Intel® 64 And IA 32 Architectures Software Developer’s Manual, Volume 3 (3A, 3B, 3C & 3D): System Programming Guide SDM Vol 3:

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Intel® 64 and IA-32 Architectures
Software Developer’s Manual
Volume 3 (3A, 3B, 3C & 3D):
System Programming Guide

NOTE: The Intel 64 and IA-32 Architectures Software Developer's Manual consists of four volumes:
Basic Architecture, Order Number 253665; Instruction Set Reference A-Z, Order Number 325383;
System Programming Guide, Order Number 325384; Model-Specific Registers, Order Number 335592.
Refer to all four volumes when evaluating your design needs.

Order Number: 325384-064US
October 2017

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Copyright © 1997-2017, Intel Corporation. All Rights Reserved.

CONTENTS
PAGE

CHAPTER 1
ABOUT THIS MANUAL
1.1
1.2
1.3
1.3.1
1.3.2
1.3.3
1.3.4
1.3.5
1.3.6
1.3.7
1.4

INTEL® 64 AND IA-32 PROCESSORS COVERED IN THIS MANUAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
OVERVIEW OF THE SYSTEM PROGRAMMING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
NOTATIONAL CONVENTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Bit and Byte Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
Reserved Bits and Software Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Instruction Operands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
Hexadecimal and Binary Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
Segmented Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
Syntax for CPUID, CR, and MSR Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
RELATED LITERATURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

CHAPTER 2
SYSTEM ARCHITECTURE OVERVIEW
2.1
2.1.1
2.1.1.1
2.1.2
2.1.2.1
2.1.3
2.1.3.1
2.1.4
2.1.4.1
2.1.5
2.1.5.1
2.1.6
2.1.6.1
2.1.7
2.2
2.2.1
2.3
2.3.1
2.4
2.4.1
2.4.2
2.4.3
2.4.4
2.5
2.5.1
2.6
2.7
2.8
2.8.1
2.8.2
2.8.3
2.8.4
2.8.5
2.8.6
2.8.6.1
2.8.7
2.8.7.1
2.8.8

OVERVIEW OF THE SYSTEM-LEVEL ARCHITECTURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Global and Local Descriptor Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Global and Local Descriptor Tables in IA-32e Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
System Segments, Segment Descriptors, and Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Gates in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Task-State Segments and Task Gates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Task-State Segments in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Interrupt and Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Interrupt and Exception Handling IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Memory Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
Memory Management in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
System Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
System Registers in IA-32e Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Other System Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
MODES OF OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
Extended Feature Enable Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
SYSTEM FLAGS AND FIELDS IN THE EFLAGS REGISTER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
System Flags and Fields in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11
MEMORY-MANAGEMENT REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11
Global Descriptor Table Register (GDTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Local Descriptor Table Register (LDTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
IDTR Interrupt Descriptor Table Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Task Register (TR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
CONTROL REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
CPUID Qualification of Control Register Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
EXTENDED CONTROL REGISTERS (INCLUDING XCR0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19
PROTECTION KEY RIGHTS REGISTER (PKRU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21
SYSTEM INSTRUCTION SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21
Loading and Storing System Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23
Verifying of Access Privileges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23
Loading and Storing Debug Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24
Invalidating Caches and TLBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-24
Controlling the Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25
Reading Performance-Monitoring and Time-Stamp Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25
Reading Counters in 64-Bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26
Reading and Writing Model-Specific Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26
Reading and Writing Model-Specific Registers in 64-Bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26
Enabling Processor Extended States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26

Vol. 3A iii

CONTENTS
PAGE

CHAPTER 3
PROTECTED-MODE MEMORY MANAGEMENT
3.1
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.3
3.3.1
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.4.5
3.4.5.1
3.5
3.5.1
3.5.2

MEMORY MANAGEMENT OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
USING SEGMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Basic Flat Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Protected Flat Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Multi-Segment Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Segmentation in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Paging and Segmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
PHYSICAL ADDRESS SPACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Intel® 64 Processors and Physical Address Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
LOGICAL AND LINEAR ADDRESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Logical Address Translation in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Segment Selectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Segment Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Segment Loading Instructions in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Segment Descriptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Code- and Data-Segment Descriptor Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
SYSTEM DESCRIPTOR TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
Segment Descriptor Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
Segment Descriptor Tables in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16

CHAPTER 4
PAGING
4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.2
4.3
4.4
4.4.1
4.4.2
4.5
4.6
4.6.1
4.6.2
4.7
4.8
4.9
4.9.1
4.9.2
4.9.3
4.10
4.10.1
4.10.2
4.10.2.1
4.10.2.2
4.10.2.3
4.10.2.4
4.10.3
4.10.3.1
4.10.3.2
4.10.3.3
4.10.4
4.10.4.1
4.10.4.2
4.10.4.3
4.10.4.4
4.10.5
4.11
4.11.1

PAGING MODES AND CONTROL BITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Three Paging Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Paging-Mode Enabling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Paging-Mode Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Enumeration of Paging Features by CPUID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
HIERARCHICAL PAGING STRUCTURES: AN OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
32-BIT PAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
PAE PAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
PDPTE Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
Linear-Address Translation with PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
4-LEVEL PAGING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19
ACCESS RIGHTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28
Determination of Access Rights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29
Protection Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31
PAGE-FAULT EXCEPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-31
ACCESSED AND DIRTY FLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-33
PAGING AND MEMORY TYPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-34
Paging and Memory Typing When the PAT is Not Supported (Pentium Pro and Pentium II Processors) . . . . . . . . . . . . . . 4-34
Paging and Memory Typing When the PAT is Supported (Pentium III and More Recent Processor Families). . . . . . . . . . 4-34
Caching Paging-Related Information about Memory Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-35
CACHING TRANSLATION INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-35
Process-Context Identifiers (PCIDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-35
Translation Lookaside Buffers (TLBs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36
Page Numbers, Page Frames, and Page Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36
Caching Translations in TLBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-37
Details of TLB Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-37
Global Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-38
Paging-Structure Caches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-38
Caches for Paging Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-38
Using the Paging-Structure Caches to Translate Linear Addresses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-40
Multiple Cached Entries for a Single Paging-Structure Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-41
Invalidation of TLBs and Paging-Structure Caches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-41
Operations that Invalidate TLBs and Paging-Structure Caches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-41
Recommended Invalidation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-43
Optional Invalidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44
Delayed Invalidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-45
Propagation of Paging-Structure Changes to Multiple Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-46
INTERACTIONS WITH VIRTUAL-MACHINE EXTENSIONS (VMX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-47
VMX Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-47

iv Vol. 3A

CONTENTS
PAGE

4.11.2
4.12
4.13

VMX Support for Address Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-47
USING PAGING FOR VIRTUAL MEMORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-47
MAPPING SEGMENTS TO PAGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-48

CHAPTER 5
PROTECTION
5.1
5.2

5.2.1
5.3
5.3.1
5.4
5.4.1
5.4.1.1
5.5
5.6
5.6.1
5.7
5.8
5.8.1
5.8.1.1
5.8.1.2
5.8.2
5.8.3
5.8.3.1
5.8.4
5.8.5
5.8.5.1
5.8.6
5.8.7
5.8.7.1
5.8.8
5.9
5.10
5.10.1
5.10.2
5.10.3
5.10.4
5.10.5
5.11
5.11.1
5.11.2
5.11.3
5.11.4
5.11.5
5.12
5.13
5.13.1
5.13.2
5.13.3
5.13.4

ENABLING AND DISABLING SEGMENT AND PAGE PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
FIELDS AND FLAGS USED FOR SEGMENT-LEVEL AND
PAGE-LEVEL PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
Code-Segment Descriptor in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
LIMIT CHECKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Limit Checking in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
TYPE CHECKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
Null Segment Selector Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
NULL Segment Checking in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
PRIVILEGE LEVELS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
PRIVILEGE LEVEL CHECKING WHEN ACCESSING DATA SEGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
Accessing Data in Code Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
PRIVILEGE LEVEL CHECKING WHEN LOADING THE SS REGISTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
PRIVILEGE LEVEL CHECKING WHEN TRANSFERRING PROGRAM CONTROL BETWEEN CODE SEGMENTS . . . . . . . . . . . . . . . . 5-10
Direct Calls or Jumps to Code Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10
Accessing Nonconforming Code Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11
Accessing Conforming Code Segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12
Gate Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
Call Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
IA-32e Mode Call Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14
Accessing a Code Segment Through a Call Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15
Stack Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17
Stack Switching in 64-bit Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19
Returning from a Called Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20
Performing Fast Calls to System Procedures with the SYSENTER and SYSEXIT Instructions . . . . . . . . . . . . . . . . . . . . . . . 5-20
SYSENTER and SYSEXIT Instructions in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21
Fast System Calls in 64-Bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22
PRIVILEGED INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23
POINTER VALIDATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24
Checking Access Rights (LAR Instruction) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24
Checking Read/Write Rights (VERR and VERW Instructions) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25
Checking That the Pointer Offset Is Within Limits (LSL Instruction) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25
Checking Caller Access Privileges (ARPL Instruction) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26
Checking Alignment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27
PAGE-LEVEL PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27
Page-Protection Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Restricting Addressable Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Page Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Combining Protection of Both Levels of Page Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28
Overrides to Page Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29
COMBINING PAGE AND SEGMENT PROTECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29
PAGE-LEVEL PROTECTION AND EXECUTE-DISABLE BIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Detecting and Enabling the Execute-Disable Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Execute-Disable Page Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Reserved Bit Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31
Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

CHAPTER 6
INTERRUPT AND EXCEPTION HANDLING
6.1
6.2
6.3
6.3.1
6.3.2
6.3.3
6.4

INTERRUPT AND EXCEPTION OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EXCEPTION AND INTERRUPT VECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SOURCES OF INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maskable Hardware Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Software-Generated Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SOURCES OF EXCEPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6-1
6-1
6-2
6-2
6-3
6-4
6-4

Vol. 3A v

CONTENTS
PAGE

6.4.1
6.4.2
6.4.3
6.5
6.6
6.7
6.7.1
6.8
6.8.1
6.8.2
6.8.3
6.9
6.10
6.11
6.12
6.12.1
6.12.1.1
6.12.1.2
6.12.2
6.13
6.14
6.14.1
6.14.2
6.14.3
6.14.4
6.14.5
6.15

Program-Error Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
Software-Generated Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
Machine-Check Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
EXCEPTION CLASSIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
PROGRAM OR TASK RESTART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5
NONMASKABLE INTERRUPT (NMI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
Handling Multiple NMIs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
ENABLING AND DISABLING INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
Masking Maskable Hardware Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6
Masking Instruction Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
Masking Exceptions and Interrupts When Switching Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
PRIORITY AMONG SIMULTANEOUS EXCEPTIONS AND INTERRUPTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8
INTERRUPT DESCRIPTOR TABLE (IDT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9
IDT DESCRIPTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
EXCEPTION AND INTERRUPT HANDLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
Exception- or Interrupt-Handler Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
Protection of Exception- and Interrupt-Handler Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13
Flag Usage By Exception- or Interrupt-Handler Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14
Interrupt Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14
ERROR CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
EXCEPTION AND INTERRUPT HANDLING IN 64-BIT MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16
64-Bit Mode IDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16
64-Bit Mode Stack Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17
IRET in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18
Stack Switching in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18
Interrupt Stack Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19
EXCEPTION AND INTERRUPT REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19
Interrupt 0—Divide Error Exception (#DE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20
Interrupt 1—Debug Exception (#DB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
Interrupt 2—NMI Interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
Interrupt 3—Breakpoint Exception (#BP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23
Interrupt 4—Overflow Exception (#OF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24
Interrupt 5—BOUND Range Exceeded Exception (#BR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-25
Interrupt 6—Invalid Opcode Exception (#UD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26
Interrupt 7—Device Not Available Exception (#NM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27
Interrupt 8—Double Fault Exception (#DF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28
Interrupt 9—Coprocessor Segment Overrun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-30
Interrupt 10—Invalid TSS Exception (#TS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31
Interrupt 11—Segment Not Present (#NP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-33
Interrupt 12—Stack Fault Exception (#SS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-35
Interrupt 13—General Protection Exception (#GP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-36
Interrupt 14—Page-Fault Exception (#PF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-39
Interrupt 16—x87 FPU Floating-Point Error (#MF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-42
Interrupt 17—Alignment Check Exception (#AC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-44
Interrupt 18—Machine-Check Exception (#MC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-46
Interrupt 19—SIMD Floating-Point Exception (#XM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-47
Interrupt 20—Virtualization Exception (#VE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-49
Interrupts 32 to 255—User Defined Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-50

CHAPTER 7
TASK MANAGEMENT
7.1
7.1.1
7.1.2
7.1.3
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5

TASK MANAGEMENT OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Task Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Task State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Executing a Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TASK MANAGEMENT DATA STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Task-State Segment (TSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TSS Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TSS Descriptor in 64-bit mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Task Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Task-Gate Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

vi Vol. 3A

7-1
7-1
7-2
7-2
7-3
7-3
7-5
7-6
7-7
7-8

CONTENTS
PAGE

7.3
7.4
7.4.1
7.4.2
7.5
7.5.1
7.5.2
7.6
7.7

TASK SWITCHING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9
TASK LINKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12
Use of Busy Flag To Prevent Recursive Task Switching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
Modifying Task Linkages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
TASK ADDRESS SPACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14
Mapping Tasks to the Linear and Physical Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14
Task Logical Address Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15
16-BIT TASK-STATE SEGMENT (TSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15
TASK MANAGEMENT IN 64-BIT MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

CHAPTER 8
MULTIPLE-PROCESSOR MANAGEMENT

8.1
8.1.1
8.1.2
8.1.2.1
8.1.2.2
8.1.3
8.1.4
8.2
8.2.1
8.2.2
8.2.3
8.2.3.1
8.2.3.2
8.2.3.3
8.2.3.4
8.2.3.5
8.2.3.6
8.2.3.7
8.2.3.8
8.2.3.9
8.2.4
8.2.4.1
8.2.4.2
8.2.5
8.3
8.4
8.4.1
8.4.2
8.4.3
8.4.4
8.4.4.1
8.4.4.2
8.4.5
8.5
8.6
8.6.1
8.6.2
8.6.3
8.6.4
8.7
8.7.1
8.7.2
8.7.3
8.7.4
8.7.5
8.7.6
8.7.7
8.7.8
8.7.9
8.7.10
8.7.11
8.7.12

LOCKED ATOMIC OPERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
Guaranteed Atomic Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2
Bus Locking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3
Automatic Locking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3
Software Controlled Bus Locking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3
Handling Self- and Cross-Modifying Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4
Effects of a LOCK Operation on Internal Processor Caches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5
MEMORY ORDERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5
Memory Ordering in the Intel® Pentium® and Intel486™ Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6
Memory Ordering in P6 and More Recent Processor Families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6
Examples Illustrating the Memory-Ordering Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7
Assumptions, Terminology, and Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8
Neither Loads Nor Stores Are Reordered with Like Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9
Stores Are Not Reordered With Earlier Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9
Loads May Be Reordered with Earlier Stores to Different Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9
Intra-Processor Forwarding Is Allowed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10
Stores Are Transitively Visible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-10
Stores Are Seen in a Consistent Order by Other Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11
Locked Instructions Have a Total Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11
Loads and Stores Are Not Reordered with Locked Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12
Fast-String Operation and Out-of-Order Stores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12
Memory-Ordering Model for String Operations on Write-Back (WB) Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13
Examples Illustrating Memory-Ordering Principles for String Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13
Strengthening or Weakening the Memory-Ordering Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15
SERIALIZING INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17
MULTIPLE-PROCESSOR (MP) INITIALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18
BSP and AP Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18
MP Initialization Protocol Requirements and Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19
MP Initialization Protocol Algorithm for MP Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19
MP Initialization Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-20
Typical BSP Initialization Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21
Typical AP Initialization Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22
Identifying Logical Processors in an MP System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-23
INTEL® HYPER-THREADING TECHNOLOGY AND INTEL® MULTI-CORE TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24
DETECTING HARDWARE MULTI-THREADING SUPPORT AND TOPOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24
Initializing Processors Supporting Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-25
Initializing Multi-Core Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-26
Executing Multiple Threads on an Intel® 64 or IA-32 Processor Supporting Hardware Multi-Threading . . . . . . . . . . . . 8-26
Handling Interrupts on an IA-32 Processor Supporting Hardware Multi-Threading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-26
INTEL® HYPER-THREADING TECHNOLOGY ARCHITECTURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-27
State of the Logical Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
APIC Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Memory Type Range Registers (MTRR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Page Attribute Table (PAT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Machine Check Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29
Debug Registers and Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Performance Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
IA32_MISC_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Memory Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Serializing Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Microcode Update Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30
Self Modifying Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-31
Vol. 3A vii

CONTENTS
PAGE

8.7.13
8.7.13.1
8.7.13.2
8.7.13.3
8.7.13.4
8.8
8.8.1
8.8.2
8.8.3
8.8.4
8.8.5
8.9
8.9.1
8.9.2
8.9.3
8.9.3.1
8.9.4
8.9.5
8.10
8.10.1
8.10.2
8.10.3
8.10.4
8.10.5
8.10.6
8.10.6.1
8.10.6.2
8.10.6.3
8.10.6.4
8.10.6.5
8.10.6.6
8.10.6.7
8.11
8.11.1
8.11.2
8.11.2.1

Implementation-Specific Intel HT Technology Facilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-31
Processor Caches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-31
Processor Translation Lookaside Buffers (TLBs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-31
Thermal Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
External Signal Compatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
MULTI-CORE ARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32
Logical Processor Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-33
Memory Type Range Registers (MTRR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-33
Performance Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-33
IA32_MISC_ENABLE MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-33
Microcode Update Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-33
PROGRAMMING CONSIDERATIONS FOR HARDWARE MULTI-THREADING CAPABLE PROCESSORS . . . . . . . . . . . . . . . . . . . . . 8-34
Hierarchical Mapping of Shared Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-34
Hierarchical Mapping of CPUID Extended Topology Leaf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-35
Hierarchical ID of Logical Processors in an MP System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-36
Hierarchical ID of Logical Processors with x2APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-38
Algorithm for Three-Level Mappings of APIC_ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-38
Identifying Topological Relationships in a MP System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-43
MANAGEMENT OF IDLE AND BLOCKED CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-47
HLT Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-47
PAUSE Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-47
Detecting Support MONITOR/MWAIT Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-47
MONITOR/MWAIT Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-48
Monitor/Mwait Address Range Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-49
Required Operating System Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-49
Use the PAUSE Instruction in Spin-Wait Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-50
Potential Usage of MONITOR/MWAIT in C0 Idle Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-50
Halt Idle Logical Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-51
Potential Usage of MONITOR/MWAIT in C1 Idle Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-52
Guidelines for Scheduling Threads on Logical Processors Sharing Execution Resources . . . . . . . . . . . . . . . . . . . . . . . . . 8-52
Eliminate Execution-Based Timing Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-53
Place Locks and Semaphores in Aligned, 128-Byte Blocks of Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-53
MP INITIALIZATION FOR P6 FAMILY PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-53
Overview of the MP Initialization Process For P6 Family Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-53
MP Initialization Protocol Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-54
Error Detection and Handling During the MP Initialization Protocol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-55

CHAPTER 9
PROCESSOR MANAGEMENT AND INITIALIZATION
9.1
9.1.1
9.1.2
9.1.3
9.1.4
9.2
9.2.1
9.2.2
9.3
9.4
9.5
9.6
9.7
9.7.1
9.7.2
9.8
9.8.1
9.8.2
9.8.3
9.8.4
9.8.5
9.8.5.1
9.8.5.2
9.8.5.3
9.8.5.4

INITIALIZATION OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1
Processor State After Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2
Processor Built-In Self-Test (BIST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
Model and Stepping Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
First Instruction Executed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
X87 FPU INITIALIZATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5
Configuring the x87 FPU Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6
Setting the Processor for x87 FPU Software Emulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6
CACHE ENABLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
MODEL-SPECIFIC REGISTERS (MSRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
MEMORY TYPE RANGE REGISTERS (MTRRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
INITIALIZING SSE/SSE2/SSE3/SSSE3 EXTENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
SOFTWARE INITIALIZATION FOR REAL-ADDRESS MODE OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
Real-Address Mode IDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8
NMI Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9
SOFTWARE INITIALIZATION FOR PROTECTED-MODE OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9
Protected-Mode System Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9
Initializing Protected-Mode Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
Initializing Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
Initializing Multitasking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10
Initializing IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11
IA-32e Mode System Data Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11
IA-32e Mode Interrupts and Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12
64-bit Mode and Compatibility Mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12
Switching Out of IA-32e Mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12

viii Vol. 3A

CONTENTS
PAGE

9.9
MODE SWITCHING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13
9.9.1
Switching to Protected Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13
9.9.2
Switching Back to Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14
9.10
INITIALIZATION AND MODE SWITCHING EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14
9.10.1
Assembler Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16
9.10.2
STARTUP.ASM Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16
9.10.3
MAIN.ASM Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25
9.10.4
Supporting Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25
9.11
MICROCODE UPDATE FACILITIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
9.11.1
Microcode Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
9.11.2
Optional Extended Signature Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31
9.11.3
Processor Identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-32
9.11.4
Platform Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-32
9.11.5
Microcode Update Checksum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-33
9.11.6
Microcode Update Loader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-34
9.11.6.1
Hard Resets in Update Loading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.2
Update in a Multiprocessor System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.3
Update in a System Supporting Intel Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.4
Update in a System Supporting Dual-Core Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.6.5
Update Loader Enhancements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-35
9.11.7
Update Signature and Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-36
9.11.7.1
Determining the Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-36
9.11.7.2
Authenticating the Update. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
9.11.8
Optional Processor Microcode Update Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
9.11.8.1
Responsibilities of the BIOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-38
9.11.8.2
Responsibilities of the Calling Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-39
9.11.8.3
Microcode Update Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9.11.8.4
INT 15H-based Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9.11.8.5
Function 00H—Presence Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
9.11.8.6
Function 01H—Write Microcode Update Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-43
9.11.8.7
Function 02H—Microcode Update Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-46
9.11.8.8
Function 03H—Read Microcode Update Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
9.11.8.9
Return Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-48

CHAPTER 10
ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

10.1
10.2
10.3
10.4
10.4.1
10.4.2
10.4.3
10.4.4
10.4.5
10.4.6
10.4.7
10.4.7.1
10.4.7.2
10.4.7.3
10.4.7.4
10.4.8
10.5
10.5.1
10.5.2
10.5.3
10.5.4
10.5.4.1
10.5.5
10.6
10.6.1
10.6.2
10.6.2.1
10.6.2.2

LOCAL AND I/O APIC OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
SYSTEM BUS VS. APIC BUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
THE INTEL® 82489DX EXTERNAL APIC, THE APIC, THE XAPIC, AND THE X2APIC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
LOCAL APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
The Local APIC Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4
Presence of the Local APIC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8
Enabling or Disabling the Local APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8
Local APIC Status and Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-8
Relocating the Local APIC Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
Local APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
Local APIC State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10
Local APIC State After Power-Up or Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10
Local APIC State After It Has Been Software Disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
Local APIC State After an INIT Reset (“Wait-for-SIPI” State) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
Local APIC State After It Receives an INIT-Deassert IPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
Local APIC Version Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-11
HANDLING LOCAL INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12
Local Vector Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12
Valid Interrupt Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-14
Error Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15
APIC Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16
TSC-Deadline Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17
Local Interrupt Acceptance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18
ISSUING INTERPROCESSOR INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-18
Interrupt Command Register (ICR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19
Determining IPI Destination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
Physical Destination Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
Logical Destination Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23
Vol. 3A ix

CONTENTS
PAGE

10.6.2.3
Broadcast/Self Delivery Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-25
10.6.2.4
Lowest Priority Delivery Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-25
10.6.3
IPI Delivery and Acceptance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-26
10.7
SYSTEM AND APIC BUS ARBITRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-26
10.8
HANDLING INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-26
10.8.1
Interrupt Handling with the Pentium 4 and Intel Xeon Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-27
10.8.2
Interrupt Handling with the P6 Family and Pentium Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-27
10.8.3
Interrupt, Task, and Processor Priority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-28
10.8.3.1
Task and Processor Priorities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-29
10.8.4
Interrupt Acceptance for Fixed Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-30
10.8.5
Signaling Interrupt Servicing Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-31
10.8.6
Task Priority in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-31
10.8.6.1
Interaction of Task Priorities between CR8 and APIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-32
10.9
SPURIOUS INTERRUPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-32
10.10 APIC BUS MESSAGE PASSING MECHANISM AND PROTOCOL (P6 FAMILY, PENTIUM PROCESSORS) . . . . . . . . . . . . . . . . . . . 10-33
10.10.1
Bus Message Formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-34
10.11 MESSAGE SIGNALLED INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-34
10.11.1
Message Address Register Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-34
10.11.2
Message Data Register Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-35
10.12 EXTENDED XAPIC (X2APIC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-36
10.12.1
Detecting and Enabling x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-37
10.12.1.1
Instructions to Access APIC Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-37
10.12.1.2
x2APIC Register Address Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-38
10.12.1.3
Reserved Bit Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-40
10.12.2
x2APIC Register Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-40
10.12.3
MSR Access in x2APIC Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-40
10.12.4
VM-Exit Controls for MSRs and x2APIC Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-41
10.12.5
x2APIC State Transitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-41
10.12.5.1
x2APIC States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-41
x2APIC After Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-42
x2APIC Transitions From x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-42
x2APIC Transitions From Disabled Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
State Changes From xAPIC Mode to x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.6
Routing of Device Interrupts in x2APIC Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.7
Initialization by System Software. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.8
CPUID Extensions And Topology Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-43
10.12.8.1
Consistency of APIC IDs and CPUID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-44
10.12.9
ICR Operation in x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-44
10.12.10 Determining IPI Destination in x2APIC Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-45
10.12.10.1
Logical Destination Mode in x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-45
10.12.10.2
Deriving Logical x2APIC ID from the Local x2APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-46
10.12.11 SELF IPI Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-47
10.13 APIC BUS MESSAGE FORMATS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-47
10.13.1
Bus Message Formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-47
10.13.2
EOI Message. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-47
10.13.2.1
Short Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-48
10.13.2.2
Non-focused Lowest Priority Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-49
10.13.2.3
APIC Bus Status Cycles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-50

CHAPTER 11
MEMORY CACHE CONTROL
11.1
11.2
11.3
11.3.1
11.3.2
11.3.3
11.4
11.5
11.5.1
11.5.2
11.5.2.1
11.5.2.2

x Vol. 3A

INTERNAL CACHES, TLBS, AND BUFFERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1
CACHING TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5
METHODS OF CACHING AVAILABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6
Buffering of Write Combining Memory Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7
Choosing a Memory Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-8
Code Fetches in Uncacheable Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9
CACHE CONTROL PROTOCOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9
CACHE CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-10
Cache Control Registers and Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-10
Precedence of Cache Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-13
Selecting Memory Types for Pentium Pro and Pentium II Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-14
Selecting Memory Types for Pentium III and More Recent Processor Families . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-15

CONTENTS
PAGE

11.5.2.3
Writing Values Across Pages with Different Memory Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-16
11.5.3
Preventing Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-16
11.5.4
Disabling and Enabling the L3 Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-17
11.5.5
Cache Management Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-17
11.5.6
L1 Data Cache Context Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.5.6.1
Adaptive Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.5.6.2
Shared Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.6
SELF-MODIFYING CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-18
11.7
IMPLICIT CACHING (PENTIUM 4, INTEL XEON, AND P6 FAMILY PROCESSORS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-19
11.8
EXPLICIT CACHING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-19
11.9
INVALIDATING THE TRANSLATION LOOKASIDE BUFFERS (TLBS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-19
11.10 STORE BUFFER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-20
11.11 MEMORY TYPE RANGE REGISTERS (MTRRS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-20
11.11.1
MTRR Feature Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-21
11.11.2
Setting Memory Ranges with MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-22
11.11.2.1
IA32_MTRR_DEF_TYPE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-22
11.11.2.2
Fixed Range MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-23
11.11.2.3
Variable Range MTRRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-23
11.11.2.4
System-Management Range Register Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-25
11.11.3
Example Base and Mask Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-26
11.11.3.1
Base and Mask Calculations for Greater-Than 36-bit Physical Address Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-27
11.11.4
Range Size and Alignment Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-28
11.11.4.1
MTRR Precedences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-28
11.11.5
MTRR Initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.6
Remapping Memory Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.7
MTRR Maintenance Programming Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.7.1
MemTypeGet() Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-29
11.11.7.2
MemTypeSet() Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-31
11.11.8
MTRR Considerations in MP Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-32
11.11.9
Large Page Size Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-33
11.12 PAGE ATTRIBUTE TABLE (PAT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-33
11.12.1
Detecting Support for the PAT Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34
11.12.2
IA32_PAT MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34
11.12.3
Selecting a Memory Type from the PAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35
11.12.4
Programming the PAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35
11.12.5
PAT Compatibility with Earlier IA-32 Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-36

CHAPTER 12
INTEL® MMX™ TECHNOLOGY SYSTEM PROGRAMMING
12.1
12.2
12.2.1
12.3
12.4
12.5
12.5.1
12.6

EMULATION OF THE MMX INSTRUCTION SET. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
THE MMX STATE AND MMX REGISTER ALIASING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
Effect of MMX, x87 FPU, FXSAVE, and FXRSTOR Instructions on the x87 FPU Tag Word . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
SAVING AND RESTORING THE MMX STATE AND REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
SAVING MMX STATE ON TASK OR CONTEXT SWITCHES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4
EXCEPTIONS THAT CAN OCCUR WHEN EXECUTING MMX INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-4
Effect of MMX Instructions on Pending x87 Floating-Point Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5
DEBUGGING MMX CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5

CHAPTER 13
SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND PROCESSOR EXTENDED
STATES

13.1
13.1.1
13.1.2
13.1.3
13.1.4
13.1.5
13.1.5.1
13.2
13.3
13.4
13.4.1

PROVIDING OPERATING SYSTEM SUPPORT FOR SSE EXTENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1
Adding Support to an Operating System for SSE Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2
Checking for CPU Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2
Initialization of the SSE Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2
Providing Non-Numeric Exception Handlers for Exceptions Generated by the SSE Instructions. . . . . . . . . . . . . . . . . . . . . 13-4
Providing a Handler for the SIMD Floating-Point Exception (#XM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-5
Numeric Error flag and IGNNE#. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-6
EMULATION OF SSE EXTENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-6
SAVING AND RESTORING SSE STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-6
DESIGNING OS FACILITIES FOR SAVING X87 FPU, SSE AND EXTENDED STATES ON TASK OR CONTEXT SWITCHES . . . . . 13-6
Using the TS Flag to Control the Saving of the x87 FPU and SSE State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-7
Vol. 3A xi

CONTENTS
PAGE

13.5
13.5.1
13.5.2
13.5.3
13.5.4
13.5.5
13.6
13.7
13.8
13.8.1
13.8.2

THE XSAVE FEATURE SET AND PROCESSOR EXTENDED STATE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-7
Checking the Support for XSAVE Feature Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-8
Determining the XSAVE Managed Feature States And The Required Buffer Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-8
Enable the Use Of XSAVE Feature Set And XSAVE State Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9
Provide an Initialization for the XSAVE State Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9
Providing the Required Exception Handlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9
INTEROPERABILITY OF THE XSAVE FEATURE SET AND FXSAVE/FXRSTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-9
THE XSAVE FEATURE SET AND PROCESSOR SUPERVISOR STATE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-10
SYSTEM PROGRAMMING FOR XSAVE MANAGED FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-10
Intel® Advanced Vector Extensions (Intel® AVX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-11
Intel® Advanced Vector Extensions 512 (Intel® AVX-512) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13-11

CHAPTER 14
POWER AND THERMAL MANAGEMENT

14.1
14.1.1
14.2
14.3
14.3.1
14.3.2
14.3.2.1
14.3.2.2
14.3.2.3
14.3.3
14.3.4
14.4
14.4.1
14.4.2
14.4.3
14.4.4
14.4.5
14.4.5.1
14.4.6
14.4.7
14.5
14.5.1
14.5.2
14.5.3
14.5.4
14.5.4.1
14.5.4.2
14.5.5
14.6
14.7
14.7.1
14.7.2
14.7.2.1
14.7.2.2
14.7.2.3
14.7.2.4
14.7.2.5
14.7.2.6
14.7.3
14.7.3.1
14.7.4
14.7.4.1
14.7.5
14.7.5.1
14.7.5.2
14.7.6
14.8
14.8.1
14.9
14.9.1

ENHANCED INTEL SPEEDSTEP® TECHNOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1
Software Interface For Initiating Performance State Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1
P-STATE HARDWARE COORDINATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-1
SYSTEM SOFTWARE CONSIDERATIONS AND OPPORTUNISTIC PROCESSOR PERFORMANCE OPERATION . . . . . . . . . . . . . . 14-3
Intel Dynamic Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-3
System Software Interfaces for Opportunistic Processor Performance Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-3
Discover Hardware Support and Enabling of Opportunistic Processor Performance Operation. . . . . . . . . . . . . . . . . . . 14-3
OS Control of Opportunistic Processor Performance Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
Required Changes to OS Power Management P-state Policy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
Intel Turbo Boost Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-5
Performance and Energy Bias Hint support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-5
HARDWARE-CONTROLLED PERFORMANCE STATES (HWP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-5
HWP Programming Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-6
Enabling HWP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7
HWP Performance Range and Dynamic Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7
Managing HWP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-8
HWP Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-9
Non-Architectural HWP Feedback. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-11
HWP Notifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-11
Recommendations for OS use of HWP Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-12
HARDWARE DUTY CYCLING (HDC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-13
Hardware Duty Cycling Programming Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-13
Package level Enabling HDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-14
Logical-Processor Level HDC Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-14
HDC Residency Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-15
IA32_THREAD_STALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-15
Non-Architectural HDC Residency Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-16
MPERF and APERF Counters Under HDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-18
MWAIT EXTENSIONS FOR ADVANCED POWER MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-18
THERMAL MONITORING AND PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-19
Catastrophic Shutdown Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-20
Thermal Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-20
Thermal Monitor 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-20
Thermal Monitor 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-20
Two Methods for Enabling TM2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-20
Performance State Transitions and Thermal Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-21
Thermal Status Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-21
Adaptive Thermal Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-22
Software Controlled Clock Modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-23
Extension of Software Controlled Clock Modulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-24
Detection of Thermal Monitor and Software Controlled Clock Modulation Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-24
Detection of Software Controlled Clock Modulation Extension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-24
On Die Digital Thermal Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-24
Digital Thermal Sensor Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-25
Reading the Digital Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-25
Power Limit Notification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-28
PACKAGE LEVEL THERMAL MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-28
Support for Passive and Active cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-30
PLATFORM SPECIFIC POWER MANAGEMENT SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-31
RAPL Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14-31

xii Vol. 3A

CONTENTS
PAGE

14.9.2
14.9.3
14.9.4
14.9.5

RAPL Domains and Platform Specificity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-32
Package RAPL Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-33
PP0/PP1 RAPL Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-35
DRAM RAPL Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-37

CHAPTER 15
MACHINE-CHECK ARCHITECTURE

15.1
MACHINE-CHECK ARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1
15.2
COMPATIBILITY WITH PENTIUM PROCESSOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-1
15.3
MACHINE-CHECK MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
15.3.1
Machine-Check Global Control MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
15.3.1.1
IA32_MCG_CAP MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
15.3.1.2
IA32_MCG_STATUS MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
15.3.1.3
IA32_MCG_CTL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
15.3.1.4
IA32_MCG_EXT_CTL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
15.3.1.5
Enabling Local Machine Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
15.3.2
Error-Reporting Register Banks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
15.3.2.1
IA32_MCi_CTL MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
15.3.2.2
IA32_MCi_STATUS MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-6
15.3.2.3
IA32_MCi_ADDR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-9
15.3.2.4
IA32_MCi_MISC MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-9
15.3.2.5
IA32_MCi_CTL2 MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-11
15.3.2.6
IA32_MCG Extended Machine Check State MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-12
15.3.3
Mapping of the Pentium Processor Machine-Check Errors to the Machine-Check Architecture . . . . . . . . . . . . . . . . . . . . . 15-13
15.4
ENHANCED CACHE ERROR REPORTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-13
15.5
CORRECTED MACHINE CHECK ERROR INTERRUPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-14
15.5.1
CMCI Local APIC Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-14
15.5.2
System Software Recommendation for Managing CMCI and Machine Check Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-15
15.5.2.1
CMCI Initialization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-15
15.5.2.2
CMCI Threshold Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-16
15.5.2.3
CMCI Interrupt Handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-16
15.6
RECOVERY OF UNCORRECTED RECOVERABLE (UCR) ERRORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-16
15.6.1
Detection of Software Error Recovery Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-16
15.6.2
UCR Error Reporting and Logging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-17
15.6.3
UCR Error Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-17
15.6.4
UCR Error Overwrite Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-18
15.7
MACHINE-CHECK AVAILABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-19
15.8
MACHINE-CHECK INITIALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-19
15.9
INTERPRETING THE MCA ERROR CODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-20
15.9.1
Simple Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
15.9.2
Compound Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
15.9.2.1
Correction Report Filtering (F) Bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
15.9.2.2
Transaction Type (TT) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
15.9.2.3
Level (LL) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
15.9.2.4
Request (RRRR) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
15.9.2.5
Bus and Interconnect Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-23
15.9.2.6
Memory Controller Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-23
15.9.3
Architecturally Defined UCR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-24
15.9.3.1
Architecturally Defined SRAO Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-24
15.9.3.2
Architecturally Defined SRAR Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-25
15.9.4
Multiple MCA Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-27
15.9.5
Machine-Check Error Codes Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-27
15.10 GUIDELINES FOR WRITING MACHINE-CHECK SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-27
15.10.1
Machine-Check Exception Handler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-27
15.10.2
Pentium Processor Machine-Check Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-29
15.10.3
Logging Correctable Machine-Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-29
15.10.4
Machine-Check Software Handler Guidelines for Error Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-31
15.10.4.1
Machine-Check Exception Handler for Error Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-31
15.10.4.2
Corrected Machine-Check Handler for Error Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-35

Vol. 3A xiii

CONTENTS
PAGE

CHAPTER 16
INTERPRETING MACHINE-CHECK ERROR CODES
16.1
16.2

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY 06H MACHINE ERROR CODES FOR MACHINE CHECK . . . 16-1
INCREMENTAL DECODING INFORMATION: INTEL CORE 2 PROCESSOR FAMILY MACHINE ERROR CODES FOR MACHINE
CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-3
16.2.1
Model-Specific Machine Check Error Codes for Intel Xeon Processor 7400 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-5
16.2.1.1
Processor Machine Check Status Register Incremental MCA Error Code Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
16.2.2
Intel Xeon Processor 7400 Model Specific Error Code Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
16.2.2.1
Processor Model Specific Error Code Field Type B: Bus and Interconnect Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
16.2.2.2
Processor Model Specific Error Code Field Type C: Cache Bus Controller Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7
16.3
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_1AH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7
16.3.1
Intel QPI Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
16.3.2
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
16.3.3
Memory Controller Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-9
16.4
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_2DH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-10
16.4.1
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-10
16.4.2
Intel QPI Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-11
16.4.3
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-11
16.5
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_3EH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-13
16.5.1
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-13
16.5.2
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-14
16.6
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_3FH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-15
16.6.1
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-16
16.6.2
Intel QPI Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-17
16.6.3
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-17
16.7
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_56H, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19
16.7.1
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-19
16.7.2
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-20
16.8
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_4FH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-21
16.8.1
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-21
16.8.2
Home Agent Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-22
16.9
INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_55H, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-22
16.9.1
Internal Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-22
16.9.2
Interconnect Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-24
16.9.3
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-25
16.9.4
M2M Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-26
16.9.5
Home Agent Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-27
16.10 INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE
06_5FH, MACHINE ERROR CODES FOR MACHINE CHECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-28
16.10.1
Integrated Memory Controller Machine Check Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-28
16.11 INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY 0FH MACHINE ERROR CODES FOR MACHINE CHECK . . 16-29
16.11.1
Model-Specific Machine Check Error Codes for Intel Xeon Processor MP 7100 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-29
16.11.1.1
Processor Machine Check Status Register
MCA Error Code Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-30
16.11.2
Other_Info Field (all MCA Error Types) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-31
16.11.3
Processor Model Specific Error Code Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-32
16.11.3.1
MCA Error Type A: L3 Error. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-32
16.11.3.2
Processor Model Specific Error Code Field Type B: Bus and Interconnect Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-32
16.11.3.3
Processor Model Specific Error Code Field Type C: Cache Bus Controller Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-33

CHAPTER 17
DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES
17.1
17.2
17.2.1
17.2.2

OVERVIEW OF DEBUG SUPPORT FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-1
DEBUG REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-2
Debug Address Registers (DR0-DR3). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-3
Debug Registers DR4 and DR5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-3

xiv Vol. 3A

CONTENTS
PAGE

17.2.3
17.2.4
17.2.5
17.2.6
17.3
17.3.1
17.3.1.1
17.3.1.2
17.3.1.3
17.3.1.4
17.3.1.5
17.3.2
17.3.3
17.4
17.4.1
17.4.2
17.4.3
17.4.4
17.4.4.1
17.4.5
17.4.6
17.4.7
17.4.8
17.4.8.1
17.4.8.2
17.4.8.3
17.4.9
17.4.9.1
17.4.9.2
17.4.9.3
17.4.9.4
17.4.9.5
17.5
17.5.1
17.5.2
17.6
17.7
17.8
17.9
17.9.1
17.9.2
17.10
17.11
17.11.1
17.12
17.12.1
17.12.2
17.12.3
17.13
17.13.1
17.13.2
17.13.3
17.14
17.15
17.16
17.16.1
17.16.2
17.16.3

Debug Status Register (DR6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-3
Debug Control Register (DR7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-4
Breakpoint Field Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-5
Debug Registers and Intel® 64 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-6
DEBUG EXCEPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-6
Debug Exception (#DB)—Interrupt Vector 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-7
Instruction-Breakpoint Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-8
Data Memory and I/O Breakpoint Exception Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
General-Detect Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
Single-Step Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-9
Task-Switch Exception Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-10
Breakpoint Exception (#BP)—Interrupt Vector 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-10
Debug Exceptions, Breakpoint Exceptions, and Restricted Transactional Memory (RTM) . . . . . . . . . . . . . . . . . . . . . . . . . . 17-10
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-11
IA32_DEBUGCTL MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-11
Monitoring Branches, Exceptions, and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-12
Single-Stepping on Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-13
Branch Trace Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-13
Branch Trace Message Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-13
Branch Trace Store (BTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-13
CPL-Qualified Branch Trace Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-14
Freezing LBR and Performance Counters on PMI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-14
LBR Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-15
LBR Stack and Intel® 64 Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-16
LBR Stack and IA-32 Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-17
Last Exception Records and Intel 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-17
BTS and DS Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-17
64 Bit Format of the DS Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-20
Setting Up the DS Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-22
Setting Up the BTS Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-23
Setting Up CPL-Qualified BTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-24
Writing the DS Interrupt Service Routine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-24
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (INTEL® CORE™ 2 DUO AND INTEL® ATOM™ PROCESSORS) . 17-25
LBR Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-25
LBR Stack in Intel Atom Processors based on the Silvermont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-26
LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON GOLDMONT
MICROARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-26
LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON GOLDMONT PLUS
MICROARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-27
LAST BRANCH, INTERRUPT AND EXCEPTION RECORDING FOR INTEL® XEON PHI™ PROCESSOR 7200/5200/3200 . . . 17-27
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE
NAME NEHALEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-27
LBR Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-29
Filtering of Last Branch Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-29
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE
CODE NAME SANDY BRIDGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-30
LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON HASWELL
MICROARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-30
LBR Stack Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-31
LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING FOR PROCESSORS BASED ON SKYLAKE
MICROARCHITECTURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-32
MSR_LBR_INFO_x MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-32
Streamlined Freeze_LBRs_On_PMI Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-33
LBR Behavior and Deep C-State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-33
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (PROCESSORS BASED ON INTEL NETBURST®
MICROARCHITECTURE). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-33
MSR_DEBUGCTLA MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-34
LBR Stack for Processors Based on Intel NetBurst® Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-35
Last Exception Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-36
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (INTEL® CORE™ SOLO AND INTEL® CORE™ DUO PROCESSORS) 17-36
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (PENTIUM M PROCESSORS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-38
LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (P6 FAMILY PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-39
DEBUGCTLMSR Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-39
Last Branch and Last Exception MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-40
Monitoring Branches, Exceptions, and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-40
Vol. 3A xv

CONTENTS
PAGE

17.17 TIME-STAMP COUNTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-41
17.17.1
Invariant TSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-42
17.17.2
IA32_TSC_AUX Register and RDTSCP Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-42
17.17.3
Time-Stamp Counter Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-43
17.17.4
Invariant Time-Keeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-43
17.18 INTEL® RESOURCE DIRECTOR TECHNOLOGY (INTEL® RDT) MONITORING FEATURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-43
17.18.1
Overview of Cache Monitoring Technology and Memory Bandwidth Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-44
17.18.2
Enabling Monitoring: Usage Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-44
17.18.3
Enumeration and Detecting Support of Cache Monitoring Technology and Memory Bandwidth Monitoring . . . . . . . . .17-45
17.18.4
Monitoring Resource Type and Capability Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-45
17.18.5
Feature-Specific Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-46
17.18.5.1
Cache Monitoring Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-47
17.18.5.2
Memory Bandwidth Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-47
17.18.6
Monitoring Resource RMID Association. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-47
17.18.7
Monitoring Resource Selection and Reporting Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-48
17.18.8
Monitoring Programming Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-49
17.18.8.1
Monitoring Dynamic Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-50
17.18.8.2
Monitoring Operation With Power Saving Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-50
17.18.8.3
Monitoring Operation with Other Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-50
17.18.8.4
Monitoring Operation with RAS Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-50
17.19 INTEL® RESOURCE DIRECTOR TECHNOLOGY (INTEL® RDT) ALLOCATION FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-50
17.19.1
Introduction to Cache Allocation Technology (CAT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-50
17.19.2
Cache Allocation Technology Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-51
17.19.3
Code and Data Prioritization (CDP) Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-54
17.19.4
Enabling Cache Allocation Technology Usage Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-55
17.19.4.1
Enumeration and Detection Support of Cache Allocation Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-56
17.19.4.2
Cache Allocation Technology: Resource Type and Capability Enumeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-56
17.19.4.3
Cache Allocation Technology: Cache Mask Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-59
17.19.4.4
Class of Service to Cache Mask Association: Common Across Allocation Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-59
17.19.5
Code and Data Prioritization (CDP): Enumerating and Enabling L3 CDP Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-60
17.19.5.1
Mapping Between L3 CDP Masks and CAT Masks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-61
17.19.5.2
L3 CAT: Disabling CDP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-61
17.19.6
Cache Allocation Technology Programming Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-61
17.19.6.1
Cache Allocation Technology Dynamic Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-61
17.19.6.2
Cache Allocation Technology Operation With Power Saving Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-62
17.19.6.3
Cache Allocation Technology Operation with Other Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-62
17.19.6.4
Associating Threads with CAT/CDP Classes of Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-63
17.19.7
Introduction to Memory Bandwidth Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-63
17.19.7.1
Memory Bandwidth Allocation Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-64
17.19.7.2
Memory Bandwidth Allocation Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-65
17.19.7.3
Memory Bandwidth Allocation Usage Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-66

CHAPTER 18
PERFORMANCE MONITORING

18.1
PERFORMANCE MONITORING OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-1
18.2
ARCHITECTURAL PERFORMANCE MONITORING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-2
18.2.1
Architectural Performance Monitoring Version 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-3
18.2.1.1
Architectural Performance Monitoring Version 1 Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-3
18.2.1.2
Pre-defined Architectural Performance Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-5
18.2.2
Architectural Performance Monitoring Version 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-6
18.2.3
Architectural Performance Monitoring Version 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-10
18.2.3.1
AnyThread Counting and Software Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-13
18.2.4
Architectural Performance Monitoring Version 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-13
18.2.4.1
Enhancement in IA32_PERF_GLOBAL_STATUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-13
18.2.4.2
IA32_PERF_GLOBAL_STATUS_RESET and IA32_PERF_GLOBAL_STATUS_SET MSRS. . . . . . . . . . . . . . . . . . . . . . . . . .18-15
18.2.4.3
IA32_PERF_GLOBAL_INUSE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-15
18.2.5
Full-Width Writes to Performance Counter Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-17
18.3
PERFORMANCE MONITORING (INTEL® CORE™ PROCESSORS AND INTEL® XEON® PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . 18-17
18.3.1
Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name Nehalem . . . . . . . . . . . . . . . . .18-17
18.3.1.1
Enhancements of Performance Monitoring in the Processor Core. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-18
18.3.1.2
Performance Monitoring Facility in the Uncore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-25
18.3.1.3
Intel® Xeon® Processor 7500 Series Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-30
18.3.2
Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name Westmere . . . . . . . . . . . . . . .18-32
18.3.3
Intel® Xeon® Processor E7 Family Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-32
xvi Vol. 3A

CONTENTS
PAGE

18.3.4
18.3.4.1
18.3.4.2
18.3.4.3
18.3.4.4
18.3.4.5
18.3.4.6
18.3.4.7
18.3.4.8
18.3.5
18.3.5.1
18.3.6
18.3.6.1
18.3.6.2
18.3.6.3
18.3.6.4
18.3.6.5
18.3.6.6
18.3.6.7
18.3.7
18.3.8
18.3.8.1
18.3.8.2
18.4
18.4.1
18.4.1.1
18.5
18.5.1
18.5.2
18.5.2.1
18.5.2.2
18.5.2.3
18.5.3
18.5.3.1
18.5.3.2
18.5.3.3
18.5.4
18.5.4.1
18.5.4.2
18.6
18.6.1
18.6.2
18.6.2.1
18.6.2.2
18.6.2.3
18.6.2.4
18.6.3
18.6.3.1
18.6.3.2
18.6.3.3
18.6.3.4
18.6.3.5
18.6.3.6
18.6.3.7
18.6.3.8
18.6.3.9
18.6.4
18.6.4.1
18.6.4.2
18.6.4.3
18.6.4.4

Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . 18-33
Global Counter Control Facilities In Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . 18-34
Counter Coalescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-36
Full Width Writes to Performance Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-36
PEBS Support in Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-36
Off-core Response Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-40
Uncore Performance Monitoring Facilities In Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx
Processor Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-43
Intel® Xeon® Processor E5 Family Performance Monitoring Facility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-45
Intel® Xeon® Processor E5 Family Uncore Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-46
3rd Generation Intel® Core™ Processor Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-46
Intel® Xeon® Processor E5 v2 and E7 v2 Family Uncore Performance Monitoring Facility. . . . . . . . . . . . . . . . . . . . 18-46
4th Generation Intel® Core™ Processor Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-47
Processor Event Based Sampling (PEBS) Facility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-47
PEBS Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-48
PEBS Data Address Profiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-49
Off-core Response Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-50
Performance Monitoring and Intel® TSX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-52
Uncore Performance Monitoring Facilities in the 4th Generation Intel® Core™ Processors . . . . . . . . . . . . . . . . . . . . 18-54
Intel® Xeon® Processor E5 v3 Family Uncore Performance Monitoring Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-55
5th Generation Intel® Core™ Processor and Intel® Core™ M Processor Performance Monitoring Facility. . . . . . . . . . . 18-55
6th Generation Intel® Core™ Processor and 7th Generation Intel® Core™ Processor Performance Monitoring
Facility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-56
Processor Event Based Sampling (PEBS) Facility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-57
Off-core Response Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-62
PERFORMANCE MONITORING (INTEL® XEON™ PHI PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-66
Intel® Xeon Phi™ Processor 7200/5200/3200 Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-66
Enhancements of Performance Monitoring in the Intel® Xeon Phi™ processor Tile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-66
PERFORMANCE MONITORING (INTEL® ATOM™ PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-70
Performance Monitoring (45 nm and 32 nm Intel® Atom™ Processors). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-70
Performance Monitoring for Silvermont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-70
Enhancements of Performance Monitoring in the Processor Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-70
Offcore Response Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-72
Average Offcore Request Latency Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-74
Performance Monitoring for Goldmont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-75
Processor Event Based Sampling (PEBS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-76
Offcore Response Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-79
Average Offcore Request Latency Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-80
Performance Monitoring for Goldmont Plus Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-80
Extended PEBS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-81
Reduced Skid PEBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-83
PERFORMANCE MONITORING (LEGACY INTEL PROCESSORS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-83
Performance Monitoring (Intel® Core™ Solo and Intel® Core™ Duo Processors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-83
Performance Monitoring (Processors Based on Intel® Core™ Microarchitecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-84
Fixed-function Performance Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-85
Global Counter Control Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-86
At-Retirement Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-87
Processor Event Based Sampling (PEBS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-88
Performance Monitoring (Processors Based on Intel NetBurst® Microarchitecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-90
ESCR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-93
Performance Counters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-94
CCCR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-95
Debug Store (DS) Mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-97
Programming the Performance Counters for Non-Retirement Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-97
At-Retirement Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-103
Tagging Mechanism for Replay_event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-105
Processor Event-Based Sampling (PEBS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-105
Operating System Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-106
Performance Monitoring and Intel Hyper-Threading Technology in Processors Based on Intel NetBurst®
Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-107
ESCR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-107
CCCR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-108
IA32_PEBS_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-109
Performance Monitoring Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-110

Vol. 3A xvii

CONTENTS
PAGE

18.6.4.5
18.6.5
18.6.6
18.6.7
18.6.7.1
18.6.7.2
18.6.7.3
18.6.7.4
18.6.7.5
18.6.8
18.6.8.1
18.6.8.2
18.6.8.3
18.6.8.4
18.6.8.5
18.6.9
18.6.9.1
18.6.9.2
18.6.9.3
18.7
18.7.1
18.7.2
18.7.3
18.7.3.1
18.7.3.2
18.7.3.3
18.7.3.4
18.8
18.8.1

Counting Clocks on systems with Intel Hyper-Threading Technology in Processors Based on Intel NetBurst®
Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-111
Performance Monitoring and Dual-Core Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-112
Performance Monitoring on 64-bit Intel Xeon Processor MP with Up to 8-MByte L3 Cache. . . . . . . . . . . . . . . . . . . . . . 18-112
Performance Monitoring on L3 and Caching Bus Controller Sub-Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-114
Overview of Performance Monitoring with L3/Caching Bus Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-116
GBSQ Event Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-117
GSNPQ Event Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-118
FSB Event Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-119
Common Event Control Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-120
Performance Monitoring (P6 Family Processor) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-120
PerfEvtSel0 and PerfEvtSel1 MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-121
PerfCtr0 and PerfCtr1 MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-122
Starting and Stopping the Performance-Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-122
Event and Time-Stamp Monitoring Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-122
Monitoring Counter Overflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-123
Performance Monitoring (Pentium Processors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-123
Control and Event Select Register (CESR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-124
Use of the Performance-Monitoring Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-124
Events Counted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-125
COUNTING CLOCKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-125
Non-Halted Reference Clockticks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-126
Cycle Counting and Opportunistic Processor Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-126
Determining the Processor Base Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-127
For Intel® Processors Based on Microarchitecture Code Name Sandy Bridge, Ivy Bridge, Haswell and Broadwell18-127
For Intel® Processors Based on Microarchitecture Code Name Nehalem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-127
For Intel® Atom™ Processors Based on the Silvermont Microarchitecture (Including Intel Processors Based on
Airmont Microarchitecture). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-127
For Intel® Core™ 2 Processor Family and for Intel® Xeon® Processors Based on Intel Core Microarchitecture . . . 18-128
IA32_PERF_CAPABILITIES MSR ENUMERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-129
Filtering of SMM Handler Overhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-129

CHAPTER 19
PERFORMANCE MONITORING EVENTS
19.1
19.2
19.3

ARCHITECTURAL PERFORMANCE MONITORING EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2
PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR SCALABLE FAMILY . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-3
PERFORMANCE MONITORING EVENTS FOR 6TH GENERATION INTEL® CORE™ PROCESSOR AND 7TH GENERATION INTEL® CORE™
PROCESSOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-23
19.4
PERFORMANCE MONITORING EVENTS FOR INTEL® XEON PHI™ PROCESSOR 3200, 5200, 7200 SERIES . . . . . . . . . . . . . . 19-33
19.5
PERFORMANCE MONITORING EVENTS FOR THE INTEL® CORE™ M AND 5TH GENERATION INTEL® CORE™
PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-38
19.6
PERFORMANCE MONITORING EVENTS FOR THE 4TH GENERATION INTEL® CORE™ PROCESSORS . . . . . . . . . . . . . . . . . . 19-46
19.6.1
Performance Monitoring Events in the Processor Core of Intel Xeon Processor E5 v3 Family. . . . . . . . . . . . . . . . . . . . . .19-57
19.7
PERFORMANCE MONITORING EVENTS FOR 3RD GENERATION INTEL® CORE™ PROCESSORS. . . . . . . . . . . . . . . . . . . . . . . 19-58
19.7.1
Performance Monitoring Events in the Processor Core of Intel Xeon Processor E5 v2 Family and Intel Xeon Processor
E7 v2 Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-66
19.8
PERFORMANCE MONITORING EVENTS FOR 2ND GENERATION INTEL® CORE™ I7-2XXX, INTEL® CORE™ I5-2XXX,
INTEL® CORE™ I3-2XXX PROCESSOR SERIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-67
19.9
PERFORMANCE MONITORING EVENTS FOR INTEL® CORE™ I7 PROCESSOR FAMILY AND INTEL® XEON® PROCESSOR
FAMILY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-81
19.10 PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE NAME
WESTMERE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-109
19.11 PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR 5200, 5400 SERIES AND INTEL® CORE™2
EXTREME PROCESSORS QX 9000 SERIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-141
19.12 PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR 3000, 3200, 5100, 5300 SERIES AND
INTEL® CORE™2 DUO PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-141
19.13 PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON THE GOLDMONT PLUS MICROARCHITECTURE . 19-167
19.14 PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON THE GOLDMONT MICROARCHITECTURE . . . . . . . 19-168
19.15 PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON THE SILVERMONT MICROARCHITECTURE. . . . . . 19-175
19.15.1
Performance Monitoring Events for Processors Based on the Airmont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . 19-180
19.16 PERFORMANCE MONITORING EVENTS FOR 45 NM AND 32 NM INTEL® ATOM™ PROCESSORS . . . . . . . . . . . . . . . . . . . . 19-180
19.17 PERFORMANCE MONITORING EVENTS FOR INTEL® CORE™ SOLO AND INTEL® CORE™ DUO PROCESSORS . . . . . . . 19-194
19.18 PENTIUM® 4 AND INTEL® XEON® PROCESSOR PERFORMANCE MONITORING EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-199
19.19 PERFORMANCE MONITORING EVENTS FOR INTEL® PENTIUM® M PROCESSORS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-228
xviii Vol. 3A

CONTENTS
PAGE

19.20
19.21

P6 FAMILY PROCESSOR PERFORMANCE MONITORING EVENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-230
PENTIUM PROCESSOR PERFORMANCE MONITORING EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-239

CHAPTER 20
8086 EMULATION
20.1
20.1.1
20.1.2
20.1.3
20.1.4
20.2
20.2.1
20.2.2
20.2.3
20.2.4
20.2.5
20.2.6
20.2.7
20.2.8
20.2.8.1
20.2.8.2
20.2.8.3
20.3
20.3.1
20.3.1.1
20.3.1.2
20.3.1.3
20.3.2
20.3.3
20.3.3.1
20.3.3.2
20.3.3.3
20.3.3.4
20.3.3.5
20.4

REAL-ADDRESS MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-1
Address Translation in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-2
Registers Supported in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-3
Instructions Supported in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-3
Interrupt and Exception Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-4
VIRTUAL-8086 MODE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-5
Enabling Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-6
Structure of a Virtual-8086 Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-7
Paging of Virtual-8086 Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-7
Protection within a Virtual-8086 Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-8
Entering Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-8
Leaving Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-9
Sensitive Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-10
Virtual-8086 Mode I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-10
I/O-Port-Mapped I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-11
Memory-Mapped I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-11
Special I/O Buffers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-11
INTERRUPT AND EXCEPTION HANDLING IN VIRTUAL-8086 MODE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-11
Class 1—Hardware Interrupt and Exception Handling in Virtual-8086 Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-12
Handling an Interrupt or Exception Through a Protected-Mode Trap or Interrupt Gate. . . . . . . . . . . . . . . . . . . . . . . . . 20-12
Handling an Interrupt or Exception With an 8086 Program Interrupt or Exception Handler . . . . . . . . . . . . . . . . . . . . 20-14
Handling an Interrupt or Exception Through a Task Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-14
Class 2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the Virtual Interrupt Mechanism . . . . . 20-15
Class 3—Software Interrupt Handling in Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-16
Method 1: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-18
Methods 2 and 3: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-18
Method 4: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-19
Method 5: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-19
Method 6: Software Interrupt Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-19
PROTECTED-MODE VIRTUAL INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-20

CHAPTER 21
MIXING 16-BIT AND 32-BIT CODE
21.1
21.2
21.3
21.4
21.4.1
21.4.2
21.4.2.1
21.4.2.2
21.4.3
21.4.4
21.4.5

DEFINING 16-BIT AND 32-BIT PROGRAM MODULES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1
MIXING 16-BIT AND 32-BIT OPERATIONS WITHIN A CODE SEGMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-2
SHARING DATA AMONG MIXED-SIZE CODE SEGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-3
TRANSFERRING CONTROL AMONG MIXED-SIZE CODE SEGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-3
Code-Segment Pointer Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-4
Stack Management for Control Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-4
Controlling the Operand-Size Attribute For a Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-5
Passing Parameters With a Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6
Interrupt Control Transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6
Parameter Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6
Writing Interface Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-6

CHAPTER 22
ARCHITECTURE COMPATIBILITY
22.1
22.2
22.3
22.4
22.5
22.6
22.7
22.8
22.9

PROCESSOR FAMILIES AND CATEGORIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-1
RESERVED BITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2
ENABLING NEW FUNCTIONS AND MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2
DETECTING THE PRESENCE OF NEW FEATURES THROUGH SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2
INTEL MMX TECHNOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-2
STREAMING SIMD EXTENSIONS (SSE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
STREAMING SIMD EXTENSIONS 2 (SSE2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
STREAMING SIMD EXTENSIONS 3 (SSE3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
ADDITIONAL STREAMING SIMD EXTENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3

Vol. 3A xix

CONTENTS
PAGE

22.10 INTEL HYPER-THREADING TECHNOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-3
22.11 MULTI-CORE TECHNOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
22.12 SPECIFIC FEATURES OF DUAL-CORE PROCESSOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
22.13 NEW INSTRUCTIONS IN THE PENTIUM AND LATER IA-32 PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
22.13.1
Instructions Added Prior to the Pentium Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
22.14 OBSOLETE INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5
22.15 UNDEFINED OPCODES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-5
22.16 NEW FLAGS IN THE EFLAGS REGISTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6
22.16.1
Using EFLAGS Flags to Distinguish Between 32-Bit IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-6
22.17 STACK OPERATIONS AND USER SOFTWARE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
22.17.1
PUSH SP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
22.17.2
EFLAGS Pushed on the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
22.18 X87 FPU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
22.18.1
Control Register CR0 Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-7
22.18.2
x87 FPU Status Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.2.1
Condition Code Flags (C0 through C3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.2.2
Stack Fault Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.3
x87 FPU Control Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-8
22.18.4
x87 FPU Tag Word. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.5
Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.5.1
NaNs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.5.2
Pseudo-zero, Pseudo-NaN, Pseudo-infinity, and Unnormal Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.6
Floating-Point Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-9
22.18.6.1
Denormal Operand Exception (#D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-10
22.18.6.2
Numeric Overflow Exception (#O) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-10
22.18.6.3
Numeric Underflow Exception (#U) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-10
22.18.6.4
Exception Precedence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-10
22.18.6.5
CS and EIP For FPU Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-10
22.18.6.6
FPU Error Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-11
22.18.6.7
Assertion of the FERR# Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-11
22.18.6.8
Invalid Operation Exception On Denormals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-11
22.18.6.9
Alignment Check Exceptions (#AC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-11
22.18.6.10
Segment Not Present Exception During FLDENV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-11
22.18.6.11
Device Not Available Exception (#NM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.6.12
Coprocessor Segment Overrun Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.6.13
General Protection Exception (#GP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.6.14
Floating-Point Error Exception (#MF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.7
Changes to Floating-Point Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.7.1
FDIV, FPREM, and FSQRT Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.7.2
FSCALE Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.7.3
FPREM1 Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-12
22.18.7.4
FPREM Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.5
FUCOM, FUCOMP, and FUCOMPP Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.6
FPTAN Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.7
Stack Overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.8
FSIN, FCOS, and FSINCOS Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.9
FPATAN Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.10
F2XM1 Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.11
FLD Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-13
22.18.7.12
FXTRACT Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-14
22.18.7.13
Load Constant Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-14
22.18.7.14
FXAM Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-14
22.18.7.15
FSAVE and FSTENV Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-14
22.18.8
Transcendental Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-14
22.18.9
Obsolete Instructions and Undefined Opcodes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-15
22.18.10 WAIT/FWAIT Prefix Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-15
22.18.11 Operands Split Across Segments and/or Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-15
22.18.12 FPU Instruction Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-15
22.19 SERIALIZING INSTRUCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-16
22.20 FPU AND MATH COPROCESSOR INITIALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-16
22.20.1
Intel® 387 and Intel® 287 Math Coprocessor Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-16
22.20.2
Intel486 SX Processor and Intel 487 SX Math Coprocessor Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-16
22.21 CONTROL REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-17
22.22 MEMORY MANAGEMENT FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.22.1
New Memory Management Control Flags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-19
xx Vol. 3A

CONTENTS
PAGE

22.22.1.1
Physical Memory Addressing Extension. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.22.1.2
Global Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.22.1.3
Larger Page Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.22.2
CD and NW Cache Control Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.22.3
Descriptor Types and Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-19
22.22.4
Changes in Segment Descriptor Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20
22.23 DEBUG FACILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20
22.23.1
Differences in Debug Register DR6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20
22.23.2
Differences in Debug Register DR7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20
22.23.3
Debug Registers DR4 and DR5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20
22.24 RECOGNITION OF BREAKPOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-20
22.25 EXCEPTIONS AND/OR EXCEPTION CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-21
22.25.1
Machine-Check Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-22
22.25.2
Priority of Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-22
22.25.3
Exception Conditions of Legacy SIMD Instructions Operating on MMX Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-22
22.26 INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27
22.26.1
Interrupt Propagation Delay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27
22.26.2
NMI Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27
22.26.3
IDT Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27
22.27 ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-27
22.27.1
Software Visible Differences Between the Local APIC and the 82489DX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-28
22.27.2
New Features Incorporated in the Local APIC for the P6 Family and Pentium Processors . . . . . . . . . . . . . . . . . . . . . . . . . 22-28
22.27.3
New Features Incorporated in the Local APIC of the Pentium 4 and Intel Xeon Processors. . . . . . . . . . . . . . . . . . . . . . . . 22-28
22.28 TASK SWITCHING AND TSS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-28
22.28.1
P6 Family and Pentium Processor TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29
22.28.2
TSS Selector Writes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29
22.28.3
Order of Reads/Writes to the TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29
22.28.4
Using A 16-Bit TSS with 32-Bit Constructs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29
22.28.5
Differences in I/O Map Base Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-29
22.29 CACHE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-30
22.29.1
Self-Modifying Code with Cache Enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-30
22.29.2
Disabling the L3 Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-31
22.30 PAGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-31
22.30.1
Large Pages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-31
22.30.2
PCD and PWT Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-31
22.30.3
Enabling and Disabling Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-32
22.31 STACK OPERATIONS AND SUPERVISOR SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-32
22.31.1
Selector Pushes and Pops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-32
22.31.2
Error Code Pushes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-32
22.31.3
Fault Handling Effects on the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-33
22.31.4
Interlevel RET/IRET From a 16-Bit Interrupt or Call Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-33
22.32
MIXING 16- AND 32-BIT SEGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-33
22.33
SEGMENT AND ADDRESS WRAPAROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-33
22.33.1
Segment Wraparound. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-34
22.34
STORE BUFFERS AND MEMORY ORDERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-34
22.35
BUS LOCKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-35
22.36
BUS HOLD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-35
22.37
MODEL-SPECIFIC EXTENSIONS TO THE IA-32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-35
22.37.1
Model-Specific Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-36
22.37.2
RDMSR and WRMSR Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-36
22.37.3
Memory Type Range Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-36
22.37.4
Machine-Check Exception and Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-36
22.37.5
Performance-Monitoring Counters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-37
22.38 TWO WAYS TO RUN INTEL 286 PROCESSOR TASKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-37
22.39 INITIAL STATE OF PENTIUM, PENTIUM PRO AND PENTIUM 4 PROCESSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-37

CHAPTER 23
INTRODUCTION TO VIRTUAL MACHINE EXTENSIONS
23.1
23.2
23.3
23.4
23.5
23.6

OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1
VIRTUAL MACHINE ARCHITECTURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1
INTRODUCTION TO VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-1
LIFE CYCLE OF VMM SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2
VIRTUAL-MACHINE CONTROL STRUCTURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2
DISCOVERING SUPPORT FOR VMX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2
Vol. 3A xxi

CONTENTS
PAGE

23.7
23.8

ENABLING AND ENTERING VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-3
RESTRICTIONS ON VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-3

CHAPTER 24
VIRTUAL MACHINE CONTROL STRUCTURES
24.1
24.2
24.3
24.4
24.4.1
24.4.2
24.5
24.6
24.6.1
24.6.2
24.6.3
24.6.4
24.6.5
24.6.6
24.6.7
24.6.8
24.6.9
24.6.10
24.6.11
24.6.12
24.6.13
24.6.14
24.6.15
24.6.16
24.6.17
24.6.18
24.6.19
24.7
24.7.1
24.7.2
24.8
24.8.1
24.8.2
24.8.3
24.9
24.9.1
24.9.2
24.9.3
24.9.4
24.9.5
24.10
24.11
24.11.1
24.11.2
24.11.3
24.11.4
24.11.5

OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-1
FORMAT OF THE VMCS REGION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-2
ORGANIZATION OF VMCS DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-3
GUEST-STATE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-4
Guest Register State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-4
Guest Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-5
HOST-STATE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-8
VM-EXECUTION CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-8
Pin-Based VM-Execution Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-8
Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-9
Exception Bitmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-12
I/O-Bitmap Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-12
Time-Stamp Counter Offset and Multiplier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-12
Guest/Host Masks and Read Shadows for CR0 and CR4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-12
CR3-Target Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-13
Controls for APIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-13
MSR-Bitmap Address. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-14
Executive-VMCS Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-14
Extended-Page-Table Pointer (EPTP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-15
Virtual-Processor Identifier (VPID) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-15
Controls for PAUSE-Loop Exiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-15
VM-Function Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-16
VMCS Shadowing Bitmap Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-16
ENCLS-Exiting Bitmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-16
Control Field for Page-Modification Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-16
Controls for Virtualization Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-16
XSS-Exiting Bitmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-17
VM-EXIT CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-17
VM-Exit Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-17
VM-Exit Controls for MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-18
VM-ENTRY CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-18
VM-Entry Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-19
VM-Entry Controls for MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-19
VM-Entry Controls for Event Injection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-20
VM-EXIT INFORMATION FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-21
Basic VM-Exit Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-21
Information for VM Exits Due to Vectored Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-22
Information for VM Exits That Occur During Event Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-22
Information for VM Exits Due to Instruction Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-23
VM-Instruction Error Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-23
VMCS TYPES: ORDINARY AND SHADOW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-24
SOFTWARE USE OF THE VMCS AND RELATED STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-24
Software Use of Virtual-Machine Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-24
VMREAD, VMWRITE, and Encodings of VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-25
Initializing a VMCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-27
Software Access to Related Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-27
VMXON Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-27

CHAPTER 25
VMX NON-ROOT OPERATION
25.1
25.1.1
25.1.2
25.1.3
25.2
25.3
25.4

INSTRUCTIONS THAT CAUSE VM EXITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-1
Relative Priority of Faults and VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-1
Instructions That Cause VM Exits Unconditionally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2
Instructions That Cause VM Exits Conditionally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-2
OTHER CAUSES OF VM EXITS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-5
CHANGES TO INSTRUCTION BEHAVIOR IN VMX NON-ROOT OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-6
OTHER CHANGES IN VMX NON-ROOT OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-10

xxii Vol. 3A

CONTENTS
PAGE

25.4.1
Event Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-10
25.4.2
Treatment of Task Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-10
25.5
FEATURES SPECIFIC TO VMX NON-ROOT OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-11
25.5.1
VMX-Preemption Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-11
25.5.2
Monitor Trap Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-12
25.5.3
Translation of Guest-Physical Addresses Using EPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-13
25.5.4
APIC Virtualization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-13
25.5.5
VM Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-13
25.5.5.1
Enabling VM Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-13
25.5.5.2
General Operation of the VMFUNC Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-13
25.5.5.3
EPTP Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-14
25.5.6
Virtualization Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-15
25.5.6.1
Convertible EPT Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-15
25.5.6.2
Virtualization-Exception Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-16
25.5.6.3
Delivery of Virtualization Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-16
25.6
UNRESTRICTED GUESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-17

CHAPTER 26
VM ENTRIES
26.1
26.2
26.2.1
26.2.1.1
26.2.1.2
26.2.1.3
26.2.2
26.2.3
26.2.4
26.3
26.3.1
26.3.1.1
26.3.1.2
26.3.1.3
26.3.1.4
26.3.1.5
26.3.1.6
26.3.2
26.3.2.1
26.3.2.2
26.3.2.3
26.3.2.4
26.3.2.5
26.3.3
26.4
26.5
26.5.1
26.5.1.1
26.5.1.2
26.5.1.3
26.5.2
26.6
26.6.1
26.6.2
26.6.3
26.6.4
26.6.5
26.6.6
26.6.7
26.6.8
26.6.9
26.7
26.8

BASIC VM-ENTRY CHECKS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
CHECKS ON VMX CONTROLS AND HOST-STATE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
Checks on VMX Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
VM-Execution Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-2
VM-Exit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-5
VM-Entry Control Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-6
Checks on Host Control Registers and MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-6
Checks on Host Segment and Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-7
Checks Related to Address-Space Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-7
CHECKING AND LOADING GUEST STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-8
Checks on the Guest State Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-8
Checks on Guest Control Registers, Debug Registers, and MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-8
Checks on Guest Segment Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-9
Checks on Guest Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-11
Checks on Guest RIP and RFLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-11
Checks on Guest Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-12
Checks on Guest Page-Directory-Pointer-Table Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-14
Loading Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-14
Loading Guest Control Registers, Debug Registers, and MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-15
Loading Guest Segment Registers and Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-16
Loading Guest RIP, RSP, and RFLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-16
Loading Page-Directory-Pointer-Table Entries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-17
Updating Non-Register State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-17
Clearing Address-Range Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-17
LOADING MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-17
EVENT INJECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-18
Vectored-Event Injection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-18
Details of Vectored-Event Injection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-19
VM Exits During Event Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-20
Event Injection for VM Entries to Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-20
Injection of Pending MTF VM Exits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-21
SPECIAL FEATURES OF VM ENTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-21
Interruptibility State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-21
Activity State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-22
Delivery of Pending Debug Exceptions after VM Entry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-22
VMX-Preemption Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-23
Interrupt-Window Exiting and Virtual-Interrupt Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-23
NMI-Window Exiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-24
VM Exits Induced by the TPR Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-24
Pending MTF VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-24
VM Entries and Advanced Debugging Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-24
VM-ENTRY FAILURES DURING OR AFTER LOADING GUEST STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-25
MACHINE-CHECK EVENTS DURING VM ENTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26-25

Vol. 3A xxiii

CONTENTS
PAGE

CHAPTER 27
VM EXITS
27.1
27.2
27.2.1
27.2.2
27.2.3
27.2.4
27.3
27.3.1
27.3.2
27.3.3
27.3.4
27.4
27.5
27.5.1
27.5.2
27.5.3
27.5.4
27.5.5
27.5.6
27.6
27.7
27.8

ARCHITECTURAL STATE BEFORE A VM EXIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-1
RECORDING VM-EXIT INFORMATION AND UPDATING VM-ENTRY CONTROL FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-4
Basic VM-Exit Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-4
Information for VM Exits Due to Vectored Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-11
Information for VM Exits During Event Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-12
Information for VM Exits Due to Instruction Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-13
SAVING GUEST STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-20
Saving Control Registers, Debug Registers, and MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-21
Saving Segment Registers and Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-21
Saving RIP, RSP, and RFLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-21
Saving Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-23
SAVING MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-25
LOADING HOST STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-25
Loading Host Control Registers, Debug Registers, MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-25
Loading Host Segment and Descriptor-Table Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-26
Loading Host RIP, RSP, and RFLAGS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-28
Checking and Loading Host Page-Directory-Pointer-Table Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-28
Updating Non-Register State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-28
Clearing Address-Range Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27-29
LOADING MSRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-29
VMX ABORTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-29
MACHINE-CHECK EVENTS DURING VM EXIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-30

CHAPTER 28
VMX SUPPORT FOR ADDRESS TRANSLATION

28.1
VIRTUAL PROCESSOR IDENTIFIERS (VPIDS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-1
28.2
THE EXTENDED PAGE TABLE MECHANISM (EPT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-1
28.2.1
EPT Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-1
28.2.2
EPT Translation Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-3
28.2.3
EPT-Induced VM Exits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-9
28.2.3.1
EPT Misconfigurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-10
28.2.3.2
EPT Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-10
28.2.3.3
Prioritization of EPT Misconfigurations and EPT Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-12
28.2.4
Accessed and Dirty Flags for EPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-13
28.2.5
Page-Modification Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-14
28.2.6
EPT and Memory Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-14
28.2.6.1
Memory Type Used for Accessing EPT Paging Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-14
28.2.6.2
Memory Type Used for Translated Guest-Physical Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-15
28.3
CACHING TRANSLATION INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-15
28.3.1
Information That May Be Cached . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-15
28.3.2
Creating and Using Cached Translation Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-16
28.3.3
Invalidating Cached Translation Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-17
28.3.3.1
Operations that Invalidate Cached Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-17
28.3.3.2
Operations that Need Not Invalidate Cached Mappings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-19
28.3.3.3
Guidelines for Use of the INVVPID Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-19
28.3.3.4
Guidelines for Use of the INVEPT Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28-20

CHAPTER 29
APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS
29.1
29.1.1
29.1.2
29.1.3
29.1.4
29.1.5
29.2
29.2.1
29.2.2
29.3
29.4

VIRTUAL APIC STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-1
Virtualized APIC Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-1
TPR Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-2
PPR Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-2
EOI Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
Self-IPI Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
EVALUATION AND DELIVERY OF VIRTUAL INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
Evaluation of Pending Virtual Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-3
Virtual-Interrupt Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-4
VIRTUALIZING CR8-BASED TPR ACCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-5
VIRTUALIZING MEMORY-MAPPED APIC ACCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-5

xxiv Vol. 3A

CONTENTS
PAGE

29.4.1
Priority of APIC-Access VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-6
29.4.2
Virtualizing Reads from the APIC-Access Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-6
29.4.3
Virtualizing Writes to the APIC-Access Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-7
29.4.3.1
Determining Whether a Write Access is Virtualized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-7
29.4.3.2
APIC-Write Emulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-8
29.4.3.3
APIC-Write VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-9
29.4.4
Instruction-Specific Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-9
29.4.5
Issues Pertaining to Page Size and TLB Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-10
29.4.6
APIC Accesses Not Directly Resulting From Linear Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-10
29.4.6.1
Guest-Physical Accesses to the APIC-Access Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-11
29.4.6.2
Physical Accesses to the APIC-Access Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-11
29.5
VIRTUALIZING MSR-BASED APIC ACCESSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-12
29.6
POSTED-INTERRUPT PROCESSING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-13

CHAPTER 30
VMX INSTRUCTION REFERENCE
30.1
30.2
30.3

30.4

OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-1
CONVENTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2
VMX INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-2
INVEPT— Invalidate Translations Derived from EPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-3
INVVPID— Invalidate Translations Based on VPID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-6
VMCALL—Call to VM Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-9
VMCLEAR—Clear Virtual-Machine Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-11
VMFUNC—Invoke VM function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-13
VMLAUNCH/VMRESUME—Launch/Resume Virtual Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-14
VMPTRLD—Load Pointer to Virtual-Machine Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-16
VMPTRST—Store Pointer to Virtual-Machine Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-18
VMREAD—Read Field from Virtual-Machine Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-20
VMRESUME—Resume Virtual Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-22
VMWRITE—Write Field to Virtual-Machine Control Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-23
VMXOFF—Leave VMX Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-25
VMXON—Enter VMX Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-27
VM INSTRUCTION ERROR NUMBERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-29

CHAPTER 31
VIRTUAL-MACHINE MONITOR PROGRAMMING CONSIDERATIONS
31.1
31.2
31.2.1
31.3
31.4
31.5
31.5.1
31.6
31.7
31.7.1
31.7.1.1
31.7.1.2
31.8
31.8.1
31.8.2
31.8.3
31.8.4
31.8.5
31.9
31.9.1
31.9.2
31.9.2.1
31.9.2.2
31.9.3
31.9.4

VMX SYSTEM PROGRAMMING OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-1
SUPPORTING PROCESSOR OPERATING MODES IN GUEST ENVIRONMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-1
Using Unrestricted Guest Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-1
MANAGING VMCS REGIONS AND POINTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-2
USING VMX INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-2
VMM SETUP & TEAR DOWN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-4
Algorithms for Determining VMX Capabilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-5
PREPARATION AND LAUNCHING A VIRTUAL MACHINE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-6
HANDLING OF VM EXITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-7
Handling VM Exits Due to Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-8
Reflecting Exceptions to Guest Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-8
Resuming Guest Software after Handling an Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-9
MULTI-PROCESSOR CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-10
Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-11
Moving a VMCS Between Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-11
Paired Index-Data Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-11
External Data Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-11
CPUID Emulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-12
32-BIT AND 64-BIT GUEST ENVIRONMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-12
Operating Modes of Guest Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-12
Handling Widths of VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-12
Natural-Width VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-13
64-Bit VMCS Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-13
IA-32e Mode Hosts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-13
IA-32e Mode Guests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-13
Vol. 3A xxv

CONTENTS
PAGE

31.9.5
32-Bit Guests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-14
31.10 HANDLING MODEL SPECIFIC REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-14
31.10.1
Using VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-14
31.10.2
Using VM-Exit Controls for MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-15
31.10.3
Using VM-Entry Controls for MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-15
31.10.4
Handling Special-Case MSRs and Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-15
31.10.4.1
Handling IA32_EFER MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.2
Handling the SYSENTER and SYSEXIT Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.3
Handling the SYSCALL and SYSRET Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.4
Handling the SWAPGS Instruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.4.5
Implementation Specific Behavior on Writing to Certain MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-16
31.10.5
Handling Accesses to Reserved MSR Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31-17
31.11 HANDLING ACCESSES TO CONTROL REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-17
31.12 PERFORMANCE CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-17
31.13 USE OF THE VMX-PREEMPTION TIMER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-17

CHAPTER 32
VIRTUALIZATION OF SYSTEM RESOURCES
32.1
32.2
32.2.1
32.3
32.3.1
32.3.2
32.3.3
32.3.4
32.3.5
32.3.5.1
32.3.5.2
32.3.5.3
32.3.5.4
32.4
32.4.1
32.4.2

OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1
VIRTUALIZATION SUPPORT FOR DEBUGGING FACILITIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1
Debug Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-1
MEMORY VIRTUALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-2
Processor Operating Modes & Memory Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-2
Guest & Host Physical Address Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-2
Virtualizing Virtual Memory by Brute Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-3
Alternate Approach to Memory Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-3
Details of Virtual TLB Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-4
Initialization of Virtual TLB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-5
Response to Page Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-5
Response to Uses of INVLPG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-7
Response to CR3 Writes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8
MICROCODE UPDATE FACILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8
Early Load of Microcode Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8
Late Load of Microcode Updates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-8

CHAPTER 33
HANDLING BOUNDARY CONDITIONS IN A VIRTUAL MACHINE MONITOR
33.1
33.2
33.3
33.3.1
33.3.2
33.3.2.1
33.3.2.2
33.3.2.3
33.3.2.4
33.3.2.5
33.3.3
33.3.3.1
33.3.3.2
33.3.3.3
33.3.3.4
33.4
33.4.1
33.4.2
33.4.3
33.4.3.1
33.4.3.2
33.4.3.3
33.4.3.4
33.4.3.5
33.5

OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1
INTERRUPT HANDLING IN VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-1
EXTERNAL INTERRUPT VIRTUALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-2
Virtualization of Interrupt Vector Space. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-3
Control of Platform Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-4
PIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-4
xAPIC Virtualization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-5
Local APIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-5
I/O APIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Virtualization of Message Signaled Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Examples of Handling of External Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Guest Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Processor Treatment of External Interrupt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-6
Processing of External Interrupts by VMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-7
Generation of Virtual Interrupt Events by VMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-7
ERROR HANDLING BY VMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-8
VM-Exit Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-8
Machine-Check Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-8
MCA Error Handling Guidelines for VMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-9
VMM Error Handling Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33-10
Basic VMM MCA error recovery handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33-10
Implementation Considerations for the Basic Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33-10
MCA Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33-10
Implementation Considerations for the MCA Virtualization Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33-11
HANDLING ACTIVITY STATES BY VMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-11

xxvi Vol. 3A

CONTENTS
PAGE

CHAPTER 34
SYSTEM MANAGEMENT MODE

34.1
SYSTEM MANAGEMENT MODE OVERVIEW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1
34.1.1
System Management Mode and VMX Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-1
34.2
SYSTEM MANAGEMENT INTERRUPT (SMI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-2
34.3
SWITCHING BETWEEN SMM AND THE OTHER PROCESSOR OPERATING MODES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-2
34.3.1
Entering SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-2
34.3.2
Exiting From SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-3
34.4
SMRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-3
34.4.1
SMRAM State Save Map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-4
34.4.1.1
SMRAM State Save Map and Intel 64 Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-6
34.4.2
SMRAM Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-8
34.4.2.1
System Management Range Registers (SMRR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
34.5
SMI HANDLER EXECUTION ENVIRONMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
34.5.1
Initial SMM Execution Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
34.5.2
SMI Handler Operating Mode Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-10
34.6
EXCEPTIONS AND INTERRUPTS WITHIN SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-10
34.7
MANAGING SYNCHRONOUS AND ASYNCHRONOUS SYSTEM MANAGEMENT INTERRUPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-11
34.7.1
I/O State Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-12
34.8
NMI HANDLING WHILE IN SMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
34.9
SMM REVISION IDENTIFIER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
34.10 AUTO HALT RESTART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
34.10.1
Executing the HLT Instruction in SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-14
34.11 SMBASE RELOCATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-14
34.12 I/O INSTRUCTION RESTART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-15
34.12.1
Back-to-Back SMI Interrupts When I/O Instruction Restart Is Being Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-16
34.13 SMM MULTIPLE-PROCESSOR CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-16
34.14 DEFAULT TREATMENT OF SMIS AND SMM WITH VMX OPERATION AND SMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . 34-16
34.14.1
Default Treatment of SMI Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-16
34.14.2
Default Treatment of RSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-17
34.14.3
Protection of CR4.VMXE in SMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-18
34.14.4
VMXOFF and SMI Unblocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-18
34.15 DUAL-MONITOR TREATMENT OF SMIs AND SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-19
34.15.1
Dual-Monitor Treatment Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-19
34.15.2
SMM VM Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-19
34.15.2.1
Architectural State Before a VM Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-20
34.15.2.2
Updating the Current-VMCS and Executive-VMCS Pointers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-20
34.15.2.3
Recording VM-Exit Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-20
34.15.2.4
Saving Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-21
34.15.2.5
Updating Non-Register State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-21
34.15.3
Operation of the SMM-Transfer Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-21
34.15.4
VM Entries that Return from SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-22
34.15.4.1
Checks on the Executive-VMCS Pointer Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-22
34.15.4.2
Checks on VM-Execution Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-22
34.15.4.3
Checks on VM-Entry Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-22
34.15.4.4
Checks on the Guest State Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-23
34.15.4.5
Loading Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-23
34.15.4.6
VMX-Preemption Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-23
34.15.4.7
Updating the Current-VMCS and SMM-Transfer VMCS Pointers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-23
34.15.4.8
VM Exits Induced by VM Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-24
34.15.4.9
SMI Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-24
34.15.4.10
Failures of VM Entries That Return from SMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-24
34.15.5
Enabling the Dual-Monitor Treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-24
34.15.6
Activating the Dual-Monitor Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-26
34.15.6.1
Initial Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-26
34.15.6.2
Updating the Current-VMCS and Executive-VMCS Pointers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-27
34.15.6.3
Saving Guest State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-27
34.15.6.4
Saving MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-27
34.15.6.5
Loading Host State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-27
34.15.6.6
Loading MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-28
34.15.7
Deactivating the Dual-Monitor Treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-29
34.16 SMI AND PROCESSOR EXTENDED STATE MANAGEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-29
34.17 MODEL-SPECIFIC SYSTEM MANAGEMENT ENHANCEMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-29
34.17.1
SMM Handler Code Access Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-29
Vol. 3A xxvii

CONTENTS
PAGE

34.17.2
34.17.3

SMI Delivery Delay Reporting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-30
Blocked SMI Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-30

CHAPTER 35
INTEL® PROCESSOR TRACE

35.1
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1
35.1.1
Features and Capabilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1
35.1.1.1
Packet Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-1
35.2
INTEL® PROCESSOR TRACE OPERATIONAL MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2
35.2.1
Change of Flow Instruction (COFI) Tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2
35.2.1.1
Direct Transfer COFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-3
35.2.1.2
Indirect Transfer COFI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-3
35.2.1.3
Far Transfer COFI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4
35.2.2
Software Trace Instrumentation with PTWRITE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4
35.2.3
Power Event Tracing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4
35.2.4
Trace Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4
35.2.4.1
Filtering by Current Privilege Level (CPL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-4
35.2.4.2
Filtering by CR3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-5
35.2.4.3
Filtering by IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-5
35.2.5
Packet Generation Enable Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-6
35.2.5.1
Packet Enable (PacketEn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-7
35.2.5.2
Trigger Enable (TriggerEn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-7
35.2.5.3
Context Enable (ContextEn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-7
35.2.5.4
Branch Enable (BranchEn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-7
35.2.5.5
Filter Enable (FilterEn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-8
35.2.6
Trace Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-8
35.2.6.1
Single Range Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-8
35.2.6.2
Table of Physical Addresses (ToPA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-9
Single Output Region ToPA Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-11
ToPA Table Entry Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-11
ToPA STOP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-12
ToPA PMI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-12
ToPA PMI and Single Output Region ToPA Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-13
ToPA PMI and XSAVES/XRSTORS State Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-13
ToPA Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-14
35.2.6.3
Trace Transport Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-15
35.2.6.4
Restricted Memory Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-15
Modifications to Restricted Memory Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-15
35.2.7
Enabling and Configuration MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-15
35.2.7.1
General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-15
35.2.7.2
IA32_RTIT_CTL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-16
35.2.7.3
Enabling and Disabling Packet Generation with TraceEn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-19
Disabling Packet Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-19
Other Writes to IA32_RTIT_CTL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-19
35.2.7.4
IA32_RTIT_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-19
35.2.7.5
IA32_RTIT_ADDRn_A and IA32_RTIT_ADDRn_B MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-20
35.2.7.6
IA32_RTIT_CR3_MATCH MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-21
35.2.7.7
IA32_RTIT_OUTPUT_BASE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-21
35.2.7.8
IA32_RTIT_OUTPUT_MASK_PTRS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-22
35.2.8
Interaction of Intel® Processor Trace and Other Processor Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-23
35.2.8.1
Intel® Transactional Synchronization Extensions (Intel® TSX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-23
35.2.8.2
Virtual-Machine Extensions (VMX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-24
35.2.8.3
Intel Software Guard Extensions (SGX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-24
35.2.8.4
SENTER/ENTERACCS and ACM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-25
35.2.8.5
Intel® Memory Protection Extensions (Intel® MPX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-25
35.3
CONFIGURATION AND PROGRAMMING GUIDELINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-25
35.3.1
Detection of Intel Processor Trace and Capability Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-25
35.3.1.1
Packet Decoding of RIP versus LIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-29
35.3.1.2
Model Specific Capability Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-29
35.3.2
Enabling and Configuration of Trace Packet Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-29
35.3.2.1
Enabling Packet Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-29
35.3.2.2
Disabling Packet Generation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-30
35.3.3
Flushing Trace Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-30
xxviii Vol. 3A

CONTENTS
PAGE

35.3.4
Warm Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-30
35.3.5
Context Switch Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-30
35.3.5.1
Manual Trace Configuration Context Switch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-30
35.3.5.2
Trace Configuration Context Switch Using XSAVES/XRSTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-31
35.3.6
Cycle-Accurate Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-31
35.3.6.1
Cycle Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-32
35.3.6.2
Cycle Packet Semantics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-32
35.3.6.3
Cycle Thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-33
35.3.7
Decoder Synchronization (PSB+) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-33
35.3.8
Internal Buffer Overflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-34
35.3.8.1
Overflow Impact on Enables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-34
35.3.8.2
Overflow Impact on Timing Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-35
35.3.9
Operational Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-35
35.4
TRACE PACKETS AND DATA TYPES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-35
35.4.1
Packet Relationships and Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-35
35.4.2
Packet Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-36
35.4.2.1
Taken/Not-taken (TNT) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-36
35.4.2.2
Target IP (TIP) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-38
IP Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-38
35.4.2.3
Deferred TIPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-40
35.4.2.4
Packet Generation Enable (TIP.PGE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-41
35.4.2.5
Packet Generation Disable (TIP.PGD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-42
35.4.2.6
Flow Update (FUP) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-43
FUP IP Payload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-44
35.4.2.7
Paging Information (PIP) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-45
35.4.2.8
MODE Packets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-46
MODE.Exec Packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-46
MODE.TSX Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-47
35.4.2.9
TraceStop Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-48
35.4.2.10
Core:Bus Ratio (CBR) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-48
35.4.2.11
Timestamp Counter (TSC) Packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-49
35.4.2.12
Mini Time Counter (MTC) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-50
35.4.2.13
TSC/MTC Alignment (TMA) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-51
35.4.2.14
Cycle Count Packet (CYC) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-52
35.4.2.15
VMCS Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-53
35.4.2.16
Overflow (OVF) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-54
35.4.2.17
Packet Stream Boundary (PSB) Packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-54
35.4.2.18
PSBEND Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-55
35.4.2.19
Maintenance (MNT) Packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-56
35.4.2.20
PAD Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-56
35.4.2.21
PTWRITE Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-57
35.4.2.22
Execution Stop (EXSTOP) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-58
35.4.2.23
MWAIT Packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-59
35.4.2.24
Power Entry (PWRE) Packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-60
35.4.2.25
Power Exit (PWRX) Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-61
35.5
TRACING IN VMX OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-61
35.5.1
VMX-Specific Packets and VMCS Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-62
35.5.2
Managing Trace Packet Generation Across VMX Transitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-63
35.5.2.1
System-Wide Tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-63
35.5.2.2
Host-Only Tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-63
35.5.2.3
Guest-Only Tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-64
35.5.2.4
Virtualization of Guest Output Packet Streams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-64
35.5.2.5
Emulation of Intel PT Traced State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-64
35.5.2.6
TSC Scaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-64
35.5.2.7
Failed VM Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-65
35.5.2.8
VMX Abort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-65
35.6
TRACING AND SMM TRANSFER MONITOR (STM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-65
35.7
PACKET GENERATION SCENARIOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-65
35.8
SOFTWARE CONSIDERATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-78
35.8.1
Tracing SMM Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-78
35.8.2
Cooperative Transition of Multiple Trace Collection Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-78
35.8.3
Tracking Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-79
35.8.3.1
Time Domain Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-79
35.8.3.2
Estimating TSC within Intel PT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-79
Vol. 3A xxix

CONTENTS
PAGE

35.8.3.3
35.8.3.4

VMX TSC Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-80
Calculating Frequency with Intel PT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-80

CHAPTER 36
INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS
36.1
36.2
36.3
36.4
36.5
36.5.1
36.6
36.7
36.7.1
36.7.2

OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-1
ENCLAVE INTERACTION AND PROTECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-1
ENCLAVE LIFE CYCLE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-2
DATA STRUCTURES AND ENCLAVE OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-2
ENCLAVE PAGE CACHE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-2
Enclave Page Cache Map (EPCM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-3
ENCLAVE INSTRUCTIONS AND INTEL® SGX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-3
DISCOVERING SUPPORT FOR INTEL® SGX AND ENABLING ENCLAVE INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-4
Intel® SGX Opt-In Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-4
Intel® SGX Resource Enumeration Leaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-5

CHAPTER 37
ENCLAVE ACCESS CONTROL AND DATA STRUCTURES
37.1
37.2
37.3
37.4
37.5
37.5.1
37.5.2
37.5.3
37.5.3.1
37.5.3.2
37.6
37.7
37.7.1
37.7.2
37.8
37.8.1
37.8.2
37.8.3
37.8.4
37.9
37.9.1
37.9.1.1
37.9.1.2
37.9.2
37.9.2.1
37.9.2.2
37.10
37.11
37.11.1
37.11.2
37.12
37.13
37.14
37.15
37.15.1
37.16
37.17
37.17.1
37.17.2
37.18
37.19

OVERVIEW OF ENCLAVE EXECUTION ENVIRONMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-1
TERMINOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-1
ACCESS-CONTROL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-1
SEGMENT-BASED ACCESS CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-2
PAGE-BASED ACCESS CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-2
Access-control for Accesses that Originate from non-SGX Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-2
Memory Accesses that Split across ELRANGE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-2
Implicit vs. Explicit Accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-2
Explicit Accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-3
Implicit Accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-3
INTEL® SGX DATA STRUCTURES OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-4
SGX ENCLAVE CONTROL STRUCTURE (SECS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-4
ATTRIBUTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-5
SECS.MISCSELECT Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-5
THREAD CONTROL STRUCTURE (TCS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-6
TCS.FLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-6
State Save Area Offset (OSSA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-6
Current State Save Area Frame (CSSA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-7
Number of State Save Area Frames (NSSA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-7
STATE SAVE AREA (SSA) FRAME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-7
GPRSGX Region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-8
EXITINFO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-8
VECTOR Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-9
MISC Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-9
EXINFO Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-10
Page Fault Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-10
PAGE INFORMATION (PAGEINFO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-10
SECURITY INFORMATION (SECINFO). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-11
SECINFO.FLAGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-11
PAGE_TYPE Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-12
PAGING CRYPTO METADATA (PCMD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-12
ENCLAVE SIGNATURE STRUCTURE (SIGSTRUCT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-12
EINIT TOKEN STRUCTURE (EINITTOKEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-13
REPORT (REPORT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-14
REPORTDATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-15
REPORT TARGET INFO (TARGETINFO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-15
KEY REQUEST (KEYREQUEST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-15
KEY REQUEST KeyNames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-16
Key Request Policy Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-16
VERSION ARRAY (VA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-16
ENCLAVE PAGE CACHE MAP (EPCM). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-16

xxx Vol. 3A

CONTENTS
PAGE

CHAPTER 38
ENCLAVE OPERATION
38.1
38.1.1
38.1.2
38.1.3
38.1.4
38.2
38.2.1
38.2.2
38.2.3
38.2.3.1
38.3
38.3.1
38.3.2
38.3.3
38.4
38.4.1
38.4.1.1
38.4.1.2
38.4.2
38.4.2.1
38.4.2.2
38.4.3
38.4.3.1
38.4.3.2
38.5
38.5.1
38.5.2
38.5.2.1
38.5.3
38.5.4
38.5.5
38.5.6
38.5.7
38.5.8
38.5.9
38.5.10
38.5.11
38.6
38.6.1
38.6.2
38.6.3
38.6.4
38.6.5

CONSTRUCTING AN ENCLAVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-1
ECREATE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-2
EADD and EEXTEND Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-2
EINIT Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-2
Intel® SGX Launch Control Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-3
ENCLAVE ENTRY AND EXITING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-3
Controlled Entry and Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-3
Asynchronous Enclave Exit (AEX). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-4
Resuming Execution after AEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-4
ERESUME Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-5
CALLING ENCLAVE PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-5
Calling Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-5
Register Preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-5
Returning to Caller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-5
INTEL® SGX KEY AND ATTESTATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-5
Enclave Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-5
MRENCLAVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-6
MRSIGNER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-6
Security Version Numbers (SVN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-7
Enclave Security Version. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-7
Hardware Security Version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-7
Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-7
Sealing Enclave Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-8
Using REPORTs for Local Attestation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-8
EPC AND MANAGEMENT OF EPC PAGES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-9
EPC Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-9
OS Management of EPC Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-9
Enhancement to Managing EPC Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-9
Eviction of Enclave Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-9
Loading an Enclave Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-10
Eviction of an SECS Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-10
Eviction of a Version Array Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-11
Allocating a Regular Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-11
Allocating a TCS Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-11
Trimming a Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-12
Restricting the EPCM Permissions of a Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-12
Extending the EPCM Permissions of a Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-13
CHANGES TO INSTRUCTION BEHAVIOR INSIDE AN ENCLAVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-13
Illegal Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-13
RDRAND and RDSEED Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-14
PAUSE Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-14
INT 3 Behavior Inside an Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-14
INVD Handling when Enclaves Are Enabled. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-14

CHAPTER 39
ENCLAVE EXITING EVENTS
39.1
39.2
39.3
39.3.1
39.3.2
39.3.3
39.4
39.4.1

COMPATIBLE SWITCH TO THE EXITING STACK OF AEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-1
STATE SAVING BY AEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-2
SYNTHETIC STATE ON ASYNCHRONOUS ENCLAVE EXIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-3
Processor Synthetic State on Asynchronous Enclave Exit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-3
Synthetic State for Extended Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-3
Synthetic State for MISC Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-4
AEX FLOW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-4
AEX Operational Detail. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-5

CHAPTER 40
SGX INSTRUCTION REFERENCES
40.1
40.1.1
40.1.2

INTEL® SGX INSTRUCTION SYNTAX AND OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-1
ENCLS Register Usage Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-1
ENCLU Register Usage Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-1
Vol. 3A xxxi

CONTENTS
PAGE

40.1.3
Information and Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-2
40.1.4
Internal CREGs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-3
40.1.5
Concurrent Operation Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-3
40.1.5.1
Concurrency Tables of Intel® SGX Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-4
40.2
INTEL® SGX INSTRUCTION REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-4
ENCLS—Execute an Enclave System Function of Specified Leaf Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-5
ENCLU—Execute an Enclave User Function of Specified Leaf Number. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-7
40.3
INTEL® SGX SYSTEM LEAF FUNCTION REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-10
EADD—Add a Page to an Uninitialized Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-11
EAUG—Add a Page to an Initialized Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-15
EBLOCK—Mark a page in EPC as Blocked . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-18
ECREATE—Create an SECS page in the Enclave Page Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-21
EDBGRD—Read From a Debug Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-25
EDBGWR—Write to a Debug Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-29
EEXTEND—Extend Uninitialized Enclave Measurement by 256 Bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-32
EINIT—Initialize an Enclave for Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-35
ELDB/ELDU—Load an EPC page and Marked its State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-42
EMODPR—Restrict the Permissions of an EPC Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-47
EMODT—Change the Type of an EPC Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-50
EPA—Add Version Array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-53
EREMOVE—Remove a page from the EPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-55
ETRACK—Activates EBLOCK Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-58
EWB—Invalidate an EPC Page and Write out to Main Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-60
40.4
INTEL® SGX USER LEAF FUNCTION REFERENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-65
40.4.1
Instruction Column in the Instruction Summary Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-65
EACCEPT—Accept Changes to an EPC Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-66
EACCEPTCOPY—Initialize a Pending Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-70
EENTER—Enters an Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-74
EEXIT—Exits an Enclave. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-82
EGETKEY—Retrieves a Cryptographic Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-85
EMODPE—Extend an EPC Page Permissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-92
EREPORT—Create a Cryptographic Report of the Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-95
ERESUME—Re-Enters an Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-99

CHAPTER 41
INTEL® SGX INTERACTIONS WITH IA32 AND INTEL® 64 ARCHITECTURE
41.1
41.2
41.2.1
41.2.2
41.3
41.3.1
41.3.2
41.3.3
41.3.4
41.4
41.5
41.5.1
41.5.2
41.5.3
41.6
41.7
41.7.1
41.7.2
41.7.2.1
41.7.2.2
41.7.2.3
41.7.2.4
41.7.2.5
41.7.2.6
41.7.2.7

INTEL® SGX AVAILABILITY IN VARIOUS PROCESSOR MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-1
IA32_FEATURE_CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-1
Availability of Intel SGX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-1
Intel SGX Launch Control Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-1
INTERACTIONS WITH SEGMENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-1
Scope of Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-1
Interactions of Intel® SGX Instructions with Segment, Operand, and Addressing Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . . 42-2
Interaction of Intel® SGX Instructions with Segmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-2
Interactions of Enclave Execution with Segmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-2
INTERACTIONS WITH PAGING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-2
INTERACTIONS WITH VMX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-3
VMM Controls to Configure Guest Support of Intel® SGX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-3
Interactions with the Extended Page Table Mechanism (EPT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-3
Interactions with APIC Virtualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-4
INTEL® SGX INTERACTIONS WITH ARCHITECTURALLY-VISIBLE EVENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-4
INTERACTIONS WITH THE PROCESSOR EXTENDED STATE AND MISCELLANEOUS STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-4
Requirements and Architecture Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-4
Relevant Fields in Various Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-5
SECS.ATTRIBUTES.XFRM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-5
SECS.SSAFRAMESIZE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-6
XSAVE Area in SSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-6
MISC Area in SSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-6
SIGSTRUCT Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-6
REPORT.ATTRIBUTES.XFRM and REPORT.MISCSELECT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-7
KEYREQUEST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-7

xxxii Vol. 3A

CONTENTS
PAGE

41.7.3
41.7.4
41.7.4.1
41.7.4.2
41.7.5
41.7.5.1
41.7.5.2
41.7.6
41.7.6.1
41.7.6.2
41.7.7
41.7.8
41.7.9
41.8
41.8.1
41.8.2
41.8.3
41.9
41.10
41.11
41.11.1
41.11.2
41.11.3
41.12
41.13
41.13.1
41.14
41.15
41.15.1
41.15.2
41.15.3
41.16
41.17

Processor Extended States and ENCLS[ECREATE] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-7
Processor Extended States and ENCLU[EENTER] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-7
Fault Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-7
State Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-7
Processor Extended States and AEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-8
State Saving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-8
State Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-8
Processor Extended States and ENCLU[ERESUME] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-8
Fault Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-8
State Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-8
Processor Extended States and ENCLU[EEXIT] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-8
Processor Extended States and ENCLU[EREPORT] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-9
Processor Extended States and ENCLU[EGETKEY] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-9
INTERACTIONS WITH SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-9
Availability of Intel® SGX instructions in SMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-9
SMI while Inside an Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-9
SMRAM Synthetic State of AEX Triggered by SMI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-9
INTERACTIONS OF INIT, SIPI, AND WAIT-FOR-SIPI WITH INTEL® SGX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-10
INTERACTIONS WITH DMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-10
INTERACTIONS WITH TXT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-10
Enclaves Created Prior to Execution of GETSEC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-10
Interaction of GETSEC with Intel® SGX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-10
Interactions with Authenticated Code Modules (ACMs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-11
INTERACTIONS WITH CACHING OF LINEAR-ADDRESS TRANSLATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-11
INTERACTIONS WITH INTEL® TRANSACTIONAL SYNCHRONIZATION EXTENSIONS (INTEL® TSX) . . . . . . . . . . . . . . . . . . . . . 42-11
HLE and RTM Debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-12
INTEL® SGX INTERACTIONS WITH S STATES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-12
INTEL® SGX INTERACTIONS WITH MACHINE CHECK ARCHITECTURE (MCA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-12
Interactions with MCA Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-12
Machine Check Enables (IA32_MCi_CTL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-12
CR4.MCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-12
INTEL® SGX INTERACTIONS WITH PROTECTED MODE VIRTUAL INTERRUPTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-13
INTEL SGX INTERACTION WITH PROTECTION KEYS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-13

CHAPTER 42
ENCLAVE CODE DEBUG AND PROFILING
42.1
42.1.1
42.1.2
42.2
42.2.1
42.2.2
42.2.3
42.2.3.1
42.2.3.2
42.2.4
42.2.5
42.2.6
42.3
42.3.1
42.3.2
42.3.3
42.3.4
42.4
42.4.1
42.4.2
42.4.3
42.5
42.5.1
42.5.2
42.5.2.1
42.5.2.2
42.5.2.3
42.6

CONFIGURATION AND CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-1
Debug Enclave vs. Production Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-1
Tool-Chain Opt-in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-1
SINGLE STEP DEBUG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-1
Single Stepping ENCLS Instruction Leafs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-1
Single Stepping ENCLU Instruction Leafs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-1
Single-Stepping Enclave Entry with Opt-out Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-2
Single Stepping without AEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-2
Single Step Preempted by AEX Due to Non-SMI Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-2
RFLAGS.TF Treatment on AEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-3
Restriction on Setting of TF after an Opt-Out Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-3
Trampoline Code Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-3
CODE AND DATA BREAKPOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-3
Breakpoint Suppression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-3
Reporting of Instruction Breakpoint on Next Instruction on a Debug Trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-4
RF Treatment on AEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-4
Breakpoint Matching in Intel® SGX Instruction Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-4
INT3 CONSIDERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-4
Behavior of INT3 Inside an Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-4
Debugger Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-4
VMM Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-4
BRANCH TRACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-5
BTF Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-5
LBR Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-5
LBR Stack on Opt-in Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-5
LBR Stack on Opt-out Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-6
Mispredict Bit, Record Type, and Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-7
INTERACTION WITH PERFORMANCE MONITORING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-7
Vol. 3A xxxiii

CONTENTS
PAGE

42.6.1
42.6.2
42.6.3
42.6.4
42.6.5
42.6.6
42.6.6.1

IA32_PERF_GLOBAL_STATUS Enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-7
Performance Monitoring with Opt-in Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-7
Performance Monitoring with Opt-out Entry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-8
Enclave Exit and Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-8
PEBS Record Generation on Intel® SGX Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-8
Exception-Handling on PEBS/BTS Loads/Stores after AEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-8
Other Interactions with Performance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-9

APPENDIX A
VMX CAPABILITY REPORTING FACILITY
A.1
A.2
A.3
A.3.1
A.3.2
A.3.3
A.4
A.5
A.6
A.7
A.8
A.9
A.10
A.11

BASIC VMX INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
RESERVED CONTROLS AND DEFAULT SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2
VM-EXECUTION CONTROLS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2
Pin-Based VM-Execution Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3
Primary Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3
Secondary Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4
VM-EXIT CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4
VM-ENTRY CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5
MISCELLANEOUS DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5
VMX-FIXED BITS IN CR0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6
VMX-FIXED BITS IN CR4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6
VMCS ENUMERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-7
VPID AND EPT CAPABILITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-7
VM FUNCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-8

APPENDIX B
FIELD ENCODING IN VMCS
B.1
B.1.1
B.1.2
B.1.3
B.2
B.2.1
B.2.2
B.2.3
B.2.4
B.3
B.3.1
B.3.2
B.3.3
B.3.4
B.4
B.4.1
B.4.2
B.4.3
B.4.4

16-BIT FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
16-Bit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
16-Bit Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
16-Bit Host-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
64-BIT FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
64-Bit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
64-Bit Read-Only Data Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4
64-Bit Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4
64-Bit Host-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5
32-BIT FIELDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6
32-Bit Control Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6
32-Bit Read-Only Data Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7
32-Bit Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7
32-Bit Host-State Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
NATURAL-WIDTH FIELDS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
Natural-Width Control Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
Natural-Width Read-Only Data Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9
Natural-Width Guest-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9
Natural-Width Host-State Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-10

APPENDIX C
VMX BASIC EXIT REASONS

xxxiv Vol. 3A

CONTENTS
PAGE

FIGURES
Figure 1-1.
Figure 1-2.
Figure 2-1.
Figure 2-2.
Figure 2-3.
Figure 2-4.
Figure 2-5.
Figure 2-6.
Figure 2-7.
Figure 2-8.
Figure 2-9.
Figure 2-10.
Figure 3-1.
Figure 3-2.
Figure 3-3.
Figure 3-4.
Figure 3-5.
Figure 3-6.
Figure 3-7.
Figure 3-8.
Figure 3-9.
Figure 3-10.
Figure 3-11.
Figure 4-1.
Figure 4-2.
Figure 4-3.
Figure 4-4.
Figure 4-5.
Figure 4-6.
Figure 4-7.
Figure 4-8.
Figure 4-9.
Figure 4-10.
Figure 4-11.
Figure 4-12.
Figure 4-13.
Figure 5-1.
Figure 5-2.
Figure 5-3.
Figure 5-4.
Figure 5-5.
Figure 5-6.
Figure 5-7.
Figure 5-8.
Figure 5-9.
Figure 5-10.
Figure 5-11.
Figure 5-12.
Figure 5-13.
Figure 5-14.
Figure 5-15.
Figure 6-1.
Figure 6-2.
Figure 6-3.
Figure 6-4.
Figure 6-5.
Figure 6-6.
Figure 6-7.
Figure 6-8.
Figure 6-9.
Figure 7-1.
Figure 7-2.

Bit and Byte Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7
Syntax for CPUID, CR, and MSR Data Presentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9
IA-32 System-Level Registers and Data Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
System-Level Registers and Data Structures in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Transitions Among the Processor’s Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
IA32_EFER MSR Layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
System Flags in the EFLAGS Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
Memory Management Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-14
XCR0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-20
Protection Key Rights Register for User Pages (PKRU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21
WBINVD Invalidation of Shared and Non-Shared Cache Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-25
Segmentation and Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Flat Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Protected Flat Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Multi-Segment Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Logical Address to Linear Address Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Segment Selector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Segment Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Segment Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
Segment Descriptor When Segment-Present Flag Is Clear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
Global and Local Descriptor Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15
Pseudo-Descriptor Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
Enabling and Changing Paging Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Linear-Address Translation to a 4-KByte Page using 32-Bit Paging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9
Linear-Address Translation to a 4-MByte Page using 32-Bit Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9
Formats of CR3 and Paging-Structure Entries with 32-Bit Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10
Linear-Address Translation to a 4-KByte Page using PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15
Linear-Address Translation to a 2-MByte Page using PAE Paging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
Formats of CR3 and Paging-Structure Entries with PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18
Linear-Address Translation to a 4-KByte Page using 4-Level Paging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20
Linear-Address Translation to a 2-MByte Page using 4-Level Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21
Linear-Address Translation to a 1-GByte Page using 4-Level Paging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21
Formats of CR3 and Paging-Structure Entries with 4-Level Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-28
Page-Fault Error Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-32
Memory Management Convention That Assigns a Page Table to Each Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-48
Descriptor Fields Used for Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
Descriptor Fields with Flags used in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Protection Rings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7
Privilege Check for Data Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8
Examples of Accessing Data Segments From Various Privilege Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9
Privilege Check for Control Transfer Without Using a Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11
Examples of Accessing Conforming and Nonconforming Code Segments From Various Privilege Levels. . . . . . . . . . 5-12
Call-Gate Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13
Call-Gate Descriptor in IA-32e Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14
Call-Gate Mechanism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15
Privilege Check for Control Transfer with Call Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16
Example of Accessing Call Gates At Various Privilege Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17
Stack Switching During an Interprivilege-Level Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19
MSRs Used by SYSCALL and SYSRET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23
Use of RPL to Weaken Privilege Level of Called Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26
Relationship of the IDTR and IDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10
IDT Gate Descriptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11
Interrupt Procedure Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12
Stack Usage on Transfers to Interrupt and Exception-Handling Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13
Interrupt Task Switch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
Error Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16
64-Bit IDT Gate Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17
IA-32e Mode Stack Usage After Privilege Level Change. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19
Page-Fault Error Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-40
Structure of a Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
32-Bit Task-State Segment (TSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

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xxxvi Vol. 3A

TSS Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-6
Format of TSS and LDT Descriptors in 64-bit Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-7
Task Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-8
Task-Gate Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-8
Task Gates Referencing the Same Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-9
Nested Tasks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12
Overlapping Linear-to-Physical Mappings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15
16-Bit TSS Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16
64-Bit TSS Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17
Example of Write Ordering in Multiple-Processor Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8-7
Interpretation of APIC ID in Early MP Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-24
Local APICs and I/O APIC in MP System Supporting Intel HT Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-27
IA-32 Processor with Two Logical Processors Supporting Intel HT Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28
Generalized Four level Interpretation of the APIC ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-35
Conceptual Five-level Topology and 32-bit APIC ID Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-35
Topological Relationships between Hierarchical IDs in a Hypothetical MP Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-37
MP System With Multiple Pentium III Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-55
Contents of CR0 Register after Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-2
Version Information in the EDX Register after Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-5
Processor State After Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15
Constructing Temporary GDT and Switching to Protected Mode (Lines 162-172 of List File) . . . . . . . . . . . . . . . . . . . . 9-23
Moving the GDT, IDT, and TSS from ROM to RAM (Lines 196-261 of List File) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-24
Task Switching (Lines 282-296 of List File) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-25
Applying Microcode Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
Microcode Update Write Operation Flow [1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-45
Microcode Update Write Operation Flow [2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-46
Relationship of Local APIC and I/O APIC In Single-Processor Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2
Local APICs and I/O APIC When Intel Xeon Processors Are Used in Multiple-Processor Systems . . . . . . . . . . . . . . . . . 10-3
Local APICs and I/O APIC When P6 Family Processors Are Used in Multiple-Processor Systems . . . . . . . . . . . . . . . . . . 10-3
Local APIC Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5
IA32_APIC_BASE MSR (APIC_BASE_MSR in P6 Family) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9
Local APIC ID Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10
Local APIC Version Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12
Local Vector Table (LVT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-13
Error Status Register (ESR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15
Divide Configuration Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-16
Initial Count and Current Count Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17
Interrupt Command Register (ICR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-19
Logical Destination Register (LDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24
Destination Format Register (DFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-24
Arbitration Priority Register (APR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-25
Interrupt Acceptance Flow Chart for the Local APIC (Pentium 4 and Intel Xeon Processors) . . . . . . . . . . . . . . . . . . . . 10-27
Interrupt Acceptance Flow Chart for the Local APIC (P6 Family and Pentium Processors) . . . . . . . . . . . . . . . . . . . . . . 10-28
Task-Priority Register (TPR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-29
Processor-Priority Register (PPR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-29
IRR, ISR and TMR Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-30
EOI Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31
CR8 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-32
Spurious-Interrupt Vector Register (SVR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-33
Layout of the MSI Message Address Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-34
Layout of the MSI Message Data Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-36
IA32_APIC_BASE MSR Supporting x2APIC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-37
Local x2APIC State Transitions with IA32_APIC_BASE, INIT, and Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-42
Interrupt Command Register (ICR) in x2APIC Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-45
Logical Destination Register in x2APIC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-46
SELF IPI register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-47
Cache Structure of the Pentium 4 and Intel Xeon Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1
Cache Structure of the Intel Core i7 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2
Cache-Control Registers and Bits Available in Intel 64 and IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-11
Mapping Physical Memory With MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-21
IA32_MTRRCAP Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-22
IA32_MTRR_DEF_TYPE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-23
IA32_MTRR_PHYSBASEn and IA32_MTRR_PHYSMASKn Variable-Range Register Pair . . . . . . . . . . . . . . . . . . . . . . . . 11-25
IA32_SMRR_PHYSBASE and IA32_SMRR_PHYSMASK SMRR Pair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-26
IA32_PAT MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34

CONTENTS
PAGE

Figure 12-1.
Figure 12-2.
Figure 14-1.
Figure 14-2.
Figure 14-3.
Figure 14-4.
Figure 14-5.
Figure 14-6.
Figure 14-7.
Figure 14-8.
Figure 14-9.
Figure 14-10.
Figure 14-11.
Figure 14-12.
Figure 14-13.
Figure 14-14.
Figure 14-15.
Figure 14-16.
Figure 14-17.
Figure 14-18.
Figure 14-19.
Figure 14-20.
Figure 14-21.
Figure 14-22.
Figure 14-23.
Figure 14-24.
Figure 14-25.
Figure 14-26.
Figure 14-27.
Figure 14-28.
Figure 14-29.
Figure 14-30.
Figure 14-31.
Figure 14-32.
Figure 14-33.
Figure 14-34.
Figure 14-35.
Figure 14-36.
Figure 14-37.
Figure 14-38.
Figure 14-39.
Figure 14-40.
Figure 14-41.
Figure 14-42.
Figure 14-43.
Figure 15-1.
Figure 15-2.
Figure 15-3.
Figure 15-4.
Figure 15-5.
Figure 15-6.
Figure 15-7.
Figure 15-8.
Figure 15-9.
Figure 15-10.
Figure 17-1.
Figure 17-2.
Figure 17-3.
Figure 17-4.
Figure 17-5.
Figure 17-6.
Figure 17-7.
Figure 17-8.
Figure 17-9.

Mapping of MMX Registers to Floating-Point Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-2
Mapping of MMX Registers to x87 FPU Data Register Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5
IA32_MPERF MSR and IA32_APERF MSR for P-state Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-2
IA32_PERF_CTL Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-4
IA32_ENERGY_PERF_BIAS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-5
IA32_PM_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7
IA32_HWP_CAPABILITIES Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-7
IA32_HWP_REQUEST Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-8
IA32_HWP_REQUEST_PKG Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-9
IA32_HWP_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-10
IA32_THERM_STATUS Register With HWP Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-10
MSR_PPERF MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-11
IA32_HWP_INTERRUPT MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-11
IA32_PKG_HDC_CTL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-14
IA32_PM_CTL1 MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-15
IA32_THREAD_STALL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-15
MSR_CORE_HDC_RESIDENCY MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-16
MSR_PKG_HDC_SHALLOW_RESIDENCY MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-16
MSR_PKG_HDC_DEEP_RESIDENCY MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-17
MSR_PKG_HDC_CONFIG MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-17
Example of Effective Frequency Reduction and Forced Idle Period of HDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-18
Processor Modulation Through Stop-Clock Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-19
MSR_THERM2_CTL Register On Processors with CPUID Family/Model/Stepping Signature Encoded as 0x69n
or 0x6Dn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-21
MSR_THERM2_CTL Register for Supporting TM2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-21
IA32_THERM_STATUS MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-22
IA32_THERM_INTERRUPT MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-22
IA32_CLOCK_MODULATION MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-23
IA32_CLOCK_MODULATION MSR with Clock Modulation Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-24
IA32_THERM_STATUS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-25
IA32_THERM_INTERRUPT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-27
IA32_PACKAGE_THERM_STATUS Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-28
IA32_PACKAGE_THERM_INTERRUPT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-30
MSR_RAPL_POWER_UNIT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-32
MSR_PKG_POWER_LIMIT Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-33
MSR_PKG_ENERGY_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-34
MSR_PKG_POWER_INFO Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-34
MSR_PKG_PERF_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-35
MSR_PP0_POWER_LIMIT/MSR_PP1_POWER_LIMIT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-35
MSR_PP0_ENERGY_STATUS/MSR_PP1_ENERGY_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-36
MSR_PP0_POLICY/MSR_PP1_POLICY Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-36
MSR_PP0_PERF_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-37
MSR_DRAM_POWER_LIMIT Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-37
MSR_DRAM_ENERGY_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-38
MSR_DRAM_POWER_INFO Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-38
MSR_DRAM_PERF_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-38
Machine-Check MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-2
IA32_MCG_CAP Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-3
IA32_MCG_STATUS Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-4
IA32_MCG_EXT_CTL Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-5
IA32_MCi_CTL Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-6
IA32_MCi_STATUS Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-7
IA32_MCi_ADDR MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-9
UCR Support in IA32_MCi_MISC Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-10
IA32_MCi_CTL2 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-11
CMCI Behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-14
Debug Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-2
DR6/DR7 Layout on Processors Supporting Intel® 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-7
IA32_DEBUGCTL MSR for Processors based on Intel Core microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-12
64-bit Address Layout of LBR MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-16
DS Save Area Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-19
32-bit Branch Trace Record Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-20
PEBS Record Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-20
IA-32e Mode DS Save Area Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-21
64-bit Branch Trace Record Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-21
Vol. 3A xxxvii

CONTENTS
PAGE

Figure 17-10.
Figure 17-11.
Figure 17-12.
Figure 17-13.
Figure 17-14.
Figure 17-15.
Figure 17-16.
Figure 17-17.
Figure 17-18.
Figure 17-19.
Figure 17-20.
Figure 17-21.
Figure 17-22.
Figure 17-23.
Figure 17-24.
Figure 17-25.
Figure 17-26.
Figure 17-27.
Figure 17-28.
Figure 17-29.
Figure 17-30.
Figure 17-31.
Figure 17-32.
Figure 17-33.
Figure 17-34.
Figure 17-35.
Figure 17-36.
Figure 17-37.
Figure 17-38.
Figure 17-39.
Figure 18-1.
Figure 18-2.
Figure 18-3.
Figure 18-4.
Figure 18-5.
Figure 18-6.
Figure 18-7.
Figure 18-8.
Figure 18-9.
Figure 18-10.
Figure 18-11.
Figure 18-12.
Figure 18-13.
Figure 18-14.
Figure 18-15.
Figure 18-16.
Figure 18-17.
Figure 18-18.
Figure 18-19.
Figure 18-20.
Figure 18-21.
Figure 18-22.
Figure 18-23.
Figure 18-24.
Figure 18-25.
Figure 18-26.
Figure 18-27.
Figure 18-28.
Figure 18-29.
Figure 18-30.
Figure 18-31.
Figure 18-32.
Figure 18-33.
Figure 18-34.
Figure 18-35.
xxxviii Vol. 3A

64-bit PEBS Record Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-22
IA32_DEBUGCTL MSR for Processors based on Intel microarchitecture code name Nehalem . . . . . . . . . . . . . . . . . . . 17-28
MSR_DEBUGCTLA MSR for Pentium 4 and Intel Xeon Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-34
LBR MSR Branch Record Layout for the Pentium 4 and Intel Xeon Processor Family. . . . . . . . . . . . . . . . . . . . . . . . . . . 17-36
IA32_DEBUGCTL MSR for Intel Core Solo and Intel Core Duo Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-37
LBR Branch Record Layout for the Intel Core Solo and Intel Core Duo Processor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-37
MSR_DEBUGCTLB MSR for Pentium M Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-38
LBR Branch Record Layout for the Pentium M Processor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-39
DEBUGCTLMSR Register (P6 Family Processors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-40
Platform Shared Resource Monitoring Usage Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-45
CPUID.(EAX=0FH, ECX=0H) Monitoring Resource Type Enumeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-46
L3 Cache Monitoring Capability Enumeration Data (CPUID.(EAX=0FH, ECX=1H) ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-46
L3 Cache Monitoring Capability Enumeration Event Type Bit Vector (CPUID.(EAX=0FH, ECX=1H) ). . . . . . . . . . . . . . 17-47
IA32_PQR_ASSOC MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-48
IA32_QM_EVTSEL and IA32_QM_CTR MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-49
Software Usage of Cache Monitoring Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-49
Cache Allocation Technology Allocates More Resource to High Priority Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-51
Examples of Cache Capacity Bitmasks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-52
Class of Service and Cache Capacity Bitmasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-53
Code and Data Capacity Bitmasks of CDP. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-55
Cache Allocation Technology Usage Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-56
CPUID.(EAX=10H, ECX=0H) Available Resource Type Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-57
L3 Cache Allocation Technology and CDP Enumeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-57
L2 Cache Allocation Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-58
IA32_PQR_ASSOC, IA32_L3_MASK_n MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-59
IA32_L2_MASK_n MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-59
Layout of IA32_L3_QOS_CFG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-60
A High-Level Overview of the MBA Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-63
CPUID.(EAX=10H, ECX=3H) MBA Feature Details Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-65
IA32_L2_QoS_Ext_BW_Thrtl_n MSR Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-66
Layout of IA32_PERFEVTSELx MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-4
Layout of IA32_FIXED_CTR_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-7
Layout of IA32_PERF_GLOBAL_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-8
Layout of IA32_PERF_GLOBAL_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-10
Layout of IA32_PERF_GLOBAL_OVF_CTRL MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-10
Layout of IA32_PERFEVTSELx MSRs Supporting Architectural Performance Monitoring Version 3 . . . . . . . . . . . . . 18-11
IA32_FIXED_CTR_CTRL MSR Supporting Architectural Performance Monitoring Version 3 . . . . . . . . . . . . . . . . . . . . . 18-11
Layout of Global Performance Monitoring Control MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-12
Global Performance Monitoring Overflow Status and Control MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-12
IA32_PERF_GLOBAL_STATUS MSR and Architectural Perfmon Version 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-14
IA32_PERF_GLOBAL_STATUS_RESET MSR and Architectural Perfmon Version 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-15
IA32_PERF_GLOBAL_STATUS_SET MSR and Architectural Perfmon Version 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-15
IA32_PERF_GLOBAL_INUSE MSR and Architectural Perfmon Version 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16
IA32_PERF_GLOBAL_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-18
Layout of IA32_PEBS_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-19
PEBS Programming Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-21
Layout of MSR_PEBS_LD_LAT MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-23
Layout of MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 to Configure Off-core Response Events. . . . . . . . . . 18-24
Layout of MSR_UNCORE_PERF_GLOBAL_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-26
Layout of MSR_UNCORE_PERF_GLOBAL_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-27
Layout of MSR_UNCORE_PERF_GLOBAL_OVF_CTRL MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-27
Layout of MSR_UNCORE_PERFEVTSELx MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-28
Layout of MSR_UNCORE_FIXED_CTR_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-28
Layout of MSR_UNCORE_ADDR_OPCODE_MATCH MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-29
Distributed Units of the Uncore of Intel® Xeon® Processor 7500 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-31
IA32_PERF_GLOBAL_CTRL MSR in Intel® Microarchitecture Code Name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . 18-34
IA32_PERF_GLOBAL_STATUS MSR in Intel® Microarchitecture Code Name Sandy Bridge. . . . . . . . . . . . . . . . . . . . . . . 18-35
IA32_PERF_GLOBAL_OVF_CTRL MSR in Intel microarchitecture code name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . 18-35
Layout of IA32_PEBS_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-37
Request_Type Fields for MSR_OFFCORE_RSP_x. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-41
Response_Supplier and Snoop Info Fields for MSR_OFFCORE_RSP_x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-42
Layout of Uncore PERFEVTSEL MSR for a C-Box Unit or the ARB Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-43
Layout of MSR_UNC_PERF_GLOBAL_CTRL MSR for Uncore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-44
Layout of IA32_PERFEVTSELx MSRs Supporting Intel TSX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-53
IA32_PERF_GLOBAL_STATUS MSR in Broadwell Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-55

CONTENTS
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Figure 18-36.
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Figure 39-2.
Figure 40-1.
Figure 42-1.
Figure 42-2.
Figure 42-3.
Figure 42-4.

IA32_PERF_GLOBAL_OVF_CTRL MSR in Broadwell microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-56
Request_Type Fields for MSR_OFFCORE_RSPx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-72
Response_Supplier and Snoop Info Fields for MSR_OFFCORE_RSPx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-73
Layout of IA32_PEBS_ENABLE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-81
PEBS Programming Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-82
Layout of MSR_PERF_FIXED_CTR_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-86
Layout of MSR_PERF_GLOBAL_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-86
Layout of MSR_PERF_GLOBAL_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-87
Layout of MSR_PERF_GLOBAL_OVF_CTRL MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-87
Event Selection Control Register (ESCR) for Pentium 4 and Intel Xeon Processors without Intel HT Technology
Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-94
Performance Counter (Pentium 4 and Intel Xeon Processors) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-95
Counter Configuration Control Register (CCCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-96
Effects of Edge Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-100
Event Selection Control Register (ESCR) for the Pentium 4 Processor, Intel Xeon Processor and Intel Xeon
Processor MP Supporting Hyper-Threading Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-107
Counter Configuration Control Register (CCCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-109
Block Diagram of 64-bit Intel Xeon Processor MP with 8-MByte L3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-112
MSR_IFSB_IBUSQx, Addresses: 107CCH and 107CDH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-113
MSR_IFSB_ISNPQx, Addresses: 107CEH and 107CFH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-113
MSR_EFSB_DRDYx, Addresses: 107D0H and 107D1H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-114
MSR_IFSB_CTL6, Address: 107D2H; MSR_IFSB_CNTR7, Address: 107D3H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-114
Block Diagram of Intel Xeon Processor 7400 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-115
Block Diagram of Intel Xeon Processor 7100 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-116
MSR_EMON_L3_CTR_CTL0/1, Addresses: 107CCH/107CDH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-117
MSR_EMON_L3_CTR_CTL2/3, Addresses: 107CEH/107CFH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-119
MSR_EMON_L3_CTR_CTL4/5/6/7, Addresses: 107D0H-107D3H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-119
PerfEvtSel0 and PerfEvtSel1 MSRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-121
CESR MSR (Pentium Processor Only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-124
Layout of IA32_PERF_CAPABILITIES MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-129
Real-Address Mode Address Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-3
Interrupt Vector Table in Real-Address Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-5
Entering and Leaving Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-9
Privilege Level 0 Stack After Interrupt or Exception in Virtual-8086 Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-13
Software Interrupt Redirection Bit Map in TSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-18
Stack after Far 16- and 32-Bit Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-5
I/O Map Base Address Differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-30
Interaction of a Virtual-Machine Monitor and Guests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23-2
States of VMCS X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-2
Formats of EPTP and EPT Paging-Structure Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-11
INVEPT Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-3
INVVPID Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-6
VMX Transitions and States of VMCS in a Logical Processor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-3
Virtual TLB Scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32-5
Host External Interrupts and Guest Virtual Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33-4
SMRAM Usage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-4
SMM Revision Identifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-13
Auto HALT Restart Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-14
SMBASE Relocation Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-15
I/O Instruction Restart Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-15
ToPA Memory Illustration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-10
Layout of ToPA Table Entry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-11
Interpreting Tabular Definition of Packet Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-36
An Enclave Within the Application’s Virtual Address Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-1
Enclave Memory Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-1
Measurement Flow of Enclave Build Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-6
SGX Local Attestation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-8
Exit Stack Just After Interrupt with Stack Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-1
The SSA Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-2
Relationships Between SECS, SIGSTRUCT and EINITTOKEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-35
Single Stepping with Opt-out Entry - No AEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-2
Single Stepping with Opt-out Entry -AEX Due to Non-SMI Event Before Single-Step Boundary . . . . . . . . . . . . . . . . . . 43-3
LBR Stack Interaction with Opt-in Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-6
LBR Stack Interaction with Opt-out Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43-7

Vol. 3A xxxix

CONTENTS
PAGE

TABLES
Table 2-1.
Table 2-2.
Table 2-3.
Table 3-1.
Table 3-2.
Table 4-1.
Table 4-2.
Table 4-3.
Table 4-4.
Table 4-6.
Table 4-5.
Table 4-7.
Table 4-8.
Table 4-9.
Table 4-10.
Table 4-11.
Table 4-12.
Table 4-13.
Table 4-14.
Table 4-15.
Table 4-16.
Table 4-17.
Table 4-18.
Table 4-19.
Table 5-1.
Table 5-2.
Table 5-3.
Table 5-4.
Table 5-6.
Table 5-7.
Table 5-5.
Table 5-9.
Table 5-8.
Table 6-1.
Table 6-2.
Table 6-3.
Table 6-4.
Table 6-5.
Table 6-6.
Table 6-7.
Table 6-8.
Table 7-1.
Table 7-2.
Table 8-1.
Table 8-2.
Table 8-3.
Table 8-4.
Table 8-5.
Table 9-1.
Table 9-2.
Table 9-3.
Table 9-4.
Table 9-5.
Table 9-6.
Table 9-7.
Table 9-8.
Table 9-9.
Table 9-10.
Table 9-11.

xl Vol. 3A

IA32_EFER MSR Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
Action Taken By x87 FPU Instructions for Different Combinations of EM, MP, and TS. . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16
Summary of System Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22
Code- and Data-Segment Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
System-Segment and Gate-Descriptor Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
Properties of Different Paging Modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
Paging Structures in the Different Paging Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7
Use of CR3 with 32-Bit Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10
Format of a 32-Bit Page-Directory Entry that Maps a 4-MByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11
Format of a 32-Bit Page-Table Entry that Maps a 4-KByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
Format of a 32-Bit Page-Directory Entry that References a Page Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12
Use of CR3 with PAE Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13
Format of a PAE Page-Directory-Pointer-Table Entry (PDPTE). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14
Format of a PAE Page-Directory Entry that Maps a 2-MByte Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16
Format of a PAE Page-Directory Entry that References a Page Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17
Format of a PAE Page-Table Entry that Maps a 4-KByte Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17
Use of CR3 with 4-Level Paging and CR4.PCIDE = 0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19
Use of CR3 with 4-Level Paging and CR4.PCIDE = 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19
Format of a 4-Level PML4 Entry (PML4E) that References a Page-Directory-Pointer Table . . . . . . . . . . . . . . . . . . . . . 4-23
Format of a 4-Level Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page . . . . . . . . . . . . . . . . . . . 4-24
Format of a 4-Level Page-Directory-Pointer-Table Entry (PDPTE) that References a Page Directory . . . . . . . . . . . . 4-25
Format of a 4-Level Page-Directory Entry that Maps a 2-MByte Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-25
Format of a 4-Level Page-Directory Entry that References a Page Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-26
Format of a 4-Level Page-Table Entry that Maps a 4-KByte Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-27
Privilege Check Rules for Call Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-16
64-Bit-Mode Stack Layout After Far CALL with CPL Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19
Combined Page-Directory and Page-Table Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29
Extended Feature Enable MSR (IA32_EFER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-30
Legacy PAE-Enabled 4-KByte Page Level Protection Matrix with Execute-Disable Bit Capability. . . . . . . . . . . . . . . . . 5-31
Legacy PAE-Enabled 2-MByte Page Level Protection with Execute-Disable Bit Capability . . . . . . . . . . . . . . . . . . . . . . . 5-31
IA-32e Mode Page Level Protection Matrix with Execute-Disable Bit Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31
Reserved Bit Checking WIth Execute-Disable Bit Capability Not Enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32
IA-32e Mode Page Level Protection Matrix with Execute-Disable Bit Capability Enabled . . . . . . . . . . . . . . . . . . . . . . . . 5-32
Protected-Mode Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
Priority Among Simultaneous Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8
Debug Exception Conditions and Corresponding Exception Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21
Interrupt and Exception Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28
Conditions for Generating a Double Fault. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29
Invalid TSS Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31
Alignment Requirements by Data Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-44
SIMD Floating-Point Exceptions Priority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-48
Exception Conditions Checked During a Task Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11
Effect of a Task Switch on Busy Flag, NT Flag, Previous Task Link Field, and TS Flag . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13
Broadcast INIT-SIPI-SIPI Sequence and Choice of Timeouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-22
Initial APIC IDs for the Logical Processors in a System that has Four Intel Xeon MP Processors Supporting Intel
Hyper-Threading Technology1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-37
Initial APIC IDs for the Logical Processors in a System that has Two Physical Processors Supporting Dual-Core
and Intel Hyper-Threading Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-37
Example of Possible x2APIC ID Assignment in a System that has Two Physical Processors Supporting x2APIC
and Intel Hyper-Threading Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-38
Boot Phase IPI Message Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-54
IA-32 and Intel 64 Processor States Following Power-up, Reset, or INIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2
Variance of RESET Values in Selected Intel Architecture Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4
Recommended Settings of EM and MP Flags on IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6
Software Emulation Settings of EM, MP, and NE Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7
Main Initialization Steps in STARTUP.ASM Source Listing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16
Relationship Between BLD Item and ASM Source File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27
Microcode Update Field Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28
Microcode Update Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-30
Extended Processor Signature Table Header Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31
Processor Signature Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-31
Processor Flags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-33

CONTENTS
PAGE

Table 9-12.
Table 9-13.
Table 9-14.
Table 9-15.
Table 9-16.
Table 9-17.
Table 9-18.
Table 9-19.
Table 10-1
Table 10-2.
Table 10-4
Table 10-3
Table 10-5.
Table 10-6.
Table 10-7.
Table 10-1.
Table 10-2.
Table 10-3.
Table 10-4.
Table 11-1.
Table 11-2.
Table 11-3.
Table 11-4.
Table 11-5.
Table 11-6.
Table 11-7.
Table 11-8.
Table 11-9.
Table 11-10.
Table 11-11.
Table 11-12.
Table 12-1.
Table 12-3.
Table 12-2.
Table 13-1.
Table 13-2.
Table 13-3.
Table 14-1.
Table 14-2.
Table 14-3.
Table 14-4.
Table 15-1.
Table 15-2.
Table 15-3.
Table 15-4.
Table 15-5.
Table 15-6.
Table 15-7.
Table 15-8.
Table 15-9.
Table 15-10.
Table 15-11.
Table 15-12.
Table 15-13.
Table 15-14.
Table 15-15.
Table 15-16.
Table 15-17.
Table 15-18.
Table 15-19.
Table 15-20.
Table 15-21.
Table 16-1.
Table 16-2.

Microcode Update Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-37
Microcode Update Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
Parameters for the Presence Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-42
Parameters for the Write Update Data Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-43
Parameters for the Control Update Sub-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
Mnemonic Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
Parameters for the Read Microcode Update Data Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-47
Return Code Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-49
Local APIC Register Address Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-6
Local APIC Timer Modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17
Valid Combinations for the P6 Family Processors’ Local APIC Interrupt Command Register. . . . . . . . . . . . . . . . . . . . . 10-22
Valid Combinations for the Pentium 4 and Intel Xeon Processors’ Local xAPIC Interrupt Command Register . . . . 10-22
x2APIC Operating Mode Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-37
Local APIC Register Address Map Supported by x2APIC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-38
MSR/MMIO Interface of a Local x2APIC in Different Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-40
EOI Message (14 Cycles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-47
Short Message (21 Cycles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-48
Non-Focused Lowest Priority Message (34 Cycles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-49
APIC Bus Status Cycles Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-51
Characteristics of the Caches, TLBs, Store Buffer, and Write Combining Buffer in Intel 64 and IA-32 Processors . 11-2
Memory Types and Their Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-6
Methods of Caching Available in Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium M, Pentium 4, Intel Xeon,
P6 Family, and Pentium Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-7
MESI Cache Line States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-9
Cache Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-12
Effective Page-Level Memory Type for Pentium Pro and Pentium II Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-14
Effective Page-Level Memory Types for Pentium III and More Recent Processor Families. . . . . . . . . . . . . . . . . . . . . . 11-15
Memory Types That Can Be Encoded in MTRRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-21
Address Mapping for Fixed-Range MTRRs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-24
Memory Types That Can Be Encoded With PAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-34
Selection of PAT Entries with PAT, PCD, and PWT Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35
Memory Type Setting of PAT Entries Following a Power-up or Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-35
Action Taken By MMX Instructions for Different Combinations of EM, MP and TS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
Effect of the MMX, x87 FPU, and FXSAVE/FXRSTOR Instructions on the x87 FPU Tag Word . . . . . . . . . . . . . . . . . . . 12-3
Effects of MMX Instructions on x87 FPU State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3
Action Taken for Combinations of OSFXSR, OSXMMEXCPT, SSE, SSE2, SSE3, EM, MP, and TS. . . . . . . . . . . . . . . . . . . . 13-3
Action Taken for Combinations of OSFXSR, SSSE3, SSE4, EM, and TS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-4
CPUID.(EAX=0DH, ECX=1) EAX Bit Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-8
Architectural and Non-Architectural MSRs Related to HWP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-6
Architectural and non-Architecture MSRs Related to HDC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-13
On-Demand Clock Modulation Duty Cycle Field Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-23
RAPL MSR Interfaces and RAPL Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14-32
Bits 54:53 in IA32_MCi_STATUS MSRs when IA32_MCG_CAP[11] = 1 and UC = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-7
Overwrite Rules for Enabled Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-8
Address Mode in IA32_MCi_MISC[8:6] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-10
Address Mode in IA32_MCi_MISC[8:6] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-11
Extended Machine Check State MSRs in Processors Without Support for Intel 64 Architecture. . . . . . . . . . . . . . . . . 15-12
Extended Machine Check State MSRs In Processors With Support For Intel 64 Architecture . . . . . . . . . . . . . . . . . . . 15-12
MC Error Classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-18
Overwrite Rules for UC, CE, and UCR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-19
IA32_MCi_Status [15:0] Simple Error Code Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
IA32_MCi_Status [15:0] Compound Error Code Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-21
Encoding for TT (Transaction Type) Sub-Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
Level Encoding for LL (Memory Hierarchy Level) Sub-Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
Encoding of Request (RRRR) Sub-Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-22
Encodings of PP, T, and II Sub-Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-23
Encodings of MMM and CCCC Sub-Fields. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-23
MCA Compound Error Code Encoding for SRAO Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-24
IA32_MCi_STATUS Values for SRAO Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-24
IA32_MCG_STATUS Flag Indication for SRAO Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-25
MCA Compound Error Code Encoding for SRAR Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-25
IA32_MCi_STATUS Values for SRAR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-25
IA32_MCG_STATUS Flag Indication for SRAR Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-26
CPUID DisplayFamily_DisplayModel Signatures for Processor Family 06H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-1
Incremental Decoding Information: Processor Family 06H Machine Error Codes For Machine Check. . . . . . . . . . . . . . 16-1
Vol. 3A xli

CONTENTS
PAGE

Table 16-3.
Table 16-4.
Table 16-5.
Table 16-6.
Table 16-7.
Table 16-8.
Table 16-9.
Table 16-10.
Table 16-11.
Table 16-12.
Table 16-13.
Table 16-14.
Table 16-15.
Table 16-16.
Table 16-17.
Table 16-18.
Table 16-19.
Table 16-20.
Table 16-21.
Table 16-22.
Table 16-23.
Table 16-24.
Table 16-25.
Table 16-26.
Table 16-27.
Table 16-28.
Table 16-29.
Table 16-30.
Table 16-31.
Table 16-32.
Table 16-33.
Table 16-34.
Table 16-35.
Table 16-36.
Table 16-37.
Table 16-38.
Table 16-39.
Table 16-40.
Table 16-41.
Table 17-1.
Table 17-2.
Table 17-3.
Table 17-4.
Table 17-5.
Table 17-6.
Table 17-7.
Table 17-8.
Table 17-9.
Table 17-10.
Table 17-11.
Table 17-12.
Table 17-13.
Table 17-14.
Table 17-15.
Table 17-16.
Table 17-17.
Table 17-18.
Table 17-19.
Table 17-20.
Table 18-1.
Table 18-2.
Table 18-3.
Table 18-4.
Table 18-5.
Table 18-6.
xlii Vol. 3A

CPUID DisplayFamily_DisplayModel Signatures for Processors Based on Intel Core Microarchitecture . . . . . . . . . . . 16-3
Incremental Bus Error Codes of Machine Check for Processors Based on Intel Core Microarchitecture . . . . . . . . . . . 16-4
Incremental MCA Error Code Types for Intel Xeon Processor 7400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
Type B Bus and Interconnect Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6
Type C Cache Bus Controller Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7
Intel QPI Machine Check Error Codes for IA32_MC0_STATUS and IA32_MC1_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Intel QPI Machine Check Error Codes for IA32_MC0_MISC and IA32_MC1_MISC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Machine Check Error Codes for IA32_MC7_STATUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8
Incremental Memory Controller Error Codes of Machine Check for IA32_MC8_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . 16-9
Incremental Memory Controller Error Codes of Machine Check for IA32_MC8_MISC . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-10
Machine Check Error Codes for IA32_MC4_STATUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-10
Intel QPI MC Error Codes for IA32_MC6_STATUS and IA32_MC7_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-11
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 8, 11). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-12
Intel IMC MC Error Codes for IA32_MCi_MISC (i= 8, 11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-12
Machine Check Error Codes for IA32_MC4_STATUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-13
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-16) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-14
Intel IMC MC Error Codes for IA32_MCi_MISC (i= 9-16) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-15
Machine Check Error Codes for IA32_MC4_STATUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-16
Intel QPI MC Error Codes for IA32_MCi_STATUS (i = 5, 20, 21) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-17
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-16) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-18
Intel IMC MC Error Codes for IA32_MCi_MISC (i= 9-16) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-18
Machine Check Error Codes for IA32_MC4_STATUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-19
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-10) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-20
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-16) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-21
Intel HA MC Error Codes for IA32_MCi_MISC (i= 7, 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-22
Machine Check Error Codes for IA32_MC4_STATUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-22
Interconnect MC Error Codes for IA32_MCi_STATUS, i = 5, 12, 19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-24
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 13-16). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-26
M2M MC Error Codes for IA32_MCi_STATUS (i= 7-8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-27
Intel HA MC Error Codes for IA32_MCi_MISC (i= 7, 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-27
Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 6, 7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-28
Incremental Decoding Information: Processor Family 0FH Machine Error Codes For Machine Check . . . . . . . . . . . . .16-29
MCi_STATUS Register Bit Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-30
Incremental MCA Error Code for Intel Xeon Processor MP 7100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-31
Other Information Field Bit Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-31
Type A: L3 Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-32
Type B Bus and Interconnect Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-32
Type C Cache Bus Controller Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-33
Decoding Family 0FH Machine Check Codes for Cache Hierarchy Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16-34
Breakpoint Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-6
Debug Exception Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17-8
Legacy and Streamlined Operation with Freeze_Perfmon_On_PMI = 1, Counter Overflowed . . . . . . . . . . . . . . . . . .17-15
LBR Stack Size and TOS Pointer Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-15
IA32_DEBUGCTL Flag Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-23
CPL-Qualified Branch Trace Store Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-24
MSR_LASTBRANCH_x_TO_IP for the Goldmont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-26
MSR_LASTBRANCH_x_FROM_IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-29
MSR_LASTBRANCH_x_TO_IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-29
LBR Stack Size and TOS Pointer Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-29
MSR_LBR_SELECT for Intel microarchitecture code name Nehalem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-29
MSR_LBR_SELECT for Intel® microarchitecture code name Sandy Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-30
MSR_LBR_SELECT for Intel® microarchitecture code name Haswell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-30
MSR_LASTBRANCH_x_FROM_IP with TSX Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-31
LBR Stack Size and TOS Pointer Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-32
MSR_LBR_INFO_x. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-32
LBR MSR Stack Size and TOS Pointer Range for the Pentium® 4 and the Intel® Xeon® Processor Family . . . . . . . . .17-35
Monitoring Supported Event IDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-47
Re-indexing of COS Numbers and Mapping to CAT/CDP Mask MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-61
MBA Delay Value MSRs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17-66
UMask and Event Select Encodings for Pre-Defined Architectural Performance Events . . . . . . . . . . . . . . . . . . . . . . . . . 18-5
Association of Fixed-Function Performance Counters with Architectural Performance Events . . . . . . . . . . . . . . . . . . 18-9
PEBS Record Format for Intel Core i7 Processor Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-19
Data Source Encoding for Load Latency Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-23
Off-Core Response Event Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-24
MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 Bit Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-24

CONTENTS
PAGE

Table 18-7.
Table 18-8.
Table 18-9.
Table 18-10.
Table 18-11.
Table 18-12.
Table 18-13.
Table 18-14.
Table 18-16.
Table 18-15.
Table 18-17.
Table 18-18.
Table 18-19.
Table 18-21.
Table 18-20.
Table 18-22.
Table 18-23.
Table 18-25.
Table 18-24.
Table 18-26.
Table 18-28.
Table 18-27.
Table 18-30.
Table 18-29.
Table 18-31.
Table 18-32.
Table 18-33.
Table 18-34.
Table 18-35.
Table 18-36.
Table 18-37.
Table 18-38.
Table 18-39.
Table 18-41.
Table 18-40.
Table 18-42.
Table 18-44.
Table 18-43.
Table 18-45.
Table 18-46.
Table 18-47.
Table 18-48.
Table 18-49.
Table 18-50.
Table 18-51.
Table 18-52.
Table 18-53.
Table 18-54.
Table 18-55.
Table 18-56.
Table 18-57.
Table 18-58.
Table 18-59.
Table 18-60.
Table 18-61.
Table 18-62.
Table 18-63.
Table 18-64.
Table 18-65.
Table 18-66.
Table 18-67.
Table 18-68.
Table 18-69.
Table 18-70.

Opcode Field Encoding for MSR_UNCORE_ADDR_OPCODE_MATCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-30
Uncore PMU MSR Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-31
Uncore PMU MSR Summary for Intel® Xeon® Processor E7 Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-33
Core PMU Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-33
PEBS Facility Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-36
PEBS Performance Events for Intel® Microarchitecture Code Name Sandy Bridge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-38
Layout of Data Source Field of Load Latency Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-39
Layout of Precise Store Information In PEBS Record. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-40
MSR_OFFCORE_RSP_x Request_Type Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-41
Off-Core Response Event Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-41
MSR_OFFCORE_RSP_x Response Supplier Info Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-42
MSR_OFFCORE_RSP_x Snoop Info Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-43
Uncore PMU MSR Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-45
Uncore PMU MSR Summary for Intel® Xeon® Processor E5 Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-46
MSR_OFFCORE_RSP_x Supplier Info Field Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-46
Core PMU Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-47
PEBS Facility Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-48
Precise Events That Supports Data Linear Address Profiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-49
PEBS Record Format for 4th Generation Intel Core Processor Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-49
Layout of Data Linear Address Information In PEBS Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-50
MSR_OFFCORE_RSP_x Supplier Info Field Definition (CPUID Signature 06_3CH, 06_46H). . . . . . . . . . . . . . . . . . . . . . 18-51
MSR_OFFCORE_RSP_x Request_Type Definition (Haswell microarchitecture). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-51
MSR_OFFCORE_RSP_x Supplier Info Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-52
MSR_OFFCORE_RSP_x Supplier Info Field Definition (CPUID Signature 06_45H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-52
TX Abort Information Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-54
Uncore PMU MSR Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-55
Core PMU Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-57
PEBS Facility Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-58
PEBS Record Format for 6th Generation Intel Core Processor and 7th Generation Intel Core Processor Families 18-59
Precise Events for the Skylake and Kaby Lake Microarchitectures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-60
Layout of Data Linear Address Information In PEBS Record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-61
FrontEnd_Retired Sub-Event Encodings Supported by MSR_PEBS_FRONTEND.EVTSEL . . . . . . . . . . . . . . . . . . . . . . . . 18-61
MSR_PEBS_FRONTEND Layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-62
MSR_OFFCORE_RSP_x Supplier Info Field Definition (CPUID Signature 06_4EH, 06_5EH and 06_8EH, 06_9EH) 18-63
MSR_OFFCORE_RSP_x Request_Type Definition (Skylake and Kaby Lake Microarchitectures) . . . . . . . . . . . . . . . . . 18-63
MSR_OFFCORE_RSP_x Snoop Info Field Definition (CPUID Signatures 06_4EH, 06_5EH, 06_8EH, 06_9E and
06_55H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-64
MSR_OFFCORE_RSP_x Supplier Info Field Definition (CPUID Signature 06_55H) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-65
MSR_OFFCORE_RSP_x Request_Type Definition (Intel® Xeon® Processor Scalable Family) . . . . . . . . . . . . . . . . . . . . . 18-65
PEBS Performance Events for the Knights Landing Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-67
PEBS Record Format for the Knights Landing Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-67
OffCore Response Event Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-68
Bit fields of the MSR_OFFCORE_RESP [0, 1] Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-68
PEBS Performance Events for the Silvermont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-71
PEBS Record Format for the Silvermont Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-71
OffCore Response Event Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-72
MSR_OFFCORE_RSPx Request_Type Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-73
MSR_OFFCORE_RSP_x Response Supplier Info Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-74
MSR_OFFCORE_RSPx Snoop Info Field Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-74
Core PMU Comparison Between the Goldmont and Silvermont Microarchitectures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-75
Precise Events Supported by the Goldmont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-77
PEBS Record Format for the Goldmont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-78
MSR_OFFCORE_RSPx Request_Type Field Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-79
MSR_OFFCORE_RSPx For L2 Miss and Outstanding Requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-80
Core PMU Comparison Between the Goldmont Plus and Goldmont Microarchitectures . . . . . . . . . . . . . . . . . . . . . . . . . 18-81
Core Specificity Encoding within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-83
Agent Specificity Encoding within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-83
HW Prefetch Qualification Encoding within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-84
MESI Qualification Definitions within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-84
Bus Snoop Qualification Definitions within a Non-Architectural Umask. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-84
Snoop Type Qualification Definitions within a Non-Architectural Umask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-85
At-Retirement Performance Events for Intel Core Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-88
PEBS Performance Events for Intel Core Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-88
Requirements to Program PEBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-89
Performance Counter MSRs and Associated CCCR and ESCR MSRs (Processors Based on Intel NetBurst
Vol. 3A xliii

CONTENTS
PAGE

Table 18-71.
Table 18-72.
Table 18-73.
Table 18-74.
Table 18-75.
Table 19-1.
Table 19-2.
Table 19-3.
Table 19-4.
Table 19-5.
Table 19-6.
Table 19-7.
Table 19-8.
Table 19-9.
Table 19-10.
Table 19-11.
Table 19-12.
Table 19-13.
Table 19-14.
Table 19-15.
Table 19-16.
Table 19-17.
Table 19-18.
Table 19-19.
Table 19-20.
Table 19-21.
Table 19-22.
Table 19-23.
Table 19-24.
Table 19-25.
Table 19-26.
Table 19-27.
Table 19-28.
Table 19-29.
Table 19-30.
Table 19-31.
Table 19-32.
Table 19-33.
Table 19-35.
Table 19-36.
Table 19-34.
Table 19-37.
Table 19-38.
Table 19-39.
Table 19-40.
Table 19-41.
Table 20-1.
Table 20-2.
Table 21-1.
Table 22-1.
Table 22-3.
Table 22-2.
Table 22-4.
Table 22-5.
xliv Vol. 3A

Microarchitecture) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-91
Event Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18-98
CCR Names and Bit Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-102
Effect of Logical Processor and CPL Qualification for Logical-Processor-Specific (TS) Events . . . . . . . . . . . . . . . . . 18-110
Effect of Logical Processor and CPL Qualification for Non-logical-Processor-specific (TI) Events . . . . . . . . . . . . . . 18-111
Nominal Core Crystal Clock Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-127
Architectural Performance Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2
Fixed-Function Performance Counter and Pre-defined Performance Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2
Performance Events of the Processor Core Supported in Intel® Xeon® Processor Scalable Family with Skylake
Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-3
Performance Events of the Processor Core Supported by Skylake Microarchitecture and Kaby Lake
Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-24
Intel® TSX Performance Event Addendum in Processors based on Skylake Microarchitecture. . . . . . . . . . . . . . . . . . .19-33
Performance Events of the Processor Core Supported by Knights Landing Microarchitecture . . . . . . . . . . . . . . . . . .19-34
Performance Events of the Processor Core Supported by Broadwell Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . .19-38
Intel® TSX Performance Event Addendum in Processors Based on Broadwell Microarchitecture . . . . . . . . . . . . . . . .19-45
Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors . . . . . . . . . . . . . . . . . . . . . . . . .19-46
Intel TSX Performance Events in Processors Based on Haswell Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-54
Uncore Performance Events in the 4th Generation Intel® Core™ Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-56
Performance Events Applicable only to the Processor Core of Intel® Xeon® Processor E5 v3 Family . . . . . . . . . . . .19-57
Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors . . . . . . . . . . . . . . . . .19-58
Performance Events Applicable Only to the Processor Core of Intel® Xeon® Processor E5 v2 Family and Intel® Xeon®
Processor E7 v2 Family . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-66
Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx,
Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family . . . . . . . . . . . . . . . . . . . . . . . . . .19-67
Performance Events applicable only to the Processor core for 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-76
Performance Events Applicable only to the Processor Core of Intel® Xeon® Processor E5 Family. . . . . . . . . . . . . . . .19-78
Performance Events In the Processor Uncore for 2nd Generation Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx,
Intel® Core™ i3-2xxx Processor Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-80
Performance Events In the Processor Core for Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series19-81
Performance Events In the Processor Uncore for Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500
Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19-98
Performance Events In the Processor Core for Processors Based on Intel® Microarchitecture Code Name
Westmere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-110
Performance Events In the Processor Uncore for Processors Based on Intel® Microarchitecture Code Name
Westmere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-126
Performance Events for Processors Based on Enhanced Intel Core Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . 19-141
Fixed-Function Performance Counter and Pre-defined Performance Events. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-141
Performance Events in Processors Based on Intel® Core™ Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-142
Performance Events for the Goldmont Plus Microarchitecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-167
Performance Events for the Goldmont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-168
Performance Events for Silvermont Microarchitecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-176
Performance Events for 45 nm, 32 nm Intel® Atom™ Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-180
Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-194
Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture for Non-Retirement Counting19-199
Performance Monitoring Events For Intel NetBurst® Microarchitecture for At-Retirement Counting . . . . . . . . . . 19-217
Intel NetBurst® Microarchitecture Model-Specific Performance Monitoring Events (For Model Encoding 3, 4 or 6)19-221
List of Metrics Available for Execution Tagging (For Execution Event Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-222
List of Metrics Available for Replay Tagging (For Replay Event Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-222
List of Metrics Available for Front_end Tagging (For Front_end Event Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-222
Event Mask Qualification for Logical Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-224
Performance Monitoring Events on Intel® Pentium® M Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-229
Performance Monitoring Events Modified on Intel® Pentium® M Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-230
Events That Can Be Counted with the P6 Family Performance Monitoring Counters . . . . . . . . . . . . . . . . . . . . . . . . . 19-231
Events That Can Be Counted with Pentium Processor Performance Monitoring Counters . . . . . . . . . . . . . . . . . . . . 19-240
Real-Address Mode Exceptions and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20-6
Software Interrupt Handling Methods While in Virtual-8086 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20-17
Characteristics of 16-Bit and 32-Bit Program Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21-1
New Instruction in the Pentium Processor and Later IA-32 Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-4
EM and MP Flag Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-17
Recommended Values of the EM, MP, and NE Flags for Intel486 SX Microprocessor/Intel 487 SX Math Coprocessor
System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22-17
Exception Conditions for Legacy SIMD/MMX Instructions with FP Exception and 16-Byte Alignment . . . . . . . . . . .22-22
Exception Conditions for Legacy SIMD/MMX Instructions with XMM and FP Exception . . . . . . . . . . . . . . . . . . . . . . . . .22-23

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Table 22-6.
Table 22-7.
Table 22-8.
Table 22-9.
Table 22-10.
Table 24-1.
Table 24-2.
Table 24-3.
Table 24-4.
Table 24-5.
Table 24-6.
Table 24-7.
Table 24-8.
Table 24-9.
Table 24-10.
Table 24-11.
Table 24-12.
Table 24-13.
Table 24-14.
Table 24-15.
Table 24-16.
Table 24-17.
Table 25-1.
Table 27-1.
Table 27-2.
Table 27-3.
Table 27-4.
Table 27-5.
Table 27-6.
Table 27-7.
Table 27-8.
Table 27-9.
Table 27-10.
Table 27-11.
Table 27-12.
Table 27-13.
Table 27-14.
Table 28-1.
Table 28-2.
Table 28-3.
Table 28-4.
Table 28-5.
Table 28-6.
Table 29-1.
Table 30-1.
Table 31-1.
Table 34-1.
Table 34-2.
Table 34-3.
Table 34-4.
Table 34-5.
Table 34-6.
Table 34-7.
Table 34-8.
Table 34-9.
Table 34-10.
Table 35-1.
Table 35-2.
Table 35-3.
Table 35-4.
Table 35-5.
Table 35-6.
Table 35-7.
Table 35-9.

Exception Conditions for Legacy SIMD/MMX Instructions with XMM and without FP Exception. . . . . . . . . . . . . . . . . 22-24
Exception Conditions for SIMD/MMX Instructions with Memory Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-25
Exception Conditions for Legacy SIMD/MMX Instructions without FP Exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22-26
Exception Conditions for Legacy SIMD/MMX Instructions without Memory Reference . . . . . . . . . . . . . . . . . . . . . . . . . 22-27
Processor State Following Power-up/Reset/INIT for Pentium, Pentium Pro and Pentium 4 Processors . . . . . . . . . 22-37
Format of the VMCS Region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-2
Format of Access Rights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-4
Format of Interruptibility State. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-6
Format of Pending-Debug-Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-7
Definitions of Pin-Based VM-Execution Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-9
Definitions of Primary Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-9
Definitions of Secondary Processor-Based VM-Execution Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-11
Format of Extended-Page-Table Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-15
Definitions of VM-Function Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-16
Definitions of VM-Exit Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-17
Format of an MSR Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-18
Definitions of VM-Entry Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-19
Format of the VM-Entry Interruption-Information Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-20
Format of Exit Reason . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-21
Format of the VM-Exit Interruption-Information Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-22
Format of the IDT-Vectoring Information Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-23
Structure of VMCS Component Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24-25
Format of the Virtualization-Exception Information Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25-16
Exit Qualification for Debug Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-4
Exit Qualification for Task Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-5
Exit Qualification for Control-Register Accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-6
Exit Qualification for MOV DR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-7
Exit Qualification for I/O Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-8
Exit Qualification for APIC-Access VM Exits from Linear Accesses and Guest-Physical Accesses. . . . . . . . . . . . . . . . . 27-8
Exit Qualification for EPT Violations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-9
Format of the VM-Exit Instruction-Information Field as Used for INS and OUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-14
Format of the VM-Exit Instruction-Information Field as Used for INVEPT, INVPCID, and INVVPID . . . . . . . . . . . . . . . 27-15
Format of the VM-Exit Instruction-Information Field as Used for LIDT, LGDT, SIDT, or SGDT. . . . . . . . . . . . . . . . . . . . 27-16
Format of the VM-Exit Instruction-Information Field as Used for LLDT, LTR, SLDT, and STR. . . . . . . . . . . . . . . . . . . . 27-17
Format of the VM-Exit Instruction-Information Field as Used for RDRAND and RDSEED. . . . . . . . . . . . . . . . . . . . . . . . 27-18
Format of the VM-Exit Instruction-Information Field as Used for VMCLEAR, VMPTRLD, VMPTRST, VMXON,
XRSTORS, and XSAVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27-18
Format of the VM-Exit Instruction-Information Field as Used for VMREAD and VMWRITE . . . . . . . . . . . . . . . . . . . . . . 27-19
Format of an EPT PML4 Entry (PML4E) that References an EPT Page-Directory-Pointer Table . . . . . . . . . . . . . . . . . . 28-3
Format of an EPT Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page . . . . . . . . . . . . . . . . . . . . . 28-5
Format of an EPT Page-Directory-Pointer-Table Entry (PDPTE) that References an EPT Page Directory . . . . . . . . . 28-6
Format of an EPT Page-Directory Entry (PDE) that Maps a 2-MByte Page. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-7
Format of an EPT Page-Directory Entry (PDE) that References an EPT Page Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-8
Format of an EPT Page-Table Entry that Maps a 4-KByte Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28-9
Format of Posted-Interrupt Descriptor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29-13
VM-Instruction Error Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30-29
Operating Modes for Host and Guest Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31-12
SMRAM State Save Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-5
Processor Signatures and 64-bit SMRAM State Save Map Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-6
SMRAM State Save Map for Intel 64 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-7
Processor Register Initialization in SMM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-9
I/O Instruction Information in the SMM State Save Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-12
I/O Instruction Type Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-12
Auto HALT Restart Flag Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-14
I/O Instruction Restart Field Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-15
Exit Qualification for SMIs That Arrive Immediately After the Retirement of an I/O Instruction. . . . . . . . . . . . . . . . . 34-20
Format of MSEG Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34-25
COFI Type for Branch Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-2
IP Filtering Packet Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-6
ToPA Table Entry Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-11
Algorithm to Manage Intel PT ToPA PMI and XSAVES/XRSTORS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-14
Behavior on Restricted Memory Access. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-15
IA32_RTIT_CTL MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-16
IA32_RTIT_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-20
IA32_RTIT_OUTPUT_MASK_PTRS MSR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35-22
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Table 35-8.
Table 35-10.
Table 35-11.
Table 35-12.
Table 35-13.
Table 35-14.
Table 35-15.
Table 35-16.
Table 35-17.
Table 35-18.
Table 35-19.
Table 35-20.
Table 35-21.
Table 35-22.
Table 35-23.
Table 35-24.
Table 35-25.
Table 35-26.
Table 35-27.
Table 35-28.
Table 35-29.
Table 35-30.
Table 35-31.
Table 35-32.
Table 35-33.
Table 35-34.
Table 35-35.
Table 35-36.
Table 35-37.
Table 35-38.
Table 35-39.
Table 35-40.
Table 35-41.
Table 35-42.
Table 35-43.
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Table 35-46.
Table 35-45.
Table 35-47.
Table 35-48.
Table 35-49.
Table 35-50.
Table 35-51.
Table 35-52.
Table 36-1.
Table 36-2.
Table 36-3.
Table 36-4.
Table 36-5.
Table 36-6.
Table 37-1.
Table 37-2.
Table 37-3.
Table 37-4.
Table 37-5.
Table 37-6.
Table 37-7.
Table 37-8.
Table 37-10.
Table 37-9.
Table 37-11.
Table 37-12.
Table 37-13.
Table 37-14.
Table 37-15.
xlvi Vol. 3A

IA32_RTIT_OUTPUT_BASE MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-22
TSX Packet Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-23
CPUID Leaf 14H Enumeration of Intel Processor Trace Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-26
CPUID Leaf 14H, sub-leaf 1H Enumeration of Intel Processor Trace Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-28
Memory Layout of the Trace Configuration State Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-31
An Illustrative CYC Packet Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-33
Compound Packet Event Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-36
TNT Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-36
IP Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-38
FUP/TIP IP Reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-39
TNT Examples with Deferred TIPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-40
TIP.PGE Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-41
TIP.PGD Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-42
FUP Packet Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-43
FUP Cases and IP Payload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-44
PIP Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-45
General Form of MODE Packets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-46
MODE.Exec Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-46
MODE.TSX Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-47
TraceStop Packet Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-48
CBR Packet Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-48
TSC Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-49
MTC Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-50
TMA Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-51
Cycle Count Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-52
VMCS Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-53
OVF Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-54
PSB Packet Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-54
PSBEND Packet Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-55
MNT Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-56
PAD Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-56
PTW Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-57
EXSTOP Packet Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-58
MWAIT Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-59
PWRE Packet Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-60
PWRX Packet Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-61
VMCS Controls For Intel Processor Trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-62
Common Usages of Intel PT and VMX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-62
Packets on VMX Transitions (System-Wide Tracing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-63
Packets on VMX Transitions (Host-Only Tracing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-64
Packets on a Failed VM Entry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-65
Packet Generation under Different Enable Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-65
PwrEvtEn and PTWEn Packet Generation under Different Enable Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-74
PwrEvtEn and PTWEn Packet Generation under Different Enable Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35-78
Supervisor and User Mode Enclave Instruction Leaf Functions in Long-Form of SGX1. . . . . . . . . . . . . . . . . . . . . . . . . . . 37-3
Supervisor and User Mode Enclave Instruction Leaf Functions in Long-Form of SGX2. . . . . . . . . . . . . . . . . . . . . . . . . . . 37-4
Intel® SGX Opt-in and Enabling Behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-4
CPUID Leaf 12H, Sub-Leaf 0 Enumeration of Intel® SGX Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-5
CPUID Leaf 12H, Sub-Leaf 1 Enumeration of Intel® SGX Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-5
CPUID Leaf 12H, Sub-Leaf Index 2 or Higher Enumeration of Intel® SGX Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37-6
List of Implicit and Explicit Memory Access by Intel® SGX Enclave Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-3
Layout of SGX Enclave Control Structure (SECS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-4
Layout of ATTRIBUTES Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-5
Bit Vector Layout of MISCSELECT Field of Extended Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-6
Layout of Thread Control Structure (TCS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-6
Layout of TCS.FLAGS Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-6
Top-to-Bottom Layout of an SSA Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-7
Layout of GPRSGX Portion of the State Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-8
Exception Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-9
Layout of EXITINFO Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-9
Layout of MISC region of the State Save Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-10
Layout of EXINFO Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-10
Page Fault Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-10
Layout of PAGEINFO Data Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-11
Layout of SECINFO Data Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38-11

CONTENTS
PAGE

Table 37-16.
Table 37-17.
Table 37-18.
Table 37-19.
Table 37-21.
Table 37-20.
Table 37-22.
Table 37-23.
Table 37-24.
Table 37-25.
Table 37-26.
Table 37-27.
Table 38-1.
Table 39-1.
Table 40-1.
Table 40-2.
Table 40-3.
Table 40-4.
Table 40-5.
Table 40-6.
Table 40-7.
Table 40-8.
Table 40-9.
Table 40-10.
Table 40-11.
Table 40-12.
Table 40-13.
Table 40-14.
Table 40-15.
Table 40-16.
Table 40-17.
Table 40-18.
Table 40-19.
Table 40-20.
Table 40-21.
Table 40-22.
Table 40-23.
Table 40-24.
Table 40-25.
Table 40-26.
Table 40-27.
Table 40-28.
Table 40-29.
Table 40-30.
Table 40-31.
Table 40-32.
Table 40-33.
Table 40-34.
Table 40-35.
Table 40-36.
Table 40-37.
Table 40-38.
Table 40-39.
Table 40-40.
Table 40-41.
Table 40-42.
Table 40-43.
Table 40-44.
Table 40-45.
Table 40-46.
Table 40-47.
Table 40-48.
Table 40-49.
Table 40-50.
Table 40-51.

Layout of SECINFO.FLAGS Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-11
Supported PAGE_TYPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-12
Layout of PCMD Data Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-12
Layout of Enclave Signature Structure (SIGSTRUCT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-13
Layout of REPORT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-14
Layout of EINIT Token (EINITTOKEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-14
Layout of TARGETINFO Data Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-15
Layout of KEYREQUEST Data Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-15
Supported KEYName Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-16
Layout of KEYPOLICY Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-16
Layout of Version Array Data Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-16
Content of an Enclave Page Cache Map Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38-17
Illegal Instructions Inside an Enclave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39-13
GPR, x87 Synthetic States on Asynchronous Enclave Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40-3
Register Usage of Privileged Enclave Instruction Leaf Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-1
Register Usage of Unprivileged Enclave Instruction Leaf Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-2
Error or Information Codes for Intel® SGX Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-2
List of Internal CREG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-3
Concurrency Restrictions of EADD with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-11
Concurrency Restrictions of EADD with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-12
Concurrency Restrictions of EAUG with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-15
Concurrency Restrictions of EAUG with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-16
EBLOCK Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-18
Concurrency Restrictions of EBLOCK with Other Intel® SGX Operations 1 of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-18
Concurrency Restrictions of EBLOCK with Other Intel® SGX Operations 2 of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-19
Concurrency Restrictions of ECREATE with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-21
Concurrency Restrictions of ECREATE with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-21
EDBGRD Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-25
Concurrency Restrictions of EDBGRD with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-26
Concurrency Restrictions of EDBGRD with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-26
EDBGWR Return Value in RAX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-29
Concurrency Restrictions of EDBGWR with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-30
Concurrency Restrictions of EDBGWR with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-30
Concurrency Restrictions of EEXTEND with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-32
Concurrency Restrictions of EEXTEND with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-33
EINIT Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-36
Concurrency Restrictions of EINIT with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-37
Concurrency Restrictions of EINIT with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-37
ELDB/ELDU Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-42
Concurrency Restrictions of ELDB/ELDU with Intel® SGX Instructions - 1of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-42
Concurrency Restrictions of ELDB/ELDU with Intel® SGX Instructions - 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-43
EMODPR Return Value in RAX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-47
Concurrency Restrictions of EMODPR with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-47
Concurrency Restrictions of EMODPR with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-48
EMODT Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-50
Concurrency Restrictions of EMODT with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-50
Concurrency Restrictions of EMODT with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-51
Concurrency Restrictions of EPA with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-53
Concurrency Restrictions of EPA with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-53
EREMOVE Return Value in RAX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-55
Concurrency Restrictions of EREMOVE with Other Intel® SGX Operations 1 of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-56
Concurrency Restrictions of EREMOVE with Other Intel® SGX Operations 2 of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-56
ETRACK Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-58
Concurrency Restrictions of ETRACK with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-58
Concurrency Restrictions of ETRACK with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-58
ETRACK Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-59
EWB Return Value in RAX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-60
Concurrency Restrictions of EWB with Intel® SGX Instructions - 1of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-60
Concurrency Restrictions of EWB with Intel® SGX Instructions - 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-60
EACCEPT Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-66
Concurrency Restrictions of EACCEPT with Intel® SGX Instructions - 1of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-66
Concurrency Restrictions of EACCEPT with Intel® SGX Instructions - 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-67
EACCEPTCOPY Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-70
Concurrency Restrictions of EACCEPTCOPY with Intel® SGX Instructions - 1of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-71
Concurrency Restrictions of EACCEPTCOPY with Intel® SGX Instructions - 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-71
Vol. 3A xlvii

CONTENTS
PAGE

Table 40-52.
Table 40-53.
Table 40-54.
Table 40-55.
Table 40-56.
Table 40-57.
Table 40-58.
Table 40-59.
Table 40-60.
Table 40-61.
Table 40-62.
Table 40-63.
Table 40-64.
Table 40-65.
Table 41-1.
Table 41-2.
Table A-1.
Table B-1.
Table B-2.
Table B-3.
Table B-4.
Table B-5.
Table B-6.
Table B-7.
Table B-8.
Table B-9.
Table B-10.
Table B-11.
Table B-12.
Table B-13.
Table B-14.
Table B-15.
Table C-1.

xlviii Vol. 3A

Concurrency Restrictions of EENTER with Intel® SGX Instructions - 1of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-75
Concurrency Restrictions of EENTER with Intel® SGX Instructions - 2 of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-75
Concurrency Restrictions of EEXIT with Intel® SGX Instructions - 1of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-82
Concurrency Restrictions of EEXIT with Intel® SGX Instructions - 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-82
Key Derivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-86
EGETKEY Return Value in RAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-86
Concurrency Restrictions of EGETKEY with Other Intel® SGX Operations 1 of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-86
Concurrency Restrictions of EGETKEY with Other Intel® SGX Operations 2 of 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-87
Concurrency Restrictions of EMODPE with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-92
Concurrency Restrictions of EMODPE with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-92
Concurrency Restrictions of EREPORT with Other Intel® SGX Operations 1 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-96
Concurrency Restrictions of EREPORT with Other Intel® SGX Operations 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41-96
Concurrency Restrictions of ERESUME with Intel® SGX Instructions - 1of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-100
Concurrency Restrictions of ERESUME with Intel® SGX Instructions - 2 of 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41-100
SMRAM Synthetic States on Asynchronous Enclave Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42-9
Layout of the IA32_SGX_SVN_STATUS MSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42-11
Memory Types Recommended for VMCS and Related Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1
Encoding for 16-Bit Control Fields (0000_00xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
Encodings for 16-Bit Guest-State Fields (0000_10xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1
Encodings for 16-Bit Host-State Fields (0000_11xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
Encodings for 64-Bit Control Fields (0010_00xx_xxxx_xxxAb) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2
Encodings for 64-Bit Read-Only Data Field (0010_01xx_xxxx_xxxAb) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4
Encodings for 64-Bit Guest-State Fields (0010_10xx_xxxx_xxxAb). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-4
Encodings for 64-Bit Host-State Fields (0010_11xx_xxxx_xxxAb). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-5
Encodings for 32-Bit Control Fields (0100_00xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6
Encodings for 32-Bit Read-Only Data Fields (0100_01xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7
Encodings for 32-Bit Guest-State Fields (0100_10xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7
Encoding for 32-Bit Host-State Field (0100_11xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
Encodings for Natural-Width Control Fields (0110_00xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8
Encodings for Natural-Width Read-Only Data Fields (0110_01xx_xxxx_xxx0B). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9
Encodings for Natural-Width Guest-State Fields (0110_10xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9
Encodings for Natural-Width Host-State Fields (0110_11xx_xxxx_xxx0B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-10
Basic Exit Reasons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .C-1

CHAPTER 1
ABOUT THIS MANUAL
The Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A: System Programming Guide,
Part 1 (order number 253668), the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3B:
System Programming Guide, Part 2 (order number 253669), the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 3C: System Programming Guide, Part 3 (order number 326019), and the Intel® 64
and IA-32 Architectures Software Developer’s Manual, Volume 3D:System Programming Guide, Part 4 (order
number 332831) are part of a set that describes the architecture and programming environment of Intel 64 and IA32 Architecture processors. The other volumes in this set are:

•

Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1: Basic Architecture (order number
253665).

•

Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C & 2D: Instruction Set
Reference (order numbers 253666, 253667, 326018 and 334569).

•

The Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4: Model-Specific Registers
(order number 335592).

The Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, describes the basic architecture
and programming environment of Intel 64 and IA-32 processors. The Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volumes 2A, 2B, 2C & 2D, describe the instruction set of the processor and the opcode structure. These volumes apply to application programmers and to programmers who write operating systems or executives. The Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 3A, 3B, 3C & 3D, describe
the operating-system support environment of Intel 64 and IA-32 processors. These volumes target operatingsystem and BIOS designers. In addition, Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
3B, and Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C address the programming
environment for classes of software that host operating systems. The Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 4, describes the model-specific registers of Intel 64 and IA-32 processors.

1.1

INTEL® 64 AND IA-32 PROCESSORS COVERED IN THIS MANUAL

This manual set includes information pertaining primarily to the most recent Intel 64 and IA-32 processors, which
include:

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Pentium® processors
P6 family processors
Pentium® 4 processors
Pentium® M processors
Intel® Xeon® processors
Pentium® D processors
Pentium® processor Extreme Editions
64-bit Intel® Xeon® processors
Intel® Core™ Duo processor
Intel® Core™ Solo processor
Dual-Core Intel® Xeon® processor LV
Intel® Core™2 Duo processor
Intel® Core™2 Quad processor Q6000 series
Intel® Xeon® processor 3000, 3200 series
Intel® Xeon® processor 5000 series
Intel® Xeon® processor 5100, 5300 series

Vol. 3A 1-1

ABOUT THIS MANUAL

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Intel® Core™2 Extreme processor X7000 and X6800 series

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Intel® Core™ i7 processor

Intel® Core™2 Extreme QX6000 series
Intel® Xeon® processor 7100 series
Intel® Pentium® Dual-Core processor
Intel® Xeon® processor 7200, 7300 series
Intel® Core™2 Extreme QX9000 series
Intel® Xeon® processor 5200, 5400, 7400 series
Intel® Core™2 Extreme processor QX9000 and X9000 series
Intel® Core™2 Quad processor Q9000 series
Intel® Core™2 Duo processor E8000, T9000 series
Intel® Atom™ processors 200, 300, D400, D500, D2000, N200, N400, N2000, E2000, Z500, Z600, Z2000,
C1000 series are built from 45 nm and 32 nm processes.
Intel® Core™ i5 processor
Intel® Xeon® processor E7-8800/4800/2800 product families
Intel® Core™ i7-3930K processor
2nd generation Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx processor series
Intel® Xeon® processor E3-1200 product family
Intel® Xeon® processor E5-2400/1400 product family
Intel® Xeon® processor E5-4600/2600/1600 product family
3rd generation Intel® Core™ processors
Intel® Xeon® processor E3-1200 v2 product family
Intel® Xeon® processor E5-2400/1400 v2 product families
Intel® Xeon® processor E5-4600/2600/1600 v2 product families
Intel® Xeon® processor E7-8800/4800/2800 v2 product families
4th generation Intel® Core™ processors
The Intel® Core™ M processor family
Intel® Core™ i7-59xx Processor Extreme Edition
Intel® Core™ i7-49xx Processor Extreme Edition
Intel® Xeon® processor E3-1200 v3 product family
Intel® Xeon® processor E5-2600/1600 v3 product families
5th generation Intel® Core™ processors
Intel® Xeon® processor D-1500 product family
Intel® Xeon® processor E5 v4 family
Intel® Atom™ processor X7-Z8000 and X5-Z8000 series
Intel® Atom™ processor Z3400 series
Intel® Atom™ processor Z3500 series
6th generation Intel® Core™ processors
Intel® Xeon® processor E3-1500m v5 product family
7th generation Intel® Core™ processors
Intel® Xeon Phi™ Processor 3200, 5200, 7200 Series
Intel® Xeon® Processor Scalable Family

1-2 Vol. 3A

ABOUT THIS MANUAL
The Pentium® 4, Pentium® D, and Pentium® processor Extreme Editions are based on the Intel NetBurst® microarchitecture. Most early Intel® Xeon® processors are based on the Intel NetBurst® microarchitecture. Intel Xeon
processor 5000, 7100 series are based on the Intel NetBurst® microarchitecture.
The Intel® Core™ Duo, Intel® Core™ Solo and dual-core Intel® Xeon® processor LV are based on an improved
Pentium® M processor microarchitecture.
The Intel® Xeon® processor 3000, 3200, 5100, 5300, 7200, and 7300 series, Intel® Pentium® dual-core, Intel®
Core™2 Duo, Intel® Core™2 Quad, and Intel® Core™2 Extreme processors are based on Intel® Core™ microarchitecture.
The Intel® Xeon® processor 5200, 5400, 7400 series, Intel® Core™2 Quad processor Q9000 series, and Intel®
Core™2 Extreme processors QX9000, X9000 series, Intel® Core™2 processor E8000 series are based on Enhanced
Intel® Core™ microarchitecture.
The Intel® Atom™ processors 200, 300, D400, D500, D2000, N200, N400, N2000, E2000, Z500, Z600, Z2000,
C1000 series are based on the Intel® Atom™ microarchitecture and supports Intel 64 architecture.
P6 family, Pentium® M, Intel® Core™ Solo, Intel® Core™ Duo processors, dual-core Intel® Xeon® processor LV,
and early generations of Pentium 4 and Intel Xeon processors support IA-32 architecture. The Intel® AtomTM
processor Z5xx series support IA-32 architecture.
The Intel® Xeon® processor 3000, 3200, 5000, 5100, 5200, 5300, 5400, 7100, 7200, 7300, 7400 series, Intel®
Core™2 Duo, Intel® Core™2 Extreme, Intel® Core™2 Quad processors, Pentium® D processors, Pentium® DualCore processor, newer generations of Pentium 4 and Intel Xeon processor family support Intel® 64 architecture.
The Intel® Core™ i7 processor and Intel® Xeon® processor 3400, 5500, 7500 series are based on 45 nm Intel®
microarchitecture code name Nehalem. Intel® microarchitecture code name Westmere is a 32 nm version of Intel®
microarchitecture code name Nehalem. Intel® Xeon® processor 5600 series, Intel Xeon processor E7 and various
Intel Core i7, i5, i3 processors are based on Intel® microarchitecture code name Westmere. These processors
support Intel 64 architecture.
The Intel® Xeon® processor E5 family, Intel® Xeon® processor E3-1200 family, Intel® Xeon® processor E78800/4800/2800 product families, Intel® Core™ i7-3930K processor, and 2nd generation Intel® Core™ i7-2xxx,
Intel® CoreTM i5-2xxx, Intel® Core™ i3-2xxx processor series are based on the Intel® microarchitecture code name
Sandy Bridge and support Intel 64 architecture.
The Intel® Xeon® processor E7-8800/4800/2800 v2 product families, Intel® Xeon® processor E3-1200 v2 product
family and 3rd generation Intel® Core™ processors are based on the Intel® microarchitecture code name Ivy
Bridge and support Intel 64 architecture.
The Intel® Xeon® processor E5-4600/2600/1600 v2 product families, Intel® Xeon® processor E5-2400/1400 v2
product families and Intel® Core™ i7-49xx Processor Extreme Edition are based on the Intel® microarchitecture
code name Ivy Bridge-E and support Intel 64 architecture.
The Intel® Xeon® processor E3-1200 v3 product family and 4th Generation Intel® Core™ processors are based on
the Intel® microarchitecture code name Haswell and support Intel 64 architecture.
The Intel® Xeon® processor E5-2600/1600 v3 product families and the Intel® Core™ i7-59xx Processor Extreme
Edition are based on the Intel® microarchitecture code name Haswell-E and support Intel 64 architecture.
The Intel® Atom™ processor Z8000 series is based on the Intel microarchitecture code name Airmont.
The Intel® Atom™ processor Z3400 series and the Intel® Atom™ processor Z3500 series are based on the Intel
microarchitecture code name Silvermont.
The Intel® Core™ M processor family, 5th generation Intel® Core™ processors, Intel® Xeon® processor D-1500
product family and the Intel® Xeon® processor E5 v4 family are based on the Intel® microarchitecture code name
Broadwell and support Intel 64 architecture.
The Intel® Xeon® Processor Scalable Family, Intel® Xeon® processor E3-1500m v5 product family and 6th generation Intel® Core™ processors are based on the Intel® microarchitecture code name Skylake and support Intel 64
architecture.
The 7th generation Intel® Core™ processors are based on the Intel® microarchitecture code name Kaby Lake and
support Intel 64 architecture.
The Intel® Xeon Phi™ Processor 3200, 5200, 7200 Series is based on the Intel® microarchitecture code name
Knights Landing and supports Intel 64 architecture.
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IA-32 architecture is the instruction set architecture and programming environment for Intel's 32-bit microprocessors. Intel® 64 architecture is the instruction set architecture and programming environment which is the superset
of Intel’s 32-bit and 64-bit architectures. It is compatible with the IA-32 architecture.

1.2

OVERVIEW OF THE SYSTEM PROGRAMMING GUIDE

A description of this manual’s content follows1:
Chapter 1 — About This Manual. Gives an overview of all eight volumes of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual. It also describes the notational conventions in these manuals and lists related Intel
manuals and documentation of interest to programmers and hardware designers.
Chapter 2 — System Architecture Overview. Describes the modes of operation used by Intel 64 and IA-32
processors and the mechanisms provided by the architectures to support operating systems and executives,
including the system-oriented registers and data structures and the system-oriented instructions. The steps necessary for switching between real-address and protected modes are also identified.
Chapter 3 — Protected-Mode Memory Management. Describes the data structures, registers, and instructions
that support segmentation and paging. The chapter explains how they can be used to implement a “flat” (unsegmented) memory model or a segmented memory model.
Chapter 4 — Paging. Describes the paging modes supported by Intel 64 and IA-32 processors.
Chapter 5 — Protection. Describes the support for page and segment protection provided in the Intel 64 and IA32 architectures. This chapter also explains the implementation of privilege rules, stack switching, pointer validation, user and supervisor modes.
Chapter 6 — Interrupt and Exception Handling. Describes the basic interrupt mechanisms defined in the Intel
64 and IA-32 architectures, shows how interrupts and exceptions relate to protection, and describes how the architecture handles each exception type. Reference information for each exception is given in this chapter. Includes
programming the LINT0 and LINT1 inputs and gives an example of how to program the LINT0 and LINT1 pins for
specific interrupt vectors.
Chapter 7 — Task Management. Describes mechanisms the Intel 64 and IA-32 architectures provide to support
multitasking and inter-task protection.
Chapter 8 — Multiple-Processor Management. Describes the instructions and flags that support multiple
processors with shared memory, memory ordering, and Intel® Hyper-Threading Technology. Includes MP initialization for P6 family processors and gives an example of how to use the MP protocol to boot P6 family processors in an
MP system.
Chapter 9 — Processor Management and Initialization. Defines the state of an Intel 64 or IA-32 processor
after reset initialization. This chapter also explains how to set up an Intel 64 or IA-32 processor for real-address
mode operation and protected- mode operation, and how to switch between modes.
Chapter 10 — Advanced Programmable Interrupt Controller (APIC). Describes the programming interface
to the local APIC and gives an overview of the interface between the local APIC and the I/O APIC. Includes APIC bus
message formats and describes the message formats for messages transmitted on the APIC bus for P6 family and
Pentium processors.
Chapter 11 — Memory Cache Control. Describes the general concept of caching and the caching mechanisms
supported by the Intel 64 or IA-32 architectures. This chapter also describes the memory type range registers
(MTRRs) and how they can be used to map memory types of physical memory. Information on using the new cache
control and memory streaming instructions introduced with the Pentium III, Pentium 4, and Intel Xeon processors is
also given.
Chapter 12 — Intel® MMX™ Technology System Programming. Describes those aspects of the Intel® MMX™
technology that must be handled and considered at the system programming level, including: task switching,
exception handling, and compatibility with existing system environments.

1. Model-Specific Registers have been moved out of this volume and into a separate volume: Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4.
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Chapter 13 — System Programming For Instruction Set Extensions And Processor Extended States.
Describes the operating system requirements to support SSE/SSE2/SSE3/SSSE3/SSE4 extensions, including task
switching, exception handling, and compatibility with existing system environments. The latter part of this chapter
describes the extensible framework of operating system requirements to support processor extended states.
Processor extended state may be required by instruction set extensions beyond those of
SSE/SSE2/SSE3/SSSE3/SSE4 extensions.
Chapter 14 — Power and Thermal Management. Describes facilities of Intel 64 and IA-32 architecture used for
power management and thermal monitoring.
Chapter 15 — Machine-Check Architecture. Describes the machine-check architecture and machine-check
exception mechanism found in the Pentium 4, Intel Xeon, and P6 family processors. Additionally, a signaling mechanism for software to respond to hardware corrected machine check error is covered.
Chapter 16 — Interpreting Machine-Check Error Codes. Gives an example of how to interpret the error codes
for a machine-check error that occurred on a P6 family processor.
Chapter 17 — Debug, Branch Profile, TSC, and Resource Monitoring Features. Describes the debugging
registers and other debug mechanism provided in Intel 64 or IA-32 processors. This chapter also describes the
time-stamp counter.
Chapter 18 — Performance Monitoring. Describes the Intel 64 and IA-32 architectures’ facilities for monitoring
performance.
Chapter 19 — Performance-Monitoring Events. Lists architectural performance events. Non-architectural
performance events (i.e. model-specific events) are listed for each generation of microarchitecture.
Chapter 20 — 8086 Emulation. Describes the real-address and virtual-8086 modes of the IA-32 architecture.
Chapter 21 — Mixing 16-Bit and 32-Bit Code. Describes how to mix 16-bit and 32-bit code modules within the
same program or task.
Chapter 22 — IA-32 Architecture Compatibility. Describes architectural compatibility among IA-32 processors.
Chapter 23 — Introduction to Virtual Machine Extensions. Describes the basic elements of virtual machine
architecture and the virtual machine extensions for Intel 64 and IA-32 Architectures.
Chapter 24 — Virtual Machine Control Structures. Describes components that manage VMX operation. These
include the working-VMCS pointer and the controlling-VMCS pointer.
Chapter 25 — VMX Non-Root Operation. Describes the operation of a VMX non-root operation. Processor operation in VMX non-root mode can be restricted programmatically such that certain operations, events or conditions
can cause the processor to transfer control from the guest (running in VMX non-root mode) to the monitor software
(running in VMX root mode).
Chapter 26 — VM Entries. Describes VM entries. VM entry transitions the processor from the VMM running in
VMX root-mode to a VM running in VMX non-root mode. VM-Entry is performed by the execution of VMLAUNCH or
VMRESUME instructions.
Chapter 27 — VM Exits. Describes VM exits. Certain events, operations or situations while the processor is in VMX
non-root operation may cause VM-exit transitions. In addition, VM exits can also occur on failed VM entries.
Chapter 28 — VMX Support for Address Translation. Describes virtual-machine extensions that support
address translation and the virtualization of physical memory.
Chapter 29 — APIC Virtualization and Virtual Interrupts. Describes the VMCS including controls that enable
the virtualization of interrupts and the Advanced Programmable Interrupt Controller (APIC).
Chapter 30 — VMX Instruction Reference. Describes the virtual-machine extensions (VMX). VMX is intended
for a system executive to support virtualization of processor hardware and a system software layer acting as a host
to multiple guest software environments.
Chapter 31 — Virtual-Machine Monitor Programming Considerations. Describes programming considerations for VMMs. VMMs manage virtual machines (VMs).
Chapter 32 — Virtualization of System Resources. Describes the virtualization of the system resources. These
include: debugging facilities, address translation, physical memory, and microcode update facilities.

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Chapter 33 — Handling Boundary Conditions in a Virtual Machine Monitor. Describes what a VMM must
consider when handling exceptions, interrupts, error conditions, and transitions between activity states.
Chapter 34 — System Management Mode. Describes Intel 64 and IA-32 architectures’ system management
mode (SMM) facilities.
Chapter 35 — Intel® Processor Trace. Describes details of Intel® Processor Trace.
Chapter 36 — Introduction to Intel® Software Guard Extensions. Provides an overview of the Intel® Software Guard Extensions (Intel® SGX) set of instructions.
Chapter 37 — Enclave Access Control and Data Structures. Describes Enclave Access Control procedures and
defines various Intel SGX data structures.
Chapter 38 — Enclave Operation. Describes enclave creation and initialization, adding pages and measuring an
enclave, and enclave entry and exit.
Chapter 39 — Enclave Exiting Events. Describes enclave-exiting events (EEE) and asynchronous enclave exit
(AEX).
Chapter 40 — SGX Instruction References. Describes the supervisor and user level instructions provided by
Intel SGX.
Chapter 41 — Intel® SGX Interactions with IA32 and Intel® 64 Architecture. Describes the Intel SGX
collection of enclave instructions for creating protected execution environments on processors supporting IA32 and
Intel 64 architectures.
Chapter 42 — Enclave Code Debug and Profiling. Describes enclave code debug processes and options.
Appendix A — VMX Capability Reporting Facility. Describes the VMX capability MSRs. Support for specific VMX
features is determined by reading capability MSRs.
Appendix B — Field Encoding in VMCS. Enumerates all fields in the VMCS and their encodings. Fields are
grouped by width (16-bit, 32-bit, etc.) and type (guest-state, host-state, etc.).
Appendix C — VM Basic Exit Reasons. Describes the 32-bit fields that encode reasons for a VM exit. Examples
of exit reasons include, but are not limited to: software interrupts, processor exceptions, software traps, NMIs,
external interrupts, and triple faults.

1.3

NOTATIONAL CONVENTIONS

This manual uses specific notation for data-structure formats, for symbolic representation of instructions, and for
hexadecimal and binary numbers. A review of this notation makes the manual easier to read.

1.3.1

Bit and Byte Order

In illustrations of data structures in memory, smaller addresses appear toward the bottom of the figure; addresses
increase toward the top. Bit positions are numbered from right to left. The numerical value of a set bit is equal to
two raised to the power of the bit position. Intel 64 and IA-32 processors are “little endian” machines; this means
the bytes of a word are numbered starting from the least significant byte. Figure 1-1 illustrates these conventions.

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1.3.2

Reserved Bits and Software Compatibility

In many register and memory layout descriptions, certain bits are marked as reserved. When bits are marked as
reserved, it is essential for compatibility with future processors that software treat these bits as having a future,
though unknown, effect. The behavior of reserved bits should be regarded as not only undefined, but unpredictable. Software should follow these guidelines in dealing with reserved bits:

•

Do not depend on the states of any reserved bits when testing the values of registers which contain such bits.
Mask out the reserved bits before testing.

•
•
•

Do not depend on the states of any reserved bits when storing to memory or to a register.
Do not depend on the ability to retain information written into any reserved bits.
When loading a register, always load the reserved bits with the values indicated in the documentation, if any,
or reload them with values previously read from the same register.

NOTE
Avoid any software dependence upon the state of reserved bits in Intel 64 and IA-32 registers.
Depending upon the values of reserved register bits will make software dependent upon the
unspecified manner in which the processor handles these bits. Programs that depend upon
reserved values risk incompatibility with future processors.

Highest
31
Address

Data Structure
8 7
24 23
16 15

Byte 3

Byte 2

Byte 1

Bit offset

0

Byte 0

28
24
20
16
12
8
4
0

Lowest
Address

Byte Offset

Figure 1-1. Bit and Byte Order

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1.3.3

Instruction Operands

When instructions are represented symbolically, a subset of assembly language is used. In this subset, an instruction has the following format:
label: mnemonic argument1, argument2, argument3
where:

•
•
•

A label is an identifier which is followed by a colon.
A mnemonic is a reserved name for a class of instruction opcodes which have the same function.
The operands argument1, argument2, and argument3 are optional. There may be from zero to three
operands, depending on the opcode. When present, they take the form of either literals or identifiers for data
items. Operand identifiers are either reserved names of registers or are assumed to be assigned to data items
declared in another part of the program (which may not be shown in the example).

When two operands are present in an arithmetic or logical instruction, the right operand is the source and the left
operand is the destination.
For example:
LOADREG: MOV EAX, SUBTOTAL
In this example LOADREG is a label, MOV is the mnemonic identifier of an opcode, EAX is the destination operand,
and SUBTOTAL is the source operand. Some assembly languages put the source and destination in reverse order.

1.3.4

Hexadecimal and Binary Numbers

Base 16 (hexadecimal) numbers are represented by a string of hexadecimal digits followed by the character H (for
example, F82EH). A hexadecimal digit is a character from the following set: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D,
E, and F.
Base 2 (binary) numbers are represented by a string of 1s and 0s, sometimes followed by the character B (for
example, 1010B). The “B” designation is only used in situations where confusion as to the type of number might
arise.

1.3.5

Segmented Addressing

The processor uses byte addressing. This means memory is organized and accessed as a sequence of bytes.
Whether one or more bytes are being accessed, a byte address is used to locate the byte or bytes memory. The
range of memory that can be addressed is called an address space.
The processor also supports segmented addressing. This is a form of addressing where a program may have many
independent address spaces, called segments. For example, a program can keep its code (instructions) and stack
in separate segments. Code addresses would always refer to the code space, and stack addresses would always
refer to the stack space. The following notation is used to specify a byte address within a segment:
Segment-register:Byte-address
For example, the following segment address identifies the byte at address FF79H in the segment pointed by the DS
register:
DS:FF79H
The following segment address identifies an instruction address in the code segment. The CS register points to the
code segment and the EIP register contains the address of the instruction.
CS:EIP

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1.3.6

Syntax for CPUID, CR, and MSR Values

Obtain feature flags, status, and system information by using the CPUID instruction, by checking control register
bits, and by reading model-specific registers. We are moving toward a single syntax to represent this type of information. See Figure 1-2.

CPUID Input and Output
CPUID.01H:EDX.SSE[bit 25] = 1

Input value for EAX register
Output register and feature flag or field
name with bit position(s)
Value (or range) of output

Control Register Values
CR4.OSFXSR[bit 9] = 1

Example CR name
Feature flag or field name
with bit position(s)
Value (or range) of output

Model-Specific Register Values
IA32_MISC_ENABLE.ENABLEFOPCODE[bit 2] = 1

Example MSR name
Feature flag or field name with bit position(s)
Value (or range) of output

S

Figure 1-2. Syntax for CPUID, CR, and MSR Data Presentation

1.3.7

29002

Exceptions

An exception is an event that typically occurs when an instruction causes an error. For example, an attempt to
divide by zero generates an exception. However, some exceptions, such as breakpoints, occur under other conditions. Some types of exceptions may provide error codes. An error code reports additional information about the
error. An example of the notation used to show an exception and error code is shown below:
#PF(fault code)
This example refers to a page-fault exception under conditions where an error code naming a type of fault is
reported. Under some conditions, exceptions which produce error codes may not be able to report an accurate
code. In this case, the error code is zero, as shown below for a general-protection exception:
#GP(0)

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1.4

RELATED LITERATURE

Literature related to Intel 64 and IA-32 processors is listed and viewable on-line at:
http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html
See also:

•
•
•

The data sheet for a particular Intel 64 or IA-32 processor

•

Intel® Fortran Compiler documentation and online help:
http://software.intel.com/en-us/articles/intel-compilers/

•

Intel® Software Development Tools:
https://software.intel.com/en-us/intel-sdp-home

•

Intel® 64 and IA-32 Architectures Software Developer’s Manual (in one, four or ten volumes):
https://software.intel.com/en-us/articles/intel-sdm

•

Intel® 64 and IA-32 Architectures Optimization Reference Manual:
https://software.intel.com/en-us/articles/intel-sdm#optimization

•

Intel 64 Architecture x2APIC Specification:

The specification update for a particular Intel 64 or IA-32 processor
Intel® C++ Compiler documentation and online help:
http://software.intel.com/en-us/articles/intel-compilers/

http://www.intel.com/content/www/us/en/architecture-and-technology/64-architecture-x2apic-specification.html

•

Intel® Trusted Execution Technology Measured Launched Environment Programming Guide:
http://www.intel.com/content/www/us/en/software-developers/intel-txt-software-development-guide.html

•

Developing Multi-threaded Applications: A Platform Consistent Approach:
https://software.intel.com/sites/default/files/article/147714/51534-developing-multithreaded-applications.pdf

•

Using Spin-Loops on Intel® Pentium® 4 Processor and Intel® Xeon® Processor:
https://software.intel.com/sites/default/files/22/30/25602

•

Performance Monitoring Unit Sharing Guide
http://software.intel.com/file/30388

Literature related to selected features in future Intel processors are available at:

•

Intel® Architecture Instruction Set Extensions Programming Reference
https://software.intel.com/en-us/isa-extensions

•

Intel® Software Guard Extensions (Intel® SGX) Programming Reference
https://software.intel.com/en-us/isa-extensions/intel-sgx

More relevant links are:

•

Intel® Developer Zone:

•

Developer centers:

https://software.intel.com/en-us
http://www.intel.com/content/www/us/en/hardware-developers/developer-centers.html

•

Processor support general link:
http://www.intel.com/support/processors/

•

Intel® Hyper-Threading Technology (Intel® HT Technology):
http://www.intel.com/technology/platform-technology/hyper-threading/index.htm

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CHAPTER 2
SYSTEM ARCHITECTURE OVERVIEW
IA-32 architecture (beginning with the Intel386 processor family) provides extensive support for operating-system
and system-development software. This support offers multiple modes of operation, which include:

•

Real mode, protected mode, virtual 8086 mode, and system management mode. These are sometimes
referred to as legacy modes.

Intel 64 architecture supports almost all the system programming facilities available in IA-32 architecture and
extends them to a new operating mode (IA-32e mode) that supports a 64-bit programming environment. IA-32e
mode allows software to operate in one of two sub-modes:

•
•

64-bit mode supports 64-bit OS and 64-bit applications
Compatibility mode allows most legacy software to run; it co-exists with 64-bit applications under a 64-bit OS.

The IA-32 system-level architecture includes features to assist in the following operations:

•
•
•
•
•
•
•
•

Memory management
Protection of software modules
Multitasking
Exception and interrupt handling
Multiprocessing
Cache management
Hardware resource and power management
Debugging and performance monitoring

This chapter provides a description of each part of this architecture. It also describes the system registers that are
used to set up and control the processor at the system level and gives a brief overview of the processor’s systemlevel (operating system) instructions.
Many features of the system-level architecture are used only by system programmers. However, application
programmers may need to read this chapter and the following chapters in order to create a reliable and secure
environment for application programs.
This overview and most subsequent chapters of this book focus on protected-mode operation of the IA-32 architecture. IA-32e mode operation of the Intel 64 architecture, as it differs from protected mode operation, is also
described.
All Intel 64 and IA-32 processors enter real-address mode following a power-up or reset (see Chapter 9, “Processor
Management and Initialization”). Software then initiates the switch from real-address mode to protected mode. If
IA-32e mode operation is desired, software also initiates a switch from protected mode to IA-32e mode.

2.1

OVERVIEW OF THE SYSTEM-LEVEL ARCHITECTURE

System-level architecture consists of a set of registers, data structures, and instructions designed to support basic
system-level operations such as memory management, interrupt and exception handling, task management, and
control of multiple processors.
Figure 2-1 provides a summary of system registers and data structures that applies to 32-bit modes. System registers and data structures that apply to IA-32e mode are shown in Figure 2-2.

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SYSTEM ARCHITECTURE OVERVIEW

Physical Address

EFLAGS Register
Control Registers
CR4
CR3
CR2
CR1
CR0
Task Register

Interrupt
Vector

Code, Data or
Stack Segment

Linear Address

Task-State
Segment (TSS)

Segment Selector
Register
Global Descriptor
Table (GDT)

Segment Sel.

Seg. Desc.

TSS Seg. Sel.

TSS Desc.

Interrupt Handler
Code
Current
Stack
TSS

Seg. Desc.

Interrupt Descriptor
Table (IDT)

Task-State
Segment (TSS)

TSS Desc.

Interrupt Gate

LDT Desc.

Task Gate

Task
Code
Data
Stack

GDTR

Trap Gate

IDTR

Task
Code
Data
Stack

Local Descriptor
Table (LDT)

Call-Gate
Segment Selector

Seg. Desc.
Call Gate

XCR0 (XFEM)

Protected Procedure
Code
Current
Stack
TSS

LDTR

Linear Address Space
Dir
Linear Addr.

0
CR3*

Exception Handler
Code
Current
Stack
TSS

Linear Address
Table
Offset

Page Directory

Page Table

Pg. Dir. Entry

Pg. Tbl. Entry

Page
Physical Addr.

This page mapping example is for 4-KByte pages
and the normal 32-bit physical address size.

*Physical Address

Figure 2-1. IA-32 System-Level Registers and Data Structures

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RFLAGS
Physical Address
Control Register
CR8
CR4
CR3
CR2
CR1
CR0
Task Register

Interrupt
Vector

Task-State
Segment (TSS)

Segment Selector
Register
Global Descriptor
Table (GDT)

Segment Sel.

Seg. Desc.

TR

TSS Desc.

NULL

Interrupt Handler
Code
Stack

Seg. Desc.

Interrupt Descriptor
Table (IDT)

Interr. Handler

Seg. Desc.

Interrupt Gate

LDT Desc.

Code

Current TSS

Stack

Interrupt Gate

GDTR

Trap Gate

IDTR

Code, Data or Stack
Segment (Base =0)

Linear Address

IST

Local Descriptor
Table (LDT)

Call-Gate
Segment Selector

NULL

Seg. Desc.
Call Gate

XCR0 (XFEM)

NULL

LDTR

Exception Handler
Code
Stack
Protected Procedure
Code
Stack

PKRU

Linear Address Space

Linear Addr.

Linear Address
PML4 Dir. Pointer Directory

PML4

Pg. Dir. Ptr.

Pg. Dir.
Entry

PML4.
Entry
0
CR3*

Page Dir.

Table

Offset

Page Table
Page Tbl
Entry

Page
Physical
Addr.

This page mapping example is for 4-KByte pages
and 40-bit physical address size.

*Physical Address

Figure 2-2. System-Level Registers and Data Structures in IA-32e Mode

2.1.1

Global and Local Descriptor Tables

When operating in protected mode, all memory accesses pass through either the global descriptor table (GDT) or
an optional local descriptor table (LDT) as shown in Figure 2-1. These tables contain entries called segment
descriptors. Segment descriptors provide the base address of segments well as access rights, type, and usage
information.

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Each segment descriptor has an associated segment selector. A segment selector provides the software that uses
it with an index into the GDT or LDT (the offset of its associated segment descriptor), a global/local flag (determines whether the selector points to the GDT or the LDT), and access rights information.
To access a byte in a segment, a segment selector and an offset must be supplied. The segment selector provides
access to the segment descriptor for the segment (in the GDT or LDT). From the segment descriptor, the processor
obtains the base address of the segment in the linear address space. The offset then provides the location of the
byte relative to the base address. This mechanism can be used to access any valid code, data, or stack segment,
provided the segment is accessible from the current privilege level (CPL) at which the processor is operating. The
CPL is defined as the protection level of the currently executing code segment.
See Figure 2-1. The solid arrows in the figure indicate a linear address, dashed lines indicate a segment selector,
and the dotted arrows indicate a physical address. For simplicity, many of the segment selectors are shown as
direct pointers to a segment. However, the actual path from a segment selector to its associated segment is always
through a GDT or LDT.
The linear address of the base of the GDT is contained in the GDT register (GDTR); the linear address of the LDT is
contained in the LDT register (LDTR).

2.1.1.1

Global and Local Descriptor Tables in IA-32e Mode

GDTR and LDTR registers are expanded to 64-bits wide in both IA-32e sub-modes (64-bit mode and compatibility
mode). For more information: see Section 3.5.2, “Segment Descriptor Tables in IA-32e Mode.”
Global and local descriptor tables are expanded in 64-bit mode to support 64-bit base addresses, (16-byte LDT
descriptors hold a 64-bit base address and various attributes). In compatibility mode, descriptors are not
expanded.

2.1.2

System Segments, Segment Descriptors, and Gates

Besides code, data, and stack segments that make up the execution environment of a program or procedure, the
architecture defines two system segments: the task-state segment (TSS) and the LDT. The GDT is not considered
a segment because it is not accessed by means of a segment selector and segment descriptor. TSSs and LDTs have
segment descriptors defined for them.
The architecture also defines a set of special descriptors called gates (call gates, interrupt gates, trap gates, and
task gates). These provide protected gateways to system procedures and handlers that may operate at a different
privilege level than application programs and most procedures. For example, a CALL to a call gate can provide
access to a procedure in a code segment that is at the same or a numerically lower privilege level (more privileged)
than the current code segment. To access a procedure through a call gate, the calling procedure1 supplies the
selector for the call gate. The processor then performs an access rights check on the call gate, comparing the CPL
with the privilege level of the call gate and the destination code segment pointed to by the call gate.
If access to the destination code segment is allowed, the processor gets the segment selector for the destination
code segment and an offset into that code segment from the call gate. If the call requires a change in privilege
level, the processor also switches to the stack for the targeted privilege level. The segment selector for the new
stack is obtained from the TSS for the currently running task. Gates also facilitate transitions between 16-bit and
32-bit code segments, and vice versa.

2.1.2.1

Gates in IA-32e Mode

In IA-32e mode, the following descriptors are 16-byte descriptors (expanded to allow a 64-bit base): LDT descriptors, 64-bit TSSs, call gates, interrupt gates, and trap gates.
Call gates facilitate transitions between 64-bit mode and compatibility mode. Task gates are not supported in IA32e mode. On privilege level changes, stack segment selectors are not read from the TSS. Instead, they are set to
NULL.
1. The word “procedure” is commonly used in this document as a general term for a logical unit or block of code (such as a program, procedure, function, or routine).
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2.1.3

Task-State Segments and Task Gates

The TSS (see Figure 2-1) defines the state of the execution environment for a task. It includes the state of generalpurpose registers, segment registers, the EFLAGS register, the EIP register, and segment selectors with stack
pointers for three stack segments (one stack for each privilege level). The TSS also includes the segment selector
for the LDT associated with the task and the base address of the paging-structure hierarchy.
All program execution in protected mode happens within the context of a task (called the current task). The
segment selector for the TSS for the current task is stored in the task register. The simplest method for switching
to a task is to make a call or jump to the new task. Here, the segment selector for the TSS of the new task is given
in the CALL or JMP instruction. In switching tasks, the processor performs the following actions:
1. Stores the state of the current task in the current TSS.
2. Loads the task register with the segment selector for the new task.
3. Accesses the new TSS through a segment descriptor in the GDT.
4. Loads the state of the new task from the new TSS into the general-purpose registers, the segment registers,
the LDTR, control register CR3 (base address of the paging-structure hierarchy), the EFLAGS register, and the
EIP register.
5. Begins execution of the new task.
A task can also be accessed through a task gate. A task gate is similar to a call gate, except that it provides access
(through a segment selector) to a TSS rather than a code segment.

2.1.3.1

Task-State Segments in IA-32e Mode

Hardware task switches are not supported in IA-32e mode. However, TSSs continue to exist. The base address of
a TSS is specified by its descriptor.
A 64-bit TSS holds the following information that is important to 64-bit operation:

•
•
•

Stack pointer addresses for each privilege level
Pointer addresses for the interrupt stack table
Offset address of the IO-permission bitmap (from the TSS base)

The task register is expanded to hold 64-bit base addresses in IA-32e mode. See also: Section 7.7, “Task Management in 64-bit Mode.”

2.1.4

Interrupt and Exception Handling

External interrupts, software interrupts and exceptions are handled through the interrupt descriptor table (IDT).
The IDT stores a collection of gate descriptors that provide access to interrupt and exception handlers. Like the
GDT, the IDT is not a segment. The linear address for the base of the IDT is contained in the IDT register (IDTR).
Gate descriptors in the IDT can be interrupt, trap, or task gate descriptors. To access an interrupt or exception
handler, the processor first receives an interrupt vector from internal hardware, an external interrupt controller, or
from software by means of an INT, INTO, INT 3, or BOUND instruction. The interrupt vector provides an index into
the IDT. If the selected gate descriptor is an interrupt gate or a trap gate, the associated handler procedure is
accessed in a manner similar to calling a procedure through a call gate. If the descriptor is a task gate, the handler
is accessed through a task switch.

2.1.4.1

Interrupt and Exception Handling IA-32e Mode

In IA-32e mode, interrupt gate descriptors are expanded to 16 bytes to support 64-bit base addresses. This is true
for 64-bit mode and compatibility mode.
The IDTR register is expanded to hold a 64-bit base address. Task gates are not supported.

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2.1.5

Memory Management

System architecture supports either direct physical addressing of memory or virtual memory (through paging).
When physical addressing is used, a linear address is treated as a physical address. When paging is used: all code,
data, stack, and system segments (including the GDT and IDT) can be paged with only the most recently accessed
pages being held in physical memory.
The location of pages (sometimes called page frames) in physical memory is contained in the paging structures.
These structures reside in physical memory (see Figure 2-1 for the case of 32-bit paging).
The base physical address of the paging-structure hierarchy is contained in control register CR3. The entries in the
paging structures determine the physical address of the base of a page frame, access rights and memory management information.
To use this paging mechanism, a linear address is broken into parts. The parts provide separate offsets into the
paging structures and the page frame. A system can have a single hierarchy of paging structures or several. For
example, each task can have its own hierarchy.

2.1.5.1

Memory Management in IA-32e Mode

In IA-32e mode, physical memory pages are managed by a set of system data structures. In compatibility mode
and 64-bit mode, four levels of system data structures are used. These include:

•

The page map level 4 (PML4) — An entry in a PML4 table contains the physical address of the base of a page
directory pointer table, access rights, and memory management information. The base physical address of the
PML4 is stored in CR3.

•

A set of page directory pointer tables — An entry in a page directory pointer table contains the physical
address of the base of a page directory table, access rights, and memory management information.

•

Sets of page directories — An entry in a page directory table contains the physical address of the base of a
page table, access rights, and memory management information.

•

Sets of page tables — An entry in a page table contains the physical address of a page frame, access rights,
and memory management information.

2.1.6

System Registers

To assist in initializing the processor and controlling system operations, the system architecture provides system
flags in the EFLAGS register and several system registers:

•

The system flags and IOPL field in the EFLAGS register control task and mode switching, interrupt handling,
instruction tracing, and access rights. See also: Section 2.3, “System Flags and Fields in the EFLAGS Register.”

•

The control registers (CR0, CR2, CR3, and CR4) contain a variety of flags and data fields for controlling systemlevel operations. Other flags in these registers are used to indicate support for specific processor capabilities
within the operating system or executive. See also: Section 2.5, “Control Registers” and Section 2.6, “Extended
Control Registers (Including XCR0).”

•

The debug registers (not shown in Figure 2-1) allow the setting of breakpoints for use in debugging programs
and systems software. See also: Chapter 17, “Debug, Branch Profile, TSC, and Resource Monitoring Features.”

•

The GDTR, LDTR, and IDTR registers contain the linear addresses and sizes (limits) of their respective tables.
See also: Section 2.4, “Memory-Management Registers.”

•

The task register contains the linear address and size of the TSS for the current task. See also: Section 2.4,
“Memory-Management Registers.”

•

Model-specific registers (not shown in Figure 2-1).

The model-specific registers (MSRs) are a group of registers available primarily to operating-system or executive
procedures (that is, code running at privilege level 0). These registers control items such as the debug extensions,
the performance-monitoring counters, the machine- check architecture, and the memory type ranges (MTRRs).
The number and function of these registers varies among different members of the Intel 64 and IA-32 processor
families. See also: Section 9.4, “Model-Specific Registers (MSRs),” and Chapter 2, “Model-Specific Registers
(MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4.
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Most systems restrict access to system registers (other than the EFLAGS register) by application programs.
Systems can be designed, however, where all programs and procedures run at the most privileged level (privilege
level 0). In such a case, application programs would be allowed to modify the system registers.

2.1.6.1

System Registers in IA-32e Mode

In IA-32e mode, the four system-descriptor-table registers (GDTR, IDTR, LDTR, and TR) are expanded in hardware
to hold 64-bit base addresses. EFLAGS becomes the 64-bit RFLAGS register. CR0–CR4 are expanded to 64 bits.
CR8 becomes available. CR8 provides read-write access to the task priority register (TPR) so that the operating
system can control the priority classes of external interrupts.
In 64-bit mode, debug registers DR0–DR7 are 64 bits. In compatibility mode, address-matching in DR0–DR3 is
also done at 64-bit granularity.
On systems that support IA-32e mode, the extended feature enable register (IA32_EFER) is available. This modelspecific register controls activation of IA-32e mode and other IA-32e mode operations. In addition, there are
several model-specific registers that govern IA-32e mode instructions:

•
•
•
•

IA32_KERNEL_GS_BASE — Used by SWAPGS instruction.
IA32_LSTAR — Used by SYSCALL instruction.
IA32_FMASK — Used by SYSCALL instruction.
IA32_STAR — Used by SYSCALL and SYSRET instruction.

2.1.7

Other System Resources

Besides the system registers and data structures described in the previous sections, system architecture provides
the following additional resources:

•
•
•

Operating system instructions (see also: Section 2.8, “System Instruction Summary”).
Performance-monitoring counters (not shown in Figure 2-1).
Internal caches and buffers (not shown in Figure 2-1).

Performance-monitoring counters are event counters that can be programmed to count processor events such as
the number of instructions decoded, the number of interrupts received, or the number of cache loads. See also:
Chapter 19, “Performance Monitoring Events.”
The processor provides several internal caches and buffers. The caches are used to store both data and instructions. The buffers are used to store things like decoded addresses to system and application segments and write
operations waiting to be performed. See also: Chapter 11, “Memory Cache Control.”

2.2

MODES OF OPERATION

The IA-32 architecture supports three operating modes and one quasi-operating mode:

•

Protected mode — This is the native operating mode of the processor. It provides a rich set of architectural
features, flexibility, high performance and backward compatibility to existing software base.

•

Real-address mode — This operating mode provides the programming environment of the Intel 8086
processor, with a few extensions (such as the ability to switch to protected or system management mode).

•

System management mode (SMM) — SMM is a standard architectural feature in all IA-32 processors,
beginning with the Intel386 SL processor. This mode provides an operating system or executive with a
transparent mechanism for implementing power management and OEM differentiation features. SMM is
entered through activation of an external system interrupt pin (SMI#), which generates a system management
interrupt (SMI). In SMM, the processor switches to a separate address space while saving the context of the
currently running program or task. SMM-specific code may then be executed transparently. Upon returning
from SMM, the processor is placed back into its state prior to the SMI.

•

Virtual-8086 mode — In protected mode, the processor supports a quasi-operating mode known as virtual8086 mode. This mode allows the processor execute 8086 software in a protected, multitasking environment.

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Intel 64 architecture supports all operating modes of IA-32 architecture and IA-32e modes:

•

IA-32e mode — In IA-32e mode, the processor supports two sub-modes: compatibility mode and 64-bit
mode. 64-bit mode provides 64-bit linear addressing and support for physical address space larger than 64
GBytes. Compatibility mode allows most legacy protected-mode applications to run unchanged.

Figure 2-3 shows how the processor moves between operating modes.

Real-Address
Mode
Reset or
PE=0

PE=1

SMI#
Reset
or
RSM
SMI#

Reset

Protected Mode

See**
VM=0

RSM
LME=1, CR0.PG=1*

SMI#

IA-32e
Mode

RSM

System
Management
Mode

VM=1
* See Section 9.8.5

Virtual-8086
Mode

SMI#

** See Section 9.8.5.4

RSM

Figure 2-3. Transitions Among the Processor’s Operating Modes
The processor is placed in real-address mode following power-up or a reset. The PE flag in control register CR0 then
controls whether the processor is operating in real-address or protected mode. See also: Section 9.9, “Mode
Switching.” and Section 4.1.2, “Paging-Mode Enabling.”
The VM flag in the EFLAGS register determines whether the processor is operating in protected mode or virtual8086 mode. Transitions between protected mode and virtual-8086 mode are generally carried out as part of a task
switch or a return from an interrupt or exception handler. See also: Section 20.2.5, “Entering Virtual-8086 Mode.”
The LMA bit (IA32_EFER.LMA[bit 10]) determines whether the processor is operating in IA-32e mode. When
running in IA-32e mode, 64-bit or compatibility sub-mode operation is determined by CS.L bit of the code segment.
The processor enters into IA-32e mode from protected mode by enabling paging and setting the LME bit
(IA32_EFER.LME[bit 8]). See also: Chapter 9, “Processor Management and Initialization.”
The processor switches to SMM whenever it receives an SMI while the processor is in real-address, protected,
virtual-8086, or IA-32e modes. Upon execution of the RSM instruction, the processor always returns to the mode
it was in when the SMI occurred.

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2.2.1

Extended Feature Enable Register

The IA32_EFER MSR provides several fields related to IA-32e mode enabling and operation. It also provides one
field that relates to page-access right modification (see Section 4.6, “Access Rights”). The layout of the
IA32_EFER MSR is shown in Figure 2-4.

63

12 11 10 9 8 7

1

0

IA32_EFER

Execute Disable Bit Enable
IA-32e Mode Active
IA-32e Mode Enable
SYSCALL Enable

Reserved

Figure 2-4. IA32_EFER MSR Layout

Table 2-1. IA32_EFER MSR Information
Bit

Description

0

SYSCALL Enable: IA32_EFER.SCE (R/W)
Enables SYSCALL/SYSRET instructions in 64-bit mode.

7:1

Reserved.

8

IA-32e Mode Enable: IA32_EFER.LME (R/W)
Enables IA-32e mode operation.

9

Reserved.

10

IA-32e Mode Active: IA32_EFER.LMA (R)
Indicates IA-32e mode is active when set.

11

Execute Disable Bit Enable: IA32_EFER.NXE (R/W)
Enables page access restriction by preventing instruction fetches from PAE pages with the XD bit set (See Section 4.6).

63:12

2.3

Reserved.

SYSTEM FLAGS AND FIELDS IN THE EFLAGS REGISTER

The system flags and IOPL field of the EFLAGS register control I/O, maskable hardware interrupts, debugging, task
switching, and the virtual-8086 mode (see Figure 2-5). Only privileged code (typically operating system or executive code) should be allowed to modify these bits.
The system flags and IOPL are:
TF

Trap (bit 8) — Set to enable single-step mode for debugging; clear to disable single-step mode. In singlestep mode, the processor generates a debug exception after each instruction. This allows the execution
state of a program to be inspected after each instruction. If an application program sets the TF flag using a

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POPF, POPFD, or IRET instruction, a debug exception is generated after the instruction that follows the
POPF, POPFD, or IRET.

31

22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Reserved (set to 0)

V V
I I I A V R 0 N
T
D
C M F
P F

I
O
P
L

O D I T S Z
P
C
A
F F F F F F 0 F 0 F 1 F

ID — Identification Flag
VIP — Virtual Interrupt Pending
VIF — Virtual Interrupt Flag
AC — Alignment Check / Access Control
VM — Virtual-8086 Mode
RF — Resume Flag
NT — Nested Task Flag
IOPL— I/O Privilege Level
IF — Interrupt Enable Flag
TF — Trap Flag
Reserved

Figure 2-5. System Flags in the EFLAGS Register
IF

Interrupt enable (bit 9) — Controls the response of the processor to maskable hardware interrupt
requests (see also: Section 6.3.2, “Maskable Hardware Interrupts”). The flag is set to respond to maskable
hardware interrupts; cleared to inhibit maskable hardware interrupts. The IF flag does not affect the generation of exceptions or nonmaskable interrupts (NMI interrupts). The CPL, IOPL, and the state of the VME
flag in control register CR4 determine whether the IF flag can be modified by the CLI, STI, POPF, POPFD,
and IRET.

IOPL

I/O privilege level field (bits 12 and 13) — Indicates the I/O privilege level (IOPL) of the currently
running program or task. The CPL of the currently running program or task must be less than or equal to
the IOPL to access the I/O address space. The POPF and IRET instructions can modify this field only when
operating at a CPL of 0.
The IOPL is also one of the mechanisms that controls the modification of the IF flag and the handling of
interrupts in virtual-8086 mode when virtual mode extensions are in effect (when CR4.VME = 1). See also:
Chapter 18, “Input/Output,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 1.

NT

Nested task (bit 14) — Controls the chaining of interrupted and called tasks. The processor sets this flag
on calls to a task initiated with a CALL instruction, an interrupt, or an exception. It examines and modifies
this flag on returns from a task initiated with the IRET instruction. The flag can be explicitly set or cleared
with the POPF/POPFD instructions; however, changing to the state of this flag can generate unexpected
exceptions in application programs.
See also: Section 7.4, “Task Linking.”

RF

Resume (bit 16) — Controls the processor’s response to instruction-breakpoint conditions. When set, this
flag temporarily disables debug exceptions (#DB) from being generated for instruction breakpoints
(although other exception conditions can cause an exception to be generated). When clear, instruction
breakpoints will generate debug exceptions.
The primary function of the RF flag is to allow the restarting of an instruction following a debug exception
that was caused by an instruction breakpoint condition. Here, debug software must set this flag in the
EFLAGS image on the stack just prior to returning to the interrupted program with IRETD (to prevent the
instruction breakpoint from causing another debug exception). The processor then automatically clears
this flag after the instruction returned to has been successfully executed, enabling instruction breakpoint
faults again.
See also: Section 17.3.1.1, “Instruction-Breakpoint Exception Condition.”

VM

Virtual-8086 mode (bit 17) — Set to enable virtual-8086 mode; clear to return to protected mode.

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See also: Section 20.2.1, “Enabling Virtual-8086 Mode.”
AC

Alignment check or access control (bit 18) — If the AM bit is set in the CR0 register, alignment
checking of user-mode data accesses is enabled if and only if this flag is 1. An alignment-check exception
is generated when reference is made to an unaligned operand, such as a word at an odd byte address or a
doubleword at an address which is not an integral multiple of four. Alignment-check exceptions are generated only in user mode (privilege level 3). Memory references that default to privilege level 0, such as
segment descriptor loads, do not generate this exception even when caused by instructions executed in
user-mode.
The alignment-check exception can be used to check alignment of data. This is useful when exchanging
data with processors which require all data to be aligned. The alignment-check exception can also be used
by interpreters to flag some pointers as special by misaligning the pointer. This eliminates overhead of
checking each pointer and only handles the special pointer when used.
If the SMAP bit is set in the CR4 register, explicit supervisor-mode data accesses to user-mode pages are
allowed if and only if this bit is 1. See Section 4.6, “Access Rights.”

VIF

Virtual Interrupt (bit 19) — Contains a virtual image of the IF flag. This flag is used in conjunction with
the VIP flag. The processor only recognizes the VIF flag when either the VME flag or the PVI flag in control
register CR4 is set and the IOPL is less than 3. (The VME flag enables the virtual-8086 mode extensions;
the PVI flag enables the protected-mode virtual interrupts.)
See also: Section 20.3.3.5, “Method 6: Software Interrupt Handling,” and Section 20.4, “Protected-Mode
Virtual Interrupts.”

VIP

Virtual interrupt pending (bit 20) — Set by software to indicate that an interrupt is pending; cleared to
indicate that no interrupt is pending. This flag is used in conjunction with the VIF flag. The processor reads
this flag but never modifies it. The processor only recognizes the VIP flag when either the VME flag or the
PVI flag in control register CR4 is set and the IOPL is less than 3. The VME flag enables the virtual-8086
mode extensions; the PVI flag enables the protected-mode virtual interrupts.
See Section 20.3.3.5, “Method 6: Software Interrupt Handling,” and Section 20.4, “Protected-Mode Virtual
Interrupts.”

ID

2.3.1

Identification (bit 21) — The ability of a program or procedure to set or clear this flag indicates support
for the CPUID instruction.

System Flags and Fields in IA-32e Mode

In 64-bit mode, the RFLAGS register expands to 64 bits with the upper 32 bits reserved. System flags in RFLAGS
(64-bit mode) or EFLAGS (compatibility mode) are shown in Figure 2-5.
In IA-32e mode, the processor does not allow the VM bit to be set because virtual-8086 mode is not supported
(attempts to set the bit are ignored). Also, the processor will not set the NT bit. The processor does, however, allow
software to set the NT bit (note that an IRET causes a general protection fault in IA-32e mode if the NT bit is set).
In IA-32e mode, the SYSCALL/SYSRET instructions have a programmable method of specifying which bits are
cleared in RFLAGS/EFLAGS. These instructions save/restore EFLAGS/RFLAGS.

2.4

MEMORY-MANAGEMENT REGISTERS

The processor provides four memory-management registers (GDTR, LDTR, IDTR, and TR) that specify the locations
of the data structures which control segmented memory management (see Figure 2-6). Special instructions are
provided for loading and storing these registers.

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SYSTEM ARCHITECTURE OVERVIEW

47(79)

System Table Registers
16 15

0

GDTR

32(64)-bit Linear Base Address

16-Bit Table Limit

IDTR

32(64)-bit Linear Base Address

16-Bit Table Limit

Task
Register
LDTR

System Segment
Registers
15
0

Segment Descriptor Registers (Automatically Loaded)

Attributes

Seg. Sel.

32(64)-bit Linear Base Address

Segment Limit

Seg. Sel.

32(64)-bit Linear Base Address

Segment Limit

Figure 2-6. Memory Management Registers

2.4.1

Global Descriptor Table Register (GDTR)

The GDTR register holds the base address (32 bits in protected mode; 64 bits in IA-32e mode) and the 16-bit table
limit for the GDT. The base address specifies the linear address of byte 0 of the GDT; the table limit specifies the
number of bytes in the table.
The LGDT and SGDT instructions load and store the GDTR register, respectively. On power up or reset of the
processor, the base address is set to the default value of 0 and the limit is set to 0FFFFH. A new base address must
be loaded into the GDTR as part of the processor initialization process for protected-mode operation.
See also: Section 3.5.1, “Segment Descriptor Tables.”

2.4.2

Local Descriptor Table Register (LDTR)

The LDTR register holds the 16-bit segment selector, base address (32 bits in protected mode; 64 bits in IA-32e
mode), segment limit, and descriptor attributes for the LDT. The base address specifies the linear address of byte
0 of the LDT segment; the segment limit specifies the number of bytes in the segment. See also: Section 3.5.1,
“Segment Descriptor Tables.”
The LLDT and SLDT instructions load and store the segment selector part of the LDTR register, respectively. The
segment that contains the LDT must have a segment descriptor in the GDT. When the LLDT instruction loads a
segment selector in the LDTR: the base address, limit, and descriptor attributes from the LDT descriptor are automatically loaded in the LDTR.
When a task switch occurs, the LDTR is automatically loaded with the segment selector and descriptor for the LDT
for the new task. The contents of the LDTR are not automatically saved prior to writing the new LDT information
into the register.
On power up or reset of the processor, the segment selector and base address are set to the default value of 0 and
the limit is set to 0FFFFH.

2.4.3

IDTR Interrupt Descriptor Table Register

The IDTR register holds the base address (32 bits in protected mode; 64 bits in IA-32e mode) and 16-bit table limit
for the IDT. The base address specifies the linear address of byte 0 of the IDT; the table limit specifies the number
of bytes in the table. The LIDT and SIDT instructions load and store the IDTR register, respectively. On power up or
reset of the processor, the base address is set to the default value of 0 and the limit is set to 0FFFFH. The base
address and limit in the register can then be changed as part of the processor initialization process.
See also: Section 6.10, “Interrupt Descriptor Table (IDT).”

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2.4.4

Task Register (TR)

The task register holds the 16-bit segment selector, base address (32 bits in protected mode; 64 bits in IA-32e
mode), segment limit, and descriptor attributes for the TSS of the current task. The selector references the TSS
descriptor in the GDT. The base address specifies the linear address of byte 0 of the TSS; the segment limit specifies the number of bytes in the TSS. See also: Section 7.2.4, “Task Register.”
The LTR and STR instructions load and store the segment selector part of the task register, respectively. When the
LTR instruction loads a segment selector in the task register, the base address, limit, and descriptor attributes from
the TSS descriptor are automatically loaded into the task register. On power up or reset of the processor, the base
address is set to the default value of 0 and the limit is set to 0FFFFH.
When a task switch occurs, the task register is automatically loaded with the segment selector and descriptor for
the TSS for the new task. The contents of the task register are not automatically saved prior to writing the new TSS
information into the register.

2.5

CONTROL REGISTERS

Control registers (CR0, CR1, CR2, CR3, and CR4; see Figure 2-7) determine operating mode of the processor and
the characteristics of the currently executing task. These registers are 32 bits in all 32-bit modes and compatibility
mode.
In 64-bit mode, control registers are expanded to 64 bits. The MOV CRn instructions are used to manipulate the
register bits. Operand-size prefixes for these instructions are ignored. The following is also true:

•

The control registers can be read and loaded (or modified) using the move-to-or-from-control-registers forms
of the MOV instruction. In protected mode, the MOV instructions allow the control registers to be read or loaded
(at privilege level 0 only). This restriction means that application programs or operating-system procedures
(running at privilege levels 1, 2, or 3) are prevented from reading or loading the control registers.

•

Bits 63:32 of CR0 and CR4 are reserved and must be written with zeros. Writing a nonzero value to any of the
upper 32 bits results in a general-protection exception, #GP(0).

•
•
•

All 64 bits of CR2 are writable by software.

•

Register CR8 is available in 64-bit mode only.

Bits 51:40 of CR3 are reserved and must be 0.
The MOV CRn instructions do not check that addresses written to CR2 and CR3 are within the linear-address or
physical-address limitations of the implementation.

The control registers are summarized below, and each architecturally defined control field in these control registers
is described individually. In Figure 2-7, the width of the register in 64-bit mode is indicated in parenthesis (except
for CR0).

•
•
•
•

CR0 — Contains system control flags that control operating mode and states of the processor.
CR1 — Reserved.
CR2 — Contains the page-fault linear address (the linear address that caused a page fault).
CR3 — Contains the physical address of the base of the paging-structure hierarchy and two flags (PCD and
PWT). Only the most-significant bits (less the lower 12 bits) of the base address are specified; the lower 12 bits
of the address are assumed to be 0. The first paging structure must thus be aligned to a page (4-KByte)
boundary. The PCD and PWT flags control caching of that paging structure in the processor’s internal data
caches (they do not control TLB caching of page-directory information).
When using the physical address extension, the CR3 register contains the base address of the page-directorypointer table. In IA-32e mode, the CR3 register contains the base address of the PML4 table.
See also: Chapter 4, “Paging.”

•

CR4 — Contains a group of flags that enable several architectural extensions, and indicate operating system or
executive support for specific processor capabilities.

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SYSTEM ARCHITECTURE OVERVIEW

•

CR8 — Provides read and write access to the Task Priority Register (TPR). It specifies the priority threshold
value that operating systems use to control the priority class of external interrupts allowed to interrupt the
processor. This register is available only in 64-bit mode. However, interrupt filtering continues to apply in
compatibility mode.

22 21 20

31(63)

18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

P S S
K M M
E A E
P P

Reserved

S
M
X
E

OSXSAVE

V
M
X
E

U
M
I
P

T P V
P P M P P
C G C A S D S V M
E D I E
E E E E E

FSGSBASE
PCIDE

OSFXSR
OSXMMEXCPT

12 11

5 4 3 2

31(63)

P P
C W
D T

Page-Directory Base
31(63)

CR4

CR3
(PDBR)
0

Page-Fault Linear Address
31(63)

CR2
0

CR1
31 30 29 28
P C N
G D W

19 18 17 16 15
A
M

W
P

6 5 4 3 2 1 0
N E T E M P
E T S M P E

CR0

Reserved

Figure 2-7. Control Registers
When loading a control register, reserved bits should always be set to the values previously read. The flags in
control registers are:
CR0.PG
Paging (bit 31 of CR0) — Enables paging when set; disables paging when clear. When paging is
disabled, all linear addresses are treated as physical addresses. The PG flag has no effect if the PE flag (bit
0 of register CR0) is not also set; setting the PG flag when the PE flag is clear causes a general-protection
exception (#GP). See also: Chapter 4, “Paging.”
On Intel 64 processors, enabling and disabling IA-32e mode operation also requires modifying CR0.PG.
CR0.CD
Cache Disable (bit 30 of CR0) — When the CD and NW flags are clear, caching of memory locations for
the whole of physical memory in the processor’s internal (and external) caches is enabled. When the CD
flag is set, caching is restricted as described in Table 11-5. To prevent the processor from accessing and
updating its caches, the CD flag must be set and the caches must be invalidated so that no cache hits can
occur.
See also: Section 11.5.3, “Preventing Caching,” and Section 11.5, “Cache Control.”
CR0.NW
Not Write-through (bit 29 of CR0) — When the NW and CD flags are clear, write-back (for Pentium 4,
Intel Xeon, P6 family, and Pentium processors) or write-through (for Intel486 processors) is enabled for
writes that hit the cache and invalidation cycles are enabled. See Table 11-5 for detailed information about
the effect of the NW flag on caching for other settings of the CD and NW flags.

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SYSTEM ARCHITECTURE OVERVIEW

CR0.AM
Alignment Mask (bit 18 of CR0) — Enables automatic alignment checking when set; disables alignment
checking when clear. Alignment checking is performed only when the AM flag is set, the AC flag in the
EFLAGS register is set, CPL is 3, and the processor is operating in either protected or virtual-8086 mode.
CR0.WP
Write Protect (bit 16 of CR0) — When set, inhibits supervisor-level procedures from writing into readonly pages; when clear, allows supervisor-level procedures to write into read-only pages (regardless of the
U/S bit setting; see Section 4.1.3 and Section 4.6). This flag facilitates implementation of the copy-onwrite method of creating a new process (forking) used by operating systems such as UNIX.
CR0.NE
Numeric Error (bit 5 of CR0) — Enables the native (internal) mechanism for reporting x87 FPU errors
when set; enables the PC-style x87 FPU error reporting mechanism when clear. When the NE flag is clear
and the IGNNE# input is asserted, x87 FPU errors are ignored. When the NE flag is clear and the IGNNE#
input is deasserted, an unmasked x87 FPU error causes the processor to assert the FERR# pin to generate
an external interrupt and to stop instruction execution immediately before executing the next waiting
floating-point instruction or WAIT/FWAIT instruction.
The FERR# pin is intended to drive an input to an external interrupt controller (the FERR# pin emulates the
ERROR# pin of the Intel 287 and Intel 387 DX math coprocessors). The NE flag, IGNNE# pin, and FERR#
pin are used with external logic to implement PC-style error reporting. Using FERR# and IGNNE# to handle
floating-point exceptions is deprecated by modern operating systems; this non-native approach also limits
newer processors to operate with one logical processor active.
See also: Section 8.7, “Handling x87 FPU Exceptions in Software” in Chapter 8, “Programming with the x87
FPU,” and Appendix A, “EFLAGS Cross-Reference,” in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1.
CR0.ET
Extension Type (bit 4 of CR0) — Reserved in the Pentium 4, Intel Xeon, P6 family, and Pentium processors. In the Pentium 4, Intel Xeon, and P6 family processors, this flag is hardcoded to 1. In the Intel386
and Intel486 processors, this flag indicates support of Intel 387 DX math coprocessor instructions when
set.
CR0.TS
Task Switched (bit 3 of CR0) — Allows the saving of the x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4
context on a task switch to be delayed until an x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction is
actually executed by the new task. The processor sets this flag on every task switch and tests it when
executing x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instructions.

•

If the TS flag is set and the EM flag (bit 2 of CR0) is clear, a device-not-available exception (#NM) is
raised prior to the execution of any x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction; with the
exception of PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, MOVNTI, CLFLUSH, CRC32, and POPCNT.
See the paragraph below for the special case of the WAIT/FWAIT instructions.

•

If the TS flag is set and the MP flag (bit 1 of CR0) and EM flag are clear, an #NM exception is not raised
prior to the execution of an x87 FPU WAIT/FWAIT instruction.

•

If the EM flag is set, the setting of the TS flag has no effect on the execution of x87
FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instructions.

Table 2-2 shows the actions taken when the processor encounters an x87 FPU instruction based on the
settings of the TS, EM, and MP flags. Table 12-1 and 13-1 show the actions taken when the processor
encounters an MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction.
The processor does not automatically save the context of the x87 FPU, XMM, and MXCSR registers on a
task switch. Instead, it sets the TS flag, which causes the processor to raise an #NM exception whenever
it encounters an x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction in the instruction stream for the
new task (with the exception of the instructions listed above).
The fault handler for the #NM exception can then be used to clear the TS flag (with the CLTS instruction)
and save the context of the x87 FPU, XMM, and MXCSR registers. If the task never encounters an x87
FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instruction, the x87 FPU/MMX/SSE/SSE2/SSE3/SSSE3/SSE4
context is never saved.
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SYSTEM ARCHITECTURE OVERVIEW

Table 2-2. Action Taken By x87 FPU Instructions for Different Combinations of EM, MP, and TS
CR0 Flags

x87 FPU Instruction Type

EM

MP

TS

0

0

0

Execute

Floating-Point
Execute.

WAIT/FWAIT

0

0

1

#NM Exception

Execute.

0

1

0

Execute

Execute.

0

1

1

#NM Exception

#NM exception.

1

0

0

#NM Exception

Execute.

1

0

1

#NM Exception

Execute.

1

1

0

#NM Exception

Execute.

1

1

1

#NM Exception

#NM exception.

CR0.EM
Emulation (bit 2 of CR0) — Indicates that the processor does not have an internal or external x87 FPU
when set; indicates an x87 FPU is present when clear. This flag also affects the execution of
MMX/SSE/SSE2/SSE3/SSSE3/SSE4 instructions.
When the EM flag is set, execution of an x87 FPU instruction generates a device-not-available exception
(#NM). This flag must be set when the processor does not have an internal x87 FPU or is not connected to
an external math coprocessor. Setting this flag forces all floating-point instructions to be handled by software emulation. Table 9-3 shows the recommended setting of this flag, depending on the IA-32 processor
and x87 FPU or math coprocessor present in the system. Table 2-2 shows the interaction of the EM, MP, and
TS flags.
Also, when the EM flag is set, execution of an MMX instruction causes an invalid-opcode exception (#UD)
to be generated (see Table 12-1). Thus, if an IA-32 or Intel 64 processor incorporates MMX technology, the
EM flag must be set to 0 to enable execution of MMX instructions.
Similarly for SSE/SSE2/SSE3/SSSE3/SSE4 extensions, when the EM flag is set, execution of most
SSE/SSE2/SSE3/SSSE3/SSE4 instructions causes an invalid opcode exception (#UD) to be generated (see
Table 13-1). If an IA-32 or Intel 64 processor incorporates the SSE/SSE2/SSE3/SSSE3/SSE4 extensions,
the EM flag must be set to 0 to enable execution of these extensions. SSE/SSE2/SSE3/SSSE3/SSE4
instructions not affected by the EM flag include: PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, MOVNTI,
CLFLUSH, CRC32, and POPCNT.
CR0.MP
Monitor Coprocessor (bit 1 of CR0) — Controls the interaction of the WAIT (or FWAIT) instruction with
the TS flag (bit 3 of CR0). If the MP flag is set, a WAIT instruction generates a device-not-available exception
(#NM) if the TS flag is also set. If the MP flag is clear, the WAIT instruction ignores the setting of the TS flag.
Table 9-3 shows the recommended setting of this flag, depending on the IA-32 processor and x87 FPU or
math coprocessor present in the system. Table 2-2 shows the interaction of the MP, EM, and TS flags.
CR0.PE
Protection Enable (bit 0 of CR0) — Enables protected mode when set; enables real-address mode when
clear. This flag does not enable paging directly. It only enables segment-level protection. To enable paging,
both the PE and PG flags must be set.
See also: Section 9.9, “Mode Switching.”
CR3.PCD
Page-level Cache Disable (bit 4 of CR3) — Controls the memory type used to access the first paging
structure of the current paging-structure hierarchy. See Section 4.9, “Paging and Memory Typing”. This bit
is not used if paging is disabled, with PAE paging, or with 4-level paging2 if CR4.PCIDE=1.

2. Earlier versions of this manual used the term “IA-32e paging” to identify 4-level paging.
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CR3.PWT
Page-level Write-Through (bit 3 of CR3) — Controls the memory type used to access the first paging
structure of the current paging-structure hierarchy. See Section 4.9, “Paging and Memory Typing”. This bit
is not used if paging is disabled, with PAE paging, or with 4-level paging if CR4.PCIDE=1.
CR4.VME
Virtual-8086 Mode Extensions (bit 0 of CR4) — Enables interrupt- and exception-handling extensions
in virtual-8086 mode when set; disables the extensions when clear. Use of the virtual mode extensions can
improve the performance of virtual-8086 applications by eliminating the overhead of calling the virtual8086 monitor to handle interrupts and exceptions that occur while executing an 8086 program and,
instead, redirecting the interrupts and exceptions back to the 8086 program’s handlers. It also provides
hardware support for a virtual interrupt flag (VIF) to improve reliability of running 8086 programs in multitasking and multiple-processor environments.
See also: Section 20.3, “Interrupt and Exception Handling in Virtual-8086 Mode.”
CR4.PVI
Protected-Mode Virtual Interrupts (bit 1 of CR4) — Enables hardware support for a virtual interrupt
flag (VIF) in protected mode when set; disables the VIF flag in protected mode when clear.
See also: Section 20.4, “Protected-Mode Virtual Interrupts.”
CR4.TSD
Time Stamp Disable (bit 2 of CR4) — Restricts the execution of the RDTSC instruction to procedures
running at privilege level 0 when set; allows RDTSC instruction to be executed at any privilege level when
clear. This bit also applies to the RDTSCP instruction if supported (if CPUID.80000001H:EDX[27] = 1).
CR4.DE
Debugging Extensions (bit 3 of CR4) — References to debug registers DR4 and DR5 cause an undefined opcode (#UD) exception to be generated when set; when clear, processor aliases references to registers DR4 and DR5 for compatibility with software written to run on earlier IA-32 processors.
See also: Section 17.2.2, “Debug Registers DR4 and DR5.”
CR4.PSE
Page Size Extensions (bit 4 of CR4) — Enables 4-MByte pages with 32-bit paging when set; restricts
32-bit paging to pages of 4 KBytes when clear.
See also: Section 4.3, “32-Bit Paging.”
CR4.PAE
Physical Address Extension (bit 5 of CR4) — When set, enables paging to produce physical addresses
with more than 32 bits. When clear, restricts physical addresses to 32 bits. PAE must be set before entering
IA-32e mode.
See also: Chapter 4, “Paging.”
CR4.MCE
Machine-Check Enable (bit 6 of CR4) — Enables the machine-check exception when set; disables the
machine-check exception when clear.
See also: Chapter 15, “Machine-Check Architecture.”
CR4.PGE
Page Global Enable (bit 7 of CR4) — (Introduced in the P6 family processors.) Enables the global page
feature when set; disables the global page feature when clear. The global page feature allows frequently
used or shared pages to be marked as global to all users (done with the global flag, bit 8, in a page-directory or page-table entry). Global pages are not flushed from the translation-lookaside buffer (TLB) on a
task switch or a write to register CR3.
When enabling the global page feature, paging must be enabled (by setting the PG flag in control register
CR0) before the PGE flag is set. Reversing this sequence may affect program correctness, and processor
performance will be impacted.
See also: Section 4.10, “Caching Translation Information.”

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SYSTEM ARCHITECTURE OVERVIEW

CR4.PCE
Performance-Monitoring Counter Enable (bit 8 of CR4) — Enables execution of the RDPMC instruction for programs or procedures running at any protection level when set; RDPMC instruction can be
executed only at protection level 0 when clear.
CR4.OSFXSR
Operating System Support for FXSAVE and FXRSTOR instructions (bit 9 of CR4) — When set, this
flag: (1) indicates to software that the operating system supports the use of the FXSAVE and FXRSTOR
instructions, (2) enables the FXSAVE and FXRSTOR instructions to save and restore the contents of the
XMM and MXCSR registers along with the contents of the x87 FPU and MMX registers, and (3) enables the
processor to execute SSE/SSE2/SSE3/SSSE3/SSE4 instructions, with the exception of the PAUSE,
PREFETCHh, SFENCE, LFENCE, MFENCE, MOVNTI, CLFLUSH, CRC32, and POPCNT.
If this flag is clear, the FXSAVE and FXRSTOR instructions will save and restore the contents of the x87 FPU
and MMX registers, but they may not save and restore the contents of the XMM and MXCSR registers. Also,
the processor will generate an invalid opcode exception (#UD) if it attempts to execute any
SSE/SSE2/SSE3 instruction, with the exception of PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE,
MOVNTI, CLFLUSH, CRC32, and POPCNT. The operating system or executive must explicitly set this flag.

NOTE
CPUID feature flag FXSR indicates availability of the FXSAVE/FXRSTOR instructions. The OSFXSR
bit provides operating system software with a means of enabling FXSAVE/FXRSTOR to save/restore
the contents of the X87 FPU, XMM and MXCSR registers. Consequently OSFXSR bit indicates that
the operating system provides context switch support for SSE/SSE2/SSE3/SSSE3/SSE4.
CR4.OSXMMEXCPT
Operating System Support for Unmasked SIMD Floating-Point Exceptions (bit 10 of CR4) —
When set, indicates that the operating system supports the handling of unmasked SIMD floating-point
exceptions through an exception handler that is invoked when a SIMD floating-point exception (#XM) is
generated. SIMD floating-point exceptions are only generated by SSE/SSE2/SSE3/SSE4.1 SIMD floatingpoint instructions.
The operating system or executive must explicitly set this flag. If this flag is not set, the processor will
generate an invalid opcode exception (#UD) whenever it detects an unmasked SIMD floating-point exception.
CR4.UMIP
User-Mode Instruction Prevention (bit 11 of CR4) — When set, the following instructions cannot be
executed if CPL > 0: SGDT, SIDT, SLDT, SMSW, and STR. An attempt at such execution causes a generalprotection exception (#GP).
CR4.VMXE
VMX-Enable Bit (bit 13 of CR4) — Enables VMX operation when set. See Chapter 23, “Introduction to
Virtual Machine Extensions.”
CR4.SMXE
SMX-Enable Bit (bit 14 of CR4) — Enables SMX operation when set. See Chapter 6, “Safer Mode Extensions Reference” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2D.
CR4.FSGSBASE
FSGSBASE-Enable Bit (bit 16 of CR4) — Enables the instructions RDFSBASE, RDGSBASE, WRFSBASE,
and WRGSBASE.
CR4.PCIDE
PCID-Enable Bit (bit 17 of CR4) — Enables process-context identifiers (PCIDs) when set. See Section
4.10.1, “Process-Context Identifiers (PCIDs)”. Can be set only in IA-32e mode (if IA32_EFER.LMA = 1).

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SYSTEM ARCHITECTURE OVERVIEW

CR4.OSXSAVE
XSAVE and Processor Extended States-Enable Bit (bit 18 of CR4) — When set, this flag: (1) indicates (via CPUID.01H:ECX.OSXSAVE[bit 27]) that the operating system supports the use of the XGETBV,
XSAVE and XRSTOR instructions by general software; (2) enables the XSAVE and XRSTOR instructions to
save and restore the x87 FPU state (including MMX registers), the SSE state (XMM registers and MXCSR),
along with other processor extended states enabled in XCR0; (3) enables the processor to execute XGETBV
and XSETBV instructions in order to read and write XCR0. See Section 2.6 and Chapter 13, “System
Programming for Instruction Set Extensions and Processor Extended States”.
CR4.SMEP
SMEP-Enable Bit (bit 20 of CR4) — Enables supervisor-mode execution prevention (SMEP) when set.
See Section 4.6, “Access Rights”.
CR4.SMAP
SMAP-Enable Bit (bit 21 of CR4) — Enables supervisor-mode access prevention (SMAP) when set. See
Section 4.6, “Access Rights.”
CR4.PKE
Protection-Key-Enable Bit (bit 22 of CR4) — Enables 4-level paging to associate each linear address
with a protection key. The PKRU register specifies, for each protection key, whether user-mode linear
addresses with that protection key can be read or written. This bit also enables access to the PKRU register
using the RDPKRU and WRPKRU instructions.
CR8.TPL
Task Priority Level (bit 3:0 of CR8) — This sets the threshold value corresponding to the highestpriority interrupt to be blocked. A value of 0 means all interrupts are enabled. This field is available in 64bit mode. A value of 15 means all interrupts will be disabled.

2.5.1

CPUID Qualification of Control Register Flags

Not all flags in control register CR4 are implemented on all processors. With the exception of the PCE flag, they can
be qualified with the CPUID instruction to determine if they are implemented on the processor before they are
used.
The CR8 register is available on processors that support Intel 64 architecture.

2.6

EXTENDED CONTROL REGISTERS (INCLUDING XCR0)

If CPUID.01H:ECX.XSAVE[bit 26] is 1, the processor supports one or more extended control registers (XCRs).
Currently, the only such register defined is XCR0. This register specifies the set of processor state components for
which the operating system provides context management, e.g. x87 FPU state, SSE state, AVX state. The OS
programs XCR0 to reflect the features for which it provides context management.

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SYSTEM ARCHITECTURE OVERVIEW

63

9

Reserved (must be 0)

7 6 5 4 3

2 1 0
1

Reserved for XCR0 bit vector expansion
Reserved / Future processor extended states
PKRU state
Hi16_ZMM state
ZMM_Hi256 state
Opmask state
BNDCSR state
BNDREG state
AVX state
SSE state
x87 FPU/MMX state (must be 1)

Figure 2-8. XCR0
Software can access XCR0 only if CR4.OSXSAVE[bit 18] = 1. (This bit is also readable as
CPUID.01H:ECX.OSXSAVE[bit 27].) Software can use CPUID leaf function 0DH to enumerate the bits in XCR0 that
the processor supports (see CPUID instruction in Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 2A). Each supported state component is represented by a bit in XCR0. System software enables state
components by loading an appropriate bit mask value into XCR0 using the XSETBV instruction.
As each bit in XCR0 (except bit 63) corresponds to a processor state component, XCR0 thus provides support for
up to 63 sets of processor state components. Bit 63 of XCR0 is reserved for future expansion and will not represent
a processor state component.
Currently, XCR0 defines support for the following state components:

•
•

XCR0.X87 (bit 0): This bit 0 must be 1. An attempt to write 0 to this bit causes a #GP exception.

•

XCR0.AVX (bit 2): If 1, AVX instructions can be executed and the XSAVE feature set can be used to manage the
upper halves of the YMM registers (YMM0-YMM15 in 64-bit mode; otherwise YMM0-YMM7).

•

XCR0.BNDREG (bit 3): If 1, MPX instructions can be executed and the XSAVE feature set can be used to
manage the bounds registers BND0–BND3.

•

XCR0.BNDCSR (bit 4): If 1, MPX instructions can be executed and the XSAVE feature set can be used to
manage the BNDCFGU and BNDSTATUS registers.

•

XCR0.opmask (bit 5): If 1, AVX-512 instructions can be executed and the XSAVE feature set can be used to
manage the opmask registers k0–k7.

•

XCR0.ZMM_Hi256 (bit 6): If 1, AVX-512 instructions can be executed and the XSAVE feature set can be used to
manage the upper halves of the lower ZMM registers (ZMM0-ZMM15 in 64-bit mode; otherwise ZMM0-ZMM7).

•

XCR0.Hi16_ZMM (bit 7): If 1, AVX-512 instructions can be executed and the XSAVE feature set can be used to
manage the upper ZMM registers (ZMM16-ZMM31, only in 64-bit mode).

•

XCR0.PKRU (bit 9): If 1, the XSAVE feature set can be used to manage the PKRU register (see Section 2.7).

XCR0.SSE (bit 1): If 1, the XSAVE feature set can be used to manage MXCSR and the XMM registers (XMM0XMM15 in 64-bit mode; otherwise XMM0-XMM7).

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SYSTEM ARCHITECTURE OVERVIEW

An attempt to use XSETBV to write to XCR0 results in general-protection exceptions (#GP) if it would do any of the
following:

•

Set a bit reserved in XCR0 for a given processor (as determined by the contents of EAX and EDX after executing
CPUID with EAX=0DH, ECX= 0H).

•
•
•
•
•

Clear XCR0.x87.
Clear XCR0.SSE and set XCR0.AVX.
Clear XCR0.AVX and set any of XCR0.opmask, XCR0.ZMM_Hi256, and XCR0.Hi16_ZMM.
Set either XCR0.BNDREG and XCR0.BNDCSR while not setting the other.
Set any of XCR0.opmask, XCR0.ZMM_Hi256, and XCR0.Hi16_ZMM while not setting all of them.

After reset, all bits (except bit 0) in XCR0 are cleared to zero; XCR0[0] is set to 1.

2.7

PROTECTION KEY RIGHTS REGISTER (PKRU)

If CPUID.(EAX=07H,ECX=0H):ECX.PKU [bit 3] = 1, the processor supports the protection-key feature for 4-level
paging. The feature allows selective protection of user-mode pages depending on the 4-bit protection key assigned
to each page. The protection key rights register for user pages (PKRU) allows software to specify the access
rights for each protection key.

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Bit Position

W A W A W A W A W A W A W A W A W A W A W A W A W A W A W A W A
D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D
15 15 14 14 13 13 12 12 11 11 10 10 9 9 8 8 7 7 6 6 5 5 4 4 3 3 2 2 1 1 0 0

Figure 2-9. Protection Key Rights Register for User Pages (PKRU)
The layout of the PKRU register is shown in Figure 2-9. It contains 16 pairs of disable controls to prevent data
accesses to user-mode linear addresses based on their protection keys. Each protection key i is associated with
two bits in the PKRU register:

•

Bit 2i, shown as “ADi” (access disable): if set, the processor prevents any data accesses to user-mode linear
addresses with protection key i.

•

Bit 2i+1, shown as “WDi” (write disable): if set, the processor prevents write accesses to user-mode linear
addresses with protection key i.

See Section 4.6.2, “Protection Keys,” for details of how the processor uses the PKRU register to control accesses to
user-mode linear addresses.

2.8

SYSTEM INSTRUCTION SUMMARY

System instructions handle system-level functions such as loading system registers, managing the cache,
managing interrupts, or setting up the debug registers. Many of these instructions can be executed only by operating-system or executive procedures (that is, procedures running at privilege level 0). Others can be executed at
any privilege level and are thus available to application programs.
Table 2-3 lists the system instructions and indicates whether they are available and useful for application
programs. These instructions are described in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volumes 2A, 2B, 2C & 2D.

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SYSTEM ARCHITECTURE OVERVIEW

Table 2-3. Summary of System Instructions
Useful to
Application?

Protected from
Application?

Instruction

Description

LLDT

Load LDT Register

No

Yes

SLDT

Store LDT Register

No

If CR4.UMIP = 1

LGDT

Load GDT Register

No

Yes

SGDT

Store GDT Register

No

If CR4.UMIP = 1

LTR

Load Task Register

No

Yes

STR

Store Task Register

No

If CR4.UMIP = 1

LIDT

Load IDT Register

No

Yes

SIDT

Store IDT Register

No

If CR4.UMIP = 1

MOV CRn

Load and store control registers

No

Yes

SMSW

Store MSW

Yes

If CR4.UMIP = 1

LMSW

Load MSW

No

Yes

CLTS

Clear TS flag in CR0

No

Yes

ARPL

Adjust RPL

LAR

Load Access Rights

Yes

No

LSL

Load Segment Limit

Yes

No

VERR

Verify for Reading

Yes

No

VERW

Verify for Writing

Yes

No

MOV DRn

Load and store debug registers

No

Yes

INVD

Invalidate cache, no writeback

No

Yes

WBINVD

Invalidate cache, with writeback

No

Yes

INVLPG

Invalidate TLB entry

No

Yes

HLT

Halt Processor

No

Yes

LOCK (Prefix)

Bus Lock

Yes

No

RSM

Return from system management mode

No

Yes

RDMSR3

Read Model-Specific Registers

No

Yes

WRMSR3

Write Model-Specific Registers

No

Yes

RDPMC4

Read Performance-Monitoring Counter

Yes

Yes2

RDTSC3

Read Time-Stamp Counter

Yes

Yes2

RDTSCP7

Read Serialized Time-Stamp Counter

Yes

Yes2

2-22 Vol. 3A

Yes

1, 5

No

SYSTEM ARCHITECTURE OVERVIEW

Table 2-3. Summary of System Instructions (Contd.)
Useful to
Application?

Protected from
Application?

Instruction

Description

XGETBV

Return the state of XCR0

Yes

No

XSETBV

Enable one or more processor extended states

No

Yes

6

NOTES:
1.
2.
3.
4.

Useful to application programs running at a CPL of 1 or 2.
The TSD and PCE flags in control register CR4 control access to these instructions by application programs running at a CPL of 3.
These instructions were introduced into the IA-32 Architecture with the Pentium processor.
This instruction was introduced into the IA-32 Architecture with the Pentium Pro processor and the Pentium processor with MMX technology.
5. This instruction is not supported in 64-bit mode.
6. Application uses XGETBV to query which set of processor extended states are enabled.
7. RDTSCP is introduced in Intel Core i7 processor.

2.8.1

Loading and Storing System Registers

The GDTR, LDTR, IDTR, and TR registers each have a load and store instruction for loading data into and storing
data from the register:

•
•
•
•
•

LGDT (Load GDTR Register) — Loads the GDT base address and limit from memory into the GDTR register.
SGDT (Store GDTR Register) — Stores the GDT base address and limit from the GDTR register into memory.
LIDT (Load IDTR Register) — Loads the IDT base address and limit from memory into the IDTR register.
SIDT (Store IDTR Register) — Stores the IDT base address and limit from the IDTR register into memory.
LLDT (Load LDTR Register) — Loads the LDT segment selector and segment descriptor from memory into
the LDTR. (The segment selector operand can also be located in a general-purpose register.)

•

SLDT (Store LDTR Register) — Stores the LDT segment selector from the LDTR register into memory or a
general-purpose register.

•

LTR (Load Task Register) — Loads segment selector and segment descriptor for a TSS from memory into the
task register. (The segment selector operand can also be located in a general-purpose register.)

•

STR (Store Task Register) — Stores the segment selector for the current task TSS from the task register into
memory or a general-purpose register.

The LMSW (load machine status word) and SMSW (store machine status word) instructions operate on bits 0
through 15 of control register CR0. These instructions are provided for compatibility with the 16-bit Intel 286
processor. Programs written to run on 32-bit IA-32 processors should not use these instructions. Instead, they
should access the control register CR0 using the MOV CR instruction.
The CLTS (clear TS flag in CR0) instruction is provided for use in handling a device-not-available exception (#NM)
that occurs when the processor attempts to execute a floating-point instruction when the TS flag is set. This
instruction allows the TS flag to be cleared after the x87 FPU context has been saved, preventing further #NM
exceptions. See Section 2.5, “Control Registers,” for more information on the TS flag.
The control registers (CR0, CR1, CR2, CR3, CR4, and CR8) are loaded using the MOV instruction. The instruction
loads a control register from a general-purpose register or stores the content of a control register in a generalpurpose register.

2.8.2

Verifying of Access Privileges

The processor provides several instructions for examining segment selectors and segment descriptors to determine if access to their associated segments is allowed. These instructions duplicate some of the automatic access
rights and type checking done by the processor, thus allowing operating-system or executive software to prevent
exceptions from being generated.

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SYSTEM ARCHITECTURE OVERVIEW

The ARPL (adjust RPL) instruction adjusts the RPL (requestor privilege level) of a segment selector to match that of
the program or procedure that supplied the segment selector. See Section 5.10.4, “Checking Caller Access Privileges (ARPL Instruction)” for a detailed explanation of the function and use of this instruction. Note that ARPL is not
supported in 64-bit mode.
The LAR (load access rights) instruction verifies the accessibility of a specified segment and loads access rights
information from the segment’s segment descriptor into a general-purpose register. Software can then examine
the access rights to determine if the segment type is compatible with its intended use. See Section 5.10.1,
“Checking Access Rights (LAR Instruction)” for a detailed explanation of the function and use of this instruction.
The LSL (load segment limit) instruction verifies the accessibility of a specified segment and loads the segment
limit from the segment’s segment descriptor into a general-purpose register. Software can then compare the
segment limit with an offset into the segment to determine whether the offset lies within the segment. See Section
5.10.3, “Checking That the Pointer Offset Is Within Limits (LSL Instruction)” for a detailed explanation of the function and use of this instruction.
The VERR (verify for reading) and VERW (verify for writing) instructions verify if a selected segment is readable or
writable, respectively, at a given CPL. See Section 5.10.2, “Checking Read/Write Rights (VERR and VERW Instructions)” for a detailed explanation of the function and use of these instructions.

2.8.3

Loading and Storing Debug Registers

Internal debugging facilities in the processor are controlled by a set of 8 debug registers (DR0-DR7). The MOV
instruction allows setup data to be loaded to and stored from these registers.
On processors that support Intel 64 architecture, debug registers DR0-DR7 are 64 bits. In 32-bit modes and
compatibility mode, writes to a debug register fill the upper 32 bits with zeros. Reads return the lower 32 bits. In
64-bit mode, the upper 32 bits of DR6-DR7 are reserved and must be written with zeros. Writing one to any of the
upper 32 bits causes an exception, #GP(0).
In 64-bit mode, MOV DRn instructions read or write all 64 bits of a debug register (operand-size prefixes are
ignored). All 64 bits of DR0-DR3 are writable by software. However, MOV DRn instructions do not check that
addresses written to DR0-DR3 are in the limits of the implementation. Address matching is supported only on valid
addresses generated by the processor implementation.

2.8.4

Invalidating Caches and TLBs

The processor provides several instructions for use in explicitly invalidating its caches and TLB entries. The INVD
(invalidate cache with no writeback) instruction invalidates all data and instruction entries in the internal caches
and sends a signal to the external caches indicating that they should also be invalidated.
The WBINVD (invalidate cache with writeback) instruction performs the same function as the INVD instruction,
except that it writes back modified lines in its internal caches to memory before it invalidates the caches. After
invalidating the caches local to the executing logical processor or processor core, WBINVD signals caches higher in
the cache hierarchy (caches shared with the invalidating logical processor or core) to write back any data they have
in modified state at the time of instruction execution and to invalidate their contents.
Note, non-shared caches may not be written back nor invalidated. In Figure 2-10 below, if code executing on either
LP0 or LP1 were to execute a WBINVD, the shared L1 and L2 for LP0/LP1 will be written back and invalidated as will
the shared L3. However, the L1 and L2 caches not shared with LP0 and LP1 will not be written back nor invalidated.

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Logical Processors
L1 & L2 Cache

LP0

LP1

LP2

LP3

LP4

LP5

LP6

Not Written back and
not Invalidated
LP7

Written back
& Invalidated

Execution Engine
L3 Cache

Written back and Invalidated

Uncore
QPI
DDR3

Figure 2-10. WBINVD Invalidation of Shared and Non-Shared Cache Hierarchy
The INVLPG (invalidate TLB entry) instruction invalidates (flushes) the TLB entry for a specified page.

2.8.5

Controlling the Processor

The HLT (halt processor) instruction stops the processor until an enabled interrupt (such as NMI or SMI, which are
normally enabled), a debug exception, the BINIT# signal, the INIT# signal, or the RESET# signal is received. The
processor generates a special bus cycle to indicate that the halt mode has been entered.
Hardware may respond to this signal in a number of ways. An indicator light on the front panel may be turned on.
An NMI interrupt for recording diagnostic information may be generated. Reset initialization may be invoked (note
that the BINIT# pin was introduced with the Pentium Pro processor). If any non-wake events are pending during
shutdown, they will be handled after the wake event from shutdown is processed (for example, A20M# interrupts).
The LOCK prefix invokes a locked (atomic) read-modify-write operation when modifying a memory operand. This
mechanism is used to allow reliable communications between processors in multiprocessor systems, as described
below:

•

In the Pentium processor and earlier IA-32 processors, the LOCK prefix causes the processor to assert the
LOCK# signal during the instruction. This always causes an explicit bus lock to occur.

•

In the Pentium 4, Intel Xeon, and P6 family processors, the locking operation is handled with either a cache lock
or bus lock. If a memory access is cacheable and affects only a single cache line, a cache lock is invoked and
the system bus and the actual memory location in system memory are not locked during the operation. Here,
other Pentium 4, Intel Xeon, or P6 family processors on the bus write-back any modified data and invalidate
their caches as necessary to maintain system memory coherency. If the memory access is not cacheable
and/or it crosses a cache line boundary, the processor’s LOCK# signal is asserted and the processor does not
respond to requests for bus control during the locked operation.

The RSM (return from SMM) instruction restores the processor (from a context dump) to the state it was in prior to
a system management mode (SMM) interrupt.

2.8.6

Reading Performance-Monitoring and Time-Stamp Counters

The RDPMC (read performance-monitoring counter) and RDTSC (read time-stamp counter) instructions allow
application programs to read the processor’s performance-monitoring and time-stamp counters, respectively.
Processors based on Intel NetBurst® microarchitecture have eighteen 40-bit performance-monitoring counters; P6
family processors have two 40-bit counters. Intel® Atom™ processors and most of the processors based on the
Intel Core microarchitecture support two types of performance monitoring counters: programmable performance
counters similar to those available in the P6 family, and three fixed-function performance monitoring counters.

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Details of programmable and fixed-function performance monitoring counters for each processor generation are
described in Chapter 18, “Performance Monitoring”.
The programmable performance counters can support counting either the occurrence or duration of events. Events
that can be monitored on programmable counters generally are model specific (except for architectural performance events enumerated by CPUID leaf 0AH); they may include the number of instructions decoded, interrupts
received, or the number of cache loads. Individual counters can be set up to monitor different events. Use the
system instruction WRMSR to set up values in one of the IA32_PERFEVTSELx MSR, in one of the 45 ESCRs and one
of the 18 CCCR MSRs (for Pentium 4 and Intel Xeon processors); or in the PerfEvtSel0 or the PerfEvtSel1 MSR (for
the P6 family processors). The RDPMC instruction loads the current count from the selected counter into the
EDX:EAX registers.
Fixed-function performance counters record only specific events that are defined in Chapter 19, “Performance
Monitoring Events”, and the width/number of fixed-function counters are enumerated by CPUID leaf 0AH.
The time-stamp counter is a model-specific 64-bit counter that is reset to zero each time the processor is reset. If
not reset, the counter will increment ~9.5 x 1016 times per year when the processor is operating at a clock rate
of 3GHz. At this clock frequency, it would take over 190 years for the counter to wrap around. The RDTSC
instruction loads the current count of the time-stamp counter into the EDX:EAX registers.
See Section 18.1, “Performance Monitoring Overview,” and Section 17.17, “Time-Stamp Counter,” for more information about the performance monitoring and time-stamp counters.
The RDTSC instruction was introduced into the IA-32 architecture with the Pentium processor. The RDPMC instruction was introduced into the IA-32 architecture with the Pentium Pro processor and the Pentium processor with
MMX technology. Earlier Pentium processors have two performance-monitoring counters, but they can be read only
with the RDMSR instruction, and only at privilege level 0.

2.8.6.1

Reading Counters in 64-Bit Mode

In 64-bit mode, RDTSC operates the same as in protected mode. The count in the time-stamp counter is stored in
EDX:EAX (or RDX[31:0]:RAX[31:0] with RDX[63:32]:RAX[63:32] cleared).
RDPMC requires an index to specify the offset of the performance-monitoring counter. In 64-bit mode for Pentium
4 or Intel Xeon processor families, the index is specified in ECX[30:0]. The current count of the performance-monitoring counter is stored in EDX:EAX (or RDX[31:0]:RAX[31:0] with RDX[63:32]:RAX[63:32] cleared).

2.8.7

Reading and Writing Model-Specific Registers

The RDMSR (read model-specific register) and WRMSR (write model-specific register) instructions allow a
processor’s 64-bit model-specific registers (MSRs) to be read and written, respectively. The MSR to be read or
written is specified by the value in the ECX register.
RDMSR reads the value from the specified MSR to the EDX:EAX registers; WRMSR writes the value in the EDX:EAX
registers to the specified MSR. RDMSR and WRMSR were introduced into the IA-32 architecture with the Pentium
processor.
See Section 9.4, “Model-Specific Registers (MSRs),” for more information.

2.8.7.1

Reading and Writing Model-Specific Registers in 64-Bit Mode

RDMSR and WRMSR require an index to specify the address of an MSR. In 64-bit mode, the index is 32 bits; it is
specified using ECX.

2.8.8

Enabling Processor Extended States

The XSETBV instruction is required to enable OS support of individual processor extended states in XCR0 (see
Section 2.6).

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CHAPTER 3
PROTECTED-MODE MEMORY MANAGEMENT
This chapter describes the Intel 64 and IA-32 architecture’s protected-mode memory management facilities,
including the physical memory requirements, segmentation mechanism, and paging mechanism.
See also: Chapter 5, “Protection” (for a description of the processor’s protection mechanism) and Chapter 20,
“8086 Emulation” (for a description of memory addressing protection in real-address and virtual-8086 modes).

3.1

MEMORY MANAGEMENT OVERVIEW

The memory management facilities of the IA-32 architecture are divided into two parts: segmentation and paging.
Segmentation provides a mechanism of isolating individual code, data, and stack modules so that multiple
programs (or tasks) can run on the same processor without interfering with one another. Paging provides a mechanism for implementing a conventional demand-paged, virtual-memory system where sections of a program’s
execution environment are mapped into physical memory as needed. Paging can also be used to provide isolation
between multiple tasks. When operating in protected mode, some form of segmentation must be used. There is
no mode bit to disable segmentation. The use of paging, however, is optional.
These two mechanisms (segmentation and paging) can be configured to support simple single-program (or singletask) systems, multitasking systems, or multiple-processor systems that used shared memory.
As shown in Figure 3-1, segmentation provides a mechanism for dividing the processor’s addressable memory
space (called the linear address space) into smaller protected address spaces called segments. Segments can
be used to hold the code, data, and stack for a program or to hold system data structures (such as a TSS or LDT).
If more than one program (or task) is running on a processor, each program can be assigned its own set of
segments. The processor then enforces the boundaries between these segments and insures that one program
does not interfere with the execution of another program by writing into the other program’s segments. The
segmentation mechanism also allows typing of segments so that the operations that may be performed on a particular type of segment can be restricted.
All the segments in a system are contained in the processor’s linear address space. To locate a byte in a particular
segment, a logical address (also called a far pointer) must be provided. A logical address consists of a segment
selector and an offset. The segment selector is a unique identifier for a segment. Among other things it provides an
offset into a descriptor table (such as the global descriptor table, GDT) to a data structure called a segment
descriptor. Each segment has a segment descriptor, which specifies the size of the segment, the access rights and
privilege level for the segment, the segment type, and the location of the first byte of the segment in the linear
address space (called the base address of the segment). The offset part of the logical address is added to the base
address for the segment to locate a byte within the segment. The base address plus the offset thus forms a linear
address in the processor’s linear address space.

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Logical Address
(or Far Pointer)
Segment
Selector

Offset

Linear Address
Space

Global Descriptor
Table (GDT)

Dir

Linear Address
Table
Offset

Segment
Segment
Descriptor
Lin. Addr.

Page Table
Page Directory

Physical
Address
Space
Page
Phy. Addr.

Entry
Entry

Segment
Base Address
Page

Segmentation

Paging

Figure 3-1. Segmentation and Paging
If paging is not used, the linear address space of the processor is mapped directly into the physical address space
of processor. The physical address space is defined as the range of addresses that the processor can generate on
its address bus.
Because multitasking computing systems commonly define a linear address space much larger than it is economically feasible to contain all at once in physical memory, some method of “virtualizing” the linear address space is
needed. This virtualization of the linear address space is handled through the processor’s paging mechanism.
Paging supports a “virtual memory” environment where a large linear address space is simulated with a small
amount of physical memory (RAM and ROM) and some disk storage. When using paging, each segment is divided
into pages (typically 4 KBytes each in size), which are stored either in physical memory or on the disk. The operating system or executive maintains a page directory and a set of page tables to keep track of the pages. When a
program (or task) attempts to access an address location in the linear address space, the processor uses the page
directory and page tables to translate the linear address into a physical address and then performs the requested
operation (read or write) on the memory location.
If the page being accessed is not currently in physical memory, the processor interrupts execution of the program
(by generating a page-fault exception). The operating system or executive then reads the page into physical
memory from the disk and continues executing the program.
When paging is implemented properly in the operating-system or executive, the swapping of pages between physical memory and the disk is transparent to the correct execution of a program. Even programs written for 16-bit IA32 processors can be paged (transparently) when they are run in virtual-8086 mode.

3.2

USING SEGMENTS

The segmentation mechanism supported by the IA-32 architecture can be used to implement a wide variety of
system designs. These designs range from flat models that make only minimal use of segmentation to protect
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programs to multi-segmented models that employ segmentation to create a robust operating environment in
which multiple programs and tasks can be executed reliably.
The following sections give several examples of how segmentation can be employed in a system to improve
memory management performance and reliability.

3.2.1

Basic Flat Model

The simplest memory model for a system is the basic “flat model,” in which the operating system and application
programs have access to a continuous, unsegmented address space. To the greatest extent possible, this basic flat
model hides the segmentation mechanism of the architecture from both the system designer and the application
programmer.
To implement a basic flat memory model with the IA-32 architecture, at least two segment descriptors must be
created, one for referencing a code segment and one for referencing a data segment (see Figure 3-2). Both of
these segments, however, are mapped to the entire linear address space: that is, both segment descriptors have
the same base address value of 0 and the same segment limit of 4 GBytes. By setting the segment limit to 4
GBytes, the segmentation mechanism is kept from generating exceptions for out of limit memory references, even
if no physical memory resides at a particular address. ROM (EPROM) is generally located at the top of the physical
address space, because the processor begins execution at FFFF_FFF0H. RAM (DRAM) is placed at the bottom of the
address space because the initial base address for the DS data segment after reset initialization is 0.

3.2.2

Protected Flat Model

The protected flat model is similar to the basic flat model, except the segment limits are set to include only the
range of addresses for which physical memory actually exists (see Figure 3-3). A general-protection exception
(#GP) is then generated on any attempt to access nonexistent memory. This model provides a minimum level of
hardware protection against some kinds of program bugs.

Linear Address Space
(or Physical Memory)
Segment
Registers
CS
SS
DS
ES

Code
Code- and Data-Segment
Descriptors
Access
Limit
Base Address

FFFFFFFFH

Not Present
Data and
Stack

0

FS
GS

Figure 3-2. Flat Model

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PROTECTED-MODE MEMORY MANAGEMENT

Segment
Registers
CS

Segment
Descriptors

Linear Address Space
(or Physical Memory)

Access
Limit
Base Address

Code

FFFFFFFFH

Not Present

ES
SS
DS
FS

Access
Limit
Base Address

Memory I/O
Data and
Stack

GS

0

Figure 3-3. Protected Flat Model
More complexity can be added to this protected flat model to provide more protection. For example, for the paging
mechanism to provide isolation between user and supervisor code and data, four segments need to be defined:
code and data segments at privilege level 3 for the user, and code and data segments at privilege level 0 for the
supervisor. Usually these segments all overlay each other and start at address 0 in the linear address space. This
flat segmentation model along with a simple paging structure can protect the operating system from applications,
and by adding a separate paging structure for each task or process, it can also protect applications from each other.
Similar designs are used by several popular multitasking operating systems.

3.2.3

Multi-Segment Model

A multi-segment model (such as the one shown in Figure 3-4) uses the full capabilities of the segmentation mechanism to provide hardware enforced protection of code, data structures, and programs and tasks. Here, each
program (or task) is given its own table of segment descriptors and its own segments. The segments can be
completely private to their assigned programs or shared among programs. Access to all segments and to the
execution environments of individual programs running on the system is controlled by hardware.

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Segment
Registers

Segment
Descriptors

Linear Address Space
(or Physical Memory)

CS

Access
Limit
Base Address

Stack

SS

Access
Limit
Base Address

DS

Access
Limit
Base Address

ES

Access
Limit
Base Address

FS

Access
Limit
Base Address

GS

Access
Limit
Base Address
Access
Limit
Base Address

Code

Data
Data

Data

Access
Limit
Base Address
Access
Limit
Base Address

Data

Access
Limit
Base Address

Figure 3-4. Multi-Segment Model
Access checks can be used to protect not only against referencing an address outside the limit of a segment, but
also against performing disallowed operations in certain segments. For example, since code segments are designated as read-only segments, hardware can be used to prevent writes into code segments. The access rights information created for segments can also be used to set up protection rings or levels. Protection levels can be used to
protect operating-system procedures from unauthorized access by application programs.

3.2.4

Segmentation in IA-32e Mode

In IA-32e mode of Intel 64 architecture, the effects of segmentation depend on whether the processor is running
in compatibility mode or 64-bit mode. In compatibility mode, segmentation functions just as it does using legacy
16-bit or 32-bit protected mode semantics.
In 64-bit mode, segmentation is generally (but not completely) disabled, creating a flat 64-bit linear-address
space. The processor treats the segment base of CS, DS, ES, SS as zero, creating a linear address that is equal to
the effective address. The FS and GS segments are exceptions. These segment registers (which hold the segment
base) can be used as additional base registers in linear address calculations. They facilitate addressing local data
and certain operating system data structures.
Note that the processor does not perform segment limit checks at runtime in 64-bit mode.

3.2.5

Paging and Segmentation

Paging can be used with any of the segmentation models described in Figures 3-2, 3-3, and 3-4. The processor’s
paging mechanism divides the linear address space (into which segments are mapped) into pages (as shown in
Figure 3-1). These linear-address-space pages are then mapped to pages in the physical address space. The
paging mechanism offers several page-level protection facilities that can be used with or instead of the segment-

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protection facilities. For example, it lets read-write protection be enforced on a page-by-page basis. The paging
mechanism also provides two-level user-supervisor protection that can also be specified on a page-by-page basis.

3.3

PHYSICAL ADDRESS SPACE

In protected mode, the IA-32 architecture provides a normal physical address space of 4 GBytes (232 bytes). This
is the address space that the processor can address on its address bus. This address space is flat (unsegmented),
with addresses ranging continuously from 0 to FFFFFFFFH. This physical address space can be mapped to readwrite memory, read-only memory, and memory mapped I/O. The memory mapping facilities described in this
chapter can be used to divide this physical memory up into segments and/or pages.
Starting with the Pentium Pro processor, the IA-32 architecture also supports an extension of the physical address
space to 236 bytes (64 GBytes); with a maximum physical address of FFFFFFFFFH. This extension is invoked in
either of two ways:

•
•

Using the physical address extension (PAE) flag, located in bit 5 of control register CR4.
Using the 36-bit page size extension (PSE-36) feature (introduced in the Pentium III processors).

Physical address support has since been extended beyond 36 bits. See Chapter 4, “Paging” for more information
about 36-bit physical addressing.

3.3.1

Intel® 64 Processors and Physical Address Space

On processors that support Intel 64 architecture (CPUID.80000001H:EDX[29] = 1), the size of the physical
address range is implementation-specific and indicated by CPUID.80000008H:EAX[bits 7-0].
For the format of information returned in EAX, see “CPUID—CPU Identification” in Chapter 3 of the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 2A. See also: Chapter 4, “Paging.”

3.4

LOGICAL AND LINEAR ADDRESSES

At the system-architecture level in protected mode, the processor uses two stages of address translation to arrive
at a physical address: logical-address translation and linear address space paging.
Even with the minimum use of segments, every byte in the processor’s address space is accessed with a logical
address. A logical address consists of a 16-bit segment selector and a 32-bit offset (see Figure 3-5). The segment
selector identifies the segment the byte is located in and the offset specifies the location of the byte in the segment
relative to the base address of the segment.
The processor translates every logical address into a linear address. A linear address is a 32-bit address in the
processor’s linear address space. Like the physical address space, the linear address space is a flat (unsegmented),
232-byte address space, with addresses ranging from 0 to FFFFFFFFH. The linear address space contains all the
segments and system tables defined for a system.
To translate a logical address into a linear address, the processor does the following:
1. Uses the offset in the segment selector to locate the segment descriptor for the segment in the GDT or LDT and
reads it into the processor. (This step is needed only when a new segment selector is loaded into a segment
register.)
2. Examines the segment descriptor to check the access rights and range of the segment to insure that the
segment is accessible and that the offset is within the limits of the segment.
3. Adds the base address of the segment from the segment descriptor to the offset to form a linear address.

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Logical
Address

31(63)
0
Offset (Effective Address)

15
0
Seg. Selector
Descriptor Table

Segment
Descriptor

Base Address

+

31(63)

0
Linear Address

Figure 3-5. Logical Address to Linear Address Translation
If paging is not used, the processor maps the linear address directly to a physical address (that is, the linear
address goes out on the processor’s address bus). If the linear address space is paged, a second level of address
translation is used to translate the linear address into a physical address.
See also: Chapter 4, “Paging.”

3.4.1

Logical Address Translation in IA-32e Mode

In IA-32e mode, an Intel 64 processor uses the steps described above to translate a logical address to a linear
address. In 64-bit mode, the offset and base address of the segment are 64-bits instead of 32 bits. The linear
address format is also 64 bits wide and is subject to the canonical form requirement.
Each code segment descriptor provides an L bit. This bit allows a code segment to execute 64-bit code or legacy
32-bit code by code segment.

3.4.2

Segment Selectors

A segment selector is a 16-bit identifier for a segment (see Figure 3-6). It does not point directly to the segment,
but instead points to the segment descriptor that defines the segment. A segment selector contains the following
items:
Index

(Bits 3 through 15) — Selects one of 8192 descriptors in the GDT or LDT. The processor multiplies
the index value by 8 (the number of bytes in a segment descriptor) and adds the result to the base
address of the GDT or LDT (from the GDTR or LDTR register, respectively).

TI (table indicator) flag
(Bit 2) — Specifies the descriptor table to use: clearing this flag selects the GDT; setting this flag
selects the current LDT.

15

3 2 1 0

Index

T RPL
I

Table Indicator
0 = GDT
1 = LDT
Requested Privilege Level (RPL)

Figure 3-6. Segment Selector

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PROTECTED-MODE MEMORY MANAGEMENT

Requested Privilege Level (RPL)
(Bits 0 and 1) — Specifies the privilege level of the selector. The privilege level can range from 0 to
3, with 0 being the most privileged level. See Section 5.5, “Privilege Levels”, for a description of the
relationship of the RPL to the CPL of the executing program (or task) and the descriptor privilege
level (DPL) of the descriptor the segment selector points to.
The first entry of the GDT is not used by the processor. A segment selector that points to this entry of the GDT (that
is, a segment selector with an index of 0 and the TI flag set to 0) is used as a “null segment selector.” The processor
does not generate an exception when a segment register (other than the CS or SS registers) is loaded with a null
selector. It does, however, generate an exception when a segment register holding a null selector is used to access
memory. A null selector can be used to initialize unused segment registers. Loading the CS or SS register with a null
segment selector causes a general-protection exception (#GP) to be generated.
Segment selectors are visible to application programs as part of a pointer variable, but the values of selectors are
usually assigned or modified by link editors or linking loaders, not application programs.

3.4.3

Segment Registers

To reduce address translation time and coding complexity, the processor provides registers for holding up to 6
segment selectors (see Figure 3-7). Each of these segment registers support a specific kind of memory reference
(code, stack, or data). For virtually any kind of program execution to take place, at least the code-segment (CS),
data-segment (DS), and stack-segment (SS) registers must be loaded with valid segment selectors. The processor
also provides three additional data-segment registers (ES, FS, and GS), which can be used to make additional data
segments available to the currently executing program (or task).
For a program to access a segment, the segment selector for the segment must have been loaded in one of the
segment registers. So, although a system can define thousands of segments, only 6 can be available for immediate
use. Other segments can be made available by loading their segment selectors into these registers during program
execution.

Visible Part
Segment Selector

Hidden Part
Base Address, Limit, Access Information

CS
SS
DS
ES
FS
GS

Figure 3-7. Segment Registers
Every segment register has a “visible” part and a “hidden” part. (The hidden part is sometimes referred to as a
“descriptor cache” or a “shadow register.”) When a segment selector is loaded into the visible part of a segment
register, the processor also loads the hidden part of the segment register with the base address, segment limit, and
access control information from the segment descriptor pointed to by the segment selector. The information cached
in the segment register (visible and hidden) allows the processor to translate addresses without taking extra bus
cycles to read the base address and limit from the segment descriptor. In systems in which multiple processors
have access to the same descriptor tables, it is the responsibility of software to reload the segment registers when
the descriptor tables are modified. If this is not done, an old segment descriptor cached in a segment register might
be used after its memory-resident version has been modified.
Two kinds of load instructions are provided for loading the segment registers:
1. Direct load instructions such as the MOV, POP, LDS, LES, LSS, LGS, and LFS instructions. These instructions
explicitly reference the segment registers.

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PROTECTED-MODE MEMORY MANAGEMENT

2. Implied load instructions such as the far pointer versions of the CALL, JMP, and RET instructions, the SYSENTER
and SYSEXIT instructions, and the IRET, INTn, INTO and INT3 instructions. These instructions change the
contents of the CS register (and sometimes other segment registers) as an incidental part of their operation.
The MOV instruction can also be used to store the visible part of a segment register in a general-purpose register.

3.4.4

Segment Loading Instructions in IA-32e Mode

Because ES, DS, and SS segment registers are not used in 64-bit mode, their fields (base, limit, and attribute) in
segment descriptor registers are ignored. Some forms of segment load instructions are also invalid (for example,
LDS, POP ES). Address calculations that reference the ES, DS, or SS segments are treated as if the segment base
is zero.
The processor checks that all linear-address references are in canonical form instead of performing limit checks.
Mode switching does not change the contents of the segment registers or the associated descriptor registers.
These registers are also not changed during 64-bit mode execution, unless explicit segment loads are performed.
In order to set up compatibility mode for an application, segment-load instructions (MOV to Sreg, POP Sreg) work
normally in 64-bit mode. An entry is read from the system descriptor table (GDT or LDT) and is loaded in the hidden
portion of the segment register. The descriptor-register base, limit, and attribute fields are all loaded. However, the
contents of the data and stack segment selector and the descriptor registers are ignored.
When FS and GS segment overrides are used in 64-bit mode, their respective base addresses are used in the linear
address calculation: (FS or GS).base + index + displacement. FS.base and GS.base are then expanded to the full
linear-address size supported by the implementation. The resulting effective address calculation can wrap across
positive and negative addresses; the resulting linear address must be canonical.
In 64-bit mode, memory accesses using FS-segment and GS-segment overrides are not checked for a runtime limit
nor subjected to attribute-checking. Normal segment loads (MOV to Sreg and POP Sreg) into FS and GS load a
standard 32-bit base value in the hidden portion of the segment register. The base address bits above the standard
32 bits are cleared to 0 to allow consistency for implementations that use less than 64 bits.
The hidden descriptor register fields for FS.base and GS.base are physically mapped to MSRs in order to load all
address bits supported by a 64-bit implementation. Software with CPL = 0 (privileged software) can load all
supported linear-address bits into FS.base or GS.base using WRMSR. Addresses written into the 64-bit FS.base
and GS.base registers must be in canonical form. A WRMSR instruction that attempts to write a non-canonical
address to those registers causes a #GP fault.
When in compatibility mode, FS and GS overrides operate as defined by 32-bit mode behavior regardless of the
value loaded into the upper 32 linear-address bits of the hidden descriptor register base field. Compatibility mode
ignores the upper 32 bits when calculating an effective address.
A new 64-bit mode instruction, SWAPGS, can be used to load GS base. SWAPGS exchanges the kernel data structure pointer from the IA32_KERNEL_GS_BASE MSR with the GS base register. The kernel can then use the GS
prefix on normal memory references to access the kernel data structures. An attempt to write a non-canonical
value (using WRMSR) to the IA32_KERNEL_GS_BASE MSR causes a #GP fault.

3.4.5

Segment Descriptors

A segment descriptor is a data structure in a GDT or LDT that provides the processor with the size and location of
a segment, as well as access control and status information. Segment descriptors are typically created by
compilers, linkers, loaders, or the operating system or executive, but not application programs. Figure 3-8 illustrates the general descriptor format for all types of segment descriptors.

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PROTECTED-MODE MEMORY MANAGEMENT

31

24 23 22 21 20 19

Base 31:24

D
A
G / L V
B
L

31

16 15 14 13 12 11

Seg.
Limit
19:16

P

D
P
L

S

0

8 7

Type

16 15

Base Address 15:00

4

Base 23:16

0

Segment Limit 15:00

0

L
— 64-bit code segment (IA-32e mode only)
AVL — Available for use by system software
BASE — Segment base address
D/B — Default operation size (0 = 16-bit segment; 1 = 32-bit segment)
DPL — Descriptor privilege level
G
— Granularity
LIMIT — Segment Limit
P
— Segment present
S
— Descriptor type (0 = system; 1 = code or data)
TYPE — Segment type

Figure 3-8. Segment Descriptor
The flags and fields in a segment descriptor are as follows:
Segment limit field
Specifies the size of the segment. The processor puts together the two segment limit fields to form
a 20-bit value. The processor interprets the segment limit in one of two ways, depending on the
setting of the G (granularity) flag:
•

If the granularity flag is clear, the segment size can range from 1 byte to 1 MByte, in byte increments.

•

If the granularity flag is set, the segment size can range from 4 KBytes to 4 GBytes, in 4-KByte
increments.

The processor uses the segment limit in two different ways, depending on whether the segment is
an expand-up or an expand-down segment. See Section 3.4.5.1, “Code- and Data-Segment
Descriptor Types”, for more information about segment types. For expand-up segments, the offset
in a logical address can range from 0 to the segment limit. Offsets greater than the segment limit
generate general-protection exceptions (#GP, for all segments other than SS) or stack-fault exceptions (#SS for the SS segment). For expand-down segments, the segment limit has the reverse
function; the offset can range from the segment limit plus 1 to FFFFFFFFH or FFFFH, depending on
the setting of the B flag. Offsets less than or equal to the segment limit generate general-protection
exceptions or stack-fault exceptions. Decreasing the value in the segment limit field for an expanddown segment allocates new memory at the bottom of the segment's address space, rather than at
the top. IA-32 architecture stacks always grow downwards, making this mechanism convenient for
expandable stacks.
Base address fields
Defines the location of byte 0 of the segment within the 4-GByte linear address space. The
processor puts together the three base address fields to form a single 32-bit value. Segment base
addresses should be aligned to 16-byte boundaries. Although 16-byte alignment is not required,
this alignment allows programs to maximize performance by aligning code and data on 16-byte
boundaries.
Type field

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Indicates the segment or gate type and specifies the kinds of access that can be made to the
segment and the direction of growth. The interpretation of this field depends on whether the
descriptor type flag specifies an application (code or data) descriptor or a system descriptor. The
encoding of the type field is different for code, data, and system descriptors (see Figure 5-1). See
Section 3.4.5.1, “Code- and Data-Segment Descriptor Types”, for a description of how this field is
used to specify code and data-segment types.

PROTECTED-MODE MEMORY MANAGEMENT

S (descriptor type) flag
Specifies whether the segment descriptor is for a system segment (S flag is clear) or a code or data
segment (S flag is set).
DPL (descriptor privilege level) field
Specifies the privilege level of the segment. The privilege level can range from 0 to 3, with 0 being
the most privileged level. The DPL is used to control access to the segment. See Section 5.5, “Privilege Levels”, for a description of the relationship of the DPL to the CPL of the executing code
segment and the RPL of a segment selector.
P (segment-present) flag
Indicates whether the segment is present in memory (set) or not present (clear). If this flag is clear,
the processor generates a segment-not-present exception (#NP) when a segment selector that
points to the segment descriptor is loaded into a segment register. Memory management software
can use this flag to control which segments are actually loaded into physical memory at a given
time. It offers a control in addition to paging for managing virtual memory.
Figure 3-9 shows the format of a segment descriptor when the segment-present flag is clear. When
this flag is clear, the operating system or executive is free to use the locations marked “Available” to
store its own data, such as information regarding the whereabouts of the missing segment.
D/B (default operation size/default stack pointer size and/or upper bound) flag
Performs different functions depending on whether the segment descriptor is an executable code
segment, an expand-down data segment, or a stack segment. (This flag should always be set to 1
for 32-bit code and data segments and to 0 for 16-bit code and data segments.)
•

Executable code segment. The flag is called the D flag and it indicates the default length for
effective addresses and operands referenced by instructions in the segment. If the flag is set,
32-bit addresses and 32-bit or 8-bit operands are assumed; if it is clear, 16-bit addresses and
16-bit or 8-bit operands are assumed.
The instruction prefix 66H can be used to select an operand size other than the default, and the
prefix 67H can be used select an address size other than the default.

•

Stack segment (data segment pointed to by the SS register). The flag is called the B (big)
flag and it specifies the size of the stack pointer used for implicit stack operations (such as
pushes, pops, and calls). If the flag is set, a 32-bit stack pointer is used, which is stored in the
32-bit ESP register; if the flag is clear, a 16-bit stack pointer is used, which is stored in the 16bit SP register. If the stack segment is set up to be an expand-down data segment (described in
the next paragraph), the B flag also specifies the upper bound of the stack segment.

•

Expand-down data segment. The flag is called the B flag and it specifies the upper bound of
the segment. If the flag is set, the upper bound is FFFFFFFFH (4 GBytes); if the flag is clear, the
upper bound is FFFFH (64 KBytes).

31

16 15 14 13 12 11

Available

0

D
P
L

31

S

0

8 7

Type

4

Available

0

Available

0

Figure 3-9. Segment Descriptor When Segment-Present Flag Is Clear
G (granularity) flag
Determines the scaling of the segment limit field. When the granularity flag is clear, the segment
limit is interpreted in byte units; when flag is set, the segment limit is interpreted in 4-KByte units.
(This flag does not affect the granularity of the base address; it is always byte granular.) When the
granularity flag is set, the twelve least significant bits of an offset are not tested when checking the

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PROTECTED-MODE MEMORY MANAGEMENT

offset against the segment limit. For example, when the granularity flag is set, a limit of 0 results in
valid offsets from 0 to 4095.
L (64-bit code segment) flag
In IA-32e mode, bit 21 of the second doubleword of the segment descriptor indicates whether a
code segment contains native 64-bit code. A value of 1 indicates instructions in this code segment
are executed in 64-bit mode. A value of 0 indicates the instructions in this code segment are
executed in compatibility mode. If L-bit is set, then D-bit must be cleared. When not in IA-32e mode
or for non-code segments, bit 21 is reserved and should always be set to 0.
Available and reserved bits
Bit 20 of the second doubleword of the segment descriptor is available for use by system software.

3.4.5.1

Code- and Data-Segment Descriptor Types

When the S (descriptor type) flag in a segment descriptor is set, the descriptor is for either a code or a data
segment. The highest order bit of the type field (bit 11 of the second double word of the segment descriptor) then
determines whether the descriptor is for a data segment (clear) or a code segment (set).
For data segments, the three low-order bits of the type field (bits 8, 9, and 10) are interpreted as accessed (A),
write-enable (W), and expansion-direction (E). See Table 3-1 for a description of the encoding of the bits in the
type field for code and data segments. Data segments can be read-only or read/write segments, depending on the
setting of the write-enable bit.

Table 3-1. Code- and Data-Segment Types
Type Field

Descriptor
Type

Description

Decimal

11

10
E

9
W

8
A

0

0

0

0

0

Data

Read-Only

1

0

0

0

1

Data

Read-Only, accessed

2

0

0

1

0

Data

Read/Write

3

0

0

1

1

Data

Read/Write, accessed

4

0

1

0

0

Data

Read-Only, expand-down

5

0

1

0

1

Data

Read-Only, expand-down, accessed

6

0

1

1

0

Data

Read/Write, expand-down

7

0

1

1

1

Data

Read/Write, expand-down, accessed

C

R

A

8

1

0

0

0

Code

Execute-Only

9

1

0

0

1

Code

Execute-Only, accessed

10

1

0

1

0

Code

Execute/Read

11

1

0

1

1

Code

Execute/Read, accessed

12

1

1

0

0

Code

Execute-Only, conforming

13

1

1

0

1

Code

Execute-Only, conforming, accessed

14

1

1

1

0

Code

Execute/Read, conforming

15

1

1

1

1

Code

Execute/Read, conforming, accessed

Stack segments are data segments which must be read/write segments. Loading the SS register with a segment
selector for a nonwritable data segment generates a general-protection exception (#GP). If the size of a stack
segment needs to be changed dynamically, the stack segment can be an expand-down data segment (expansiondirection flag set). Here, dynamically changing the segment limit causes stack space to be added to the bottom of

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PROTECTED-MODE MEMORY MANAGEMENT

the stack. If the size of a stack segment is intended to remain static, the stack segment may be either an expandup or expand-down type.
The accessed bit indicates whether the segment has been accessed since the last time the operating-system or
executive cleared the bit. The processor sets this bit whenever it loads a segment selector for the segment into a
segment register, assuming that the type of memory that contains the segment descriptor supports processor
writes. The bit remains set until explicitly cleared. This bit can be used both for virtual memory management and
for debugging.
For code segments, the three low-order bits of the type field are interpreted as accessed (A), read enable (R), and
conforming (C). Code segments can be execute-only or execute/read, depending on the setting of the read-enable
bit. An execute/read segment might be used when constants or other static data have been placed with instruction
code in a ROM. Here, data can be read from the code segment either by using an instruction with a CS override
prefix or by loading a segment selector for the code segment in a data-segment register (the DS, ES, FS, or GS
registers). In protected mode, code segments are not writable.
Code segments can be either conforming or nonconforming. A transfer of execution into a more-privileged
conforming segment allows execution to continue at the current privilege level. A transfer into a nonconforming
segment at a different privilege level results in a general-protection exception (#GP), unless a call gate or task gate
is used (see Section 5.8.1, “Direct Calls or Jumps to Code Segments”, for more information on conforming and
nonconforming code segments). System utilities that do not access protected facilities and handlers for some types
of exceptions (such as, divide error or overflow) may be loaded in conforming code segments. Utilities that need to
be protected from less privileged programs and procedures should be placed in nonconforming code segments.

NOTE
Execution cannot be transferred by a call or a jump to a less-privileged (numerically higher
privilege level) code segment, regardless of whether the target segment is a conforming or
nonconforming code segment. Attempting such an execution transfer will result in a generalprotection exception.
All data segments are nonconforming, meaning that they cannot be accessed by less privileged programs or procedures (code executing at numerically higher privilege levels). Unlike code segments, however, data segments can
be accessed by more privileged programs or procedures (code executing at numerically lower privilege levels)
without using a special access gate.
If the segment descriptors in the GDT or an LDT are placed in ROM, the processor can enter an indefinite loop if
software or the processor attempts to update (write to) the ROM-based segment descriptors. To prevent this
problem, set the accessed bits for all segment descriptors placed in a ROM. Also, remove operating-system or
executive code that attempts to modify segment descriptors located in ROM.

3.5

SYSTEM DESCRIPTOR TYPES

When the S (descriptor type) flag in a segment descriptor is clear, the descriptor type is a system descriptor. The
processor recognizes the following types of system descriptors:

•
•
•
•
•
•

Local descriptor-table (LDT) segment descriptor.
Task-state segment (TSS) descriptor.
Call-gate descriptor.
Interrupt-gate descriptor.
Trap-gate descriptor.
Task-gate descriptor.

These descriptor types fall into two categories: system-segment descriptors and gate descriptors. Systemsegment descriptors point to system segments (LDT and TSS segments). Gate descriptors are in themselves
“gates,” which hold pointers to procedure entry points in code segments (call, interrupt, and trap gates) or which
hold segment selectors for TSS’s (task gates).

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PROTECTED-MODE MEMORY MANAGEMENT

Table 3-2 shows the encoding of the type field for system-segment descriptors and gate descriptors. Note that
system descriptors in IA-32e mode are 16 bytes instead of 8 bytes.

Table 3-2. System-Segment and Gate-Descriptor Types
Type Field

Description

Decimal

11

10

9

8

32-Bit Mode

IA-32e Mode

0

0

0

0

0

Reserved

1

0

0

0

1

16-bit TSS (Available)

Reserved

2

0

0

1

0

LDT

LDT

3

0

0

1

1

16-bit TSS (Busy)

Reserved

4

0

1

0

0

16-bit Call Gate

Reserved

5

0

1

0

1

Task Gate

Reserved

6

0

1

1

0

16-bit Interrupt Gate

Reserved

7

0

1

1

1

16-bit Trap Gate

Reserved

8

1

0

0

0

Reserved

Reserved

9

1

0

0

1

32-bit TSS (Available)

64-bit TSS (Available)

10

1

0

1

0

Reserved

Reserved

11

1

0

1

1

32-bit TSS (Busy)

64-bit TSS (Busy)

12

1

1

0

0

32-bit Call Gate

64-bit Call Gate

13

1

1

0

1

Reserved

Reserved

14

1

1

1

0

32-bit Interrupt Gate

64-bit Interrupt Gate

15

1

1

1

1

32-bit Trap Gate

64-bit Trap Gate

Reserved

See also: Section 3.5.1, “Segment Descriptor Tables”, and Section 7.2.2, “TSS Descriptor” (for more information
on the system-segment descriptors); see Section 5.8.3, “Call Gates”, Section 6.11, “IDT Descriptors”, and Section
7.2.5, “Task-Gate Descriptor” (for more information on the gate descriptors).

3.5.1

Segment Descriptor Tables

A segment descriptor table is an array of segment descriptors (see Figure 3-10). A descriptor table is variable in
length and can contain up to 8192 (213) 8-byte descriptors. There are two kinds of descriptor tables:

•
•

The global descriptor table (GDT)
The local descriptor tables (LDT)

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T
I

Segment
Selector

Global
Descriptor
Table (GDT)

Local
Descriptor
Table (LDT)

TI = 0

TI = 1

First Descriptor in
GDT is Not Used

56

56

48

48

40

40

32

32

24

24

16

16

8

8

0

0

GDTR Register

LDTR Register

Limit
Base Address

Limit
Base Address
Seg. Sel.

Figure 3-10. Global and Local Descriptor Tables
Each system must have one GDT defined, which may be used for all programs and tasks in the system. Optionally,
one or more LDTs can be defined. For example, an LDT can be defined for each separate task being run, or some or
all tasks can share the same LDT.
The GDT is not a segment itself; instead, it is a data structure in linear address space. The base linear address and
limit of the GDT must be loaded into the GDTR register (see Section 2.4, “Memory-Management Registers”). The
base address of the GDT should be aligned on an eight-byte boundary to yield the best processor performance. The
limit value for the GDT is expressed in bytes. As with segments, the limit value is added to the base address to get
the address of the last valid byte. A limit value of 0 results in exactly one valid byte. Because segment descriptors
are always 8 bytes long, the GDT limit should always be one less than an integral multiple of eight (that is, 8N – 1).
The first descriptor in the GDT is not used by the processor. A segment selector to this “null descriptor” does not
generate an exception when loaded into a data-segment register (DS, ES, FS, or GS), but it always generates a
general-protection exception (#GP) when an attempt is made to access memory using the descriptor. By initializing
the segment registers with this segment selector, accidental reference to unused segment registers can be guaranteed to generate an exception.
The LDT is located in a system segment of the LDT type. The GDT must contain a segment descriptor for the LDT
segment. If the system supports multiple LDTs, each must have a separate segment selector and segment
descriptor in the GDT. The segment descriptor for an LDT can be located anywhere in the GDT. See Section 3.5,
“System Descriptor Types”, for information on the LDT segment-descriptor type.
An LDT is accessed with its segment selector. To eliminate address translations when accessing the LDT, the
segment selector, base linear address, limit, and access rights of the LDT are stored in the LDTR register (see
Section 2.4, “Memory-Management Registers”).
When the GDTR register is stored (using the SGDT instruction), a 48-bit “pseudo-descriptor” is stored in memory
(see top diagram in Figure 3-11). To avoid alignment check faults in user mode (privilege level 3), the pseudodescriptor should be located at an odd word address (that is, address MOD 4 is equal to 2). This causes the
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PROTECTED-MODE MEMORY MANAGEMENT

processor to store an aligned word, followed by an aligned doubleword. User-mode programs normally do not store
pseudo-descriptors, but the possibility of generating an alignment check fault can be avoided by aligning pseudodescriptors in this way. The same alignment should be used when storing the IDTR register using the SIDT instruction. When storing the LDTR or task register (using the SLDT or STR instruction, respectively), the pseudodescriptor should be located at a doubleword address (that is, address MOD 4 is equal to 0).

47

16 15

79

0
Limit

32-bit Base Address

0

16 15
64-bit Base Address

Limit

Figure 3-11. Pseudo-Descriptor Formats

3.5.2

Segment Descriptor Tables in IA-32e Mode

In IA-32e mode, a segment descriptor table can contain up to 8192 (213) 8-byte descriptors. An entry in the
segment descriptor table can be 8 bytes. System descriptors are expanded to 16 bytes (occupying the space of two
entries).
GDTR and LDTR registers are expanded to hold 64-bit base address. The corresponding pseudo-descriptor is 80
bits. (see the bottom diagram in Figure 3-11).
The following system descriptors expand to 16 bytes:
— Call gate descriptors (see Section 5.8.3.1, “IA-32e Mode Call Gates”)
— IDT gate descriptors (see Section 6.14.1, “64-Bit Mode IDT”)
— LDT and TSS descriptors (see Section 7.2.3, “TSS Descriptor in 64-bit mode”).

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CHAPTER 4
PAGING
Chapter 3 explains how segmentation converts logical addresses to linear addresses. Paging (or linear-address
translation) is the process of translating linear addresses so that they can be used to access memory or I/O
devices. Paging translates each linear address to a physical address and determines, for each translation, what
accesses to the linear address are allowed (the address’s access rights) and the type of caching used for such
accesses (the address’s memory type).
Intel-64 processors support three different paging modes. These modes are identified and defined in Section 4.1.
Section 4.2 gives an overview of the translation mechanism that is used in all modes. Section 4.3, Section 4.4, and
Section 4.5 discuss the three paging modes in detail.
Section 4.6 details how paging determines and uses access rights. Section 4.7 discusses exceptions that may be
generated by paging (page-fault exceptions). Section 4.8 considers data which the processor writes in response to
linear-address accesses (accessed and dirty flags).
Section 4.9 describes how paging determines the memory types used for accesses to linear addresses. Section
4.10 provides details of how a processor may cache information about linear-address translation. Section 4.11
outlines interactions between paging and certain VMX features. Section 4.12 gives an overview of how paging can
be used to implement virtual memory.

4.1

PAGING MODES AND CONTROL BITS

Paging behavior is controlled by the following control bits:

•
•

The WP and PG flags in control register CR0 (bit 16 and bit 31, respectively).

•
•

The LME and NXE flags in the IA32_EFER MSR (bit 8 and bit 11, respectively).

The PSE, PAE, PGE, PCIDE, SMEP, SMAP, and PKE flags in control register CR4 (bit 4, bit 5, bit 7, bit 17, bit 20,
bit 21, and bit 22, respectively).
The AC flag in the EFLAGS register (bit 18).

Software enables paging by using the MOV to CR0 instruction to set CR0.PG. Before doing so, software should
ensure that control register CR3 contains the physical address of the first paging structure that the processor will
use for linear-address translation (see Section 4.2) and that structure is initialized as desired. See Table 4-3,
Table 4-7, and Table 4-12 for the use of CR3 in the different paging modes.
Section 4.1.1 describes how the values of CR0.PG, CR4.PAE, and IA32_EFER.LME determine whether paging is in
use and, if so, which of three paging modes is in use. Section 4.1.2 explains how to manage these bits to establish
or make changes in paging modes. Section 4.1.3 discusses how CR0.WP, CR4.PSE, CR4.PGE, CR4.PCIDE,
CR4.SMEP, CR4.SMAP, CR4.PKE, and IA32_EFER.NXE modify the operation of the different paging modes.

4.1.1

Three Paging Modes

If CR0.PG = 0, paging is not used. The logical processor treats all linear addresses as if they were physical
addresses. CR4.PAE and IA32_EFER.LME are ignored by the processor, as are CR0.WP, CR4.PSE, CR4.PGE,
CR4.SMEP, CR4.SMAP, and IA32_EFER.NXE.
Paging is enabled if CR0.PG = 1. Paging can be enabled only if protection is enabled (CR0.PE = 1). If paging is
enabled, one of three paging modes is used. The values of CR4.PAE and IA32_EFER.LME determine which paging
mode is used:

•

If CR0.PG = 1 and CR4.PAE = 0, 32-bit paging is used. 32-bit paging is detailed in Section 4.3. 32-bit paging
uses CR0.WP, CR4.PSE, CR4.PGE, CR4.SMEP, and CR4.SMAP as described in Section 4.1.3.

•

If CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 0, PAE paging is used. PAE paging is detailed in Section
4.4. PAE paging uses CR0.WP, CR4.PGE, CR4.SMEP, CR4.SMAP, and IA32_EFER.NXE as described in Section
4.1.3.
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PAGING

•

If CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 1, 4-level paging1 is used.2 4-level paging is detailed in
Section 4.5. 4-level paging uses CR0.WP, CR4.PGE, CR4.PCIDE, CR4.SMEP, CR4.SMAP, CR4.PKE, and
IA32_EFER.NXE as described in Section 4.1.3. 4-level paging is available only on processors that support the
Intel 64 architecture.

The three paging modes differ with regard to the following details:

•
•
•

Linear-address width. The size of the linear addresses that can be translated.

•

Support for execute-disable access rights. In some paging modes, software can be prevented from fetching
instructions from pages that are otherwise readable.

•

Support for PCIDs. With 4-level paging, software can enable a facility by which a logical processor caches
information for multiple linear-address spaces. The processor may retain cached information when software
switches between different linear-address spaces.

•

Support for protection keys. With 4-level paging, software can enable a facility by which each linear address is
associated with a protection key. Software can use a new control register to determine, for each protection
keys, how software can access linear addresses associated with that protection key.

Physical-address width. The size of the physical addresses produced by paging.
Page size. The granularity at which linear addresses are translated. Linear addresses on the same page are
translated to corresponding physical addresses on the same page.

Table 4-1 illustrates the principal differences between the three paging modes.

Table 4-1. Properties of Different Paging Modes
Paging
Mode

PG in
CR0

PAE in
CR4

LME in
IA32_EFER

Lin.Addr.
Width

Phys.Addr.
Width1

Page
Sizes

Supports
ExecuteDisable?

Supports
PCIDs and
protection
keys?

None

0

N/A

N/A

32

32

N/A

No

No

32-bit

1

0

02

32

Up to
403

4 KB
4 MB4

No

No

PAE

1

1

0

32

Up to
52

4 KB
2 MB

Yes5

No

4-level

1

1

1

48

Up to
52

4 KB
2 MB
1 GB6

Yes5

Yes7

NOTES:
1. The physical-address width is always bounded by MAXPHYADDR; see Section 4.1.4.
2. The processor ensures that IA32_EFER.LME must be 0 if CR0.PG = 1 and CR4.PAE = 0.
3. 32-bit paging supports physical-address widths of more than 32 bits only for 4-MByte pages and only if the PSE-36 mechanism is
supported; see Section 4.1.4 and Section 4.3.
4. 4-MByte pages are used with 32-bit paging only if CR4.PSE = 1; see Section 4.3.
5. Execute-disable access rights are applied only if IA32_EFER.NXE = 1; see Section 4.6.
6. Not all processors that support 4-level paging support 1-GByte pages; see Section 4.1.4.
7. PCIDs are used only if CR4.PCIDE = 1; see Section 4.10.1. Protection keys are used only if certain conditions hold; see Section 4.6.2.

1. Earlier versions of this manual used the term “IA-32e paging” to identify 4-level paging.
2. The LMA flag in the IA32_EFER MSR (bit 10) is a status bit that indicates whether the logical processor is in IA-32e mode (and thus
using 4-level paging). The processor always sets IA32_EFER.LMA to CR0.PG & IA32_EFER.LME. Software cannot directly modify
IA32_EFER.LMA; an execution of WRMSR to the IA32_EFER MSR ignores bit 10 of its source operand.
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PAGING

Because they are used only if IA32_EFER.LME = 0, 32-bit paging and PAE paging are used only in legacy protected
mode. Because legacy protected mode cannot produce linear addresses larger than 32 bits, 32-bit paging and PAE
paging translate 32-bit linear addresses.
Because it is used only if IA32_EFER.LME = 1, 4-level paging is used only in IA-32e mode. (In fact, it is the use of
4-level paging that defines IA-32e mode.) IA-32e mode has two sub-modes:

•

Compatibility mode. This mode uses only 32-bit linear addresses. 4-level paging treats bits 47:32 of such an
address as all 0.

•

64-bit mode. While this mode produces 64-bit linear addresses, the processor ensures that bits 63:47 of such
an address are identical.1 4-level paging does not use bits 63:48 of such addresses.

4.1.2

Paging-Mode Enabling

If CR0.PG = 1, a logical processor is in one of three paging modes, depending on the values of CR4.PAE and
IA32_EFER.LME. Figure 4-1 illustrates how software can enable these modes and make transitions between them.
The following items identify certain limitations and other details:
#GP

#GP

Set LME
No Paging

Set PG

PG = 0
PAE = 0
LME = 0

Clear PG

Set LME

32-bit Paging
PG = 1
PAE = 0
LME = 0

PAE Paging
PG = 1
PAE = 1
LME = 0

Clear PAE

Clear LME

Setr LME

#GP
Clear PAE

Set PG

Set PAE

Clear PG

No Paging
PG = 0
PAE = 0
LME = 1

Clear PAE

No Paging
PG = 0
PAE = 1
LME = 0

Clear PG

Clear LME

Clear PAE

4-level Paging
PG = 1
PAE = 1
LME = 1
Set PG

Clear LME

Setr LME

Set PG

#GP

Set PAE

Set PAE

#GP
No Paging
PG = 0
PAE = 1
LME = 1

Figure 4-1. Enabling and Changing Paging Modes

•

IA32_EFER.LME cannot be modified while paging is enabled (CR0.PG = 1). Attempts to do so using WRMSR
cause a general-protection exception (#GP(0)).

1. Such an address is called canonical. Use of a non-canonical linear address in 64-bit mode produces a general-protection exception
(#GP(0)); the processor does not attempt to translate non-canonical linear addresses using 4-level paging.
Vol. 3A 4-3

PAGING

•

Paging cannot be enabled (by setting CR0.PG to 1) while CR4.PAE = 0 and IA32_EFER.LME = 1. Attempts to do
so using MOV to CR0 cause a general-protection exception (#GP(0)).

•

CR4.PAE cannot be cleared while 4-level paging is active (CR0.PG = 1 and IA32_EFER.LME = 1). Attempts to
do so using MOV to CR4 cause a general-protection exception (#GP(0)).

•
•

Regardless of the current paging mode, software can disable paging by clearing CR0.PG with MOV to CR0.1

•

Software cannot make transitions directly between 4-level paging and either of the other two paging modes. It
must first disable paging (by clearing CR0.PG with MOV to CR0), then set CR4.PAE and IA32_EFER.LME to the
desired values (with MOV to CR4 and WRMSR), and then re-enable paging (by setting CR0.PG with MOV to
CR0). As noted earlier, an attempt to clear either CR4.PAE or IA32_EFER.LME cause a general-protection
exception (#GP(0)).

•

VMX transitions allow transitions between paging modes that are not possible using MOV to CR or WRMSR. This
is because VMX transitions can load CR0, CR4, and IA32_EFER in one operation. See Section 4.11.1.

Software can make transitions between 32-bit paging and PAE paging by changing the value of CR4.PAE with
MOV to CR4.

4.1.3

Paging-Mode Modifiers

Details of how each paging mode operates are determined by the following control bits:

•
•

The WP flag in CR0 (bit 16).

•

The NXE flag in the IA32_EFER MSR (bit 11).

The PSE, PGE, PCIDE, SMEP, SMAP, and PKE flags in CR4 (bit 4, bit 7, bit 17, bit 20, bit 21, and bit 22 respectively).

CR0.WP allows pages to be protected from supervisor-mode writes. If CR0.WP = 0, supervisor-mode write
accesses are allowed to linear addresses with read-only access rights; if CR0.WP = 1, they are not. (User-mode
write accesses are never allowed to linear addresses with read-only access rights, regardless of the value of
CR0.WP.) Section 4.6 explains how access rights are determined, including the definition of supervisor-mode and
user-mode accesses.
CR4.PSE enables 4-MByte pages for 32-bit paging. If CR4.PSE = 0, 32-bit paging can use only 4-KByte pages; if
CR4.PSE = 1, 32-bit paging can use both 4-KByte pages and 4-MByte pages. See Section 4.3 for more information.
(PAE paging and 4-level paging can use multiple page sizes regardless of the value of CR4.PSE.)
CR4.PGE enables global pages. If CR4.PGE = 0, no translations are shared across address spaces; if CR4.PGE = 1,
specified translations may be shared across address spaces. See Section 4.10.2.4 for more information.
CR4.PCIDE enables process-context identifiers (PCIDs) for 4-level paging (CR4.PCIDE can be 1 only when 4-level
paging is in use). PCIDs allow a logical processor to cache information for multiple linear-address spaces. See
Section 4.10.1 for more information.
CR4.SMEP allows pages to be protected from supervisor-mode instruction fetches. If CR4.SMEP = 1, software
operating in supervisor mode cannot fetch instructions from linear addresses that are accessible in user mode.
Section 4.6 explains how access rights are determined, including the definition of supervisor-mode accesses and
user-mode accessibility.
CR4.SMAP allows pages to be protected from supervisor-mode data accesses. If CR4.SMAP = 1, software operating
in supervisor mode cannot access data at linear addresses that are accessible in user mode. Software can override
this protection by setting EFLAGS.AC. Section 4.6 explains how access rights are determined, including the definition of supervisor-mode accesses and user-mode accessibility.
CR4.PKE allows each linear address to be associated with a protection key. The PKRU register specifies, for each
protection key, whether linear addresses with that protection key can be read or written by software. See Section
4.6 for more information.
IA32_EFER.NXE enables execute-disable access rights for PAE paging and 4-level paging. If IA32_EFER.NXE = 1,
instruction fetches can be prevented from specified linear addresses (even if data reads from the addresses are
1. If CR4.PCIDE = 1, an attempt to clear CR0.PG causes a general-protection exception (#GP); software should clear CR4.PCIDE before
attempting to disable paging.
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PAGING

allowed). Section 4.6 explains how access rights are determined. (IA32_EFER.NXE has no effect with 32-bit
paging. Software that wants to use this feature to limit instruction fetches from readable pages must use either PAE
paging or 4-level paging.)

4.1.4

Enumeration of Paging Features by CPUID

Software can discover support for different paging features using the CPUID instruction:

•

PSE: page-size extensions for 32-bit paging.
If CPUID.01H:EDX.PSE [bit 3] = 1, CR4.PSE may be set to 1, enabling support for 4-MByte pages with 32-bit
paging (see Section 4.3).

•

PAE: physical-address extension.
If CPUID.01H:EDX.PAE [bit 6] = 1, CR4.PAE may be set to 1, enabling PAE paging (this setting is also required
for 4-level paging).

•

PGE: global-page support.
If CPUID.01H:EDX.PGE [bit 13] = 1, CR4.PGE may be set to 1, enabling the global-page feature (see Section
4.10.2.4).

•

PAT: page-attribute table.
If CPUID.01H:EDX.PAT [bit 16] = 1, the 8-entry page-attribute table (PAT) is supported. When the PAT is
supported, three bits in certain paging-structure entries select a memory type (used to determine type of
caching used) from the PAT (see Section 4.9.2).

•

PSE-36: page-size extensions with 40-bit physical-address extension.
If CPUID.01H:EDX.PSE-36 [bit 17] = 1, the PSE-36 mechanism is supported, indicating that translations using
4-MByte pages with 32-bit paging may produce physical addresses with up to 40 bits (see Section 4.3).

•

PCID: process-context identifiers.
If CPUID.01H:ECX.PCID [bit 17] = 1, CR4.PCIDE may be set to 1, enabling process-context identifiers (see
Section 4.10.1).

•

SMEP: supervisor-mode execution prevention.
If CPUID.(EAX=07H,ECX=0H):EBX.SMEP [bit 7] = 1, CR4.SMEP may be set to 1, enabling supervisor-mode
execution prevention (see Section 4.6).

•

SMAP: supervisor-mode access prevention.
If CPUID.(EAX=07H,ECX=0H):EBX.SMAP [bit 20] = 1, CR4.SMAP may be set to 1, enabling supervisor-mode
access prevention (see Section 4.6).

•

PKU: protection keys.
If CPUID.(EAX=07H,ECX=0H):ECX.PKU [bit 3] = 1, CR4.PKE may be set to 1, enabling protection keys (see
Section 4.6).

•

NX: execute disable.
If CPUID.80000001H:EDX.NX [bit 20] = 1, IA32_EFER.NXE may be set to 1, allowing PAE paging and 4-level
paging to disable execute access to selected pages (see Section 4.6). (Processors that do not support CPUID
function 80000001H do not allow IA32_EFER.NXE to be set to 1.)

•

Page1GB: 1-GByte pages.
If CPUID.80000001H:EDX.Page1GB [bit 26] = 1, 1-GByte pages are supported with 4-level paging (see
Section 4.5).

•

LM: IA-32e mode support.
If CPUID.80000001H:EDX.LM [bit 29] = 1, IA32_EFER.LME may be set to 1, enabling 4-level paging.
(Processors that do not support CPUID function 80000001H do not allow IA32_EFER.LME to be set to 1.)

•

CPUID.80000008H:EAX[7:0] reports the physical-address width supported by the processor. (For processors
that do not support CPUID function 80000008H, the width is generally 36 if CPUID.01H:EDX.PAE [bit 6] = 1
and 32 otherwise.) This width is referred to as MAXPHYADDR. MAXPHYADDR is at most 52.

•

CPUID.80000008H:EAX[15:8] reports the linear-address width supported by the processor. Generally, this
value is 48 if CPUID.80000001H:EDX.LM [bit 29] = 1 and 32 otherwise. (Processors that do not support CPUID
function 80000008H, support a linear-address width of 32.)

Vol. 3A 4-5

PAGING

4.2

HIERARCHICAL PAGING STRUCTURES: AN OVERVIEW

All three paging modes translate linear addresses using hierarchical paging structures. This section provides an
overview of their operation. Section 4.3, Section 4.4, and Section 4.5 provide details for the three paging modes.
Every paging structure is 4096 Bytes in size and comprises a number of individual entries. With 32-bit paging,
each entry is 32 bits (4 bytes); there are thus 1024 entries in each structure. With PAE paging and 4-level paging,
each entry is 64 bits (8 bytes); there are thus 512 entries in each structure. (PAE paging includes one exception, a
paging structure that is 32 bytes in size, containing 4 64-bit entries.)
The processor uses the upper portion of a linear address to identify a series of paging-structure entries. The last of
these entries identifies the physical address of the region to which the linear address translates (called the page
frame). The lower portion of the linear address (called the page offset) identifies the specific address within that
region to which the linear address translates.
Each paging-structure entry contains a physical address, which is either the address of another paging structure or
the address of a page frame. In the first case, the entry is said to reference the other paging structure; in the
latter, the entry is said to map a page.
The first paging structure used for any translation is located at the physical address in CR3. A linear address is
translated using the following iterative procedure. A portion of the linear address (initially the uppermost bits)
selects an entry in a paging structure (initially the one located using CR3). If that entry references another paging
structure, the process continues with that paging structure and with the portion of the linear address immediately
below that just used. If instead the entry maps a page, the process completes: the physical address in the entry is
that of the page frame and the remaining lower portion of the linear address is the page offset.
The following items give an example for each of the three paging modes (each example locates a 4-KByte page
frame):

•

With 32-bit paging, each paging structure comprises 1024 = 210 entries. For this reason, the translation
process uses 10 bits at a time from a 32-bit linear address. Bits 31:22 identify the first paging-structure entry
and bits 21:12 identify a second. The latter identifies the page frame. Bits 11:0 of the linear address are the
page offset within the 4-KByte page frame. (See Figure 4-2 for an illustration.)

•

With PAE paging, the first paging structure comprises only 4 = 22 entries. Translation thus begins by using
bits 31:30 from a 32-bit linear address to identify the first paging-structure entry. Other paging structures
comprise 512 =29 entries, so the process continues by using 9 bits at a time. Bits 29:21 identify a second
paging-structure entry and bits 20:12 identify a third. This last identifies the page frame. (See Figure 4-5 for
an illustration.)

•

With 4-level paging, each paging structure comprises 512 = 29 entries and translation uses 9 bits at a time
from a 48-bit linear address. Bits 47:39 identify the first paging-structure entry, bits 38:30 identify a second,
bits 29:21 a third, and bits 20:12 identify a fourth. Again, the last identifies the page frame. (See Figure 4-8
for an illustration.)

The translation process in each of the examples above completes by identifying a page frame; the page frame is
part of the translation of the original linear address. In some cases, however, the paging structures may be
configured so that the translation process terminates before identifying a page frame. This occurs if the process
encounters a paging-structure entry that is marked “not present” (because its P flag — bit 0 — is clear) or in which
a reserved bit is set. In this case, there is no translation for the linear address; an access to that address causes a
page-fault exception (see Section 4.7).
In the examples above, a paging-structure entry maps a page with a 4-KByte page frame when only 12 bits remain
in the linear address; entries identified earlier always reference other paging structures. That may not apply in
other cases. The following items identify when an entry maps a page and when it references another paging structure:

•

If more than 12 bits remain in the linear address, bit 7 (PS — page size) of the current paging-structure entry
is consulted. If the bit is 0, the entry references another paging structure; if the bit is 1, the entry maps a page.

•

If only 12 bits remain in the linear address, the current paging-structure entry always maps a page (bit 7 is
used for other purposes).

If a paging-structure entry maps a page when more than 12 bits remain in the linear address, the entry identifies
a page frame larger than 4 KBytes. For example, 32-bit paging uses the upper 10 bits of a linear address to locate
the first paging-structure entry; 22 bits remain. If that entry maps a page, the page frame is 222 Bytes = 4 MBytes.

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PAGING

32-bit paging supports 4-MByte pages if CR4.PSE = 1. PAE paging and 4-level paging support 2-MByte pages
(regardless of the value of CR4.PSE). 4-level paging may support 1-GByte pages (see Section 4.1.4).
Paging structures are given different names based on their uses in the translation process. Table 4-2 gives the
names of the different paging structures. It also provides, for each structure, the source of the physical address
used to locate it (CR3 or a different paging-structure entry); the bits in the linear address used to select an entry
from the structure; and details of whether and how such an entry can map a page.

Table 4-2. Paging Structures in the Different Paging Modes
Paging Structure

Entry
Name

PML4 table

PML4E

Paging Mode

Physical
Address of
Structure

Bits Selecting
Entry

32-bit, PAE
4-level

N/A
CR3

47:39

32-bit
Page-directorypointer table

PDPTE

Page directory

PDE

Page table

PTE

Page Mapping

N/A (PS must be 0)
N/A

PAE

CR3

31:30

N/A (PS must be 0)

4-level

PML4E

38:30

1-GByte page if PS=11

32-bit

CR3

31:22

4-MByte page if PS=12

PAE, 4-level

PDPTE

29:21

2-MByte page if PS=1

21:12

4-KByte page

20:12

4-KByte page

32-bit
PAE, 4-level

PDE

NOTES:
1. Not all processors allow the PS flag to be 1 in PDPTEs; see Section 4.1.4 for how to determine whether 1-GByte pages are supported.
2. 32-bit paging ignores the PS flag in a PDE (and uses the entry to reference a page table) unless CR4.PSE = 1. Not all processors allow
CR4.PSE to be 1; see Section 4.1.4 for how to determine whether 4-MByte pages are supported with 32-bit paging.

4.3

32-BIT PAGING

A logical processor uses 32-bit paging if CR0.PG = 1 and CR4.PAE = 0. 32-bit paging translates 32-bit linear
addresses to 40-bit physical addresses.1 Although 40 bits corresponds to 1 TByte, linear addresses are limited to
32 bits; at most 4 GBytes of linear-address space may be accessed at any given time.
32-bit paging uses a hierarchy of paging structures to produce a translation for a linear address. CR3 is used to
locate the first paging-structure, the page directory. Table 4-3 illustrates how CR3 is used with 32-bit paging.
32-bit paging may map linear addresses to either 4-KByte pages or 4-MByte pages. Figure 4-2 illustrates the
translation process when it uses a 4-KByte page; Figure 4-3 covers the case of a 4-MByte page. The following
items describe the 32-bit paging process in more detail as well has how the page size is determined:

•

A 4-KByte naturally aligned page directory is located at the physical address specified in bits 31:12 of CR3 (see
Table 4-3). A page directory comprises 1024 32-bit entries (PDEs). A PDE is selected using the physical address
defined as follows:
— Bits 39:32 are all 0.
— Bits 31:12 are from CR3.

1. Bits in the range 39:32 are 0 in any physical address used by 32-bit paging except those used to map 4-MByte pages. If the processor does not support the PSE-36 mechanism, this is true also for physical addresses used to map 4-MByte pages. If the processor
does support the PSE-36 mechanism and MAXPHYADDR < 40, bits in the range 39:MAXPHYADDR are 0 in any physical address used
to map a 4-MByte page. (The corresponding bits are reserved in PDEs.) See Section 4.1.4 for how to determine MAXPHYADDR and
whether the PSE-36 mechanism is supported.
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PAGING

— Bits 11:2 are bits 31:22 of the linear address.
— Bits 1:0 are 0.
Because a PDE is identified using bits 31:22 of the linear address, it controls access to a 4-Mbyte region of the
linear-address space. Use of the PDE depends on CR4.PSE and the PDE’s PS flag (bit 7):

•

If CR4.PSE = 1 and the PDE’s PS flag is 1, the PDE maps a 4-MByte page (see Table 4-4). The final physical
address is computed as follows:
— Bits 39:32 are bits 20:13 of the PDE.
— Bits 31:22 are bits 31:22 of the PDE.1
— Bits 21:0 are from the original linear address.

•

If CR4.PSE = 0 or the PDE’s PS flag is 0, a 4-KByte naturally aligned page table is located at the physical
address specified in bits 31:12 of the PDE (see Table 4-5). A page table comprises 1024 32-bit entries (PTEs).
A PTE is selected using the physical address defined as follows:
— Bits 39:32 are all 0.
— Bits 31:12 are from the PDE.
— Bits 11:2 are bits 21:12 of the linear address.
— Bits 1:0 are 0.

•

Because a PTE is identified using bits 31:12 of the linear address, every PTE maps a 4-KByte page (see
Table 4-6). The final physical address is computed as follows:
— Bits 39:32 are all 0.
— Bits 31:12 are from the PTE.
— Bits 11:0 are from the original linear address.

If a paging-structure entry’s P flag (bit 0) is 0 or if the entry sets any reserved bit, the entry is used neither to reference another paging-structure entry nor to map a page. There is no translation for a linear address whose translation would use such a paging-structure entry; a reference to such a linear address causes a page-fault exception
(see Section 4.7).
With 32-bit paging, there are reserved bits only if CR4.PSE = 1:

•

If the P flag and the PS flag (bit 7) of a PDE are both 1, the bits reserved depend on MAXPHYADDR, and whether
the PSE-36 mechanism is supported:2
— If the PSE-36 mechanism is not supported, bits 21:13 are reserved.
— If the PSE-36 mechanism is supported, bits 21:(M–19) are reserved, where M is the minimum of 40 and
MAXPHYADDR.

•

If the PAT is not supported:3
— If the P flag of a PTE is 1, bit 7 is reserved.
— If the P flag and the PS flag of a PDE are both 1, bit 12 is reserved.

(If CR4.PSE = 0, no bits are reserved with 32-bit paging.)
A reference using a linear address that is successfully translated to a physical address is performed only if allowed
by the access rights of the translation; see Section 4.6.

1. The upper bits in the final physical address do not all come from corresponding positions in the PDE; the physical-address bits in the
PDE are not all contiguous.
2. See Section 4.1.4 for how to determine MAXPHYADDR and whether the PSE-36 mechanism is supported.
3. See Section 4.1.4 for how to determine whether the PAT is supported.
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PAGING

Linear Address
31
22 21
12 11
Table
Directory

0
Offset
12

Page Table

10

10

4-KByte Page
Physical Address

Page Directory

PTE
PDE with PS=0
32

20

20

CR3

Figure 4-2. Linear-Address Translation to a 4-KByte Page using 32-Bit Paging

31

Linear Address
22 21
Offset
Directory
22

10

Page Directory

PDE with PS=1
32

0

4-MByte Page
Physical Address

18

CR3

Figure 4-3. Linear-Address Translation to a 4-MByte Page using 32-Bit Paging
Figure 4-4 gives a summary of the formats of CR3 and the paging-structure entries with 32-bit paging. For the
paging structure entries, it identifies separately the format of entries that map pages, those that reference other
paging structures, and those that do neither because they are “not present”; bit 0 (P) and bit 7 (PS) are highlighted because they determine how such an entry is used.

Vol. 3A 4-9

PAGING

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9

Address of page directory1
Bits 31:22 of address
of 4MB page frame

Reserved
(must be 0)

P
Bits 39:32 of A
2
address
T

Address of page table

8

7

6

5

4

3

1

0

Ignored

CR3

G

1 D A

P PW U R
C
/ / 1
D T S W

PDE:
4MB
page

I
g
n

P PW U R
C
/ / 1
D T S W

PDE:
page
table

Ignored

Ignored

0

A

Ignored

Address of 4KB page frame

2

P PW
C
Ignored
D T

0

Ignored

G

P
P
U R
A D A C PW
/ / 1
T
D T S W

Ignored

0

PDE:
not
present
PTE:
4KB
page
PTE:
not
present

Figure 4-4. Formats of CR3 and Paging-Structure Entries with 32-Bit Paging
NOTES:
1. CR3 has 64 bits on processors supporting the Intel-64 architecture. These bits are ignored with 32-bit paging.
2. This example illustrates a processor in which MAXPHYADDR is 36. If this value is larger or smaller, the number of bits reserved in
positions 20:13 of a PDE mapping a 4-MByte page will change.

Table 4-3. Use of CR3 with 32-Bit Paging
Bit
Position(s)

Contents

2:0

Ignored

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page directory during linearaddress translation (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page directory during linearaddress translation (see Section 4.9)

11:5

Ignored

31:12

Physical address of the 4-KByte aligned page directory used for linear-address translation

63:32

Ignored (these bits exist only on processors supporting the Intel-64 architecture)

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Table 4-4. Format of a 32-Bit Page-Directory Entry that Maps a 4-MByte Page
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to map a 4-MByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 4-MByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 4-MByte page referenced by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 4-MByte page referenced by
this entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 4-MByte page referenced by
this entry (see Section 4.9)

5 (A)

Accessed; indicates whether software has accessed the 4-MByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 4-MByte page referenced by this entry (see Section 4.8)

7 (PS)

Page size; must be 1 (otherwise, this entry references a page table; see Table 4-5)

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise

11:9

Ignored

12 (PAT)

If the PAT is supported, indirectly determines the memory type used to access the 4-MByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1

(M–20):13

Bits (M–1):32 of physical address of the 4-MByte page referenced by this entry2

21:(M–19)

Reserved (must be 0)

31:22

Bits 31:22 of physical address of the 4-MByte page referenced by this entry

NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.
2. If the PSE-36 mechanism is not supported, M is 32, and this row does not apply. If the PSE-36 mechanism is supported, M is the minimum of 40 and MAXPHYADDR (this row does not apply if MAXPHYADDR = 32). See Section 4.1.4 for how to determine MAXPHYADDR and whether the PSE-36 mechanism is supported.

Vol. 3A 4-11

PAGING

Table 4-5. Format of a 32-Bit Page-Directory Entry that References a Page Table
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to reference a page table

1 (R/W)

Read/write; if 0, writes may not be allowed to the 4-MByte region controlled by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 4-MByte region controlled by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)

5 (A)

Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)

6

Ignored

7 (PS)

If CR4.PSE = 1, must be 0 (otherwise, this entry maps a 4-MByte page; see Table 4-4); otherwise, ignored

11:8

Ignored

31:12

Physical address of 4-KByte aligned page table referenced by this entry

Table 4-6. Format of a 32-Bit Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to map a 4-KByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9)

5 (A)

Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)

7 (PAT)

If the PAT is supported, indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise

11:9

Ignored

31:12

Physical address of the 4-KByte page referenced by this entry

NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.

4-12 Vol. 3A

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4.4

PAE PAGING

A logical processor uses PAE paging if CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 0. PAE paging translates
32-bit linear addresses to 52-bit physical addresses.1 Although 52 bits corresponds to 4 PBytes, linear addresses
are limited to 32 bits; at most 4 GBytes of linear-address space may be accessed at any given time.
With PAE paging, a logical processor maintains a set of four (4) PDPTE registers, which are loaded from an address
in CR3. Linear address are translated using 4 hierarchies of in-memory paging structures, each located using one
of the PDPTE registers. (This is different from the other paging modes, in which there is one hierarchy referenced
by CR3.)
Section 4.4.1 discusses the PDPTE registers. Section 4.4.2 describes linear-address translation with PAE paging.

4.4.1

PDPTE Registers

When PAE paging is used, CR3 references the base of a 32-Byte page-directory-pointer table. Table 4-7 illustrates how CR3 is used with PAE paging.

Table 4-7. Use of CR3 with PAE Paging
Bit
Position(s)

Contents

4:0

Ignored

31:5

Physical address of the 32-Byte aligned page-directory-pointer table used for linear-address translation

63:32

Ignored (these bits exist only on processors supporting the Intel-64 architecture)

The page-directory-pointer-table comprises four (4) 64-bit entries called PDPTEs. Each PDPTE controls access to a
1-GByte region of the linear-address space. Corresponding to the PDPTEs, the logical processor maintains a set of
four (4) internal, non-architectural PDPTE registers, called PDPTE0, PDPTE1, PDPTE2, and PDPTE3. The logical
processor loads these registers from the PDPTEs in memory as part of certain operations:

•

If PAE paging would be in use following an execution of MOV to CR0 or MOV to CR4 (see Section 4.1.1) and the
instruction is modifying any of CR0.CD, CR0.NW, CR0.PG, CR4.PAE, CR4.PGE, CR4.PSE, or CR4.SMEP; then the
PDPTEs are loaded from the address in CR3.

•

If MOV to CR3 is executed while the logical processor is using PAE paging, the PDPTEs are loaded from the
address being loaded into CR3.

•

If PAE paging is in use and a task switch changes the value of CR3, the PDPTEs are loaded from the address in
the new CR3 value.

•

Certain VMX transitions load the PDPTE registers. See Section 4.11.1.

Table 4-8 gives the format of a PDPTE. If any of the PDPTEs sets both the P flag (bit 0) and any reserved bit, the
MOV to CR instruction causes a general-protection exception (#GP(0)) and the PDPTEs are not loaded.2 As shown
in Table 4-8, bits 2:1, 8:5, and 63:MAXPHYADDR are reserved in the PDPTEs.

1. If MAXPHYADDR < 52, bits in the range 51:MAXPHYADDR will be 0 in any physical address used by PAE paging. (The corresponding
bits are reserved in the paging-structure entries.) See Section 4.1.4 for how to determine MAXPHYADDR.
2. On some processors, reserved bits are checked even in PDPTEs in which the P flag (bit 0) is 0.
Vol. 3A 4-13

PAGING

Table 4-8. Format of a PAE Page-Directory-Pointer-Table Entry (PDPTE)
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to reference a page directory

2:1

Reserved (must be 0)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9)

8:5

Reserved (must be 0)

11:9

Ignored

(M–1):12

Physical address of 4-KByte aligned page directory referenced by this entry1

63:M

Reserved (must be 0)

NOTES:
1. M is an abbreviation for MAXPHYADDR, which is at most 52; see Section 4.1.4.

4.4.2

Linear-Address Translation with PAE Paging

PAE paging may map linear addresses to either 4-KByte pages or 2-MByte pages. Figure 4-5 illustrates the translation process when it produces a 4-KByte page; Figure 4-6 covers the case of a 2-MByte page. The following items
describe the PAE paging process in more detail as well has how the page size is determined:

•

Bits 31:30 of the linear address select a PDPTE register (see Section 4.4.1); this is PDPTEi, where i is the value
of bits 31:30.1 Because a PDPTE register is identified using bits 31:30 of the linear address, it controls access
to a 1-GByte region of the linear-address space. If the P flag (bit 0) of PDPTEi is 0, the processor ignores bits
63:1, and there is no mapping for the 1-GByte region controlled by PDPTEi. A reference using a linear address
in this region causes a page-fault exception (see Section 4.7).

•

If the P flag of PDPTEi is 1, 4-KByte naturally aligned page directory is located at the physical address specified
in bits 51:12 of PDPTEi (see Table 4-8 in Section 4.4.1). A page directory comprises 512 64-bit entries (PDEs).
A PDE is selected using the physical address defined as follows:
— Bits 51:12 are from PDPTEi.
— Bits 11:3 are bits 29:21 of the linear address.
— Bits 2:0 are 0.

Because a PDE is identified using bits 31:21 of the linear address, it controls access to a 2-Mbyte region of the
linear-address space. Use of the PDE depends on its PS flag (bit 7):

•

If the PDE’s PS flag is 1, the PDE maps a 2-MByte page (see Table 4-9). The final physical address is computed
as follows:
— Bits 51:21 are from the PDE.
— Bits 20:0 are from the original linear address.

•

If the PDE’s PS flag is 0, a 4-KByte naturally aligned page table is located at the physical address specified in
bits 51:12 of the PDE (see Table 4-10). A page table comprises 512 64-bit entries (PTEs). A PTE is selected
using the physical address defined as follows:
— Bits 51:12 are from the PDE.

1. With PAE paging, the processor does not use CR3 when translating a linear address (as it does in the other paging modes). It does
not access the PDPTEs in the page-directory-pointer table during linear-address translation.
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PAGING

— Bits 11:3 are bits 20:12 of the linear address.
— Bits 2:0 are 0.

•

Because a PTE is identified using bits 31:12 of the linear address, every PTE maps a 4-KByte page (see
Table 4-11). The final physical address is computed as follows:
— Bits 51:12 are from the PTE.
— Bits 11:0 are from the original linear address.

If the P flag (bit 0) of a PDE or a PTE is 0 or if a PDE or a PTE sets any reserved bit, the entry is used neither to
reference another paging-structure entry nor to map a page. There is no translation for a linear address whose
translation would use such a paging-structure entry; a reference to such a linear address causes a page-fault
exception (see Section 4.7).
The following bits are reserved with PAE paging:

•
•
•
•

If the P flag (bit 0) of a PDE or a PTE is 1, bits 62:MAXPHYADDR are reserved.
If the P flag and the PS flag (bit 7) of a PDE are both 1, bits 20:13 are reserved.
If IA32_EFER.NXE = 0 and the P flag of a PDE or a PTE is 1, the XD flag (bit 63) is reserved.
If the PAT is not supported:1
— If the P flag of a PTE is 1, bit 7 is reserved.
— If the P flag and the PS flag of a PDE are both 1, bit 12 is reserved.

A reference using a linear address that is successfully translated to a physical address is performed only if allowed
by the access rights of the translation; see Section 4.6.

Directory Pointer

Linear Address
31 30 29
21 20
12 11
Table
Directory

0
Offset
12

Page Table
PTE

9
2

Physical Address

9

Page Directory
PDE with PS=0

4-KByte Page

40

40

PDPTE Registers
40
PDPTE value

Figure 4-5. Linear-Address Translation to a 4-KByte Page using PAE Paging

1. See Section 4.1.4 for how to determine whether the PAT is supported.
Vol. 3A 4-15

PAGING

Directory
Pointer

Linear Address
31 30 29
21 20
Offset
Directory

0

21
9

Page Directory

2-MByte Page
Physical Address

PDPTE Registers
2
PDE with PS=1
PDPTE value

31

40

Figure 4-6. Linear-Address Translation to a 2-MByte Page using PAE Paging

Table 4-9. Format of a PAE Page-Directory Entry that Maps a 2-MByte Page
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to map a 2-MByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 2-MByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte page referenced by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 2-MByte page referenced by
this entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 2-MByte page referenced by this
entry (see Section 4.9)

5 (A)

Accessed; indicates whether software has accessed the 2-MByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 2-MByte page referenced by this entry (see Section 4.8)

7 (PS)

Page size; must be 1 (otherwise, this entry references a page table; see Table 4-10)

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise

11:9

Ignored

12 (PAT)

If the PAT is supported, indirectly determines the memory type used to access the 2-MByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1

20:13

Reserved (must be 0)

(M–1):21

Physical address of the 2-MByte page referenced by this entry

62:M

Reserved (must be 0)

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)

NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.

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PAGING

Table 4-10. Format of a PAE Page-Directory Entry that References a Page Table
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to reference a page table

1 (R/W)

Read/write; if 0, writes may not be allowed to the 2-MByte region controlled by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte region controlled by this entry (see
Section 4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)

5 (A)

Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)

6

Ignored

7 (PS)

Page size; must be 0 (otherwise, this entry maps a 2-MByte page; see Table 4-9)

11:8

Ignored

(M–1):12

Physical address of 4-KByte aligned page table referenced by this entry

62:M

Reserved (must be 0)

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte region controlled
by this entry; see Section 4.6); otherwise, reserved (must be 0)

Table 4-11. Format of a PAE Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to map a 4-KByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by
this entry (see Section 4.9)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9)

5 (A)

Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)

7 (PAT)

If the PAT is supported, indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)1

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise

Vol. 3A 4-17

PAGING

Table 4-11. Format of a PAE Page-Table Entry that Maps a 4-KByte Page (Contd.)
Bit
Position(s)

Contents

11:9

Ignored

(M–1):12

Physical address of the 4-KByte page referenced by this entry

62:M

Reserved (must be 0)

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 4-KByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)

NOTES:
1. See Section 4.1.4 for how to determine whether the PAT is supported.
Figure 4-7 gives a summary of the formats of CR3 and the paging-structure entries with PAE paging. For the paging
structure entries, it identifies separately the format of entries that map pages, those that reference other paging
structures, and those that do neither because they are “not present”; bit 0 (P) and bit 7 (PS) are highlighted
because they determine how a paging-structure entry is used.
6666555555555
3210987654321
Ignored2

Reserved3

M1 M-1

33322222222221111111111
210987654321098765432109876543210
Address of page-directory-pointer table

Address of page directory

Ign.

Ignored

Rsvd.

P P Rs
PDPTE:
CW
1
present
D T vd

Ignored
X
D
4

X
D

Reserved

Reserved

Address of
2MB page frame

0

Reserved

Address of page table

Reserved

Address of 4KB page frame

PDE:
2MB
page

I PPUR
0 g A C W /S
/ 1
n DT W

PDE:
page
table

Ign.

0
P
PPUR
Ign. G A D A C W /S
/ 1
T
DT W

Ignored

Figure 4-7. Formats of CR3 and Paging-Structure Entries with PAE Paging
NOTES:
1. M is an abbreviation for MAXPHYADDR.
2. CR3 has 64 bits only on processors supporting the Intel-64 architecture. These bits are ignored with PAE paging.
3. Reserved fields must be 0.
4. If IA32_EFER.NXE = 0 and the P flag of a PDE or a PTE is 1, the XD flag (bit 63) is reserved.

4-18 Vol. 3A

PDTPE:
not
present

P
PPUR
A Ign. G 1 D A C W /S
/ 1
T
DT W

Ignored
X
D

CR3

0

PDE:
not
present
PTE:
4KB
page
PTE:
not
present

PAGING

4.5

4-LEVEL PAGING

A logical processor uses 4-level paging if CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LME = 1. With 4-level paging,
linear address are translated using a hierarchy of in-memory paging structures located using the contents of CR3.
4-level paging translates 48-bit linear addresses to 52-bit physical addresses.1 Although 52 bits corresponds to 4
PBytes, linear addresses are limited to 48 bits; at most 256 TBytes of linear-address space may be accessed at any
given time.
4-level paging uses a hierarchy of paging structures to produce a translation for a linear address. CR3 is used to
locate the first paging-structure, the PML4 table. Use of CR3 with 4-level paging depends on whether processcontext identifiers (PCIDs) have been enabled by setting CR4.PCIDE:

•

Table 4-12 illustrates how CR3 is used with 4-level paging if CR4.PCIDE = 0.

Table 4-12. Use of CR3 with 4-Level Paging and CR4.PCIDE = 0
Bit
Position(s)

Contents

2:0

Ignored

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the PML4 table during linearaddress translation (see Section 4.9.2)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the PML4 table during linear-address
translation (see Section 4.9.2)

11:5

Ignored

M–1:12

Physical address of the 4-KByte aligned PML4 table used for linear-address translation1

63:M

Reserved (must be 0)

NOTES:
1. M is an abbreviation for MAXPHYADDR, which is at most 52; see Section 4.1.4.

•

Table 4-13 illustrates how CR3 is used with 4-level paging if CR4.PCIDE = 1.

Table 4-13. Use of CR3 with 4-Level Paging and CR4.PCIDE = 1
Bit
Position(s)

Contents

11:0

PCID (see Section 4.10.1)1

M–1:12

Physical address of the 4-KByte aligned PML4 table used for linear-address translation2

63:M

Reserved (must be 0)3

NOTES:
1. Section 4.9.2 explains how the processor determines the memory type used to access the PML4 table during linear-address translation with CR4.PCIDE = 1.
2. M is an abbreviation for MAXPHYADDR, which is at most 52; see Section 4.1.4.
3. See Section 4.10.4.1 for use of bit 63 of the source operand of the MOV to CR3 instruction.
After software modifies the value of CR4.PCIDE, the logical processor immediately begins using CR3 as specified
for the new value. For example, if software changes CR4.PCIDE from 1 to 0, the current PCID immediately changes

1. If MAXPHYADDR < 52, bits in the range 51:MAXPHYADDR will be 0 in any physical address used by 4-level paging. (The corresponding bits are reserved in the paging-structure entries.) See Section 4.1.4 for how to determine MAXPHYADDR.
Vol. 3A 4-19

PAGING

from CR3[11:0] to 000H (see also Section 4.10.4.1). In addition, the logical processor subsequently determines
the memory type used to access the PML4 table using CR3.PWT and CR3.PCD, which had been bits 4:3 of the PCID.
4-level paging may map linear addresses to 4-KByte pages, 2-MByte pages, or 1-GByte pages.1 Figure 4-8 illustrates the translation process when it produces a 4-KByte page; Figure 4-9 covers the case of a 2-MByte page, and
Figure 4-10 the case of a 1-GByte page.

47

Linear Address
39 38
30 29
21 20
Directory
Table
PML4
Directory Ptr
9

9

9

12 11

0
Offset

12 4-KByte Page
Physical Addr

PTE
Page-DirectoryPointer Table
PDPTE

PDE with PS=0

40
Page-Directory

40
Page Table

40

9
40
PML4E

40
CR3

Figure 4-8. Linear-Address Translation to a 4-KByte Page using 4-Level Paging

1. Not all processors support 1-GByte pages; see Section 4.1.4.
4-20 Vol. 3A

PAGING

47

Linear Address
39 38
21 20
30 29
Directory
PML4
Directory Ptr

0
Offset
21

9

9

2-MByte Page
Physical Addr
Page-DirectoryPointer Table

PDE with PS=1

31

Page-Directory
PDPTE

40

9

40
PML4E

40
CR3

Figure 4-9. Linear-Address Translation to a 2-MByte Page using 4-Level Paging

47

Linear Address
39 38
30 29
PML4
Directory Ptr

0
Offset
30

9

1-GByte Page

Page-DirectoryPointer Table

Physical Addr
PDPTE with PS=1

22

9
40
PML4E

40
CR3

Figure 4-10. Linear-Address Translation to a 1-GByte Page using 4-Level Paging

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PAGING

If CR4.PKE = 1, 4-level paging associates with each linear address a protection key. Section 4.6 explains how the
processor uses the protection key in its determination of the access rights of each linear address.
The following items describe the 4-level paging process in more detail as well has how the page size and protection
key are determined.

•

A 4-KByte naturally aligned PML4 table is located at the physical address specified in bits 51:12 of CR3 (see
Table 4-12). A PML4 table comprises 512 64-bit entries (PML4Es). A PML4E is selected using the physical
address defined as follows:
— Bits 51:12 are from CR3.
— Bits 11:3 are bits 47:39 of the linear address.
— Bits 2:0 are all 0.
Because a PML4E is identified using bits 47:39 of the linear address, it controls access to a 512-GByte region of
the linear-address space.

•

A 4-KByte naturally aligned page-directory-pointer table is located at the physical address specified in
bits 51:12 of the PML4E (see Table 4-14). A page-directory-pointer table comprises 512 64-bit entries
(PDPTEs). A PDPTE is selected using the physical address defined as follows:
— Bits 51:12 are from the PML4E.
— Bits 11:3 are bits 38:30 of the linear address.
— Bits 2:0 are all 0.

Because a PDPTE is identified using bits 47:30 of the linear address, it controls access to a 1-GByte region of the
linear-address space. Use of the PDPTE depends on its PS flag (bit 7):1

•

If the PDPTE’s PS flag is 1, the PDPTE maps a 1-GByte page (see Table 4-15). The final physical address is
computed as follows:
— Bits 51:30 are from the PDPTE.
— Bits 29:0 are from the original linear address.
If CR4.PKE = 1, the linear address’s protection key is the value of bits 62:59 of the PDPTE.

•

If the PDPTE’s PS flag is 0, a 4-KByte naturally aligned page directory is located at the physical address
specified in bits 51:12 of the PDPTE (see Table 4-16). A page directory comprises 512 64-bit entries (PDEs). A
PDE is selected using the physical address defined as follows:
— Bits 51:12 are from the PDPTE.
— Bits 11:3 are bits 29:21 of the linear address.
— Bits 2:0 are all 0.

Because a PDE is identified using bits 47:21 of the linear address, it controls access to a 2-MByte region of the
linear-address space. Use of the PDE depends on its PS flag:

•

If the PDE's PS flag is 1, the PDE maps a 2-MByte page (see Table 4-17). The final physical address is computed
as follows:
— Bits 51:21 are from the PDE.
— Bits 20:0 are from the original linear address.
If CR4.PKE = 1, the linear address’s protection key is the value of bits 62:59 of the PDE.

•

If the PDE’s PS flag is 0, a 4-KByte naturally aligned page table is located at the physical address specified in
bits 51:12 of the PDE (see Table 4-18). A page table comprises 512 64-bit entries (PTEs). A PTE is selected
using the physical address defined as follows:
— Bits 51:12 are from the PDE.
— Bits 11:3 are bits 20:12 of the linear address.
— Bits 2:0 are all 0.

1. The PS flag of a PDPTE is reserved and must be 0 (if the P flag is 1) if 1-GByte pages are not supported. See Section 4.1.4 for how
to determine whether 1-GByte pages are supported.
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•

Because a PTE is identified using bits 47:12 of the linear address, every PTE maps a 4-KByte page (see
Table 4-19). The final physical address is computed as follows:
— Bits 51:12 are from the PTE.
— Bits 11:0 are from the original linear address.
If CR4.PKE = 1, the linear address’s protection key is the value of bits 62:59 of the PTE.

If a paging-structure entry’s P flag (bit 0) is 0 or if the entry sets any reserved bit, the entry is used neither to reference another paging-structure entry nor to map a page. There is no translation for a linear address whose translation would use such a paging-structure entry; a reference to such a linear address causes a page-fault exception
(see Section 4.7).
The following bits are reserved with 4-level paging:

•
•
•
•
•
•

If the P flag of a paging-structure entry is 1, bits 51:MAXPHYADDR are reserved.
If the P flag of a PML4E is 1, the PS flag is reserved.
If 1-GByte pages are not supported and the P flag of a PDPTE is 1, the PS flag is reserved.1
If the P flag and the PS flag of a PDPTE are both 1, bits 29:13 are reserved.
If the P flag and the PS flag of a PDE are both 1, bits 20:13 are reserved.
If IA32_EFER.NXE = 0 and the P flag of a paging-structure entry is 1, the XD flag (bit 63) is reserved.

A reference using a linear address that is successfully translated to a physical address is performed only if allowed
by the access rights of the translation; see Section 4.6.
Figure 4-11 gives a summary of the formats of CR3 and the 4-level paging-structure entries. For the paging structure entries, it identifies separately the format of entries that map pages, those that reference other paging structures, and those that do neither because they are “not present”; bit 0 (P) and bit 7 (PS) are highlighted because
they determine how a paging-structure entry is used.

Table 4-14. Format of a 4-Level PML4 Entry (PML4E) that References a Page-Directory-Pointer Table
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to reference a page-directory-pointer table

1 (R/W)

Read/write; if 0, writes may not be allowed to the 512-GByte region controlled by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 512-GByte region controlled by this entry (see
Section 4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page-directory-pointer table
referenced by this entry (see Section 4.9.2)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page-directory-pointer table
referenced by this entry (see Section 4.9.2)

5 (A)

Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)

6

Ignored

7 (PS)

Reserved (must be 0)

11:8

Ignored

1. See Section 4.1.4 for how to determine whether 1-GByte pages are supported.
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Table 4-14. Format of a 4-Level PML4 Entry (PML4E) that References a Page-Directory-Pointer Table (Contd.)
Bit
Position(s)

Contents

M–1:12

Physical address of 4-KByte aligned page-directory-pointer table referenced by this entry

51:M

Reserved (must be 0)

62:52

Ignored

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 512-GByte region
controlled by this entry; see Section 4.6); otherwise, reserved (must be 0)

Table 4-15. Format of a 4-Level Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to map a 1-GByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 1-GByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 1-GByte page referenced by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 1-GByte page referenced by this
entry (see Section 4.9.2)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 1-GByte page referenced by this
entry (see Section 4.9.2)

5 (A)

Accessed; indicates whether software has accessed the 1-GByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 1-GByte page referenced by this entry (see Section 4.8)

7 (PS)

Page size; must be 1 (otherwise, this entry references a page directory; see Table 4-16)

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise

11:9

Ignored

12 (PAT)

Indirectly determines the memory type used to access the 1-GByte page referenced by this entry (see Section
4.9.2)1

29:13

Reserved (must be 0)

(M–1):30

Physical address of the 1-GByte page referenced by this entry

51:M

Reserved (must be 0)

58:52

Ignored

62:59

Protection key; if CR4.PKE = 1, determines the protection key of the page (see Section 4.6.2); ignored otherwise

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 1-GByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)

NOTES:
1. The PAT is supported on all processors that support 4-level paging.

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Table 4-16. Format of a 4-Level Page-Directory-Pointer-Table Entry (PDPTE) that References a Page Directory
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to reference a page directory

1 (R/W)

Read/write; if 0, writes may not be allowed to the 1-GByte region controlled by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 1-GByte region controlled by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9.2)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page directory referenced by
this entry (see Section 4.9.2)

5 (A)

Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)

6

Ignored

7 (PS)

Page size; must be 0 (otherwise, this entry maps a 1-GByte page; see Table 4-15)

11:8

Ignored

(M–1):12

Physical address of 4-KByte aligned page directory referenced by this entry

51:M

Reserved (must be 0)

62:52

Ignored

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 1-GByte region controlled
by this entry; see Section 4.6); otherwise, reserved (must be 0)

Table 4-17. Format of a 4-Level Page-Directory Entry that Maps a 2-MByte Page
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to map a 2-MByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 2-MByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte page referenced by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 2-MByte page referenced by
this entry (see Section 4.9.2)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 2-MByte page referenced by
this entry (see Section 4.9.2)

5 (A)

Accessed; indicates whether software has accessed the 2-MByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 2-MByte page referenced by this entry (see Section 4.8)

7 (PS)

Page size; must be 1 (otherwise, this entry references a page table; see Table 4-18)

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise

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Table 4-17. Format of a 4-Level Page-Directory Entry that Maps a 2-MByte Page (Contd.)
Bit
Position(s)

Contents

11:9

Ignored

12 (PAT)

Indirectly determines the memory type used to access the 2-MByte page referenced by this entry (see Section
4.9.2)

20:13

Reserved (must be 0)

(M–1):21

Physical address of the 2-MByte page referenced by this entry

51:M

Reserved (must be 0)

58:52

Ignored

62:59

Protection key; if CR4.PKE = 1, determines the protection key of the page (see Section 4.6.2); ignored otherwise

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)

Table 4-18. Format of a 4-Level Page-Directory Entry that References a Page Table
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to reference a page table

1 (R/W)

Read/write; if 0, writes may not be allowed to the 2-MByte region controlled by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte region controlled by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9.2)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9.2)

5 (A)

Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)

6

Ignored

7 (PS)

Page size; must be 0 (otherwise, this entry maps a 2-MByte page; see Table 4-17)

11:8

Ignored

(M–1):12

Physical address of 4-KByte aligned page table referenced by this entry

51:M

Reserved (must be 0)

62:52

Ignored

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte region controlled
by this entry; see Section 4.6); otherwise, reserved (must be 0)

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Table 4-19. Format of a 4-Level Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)

Contents

0 (P)

Present; must be 1 to map a 4-KByte page

1 (R/W)

Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)

2 (U/S)

User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section
4.6)

3 (PWT)

Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by
this entry (see Section 4.9.2)

4 (PCD)

Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9.2)

5 (A)

Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)

6 (D)

Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)

7 (PAT)

Indirectly determines the memory type used to access the 4-KByte page referenced by this entry (see Section 4.9.2)

8 (G)

Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise

11:9

Ignored

(M–1):12

Physical address of the 4-KByte page referenced by this entry

51:M

Reserved (must be 0)

58:52

Ignored

62:59

Protection key; if CR4.PKE = 1, determines the protection key of the page (see Section 4.6.2); ignored otherwise

63 (XD)

If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 4-KByte page controlled by
this entry; see Section 4.6); otherwise, reserved (must be 0)

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.
6666555555555
3210987654321

M1 M-1

33322222222221111111111
210987654321098765432109876543210

Reserved2
X
D

Ignored

3

Address of PML4 table

Rsvd.

Ignored

Address of page-directory-pointer table

Ign.

PP
C W Ign.
DT

PUR
Rs gI A P
PML4E:
C
W
/ 1 present
vd n D T /S W
0

PML4E:
not
present

P
PP R
A Ign. G 1 D A C W U / 1
T
D T /S W

PDPTE:
1GB
page

Ignored
X
D

Prot.
Key4

X
D

Ignored

Ignored

Rsvd.

Address of
1GB page frame

Rsvd.

Reserved

Address of page directory

Ign.

I PPUR
PDPTE:
page
0 g A C W /S / 1
n DT W
directory

Ignored
X
D

Prot.
Key4

X
D

Ignored

Ignored

Rsvd.

Rsvd.

Address of
2MB page frame

0

Reserved

Address of page table

Prot.
Key4

Ignored

Rsvd.

Address of 4KB page frame

PDTPE:
not
present

P
PPUR
A Ign. G 1 D A C W /S
/ 1
T
DT W

PDE:
2MB
page

I PPUR
0 g A C W /S / 1
n DT W

PDE:
page
table

Ign.

Ignored
X
D

CR3

0
P
PPUR
Ign. G A D A C W /S
/ 1
T
DT W

Ignored

0

PDE:
not
present
PTE:
4KB
page
PTE:
not
present

Figure 4-11. Formats of CR3 and Paging-Structure Entries with 4-Level Paging
NOTES:
1. M is an abbreviation for MAXPHYADDR.
2. Reserved fields must be 0.
3. If IA32_EFER.NXE = 0 and the P flag of a paging-structure entry is 1, the XD flag (bit 63) is reserved.
4. If CR4.PKE = 0, the protection key is ignored.

4.6

ACCESS RIGHTS

There is a translation for a linear address if the processes described in Section 4.3, Section 4.4.2, and Section 4.5
(depending upon the paging mode) completes and produces a physical address. Whether an access is permitted by
a translation is determined by the access rights specified by the paging-structure entries controlling the translation;1 paging-mode modifiers in CR0, CR4, and the IA32_EFER MSR; EFLAGS.AC; and the mode of the access.
1. With PAE paging, the PDPTEs do not determine access rights.
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Section 4.6.1 describes how the processor determines the access rights for each linear address. Section 4.6.2
provides additional information about how protection keys contribute to access-rights determination. (They do so
only with 4-level paging and only if CR4.PKE = 1.)

4.6.1

Determination of Access Rights

Every access to a linear address is either a supervisor-mode access or a user-mode access. For all instruction
fetches and most data accesses, this distinction is determined by the current privilege level (CPL): accesses made
while CPL < 3 are supervisor-mode accesses, while accesses made while CPL = 3 are user-mode accesses.
Some operations implicitly access system data structures with linear addresses; the resulting accesses to those
data structures are supervisor-mode accesses regardless of CPL. Examples of such accesses include the following:
accesses to the global descriptor table (GDT) or local descriptor table (LDT) to load a segment descriptor; accesses
to the interrupt descriptor table (IDT) when delivering an interrupt or exception; and accesses to the task-state
segment (TSS) as part of a task switch or change of CPL. All these accesses are called implicit supervisor-mode
accesses regardless of CPL. Other accesses made while CPL < 3 are called explicit supervisor-mode accesses.
Access rights are also controlled by the mode of a linear address as specified by the paging-structure entries
controlling the translation of the linear address. If the U/S flag (bit 2) is 0 in at least one of the paging-structure
entries, the address is a supervisor-mode address. Otherwise, the address is a user-mode address.
The following items detail how paging determines access rights:

•

For supervisor-mode accesses:
— Data may be read (implicitly or explicitly) from any supervisor-mode address.
— Data reads from user-mode pages.
Access rights depend on the value of CR4.SMAP:

•

If CR4.SMAP = 0, data may be read from any user-mode address with a protection key for which read
access is permitted.

•

If CR4.SMAP = 1, access rights depend on the value of EFLAGS.AC and whether the access is implicit or
explicit:
—

If EFLAGS.AC = 1 and the access is explicit, data may be read from any user-mode address with a
protection key for which read access is permitted.

—

If EFLAGS.AC = 0 or the access is implicit, data may not be read from any user-mode address.

Section 4.6.2 explains how protection keys are associated with user-mode addresses and the accesses that
are permitted for each protection key.
— Data writes to supervisor-mode addresses.
Access rights depend on the value of CR0.WP:

•
•

If CR0.WP = 0, data may be written to any supervisor-mode address.
If CR0.WP = 1, data may be written to any supervisor-mode address with a translation for which the
R/W flag (bit 1) is 1 in every paging-structure entry controlling the translation; data may not be written
to any supervisor-mode address with a translation for which the R/W flag is 0 in any paging-structure
entry controlling the translation.

— Data writes to user-mode addresses.
Access rights depend on the value of CR0.WP:

•

If CR0.WP = 0, access rights depend on the value of CR4.SMAP:
—

If CR4.SMAP = 0, data may be written to any user-mode address with a protection key for which
write access is permitted.

—

If CR4.SMAP = 1, access rights depend on the value of EFLAGS.AC and whether the access is
implicit or explicit:
•

If EFLAGS.AC = 1 and the access is explicit, data may be written to any user-mode address
with a protection key for which write access is permitted.

•

If EFLAGS.AC = 0 or the access is implicit, data may not be written to any user-mode address.
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•

If CR0.WP = 1, access rights depend on the value of CR4.SMAP:
—

If CR4.SMAP = 0, data may be written to any user-mode address with a translation for which the
R/W flag is 1 in every paging-structure entry controlling the translation and with a protection key
for which write access is permitted; data may not be written to any user-mode address with a
translation for which the R/W flag is 0 in any paging-structure entry controlling the translation.

—

If CR4.SMAP = 1, access rights depend on the value of EFLAGS.AC and whether the access is
implicit or explicit:
•

If EFLAGS.AC = 1 and the access is explicit, data may be written to any user-mode address
with a translation for which the R/W flag is 1 in every paging-structure entry controlling the
translation and with a protection key for which write access is permitted; data may not be
written to any user-mode address with a translation for which the R/W flag is 0 in any pagingstructure entry controlling the translation.

•

If EFLAGS.AC = 0 or the access is implicit, data may not be written to any user-mode address.

Section 4.6.2 explains how protection keys are associated with user-mode addresses and the accesses that
are permitted for each protection key.
— Instruction fetches from supervisor-mode addresses.

•

For 32-bit paging or if IA32_EFER.NXE = 0, instructions may be fetched from any supervisor-mode
address.

•

For PAE paging or 4-level paging with IA32_EFER.NXE = 1, instructions may be fetched from any
supervisor-mode address with a translation for which the XD flag (bit 63) is 0 in every paging-structure
entry controlling the translation; instructions may not be fetched from any supervisor-mode address
with a translation for which the XD flag is 1 in any paging-structure entry controlling the translation.

— Instruction fetches from user-mode addresses.
Access rights depend on the values of CR4.SMEP:

•

•

•

If CR4.SMEP = 0, access rights depend on the paging mode and the value of IA32_EFER.NXE:
—

For 32-bit paging or if IA32_EFER.NXE = 0, instructions may be fetched from any user-mode
address.

—

For PAE paging or 4-level paging with IA32_EFER.NXE = 1, instructions may be fetched from any
user-mode address with a translation for which the XD flag is 0 in every paging-structure entry
controlling the translation; instructions may not be fetched from any user-mode address with a
translation for which the XD flag is 1 in any paging-structure entry controlling the translation.

If CR4.SMEP = 1, instructions may not be fetched from any user-mode address.

For user-mode accesses:
— Data reads.
Access rights depend on the mode of the linear address:

•

Data may be read from any user-mode address with a protection key for which read access is
permitted. Section 4.6.2 explains how protection keys are associated with user-mode addresses and
the accesses that are permitted for each protection key.

•

Data may not be read from any supervisor-mode address.

— Data writes.
Access rights depend on the mode of the linear address:

•

Data may be written to any user-mode address with a translation for which the R/W flag is 1 in every
paging-structure entry controlling the translation and with a protection key for which write access is
permitted. Section 4.6.2 explains how protection keys are associated with user-mode addresses and
the accesses that are permitted for each protection key.

•

Data may not be written to any supervisor-mode address.

— Instruction fetches.
Access rights depend on the mode of the linear address, the paging mode, and the value of
IA32_EFER.NXE:

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PAGING

•
•
•

For 32-bit paging or if IA32_EFER.NXE = 0, instructions may be fetched from any user-mode address.
For PAE paging or 4-level paging with IA32_EFER.NXE = 1, instructions may be fetched from any usermode address with a translation for which the XD flag is 0 in every paging-structure entry controlling
the translation.
Instructions may not be fetched from any supervisor-mode address.

A processor may cache information from the paging-structure entries in TLBs and paging-structure caches (see
Section 4.10). These structures may include information about access rights. The processor may enforce access
rights based on the TLBs and paging-structure caches instead of on the paging structures in memory.
This fact implies that, if software modifies a paging-structure entry to change access rights, the processor might
not use that change for a subsequent access to an affected linear address (see Section 4.10.4.3). See Section
4.10.4.2 for how software can ensure that the processor uses the modified access rights.

4.6.2

Protection Keys

The protection-key feature provides an additional mechanism by which 4-level paging controls access to usermode addresses. When CR4.PKE = 1, every linear address is associated with the 4-bit protection key located in
bits 62:59 of the paging-structure entry that mapped the page containing the linear address (see Section 4.5). The
PKRU register determines, for each protection key, whether user-mode addresses with that protection key may be
read or written.
If CR4.PKE = 0, or if 4-level paging is not active, the processor does not associate linear addresses with protection
keys and does not use the access-control mechanism described in this section. In either of these cases, a reference
in Section 4.6.1 to a user-mode address with a protection key should be considered a reference to any user-mode
address.
The PKRU register (protection key rights for user pages) is a 32-bit register with the following format: for each i
(0 ≤ i ≤ 15), PKRU[2i] is the access-disable bit for protection key i (ADi); PKRU[2i+1] is the write-disable bit
for protection key i (WDi).
Software can use the RDPKRU and WRPKRU instructions with ECX = 0 to read and write PKRU. In addition, the
PKRU register is XSAVE-managed state and can thus be read and written by instructions in the XSAVE feature set.
See Chapter 13, “Managing State Using the XSAVE Feature Set,” of Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1 for more information about the XSAVE feature set.
How a linear address’s protection key controls access to the address depends on the mode of the linear address:

•

A linear address’s protection key controls only data accesses to the address. It does not in any way affect
instructions fetches from the address.

•

The protection key of a supervisor-mode address is ignored and does not control data accesses to the address.
Because of this, Section 4.6.1 does not refer to protection keys when specifying the access rights for
supervisor-mode addresses.

•

Use of the protection key i of a user-mode address depends on the value of the PKRU register:
— If ADi = 1, no data accesses are permitted.
— If WDi = 1, permission may be denied to certain data write accesses:

•
•

4.7

User-mode write accesses are not permitted.
Supervisor-mode write accesses are not permitted if CR0.WP = 1. (If CR0.WP = 0, WDi does not affect
supervisor-mode write accesses to user-mode addresses with protection key i.)

PAGE-FAULT EXCEPTIONS

Accesses using linear addresses may cause page-fault exceptions (#PF; exception 14). An access to a linear
address may cause a page-fault exception for either of two reasons: (1) there is no translation for the linear
address; or (2) there is a translation for the linear address, but its access rights do not permit the access.

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As noted in Section 4.3, Section 4.4.2, and Section 4.5, there is no translation for a linear address if the translation
process for that address would use a paging-structure entry in which the P flag (bit 0) is 0 or one that sets a
reserved bit. If there is a translation for a linear address, its access rights are determined as specified in Section
4.6.
When Intel® Software Guard Extensions (Intel® SGX) are enabled, the processor may deliver exception 14 for
reasons unrelated to paging. See Section 37.3, “Access-control Requirements” and Section 37.19, “Enclave Page
Cache Map (EPCM)” in Chapter 37, “Enclave Access Control and Data Structures.” Such an exception is called an
SGX-induced page fault. The processor uses the error code to distinguish SGX-induced page faults from ordinary
page faults.
Figure 4-12 illustrates the error code that the processor provides on delivery of a page-fault exception. The
following items explain how the bits in the error code describe the nature of the page-fault exception:
31

5 4 3 2 1 0

15

Reserved

P
W/R
U/S
RSVD
I/D
PK

SGX

Reserved
P

0 The fault was caused by a non-present page.
1 The fault was caused by a page-level protection violation.

W/R

0 The access causing the fault was a read.
1 The access causing the fault was a write.

U/S

0 A supervisor-mode access caused the fault.
1 A user-mode access caused the fault.

RSVD

0 The fault was not caused by reserved bit violation.
1 The fault was caused by a reserved bit set to 1 in some
paging-structure entry.

I/D

0 The fault was not caused by an instruction fetch.
1 The fault was caused by an instruction fetch.

PK

0 The fault was not caused by protection keys.
1 There was a protection-key violation.

SGX

0 The fault is not related to SGX.
1 The fault resulted from violation of SGX-specific access-control
requirements.

Figure 4-12. Page-Fault Error Code

•

P flag (bit 0).
This flag is 0 if there is no translation for the linear address because the P flag was 0 in one of the pagingstructure entries used to translate that address.

•

W/R (bit 1).
If the access causing the page-fault exception was a write, this flag is 1; otherwise, it is 0. This flag describes
the access causing the page-fault exception, not the access rights specified by paging.

•

U/S (bit 2).
If a user-mode access caused the page-fault exception, this flag is 1; it is 0 if a supervisor-mode access did so.
This flag describes the access causing the page-fault exception, not the access rights specified by paging. Usermode and supervisor-mode accesses are defined in Section 4.6.

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•

RSVD flag (bit 3).
This flag is 1 if there is no translation for the linear address because a reserved bit was set in one of the pagingstructure entries used to translate that address. (Because reserved bits are not checked in a paging-structure
entry whose P flag is 0, bit 3 of the error code can be set only if bit 0 is also set.1)
Bits reserved in the paging-structure entries are reserved for future functionality. Software developers should
be aware that such bits may be used in the future and that a paging-structure entry that causes a page-fault
exception on one processor might not do so in the future.

•

I/D flag (bit 4).
This flag is 1 if (1) the access causing the page-fault exception was an instruction fetch; and (2) either
(a) CR4.SMEP = 1; or (b) both (i) CR4.PAE = 1 (either PAE paging or 4-level paging is in use); and
(ii) IA32_EFER.NXE = 1. Otherwise, the flag is 0. This flag describes the access causing the page-fault
exception, not the access rights specified by paging.

•

PK flag (bit 5).
This flag is 1 if (1) IA32_EFER.LMA = CR4.PKE = 1; (2) the access causing the page-fault exception was a data
access; (3) the linear address was a user-mode address with protection key i; and (5) the PKRU register (see
Section 4.6.2) is such that either (a) ADi = 1; or (b) the following all hold: (i) WDi = 1; (ii) the access is a write
access; and (iii) either CR0.WP = 1 or the access causing the page-fault exception was a user-mode access.

•

SGX flag (bit 15).
This flag is 1 if the exception is unrelated to paging and resulted from violation of SGX-specific access-control
requirements. Because such a violation can occur only if there is no ordinary page fault, this flag is set only if
the P flag (bit 0) is 1 and the RSVD flag (bit 3) and the PK flag (bit 5) are both 0.

Page-fault exceptions occur only due to an attempt to use a linear address. Failures to load the PDPTE registers
with PAE paging (see Section 4.4.1) cause general-protection exceptions (#GP(0)) and not page-fault exceptions.

4.8

ACCESSED AND DIRTY FLAGS

For any paging-structure entry that is used during linear-address translation, bit 5 is the accessed flag.2 For
paging-structure entries that map a page (as opposed to referencing another paging structure), bit 6 is the dirty
flag. These flags are provided for use by memory-management software to manage the transfer of pages and
paging structures into and out of physical memory.
Whenever the processor uses a paging-structure entry as part of linear-address translation, it sets the accessed
flag in that entry (if it is not already set).
Whenever there is a write to a linear address, the processor sets the dirty flag (if it is not already set) in the pagingstructure entry that identifies the final physical address for the linear address (either a PTE or a paging-structure
entry in which the PS flag is 1).
Memory-management software may clear these flags when a page or a paging structure is initially loaded into
physical memory. These flags are “sticky,” meaning that, once set, the processor does not clear them; only software can clear them.
A processor may cache information from the paging-structure entries in TLBs and paging-structure caches (see
Section 4.10). This fact implies that, if software changes an accessed flag or a dirty flag from 1 to 0, the processor
might not set the corresponding bit in memory on a subsequent access using an affected linear address (see
Section 4.10.4.3). See Section 4.10.4.2 for how software can ensure that these bits are updated as desired.

NOTE
The accesses used by the processor to set these flags may or may not be exposed to the
processor’s self-modifying code detection logic. If the processor is executing code from the same
1. Some past processors had errata for some page faults that occur when there is no translation for the linear address because the P
flag was 0 in one of the paging-structure entries used to translate that address. Due to these errata, some such page faults produced error codes that cleared bit 0 (P flag) and set bit 3 (RSVD flag).
2. With PAE paging, the PDPTEs are not used during linear-address translation but only to load the PDPTE registers for some executions of the MOV CR instruction (see Section 4.4.1). For this reason, the PDPTEs do not contain accessed flags with PAE paging.
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memory area that is being used for the paging structures, the setting of these flags may or may not
result in an immediate change to the executing code stream.

4.9

PAGING AND MEMORY TYPING

The memory type of a memory access refers to the type of caching used for that access. Chapter 11, “Memory
Cache Control” provides many details regarding memory typing in the Intel-64 and IA-32 architectures. This
section describes how paging contributes to the determination of memory typing.
The way in which paging contributes to memory typing depends on whether the processor supports the Page
Attribute Table (PAT; see Section 11.12).1 Section 4.9.1 and Section 4.9.2 explain how paging contributes to
memory typing depending on whether the PAT is supported.

4.9.1

Paging and Memory Typing When the PAT is Not Supported (Pentium Pro and Pentium
II Processors)
NOTE
The PAT is supported on all processors that support 4-level paging. Thus, this section applies only
to 32-bit paging and PAE paging.

If the PAT is not supported, paging contributes to memory typing in conjunction with the memory-type range registers (MTRRs) as specified in Table 11-6 in Section 11.5.2.1.
For any access to a physical address, the table combines the memory type specified for that physical address by the
MTRRs with a PCD value and a PWT value. The latter two values are determined as follows:

•
•
•
•

For an access to a PDE with 32-bit paging, the PCD and PWT values come from CR3.

•

With PAE paging, the UC memory type is used when loading the PDPTEs (see Section 4.4.1).

For an access to a PDE with PAE paging, the PCD and PWT values come from the relevant PDPTE register.
For an access to a PTE, the PCD and PWT values come from the relevant PDE.
For an access to the physical address that is the translation of a linear address, the PCD and PWT values come
from the relevant PTE (if the translation uses a 4-KByte page) or the relevant PDE (otherwise).

4.9.2

Paging and Memory Typing When the PAT is Supported (Pentium III and More Recent
Processor Families)

If the PAT is supported, paging contributes to memory typing in conjunction with the PAT and the memory-type
range registers (MTRRs) as specified in Table 11-7 in Section 11.5.2.2.
The PAT is a 64-bit MSR (IA32_PAT; MSR index 277H) comprising eight (8) 8-bit entries (entry i comprises
bits 8i+7:8i of the MSR).

1. The PAT is supported on Pentium III and more recent processor families. See Section 4.1.4 for how to determine whether the PAT is
supported.
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For any access to a physical address, the table combines the memory type specified for that physical address by
the MTRRs with a memory type selected from the PAT. Table 11-11 in Section 11.12.3 specifies how a memory type
is selected from the PAT. Specifically, it comes from entry i of the PAT, where i is defined as follows:

•

For an access to an entry in a paging structure whose address is in CR3 (e.g., the PML4 table with 4-level
paging):
— For 4-level paging with CR4.PCIDE = 1, i = 0.
— Otherwise, i = 2*PCD+PWT, where the PCD and PWT values come from CR3.

•

For an access to a PDE with PAE paging, i = 2*PCD+PWT, where the PCD and PWT values come from the
relevant PDPTE register.

•

For an access to a paging-structure entry X whose address is in another paging-structure entry Y, i =
2*PCD+PWT, where the PCD and PWT values come from Y.

•

For an access to the physical address that is the translation of a linear address, i = 4*PAT+2*PCD+PWT, where
the PAT, PCD, and PWT values come from the relevant PTE (if the translation uses a 4-KByte page), the relevant
PDE (if the translation uses a 2-MByte page or a 4-MByte page), or the relevant PDPTE (if the translation uses
a 1-GByte page).

•

With PAE paging, the WB memory type is used when loading the PDPTEs (see Section 4.4.1).1

4.9.3

Caching Paging-Related Information about Memory Typing

A processor may cache information from the paging-structure entries in TLBs and paging-structure caches (see
Section 4.10). These structures may include information about memory typing. The processor may use memorytyping information from the TLBs and paging-structure caches instead of from the paging structures in memory.
This fact implies that, if software modifies a paging-structure entry to change the memory-typing bits, the
processor might not use that change for a subsequent translation using that entry or for access to an affected
linear address. See Section 4.10.4.2 for how software can ensure that the processor uses the modified memory
typing.

4.10

CACHING TRANSLATION INFORMATION

The Intel-64 and IA-32 architectures may accelerate the address-translation process by caching data from the
paging structures on the processor. Because the processor does not ensure that the data that it caches are always
consistent with the structures in memory, it is important for software developers to understand how and when the
processor may cache such data. They should also understand what actions software can take to remove cached
data that may be inconsistent and when it should do so. This section provides software developers information
about the relevant processor operation.
Section 4.10.1 introduces process-context identifiers (PCIDs), which a logical processor may use to distinguish
information cached for different linear-address spaces. Section 4.10.2 and Section 4.10.3 describe how the
processor may cache information in translation lookaside buffers (TLBs) and paging-structure caches, respectively.
Section 4.10.4 explains how software can remove inconsistent cached information by invalidating portions of the
TLBs and paging-structure caches. Section 4.10.5 describes special considerations for multiprocessor systems.

4.10.1

Process-Context Identifiers (PCIDs)

Process-context identifiers (PCIDs) are a facility by which a logical processor may cache information for multiple
linear-address spaces. The processor may retain cached information when software switches to a different linearaddress space with a different PCID (e.g., by loading CR3; see Section 4.10.4.1 for details).

1. Some older IA-32 processors used the UC memory type when loading the PDPTEs. Some processors may use the UC memory type if
CR0.CD = 1 or if the MTRRs are disabled. These behaviors are model-specific and not architectural.
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A PCID is a 12-bit identifier. Non-zero PCIDs are enabled by setting the PCIDE flag (bit 17) of CR4. If CR4.PCIDE =
0, the current PCID is always 000H; otherwise, the current PCID is the value of bits 11:0 of CR3. Not all processors
allow CR4.PCIDE to be set to 1; see Section 4.1.4 for how to determine whether this is allowed.
The processor ensures that CR4.PCIDE can be 1 only in IA-32e mode (thus, 32-bit paging and PAE paging use only
PCID 000H). In addition, software can change CR4.PCIDE from 0 to 1 only if CR3[11:0] = 000H. These requirements are enforced by the following limitations on the MOV CR instruction:

•
•

MOV to CR4 causes a general-protection exception (#GP) if it would change CR4.PCIDE from 0 to 1 and either
IA32_EFER.LMA = 0 or CR3[11:0] ≠ 000H.
MOV to CR0 causes a general-protection exception if it would clear CR0.PG to 0 while CR4.PCIDE = 1.

When a logical processor creates entries in the TLBs (Section 4.10.2) and paging-structure caches (Section
4.10.3), it associates those entries with the current PCID. When using entries in the TLBs and paging-structure
caches to translate a linear address, a logical processor uses only those entries associated with the current PCID
(see Section 4.10.2.4 for an exception).
If CR4.PCIDE = 0, a logical processor does not cache information for any PCID other than 000H. This is because
(1) if CR4.PCIDE = 0, the logical processor will associate any newly cached information with the current PCID,
000H; and (2) if MOV to CR4 clears CR4.PCIDE, all cached information is invalidated (see Section 4.10.4.1).

NOTE
In revisions of this manual that were produced when no processors allowed CR4.PCIDE to be set to
1, Section 4.10 discussed the caching of translation information without any reference to PCIDs.
While the section now refers to PCIDs in its specification of this caching, this documentation change
is not intended to imply any change to the behavior of processors that do not allow CR4.PCIDE to
be set to 1.

4.10.2

Translation Lookaside Buffers (TLBs)

A processor may cache information about the translation of linear addresses in translation lookaside buffers (TLBs).
In general, TLBs contain entries that map page numbers to page frames; these terms are defined in Section
4.10.2.1. Section 4.10.2.2 describes how information may be cached in TLBs, and Section 4.10.2.3 gives details of
TLB usage. Section 4.10.2.4 explains the global-page feature, which allows software to indicate that certain translations should receive special treatment when cached in the TLBs.

4.10.2.1

Page Numbers, Page Frames, and Page Offsets

Section 4.3, Section 4.4.2, and Section 4.5 give details of how the different paging modes translate linear
addresses to physical addresses. Specifically, the upper bits of a linear address (called the page number) determine the upper bits of the physical address (called the page frame); the lower bits of the linear address (called the
page offset) determine the lower bits of the physical address. The boundary between the page number and the
page offset is determined by the page size. Specifically:

•

32-bit paging:
— If the translation does not use a PTE (because CR4.PSE = 1 and the PS flag is 1 in the PDE used), the page
size is 4 MBytes and the page number comprises bits 31:22 of the linear address.
— If the translation does use a PTE, the page size is 4 KBytes and the page number comprises bits 31:12 of
the linear address.

•

PAE paging:
— If the translation does not use a PTE (because the PS flag is 1 in the PDE used), the page size is 2 MBytes
and the page number comprises bits 31:21 of the linear address.
— If the translation does uses a PTE, the page size is 4 KBytes and the page number comprises bits 31:12 of
the linear address.

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•

4-level paging:
— If the translation does not use a PDE (because the PS flag is 1 in the PDPTE used), the page size is 1 GByte
and the page number comprises bits 47:30 of the linear address.
— If the translation does use a PDE but does not uses a PTE (because the PS flag is 1 in the PDE used), the
page size is 2 MBytes and the page number comprises bits 47:21 of the linear address.
— If the translation does use a PTE, the page size is 4 KBytes and the page number comprises bits 47:12 of
the linear address.

4.10.2.2

Caching Translations in TLBs

The processor may accelerate the paging process by caching individual translations in translation lookaside
buffers (TLBs). Each entry in a TLB is an individual translation. Each translation is referenced by a page number.
It contains the following information from the paging-structure entries used to translate linear addresses with the
page number:

•
•

The physical address corresponding to the page number (the page frame).
The access rights from the paging-structure entries used to translate linear addresses with the page number
(see Section 4.6):
— The logical-AND of the R/W flags.
— The logical-AND of the U/S flags.
— The logical-OR of the XD flags (necessary only if IA32_EFER.NXE = 1).
— The protection key (necessary only with 4-level paging and CR4.PKE = 1).

•

Attributes from a paging-structure entry that identifies the final page frame for the page number (either a PTE
or a paging-structure entry in which the PS flag is 1):
— The dirty flag (see Section 4.8).
— The memory type (see Section 4.9).

(TLB entries may contain other information as well. A processor may implement multiple TLBs, and some of these
may be for special purposes, e.g., only for instruction fetches. Such special-purpose TLBs may not contain some of
this information if it is not necessary. For example, a TLB used only for instruction fetches need not contain information about the R/W and dirty flags.)
As noted in Section 4.10.1, any TLB entries created by a logical processor are associated with the current PCID.
Processors need not implement any TLBs. Processors that do implement TLBs may invalidate any TLB entry at any
time. Software should not rely on the existence of TLBs or on the retention of TLB entries.

4.10.2.3

Details of TLB Use

Because the TLBs cache entries only for linear addresses with translations, there can be a TLB entry for a page
number only if the P flag is 1 and the reserved bits are 0 in each of the paging-structure entries used to translate
that page number. In addition, the processor does not cache a translation for a page number unless the accessed
flag is 1 in each of the paging-structure entries used during translation; before caching a translation, the processor
sets any of these accessed flags that is not already 1.
The processor may cache translations required for prefetches and for accesses that are a result of speculative
execution that would never actually occur in the executed code path.
If the page number of a linear address corresponds to a TLB entry associated with the current PCID, the processor
may use that TLB entry to determine the page frame, access rights, and other attributes for accesses to that linear
address. In this case, the processor may not actually consult the paging structures in memory. The processor may
retain a TLB entry unmodified even if software subsequently modifies the relevant paging-structure entries in
memory. See Section 4.10.4.2 for how software can ensure that the processor uses the modified paging-structure
entries.
If the paging structures specify a translation using a page larger than 4 KBytes, some processors may cache
multiple smaller-page TLB entries for that translation. Each such TLB entry would be associated with a page
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number corresponding to the smaller page size (e.g., bits 47:12 of a linear address with 4-level paging), even
though part of that page number (e.g., bits 20:12) is part of the offset with respect to the page specified by the
paging structures. The upper bits of the physical address in such a TLB entry are derived from the physical address
in the PDE used to create the translation, while the lower bits come from the linear address of the access for which
the translation is created. There is no way for software to be aware that multiple translations for smaller pages
have been used for a large page. For example, an execution of INVLPG for a linear address on such a page invalidates any and all smaller-page TLB entries for the translation of any linear address on that page.
If software modifies the paging structures so that the page size used for a 4-KByte range of linear addresses
changes, the TLBs may subsequently contain multiple translations for the address range (one for each page size).
A reference to a linear address in the address range may use any of these translations. Which translation is used
may vary from one execution to another, and the choice may be implementation-specific.

4.10.2.4

Global Pages

The Intel-64 and IA-32 architectures also allow for global pages when the PGE flag (bit 7) is 1 in CR4. If the G flag
(bit 8) is 1 in a paging-structure entry that maps a page (either a PTE or a paging-structure entry in which the PS
flag is 1), any TLB entry cached for a linear address using that paging-structure entry is considered to be global.
Because the G flag is used only in paging-structure entries that map a page, and because information from such
entries is not cached in the paging-structure caches, the global-page feature does not affect the behavior of the
paging-structure caches.
A logical processor may use a global TLB entry to translate a linear address, even if the TLB entry is associated with
a PCID different from the current PCID.

4.10.3

Paging-Structure Caches

In addition to the TLBs, a processor may cache other information about the paging structures in memory.

4.10.3.1

Caches for Paging Structures

A processor may support any or all of the following paging-structure caches:

•

PML4 cache (4-level paging only). Each PML4-cache entry is referenced by a 9-bit value and is used for linear
addresses for which bits 47:39 have that value. The entry contains information from the PML4E used to
translate such linear addresses:
— The physical address from the PML4E (the address of the page-directory-pointer table).
— The value of the R/W flag of the PML4E.
— The value of the U/S flag of the PML4E.
— The value of the XD flag of the PML4E.
— The values of the PCD and PWT flags of the PML4E.
The following items detail how a processor may use the PML4 cache:
— If the processor has a PML4-cache entry for a linear address, it may use that entry when translating the
linear address (instead of the PML4E in memory).
— The processor does not create a PML4-cache entry unless the P flag is 1 and all reserved bits are 0 in the
PML4E in memory.
— The processor does not create a PML4-cache entry unless the accessed flag is 1 in the PML4E in memory;
before caching a translation, the processor sets the accessed flag if it is not already 1.
— The processor may create a PML4-cache entry even if there are no translations for any linear address that
might use that entry (e.g., because the P flags are 0 in all entries in the referenced page-directory-pointer
table).
— If the processor creates a PML4-cache entry, the processor may retain it unmodified even if software subsequently modifies the corresponding PML4E in memory.

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•

PDPTE cache (4-level paging only).1 Each PDPTE-cache entry is referenced by an 18-bit value and is used for
linear addresses for which bits 47:30 have that value. The entry contains information from the PML4E and
PDPTE used to translate such linear addresses:
— The physical address from the PDPTE (the address of the page directory). (No PDPTE-cache entry is created
for a PDPTE that maps a 1-GByte page.)
— The logical-AND of the R/W flags in the PML4E and the PDPTE.
— The logical-AND of the U/S flags in the PML4E and the PDPTE.
— The logical-OR of the XD flags in the PML4E and the PDPTE.
— The values of the PCD and PWT flags of the PDPTE.
The following items detail how a processor may use the PDPTE cache:
— If the processor has a PDPTE-cache entry for a linear address, it may use that entry when translating the
linear address (instead of the PML4E and the PDPTE in memory).
— The processor does not create a PDPTE-cache entry unless the P flag is 1, the PS flag is 0, and the reserved
bits are 0 in the PML4E and the PDPTE in memory.
— The processor does not create a PDPTE-cache entry unless the accessed flags are 1 in the PML4E and the
PDPTE in memory; before caching a translation, the processor sets any accessed flags that are not already
1.
— The processor may create a PDPTE-cache entry even if there are no translations for any linear address that
might use that entry.
— If the processor creates a PDPTE-cache entry, the processor may retain it unmodified even if software
subsequently modifies the corresponding PML4E or PDPTE in memory.

•

PDE cache. The use of the PDE cache depends on the paging mode:
— For 32-bit paging, each PDE-cache entry is referenced by a 10-bit value and is used for linear addresses for
which bits 31:22 have that value.
— For PAE paging, each PDE-cache entry is referenced by an 11-bit value and is used for linear addresses for
which bits 31:21 have that value.
— For 4-level paging, each PDE-cache entry is referenced by a 27-bit value and is used for linear addresses
for which bits 47:21 have that value.
A PDE-cache entry contains information from the PML4E, PDPTE, and PDE used to translate the relevant linear
addresses (for 32-bit paging and PAE paging, only the PDE applies):
— The physical address from the PDE (the address of the page table). (No PDE-cache entry is created for a
PDE that maps a page.)
— The logical-AND of the R/W flags in the PML4E, PDPTE, and PDE.
— The logical-AND of the U/S flags in the PML4E, PDPTE, and PDE.
— The logical-OR of the XD flags in the PML4E, PDPTE, and PDE.
— The values of the PCD and PWT flags of the PDE.

1. With PAE paging, the PDPTEs are stored in internal, non-architectural registers. The operation of these registers is described in Section 4.4.1 and differs from that described here.
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The following items detail how a processor may use the PDE cache (references below to PML4Es and PDPTEs
apply only to 4-level paging):
— If the processor has a PDE-cache entry for a linear address, it may use that entry when translating the
linear address (instead of the PML4E, the PDPTE, and the PDE in memory).
— The processor does not create a PDE-cache entry unless the P flag is 1, the PS flag is 0, and the reserved
bits are 0 in the PML4E, the PDPTE, and the PDE in memory.
— The processor does not create a PDE-cache entry unless the accessed flag is 1 in the PML4E, the PDPTE, and
the PDE in memory; before caching a translation, the processor sets any accessed flags that are not already
1.
— The processor may create a PDE-cache entry even if there are no translations for any linear address that
might use that entry.
— If the processor creates a PDE-cache entry, the processor may retain it unmodified even if software subsequently modifies the corresponding PML4E, the PDPTE, or the PDE in memory.
Information from a paging-structure entry can be included in entries in the paging-structure caches for other
paging-structure entries referenced by the original entry. For example, if the R/W flag is 0 in a PML4E, then the R/W
flag will be 0 in any PDPTE-cache entry for a PDPTE from the page-directory-pointer table referenced by that
PML4E. This is because the R/W flag of each such PDPTE-cache entry is the logical-AND of the R/W flags in the
appropriate PML4E and PDPTE.
The paging-structure caches contain information only from paging-structure entries that reference other paging
structures (and not those that map pages). Because the G flag is not used in such paging-structure entries, the
global-page feature does not affect the behavior of the paging-structure caches.
The processor may create entries in paging-structure caches for translations required for prefetches and for
accesses that are a result of speculative execution that would never actually occur in the executed code path.
As noted in Section 4.10.1, any entries created in paging-structure caches by a logical processor are associated
with the current PCID.
A processor may or may not implement any of the paging-structure caches. Software should rely on neither their
presence nor their absence. The processor may invalidate entries in these caches at any time. Because the
processor may create the cache entries at the time of translation and not update them following subsequent modifications to the paging structures in memory, software should take care to invalidate the cache entries appropriately when causing such modifications. The invalidation of TLBs and the paging-structure caches is described in
Section 4.10.4.

4.10.3.2

Using the Paging-Structure Caches to Translate Linear Addresses

When a linear address is accessed, the processor uses a procedure such as the following to determine the physical
address to which it translates and whether the access should be allowed:

•

If the processor finds a TLB entry that is for the page number of the linear address and that is associated with
the current PCID (or which is global), it may use the physical address, access rights, and other attributes from
that entry.

•

If the processor does not find a relevant TLB entry, it may use the upper bits of the linear address to select an
entry from the PDE cache that is associated with the current PCID (Section 4.10.3.1 indicates which bits are
used in each paging mode). It can then use that entry to complete the translation process (locating a PTE, etc.)
as if it had traversed the PDE (and, for 4-level paging, the PDPTE and PML4E) corresponding to the PDE-cache
entry.

•

The following items apply when 4-level paging is used:
— If the processor does not find a relevant TLB entry or a relevant PDE-cache entry, it may use bits 47:30 of
the linear address to select an entry from the PDPTE cache that is associated with the current PCID. It can
then use that entry to complete the translation process (locating a PDE, etc.) as if it had traversed the
PDPTE and the PML4E corresponding to the PDPTE-cache entry.
— If the processor does not find a relevant TLB entry, a relevant PDE-cache entry, or a relevant PDPTE-cache
entry, it may use bits 47:39 of the linear address to select an entry from the PML4 cache that is associated

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with the current PCID. It can then use that entry to complete the translation process (locating a PDPTE,
etc.) as if it had traversed the corresponding PML4E.
(Any of the above steps would be skipped if the processor does not support the cache in question.)
If the processor does not find a TLB or paging-structure-cache entry for the linear address, it uses the linear
address to traverse the entire paging-structure hierarchy, as described in Section 4.3, Section 4.4.2, and Section
4.5.

4.10.3.3

Multiple Cached Entries for a Single Paging-Structure Entry

The paging-structure caches and TLBs may contain multiple entries associated with a single PCID and with information derived from a single paging-structure entry. The following items give some examples for 4-level paging:

•

•

Suppose that two PML4Es contain the same physical address and thus reference the same page-directorypointer table. Any PDPTE in that table may result in two PDPTE-cache entries, each associated with a different
set of linear addresses. Specifically, suppose that the n1th and n2th entries in the PML4 table contain the same
physical address. This implies that the physical address in the mth PDPTE in the page-directory-pointer table
would appear in the PDPTE-cache entries associated with both p1 and p2, where (p1 » 9) = n1, (p2 » 9) = n2,
and (p1 & 1FFH) = (p2 & 1FFH) = m. This is because both PDPTE-cache entries use the same PDPTE, one
resulting from a reference from the n1th PML4E and one from the n2th PML4E.
Suppose that the first PML4E (i.e., the one in position 0) contains the physical address X in CR3 (the physical
address of the PML4 table). This implies the following:
— Any PML4-cache entry associated with linear addresses with 0 in bits 47:39 contains address X.
— Any PDPTE-cache entry associated with linear addresses with 0 in bits 47:30 contains address X. This is
because the translation for a linear address for which the value of bits 47:30 is 0 uses the value of
bits 47:39 (0) to locate a page-directory-pointer table at address X (the address of the PML4 table). It then
uses the value of bits 38:30 (also 0) to find address X again and to store that address in the PDPTE-cache
entry.
— Any PDE-cache entry associated with linear addresses with 0 in bits 47:21 contains address X for similar
reasons.
— Any TLB entry for page number 0 (associated with linear addresses with 0 in bits 47:12) translates to page
frame X » 12 for similar reasons.
The same PML4E contributes its address X to all these cache entries because the self-referencing nature of the
entry causes it to be used as a PML4E, a PDPTE, a PDE, and a PTE.

4.10.4

Invalidation of TLBs and Paging-Structure Caches

As noted in Section 4.10.2 and Section 4.10.3, the processor may create entries in the TLBs and the paging-structure caches when linear addresses are translated, and it may retain these entries even after the paging structures
used to create them have been modified. To ensure that linear-address translation uses the modified paging structures, software should take action to invalidate any cached entries that may contain information that has since
been modified.

4.10.4.1

Operations that Invalidate TLBs and Paging-Structure Caches

The following instructions invalidate entries in the TLBs and the paging-structure caches:

•

INVLPG. This instruction takes a single operand, which is a linear address. The instruction invalidates any TLB
entries that are for a page number corresponding to the linear address and that are associated with the current
PCID. It also invalidates any global TLB entries with that page number, regardless of PCID (see Section
4.10.2.4).1 INVLPG also invalidates all entries in all paging-structure caches associated with the current PCID,
regardless of the linear addresses to which they correspond.

1. If the paging structures map the linear address using a page larger than 4 KBytes and there are multiple TLB entries for that page
(see Section 4.10.2.3), the instruction invalidates all of them.
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•

INVPCID. The operation of this instruction is based on instruction operands, called the INVPCID type and the
INVPCID descriptor. Four INVPCID types are currently defined:
— Individual-address. If the INVPCID type is 0, the logical processor invalidates mappings—except global
translations—associated with the PCID specified in the INVPCID descriptor and that would be used to
translate the linear address specified in the INVPCID descriptor.1 (The instruction may also invalidate global
translations, as well as mappings associated with other PCIDs and for other linear addresses.)
— Single-context. If the INVPCID type is 1, the logical processor invalidates all mappings—except global
translations—associated with the PCID specified in the INVPCID descriptor. (The instruction may also
invalidate global translations, as well as mappings associated with other PCIDs.)
— All-context, including globals. If the INVPCID type is 2, the logical processor invalidates
mappings—including global translations—associated with all PCIDs.
— All-context. If the INVPCID type is 3, the logical processor invalidates mappings—except global translations—associated with all PCIDs. (The instruction may also invalidate global translations.)
See Chapter 3 of the Intel 64 and IA-32 Architecture Software Developer’s Manual, Volume 2A for details of the
INVPCID instruction.

•

MOV to CR0. The instruction invalidates all TLB entries (including global entries) and all entries in all pagingstructure caches (for all PCIDs) if it changes the value of CR0.PG from 1 to 0.

•

MOV to CR3. The behavior of the instruction depends on the value of CR4.PCIDE:
— If CR4.PCIDE = 0, the instruction invalidates all TLB entries associated with PCID 000H except those for
global pages. It also invalidates all entries in all paging-structure caches associated with PCID 000H.
— If CR4.PCIDE = 1 and bit 63 of the instruction’s source operand is 0, the instruction invalidates all TLB
entries associated with the PCID specified in bits 11:0 of the instruction’s source operand except those for
global pages. It also invalidates all entries in all paging-structure caches associated with that PCID. It is not
required to invalidate entries in the TLBs and paging-structure caches that are associated with other PCIDs.
— If CR4.PCIDE = 1 and bit 63 of the instruction’s source operand is 1, the instruction is not required to
invalidate any TLB entries or entries in paging-structure caches.

•

MOV to CR4. The behavior of the instruction depends on the bits being modified:
— The instruction invalidates all TLB entries (including global entries) and all entries in all paging-structure
caches (for all PCIDs) if (1) it changes the value of CR4.PGE;2 or (2) it changes the value of the CR4.PCIDE
from 1 to 0.
— The instruction invalidates all TLB entries and all entries in all paging-structure caches for the current PCID
if (1) it changes the value of CR4.PAE; or (2) it changes the value of CR4.SMEP from 0 to 1.

•

Task switch. If a task switch changes the value of CR3, it invalidates all TLB entries associated with PCID 000H
except those for global pages. It also invalidates all entries in all paging-structure caches associated with PCID
000H.3

•

VMX transitions. See Section 4.11.1.

The processor is always free to invalidate additional entries in the TLBs and paging-structure caches. The following
are some examples:

•

INVLPG may invalidate TLB entries for pages other than the one corresponding to its linear-address operand. It
may invalidate TLB entries and paging-structure-cache entries associated with PCIDs other than the current
PCID.

1. If the paging structures map the linear address using a page larger than 4 KBytes and there are multiple TLB entries for that page
(see Section 4.10.2.3), the instruction invalidates all of them.
2. If CR4.PGE is changing from 0 to 1, there were no global TLB entries before the execution; if CR4.PGE is changing from 1 to 0, there
will be no global TLB entries after the execution.
3. Task switches do not occur in IA-32e mode and thus cannot occur with 4-level paging. Since CR4.PCIDE can be set only with 4-level
paging, task switches occur only with CR4.PCIDE = 0.
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•

INVPCID may invalidate TLB entries for pages other than the one corresponding to the specified linear address.
It may invalidate TLB entries and paging-structure-cache entries associated with PCIDs other than the
specified PCID.

•

MOV to CR0 may invalidate TLB entries even if CR0.PG is not changing. For example, this may occur if either
CR0.CD or CR0.NW is modified.

•

MOV to CR3 may invalidate TLB entries for global pages. If CR4.PCIDE = 1 and bit 63 of the instruction’s source
operand is 0, it may invalidate TLB entries and entries in the paging-structure caches associated with PCIDs
other than the PCID it is establishing. It may invalidate entries if CR4.PCIDE = 1 and bit 63 of the instruction’s
source operand is 1.

•
•

MOV to CR4 may invalidate TLB entries when changing CR4.PSE or when changing CR4.SMEP from 1 to 0.
On a processor supporting Hyper-Threading Technology, invalidations performed on one logical processor may
invalidate entries in the TLBs and paging-structure caches used by other logical processors.

(Other instructions and operations may invalidate entries in the TLBs and the paging-structure caches, but the
instructions identified above are recommended.)
In addition to the instructions identified above, page faults invalidate entries in the TLBs and paging-structure
caches. In particular, a page-fault exception resulting from an attempt to use a linear address will invalidate any
TLB entries that are for a page number corresponding to that linear address and that are associated with the
current PCID. It also invalidates all entries in the paging-structure caches that would be used for that linear address
and that are associated with the current PCID.1 These invalidations ensure that the page-fault exception will not
recur (if the faulting instruction is re-executed) if it would not be caused by the contents of the paging structures
in memory (and if, therefore, it resulted from cached entries that were not invalidated after the paging structures
were modified in memory).
As noted in Section 4.10.2, some processors may choose to cache multiple smaller-page TLB entries for a translation specified by the paging structures to use a page larger than 4 KBytes. There is no way for software to be aware
that multiple translations for smaller pages have been used for a large page. The INVLPG instruction and page
faults provide the same assurances that they provide when a single TLB entry is used: they invalidate all TLB
entries corresponding to the translation specified by the paging structures.

4.10.4.2

Recommended Invalidation

The following items provide some recommendations regarding when software should perform invalidations:

•

If software modifies a paging-structure entry that maps a page (rather than referencing another paging
structure), it should execute INVLPG for any linear address with a page number whose translation uses that
paging-structure entry.2
(If the paging-structure entry may be used in the translation of different page numbers — see Section 4.10.3.3
— software should execute INVLPG for linear addresses with each of those page numbers; alternatively, it could
use MOV to CR3 or MOV to CR4.)

•

If software modifies a paging-structure entry that references another paging structure, it may use one of the
following approaches depending upon the types and number of translations controlled by the modified entry:
— Execute INVLPG for linear addresses with each of the page numbers with translations that would use the
entry. However, if no page numbers that would use the entry have translations (e.g., because the P flags
are 0 in all entries in the paging structure referenced by the modified entry), it remains necessary to
execute INVLPG at least once.
— Execute MOV to CR3 if the modified entry controls no global pages.
— Execute MOV to CR4 to modify CR4.PGE.

•

If CR4.PCIDE = 1 and software modifies a paging-structure entry that does not map a page or in which the G
flag (bit 8) is 0, additional steps are required if the entry may be used for PCIDs other than the current one. Any
one of the following suffices:

1. Unlike INVLPG, page faults need not invalidate all entries in the paging-structure caches, only those that would be used to translate
the faulting linear address.
2. One execution of INVLPG is sufficient even for a page with size greater than 4 KBytes.
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— Execute MOV to CR4 to modify CR4.PGE, either immediately or before again using any of the affected
PCIDs. For example, software could use different (previously unused) PCIDs for the processes that used the
affected PCIDs.
— For each affected PCID, execute MOV to CR3 to make that PCID current (and to load the address of the
appropriate PML4 table). If the modified entry controls no global pages and bit 63 of the source operand to
MOV to CR3 was 0, no further steps are required. Otherwise, execute INVLPG for linear addresses with each
of the page numbers with translations that would use the entry; if no page numbers that would use the
entry have translations, execute INVLPG at least once.

•

If software using PAE paging modifies a PDPTE, it should reload CR3 with the register’s current value to ensure
that the modified PDPTE is loaded into the corresponding PDPTE register (see Section 4.4.1).

•

If the nature of the paging structures is such that a single entry may be used for multiple purposes (see Section
4.10.3.3), software should perform invalidations for all of these purposes. For example, if a single entry might
serve as both a PDE and PTE, it may be necessary to execute INVLPG with two (or more) linear addresses, one
that uses the entry as a PDE and one that uses it as a PTE. (Alternatively, software could use MOV to CR3 or
MOV to CR4.)

•

As noted in Section 4.10.2, the TLBs may subsequently contain multiple translations for the address range if
software modifies the paging structures so that the page size used for a 4-KByte range of linear addresses
changes. A reference to a linear address in the address range may use any of these translations.
Software wishing to prevent this uncertainty should not write to a paging-structure entry in a way that would
change, for any linear address, both the page size and either the page frame, access rights, or other attributes.
It can instead use the following algorithm: first clear the P flag in the relevant paging-structure entry (e.g.,
PDE); then invalidate any translations for the affected linear addresses (see above); and then modify the
relevant paging-structure entry to set the P flag and establish modified translation(s) for the new page size.

•

Software should clear bit 63 of the source operand to a MOV to CR3 instruction that establishes a PCID that had
been used earlier for a different linear-address space (e.g., with a different value in bits 51:12 of CR3). This
ensures invalidation of any information that may have been cached for the previous linear-address space.
This assumes that both linear-address spaces use the same global pages and that it is thus not necessary to
invalidate any global TLB entries. If that is not the case, software should invalidate those entries by executing
MOV to CR4 to modify CR4.PGE.

4.10.4.3

Optional Invalidation

The following items describe cases in which software may choose not to invalidate and the potential consequences
of that choice:

•

If a paging-structure entry is modified to change the P flag from 0 to 1, no invalidation is necessary. This is
because no TLB entry or paging-structure cache entry is created with information from a paging-structure entry
in which the P flag is 0.1

•

If a paging-structure entry is modified to change the accessed flag from 0 to 1, no invalidation is necessary
(assuming that an invalidation was performed the last time the accessed flag was changed from 1 to 0). This is
because no TLB entry or paging-structure cache entry is created with information from a paging-structure entry
in which the accessed flag is 0.

•

If a paging-structure entry is modified to change the R/W flag from 0 to 1, failure to perform an invalidation
may result in a “spurious” page-fault exception (e.g., in response to an attempted write access) but no other
adverse behavior. Such an exception will occur at most once for each affected linear address (see Section
4.10.4.1).

•

If CR4.SMEP = 0 and a paging-structure entry is modified to change the U/S flag from 0 to 1, failure to perform
an invalidation may result in a “spurious” page-fault exception (e.g., in response to an attempted user-mode
access) but no other adverse behavior. Such an exception will occur at most once for each affected linear
address (see Section 4.10.4.1).

•

If a paging-structure entry is modified to change the XD flag from 1 to 0, failure to perform an invalidation may
result in a “spurious” page-fault exception (e.g., in response to an attempted instruction fetch) but no other

1. If it is also the case that no invalidation was performed the last time the P flag was changed from 1 to 0, the processor may use a
TLB entry or paging-structure cache entry that was created when the P flag had earlier been 1.
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adverse behavior. Such an exception will occur at most once for each affected linear address (see Section
4.10.4.1).

•

If a paging-structure entry is modified to change the accessed flag from 1 to 0, failure to perform an invalidation may result in the processor not setting that bit in response to a subsequent access to a linear address
whose translation uses the entry. Software cannot interpret the bit being clear as an indication that such an
access has not occurred.

•

If software modifies a paging-structure entry that identifies the final physical address for a linear address
(either a PTE or a paging-structure entry in which the PS flag is 1) to change the dirty flag from 1 to 0, failure
to perform an invalidation may result in the processor not setting that bit in response to a subsequent write to
a linear address whose translation uses the entry. Software cannot interpret the bit being clear as an indication
that such a write has not occurred.

•

The read of a paging-structure entry in translating an address being used to fetch an instruction may appear to
execute before an earlier write to that paging-structure entry if there is no serializing instruction between the
write and the instruction fetch. Note that the invalidating instructions identified in Section 4.10.4.1 are all
serializing instructions.

•

Section 4.10.3.3 describes situations in which a single paging-structure entry may contain information cached
in multiple entries in the paging-structure caches. Because all entries in these caches are invalidated by any
execution of INVLPG, it is not necessary to follow the modification of such a paging-structure entry by
executing INVLPG multiple times solely for the purpose of invalidating these multiple cached entries. (It may be
necessary to do so to invalidate multiple TLB entries.)

4.10.4.4

Delayed Invalidation

Required invalidations may be delayed under some circumstances. Software developers should understand that,
between the modification of a paging-structure entry and execution of the invalidation instruction recommended in
Section 4.10.4.2, the processor may use translations based on either the old value or the new value of the pagingstructure entry. The following items describe some of the potential consequences of delayed invalidation:

•

If a paging-structure entry is modified to change the P flag from 1 to 0, an access to a linear address whose
translation is controlled by this entry may or may not cause a page-fault exception.

•

If a paging-structure entry is modified to change the R/W flag from 0 to 1, write accesses to linear addresses
whose translation is controlled by this entry may or may not cause a page-fault exception.

•

If a paging-structure entry is modified to change the U/S flag from 0 to 1, user-mode accesses to linear
addresses whose translation is controlled by this entry may or may not cause a page-fault exception.

•

If a paging-structure entry is modified to change the XD flag from 1 to 0, instruction fetches from linear
addresses whose translation is controlled by this entry may or may not cause a page-fault exception.

As noted in Section 8.1.1, an x87 instruction or an SSE instruction that accesses data larger than a quadword may
be implemented using multiple memory accesses. If such an instruction stores to memory and invalidation has
been delayed, some of the accesses may complete (writing to memory) while another causes a page-fault exception.1 In this case, the effects of the completed accesses may be visible to software even though the overall
instruction caused a fault.
In some cases, the consequences of delayed invalidation may not affect software adversely. For example, when
freeing a portion of the linear-address space (by marking paging-structure entries “not present”), invalidation
using INVLPG may be delayed if software does not re-allocate that portion of the linear-address space or the
memory that had been associated with it. However, because of speculative execution (or errant software), there
may be accesses to the freed portion of the linear-address space before the invalidations occur. In this case, the
following can happen:

•

Reads can occur to the freed portion of the linear-address space. Therefore, invalidation should not be delayed
for an address range that has read side effects.

•

The processor may retain entries in the TLBs and paging-structure caches for an extended period of time.
Software should not assume that the processor will not use entries associated with a linear address simply
because time has passed.

1. If the accesses are to different pages, this may occur even if invalidation has not been delayed.
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•

As noted in Section 4.10.3.1, the processor may create an entry in a paging-structure cache even if there are
no translations for any linear address that might use that entry. Thus, if software has marked “not present” all
entries in a page table, the processor may subsequently create a PDE-cache entry for the PDE that references
that page table (assuming that the PDE itself is marked “present”).

•

If software attempts to write to the freed portion of the linear-address space, the processor might not generate
a page fault. (Such an attempt would likely be the result of a software error.) For that reason, the page frames
previously associated with the freed portion of the linear-address space should not be reallocated for another
purpose until the appropriate invalidations have been performed.

4.10.5

Propagation of Paging-Structure Changes to Multiple Processors

As noted in Section 4.10.4, software that modifies a paging-structure entry may need to invalidate entries in the
TLBs and paging-structure caches that were derived from the modified entry before it was modified. In a system
containing more than one logical processor, software must account for the fact that there may be entries in the
TLBs and paging-structure caches of logical processors other than the one used to modify the paging-structure
entry. The process of propagating the changes to a paging-structure entry is commonly referred to as “TLB shootdown.”
TLB shootdown can be done using memory-based semaphores and/or interprocessor interrupts (IPI). The following
items describe a simple but inefficient example of a TLB shootdown algorithm for processors supporting the
Intel-64 and IA-32 architectures:
1. Begin barrier: Stop all but one logical processor; that is, cause all but one to execute the HLT instruction or to
enter a spin loop.
2. Allow the active logical processor to change the necessary paging-structure entries.
3. Allow all logical processors to perform invalidations appropriate to the modifications to the paging-structure
entries.
4. Allow all logical processors to resume normal operation.
Alternative, performance-optimized, TLB shootdown algorithms may be developed; however, software developers
must take care to ensure that the following conditions are met:

•

All logical processors that are using the paging structures that are being modified must participate and perform
appropriate invalidations after the modifications are made.

•

If the modifications to the paging-structure entries are made before the barrier or if there is no barrier, the
operating system must ensure one of the following: (1) that the affected linear-address range is not used
between the time of modification and the time of invalidation; or (2) that it is prepared to deal with the consequences of the affected linear-address range being used during that period. For example, if the operating
system does not allow pages being freed to be reallocated for another purpose until after the required invalidations, writes to those pages by errant software will not unexpectedly modify memory that is in use.

•

Software must be prepared to deal with reads, instruction fetches, and prefetch requests to the affected linearaddress range that are a result of speculative execution that would never actually occur in the executed code
path.

When multiple logical processors are using the same linear-address space at the same time, they must coordinate
before any request to modify the paging-structure entries that control that linear-address space. In these cases,
the barrier in the TLB shootdown routine may not be required. For example, when freeing a range of linear
addresses, some other mechanism can assure no logical processor is using that range before the request to free it
is made. In this case, a logical processor freeing the range can clear the P flags in the PTEs associated with the
range, free the physical page frames associated with the range, and then signal the other logical processors using
that linear-address space to perform the necessary invalidations. All the affected logical processors must complete
their invalidations before the linear-address range and the physical page frames previously associated with that
range can be reallocated.

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4.11

INTERACTIONS WITH VIRTUAL-MACHINE EXTENSIONS (VMX)

The architecture for virtual-machine extensions (VMX) includes features that interact with paging. Section 4.11.1
discusses ways in which VMX-specific control transfers, called VMX transitions specially affect paging. Section
4.11.2 gives an overview of VMX features specifically designed to support address translation.

4.11.1

VMX Transitions

The VMX architecture defines two control transfers called VM entries and VM exits; collectively, these are called
VMX transitions. VM entries and VM exits are described in detail in Chapter 26 and Chapter 27, respectively, in
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C. The following items identify
paging-related details:

•

VMX transitions modify the CR0 and CR4 registers and the IA32_EFER MSR concurrently. For this reason, they
allow transitions between paging modes that would not otherwise be possible:
— VM entries allow transitions from 4-level paging directly to either 32-bit paging or PAE paging.
— VM exits allow transitions from either 32-bit paging or PAE paging directly to 4-level paging.

•

VMX transitions that result in PAE paging load the PDPTE registers (see Section 4.4.1) as follows:
— VM entries load the PDPTE registers either from the physical address being loaded into CR3 or from the
virtual-machine control structure (VMCS); see Section 26.3.2.4.
— VM exits load the PDPTE registers from the physical address being loaded into CR3; see Section 27.5.4.

•

VMX transitions invalidate the TLBs and paging-structure caches based on certain control settings. See Section
26.3.2.5 and Section 27.5.5 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
3C.

4.11.2

VMX Support for Address Translation

Chapter 28, “VMX Support for Address Translation,” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3C describe two features of the virtual-machine extensions (VMX) that interact directly with
paging. These are virtual-processor identifiers (VPIDs) and the extended page table mechanism (EPT).
VPIDs provide a way for software to identify to the processor the address spaces for different “virtual processors.”
The processor may use this identification to maintain concurrently information for multiple address spaces in its
TLBs and paging-structure caches, even when non-zero PCIDs are not being used. See Section 28.1 for details.
When EPT is in use, the addresses in the paging-structures are not used as physical addresses to access memory
and memory-mapped I/O. Instead, they are treated as guest-physical addresses and are translated through a
set of EPT paging structures to produce physical addresses. EPT can also specify its own access rights and memory
typing; these are used on conjunction with those specified in this chapter. See Section 28.2 for more information.
Both VPIDs and EPT may change the way that a processor maintains information in TLBs and paging structure
caches and the ways in which software can manage that information. Some of the behaviors documented in
Section 4.10 may change. See Section 28.3 for details.

4.12

USING PAGING FOR VIRTUAL MEMORY

With paging, portions of the linear-address space need not be mapped to the physical-address space; data for the
unmapped addresses can be stored externally (e.g., on disk). This method of mapping the linear-address space is
referred to as virtual memory or demand-paged virtual memory.
Paging divides the linear address space into fixed-size pages that can be mapped into the physical-address space
and/or external storage. When a program (or task) references a linear address, the processor uses paging to translate the linear address into a corresponding physical address if such an address is defined.
If the page containing the linear address is not currently mapped into the physical-address space, the processor
generates a page-fault exception as described in Section 4.7. The handler for page-fault exceptions typically

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directs the operating system or executive to load data for the unmapped page from external storage into physical
memory (perhaps writing a different page from physical memory out to external storage in the process) and to map
it using paging (by updating the paging structures). When the page has been loaded into physical memory, a return
from the exception handler causes the instruction that generated the exception to be restarted.
Paging differs from segmentation through its use of fixed-size pages. Unlike segments, which usually are the same
size as the code or data structures they hold, pages have a fixed size. If segmentation is the only form of address
translation used, a data structure present in physical memory will have all of its parts in memory. If paging is used,
a data structure can be partly in memory and partly in disk storage.

4.13

MAPPING SEGMENTS TO PAGES

The segmentation and paging mechanisms provide support for a wide variety of approaches to memory management. When segmentation and paging are combined, segments can be mapped to pages in several ways. To implement a flat (unsegmented) addressing environment, for example, all the code, data, and stack modules can be
mapped to one or more large segments (up to 4-GBytes) that share same range of linear addresses (see Figure 3-2
in Section 3.2.2). Here, segments are essentially invisible to applications and the operating-system or executive. If
paging is used, the paging mechanism can map a single linear-address space (contained in a single segment) into
virtual memory. Alternatively, each program (or task) can have its own large linear-address space (contained in its
own segment), which is mapped into virtual memory through its own paging structures.
Segments can be smaller than the size of a page. If one of these segments is placed in a page which is not shared
with another segment, the extra memory is wasted. For example, a small data structure, such as a 1-Byte semaphore, occupies 4 KBytes if it is placed in a page by itself. If many semaphores are used, it is more efficient to pack
them into a single page.
The Intel-64 and IA-32 architectures do not enforce correspondence between the boundaries of pages and
segments. A page can contain the end of one segment and the beginning of another. Similarly, a segment can
contain the end of one page and the beginning of another.
Memory-management software may be simpler and more efficient if it enforces some alignment between page and
segment boundaries. For example, if a segment which can fit in one page is placed in two pages, there may be
twice as much paging overhead to support access to that segment.
One approach to combining paging and segmentation that simplifies memory-management software is to give each
segment its own page table, as shown in Figure 4-13. This convention gives the segment a single entry in the page
directory, and this entry provides the access control information for paging the entire segment.

Page Frames
LDT

Page Directory

Page Tables
PTE
PTE
PTE

Seg. Descript.
Seg. Descript.

PDE
PDE

PTE
PTE

Figure 4-13. Memory Management Convention That Assigns a Page Table
to Each Segment

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CHAPTER 5
PROTECTION
In protected mode, the Intel 64 and IA-32 architectures provide a protection mechanism that operates at both the
segment level and the page level. This protection mechanism provides the ability to limit access to certain
segments or pages based on privilege levels (four privilege levels for segments and two privilege levels for pages).
For example, critical operating-system code and data can be protected by placing them in more privileged
segments than those that contain applications code. The processor’s protection mechanism will then prevent application code from accessing the operating-system code and data in any but a controlled, defined manner.
Segment and page protection can be used at all stages of software development to assist in localizing and detecting
design problems and bugs. It can also be incorporated into end-products to offer added robustness to operating
systems, utilities software, and applications software.
When the protection mechanism is used, each memory reference is checked to verify that it satisfies various
protection checks. All checks are made before the memory cycle is started; any violation results in an exception.
Because checks are performed in parallel with address translation, there is no performance penalty. The protection
checks that are performed fall into the following categories:

•
•
•
•
•
•

Limit checks.
Type checks.
Privilege level checks.
Restriction of addressable domain.
Restriction of procedure entry-points.
Restriction of instruction set.

All protection violation results in an exception being generated. See Chapter 6, “Interrupt and Exception Handling,”
for an explanation of the exception mechanism. This chapter describes the protection mechanism and the violations which lead to exceptions.
The following sections describe the protection mechanism available in protected mode. See Chapter 20, “8086
Emulation,” for information on protection in real-address and virtual-8086 mode.

5.1

ENABLING AND DISABLING SEGMENT AND PAGE PROTECTION

Setting the PE flag in register CR0 causes the processor to switch to protected mode, which in turn enables the
segment-protection mechanism. Once in protected mode, there is no control bit for turning the protection mechanism on or off. The part of the segment-protection mechanism that is based on privilege levels can essentially be
disabled while still in protected mode by assigning a privilege level of 0 (most privileged) to all segment selectors
and segment descriptors. This action disables the privilege level protection barriers between segments, but other
protection checks such as limit checking and type checking are still carried out.
Page-level protection is automatically enabled when paging is enabled (by setting the PG flag in register CR0). Here
again there is no mode bit for turning off page-level protection once paging is enabled. However, page-level protection can be disabled by performing the following operations:

•
•

Clear the WP flag in control register CR0.
Set the read/write (R/W) and user/supervisor (U/S) flags for each page-directory and page-table entry.

This action makes each page a writable, user page, which in effect disables page-level protection.

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5.2

FIELDS AND FLAGS USED FOR SEGMENT-LEVEL AND
PAGE-LEVEL PROTECTION

The processor’s protection mechanism uses the following fields and flags in the system data structures to control
access to segments and pages:

•

Descriptor type (S) flag — (Bit 12 in the second doubleword of a segment descriptor.) Determines if the
segment descriptor is for a system segment or a code or data segment.

•

Type field — (Bits 8 through 11 in the second doubleword of a segment descriptor.) Determines the type of
code, data, or system segment.

•

Limit field — (Bits 0 through 15 of the first doubleword and bits 16 through 19 of the second doubleword of a
segment descriptor.) Determines the size of the segment, along with the G flag and E flag (for data segments).

•

G flag — (Bit 23 in the second doubleword of a segment descriptor.) Determines the size of the segment, along
with the limit field and E flag (for data segments).

•

E flag — (Bit 10 in the second doubleword of a data-segment descriptor.) Determines the size of the segment,
along with the limit field and G flag.

•

Descriptor privilege level (DPL) field — (Bits 13 and 14 in the second doubleword of a segment descriptor.)
Determines the privilege level of the segment.

•

Requested privilege level (RPL) field — (Bits 0 and 1 of any segment selector.) Specifies the requested
privilege level of a segment selector.

•

Current privilege level (CPL) field — (Bits 0 and 1 of the CS segment register.) Indicates the privilege level
of the currently executing program or procedure. The term current privilege level (CPL) refers to the setting of
this field.

•

User/supervisor (U/S) flag — (Bit 2 of paging-structure entries.) Determines the type of page: user or
supervisor.

•

Read/write (R/W) flag — (Bit 1 of paging-structure entries.) Determines the type of access allowed to a
page: read-only or read/write.

•

Execute-disable (XD) flag — (Bit 63 of certain paging-structure entries.) Determines the type of access
allowed to a page: executable or not-executable.

Figure 5-1 shows the location of the various fields and flags in the data-, code-, and system-segment descriptors;
Figure 3-6 shows the location of the RPL (or CPL) field in a segment selector (or the CS register); and Chapter 4
identifies the locations of the U/S, R/W, and XD flags in the paging-structure entries.

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PROTECTION

Data-Segment Descriptor
31

Base 31:24

24 23 22 21 20 19

16 15 14 13 12 11

A
G B 0 V
L

D
P
L

Limit
19:16

31

P

0

8 7

Type

4

Base 23:16

1 0 E W A

16 15

0

Base Address 15:00

0

Segment Limit 15:00

Code-Segment Descriptor
31

Base 31:24

24 23 22 21 20 19

16 15 14 13 12 11

A
G D 0 V
L

D
P
L

Limit
19:16

31

P

0

8 7

Type

4

Base 23:16

1 1 C R A

16 15

0

Base Address 15:00

0

Segment Limit 15:00

System-Segment Descriptor
31

24 23 22 21 20 19

Base 31:24

G

0

31

16 15 14 13 12 11

Limit
19:16

P

D
P
L

0

0

8 7

Type

16 15

Base Address 15:00

A
AVL
B
C
D
DPL

Accessed
Available to Sys. Programmers
Big
Conforming
Default
Descriptor Privilege Level

4

Base 23:16
0

Segment Limit 15:00

E
G
R
LIMIT
W
P

0

Expansion Direction
Granularity
Readable
Segment Limit
Writable
Present

Reserved

Figure 5-1. Descriptor Fields Used for Protection
Many different styles of protection schemes can be implemented with these fields and flags. When the operating
system creates a descriptor, it places values in these fields and flags in keeping with the particular protection style
chosen for an operating system or executive. Application programs do not generally access or modify these fields
and flags.
The following sections describe how the processor uses these fields and flags to perform the various categories of
checks described in the introduction to this chapter.

5.2.1

Code-Segment Descriptor in 64-bit Mode

Code segments continue to exist in 64-bit mode even though, for address calculations, the segment base is treated
as zero. Some code-segment (CS) descriptor content (the base address and limit fields) is ignored; the remaining
fields function normally (except for the readable bit in the type field).
Code segment descriptors and selectors are needed in IA-32e mode to establish the processor’s operating mode
and execution privilege-level. The usage is as follows:

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PROTECTION

•

IA-32e mode uses a previously unused bit in the CS descriptor. Bit 53 is defined as the 64-bit (L) flag and is
used to select between 64-bit mode and compatibility mode when IA-32e mode is active (IA32_EFER.LMA = 1).
See Figure 5-2.
— If CS.L = 0 and IA-32e mode is active, the processor is running in compatibility mode. In this case, CS.D
selects the default size for data and addresses. If CS.D = 0, the default data and address size is 16 bits. If
CS.D = 1, the default data and address size is 32 bits.
— If CS.L = 1 and IA-32e mode is active, the only valid setting is CS.D = 0. This setting indicates a default
operand size of 32 bits and a default address size of 64 bits. The CS.L = 1 and CS.D = 1 bit combination is
reserved for future use and a #GP fault will be generated on an attempt to use a code segment with these
bits set in IA-32e mode.

•

In IA-32e mode, the CS descriptor’s DPL is used for execution privilege checks (as in legacy 32-bit mode).

Code-Segment Descriptor
31

24 23 22 21 20 19

16 15 14 13 12 11

A
G D L V
L

D
P
L

P

8 7

0

Type

4

1 1 C R A
0

31

0

A
AVL
C
D
DPL
L

Accessed
Available to Sys. Programmer’s
Conforming
Default
Descriptor Privilege Level
64-Bit Flag

G
R
P

Granularity
Readable
Present

Figure 5-2. Descriptor Fields with Flags used in IA-32e Mode

5.3

LIMIT CHECKING

The limit field of a segment descriptor prevents programs or procedures from addressing memory locations outside
the segment. The effective value of the limit depends on the setting of the G (granularity) flag (see Figure 5-1). For
data segments, the limit also depends on the E (expansion direction) flag and the B (default stack pointer size
and/or upper bound) flag. The E flag is one of the bits in the type field when the segment descriptor is for a datasegment type.
When the G flag is clear (byte granularity), the effective limit is the value of the 20-bit limit field in the segment
descriptor. Here, the limit ranges from 0 to FFFFFH (1 MByte). When the G flag is set (4-KByte page granularity),
the processor scales the value in the limit field by a factor of 212 (4 KBytes). In this case, the effective limit ranges
from FFFH (4 KBytes) to FFFFFFFFH (4 GBytes). Note that when scaling is used (G flag is set), the lower 12 bits of
a segment offset (address) are not checked against the limit; for example, note that if the segment limit is 0,
offsets 0 through FFFH are still valid.
For all types of segments except expand-down data segments, the effective limit is the last address that is allowed
to be accessed in the segment, which is one less than the size, in bytes, of the segment. The processor causes a
general-protection exception (or, if the segment is SS, a stack-fault exception) any time an attempt is made to
access the following addresses in a segment:

•
•
•
•

A byte at an offset greater than the effective limit
A word at an offset greater than the (effective-limit – 1)
A doubleword at an offset greater than the (effective-limit – 3)
A quadword at an offset greater than the (effective-limit – 7)

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PROTECTION

•

A double quadword at an offset greater than the (effective limit – 15)

When the effective limit is FFFFFFFFH (4 GBytes), these accesses may or may not cause the indicated exceptions.
Behavior is implementation-specific and may vary from one execution to another.
For expand-down data segments, the segment limit has the same function but is interpreted differently. Here, the
effective limit specifies the last address that is not allowed to be accessed within the segment; the range of valid
offsets is from (effective-limit + 1) to FFFFFFFFH if the B flag is set and from (effective-limit + 1) to FFFFH if the B
flag is clear. An expand-down segment has maximum size when the segment limit is 0.
Limit checking catches programming errors such as runaway code, runaway subscripts, and invalid pointer calculations. These errors are detected when they occur, so identification of the cause is easier. Without limit checking,
these errors could overwrite code or data in another segment.
In addition to checking segment limits, the processor also checks descriptor table limits. The GDTR and IDTR registers contain 16-bit limit values that the processor uses to prevent programs from selecting a segment descriptors
outside the respective descriptor tables. The LDTR and task registers contain 32-bit segment limit value (read from
the segment descriptors for the current LDT and TSS, respectively). The processor uses these segment limits to
prevent accesses beyond the bounds of the current LDT and TSS. See Section 3.5.1, “Segment Descriptor Tables,”
for more information on the GDT and LDT limit fields; see Section 6.10, “Interrupt Descriptor Table (IDT),” for more
information on the IDT limit field; and see Section 7.2.4, “Task Register,” for more information on the TSS segment
limit field.

5.3.1

Limit Checking in 64-bit Mode

In 64-bit mode, the processor does not perform runtime limit checking on code or data segments. However, the
processor does check descriptor-table limits.

5.4

TYPE CHECKING

Segment descriptors contain type information in two places:

•
•

The S (descriptor type) flag.
The type field.

The processor uses this information to detect programming errors that result in an attempt to use a segment or
gate in an incorrect or unintended manner.
The S flag indicates whether a descriptor is a system type or a code or data type. The type field provides 4 additional bits for use in defining various types of code, data, and system descriptors. Table 3-1 shows the encoding of
the type field for code and data descriptors; Table 3-2 shows the encoding of the field for system descriptors.
The processor examines type information at various times while operating on segment selectors and segment
descriptors. The following list gives examples of typical operations where type checking is performed (this list is not
exhaustive):

•

When a segment selector is loaded into a segment register — Certain segment registers can contain only
certain descriptor types, for example:
— The CS register only can be loaded with a selector for a code segment.
— Segment selectors for code segments that are not readable or for system segments cannot be loaded into
data-segment registers (DS, ES, FS, and GS).
— Only segment selectors of writable data segments can be loaded into the SS register.

•

When a segment selector is loaded into the LDTR or task register — For example:
— The LDTR can only be loaded with a selector for an LDT.
— The task register can only be loaded with a segment selector for a TSS.

•

When instructions access segments whose descriptors are already loaded into segment registers —
Certain segments can be used by instructions only in certain predefined ways, for example:
— No instruction may write into an executable segment.
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PROTECTION

— No instruction may write into a data segment if it is not writable.
— No instruction may read an executable segment unless the readable flag is set.

•

When an instruction operand contains a segment selector — Certain instructions can access segments
or gates of only a particular type, for example:
— A far CALL or far JMP instruction can only access a segment descriptor for a conforming code segment,
nonconforming code segment, call gate, task gate, or TSS.
— The LLDT instruction must reference a segment descriptor for an LDT.
— The LTR instruction must reference a segment descriptor for a TSS.
— The LAR instruction must reference a segment or gate descriptor for an LDT, TSS, call gate, task gate, code
segment, or data segment.
— The LSL instruction must reference a segment descriptor for a LDT, TSS, code segment, or data segment.
— IDT entries must be interrupt, trap, or task gates.

•

During certain internal operations — For example:
— On a far call or far jump (executed with a far CALL or far JMP instruction), the processor determines the
type of control transfer to be carried out (call or jump to another code segment, a call or jump through a
gate, or a task switch) by checking the type field in the segment (or gate) descriptor pointed to by the
segment (or gate) selector given as an operand in the CALL or JMP instruction. If the descriptor type is for
a code segment or call gate, a call or jump to another code segment is indicated; if the descriptor type is for
a TSS or task gate, a task switch is indicated.
— On a call or jump through a call gate (or on an interrupt- or exception-handler call through a trap or
interrupt gate), the processor automatically checks that the segment descriptor being pointed to by the
gate is for a code segment.
— On a call or jump to a new task through a task gate (or on an interrupt- or exception-handler call to a new
task through a task gate), the processor automatically checks that the segment descriptor being pointed to
by the task gate is for a TSS.
— On a call or jump to a new task by a direct reference to a TSS, the processor automatically checks that the
segment descriptor being pointed to by the CALL or JMP instruction is for a TSS.
— On return from a nested task (initiated by an IRET instruction), the processor checks that the previous task
link field in the current TSS points to a TSS.

5.4.1

Null Segment Selector Checking

Attempting to load a null segment selector (see Section 3.4.2, “Segment Selectors”) into the CS or SS segment
register generates a general-protection exception (#GP). A null segment selector can be loaded into the DS, ES,
FS, or GS register, but any attempt to access a segment through one of these registers when it is loaded with a null
segment selector results in a #GP exception being generated. Loading unused data-segment registers with a null
segment selector is a useful method of detecting accesses to unused segment registers and/or preventing
unwanted accesses to data segments.

5.4.1.1

NULL Segment Checking in 64-bit Mode

In 64-bit mode, the processor does not perform runtime checking on NULL segment selectors. The processor does
not cause a #GP fault when an attempt is made to access memory where the referenced segment register has a
NULL segment selector.

5.5

PRIVILEGE LEVELS

The processor’s segment-protection mechanism recognizes 4 privilege levels, numbered from 0 to 3. The greater
numbers mean lesser privileges. Figure 5-3 shows how these levels of privilege can be interpreted as rings of
protection.
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PROTECTION

The center (reserved for the most privileged code, data, and stacks) is used for the segments containing the critical
software, usually the kernel of an operating system. Outer rings are used for less critical software. (Systems that
use only 2 of the 4 possible privilege levels should use levels 0 and 3.)

Protection Rings

Operating
System
Kernel

Level 0

Operating System
Services

Level 1
Level 2

Applications

Level 3

Figure 5-3. Protection Rings
The processor uses privilege levels to prevent a program or task operating at a lesser privilege level from accessing
a segment with a greater privilege, except under controlled situations. When the processor detects a privilege level
violation, it generates a general-protection exception (#GP).
To carry out privilege-level checks between code segments and data segments, the processor recognizes the
following three types of privilege levels:

•

Current privilege level (CPL) — The CPL is the privilege level of the currently executing program or task. It
is stored in bits 0 and 1 of the CS and SS segment registers. Normally, the CPL is equal to the privilege level of
the code segment from which instructions are being fetched. The processor changes the CPL when program
control is transferred to a code segment with a different privilege level. The CPL is treated slightly differently
when accessing conforming code segments. Conforming code segments can be accessed from any privilege
level that is equal to or numerically greater (less privileged) than the DPL of the conforming code segment.
Also, the CPL is not changed when the processor accesses a conforming code segment that has a different
privilege level than the CPL.

•

Descriptor privilege level (DPL) — The DPL is the privilege level of a segment or gate. It is stored in the DPL
field of the segment or gate descriptor for the segment or gate. When the currently executing code segment
attempts to access a segment or gate, the DPL of the segment or gate is compared to the CPL and RPL of the
segment or gate selector (as described later in this section). The DPL is interpreted differently, depending on
the type of segment or gate being accessed:
— Data segment — The DPL indicates the numerically highest privilege level that a program or task can have
to be allowed to access the segment. For example, if the DPL of a data segment is 1, only programs running
at a CPL of 0 or 1 can access the segment.
— Nonconforming code segment (without using a call gate) — The DPL indicates the privilege level that
a program or task must be at to access the segment. For example, if the DPL of a nonconforming code
segment is 0, only programs running at a CPL of 0 can access the segment.
— Call gate — The DPL indicates the numerically highest privilege level that the currently executing program
or task can be at and still be able to access the call gate. (This is the same access rule as for a data
segment.)
— Conforming code segment and nonconforming code segment accessed through a call gate — The
DPL indicates the numerically lowest privilege level that a program or task can have to be allowed to access
the segment. For example, if the DPL of a conforming code segment is 2, programs running at a CPL of 0 or
1 cannot access the segment.

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PROTECTION

— TSS — The DPL indicates the numerically highest privilege level that the currently executing program or
task can be at and still be able to access the TSS. (This is the same access rule as for a data segment.)

•

Requested privilege level (RPL) — The RPL is an override privilege level that is assigned to segment
selectors. It is stored in bits 0 and 1 of the segment selector. The processor checks the RPL along with the CPL
to determine if access to a segment is allowed. Even if the program or task requesting access to a segment has
sufficient privilege to access the segment, access is denied if the RPL is not of sufficient privilege level. That is,
if the RPL of a segment selector is numerically greater than the CPL, the RPL overrides the CPL, and vice versa.
The RPL can be used to insure that privileged code does not access a segment on behalf of an application
program unless the program itself has access privileges for that segment. See Section 5.10.4, “Checking Caller
Access Privileges (ARPL Instruction),” for a detailed description of the purpose and typical use of the RPL.

Privilege levels are checked when the segment selector of a segment descriptor is loaded into a segment register.
The checks used for data access differ from those used for transfers of program control among code segments;
therefore, the two kinds of accesses are considered separately in the following sections.

5.6

PRIVILEGE LEVEL CHECKING WHEN ACCESSING DATA SEGMENTS

To access operands in a data segment, the segment selector for the data segment must be loaded into the datasegment registers (DS, ES, FS, or GS) or into the stack-segment register (SS). (Segment registers can be loaded
with the MOV, POP, LDS, LES, LFS, LGS, and LSS instructions.) Before the processor loads a segment selector into
a segment register, it performs a privilege check (see Figure 5-4) by comparing the privilege levels of the currently
running program or task (the CPL), the RPL of the segment selector, and the DPL of the segment’s segment
descriptor. The processor loads the segment selector into the segment register if the DPL is numerically greater
than or equal to both the CPL and the RPL. Otherwise, a general-protection fault is generated and the segment
register is not loaded.

CS Register
CPL
Segment Selector
For Data Segment
RPL
Data-Segment Descriptor

Privilege
Check

DPL

Figure 5-4. Privilege Check for Data Access
Figure 5-5 shows four procedures (located in codes segments A, B, C, and D), each running at different privilege
levels and each attempting to access the same data segment.
1. The procedure in code segment A is able to access data segment E using segment selector E1, because the CPL
of code segment A and the RPL of segment selector E1 are equal to the DPL of data segment E.
2. The procedure in code segment B is able to access data segment E using segment selector E2, because the CPL
of code segment B and the RPL of segment selector E2 are both numerically lower than (more privileged) than
the DPL of data segment E. A code segment B procedure can also access data segment E using segment
selector E1.
3. The procedure in code segment C is not able to access data segment E using segment selector E3 (dotted line),
because the CPL of code segment C and the RPL of segment selector E3 are both numerically greater than (less
privileged) than the DPL of data segment E. Even if a code segment C procedure were to use segment selector

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E1 or E2, such that the RPL would be acceptable, it still could not access data segment E because its CPL is not
privileged enough.
4. The procedure in code segment D should be able to access data segment E because code segment D’s CPL is
numerically less than the DPL of data segment E. However, the RPL of segment selector E3 (which the code
segment D procedure is using to access data segment E) is numerically greater than the DPL of data segment
E, so access is not allowed. If the code segment D procedure were to use segment selector E1 or E2 to access
the data segment, access would be allowed.

3

2

1

0

Code
Segment C
CPL=3
Lowest Privilege

Segment Sel. E3
RPL=3

Code
Segment A
CPL=2

Segment Sel. E1
RPL=2

Code
Segment B
CPL=1

Segment Sel. E2
RPL=1

Data
Segment E
DPL=2

Highest Privilege

Code
Segment D
CPL=0

Figure 5-5. Examples of Accessing Data Segments From Various Privilege Levels
As demonstrated in the previous examples, the addressable domain of a program or task varies as its CPL changes.
When the CPL is 0, data segments at all privilege levels are accessible; when the CPL is 1, only data segments at
privilege levels 1 through 3 are accessible; when the CPL is 3, only data segments at privilege level 3 are accessible.
The RPL of a segment selector can always override the addressable domain of a program or task. When properly
used, RPLs can prevent problems caused by accidental (or intensional) use of segment selectors for privileged data
segments by less privileged programs or procedures.
It is important to note that the RPL of a segment selector for a data segment is under software control. For
example, an application program running at a CPL of 3 can set the RPL for a data- segment selector to 0. With the
RPL set to 0, only the CPL checks, not the RPL checks, will provide protection against deliberate, direct attempts to
violate privilege-level security for the data segment. To prevent these types of privilege-level-check violations, a
program or procedure can check access privileges whenever it receives a data-segment selector from another
procedure (see Section 5.10.4, “Checking Caller Access Privileges (ARPL Instruction)”).

5.6.1

Accessing Data in Code Segments

In some instances it may be desirable to access data structures that are contained in a code segment. The
following methods of accessing data in code segments are possible:

•
•
•

Load a data-segment register with a segment selector for a nonconforming, readable, code segment.
Load a data-segment register with a segment selector for a conforming, readable, code segment.
Use a code-segment override prefix (CS) to read a readable, code segment whose selector is already loaded in
the CS register.

The same rules for accessing data segments apply to method 1. Method 2 is always valid because the privilege
level of a conforming code segment is effectively the same as the CPL, regardless of its DPL. Method 3 is always
valid because the DPL of the code segment selected by the CS register is the same as the CPL.
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5.7

PRIVILEGE LEVEL CHECKING WHEN LOADING THE SS REGISTER

Privilege level checking also occurs when the SS register is loaded with the segment selector for a stack segment.
Here all privilege levels related to the stack segment must match the CPL; that is, the CPL, the RPL of the stacksegment selector, and the DPL of the stack-segment descriptor must be the same. If the RPL and DPL are not equal
to the CPL, a general-protection exception (#GP) is generated.

5.8

PRIVILEGE LEVEL CHECKING WHEN TRANSFERRING PROGRAM CONTROL
BETWEEN CODE SEGMENTS

To transfer program control from one code segment to another, the segment selector for the destination code
segment must be loaded into the code-segment register (CS). As part of this loading process, the processor examines the segment descriptor for the destination code segment and performs various limit, type, and privilege
checks. If these checks are successful, the CS register is loaded, program control is transferred to the new code
segment, and program execution begins at the instruction pointed to by the EIP register.
Program control transfers are carried out with the JMP, CALL, RET, SYSENTER, SYSEXIT, SYSCALL, SYSRET, INT n,
and IRET instructions, as well as by the exception and interrupt mechanisms. Exceptions, interrupts, and the IRET
instruction are special cases discussed in Chapter 6, “Interrupt and Exception Handling.” This chapter discusses
only the JMP, CALL, RET, SYSENTER, SYSEXIT, SYSCALL, and SYSRET instructions.
A JMP or CALL instruction can reference another code segment in any of four ways:

•
•

The target operand contains the segment selector for the target code segment.

•
•

The target operand points to a TSS, which contains the segment selector for the target code segment.

The target operand points to a call-gate descriptor, which contains the segment selector for the target code
segment.
The target operand points to a task gate, which points to a TSS, which in turn contains the segment selector for
the target code segment.

The following sections describe first two types of references. See Section 7.3, “Task Switching,” for information on
transferring program control through a task gate and/or TSS.
The SYSENTER and SYSEXIT instructions are special instructions for making fast calls to and returns from operating
system or executive procedures. These instructions are discussed in Section 5.8.7, “Performing Fast Calls to
System Procedures with the SYSENTER and SYSEXIT Instructions.”
The SYCALL and SYSRET instructions are special instructions for making fast calls to and returns from operating
system or executive procedures in 64-bit mode. These instructions are discussed in Section 5.8.8, “Fast System
Calls in 64-Bit Mode.”

5.8.1

Direct Calls or Jumps to Code Segments

The near forms of the JMP, CALL, and RET instructions transfer program control within the current code segment,
so privilege-level checks are not performed. The far forms of the JMP, CALL, and RET instructions transfer control
to other code segments, so the processor does perform privilege-level checks.
When transferring program control to another code segment without going through a call gate, the processor
examines four kinds of privilege level and type information (see Figure 5-6):

•

The CPL. (Here, the CPL is the privilege level of the calling code segment; that is, the code segment that
contains the procedure that is making the call or jump.)

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CS Register
CPL
Segment Selector
For Code Segment
RPL
Destination Code
Segment Descriptor
DPL

Privilege
Check

C

Figure 5-6. Privilege Check for Control Transfer Without Using a Gate

•
•
•

The DPL of the segment descriptor for the destination code segment that contains the called procedure.
The RPL of the segment selector of the destination code segment.
The conforming (C) flag in the segment descriptor for the destination code segment, which determines whether
the segment is a conforming (C flag is set) or nonconforming (C flag is clear) code segment. See Section
3.4.5.1, “Code- and Data-Segment Descriptor Types,” for more information about this flag.

The rules that the processor uses to check the CPL, RPL, and DPL depends on the setting of the C flag, as described
in the following sections.

5.8.1.1

Accessing Nonconforming Code Segments

When accessing nonconforming code segments, the CPL of the calling procedure must be equal to the DPL of the
destination code segment; otherwise, the processor generates a general-protection exception (#GP). For example
in Figure 5-7:

•

Code segment C is a nonconforming code segment. A procedure in code segment A can call a procedure in code
segment C (using segment selector C1) because they are at the same privilege level (CPL of code segment A is
equal to the DPL of code segment C).

•

A procedure in code segment B cannot call a procedure in code segment C (using segment selector C2 or C1)
because the two code segments are at different privilege levels.

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PROTECTION

Code
Segment B
CPL=3

3

Segment Sel. D2
RPL=3
Segment Sel. C2
RPL=3

Lowest Privilege
Code
Segment A
CPL=2

2

Segment Sel. C1
RPL=2
Segment Sel. D1
RPL=2

Code
Segment C
DPL=2
Nonconforming
Code Segment

Code
Segment D
DPL=1
Conforming
Code Segment

1

0

Highest Privilege

Figure 5-7. Examples of Accessing Conforming and Nonconforming Code Segments From Various Privilege Levels
The RPL of the segment selector that points to a nonconforming code segment has a limited effect on the privilege
check. The RPL must be numerically less than or equal to the CPL of the calling procedure for a successful control
transfer to occur. So, in the example in Figure 5-7, the RPLs of segment selectors C1 and C2 could legally be set to
0, 1, or 2, but not to 3.
When the segment selector of a nonconforming code segment is loaded into the CS register, the privilege level field
is not changed; that is, it remains at the CPL (which is the privilege level of the calling procedure). This is true, even
if the RPL of the segment selector is different from the CPL.

5.8.1.2

Accessing Conforming Code Segments

When accessing conforming code segments, the CPL of the calling procedure may be numerically equal to or
greater than (less privileged) the DPL of the destination code segment; the processor generates a general-protection exception (#GP) only if the CPL is less than the DPL. (The segment selector RPL for the destination code
segment is not checked if the segment is a conforming code segment.)
In the example in Figure 5-7, code segment D is a conforming code segment. Therefore, calling procedures in both
code segment A and B can access code segment D (using either segment selector D1 or D2, respectively), because
they both have CPLs that are greater than or equal to the DPL of the conforming code segment. For conforming
code segments, the DPL represents the numerically lowest privilege level that a calling procedure may
be at to successfully make a call to the code segment.
(Note that segments selectors D1 and D2 are identical except for their respective RPLs. But since RPLs are not
checked when accessing conforming code segments, the two segment selectors are essentially interchangeable.)
When program control is transferred to a conforming code segment, the CPL does not change, even if the DPL of
the destination code segment is less than the CPL. This situation is the only one where the CPL may be different
from the DPL of the current code segment. Also, since the CPL does not change, no stack switch occurs.
Conforming segments are used for code modules such as math libraries and exception handlers, which support
applications but do not require access to protected system facilities. These modules are part of the operating
system or executive software, but they can be executed at numerically higher privilege levels (less privileged
levels). Keeping the CPL at the level of a calling code segment when switching to a conforming code segment
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prevents an application program from accessing nonconforming code segments while at the privilege level (DPL) of
a conforming code segment and thus prevents it from accessing more privileged data.
Most code segments are nonconforming. For these segments, program control can be transferred only to code
segments at the same level of privilege, unless the transfer is carried out through a call gate, as described in the
following sections.

5.8.2

Gate Descriptors

To provide controlled access to code segments with different privilege levels, the processor provides special set of
descriptors called gate descriptors. There are four kinds of gate descriptors:

•
•
•
•

Call gates
Trap gates
Interrupt gates
Task gates

Task gates are used for task switching and are discussed in Chapter 7, “Task Management”. Trap and interrupt
gates are special kinds of call gates used for calling exception and interrupt handlers. The are described in Chapter
6, “Interrupt and Exception Handling.” This chapter is concerned only with call gates.

5.8.3

Call Gates

Call gates facilitate controlled transfers of program control between different privilege levels. They are typically
used only in operating systems or executives that use the privilege-level protection mechanism. Call gates are also
useful for transferring program control between 16-bit and 32-bit code segments, as described in Section 21.4,
“Transferring Control Among Mixed-Size Code Segments.”
Figure 5-8 shows the format of a call-gate descriptor. A call-gate descriptor may reside in the GDT or in an LDT, but
not in the interrupt descriptor table (IDT). It performs six functions:

•
•
•

It specifies the code segment to be accessed.
It defines an entry point for a procedure in the specified code segment.
It specifies the privilege level required for a caller trying to access the procedure.

31

16 15 14 13 12 11

Offset in Segment 31:16
31

P

D
P
L

8 7

Type

6
0 0 0

0 1 1 0 0

16 15

Segment Selector

0

5 4

Param.
Count

4
0

Offset in Segment 15:00

0

DPL Descriptor Privilege Level
P
Gate Valid

Figure 5-8. Call-Gate Descriptor

•
•

If a stack switch occurs, it specifies the number of optional parameters to be copied between stacks.

•

It specifies whether the call-gate descriptor is valid.

It defines the size of values to be pushed onto the target stack: 16-bit gates force 16-bit pushes and 32-bit
gates force 32-bit pushes.

The segment selector field in a call gate specifies the code segment to be accessed. The offset field specifies the
entry point in the code segment. This entry point is generally to the first instruction of a specific procedure. The DPL
field indicates the privilege level of the call gate, which in turn is the privilege level required to access the selected
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procedure through the gate. The P flag indicates whether the call-gate descriptor is valid. (The presence of the code
segment to which the gate points is indicated by the P flag in the code segment’s descriptor.) The parameter count
field indicates the number of parameters to copy from the calling procedures stack to the new stack if a stack
switch occurs (see Section 5.8.5, “Stack Switching”). The parameter count specifies the number of words for 16bit call gates and doublewords for 32-bit call gates.
Note that the P flag in a gate descriptor is normally always set to 1. If it is set to 0, a not present (#NP) exception
is generated when a program attempts to access the descriptor. The operating system can use the P flag for special
purposes. For example, it could be used to track the number of times the gate is used. Here, the P flag is initially
set to 0 causing a trap to the not-present exception handler. The exception handler then increments a counter and
sets the P flag to 1, so that on returning from the handler, the gate descriptor will be valid.

5.8.3.1

IA-32e Mode Call Gates

Call-gate descriptors in 32-bit mode provide a 32-bit offset for the instruction pointer (EIP); 64-bit extensions
double the size of 32-bit mode call gates in order to store 64-bit instruction pointers (RIP). See Figure 5-9:

•

The first eight bytes (bytes 7:0) of a 64-bit mode call gate are similar but not identical to legacy 32-bit mode
call gates. The parameter-copy-count field has been removed.

•

Bytes 11:8 hold the upper 32 bits of the target-segment offset in canonical form. A general-protection
exception (#GP) is generated if software attempts to use a call gate with a target offset that is not in canonical
form.

•

16-byte descriptors may reside in the same descriptor table with 16-bit and 32-bit descriptors. A type field,
used for consistency checking, is defined in bits 12:8 of the 64-bit descriptor’s highest dword (cleared to zero).
A general-protection exception (#GP) results if an attempt is made to access the upper half of a 64-bit mode
descriptor as a 32-bit mode descriptor.

13 12 11 10 9 8 7

31

Type

Reserved

0

Reserved

12

0 0 0 0 0
31

0

8

Offset in Segment 63:31

31

Offset in Segment 31:16
31

P

D
P
L

0

8 7

16 15 14 13 12 11

Type

0

16 15

Segment Selector

.

4

0 1 1 0 0
0

Offset in Segment 15:00

0

DPL Descriptor Privilege Level
P
Gate Valid

Figure 5-9. Call-Gate Descriptor in IA-32e Mode

•

Target code segments referenced by a 64-bit call gate must be 64-bit code segments (CS.L = 1, CS.D = 0). If
not, the reference generates a general-protection exception, #GP (CS selector).

•

Only 64-bit mode call gates can be referenced in IA-32e mode (64-bit mode and compatibility mode). The
legacy 32-bit mode call gate type (0CH) is redefined in IA-32e mode as a 64-bit call-gate type; no 32-bit callgate type exists in IA-32e mode.

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•

If a far call references a 16-bit call gate type (04H) in IA-32e mode, a general-protection exception (#GP) is
generated.

When a call references a 64-bit mode call gate, actions taken are identical to those taken in 32-bit mode, with the
following exceptions:

•
•
•

Stack pushes are made in eight-byte increments.
A 64-bit RIP is pushed onto the stack.
Parameter copying is not performed.

Use a matching far-return instruction size for correct operation (returns from 64-bit calls must be performed with
a 64-bit operand-size return to process the stack correctly).

5.8.4

Accessing a Code Segment Through a Call Gate

To access a call gate, a far pointer to the gate is provided as a target operand in a CALL or JMP instruction. The
segment selector from this pointer identifies the call gate (see Figure 5-10); the offset from the pointer is required,
but not used or checked by the processor. (The offset can be set to any value.)
When the processor has accessed the call gate, it uses the segment selector from the call gate to locate the
segment descriptor for the destination code segment. (This segment descriptor can be in the GDT or the LDT.) It
then combines the base address from the code-segment descriptor with the offset from the call gate to form the
linear address of the procedure entry point in the code segment.
As shown in Figure 5-11, four different privilege levels are used to check the validity of a program control transfer
through a call gate:

•
•
•
•

The CPL (current privilege level).
The RPL (requestor's privilege level) of the call gate’s selector.
The DPL (descriptor privilege level) of the call gate descriptor.
The DPL of the segment descriptor of the destination code segment.

The C flag (conforming) in the segment descriptor for the destination code segment is also checked.

Far Pointer to Call Gate
Segment Selector

Offset
Required but not used by processor

Descriptor Table

Offset
Segment Selector

+

Base

Offset

Base

Base

Call-Gate
Descriptor

Code-Segment
Descriptor

Procedure
Entry Point

Figure 5-10. Call-Gate Mechanism

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CS Register
CPL

Call-Gate Selector
RPL

Call Gate (Descriptor)
DPL

Privilege
Check

Destination CodeSegment Descriptor
DPL

Figure 5-11. Privilege Check for Control Transfer with Call Gate
The privilege checking rules are different depending on whether the control transfer was initiated with a CALL or a
JMP instruction, as shown in Table 5-1.

Table 5-1. Privilege Check Rules for Call Gates
Instruction

Privilege Check Rules

CALL

CPL ≤ call gate DPL; RPL ≤ call gate DPL
Destination conforming code segment DPL ≤ CPL
Destination nonconforming code segment DPL ≤ CPL

JMP

CPL ≤ call gate DPL; RPL ≤ call gate DPL
Destination conforming code segment DPL ≤ CPL
Destination nonconforming code segment DPL = CPL

The DPL field of the call-gate descriptor specifies the numerically highest privilege level from which a calling procedure can access the call gate; that is, to access a call gate, the CPL of a calling procedure must be equal to or less
than the DPL of the call gate. For example, in Figure 5-15, call gate A has a DPL of 3. So calling procedures at all
CPLs (0 through 3) can access this call gate, which includes calling procedures in code segments A, B, and C. Call
gate B has a DPL of 2, so only calling procedures at a CPL or 0, 1, or 2 can access call gate B, which includes calling
procedures in code segments B and C. The dotted line shows that a calling procedure in code segment A cannot
access call gate B.
The RPL of the segment selector to a call gate must satisfy the same test as the CPL of the calling procedure; that
is, the RPL must be less than or equal to the DPL of the call gate. In the example in Figure 5-15, a calling procedure
in code segment C can access call gate B using gate selector B2 or B1, but it could not use gate selector B3 to
access call gate B.
If the privilege checks between the calling procedure and call gate are successful, the processor then checks the
DPL of the code-segment descriptor against the CPL of the calling procedure. Here, the privilege check rules vary
between CALL and JMP instructions. Only CALL instructions can use call gates to transfer program control to more
privileged (numerically lower privilege level) nonconforming code segments; that is, to nonconforming code
segments with a DPL less than the CPL. A JMP instruction can use a call gate only to transfer program control to a
nonconforming code segment with a DPL equal to the CPL. CALL and JMP instruction can both transfer program
control to a more privileged conforming code segment; that is, to a conforming code segment with a DPL less than
or equal to the CPL.
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If a call is made to a more privileged (numerically lower privilege level) nonconforming destination code segment,
the CPL is lowered to the DPL of the destination code segment and a stack switch occurs (see Section 5.8.5, “Stack
Switching”). If a call or jump is made to a more privileged conforming destination code segment, the CPL is not
changed and no stack switch occurs.

3

Code
Segment A

Gate Selector A
RPL=3

CPL=3

Gate Selector B3
RPL=3

Call
Gate A
DPL=3

Lowest Privilege
Code
Segment B
CPL=2

Gate Selector B1
RPL=2

Call
Gate B
DPL=2

2
Code
Segment C
CPL=1

Gate Selector B2
RPL=1
No Stack
Switch Occurs

1

Stack Switch
Occurs

Code
Segment D
DPL=0

0

Highest Privilege

Conforming
Code Segment

Code
Segment E
DPL=0
Nonconforming
Code Segment

Figure 5-12. Example of Accessing Call Gates At Various Privilege Levels
Call gates allow a single code segment to have procedures that can be accessed at different privilege levels. For
example, an operating system located in a code segment may have some services which are intended to be used
by both the operating system and application software (such as procedures for handling character I/O). Call gates
for these procedures can be set up that allow access at all privilege levels (0 through 3). More privileged call gates
(with DPLs of 0 or 1) can then be set up for other operating system services that are intended to be used only by
the operating system (such as procedures that initialize device drivers).

5.8.5

Stack Switching

Whenever a call gate is used to transfer program control to a more privileged nonconforming code segment (that
is, when the DPL of the nonconforming destination code segment is less than the CPL), the processor automatically
switches to the stack for the destination code segment’s privilege level. This stack switching is carried out to
prevent more privileged procedures from crashing due to insufficient stack space. It also prevents less privileged
procedures from interfering (by accident or intent) with more privileged procedures through a shared stack.
Each task must define up to 4 stacks: one for applications code (running at privilege level 3) and one for each of
the privilege levels 2, 1, and 0 that are used. (If only two privilege levels are used [3 and 0], then only two stacks
must be defined.) Each of these stacks is located in a separate segment and is identified with a segment selector
and an offset into the stack segment (a stack pointer).
The segment selector and stack pointer for the privilege level 3 stack is located in the SS and ESP registers, respectively, when privilege-level-3 code is being executed and is automatically stored on the called procedure’s stack
when a stack switch occurs.
Pointers to the privilege level 0, 1, and 2 stacks are stored in the TSS for the currently running task (see
Figure 7-2). Each of these pointers consists of a segment selector and a stack pointer (loaded into the ESP
register). These initial pointers are strictly read-only values. The processor does not change them while the task is
running. They are used only to create new stacks when calls are made to more privileged levels (numerically lower

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privilege levels). These stacks are disposed of when a return is made from the called procedure. The next time the
procedure is called, a new stack is created using the initial stack pointer. (The TSS does not specify a stack for privilege level 3 because the processor does not allow a transfer of program control from a procedure running at a CPL
of 0, 1, or 2 to a procedure running at a CPL of 3, except on a return.)
The operating system is responsible for creating stacks and stack-segment descriptors for all the privilege levels to
be used and for loading initial pointers for these stacks into the TSS. Each stack must be read/write accessible (as
specified in the type field of its segment descriptor) and must contain enough space (as specified in the limit field)
to hold the following items:

•
•
•

The contents of the SS, ESP, CS, and EIP registers for the calling procedure.
The parameters and temporary variables required by the called procedure.
The EFLAGS register and error code, when implicit calls are made to an exception or interrupt handler.

The stack will need to require enough space to contain many frames of these items, because procedures often call
other procedures, and an operating system may support nesting of multiple interrupts. Each stack should be large
enough to allow for the worst case nesting scenario at its privilege level.
(If the operating system does not use the processor’s multitasking mechanism, it still must create at least one TSS
for this stack-related purpose.)
When a procedure call through a call gate results in a change in privilege level, the processor performs the following
steps to switch stacks and begin execution of the called procedure at a new privilege level:
1. Uses the DPL of the destination code segment (the new CPL) to select a pointer to the new stack (segment
selector and stack pointer) from the TSS.
2. Reads the segment selector and stack pointer for the stack to be switched to from the current TSS. Any limit
violations detected while reading the stack-segment selector, stack pointer, or stack-segment descriptor cause
an invalid TSS (#TS) exception to be generated.
3. Checks the stack-segment descriptor for the proper privileges and type and generates an invalid TSS (#TS)
exception if violations are detected.
4. Temporarily saves the current values of the SS and ESP registers.
5. Loads the segment selector and stack pointer for the new stack in the SS and ESP registers.
6. Pushes the temporarily saved values for the SS and ESP registers (for the calling procedure) onto the new stack
(see Figure 5-13).
7. Copies the number of parameter specified in the parameter count field of the call gate from the calling
procedure’s stack to the new stack. If the count is 0, no parameters are copied.
8. Pushes the return instruction pointer (the current contents of the CS and EIP registers) onto the new stack.
9. Loads the segment selector for the new code segment and the new instruction pointer from the call gate into
the CS and EIP registers, respectively, and begins execution of the called procedure.
See the description of the CALL instruction in Chapter 3, Instruction Set Reference, in the IA-32 Intel Architecture
Software Developer’s Manual, Volume 2, for a detailed description of the privilege level checks and other protection
checks that the processor performs on a far call through a call gate.

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Calling Procedure’s Stack

Called Procedure’s Stack
Calling SS

Parameter 1

Calling ESP

Parameter 2

Parameter 1

Parameter 3

ESP

Parameter 2
Parameter 3
Calling CS
Calling EIP

ESP

Figure 5-13. Stack Switching During an Interprivilege-Level Call
The parameter count field in a call gate specifies the number of data items (up to 31) that the processor should
copy from the calling procedure’s stack to the stack of the called procedure. If more than 31 data items need to be
passed to the called procedure, one of the parameters can be a pointer to a data structure, or the saved contents
of the SS and ESP registers may be used to access parameters in the old stack space. The size of the data items
passed to the called procedure depends on the call gate size, as described in Section 5.8.3, “Call Gates.”

5.8.5.1

Stack Switching in 64-bit Mode

Although protection-check rules for call gates are unchanged from 32-bit mode, stack-switch changes in 64-bit
mode are different.
When stacks are switched as part of a 64-bit mode privilege-level change through a call gate, a new SS (stack
segment) descriptor is not loaded; 64-bit mode only loads an inner-level RSP from the TSS. The new SS is forced
to NULL and the SS selector’s RPL field is forced to the new CPL. The new SS is set to NULL in order to handle
nested far transfers (far CALL, INTn, interrupts and exceptions). The old SS and RSP are saved on the new stack.
On a subsequent far RET, the old SS is popped from the stack and loaded into the SS register. See Table 5-2.

Table 5-2. 64-Bit-Mode Stack Layout After Far CALL with CPL Change
32-bit Mode

IA-32e mode

Old SS Selector

+12

+24

Old SS Selector

Old ESP

+8

+16

Old RSP

CS Selector

+4

+8

Old CS Selector

EIP

0

0

RIP

< 4 Bytes >

ESP

RSP

< 8 Bytes >

In 64-bit mode, stack operations resulting from a privilege-level-changing far call or far return are eight-bytes wide
and change the RSP by eight. The mode does not support the automatic parameter-copy feature found in 32-bit
mode. The call-gate count field is ignored. Software can access the old stack, if necessary, by referencing the old
stack-segment selector and stack pointer saved on the new process stack.
In 64-bit mode, far RET is allowed to load a NULL SS under certain conditions. If the target mode is 64-bit mode
and the target CPL ≠ 3, IRET allows SS to be loaded with a NULL selector. If the called procedure itself is interrupted, the NULL SS is pushed on the stack frame. On the subsequent far RET, the NULL SS on the stack acts as a
flag to tell the processor not to load a new SS descriptor.
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5.8.6

Returning from a Called Procedure

The RET instruction can be used to perform a near return, a far return at the same privilege level, and a far return
to a different privilege level. This instruction is intended to execute returns from procedures that were called with
a CALL instruction. It does not support returns from a JMP instruction, because the JMP instruction does not save a
return instruction pointer on the stack.
A near return only transfers program control within the current code segment; therefore, the processor performs
only a limit check. When the processor pops the return instruction pointer from the stack into the EIP register, it
checks that the pointer does not exceed the limit of the current code segment.
On a far return at the same privilege level, the processor pops both a segment selector for the code segment being
returned to and a return instruction pointer from the stack. Under normal conditions, these pointers should be
valid, because they were pushed on the stack by the CALL instruction. However, the processor performs privilege
checks to detect situations where the current procedure might have altered the pointer or failed to maintain the
stack properly.
A far return that requires a privilege-level change is only allowed when returning to a less privileged level (that is,
the DPL of the return code segment is numerically greater than the CPL). The processor uses the RPL field from the
CS register value saved for the calling procedure (see Figure 5-13) to determine if a return to a numerically higher
privilege level is required. If the RPL is numerically greater (less privileged) than the CPL, a return across privilege
levels occurs.
The processor performs the following steps when performing a far return to a calling procedure (see Figures 6-2
and 6-4 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for an illustration of the
stack contents prior to and after a return):
1. Checks the RPL field of the saved CS register value to determine if a privilege level change is required on the
return.
2. Loads the CS and EIP registers with the values on the called procedure’s stack. (Type and privilege level checks
are performed on the code-segment descriptor and RPL of the code- segment selector.)
3. (If the RET instruction includes a parameter count operand and the return requires a privilege level change.)
Adds the parameter count (in bytes obtained from the RET instruction) to the current ESP register value (after
popping the CS and EIP values), to step past the parameters on the called procedure’s stack. The resulting
value in the ESP register points to the saved SS and ESP values for the calling procedure’s stack. (Note that the
byte count in the RET instruction must be chosen to match the parameter count in the call gate that the calling
procedure referenced when it made the original call multiplied by the size of the parameters.)
4. (If the return requires a privilege level change.) Loads the SS and ESP registers with the saved SS and ESP
values and switches back to the calling procedure’s stack. The SS and ESP values for the called procedure’s
stack are discarded. Any limit violations detected while loading the stack-segment selector or stack pointer
cause a general-protection exception (#GP) to be generated. The new stack-segment descriptor is also checked
for type and privilege violations.
5. (If the RET instruction includes a parameter count operand.) Adds the parameter count (in bytes obtained from
the RET instruction) to the current ESP register value, to step past the parameters on the calling procedure’s
stack. The resulting ESP value is not checked against the limit of the stack segment. If the ESP value is beyond
the limit, that fact is not recognized until the next stack operation.
6. (If the return requires a privilege level change.) Checks the contents of the DS, ES, FS, and GS segment
registers. If any of these registers refer to segments whose DPL is less than the new CPL (excluding conforming
code segments), the segment register is loaded with a null segment selector.
See the description of the RET instruction in Chapter 4 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B, for a detailed description of the privilege level checks and other protection checks that
the processor performs on a far return.

5.8.7

Performing Fast Calls to System Procedures with the
SYSENTER and SYSEXIT Instructions

The SYSENTER and SYSEXIT instructions were introduced into the IA-32 architecture in the Pentium II processors
for the purpose of providing a fast (low overhead) mechanism for calling operating system or executive procedures.
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SYSENTER is intended for use by user code running at privilege level 3 to access operating system or executive
procedures running at privilege level 0. SYSEXIT is intended for use by privilege level 0 operating system or executive procedures for fast returns to privilege level 3 user code. SYSENTER can be executed from privilege levels 3,
2, 1, or 0; SYSEXIT can only be executed from privilege level 0.
The SYSENTER and SYSEXIT instructions are companion instructions, but they do not constitute a call/return pair.
This is because SYSENTER does not save any state information for use by SYSEXIT on a return.
The target instruction and stack pointer for these instructions are not specified through instruction operands.
Instead, they are specified through parameters entered in MSRs and general-purpose registers.
For SYSENTER, target fields are generated using the following sources:

•
•
•
•

Target code segment — Reads this from IA32_SYSENTER_CS.
Target instruction — Reads this from IA32_SYSENTER_EIP.
Stack segment — Computed by adding 8 to the value in IA32_SYSENTER_CS.
Stack pointer — Reads this from the IA32_SYSENTER_ESP.

For SYSEXIT, target fields are generated using the following sources:

•
•
•
•

Target code segment — Computed by adding 16 to the value in the IA32_SYSENTER_CS.
Target instruction — Reads this from EDX.
Stack segment — Computed by adding 24 to the value in IA32_SYSENTER_CS.
Stack pointer — Reads this from ECX.

The SYSENTER and SYSEXIT instructions preform “fast” calls and returns because they force the processor into a
predefined privilege level 0 state when SYSENTER is executed and into a predefined privilege level 3 state when
SYSEXIT is executed. By forcing predefined and consistent processor states, the number of privilege checks ordinarily required to perform a far call to another privilege levels are greatly reduced. Also, by predefining the target
context state in MSRs and general-purpose registers eliminates all memory accesses except when fetching the
target code.
Any additional state that needs to be saved to allow a return to the calling procedure must be saved explicitly by
the calling procedure or be predefined through programming conventions.

5.8.7.1

SYSENTER and SYSEXIT Instructions in IA-32e Mode

For Intel 64 processors, the SYSENTER and SYSEXIT instructions are enhanced to allow fast system calls from user
code running at privilege level 3 (in compatibility mode or 64-bit mode) to 64-bit executive procedures running at
privilege level 0. IA32_SYSENTER_EIP MSR and IA32_SYSENTER_ESP MSR are expanded to hold 64-bit addresses.
If IA-32e mode is inactive, only the lower 32-bit addresses stored in these MSRs are used. The WRMSR instruction
ensures that the addresses stored in these MSRs are canonical. Note that, in 64-bit mode, IA32_SYSENTER_CS
must not contain a NULL selector.
When SYSENTER transfers control, the following fields are generated and bits set:

•
•
•
•
•
•

Target code segment — Reads non-NULL selector from IA32_SYSENTER_CS.
New CS attributes — CS base = 0, CS limit = FFFFFFFFH.
Target instruction — Reads 64-bit canonical address from IA32_SYSENTER_EIP.
Stack segment — Computed by adding 8 to the value from IA32_SYSENTER_CS.
Stack pointer — Reads 64-bit canonical address from IA32_SYSENTER_ESP.
New SS attributes — SS base = 0, SS limit = FFFFFFFFH.

When the SYSEXIT instruction transfers control to 64-bit mode user code using REX.W, the following fields are
generated and bits set:

•
•
•
•

Target code segment — Computed by adding 32 to the value in IA32_SYSENTER_CS.
New CS attributes — L-bit = 1 (go to 64-bit mode).
Target instruction — Reads 64-bit canonical address in RDX.
Stack segment — Computed by adding 40 to the value of IA32_SYSENTER_CS.

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•

Stack pointer — Update RSP using 64-bit canonical address in RCX.

When SYSEXIT transfers control to compatibility mode user code when the operand size attribute is 32 bits, the
following fields are generated and bits set:

•
•
•
•
•

Target code segment — Computed by adding 16 to the value in IA32_SYSENTER_CS.
New CS attributes — L-bit = 0 (go to compatibility mode).
Target instruction — Fetch the target instruction from 32-bit address in EDX.
Stack segment — Computed by adding 24 to the value in IA32_SYSENTER_CS.
Stack pointer — Update ESP from 32-bit address in ECX.

5.8.8

Fast System Calls in 64-Bit Mode

The SYSCALL and SYSRET instructions are designed for operating systems that use a flat memory model (segmentation is not used). The instructions, along with SYSENTER and SYSEXIT, are suited for IA-32e mode operation.
SYSCALL and SYSRET, however, are not supported in compatibility mode (or in protected mode). Use CPUID to
check if SYSCALL and SYSRET are available (CPUID.80000001H.EDX[bit 11] = 1).
SYSCALL is intended for use by user code running at privilege level 3 to access operating system or executive
procedures running at privilege level 0. SYSRET is intended for use by privilege level 0 operating system or executive procedures for fast returns to privilege level 3 user code.
Stack pointers for SYSCALL/SYSRET are not specified through model specific registers. The clearing of bits in
RFLAGS is programmable rather than fixed. SYSCALL/SYSRET save and restore the RFLAGS register.
For SYSCALL, the processor saves RFLAGS into R11 and the RIP of the next instruction into RCX; it then gets the
privilege-level 0 target code segment, instruction pointer, stack segment, and flags as follows:

•
•

Target code segment — Reads a non-NULL selector from IA32_STAR[47:32].

•
•

Stack segment — Computed by adding 8 to the value in IA32_STAR[47:32].

Target instruction pointer — Reads a 64-bit address from IA32_LSTAR. (The WRMSR instruction ensures
that the value of the IA32_LSTAR MSR is canonical.)
Flags — The processor sets RFLAGS to the logical-AND of its current value with the complement of the value in
the IA32_FMASK MSR.

When SYSRET transfers control to 64-bit mode user code using REX.W, the processor gets the privilege level 3
target code segment, instruction pointer, stack segment, and flags as follows:

•
•
•
•

Target code segment — Reads a non-NULL selector from IA32_STAR[63:48] + 16.
Target instruction pointer — Copies the value in RCX into RIP.
Stack segment — IA32_STAR[63:48] + 8.
EFLAGS — Loaded from R11.

When SYSRET transfers control to 32-bit mode user code using a 32-bit operand size, the processor gets the privilege level 3 target code segment, instruction pointer, stack segment, and flags as follows:

•
•
•
•

Target code segment — Reads a non-NULL selector from IA32_STAR[63:48].
Target instruction pointer — Copies the value in ECX into EIP.
Stack segment — IA32_STAR[63:48] + 8.
EFLAGS — Loaded from R11.

It is the responsibility of the OS to ensure the descriptors in the GDT/LDT correspond to the selectors loaded by
SYSCALL/SYSRET (consistent with the base, limit, and attribute values forced by the instructions).
See Figure 5-14 for the layout of IA32_STAR, IA32_LSTAR and IA32_FMASK.

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63

0

32 31
SYSCALL EFLAGS Mask

Reserved

IA32_FMASK
63

0

Target RIP for 64-bit Mode Calling Program

IA32_LSTAR
63

32 31

48 47

SYSRET CS and SS

SYSCALL CS and SS

0
Reserved

IA32_STAR

Figure 5-14. MSRs Used by SYSCALL and SYSRET
The SYSCALL instruction does not save the stack pointer, and the SYSRET instruction does not restore it. It is likely
that the OS system-call handler will change the stack pointer from the user stack to the OS stack. If so, it is the
responsibility of software first to save the user stack pointer. This might be done by user code, prior to executing
SYSCALL, or by the OS system-call handler after SYSCALL.
Because the SYSRET instruction does not modify the stack pointer, it is necessary for software to switch back to the
user stack. The OS may load the user stack pointer (if it was saved after SYSCALL) before executing SYSRET; alternatively, user code may load the stack pointer (if it was saved before SYSCALL) after receiving control from
SYSRET.
If the OS loads the stack pointer before executing SYSRET, it must ensure that the handler of any interrupt or
exception delivered between restoring the stack pointer and successful execution of SYSRET is not invoked with the
user stack. It can do so using approaches such as the following:

•

External interrupts. The OS can prevent an external interrupt from being delivered by clearing EFLAGS.IF
before loading the user stack pointer.

•

Nonmaskable interrupts (NMIs). The OS can ensure that the NMI handler is invoked with the correct stack by
using the interrupt stack table (IST) mechanism for gate 2 (NMI) in the IDT (see Section 6.14.5, “Interrupt
Stack Table”).

•

General-protection exceptions (#GP). The SYSRET instruction generates #GP(0) if the value of RCX is not
canonical. The OS can address this possibility using one or more of the following approaches:
— Confirming that the value of RCX is canonical before executing SYSRET.
— Using paging to ensure that the SYSCALL instruction will never save a non-canonical value into RCX.
— Using the IST mechanism for gate 13 (#GP) in the IDT.

5.9

PRIVILEGED INSTRUCTIONS

Some of the system instructions (called “privileged instructions”) are protected from use by application programs.
The privileged instructions control system functions (such as the loading of system registers). They can be
executed only when the CPL is 0 (most privileged). If one of these instructions is executed when the CPL is not 0,
a general-protection exception (#GP) is generated. The following system instructions are privileged instructions:

•
•

LGDT — Load GDT register.
LLDT — Load LDT register.
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•
•
•
•
•
•
•
•
•
•
•
•
•
•

LTR — Load task register.
LIDT — Load IDT register.
MOV (control registers) — Load and store control registers.
LMSW — Load machine status word.
CLTS — Clear task-switched flag in register CR0.
MOV (debug registers) — Load and store debug registers.
INVD — Invalidate cache, without writeback.
WBINVD — Invalidate cache, with writeback.
INVLPG —Invalidate TLB entry.
HLT— Halt processor.
RDMSR — Read Model-Specific Registers.
WRMSR —Write Model-Specific Registers.
RDPMC — Read Performance-Monitoring Counter.
RDTSC — Read Time-Stamp Counter.

Some of the privileged instructions are available only in the more recent families of Intel 64 and IA-32 processors
(see Section 22.13, “New Instructions In the Pentium and Later IA-32 Processors”).
The PCE and TSD flags in register CR4 (bits 4 and 2, respectively) enable the RDPMC and RDTSC instructions,
respectively, to be executed at any CPL.

5.10

POINTER VALIDATION

When operating in protected mode, the processor validates all pointers to enforce protection between segments
and maintain isolation between privilege levels. Pointer validation consists of the following checks:
1. Checking access rights to determine if the segment type is compatible with its use.
2. Checking read/write rights.
3. Checking if the pointer offset exceeds the segment limit.
4. Checking if the supplier of the pointer is allowed to access the segment.
5. Checking the offset alignment.
The processor automatically performs first, second, and third checks during instruction execution. Software must
explicitly request the fourth check by issuing an ARPL instruction. The fifth check (offset alignment) is performed
automatically at privilege level 3 if alignment checking is turned on. Offset alignment does not affect isolation of
privilege levels.

5.10.1

Checking Access Rights (LAR Instruction)

When the processor accesses a segment using a far pointer, it performs an access rights check on the segment
descriptor pointed to by the far pointer. This check is performed to determine if type and privilege level (DPL) of the
segment descriptor are compatible with the operation to be performed. For example, when making a far call in
protected mode, the segment-descriptor type must be for a conforming or nonconforming code segment, a call
gate, a task gate, or a TSS. Then, if the call is to a nonconforming code segment, the DPL of the code segment must
be equal to the CPL, and the RPL of the code segment’s segment selector must be less than or equal to the DPL. If
type or privilege level are found to be incompatible, the appropriate exception is generated.
To prevent type incompatibility exceptions from being generated, software can check the access rights of a
segment descriptor using the LAR (load access rights) instruction. The LAR instruction specifies the segment
selector for the segment descriptor whose access rights are to be checked and a destination register. The instruction then performs the following operations:
1. Check that the segment selector is not null.
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2. Checks that the segment selector points to a segment descriptor that is within the descriptor table limit (GDT
or LDT).
3. Checks that the segment descriptor is a code, data, LDT, call gate, task gate, or TSS segment-descriptor type.
4. If the segment is not a conforming code segment, checks if the segment descriptor is visible at the CPL (that
is, if the CPL and the RPL of the segment selector are less than or equal to the DPL).
5. If the privilege level and type checks pass, loads the second doubleword of the segment descriptor into the
destination register (masked by the value 00FXFF00H, where X indicates that the corresponding 4 bits are
undefined) and sets the ZF flag in the EFLAGS register. If the segment selector is not visible at the current
privilege level or is an invalid type for the LAR instruction, the instruction does not modify the destination
register and clears the ZF flag.
Once loaded in the destination register, software can preform additional checks on the access rights information.

5.10.2

Checking Read/Write Rights (VERR and VERW Instructions)

When the processor accesses any code or data segment it checks the read/write privileges assigned to the
segment to verify that the intended read or write operation is allowed. Software can check read/write rights using
the VERR (verify for reading) and VERW (verify for writing) instructions. Both these instructions specify the
segment selector for the segment being checked. The instructions then perform the following operations:
1. Check that the segment selector is not null.
2. Checks that the segment selector points to a segment descriptor that is within the descriptor table limit (GDT
or LDT).
3. Checks that the segment descriptor is a code or data-segment descriptor type.
4. If the segment is not a conforming code segment, checks if the segment descriptor is visible at the CPL (that
is, if the CPL and the RPL of the segment selector are less than or equal to the DPL).
5. Checks that the segment is readable (for the VERR instruction) or writable (for the VERW) instruction.
The VERR instruction sets the ZF flag in the EFLAGS register if the segment is visible at the CPL and readable; the
VERW sets the ZF flag if the segment is visible and writable. (Code segments are never writable.) The ZF flag is
cleared if any of these checks fail.

5.10.3

Checking That the Pointer Offset Is Within Limits (LSL Instruction)

When the processor accesses any segment it performs a limit check to insure that the offset is within the limit of
the segment. Software can perform this limit check using the LSL (load segment limit) instruction. Like the LAR
instruction, the LSL instruction specifies the segment selector for the segment descriptor whose limit is to be
checked and a destination register. The instruction then performs the following operations:
1. Check that the segment selector is not null.
2. Checks that the segment selector points to a segment descriptor that is within the descriptor table limit (GDT
or LDT).
3. Checks that the segment descriptor is a code, data, LDT, or TSS segment-descriptor type.
4. If the segment is not a conforming code segment, checks if the segment descriptor is visible at the CPL (that
is, if the CPL and the RPL of the segment selector less than or equal to the DPL).
5. If the privilege level and type checks pass, loads the unscrambled limit (the limit scaled according to the setting
of the G flag in the segment descriptor) into the destination register and sets the ZF flag in the EFLAGS register.
If the segment selector is not visible at the current privilege level or is an invalid type for the LSL instruction,
the instruction does not modify the destination register and clears the ZF flag.
Once loaded in the destination register, software can compare the segment limit with the offset of a pointer.

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5.10.4

Checking Caller Access Privileges (ARPL Instruction)

The requestor’s privilege level (RPL) field of a segment selector is intended to carry the privilege level of a calling
procedure (the calling procedure’s CPL) to a called procedure. The called procedure then uses the RPL to determine
if access to a segment is allowed. The RPL is said to “weaken” the privilege level of the called procedure to that of
the RPL.
Operating-system procedures typically use the RPL to prevent less privileged application programs from accessing
data located in more privileged segments. When an operating-system procedure (the called procedure) receives a
segment selector from an application program (the calling procedure), it sets the segment selector’s RPL to the
privilege level of the calling procedure. Then, when the operating system uses the segment selector to access its
associated segment, the processor performs privilege checks using the calling procedure’s privilege level (stored in
the RPL) rather than the numerically lower privilege level (the CPL) of the operating-system procedure. The RPL
thus insures that the operating system does not access a segment on behalf of an application program unless that
program itself has access to the segment.
Figure 5-15 shows an example of how the processor uses the RPL field. In this example, an application program
(located in code segment A) possesses a segment selector (segment selector D1) that points to a privileged data
structure (that is, a data structure located in a data segment D at privilege level 0).
The application program cannot access data segment D, because it does not have sufficient privilege, but the operating system (located in code segment C) can. So, in an attempt to access data segment D, the application
program executes a call to the operating system and passes segment selector D1 to the operating system as a
parameter on the stack. Before passing the segment selector, the (well behaved) application program sets the RPL
of the segment selector to its current privilege level (which in this example is 3). If the operating system attempts
to access data segment D using segment selector D1, the processor compares the CPL (which is now 0 following
the call), the RPL of segment selector D1, and the DPL of data segment D (which is 0). Since the RPL is greater than
the DPL, access to data segment D is denied. The processor’s protection mechanism thus protects data segment D
from access by the operating system, because application program’s privilege level (represented by the RPL of
segment selector B) is greater than the DPL of data segment D.

Passed as a
parameter on
the stack.
Application Program

3

Code
Segment A
CPL=3
Lowest Privilege

Gate Selector B
RPL=3

Call
Gate B
DPL=3

Segment Sel. D1
RPL=3

2
Access
not
allowed

1
Code
Operating Segment C
System
DPL=0

0

Highest Privilege

Segment Sel. D2
RPL=0
Access
allowed

Data
Segment D
DPL=0

Figure 5-15. Use of RPL to Weaken Privilege Level of Called Procedure

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Now assume that instead of setting the RPL of the segment selector to 3, the application program sets the RPL to
0 (segment selector D2). The operating system can now access data segment D, because its CPL and the RPL of
segment selector D2 are both equal to the DPL of data segment D.
Because the application program is able to change the RPL of a segment selector to any value, it can potentially use
a procedure operating at a numerically lower privilege level to access a protected data structure. This ability to
lower the RPL of a segment selector breaches the processor’s protection mechanism.
Because a called procedure cannot rely on the calling procedure to set the RPL correctly, operating-system procedures (executing at numerically lower privilege-levels) that receive segment selectors from numerically higher
privilege-level procedures need to test the RPL of the segment selector to determine if it is at the appropriate level.
The ARPL (adjust requested privilege level) instruction is provided for this purpose. This instruction adjusts the RPL
of one segment selector to match that of another segment selector.
The example in Figure 5-15 demonstrates how the ARPL instruction is intended to be used. When the operatingsystem receives segment selector D2 from the application program, it uses the ARPL instruction to compare the
RPL of the segment selector with the privilege level of the application program (represented by the code-segment
selector pushed onto the stack). If the RPL is less than application program’s privilege level, the ARPL instruction
changes the RPL of the segment selector to match the privilege level of the application program (segment selector
D1). Using this instruction thus prevents a procedure running at a numerically higher privilege level from
accessing numerically lower privilege-level (more privileged) segments by lowering the RPL of a segment selector.
Note that the privilege level of the application program can be determined by reading the RPL field of the segment
selector for the application-program’s code segment. This segment selector is stored on the stack as part of the call
to the operating system. The operating system can copy the segment selector from the stack into a register for
use as an operand for the ARPL instruction.

5.10.5

Checking Alignment

When the CPL is 3, alignment of memory references can be checked by setting the AM flag in the CR0 register and
the AC flag in the EFLAGS register. Unaligned memory references generate alignment exceptions (#AC). The
processor does not generate alignment exceptions when operating at privilege level 0, 1, or 2. See Table 6-7 for a
description of the alignment requirements when alignment checking is enabled.

5.11

PAGE-LEVEL PROTECTION

Page-level protection can be used alone or applied to segments. When page-level protection is used with the flat
memory model, it allows supervisor code and data (the operating system or executive) to be protected from user
code and data (application programs). It also allows pages containing code to be write protected. When the
segment- and page-level protection are combined, page-level read/write protection allows more protection granularity within segments.
With page-level protection (as with segment-level protection) each memory reference is checked to verify that
protection checks are satisfied. All checks are made before the memory cycle is started, and any violation prevents
the cycle from starting and results in a page-fault exception being generated. Because checks are performed in
parallel with address translation, there is no performance penalty.
The processor performs two page-level protection checks:

•
•

Restriction of addressable domain (supervisor and user modes).
Page type (read only or read/write).

Violations of either of these checks results in a page-fault exception being generated. See Chapter 6, “Interrupt
14—Page-Fault Exception (#PF),” for an explanation of the page-fault exception mechanism. This chapter
describes the protection violations which lead to page-fault exceptions.

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5.11.1

Page-Protection Flags

Protection information for pages is contained in two flags in a paging-structure entry (see Chapter 4): the
read/write flag (bit 1) and the user/supervisor flag (bit 2). The protection checks use the flags in all paging structures.

5.11.2

Restricting Addressable Domain

The page-level protection mechanism allows restricting access to pages based on two privilege levels:

•

Supervisor mode (U/S flag is 0)—(Most privileged) For the operating system or executive, other system
software (such as device drivers), and protected system data (such as page tables).

•

User mode (U/S flag is 1)—(Least privileged) For application code and data.

The segment privilege levels map to the page privilege levels as follows. If the processor is currently operating at
a CPL of 0, 1, or 2, it is in supervisor mode; if it is operating at a CPL of 3, it is in user mode. When the processor is
in supervisor mode, it can access all pages; when in user mode, it can access only user-level pages. (Note that the
WP flag in control register CR0 modifies the supervisor permissions, as described in Section 5.11.3, “Page Type.”)
Note that to use the page-level protection mechanism, code and data segments must be set up for at least two
segment-based privilege levels: level 0 for supervisor code and data segments and level 3 for user code and data
segments. (In this model, the stacks are placed in the data segments.) To minimize the use of segments, a flat
memory model can be used (see Section 3.2.1, “Basic Flat Model”).
Here, the user and supervisor code and data segments all begin at address zero in the linear address space and
overlay each other. With this arrangement, operating-system code (running at the supervisor level) and application
code (running at the user level) can execute as if there are no segments. Protection between operating-system and
application code and data is provided by the processor’s page-level protection mechanism.

5.11.3

Page Type

The page-level protection mechanism recognizes two page types:

•
•

Read-only access (R/W flag is 0).
Read/write access (R/W flag is 1).

When the processor is in supervisor mode and the WP flag in register CR0 is clear (its state following reset initialization), all pages are both readable and writable (write-protection is ignored). When the processor is in user mode,
it can write only to user-mode pages that are read/write accessible. User-mode pages which are read/write or
read-only are readable; supervisor-mode pages are neither readable nor writable from user mode. A page-fault
exception is generated on any attempt to violate the protection rules.
Starting with the P6 family, Intel processors allow user-mode pages to be write-protected against supervisor-mode
access. Setting CR0.WP = 1 enables supervisor-mode sensitivity to write protected pages. If CR0.WP = 1, readonly pages are not writable from any privilege level. This supervisor write-protect feature is useful for implementing a “copy-on-write” strategy used by some operating systems, such as UNIX*, for task creation (also called
forking or spawning). When a new task is created, it is possible to copy the entire address space of the parent task.
This gives the child task a complete, duplicate set of the parent's segments and pages. An alternative copy-onwrite strategy saves memory space and time by mapping the child's segments and pages to the same segments
and pages used by the parent task. A private copy of a page gets created only when one of the tasks writes to the
page. By using the WP flag and marking the shared pages as read-only, the supervisor can detect an attempt to
write to a page, and can copy the page at that time.

5.11.4

Combining Protection of Both Levels of Page Tables

For any one page, the protection attributes of its page-directory entry (first-level page table) may differ from those
of its page-table entry (second-level page table). The processor checks the protection for a page in both its pagedirectory and the page-table entries. Table 5-3 shows the protection provided by the possible combinations of
protection attributes when the WP flag is clear.

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5.11.5

Overrides to Page Protection

The following types of memory accesses are checked as if they are privilege-level 0 accesses, regardless of the CPL
at which the processor is currently operating:

•
•

Access to segment descriptors in the GDT, LDT, or IDT.
Access to an inner-privilege-level stack during an inter-privilege-level call or a call to in exception or interrupt
handler, when a change of privilege level occurs.

5.12

COMBINING PAGE AND SEGMENT PROTECTION

When paging is enabled, the processor evaluates segment protection first, then evaluates page protection. If the
processor detects a protection violation at either the segment level or the page level, the memory access is not
carried out and an exception is generated. If an exception is generated by segmentation, no paging exception is
generated.
Page-level protections cannot be used to override segment-level protection. For example, a code segment is by
definition not writable. If a code segment is paged, setting the R/W flag for the pages to read-write does not make
the pages writable. Attempts to write into the pages will be blocked by segment-level protection checks.
Page-level protection can be used to enhance segment-level protection. For example, if a large read-write data
segment is paged, the page-protection mechanism can be used to write-protect individual pages.

Table 5-3. Combined Page-Directory and Page-Table Protection
Page-Directory Entry

Page-Table Entry

Combined Effect

Privilege

Access Type

Privilege

Access Type

Privilege

Access Type

User

Read-Only

User

Read-Only

User

Read-Only

User

Read-Only

User

Read-Write

User

Read-Only

User

Read-Write

User

Read-Only

User

Read-Only

User

Read-Write

User

Read-Write

User

Read/Write

User

Read-Only

Supervisor

Read-Only

Supervisor

Read/Write*

User

Read-Only

Supervisor

Read-Write

Supervisor

Read/Write*

User

Read-Write

Supervisor

Read-Only

Supervisor

Read/Write*

User

Read-Write

Supervisor

Read-Write

Supervisor

Read/Write

Supervisor

Read-Only

User

Read-Only

Supervisor

Read/Write*

Supervisor

Read-Only

User

Read-Write

Supervisor

Read/Write*

Supervisor

Read-Write

User

Read-Only

Supervisor

Read/Write*

Supervisor

Read-Write

User

Read-Write

Supervisor

Read/Write

Supervisor

Read-Only

Supervisor

Read-Only

Supervisor

Read/Write*

Supervisor

Read-Only

Supervisor

Read-Write

Supervisor

Read/Write*

Supervisor

Read-Write

Supervisor

Read-Only

Supervisor

Read/Write*

Supervisor

Read-Write

Supervisor

Read-Write

Supervisor

Read/Write

NOTE:
* If CR0.WP = 1, access type is determined by the R/W flags of the page-directory and page-table entries. IF CR0.WP = 0, supervisor
privilege permits read-write access.

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5.13

PAGE-LEVEL PROTECTION AND EXECUTE-DISABLE BIT

In addition to page-level protection offered by the U/S and R/W flags, paging structures used with PAE paging and
4-level paging1 (see Chapter 4) provide the execute-disable bit. This bit offers additional protection for data pages.
An Intel 64 or IA-32 processor with the execute-disable bit capability can prevent data pages from being used by
malicious software to execute code. This capability is provided in:

•
•

32-bit protected mode with PAE enabled.
IA-32e mode.

While the execute-disable bit capability does not introduce new instructions, it does require operating systems to
use a PAE-enabled environment and establish a page-granular protection policy for memory pages.
If the execute-disable bit of a memory page is set, that page can be used only as data. An attempt to execute code
from a memory page with the execute-disable bit set causes a page-fault exception.
The execute-disable capability is supported only with PAE paging and 4-level paging. It is not supported with 32-bit
paging. Existing page-level protection mechanisms (see Section 5.11, “Page-Level Protection”) continue to apply
to memory pages independent of the execute-disable setting.

5.13.1

Detecting and Enabling the Execute-Disable Capability

Software can detect the presence of the execute-disable capability using the CPUID instruction.
CPUID.80000001H:EDX.NX [bit 20] = 1 indicates the capability is available.
If the capability is available, software can enable it by setting IA32_EFER.NXE[bit 11] to 1. IA32_EFER is available
if CPUID.80000001H.EDX[bit 20 or 29] = 1.
If the execute-disable capability is not available, a write to set IA32_EFER.NXE produces a #GP exception. See
Table 5-4.

Table 5-4. Extended Feature Enable MSR (IA32_EFER)
63:12

11

10

9

8

7:1

0

Reserved

Execute-disable bit
enable (NXE)

IA-32e mode
active (LMA)

Reserved

IA-32e mode
enable (LME)

Reserved

SysCall enable (SCE)

5.13.2

Execute-Disable Page Protection

The execute-disable bit in the paging structures enhances page protection for data pages. Instructions cannot be
fetched from a memory page if IA32_EFER.NXE =1 and the execute-disable bit is set in any of the paging-structure
entries used to map the page. Table 5-5 lists the valid usage of a page in relation to the value of execute-disable bit
(bit 63) of the corresponding entry in each level of the paging structures. Execute-disable protection can be activated using the execute-disable bit at any level of the paging structure, irrespective of the corresponding entry in
other levels. When execute-disable protection is not activated, the page can be used as code or data.

1. Earlier versions of this manual used the term “IA-32e paging” to identify 4-level paging.
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PROTECTION

Table 5-5. IA-32e Mode Page Level Protection Matrix
with Execute-Disable Bit Capability
Execute Disable Bit Value (Bit 63)

Valid Usage

PML4

PDP

PDE

PTE

Bit 63 = 1

*

*

*

Data

*

Bit 63 = 1

*

*

Data

*

*

Bit 63 = 1

*

Data

*

*

*

Bit 63 = 1

Data

Bit 63 = 0

Bit 63 = 0

Bit 63 = 0

Bit 63 = 0

Data/Code

NOTES:
* Value not checked.
In legacy PAE-enabled mode, Table 5-6 and Table 5-7 show the effect of setting the execute-disable bit for code
and data pages.

Table 5-6. Legacy PAE-Enabled 4-KByte Page Level Protection Matrix
with Execute-Disable Bit Capability
Execute Disable Bit Value (Bit 63)

Valid Usage

PDE

PTE

Bit 63 = 1

*

Data

*

Bit 63 = 1

Data

Bit 63 = 0

Bit 63 = 0

Data/Code

NOTE:
* Value not checked.

Table 5-7. Legacy PAE-Enabled 2-MByte Page Level Protection
with Execute-Disable Bit Capability
Execute Disable Bit Value (Bit 63)

Valid Usage

PDE
Bit 63 = 1

Data

Bit 63 = 0

Data/Code

5.13.3

Reserved Bit Checking

The processor enforces reserved bit checking in paging data structure entries. The bits being checked varies with
paging mode and may vary with the size of physical address space.
Table 5-8 shows the reserved bits that are checked when the execute disable bit capability is enabled (CR4.PAE = 1
and IA32_EFER.NXE = 1). Table 5-8 and Table 5-9 show the following paging modes:

•
•
•

Non-PAE 4-KByte paging: 4-KByte-page only paging (CR4.PAE = 0, CR4.PSE = 0).
PSE36: 4-KByte and 4-MByte pages (CR4.PAE = 0, CR4.PSE = 1).
PAE: 4-KByte and 2-MByte pages (CR4.PAE = 1, CR4.PSE = X).

The reserved bit checking depends on the physical address size supported by the implementation, which is
reported in CPUID.80000008H. See the table note.

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PROTECTION

Table 5-8. IA-32e Mode Page Level Protection Matrix with Execute-Disable Bit Capability Enabled
Mode

Paging Mode

Check Bits

32-bit

4-KByte paging (non-PAE)

No reserved bits checked

64-bit

PSE36 - PDE, 4-MByte page

Bit [21]

PSE36 - PDE, 4-KByte page

No reserved bits checked

PSE36 - PTE

No reserved bits checked

PAE - PDP table entry

Bits [63:MAXPHYADDR] & [8:5] & [2:1] *

PAE - PDE, 2-MByte page

Bits [62:MAXPHYADDR] & [20:13] *

PAE - PDE, 4-KByte page

Bits [62:MAXPHYADDR] *

PAE - PTE

Bits [62:MAXPHYADDR] *

PML4E

Bits [51:MAXPHYADDR] *

PDPTE

Bits [51:MAXPHYADDR] *

PDE, 2-MByte page

Bits [51:MAXPHYADDR] & [20:13] *

PDE, 4-KByte page

Bits [51:MAXPHYADDR] *

PTE

Bits [51:MAXPHYADDR] *

NOTES:
* MAXPHYADDR is the maximum physical address size and is indicated by CPUID.80000008H:EAX[bits 7-0].
If execute disable bit capability is not enabled or not available, reserved bit checking in 64-bit mode includes bit 63
and additional bits. This and reserved bit checking for legacy 32-bit paging modes are shown in Table 5-10.

Table 5-9. Reserved Bit Checking WIth Execute-Disable Bit Capability Not Enabled
Mode

Paging Mode

Check Bits

32-bit

KByte paging (non-PAE)

No reserved bits checked

PSE36 - PDE, 4-MByte page

Bit [21]

PSE36 - PDE, 4-KByte page

No reserved bits checked

PSE36 - PTE

No reserved bits checked

PAE - PDP table entry

Bits [63:MAXPHYADDR] & [8:5] & [2:1]*

PAE - PDE, 2-MByte page

Bits [63:MAXPHYADDR] & [20:13]*

PAE - PDE, 4-KByte page

Bits [63:MAXPHYADDR]*

PAE - PTE

Bits [63:MAXPHYADDR]*

PML4E

Bit [63], bits [51:MAXPHYADDR]*

64-bit

PDPTE

Bit [63], bits [51:MAXPHYADDR]*

PDE, 2-MByte page

Bit [63], bits [51:MAXPHYADDR] & [20:13]*

PDE, 4-KByte page

Bit [63], bits [51:MAXPHYADDR]*

PTE

Bit [63], bits [51:MAXPHYADDR]*

NOTES:
* MAXPHYADDR is the maximum physical address size and is indicated by CPUID.80000008H:EAX[bits 7-0].

5.13.4

Exception Handling

When execute disable bit capability is enabled (IA32_EFER.NXE = 1), conditions for a page fault to occur include
the same conditions that apply to an Intel 64 or IA-32 processor without execute disable bit capability plus the
following new condition: an instruction fetch to a linear address that translates to physical address in a memory
page that has the execute-disable bit set.

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PROTECTION

An Execute Disable Bit page fault can occur at all privilege levels. It can occur on any instruction fetch, including
(but not limited to): near branches, far branches, CALL/RET/INT/IRET execution, sequential instruction fetches,
and task switches. The execute-disable bit in the page translation mechanism is checked only when:

•
•

IA32_EFER.NXE = 1.
The instruction translation look-aside buffer (ITLB) is loaded with a page that is not already present in the ITLB.

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5-34 Vol. 3A

CHAPTER 6
INTERRUPT AND EXCEPTION HANDLING
This chapter describes the interrupt and exception-handling mechanism when operating in protected mode on an
Intel 64 or IA-32 processor. Most of the information provided here also applies to interrupt and exception mechanisms used in real-address, virtual-8086 mode, and 64-bit mode.
Chapter 20, “8086 Emulation,” describes information specific to interrupt and exception mechanisms in realaddress and virtual-8086 mode. Section 6.14, “Exception and Interrupt Handling in 64-bit Mode,” describes information specific to interrupt and exception mechanisms in IA-32e mode and 64-bit sub-mode.

6.1

INTERRUPT AND EXCEPTION OVERVIEW

Interrupts and exceptions are events that indicate that a condition exists somewhere in the system, the processor,
or within the currently executing program or task that requires the attention of a processor. They typically result in
a forced transfer of execution from the currently running program or task to a special software routine or task
called an interrupt handler or an exception handler. The action taken by a processor in response to an interrupt or
exception is referred to as servicing or handling the interrupt or exception.
Interrupts occur at random times during the execution of a program, in response to signals from hardware. System
hardware uses interrupts to handle events external to the processor, such as requests to service peripheral devices.
Software can also generate interrupts by executing the INT n instruction.
Exceptions occur when the processor detects an error condition while executing an instruction, such as division by
zero. The processor detects a variety of error conditions including protection violations, page faults, and internal
machine faults. The machine-check architecture of the Pentium 4, Intel Xeon, P6 family, and Pentium processors
also permits a machine-check exception to be generated when internal hardware errors and bus errors are
detected.
When an interrupt is received or an exception is detected, the currently running procedure or task is suspended
while the processor executes an interrupt or exception handler. When execution of the handler is complete, the
processor resumes execution of the interrupted procedure or task. The resumption of the interrupted procedure or
task happens without loss of program continuity, unless recovery from an exception was not possible or an interrupt caused the currently running program to be terminated.
This chapter describes the processor’s interrupt and exception-handling mechanism, when operating in protected
mode. A description of the exceptions and the conditions that cause them to be generated is given at the end of this
chapter.

6.2

EXCEPTION AND INTERRUPT VECTORS

To aid in handling exceptions and interrupts, each architecturally defined exception and each interrupt condition
requiring special handling by the processor is assigned a unique identification number, called a vector number. The
processor uses the vector number assigned to an exception or interrupt as an index into the interrupt descriptor
table (IDT). The table provides the entry point to an exception or interrupt handler (see Section 6.10, “Interrupt
Descriptor Table (IDT)”).
The allowable range for vector numbers is 0 to 255. Vector numbers in the range 0 through 31 are reserved by the
Intel 64 and IA-32 architectures for architecture-defined exceptions and interrupts. Not all of the vector numbers
in this range have a currently defined function. The unassigned vector numbers in this range are reserved. Do not
use the reserved vector numbers.
Vector numbers in the range 32 to 255 are designated as user-defined interrupts and are not reserved by the Intel
64 and IA-32 architecture. These interrupts are generally assigned to external I/O devices to enable those devices
to send interrupts to the processor through one of the external hardware interrupt mechanisms (see Section 6.3,
“Sources of Interrupts”).

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INTERRUPT AND EXCEPTION HANDLING

Table 6-1 shows vector number assignments for architecturally defined exceptions and for the NMI interrupt. This
table gives the exception type (see Section 6.5, “Exception Classifications”) and indicates whether an error code is
saved on the stack for the exception. The source of each predefined exception and the NMI interrupt is also given.

6.3

SOURCES OF INTERRUPTS

The processor receives interrupts from two sources:

•
•

External (hardware generated) interrupts.
Software-generated interrupts.

6.3.1

External Interrupts

External interrupts are received through pins on the processor or through the local APIC. The primary interrupt pins
on Pentium 4, Intel Xeon, P6 family, and Pentium processors are the LINT[1:0] pins, which are connected to the
local APIC (see Chapter 10, “Advanced Programmable Interrupt Controller (APIC)”). When the local APIC is
enabled, the LINT[1:0] pins can be programmed through the APIC’s local vector table (LVT) to be associated with
any of the processor’s exception or interrupt vectors.
When the local APIC is global/hardware disabled, these pins are configured as INTR and NMI pins, respectively.
Asserting the INTR pin signals the processor that an external interrupt has occurred. The processor reads from the
system bus the interrupt vector number provided by an external interrupt controller, such as an 8259A (see Section
6.2, “Exception and Interrupt Vectors”). Asserting the NMI pin signals a non-maskable interrupt (NMI), which is
assigned to interrupt vector 2.

Table 6-1. Protected-Mode Exceptions and Interrupts
Vector

Mnemonic

Description

Type

Error
Code

Source

0

#DE

Divide Error

Fault

No

DIV and IDIV instructions.

1

#DB

Debug Exception

Fault/ Trap

No

Instruction, data, and I/O breakpoints;
single-step; and others.

2

—

NMI Interrupt

Interrupt

No

Nonmaskable external interrupt.

3

#BP

Breakpoint

Trap

No

INT 3 instruction.

4

#OF

Overflow

Trap

No

INTO instruction.

5

#BR

BOUND Range Exceeded

Fault

No

BOUND instruction.

6

#UD

Invalid Opcode (Undefined Opcode)

Fault

No

UD instruction or reserved opcode.

7

#NM

Device Not Available (No Math
Coprocessor)

Fault

No

Floating-point or WAIT/FWAIT instruction.

8

#DF

Double Fault

Abort

Yes
(zero)

Any instruction that can generate an
exception, an NMI, or an INTR.

Coprocessor Segment Overrun
(reserved)

Fault

No

Floating-point instruction.1

9
10

#TS

Invalid TSS

Fault

Yes

Task switch or TSS access.

11

#NP

Segment Not Present

Fault

Yes

Loading segment registers or accessing
system segments.

12

#SS

Stack-Segment Fault

Fault

Yes

Stack operations and SS register loads.

13

#GP

General Protection

Fault

Yes

Any memory reference and other
protection checks.

14

#PF

Page Fault

Fault

Yes

Any memory reference.

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INTERRUPT AND EXCEPTION HANDLING

Table 6-1. Protected-Mode Exceptions and Interrupts (Contd.)
15

—

(Intel reserved. Do not use.)

16

#MF

x87 FPU Floating-Point Error (Math
Fault)

Fault

No

x87 FPU floating-point or WAIT/FWAIT
instruction.

17

#AC

Alignment Check

Fault

Yes
(Zero)

Any data reference in memory.2

18

#MC

Machine Check

Abort

No

Error codes (if any) and source are model
dependent.3

19

#XM

SIMD Floating-Point Exception

Fault

No

SSE/SSE2/SSE3 floating-point
instructions4

20

#VE

Virtualization Exception

Fault

No

EPT violations5

21-31

—

Intel reserved. Do not use.

32-255

—

User Defined (Non-reserved)
Interrupts

No

Interrupt

External interrupt or INT n instruction.

NOTES:
1. Processors after the Intel386 processor do not generate this exception.
2. This exception was introduced in the Intel486 processor.
3. This exception was introduced in the Pentium processor and enhanced in the P6 family processors.
4. This exception was introduced in the Pentium III processor.
5. This exception can occur only on processors that support the 1-setting of the “EPT-violation #VE” VM-execution control.
The processor’s local APIC is normally connected to a system-based I/O APIC. Here, external interrupts received at
the I/O APIC’s pins can be directed to the local APIC through the system bus (Pentium 4, Intel Core Duo, Intel Core
2, Intel® Atom™, and Intel Xeon processors) or the APIC serial bus (P6 family and Pentium processors). The I/O
APIC determines the vector number of the interrupt and sends this number to the local APIC. When a system
contains multiple processors, processors can also send interrupts to one another by means of the system bus
(Pentium 4, Intel Core Duo, Intel Core 2, Intel Atom, and Intel Xeon processors) or the APIC serial bus (P6 family
and Pentium processors).
The LINT[1:0] pins are not available on the Intel486 processor and earlier Pentium processors that do not contain
an on-chip local APIC. These processors have dedicated NMI and INTR pins. With these processors, external interrupts are typically generated by a system-based interrupt controller (8259A), with the interrupts being signaled
through the INTR pin.
Note that several other pins on the processor can cause a processor interrupt to occur. However, these interrupts
are not handled by the interrupt and exception mechanism described in this chapter. These pins include the
RESET#, FLUSH#, STPCLK#, SMI#, R/S#, and INIT# pins. Whether they are included on a particular processor is
implementation dependent. Pin functions are described in the data books for the individual processors. The SMI#
pin is described in Chapter 34, “System Management Mode.”

6.3.2

Maskable Hardware Interrupts

Any external interrupt that is delivered to the processor by means of the INTR pin or through the local APIC is called
a maskable hardware interrupt. Maskable hardware interrupts that can be delivered through the INTR pin include
all IA-32 architecture defined interrupt vectors from 0 through 255; those that can be delivered through the local
APIC include interrupt vectors 16 through 255.
The IF flag in the EFLAGS register permits all maskable hardware interrupts to be masked as a group (see Section
6.8.1, “Masking Maskable Hardware Interrupts”). Note that when interrupts 0 through 15 are delivered through the
local APIC, the APIC indicates the receipt of an illegal vector.

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INTERRUPT AND EXCEPTION HANDLING

6.3.3

Software-Generated Interrupts

The INT n instruction permits interrupts to be generated from within software by supplying an interrupt vector
number as an operand. For example, the INT 35 instruction forces an implicit call to the interrupt handler for interrupt 35.
Any of the interrupt vectors from 0 to 255 can be used as a parameter in this instruction. If the processor’s
predefined NMI vector is used, however, the response of the processor will not be the same as it would be from an
NMI interrupt generated in the normal manner. If vector number 2 (the NMI vector) is used in this instruction, the
NMI interrupt handler is called, but the processor’s NMI-handling hardware is not activated.
Interrupts generated in software with the INT n instruction cannot be masked by the IF flag in the EFLAGS register.

6.4

SOURCES OF EXCEPTIONS

The processor receives exceptions from three sources:

•
•
•

Processor-detected program-error exceptions.
Software-generated exceptions.
Machine-check exceptions.

6.4.1

Program-Error Exceptions

The processor generates one or more exceptions when it detects program errors during the execution in an application program or the operating system or executive. Intel 64 and IA-32 architectures define a vector number for
each processor-detectable exception. Exceptions are classified as faults, traps, and aborts (see Section 6.5,
“Exception Classifications”).

6.4.2

Software-Generated Exceptions

The INTO, INT 3, and BOUND instructions permit exceptions to be generated in software. These instructions allow
checks for exception conditions to be performed at points in the instruction stream. For example, INT 3 causes a
breakpoint exception to be generated.
The INT n instruction can be used to emulate exceptions in software; but there is a limitation. If INT n provides a
vector for one of the architecturally-defined exceptions, the processor generates an interrupt to the correct vector
(to access the exception handler) but does not push an error code on the stack. This is true even if the associated
hardware-generated exception normally produces an error code. The exception handler will still attempt to pop an
error code from the stack while handling the exception. Because no error code was pushed, the handler will pop off
and discard the EIP instead (in place of the missing error code). This sends the return to the wrong location.

6.4.3

Machine-Check Exceptions

The P6 family and Pentium processors provide both internal and external machine-check mechanisms for checking
the operation of the internal chip hardware and bus transactions. These mechanisms are implementation dependent. When a machine-check error is detected, the processor signals a machine-check exception (vector 18) and
returns an error code.
See Chapter 6, “Interrupt 18—Machine-Check Exception (#MC)” and Chapter 15, “Machine-Check Architecture,”
for more information about the machine-check mechanism.

6.5

EXCEPTION CLASSIFICATIONS

Exceptions are classified as faults, traps, or aborts depending on the way they are reported and whether the
instruction that caused the exception can be restarted without loss of program or task continuity.

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INTERRUPT AND EXCEPTION HANDLING

•

Faults — A fault is an exception that can generally be corrected and that, once corrected, allows the program
to be restarted with no loss of continuity. When a fault is reported, the processor restores the machine state to
the state prior to the beginning of execution of the faulting instruction. The return address (saved contents of
the CS and EIP registers) for the fault handler points to the faulting instruction, rather than to the instruction
following the faulting instruction.

•

Traps — A trap is an exception that is reported immediately following the execution of the trapping instruction.
Traps allow execution of a program or task to be continued without loss of program continuity. The return
address for the trap handler points to the instruction to be executed after the trapping instruction.

•

Aborts — An abort is an exception that does not always report the precise location of the instruction causing
the exception and does not allow a restart of the program or task that caused the exception. Aborts are used to
report severe errors, such as hardware errors and inconsistent or illegal values in system tables.

NOTE
One exception subset normally reported as a fault is not restartable. Such exceptions result in loss
of some processor state. For example, executing a POPAD instruction where the stack frame
crosses over the end of the stack segment causes a fault to be reported. In this situation, the
exception handler sees that the instruction pointer (CS:EIP) has been restored as if the POPAD
instruction had not been executed. However, internal processor state (the general-purpose
registers) will have been modified. Such cases are considered programming errors. An application
causing this class of exceptions should be terminated by the operating system.

6.6

PROGRAM OR TASK RESTART

To allow the restarting of program or task following the handling of an exception or an interrupt, all exceptions
(except aborts) are guaranteed to report exceptions on an instruction boundary. All interrupts are guaranteed to be
taken on an instruction boundary.
For fault-class exceptions, the return instruction pointer (saved when the processor generates an exception) points
to the faulting instruction. So, when a program or task is restarted following the handling of a fault, the faulting
instruction is restarted (re-executed). Restarting the faulting instruction is commonly used to handle exceptions
that are generated when access to an operand is blocked. The most common example of this type of fault is a pagefault exception (#PF) that occurs when a program or task references an operand located on a page that is not in
memory. When a page-fault exception occurs, the exception handler can load the page into memory and resume
execution of the program or task by restarting the faulting instruction. To insure that the restart is handled transparently to the currently executing program or task, the processor saves the necessary registers and stack pointers
to allow a restart to the state prior to the execution of the faulting instruction.
For trap-class exceptions, the return instruction pointer points to the instruction following the trapping instruction.
If a trap is detected during an instruction which transfers execution, the return instruction pointer reflects the
transfer. For example, if a trap is detected while executing a JMP instruction, the return instruction pointer points
to the destination of the JMP instruction, not to the next address past the JMP instruction. All trap exceptions allow
program or task restart with no loss of continuity. For example, the overflow exception is a trap exception. Here,
the return instruction pointer points to the instruction following the INTO instruction that tested EFLAGS.OF (overflow) flag. The trap handler for this exception resolves the overflow condition. Upon return from the trap handler,
program or task execution continues at the instruction following the INTO instruction.
The abort-class exceptions do not support reliable restarting of the program or task. Abort handlers are designed
to collect diagnostic information about the state of the processor when the abort exception occurred and then shut
down the application and system as gracefully as possible.
Interrupts rigorously support restarting of interrupted programs and tasks without loss of continuity. The return
instruction pointer saved for an interrupt points to the next instruction to be executed at the instruction boundary
where the processor took the interrupt. If the instruction just executed has a repeat prefix, the interrupt is taken
at the end of the current iteration with the registers set to execute the next iteration.
The ability of a P6 family processor to speculatively execute instructions does not affect the taking of interrupts by
the processor. Interrupts are taken at instruction boundaries located during the retirement phase of instruction
execution; so they are always taken in the “in-order” instruction stream. See Chapter 2, “Intel® 64 and IA-32

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INTERRUPT AND EXCEPTION HANDLING

Architectures,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for more information about the P6 family processors’ microarchitecture and its support for out-of-order instruction execution.
Note that the Pentium processor and earlier IA-32 processors also perform varying amounts of prefetching and
preliminary decoding. With these processors as well, exceptions and interrupts are not signaled until actual “inorder” execution of the instructions. For a given code sample, the signaling of exceptions occurs uniformly when
the code is executed on any family of IA-32 processors (except where new exceptions or new opcodes have been
defined).

6.7

NONMASKABLE INTERRUPT (NMI)

The nonmaskable interrupt (NMI) can be generated in either of two ways:

•
•

External hardware asserts the NMI pin.
The processor receives a message on the system bus (Pentium 4, Intel Core Duo, Intel Core 2, Intel Atom, and
Intel Xeon processors) or the APIC serial bus (P6 family and Pentium processors) with a delivery mode NMI.

When the processor receives a NMI from either of these sources, the processor handles it immediately by calling
the NMI handler pointed to by interrupt vector number 2. The processor also invokes certain hardware conditions
to insure that no other interrupts, including NMI interrupts, are received until the NMI handler has completed
executing (see Section 6.7.1, “Handling Multiple NMIs”).
Also, when an NMI is received from either of the above sources, it cannot be masked by the IF flag in the EFLAGS
register.
It is possible to issue a maskable hardware interrupt (through the INTR pin) to vector 2 to invoke the NMI interrupt
handler; however, this interrupt will not truly be an NMI interrupt. A true NMI interrupt that activates the
processor’s NMI-handling hardware can only be delivered through one of the mechanisms listed above.

6.7.1

Handling Multiple NMIs

While an NMI interrupt handler is executing, the processor blocks delivery of subsequent NMIs until the next execution of the IRET instruction. This blocking of NMIs prevents nested execution of the NMI handler. It is recommended
that the NMI interrupt handler be accessed through an interrupt gate to disable maskable hardware interrupts (see
Section 6.8.1, “Masking Maskable Hardware Interrupts”).
An execution of the IRET instruction unblocks NMIs even if the instruction causes a fault. For example, if the IRET
instruction executes with EFLAGS.VM = 1 and IOPL of less than 3, a general-protection exception is generated (see
Section 20.2.7, “Sensitive Instructions”). In such a case, NMIs are unmasked before the exception handler is
invoked.

6.8

ENABLING AND DISABLING INTERRUPTS

The processor inhibits the generation of some interrupts, depending on the state of the processor and of the IF and
RF flags in the EFLAGS register, as described in the following sections.

6.8.1

Masking Maskable Hardware Interrupts

The IF flag can disable the servicing of maskable hardware interrupts received on the processor’s INTR pin or
through the local APIC (see Section 6.3.2, “Maskable Hardware Interrupts”). When the IF flag is clear, the
processor inhibits interrupts delivered to the INTR pin or through the local APIC from generating an internal interrupt request; when the IF flag is set, interrupts delivered to the INTR or through the local APIC pin are processed
as normal external interrupts.
The IF flag does not affect non-maskable interrupts (NMIs) delivered to the NMI pin or delivery mode NMI
messages delivered through the local APIC, nor does it affect processor generated exceptions. As with the other
flags in the EFLAGS register, the processor clears the IF flag in response to a hardware reset.

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INTERRUPT AND EXCEPTION HANDLING

The fact that the group of maskable hardware interrupts includes the reserved interrupt and exception vectors 0
through 32 can potentially cause confusion. Architecturally, when the IF flag is set, an interrupt for any of the
vectors from 0 through 32 can be delivered to the processor through the INTR pin and any of the vectors from 16
through 32 can be delivered through the local APIC. The processor will then generate an interrupt and call the
interrupt or exception handler pointed to by the vector number. So for example, it is possible to invoke the pagefault handler through the INTR pin (by means of vector 14); however, this is not a true page-fault exception. It is
an interrupt. As with the INT n instruction (see Section 6.4.2, “Software-Generated Exceptions”), when an interrupt is generated through the INTR pin to an exception vector, the processor does not push an error code on the
stack, so the exception handler may not operate correctly.
The IF flag can be set or cleared with the STI (set interrupt-enable flag) and CLI (clear interrupt-enable flag)
instructions, respectively. These instructions may be executed only if the CPL is equal to or less than the IOPL. A
general-protection exception (#GP) is generated if they are executed when the CPL is greater than the IOPL. (The
effect of the IOPL on these instructions is modified slightly when the virtual mode extension is enabled by setting
the VME flag in control register CR4: see Section 20.3, “Interrupt and Exception Handling in Virtual-8086 Mode.”
Behavior is also impacted by the PVI flag: see Section 20.4, “Protected-Mode Virtual Interrupts.”
The IF flag is also affected by the following operations:

•

The PUSHF instruction stores all flags on the stack, where they can be examined and modified. The POPF
instruction can be used to load the modified flags back into the EFLAGS register.

•

Task switches and the POPF and IRET instructions load the EFLAGS register; therefore, they can be used to
modify the setting of the IF flag.

•

When an interrupt is handled through an interrupt gate, the IF flag is automatically cleared, which disables
maskable hardware interrupts. (If an interrupt is handled through a trap gate, the IF flag is not cleared.)

See the descriptions of the CLI, STI, PUSHF, POPF, and IRET instructions in Chapter 3, “Instruction Set Reference,
A-L,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A, and Chapter 4, “Instruction Set Reference, M-U,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B, for a
detailed description of the operations these instructions are allowed to perform on the IF flag.

6.8.2

Masking Instruction Breakpoints

The RF (resume) flag in the EFLAGS register controls the response of the processor to instruction-breakpoint conditions (see the description of the RF flag in Section 2.3, “System Flags and Fields in the EFLAGS Register”).
When set, it prevents an instruction breakpoint from generating a debug exception (#DB); when clear, instruction
breakpoints will generate debug exceptions. The primary function of the RF flag is to prevent the processor from
going into a debug exception loop on an instruction-breakpoint. See Section 17.3.1.1, “Instruction-Breakpoint
Exception Condition,” for more information on the use of this flag.

6.8.3

Masking Exceptions and Interrupts When Switching Stacks

To switch to a different stack segment, software often uses a pair of instructions, for example:
MOV SS, AX
MOV ESP, StackTop
If an interrupt or exception occurs after the segment selector has been loaded into the SS register but before the
ESP register has been loaded, these two parts of the logical address into the stack space are inconsistent for the
duration of the interrupt or exception handler.
To prevent this situation, the processor inhibits interrupts, debug exceptions, and single-step trap exceptions after
either a MOV to SS instruction or a POP to SS instruction, until the instruction boundary following the next instruction is reached. All other faults may still be generated. If the LSS instruction is used to modify the contents of the
SS register (which is the recommended method of modifying this register), this problem does not occur.

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6.9

PRIORITY AMONG SIMULTANEOUS EXCEPTIONS AND INTERRUPTS

If more than one exception or interrupt is pending at an instruction boundary, the processor services them in a
predictable order. Table 6-2 shows the priority among classes of exception and interrupt sources.

Table 6-2. Priority Among Simultaneous Exceptions and Interrupts
Priority
1 (Highest)

Description
Hardware Reset and Machine Checks
- RESET
- Machine Check

2

Trap on Task Switch
- T flag in TSS is set

3

External Hardware Interventions
- FLUSH
- STOPCLK
- SMI
- INIT

4

Traps on the Previous Instruction
- Breakpoints
- Debug Trap Exceptions (TF flag set or data/I-O breakpoint)

5

Nonmaskable Interrupts (NMI) 1

6

Maskable Hardware Interrupts 1

7

Code Breakpoint Fault

8

Faults from Fetching Next Instruction
- Code-Segment Limit Violation
- Code Page Fault

9

Faults from Decoding the Next Instruction
- Instruction length > 15 bytes
- Invalid Opcode
- Coprocessor Not Available

10 (Lowest)

Faults on Executing an Instruction
- Overflow
- Bound error
- Invalid TSS
- Segment Not Present
- Stack fault
- General Protection
- Data Page Fault
- Alignment Check
- x87 FPU Floating-point exception
- SIMD floating-point exception
- Virtualization exception

NOTE
1. The Intel® 486 processor and earlier processors group nonmaskable and maskable interrupts in the same priority class.
While priority among these classes listed in Table 6-2 is consistent throughout the architecture, exceptions within
each class are implementation-dependent and may vary from processor to processor. The processor first services
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INTERRUPT AND EXCEPTION HANDLING

a pending exception or interrupt from the class which has the highest priority, transferring execution to the first
instruction of the handler. Lower priority exceptions are discarded; lower priority interrupts are held pending.
Discarded exceptions are re-generated when the interrupt handler returns execution to the point in the program or
task where the exceptions and/or interrupts occurred.

6.10

INTERRUPT DESCRIPTOR TABLE (IDT)

The interrupt descriptor table (IDT) associates each exception or interrupt vector with a gate descriptor for the
procedure or task used to service the associated exception or interrupt. Like the GDT and LDTs, the IDT is an array
of 8-byte descriptors (in protected mode). Unlike the GDT, the first entry of the IDT may contain a descriptor. To
form an index into the IDT, the processor scales the exception or interrupt vector by eight (the number of bytes in
a gate descriptor). Because there are only 256 interrupt or exception vectors, the IDT need not contain more than
256 descriptors. It can contain fewer than 256 descriptors, because descriptors are required only for the interrupt
and exception vectors that may occur. All empty descriptor slots in the IDT should have the present flag for the
descriptor set to 0.
The base addresses of the IDT should be aligned on an 8-byte boundary to maximize performance of cache line
fills. The limit value is expressed in bytes and is added to the base address to get the address of the last valid byte.
A limit value of 0 results in exactly 1 valid byte. Because IDT entries are always eight bytes long, the limit should
always be one less than an integral multiple of eight (that is, 8N – 1).
The IDT may reside anywhere in the linear address space. As shown in Figure 6-1, the processor locates the IDT
using the IDTR register. This register holds both a 32-bit base address and 16-bit limit for the IDT.
The LIDT (load IDT register) and SIDT (store IDT register) instructions load and store the contents of the IDTR
register, respectively. The LIDT instruction loads the IDTR register with the base address and limit held in a
memory operand. This instruction can be executed only when the CPL is 0. It normally is used by the initialization
code of an operating system when creating an IDT. An operating system also may use it to change from one IDT to
another. The SIDT instruction copies the base and limit value stored in IDTR to memory. This instruction can be
executed at any privilege level.
If a vector references a descriptor beyond the limit of the IDT, a general-protection exception (#GP) is generated.

NOTE
Because interrupts are delivered to the processor core only once, an incorrectly configured IDT
could result in incomplete interrupt handling and/or the blocking of interrupt delivery.
IA-32 architecture rules need to be followed for setting up IDTR base/limit/access fields and each
field in the gate descriptors. The same apply for the Intel 64 architecture. This includes implicit
referencing of the destination code segment through the GDT or LDT and accessing the stack.

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INTERRUPT AND EXCEPTION HANDLING

IDTR Register
47

16 15

IDT Base Address

0

IDT Limit

+

Interrupt
Descriptor Table (IDT)
Gate for
Interrupt #n

(n−1)∗8

Gate for
Interrupt #3

16

Gate for
Interrupt #2

8

Gate for
Interrupt #1
31

0
0

Figure 6-1. Relationship of the IDTR and IDT

6.11

IDT DESCRIPTORS

The IDT may contain any of three kinds of gate descriptors:

•
•
•

Task-gate descriptor
Interrupt-gate descriptor
Trap-gate descriptor

Figure 6-2 shows the formats for the task-gate, interrupt-gate, and trap-gate descriptors. The format of a task
gate used in an IDT is the same as that of a task gate used in the GDT or an LDT (see Section 7.2.5, “Task-Gate
Descriptor”). The task gate contains the segment selector for a TSS for an exception and/or interrupt handler task.
Interrupt and trap gates are very similar to call gates (see Section 5.8.3, “Call Gates”). They contain a far pointer
(segment selector and offset) that the processor uses to transfer program execution to a handler procedure in an
exception- or interrupt-handler code segment. These gates differ in the way the processor handles the IF flag in the
EFLAGS register (see Section 6.12.1.2, “Flag Usage By Exception- or Interrupt-Handler Procedure”).

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INTERRUPT AND EXCEPTION HANDLING

Task Gate
31

16 15 14 13 12
P

31

D
P
L

0

8 7

4

0 0 1 0 1

16 15

0

0

TSS Segment Selector

Interrupt Gate
31

16 15 14 13 12

Offset 31..16
31

P

D
P
L

8 7

0 D 1 1 0

5 4

0

4

0 0 0

16 15

0

Segment Selector

0

Offset 15..0

Trap Gate
31

16 15 14 13 12

Offset 31..16
31

P

D
P
L

8 7

0 D 1 1 1

5 4

DPL
Offset
P
Selector
D

4

0 0 0

16 15

Segment Selector

0

0

Offset 15..0

0

Descriptor Privilege Level
Offset to procedure entry point
Segment Present flag
Segment Selector for destination code segment
Size of gate: 1 = 32 bits; 0 = 16 bits

Reserved

Figure 6-2. IDT Gate Descriptors

6.12

EXCEPTION AND INTERRUPT HANDLING

The processor handles calls to exception- and interrupt-handlers similar to the way it handles calls with a CALL
instruction to a procedure or a task. When responding to an exception or interrupt, the processor uses the exception or interrupt vector as an index to a descriptor in the IDT. If the index points to an interrupt gate or trap gate,
the processor calls the exception or interrupt handler in a manner similar to a CALL to a call gate (see Section
5.8.2, “Gate Descriptors,” through Section 5.8.6, “Returning from a Called Procedure”). If index points to a task
gate, the processor executes a task switch to the exception- or interrupt-handler task in a manner similar to a CALL
to a task gate (see Section 7.3, “Task Switching”).

6.12.1

Exception- or Interrupt-Handler Procedures

An interrupt gate or trap gate references an exception- or interrupt-handler procedure that runs in the context of
the currently executing task (see Figure 6-3). The segment selector for the gate points to a segment descriptor for
an executable code segment in either the GDT or the current LDT. The offset field of the gate descriptor points to
the beginning of the exception- or interrupt-handling procedure.

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INTERRUPT AND EXCEPTION HANDLING

Destination
Code Segment

IDT

Interrupt
Vector

Interrupt or
Trap Gate

Offset

+

Interrupt
Procedure

Segment Selector
GDT or LDT
Base
Address
Segment
Descriptor

Figure 6-3. Interrupt Procedure Call
When the processor performs a call to the exception- or interrupt-handler procedure:

•

If the handler procedure is going to be executed at a numerically lower privilege level, a stack switch occurs.
When the stack switch occurs:
a. The segment selector and stack pointer for the stack to be used by the handler are obtained from the TSS
for the currently executing task. On this new stack, the processor pushes the stack segment selector and
stack pointer of the interrupted procedure.
b. The processor then saves the current state of the EFLAGS, CS, and EIP registers on the new stack (see
Figures 6-4).
c.

•

If an exception causes an error code to be saved, it is pushed on the new stack after the EIP value.

If the handler procedure is going to be executed at the same privilege level as the interrupted procedure:
a. The processor saves the current state of the EFLAGS, CS, and EIP registers on the current stack (see
Figures 6-4).
b. If an exception causes an error code to be saved, it is pushed on the current stack after the EIP value.

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INTERRUPT AND EXCEPTION HANDLING

Stack Usage with No
Privilege-Level Change

Interrupted Procedure’s
and Handler’s Stack

EFLAGS
CS
EIP
Error Code

ESP Before
Transfer to Handler

ESP After
Transfer to Handler

Stack Usage with
Privilege-Level Change

Interrupted Procedure’s
Stack

Handler’s Stack
ESP Before
Transfer to Handler

ESP After
Transfer to Handler

SS
ESP
EFLAGS
CS
EIP
Error Code

Figure 6-4. Stack Usage on Transfers to Interrupt and Exception-Handling Routines
To return from an exception- or interrupt-handler procedure, the handler must use the IRET (or IRETD) instruction.
The IRET instruction is similar to the RET instruction except that it restores the saved flags into the EFLAGS
register. The IOPL field of the EFLAGS register is restored only if the CPL is 0. The IF flag is changed only if the CPL
is less than or equal to the IOPL. See Chapter 3, “Instruction Set Reference, A-L,” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A, for a description of the complete operation performed by the
IRET instruction.
If a stack switch occurred when calling the handler procedure, the IRET instruction switches back to the interrupted
procedure’s stack on the return.

6.12.1.1

Protection of Exception- and Interrupt-Handler Procedures

The privilege-level protection for exception- and interrupt-handler procedures is similar to that used for ordinary
procedure calls when called through a call gate (see Section 5.8.4, “Accessing a Code Segment Through a Call
Gate”). The processor does not permit transfer of execution to an exception- or interrupt-handler procedure in a
less privileged code segment (numerically greater privilege level) than the CPL.
An attempt to violate this rule results in a general-protection exception (#GP). The protection mechanism for
exception- and interrupt-handler procedures is different in the following ways:

•

Because interrupt and exception vectors have no RPL, the RPL is not checked on implicit calls to exception and
interrupt handlers.

•

The processor checks the DPL of the interrupt or trap gate only if an exception or interrupt is generated with an
INT n, INT 3, or INTO instruction. Here, the CPL must be less than or equal to the DPL of the gate. This
restriction prevents application programs or procedures running at privilege level 3 from using a software
interrupt to access critical exception handlers, such as the page-fault handler, providing that those handlers are
placed in more privileged code segments (numerically lower privilege level). For hardware-generated
interrupts and processor-detected exceptions, the processor ignores the DPL of interrupt and trap gates.

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INTERRUPT AND EXCEPTION HANDLING

Because exceptions and interrupts generally do not occur at predictable times, these privilege rules effectively
impose restrictions on the privilege levels at which exception and interrupt- handling procedures can run. Either of
the following techniques can be used to avoid privilege-level violations.

•

The exception or interrupt handler can be placed in a conforming code segment. This technique can be used for
handlers that only need to access data available on the stack (for example, divide error exceptions). If the
handler needs data from a data segment, the data segment needs to be accessible from privilege level 3, which
would make it unprotected.

•

The handler can be placed in a nonconforming code segment with privilege level 0. This handler would always
run, regardless of the CPL that the interrupted program or task is running at.

6.12.1.2

Flag Usage By Exception- or Interrupt-Handler Procedure

When accessing an exception or interrupt handler through either an interrupt gate or a trap gate, the processor
clears the TF flag in the EFLAGS register after it saves the contents of the EFLAGS register on the stack. (On calls
to exception and interrupt handlers, the processor also clears the VM, RF, and NT flags in the EFLAGS register, after
they are saved on the stack.) Clearing the TF flag prevents instruction tracing from affecting interrupt response. A
subsequent IRET instruction restores the TF (and VM, RF, and NT) flags to the values in the saved contents of the
EFLAGS register on the stack.
The only difference between an interrupt gate and a trap gate is the way the processor handles the IF flag in the
EFLAGS register. When accessing an exception- or interrupt-handling procedure through an interrupt gate, the
processor clears the IF flag to prevent other interrupts from interfering with the current interrupt handler. A subsequent IRET instruction restores the IF flag to its value in the saved contents of the EFLAGS register on the stack.
Accessing a handler procedure through a trap gate does not affect the IF flag.

6.12.2

Interrupt Tasks

When an exception or interrupt handler is accessed through a task gate in the IDT, a task switch results. Handling
an exception or interrupt with a separate task offers several advantages:

•
•

The entire context of the interrupted program or task is saved automatically.

•

The handler can be further isolated from other tasks by giving it a separate address space. This is done by
giving it a separate LDT.

A new TSS permits the handler to use a new privilege level 0 stack when handling the exception or interrupt. If
an exception or interrupt occurs when the current privilege level 0 stack is corrupted, accessing the handler
through a task gate can prevent a system crash by providing the handler with a new privilege level 0 stack.

The disadvantage of handling an interrupt with a separate task is that the amount of machine state that must be
saved on a task switch makes it slower than using an interrupt gate, resulting in increased interrupt latency.
A task gate in the IDT references a TSS descriptor in the GDT (see Figure 6-5). A switch to the handler task is
handled in the same manner as an ordinary task switch (see Section 7.3, “Task Switching”). The link back to the
interrupted task is stored in the previous task link field of the handler task’s TSS. If an exception caused an error
code to be generated, this error code is copied to the stack of the new task.
When exception- or interrupt-handler tasks are used in an operating system, there are actually two mechanisms
that can be used to dispatch tasks: the software scheduler (part of the operating system) and the hardware scheduler (part of the processor's interrupt mechanism). The software scheduler needs to accommodate interrupt tasks
that may be dispatched when interrupts are enabled.

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INTERRUPT AND EXCEPTION HANDLING

NOTE
Because IA-32 architecture tasks are not re-entrant, an interrupt-handler task must disable
interrupts between the time it completes handling the interrupt and the time it executes the IRET
instruction. This action prevents another interrupt from occurring while the interrupt task’s TSS is
still marked busy, which would cause a general-protection (#GP) exception.

IDT

Interrupt
Vector

TSS for InterruptHandling Task

Task Gate

TSS Selector
GDT

TSS
Base
Address

TSS Descriptor

Figure 6-5. Interrupt Task Switch

6.13

ERROR CODE

When an exception condition is related to a specific segment selector or IDT vector, the processor pushes an error
code onto the stack of the exception handler (whether it is a procedure or task). The error code has the format
shown in Figure 6-6. The error code resembles a segment selector; however, instead of a TI flag and RPL field, the
error code contains 3 flags:
EXT

External event (bit 0) — When set, indicates that the exception occurred during delivery of an
event external to the program, such as an interrupt or an earlier exception.

IDT

Descriptor location (bit 1) — When set, indicates that the index portion of the error code refers
to a gate descriptor in the IDT; when clear, indicates that the index refers to a descriptor in the GDT
or the current LDT.

TI

GDT/LDT (bit 2) — Only used when the IDT flag is clear. When set, the TI flag indicates that the
index portion of the error code refers to a segment or gate descriptor in the LDT; when clear, it indicates that the index refers to a descriptor in the current GDT.

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INTERRUPT AND EXCEPTION HANDLING

31

3 2 1 0

Reserved

Segment Selector Index

T I E
X
I D
T T

Figure 6-6. Error Code
The segment selector index field provides an index into the IDT, GDT, or current LDT to the segment or gate
selector being referenced by the error code. In some cases the error code is null (all bits are clear except possibly
EXT). A null error code indicates that the error was not caused by a reference to a specific segment or that a null
segment selector was referenced in an operation.
The format of the error code is different for page-fault exceptions (#PF). See the “Interrupt 14—Page-Fault Exception (#PF)” section in this chapter.
The error code is pushed on the stack as a doubleword or word (depending on the default interrupt, trap, or task
gate size). To keep the stack aligned for doubleword pushes, the upper half of the error code is reserved. Note that
the error code is not popped when the IRET instruction is executed to return from an exception handler, so the
handler must remove the error code before executing a return.
Error codes are not pushed on the stack for exceptions that are generated externally (with the INTR or LINT[1:0]
pins) or the INT n instruction, even if an error code is normally produced for those exceptions.

6.14

EXCEPTION AND INTERRUPT HANDLING IN 64-BIT MODE

In 64-bit mode, interrupt and exception handling is similar to what has been described for non-64-bit modes. The
following are the exceptions:

•
•
•

All interrupt handlers pointed by the IDT are in 64-bit code (this does not apply to the SMI handler).

•
•
•
•

The new SS is set to NULL if there is a change in CPL.

The size of interrupt-stack pushes is fixed at 64 bits; and the processor uses 8-byte, zero extended stores.
The stack pointer (SS:RSP) is pushed unconditionally on interrupts. In legacy modes, this push is conditional
and based on a change in current privilege level (CPL).
IRET behavior changes.
There is a new interrupt stack-switch mechanism.
The alignment of interrupt stack frame is different.

6.14.1

64-Bit Mode IDT

Interrupt and trap gates are 16 bytes in length to provide a 64-bit offset for the instruction pointer (RIP). The 64bit RIP referenced by interrupt-gate descriptors allows an interrupt service routine to be located anywhere in the
linear-address space. See Figure 6-7.

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INTERRUPT AND EXCEPTION HANDLING

Interrupt/Trap Gate
31

0

Reserved

12

31

0

Offset 63..32
31

8

16 15 14 13 12 11

Offset 31..16
31

P

D
P

L

0

8 7

TYPE

5 4

0 0 0 0 0

16 15

Segment Selector

DPL
Offset
P
Selector
IST

0

2

4

IST
0

Offset 15..0

0

Descriptor Privilege Level
Offset to procedure entry point
Segment Present flag
Segment Selector for destination code segment
Interrupt Stack Table

Figure 6-7. 64-Bit IDT Gate Descriptors
In 64-bit mode, the IDT index is formed by scaling the interrupt vector by 16. The first eight bytes (bytes 7:0) of a
64-bit mode interrupt gate are similar but not identical to legacy 32-bit interrupt gates. The type field (bits 11:8 in
bytes 7:4) is described in Table 3-2. The Interrupt Stack Table (IST) field (bits 4:0 in bytes 7:4) is used by the stack
switching mechanisms described in Section 6.14.5, “Interrupt Stack Table.” Bytes 11:8 hold the upper 32 bits of
the target RIP (interrupt segment offset) in canonical form. A general-protection exception (#GP) is generated if
software attempts to reference an interrupt gate with a target RIP that is not in canonical form.
The target code segment referenced by the interrupt gate must be a 64-bit code segment (CS.L = 1, CS.D = 0). If
the target is not a 64-bit code segment, a general-protection exception (#GP) is generated with the IDT vector
number reported as the error code.
Only 64-bit interrupt and trap gates can be referenced in IA-32e mode (64-bit mode and compatibility mode).
Legacy 32-bit interrupt or trap gate types (0EH or 0FH) are redefined in IA-32e mode as 64-bit interrupt and trap
gate types. No 32-bit interrupt or trap gate type exists in IA-32e mode. If a reference is made to a 16-bit interrupt
or trap gate (06H or 07H), a general-protection exception (#GP(0)) is generated.

6.14.2

64-Bit Mode Stack Frame

In legacy mode, the size of an IDT entry (16 bits or 32 bits) determines the size of interrupt-stack-frame pushes.
SS:ESP is pushed only on a CPL change. In 64-bit mode, the size of interrupt stack-frame pushes is fixed at eight
bytes. This is because only 64-bit mode gates can be referenced. 64-bit mode also pushes SS:RSP unconditionally,
rather than only on a CPL change.
Aside from error codes, pushing SS:RSP unconditionally presents operating systems with a consistent interruptstackframe size across all interrupts. Interrupt service-routine entry points that handle interrupts generated by the
INTn instruction or external INTR# signal can push an additional error code place-holder to maintain consistency.
In legacy mode, the stack pointer may be at any alignment when an interrupt or exception causes a stack frame to
be pushed. This causes the stack frame and succeeding pushes done by an interrupt handler to be at arbitrary
alignments. In IA-32e mode, the RSP is aligned to a 16-byte boundary before pushing the stack frame. The stack
frame itself is aligned on a 16-byte boundary when the interrupt handler is called. The processor can arbitrarily
realign the new RSP on interrupts because the previous (possibly unaligned) RSP is unconditionally saved on the
newly aligned stack. The previous RSP will be automatically restored by a subsequent IRET.
Aligning the stack permits exception and interrupt frames to be aligned on a 16-byte boundary before interrupts
are re-enabled. This allows the stack to be formatted for optimal storage of 16-byte XMM registers, which enables

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INTERRUPT AND EXCEPTION HANDLING

the interrupt handler to use faster 16-byte aligned loads and stores (MOVAPS rather than MOVUPS) to save and
restore XMM registers.
Although the RSP alignment is always performed when LMA = 1, it is only of consequence for the kernel-mode case
where there is no stack switch or IST used. For a stack switch or IST, the OS would have presumably put suitably
aligned RSP values in the TSS.

6.14.3

IRET in IA-32e Mode

In IA-32e mode, IRET executes with an 8-byte operand size. There is nothing that forces this requirement. The
stack is formatted in such a way that for actions where IRET is required, the 8-byte IRET operand size works
correctly.
Because interrupt stack-frame pushes are always eight bytes in IA-32e mode, an IRET must pop eight byte items
off the stack. This is accomplished by preceding the IRET with a 64-bit operand-size prefix. The size of the pop is
determined by the address size of the instruction. The SS/ESP/RSP size adjustment is determined by the stack size.
IRET pops SS:RSP unconditionally off the interrupt stack frame only when it is executed in 64-bit mode. In compatibility mode, IRET pops SS:RSP off the stack only if there is a CPL change. This allows legacy applications to execute
properly in compatibility mode when using the IRET instruction. 64-bit interrupt service routines that exit with an
IRET unconditionally pop SS:RSP off of the interrupt stack frame, even if the target code segment is running in 64bit mode or at CPL = 0. This is because the original interrupt always pushes SS:RSP.
In IA-32e mode, IRET is allowed to load a NULL SS under certain conditions. If the target mode is 64-bit mode and
the target CPL ≠ 3, IRET allows SS to be loaded with a NULL selector. As part of the stack switch mechanism, an
interrupt or exception sets the new SS to NULL, instead of fetching a new SS selector from the TSS and loading the
corresponding descriptor from the GDT or LDT. The new SS selector is set to NULL in order to properly handle
returns from subsequent nested far transfers. If the called procedure itself is interrupted, the NULL SS is pushed on
the stack frame. On the subsequent IRET, the NULL SS on the stack acts as a flag to tell the processor not to load
a new SS descriptor.

6.14.4

Stack Switching in IA-32e Mode

The IA-32 architecture provides a mechanism to automatically switch stack frames in response to an interrupt. The
64-bit extensions of Intel 64 architecture implement a modified version of the legacy stack-switching mechanism
and an alternative stack-switching mechanism called the interrupt stack table (IST).
In IA-32 modes, the legacy IA-32 stack-switch mechanism is unchanged. In IA-32e mode, the legacy stack-switch
mechanism is modified. When stacks are switched as part of a 64-bit mode privilege-level change (resulting from
an interrupt), a new SS descriptor is not loaded. IA-32e mode loads only an inner-level RSP from the TSS. The new
SS selector is forced to NULL and the SS selector’s RPL field is set to the new CPL. The new SS is set to NULL in
order to handle nested far transfers (far CALL, INT, interrupts and exceptions). The old SS and RSP are saved on
the new stack (Figure 6-8). On the subsequent IRET, the old SS is popped from the stack and loaded into the SS
register.
In summary, a stack switch in IA-32e mode works like the legacy stack switch, except that a new SS selector is not
loaded from the TSS. Instead, the new SS is forced to NULL.

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INTERRUPT AND EXCEPTION HANDLING

Legacy Mode

+20
+16
+12
+8
+4
0

Stack Usage with
Privilege-Level Change

IA-32e Mode

Handler’s Stack

Handler’s Stack

SS
ESP
EFLAGS
CS
EIP
Error Code

SS
RSP
RFLAGS
CS
RIP
Error Code

Stack Pointer After
Transfer to Handler

+40
+32
+24
+16
+8
0

Figure 6-8. IA-32e Mode Stack Usage After Privilege Level Change

6.14.5

Interrupt Stack Table

In IA-32e mode, a new interrupt stack table (IST) mechanism is available as an alternative to the modified legacy
stack-switching mechanism described above. This mechanism unconditionally switches stacks when it is enabled.
It can be enabled on an individual interrupt-vector basis using a field in the IDT entry. This means that some interrupt vectors can use the modified legacy mechanism and others can use the IST mechanism.
The IST mechanism is only available in IA-32e mode. It is part of the 64-bit mode TSS. The motivation for the IST
mechanism is to provide a method for specific interrupts (such as NMI, double-fault, and machine-check) to always
execute on a known good stack. In legacy mode, interrupts can use the task-switch mechanism to set up a knowngood stack by accessing the interrupt service routine through a task gate located in the IDT. However, the legacy
task-switch mechanism is not supported in IA-32e mode.
The IST mechanism provides up to seven IST pointers in the TSS. The pointers are referenced by an interrupt-gate
descriptor in the interrupt-descriptor table (IDT); see Figure 6-7. The gate descriptor contains a 3-bit IST index
field that provides an offset into the IST section of the TSS. Using the IST mechanism, the processor loads the
value pointed by an IST pointer into the RSP.
When an interrupt occurs, the new SS selector is forced to NULL and the SS selector’s RPL field is set to the new
CPL. The old SS, RSP, RFLAGS, CS, and RIP are pushed onto the new stack. Interrupt processing then proceeds as
normal. If the IST index is zero, the modified legacy stack-switching mechanism described above is used.

6.15

EXCEPTION AND INTERRUPT REFERENCE

The following sections describe conditions which generate exceptions and interrupts. They are arranged in the
order of vector numbers. The information contained in these sections are as follows:

•

Exception Class — Indicates whether the exception class is a fault, trap, or abort type. Some exceptions can
be either a fault or trap type, depending on when the error condition is detected. (This section is not applicable
to interrupts.)

•

Description — Gives a general description of the purpose of the exception or interrupt type. It also describes
how the processor handles the exception or interrupt.

•

Exception Error Code — Indicates whether an error code is saved for the exception. If one is saved, the
contents of the error code are described. (This section is not applicable to interrupts.)

•

Saved Instruction Pointer — Describes which instruction the saved (or return) instruction pointer points to.
It also indicates whether the pointer can be used to restart a faulting instruction.

•

Program State Change — Describes the effects of the exception or interrupt on the state of the currently
running program or task and the possibilities of restarting the program or task without loss of continuity.

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Interrupt 0—Divide Error Exception (#DE)
Exception Class

Fault.

Description
Indicates the divisor operand for a DIV or IDIV instruction is 0 or that the result cannot be represented in the
number of bits specified for the destination operand.

Exception Error Code
None.

Saved Instruction Pointer
Saved contents of CS and EIP registers point to the instruction that generated the exception.

Program State Change
A program-state change does not accompany the divide error, because the exception occurs before the faulting
instruction is executed.

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Interrupt 1—Debug Exception (#DB)
Trap or Fault. The exception handler can distinguish between traps or faults by examining the contents of DR6 and the other debug registers.

Exception Class

Description
Indicates that one or more of several debug-exception conditions has been detected. Whether the exception is a
fault or a trap depends on the condition (see Table 6-3). See Chapter 17, “Debug, Branch Profile, TSC, and
Resource Monitoring Features,” for detailed information about the debug exceptions.

Table 6-3. Debug Exception Conditions and Corresponding Exception Classes
Exception Condition

Exception Class

Instruction fetch breakpoint

Fault

Data read or write breakpoint

Trap

I/O read or write breakpoint

Trap

General detect condition (in conjunction with in-circuit emulation)

Fault

Single-step

Trap

Task-switch

Trap

Exception Error Code
None. An exception handler can examine the debug registers to determine which condition caused the exception.

Saved Instruction Pointer
Fault — Saved contents of CS and EIP registers point to the instruction that generated the exception.
Trap — Saved contents of CS and EIP registers point to the instruction following the instruction that generated the
exception.

Program State Change
Fault — A program-state change does not accompany the debug exception, because the exception occurs before
the faulting instruction is executed. The program can resume normal execution upon returning from the debug
exception handler.
Trap — A program-state change does accompany the debug exception, because the instruction or task switch being
executed is allowed to complete before the exception is generated. However, the new state of the program is not
corrupted and execution of the program can continue reliably.
Any debug exception inside an RTM region causes a transactional abort and, by default, redirects control flow to the
fallback instruction address. If advanced debugging of RTM transactional regions has been enabled, any transactional abort due to a debug exception instead causes execution to roll back to just before the XBEGIN instruction
and then delivers a #DB. See Section 16.3.7, “RTM-Enabled Debugger Support,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.

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Interrupt 2—NMI Interrupt
Exception Class

Not applicable.

Description
The nonmaskable interrupt (NMI) is generated externally by asserting the processor’s NMI pin or through an NMI
request set by the I/O APIC to the local APIC. This interrupt causes the NMI interrupt handler to be called.

Exception Error Code
Not applicable.
Saved Instruction Pointer
The processor always takes an NMI interrupt on an instruction boundary. The saved contents of CS and EIP registers point to the next instruction to be executed at the point the interrupt is taken. See Section 6.5, “Exception
Classifications,” for more information about when the processor takes NMI interrupts.

Program State Change
The instruction executing when an NMI interrupt is received is completed before the NMI is generated. A program
or task can thus be restarted upon returning from an interrupt handler without loss of continuity, provided the
interrupt handler saves the state of the processor before handling the interrupt and restores the processor’s state
prior to a return.

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Interrupt 3—Breakpoint Exception (#BP)
Exception Class

Trap.

Description
Indicates that a breakpoint instruction (INT 3, opcode CCH) was executed, causing a breakpoint trap to be generated. Typically, a debugger sets a breakpoint by replacing the first opcode byte of an instruction with the opcode
for the INT 3 instruction. (The INT 3 instruction is one byte long, which makes it easy to replace an opcode in a code
segment in RAM with the breakpoint opcode.) The operating system or a debugging tool can use a data segment
mapped to the same physical address space as the code segment to place an INT 3 instruction in places where it is
desired to call the debugger.
With the P6 family, Pentium, Intel486, and Intel386 processors, it is more convenient to set breakpoints with the
debug registers. (See Section 17.3.2, “Breakpoint Exception (#BP)—Interrupt Vector 3,” for information about the
breakpoint exception.) If more breakpoints are needed beyond what the debug registers allow, the INT 3 instruction can be used.
Any breakpoint exception inside an RTM region causes a transactional abort and, by default, redirects control flow
to the fallback instruction address. If advanced debugging of RTM transactional regions has been enabled, any
transactional abort due to a break exception instead causes execution to roll back to just before the XBEGIN
instruction and then delivers a debug exception (#DB) — not a breakpoint exception. See Section 16.3.7, “RTMEnabled Debugger Support,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.
A breakpoint exception can also be generated by executing the INT n instruction with an operand of 3. The action
of this instruction (INT 3) is slightly different than that of the INT 3 instruction (see “INTn/INTO/INT3—Call to
Interrupt Procedure” in Chapter 3 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
2A).

Exception Error Code
None.

Saved Instruction Pointer
Saved contents of CS and EIP registers point to the instruction following the INT 3 instruction.

Program State Change
Even though the EIP points to the instruction following the breakpoint instruction, the state of the program is
essentially unchanged because the INT 3 instruction does not affect any register or memory locations. The
debugger can thus resume the suspended program by replacing the INT 3 instruction that caused the breakpoint
with the original opcode and decrementing the saved contents of the EIP register. Upon returning from the
debugger, program execution resumes with the replaced instruction.

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Interrupt 4—Overflow Exception (#OF)
Exception Class

Trap.

Description
Indicates that an overflow trap occurred when an INTO instruction was executed. The INTO instruction checks the
state of the OF flag in the EFLAGS register. If the OF flag is set, an overflow trap is generated.
Some arithmetic instructions (such as the ADD and SUB) perform both signed and unsigned arithmetic. These
instructions set the OF and CF flags in the EFLAGS register to indicate signed overflow and unsigned overflow,
respectively. When performing arithmetic on signed operands, the OF flag can be tested directly or the INTO
instruction can be used. The benefit of using the INTO instruction is that if the overflow exception is detected, an
exception handler can be called automatically to handle the overflow condition.

Exception Error Code
None.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction following the INTO instruction.

Program State Change
Even though the EIP points to the instruction following the INTO instruction, the state of the program is essentially
unchanged because the INTO instruction does not affect any register or memory locations. The program can thus
resume normal execution upon returning from the overflow exception handler.

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Interrupt 5—BOUND Range Exceeded Exception (#BR)
Exception Class

Fault.

Description
Indicates that a BOUND-range-exceeded fault occurred when a BOUND instruction was executed. The BOUND
instruction checks that a signed array index is within the upper and lower bounds of an array located in memory. If
the array index is not within the bounds of the array, a BOUND-range-exceeded fault is generated.

Exception Error Code
None.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the BOUND instruction that generated the exception.

Program State Change
A program-state change does not accompany the bounds-check fault, because the operands for the BOUND
instruction are not modified. Returning from the BOUND-range-exceeded exception handler causes the BOUND
instruction to be restarted.

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Interrupt 6—Invalid Opcode Exception (#UD)
Exception Class

Fault.

Description
Indicates that the processor did one of the following things:

•
•

Attempted to execute an invalid or reserved opcode.

•

Attempted to execute an MMX or SSE/SSE2/SSE3 instruction on an Intel 64 or IA-32 processor that does not
support the MMX technology or SSE/SSE2/SSE3/SSSE3 extensions, respectively. CPUID feature flags MMX (bit
23), SSE (bit 25), SSE2 (bit 26), SSE3 (ECX, bit 0), SSSE3 (ECX, bit 9) indicate support for these extensions.

•

Attempted to execute an MMX instruction or SSE/SSE2/SSE3/SSSE3 SIMD instruction (with the exception of
the MOVNTI, PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, CLFLUSH, MONITOR, and MWAIT instructions)
when the EM flag in control register CR0 is set (1).

•

Attempted to execute an SSE/SE2/SSE3/SSSE3 instruction when the OSFXSR bit in control register CR4 is clear
(0). Note this does not include the following SSE/SSE2/SSE3 instructions: MASKMOVQ, MOVNTQ, MOVNTI,
PREFETCHh, SFENCE, LFENCE, MFENCE, and CLFLUSH; or the 64-bit versions of the PAVGB, PAVGW, PEXTRW,
PINSRW, PMAXSW, PMAXUB, PMINSW, PMINUB, PMOVMSKB, PMULHUW, PSADBW, PSHUFW, PADDQ, PSUBQ,
PALIGNR, PABSB, PABSD, PABSW, PHADDD, PHADDSW, PHADDW, PHSUBD, PHSUBSW, PHSUBW,
PMADDUBSM, PMULHRSW, PSHUFB, PSIGNB, PSIGND, and PSIGNW.

•

Attempted to execute an SSE/SSE2/SSE3/SSSE3 instruction on an Intel 64 or IA-32 processor that caused a
SIMD floating-point exception when the OSXMMEXCPT bit in control register CR4 is clear (0).

•

Executed a UD2 instruction. Note that even though it is the execution of the UD2 instruction that causes the
invalid opcode exception, the saved instruction pointer will still points at the UD2 instruction.

•

Detected a LOCK prefix that precedes an instruction that may not be locked or one that may be locked but the
destination operand is not a memory location.

•

Attempted to execute an LLDT, SLDT, LTR, STR, LSL, LAR, VERR, VERW, or ARPL instruction while in realaddress or virtual-8086 mode.

•

Attempted to execute the RSM instruction when not in SMM mode.

Attempted to execute an instruction with an operand type that is invalid for its accompanying opcode; for
example, the source operand for a LES instruction is not a memory location.

In Intel 64 and IA-32 processors that implement out-of-order execution microarchitectures, this exception is not
generated until an attempt is made to retire the result of executing an invalid instruction; that is, decoding and
speculatively attempting to execute an invalid opcode does not generate this exception. Likewise, in the Pentium
processor and earlier IA-32 processors, this exception is not generated as the result of prefetching and preliminary
decoding of an invalid instruction. (See Section 6.5, “Exception Classifications,” for general rules for taking of interrupts and exceptions.)
The opcodes D6 and F1 are undefined opcodes reserved by the Intel 64 and IA-32 architectures. These opcodes,
even though undefined, do not generate an invalid opcode exception.
The UD2 instruction is guaranteed to generate an invalid opcode exception.

Exception Error Code
None.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.

Program State Change
A program-state change does not accompany an invalid-opcode fault, because the invalid instruction is not
executed.

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Interrupt 7—Device Not Available Exception (#NM)
Exception Class

Fault.

Description
Indicates one of the following things:
The device-not-available exception is generated by either of three conditions:

•

The processor executed an x87 FPU floating-point instruction while the EM flag in control register CR0 was set
(1). See the paragraph below for the special case of the WAIT/FWAIT instruction.

•

The processor executed a WAIT/FWAIT instruction while the MP and TS flags of register CR0 were set,
regardless of the setting of the EM flag.

•

The processor executed an x87 FPU, MMX, or SSE/SSE2/SSE3 instruction (with the exception of MOVNTI,
PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, and CLFLUSH) while the TS flag in control register CR0 was set
and the EM flag is clear.

The EM flag is set when the processor does not have an internal x87 FPU floating-point unit. A device-not-available
exception is then generated each time an x87 FPU floating-point instruction is encountered, allowing an exception
handler to call floating-point instruction emulation routines.
The TS flag indicates that a context switch (task switch) has occurred since the last time an x87 floating-point,
MMX, or SSE/SSE2/SSE3 instruction was executed; but that the context of the x87 FPU, XMM, and MXCSR registers
were not saved. When the TS flag is set and the EM flag is clear, the processor generates a device-not-available
exception each time an x87 floating-point, MMX, or SSE/SSE2/SSE3 instruction is encountered (with the exception
of the instructions listed above). The exception handler can then save the context of the x87 FPU, XMM, and MXCSR
registers before it executes the instruction. See Section 2.5, “Control Registers,” for more information about the TS
flag.
The MP flag in control register CR0 is used along with the TS flag to determine if WAIT or FWAIT instructions should
generate a device-not-available exception. It extends the function of the TS flag to the WAIT and FWAIT instructions, giving the exception handler an opportunity to save the context of the x87 FPU before the WAIT or FWAIT
instruction is executed. The MP flag is provided primarily for use with the Intel 286 and Intel386 DX processors. For
programs running on the Pentium 4, Intel Xeon, P6 family, Pentium, or Intel486 DX processors, or the Intel 487 SX
coprocessors, the MP flag should always be set; for programs running on the Intel486 SX processor, the MP flag
should be clear.

Exception Error Code
None.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the floating-point instruction or the WAIT/FWAIT instruction
that generated the exception.

Program State Change
A program-state change does not accompany a device-not-available fault, because the instruction that generated
the exception is not executed.
If the EM flag is set, the exception handler can then read the floating-point instruction pointed to by the EIP and
call the appropriate emulation routine.
If the MP and TS flags are set or the TS flag alone is set, the exception handler can save the context of the x87 FPU,
clear the TS flag, and continue execution at the interrupted floating-point or WAIT/FWAIT instruction.

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Interrupt 8—Double Fault Exception (#DF)
Exception Class

Abort.

Description
Indicates that the processor detected a second exception while calling an exception handler for a prior exception.
Normally, when the processor detects another exception while trying to call an exception handler, the two exceptions can be handled serially. If, however, the processor cannot handle them serially, it signals the double-fault
exception. To determine when two faults need to be signalled as a double fault, the processor divides the exceptions into three classes: benign exceptions, contributory exceptions, and page faults (see Table 6-4).

Table 6-4. Interrupt and Exception Classes
Class

Vector Number

Description

Benign Exceptions and Interrupts

1
2
3
4
5
6
7
9
16
17
18

Debug
NMI Interrupt
Breakpoint
Overflow
BOUND Range Exceeded
Invalid Opcode
Device Not Available
Coprocessor Segment Overrun
Floating-Point Error
Alignment Check
Machine Check

19
All
All

SIMD floating-point
INT n
INTR

Contributory Exceptions

0
10
11
12
13

Divide Error
Invalid TSS
Segment Not Present
Stack Fault
General Protection

Page Faults

14
20

Page Fault
Virtualization Exception

Table 6-5 shows the various combinations of exception classes that cause a double fault to be generated. A doublefault exception falls in the abort class of exceptions. The program or task cannot be restarted or resumed. The
double-fault handler can be used to collect diagnostic information about the state of the machine and/or, when
possible, to shut the application and/or system down gracefully or restart the system.

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A segment or page fault may be encountered while prefetching instructions; however, this behavior is outside the
domain of Table 6-5. Any further faults generated while the processor is attempting to transfer control to the
appropriate fault handler could still lead to a double-fault sequence.

Table 6-5. Conditions for Generating a Double Fault
Second Exception
First Exception

Benign

Contributory

Page Fault

Benign

Handle Exceptions Serially

Handle Exceptions Serially

Handle Exceptions Serially

Contributory

Handle Exceptions Serially

Generate a Double Fault

Handle Exceptions Serially

Page Fault

Handle Exceptions Serially

Generate a Double Fault

Generate a Double Fault

Double Fault

Handle Exceptions Serially

Enter Shutdown Mode

Enter Shutdown Mode

If another contributory or page fault exception occurs while attempting to call the double-fault handler, the
processor enters shutdown mode. This mode is similar to the state following execution of an HLT instruction. In this
mode, the processor stops executing instructions until an NMI interrupt, SMI interrupt, hardware reset, or INIT# is
received. The processor generates a special bus cycle to indicate that it has entered shutdown mode. Software
designers may need to be aware of the response of hardware when it goes into shutdown mode. For example,
hardware may turn on an indicator light on the front panel, generate an NMI interrupt to record diagnostic information, invoke reset initialization, generate an INIT initialization, or generate an SMI. If any events are pending
during shutdown, they will be handled after an wake event from shutdown is processed (for example, A20M# interrupts).
If a shutdown occurs while the processor is executing an NMI interrupt handler, then only a hardware reset can
restart the processor. Likewise, if the shutdown occurs while executing in SMM, a hardware reset must be used to
restart the processor.

Exception Error Code
Zero. The processor always pushes an error code of 0 onto the stack of the double-fault handler.

Saved Instruction Pointer
The saved contents of CS and EIP registers are undefined.

Program State Change
A program-state following a double-fault exception is undefined. The program or task cannot be resumed or
restarted. The only available action of the double-fault exception handler is to collect all possible context information for use in diagnostics and then close the application and/or shut down or reset the processor.
If the double fault occurs when any portion of the exception handling machine state is corrupted, the handler
cannot be invoked and the processor must be reset.

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INTERRUPT AND EXCEPTION HANDLING

Interrupt 9—Coprocessor Segment Overrun
Exception Class

Abort. (Intel reserved; do not use. Recent IA-32 processors do not generate this
exception.)

Description
Indicates that an Intel386 CPU-based systems with an Intel 387 math coprocessor detected a page or segment
violation while transferring the middle portion of an Intel 387 math coprocessor operand. The P6 family, Pentium,
and Intel486 processors do not generate this exception; instead, this condition is detected with a general protection exception (#GP), interrupt 13.

Exception Error Code
None.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.

Program State Change
A program-state following a coprocessor segment-overrun exception is undefined. The program or task cannot
be resumed or restarted. The only available action of the exception handler is to save the instruction pointer and
reinitialize the x87 FPU using the FNINIT instruction.

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Interrupt 10—Invalid TSS Exception (#TS)
Exception Class

Fault.

Description
Indicates that there was an error related to a TSS. Such an error might be detected during a task switch or during
the execution of instructions that use information from a TSS. Table 6-6 shows the conditions that cause an invalid
TSS exception to be generated.

Table 6-6. Invalid TSS Conditions
Error Code Index

Invalid Condition

TSS segment selector index

The TSS segment limit is less than 67H for 32-bit TSS or less than 2CH for 16-bit TSS.

TSS segment selector index

During an IRET task switch, the TI flag in the TSS segment selector indicates the LDT.

TSS segment selector index

During an IRET task switch, the TSS segment selector exceeds descriptor table limit.

TSS segment selector index

During an IRET task switch, the busy flag in the TSS descriptor indicates an inactive task.

TSS segment selector index

During a task switch, an attempt to access data in a TSS results in a limit violation or
canonical fault.

TSS segment selector index

During an IRET task switch, the backlink is a NULL selector.

TSS segment selector index

During an IRET task switch, the backlink points to a descriptor which is not a busy TSS.

TSS segment selector index

The new TSS descriptor is beyond the GDT limit.

TSS segment selector index

The new TSS selector is null on an attempt to lock the new TSS.

TSS segment selector index

The new TSS selector has the TI bit set on an attempt to lock the new TSS.

TSS segment selector index

The new TSS descriptor is not an available TSS descriptor on an attempt to lock the new
TSS.

LDT segment selector index

LDT not valid or not present.

Stack segment selector index

The stack segment selector exceeds descriptor table limit.

Stack segment selector index

The stack segment selector is NULL.

Stack segment selector index

The stack segment descriptor is a non-data segment.

Stack segment selector index

The stack segment is not writable.

Stack segment selector index

The stack segment DPL ≠ CPL.

Stack segment selector index

The stack segment selector RPL ≠ CPL.

Code segment selector index

The code segment selector exceeds descriptor table limit.

Code segment selector index

The code segment selector is NULL.

Code segment selector index

The code segment descriptor is not a code segment type.

Code segment selector index

The nonconforming code segment DPL ≠ CPL.

Code segment selector index

The conforming code segment DPL is greater than CPL.

Data segment selector index

The data segment selector exceeds the descriptor table limit.

Data segment selector index

The data segment descriptor is not a readable code or data type.

Data segment selector index

The data segment descriptor is a nonconforming code type and RPL > DPL.

Data segment selector index

The data segment descriptor is a nonconforming code type and CPL > DPL.

TSS segment selector index

The TSS segment descriptor/upper descriptor is beyond the GDT segment limit.

TSS segment selector index

The TSS segment descriptor is not an available TSS type.

TSS segment selector index

The TSS segment descriptor is an available 286 TSS type in IA-32e mode.
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INTERRUPT AND EXCEPTION HANDLING

Table 6-6. Invalid TSS Conditions (Contd.)
Error Code Index

Invalid Condition

TSS segment selector index

The TSS segment upper descriptor is not the correct type.

TSS segment selector index

The TSS segment descriptor contains a non-canonical base.

This exception can generated either in the context of the original task or in the context of the new task (see Section
7.3, “Task Switching”). Until the processor has completely verified the presence of the new TSS, the exception is
generated in the context of the original task. Once the existence of the new TSS is verified, the task switch is
considered complete. Any invalid-TSS conditions detected after this point are handled in the context of the new
task. (A task switch is considered complete when the task register is loaded with the segment selector for the new
TSS and, if the switch is due to a procedure call or interrupt, the previous task link field of the new TSS references
the old TSS.)
The invalid-TSS handler must be a task called using a task gate. Handling this exception inside the faulting TSS
context is not recommended because the processor state may not be consistent.

Exception Error Code
An error code containing the segment selector index for the segment descriptor that caused the violation is pushed
onto the stack of the exception handler. If the EXT flag is set, it indicates that the exception was caused by an event
external to the currently running program (for example, if an external interrupt handler using a task gate
attempted a task switch to an invalid TSS).

Saved Instruction Pointer
If the exception condition was detected before the task switch was carried out, the saved contents of CS and EIP
registers point to the instruction that invoked the task switch. If the exception condition was detected after the task
switch was carried out, the saved contents of CS and EIP registers point to the first instruction of the new task.

Program State Change
The ability of the invalid-TSS handler to recover from the fault depends on the error condition than causes the fault.
See Section 7.3, “Task Switching,” for more information on the task switch process and the possible recovery
actions that can be taken.
If an invalid TSS exception occurs during a task switch, it can occur before or after the commit-to-new-task point.
If it occurs before the commit point, no program state change occurs. If it occurs after the commit point (when the
segment descriptor information for the new segment selectors have been loaded in the segment registers), the
processor will load all the state information from the new TSS before it generates the exception. During a task
switch, the processor first loads all the segment registers with segment selectors from the TSS, then checks their
contents for validity. If an invalid TSS exception is discovered, the remaining segment registers are loaded but not
checked for validity and therefore may not be usable for referencing memory. The invalid TSS handler should not
rely on being able to use the segment selectors found in the CS, SS, DS, ES, FS, and GS registers without causing
another exception. The exception handler should load all segment registers before trying to resume the new task;
otherwise, general-protection exceptions (#GP) may result later under conditions that make diagnosis more difficult. The Intel recommended way of dealing situation is to use a task for the invalid TSS exception handler. The task
switch back to the interrupted task from the invalid-TSS exception-handler task will then cause the processor to
check the registers as it loads them from the TSS.

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Interrupt 11—Segment Not Present (#NP)
Exception Class

Fault.

Description
Indicates that the present flag of a segment or gate descriptor is clear. The processor can generate this exception
during any of the following operations:

•

While attempting to load CS, DS, ES, FS, or GS registers. [Detection of a not-present segment while loading the
SS register causes a stack fault exception (#SS) to be generated.] This situation can occur while performing a
task switch.

•

While attempting to load the LDTR using an LLDT instruction. Detection of a not-present LDT while loading the
LDTR during a task switch operation causes an invalid-TSS exception (#TS) to be generated.

•
•

When executing the LTR instruction and the TSS is marked not present.
While attempting to use a gate descriptor or TSS that is marked segment-not-present, but is otherwise valid.

An operating system typically uses the segment-not-present exception to implement virtual memory at the
segment level. If the exception handler loads the segment and returns, the interrupted program or task resumes
execution.
A not-present indication in a gate descriptor, however, does not indicate that a segment is not present (because
gates do not correspond to segments). The operating system may use the present flag for gate descriptors to
trigger exceptions of special significance to the operating system.
A contributory exception or page fault that subsequently referenced a not-present segment would cause a double
fault (#DF) to be generated instead of #NP.

Exception Error Code
An error code containing the segment selector index for the segment descriptor that caused the violation is pushed
onto the stack of the exception handler. If the EXT flag is set, it indicates that the exception resulted from either:

•

an external event (NMI or INTR) that caused an interrupt, which subsequently referenced a not-present
segment

•

a benign exception that subsequently referenced a not-present segment

The IDT flag is set if the error code refers to an IDT entry. This occurs when the IDT entry for an interrupt being
serviced references a not-present gate. Such an event could be generated by an INT instruction or a hardware
interrupt.

Saved Instruction Pointer
The saved contents of CS and EIP registers normally point to the instruction that generated the exception. If the
exception occurred while loading segment descriptors for the segment selectors in a new TSS, the CS and EIP
registers point to the first instruction in the new task. If the exception occurred while accessing a gate descriptor,
the CS and EIP registers point to the instruction that invoked the access (for example a CALL instruction that references a call gate).

Program State Change
If the segment-not-present exception occurs as the result of loading a register (CS, DS, SS, ES, FS, GS, or LDTR),
a program-state change does accompany the exception because the register is not loaded. Recovery from this
exception is possible by simply loading the missing segment into memory and setting the present flag in the
segment descriptor.
If the segment-not-present exception occurs while accessing a gate descriptor, a program-state change does not
accompany the exception. Recovery from this exception is possible merely by setting the present flag in the gate
descriptor.
If a segment-not-present exception occurs during a task switch, it can occur before or after the commit-to-newtask point (see Section 7.3, “Task Switching”). If it occurs before the commit point, no program state change
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INTERRUPT AND EXCEPTION HANDLING

occurs. If it occurs after the commit point, the processor will load all the state information from the new TSS
(without performing any additional limit, present, or type checks) before it generates the exception. The segmentnot-present exception handler should not rely on being able to use the segment selectors found in the CS, SS, DS,
ES, FS, and GS registers without causing another exception. (See the Program State Change description for “Interrupt 10—Invalid TSS Exception (#TS)” in this chapter for additional information on how to handle this situation.)

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Interrupt 12—Stack Fault Exception (#SS)
Exception Class

Fault.

Description
Indicates that one of the following stack related conditions was detected:

•

A limit violation is detected during an operation that refers to the SS register. Operations that can cause a limit
violation include stack-oriented instructions such as POP, PUSH, CALL, RET, IRET, ENTER, and LEAVE, as well as
other memory references which implicitly or explicitly use the SS register (for example, MOV AX, [BP+6] or
MOV AX, SS:[EAX+6]). The ENTER instruction generates this exception when there is not enough stack space
for allocating local variables.

•

A not-present stack segment is detected when attempting to load the SS register. This violation can occur
during the execution of a task switch, a CALL instruction to a different privilege level, a return to a different
privilege level, an LSS instruction, or a MOV or POP instruction to the SS register.

•

A canonical violation is detected in 64-bit mode during an operation that reference memory using the stack
pointer register containing a non-canonical memory address.

Recovery from this fault is possible by either extending the limit of the stack segment (in the case of a limit violation) or loading the missing stack segment into memory (in the case of a not-present violation.
In the case of a canonical violation that was caused intentionally by software, recovery is possible by loading the
correct canonical value into RSP. Otherwise, a canonical violation of the address in RSP likely reflects some register
corruption in the software.

Exception Error Code
If the exception is caused by a not-present stack segment or by overflow of the new stack during an inter-privilegelevel call, the error code contains a segment selector for the segment that caused the exception. Here, the exception handler can test the present flag in the segment descriptor pointed to by the segment selector to determine
the cause of the exception. For a normal limit violation (on a stack segment already in use) the error code is set to
0.

Saved Instruction Pointer
The saved contents of CS and EIP registers generally point to the instruction that generated the exception.
However, when the exception results from attempting to load a not-present stack segment during a task switch,
the CS and EIP registers point to the first instruction of the new task.

Program State Change
A program-state change does not generally accompany a stack-fault exception, because the instruction that generated the fault is not executed. Here, the instruction can be restarted after the exception handler has corrected the
stack fault condition.
If a stack fault occurs during a task switch, it occurs after the commit-to-new-task point (see Section 7.3, “Task
Switching”). Here, the processor loads all the state information from the new TSS (without performing any additional limit, present, or type checks) before it generates the exception. The stack fault handler should thus not rely
on being able to use the segment selectors found in the CS, SS, DS, ES, FS, and GS registers without causing
another exception. The exception handler should check all segment registers before trying to resume the new
task; otherwise, general protection faults may result later under conditions that are more difficult to diagnose.
(See the Program State Change description for “Interrupt 10—Invalid TSS Exception (#TS)” in this chapter for
additional information on how to handle this situation.)

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Interrupt 13—General Protection Exception (#GP)
Exception Class

Fault.

Description
Indicates that the processor detected one of a class of protection violations called “general-protection violations.”
The conditions that cause this exception to be generated comprise all the protection violations that do not cause
other exceptions to be generated (such as, invalid-TSS, segment-not-present, stack-fault, or page-fault exceptions). The following conditions cause general-protection exceptions to be generated:

•
•

Exceeding the segment limit when accessing the CS, DS, ES, FS, or GS segments.

•
•
•
•

Transferring execution to a segment that is not executable.

•
•
•
•
•
•
•

Loading the SS, DS, ES, FS, or GS register with a segment selector for a system segment.

•
•

Violating any of the privilege rules described in Chapter 5, “Protection.”

•
•
•
•

Loading the CR0 register with a set PG flag (paging enabled) and a clear PE flag (protection disabled).

•
•

Attempting to write a 1 into a reserved bit of CR4.

•
•
•
•

Attempting to execute SGDT, SIDT, SLDT, SMSW, or STR when CR4.UMIP = 1 and the CPL is not equal to 0.

Exceeding the segment limit when referencing a descriptor table (except during a task switch or a stack
switch).
Writing to a code segment or a read-only data segment.
Reading from an execute-only code segment.
Loading the SS register with a segment selector for a read-only segment (unless the selector comes from a TSS
during a task switch, in which case an invalid-TSS exception occurs).
Loading the DS, ES, FS, or GS register with a segment selector for an execute-only code segment.
Loading the SS register with the segment selector of an executable segment or a null segment selector.
Loading the CS register with a segment selector for a data segment or a null segment selector.
Accessing memory using the DS, ES, FS, or GS register when it contains a null segment selector.
Switching to a busy task during a call or jump to a TSS.
Using a segment selector on a non-IRET task switch that points to a TSS descriptor in the current LDT. TSS
descriptors can only reside in the GDT. This condition causes a #TS exception during an IRET task switch.
Exceeding the instruction length limit of 15 bytes (this only can occur when redundant prefixes are placed
before an instruction).
Loading the CR0 register with a set NW flag and a clear CD flag.
Referencing an entry in the IDT (following an interrupt or exception) that is not an interrupt, trap, or task gate.
Attempting to access an interrupt or exception handler through an interrupt or trap gate from virtual-8086
mode when the handler’s code segment DPL is greater than 0.
Attempting to execute a privileged instruction when the CPL is not equal to 0 (see Section 5.9, “Privileged
Instructions,” for a list of privileged instructions).
Writing to a reserved bit in an MSR.
Accessing a gate that contains a null segment selector.
Executing the INT n instruction when the CPL is greater than the DPL of the referenced interrupt, trap, or task
gate.

•
•

The segment selector in a call, interrupt, or trap gate does not point to a code segment.

•
•

The segment selector operand in the LTR instruction is local or points to a TSS that is not available.

The segment selector operand in the LLDT instruction is a local type (TI flag is set) or does not point to a
segment descriptor of the LDT type.
The target code-segment selector for a call, jump, or return is null.

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•

If the PAE and/or PSE flag in control register CR4 is set and the processor detects any reserved bits in a pagedirectory-pointer-table entry set to 1. These bits are checked during a write to control registers CR0, CR3, or
CR4 that causes a reloading of the page-directory-pointer-table entry.

•
•

Attempting to write a non-zero value into the reserved bits of the MXCSR register.
Executing an SSE/SSE2/SSE3 instruction that attempts to access a 128-bit memory location that is not aligned
on a 16-byte boundary when the instruction requires 16-byte alignment. This condition also applies to the
stack segment.

A program or task can be restarted following any general-protection exception. If the exception occurs while
attempting to call an interrupt handler, the interrupted program can be restartable, but the interrupt may be lost.

Exception Error Code
The processor pushes an error code onto the exception handler's stack. If the fault condition was detected while
loading a segment descriptor, the error code contains a segment selector to or IDT vector number for the
descriptor; otherwise, the error code is 0. The source of the selector in an error code may be any of the following:

•
•
•
•

An operand of the instruction.
A selector from a gate which is the operand of the instruction.
A selector from a TSS involved in a task switch.
IDT vector number.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.

Program State Change
In general, a program-state change does not accompany a general-protection exception, because the invalid
instruction or operation is not executed. An exception handler can be designed to correct all of the conditions that
cause general-protection exceptions and restart the program or task without any loss of program continuity.
If a general-protection exception occurs during a task switch, it can occur before or after the commit-to-new-task
point (see Section 7.3, “Task Switching”). If it occurs before the commit point, no program state change occurs. If
it occurs after the commit point, the processor will load all the state information from the new TSS (without
performing any additional limit, present, or type checks) before it generates the exception. The general-protection
exception handler should thus not rely on being able to use the segment selectors found in the CS, SS, DS, ES, FS,
and GS registers without causing another exception. (See the Program State Change description for “Interrupt
10—Invalid TSS Exception (#TS)” in this chapter for additional information on how to handle this situation.)

General Protection Exception in 64-bit Mode
The following conditions cause general-protection exceptions in 64-bit mode:

•
•
•
•
•

If the memory address is in a non-canonical form.

•
•
•
•
•

If the EFLAGS.NT bit is set in IRET.

If a segment descriptor memory address is in non-canonical form.
If the target offset in a destination operand of a call or jmp is in a non-canonical form.
If a code segment or 64-bit call gate overlaps non-canonical space.
If the code segment descriptor pointed to by the selector in the 64-bit gate doesn't have the L-bit set and the
D-bit clear.
If the stack segment selector of IRET is null when going back to compatibility mode.
If the stack segment selector of IRET is null going back to CPL3 and 64-bit mode.
If a null stack segment selector RPL of IRET is not equal to CPL going back to non-CPL3 and 64-bit mode.
If the proposed new code segment descriptor of IRET has both the D-bit and the L-bit set.

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INTERRUPT AND EXCEPTION HANDLING

•

If the segment descriptor pointed to by the segment selector in the destination operand is a code segment and
it has both the D-bit and the L-bit set.

•
•
•
•
•
•

If the segment descriptor from a 64-bit call gate is in non-canonical space.

•
•

If an attempt is made to clear CR0.PG while IA-32e mode is enabled.

If the DPL from a 64-bit call-gate is less than the CPL or than the RPL of the 64-bit call-gate.
If the type field of the upper 64 bits of a 64-bit call gate is not 0.
If an attempt is made to load a null selector in the SS register in compatibility mode.
If an attempt is made to load null selector in the SS register in CPL3 and 64-bit mode.
If an attempt is made to load a null selector in the SS register in non-CPL3 and 64-bit mode where RPL is not
equal to CPL.
If an attempt is made to set a reserved bit in CR3, CR4 or CR8.

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Interrupt 14—Page-Fault Exception (#PF)
Exception Class

Fault.

Description
Indicates that, with paging enabled (the PG flag in the CR0 register is set), the processor detected one of the
following conditions while using the page-translation mechanism to translate a linear address to a physical
address:

•

The P (present) flag in a page-directory or page-table entry needed for the address translation is clear,
indicating that a page table or the page containing the operand is not present in physical memory.

•

The procedure does not have sufficient privilege to access the indicated page (that is, a procedure running in
user mode attempts to access a supervisor-mode page). If the SMAP flag is set in CR4, a page fault may also
be triggered by code running in supervisor mode that tries to access data at a user-mode address. If the PKE
flag is set in CR4, the PKRU register may cause page faults on data accesses to user-mode addresses with
certain protection keys.

•

Code running in user mode attempts to write to a read-only page. If the WP flag is set in CR0, the page fault
will also be triggered by code running in supervisor mode that tries to write to a read-only page.

•

An instruction fetch to a linear address that translates to a physical address in a memory page with the
execute-disable bit set (for information about the execute-disable bit, see Chapter 4, “Paging”). If the SMEP
flag is set in CR4, a page fault will also be triggered by code running in supervisor mode that tries to fetch an
instruction from a user-mode address.

•
•

One or more reserved bits in paging-structure entry are set to 1. See description below of RSVD error code flag.
An enclave access violates one of the specified access-control requirements. See Section 37.3, “Access-control
Requirements” and Section 37.19, “Enclave Page Cache Map (EPCM)” in Chapter 37, “Enclave Access Control
and Data Structures.” In this case, the exception is called an SGX-induced page fault. The processor uses the
error code (below) to distinguish SGX-induced page faults from ordinary page faults.

The exception handler can recover from page-not-present conditions and restart the program or task without any
loss of program continuity. It can also restart the program or task after a privilege violation, but the problem that
caused the privilege violation may be uncorrectable.
See also: Section 4.7, “Page-Fault Exceptions.”

Exception Error Code
Yes (special format). The processor provides the page-fault handler with two items of information to aid in diagnosing the exception and recovering from it:

•

An error code on the stack. The error code for a page fault has a format different from that for other exceptions
(see Figure 6-9). The processor establishes the bits in the error code as follows:
— P flag (bit 0).
This flag is 0 if there is no translation for the linear address because the P flag was 0 in one of the pagingstructure entries used to translate that address.
— W/R (bit 1).
If the access causing the page-fault exception was a write, this flag is 1; otherwise, it is 0. This flag
describes the access causing the page-fault exception, not the access rights specified by paging.
— U/S (bit 2).
If a user-mode access caused the page-fault exception, this flag is 1; it is 0 if a supervisor-mode access did
so. This flag describes the access causing the page-fault exception, not the access rights specified by
paging.
— RSVD flag (bit 3).
This flag is 1 if there is no translation for the linear address because a reserved bit was set in one of the
paging-structure entries used to translate that address.

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— I/D flag (bit 4).
This flag is 1 if the access causing the page-fault exception was an instruction fetch. This flag describes the
access causing the page-fault exception, not the access rights specified by paging.
— PK flag (bit 5).
This flag is 1 if the access causing the page-fault exception was a data access to a user-mode address with
protection key disallowed by the value of the PKRU register.
— SGX flag (bit 15).
This flag is 1 if the exception is unrelated to paging and resulted from violation of SGX-specific accesscontrol requirements. Because such a violation can occur only if there is no ordinary page fault, this flag is
set only if the P flag (bit 0) is 1 and the RSVD flag (bit 3) and the PK flag (bit 5) are both 0.
See Section 4.6, “Access Rights” and Section 4.7, “Page-Fault Exceptions” for more information about pagefault exceptions and the error codes that they produce.

31

5 4 3 2 1 0

15

Reserved

P
W/R
U/S
RSVD
I/D
PK

SGX

Reserved
P

0 The fault was caused by a non-present page.
1 The fault was caused by a page-level protection violation.

W/R

0 The access causing the fault was a read.
1 The access causing the fault was a write.

U/S

0 A supervisor-mode access caused the fault.
1 A user-mode access caused the fault.

RSVD

0 The fault was not caused by reserved bit violation.
1 The fault was caused by a reserved bit set to 1 in some
paging-structure entry.

I/D

0 The fault was not caused by an instruction fetch.
1 The fault was caused by an instruction fetch.

PK

0 The fault was not caused by protection keys.
1 There was a protection-key violation.

SGX

0 The fault is not related to SGX.
1 The fault resulted from violation of SGX-specific access-control
requirements.

Figure 6-9. Page-Fault Error Code

•

The contents of the CR2 register. The processor loads the CR2 register with the 32-bit linear address that
generated the exception. The page-fault handler can use this address to locate the corresponding page
directory and page-table entries. Another page fault can potentially occur during execution of the page-fault
handler; the handler should save the contents of the CR2 register before a second page fault can occur.1 If a
page fault is caused by a page-level protection violation, the access flag in the page-directory entry is set when
the fault occurs. The behavior of IA-32 processors regarding the access flag in the corresponding page-table
entry is model specific and not architecturally defined.

1. Processors update CR2 whenever a page fault is detected. If a second page fault occurs while an earlier page fault is being delivered, the faulting linear address of the second fault will overwrite the contents of CR2 (replacing the previous address). These
updates to CR2 occur even if the page fault results in a double fault or occurs during the delivery of a double fault.
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Saved Instruction Pointer
The saved contents of CS and EIP registers generally point to the instruction that generated the exception. If the
page-fault exception occurred during a task switch, the CS and EIP registers may point to the first instruction of the
new task (as described in the following “Program State Change” section).

Program State Change
A program-state change does not normally accompany a page-fault exception, because the instruction that causes
the exception to be generated is not executed. After the page-fault exception handler has corrected the violation
(for example, loaded the missing page into memory), execution of the program or task can be resumed.
When a page-fault exception is generated during a task switch, the program-state may change, as follows. During
a task switch, a page-fault exception can occur during any of following operations:

•
•
•
•
•

While writing the state of the original task into the TSS of that task.
While reading the GDT to locate the TSS descriptor of the new task.
While reading the TSS of the new task.
While reading segment descriptors associated with segment selectors from the new task.
While reading the LDT of the new task to verify the segment registers stored in the new TSS.

In the last two cases the exception occurs in the context of the new task. The instruction pointer refers to the first
instruction of the new task, not to the instruction which caused the task switch (or the last instruction to be
executed, in the case of an interrupt). If the design of the operating system permits page faults to occur during
task-switches, the page-fault handler should be called through a task gate.
If a page fault occurs during a task switch, the processor will load all the state information from the new TSS
(without performing any additional limit, present, or type checks) before it generates the exception. The page-fault
handler should thus not rely on being able to use the segment selectors found in the CS, SS, DS, ES, FS, and GS
registers without causing another exception. (See the Program State Change description for “Interrupt 10—Invalid
TSS Exception (#TS)” in this chapter for additional information on how to handle this situation.)

Additional Exception-Handling Information
Special care should be taken to ensure that an exception that occurs during an explicit stack switch does not cause
the processor to use an invalid stack pointer (SS:ESP). Software written for 16-bit IA-32 processors often use a
pair of instructions to change to a new stack, for example:
MOV SS, AX
MOV SP, StackTop
When executing this code on one of the 32-bit IA-32 processors, it is possible to get a page fault, general-protection fault (#GP), or alignment check fault (#AC) after the segment selector has been loaded into the SS register
but before the ESP register has been loaded. At this point, the two parts of the stack pointer (SS and ESP) are
inconsistent. The new stack segment is being used with the old stack pointer.
The processor does not use the inconsistent stack pointer if the exception handler switches to a well defined stack
(that is, the handler is a task or a more privileged procedure). However, if the exception handler is called at the
same privilege level and from the same task, the processor will attempt to use the inconsistent stack pointer.
In systems that handle page-fault, general-protection, or alignment check exceptions within the faulting task (with
trap or interrupt gates), software executing at the same privilege level as the exception handler should initialize a
new stack by using the LSS instruction rather than a pair of MOV instructions, as described earlier in this note.
When the exception handler is running at privilege level 0 (the normal case), the problem is limited to procedures
or tasks that run at privilege level 0, typically the kernel of the operating system.

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Interrupt 16—x87 FPU Floating-Point Error (#MF)
Exception Class

Fault.

Description
Indicates that the x87 FPU has detected a floating-point error. The NE flag in the register CR0 must be set for an
interrupt 16 (floating-point error exception) to be generated. (See Section 2.5, “Control Registers,” for a detailed
description of the NE flag.)

NOTE
SIMD floating-point exceptions (#XM) are signaled through interrupt 19.
While executing x87 FPU instructions, the x87 FPU detects and reports six types of floating-point error conditions:

•

Invalid operation (#I)
— Stack overflow or underflow (#IS)
— Invalid arithmetic operation (#IA)

•
•
•
•
•

Divide-by-zero (#Z)
Denormalized operand (#D)
Numeric overflow (#O)
Numeric underflow (#U)
Inexact result (precision) (#P)

Each of these error conditions represents an x87 FPU exception type, and for each of exception type, the x87 FPU
provides a flag in the x87 FPU status register and a mask bit in the x87 FPU control register. If the x87 FPU detects
a floating-point error and the mask bit for the exception type is set, the x87 FPU handles the exception automatically by generating a predefined (default) response and continuing program execution. The default responses have
been designed to provide a reasonable result for most floating-point applications.
If the mask for the exception is clear and the NE flag in register CR0 is set, the x87 FPU does the following:
1. Sets the necessary flag in the FPU status register.
2. Waits until the next “waiting” x87 FPU instruction or WAIT/FWAIT instruction is encountered in the program’s
instruction stream.
3. Generates an internal error signal that cause the processor to generate a floating-point exception (#MF).
Prior to executing a waiting x87 FPU instruction or the WAIT/FWAIT instruction, the x87 FPU checks for pending x87
FPU floating-point exceptions (as described in step 2 above). Pending x87 FPU floating-point exceptions are
ignored for “non-waiting” x87 FPU instructions, which include the FNINIT, FNCLEX, FNSTSW, FNSTSW AX, FNSTCW,
FNSTENV, and FNSAVE instructions. Pending x87 FPU exceptions are also ignored when executing the state
management instructions FXSAVE and FXRSTOR.
All of the x87 FPU floating-point error conditions can be recovered from. The x87 FPU floating-point-error exception
handler can determine the error condition that caused the exception from the settings of the flags in the x87 FPU
status word. See “Software Exception Handling” in Chapter 8 of the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1, for more information on handling x87 FPU floating-point exceptions.

Exception Error Code
None. The x87 FPU provides its own error information.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the floating-point or WAIT/FWAIT instruction that was about to
be executed when the floating-point-error exception was generated. This is not the faulting instruction in which the
error condition was detected. The address of the faulting instruction is contained in the x87 FPU instruction pointer
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register. See Section 8.1.8, “x87 FPU Instruction and Data (Operand) Pointers” in Chapter 8 of the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 1, for more information about information the FPU saves
for use in handling floating-point-error exceptions.

Program State Change
A program-state change generally accompanies an x87 FPU floating-point exception because the handling of the
exception is delayed until the next waiting x87 FPU floating-point or WAIT/FWAIT instruction following the faulting
instruction. The x87 FPU, however, saves sufficient information about the error condition to allow recovery from the
error and re-execution of the faulting instruction if needed.
In situations where non- x87 FPU floating-point instructions depend on the results of an x87 FPU floating-point
instruction, a WAIT or FWAIT instruction can be inserted in front of a dependent instruction to force a pending x87
FPU floating-point exception to be handled before the dependent instruction is executed. See “x87 FPU Exception
Synchronization” in Chapter 8 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1,
for more information about synchronization of x87 floating-point-error exceptions.

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Interrupt 17—Alignment Check Exception (#AC)
Exception Class

Fault.

Description
Indicates that the processor detected an unaligned memory operand when alignment checking was enabled. Alignment checks are only carried out in data (or stack) accesses (not in code fetches or system segment accesses). An
example of an alignment-check violation is a word stored at an odd byte address, or a doubleword stored at an
address that is not an integer multiple of 4. Table 6-7 lists the alignment requirements various data types recognized by the processor.

Table 6-7. Alignment Requirements by Data Type
Data Type

Address Must Be Divisible By

Word

2

Doubleword

4

Single-precision floating-point (32-bits)

4

Double-precision floating-point (64-bits)

8

Double extended-precision floating-point (80-bits)

8

Quadword

8

Double quadword

16

Segment Selector

2

32-bit Far Pointer

2

48-bit Far Pointer

4

32-bit Pointer

4

GDTR, IDTR, LDTR, or Task Register Contents

4

FSTENV/FLDENV Save Area

4 or 2, depending on operand size

FSAVE/FRSTOR Save Area

4 or 2, depending on operand size

Bit String

2 or 4 depending on the operand-size attribute.

Note that the alignment check exception (#AC) is generated only for data types that must be aligned on word,
doubleword, and quadword boundaries. A general-protection exception (#GP) is generated 128-bit data types that
are not aligned on a 16-byte boundary.
To enable alignment checking, the following conditions must be true:

•
•
•

AM flag in CR0 register is set.
AC flag in the EFLAGS register is set.
The CPL is 3 (protected mode or virtual-8086 mode).

Alignment-check exceptions (#AC) are generated only when operating at privilege level 3 (user mode). Memory
references that default to privilege level 0, such as segment descriptor loads, do not generate alignment-check
exceptions, even when caused by a memory reference made from privilege level 3.
Storing the contents of the GDTR, IDTR, LDTR, or task register in memory while at privilege level 3 can generate
an alignment-check exception. Although application programs do not normally store these registers, the fault can
be avoided by aligning the information stored on an even word-address.
The FXSAVE/XSAVE and FXRSTOR/XRSTOR instructions save and restore a 512-byte data structure, the first byte
of which must be aligned on a 16-byte boundary. If the alignment-check exception (#AC) is enabled when
executing these instructions (and CPL is 3), a misaligned memory operand can cause either an alignment-check
exception or a general-protection exception (#GP) depending on the processor implementation (see “FXSAVE-Save
x87 FPU, MMX, SSE, and SSE2 State” and “FXRSTOR-Restore x87 FPU, MMX, SSE, and SSE2 State” in Chapter 3

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of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A; see “XSAVE—Save Processor
Extended States” and “XRSTOR—Restore Processor Extended States” in Chapter 5 of the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 2C).
The MOVDQU, MOVUPS, and MOVUPD instructions perform 128-bit unaligned loads or stores. The LDDQU instructions loads 128-bit unaligned data. They do not generate general-protection exceptions (#GP) when operands are
not aligned on a 16-byte boundary. If alignment checking is enabled, alignment-check exceptions (#AC) may or
may not be generated depending on processor implementation when data addresses are not aligned on an 8-byte
boundary.
FSAVE and FRSTOR instructions can generate unaligned references, which can cause alignment-check faults.
These instructions are rarely needed by application programs.

Exception Error Code
Yes. The error code is null; all bits are clear except possibly bit 0 — EXT; see Section 6.13. EXT is set if the #AC is
recognized during delivery of an event other than a software interrupt (see “INT n/INTO/INT 3—Call to Interrupt
Procedure” in Chapter 3 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A).

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that generated the exception.

Program State Change
A program-state change does not accompany an alignment-check fault, because the instruction is not executed.

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Interrupt 18—Machine-Check Exception (#MC)
Exception Class

Abort.

Description
Indicates that the processor detected an internal machine error or a bus error, or that an external agent detected
a bus error. The machine-check exception is model-specific, available on the Pentium and later generations of
processors. The implementation of the machine-check exception is different between different processor families,
and these implementations may not be compatible with future Intel 64 or IA-32 processors. (Use the CPUID
instruction to determine whether this feature is present.)
Bus errors detected by external agents are signaled to the processor on dedicated pins: the BINIT# and MCERR#
pins on the Pentium 4, Intel Xeon, and P6 family processors and the BUSCHK# pin on the Pentium processor. When
one of these pins is enabled, asserting the pin causes error information to be loaded into machine-check registers
and a machine-check exception is generated.
The machine-check exception and machine-check architecture are discussed in detail in Chapter 15, “MachineCheck Architecture.” Also, see the data books for the individual processors for processor-specific hardware information.

Exception Error Code
None. Error information is provide by machine-check MSRs.

Saved Instruction Pointer
For the Pentium 4 and Intel Xeon processors, the saved contents of extended machine-check state registers are
directly associated with the error that caused the machine-check exception to be generated (see Section 15.3.1.2,
“IA32_MCG_STATUS MSR,” and Section 15.3.2.6, “IA32_MCG Extended Machine Check State MSRs”).
For the P6 family processors, if the EIPV flag in the MCG_STATUS MSR is set, the saved contents of CS and EIP
registers are directly associated with the error that caused the machine-check exception to be generated; if the flag
is clear, the saved instruction pointer may not be associated with the error (see Section 15.3.1.2,
“IA32_MCG_STATUS MSR”).
For the Pentium processor, contents of the CS and EIP registers may not be associated with the error.

Program State Change
The machine-check mechanism is enabled by setting the MCE flag in control register CR4.
For the Pentium 4, Intel Xeon, P6 family, and Pentium processors, a program-state change always accompanies a
machine-check exception, and an abort class exception is generated. For abort exceptions, information about the
exception can be collected from the machine-check MSRs, but the program cannot generally be restarted.
If the machine-check mechanism is not enabled (the MCE flag in control register CR4 is clear), a machine-check
exception causes the processor to enter the shutdown state.

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INTERRUPT AND EXCEPTION HANDLING

Interrupt 19—SIMD Floating-Point Exception (#XM)
Exception Class

Fault.

Description
Indicates the processor has detected an SSE/SSE2/SSE3 SIMD floating-point exception. The appropriate status
flag in the MXCSR register must be set and the particular exception unmasked for this interrupt to be generated.
There are six classes of numeric exception conditions that can occur while executing an SSE/ SSE2/SSE3 SIMD
floating-point instruction:

•
•
•
•
•
•

Invalid operation (#I)
Divide-by-zero (#Z)
Denormal operand (#D)
Numeric overflow (#O)
Numeric underflow (#U)
Inexact result (Precision) (#P)

The invalid operation, divide-by-zero, and denormal-operand exceptions are pre-computation exceptions; that is,
they are detected before any arithmetic operation occurs. The numeric underflow, numeric overflow, and inexact
result exceptions are post-computational exceptions.
See “SIMD Floating-Point Exceptions” in Chapter 11 of the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1, for additional information about the SIMD floating-point exception classes.
When a SIMD floating-point exception occurs, the processor does either of the following things:

•

It handles the exception automatically by producing the most reasonable result and allowing program
execution to continue undisturbed. This is the response to masked exceptions.

•

It generates a SIMD floating-point exception, which in turn invokes a software exception handler. This is the
response to unmasked exceptions.

Each of the six SIMD floating-point exception conditions has a corresponding flag bit and mask bit in the MXCSR
register. If an exception is masked (the corresponding mask bit in the MXCSR register is set), the processor takes
an appropriate automatic default action and continues with the computation. If the exception is unmasked (the
corresponding mask bit is clear) and the operating system supports SIMD floating-point exceptions (the OSXMMEXCPT flag in control register CR4 is set), a software exception handler is invoked through a SIMD floating-point
exception. If the exception is unmasked and the OSXMMEXCPT bit is clear (indicating that the operating system
does not support unmasked SIMD floating-point exceptions), an invalid opcode exception (#UD) is signaled instead
of a SIMD floating-point exception.
Note that because SIMD floating-point exceptions are precise and occur immediately, the situation does not arise
where an x87 FPU instruction, a WAIT/FWAIT instruction, or another SSE/SSE2/SSE3 instruction will catch a
pending unmasked SIMD floating-point exception.
In situations where a SIMD floating-point exception occurred while the SIMD floating-point exceptions were
masked (causing the corresponding exception flag to be set) and the SIMD floating-point exception was subsequently unmasked, then no exception is generated when the exception is unmasked.
When SSE/SSE2/SSE3 SIMD floating-point instructions operate on packed operands (made up of two or four suboperands), multiple SIMD floating-point exception conditions may be detected. If no more than one exception
condition is detected for one or more sets of sub-operands, the exception flags are set for each exception condition
detected. For example, an invalid exception detected for one sub-operand will not prevent the reporting of a divideby-zero exception for another sub-operand. However, when two or more exceptions conditions are generated for
one sub-operand, only one exception condition is reported, according to the precedences shown in Table 6-8. This
exception precedence sometimes results in the higher priority exception condition being reported and the lower
priority exception conditions being ignored.

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INTERRUPT AND EXCEPTION HANDLING

Table 6-8. SIMD Floating-Point Exceptions Priority
Priority

Description

1 (Highest)

Invalid operation exception due to SNaN operand (or any NaN operand for maximum, minimum, or certain compare and
convert operations).

2

QNaN operand1.

3

Any other invalid operation exception not mentioned above or a divide-by-zero exception2.

4

Denormal operand exception2.

5

Numeric overflow and underflow exceptions possibly in conjunction with the inexact result exception2.

6 (Lowest)

Inexact result exception.

NOTES:
1. Though a QNaN this is not an exception, the handling of a QNaN operand has precedence over lower priority exceptions. For example, a QNaN divided by zero results in a QNaN, not a divide-by-zero- exception.
2. If masked, then instruction execution continues, and a lower priority exception can occur as well.

Exception Error Code
None.

Saved Instruction Pointer
The saved contents of CS and EIP registers point to the SSE/SSE2/SSE3 instruction that was executed when the
SIMD floating-point exception was generated. This is the faulting instruction in which the error condition was
detected.

Program State Change
A program-state change does not accompany a SIMD floating-point exception because the handling of the exception is immediate unless the particular exception is masked. The available state information is often sufficient to
allow recovery from the error and re-execution of the faulting instruction if needed.

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INTERRUPT AND EXCEPTION HANDLING

Interrupt 20—Virtualization Exception (#VE)
Exception Class

Fault.

Description
Indicates that the processor detected an EPT violation in VMX non-root operation. Not all EPT violations cause
virtualization exceptions. See Section 25.5.6.2 for details.
The exception handler can recover from EPT violations and restart the program or task without any loss of program
continuity. In some cases, however, the problem that caused the EPT violation may be uncorrectable.

Exception Error Code
None.

Saved Instruction Pointer
The saved contents of CS and EIP registers generally point to the instruction that generated the exception.

Program State Change
A program-state change does not normally accompany a virtualization exception, because the instruction that
causes the exception to be generated is not executed. After the virtualization exception handler has corrected the
violation (for example, by executing the EPTP-switching VM function), execution of the program or task can be
resumed.

Additional Exception-Handling Information
The processor saves information about virtualization exceptions in the virtualization-exception information area.
See Section 25.5.6.2 for details.

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INTERRUPT AND EXCEPTION HANDLING

Interrupts 32 to 255—User Defined Interrupts
Exception Class

Not applicable.

Description
Indicates that the processor did one of the following things:

•
•

Executed an INT n instruction where the instruction operand is one of the vector numbers from 32 through 255.
Responded to an interrupt request at the INTR pin or from the local APIC when the interrupt vector number
associated with the request is from 32 through 255.

Exception Error Code
Not applicable.
Saved Instruction Pointer
The saved contents of CS and EIP registers point to the instruction that follows the INT n instruction or instruction
following the instruction on which the INTR signal occurred.

Program State Change
A program-state change does not accompany interrupts generated by the INT n instruction or the INTR signal. The
INT n instruction generates the interrupt within the instruction stream. When the processor receives an INTR
signal, it commits all state changes for all previous instructions before it responds to the interrupt; so, program
execution can resume upon returning from the interrupt handler.

6-50 Vol. 3A

CHAPTER 7
TASK MANAGEMENT
This chapter describes the IA-32 architecture’s task management facilities. These facilities are only available when
the processor is running in protected mode.
This chapter focuses on 32-bit tasks and the 32-bit TSS structure. For information on 16-bit tasks and the 16-bit
TSS structure, see Section 7.6, “16-Bit Task-State Segment (TSS).” For information specific to task management in
64-bit mode, see Section 7.7, “Task Management in 64-bit Mode.”

7.1

TASK MANAGEMENT OVERVIEW

A task is a unit of work that a processor can dispatch, execute, and suspend. It can be used to execute a program,
a task or process, an operating-system service utility, an interrupt or exception handler, or a kernel or executive
utility.
The IA-32 architecture provides a mechanism for saving the state of a task, for dispatching tasks for execution, and
for switching from one task to another. When operating in protected mode, all processor execution takes place from
within a task. Even simple systems must define at least one task. More complex systems can use the processor’s
task management facilities to support multitasking applications.

7.1.1

Task Structure

A task is made up of two parts: a task execution space and a task-state segment (TSS). The task execution space
consists of a code segment, a stack segment, and one or more data segments (see Figure 7-1). If an operating
system or executive uses the processor’s privilege-level protection mechanism, the task execution space also
provides a separate stack for each privilege level.
The TSS specifies the segments that make up the task execution space and provides a storage place for task state
information. In multitasking systems, the TSS also provides a mechanism for linking tasks.
A task is identified by the segment selector for its TSS. When a task is loaded into the processor for execution, the
segment selector, base address, limit, and segment descriptor attributes for the TSS are loaded into the task
register (see Section 2.4.4, “Task Register (TR)”).
If paging is implemented for the task, the base address of the page directory used by the task is loaded into control
register CR3.

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TASK MANAGEMENT

Code
Segment
Data
Segment

Task-State
Segment
(TSS)

Stack
Segment
(Current Priv.
Level)
Stack Seg.
Priv. Level 0
Stack Seg.
Priv. Level 1

Task Register
CR3

Stack
Segment
(Priv. Level 2)

Figure 7-1. Structure of a Task

7.1.2

Task State

The following items define the state of the currently executing task:

•

The task’s current execution space, defined by the segment selectors in the segment registers (CS, DS, SS, ES,
FS, and GS).

•
•
•
•
•
•
•
•
•

The state of the general-purpose registers.
The state of the EFLAGS register.
The state of the EIP register.
The state of control register CR3.
The state of the task register.
The state of the LDTR register.
The I/O map base address and I/O map (contained in the TSS).
Stack pointers to the privilege 0, 1, and 2 stacks (contained in the TSS).
Link to previously executed task (contained in the TSS).

Prior to dispatching a task, all of these items are contained in the task’s TSS, except the state of the task register.
Also, the complete contents of the LDTR register are not contained in the TSS, only the segment selector for the
LDT.

7.1.3

Executing a Task

Software or the processor can dispatch a task for execution in one of the following ways:

•
•
•
•
•

A explicit call to a task with the CALL instruction.
A explicit jump to a task with the JMP instruction.
An implicit call (by the processor) to an interrupt-handler task.
An implicit call to an exception-handler task.
A return (initiated with an IRET instruction) when the NT flag in the EFLAGS register is set.

All of these methods for dispatching a task identify the task to be dispatched with a segment selector that points to
a task gate or the TSS for the task. When dispatching a task with a CALL or JMP instruction, the selector in the
instruction may select the TSS directly or a task gate that holds the selector for the TSS. When dispatching a task

7-2 Vol. 3A

TASK MANAGEMENT

to handle an interrupt or exception, the IDT entry for the interrupt or exception must contain a task gate that holds
the selector for the interrupt- or exception-handler TSS.
When a task is dispatched for execution, a task switch occurs between the currently running task and the
dispatched task. During a task switch, the execution environment of the currently executing task (called the task’s
state or context) is saved in its TSS and execution of the task is suspended. The context for the dispatched task is
then loaded into the processor and execution of that task begins with the instruction pointed to by the newly loaded
EIP register. If the task has not been run since the system was last initialized, the EIP will point to the first instruction of the task’s code; otherwise, it will point to the next instruction after the last instruction that the task
executed when it was last active.
If the currently executing task (the calling task) called the task being dispatched (the called task), the TSS
segment selector for the calling task is stored in the TSS of the called task to provide a link back to the calling task.
For all IA-32 processors, tasks are not recursive. A task cannot call or jump to itself.
Interrupts and exceptions can be handled with a task switch to a handler task. Here, the processor performs a task
switch to handle the interrupt or exception and automatically switches back to the interrupted task upon returning
from the interrupt-handler task or exception-handler task. This mechanism can also handle interrupts that occur
during interrupt tasks.
As part of a task switch, the processor can also switch to another LDT, allowing each task to have a different logicalto-physical address mapping for LDT-based segments. The page-directory base register (CR3) also is reloaded on a
task switch, allowing each task to have its own set of page tables. These protection facilities help isolate tasks and
prevent them from interfering with one another.
If protection mechanisms are not used, the processor provides no protection between tasks. This is true even with
operating systems that use multiple privilege levels for protection. A task running at privilege level 3 that uses the
same LDT and page tables as other privilege-level-3 tasks can access code and corrupt data and the stack of other
tasks.
Use of task management facilities for handling multitasking applications is optional. Multitasking can be handled in
software, with each software defined task executed in the context of a single IA-32 architecture task.

7.2

TASK MANAGEMENT DATA STRUCTURES

The processor defines five data structures for handling task-related activities:

•
•
•
•
•

Task-state segment (TSS).
Task-gate descriptor.
TSS descriptor.
Task register.
NT flag in the EFLAGS register.

When operating in protected mode, a TSS and TSS descriptor must be created for at least one task, and the
segment selector for the TSS must be loaded into the task register (using the LTR instruction).

7.2.1

Task-State Segment (TSS)

The processor state information needed to restore a task is saved in a system segment called the task-state
segment (TSS). Figure 7-2 shows the format of a TSS for tasks designed for 32-bit CPUs. The fields of a TSS are
divided into two main categories: dynamic fields and static fields.
For information about 16-bit Intel 286 processor task structures, see Section 7.6, “16-Bit Task-State Segment
(TSS).” For information about 64-bit mode task structures, see Section 7.7, “Task Management in 64-bit Mode.”

Vol. 3A 7-3

TASK MANAGEMENT

31

0

15
Reserved

I/O Map Base Address

T 100

LDT Segment Selector

Reserved

96

Reserved

GS

92

Reserved

FS

88

Reserved

DS

84

Reserved

SS

80

Reserved

CS

76

Reserved

ES

72

EDI

68

ESI

64

EBP

60

ESP

56

EBX

52

EDX

48

ECX

44

EAX

40

EFLAGS

36

EIP

32

CR3 (PDBR)

28

Reserved

SS2

Reserved

SS1
SS0

8
4

ESP0
Reserved

16
12

ESP1
Reserved

24
20

ESP2

Previous Task Link

0

Reserved bits. Set to 0.

Figure 7-2. 32-Bit Task-State Segment (TSS)
The processor updates dynamic fields when a task is suspended during a task switch. The following are dynamic
fields:

•

General-purpose register fields — State of the EAX, ECX, EDX, EBX, ESP, EBP, ESI, and EDI registers prior
to the task switch.

•

Segment selector fields — Segment selectors stored in the ES, CS, SS, DS, FS, and GS registers prior to the
task switch.

•
•
•

EFLAGS register field — State of the EFAGS register prior to the task switch.
EIP (instruction pointer) field — State of the EIP register prior to the task switch.
Previous task link field — Contains the segment selector for the TSS of the previous task (updated on a task
switch that was initiated by a call, interrupt, or exception). This field (which is sometimes called the back link
field) permits a task switch back to the previous task by using the IRET instruction.

The processor reads the static fields, but does not normally change them. These fields are set up when a task is
created. The following are static fields:

•

LDT segment selector field — Contains the segment selector for the task's LDT.

7-4 Vol. 3A

TASK MANAGEMENT

•

CR3 control register field — Contains the base physical address of the page directory to be used by the task.
Control register CR3 is also known as the page-directory base register (PDBR).

•

Privilege level-0, -1, and -2 stack pointer fields — These stack pointers consist of a logical address made
up of the segment selector for the stack segment (SS0, SS1, and SS2) and an offset into the stack (ESP0,
ESP1, and ESP2). Note that the values in these fields are static for a particular task; whereas, the SS and ESP
values will change if stack switching occurs within the task.

•

T (debug trap) flag (byte 100, bit 0) — When set, the T flag causes the processor to raise a debug exception
when a task switch to this task occurs (see Section 17.3.1.5, “Task-Switch Exception Condition”).

•

I/O map base address field — Contains a 16-bit offset from the base of the TSS to the I/O permission bit
map and interrupt redirection bitmap. When present, these maps are stored in the TSS at higher addresses.
The I/O map base address points to the beginning of the I/O permission bit map and the end of the interrupt
redirection bit map. See Chapter 18, “Input/Output,” in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1, for more information about the I/O permission bit map. See Section 20.3,
“Interrupt and Exception Handling in Virtual-8086 Mode,” for a detailed description of the interrupt redirection
bit map.

If paging is used:

•

Avoid placing a page boundary in the part of the TSS that the processor reads during a task switch (the first 104
bytes). The processor may not correctly perform address translations if a boundary occurs in this area. During
a task switch, the processor reads and writes into the first 104 bytes of each TSS (using contiguous physical
addresses beginning with the physical address of the first byte of the TSS). So, after TSS access begins, if part
of the 104 bytes is not physically contiguous, the processor will access incorrect information without generating
a page-fault exception.

•

Pages corresponding to the previous task’s TSS, the current task’s TSS, and the descriptor table entries for
each all should be marked as read/write.

•

Task switches are carried out faster if the pages containing these structures are present in memory before the
task switch is initiated.

7.2.2

TSS Descriptor

The TSS, like all other segments, is defined by a segment descriptor. Figure 7-3 shows the format of a TSS
descriptor. TSS descriptors may only be placed in the GDT; they cannot be placed in an LDT or the IDT.
An attempt to access a TSS using a segment selector with its TI flag set (which indicates the current LDT) causes
a general-protection exception (#GP) to be generated during CALLs and JMPs; it causes an invalid TSS exception
(#TS) during IRETs. A general-protection exception is also generated if an attempt is made to load a segment
selector for a TSS into a segment register.
The busy flag (B) in the type field indicates whether the task is busy. A busy task is currently running or suspended.
A type field with a value of 1001B indicates an inactive task; a value of 1011B indicates a busy task. Tasks are not
recursive. The processor uses the busy flag to detect an attempt to call a task whose execution has been interrupted. To insure that there is only one busy flag is associated with a task, each TSS should have only one TSS
descriptor that points to it.

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TASK MANAGEMENT

TSS Descriptor
31

24 23 22 21 20 19

Base 31:24

A
G 0 0 V
L

31

16 15 14 13 12 11

Limit
19:16

P

D
P
L

0

8 7

Type

16 15

Base Address 15:00

AVL
B
BASE
DPL
G
LIMIT
P
TYPE

4

Base 23:16

0 1 0 B 1
0

Segment Limit 15:00

0

Available for use by system software
Busy flag
Segment Base Address
Descriptor Privilege Level
Granularity
Segment Limit
Segment Present
Segment Type

Figure 7-3. TSS Descriptor
The base, limit, and DPL fields and the granularity and present flags have functions similar to their use in datasegment descriptors (see Section 3.4.5, “Segment Descriptors”). When the G flag is 0 in a TSS descriptor for a 32bit TSS, the limit field must have a value equal to or greater than 67H, one byte less than the minimum size of a
TSS. Attempting to switch to a task whose TSS descriptor has a limit less than 67H generates an invalid-TSS exception (#TS). A larger limit is required if an I/O permission bit map is included or if the operating system stores additional data. The processor does not check for a limit greater than 67H on a task switch; however, it does check
when accessing the I/O permission bit map or interrupt redirection bit map.
Any program or procedure with access to a TSS descriptor (that is, whose CPL is numerically equal to or less than
the DPL of the TSS descriptor) can dispatch the task with a call or a jump.
In most systems, the DPLs of TSS descriptors are set to values less than 3, so that only privileged software can
perform task switching. However, in multitasking applications, DPLs for some TSS descriptors may be set to 3 to
allow task switching at the application (or user) privilege level.

7.2.3

TSS Descriptor in 64-bit mode

In 64-bit mode, task switching is not supported, but TSS descriptors still exist. The format of a 64-bit TSS is
described in Section 7.7.
In 64-bit mode, the TSS descriptor is expanded to 16 bytes (see Figure 7-4). This expansion also applies to an LDT
descriptor in 64-bit mode. Table 3-2 provides the encoding information for the segment type field.

7-6 Vol. 3A

TASK MANAGEMENT

TSS (or LDT) Descriptor
31

13 12

Reserved

0

8 7
0

12

Reserved

31

0

8

Base Address 63:32

31

24 23 22 21 20 19

Base 31:24

A
G 0 0 V
L

31

16 15 14 13 12 11

Limit
19:16

P

D
P
L

0

8 7

Type

16 15

Base Address 15:00

AVL
B
BASE
DPL
G
LIMIT
P
TYPE

4

Base 23:16

0
0

Segment Limit 15:00

0

Available for use by system software
Busy flag
Segment Base Address
Descriptor Privilege Level
Granularity
Segment Limit
Segment Present
Segment Type

Figure 7-4. Format of TSS and LDT Descriptors in 64-bit Mode

7.2.4

Task Register

The task register holds the 16-bit segment selector and the entire segment descriptor (32-bit base address (64 bits
in IA-32e mode), 16-bit segment limit, and descriptor attributes) for the TSS of the current task (see Figure 2-6).
This information is copied from the TSS descriptor in the GDT for the current task. Figure 7-5 shows the path the
processor uses to access the TSS (using the information in the task register).
The task register has a visible part (that can be read and changed by software) and an invisible part (maintained
by the processor and is inaccessible by software). The segment selector in the visible portion points to a TSS
descriptor in the GDT. The processor uses the invisible portion of the task register to cache the segment descriptor
for the TSS. Caching these values in a register makes execution of the task more efficient. The LTR (load task
register) and STR (store task register) instructions load and read the visible portion of the task register:
The LTR instruction loads a segment selector (source operand) into the task register that points to a TSS descriptor
in the GDT. It then loads the invisible portion of the task register with information from the TSS descriptor. LTR is a
privileged instruction that may be executed only when the CPL is 0. It’s used during system initialization to put an
initial value in the task register. Afterwards, the contents of the task register are changed implicitly when a task
switch occurs.
The STR (store task register) instruction stores the visible portion of the task register in a general-purpose register
or memory. This instruction can be executed by code running at any privilege level in order to identify the currently
running task. However, it is normally used only by operating system software. (If CR4.UMIP = 1, STR can be
executed only when CPL = 0.)
On power up or reset of the processor, segment selector and base address are set to the default value of 0; the limit
is set to FFFFH.

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TASK MANAGEMENT

TSS

Task
Register

+

Visible Part
Selector

Invisible Part
Base Address

Segment Limit

GDT

TSS Descriptor

0

Figure 7-5. Task Register

7.2.5

Task-Gate Descriptor

A task-gate descriptor provides an indirect, protected reference to a task (see Figure 7-6). It can be placed in the
GDT, an LDT, or the IDT. The TSS segment selector field in a task-gate descriptor points to a TSS descriptor in the
GDT. The RPL in this segment selector is not used.
The DPL of a task-gate descriptor controls access to the TSS descriptor during a task switch. When a program or
procedure makes a call or jump to a task through a task gate, the CPL and the RPL field of the gate selector pointing
to the task gate must be less than or equal to the DPL of the task-gate descriptor. Note that when a task gate is
used, the DPL of the destination TSS descriptor is not used.

31

16 15 14 13 12 11

Reserved
31

P

D
P
L

Type

DPL
P
TYPE

4
0

Reserved

Descriptor Privilege Level
Segment Present
Segment Type

Figure 7-6. Task-Gate Descriptor
7-8 Vol. 3A

Reserved

0 0 1 0 1

16 15

TSS Segment Selector

0

8 7

0

TASK MANAGEMENT

A task can be accessed either through a task-gate descriptor or a TSS descriptor. Both of these structures satisfy
the following needs:

•

Need for a task to have only one busy flag — Because the busy flag for a task is stored in the TSS
descriptor, each task should have only one TSS descriptor. There may, however, be several task gates that
reference the same TSS descriptor.

•

Need to provide selective access to tasks — Task gates fill this need, because they can reside in an LDT and
can have a DPL that is different from the TSS descriptor's DPL. A program or procedure that does not have
sufficient privilege to access the TSS descriptor for a task in the GDT (which usually has a DPL of 0) may be
allowed access to the task through a task gate with a higher DPL. Task gates give the operating system greater
latitude for limiting access to specific tasks.

•

Need for an interrupt or exception to be handled by an independent task — Task gates may also reside
in the IDT, which allows interrupts and exceptions to be handled by handler tasks. When an interrupt or
exception vector points to a task gate, the processor switches to the specified task.

Figure 7-7 illustrates how a task gate in an LDT, a task gate in the GDT, and a task gate in the IDT can all point to
the same task.

LDT

GDT

TSS

Task Gate

Task Gate

TSS Descriptor

IDT

Task Gate

Figure 7-7. Task Gates Referencing the Same Task

7.3

TASK SWITCHING

The processor transfers execution to another task in one of four cases:

•
•

The current program, task, or procedure executes a JMP or CALL instruction to a TSS descriptor in the GDT.
The current program, task, or procedure executes a JMP or CALL instruction to a task-gate descriptor in the
GDT or the current LDT.

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TASK MANAGEMENT

•
•

An interrupt or exception vector points to a task-gate descriptor in the IDT.
The current task executes an IRET when the NT flag in the EFLAGS register is set.

JMP, CALL, and IRET instructions, as well as interrupts and exceptions, are all mechanisms for redirecting a
program. The referencing of a TSS descriptor or a task gate (when calling or jumping to a task) or the state of the
NT flag (when executing an IRET instruction) determines whether a task switch occurs.
The processor performs the following operations when switching to a new task:
1. Obtains the TSS segment selector for the new task as the operand of the JMP or CALL instruction, from a task
gate, or from the previous task link field (for a task switch initiated with an IRET instruction).
2. Checks that the current (old) task is allowed to switch to the new task. Data-access privilege rules apply to JMP
and CALL instructions. The CPL of the current (old) task and the RPL of the segment selector for the new task
must be less than or equal to the DPL of the TSS descriptor or task gate being referenced. Exceptions,
interrupts (except for interrupts generated by the INT n instruction), and the IRET instruction are permitted to
switch tasks regardless of the DPL of the destination task-gate or TSS descriptor. For interrupts generated by
the INT n instruction, the DPL is checked.
3. Checks that the TSS descriptor of the new task is marked present and has a valid limit (greater than or equal
to 67H).
4. Checks that the new task is available (call, jump, exception, or interrupt) or busy (IRET return).
5. Checks that the current (old) TSS, new TSS, and all segment descriptors used in the task switch are paged into
system memory.
6. If the task switch was initiated with a JMP or IRET instruction, the processor clears the busy (B) flag in the
current (old) task’s TSS descriptor; if initiated with a CALL instruction, an exception, or an interrupt: the busy
(B) flag is left set. (See Table 7-2.)
7. If the task switch was initiated with an IRET instruction, the processor clears the NT flag in a temporarily saved
image of the EFLAGS register; if initiated with a CALL or JMP instruction, an exception, or an interrupt, the NT
flag is left unchanged in the saved EFLAGS image.
8. Saves the state of the current (old) task in the current task’s TSS. The processor finds the base address of the
current TSS in the task register and then copies the states of the following registers into the current TSS: all the
general-purpose registers, segment selectors from the segment registers, the temporarily saved image of the
EFLAGS register, and the instruction pointer register (EIP).
9. If the task switch was initiated with a CALL instruction, an exception, or an interrupt, the processor will set the
NT flag in the EFLAGS loaded from the new task. If initiated with an IRET instruction or JMP instruction, the NT
flag will reflect the state of NT in the EFLAGS loaded from the new task (see Table 7-2).
10. If the task switch was initiated with a CALL instruction, JMP instruction, an exception, or an interrupt, the
processor sets the busy (B) flag in the new task’s TSS descriptor; if initiated with an IRET instruction, the busy
(B) flag is left set.
11. Loads the task register with the segment selector and descriptor for the new task's TSS.
12. The TSS state is loaded into the processor. This includes the LDTR register, the PDBR (control register CR3), the
EFLAGS register, the EIP register, the general-purpose registers, and the segment selectors. A fault during the
load of this state may corrupt architectural state. (If paging is not enabled, a PDBR value is read from the new
task's TSS, but it is not loaded into CR3.)
13. The descriptors associated with the segment selectors are loaded and qualified. Any errors associated with this
loading and qualification occur in the context of the new task and may corrupt architectural state.

NOTES
If all checks and saves have been carried out successfully, the processor commits to the task
switch. If an unrecoverable error occurs in steps 1 through 11, the processor does not complete the
task switch and insures that the processor is returned to its state prior to the execution of the
instruction that initiated the task switch.
If an unrecoverable error occurs in step 12, architectural state may be corrupted, but an attempt
will be made to handle the error in the prior execution environment. If an unrecoverable error
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occurs after the commit point (in step 13), the processor completes the task switch (without
performing additional access and segment availability checks) and generates the appropriate
exception prior to beginning execution of the new task.
If exceptions occur after the commit point, the exception handler must finish the task switch itself
before allowing the processor to begin executing the new task. See Chapter 6, “Interrupt
10—Invalid TSS Exception (#TS),” for more information about the affect of exceptions on a task
when they occur after the commit point of a task switch.
14. Begins executing the new task. (To an exception handler, the first instruction of the new task appears not to
have been executed.)
The state of the currently executing task is always saved when a successful task switch occurs. If the task is
resumed, execution starts with the instruction pointed to by the saved EIP value, and the registers are restored to
the values they held when the task was suspended.
When switching tasks, the privilege level of the new task does not inherit its privilege level from the suspended
task. The new task begins executing at the privilege level specified in the CPL field of the CS register, which is
loaded from the TSS. Because tasks are isolated by their separate address spaces and TSSs and because privilege
rules control access to a TSS, software does not need to perform explicit privilege checks on a task switch.
Table 7-1 shows the exception conditions that the processor checks for when switching tasks. It also shows the
exception that is generated for each check if an error is detected and the segment that the error code references.
(The order of the checks in the table is the order used in the P6 family processors. The exact order is model specific
and may be different for other IA-32 processors.) Exception handlers designed to handle these exceptions may be
subject to recursive calls if they attempt to reload the segment selector that generated the exception. The cause of
the exception (or the first of multiple causes) should be fixed before reloading the selector.

Table 7-1. Exception Conditions Checked During a Task Switch
Condition Checked
Segment selector for a TSS descriptor references
the GDT and is within the limits of the table.

Exception1
#GP

Error Code Reference2
New Task’s TSS

#TS (for IRET)

P bit is set in TSS descriptor.

#NP

TSS descriptor is not busy (for task switch initiated by a call, interrupt, or
exception).

#GP (for JMP, CALL, INT) Task’s back-link TSS

New Task’s TSS

TSS descriptor is not busy (for task switch initiated by an IRET instruction).

#TS (for IRET)

New Task’s TSS

TSS segment limit greater than or equal to 108 (for 32-bit TSS) or 44 (for 16-bit
TSS).

#TS

New Task’s TSS

#TS

New Task’s LDT

Registers are loaded from the values in the TSS.
LDT segment selector of new task is valid 3.
If code segment is non-conforming, its DPL should equal its RPL.

#TS

New Code Segment

If code segment is conforming, its DPL should be less than or equal to its RPL.

#TS

New Code Segment

SS segment selector is valid 2.

#TS

New Stack Segment

P bit is set in stack segment descriptor.

#SS

New Stack Segment

Stack segment DPL should equal CPL.

#TS

New stack segment

P bit is set in new task's LDT descriptor.

#TS

New Task’s LDT

CS segment selector is valid

#TS

New Code Segment

#NP

New Code Segment

Stack segment DPL should equal its RPL.

#TS

New Stack Segment

DS, ES, FS, and GS segment selectors are valid 3.

#TS

New Data Segment

DS, ES, FS, and GS segments are readable.

#TS

New Data Segment

3

.

P bit is set in code segment descriptor.

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Table 7-1. Exception Conditions Checked During a Task Switch (Contd.)
Condition Checked

Exception1

Error Code Reference2

P bits are set in descriptors of DS, ES, FS, and GS segments.

#NP

New Data Segment

DS, ES, FS, and GS segment DPL greater than or equal to CPL (unless these are
conforming segments).

#TS

New Data Segment

NOTES:
1. #NP is segment-not-present exception, #GP is general-protection exception, #TS is invalid-TSS exception, and #SS is stack-fault
exception.
2. The error code contains an index to the segment descriptor referenced in this column.
3. A segment selector is valid if it is in a compatible type of table (GDT or LDT), occupies an address within the table's segment limit,
and refers to a compatible type of descriptor (for example, a segment selector in the CS register only is valid when it points to a
code-segment descriptor).
The TS (task switched) flag in the control register CR0 is set every time a task switch occurs. System software uses
the TS flag to coordinate the actions of floating-point unit when generating floating-point exceptions with the rest
of the processor. The TS flag indicates that the context of the floating-point unit may be different from that of the
current task. See Section 2.5, “Control Registers”, for a detailed description of the function and use of the TS flag.

7.4

TASK LINKING

The previous task link field of the TSS (sometimes called the “backlink”) and the NT flag in the EFLAGS register are
used to return execution to the previous task. EFLAGS.NT = 1 indicates that the currently executing task is nested
within the execution of another task.
When a CALL instruction, an interrupt, or an exception causes a task switch: the processor copies the segment
selector for the current TSS to the previous task link field of the TSS for the new task; it then sets EFLAGS.NT = 1.
If software uses an IRET instruction to suspend the new task, the processor checks for EFLAGS.NT = 1; it then uses
the value in the previous task link field to return to the previous task. See Figures 7-8.
When a JMP instruction causes a task switch, the new task is not nested. The previous task link field is not used and
EFLAGS.NT = 0. Use a JMP instruction to dispatch a new task when nesting is not desired.

Top Level
Task

Nested
Task

More Deeply
Nested Task

Currently Executing
Task

TSS

TSS

TSS

EFLAGS
NT=1

NT=0
Previous
Task Link

NT=1
Previous
Task Link

NT=1
Previous
Task Link

Task Register

Figure 7-8. Nested Tasks
Table 7-2 shows the busy flag (in the TSS segment descriptor), the NT flag, the previous task link field, and TS flag
(in control register CR0) during a task switch.
The NT flag may be modified by software executing at any privilege level. It is possible for a program to set the NT
flag and execute an IRET instruction. This might randomly invoke the task specified in the previous link field of the
current task's TSS. To keep such spurious task switches from succeeding, the operating system should initialize the
previous task link field in every TSS that it creates to 0.

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Table 7-2. Effect of a Task Switch on Busy Flag, NT Flag, Previous Task Link Field, and TS Flag
Flag or Field

Effect of JMP instruction

Effect of CALL Instruction or
Interrupt

Effect of IRET
Instruction

Busy (B) flag of new task.

Flag is set. Must have been
clear before.

Flag is set. Must have been
clear before.

No change. Must have been set.

Busy flag of old task.

Flag is cleared.

No change. Flag is currently
set.

Flag is cleared.

NT flag of new task.

Set to value from TSS of new
task.

Flag is set.

Set to value from TSS of new
task.

NT flag of old task.

No change.

No change.

Flag is cleared.

Previous task link field of new
task.

No change.

Loaded with selector
for old task’s TSS.

No change.

Previous task link field of old
task.

No change.

No change.

No change.

TS flag in control register CR0.

Flag is set.

Flag is set.

Flag is set.

7.4.1

Use of Busy Flag To Prevent Recursive Task Switching

A TSS allows only one context to be saved for a task; therefore, once a task is called (dispatched), a recursive (or
re-entrant) call to the task would cause the current state of the task to be lost. The busy flag in the TSS segment
descriptor is provided to prevent re-entrant task switching and a subsequent loss of task state information. The
processor manages the busy flag as follows:
1. When dispatching a task, the processor sets the busy flag of the new task.
2. If during a task switch, the current task is placed in a nested chain (the task switch is being generated by a
CALL instruction, an interrupt, or an exception), the busy flag for the current task remains set.
3. When switching to the new task (initiated by a CALL instruction, interrupt, or exception), the processor
generates a general-protection exception (#GP) if the busy flag of the new task is already set. If the task switch
is initiated with an IRET instruction, the exception is not raised because the processor expects the busy flag to
be set.
4. When a task is terminated by a jump to a new task (initiated with a JMP instruction in the task code) or by an
IRET instruction in the task code, the processor clears the busy flag, returning the task to the “not busy” state.
The processor prevents recursive task switching by preventing a task from switching to itself or to any task in a
nested chain of tasks. The chain of nested suspended tasks may grow to any length, due to multiple calls, interrupts, or exceptions. The busy flag prevents a task from being invoked if it is in this chain.
The busy flag may be used in multiprocessor configurations, because the processor follows a LOCK protocol (on the
bus or in the cache) when it sets or clears the busy flag. This lock keeps two processors from invoking the same
task at the same time. See Section 8.1.2.1, “Automatic Locking,” for more information about setting the busy flag
in a multiprocessor applications.

7.4.2

Modifying Task Linkages

In a uniprocessor system, in situations where it is necessary to remove a task from a chain of linked tasks, use the
following procedure to remove the task:
1. Disable interrupts.
2. Change the previous task link field in the TSS of the pre-empting task (the task that suspended the task to be
removed). It is assumed that the pre-empting task is the next task (newer task) in the chain from the task to
be removed. Change the previous task link field to point to the TSS of the next oldest task in the chain or to an
even older task in the chain.
3. Clear the busy (B) flag in the TSS segment descriptor for the task being removed from the chain. If more than
one task is being removed from the chain, the busy flag for each task being remove must be cleared.
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TASK MANAGEMENT

4. Enable interrupts.
In a multiprocessing system, additional synchronization and serialization operations must be added to this procedure to insure that the TSS and its segment descriptor are both locked when the previous task link field is changed
and the busy flag is cleared.

7.5

TASK ADDRESS SPACE

The address space for a task consists of the segments that the task can access. These segments include the code,
data, stack, and system segments referenced in the TSS and any other segments accessed by the task code. The
segments are mapped into the processor’s linear address space, which is in turn mapped into the processor’s physical address space (either directly or through paging).
The LDT segment field in the TSS can be used to give each task its own LDT. Giving a task its own LDT allows the
task address space to be isolated from other tasks by placing the segment descriptors for all the segments associated with the task in the task’s LDT.
It also is possible for several tasks to use the same LDT. This is a memory-efficient way to allow specific tasks to
communicate with or control each other, without dropping the protection barriers for the entire system.
Because all tasks have access to the GDT, it also is possible to create shared segments accessed through segment
descriptors in this table.
If paging is enabled, the CR3 register (PDBR) field in the TSS allows each task to have its own set of page tables for
mapping linear addresses to physical addresses. Or, several tasks can share the same set of page tables.

7.5.1

Mapping Tasks to the Linear and Physical Address Spaces

Tasks can be mapped to the linear address space and physical address space in one of two ways:

•

One linear-to-physical address space mapping is shared among all tasks. — When paging is not
enabled, this is the only choice. Without paging, all linear addresses map to the same physical addresses. When
paging is enabled, this form of linear-to-physical address space mapping is obtained by using one page
directory for all tasks. The linear address space may exceed the available physical space if demand-paged
virtual memory is supported.

•

Each task has its own linear address space that is mapped to the physical address space. — This form
of mapping is accomplished by using a different page directory for each task. Because the PDBR (control
register CR3) is loaded on task switches, each task may have a different page directory.

The linear address spaces of different tasks may map to completely distinct physical addresses. If the entries of
different page directories point to different page tables and the page tables point to different pages of physical
memory, then the tasks do not share physical addresses.
With either method of mapping task linear address spaces, the TSSs for all tasks must lie in a shared area of the
physical space, which is accessible to all tasks. This mapping is required so that the mapping of TSS addresses does
not change while the processor is reading and updating the TSSs during a task switch. The linear address space
mapped by the GDT also should be mapped to a shared area of the physical space; otherwise, the purpose of the
GDT is defeated. Figure 7-9 shows how the linear address spaces of two tasks can overlap in the physical space by
sharing page tables.

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TASK MANAGEMENT

TSS

Page Directories

Page Tables

Page Frames

Task A
Task A TSS

PDBR

PTE
PTE
PTE

PDE
PDE

Task A
Task A

Shared PT

Shared
PTE
PTE

Task B TSS

Shared
Task B

PDBR

PDE
PDE

PTE
PTE

Task B

Figure 7-9. Overlapping Linear-to-Physical Mappings

7.5.2

Task Logical Address Space

To allow the sharing of data among tasks, use the following techniques to create shared logical-to-physical
address-space mappings for data segments:

•

Through the segment descriptors in the GDT — All tasks must have access to the segment descriptors in
the GDT. If some segment descriptors in the GDT point to segments in the linear-address space that are
mapped into an area of the physical-address space common to all tasks, then all tasks can share the data and
code in those segments.

•

Through a shared LDT — Two or more tasks can use the same LDT if the LDT fields in their TSSs point to the
same LDT. If some segment descriptors in a shared LDT point to segments that are mapped to a common area
of the physical address space, the data and code in those segments can be shared among the tasks that share
the LDT. This method of sharing is more selective than sharing through the GDT, because the sharing can be
limited to specific tasks. Other tasks in the system may have different LDTs that do not give them access to the
shared segments.

•

Through segment descriptors in distinct LDTs that are mapped to common addresses in linear
address space — If this common area of the linear address space is mapped to the same area of the physical
address space for each task, these segment descriptors permit the tasks to share segments. Such segment
descriptors are commonly called aliases. This method of sharing is even more selective than those listed above,
because, other segment descriptors in the LDTs may point to independent linear addresses which are not
shared.

7.6

16-BIT TASK-STATE SEGMENT (TSS)

The 32-bit IA-32 processors also recognize a 16-bit TSS format like the one used in Intel 286 processors (see
Figure 7-10). This format is supported for compatibility with software written to run on earlier IA-32 processors.
The following information is important to know about the 16-bit TSS.

•
•

Do not use a 16-bit TSS to implement a virtual-8086 task.
The valid segment limit for a 16-bit TSS is 2CH.

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TASK MANAGEMENT

•

The 16-bit TSS does not contain a field for the base address of the page directory, which is loaded into control
register CR3. A separate set of page tables for each task is not supported for 16-bit tasks. If a 16-bit task is
dispatched, the page-table structure for the previous task is used.

•
•
•

The I/O base address is not included in the 16-bit TSS. None of the functions of the I/O map are supported.
When task state is saved in a 16-bit TSS, the upper 16 bits of the EFLAGS register and the EIP register are lost.
When the general-purpose registers are loaded or saved from a 16-bit TSS, the upper 16 bits of the registers
are modified and not maintained.

15

0
Task LDT Selector

42

DS Selector

40

SS Selector

38

CS Selector
ES Selector

36
34

DI

32

SI

30

BP

28

SP

26

BX

24

DX

22

CX

20

AX

18

FLAG Word

16

IP (Entry Point)

14

SS2

12

SP2

10

SS1

8

SP1

6

SS0

4

SP0

2

Previous Task Link

0

Figure 7-10. 16-Bit TSS Format

7.7

TASK MANAGEMENT IN 64-BIT MODE

In 64-bit mode, task structure and task state are similar to those in protected mode. However, the task switching
mechanism available in protected mode is not supported in 64-bit mode. Task management and switching must be
performed by software. The processor issues a general-protection exception (#GP) if the following is attempted in
64-bit mode:

•
•

Control transfer to a TSS or a task gate using JMP, CALL, INTn, or interrupt.
An IRET with EFLAGS.NT (nested task) set to 1.

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TASK MANAGEMENT

Although hardware task-switching is not supported in 64-bit mode, a 64-bit task state segment (TSS) must exist.
Figure 7-11 shows the format of a 64-bit TSS. The TSS holds information important to 64-bit mode and that is not
directly related to the task-switch mechanism. This information includes:

•
•
•

RSPn — The full 64-bit canonical forms of the stack pointers (RSP) for privilege levels 0-2.
ISTn — The full 64-bit canonical forms of the interrupt stack table (IST) pointers.
I/O map base address — The 16-bit offset to the I/O permission bit map from the 64-bit TSS base.

The operating system must create at least one 64-bit TSS after activating IA-32e mode. It must execute the LTR
instruction (in 64-bit mode) to load the TR register with a pointer to the 64-bit TSS responsible for both 64-bitmode programs and compatibility-mode programs.

31

0

15
Reserved

I/O Map Base Address
Reserved

100
96

Reserved

92

IST7 (upper 32 bits)

88

IST7 (lower 32 bits)

84

IST6 (upper 32 bits)

80

IST6 (lower 32 bits)

76

IST5 (upper 32 bits)

72

IST5 (lower 32 bits)

68

IST4 (upper 32 bits)

64

IST4 (lower 32 bits)

60

IST3 (upper 32 bits)

56

IST3 (lower 32 bits)

52

IST2 (upper 32 bits)

48

IST2 (lower 32 bits)

44

IST1 (upper 32 bits)

40

IST1 (lower 32 bits)

36

Reserved

32

Reserved

28

RSP2 (upper 32 bits)

24

RSP2 (lower 32 bits)

20

RSP1 (upper 32 bits)

16

RSP1 (lower 32 bits)

12

RSP0 (upper 32 bits)

8

RSP0 (lower 32 bits)

4

Reserved

0

Reserved bits. Set to 0.

Figure 7-11. 64-Bit TSS Format

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CHAPTER 8
MULTIPLE-PROCESSOR MANAGEMENT
The Intel 64 and IA-32 architectures provide mechanisms for managing and improving the performance of multiple
processors connected to the same system bus. These include:

•
•
•

Bus locking and/or cache coherency management for performing atomic operations on system memory.

•

A second-level cache (level 2, L2). For the Pentium 4, Intel Xeon, and P6 family processors, the L2 cache is
included in the processor package and is tightly coupled to the processor. For the Pentium and Intel486
processors, pins are provided to support an external L2 cache.

•

A third-level cache (level 3, L3). For Intel Xeon processors, the L3 cache is included in the processor package
and is tightly coupled to the processor.

•

Intel Hyper-Threading Technology. This extension to the Intel 64 and IA-32 architectures enables a single
processor core to execute two or more threads concurrently (see Section 8.5, “Intel® Hyper-Threading
Technology and Intel® Multi-Core Technology”).

Serializing instructions.
An advance programmable interrupt controller (APIC) located on the processor chip (see Chapter 10,
“Advanced Programmable Interrupt Controller (APIC)”). This feature was introduced by the Pentium processor.

These mechanisms are particularly useful in symmetric-multiprocessing (SMP) systems. However, they can also be
used when an Intel 64 or IA-32 processor and a special-purpose processor (such as a communications, graphics,
or video processor) share the system bus.
These multiprocessing mechanisms have the following characteristics:

•

To maintain system memory coherency — When two or more processors are attempting simultaneously to
access the same address in system memory, some communication mechanism or memory access protocol
must be available to promote data coherency and, in some instances, to allow one processor to temporarily lock
a memory location.

•

To maintain cache consistency — When one processor accesses data cached on another processor, it must not
receive incorrect data. If it modifies data, all other processors that access that data must receive the modified
data.

•

To allow predictable ordering of writes to memory — In some circumstances, it is important that memory writes
be observed externally in precisely the same order as programmed.

•

To distribute interrupt handling among a group of processors — When several processors are operating in a
system in parallel, it is useful to have a centralized mechanism for receiving interrupts and distributing them to
available processors for servicing.

•

To increase system performance by exploiting the multi-threaded and multi-process nature of contemporary
operating systems and applications.

The caching mechanism and cache consistency of Intel 64 and IA-32 processors are discussed in Chapter 11. The
APIC architecture is described in Chapter 10. Bus and memory locking, serializing instructions, memory ordering,
and Intel Hyper-Threading Technology are discussed in the following sections.

8.1

LOCKED ATOMIC OPERATIONS

The 32-bit IA-32 processors support locked atomic operations on locations in system memory. These operations
are typically used to manage shared data structures (such as semaphores, segment descriptors, system segments,
or page tables) in which two or more processors may try simultaneously to modify the same field or flag. The
processor uses three interdependent mechanisms for carrying out locked atomic operations:

•
•

Guaranteed atomic operations
Bus locking, using the LOCK# signal and the LOCK instruction prefix

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MULTIPLE-PROCESSOR MANAGEMENT

•

Cache coherency protocols that ensure that atomic operations can be carried out on cached data structures
(cache lock); this mechanism is present in the Pentium 4, Intel Xeon, and P6 family processors

These mechanisms are interdependent in the following ways. Certain basic memory transactions (such as reading
or writing a byte in system memory) are always guaranteed to be handled atomically. That is, once started, the
processor guarantees that the operation will be completed before another processor or bus agent is allowed access
to the memory location. The processor also supports bus locking for performing selected memory operations (such
as a read-modify-write operation in a shared area of memory) that typically need to be handled atomically, but are
not automatically handled this way. Because frequently used memory locations are often cached in a processor’s L1
or L2 caches, atomic operations can often be carried out inside a processor’s caches without asserting the bus lock.
Here the processor’s cache coherency protocols ensure that other processors that are caching the same memory
locations are managed properly while atomic operations are performed on cached memory locations.

NOTE
Where there are contested lock accesses, software may need to implement algorithms that ensure
fair access to resources in order to prevent lock starvation. The hardware provides no resource that
guarantees fairness to participating agents. It is the responsibility of software to manage the
fairness of semaphores and exclusive locking functions.
The mechanisms for handling locked atomic operations have evolved with the complexity of IA-32 processors. More
recent IA-32 processors (such as the Pentium 4, Intel Xeon, and P6 family processors) and Intel 64 provide a more
refined locking mechanism than earlier processors. These mechanisms are described in the following sections.

8.1.1

Guaranteed Atomic Operations

The Intel486 processor (and newer processors since) guarantees that the following basic memory operations will
always be carried out atomically:

•
•
•

Reading or writing a byte
Reading or writing a word aligned on a 16-bit boundary
Reading or writing a doubleword aligned on a 32-bit boundary

The Pentium processor (and newer processors since) guarantees that the following additional memory operations
will always be carried out atomically:

•
•

Reading or writing a quadword aligned on a 64-bit boundary
16-bit accesses to uncached memory locations that fit within a 32-bit data bus

The P6 family processors (and newer processors since) guarantee that the following additional memory operation
will always be carried out atomically:

•

Unaligned 16-, 32-, and 64-bit accesses to cached memory that fit within a cache line

Accesses to cacheable memory that are split across cache lines and page boundaries are not guaranteed to be
atomic by the Intel Core 2 Duo, Intel® Atom™, Intel Core Duo, Pentium M, Pentium 4, Intel Xeon, P6 family,
Pentium, and Intel486 processors. The Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium M, Pentium 4, Intel
Xeon, and P6 family processors provide bus control signals that permit external memory subsystems to make split
accesses atomic; however, nonaligned data accesses will seriously impact the performance of the processor and
should be avoided.
An x87 instruction or an SSE instructions that accesses data larger than a quadword may be implemented using
multiple memory accesses. If such an instruction stores to memory, some of the accesses may complete (writing
to memory) while another causes the operation to fault for architectural reasons (e.g. due an page-table entry that
is marked “not present”). In this case, the effects of the completed accesses may be visible to software even
though the overall instruction caused a fault. If TLB invalidation has been delayed (see Section 4.10.4.4), such
page faults may occur even if all accesses are to the same page.

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8.1.2

Bus Locking

Intel 64 and IA-32 processors provide a LOCK# signal that is asserted automatically during certain critical memory
operations to lock the system bus or equivalent link. While this output signal is asserted, requests from other
processors or bus agents for control of the bus are blocked. Software can specify other occasions when the LOCK
semantics are to be followed by prepending the LOCK prefix to an instruction.
In the case of the Intel386, Intel486, and Pentium processors, explicitly locked instructions will result in the assertion of the LOCK# signal. It is the responsibility of the hardware designer to make the LOCK# signal available in
system hardware to control memory accesses among processors.
For the P6 and more recent processor families, if the memory area being accessed is cached internally in the
processor, the LOCK# signal is generally not asserted; instead, locking is only applied to the processor’s caches
(see Section 8.1.4, “Effects of a LOCK Operation on Internal Processor Caches”).

8.1.2.1

Automatic Locking

The operations on which the processor automatically follows the LOCK semantics are as follows:

•
•
•

When executing an XCHG instruction that references memory.
When setting the B (busy) flag of a TSS descriptor — The processor tests and sets the busy flag in the
type field of the TSS descriptor when switching to a task. To ensure that two processors do not switch to the
same task simultaneously, the processor follows the LOCK semantics while testing and setting this flag.
When updating segment descriptors — When loading a segment descriptor, the processor will set the
accessed flag in the segment descriptor if the flag is clear. During this operation, the processor follows the LOCK
semantics so that the descriptor will not be modified by another processor while it is being updated. For this
action to be effective, operating-system procedures that update descriptors should use the following steps:
— Use a locked operation to modify the access-rights byte to indicate that the segment descriptor is notpresent, and specify a value for the type field that indicates that the descriptor is being updated.
— Update the fields of the segment descriptor. (This operation may require several memory accesses;
therefore, locked operations cannot be used.)
— Use a locked operation to modify the access-rights byte to indicate that the segment descriptor is valid and
present.

•

The Intel386 processor always updates the accessed flag in the segment descriptor, whether it is clear or not.
The Pentium 4, Intel Xeon, P6 family, Pentium, and Intel486 processors only update this flag if it is not already
set.

•

When updating page-directory and page-table entries — When updating page-directory and page-table
entries, the processor uses locked cycles to set the accessed and dirty flag in the page-directory and page-table
entries.

•

Acknowledging interrupts — After an interrupt request, an interrupt controller may use the data bus to send
the interrupt’s vector to the processor. The processor follows the LOCK semantics during this time to ensure
that no other data appears on the data bus while the vector is being transmitted.

8.1.2.2

Software Controlled Bus Locking

To explicitly force the LOCK semantics, software can use the LOCK prefix with the following instructions when they
are used to modify a memory location. An invalid-opcode exception (#UD) is generated when the LOCK prefix is
used with any other instruction or when no write operation is made to memory (that is, when the destination
operand is in a register).

•
•
•
•
•

The bit test and modify instructions (BTS, BTR, and BTC).
The exchange instructions (XADD, CMPXCHG, and CMPXCHG8B).
The LOCK prefix is automatically assumed for XCHG instruction.
The following single-operand arithmetic and logical instructions: INC, DEC, NOT, and NEG.
The following two-operand arithmetic and logical instructions: ADD, ADC, SUB, SBB, AND, OR, and XOR.

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A locked instruction is guaranteed to lock only the area of memory defined by the destination operand, but may be
interpreted by the system as a lock for a larger memory area.
Software should access semaphores (shared memory used for signalling between multiple processors) using identical addresses and operand lengths. For example, if one processor accesses a semaphore using a word access,
other processors should not access the semaphore using a byte access.

NOTE
Do not implement semaphores using the WC memory type. Do not perform non-temporal stores to
a cache line containing a location used to implement a semaphore.
The integrity of a bus lock is not affected by the alignment of the memory field. The LOCK semantics are followed
for as many bus cycles as necessary to update the entire operand. However, it is recommend that locked accesses
be aligned on their natural boundaries for better system performance:

•
•
•
•

Any boundary for an 8-bit access (locked or otherwise).
16-bit boundary for locked word accesses.
32-bit boundary for locked doubleword accesses.
64-bit boundary for locked quadword accesses.

Locked operations are atomic with respect to all other memory operations and all externally visible events. Only
instruction fetch and page table accesses can pass locked instructions. Locked instructions can be used to synchronize data written by one processor and read by another processor.
For the P6 family processors, locked operations serialize all outstanding load and store operations (that is, wait for
them to complete). This rule is also true for the Pentium 4 and Intel Xeon processors, with one exception. Load
operations that reference weakly ordered memory types (such as the WC memory type) may not be serialized.
Locked instructions should not be used to ensure that data written can be fetched as instructions.

NOTE
The locked instructions for the current versions of the Pentium 4, Intel Xeon, P6 family, Pentium,
and Intel486 processors allow data written to be fetched as instructions. However, Intel
recommends that developers who require the use of self-modifying code use a different synchronizing mechanism, described in the following sections.

8.1.3

Handling Self- and Cross-Modifying Code

The act of a processor writing data into a currently executing code segment with the intent of executing that data
as code is called self-modifying code. IA-32 processors exhibit model-specific behavior when executing selfmodified code, depending upon how far ahead of the current execution pointer the code has been modified.
As processor microarchitectures become more complex and start to speculatively execute code ahead of the retirement point (as in P6 and more recent processor families), the rules regarding which code should execute, pre- or
post-modification, become blurred. To write self-modifying code and ensure that it is compliant with current and
future versions of the IA-32 architectures, use one of the following coding options:
(* OPTION 1 *)
Store modified code (as data) into code segment;
Jump to new code or an intermediate location;
Execute new code;
(* OPTION 2 *)
Store modified code (as data) into code segment;
Execute a serializing instruction; (* For example, CPUID instruction *)
Execute new code;
The use of one of these options is not required for programs intended to run on the Pentium or Intel486 processors,
but are recommended to ensure compatibility with the P6 and more recent processor families.
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Self-modifying code will execute at a lower level of performance than non-self-modifying or normal code. The
degree of the performance deterioration will depend upon the frequency of modification and specific characteristics
of the code.
The act of one processor writing data into the currently executing code segment of a second processor with the
intent of having the second processor execute that data as code is called cross-modifying code. As with selfmodifying code, IA-32 processors exhibit model-specific behavior when executing cross-modifying code,
depending upon how far ahead of the executing processors current execution pointer the code has been modified.
To write cross-modifying code and ensure that it is compliant with current and future versions of the IA-32 architecture, the following processor synchronization algorithm must be implemented:
(* Action of Modifying Processor *)
Memory_Flag ← 0; (* Set Memory_Flag to value other than 1 *)
Store modified code (as data) into code segment;
Memory_Flag ← 1;
(* Action of Executing Processor *)
WHILE (Memory_Flag ≠ 1)
Wait for code to update;
ELIHW;
Execute serializing instruction; (* For example, CPUID instruction *)
Begin executing modified code;
(The use of this option is not required for programs intended to run on the Intel486 processor, but is recommended
to ensure compatibility with the Pentium 4, Intel Xeon, P6 family, and Pentium processors.)
Like self-modifying code, cross-modifying code will execute at a lower level of performance than non-cross-modifying (normal) code, depending upon the frequency of modification and specific characteristics of the code.
The restrictions on self-modifying code and cross-modifying code also apply to the Intel 64 architecture.

8.1.4

Effects of a LOCK Operation on Internal Processor Caches

For the Intel486 and Pentium processors, the LOCK# signal is always asserted on the bus during a LOCK operation,
even if the area of memory being locked is cached in the processor.
For the P6 and more recent processor families, if the area of memory being locked during a LOCK operation is
cached in the processor that is performing the LOCK operation as write-back memory and is completely contained
in a cache line, the processor may not assert the LOCK# signal on the bus. Instead, it will modify the memory location internally and allow it’s cache coherency mechanism to ensure that the operation is carried out atomically. This
operation is called “cache locking.” The cache coherency mechanism automatically prevents two or more processors that have cached the same area of memory from simultaneously modifying data in that area.

8.2

MEMORY ORDERING

The term memory ordering refers to the order in which the processor issues reads (loads) and writes (stores)
through the system bus to system memory. The Intel 64 and IA-32 architectures support several memory-ordering
models depending on the implementation of the architecture. For example, the Intel386 processor enforces
program ordering (generally referred to as strong ordering), where reads and writes are issued on the system
bus in the order they occur in the instruction stream under all circumstances.
To allow performance optimization of instruction execution, the IA-32 architecture allows departures from strongordering model called processor ordering in Pentium 4, Intel Xeon, and P6 family processors. These processorordering variations (called here the memory-ordering model) allow performance enhancing operations such as
allowing reads to go ahead of buffered writes. The goal of any of these variations is to increase instruction execution speeds, while maintaining memory coherency, even in multiple-processor systems.
Section 8.2.1 and Section 8.2.2 describe the memory-ordering implemented by Intel486, Pentium, Intel Core 2
Duo, Intel Atom, Intel Core Duo, Pentium 4, Intel Xeon, and P6 family processors. Section 8.2.3 gives examples

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illustrating the behavior of the memory-ordering model on IA-32 and Intel-64 processors. Section 8.2.4 considers
the special treatment of stores for string operations and Section 8.2.5 discusses how memory-ordering behavior
may be modified through the use of specific instructions.

8.2.1

Memory Ordering in the Intel® Pentium® and Intel486™ Processors

The Pentium and Intel486 processors follow the processor-ordered memory model; however, they operate as
strongly-ordered processors under most circumstances. Reads and writes always appear in programmed order at
the system bus—except for the following situation where processor ordering is exhibited. Read misses are
permitted to go ahead of buffered writes on the system bus when all the buffered writes are cache hits and, therefore, are not directed to the same address being accessed by the read miss.
In the case of I/O operations, both reads and writes always appear in programmed order.
Software intended to operate correctly in processor-ordered processors (such as the Pentium 4, Intel Xeon, and P6
family processors) should not depend on the relatively strong ordering of the Pentium or Intel486 processors.
Instead, it should ensure that accesses to shared variables that are intended to control concurrent execution
among processors are explicitly required to obey program ordering through the use of appropriate locking or serializing operations (see Section 8.2.5, “Strengthening or Weakening the Memory-Ordering Model”).

8.2.2

Memory Ordering in P6 and More Recent Processor Families

The Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium 4, and P6 family processors also use a processor-ordered
memory-ordering model that can be further defined as “write ordered with store-buffer forwarding.” This model can
be characterized as follows.
In a single-processor system for memory regions defined as write-back cacheable, the memory-ordering model
respects the following principles (Note the memory-ordering principles for single-processor and multipleprocessor systems are written from the perspective of software executing on the processor, where the term
“processor” refers to a logical processor. For example, a physical processor supporting multiple cores and/or Intel
Hyper-Threading Technology is treated as a multi-processor systems.):

•
•
•

Reads are not reordered with other reads.
Writes are not reordered with older reads.
Writes to memory are not reordered with other writes, with the following exceptions:
— streaming stores (writes) executed with the non-temporal move instructions (MOVNTI, MOVNTQ,
MOVNTDQ, MOVNTPS, and MOVNTPD); and
— string operations (see Section 8.2.4.1).

•

No write to memory may be reordered with an execution of the CLFLUSH instruction; a write may be reordered
with an execution of the CLFLUSHOPT instruction that flushes a cache line other than the one being written.1
Executions of the CLFLUSH instruction are not reordered with each other. Executions of CLFLUSHOPT that
access different cache lines may be reordered with each other. An execution of CLFLUSHOPT may be reordered
with an execution of CLFLUSH that accesses a different cache line.

•
•
•
•

Reads may be reordered with older writes to different locations but not with older writes to the same location.

•
•
•

LFENCE instructions cannot pass earlier reads.

Reads or writes cannot be reordered with I/O instructions, locked instructions, or serializing instructions.
Reads cannot pass earlier LFENCE and MFENCE instructions.
Writes and executions of CLFLUSH and CLFLUSHOPT cannot pass earlier LFENCE, SFENCE, and MFENCE
instructions.
SFENCE instructions cannot pass earlier writes or executions of CLFLUSH and CLFLUSHOPT.
MFENCE instructions cannot pass earlier reads, writes, or executions of CLFLUSH and CLFLUSHOPT.

1. Earlier versions of this manual specified that writes to memory may be reordered with executions of the CLFLUSH instruction. No
processors implementing the CLFLUSH instruction allow such reordering.
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In a multiple-processor system, the following ordering principles apply:

•
•
•
•
•
•

Individual processors use the same ordering principles as in a single-processor system.
Writes by a single processor are observed in the same order by all processors.
Writes from an individual processor are NOT ordered with respect to the writes from other processors.
Memory ordering obeys causality (memory ordering respects transitive visibility).
Any two stores are seen in a consistent order by processors other than those performing the stores
Locked instructions have a total order.

See the example in Figure 8-1. Consider three processors in a system and each processor performs three writes,
one to each of three defined locations (A, B, and C). Individually, the processors perform the writes in the same
program order, but because of bus arbitration and other memory access mechanisms, the order that the three
processors write the individual memory locations can differ each time the respective code sequences are executed
on the processors. The final values in location A, B, and C would possibly vary on each execution of the write
sequence.
The processor-ordering model described in this section is virtually identical to that used by the Pentium and
Intel486 processors. The only enhancements in the Pentium 4, Intel Xeon, and P6 family processors are:

•
•
•

Added support for speculative reads, while still adhering to the ordering principles above.
Store-buffer forwarding, when a read passes a write to the same memory location.
Out of order store from long string store and string move operations (see Section 8.2.4, “Fast-String Operation
and Out-of-Order Stores,” below).

Order of Writes From Individual Processors

Processor #1
Each processor
is guaranteed to
perform writes in
program order.

Write A.1
Write B.1
Write C.1

Processor #2
Write A.2
Write B.2
Write C.2

Processor #3
Write A.3
Write B.3
Write C.3

Example of order of actual writes
from all processors to memory
Writes are in order
with respect to
individual processes.

Write A.1
Write B.1
Write A.2
Write A.3
Write C.1
Write B.2
Write C.2
Write B.3
Write C.3

Writes from all
processors are
not guaranteed
to occur in a
particular order.

Figure 8-1. Example of Write Ordering in Multiple-Processor Systems

NOTE
In P6 processor family, store-buffer forwarding to reads of WC memory from streaming stores to the same address
does not occur due to errata.

8.2.3

Examples Illustrating the Memory-Ordering Principles

This section provides a set of examples that illustrate the behavior of the memory-ordering principles introduced in
Section 8.2.2. They are designed to give software writers an understanding of how memory ordering may affect
the results of different sequences of instructions.

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These examples are limited to accesses to memory regions defined as write-back cacheable (WB). (Section 8.2.3.1
describes other limitations on the generality of the examples.) The reader should understand that they describe
only software-visible behavior. A logical processor may reorder two accesses even if one of examples indicates that
they may not be reordered. Such an example states only that software cannot detect that such a reordering
occurred. Similarly, a logical processor may execute a memory access more than once as long as the behavior
visible to software is consistent with a single execution of the memory access.

8.2.3.1

Assumptions, Terminology, and Notation

As noted above, the examples in this section are limited to accesses to memory regions defined as write-back
cacheable (WB). They apply only to ordinary loads stores and to locked read-modify-write instructions. They do not
necessarily apply to any of the following: out-of-order stores for string instructions (see Section 8.2.4); accesses
with a non-temporal hint; reads from memory by the processor as part of address translation (e.g., page walks);
and updates to segmentation and paging structures by the processor (e.g., to update “accessed” bits).
The principles underlying the examples in this section apply to individual memory accesses and to locked readmodify-write instructions. The Intel-64 memory-ordering model guarantees that, for each of the following
memory-access instructions, the constituent memory operation appears to execute as a single memory access:

•
•
•
•

Instructions that read or write a single byte.
Instructions that read or write a word (2 bytes) whose address is aligned on a 2 byte boundary.
Instructions that read or write a doubleword (4 bytes) whose address is aligned on a 4 byte boundary.
Instructions that read or write a quadword (8 bytes) whose address is aligned on an 8 byte boundary.

Any locked instruction (either the XCHG instruction or another read-modify-write instruction with a LOCK prefix)
appears to execute as an indivisible and uninterruptible sequence of load(s) followed by store(s) regardless of
alignment.
Other instructions may be implemented with multiple memory accesses. From a memory-ordering point of view,
there are no guarantees regarding the relative order in which the constituent memory accesses are made. There is
also no guarantee that the constituent operations of a store are executed in the same order as the constituent
operations of a load.
Section 8.2.3.2 through Section 8.2.3.7 give examples using the MOV instruction. The principles that underlie
these examples apply to load and store accesses in general and to other instructions that load from or store to
memory. Section 8.2.3.8 and Section 8.2.3.9 give examples using the XCHG instruction. The principles that
underlie these examples apply to other locked read-modify-write instructions.
This section uses the term “processor” is to refer to a logical processor. The examples are written using Intel-64
assembly-language syntax and use the following notational conventions:

•

Arguments beginning with an “r”, such as r1 or r2 refer to registers (e.g., EAX) visible only to the processor
being considered.

•
•
•

Memory locations are denoted with x, y, z.
Stores are written as mov [ _x], val, which implies that val is being stored into the memory location x.
Loads are written as mov r, [ _x], which implies that the contents of the memory location x are being loaded
into the register r.

As noted earlier, the examples refer only to software visible behavior. When the succeeding sections make statement such as “the two stores are reordered,” the implication is only that “the two stores appear to be reordered
from the point of view of software.”

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8.2.3.2

Neither Loads Nor Stores Are Reordered with Like Operations

The Intel-64 memory-ordering model allows neither loads nor stores to be reordered with the same kind of operation. That is, it ensures that loads are seen in program order and that stores are seen in program order. This is illustrated by the following example:
Example 8-1. Stores Are Not Reordered with Other Stores
Processor 0

Processor 1

mov [ _x], 1

mov r1, [ _y]

mov [ _y], 1

mov r2, [ _x]

Initially x = y = 0
r1 = 1 and r2 = 0 is not allowed
The disallowed return values could be exhibited only if processor 0’s two stores are reordered (with the two loads
occurring between them) or if processor 1’s two loads are reordered (with the two stores occurring between them).
If r1 = 1, the store to y occurs before the load from y. Because the Intel-64 memory-ordering model does not allow
stores to be reordered, the earlier store to x occurs before the load from y. Because the Intel-64 memory-ordering
model does not allow loads to be reordered, the store to x also occurs before the later load from x. This r2 = 1.

8.2.3.3

Stores Are Not Reordered With Earlier Loads

The Intel-64 memory-ordering model ensures that a store by a processor may not occur before a previous load by
the same processor. This is illustrated by the following example:
Example 8-2. Stores Are Not Reordered with Older Loads
Processor 0

Processor 1

mov r1, [ _x]

mov r2, [ _y]

mov [ _y], 1

mov [ _x], 1

Initially x = y = 0
r1 = 1 and r2 = 1 is not allowed
Assume r1 = 1.

•
•

Because r1 = 1, processor 1’s store to x occurs before processor 0’s load from x.

•
•

Similarly, processor 0’s load from x occurs before its store to y.

Because the Intel-64 memory-ordering model prevents each store from being reordered with the earlier load
by the same processor, processor 1’s load from y occurs before its store to x.
Thus, processor 1’s load from y occurs before processor 0’s store to y, implying r2 = 0.

8.2.3.4

Loads May Be Reordered with Earlier Stores to Different Locations

The Intel-64 memory-ordering model allows a load to be reordered with an earlier store to a different location.
However, loads are not reordered with stores to the same location.
The fact that a load may be reordered with an earlier store to a different location is illustrated by the following
example:
Example 8-3. Loads May be Reordered with Older Stores
Processor 0

Processor 1

mov [ _x], 1

mov [ _y], 1

mov r1, [ _y]

mov r2, [ _x]

Initially x = y = 0
r1 = 0 and r2 = 0 is allowed

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At each processor, the load and the store are to different locations and hence may be reordered. Any interleaving
of the operations is thus allowed. One such interleaving has the two loads occurring before the two stores. This
would result in each load returning value 0.
The fact that a load may not be reordered with an earlier store to the same location is illustrated by the following
example:
Example 8-4. Loads Are not Reordered with Older Stores to the Same Location
Processor 0
mov [ _x], 1
mov r1, [ _x]
Initially x = 0
r1 = 0 is not allowed
The Intel-64 memory-ordering model does not allow the load to be reordered with the earlier store because the
accesses are to the same location. Therefore, r1 = 1 must hold.

8.2.3.5

Intra-Processor Forwarding Is Allowed

The memory-ordering model allows concurrent stores by two processors to be seen in different orders by those two
processors; specifically, each processor may perceive its own store occurring before that of the other. This is illustrated by the following example:
Example 8-5. Intra-Processor Forwarding is Allowed
Processor 0

Processor 1

mov [ _x], 1

mov [ _y], 1

mov r1, [ _x]

mov r3, [ _y]

mov r2, [ _y]

mov r4, [ _x]

Initially x = y = 0
r2 = 0 and r4 = 0 is allowed
The memory-ordering model imposes no constraints on the order in which the two stores appear to execute by the
two processors. This fact allows processor 0 to see its store before seeing processor 1's, while processor 1 sees its
store before seeing processor 0's. (Each processor is self consistent.) This allows r2 = 0 and r4 = 0.
In practice, the reordering in this example can arise as a result of store-buffer forwarding. While a store is temporarily held in a processor's store buffer, it can satisfy the processor's own loads but is not visible to (and cannot
satisfy) loads by other processors.

8.2.3.6

Stores Are Transitively Visible

The memory-ordering model ensures transitive visibility of stores; stores that are causally related appear to all
processors to occur in an order consistent with the causality relation. This is illustrated by the following example:
Example 8-6. Stores Are Transitively Visible
Processor 0
mov [ _x], 1

Processor 1

Processor 2

mov r1, [ _x]
mov [ _y], 1

mov r2, [ _y]
mov r3, [_x]

Initially x = y = 0
r1 = 1, r2 = 1, r3 = 0 is not allowed
Assume that r1 = 1 and r2 = 1.

•

Because r1 = 1, processor 0’s store occurs before processor 1’s load.

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•

Because the memory-ordering model prevents a store from being reordered with an earlier load (see Section
8.2.3.3), processor 1’s load occurs before its store. Thus, processor 0’s store causally precedes processor 1’s
store.

•

Because processor 0’s store causally precedes processor 1’s store, the memory-ordering model ensures that
processor 0’s store appears to occur before processor 1’s store from the point of view of all processors.

•
•

Because r2 = 1, processor 1’s store occurs before processor 2’s load.

•

The above items imply that processor 0’s store to x occurs before processor 2’s load from x. This implies that
r3 = 1.

Because the Intel-64 memory-ordering model prevents loads from being reordered (see Section 8.2.3.2),
processor 2’s load occur in order.

8.2.3.7

Stores Are Seen in a Consistent Order by Other Processors

As noted in Section 8.2.3.5, the memory-ordering model allows stores by two processors to be seen in different
orders by those two processors. However, any two stores must appear to execute in the same order to all processors other than those performing the stores. This is illustrated by the following example:
Example 8-7. Stores Are Seen in a Consistent Order by Other Processors
Processor 0
Processor 1
Processor 2
mov [ _x], 1

mov [ _y], 1

Processor 3

mov r1, [ _x]

mov r3, [_y]

mov r2, [ _y]

mov r4, [_x]

Initially x = y =0
r1 = 1, r2 = 0, r3 = 1, r4 = 0 is not allowed
By the principles discussed in Section 8.2.3.2,

•
•
•
•

processor 2’s first and second load cannot be reordered,
processor 3’s first and second load cannot be reordered.
If r1 = 1 and r2 = 0, processor 0’s store appears to precede processor 1’s store with respect to processor 2.
Similarly, r3 = 1 and r4 = 0 imply that processor 1’s store appears to precede processor 0’s store with respect
to processor 1.

Because the memory-ordering model ensures that any two stores appear to execute in the same order to all
processors (other than those performing the stores), this set of return values is not allowed

8.2.3.8

Locked Instructions Have a Total Order

The memory-ordering model ensures that all processors agree on a single execution order of all locked instructions, including those that are larger than 8 bytes or are not naturally aligned. This is illustrated by the following
example:
Example 8-8. Locked Instructions Have a Total Order
Processor 0
Processor 1
xchg [ _x], r1

Processor 2

Processor 3

xchg [ _y], r2
mov r3, [ _x]

mov r5, [_y]

mov r4, [ _y]

mov r6, [_x]

Initially r1 = r2 = 1, x = y = 0
r3 = 1, r4 = 0, r5 = 1, r6 = 0 is not allowed
Processor 2 and processor 3 must agree on the order of the two executions of XCHG. Without loss of generality,
suppose that processor 0’s XCHG occurs first.

•

If r5 = 1, processor 1’s XCHG into y occurs before processor 3’s load from y.
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•

Because the Intel-64 memory-ordering model prevents loads from being reordered (see Section 8.2.3.2),
processor 3’s loads occur in order and, therefore, processor 1’s XCHG occurs before processor 3’s load from x.

•

Since processor 0’s XCHG into x occurs before processor 1’s XCHG (by assumption), it occurs before
processor 3’s load from x. Thus, r6 = 1.

A similar argument (referring instead to processor 2’s loads) applies if processor 1’s XCHG occurs before
processor 0’s XCHG.

8.2.3.9

Loads and Stores Are Not Reordered with Locked Instructions

The memory-ordering model prevents loads and stores from being reordered with locked instructions that execute
earlier or later. The examples in this section illustrate only cases in which a locked instruction is executed before a
load or a store. The reader should note that reordering is prevented also if the locked instruction is executed after
a load or a store.
The first example illustrates that loads may not be reordered with earlier locked instructions:
Example 8-9. Loads Are not Reordered with Locks
Processor 0

Processor 1

xchg [ _x], r1

xchg [ _y], r3

mov r2, [ _y]

mov r4, [ _x]

Initially x = y = 0, r1 = r3 = 1
r2 = 0 and r4 = 0 is not allowed
As explained in Section 8.2.3.8, there is a total order of the executions of locked instructions. Without loss of
generality, suppose that processor 0’s XCHG occurs first.
Because the Intel-64 memory-ordering model prevents processor 1’s load from being reordered with its earlier
XCHG, processor 0’s XCHG occurs before processor 1’s load. This implies r4 = 1.
A similar argument (referring instead to processor 2’s accesses) applies if processor 1’s XCHG occurs before
processor 0’s XCHG.
The second example illustrates that a store may not be reordered with an earlier locked instruction:
Example 8-10. Stores Are not Reordered with Locks
Processor 0

Processor 1

xchg [ _x], r1

mov r2, [ _y]

mov [ _y], 1

mov r3, [ _x]

Initially x = y = 0, r1 = 1
r2 = 1 and r3 = 0 is not allowed
Assume r2 = 1.

•
•

Because r2 = 1, processor 0’s store to y occurs before processor 1’s load from y.

•

Because the memory-ordering model prevents loads from being reordered (see Section 8.2.3.2), processor 1’s
loads occur in order and, therefore, processor 1’s XCHG into x occurs before processor 1’s load from x. Thus,
r3 = 1.

Because the memory-ordering model prevents a store from being reordered with an earlier locked instruction,
processor 0’s XCHG into x occurs before its store to y. Thus, processor 0’s XCHG into x occurs before
processor 1’s load from y.

8.2.4

Fast-String Operation and Out-of-Order Stores

Section 7.3.9.3 of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 described an optimization of repeated string operations called fast-string operation.

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As explained in that section, the stores produced by fast-string operation may appear to execute out of order. Software dependent upon sequential store ordering should not use string operations for the entire data structure to be
stored. Data and semaphores should be separated. Order-dependent code should write to a discrete semaphore
variable after any string operations to allow correctly ordered data to be seen by all processors. Atomicity of load
and store operations is guaranteed only for native data elements of the string with native data size, and only if they
are included in a single cache line.
Section 8.2.4.1 and Section 8.2.4.2 provide further explain and examples.

8.2.4.1

Memory-Ordering Model for String Operations on Write-Back (WB) Memory

This section deals with the memory-ordering model for string operations on write-back (WB) memory for the Intel
64 architecture.
The memory-ordering model respects the follow principles:
1. Stores within a single string operation may be executed out of order.
2. Stores from separate string operations (for example, stores from consecutive string operations) do not execute
out of order. All the stores from an earlier string operation will complete before any store from a later string
operation.
3. String operations are not reordered with other store operations.
Fast string operations (e.g. string operations initiated with the MOVS/STOS instructions and the REP prefix) may be
interrupted by exceptions or interrupts. The interrupts are precise but may be delayed - for example, the interruptions may be taken at cache line boundaries, after every few iterations of the loop, or after operating on every few
bytes. Different implementations may choose different options, or may even choose not to delay interrupt
handling, so software should not rely on the delay. When the interrupt/trap handler is reached, the source/destination registers point to the next string element to be operated on, while the EIP stored in the stack points to the
string instruction, and the ECX register has the value it held following the last successful iteration. The return from
that trap/interrupt handler should cause the string instruction to be resumed from the point where it was interrupted.
The string operation memory-ordering principles, (item 2 and 3 above) should be interpreted by taking the incorruptibility of fast string operations into account. For example, if a fast string operation gets interrupted after k iterations, then stores performed by the interrupt handler will become visible after the fast string stores from iteration
0 to k, and before the fast string stores from the (k+1)th iteration onward.
Stores within a single string operation may execute out of order (item 1 above) only if fast string operation is
enabled. Fast string operations are enabled/disabled through the IA32_MISC_ENABLE model specific register.

8.2.4.2

Examples Illustrating Memory-Ordering Principles for String Operations

The following examples uses the same notation and convention as described in Section 8.2.3.1.
In Example 8-11, processor 0 does one round of (128 iterations) doubleword string store operation via rep:stosd,
writing the value 1 (value in EAX) into a block of 512 bytes from location _x (kept in ES:EDI) in ascending order.
Since each operation stores a doubleword (4 bytes), the operation is repeated 128 times (value in ECX). The block
of memory initially contained 0. Processor 1 is reading two memory locations that are part of the memory block
being updated by processor 0, i.e, reading locations in the range _x to (_x+511).
Example 8-11. Stores Within a String Operation May be Reordered
Processor 0
rep:stosd [ _x]

Processor 1

mov r1, [ _z]
mov r2, [ _y]

Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_x] to 511[_x]= 0, _x <= _y < _z < _x+512
r1 = 1 and r2 = 0 is allowed

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It is possible for processor 1 to perceive that the repeated string stores in processor 0 are happening out of order.
Assume that fast string operations are enabled on processor 0.
In Example 8-12, processor 0 does two separate rounds of rep stosd operation of 128 doubleword stores, writing
the value 1 (value in EAX) into the first block of 512 bytes from location _x (kept in ES:EDI) in ascending order. It
then writes 1 into a second block of memory from (_x+512) to (_x+1023). All of the memory locations initially
contain 0. The block of memory initially contained 0. Processor 1 performs two load operations from the two blocks
of memory.
Example 8-12. Stores Across String Operations Are not Reordered
Processor 0

Processor 1

rep:stosd [ _x]
mov r1, [ _z]
mov ecx, $128
mov r2, [ _y]
rep:stosd 512[ _x]
Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_x] to 1023[_x]= 0, _x <= _y < _x+512 < _z < _x+1024
r1 = 1 and r2 = 0 is not allowed
It is not possible in the above example for processor 1 to perceive any of the stores from the later string operation
(to the second 512 block) in processor 0 before seeing the stores from the earlier string operation to the first 512
block.
The above example assumes that writes to the second block (_x+512 to _x+1023) does not get executed while
processor 0’s string operation to the first block has been interrupted. If the string operation to the first block by
processor 0 is interrupted, and a write to the second memory block is executed by the interrupt handler, then that
change in the second memory block will be visible before the string operation to the first memory block resumes.
In Example 8-13, processor 0 does one round of (128 iterations) doubleword string store operation via rep:stosd,
writing the value 1 (value in EAX) into a block of 512 bytes from location _x (kept in ES:EDI) in ascending order. It
then writes to a second memory location outside the memory block of the previous string operation. Processor 1
performs two read operations, the first read is from an address outside the 512-byte block but to be updated by
processor 0, the second ready is from inside the block of memory of string operation.
Example 8-13. String Operations Are not Reordered with later Stores
Processor 0
rep:stosd [ _x]

mov r1, [ _z]

mov [_z], $1

mov r2, [ _y]

Processor 1

Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_y] = [_z] = 0, [_x] to 511[_x]= 0, _x <= _y < _x+512, _z is a separate memory location
r1 = 1 and r2 = 0 is not allowed
Processor 1 cannot perceive the later store by processor 0 until it sees all the stores from the string operation.
Example 8-13 assumes that processor 0’s store to [_z] is not executed while the string operation has been interrupted. If the string operation is interrupted and the store to [_z] by processor 0 is executed by the interrupt
handler, then changes to [_z] will become visible before the string operation resumes.
Example 8-14 illustrates the visibility principle when a string operation is interrupted.

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Example 8-14. Interrupted String Operation
Processor 0

Processor 1

rep:stosd [ _x] // interrupted before es:edi reach _y

mov r1, [ _z]

mov [_z], $1 // interrupt handler

mov r2, [ _y]

Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_y] = [_z] = 0, [_x] to 511[_x]= 0, _x <= _y < _x+512, _z is a separate memory location
r1 = 1 and r2 = 0 is allowed
In Example 8-14, processor 0 started a string operation to write to a memory block of 512 bytes starting at address
_x. Processor 0 got interrupted after k iterations of store operations. The address _y has not yet been updated by
processor 0 when processor 0 got interrupted. The interrupt handler that took control on processor 0 writes to the
address _z. Processor 1 may see the store to _z from the interrupt handler, before seeing the remaining stores to
the 512-byte memory block that are executed when the string operation resumes.
Example 8-15 illustrates the ordering of string operations with earlier stores. No store from a string operation can
be visible before all prior stores are visible.
Example 8-15. String Operations Are not Reordered with Earlier Stores
Processor 0
mov [_z], $1

mov r1, [ _y]

rep:stosd [ _x]

mov r2, [ _z]

Processor 1

Initially on processor 0: EAX = 1, ECX=128, ES:EDI =_x
Initially [_y] = [_z] = 0, [_x] to 511[_x]= 0, _x <= _y < _x+512, _z is a separate memory location
r1 = 1 and r2 = 0 is not allowed

8.2.5

Strengthening or Weakening the Memory-Ordering Model

The Intel 64 and IA-32 architectures provide several mechanisms for strengthening or weakening the memoryordering model to handle special programming situations. These mechanisms include:

•

The I/O instructions, locking instructions, the LOCK prefix, and serializing instructions force stronger ordering
on the processor.

•

The SFENCE instruction (introduced to the IA-32 architecture in the Pentium III processor) and the LFENCE and
MFENCE instructions (introduced in the Pentium 4 processor) provide memory-ordering and serialization
capabilities for specific types of memory operations.

•

The memory type range registers (MTRRs) can be used to strengthen or weaken memory ordering for specific
area of physical memory (see Section 11.11, “Memory Type Range Registers (MTRRs)”). MTRRs are available
only in the Pentium 4, Intel Xeon, and P6 family processors.

•

The page attribute table (PAT) can be used to strengthen memory ordering for a specific page or group of pages
(see Section 11.12, “Page Attribute Table (PAT)”). The PAT is available only in the Pentium 4, Intel Xeon, and
Pentium III processors.

These mechanisms can be used as follows:
Memory mapped devices and other I/O devices on the bus are often sensitive to the order of writes to their I/O
buffers. I/O instructions can be used to (the IN and OUT instructions) impose strong write ordering on such
accesses as follows. Prior to executing an I/O instruction, the processor waits for all previous instructions in the
program to complete and for all buffered writes to drain to memory. Only instruction fetch and page tables walks
can pass I/O instructions. Execution of subsequent instructions do not begin until the processor determines that
the I/O instruction has been completed.

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Synchronization mechanisms in multiple-processor systems may depend upon a strong memory-ordering model.
Here, a program can use a locking instruction such as the XCHG instruction or the LOCK prefix to ensure that a
read-modify-write operation on memory is carried out atomically. Locking operations typically operate like I/O
operations in that they wait for all previous instructions to complete and for all buffered writes to drain to memory
(see Section 8.1.2, “Bus Locking”).
Program synchronization can also be carried out with serializing instructions (see Section 8.3). These instructions
are typically used at critical procedure or task boundaries to force completion of all previous instructions before a
jump to a new section of code or a context switch occurs. Like the I/O and locking instructions, the processor waits
until all previous instructions have been completed and all buffered writes have been drained to memory before
executing the serializing instruction.
The SFENCE, LFENCE, and MFENCE instructions provide a performance-efficient way of ensuring load and store
memory ordering between routines that produce weakly-ordered results and routines that consume that data. The
functions of these instructions are as follows:

•

SFENCE — Serializes all store (write) operations that occurred prior to the SFENCE instruction in the program
instruction stream, but does not affect load operations.

•

LFENCE — Serializes all load (read) operations that occurred prior to the LFENCE instruction in the program
instruction stream, but does not affect store operations.2

•

MFENCE — Serializes all store and load operations that occurred prior to the MFENCE instruction in the
program instruction stream.

Note that the SFENCE, LFENCE, and MFENCE instructions provide a more efficient method of controlling memory
ordering than the CPUID instruction.
The MTRRs were introduced in the P6 family processors to define the cache characteristics for specified areas of
physical memory. The following are two examples of how memory types set up with MTRRs can be used strengthen
or weaken memory ordering for the Pentium 4, Intel Xeon, and P6 family processors:

•

The strong uncached (UC) memory type forces a strong-ordering model on memory accesses. Here, all reads
and writes to the UC memory region appear on the bus and out-of-order or speculative accesses are not
performed. This memory type can be applied to an address range dedicated to memory mapped I/O devices to
force strong memory ordering.

•

For areas of memory where weak ordering is acceptable, the write back (WB) memory type can be chosen.
Here, reads can be performed speculatively and writes can be buffered and combined. For this type of memory,
cache locking is performed on atomic (locked) operations that do not split across cache lines, which helps to
reduce the performance penalty associated with the use of the typical synchronization instructions, such as
XCHG, that lock the bus during the entire read-modify-write operation. With the WB memory type, the XCHG
instruction locks the cache instead of the bus if the memory access is contained within a cache line.

The PAT was introduced in the Pentium III processor to enhance the caching characteristics that can be assigned to
pages or groups of pages. The PAT mechanism typically used to strengthen caching characteristics at the page level
with respect to the caching characteristics established by the MTRRs. Table 11-7 shows the interaction of the PAT
with the MTRRs.
Intel recommends that software written to run on Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium 4, Intel
Xeon, and P6 family processors assume the processor-ordering model or a weaker memory-ordering model. The
Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium 4, Intel Xeon, and P6 family processors do not implement a
strong memory-ordering model, except when using the UC memory type. Despite the fact that Pentium 4, Intel
Xeon, and P6 family processors support processor ordering, Intel does not guarantee that future processors will
support this model. To make software portable to future processors, it is recommended that operating systems
provide critical region and resource control constructs and API’s (application program interfaces) based on I/O,
locking, and/or serializing instructions be used to synchronize access to shared areas of memory in multipleprocessor systems. Also, software should not depend on processor ordering in situations where the system hardware does not support this memory-ordering model.
2. Specifically, LFENCE does not execute until all prior instructions have completed locally, and no later instruction begins execution
until LFENCE completes. As a result, an instruction that loads from memory and that precedes an LFENCE receives data from memory prior to completion of the LFENCE. An LFENCE that follows an instruction that stores to memory might complete before the data
being stored have become globally visible. Instructions following an LFENCE may be fetched from memory before the LFENCE, but
they will not execute until the LFENCE completes.
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8.3

SERIALIZING INSTRUCTIONS

The Intel 64 and IA-32 architectures define several serializing instructions. These instructions force the
processor to complete all modifications to flags, registers, and memory by previous instructions and to drain all
buffered writes to memory before the next instruction is fetched and executed. For example, when a MOV to
control register instruction is used to load a new value into control register CR0 to enable protected mode, the
processor must perform a serializing operation before it enters protected mode. This serializing operation ensures
that all operations that were started while the processor was in real-address mode are completed before the switch
to protected mode is made.
The concept of serializing instructions was introduced into the IA-32 architecture with the Pentium processor to
support parallel instruction execution. Serializing instructions have no meaning for the Intel486 and earlier processors that do not implement parallel instruction execution.
It is important to note that executing of serializing instructions on P6 and more recent processor families constrain
speculative execution because the results of speculatively executed instructions are discarded. The following
instructions are serializing instructions:

•

Privileged serializing instructions — INVD, INVEPT, INVLPG, INVVPID, LGDT, LIDT, LLDT, LTR, MOV (to
control register, with the exception of MOV CR83), MOV (to debug register), WBINVD, and WRMSR4.

•

Non-privileged serializing instructions — CPUID, IRET, and RSM.

When the processor serializes instruction execution, it ensures that all pending memory transactions are
completed (including writes stored in its store buffer) before it executes the next instruction. Nothing can pass a
serializing instruction and a serializing instruction cannot pass any other instruction (read, write, instruction fetch,
or I/O). For example, CPUID can be executed at any privilege level to serialize instruction execution with no effect
on program flow, except that the EAX, EBX, ECX, and EDX registers are modified.
The following instructions are memory-ordering instructions, not serializing instructions. These drain the data
memory subsystem. They do not serialize the instruction execution stream:5

•

Non-privileged memory-ordering instructions — SFENCE, LFENCE, and MFENCE.

The SFENCE, LFENCE, and MFENCE instructions provide more granularity in controlling the serialization of memory
loads and stores (see Section 8.2.5, “Strengthening or Weakening the Memory-Ordering Model”).
The following additional information is worth noting regarding serializing instructions:

•

The processor does not write back the contents of modified data in its data cache to external memory when it
serializes instruction execution. Software can force modified data to be written back by executing the WBINVD
instruction, which is a serializing instruction. The amount of time or cycles for WBINVD to complete will vary
due to the size of different cache hierarchies and other factors. As a consequence, the use of the WBINVD
instruction can have an impact on interrupt/event response time.

•

When an instruction is executed that enables or disables paging (that is, changes the PG flag in control register
CR0), the instruction should be followed by a jump instruction. The target instruction of the jump instruction is
fetched with the new setting of the PG flag (that is, paging is enabled or disabled), but the jump instruction
itself is fetched with the previous setting. The Pentium 4, Intel Xeon, and P6 family processors do not require
the jump operation following the move to register CR0 (because any use of the MOV instruction in a Pentium 4,
Intel Xeon, or P6 family processor to write to CR0 is completely serializing). However, to maintain backwards
and forward compatibility with code written to run on other IA-32 processors, it is recommended that the jump
operation be performed.

•

Whenever an instruction is executed to change the contents of CR3 while paging is enabled, the next
instruction is fetched using the translation tables that correspond to the new value of CR3. Therefore the next
instruction and the sequentially following instructions should have a mapping based upon the new value of
CR3. (Global entries in the TLBs are not invalidated, see Section 4.10.4, “Invalidation of TLBs and PagingStructure Caches.”)

3. MOV CR8 is not defined architecturally as a serializing instruction.
4. WRMSR to the IA32_TSC_DEADLINE MSR (MSR index 6E0H) and the X2APIC MSRs (MSR indices 802H to 83FH) are not serializing.
5. LFENCE does provide some guarantees on instruction ordering. It does not execute until all prior instructions have completed locally,
and no later instruction begins execution until LFENCE completes.
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•

The Pentium processor and more recent processor families use branch-prediction techniques to improve
performance by prefetching the destination of a branch instruction before the branch instruction is executed.
Consequently, instruction execution is not deterministically serialized when a branch instruction is executed.

8.4

MULTIPLE-PROCESSOR (MP) INITIALIZATION

The IA-32 architecture (beginning with the P6 family processors) defines a multiple-processor (MP) initialization
protocol called the Multiprocessor Specification Version 1.4. This specification defines the boot protocol to be used
by IA-32 processors in multiple-processor systems. (Here, multiple processors is defined as two or more processors.) The MP initialization protocol has the following important features:

•
•

It supports controlled booting of multiple processors without requiring dedicated system hardware.

•

It allows all IA-32 processors to be booted in the same manner, including those supporting Intel HyperThreading Technology.

•

The MP initialization protocol also applies to MP systems using Intel 64 processors.

It allows hardware to initiate the booting of a system without the need for a dedicated signal or a predefined
boot processor.

The mechanism for carrying out the MP initialization protocol differs depending on the Intel processor generations.
The following bullets summarizes the evolution of the changes:

•

For P6 family or older processors supporting MP operations— The selection of the BSP and APs (see
Section 8.4.1, “BSP and AP Processors”) is handled through arbitration on the APIC bus, using BIPI and FIPI
messages. These processor generations have CPUID signatures of (family=06H, extended_model=0,
model<=0DH), or family <06H. See Section 8.11.1, “Overview of the MP Initialization Process For P6 Family
Processors” for a complete discussion of MP initialization for P6 family processors.

•

Early generations of IA processors with family 0FH — The selection of the BSP and APs (see Section
8.4.1, “BSP and AP Processors”) is handled through arbitration on the system bus, using BIPI and FIPI
messages (see Section 8.4.3, “MP Initialization Protocol Algorithm for MP Systems”). These processor
generations have CPUID signatures of family=0FH, model=0H, stepping<=09H.

•

Later generations of IA processors with family 0FH, and IA processors with system bus — The
selection of the BSP and APs is handled through a special system bus cycle, without using BIPI and FIPI
message arbitration (see Section 8.4.3, “MP Initialization Protocol Algorithm for MP Systems”). These
processor generations have CPUID signatures of family=0FH with (model=0H, stepping>=0AH) or (model >0,
all steppings); or family=06H, extended_model=0, model>=0EH.

•

All other modern IA processor generations supporting MP operations— The selection of the BSP and
APs in the system is handled by platform-specific arrangement of the combination of hardware, BIOS, and/or
configuration input options. The basis of the selection mechanism is similar to those of the Later generations of
family 0FH and other Intel processor using system bus (see Section 8.4.3, “MP Initialization Protocol Algorithm
for MP Systems”). These processor generations have CPUID signatures of family=06H, extended_model>0.

The family, model, and stepping ID for a processor is given in the EAX register when the CPUID instruction is
executed with a value of 1 in the EAX register.

8.4.1

BSP and AP Processors

The MP initialization protocol defines two classes of processors: the bootstrap processor (BSP) and the application
processors (APs). Following a power-up or RESET of an MP system, system hardware dynamically selects one of the
processors on the system bus as the BSP. The remaining processors are designated as APs.
As part of the BSP selection mechanism, the BSP flag is set in the IA32_APIC_BASE MSR (see Figure 10-5) of the
BSP, indicating that it is the BSP. This flag is cleared for all other processors.
The BSP executes the BIOS’s boot-strap code to configure the APIC environment, sets up system-wide data structures, and starts and initializes the APs. When the BSP and APs are initialized, the BSP then begins executing the
operating-system initialization code.

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Following a power-up or reset, the APs complete a minimal self-configuration, then wait for a startup signal (a SIPI
message) from the BSP processor. Upon receiving a SIPI message, an AP executes the BIOS AP configuration code,
which ends with the AP being placed in halt state.
For Intel 64 and IA-32 processors supporting Intel Hyper-Threading Technology, the MP initialization protocol treats
each of the logical processors on the system bus or coherent link domain as a separate processor (with a unique
APIC ID). During boot-up, one of the logical processors is selected as the BSP and the remainder of the logical
processors are designated as APs.

8.4.2

MP Initialization Protocol Requirements and Restrictions

The MP initialization protocol imposes the following requirements and restrictions on the system:

•

The MP protocol is executed only after a power-up or RESET. If the MP protocol has completed and a BSP is
chosen, subsequent INITs (either to a specific processor or system wide) do not cause the MP protocol to be
repeated. Instead, each logical processor examines its BSP flag (in the IA32_APIC_BASE MSR) to determine
whether it should execute the BIOS boot-strap code (if it is the BSP) or enter a wait-for-SIPI state (if it is an
AP).

•

All devices in the system that are capable of delivering interrupts to the processors must be inhibited from
doing so for the duration of the MP initialization protocol. The time during which interrupts must be inhibited
includes the window between when the BSP issues an INIT-SIPI-SIPI sequence to an AP and when the AP
responds to the last SIPI in the sequence.

8.4.3

MP Initialization Protocol Algorithm for MP Systems

Following a power-up or RESET of an MP system, the processors in the system execute the MP initialization protocol
algorithm to initialize each of the logical processors on the system bus or coherent link domain. In the course of
executing this algorithm, the following boot-up and initialization operations are carried out:
1. Each logical processor is assigned a unique APIC ID, based on system topology. The unique ID is a 32-bit value
if the processor supports CPUID leaf 0BH, otherwise the unique ID is an 8-bit value. (see Section 8.4.5, “Identifying Logical Processors in an MP System”).
2. Each logical processor is assigned a unique arbitration priority based on its APIC ID.
3. Each logical processor executes its internal BIST simultaneously with the other logical processors in the
system.
4. Upon completion of the BIST, the logical processors use a hardware-defined selection mechanism to select the
BSP and the APs from the available logical processors on the system bus. The BSP selection mechanism differs
depending on the family, model, and stepping IDs of the processors, as follows:
— Later generations of IA processors within family 0FH (see Section 8.4), IA processors with system bus
(family=06H, extended_model=0, model>=0EH), or all other modern Intel processors (family=06H,
extended_model>0):

•

The logical processors begin monitoring the BNR# signal, which is toggling. When the BNR# pin stops
toggling, each processor attempts to issue a NOP special cycle on the system bus.

•

The logical processor with the highest arbitration priority succeeds in issuing a NOP special cycle and is
nominated the BSP. This processor sets the BSP flag in its IA32_APIC_BASE MSR, then fetches and
begins executing BIOS boot-strap code, beginning at the reset vector (physical address FFFF FFF0H).

•

The remaining logical processors (that failed in issuing a NOP special cycle) are designated as APs. They
leave their BSP flags in the clear state and enter a “wait-for-SIPI state.”

— Early generations of IA processors within family 0FH (family=0FH, model=0H, stepping<=09H), P6 family
or older processors supporting MP operations (family=06H, extended_model=0, model<=0DH; or family
<06H):

•

Each processor broadcasts a BIPI to “all including self.” The first processor that broadcasts a BIPI (and
thus receives its own BIPI vector), selects itself as the BSP and sets the BSP flag in its IA32_APIC_BASE

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MSR. (See Section 8.11.1, “Overview of the MP Initialization Process For P6 Family Processors” for a
description of the BIPI, FIPI, and SIPI messages.)

•

The remainder of the processors (which were not selected as the BSP) are designated as APs. They
leave their BSP flags in the clear state and enter a “wait-for-SIPI state.”

•

The newly established BSP broadcasts an FIPI message to “all including self,” which the BSP and APs
treat as an end of MP initialization signal. Only the processor with its BSP flag set responds to the FIPI
message. It responds by fetching and executing the BIOS boot-strap code, beginning at the reset vector
(physical address FFFF FFF0H).

5. As part of the boot-strap code, the BSP creates an ACPI table and/or an MP table and adds its initial APIC ID to
these tables as appropriate.
6. At the end of the boot-strap procedure, the BSP sets a processor counter to 1, then broadcasts a SIPI message
to all the APs in the system. Here, the SIPI message contains a vector to the BIOS AP initialization code (at
000VV000H, where VV is the vector contained in the SIPI message).
7. The first action of the AP initialization code is to set up a race (among the APs) to a BIOS initialization
semaphore. The first AP to the semaphore begins executing the initialization code. (See Section 8.4.4, “MP
Initialization Example,” for semaphore implementation details.) As part of the AP initialization procedure, the
AP adds its APIC ID number to the ACPI and/or MP tables as appropriate and increments the processor counter
by 1. At the completion of the initialization procedure, the AP executes a CLI instruction and halts itself.
8. When each of the APs has gained access to the semaphore and executed the AP initialization code, the BSP
establishes a count for the number of processors connected to the system bus, completes executing the BIOS
boot-strap code, and then begins executing operating-system boot-strap and start-up code.
9. While the BSP is executing operating-system boot-strap and start-up code, the APs remain in the halted state.
In this state they will respond only to INITs, NMIs, and SMIs. They will also respond to snoops and to assertions
of the STPCLK# pin.
The following section gives an example (with code) of the MP initialization protocol for of multiple processors operating in an MP configuration.
Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 4 describes how to program the LINT[0:1] pins of the processor’s local APICs after an MP configuration has been completed.

8.4.4

MP Initialization Example

The following example illustrates the use of the MP initialization protocol used to initialize processors in an MP
system after the BSP and APs have been established. The code runs on Intel 64 or IA-32 processors that use a
protocol. This includes P6 Family processors, Pentium 4 processors, Intel Core Duo, Intel Core 2 Duo and Intel Xeon
processors.
The following constants and data definitions are used in the accompanying
code examples. They are based on the addresses of the APIC registers defined in Table 10-1.
ICR_LOW
SVR
APIC_ID
LVT3
APIC_ENABLED
BOOT_ID
COUNT
VACANT

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EQU 0FEE00300H
EQU 0FEE000F0H
EQU 0FEE00020H
EQU 0FEE00370H
EQU 0100H
DD ?
EQU 00H
EQU 00H

MULTIPLE-PROCESSOR MANAGEMENT

8.4.4.1

Typical BSP Initialization Sequence

After the BSP and APs have been selected (by means of a hardware protocol, see Section 8.4.3, “MP Initialization
Protocol Algorithm for MP Systems”), the BSP begins executing BIOS boot-strap code (POST) at the normal IA-32
architecture starting address (FFFF FFF0H). The boot-strap code typically performs the following operations:
1. Initializes memory.
2. Loads the microcode update into the processor.
3. Initializes the MTRRs.
4. Enables the caches.
5. Executes the CPUID instruction with a value of 0H in the EAX register, then reads the EBX, ECX, and EDX
registers to determine if the BSP is “GenuineIntel.”
6. Executes the CPUID instruction with a value of 1H in the EAX register, then saves the values in the EAX, ECX,
and EDX registers in a system configuration space in RAM for use later.
7. Loads start-up code for the AP to execute into a 4-KByte page in the lower 1 MByte of memory.
8. Switches to protected mode and ensures that the APIC address space is mapped to the strong uncacheable
(UC) memory type.
9. Determine the BSP’s APIC ID from the local APIC ID register (default is 0), the code snippet below is an
example that applies to logical processors in a system whose local APIC units operate in xAPIC mode that APIC
registers are accessed using memory mapped interface:
MOV ESI, APIC_ID; Address of local APIC ID register
MOV EAX, [ESI];
AND EAX, 0FF000000H; Zero out all other bits except APIC ID
MOV BOOT_ID, EAX; Save in memory
Saves the APIC ID in the ACPI and/or MP tables and optionally in the system configuration space in RAM.
10. Converts the base address of the 4-KByte page for the AP’s bootup code into 8-bit vector. The 8-bit vector
defines the address of a 4-KByte page in the real-address mode address space (1-MByte space). For example,
a vector of 0BDH specifies a start-up memory address of 000BD000H.
11. Enables the local APIC by setting bit 8 of the APIC spurious vector register (SVR).
MOV ESI, SVR; Address of SVR
MOV EAX, [ESI];
OR EAX, APIC_ENABLED; Set bit 8 to enable (0 on reset)
MOV [ESI], EAX;
12. Sets up the LVT error handling entry by establishing an 8-bit vector for the APIC error handler.
MOV ESI, LVT3;
MOV EAX, [ESI];
AND EAX, FFFFFF00H; Clear out previous vector.
OR EAX, 000000xxH; xx is the 8-bit vector the APIC error handler.
MOV [ESI], EAX;
13. Initializes the Lock Semaphore variable VACANT to 00H. The APs use this semaphore to determine the order in
which they execute BIOS AP initialization code.
14. Performs the following operation to set up the BSP to detect the presence of APs in the system and the number
of processors (within a finite duration, minimally 100 milliseconds):
— Sets the value of the COUNT variable to 1.
— In the AP BIOS initialization code, the AP will increment the COUNT variable to indicate its presence. The
finite duration while waiting for the COUNT to be updated can be accomplished with a timer. When the timer
expires, the BSP checks the value of the COUNT variable. If the timer expires and the COUNT variable has
not been incremented, no APs are present or some error has occurred.

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15. Broadcasts an INIT-SIPI-SIPI IPI sequence to the APs to wake them up and initialize them. If software knows
how many logical processors it expects to wake up, it may choose to poll the COUNT variable. If the expected
processors show up before the 100 millisecond timer expires, the timer can be canceled and skip to step 16.
The left-hand-side of the procedure illustrated in Table 8-1 provides an algorithm when the expected processor
count is unknown. The right-hand-side of Table 8-1 can be used when the expected processor count is known.

Table 8-1. Broadcast INIT-SIPI-SIPI Sequence and Choice of Timeouts
INIT-SIPI-SIPI when the expected processor count is unknown

INIT-SIPI-SIPI when the expected processor count is known

MOV ESI, ICR_LOW; Load address of ICR low dword into ESI.

MOV ESI, ICR_LOW; Load address of ICR low dword into ESI.

MOV EAX, 000C4500H; Load ICR encoding for broadcast INIT IPI

MOV EAX, 000C4500H; Load ICR encoding for broadcast INIT IPI

; to all APs into EAX.

; to all APs into EAX.

MOV [ESI], EAX; Broadcast INIT IPI to all APs

MOV [ESI], EAX; Broadcast INIT IPI to all APs

; 10-millisecond delay loop.

; 10-millisecond delay loop.

MOV EAX, 000C46XXH; Load ICR encoding for broadcast SIPI IP

MOV EAX, 000C46XXH; Load ICR encoding for broadcast SIPI IP

; to all APs into EAX, where xx is the vector computed in step 10.

; to all APs into EAX, where xx is the vector computed in step 10.

MOV [ESI], EAX; Broadcast SIPI IPI to all APs

MOV [ESI], EAX; Broadcast SIPI IPI to all APs

; 200-microsecond delay loop

; 200 microsecond delay loop with check to see if COUNT has

MOV [ESI], EAX; Broadcast second SIPI IPI to all APs

; reached the expected processor count. If COUNT reaches

;Waits for the timer interrupt until the timer expires

; expected processor count, cancel timer and go to step 16.
MOV [ESI], EAX; Broadcast second SIPI IPI to all APs
; Wait for the timer interrupt polling COUNT. If COUNT reaches
; expected processor count, cancel timer and go to step 16.
; If timer expires, go to step 16.

16. Reads and evaluates the COUNT variable and establishes a processor count.
17. If necessary, reconfigures the APIC and continues with the remaining system diagnostics as appropriate.

8.4.4.2

Typical AP Initialization Sequence

When an AP receives the SIPI, it begins executing BIOS AP initialization code at the vector encoded in the SIPI. The
AP initialization code typically performs the following operations:
1. Waits on the BIOS initialization Lock Semaphore. When control of the semaphore is attained, initialization
continues.
2. Loads the microcode update into the processor.
3. Initializes the MTRRs (using the same mapping that was used for the BSP).
4. Enables the cache.
5. Executes the CPUID instruction with a value of 0H in the EAX register, then reads the EBX, ECX, and EDX
registers to determine if the AP is “GenuineIntel.”
6. Executes the CPUID instruction with a value of 1H in the EAX register, then saves the values in the EAX, ECX,
and EDX registers in a system configuration space in RAM for use later.
7. Switches to protected mode and ensures that the APIC address space is mapped to the strong uncacheable
(UC) memory type.
8. Determines the AP’s APIC ID from the local APIC ID register, and adds it to the MP and ACPI tables and
optionally to the system configuration space in RAM.
9. Initializes and configures the local APIC by setting bit 8 in the SVR register and setting up the LVT3 (error LVT)
for error handling (as described in steps 9 and 10 in Section 8.4.4.1, “Typical BSP Initialization Sequence”).

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10. Configures the APs SMI execution environment. (Each AP and the BSP must have a different SMBASE address.)
11. Increments the COUNT variable by 1.
12. Releases the semaphore.
13. Executes one of the following:
— the CLI and HLT instructions (if MONITOR/MWAIT is not supported), or
— the CLI, MONITOR and MWAIT sequence to enter a deep C-state.
14. Waits for an INIT IPI.

8.4.5

Identifying Logical Processors in an MP System

After the BIOS has completed the MP initialization protocol, each logical processor can be uniquely identified by its
local APIC ID. Software can access these APIC IDs in either of the following ways:

•

Read APIC ID for a local APIC — Code running on a logical processor can read APIC ID in one of two ways
depending on the local APIC unit is operating in x2APIC mode (see Intel® 64 Architecture x2APIC Specification)or in xAPIC mode:
— If the local APIC unit supports x2APIC and is operating in x2APIC mode, 32-bit APIC ID can be read by
executing a RDMSR instruction to read the processor’s x2APIC ID register. This method is equivalent to
executing CPUID leaf 0BH described below.
— If the local APIC unit is operating in xAPIC mode, 8-bit APIC ID can be read by executing a MOV instruction
to read the processor’s local APIC ID register (see Section 10.4.6, “Local APIC ID”). This is the ID to use for
directing physical destination mode interrupts to the processor.

•

Read ACPI or MP table — As part of the MP initialization protocol, the BIOS creates an ACPI table and an MP
table. These tables are defined in the Multiprocessor Specification Version 1.4 and provide software with a list
of the processors in the system and their local APIC IDs. The format of the ACPI table is derived from the ACPI
specification, which is an industry standard power management and platform configuration specification for MP
systems.

•

Read Initial APIC ID (If the process does not support CPUID leaf 0BH) — An APIC ID is assigned to a logical
processor during power up. This is the initial APIC ID reported by CPUID.1:EBX[31:24] and may be different
from the current value read from the local APIC. The initial APIC ID can be used to determine the topological
relationship between logical processors for multi-processor systems that do not support CPUID leaf 0BH.
Bits in the 8-bit initial APIC ID can be interpreted using several bit masks. Each bit mask can be used to extract
an identifier to represent a hierarchical level of the multi-threading resource topology in an MP system (See
Section 8.9.1, “Hierarchical Mapping of Shared Resources”). The initial APIC ID may consist of up to four bitfields. In a non-clustered MP system, the field consists of up to three bit fields.

•

Read 32-bit APIC ID from CPUID leaf 0BH (If the processor supports CPUID leaf 0BH) — A unique APIC ID
is assigned to a logical processor during power up. This APIC ID is reported by CPUID.0BH:EDX[31:0] as a 32bit value. Use the 32-bit APIC ID and CPUID leaf 0BH to determine the topological relationship between logical
processors if the processor supports CPUID leaf 0BH.
Bits in the 32-bit x2APIC ID can be extracted into sub-fields using CPUID leaf 0BH parameters. (See Section
8.9.1, “Hierarchical Mapping of Shared Resources”).

Figure 8-2 shows two examples of APIC ID bit fields in earlier single-core processors. In single-core Intel Xeon
processors, the APIC ID assigned to a logical processor during power-up and initialization is 8 bits. Bits 2:1 form a
2-bit physical package identifier (which can also be thought of as a socket identifier). In systems that configure
physical processors in clusters, bits 4:3 form a 2-bit cluster ID. Bit 0 is used in the Intel Xeon processor MP to identify the two logical processors within the package (see Section 8.9.3, “Hierarchical ID of Logical Processors in an MP
System”). For Intel Xeon processors that do not support Intel Hyper-Threading Technology, bit 0 is always set to 0;
for Intel Xeon processors supporting Intel Hyper-Threading Technology, bit 0 performs the same function as it does
for Intel Xeon processor MP.
For more recent multi-core processors, see Section 8.9.1, “Hierarchical Mapping of Shared Resources” for a
complete description of the topological relationships between logical processors and bit field locations within an
initial APIC ID across Intel 64 and IA-32 processor families.

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Note the number of bit fields and the width of bit-fields are dependent on processor and platform hardware capabilities. Software should determine these at runtime. When initial APIC IDs are assigned to logical processors, the
value of APIC ID assigned to a logical processor will respect the bit-field boundaries corresponding core, physical
package, etc. Additional examples of the bit fields in the initial APIC ID of multi-threading capable systems are
shown in Section 8.9.

APIC ID Format for Intel Xeon Processors that
do not Support Intel Hyper-Threading Technology
7

5

4

3

2

1

Reserved

0
0

Cluster
Processor ID
APIC ID Format for P6 Family Processors
7

4

3

2

1

0

Reserved

Cluster
Processor ID

Figure 8-2. Interpretation of APIC ID in Early MP Systems
For P6 family processors, the APIC ID that is assigned to a processor during power-up and initialization is 4 bits
(see Figure 8-2). Here, bits 0 and 1 form a 2-bit processor (or socket) identifier and bits 2 and 3 form a 2-bit cluster
ID.

8.5

INTEL® HYPER-THREADING TECHNOLOGY AND INTEL® MULTI-CORE
TECHNOLOGY

Intel Hyper-Threading Technology and Intel multi-core technology are extensions to Intel 64 and IA-32 architectures that enable a single physical processor to execute two or more separate code streams (called threads)
concurrently. In Intel Hyper-Threading Technology, a single processor core provides two logical processors that
share execution resources (see Section 8.7, “Intel® Hyper-Threading Technology Architecture”). In Intel multi-core
technology, a physical processor package provides two or more processor cores. Both configurations require chipsets and a BIOS that support the technologies.
Software should not rely on processor names to determine whether a processor supports Intel Hyper-Threading
Technology or Intel multi-core technology. Use the CPUID instruction to determine processor capability (see
Section 8.6.2, “Initializing Multi-Core Processors”).

8.6

DETECTING HARDWARE MULTI-THREADING SUPPORT AND TOPOLOGY

Use the CPUID instruction to detect the presence of hardware multi-threading support in a physical processor.
Hardware multi-threading can support several varieties of multigrade and/or Intel Hyper-Threading Technology.
CPUID instruction provides several sets of parameter information to aid software enumerating topology information. The relevant topology enumeration parameters provided by CPUID include:

•

Hardware Multi-Threading feature flag (CPUID.1:EDX[28] = 1) — Indicates when set that the physical
package is capable of supporting Intel Hyper-Threading Technology and/or multiple cores.

•

Processor topology enumeration parameters for 8-bit APIC ID:

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— Addressable IDs for Logical processors in the same Package (CPUID.1:EBX[23:16]) — Indicates
the maximum number of addressable ID for logical processors in a physical package. Within a physical
package, there may be addressable IDs that are not occupied by any logical processors. This parameter
does not represents the hardware capability of the physical processor.6

•

Addressable IDs for processor cores in the same Package7 (CPUID.(EAX=4, ECX=08):EAX[31:26] +
1 = Y) — Indicates the maximum number of addressable IDs attributable to processor cores (Y) in the physical
package.

•

Extended Processor Topology Enumeration parameters for 32-bit APIC ID: Intel 64 processors
supporting CPUID leaf 0BH will assign unique APIC IDs to each logical processor in the system. CPUID leaf 0BH
reports the 32-bit APIC ID and provide topology enumeration parameters. See CPUID instruction reference
pages in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A.

The CPUID feature flag may indicate support for hardware multi-threading when only one logical processor available in the package. In this case, the decimal value represented by bits 16 through 23 in the EBX register will have
a value of 1.
Software should note that the number of logical processors enabled by system software may be less than the value
of “Addressable IDs for Logical processors”. Similarly, the number of cores enabled by system software may be less
than the value of “Addressable IDs for processor cores”.
Software can detect the availability of the CPUID extended topology enumeration leaf (0BH) by performing two
steps:

•

Check maximum input value for basic CPUID information by executing CPUID with EAX= 0. If CPUID.0H:EAX is
greater than or equal or 11 (0BH), then proceed to next step,

•

Check CPUID.EAX=0BH, ECX=0H:EBX is non-zero.

If both of the above conditions are true, extended topology enumeration leaf is available. Note the presence of
CPUID leaf 0BH in a processor does not guarantee support that the local APIC supports x2APIC. If
CPUID.(EAX=0BH, ECX=0H):EBX returns zero and maximum input value for basic CPUID information is greater
than 0BH, then CPUID.0BH leaf is not supported on that processor.

8.6.1

Initializing Processors Supporting Hyper-Threading Technology

The initialization process for an MP system that contains processors supporting Intel Hyper-Threading Technology
is the same as for conventional MP systems (see Section 8.4, “Multiple-Processor (MP) Initialization”). One logical
processor in the system is selected as the BSP and other processors (or logical processors) are designated as APs.
The initialization process is identical to that described in Section 8.4.3, “MP Initialization Protocol Algorithm for MP
Systems,” and Section 8.4.4, “MP Initialization Example.”
During initialization, each logical processor is assigned an APIC ID that is stored in the local APIC ID register for
each logical processor. If two or more processors supporting Intel Hyper-Threading Technology are present, each
logical processor on the system bus is assigned a unique ID (see Section 8.9.3, “Hierarchical ID of Logical Processors in an MP System”). Once logical processors have APIC IDs, software communicates with them by sending APIC
IPI messages.

6. Operating system and BIOS may implement features that reduce the number of logical processors available in a platform to applications at runtime to less than the number of physical packages times the number of hardware-capable logical processors per package.
7. Software must check CPUID for its support of leaf 4 when implementing support for multi-core. If CPUID leaf 4 is not available at
runtime, software should handle the situation as if there is only one core per package.
8. Maximum number of cores in the physical package must be queried by executing CPUID with EAX=4 and a valid ECX input value.
Valid ECX input values start from 0.
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8.6.2

Initializing Multi-Core Processors

The initialization process for an MP system that contains multi-core Intel 64 or IA-32 processors is the same as for
conventional MP systems (see Section 8.4, “Multiple-Processor (MP) Initialization”). A logical processor in one core
is selected as the BSP; other logical processors are designated as APs.
During initialization, each logical processor is assigned an APIC ID. Once logical processors have APIC IDs, software
may communicate with them by sending APIC IPI messages.

8.6.3

Executing Multiple Threads on an Intel® 64 or IA-32 Processor Supporting Hardware
Multi-Threading

Upon completing the operating system boot-up procedure, the bootstrap processor (BSP) executes operating
system code. Other logical processors are placed in the halt state. To execute a code stream (thread) on a halted
logical processor, the operating system issues an interprocessor interrupt (IPI) addressed to the halted logical
processor. In response to the IPI, the processor wakes up and begins executing the code identified by the vector
received as part of the IPI.
To manage execution of multiple threads on logical processors, an operating system can use conventional
symmetric multiprocessing (SMP) techniques. For example, the operating-system can use a time-slice or load
balancing mechanism to periodically interrupt each of the active logical processors. Upon interrupting a logical
processor, the operating system checks its run queue for a thread waiting to be executed and dispatches the thread
to the interrupted logical processor.

8.6.4

Handling Interrupts on an IA-32 Processor Supporting Hardware Multi-Threading

Interrupts are handled on processors supporting Intel Hyper-Threading Technology as they are on conventional MP
systems. External interrupts are received by the I/O APIC, which distributes them as interrupt messages to specific
logical processors (see Figure 8-3).
Logical processors can also send IPIs to other logical processors by writing to the ICR register of its local APIC (see
Section 10.6, “Issuing Interprocessor Interrupts”). This also applies to dual-core processors.

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Intel Processor with Intel
Intel Processor with Intel
Hyper-Threading Technology Hyper-Threading Technology

Logical
Logical
Processor 0 Processor 1

Logical
Logical
Processor 0 Processor 1

Processor Core

Processor Core

Local APIC Local APIC

Local APIC Local APIC

Bus Interface

Bus Interface

IPIs

Interrupt
Messages

Interrupt
Messages

IPIs
Interrupt Messages

Bridge
PCI

I/O APIC

External
Interrupts

System Chip Set

Figure 8-3. Local APICs and I/O APIC in MP System Supporting Intel HT Technology

8.7

INTEL® HYPER-THREADING TECHNOLOGY ARCHITECTURE

Figure 8-4 shows a generalized view of an Intel processor supporting Intel Hyper-Threading Technology, using the
original Intel Xeon processor MP as an example. This implementation of the Intel Hyper-Threading Technology
consists of two logical processors (each represented by a separate architectural state) which share the processor’s
execution engine and the bus interface. Each logical processor also has its own advanced programmable interrupt
controller (APIC).

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Logical
Processor 0
Architectural
State

Logical
Processor 1
Architectural
State

Execution Engine

Local APIC

Local APIC

Bus Interface

System Bus

Figure 8-4. IA-32 Processor with Two Logical Processors Supporting Intel HT Technology

8.7.1

State of the Logical Processors

The following features are part of the architectural state of logical processors within Intel 64 or IA-32 processors
supporting Intel Hyper-Threading Technology. The features can be subdivided into three groups:

•
•
•

Duplicated for each logical processor
Shared by logical processors in a physical processor
Shared or duplicated, depending on the implementation

The following features are duplicated for each logical processor:

•
•
•

General purpose registers (EAX, EBX, ECX, EDX, ESI, EDI, ESP, and EBP)

•

x87 FPU registers (ST0 through ST7, status word, control word, tag word, data operand pointer, and instruction
pointer)

•
•
•
•
•
•
•
•
•
•

MMX registers (MM0 through MM7)

Segment registers (CS, DS, SS, ES, FS, and GS)
EFLAGS and EIP registers. Note that the CS and EIP/RIP registers for each logical processor point to the
instruction stream for the thread being executed by the logical processor.

XMM registers (XMM0 through XMM7) and the MXCSR register
Control registers and system table pointer registers (GDTR, LDTR, IDTR, task register)
Debug registers (DR0, DR1, DR2, DR3, DR6, DR7) and the debug control MSRs
Machine check global status (IA32_MCG_STATUS) and machine check capability (IA32_MCG_CAP) MSRs
Thermal clock modulation and ACPI Power management control MSRs
Time stamp counter MSRs
Most of the other MSR registers, including the page attribute table (PAT). See the exceptions below.
Local APIC registers.
Additional general purpose registers (R8-R15), XMM registers (XMM8-XMM15), control register, IA32_EFER on
Intel 64 processors.

The following features are shared by logical processors:

•

Memory type range registers (MTRRs)

Whether the following features are shared or duplicated is implementation-specific:

•

IA32_MISC_ENABLE MSR (MSR address 1A0H)

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•
•

Machine check architecture (MCA) MSRs (except for the IA32_MCG_STATUS and IA32_MCG_CAP MSRs)
Performance monitoring control and counter MSRs

8.7.2

APIC Functionality

When a processor supporting Intel Hyper-Threading Technology support is initialized, each logical processor is
assigned a local APIC ID (see Table 10-1). The local APIC ID serves as an ID for the logical processor and is stored
in the logical processor’s APIC ID register. If two or more processors supporting Intel Hyper-Threading Technology
are present in a dual processor (DP) or MP system, each logical processor on the system bus is assigned a unique
local APIC ID (see Section 8.9.3, “Hierarchical ID of Logical Processors in an MP System”).
Software communicates with local processors using the APIC’s interprocessor interrupt (IPI) messaging facility.
Setup and programming for APICs is identical in processors that support and do not support Intel Hyper-Threading
Technology. See Chapter 10, “Advanced Programmable Interrupt Controller (APIC),” for a detailed discussion.

8.7.3

Memory Type Range Registers (MTRR)

MTRRs in a processor supporting Intel Hyper-Threading Technology are shared by logical processors. When one
logical processor updates the setting of the MTRRs, settings are automatically shared with the other logical processors in the same physical package.
The architectures require that all MP systems based on Intel 64 and IA-32 processors (this includes logical processors) must use an identical MTRR memory map. This gives software a consistent view of memory, independent of
the processor on which it is running. See Section 11.11, “Memory Type Range Registers (MTRRs),” for information
on setting up MTRRs.

8.7.4

Page Attribute Table (PAT)

Each logical processor has its own PAT MSR (IA32_PAT). However, as described in Section 11.12, “Page Attribute
Table (PAT),” the PAT MSR settings must be the same for all processors in a system, including the logical processors.

8.7.5

Machine Check Architecture

In the Intel HT Technology context as implemented by processors based on Intel NetBurst® microarchitecture, all
of the machine check architecture (MCA) MSRs (except for the IA32_MCG_STATUS and IA32_MCG_CAP MSRs) are
duplicated for each logical processor. This permits logical processors to initialize, configure, query, and handle
machine-check exceptions simultaneously within the same physical processor. The design is compatible with
machine check exception handlers that follow the guidelines given in Chapter 15, “Machine-Check Architecture.”
The IA32_MCG_STATUS MSR is duplicated for each logical processor so that its machine check in progress bit field
(MCIP) can be used to detect recursion on the part of MCA handlers. In addition, the MSR allows each logical
processor to determine that a machine-check exception is in progress independent of the actions of another logical
processor in the same physical package.
Because the logical processors within a physical package are tightly coupled with respect to shared hardware
resources, both logical processors are notified of machine check errors that occur within a given physical processor.
If machine-check exceptions are enabled when a fatal error is reported, all the logical processors within a physical
package are dispatched to the machine-check exception handler. If machine-check exceptions are disabled, the
logical processors enter the shutdown state and assert the IERR# signal.
When enabling machine-check exceptions, the MCE flag in control register CR4 should be set for each logical
processor.
On Intel Atom family processors that support Intel Hyper-Threading Technology, the MCA facilities are shared
between all logical processors on the same processor core.

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8.7.6

Debug Registers and Extensions

Each logical processor has its own set of debug registers (DR0, DR1, DR2, DR3, DR6, DR7) and its own debug
control MSR. These can be set to control and record debug information for each logical processor independently.
Each logical processor also has its own last branch records (LBR) stack.

8.7.7

Performance Monitoring Counters

Performance counters and their companion control MSRs are shared between the logical processors within a
processor core for processors based on Intel NetBurst microarchitecture. As a result, software must manage the
use of these resources. The performance counter interrupts, events, and precise event monitoring support can be
set up and allocated on a per thread (per logical processor) basis.
See Section 18.6.4, “Performance Monitoring and Intel Hyper-Threading Technology in Processors Based on Intel
NetBurst® Microarchitecture,” for a discussion of performance monitoring in the Intel Xeon processor MP.
In Intel Atom processor family that support Intel Hyper-Threading Technology, the performance counters (generalpurpose and fixed-function counters) and their companion control MSRs are duplicated for each logical processor.

8.7.8

IA32_MISC_ENABLE MSR

The IA32_MISC_ENABLE MSR (MSR address 1A0H) is generally shared between the logical processors in a
processor core supporting Intel Hyper-Threading Technology. However, some bit fields within IA32_MISC_ENABLE
MSR may be duplicated per logical processor. The partition of shared or duplicated bit fields within
IA32_MISC_ENABLE is implementation dependent. Software should program duplicated fields carefully on all
logical processors in the system to ensure consistent behavior.

8.7.9

Memory Ordering

The logical processors in an Intel 64 or IA-32 processor supporting Intel Hyper-Threading Technology obey the
same rules for memory ordering as Intel 64 or IA-32 processors without Intel HT Technology (see Section 8.2,
“Memory Ordering”). Each logical processor uses a processor-ordered memory model that can be further defined
as “write-ordered with store buffer forwarding.” All mechanisms for strengthening or weakening the memoryordering model to handle special programming situations apply to each logical processor.

8.7.10

Serializing Instructions

As a general rule, when a logical processor in a processor supporting Intel Hyper-Threading Technology executes a
serializing instruction, only that logical processor is affected by the operation. An exception to this rule is the execution of the WBINVD, INVD, and WRMSR instructions; and the MOV CR instruction when the state of the CD flag in
control register CR0 is modified. Here, both logical processors are serialized.

8.7.11

Microcode Update Resources

In an Intel processor supporting Intel Hyper-Threading Technology, the microcode update facilities are shared
between the logical processors; either logical processor can initiate an update. Each logical processor has its own
BIOS signature MSR (IA32_BIOS_SIGN_ID at MSR address 8BH). When a logical processor performs an update for
the physical processor, the IA32_BIOS_SIGN_ID MSRs for resident logical processors are updated with identical
information. If logical processors initiate an update simultaneously, the processor core provides the necessary
synchronization needed to ensure that only one update is performed at a time.

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NOTE
Some processors (prior to the introduction of Intel 64 Architecture and based on Intel NetBurst
microarchitecture) do not support simultaneous loading of microcode update to the sibling logical
processors in the same core. All other processors support logical processors initiating an update
simultaneously. Intel recommends a common approach that the microcode loader use the
sequential technique described in Section 9.11.6.3.

8.7.12

Self Modifying Code

Intel processors supporting Intel Hyper-Threading Technology support self-modifying code, where data writes
modify instructions cached or currently in flight. They also support cross-modifying code, where on an MP system
writes generated by one processor modify instructions cached or currently in flight on another. See Section 8.1.3,
“Handling Self- and Cross-Modifying Code,” for a description of the requirements for self- and cross-modifying code
in an IA-32 processor.

8.7.13

Implementation-Specific Intel HT Technology Facilities

The following non-architectural facilities are implementation-specific in IA-32 processors supporting Intel HyperThreading Technology:

•
•
•

Caches
Translation lookaside buffers (TLBs)
Thermal monitoring facilities

The Intel Xeon processor MP implementation is described in the following sections.

8.7.13.1

Processor Caches

For processors supporting Intel Hyper-Threading Technology, the caches are shared. Any cache manipulation
instruction that is executed on one logical processor has a global effect on the cache hierarchy of the physical
processor. Note the following:

•

WBINVD instruction — The entire cache hierarchy is invalidated after modified data is written back to
memory. All logical processors are stopped from executing until after the write-back and invalidate operation is
completed. A special bus cycle is sent to all caching agents. The amount of time or cycles for WBINVD to
complete will vary due to the size of different cache hierarchies and other factors. As a consequence, the use of
the WBINVD instruction can have an impact on interrupt/event response time.

•

INVD instruction — The entire cache hierarchy is invalidated without writing back modified data to memory.
All logical processors are stopped from executing until after the invalidate operation is completed. A special bus
cycle is sent to all caching agents.

•

CLFLUSH and CLFLUSHOPT instructions — The specified cache line is invalidated from the cache hierarchy
after any modified data is written back to memory and a bus cycle is sent to all caching agents, regardless of
which logical processor caused the cache line to be filled.

•

CD flag in control register CR0 — Each logical processor has its own CR0 control register, and thus its own
CD flag in CR0. The CD flags for the two logical processors are ORed together, such that when any logical
processor sets its CD flag, the entire cache is nominally disabled.

8.7.13.2

Processor Translation Lookaside Buffers (TLBs)

In processors supporting Intel Hyper-Threading Technology, data cache TLBs are shared. The instruction cache TLB
may be duplicated or shared in each logical processor, depending on implementation specifics of different
processor families.
Entries in the TLBs are tagged with an ID that indicates the logical processor that initiated the translation. This tag
applies even for translations that are marked global using the page-global feature for memory paging. See Section
4.10, “Caching Translation Information,” for information about global translations.

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When a logical processor performs a TLB invalidation operation, only the TLB entries that are tagged for that logical
processor are guaranteed to be flushed. This protocol applies to all TLB invalidation operations, including writes to
control registers CR3 and CR4 and uses of the INVLPG instruction.

8.7.13.3

Thermal Monitor

In a processor that supports Intel Hyper-Threading Technology, logical processors share the catastrophic shutdown
detector and the automatic thermal monitoring mechanism (see Section 14.7, “Thermal Monitoring and Protection”). Sharing results in the following behavior:

•

If the processor’s core temperature rises above the preset catastrophic shutdown temperature, the processor
core halts execution, which causes both logical processors to stop execution.

•

When the processor’s core temperature rises above the preset automatic thermal monitor trip temperature, the
frequency of the processor core is automatically modulated, which effects the execution speed of both logical
processors.

For software controlled clock modulation, each logical processor has its own IA32_CLOCK_MODULATION MSR,
allowing clock modulation to be enabled or disabled on a logical processor basis. Typically, if software controlled
clock modulation is going to be used, the feature must be enabled for all the logical processors within a physical
processor and the modulation duty cycle must be set to the same value for each logical processor. If the duty cycle
values differ between the logical processors, the processor clock will be modulated at the highest duty cycle
selected.

8.7.13.4

External Signal Compatibility

This section describes the constraints on external signals received through the pins of a processor supporting Intel
Hyper-Threading Technology and how these signals are shared between its logical processors.

•

STPCLK# — A single STPCLK# pin is provided on the physical package of the Intel Xeon processor MP. External
control logic uses this pin for power management within the system. When the STPCLK# signal is asserted, the
processor core transitions to the stop-grant state, where instruction execution is halted but the processor core
continues to respond to snoop transactions. Regardless of whether the logical processors are active or halted
when the STPCLK# signal is asserted, execution is stopped on both logical processors and neither will respond
to interrupts.
In MP systems, the STPCLK# pins on all physical processors are generally tied together. As a result this signal
affects all the logical processors within the system simultaneously.

•

LINT0 and LINT1 pins — A processor supporting Intel Hyper-Threading Technology has only one set of LINT0
and LINT1 pins, which are shared between the logical processors. When one of these pins is asserted, both
logical processors respond unless the pin has been masked in the APIC local vector tables for one or both of the
logical processors.
Typically in MP systems, the LINT0 and LINT1 pins are not used to deliver interrupts to the logical processors.
Instead all interrupts are delivered to the local processors through the I/O APIC.

•

A20M# pin — On an IA-32 processor, the A20M# pin is typically provided for compatibility with the Intel 286
processor. Asserting this pin causes bit 20 of the physical address to be masked (forced to zero) for all external
bus memory accesses. Processors supporting Intel Hyper-Threading Technology provide one A20M# pin, which
affects the operation of both logical processors within the physical processor.
The functionality of A20M# is used primarily by older operating systems and not used by modern operating
systems. On newer Intel 64 processors, A20M# may be absent.

8.8

MULTI-CORE ARCHITECTURE

This section describes the architecture of Intel 64 and IA-32 processors supporting dual-core and quad-core technology. The discussion is applicable to the Intel Pentium processor Extreme Edition, Pentium D, Intel Core Duo,
Intel Core 2 Duo, Dual-core Intel Xeon processor, Intel Core 2 Quad processors, and quad-core Intel Xeon processors. Features vary across different microarchitectures and are detectable using CPUID.
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In general, each processor core has dedicated microarchitectural resources identical to a single-processor implementation of the underlying microarchitecture without hardware multi-threading capability. Each logical processor
in a dual-core processor (whether supporting Intel Hyper-Threading Technology or not) has its own APIC functionality, PAT, machine check architecture, debug registers and extensions. Each logical processor handles serialization
instructions or self-modifying code on its own. Memory order is handled the same way as in Intel Hyper-Threading
Technology.
The topology of the cache hierarchy (with respect to whether a given cache level is shared by one or more
processor cores or by all logical processors in the physical package) depends on the processor implementation.
Software must use the deterministic cache parameter leaf of CPUID instruction to discover the cache-sharing
topology between the logical processors in a multi-threading environment.

8.8.1

Logical Processor Support

The topological composition of processor cores and logical processors in a multi-core processor can be discovered
using CPUID. Within each processor core, one or more logical processors may be available.
System software must follow the requirement MP initialization sequences (see Section 8.4, “Multiple-Processor
(MP) Initialization”) to recognize and enable logical processors. At runtime, software can enumerate those logical
processors enabled by system software to identify the topological relationships between these logical processors.
(See Section 8.9.5, “Identifying Topological Relationships in a MP System”).

8.8.2

Memory Type Range Registers (MTRR)

MTRR is shared between two logical processors sharing a processor core if the physical processor supports Intel
Hyper-Threading Technology. MTRR is not shared between logical processors located in different cores or different
physical packages.
The Intel 64 and IA-32 architectures require that all logical processors in an MP system use an identical MTRR
memory map. This gives software a consistent view of memory, independent of the processor on which it is
running.
See Section 11.11, “Memory Type Range Registers (MTRRs).”

8.8.3

Performance Monitoring Counters

Performance counters and their companion control MSRs are shared between two logical processors sharing a
processor core if the processor core supports Intel Hyper-Threading Technology and is based on Intel NetBurst
microarchitecture. They are not shared between logical processors in different cores or different physical packages.
As a result, software must manage the use of these resources, based on the topology of performance monitoring
resources. Performance counter interrupts, events, and precise event monitoring support can be set up and allocated on a per thread (per logical processor) basis.
See Section 18.6.4, “Performance Monitoring and Intel Hyper-Threading Technology in Processors Based on Intel
NetBurst® Microarchitecture.”

8.8.4

IA32_MISC_ENABLE MSR

Some bit fields in IA32_MISC_ENABLE MSR (MSR address 1A0H) may be shared between two logical processors
sharing a processor core, or may be shared between different cores in a physical processor. See Chapter 2, “ModelSpecific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4.

8.8.5

Microcode Update Resources

Microcode update facilities are shared between two logical processors sharing a processor core if the physical
package supports Intel Hyper-Threading Technology. They are not shared between logical processors in different

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cores or different physical packages. Either logical processor that has access to the microcode update facility can
initiate an update.
Each logical processor has its own BIOS signature MSR (IA32_BIOS_SIGN_ID at MSR address 8BH). When a logical
processor performs an update for the physical processor, the IA32_BIOS_SIGN_ID MSRs for resident logical
processors are updated with identical information.
All microcode update steps during processor initialization should use the same update data on all cores in all physical packages of the same stepping. Any subsequent microcode update must apply consistent update data to all
cores in all physical packages of the same stepping. If the processor detects an attempt to load an older microcode
update when a newer microcode update had previously been loaded, it may reject the older update to stay with the
newer update.

NOTE
Some processors (prior to the introduction of Intel 64 Architecture and based on Intel NetBurst
microarchitecture) do not support simultaneous loading of microcode update to the sibling logical
processors in the same core. All other processors support logical processors initiating an update
simultaneously. Intel recommends a common approach that the microcode loader use the
sequential technique described in Section 9.11.6.3.

8.9

PROGRAMMING CONSIDERATIONS FOR HARDWARE MULTI-THREADING
CAPABLE PROCESSORS

In a multi-threading environment, there may be certain hardware resources that are physically shared at some
level of the hardware topology. In the multi-processor systems, typically bus and memory sub-systems are physically shared between multiple sockets. Within a hardware multi-threading capable processors, certain resources
are provided for each processor core, while other resources may be provided for each logical processors (see
Section 8.7, “Intel® Hyper-Threading Technology Architecture,” and Section 8.8, “Multi-Core Architecture”).
From a software programming perspective, control transfer of processor operation is managed at the granularity of
logical processor (operating systems dispatch a runnable task by allocating an available logical processor on the
platform). To manage the topology of shared resources in a multi-threading environment, it may be useful for software to understand and manage resources that are shared by more than one logical processors.

8.9.1

Hierarchical Mapping of Shared Resources

The APIC_ID value associated with each logical processor in a multi-processor system is unique (see Section 8.6,
“Detecting Hardware Multi-Threading Support and Topology”). This 8-bit or 32-bit value can be decomposed into
sub-fields, where each sub-field corresponds a hierarchical level of the topological mapping of hardware resources.
The decomposition of an APIC_ID may consist of several sub fields representing the topology within a physical
processor package, the higher-order bits of an APIC ID may also be used by cluster vendors to represent the
topology of cluster nodes of each coherent multiprocessor systems. If the processor does not support CPUID leaf
0BH, the 8-bit initial APIC ID can represent 4 levels of hierarchy:

•

Cluster — Some multi-threading environments consists of multiple clusters of multi-processor systems. The
CLUSTER_ID sub-field is usually supported by vendor firmware to distinguish different clusters. For nonclustered systems, CLUSTER_ID is usually 0 and system topology is reduced to three levels of hierarchy.

•

Package — A multi-processor system consists of two or more sockets, each mates with a physical processor
package. The PACKAGE_ID sub-field distinguishes different physical packages within a cluster.

•

Core — A physical processor package consists of one or more processor cores. The CORE_ID sub-field distinguishes processor cores in a package. For a single-core processor, the width of this bit field is 0.

•

SMT — A processor core provides one or more logical processors sharing execution resources. The SMT_ID
sub-field distinguishes logical processors in a core. The width of this bit field is non-zero if a processor core
provides more than one logical processors.

SMT and CORE sub-fields are bit-wise contiguous in the APIC_ID field (see Figure 8-5).

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X=31 if x2APIC is supported

X

Otherwise X= 7

Reserved

0

Cluster ID
Package ID
Core ID
SMT ID

Figure 8-5. Generalized Four level Interpretation of the APIC ID
If the processor supports CPUID leaf 0BH, the 32-bit APIC ID can represent cluster plus several levels of topology
within the physical processor package. The exact number of hierarchical levels within a physical processor package
must be enumerated through CPUID leaf 0BH. Common processor families may employ topology similar to that
represented by 8-bit Initial APIC ID. In general, CPUID leaf 0BH can support topology enumeration algorithm that
decompose a 32-bit APIC ID into more than four sub-fields (see Figure 8-6).
The width of each sub-field depends on hardware and software configurations. Field widths can be determined at
runtime using the algorithm discussed below (Example 8-16 through Example 8-20).
Figure 7-6 depicts the relationships of three of the hierarchical sub-fields in a hypothetical MP system. The value of
valid APIC_IDs need not be contiguous across package boundary or core boundaries.

0

31

Package

SMT

R

Q

Physical Processor Topology

Reserved
Cluster ID
Package ID
Q ID
R ID
SMT ID
32-bit APIC ID Composition

Figure 8-6. Conceptual Five-level Topology and 32-bit APIC ID Composition

8.9.2

Hierarchical Mapping of CPUID Extended Topology Leaf

CPUID leaf 0BH provides enumeration parameters for software to identify each hierarchy of the processor topology
in a deterministic manner. Each hierarchical level of the topology starting from the SMT level is represented numerically by a sub-leaf index within the CPUID 0BH leaf. Each level of the topology is mapped to a sub-field in the APIC
ID, following the general relationship depicted in Figure 8-6. This mechanism allows software to query the exact
number of levels within a physical processor package and the bit-width of each sub-field of x2APIC ID directly. For
example,

•

Starting from sub-leaf index 0 and incrementing ECX until CPUID.(EAX=0BH, ECX=N):ECX[15:8] returns an
invalid “level type” encoding. The number of levels within the physical processor package is “N” (excluding
PACKAGE). Using Figure 8-6 as an example, CPUID.(EAX=0BH, ECX=3):ECX[15:8] will report 00H, indicating
sub leaf 03H is invalid. This is also depicted by a pseudo code example:

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Example 8-16. Number of Levels Below the Physical Processor Package
Byte type = 1;
s = 0;
While ( type ) {
EAX = 0BH; // query each sub leaf of CPUID leaf 0BH
ECX = s;
CPUID;
type = ECX[15:8]; // examine level type encoding
s ++;
}
N = ECX[7:0];

•

Sub-leaf index 0 (ECX= 0 as input) provides enumeration parameters to extract the SMT sub-field of x2APIC
ID. If EAX = 0BH, and ECX =0 is specified as input when executing CPUID, CPUID.(EAX=0BH,
ECX=0):EAX[4:0] reports a value (a right-shift count) that allow software to extract part of x2APIC ID to
distinguish the next higher topological entities above the SMT level. This value also corresponds to the bit-width
of the sub-field of x2APIC ID corresponding the hierarchical level with sub-leaf index 0.

•

For each subsequent higher sub-leaf index m, CPUID.(EAX=0BH, ECX=m):EAX[4:0] reports the right-shift
count that will allow software to extract part of x2APIC ID to distinguish higher-level topological entities. This
means the right-shift value at of sub-leaf m, corresponds to the least significant (m+1) subfields of the 32-bit
x2APIC ID.

Example 8-17. BitWidth Determination of x2APIC ID Subfields
For m = 0, m < N, m ++;
{ cumulative_width[m] = CPUID.(EAX=0BH, ECX= m): EAX[4:0]; }
BitWidth[0] = cumulative_width[0];
For m = 1, m < N, m ++;
BitWidth[m] = cumulative_width[m] - cumulative_width[m-1];
Currently, only the following encoding of hierarchical level type are defined: 0 (invalid), 1 (SMT), and 2 (core). Software must not assume any “level type“ encoding value to be related to any sub-leaf index, except sub-leaf 0.
Example 8-16 and Example 8-17 represent the general technique for using CPUID leaf 0BH to enumerate processor
topology of more than two levels of hierarchy inside a physical package. Most processor families to date requires
only “SMT” and “CORE” levels within a physical package. The examples in later sections will focus on these threelevel topology only.

8.9.3

Hierarchical ID of Logical Processors in an MP System

For Intel 64 and IA-32 processors, system hardware establishes an 8-bit initial APIC ID (or 32-bit APIC ID if the
processor supports CPUID leaf 0BH) that is unique for each logical processor following power-up or RESET (see
Section 8.6.1). Each logical processor on the system is allocated an initial APIC ID. BIOS may implement features
that tell the OS to support less than the total number of logical processors on the system bus. Those logical processors that are not available to applications at runtime are halted during the OS boot process. As a result, the number
valid local APIC_IDs that can be queried by affinitizing-current-thread-context (See Example 8-22) is limited to the
number of logical processors enabled at runtime by the OS boot process.
Table 8-2 shows an example of the 8-bit APIC IDs that are initially reported for logical processors in a system with
four Intel Xeon MP processors that support Intel Hyper-Threading Technology (a total of 8 logical processors, each
physical package has two processor cores and supports Intel Hyper-Threading Technology). Of the two logical
processors within a Intel Xeon processor MP, logical processor 0 is designated the primary logical processor and
logical processor 1 as the secondary logical processor.

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T0

T1

Core 0

T0

T1

T0

Core1

T1

Core 0

T1

T0

Core1

Core ID
Package ID

Package 1

Package 0

SMT_ID

Figure 8-7. Topological Relationships between Hierarchical IDs in a Hypothetical MP Platform

Table 8-2. Initial APIC IDs for the Logical Processors in a System that has Four Intel Xeon MP Processors Supporting
Intel Hyper-Threading Technology1
Initial APIC ID

Package ID

Core ID

SMT ID

0H

0H

0H

0H

1H

0H

0H

1H

2H

1H

0H

0H

3H

1H

0H

1H

4H

2H

0H

0H

5H

2H

0H

1H

6H

3H

0H

0H

7H

3H

0H

1H

NOTE:
1. Because information on the number of processor cores in a physical package was not available in early single-core processors supporting Intel Hyper-Threading Technology, the core ID can be treated as 0.
Table 8-3 shows the initial APIC IDs for a hypothetical situation with a dual processor system. Each physical
package providing two processor cores, and each processor core also supporting Intel Hyper-Threading Technology.

Table 8-3. Initial APIC IDs for the Logical Processors in a System that has Two Physical Processors Supporting DualCore and Intel Hyper-Threading Technology
Initial APIC ID

Package ID

Core ID

SMT ID

0H

0H

0H

0H

1H

0H

0H

1H

2H

0H

1H

0H

3H

0H

1H

1H

4H

1H

0H

0H

5H

1H

0H

1H

6H

1H

1H

0H

7H

1H

1H

1H

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8.9.3.1

Hierarchical ID of Logical Processors with x2APIC ID

Table 8-4 shows an example of possible x2APIC ID assignments for a dual processor system that support x2APIC.
Each physical package providing four processor cores, and each processor core also supporting Intel HyperThreading Technology. Note that the x2APIC ID need not be contiguous in the system.

Table 8-4. Example of Possible x2APIC ID Assignment in a System that has Two Physical Processors Supporting
x2APIC and Intel Hyper-Threading Technology

8.9.4

x2APIC ID

Package ID

Core ID

SMT ID

0H

0H

0H

0H

1H

0H

0H

1H

2H

0H

1H

0H

3H

0H

1H

1H

4H

0H

2H

0H

5H

0H

2H

1H

6H

0H

3H

0H

7H

0H

3H

1H

10H

1H

0H

0H

11H

1H

0H

1H

12H

1H

1H

0H

13H

1H

1H

1H

14H

1H

2H

0H

15H

1H

2H

1H

16H

1H

3H

0H

17H

1H

3H

1H

Algorithm for Three-Level Mappings of APIC_ID

Software can gather the initial APIC_IDs for each logical processor supported by the operating system at runtime9
and extract identifiers corresponding to the three levels of sharing topology (package, core, and SMT). The threelevel algorithms below focus on a non-clustered MP system for simplicity. They do not assume APIC IDs are contiguous or that all logical processors on the platform are enabled.
Intel supports multi-threading systems where all physical processors report identical values in CPUID leaf 0BH,
CPUID.1:EBX[23:16]), CPUID.410:EAX[31:26], and CPUID.411:EAX[25:14]. The algorithms below assume the
target system has symmetry across physical package boundaries with respect to the number of logical processors
per package, number of cores per package, and cache topology within a package.
The extraction algorithm (for three-level mappings from an APIC ID) uses the general procedure depicted in
Example 8-18, and is supplemented by more detailed descriptions on the derivation of topology enumeration
parameters for extraction bit masks:
1. Detect hardware multi-threading support in the processor.
9. As noted in Section 8.6 and Section 8.9.3, the number of logical processors supported by the OS at runtime may be less than the
total number logical processors available in the platform hardware.
10. Maximum number of addressable ID for processor cores in a physical processor is obtained by executing CPUID with EAX=4 and a
valid ECX index, The ECX index start at 0.
11. Maximum number addressable ID for processor cores sharing the target cache level is obtained by executing CPUID with EAX = 4
and the ECX index corresponding to the target cache level.
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2. Derive a set of bit masks that can extract the sub ID of each hierarchical level of the topology. The algorithm to
derive extraction bit masks for SMT_ID/CORE_ID/PACKAGE_ID differs based on APIC ID is 32-bit (see step 3
below) or 8-bit (see step 4 below):
3. If the processor supports CPUID leaf 0BH, each APIC ID contains a 32-bit value, the topology enumeration
parameters needed to derive three-level extraction bit masks are:
a. Query the right-shift value for the SMT level of the topology using CPUID leaf 0BH with ECX =0H as input.
The number of bits to shift-right on x2APIC ID (EAX[4:0]) can distinguish different higher-level entities
above SMT (e.g. processor cores) in the same physical package. This is also the width of the bit mask to
extract the SMT_ID.
b. Query CPUID leaf 0BH for the amount of bit shift to distinguish next higher-level entities (e.g. physical
processor packages) in the system. This describes an explicit three-level-topology situation for commonly
available processors. Consult Example 8-17 to adapt to situations beyond three-level topology of a physical
processor. The width of the extraction bit mask can be used to derive the cumulative extraction bitmask to
extract the sub IDs of logical processors (including different processor cores) in the same physical package.
The extraction bit mask to distinguish merely different processor cores can be derived by xor’ing the SMT
extraction bit mask from the cumulative extraction bit mask.
c.

Query the 32-bit x2APIC ID for the logical processor where the current thread is executing.

d. Derive the extraction bit masks corresponding to SMT_ID, CORE_ID, and PACKAGE_ID, starting from
SMT_ID.
e. Apply each extraction bit mask to the 32-bit x2APIC ID to extract sub-field IDs.
4. If the processor does not support CPUID leaf 0BH, each initial APIC ID contains an 8-bit value, the topology
enumeration parameters needed to derive extraction bit masks are:
a. Query the size of address space for sub IDs that can accommodate logical processors in a physical
processor package. This size parameters (CPUID.1:EBX[23:16]) can be used to derive the width of an
extraction bitmask to enumerate the sub IDs of different logical processors in the same physical package.
b. Query the size of address space for sub IDs that can accommodate processor cores in a physical processor
package. This size parameters can be used to derive the width of an extraction bitmask to enumerate the
sub IDs of processor cores in the same physical package.
c.

Query the 8-bit initial APIC ID for the logical processor where the current thread is executing.

d. Derive the extraction bit masks using respective address sizes corresponding to SMT_ID, CORE_ID, and
PACKAGE_ID, starting from SMT_ID.
e. Apply each extraction bit mask to the 8-bit initial APIC ID to extract sub-field IDs.

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Example 8-18. Support Routines for Detecting Hardware Multi-Threading and Identifying the Relationships Between Package,
Core and Logical Processors
1.
//
//
//
//
//

Detect support for Hardware Multi-Threading Support in a processor.
Returns a non-zero value if CPUID reports the presence of hardware multi-threading
support in the physical package where the current logical processor is located.
This does not guarantee BIOS or OS will enable all logical processors in the physical
package and make them available to applications.
Returns zero if hardware multi-threading is not present.

#define HWMT_BIT 10000000H
unsigned int HWMTSupported(void)
{
// ensure cpuid instruction is supported
execute cpuid with eax = 0 to get vendor string
execute cpuid with eax = 1 to get feature flag and signature

// Check to see if this a Genuine Intel Processor
if (vendor string EQ GenuineIntel) {
return (feature_flag_edx & HWMT_BIT); // bit 28
}
return 0;
}
Example 8-19. Support Routines for Identifying Package, Core and Logical Processors from 32-bit x2APIC ID
a.

Derive the extraction bitmask for logical processors in a processor core and associated mask offset for different
cores.

int DeriveSMT_Mask_Offsets (void)
{
if (!HWMTSupported()) return -1;
execute cpuid with eax = 11, ECX = 0;
If (returned level type encoding in ECX[15:8] does not match SMT) return -1;
Mask_SMT_shift = EAX[4:0]; // # bits shift right of APIC ID to distinguish different cores
SMT_MASK = ~( (-1) << Mask_SMT_shift); // shift left to derive extraction bitmask for SMT_ID
return 0;
}

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b.

Derive the extraction bitmask for processor cores in a physical processor package and associated mask offset for
different packages.

int DeriveCore_Mask_Offsets (void)
{
if (!HWMTSupported()) return -1;
execute cpuid with eax = 11, ECX = 0;
while( ECX[15:8] ) { // level type encoding is valid
If (returned level type encoding in ECX[15:8] matches CORE) {
Mask_Core_shift = EAX[4:0]; // needed to distinguish different physical packages
COREPlusSMT_MASK = ~( (-1) << Mask_Core_shift);
CORE_MASK = COREPlusSMT_MASK ^ SMT_MASK;
PACKAGE_MASK = (-1) << Mask_Core_shift;
return 0
}
ECX ++;
execute cpuid with eax = 11;
}
return -1;
}
c.

Query the x2APIC ID of a logical processor.

APIC_IDs for each logical processor.
unsigned char Getx2APIC_ID (void)
{
unsigned reg_edx = 0;
execute cpuid with eax = 11, ECX = 0
store returned value of edx
return (unsigned) (reg_edx) ;
}

Example 8-20. Support Routines for Identifying Package, Core and Logical Processors from 8-bit Initial APIC ID
a.

Find the size of address space for logical processors in a physical processor package.

#define NUM_LOGICAL_BITS 00FF0000H
// Use the mask above and CPUID.1.EBX[23:16] to obtain the max number of addressable IDs
// for logical processors in a physical package,
//Returns the size of address space of logical processors in a physical processor package;
// Software should not assume the value to be a power of 2.
unsigned char MaxLPIDsPerPackage(void)
{
if (!HWMTSupported()) return 1;
execute cpuid with eax = 1
store returned value of ebx
return (unsigned char) ((reg_ebx & NUM_LOGICAL_BITS) >> 16);
}

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b.

Find the size of address space for processor cores in a physical processor package.

// Returns the max number of addressable IDs for processor cores in a physical processor package;
// Software should not assume cpuid reports this value to be a power of 2.
unsigned MaxCoreIDsPerPackage(void)
{
if (!HWMTSupported()) return (unsigned char) 1;
if cpuid supports leaf number 4
{ // we can retrieve multi-core topology info using leaf 4
execute cpuid with eax = 4, ecx = 0
store returned value of eax
return (unsigned) ((reg_eax >> 26) +1);
}
else // must be a single-core processor
return 1;
}
c.

Query the initial APIC ID of a logical processor.

#define INITIAL_APIC_ID_BITS FF000000H // CPUID.1.EBX[31:24] initial APIC ID
// Returns the 8-bit unique initial APIC ID for the processor running the code.
// Software can use OS services to affinitize the current thread to each logical processor
// available under the OS to gather the initial APIC_IDs for each logical processor.
unsigned GetInitAPIC_ID (void)
{
unsigned int reg_ebx = 0;
execute cpuid with eax = 1
store returned value of ebx
return (unsigned) ((reg_ebx & INITIAL_APIC_ID_BITS) >> 24;
}

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d.

Find the width of an extraction bitmask from the maximum count of the bit-field (address size).

// Returns the mask bit width of a bit field from the maximum count that bit field can represent.
// This algorithm does not assume ‘address size’ to have a value equal to power of 2.
// Address size for SMT_ID can be calculated from MaxLPIDsPerPackage()/MaxCoreIDsPerPackage()
// Then use the routine below to derive the corresponding width of SMT extraction bitmask
// Address size for CORE_ID is MaxCoreIDsPerPackage(),
// Derive the bitwidth for CORE extraction mask similarly
unsigned FindMaskWidth(Unsigned Max_Count)
{unsigned int mask_width, cnt = Max_Count;
__asm {
mov eax, cnt
mov ecx, 0
mov mask_width, ecx
dec eax
bsr cx, ax
jz next
inc cx
mov mask_width, ecx
next:
mov eax, mask_width
}
return mask_width;
}
e.

Extract a sub ID from an 8-bit full ID, using address size of the sub ID and shift count.

// The routine below can extract SMT_ID, CORE_ID, and PACKAGE_ID respectively from the init APIC_ID
// To extract SMT_ID, MaxSubIDvalue is set to the address size of SMT_ID, Shift_Count = 0
// To extract CORE_ID, MaxSubIDvalue is the address size of CORE_ID, Shift_Count is width of SMT extraction bitmask.
// Returns the value of the sub ID, this is not a zero-based value
Unsigned char GetSubID(unsigned char Full_ID, unsigned char MaxSubIDvalue, unsigned char Shift_Count)
{
MaskWidth = FindMaskWidth(MaxSubIDValue);
MaskBits = ((uchar) (FFH << Shift_Count)) ^ ((uchar) (FFH << Shift_Count + MaskWidth)) ;
SubID = Full_ID & MaskBits;
Return SubID;
}
Software must not assume local APIC_ID values in an MP system are consecutive. Non-consecutive local APIC_IDs
may be the result of hardware configurations or debug features implemented in the BIOS or OS.
An identifier for each hierarchical level can be extracted from an 8-bit APIC_ID using the support routines illustrated in Example 8-20. The appropriate bit mask and shift value to construct the appropriate bit mask for each
level must be determined dynamically at runtime.

8.9.5

Identifying Topological Relationships in a MP System

To detect the number of physical packages, processor cores, or other topological relationships in a MP system, the
following procedures are recommended:

•

Extract the three-level identifiers from the APIC ID of each logical processor enabled by system software. The
sequence is as follows (See the pseudo code shown in Example 8-21 and support routines shown in Example
8-18):

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•

The extraction start from the right-most bit field, corresponding to SMT_ID, the innermost hierarchy in
a three-level topology (See Figure 8-7). For the right-most bit field, the shift value of the working mask
is zero. The width of the bit field is determined dynamically using the maximum number of logical
processor per core, which can be derived from information provided from CPUID.

•

To extract the next bit-field, the shift value of the working mask is determined from the width of the bit
mask of the previous step. The width of the bit field is determined dynamically using the maximum
number of cores per package.

•

To extract the remaining bit-field, the shift value of the working mask is determined from the maximum
number of logical processor per package. So the remaining bits in the APIC ID (excluding those bits
already extracted in the two previous steps) are extracted as the third identifier. This applies to a nonclustered MP system, or if there is no need to distinguish between PACKAGE_ID and CLUSTER_ID.
If there is need to distinguish between PACKAGE_ID and CLUSTER_ID, PACKAGE_ID can be extracted
using an algorithm similar to the extraction of CORE_ID, assuming the number of physical packages in
each node of a clustered system is symmetric.

•

Assemble the three-level identifiers of SMT_ID, CORE_ID, PACKAGE_IDs into arrays for each enabled logical
processor. This is shown in Example 8-22a.

•

To detect the number of physical packages: use PACKAGE_ID to identify those logical processors that reside in
the same physical package. This is shown in Example 8-22b. This example also depicts a technique to construct
a mask to represent the logical processors that reside in the same package.

•

To detect the number of processor cores: use CORE_ID to identify those logical processors that reside in the
same core. This is shown in Example 8-22. This example also depicts a technique to construct a mask to
represent the logical processors that reside in the same core.

In Example 8-21, the numerical ID value can be obtained from the value extracted with the mask by shifting it right
by shift count. Algorithms below do not shift the value. The assumption is that the SubID values can be compared
for equivalence without the need to shift.
Example 8-21. Pseudo Code Depicting Three-level Extraction Algorithm
For Each local_APIC_ID{
// Calculate SMT_MASK, the bit mask pattern to extract SMT_ID,
// SMT_MASK is determined using topology enumertaion parameters
// from CPUID leaf 0BH (Example 8-19);
// otherwise, SMT_MASK is determined using CPUID leaf 01H and leaf 04H (Example 8-20).
// This algorithm assumes there is symmetry across core boundary, i.e. each core within a
// package has the same number of logical processors
// SMT_ID always starts from bit 0, corresponding to the right-most bit-field
SMT_ID = APIC_ID & SMT_MASK;
// Extract CORE_ID:
// CORE_MASK is determined in Example 8-19 or Example 8-20
CORE_ID = (APIC_ID & CORE_MASK) ;
// Extract PACKAGE_ID:
// Assume single cluster.
// Shift out the mask width for maximum logical processors per package
// PACKAGE_MASK is determined in Example 8-19 or Example 8-20
PACKAGE_ID = (APIC_ID & PACKAGE_MASK) ;
}

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Example 8-22. Compute the Number of Packages, Cores, and Processor Relationships in a MP System
a) Assemble lists of PACKAGE_ID, CORE_ID, and SMT_ID of each enabled logical processors
//The BIOS and/or OS may limit the number of logical processors available to applications
// after system boot. The below algorithm will compute topology for the processors visible
// to the thread that is computing it.
// Extract the 3-levels of IDs on every processor
// SystemAffinity is a bitmask of all the processors started by the OS. Use OS specific APIs to
// obtain it.
// ThreadAffinityMask is used to affinitize the topology enumeration thread to each processor
using OS specific APIs.
// Allocate per processor arrays to store the Package_ID, Core_ID and SMT_ID for every started
// processor.
ThreadAffinityMask = 1;
ProcessorNum = 0;
while (ThreadAffinityMask ≠ 0 && ThreadAffinityMask <= SystemAffinity) {
// Check to make sure we can utilize this processor first.
if (ThreadAffinityMask & SystemAffinity){
Set thread to run on the processor specified in ThreadAffinityMask
Wait if necessary and ensure thread is running on specified processor
APIC_ID = GetAPIC_ID(); // 32 bit ID in Example 8-19 or 8-bit ID in Example 8-20
Extract the Package_ID, Core_ID and SMT_ID as explained in three level extraction
algorithm of Example 8-21
PackageID[ProcessorNUM] = PACKAGE_ID;
CoreID[ProcessorNum] = CORE_ID;
SmtID[ProcessorNum] = SMT_ID;
ProcessorNum++;
}
ThreadAffinityMask <<= 1;
}
NumStartedLPs = ProcessorNum;
b) Using the list of PACKAGE_ID to count the number of physical packages in a MP system and construct, for each package, a multi-bit
mask corresponding to those logical processors residing in the same package.
// Compute the number of packages by counting the number of processors
// with unique PACKAGE_IDs in the PackageID array.
// Compute the mask of processors in each package.
PackageIDBucket is an array of unique PACKAGE_ID values. Allocate an array of
NumStartedLPs count of entries in this array.
PackageProcessorMask is a corresponding array of the bit mask of processors belonging to
the same package, these are processors with the same PACKAGE_ID
The algorithm below assumes there is symmetry across package boundary if more than
one socket is populated in an MP system.
// Bucket Package IDs and compute processor mask for every package.
PackageNum = 1;
PackageIDBucket[0] = PackageID[0];
ProcessorMask = 1;
PackageProcessorMask[0] = ProcessorMask;

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For (ProcessorNum = 1; ProcessorNum < NumStartedLPs; ProcessorNum++) {
ProcessorMask << = 1;
For (i=0; i < PackageNum; i++) {
// we may be comparing bit-fields of logical processors residing in different
// packages, the code below assume package symmetry
If (PackageID[ProcessorNum] = PackageIDBucket[i]) {
PackageProcessorMask[i] |= ProcessorMask;
Break; // found in existing bucket, skip to next iteration
}
}
if (i =PackageNum) {
//PACKAGE_ID did not match any bucket, start new bucket
PackageIDBucket[i] = PackageID[ProcessorNum];
PackageProcessorMask[i] = ProcessorMask;
PackageNum++;
}
}
// PackageNum has the number of Packages started in OS
// PackageProcessorMask[] array has the processor set of each package
c) Using the list of CORE_ID to count the number of cores in a MP system and construct, for each core, a multi-bit mask corresponding
to those logical processors residing in the same core.
Processors in the same core can be determined by bucketing the processors with the same PACKAGE_ID and CORE_ID. Note that code
below can BIT OR the values of PACKGE and CORE ID because they have not been shifted right.
The algorithm below assumes there is symmetry across package boundary if more than one socket is populated in an MP system.
//Bucketing PACKAGE and CORE IDs and computing processor mask for every core
CoreNum = 1;
CoreIDBucket[0] = PackageID[0] | CoreID[0];
ProcessorMask = 1;
CoreProcessorMask[0] = ProcessorMask;
For (ProcessorNum = 1; ProcessorNum < NumStartedLPs; ProcessorNum++) {
ProcessorMask << = 1;
For (i=0; i < CoreNum; i++) {
// we may be comparing bit-fields of logical processors residing in different
// packages, the code below assume package symmetry
If ((PackageID[ProcessorNum] | CoreID[ProcessorNum]) = CoreIDBucket[i]) {
CoreProcessorMask[i] |= ProcessorMask;
Break; // found in existing bucket, skip to next iteration
}
}
if (i = CoreNum) {
//Did not match any bucket, start new bucket
CoreIDBucket[i] = PackageID[ProcessorNum] | CoreID[ProcessorNum];
CoreProcessorMask[i] = ProcessorMask;
CoreNum++;
}
}
// CoreNum has the number of cores started in the OS
// CoreProcessorMask[] array has the processor set of each core
Other processor relationships such as processor mask of sibling cores can be computed from set operations of the
PackageProcessorMask[] and CoreProcessorMask[].
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The algorithm shown above can be adapted to work with earlier generations of single-core IA-32 processors that
support Intel Hyper-Threading Technology and in situations that the deterministic cache parameter leaf is not
supported (provided CPUID supports initial APIC ID). A reference code example is available (see Intel® 64 Architecture Processor Topology Enumeration).

8.10

MANAGEMENT OF IDLE AND BLOCKED CONDITIONS

When a logical processor in an MP system (including multi-core processor or processors supporting Intel HyperThreading Technology) is idle (no work to do) or blocked (on a lock or semaphore), additional management of the
core execution engine resource can be accomplished by using the HLT (halt), PAUSE, or the MONITOR/MWAIT
instructions.

8.10.1

HLT Instruction

The HLT instruction stops the execution of the logical processor on which it is executed and places it in a halted
state until further notice (see the description of the HLT instruction in Chapter 3 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A). When a logical processor is halted, active logical processors
continue to have full access to the shared resources within the physical package. Here shared resources that were
being used by the halted logical processor become available to active logical processors, allowing them to execute
at greater efficiency. When the halted logical processor resumes execution, shared resources are again shared
among all active logical processors. (See Section 8.10.6.3, “Halt Idle Logical Processors,” for more information
about using the HLT instruction with processors supporting Intel Hyper-Threading Technology.)

8.10.2

PAUSE Instruction

The PAUSE instruction can improves the performance of processors supporting Intel Hyper-Threading Technology
when executing “spin-wait loops” and other routines where one thread is accessing a shared lock or semaphore in
a tight polling loop. When executing a spin-wait loop, the processor can suffer a severe performance penalty when
exiting the loop because it detects a possible memory order violation and flushes the core processor’s pipeline. The
PAUSE instruction provides a hint to the processor that the code sequence is a spin-wait loop. The processor uses
this hint to avoid the memory order violation and prevent the pipeline flush. In addition, the PAUSE instruction depipelines the spin-wait loop to prevent it from consuming execution resources excessively and consume power
needlessly. (See Section 8.10.6.1, “Use the PAUSE Instruction in Spin-Wait Loops,” for more information about
using the PAUSE instruction with IA-32 processors supporting Intel Hyper-Threading Technology.)

8.10.3

Detecting Support MONITOR/MWAIT Instruction

Streaming SIMD Extensions 3 introduced two instructions (MONITOR and MWAIT) to help multithreaded software
improve thread synchronization. In the initial implementation, MONITOR and MWAIT are available to software at
ring 0. The instructions are conditionally available at levels greater than 0. Use the following steps to detect the
availability of MONITOR and MWAIT:

•
•

Use CPUID to query the MONITOR bit (CPUID.1.ECX[3] = 1).
If CPUID indicates support, execute MONITOR inside a TRY/EXCEPT exception handler and trap for an
exception. If an exception occurs, MONITOR and MWAIT are not supported at a privilege level greater than 0.
See Example 8-23.

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Example 8-23. Verifying MONITOR/MWAIT Support
boolean MONITOR_MWAIT_works = TRUE;
try {
_asm {
xor ecx, ecx
xor edx, edx
mov eax, MemArea
monitor
}
// Use monitor
} except (UNWIND) {
// if we get here, MONITOR/MWAIT is not supported
MONITOR_MWAIT_works = FALSE;
}

8.10.4

MONITOR/MWAIT Instruction

Operating systems usually implement idle loops to handle thread synchronization. In a typical idle-loop scenario,
there could be several “busy loops” and they would use a set of memory locations. An impacted processor waits in
a loop and poll a memory location to determine if there is available work to execute. The posting of work is typically
a write to memory (the work-queue of the waiting processor). The time for initiating a work request and getting it
scheduled is on the order of a few bus cycles.
From a resource sharing perspective (logical processors sharing execution resources), use of the HLT instruction in
an OS idle loop is desirable but has implications. Executing the HLT instruction on a idle logical processor puts the
targeted processor in a non-execution state. This requires another processor (when posting work for the halted
logical processor) to wake up the halted processor using an inter-processor interrupt. The posting and servicing of
such an interrupt introduces a delay in the servicing of new work requests.
In a shared memory configuration, exits from busy loops usually occur because of a state change applicable to a
specific memory location; such a change tends to be triggered by writes to the memory location by another agent
(typically a processor).
MONITOR/MWAIT complement the use of HLT and PAUSE to allow for efficient partitioning and un-partitioning of
shared resources among logical processors sharing physical resources. MONITOR sets up an effective address
range that is monitored for write-to-memory activities; MWAIT places the processor in an optimized state (this may
vary between different implementations) until a write to the monitored address range occurs.
In the initial implementation of MONITOR and MWAIT, they are available at CPL = 0 only.
Both instructions rely on the state of the processor’s monitor hardware. The monitor hardware can be either armed
(by executing the MONITOR instruction) or triggered (due to a variety of events, including a store to the monitored
memory region). If upon execution of MWAIT, monitor hardware is in a triggered state: MWAIT behaves as a NOP
and execution continues at the next instruction in the execution stream. The state of monitor hardware is not architecturally visible except through the behavior of MWAIT.
Multiple events other than a write to the triggering address range can cause a processor that executed MWAIT to
wake up. These include events that would lead to voluntary or involuntary context switches, such as:

•
•
•

External interrupts, including NMI, SMI, INIT, BINIT, MCERR, A20M#

•

Voluntary transitions due to fast system call and far calls (occurring prior to issuing MWAIT but after setting the
monitor)

Faults, Aborts (including Machine Check)
Architectural TLB invalidations including writes to CR0, CR3, CR4 and certain MSR writes; execution of LMSW
(occurring prior to issuing MWAIT but after setting the monitor)

Power management related events (such as Thermal Monitor 2 or chipset driven STPCLK# assertion) will not cause
the monitor event pending flag to be cleared. Faults will not cause the monitor event pending flag to be cleared.

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Software should not allow for voluntary context switches in between MONITOR/MWAIT in the instruction flow. Note
that execution of MWAIT does not re-arm the monitor hardware. This means that MONITOR/MWAIT need to be
executed in a loop. Also note that exits from the MWAIT state could be due to a condition other than a write to the
triggering address; software should explicitly check the triggering data location to determine if the write occurred.
Software should also check the value of the triggering address following the execution of the monitor instruction
(and prior to the execution of the MWAIT instruction). This check is to identify any writes to the triggering address
that occurred during the course of MONITOR execution.
The address range provided to the MONITOR instruction must be of write-back caching type. Only write-back
memory type stores to the monitored address range will trigger the monitor hardware. If the address range is not
in memory of write-back type, the address monitor hardware may not be set up properly or the monitor hardware
may not be armed. Software is also responsible for ensuring that

•

Writes that are not intended to cause the exit of a busy loop do not write to a location within the address region
being monitored by the monitor hardware,

•

Writes intended to cause the exit of a busy loop are written to locations within the monitored address region.

Not doing so will lead to more false wakeups (an exit from the MWAIT state not due to a write to the intended data
location). These have negative performance implications. It might be necessary for software to use padding to
prevent false wakeups. CPUID provides a mechanism for determining the size data locations for monitoring as well
as a mechanism for determining the size of a the pad.

8.10.5

Monitor/Mwait Address Range Determination

To use the MONITOR/MWAIT instructions, software should know the length of the region monitored by the
MONITOR/MWAIT instructions and the size of the coherence line size for cache-snoop traffic in a multiprocessor
system. This information can be queried using the CPUID monitor leaf function (EAX = 05H). You will need the
smallest and largest monitor line size:

•

To avoid missed wake-ups: make sure that the data structure used to monitor writes fits within the smallest
monitor line-size. Otherwise, the processor may not wake up after a write intended to trigger an exit from
MWAIT.

•

To avoid false wake-ups; use the largest monitor line size to pad the data structure used to monitor writes.
Software must make sure that beyond the data structure, no unrelated data variable exists in the triggering
area for MWAIT. A pad may be needed to avoid this situation.

These above two values bear no relationship to cache line size in the system and software should not make any
assumptions to that effect. Within a single-cluster system, the two parameters should default to be the same (the
size of the monitor triggering area is the same as the system coherence line size).
Based on the monitor line sizes returned by the CPUID, the OS should dynamically allocate structures with appropriate padding. If static data structures must be used by an OS, attempt to adapt the data structure and use a
dynamically allocated data buffer for thread synchronization. When the latter technique is not possible, consider
not using MONITOR/MWAIT when using static data structures.
To set up the data structure correctly for MONITOR/MWAIT on multi-clustered systems: interaction between
processors, chipsets, and the BIOS is required (system coherence line size may depend on the chipset used in the
system; the size could be different from the processor’s monitor triggering area). The BIOS is responsible to set the
correct value for system coherence line size using the IA32_MONITOR_FILTER_LINE_SIZE MSR. Depending on the
relative magnitude of the size of the monitor triggering area versus the value written into the
IA32_MONITOR_FILTER_LINE_SIZE MSR, the smaller of the parameters will be reported as the Smallest Monitor
Line Size. The larger of the parameters will be reported as the Largest Monitor Line Size.

8.10.6

Required Operating System Support

This section describes changes that must be made to an operating system to run on processors supporting Intel
Hyper-Threading Technology. It also describes optimizations that can help an operating system make more efficient use of the logical processors sharing execution resources. The required changes and suggested optimizations
are representative of the types of modifications that appear in Windows* XP and Linux* kernel 2.4.0 operating
systems for Intel processors supporting Intel Hyper-Threading Technology. Additional optimizations for processors

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supporting Intel Hyper-Threading Technology are described in the Intel® 64 and IA-32 Architectures Optimization
Reference Manual.

8.10.6.1

Use the PAUSE Instruction in Spin-Wait Loops

Intel recommends that a PAUSE instruction be placed in all spin-wait loops that run on Intel processors supporting
Intel Hyper-Threading Technology and multi-core processors.
Software routines that use spin-wait loops include multiprocessor synchronization primitives (spin-locks, semaphores, and mutex variables) and idle loops. Such routines keep the processor core busy executing a load-comparebranch loop while a thread waits for a resource to become available. Including a PAUSE instruction in such a loop
greatly improves efficiency (see Section 8.10.2, “PAUSE Instruction”). The following routine gives an example of a
spin-wait loop that uses a PAUSE instruction:
Spin_Lock:
CMP lockvar, 0
;Check if lock is free
JE Get_Lock
PAUSE
;Short delay
JMP Spin_Lock
Get_Lock:
MOV EAX, 1
XCHG EAX, lockvar ;Try to get lock
CMP EAX, 0
;Test if successful
JNE Spin_Lock
Critical_Section:

MOV lockvar, 0
...
Continue:
The spin-wait loop above uses a “test, test-and-set” technique for determining the availability of the synchronization variable. This technique is recommended when writing spin-wait loops.
In IA-32 processor generations earlier than the Pentium 4 processor, the PAUSE instruction is treated as a NOP
instruction.

8.10.6.2

Potential Usage of MONITOR/MWAIT in C0 Idle Loops

An operating system may implement different handlers for different idle states. A typical OS idle loop on an ACPIcompatible OS is shown in Example 8-24:
Example 8-24. A Typical OS Idle Loop
// WorkQueue is a memory location indicating there is a thread
// ready to run. A non-zero value for WorkQueue is assumed to
// indicate the presence of work to be scheduled on the processor.
// The idle loop is entered with interrupts disabled.
WHILE (1) {
IF (WorkQueue) THEN {
// Schedule work at WorkQueue.
}
ELSE {
// No work to do - wait in appropriate C-state handler depending
// on Idle time accumulated
IF (IdleTime >= IdleTimeThreshhold) THEN {
// Call appropriate C1, C2, C3 state handler, C1 handler
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// shown below
}
}
}
// C1 handler uses a Halt instruction
VOID C1Handler()
{ STI
HLT
}
The MONITOR and MWAIT instructions may be considered for use in the C0 idle state loops, if MONITOR and MWAIT are supported.
Example 8-25. An OS Idle Loop with MONITOR/MWAIT in the C0 Idle Loop
// WorkQueue is a memory location indicating there is a thread
// ready to run. A non-zero value for WorkQueue is assumed to
// indicate the presence of work to be scheduled on the processor.
// The following example assumes that the necessary padding has been
// added surrounding WorkQueue to eliminate false wakeups
// The idle loop is entered with interrupts disabled.
WHILE (1) {
IF (WorkQueue) THEN {
// Schedule work at WorkQueue.
}
ELSE {
// No work to do - wait in appropriate C-state handler depending
// on Idle time accumulated.
IF (IdleTime >= IdleTimeThreshhold) THEN {
// Call appropriate C1, C2, C3 state handler, C1
// handler shown below
MONITOR WorkQueue // Setup of eax with WorkQueue
// LinearAddress,
// ECX, EDX = 0
IF (WorkQueue ≠ 0) THEN {
MWAIT
}
}
}
}
// C1 handler uses a Halt instruction.
VOID C1Handler()
{ STI
HLT
}

8.10.6.3

Halt Idle Logical Processors

If one of two logical processors is idle or in a spin-wait loop of long duration, explicitly halt that processor by means
of a HLT instruction.
In an MP system, operating systems can place idle processors into a loop that continuously checks the run queue
for runnable software tasks. Logical processors that execute idle loops consume a significant amount of core’s
execution resources that might otherwise be used by the other logical processors in the physical package. For this
reason, halting idle logical processors optimizes the performance.12 If all logical processors within a physical
package are halted, the processor will enter a power-saving state.
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8.10.6.4

Potential Usage of MONITOR/MWAIT in C1 Idle Loops

An operating system may also consider replacing HLT with MONITOR/MWAIT in its C1 idle loop. An example is
shown in Example 8-26:
Example 8-26. An OS Idle Loop with MONITOR/MWAIT in the C1 Idle Loop
// WorkQueue is a memory location indicating there is a thread
// ready to run. A non-zero value for WorkQueue is assumed to
// indicate the presence of work to be scheduled on the processor.
// The following example assumes that the necessary padding has been
// added surrounding WorkQueue to eliminate false wakeups
// The idle loop is entered with interrupts disabled.
WHILE (1) {
IF (WorkQueue) THEN {
// Schedule work at WorkQueue
}
ELSE {
// No work to do - wait in appropriate C-state handler depending
// on Idle time accumulated
IF (IdleTime >= IdleTimeThreshhold) THEN {
// Call appropriate C1, C2, C3 state handler, C1
// handler shown below
}
}
}
VOID C1Handler()
{

MONITOR WorkQueue // Setup of eax with WorkQueue LinearAddress,
// ECX, EDX = 0
IF (WorkQueue ≠ 0) THEN {
STI
MWAIT
// EAX, ECX = 0
}

}

8.10.6.5

Guidelines for Scheduling Threads on Logical Processors Sharing Execution Resources

Because the logical processors, the order in which threads are dispatched to logical processors for execution can
affect the overall efficiency of a system. The following guidelines are recommended for scheduling threads for
execution.

•

Dispatch threads to one logical processor per processor core before dispatching threads to the other logical
processor sharing execution resources in the same processor core.

•

In an MP system with two or more physical packages, distribute threads out over all the physical processors,
rather than concentrate them in one or two physical processors.

•

Use processor affinity to assign a thread to a specific processor core or package, depending on the cachesharing topology. The practice increases the chance that the processor’s caches will contain some of the
thread’s code and data when it is dispatched for execution after being suspended.

12. Excessive transitions into and out of the HALT state could also incur performance penalties. Operating systems should evaluate the
performance trade-offs for their operating system.
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8.10.6.6

Eliminate Execution-Based Timing Loops

Intel discourages the use of timing loops that depend on a processor’s execution speed to measure time. There are
several reasons:

•

Timing loops cause problems when they are calibrated on a IA-32 processor running at one frequency and then
executed on a processor running at another frequency.

•

Routines for calibrating execution-based timing loops produce unpredictable results when run on an IA-32
processor supporting Intel Hyper-Threading Technology. This is due to the sharing of execution resources
between the logical processors within a physical package.

To avoid the problems described, timing loop routines must use a timing mechanism for the loop that does not
depend on the execution speed of the logical processors in the system. The following sources are generally available:

•
•

A high resolution system timer (for example, an Intel 8254).
A high resolution timer within the processor (such as, the local APIC timer or the time-stamp counter).

For additional information, see the Intel® 64 and IA-32 Architectures Optimization Reference Manual.

8.10.6.7

Place Locks and Semaphores in Aligned, 128-Byte Blocks of Memory

When software uses locks or semaphores to synchronize processes, threads, or other code sections; Intel recommends that only one lock or semaphore be present within a cache line (or 128 byte sector, if 128-byte sector is
supported). In processors based on Intel NetBurst microarchitecture (which support 128-byte sector consisting of
two cache lines), following this recommendation means that each lock or semaphore should be contained in a 128byte block of memory that begins on a 128-byte boundary. The practice minimizes the bus traffic required to
service locks.

8.11

MP INITIALIZATION FOR P6 FAMILY PROCESSORS

This section describes the MP initialization process for systems that use multiple P6 family processors. This process
uses the MP initialization protocol that was introduced with the Pentium Pro processor (see Section 8.4, “MultipleProcessor (MP) Initialization”). For P6 family processors, this protocol is typically used to boot 2 or 4 processors
that reside on single system bus; however, it can support from 2 to 15 processors in a multi-clustered system when
the APIC busses are tied together. Larger systems are not supported.

8.11.1

Overview of the MP Initialization Process For P6 Family Processors

During the execution of the MP initialization protocol, one processor is selected as the bootstrap processor (BSP)
and the remaining processors are designated as application processors (APs), see Section 8.4.1, “BSP and AP
Processors.” Thereafter, the BSP manages the initialization of itself and the APs. This initialization includes
executing BIOS initialization code and operating-system initialization code.
The MP protocol imposes the following requirements and restrictions on the system:

•
•

An APIC clock (APICLK) must be provided.

•

All devices in the system that are capable of delivering interrupts to the processors must be inhibited from
doing so for the duration of the MP initialization protocol. The time during which interrupts must be inhibited
includes the window between when the BSP issues an INIT-SIPI-SIPI sequence to an AP and when the AP
responds to the last SIPI in the sequence.

The MP protocol will be executed only after a power-up or RESET. If the MP protocol has been completed and a
BSP has been chosen, subsequent INITs (either to a specific processor or system wide) do not cause the MP
protocol to be repeated. Instead, each processor examines its BSP flag (in the APIC_BASE MSR) to determine
whether it should execute the BIOS boot-strap code (if it is the BSP) or enter a wait-for-SIPI state (if it is an
AP).

The following special-purpose interprocessor interrupts (IPIs) are used during the boot phase of the MP initialization protocol. These IPIs are broadcast on the APIC bus.
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MULTIPLE-PROCESSOR MANAGEMENT

•

Boot IPI (BIPI)—Initiates the arbitration mechanism that selects a BSP from the group of processors on the
system bus and designates the remainder of the processors as APs. Each processor on the system bus
broadcasts a BIPI to all the processors following a power-up or RESET.

•

Final Boot IPI (FIPI)—Initiates the BIOS initialization procedure for the BSP. This IPI is broadcast to all the
processors on the system bus, but only the BSP responds to it. The BSP responds by beginning execution of the
BIOS initialization code at the reset vector.

•

Startup IPI (SIPI)—Initiates the initialization procedure for an AP. The SIPI message contains a vector to the AP
initialization code in the BIOS.

Table 8-5 describes the various fields of the boot phase IPIs.

Table 8-5. Boot Phase IPI Message Format
Type

Destination
Field

Destination
Shorthand

Trigger
Mode

Level

Destination
Mode

Delivery
Mode

Vector
(Hex)

BIPI

Not used

All including self

Edge

Deassert

Don’t Care

Fixed
(000)

40 to 4E*

FIPI

Not used

All including self

Edge

Deassert

Don’t Care

Fixed
(000)

10

SIPI

Used

All excluding self

Edge

Assert

Physical

StartUp
(110)

00 to FF

NOTE:
* For all P6 family processors.
For BIPI messages, the lower 4 bits of the vector field contain the APIC ID of the processor issuing the message and
the upper 4 bits contain the “generation ID” of the message. All P6 family processor will have a generation ID of 4H.
BIPIs will therefore use vector values ranging from 40H to 4EH (4FH can not be used because FH is not a valid APIC
ID).

8.11.2

MP Initialization Protocol Algorithm

Following a power-up or RESET of a system, the P6 family processors in the system execute the MP initialization
protocol algorithm to initialize each of the processors on the system bus. In the course of executing this algorithm,
the following boot-up and initialization operations are carried out:
1. Each processor on the system bus is assigned a unique APIC ID, based on system topology (see Section 8.4.5,
“Identifying Logical Processors in an MP System”). This ID is written into the local APIC ID register for each
processor.
2. Each processor executes its internal BIST simultaneously with the other processors on the system bus. Upon
completion of the BIST (at T0), each processor broadcasts a BIPI to “all including self” (see Figure 8-1).
3. APIC arbitration hardware causes all the APICs to respond to the BIPIs one at a time (at T1, T2, T3, and T4).
4. When the first BIPI is received (at time T1), each APIC compares the four least significant bits of the BIPI’s
vector field with its APIC ID. If the vector and APIC ID match, the processor selects itself as the BSP by setting
the BSP flag in its IA32_APIC_BASE MSR. If the vector and APIC ID do not match, the processor selects itself
as an AP by entering the “wait for SIPI” state. (Note that in Figure 8-1, the BIPI from processor 1 is the first
BIPI to be handled, so processor 1 becomes the BSP.)
5. The newly established BSP broadcasts an FIPI message to “all including self.” The FIPI is guaranteed to be
handled only after the completion of the BIPIs that were issued by the non-BSP processors.

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System (CPU) Bus

Pentium III
Processor 0

Pentium III
Processor 1

Pentium III
Processor 2

Pentium III
Processor 3

APIC Bus
Processor 1
Becomes BSP
T0

T1

BIPI.1

T2

BIPI.0

T3

BIPI.3

T4

BIPI.2

T5

FIPI

Serial Bus Activity

Figure 8-1. MP System With Multiple Pentium III Processors
6. After the BSP has been established, the outstanding BIPIs are received one at a time (at T2, T3, and T4) and
ignored by all processors.
7. When the FIPI is finally received (at T5), only the BSP responds to it. It responds by fetching and executing
BIOS boot-strap code, beginning at the reset vector (physical address FFFF FFF0H).
8. As part of the boot-strap code, the BSP creates an ACPI table and an MP table and adds its initial APIC ID to
these tables as appropriate.
9. At the end of the boot-strap procedure, the BSP broadcasts a SIPI message to all the APs in the system. Here,
the SIPI message contains a vector to the BIOS AP initialization code (at 000V V000H, where VV is the vector
contained in the SIPI message).
10. All APs respond to the SIPI message by racing to a BIOS initialization semaphore. The first one to the
semaphore begins executing the initialization code. (See MP init code for semaphore implementation details.)
As part of the AP initialization procedure, the AP adds its APIC ID number to the ACPI and MP tables as appropriate. At the completion of the initialization procedure, the AP executes a CLI instruction (to clear the IF flag in
the EFLAGS register) and halts itself.
11. When each of the APs has gained access to the semaphore and executed the AP initialization code and all
written their APIC IDs into the appropriate places in the ACPI and MP tables, the BSP establishes a count for the
number of processors connected to the system bus, completes executing the BIOS boot-strap code, and then
begins executing operating-system boot-strap and start-up code.
12. While the BSP is executing operating-system boot-strap and start-up code, the APs remain in the halted state.
In this state they will respond only to INITs, NMIs, and SMIs. They will also respond to snoops and to assertions
of the STPCLK# pin.
See Section 8.4.4, “MP Initialization Example,” for an annotated example the use of the MP protocol to boot IA-32
processors in an MP. This code should run on any IA-32 processor that used the MP protocol.

8.11.2.1

Error Detection and Handling During the MP Initialization Protocol

Errors may occur on the APIC bus during the MP initialization phase. These errors may be transient or permanent
and can be caused by a variety of failure mechanisms (for example, broken traces, soft errors during bus usage,
etc.). All serial bus related errors will result in an APIC checksum or acceptance error.
The MP initialization protocol makes the following assumptions regarding errors that occur during initialization:

•

If errors are detected on the APIC bus during execution of the MP initialization protocol, the processors that
detect the errors are shut down.

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MULTIPLE-PROCESSOR MANAGEMENT

•

The MP initialization protocol will be executed by processors even if they fail their BIST sequences.

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CHAPTER 9
PROCESSOR MANAGEMENT AND INITIALIZATION
This chapter describes the facilities provided for managing processor wide functions and for initializing the
processor. The subjects covered include: processor initialization, x87 FPU initialization, processor configuration,
feature determination, mode switching, the MSRs (in the Pentium, P6 family, Pentium 4, and Intel Xeon processors), and the MTRRs (in the P6 family, Pentium 4, and Intel Xeon processors).

9.1

INITIALIZATION OVERVIEW

Following power-up or an assertion of the RESET# pin, each processor on the system bus performs a hardware
initialization of the processor (known as a hardware reset) and an optional built-in self-test (BIST). A hardware
reset sets each processor’s registers to a known state and places the processor in real-address mode. It also invalidates the internal caches, translation lookaside buffers (TLBs) and the branch target buffer (BTB). At this point,
the action taken depends on the processor family:

•

Pentium 4 processors (CPUID DisplayFamily 0FH) — All the processors on the system bus (including a
single processor in a uniprocessor system) execute the multiple processor (MP) initialization protocol. The
processor that is selected through this protocol as the bootstrap processor (BSP) then immediately starts
executing software-initialization code in the current code segment beginning at the offset in the EIP register.
The application (non-BSP) processors (APs) go into a Wait For Startup IPI (SIPI) state while the BSP is
executing initialization code. See Section 8.4, “Multiple-Processor (MP) Initialization,” for more details. Note
that in a uniprocessor system, the single Pentium 4 or Intel Xeon processor automatically becomes the BSP.

•

IA-32 and Intel 64 processors (CPUID DisplayFamily 06H) — The action taken is the same as for the
Pentium 4 processors (as described in the previous paragraph).

•

Pentium processors — In either a single- or dual- processor system, a single Pentium processor is always
pre-designated as the primary processor. Following a reset, the primary processor behaves as follows in both
single- and dual-processor systems. Using the dual-processor (DP) ready initialization protocol, the primary
processor immediately starts executing software-initialization code in the current code segment beginning at
the offset in the EIP register. The secondary processor (if there is one) goes into a halt state.

•

Intel486 processor — The primary processor (or single processor in a uniprocessor system) immediately
starts executing software-initialization code in the current code segment beginning at the offset in the EIP
register. (The Intel486 does not automatically execute a DP or MP initialization protocol to determine which
processor is the primary processor.)

The software-initialization code performs all system-specific initialization of the BSP or primary processor and the
system logic.
At this point, for MP (or DP) systems, the BSP (or primary) processor wakes up each AP (or secondary) processor
to enable those processors to execute self-configuration code.
When all processors are initialized, configured, and synchronized, the BSP or primary processor begins executing
an initial operating-system or executive task.
The x87 FPU is also initialized to a known state during hardware reset. x87 FPU software initialization code can then
be executed to perform operations such as setting the precision of the x87 FPU and the exception masks. No special
initialization of the x87 FPU is required to switch operating modes.
Asserting the INIT# pin on the processor invokes a similar response to a hardware reset. The major difference is
that during an INIT, the internal caches, MSRs, MTRRs, and x87 FPU state are left unchanged (although, the TLBs
and BTB are invalidated as with a hardware reset). An INIT provides a method for switching from protected to realaddress mode while maintaining the contents of the internal caches.

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PROCESSOR MANAGEMENT AND INITIALIZATION

9.1.1

Processor State After Reset

Following power-up, The state of control register CR0 is 60000010H (see Figure 9-1). This places the processor is
in real-address mode with paging disabled.
Paging disabled: 0
Caching disabled: 1
Not write-through disabled: 1
Alignment check disabled: 0
Write-protect disabled: 0
31 30 29 28

P C N
G DW

19 18 17 16 15

Reserved

A
M

W
P

6 5 4 3 2 1 0

Reserved

N
T E M P
1
E
S MP E

External x87 FPU error reporting: 0
(Not used): 1
No task switch: 0
x87 FPU instructions not trapped: 0
WAIT/FWAIT instructions not trapped: 0
Real-address mode: 0

Figure 9-1. Contents of CR0 Register after Reset
The state of the flags and other registers following power-up for the Pentium 4, Pentium Pro, and Pentium processors are shown in Section 22.39, “Initial State of Pentium, Pentium Pro and Pentium 4 Processors” of the Intel® 64
and IA-32 Architectures Software Developer’s Manual, Volume 3B.
Table 9-1 shows processor states of IA-32 and Intel 64 processors with CPUID DisplayFamily signature of 06H at
the following events: power-up, RESET, and INIT. In a few cases, the behavior of some registers behave slightly
different across warm RESET, the variant cases are marked in Table 9-1 and described in more detail in Table 9-2.

Table 9-1. IA-32 and Intel 64 Processor States Following Power-up, Reset, or INIT
Register

Power up

Reset

INIT

EFLAGS1

00000002H

00000002H

00000002H

EIP

0000FFF0H

0000FFF0H

0000FFF0H

CR0

60000010H2

60000010H2

60000010H2

CR2, CR3, CR4

00000000H

00000000H

00000000H

CS

Selector = F000H
Base = FFFF0000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = F000H
Base = FFFF0000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = F000H
Base = FFFF0000H
Limit = FFFFH
AR = Present, R/W, Accessed

SS, DS, ES, FS, GS

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W, Accessed

EDX

000n06xxH3

000n06xxH3

000n06xxH3

EAX

04

04

04

EBX, ECX, ESI, EDI, EBP, ESP

00000000H

00000000H

00000000H

ST0 through ST7

+0.0

+0.0

FINIT/FNINIT: Unchanged

9-2 Vol. 3A

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PROCESSOR MANAGEMENT AND INITIALIZATION

Table 9-1. IA-32 and Intel 64 Processor States Following Power-up, Reset, or INIT (Contd.)
Register

Power up

Reset

INIT

x87 FPU Control Word5

0040H

0040H

FINIT/FNINIT: 037FH

x87 FPU Status Word

0000H

0000H

FINIT/FNINIT: 0000H

x87 FPU Tag Word5

5555H

5555H

FINIT/FNINIT: FFFFH

x87 FPU Data Operand and
CS Seg. Selectors5

0000H

0000H

FINIT/FNINIT: 0000H

x87 FPU Data Operand and
Inst. Pointers5

00000000H

00000000H

FINIT/FNINIT: 00000000H

MM0 through MM75

0000000000000000H

0000000000000000H

INIT or FINIT/FNINIT: Unchanged

XMM0 through XMM7

0H

0H

Unchanged

MXCSR

1F80H

1F80H

Unchanged

GDTR, IDTR

Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Base = 00000000H
Limit = FFFFH
AR = Present, R/W

LDTR, Task Register

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W

DR0, DR1, DR2, DR3

00000000H

00000000H

00000000H

DR6

FFFF0FF0H

FFFF0FF0H

FFFF0FF0H

DR7

00000400H

00000400H

00000400H

R8-R15

0000000000000000H

0000000000000000H

0000000000000000H

XMM8-XMM15

0H

0H

Unchanged

XCR0

1H

1H

Unchanged

IA32_XSS

0H

0H

0H

YMM_H[255:128]

0H

0H

Unchanged

BNDCFGU

0H

0H

0H

BND0-BND3

0H

0H

0H

IA32_BNDCFGS

0H

0H

0H

OPMASK

0H

0H

Unchanged

ZMM_H[511:256]

0H

0H

Unchanged

ZMMHi16[511:0]

0H

0H

Unchanged

PKRU

0H

0H

Unchanged

Intel Processor Trace MSRs

0H

Time-Stamp Counter

5

0H

W

Unchanged

0H

0H

W

Unchanged

IA32_TSC_AUX

0H

0H

Unchanged

IA32_TSC_ADJUST

0H

0H

Unchanged

IA32_TSC_DEADLINE

0H

0H

Unchanged

IA32_SYSENTER_CS/ESP/EIP

0H

0H

Unchanged

IA32_EFER

0000000000000000H

0000000000000000H

0000000000000000H

IA32_STAR/LSTAR

0H

0H

Unchanged

IA32_FS_BASE/GS_BASE

0H

0H

0H
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PROCESSOR MANAGEMENT AND INITIALIZATION

Table 9-1. IA-32 and Intel 64 Processor States Following Power-up, Reset, or INIT (Contd.)
Register

Power up

Reset

INIT

IA32_PMCx,
IA32_PERFEVTSELx

0H

0H

Unchanged

IA32_FIXED_CTRx,
IA32_FIXED_CTR_CTRL,

0H

0H

Unchanged

Data and Code Cache, TLBs

Invalid6

Invalid6

Unchanged

Fixed MTRRs

Disabled

Disabled

Unchanged

Global Perf Counter Controls

Variable MTRRs

Disabled

Disabled

Unchanged

Machine-Check Banks

Undefined

UndefinedW

Unchanged

Last Branch Record Stack

0

0W

Unchanged

APIC

Enabled

Enabled

Unchanged

X2APIC

Disabled

Disabled

Unchanged

IA32_DEBUG_INTERFACE

0

0W

Unchanged

NOTES:
1. The 10 most-significant bits of the EFLAGS register are undefined following a reset. Software should not depend on the states of
any of these bits.
2. The CD and NW flags are unchanged, bit 4 is set to 1, all other bits are cleared.
3. Where “n” is the Extended Model Value for the respective processor, and “xx” = don’t care.
4. If Built-In Self-Test (BIST) is invoked on power up or reset, EAX is 0 only if all tests passed. (BIST cannot be invoked during an INIT.)
5. The state of the x87 FPU and MMX registers is not changed by the execution of an INIT.
6. Internal caches are invalid after power-up and RESET, but left unchanged with an INIT.
W: Warm RESET behavior differs from power-on RESET with details listed in Table 9-2.

Table 9-2. Variance of RESET Values in Selected Intel Architecture Processors
State

XREF

Value

Feature Flag or DisplayFamily_DisplayModel Signatures

Time-Stamp Counter

Warm RESET Unmodified across warm
Reset

06_2DH, 06_3EH

Machine-Check Banks

Warm RESET IA32_MCi_Status banks are
unmodified across warm
Reset

06_2DH, 06_3EH, 06_3FH, 06_4FH, 06_56H

Last Branch Record Stack

Warm RESET LBR stack MSRs are
unmodified across warm
Reset

06_1AH, 06_1CH, DisplayFamiy= 06 and DisplayModel >1DH

Intel Processor Trace
MSRs

Warm RESET Clears
IA32_RTIT_CTL.TraceEn,
the rest of MSRs are
unmodified

If CPUID.(EAX=14H, ECX=0H):EBX[bit 2] = 1

IA32_DEBUG_INTERFACE

Warm RESET Unmodified across warm
Reset

If CPUID.01H:ECX.[11] = 1

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PROCESSOR MANAGEMENT AND INITIALIZATION

9.1.2

Processor Built-In Self-Test (BIST)

Hardware may request that the BIST be performed at power-up. The EAX register is cleared (0H) if the processor
passes the BIST. A nonzero value in the EAX register after the BIST indicates that a processor fault was detected.
If the BIST is not requested, the contents of the EAX register after a hardware reset is 0H.
The overhead for performing a BIST varies between processor families. For example, the BIST takes approximately
30 million processor clock periods to execute on the Pentium 4 processor. This clock count is model-specific; Intel
reserves the right to change the number of periods for any Intel 64 or IA-32 processor, without notification.

9.1.3

Model and Stepping Information

Following a hardware reset, the EDX register contains component identification and revision information (see
Figure 9-2). For example, the model, family, and processor type returned for the first processor in the Intel
Pentium 4 family is as follows: model (0000B), family (1111B), and processor type (00B).
31

EDX

28 27

20 19

Extended
Family

16 15 14 13 12 11

Extended
Model

Family

8 7

4 3

Model

0

Stepping
ID

Processor Type
Family (1111B for the Pentium 4 Processor Family)
Model (Beginning with 0000B)
Reserved

Figure 9-2. Version Information in the EDX Register after Reset
The stepping ID field contains a unique identifier for the processor’s stepping ID or revision level. The extended
family and extended model fields were added to the IA-32 architecture in the Pentium 4 processors.

9.1.4

First Instruction Executed

The first instruction that is fetched and executed following a hardware reset is located at physical address
FFFFFFF0H. This address is 16 bytes below the processor’s uppermost physical address. The EPROM containing the
software-initialization code must be located at this address.
The address FFFFFFF0H is beyond the 1-MByte addressable range of the processor while in real-address mode. The
processor is initialized to this starting address as follows. The CS register has two parts: the visible segment
selector part and the hidden base address part. In real-address mode, the base address is normally formed by
shifting the 16-bit segment selector value 4 bits to the left to produce a 20-bit base address. However, during a
hardware reset, the segment selector in the CS register is loaded with F000H and the base address is loaded with
FFFF0000H. The starting address is thus formed by adding the base address to the value in the EIP register (that
is, FFFF0000 + FFF0H = FFFFFFF0H).
The first time the CS register is loaded with a new value after a hardware reset, the processor will follow the normal
rule for address translation in real-address mode (that is, [CS base address = CS segment selector * 16]). To
insure that the base address in the CS register remains unchanged until the EPROM based software-initialization
code is completed, the code must not contain a far jump or far call or allow an interrupt to occur (which would
cause the CS selector value to be changed).

9.2

X87 FPU INITIALIZATION

Software-initialization code can determine the whether the processor contains an x87 FPU by using the CPUID
instruction. The code must then initialize the x87 FPU and set flags in control register CR0 to reflect the state of the
x87 FPU environment.
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PROCESSOR MANAGEMENT AND INITIALIZATION

A hardware reset places the x87 FPU in the state shown in Table 9-1. This state is different from the state the x87
FPU is placed in following the execution of an FINIT or FNINIT instruction (also shown in Table 9-1). If the x87 FPU
is to be used, the software-initialization code should execute an FINIT/FNINIT instruction following a hardware
reset. These instructions, tag all data registers as empty, clear all the exception masks, set the TOP-of-stack value
to 0, and select the default rounding and precision controls setting (round to nearest and 64-bit precision).
If the processor is reset by asserting the INIT# pin, the x87 FPU state is not changed.

9.2.1

Configuring the x87 FPU Environment

Initialization code must load the appropriate values into the MP, EM, and NE flags of control register CR0. These bits
are cleared on hardware reset of the processor. Figure 9-3 shows the suggested settings for these flags, depending
on the IA-32 processor being initialized. Initialization code can test for the type of processor present before setting
or clearing these flags.

Table 9-3. Recommended Settings of EM and MP Flags on IA-32 Processors
EM

MP

NE

IA-32 processor

1

0

1

Intel486™ SX, Intel386™ DX, and Intel386™ SX processors only, without the presence of a math
coprocessor.

0

1

1 or 0*

Pentium 4, Intel Xeon, P6 family, Pentium, Intel486™ DX, and Intel 487 SX processors, and
Intel386 DX and Intel386 SX processors when a companion math coprocessor is present.

0

1

1 or 0*

More recent Intel 64 or IA-32 processors

NOTE:
* The setting of the NE flag depends on the operating system being used.
The EM flag determines whether floating-point instructions are executed by the x87 FPU (EM is cleared) or a
device-not-available exception (#NM) is generated for all floating-point instructions so that an exception handler
can emulate the floating-point operation (EM = 1). Ordinarily, the EM flag is cleared when an x87 FPU or math
coprocessor is present and set if they are not present. If the EM flag is set and no x87 FPU, math coprocessor, or
floating-point emulator is present, the processor will hang when a floating-point instruction is executed.
The MP flag determines whether WAIT/FWAIT instructions react to the setting of the TS flag. If the MP flag is clear,
WAIT/FWAIT instructions ignore the setting of the TS flag; if the MP flag is set, they will generate a device-notavailable exception (#NM) if the TS flag is set. Generally, the MP flag should be set for processors with an integrated x87 FPU and clear for processors without an integrated x87 FPU and without a math coprocessor present.
However, an operating system can choose to save the floating-point context at every context switch, in which case
there would be no need to set the MP bit.
Table 2-2 shows the actions taken for floating-point and WAIT/FWAIT instructions based on the settings of the EM,
MP, and TS flags.
The NE flag determines whether unmasked floating-point exceptions are handled by generating a floating-point
error exception internally (NE is set, native mode) or through an external interrupt (NE is cleared). In systems
where an external interrupt controller is used to invoke numeric exception handlers (such as MS-DOS-based
systems), the NE bit should be cleared.

9.2.2

Setting the Processor for x87 FPU Software Emulation

Setting the EM flag causes the processor to generate a device-not-available exception (#NM) and trap to a software
exception handler whenever it encounters a floating-point instruction. (Table 9-3 shows when it is appropriate to
use this flag.) Setting this flag has two functions:

•

It allows x87 FPU code to run on an IA-32 processor that has neither an integrated x87 FPU nor is connected to
an external math coprocessor, by using a floating-point emulator.

•

It allows floating-point code to be executed using a special or nonstandard floating-point emulator, selected for
a particular application, regardless of whether an x87 FPU or math coprocessor is present.

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To emulate floating-point instructions, the EM, MP, and NE flag in control register CR0 should be set as shown in
Table 9-4.

Table 9-4. Software Emulation Settings of EM, MP, and NE Flags
CR0 Bit

Value

EM

1

MP

0

NE

1

Regardless of the value of the EM bit, the Intel486 SX processor generates a device-not-available exception (#NM)
upon encountering any floating-point instruction.

9.3

CACHE ENABLING

IA-32 processors (beginning with the Intel486 processor) and Intel 64 processors contain internal instruction and
data caches. These caches are enabled by clearing the CD and NW flags in control register CR0. (They are set
during a hardware reset.) Because all internal cache lines are invalid following reset initialization, it is not necessary to invalidate the cache before enabling caching. Any external caches may require initialization and invalidation
using a system-specific initialization and invalidation code sequence.
Depending on the hardware and operating system or executive requirements, additional configuration of the
processor’s caching facilities will probably be required. Beginning with the Intel486 processor, page-level caching
can be controlled with the PCD and PWT flags in page-directory and page-table entries. Beginning with the P6
family processors, the memory type range registers (MTRRs) control the caching characteristics of the regions of
physical memory. (For the Intel486 and Pentium processors, external hardware can be used to control the caching
characteristics of regions of physical memory.) See Chapter 11, “Memory Cache Control,” for detailed information
on configuration of the caching facilities in the Pentium 4, Intel Xeon, and P6 family processors and system
memory.

9.4

MODEL-SPECIFIC REGISTERS (MSRS)

Most IA-32 processors (starting from Pentium processors) and Intel 64 processors contain a model-specific registers (MSRs). A given MSR may not be supported across all families and models for Intel 64 and IA-32 processors.
Some MSRs are designated as architectural to simplify software programming; a feature introduced by an architectural MSR is expected to be supported in future processors. Non-architectural MSRs are not guaranteed to be
supported or to have the same functions on future processors.
MSRs that provide control for a number of hardware and software-related features, include:

•
•
•

Performance-monitoring counters (see Chapter 23, “Introduction to Virtual Machine Extensions”).

•
•
•
•

MTRRs (see Section 11.11, “Memory Type Range Registers (MTRRs)”).

Debug extensions (see Chapter 23, “Introduction to Virtual Machine Extensions.”).
Machine-check exception capability and its accompanying machine-check architecture (see Chapter 15,
“Machine-Check Architecture”).
Thermal and power management.
Instruction-specific support (for example: SYSENTER, SYSEXIT, SWAPGS, etc.).
Processor feature/mode support (for example: IA32_EFER, IA32_FEATURE_CONTROL).

The MSRs can be read and written to using the RDMSR and WRMSR instructions, respectively.
When performing software initialization of an IA-32 or Intel 64 processor, many of the MSRs will need to be initialized to set up things like performance-monitoring events, run-time machine checks, and memory types for physical memory.

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Lists of available performance-monitoring events are given in Chapter 19, “Performance Monitoring Events”, and
lists of available MSRs are given in Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4. The references earlier in this section show where the functions of
the various groups of MSRs are described in this manual.

9.5

MEMORY TYPE RANGE REGISTERS (MTRRS)

Memory type range registers (MTRRs) were introduced into the IA-32 architecture with the Pentium Pro processor.
They allow the type of caching (or no caching) to be specified in system memory for selected physical address
ranges. They allow memory accesses to be optimized for various types of memory such as RAM, ROM, frame buffer
memory, and memory-mapped I/O devices.
In general, initializing the MTRRs is normally handled by the software initialization code or BIOS and is not an operating system or executive function. At the very least, all the MTRRs must be cleared to 0, which selects the
uncached (UC) memory type. See Section 11.11, “Memory Type Range Registers (MTRRs),” for detailed information on the MTRRs.

9.6

INITIALIZING SSE/SSE2/SSE3/SSSE3 EXTENSIONS

For processors that contain SSE/SSE2/SSE3/SSSE3 extensions, steps must be taken when initializing the
processor to allow execution of these instructions.
1. Check the CPUID feature flags for the presence of the SSE/SSE2/SSE3/SSSE3 extensions (respectively: EDX
bits 25 and 26, ECX bit 0 and 9) and support for the FXSAVE and FXRSTOR instructions (EDX bit 24). Also check
for support for the CLFLUSH instruction (EDX bit 19). The CPUID feature flags are loaded in the EDX and ECX
registers when the CPUID instruction is executed with a 1 in the EAX register.
2. Set the OSFXSR flag (bit 9 in control register CR4) to indicate that the operating system supports saving and
restoring the SSE/SSE2/SSE3/SSSE3 execution environment (XMM and MXCSR registers) with the FXSAVE and
FXRSTOR instructions, respectively. See Section 2.5, “Control Registers,” for a description of the OSFXSR flag.
3. Set the OSXMMEXCPT flag (bit 10 in control register CR4) to indicate that the operating system supports the
handling of SSE/SSE2/SSE3 SIMD floating-point exceptions (#XM). See Section 2.5, “Control Registers,” for a
description of the OSXMMEXCPT flag.
4. Set the mask bits and flags in the MXCSR register according to the mode of operation desired for
SSE/SSE2/SSE3 SIMD floating-point instructions. See “MXCSR Control and Status Register” in Chapter 10,
“Programming with Streaming SIMD Extensions (SSE),” of the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1, for a detailed description of the bits and flags in the MXCSR register.

9.7

SOFTWARE INITIALIZATION FOR REAL-ADDRESS MODE OPERATION

Following a hardware reset (either through a power-up or the assertion of the RESET# pin) the processor is placed
in real-address mode and begins executing software initialization code from physical address FFFFFFF0H. Software
initialization code must first set up the necessary data structures for handling basic system functions, such as a
real-mode IDT for handling interrupts and exceptions. If the processor is to remain in real-address mode, software
must then load additional operating-system or executive code modules and data structures to allow reliable execution of application programs in real-address mode.
If the processor is going to operate in protected mode, software must load the necessary data structures to operate
in protected mode and then switch to protected mode. The protected-mode data structures that must be loaded
are described in Section 9.8, “Software Initialization for Protected-Mode Operation.”

9.7.1

Real-Address Mode IDT

In real-address mode, the only system data structure that must be loaded into memory is the IDT (also called the
“interrupt vector table”). By default, the address of the base of the IDT is physical address 0H. This address can be
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changed by using the LIDT instruction to change the base address value in the IDTR. Software initialization code
needs to load interrupt- and exception-handler pointers into the IDT before interrupts can be enabled.
The actual interrupt- and exception-handler code can be contained either in EPROM or RAM; however, the code
must be located within the 1-MByte addressable range of the processor in real-address mode. If the handler code
is to be stored in RAM, it must be loaded along with the IDT.

9.7.2

NMI Interrupt Handling

The NMI interrupt is always enabled (except when multiple NMIs are nested). If the IDT and the NMI interrupt
handler need to be loaded into RAM, there will be a period of time following hardware reset when an NMI interrupt
cannot be handled. During this time, hardware must provide a mechanism to prevent an NMI interrupt from halting
code execution until the IDT and the necessary NMI handler software is loaded. Here are two examples of how
NMIs can be handled during the initial states of processor initialization:

•

A simple IDT and NMI interrupt handler can be provided in EPROM. This allows an NMI interrupt to be handled
immediately after reset initialization.

•

The system hardware can provide a mechanism to enable and disable NMIs by passing the NMI# signal through
an AND gate controlled by a flag in an I/O port. Hardware can clear the flag when the processor is reset, and
software can set the flag when it is ready to handle NMI interrupts.

9.8

SOFTWARE INITIALIZATION FOR PROTECTED-MODE OPERATION

The processor is placed in real-address mode following a hardware reset. At this point in the initialization process,
some basic data structures and code modules must be loaded into physical memory to support further initialization
of the processor, as described in Section 9.7, “Software Initialization for Real-Address Mode Operation.” Before the
processor can be switched to protected mode, the software initialization code must load a minimum number of
protected mode data structures and code modules into memory to support reliable operation of the processor in
protected mode. These data structures include the following:

•
•
•
•
•
•
•

A IDT.
A GDT.
A TSS.
(Optional) An LDT.
If paging is to be used, at least one page directory and one page table.
A code segment that contains the code to be executed when the processor switches to protected mode.
One or more code modules that contain the necessary interrupt and exception handlers.

Software initialization code must also initialize the following system registers before the processor can be switched
to protected mode:

•
•

The GDTR.

•
•

Control registers CR1 through CR4.

(Optional.) The IDTR. This register can also be initialized immediately after switching to protected mode, prior
to enabling interrupts.
(Pentium 4, Intel Xeon, and P6 family processors only.) The memory type range registers (MTRRs).

With these data structures, code modules, and system registers initialized, the processor can be switched to
protected mode by loading control register CR0 with a value that sets the PE flag (bit 0).

9.8.1

Protected-Mode System Data Structures

The contents of the protected-mode system data structures loaded into memory during software initialization,
depend largely on the type of memory management the protected-mode operating-system or executive is going to
support: flat, flat with paging, segmented, or segmented with paging.

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To implement a flat memory model without paging, software initialization code must at a minimum load a GDT with
one code and one data-segment descriptor. A null descriptor in the first GDT entry is also required. The stack can
be placed in a normal read/write data segment, so no dedicated descriptor for the stack is required. A flat memory
model with paging also requires a page directory and at least one page table (unless all pages are 4 MBytes in
which case only a page directory is required). See Section 9.8.3, “Initializing Paging.”
Before the GDT can be used, the base address and limit for the GDT must be loaded into the GDTR register using
an LGDT instruction.
A multi-segmented model may require additional segments for the operating system, as well as segments and LDTs
for each application program. LDTs require segment descriptors in the GDT. Some operating systems allocate new
segments and LDTs as they are needed. This provides maximum flexibility for handling a dynamic programming
environment. However, many operating systems use a single LDT for all tasks, allocating GDT entries in advance.
An embedded system, such as a process controller, might pre-allocate a fixed number of segments and LDTs for a
fixed number of application programs. This would be a simple and efficient way to structure the software environment of a real-time system.

9.8.2

Initializing Protected-Mode Exceptions and Interrupts

Software initialization code must at a minimum load a protected-mode IDT with gate descriptor for each exception
vector that the processor can generate. If interrupt or trap gates are used, the gate descriptors can all point to the
same code segment, which contains the necessary exception handlers. If task gates are used, one TSS and accompanying code, data, and task segments are required for each exception handler called with a task gate.
If hardware allows interrupts to be generated, gate descriptors must be provided in the IDT for one or more interrupt handlers.
Before the IDT can be used, the base address and limit for the IDT must be loaded into the IDTR register using an
LIDT instruction. This operation is typically carried out immediately after switching to protected mode.

9.8.3

Initializing Paging

Paging is controlled by the PG flag in control register CR0. When this flag is clear (its state following a hardware
reset), the paging mechanism is turned off; when it is set, paging is enabled. Before setting the PG flag, the
following data structures and registers must be initialized:

•

Software must load at least one page directory and one page table into physical memory. The page table can
be eliminated if the page directory contains a directory entry pointing to itself (here, the page directory and
page table reside in the same page), or if only 4-MByte pages are used.

•

Control register CR3 (also called the PDBR register) is loaded with the physical base address of the page
directory.

•

(Optional) Software may provide one set of code and data descriptors in the GDT or in an LDT for supervisor
mode and another set for user mode.

With this paging initialization complete, paging is enabled and the processor is switched to protected mode at the
same time by loading control register CR0 with an image in which the PG and PE flags are set. (Paging cannot be
enabled before the processor is switched to protected mode.)

9.8.4

Initializing Multitasking

If the multitasking mechanism is not going to be used and changes between privilege levels are not allowed, it is
not necessary load a TSS into memory or to initialize the task register.
If the multitasking mechanism is going to be used and/or changes between privilege levels are allowed, software
initialization code must load at least one TSS and an accompanying TSS descriptor. (A TSS is required to change
privilege levels because pointers to the privileged-level 0, 1, and 2 stack segments and the stack pointers for these
stacks are obtained from the TSS.) TSS descriptors must not be marked as busy when they are created; they
should be marked busy by the processor only as a side-effect of performing a task switch. As with descriptors for
LDTs, TSS descriptors reside in the GDT.

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After the processor has switched to protected mode, the LTR instruction can be used to load a segment selector for
a TSS descriptor into the task register. This instruction marks the TSS descriptor as busy, but does not perform a
task switch. The processor can, however, use the TSS to locate pointers to privilege-level 0, 1, and 2 stacks. The
segment selector for the TSS must be loaded before software performs its first task switch in protected mode,
because a task switch copies the current task state into the TSS.
After the LTR instruction has been executed, further operations on the task register are performed by task
switching. As with other segments and LDTs, TSSs and TSS descriptors can be either pre-allocated or allocated as
needed.

9.8.5

Initializing IA-32e Mode

On Intel 64 processors, the IA32_EFER MSR is cleared on system reset. The operating system must be in protected
mode with paging enabled before attempting to initialize IA-32e mode. IA-32e mode operation also requires physical-address extensions with four levels of enhanced paging structures (see Section 4.5, “4-Level Paging”).
Operating systems should follow this sequence to initialize IA-32e mode:
1. Starting from protected mode, disable paging by setting CR0.PG = 0. Use the MOV CR0 instruction to disable
paging (the instruction must be located in an identity-mapped page).
2. Enable physical-address extensions (PAE) by setting CR4.PAE = 1. Failure to enable PAE will result in a #GP
fault when an attempt is made to initialize IA-32e mode.
3. Load CR3 with the physical base address of the Level 4 page map table (PML4).
4. Enable IA-32e mode by setting IA32_EFER.LME = 1.
5. Enable paging by setting CR0.PG = 1. This causes the processor to set the IA32_EFER.LMA bit to 1. The MOV
CR0 instruction that enables paging and the following instructions must be located in an identity-mapped page
(until such time that a branch to non-identity mapped pages can be effected).
64-bit mode paging tables must be located in the first 4 GBytes of physical-address space prior to activating IA-32e
mode. This is necessary because the MOV CR3 instruction used to initialize the page-directory base must be
executed in legacy mode prior to activating IA-32e mode (setting CR0.PG = 1 to enable paging). Because MOV CR3
is executed in protected mode, only the lower 32 bits of the register are written, limiting the table location to the
low 4 GBytes of memory. Software can relocate the page tables anywhere in physical memory after IA-32e mode
is activated.
The processor performs 64-bit mode consistency checks whenever software attempts to modify any of the enable
bits directly involved in activating IA-32e mode (IA32_EFER.LME, CR0.PG, and CR4.PAE). It will generate a general
protection fault (#GP) if consistency checks fail. 64-bit mode consistency checks ensure that the processor does
not enter an undefined mode or state with unpredictable behavior.
64-bit mode consistency checks fail in the following circumstances:

•
•
•
•
•

An attempt is made to enable or disable IA-32e mode while paging is enabled.
IA-32e mode is enabled and an attempt is made to enable paging prior to enabling physical-address extensions
(PAE).
IA-32e mode is active and an attempt is made to disable physical-address extensions (PAE).
If the current CS has the L-bit set on an attempt to activate IA-32e mode.
If the TR contains a 16-bit TSS.

9.8.5.1

IA-32e Mode System Data Structures

After activating IA-32e mode, the system-descriptor-table registers (GDTR, LDTR, IDTR, TR) continue to reference
legacy protected-mode descriptor tables. Tables referenced by the descriptors all reside in the lower 4 GBytes of
linear-address space. After activating IA-32e mode, 64-bit operating-systems should use the LGDT, LLDT, LIDT,
and LTR instructions to load the system-descriptor-table registers with references to 64-bit descriptor tables.

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9.8.5.2

IA-32e Mode Interrupts and Exceptions

Software must not allow exceptions or interrupts to occur between the time IA-32e mode is activated and the
update of the interrupt-descriptor-table register (IDTR) that establishes references to a 64-bit interrupt-descriptor
table (IDT). This is because the IDT remains in legacy form immediately after IA-32e mode is activated.
If an interrupt or exception occurs prior to updating the IDTR, a legacy 32-bit interrupt gate will be referenced and
interpreted as a 64-bit interrupt gate with unpredictable results. External interrupts can be disabled by using the
CLI instruction.
Non-maskable interrupts (NMI) must be disabled using external hardware.

9.8.5.3

64-bit Mode and Compatibility Mode Operation

IA-32e mode uses two code segment-descriptor bits (CS.L and CS.D, see Figure 3-8) to control the operating modes
after IA-32e mode is initialized. If CS.L = 1 and CS.D = 0, the processor is running in 64-bit mode. With this
encoding, the default operand size is 32 bits and default address size is 64 bits. Using instruction prefixes, operand
size can be changed to 64 bits or 16 bits; address size can be changed to 32 bits.
When IA-32e mode is active and CS.L = 0, the processor operates in compatibility mode. In this mode, CS.D
controls default operand and address sizes exactly as it does in the IA-32 architecture. Setting CS.D = 1 specifies
default operand and address size as 32 bits. Clearing CS.D to 0 specifies default operand and address size as 16
bits (the CS.L = 1, CS.D = 1 bit combination is reserved).
Compatibility mode execution is selected on a code-segment basis. This mode allows legacy applications to coexist
with 64-bit applications running in 64-bit mode. An operating system running in IA-32e mode can execute existing
16-bit and 32-bit applications by clearing their code-segment descriptor’s CS.L bit to 0.
In compatibility mode, the following system-level mechanisms continue to operate using the IA-32e-mode architectural semantics:

•
•
•

Linear-to-physical address translation uses the 64-bit mode extended page-translation mechanism.
Interrupts and exceptions are handled using the 64-bit mode mechanisms.
System calls (calls through call gates and SYSENTER/SYSEXIT) are handled using the IA-32e mode
mechanisms.

9.8.5.4

Switching Out of IA-32e Mode Operation

To return from IA-32e mode to paged-protected mode operation operating systems must use the following
sequence:
1. Switch to compatibility mode.
2. Deactivate IA-32e mode by clearing CR0.PG = 0. This causes the processor to set IA32_EFER.LMA = 0. The
MOV CR0 instruction used to disable paging and subsequent instructions must be located in an identity-mapped
page.
3. Load CR3 with the physical base address of the legacy page-table-directory base address.
4. Disable IA-32e mode by setting IA32_EFER.LME = 0.
5. Enable legacy paged-protected mode by setting CR0.PG = 1
6. A branch instruction must follow the MOV CR0 that enables paging. Both the MOV CR0 and the branch
instruction must be located in an identity-mapped page.
Registers only available in 64-bit mode (R8-R15 and XMM8-XMM15) are preserved across transitions from 64-bit
mode into compatibility mode then back into 64-bit mode. However, values of R8-R15 and XMM8-XMM15 are undefined after transitions from 64-bit mode through compatibility mode to legacy or real mode and then back through
compatibility mode to 64-bit mode.

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9.9

MODE SWITCHING

To use the processor in protected mode after hardware or software reset, a mode switch must be performed from
real-address mode. Once in protected mode, software generally does not need to return to real-address mode. To
run software written to run in real-address mode (8086 mode), it is generally more convenient to run the software
in virtual-8086 mode, than to switch back to real-address mode.

9.9.1

Switching to Protected Mode

Before switching to protected mode from real mode, a minimum set of system data structures and code modules
must be loaded into memory, as described in Section 9.8, “Software Initialization for Protected-Mode Operation.”
Once these tables are created, software initialization code can switch into protected mode.
Protected mode is entered by executing a MOV CR0 instruction that sets the PE flag in the CR0 register. (In the
same instruction, the PG flag in register CR0 can be set to enable paging.) Execution in protected mode begins with
a CPL of 0.
Intel 64 and IA-32 processors have slightly different requirements for switching to protected mode. To insure
upwards and downwards code compatibility with Intel 64 and IA-32 processors, we recommend that you follow
these steps:
1. Disable interrupts. A CLI instruction disables maskable hardware interrupts. NMI interrupts can be disabled
with external circuitry. (Software must guarantee that no exceptions or interrupts are generated during the
mode switching operation.)
2. Execute the LGDT instruction to load the GDTR register with the base address of the GDT.
3. Execute a MOV CR0 instruction that sets the PE flag (and optionally the PG flag) in control register CR0.
4. Immediately following the MOV CR0 instruction, execute a far JMP or far CALL instruction. (This operation is
typically a far jump or call to the next instruction in the instruction stream.)
5. The JMP or CALL instruction immediately after the MOV CR0 instruction changes the flow of execution and
serializes the processor.
6. If paging is enabled, the code for the MOV CR0 instruction and the JMP or CALL instruction must come from a
page that is identity mapped (that is, the linear address before the jump is the same as the physical address
after paging and protected mode is enabled). The target instruction for the JMP or CALL instruction does not
need to be identity mapped.
7. If a local descriptor table is going to be used, execute the LLDT instruction to load the segment selector for the
LDT in the LDTR register.
8. Execute the LTR instruction to load the task register with a segment selector to the initial protected-mode task
or to a writable area of memory that can be used to store TSS information on a task switch.
9. After entering protected mode, the segment registers continue to hold the contents they had in real-address
mode. The JMP or CALL instruction in step 4 resets the CS register. Perform one of the following operations to
update the contents of the remaining segment registers.
— Reload segment registers DS, SS, ES, FS, and GS. If the ES, FS, and/or GS registers are not going to be
used, load them with a null selector.
— Perform a JMP or CALL instruction to a new task, which automatically resets the values of the segment
registers and branches to a new code segment.
10. Execute the LIDT instruction to load the IDTR register with the address and limit of the protected-mode IDT.
11. Execute the STI instruction to enable maskable hardware interrupts and perform the necessary hardware
operation to enable NMI interrupts.
Random failures can occur if other instructions exist between steps 3 and 4 above. Failures will be readily seen in
some situations, such as when instructions that reference memory are inserted between steps 3 and 4 while in
system management mode.

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9.9.2

Switching Back to Real-Address Mode

The processor switches from protected mode back to real-address mode if software clears the PE bit in the CR0
register with a MOV CR0 instruction. A procedure that re-enters real-address mode should perform the following
steps:
1. Disable interrupts. A CLI instruction disables maskable hardware interrupts. NMI interrupts can be disabled
with external circuitry.
2. If paging is enabled, perform the following operations:
— Transfer program control to linear addresses that are identity mapped to physical addresses (that is, linear
addresses equal physical addresses).
— Insure that the GDT and IDT are in identity mapped pages.
— Clear the PG bit in the CR0 register.
— Move 0H into the CR3 register to flush the TLB.
3. Transfer program control to a readable segment that has a limit of 64 KBytes (FFFFH). This operation loads the
CS register with the segment limit required in real-address mode.
4. Load segment registers SS, DS, ES, FS, and GS with a selector for a descriptor containing the following values,
which are appropriate for real-address mode:
— Limit = 64 KBytes (0FFFFH)
— Byte granular (G = 0)
— Expand up (E = 0)
— Writable (W = 1)
— Present (P = 1)
— Base = any value
The segment registers must be loaded with non-null segment selectors or the segment registers will be
unusable in real-address mode. Note that if the segment registers are not reloaded, execution continues using
the descriptor attributes loaded during protected mode.
5. Execute an LIDT instruction to point to a real-address mode interrupt table that is within the 1-MByte realaddress mode address range.
6. Clear the PE flag in the CR0 register to switch to real-address mode.
7. Execute a far JMP instruction to jump to a real-address mode program. This operation flushes the instruction
queue and loads the appropriate base-address value in the CS register.
8. Load the SS, DS, ES, FS, and GS registers as needed by the real-address mode code. If any of the registers are
not going to be used in real-address mode, write 0s to them.
9. Execute the STI instruction to enable maskable hardware interrupts and perform the necessary hardware
operation to enable NMI interrupts.

NOTE
All the code that is executed in steps 1 through 9 must be in a single page and the linear addresses
in that page must be identity mapped to physical addresses.

9.10

INITIALIZATION AND MODE SWITCHING EXAMPLE

This section provides an initialization and mode switching example that can be incorporated into an application.
This code was originally written to initialize the Intel386 processor, but it will execute successfully on the Pentium
4, Intel Xeon, P6 family, Pentium, and Intel486 processors. The code in this example is intended to reside in EPROM
and to run following a hardware reset of the processor. The function of the code is to do the following:

•

Establish a basic real-address mode operating environment.

9-14 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

•
•

Load the necessary protected-mode system data structures into RAM.

•

Switch the processor to protected mode.

Load the system registers with the necessary pointers to the data structures and the appropriate flag settings
for protected-mode operation.

Figure 9-3 shows the physical memory layout for the processor following a hardware reset and the starting point of
this example. The EPROM that contains the initialization code resides at the upper end of the processor’s physical
memory address range, starting at address FFFFFFFFH and going down from there. The address of the first instruction to be executed is at FFFFFFF0H, the default starting address for the processor following a hardware reset.
The main steps carried out in this example are summarized in Table 9-5. The source listing for the example (with
the filename STARTUP.ASM) is given in Example 9-1. The line numbers given in Table 9-5 refer to the source listing.
The following are some additional notes concerning this example:

•

When the processor is switched into protected mode, the original code segment base-address value of
FFFF0000H (located in the hidden part of the CS register) is retained and execution continues from the current
offset in the EIP register. The processor will thus continue to execute code in the EPROM until a far jump or call
is made to a new code segment, at which time, the base address in the CS register will be changed.

•

Maskable hardware interrupts are disabled after a hardware reset and should remain disabled until the
necessary interrupt handlers have been installed. The NMI interrupt is not disabled following a reset. The NMI#
pin must thus be inhibited from being asserted until an NMI handler has been loaded and made available to the
processor.

•

The use of a temporary GDT allows simple transfer of tables from the EPROM to anywhere in the RAM area. A
GDT entry is constructed with its base pointing to address 0 and a limit of 4 GBytes. When the DS and ES
registers are loaded with this descriptor, the temporary GDT is no longer needed and can be replaced by the
application GDT.

•

This code loads one TSS and no LDTs. If more TSSs exist in the application, they must be loaded into RAM. If
there are LDTs they may be loaded as well.

After Reset
[CS.BASE+EIP]

FFFF FFFFH
FFFF FFF0H
64K EPROM

EIP = 0000 FFF0H
CS.BASE = FFFF 0000H
DS.BASE = 0H
ES.BASE = 0H
SS.BASE = 0H
ESP = 0H

[SP, DS, SS, ES]

FFFF 0000H

0

Figure 9-3. Processor State After Reset

Vol. 3A 9-15

PROCESSOR MANAGEMENT AND INITIALIZATION

Table 9-5. Main Initialization Steps in STARTUP.ASM Source Listing
STARTUP.ASM Line
Numbers

Description

From

To

157

157

Jump (short) to the entry code in the EPROM

162

169

Construct a temporary GDT in RAM with one entry:
0 - null
1 - R/W data segment, base = 0, limit = 4 GBytes

171

172

Load the GDTR to point to the temporary GDT

174

177

Load CR0 with PE flag set to switch to protected mode

179

181

Jump near to clear real mode instruction queue

184

186

Load DS, ES registers with GDT[1] descriptor, so both point to the entire physical memory space

188

195

Perform specific board initialization that is imposed by the new protected mode

196

218

Copy the application's GDT from ROM into RAM

220

238

Copy the application's IDT from ROM into RAM

241

243

Load application's GDTR

244

245

Load application's IDTR

247

261

Copy the application's TSS from ROM into RAM

263

267

Update TSS descriptor and other aliases in GDT (GDT alias or IDT alias)

277

277

Load the task register (without task switch) using LTR instruction

282

286

Load SS, ESP with the value found in the application's TSS

287

287

Push EFLAGS value found in the application's TSS

288

288

Push CS value found in the application's TSS

289

289

Push EIP value found in the application's TSS

290

293

Load DS, ES with the value found in the application's TSS

296

296

Perform IRET; pop the above values and enter the application code

9.10.1

Assembler Usage

In this example, the Intel assembler ASM386 and build tools BLD386 are used to assemble and build the initialization code module. The following assumptions are used when using the Intel ASM386 and BLD386 tools.

•

The ASM386 will generate the right operand size opcodes according to the code-segment attribute. The
attribute is assigned either by the ASM386 invocation controls or in the code-segment definition.

•

If a code segment that is going to run in real-address mode is defined, it must be set to a USE 16 attribute. If
a 32-bit operand is used in an instruction in this code segment (for example, MOV EAX, EBX), the assembler
automatically generates an operand prefix for the instruction that forces the processor to execute a 32-bit
operation, even though its default code-segment attribute is 16-bit.

•

Intel's ASM386 assembler allows specific use of the 16- or 32-bit instructions, for example, LGDTW, LGDTD,
IRETD. If the generic instruction LGDT is used, the default- segment attribute will be used to generate the right
opcode.

9.10.2

STARTUP.ASM Listing

Example 9-1 provides high-level sample code designed to move the processor into protected mode. This listing
does not include any opcode and offset information.

9-16 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

Example 9-1. STARTUP.ASM
MS-DOS* 5.0(045-N) 386(TM) MACRO ASSEMBLER STARTUP

09:44:51 08/19/92 PAGE 1

MS-DOS 5.0(045-N) 386(TM) MACRO ASSEMBLER V4.0, ASSEMBLY OF MODULE STARTUP
OBJECT MODULE PLACED IN startup.obj
ASSEMBLER INVOKED BY: f:\386tools\ASM386.EXE startup.a58 pw (132 )
LINE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45

SOURCE
NAME

STARTUP

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
;
ASSUMPTIONS:
;
;
1. The bottom 64K of memory is ram, and can be used for
;
scratch space by this module.
;
;
2. The system has sufficient free usable ram to copy the
;
initial GDT, IDT, and TSS
;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; configuration data - must match with build definition
CS_BASE

EQU

0FFFF0000H

; CS_BASE is the linear address of the segment STARTUP_CODE
; - this is specified in the build language file
RAM_START
;
;
;
;
;
;
;

EQU

400H

RAM_START is the start of free, usable ram in the linear
memory space.
The GDT, IDT, and initial TSS will be
copied above this space, and a small data segment will be
discarded at this linear address.
The 32-bit word at
RAM_START will contain the linear address of the first
free byte above the copied tables - this may be useful if
a memory manager is used.

TSS_INDEX

EQU

10

; TSS_INDEX is the index of the
; run after startup

TSS of the

first task to

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; ------------------------- STRUCTURES and EQU --------------; structures for system data
; TSS structure
TASK_STATE STRUC
link
DW ?
Vol. 3A 9-17

PROCESSOR MANAGEMENT AND INITIALIZATION

46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99

link_h
DW ?
ESP0
DD ?
SS0
DW ?
SS0_h
DW ?
ESP1
DD ?
SS1
DW ?
SS1_h
DW ?
ESP2
DD ?
SS2
DW ?
SS2_h
DW ?
CR3_reg DD ?
EIP_reg DD ?
EFLAGS_regDD ?
EAX_reg DD ?
ECX_reg DD ?
EDX_reg DD ?
EBX_reg DD ?
ESP_reg DD ?
EBP_reg DD ?
ESI_reg DD ?
EDI_reg DD ?
ES_reg
DW ?
ES_h
DW ?
CS_reg
DW ?
CS_h
DW ?
SS_reg
DW ?
SS_h
DW ?
DS_reg
DW ?
DS_h
DW ?
FS_reg
DW ?
FS_h
DW ?
GS_reg
DW ?
GS_h
DW ?
LDT_reg DW ?
LDT_h
DW ?
TRAP_reg DW ?
IO_map_baseDW ?
TASK_STATE ENDS
; basic structure of a descriptor
DESC
STRUC
lim_0_15 DW ?
bas_0_15 DW ?
bas_16_23 DB ?
access
DB ?
gran
DB ?
bas_24_31 DB ?
DESC
ENDS
; structure for use with LGDT and LIDT instructions
TABLE_REG
STRUC
table_lim DW ?
table_linearDD ?
TABLE_REG
ENDS

9-18 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153

; offset of GDT and IDT descriptors in builder generated GDT
GDT_DESC_OFF
EQU 1*SIZE(DESC)
IDT_DESC_OFF
EQU 2*SIZE(DESC)
; equates for building temporary GDT in RAM
LINEAR_SEL
EQU
1*SIZE (DESC)
LINEAR_PROTO_LO
EQU
00000FFFFH ; LINEAR_ALIAS
LINEAR_PROTO_HI
EQU
000CF9200H
; Protection Enable Bit in CR0
PE_BIT EQU 1B
; -----------------------------------------------------------; ------------------------- DATA SEGMENT---------------------; Initially, this data segment starts at linear 0, according
; to the processor’s power-up state.
STARTUP_DATA

SEGMENT RW

free_mem_linear_base
LABEL
DWORD
TEMP_GDT
LABEL
BYTE ; must be first in segment
TEMP_GDT_NULL_DESC
DESC
<>
TEMP_GDT_LINEAR_DESC DESC
<>
; scratch areas for LGDT and
TEMP_GDT_SCRATCH TABLE_REG
APP_GDT_RAM
TABLE_REG
APP_IDT_RAM
TABLE_REG
; align end_data
fill
DW
?

LIDT instructions
<>
<>
<>

; last thing in this segment - should be on a dword boundary
end_data
LABEL
BYTE
STARTUP_DATA
ENDS
; ------------------------------------------------------------

; ------------------------- CODE SEGMENT---------------------STARTUP_CODE SEGMENT ER PUBLIC USE16
; filled in by builder
PUBLIC GDT_EPROM
GDT_EPROM
TABLE_REG

<>

; filled in by builder
PUBLIC IDT_EPROM
IDT_EPROM
TABLE_REG

<>

; entry point into startup code - the bootstrap will vector
; here with a near JMP generated by the builder.
This
Vol. 3A 9-19

PROCESSOR MANAGEMENT AND INITIALIZATION

154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178

; label must be in the top 64K of linear memory.

179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206

; clear prefetch queue
JMP
CLEAR_LABEL
CLEAR_LABEL:

PUBLIC
STARTUP:

STARTUP

; DS,ES address the bottom 64K of flat linear memory
ASSUME DS:STARTUP_DATA, ES:STARTUP_DATA
; See Figure 9-4
; load GDTR with temporary GDT
LEA
EBX,TEMP_GDT ; build the TEMP_GDT in low ram,
MOV
DWORD PTR [EBX],0
; where we can address
MOV
DWORD PTR [EBX]+4,0
MOV
DWORD PTR [EBX]+8, LINEAR_PROTO_LO
MOV
DWORD PTR [EBX]+12, LINEAR_PROTO_HI
MOV
TEMP_GDT_scratch.table_linear,EBX
MOV
TEMP_GDT_scratch.table_lim,15
DB 66H; execute a 32 bit LGDT
LGDT
TEMP_GDT_scratch
; enter protected mode
MOV
EBX,CR0
OR
EBX,PE_BIT
MOV
CR0,EBX

; make DS and ES address 4G of linear memory
MOV
CX,LINEAR_SEL
MOV
DS,CX
MOV
ES,CX
; do board specific initialization
;
;
; ......
;

9-20 Vol. 3A

; See Figure 9-5
; copy EPROM GDT to ram at:
;
RAM_START + size (STARTUP_DATA)
MOV
EAX,RAM_START
ADD
EAX,OFFSET (end_data)
MOV
EBX,RAM_START
MOV
ECX, CS_BASE
ADD
ECX, OFFSET (GDT_EPROM)
MOV
ESI, [ECX].table_linear
MOV
EDI,EAX
MOVZX
ECX, [ECX].table_lim
MOV
APP_GDT_ram[EBX].table_lim,CX

PROCESSOR MANAGEMENT AND INITIALIZATION

207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260

INC
MOV
MOV
ADD
REP MOVS
; fixup
MOV
MOV
ROR
MOV
MOV

ECX
EDX,EAX
APP_GDT_ram[EBX].table_linear,EAX
EAX,ECX
BYTE PTR ES:[EDI],BYTE PTR DS:[ESI]
GDT base in descriptor
ECX,EDX
[EDX].bas_0_15+GDT_DESC_OFF,CX
ECX,16
[EDX].bas_16_23+GDT_DESC_OFF,CL
[EDX].bas_24_31+GDT_DESC_OFF,CH

; copy EPROM IDT to ram at:
; RAM_START+size(STARTUP_DATA)+SIZE (EPROM GDT)
MOV
ECX, CS_BASE
ADD
ECX, OFFSET (IDT_EPROM)
MOV
ESI, [ECX].table_linear
MOV
EDI,EAX
MOVZX
ECX, [ECX].table_lim
MOV
APP_IDT_ram[EBX].table_lim,CX
INC
ECX
MOV
APP_IDT_ram[EBX].table_linear,EAX
MOV
EBX,EAX
ADD
EAX,ECX
REP MOVS
BYTE PTR ES:[EDI],BYTE PTR DS:[ESI]

MOV
ROR
MOV
MOV

; fixup IDT pointer in GDT
[EDX].bas_0_15+IDT_DESC_OFF,BX
EBX,16
[EDX].bas_16_23+IDT_DESC_OFF,BL
[EDX].bas_24_31+IDT_DESC_OFF,BH

LIDT

; load GDTR and IDTR
EBX,RAM_START
DB
66H
; execute a 32 bit LGDT
APP_GDT_ram[EBX]
DB
66H
; execute a 32 bit LIDT
APP_IDT_ram[EBX]

MOV
MOV
MOV
MOV
MOV
MOV
ROL
MOV
MOV
LSL
INC
MOV
ADD

; move the TSS
EDI,EAX
EBX,TSS_INDEX*SIZE(DESC)
ECX,GDT_DESC_OFF ;build linear address for TSS
GS,CX
DH,GS:[EBX].bas_24_31
DL,GS:[EBX].bas_16_23
EDX,16
DX,GS:[EBX].bas_0_15
ESI,EDX
ECX,EBX
ECX
EDX,EAX
EAX,ECX

MOV
LGDT

Vol. 3A 9-21

PROCESSOR MANAGEMENT AND INITIALIZATION

261
REP MOVS
BYTE PTR ES:[EDI],BYTE PTR DS:[ESI]
262
263
; fixup TSS pointer
264
MOV
GS:[EBX].bas_0_15,DX
265
ROL
EDX,16
266
MOV
GS:[EBX].bas_24_31,DH
267
MOV
GS:[EBX].bas_16_23,DL
268
ROL
EDX,16
269
;save start of free ram at linear location RAMSTART
270
MOV
free_mem_linear_base+RAM_START,EAX
271
272
;assume no LDT used in the initial task - if necessary,
273
;code to move the LDT could be added, and should resemble
274
;that used to move the TSS
275
276
; load task register
277
LTR
BX
; No task switch, only descriptor loading
278
; See Figure 9-6
279
; load minimal set of registers necessary to simulate task
280
; switch
281
282
283
MOV
AX,[EDX].SS_reg
; start loading registers
284
MOV
EDI,[EDX].ESP_reg
285
MOV
SS,AX
286
MOV
ESP,EDI
; stack now valid
287
PUSH
DWORD PTR [EDX].EFLAGS_reg
288
PUSH
DWORD PTR [EDX].CS_reg
289
PUSH
DWORD PTR [EDX].EIP_reg
290
MOV
AX,[EDX].DS_reg
291
MOV
BX,[EDX].ES_reg
292
MOV
DS,AX
; DS and ES no longer linear memory
293
MOV
ES,BX
294
295
; simulate far jump to initial task
296
IRETD
297
298 STARTUP_CODE ENDS
*** WARNING #377 IN 298, (PASS 2) SEGMENT CONTAINS PRIVILEGED INSTRUCTION(S)
299
300 END STARTUP, DS:STARTUP_DATA, SS:STARTUP_DATA
301
302
ASSEMBLY COMPLETE,

9-22 Vol. 3A

1 WARNING,

NO ERRORS.

PROCESSOR MANAGEMENT AND INITIALIZATION

FFFF FFFFH

START: [CS.BASE+EIP]

FFFF 0000H

• Jump near start
• Construct TEMP_GDT
• LGDT
• Move to protected mode

DS, ES = GDT[1]

4 GB

Base
Limit
GDT [1]
GDT [0]

Base=0, Limit=4G
0

GDT_SCRATCH

TEMP_GDT

Figure 9-4. Constructing Temporary GDT and Switching to Protected Mode (Lines 162-172 of List File)

Vol. 3A 9-23

PROCESSOR MANAGEMENT AND INITIALIZATION

FFFF FFFFH

TSS
IDT
GDT

• Move the GDT, IDT, TSS
from ROM to RAM
• Fix Aliases
• LTR

TSS RAM
IDT RAM
GDT RAM

RAM_START

0

Figure 9-5. Moving the GDT, IDT, and TSS from ROM to RAM (Lines 196-261 of List File)

9-24 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

SS = TSS.SS
ESP = TSS.ESP
PUSH TSS.EFLAG
PUSH TSS.CS
PUSH TSS.EIP
ES = TSS.ES
DS = TSS.DS
IRET

•
•
EIP
EFLAGS
•
•
•
ESP
•
ES
CS
SS
DS

GDT

IDT Alias
GDT Alias
0

TSS RAM
IDT RAM
GDT RAM

RAM_START

Figure 9-6. Task Switching (Lines 282-296 of List File)

9.10.3

MAIN.ASM Source Code

The file MAIN.ASM shown in Example 9-2 defines the data and stack segments for this application and can be
substituted with the main module task written in a high-level language that is invoked by the IRET instruction
executed by STARTUP.ASM.
Example 9-2. MAIN.ASM
NAME
main_module
data
SEGMENT RW
dw 1000 dup(?)
DATA
ENDS
stack stackseg 800
CODE SEGMENT ER use32 PUBLIC
main_start:
nop
nop
nop
CODE ENDS
END main_start, ds:data, ss:stack

9.10.4

Supporting Files

The batch file shown in Example 9-3 can be used to assemble the source code files STARTUP.ASM and MAIN.ASM
and build the final application.

Vol. 3A 9-25

PROCESSOR MANAGEMENT AND INITIALIZATION

Example 9-3. Batch File to Assemble and Build the Application
ASM386 STARTUP.ASM
ASM386 MAIN.ASM
BLD386 STARTUP.OBJ, MAIN.OBJ buildfile(EPROM.BLD) bootstrap(STARTUP) Bootload
BLD386 performs several operations in this example:
It allocates physical memory location to segments and tables.
It generates tables using the build file and the input files.
It links object files and resolves references.
It generates a boot-loadable file to be programmed into the EPROM.
Example 9-4 shows the build file used as an input to BLD386 to perform the above functions.
Example 9-4. Build File
INIT_BLD_EXAMPLE;
SEGMENT
,
;

*SEGMENTS(DPL = 0)
startup.startup_code(BASE = 0FFFF0000H)

TASK
BOOT_TASK(OBJECT = startup, INITIAL,DPL = 0,
NOT INTENABLED)
PROTECTED_MODE_TASK(OBJECT = main_module,DPL = 0,
NOT INTENABLED)

,
;

TABLE
GDT (
LOCATION = GDT_EPROM
,
ENTRY = (
10:
PROTECTED_MODE_TASK
,
startup.startup_code
,
startup.startup_data
,
main_module.data
,
main_module.code
,
main_module.stack
)
),
IDT (
LOCATION = IDT_EPROM
);
MEMORY
(

,
,
,

RESERVE = (0..3FFFH
-- Area for the GDT, IDT, TSS copied from ROM
60000H..0FFFEFFFFH)
RANGE = (ROM_AREA = ROM (0FFFF0000H..0FFFFFFFFH))
-- Eprom size 64K
RANGE = (RAM_AREA = RAM (4000H..05FFFFH))

9-26 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

);
END
Table 9-6 shows the relationship of each build item with an ASM source file.

Table 9-6. Relationship Between BLD Item and ASM Source File
Item

ASM386 and Startup.A58

BLD386 Controls
and BLD file

Effect

Bootstrap

public startup
startup:

bootstrap
start(startup)

Near jump at 0FFFFFFF0H to
start.

GDT location

public GDT_EPROM
GDT_EPROM TABLE_REG <>

TABLE
GDT(location = GDT_EPROM)

The location of the GDT will be
programmed into the
GDT_EPROM location.

IDT location

public IDT_EPROM
IDT_EPROM TABLE_REG <>

TABLE
IDT(location = IDT_EPROM

The location of the IDT will be
programmed into the
IDT_EPROM location.

RAM start

RAM_START equ 400H

memory (reserve = (0..3FFFH))

RAM_START is used as the ram
destination for moving the
tables. It must be excluded from
the application's segment area.

Location of the
application TSS in
the GDT

TSS_INDEX EQU 10

TABLE GDT(
ENTRY = (10: PROTECTED_MODE_
TASK))

Put the descriptor of the
application TSS in GDT entry 10.

EPROM size and
location

size and location of the initialization
code

SEGMENT startup.code (base =
0FFFF0000H) ...memory (RANGE(
ROM_AREA = ROM(x..y))

Initialization code size must be
less than 64K and resides at
upper most 64K of the 4-GByte
memory space.

9.11

MICROCODE UPDATE FACILITIES

The P6 family and later processors have the capability to correct errata by loading an Intel-supplied data block into
the processor. The data block is called a microcode update. This section describes the mechanisms the BIOS needs
to provide in order to use this feature during system initialization. It also describes a specification that permits the
incorporation of future updates into a system BIOS.
Intel considers the release of a microcode update for a silicon revision to be the equivalent of a processor stepping
and completes a full-stepping level validation for releases of microcode updates.
A microcode update is used to correct errata in the processor. The BIOS, which has an update loader, is responsible
for loading the update on processors during system initialization (Figure 9-7). There are two steps to this process:
the first is to incorporate the necessary update data blocks into the BIOS; the second is to load update data blocks
into the processor.

Vol. 3A 9-27

PROCESSOR MANAGEMENT AND INITIALIZATION

Update
Loader

New Update

Update
Blocks

CPU

BIOS

Figure 9-7. Applying Microcode Updates

9.11.1

Microcode Update

A microcode update consists of an Intel-supplied binary that contains a descriptive header and data. No executable
code resides within the update. Each microcode update is tailored for a specific list of processor signatures. A
mismatch of the processor’s signature with the signature contained in the update will result in a failure to load. A
processor signature includes the extended family, extended model, type, family, model, and stepping of the
processor (starting with processor family 0fH, model 03H, a given microcode update may be associated with one of
multiple processor signatures; see Section 9.11.2 for details).
Microcode updates are composed of a multi-byte header, followed by encrypted data and then by an optional
extended signature table. Table 9-7 provides a definition of the fields; Table 9-8 shows the format of an update.
The header is 48 bytes. The first 4 bytes of the header contain the header version. The update header and its
reserved fields are interpreted by software based upon the header version. An encoding scheme guards against
tampering and provides a means for determining the authenticity of any given update. For microcode updates with
a data size field equal to 00000000H, the size of the microcode update is 2048 bytes. The first 48 bytes contain the
microcode update header. The remaining 2000 bytes contain encrypted data.
For microcode updates with a data size not equal to 00000000H, the total size field specifies the size of the microcode update. The first 48 bytes contain the microcode update header. The second part of the microcode update is
the encrypted data. The data size field of the microcode update header specifies the encrypted data size, its value
must be a multiple of the size of DWORD. The total size field of the microcode update header specifies the
encrypted data size plus the header size; its value must be in multiples of 1024 bytes (1 KBytes). The optional
extended signature table if implemented follows the encrypted data, and its size is calculated by (Total Size – (Data
Size + 48)).

NOTE
The optional extended signature table is supported starting with processor family 0FH, model 03H.
.

Table 9-7. Microcode Update Field Definitions
Field Name

Offset (bytes)

Length
(bytes)

Description

Header Version

0

4

Version number of the update header.

Update Revision

4

4

Unique version number for the update, the basis for the update
signature provided by the processor to indicate the current update
functioning within the processor. Used by the BIOS to authenticate
the update and verify that the processor loads successfully. The
value in this field cannot be used for processor stepping identification
alone. This is a signed 32-bit number.

Date

8

4

Date of the update creation in binary format: mmddyyyy (e.g.
07/18/98 is 07181998H).

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Table 9-7. Microcode Update Field Definitions (Contd.)
Field Name

Offset (bytes)

Length
(bytes)

Description

Processor Signature

12

4

Extended family, extended model, type, family, model, and stepping
of processor that requires this particular update revision (e.g.,
00000650H). Each microcode update is designed specifically for a
given extended family, extended model, type, family, model, and
stepping of the processor.
Software should use the processor signature field in conjunction with
the CPUID instruction to determine whether or not an update is
appropriate to load on a processor. The information encoded within
this field exactly corresponds to the bit representations returned by
the CPUID instruction.

Checksum

16

4

Checksum of Update Data and Header. Used to verify the integrity of
the update header and data. Checksum is correct when the
summation of all the DWORDs (including the extended Processor
Signature Table) that comprise the microcode update result in
00000000H.

Loader Revision

20

4

Version number of the loader program needed to correctly load this
update. The initial version is 00000001H.

Processor Flags

24

4

Platform type information is encoded in the lower 8 bits of this 4byte field. Each bit represents a particular platform type for a given
CPUID. Software should use the processor flags field in conjunction
with the platform Id bits in MSR (17H) to determine whether or not
an update is appropriate to load on a processor. Multiple bits may be
set representing support for multiple platform IDs.

Data Size

28

4

Specifies the size of the encrypted data in bytes, and must be a
multiple of DWORDs. If this value is 00000000H, then the microcode
update encrypted data is 2000 bytes (or 500 DWORDs).

Total Size

32

4

Specifies the total size of the microcode update in bytes. It is the
summation of the header size, the encrypted data size and the size of
the optional extended signature table. This value is always a multiple
of 1024.

Reserved

36

12

Reserved fields for future expansion.

Update Data

48

Data Size or
2000

Update data.

Extended Signature
Count

Data Size + 48

4

Specifies the number of extended signature structures (Processor
Signature[n], processor flags[n] and checksum[n]) that exist in this
microcode update.

Extended Checksum

Data Size + 52

4

Checksum of update extended processor signature table. Used to
verify the integrity of the extended processor signature table.
Checksum is correct when the summation of the DWORDs that
comprise the extended processor signature table results in
00000000H.

Reserved

Data Size + 56

12

Reserved fields.

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Table 9-7. Microcode Update Field Definitions (Contd.)
Field Name

Offset (bytes)

Length
(bytes)

Description

Processor Signature[n]

Data Size + 68 +
(n * 12)

4

Extended family, extended model, type, family, model, and stepping
of processor that requires this particular update revision (e.g.,
00000650H). Each microcode update is designed specifically for a
given extended family, extended model, type, family, model, and
stepping of the processor.
Software should use the processor signature field in conjunction with
the CPUID instruction to determine whether or not an update is
appropriate to load on a processor. The information encoded within
this field exactly corresponds to the bit representations returned by
the CPUID instruction.

Processor Flags[n]

Data Size + 72 +
(n * 12)

4

Platform type information is encoded in the lower 8 bits of this 4byte field. Each bit represents a particular platform type for a given
CPUID. Software should use the processor flags field in conjunction
with the platform Id bits in MSR (17H) to determine whether or not
an update is appropriate to load on a processor. Multiple bits may be
set representing support for multiple platform IDs.

Checksum[n]

Data Size + 76 +
(n * 12)

4

Used by utility software to decompose a microcode update into
multiple microcode updates where each of the new updates is
constructed without the optional Extended Processor Signature
Table.
To calculate the Checksum, substitute the Primary Processor
Signature entry and the Processor Flags entry with the
corresponding Extended Patch entry. Delete the Extended Processor
Signature Table entries. The Checksum is correct when the
summation of all DWORDs that comprise the created Extended
Processor Patch results in 00000000H.

Table 9-8. Microcode Update Format
31

24

16

8

0

Bytes

Header Version

0

Update Revision

4

Month: 8

Day: 8

Year: 16

8

Processor Signature (CPUID)

12
Stepping: 4

Model: 4

Family: 4

Type: 2

Reserved: 2

Extended
Mode: 4

Extended

Family: 8

Res: 4
Checksum

16

Loader Revision

20

Processor Flags

24
P0

P1

P2

P3

P4

P5

P6

P7

Reserved (24 bits)
Data Size

28

Total Size

32

Reserved (12 Bytes)

36

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Table 9-8. Microcode Update Format (Contd.)
31

24

16

8

0

Bytes

Update Data (Data Size bytes, or 2000 Bytes if Data Size = 00000000H)

48

Extended Signature Count ‘n’

Data Size +
48

Extended Processor Signature Table Checksum

Data Size +
52

Reserved (12 Bytes)

Data Size +
56

Processor Signature[n]

Data Size +
68 +
(n * 12)

Processor Flags[n]

Data Size +
72 +
(n * 12)

Checksum[n]

Data Size +
76 +
(n * 12)

9.11.2

Optional Extended Signature Table

The extended signature table is a structure that may be appended to the end of the encrypted data when the
encrypted data only supports a single processor signature (optional case). The extended signature table will always
be present when the encrypted data supports multiple processor steppings and/or models (required case).
The extended signature table consists of a 20-byte extended signature header structure, which contains the
extended signature count, the extended processor signature table checksum, and 12 reserved bytes (Table 9-9).
Following the extended signature header structure, the extended signature table contains 0-to-n extended
processor signature structures.
Each processor signature structure consist of the processor signature, processor flags, and a checksum
(Table 9-10).
The extended signature count in the extended signature header structure indicates the number of processor signature structures that exist in the extended signature table.
The extended processor signature table checksum is a checksum of all DWORDs that comprise the extended signature table. That includes the extended signature count, extended processor signature table checksum, 12 reserved
bytes and the n processor signature structures. A valid extended signature table exists when the result of a
DWORD checksum is 00000000H.

Table 9-9. Extended Processor Signature Table Header Structure
Extended Signature Count ‘n’
Extended Processor Signature Table Checksum
Reserved (12 Bytes)

Data Size + 48
Data Size + 52
Data Size + 56

Table 9-10. Processor Signature Structure
Processor Signature[n]
Processor Flags[n]
Checksum[n]

Data Size + 68 + (n * 12)
Data Size + 72 + (n * 12)
Data Size + 76 + (n * 12)

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9.11.3

Processor Identification

Each microcode update is designed to for a specific processor or set of processors. To determine the correct microcode update to load, software must ensure that one of the processor signatures embedded in the microcode update
matches the 32-bit processor signature returned by the CPUID instruction when executed by the target processor
with EAX = 1. Attempting to load a microcode update that does not match a processor signature embedded in the
microcode update with the processor signature returned by CPUID will cause the BIOS to reject the update.
Example 9-5 shows how to check for a valid processor signature match between the processor and microcode
update.
Example 9-5. Pseudo Code to Validate the Processor Signature
ProcessorSignature ← CPUID(1):EAX
If (Update.HeaderVersion = 00000001h)
{
// first check the ProcessorSignature field
If (ProcessorSignature = Update.ProcessorSignature)
Success
// if extended signature is present
Else If (Update.TotalSize > (Update.DataSize + 48))
{
//
// Assume the Data Size has been used to calculate the
// location of Update.ProcessorSignature[0].
//
For (N ← 0; ((N < Update.ExtendedSignatureCount) AND
(ProcessorSignature ≠ Update.ProcessorSignature[N])); N++);
// if the loops ended when the iteration count is
// less than the number of processor signatures in
// the table, we have a match
If (N < Update.ExtendedSignatureCount)
Success
Else
Fail
}
Else
Fail
Else
Fail

9.11.4

Platform Identification

In addition to verifying the processor signature, the intended processor platform type must be determined to properly target the microcode update. The intended processor platform type is determined by reading the
IA32_PLATFORM_ID register, (MSR 17H). This 64-bit register must be read using the RDMSR instruction.
The three platform ID bits, when read as a binary coded decimal (BCD) number, indicate the bit position in the
microcode update header’s processor flags field associated with the installed processor. The processor flags in the
48-byte header and the processor flags field associated with the extended processor signature structures may have
multiple bits set. Each set bit represents a different platform ID that the update supports.
Register Name:
MSR Address:

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PROCESSOR MANAGEMENT AND INITIALIZATION

Access:

Read Only

IA32_PLATFORM_ID is a 64-bit register accessed only when referenced as a Qword through a RDMSR instruction.

Table 9-11. Processor Flags
Bit
63:53
52:50

Descriptions
Reserved
Platform Id Bits (RO). The field gives information concerning the intended platform for the processor. See also Table 9-8.
52
0
0
0
0
1
1
1
1

49:0

51
0
0
1
1
0
0
1
1

50
0
1
0
1
0
1
0
1

Processor Flag 0
Processor Flag 1
Processor Flag 2
Processor Flag 3
Processor Flag 4
Processor Flag 5
Processor Flag 6
Processor Flag 7

Reserved

To validate the platform information, software may implement an algorithm similar to the algorithms in
Example 9-6.
Example 9-6. Pseudo Code Example of Processor Flags Test
Flag ← 1 << IA32_PLATFORM_ID[52:50]
If (Update.HeaderVersion = 00000001h)
{
If (Update.ProcessorFlags & Flag)
{
Load Update
}
Else
{
//
// Assume the Data Size has been used to calculate the
// location of Update.ProcessorSignature[N] and a match
// on Update.ProcessorSignature[N] has already succeeded
//
If (Update.ProcessorFlags[n] & Flag)
{
Load Update
}
}
}

9.11.5

Microcode Update Checksum

Each microcode update contains a DWORD checksum located in the update header. It is software’s responsibility to
ensure that a microcode update is not corrupt. To check for a corrupt microcode update, software must perform a
unsigned DWORD (32-bit) checksum of the microcode update. Even though some fields are signed, the checksum
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procedure treats all DWORDs as unsigned. Microcode updates with a header version equal to 00000001H must sum
all DWORDs that comprise the microcode update. A valid checksum check will yield a value of 00000000H. Any
other value indicates the microcode update is corrupt and should not be loaded.
The checksum algorithm shown by the pseudo code in Example 9-7 treats the microcode update as an array of
unsigned DWORDs. If the data size DWORD field at byte offset 32 equals 00000000H, the size of the encrypted
data is 2000 bytes, resulting in 500 DWORDs. Otherwise the microcode update size in DWORDs = (Total Size / 4),
where the total size is a multiple of 1024 bytes (1 KBytes).
Example 9-7. Pseudo Code Example of Checksum Test
N ← 512
If (Update.DataSize ≠ 00000000H)
N ← Update.TotalSize / 4
ChkSum ← 0
For (I ← 0; I < N; I++)
{
ChkSum ← ChkSum + MicrocodeUpdate[I]
}
If (ChkSum = 00000000H)
Success
Else
Fail

9.11.6

Microcode Update Loader

This section describes an update loader used to load an update into a P6 family or later processors. It also discusses
the requirements placed on the BIOS to ensure proper loading. The update loader described contains the minimal
instructions needed to load an update. The specific instruction sequence that is required to load an update is
dependent upon the loader revision field contained within the update header. This revision is expected to change
infrequently (potentially, only when new processor models are introduced).
Example 9-8 below represents the update loader with a loader revision of 00000001H. Note that the microcode
update must be aligned on a 16-byte boundary and the size of the microcode update must be 1-KByte granular.
Example 9-8. Assembly Code Example of Simple Microcode Update Loader
mov ecx,79h
xor eax,eax
xor ebx,ebx
mov ax,cs
shl eax,4
mov bx,offset Update
add eax,ebx
add eax,48d
xor edx,edx
WRMSR

;
;
;
;

MSR to write in ECX
clear EAX
clear EBX
Segment of microcode update

; Offset of microcode update
; Linear Address of Update in EAX
; Offset of the Update Data within the Update
; Zero in EDX
; microcode update trigger

The loader shown in Example 9-8 assumes that update is the address of a microcode update (header and data)
embedded within the code segment of the BIOS. It also assumes that the processor is operating in real mode. The
data may reside anywhere in memory, aligned on a 16-byte boundary, that is accessible by the processor within its
current operating mode.
Before the BIOS executes the microcode update trigger (WRMSR) instruction, the following must be true:

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•

In 64-bit mode, EAX contains the lower 32-bits of the microcode update linear address. In protected mode, EAX
contains the full 32-bit linear address of the microcode update.

•

In 64-bit mode, EDX contains the upper 32-bits of the microcode update linear address. In protected mode,
EDX equals zero.

•

ECX contains 79H (address of IA32_BIOS_UPDT_TRIG).

Other requirements are:

•
•
•

The addresses for the microcode update data must be in canonical form.
If paging is enabled, the microcode update data must map that data as present.
The microcode update data must start at a 16-byte aligned linear address.

9.11.6.1

Hard Resets in Update Loading

The effects of a loaded update are cleared from the processor upon a hard reset. Therefore, each time a hard reset
is asserted during the BIOS POST, the update must be reloaded on all processors that observed the reset. The
effects of a loaded update are, however, maintained across a processor INIT. There are no side effects caused by
loading an update into a processor multiple times.

9.11.6.2

Update in a Multiprocessor System

A multiprocessor (MP) system requires loading each processor with update data appropriate for its CPUID and platform ID bits. The BIOS is responsible for ensuring that this requirement is met and that the loader is located in a
module executed by all processors in the system. If a system design permits multiple steppings of Pentium 4, Intel
Xeon, and P6 family processors to exist concurrently; then the BIOS must verify individual processors against the
update header information to ensure appropriate loading. Given these considerations, it is most practical to load
the update during MP initialization.

9.11.6.3

Update in a System Supporting Intel Hyper-Threading Technology

Intel Hyper-Threading Technology has implications on the loading of the microcode update. The update must be
loaded for each core in a physical processor. Thus, for a processor supporting Intel Hyper-Threading Technology,
only one logical processor per core is required to load the microcode update. Each individual logical processor can
independently load the update. However, MP initialization must provide some mechanism (e.g. a software semaphore) to force serialization of microcode update loads and to prevent simultaneous load attempts to the same
core.

9.11.6.4

Update in a System Supporting Dual-Core Technology

Dual-core technology has implications on the loading of the microcode update. The microcode update facility is not
shared between processor cores in the same physical package. The update must be loaded for each core in a physical processor.
If processor core supports Intel Hyper-Threading Technology, the guideline described in Section 9.11.6.3 also
applies.

9.11.6.5

Update Loader Enhancements

The update loader presented in Section 9.11.6, “Microcode Update Loader,” is a minimal implementation that can
be enhanced to provide additional functionality. Potential enhancements are described below:

•

BIOS can incorporate multiple updates to support multiple steppings of the Pentium 4, Intel Xeon, and P6
family processors. This feature provides for operating in a mixed stepping environment on an MP system and
enables a user to upgrade to a later version of the processor. In this case, modify the loader to check the CPUID
and platform ID bits of the processor that it is running on against the available headers before loading a
particular update. The number of updates is only limited by available BIOS space.

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•

A loader can load the update and test the processor to determine if the update was loaded correctly. See
Section 9.11.7, “Update Signature and Verification.”

•

A loader can verify the integrity of the update data by performing a checksum on the double words of the
update summing to zero. See Section 9.11.5, “Microcode Update Checksum.”

•

A loader can provide power-on messages indicating successful loading of an update.

9.11.7

Update Signature and Verification

The P6 family and later processors provide capabilities to verify the authenticity of a particular update and to identify the current update revision. This section describes the model-specific extensions of processors that support
this feature. The update verification method below assumes that the BIOS will only verify an update that is more
recent than the revision currently loaded in the processor.
CPUID returns a value in a model specific register in addition to its usual register return values. The semantics of
CPUID cause it to deposit an update ID value in the 64-bit model-specific register at address 08BH
(IA32_BIOS_SIGN_ID). If no update is present in the processor, the value in the MSR remains unmodified. The
BIOS must pre-load a zero into the MSR before executing CPUID. If a read of the MSR at 8BH still returns zero after
executing CPUID, this indicates that no update is present.
The update ID value returned in the EDX register after RDMSR executes indicates the revision of the update loaded
in the processor. This value, in combination with the CPUID value returned in the EAX register, uniquely identifies a
particular update. The signature ID can be directly compared with the update revision field in a microcode update
header for verification of a correct load. No consecutive updates released for a given stepping of a processor may
share the same signature. The processor signature returned by CPUID differentiates updates for different steppings.

9.11.7.1

Determining the Signature

An update that is successfully loaded into the processor provides a signature that matches the update revision of
the currently functioning revision. This signature is available any time after the actual update has been loaded.
Requesting the signature does not have a negative impact upon a loaded update.
The procedure for determining this signature shown in Example 9-9.
Example 9-9. Assembly Code to Retrieve the Update Revision
MOV
XOR
XOR
WRMSR
MOV
cpuid
MOV
rdmsr

ECX, 08BH
EAX, EAX
EDX, EDX

;IA32_BIOS_SIGN_ID
;clear EAX
;clear EDX
;Load 0 to MSR at 8BH

EAX, 1
ECX, 08BH

;IA32_BIOS_SIGN_ID
;Read Model Specific Register

If there is an update active in the processor, its revision is returned in the EDX register after the RDMSR instruction
executes.
IA32_BIOS_SIGN_ID
MSR Address:
Default Value:
Access:

Microcode Update Signature Register
08BH Accessed as a Qword
XXXX XXXX XXXX XXXXh
Read/Write

The IA32_BIOS_SIGN_ID register is used to report the microcode update signature when CPUID executes. The
signature is returned in the upper DWORD (Table 9-12).

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Table 9-12. Microcode Update Signature
Bit

Description

63:32

Microcode update signature. This field contains the signature of the currently loaded microcode update when read following
the execution of the CPUID instruction, function 1. It is required that this register field be pre-loaded with zero prior to
executing the CPUID, function 1. If the field remains equal to zero, then there is no microcode update loaded. Another nonzero value will be the signature.

31:0

Reserved.

9.11.7.2

Authenticating the Update

An update may be authenticated by the BIOS using the signature primitive, described above, and the algorithm in
Example 9-10.
Example 9-10. Pseudo Code to Authenticate the Update
Z ← Obtain Update Revision from the Update Header to be authenticated;
X ← Obtain Current Update Signature from MSR 8BH;
If (Z > X)
{
Load Update that is to be authenticated;
Y ← Obtain New Signature from MSR 8BH;
If (Z = Y)
Success
Else
Fail
}
Else
Fail
Example 9-10 requires that the BIOS only authenticate updates that contain a numerically larger revision than the
currently loaded revision, where Current Signature (X) < New Update Revision (Z). A processor with no loaded
update is considered to have a revision equal to zero.
This authentication procedure relies upon the decoding provided by the processor to verify an update from a potentially hostile source. As an example, this mechanism in conjunction with other safeguards provides security for
dynamically incorporating field updates into the BIOS.

9.11.8

Optional Processor Microcode Update Specifications

This section an interface that an OEM-BIOS may provide to its client system software to manage processor microcode updates. System software may choose to build its own facility to manage microcode updates (e.g. similar to
the facility described in Section 9.11.6) or rely on a facility provided by the BIOS to perform microcode updates.
Sections 9.11.8.1-9.11.8.9 describes an extension (Function 0D042H) to the real mode INT 15H service. INT 15H
0D042H function is one of several alternatives that a BIOS may choose to implement microcode update facility and
offer to its client application (e.g. an OS). Other alternative microcode update facility that BIOS can choose are
dependent on platform-specific capabilities, including the Capsule Update mechanism from the UEFI specification
(www.uefi.org). In this discussion, the application is referred to as the calling program or caller.
The real mode INT15 call specification described here is an Intel extension to an OEM BIOS. This extension allows
an application to read and modify the contents of the microcode update data in NVRAM. The update loader, which
is part of the system BIOS, cannot be updated by the interface. All of the functions defined in the specification must
be implemented for a system to be considered compliant with the specification. The INT15 functions are accessible
only from real mode.

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9.11.8.1

Responsibilities of the BIOS

If a BIOS passes the presence test (INT 15H, AX = 0D042H, BL = 0H), it must implement all of the sub-functions
defined in the INT 15H, AX = 0D042H specification. There are no optional functions. BIOS must load the appropriate
update for each processor during system initialization.
A Header Version of an update block containing the value 0FFFFFFFFH indicates that the update block is unused and
available for storing a new update.
The BIOS is responsible for providing a region of non-volatile storage (NVRAM) for each potential processor stepping within a system. This storage unit consists of one or more update blocks. An update block is a contiguous
2048-byte block of memory. The BIOS for a single processor system need only provide update blocks to store one
microcode update. If the BIOS for a multiple processor system is intended to support mixed processor steppings,
then the BIOS needs to provide enough update blocks to store each unique microcode update or for each processor
socket on the OEM’s system board.
The BIOS is responsible for managing the NVRAM update blocks. This includes garbage collection, such as
removing microcode updates that exist in NVRAM for which a corresponding processor does not exist in the system.
This specification only provides the mechanism for ensuring security, the uniqueness of an entry, and that stale
entries are not loaded. The actual update block management is implementation specific on a per-BIOS basis.
As an example, the BIOS may use update blocks sequentially in ascending order with CPU signatures sorted versus
the first available block. In addition, garbage collection may be implemented as a setup option to clear all NVRAM
slots or as BIOS code that searches and eliminates unused entries during boot.

NOTES
For IA-32 processors starting with family 0FH and model 03H and Intel 64 processors, the
microcode update may be as large as 16 KBytes. Thus, BIOS must allocate 8 update blocks for each
microcode update. In a MP system, a common microcode update may be sufficient for each socket
in the system.
For IA-32 processors earlier than family 0FH and model 03H, the microcode update is 2 KBytes. An
MP-capable BIOS that supports multiple steppings must allocate a block for each socket in the
system.
A single-processor BIOS that supports variable-sized microcode update and fixed-sized microcode
update must allocate one 16-KByte region and a second region of at least 2 KBytes.
The following algorithm (Example 9-11) describes the steps performed during BIOS initialization used to load the
updates into the processor(s). The algorithm assumes:

•

The BIOS ensures that no update contained within NVRAM has a header version or loader version that does not
match one currently supported by the BIOS.

•
•
•

The update contains a correct checksum.
The BIOS ensures that (at most) one update exists for each processor stepping.
Older update revisions are not allowed to overwrite more recent ones.

These requirements are checked by the BIOS during the execution of the write update function of this interface.
The BIOS sequentially scans through all of the update blocks in NVRAM starting with index 0. The BIOS scans until
it finds an update where the processor fields in the header match the processor signature (extended family,
extended model, type, family, model, and stepping) as well as the platform bits of the current processor.
Example 9-11. Pseudo Code, Checks Required Prior to Loading an Update
For each processor in the system
{
Determine the Processor Signature via CPUID function 1;
Determine the Platform Bits ← 1 << IA32_PLATFORM_ID[52:50];
For (I ← UpdateBlock 0, I < NumOfBlocks; I++)
{
If (Update.Header_Version = 00000001H)
{
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If ((Update.ProcessorSignature = Processor Signature) &&
(Update.ProcessorFlags & Platform Bits))
{
Load Update.UpdateData into the Processor;
Verify update was correctly loaded into the processor
Go on to next processor
Break;
}
Else If (Update.TotalSize > (Update.DataSize + 48))
{
N ← 0
While (N < Update.ExtendedSignatureCount)
{
If ((Update.ProcessorSignature[N] =
Processor Signature) &&
(Update.ProcessorFlags[N] & Platform Bits))
{
Load Update.UpdateData into the Processor;
Verify update correctly loaded into the processor
Go on to next processor
Break;
}
N ← N + 1
}
I ← I + (Update.TotalSize / 2048)
If ((Update.TotalSize MOD 2048) = 0)
I ← I + 1
}
}
}
}

NOTES
The platform Id bits in IA32_PLATFORM_ID are encoded as a three-bit binary coded decimal field.
The platform bits in the microcode update header are individually bit encoded. The algorithm must
do a translation from one format to the other prior to doing a check.
When performing the INT 15H, 0D042H functions, the BIOS must assume that the caller has no knowledge of platform specific requirements. It is the responsibility of BIOS calls to manage all chipset and platform specific prerequisites for managing the NVRAM device. When writing the update data using the Write Update sub-function, the
BIOS must maintain implementation specific data requirements (such as the update of NVRAM checksum). The
BIOS should also attempt to verify the success of write operations on the storage device used to record the update.

9.11.8.2

Responsibilities of the Calling Program

This section of the document lists the responsibilities of a calling program using the interface specifications to load
microcode update(s) into BIOS NVRAM.

•

The calling program should call the INT 15H, 0D042H functions from a pure real mode program and should be
executing on a system that is running in pure real mode.

•

The caller should issue the presence test function (sub function 0) and verify the signature and return codes of
that function.

•

It is important that the calling program provides the required scratch RAM buffers for the BIOS and the proper
stack size as specified in the interface definition.

•

The calling program should read any update data that already exists in the BIOS in order to make decisions
about the appropriateness of loading the update. The BIOS must refuse to overwrite a newer update with an

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PROCESSOR MANAGEMENT AND INITIALIZATION

older version. The update header contains information about version and processor specifics for the calling
program to make an intelligent decision about loading.

•

There can be no ambiguous updates. The BIOS must refuse to allow multiple updates for the same CPU to exist
at the same time; it also must refuse to load updates for processors that don’t exist on the system.

•

The calling application should implement a verify function that is run after the update write function successfully completes. This function reads back the update and verifies that the BIOS returned an image identical to
the one that was written.

Example 9-12 represents a calling program.
Example 9-12. INT 15 DO42 Calling Program Pseudo-code
//
// We must be in real mode
//
If the system is not in Real mode exit
//
// Detect presence of Genuine Intel processor(s) that can be updated
// using(CPUID)
//
If no Intel processors exist that can be updated exit
//
// Detect the presence of the Intel microcode update extensions
//
If the BIOS fails the PresenceTestexit
//
// If the APIC is enabled, see if any other processors are out there
//
Read IA32_APICBASE
If APIC enabled
{
Send Broadcast Message to all processors except self via APIC
Have all processors execute CPUID, record the Processor Signature
(i.e.,Extended Family, Extended Model, Type, Family, Model, Stepping)
Have all processors read IA32_PLATFORM_ID[52:50], record Platform
Id Bits
If current processor cannot be updated
exit
}
//
// Determine the number of unique update blocks needed for this system
//
NumBlocks = 0
For each processor
{
If ((this is a unique processor stepping) AND
(we have a unique update in the database for this processor))
{
Checksum the update from the database;
If Checksum fails
exit
NumBlocks ← NumBlocks + size of microcode update / 2048
}
}
//
// Do we have enough update slots for all CPUs?
//
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PROCESSOR MANAGEMENT AND INITIALIZATION

If there are more blocks required to support the unique processor steppings than update blocks
provided by the BIOS exit
//
// Do we need any update blocks at all? If not, we are done
//
If (NumBlocks = 0)
exit
//
// Record updates for processors in NVRAM.
//
For (I=0; I ISRV[7:4])
THEN
APR[7:0] ← TPR[7:0]
ELSE
APR[7:4] ← max(TPR[7:4] AND ISRV[7:4], IRRV[7:4])
APR[3:0] ← 0.

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

Here, the TPR value is the task priority value in the TPR (see Figure 10-18), the IRRV value is the vector number
for the highest priority bit that is set in the IRR (see Figure 10-20) or 00H (if no IRR bit is set), and the ISRV value
is the vector number for the highest priority bit that is set in the ISR (see Figure 10-20). Following arbitration
among the destination processors, the processor with the lowest value in its APR handles the IPI and the other
processors ignore it.
(P6 family and Pentium processors.) For these processors, if a focus processor exists, it may accept the interrupt,
regardless of its priority. A processor is said to be the focus of an interrupt if it is currently servicing that interrupt
or if it has a pending request for that interrupt. For Intel Xeon processors, the concept of a focus processor is not
supported.
In operating systems that use the lowest priority delivery mode but do not update the TPR, the TPR information
saved in the chipset will potentially cause the interrupt to be always delivered to the same processor from the
logical set. This behavior is functionally backward compatible with the P6 family processor but may result in unexpected performance implications.

10.6.3

IPI Delivery and Acceptance

When the low double-word of the ICR is written to, the local APIC creates an IPI message from the information
contained in the ICR and sends the message out on the system bus (Pentium 4 and Intel Xeon processors) or the
APIC bus (P6 family and Pentium processors). The manner in which these IPIs are handled after being issues in
described in Section 10.8, “Handling Interrupts.”

10.7

SYSTEM AND APIC BUS ARBITRATION

When several local APICs and the I/O APIC are sending IPI and interrupt messages on the system bus (or APIC
bus), the order in which the messages are sent and handled is determined through bus arbitration.
For the Pentium 4 and Intel Xeon processors, the local and I/O APICs use the arbitration mechanism defined for the
system bus to determine the order in which IPIs are handled. This mechanism is non-architectural and cannot be
controlled by software.
For the P6 family and Pentium processors, the local and I/O APICs use an APIC-based arbitration mechanism to
determine the order in which IPIs are handled. Here, each local APIC is given an arbitration priority of from 0 to 15,
which the I/O APIC uses during arbitration to determine which local APIC should be given access to the APIC bus.
The local APIC with the highest arbitration priority always wins bus access. Upon completion of an arbitration
round, the winning local APIC lowers its arbitration priority to 0 and the losing local APICs each raise theirs by 1.
The current arbitration priority for a local APIC is stored in a 4-bit, software-transparent arbitration ID (Arb ID)
register. During reset, this register is initialized to the APIC ID number (stored in the local APIC ID register). The
INIT level-deassert IPI, which is issued with and ICR command, can be used to resynchronize the arbitration priorities of the local APICs by resetting Arb ID register of each agent to its current APIC ID value. (The Pentium 4 and
Intel Xeon processors do not implement the Arb ID register.)
Section 10.10, “APIC Bus Message Passing Mechanism and Protocol (P6 Family, Pentium Processors),” describes the
APIC bus arbitration protocols and bus message formats, while Section 10.6.1, “Interrupt Command Register
(ICR),” describes the INIT level de-assert IPI message.
Note that except for the SIPI IPI (see Section 10.6.1, “Interrupt Command Register (ICR)”), all bus messages that
fail to be delivered to their specified destination or destinations are automatically retried. Software should avoid
situations in which IPIs are sent to disabled or nonexistent local APICs, causing the messages to be resent repeatedly. Additionally, interrupt sources that target the APIC should be masked or changed to no longer target the APIC.

10.8

HANDLING INTERRUPTS

When a local APIC receives an interrupt from a local source, an interrupt message from an I/O APIC, or an IPI, the
manner in which it handles the message depends on processor implementation, as described in the following
sections.

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10.8.1

Interrupt Handling with the Pentium 4 and Intel Xeon Processors

With the Pentium 4 and Intel Xeon processors, the local APIC handles the local interrupts, interrupt messages, and
IPIs it receives as follows:
1. It determines if it is the specified destination or not (see Figure 10-16). If it is the specified destination, it
accepts the message; if it is not, it discards the message.

Wait to Receive
Bus Message

Discard
Message

No

Belong to
Destination?

Yes

Accept
Message

Figure 10-16. Interrupt Acceptance Flow Chart for the Local APIC (Pentium 4 and Intel Xeon Processors)
2. If the local APIC determines that it is the designated destination for the interrupt and if the interrupt request is
an NMI, SMI, INIT, ExtINT, or SIPI, the interrupt is sent directly to the processor core for handling.
3. If the local APIC determines that it is the designated destination for the interrupt but the interrupt request is
not one of the interrupts given in step 2, the local APIC sets the appropriate bit in the IRR.
4. When interrupts are pending in the IRR register, the local APIC dispatches them to the processor one at a time,
based on their priority and the current processor priority in the PPR (see Section 10.8.3.1, “Task and Processor
Priorities”).
5. When a fixed interrupt has been dispatched to the processor core for handling, the completion of the handler
routine is indicated with an instruction in the instruction handler code that writes to the end-of-interrupt (EOI)
register in the local APIC (see Section 10.8.5, “Signaling Interrupt Servicing Completion”). The act of writing to
the EOI register causes the local APIC to delete the interrupt from its ISR queue and (for level-triggered
interrupts) send a message on the bus indicating that the interrupt handling has been completed. (A write to
the EOI register must not be included in the handler routine for an NMI, SMI, INIT, ExtINT, or SIPI.)

10.8.2

Interrupt Handling with the P6 Family and Pentium Processors

With the P6 family and Pentium processors, the local APIC handles the local interrupts, interrupt messages, and
IPIs it receives as follows (see Figure 10-17).
1. (IPIs only) The local APIC examines the IPI message to determines if it is the specified destination for the IPI
as described in Section 10.6.2, “Determining IPI Destination.” If it is the specified destination, it continues its
acceptance procedure; if it is not the destination, it discards the IPI message. When the message specifies
lowest-priority delivery mode, the local APIC will arbitrate with the other processors that were designated as
recipients of the IPI message (see Section 10.6.2.4, “Lowest Priority Delivery Mode”).
2. If the local APIC determines that it is the designated destination for the interrupt and if the interrupt request is
an NMI, SMI, INIT, ExtINT, or INIT-deassert interrupt, or one of the MP protocol IPI messages (BIPI, FIPI, and
SIPI), the interrupt is sent directly to the processor core for handling.
3. If the local APIC determines that it is the designated destination for the interrupt but the interrupt request is
not one of the interrupts given in step 2, the local APIC looks for an open slot in one of its two pending interrupt
queues contained in the IRR and ISR registers (see Figure 10-20). If a slot is available (see Section 10.8.4,
“Interrupt Acceptance for Fixed Interrupts”), places the interrupt in the slot. If a slot is not available, it rejects
the interrupt request and sends it back to the sender with a retry message.
4. When interrupts are pending in the IRR register, the local APIC dispatches them to the processor one at a time,
based on their priority and the current processor priority in the PPR (see Section 10.8.3.1, “Task and Processor
Priorities”).
5. When a fixed interrupt has been dispatched to the processor core for handling, the completion of the handler
routine is indicated with an instruction in the instruction handler code that writes to the end-of-interrupt (EOI)
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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

Wait to Receive
Bus Message

No

Discard
Message

Belong
to
Destination?
Yes
Is it
NMI/SMI/INIT
/ExtINT?

Yes

Accept
Message

No
Fixed

Delivery

Lowest
Priority
P6 Family
Processor Specific

No

Set Status
to Retry

Am I
Focus?

Is Interrupt Slot
Available?
Yes

Yes

Is Status a
Retry?

Yes

Accept
Message

Yes

Discard
Message

No
No

Other
Focus?

No

Set Status
to Retry

No

Accept
Message
Is Interrupt
Slot Available?

Yes

No

Arbitrate

Am I Winner?

Yes

Accept
Message

Figure 10-17. Interrupt Acceptance Flow Chart for the Local APIC (P6 Family and Pentium Processors)
register in the local APIC (see Section 10.8.5, “Signaling Interrupt Servicing Completion”). The act of writing to
the EOI register causes the local APIC to delete the interrupt from its queue and (for level-triggered interrupts)
send a message on the bus indicating that the interrupt handling has been completed. (A write to the EOI
register must not be included in the handler routine for an NMI, SMI, INIT, ExtINT, or SIPI.)
The following sections describe the acceptance of interrupts and their handling by the local APIC and processor in
greater detail.

10.8.3

Interrupt, Task, and Processor Priority

Each interrupt delivered to the processor through the local APIC has a priority based on its vector number. The local
APIC uses this priority to determine when to service the interrupt relative to the other activities of the processor,
including the servicing of other interrupts.
Each interrupt vector is an 8-bit value. The interrupt-priority class is the value of bits 7:4 of the interrupt vector.
The lowest interrupt-priority class is 1 and the highest is 15; interrupts with vectors in the range 0–15 (with interrupt-priority class 0) are illegal and are never delivered. Because vectors 0–31 are reserved for dedicated uses by
the Intel 64 and IA-32 architectures, software should configure interrupt vectors to use interrupt-priority classes in
the range 2–15.
Each interrupt-priority class encompasses 16 vectors. The relative priority of interrupts within an interrupt-priority
class is determined by the value of bits 3:0 of the vector number. The higher the value of those bits, the higher the

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

priority within that interrupt-priority class. Thus, each interrupt vector comprises two parts, with the high 4 bits
indicating its interrupt-priority class and the low 4 bits indicating its ranking within the interrupt-priority class.

10.8.3.1

Task and Processor Priorities

The local APIC also defines a task priority and a processor priority that determine the order in which interrupts
are handled. The task-priority class is the value of bits 7:4 of the task-priority register (TPR), which can be
written by software (TPR is a read/write register); see Figure 10-18.
31

8 7

4 3

0

Reserved

Address: FEE0 0080H
Value after reset: 0H

Task-Priority Class
Task-Priority Sub-Class

Figure 10-18. Task-Priority Register (TPR)

NOTE
In this discussion, the term “task” refers to a software defined task, process, thread, program, or
routine that is dispatched to run on the processor by the operating system. It does not refer to an
IA-32 architecture defined task as described in Chapter 7, “Task Management.”
The task priority allows software to set a priority threshold for interrupting the processor. This mechanism enables
the operating system to temporarily block low priority interrupts from disturbing high-priority work that the
processor is doing. The ability to block such interrupts using task priority results from the way that the TPR controls
the value of the processor-priority register (PPR).7
The processor-priority class is a value in the range 0–15 that is maintained in bits 7:4 of the processor-priority
register (PPR); see Figure 10-19. The PPR is a read-only register. The processor-priority class represents the
current priority at which the processor is executing.
31

8 7

4 3

0

Reserved

Address: FEE0 00A0H
Value after reset: 0H

Processor-Priority Class
Processor-Priority Sub-Class

Figure 10-19. Processor-Priority Register (PPR)
The value of the PPR is based on the value of TPR and the value ISRV; ISRV is the vector number of the highest
priority bit that is set in the ISR or 00H if no bit is set in the ISR. (See Section 10.8.4 for more details on the ISR.)
The value of PPR is determined as follows:

•

PPR[7:4] (the processor-priority class) the maximum of TPR[7:4] (the task- priority class) and ISRV[7:4] (the
priority of the highest priority interrupt in service).

•

PPR[3:0] (the processor-priority sub-class) is determined as follows:
— If TPR[7:4] > ISRV[7:4], PPR[3:0] is TPR[3:0] (the task-priority sub-class).
— If TPR[7:4] < ISRV[7:4], PPR[3:0] is 0.
— If TPR[7:4] = ISRV[7:4], PPR[3:0] may be either TPR[3:0] or 0. The actual behavior is model-specific.

7. The TPR also determines the arbitration priority of the local processor; see Section 10.6.2.4, “Lowest Priority Delivery Mode.”
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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

The processor-priority class determines the priority threshold for interrupting the processor. The processor will
deliver only those interrupts that have an interrupt-priority class higher than the processor-priority class in the
PPR. If the processor-priority class is 0, the PPR does not inhibit the delivery any interrupt; if it is 15, the processor
inhibits the delivery of all interrupts. (The processor-priority mechanism does not affect the delivery of interrupts
with the NMI, SMI, INIT, ExtINT, INIT-deassert, and start-up delivery modes.)
The processor does not use the processor-priority sub-class to determine which interrupts to delivery and which to
inhibit. (The processor uses the processor-priority sub-class only to satisfy reads of the PPR.)

10.8.4

Interrupt Acceptance for Fixed Interrupts

The local APIC queues the fixed interrupts that it accepts in one of two interrupt pending registers: the interrupt
request register (IRR) or in-service register (ISR). These two 256-bit read-only registers are shown in
Figure 10-20. The 256 bits in these registers represent the 256 possible vectors; vectors 0 through 15 are reserved
by the APIC (see also: Section 10.5.2, “Valid Interrupt Vectors”).

NOTE
All interrupts with an NMI, SMI, INIT, ExtINT, start-up, or INIT-deassert delivery mode bypass the
IRR and ISR registers and are sent directly to the processor core for servicing.

255

16 15

0

Reserved

IRR

Reserved

ISR

Reserved

TMR

Addresses: IRR FEE0 0200H - FEE0 0270H
ISR FEE0 0100H - FEE0 0170H
TMR FEE0 0180H - FEE0 01F0H
Value after reset: 0H

Figure 10-20. IRR, ISR and TMR Registers
The IRR contains the active interrupt requests that have been accepted, but not yet dispatched to the processor for
servicing. When the local APIC accepts an interrupt, it sets the bit in the IRR that corresponds the vector of the
accepted interrupt. When the processor core is ready to handle the next interrupt, the local APIC clears the highest
priority IRR bit that is set and sets the corresponding ISR bit. The vector for the highest priority bit set in the ISR is
then dispatched to the processor core for servicing.
While the processor is servicing the highest priority interrupt, the local APIC can send additional fixed interrupts by
setting bits in the IRR. When the interrupt service routine issues a write to the EOI register (see Section 10.8.5,
“Signaling Interrupt Servicing Completion”), the local APIC responds by clearing the highest priority ISR bit that is
set. It then repeats the process of clearing the highest priority bit in the IRR and setting the corresponding bit in
the ISR. The processor core then begins executing the service routing for the highest priority bit set in the ISR.
If more than one interrupt is generated with the same vector number, the local APIC can set the bit for the vector
both in the IRR and the ISR. This means that for the Pentium 4 and Intel Xeon processors, the IRR and ISR can
queue two interrupts for each interrupt vector: one in the IRR and one in the ISR. Any additional interrupts issued
for the same interrupt vector are collapsed into the single bit in the IRR.
For the P6 family and Pentium processors, the IRR and ISR registers can queue no more than two interrupts per
interrupt vector and will reject other interrupts that are received within the same vector.
If the local APIC receives an interrupt with an interrupt-priority class higher than that of the interrupt currently in
service, and interrupts are enabled in the processor core, the local APIC dispatches the higher priority interrupt to
the processor immediately (without waiting for a write to the EOI register). The currently executing interrupt
handler is then interrupted so the higher-priority interrupt can be handled. When the handling of the higher-priority
interrupt has been completed, the servicing of the interrupted interrupt is resumed.

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The trigger mode register (TMR) indicates the trigger mode of the interrupt (see Figure 10-20). Upon acceptance
of an interrupt into the IRR, the corresponding TMR bit is cleared for edge-triggered interrupts and set for leveltriggered interrupts. If a TMR bit is set when an EOI cycle for its corresponding interrupt vector is generated, an
EOI message is sent to all I/O APICs.

10.8.5

Signaling Interrupt Servicing Completion

For all interrupts except those delivered with the NMI, SMI, INIT, ExtINT, the start-up, or INIT-Deassert delivery
mode, the interrupt handler must include a write to the end-of-interrupt (EOI) register (see Figure 10-21). This
write must occur at the end of the handler routine, sometime before the IRET instruction. This action indicates that
the servicing of the current interrupt is complete and the local APIC can issue the next interrupt from the ISR.

31

0

Address: 0FEE0 00B0H
Value after reset: 0H

Figure 10-21. EOI Register
Upon receiving an EOI, the APIC clears the highest priority bit in the ISR and dispatches the next highest priority
interrupt to the processor. If the terminated interrupt was a level-triggered interrupt, the local APIC also sends an
end-of-interrupt message to all I/O APICs.
System software may prefer to direct EOIs to specific I/O APICs rather than having the local APIC send end-ofinterrupt messages to all I/O APICs.
Software can inhibit the broadcast of EOI message by setting bit 12 of the Spurious Interrupt Vector Register (see
Section 10.9). If this bit is set, a broadcast EOI is not generated on an EOI cycle even if the associated TMR bit indicates that the current interrupt was level-triggered. The default value for the bit is 0, indicating that EOI broadcasts
are performed.
Bit 12 of the Spurious Interrupt Vector Register is reserved to 0 if the processor does not support suppression of
EOI broadcasts. Support for EOI-broadcast suppression is reported in bit 24 in the Local APIC Version Register (see
Section 10.4.8); the feature is supported if that bit is set to 1. When supported, the feature is available in both
xAPIC mode and x2APIC mode.
System software desiring to perform directed EOIs for level-triggered interrupts should set bit 12 of the Spurious
Interrupt Vector Register and follow each the EOI to the local xAPIC for a level triggered interrupt with a directed
EOI to the I/O APIC generating the interrupt (this is done by writing to the I/O APIC’s EOI register). System software performing directed EOIs must retain a mapping associating level-triggered interrupts with the I/O APICs in
the system.

10.8.6

Task Priority in IA-32e Mode

In IA-32e mode, operating systems can manage the 16 interrupt-priority classes (see Section 10.8.3, “Interrupt,
Task, and Processor Priority”) explicitly using the task priority register (TPR). Operating systems can use the TPR
to temporarily block specific (low-priority) interrupts from interrupting a high-priority task. This is done by loading
TPR with a value in which the task-priority class corresponds to the highest interrupt-priority class that is to be
blocked. For example:

•

Loading the TPR with a task-priority class of 8 (01000B) blocks all interrupts with an interrupt-priority class of
8 or less while allowing all interrupts with an interrupt-priority class of 9 or more to be recognized.

•
•

Loading the TPR with a task-priority class of 0 enables all external interrupts.
Loading the TPR with a task-priority class of 0FH (01111B) disables all external interrupts.

The TPR (shown in Figure 10-18) is cleared to 0 on reset. In 64-bit mode, software can read and write the TPR
using an alternate interface, MOV CR8 instruction. The new task-priority class is established when the MOV CR8
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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

instruction completes execution. Software does not need to force serialization after loading the TPR using MOV
CR8.
Use of the MOV CRn instruction requires a privilege level of 0. Programs running at privilege level greater than 0
cannot read or write the TPR. An attempt to do so causes a general-protection exception. The TPR is abstracted
from the interrupt controller (IC), which prioritizes and manages external interrupt delivery to the processor. The
IC can be an external device, such as an APIC or 8259. Typically, the IC provides a priority mechanism similar or
identical to the TPR. The IC, however, is considered implementation-dependent with the under-lying priority mechanisms subject to change. CR8, by contrast, is part of the Intel 64 architecture. Software can depend on this definition remaining unchanged.
Figure 10-22 shows the layout of CR8; only the low four bits are used. The remaining 60 bits are reserved and must
be written with zeros. Failure to do this causes a general-protection exception.

63

4 3

0

Reserved

Value after reset: 0H

Figure 10-22. CR8 Register

10.8.6.1

Interaction of Task Priorities between CR8 and APIC

The first implementation of Intel 64 architecture includes a local advanced programmable interrupt controller
(APIC) that is similar to the APIC used with previous IA-32 processors. Some aspects of the local APIC affect the
operation of the architecturally defined task priority register and the programming interface using CR8.
Notable CR8 and APIC interactions are:

•
•

The processor powers up with the local APIC enabled.

•

APIC.TPR[bits 7:4] = CR8[bits 3:0], APIC.TPR[bits 3:0] = 0. A read of CR8 returns a 64-bit value which is the
value of TPR[bits 7:4], zero extended to 64 bits.

The APIC must be enabled for CR8 to function as the TPR. Writes to CR8 are reflected into the APIC Task Priority
Register.

There are no ordering mechanisms between direct updates of the APIC.TPR and CR8. Operating software should
implement either direct APIC TPR updates or CR8 style TPR updates but not mix them. Software can use a serializing instruction (for example, CPUID) to serialize updates between MOV CR8 and stores to the APIC.

10.9

SPURIOUS INTERRUPT

A special situation may occur when a processor raises its task priority to be greater than or equal to the level of the
interrupt for which the processor INTR signal is currently being asserted. If at the time the INTA cycle is issued, the
interrupt that was to be dispensed has become masked (programmed by software), the local APIC will deliver a
spurious-interrupt vector. Dispensing the spurious-interrupt vector does not affect the ISR, so the handler for this
vector should return without an EOI.
The vector number for the spurious-interrupt vector is specified in the spurious-interrupt vector register (see
Figure 10-23). The functions of the fields in this register are as follows:
Spurious Vector

Determines the vector number to be delivered to the processor when the local APIC generates
a spurious vector.
(Pentium 4 and Intel Xeon processors.) Bits 0 through 7 of the this field are programmable by
software.
(P6 family and Pentium processors). Bits 4 through 7 of the this field are programmable by
software, and bits 0 through 3 are hardwired to logical ones. Software writes to bits 0 through
3 have no effect.

APIC Software Enable/Disable
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Allows software to temporarily enable (1) or disable (0) the local APIC (see Section 10.4.3,
“Enabling or Disabling the Local APIC”).
Focus Processor Checking
Determines if focus processor checking is enabled (0) or disabled (1) when using the lowestpriority delivery mode. In Pentium 4 and Intel Xeon processors, this bit is reserved and should
be cleared to 0.
Suppress EOI Broadcasts
Determines whether an EOI for a level-triggered interrupt causes EOI messages to be broadcast to the I/O APICs (0) or not (1). See Section 10.8.5. The default value for this bit is 0, indicating that EOI broadcasts are performed. This bit is reserved to 0 if the processor does not
support EOI-broadcast suppression.

NOTE
Do not program an LVT or IOAPIC RTE with a spurious vector even if you set the mask bit. A
spurious vector ISR does not do an EOI. If for some reason an interrupt is generated by an LVT or
RTE entry, the bit in the in-service register will be left set for the spurious vector. This will mask all
interrupts at the same or lower priority
31

12 11 10 9 8 7

0

Reserved

EOI-Broadcast Suppression1
0: Disabled
1: Enabled
Focus Processor Checking2
0: Enabled
1: Disabled
APIC Software Enable/Disable
0: APIC Disabled
1: APIC Enabled
Spurious Vector3
Address: FEE0 00F0H
Value after reset: 0000 00FFH
1. Not supported on all processors. See bit 24 of Local APIC Version Register.
2. Not supported in Pentium 4 and Intel Xeon processors.
3. For the P6 family and Pentium processors, bits 0 through 3
are always 0.

Figure 10-23. Spurious-Interrupt Vector Register (SVR)

10.10

APIC BUS MESSAGE PASSING MECHANISM AND
PROTOCOL (P6 FAMILY, PENTIUM PROCESSORS)

The Pentium 4 and Intel Xeon processors pass messages among the local and I/O APICs on the system bus, using
the system bus message passing mechanism and protocol.
The P6 family and Pentium processors, pass messages among the local and I/O APICs on the serial APIC bus, as
follows. Because only one message can be sent at a time on the APIC bus, the I/O APIC and local APICs employ a
“rotating priority” arbitration protocol to gain permission to send a message on the APIC bus. One or more APICs
may start sending their messages simultaneously. At the beginning of every message, each APIC presents the type
of the message it is sending and its current arbitration priority on the APIC bus. This information is used for arbitration. After each arbitration cycle (within an arbitration round), only the potential winners keep driving the bus.

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By the time all arbitration cycles are completed, there will be only one APIC left driving the bus. Once a winner is
selected, it is granted exclusive use of the bus, and will continue driving the bus to send its actual message.
After each successfully transmitted message, all APICs increase their arbitration priority by 1. The previous winner
(that is, the one that has just successfully transmitted its message) assumes a priority of 0 (lowest). An agent
whose arbitration priority was 15 (highest) during arbitration, but did not send a message, adopts the previous
winner’s arbitration priority, incremented by 1.
Note that the arbitration protocol described above is slightly different if one of the APICs issues a special End-OfInterrupt (EOI). This high-priority message is granted the bus regardless of its sender’s arbitration priority, unless
more than one APIC issues an EOI message simultaneously. In the latter case, the APICs sending the EOI
messages arbitrate using their arbitration priorities.
If the APICs are set up to use “lowest priority” arbitration (see Section 10.6.2.4, “Lowest Priority Delivery Mode”)
and multiple APICs are currently executing at the lowest priority (the value in the APR register), the arbitration
priorities (unique values in the Arb ID register) are used to break ties. All 8 bits of the APR are used for the lowest
priority arbitration.

10.10.1 Bus Message Formats
See Section 10.13, “APIC Bus Message Formats,” for a description of bus message formats used to transmit
messages on the serial APIC bus.

10.11

MESSAGE SIGNALLED INTERRUPTS

The PCI Local Bus Specification, Rev 2.2 (www.pcisig.com) introduces the concept of message signalled interrupts.
As the specification indicates:
“Message signalled interrupts (MSI) is an optional feature that enables PCI devices to request
service by writing a system-specified message to a system-specified address (PCI DWORD memory
write transaction). The transaction address specifies the message destination while the transaction
data specifies the message. System software is expected to initialize the message destination and
message during device configuration, allocating one or more non-shared messages to each MSI
capable function.”
The capabilities mechanism provided by the PCI Local Bus Specification is used to identify and configure MSI
capable PCI devices. Among other fields, this structure contains a Message Data Register and a Message Address
Register. To request service, the PCI device function writes the contents of the Message Data Register to the
address contained in the Message Address Register (and the Message Upper Address register for 64-bit message
addresses).
Section 10.11.1 and Section 10.11.2 provide layout details for the Message Address Register and the Message Data
Register. The operation issued by the device is a PCI write command to the Message Address Register with the
Message Data Register contents. The operation follows semantic rules as defined for PCI write operations and is a
DWORD operation.

10.11.1 Message Address Register Format
The format of the Message Address Register (lower 32-bits) is shown in Figure 10-24.

31

20 19
0FEEH

12 11

Destination ID

4

Reserved

3

2

RH

DM

1

0
XX

Figure 10-24. Layout of the MSI Message Address Register
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Fields in the Message Address Register are as follows:
1. Bits 31-20 — These bits contain a fixed value for interrupt messages (0FEEH). This value locates interrupts at
the 1-MByte area with a base address of 4G – 18M. All accesses to this region are directed as interrupt
messages. Care must to be taken to ensure that no other device claims the region as I/O space.
2. Destination ID — This field contains an 8-bit destination ID. It identifies the message’s target processor(s).
The destination ID corresponds to bits 63:56 of the I/O APIC Redirection Table Entry if the IOAPIC is used to
dispatch the interrupt to the processor(s).
3. Redirection hint indication (RH) — When this bit is set, the message is directed to the processor with the
lowest interrupt priority among processors that can receive the interrupt.

•
•

When RH is 0, the interrupt is directed to the processor listed in the Destination ID field.
When RH is 1 and the physical destination mode is used, the Destination ID field must not be set to FFH;
it must point to a processor that is present and enabled to receive the interrupt.

•

When RH is 1 and the logical destination mode is active in a system using a flat addressing model, the
Destination ID field must be set so that bits set to 1 identify processors that are present and enabled to
receive the interrupt.

•

If RH is set to 1 and the logical destination mode is active in a system using cluster addressing model,
then Destination ID field must not be set to FFH; the processors identified with this field must be
present and enabled to receive the interrupt.

4. Destination mode (DM) — This bit indicates whether the Destination ID field should be interpreted as logical
or physical APIC ID for delivery of the lowest priority interrupt.

•

If RH is 1 and DM is 0, the Destination ID field is in physical destination mode and only the processor in
the system that has the matching APIC ID is considered for delivery of that interrupt (this means no redirection).

•

If RH is 1 and DM is 1, the Destination ID Field is interpreted as in logical destination mode and the
redirection is limited to only those processors that are part of the logical group of processors based on
the processor’s logical APIC ID and the Destination ID field in the message. The logical group of
processors consists of those identified by matching the 8-bit Destination ID with the logical destination
identified by the Destination Format Register and the Logical Destination Register in each local APIC.
The details are similar to those described in Section 10.6.2, “Determining IPI Destination.”

•

If RH is 0, then the DM bit is ignored and the message is sent ahead independent of whether the
physical or logical destination mode is used.

10.11.2 Message Data Register Format
The layout of the Message Data Register is shown in Figure 10-25.
Reserved fields are not assumed to be any value. Software must preserve their contents on writes. Other fields in
the Message Data Register are described below.
1. Vector — This 8-bit field contains the interrupt vector associated with the message. Values range from 010H
to 0FEH. Software must guarantee that the field is not programmed with vector 00H to 0FH.
2. Delivery Mode — This 3-bit field specifies how the interrupt receipt is handled. Delivery Modes operate only in
conjunction with specified Trigger Modes. Correct Trigger Modes must be guaranteed by software. Restrictions
are indicated below:
a. 000B (Fixed Mode) — Deliver the signal to all the agents listed in the destination. The Trigger Mode for
fixed delivery mode can be edge or level.
b. 001B (Lowest Priority) — Deliver the signal to the agent that is executing at the lowest priority of all
agents listed in the destination field. The trigger mode can be edge or level.
c.

010B (System Management Interrupt or SMI) — The delivery mode is edge only. For systems that rely
on SMI semantics, the vector field is ignored but must be programmed to all zeroes for future compatibility.

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

63

32

Reserved
31

16

15

Reserved

Trigger Mode
0 - Edge
1 - Level
Level for Trigger Mode = 0
X - Don’t care
Level for Trigger Mode = 1
0 - Deassert
1 - Assert

14

13

11 10

Reserved

8

7

0

Vector

Delivery Mode
000 - Fixed
001 - Lowest Priority
010 - SMI
011 - Reserved
100 - NMI
101 - INIT
110 - Reserved
111 - ExtINT

Figure 10-25. Layout of the MSI Message Data Register
d. 100B (NMI) — Deliver the signal to all the agents listed in the destination field. The vector information is
ignored. NMI is an edge triggered interrupt regardless of the Trigger Mode Setting.
e. 101B (INIT) — Deliver this signal to all the agents listed in the destination field. The vector information is
ignored. INIT is an edge triggered interrupt regardless of the Trigger Mode Setting.
f.

111B (ExtINT) — Deliver the signal to the INTR signal of all agents in the destination field (as an interrupt
that originated from an 8259A compatible interrupt controller). The vector is supplied by the INTA cycle
issued by the activation of the ExtINT. ExtINT is an edge triggered interrupt.

3. Level — Edge triggered interrupt messages are always interpreted as assert messages. For edge triggered
interrupts this field is not used. For level triggered interrupts, this bit reflects the state of the interrupt input.
4. Trigger Mode — This field indicates the signal type that will trigger a message.
a. 0 — Indicates edge sensitive.
b. 1 — Indicates level sensitive.

10.12

EXTENDED XAPIC (X2APIC)

The x2APIC architecture extends the xAPIC architecture (described in Section 10.4) in a backward compatible
manner and provides forward extendability for future Intel platform innovations. Specifically, the x2APIC architecture does the following.

•

Retains all key elements of compatibility to the xAPIC architecture.
— Delivery modes.
— Interrupt and processor priorities.
— Interrupt sources.
— Interrupt destination types.

•

Provides extensions to scale processor addressability for both the logical and physical destination modes.

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

•
•
•

Adds new features to enhance performance of interrupt delivery.
Reduces complexity of logical destination mode interrupt delivery on link based platform architectures.
Uses MSR programming interface to access APIC registers in x2APIC mode instead of memory-mapped
interfaces. Memory-mapped interface is supported when operating in xAPIC mode.

10.12.1 Detecting and Enabling x2APIC Mode
Processor support for x2APIC mode can be detected by executing CPUID with EAX=1 and then checking ECX, bit
21 ECX. If CPUID.(EAX=1):ECX.21 is set , the processor supports the x2APIC capability and can be placed into the
x2APIC mode.
System software can place the local APIC in the x2APIC mode by setting the x2APIC mode enable bit (bit 10) in the
IA32_APIC_BASE MSR at MSR address 01BH. The layout for the IA32_APIC_BASE MSR is shown in Figure 10-26.
63

36 35

Reserved

12 11 10 9 8 7

0

APIC Base

APIC Base—Base physical address
EN—xAPIC global enable/disable
EXTD—Enable x2APIC mode
BSP—Processor is BSP
Reserved

Figure 10-26. IA32_APIC_BASE MSR Supporting x2APIC
Table 10-5, “x2APIC operating mode configurations” describe the possible combinations of the enable bit (EN - bit
11) and the extended mode bit (EXTD - bit 10) in the IA32_APIC_BASE MSR.

Table 10-5. x2APIC Operating Mode Configurations
xAPIC global enable
(IA32_APIC_BASE[11])

x2APIC enable
(IA32_APIC_BASE[10])

Description

0

0

local APIC is disabled

0

1

Invalid

1

0

local APIC is enabled in xAPIC mode

1

1

local APIC is enabled in x2APIC mode

Once the local APIC has been switched to x2APIC mode (EN = 1, EXTD = 1), switching back to xAPIC mode would
require system software to disable the local APIC unit. Specifically, attempting to write a value to the
IA32_APIC_BASE MSR that has (EN= 1, EXTD = 0) when the local APIC is enabled and in x2APIC mode causes a
general-protection exception. Once bit 10 in IA32_APIC_BASE MSR is set, the only way to leave x2APIC mode
using IA32_APIC_BASE would require a WRMSR to set both bit 11 and bit 10 to zero. Section 10.12.5, “x2APIC
State Transitions” provides a detailed state diagram for the state transitions allowed for the local APIC.

10.12.1.1 Instructions to Access APIC Registers
In x2APIC mode, system software uses RDMSR and WRMSR to access the APIC registers. The MSR addresses for
accessing the x2APIC registers are architecturally defined and specified in Section 10.12.1.2, “x2APIC Register
Address Space”. Executing the RDMSR instruction with the APIC register address specified in ECX returns the
content of bits 0 through 31 of the APIC registers in EAX. Bits 32 through 63 are returned in register EDX - these
bits are reserved if the APIC register being read is a 32-bit register. Similarly executing the WRMSR instruction with
the APIC register address in ECX, writes bits 0 to 31 of register EAX to bits 0 to 31 of the specified APIC register. If
the register is a 64-bit register then bits 0 to 31 of register EDX are written to bits 32 to 63 of the APIC register. The

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Interrupt Command Register is the only APIC register that is implemented as a 64-bit MSR. The semantics of
handling reserved bits are defined in Section 10.12.1.3, “Reserved Bit Checking”.

10.12.1.2 x2APIC Register Address Space
The MSR address range 800H through BFFH is architecturally reserved and dedicated for accessing APIC registers
in x2APIC mode. Table 10-6 lists the APIC registers that are available in x2APIC mode. When appropriate, the table
also gives the offset at which each register is available on the page referenced by IA32_APIC_BASE[35:12] in
xAPIC mode.
There is a one-to-one mapping between the x2APIC MSRs and the legacy xAPIC register offsets with the following
exceptions:

•

The Destination Format Register (DFR): The DFR, supported at offset 0E0H in xAPIC mode, is not supported in
x2APIC mode. There is no MSR with address 80EH.

•

The Interrupt Command Register (ICR): The two 32-bit registers in xAPIC mode (at offsets 300H and 310H) are
merged into a single 64-bit MSR in x2APIC mode (with MSR address 830H). There is no MSR with address
831H.

•

The SELF IPI register. This register is available only in x2APIC mode at address 83FH. In xAPIC mode, there is
no register defined at offset 3F0H.

MSR addresses in the range 800H–BFFH that are not listed in Table 10-6 (including 80EH and 831H) are reserved.
Executions of RDMSR and WRMSR that attempt to access such addresses cause general-protection exceptions.
The MSR address space is compressed to allow for future growth. Every 32 bit register on a 128-bit boundary in the
legacy MMIO space is mapped to a single MSR in the local x2APIC MSR address space. The upper 32-bits of all
x2APIC MSRs (except for the ICR) are reserved.

Table 10-6. Local APIC Register Address Map Supported by x2APIC
MSR Address
(x2APIC mode)

MMIO Offset
(xAPIC mode)

Register Name

MSR R/W
Semantics

802H

020H

Local APIC ID register

Read-only1

See Section 10.12.5.1 for initial
values.

803H

030H

Local APIC Version register

Read-only

Same version used in xAPIC mode
and x2APIC mode.

808H

080H

Task Priority Register (TPR)

Read/write

Bits 31:8 are reserved.2

80AH

0A0H

Processor Priority Register
(PPR)

Read-only

80BH

0B0H

EOI register

Write-only3

WRMSR of a non-zero value causes
#GP(0).

80DH

0D0H

Logical Destination Register
(LDR)

Read-only

Read/write in xAPIC mode.

80FH

0F0H

Spurious Interrupt Vector
Register (SVR)

Read/write

See Section 10.9 for reserved bits.

810H

100H

In-Service Register (ISR); bits
31:0

Read-only

811H

110H

ISR bits 63:32

Read-only

812H

120H

ISR bits 95:64

Read-only

813H

130H

ISR bits 127:96

Read-only

814H

140H

ISR bits 159:128

Read-only

815H

150H

ISR bits 191:160

Read-only

816H

160H

ISR bits 223:192

Read-only

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Comments

ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

Table 10-6. Local APIC Register Address Map Supported by x2APIC (Contd.)
MSR Address
(x2APIC mode)

MMIO Offset
(xAPIC mode)

Register Name

MSR R/W
Semantics

817H

170H

ISR bits 255:224

Read-only

818H

180H

Trigger Mode Register (TMR);
bits 31:0

Read-only

819H

190H

TMR bits 63:32

Read-only

81AH

1A0H

TMR bits 95:64

Read-only

81BH

1B0H

TMR bits 127:96

Read-only

81CH

1C0H

TMR bits 159:128

Read-only

81DH

1D0H

TMR bits 191:160

Read-only

81EH

1E0H

TMR bits 223:192

Read-only

81FH

1F0H

TMR bits 255:224

Read-only

820H

200H

Interrupt Request Register
(IRR); bits 31:0

Read-only

821H

210H

IRR bits 63:32

Read-only

822H

220H

IRR bits 95:64

Read-only

823H

230H

IRR bits 127:96

Read-only

824H

240H

IRR bits 159:128

Read-only

825H

250H

IRR bits 191:160

Read-only

826H

260H

IRR bits 223:192

Read-only

827H

270H

IRR bits 255:224

Read-only

828H

280H

Error Status Register (ESR)

Read/write

WRMSR of a non-zero value causes
#GP(0). See Section 10.5.3.

82FH

2F0H

LVT CMCI register

Read/write

See Figure 10-8 for reserved bits.

830H4

300H and 310H

Interrupt Command Register
(ICR)

Read/write

See Figure 10-28 for reserved bits

832H

320H

LVT Timer register

Read/write

See Figure 10-8 for reserved bits.

833H

330H

LVT Thermal Sensor register

Read/write

See Figure 10-8 for reserved bits.

834H

340H

LVT Performance Monitoring
register

Read/write

See Figure 10-8 for reserved bits.

835H

350H

LVT LINT0 register

Read/write

See Figure 10-8 for reserved bits.

836H

360H

LVT LINT1 register

Read/write

See Figure 10-8 for reserved bits.

837H

370H

LVT Error register

Read/write

See Figure 10-8 for reserved bits.

838H

380H

Initial Count register (for
Timer)

Read/write

839H

390H

Current Count register (for
Timer)

Read-only

83EH

3E0H

Divide Configuration Register
(DCR; for Timer)

Read/write

See Figure 10-10 for reserved bits.

83FH

Not available

SELF IPI5

Write-only

Available only in x2APIC mode.

Comments

NOTES:
1. WRMSR causes #GP(0) for read-only registers.

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

2. WRMSR causes #GP(0) for attempts to set a reserved bit to 1 in a read/write register (including bits 63:32 of each register).
3. RDMSR causes #GP(0) for write-only registers.
4. MSR 831H is reserved; read/write operations cause general-protection exceptions. The contents of the APIC register at MMIO offset
310H are accessible in x2APIC mode through the MSR at address 830H.
5. SELF IPI register is supported only in x2APIC mode.

10.12.1.3 Reserved Bit Checking
Section 10.12.1.2 and Table 10-6 specifies the reserved bit definitions for the APIC registers in x2APIC mode. Nonzero writes (by WRMSR instruction) to reserved bits to these registers will raise a general protection fault exception
while reads return zeros (RsvdZ semantics).
In x2APIC mode, the local APIC ID register is increased to 32 bits wide. This enables 232–1 processors to be
addressable in physical destination mode. This 32-bit value is referred to as “x2APIC ID”. A processor implementation may choose to support less than 32 bits in its hardware. System software should be agnostic to the actual
number of bits that are implemented. All non-implemented bits will return zeros on reads by software.
The APIC ID value of FFFF_FFFFH and the highest value corresponding to the implemented bit-width of the local
APIC ID register in the system are reserved and cannot be assigned to any logical processor.
In x2APIC mode, the local APIC ID register is a read-only register to system software and will be initialized by hardware. It is accessed via the RDMSR instruction reading the MSR at address 0802H.
Each logical processor in the system (including clusters with a communication fabric) must be configured with an
unique x2APIC ID to avoid collisions of x2APIC IDs. On DP and high-end MP processors targeted to specific market
segments and depending on the system configuration, it is possible that logical processors in different and “unconnected” clusters power up initialized with overlapping x2APIC IDs. In these configurations, a model-specific
means may be provided in those product segments to enable BIOS and/or platform firmware to re-configure the
x2APIC IDs in some clusters to provide for unique and non-overlapping system wide IDs before configuring the
disconnected components into a single system.

10.12.2 x2APIC Register Availability
The local APIC registers can be accessed via the MSR interface only when the local APIC has been switched to the
x2APIC mode as described in Section 10.12.1. Accessing any APIC register in the MSR address range 0800H
through 0BFFH via RDMSR or WRMSR when the local APIC is not in x2APIC mode causes a general-protection
exception. In x2APIC mode, the memory mapped interface is not available and any access to the MMIO interface
will behave similar to that of a legacy xAPIC in globally disabled state. Table 10-7 provides the interactions between
the legacy & extended modes and the legacy and register interfaces.

Table 10-7. MSR/MMIO Interface of a Local x2APIC in Different Modes of Operation
MMIO Interface

MSR Interface

xAPIC mode

Available

General-protection exception

x2APIC mode

Behavior identical to xAPIC in globally disabled state

Available

10.12.3 MSR Access in x2APIC Mode
To allow for efficient access to the APIC registers in x2APIC mode, the serializing semantics of WRMSR are relaxed
when writing to the APIC registers. Thus, system software should not use “WRMSR to APIC registers in x2APIC
mode” as a serializing instruction. Read and write accesses to the APIC registers will occur in program order. A
WRMSR to an APIC register may complete before all preceding stores are globally visible; software can prevent this
by inserting a serializing instruction, an SFENCE, or an MFENCE before the WRMSR.
The RDMSR instruction is not serializing and this behavior is unchanged when reading APIC registers in x2APIC
mode. System software accessing the APIC registers using the RDMSR instruction should not expect a serializing
behavior. (Note: The MMIO-based xAPIC interface is mapped by system software as an un-cached region. Consequently, read/writes to the xAPIC-MMIO interface have serializing semantics in the xAPIC mode.)
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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

10.12.4 VM-Exit Controls for MSRs and x2APIC Registers
The VMX architecture allows a VMM to specify lists of MSRs to be loaded or stored on VMX transitions using the
VMX-transition MSR areas (see VM-exit MSR-store address field, VM-exit MSR-load address field, and VM-entry
MSR-load address field in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C).
The X2APIC MSRs cannot to be loaded and stored on VMX transitions. A VMX transition fails if the VMM has specified that the transition should access any MSRs in the address range from 0000_0800H to 0000_08FFH (the range
used for accessing the X2APIC registers). Specifically, processing of an 128-bit entry in any of the VMX-transition
MSR areas fails if bits 31:0 of that entry (represented as ENTRY_LOW_DW) satisfies the expression:
“ENTRY_LOW_DW & FFFFF800H = 00000800H”. Such a failure causes an associated VM entry to fail (by reloading
host state) and causes an associated VM exit to lead to VMX abort.

10.12.5 x2APIC State Transitions
This section provides a detailed description of the x2APIC states of a local x2APIC unit, transitions between these
states as well as interactions of these states with INIT and reset.

10.12.5.1 x2APIC States
The valid states for a local x2APIC unit are listed in Table 10-5.

•
•
•
•

APIC disabled: IA32_APIC_BASE[EN]=0 and IA32_APIC_BASE[EXTD]=0.
xAPIC mode: IA32_APIC_BASE[EN]=1 and IA32_APIC_BASE[EXTD]=0.
x2APIC mode: IA32_APIC_BASE[EN]=1 and IA32_APIC_BASE[EXTD]=1.
Invalid: IA32_APIC_BASE[EN]=0 and IA32_APIC_BASE[EXTD]=1.

The state corresponding to EXTD=1 and EN=0 is not valid and it is not possible to get into this state. An execution
of WRMSR to the IA32_APIC_BASE_MSR that attempts a transition from a valid state to this invalid state causes a
general-protection exception. Figure 10-27 shows the comprehensive state transition diagram for a local x2APIC
unit.
On coming out of reset, the local APIC unit is enabled and is in the xAPIC mode: IA32_APIC_BASE[EN]=1 and
IA32_APIC_BASE[EXTD]=0. The APIC registers are initialized as follows.

•

The local APIC ID is initialized by hardware with a 32 bit ID (x2APIC ID). The lowest 8 bits of the x2APIC ID are
the legacy local xAPIC ID, and are stored in the upper 8 bits of the APIC register for access in xAPIC mode.

•

The following APIC registers are reset to all zeros for those fields that are defined in the xAPIC mode.
— IRR, ISR, TMR, ICR, LDR, TPR, Divide Configuration Register (See Section 10.4 through Section 10.6 for
details of individual APIC registers).
— Timer initial count and timer current count registers.

•
•
•
•
•

The LVT registers are reset to 0s except for the mask bits; these are set to 1s.
The local APIC version register is not affected.
The Spurious Interrupt Vector Register is initialized to 000000FFH.
The DFR (available only in xAPIC mode) is reset to all 1s.
SELF IPI register is reset to zero.

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Reset
Init

Disabled
EN = 0
Extd = 0

EN =1

xAPIC Mode

EN = 0

EN=1, Extd=0

Reset

Extd = 1

Init

EN = 0
Extd = 0

Illegal
Transition
Extd = 1
Illegal
Transition
Extd = 1

Illegal
Transition
Extd = 0

Invalid
State

EN = 0
Illegal
Transition
EN = 0

Extended

Mode
EN=1, Extd=1

Reset

Init

Figure 10-27. Local x2APIC State Transitions with IA32_APIC_BASE, INIT, and Reset

x2APIC After Reset
The valid transitions from the xAPIC mode state are:

•

to the x2APIC mode by setting EXT to 1 (resulting EN=1, EXTD= 1). The physical x2APIC ID (see Figure 10-6)
is preserved across this transition and the logical x2APIC ID (see Figure 10-29) is initialized by hardware during
this transition as documented in Section 10.12.10.2. The state of the extended fields in other APIC registers,
which was not initialized at reset, is not architecturally defined across this transition and system software
should explicitly initialize those programmable APIC registers.

•

to the disabled state by setting EN to 0 (resulting EN=0, EXTD= 0).

The result of an INIT in the xAPIC state places the APIC in the state with EN= 1, EXTD= 0. The state of the local
APIC ID register is preserved (the 8-bit xAPIC ID is in the upper 8 bits of the APIC ID register). All the other APIC
registers are initialized as a result of INIT.
A reset in this state places the APIC in the state with EN= 1, EXTD= 0. The state of the local APIC ID register is
initialized as described in Section 10.12.5.1. All the other APIC registers are initialized described in Section
10.12.5.1.

x2APIC Transitions From x2APIC Mode
From the x2APIC mode, the only valid x2APIC transition using IA32_APIC_BASE is to the state where the x2APIC
is disabled by setting EN to 0 and EXTD to 0. The x2APIC ID (32 bits) and the legacy local xAPIC ID (8 bits) are
preserved across this transition. A transition from the x2APIC mode to xAPIC mode is not valid, and the corresponding WRMSR to the IA32_APIC_BASE MSR causes a general-protection exception.
A reset in this state places the x2APIC in xAPIC mode. All APIC registers (including the local APIC ID register) are
initialized as described in Section 10.12.5.1.
An INIT in this state keeps the x2APIC in the x2APIC mode. The state of the local APIC ID register is preserved (all
32 bits). However, all the other APIC registers are initialized as a result of the INIT transition.

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x2APIC Transitions From Disabled Mode
From the disabled state, the only valid x2APIC transition using IA32_APIC_BASE is to the xAPIC mode (EN= 1,
EXTD = 0). Thus the only means to transition from x2APIC mode to xAPIC mode is a two-step process:

•
•

first transition from x2APIC mode to local APIC disabled mode (EN= 0, EXTD = 0),
followed by another transition from disabled mode to xAPIC mode (EN= 1, EXTD= 0).

Consequently, all the APIC register states in the x2APIC, except for the x2APIC ID (32 bits), are not preserved
across mode transitions.
A reset in the disabled state places the x2APIC in the xAPIC mode. All APIC registers (including the local APIC ID
register) are initialized as described in Section 10.12.5.1.
An INIT in the disabled state keeps the x2APIC in the disabled state.

State Changes From xAPIC Mode to x2APIC Mode
After APIC register states have been initialized by software in xAPIC mode, a transition from xAPIC mode to x2APIC
mode does not affect most of the APIC register states, except the following:

•
•
•

The Logical Destination Register is not preserved.
Any APIC ID value written to the memory-mapped local APIC ID register is not preserved.
The high half of the Interrupt Command Register is not preserved.

10.12.6 Routing of Device Interrupts in x2APIC Mode
The x2APIC architecture is intended to work with all existing IOxAPIC units as well as all PCI and PCI Express
(PCIe) devices that support the capability for message-signaled interrupts (MSI). Support for x2APIC modifies only
the following:

•
•
•

the local APIC units;
the interconnects joining IOxAPIC units to the local APIC units; and
the interconnects joining MSI-capable PCI and PCIe devices to the local APIC units.

No modifications are required to MSI-capable PCI and PCIe devices. Similarly, no modifications are required to
IOxAPIC units. This made possible through use of the interrupt-remapping architecture specified in the Intel®
Virtualization Technology for Directed I/O, Revision 1.3 for the routing of interrupts from MSI-capable devices to
local APIC units operating in x2APIC mode.

10.12.7 Initialization by System Software
Routing of device interrupts to local APIC units operating in x2APIC mode requires use of the interrupt-remapping
architecture specified in the Intel® Virtualization Technology for Directed I/O (Revision 1.3 and/or later versions).
Because of this, BIOS must enumerate support for and software must enable this interrupt remapping with
Extended Interrupt Mode Enabled before it enabling x2APIC mode in the local APIC units.
The ACPI interfaces for the x2APIC are described in Section 5.2, “ACPI System Description Tables,” of the Advanced
Configuration and Power Interface Specification, Revision 4.0a (http://www.acpi.info/spec.htm). The default
behavior for BIOS is to pass the control to the operating system with the local x2APICs in xAPIC mode if all APIC
IDs reported by CPUID.0BH:EDX are less than 255, and in x2APIC mode if there are any logical processor reporting
an APIC ID of 255 or greater.

10.12.8 CPUID Extensions And Topology Enumeration
For Intel 64 and IA-32 processors that support x2APIC, a value of 1 reported by CPUID.01H:ECX[21] indicates that
the processor supports x2APIC and the extended topology enumeration leaf (CPUID.0BH).

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

The extended topology enumeration leaf can be accessed by executing CPUID with EAX = 0BH. Processors that do
not support x2APIC may support CPUID leaf 0BH. Software can detect the availability of the extended topology
enumeration leaf (0BH) by performing two steps:

•

Check maximum input value for basic CPUID information by executing CPUID with EAX= 0. If CPUID.0H:EAX is
greater than or equal or 11 (0BH), then proceed to next step

•

Check CPUID.EAX=0BH, ECX=0H:EBX is non-zero.

If both of the above conditions are true, extended topology enumeration leaf is available. If available, the extended
topology enumeration leaf is the preferred mechanism for enumerating topology. The presence of CPUID leaf 0BH
in a processor does not guarantee support for x2APIC. If CPUID.EAX=0BH, ECX=0H:EBX returns zero and
maximum input value for basic CPUID information is greater than 0BH, then CPUID.0BH leaf is not supported on
that processor.
The extended topology enumeration leaf is intended to assist software with enumerating processor topology on
systems that requires 32-bit x2APIC IDs to address individual logical processors. Details of CPUID leaf 0BH can be
found in the reference pages of CPUID in Chapter 3 of Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 2A.
Processor topology enumeration algorithm for processors supporting the extended topology enumeration leaf of
CPUID and processors that do not support CPUID leaf 0BH are treated in Section 8.9.4, “Algorithm for Three-Level
Mappings of APIC_ID”.

10.12.8.1 Consistency of APIC IDs and CPUID
The consistency of physical x2APIC ID in MSR 802H in x2APIC mode and the 32-bit value returned in
CPUID.0BH:EDX is facilitated by processor hardware.
CPUID.0BH:EDX will report the full 32 bit ID, in xAPIC and x2APIC mode. This allows BIOS to determine if a system
has processors with IDs exceeding the 8-bit initial APIC ID limit (CPUID.01H:EBX[31:24]). Initial APIC ID
(CPUID.01H:EBX[31:24]) is always equal to CPUID.0BH:EDX[7:0].
If the values of CPUID.0BH:EDX reported by all logical processors in a system are less than 255, BIOS can transfer
control to OS in xAPIC mode.
If the values of CPUID.0BH:EDX reported by some logical processors in a system are greater than or equal to 255,
BIOS must support two options to hand off to OS.

•

If BIOS enables logical processors with x2APIC IDs greater than 255, then it should enable x2APIC in the Boot
Strap Processor (BSP) and all Application Processors (AP) before passing control to the OS. Applications
requiring processor topology information must use OS provided services based on x2APIC IDs or CPUID.0BH
leaf.

•

If a BIOS transfers control to OS in xAPIC mode, then the BIOS must ensure that only logical processors with
CPUID.0BH.EDX value less than 255 are enabled. BIOS initialization on all logical processors with
CPUID.0B.EDX values greater than or equal to 255 must (a) disable APIC and execute CLI in each logical
processor, and (b) leave these logical processor in the lowest power state so that these processors do not
respond to INIT IPI during OS boot. The BSP and all the enabled logical processor operate in xAPIC mode after
BIOS passed control to OS. Application requiring processor topology information can use OS provided legacy
services based on 8-bit initial APIC IDs or legacy topology information from CPUID.01H and CPUID 04H leaves.
Even if the BIOS passes control in xAPIC mode, an OS can switch the processors to x2APIC mode later. BIOS
SMM handler should always read the APIC_BASE_MSR, determine the APIC mode and use the corresponding
access method.

10.12.9 ICR Operation in x2APIC Mode
In x2APIC mode, the layout of the Interrupt Command Register is shown in Figure 10-12. The lower 32 bits of ICR
in x2APIC mode is identical to the lower half of the ICR in xAPIC mode, except the Delivery Status bit is removed
since it is not needed in x2APIC mode. The destination ID field is expanded to 32 bits in x2APIC mode.
To send an IPI using the ICR, software must set up the ICR to indicate the type of IPI message to be sent and the
destination processor or processors. Self IPIs can also be sent using the SELF IPI register (see Section 10.12.11).

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

63

32

Destination Field

31

20 19 18 17 16 15 14 13 12 11 10

Reserved

Destination Shorthand
00: No Shorthand
01: Self
10: All Including Self
11: All Excluding Self

Reserved

8 7

0

Vector

Delivery Mode
000: Fixed
001: Reserved
010: SMI
011: Reserved
100: NMI
101: INIT
110: Start Up
111: Reserved
Destination Mode
0: Physical
1: Logical

Address: 830H (63 - 0)
Value after Reset: 0H

Level
0 = De-assert
1 = Assert
Trigger Mode
0: Edge
1: Level

Figure 10-28. Interrupt Command Register (ICR) in x2APIC Mode
A single MSR write to the Interrupt Command Register is required for dispatching an interrupt in x2APIC mode.
With the removal of the Delivery Status bit, system software no longer has a reason to read the ICR. It remains
readable only to aid in debugging; however, software should not assume the value returned by reading the ICR is
the last written value.
A destination ID value of FFFF_FFFFH is used for broadcast of interrupts in both logical destination and physical
destination modes.

10.12.10 Determining IPI Destination in x2APIC Mode
10.12.10.1 Logical Destination Mode in x2APIC Mode
In x2APIC mode, the Logical Destination Register (LDR) is increased to 32 bits wide. It is a read-only register to
system software. This 32-bit value is referred to as “logical x2APIC ID”. System software accesses this register via
the RDMSR instruction reading the MSR at address 80DH. Figure 10-29 provides the layout of the Logical Destination Register in x2APIC mode.

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

MSR Address: 80DH
31

0

Logical x2APIC ID

Figure 10-29. Logical Destination Register in x2APIC Mode
In the xAPIC mode, the Destination Format Register (DFR) through the MMIO interface determines the choice of a
flat logical mode or a clustered logical mode. Flat logical mode is not supported in the x2APIC mode. Hence the
Destination Format Register (DFR) is eliminated in x2APIC mode.
The 32-bit logical x2APIC ID field of LDR is partitioned into two sub-fields:

•
•

Cluster ID (LDR[31:16]): is the address of the destination cluster
Logical ID (LDR[15:0]): defines a logical ID of the individual local x2APIC within the cluster specified by
LDR[31:16].

This layout enables 2^16-1 clusters each with up to 16 unique logical IDs - effectively providing an addressability
of ((2^20) - 16) processors in logical destination mode.
It is likely that processor implementations may choose to support less than 16 bits of the cluster ID or less than 16bits of the Logical ID in the Logical Destination Register. However system software should be agnostic to the
number of bits implemented in the cluster ID and logical ID sub-fields. The x2APIC hardware initialization will
ensure that the appropriately initialized logical x2APIC IDs are available to system software and reads of nonimplemented bits return zero. This is a read-only register that software must read to determine the logical x2APIC
ID of the processor. Specifically, software can apply a 16-bit mask to the lowest 16 bits of the logical x2APIC ID to
identify the logical address of a processor within a cluster without needing to know the number of implemented bits
in cluster ID and Logical ID sub-fields. Similarly, software can create a message destination address for cluster
model, by bit-Oring the Logical X2APIC ID (31:0) of processors that have matching Cluster ID(31:16).
To enable cluster ID assignment in a fashion that matches the system topology characteristics and to enable efficient routing of logical mode lowest priority device interrupts in link based platform interconnects, the LDR are
initialized by hardware based on the value of x2APIC ID upon x2APIC state transitions. Details of this initialization
are provided in Section 10.12.10.2.

10.12.10.2 Deriving Logical x2APIC ID from the Local x2APIC ID
In x2APIC mode, the 32-bit logical x2APIC ID, which can be read from LDR, is derived from the 32-bit local x2APIC
ID. Specifically, the 16-bit logical ID sub-field is derived by shifting 1 by the lowest 4 bits of the x2APIC ID, i.e.
Logical ID = 1 « x2APIC ID[3:0]. The remaining bits of the x2APIC ID then form the cluster ID portion of the logical
x2APIC ID:
Logical x2APIC ID = [(x2APIC ID[19:4] « 16) | (1 « x2APIC ID[3:0])]
The use of the lowest 4 bits in the x2APIC ID implies that at least 16 APIC IDs are reserved for logical processors
within a socket in multi-socket configurations. If more than 16 APIC IDS are reserved for logical processors in a
socket/package then multiple cluster IDs can exist within the package.
The LDR initialization occurs whenever the x2APIC mode is enabled (see Section 10.12.5).

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

10.12.11 SELF IPI Register
SELF IPIs are used extensively by some system software. The x2APIC architecture introduces a new register interface. This new register is dedicated to the purpose of sending self-IPIs with the intent of enabling a highly optimized path for sending self-IPIs.
Figure 10-30 provides the layout of the SELF IPI register. System software only specifies the vector associated with
the interrupt to be sent. The semantics of sending a self-IPI via the SELF IPI register are identical to sending a self
targeted edge triggered fixed interrupt with the specified vector. Specifically the semantics are identical to the
following settings for an inter-processor interrupt sent via the ICR - Destination Shorthand (ICR[19:18] = 01
(Self)), Trigger Mode (ICR[15] = 0 (Edge)), Delivery Mode (ICR[10:8] = 000 (Fixed)), Vector (ICR[7:0] = Vector).

MSR Address: 083FH
31

8 7

0

Vector

Reserved

Figure 10-30. SELF IPI register
The SELF IPI register is a write-only register. A RDMSR instruction with address of the SELF IPI register causes a
general-protection exception.
The handling and prioritization of a self-IPI sent via the SELF IPI register is architecturally identical to that for an
IPI sent via the ICR from a legacy xAPIC unit. Specifically the state of the interrupt would be tracked via the Interrupt Request Register (IRR) and In Service Register (ISR) and Trigger Mode Register (TMR) as if it were received
from the system bus. Also sending the IPI via the Self Interrupt Register ensures that interrupt is delivered to the
processor core. Specifically completion of the WRMSR instruction to the SELF IPI register implies that the interrupt
has been logged into the IRR. As expected for edge triggered interrupts, depending on the processor priority and
readiness to accept interrupts, it is possible that interrupts sent via the SELF IPI register or via the ICR with identical vectors can be combined.

10.13

APIC BUS MESSAGE FORMATS

This section describes the message formats used when transmitting messages on the serial APIC bus. The information described here pertains only to the Pentium and P6 family processors.

10.13.1 Bus Message Formats
The local and I/O APICs transmit three types of messages on the serial APIC bus: EOI message, short message,
and non-focused lowest priority message. The purpose of each type of message and its format are described
below.

10.13.2 EOI Message
Local APICs send 14-cycle EOI messages to the I/O APIC to indicate that a level triggered interrupt has been
accepted by the processor. This interrupt, in turn, is a result of software writing into the EOI register of the local
APIC. Table 10-1 shows the cycles in an EOI message.

Table 10-1. EOI Message (14 Cycles)
Cycle

Bit1

Bit0

1

1

1

11 = EOI

2

ArbID3

0

Arbitration ID bits 3 through 0

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

Table 10-1. EOI Message (14 Cycles) (Contd.)
Cycle

Bit1

Bit0

3

ArbID2

0

4

ArbID1

0

5

ArbID0

0

6

V7

V6

7

V5

V4

8

V3

V2

9

V1

V0

Interrupt vector V7 - V0

10

C

C

11

0

0

Checksum for cycles 6 - 9

12

A

A

Status Cycle 0

13

A1

A1

Status Cycle 1

14

0

0

Idle

The checksum is computed for cycles 6 through 9. It is a cumulative sum of the 2-bit (Bit1:Bit0) logical data values.
The carry out of all but the last addition is added to the sum. If any APIC computes a different checksum than the
one appearing on the bus in cycle 10, it signals an error, driving 11 on the APIC bus during cycle 12. In this case,
the APICs disregard the message. The sending APIC will receive an appropriate error indication (see Section
10.5.3, “Error Handling”) and resend the message. The status cycles are defined in Table 10-4.

10.13.2.1 Short Message
Short messages (21-cycles) are used for sending fixed, NMI, SMI, INIT, start-up, ExtINT and lowest-priority-withfocus interrupts. Table 10-2 shows the cycles in a short message.

Table 10-2. Short Message (21 Cycles)
Cycle

Bit1

Bit0

1

0

1

0 1 = normal

2

ArbID3

0

Arbitration ID bits 3 through 0

3

ArbID2

0

4

ArbID1

0

5

ArbID0

0

6

DM

M2

DM = Destination Mode

7

M1

M0

M2-M0 = Delivery mode

8

L

TM

L = Level, TM = Trigger Mode

9

V7

V6

V7-V0 = Interrupt Vector

10

V5

V4

11

V3

V2

12

V1

V0

13

D7

D6

14

D5

D4

15

D3

D2

16

D1

D0

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

Table 10-2. Short Message (21 Cycles) (Contd.)
Cycle

Bit1

Bit0

17

C

C

Checksum for cycles 6-16

18

0

0

19

A

A

Status cycle 0

20

A1

A1

Status cycle 1

21

0

0

Idle

If the physical delivery mode is being used, then cycles 15 and 16 represent the APIC ID and cycles 13 and 14 are
considered don't care by the receiver. If the logical delivery mode is being used, then cycles 13 through 16 are the
8-bit logical destination field.
For shorthands of “all-incl-self” and “all-excl-self,” the physical delivery mode and an arbitration priority of 15
(D0:D3 = 1111) are used. The agent sending the message is the only one required to distinguish between the two
cases. It does so using internal information.
When using lowest priority delivery with an existing focus processor, the focus processor identifies itself by driving
10 during cycle 19 and accepts the interrupt. This is an indication to other APICs to terminate arbitration. If the
focus processor has not been found, the short message is extended on-the-fly to the non-focused lowest-priority
message. Note that except for the EOI message, messages generating a checksum or an acceptance error (see
Section 10.5.3, “Error Handling”) terminate after cycle 21.

10.13.2.2 Non-focused Lowest Priority Message
These 34-cycle messages (see Table 10-3) are used in the lowest priority delivery mode when a focus processor is
not present. Cycles 1 through 20 are same as for the short message. If during the status cycle (cycle 19) the state
of the (A:A) flags is 10B, a focus processor has been identified, and the short message format is used (see Table
10-2). If the (A:A) flags are set to 00B, lowest priority arbitration is started and the 34-cycles of the non-focused
lowest priority message are competed. For other combinations of status flags, refer to Section 10.13.2.3, “APIC
Bus Status Cycles.”

Table 10-3. Non-Focused Lowest Priority Message (34 Cycles)
Cycle

Bit0

Bit1

1

0

1

0 1 = normal

2

ArbID3

0

Arbitration ID bits 3 through 0

3

ArbID2

0

4

ArbID1

0

5

ArbID0

0

6

DM

M2

DM = Destination mode

7

M1

M0

M2-M0 = Delivery mode

8

L

TM

L = Level, TM = Trigger Mode

9

V7

V6

V7-V0 = Interrupt Vector

10

V5

V4

11

V3

V2

12

V1

V0

13

D7

D6

14

D5

D4

15

D3

D2

16

D1

D0

D7-D0 = Destination

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

Table 10-3. Non-Focused Lowest Priority Message (34 Cycles) (Contd.)
Cycle

Bit0

Bit1

17

C

C

Checksum for cycles 6-16

18

0

0

19

A

A

Status cycle 0

20

A1

A1

Status cycle 1

21

P7

0

22

P6

0

23

P5

0

24

P4

0

25

P3

0

26

P2

0

27

P1

0

28

P0

0

29

ArbID3

0

30

ArbID2

0

31

ArbID1

0

32

ArbID0

0

33

A2

A2

34

0

0

P7 - P0 = Inverted Processor Priority

Arbitration ID 3 -0

Status Cycle
Idle

Cycles 21 through 28 are used to arbitrate for the lowest priority processor. The processors participating in the arbitration drive their inverted processor priority on the bus. Only the local APICs having free interrupt slots participate
in the lowest priority arbitration. If no such APIC exists, the message will be rejected, requiring it to be tried at a
later time.
Cycles 29 through 32 are also used for arbitration in case two or more processors have the same lowest priority. In
the lowest priority delivery mode, all combinations of errors in cycle 33 (A2 A2) will set the “accept error” bit in the
error status register (see Figure 10-9). Arbitration priority update is performed in cycle 20, and is not affected by
errors detected in cycle 33. Only the local APIC that wins in the lowest priority arbitration, drives cycle 33. An error
in cycle 33 will force the sender to resend the message.

10.13.2.3 APIC Bus Status Cycles
Certain cycles within an APIC bus message are status cycles. During these cycles the status flags (A:A) and
(A1:A1) are examined. Table 10-4 shows how these status flags are interpreted, depending on the current delivery
mode and existence of a focus processor.

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ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

Table 10-4. APIC Bus Status Cycles Interpretation
Delivery
Mode

A Status

A1 Status

A2 Status

Update ArbID Message
and Cycle#
Length

EOI

00: CS_OK

10: Accept

XX:

Yes, 13

14 Cycle

No

00: CS_OK

11: Retry

XX:

Yes, 13

14 Cycle

Yes

00: CS_OK

0X: Accept Error

XX:

No

14 Cycle

Yes

11: CS_Error

XX:

XX:

No

14 Cycle

Yes

10: Error

XX:

XX:

No

14 Cycle

Yes

01: Error

XX:

XX:

No

14 Cycle

Yes

00: CS_OK

10: Accept

XX:

Yes, 20

21 Cycle

No

00: CS_OK

11: Retry

XX:

Yes, 20

21 Cycle

Yes

00: CS_OK

0X: Accept Error

XX:

No

21 Cycle

Yes

11: CS_Error

XX:

XX:

No

21 Cycle

Yes

10: Error

XX:

XX:

No

21 Cycle

Yes

Fixed

NMI, SMI, INIT,
ExtINT,
Start-Up

Lowest

Retry

01: Error

XX:

XX:

No

21 Cycle

Yes

00: CS_OK

10: Accept

XX:

Yes, 20

21 Cycle

No

00: CS_OK

11: Retry

XX:

Yes, 20

21 Cycle

Yes

00: CS_OK

0X: Accept Error

XX:

No

21 Cycle

Yes

11: CS_Error

XX:

XX:

No

21 Cycle

Yes

10: Error

XX:

XX:

No

21 Cycle

Yes

01: Error

XX:

XX:

No

21 Cycle

Yes

00: CS_OK, NoFocus

11: Do Lowest

10: Accept

Yes, 20

34 Cycle

No

00: CS_OK, NoFocus

11: Do Lowest

11: Error

Yes, 20

34 Cycle

Yes

00: CS_OK, NoFocus

11: Do Lowest

0X: Error

Yes, 20

34 Cycle

Yes

00: CS_OK, NoFocus

10: End and Retry

XX:

Yes, 20

34 Cycle

Yes

00: CS_OK, NoFocus

0X: Error

XX:

No

34 Cycle

Yes

10: CS_OK, Focus

XX:

XX:

Yes, 20

34 Cycle

No

11: CS_Error

XX:

XX:

No

21 Cycle

Yes

01: Error

XX:

XX:

No

21 Cycle

Yes

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10-52 Vol. 3A

CHAPTER 11
MEMORY CACHE CONTROL
This chapter describes the memory cache and cache control mechanisms, the TLBs, and the store buffer in Intel 64
and IA-32 processors. It also describes the memory type range registers (MTRRs) introduced in the P6 family
processors and how they are used to control caching of physical memory locations.

11.1

INTERNAL CACHES, TLBS, AND BUFFERS

The Intel 64 and IA-32 architectures support cache, translation look aside buffers (TLBs), and a store buffer for
temporary on-chip (and external) storage of instructions and data. (Figure 11-1 shows the arrangement of caches,
TLBs, and the store buffer for the Pentium 4 and Intel Xeon processors.) Table 11-1 shows the characteristics of
these caches and buffers for the Pentium 4, Intel Xeon, P6 family, and Pentium processors. The sizes and characteristics of these units are machine specific and may change in future versions of the processor. The
CPUID instruction returns the sizes and characteristics of the caches and buffers for the processor on which the
instruction is executed. See “CPUID—CPU Identification” in Chapter 3, “Instruction Set Reference, A-L,” of the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A.

Physical
Memory

System Bus
(External)
L3 Cache†

L2 Cache

Data Cache
Unit (L1)
Instruction
TLBs

Bus Interface Unit
Data TLBs

Instruction Decoder

Trace Cache

Store Buffer

† Intel Xeon processors only

Figure 11-1. Cache Structure of the Pentium 4 and Intel Xeon Processors

Vol. 3A 11-1

MEMORY CACHE CONTROL

Instruction Decoder and front end

ITLB

Instruction
Cache

Chipset

Out-of-Order Engine
QPI

Data TLB

Data Cache
Unit (L1)

STLB

IMC

L2 Cache
L3 Cache

Figure 11-2. Cache Structure of the Intel Core i7 Processors
Figure 11-2 shows the cache arrangement of Intel Core i7 processor.

Table 11-1. Characteristics of the Caches, TLBs, Store Buffer, and
Write Combining Buffer in Intel 64 and IA-32 Processors
Cache or Buffer
Trace

Cache1

Characteristics
• Pentium 4 and Intel Xeon processors (Based on Intel NetBurst® microarchitecture): 12 Kμops, 8-way set
associative.
• Intel Core i7, Intel Core 2 Duo, Intel® Atom™, Intel Core Duo, Intel Core Solo, Pentium M processor: not
implemented.
• P6 family and Pentium processors: not implemented.

L1 Instruction Cache • Pentium 4 and Intel Xeon processors (Based on Intel NetBurst microarchitecture): not implemented.
• Intel Core i7 processor: 32-KByte, 4-way set associative.
• Intel Core 2 Duo, Intel Atom, Intel Core Duo, Intel Core Solo, Pentium M processor: 32-KByte, 8-way set
associative.
• P6 family and Pentium processors: 8- or 16-KByte, 4-way set associative, 32-byte cache line size; 2-way set
associative for earlier Pentium processors.
L1 Data Cache

11-2 Vol. 3A

• Pentium 4 and Intel Xeon processors (Based on Intel NetBurst microarchitecture): 8-KByte, 4-way set
associative, 64-byte cache line size.
• Pentium 4 and Intel Xeon processors (Based on Intel NetBurst microarchitecture): 16-KByte, 8-way set
associative, 64-byte cache line size.
• Intel Atom processors: 24-KByte, 6-way set associative, 64-byte cache line size.
• Intel Core i7, Intel Core 2 Duo, Intel Core Duo, Intel Core Solo, Pentium M and Intel Xeon processors: 32KByte, 8-way set associative, 64-byte cache line size.
• P6 family processors: 16-KByte, 4-way set associative, 32-byte cache line size; 8-KBytes, 2-way set
associative for earlier P6 family processors.
• Pentium processors: 16-KByte, 4-way set associative, 32-byte cache line size; 8-KByte, 2-way set
associative for earlier Pentium processors.

MEMORY CACHE CONTROL

Table 11-1. Characteristics of the Caches, TLBs, Store Buffer, and
Write Combining Buffer in Intel 64 and IA-32 Processors (Contd.)
Cache or Buffer

Characteristics

L2 Unified Cache

• Intel Core 2 Duo and Intel Xeon processors: up to 4-MByte (or 4MBx2 in quadcore processors), 16-way set
associative, 64-byte cache line size.
• Intel Core 2 Duo and Intel Xeon processors: up to 6-MByte (or 6MBx2 in quadcore processors), 24-way set
associative, 64-byte cache line size.
• Intel Core i7, i5, i3 processors: 256KBbyte, 8-way set associative, 64-byte cache line size.
• Intel Atom processors: 512-KByte, 8-way set associative, 64-byte cache line size.
• Intel Core Duo, Intel Core Solo processors: 2-MByte, 8-way set associative, 64-byte cache line size
• Pentium 4 and Intel Xeon processors: 256, 512, 1024, or 2048-KByte, 8-way set associative, 64-byte cache
line size, 128-byte sector size.
• Pentium M processor: 1 or 2-MByte, 8-way set associative, 64-byte cache line size.
• P6 family processors: 128-KByte, 256-KByte, 512-KByte, 1-MByte, or 2-MByte, 4-way set associative,
32-byte cache line size.
• Pentium processor (external optional): System specific, typically 256- or 512-KByte, 4-way set associative,
32-byte cache line size.

L3 Unified Cache

• Intel Xeon processors: 512-KByte, 1-MByte, 2-MByte, or 4-MByte, 8-way set associative, 64-byte cache line
size, 128-byte sector size.
• Intel Core i7 processor, Intel Xeon processor 5500: Up to 8MByte, 16-way set associative, 64-byte cache
line size.
• Intel Xeon processor 5600: Up to 12MByte, 64-byte cache line size.
• Intel Xeon processor 7500: Up to 24MByte, 64-byte cache line size.

Instruction TLB
(4-KByte Pages)

• Pentium 4 and Intel Xeon processors (Based on Intel NetBurst microarchitecture): 128 entries, 4-way set
associative.
• Intel Atom processors: 32-entries, fully associative.
• Intel Core i7, i5, i3 processors: 64-entries per thread (128-entries per core), 4-way set associative.
• Intel Core 2 Duo, Intel Core Duo, Intel Core Solo processors, Pentium M processor: 128 entries, 4-way set
associative.
• P6 family processors: 32 entries, 4-way set associative.
• Pentium processor: 32 entries, 4-way set associative; fully set associative for Pentium processors with MMX
technology.

Data TLB (4-KByte
Pages)

• Intel Core i7, i5, i3 processors, DTLB0: 64-entries, 4-way set associative.
• Intel Core 2 Duo processors: DTLB0, 16 entries, DTLB1, 256 entries, 4 ways.
• Intel Atom processors: 16-entry-per-thread micro-TLB, fully associative; 64-entry DTLB, 4-way set
associative; 16-entry PDE cache, fully associative.
• Pentium 4 and Intel Xeon processors (Based on Intel NetBurst microarchitecture): 64 entry, fully set
associative, shared with large page DTLB.
• Intel Core Duo, Intel Core Solo processors, Pentium M processor: 128 entries, 4-way set associative.
• Pentium and P6 family processors: 64 entries, 4-way set associative; fully set, associative for Pentium
processors with MMX technology.

Instruction TLB
(Large Pages)

•
•
•
•
•
•

Intel Core i7, i5, i3 processors: 7-entries per thread, fully associative.
Intel Core 2 Duo processors: 4 entries, 4 ways.
Pentium 4 and Intel Xeon processors: large pages are fragmented.
Intel Core Duo, Intel Core Solo, Pentium M processor: 2 entries, fully associative.
P6 family processors: 2 entries, fully associative.
Pentium processor: Uses same TLB as used for 4-KByte pages.

Data TLB (Large
Pages)

•
•
•
•
•
•
•

Intel Core i7, i5, i3 processors, DTLB0: 32-entries, 4-way set associative.
Intel Core 2 Duo processors: DTLB0, 16 entries, DTLB1, 32 entries, 4 ways.
Intel Atom processors: 8 entries, 4-way set associative.
Pentium 4 and Intel Xeon processors: 64 entries, fully set associative; shared with small page data TLBs.
Intel Core Duo, Intel Core Solo, Pentium M processor: 8 entries, fully associative.
P6 family processors: 8 entries, 4-way set associative.
Pentium processor: 8 entries, 4-way set associative; uses same TLB as used for 4-KByte pages in Pentium
processors with MMX technology.

Second-level Unified
TLB (4-KByte
Pages)

• Intel Core i7, i5, i3 processor, STLB: 512-entries, 4-way set associative.

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MEMORY CACHE CONTROL

Table 11-1. Characteristics of the Caches, TLBs, Store Buffer, and
Write Combining Buffer in Intel 64 and IA-32 Processors (Contd.)
Cache or Buffer

Characteristics

Store Buffer

•
•
•
•
•
•
•

Intel Core i7, i5, i3 processors: 32entries.
Intel Core 2 Duo processors: 20 entries.
Intel Atom processors: 8 entries, used for both WC and store buffers.
Pentium 4 and Intel Xeon processors: 24 entries.
Pentium M processor: 16 entries.
P6 family processors: 12 entries.
Pentium processor: 2 buffers, 1 entry each (Pentium processors with MMX technology have 4 buffers for 4
entries).

Write Combining
(WC) Buffer

•
•
•
•
•

Intel Core 2 Duo processors: 8 entries.
Intel Atom processors: 8 entries, used for both WC and store buffers.
Pentium 4 and Intel Xeon processors: 6 or 8 entries.
Intel Core Duo, Intel Core Solo, Pentium M processors: 6 entries.
P6 family processors: 4 entries.

NOTES:
1 Introduced to the IA-32 architecture in the Pentium 4 and Intel Xeon processors.
Intel 64 and IA-32 processors may implement four types of caches: the trace cache, the level 1 (L1) cache, the
level 2 (L2) cache, and the level 3 (L3) cache. See Figure 11-1. Cache availability is described below:

•

Intel Core i7, i5, i3 processor Family and Intel Xeon processor Family based on Intel® microarchitecture code name Nehalem and Intel® microarchitecture code name Westmere — The L1 cache is
divided into two sections: one section is dedicated to caching instructions (pre-decoded instructions) and the
other caches data. The L2 cache is a unified data and instruction cache. Each processor core has its own L1 and
L2. The L3 cache is an inclusive, unified data and instruction cache, shared by all processor cores inside a
physical package. No trace cache is implemented.

•

Intel® Core™ 2 processor family and Intel® Xeon® processor family based on Intel® Core™ microarchitecture — The L1 cache is divided into two sections: one section is dedicated to caching instructions (predecoded instructions) and the other caches data. The L2 cache is a unified data and instruction cache located
on the processor chip; it is shared between two processor cores in a dual-core processor implementation.
Quad-core processors have two L2, each shared by two processor cores. No trace cache is implemented.

•

Intel® Atom™ processor — The L1 cache is divided into two sections: one section is dedicated to caching
instructions (pre-decoded instructions) and the other caches data. The L2 cache is a unified data and
instruction cache is located on the processor chip. No trace cache is implemented.

•

Intel® Core™ Solo and Intel® Core™ Duo processors — The L1 cache is divided into two sections: one
section is dedicated to caching instructions (pre-decoded instructions) and the other caches data. The L2 cache
is a unified data and instruction cache located on the processor chip. It is shared between two processor cores
in a dual-core processor implementation. No trace cache is implemented.

•

Pentium® 4 and Intel® Xeon® processors Based on Intel NetBurst® microarchitecture — The trace
cache caches decoded instructions (μops) from the instruction decoder and the L1 cache contains data. The L2
and L3 caches are unified data and instruction caches located on the processor chip. Dualcore processors have
two L2, one in each processor core. Note that the L3 cache is only implemented on some Intel Xeon processors.

•

P6 family processors — The L1 cache is divided into two sections: one dedicated to caching instructions (predecoded instructions) and the other to caching data. The L2 cache is a unified data and instruction cache
located on the processor chip. P6 family processors do not implement a trace cache.

•

Pentium® processors — The L1 cache has the same structure as on P6 family processors. There is no trace
cache. The L2 cache is a unified data and instruction cache external to the processor chip on earlier Pentium
processors and implemented on the processor chip in later Pentium processors. For Pentium processors where
the L2 cache is external to the processor, access to the cache is through the system bus.

For Intel Core i7 processors and processors based on Intel Core, Intel Atom, and Intel NetBurst microarchitectures,
Intel Core Duo, Intel Core Solo and Pentium M processors, the cache lines for the L1 and L2 caches (and L3 caches
if supported) are 64 bytes wide. The processor always reads a cache line from system memory beginning on a 64byte boundary. (A 64-byte aligned cache line begins at an address with its 6 least-significant bits clear.) A cache

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MEMORY CACHE CONTROL

line can be filled from memory with a 8-transfer burst transaction. The caches do not support partially-filled cache
lines, so caching even a single doubleword requires caching an entire line.
The L1 and L2 cache lines in the P6 family and Pentium processors are 32 bytes wide, with cache line reads from
system memory beginning on a 32-byte boundary (5 least-significant bits of a memory address clear.) A cache line
can be filled from memory with a 4-transfer burst transaction. Partially-filled cache lines are not supported.
The trace cache in processors based on Intel NetBurst microarchitecture is available in all execution modes:
protected mode, system management mode (SMM), and real-address mode. The L1,L2, and L3 caches are also
available in all execution modes; however, use of them must be handled carefully in SMM (see Section 34.4.2,
“SMRAM Caching”).
The TLBs store the most recently used page-directory and page-table entries. They speed up memory accesses
when paging is enabled by reducing the number of memory accesses that are required to read the page tables
stored in system memory. The TLBs are divided into four groups: instruction TLBs for 4-KByte pages, data TLBs for
4-KByte pages; instruction TLBs for large pages (2-MByte, 4-MByte or 1-GByte pages), and data TLBs for large
pages. The TLBs are normally active only in protected mode with paging enabled. When paging is disabled or the
processor is in real-address mode, the TLBs maintain their contents until explicitly or implicitly flushed (see Section
11.9, “Invalidating the Translation Lookaside Buffers (TLBs)”).
Processors based on Intel Core microarchitectures implement one level of instruction TLB and two levels of data
TLB. Intel Core i7 processor provides a second-level unified TLB.
The store buffer is associated with the processors instruction execution units. It allows writes to system memory
and/or the internal caches to be saved and in some cases combined to optimize the processor’s bus accesses. The
store buffer is always enabled in all execution modes.
The processor’s caches are for the most part transparent to software. When enabled, instructions and data flow
through these caches without the need for explicit software control. However, knowledge of the behavior of these
caches may be useful in optimizing software performance. For example, knowledge of cache dimensions and
replacement algorithms gives an indication of how large of a data structure can be operated on at once without
causing cache thrashing.
In multiprocessor systems, maintenance of cache consistency may, in rare circumstances, require intervention by
system software. For these rare cases, the processor provides privileged cache control instructions for use in
flushing caches and forcing memory ordering.
There are several instructions that software can use to improve the performance of the L1, L2, and L3 caches,
including the PREFETCHh, CLFLUSH, and CLFLUSHOPT instructions and the non-temporal move instructions
(MOVNTI, MOVNTQ, MOVNTDQ, MOVNTPS, and MOVNTPD). The use of these instructions are discussed in Section
11.5.5, “Cache Management Instructions.”

11.2

CACHING TERMINOLOGY

IA-32 processors (beginning with the Pentium processor) and Intel 64 processors use the MESI (modified, exclusive, shared, invalid) cache protocol to maintain consistency with internal caches and caches in other processors
(see Section 11.4, “Cache Control Protocol”).
When the processor recognizes that an operand being read from memory is cacheable, the processor reads an
entire cache line into the appropriate cache (L1, L2, L3, or all). This operation is called a cache line fill. If the
memory location containing that operand is still cached the next time the processor attempts to access the
operand, the processor can read the operand from the cache instead of going back to memory. This operation is
called a cache hit.
When the processor attempts to write an operand to a cacheable area of memory, it first checks if a cache line for
that memory location exists in the cache. If a valid cache line does exist, the processor (depending on the write
policy currently in force) can write the operand into the cache instead of writing it out to system memory. This
operation is called a write hit. If a write misses the cache (that is, a valid cache line is not present for area of
memory being written to), the processor performs a cache line fill, write allocation. Then it writes the operand into
the cache line and (depending on the write policy currently in force) can also write it out to memory. If the operand
is to be written out to memory, it is written first into the store buffer, and then written from the store buffer to
memory when the system bus is available. (Note that for the Pentium processor, write misses do not result in a
cache line fill; they always result in a write to memory. For this processor, only read misses result in cache line fills.)
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MEMORY CACHE CONTROL

When operating in an MP system, IA-32 processors (beginning with the Intel486 processor) and Intel 64 processors
have the ability to snoop other processor’s accesses to system memory and to their internal caches. They use this
snooping ability to keep their internal caches consistent both with system memory and with the caches in other
processors on the bus. For example, in the Pentium and P6 family processors, if through snooping one processor
detects that another processor intends to write to a memory location that it currently has cached in shared state,
the snooping processor will invalidate its cache line forcing it to perform a cache line fill the next time it accesses
the same memory location.
Beginning with the P6 family processors, if a processor detects (through snooping) that another processor is trying
to access a memory location that it has modified in its cache, but has not yet written back to system memory, the
snooping processor will signal the other processor (by means of the HITM# signal) that the cache line is held in
modified state and will preform an implicit write-back of the modified data. The implicit write-back is transferred
directly to the initial requesting processor and snooped by the memory controller to assure that system memory
has been updated. Here, the processor with the valid data may pass the data to the other processors without actually writing it to system memory; however, it is the responsibility of the memory controller to snoop this operation
and update memory.

11.3

METHODS OF CACHING AVAILABLE

The processor allows any area of system memory to be cached in the L1, L2, and L3 caches. In individual pages or
regions of system memory, it allows the type of caching (also called memory type) to be specified (see Section
11.5). Memory types currently defined for the Intel 64 and IA-32 architectures are (see Table 11-2):

•

Strong Uncacheable (UC) —System memory locations are not cached. All reads and writes appear on the
system bus and are executed in program order without reordering. No speculative memory accesses, pagetable walks, or prefetches of speculated branch targets are made. This type of cache-control is useful for
memory-mapped I/O devices. When used with normal RAM, it greatly reduces processor performance.

NOTE
The behavior of FP and SSE/SSE2 operations on operands in UC memory is implementation
dependent. In some implementations, accesses to UC memory may occur more than once. To
ensure predictable behavior, use loads and stores of general purpose registers to access UC
memory that may have read or write side effects.

Table 11-2. Memory Types and Their Properties
Memory Type and
Mnemonic

Cacheable

Writeback Allows
Cacheable Speculative
Reads

Memory Ordering Model

Strong Uncacheable
(UC)

No

No

No

Strong Ordering

Uncacheable (UC-)

No

No

No

Strong Ordering. Can only be selected through the PAT. Can be
overridden by WC in MTRRs.

Write Combining (WC) No

No

Yes

Weak Ordering. Available by programming MTRRs or by selecting it
through the PAT.

Write Through (WT)

Yes

No

Yes

Speculative Processor Ordering.

Write Back (WB)

Yes

Yes

Yes

Speculative Processor Ordering.

Write Protected (WP)

Yes for
reads; no for
writes

No

Yes

Speculative Processor Ordering. Available by programming MTRRs.

•

Uncacheable (UC-) — Has same characteristics as the strong uncacheable (UC) memory type, except that
this memory type can be overridden by programming the MTRRs for the WC memory type. This memory type
is available in processor families starting from the Pentium III processors and can only be selected through the
PAT.

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MEMORY CACHE CONTROL

•

Write Combining (WC) — System memory locations are not cached (as with uncacheable memory) and
coherency is not enforced by the processor’s bus coherency protocol. Speculative reads are allowed. Writes
may be delayed and combined in the write combining buffer (WC buffer) to reduce memory accesses. If the WC
buffer is partially filled, the writes may be delayed until the next occurrence of a serializing event; such as, an
SFENCE or MFENCE instruction, CPUID execution, a read or write to uncached memory, an interrupt
occurrence, or a LOCK instruction execution. This type of cache-control is appropriate for video frame buffers,
where the order of writes is unimportant as long as the writes update memory so they can be seen on the
graphics display. See Section 11.3.1, “Buffering of Write Combining Memory Locations,” for more information
about caching the WC memory type. This memory type is available in the Pentium Pro and Pentium II
processors by programming the MTRRs; or in processor families starting from the Pentium III processors by
programming the MTRRs or by selecting it through the PAT.

•

Write-through (WT) — Writes and reads to and from system memory are cached. Reads come from cache
lines on cache hits; read misses cause cache fills. Speculative reads are allowed. All writes are written to a
cache line (when possible) and through to system memory. When writing through to memory, invalid cache
lines are never filled, and valid cache lines are either filled or invalidated. Write combining is allowed. This type
of cache-control is appropriate for frame buffers or when there are devices on the system bus that access
system memory, but do not perform snooping of memory accesses. It enforces coherency between caches in
the processors and system memory.

•

Write-back (WB) — Writes and reads to and from system memory are cached. Reads come from cache lines
on cache hits; read misses cause cache fills. Speculative reads are allowed. Write misses cause cache line fills
(in processor families starting with the P6 family processors), and writes are performed entirely in the cache,
when possible. Write combining is allowed. The write-back memory type reduces bus traffic by eliminating
many unnecessary writes to system memory. Writes to a cache line are not immediately forwarded to system
memory; instead, they are accumulated in the cache. The modified cache lines are written to system memory
later, when a write-back operation is performed. Write-back operations are triggered when cache lines need to
be deallocated, such as when new cache lines are being allocated in a cache that is already full. They also are
triggered by the mechanisms used to maintain cache consistency. This type of cache-control provides the best
performance, but it requires that all devices that access system memory on the system bus be able to snoop
memory accesses to insure system memory and cache coherency.

•

Write protected (WP) — Reads come from cache lines when possible, and read misses cause cache fills.
Writes are propagated to the system bus and cause corresponding cache lines on all processors on the bus to
be invalidated. Speculative reads are allowed. This memory type is available in processor families starting from
the P6 family processors by programming the MTRRs (see Table 11-6).

Table 11-3 shows which of these caching methods are available in the Pentium, P6 Family, Pentium 4, and Intel
Xeon processors.

Table 11-3. Methods of Caching Available in Intel Core 2 Duo, Intel Atom, Intel Core Duo, Pentium M, Pentium 4,
Intel Xeon, P6 Family, and Pentium Processors
Memory Type

Intel Core 2 Duo, Intel Atom, Intel Core Duo,
P6 Family
Pentium M, Pentium 4 and Intel Xeon Processors Processors

Pentium
Processor

Strong Uncacheable (UC)

Yes

Yes

Yes

Uncacheable (UC-)

Yes

Yes*

No

Write Combining (WC)

Yes

Yes

No

Write Through (WT)

Yes

Yes

Yes

Write Back (WB)

Yes

Yes

Yes

Write Protected (WP)

Yes

Yes

No

NOTE:
* Introduced in the Pentium III processor; not available in the Pentium Pro or Pentium II processors

11.3.1

Buffering of Write Combining Memory Locations

Writes to the WC memory type are not cached in the typical sense of the word cached. They are retained in an
internal write combining buffer (WC buffer) that is separate from the internal L1, L2, and L3 caches and the store
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MEMORY CACHE CONTROL

buffer. The WC buffer is not snooped and thus does not provide data coherency. Buffering of writes to WC memory
is done to allow software a small window of time to supply more modified data to the WC buffer while remaining as
non-intrusive to software as possible. The buffering of writes to WC memory also causes data to be collapsed; that
is, multiple writes to the same memory location will leave the last data written in the location and the other writes
will be lost.
The size and structure of the WC buffer is not architecturally defined. For the Intel Core 2 Duo, Intel Atom, Intel
Core Duo, Pentium M, Pentium 4 and Intel Xeon processors; the WC buffer is made up of several 64-byte WC
buffers. For the P6 family processors, the WC buffer is made up of several 32-byte WC buffers.
When software begins writing to WC memory, the processor begins filling the WC buffers one at a time. When one
or more WC buffers has been filled, the processor has the option of evicting the buffers to system memory. The
protocol for evicting the WC buffers is implementation dependent and should not be relied on by software for
system memory coherency. When using the WC memory type, software must be sensitive to the fact that the
writing of data to system memory is being delayed and must deliberately empty the WC buffers when system
memory coherency is required.
Once the processor has started to evict data from the WC buffer into system memory, it will make a bus-transaction
style decision based on how much of the buffer contains valid data. If the buffer is full (for example, all bytes are
valid), the processor will execute a burst-write transaction on the bus. This results in all 32 bytes (P6 family processors) or 64 bytes (Pentium 4 and more recent processor) being transmitted on the data bus in a single burst transaction. If one or more of the WC buffer’s bytes are invalid (for example, have not been written by software), the
processor will transmit the data to memory using “partial write” transactions (one chunk at a time, where a “chunk”
is 8 bytes).
This will result in a maximum of 4 partial write transactions (for P6 family processors) or 8 partial write transactions
(for the Pentium 4 and more recent processors) for one WC buffer of data sent to memory.
The WC memory type is weakly ordered by definition. Once the eviction of a WC buffer has started, the data is
subject to the weak ordering semantics of its definition. Ordering is not maintained between the successive allocation/deallocation of WC buffers (for example, writes to WC buffer 1 followed by writes to WC buffer 2 may appear
as buffer 2 followed by buffer 1 on the system bus). When a WC buffer is evicted to memory as partial writes there
is no guaranteed ordering between successive partial writes (for example, a partial write for chunk 2 may appear
on the bus before the partial write for chunk 1 or vice versa).
The only elements of WC propagation to the system bus that are guaranteed are those provided by transaction
atomicity. For example, with a P6 family processor, a completely full WC buffer will always be propagated as a
single 32-bit burst transaction using any chunk order. In a WC buffer eviction where data will be evicted as partials,
all data contained in the same chunk (0 mod 8 aligned) will be propagated simultaneously. Likewise, for more
recent processors starting with those based on Intel NetBurst microarchitectures, a full WC buffer will always be
propagated as a single burst transactions, using any chunk order within a transaction. For partial buffer propagations, all data contained in the same chunk will be propagated simultaneously.

11.3.2

Choosing a Memory Type

The simplest system memory model does not use memory-mapped I/O with read or write side effects, does not
include a frame buffer, and uses the write-back memory type for all memory. An I/O agent can perform direct
memory access (DMA) to write-back memory and the cache protocol maintains cache coherency.
A system can use strong uncacheable memory for other memory-mapped I/O, and should always use strong uncacheable memory for memory-mapped I/O with read side effects.
Dual-ported memory can be considered a write side effect, making relatively prompt writes desirable, because
those writes cannot be observed at the other port until they reach the memory agent. A system can use strong
uncacheable, uncacheable, write-through, or write-combining memory for frame buffers or dual-ported memory
that contains pixel values displayed on a screen. Frame buffer memory is typically large (a few megabytes) and is
usually written more than it is read by the processor. Using strong uncacheable memory for a frame buffer generates very large amounts of bus traffic, because operations on the entire buffer are implemented using partial writes
rather than line writes. Using write-through memory for a frame buffer can displace almost all other useful cached
lines in the processor's L2 and L3 caches and L1 data cache. Therefore, systems should use write-combining
memory for frame buffers whenever possible.

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Software can use page-level cache control, to assign appropriate effective memory types when software will not
access data structures in ways that benefit from write-back caching. For example, software may read a large data
structure once and not access the structure again until the structure is rewritten by another agent. Such a large
data structure should be marked as uncacheable, or reading it will evict cached lines that the processor will be
referencing again.
A similar example would be a write-only data structure that is written to (to export the data to another agent), but
never read by software. Such a structure can be marked as uncacheable, because software never reads the values
that it writes (though as uncacheable memory, it will be written using partial writes, while as write-back memory,
it will be written using line writes, which may not occur until the other agent reads the structure and triggers
implicit write-backs).
On the Pentium III, Pentium 4, and more recent processors, new instructions are provided that give software
greater control over the caching, prefetching, and the write-back characteristics of data. These instructions allow
software to use weakly ordered or processor ordered memory types to improve processor performance, but when
necessary to force strong ordering on memory reads and/or writes. They also allow software greater control over
the caching of data. For a description of these instructions and there intended use, see Section 11.5.5, “Cache
Management Instructions.”

11.3.3

Code Fetches in Uncacheable Memory

Programs may execute code from uncacheable (UC) memory, but the implications are different from accessing
data in UC memory. When doing code fetches, the processor never transitions from cacheable code to UC code
speculatively. It also never speculatively fetches branch targets that result in UC code.
The processor may fetch the same UC cache line multiple times in order to decode an instruction once. It may
decode consecutive UC instructions in a cacheline without fetching between each instruction. It may also fetch
additional cachelines from the same or a consecutive 4-KByte page in order to decode one non-speculative UC
instruction (this can be true even when the instruction is contained fully in one line).
Because of the above and because cacheline sizes may change in future processors, software should avoid placing
memory-mapped I/O with read side effects in the same page or in a subsequent page used to execute UC code.

11.4

CACHE CONTROL PROTOCOL

The following section describes the cache control protocol currently defined for the Intel 64 and IA-32 architectures.
In the L1 data cache and in the L2/L3 unified caches, the MESI (modified, exclusive, shared, invalid) cache protocol
maintains consistency with caches of other processors. The L1 data cache and the L2/L3 unified caches have two
MESI status flags per cache line. Each line can be marked as being in one of the states defined in Table 11-4. In
general, the operation of the MESI protocol is transparent to programs.

Table 11-4. MESI Cache Line States
Cache Line State

M (Modified)

E (Exclusive)

S (Shared)

I (Invalid)

This cache line is valid?

Yes

Yes

Yes

No

The memory copy is…

Out of date

Valid

Valid

—

Copies exist in caches of other
processors?

No

No

Maybe

Maybe

A write to this line …

Does not go to the
system bus.

Does not go to the
system bus.

Causes the processor to
gain exclusive ownership
of the line.

Goes directly to the
system bus.

The L1 instruction cache in P6 family processors implements only the “SI” part of the MESI protocol, because the
instruction cache is not writable. The instruction cache monitors changes in the data cache to maintain consistency
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MEMORY CACHE CONTROL

between the caches when instructions are modified. See Section 11.6, “Self-Modifying Code,” for more information
on the implications of caching instructions.

11.5

CACHE CONTROL

The Intel 64 and IA-32 architectures provide a variety of mechanisms for controlling the caching of data and
instructions and for controlling the ordering of reads and writes between the processor, the caches, and memory.
These mechanisms can be divided into two groups:

•

Cache control registers and bits — The Intel 64 and IA-32 architectures define several dedicated registers
and various bits within control registers and page- and directory-table entries that control the caching system
memory locations in the L1, L2, and L3 caches. These mechanisms control the caching of virtual memory pages
and of regions of physical memory.

•

Cache control and memory ordering instructions — The Intel 64 and IA-32 architectures provide several
instructions that control the caching of data, the ordering of memory reads and writes, and the prefetching of
data. These instructions allow software to control the caching of specific data structures, to control memory
coherency for specific locations in memory, and to force strong memory ordering at specific locations in a
program.

The following sections describe these two groups of cache control mechanisms.

11.5.1

Cache Control Registers and Bits

Figure 11-3 depicts cache-control mechanisms in IA-32 processors. Other than for the matter of memory address
space, these work the same in Intel 64 processors.
The Intel 64 and IA-32 architectures provide the following cache-control registers and bits for use in enabling or
restricting caching to various pages or regions in memory:

•

CD flag, bit 30 of control register CR0 — Controls caching of system memory locations (see Section 2.5,
“Control Registers”). If the CD flag is clear, caching is enabled for the whole of system memory, but may be
restricted for individual pages or regions of memory by other cache-control mechanisms. When the CD flag is
set, caching is restricted in the processor’s caches (cache hierarchy) for the P6 and more recent processor
families and prevented for the Pentium processor (see note below). With the CD flag set, however, the caches
will still respond to snoop traffic. Caches should be explicitly flushed to insure memory coherency. For highest
processor performance, both the CD and the NW flags in control register CR0 should be cleared. Table 11-5
shows the interaction of the CD and NW flags.
The effect of setting the CD flag is somewhat different for processor families starting with P6 family than the
Pentium processor (see Table 11-5). To insure memory coherency after the CD flag is set, the caches should
be explicitly flushed (see Section 11.5.3, “Preventing Caching”). Setting the CD flag for the P6 and more
recent processor families modify cache line fill and update behaviour. Also, setting the CD flag on these
processors do not force strict ordering of memory accesses unless the MTRRs are disabled and/or all memory
is referenced as uncached (see Section 8.2.5, “Strengthening or Weakening the Memory-Ordering Model”).

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MEMORY CACHE CONTROL

CR4
P
G
E

Enables global pages
designated with G flag

CR3
P P
C W
D T

CR0
C N
D W

CD and NW Flags
control overall caching
of system memory

FFFFFFFFH2
PAT4

Control caching of
page directory

PAT controls caching
of virtual memory
pages

Page-Directory or
Page-Table Entry
P P
P4
A G1 C W
T
D T

MTRRs3

PCD and PWT flags
control page-level
caching
G flag controls pagelevel flushing of TLBs

Store Buffer

Physical Memory

0

MTRRs control caching
of selected regions of
physical memory

TLBs
1. G flag only available in P6 and later processor families
2. The maximum physical address size is reported by CPUID leaf
function 80000008H. The maximum physical address size of
FFFFFFFFFH applies only If 36-bit physical addressing is used.
3. MTRRs available only in P6 and later processor families;
similar control available in Pentium processor with the KEN#
and WB/WT# pins.
4. PAT available only in Pentium III and later processor families.
5. L3 in processors based on Intel NetBurst microarchitecture can
be disabled using IA32_MISC_ENABLE MSR.

Figure 11-3. Cache-Control Registers and Bits Available in Intel 64 and IA-32 Processors

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MEMORY CACHE CONTROL

Table 11-5. Cache Operating Modes
CD

NW

0

0

0

1

L1

L2/L31

• Read hits access the cache; read misses may cause replacement.
• Write hits update the cache.
• Only writes to shared lines and write misses update system memory.

Yes
Yes
Yes

Yes
Yes
Yes

• Write misses cause cache line fills.
• Write hits can change shared lines to modified under control of the MTRRs and with associated
read invalidation cycle.
• (Pentium processor only.) Write misses do not cause cache line fills.

Yes
Yes

Yes

• (Pentium processor only.) Write hits can change shared lines to exclusive under control of WB/WT#.
• Invalidation is allowed.
• External snoop traffic is supported.

Yes

Caching and Read/Write Policy
Normal Cache Mode. Highest performance cache operation.

Yes
Yes

Yes
Yes

NA

NA

Yes

Yes

Yes

Yes

Yes
Yes

Yes
Yes

• Write misses access memory.
• Write hits can change shared lines to exclusive under control of the MTRRs and with associated
read invalidation cycle.
• (Pentium processor only.) Write hits can change shared lines to exclusive under control of the
WB/WT#.

Yes
Yes

Yes
Yes

• (P6 and later processor families only.) Strict memory ordering is not enforced unless the MTRRs are
disabled and/or all memory is referenced as uncached (see Section 7.2.4., “Strengthening or
Weakening the Memory Ordering Model”).
• Invalidation is allowed.
• External snoop traffic is supported.

Yes

Yes

Yes
Yes

Yes
Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes
Yes
Yes

Yes
Yes
Yes

No

Yes

Invalid setting.
Generates a general-protection exception (#GP) with an error code of 0.

1

0

No-fill Cache Mode. Memory coherency is maintained.3
• (Pentium 4 and later processor families.) State of processor after a power up or reset.
• Read hits access the cache; read misses do not cause replacement (see Pentium 4 and Intel Xeon
processors reference below).
• Write hits update the cache.
• Only writes to shared lines and write misses update system memory.

1

1

Yes

Memory coherency is not maintained.2, 3
• (P6 family and Pentium processors.) State of the processor after a power up or reset.
• Read hits access the cache; read misses do not cause replacement.
• Write hits update the cache and change exclusive lines to modified.

•
•
•
•

Shared lines remain shared after write hit.
Write misses access memory.
Invalidation is inhibited when snooping; but is allowed with INVD and WBINVD instructions.
External snoop traffic is supported.

Yes

NOTES:
1. The L2/L3 column in this table is definitive for the Pentium 4, Intel Xeon, and P6 family processors. It is intended to represent what
could be implemented in a system based on a Pentium processor with an external, platform specific, write-back L2 cache.
2. The Pentium 4 and more recent processor families do not support this mode; setting the CD and NW bits to 1 selects the no-fill
cache mode.
3. Not supported In Intel Atom processors. If CD = 1 in an Intel Atom processor, caching is disabled.

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MEMORY CACHE CONTROL

•

NW flag, bit 29 of control register CR0 — Controls the write policy for system memory locations (see
Section 2.5, “Control Registers”). If the NW and CD flags are clear, write-back is enabled for the whole of
system memory, but may be restricted for individual pages or regions of memory by other cache-control
mechanisms. Table 11-5 shows how the other combinations of CD and NW flags affects caching.

NOTES
For the Pentium 4 and Intel Xeon processors, the NW flag is a don’t care flag; that is, when the CD
flag is set, the processor uses the no-fill cache mode, regardless of the setting of the NW flag.
For Intel Atom processors, the NW flag is a don’t care flag; that is, when the CD flag is set, the
processor disables caching, regardless of the setting of the NW flag.
For the Pentium processor, when the L1 cache is disabled (the CD and NW flags in control register
CR0 are set), external snoops are accepted in DP (dual-processor) systems and inhibited in uniprocessor systems.
When snoops are inhibited, address parity is not checked and APCHK# is not asserted for a corrupt
address; however, when snoops are accepted, address parity is checked and APCHK# is asserted
for corrupt addresses.

•

PCD and PWT flags in paging-structure entries — Control the memory type used to access paging
structures and pages (see Section 4.9, “Paging and Memory Typing”).

•

PCD and PWT flags in control register CR3 — Control the memory type used to access the first paging
structure of the current paging-structure hierarchy (see Section 4.9, “Paging and Memory Typing”).

•

G (global) flag in the page-directory and page-table entries (introduced to the IA-32 architecture in
the P6 family processors) — Controls the flushing of TLB entries for individual pages. See Section 4.10,
“Caching Translation Information,” for more information about this flag.

•

PGE (page global enable) flag in control register CR4 — Enables the establishment of global pages with
the G flag. See Section 4.10, “Caching Translation Information,” for more information about this flag.

•

Memory type range registers (MTRRs) (introduced in P6 family processors) — Control the type of
caching used in specific regions of physical memory. Any of the caching types described in Section 11.3,
“Methods of Caching Available,” can be selected. See Section 11.11, “Memory Type Range Registers (MTRRs),”
for a detailed description of the MTRRs.

•

Page Attribute Table (PAT) MSR (introduced in the Pentium III processor) — Extends the memory
typing capabilities of the processor to permit memory types to be assigned on a page-by-page basis (see
Section 11.12, “Page Attribute Table (PAT)”).

•

Third-Level Cache Disable flag, bit 6 of the IA32_MISC_ENABLE MSR (Available only in processors
based on Intel NetBurst microarchitecture) — Allows the L3 cache to be disabled and enabled, independently of the L1 and L2 caches.

•

KEN# and WB/WT# pins (Pentium processor) — Allow external hardware to control the caching method
used for specific areas of memory. They perform similar (but not identical) functions to the MTRRs in the P6
family processors.

•

PCD and PWT pins (Pentium processor) — These pins (which are associated with the PCD and PWT flags in
control register CR3 and in the page-directory and page-table entries) permit caching in an external L2 cache
to be controlled on a page-by-page basis, consistent with the control exercised on the L1 cache of these
processors. The P6 and more recent processor families do not provide these pins because the L2 cache in
internal to the chip package.

11.5.2

Precedence of Cache Controls

The cache control flags and MTRRs operate hierarchically for restricting caching. That is, if the CD flag is set,
caching is prevented globally (see Table 11-5). If the CD flag is clear, the page-level cache control flags and/or the
MTRRs can be used to restrict caching. If there is an overlap of page-level and MTRR caching controls, the mechanism that prevents caching has precedence. For example, if an MTRR makes a region of system memory uncacheable, a page-level caching control cannot be used to enable caching for a page in that region. The converse is also

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MEMORY CACHE CONTROL

true; that is, if a page-level caching control designates a page as uncacheable, an MTRR cannot be used to make
the page cacheable.
In cases where there is a overlap in the assignment of the write-back and write-through caching policies to a page
and a region of memory, the write-through policy takes precedence. The write-combining policy (which can only be
assigned through an MTRR or the PAT) takes precedence over either write-through or write-back.
The selection of memory types at the page level varies depending on whether PAT is being used to select memory
types for pages, as described in the following sections.
On processors based on Intel NetBurst microarchitecture, the third-level cache can be disabled by bit 6 of the
IA32_MISC_ENABLE MSR. Using IA32_MISC_ENABLE[bit 6] takes precedence over the CD flag, MTRRs, and PAT
for the L3 cache in those processors. That is, when the third-level cache disable flag is set (cache disabled), the
other cache controls have no affect on the L3 cache; when the flag is clear (enabled), the cache controls have the
same affect on the L3 cache as they have on the L1 and L2 caches.
IA32_MISC_ENABLE[bit 6] is not supported in Intel Core i7 processors, nor processors based on Intel Core, and
Intel Atom microarchitectures.

11.5.2.1

Selecting Memory Types for Pentium Pro and Pentium II Processors

The Pentium Pro and Pentium II processors do not support the PAT. Here, the effective memory type for a page is
selected with the MTRRs and the PCD and PWT bits in the page-table or page-directory entry for the page. Table
11-6 describes the mapping of MTRR memory types and page-level caching attributes to effective memory types,
when normal caching is in effect (the CD and NW flags in control register CR0 are clear). Combinations that appear
in gray are implementation-defined for the Pentium Pro and Pentium II processors. System designers are encouraged to avoid these implementation-defined combinations.

Table 11-6. Effective Page-Level Memory Type for Pentium Pro and Pentium II Processors
MTRR Memory Type1

PCD Value

PWT Value

Effective Memory Type

UC

X

X

UC

WC

0

0

WC

0

1

WC

1

0

WC

1

1

UC

0

X

WT

1

X

UC

0

0

WP

0

1

WP

1

0

WC

1

1

UC

0

0

WB

0

1

WT

1

X

UC

WT
WP

WB

NOTE:
1. These effective memory types also apply to the Pentium 4, Intel Xeon, and Pentium III processors when the PAT bit is not used
(set to 0) in page-table and page-directory entries.
When normal caching is in effect, the effective memory type shown in Table 11-6 is determined using the following
rules:
1. If the PCD and PWT attributes for the page are both 0, then the effective memory type is identical to the
MTRR-defined memory type.

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2. If the PCD flag is set, then the effective memory type is UC.
3. If the PCD flag is clear and the PWT flag is set, the effective memory type is WT for the WB memory type and
the MTRR-defined memory type for all other memory types.
4. Setting the PCD and PWT flags to opposite values is considered model-specific for the WP and WC memory
types and architecturally-defined for the WB, WT, and UC memory types.

11.5.2.2

Selecting Memory Types for Pentium III and More Recent Processor Families

The Intel Core 2 Duo, Intel Atom, Intel Core Duo, Intel Core Solo, Pentium M, Pentium 4, Intel Xeon, and Pentium
III processors use the PAT to select effective page-level memory types. Here, a memory type for a page is selected
by the MTRRs and the value in a PAT entry that is selected with the PAT, PCD and PWT bits in a page-table or pagedirectory entry (see Section 11.12.3, “Selecting a Memory Type from the PAT”). Table 11-7 describes the mapping
of MTRR memory types and PAT entry types to effective memory types, when normal caching is in effect (the CD
and NW flags in control register CR0 are clear).

Table 11-7. Effective Page-Level Memory Types for Pentium III and More Recent Processor Families
MTRR Memory Type

PAT Entry Value

Effective Memory Type

UC

UC

UC1

UC-

UC1

WC

WC

WT

UC1

WB

UC1

WP

UC1

UC

UC2

UC-

WC

WC

WC

WT

UC2,3

WB

WC

WP

UC2,3

UC

UC2

UC-

UC2

WC

WC

WT

WT

WB

WT

WP

WP3

UC

UC2

UC-

UC2

WC

WC

WC

WT

WB

WT

WT

WB

WB

WP

WP

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MEMORY CACHE CONTROL

Table 11-7. Effective Page-Level Memory Types for Pentium III and More Recent Processor Families (Contd.)
MTRR Memory Type

PAT Entry Value

Effective Memory Type

WP

UC

UC2

UC-

WC3

WC

WC

WT

WT3

WB

WP

WP

WP

NOTES:
1. The UC attribute comes from the MTRRs and the processors are not required to snoop their caches since the data could never have
been cached. This attribute is preferred for performance reasons.
2. The UC attribute came from the page-table or page-directory entry and processors are required to check their caches because the
data may be cached due to page aliasing, which is not recommended.
3. These combinations were specified as “undefined” in previous editions of the Intel® 64 and IA-32 Architectures Software Developer’s Manual. However, all processors that support both the PAT and the MTRRs determine the effective page-level memory
types for these combinations as given.

11.5.2.3

Writing Values Across Pages with Different Memory Types

If two adjoining pages in memory have different memory types, and a word or longer operand is written to a
memory location that crosses the page boundary between those two pages, the operand might be written to
memory twice. This action does not present a problem for writes to actual memory; however, if a device is mapped
the memory space assigned to the pages, the device might malfunction.

11.5.3

Preventing Caching

To disable the L1, L2, and L3 caches after they have been enabled and have received cache fills, perform the
following steps:
1. Enter the no-fill cache mode. (Set the CD flag in control register CR0 to 1 and the NW flag to 0.
2. Flush all caches using the WBINVD instruction.
3. Disable the MTRRs and set the default memory type to uncached or set all MTRRs for the uncached memory
type (see the discussion of the discussion of the TYPE field and the E flag in Section 11.11.2.1,
“IA32_MTRR_DEF_TYPE MSR”).
The caches must be flushed (step 2) after the CD flag is set to insure system memory coherency. If the caches are
not flushed, cache hits on reads will still occur and data will be read from valid cache lines.
The intent of the three separate steps listed above address three distinct requirements: (i) discontinue new data
replacing existing data in the cache (ii) ensure data already in the cache are evicted to memory, (iii) ensure subsequent memory references observe UC memory type semantics. Different processor implementation of caching
control hardware may allow some variation of software implementation of these three requirements. See note
below.

NOTES
Setting the CD flag in control register CR0 modifies the processor’s caching behaviour as indicated
in Table 11-5, but setting the CD flag alone may not be sufficient across all processor families to
force the effective memory type for all physical memory to be UC nor does it force strict memory
ordering, due to hardware implementation variations across different processor families. To force
the UC memory type and strict memory ordering on all of physical memory, it is sufficient to either
program the MTRRs for all physical memory to be UC memory type or disable all MTRRs.
For the Pentium 4 and Intel Xeon processors, after the sequence of steps given above has been
executed, the cache lines containing the code between the end of the WBINVD instruction and
before the MTRRS have actually been disabled may be retained in the cache hierarchy. Here, to
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MEMORY CACHE CONTROL

remove code from the cache completely, a second WBINVD instruction must be executed after the
MTRRs have been disabled.
For Intel Atom processors, setting the CD flag forces all physical memory to observe UC semantics
(without requiring memory type of physical memory to be set explicitly). Consequently, software
does not need to issue a second WBINVD as some other processor generations might require.

11.5.4

Disabling and Enabling the L3 Cache

On processors based on Intel NetBurst microarchitecture, the third-level cache can be disabled by bit 6 of the
IA32_MISC_ENABLE MSR. The third-level cache disable flag (bit 6 of the IA32_MISC_ENABLE MSR) allows the L3
cache to be disabled and enabled, independently of the L1 and L2 caches. Prior to using this control to disable or
enable the L3 cache, software should disable and flush all the processor caches, as described earlier in Section
11.5.3, “Preventing Caching,” to prevent of loss of information stored in the L3 cache. After the L3 cache has been
disabled or enabled, caching for the whole processor can be restored.
Newer Intel 64 processor with L3 do not support IA32_MISC_ENABLE[bit 6], the procedure described in Section
11.5.3, “Preventing Caching,” apply to the entire cache hierarchy.

11.5.5

Cache Management Instructions

The Intel 64 and IA-32 architectures provide several instructions for managing the L1, L2, and L3 caches. The INVD
and WBINVD instructions are privileged instructions and operate on the L1, L2 and L3 caches as a whole. The
PREFETCHh, CLFLUSH and CLFLUSHOPT instructions and the non-temporal move instructions (MOVNTI, MOVNTQ,
MOVNTDQ, MOVNTPS, and MOVNTPD) offer more granular control over caching, and are available to all privileged
levels.
The INVD and WBINVD instructions are used to invalidate the contents of the L1, L2, and L3 caches. The INVD
instruction invalidates all internal cache entries, then generates a special-function bus cycle that indicates that
external caches also should be invalidated. The INVD instruction should be used with care. It does not force a
write-back of modified cache lines; therefore, data stored in the caches and not written back to system memory
will be lost. Unless there is a specific requirement or benefit to invalidating the caches without writing back the
modified lines (such as, during testing or fault recovery where cache coherency with main memory is not a
concern), software should use the WBINVD instruction.
The WBINVD instruction first writes back any modified lines in all the internal caches, then invalidates the contents
of both the L1, L2, and L3 caches. It ensures that cache coherency with main memory is maintained regardless of
the write policy in effect (that is, write-through or write-back). Following this operation, the WBINVD instruction
generates one (P6 family processors) or two (Pentium and Intel486 processors) special-function bus cycles to indicate to external cache controllers that write-back of modified data followed by invalidation of external caches
should occur. The amount of time or cycles for WBINVD to complete will vary due to the size of different cache hierarchies and other factors. As a consequence, the use of the WBINVD instruction can have an impact on interrupt/event response time.
The PREFETCHh instructions allow a program to suggest to the processor that a cache line from a specified location
in system memory be prefetched into the cache hierarchy (see Section 11.8, “Explicit Caching”).
The CLFLUSH and CLFLUSHOPT instructions allow selected cache lines to be flushed from memory. These instructions give a program the ability to explicitly free up cache space, when it is known that cached section of system
memory will not be accessed in the near future.
The non-temporal move instructions (MOVNTI, MOVNTQ, MOVNTDQ, MOVNTPS, and MOVNTPD) allow data to be
moved from the processor’s registers directly into system memory without being also written into the L1, L2,
and/or L3 caches. These instructions can be used to prevent cache pollution when operating on data that is going
to be modified only once before being stored back into system memory. These instructions operate on data in the
general-purpose, MMX, and XMM registers.

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MEMORY CACHE CONTROL

11.5.6

L1 Data Cache Context Mode

L1 data cache context mode is a feature of processors based on the Intel NetBurst microarchitecture that support
Intel Hyper-Threading Technology. When CPUID.1:ECX[bit 10] = 1, the processor supports setting L1 data cache
context mode using the L1 data cache context mode flag ( IA32_MISC_ENABLE[bit 24] ). Selectable modes are
adaptive mode (default) and shared mode.
The BIOS is responsible for configuring the L1 data cache context mode.

11.5.6.1

Adaptive Mode

Adaptive mode facilitates L1 data cache sharing between logical processors. When running in adaptive mode, the
L1 data cache is shared across logical processors in the same core if:

•
•

CR3 control registers for logical processors sharing the cache are identical.
The same paging mode is used by logical processors sharing the cache.

In this situation, the entire L1 data cache is available to each logical processor (instead of being competitively
shared).
If CR3 values are different for the logical processors sharing an L1 data cache or the logical processors use different
paging modes, processors compete for cache resources. This reduces the effective size of the cache for each logical
processor. Aliasing of the cache is not allowed (which prevents data thrashing).

11.5.6.2

Shared Mode

In shared mode, the L1 data cache is competitively shared between logical processors. This is true even if the
logical processors use identical CR3 registers and paging modes.
In shared mode, linear addresses in the L1 data cache can be aliased, meaning that one linear address in the cache
can point to different physical locations. The mechanism for resolving aliasing can lead to thrashing. For this
reason, IA32_MISC_ENABLE[bit 24] = 0 is the preferred configuration for processors based on the Intel NetBurst
microarchitecture that support Intel Hyper-Threading Technology.

11.6

SELF-MODIFYING CODE

A write to a memory location in a code segment that is currently cached in the processor causes the associated
cache line (or lines) to be invalidated. This check is based on the physical address of the instruction. In addition,
the P6 family and Pentium processors check whether a write to a code segment may modify an instruction that has
been prefetched for execution. If the write affects a prefetched instruction, the prefetch queue is invalidated. This
latter check is based on the linear address of the instruction. For the Pentium 4 and Intel Xeon processors, a write
or a snoop of an instruction in a code segment, where the target instruction is already decoded and resident in the
trace cache, invalidates the entire trace cache. The latter behavior means that programs that self-modify code can
cause severe degradation of performance when run on the Pentium 4 and Intel Xeon processors.
In practice, the check on linear addresses should not create compatibility problems among IA-32 processors. Applications that include self-modifying code use the same linear address for modifying and fetching the instruction.
Systems software, such as a debugger, that might possibly modify an instruction using a different linear address
than that used to fetch the instruction, will execute a serializing operation, such as a CPUID instruction, before the
modified instruction is executed, which will automatically resynchronize the instruction cache and prefetch queue.
(See Section 8.1.3, “Handling Self- and Cross-Modifying Code,” for more information about the use of self-modifying code.)
For Intel486 processors, a write to an instruction in the cache will modify it in both the cache and memory, but if
the instruction was prefetched before the write, the old version of the instruction could be the one executed. To
prevent the old instruction from being executed, flush the instruction prefetch unit by coding a jump instruction
immediately after any write that modifies an instruction.

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11.7

IMPLICIT CACHING (PENTIUM 4, INTEL XEON,
AND P6 FAMILY PROCESSORS)

Implicit caching occurs when a memory element is made potentially cacheable, although the element may never
have been accessed in the normal von Neumann sequence. Implicit caching occurs on the P6 and more recent
processor families due to aggressive prefetching, branch prediction, and TLB miss handling. Implicit caching is an
extension of the behavior of existing Intel386, Intel486, and Pentium processor systems, since software running
on these processor families also has not been able to deterministically predict the behavior of instruction prefetch.
To avoid problems related to implicit caching, the operating system must explicitly invalidate the cache when
changes are made to cacheable data that the cache coherency mechanism does not automatically handle. This
includes writes to dual-ported or physically aliased memory boards that are not detected by the snooping mechanisms of the processor, and changes to page- table entries in memory.
The code in Example 11-1 shows the effect of implicit caching on page-table entries. The linear address F000H
points to physical location B000H (the page-table entry for F000H contains the value B000H), and the page-table
entry for linear address F000 is PTE_F000.
Example 11-1. Effect of Implicit Caching on Page-Table Entries
mov EAX, CR3; Invalidate the TLB
mov CR3, EAX; by copying CR3 to itself
mov PTE_F000, A000H; Change F000H to point to A000H
mov EBX, [F000H];
Because of speculative execution in the P6 and more recent processor families, the last MOV instruction performed
would place the value at physical location B000H into EBX, rather than the value at the new physical address
A000H. This situation is remedied by placing a TLB invalidation between the load and the store.

11.8

EXPLICIT CACHING

The Pentium III processor introduced four new instructions, the PREFETCHh instructions, that provide software with
explicit control over the caching of data. These instructions provide “hints” to the processor that the data requested
by a PREFETCHh instruction should be read into cache hierarchy now or as soon as possible, in anticipation of its
use. The instructions provide different variations of the hint that allow selection of the cache level into which data
will be read.
The PREFETCHh instructions can help reduce the long latency typically associated with reading data from memory
and thus help prevent processor “stalls.” However, these instructions should be used judiciously. Overuse can lead
to resource conflicts and hence reduce the performance of an application. Also, these instructions should only be
used to prefetch data from memory; they should not be used to prefetch instructions. For more detailed information on the proper use of the prefetch instruction, refer to Chapter 7, “Optimizing Cache Usage,” in the Intel® 64
and IA-32 Architectures Optimization Reference Manual.

11.9

INVALIDATING THE TRANSLATION LOOKASIDE BUFFERS (TLBS)

The processor updates its address translation caches (TLBs) transparently to software. Several mechanisms are
available, however, that allow software and hardware to invalidate the TLBs either explicitly or as a side effect of
another operation. Most details are given in Section 4.10.4, “Invalidation of TLBs and Paging-Structure Caches.” In
addition, the following operations invalidate all TLB entries, irrespective of the setting of the G flag:

•
•
•

Asserting or de-asserting the FLUSH# pin.
(Pentium 4, Intel Xeon, and later processors only.) Writing to an MTRR (with a WRMSR instruction).
Writing to control register CR0 to modify the PG or PE flag.

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MEMORY CACHE CONTROL

•

(Pentium 4, Intel Xeon, and later processors only.) Writing to control register CR4 to modify the PSE, PGE, or
PAE flag.

•

Writing to control register CR4 to change the PCIDE flag from 1 to 0.

See Section 4.10, “Caching Translation Information,” for additional information about the TLBs.

11.10

STORE BUFFER

Intel 64 and IA-32 processors temporarily store each write (store) to memory in a store buffer. The store buffer
improves processor performance by allowing the processor to continue executing instructions without having to
wait until a write to memory and/or to a cache is complete. It also allows writes to be delayed for more efficient use
of memory-access bus cycles.
In general, the existence of the store buffer is transparent to software, even in systems that use multiple processors. The processor ensures that write operations are always carried out in program order. It also insures that the
contents of the store buffer are always drained to memory in the following situations:

•
•
•
•
•
•
•

When an exception or interrupt is generated.
(P6 and more recent processor families only) When a serializing instruction is executed.
When an I/O instruction is executed.
When a LOCK operation is performed.
(P6 and more recent processor families only) When a BINIT operation is performed.
(Pentium III, and more recent processor families only) When using an SFENCE instruction to order stores.
(Pentium 4 and more recent processor families only) When using an MFENCE instruction to order stores.

The discussion of write ordering in Section 8.2, “Memory Ordering,” gives a detailed description of the operation of
the store buffer.

11.11

MEMORY TYPE RANGE REGISTERS (MTRRS)

The following section pertains only to the P6 and more recent processor families.
The memory type range registers (MTRRs) provide a mechanism for associating the memory types (see Section
11.3, “Methods of Caching Available”) with physical-address ranges in system memory. They allow the processor to
optimize operations for different types of memory such as RAM, ROM, frame-buffer memory, and memory-mapped
I/O devices. They also simplify system hardware design by eliminating the memory control pins used for this function on earlier IA-32 processors and the external logic needed to drive them.
The MTRR mechanism allows up to 96 memory ranges to be defined in physical memory, and it defines a set of
model-specific registers (MSRs) for specifying the type of memory that is contained in each range. Table 11-8
shows the memory types that can be specified and their properties; Figure 11-4 shows the mapping of physical
memory with MTRRs. See Section 11.3, “Methods of Caching Available,” for a more detailed description of each
memory type.
Following a hardware reset, the P6 and more recent processor families disable all the fixed and variable MTRRs,
which in effect makes all of physical memory uncacheable. Initialization software should then set the MTRRs to a
specific, system-defined memory map. Typically, the BIOS (basic input/output system) software configures the
MTRRs. The operating system or executive is then free to modify the memory map using the normal page-level
cacheability attributes.
In a multiprocessor system using a processor in the P6 family or a more recent family, each processor MUST use
the identical MTRR memory map so that software will have a consistent view of memory.

NOTE
In multiple processor systems, the operating system must maintain MTRR consistency between all
the processors in the system (that is, all processors must use the same MTRR values). The P6 and
more recent processor families provide no hardware support for maintaining this consistency.
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Table 11-8. Memory Types That Can Be Encoded in MTRRs
Memory Type and Mnemonic

Encoding in MTRR

Uncacheable (UC)

00H

Write Combining (WC)

01H

Reserved*

02H

Reserved*

03H

Write-through (WT)

04H

Write-protected (WP)

05H

Writeback (WB)

06H

Reserved*

7H through FFH

NOTE:
*

Use of these encodings results in a general-protection exception (#GP).

Physical Memory
FFFFFFFFH

Address ranges not
mapped by an MTRR
are set to a default type

Variable ranges
(from 4 KBytes to
maximum size of
physical memory)

64 fixed ranges
(4 KBytes each)
16 fixed ranges
(16 KBytes each)
8 fixed ranges
(64-KBytes each)

256 KBytes
256 KBytes

100000H
FFFFFH
C0000H
BFFFFH
80000H
7FFFFH

512 KBytes
0

Figure 11-4. Mapping Physical Memory With MTRRs

11.11.1 MTRR Feature Identification
The availability of the MTRR feature is model-specific. Software can determine if MTRRs are supported on a
processor by executing the CPUID instruction and reading the state of the MTRR flag (bit 12) in the feature information register (EDX).
If the MTRR flag is set (indicating that the processor implements MTRRs), additional information about MTRRs can
be obtained from the 64-bit IA32_MTRRCAP MSR (named MTRRcap MSR for the P6 family processors). The
IA32_MTRRCAP MSR is a read-only MSR that can be read with the RDMSR instruction. Figure 11-5 shows the
contents of the IA32_MTRRCAP MSR. The functions of the flags and field in this register are as follows:

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MEMORY CACHE CONTROL

•

VCNT (variable range registers count) field, bits 0 through 7 — Indicates the number of variable ranges
implemented on the processor.

•

FIX (fixed range registers supported) flag, bit 8 — Fixed range MTRRs (IA32_MTRR_FIX64K_00000
through IA32_MTRR_FIX4K_0F8000) are supported when set; no fixed range registers are supported when
clear.

•

WC (write combining) flag, bit 10 — The write-combining (WC) memory type is supported when set; the
WC type is not supported when clear.

•

SMRR (System-Management Range Register) flag, bit 11 — The system-management range register
(SMRR) interface is supported when bit 11 is set; the SMRR interface is not supported when clear.

Bit 9 and bits 12 through 63 in the IA32_MTRRCAP MSR are reserved. If software attempts to write to the
IA32_MTRRCAP MSR, a general-protection exception (#GP) is generated.
Software must read IA32_MTRRCAP VCNT field to determine the number of variable MTRRs and query other
feature bits in IA32_MTRRCAP to determine additional capabilities that are supported in a processor. For example,
some processors may report a value of ‘8’ in the VCNT field, other processors may report VCNT with different
values.
63

0

11 10 9 8 7

Reserved

W
C

F
I
X

VCNT

SMRR — SMRR interface supported
WC — Write-combining memory type supported
FIX — Fixed range registers supported
VCNT — Number of variable range registers
Reserved

Figure 11-5. IA32_MTRRCAP Register

11.11.2 Setting Memory Ranges with MTRRs
The memory ranges and the types of memory specified in each range are set by three groups of registers: the
IA32_MTRR_DEF_TYPE MSR, the fixed-range MTRRs, and the variable range MTRRs. These registers can be read
and written to using the RDMSR and WRMSR instructions, respectively. The IA32_MTRRCAP MSR indicates the
availability of these registers on the processor (see Section 11.11.1, “MTRR Feature Identification”).

11.11.2.1 IA32_MTRR_DEF_TYPE MSR
The IA32_MTRR_DEF_TYPE MSR (named MTRRdefType MSR for the P6 family processors) sets the default properties of the regions of physical memory that are not encompassed by MTRRs. The functions of the flags and field in
this register are as follows:

•

Type field, bits 0 through 7 — Indicates the default memory type used for those physical memory address
ranges that do not have a memory type specified for them by an MTRR (see Table 11-8 for the encoding of this
field). The legal values for this field are 0, 1, 4, 5, and 6. All other values result in a general-protection
exception (#GP) being generated.
Intel recommends the use of the UC (uncached) memory type for all physical memory addresses where
memory does not exist. To assign the UC type to nonexistent memory locations, it can either be specified as the
default type in the Type field or be explicitly assigned with the fixed and variable MTRRs.

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MEMORY CACHE CONTROL

63

0

12 11 10 9 8 7

Reserved

E F
E

Type

E — MTRR enable/disable
FE — Fixed-range MTRRs enable/disable
Type — Default memory type
Reserved

Figure 11-6. IA32_MTRR_DEF_TYPE MSR

•

FE (fixed MTRRs enabled) flag, bit 10 — Fixed-range MTRRs are enabled when set; fixed-range MTRRs are
disabled when clear. When the fixed-range MTRRs are enabled, they take priority over the variable-range
MTRRs when overlaps in ranges occur. If the fixed-range MTRRs are disabled, the variable-range MTRRs can
still be used and can map the range ordinarily covered by the fixed-range MTRRs.

•

E (MTRRs enabled) flag, bit 11 — MTRRs are enabled when set; all MTRRs are disabled when clear, and the
UC memory type is applied to all of physical memory. When this flag is set, the FE flag can disable the fixedrange MTRRs; when the flag is clear, the FE flag has no affect. When the E flag is set, the type specified in the
default memory type field is used for areas of memory not already mapped by either a fixed or variable MTRR.

Bits 8 and 9, and bits 12 through 63, in the IA32_MTRR_DEF_TYPE MSR are reserved; the processor generates a
general-protection exception (#GP) if software attempts to write nonzero values to them.

11.11.2.2 Fixed Range MTRRs
The fixed memory ranges are mapped with 11 fixed-range registers of 64 bits each. Each of these registers is
divided into 8-bit fields that are used to specify the memory type for each of the sub-ranges the register controls:

•

Register IA32_MTRR_FIX64K_00000 — Maps the 512-KByte address range from 0H to 7FFFFH. This range
is divided into eight 64-KByte sub-ranges.

•

Registers IA32_MTRR_FIX16K_80000 and IA32_MTRR_FIX16K_A0000 — Maps the two 128-KByte
address ranges from 80000H to BFFFFH. This range is divided into sixteen 16-KByte sub-ranges, 8 ranges per
register.

•

Registers IA32_MTRR_FIX4K_C0000 through IA32_MTRR_FIX4K_F8000 — Maps eight 32-KByte
address ranges from C0000H to FFFFFH. This range is divided into sixty-four 4-KByte sub-ranges, 8 ranges per
register.

Table 11-9 shows the relationship between the fixed physical-address ranges and the corresponding fields of the
fixed-range MTRRs; Table 11-8 shows memory type encoding for MTRRs.
For the P6 family processors, the prefix for the fixed range MTRRs is MTRRfix.

11.11.2.3 Variable Range MTRRs
The Pentium 4, Intel Xeon, and P6 family processors permit software to specify the memory type for m variablesize address ranges, using a pair of MTRRs for each range. The number m of ranges supported is given in bits 7:0
of the IA32_MTRRCAP MSR (see Figure 11-5 in Section 11.11.1).
The first entry in each pair (IA32_MTRR_PHYSBASEn) defines the base address and memory type for the range;
the second entry (IA32_MTRR_PHYSMASKn) contains a mask used to determine the address range. The “n” suffix
is in the range 0 through m–1 and identifies a specific register pair.
For P6 family processors, the prefixes for these variable range MTRRs are MTRRphysBase and MTRRphysMask.

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Table 11-9. Address Mapping for Fixed-Range MTRRs
Address Range (hexadecimal)

MTRR

63 56

55 48

47 40

39 32

31

24

23

16

15

8

7

0

700007FFFF

600006FFFF

500005FFFF

400004FFFF

300003FFFF

200002FFFF

100001FFFF

000000FFFF

IA32_MTRR_
FIX64K_00000

9C000
9FFFF

980009BFFF

9400097FFF

9000093FFF

8C0008FFFF

880008BFFF

8400087FFF

8000083FFF

IA32_MTRR_
FIX16K_80000

BC000
BFFFF

B8000BBFFF

B4000B7FFF

B0000B3FFF

AC000AFFFF

A8000ABFFF

A4000A7FFF

A0000A3FFF

IA32_MTRR_
FIX16K_A0000

C7000
C7FFF

C6000C6FFF

C5000C5FFF

C4000C4FFF

C3000C3FFF

C2000C2FFF

C1000C1FFF

C0000C0FFF

IA32_MTRR_
FIX4K_C0000

CF000
CFFFF

CE000CEFFF

CD000CDFFF

CC000CCFFF

CB000CBFFF

CA000CAFFF

C9000C9FFF

C8000C8FFF

IA32_MTRR_
FIX4K_C8000

D7000
D7FFF

D6000D6FFF

D5000D5FFF

D4000D4FFF

D3000D3FFF

D2000D2FFF

D1000D1FFF

D0000D0FFF

IA32_MTRR_
FIX4K_D0000

DF000
DFFFF

DE000DEFFF

DD000DDFFF

DC000DCFFF

DB000DBFFF

DA000DAFFF

D9000D9FFF

D8000D8FFF

IA32_MTRR_
FIX4K_D8000

E7000
E7FFF

E6000E6FFF

E5000E5FFF

E4000E4FFF

E3000E3FFF

E2000E2FFF

E1000E1FFF

E0000E0FFF

IA32_MTRR_
FIX4K_E0000

EF000
EFFFF

EE000EEFFF

ED000EDFFF

EC000ECFFF

EB000EBFFF

EA000EAFFF

E9000E9FFF

E8000E8FFF

IA32_MTRR_
FIX4K_E8000

F7000
F7FFF

F6000F6FFF

F5000F5FFF

F4000F4FFF

F3000F3FFF

F2000F2FFF

F1000F1FFF

F0000F0FFF

IA32_MTRR_
FIX4K_F0000

FF000
FFFFF

FE000FEFFF

FD000FDFFF

FC000FCFFF

FB000FBFFF

FA000FAFFF

F9000F9FFF

F8000F8FFF

IA32_MTRR_
FIX4K_F8000

Figure 11-7 shows flags and fields in these registers. The functions of these flags and fields are:

•

Type field, bits 0 through 7 — Specifies the memory type for the range (see Table 11-8 for the encoding of
this field).

•

PhysBase field, bits 12 through (MAXPHYADDR-1) — Specifies the base address of the address range.
This 24-bit value, in the case where MAXPHYADDR is 36 bits, is extended by 12 bits at the low end to form the
base address (this automatically aligns the address on a 4-KByte boundary).

•

PhysMask field, bits 12 through (MAXPHYADDR-1) — Specifies a mask (24 bits if the maximum physical
address size is 36 bits, 28 bits if the maximum physical address size is 40 bits). The mask determines the range
of the region being mapped, according to the following relationships:
— Address_Within_Range AND PhysMask = PhysBase AND PhysMask
— This value is extended by 12 bits at the low end to form the mask value. For more information: see Section
11.11.3, “Example Base and Mask Calculations.”
— The width of the PhysMask field depends on the maximum physical address size supported by the
processor.
CPUID.80000008H reports the maximum physical address size supported by the processor. If
CPUID.80000008H is not available, software may assume that the processor supports a 36-bit physical
address size (then PhysMask is 24 bits wide and the upper 28 bits of IA32_MTRR_PHYSMASKn are
reserved). See the Note below.

•

V (valid) flag, bit 11 — Enables the register pair when set; disables register pair when clear.

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IA32_MTRR_PHYSBASEn Register
63

MAXPHYADDR 12 11

Reserved

0

8 7

PhysBase

Type

PhysBase — Base address of range
Type — Memory type for range

IA32_MTRR_PHYSMASKn Register
63

MAXPHYADDR

Reserved

0

12 11 10

PhysMask

V

Reserved

PhysMask — Sets range mask
V — Valid
Reserved
MAXPHYADDR: The bit position indicated by MAXPHYADDR depends on the maximum
physical address range supported by the processor. It is reported by CPUID leaf
function 80000008H. If CPUID does not support leaf 80000008H, the processor
supports 36-bit physical address size, then bit PhysMask consists of bits 35:12, and
bits 63:36 are reserved.

Figure 11-7. IA32_MTRR_PHYSBASEn and IA32_MTRR_PHYSMASKn Variable-Range Register Pair
All other bits in the IA32_MTRR_PHYSBASEn and IA32_MTRR_PHYSMASKn registers are reserved; the processor
generates a general-protection exception (#GP) if software attempts to write to them.
Some mask values can result in ranges that are not continuous. In such ranges, the area not mapped by the mask
value is set to the default memory type, unless some other MTRR specifies a type for that range. Intel does not
encourage the use of “discontinuous” ranges.

NOTE
It is possible for software to parse the memory descriptions that BIOS provides by using the
ACPI/INT15 e820 interface mechanism. This information then can be used to determine how
MTRRs are initialized (for example: allowing the BIOS to define valid memory ranges and the
maximum memory range supported by the platform, including the processor).
See Section 11.11.4.1, “MTRR Precedences,” for information on overlapping variable MTRR ranges.

11.11.2.4 System-Management Range Register Interface
If IA32_MTRRCAP[bit 11] is set, the processor supports the SMRR interface to restrict access to a specified
memory address range used by system-management mode (SMM) software (see Section 34.4.2.1). If the SMRR
interface is supported, SMM software is strongly encouraged to use it to protect the SMI code and data stored by
SMI handler in the SMRAM region.
The system-management range registers consist of a pair of MSRs (see Figure 11-8). The IA32_SMRR_PHYSBASE
MSR defines the base address for the SMRAM memory range and the memory type used to access it in SMM. The
IA32_SMRR_PHYSMASK MSR contains a valid bit and a mask that determines the SMRAM address range protected
by the SMRR interface. These MSRs may be written only in SMM; an attempt to write them outside of SMM causes
a general-protection exception.1
Figure 11-8 shows flags and fields in these registers. The functions of these flags and fields are the following:

1. For some processor models, these MSRs can be accessed by RDMSR and WRMSR only if the SMRR interface has been enabled using
a model-specific bit in the IA32_FEATURE_CONTROL MSR.
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MEMORY CACHE CONTROL

•

Type field, bits 0 through 7 — Specifies the memory type for the range (see Table 11-8 for the encoding of
this field).

•

PhysBase field, bits 12 through 31 — Specifies the base address of the address range. The address must be
less than 4 GBytes and is automatically aligned on a 4-KByte boundary.

•

PhysMask field, bits 12 through 31 — Specifies a mask that determines the range of the region being
mapped, according to the following relationships:
— Address_Within_Range AND PhysMask = PhysBase AND PhysMask
— This value is extended by 12 bits at the low end to form the mask value. For more information: see Section
11.11.3, “Example Base and Mask Calculations.”

•

V (valid) flag, bit 11 — Enables the register pair when set; disables register pair when clear.

Before attempting to access these SMRR registers, software must test bit 11 in the IA32_MTRRCAP register. If
SMRR is not supported, reads from or writes to registers cause general-protection exceptions.
When the valid flag in the IA32_SMRR_PHYSMASK MSR is 1, accesses to the specified address range are treated as
follows:

•
•

If the logical processor is in SMM, accesses uses the memory type in the IA32_SMRR_PHYSBASE MSR.
If the logical processor is not in SMM, write accesses are ignored and read accesses return a fixed value for each
byte. The uncacheable memory type (UC) is used in this case.

The above items apply even if the address range specified overlaps with a range specified by the MTRRs.

IA32_SMRR_PHYSBASE Register
63

31

Reserved

12 11

0

8 7

PhysBase

Type

PhysBase — Base address of range
Type — Memory type for range

IA32_SMRR_PHYSMASK Register
63

31

Reserved

12 11 10

PhysMask

V

0

Reserved

PhysMask — Sets range mask
V — Valid
Reserved

Figure 11-8. IA32_SMRR_PHYSBASE and IA32_SMRR_PHYSMASK SMRR Pair

11.11.3 Example Base and Mask Calculations
The examples in this section apply to processors that support a maximum physical address size of 36 bits. The base
and mask values entered in variable-range MTRR pairs are 24-bit values that the processor extends to 36-bits.
For example, to enter a base address of 2 MBytes (200000H) in the IA32_MTRR_PHYSBASE3 register, the 12 leastsignificant bits are truncated and the value 000200H is entered in the PhysBase field. The same operation must be
performed on mask values. For example, to map the address range from 200000H to 3FFFFFH (2 MBytes to 4
MBytes), a mask value of FFFE00000H is required. Again, the 12 least-significant bits of this mask value are truncated, so that the value entered in the PhysMask field of IA32_MTRR_PHYSMASK3 is FFFE00H. This mask is chosen
so that when any address in the 200000H to 3FFFFFH range is AND’d with the mask value, it will return the same
value as when the base address is AND’d with the mask value (which is 200000H).

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To map the address range from 400000H to 7FFFFFH (4 MBytes to 8 MBytes), a base value of 000400H is entered
in the PhysBase field and a mask value of FFFC00H is entered in the PhysMask field.
Example 11-2. Setting-Up Memory for a System
Here is an example of setting up the MTRRs for an system. Assume that the system has the following characteristics:

•
•

96 MBytes of system memory is mapped as write-back memory (WB) for highest system performance.

•
•

An 8-MByte graphics card is mapped to write-combining memory (WC) beginning at address A0000000H.

A custom 4-MByte I/O card is mapped to uncached memory (UC) at a base address of 64 MBytes. This
restriction forces the 96 MBytes of system memory to be addressed from 0 to 64 MBytes and from 68 MBytes
to 100 MBytes, leaving a 4-MByte hole for the I/O card.
The BIOS area from 15 MBytes to 16 MBytes is mapped to UC memory.

The following settings for the MTRRs will yield the proper mapping of the physical address space for this system
configuration.
IA32_MTRR_PHYSBASE0 = 0000 0000 0000 0006H
IA32_MTRR_PHYSMASK0 = 0000 000F FC00 0800H
Caches 0-64 MByte as WB cache type.
IA32_MTRR_PHYSBASE1 = 0000 0000 0400 0006H
IA32_MTRR_PHYSMASK1 = 0000 000F FE00 0800H
Caches 64-96 MByte as WB cache type.
IA32_MTRR_PHYSBASE2 = 0000 0000 0600 0006H
IA32_MTRR_PHYSMASK2 = 0000 000F FFC0 0800H
Caches 96-100 MByte as WB cache type.
IA32_MTRR_PHYSBASE3 = 0000 0000 0400 0000H
IA32_MTRR_PHYSMASK3 = 0000 000F FFC0 0800H
Caches 64-68 MByte as UC cache type.
IA32_MTRR_PHYSBASE4 = 0000 0000 00F0 0000H
IA32_MTRR_PHYSMASK4 = 0000 000F FFF0 0800H
Caches 15-16 MByte as UC cache type.
IA32_MTRR_PHYSBASE5 = 0000 0000 A000 0001H
IA32_MTRR_PHYSMASK5 = 0000 000F FF80 0800H
Caches A0000000-A0800000 as WC type.
This MTRR setup uses the ability to overlap any two memory ranges (as long as the ranges are mapped to WB and
UC memory types) to minimize the number of MTRR registers that are required to configure the memory environment. This setup also fulfills the requirement that two register pairs are left for operating system usage.

11.11.3.1 Base and Mask Calculations for Greater-Than 36-bit Physical Address Support
For Intel 64 and IA-32 processors that support greater than 36 bits of physical address size, software should query
CPUID.80000008H to determine the maximum physical address. See the example.
Example 11-3. Setting-Up Memory for a System with a 40-Bit Address Size
If a processor supports 40-bits of physical address size, then the PhysMask field (in IA32_MTRR_PHYSMASKn
registers) is 28 bits instead of 24 bits. For this situation, Example 11-2 should be modified as follows:
IA32_MTRR_PHYSBASE0 = 0000 0000 0000 0006H
IA32_MTRR_PHYSMASK0 = 0000 00FF FC00 0800H
Caches 0-64 MByte as WB cache type.

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IA32_MTRR_PHYSBASE1 = 0000 0000 0400 0006H
IA32_MTRR_PHYSMASK1 = 0000 00FF FE00 0800H
Caches 64-96 MByte as WB cache type.
IA32_MTRR_PHYSBASE2 = 0000 0000 0600 0006H
IA32_MTRR_PHYSMASK2 = 0000 00FF FFC0 0800H
Caches 96-100 MByte as WB cache type.
IA32_MTRR_PHYSBASE3 = 0000 0000 0400 0000H
IA32_MTRR_PHYSMASK3 = 0000 00FF FFC0 0800H
Caches 64-68 MByte as UC cache type.
IA32_MTRR_PHYSBASE4 = 0000 0000 00F0 0000H
IA32_MTRR_PHYSMASK4 = 0000 00FF FFF0 0800H
Caches 15-16 MByte as UC cache type.
IA32_MTRR_PHYSBASE5 = 0000 0000 A000 0001H
IA32_MTRR_PHYSMASK5 = 0000 00FF FF80 0800H
Caches A0000000-A0800000 as WC type.

11.11.4 Range Size and Alignment Requirement
A range that is to be mapped to a variable-range MTRR must meet the following “power of 2” size and alignment
rules:
1. The minimum range size is 4 KBytes and the base address of the range must be on at least a 4-KByte
boundary.
2. For ranges greater than 4 KBytes, each range must be of length 2n and its base address must be aligned on a
2n boundary, where n is a value equal to or greater than 12. The base-address alignment value cannot be less
than its length. For example, an 8-KByte range cannot be aligned on a 4-KByte boundary. It must be aligned on
at least an 8-KByte boundary.

11.11.4.1 MTRR Precedences
If the MTRRs are not enabled (by setting the E flag in the IA32_MTRR_DEF_TYPE MSR), then all memory accesses
are of the UC memory type. If the MTRRs are enabled, then the memory type used for a memory access is determined as follows:
1. If the physical address falls within the first 1 MByte of physical memory and fixed MTRRs are enabled, the
processor uses the memory type stored for the appropriate fixed-range MTRR.
2. Otherwise, the processor attempts to match the physical address with a memory type set by the variable-range
MTRRs:
— If one variable memory range matches, the processor uses the memory type stored in the
IA32_MTRR_PHYSBASEn register for that range.
— If two or more variable memory ranges match and the memory types are identical, then that memory type
is used.
— If two or more variable memory ranges match and one of the memory types is UC, the UC memory type
used.
— If two or more variable memory ranges match and the memory types are WT and WB, the WT memory type
is used.
— For overlaps not defined by the above rules, processor behavior is undefined.
3. If no fixed or variable memory range matches, the processor uses the default memory type.

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MEMORY CACHE CONTROL

11.11.5 MTRR Initialization
On a hardware reset, the P6 and more recent processors clear the valid flags in variable-range MTRRs and clear the
E flag in the IA32_MTRR_DEF_TYPE MSR to disable all MTRRs. All other bits in the MTRRs are undefined.
Prior to initializing the MTRRs, software (normally the system BIOS) must initialize all fixed-range and variablerange MTRR register fields to 0. Software can then initialize the MTRRs according to known types of memory,
including memory on devices that it auto-configures. Initialization is expected to occur prior to booting the operating system.
See Section 11.11.8, “MTRR Considerations in MP Systems,” for information on initializing MTRRs in MP (multipleprocessor) systems.

11.11.6 Remapping Memory Types
A system designer may re-map memory types to tune performance or because a future processor may not implement all memory types supported by the Pentium 4, Intel Xeon, and P6 family processors. The following rules
support coherent memory-type re-mappings:
1. A memory type should not be mapped into another memory type that has a weaker memory ordering model.
For example, the uncacheable type cannot be mapped into any other type, and the write-back, write-through,
and write-protected types cannot be mapped into the weakly ordered write-combining type.
2. A memory type that does not delay writes should not be mapped into a memory type that does delay writes,
because applications of such a memory type may rely on its write-through behavior. Accordingly, the writeback type cannot be mapped into the write-through type.
3. A memory type that views write data as not necessarily stored and read back by a subsequent read, such as
the write-protected type, can only be mapped to another type with the same behaviour (and there are no
others for the Pentium 4, Intel Xeon, and P6 family processors) or to the uncacheable type.
In many specific cases, a system designer can have additional information about how a memory type is used,
allowing additional mappings. For example, write-through memory with no associated write side effects can be
mapped into write-back memory.

11.11.7 MTRR Maintenance Programming Interface
The operating system maintains the MTRRs after booting and sets up or changes the memory types for memorymapped devices. The operating system should provide a driver and application programming interface (API) to
access and set the MTRRs. The function calls MemTypeGet() and MemTypeSet() define this interface.

11.11.7.1 MemTypeGet() Function
The MemTypeGet() function returns the memory type of the physical memory range specified by the parameters
base and size. The base address is the starting physical address and the size is the number of bytes for the memory
range. The function automatically aligns the base address and size to 4-KByte boundaries. Pseudocode for the
MemTypeGet() function is given in Example 11-4.

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MEMORY CACHE CONTROL

Example 11-4. MemTypeGet() Pseudocode
#define MIXED_TYPES -1

/* 0 < MIXED_TYPES || MIXED_TYPES > 256 */

IF CPU_FEATURES.MTRR /* processor supports MTRRs */
THEN
Align BASE and SIZE to 4-KByte boundary;
IF (BASE + SIZE) wrap 4-GByte address space
THEN return INVALID;
FI;
IF MTRRdefType.E = 0
THEN return UC;
FI;
FirstType ¨ Get4KMemType (BASE);
/* Obtains memory type for first 4-KByte range. */
/* See Get4KMemType (4KByteRange) in Example 11-5. */
FOR each additional 4-KByte range specified in SIZE
NextType ¨ Get4KMemType (4KByteRange);
IF NextType ¼ FirstType
THEN return MixedTypes;
FI;
ROF;
return FirstType;
ELSE return UNSUPPORTED;
FI;
If the processor does not support MTRRs, the function returns UNSUPPORTED. If the MTRRs are not enabled, then
the UC memory type is returned. If more than one memory type corresponds to the specified range, a status of
MIXED_TYPES is returned. Otherwise, the memory type defined for the range (UC, WC, WT, WB, or WP) is
returned.
The pseudocode for the Get4KMemType() function in Example 11-5 obtains the memory type for a single 4-KByte
range at a given physical address. The sample code determines whether an PHY_ADDRESS falls within a fixed
range by comparing the address with the known fixed ranges: 0 to 7FFFFH (64-KByte regions), 80000H to BFFFFH
(16-KByte regions), and C0000H to FFFFFH (4-KByte regions). If an address falls within one of these ranges, the
appropriate bits within one of its MTRRs determine the memory type.
Example 11-5. Get4KMemType() Pseudocode
IF IA32_MTRRCAP.FIX AND MTRRdefType.FE /* fixed registers enabled */
THEN IF PHY_ADDRESS is within a fixed range
return IA32_MTRR_FIX.Type;
FI;
FOR each variable-range MTRR in IA32_MTRRCAP.VCNT
IF IA32_MTRR_PHYSMASK.V = 0
THEN continue;
FI;
IF (PHY_ADDRESS AND IA32_MTRR_PHYSMASK.Mask) =
(IA32_MTRR_PHYSBASE.Base
AND IA32_MTRR_PHYSMASK.Mask)
THEN
return IA32_MTRR_PHYSBASE.Type;
FI;
ROF;
return MTRRdefType.Type;

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MEMORY CACHE CONTROL

11.11.7.2 MemTypeSet() Function
The MemTypeSet() function in Example 11-6 sets a MTRR for the physical memory range specified by the parameters base and size to the type specified by type. The base address and size are multiples of 4 KBytes and the size
is not 0.
Example 11-6. MemTypeSet Pseudocode
IF CPU_FEATURES.MTRR (* processor supports MTRRs *)
THEN
IF BASE and SIZE are not 4-KByte aligned or size is 0
THEN return INVALID;
FI;
IF (BASE + SIZE) wrap 4-GByte address space
THEN return INVALID;
FI;
IF TYPE is invalid for Pentium 4, Intel Xeon, and P6 family
processors
THEN return UNSUPPORTED;
FI;
IF TYPE is WC and not supported
THEN return UNSUPPORTED;
FI;
IF IA32_MTRRCAP.FIX is set AND range can be mapped using a
fixed-range MTRR
THEN
pre_mtrr_change();
update affected MTRR;
post_mtrr_change();
FI;
ELSE (* try to map using a variable MTRR pair *)
IF IA32_MTRRCAP.VCNT = 0
THEN return UNSUPPORTED;
FI;
IF conflicts with current variable ranges
THEN return RANGE_OVERLAP;
FI;
IF no MTRRs available
THEN return VAR_NOT_AVAILABLE;
FI;
IF BASE and SIZE do not meet the power of 2 requirements for
variable MTRRs
THEN return INVALID_VAR_REQUEST;
FI;
pre_mtrr_change();
Update affected MTRRs;
post_mtrr_change();
FI;
pre_mtrr_change()
BEGIN
disable interrupts;
Save current value of CR4;
disable and flush caches;
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MEMORY CACHE CONTROL

flush TLBs;
disable MTRRs;
IF multiprocessing
THEN maintain consistency through IPIs;
FI;
END
post_mtrr_change()
BEGIN
flush caches and TLBs;
enable MTRRs;
enable caches;
restore value of CR4;
enable interrupts;
END
The physical address to variable range mapping algorithm in the MemTypeSet function detects conflicts with
current variable range registers by cycling through them and determining whether the physical address in question
matches any of the current ranges. During this scan, the algorithm can detect whether any current variable ranges
overlap and can be concatenated into a single range.
The pre_mtrr_change() function disables interrupts prior to changing the MTRRs, to avoid executing code with a
partially valid MTRR setup. The algorithm disables caching by setting the CD flag and clearing the NW flag in control
register CR0. The caches are invalidated using the WBINVD instruction. The algorithm flushes all TLB entries either
by clearing the page-global enable (PGE) flag in control register CR4 (if PGE was already set) or by updating control
register CR3 (if PGE was already clear). Finally, it disables MTRRs by clearing the E flag in the
IA32_MTRR_DEF_TYPE MSR.
After the memory type is updated, the post_mtrr_change() function re-enables the MTRRs and again invalidates
the caches and TLBs. This second invalidation is required because of the processor's aggressive prefetch of both
instructions and data. The algorithm restores interrupts and re-enables caching by setting the CD flag.
An operating system can batch multiple MTRR updates so that only a single pair of cache invalidations occur.

11.11.8 MTRR Considerations in MP Systems
In MP (multiple-processor) systems, the operating systems must maintain MTRR consistency between all the
processors in the system. The Pentium 4, Intel Xeon, and P6 family processors provide no hardware support to
maintain this consistency. In general, all processors must have the same MTRR values.
This requirement implies that when the operating system initializes an MP system, it must load the MTRRs of the
boot processor while the E flag in register MTRRdefType is 0. The operating system then directs other processors to
load their MTRRs with the same memory map. After all the processors have loaded their MTRRs, the operating
system signals them to enable their MTRRs. Barrier synchronization is used to prevent further memory accesses
until all processors indicate that the MTRRs are enabled. This synchronization is likely to be a shoot-down style
algorithm, with shared variables and interprocessor interrupts.
Any change to the value of the MTRRs in an MP system requires the operating system to repeat the loading and
enabling process to maintain consistency, using the following procedure:
1. Broadcast to all processors to execute the following code sequence.
2. Disable interrupts.
3. Wait for all processors to reach this point.
4. Enter the no-fill cache mode. (Set the CD flag in control register CR0 to 1 and the NW flag to 0.)
5. Flush all caches using the WBINVD instructions. Note on a processor that supports self-snooping, CPUID
feature flag bit 27, this step is unnecessary.
6. If the PGE flag is set in control register CR4, flush all TLBs by clearing that flag.

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MEMORY CACHE CONTROL

7. If the PGE flag is clear in control register CR4, flush all TLBs by executing a MOV from control register CR3 to
another register and then a MOV from that register back to CR3.
8. Disable all range registers (by clearing the E flag in register MTRRdefType). If only variable ranges are being
modified, software may clear the valid bits for the affected register pairs instead.
9. Update the MTRRs.
10. Enable all range registers (by setting the E flag in register MTRRdefType). If only variable-range registers were
modified and their individual valid bits were cleared, then set the valid bits for the affected ranges instead.
11. Flush all caches and all TLBs a second time. (The TLB flush is required for Pentium 4, Intel Xeon, and P6 family
processors. Executing the WBINVD instruction is not needed when using Pentium 4, Intel Xeon, and P6 family
processors, but it may be needed in future systems.)
12. Enter the normal cache mode to re-enable caching. (Set the CD and NW flags in control register CR0 to 0.)
13. Set PGE flag in control register CR4, if cleared in Step 6 (above).
14. Wait for all processors to reach this point.
15. Enable interrupts.

11.11.9 Large Page Size Considerations
The MTRRs provide memory typing for a limited number of regions that have a 4 KByte granularity (the same granularity as 4-KByte pages). The memory type for a given page is cached in the processor’s TLBs. When using large
pages (2 MBytes, 4 MBytes, or 1 GBytes), a single page-table entry covers multiple 4-KByte granules, each with a
single memory type. Because the memory type for a large page is cached in the TLB, the processor can behave in
an undefined manner if a large page is mapped to a region of memory that MTRRs have mapped with multiple
memory types.
Undefined behavior can be avoided by insuring that all MTRR memory-type ranges within a large page are of the
same type. If a large page maps to a region of memory containing different MTRR-defined memory types, the PCD
and PWT flags in the page-table entry should be set for the most conservative memory type for that range. For
example, a large page used for memory mapped I/O and regular memory is mapped as UC memory. Alternatively,
the operating system can map the region using multiple 4-KByte pages each with its own memory type.
The requirement that all 4-KByte ranges in a large page are of the same memory type implies that large pages with
different memory types may suffer a performance penalty, since they must be marked with the lowest common
denominator memory type. The same consideration apply to 1 GByte pages, each of which may consist of multiple
2-Mbyte ranges.
The Pentium 4, Intel Xeon, and P6 family processors provide special support for the physical memory range from 0
to 4 MBytes, which is potentially mapped by both the fixed and variable MTRRs. This support is invoked when a
Pentium 4, Intel Xeon, or P6 family processor detects a large page overlapping the first 1 MByte of this memory
range with a memory type that conflicts with the fixed MTRRs. Here, the processor maps the memory range as
multiple 4-KByte pages within the TLB. This operation insures correct behavior at the cost of performance. To avoid
this performance penalty, operating-system software should reserve the large page option for regions of memory
at addresses greater than or equal to 4 MBytes.

11.12

PAGE ATTRIBUTE TABLE (PAT)

The Page Attribute Table (PAT) extends the IA-32 architecture’s page-table format to allow memory types to be
assigned to regions of physical memory based on linear address mappings. The PAT is a companion feature to the
MTRRs; that is, the MTRRs allow mapping of memory types to regions of the physical address space, where the PAT
allows mapping of memory types to pages within the linear address space. The MTRRs are useful for statically
describing memory types for physical ranges, and are typically set up by the system BIOS. The PAT extends the
functions of the PCD and PWT bits in page tables to allow all five of the memory types that can be assigned with the
MTRRs (plus one additional memory type) to also be assigned dynamically to pages of the linear address space.
The PAT was introduced to IA-32 architecture on the Pentium III processor. It is also available in the Pentium 4 and
Intel Xeon processors.
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MEMORY CACHE CONTROL

11.12.1 Detecting Support for the PAT Feature
An operating system or executive can detect the availability of the PAT by executing the CPUID instruction with a
value of 1 in the EAX register. Support for the PAT is indicated by the PAT flag (bit 16 of the values returned to EDX
register). If the PAT is supported, the operating system or executive can use the IA32_PAT MSR to program the PAT.
When memory types have been assigned to entries in the PAT, software can then use of the PAT-index bit (PAT) in
the page-table and page-directory entries along with the PCD and PWT bits to assign memory types from the PAT
to individual pages.
Note that there is no separate flag or control bit in any of the control registers that enables the PAT. The PAT is
always enabled on all processors that support it, and the table lookup always occurs whenever paging is enabled,
in all paging modes.

11.12.2 IA32_PAT MSR
The IA32_PAT MSR is located at MSR address 277H (see Chapter 2, “Model-Specific Registers (MSRs)” in the Intel®
64 and IA-32 Architectures Software Developer’s Manual, Volume 4). Figure 11-9. shows the format of the 64-bit
IA32_PAT MSR.
The IA32_PAT MSR contains eight page attribute fields: PA0 through PA7. The three low-order bits of each field are
used to specify a memory type. The five high-order bits of each field are reserved, and must be set to all 0s. Each
of the eight page attribute fields can contain any of the memory type encodings specified in Table 11-10.

31
27
Reserved

26
PA3

24

23
19
Reserved

18
PA2

16

15
11
Reserved

10
PA1

8

7
3
Reserved

2
PA0

0

63
59
Reserved

58
PA7

56

55
51
Reserved

50
PA6

48

47
43
Reserved

42
PA5

40

39
35
Reserved

34
PA4

32

Figure 11-9. IA32_PAT MSR
Note that for the P6 family processors, the IA32_PAT MSR is named the PAT MSR.

Table 11-10. Memory Types That Can Be Encoded With PAT
Encoding

Mnemonic

00H

Uncacheable (UC)

01H

Write Combining (WC)

02H

Reserved*

03H

Reserved*

04H

Write Through (WT)

05H

Write Protected (WP)

06H

Write Back (WB)

07H

Uncached (UC-)

08H - FFH

Reserved*

NOTE:
* Using these encodings will result in a general-protection exception (#GP).

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MEMORY CACHE CONTROL

11.12.3 Selecting a Memory Type from the PAT
To select a memory type for a page from the PAT, a 3-bit index made up of the PAT, PCD, and PWT bits must be
encoded in the page-table or page-directory entry for the page. Table 11-11 shows the possible encodings of the
PAT, PCD, and PWT bits and the PAT entry selected with each encoding. The PAT bit is bit 7 in page-table entries that
point to 4-KByte pages and bit 12 in paging-structure entries that point to larger pages. The PCD and PWT bits are
bits 4 and 3, respectively, in paging-structure entries that point to pages of any size.
The PAT entry selected for a page is used in conjunction with the MTRR setting for the region of physical memory
in which the page is mapped to determine the effective memory type for the page, as shown in Table 11-7.

Table 11-11. Selection of PAT Entries with PAT, PCD, and PWT Flags
PAT

PCD

PWT

PAT Entry

0

0

0

PAT0

0

0

1

PAT1

0

1

0

PAT2

0

1

1

PAT3

1

0

0

PAT4

1

0

1

PAT5

1

1

0

PAT6

1

1

1

PAT7

11.12.4 Programming the PAT
Table 11-12 shows the default setting for each PAT entry following a power up or reset of the processor. The setting
remain unchanged following a soft reset (INIT reset).

Table 11-12. Memory Type Setting of PAT Entries Following a Power-up or Reset
PAT Entry

Memory Type Following Power-up or Reset

PAT0

WB

PAT1

WT

PAT2

UC-

PAT3

UC

PAT4

WB

PAT5

WT

PAT6

UC-

PAT7

UC

The values in all the entries of the PAT can be changed by writing to the IA32_PAT MSR using the WRMSR instruction. The IA32_PAT MSR is read and write accessible (use of the RDMSR and WRMSR instructions, respectively) to
software operating at a CPL of 0. Table 11-10 shows the allowable encoding of the entries in the PAT. Attempting to
write an undefined memory type encoding into the PAT causes a general-protection (#GP) exception to be generated.
The operating system is responsible for insuring that changes to a PAT entry occur in a manner that maintains the
consistency of the processor caches and translation lookaside buffers (TLB). This is accomplished by following the
procedure as specified in Section 11.11.8, “MTRR Considerations in MP Systems,” for changing the value of an
MTRR in a multiple processor system. It requires a specific sequence of operations that includes flushing the
processors caches and TLBs.
The PAT allows any memory type to be specified in the page tables, and therefore it is possible to have a single
physical page mapped to two or more different linear addresses, each with different memory types. Intel does not
support this practice because it may lead to undefined operations that can result in a system failure. In particular,
a WC page must never be aliased to a cacheable page because WC writes may not check the processor caches.
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MEMORY CACHE CONTROL

When remapping a page that was previously mapped as a cacheable memory type to a WC page, an operating
system can avoid this type of aliasing by doing the following:
1. Remove the previous mapping to a cacheable memory type in the page tables; that is, make them not
present.
2. Flush the TLBs of processors that may have used the mapping, even speculatively.
3. Create a new mapping to the same physical address with a new memory type, for instance, WC.
4. Flush the caches on all processors that may have used the mapping previously. Note on processors that support
self-snooping, CPUID feature flag bit 27, this step is unnecessary.
Operating systems that use a page directory as a page table (to map large pages) and enable page size extensions
must carefully scrutinize the use of the PAT index bit for the 4-KByte page-table entries. The PAT index bit for a
page-table entry (bit 7) corresponds to the page size bit in a page-directory entry. Therefore, the operating system
can only use PAT entries PA0 through PA3 when setting the caching type for a page table that is also used as a page
directory. If the operating system attempts to use PAT entries PA4 through PA7 when using this memory as a page
table, it effectively sets the PS bit for the access to this memory as a page directory.
For compatibility with earlier IA-32 processors that do not support the PAT, care should be taken in selecting the
encodings for entries in the PAT (see Section 11.12.5, “PAT Compatibility with Earlier IA-32 Processors”).

11.12.5 PAT Compatibility with Earlier IA-32 Processors
For IA-32 processors that support the PAT, the IA32_PAT MSR is always active. That is, the PCD and PWT bits in
page-table entries and in page-directory entries (that point to pages) are always select a memory type for a page
indirectly by selecting an entry in the PAT. They never select the memory type for a page directly as they do in
earlier IA-32 processors that do not implement the PAT (see Table 11-6).
To allow compatibility for code written to run on earlier IA-32 processor that do not support the PAT, the PAT mechanism has been designed to allow backward compatibility to earlier processors. This compatibility is provided
through the ordering of the PAT, PCD, and PWT bits in the 3-bit PAT entry index. For processors that do not implement the PAT, the PAT index bit (bit 7 in the page-table entries and bit 12 in the page-directory entries) is reserved
and set to 0. With the PAT bit reserved, only the first four entries of the PAT can be selected with the PCD and PWT
bits. At power-up or reset (see Table 11-12), these first four entries are encoded to select the same memory types
as the PCD and PWT bits would normally select directly in an IA-32 processor that does not implement the PAT. So,
if encodings of the first four entries in the PAT are left unchanged following a power-up or reset, code written to run
on earlier IA-32 processors that do not implement the PAT will run correctly on IA-32 processors that do implement
the PAT.

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CHAPTER 12
INTEL MMX TECHNOLOGY SYSTEM PROGRAMMING
®

™

This chapter describes those features of the Intel® MMX™ technology that must be considered when designing or
enhancing an operating system to support MMX technology. It covers MMX instruction set emulation, the MMX
state, aliasing of MMX registers, saving MMX state, task and context switching considerations, exception handling,
and debugging.

12.1

EMULATION OF THE MMX INSTRUCTION SET

The IA-32 or Intel 64 architecture does not support emulation of the MMX instructions, as it does for x87 FPU
instructions. The EM flag in control register CR0 (provided to invoke emulation of x87 FPU instructions) cannot be
used for MMX instruction emulation. If an MMX instruction is executed when the EM flag is set, an invalid opcode
exception (UD#) is generated. Table 12-1 shows the interaction of the EM, MP, and TS flags in control register CR0
when executing MMX instructions.

Table 12-1. Action Taken By MMX Instructions for Different Combinations of EM, MP and TS
CR0 Flags
EM

MP*

TS

Action

0

1

0

Execute.

0

1

1

#NM exception.

1

1

0

#UD exception.

1

1

1

#UD exception.

NOTE:
* For processors that support the MMX instructions, the MP flag should be set.

12.2

THE MMX STATE AND MMX REGISTER ALIASING

The MMX state consists of eight 64-bit registers (MM0 through MM7). These registers are aliased to the low 64-bits
(bits 0 through 63) of floating-point registers R0 through R7 (see Figure 12-1). Note that the MMX registers are
mapped to the physical locations of the floating-point registers (R0 through R7), not to the relative locations of the
registers in the floating-point register stack (ST0 through ST7). As a result, the MMX register mapping is fixed and
is not affected by value in the Top Of Stack (TOS) field in the floating-point status word (bits 11 through 13).

Vol. 3A 12-1

INTEL® MMX™ TECHNOLOGY SYSTEM PROGRAMMING

x87 FPU Tag
Register
79

64 63

Floating-Point Registers

0

00

R7

00

R6

00

R5

00

R4

00

R3

00

R2

00

R1

00

R0

x87 FPU Status Register
13 11
000
63

TOS

MMX Registers

0
MM7
MM6
MM5
MM4
MM3
MM2

TOS = 0

MM1
MM0

Figure 12-1. Mapping of MMX Registers to Floating-Point Registers
When a value is written into an MMX register using an MMX instruction, the value also appears in the corresponding
floating-point register in bits 0 through 63. Likewise, when a floating-point value written into a floating-point
register by a x87 FPU, the low 64 bits of that value also appears in a the corresponding MMX register.
The execution of MMX instructions have several side effects on the x87 FPU state contained in the floating-point
registers, the x87 FPU tag word, and the x87 FPU status word. These side effects are as follows:

•

When an MMX instruction writes a value into an MMX register, at the same time, bits 64 through 79 of the corresponding floating-point register are set to all 1s.

•

When an MMX instruction (other than the EMMS instruction) is executed, each of the tag fields in the x87 FPU
tag word is set to 00B (valid). (See also Section 12.2.1, “Effect of MMX, x87 FPU, FXSAVE, and FXRSTOR
Instructions on the x87 FPU Tag Word.”)

•
•

When the EMMS instruction is executed, each tag field in the x87 FPU tag word is set to 11B (empty).
Each time an MMX instruction is executed, the TOS value is set to 000B.

Execution of MMX instructions does not affect the other bits in the x87 FPU status word (bits 0 through 10 and bits
14 and 15) or the contents of the other x87 FPU registers that comprise the x87 FPU state (the x87 FPU control
word, instruction pointer, data pointer, or opcode registers).
Table 12-2 summarizes the effects of the MMX instructions on the x87 FPU state.

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INTEL® MMX™ TECHNOLOGY SYSTEM PROGRAMMING

Table 12-2. Effects of MMX Instructions on x87 FPU State
MMX Instruction
Type

x87 FPU Tag
Word

TOS Field of x87 Other x87 FPU
FPU Status Word Registers

Bits 64 Through 79
of x87 FPU Data
Registers

Bits 0 Through 63
of x87 FPU Data
Registers

Read from MMX
register

All tags set to 00B
(Valid)

000B

Unchanged

Unchanged

Unchanged

Write to MMX
register

All tags set to 00B
(Valid)

000B

Unchanged

Set to all 1s

Overwritten with
MMX data

EMMS

All fields set to
11B (Empty)

000B

Unchanged

Unchanged

Unchanged

12.2.1

Effect of MMX, x87 FPU, FXSAVE, and FXRSTOR
Instructions on the x87 FPU Tag Word

Table 12-3 summarizes the effect of MMX and x87 FPU instructions and the FXSAVE and FXRSTOR instructions on
the tags in the x87 FPU tag word and the corresponding tags in an image of the tag word stored in memory.
The values in the fields of the x87 FPU tag word do not affect the contents of the MMX registers or the execution of
MMX instructions. However, the MMX instructions do modify the contents of the x87 FPU tag word, as is described
in Section 12.2, “The MMX State and MMX Register Aliasing.” These modifications may affect the operation of the
x87 FPU when executing x87 FPU instructions, if the x87 FPU state is not initialized or restored prior to beginning
x87 FPU instruction execution.
Note that the FSAVE, FXSAVE, and FSTENV instructions (which save x87 FPU state information) read the x87 FPU
tag register and contents of each of the floating-point registers, determine the actual tag values for each register
(empty, nonzero, zero, or special), and store the updated tag word in memory. After executing these instructions,
all the tags in the x87 FPU tag word are set to empty (11B). Likewise, the EMMS instruction clears MMX state from
the MMX/floating-point registers by setting all the tags in the x87 FPU tag word to 11B.

Table 12-3. Effect of the MMX, x87 FPU, and FXSAVE/FXRSTOR Instructions on the x87 FPU Tag Word
Instruction
Type

Instruction

x87 FPU Tag Word

Image of x87 FPU Tag Word Stored in
Memory

MMX

All (except EMMS)

All tags are set to 00B (valid).

Not affected.

MMX

EMMS

All tags are set to 11B (empty).

Not affected.

x87 FPU

All (except FSAVE,
FSTENV, FRSTOR,
FLDENV)

Tag for modified floating-point register is
set to 00B or 11B.

Not affected.

x87 FPU and
FXSAVE

FSAVE, FSTENV, FXSAVE

Tags and register values are read and
interpreted; then all tags are set to 11B.

Tags are set according to the actual
values in the floating-point registers;
that is, empty registers are marked 11B
and valid registers are marked 00B
(nonzero), 01B (zero), or 10B (special).

x87 FPU and
FXRSTOR

FRSTOR, FLDENV,
FXRSTOR

All tags marked 11B in memory are set
to 11B; all other tags are set according
to the value in the corresponding
floating-point register: 00B (nonzero),
01B (zero), or 10B (special).

Tags are read and interpreted, but not
modified.

12.3

SAVING AND RESTORING THE MMX STATE AND REGISTERS

Because the MMX registers are aliased to the x87 FPU data registers, the MMX state can be saved to memory and
restored from memory as follows:

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INTEL® MMX™ TECHNOLOGY SYSTEM PROGRAMMING

•

Execute an FSAVE, FNSAVE, or FXSAVE instruction to save the MMX state to memory. (The FXSAVE instruction
also saves the state of the XMM and MXCSR registers.)

•

Execute an FRSTOR or FXRSTOR instruction to restore the MMX state from memory. (The FXRSTOR instruction
also restores the state of the XMM and MXCSR registers.)

The save and restore methods described above are required for operating systems (see Section 12.4, “Saving MMX
State on Task or Context Switches”). Applications can in some cases save and restore only the MMX registers in the
following way:

•

Execute eight MOVQ instructions to save the contents of the MMX0 through MMX7 registers to memory. An
EMMS instruction may then (optionally) be executed to clear the MMX state in the x87 FPU.

•

Execute eight MOVQ instructions to read the saved contents of MMX registers from memory into the MMX0
through MMX7 registers.

NOTE
The IA-32 architecture does not support scanning the x87 FPU tag word and then only saving valid
entries.

12.4

SAVING MMX STATE ON TASK OR CONTEXT SWITCHES

When switching from one task or context to another, it is often necessary to save the MMX state. As a general rule,
if the existing task switching code for an operating system includes facilities for saving the state of the x87 FPU,
these facilities can also be relied upon to save the MMX state, without rewriting the task switch code. This reliance
is possible because the MMX state is aliased to the x87 FPU state (see Section 12.2, “The MMX State and MMX
Register Aliasing”).
With the introduction of the FXSAVE and FXRSTOR instructions and of SSE/SSE2/SSE3/SSSE3 extensions, it is
possible (and more efficient) to create state saving facilities in the operating system or executive that save the x87
FPU/MMX/SSE/SSE2/SSE3/SSSE3 state in one operation. Section 13.4, “Designing OS Facilities for Saving x87
FPU, SSE AND EXTENDED States on Task or Context Switches,” describes how to design such facilities. The techniques describes in this section can be adapted to saving only the MMX and x87 FPU state if needed.

12.5

EXCEPTIONS THAT CAN OCCUR WHEN EXECUTING MMX INSTRUCTIONS

MMX instructions do not generate x87 FPU floating-point exceptions, nor do they affect the processor’s status flags
in the EFLAGS register or the x87 FPU status word. The following exceptions can be generated during the execution
of an MMX instruction:

•

Exceptions during memory accesses:
— Stack-segment fault (#SS).
— General protection (#GP).
— Page fault (#PF).
— Alignment check (#AC), if alignment checking is enabled.

•

System exceptions:
— Invalid Opcode (#UD), if the EM flag in control register CR0 is set when an MMX instruction is executed (see
Section 12.1, “Emulation of the MMX Instruction Set”).
— Device not available (#NM), if an MMX instruction is executed when the TS flag in control register CR0 is
set. (See Section 13.4.1, “Using the TS Flag to Control the Saving of the x87 FPU and SSE State.”)

•

Floating-point error (#MF). (See Section 12.5.1, “Effect of MMX Instructions on Pending x87 Floating-Point
Exceptions.”)

•

Other exceptions can occur indirectly due to the faulty execution of the exception handlers for the above
exceptions.

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12.5.1

Effect of MMX Instructions on Pending x87 Floating-Point Exceptions

If an x87 FPU floating-point exception is pending and the processor encounters an MMX instruction, the processor
generates a x87 FPU floating-point error (#MF) prior to executing the MMX instruction, to allow the pending exception to be handled by the x87 FPU floating-point error exception handler. While this exception handler is executing,
the x87 FPU state is maintained and is visible to the handler. Upon returning from the exception handler, the MMX
instruction is executed, which will alter the x87 FPU state, as described in Section 12.2, “The MMX State and MMX
Register Aliasing.”

12.6

DEBUGGING MMX CODE

The debug facilities operate in the same manner when executing MMX instructions as when executing other IA-32
or Intel 64 architecture instructions.
To correctly interpret the contents of the MMX or x87 FPU registers from the FSAVE/FNSAVE or FXSAVE image in
memory, a debugger needs to take account of the relationship between the x87 FPU register’s logical locations
relative to TOS and the MMX register’s physical locations.
In the x87 FPU context, STn refers to an x87 FPU register at location n relative to the TOS. However, the tags in the
x87 FPU tag word are associated with the physical locations of the x87 FPU registers (R0 through R7). The MMX
registers always refer to the physical locations of the registers (with MM0 through MM7 being mapped to R0
through R7). Figure 12-2 shows this relationship. Here, the inner circle refers to the physical location of the x87
FPU and MMX registers. The outer circle refers to the x87 FPU registers’s relative location to the current TOS.
When the TOS equals 0 (case A in Figure 12-2), ST0 points to the physical location R0 on the floating-point stack.
MM0 maps to ST0, MM1 maps to ST1, and so on.
When the TOS equals 2 (case B in Figure 12-2), ST0 points to the physical location R2. MM0 maps to ST6, MM1
maps to ST7, MM2 maps to ST0, and so on.
x87 FPU “push”
ST7
MM7
MM6

ST0
MM0
(R0)
TOS

x87 FPU “pop”

ST6

ST1
MM7

MM1
MM2
(R2)

ST2

MM6

ST7
MM1
MM2
(R2)

ST0

MM3
MM4

MM4
Case A: TOS=0

TOS

MM5

MM3

MM5

MM0
(R0)

x87 FPU “push”

x87 FPU “pop”
ST1

Case B: TOS=2

Outer circle = x87 FPU data register’s logical location relative to TOS
Inner circle = x87 FPU tags = MMX register’s location = FP registers’s physical location

Figure 12-2. Mapping of MMX Registers to x87 FPU Data Register Stack

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CHAPTER 13
SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND
PROCESSOR EXTENDED STATES
This chapter describes system programming features for instruction set extensions operating on the processor
state extension known as the SSE state (XMM registers, MXCSR) and for other processor extended states. Instruction set extensions operating on the SSE state include the streaming SIMD extensions (SSE), streaming SIMD
extensions 2 (SSE2), streaming SIMD extensions 3 (SSE3), Supplemental SSE3 (SSSE3), and SSE4. Collectively,
these are called SSE extensions1 and the corresponding instructions SSE instructions. FXSAVE/FXRSTOR
instructions can be used save/restore SSE state along with FP state. See Section 10.5 in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 1 for information about FXSAVE and FXRSTOR.
Sections 13.1 through 13.4 cover system programming requirements to enable the SSE extensions, providing
operating system or executive support for the SSE extensions, SIMD floating-point exceptions, exception handling,
and task (context) switching. These sections primarily discuss use of FXSAVE/FXRSTOR to save/restore SSE state.
XSAVE feature set refers to extensions to the Intel architecture that will allow system executives to implement
support for multiple processor extended states along with FP/SSE states that may be introduced over time without
requiring the system executive to be modified each time a new processor state extension is introduced. XSAVE
feature set provide mechanisms to enumerate the supported extended states, enable some or all of them for software use, instructions to save/restore the states and enumerate the layout of the states when saved to memory.
XSAVE/XRSTOR instructions are part of the XSAVE feature set. These instructions are introduced after the introduction of FP/SSE states but can be used to manage legacy FP/SSE state along with processor extended states. See
CHAPTER 13 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 for information
about XSAVE feature set.
System programming for managing processor extended states is described in sections 13.5 through 13.6. XSAVE
feature set is designed to be compatible with FXSAVE/FXRSTOR and hence much of the material through sections
13.1 to 13.4 related to SSE state also applies to XSAVE feature set with the exception of enumeration and
saving/restoring state.
XSAVE Compaction is an XSAVE feature that allows operating systems to allocate space for only the states saved
to conserve memory usage. A new instruction called XSAVEC is introduced to save extended states in compacted
format and XRSTOR instruction is enhanced to comprehend compacted format. System programming for managing
processor extended states in compacted format is also described in section 13.5.
Supervisor state is an extended state that can only be accessed in ring 0. XSAVE feature set has been enhanced
to manage supervisor states. Two new ring 0 instructions, XSAVES/XRSTORS, are introduced to save/restore
supervisor states along with other XSAVE managed states. They are privileged instruction and only operate in
compacted format. System programming for managing supervisor states in described in section 13.7.
Each XSAVE managed features may have additional feature specific system programming requirements such as
exception handlers etc. Feature specific system programming requirements for XSAVE managed features are
described in section 13.8.

13.1

PROVIDING OPERATING SYSTEM SUPPORT FOR SSE EXTENSIONS

To use SSE extensions, the operating system or executive must provide support for initializing the processor to use
these extensions, for handling SIMD floating-point exceptions, and for using FXSAVE and FXRSTOR (Section 10.5
of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1) to manage context. XSAVE
feature set can also be used to manage SSE state along with other processor extended states as described in 13.5.
This section primarily focuses on using FXSAVE/FXRSTOR to manage SSE state. Because SSE extensions share the
same state, experience the same sets of non-numerical and numerical exception behavior, these guidelines that
apply to SSE also apply to other sets of SIMD extensions that operate on the same processor state and subject to
the same sets of non-numerical and numerical exception behavior.
1. The collection also includes PCLMULQDQ and AES instructions operating on XMM state.
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Chapter 11, “Programming with Streaming SIMD Extensions 2 (SSE2)” and Chapter 12, “Programming with SSE3,
SSSE3 and SSE4,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, provide
details on SSE instruction set.

13.1.1

Adding Support to an Operating System for SSE Extensions

The following guidelines describe functions that an operating system or executive must perform to support SSE
extensions:
1. Check that the processor supports the SSE extensions.
2. Check that the processor supports the FXSAVE and FXRSTOR instructions or the XSAVE feature set.
3. Provide an initialization for the SSE states.
4. Provide support for the FXSAVE and FXRSTOR instructions or the XSAVE feature set.
5. Provide support (if necessary) in non-numeric exception handlers for exceptions generated by the SSE instructions.
6. Provide an exception handler for the SIMD floating-point exception (#XM).
The following sections describe how to implement each of these guidelines.

13.1.2

Checking for CPU Support

If the processor attempts to execute an unsupported SSE instruction, the processor generates an invalid-opcode
exception (#UD). Before an operating system or executive attempts to use SSE extensions, it should check that
support is present by confirming the following bit values returned by the CPUID instruction:

•
•
•
•
•
•

CPUID.1:EDX.SSE[bit 25] = 1
CPUID.1:EDX.SSE2[bit 26] = 1
CPUID.1:ECX.SSE3[bit 0] = 1
CPUID.1:ECX.SSSE3[bit 9] = 1
CPUID.1:ECX.SSE4_1[bit 19] = 1
CPUID.1:ECX.SSE4_2[bit 20] = 1

(To use POPCNT instruction, software must check CPUID.1:ECX.POPCNT[bit 23] = 1.)
Separate checks must be made to ensure that the processor supports either FXSAVE and FXRSTOR or the XSAVE
feature set. See Section 10.5 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 and
Chapter 13 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, respectively.

13.1.3

Initialization of the SSE Extensions

The operating system or executive should carry out the following steps to set up SSE extensions for use by application programs:
1. Set CR4.OSFXSR[bit 9] = 1. Setting this flag implies that the operating system provides facilities for saving
and restoring SSE state using FXSAVE and FXRSTOR instructions. These instructions may be used to save the
SSE state during task switches and when invoking the SIMD floating-point exception (#XM) handler (see
Section 13.1.5, “Providing a Handler for the SIMD Floating-Point Exception (#XM)”).
If the processor does not support the FXSAVE and FXRSTOR instructions, attempting to set the OSFXSR flag
causes a general-protection exception (#GP) to be generated.

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2. Set CR4.OSXMMEXCPT[bit 10] = 1. Setting this flag implies that the operating system provides a SIMD
floating-point exception (#XM) handler (see Section 13.1.5, “Providing a Handler for the SIMD Floating-Point
Exception (#XM)”).

NOTE
The OSFXSR and OSXMMEXCPT bits in control register CR4 must be set by the operating system.
The processor has no other way of detecting operating-system support for the FXSAVE and
FXRSTOR instructions or for handling SIMD floating-point exceptions.
3. Clear CR0.EM[bit 2] = 0. This action disables emulation of the x87 FPU, which is required when executing SSE
instructions (see Section 2.5, “Control Registers”).
4. Set CR0.MP[bit 1] = 1. This setting is required for Intel 64 and IA-32 processors that support the SSE
extensions (see Section 9.2.1, “Configuring the x87 FPU Environment”).
Table 13-1 and Table 13-2 show the actions of the processor when an SSE instruction is executed, depending on
the following:

•
•
•

OSFXSR and OSXMMEXCPT flags in control register CR4
SSE/SSE2/SSE3/SSSE3/SSE4 feature flags returned by CPUID
EM, MP, and TS flags in control register CR0

Table 13-1. Action Taken for Combinations of OSFXSR, OSXMMEXCPT, SSE, SSE2, SSE3, EM, MP, and TS1
CR4

CPUID

CR0 Flags

OSFXSR

OSXMMEXCPT

SSE, SSE2,
SSE32,
SSE4_13

EM

MP4

TS

0

X5

X

X

1

X

#UD exception.

1

X

0

X

1

X

#UD exception.

1

X

1

1

1

X

#UD exception.

1

0

1

0

1

0

Execute instruction; #UD exception if unmasked
SIMD floating-point exception is detected.

1

1

1

0

1

0

Execute instruction; #XM exception if unmasked
SIMD floating-point exception is detected.

1

X

1

0

1

1

#NM exception.

Action

NOTES:
1. For execution of any SSE instruction except the PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, MOVNTI, and CLFLUSH instructions.
2. Exception conditions due to CR4.OSFXSR or CR4.OSXMMEXCPT do not apply to FISTTP.
3. Only applies to DPPS, DPPD, ROUNDPS, ROUNDPD, ROUNDSS, ROUNDSD.
4. For processors that support the MMX instructions, the MP flag should be set.
5. X = Don’t care.

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Table 13-2. Action Taken for Combinations of OSFXSR, SSSE3, SSE4, EM, and TS
CR4

CPUID

CR0 Flags

OSFXSR

SSSE3
SSE4_11
SSE4_22

EM

TS

0

X3

X

X

#UD exception.

1

0

X

X

#UD exception.

1

1

1

X

#UD exception.

1

1

0

1

#NM exception.

Action

NOTES:
1. Applies to SSE4_1 instructions except DPPS, DPPD, ROUNDPS, ROUNDPD, ROUNDSS, ROUNDSD.
2. Applies to SSE4_2 instructions except CRC32 and POPCNT.
3. X = Don’t care.
The SIMD floating-point exception mask bits (bits 7 through 12), the flush-to-zero flag (bit 15), the denormals-arezero flag (bit 6), and the rounding control field (bits 13 and 14) in the MXCSR register should be left in their default
values of 0. This permits the application to determine how these features are to be used.

13.1.4

Providing Non-Numeric Exception Handlers for Exceptions Generated by the SSE
Instructions

SSE instructions can generate the same type of memory-access exceptions (such as page faults and limit violations) and other non-numeric exceptions as other Intel 64 and IA-32 architecture instructions generate.
Ordinarily, existing exception handlers can handle these and other non-numeric exceptions without code modification. However, depending on the mechanisms used in existing exception handlers, some modifications might need
to be made.
The SSE extensions can generate the non-numeric exceptions listed below:

•

Memory Access Exceptions:
— Stack-segment fault (#SS).
— General protection exception (#GP). Executing most SSE instructions with an unaligned 128-bit memory
reference generates a general-protection exception. (The MOVUPS and MOVUPD instructions allow
unaligned a loads or stores of 128-bit memory locations, without generating a general-protection
exception.) A 128-bit reference within the stack segment that is not aligned to a 16-byte boundary will also
generate a general-protection exception, instead a stack-segment fault exception (#SS).
— Page fault (#PF).
— Alignment check (#AC). When enabled, this type of alignment check operates on operands that are less
than 128-bits in size: 16-bit, 32-bit, and 64-bit. To enable the generation of alignment check exceptions, do
the following:

•
•
•

Set the AM flag (bit 18 of control register CR0)
Set the AC flag (bit 18 of the EFLAGS register)
CPL must be 3

If alignment check exceptions are enabled, 16-bit, 32-bit, and 64-bit misalignment will be detected for the
MOVUPD and MOVUPS instructions; detection of 128-bit misalignment is not guaranteed and may vary
with implementation.

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•

System Exceptions:
— Invalid-opcode exception (#UD). This exception is generated when executing SSE instructions under the
following conditions:

•

SSE/SSE2/SSE3/SSSE3/SSE4_1/SSE4_2 feature flags returned by CPUID are set to 0. This condition
does not affect the CLFLUSH instruction, nor POPCNT.

•

The CLFSH feature flag returned by the CPUID instruction is set to 0. This exception condition only
pertains to the execution of the CLFLUSH instruction.

•

The POPCNT feature flag returned by the CPUID instruction is set to 0. This exception condition only
pertains to the execution of the POPCNT instruction.

•

The EM flag (bit 2) in control register CR0 is set to 1, regardless of the value of TS flag (bit 3) of CR0.
This condition does not affect the PAUSE, PREFETCHh, MOVNTI, SFENCE, LFENCE, MFENCE, CLFLUSH,
CRC32 and POPCNT instructions.

•

The OSFXSR flag (bit 9) in control register CR4 is set to 0. This condition does not affect the PSHUFW,
MOVNTQ, MOVNTI, PAUSE, PREFETCHh, SFENCE, LFENCE, MFENCE, CLFLUSH, CRC32 and POPCNT
instructions.

•

Executing an instruction that causes a SIMD floating-point exception when the OSXMMEXCPT flag (bit
10) in control register CR4 is set to 0. See Section 13.4.1, “Using the TS Flag to Control the Saving of
the x87 FPU and SSE State.”

— Device not available (#NM). This exception is generated by executing a SSE instruction when the TS flag
(bit 3) of CR0 is set to 1.
Other exceptions can occur during delivery of the above exceptions.

13.1.5

Providing a Handler for the SIMD Floating-Point Exception (#XM)

SSE instructions do not generate numeric exceptions on packed integer operations. They can generate the
following numeric (SIMD floating-point) exceptions on packed and scalar single-precision and double-precision
floating-point operations.

•
•
•
•
•
•

Invalid operation (#I)
Divide-by-zero (#Z)
Denormal operand (#D)
Numeric overflow (#O)
Numeric underflow (#U)
Inexact result (Precision) (#P)

These SIMD floating-point exceptions (with the exception of the denormal operand exception) are defined in the
IEEE Standard 754 for Binary Floating-Point Arithmetic and represent the same conditions that cause x87 FPU
floating-point error exceptions (#MF) to be generated for x87 FPU instructions.
Each of these exceptions can be masked, in which case the processor returns a reasonable result to the destination
operand without invoking an exception handler. However, if any of these exceptions are left unmasked, detection
of the exception condition results in a SIMD floating-point exception (#XM) being generated. See Chapter 6,
“Interrupt 19—SIMD Floating-Point Exception (#XM).”
To handle unmasked SIMD floating-point exceptions, the operating system or executive must provide an exception
handler. The section titled “SSE and SSE2 SIMD Floating-Point Exceptions” in Chapter 11, “Programming with
Streaming SIMD Extensions 2 (SSE2),” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 1, describes the SIMD floating-point exception classes and gives suggestions for writing an exception
handler to handle them.
To indicate that the operating system provides a handler for SIMD floating-point exceptions (#XM), the OSXMMEXCPT flag (bit 10) must be set in control register CR4.

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SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND PROCESSOR EXTENDED STATES

13.1.5.1

Numeric Error flag and IGNNE#

SSE extensions ignore the NE flag in control register CR0 (that is, they treat it as if it were always set) and the
IGNNE# pin. When an unmasked SIMD floating-point exception is detected, it is always reported by generating a
SIMD floating-point exception (#XM).

13.2

EMULATION OF SSE EXTENSIONS

The Intel 64 and IA-32 architectures do not support emulation of the SSE instructions, as they do for x87 FPU
instructions.
The EM flag in control register CR0 (provided to invoke emulation of x87 FPU instructions) cannot be used to invoke
emulation of SSE instructions. If an SSE instruction is executed when CR0.EM = 1, an invalid opcode exception
(#UD) is generated. See Table 13-1.

13.3

SAVING AND RESTORING SSE STATE

The SSE state consists of the state of the XMM and MXCSR registers. Intel recommends the following method for
saving and restoring this state:

•
•

Execute the FXSAVE instruction to save the state of the XMM and MXCSR registers to memory.
Execute the FXRSTOR instruction to restore the state of the XMM and MXCSR registers from the image saved in
memory earlier.

This save and restore method is required for all operating systems. XSAVE feature set can also be used to
save/restore SSE state. See Section 13.5, “The XSAVE Feature Set and Processor Extended State Management,”
for using the XSAVE feature set to save/restore SSE state.
In some cases, applications may choose to save only the XMM and MXCSR registers in the following manner:

•
•

Execute MOVDQ instructions to save the contents of the XMM registers to memory.
Execute a STMXCSR instruction to save the state of the MXCSR register to memory.

Such applications must restore the XMM and MXCSR registers as follows:

•

Execute MOVDQ instructions to load the saved contents of the XMM registers from memory into the XMM
registers.

•

Execute a LDMXCSR instruction to restore the state of the MXCSR register from memory.

13.4

DESIGNING OS FACILITIES FOR SAVING X87 FPU, SSE AND EXTENDED
STATES ON TASK OR CONTEXT SWITCHES

The x87 FPU and SSE state consist of the state of the x87 FPU, XMM, and MXCSR registers. The FXSAVE and
FXRSTOR instructions provide a fast method for saving and restoring this state. The XSAVE feature set can also be
used to save FP and SSE state along with other extended states (see Section 13.5).
Older operating systems may use FSAVE/FNSAVE and FRSTOR to save the x87 FPU state. These facilities can be
extended to save and restore SSE state by substituting FXSAVE and FXRSTOR or the XSAVE feature set in place of
FSAVE/FNSAVE and FRSTOR.
If task or context switching facilities are written from scratch, any of several approaches may be taken for using the
FXSAVE and FXRSTOR instructions or the XSAVE feature set to save and restore x87 FPU and SSE state:

•

The operating system can require applications that are intended to be run as tasks take responsibility for saving
the states prior to a task suspension during a task switch and for restoring the states when the task is resumed.
This approach is appropriate for cooperative multitasking operating systems, where the application has control
over (or is able to determine) when a task switch is about to occur and can save state prior to the task switch.

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•

The operating system can take the responsibility for saving the states as part of the task switch process and
restoring the state of the registers when a suspended task is resumed. This approach is appropriate for
preemptive multitasking operating systems, where the application cannot know when it is going to be
preempted and cannot prepare in advance for task switching.

•

The operating system can take the responsibility for saving the states as part of the task switch process, but
delay the restoring of the states until an instruction operating on the states is actually executed by the new
task. See Section 13.4.1, “Using the TS Flag to Control the Saving of the x87 FPU and SSE State,” for more
information. This approach is called lazy restore.
The use of lazy restore mechanism in context switches is not recommended when XSAVE feature set is used to
save/restore states for the following reasons.
— With XSAVE feature set, Intel processors have optimizations in place to avoid saving the state components
that are in their initial configurations or when they have not been modified since they were restored last.
These optimizations eliminate the need for lazy restore. See section 13.5.4 in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.
— Intel processors have power optimizations when state components are in their initial configurations. Use of
lazy restore retains the non-initial configuration of the last thread and is not power efficient.
— Not all extended states support lazy restore mechanisms. As such, when one or more such states are
enabled it becomes very inefficient to use lazy restore as it results in two separate state restore, one in
context switch for the states that does not support lazy restore and one in the #NM handler for states that
support lazy restore.

13.4.1

Using the TS Flag to Control the Saving of the x87 FPU and SSE State

The TS flag in control register CR0 is provided to allow the operating system to delay saving/restoring the x87 FPU
and SSE state until an instruction that actually accesses this state is encountered in a new task. When the TS flag
is set, the processor monitors the instruction stream for x87 FPU, MMX, SSE instructions. When the processor
detects one of these instructions, it raises a device-not-available exception (#NM) prior to executing the instruction. The #NM exception handler can then be used to save the x87 FPU and SSE state for the previous task (using
an FXSAVE, XSAVE, or XSAVEOPT instruction) and load the x87 FPU and SSE state for the current task (using an
FXRSTOR or XRSOTR instruction). If the task never encounters an x87 FPU, MMX, or SSE instruction, the devicenot-available exception will not be raised and a task state will not be saved/restored unnecessarily.

NOTE
The CRC32 and POPCNT instructions do not operate on the x87 FPU or SSE state. They operate on
the general-purpose registers and are not involved with the techniques described above.
The TS flag can be set either explicitly (by executing a MOV instruction to control register CR0) or implicitly (using
the IA-32 architecture’s native task switching mechanism). When the native task switching mechanism is used, the
processor automatically sets the TS flag on a task switch. After the device-not-available handler has saved the x87
FPU and SSE state, it should execute the CLTS instruction to clear the TS flag.

13.5

THE XSAVE FEATURE SET AND PROCESSOR EXTENDED STATE
MANAGEMENT

The architecture of XSAVE feature set is described in CHAPTER 13 of Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 1. The XSAVE feature set includes the following:

•

An extensible data layout for existing and future processor state extensions. The layout of the XSAVE area
extends from the 512-byte FXSAVE/FXRSTOR layout to provide compatibility and migration path from
managing the legacy FXSAVE/FXRSTOR area. The XSAVE area is described in more detail in Section 13.4 of the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.

•

CPUID enhancements for feature enumeration. See Section 13.2 of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1.

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SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND PROCESSOR EXTENDED STATES

•

Control register enhancement and dedicated register for enabling each processor extended state. See Section
13.3 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.

•

Instructions to save state to and restore state from the XSAVE area. See Section 13.7 through Section 13.9 of
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.

Operating systems can utilize XSAVE feature set to manage both FP/SSE state and processor extended states.
CPUID leaf 0DH enumerates XSAVE feature set related information. The following guidelines provide the steps an
operating system needs to take to support legacy FP/SSE states and processor extended states.
1. Check that the processor supports the XSAVE feature set
2. Determine the set of XSAVE managed features that the operating system intends to enable and calculate the
size of the buffer needed to save/restore the states during context switch and other flows
3. Enable use of XSAVE feature set and XSAVE managed features
4. Provide an initialization for the XSAVE managed feature state components
5. Provide (if necessary) required exception handlers for exceptions generated each of the XSAVE managed
features.

13.5.1

Checking the Support for XSAVE Feature Set

Support for XSAVE Feature set is enumerated in CPUID.1.ECX.XSAVE[bit 26]. Enumeration of this bit indicates that
the processor supports XSAVE/XRSTOR instructions to manage state and XSETBV/XGETBV on XCR0 to enable and
get enabled states. An operating system needs to enable XSAVE feature set as described later.
Additionally CPUID.(EAX=0DH, ECX=1).EAX enumerates additional XSAVE sub features such as optimized save,
compaction and supervisor state support. The following table summarizes XSAVE sub features. Once an operating
system enables XSAVE feature set, all the sub-features enumerated are also available. There is no need to enable
each additional sub feature.

Table 13-3. CPUID.(EAX=0DH, ECX=1) EAX Bit Assignment
EAX Bit Position
0

If set, indicates availability of the XSAVEOPT instruction.

1

If set, indicates availability of the XSAVEC instruction and the corresponding compaction enhancements
to the legacy XRSTOR instruction.

2

If set, indicates support for execution of XGETBV with ECX=1. This execution returns the state-component bitmap XINUSE. If XINUSE[i] = 0, state component i is in its initial configuration. Execution of
XSETBV with ECX=1 causes a #GP.

3

If set, indicates support for XSAVES/XRSTORS and IA32_XSS MSR

31:4

13.5.2

Meaning

Reserved

Determining the XSAVE Managed Feature States And The Required Buffer Size

Each XSAVE managed feature has one or more state components associated with it. An operating system policy
needs to determine the XSAVE managed features to support and determine the corresponding state components to
enable. When determining the XSAVE managed features to support, operating system needs to take into account
the dependencies between them (e.g. AVX feature depends on SSE feature). Similarly, when a XSAVE managed
feature has more than one state component, all of them need to be enabled. Each logical processor enumerates
supported XSAVE state components in CPUID.(EAX=0DH, ECX=0).EDX:EAX. An operating system may enable all
or a subset of the state components enumerated by the processor based on the OS policy.
The size of the memory buffer needed to save enabled XSAVE state components depends on whether the OS optsin to use compacted format or not. Section 13.4.3 of the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1 describes the layout of the extended region of the XSAVE area.

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13.5.3

Enable the Use Of XSAVE Feature Set And XSAVE State Components

Operating systems need to enable the use of XSAVE feature set by writing to CR4.OSXSAVE[bit 18] to enable
XSETBV/XGETBV instructions to access XCR0 and to support processor extended state management using
XSAVE/XRSTOR. When XSAVE feature set is enabled, all enumerated XSAVE sub features such as optimized save,
compaction and supervisor state support are also enabled. Operating systems also need to enable the XSAVE state
components in XCR0 using XSETBV instruction.
XSAVE state components can subsequently be disabled in XCR0. However, disabling state components of AVX or
AVX-512 that are not in initial configuration may incur power and performance penalty on SSE and AVX instructions
respectively. If AVX state is disabled when it is not in its initial configuration, subsequent SSE instructions may
incur a penalty. If AVX-512 state is disabled when it is not in its initial configuration, subsequent SSE and AVX
instructions may incur a penalty. It is recommended that the operating systems and VMM set AVX or AVX-512 state
components to their initial configuration before disabling them. This can be achieved by one of the two methods
below.

•

Using XRSTOR: Operating system or VMM can set the state of AVX or AVX-512 state components using XRSTOR
instruction before disabling them in XCR0.

•

Using VZEROUPPER: Operating system or VMM can set AVX and AVX-512 state components to their initial
configuration using VZEROUPPER instruction before disabling them in XCR0. Note that this will set both AVX
and AVX-512 state components to their initial configuration. If the intent is to only disable AVX-512 state,
Operating system or VMM will need to save AVX state before executing VZEROUPPER and restore it afterwards.

13.5.4

Provide an Initialization for the XSAVE State Components

The XSAVE header of a newly allocated XSAVE area should be initialized to all zeroes before saving context. An
operating system may choose to establish beginning state-component values for a task by executing XRSTOR from
an XSAVE area that the OS has configured. If it is desired to begin state component i in its initial configuration, the
OS should clear bit i in the XSTATE_BV field in the XSAVE header; otherwise, it should set that bit and place the
desired beginning value in the appropriate location in the XSAVE area.
When a buffer is allocated for compacted size, software must ensure that the XCOMP_BV field is setup correctly
before restoring from the buffer. Bit 63 of the XCOMP_BV field indicates that the save area is in the compacted
format and the remaining bits indicate the states that have space allocated in the save area. If the buffer is first
used to save the state in compacted format, then the save instructions will setup the XCOMP_BV field appropriately. If the buffer is first used to restore the state, then software must set up the XCOMP_BV field.

13.5.5

Providing the Required Exception Handlers

Instructions part of each XSAVE managed features may generate exceptions and operating system may need to
enable such exceptions and provide handlers for them. Section 13.8 describes feature specific OS requirements for
each XSAVE managed features.

13.6

INTEROPERABILITY OF THE XSAVE FEATURE SET AND FXSAVE/FXRSTOR

The FXSAVE instruction writes x87 FPU and SSE state information to a 512-byte FXSAVE save area. FXRSTOR
restores the processor’s x87 FPU and SSE states from an FXSAVE area. The XSAVE features set supports x87 FPU
and SSE states using the same layout as the FXSAVE area to provide interoperability of FXSAVE versus XSAVE, and
FXRSTOR versus XRSTOR. The XSAVE feature set allows system software to manage SSE state independent of x87
FPU states. Thus system software that had been using FXSAVE and FXRSTOR to manage x87 FPU and SSE states
can transition to using the XSAVE feature set to manage x87 FPU, SSE and other processor extended states in a
systematic and forward-looking manner. See Section 10.5 and Chapter 13 of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1 for more details.
System software can implement forward-looking processor extended state management using the XSAVE feature
set. In this case, system software must specify the bit vector mask in EDX:EAX appropriately when executing
XSAVE/XRSTOR instructions.

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SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND PROCESSOR EXTENDED STATES

For instance, the OS can supply instructions in the XSAVE feature set with a bit vector in EDX:EAX with the two
least significant bits (corresponding to x87 FPU and SSE state) equal to 0. Then, the XSAVE instruction will not
write the processor’s x87 FPU and SSE state into memory. Similarly, the XRSTOR instruction executed with a value
in EDX:EAX with the least two significant bit equal to 0 will not restore nor initialize the processor’s x87 FPU and
SSE state.
The processor’s action as a result of executing XRSTOR is given in Section 13.8 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1. The instruction may be used to initialize x87 FPU or XMM registers. When the MXCSR register is updated from memory, reserved bit checking is enforced. The saving/restoring of
MXCSR is bound to the SSE state, independent of the x87 FPU state. The action of XSAVE is given in Section 13.7
of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.

13.7

THE XSAVE FEATURE SET AND PROCESSOR SUPERVISOR STATE
MANAGEMENT

Supervisor state is a processor state that is only accessible in ring 0. An extension to XSAVE feature set, enumerated by CPUID.(EAX=0DH, ECX=1).EAX[bit 3] allows the management of the supervisor states using XSAVE
feature set. See Chapter 13 of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 for the
details of the supervisor state XSAVE feature set extension. The supervisor state extension includes the following:

•

CPUID enhancements to enumerate the set of supervisor states and their sizes that can be managed by XSAVE
feature set.

•
•

A new MSR IA32_XSS to enable XSAVE feature set to manage one or more enumerated supervisor states.
A new pair of privileged save/restore instructions, XSAVES and XRSTORS, to save/restore supervisor states
along with other XSAVE managed feature states.

The guidelines to enable XSAVE feature set to manage supervisor state are very similar to the steps outlines in
Section 13.6 with the differences outline below. The set of supervisor states that can be managed by XSAVE feature
set is enumerated in (EAX=0DH, ECX=1).EDX:ECX. XSAVE managed supervisor states are enabled in IA32_XSS
MSR instead of XCR0 control register. There are semantic differences between user states enabled in XCR0 and
supervisor state enabled in IA32_XSS MSR. A supervisor state enabled in IA32_XSS MSR:

•

May be accessed via other mechanisms such as RDMSR/WRMSR even when they are not enabled in IA32_XSS
MSR. Enabling a supervisor state in the IA32_XSS MSR merely indicates that the state can be saved/restored
using XSAVES/XRSTORS instructions.

•

May have side effects when saving/restoring the state such as disabling/enabling feature associated with the
state. This behavior is feature specific and will be documented along with the feature description.

•

May generate faults when saving/restoring the state. XSAVES/XRSTORS will follow the faulting behavior of
RDMSR/WRMSR respectively if the corresponding state is also accessible using RDMSR/WRMSR.

•

XRSTORS may fault when restoring the state for supervisor features that are already enabled via feature
specific mechanisms. This behavior is feature specific and will be documented along with the feature
description.

When a supervisor state is disabled via a feature specific mechanism, the state does not automatically get marked
as INIT. Hence XSAVES/XRSTORS will continue to save/restore the state subject to available optimizations. If the
software does not intend to preserve the state when it disables the feature, it should initialize it to hardware INIT
value with XRSTORS instruction so that XSAVES/XRSTORS perform optimally for that state.

13.8

SYSTEM PROGRAMMING FOR XSAVE MANAGED FEATURES

This section describes system programming requirement for each XSAVE managed features that are feature
specific such as exception handling.

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SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND PROCESSOR EXTENDED STATES

13.8.1

Intel® Advanced Vector Extensions (Intel® AVX)

Intel AVX instructions comprises of 256-bit and 128-bit instructions that operates on 256-bit YMM registers. The
XSAVE feature set allows software to save and restore the state of these registers. See Chapter 13 of the Intel® 64
and IA-32 Architectures Software Developer’s Manual, Volume 1.
For processors that support YMM states, the YMM state exists in all operating modes. However, the available
instruction interfaces to access YMM states may vary in different modes.
Operating systems must use the XSAVE feature set for YMM state management. The XSAVE feature set also
provides flexible and efficient interface to manage XMM/MXCSR states and x87 FPU states in conjunction with
newer processor extended states like YMM states. Operating systems may need to be aware of the following when
supporting AVX.

•

Saving/Restoring AVX state in non-compacted format without SSE state will also save/restore MXCSR even
though MXCSR is not part of AVX state. This does not happen when compacted format is used.

•

Few AVX instructions such as VZEROUPPER/VZEROALL may operate on future expansion of YMM registers.

An operating system must enable its YMM state management to support AVX and any 256-bit extensions that
operate on YMM registers. Otherwise, an attempt to execute an instruction in AVX extensions (including an
enhanced 128-bit SIMD instructions using VEX encoding) will cause a #UD exception.
AVX instructions may generate SIMD floating-point exceptions. An OS must enable SIMD floating-point exception
support by setting CR4.OSXMMEXCPT[bit 10]=1.

13.8.2

Intel® Advanced Vector Extensions 512 (Intel® AVX-512)

Intel AVX-512 instructions are encoded using EVEX prefix. The EVEX encoding scheme can support 512-bit, 256bit and 128-bit instructions that operate on opmask, ZMM, YMM and XMM registers.
For processors that support the Intel AVX-512 family of instructions, the extended processor states (ZMM and
opmask registers) exist in all operating modes. However, the access to these states may vary in different modes.
The processor's support for instruction extensions that employ EVEX prefix encoding is independent of the
processor's support for using XSAVE feature set on those states.
Instructions requiring EVEX prefix encoding are generally supported in 64-bit, 32-bit modes, and 16-bit protected
mode. They are not supported in Real mode, Virtual-8086 mode or entering into SMM mode. Note that bits MAXVL1:256 (511:256) of ZMM register state are maintained across transitions into and out of these modes. Because the
XSAVE feature set instruction can operate in all operating modes, it is possible that the processor's ZMM register
state can be modified by software in any operating mode by executing XRSTOR.
Operating systems must use the XSAVE/XRSTOR/XSAVEOPT instructions for ZMM and opmask state management.
An OS must enable its ZMM and opmask state management to support Intel AVX-512 Foundation instructions.
Otherwise, an attempt to execute an instruction in Intel AVX-512 Foundation instructions (including a scalar 128bit SIMD instructions using EVEX encoding) will cause a #UD exception. An operating system, which enables the
AVX-512 state to support Intel AVX-512 Foundation instructions, is also sufficient to support the rest of the Intel
AVX-512 family of instructions. Note that even though ZMM8-ZMM31 are not accessible in 32 bit mode, a 32 bit OS
is still required to allocate memory for the entire ZMM state.
Intel AVX-512 Foundation instructions may generate SIMD floating-point exceptions. An OS must enable SIMD
floating point exception support by setting CR4.OSXMMEXCPT[bit 10]=1.

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SYSTEM PROGRAMMING FOR INSTRUCTION SET EXTENSIONS AND PROCESSOR EXTENDED STATES

13-12 Vol. 3A

CHAPTER 14
POWER AND THERMAL MANAGEMENT
This chapter describes facilities of Intel 64 and IA-32 architecture used for power management and thermal monitoring.

14.1

ENHANCED INTEL SPEEDSTEP® TECHNOLOGY

Enhanced Intel SpeedStep® Technology was introduced in the Pentium M processor. The technology enables the
management of processor power consumption via performance state transitions. These states are defined as
discrete operating points associated with different voltages and frequencies.
Enhanced Intel SpeedStep Technology differs from previous generations of Intel SpeedStep Technology in two
ways:

•

Centralization of the control mechanism and software interface in the processor by using model-specific
registers.

•

Reduced hardware overhead; this permits more frequent performance state transitions.

Previous generations of the Intel SpeedStep Technology require processors to be a deep sleep state, holding off bus
master transfers for the duration of a performance state transition. Performance state transitions under the
Enhanced Intel SpeedStep Technology are discrete transitions to a new target frequency.
Support is indicated by CPUID, using ECX feature bit 07. Enhanced Intel SpeedStep Technology is enabled by
setting IA32_MISC_ENABLE MSR, bit 16. On reset, bit 16 of IA32_MISC_ENABLE MSR is cleared.

14.1.1

Software Interface For Initiating Performance State Transitions

State transitions are initiated by writing a 16-bit value to the IA32_PERF_CTL register, see Figure 14-2. If a transition is already in progress, transition to a new value will subsequently take effect.
Reads of IA32_PERF_CTL determine the last targeted operating point. The current operating point can be read from
IA32_PERF_STATUS. IA32_PERF_STATUS is updated dynamically.
The 16-bit encoding that defines valid operating points is model-specific. Applications and performance tools are
not expected to use either IA32_PERF_CTL or IA32_PERF_STATUS and should treat both as reserved. Performance
monitoring tools can access model-specific events and report the occurrences of state transitions.

14.2

P-STATE HARDWARE COORDINATION

The Advanced Configuration and Power Interface (ACPI) defines performance states (P-states) that are used to
facilitate system software’s ability to manage processor power consumption. Different P-states correspond to
different performance levels that are applied while the processor is actively executing instructions. Enhanced Intel
SpeedStep Technology supports P-states by providing software interfaces that control the operating frequency and
voltage of a processor.
With multiple processor cores residing in the same physical package, hardware dependencies may exist for a
subset of logical processors on a platform. These dependencies may impose requirements that impact the coordination of P-state transitions. As a result, multi-core processors may require an OS to provide additional software
support for coordinating P-state transitions for those subsets of logical processors.
ACPI firmware can choose to expose P-states as dependent and hardware-coordinated to OS power management
(OSPM) policy. To support OSPMs, multi-core processors must have additional built-in support for P-state hardware
coordination and feedback.
Intel 64 and IA-32 processors with dependent P-states amongst a subset of logical processors permit hardware
coordination of P-states and provide a hardware-coordination feedback mechanism using IA32_MPERF MSR and
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POWER AND THERMAL MANAGEMENT

IA32_APERF MSR. See Figure 14-1 for an overview of the two 64-bit MSRs and the bullets below for a detailed
description:

63

0

IA32_MPERF (Addr: E7H)

63

0

IA32_APERF (Addr: E8H)

Figure 14-1. IA32_MPERF MSR and IA32_APERF MSR for P-state Coordination

•

Use CPUID to check the P-State hardware coordination feedback capability bit. CPUID.06H.ECX[Bit 0] = 1
indicates IA32_MPERF MSR and IA32_APERF MSR are present.

•

IA32_MPERF MSR (E7H) increments in proportion to a fixed frequency, which is configured when the processor
is booted.

•

IA32_APERF MSR (E8H) increments in proportion to actual performance, while accounting for hardware coordination of P-state and TM1/TM2; or software initiated throttling.

•

The MSRs are per logical processor; they measure performance only when the targeted processor is in the C0
state.

•

Only the IA32_APERF/IA32_MPERF ratio is architecturally defined; software should not attach meaning to the
content of the individual of IA32_APERF or IA32_MPERF MSRs.

•
•

When either MSR overflows, both MSRs are reset to zero and continue to increment.
Both MSRs are full 64-bits counters. Each MSR can be written to independently. However, software should
follow the guidelines illustrated in Example 14-1.

If P-states are exposed by the BIOS as hardware coordinated, software is expected to confirm processor support
for P-state hardware coordination feedback and use the feedback mechanism to make P-state decisions. The OSPM
is expected to either save away the current MSR values (for determination of the delta of the counter ratio at a later
time) or reset both MSRs (execute WRMSR with 0 to these MSRs individually) at the start of the time window used
for making the P-state decision. When not resetting the values, overflow of the MSRs can be detected by checking
whether the new values read are less than the previously saved values.
Example 14-1 demonstrates steps for using the hardware feedback mechanism provided by IA32_APERF MSR and
IA32_MPERF MSR to determine a target P-state.
Example 14-1. Determine Target P-state From Hardware Coordinated Feedback
DWORD PercentBusy; // Percentage of processor time not idle.
// Measure “PercentBusy“ during previous sampling window.
// Typically, “PercentBusy“ is measure over a time scale suitable for
// power management decisions
//
// RDMSR of MCNT and ACNT should be performed without delay.
// Software needs to exercise care to avoid delays between
// the two RDMSRs (for example, interrupts).
MCNT = RDMSR(IA32_MPERF);
ACNT = RDMSR(IA32_APERF);
// PercentPerformance indicates the percentage of the processor
// that is in use. The calculation is based on the PercentBusy,
// that is the percentage of processor time not idle and the P-state
// hardware coordinated feedback using the ACNT/MCNT ratio.
// Note that both values need to be calculated over the same

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POWER AND THERMAL MANAGEMENT

// time window.
PercentPerformance = PercentBusy * (ACNT/MCNT);

// This example does not cover the additional logic or algorithms
// necessary to coordinate multiple logical processors to a target P-state.
TargetPstate = FindPstate(PercentPerformance);
if (TargetPstate ≠ currentPstate) {
SetPState(TargetPstate);
}
// WRMSR of MCNT and ACNT should be performed without delay.
// Software needs to exercise care to avoid delays between
// the two WRMSRs (for example, interrupts).
WRMSR(IA32_MPERF, 0);
WRMSR(IA32_APERF, 0);

14.3

SYSTEM SOFTWARE CONSIDERATIONS AND OPPORTUNISTIC PROCESSOR
PERFORMANCE OPERATION

An Intel 64 processor may support a form of processor operation that takes advantage of design headroom to
opportunistically increase performance. The Intel Turbo Boost Technology can convert thermal headroom into
higher performance across multi-threaded and single-threaded workloads. The Intel Dynamic Acceleration feature
can convert thermal headroom into higher performance if only one thread is active.

14.3.1

Intel Dynamic Acceleration

Intel Core 2 Duo processor T 7700 introduces Intel Dynamic Acceleration (IDA). IDA takes advantage of thermal
design headroom and opportunistically allows a single core to operate at a higher performance level when the
operating system requests increased performance.

14.3.2

System Software Interfaces for Opportunistic Processor Performance Operation

Opportunistic processor performance operation, applicable to Intel Dynamic Acceleration and Intel Turbo Boost
Technology, has the following characteristics:

•

A transition from a normal state of operation (e.g. IDA/Turbo mode disengaged) to a target state is not
guaranteed, but may occur opportunistically after the corresponding enable mechanism is activated, the
headroom is available and certain criteria are met.

•
•

The opportunistic processor performance operation is generally transparent to most application software.

•

When opportunistic processor performance operation is engaged, the OS should use hardware coordination
feedback mechanisms to prevent un-intended policy effects if it is activated during inappropriate situations.

System software (BIOS and Operating system) must be aware of hardware support for opportunistic processor
performance operation and may need to temporarily disengage opportunistic processor performance operation
when it requires more predictable processor operation.

14.3.2.1

Discover Hardware Support and Enabling of Opportunistic Processor Performance Operation

If an Intel 64 processor has hardware support for opportunistic processor performance operation, the power-on
default state of IA32_MISC_ENABLE[38] indicates the presence of such hardware support. For Intel 64 processors
that support opportunistic processor performance operation, the default value is 1, indicating its presence. For
processors that do not support opportunistic processor performance operation, the default value is 0. The powerVol. 3B 14-3

POWER AND THERMAL MANAGEMENT

on default value of IA32_MISC_ENABLE[38] allows BIOS to detect the presence of hardware support of opportunistic processor performance operation.
IA32_MISC_ENABLE[38] is shared across all logical processors in a physical package. It is written by BIOS during
platform initiation to enable/disable opportunistic processor performance operation in conjunction of OS power
management capabilities, see Section 14.3.2.2. BIOS can set IA32_MISC_ENABLE[38] with 1 to disable opportunistic processor performance operation; it must clear the default value of IA32_MISC_ENABLE[38] to 0 to enable
opportunistic processor performance operation. OS and applications must use CPUID leaf 06H if it needs to detect
processors that have opportunistic processor performance operation enabled.
When CPUID is executed with EAX = 06H on input, Bit 1 of EAX in Leaf 06H (i.e. CPUID.06H:EAX[1]) indicates
opportunistic processor performance operation, such as IDA, has been enabled by BIOS.
Opportunistic processor performance operation can be disabled by setting bit 38 of IA32_MISC_ENABLE. This
mechanism is intended for BIOS only. If IA32_MISC_ENABLE[38] is set, CPUID.06H:EAX[1] will return 0.

14.3.2.2

OS Control of Opportunistic Processor Performance Operation

There may be phases of software execution in which system software cannot tolerate the non-deterministic aspects
of opportunistic processor performance operation. For example, when calibrating a real-time workload to make a
CPU reservation request to the OS, it may be undesirable to allow the possibility of the processor delivering
increased performance that cannot be sustained after the calibration phase.
System software can temporarily disengage opportunistic processor performance operation by setting bit 32 of the
IA32_PERF_CTL MSR (0199H), using a read-modify-write sequence on the MSR. The opportunistic processor
performance operation can be re-engaged by clearing bit 32 in IA32_PERF_CTL MSR, using a read-modify-write
sequence. The DISENAGE bit in IA32_PERF_CTL is not reflected in bit 32 of the IA32_PERF_STATUS MSR (0198H),
and it is not shared between logical processors in a physical package. In order for OS to engage IDA/Turbo mode,
the BIOS must

•
•

enable opportunistic processor performance operation, as described in Section 14.3.2.1,
expose the operating points associated with IDA/Turbo mode to the OS.

33 32 31

63

16 15

0

Reserved
IDA/Turbo DISENGAGE
Enhanced Intel Speedstep Technology Transition Target

Figure 14-2. IA32_PERF_CTL Register

14.3.2.3

Required Changes to OS Power Management P-state Policy

Intel Dynamic Acceleration (IDA) and Intel Turbo Boost Technology can provide opportunistic performance greater
than the performance level corresponding to the Processor Base frequency of the processor (see CPUID’s processor
frequency information). System software can use a pair of MSRs to observe performance feedback. Software must
query for the presence of IA32_APERF and IA32_MPERF (see Section 14.2). The ratio between IA32_APERF and
IA32_MPERF is architecturally defined and a value greater than unity indicates performance increase occurred
during the observation period due to IDA. Without incorporating such performance feedback, the target P-state
evaluation algorithm can result in a non-optimal P-state target.
There are other scenarios under which OS power management may want to disable IDA, some of these are listed
below:

•

When engaging ACPI defined passive thermal management, it may be more effective to disable IDA for the
duration of passive thermal management.

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POWER AND THERMAL MANAGEMENT

•

When the user has indicated a policy preference of power savings over performance, OS power management
may want to disable IDA while that policy is in effect.

14.3.3

Intel Turbo Boost Technology

Intel Turbo Boost Technology is supported in Intel Core i7 processors and Intel Xeon processors based on Intel®
microarchitecture code name Nehalem. It uses the same principle of leveraging thermal headroom to dynamically
increase processor performance for single-threaded and multi-threaded/multi-tasking environment. The programming interface described in Section 14.3.2 also applies to Intel Turbo Boost Technology.

14.3.4

Performance and Energy Bias Hint support

Intel 64 processors may support additional software hint to guide the hardware heuristic of power management
features to favor increasing dynamic performance or conserve energy consumption.
Software can detect the processor's capability to support the performance-energy bias preference hint by examining bit 3 of ECX in CPUID leaf 6. The processor supports this capability if CPUID.06H:ECX.SETBH[bit 3] is set and
it also implies the presence of a new architectural MSR called IA32_ENERGY_PERF_BIAS (1B0H).
Software can program the lowest four bits of IA32_ENERGY_PERF_BIAS MSR with a value from 0 - 15. The values
represent a sliding scale, where a value of 0 (the default reset value) corresponds to a hint preference for highest
performance and a value of 15 corresponds to the maximum energy savings. A value of 7 roughly translates into a
hint to balance performance with energy consumption.

4 3

63

0

Reserved

Energy Policy Preference Hint

Figure 14-3. IA32_ENERGY_PERF_BIAS Register
The layout of IA32_ENERGY_PERF_BIAS is shown in Figure 14-3. The scope of IA32_ENERGY_PERF_BIAS is per
logical processor, which means that each of the logical processors in the package can be programmed with a
different value. This may be especially important in virtualization scenarios, where the performance / energy
requirements of one logical processor may differ from the other. Conflicting “hints” from various logical processors
at higher hierarchy level will be resolved in favor of performance over energy savings.
Software can use whatever criteria it sees fit to program the MSR with an appropriate value. However, the value
only serves as a hint to the hardware and the actual impact on performance and energy savings is model specific.

14.4

HARDWARE-CONTROLLED PERFORMANCE STATES (HWP)

Intel processors may contain support for Hardware-Controlled Performance States (HWP), which autonomously
selects performance states while utilizing OS supplied performance guidance hints. The Enhanced Intel SpeedStep® Technology provides a means for the OS to control and monitor discrete frequency-based operating points
via the IA32_PERF_CTL and IA32_PERF_STATUS MSRs.
In contrast, HWP is an implementation of the ACPI-defined Collaborative Processor Performance Control (CPPC),
which specifies that the platform enumerate a continuous, abstract unit-less, performance value scale that is not
tied to a specific performance state / frequency by definition. While the enumerated scale is roughly linear in terms
of a delivered integer workload performance result, the OS is required to characterize the performance value range
to comprehend the delivered performance for an applied workload.
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When HWP is enabled, the processor autonomously selects performance states as deemed appropriate for the
applied workload and with consideration of constraining hints that are programmed by the OS. These OS-provided
hints include minimum and maximum performance limits, preference towards energy efficiency or performance,
and the specification of a relevant workload history observation time window. The means for the OS to override
HWP's autonomous selection of performance state with a specific desired performance target is also provided,
however, the effective frequency delivered is subject to the result of energy efficiency and performance optimizations.

14.4.1

HWP Programming Interfaces

The programming interfaces provided by HWP include the following:

•

The CPUID instruction allows software to discover the presence of HWP support in an Intel processor. Specifically, execute CPUID instruction with EAX=06H as input will return 5 bit flags covering the following aspects in
bits 7 through 11 of CPUID.06H:EAX:
— Availability of HWP baseline resource and capability, CPUID.06H:EAX[bit 7]: If this bit is set, HWP provides
several new architectural MSRs: IA32_PM_ENABLE, IA32_HWP_CAPABILITIES, IA32_HWP_REQUEST,
IA32_HWP_STATUS.
— Availability of HWP Notification upon dynamic Guaranteed Performance change, CPUID.06H:EAX[bit 8]: If
this bit is set, HWP provides IA32_HWP_INTERRUPT MSR to enable interrupt generation due to dynamic
Performance changes and excursions.
— Availability of HWP Activity window control, CPUID.06H:EAX[bit 9]: If this bit is set, HWP allows software to
program activity window in the IA32_HWP_REQUEST MSR.
— Availability of HWP energy/performance preference control, CPUID.06H:EAX[bit 10]: If this bit is set, HWP
allows software to set an energy/performance preference hint in the IA32_HWP_REQUEST MSR.
— Availability of HWP package level control, CPUID.06H:EAX[bit 11]:If this bit is set, HWP provides the
IA32_HWP_REQUEST_PKG MSR to convey OS Power Management’s control hints for all logical processors
in the physical package.

Table 14-1. Architectural and Non-Architectural MSRs Related to HWP

•

Address

Archite
ctural

Register Name

Description

770H

Y

IA32_PM_ENABLE

771H

Y

IA32_HWP_CAPABILITIES

Enumerates the HWP performance range (static and dynamic).

772H

Y

IA32_HWP_REQUEST_PKG

Conveys OSPM's control hints (Min, Max, Activity Window, Energy
Performance Preference, Desired) for all logical processor in the physical
package.

773H

Y

IA32_HWP_INTERRUPT

774H

Y

IA32_HWP_REQUEST

777H

Y

IA32_HWP_STATUS

19CH

Y

IA32_THERM_STATUS[bits 15:12]

64EH

N

MSR_PPERF

Enable/Disable HWP.

Controls HWP native interrupt generation (Guaranteed Performance
changes, excursions).
Conveys OSPM's control hints (Min, Max, Activity Window, Energy
Performance Preference, Desired) for a single logical processor.
Status bits indicating changes to Guaranteed Performance and
excursions to Minimum Performance.
Conveys reasons for performance excursions
Productive Performance Count.

Additionally, HWP may provide a non-architectural MSR, MSR_PPERF, which provides a quantitative metric to
software of hardware’s view of workload scalability. This hardware’s view of workload scalability is implementation specific.

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14.4.2

Enabling HWP

The layout of the IA32_PM_ENABLE MSR is shown in Figure 14-4. The bit fields are described below:
63

1 0

Reserved
HWP_ENABLE

Reserved

Figure 14-4. IA32_PM_ENABLE MSR

•

HWP_ENABLE (bit 0, R/W1Once) — Software sets this bit to enable HWP with autonomous selection. When
set, the processor will disregard input from the legacy performance control interface (IA32_PERF_CTL). Note
this bit can only be enabled once from the default value. Once set, writes to the HWP_ENABLE bit are ignored.
Only RESET will clear this bit. Default = zero (0).

•

Bits 63:1 are reserved and must be zero.

After software queries CPUID and verifies the processor’s support of HWP, system software can write 1 to
IA32_PM_ENABLE.HWP_ENABLE (bit 0) to enable hardware controlled performance states. The default value of
IA32_PM_ENABLE MSR at power-on is 0, i.e. HWP is disabled.
Additional MSRs associated with HWP may only be accessed after HWP is enabled, with the exception of
IA32_HWP_INTERRUPT and MSR_PPERF. Accessing the IA32_HWP_INTERRUPT MSR requires only HWP is present
as enumerated by CPUID but does not require enabling HWP.
IA32_PM_ENABLE is a package level MSR, i.e. writing to it from any logical processor within a package affects all
logical processors within that package.

14.4.3

HWP Performance Range and Dynamic Capabilities

The OS reads the IA32_HWP_CAPABILITIES MSR to comprehend the limits of the HWP-managed performance
range as well as the dynamic capability, which may change during processor operation. The enumerated performance range values reported by IA32_HWP_CAPABILITIES directly map to initial frequency targets (prior to workload-specific frequency optimizations of HWP). However the mapping is processor family specific.
The layout of the IA32_HWP_CAPABILITIES MSR is shown in Figure 14-5. The bit fields are described below:

63

32 31

24 23

16 15

8

7

0

Reserved

Lowest_Performance
Most_Efficient_Performance
Guaranteed_Performance
Highest_Performance

Figure 14-5. IA32_HWP_CAPABILITIES Register

•
•

Highest_Performance (bits 7:0, RO) — Value for the maximum non-guaranteed performance level.

•

Most_Efficient_Performance (bits 23:16, RO) — Current value of the most efficient performance level.
This value can change dynamically as a result of workload characteristics.

Guaranteed_Performance (bits 15:8, RO) — Current value for the guaranteed performance level. This
value can change dynamically as a result of internal or external constraints, e.g. thermal or power limits.

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POWER AND THERMAL MANAGEMENT

•

Lowest_Performance (bits 31:24, RO) — Value for the lowest performance level that software can program
to IA32_HWP_REQUEST.

•

Bits 63:32 are reserved and must be zero.

The value returned in the Guaranteed_Performance field is hardware's best-effort approximation of the available performance given current operating constraints. Changes to the Guaranteed_Performance value will
primarily occur due to a shift in operational mode. This includes a power or other limit applied by an external agent,
e.g. RAPL (see Figure 14.9.1), or the setting of a Configurable TDP level (see model-specific controls related to
Programmable TDP Limit in Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 4.). Notification of a change to the Guaranteed_Performance occurs via
interrupt (if configured) and the IA32_HWP_Status MSR. Changes to Guaranteed_Performance are indicated when
a macroscopically meaningful change in performance occurs i.e. sustained for greater than one second. Consequently, notification of a change in Guaranteed Performance will typically occur no more frequently than once per
second. Rapid changes in platform configuration, e.g. docking / undocking, with corresponding changes to a
Configurable TDP level could potentially cause more frequent notifications.
The value returned by the Most_Efficient_Performance field provides the OS with an indication of the practical
lower limit for the IA32_HWP_REQUEST. The processor may not honor IA32_HWP_REQUEST.Maximum Performance settings below this value.

14.4.4

Managing HWP

Typically, the OS controls HWP operation for each logical processor via the writing of control hints / constraints to
the IA32_HWP_REQUEST MSR. The layout of the IA32_HWP_REQUEST MSR is shown in Figure 14-6. The bit fields
are described below:

63

43 42 41

32 31

24 23

16 15

8

7

0

Reserved
Package_Control
Activity_Window
Energy_Performance_Preference
Desired_Performance
Maximum_Performance
Minimum_Performance

Figure 14-6. IA32_HWP_REQUEST Register

•

Minimum_Performance (bits 7:0, RW) — Conveys a hint to the HWP hardware. The OS programs the
minimum performance hint to achieve the required quality of service (QOS) or to meet a service level
agreement (SLA) as needed. Note that an excursion below the level specified is possible due to hardware
constraints. The default value of this field is IA32_HWP_CAPABILITIES.Lowest_Performance.

•

Maximum_Performance (bits 15:8, RW) — Conveys a hint to the HWP hardware. The OS programs this
field to limit the maximum performance that is expected to be supplied by the HWP hardware. Excursions above
the limit requested by OS are possible due to hardware coordination between the processor cores and other
components in the package. The default value of this field is IA32_HWP_CAPABILITIES.Highest_Performance.

•

Desired_Performance (bits 23:16, RW) — Conveys a hint to the HWP hardware. When set to zero,
hardware autonomous selection determines the performance target. When set to a non-zero value (between
the range of Lowest_Performance and Highest_Performance of IA32_HWP_CAPABILITIES) conveys an explicit
performance request hint to the hardware; effectively disabling HW Autonomous selection. The
Desired_Performance input is non-constraining in terms of Performance and Energy Efficiency optimizations,
which are independently controlled. The default value of this field is 0.

•

Energy_Performance_Preference (bits 31:24, RW) — Conveys a hint to the HWP hardware. The OS may
write a range of values from 0 (performance preference) to 0FFH (energy efficiency preference) to influence the
rate of performance increase /decrease and the result of the hardware's energy efficiency and performance

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optimizations. The default value of this field is 80H. Note: If CPUID.06H:EAX[bit 10] indicates that this field is
not supported, HWP uses the value of the IA32_ENERGY_PERF_BIAS MSR to determine the energy efficiency /
performance preference.

•

Activity_Window (bits 41:32, RW) — Conveys a hint to the HWP hardware specifying a moving workload
history observation window for performance/frequency optimizations. If 0, the hardware will determine the
appropriate window size. When writing a non-zero value to this field, this field is encoded in the format of bits
38:32 as a 7-bit mantissa and bits 41:39 as a 3-bit exponent value in powers of 10. The resultant value is in
microseconds. Thus, the minimal/maximum activity window size is 1 microsecond/1270 seconds. Combined
with the Energy_Performance_Preference input, Activity_Window influences the rate of performance increase
/ decrease. This non-zero hint only has meaning when Desired_Performance = 0. The default value of this field
is 0.

•

Package_Control (bit 42, RW) — When set causes this logical processor's IA32_HWP_REQUEST control
inputs to be derived from IA32_HWP_REQUEST_PKG

•

Bits 63:43 are reserved and must be zero.

The HWP hardware clips and resolves the field values as necessary to the valid range. Reads return the last value
written not the clipped values.
Processors may support a subset of IA32_HWP_REQUEST fields as indicated by CPUID. Reads of non-supported
fields will return 0. Writes to non-supported fields are ignored.
The OS may override HWP's autonomous selection of performance state with a specific performance target by
setting the Desired_Performance field to a non zero value, however, the effective frequency delivered is subject to
the result of energy efficiency and performance optimizations, which are influenced by the Energy Performance
Preference field.
Software may disable all hardware optimizations by setting Minimum_Performance = Maximum_Performance
(subject to package coordination).
Note: The processor may run below the Minimum_Performance level due to hardware constraints including: power,
thermal, and package coordination constraints. The processor may also run below the Minimum_Performance level
for short durations (few milliseconds) following C-state exit, and when Hardware Duty Cycling (see Section 14.5)
is enabled.

63

42 41

32 31

24 23

16 15

8

7

0

Reserved

Activity_Window
Energy_Performance_Preference
Desired_Performance
Maximum_Performance
Minimum_Performance

Figure 14-7. IA32_HWP_REQUEST_PKG Register
The structure of the IA32_HWP_REQUEST_PKG MSR (package-level) is identical to the IA32_HWP_REQUEST MSR
with the exception of the Package Control field, which does not exist. Field values written to this MSR apply to all
logical processors within the physical package with the exception of logical processors whose
IA32_HWP_REQUEST.Package Control field is clear (zero). Single P-state Control mode is only supported when
IA32_HWP_REQUEST_PKG is not supported.

14.4.5

HWP Feedback

The processor provides several types of feedback to the OS during HWP operation.

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The IA32_MPERF MSR and IA32_APERF MSR mechanism (see Section 14.2) allows the OS to calculate the resultant
effective frequency delivered over a time period. Energy efficiency and performance optimizations directly impact
the resultant effective frequency delivered.
The layout of the IA32_HWP_STATUS MSR is shown in Figure 14-8. It provides feedback regarding changes to
IA32_HWP_CAPABILITIES.Guaranteed_Performance and excursions to
IA32_HWP_CAPABILITIES.Minimum_Performance. The bit fields are described below:

•

Guaranteed_Performance_Change (bit 0, RWC0) — If set (1), a change to Guaranteed_Performance has
occurred. Software should query IA32_HWP_CAPABILITIES.Guaranteed_Performance value to ascertain the
new Guaranteed Performance value and to assess whether to re-adjust HWP hints via IA32_HWP_REQUEST.
Software must clear this bit by writing a zero (0).

•

Excursion_To_Minimum (bit 2, RWC0) — If set (1), an excursion to Minimum_Performance of
IA32_HWP_REQUEST has occurred. Software must clear this bit by writing a zero (0).

•

Bits 63:3, and bit 1 are reserved and must be zero.
63

3 2 1 0

Reserved
Excursion_To_Minimum
Reserved
Guaranteed_Performance_Change

Figure 14-8. IA32_HWP_STATUS MSR
The status bits of IA32_HWP_STATUS must be cleared (0) by software so that a new status condition change will
cause the hardware to set the bit again and issue the notification. Status bits are not set for “normal” excursions
e.g. running below Minimum Performance for short durations during C-state exit. Changes to
Guaranteed_Performance and excursions to Minimum_Performance will occur no more than once per second.
The OS can determine the specific reasons for a Guaranteed_Performance change or an excursion to
Minimum_Performance in IA32_HWP_REQUEST by examining the associated status and log bits reported in the
IA32_THERM_STATUS MSR. The layout of the IA32_HWP_STATUS MSR that HWP uses to support software query of
HWP feedback is shown in Figure 14-9. The bit fields of IA32_THERM_STATUS associated with HWP feedback are
described below (Bit fields of IA32_THERM_STATUS unrelated to HWP can be found in Section 14.7.5.2).

63

32 31

27

23 22

16 15 14 13 12 11 10 9 8 7

6 5

4

3

2

Reserved
Reading Valid
Resolution in Deg. Celsius
Digital Readout
Cross-domain Limit Log
Cross-domain Limit Status
Current Limit Log
Current Limit Status
Power Limit Notification Log
Power Limit Notification Status
Thermal Threshold #2 Log
Thermal Threshold #2 Status
Thermal Threshold #1 Log
Thermal Threshold #1 Status
Critical Temperature Log
Critical Temperature Status
PROCHOT# or FORCEPR# Log
PROCHOT# or FORCEPR# Event
Thermal Status Log
Thermal Status

Figure 14-9. IA32_THERM_STATUS Register With HWP Feedback

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POWER AND THERMAL MANAGEMENT

•
•

Bits 11:0, See Section 14.7.5.2.

•

Current Limit Log (bit 13, RWC0) — If set (1), an electrical current limit has been exceeded that has
adversely impacted energy efficiency optimizations since the last clearing of this bit or a reset. This bit is sticky,
software may clear this bit by writing a zero (0).

•

Cross-domain Limit Status (bit 14, RO) — If set (1), indicates another hardware domain (e.g. processor
graphics) is currently limiting energy efficiency optimizations in the processor core domain.

•

Cross-domain Limit Log (bit 15, RWC0) — If set (1), indicates another hardware domain (e.g. processor
graphics) has limited energy efficiency optimizations in the processor core domain since the last clearing of this
bit or a reset. This bit is sticky, software may clear this bit by writing a zero (0).

•

Bits 63:16, See Section 14.7.5.2.

Current Limit Status (bit 12, RO) — If set (1), indicates an electrical current limit (e.g. Electrical Design
Point/IccMax) is being exceeded and is adversely impacting energy efficiency optimizations.

14.4.5.1

Non-Architectural HWP Feedback

The Productive Performance (MSR_PPERF) MSR (non-architectural) provides hardware's view of workload scalability, which is a rough assessment of the relationship between frequency and workload performance, to software.
The layout of the MSR_PPERF is shown in Figure 14-10.
63

0

PCNT - Productive Performance Count

Figure 14-10. MSR_PPERF MSR

•

PCNT (bits 63:0, RO) — Similar to IA32_APERF but only counts cycles perceived by hardware as contributing
to instruction execution (e.g. unhalted and unstalled cycles). This counter increments at the same rate as
IA32_APERF, where the ratio of (ΔPCNT/ΔACNT) is an indicator of workload scalability (0% to 100%). Note that
values in this register are valid even when HWP is not enabled.

14.4.6

HWP Notifications

Processors may support interrupt-based notification of changes to HWP status as indicated by CPUID. If supported,
the IA32_HWP_INTERRUPT MSR is used to enable interrupt-based notifications. Notification events, when enabled,
are delivered using the existing thermal LVT entry. The layout of the IA32_HWP_INTERRUPT is shown in
Figure 14-11. The bit fields are described below:

63

2 1 0

Reserved
EN_Excursion_Minimum
EN_Guaranteed_Performance_Change

Figure 14-11. IA32_HWP_INTERRUPT MSR

•

EN_Guaranteed_Performance_Change (bit 0, RW) — When set (1), an HWP Interrupt will be generated
whenever a change to the IA32_HWP_CAPABILITIES.Guaranteed_Performance occurs. The default value is 0
(Interrupt generation is disabled).

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POWER AND THERMAL MANAGEMENT

•

EN_Excursion_Minimum (bit 1, RW) — When set (1), an HWP Interrupt will be generated whenever the
HWP hardware is unable to meet the IA32_HWP_REQUEST.Minimum_Performance setting. The default value is
0 (Interrupt generation is disabled).

•

Bits 63:2, and bit 1 are reserved and must be zero.

14.4.7

Recommendations for OS use of HWP Controls

Common Cases of Using HWP
The default HWP control field values are expected to be suitable for many applications. The OS can enable autonomous HWP for these common cases by

•

Setting IA32_HWP_REQUEST.Desired Performance = 0 (hardware autonomous selection determines the
performance target). Set IA32_HWP_REQUEST.Activity Window = 0 (enable HW dynamic selection of window
size).

To maximize HWP benefit for the common cases, the OS should set

•
•

IA32_HWP_REQUEST.Minimum_Performance = IA32_HWP_CAPABILITIES.Lowest_Performance and
IA32_HWP_REQUEST.Maximum_Performance = IA32_HWP_CAPABILITIES.Highest_Performance.

Setting IA32_HWP_REQUEST.Minimum_Performance = IA32_HWP_REQUEST.Maximum_Performance is functionally equivalent to using of the IA32_PERF_CTL interface and is therefore not recommended (bypassing HWP).

Calibrating HWP for Application-Specific HWP Optimization
In some applications, the OS may have Quality of Service requirements that may not be met by the default values.
The OS can characterize HWP by:

•

keeping IA32_HWP_REQUEST.Minimum_Performance = IA32_HWP_REQUEST.Maximum_Performance to
prevent non-linearity in the characterization process,

•

utilizing the range values enumerated from the IA32_HWP_CAPABILITIES MSR to program
IA32_HWP_REQUEST while executing workloads of interest and observing the power and performance result.

The power and performance result of characterization is also influenced by the IA32_HWP_REQUEST.Energy
Performance Preference field, which must also be characterized.
Characterization can be used to set IA32_HWP_REQUEST.Minimum_Performance to achieve the required QOS in
terms of performance. If IA32_HWP_REQUEST.Minimum_Performance is set higher than
IA32_HWP_CAPABILITIES.Guaranteed Performance then notification of excursions to Minimum Performance may
be continuous.
If autonomous selection does not deliver the required workload performance, the OS should assess the current
delivered effective frequency and for the duration of the specific performance requirement set
IA32_HWP_REQUEST.Desired_Performance ≠ 0 and adjust IA32_HWP_REQUEST.Energy_Performance_Preference
as necessary to achieve the required workload performance. The MSR_PPERF.PCNT value can be used to better
comprehend the potential performance result from adjustments to IA32_HWP_REQUEST.Desired_Performance.
The OS should set IA32_HWP_REQUEST.Desired_Performance = 0 to re-enable autonomous selection.

Tuning for Maximum Performance or Lowest Power Consumption
Maximum performance will be delivered by setting IA32_HWP_REQUEST.Minimum_Performance =
IA32_HWP_REQUEST.Maximum_Performance = IA32_HWP_CAPABILITIES.Highest_Performance and setting
IA32_HWP_REQUEST.Energy_Performance_Preference = 0 (performance preference).
Lowest power will be achieved by setting IA32_HWP_REQUEST.Minimum_Performance =
IA32_HWP_REQUEST.Maximum_Performance = IA32_HWP_CAPABILITIES.Lowest_Performance and setting
IA32_HWP_REQUEST.Energy_Performance_Preference = 0FFH (energy efficiency preference).

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Additional Guidelines
Set IA32_HWP_REQUEST.Energy_Performance_Preference as appropriate for the platform's current mode of operation. For example, a mobile platforms' setting may be towards performance preference when on AC power and
more towards energy efficiency when on DC power.
The use of the Running Average Power Limit (RAPL) processor capability (see section 14.7.1) is highly recommended when HWP is enabled. Use of IA32_HWP_Request.Maximum_Performance for thermal control is subject to
limitations and can adversely impact the performance of other processor components e.g. Graphics
If default values deliver undesirable performance latency in response to events, the OS should set
IA32_HWP_REQUEST. Activity_Window to a low (non zero) value and
IA32_HWP_REQUEST.Energy_Performance_Preference towards performance (0) for the event duration.
Similarly, for “real-time” threads, set IA32_HWP_REQUEST.Energy_Performance_Preference towards performance
(0) and IA32_HWP_REQUEST. Activity_Window to a low value, e.g. 01H, for the duration of their execution.
When executing low priority work that may otherwise cause the hardware to deliver high performance, set
IA32_HWP_REQUEST. Activity_Window to a longer value and reduce the
IA32_HWP_Request.Maximum_Performance value as appropriate to control energy efficiency. Adjustments to
IA32_HWP_REQUEST.Energy_Performance_Preference may also be necessary.

14.5

HARDWARE DUTY CYCLING (HDC)

Intel processors may contain support for Hardware Duty Cycling (HDC), which enables the processor to autonomously force its components inside the physical package into idle state. For example, the processor may selectively
force only the processor cores into an idle state.
HDC is disabled by default on processors that support it. System software can dynamically enable or disable HDC
to force one or more components into an idle state or wake up those components previously forced into an idle
state. Forced Idling (and waking up) of multiple components in a physical package can be done with one WRMSR
to a packaged-scope MSR from any logical processor within the same package.
HDC does not delay events such as timer expiration, but it may affect the latency of short (less than 1 msec) software threads, e.g. if a thread is forced to idle state just before completion and entering a “natural idle”.
HDC forced idle operation can be thought of as operating at a lower effective frequency. The effective average
frequency computed by software will include the impact of HDC forced idle.
The primary use of HDC is enable system software to manage low active workloads to increase the package level
C6 residency. Additionally, HDC can lower the effective average frequency in case or power or thermal limitation.
When HDC forces a logical processor, a processor core or a physical package to enter an idle state, its C-State is set
to C3 or deeper. The deep “C-states” referred to in this section are processor-specific C-states.

14.5.1

Hardware Duty Cycling Programming Interfaces

The programming interfaces provided by HDC include the following:

•

The CPUID instruction allows software to discover the presence of HDC support in an Intel processor. Specifically, execute CPUID instruction with EAX=06H as input, bit 13 of EAX indicates the processor’s support of the
following aspects of HDC.
— Availability of HDC baseline resource, CPUID.06H:EAX[bit 13]: If this bit is set, HDC provides the following
architectural MSRs: IA32_PKG_HDC_CTL, IA32_PM_CTL1, and the IA32_THREAD_STALL MSRs.

•

Additionally, HDC may provide several non-architectural MSR.

Table 14-2. Architectural and non-Architecture MSRs Related to HDC
Address

Architec
tural

Register Name

Description

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POWER AND THERMAL MANAGEMENT

Table 14-2. Architectural and non-Architecture MSRs Related to HDC
DB0H

Y

IA32_PKG_HDC_CTL

DB1H

Y

IA32_PM_CTL1

Package Enable/Disable HDC.
Per-logical-processor select control to allow/block HDC forced idling.

DB2H

Y

IA32_THREAD_STALL

653H

N

MSR_CORE_HDC_RESIDENCY

Accumulate stalled cycles on this logical processor due to HDC forced idling.
Core level stalled cycle counter due to HDC forced idling on one or more
logical processor.

655H

N

MSR_PKG_HDC_SHALLOW_RE
SIDENCY

Accumulate the cycles the package was in C21 state and at least one logical
processor was in forced idle

656H

N

MSR_PKG_HDC_DEEP_RESIDE
NCY

Accumulate the cycles the package was in the software specified Cx1 state
and at least one logical processor was in forced idle. Cx is specified in
MSR_PKG_HDC_CONFIG_CTL.

652H

N

MSR_PKG_HDC_CONFIG_CTL

HDC configuration controls

NOTES:
1. The package “C-states” referred to in this section are processor-specific C-states.

14.5.2

Package level Enabling HDC

The layout of the IA32_PKG_HDC_CTL MSR is shown in Figure 14-12. IA32_PKG_HDC_CTL is a writable MSR from
any logical processor in a package. The bit fields are described below:
63

1 0

Reserved
Reserved

HDC_PKG_Enable

Figure 14-12. IA32_PKG_HDC_CTL MSR

•

HDC_PKG_Enable (bit 0, R/W) — Software sets this bit to enable HDC operation by allowing the processor
to force to idle all “HDC-allowed” (see Figure 14.5.3) logical processors in the package. Clearing this bit
disables HDC operation in the package by waking up all the processor cores that were forced into idle by a
previous ‘0’-to-’1’ transition in IA32_PKG_HDC_CTL.HDC_PKG_Enable. This bit is writable only if
CPUID.06H:EAX[bit 13] = 1. Default = zero (0).

•

Bits 63:1 are reserved and must be zero.

After processor support is determined via CPUID, system software can enable HDC operation by setting
IA32_PKG_HDC_CTL.HDC_PKG_Enable to 1. At reset, IA32_PKG_HDC_CTL.HDC_PKG_Enable is cleared to 0. A
'0'-to-'1' transition in HDC_PKG_Enable allows the processor to force to idle all HDC-allowed (indicated by the nonzero state of IA32_PM_CTL1[bit 0]) logical processors in the package. A ‘1’-to-’0’ transition wakes up those HDC
force-idled logical processors.
Software can enable or disable HDC using this package level control multiple times from any logical processor in the
package. Note the latency of writing a value to the package-visible IA32_PKG_HDC_CTL.HDC_PKG_Enable is
longer than the latency of a WRMSR operation to a Logical Processor MSR (as opposed to package level MSR) such
as: IA32_PM_CTL1 (described in Section 14.5.3). Propagation of the change in
IA32_PKG_HDC_CTL.HDC_PKG_Enable and reaching all HDC idled logical processor to be woken up may take on
the order of core C6 exit latency.

14.5.3

Logical-Processor Level HDC Control

The layout of the IA32_PM_CTL1 MSR is shown in Figure 14-13. Each logical processor in a package has its own
IA32_PM_CTL1 MSR. The bit fields are described below:

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POWER AND THERMAL MANAGEMENT

63

1 0

Reserved
HDC_Allow_Block

Reserved

Figure 14-13. IA32_PM_CTL1 MSR

•

HDC_Allow_Block (bit 0, R/W) — Software sets this bit to allow this logical processors to honor the
package-level IA32_PKG_HDC_CTL.HDC_PKG_Enable control. Clearing this bit prevents this logical processor
from using the HDC. This bit is writable only if CPUID.06H:EAX[bit 13] = 1. Default = one (1).

•

Bits 63:1 are reserved and must be zero.

Fine-grain OS control of HDC operation at the granularity of per-logical-processor is provided by IA32_PM_CTL1.
At RESET, all logical processors are allowed to participate in HDC operation such that OS can manage HDC using
the package-level IA32_PKG_HDC_CTL.
Writes to IA32_PM_CTL1 complete with the latency that is typical to WRMSR to a Logical Processor level MSR.
When the OS chooses to manage HDC operation at per-logical-processor granularity, it can write to IA32_PM_CTL1
on one or more logical processors as desired. Each write to IA32_PM_CTL1 must be done by code that executes on
the logical processor targeted to be allowed into or blocked from HDC operation.
Blocking one logical processor for HDC operation may have package level impact. For example, the processor may
decide to stop duty cycling of all other Logical Processors as well.
The propagation of IA32_PKG_HDC_CTL.HDC_PKG_Enable in a package takes longer than a WRMSR to
IA32_PM_CTL1. The last completed write to IA32_PM_CTL1 on a logical processor will be honored when a ‘0’-to-’1’
transition of IA32_PKG_HDC_CTL.HDC_PKG_Enable arrives to a logical processor.

14.5.4

HDC Residency Counters

There is a collection of counters available for software to track various residency metrics related to HDC operation.
In general, HDC residency time is defined as the time in HDC forced idle state at the granularity of per-logicalprocessor, per-core, or package. At the granularity of per-core/package-level HDC residency, at least one of the
logical processor in a core/package must be in the HDC forced idle state.

14.5.4.1

IA32_THREAD_STALL

Software can track per-logical-processor HDC residency using the architectural MSR IA32_THREAD_STALL.The
layout of the IA32_THREAD_STALL MSR is shown in Figure 14-14. Each logical processor in a package has its own
IA32_THREAD_STALL MSR. The bit fields are described below:
63

0

Stall_cycle_cnt

Figure 14-14. IA32_THREAD_STALL MSR

•

Stall_Cycle_Cnt (bits 63:0, R/O) — Stores accumulated HDC forced-idle cycle count of this processor core
since last RESET. This counter increments at the same rate of the TSC. The count is updated only after the
logical processor exits from the forced idled C-state. At each update, the number of cycles that the logical
processor was stalled due to forced-idle will be added to the counter. This counter is available only if
CPUID.06H:EAX[bit 13] = 1. Default = zero (0).
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POWER AND THERMAL MANAGEMENT

A value of zero in IA32_THREAD_STALL indicates either HDC is not supported or the logical processor never
serviced any forced HDC idle. A non-zero value in IA32_THREAD_STALL indicates the HDC forced-idle residency
times of the logical processor. It also indicates the forced-idle cycles due to HDC that could appear as C0 time to
traditional OS accounting mechanisms (e.g. time-stamping OS idle/exit events).
Software can read IA32_THREAD_STALL irrespective of the state of IA32_PKG_HDC_CTL and IA32_PM_CTL1, as
long as CPUID.06H:EAX[bit 13] = 1.

14.5.4.2

Non-Architectural HDC Residency Counters

Processors that support HDC operation may provide the following model-specific HDC residency counters.

MSR_CORE_HDC_RESIDENCY
Software can track per-core HDC residency using the counter MSR_CORE_HDC_RESIDENCY. This counter increments when the core is in C3 state or deeper (all logical processors in this core are idle due to either HDC or other
mechanisms) and at least one of the logical processors is in HDC forced idle state. The layout of the
MSR_CORE_HDC_RESIDENCY is shown in Figure 14-15. Each processor core in a package has its own
MSR_CORE_HDC_RESIDENCY MSR. The bit fields are described below:
63

0

Core_Cx_duty_cycle_cnt

Figure 14-15. MSR_CORE_HDC_RESIDENCY MSR

•

Core_Cx_Duty_Cycle_Cnt (bits 63:0, R/O) — Stores accumulated HDC forced-idle cycle count of this
processor core since last RESET. This counter increments at the same rate of the TSC. The count is updated only
after core C-state exit from a forced idled C-state. At each update, the increment counts cycles when the core
is in a Cx state (all its logical processor are idle) and at least one logical processor in this core was forced into
idle state due to HDC. If CPUID.06H:EAX[bit 13] = 0, attempt to access this MSR will cause a #GP fault. Default
= zero (0).

A value of zero in MSR_CORE_HDC_RESIDENCY indicates either HDC is not supported or this processor core never
serviced any forced HDC idle.

MSR_PKG_HDC_SHALLOW_RESIDENCY
The counter MSR_PKG_HDC_SHALLOW_RESIDENCY allows software to track HDC residency time when the
package is in C2 state, all processor cores in the package are not active and at least one logical processor was
forced into idle state due to HDC. The layout of the MSR_PKG_HDC_SHALLOW_RESIDENCY is shown in
Figure 14-16. There is one MSR_PKG_HDC_SHALLOW_RESIDENCY per package. The bit fields are described
below:
63

0

Pkg_Duty_cycle_cnt

Figure 14-16. MSR_PKG_HDC_SHALLOW_RESIDENCY MSR

•

Pkg_Duty_Cycle_Cnt (bits 63:0, R/O) — Stores accumulated HDC forced-idle cycle count of this processor
core since last RESET. This counter increments at the same rate of the TSC. Package shallow residency may be
implementation specific. In the initial implementation, the threshold is package C2-state. The count is
updated only after package C2-state exit from a forced idled C-state. At each update, the increment counts

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POWER AND THERMAL MANAGEMENT

cycles when the package is in C2 state and at least one processor core in this package was forced into idle state
due to HDC. If CPUID.06H:EAX[bit 13] = 0, attempt to access this MSR may cause a #GP fault. Default = zero
(0).
A value of zero in MSR_PKG_HDC_SHALLOW_RESIDENCY indicates either HDC is not supported or this processor
package never serviced any forced HDC idle.

MSR_PKG_HDC_DEEP_RESIDENCY
The counter MSR_PKG_HDC_DEEP_RESIDENCY allows software to track HDC residency time when the package is
in a software-specified package Cx state, all processor cores in the package are not active and at least one logical
processor was forced into idle state due to HDC. Selection of a specific package Cx state can be configured using
MSR_PKG_HDC_CONFIG. The layout of the MSR_PKG_HDC_DEEP_RESIDENCY is shown in Figure 14-17. There is
one MSR_PKG_HDC_DEEP_RESIDENCY per package. The bit fields are described below:
63

0

Pkg_Cx_duty_cycle_cnt

Figure 14-17. MSR_PKG_HDC_DEEP_RESIDENCY MSR

•

Pkg_Cx_Duty_Cycle_Cnt (bits 63:0, R/O) — Stores accumulated HDC forced-idle cycle count of this
processor core since last RESET. This counter increments at the same rate of the TSC. The count is updated
only after package C-state exit from a forced idle state. At each update, the increment counts cycles when the
package is in the software-configured Cx state and at least one processor core in this package was forced into
idle state due to HDC. If CPUID.06H:EAX[bit 13] = 0, attempt to access this MSR may cause a #GP fault.
Default = zero (0).

A value of zero in MSR_PKG_HDC_SHALLOW_RESIDENCY indicates either HDC is not supported or this processor
package never serviced any forced HDC idle.

MSR_PKG_HDC_CONFIG
MSR_PKG_HDC_CONFIG allows software to configure the package Cx state that the counter
MSR_PKG_HDC_DEEP_RESIDENCY monitors. The layout of the MSR_PKG_HDC_CONFIG is shown in Figure 14-18.
There is one MSR_PKG_HDC_CONFIG per package. The bit fields are described below:

2

63

0

Reserved

Reserved

HDC_Cx_Monitor

Figure 14-18. MSR_PKG_HDC_CONFIG MSR

•

Pkg_Cx_Monitor (bits 2:0, R/W) — Selects which package C-state the MSR_HDC_DEEP_RESIDENCY
counter will monitor. The encoding of the HDC_Cx_Monitor field are: 0: no-counting; 1: count package C2 only,
2: count package C3 and deeper; 3: count package C6 and deeper; 4: count package C7 and deeper; other
encodings are reserved. If CPUID.06H:EAX[bit 13] = 0, attempt to access this MSR may cause a #GP fault.
Default = zero (0).

•

Bits 63:3 are reserved and must be zero.

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POWER AND THERMAL MANAGEMENT

14.5.5

MPERF and APERF Counters Under HDC

HDC operation can be thought of as an average effective frequency drop due to all or some of the Logical Processors enter an idle state period.
1600 MHz: 25% Utilization /75% Forced Idle

Effective Frequency @ 100% Utilization: 400 MHz

Figure 14-19. Example of Effective Frequency Reduction and Forced Idle Period of HDC
By default, the IA32_MPERF counter counts during forced idle periods as if the logical processor was active. The
IA32_APERF counter does not count during forced idle state. This counting convention allows the OS to compute
the average effective frequency of the Logical Processor between the last MWAIT exit and the next MWAIT entry
(OS visible C0) by ΔACNT/ΔMCNT * TSC Frequency.

14.6

MWAIT EXTENSIONS FOR ADVANCED POWER MANAGEMENT

IA-32 processors may support a number of C-states1 that reduce power consumption for inactive states. Intel Core
Solo and Intel Core Duo processors support both deeper C-state and MWAIT extensions that can be used by OS to
implement power management policy.
Software should use CPUID to discover if a target processor supports the enumeration of MWAIT extensions. If
CPUID.05H.ECX[Bit 0] = 1, the target processor supports MWAIT extensions and their enumeration (see Chapter
4, “Instruction Set Reference, M-U,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
2B).
If CPUID.05H.ECX[Bit 1] = 1, the target processor supports using interrupts as break-events for MWAIT, even
when interrupts are disabled. Use this feature to measure C-state residency as follows:

•

Software can write to bit 0 in the MWAIT Extensions register (ECX) when issuing an MWAIT to enter into a
processor-specific C-state or sub C-state.

•

When a processor comes out of an inactive C-state or sub C-state, software can read a timestamp before an
interrupt service routine (ISR) is potentially executed.

CPUID.05H.EDX allows software to enumerate processor-specific C-states and sub C-states available for use with
MWAIT extensions. IA-32 processors may support more than one C-state of a given C-state type. These are called
sub C-states. Numerically higher C-state have higher power savings and latency (upon entering and exiting) than
lower-numbered C-state.
At CPL = 0, system software can specify desired C-state and sub C-state by using the MWAIT hints register (EAX).
Processors will not go to C-state and sub C-state deeper than what is specified by the hint register. If CPL > 0 and
if MONITOR/MWAIT is supported at CPL > 0, the processor will only enter C1-state (regardless of the C-state
request in the hints register).
Executing MWAIT generates an exception on processors operating at a privilege level where MONITOR/MWAIT are
not supported.

1. The processor-specific C-states defined in MWAIT extensions can map to ACPI defined C-state types (C0, C1, C2, C3). The mapping
relationship depends on the definition of a C-state by processor implementation and is exposed to OSPM by the BIOS using the ACPI
defined _CST table.
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POWER AND THERMAL MANAGEMENT

NOTE
If MWAIT is used to enter a C-state (including sub C-state) that is numerically higher than C1, a
store to the address range armed by MONITOR instruction will cause the processor to exit MWAIT if
the store was originated by other processor agents. A store from non-processor agent may not
cause the processor to exit MWAIT.

14.7

THERMAL MONITORING AND PROTECTION

The IA-32 architecture provides the following mechanisms for monitoring temperature and controlling thermal
power:
1. The catastrophic shutdown detector forces processor execution to stop if the processor’s core temperature
rises above a preset limit.
2. Automatic and adaptive thermal monitoring mechanisms force the processor to reduce it’s power
consumption in order to operate within predetermined temperature limits.
3. The software controlled clock modulation mechanism permits operating systems to implement power
management policies that reduce power consumption; this is in addition to the reduction offered by automatic
thermal monitoring mechanisms.
4. On-die digital thermal sensor and interrupt mechanisms permit the OS to manage thermal conditions
natively without relying on BIOS or other system board components.
The first mechanism is not visible to software. The other three mechanisms are visible to software using processor
feature information returned by executing CPUID with EAX = 1.
The second mechanism includes:

•

Automatic thermal monitoring provides two modes of operation. One mode modulates the clock duty cycle;
the second mode changes the processor’s frequency. Both modes are used to control the core temperature of
the processor.

•

Adaptive thermal monitoring can provide flexible thermal management on processors made of multiple
cores.

The third mechanism modulates the clock duty cycle of the processor. As shown in Figure 14-20, the phrase ‘duty
cycle’ does not refer to the actual duty cycle of the clock signal. Instead it refers to the time period during which
the clock signal is allowed to drive the processor chip. By using the stop clock mechanism to control how often the
processor is clocked, processor power consumption can be modulated.
Clock Applied to Processor

Stop-Clock Duty Cycle

25% Duty Cycle (example only)

Figure 14-20. Processor Modulation Through Stop-Clock Mechanism
For previous automatic thermal monitoring mechanisms, software controlled mechanisms that changed processor
operating parameters to impact changes in thermal conditions. Software did not have native access to the native
thermal condition of the processor; nor could software alter the trigger condition that initiated software program
control.
The fourth mechanism (listed above) provides access to an on-die digital thermal sensor using a model-specific
register and uses an interrupt mechanism to alert software to initiate digital thermal monitoring.

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14.7.1

Catastrophic Shutdown Detector

P6 family processors introduced a thermal sensor that acts as a catastrophic shutdown detector. This catastrophic
shutdown detector was also implemented in Pentium 4, Intel Xeon and Pentium M processors. It is always enabled.
When processor core temperature reaches a factory preset level, the sensor trips and processor execution is halted
until after the next reset cycle.

14.7.2

Thermal Monitor

Pentium 4, Intel Xeon and Pentium M processors introduced a second temperature sensor that is factory-calibrated
to trip when the processor’s core temperature crosses a level corresponding to the recommended thermal design
envelop. The trip-temperature of the second sensor is calibrated below the temperature assigned to the catastrophic shutdown detector.

14.7.2.1

Thermal Monitor 1

The Pentium 4 processor uses the second temperature sensor in conjunction with a mechanism called Thermal
Monitor 1 (TM1) to control the core temperature of the processor. TM1 controls the processor’s temperature by
modulating the duty cycle of the processor clock. Modulation of duty cycles is processor model specific. Note that
the processors STPCLK# pin is not used here; the stop-clock circuitry is controlled internally.
Support for TM1 is indicated by CPUID.1:EDX.TM[bit 29] = 1.
TM1 is enabled by setting the thermal-monitor enable flag (bit 3) in IA32_MISC_ENABLE [see Chapter 2, “ModelSpecific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4].
Following a power-up or reset, the flag is cleared, disabling TM1. BIOS is required to enable only one automatic
thermal monitoring modes. Operating systems and applications must not disable the operation of these mechanisms.

14.7.2.2

Thermal Monitor 2

An additional automatic thermal protection mechanism, called Thermal Monitor 2 (TM2), was introduced in the
Intel Pentium M processor and also incorporated in newer models of the Pentium 4 processor family. Intel Core Duo
and Solo processors, and Intel Core 2 Duo processor family all support TM1 and TM2. TM2 controls the core
temperature of the processor by reducing the operating frequency and voltage of the processor and offers a higher
performance level for a given level of power reduction than TM1.
TM2 is triggered by the same temperature sensor as TM1. The mechanism to enable TM2 may be implemented
differently across various IA-32 processor families with different CPUID signatures in the family encoding value, but
will be uniform within an IA-32 processor family.
Support for TM2 is indicated by CPUID.1:ECX.TM2[bit 8] = 1.

14.7.2.3

Two Methods for Enabling TM2

On processors with CPUID family/model/stepping signature encoded as 0x69n or 0x6Dn (early Pentium M processors), TM2 is enabled if the TM_SELECT flag (bit 16) of the MSR_THERM2_CTL register is set to 1 (Figure 14-21)
and bit 3 of the IA32_MISC_ENABLE register is set to 1.
Following a power-up or reset, the TM_SELECT flag may be cleared. BIOS is required to enable either TM1 or TM2.
Operating systems and applications must not disable mechanisms that enable TM1 or TM2. If bit 3 of the
IA32_MISC_ENABLE register is set and TM_SELECT flag of the MSR_THERM2_CTL register is cleared, TM1 is
enabled.

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POWER AND THERMAL MANAGEMENT

31

0

16
Reserved

Reserved
TM_SELECT

Figure 14-21. MSR_THERM2_CTL Register On Processors with CPUID Family/Model/Stepping Signature Encoded
as 0x69n or 0x6Dn
On processors introduced after the Pentium 4 processor (this includes most Pentium M processors), the method
used to enable TM2 is different. TM2 is enable by setting bit 13 of IA32_MISC_ENABLE register to 1. This applies to
Intel Core Duo, Core Solo, and Intel Core 2 processor family.
The target operating frequency and voltage for the TM2 transition after TM2 is triggered is specified by the value
written to MSR_THERM2_CTL, bits 15:0 (Figure 14-22). Following a power-up or reset, BIOS is required to enable
at least one of these two thermal monitoring mechanisms. If both TM1 and TM2 are supported, BIOS may choose
to enable TM2 instead of TM1. Operating systems and applications must not disable the mechanisms that enable
TM1or TM2; and they must not alter the value in bits 15:0 of the MSR_THERM2_CTL register.

15

63

0

Reserved

TM2 Transition Target

Figure 14-22. MSR_THERM2_CTL Register for Supporting TM2

14.7.2.4

Performance State Transitions and Thermal Monitoring

If the thermal control circuitry (TCC) for thermal monitor (TM1/TM2) is active, writes to the IA32_PERF_CTL will
effect a new target operating point as follows:

•

If TM1 is enabled and the TCC is engaged, the performance state transition can commence before the TCC is
disengaged.

•

If TM2 is enabled and the TCC is engaged, the performance state transition specified by a write to the
IA32_PERF_CTL will commence after the TCC has disengaged.

14.7.2.5

Thermal Status Information

The status of the temperature sensor that triggers the thermal monitor (TM1/TM2) is indicated through the thermal
status flag and thermal status log flag in the IA32_THERM_STATUS MSR (see Figure 14-23).
The functions of these flags are:

•

Thermal Status flag, bit 0 — When set, indicates that the processor core temperature is currently at the trip
temperature of the thermal monitor and that the processor power consumption is being reduced via either TM1
or TM2, depending on which is enabled. When clear, the flag indicates that the core temperature is below the
thermal monitor trip temperature. This flag is read only.

•

Thermal Status Log flag, bit 1 — When set, indicates that the thermal sensor has tripped since the last
power-up or reset or since the last time that software cleared this flag. This flag is a sticky bit; once set it
remains set until cleared by software or until a power-up or reset of the processor. The default state is clear.

Vol. 3B 14-21

POWER AND THERMAL MANAGEMENT

63

210

Reserved
Thermal Status Log
Thermal Status

Figure 14-23. IA32_THERM_STATUS MSR
After the second temperature sensor has been tripped, the thermal monitor (TM1/TM2) will remain engaged for a
minimum time period (on the order of 1 ms). The thermal monitor will remain engaged until the processor core
temperature drops below the preset trip temperature of the temperature sensor, taking hysteresis into account.
While the processor is in a stop-clock state, interrupts will be blocked from interrupting the processor. This holding
off of interrupts increases the interrupt latency, but does not cause interrupts to be lost. Outstanding interrupts
remain pending until clock modulation is complete.
The thermal monitor can be programmed to generate an interrupt to the processor when the thermal sensor is
tripped. The delivery mode, mask and vector for this interrupt can be programmed through the thermal entry in the
local APIC’s LVT (see Section 10.5.1, “Local Vector Table”). The low-temperature interrupt enable and high-temperature interrupt enable flags in the IA32_THERM_INTERRUPT MSR (see Figure 14-24) control when the interrupt is
generated; that is, on a transition from a temperature below the trip point to above and/or vice-versa.
63

210

Reserved
Low-Temperature Interrupt Enable
High-Temperature Interrupt Enable

Figure 14-24. IA32_THERM_INTERRUPT MSR

•

High-Temperature Interrupt Enable flag, bit 0 — Enables an interrupt to be generated on the transition
from a low-temperature to a high-temperature when set; disables the interrupt when clear.(R/W).

•

Low-Temperature Interrupt Enable flag, bit 1 — Enables an interrupt to be generated on the transition
from a high-temperature to a low-temperature when set; disables the interrupt when clear.

The thermal monitor interrupt can be masked by the thermal LVT entry. After a power-up or reset, the low-temperature interrupt enable and high-temperature interrupt enable flags in the IA32_THERM_INTERRUPT MSR are
cleared (interrupts are disabled) and the thermal LVT entry is set to mask interrupts. This interrupt should be
handled either by the operating system or system management mode (SMM) code.
Note that the operation of the thermal monitoring mechanism has no effect upon the clock rate of the processor's
internal high-resolution timer (time stamp counter).

14.7.2.6

Adaptive Thermal Monitor

The Intel Core 2 Duo processor family supports enhanced thermal management mechanism, referred to as Adaptive Thermal Monitor (Adaptive TM).
Unlike TM2, Adaptive TM is not limited to one TM2 transition target. During a thermal trip event, Adaptive TM (if
enabled) selects an optimal target operating point based on whether or not the current operating point has effectively cooled the processor.
Similar to TM2, Adaptive TM is enable by BIOS. The BIOS is required to test the TM1 and TM2 feature flags and
enable all available thermal control mechanisms (including Adaptive TM) at platform initiation.
Adaptive TM is available only to a subset of processors that support TM2.

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POWER AND THERMAL MANAGEMENT

In each chip-multiprocessing (CMP) silicon die, each core has a unique thermal sensor that triggers independently.
These thermal sensor can trigger TM1 or TM2 transitions in the same manner as described in Section 14.7.2.1 and
Section 14.7.2.2. The trip point of the thermal sensor is not programmable by software since it is set during the
fabrication of the processor.
Each thermal sensor in a processor core may be triggered independently to engage thermal management features.
In Adaptive TM, both cores will transition to a lower frequency and/or lower voltage level if one sensor is triggered.
Triggering of this sensor is visible to software via the thermal interrupt LVT entry in the local APIC of a given core.

14.7.3

Software Controlled Clock Modulation

Pentium 4, Intel Xeon and Pentium M processors also support software-controlled clock modulation. This provides
a means for operating systems to implement a power management policy to reduce the power consumption of the
processor. Here, the stop-clock duty cycle is controlled by software through the IA32_CLOCK_MODULATION MSR
(see Figure 14-25).
63

543

10

Reserved
On-Demand Clock Modulation Enable
On-Demand Clock Modulation Duty Cycle

Reserved

Figure 14-25. IA32_CLOCK_MODULATION MSR
The IA32_CLOCK_MODULATION MSR contains the following flag and field used to enable software-controlled clock
modulation and to select the clock modulation duty cycle:

•

On-Demand Clock Modulation Enable, bit 4 — Enables on-demand software controlled clock modulation
when set; disables software-controlled clock modulation when clear.

•

On-Demand Clock Modulation Duty Cycle, bits 1 through 3 — Selects the on-demand clock modulation
duty cycle (see Table 14-3). This field is only active when the on-demand clock modulation enable flag is set.

Note that the on-demand clock modulation mechanism (like the thermal monitor) controls the processor’s stopclock circuitry internally to modulate the clock signal. The STPCLK# pin is not used in this mechanism.

Table 14-3. On-Demand Clock Modulation Duty Cycle Field Encoding
Duty Cycle Field Encoding

Duty Cycle

000B

Reserved

001B

12.5% (Default)

010B

25.0%

011B

37.5%

100B

50.0%

101B

63.5%

110B

75%

111B

87.5%

The on-demand clock modulation mechanism can be used to control processor power consumption. Power
management software can write to the IA32_CLOCK_MODULATION MSR to enable clock modulation and to select
a modulation duty cycle. If on-demand clock modulation and TM1 are both enabled and the thermal status of the
processor is hot (bit 0 of the IA32_THERM_STATUS MSR is set), clock modulation at the duty cycle specified by TM1
takes precedence, regardless of the setting of the on-demand clock modulation duty cycle.
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For Hyper-Threading Technology enabled processors, the IA32_CLOCK_MODULATION register is duplicated for
each logical processor. In order for the On-demand clock modulation feature to work properly, the feature must be
enabled on all the logical processors within a physical processor. If the programmed duty cycle is not identical for
all the logical processors, the processor core clock will modulate to the highest duty cycle programmed for processors with any of the following CPUID DisplayFamily_DisplayModel signatures (see CPUID instruction in Chapter3,
“Instruction Set Reference, A-L” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
2A): 06_1A, 06_1C, 06_1E, 06_1F, 06_25, 06_26, 06_27, 06_2C, 06_2E, 06_2F, 06_35, 06_36, and 0F_xx. For all
other processors, if the programmed duty cycle is not identical for all logical processors in the same core, the
processor core will modulate at the lowest programmed duty cycle.
For multiple processor cores in a physical package, each processor core can modulate to a programmed duty cycle
independently.
For the P6 family processors, on-demand clock modulation was implemented through the chipset, which controlled
clock modulation through the processor’s STPCLK# pin.

14.7.3.1

Extension of Software Controlled Clock Modulation

Extension of the software controlled clock modulation facility supports on-demand clock modulation duty cycle with
4-bit dynamic range (increased from 3-bit range). Granularity of clock modulation duty cycle is increased to 6.25%
(compared to 12.5%).
Four bit dynamic range control is provided by using bit 0 in conjunction with bits 3:1 of the
IA32_CLOCK_MODULATION MSR (see Figure 14-26).
63

543

0

Reserved
On-Demand Clock Modulation Enable
Extended On-Demand Clock Modulation Duty Cycle
Reserved

Figure 14-26. IA32_CLOCK_MODULATION MSR with Clock Modulation Extension
Extension to software controlled clock modulation is supported only if CPUID.06H:EAX[Bit 5] = 1. If
CPUID.06H:EAX[Bit 5] = 0, then bit 0 of IA32_CLOCK_MODULATION is reserved.

14.7.4

Detection of Thermal Monitor and Software Controlled
Clock Modulation Facilities

The ACPI flag (bit 22) of the CPUID feature flags indicates the presence of the IA32_THERM_STATUS,
IA32_THERM_INTERRUPT, IA32_CLOCK_MODULATION MSRs, and the xAPIC thermal LVT entry.
The TM1 flag (bit 29) of the CPUID feature flags indicates the presence of the automatic thermal monitoring facilities that modulate clock duty cycles.

14.7.4.1

Detection of Software Controlled Clock Modulation Extension

Processor’s support of software controlled clock modulation extension is indicated by CPUID.06H:EAX[Bit 5] = 1.

14.7.5

On Die Digital Thermal Sensors

On die digital thermal sensor can be read using an MSR (no I/O interface). In Intel Core Duo processors, each core
has a unique digital sensor whose temperature is accessible using an MSR. The digital thermal sensor is the
preferred method for reading the die temperature because (a) it is located closer to the hottest portions of the die,
(b) it enables software to accurately track the die temperature and the potential activation of thermal throttling.

14-24 Vol. 3B

POWER AND THERMAL MANAGEMENT

14.7.5.1

Digital Thermal Sensor Enumeration

The processor supports a digital thermal sensor if CPUID.06H.EAX[0] = 1. If the processor supports digital thermal
sensor, EBX[bits 3:0] determine the number of thermal thresholds that are available for use.
Software sets thermal thresholds by using the IA32_THERM_INTERRUPT MSR. Software reads output of the digital
thermal sensor using the IA32_THERM_STATUS MSR.

14.7.5.2

Reading the Digital Sensor

Unlike traditional analog thermal devices, the output of the digital thermal sensor is a temperature relative to the
maximum supported operating temperature of the processor.
Temperature measurements returned by digital thermal sensors are always at or below TCC activation temperature. Critical temperature conditions are detected using the “Critical Temperature Status” bit. When this bit is set,
the processor is operating at a critical temperature and immediate shutdown of the system should occur. Once the
“Critical Temperature Status” bit is set, reliable operation is not guaranteed.
See Figure 14-27 for the layout of IA32_THERM_STATUS MSR. Bit fields include:

•

Thermal Status (bit 0, RO) — This bit indicates whether the digital thermal sensor high-temperature output
signal (PROCHOT#) is currently active. Bit 0 = 1 indicates the feature is active. This bit may not be written by
software; it reflects the state of the digital thermal sensor.

•

Thermal Status Log (bit 1, R/WC0) — This is a sticky bit that indicates the history of the thermal sensor
high temperature output signal (PROCHOT#). Bit 1 = 1 if PROCHOT# has been asserted since a previous
RESET or the last time software cleared the bit. Software may clear this bit by writing a zero.

•

PROCHOT# or FORCEPR# Event (bit 2, RO) — Indicates whether PROCHOT# or FORCEPR# is being
asserted by another agent on the platform.

63

32 31

27

23 22

16 15

11 10 9 8 7

6 5

4

3

2

1 0

Reserved

Reading Valid
Resolution in Deg. Celsius
Digital Readout
Power Limit Notification Log
Power Limit Notification Status
Thermal Threshold #2 Log
Thermal Threshold #2 Status
Thermal Threshold #1 Log
Thermal Threshold #1 Status
Critical Temperature Log
Critical Temperature Status
PROCHOT# or FORCEPR# Log
PROCHOT# or FORCEPR# Event
Thermal Status Log
Thermal Status

Figure 14-27. IA32_THERM_STATUS Register

•

PROCHOT# or FORCEPR# Log (bit 3, R/WC0) — Sticky bit that indicates whether PROCHOT# or
FORCEPR# has been asserted by another agent on the platform since the last clearing of this bit or a reset. If
bit 3 = 1, PROCHOT# or FORCEPR# has been externally asserted. Software may clear this bit by writing a zero.
External PROCHOT# assertions are only acknowledged if the Bidirectional Prochot feature is enabled.

•

Critical Temperature Status (bit 4, RO) — Indicates whether the critical temperature detector output signal
is currently active. If bit 4 = 1, the critical temperature detector output signal is currently active.

Vol. 3B 14-25

POWER AND THERMAL MANAGEMENT

•

Critical Temperature Log (bit 5, R/WC0) — Sticky bit that indicates whether the critical temperature
detector output signal has been asserted since the last clearing of this bit or reset. If bit 5 = 1, the output
signal has been asserted. Software may clear this bit by writing a zero.

•

Thermal Threshold #1 Status (bit 6, RO) — Indicates whether the actual temperature is currently higher
than or equal to the value set in Thermal Threshold #1. If bit 6 = 0, the actual temperature is lower. If
bit 6 = 1, the actual temperature is greater than or equal to TT#1. Quantitative information of actual
temperature can be inferred from Digital Readout, bits 22:16.

•

Thermal Threshold #1 Log (bit 7, R/WC0) — Sticky bit that indicates whether the Thermal Threshold #1
has been reached since the last clearing of this bit or a reset. If bit 7 = 1, the Threshold #1 has been reached.
Software may clear this bit by writing a zero.

•

Thermal Threshold #2 Status (bit 8, RO) — Indicates whether actual temperature is currently higher than
or equal to the value set in Thermal Threshold #2. If bit 8 = 0, the actual temperature is lower. If bit 8 = 1, the
actual temperature is greater than or equal to TT#2. Quantitative information of actual temperature can be
inferred from Digital Readout, bits 22:16.

•

Thermal Threshold #2 Log (bit 9, R/WC0) — Sticky bit that indicates whether the Thermal Threshold #2
has been reached since the last clearing of this bit or a reset. If bit 9 = 1, the Thermal Threshold #2 has been
reached. Software may clear this bit by writing a zero.

•

Power Limitation Status (bit 10, RO) — Indicates whether the processor is currently operating below OSrequested P-state (specified in IA32_PERF_CTL) or OS-requested clock modulation duty cycle (specified in
IA32_CLOCK_MODULATION). This field is supported only if CPUID.06H:EAX[bit 4] = 1. Package level power
limit notification can be delivered independently to IA32_PACKAGE_THERM_STATUS MSR.

•

Power Notification Log (bit 11, R/WCO) — Sticky bit that indicates the processor went below OS-requested
P-state or OS-requested clock modulation duty cycle since the last clearing of this or RESET. This field is
supported only if CPUID.06H:EAX[bit 4] = 1. Package level power limit notification is indicated independently
in IA32_PACKAGE_THERM_STATUS MSR.

•

Digital Readout (bits 22:16, RO) — Digital temperature reading in 1 degree Celsius relative to the TCC
activation temperature.
0: TCC Activation temperature,
1: (TCC Activation - 1) , etc. See the processor’s data sheet for details regarding TCC activation.
A lower reading in the Digital Readout field (bits 22:16) indicates a higher actual temperature.

•

Resolution in Degrees Celsius (bits 30:27, RO) — Specifies the resolution (or tolerance) of the digital
thermal sensor. The value is in degrees Celsius. It is recommended that new threshold values be offset from the
current temperature by at least the resolution + 1 in order to avoid hysteresis of interrupt generation.

•

Reading Valid (bit 31, RO) — Indicates if the digital readout in bits 22:16 is valid. The readout is valid if
bit 31 = 1.

Changes to temperature can be detected using two thresholds (see Figure 14-28); one is set above and the other
below the current temperature. These thresholds have the capability of generating interrupts using the core's local
APIC which software must then service. Note that the local APIC entries used by these thresholds are also used by
the Intel® Thermal Monitor; it is up to software to determine the source of a specific interrupt.

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POWER AND THERMAL MANAGEMENT

63

25 24 23 22

16 15 14

8

5

4

3

2

1

0

Reserved
Power Limit Notification Enable
Threshold #2 Interrupt Enable
Threshold #2 Value
Threshold #1 Interrupt Enable
Threshold #1 Value
Overheat Interrupt Enable
FORCPR# Interrupt Enable
PROCHOT# Interrupt Enable
Low Temp. Interrupt Enable
High Temp. Interrupt Enable

Figure 14-28. IA32_THERM_INTERRUPT Register

See Figure 14-28 for the layout of IA32_THERM_INTERRUPT MSR. Bit fields include:

•

High-Temperature Interrupt Enable (bit 0, R/W) — This bit allows the BIOS to enable the generation of
an interrupt on the transition from low-temperature to a high-temperature threshold. Bit 0 = 0 (default)
disables interrupts; bit 0 = 1 enables interrupts.

•

Low-Temperature Interrupt Enable (bit 1, R/W) — This bit allows the BIOS to enable the generation of an
interrupt on the transition from high-temperature to a low-temperature (TCC de-activation). Bit 1 = 0 (default)
disables interrupts; bit 1 = 1 enables interrupts.

•

PROCHOT# Interrupt Enable (bit 2, R/W) — This bit allows the BIOS or OS to enable the generation of an
interrupt when PROCHOT# has been asserted by another agent on the platform and the Bidirectional Prochot
feature is enabled. Bit 2 = 0 disables the interrupt; bit 2 = 1 enables the interrupt.

•

FORCEPR# Interrupt Enable (bit 3, R/W) — This bit allows the BIOS or OS to enable the generation of an
interrupt when FORCEPR# has been asserted by another agent on the platform. Bit 3 = 0 disables the
interrupt; bit 3 = 1 enables the interrupt.

•

Critical Temperature Interrupt Enable (bit 4, R/W) — Enables the generation of an interrupt when the
Critical Temperature Detector has detected a critical thermal condition. The recommended response to this
condition is a system shutdown. Bit 4 = 0 disables the interrupt; bit 4 = 1 enables the interrupt.

•

Threshold #1 Value (bits 14:8, R/W) — A temperature threshold, encoded relative to the TCC Activation
temperature (using the same format as the Digital Readout). This threshold is compared against the Digital
Readout and is used to generate the Thermal Threshold #1 Status and Log bits as well as the Threshold #1
thermal interrupt delivery.

•

Threshold #1 Interrupt Enable (bit 15, R/W) — Enables the generation of an interrupt when the actual
temperature crosses the Threshold #1 setting in any direction. Bit 15 = 1 enables the interrupt; bit 15 = 0
disables the interrupt.

•

Threshold #2 Value (bits 22:16, R/W) —A temperature threshold, encoded relative to the TCC Activation
temperature (using the same format as the Digital Readout). This threshold is compared against the Digital
Readout and is used to generate the Thermal Threshold #2 Status and Log bits as well as the Threshold #2
thermal interrupt delivery.

•

Threshold #2 Interrupt Enable (bit 23, R/W) — Enables the generation of an interrupt when the actual
temperature crosses the Threshold #2 setting in any direction. Bit 23 = 1enables the interrupt; bit 23 = 0
disables the interrupt.

•

Power Limit Notification Enable (bit 24, R/W) — Enables the generation of power notification events when
the processor went below OS-requested P-state or OS-requested clock modulation duty cycle. This field is
supported only if CPUID.06H:EAX[bit 4] = 1. Package level power limit notification can be enabled independently by IA32_PACKAGE_THERM_INTERRUPT MSR.

Vol. 3B 14-27

POWER AND THERMAL MANAGEMENT

14.7.6

Power Limit Notification

Platform firmware may be capable of specifying a power limit to restrict power delivered to a platform component,
such as a physical processor package. This constraint imposed by platform firmware may occasionally cause the
processor to operate below OS-requested P or T-state. A power limit notification event can be delivered using the
existing thermal LVT entry in the local APIC.
Software can enumerate the presence of the processor’s support for power limit notification by verifying
CPUID.06H:EAX[bit 4] = 1.
If CPUID.06H:EAX[bit 4] = 1, then IA32_THERM_INTERRUPT and IA32_THERM_STATUS provides the following
facility to manage power limit notification:

•

Bits 10 and 11 in IA32_THERM_STATUS informs software of the occurrence of processor operating below OSrequested P-state or clock modulation duty cycle setting (see Figure 14-27).

•

Bit 24 in IA32_THERM_INTERRUPT enables the local APIC to deliver a thermal event when the processor went
below OS-requested P-state or clock modulation duty cycle setting (see Figure 14-28).

14.8

PACKAGE LEVEL THERMAL MANAGEMENT

The thermal management facilities like IA32_THERM_INTERRUPT and IA32_THERM_STATUS are often implemented with a processor core granularity. To facilitate software manage thermal events from a package level granularity, two architectural MSR is provided for package level thermal management. The
IA32_PACKAGE_THERM_STATUS and IA32_PACKAGE_THERM_INTERRUPT MSRs use similar interfaces as
IA32_THERM_STATUS and IA32_THERM_INTERRUPT, but are shared in each physical processor package.
Software can enumerate the presence of the processor’s support for package level thermal management facility
(IA32_PACKAGE_THERM_STATUS and IA32_PACKAGE_THERM_INTERRUPT) by verifying CPUID.06H:EAX[bit 6] =
1.
The layout of IA32_PACKAGE_THERM_STATUS MSR is shown in Figure 14-29.

63

32 31

27

23 22

16 15

11 10 9 8 7

6 5

4

3

2

1 0

Reserved

PKG Digital Readout
PKG Power Limit Notification Log
PKG Power Limit Notification Status
PKG Thermal Threshold #2 Log
PKG Thermal Threshold #2 Status
PKG Thermal Threshold #1 Log
PKG Thermal Threshold #1 Status
PKG Critical Temperature Log
PKG Critical Temperature Status
PKG PROCHOT# or FORCEPR# Log
PKG PROCHOT# or FORCEPR# Event
PKG Thermal Status Log
PKG Thermal Status

Figure 14-29. IA32_PACKAGE_THERM_STATUS Register

•

Package Thermal Status (bit 0, RO) — This bit indicates whether the digital thermal sensor hightemperature output signal (PROCHOT#) for the package is currently active. Bit 0 = 1 indicates the feature is
active. This bit may not be written by software; it reflects the state of the digital thermal sensor.

14-28 Vol. 3B

POWER AND THERMAL MANAGEMENT

•

Package Thermal Status Log (bit 1, R/WC0) — This is a sticky bit that indicates the history of the thermal
sensor high temperature output signal (PROCHOT#) of the package. Bit 1 = 1 if package PROCHOT# has been
asserted since a previous RESET or the last time software cleared the bit. Software may clear this bit by writing
a zero.

•

Package PROCHOT# Event (bit 2, RO) — Indicates whether package PROCHOT# is being asserted by
another agent on the platform.

•

Package PROCHOT# Log (bit 3, R/WC0) — Sticky bit that indicates whether package PROCHOT# has been
asserted by another agent on the platform since the last clearing of this bit or a reset. If bit 3 = 1, package
PROCHOT# has been externally asserted. Software may clear this bit by writing a zero.

•

Package Critical Temperature Status (bit 4, RO) — Indicates whether the package critical temperature
detector output signal is currently active. If bit 4 = 1, the package critical temperature detector output signal
is currently active.

•

Package Critical Temperature Log (bit 5, R/WC0) — Sticky bit that indicates whether the package critical
temperature detector output signal has been asserted since the last clearing of this bit or reset. If bit 5 = 1, the
output signal has been asserted. Software may clear this bit by writing a zero.

•

Package Thermal Threshold #1 Status (bit 6, RO) — Indicates whether the actual package temperature is
currently higher than or equal to the value set in Package Thermal Threshold #1. If bit 6 = 0, the actual
temperature is lower. If bit 6 = 1, the actual temperature is greater than or equal to PTT#1. Quantitative
information of actual package temperature can be inferred from Package Digital Readout, bits 22:16.

•

Package Thermal Threshold #1 Log (bit 7, R/WC0) — Sticky bit that indicates whether the Package
Thermal Threshold #1 has been reached since the last clearing of this bit or a reset. If bit 7 = 1, the Package
Threshold #1 has been reached. Software may clear this bit by writing a zero.

•

Package Thermal Threshold #2 Status (bit 8, RO) — Indicates whether actual package temperature is
currently higher than or equal to the value set in Package Thermal Threshold #2. If bit 8 = 0, the actual
temperature is lower. If bit 8 = 1, the actual temperature is greater than or equal to PTT#2. Quantitative
information of actual temperature can be inferred from Package Digital Readout, bits 22:16.

•

Package Thermal Threshold #2 Log (bit 9, R/WC0) — Sticky bit that indicates whether the Package
Thermal Threshold #2 has been reached since the last clearing of this bit or a reset. If bit 9 = 1, the Package
Thermal Threshold #2 has been reached. Software may clear this bit by writing a zero.

•

Package Power Limitation Status (bit 10, RO) — Indicates package power limit is forcing one ore more
processors to operate below OS-requested P-state. Note that package power limit violation may be caused by
processor cores or by devices residing in the uncore. Software can examine IA32_THERM_STATUS to
determine if the cause originates from a processor core (see Figure 14-27).

•

Package Power Notification Log (bit 11, R/WCO) — Sticky bit that indicates any processor in the package
went below OS-requested P-state or OS-requested clock modulation duty cycle since the last clearing of this or
RESET.

•

Package Digital Readout (bits 22:16, RO) — Package digital temperature reading in 1 degree Celsius
relative to the package TCC activation temperature.
0: Package TCC Activation temperature,
1: (PTCC Activation - 1) , etc. See the processor’s data sheet for details regarding PTCC activation.
A lower reading in the Package Digital Readout field (bits 22:16) indicates a higher actual temperature.

The layout of IA32_PACKAGE_THERM_INTERRUPT MSR is shown in Figure 14-30.

Vol. 3B 14-29

POWER AND THERMAL MANAGEMENT

63

25 24 23 22

16 15 14

8

5

4

3

2

1

0

Reserved
Pkg Power Limit Notification Enable
Pkg Threshold #2 Interrupt Enable
Pkg Threshold #2 Value
Pkg Threshold #1 Interrupt Enable
Pkg Threshold #1 Value
Pkg Overheat Interrupt Enable
Pkg PROCHOT# Interrupt Enable
Pkg Low Temp. Interrupt Enable
Pkg High Temp. Interrupt Enable

Figure 14-30. IA32_PACKAGE_THERM_INTERRUPT Register

•

Package High-Temperature Interrupt Enable (bit 0, R/W) — This bit allows the BIOS to enable the
generation of an interrupt on the transition from low-temperature to a package high-temperature threshold.
Bit 0 = 0 (default) disables interrupts; bit 0 = 1 enables interrupts.

•

Package Low-Temperature Interrupt Enable (bit 1, R/W) — This bit allows the BIOS to enable the
generation of an interrupt on the transition from high-temperature to a low-temperature (TCC de-activation).
Bit 1 = 0 (default) disables interrupts; bit 1 = 1 enables interrupts.

•

Package PROCHOT# Interrupt Enable (bit 2, R/W) — This bit allows the BIOS or OS to enable the
generation of an interrupt when Package PROCHOT# has been asserted by another agent on the platform and
the Bidirectional Prochot feature is enabled. Bit 2 = 0 disables the interrupt; bit 2 = 1 enables the interrupt.

•

Package Critical Temperature Interrupt Enable (bit 4, R/W) — Enables the generation of an interrupt
when the Package Critical Temperature Detector has detected a critical thermal condition. The recommended
response to this condition is a system shutdown. Bit 4 = 0 disables the interrupt; bit 4 = 1 enables the
interrupt.

•

Package Threshold #1 Value (bits 14:8, R/W) — A temperature threshold, encoded relative to the
Package TCC Activation temperature (using the same format as the Digital Readout). This threshold is
compared against the Package Digital Readout and is used to generate the Package Thermal Threshold #1
Status and Log bits as well as the Package Threshold #1 thermal interrupt delivery.

•

Package Threshold #1 Interrupt Enable (bit 15, R/W) — Enables the generation of an interrupt when the
actual temperature crosses the Package Threshold #1 setting in any direction. Bit 15 = 1 enables the interrupt;
bit 15 = 0 disables the interrupt.

•

Package Threshold #2 Value (bits 22:16, R/W) —A temperature threshold, encoded relative to the PTCC
Activation temperature (using the same format as the Package Digital Readout). This threshold is compared
against the Package Digital Readout and is used to generate the Package Thermal Threshold #2 Status and Log
bits as well as the Package Threshold #2 thermal interrupt delivery.

•

Package Threshold #2 Interrupt Enable (bit 23, R/W) — Enables the generation of an interrupt when the
actual temperature crosses the Package Threshold #2 setting in any direction. Bit 23 = 1 enables the interrupt;
bit 23 = 0 disables the interrupt.

•

Package Power Limit Notification Enable (bit 24, R/W) — Enables the generation of package power
notification events.

14.8.1

Support for Passive and Active cooling

Passive and active cooling may be controlled by the OS power management agent through ACPI control methods.
On platforms providing package level thermal management facility described in the previous section, it is recommended that active cooling (FAN control) should be driven by measuring the package temperature using the
IA32_PACKAGE_THERM_INTERRUPT MSR.

14-30 Vol. 3B

POWER AND THERMAL MANAGEMENT

Passive cooling (frequency throttling) should be driven by measuring (a) the core and package temperatures, or
(b) only the package temperature. If measured package temperature led the power management agent to choose
which core to execute passive cooling, then all cores need to execute passive cooling. Core temperature is
measured using the IA32_THERMAL_STATUS and IA32_THERMAL_INTERRUPT MSRs. The exact implementation
details depend on the platform firmware and possible solutions include defining two different thermal zones (one
for core temperature and passive cooling and the other for package temperature and active cooling).

14.9

PLATFORM SPECIFIC POWER MANAGEMENT SUPPORT

This section covers power management interfaces that are not architectural but addresses the power management
needs of several platform specific components. Specifically, RAPL (Running Average Power Limit) interfaces provide
mechanisms to enforce power consumption limit. Power limiting usages have specific usages in client and server
platforms.
For client platform power limit control and for server platforms used in a data center, the following power and
thermal related usages are desirable:

•

Platform Thermal Management: Robust mechanisms to manage component, platform, and group-level
thermals, either proactively or reactively (e.g., in response to a platform-level thermal trip point).

•

Platform Power Limiting: More deterministic control over the system's power consumption, for example to
meet battery life targets on rack-level or container-level power consumption goals within a datacenter.

•

Power/Performance Budgeting: Efficient means to control the power consumed (and therefore the sustained
performance delivered) within and across platforms.

The server and client usage models are addressed by RAPL interfaces, which expose multiple domains of power
rationing within each processor socket. Generally, these RAPL domains may be viewed to include hierarchically:

•
•

Package domain is the processor die.
Memory domain includes the directly-attached DRAM; an additional power plane may constitute a separate
domain.

In order to manage the power consumed across multiple sockets via RAPL, individual limits must be programmed
for each processor complex. Programming specific RAPL domain across multiple sockets is not supported.

14.9.1

RAPL Interfaces

RAPL interfaces consist of non-architectural MSRs. Each RAPL domain supports the following set of capabilities,
some of which are optional as stated below.

•
•
•

Power limit - MSR interfaces to specify power limit, time window; lock bit, clamp bit etc.

•

Power Info (Optional) - Interface providing information on the range of parameters for a given domain,
minimum power, maximum power etc.

•

Policy (Optional) - 4-bit priority information that is a hint to hardware for dividing budget between sub-domains
in a parent domain.

Energy Status - Power metering interface providing energy consumption information.
Perf Status (Optional) - Interface providing information on the performance effects (regression) due to power
limits. It is defined as a duration metric that measures the power limit effect in the respective domain. The
meaning of duration is domain specific.

Each of the above capabilities requires specific units in order to describe them. Power is expressed in Watts, Time
is expressed in Seconds, and Energy is expressed in Joules. Scaling factors are supplied to each unit to make the
information presented meaningful in a finite number of bits. Units for power, energy, and time are exposed in the
read-only MSR_RAPL_POWER_UNIT MSR.

Vol. 3B 14-31

POWER AND THERMAL MANAGEMENT

63

20 19

16 15 13 12

8 7

4

3

0

Reserved

Time units
Energy status units
Power units

Figure 14-31. MSR_RAPL_POWER_UNIT Register
MSR_RAPL_POWER_UNIT (Figure 14-31) provides the following information across all RAPL domains:

•

Power Units (bits 3:0): Power related information (in Watts) is based on the multiplier, 1/ 2^PU; where PU is
an unsigned integer represented by bits 3:0. Default value is 0011b, indicating power unit is in 1/8 Watts
increment.

•

Energy Status Units (bits 12:8): Energy related information (in Joules) is based on the multiplier, 1/2^ESU;
where ESU is an unsigned integer represented by bits 12:8. Default value is 10000b, indicating energy status
unit is in 15.3 micro-Joules increment.

•

Time Units (bits 19:16): Time related information (in Seconds) is based on the multiplier, 1/ 2^TU; where TU
is an unsigned integer represented by bits 19:16. Default value is 1010b, indicating time unit is in 976 microseconds increment.

14.9.2

RAPL Domains and Platform Specificity

The specific RAPL domains available in a platform vary across product segments. Platforms targeting the client
segment support the following RAPL domain hierarchy:

•
•

Package
Two power planes: PP0 and PP1 (PP1 may reflect to uncore devices)

Platforms targeting the server segment support the following RAPL domain hierarchy:

•
•
•

Package
Power plane: PP0
DRAM

Each level of the RAPL hierarchy provides a respective set of RAPL interface MSRs. Table 14-4 lists the RAPL MSR
interfaces available for each RAPL domain. The power limit MSR of each RAPL domain is located at offset 0 relative
to an MSR base address which is non-architectural (see Chapter 2, “Model-Specific Registers (MSRs)” in the Intel®
64 and IA-32 Architectures Software Developer’s Manual, Volume 4). The energy status MSR of each domain is
located at offset 1 relative to the MSR base address of respective domain.

Table 14-4. RAPL MSR Interfaces and RAPL Domains
Domain
PKG
DRAM
PP0

14-32 Vol. 3B

Power Limit
(Offset 0)
MSR_PKG_POWER_
LIMIT

Energy Status (Offset
1)

MSR_PKG_ENERGY_STA RESERVED
TUS

MSR_DRAM_POWER MSR_DRAM_ENERGY_S
_LIMIT
TATUS
MSR_PP0_POWER_
LIMIT

Policy
(Offset 2)

RESERVED

MSR_PP0_ENERGY_STA MSR_PP0_POLICY
TUS

Perf Status
(Offset 3)

Power Info
(Offset 4)

MSR_PKG_PERF_STATUS

MSR_PKG_POWER_I
NFO

MSR_DRAM_PERF_STATUS

MSR_DRAM_POWER
_INFO

MSR_PP0_PERF_STATUS

RESERVED

POWER AND THERMAL MANAGEMENT

Table 14-4. RAPL MSR Interfaces and RAPL Domains
PP1

MSR_PP1_POWER_
LIMIT

MSR_PP1_ENERGY_STA MSR_PP1_POLICY
TUS

RESERVED

RESERVED

The presence of the optional MSR interfaces (the three right-most columns of Table 14-4) may be model-specific.
See Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 4 for details.

14.9.3

Package RAPL Domain

The MSR interfaces defined for the package RAPL domain are:

•

MSR_PKG_POWER_LIMIT allows software to set power limits for the package and measurement attributes
associated with each limit,

•
•

MSR_PKG_ENERGY_STATUS reports measured actual energy usage,
MSR_PKG_POWER_INFO reports the package power range information for RAPL usage.

MSR_PKG_PERF_STATUS can report the performance impact of power limiting, but its availability may be modelspecific.

63 62
L
O
C
K

56 55

49 48 47 46

Time window
Power Limit #2

32 31

24 23

Pkg Power Limit #2

17 16 15 14

Time window
Power Limit #1

0

Pkg Power Limit #1

Enable limit #1
Pkg clamping limit #1
Enable limit #2
Pkg clamping limit #2

Figure 14-32. MSR_PKG_POWER_LIMIT Register
MSR_PKG_POWER_LIMIT allows a software agent to define power limitation for the package domain. Power limitation is defined in terms of average power usage (Watts) over a time window specified in MSR_PKG_POWER_LIMIT.
Two power limits can be specified, corresponding to time windows of different sizes. Each power limit provides
independent clamping control that would permit the processor cores to go below OS-requested state to meet the
power limits. A lock mechanism allow the software agent to enforce power limit settings. Once the lock bit is set,
the power limit settings are static and un-modifiable until next RESET.
The bit fields of MSR_PKG_POWER_LIMIT (Figure 14-32) are:

•

Package Power Limit #1(bits 14:0): Sets the average power usage limit of the package domain corresponding to time window # 1. The unit of this field is specified by the “Power Units” field of
MSR_RAPL_POWER_UNIT.

•
•

Enable Power Limit #1(bit 15): 0 = disabled; 1 = enabled.

•

Time Window for Power Limit #1 (bits 23:17): Indicates the time window for power limit #1

Package Clamping Limitation #1 (bit 16): Allow going below OS-requested P/T state setting during time
window specified by bits 23:17.
Time limit = 2^Y * (1.0 + Z/4.0) * Time_Unit
Here “Y” is the unsigned integer value represented. by bits 21:17, “Z” is an unsigned integer represented by
bits 23:22. “Time_Unit” is specified by the “Time Units” field of MSR_RAPL_POWER_UNIT.

Vol. 3B 14-33

POWER AND THERMAL MANAGEMENT

•

Package Power Limit #2(bits 46:32): Sets the average power usage limit of the package domain corresponding to time window # 2. The unit of this field is specified by the “Power Units” field of
MSR_RAPL_POWER_UNIT.

•
•

Enable Power Limit #2(bit 47): 0 = disabled; 1 = enabled.

•

Time Window for Power Limit #2 (bits 55:49): Indicates the time window for power limit #2

Package Clamping Limitation #2 (bit 48): Allow going below OS-requested P/T state setting during time
window specified by bits 23:17.
Time limit = 2^Y * (1.0 + Z/4.0) * Time_Unit
Here “Y” is the unsigned integer value represented. by bits 53:49, “Z” is an unsigned integer represented by
bits 55:54. “Time_Unit” is specified by the “Time Units” field of MSR_RAPL_POWER_UNIT. This field may have
a hard-coded value in hardware and ignores values written by software.

•

Lock (bit 63): If set, all write attempts to this MSR are ignored until next RESET.

MSR_PKG_ENERGY_STATUS is a read-only MSR. It reports the actual energy use for the package domain. This MSR
is updated every ~1msec. It has a wraparound time of around 60 secs when power consumption is high, and may
be longer otherwise.
32 31

63

0

Reserved
Total Energy Consumed

Reserved

Figure 14-33. MSR_PKG_ENERGY_STATUS MSR

•

Total Energy Consumed (bits 31:0): The unsigned integer value represents the total amount of energy
consumed since that last time this register is cleared. The unit of this field is specified by the “Energy Status
Units” field of MSR_RAPL_POWER_UNIT.

MSR_PKG_POWER_INFO is a read-only MSR. It reports the package power range information for RAPL usage. This
MSR provides maximum/minimum values (derived from electrical specification), thermal specification power of the
package domain. It also provides the largest possible time window for software to program the RAPL interface.

63

54 53

48 47 46

Maximum Time window

32 31 30

Maximum Power

Minimum Power

16 15 14

0

Thermal Spec Power

Figure 14-34. MSR_PKG_POWER_INFO Register

•

Thermal Spec Power (bits 14:0): The unsigned integer value is the equivalent of thermal specification power
of the package domain. The unit of this field is specified by the “Power Units” field of MSR_RAPL_POWER_UNIT.

•

Minimum Power (bits 30:16): The unsigned integer value is the equivalent of minimum power derived from
electrical spec of the package domain. The unit of this field is specified by the “Power Units” field of
MSR_RAPL_POWER_UNIT.

•

Maximum Power (bits 46:32): The unsigned integer value is the equivalent of maximum power derived from
the electrical spec of the package domain. The unit of this field is specified by the “Power Units” field of
MSR_RAPL_POWER_UNIT.

14-34 Vol. 3B

POWER AND THERMAL MANAGEMENT

•

Maximum Time Window (bits 53:48): The unsigned integer value is the equivalent of largest acceptable
value to program the time window of MSR_PKG_POWER_LIMIT. The unit of this field is specified by the “Time
Units” field of MSR_RAPL_POWER_UNIT.

MSR_PKG_PERF_STATUS is a read-only MSR. It reports the total time for which the package was throttled due to
the RAPL power limits. Throttling in this context is defined as going below the OS-requested P-state or T-state. It
has a wrap-around time of many hours. The availability of this MSR is platform specific (see Chapter 2, “ModelSpecific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4).
32 31

63

0

Reserved
Accumulated pkg throttled time

Reserved

Figure 14-35. MSR_PKG_PERF_STATUS MSR

•

Accumulated Package Throttled Time (bits 31:0): The unsigned integer value represents the cumulative
time (since the last time this register is cleared) that the package has throttled. The unit of this field is specified
by the “Time Units” field of MSR_RAPL_POWER_UNIT.

14.9.4

PP0/PP1 RAPL Domains

The MSR interfaces defined for the PP0 and PP1 domains are identical in layout. Generally, PP0 refers to the
processor cores. The availability of PP1 RAPL domain interface is platform-specific. For a client platform, the PP1
domain refers to the power plane of a specific device in the uncore. For server platforms, the PP1 domain is not
supported, but its PP0 domain supports the MSR_PP0_PERF_STATUS interface.

•

MSR_PP0_POWER_LIMIT/MSR_PP1_POWER_LIMIT allow software to set power limits for the respective power
plane domain.

•
•

MSR_PP0_ENERGY_STATUS/MSR_PP1_ENERGY_STATUS report actual energy usage on a power plane.
MSR_PP0_POLICY/MSR_PP1_POLICY allow software to adjust balance for respective power plane.

MSR_PP0_PERF_STATUS can report the performance impact of power limiting, but it is not available in client platforms.

63

32 31 30
L
O
C
K

24 23
Time window
Power Limit

17 16 15 14

0

Power Limit

Enable limit
Clamping limit

Figure 14-36. MSR_PP0_POWER_LIMIT/MSR_PP1_POWER_LIMIT Register
MSR_PP0_POWER_LIMIT/MSR_PP1_POWER_LIMIT allow a software agent to define power limitation for the
respective power plane domain. A lock mechanism in each power plane domain allows the software agent to
enforce power limit settings independently. Once a lock bit is set, the power limit settings in that power plane are
static and un-modifiable until next RESET.
The bit fields of MSR_PP0_POWER_LIMIT/MSR_PP1_POWER_LIMIT (Figure 14-36) are:

Vol. 3B 14-35

POWER AND THERMAL MANAGEMENT

•

Power Limit (bits 14:0): Sets the average power usage limit of the respective power plane domain. The unit
of this field is specified by the “Power Units” field of MSR_RAPL_POWER_UNIT.

•
•

Enable Power Limit (bit 15): 0 = disabled; 1 = enabled.

•

Time Window for Power Limit (bits 23:17): Indicates the length of time window over which the power limit
#1 will be used by the processor. The numeric value encoded by bits 23:17 is represented by the product of
2^Y *F; where F is a single-digit decimal floating-point value between 1.0 and 1.3 with the fraction digit
represented by bits 23:22, Y is an unsigned integer represented by bits 21:17. The unit of this field is specified
by the “Time Units” field of MSR_RAPL_POWER_UNIT.

•

Lock (bit 31): If set, all write attempts to the MSR and corresponding policy
MSR_PP0_POLICY/MSR_PP1_POLICY are ignored until next RESET.

Clamping Limitation (bit 16): Allow going below OS-requested P/T state setting during time window specified
by bits 23:17.

MSR_PP0_ENERGY_STATUS/MSR_PP1_ENERGY_STATUS are read-only MSRs. They report the actual energy use
for the respective power plane domains. These MSRs are updated every ~1msec.
32 31

63

0

Reserved
Total Energy Consumed

Reserved

Figure 14-37. MSR_PP0_ENERGY_STATUS/MSR_PP1_ENERGY_STATUS MSR

•

Total Energy Consumed (bits 31:0): The unsigned integer value represents the total amount of energy
consumed since the last time this register was cleared. The unit of this field is specified by the “Energy Status
Units” field of MSR_RAPL_POWER_UNIT.

MSR_PP0_POLICY/MSR_PP1_POLICY provide balance power policy control for each power plane by providing
inputs to the power budgeting management algorithm. On platforms that support PP0 (IA cores) and PP1 (uncore
graphic device), the default values give priority to the non-IA power plane. These MSRs enable the PCU to balance
power consumption between the IA cores and uncore graphic device.

63

5 4

0

Priority Level

Figure 14-38. MSR_PP0_POLICY/MSR_PP1_POLICY Register

•

Priority Level (bits 4:0): Priority level input to the PCU for respective power plane. PP0 covers the IA
processor cores, PP1 covers the uncore graphic device. The value 31 is considered highest priority.

MSR_PP0_PERF_STATUS is a read-only MSR. It reports the total time for which the PP0 domain was throttled due
to the power limits. This MSR is supported only in server platform. Throttling in this context is defined as going
below the OS-requested P-state or T-state.

14-36 Vol. 3B

POWER AND THERMAL MANAGEMENT

32 31

63

0

Reserved
Accumulated PP0 throttled time

Reserved

Figure 14-39. MSR_PP0_PERF_STATUS MSR

•

Accumulated PP0 Throttled Time (bits 31:0): The unsigned integer value represents the cumulative time
(since the last time this register is cleared) that the PP0 domain has throttled. The unit of this field is specified
by the “Time Units” field of MSR_RAPL_POWER_UNIT.

14.9.5

DRAM RAPL Domain

The MSR interfaces defined for the DRAM domains are supported only in the server platform. The MSR interfaces
are:

•

MSR_DRAM_POWER_LIMIT allows software to set power limits for the DRAM domain and measurement
attributes associated with each limit.

•
•
•

MSR_DRAM_ENERGY_STATUS reports measured actual energy usage.
MSR_DRAM_POWER_INFO reports the DRAM domain power range information for RAPL usage.
MSR_DRAM_PERF_STATUS can report the performance impact of power limiting.

63

32 31 30

24 23

L
O
C
K

Time window
Power Limit

17 16 15 14

0

Power Limit

Enable limit
Clamping limit

Figure 14-40. MSR_DRAM_POWER_LIMIT Register
MSR_DRAM_POWER_LIMIT allows a software agent to define power limitation for the DRAM domain. Power limitation is defined in terms of average power usage (Watts) over a time window specified in
MSR_DRAM_POWER_LIMIT. A power limit can be specified along with a time window. A lock mechanism allow the
software agent to enforce power limit settings. Once the lock bit is set, the power limit settings are static and unmodifiable until next RESET.
The bit fields of MSR_DRAM_POWER_LIMIT (Figure 14-40) are:

•

DRAM Power Limit #1(bits 14:0): Sets the average power usage limit of the DRAM domain corresponding to
time window # 1. The unit of this field is specified by the “Power Units” field of MSR_RAPL_POWER_UNIT.

•
•

Enable Power Limit #1(bit 15): 0 = disabled; 1 = enabled.

•

Time Window for Power Limit (bits 23:17): Indicates the length of time window over which the power limit
will be used by the processor. The numeric value encoded by bits 23:17 is represented by the product of 2^Y
*F; where F is a single-digit decimal floating-point value between 1.0 and 1.3 with the fraction digit
represented by bits 23:22, Y is an unsigned integer represented by bits 21:17. The unit of this field is specified
by the “Time Units” field of MSR_RAPL_POWER_UNIT.
Lock (bit 31): If set, all write attempts to this MSR are ignored until next RESET.

Vol. 3B 14-37

POWER AND THERMAL MANAGEMENT

MSR_DRAM_ENERGY_STATUS is a read-only MSR. It reports the actual energy use for the DRAM domain. This MSR
is updated every ~1msec.
32 31

63

0

Reserved
Total Energy Consumed

Reserved

Figure 14-41. MSR_DRAM_ENERGY_STATUS MSR

•

Total Energy Consumed (bits 31:0): The unsigned integer value represents the total amount of energy
consumed since that last time this register is cleared. The unit of this field is specified by the “Energy Status
Units” field of MSR_RAPL_POWER_UNIT.

MSR_DRAM_POWER_INFO is a read-only MSR. It reports the DRAM power range information for RAPL usage. This
MSR provides maximum/minimum values (derived from electrical specification), thermal specification power of the
DRAM domain. It also provides the largest possible time window for software to program the RAPL interface.

63

54 53

48 47 46

Maximum Time window

32 31 30

Maximum Power

Minimum Power

16 15 14

0

Thermal Spec Power

Figure 14-42. MSR_DRAM_POWER_INFO Register

•

Thermal Spec Power (bits 14:0): The unsigned integer value is the equivalent of thermal specification power
of the DRAM domain. The unit of this field is specified by the “Power Units” field of MSR_RAPL_POWER_UNIT.

•

Minimum Power (bits 30:16): The unsigned integer value is the equivalent of minimum power derived from
electrical spec of the DRAM domain. The unit of this field is specified by the “Power Units” field of
MSR_RAPL_POWER_UNIT.

•

Maximum Power (bits 46:32): The unsigned integer value is the equivalent of maximum power derived from
the electrical spec of the DRAM domain. The unit of this field is specified by the “Power Units” field of
MSR_RAPL_POWER_UNIT.

•

Maximum Time Window (bits 53:48): The unsigned integer value is the equivalent of largest acceptable
value to program the time window of MSR_DRAM_POWER_LIMIT. The unit of this field is specified by the “Time
Units” field of MSR_RAPL_POWER_UNIT.

MSR_DRAM_PERF_STATUS is a read-only MSR. It reports the total time for which the package was throttled due to
the RAPL power limits. Throttling in this context is defined as going below the OS-requested P-state or T-state. It
has a wrap-around time of many hours. The availability of this MSR is platform specific (see Chapter 2, “ModelSpecific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4).
32 31

63

Reserved
Accumulated DRAM throttled time

Reserved

Figure 14-43. MSR_DRAM_PERF_STATUS MSR
14-38 Vol. 3B

0

POWER AND THERMAL MANAGEMENT

•

Accumulated Package Throttled Time (bits 31:0): The unsigned integer value represents the cumulative
time (since the last time this register is cleared) that the DRAM domain has throttled. The unit of this field is
specified by the “Time Units” field of MSR_RAPL_POWER_UNIT.

Vol. 3B 14-39

POWER AND THERMAL MANAGEMENT

14-40 Vol. 3B

CHAPTER 15
MACHINE-CHECK ARCHITECTURE
This chapter describes the machine-check architecture and machine-check exception mechanism found in the
Pentium 4, Intel Xeon, Intel Atom, and P6 family processors. See Chapter 6, “Interrupt 18—Machine-Check Exception (#MC),” for more information on machine-check exceptions. A brief description of the Pentium processor’s
machine check capability is also given.
Additionally, a signaling mechanism for software to respond to hardware corrected machine check error is covered.

15.1

MACHINE-CHECK ARCHITECTURE

The Pentium 4, Intel Xeon, Intel Atom, and P6 family processors implement a machine-check architecture that
provides a mechanism for detecting and reporting hardware (machine) errors, such as: system bus errors, ECC
errors, parity errors, cache errors, and TLB errors. It consists of a set of model-specific registers (MSRs) that are
used to set up machine checking and additional banks of MSRs used for recording errors that are detected.
The processor signals the detection of an uncorrected machine-check error by generating a machine-check exception (#MC), which is an abort class exception. The implementation of the machine-check architecture does not
ordinarily permit the processor to be restarted reliably after generating a machine-check exception. However, the
machine-check-exception handler can collect information about the machine-check error from the machine-check
MSRs.
Starting with 45 nm Intel 64 processor on which CPUID reports DisplayFamily_DisplayModel as 06H_1AH (see
CPUID instruction in Chapter 3, “Instruction Set Reference, A-L” in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 2A), the processor can report information on corrected machine-check errors and
deliver a programmable interrupt for software to respond to MC errors, referred to as corrected machine-check
error interrupt (CMCI). See Section 15.5 for detail.
Intel 64 processors supporting machine-check architecture and CMCI may also support an additional enhancement, namely, support for software recovery from certain uncorrected recoverable machine check errors. See
Section 15.6 for detail.

15.2

COMPATIBILITY WITH PENTIUM PROCESSOR

The Pentium 4, Intel Xeon, Intel Atom, and P6 family processors support and extend the machine-check exception
mechanism introduced in the Pentium processor. The Pentium processor reports the following machine-check
errors:

•
•

data parity errors during read cycles
unsuccessful completion of a bus cycle

The above errors are reported using the P5_MC_TYPE and P5_MC_ADDR MSRs (implementation specific for the
Pentium processor). Use the RDMSR instruction to read these MSRs. See Chapter 2, “Model-Specific Registers
(MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4 for the addresses.
The machine-check error reporting mechanism that Pentium processors use is similar to that used in Pentium 4,
Intel Xeon, Intel Atom, and P6 family processors. When an error is detected, it is recorded in P5_MC_TYPE and
P5_MC_ADDR; the processor then generates a machine-check exception (#MC).
See Section 15.3.3, “Mapping of the Pentium Processor Machine-Check Errors to the Machine-Check Architecture,”
and Section 15.10.2, “Pentium Processor Machine-Check Exception Handling,” for information on compatibility
between machine-check code written to run on the Pentium processors and code written to run on P6 family
processors.

Vol. 3B 15-1

MACHINE-CHECK ARCHITECTURE

15.3

MACHINE-CHECK MSRS

Machine check MSRs in the Pentium 4, Intel Atom, Intel Xeon, and P6 family processors consist of a set of global
control and status registers and several error-reporting register banks. See Figure 15-1.

Error-Reporting Bank Registers
(One Set for Each Hardware Unit)

Global Control MSRs
63

0

63

IA32_MCG_CAP MSR
63

0

63

IA32_MCG_STATUS MSR
63

0
IA32_MCi_ADDR MSR

IA32_MCG_CTL MSR
0

63

0
IA32_MCi_STATUS MSR

0

63

0
IA32_MCi_CTL MSR

63

IA32_MCG_EXT_CTL MSR

0
IA32_MCi_MISC MSR
0

63
IA32_MCi_CTL2 MSR

Figure 15-1. Machine-Check MSRs
Each error-reporting bank is associated with a specific hardware unit (or group of hardware units) in the processor.
Use RDMSR and WRMSR to read and to write these registers.

15.3.1

Machine-Check Global Control MSRs

The machine-check global control MSRs include the IA32_MCG_CAP, IA32_MCG_STATUS, and optionally
IA32_MCG_CTL and IA32_MCG_EXT_CTL. See Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 4 for the addresses of these registers.

15.3.1.1

IA32_MCG_CAP MSR

The IA32_MCG_CAP MSR is a read-only register that provides information about the machine-check architecture of
the processor. Figure 15-2 shows the layout of the register.

15-2 Vol. 3B

MACHINE-CHECK ARCHITECTURE

63

27 26

25 24 23

16 15

0

12 11 10 9 8 7

Count

Reserved
MCG_LMCE_P[27]
MCG_ELOG_P[26]
MCG_EMC_P[25]
MCG_SER_P[24]
MCG_EXT_CNT[23:16]
MCG_TES_P[11]
MCG_CMCI_P[10]
MCG_EXT_P[9]
MCG_CTL_P[8]

Figure 15-2. IA32_MCG_CAP Register
Where:

•

Count field, bits 7:0 — Indicates the number of hardware unit error-reporting banks available in a particular
processor implementation.

•

MCG_CTL_P (control MSR present) flag, bit 8 — Indicates that the processor implements the
IA32_MCG_CTL MSR when set; this register is absent when clear.

•

MCG_EXT_P (extended MSRs present) flag, bit 9 — Indicates that the processor implements the extended
machine-check state registers found starting at MSR address 180H; these registers are absent when clear.

•

MCG_CMCI_P (Corrected MC error counting/signaling extension present) flag, bit 10 — Indicates
(when set) that extended state and associated MSRs necessary to support the reporting of an interrupt on a
corrected MC error event and/or count threshold of corrected MC errors, is present. When this bit is set, it does
not imply this feature is supported across all banks. Software should check the availability of the necessary
logic on a bank by bank basis when using this signaling capability (i.e. bit 30 settable in individual
IA32_MCi_CTL2 register).

•

MCG_TES_P (threshold-based error status present) flag, bit 11 — Indicates (when set) that bits 56:53
of the IA32_MCi_STATUS MSR are part of the architectural space. Bits 56:55 are reserved, and bits 54:53 are
used to report threshold-based error status. Note that when MCG_TES_P is not set, bits 56:53 of the
IA32_MCi_STATUS MSR are model-specific.

•

MCG_EXT_CNT, bits 23:16 — Indicates the number of extended machine-check state registers present. This
field is meaningful only when the MCG_EXT_P flag is set.

•

MCG_SER_P (software error recovery support present) flag, bit 24 — Indicates (when set) that the
processor supports software error recovery (see Section 15.6), and IA32_MCi_STATUS MSR bits 56:55 are
used to report the signaling of uncorrected recoverable errors and whether software must take recovery
actions for uncorrected errors. Note that when MCG_TES_P is not set, bits 56:53 of the IA32_MCi_STATUS MSR
are model-specific. If MCG_TES_P is set but MCG_SER_P is not set, bits 56:55 are reserved.

•

MCG_EMC_P (Enhanced Machine Check Capability) flag, bit 25 — Indicates (when set) that the
processor supports enhanced machine check capabilities for firmware first signaling.

•

MCG_ELOG_P (extended error logging) flag, bit 26 — Indicates (when set) that the processor allows
platform firmware to be invoked when an error is detected so that it may provide additional platform specific
information in an ACPI format “Generic Error Data Entry” that augments the data included in machine check
bank registers.
For additional information about extended error logging interface, see
https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/enhanced-mca-loggingxeon-paper.pdf.

Vol. 3B 15-3

MACHINE-CHECK ARCHITECTURE

•

MCG_LMCE_P (local machine check exception) flag, bit 27 — Indicates (when set) that the following
interfaces are present:
— an extended state LMCE_S (located in bit 3 of IA32_MCG_STATUS), and
— the IA32_MCG_EXT_CTL MSR, necessary to support Local Machine Check Exception (LMCE).
A non-zero MCG_LMCE_P indicates that, when LMCE is enabled as described in Section 15.3.1.5, some machine
check errors may be delivered to only a single logical processor.

The effect of writing to the IA32_MCG_CAP MSR is undefined.

15.3.1.2

IA32_MCG_STATUS MSR

The IA32_MCG_STATUS MSR describes the current state of the processor after a machine-check exception has
occurred (see Figure 15-3).

63

3 2 1 0

Reserved

M
C
I
P

E R
I I
P P
V V

LMCE_S—Local machine check exception signaled
MCIP—Machine check in progress flag
EIPV—Error IP valid flag
RIPV—Restart IP valid flag

Figure 15-3. IA32_MCG_STATUS Register
Where:

•

RIPV (restart IP valid) flag, bit 0 — Indicates (when set) that program execution can be restarted reliably
at the instruction pointed to by the instruction pointer pushed on the stack when the machine-check exception
is generated. When clear, the program cannot be reliably restarted at the pushed instruction pointer.

•

EIPV (error IP valid) flag, bit 1 — Indicates (when set) that the instruction pointed to by the instruction
pointer pushed onto the stack when the machine-check exception is generated is directly associated with the
error. When this flag is cleared, the instruction pointed to may not be associated with the error.

•

MCIP (machine check in progress) flag, bit 2 — Indicates (when set) that a machine-check exception was
generated. Software can set or clear this flag. The occurrence of a second Machine-Check Event while MCIP is
set will cause the processor to enter a shutdown state. For information on processor behavior in the shutdown
state, please refer to the description in Chapter 6, “Interrupt and Exception Handling”: “Interrupt 8—Double
Fault Exception (#DF)”.

•

LMCE_S (local machine check exception signaled), bit 3 — Indicates (when set) that a local machinecheck exception was generated. This indicates that the current machine-check event was delivered to only this
logical processor.

Bits 63:04 in IA32_MCG_STATUS are reserved. An attempt to write to IA32_MCG_STATUS with any value other
than 0 would result in #GP.

15.3.1.3

IA32_MCG_CTL MSR

The IA32_MCG_CTL MSR is present if the capability flag MCG_CTL_P is set in the IA32_MCG_CAP MSR.
IA32_MCG_CTL controls the reporting of machine-check exceptions. If present, writing 1s to this register enables
machine-check features and writing all 0s disables machine-check features. All other values are undefined and/or
implementation specific.

15-4 Vol. 3B

MACHINE-CHECK ARCHITECTURE

15.3.1.4

IA32_MCG_EXT_CTL MSR

The IA32_MCG_EXT_CTL MSR is present if the capability flag MCG_LMCE_P is set in the IA32_MCG_CAP MSR.
IA32_MCG_EXT_CTL.LMCE_EN (bit 0) allows the processor to signal some MCEs to only a single logical processor
in the system.
If MCG_LMCE_P is not set in IA32_MCG_CAP, or platform software has not enabled LMCE by setting
IA32_FEATURE_CONTROL.LMCE_ON (bit 20), any attempt to write or read IA32_MCG_EXT_CTL will result in #GP.
The IA32_MCG_EXT_CTL MSR is cleared on RESET.
Figure 15-4 shows the layout of the IA32_MCG_EXT_CTL register

63

1 0

Reserved

LMCE_EN - system software control to enable/disable LMCE

Figure 15-4. IA32_MCG_EXT_CTL Register
where

•

LMCE_EN (local machine check exception enable) flag, bit 0 - System software sets this to allow
hardware to signal some MCEs to only a single logical processor. System software can set LMCE_EN only if the
platform software has configured IA32_FEATURE_CONTROL as described in Section 15.3.1.5.

15.3.1.5

Enabling Local Machine Check

The intended usage of LMCE requires proper configuration by both platform software and system software. Platform software can turn LMCE on by setting bit 20 (LMCE_ON) in IA32_FEATURE_CONTROL MSR (MSR address
3AH).
System software must ensure that both IA32_FEATURE_CONTROL.Lock (bit 0)and
IA32_FEATURE_CONTROL.LMCE_ON (bit 20) are set before attempting to set IA32_MCG_EXT_CTL.LMCE_EN (bit
0). When system software has enabled LMCE, then hardware will determine if a particular error can be delivered
only to a single logical processor. Software should make no assumptions about the type of error that hardware can
choose to deliver as LMCE. The severity and override rules stay the same as described in Table 15-8 to determine
the recovery actions.

15.3.2

Error-Reporting Register Banks

Each error-reporting register bank can contain the IA32_MCi_CTL, IA32_MCi_STATUS, IA32_MCi_ADDR, and
IA32_MCi_MISC MSRs. The number of reporting banks is indicated by bits [7:0] of IA32_MCG_CAP MSR (address
0179H). The first error-reporting register (IA32_MC0_CTL) always starts at address 400H.
See Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 4 for addresses of the error-reporting registers in the Pentium 4, Intel Atom, and Intel Xeon
processors; and for addresses of the error-reporting registers P6 family processors.

15.3.2.1

IA32_MCi_CTL MSRs

The IA32_MCi_CTL MSR controls signaling of #MC for errors produced by a particular hardware unit (or group of
hardware units). Each of the 64 flags (EEj) represents a potential error. Setting an EEj flag enables signaling #MC
of the associated error and clearing it disables signaling of the error. Error logging happens regardless of the setting
of these bits. The processor drops writes to bits that are not implemented. Figure 15-5 shows the bit fields of
IA32_MCi_CTL.
Vol. 3B 15-5

MACHINE-CHECK ARCHITECTURE

63 62 61
E
E
6
3

E
E
6
2

.....

E
E
6
1

3 2 1 0
E
E
0
2

E
E
0
1

E
E
0
0

EEj—Error reporting enable flag
(where j is 00 through 63)

Figure 15-5. IA32_MCi_CTL Register

NOTE
For P6 family processors, processors based on Intel Core microarchitecture (excluding those on
which on which CPUID reports DisplayFamily_DisplayModel as 06H_1AH and onward): the
operating system or executive software must not modify the contents of the IA32_MC0_CTL MSR.
This MSR is internally aliased to the EBL_CR_POWERON MSR and controls platform-specific error
handling features. System specific firmware (the BIOS) is responsible for the appropriate initialization of the IA32_MC0_CTL MSR. P6 family processors only allow the writing of all 1s or all 0s to
the IA32_MCi_CTL MSR.

15.3.2.2

IA32_MCi_STATUS MSRS

Each IA32_MCi_STATUS MSR contains information related to a machine-check error if its VAL (valid) flag is set (see
Figure 15-6). Software is responsible for clearing IA32_MCi_STATUS MSRs by explicitly writing 0s to them; writing
1s to them causes a general-protection exception.

NOTE
Figure 15-6 depicts the IA32_MCi_STATUS MSR when IA32_MCG_CAP[24] = 1,
IA32_MCG_CAP[11] = 1 and IA32_MCG_CAP[10] = 1. When IA32_MCG_CAP[24] = 0 and
IA32_MCG_CAP[11] = 1, bits 56:55 is reserved and bits 54:53 for threshold-based error reporting.
When IA32_MCG_CAP[11] = 0, bits 56:53 are part of the “Other Information” field. The use of bits
54:53 for threshold-based error reporting began with Intel Core Duo processors, and is currently
used for cache memory. See Section 15.4, “Enhanced Cache Error reporting,” for more information.
When IA32_MCG_CAP[10] = 0, bits 52:38 are part of the “Other Information” field. The use of bits
52:38 for corrected MC error count is introduced with Intel 64 processor on which CPUID reports
DisplayFamily_DisplayModel as 06H_1AH.
Where:

•

MCA (machine-check architecture) error code field, bits 15:0 — Specifies the machine-check architecture-defined error code for the machine-check error condition detected. The machine-check architecturedefined error codes are guaranteed to be the same for all IA-32 processors that implement the machine-check
architecture. See Section 15.9, “Interpreting the MCA Error Codes,” and Chapter 16, “Interpreting MachineCheck Error Codes”, for information on machine-check error codes.

•

Model-specific error code field, bits 31:16 — Specifies the model-specific error code that uniquely
identifies the machine-check error condition detected. The model-specific error codes may differ among IA-32
processors for the same machine-check error condition. See Chapter 16, “Interpreting Machine-Check Error
Codes”for information on model-specific error codes.

•

Reserved, Error Status, and Other Information fields, bits 56:32 —

•

If IA32_MCG_CAP.MCG_EMC_P[bit 25] is 0, bits 37:32 contain “Other Information” that is implementation-specific and is not part of the machine-check architecture.

•

If IA32_MCG_CAP.MCG_EMC_P is 1, “Other Information” is in bits 36:32. If bit 37 is 0, system firmware
has not changed the contents of IA32_MCi_STATUS. If bit 37 is 1, system firmware may have edited the
contents of IA32_MCi_STATUS.

•

If IA32_MCG_CAP.MCG_CMCI_P[bit 10] is 0, bits 52:38 also contain “Other Information” (in the same
sense as bits 37:32).

15-6 Vol. 3B

MACHINE-CHECK ARCHITECTURE

63 62 61 60 59 58 57 56 55 54 53 52
V O U E
A V C N
L E
R

P S A
R
C
C

Corrected Error
Count

38 37 36

32 31

Other
Info

16 15

MSCOD Model
Specific Error Code

0

MCA Error Code

Firmware updated error status indicator (37)*
Threshold-based error status (54:53)**
AR — Recovery action required for UCR error (55)***
S — Signaling an uncorrected recoverable (UCR) error (56)***
PCC — Processor context corrupted (57)
ADDRV — MCi_ADDR register valid (58)
MISCV — MCi_MISC register valid (59)
EN — Error reporting enabled (60)
UC — Uncorrected error (61)
OVER — Error overflow (62)
VAL — MCi_STATUS register valid (63)
* When IA32_MCG_CAP[25] (MCG_EMC_P) is set, bit 37 is not part of “Other Information”.
** When IA32_MCG_CAP[11] (MCG_TES_P) is not set, these bits are model-specific
(part of “Other Information”).
*** When IA32_MCG_CAP[11] or IA32_MCG_CAP[24] are not set, these bits are reserved, or
model-specific (part of “Other Information”).

Figure 15-6. IA32_MCi_STATUS Register

•

If IA32_MCG_CAP[10] is 1, bits 52:38 are architectural (not model-specific). In this case, bits 52:38
reports the value of a 15 bit counter that increments each time a corrected error is observed by the MCA
recording bank. This count value will continue to increment until cleared by software. The most
significant bit, 52, is a sticky count overflow bit.

•
•

If IA32_MCG_CAP[11] is 0, bits 56:53 also contain “Other Information” (in the same sense).
If IA32_MCG_CAP[11] is 1, bits 56:53 are architectural (not model-specific). In this case, bits 56:53
have the following functionality:

•
•
•

If IA32_MCG_CAP[24] is 0, bits 56:55 are reserved.
If IA32_MCG_CAP[24] is 1, bits 56:55 are defined as follows:
S (Signaling) flag, bit 56 - Signals the reporting of UCR errors in this MC bank. See Section 15.6.2
for additional detail.

•

AR (Action Required) flag, bit 55 - Indicates (when set) that MCA error code specific recovery
action must be performed by system software at the time this error was signaled. See Section
15.6.2 for additional detail.

•
•

If the UC bit (Figure 15-6) is 1, bits 54:53 are undefined.
If the UC bit (Figure 15-6) is 0, bits 54:53 indicate the status of the hardware structure that
reported the threshold-based error. See Table 15-1.

Table 15-1. Bits 54:53 in IA32_MCi_STATUS MSRs when IA32_MCG_CAP[11] = 1 and UC = 0
Bits 54:53

Meaning

00

No tracking - No hardware status tracking is provided for the structure reporting this event.

01

Green - Status tracking is provided for the structure posting the event; the current status is green (below threshold).
For more information, see Section 15.4, “Enhanced Cache Error reporting”.

10

Yellow - Status tracking is provided for the structure posting the event; the current status is yellow (above threshold).
For more information, see Section 15.4, “Enhanced Cache Error reporting”.

11

Reserved

Vol. 3B 15-7

MACHINE-CHECK ARCHITECTURE

•

PCC (processor context corrupt) flag, bit 57 — Indicates (when set) that the state of the processor might
have been corrupted by the error condition detected and that reliable restarting of the processor may not be
possible. When clear, this flag indicates that the error did not affect the processor’s state, and software may be
able to restart. When system software supports recovery, consult Section 15.10.4, “Machine-Check Software
Handler Guidelines for Error Recovery” for additional rules that apply.

•

ADDRV (IA32_MCi_ADDR register valid) flag, bit 58 — Indicates (when set) that the IA32_MCi_ADDR
register contains the address where the error occurred (see Section 15.3.2.3, “IA32_MCi_ADDR MSRs”). When
clear, this flag indicates that the IA32_MCi_ADDR register is either not implemented or does not contain the
address where the error occurred. Do not read these registers if they are not implemented in the processor.

•

MISCV (IA32_MCi_MISC register valid) flag, bit 59 — Indicates (when set) that the IA32_MCi_MISC
register contains additional information regarding the error. When clear, this flag indicates that the
IA32_MCi_MISC register is either not implemented or does not contain additional information regarding the
error. Do not read these registers if they are not implemented in the processor.

•

EN (error enabled) flag, bit 60 — Indicates (when set) that the error was enabled by the associated EEj bit
of the IA32_MCi_CTL register.

•

UC (error uncorrected) flag, bit 61 — Indicates (when set) that the processor did not or was not able to
correct the error condition. When clear, this flag indicates that the processor was able to correct the error
condition.

•

OVER (machine check overflow) flag, bit 62 — Indicates (when set) that a machine-check error occurred
while the results of a previous error were still in the error-reporting register bank (that is, the VAL bit was
already set in the IA32_MCi_STATUS register). The processor sets the OVER flag and software is responsible for
clearing it. In general, enabled errors are written over disabled errors, and uncorrected errors are written over
corrected errors. Uncorrected errors are not written over previous valid uncorrected errors. When
MCG_CMCI_P is set, corrected errors may not set the OVER flag. Software can rely on corrected error count in
IA32_MCi_Status[52:38] to determine if any additional corrected errors may have occurred. For more information, see Section 15.3.2.2.1, “Overwrite Rules for Machine Check Overflow”.

•

VAL (IA32_MCi_STATUS register valid) flag, bit 63 — Indicates (when set) that the information within the
IA32_MCi_STATUS register is valid. When this flag is set, the processor follows the rules given for the OVER flag
in the IA32_MCi_STATUS register when overwriting previously valid entries. The processor sets the VAL flag
and software is responsible for clearing it.

15.3.2.2.1 Overwrite Rules for Machine Check Overflow
Table 15-2 shows the overwrite rules for how to treat a second event if the cache has already posted an event to
the MC bank – that is, what to do if the valid bit for an MC bank already is set to 1. When more than one structure
posts events in a given bank, these rules specify whether a new event will overwrite a previous posting or not.
These rules define a priority for uncorrected (highest priority), yellow, and green/unmonitored (lowest priority)
status.
In Table 15-2, the values in the two left-most columns are IA32_MCi_STATUS[54:53].

Table 15-2. Overwrite Rules for Enabled Errors

First Event

Second Event

UC bit

Color

MCA Info

00/green

00/green

0

00/green

either

00/green

yellow

0

yellow

second error

yellow

00/green

0

yellow

first error

yellow

yellow

0

yellow

either

00/green/yellow

UC

1

undefined

second

UC

00/green/yellow

1

undefined

first

If a second event overwrites a previously posted event, the information (as guarded by individual valid bits) in the
MCi bank is entirely from the second event. Similarly, if a first event is retained, all of the information previously
posted for that event is retained. In general, when the logged error or the recent error is a corrected error, the
OVER bit (MCi_Status[62]) may be set to indicate an overflow. When MCG_CMCI_P is set in IA32_MCG_CAP,
system software should consult IA32_MCi_STATUS[52:38] to determine if additional corrected errors may have

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MACHINE-CHECK ARCHITECTURE

occurred. Software may re-read IA32_MCi_STATUS, IA32_MCi_ADDR and IA32_MCi_MISC appropriately to ensure
data collected represent the last error logged.
After software polls a posting and clears the register, the valid bit is no longer set and therefore the meaning of the
rest of the bits, including the yellow/green/00 status field in bits 54:53, is undefined. The yellow/green indication
will only be posted for events associated with monitored structures – otherwise the unmonitored (00) code will be
posted in IA32_MCi_STATUS[54:53].

15.3.2.3

IA32_MCi_ADDR MSRs

The IA32_MCi_ADDR MSR contains the address of the code or data memory location that produced the machinecheck error if the ADDRV flag in the IA32_MCi_STATUS register is set (see Section 15-7, “IA32_MCi_ADDR MSR”).
The IA32_MCi_ADDR register is either not implemented or contains no address if the ADDRV flag in the
IA32_MCi_STATUS register is clear. When not implemented in the processor, all reads and writes to this MSR will
cause a general protection exception.
The address returned is an offset into a segment, linear address, or physical address. This depends on the error
encountered. When these registers are implemented, these registers can be cleared by explicitly writing 0s to
these registers. Writing 1s to these registers will cause a general-protection exception. See Figure 15-7.

Processor Without Support For Intel 64 Architecture
63

0

36 35

Address

Reserved

Processor With Support for Intel 64 Architecture
63

0

Address*

* Useful bits in this field depend on the address methodology in use when the
the register state is saved.

Figure 15-7. IA32_MCi_ADDR MSR

15.3.2.4

IA32_MCi_MISC MSRs

The IA32_MCi_MISC MSR contains additional information describing the machine-check error if the MISCV flag in
the IA32_MCi_STATUS register is set. The IA32_MCi_MISC_MSR is either not implemented or does not contain
additional information if the MISCV flag in the IA32_MCi_STATUS register is clear.
When not implemented in the processor, all reads and writes to this MSR will cause a general protection exception.
When implemented in a processor, these registers can be cleared by explicitly writing all 0s to them; writing 1s to
them causes a general-protection exception to be generated. This register is not implemented in any of the errorreporting register banks for the P6 or Intel Atom family processors.
If both MISCV and IA32_MCG_CAP[24] are set, the IA32_MCi_MISC_MSR is defined according to Figure 15-8 to
support software recovery of uncorrected errors (see Section 15.6).

Vol. 3B 15-9

MACHINE-CHECK ARCHITECTURE

9 8

63

6 5

0

Model Specific Information

Address Mode
Recoverable Address LSB

Figure 15-8. UCR Support in IA32_MCi_MISC Register

•

Recoverable Address LSB (bits 5:0): The lowest valid recoverable address bit. Indicates the position of the least
significant bit (LSB) of the recoverable error address. For example, if the processor logs bits [43:9] of the
address, the LSB sub-field in IA32_MCi_MISC is 01001b (9 decimal). For this example, bits [8:0] of the
recoverable error address in IA32_MCi_ADDR should be ignored.

•

Address Mode (bits 8:6): Address mode for the address logged in IA32_MCi_ADDR. The supported address
modes are given in Table 15-3.

Table 15-3. Address Mode in IA32_MCi_MISC[8:6]
IA32_MCi_MISC[8:6] Encoding
000

Segment Offset

001

Linear Address

010

Physical Address

011

Memory Address

100 to 110
111

•

Definition

Reserved
Generic

Model Specific Information (bits 63:9): Not architecturally defined.

15.3.2.4.2 IOMCA
Logging and Signaling of errors from PCI Express domain is governed by PCI Express Advanced Error Reporting
(AER) architecture. PCI Express architecture divides errors in two categories: Uncorrectable errors and Correctable
errors. Uncorrectable errors can further be classified as Fatal or Non-Fatal. Uncorrected IO errors are signaled to
the system software either as AER Message Signaled Interrupt (MSI) or via platform specific mechanisms such as
NMI. Generally, the signaling mechanism is controlled by BIOS and/or platform firmware. Certain processors
support an error handling mode, called IOMCA mode, where Uncorrected PCI Express errors are signaled in the
form of machine check exception and logged in machine check banks.
When a processor is in this mode, Uncorrected PCI Express errors are logged in the MCACOD field of the
IA32_MCi_STATUS register as Generic I/O error. The corresponding MCA error code is defined in Table 15-8.
IA32_MCi_Status [15:0] Simple Error Code Encoding. Machine check logging complements and does not replace
AER logging that occurs inside the PCI Express hierarchy. The PCI Express Root Complex and Endpoints continue to
log the error in accordance with PCI Express AER mechanism. In IOMCA mode, MCi_MISC register in the bank that
logged IOMCA can optionally contain information that link the Machine Check logs with the AER logs or proprietary
logs. In such a scenario, the machine check handler can utilize the contents of MCi_MISC to locate the next level of
error logs corresponding to the same error. Specifically, if MCi_Status.MISCV is 1 and MCACOD is 0x0E0B,
MCi_MISC contains the PCI Express address of the Root Complex device containing the AER Logs. Software can
consult the header type and class code registers in the Root Complex device's PCIe Configuration space to determine what type of device it is. This Root Complex device can either be a PCI Express Root Port, PCI Express Root
Complex Event Collector or a proprietary device.

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MACHINE-CHECK ARCHITECTURE

Errors that originate from PCI Express or Legacy Endpoints are logged in the corresponding Root Port in addition to
the generating device. If MISCV=1 and MCi_MISC contains the address of the Root Port or a Root Complex Event
collector, software can parse the AER logs to learn more about the error.
If MISCV=1 and MCi_MISC points to a device that is neither a Root Complex Event Collector not a Root Port, software must consult the Vendor ID/Device ID and use device specific knowledge to locate and interpret the error log
registers. In some cases, the Root Complex device configuration space may not be accessible to the software and
both the Vendor and Device ID read as 0xFFFF.

•

The format of MCi_MISC for IOMCA errors is shown in Table 15-4.

Table 15-4. Address Mode in IA32_MCi_MISC[8:6]
63:40
RSVD

39:32
PCI Express Segment
number

31:16

15:9

PCI Express
Requestor ID

8:6

RSVD

ADDR MODE

5:0
1

RECOV ADDR LSB1

NOTES:
1. Not Applicable if ADDRV=0.
Refer to PCI Express Specification 3.0 for definition of PCI Express Requestor ID and AER architecture. Refer to PCI
Firmware Specification 3.0 for an explanation of PCI Ex-press Segment number and how software can access
configuration space of a PCI Ex-press device given the segment number and Requestor ID.

15.3.2.5

IA32_MCi_CTL2 MSRs

The IA32_MCi_CTL2 MSR provides the programming interface to use corrected MC error signaling capability that is
indicated by IA32_MCG_CAP[10] = 1. Software must check for the presence of IA32_MCi_CTL2 on a per-bank
basis.
When IA32_MCG_CAP[10] = 1, the IA32_MCi_CTL2 MSR for each bank exists, i.e. reads and writes to these MSR
are supported. However, signaling interface for corrected MC errors may not be supported in all banks.
The layout of IA32_MCi_CTL2 is shown in Figure 15-9:

63

31 30 29

15 14

0

Reserved

Reserved

CMCI_EN—Enable/disable CMCI
Corrected error count threshold

Figure 15-9. IA32_MCi_CTL2 Register

•

Corrected error count threshold, bits 14:0 — Software must initialize this field. The value is compared with
the corrected error count field in IA32_MCi_STATUS, bits 38 through 52. An overflow event is signaled to the
CMCI LVT entry (see Table 10-1) in the APIC when the count value equals the threshold value. The new LVT
entry in the APIC is at 02F0H offset from the APIC_BASE. If CMCI interface is not supported for a particular
bank (but IA32_MCG_CAP[10] = 1), this field will always read 0.

•

CMCI_EN (Corrected error interrupt enable/disable/indicator), bits 30 — Software sets this bit to
enable the generation of corrected machine-check error interrupt (CMCI). If CMCI interface is not supported for
a particular bank (but IA32_MCG_CAP[10] = 1), this bit is writeable but will always return 0 for that bank. This
bit also indicates CMCI is supported or not supported in the corresponding bank. See Section 15.5 for details of
software detection of CMCI facility.

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MACHINE-CHECK ARCHITECTURE

Some microarchitectural sub-systems that are the source of corrected MC errors may be shared by more than one
logical processors. Consequently, the facilities for reporting MC errors and controlling mechanisms may be shared
by more than one logical processors. For example, the IA32_MCi_CTL2 MSR is shared between logical processors
sharing a processor core. Software is responsible to program IA32_MCi_CTL2 MSR in a consistent manner with
CMCI delivery and usage.
After processor reset, IA32_MCi_CTL2 MSRs are zero’ed.

15.3.2.6

IA32_MCG Extended Machine Check State MSRs

The Pentium 4 and Intel Xeon processors implement a variable number of extended machine-check state MSRs.
The MCG_EXT_P flag in the IA32_MCG_CAP MSR indicates the presence of these extended registers, and the
MCG_EXT_CNT field indicates the number of these registers actually implemented. See Section 15.3.1.1,
“IA32_MCG_CAP MSR.” Also see Table 15-5.

Table 15-5. Extended Machine Check State MSRs
in Processors Without Support for Intel 64 Architecture
MSR

Address

Description

IA32_MCG_EAX

180H

Contains state of the EAX register at the time of the machine-check error.

IA32_MCG_EBX

181H

Contains state of the EBX register at the time of the machine-check error.

IA32_MCG_ECX

182H

Contains state of the ECX register at the time of the machine-check error.

IA32_MCG_EDX

183H

Contains state of the EDX register at the time of the machine-check error.

IA32_MCG_ESI

184H

Contains state of the ESI register at the time of the machine-check error.

IA32_MCG_EDI

185H

Contains state of the EDI register at the time of the machine-check error.

IA32_MCG_EBP

186H

Contains state of the EBP register at the time of the machine-check error.

IA32_MCG_ESP

187H

Contains state of the ESP register at the time of the machine-check error.

IA32_MCG_EFLAGS

188H

Contains state of the EFLAGS register at the time of the machine-check error.

IA32_MCG_EIP

189H

Contains state of the EIP register at the time of the machine-check error.

IA32_MCG_MISC

18AH

When set, indicates that a page assist or page fault occurred during DS normal
operation.

In processors with support for Intel 64 architecture, 64-bit machine check state MSRs are aliased to the legacy
MSRs. In addition, there may be registers beyond IA32_MCG_MISC. These may include up to five reserved MSRs
(IA32_MCG_RESERVED[1:5]) and save-state MSRs for registers introduced in 64-bit mode. See Table 15-6.

Table 15-6. Extended Machine Check State MSRs
In Processors With Support For Intel 64 Architecture
MSR

Address

Description

IA32_MCG_RAX

180H

Contains state of the RAX register at the time of the machine-check error.

IA32_MCG_RBX

181H

Contains state of the RBX register at the time of the machine-check error.

IA32_MCG_RCX

182H

Contains state of the RCX register at the time of the machine-check error.

IA32_MCG_RDX

183H

Contains state of the RDX register at the time of the machine-check error.

IA32_MCG_RSI

184H

Contains state of the RSI register at the time of the machine-check error.

IA32_MCG_RDI

185H

Contains state of the RDI register at the time of the machine-check error.

IA32_MCG_RBP

186H

Contains state of the RBP register at the time of the machine-check error.

IA32_MCG_RSP

187H

Contains state of the RSP register at the time of the machine-check error.

IA32_MCG_RFLAGS

188H

Contains state of the RFLAGS register at the time of the machine-check error.

IA32_MCG_RIP

189H

Contains state of the RIP register at the time of the machine-check error.

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MACHINE-CHECK ARCHITECTURE

Table 15-6. Extended Machine Check State MSRs
In Processors With Support For Intel 64 Architecture (Contd.)
MSR

Address

Description

IA32_MCG_MISC

18AH

When set, indicates that a page assist or page fault occurred during DS normal
operation.

IA32_MCG_
RSERVED[1:5]

18BH18FH

These registers, if present, are reserved.

IA32_MCG_R8

190H

Contains state of the R8 register at the time of the machine-check error.

IA32_MCG_R9

191H

Contains state of the R9 register at the time of the machine-check error.

IA32_MCG_R10

192H

Contains state of the R10 register at the time of the machine-check error.

IA32_MCG_R11

193H

Contains state of the R11 register at the time of the machine-check error.

IA32_MCG_R12

194H

Contains state of the R12 register at the time of the machine-check error.

IA32_MCG_R13

195H

Contains state of the R13 register at the time of the machine-check error.

IA32_MCG_R14

196H

Contains state of the R14 register at the time of the machine-check error.

IA32_MCG_R15

197H

Contains state of the R15 register at the time of the machine-check error.

When a machine-check error is detected on a Pentium 4 or Intel Xeon processor, the processor saves the state of
the general-purpose registers, the R/EFLAGS register, and the R/EIP in these extended machine-check state MSRs.
This information can be used by a debugger to analyze the error.
These registers are read/write to zero registers. This means software can read them; but if software writes to
them, only all zeros is allowed. If software attempts to write a non-zero value into one of these registers, a generalprotection (#GP) exception is generated. These registers are cleared on a hardware reset (power-up or RESET),
but maintain their contents following a soft reset (INIT reset).

15.3.3

Mapping of the Pentium Processor Machine-Check Errors
to the Machine-Check Architecture

The Pentium processor reports machine-check errors using two registers: P5_MC_TYPE and P5_MC_ADDR. The
Pentium 4, Intel Xeon, Intel Atom, and P6 family processors map these registers to the IA32_MCi_STATUS and
IA32_MCi_ADDR in the error-reporting register bank. This bank reports on the same type of external bus errors
reported in P5_MC_TYPE and P5_MC_ADDR.
The information in these registers can then be accessed in two ways:

•

By reading the IA32_MCi_STATUS and IA32_MCi_ADDR registers as part of a general machine-check exception
handler written for Pentium 4, Intel Atom and P6 family processors.

•

By reading the P5_MC_TYPE and P5_MC_ADDR registers using the RDMSR instruction.

The second capability permits a machine-check exception handler written to run on a Pentium processor to be run
on a Pentium 4, Intel Xeon, Intel Atom, or P6 family processor. There is a limitation in that information returned by
the Pentium 4, Intel Xeon, Intel Atom, and P6 family processors is encoded differently than information returned
by the Pentium processor. To run a Pentium processor machine-check exception handler on a Pentium 4, Intel
Xeon, Intel Atom, or P6 family processor; the handler must be written to interpret P5_MC_TYPE encodings
correctly.

15.4

ENHANCED CACHE ERROR REPORTING

Starting with Intel Core Duo processors, cache error reporting was enhanced. In earlier Intel processors, cache
status was based on the number of correction events that occurred in a cache. In the new paradigm, called
“threshold-based error status”, cache status is based on the number of lines (ECC blocks) in a cache that incur
repeated corrections. The threshold is chosen by Intel, based on various factors. If a processor supports thresholdbased error status, it sets IA32_MCG_CAP[11] (MCG_TES_P) to 1; if not, to 0.

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A processor that supports enhanced cache error reporting contains hardware that tracks the operating status of
certain caches and provides an indicator of their “health”. The hardware reports a “green” status when the number
of lines that incur repeated corrections is at or below a pre-defined threshold, and a “yellow” status when the
number of affected lines exceeds the threshold. Yellow status means that the cache reporting the event is operating
correctly, but you should schedule the system for servicing within a few weeks.
Intel recommends that you rely on this mechanism for structures supported by threshold-base error reporting.
The CPU/system/platform response to a yellow event should be less severe than its response to an uncorrected
error. An uncorrected error means that a serious error has actually occurred, whereas the yellow condition is a
warning that the number of affected lines has exceeded the threshold but is not, in itself, a serious event: the error
was corrected and system state was not compromised.
The green/yellow status indicator is not a foolproof early warning for an uncorrected error resulting from the failure
of two bits in the same ECC block. Such a failure can occur and cause an uncorrected error before the yellow
threshold is reached. However, the chance of an uncorrected error increases as the number of affected lines
increases.

15.5

CORRECTED MACHINE CHECK ERROR INTERRUPT

Corrected machine-check error interrupt (CMCI) is an architectural enhancement to the machine-check architecture. It provides capabilities beyond those of threshold-based error reporting (Section 15.4). With threshold-based
error reporting, software is limited to use periodic polling to query the status of hardware corrected MC errors.
CMCI provides a signaling mechanism to deliver a local interrupt based on threshold values that software can
program using the IA32_MCi_CTL2 MSRs.
CMCI is disabled by default. System software is required to enable CMCI for each IA32_MCi bank that support the
reporting of hardware corrected errors if IA32_MCG_CAP[10] = 1.
System software use IA32_MCi_CTL2 MSR to enable/disable the CMCI capability for each bank and program
threshold values into IA32_MCi_CTL2 MSR. CMCI is not affected by the CR4.MCE bit, and it is not affected by the
IA32_MCi_CTL MSRs.
To detect the existence of thresholding for a given bank, software writes only bits 14:0 with the threshold value. If
the bits persist, then thresholding is available (and CMCI is available). If the bits are all 0's, then no thresholding
exists. To detect that CMCI signaling exists, software writes a 1 to bit 30 of the MCi_CTL2 register. Upon subsequent
read, if bit 30 = 0, no CMCI is available for this bank and no corrected or UCNA errors will be reported on this bank.
If bit 30 = 1, then CMCI is available and enabled.

15.5.1

CMCI Local APIC Interface

The operation of CMCI is depicted in Figure 15-10.

63

Software write 1 to enable
31 30 29

Error threshold

?=
53 52
MCi_STATUS

0

14

MCi_CTL2

Count overflow threshold -> CMCI LVT in local APIC

38 37

0

Error count

Figure 15-10. CMCI Behavior

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CMCI interrupt delivery is configured by writing to the LVT CMCI register entry in the local APIC register space at
default address of APIC_BASE + 2F0H. A CMCI interrupt can be delivered to more than one logical processors if
multiple logical processors are affected by the associated MC errors. For example, if a corrected bit error in a cache
shared by two logical processors caused a CMCI, the interrupt will be delivered to both logical processors sharing
that microarchitectural sub-system. Similarly, package level errors may cause CMCI to be delivered to all logical
processors within the package. However, system level errors will not be handled by CMCI.
See Section 10.5.1, “Local Vector Table” for details regarding the LVT CMCI register.

15.5.2

System Software Recommendation for Managing CMCI and Machine Check Resources

System software must enable and manage CMCI, set up interrupt handlers to service CMCI interrupts delivered to
affected logical processors, program CMCI LVT entry, and query machine check banks that are shared by more
than one logical processors.
This section describes techniques system software can implement to manage CMCI initialization, service CMCI
interrupts in a efficient manner to minimize contentions to access shared MSR resources.

15.5.2.1

CMCI Initialization

Although a CMCI interrupt may be delivered to more than one logical processors depending on the nature of the
corrected MC error, only one instance of the interrupt service routine needs to perform the necessary service and
make queries to the machine-check banks. The following steps describes a technique that limits the amount of
work the system has to do in response to a CMCI.

•

To provide maximum flexibility, system software should define per-thread data structure for each logical
processor to allow equal-opportunity and efficient response to interrupt delivery. Specifically, the per-thread
data structure should include a set of per-bank fields to track which machine check bank it needs to access in
response to a delivered CMCI interrupt. The number of banks that needs to be tracked is determined by
IA32_MCG_CAP[7:0].

•

Initialization of per-thread data structure. The initialization of per-thread data structure must be done serially
on each logical processor in the system. The sequencing order to start the per-thread initialization between
different logical processor is arbitrary. But it must observe the following specific detail to satisfy the shared
nature of specific MSR resources:
a. Each thread initializes its data structure to indicate that it does not own any MC bank registers.
b. Each thread examines IA32_MCi_CTL2[30] indicator for each bank to determine if another thread has
already claimed ownership of that bank.

c.

•

•

If IA32_MCi_CTL2[30] had been set by another thread. This thread can not own bank i and should
proceed to step b. and examine the next machine check bank until all of the machine check banks are
exhausted.

•

If IA32_MCi_CTL2[30] = 0, proceed to step c.

Check whether writing a 1 into IA32_MCi_CTL2[30] can return with 1 on a subsequent read to determine
this bank can support CMCI.

•

If IA32_MCi_CTL2[30] = 0, this bank does not support CMCI. This thread can not own bank i and should
proceed to step b. and examine the next machine check bank until all of the machine check banks are
exhausted.

•

If IA32_MCi_CTL2[30] = 1, modify the per-thread data structure to indicate this thread claims
ownership to the MC bank; proceed to initialize the error threshold count (bits 15:0) of that bank as
described in Chapter 15, “CMCI Threshold Management”. Then proceed to step b. and examine the next
machine check bank until all of the machine check banks are exhausted.

After the thread has examined all of the machine check banks, it sees if it owns any MC banks to service CMCI.
If any bank has been claimed by this thread:
— Ensure that the CMCI interrupt handler has been set up as described in Chapter 15, “CMCI Interrupt
Handler”.
— Initialize the CMCI LVT entry, as described in Section 15.5.1, “CMCI Local APIC Interface”.
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— Log and clear all of IA32_MCi_Status registers for the banks that this thread owns. This will allow new
errors to be logged.

15.5.2.2

CMCI Threshold Management

The Corrected MC error threshold field, IA32_MCi_CTL2[15:0], is architecturally defined. Specifically, all these bits
are writable by software, but different processor implementations may choose to implement less than 15 bits as
threshold for the overflow comparison with IA32_MCi_STATUS[52:38]. The following describes techniques that
software can manage CMCI threshold to be compatible with changes in implementation characteristics:

•

Software can set the initial threshold value to 1 by writing 1 to IA32_MCi_CTL2[15:0]. This will cause overflow
condition on every corrected MC error and generates a CMCI interrupt.

•

To increase the threshold and reduce the frequency of CMCI servicing:
a. Find the maximum threshold value a given processor implementation supports. The steps are:

•
•

Write 7FFFH to IA32_MCi_CTL2[15:0],
Read back IA32_MCi_CTL2[15:0], the lower 15 bits (14:0) is the maximum threshold supported by the
processor.

b. Increase the threshold to a value below the maximum value discovered using step a.

15.5.2.3

CMCI Interrupt Handler

The following describes techniques system software may consider to implement a CMCI service routine:

•

The service routine examines its private per-thread data structure to check which set of MC banks it has
ownership. If the thread does not have ownership of a given MC bank, proceed to the next MC bank. Ownership
is determined at initialization time which is described in Section [Cross Reference to 14.5.2.1].

If the thread had claimed ownership to an MC bank, this technique will allow each logical processors to handle
corrected MC errors independently and requires no synchronization to access shared MSR resources. Consult
Example 15-5 for guidelines on logging when processing CMCI.

15.6

RECOVERY OF UNCORRECTED RECOVERABLE (UCR) ERRORS

Recovery of uncorrected recoverable machine check errors is an enhancement in machine-check architecture. The
first processor that supports this feature is 45 nm Intel 64 processor on which CPUID reports
DisplayFamily_DisplayModel as 06H_2EH (see CPUID instruction in Chapter 3, “Instruction Set Reference, A-L” in
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A). This allow system software to
perform recovery action on certain class of uncorrected errors and continue execution.

15.6.1

Detection of Software Error Recovery Support

Software must use bit 24 of IA32_MCG_CAP (MCG_SER_P) to detect the presence of software error recovery
support (see Figure 15-2). When IA32_MCG_CAP[24] is set, this indicates that the processor supports software
error recovery. When this bit is clear, this indicates that there is no support for error recovery from the processor
and the primary responsibility of the machine check handler is logging the machine check error information and
shutting down the system.
The new class of architectural MCA errors from which system software can attempt recovery is called Uncorrected
Recoverable (UCR) Errors. UCR errors are uncorrected errors that have been detected and signaled but have not
corrupted the processor context. For certain UCR errors, this means that once system software has performed a
certain recovery action, it is possible to continue execution on this processor. UCR error reporting provides an error
containment mechanism for data poisoning. The machine check handler will use the error log information from the
error reporting registers to analyze and implement specific error recovery actions for UCR errors.

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15.6.2

UCR Error Reporting and Logging

IA32_MCi_STATUS MSR is used for reporting UCR errors and existing corrected or uncorrected errors. The definitions of IA32_MCi_STATUS, including bit fields to identify UCR errors, is shown in Figure 15-6. UCR errors can be
signaled through either the corrected machine check interrupt (CMCI) or machine check exception (MCE) path
depending on the type of the UCR error.
When IA32_MCG_CAP[24] is set, a UCR error is indicated by the following bit settings in the IA32_MCi_STATUS
register:

•
•
•

Valid (bit 63) = 1
UC (bit 61) = 1
PCC (bit 57) = 0

Additional information from the IA32_MCi_MISC and the IA32_MCi_ADDR registers for the UCR error are available
when the ADDRV and the MISCV flags in the IA32_MCi_STATUS register are set (see Section 15.3.2.4). The MCA
error code field of the IA32_MCi_STATUS register indicates the type of UCR error. System software can interpret
the MCA error code field to analyze and identify the necessary recovery action for the given UCR error.
In addition, the IA32_MCi_STATUS register bit fields, bits 56:55, are defined (see Figure 15-6) to provide additional information to help system software to properly identify the necessary recovery action for the UCR error:

•

S (Signaling) flag, bit 56 - Indicates (when set) that a machine check exception was generated for the UCR
error reported in this MC bank and system software needs to check the AR flag and the MCA error code fields in
the IA32_MCi_STATUS register to identify the necessary recovery action for this error. When the S flag in the
IA32_MCi_STATUS register is clear, this UCR error was not signaled via a machine check exception and instead
was reported as a corrected machine check (CMC). System software is not required to take any recovery action
when the S flag in the IA32_MCi_STATUS register is clear.

•

AR (Action Required) flag, bit 55 - Indicates (when set) that MCA error code specific recovery action must be
performed by system software at the time this error was signaled. This recovery action must be completed
successfully before any additional work is scheduled for this processor. When the RIPV flag in the
IA32_MCG_STATUS is clear, an alternative execution stream needs to be provided; when the MCA error code
specific recovery specific recovery action cannot be successfully completed, system software must shut down
the system. When the AR flag in the IA32_MCi_STATUS register is clear, system software may still take MCA
error code specific recovery action but this is optional; system software can safely resume program execution
at the instruction pointer saved on the stack from the machine check exception when the RIPV flag in the
IA32_MCG_STATUS register is set.

Both the S and the AR flags in the IA32_MCi_STATUS register are defined to be sticky bits, which mean that once
set, the processor does not clear them. Only software and good power-on reset can clear the S and the AR-flags.
Both the S and the AR flags are only set when the processor reports the UCR errors (MCG_CAP[24] is set).

15.6.3

UCR Error Classification

With the S and AR flag encoding in the IA32_MCi_STATUS register, UCR errors can be classified as:

•

Uncorrected no action required (UCNA) - is a UCR error that is not signaled via a machine check exception and,
instead, is reported to system software as a corrected machine check error. UCNA errors indicate that some
data in the system is corrupted, but the data has not been consumed and the processor state is valid and you
may continue execution on this processor. UCNA errors require no action from system software to continue
execution. A UNCA error is indicated with UC=1, PCC=0, S=0 and AR=0 in the IA32_MCi_STATUS register.

•

Software recoverable action optional (SRAO) - a UCR error is signaled either via a machine check exception or
CMCI. System software recovery action is optional and not required to continue execution from this machine
check exception. SRAO errors indicate that some data in the system is corrupt, but the data has not been
consumed and the processor state is valid. SRAO errors provide the additional error information for system
software to perform a recovery action. An SRAO error when signaled as a machine check is indicated with
UC=1, PCC=0, S=1, EN=1 and AR=0 in the IA32_MCi_STATUS register. In cases when SRAO is signaled via
CMCI the error signature is indicated via UC=1, PCC=0, S=0. Recovery actions for SRAO errors are MCA error
code specific. The MISCV and the ADDRV flags in the IA32_MCi_STATUS register are set when the additional
error information is available from the IA32_MCi_MISC and the IA32_MCi_ADDR registers. System software
needs to inspect the MCA error code fields in the IA32_MCi_STATUS register to identify the specific recovery

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MACHINE-CHECK ARCHITECTURE

action for a given SRAO error. If MISCV and ADDRV are not set, it is recommended that no system software
error recovery be performed however, system software can resume execution.

•

Software recoverable action required (SRAR) - a UCR error that requires system software to take a recovery
action on this processor before scheduling another stream of execution on this processor. SRAR errors indicate
that the error was detected and raised at the point of the consumption in the execution flow. An SRAR error is
indicated with UC=1, PCC=0, S=1, EN=1 and AR=1 in the IA32_MCi_STATUS register. Recovery actions are
MCA error code specific. The MISCV and the ADDRV flags in the IA32_MCi_STATUS register are set when the
additional error information is available from the IA32_MCi_MISC and the IA32_MCi_ADDR registers. System
software needs to inspect the MCA error code fields in the IA32_MCi_STATUS register to identify the specific
recovery action for a given SRAR error. If MISCV and ADDRV are not set, it is recommended that system
software shutdown the system.

Table 15-7 summarizes UCR, corrected, and uncorrected errors.

Table 15-7. MC Error Classifications

Type of Error1

UC

EN

PCC

S

AR

Signaling Software Action

Uncorrected Error (UC)

1

1

1

x

x

MCE

If EN=1, reset the system, else log
and OK to keep the system running.

SRAR

1

1

0

1

1

MCE

For known MCACOD, take specific
recovery action;

Example

Cache to processor load
error.

For unknown MCACOD, must
bugcheck.
If OVER=1, reset system, else take
specific recovery action.
SRAO

1

x2

0

x2 0

MCE/CMC

For known MCACOD, take specific
recovery action;

Patrol scrub and explicit
writeback poison errors.

For unknown MCACOD, OK to keep
the system running.
UCNA

1

x

0

0

0

CMC

Log the error and Ok to keep the
system running.

Poison detection error.

Corrected Error (CE)

0

x

x

x

x

CMC

Log the error and no corrective
action required.

ECC in caches and
memory.

NOTES:
1. SRAR, SRAO and UCNA errors are supported by the processor only when IA32_MCG_CAP[24] (MCG_SER_P) is set.
2. EN=1, S=1 when signaled via MCE. EN=x, S=0 when signaled via CMC.

15.6.4

UCR Error Overwrite Rules

In general, the overwrite rules are as follows:

•
•
•
•

UCR errors will overwrite corrected errors.
Uncorrected (PCC=1) errors overwrite UCR (PCC=0) errors.
UCR errors are not written over previous UCR errors.
Corrected errors do not write over previous UCR errors.

Regardless of whether the 1st error is retained or the 2nd error is overwritten over the 1st error, the OVER flag in
the IA32_MCi_STATUS register will be set to indicate an overflow condition. As the S flag and AR flag in the
IA32_MCi_STATUS register are defined to be sticky flags, a second event cannot clear these 2 flags once set,
however the MC bank information may be filled in for the 2nd error. The table below shows the overwrite rules and
how to treat a second error if the first event is already logged in a MC bank along with the resulting bit setting of
the UC, PCC, and AR flags in the IA32_MCi_STATUS register. As UCNA and SRA0 errors do not require recovery
action from system software to continue program execution, a system reset by system software is not required
unless the AR flag or PCC flag is set for the UCR overflow case (OVER=1, VAL=1, UC=1, PCC=0).

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MACHINE-CHECK ARCHITECTURE

Table 15-8 lists overwrite rules for uncorrected errors, corrected errors, and uncorrected recoverable errors.

Table 15-8. Overwrite Rules for UC, CE, and UCR Errors

First Event

Second Event

UC

PCC

S

MCA Bank

Reset System

CE

UCR

1

0

0 if UCNA, else 1 1 if SRAR, else 0

AR

second

yes, if AR=1

UCR

CE

1

0

0 if UCNA, else 1 1 if SRAR, else 0

first

yes, if AR=1

UCNA

UCNA

1

0

0

first

no

0

UCNA

SRAO

1

0

1

0

first

no

UCNA

SRAR

1

0

1

1

first

yes

SRAO

UCNA

1

0

1

0

first

no

SRAO

SRAO

1

0

1

0

first

no

SRAO

SRAR

1

0

1

1

first

yes

SRAR

UCNA

1

0

1

1

first

yes

SRAR

SRAO

1

0

1

1

first

yes

SRAR

SRAR

1

0

1

1

first

yes

UCR

UC

1

1

undefined

undefined

second

yes

UC

UCR

1

1

undefined

undefined

first

yes

15.7

MACHINE-CHECK AVAILABILITY

The machine-check architecture and machine-check exception (#MC) are model-specific features. Software can
execute the CPUID instruction to determine whether a processor implements these features. Following the execution of the CPUID instruction, the settings of the MCA flag (bit 14) and MCE flag (bit 7) in EDX indicate whether the
processor implements the machine-check architecture and machine-check exception.

15.8

MACHINE-CHECK INITIALIZATION

To use the processors machine-check architecture, software must initialize the processor to activate the machinecheck exception and the error-reporting mechanism.
Example 15-1 gives pseudocode for performing this initialization. This pseudocode checks for the existence of the
machine-check architecture and exception; it then enables machine-check exception and the error-reporting
register banks. The pseudocode shown is compatible with the Pentium 4, Intel Xeon, Intel Atom, P6 family, and
Pentium processors.
Following power up or power cycling, IA32_MCi_STATUS registers are not guaranteed to have valid data until after
they are initially cleared to zero by software (as shown in the initialization pseudocode in Example 15-1). In addition, when using P6 family processors, software must set MCi_STATUS registers to zero when doing a soft-reset.
Example 15-1. Machine-Check Initialization Pseudocode
Check CPUID Feature Flags for MCE and MCA support
IF CPU supports MCE
THEN
IF CPU supports MCA
THEN
IF (IA32_MCG_CAP.MCG_CTL_P = 1)
(* IA32_MCG_CTL register is present *)
THEN
IA32_MCG_CTL ← FFFFFFFFFFFFFFFFH;
(* enables all MCA features *)
FI
IF (IA32_MCG_CAP.MCG_LMCE_P = 1 and IA32_FEATURE_CONTROL.LOCK = 1 and IA32_FEATURE_CONTROL.LMCE_ON= 1)

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(* IA32_MCG_EXT_CTL register is present and platform has enabled LMCE to permit system software to use LMCE *)
THEN
IA32_MCG_EXT_CTL ← IA32_MCG_EXT_CTL | 01H;
(* System software enables LMCE capability for hardware to signal MCE to a single logical processor*)
FI
(* Determine number of error-reporting banks supported *)
COUNT← IA32_MCG_CAP.Count;
MAX_BANK_NUMBER ← COUNT - 1;
IF (Processor Family is 6H and Processor EXTMODEL:MODEL is less than 1AH)
THEN
(* Enable logging of all errors except for MC0_CTL register *)
FOR error-reporting banks (1 through MAX_BANK_NUMBER)
DO
IA32_MCi_CTL ← 0FFFFFFFFFFFFFFFFH;
OD
ELSE
(* Enable logging of all errors including MC0_CTL register *)
FOR error-reporting banks (0 through MAX_BANK_NUMBER)
DO
IA32_MCi_CTL ← 0FFFFFFFFFFFFFFFFH;
OD
FI
(* BIOS clears all errors only on power-on reset *)
IF (BIOS detects Power-on reset)
THEN
FOR error-reporting banks (0 through MAX_BANK_NUMBER)
DO
IA32_MCi_STATUS ← 0;
OD
ELSE
FOR error-reporting banks (0 through MAX_BANK_NUMBER)
DO
(Optional for BIOS and OS) Log valid errors
(OS only) IA32_MCi_STATUS ← 0;
OD

FI

FI

Setup the Machine Check Exception (#MC) handler for vector 18 in IDT
Set the MCE bit (bit 6) in CR4 register to enable Machine-Check Exceptions
FI

15.9

INTERPRETING THE MCA ERROR CODES

When the processor detects a machine-check error condition, it writes a 16-bit error code to the MCA error code
field of one of the IA32_MCi_STATUS registers and sets the VAL (valid) flag in that register. The processor may also
write a 16-bit model-specific error code in the IA32_MCi_STATUS register depending on the implementation of the
machine-check architecture of the processor.
The MCA error codes are architecturally defined for Intel 64 and IA-32 processors. To determine the cause of a
machine-check exception, the machine-check exception handler must read the VAL flag for each
IA32_MCi_STATUS register. If the flag is set, the machine check-exception handler must then read the MCA error
code field of the register. It is the encoding of the MCA error code field [15:0] that determines the type of error
being reported and not the register bank reporting it.
There are two types of MCA error codes: simple error codes and compound error codes.

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15.9.1

Simple Error Codes

Table 15-9 shows the simple error codes. These unique codes indicate global error information.

Table 15-9. IA32_MCi_Status [15:0] Simple Error Code Encoding
Error Code

Binary Encoding

Meaning

No Error

0000 0000 0000 0000

No error has been reported to this bank of error-reporting
registers.

Unclassified

0000 0000 0000 0001

This error has not been classified into the MCA error classes.

Microcode ROM Parity Error

0000 0000 0000 0010

Parity error in internal microcode ROM

External Error

0000 0000 0000 0011

The BINIT# from another processor caused this processor to
enter machine check.1

FRC Error

0000 0000 0000 0100

FRC (functional redundancy check) master/slave error

Internal Parity Error

0000 0000 0000 0101

Internal parity error.

SMM Handler Code Access
Violation

0000 0000 0000 0110

An attempt was made by the SMM Handler to execute
outside the ranges specified by SMRR.

Internal Timer Error

0000 0100 0000 0000

Internal timer error.

I/O Error

0000 1110 0000 1011

generic I/O error.

Internal Unclassified

0000 01xx xxxx xxxx

Internal unclassified errors. 2

NOTES:
1. BINIT# assertion will cause a machine check exception if the processor (or any processor on the same external bus) has BINIT#
observation enabled during power-on configuration (hardware strapping) and if machine check exceptions are enabled (by setting
CR4.MCE = 1).
2. At least one X must equal one. Internal unclassified errors have not been classified.

15.9.2

Compound Error Codes

Compound error codes describe errors related to the TLBs, memory, caches, bus and interconnect logic, and
internal timer. A set of sub-fields is common to all of compound errors. These sub-fields describe the type of
access, level in the cache hierarchy, and type of request. Table 15-10 shows the general form of the compound
error codes.

Table 15-10. IA32_MCi_Status [15:0] Compound Error Code Encoding
Type

Form

Interpretation

Generic Cache Hierarchy

000F 0000 0000 11LL

Generic cache hierarchy error

TLB Errors

000F 0000 0001 TTLL

{TT}TLB{LL}_ERR

Memory Controller Errors

000F 0000 1MMM CCCC

{MMM}_CHANNEL{CCCC}_ERR

Cache Hierarchy Errors

000F 0001 RRRR TTLL

{TT}CACHE{LL}_{RRRR}_ERR

Bus and Interconnect Errors

000F 1PPT RRRR IILL

BUS{LL}_{PP}_{RRRR}_{II}_{T}_ERR

The “Interpretation” column in the table indicates the name of a compound error. The name is constructed by
substituting mnemonics for the sub-field names given within curly braces. For example, the error code
ICACHEL1_RD_ERR is constructed from the form:
{TT}CACHE{LL}_{RRRR}_ERR,
where {TT} is replaced by I, {LL} is replaced by L1, and {RRRR} is replaced by RD.

For more information on the “Form” and “Interpretation” columns, see Sections Section 15.9.2.1, “Correction
Report Filtering (F) Bit” through Section 15.9.2.5, “Bus and Interconnect Errors”.

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15.9.2.1

Correction Report Filtering (F) Bit

Starting with Intel Core Duo processors, bit 12 in the “Form” column in Table 15-10 is used to indicate that a particular posting to a log may be the last posting for corrections in that line/entry, at least for some time:

•
•

0 in bit 12 indicates “normal” filtering (original P6/Pentium4/Atom/Xeon processor meaning).
1 in bit 12 indicates “corrected” filtering (filtering is activated for the line/entry in the posting). Filtering means
that some or all of the subsequent corrections to this entry (in this structure) will not be posted. The enhanced
error reporting introduced with the Intel Core Duo processors is based on tracking the lines affected by
repeated corrections (see Section 15.4, “Enhanced Cache Error reporting”). This capability is indicated by
IA32_MCG_CAP[11]. Only the first few correction events for a line are posted; subsequent redundant
correction events to the same line are not posted. Uncorrected events are always posted.

The behavior of error filtering after crossing the yellow threshold is model-specific. Filtering has meaning only for
corrected errors (UC=0 in IA32_MCi_STATUS MSR). System software must ignore filtering bit (12) for uncorrected
errors.

15.9.2.2

Transaction Type (TT) Sub-Field

The 2-bit TT sub-field (Table 15-11) indicates the type of transaction (data, instruction, or generic). The sub-field
applies to the TLB, cache, and interconnect error conditions. Note that interconnect error conditions are primarily
associated with P6 family and Pentium processors, which utilize an external APIC bus separate from the system
bus. The generic type is reported when the processor cannot determine the transaction type.

Table 15-11. Encoding for TT (Transaction Type) Sub-Field
Transaction Type

Mnemonic

Binary Encoding

Instruction

I

00

Data

D

01

Generic

G

10

15.9.2.3

Level (LL) Sub-Field

The 2-bit LL sub-field (see Table 15-12) indicates the level in the memory hierarchy where the error occurred (level
0, level 1, level 2, or generic). The LL sub-field also applies to the TLB, cache, and interconnect error conditions.
The Pentium 4, Intel Xeon, Intel Atom, and P6 family processors support two levels in the cache hierarchy and one
level in the TLBs. Again, the generic type is reported when the processor cannot determine the hierarchy level.

Table 15-12. Level Encoding for LL (Memory Hierarchy Level) Sub-Field
Hierarchy Level

Mnemonic

Binary Encoding

Level 0

L0

00

Level 1

L1

01

Level 2

L2

10

Generic

LG

11

15.9.2.4

Request (RRRR) Sub-Field

The 4-bit RRRR sub-field (see Table 15-13) indicates the type of action associated with the error. Actions include
read and write operations, prefetches, cache evictions, and snoops. Generic error is returned when the type of
error cannot be determined. Generic read and generic write are returned when the processor cannot determine the
type of instruction or data request that caused the error. Eviction and snoop requests apply only to the caches. All
of the other requests apply to TLBs, caches and interconnects.

Table 15-13. Encoding of Request (RRRR) Sub-Field
Request Type

Mnemonic

Binary Encoding

Generic Error

ERR

0000

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Table 15-13. Encoding of Request (RRRR) Sub-Field (Contd.)
Generic Read

RD

0001

Generic Write

WR

0010

Data Read

DRD

0011

Data Write

DWR

0100

Instruction Fetch

IRD

0101

Prefetch

PREFETCH

0110

Eviction

EVICT

0111

Snoop

SNOOP

1000

15.9.2.5

Bus and Interconnect Errors

The bus and interconnect errors are defined with the 2-bit PP (participation), 1-bit T (time-out), and 2-bit II
(memory or I/O) sub-fields, in addition to the LL and RRRR sub-fields (see Table 15-14). The bus error conditions
are implementation dependent and related to the type of bus implemented by the processor. Likewise, the interconnect error conditions are predicated on a specific implementation-dependent interconnect model that describes
the connections between the different levels of the storage hierarchy. The type of bus is implementation dependent, and as such is not specified in this document. A bus or interconnect transaction consists of a request involving
an address and a response.

Table 15-14. Encodings of PP, T, and II Sub-Fields
Sub-Field

Transaction

Mnemonic

Binary Encoding

PP (Participation)

Local processor* originated request

SRC

00

Local processor* responded to request

RES

01

Local processor* observed error as third party

OBS

10

Request timed out

TIMEOUT

1

Request did not time out

NOTIMEOUT

0

Memory Access

M

00

IO

10

Generic
T (Time-out)
II (Memory or I/O)

11

Reserved
I/O

01

Other transaction

11

NOTE:
* Local processor differentiates the processor reporting the error from other system components (including the APIC, other processors, etc.).

15.9.2.6

Memory Controller Errors

The memory controller errors are defined with the 3-bit MMM (memory transaction type), and 4-bit CCCC
(channel) sub-fields. The encodings for MMM and CCCC are defined in Table 15-15.

Table 15-15. Encodings of MMM and CCCC Sub-Fields
Sub-Field

Transaction

Mnemonic

Binary Encoding

MMM

Generic undefined request

GEN

000

Memory read error

RD

001

Memory write error

WR

010

Address/Command Error

AC

011

Memory Scrubbing Error

MS

100

Reserved

101-111
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Table 15-15. Encodings of MMM and CCCC Sub-Fields (Contd.)
CCCC

Channel number

CHN

0000-1110

Channel not specified

15.9.3

1111

Architecturally Defined UCR Errors

Software recoverable compound error code are defined in this section.

15.9.3.1

Architecturally Defined SRAO Errors

The following two SRAO errors are architecturally defined.

•
•

UCR Errors detected by memory controller scrubbing; and
UCR Errors detected during L3 cache (L3) explicit writebacks.

The MCA error code encodings for these two architecturally-defined UCR errors corresponds to sub-classes of
compound MCA error codes (see Table 15-10). Their values and compound encoding format are given in Table
15-16.

Table 15-16. MCA Compound Error Code Encoding for SRAO Errors
Type

MCACOD Value

MCA Error Code Encoding1

Memory Scrubbing

C0H - CFH

0000_0000_1100_CCCC
000F 0000 1MMM CCCC (Memory Controller Error), where
Memory subfield MMM = 100B (memory scrubbing)
Channel subfield CCCC = channel # or generic

L3 Explicit Writeback 17AH

0000_0001_0111_1010
000F 0001 RRRR TTLL (Cache Hierarchy Error) where
Request subfields RRRR = 0111B (Eviction)
Transaction Type subfields TT = 10B (Generic)
Level subfields LL = 10B

NOTES:
1. Note that for both of these errors the correction report filtering (F) bit (bit 12) of the MCA error must be ignored.
Table 15-17 lists values of relevant bit fields of IA32_MCi_STATUS for architecturally defined SRAO errors.

Table 15-17. IA32_MCi_STATUS Values for SRAO Errors

SRAO Error

Valid

OVER

UC

EN

MISCV

ADDRV

PCC

S

AR

MCACOD

Memory Scrubbing

1

0

1

x1

1

1

0

x1

0

C0H-CFH

L3 Explicit Writeback

1

0

1

x1

1

1

0

x1

0

17AH

NOTES:
1. When signaled as MCE, EN=1 and S=1. If error was signaled via CMC, then EN=x, and S=0.
For both the memory scrubbing and L3 explicit writeback errors, the ADDRV and MISCV flags in the
IA32_MCi_STATUS register are set to indicate that the offending physical address information is available from the
IA32_MCi_MISC and the IA32_MCi_ADDR registers. For the memory scrubbing and L3 explicit writeback errors,
the address mode in the IA32_MCi_MISC register should be set as physical address mode (010b) and the address
LSB information in the IA32_MCi_MISC register should indicate the lowest valid address bit in the address information provided from the IA32_MCi_ADDR register.
MCE signal is broadcast to all logical processors as outlined in Section 15.10.4.1. If LMCE is supported and enabled,
some errors (not limited to UCR errors) may be delivered to only a single logical processor. System software should
consult IA32_MCG_STATUS.LMCE_S to determine if the MCE signaled is only to this logical processor.

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IA32_MCi_STATUS banks can be shared by logical processors within a core or within the same package. So several
logical processors may find an SRAO error in the shared IA32_MCi_STATUS bank but other processors do not find
it in any of the IA32_MCi_STATUS banks. Table 15-18 shows the RIPV and EIPV flag indication in the
IA32_MCG_STATUS register for the memory scrubbing and L3 explicit writeback errors on both the reporting and
non-reporting logical processors.

Table 15-18. IA32_MCG_STATUS Flag Indication for SRAO Errors
SRAO Type

Reporting Logical Processors

Non-reporting Logical Processors

RIPV

RIPV

EIPV

EIPV

Memory Scrubbing

1

0

1

0

L3 Explicit Writeback

1

0

1

0

15.9.3.2

Architecturally Defined SRAR Errors

The following two SRAR errors are architecturally defined.

•
•

UCR Errors detected on data load; and
UCR Errors detected on instruction fetch.

The MCA error code encodings for these two architecturally-defined UCR errors corresponds to sub-classes of
compound MCA error codes (see Table 15-10). Their values and compound encoding format are given in Table
15-19.

Table 15-19. MCA Compound Error Code Encoding for SRAR Errors
Type

MCACOD Value

MCA Error Code Encoding1

Data Load

134H

0000_0001_0011_0100
000F 0001 RRRR TTLL (Cache Hierarchy Error), where
Request subfield RRRR = 0011B (Data Load)
Transaction Type subfield TT= 01B (Data)
Level subfield LL = 00B (Level 0)

Instruction Fetch

150H

0000_0001_0101_0000
000F 0001 RRRR TTLL (Cache Hierarchy Error), where
Request subfield RRRR = 0101B (Instruction Fetch)
Transaction Type subfield TT= 00B (Instruction)
Level subfield LL = 00B (Level 0)

NOTES:
1. Note that for both of these errors the correction report filtering (F) bit (bit 12) of the MCA error must be ignored.
Table 15-20 lists values of relevant bit fields of IA32_MCi_STATUS for architecturally defined SRAR errors.

Table 15-20. IA32_MCi_STATUS Values for SRAR Errors

SRAR Error

Valid

OVER

UC

EN

MISCV

ADDRV

PCC

S

AR

MCACOD

Data Load

1

0

1

1

1

1

0

1

1

134H

Instruction Fetch

1

0

1

1

1

1

0

1

1

150H

For both the data load and instruction fetch errors, the ADDRV and MISCV flags in the IA32_MCi_STATUS register
are set to indicate that the offending physical address information is available from the IA32_MCi_MISC and the
IA32_MCi_ADDR registers. For the memory scrubbing and L3 explicit writeback errors, the address mode in the
IA32_MCi_MISC register should be set as physical address mode (010b) and the address LSB information in the
IA32_MCi_MISC register should indicate the lowest valid address bit in the address information provided from the
IA32_MCi_ADDR register.
MCE signal is broadcast to all logical processors on the system on which the UCR errors are supported, except when
the processor supports LMCE and LMCE is enabled by system software (see Section 15.3.1.5). The

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IA32_MCG_STATUS MSR allows system software to distinguish the affected logical processor of an SRAR error
amongst logical processors that observed SRAR via MCi_STATUS bank.
Table 15-21 shows the RIPV and EIPV flag indication in the IA32_MCG_STATUS register for the data load and
instruction fetch errors on both the reporting and non-reporting logical processors. The recoverable SRAR error
reported by a processor may be continuable, where the system software can interpret the context of continuable
as follows: the error was isolated, contained. If software can rectify the error condition in the current instruction
stream, the execution context on that logical processor can be continued without loss of information.

Table 15-21. IA32_MCG_STATUS Flag Indication for SRAR Errors
SRAR Type

Affected Logical Processor

Non-Affected Logical Processors

RIPV

EIPV

Continuable

Recoverablecontinuable

1

1

Yes1

Recoverable-notcontinuable

0

x

No

RIPV

EIPV

1

Continuable

0

Yes

NOTES:
1. see the definition of the context of “continuable” above and additional detail below.

SRAR Error And Affected Logical Processors
The affected logical processor is the one that has detected and raised an SRAR error at the point of the consumption in the execution flow. The affected logical processor should find the Data Load or the Instruction Fetch error
information in the IA32_MCi_STATUS register that is reporting the SRAR error.
Table 15-21 list the actionable scenarios that system software can respond to an SRAR error on an affected logical
processor according to RIPV and EIPV values:

•

Recoverable-Continuable SRAR Error (RIPV=1, EIPV=1):
For Recoverable-Continuable SRAR errors, the affected logical processor should find that both the
IA32_MCG_STATUS.RIPV and the IA32_MCG_STATUS.EIPV flags are set, indicating that system software may
be able to restart execution from the interrupted context if it is able to rectify the error condition. If system
software cannot rectify the error condition then it must treat the error as a recoverable error where restarting
execution with the interrupted context is not possible. Restarting without rectifying the error condition will
result in most cases with another SRAR error on the same instruction.

•

Recoverable-not-continuable SRAR Error (RIPV=0, EIPV=x):
For Recoverable-not-continuable errors, the affected logical processor should find that either
— IA32_MCG_STATUS.RIPV= 0, IA32_MCG_STATUS.EIPV=1, or
— IA32_MCG_STATUS.RIPV= 0, IA32_MCG_STATUS.EIPV=0.
In either case, this indicates that the error is detected at the instruction pointer saved on the stack for this
machine check exception and restarting execution with the interrupted context is not possible. System
software may take the following recovery actions for the affected logical processor:

•

The current executing thread cannot be continued. System software must terminate the interrupted
stream of execution and provide a new stream of execution on return from the machine check handler
for the affected logical processor.

SRAR Error And Non-Affected Logical Processors
The logical processors that observed but not affected by an SRAR error should find that the RIPV flag in the
IA32_MCG_STATUS register is set and the EIPV flag in the IA32_MCG_STATUS register is cleared, indicating that it
is safe to restart the execution at the instruction saved on the stack for the machine check exception on these
processors after the recovery action is successfully taken by system software.

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15.9.4

Multiple MCA Errors

When multiple MCA errors are detected within a certain detection window, the processor may aggregate the
reporting of these errors together as a single event, i.e. a single machine exception condition. If this occurs,
system software may find multiple MCA errors logged in different MC banks on one logical processor or find
multiple MCA errors logged across different processors for a single machine check broadcast event. In order to
handle multiple UCR errors reported from a single machine check event and possibly recover from multiple errors,
system software may consider the following:

•

Whether it can recover from multiple errors is determined by the most severe error reported on the system. If
the most severe error is found to be an unrecoverable error (VAL=1, UC=1, PCC=1 and EN=1) after system
software examines the MC banks of all processors to which the MCA signal is broadcast, recovery from the
multiple errors is not possible and system software needs to reset the system.

•

When multiple recoverable errors are reported and no other fatal condition (e.g. overflowed condition for SRAR
error) is found for the reported recoverable errors, it is possible for system software to recover from the
multiple recoverable errors by taking necessary recovery action for each individual recoverable error. However,
system software can no longer expect one to one relationship with the error information recorded in the
IA32_MCi_STATUS register and the states of the RIPV and EIPV flags in the IA32_MCG_STATUS register as the
states of the RIPV and the EIPV flags in the IA32_MCG_STATUS register may indicate the information for the
most severe error recorded on the processor. System software is required to use the RIPV flag indication in the
IA32_MCG_STATUS register to make a final decision of recoverability of the errors and find the restart-ability
requirement after examining each IA32_MCi_STATUS register error information in the MC banks.
In certain cases where system software observes more than one SRAR error logged for a single logical
processor, it can no longer rely on affected threads as specified in Table 15-20 above. System software is
recommended to reset the system if this condition is observed.

15.9.5

Machine-Check Error Codes Interpretation

Chapter 16, “Interpreting Machine-Check Error Codes,” provides information on interpreting the MCA error code,
model-specific error code, and other information error code fields. For P6 family processors, information has been
included on decoding external bus errors. For Pentium 4 and Intel Xeon processors; information is included on
external bus, internal timer and cache hierarchy errors.

15.10

GUIDELINES FOR WRITING MACHINE-CHECK SOFTWARE

The machine-check architecture and error logging can be used in three different ways:

•
•
•

To detect machine errors during normal instruction execution, using the machine-check exception (#MC).
To periodically check and log machine errors.
To examine recoverable UCR errors, determine software recoverability and perform recovery actions via a
machine-check exception handler or a corrected machine-check interrupt handler.

To use the machine-check exception, the operating system or executive software must provide a machine-check
exception handler. This handler may need to be designed specifically for each family of processors.
A special program or utility is required to log machine errors.
Guidelines for writing a machine-check exception handler or a machine-error logging utility are given in the
following sections.

15.10.1 Machine-Check Exception Handler
The machine-check exception (#MC) corresponds to vector 18. To service machine-check exceptions, a trap gate
must be added to the IDT. The pointer in the trap gate must point to a machine-check exception handler. Two
approaches can be taken to designing the exception handler:
1. The handler can merely log all the machine status and error information, then call a debugger or shut down the
system.

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2. The handler can analyze the reported error information and, in some cases, attempt to correct the error and
restart the processor.
For Pentium 4, Intel Xeon, Intel Atom, P6 family, and Pentium processors; virtually all machine-check conditions
cannot be corrected (they result in abort-type exceptions). The logging of status and error information is therefore
a baseline implementation requirement.
When IA32_MCG_CAP[24] is clear, consider the following when writing a machine-check exception handler:

•

To determine the nature of the error, the handler must read each of the error-reporting register banks. The
count field in the IA32_MCG_CAP register gives number of register banks. The first register of register bank 0
is at address 400H.

•

The VAL (valid) flag in each IA32_MCi_STATUS register indicates whether the error information in the register
is valid. If this flag is clear, the registers in that bank do not contain valid error information and do not need to
be checked.

•

To write a portable exception handler, only the MCA error code field in the IA32_MCi_STATUS register should be
checked. See Section 15.9, “Interpreting the MCA Error Codes,” for information that can be used to write an
algorithm to interpret this field.

•

Correctable errors are corrected automatically by the processor. The UC flag in each IA32_MCi_STATUS register indicates whether the processor automatically corrected an error.

•

The RIPV, PCC, and OVER flags in each IA32_MCi_STATUS register indicate whether recovery from the error is
possible. If PCC or OVER are set, recovery is not possible. If RIPV is not set, program execution can not be
restarted reliably. When recovery is not possible, the handler typically records the error information and signals
an abort to the operating system.

•

The RIPV flag in the IA32_MCG_STATUS register indicates whether the program can be restarted at the
instruction indicated by the instruction pointer (the address of the instruction pushed on the stack when the
exception was generated). If this flag is clear, the processor may still be able to be restarted (for debugging
purposes) but not without loss of program continuity.

•

For unrecoverable errors, the EIPV flag in the IA32_MCG_STATUS register indicates whether the instruction
indicated by the instruction pointer pushed on the stack (when the exception was generated) is related to the
error. If the flag is clear, the pushed instruction may not be related to the error.

•

The MCIP flag in the IA32_MCG_STATUS register indicates whether a machine-check exception was generated.
Before returning from the machine-check exception handler, software should clear this flag so that it can be
used reliably by an error logging utility. The MCIP flag also detects recursion. The machine-check architecture
does not support recursion. When the processor detects machine-check recursion, it enters the shutdown
state.

Example 15-2 gives typical steps carried out by a machine-check exception handler.

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Example 15-2. Machine-Check Exception Handler Pseudocode
IF CPU supports MCE
THEN
IF CPU supports MCA
THEN
call errorlogging routine; (* returns restartability *)
FI;
ELSE (* Pentium(R) processor compatible *)
READ P5_MC_ADDR
READ P5_MC_TYPE;
report RESTARTABILITY to console;
FI;
IF error is not restartable
THEN
report RESTARTABILITY to console;
abort system;
FI;
CLEAR MCIP flag in IA32_MCG_STATUS;

15.10.2 Pentium Processor Machine-Check Exception Handling
Machine-check exception handler on P6 family, Intel Atom and later processor families, should follow the guidelines
described in Section 15.10.1 and Example 15-2 that check the processor’s support of MCA.

NOTE
On processors that support MCA (CPUID.1.EDX.MCA = 1) reading the P5_MC_TYPE and
P5_MC_ADDR registers may produce invalid data.
When machine-check exceptions are enabled for the Pentium processor (MCE flag is set in control register CR4),
the machine-check exception handler uses the RDMSR instruction to read the error type from the P5_MC_TYPE
register and the machine check address from the P5_MC_ADDR register. The handler then normally reports these
register values to the system console before aborting execution (see Example 15-2).

15.10.3 Logging Correctable Machine-Check Errors
The error handling routine for servicing the machine-check exceptions is responsible for logging uncorrected
errors.
If a machine-check error is correctable, the processor does not generate a machine-check exception for it. To
detect correctable machine-check errors, a utility program must be written that reads each of the machine-check
error-reporting register banks and logs the results in an accounting file or data structure. This utility can be implemented in either of the following ways.

•
•

A system daemon that polls the register banks on an infrequent basis, such as hourly or daily.

•

An interrupt service routine servicing CMCI can read the MC banks and log the error. Please refer to Section
15.10.4.2 for guidelines on logging correctable machine checks.

A user-initiated application that polls the register banks and records the exceptions. Here, the actual polling
service is provided by an operating-system driver or through the system call interface.

Example 15-3 gives pseudocode for an error logging utility.

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Example 15-3. Machine-Check Error Logging Pseudocode
Assume that execution is restartable;
IF the processor supports MCA
THEN
FOR each bank of machine-check registers
DO
READ IA32_MCi_STATUS;
IF VAL flag in IA32_MCi_STATUS = 1
THEN
IF ADDRV flag in IA32_MCi_STATUS = 1
THEN READ IA32_MCi_ADDR;
FI;
IF MISCV flag in IA32_MCi_STATUS = 1
THEN READ IA32_MCi_MISC;
FI;
IF MCIP flag in IA32_MCG_STATUS = 1
(* Machine-check exception is in progress *)
AND PCC flag in IA32_MCi_STATUS = 1
OR RIPV flag in IA32_MCG_STATUS = 0
(* execution is not restartable *)
THEN
RESTARTABILITY = FALSE;
return RESTARTABILITY to calling procedure;
FI;
Save time-stamp counter and processor ID;
Set IA32_MCi_STATUS to all 0s;
Execute serializing instruction (i.e., CPUID);
FI;
OD;
FI;

If the processor supports the machine-check architecture, the utility reads through the banks of error-reporting
registers looking for valid register entries. It then saves the values of the IA32_MCi_STATUS, IA32_MCi_ADDR,
IA32_MCi_MISC and IA32_MCG_STATUS registers for each bank that is valid. The routine minimizes processing
time by recording the raw data into a system data structure or file, reducing the overhead associated with polling.
User utilities analyze the collected data in an off-line environment.
When the MCIP flag is set in the IA32_MCG_STATUS register, a machine-check exception is in progress and the
machine-check exception handler has called the exception logging routine.
Once the logging process has been completed the exception-handling routine must determine whether execution
can be restarted, which is usually possible when damage has not occurred (The PCC flag is clear, in the
IA32_MCi_STATUS register) and when the processor can guarantee that execution is restartable (the RIPV flag is
set in the IA32_MCG_STATUS register). If execution cannot be restarted, the system is not recoverable and the
exception-handling routine should signal the console appropriately before returning the error status to the Operating System kernel for subsequent shutdown.
The machine-check architecture allows buffering of exceptions from a given error-reporting bank although the
Pentium 4, Intel Xeon, Intel Atom, and P6 family processors do not implement this feature. The error logging
routine should provide compatibility with future processors by reading each hardware error-reporting bank's
IA32_MCi_STATUS register and then writing 0s to clear the OVER and VAL flags in this register. The error logging
utility should re-read the IA32_MCi_STATUS register for the bank ensuring that the valid bit is clear. The processor
will write the next error into the register bank and set the VAL flags.
Additional information that should be stored by the exception-logging routine includes the processor’s time-stamp
counter value, which provides a mechanism to indicate the frequency of exceptions. A multiprocessing operating
system stores the identity of the processor node incurring the exception using a unique identifier, such as the
processor’s APIC ID (see Section 10.8, “Handling Interrupts”).
The basic algorithm given in Example 15-3 can be modified to provide more robust recovery techniques. For
example, software has the flexibility to attempt recovery using information unavailable to the hardware. Specifically, the machine-check exception handler can, after logging carefully analyze the error-reporting registers when
the error-logging routine reports an error that does not allow execution to be restarted. These recovery techniques

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can use external bus related model-specific information provided with the error report to localize the source of the
error within the system and determine the appropriate recovery strategy.

15.10.4 Machine-Check Software Handler Guidelines for Error Recovery
15.10.4.1 Machine-Check Exception Handler for Error Recovery
When writing a machine-check exception (MCE) handler to support software recovery from Uncorrected Recoverable (UCR) errors, consider the following:

•

When IA32_MCG_CAP [24] is zero, there are no recoverable errors supported and all machine-check are fatal
exceptions. The logging of status and error information is therefore a baseline implementation requirement.

•

When IA32_MCG_CAP [24] is 1, certain uncorrected errors called uncorrected recoverable (UCR) errors may be
software recoverable. The handler can analyze the reported error information, and in some cases attempt to
recover from the uncorrected error and continue execution.

•

For processors on which CPUID reports DisplayFamily_DisplayModel as 06H_0EH and onward, an MCA signal is
broadcast to all logical processors in the system (see CPUID instruction in Chapter 3, “Instruction Set
Reference, A-L” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A). Due to the
potentially shared machine check MSR resources among the logical processors on the same package/core, the
MCE handler may be required to synchronize with the other processors that received a machine check error and
serialize access to the machine check registers when analyzing, logging and clearing the information in the
machine check registers.
— On processors that indicate ability for local machine-check exception (MCG_LMCE_P), hardware can choose
to report the error to only a single logical processor if system software has enabled LMCE by setting
IA32_MCG_EXT_CTL[LMCE_EN] = 1 as outlined in Section 15.3.1.5.

•

The VAL (valid) flag in each IA32_MCi_STATUS register indicates whether the error information in the register
is valid. If this flag is clear, the registers in that bank do not contain valid error information and should not be
checked.

•

The MCE handler is primarily responsible for processing uncorrected errors. The UC flag in each
IA32_MCi_Status register indicates whether the reported error was corrected (UC=0) or uncorrected (UC=1).
The MCE handler can optionally log and clear the corrected errors in the MC banks if it can implement software
algorithm to avoid the undesired race conditions with the CMCI or CMC polling handler.

•

For uncorrectable errors, the EIPV flag in the IA32_MCG_STATUS register indicates (when set) that the
instruction pointed to by the instruction pointer pushed onto the stack when the machine-check exception is
generated is directly associated with the error. When this flag is cleared, the instruction pointed to may not be
associated with the error.

•

The MCIP flag in the IA32_MCG_STATUS register indicates whether a machine-check exception was generated.
When a machine check exception is generated, it is expected that the MCIP flag in the IA32_MCG_STATUS
register is set to 1. If it is not set, this machine check was generated by either an INT 18 instruction or some
piece of hardware signaling an interrupt with vector 18.

When IA32_MCG_CAP [24] is 1, the following rules can apply when writing a machine check exception (MCE)
handler to support software recovery:

•

The PCC flag in each IA32_MCi_STATUS register indicates whether recovery from the error is possible for
uncorrected errors (UC=1). If the PCC flag is set for enabled uncorrected errors (UC=1 and EN=1), recovery is
not possible. When recovery is not possible, the MCE handler typically records the error information and signals
the operating system to reset the system.

•

The RIPV flag in the IA32_MCG_STATUS register indicates whether restarting the program execution from the
instruction pointer saved on the stack for the machine check exception is possible. When the RIPV is set,
program execution can be restarted reliably when recovery is possible. If the RIPV flag is not set, program
execution cannot be restarted reliably. In this case the recovery algorithm may involve terminating the current
program execution and resuming an alternate thread of execution upon return from the machine check handler
when recovery is possible. When recovery is not possible, the MCE handler signals the operating system to
reset the system.

Vol. 3B 15-31

MACHINE-CHECK ARCHITECTURE

•

When the EN flag is zero but the VAL and UC flags are one in the IA32_MCi_STATUS register, the reported
uncorrected error in this bank is not enabled. As uncorrected errors with the EN flag = 0 are not the source of
machine check exceptions, the MCE handler should log and clear non-enabled errors when the S bit is set and
should continue searching for enabled errors from the other IA32_MCi_STATUS registers. Note that when
IA32_MCG_CAP [24] is 0, any uncorrected error condition (VAL =1 and UC=1) including the one with the EN
flag cleared are fatal and the handler must signal the operating system to reset the system. For the errors that
do not generate machine check exceptions, the EN flag has no meaning.

•

When the VAL flag is one, the UC flag is one, the EN flag is one and the PCC flag is zero in the IA32_MCi_STATUS
register, the error in this bank is an uncorrected recoverable (UCR) error. The MCE handler needs to examine
the S flag and the AR flag to find the type of the UCR error for software recovery and determine if software error
recovery is possible.

•

When both the S and the AR flags are clear in the IA32_MCi_STATUS register for the UCR error (VAL=1, UC=1,
EN=x and PCC=0), the error in this bank is an uncorrected no-action required error (UCNA). UCNA errors are
uncorrected but do not require any OS recovery action to continue execution. These errors indicate that some
data in the system is corrupt, but that data has not been consumed and may not be consumed. If that data is
consumed a non-UNCA machine check exception will be generated. UCNA errors are signaled in the same way
as corrected machine check errors and the CMCI and CMC polling handler is primarily responsible for handling
UCNA errors. Like corrected errors, the MCA handler can optionally log and clear UCNA errors as long as it can
avoid the undesired race condition with the CMCI or CMC polling handler. As UCNA errors are not the source of
machine check exceptions, the MCA handler should continue searching for uncorrected or software recoverable
errors in all other MC banks.

•

When the S flag in the IA32_MCi_STATUS register is set for the UCR error ((VAL=1, UC=1, EN=1 and PCC=0),
the error in this bank is software recoverable and it was signaled through a machine-check exception. The AR
flag in the IA32_MCi_STATUS register further clarifies the type of the software recoverable errors.

•

When the AR flag in the IA32_MCi_STATUS register is clear for the software recoverable error (VAL=1, UC=1,
EN=1, PCC=0 and S=1), the error in this bank is a software recoverable action optional (SRAO) error. The MCE
handler and the operating system can analyze the IA32_MCi_STATUS [15:0] to implement MCA error code
specific optional recovery action, but this recovery action is optional. System software can resume the program
execution from the instruction pointer saved on the stack for the machine check exception when the RIPV flag
in the IA32_MCG_STATUS register is set.

•

Even if the OVER flag in the IA32_MCi_STATUS register is set for the SRAO error (VAL=1, UC=1, EN=1, PCC=0,
S=1 and AR=0), the MCE handler can take recovery action for the SRAO error logged in the IA32_MCi_STATUS
register. Since the recovery action for SRAO errors is optional, restarting the program execution from the
instruction pointer saved on the stack for the machine check exception is still possible for the overflowed SRAO
error if the RIPV flag in the IA32_MCG_STATUS is set.

•

When the AR flag in the IA32_MCi_STATUS register is set for the software recoverable error (VAL=1, UC=1,
EN=1, PCC=0 and S=1), the error in this bank is a software recoverable action required (SRAR) error. The MCE
handler and the operating system must take recovery action in order to continue execution after the machinecheck exception. The MCA handler and the operating system need to analyze the IA32_MCi_STATUS [15:0] to
determine the MCA error code specific recovery action. If no recovery action can be performed, the operating
system must reset the system.

•

When the OVER flag in the IA32_MCi_STATUS register is set for the SRAR error (VAL=1, UC=1, EN=1, PCC=0,
S=1 and AR=1), the MCE handler cannot take recovery action as the information of the SRAR error in the
IA32_MCi_STATUS register was potentially lost due to the overflow condition. Since the recovery action for
SRAR errors must be taken, the MCE handler must signal the operating system to reset the system.

•

When the MCE handler cannot find any uncorrected (VAL=1, UC=1 and EN=1) or any software recoverable
errors (VAL=1, UC=1, EN=1, PCC=0 and S=1) in any of the IA32_MCi banks of the processors, this is an
unexpected condition for the MCE handler and the handler should signal the operating system to reset the
system.

•

Before returning from the machine-check exception handler, software must clear the MCIP flag in the
IA32_MCG_STATUS register. The MCIP flag is used to detect recursion. The machine-check architecture does
not support recursion. When the processor receives a machine check when MCIP is set, it automatically enters
the shutdown state.

Example 15-4 gives pseudocode for an MC exception handler that supports recovery of UCR.

15-32 Vol. 3B

MACHINE-CHECK ARCHITECTURE

Example 15-4. Machine-Check Error Handler Pseudocode Supporting UCR
MACHINE CHECK HANDLER: (* Called from INT 18 handler *)
NOERROR = TRUE;
ProcessorCount = 0;
IF CPU supports MCA
THEN
RESTARTABILITY = TRUE;
IF (Processor Family = 6 AND DisplayModel ≥ 0EH) OR (Processor Family > 6)
THEN
IF ( MCG_LMCE = 1)
MCA_BROADCAST = FALSE;
ELSE
MCA_BROADCAST = TRUE;
FI;
Acquire SpinLock;
ProcessorCount++; (* Allowing one logical processor at a time to examine machine check registers *)
CALL MCA ERROR PROCESSING; (* returns RESTARTABILITY and NOERROR *)
ELSE
MCA_BROADCAST = FALSE;
(* Implement a rendezvous mechanism with the other processors if necessary *)
CALL MCA ERROR PROCESSING;
FI;
ELSE (* Pentium(R) processor compatible *)
READ P5_MC_ADDR
READ P5_MC_TYPE;
RESTARTABILITY = FALSE;
FI;
IF NOERROR = TRUE
THEN
IF NOT (MCG_RIPV = 1 AND MCG_EIPV = 0)
THEN
RESTARTABILITY = FALSE;
FI
FI;
IF RESTARTABILITY = FALSE
THEN
Report RESTARTABILITY to console;
Reset system;
FI;
IF MCA_BROADCAST = TRUE
THEN
IF ProcessorCount = MAX_PROCESSORS
AND NOERROR = TRUE
THEN
Report RESTARTABILITY to console;
Reset system;
FI;
Release SpinLock;
Wait till ProcessorCount = MAX_PROCESSRS on system;
(* implement a timeout and abort function if necessary *)
FI;
CLEAR IA32_MCG_STATUS;
RESUME Execution;
(* End of MACHINE CHECK HANDLER*)

MCA ERROR PROCESSING: (* MCA Error Processing Routine called from MCA Handler *)
IF MCIP flag in IA32_MCG_STATUS = 0
THEN (* MCIP=0 upon MCA is unexpected *)
RESTARTABILITY = FALSE;
FI;

Vol. 3B 15-33

MACHINE-CHECK ARCHITECTURE

FOR each bank of machine-check registers
DO
CLEAR_MC_BANK = FALSE;
READ IA32_MCi_STATUS;
IF VAL Flag in IA32_MCi_STATUS = 1
THEN
IF UC Flag in IA32_MCi_STATUS = 1
THEN
IF Bit 24 in IA32_MCG_CAP = 0
THEN (* the processor does not support software error recovery *)
RESTARTABILITY = FALSE;
NOERROR = FALSE;
GOTO LOG MCA REGISTER;
FI;
(* the processor supports software error recovery *)
IF EN Flag in IA32_MCi_STATUS = 0 AND OVER Flag in IA32_MCi_STATUS=0
THEN (* It is a spurious MCA Log. Log and clear the register *)
CLEAR_MC_BANK = TRUE;
GOTO LOG MCA REGISTER;
FI;
IF PCC = 1 and EN = 1 in IA32_MCi_STATUS
THEN (* processor context might have been corrupted *)
RESTARTABILITY = FALSE;
ELSE (* It is a uncorrected recoverable (UCR) error *)
IF S Flag in IA32_MCi_STATUS = 0
THEN
IF AR Flag in IA32_MCi_STATUS = 0
THEN (* It is a uncorrected no action required (UCNA) error *)
GOTO CONTINUE; (* let CMCI and CMC polling handler to process *)
ELSE
RESTARTABILITY = FALSE; (* S=0, AR=1 is illegal *)
FI
FI;
IF RESTARTABILITY = FALSE
THEN (* no need to take recovery action if RESTARTABILITY is already false *)
NOERROR = FALSE;
GOTO LOG MCA REGISTER;
FI;
(* S in IA32_MCi_STATUS = 1 *)
IF AR Flag in IA32_MCi_STATUS = 1
THEN (* It is a software recoverable and action required (SRAR) error *)
IF OVER Flag in IA32_MCi_STATUS = 1
THEN
RESTARTABILITY = FALSE;
NOERROR = FALSE;
GOTO LOG MCA REGISTER;
FI
IF MCACOD Value in IA32_MCi_STATUS is recognized
AND Current Processor is an Affected Processor
THEN
Implement MCACOD specific recovery action;
CLEAR_MC_BANK = TRUE;
ELSE
RESTARTABILITY = FALSE;
FI;
ELSE (* It is a software recoverable and action optional (SRAO) error *)
IF OVER Flag in IA32_MCi_STATUS = 0 AND
MCACOD in IA32_MCi_STATUS is recognized
THEN
Implement MCACOD specific recovery action;
FI;
CLEAR_MC_BANK = TRUE;
FI; AR
FI; PCC
NOERROR = FALSE;
15-34 Vol. 3B

MACHINE-CHECK ARCHITECTURE

GOTO LOG MCA REGISTER;
ELSE (* It is a corrected error; continue to the next IA32_MCi_STATUS *)
GOTO CONTINUE;
FI; UC

FI; VAL
LOG MCA REGISTER:
SAVE IA32_MCi_STATUS;
If MISCV in IA32_MCi_STATUS
THEN
SAVE IA32_MCi_MISC;
FI;
IF ADDRV in IA32_MCi_STATUS
THEN
SAVE IA32_MCi_ADDR;
FI;
IF CLEAR_MC_BANK = TRUE
THEN
SET all 0 to IA32_MCi_STATUS;
If MISCV in IA32_MCi_STATUS
THEN
SET all 0 to IA32_MCi_MISC;
FI;
IF ADDRV in IA32_MCi_STATUS
THEN
SET all 0 to IA32_MCi_ADDR;
FI;
FI;
CONTINUE:
OD;
( *END FOR *)
RETURN;
(* End of MCA ERROR PROCESSING*)

15.10.4.2 Corrected Machine-Check Handler for Error Recovery
When writing a corrected machine check handler, which is invoked as a result of CMCI or called from an OS CMC
Polling dispatcher, consider the following:

•

The VAL (valid) flag in each IA32_MCi_STATUS register indicates whether the error information in the register
is valid. If this flag is clear, the registers in that bank does not contain valid error information and does not need
to be checked.

•

The CMCI or CMC polling handler is responsible for logging and clearing corrected errors. The UC flag in each
IA32_MCi_Status register indicates whether the reported error was corrected (UC=0) or not (UC=1).

•

When IA32_MCG_CAP [24] is one, the CMC handler is also responsible for logging and clearing uncorrected noaction required (UCNA) errors. When the UC flag is one but the PCC, S, and AR flags are zero in the
IA32_MCi_STATUS register, the reported error in this bank is an uncorrected no-action required (UCNA) error.
In cases when SRAO error are signaled as UCNA error via CMCI, software can perform recovery for those errors
identified in Table 15-16.

•

In addition to corrected errors and UCNA errors, the CMC handler optionally logs uncorrected (UC=1 and
PCC=1), software recoverable machine check errors (UC=1, PCC=0 and S=1), but should avoid clearing those
errors from the MC banks. Clearing these errors may result in accidentally removing these errors before these
errors are actually handled and processed by the MCE handler for attempted software error recovery.

Example 15-5 gives pseudocode for a CMCI handler with UCR support.

Vol. 3B 15-35

MACHINE-CHECK ARCHITECTURE

Example 15-5. Corrected Error Handler Pseudocode with UCR Support
Corrected Error HANDLER: (* Called from CMCI handler or OS CMC Polling Dispatcher*)
IF CPU supports MCA
THEN
FOR each bank of machine-check registers
DO
READ IA32_MCi_STATUS;
IF VAL flag in IA32_MCi_STATUS = 1
THEN
IF UC Flag in IA32_MCi_STATUS = 0 (* It is a corrected error *)
THEN
GOTO LOG CMC ERROR;
ELSE
IF Bit 24 in IA32_MCG_CAP = 0
THEN
GOTO CONTINUE;
FI;
IF S Flag in IA32_MCi_STATUS = 0 AND AR Flag in IA32_MCi_STATUS = 0
THEN (* It is a uncorrected no action required error *)
GOTO LOG CMC ERROR
FI
IF EN Flag in IA32_MCi_STATUS = 0
THEN (* It is a spurious MCA error *)
GOTO LOG CMC ERROR
FI;
FI;
FI;
GOTO CONTINUE;
LOG CMC ERROR:
SAVE IA32_MCi_STATUS;
If MISCV Flag in IA32_MCi_STATUS
THEN
SAVE IA32_MCi_MISC;
SET all 0 to IA32_MCi_MISC;
FI;
IF ADDRV Flag in IA32_MCi_STATUS
THEN
SAVE IA32_MCi_ADDR;
SET all 0 to IA32_MCi_ADDR
FI;
SET all 0 to IA32_MCi_STATUS;
CONTINUE:
OD;
( *END FOR *)
FI;

15-36 Vol. 3B

CHAPTER 16
INTERPRETING MACHINE-CHECK
ERROR CODES
Encoding of the model-specific and other information fields is different across processor families. The differences
are documented in the following sections.

16.1

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY 06H
MACHINE ERROR CODES FOR MACHINE CHECK

Section 16.1 provides information for interpreting additional model-specific fields for external bus errors relating to
processor family 06H. The references to processor family 06H refers to only IA-32 processors with CPUID signatures listed in Table 16-1.

Table 16-1. CPUID DisplayFamily_DisplayModel Signatures for Processor Family 06H
DisplayFamily_DisplayModel

Processor Families/Processor Number Series

06_0EH

Intel Core Duo, Intel Core Solo processors

06_0DH

Intel Pentium M processor

06_09H

Intel Pentium M processor

06_7H, 06_08H, 06_0AH, 06_0BH

Intel Pentium III Xeon Processor, Intel Pentium III Processor

06_03H, 06_05H

Intel Pentium II Xeon Processor, Intel Pentium II Processor

06_01H

Intel Pentium Pro Processor

These errors are reported in the IA32_MCi_STATUS MSRs. They are reported architecturally as compound errors
with a general form of 0000 1PPT RRRR IILL in the MCA error code field. See Chapter 15 for information on the
interpretation of compound error codes. Incremental decoding information is listed in Table 16-2.

Table 16-2. Incremental Decoding Information: Processor Family 06H Machine Error Codes For Machine Check
Type

Bit No.

Bit Function

Bit Description

MCA error
codes1

15:0

Model specific
errors

18:16

Reserved

Reserved

Model specific
errors

24:19

Bus queue request
type

000000 for BQ_DCU_READ_TYPE error
000010 for BQ_IFU_DEMAND_TYPE error
000011 for BQ_IFU_DEMAND_NC_TYPE error
000100 for BQ_DCU_RFO_TYPE error
000101 for BQ_DCU_RFO_LOCK_TYPE error
000110 for BQ_DCU_ITOM_TYPE error
001000 for BQ_DCU_WB_TYPE error
001010 for BQ_DCU_WCEVICT_TYPE error
001011 for BQ_DCU_WCLINE_TYPE error
001100 for BQ_DCU_BTM_TYPE error

Vol. 3B 16-1

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-2. Incremental Decoding Information: Processor Family 06H Machine Error Codes For Machine Check
Type

Bit No.

Bit Function

Bit Description
001101 for BQ_DCU_INTACK_TYPE error
001110 for BQ_DCU_INVALL2_TYPE error
001111 for BQ_DCU_FLUSHL2_TYPE error
010000 for BQ_DCU_PART_RD_TYPE error
010010 for BQ_DCU_PART_WR_TYPE error
010100 for BQ_DCU_SPEC_CYC_TYPE error
011000 for BQ_DCU_IO_RD_TYPE error
011001 for BQ_DCU_IO_WR_TYPE error
011100 for BQ_DCU_LOCK_RD_TYPE error
011110 for BQ_DCU_SPLOCK_RD_TYPE error
011101 for BQ_DCU_LOCK_WR_TYPE error

Model specific
errors

27:25

Bus queue error type

000 for BQ_ERR_HARD_TYPE error
001 for BQ_ERR_DOUBLE_TYPE error
010 for BQ_ERR_AERR2_TYPE error
100 for BQ_ERR_SINGLE_TYPE error
101 for BQ_ERR_AERR1_TYPE error

Model specific
errors

Other
information

28

FRC error

1 if FRC error active

29

BERR

1 if BERR is driven

30

Internal BINIT

1 if BINIT driven for this processor

31

Reserved

Reserved

34:32

Reserved

Reserved

35

External BINIT

1 if BINIT is received from external bus.

36

Response parity error This bit is asserted in IA32_MCi_STATUS if this component has received a parity
error on the RS[2:0]# pins for a response transaction. The RS signals are checked
by the RSP# external pin.

37

Bus BINIT

This bit is asserted in IA32_MCi_STATUS if this component has received a hard
error response on a split transaction one access that has needed to be split across
the 64-bit external bus interface into two accesses).

38

Timeout BINIT

This bit is asserted in IA32_MCi_STATUS if this component has experienced a ROB
time-out, which indicates that no micro-instruction has been retired for a
predetermined period of time.
A ROB time-out occurs when the 15-bit ROB time-out counter carries a 1 out of its
high order bit. 2 The timer is cleared when a micro-instruction retires, an exception
is detected by the core processor, RESET is asserted, or when a ROB BINIT occurs.
The ROB time-out counter is prescaled by the 8-bit PIC timer which is a divide by
128 of the bus clock the bus clock is 1:2, 1:3, 1:4 of the core clock). When a carry
out of the 8-bit PIC timer occurs, the ROB counter counts up by one. While this bit
is asserted, it cannot be overwritten by another error.

16-2 Vol. 3B

41:39

Reserved

Reserved

42

Hard error

This bit is asserted in IA32_MCi_STATUS if this component has initiated a bus
transactions which has received a hard error response. While this bit is asserted, it
cannot be overwritten.

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-2. Incremental Decoding Information: Processor Family 06H Machine Error Codes For Machine Check
Type

Bit No.

Bit Function

Bit Description

43

IERR

This bit is asserted in IA32_MCi_STATUS if this component has experienced a
failure that causes the IERR pin to be asserted. While this bit is asserted, it cannot
be overwritten.

44

AERR

This bit is asserted in IA32_MCi_STATUS if this component has initiated 2 failing
bus transactions which have failed due to Address Parity Errors AERR asserted).
While this bit is asserted, it cannot be overwritten.

45

UECC

The Uncorrectable ECC error bit is asserted in IA32_MCi_STATUS for uncorrected
ECC errors. While this bit is asserted, the ECC syndrome field will not be
overwritten.

46

CECC

The correctable ECC error bit is asserted in IA32_MCi_STATUS for corrected ECC
errors.

54:47

ECC syndrome

The ECC syndrome field in IA32_MCi_STATUS contains the 8-bit ECC syndrome only
if the error was a correctable/uncorrectable ECC error and there wasn't a previous
valid ECC error syndrome logged in IA32_MCi_STATUS.
A previous valid ECC error in IA32_MCi_STATUS is indicated by
IA32_MCi_STATUS.bit45 uncorrectable error occurred) being asserted. After
processing an ECC error, machine-check handling software should clear
IA32_MCi_STATUS.bit45 so that future ECC error syndromes can be logged.

56:55
Status register
validity
indicators1

Reserved

Reserved.

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.
2. For processors with a CPUID signature of 06_0EH, a ROB time-out occurs when the 23-bit ROB time-out counter carries a 1 out of its
high order bit.

16.2

INCREMENTAL DECODING INFORMATION: INTEL CORE 2 PROCESSOR
FAMILY MACHINE ERROR CODES FOR MACHINE CHECK

Table 16-4 provides information for interpreting additional model-specific fields for external bus errors relating to
processor based on Intel Core microarchitecture, which implements the P4 bus specification. Table 16-3 lists the
CPUID signatures for Intel 64 processors that are covered by Table 16-4. These errors are reported in the
IA32_MCi_STATUS MSRs. They are reported architecturally as compound errors with a general form of
0000 1PPT RRRR IILL in the MCA error code field. See Chapter 15 for information on the interpretation of
compound error codes.

Table 16-3. CPUID DisplayFamily_DisplayModel Signatures for Processors Based on Intel Core Microarchitecture
DisplayFamily_DisplayModel Processor Families/Processor Number Series
06_1DH

Intel Xeon Processor 7400 series.

06_17H

Intel Xeon Processor 5200, 5400 series, Intel Core 2 Quad processor Q9650.

06_0FH

Intel Xeon Processor 3000, 3200, 5100, 5300, 7300 series, Intel Core 2 Quad, Intel Core 2 Extreme,
Intel Core 2 Duo processors, Intel Pentium dual-core processors.

Vol. 3B 16-3

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-4. Incremental Bus Error Codes of Machine Check for Processors
Based on Intel Core Microarchitecture
Type

Bit No.

Bit Function

Bit Description

MCA error
codes1

15:0

Model specific
errors

18:16

Reserved

Reserved

Model specific
errors

24:19

Bus queue request
type

‘000001 for BQ_PREF_READ_TYPE error
000000 for BQ_DCU_READ_TYPE error
000010 for BQ_IFU_DEMAND_TYPE error
000011 for BQ_IFU_DEMAND_NC_TYPE error
000100 for BQ_DCU_RFO_TYPE error
000101 for BQ_DCU_RFO_LOCK_TYPE error
000110 for BQ_DCU_ITOM_TYPE error
001000 for BQ_DCU_WB_TYPE error
001010 for BQ_DCU_WCEVICT_TYPE error
001011 for BQ_DCU_WCLINE_TYPE error
001100 for BQ_DCU_BTM_TYPE error
001101 for BQ_DCU_INTACK_TYPE error
001110 for BQ_DCU_INVALL2_TYPE error
001111 for BQ_DCU_FLUSHL2_TYPE error
010000 for BQ_DCU_PART_RD_TYPE error
010010 for BQ_DCU_PART_WR_TYPE error
010100 for BQ_DCU_SPEC_CYC_TYPE error
011000 for BQ_DCU_IO_RD_TYPE error
011001 for BQ_DCU_IO_WR_TYPE error
011100 for BQ_DCU_LOCK_RD_TYPE error
011110 for BQ_DCU_SPLOCK_RD_TYPE error
011101 for BQ_DCU_LOCK_WR_TYPE error
100100 for BQ_L2_WI_RFO_TYPE error
100110 for BQ_L2_WI_ITOM_TYPE error

Model specific
errors

27:25

Bus queue error type

‘001 for Address Parity Error

Model specific
errors

28

MCE Driven

1 if MCE is driven

29

MCE Observed

1 if MCE is observed

30

Internal BINIT

1 if BINIT driven for this processor

31

BINIT Observed

1 if BINIT is observed for this processor

33:32

Reserved

Reserved

34

PIC and FSB data
parity

Data Parity detected on either PIC or FSB access

35

Reserved

Reserved

‘010 for Response Hard Error
‘011 for Response Parity Error

Other
information

16-4 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-4. Incremental Bus Error Codes of Machine Check for Processors
Based on Intel Core Microarchitecture (Contd.)
Type

Bit No.

Bit Function

Bit Description

36

Response parity error This bit is asserted in IA32_MCi_STATUS if this component has received a parity
error on the RS[2:0]# pins for a response transaction. The RS signals are checked
by the RSP# external pin.

37

FSB address parity

Address parity error detected:
1 = Address parity error detected
0 = No address parity error

38

Timeout BINIT

This bit is asserted in IA32_MCi_STATUS if this component has experienced a ROB
time-out, which indicates that no micro-instruction has been retired for a
predetermined period of time.
A ROB time-out occurs when the 23-bit ROB time-out counter carries a 1 out of its
high order bit. The timer is cleared when a micro-instruction retires, an exception is
detected by the core processor, RESET is asserted, or when a ROB BINIT occurs.
The ROB time-out counter is prescaled by the 8-bit PIC timer which is a divide by
128 of the bus clock the bus clock is 1:2, 1:3, 1:4 of the core clock). When a carry
out of the 8-bit PIC timer occurs, the ROB counter counts up by one. While this bit
is asserted, it cannot be overwritten by another error.

Status register
validity
indicators1

41:39

Reserved

Reserved

42

Hard error

This bit is asserted in IA32_MCi_STATUS if this component has initiated a bus
transactions which has received a hard error response. While this bit is asserted, it
cannot be overwritten.

43

IERR

This bit is asserted in IA32_MCi_STATUS if this component has experienced a
failure that causes the IERR pin to be asserted. While this bit is asserted, it cannot
be overwritten.

44

Reserved

Reserved

45

Reserved

Reserved

46

Reserved

Reserved

54:47

Reserved

Reserved

56:55

Reserved

Reserved.

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.2.1

Model-Specific Machine Check Error Codes for Intel Xeon Processor 7400 Series

Intel Xeon processor 7400 series has machine check register banks that generally follows the description of
Chapter 15 and Section 16.2. Additional error codes specific to Intel Xeon processor 7400 series is describe in this
section.
MC4_STATUS[63:0] is the main error logging for the processor’s L3 and front side bus errors for Intel Xeon
processor 7400 series. It supports the L3 Errors, Bus and Interconnect Errors Compound Error Codes in the MCA
Error Code Field.

Vol. 3B 16-5

INTERPRETING MACHINE-CHECK ERROR CODES

16.2.1.1

Processor Machine Check Status Register
Incremental MCA Error Code Definition

Intel Xeon processor 7400 series use compound MCA Error Codes for logging its Bus internal machine check
errors, L3 Errors, and Bus/Interconnect Errors. It defines incremental Machine Check error types
(IA32_MC6_STATUS[15:0]) beyond those defined in Chapter 15. Table 16-5 lists these incremental MCA error
code types that apply to IA32_MC6_STATUS. Error code details are specified in MC6_STATUS [31:16] (see
Section 16.2.2), the “Model Specific Error Code” field. The information in the “Other_Info” field
(MC4_STATUS[56:32]) is common to the three processor error types and contains a correctable event count and
specifies the MC6_MISC register format.

Table 16-5. Incremental MCA Error Code Types for Intel Xeon Processor 7400
Processor MCA_Error_Code (MC6_STATUS[15:0])
Type

Error Code

Binary Encoding

Meaning

C

Internal Error

0000 0100 0000 0000 Internal Error Type Code

B

Bus and
Interconnect

0000 100x 0000 1111

Not used but this encoding is reserved for compatibility with other MCA
implementations

Error

0000 101x 0000 1111

Not used but this encoding is reserved for compatibility with other MCA
implementations

0000 110x 0000 1111

Not used but this encoding is reserved for compatibility with other MCA
implementations

0000 1110 0000 1111 Bus and Interconnection Error Type Code
0000 1111 0000 1111 Not used but this encoding is reserved for compatibility with other MCA
implementations
The Bold faced binary encodings are the only encodings used by the processor for MC4_STATUS[15:0].

16.2.2

Intel Xeon Processor 7400 Model Specific Error Code Field

16.2.2.1

Processor Model Specific Error Code Field
Type B: Bus and Interconnect Error

Note:

The Model Specific Error Code field in MC6_STATUS (bits 31:16).

Table 16-6. Type B Bus and Interconnect Error Codes
Bit Num

Sub-Field Name

Description

16

FSB Request Parity

Parity error detected during FSB request phase

19:17

Reserved

20

FSB Hard Fail Response

“Hard Failure“ response received for a local transaction

21

FSB Response Parity

Parity error on FSB response field detected

22

FSB Data Parity

FSB data parity error on inbound data detected

31:23

---

Reserved

16-6 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

16.2.2.2

Processor Model Specific Error Code Field
Type C: Cache Bus Controller Error
Table 16-7. Type C Cache Bus Controller Error Codes

MC4_STATUS[31:16] (MSCE) Value

Error Description

0000_0000_0000_0001 0001H

Inclusion Error from Core 0

0000_0000_0000_0010 0002H

Inclusion Error from Core 1

0000_0000_0000_0011 0003H

Write Exclusive Error from Core 0

0000_0000_0000_0100 0004H

Write Exclusive Error from Core 1

0000_0000_0000_0101 0005H

Inclusion Error from FSB

0000_0000_0000_0110 0006H

SNP Stall Error from FSB

0000_0000_0000_0111 0007H

Write Stall Error from FSB

0000_0000_0000_1000 0008H

FSB Arb Timeout Error

0000_0000_0000_1010 000AH

Inclusion Error from Core 2

0000_0000_0000_1011 000BH

Write Exclusive Error from Core 2

0000_0010_0000_0000 0200H

Internal Timeout error

0000_0011_0000_0000 0300H

Internal Timeout Error

0000_0100_0000_0000 0400H

Intel® Cache Safe Technology Queue Full Error or Disabled-ways-in-a-set overflow

0000_0101_0000_0000 0500H

Quiet cycle Timeout Error (correctable)

1100_0000_0000_0010 C002H

Correctable ECC event on outgoing Core 0 data

1100_0000_0000_0100 C004H

Correctable ECC event on outgoing Core 1 data

1100_0000_0000_1000 C008H

Correctable ECC event on outgoing Core 2 data

1110_0000_0000_0010 E002H

Uncorrectable ECC error on outgoing Core 0 data

1110_0000_0000_0100 E004H

Uncorrectable ECC error on outgoing Core 1 data

1110_0000_0000_1000 E008H

Uncorrectable ECC error on outgoing Core 2 data

— all other encodings —

Reserved

16.3

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH
CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_1AH, MACHINE
ERROR CODES FOR MACHINE CHECK

Table 16-8 through Table 16-12 provide information for interpreting additional model-specific fields for memory
controller errors relating to the processor family with CPUID DisplayFamily_DisplaySignature 06_1AH, which
supports Intel QuickPath Interconnect links. Incremental MC error codes related to the Intel QPI links are reported
in the register banks IA32_MC0 and IA32_MC1, incremental error codes for internal machine check is reported in
the register bank IA32_MC7, and incremental error codes for the memory controller unit is reported in the register
banks IA32_MC8.

Vol. 3B 16-7

INTERPRETING MACHINE-CHECK ERROR CODES

16.3.1

Intel QPI Machine Check Errors
Table 16-8. Intel QPI Machine Check Error Codes for IA32_MC0_STATUS and IA32_MC1_STATUS

Type
1

MCA error codes

Bit No.

Bit Function

Bit Description

15:0

MCACOD

Bus error format: 1PPTRRRRIILL

16

Header Parity

if 1, QPI Header had bad parity

17

Data Parity

If 1, QPI Data packet had bad parity

18

Retries Exceeded

If 1, number of QPI retries was exceeded

19

Received Poison

if 1, Received a data packet that was marked as poisoned by the sender

21:20

Reserved

Reserved

22

Unsupported Message

If 1, QPI received a message encoding it does not support

23

Unsupported Credit

If 1, QPI credit type is not supported.

24

Receive Flit Overrun

If 1, Sender sent too many QPI flits to the receiver.

25

Received Failed
Response

If 1, Indicates that sender sent a failed response to receiver.

26

Receiver Clock Jitter

If 1, clock jitter detected in the internal QPI clocking

56:27

Reserved

Reserved

Model specific errors

Status register
validity indicators1

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

Table 16-9. Intel QPI Machine Check Error Codes for IA32_MC0_MISC and IA32_MC1_MISC
Type
Model specific

Bit No.

Bit Function

Bit Description

7:0

QPI Opcode

Message class and opcode from the packet with the error

13:8

RTId

QPI Request Transaction ID

15:14

Reserved

Reserved

18:16

RHNID

QPI Requestor/Home Node ID

23:19

Reserved

Reserved

24

IIB

QPI Interleave/Head Indication Bit

errors1

NOTES:
1. Which of these fields are valid depends on the error type.

16.3.2

Internal Machine Check Errors
Table 16-10. Machine Check Error Codes for IA32_MC7_STATUS

Type

Bit No.

Bit Function

MCA error codes1

15:0

MCACOD

Model specific errors

16-8 Vol. 3B

Bit Description

INTERPRETING MACHINE-CHECK ERROR CODES

Type

Bit No.

Bit Function

Bit Description

23:16

Reserved

Reserved

31:24

Reserved except for
the following

00h - No Error
03h - Reset firmware did not complete
08h - Received an invalid CMPD
0Ah - Invalid Power Management Request
0Dh - Invalid S-state transition
11h - VID controller does not match POC controller selected
1Ah - MSID from POC does not match CPU MSID

56:32
Status register validity
indicators1

Reserved

Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.3.3

Memory Controller Errors
Table 16-11. Incremental Memory Controller Error Codes of Machine Check for IA32_MC8_STATUS

Type
MCA error

codes1

Bit No.

Bit Function

Bit Description

15:0

MCACOD

Memory error format: 1MMMCCCC

16

Read ECC error

if 1, ECC occurred on a read

17

RAS ECC error

If 1, ECC occurred on a scrub

18

Write parity error

If 1, bad parity on a write

19

Redundancy loss

if 1, Error in half of redundant memory

20

Reserved

Reserved

21

Memory range error

If 1, Memory access out of range

22

RTID out of range

If 1, Internal ID invalid

23

Address parity error

If 1, bad address parity

24

Byte enable parity
error

If 1, bad enable parity

37:25

Reserved

Reserved

52:38

CORE_ERR_CNT

Corrected error count

56:53

Reserved

Reserved

Model specific errors

Other information

Status register validity
indicators1

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

Vol. 3B 16-9

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-12. Incremental Memory Controller Error Codes of Machine Check for IA32_MC8_MISC
Type
Model specific

Bit No.

Bit Function

Bit Description

7:0

RTId

Transaction Tracker ID

15:8

Reserved

Reserved

17:16

DIMM

DIMM ID which got the error

19:18

Channel

Channel ID which got the error

31:20

Reserved

Reserved

63:32

Syndrome

ECC Syndrome

errors1

NOTES:
1. Which of these fields are valid depends on the error type.

16.4

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID
DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_2DH, MACHINE ERROR
CODES FOR MACHINE CHECK

Table 16-13 through Table 16-15 provide information for interpreting additional model-specific fields for memory
controller errors relating to the processor family with CPUID DisplayFamily_DisplaySignature 06_2DH, which
supports Intel QuickPath Interconnect links. Incremental MC error codes related to the Intel QPI links are reported
in the register banks IA32_MC6 and IA32_MC7, incremental error codes for internal machine check error from PCU
controller is reported in the register bank IA32_MC4, and incremental error codes for the memory controller unit is
reported in the register banks IA32_MC8-IA32_MC11.

16.4.1

Internal Machine Check Errors
Table 16-13. Machine Check Error Codes for IA32_MC4_STATUS

Type

Bit No.

Bit Function

MCA error
codes1

15:0

MCACOD

Model specific
errors

19:16

Reserved except for
the following

Bit Description

0000b - No Error
0001b - Non_IMem_Sel
0010b - I_Parity_Error
0011b - Bad_OpCode
0100b - I_Stack_Underflow
0101b - I_Stack_Overflow
0110b - D_Stack_Underflow
0111b - D_Stack_Overflow
1000b - Non-DMem_Sel
1001b - D_Parity_Error

16-10 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

Type

Bit No.

Bit Function

Bit Description

23:20

Reserved

Reserved

31:24

Reserved except for
the following

00h - No Error
0Dh - MC_IMC_FORCE_SR_S3_TIMEOUT
0Eh - MC_CPD_UNCPD_ST_TIMEOUT
0Fh - MC_PKGS_SAFE_WP_TIMEOUT
43h - MC_PECI_MAILBOX_QUIESCE_TIMEOUT
5Ch - MC_MORE_THAN_ONE_LT_AGENT
60h - MC_INVALID_PKGS_REQ_PCH
61h - MC_INVALID_PKGS_REQ_QPI
62h - MC_INVALID_PKGS_RES_QPI
63h - MC_INVALID_PKGC_RES_PCH
64h - MC_INVALID_PKG_STATE_CONFIG
70h - MC_WATCHDG_TIMEOUT_PKGC_SLAVE
71h - MC_WATCHDG_TIMEOUT_PKGC_MASTER
72h - MC_WATCHDG_TIMEOUT_PKGS_MASTER
7ah - MC_HA_FAILSTS_CHANGE_DETECTED
81h - MC_RECOVERABLE_DIE_THERMAL_TOO_HOT

56:32
Status register
validity
indicators1

Reserved

Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.4.2

Intel QPI Machine Check Errors
Table 16-14. Intel QPI MC Error Codes for IA32_MC6_STATUS and IA32_MC7_STATUS

Type

Bit No.

Bit Function

Bit Description

MCA error
codes1

15:0

MCACOD

Bus error format: 1PPTRRRRIILL

56:16

Reserved

Reserved

Model specific
errors
Status register
validity
indicators1

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.4.3

Integrated Memory Controller Machine Check Errors

MC error codes associated with integrated memory controllers are reported in the MSRs IA32_MC8_STATUSIA32_MC11_STATUS. The supported error codes are follows the architectural MCACOD definition type 1MMMCCCC
(see Chapter 15, “Machine-Check Architecture,”). MSR_ERROR_CONTROL.[bit 1] can enable additional informaVol. 3B 16-11

INTERPRETING MACHINE-CHECK ERROR CODES

tion logging of the IMC. The additional error information logged by the IMC is stored in IA32_MCi_STATUS and
IA32_MCi_MISC; (i = 8, 11).

Table 16-15. Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 8, 11)
Type

Bit No.

Bit Function

Bit Description

MCA error codes

15:0

MCACOD

Bus error format: 1PPTRRRRIILL

Model specific
errors

31:16

Reserved except for
the following

001H - Address parity error
002H - HA Wrt buffer Data parity error
004H - HA Wrt byte enable parity error
008H - Corrected patrol scrub error
010H - Uncorrected patrol scrub error
020H - Corrected spare error
040H - Uncorrected spare error

Model specific
errors

36:32

Other info

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log first device
error when corrected error is detected during normal read.

37

Reserved

Reserved

1

56:38
Status register
validity indicators1

See Chapter 15, “Machine-Check Architecture,”

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

Table 16-16. Intel IMC MC Error Codes for IA32_MCi_MISC (i= 8, 11)
Type

Bit No.

MCA addr info1

Bit Function

Bit Description

8:0

See Chapter 15, “Machine-Check Architecture,”

Model specific
errors

13:9

• When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log second device
error when corrected error is detected during normal read.
• Otherwise contain parity error if MCi_Status indicates HA_WB_Data or
HA_W_BE parity error.

Model specific
errors

29:14

ErrMask_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log first-device error bit
mask.

Model specific
errors

45:30

ErrMask_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log second-device error
bit mask.

50:46

FailRank_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log first-device error
failing rank.

55:51

FailRank_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log second-device error
failing rank.

58:56

Reserved

Reserved

61:59

Reserved

Reserved

62

Valid_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, indicates the iMC has logged valid data
from the first correctable error in a memory device.

63

Valid_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, indicates the iMC has logged valid data due
to a second correctable error in a memory device. Use this information only after
there is valid first error info indicated by bit 62.

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16-12 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

16.5

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH
CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_3EH, MACHINE
ERROR CODES FOR MACHINE CHECK

Intel Xeon processor E5 v2 family and Intel Xeon processor E7 v2 family are based on the Ivy Bridge-EP microarchitecture and can be identified with CPUID DisplayFamily_DisplaySignature 06_3EH. Incremental error codes for
internal machine check error from PCU controller is reported in the register bank IA32_MC4, Table lists modelspecific fields to interpret error codes applicable to IA32_MC4_STATUS. Incremental MC error codes related to the
Intel QPI links are reported in the register banks IA32_MC5. Information listed in Table 16-14 for QPI MC error code
apply to IA32_MC5_STATUS. Incremental error codes for the memory controller unit is reported in the register
banks IA32_MC9-IA32_MC16. Table 16-18 lists model-specific error codes apply to IA32_MCi_STATUS, i = 9-16.

16.5.1

Internal Machine Check Errors
Table 16-17. Machine Check Error Codes for IA32_MC4_STATUS

Type
MCA error

codes1

Model specific errors

Bit No.

Bit Function

15:0

MCACOD

19:16

Reserved except for
the following

Bit Description
0000b - No Error
0001b - Non_IMem_Sel
0010b - I_Parity_Error
0011b - Bad_OpCode
0100b - I_Stack_Underflow
0101b - I_Stack_Overflow
0110b - D_Stack_Underflow
0111b - D_Stack_Overflow
1000b - Non-DMem_Sel
1001b - D_Parity_Error

23:20

Reserved

Reserved

31:24

Reserved except for
the following

00h - No Error
0Dh - MC_IMC_FORCE_SR_S3_TIMEOUT
0Eh - MC_CPD_UNCPD_ST_TIMEOUT
0Fh - MC_PKGS_SAFE_WP_TIMEOUT
43h - MC_PECI_MAILBOX_QUIESCE_TIMEOUT
44h - MC_CRITICAL_VR_FAILED
45h - MC_ICC_MAX-NOTSUPPORTED
5Ch - MC_MORE_THAN_ONE_LT_AGENT
60h - MC_INVALID_PKGS_REQ_PCH
61h - MC_INVALID_PKGS_REQ_QPI
62h - MC_INVALID_PKGS_RES_QPI
63h - MC_INVALID_PKGC_RES_PCH
64h - MC_INVALID_PKG_STATE_CONFIG
70h - MC_WATCHDG_TIMEOUT_PKGC_SLAVE
71h - MC_WATCHDG_TIMEOUT_PKGC_MASTER
72h - MC_WATCHDG_TIMEOUT_PKGS_MASTER

Vol. 3B 16-13

INTERPRETING MACHINE-CHECK ERROR CODES

Type

Bit No.

Bit Function

Bit Description
7Ah - MC_HA_FAILSTS_CHANGE_DETECTED
7Bh - MC_PCIE_R2PCIE-RW_BLOCK_ACK_TIMEOUT
81h - MC_RECOVERABLE_DIE_THERMAL_TOO_HOT

56:32
Status register
validity indicators1

Reserved

Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.5.2

Integrated Memory Controller Machine Check Errors

MC error codes associated with integrated memory controllers are reported in the MSRs IA32_MC9_STATUSIA32_MC16_STATUS. The supported error codes are follows the architectural MCACOD definition type 1MMMCCCC
(see Chapter 15, “Machine-Check Architecture,”).
MSR_ERROR_CONTROL.[bit 1] can enable additional information logging of the IMC. The additional error information logged by the IMC is stored in IA32_MCi_STATUS and IA32_MCi_MISC; (i = 9-16).

Table 16-18. Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-16)
Type
MCA error

codes1

Model specific
errors

Bit No.

Bit Function

Bit Description

15:0

MCACOD

Memory Controller error format: 000F 0000 1MMM CCCC

31:16

Reserved except for
the following

001H - Address parity error
002H - HA Wrt buffer Data parity error
004H - HA Wrt byte enable parity error
008H - Corrected patrol scrub error
010H - Uncorrected patrol scrub error
020H - Corrected spare error
040H - Uncorrected spare error
080H - Corrected memory read error. (Only applicable with iMC’s “Additional
Error logging” Mode-1 enabled.)
100H - iMC, WDB, parity errors

36:32

Other info

When MSR_ERROR_CONTROL.[1] is set, logs an encoded value from the first error
device.

37
56:38
Status register
validity indicators1

Reserved

Reserved
See Chapter 15, “Machine-Check Architecture,”

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16-14 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-19. Intel IMC MC Error Codes for IA32_MCi_MISC (i= 9-16)
Type

Bit No.

MCA addr info1

8:0

Bit Function

See Chapter 15, “Machine-Check Architecture,”

Model specific
errors

13:9

If the error logged is MCWrDataPar error or MCWrBEPar error, this field is the WDB
ID that has the parity error. OR if the second error logged is a correctable read
error, MC logs the second error device in this field.

Model specific
errors

29:14

ErrMask_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log first-device error bit
mask.

Model specific
errors

45:30

ErrMask_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log second-device error
bit mask.

50:46

FailRank_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log first-device error
failing rank.

55:51

FailRank_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log second-device error
failing rank.

61:56

Bit Description

Reserved

62

Valid_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, indicates the iMC has logged valid data
from a correctable error from memory read associated with first error device.

63

Valid_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, indicates the iMC has logged valid data due
to a second correctable error in a memory device. Use this information only after
there is valid first error info indicated by bit 62.

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.6

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH
CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_3FH, MACHINE
ERROR CODES FOR MACHINE CHECK

Intel Xeon processor E5 v3 family is based on the Haswell-E microarchitecture and can be identified with CPUID
DisplayFamily_DisplaySignature 06_3FH. Incremental error codes for internal machine check error from PCU
controller is reported in the register bank IA32_MC4, Table 16-20 lists model-specific fields to interpret error codes
applicable to IA32_MC4_STATUS. Incremental MC error codes related to the Intel QPI links are reported in the
register banks IA32_MC5, IA32_MC20, and IA32_MC21. Information listed in Table 16-21 for QPI MC error codes.
Incremental error codes for the memory controller unit is reported in the register banks IA32_MC9-IA32_MC16.
Table 16-22 lists model-specific error codes apply to IA32_MCi_STATUS, i = 9-16.

Vol. 3B 16-15

INTERPRETING MACHINE-CHECK ERROR CODES

16.6.1

Internal Machine Check Errors
Table 16-20. Machine Check Error Codes for IA32_MC4_STATUS

Type
1

MCA error codes
2

MCACOD

Bit No.

Bit Function

15:0

MCACOD

15:0

Internal Errors

Bit Description
0402h - PCU internal Errors
0403h - PCU internal Errors
0406h - Intel TXT Errors
0407h - Other UBOX internal Errors.
On an IERR caused by a core 3-strike the IA32_MC3_STATUS (MLC) is copied
to the IA32_MC4_STATUS (After a 3-strike, the core MCA banks will be
unavailable).

Model specific errors

19:16

Reserved except for
the following

0000b - No Error

23:20

Reserved

Reserved

31:24

Reserved except for
the following

00h - No Error

00xxb - PCU internal error

09h - MC_MESSAGE_CHANNEL_TIMEOUT
13h - MC_DMI_TRAINING_TIMEOUT
15h - MC_DMI_CPU_RESET_ACK_TIMEOUT
1Eh - MC_VR_ICC_MAX_LT_FUSED_ICC_MAX
25h - MC_SVID_COMMAND_TIMEOUT
29h - MC_VR_VOUT_MAC_LT_FUSED_SVID
2Bh - MC_PKGC_WATCHDOG_HANG_CBZ_DOWN
2Ch - MC_PKGC_WATCHDOG_HANG_CBZ_UP
44h - MC_CRITICAL_VR_FAILED
46h - MC_VID_RAMP_DOWN_FAILED
49h - MC_SVID_WRITE_REG_VOUT_MAX_FAILED
4Bh - MC_BOOT_VID_TIMEOUT. Timeout setting boot VID for DRAM 0.
4Fh - MC_SVID_COMMAND_ERROR.
52h - MC_FIVR_CATAS_OVERVOL_FAULT.
53h - MC_FIVR_CATAS_OVERCUR_FAULT.
57h - MC_SVID_PKGC_REQUEST_FAILED
58h - MC_SVID_IMON_REQUEST_FAILED
59h - MC_SVID_ALERT_REQUEST_FAILED
62h - MC_INVALID_PKGS_RSP_QPI
64h - MC_INVALID_PKG_STATE_CONFIG
67h - MC_HA_IMC_RW_BLOCK_ACK_TIMEOUT
6Ah - MC_MSGCH_PMREQ_CMP_TIMEOUT
72h - MC_WATCHDG_TIMEOUT_PKGS_MASTER
81h - MC_RECOVERABLE_DIE_THERMAL_TOO_HOT

56:32
Status register
validity indicators1

Reserved

Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16-16 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

2. The internal error codes may be model-specific.

16.6.2

Intel QPI Machine Check Errors

MC error codes associated with the Intel QPI agents are reported in the MSRs IA32_MC5_STATUS,
IA32_MC20_STATUS, and IA32_MC21_STATUS. The supported error codes follow the architectural MCACOD definition type 1PPTRRRRIILL (see Chapter 15, “Machine-Check Architecture,”).
Table 16-21 lists model-specific fields to interpret error codes applicable to IA32_MC5_STATUS,
IA32_MC20_STATUS, and IA32_MC21_STATUS.

Table 16-21. Intel QPI MC Error Codes for IA32_MCi_STATUS (i = 5, 20, 21)
Type

Bit No.

Bit Function

Bit Description

MCA error
codes1

15:0

MCACOD

Bus error format: 1PPTRRRRIILL

Model specific
errors

31:16

MSCOD

02h - Intel QPI physical layer detected drift buffer alarm.
03h - Intel QPI physical layer detected latency buffer rollover.
10h - Intel QPI link layer detected control error from R3QPI.
11h - Rx entered LLR abort state on CRC error.
12h - Unsupported or undefined packet.
13h - Intel QPI link layer control error.
15h - RBT used un-initialized value.
20h - Intel QPI physical layer detected a QPI in-band reset but aborted initialization
21h - Link failover data self-healing
22h - Phy detected in-band reset (no width change).
23h - Link failover clock failover
30h -Rx detected CRC error - successful LLR after Phy re-init.
31h -Rx detected CRC error - successful LLR without Phy re-init.
All other values are reserved.

Status register
validity
indicators1

37:32

Reserved

52:38

Corrected Error Cnt

56:53

Reserved

Reserved
Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.6.3

Integrated Memory Controller Machine Check Errors

MC error codes associated with integrated memory controllers are reported in the MSRs IA32_MC9_STATUSIA32_MC16_STATUS. The supported error codes follow the architectural MCACOD definition type 1MMMCCCC (see
Chapter 15, “Machine-Check Architecture,”).
MSR_ERROR_CONTROL.[bit 1] can enable additional information logging of the IMC. The additional error information logged by the IMC is stored in IA32_MCi_STATUS and IA32_MCi_MISC; (i = 9-16).

Vol. 3B 16-17

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-22. Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-16)
Type

Bit No.

Bit Function

Bit Description

MCA error codes1

15:0

MCACOD

Memory Controller error format: 0000 0000 1MMM CCCC

Model specific
errors

31:16

Reserved except for
the following

0001H - DDR3 address parity error
0002H - Uncorrected HA write data error
0004H - Uncorrected HA data byte enable error
0008H - Corrected patrol scrub error
0010H - Uncorrected patrol scrub error
0020H - Corrected spare error
0040H - Uncorrected spare error
0080H - Corrected memory read error. (Only applicable with iMC’s “Additional
Error logging” Mode-1 enabled.)
0100H - iMC, write data buffer parity errors
0200H - DDR4 command address parity error

36:32

Other info

When MSR_ERROR_CONTROL.[1] is set, logs an encoded value from the first error
device.

37

Reserved

56:38
Status register
validity indicators1

Reserved
See Chapter 15, “Machine-Check Architecture,”

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

Table 16-23. Intel IMC MC Error Codes for IA32_MCi_MISC (i= 9-16)
Type

Bit No.

MCA addr info1

Bit Function

8:0

See Chapter 15, “Machine-Check Architecture,”

Model specific
errors

13:9

If the error logged is MCWrDataPar error or MCWrBEPar error, this field is the WDB
ID that has the parity error. OR if the second error logged is a correctable read
error, MC logs the second error device in this field.

Model specific
errors

29:14

ErrMask_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log first-device error bit
mask.

Model specific
errors

45:30

ErrMask_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log second-device error
bit mask.

50:46

FailRank_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log first-device error
failing rank.

55:51

FailRank_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, allows the iMC to log second-device error
failing rank.

61:56

16-18 Vol. 3B

Bit Description

Reserved

62

Valid_1stErrDev

When MSR_ERROR_CONTROL.[1] is set, indicates the iMC has logged valid data
from a correctable error from memory read associated with first error device.

63

Valid_2ndErrDev

When MSR_ERROR_CONTROL.[1] is set, indicates the iMC has logged valid data due
to a second correctable error in a memory device. Use this information only after
there is valid first error info indicated by bit 62.

INTERPRETING MACHINE-CHECK ERROR CODES

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.7

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH
CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_56H, MACHINE
ERROR CODES FOR MACHINE CHECK

Intel Xeon processor D family is based on the Broadwell microarchitecture and can be identified with CPUID
DisplayFamily_DisplaySignature 06_56H. Incremental error codes for internal machine check error from PCU
controller is reported in the register bank IA32_MC4, Table 16-24 lists model-specific fields to interpret error codes
applicable to IA32_MC4_STATUS. Incremental error codes for the memory controller unit is reported in the register
banks IA32_MC9-IA32_MC10. Table 16-18 lists model-specific error codes apply to IA32_MCi_STATUS, i = 9-10.

16.7.1

Internal Machine Check Errors
Table 16-24. Machine Check Error Codes for IA32_MC4_STATUS

Type
MCA error

codes1

MCACOD2

Bit No.

Bit Function

15:0

MCACOD

15:0

internal Errors

Bit Description
0402h - PCU internal Errors
0403h - internal Errors
0406h - Intel TXT Errors
0407h - Other UBOX internal Errors.
On an IERR caused by a core 3-strike the IA32_MC3_STATUS (MLC) is copied
to the IA32_MC4_STATUS (After a 3-strike, the core MCA banks will be
unavailable).

Model specific errors

19:16

Reserved except for
the following

0000b - No Error
00x1b - PCU internal error
001xb - PCU internal error

23:20

Reserved except for
the following

x1xxb - UBOX error

31:24

Reserved except for
the following

00h - No Error
09h - MC_MESSAGE_CHANNEL_TIMEOUT
13h - MC_DMI_TRAINING_TIMEOUT
15h - MC_DMI_CPU_RESET_ACK_TIMEOUT
1Eh - MC_VR_ICC_MAX_LT_FUSED_ICC_MAX
25h - MC_SVID_COMMAND_TIMEOUT
26h - MCA_PKGC_DIRECT_WAKE_RING_TIMEOUT
29h - MC_VR_VOUT_MAC_LT_FUSED_SVID
2Bh - MC_PKGC_WATCHDOG_HANG_CBZ_DOWN
2Ch - MC_PKGC_WATCHDOG_HANG_CBZ_UP
44h - MC_CRITICAL_VR_FAILED
46h - MC_VID_RAMP_DOWN_FAILED
49h - MC_SVID_WRITE_REG_VOUT_MAX_FAILED

Vol. 3B 16-19

INTERPRETING MACHINE-CHECK ERROR CODES

Type

Bit No.

Bit Function

Bit Description
4Bh - MC_PP1_BOOT_VID_TIMEOUT. Timeout setting boot VID for DRAM 0.
4Fh - MC_SVID_COMMAND_ERROR.
52h - MC_FIVR_CATAS_OVERVOL_FAULT.
53h - MC_FIVR_CATAS_OVERCUR_FAULT.
57h - MC_SVID_PKGC_REQUEST_FAILED
58h - MC_SVID_IMON_REQUEST_FAILED
59h - MC_SVID_ALERT_REQUEST_FAILED
62h - MC_INVALID_PKGS_RSP_QPI
64h - MC_INVALID_PKG_STATE_CONFIG
67h - MC_HA_IMC_RW_BLOCK_ACK_TIMEOUT
6Ah - MC_MSGCH_PMREQ_CMP_TIMEOUT
72h - MC_WATCHDG_TIMEOUT_PKGS_MASTER
81h - MC_RECOVERABLE_DIE_THERMAL_TOO_HOT

56:32
Status register
validity indicators1

Reserved

Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.
2. The internal error codes may be model-specific.

16.7.2

Integrated Memory Controller Machine Check Errors

MC error codes associated with integrated memory controllers are reported in the MSRs IA32_MC9_STATUSIA32_MC10_STATUS. The supported error codes follow the architectural MCACOD definition type 1MMMCCCC (see
Chapter 15, “Machine-Check Architecture,”).
MSR_ERROR_CONTROL.[bit 1] can enable additional information logging of the IMC. The additional error information logged by the IMC is stored in IA32_MCi_STATUS and IA32_MCi_MISC; (i = 9-10).

Table 16-25. Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-10)
Type
MCA error

codes1

Model specific
errors

Bit No.

Bit Function

Bit Description

15:0

MCACOD

Memory Controller error format: 0000 0000 1MMM CCCC

31:16

Reserved except for
the following

0001H - DDR3 address parity error
0002H - Uncorrected HA write data error
0004H - Uncorrected HA data byte enable error
0008H - Corrected patrol scrub error
0010H - Uncorrected patrol scrub error
0100H - iMC, write data buffer parity errors
0200H - DDR4 command address parity error

36:32

Other info

Reserved

37

Reserved

Reserved

56:38
Status register
validity indicators1
16-20 Vol. 3B

63:57

See Chapter 15, “Machine-Check Architecture,”

INTERPRETING MACHINE-CHECK ERROR CODES

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.8

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH
CPUID DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_4FH, MACHINE
ERROR CODES FOR MACHINE CHECK

Next Generation Intel Xeon processor E5 family is based on the Broadwell microarchitecture and can be identified
with CPUID DisplayFamily_DisplaySignature 06_4FH. Incremental error codes for internal machine check error
from PCU controller is reported in the register bank IA32_MC4, Table 16-20 in Section 16.6.1lists model-specific
fields to interpret error codes applicable to IA32_MC4_STATUS.
Incremental MC error codes related to the Intel QPI links are reported in the register banks IA32_MC5,
IA32_MC20, and IA32_MC21. Information listed in Table 16-21 of Section 16.6.1 covers QPI MC error codes.

16.8.1

Integrated Memory Controller Machine Check Errors

MC error codes associated with integrated memory controllers are reported in the MSRs IA32_MC9_STATUSIA32_MC16_STATUS. The supported error codes follow the architectural MCACOD definition type 1MMMCCCC (see
Chapter 15, “Machine-Check Architecture”).
Table 16-26 lists model-specific error codes apply to IA32_MCi_STATUS, i = 9-16.

Table 16-26. Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 9-16)
Type
MCA error

codes1

Model specific
errors

Bit No.

Bit Function

Bit Description

15:0

MCACOD

Memory Controller error format: 0000 0000 1MMM CCCC

31:16

Reserved except for
the following

0001H - DDR3 address parity error
0002H - Uncorrected HA write data error
0004H - Uncorrected HA data byte enable error
0008H - Corrected patrol scrub error
0010H - Uncorrected patrol scrub error
0020H - Corrected spare error
0040H - Uncorrected spare error
0100H - iMC, write data buffer parity errors
0200H - DDR4 command address parity error

36:32

Other info

Reserved

37

Reserved

Reserved

56:38
Status register
validity indicators1

See Chapter 15, “Machine-Check Architecture,”

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

Vol. 3B 16-21

INTERPRETING MACHINE-CHECK ERROR CODES

16.8.2

Home Agent Machine Check Errors

MC error codes associated with mirrored memory corrections are reported in the MSRs IA32_MC7_MISC and
IA32_MC8_MISC. Table 16-27 lists model-specific error codes apply to IA32_MCi_MISC, i = 7, 8.

Table 16-27. Intel HA MC Error Codes for IA32_MCi_MISC (i= 7, 8)
Bit No.

Bit Function

Bit Description

5:0

LSB

See Figure 15-8.

8:6

Address Mode

See Table 15-3.

40:9

Reserved

Reserved

41

Failover

Error occurred at a pair of mirrored memory channels. Error was corrected by mirroring with
channel failover.

42

Mirrorcorr

Error was corrected by mirroring and primary channel scrubbed successfully.

63:43

Reserved

Reserved

16.9

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID
DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_55H, MACHINE ERROR
CODES FOR MACHINE CHECK

In future Intel Xeon processors with CPUID DisplayFamily_DisplaySignature 06_55H, incremental error codes for
internal machine check errors from the PCU controller are reported in the register bank IA32_MC4. Table 16-28 in
Section 16.9.1 lists model-specific fields to interpret error codes applicable to IA32_MC4_STATUS.

16.9.1

Internal Machine Check Errors
Table 16-28. Machine Check Error Codes for IA32_MC4_STATUS

Type
MCA error

codes1

MCACOD2

Bit No.

Bit Function

15:0

MCACOD

15:0

internal Errors

Bit Description
0402h - PCU internal Errors
0403h - PCU internal Errors
0406h - Intel TXT Errors
0407h - Other UBOX internal Errors.
On an IERR caused by a core 3-strike the IA32_MC3_STATUS (MLC) is copied
to the IA32_MC4_STATUS (After a 3-strike, the core MCA banks will be
unavailable).

Model specific errors

16-22 Vol. 3B

19:16

Reserved except for
the following

0000b - No Error
00xxb - PCU internal error

INTERPRETING MACHINE-CHECK ERROR CODES

Type

Bit No.

Bit Function

Bit Description

23:20

Reserved

Reserved

31:24

Reserved except for
the following

00h - No Error
0Dh - MCA_DMI_TRAINING_TIMEOUT
0Fh - MCA_DMI_CPU_RESET_ACK_TIMEOUT
10h - MCA_MORE_THAN_ONE_LT_AGENT
1Eh - MCA_BIOS_RST_CPL_INVALID_SEQ
1Fh - MCA_BIOS_INVALID_PKG_STATE_CONFIG
25h - MCA_MESSAGE_CHANNEL_TIMEOUT
27h - MCA_MSGCH_PMREQ_CMP_TIMEOUT
30h - MCA_PKGC_DIRECT_WAKE_RING_TIMEOUT
31h - MCA_PKGC_INVALID_RSP_PCH
33h - MCA_PKGC_WATCHDOG_HANG_CBZ_DOWN
34h - MCA_PKGC_WATCHDOG_HANG_CBZ_UP
38h - MCA_PKGC_WATCHDOG_HANG_C3_UP_SF
40h - MCA_SVID_VCCIN_VR_ICC_MAX_FAILURE
41h - MCA_SVID_COMMAND_TIMEOUT
42h - MCA_SVID_VCCIN_VR_VOUT_MAX_FAILURE
43h - MCA_SVID_CPU_VR_CAPABILITY_ERROR
44h - MCA_SVID_CRITICAL_VR_FAILED
45h - MCA_SVID_SA_ITD_ERROR
46h - MCA_SVID_READ_REG_FAILED
47h - MCA_SVID_WRITE_REG_FAILED
48h - MCA_SVID_PKGC_INIT_FAILED
49h - MCA_SVID_PKGC_CONFIG_FAILED
4Ah - MCA_SVID_PKGC_REQUEST_FAILED
4Bh - MCA_SVID_IMON_REQUEST_FAILED
4Ch - MCA_SVID_ALERT_REQUEST_FAILED
4Dh - MCA_SVID_MCP_VP_ABSENT_OR_RAMP_ERROR
4Eh - MCA_SVID_UNEXPECTED_MCP_VP_DETECTED
51h - MCA_FIVR_CATAS_OVERVOL_FAULT
52h - MCA_FIVR_CATAS_OVERCUR_FAULT
58h - MCA_WATCHDG_TIMEOUT_PKGC_SLAVE
59h - MCA_WATCHDG_TIMEOUT_PKGC_MASTER
5Ah - MCA_WATCHDG_TIMEOUT_PKGS_MASTER
61h - MCA_PKGS_CPD_UNPCD_TIMEOUT
63h - MCA_PKGS_INVALID_REQ_PCH
64h - MCA_PKGS_INVALID_REQ_INTERNAL
65h - MCA_PKGS_INVALID_RSP_INTERNAL
6Bh - MCA_PKGS_SMBUS_VPP_PAUSE_TIMEOUT
81h - MC_RECOVERABLE_DIE_THERMAL_TOO_HOT

52:32

Reserved

Reserved

54:53

CORR_ERR_STATUS

Reserved

Vol. 3B 16-23

INTERPRETING MACHINE-CHECK ERROR CODES

Type
Status register
validity indicators1

Bit No.

Bit Function

Bit Description

56:55

Reserved

Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.
2. The internal error codes may be model-specific.

16.9.2

Interconnect Machine Check Errors

MC error codes associated with the link interconnect agents are reported in the MSRs IA32_MC5_STATUS,
IA32_MC12_STATUS, IA32_MC19_STATUS. The supported error codes follow the architectural MCACOD definition
type 1PPTRRRRIILL (see Chapter 15, “Machine-Check Architecture”).
Table 16-29 lists model-specific fields to interpret error codes applicable to IA32_MCi_STATUS, i= 5, 12, 19.

Table 16-29. Interconnect MC Error Codes for IA32_MCi_STATUS, i = 5, 12, 19
Type

Bit No.

Bit Function

Bit Description

MCA error
codes1

15:0

MCACOD

Bus error format: 1PPTRRRRIILL
The two supported compound error codes:
- 0x0C0F - Unsupported/Undefined Packet
- 0x0E0F - For all other corrected and uncorrected errors

Model specific
errors

21:16

MSCOD

The encoding of Uncorrectable (UC) errors are:
00h - UC Phy Initialization Failure.
01h - UC Phy detected drift buffer alarm.
02h - UC Phy detected latency buffer rollover.
10h - UC link layer Rx detected CRC error: unsuccessful LLR entered abort state
11h - UC LL Rx unsupported or undefined packet.
12h - UC LL or Phy control error.
13h - UC LL Rx parameter exchange exception.
1fh - UC LL detected control error from the link-mesh interface
The encoding of correctable (COR) errors are:
20h - COR Phy initialization abort
21h - COR Phy reset
22h - COR Phy lane failure, recovery in x8 width.
23h - COR Phy L0c error corrected without Phy reset
24h - COR Phy L0c error triggering Phy reset
25h - COR Phy L0p exit error corrected with Phy reset
30h - COR LL Rx detected CRC error - successful LLR without Phy re-init.
31h - COR LL Rx detected CRC error - successful LLR with Phy re-init.
All other values are reserved.

16-24 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

Type

Bit No.

Bit Function

31:22

MSCOD_SPARE

Bit Description
The definition below applies to MSCOD 12h (UC LL or Phy Control Errors)
[Bit 22] : Phy Control Error
[Bit 23] : Unexpected Retry.Ack flit
[Bit 24] : Unexpected Retry.Req flit
[Bit 25] : RF parity error
[Bit 26] : Routeback Table error
[Bit 27] : unexpected Tx Protocol flit (EOP, Header or Data)
[Bit 28] : Rx Header-or-Credit BGF credit overflow/underflow
[Bit 29] : Link Layer Reset still in progress when Phy enters L0 (Phy training should
not be enabled until after LL reset is complete as indicated by
KTILCL.LinkLayerReset going back to 0).
[Bit 30] : Link Layer reset initiated while protocol traffic not idle
[Bit 31] : Link Layer Tx Parity Error

Status register
validity
indicators1

37:32

Reserved

52:38

Corrected Error Cnt

56:53

Reserved

Reserved
Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.9.3

Integrated Memory Controller Machine Check Errors

MC error codes associated with integrated memory controllers are reported in the MSRs IA32_MC13_STATUSIA32_MC16_STATUS. The supported error codes follow the architectural MCACOD definition type 1MMMCCCC (see
Chapter 15, “Machine-Check Architecture”).

Vol. 3B 16-25

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-30. Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 13-16)
Type

Bit No.

Bit Function

Bit Description

MCA error codes1

15:0

MCACOD

Memory Controller error format: 0000 0000 1MMM CCCC

Model specific
errors

31:16

Reserved except for
the following

0001H - Address parity error
0002H - HA write data parity error
0004H - HA write byte enable parity error
0008H - Corrected patrol scrub error
0010H - Uncorrected patrol scrub error
0020H - Corrected spare error
0040H - Uncorrected spare error
0080H - Any HA read error
0100H - WDB read parity error
0200H - DDR4 command address parity error
0400H - Uncorrected address parity error
0800H - Unrecognized request type
0801H - Read response to an invalid scoreboard entry
0802H - Unexpected read response
0803H - DDR4 completion to an invalid scoreboard entry
0804H - Completion to an invalid scoreboard entry
0805H - Completion FIFO overflow
0806H - Correctable parity error
0807H - Uncorrectable error
0808H - Interrupt received while outstanding interrupt was not ACKed
0809H - ERID FIFO overflow
080aH - Error on Write credits
080bH - Error on Read credits
080cH - Scheduler error
080dH - Error event

36:32

Other info

MC logs the first error device. This is an encoded 5-bit value of the device.

37

Reserved

Reserved

56:38
Status register
validity indicators1

See Chapter 15, “Machine-Check Architecture,”

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.9.4

M2M Machine Check Errors

MC error codes associated with M2M are reported in the MSRs IA32_MC7_STATUS, IA32_MC8_STATUS. The
supported error codes follow the architectural MCACOD definition type 1MMMCCCC (see Chapter 15, “MachineCheck Architecture,”).

16-26 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-31. M2M MC Error Codes for IA32_MCi_STATUS (i= 7-8)
Type

Bit No.

Bit Function

Bit Description

MCA error codes1

15:0

MCACOD

Compound error format: 0000 0000 1MMM CCCC

Model specific
errors

16

MscodDataRdErr

Logged an MC read data error

17

Reserved

Reserved

18

MscodPtlWrErr

Logged an MC partial write data error

19

MscodFullWrErr

Logged a full write data error

20

MscodBgfErr

Logged an M2M clock-domain-crossing buffer (BGF) error

21

MscodTimeOut

Logged an M2M time out

22

MscodParErr

Logged an M2M tracker parity error

23

MscodBucket1Err

Logged a fatal Bucket1 error

31:24

Reserved

Reserved

36:32

Other info

MC logs the first error device. This is an encoded 5-bit value of the device.

37

Reserved

Reserved

56:38
Status register
validity indicators1

See Chapter 15, “Machine-Check Architecture,”

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16.9.5

Home Agent Machine Check Errors

MC error codes associated with mirrored memory corrections are reported in the MSRs IA32_MC7_MISC and
IA32_MC8_MISC. Table 16-32 lists model-specific error codes apply to IA32_MCi_MISC, i = 7, 8.

Table 16-32. Intel HA MC Error Codes for IA32_MCi_MISC (i= 7, 8)
Bit No.

Bit Function

Bit Description

5:0

LSB

See Figure 15-8.

8:6

Address Mode

See Table 15-3.

40:9

Reserved

Reserved

61:41

Reserved

Reserved

62

Mirrorcorr

Error was corrected by mirroring and primary channel scrubbed successfully.

63

Failover

Error occurred at a pair of mirrored memory channels. Error was corrected by mirroring with
channel failover.

Vol. 3B 16-27

INTERPRETING MACHINE-CHECK ERROR CODES

16.10

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY WITH CPUID
DISPLAYFAMILY_DISPLAYMODEL SIGNATURE 06_5FH, MACHINE ERROR
CODES FOR MACHINE CHECK

In future Intel® Atom™ processors based on Goldmont Microarchitecture with CPUID
DisplayFamily_DisplaySignature 06_5FH (code name Denverton), incremental error codes for the memory
controller unit are reported in the register banks IA32_MC6 and IA32_MC7. Table 16-33 in Section 16.10.1 lists
model-specific fields to interpret error codes applicable to IA32_MCi_STATUS, i = 6, 7.

16.10.1 Integrated Memory Controller Machine Check Errors
MC error codes associated with integrated memory controllers are reported in the MSRs IA32_MC6_STATUS and
IA32_MC7_STATUS. The supported error codes follow the architectural MCACOD definition type 1MMMCCCC (see
Chapter 15, “Machine-Check Architecture”).

Table 16-33. Intel IMC MC Error Codes for IA32_MCi_STATUS (i= 6, 7)
Type
MCA error

codes1

Model specific errors

Bit No.

Bit Function

15:0

MCACOD

31:16

Reserved except for
the following

Bit Description
01h - Cmd/Addr parity
02h - Corrected Demand/Patrol Scrub Error
04h - Uncorrected patrol scrub error
08h - Uncorrected demand read error
10h - WDB read ECC

36:32

Other info

37

Reserved

56:38
Status register
validity indicators1

See Chapter 15, “Machine-Check Architecture”.

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16-28 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

16.11

INCREMENTAL DECODING INFORMATION: PROCESSOR FAMILY 0FH
MACHINE ERROR CODES FOR MACHINE CHECK

Table 16-34 provides information for interpreting additional family 0FH model-specific fields for external bus
errors. These errors are reported in the IA32_MCi_STATUS MSRs. They are reported architecturally) as compound
errors with a general form of 0000 1PPT RRRR IILL in the MCA error code field. See Chapter 15 for information on
the interpretation of compound error codes.

Table 16-34. Incremental Decoding Information: Processor Family 0FH Machine Error Codes For Machine Check
Type

Bit No. Bit Function

MCA error
codes1

15:0

Model-specific
error codes

16

FSB address parity

Bit Description

Address parity error detected:
1 = Address parity error detected
0 = No address parity error

17

Response hard fail

Hardware failure detected on response

18

Response parity

Parity error detected on response

19

PIC and FSB data parity

Data Parity detected on either PIC or FSB access

20

Processor Signature =
00000F04H: Invalid PIC
request

Processor Signature = 00000F04H. Indicates error due to an invalid PIC
request access was made to PIC space with WB memory):
1 = Invalid PIC request error
0 = No Invalid PIC request error
Reserved

All other processors:
Reserved

Other
Information

21

Pad state machine

The state machine that tracks P and N data-strobe relative timing has
become unsynchronized or a glitch has been detected.

22

Pad strobe glitch

Data strobe glitch

23

Pad address glitch

Address strobe glitch

56:24

Reserved

Reserved

Status register 63:57
validity
indicators1
NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.
Table 16-10 provides information on interpreting additional family 0FH, model specific fields for cache hierarchy
errors. These errors are reported in one of the IA32_MCi_STATUS MSRs. These errors are reported, architecturally,
as compound errors with a general form of 0000 0001 RRRR TTLL in the MCA error code field. See Chapter 15 for
how to interpret the compound error code.

16.11.1 Model-Specific Machine Check Error Codes for Intel Xeon Processor MP 7100 Series
Intel Xeon processor MP 7100 series has 5 register banks which contains information related to Machine Check
Errors. MCi_STATUS[63:0] refers to all 5 register banks. MC0_STATUS[63:0] through MC3_STATUS[63:0] is the
same as on previous generation of Intel Xeon processors within Family 0FH. MC4_STATUS[63:0] is the main error

Vol. 3B 16-29

INTERPRETING MACHINE-CHECK ERROR CODES

logging for the processor’s L3 and front side bus errors. It supports the L3 Errors, Bus and Interconnect Errors
Compound Error Codes in the MCA Error Code Field.

Table 16-35. MCi_STATUS Register Bit Definition
Bit Field Name

Bits

Description

MCA_Error_Code

15:0

Specifies the machine check architecture defined error code for the machine check error condition
detected. The machine check architecture defined error codes are guaranteed to be the same for all
Intel Architecture processors that implement the machine check architecture. See tables below

Model_Specific_E 31:16
rror_Code

Specifies the model specific error code that uniquely identifies the machine check error condition
detected. The model specific error codes may differ among Intel Architecture processors for the same
Machine Check Error condition. See tables below

Other_Info

56:32

The functions of the bits in this field are implementation specific and are not part of the machine check
architecture. Software that is intended to be portable among Intel Architecture processors should not
rely on the values in this field.

PCC

57

Processor Context Corrupt flag indicates that the state of the processor might have been corrupted by
the error condition detected and that reliable restarting of the processor may not be possible. When
clear, this flag indicates that the error did not affect the processor's state. This bit will always be set for
MC errors which are not corrected.

ADDRV

58

MC_ADDR register valid flag indicates that the MC_ADDR register contains the address where the error
occurred. When clear, this flag indicates that the MC_ADDR register does not contain the address where
the error occurred. The MC_ADDR register should not be read if the ADDRV bit is clear.

MISCV

59

MC_MISC register valid flag indicates that the MC_MISC register contains additional
information regarding the error. When clear, this flag indicates that the MC_MISC register does not
contain additional information regarding the error. MC_MISC should not be read if the MISCV bit is not
set.

EN

60

Error enabled flag indicates that reporting of the machine check exception for this error was enabled by
the associated flag bit of the MC_CTL register. Note that correctable errors do not have associated
enable bits in the MC_CTL register so the EN bit should be clear when a correctable error is logged.

UC

61

Error uncorrected flag indicates that the processor did not correct the error condition. When clear, this
flag indicates that the processor was able to correct the event condition.

OVER

62

Machine check overflow flag indicates that a machine check error occurred while the results of a
previous error were still in the register bank (i.e., the VAL bit was already set in the
MC_STATUS register). The processor sets the OVER flag and software is responsible for clearing it.
Enabled errors are written over disabled errors, and uncorrected errors are written over corrected
events. Uncorrected errors are not written over previous valid uncorrected errors.

VAL

63

MC_STATUS register valid flag indicates that the information within the MC_STATUS register is valid.
When this flag is set, the processor follows the rules given for the OVER flag in the MC_STATUS register
when overwriting previously valid entries. The processor sets the VAL flag and software is responsible
for clearing it.

16.11.1.1 Processor Machine Check Status Register
MCA Error Code Definition
Intel Xeon processor MP 7100 series use compound MCA Error Codes for logging its CBC internal machine check
errors, L3 Errors, and Bus/Interconnect Errors. It defines additional Machine Check error types
(IA32_MC4_STATUS[15:0]) beyond those defined in Chapter 15. Table 16-36 lists these model-specific MCA error
codes. Error code details are specified in MC4_STATUS [31:16] (see Section 16.11.3), the “Model Specific Error
Code” field. The information in the “Other_Info” field (MC4_STATUS[56:32]) is common to the three processor
error types and contains a correctable event count and specifies the MC4_MISC register format.

16-30 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

Table 16-36. Incremental MCA Error Code for Intel Xeon Processor MP 7100
Processor MCA_Error_Code (MC4_STATUS[15:0])
Type

Error Code

Binary Encoding

Meaning

C

Internal Error

0000 0100 0000 0000 Internal Error Type Code

A

L3 Tag Error

0000 0001 0000 1011 L3 Tag Error Type Code

B

Bus and
Interconnect

0000 100x 0000 1111

Not used but this encoding is reserved for compatibility with other MCA
implementations

Error

0000 101x 0000 1111

Not used but this encoding is reserved for compatibility with other MCA
implementations

0000 110x 0000 1111

Not used but this encoding is reserved for compatibility with other MCA
implementations

0000 1110 0000 1111 Bus and Interconnection Error Type Code
0000 1111 0000 1111 Not used but this encoding is reserved for compatibility with other MCA
implementations
The Bold faced binary encodings are the only encodings used by the processor for MC4_STATUS[15:0].

16.11.2 Other_Info Field (all MCA Error Types)
The MC4_STATUS[56:32] field is common to the processor's three MCA error types (A, B & C).

Table 16-37. Other Information Field Bit Definition
Bit Field Name

Bits

Description

39:32

8-bit Correctable
Event Count

Holds a count of the number of correctable events since cold reset. This is a saturating counter;
the counter begins at 1 (with the first error) and saturates at a count of 255.

41:40

MC4_MISC
format type

The value in this field specifies the format of information in the MC4_MISC register. Currently,
only two values are defined. Valid only when MISCV is asserted.

43:42

–

Reserved

51:44

ECC syndrome

ECC syndrome value for a correctable ECC event when the “Valid ECC syndrome” bit is asserted

52

Valid ECC
syndrome

Set when correctable ECC event supplies the ECC syndrome

54:53

Threshold-Based 00: No tracking - No hardware status tracking is provided for the structure reporting this event.
Error Status
01: Green - Status tracking is provided for the structure posting the event; the current status is
green (below threshold).
10: Yellow - Status tracking is provided for the structure posting the event; the current status is
yellow (above threshold).
11: Reserved for future use
Valid only if Valid bit (bit 63) is set
Undefined if the UC bit (bit 61) is set

56:55

–

Reserved

Vol. 3B 16-31

INTERPRETING MACHINE-CHECK ERROR CODES

16.11.3 Processor Model Specific Error Code Field
16.11.3.1 MCA Error Type A: L3 Error
Note:

The Model Specific Error Code field in MC4_STATUS (bits 31:16).

Table 16-38. Type A: L3 Error Codes
Bit
Num

Sub-Field
Name

Description

Legal Value(s)

18:16

L3 Error
Code

Describes the L3
error
encountered

000 - No error
001 - More than one way reporting a correctable event
010 - More than one way reporting an uncorrectable error
011 - More than one way reporting a tag hit
100 - No error
101 - One way reporting a correctable event
110 - One way reporting an uncorrectable error
111 - One or more ways reporting a correctable event while one or more ways are
reporting an uncorrectable error

20:19

–

Reserved

00

31:21

–

Fixed pattern

0010_0000_000

16.11.3.2 Processor Model Specific Error Code Field Type B: Bus and Interconnect Error
Note:

The Model Specific Error Code field in MC4_STATUS (bits 31:16).

Table 16-39. Type B Bus and Interconnect Error Codes
Bit Num

Sub-Field Name

Description

16

FSB Request Parity

Parity error detected during FSB request phase

17

Core0 Addr Parity

Parity error detected on Core 0 request’s address field

18

Core1 Addr Parity

Parity error detected on Core 1 request’s address field

19

Reserved

20

FSB Response Parity

Parity error on FSB response field detected

21

FSB Data Parity

FSB data parity error on inbound data detected

22

Core0 Data Parity

Data parity error on data received from Core 0 detected

23

Core1 Data Parity

Data parity error on data received from Core 1 detected

24

IDS Parity

Detected an Enhanced Defer parity error (phase A or phase B)

25

FSB Inbound Data ECC

Data ECC event to error on inbound data (correctable or uncorrectable)

26

FSB Data Glitch

Pad logic detected a data strobe ‘glitch’ (or sequencing error)

27

FSB Address Glitch

Pad logic detected a request strobe ‘glitch’ (or sequencing error)

31:28

---

Reserved

Exactly one of the bits defined in the preceding table will be set for a Bus and Interconnect Error. The Data ECC can
be correctable or uncorrectable (the MC4_STATUS.UC bit, of course, distinguishes between correctable and uncorrectable cases with the Other_Info field possibly providing the ECC Syndrome for correctable errors). All other
errors for this processor MCA Error Type are uncorrectable.
16-32 Vol. 3B

INTERPRETING MACHINE-CHECK ERROR CODES

16.11.3.3 Processor Model Specific Error Code Field Type C: Cache Bus Controller Error
Table 16-40. Type C Cache Bus Controller Error Codes
MC4_STATUS[31:16] (MSCE) Value

Error Description

0000_0000_0000_0001 0001H

Inclusion Error from Core 0

0000_0000_0000_0010 0002H

Inclusion Error from Core 1

0000_0000_0000_0011 0003H

Write Exclusive Error from Core 0

0000_0000_0000_0100 0004H

Write Exclusive Error from Core 1

0000_0000_0000_0101 0005H

Inclusion Error from FSB

0000_0000_0000_0110 0006H

SNP Stall Error from FSB

0000_0000_0000_0111 0007H

Write Stall Error from FSB

0000_0000_0000_1000 0008H

FSB Arb Timeout Error

0000_0000_0000_1001 0009H

CBC OOD Queue Underflow/overflow

0000_0001_0000_0000 0100H

Enhanced Intel SpeedStep Technology TM1-TM2 Error

0000_0010_0000_0000 0200H

Internal Timeout error

0000_0011_0000_0000 0300H

Internal Timeout Error

0000_0100_0000_0000 0400H

Intel® Cache Safe Technology Queue Full Error or Disabled-ways-in-a-set overflow

1100_0000_0000_0001 C001H

Correctable ECC event on outgoing FSB data

1100_0000_0000_0010 C002H

Correctable ECC event on outgoing Core 0 data

1100_0000_0000_0100 C004H

Correctable ECC event on outgoing Core 1 data

1110_0000_0000_0001 E001H

Uncorrectable ECC error on outgoing FSB data

1110_0000_0000_0010 E002H

Uncorrectable ECC error on outgoing Core 0 data

1110_0000_0000_0100 E004H

Uncorrectable ECC error on outgoing Core 1 data

— all other encodings —

Reserved

Vol. 3B 16-33

INTERPRETING MACHINE-CHECK ERROR CODES

All errors - except for the correctable ECC types - in this table are uncorrectable. The correctable ECC events may
supply the ECC syndrome in the Other_Info field of the MC4_STATUS MSR.

Table 16-41. Decoding Family 0FH Machine Check Codes for Cache Hierarchy Errors
Type

Bit No.

MCA error
codes1

15:0

Model
specific error
codes

17:16

Bit Function

Bit Description

Tag Error Code

Contains the tag error code for this machine check error:
00 = No error detected
01 = Parity error on tag miss with a clean line
10 = Parity error/multiple tag match on tag hit
11 = Parity error/multiple tag match on tag miss

19:18

Data Error Code

Contains the data error code for this machine check error:
00 = No error detected
01 = Single bit error
10 = Double bit error on a clean line
11 = Double bit error on a modified line

20

L3 Error

This bit is set if the machine check error originated in the L3 it can be ignored for
invalid PIC request errors):
1 = L3 error
0 = L2 error

21

Invalid PIC Request

Indicates error due to invalid PIC request access was made to PIC space with WB
memory):
1 = Invalid PIC request error
0 = No invalid PIC request error

Other
Information

Status
register
validity
indicators1

31:22

Reserved

Reserved

39:32

8-bit Error Count

Holds a count of the number of errors since reset. The counter begins at 0 for the
first error and saturates at a count of 255.

56:40

Reserved

Reserved

63:57

NOTES:
1. These fields are architecturally defined. Refer to Chapter 15, “Machine-Check Architecture,” for more information.

16-34 Vol. 3B

CHAPTER 17
DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING
FEATURES
Intel 64 and IA-32 architectures provide debug facilities for use in debugging code and monitoring performance.
These facilities are valuable for debugging application software, system software, and multitasking operating
systems. Debug support is accessed using debug registers (DR0 through DR7) and model-specific registers
(MSRs):

•

Debug registers hold the addresses of memory and I/O locations called breakpoints. Breakpoints are userselected locations in a program, a data-storage area in memory, or specific I/O ports. They are set where a
programmer or system designer wishes to halt execution of a program and examine the state of the processor
by invoking debugger software. A debug exception (#DB) is generated when a memory or I/O access is made
to a breakpoint address.

•

MSRs monitor branches, interrupts, and exceptions; they record addresses of the last branch, interrupt or
exception taken and the last branch taken before an interrupt or exception.

•
•

Time stamp counter is described in Section 17.17, “Time-Stamp Counter”.

•

Features which enable control over shared platform resources are described in Section 17.19, “Intel® Resource
Director Technology (Intel® RDT) Allocation Features”.

Features which allow monitoring of shared platform resources such as the L3 cache are described in Section
17.18, “Intel® Resource Director Technology (Intel® RDT) Monitoring Features”.

17.1

OVERVIEW OF DEBUG SUPPORT FACILITIES

The following processor facilities support debugging and performance monitoring:

•

Debug exception (#DB) — Transfers program control to a debug procedure or task when a debug event
occurs.

•
•
•

Breakpoint exception (#BP) — See breakpoint instruction (INT 3) below.
Breakpoint-address registers (DR0 through DR3) — Specifies the addresses of up to 4 breakpoints.
Debug status register (DR6) — Reports the conditions that were in effect when a debug or breakpoint
exception was generated.

•

Debug control register (DR7) — Specifies the forms of memory or I/O access that cause breakpoints to be
generated.

•

T (trap) flag, TSS — Generates a debug exception (#DB) when an attempt is made to switch to a task with
the T flag set in its TSS.

•
•

RF (resume) flag, EFLAGS register — Suppresses multiple exceptions to the same instruction.

•

Breakpoint instruction (INT 3) — Generates a breakpoint exception (#BP) that transfers program control to
the debugger procedure or task. This instruction is an alternative way to set code breakpoints. It is especially
useful when more than four breakpoints are desired, or when breakpoints are being placed in the source code.

•

Last branch recording facilities — Store branch records in the last branch record (LBR) stack MSRs for the
most recent taken branches, interrupts, and/or exceptions in MSRs. A branch record consist of a branch-from
and a branch-to instruction address. Send branch records out on the system bus as branch trace messages
(BTMs).

TF (trap) flag, EFLAGS register — Generates a debug exception (#DB) after every execution of an
instruction.

These facilities allow a debugger to be called as a separate task or as a procedure in the context of the current
program or task. The following conditions can be used to invoke the debugger:

•
•

Task switch to a specific task.
Execution of the breakpoint instruction.
Vol. 3B 17-1

DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

•
•
•
•
•
•
•

Execution of any instruction.
Execution of an instruction at a specified address.
Read or write to a specified memory address/range.
Write to a specified memory address/range.
Input from a specified I/O address/range.
Output to a specified I/O address/range.
Attempt to change the contents of a debug register.

17.2

DEBUG REGISTERS

Eight debug registers (see Figure 17-1 for 32-bit operation and Figure 17-2 for 64-bit operation) control the debug
operation of the processor. These registers can be written to and read using the move to/from debug register form
of the MOV instruction. A debug register may be the source or destination operand for one of these instructions.

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

LEN R/W LEN R/W LEN R/W LEN R/W 0 0 G 0 R 1 G L G L G L G L G L
DR7
T
3
3
2
2
1
1
0
0
D
E E 3 3 2 2 1 1 0 0
M
31

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Reserved (set to 1)

R
T B B B 0 1 1 1 1 1 1 1 1 B B B B DR6
3 2 1 0
MT S D

31

0

DR5
31

0

DR4
31

0

DR3

Breakpoint 3 Linear Address

31

0

DR2

Breakpoint 2 Linear Address

31

0

DR1

Breakpoint 1 Linear Address

31

0

Breakpoint 0 Linear Address

Reserved

Figure 17-1. Debug Registers

17-2 Vol. 3B

DR0

DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

Debug registers are privileged resources; a MOV instruction that accesses these registers can only be executed in
real-address mode, in SMM or in protected mode at a CPL of 0. An attempt to read or write the debug registers
from any other privilege level generates a general-protection exception (#GP).
The primary function of the debug registers is to set up and monitor from 1 to 4 breakpoints, numbered 0 though
3. For each breakpoint, the following information can be specified:

•
•
•
•
•

The linear address where the breakpoint is to occur.
The length of the breakpoint location: 1, 2, 4, or 8 bytes (refer to the notes in Section 17.2.4).
The operation that must be performed at the address for a debug exception to be generated.
Whether the breakpoint is enabled.
Whether the breakpoint condition was present when the debug exception was generated.

The following paragraphs describe the functions of flags and fields in the debug registers.

17.2.1

Debug Address Registers (DR0-DR3)

Each of the debug-address registers (DR0 through DR3) holds the 32-bit linear address of a breakpoint (see
Figure 17-1). Breakpoint comparisons are made before physical address translation occurs. The contents of debug
register DR7 further specifies breakpoint conditions.

17.2.2

Debug Registers DR4 and DR5

Debug registers DR4 and DR5 are reserved when debug extensions are enabled (when the DE flag in control
register CR4 is set) and attempts to reference the DR4 and DR5 registers cause invalid-opcode exceptions (#UD).
When debug extensions are not enabled (when the DE flag is clear), these registers are aliased to debug registers
DR6 and DR7.

17.2.3

Debug Status Register (DR6)

The debug status register (DR6) reports debug conditions that were sampled at the time the last debug exception
was generated (see Figure 17-1). Updates to this register only occur when an exception is generated. The flags in
this register show the following information:

•

B0 through B3 (breakpoint condition detected) flags (bits 0 through 3) — Indicates (when set) that its
associated breakpoint condition was met when a debug exception was generated. These flags are set if the
condition described for each breakpoint by the LENn, and R/Wn flags in debug control register DR7 is true. They
may or may not be set if the breakpoint is not enabled by the Ln or the Gn flags in register DR7. Therefore on
a #DB, a debug handler should check only those B0-B3 bits which correspond to an enabled breakpoint.

•

BD (debug register access detected) flag (bit 13) — Indicates that the next instruction in the instruction
stream accesses one of the debug registers (DR0 through DR7). This flag is enabled when the GD (general
detect) flag in debug control register DR7 is set. See Section 17.2.4, “Debug Control Register (DR7),” for
further explanation of the purpose of this flag.

•

BS (single step) flag (bit 14) — Indicates (when set) that the debug exception was triggered by the singlestep execution mode (enabled with the TF flag in the EFLAGS register). The single-step mode is the highestpriority debug exception. When the BS flag is set, any of the other debug status bits also may be set.

•

BT (task switch) flag (bit 15) — Indicates (when set) that the debug exception resulted from a task switch
where the T flag (debug trap flag) in the TSS of the target task was set. See Section 7.2.1, “Task-State
Segment (TSS),” for the format of a TSS. There is no flag in debug control register DR7 to enable or disable this
exception; the T flag of the TSS is the only enabling flag.

•

RTM (restricted transactional memory) flag (bit 16) — Indicates (when clear) that a debug exception
(#DB) or breakpoint exception (#BP) occurred inside an RTM region while advanced debugging of RTM transactional regions was enabled (see Section 17.3.3). This bit is set for any other debug exception (including all
those that occur when advanced debugging of RTM transactional regions is not enabled). This bit is always 1 if
the processor does not support RTM.
Vol. 3B 17-3

DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

Certain debug exceptions may clear bits 0-3. The remaining contents of the DR6 register are never cleared by the
processor. To avoid confusion in identifying debug exceptions, debug handlers should clear the register (except
bit 16, which they should set) before returning to the interrupted task.

17.2.4

Debug Control Register (DR7)

The debug control register (DR7) enables or disables breakpoints and sets breakpoint conditions (see Figure 17-1).
The flags and fields in this register control the following things:

•

L0 through L3 (local breakpoint enable) flags (bits 0, 2, 4, and 6) — Enables (when set) the breakpoint
condition for the associated breakpoint for the current task. When a breakpoint condition is detected and its
associated Ln flag is set, a debug exception is generated. The processor automatically clears these flags on
every task switch to avoid unwanted breakpoint conditions in the new task.

•

G0 through G3 (global breakpoint enable) flags (bits 1, 3, 5, and 7) — Enables (when set) the
breakpoint condition for the associated breakpoint for all tasks. When a breakpoint condition is detected and its
associated Gn flag is set, a debug exception is generated. The processor does not clear these flags on a task
switch, allowing a breakpoint to be enabled for all tasks.

•

LE and GE (local and global exact breakpoint enable) flags (bits 8, 9) — This feature is not supported in
the P6 family processors, later IA-32 processors, and Intel 64 processors. When set, these flags cause the
processor to detect the exact instruction that caused a data breakpoint condition. For backward and forward
compatibility with other Intel processors, we recommend that the LE and GE flags be set to 1 if exact
breakpoints are required.

•

RTM (restricted transactional memory) flag (bit 11) — Enables (when set) advanced debugging of RTM
transactional regions (see Section 17.3.3). This advanced debugging is enabled only if IA32_DEBUGCTL.RTM is
also set.

•

GD (general detect enable) flag (bit 13) — Enables (when set) debug-register protection, which causes a
debug exception to be generated prior to any MOV instruction that accesses a debug register. When such a
condition is detected, the BD flag in debug status register DR6 is set prior to generating the exception. This
condition is provided to support in-circuit emulators.
When the emulator needs to access the debug registers, emulator software can set the GD flag to prevent
interference from the program currently executing on the processor.
The processor clears the GD flag upon entering to the debug exception handler, to allow the handler access to
the debug registers.

•

R/W0 through R/W3 (read/write) fields (bits 16, 17, 20, 21, 24, 25, 28, and 29) — Specifies the
breakpoint condition for the corresponding breakpoint. The DE (debug extensions) flag in control register CR4
determines how the bits in the R/Wn fields are interpreted. When the DE flag is set, the processor interprets
bits as follows:
00
01
10
11

—
—
—
—

Break
Break
Break
Break

on
on
on
on

instruction execution only.
data writes only.
I/O reads or writes.
data reads or writes but not instruction fetches.

When the DE flag is clear, the processor interprets the R/Wn bits the same as for the Intel386™ and Intel486™
processors, which is as follows:
00
01
10
11

•

—
—
—
—

Break on instruction execution only.
Break on data writes only.
Undefined.
Break on data reads or writes but not instruction fetches.

LEN0 through LEN3 (Length) fields (bits 18, 19, 22, 23, 26, 27, 30, and 31) — Specify the size of the
memory location at the address specified in the corresponding breakpoint address register (DR0 through DR3).
These fields are interpreted as follows:
00
01
10
11

17-4 Vol. 3B

—
—
—
—

1-byte length.
2-byte length.
Undefined (or 8 byte length, see note below).
4-byte length.

DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

If the corresponding RWn field in register DR7 is 00 (instruction execution), then the LENn field should also be 00.
The effect of using other lengths is undefined. See Section 17.2.5, “Breakpoint Field Recognition,” below.

NOTES
For Pentium® 4 and Intel® Xeon® processors with a CPUID signature corresponding to family 15
(model 3, 4, and 6), break point conditions permit specifying 8-byte length on data read/write with
an of encoding 10B in the LENn field.
Encoding 10B is also supported in processors based on Intel Core microarchitecture or enhanced
Intel Core microarchitecture, the respective CPUID signatures corresponding to family 6, model 15,
and family 6, DisplayModel value 23 (see CPUID instruction in Chapter 3, “Instruction Set
Reference, A-L” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
2A). The Encoding 10B is supported in processors based on Intel® Atom™ microarchitecture, with
CPUID signature of family 6, DisplayModel value 1CH. The encoding 10B is undefined for other
processors.

17.2.5

Breakpoint Field Recognition

Breakpoint address registers (debug registers DR0 through DR3) and the LENn fields for each breakpoint define a
range of sequential byte addresses for a data or I/O breakpoint. The LENn fields permit specification of a 1-, 2-, 4or 8-byte range, beginning at the linear address specified in the corresponding debug register (DRn). Two-byte
ranges must be aligned on word boundaries; 4-byte ranges must be aligned on doubleword boundaries, 8-byte
ranges must be aligned on quadword boundaries. I/O addresses are zero-extended (from 16 to 32 bits, for
comparison with the breakpoint address in the selected debug register). These requirements are enforced by the
processor; it uses LENn field bits to mask the lower address bits in the debug registers. Unaligned data or I/O
breakpoint addresses do not yield valid results.
A data breakpoint for reading or writing data is triggered if any of the bytes participating in an access is within the
range defined by a breakpoint address register and its LENn field. Table 17-1 provides an example setup of debug
registers and data accesses that would subsequently trap or not trap on the breakpoints.
A data breakpoint for an unaligned operand can be constructed using two breakpoints, where each breakpoint is
byte-aligned and the two breakpoints together cover the operand. The breakpoints generate exceptions only for
the operand, not for neighboring bytes.
Instruction breakpoint addresses must have a length specification of 1 byte (the LENn field is set to 00). Code
breakpoints for other operand sizes are undefined. The processor recognizes an instruction breakpoint address
only when it points to the first byte of an instruction. If the instruction has prefixes, the breakpoint address must
point to the first prefix.

Vol. 3B 17-5

DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

Table 17-1. Breakpoint Examples
Debug Register Setup
Debug Register

R/Wn

Breakpoint Address

LENn

DR0
DR1
DR2
DR3

R/W0 = 11 (Read/Write)
R/W1 = 01 (Write)
R/W2 = 11 (Read/Write)
R/W3 = 01 (Write)

A0001H
A0002H
B0002H
C0000H

LEN0 = 00 (1 byte)
LEN1 = 00 (1 byte)
LEN2 = 01) (2 bytes)
LEN3 = 11 (4 bytes)

Data Accesses
Operation

Address

Access Length
(In Bytes)

Data operations that trap
- Read or write
- Read or write
- Write
- Write
- Read or write
- Read or write
- Read or write
- Write
- Write
- Write

A0001H
A0001H
A0002H
A0002H
B0001H
B0002H
B0002H
C0000H
C0001H
C0003H

1
2
1
2
4
1
2
4
2
1

Data operations that do not trap
- Read or write
- Read
- Read or write
- Read or write
- Read
- Read or write

A0000H
A0002H
A0003H
B0000H
C0000H
C0004H

1
1
4
2
2
4

17.2.6

Debug Registers and Intel® 64 Processors

For Intel 64 architecture processors, debug registers DR0–DR7 are 64 bits. In 16-bit or 32-bit modes (protected
mode and compatibility mode), writes to a debug register fill the upper 32 bits with zeros. Reads from a debug
register return the lower 32 bits. In 64-bit mode, MOV DRn instructions read or write all 64 bits. Operand-size
prefixes are ignored.
In 64-bit mode, the upper 32 bits of DR6 and DR7 are reserved and must be written with zeros. Writing 1 to any of
the upper 32 bits results in a #GP(0) exception (see Figure 17-2). All 64 bits of DR0–DR3 are writable by software.
However, MOV DRn instructions do not check that addresses written to DR0–DR3 are in the linear-address limits of
the processor implementation (address matching is supported only on valid addresses generated by the processor
implementation). Break point conditions for 8-byte memory read/writes are supported in all modes.

17.3

DEBUG EXCEPTIONS

The Intel 64 and IA-32 architectures dedicate two interrupt vectors to handling debug exceptions: vector 1 (debug
exception, #DB) and vector 3 (breakpoint exception, #BP). The following sections describe how these exceptions
are generated and typical exception handler operations.

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63

32

DR7
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

LEN R/W LEN R/W LEN R/W LEN R/W 0 0 G 0 0 1 G L G L G L G L G L
DR7
3
3
2
2
1
1
0
0
D
E E 3 3 2 2 1 1 0 0
63

32

DR6
31

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Reserved (set to 1)

B B B 0 1 1 1 1 1 1 1 1 1 B B B B
DR6
T S D
3 2 1 0

63

0

DR5
63

0

DR4
63

0

DR3

Breakpoint 3 Linear Address

63

0

DR2

Breakpoint 2 Linear Address
63

0

DR1

Breakpoint 1 Linear Address

63

0

Breakpoint 0 Linear Address

DR0

Reserved

Figure 17-2. DR6/DR7 Layout on Processors Supporting Intel® 64 Architecture

17.3.1

Debug Exception (#DB)—Interrupt Vector 1

The debug-exception handler is usually a debugger program or part of a larger software system. The processor
generates a debug exception for any of several conditions. The debugger checks flags in the DR6 and DR7 registers
to determine which condition caused the exception and which other conditions might apply. Table 17-2 shows the
states of these flags following the generation of each kind of breakpoint condition.
Instruction-breakpoint and general-detect condition (see Section 17.3.1.3, “General-Detect Exception Condition”)
result in faults; other debug-exception conditions result in traps. The debug exception may report one or both at
one time. The following sections describe each class of debug exception.

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See also: Chapter 6, “Interrupt 1—Debug Exception (#DB),” in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 3A.

Table 17-2. Debug Exception Conditions
Debug or Breakpoint Condition

DR6 Flags Tested

Single-step trap

BS = 1

Instruction breakpoint, at addresses defined by DRn and
LENn

Bn = 1 and
(Gn or Ln = 1)

R/Wn = 0

Fault

Data write breakpoint, at addresses defined by DRn and
LENn

Bn = 1 and
(Gn or Ln = 1)

R/Wn = 1

Trap

I/O read or write breakpoint, at addresses defined by DRn
and LENn

Bn = 1 and
(Gn or Ln = 1)

R/Wn = 2

Trap

Data read or write (but not instruction fetches), at
addresses defined by DRn and LENn

Bn = 1 and
(Gn or Ln = 1)

R/Wn = 3

Trap

General detect fault, resulting from an attempt to modify
debug registers (usually in conjunction with in-circuit
emulation)

BD = 1

Fault

Task switch

BT = 1

Trap

17.3.1.1

DR7 Flags Tested

Exception Class
Trap

Instruction-Breakpoint Exception Condition

The processor reports an instruction breakpoint when it attempts to execute an instruction at an address specified
in a breakpoint-address register (DR0 through DR3) that has been set up to detect instruction execution (R/W flag
is set to 0). Upon reporting the instruction breakpoint, the processor generates a fault-class, debug exception
(#DB) before it executes the target instruction for the breakpoint.
Instruction breakpoints are the highest priority debug exceptions. They are serviced before any other exceptions
detected during the decoding or execution of an instruction. However, if a code instruction breakpoint is placed on
an instruction located immediately after a POP SS/MOV SS instruction, the breakpoint may not be triggered. In
most situations, POP SS/MOV SS will inhibit such interrupts (see “MOV—Move” and “POP—Pop a Value from the
Stack” in Chapter 4 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B).
Because the debug exception for an instruction breakpoint is generated before the instruction is executed, if the
instruction breakpoint is not removed by the exception handler; the processor will detect the instruction breakpoint
again when the instruction is restarted and generate another debug exception. To prevent looping on an instruction
breakpoint, the Intel 64 and IA-32 architectures provide the RF flag (resume flag) in the EFLAGS register (see
Section 2.3, “System Flags and Fields in the EFLAGS Register,” in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 3A). When the RF flag is set, the processor ignores instruction breakpoints.
All Intel 64 and IA-32 processors manage the RF flag as follows. The RF Flag is cleared at the start of the instruction
after the check for code breakpoint, CS limit violation and FP exceptions. Task Switches and IRETD/IRETQ instructions transfer the RF image from the TSS/stack to the EFLAGS register.
When calling an event handler, Intel 64 and IA-32 processors establish the value of the RF flag in the EFLAGS image
pushed on the stack:

•

For any fault-class exception except a debug exception generated in response to an instruction breakpoint, the
value pushed for RF is 1.

•

For any interrupt arriving after any iteration of a repeated string instruction but the last iteration, the value
pushed for RF is 1.

•

For any trap-class exception generated by any iteration of a repeated string instruction but the last iteration,
the value pushed for RF is 1.

•

For other cases, the value pushed for RF is the value that was in EFLAG.RF at the time the event handler was
called. This includes:
— Debug exceptions generated in response to instruction breakpoints

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— Hardware-generated interrupts arriving between instructions (including those arriving after the last
iteration of a repeated string instruction)
— Trap-class exceptions generated after an instruction completes (including those generated after the last
iteration of a repeated string instruction)
— Software-generated interrupts (RF is pushed as 0, since it was cleared at the start of the software interrupt)
As noted above, the processor does not set the RF flag prior to calling the debug exception handler for debug
exceptions resulting from instruction breakpoints. The debug exception handler can prevent recurrence of the
instruction breakpoint by setting the RF flag in the EFLAGS image on the stack. If the RF flag in the EFLAGS image
is set when the processor returns from the exception handler, it is copied into the RF flag in the EFLAGS register by
IRETD/IRETQ or a task switch that causes the return. The processor then ignores instruction breakpoints for the
duration of the next instruction. (Note that the POPF, POPFD, and IRET instructions do not transfer the RF image
into the EFLAGS register.) Setting the RF flag does not prevent other types of debug-exception conditions (such as,
I/O or data breakpoints) from being detected, nor does it prevent non-debug exceptions from being generated.
For the Pentium processor, when an instruction breakpoint coincides with another fault-type exception (such as a
page fault), the processor may generate one spurious debug exception after the second exception has been
handled, even though the debug exception handler set the RF flag in the EFLAGS image. To prevent a spurious
exception with Pentium processors, all fault-class exception handlers should set the RF flag in the EFLAGS image.

17.3.1.2

Data Memory and I/O Breakpoint Exception Conditions

Data memory and I/O breakpoints are reported when the processor attempts to access a memory or I/O address
specified in a breakpoint-address register (DR0 through DR3) that has been set up to detect data or I/O accesses
(R/W flag is set to 1, 2, or 3). The processor generates the exception after it executes the instruction that made the
access, so these breakpoint condition causes a trap-class exception to be generated.
Because data breakpoints are traps, an instruction that writes memory overwrites the original data before the
debug exception generated by a data breakpoint is generated. If a debugger needs to save the contents of a write
breakpoint location, it should save the original contents before setting the breakpoint. The handler can report the
saved value after the breakpoint is triggered. The address in the debug registers can be used to locate the new
value stored by the instruction that triggered the breakpoint.
If a data breakpoint is detected during an iteration of a string instruction executed with fast-string operation (see
Section 7.3.9.3 of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1), delivery of the
resulting debug exception may be delayed until completion of the corresponding group of iterations.
Intel486 and later processors ignore the GE and LE flags in DR7. In Intel386 processors, exact data breakpoint
matching does not occur unless it is enabled by setting the LE and/or the GE flags.
For repeated INS and OUTS instructions that generate an I/O-breakpoint debug exception, the processor generates the exception after the completion of the first iteration. Repeated INS and OUTS instructions generate a databreakpoint debug exception after the iteration in which the memory address breakpoint location is accessed.

17.3.1.3

General-Detect Exception Condition

When the GD flag in DR7 is set, the general-detect debug exception occurs when a program attempts to access any
of the debug registers (DR0 through DR7) at the same time they are being used by another application, such as an
emulator or debugger. This protection feature guarantees full control over the debug registers when required. The
debug exception handler can detect this condition by checking the state of the BD flag in the DR6 register. The
processor generates the exception before it executes the MOV instruction that accesses a debug register, which
causes a fault-class exception to be generated.

17.3.1.4

Single-Step Exception Condition

The processor generates a single-step debug exception if (while an instruction is being executed) it detects that the
TF flag in the EFLAGS register is set. The exception is a trap-class exception, because the exception is generated
after the instruction is executed. The processor will not generate this exception after the instruction that sets the
TF flag. For example, if the POPF instruction is used to set the TF flag, a single-step trap does not occur until after
the instruction that follows the POPF instruction.
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The processor clears the TF flag before calling the exception handler. If the TF flag was set in a TSS at the time of
a task switch, the exception occurs after the first instruction is executed in the new task.
The TF flag normally is not cleared by privilege changes inside a task. The INT n and INTO instructions, however,
do clear this flag. Therefore, software debuggers that single-step code must recognize and emulate INT n or INTO
instructions rather than executing them directly. To maintain protection, the operating system should check the
CPL after any single-step trap to see if single stepping should continue at the current privilege level.
The interrupt priorities guarantee that, if an external interrupt occurs, single stepping stops. When both an external
interrupt and a single-step interrupt occur together, the single-step interrupt is processed first. This operation
clears the TF flag. After saving the return address or switching tasks, the external interrupt input is examined
before the first instruction of the single-step handler executes. If the external interrupt is still pending, then it is
serviced. The external interrupt handler does not run in single-step mode. To single step an interrupt handler,
single step an INT n instruction that calls the interrupt handler.

17.3.1.5

Task-Switch Exception Condition

The processor generates a debug exception after a task switch if the T flag of the new task's TSS is set. This exception is generated after program control has passed to the new task, and prior to the execution of the first instruction of that task. The exception handler can detect this condition by examining the BT flag of the DR6 register.
If entry 1 (#DB) in the IDT is a task gate, the T bit of the corresponding TSS should not be set. Failure to observe
this rule will put the processor in a loop.

17.3.2

Breakpoint Exception (#BP)—Interrupt Vector 3

The breakpoint exception (interrupt 3) is caused by execution of an INT 3 instruction. See Chapter 6, “Interrupt
3—Breakpoint Exception (#BP).” Debuggers use break exceptions in the same way that they use the breakpoint
registers; that is, as a mechanism for suspending program execution to examine registers and memory locations.
With earlier IA-32 processors, breakpoint exceptions are used extensively for setting instruction breakpoints.
With the Intel386 and later IA-32 processors, it is more convenient to set breakpoints with the breakpoint-address
registers (DR0 through DR3). However, the breakpoint exception still is useful for breakpointing debuggers,
because a breakpoint exception can call a separate exception handler. The breakpoint exception is also useful when
it is necessary to set more breakpoints than there are debug registers or when breakpoints are being placed in the
source code of a program under development.

17.3.3

Debug Exceptions, Breakpoint Exceptions, and Restricted Transactional Memory
(RTM)

Chapter 16, “Programming with Intel® Transactional Synchronization Extensions,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 describes Restricted Transactional Memory (RTM). This is an
instruction-set interface that allows software to identify transactional regions (or critical sections) using the
XBEGIN and XEND instructions.
Execution of an RTM transactional region begins with an XBEGIN instruction. If execution of the region successfully
reaches an XEND instruction, the processor ensures that all memory operations performed within the region
appear to have occurred instantaneously when viewed from other logical processors. Execution of an RTM transaction region does not succeed if the processor cannot commit the updates atomically. When this happens, the
processor rolls back the execution, a process referred to as a transactional abort. In this case, the processor
discards all updates performed in the region, restores architectural state to appear as if the execution had not
occurred, and resumes execution at a fallback instruction address that was specified with the XBEGIN instruction.
If debug exception (#DB) or breakpoint exception (#BP) occurs within an RTM transaction region, a transactional
abort occurs, the processor sets EAX[4], and no exception is delivered.
Software can enable advanced debugging of RTM transactional regions by setting DR7.RTM[bit 11] and
IA32_DEBUGCTL.RTM[bit 15]. If these bits are both set, the transactional abort caused by a #DB or #BP within an
RTM transaction region does not resume execution at the fallback instruction address specified with the XBEGIN
instruction that begin the region. Instead, execution is resumed at that XBEGIN instruction, and a #DB is delivered.

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(A #DB is delivered even if the transactional abort was caused by a #BP.) Such a #DB will clear DR6.RTM[bit 16]
(all other debug exceptions set DR6[16]).

17.4

LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING OVERVIEW

P6 family processors introduced the ability to set breakpoints on taken branches, interrupts, and exceptions, and
to single-step from one branch to the next. This capability has been modified and extended in the Pentium 4, Intel
Xeon, Pentium M, Intel® Core™ Solo, Intel® Core™ Duo, Intel® Core™2 Duo, Intel® Core™ i7 and Intel® Atom™
processors to allow logging of branch trace messages in a branch trace store (BTS) buffer in memory.
See the following sections for processor specific implementation of last branch, interrupt and exception recording:
— Section 17.5, “Last Branch, Interrupt, and Exception Recording (Intel® Core™ 2 Duo and Intel® Atom™
Processors)”
— Section 17.6, “Last Branch, Call Stack, Interrupt, and Exception Recording for Processors based on
Goldmont Microarchitecture”
— Section 17.9, “Last Branch, Interrupt, and Exception Recording for Processors based on Intel® Microarchitecture code name Nehalem”
— Section 17.10, “Last Branch, Interrupt, and Exception Recording for Processors based on Intel® Microarchitecture code name Sandy Bridge”
— Section 17.11, “Last Branch, Call Stack, Interrupt, and Exception Recording for Processors based on
Haswell Microarchitecture”
— Section 17.12, “Last Branch, Call Stack, Interrupt, and Exception Recording for Processors based on
Skylake Microarchitecture”
— Section 17.14, “Last Branch, Interrupt, and Exception Recording (Intel® Core™ Solo and Intel® Core™
Duo Processors)”
— Section 17.15, “Last Branch, Interrupt, and Exception Recording (Pentium M Processors)”
— Section 17.16, “Last Branch, Interrupt, and Exception Recording (P6 Family Processors)”
The following subsections of Section 17.4 describe common features of profiling branches. These features are
generally enabled using the IA32_DEBUGCTL MSR (older processor may have implemented a subset or modelspecific features, see definitions of MSR_DEBUGCTLA, MSR_DEBUGCTLB, MSR_DEBUGCTL).

17.4.1

IA32_DEBUGCTL MSR

The IA32_DEBUGCTL MSR provides bit field controls to enable debug trace interrupts, debug trace stores, trace
messages enable, single stepping on branches, last branch record recording, and to control freezing of LBR stack
or performance counters on a PMI request. IA32_DEBUGCTL MSR is located at register address 01D9H.
See Figure 17-3 for the MSR layout and the bullets below for a description of the flags:

•

LBR (last branch/interrupt/exception) flag (bit 0) — When set, the processor records a running trace of
the most recent branches, interrupts, and/or exceptions taken by the processor (prior to a debug exception
being generated) in the last branch record (LBR) stack. For more information, see the Section 17.5.1, “LBR
Stack” (Intel® Core™2 Duo and Intel® Atom™ Processor Family) and Section 17.9.1, “LBR Stack” (processors
based on Intel® Microarchitecture code name Nehalem).

•

BTF (single-step on branches) flag (bit 1) — When set, the processor treats the TF flag in the EFLAGS
register as a “single-step on branches” flag rather than a “single-step on instructions” flag. This mechanism
allows single-stepping the processor on taken branches. See Section 17.4.3, “Single-Stepping on Branches,”
for more information about the BTF flag.

•

TR (trace message enable) flag (bit 6) — When set, branch trace messages are enabled. When the
processor detects a taken branch, interrupt, or exception; it sends the branch record out on the system bus as
a branch trace message (BTM). See Section 17.4.4, “Branch Trace Messages,” for more information about the
TR flag.

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•

BTS (branch trace store) flag (bit 7) — When set, the flag enables BTS facilities to log BTMs to a memoryresident BTS buffer that is part of the DS save area. See Section 17.4.9, “BTS and DS Save Area.”

•

BTINT (branch trace interrupt) flag (bit 8) — When set, the BTS facilities generate an interrupt when the
BTS buffer is full. When clear, BTMs are logged to the BTS buffer in a circular fashion. See Section 17.4.5, “Branch
Trace Store (BTS),” for a description of this mechanism.

31

15 14

12 11 10 9 8 7 6 5 4 3 2 1 0

Reserved
RTM
FREEZE_WHILE_SMM_EN
FREEZE_PERFMON_ON_PMI
FREEZE_LBRS_ON_PMI
BTS_OFF_USR — BTS off in user code
BTS_OFF_OS — BTS off in OS
BTINT — Branch trace interrupt
BTS — Branch trace store
TR — Trace messages enable
Reserved
BTF — Single-step on branches
LBR — Last branch/interrupt/exception

Figure 17-3. IA32_DEBUGCTL MSR for Processors based
on Intel Core microarchitecture

•

BTS_OFF_OS (branch trace off in privileged code) flag (bit 9) — When set, BTS or BTM is skipped if CPL
is 0. See Section 17.13.2.

•

BTS_OFF_USR (branch trace off in user code) flag (bit 10) — When set, BTS or BTM is skipped if CPL is
greater than 0. See Section 17.13.2.

•

FREEZE_LBRS_ON_PMI flag (bit 11) — When set, the LBR stack is frozen on a hardware PMI request (e.g.
when a counter overflows and is configured to trigger PMI). See Section 17.4.7 for details.

•

FREEZE_PERFMON_ON_PMI flag (bit 12) — When set, the performance counters (IA32_PMCx and
IA32_FIXED_CTRx) are frozen on a PMI request. See Section 17.4.7 for details.

•

FREEZE_WHILE_SMM_EN (bit 14) — If this bit is set, upon the delivery of an SMI, the processor will clear all
the enable bits of IA32_PERF_GLOBAL_CTRL, save a copy of the content of IA32_DEBUGCTL and disable LBR,
BTF, TR, and BTS fields of IA32_DEBUGCTL before transferring control to the SMI handler. Subsequently, the
enable bits of IA32_PERF_GLOBAL_CTRL will be set to 1, the saved copy of IA32_DEBUGCTL prior to SMI
delivery will be restored, after the SMI handler issues RSM to complete its service. Note that system software
must check if the processor supports the IA32_DEBUGCTL.FREEZE_WHILE_SMM_EN control bit.
IA32_DEBUGCTL.FREEZE_WHILE_SMM_EN is supported if
IA32_PERF_CAPABILITIES.FREEZE_WHILE_SMM[Bit 12] is reporting 1. See Section 18.8 for details of
detecting the presence of IA32_PERF_CAPABILITIES MSR.

•

RTM (bit 15) — If this bit is set, advanced debugging of RTM transactional regions is enabled if DR7.RTM is
also set. See Section 17.3.3.

17.4.2

Monitoring Branches, Exceptions, and Interrupts

When the LBR flag (bit 0) in the IA32_DEBUGCTL MSR is set, the processor automatically begins recording branch
records for taken branches, interrupts, and exceptions (except for debug exceptions) in the LBR stack MSRs.
When the processor generates a debug exception (#DB), it automatically clears the LBR flag before executing the
exception handler. This action does not clear previously stored LBR stack MSRs.
A debugger can use the linear addresses in the LBR stack to re-set breakpoints in the breakpoint address registers
(DR0 through DR3). This allows a backward trace from the manifestation of a particular bug toward its source.

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On some processors, if the LBR flag is cleared and TR flag in the IA32_DEBUGCTL MSR remains set, the processor
will continue to update LBR stack MSRs. This is because those processors use the entries in the LBR stack in the
process of generating BTM/BTS records. A #DB does not automatically clear the TR flag.

17.4.3

Single-Stepping on Branches

When software sets both the BTF flag (bit 1) in the IA32_DEBUGCTL MSR and the TF flag in the EFLAGS register,
the processor generates a single-step debug exception only after instructions that cause a branch.1 This mechanism allows a debugger to single-step on control transfers caused by branches. This “branch single stepping” helps
isolate a bug to a particular block of code before instruction single-stepping further narrows the search. The
processor clears the BTF flag when it generates a debug exception. The debugger must set the BTF flag before
resuming program execution to continue single-stepping on branches.

17.4.4

Branch Trace Messages

Setting the TR flag (bit 6) in the IA32_DEBUGCTL MSR enables branch trace messages (BTMs). Thereafter, when
the processor detects a branch, exception, or interrupt, it sends a branch record out on the system bus as a BTM.
A debugging device that is monitoring the system bus can read these messages and synchronize operations with
taken branch, interrupt, and exception events.
When interrupts or exceptions occur in conjunction with a taken branch, additional BTMs are sent out on the bus,
as described in Section 17.4.2, “Monitoring Branches, Exceptions, and Interrupts.”
For P6 processor family, Pentium M processor family, processors based on Intel Core microarchitecture, TR and LBR
bits can not be set at the same time due to hardware limitation. The content of LBR stack is undefined when TR is
set.
For processors with Intel NetBurst microarchitecture, Intel Atom processors, and Intel Core and related Intel Xeon
processors both starting with the Nehalem microarchitecture, the processor can collect branch records in the LBR
stack and at the same time send/store BTMs when both the TR and LBR flags are set in the IA32_DEBUGCTL MSR
(or the equivalent MSR_DEBUGCTLA, MSR_DEBUGCTLB).
The following exception applies:

•

BTM may not be observable on Intel Atom processor families that do not provide an externally visible system
bus (i.e., processors based on the Silvermont microarchitecture or later).

17.4.4.1

Branch Trace Message Visibility

Branch trace message (BTM) visibility is implementation specific and limited to systems with a front side bus
(FSB). BTMs may not be visible to newer system link interfaces or a system bus that deviates from a traditional
FSB.

17.4.5

Branch Trace Store (BTS)

A trace of taken branches, interrupts, and exceptions is useful for debugging code by providing a method of determining the decision path taken to reach a particular code location. The LBR flag (bit 0) of IA32_DEBUGCTL provides
a mechanism for capturing records of taken branches, interrupts, and exceptions and saving them in the last
branch record (LBR) stack MSRs, setting the TR flag for sending them out onto the system bus as BTMs. The branch
trace store (BTS) mechanism provides the additional capability of saving the branch records in a memory-resident
BTS buffer, which is part of the DS save area. The BTS buffer can be configured to be circular so that the most
recent branch records are always available or it can be configured to generate an interrupt when the buffer is
nearly full so that all the branch records can be saved. The BTINT flag (bit 8) can be used to enable the generation
of interrupt when the BTS buffer is full. See Section 17.4.9.2, “Setting Up the DS Save Area.” for additional details.
1. Executions of CALL, IRET, and JMP that cause task switches never cause single-step debug exceptions (regardless of the value of the
BTF flag). A debugger desiring debug exceptions on switches to a task should set the T flag (debug trap flag) in the TSS of that task.
See Section 7.2.1, “Task-State Segment (TSS).”
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Setting this flag (BTS) alone can greatly reduce the performance of the processor. CPL-qualified branch trace
storing mechanism can help mitigate the performance impact of sending/logging branch trace messages.

17.4.6

CPL-Qualified Branch Trace Mechanism

CPL-qualified branch trace mechanism is available to a subset of Intel 64 and IA-32 processors that support the
branch trace storing mechanism. The processor supports the CPL-qualified branch trace mechanism if
CPUID.01H:ECX[bit 4] = 1.
The CPL-qualified branch trace mechanism is described in Section 17.4.9.4. System software can selectively specify
CPL qualification to not send/store Branch Trace Messages associated with a specified privilege level. Two bit fields,
BTS_OFF_USR (bit 10) and BTS_OFF_OS (bit 9), are provided in the debug control register to specify the CPL of
BTMs that will not be logged in the BTS buffer or sent on the bus.

17.4.7

Freezing LBR and Performance Counters on PMI

Many issues may generate a performance monitoring interrupt (PMI); a PMI service handler will need to determine
cause to handle the situation. Two capabilities that allow a PMI service routine to improve branch tracing and
performance monitoring are available for processors supporting architectural performance monitoring version 2 or
greater (i.e. CPUID.0AH:EAX[7:0] > 1). These capabilities provides the following interface in IA32_DEBUGCTL to
reduce runtime overhead of PMI servicing, profiler-contributed skew effects on analysis or counter metrics:

•

Freezing LBRs on PMI (bit 11)— Allows the PMI service routine to ensure the content in the LBR stack are
associated with the target workload and not polluted by the branch flows of handling the PMI. Depending on the
version ID enumerated by CPUID.0AH:EAX.ArchPerfMonVerID[bits 7:0], two flavors are supported:
— Legacy Freeze_LBR_on_PMI is supported for ArchPerfMonVerID <= 3 and ArchPerfMonVerID >1. If
IA32_DEBUGCTL.Freeze_LBR_On_PMI = 1, the LBR is frozen on the overflowed condition of the buffer
area, the processor clears the LBR bit (bit 0) in IA32_DEBUGCTL. Software must then re-enable
IA32_DEBUGCTL.LBR to resume recording branches. When using this feature, software should be careful
about writes to IA32_DEBUGCTL to avoid re-enabling LBRs by accident if they were just disabled.
— Streamlined Freeze_LBR_on_PMI is supported for ArchPerfMonVerID >= 4. If
IA32_DEBUGCTL.Freeze_LBR_On_PMI = 1, the processor behaves as follows:

•

•

sets IA32_PERF_GLOBAL_STATUS.LBR_Frz =1 to disable recording, but does not change the LBR bit
(bit 0) in IA32_DEBUGCTL. The LBRs are frozen on the overflowed condition of the buffer area.

Freezing PMCs on PMI (bit 12) — Allows the PMI service routine to ensure the content in the performance
counters are associated with the target workload and not polluted by the PMI and activities within the PMI
service routine. Depending on the version ID enumerated by CPUID.0AH:EAX.ArchPerfMonVerID[bits 7:0], two
flavors are supported:
— Legacy Freeze_Perfmon_on_PMI is supported for ArchPerfMonVerID <= 3 and ArchPerfMonVerID >1. If
IA32_DEBUGCTL.Freeze_Perfmon_On_PMI = 1, the performance counters are frozen on the counter
overflowed condition when the processor clears the IA32_PERF_GLOBAL_CTRL MSR (see Figure 18-3). The
PMCs affected include both general-purpose counters and fixed-function counters (see Section 18.6.2.1,
“Fixed-function Performance Counters”). Software must re-enable counts by writing 1s to the corresponding enable bits in IA32_PERF_GLOBAL_CTRL before leaving a PMI service routine to continue counter
operation.
— Streamlined Freeze_Perfmon_on_PMI is supported for ArchPerfMonVerID >= 4. The processor behaves as
follows:

•

sets IA32_PERF_GLOBAL_STATUS.CTR_Frz =1 to disable counting on a counter overflow condition, but
does not change the IA32_PERF_GLOBAL_CTRL MSR.

Freezing LBRs and PMCs on PMIs (both legacy and streamlined operation) occur when one of the following applies:

•

A performance counter had an overflow and was programmed to signal a PMI in case of an overflow.
— For the general-purpose counters; enabling PMI is done by setting bit 20 of the IA32_PERFEVTSELx
register.

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— For the fixed-function counters; enabling PMI is done by setting the 3rd bit in the corresponding 4-bit
control field of the MSR_PERF_FIXED_CTR_CTRL register (see Figure 18-1) or IA32_FIXED_CTR_CTRL MSR
(see Figure 18-2).

•
•

The PEBS buffer is almost full and reaches the interrupt threshold.
The BTS buffer is almost full and reaches the interrupt threshold.

Table 17-3 compares the interaction of the processor with the PMI handler using the legacy versus streamlined
Freeza_Perfmon_On_PMI interface.

Table 17-3. Legacy and Streamlined Operation with Freeze_Perfmon_On_PMI = 1, Counter Overflowed
Legacy Freeze_Perfmon_On_PMI

Streamlined Freeze_Perfmon_On_PMI

Comment

Processor freezes the counters on overflow

Processor freezes the counters on overflow

Unchanged

Processor clears IA32_PERF_GLOBAL_CTRL

Processor set
IA32_PERF_GLOBAL_STATUS.CTR_FTZ

Handler reads IA32_PERF_GLOBAL_STATUS
mask = RDMSR(0x38E)
(0x38E) to examine which counter(s) overflowed

Similar

Handler services the PMI

Handler services the PMI

Unchanged

Handler writes 1s to
IA32_PERF_GLOBAL_OVF_CTL (0x390)

Handler writes mask into
IA32_PERF_GLOBAL_OVF_RESET (0x390)

Processor clears IA32_PERF_GLOBAL_STATUS

Processor clears IA32_PERF_GLOBAL_STATUS Unchanged

Handler re-enables IA32_PERF_GLOBAL_CTRL

None

17.4.8

Reduced software overhead

LBR Stack

The last branch record stack and top-of-stack (TOS) pointer MSRs are supported across Intel 64 and IA-32
processor families. However, the number of MSRs in the LBR stack and the valid range of TOS pointer value can
vary between different processor families. Table 17-4 lists the LBR stack size and TOS pointer range for several
processor families according to the CPUID signatures of DisplayFamily_DisplayModel encoding (see CPUID instruction in Chapter 3 of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A).

Table 17-4. LBR Stack Size and TOS Pointer Range
DisplayFamily_DisplayModel

Size of LBR Stack

Component of an LBR Entry

Range of TOS Pointer

06_5CH, 06_5FH

32

FROM_IP, TO_IP

0 to 31
1

06_4EH, 06_5EH, 06_8EH, 06_9EH, 06_55H,
06_66H, 06_7AH

32

FROM_IP, TO_IP, LBR_INFO

0 to 31

06_3DH, 06_47H, 06_4FH, 06_56H, 06_3CH,
06_45H, 06_46H, 06_3FH, 06_2AH, 06_2DH,
06_3AH, 06_3EH, 06_1AH, 06_1EH, 06_1FH,
06_2EH, 06_25H, 06_2CH, 06_2FH

16

FROM_IP, TO_IP

0 to 15

06_17H, 06_1DH, 06_0FH

4

FROM_IP, TO_IP

0 to 3

06_37H, 06_4AH, 06_4CH, 06_4DH, 06_5AH,
06_5DH, 06_1CH, 06_26H, 06_27H, 06_35H,
06_36H

8

FROM_IP, TO_IP

0 to 7

NOTES:
1. See Section 17.12.

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

The last branch recording mechanism tracks not only branch instructions (like JMP, Jcc, LOOP and CALL instructions), but also other operations that cause a change in the instruction pointer (like external interrupts, traps and
faults). The branch recording mechanisms generally employs a set of MSRs, referred to as last branch record (LBR)
stack. The size and exact locations of the LBR stack are generally model-specific (see Chapter 2, “Model-Specific
Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4 for modelspecific MSR addresses).

•

Last Branch Record (LBR) Stack — The LBR consists of N pairs of MSRs (N is listed in the LBR stack size
column of Table 17-4) that store source and destination address of recent branches (see Figure 17-3):
— MSR_LASTBRANCH_0_FROM_IP (address is model specific) through the next consecutive (N-1) MSR
address store source addresses.
— MSR_LASTBRANCH_0_TO_IP (address is model specific ) through the next consecutive (N-1) MSR address
store destination addresses.

•

Last Branch Record Top-of-Stack (TOS) Pointer — The lowest significant M bits of the TOS Pointer MSR
(MSR_LASTBRANCH_TOS, address is model specific) contains an M-bit pointer to the MSR in the LBR stack that
contains the most recent branch, interrupt, or exception recorded. The valid range of the M-bit POS pointer is
given in Table 17-4.

17.4.8.1

LBR Stack and Intel® 64 Processors

LBR MSRs are 64-bits. In 64-bit mode, last branch records store the full address. Outside of 64-bit mode, the upper
32-bits of branch addresses will be stored as 0.

MSR_LASTBRANCH_0_FROM_IP through MSR_LASTBRANCH_(N-1)_FROM_IP
0

63

Source Address
MSR_LASTBRANCH_0_TO_IP through MSR_LASTBRANCH_(N-1)_TO_IP
0

63

Destination Address

Figure 17-4. 64-bit Address Layout of LBR MSR
Software should query an architectural MSR IA32_PERF_CAPABILITIES[5:0] about the format of the address that
is stored in the LBR stack. Four formats are defined by the following encoding:
— 000000B (32-bit record format) — Stores 32-bit offset in current CS of respective source/destination,
— 000001B (64-bit LIP record format) — Stores 64-bit linear address of respective source/destination,
— 000010B (64-bit EIP record format) — Stores 64-bit offset (effective address) of respective
source/destination.
— 000011B (64-bit EIP record format) and Flags — Stores 64-bit offset (effective address) of respective
source/destination. Misprediction info is reported in the upper bit of 'FROM' registers in the LBR stack. See
LBR stack details below for flag support and definition.
— 000100B (64-bit EIP record format), Flags and TSX — Stores 64-bit offset (effective address) of
respective source/destination. Misprediction and TSX info are reported in the upper bits of ‘FROM’ registers
in the LBR stack.
— 000101B (64-bit EIP record format), Flags, TSX, LBR_INFO — Stores 64-bit offset (effective
address) of respective source/destination. Misprediction, TSX, and elapsed cycles since the last LBR update
are reported in the LBR_INFO MSR stack.
— 000110B (64-bit LIP record format), Flags, Cycles — Stores 64-bit linear address (CS.Base +
effective address) of respective source/destination. Misprediction info is reported in the upper bits of

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'FROM' registers in the LBR stack. Elapsed cycles since the last LBR update are reported in the upper 16 bits
of the 'TO' registers in the LBR stack (see Section 17.6).
— 000111B (64-bit LIP record format), Flags, TSX, LBR_INFO — Stores 64-bit linear address (CS.Base
+ effective address) of respective source/destination. Misprediction, TSX, and elapsed cycles since the last
LBR update are reported in the LBR_INFO MSR stack.
Processor’s support for the architectural MSR IA32_PERF_CAPABILITIES is provided by
CPUID.01H:ECX[PERF_CAPAB_MSR] (bit 15).

17.4.8.2

LBR Stack and IA-32 Processors

The LBR MSRs in IA-32 processors introduced prior to Intel 64 architecture store the 32-bit “To Linear Address” and
“From Linear Address“ using the high and low half of each 64-bit MSR.

17.4.8.3

Last Exception Records and Intel 64 Architecture

Intel 64 and IA-32 processors also provide MSRs that store the branch record for the last branch taken prior to an
exception or an interrupt. The location of the last exception record (LER) MSRs are model specific. The MSRs that
store last exception records are 64-bits. If IA-32e mode is disabled, only the lower 32-bits of the address is
recorded. If IA-32e mode is enabled, the processor writes 64-bit values into the MSR. In 64-bit mode, last exception records store 64-bit addresses; in compatibility mode, the upper 32-bits of last exception records are cleared.

17.4.9

BTS and DS Save Area

The Debug store (DS) feature flag (bit 21), returned by CPUID.1:EDX[21] indicates that the processor provides
the debug store (DS) mechanism. The DS mechanism allows:

•
•

BTMs to be stored in a memory-resident BTS buffer. See Section 17.4.5, “Branch Trace Store (BTS).”
Processor event-based sampling (PEBS) also uses the DS save area provided by debug store mechanism. The
capability of PEBS varies across different microarchitectures. See Section 18.6.2.4, “Processor Event Based
Sampling (PEBS),” and the relevant PEBS sub-sections across the core PMU sections in Chapter 18, “Performance Monitoring.”

When CPUID.1:EDX[21] is set:

•

The BTS_UNAVAILABLE and PEBS_UNAVAILABLE flags in the IA32_MISC_ENABLE MSR indicate (when clear)
the availability of the BTS and PEBS facilities, including the ability to set the BTS and BTINT bits in the
appropriate DEBUGCTL MSR.

•

The IA32_DS_AREA MSR exists and points to the DS save area.

The debug store (DS) save area is a software-designated area of memory that is used to collect the following two
types of information:

•

Branch records — When the BTS flag in the IA32_DEBUGCTL MSR is set, a branch record is stored in the BTS
buffer in the DS save area whenever a taken branch, interrupt, or exception is detected.

•

PEBS records — When a performance counter is configured for PEBS, a PEBS record is stored in the PEBS
buffer in the DS save area after the counter overflow occurs. This record contains the architectural state of the
processor (state of the 8 general purpose registers, EIP register, and EFLAGS register) at the next occurrence
of the PEBS event that caused the counter to overflow. When the state information has been logged, the
counter is automatically reset to a specified value, and event counting begins again. The content layout of a
PEBS record varies across different implementations that support PEBS. See Section 18.6.2.4.2 for details of
enumerating PEBS record format.

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NOTES
Prior to processors based on the Goldmont microarchitecture, PEBS facility only supports a subset
of implementation-specific precise events. See Section 18.5.3.1 for a PEBS enhancement that can
generate records for both precise and non-precise events.
The DS save area and recording mechanism are disabled on INIT, processor Reset or transition to
system-management mode (SMM) or IA-32e mode. It is similarly disabled on the generation of a
machine-check exception on 45nm and 32nm Intel Atom processors and on processors with
Netburst or Intel Core microarchitecture.
The BTS and PEBS facilities may not be available on all processors. The availability of these facilities
is indicated by the BTS_UNAVAILABLE and PEBS_UNAVAILABLE flags, respectively, in the
IA32_MISC_ENABLE MSR (see Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 4).
The DS save area is divided into three parts: buffer management area, branch trace store (BTS) buffer, and PEBS
buffer (see Figure 17-5). The buffer management area is used to define the location and size of the BTS and PEBS
buffers. The processor then uses the buffer management area to keep track of the branch and/or PEBS records in
their respective buffers and to record the performance counter reset value. The linear address of the first byte of
the DS buffer management area is specified with the IA32_DS_AREA MSR.
The fields in the buffer management area are as follows:

•

BTS buffer base — Linear address of the first byte of the BTS buffer. This address should point to a natural
doubleword boundary.

•

BTS index — Linear address of the first byte of the next BTS record to be written to. Initially, this address
should be the same as the address in the BTS buffer base field.

•

BTS absolute maximum — Linear address of the next byte past the end of the BTS buffer. This address should
be a multiple of the BTS record size (12 bytes) plus 1.

•

BTS interrupt threshold — Linear address of the BTS record on which an interrupt is to be generated. This
address must point to an offset from the BTS buffer base that is a multiple of the BTS record size. Also, it must
be several records short of the BTS absolute maximum address to allow a pending interrupt to be handled prior
to processor writing the BTS absolute maximum record.

•

PEBS buffer base — Linear address of the first byte of the PEBS buffer. This address should point to a natural
doubleword boundary.

•

PEBS index — Linear address of the first byte of the next PEBS record to be written to. Initially, this address
should be the same as the address in the PEBS buffer base field.

•

PEBS absolute maximum — Linear address of the next byte past the end of the PEBS buffer. This address
should be a multiple of the PEBS record size (40 bytes) plus 1.

•

PEBS interrupt threshold — Linear address of the PEBS record on which an interrupt is to be generated. This
address must point to an offset from the PEBS buffer base that is a multiple of the PEBS record size. Also, it
must be several records short of the PEBS absolute maximum address to allow a pending interrupt to be
handled prior to processor writing the PEBS absolute maximum record.

•

PEBS counter reset value — A 64-bit value that the counter is to be set to when a PEBS record is written. Bits
beyond the size of the counter are ignored. This value allows state information to be collected regularly every
time the specified number of events occur.

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

IA32_DS_AREA MSR
DS Buffer Management Area
BTS Buffer Base

0H

BTS Index

4H

BTS Absolute
Maximum
BTS Interrupt
Threshold

BTS Buffer
Branch Record 0

8H
Branch Record 1
CH

PEBS Buffer Base 10H
PEBS Index
PEBS Absolute
Maximum
PEBS Interrupt
Threshold
PEBS
Counter Reset
Reserved

14H
18H
1CH

Branch Record n

20H
24H

PEBS Buffer

30H

PEBS Record 0

PEBS Record 1

PEBS Record n

Figure 17-5. DS Save Area Example1
NOTES:
1. This example represents the format for a system that supports PEBS on only one counter.
Figure 17-6 shows the structure of a 12-byte branch record in the BTS buffer. The fields in each record are as
follows:

•

Last branch from — Linear address of the instruction from which the branch, interrupt, or exception was
taken.

•

Last branch to — Linear address of the branch target or the first instruction in the interrupt or exception
service routine.

•

Branch predicted — Bit 4 of field indicates whether the branch that was taken was predicted (set) or not
predicted (clear).

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

31

4

0

Last Branch From

0H

Last Branch To

4H
8H

Branch Predicted

Figure 17-6. 32-bit Branch Trace Record Format
Figure 17-7 shows the structure of the 40-byte PEBS records. Nominally the register values are those at the beginning of the instruction that caused the event. However, there are cases where the registers may be logged in a
partially modified state. The linear IP field shows the value in the EIP register translated from an offset into the
current code segment to a linear address.
31

0
EFLAGS

0H

Linear IP

4H

EAX

8H

EBX

CH

ECX

10H

EDX

14H

ESI

18H

EDI

1CH

EBP

20H

ESP

24H

Figure 17-7. PEBS Record Format

17.4.9.1

64 Bit Format of the DS Save Area

When DTES64 = 1 (CPUID.1.ECX[2] = 1), the structure of the DS save area is shown in Figure 17-8.
When DTES64 = 0 (CPUID.1.ECX[2] = 0) and IA-32e mode is active, the structure of the DS save area is shown in
Figure 17-8. If IA-32e mode is not active the structure of the DS save area is as shown in Figure 17-5.

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IA32_DS_AREA MSR
DS Buffer Management Area
BTS Buffer Base

0H

BTS Index

8H

BTS Absolute
Maximum
BTS Interrupt
Threshold

BTS Buffer
Branch Record 0

10H
Branch Record 1
18H

PEBS Buffer Base 20H
PEBS Index
PEBS Absolute
Maximum
PEBS Interrupt
Threshold
PEBS
Counter Reset
Reserved

28H
30H

Branch Record n

38H
40H
48H

PEBS Buffer

50H

PEBS Record 0

PEBS Record 1

PEBS Record n

Figure 17-8. IA-32e Mode DS Save Area Example1
NOTES:
1. This example represents the format for a system that supports PEBS on only one counter.
The IA32_DS_AREA MSR holds the 64-bit linear address of the first byte of the DS buffer management area. The
structure of a branch trace record is similar to that shown in Figure 17-6, but each field is 8 bytes in length. This
makes each BTS record 24 bytes (see Figure 17-9). The structure of a PEBS record is similar to that shown in
Figure 17-7, but each field is 8 bytes in length and architectural states include register R8 through R15. This makes
the size of a PEBS record in 64-bit mode 144 bytes (see Figure 17-10).
63

4

0

Last Branch From

0H

Last Branch To

8H
10H

Branch Predicted

Figure 17-9. 64-bit Branch Trace Record Format

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

63

0
RFLAGS

0H

RIP

8H

RAX

10H

RBX

18H

RCX

20H

RDX

28H

RSI

30H

RDI

38H

RBP

40H

RSP

48H

R8

50H

...

...

R15

88H

Figure 17-10. 64-bit PEBS Record Format

Fields in the buffer management area of a DS save area are described in Section 17.4.9.
The format of a branch trace record and a PEBS record are the same as the 64-bit record formats shown in Figures
17-9 and Figures 17-10, with the exception that the branch predicted bit is not supported by Intel Core microarchitecture or Intel Atom microarchitecture. The 64-bit record formats for BTS and PEBS apply to DS save area for all
operating modes.
The procedures used to program IA32_DEBUGCTL MSR to set up a BTS buffer or a CPL-qualified BTS are described
in Section 17.4.9.3 and Section 17.4.9.4.
Required elements for writing a DS interrupt service routine are largely the same on processors that support using
DS Save area for BTS or PEBS records. However, on processors based on Intel NetBurst® microarchitecture, reenabling counting requires writing to CCCRs. But a DS interrupt service routine on processors supporting architectural performance monitoring should:

•
•

Re-enable the enable bits in IA32_PERF_GLOBAL_CTRL MSR if it is servicing an overflow PMI due to PEBS.
Clear overflow indications by writing to IA32_PERF_GLOBAL_OVF_CTRL when a counting configuration is
changed. This includes bit 62 (ClrOvfBuffer) and the overflow indication of counters used in either PEBS or
general-purpose counting (specifically: bits 0 or 1; see Figures 18-3).

17.4.9.2

Setting Up the DS Save Area

To save branch records with the BTS buffer, the DS save area must first be set up in memory as described in the
following procedure (See Section 18.6.2.4.1, “Setting up the PEBS Buffer,” for instructions for setting up a PEBS
buffer, respectively, in the DS save area):
1. Create the DS buffer management information area in memory (see Section 17.4.9, “BTS and DS Save Area,”
and Section 17.4.9.1, “64 Bit Format of the DS Save Area”). Also see the additional notes in this section.
2. Write the base linear address of the DS buffer management area into the IA32_DS_AREA MSR.
3. Set up the performance counter entry in the xAPIC LVT for fixed delivery and edge sensitive. See Section
10.5.1, “Local Vector Table.”
4. Establish an interrupt handler in the IDT for the vector associated with the performance counter entry in the
xAPIC LVT.
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5. Write an interrupt service routine to handle the interrupt. See Section 17.4.9.5, “Writing the DS Interrupt
Service Routine.”
The following restrictions should be applied to the DS save area.

•

The three DS save area sections should be allocated from a non-paged pool, and marked accessed and dirty. It
is the responsibility of the operating system to keep the pages that contain the buffer present and to mark
them accessed and dirty. The implication is that the operating system cannot do “lazy” page-table entry
propagation for these pages.

•

The DS save area can be larger than a page, but the pages must be mapped to contiguous linear addresses.
The buffer may share a page, so it need not be aligned on a 4-KByte boundary. For performance reasons, the
base of the buffer must be aligned on a doubleword boundary and should be aligned on a cache line boundary.

•

It is recommended that the buffer size for the BTS buffer and the PEBS buffer be an integer multiple of the
corresponding record sizes.

•

The precise event records buffer should be large enough to hold the number of precise event records that can
occur while waiting for the interrupt to be serviced.

•

The DS save area should be in kernel space. It must not be on the same page as code, to avoid triggering selfmodifying code actions.

•

There are no memory type restrictions on the buffers, although it is recommended that the buffers be
designated as WB memory type for performance considerations.

•

Either the system must be prevented from entering A20M mode while DS save area is active, or bit 20 of all
addresses within buffer bounds must be 0.

•

Pages that contain buffers must be mapped to the same physical addresses for all processes, such that any
change to control register CR3 will not change the DS addresses.

•

The DS save area is expected to used only on systems with an enabled APIC. The LVT Performance Counter
entry in the APCI must be initialized to use an interrupt gate instead of the trap gate.

17.4.9.3

Setting Up the BTS Buffer

Three flags in the MSR_DEBUGCTLA MSR (see Table 17-5), IA32_DEBUGCTL (see Figure 17-3), or
MSR_DEBUGCTLB (see Figure 17-16) control the generation of branch records and storing of them in the BTS
buffer; these are TR, BTS, and BTINT. The TR flag enables the generation of BTMs. The BTS flag determines
whether the BTMs are sent out on the system bus (clear) or stored in the BTS buffer (set). BTMs cannot be simultaneously sent to the system bus and logged in the BTS buffer. The BTINT flag enables the generation of an interrupt when the BTS buffer is full. When this flag is clear, the BTS buffer is a circular buffer.

Table 17-5. IA32_DEBUGCTL Flag Encodings
TR

BTS

BTINT

Description

0

X

X

Branch trace messages (BTMs) off

1

0

X

Generate BTMs

1

1

0

Store BTMs in the BTS buffer, used here as a circular buffer

1

1

1

Store BTMs in the BTS buffer, and generate an interrupt when the buffer is nearly full

The following procedure describes how to set up a DS Save area to collect branch records in the BTS buffer:
1. Place values in the BTS buffer base, BTS index, BTS absolute maximum, and BTS interrupt threshold fields of
the DS buffer management area to set up the BTS buffer in memory.
2. Set the TR and BTS flags in the IA32_DEBUGCTL for Intel Core Solo and Intel Core Duo processors or later
processors (or MSR_DEBUGCTLA MSR for processors based on Intel NetBurst Microarchitecture; or
MSR_DEBUGCTLB for Pentium M processors).
3. Clear the BTINT flag in the corresponding IA32_DEBUGCTL (or MSR_DEBUGCTLA MSR; or MSR_DEBUGCTLB)
if a circular BTS buffer is desired.

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NOTES
If the buffer size is set to less than the minimum allowable value (i.e. BTS absolute maximum < 1
+ size of BTS record), the results of BTS is undefined.
In order to prevent generating an interrupt, when working with circular BTS buffer, SW need to set
BTS interrupt threshold to a value greater than BTS absolute maximum (fields of the DS buffer
management area). It's not enough to clear the BTINT flag itself only.

17.4.9.4

Setting Up CPL-Qualified BTS

If the processor supports CPL-qualified last branch recording mechanism, the generation of branch records and
storing of them in the BTS buffer are determined by: TR, BTS, BTS_OFF_OS, BTS_OFF_USR, and BTINT. The
encoding of these five bits are shown in Table 17-6.

Table 17-6. CPL-Qualified Branch Trace Store Encodings
TR

BTS

BTS_OFF_OS

BTS_OFF_USR

BTINT

Description

0

X

X

X

X

Branch trace messages (BTMs) off

1

0

X

X

X

Generates BTMs but do not store BTMs

1

1

0

0

0

Store all BTMs in the BTS buffer, used here as a circular buffer

1

1

1

0

0

Store BTMs with CPL > 0 in the BTS buffer

1

1

0

1

0

Store BTMs with CPL = 0 in the BTS buffer

1

1

1

1

X

Generate BTMs but do not store BTMs

1

1

0

0

1

Store all BTMs in the BTS buffer; generate an interrupt when the
buffer is nearly full

1

1

1

0

1

Store BTMs with CPL > 0 in the BTS buffer; generate an interrupt
when the buffer is nearly full

1

1

0

1

1

Store BTMs with CPL = 0 in the BTS buffer; generate an interrupt
when the buffer is nearly full

17.4.9.5

Writing the DS Interrupt Service Routine

The BTS, non-precise event-based sampling, and PEBS facilities share the same interrupt vector and interrupt
service routine (called the debug store interrupt service routine or DS ISR). To handle BTS, non-precise eventbased sampling, and PEBS interrupts: separate handler routines must be included in the DS ISR. Use the following
guidelines when writing a DS ISR to handle BTS, non-precise event-based sampling, and/or PEBS interrupts.

•

The DS interrupt service routine (ISR) must be part of a kernel driver and operate at a current privilege level of
0 to secure the buffer storage area.

•

Because the BTS, non-precise event-based sampling, and PEBS facilities share the same interrupt vector, the
DS ISR must check for all the possible causes of interrupts from these facilities and pass control on to the
appropriate handler.
BTS and PEBS buffer overflow would be the sources of the interrupt if the buffer index matches/exceeds the
interrupt threshold specified. Detection of non-precise event-based sampling as the source of the interrupt is
accomplished by checking for counter overflow.

•
•

There must be separate save areas, buffers, and state for each processor in an MP system.

•

The processor will not disable the DS save area when the buffer is full and the circular mode has not been
selected. The current DS setting must be retained and restored by the ISR on exit.

Upon entering the ISR, branch trace messages and PEBS should be disabled to prevent race conditions during
access to the DS save area. This is done by clearing TR flag in the IA32_DEBUGCTL (or MSR_DEBUGCTLA MSR)
and by clearing the precise event enable flag in the MSR_PEBS_ENABLE MSR. These settings should be
restored to their original values when exiting the ISR.

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•

After reading the data in the appropriate buffer, up to but not including the current index into the buffer, the ISR
must reset the buffer index to the beginning of the buffer. Otherwise, everything up to the index will look like
new entries upon the next invocation of the ISR.

•
•

The ISR must clear the mask bit in the performance counter LVT entry.

•

The Pentium 4 Processor and Intel Xeon Processor mask PMIs upon receiving an interrupt. Clear this condition
before leaving the interrupt handler.

The ISR must re-enable the counters to count via IA32_PERF_GLOBAL_CTRL/IA32_PERF_GLOBAL_OVF_CTRL
if it is servicing an overflow PMI due to PEBS (or via CCCR's ENABLE bit on processor based on Intel NetBurst
microarchitecture).

17.5

LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (INTEL® CORE™ 2
DUO AND INTEL® ATOM™ PROCESSORS)

The Intel Core 2 Duo processor family and Intel Xeon processors based on Intel Core microarchitecture or
enhanced Intel Core microarchitecture provide last branch interrupt and exception recording. The facilities
described in this section also apply to 45 nm and 32 nm Intel Atom processors. These capabilities are similar to
those found in Pentium 4 processors, including support for the following facilities:

•

Debug Trace and Branch Recording Control — The IA32_DEBUGCTL MSR provide bit fields for software to
configure mechanisms related to debug trace, branch recording, branch trace store, and performance counter
operations. See Section 17.4.1 for a description of the flags. See Figure 17-3 for the MSR layout.

•

Last branch record (LBR) stack — There are a collection of MSR pairs that store the source and destination
addresses related to recently executed branches. See Section 17.5.1.

•

Monitoring and single-stepping of branches, exceptions, and interrupts
— See Section 17.4.2 and Section 17.4.3. In addition, the ability to freeze the LBR stack on a PMI request is
available.
— 45 nm and 32 nm Intel Atom processors clear the TR flag when the FREEZE_LBRS_ON_PMI flag is set.

•
•
•
•
•

Branch trace messages — See Section 17.4.4.

•

FREEZE_WHILE_SMM_EN (bit 14) — FREEZE_WHILE_SMM_EN is supported if
IA32_PERF_CAPABILITIES.FREEZE_WHILE_SMM[Bit 12] is reporting 1. See Section 17.4.1.

Last exception records — See Section 17.13.3.
Branch trace store and CPL-qualified BTS — See Section 17.4.5.
FREEZE_LBRS_ON_PMI flag (bit 11) — see Section 17.4.7 for legacy Freeze_LBRs_On_PMI operation.
FREEZE_PERFMON_ON_PMI flag (bit 12) — see Section 17.4.7 for legacy Freeze_Perfmon_On_PMI
operation.

17.5.1

LBR Stack

The last branch record stack and top-of-stack (TOS) pointer MSRs are supported across Intel Core 2, Intel Atom
processor families, and Intel processors based on Intel NetBurst microarchitecture.
Four pairs of MSRs are supported in the LBR stack for Intel Core 2 processors families and Intel processors based
on Intel NetBurst microarchitecture:

•

Last Branch Record (LBR) Stack
— MSR_LASTBRANCH_0_FROM_IP (address 40H) through MSR_LASTBRANCH_3_FROM_IP (address 43H)
store source addresses
— MSR_LASTBRANCH_0_TO_IP (address 60H) through MSR_LASTBRANCH_3_TO_IP (address 63H) store
destination addresses

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•

Last Branch Record Top-of-Stack (TOS) Pointer — The lowest significant 2 bits of the TOS Pointer MSR
(MSR_LASTBRANCH_TOS, address 1C9H) contains a pointer to the MSR in the LBR stack that contains the most
recent branch, interrupt, or exception recorded.

Eight pairs of MSRs are supported in the LBR stack for 45 nm and 32 nm Intel Atom processors:

•

Last Branch Record (LBR) Stack
— MSR_LASTBRANCH_0_FROM_IP (address 40H) through MSR_LASTBRANCH_7_FROM_IP (address 47H)
store source addresses
— MSR_LASTBRANCH_0_TO_IP (address 60H) through MSR_LASTBRANCH_7_TO_IP (address 67H) store
destination addresses

•

Last Branch Record Top-of-Stack (TOS) Pointer — The lowest significant 3 bits of the TOS Pointer MSR
(MSR_LASTBRANCH_TOS, address 1C9H) contains a pointer to the MSR in the LBR stack that contains the most
recent branch, interrupt, or exception recorded.

The address format written in the FROM_IP/TO_IP MSRS may differ between processors. Software should query
IA32_PERF_CAPABILITIES[5:0] and consult Section 17.4.8.1. The behavior of the MSR_LER_TO_LIP and the
MSR_LER_FROM_LIP MSRs corresponds to that of the LastExceptionToIP and LastExceptionFromIP MSRs found in
P6 family processors.

17.5.2

LBR Stack in Intel Atom Processors based on the Silvermont Microarchitecture

The last branch record stack and top-of-stack (TOS) pointer MSRs are supported in Intel Atom processors based on
the Silvermont and Airmont microarchitectures. Eight pairs of MSRs are supported in the LBR stack.
LBR filtering is supported. Filtering of LBRs based on a combination of CPL and branch type conditions is supported.
When LBR filtering is enabled, the LBR stack only captures the subset of branches that are specified by
MSR_LBR_SELECT. The layout of MSR_LBR_SELECT is described in Table 17-11.

17.6

LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING
FOR PROCESSORS BASED ON GOLDMONT MICROARCHITECTURE

Processors based on the Goldmont microarchitecture extend the capabilities described in Section 17.5.2 with the
following enhancements:

•
•

Supports new LBR format encoding 00110b in IA32_PERF_CAPABILITIES[5:0].

•

LBR call stack filtering supported. The layout of MSR_LBR_SELECT is described in Table 17-13.

•

Elapsed cycle information is added to MSR_LASTBRANCH_x_TO_IP. Format is shown in Table 17-7.

•

Misprediction info is reported in the upper bits of MSR_LASTBRANCH_x_FROM_IP. MISPRED bit format is
shown in Table 17-8.

•

Streamlined Freeze_LBRs_On_PMI operation; see Section 17.12.2.

Size of LBR stack increased to 32. Each entry includes MSR_LASTBRANCH_x_FROM_IP (address 0x680..0x69f)
and MSR_LASTBRANCH_x_TO_IP (address 0x6c0..0x6df).

• LBR MSRs may be cleared when MWAIT is used to request a C-state that is numerically higher than C1; see
Section 17.12.3.

Table 17-7. MSR_LASTBRANCH_x_TO_IP for the Goldmont Microarchitecture
Bit Field

Bit Offset

Access

Description

Data

47:0

R/W

This is the “branch to“ address. See Section 17.4.8.1 for address format.

Cycle Count
(Saturating)

63:48

R/W

Elapsed core clocks since last update to the LBR stack.

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17.7

LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING
FOR PROCESSORS BASED ON GOLDMONT PLUS MICROARCHITECTURE

Next generation Intel Atom processors are based on the Goldmont Plus microarchitecture. Processors based on the
Goldmont Plus microarchitecture extend the capabilities described in Section 17.6 with the following changes:
• Enumeration of new LBR format: encoding 00111b in IA32_PERF_CAPABILITIES[5:0] is supported, see
Section 17.4.8.1.
•

Each LBR stack entry consists of three MSRs:
— MSR_LASTBRANCH_x_FROM_IP, the layout is simplified, see Table 17-9.
— MSR_LASTBRANCH_x_TO_IP, the layout is the same as Table 17-9.
— MSR_LBR_INFO_x, stores branch prediction flag, TSX info, and elapsed cycle data. Layout is the same as
Table 17-16.

17.8

LAST BRANCH, INTERRUPT AND EXCEPTION RECORDING FOR INTEL®
XEON PHI™ PROCESSOR 7200/5200/3200

The last branch record stack and top-of-stack (TOS) pointer MSRs are supported in the Intel® Xeon Phi™ processor
7200/5200/3200 series based on the Knights Landing microarchitecture. Eight pairs of MSRs are supported in the
LBR stack, per thread:

•

Last Branch Record (LBR) Stack
— MSR_LASTBRANCH_0_FROM_IP (address 680H) through MSR_LASTBRANCH_7_FROM_IP (address 687H)
store source addresses.
— MSR_LASTBRANCH_0_TO_IP (address 6C0H) through MSR_LASTBRANCH_7_TO_IP (address 6C7H) store
destination addresses.

•

Last Branch Record Top-of-Stack (TOS) Pointer — The lowest significant 3 bits of the TOS Pointer MSR
(MSR_LASTBRANCH_TOS, address 1C9H) contains a pointer to the MSR in the LBR stack that contains the
most recent branch, interrupt, or exception recorded.

LBR filtering is supported. Filtering of LBRs based on a combination of CPL and branch type conditions is supported.
When LBR filtering is enabled, the LBR stack only captures the subset of branches that are specified by
MSR_LBR_SELECT. The layout of MSR_LBR_SELECT is described in Table 17-11.
The address format written in the FROM_IP/TO_IP MSRS may differ between processors. Software should query
IA32_PERF_CAPABILITIES[5:0] and consult Section 17.4.8.1.The behavior of the MSR_LER_TO_LIP and the
MSR_LER_FROM_LIP MSRs corresponds to that of the LastExceptionToIP and LastExceptionFromIP MSRs found in
the P6 family processors.

17.9

LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING FOR
PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE NAME
NEHALEM

The processors based on Intel® microarchitecture code name Nehalem and Intel® microarchitecture code name
Westmere support last branch interrupt and exception recording. These capabilities are similar to those found in
Intel Core 2 processors and adds additional capabilities:

•

Debug Trace and Branch Recording Control — The IA32_DEBUGCTL MSR provides bit fields for software to
configure mechanisms related to debug trace, branch recording, branch trace store, and performance counter
operations. See Section 17.4.1 for a description of the flags. See Figure 17-11 for the MSR layout.

•

Last branch record (LBR) stack — There are 16 MSR pairs that store the source and destination addresses
related to recently executed branches. See Section 17.9.1.

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•

Monitoring and single-stepping of branches, exceptions, and interrupts — See Section 17.4.2 and
Section 17.4.3. In addition, the ability to freeze the LBR stack on a PMI request is available.

•

Branch trace messages — The IA32_DEBUGCTL MSR provides bit fields for software to enable each logical
processor to generate branch trace messages. See Section 17.4.4. However, not all BTM messages are
observable using the Intel® QPI link.

•
•
•
•

Last exception records — See Section 17.13.3.

•

UNCORE_PMI_EN (bit 13) — When set. this logical processor is enabled to receive an counter overflow
interrupt form the uncore.

•

FREEZE_WHILE_SMM_EN (bit 14) — FREEZE_WHILE_SMM_EN is supported if
IA32_PERF_CAPABILITIES.FREEZE_WHILE_SMM[Bit 12] is reporting 1. See Section 17.4.1.

Branch trace store and CPL-qualified BTS — See Section 17.4.6 and Section 17.4.5.
FREEZE_LBRS_ON_PMI flag (bit 11) — see Section 17.4.7 for legacy Freeze_LBRs_On_PMI operation.
FREEZE_PERFMON_ON_PMI flag (bit 12) — see Section 17.4.7 for legacy Freeze_Perfmon_On_PMI
operation.

Processors based on Intel microarchitecture code name Nehalem provide additional capabilities:

•

Independent control of uncore PMI — The IA32_DEBUGCTL MSR provides a bit field (see Figure 17-11) for
software to enable each logical processor to receive an uncore counter overflow interrupt.

•

LBR filtering — Processors based on Intel microarchitecture code name Nehalem support filtering of LBR
based on combination of CPL and branch type conditions. When LBR filtering is enabled, the LBR stack only
captures the subset of branches that are specified by MSR_LBR_SELECT.

31

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Reserved
FREEZE_WHILE_SMM_EN
UNCORE_PMI_EN
FREEZE_PERFMON_ON_PMI
FREEZE_LBRS_ON_PMI
BTS_OFF_USR — BTS off in user code
BTS_OFF_OS — BTS off in OS
BTINT — Branch trace interrupt
BTS — Branch trace store
TR — Trace messages enable
Reserved
BTF — Single-step on branches
LBR — Last branch/interrupt/exception

Figure 17-11. IA32_DEBUGCTL MSR for Processors based
on Intel microarchitecture code name Nehalem

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17.9.1

LBR Stack

Processors based on Intel microarchitecture code name Nehalem provide 16 pairs of MSR to record last branch
record information. The layout of each MSR pair is shown in Table 17-8 and Table 17-9.

Table 17-8. MSR_LASTBRANCH_x_FROM_IP
Bit Field

Bit Offset

Access

Description

Data

47:0

R/W

This is the “branch from” address. See Section 17.4.8.1 for address format.

SIGN_EXt

62:48

R/W

Signed extension of bit 47 of this register.

MISPRED

63

R/W

When set, indicates either the target of the branch was mispredicted and/or the
direction (taken/non-taken) was mispredicted; otherwise, the target branch was
predicted.

Table 17-9. MSR_LASTBRANCH_x_TO_IP
Bit Field

Bit Offset

Access

Description

Data

47:0

R/W

This is the “branch to” address. See Section 17.4.8.1 for address format

SIGN_EXt

63:48

R/W

Signed extension of bit 47 of this register.

Processors based on Intel microarchitecture code name Nehalem have an LBR MSR Stack as shown in Table 17-10.

Table 17-10. LBR Stack Size and TOS Pointer Range
DisplayFamily_DisplayModel

Size of LBR Stack

Range of TOS Pointer

06_1AH

16

0 to 15

17.9.2

Filtering of Last Branch Records

MSR_LBR_SELECT is cleared to zero at RESET, and LBR filtering is disabled, i.e. all branches will be captured.
MSR_LBR_SELECT provides bit fields to specify the conditions of subsets of branches that will not be captured in
the LBR. The layout of MSR_LBR_SELECT is shown in Table 17-11.

Table 17-11. MSR_LBR_SELECT for Intel microarchitecture code name Nehalem
Bit Field

Bit Offset

Access

Description

CPL_EQ_0

0

R/W

When set, do not capture branches occurring in ring 0

CPL_NEQ_0

1

R/W

When set, do not capture branches occurring in ring >0

JCC

2

R/W

When set, do not capture conditional branches

NEAR_REL_CALL

3

R/W

When set, do not capture near relative calls

NEAR_IND_CALL

4

R/W

When set, do not capture near indirect calls

NEAR_RET

5

R/W

When set, do not capture near returns

NEAR_IND_JMP

6

R/W

When set, do not capture near indirect jumps

NEAR_REL_JMP

7

R/W

When set, do not capture near relative jumps

FAR_BRANCH

8

R/W

When set, do not capture far branches

Reserved

63:9

Must be zero

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17.10

LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING FOR
PROCESSORS BASED ON INTEL® MICROARCHITECTURE CODE NAME
SANDY BRIDGE

Generally, all of the last branch record, interrupt and exception recording facility described in Section 17.9, “Last
Branch, Interrupt, and Exception Recording for Processors based on Intel® Microarchitecture code name
Nehalem”, apply to processors based on Intel microarchitecture code name Sandy Bridge. For processors based on
Intel microarchitecture code name Ivy Bridge, the same holds true.
One difference of note is that MSR_LBR_SELECT is shared between two logical processors in the same core. In Intel
microarchitecture code name Sandy Bridge, each logical processor has its own MSR_LBR_SELECT. The filtering
semantics for “Near_ind_jmp” and “Near_rel_jmp” has been enhanced, see Table 17-12.

Table 17-12. MSR_LBR_SELECT for Intel® microarchitecture code name Sandy Bridge
Bit Field

Bit Offset

Access

Description

CPL_EQ_0

0

R/W

When set, do not capture branches occurring in ring 0

CPL_NEQ_0

1

R/W

When set, do not capture branches occurring in ring >0

JCC

2

R/W

When set, do not capture conditional branches

NEAR_REL_CALL

3

R/W

When set, do not capture near relative calls

NEAR_IND_CALL

4

R/W

When set, do not capture near indirect calls

NEAR_RET

5

R/W

When set, do not capture near returns

NEAR_IND_JMP

6

R/W

When set, do not capture near indirect jumps except near indirect calls and near returns

NEAR_REL_JMP

7

R/W

When set, do not capture near relative jumps except near relative calls.

FAR_BRANCH

8

R/W

When set, do not capture far branches

Reserved

63:9

17.11

Must be zero

LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING
FOR PROCESSORS BASED ON HASWELL MICROARCHITECTURE

Generally, all of the last branch record, interrupt and exception recording facility described in Section 17.10, “Last
Branch, Interrupt, and Exception Recording for Processors based on Intel® Microarchitecture code name Sandy
Bridge”, apply to next generation processors based on Intel microarchitecture code name Haswell.
The LBR facility also supports an alternate capability to profile call stack profiles. Configuring the LBR facility to
conduct call stack profiling is by writing 1 to the MSR_LBR_SELECT.EN_CALLSTACK[bit 9]; see Table 17-13. If
MSR_LBR_SELECT.EN_CALLSTACK is clear, the LBR facility will capture branches normally as described in Section
17.10.

Table 17-13. MSR_LBR_SELECT for Intel® microarchitecture code name Haswell
Bit Field

Bit Offset

Access

Description

CPL_EQ_0

0

R/W

When set, do not capture branches occurring in ring 0

CPL_NEQ_0

1

R/W

When set, do not capture branches occurring in ring >0

JCC

2

R/W

When set, do not capture conditional branches

NEAR_REL_CALL

3

R/W

When set, do not capture near relative calls

NEAR_IND_CALL

4

R/W

When set, do not capture near indirect calls

NEAR_RET

5

R/W

When set, do not capture near returns

NEAR_IND_JMP

6

R/W

When set, do not capture near indirect jumps except near indirect calls and near returns

NEAR_REL_JMP

7

R/W

When set, do not capture near relative jumps except near relative calls.

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Table 17-13. MSR_LBR_SELECT for Intel® microarchitecture code name Haswell
Bit Field
FAR_BRANCH
1

Bit Offset

Access

Description

8

R/W

When set, do not capture far branches

EN_CALLSTACK

9

Enable LBR stack to use LIFO filtering to capture Call stack profile

Reserved

63:10

Must be zero

NOTES:
1. Must set valid combination of bits 0-8 in conjunction with bit 9 (as described below), otherwise the contents of the LBR MSRs are
undefined.
The call stack profiling capability is an enhancement of the LBR facility. The LBR stack is a ring buffer typically used
to profile control flow transitions resulting from branches. However, the finite depth of the LBR stack often become
less effective when profiling certain high-level languages (e.g. C++), where a transition of the execution flow is
accompanied by a large number of leaf function calls, each of which returns an individual parameter to form the list
of parameters for the main execution function call. A long list of such parameters returned by the leaf functions
would serve to flush the data captured in the LBR stack, often losing the main execution context.
When the call stack feature is enabled, the LBR stack will capture unfiltered call data normally, but as return
instructions are executed the last captured branch record is flushed from the on-chip registers in a last-in first-out
(LIFO) manner. Thus, branch information relative to leaf functions will not be captured, while preserving the call
stack information of the main line execution path.
The configuration of the call stack facility is summarized below:

•

Set IA32_DEBUGCTL.LBR (bit 0) to enable the LBR stack to capture branch records. The source and target
addresses of the call branches will be captured in the 16 pairs of From/To LBR MSRs that form the LBR stack.

•

Program the Top of Stack (TOS) MSR that points to the last valid from/to pair. This register is incremented by
1, modulo 16, before recording the next pair of addresses.

•
•

Program the branch filtering bits of MSR_LBR_SELECT (bits 0:8) as desired.
Program the MSR_LBR_SELECT to enable LIFO filtering of return instructions with:
— The following bits in MSR_LBR_SELECT must be set to ‘1’: JCC, NEAR_IND_JMP, NEAR_REL_JMP,
FAR_BRANCH, EN_CALLSTACK;
— The following bits in MSR_LBR_SELECT must be cleared: NEAR_REL_CALL, NEAR-IND_CALL, NEAR_RET;
— At most one of CPL_EQ_0, CPL_NEQ_0 is set.

Note that when call stack profiling is enabled, “zero length calls” are excluded from writing into the LBRs. (A “zero
length call” uses the attribute of the call instruction to push the immediate instruction pointer on to the stack and
then pops off that address into a register. This is accomplished without any matching return on the call.)

17.11.1

LBR Stack Enhancement

Processors based on Intel microarchitecture code name Haswell provide 16 pairs of MSR to record last branch
record information. The layout of each MSR pair is enumerated by IA32_PERF_CAPABILITIES[5:0] = 04H, and is
shown in Table 17-14 and Table 17-9.

Table 17-14. MSR_LASTBRANCH_x_FROM_IP with TSX Information
Bit Field

Bit Offset

Access

Description

Data

47:0

R/W

This is the “branch from” address. See Section 17.4.8.1 for address format.

SIGN_EXT

60:48

R/W

Signed extension of bit 47 of this register.

TSX_ABORT

61

R/W

When set, indicates a TSX Abort entry
LBR_FROM: EIP at the time of the TSX Abort
LBR_TO: EIP of the start of HLE region, or EIP of the RTM Abort Handler

IN_TSX

62

R/W

When set, indicates the entry occurred in a TSX region

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Table 17-14. MSR_LASTBRANCH_x_FROM_IP with TSX Information (Contd.)
Bit Field

Bit Offset

Access

Description

MISPRED

63

R/W

When set, indicates either the target of the branch was mispredicted and/or the
direction (taken/non-taken) was mispredicted; otherwise, the target branch was
predicted.

17.12

LAST BRANCH, CALL STACK, INTERRUPT, AND EXCEPTION RECORDING
FOR PROCESSORS BASED ON SKYLAKE MICROARCHITECTURE

Processors based on the Skylake microarchitecture provide a number of enhancement with storing last branch
records:

•

enumeration of new LBR format: encoding 00101b in IA32_PERF_CAPABILITIES[5:0] is supported, see Section
17.4.8.1.

•

Each LBR stack entry consists of a triplets of MSRs:
— MSR_LASTBRANCH_x_FROM_IP, the layout is simplified, see Table 17-9.
— MSR_LASTBRANCH_x_TO_IP, the layout is the same as Table 17-9.
— MSR_LBR_INFO_x, stores branch prediction flag, TSX info, and elapsed cycle data.

•

Size of LBR stack increased to 32.

Processors based on the Skylake microarchitecture supports the same LBR filtering capabilities as described in
Table 17-13.

Table 17-15. LBR Stack Size and TOS Pointer Range
DisplayFamily_DisplayModel

Size of LBR Stack

Range of TOS Pointer

06_4EH, 06_5EH

32

0 to 31

17.12.1

MSR_LBR_INFO_x MSR

The layout of each MSR_LBR_INFO_x MSR is shown in Table 17-16.

Table 17-16. MSR_LBR_INFO_x
Bit Field

Bit Offset

Access

Description

Cycle Count
(saturating)

15:0

R/W

Elapsed core clocks since last update to the LBR stack.

Reserved

60:16

R/W

Reserved

TSX_ABORT

61

R/W

When set, indicates a TSX Abort entry
LBR_FROM: EIP at the time of the TSX Abort
LBR_TO: EIP of the start of HLE region OR
EIP of the RTM Abort Handler

IN_TSX

62

R/W

When set, indicates the entry occurred in a TSX region.

MISPRED

63

R/W

When set, indicates either the target of the branch was mispredicted and/or the
direction (taken/non-taken) was mispredicted; otherwise, the target branch was
predicted.

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17.12.2

Streamlined Freeze_LBRs_On_PMI Operation

The FREEZE_LBRS_ON_PMI feature causes the LBRs to be frozen on a hardware request for a PMI. This prevents
the LBRs from being overwritten by new branches, allowing the PMI handler to examine the control flow that
preceded the PMI generation. Architectural performance monitoring version 4 and above supports a streamlined
FREEZE_LBRs_ON_PMI operation for PMI service routine that replaces the legacy FREEZE_LBRs_ON_PMI operation (see Section 17.4.7).
While the legacy FREEZE_LBRS_ON_PMI clear the LBR bit in the IA32_DEBUGCTL MSR on a PMI request, the
streamlined FREEZE_LBRS_ON_PMI will set the LBR_FRZ bit in IA32_PERF_GLOBAL_STATUS. Branches will not
cause the LBRs to be updated when LBR_FRZ is set. Software can clear LBR_FRZ at the same time as it clears overflow bits by setting the LBR_FRZ bit as well as the needed overflow bit when writing to
IA32_PERF_GLOBAL_STATUS_RESET MSR.
This streamlined behavior avoids race conditions between software and processor writes to IA32_DEBUGCTL that
are possible with FREEZE_LBRS_ON_PMI clearing of the LBR enable.

17.12.3

LBR Behavior and Deep C-State

When MWAIT is used to request a C-state that is numerically higher than C1, then LBR state may be initialized to
zero depending on optimized “waiting” state that is selected by the processor The affected LBR states include the
FROM, TO, INFO, LAST_BRANCH, LER and LBR_TOS registers. The LBR enable bit and LBR_FROZEN bit are not
affected. The LBR-time of the first LBR record inserted after an exit from such a C-state request will be zero.

17.13

LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (PROCESSORS
BASED ON INTEL NETBURST® MICROARCHITECTURE)

Pentium 4 and Intel Xeon processors based on Intel NetBurst microarchitecture provide the following methods for
recording taken branches, interrupts and exceptions:

•

Store branch records in the last branch record (LBR) stack MSRs for the most recent taken branches,
interrupts, and/or exceptions in MSRs. A branch record consist of a branch-from and a branch-to instruction
address.

•
•

Send the branch records out on the system bus as branch trace messages (BTMs).
Log BTMs in a memory-resident branch trace store (BTS) buffer.

To support these functions, the processor provides the following MSRs and related facilities:

•

MSR_DEBUGCTLA MSR — Enables last branch, interrupt, and exception recording; single-stepping on taken
branches; branch trace messages (BTMs); and branch trace store (BTS). This register is named DebugCtlMSR
in the P6 family processors.

•

Debug store (DS) feature flag (CPUID.1:EDX.DS[bit 21]) — Indicates that the processor provides the
debug store (DS) mechanism, which allows BTMs to be stored in a memory-resident BTS buffer.

•

CPL-qualified debug store (DS) feature flag (CPUID.1:ECX.DS-CPL[bit 4]) — Indicates that the
processor provides a CPL-qualified debug store (DS) mechanism, which allows software to selectively skip
sending and storing BTMs, according to specified current privilege level settings, into a memory-resident BTS
buffer.

•
•

IA32_MISC_ENABLE MSR — Indicates that the processor provides the BTS facilities.

•

Last branch record top-of-stack (TOS) pointer — The TOS Pointer MSR contains a 2-bit pointer (0-3) to
the MSR in the LBR stack that contains the most recent branch, interrupt, or exception recorded for the

Last branch record (LBR) stack — The LBR stack is a circular stack that consists of four MSRs
(MSR_LASTBRANCH_0 through MSR_LASTBRANCH_3) for the Pentium 4 and Intel Xeon processor family
[CPUID family 0FH, models 0H-02H]. The LBR stack consists of 16 MSR pairs
(MSR_LASTBRANCH_0_FROM_IP through MSR_LASTBRANCH_15_FROM_IP and
MSR_LASTBRANCH_0_TO_IP through MSR_LASTBRANCH_15_TO_IP) for the Pentium 4 and Intel Xeon
processor family [CPUID family 0FH, model 03H].

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

Pentium 4 and Intel Xeon processor family [CPUID family 0FH, models 0H-02H]. This pointer becomes a 4-bit
pointer (0-15) for the Pentium 4 and Intel Xeon processor family [CPUID family 0FH, model 03H]. See also:
Table 17-17, Figure 17-12, and Section 17.13.2, “LBR Stack for Processors Based on Intel NetBurst® Microarchitecture.”

•

Last exception record — See Section 17.13.3, “Last Exception Records.”

17.13.1

MSR_DEBUGCTLA MSR

The MSR_DEBUGCTLA MSR enables and disables the various last branch recording mechanisms described in the
previous section. This register can be written to using the WRMSR instruction, when operating at privilege level 0
or when in real-address mode. A protected-mode operating system procedure is required to provide user access to
this register. Figure 17-12 shows the flags in the MSR_DEBUGCTLA MSR. The functions of these flags are as
follows:

•

LBR (last branch/interrupt/exception) flag (bit 0) — When set, the processor records a running trace of
the most recent branches, interrupts, and/or exceptions taken by the processor (prior to a debug exception
being generated) in the last branch record (LBR) stack. Each branch, interrupt, or exception is recorded as a
64-bit branch record. The processor clears this flag whenever a debug exception is generated (for example,
when an instruction or data breakpoint or a single-step trap occurs). See Section 17.13.2, “LBR Stack for
Processors Based on Intel NetBurst® Microarchitecture.”

•

BTF (single-step on branches) flag (bit 1) — When set, the processor treats the TF flag in the EFLAGS
register as a “single-step on branches” flag rather than a “single-step on instructions” flag. This mechanism
allows single-stepping the processor on taken branches. See Section 17.4.3, “Single-Stepping on Branches.”

•

TR (trace message enable) flag (bit 2) — When set, branch trace messages are enabled. Thereafter, when
the processor detects a taken branch, interrupt, or exception, it sends the branch record out on the system bus
as a branch trace message (BTM). See Section 17.4.4, “Branch Trace Messages.”
31

7 6 5 4 3 2 1 0

Reserved

BTS_OFF_USR — Disable storing non-CPL_0 BTS
BTS_OFF_OS — Disable storing CPL_0 BTS
BTINT — Branch trace interrupt
BTS — Branch trace store
TR — Trace messages enable
BTF — Single-step on branches
LBR — Last branch/interrupt/exception

Figure 17-12. MSR_DEBUGCTLA MSR for Pentium 4 and Intel Xeon Processors

•

BTS (branch trace store) flag (bit 3) — When set, enables the BTS facilities to log BTMs to a memoryresident BTS buffer that is part of the DS save area. See Section 17.4.9, “BTS and DS Save Area.”

•

BTINT (branch trace interrupt) flag (bits 4) — When set, the BTS facilities generate an interrupt when the
BTS buffer is full. When clear, BTMs are logged to the BTS buffer in a circular fashion. See Section 17.4.5, “Branch
Trace Store (BTS).”

•

BTS_OFF_OS (disable ring 0 branch trace store) flag (bit 5) — When set, enables the BTS facilities to
skip sending/logging CPL_0 BTMs to the memory-resident BTS buffer. See Section 17.13.2, “LBR Stack for
Processors Based on Intel NetBurst® Microarchitecture.”

•

BTS_OFF_USR (disable ring 0 branch trace store) flag (bit 6) — When set, enables the BTS facilities to
skip sending/logging non-CPL_0 BTMs to the memory-resident BTS buffer. See Section 17.13.2, “LBR Stack for
Processors Based on Intel NetBurst® Microarchitecture.”

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NOTE
The initial implementation of BTS_OFF_USR and BTS_OFF_OS in MSR_DEBUGCTLA is shown in
Figure 17-12. The BTS_OFF_USR and BTS_OFF_OS fields may be implemented on other modelspecific debug control register at different locations.
See Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 4 for a detailed description of each of the last branch recording MSRs.

17.13.2

LBR Stack for Processors Based on Intel NetBurst® Microarchitecture

The LBR stack is made up of LBR MSRs that are treated by the processor as a circular stack. The TOS pointer
(MSR_LASTBRANCH_TOS MSR) points to the LBR MSR (or LBR MSR pair) that contains the most recent (last)
branch record placed on the stack. Prior to placing a new branch record on the stack, the TOS is incremented by 1.
When the TOS pointer reaches it maximum value, it wraps around to 0. See Table 17-17 and Figure 17-12.

Table 17-17. LBR MSR Stack Size and TOS Pointer Range for the Pentium® 4 and the Intel® Xeon® Processor Family
DisplayFamily_DisplayModel

Size of LBR Stack

Range of TOS Pointer

Family 0FH, Models 0H-02H; MSRs at locations 1DBH-1DEH.

4

0 to 3

Family 0FH, Models; MSRs at locations 680H-68FH.

16

0 to 15

Family 0FH, Model 03H; MSRs at locations 6C0H-6CFH.

16

0 to 15

The registers in the LBR MSR stack and the MSR_LASTBRANCH_TOS MSR are read-only and can be read using the
RDMSR instruction.
Figure 17-13 shows the layout of a branch record in an LBR MSR (or MSR pair). Each branch record consists of two
linear addresses, which represent the “from” and “to” instruction pointers for a branch, interrupt, or exception. The
contents of the from and to addresses differ, depending on the source of the branch:

•

Taken branch — If the record is for a taken branch, the “from” address is the address of the branch instruction
and the “to” address is the target instruction of the branch.

•

Interrupt — If the record is for an interrupt, the “from” address the return instruction pointer (RIP) saved for
the interrupt and the “to” address is the address of the first instruction in the interrupt handler routine. The RIP
is the linear address of the next instruction to be executed upon returning from the interrupt handler.

•

Exception — If the record is for an exception, the “from” address is the linear address of the instruction that
caused the exception to be generated and the “to” address is the address of the first instruction in the
exception handler routine.

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

CPUID Family 0FH, Models 0H-02H
MSR_LASTBRANCH_0 through MSR_LASTBRANCH_3
63

0

32 - 31

From Linear Address

To Linear Address

CPUID Family 0FH, Model 03H-04H
MSR_LASTBRANCH_0_FROM_IP through MSR_LASTBRANCH_15_FROM_IP
0

32 - 31

63

Reserved

From Linear Address

MSR_LASTBRANCH_0_TO_IP through MSR_LASTBRANCH_15_TO_IP
63

0

32 - 31

Reserved

To Linear Address

Figure 17-13. LBR MSR Branch Record Layout for the Pentium 4
and Intel Xeon Processor Family
Additional information is saved if an exception or interrupt occurs in conjunction with a branch instruction. If a
branch instruction generates a trap type exception, two branch records are stored in the LBR stack: a branch record
for the branch instruction followed by a branch record for the exception.
If a branch instruction is immediately followed by an interrupt, a branch record is stored in the LBR stack for the
branch instruction followed by a record for the interrupt.

17.13.3

Last Exception Records

The Pentium 4, Intel Xeon, Pentium M, Intel® Core™ Solo, Intel® Core™ Duo, Intel® Core™2 Duo, Intel® Core™ i7
and Intel® Atom™ processors provide two MSRs (the MSR_LER_TO_LIP and the MSR_LER_FROM_LIP MSRs) that
duplicate the functions of the LastExceptionToIP and LastExceptionFromIP MSRs found in the P6 family processors.
The MSR_LER_TO_LIP and MSR_LER_FROM_LIP MSRs contain a branch record for the last branch that the
processor took prior to an exception or interrupt being generated.

17.14

LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (INTEL® CORE™
SOLO AND INTEL® CORE™ DUO PROCESSORS)

Intel Core Solo and Intel Core Duo processors provide last branch interrupt and exception recording. This capability
is almost identical to that found in Pentium 4 and Intel Xeon processors. There are differences in the stack and in
some MSR names and locations.
Note the following:

•

IA32_DEBUGCTL MSR — Enables debug trace interrupt, debug trace store, trace messages enable,
performance monitoring breakpoint flags, single stepping on branches, and last branch. IA32_DEBUGCTL MSR
is located at register address 01D9H.
See Figure 17-14 for the layout and the entries below for a description of the flags:
— LBR (last branch/interrupt/exception) flag (bit 0) — When set, the processor records a running trace
of the most recent branches, interrupts, and/or exceptions taken by the processor (prior to a debug
exception being generated) in the last branch record (LBR) stack. For more information, see the “Last
Branch Record (LBR) Stack” below.
— BTF (single-step on branches) flag (bit 1) — When set, the processor treats the TF flag in the EFLAGS
register as a “single-step on branches” flag rather than a “single-step on instructions” flag. This mechanism

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allows single-stepping the processor on taken branches. See Section 17.4.3, “Single-Stepping on
Branches,” for more information about the BTF flag.
— TR (trace message enable) flag (bit 6) — When set, branch trace messages are enabled. When the
processor detects a taken branch, interrupt, or exception; it sends the branch record out on the system bus
as a branch trace message (BTM). See Section 17.4.4, “Branch Trace Messages,” for more information
about the TR flag.
— BTS (branch trace store) flag (bit 7) — When set, the flag enables BTS facilities to log BTMs to a
memory-resident BTS buffer that is part of the DS save area. See Section 17.4.9, “BTS and DS Save Area.”
— BTINT (branch trace interrupt) flag (bits 8) — When set, the BTS facilities generate an interrupt when
the BTS buffer is full. When clear, BTMs are logged to the BTS buffer in a circular fashion. See Section 17.4.5,
“Branch Trace Store (BTS),” for a description of this mechanism.

31

8 7 6 5 4 3 2 1 0

Reserved
BTINT — Branch trace interrupt
BTS — Branch trace store
TR — Trace messages enable
Reserved
BTF — Single-step on branches
LBR — Last branch/interrupt/exception

Figure 17-14. IA32_DEBUGCTL MSR for Intel Core Solo
and Intel Core Duo Processors

•

Debug store (DS) feature flag (bit 21), returned by the CPUID instruction — Indicates that the
processor provides the debug store (DS) mechanism, which allows BTMs to be stored in a memory-resident
BTS buffer. See Section 17.4.5, “Branch Trace Store (BTS).”

•

Last Branch Record (LBR) Stack — The LBR stack consists of 8 MSRs (MSR_LASTBRANCH_0 through
MSR_LASTBRANCH_7); bits 31-0 hold the ‘from’ address, bits 63-32 hold the ‘to’ address (MSR addresses start
at 40H). See Figure 17-15.

•

Last Branch Record Top-of-Stack (TOS) Pointer — The TOS Pointer MSR contains a 3-bit pointer (bits 20) to the MSR in the LBR stack that contains the most recent branch, interrupt, or exception recorded. For Intel
Core Solo and Intel Core Duo processors, this MSR is located at register address 01C9H.

For compatibility, the Intel Core Solo and Intel Core Duo processors provide two 32-bit MSRs (the
MSR_LER_TO_LIP and the MSR_LER_FROM_LIP MSRs) that duplicate functions of the LastExceptionToIP and LastExceptionFromIP MSRs found in P6 family processors.
For details, see Section 17.12, “Last Branch, Call Stack, Interrupt, and Exception Recording for Processors based
on Skylake Microarchitecture,” and Section 2.19, “MSRs In Intel® Core™ Solo and Intel® Core™ Duo Processors” in
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4.

MSR_LASTBRANCH_0 through MSR_LASTBRANCH_7
63

0

32 - 31

To Linear Address

From Linear Address

Figure 17-15. LBR Branch Record Layout for the Intel Core Solo
and Intel Core Duo Processor

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

17.15

LAST BRANCH, INTERRUPT, AND EXCEPTION RECORDING (PENTIUM M
PROCESSORS)

Like the Pentium 4 and Intel Xeon processor family, Pentium M processors provide last branch interrupt and exception recording. The capability operates almost identically to that found in Pentium 4 and Intel Xeon processors.
There are differences in the shape of the stack and in some MSR names and locations. Note the following:

•

MSR_DEBUGCTLB MSR — Enables debug trace interrupt, debug trace store, trace messages enable,
performance monitoring breakpoint flags, single stepping on branches, and last branch. For Pentium M
processors, this MSR is located at register address 01D9H. See Figure 17-16 and the entries below for a
description of the flags.
— LBR (last branch/interrupt/exception) flag (bit 0) — When set, the processor records a running trace
of the most recent branches, interrupts, and/or exceptions taken by the processor (prior to a debug
exception being generated) in the last branch record (LBR) stack. For more information, see the “Last
Branch Record (LBR) Stack” bullet below.
— BTF (single-step on branches) flag (bit 1) — When set, the processor treats the TF flag in the EFLAGS
register as a “single-step on branches” flag rather than a “single-step on instructions” flag. This mechanism
allows single-stepping the processor on taken branches. See Section 17.4.3, “Single-Stepping on
Branches,” for more information about the BTF flag.
— PBi (performance monitoring/breakpoint pins) flags (bits 5-2) — When these flags are set, the
performance monitoring/breakpoint pins on the processor (BP0#, BP1#, BP2#, and BP3#) report
breakpoint matches in the corresponding breakpoint-address registers (DR0 through DR3). The processor
asserts then deasserts the corresponding BPi# pin when a breakpoint match occurs. When a PBi flag is
clear, the performance monitoring/breakpoint pins report performance events. Processor execution is not
affected by reporting performance events.
— TR (trace message enable) flag (bit 6) — When set, branch trace messages are enabled. When the
processor detects a taken branch, interrupt, or exception, it sends the branch record out on the system bus
as a branch trace message (BTM). See Section 17.4.4, “Branch Trace Messages,” for more information
about the TR flag.
— BTS (branch trace store) flag (bit 7) — When set, enables the BTS facilities to log BTMs to a memoryresident BTS buffer that is part of the DS save area. See Section 17.4.9, “BTS and DS Save Area.”
— BTINT (branch trace interrupt) flag (bits 8) — When set, the BTS facilities generate an interrupt when
the BTS buffer is full. When clear, BTMs are logged to the BTS buffer in a circular fashion. See Section 17.4.5,
“Branch Trace Store (BTS),” for a description of this mechanism.

31

8 7 6 5 4 3 2 1 0

Reserved
BTINT — Branch trace interrupt
BTS — Branch trace store
TR — Trace messages enable
PB3/2/1/0 — Performance monitoring breakpoint flags
BTF — Single-step on branches
LBR — Last branch/interrupt/exception

Figure 17-16. MSR_DEBUGCTLB MSR for Pentium M Processors

•

Debug store (DS) feature flag (bit 21), returned by the CPUID instruction — Indicates that the
processor provides the debug store (DS) mechanism, which allows BTMs to be stored in a memory-resident
BTS buffer. See Section 17.4.5, “Branch Trace Store (BTS).”

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

•

Last Branch Record (LBR) Stack — The LBR stack consists of 8 MSRs (MSR_LASTBRANCH_0 through
MSR_LASTBRANCH_7); bits 31-0 hold the ‘from’ address, bits 63-32 hold the ‘to’ address. For Pentium M
Processors, these pairs are located at register addresses 040H-047H. See Figure 17-17.

•

Last Branch Record Top-of-Stack (TOS) Pointer — The TOS Pointer MSR contains a 3-bit pointer (bits 20) to the MSR in the LBR stack that contains the most recent branch, interrupt, or exception recorded. For
Pentium M Processors, this MSR is located at register address 01C9H.

MSR_LASTBRANCH_0

through MSR_LASTBRANCH_7
0

32 - 31

63

To Linear Address

From Linear Address

Figure 17-17. LBR Branch Record Layout for the Pentium M Processor
For more detail on these capabilities, see Section 17.13.3, “Last Exception Records,” and Section 2.20, “MSRs In
the Pentium M Processor” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4.

17.16

LAST BRANCH, INTERRUPT, AND EXCEPTION
RECORDING (P6 FAMILY PROCESSORS)

The P6 family processors provide five MSRs for recording the last branch, interrupt, or exception taken by the
processor: DEBUGCTLMSR, LastBranchToIP, LastBranchFromIP, LastExceptionToIP, and LastExceptionFromIP.
These registers can be used to collect last branch records, to set breakpoints on branches, interrupts, and exceptions, and to single-step from one branch to the next.
See Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 4 for a detailed description of each of the last branch recording MSRs.

17.16.1

DEBUGCTLMSR Register

The version of the DEBUGCTLMSR register found in the P6 family processors enables last branch, interrupt, and
exception recording; taken branch breakpoints; the breakpoint reporting pins; and trace messages. This register
can be written to using the WRMSR instruction, when operating at privilege level 0 or when in real-address mode.
A protected-mode operating system procedure is required to provide user access to this register. Figure 17-18
shows the flags in the DEBUGCTLMSR register for the P6 family processors. The functions of these flags are as
follows:

•

LBR (last branch/interrupt/exception) flag (bit 0) — When set, the processor records the source and
target addresses (in the LastBranchToIP, LastBranchFromIP, LastExceptionToIP, and LastExceptionFromIP
MSRs) for the last branch and the last exception or interrupt taken by the processor prior to a debug exception
being generated. The processor clears this flag whenever a debug exception, such as an instruction or data
breakpoint or single-step trap occurs.

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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

31

7 6 5 4 3 2 1 0

Reserved

P P P P B L
T B B B B T B
R 3 2 1 0 F R

TR — Trace messages enable
PBi — Performance monitoring/breakpoint pins
BTF — Single-step on branches
LBR — Last branch/interrupt/exception

Figure 17-18. DEBUGCTLMSR Register (P6 Family Processors)

•

BTF (single-step on branches) flag (bit 1) — When set, the processor treats the TF flag in the EFLAGS
register as a “single-step on branches” flag. See Section 17.4.3, “Single-Stepping on Branches.”

•

PBi (performance monitoring/breakpoint pins) flags (bits 2 through 5) — When these flags are set,
the performance monitoring/breakpoint pins on the processor (BP0#, BP1#, BP2#, and BP3#) report
breakpoint matches in the corresponding breakpoint-address registers (DR0 through DR3). The processor
asserts then deasserts the corresponding BPi# pin when a breakpoint match occurs. When a PBi flag is clear,
the performance monitoring/breakpoint pins report performance events. Processor execution is not affected by
reporting performance events.

•

TR (trace message enable) flag (bit 6) — When set, trace messages are enabled as described in Section
17.4.4, “Branch Trace Messages.” Setting this flag greatly reduces the performance of the processor. When
trace messages are enabled, the values stored in the LastBranchToIP, LastBranchFromIP, LastExceptionToIP,
and LastExceptionFromIP MSRs are undefined.

17.16.2

Last Branch and Last Exception MSRs

The LastBranchToIP and LastBranchFromIP MSRs are 32-bit registers for recording the instruction pointers for the
last branch, interrupt, or exception that the processor took prior to a debug exception being generated. When a
branch occurs, the processor loads the address of the branch instruction into the LastBranchFromIP MSR and loads
the target address for the branch into the LastBranchToIP MSR.
When an interrupt or exception occurs (other than a debug exception), the address of the instruction that was
interrupted by the exception or interrupt is loaded into the LastBranchFromIP MSR and the address of the exception
or interrupt handler that is called is loaded into the LastBranchToIP MSR.
The LastExceptionToIP and LastExceptionFromIP MSRs (also 32-bit registers) record the instruction pointers for the
last branch that the processor took prior to an exception or interrupt being generated. When an exception or interrupt occurs, the contents of the LastBranchToIP and LastBranchFromIP MSRs are copied into these registers before
the to and from addresses of the exception or interrupt are recorded in the LastBranchToIP and LastBranchFromIP
MSRs.
These registers can be read using the RDMSR instruction.
Note that the values stored in the LastBranchToIP, LastBranchFromIP, LastExceptionToIP, and LastExceptionFromIP
MSRs are offsets into the current code segment, as opposed to linear addresses, which are saved in last branch
records for the Pentium 4 and Intel Xeon processors.

17.16.3

Monitoring Branches, Exceptions, and Interrupts

When the LBR flag in the DEBUGCTLMSR register is set, the processor automatically begins recording branches that
it takes, exceptions that are generated (except for debug exceptions), and interrupts that are serviced. Each time
a branch, exception, or interrupt occurs, the processor records the to and from instruction pointers in the LastBranchToIP and LastBranchFromIP MSRs. In addition, for interrupts and exceptions, the processor copies the
contents of the LastBranchToIP and LastBranchFromIP MSRs into the LastExceptionToIP and LastExceptionFromIP
MSRs prior to recording the to and from addresses of the interrupt or exception.
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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

When the processor generates a debug exception (#DB), it automatically clears the LBR flag before executing the
exception handler, but does not touch the last branch and last exception MSRs. The addresses for the last branch,
interrupt, or exception taken are thus retained in the LastBranchToIP and LastBranchFromIP MSRs and the
addresses of the last branch prior to an interrupt or exception are retained in the LastExceptionToIP, and LastExceptionFromIP MSRs.
The debugger can use the last branch, interrupt, and/or exception addresses in combination with code-segment
selectors retrieved from the stack to reset breakpoints in the breakpoint-address registers (DR0 through DR3),
allowing a backward trace from the manifestation of a particular bug toward its source. Because the instruction
pointers recorded in the LastBranchToIP, LastBranchFromIP, LastExceptionToIP, and LastExceptionFromIP MSRs
are offsets into a code segment, software must determine the segment base address of the code segment associated with the control transfer to calculate the linear address to be placed in the breakpoint-address registers. The
segment base address can be determined by reading the segment selector for the code segment from the stack
and using it to locate the segment descriptor for the segment in the GDT or LDT. The segment base address can
then be read from the segment descriptor.
Before resuming program execution from a debug-exception handler, the handler must set the LBR flag again to reenable last branch and last exception/interrupt recording.

17.17

TIME-STAMP COUNTER

The Intel 64 and IA-32 architectures (beginning with the Pentium processor) define a time-stamp counter mechanism that can be used to monitor and identify the relative time occurrence of processor events. The counter’s architecture includes the following components:

•

TSC flag — A feature bit that indicates the availability of the time-stamp counter. The counter is available in an
if the function CPUID.1:EDX.TSC[bit 4] = 1.

•

IA32_TIME_STAMP_COUNTER MSR (called TSC MSR in P6 family and Pentium processors) — The MSR used
as the counter.

•
•

RDTSC instruction — An instruction used to read the time-stamp counter.
TSD flag — A control register flag is used to enable or disable the time-stamp counter (enabled if
CR4.TSD[bit 2] = 1).

The time-stamp counter (as implemented in the P6 family, Pentium, Pentium M, Pentium 4, Intel Xeon, Intel Core
Solo and Intel Core Duo processors and later processors) is a 64-bit counter that is set to 0 following a RESET of
the processor. Following a RESET, the counter increments even when the processor is halted by the HLT instruction
or the external STPCLK# pin. Note that the assertion of the external DPSLP# pin may cause the time-stamp
counter to stop.
Processor families increment the time-stamp counter differently:

•

For Pentium M processors (family [06H], models [09H, 0DH]); for Pentium 4 processors, Intel Xeon processors
(family [0FH], models [00H, 01H, or 02H]); and for P6 family processors: the time-stamp counter increments
with every internal processor clock cycle.
The internal processor clock cycle is determined by the current core-clock to bus-clock ratio. Intel®
SpeedStep® technology transitions may also impact the processor clock.

•

For Pentium 4 processors, Intel Xeon processors (family [0FH], models [03H and higher]); for Intel Core Solo
and Intel Core Duo processors (family [06H], model [0EH]); for the Intel Xeon processor 5100 series and Intel
Core 2 Duo processors (family [06H], model [0FH]); for Intel Core 2 and Intel Xeon processors (family [06H],
DisplayModel [17H]); for Intel Atom processors (family [06H],
DisplayModel [1CH]): the time-stamp counter increments at a constant rate. That rate may be set by the
maximum core-clock to bus-clock ratio of the processor or may be set by the maximum resolved frequency at
which the processor is booted. The maximum resolved frequency may differ from the processor base
frequency, see Section 18.7.2 for more detail. On certain processors, the TSC frequency may not be the same
as the frequency in the brand string.
The specific processor configuration determines the behavior. Constant TSC behavior ensures that the duration
of each clock tick is uniform and supports the use of the TSC as a wall clock timer even if the processor core
changes frequency. This is the architectural behavior moving forward.

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NOTE
To determine average processor clock frequency, Intel recommends the use of performance
monitoring logic to count processor core clocks over the period of time for which the average is
required. See Section 18.6.4.5, “Counting Clocks on systems with Intel Hyper-Threading
Technology in Processors Based on Intel NetBurst® Microarchitecture,” and Chapter 19, “Performance Monitoring Events,” for more information.
The RDTSC instruction reads the time-stamp counter and is guaranteed to return a monotonically increasing
unique value whenever executed, except for a 64-bit counter wraparound. Intel guarantees that the time-stamp
counter will not wraparound within 10 years after being reset. The period for counter wrap is longer for Pentium 4,
Intel Xeon, P6 family, and Pentium processors.
Normally, the RDTSC instruction can be executed by programs and procedures running at any privilege level and in
virtual-8086 mode. The TSD flag allows use of this instruction to be restricted to programs and procedures running
at privilege level 0. A secure operating system would set the TSD flag during system initialization to disable user
access to the time-stamp counter. An operating system that disables user access to the time-stamp counter should
emulate the instruction through a user-accessible programming interface.
The RDTSC instruction is not serializing or ordered with other instructions. It does not necessarily wait until all
previous instructions have been executed before reading the counter. Similarly, subsequent instructions may begin
execution before the RDTSC instruction operation is performed.
The RDMSR and WRMSR instructions read and write the time-stamp counter, treating the time-stamp counter as an
ordinary MSR (address 10H). In the Pentium 4, Intel Xeon, and P6 family processors, all 64-bits of the time-stamp
counter are read using RDMSR (just as with RDTSC). When WRMSR is used to write the time-stamp counter on
processors before family [0FH], models [03H, 04H]: only the low-order 32-bits of the time-stamp counter can be
written (the high-order 32 bits are cleared to 0). For family [0FH], models [03H, 04H, 06H]; for family [06H]],
model [0EH, 0FH]; for family [06H]], DisplayModel [17H, 1AH, 1CH, 1DH]: all 64 bits are writable.

17.17.1

Invariant TSC

The time stamp counter in newer processors may support an enhancement, referred to as invariant TSC.
Processor’s support for invariant TSC is indicated by CPUID.80000007H:EDX[8].
The invariant TSC will run at a constant rate in all ACPI P-, C-. and T-states. This is the architectural behavior
moving forward. On processors with invariant TSC support, the OS may use the TSC for wall clock timer services
(instead of ACPI or HPET timers). TSC reads are much more efficient and do not incur the overhead associated with
a ring transition or access to a platform resource.

17.17.2

IA32_TSC_AUX Register and RDTSCP Support

Processors based on Intel microarchitecture code name Nehalem provide an auxiliary TSC register, IA32_TSC_AUX
that is designed to be used in conjunction with IA32_TSC. IA32_TSC_AUX provides a 32-bit field that is initialized
by privileged software with a signature value (for example, a logical processor ID).
The primary usage of IA32_TSC_AUX in conjunction with IA32_TSC is to allow software to read the 64-bit time
stamp in IA32_TSC and signature value in IA32_TSC_AUX with the instruction RDTSCP in an atomic operation.
RDTSCP returns the 64-bit time stamp in EDX:EAX and the 32-bit TSC_AUX signature value in ECX. The atomicity
of RDTSCP ensures that no context switch can occur between the reads of the TSC and TSC_AUX values.
Support for RDTSCP is indicated by CPUID.80000001H:EDX[27]. As with RDTSC instruction, non-ring 0 access is
controlled by CR4.TSD (Time Stamp Disable flag).
User mode software can use RDTSCP to detect if CPU migration has occurred between successive reads of the TSC.
It can also be used to adjust for per-CPU differences in TSC values in a NUMA system.

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17.17.3

Time-Stamp Counter Adjustment

Software can modify the value of the time-stamp counter (TSC) of a logical processor by using the WRMSR instruction to write to the IA32_TIME_STAMP_COUNTER MSR (address 10H). Because such a write applies only to that
logical processor, software seeking to synchronize the TSC values of multiple logical processors must perform these
writes on each logical processor. It may be difficult for software to do this in a way than ensures that all logical
processors will have the same value for the TSC at a given point in time.
The synchronization of TSC adjustment can be simplified by using the 64-bit IA32_TSC_ADJUST MSR (address
3BH). Like the IA32_TIME_STAMP_COUNTER MSR, the IA32_TSC_ADJUST MSR is maintained separately for each
logical processor. A logical processor maintains and uses the IA32_TSC_ADJUST MSR as follows:

•
•

On RESET, the value of the IA32_TSC_ADJUST MSR is 0.

•

If an execution of WRMSR to the IA32_TSC_ADJUST MSR adds (or subtracts) value X from that MSR, the logical
processor also adds (or subtracts) value X from the TSC.

If an execution of WRMSR to the IA32_TIME_STAMP_COUNTER MSR adds (or subtracts) value X from the TSC,
the logical processor also adds (or subtracts) value X from the IA32_TSC_ADJUST MSR.

Unlike the TSC, the value of the IA32_TSC_ADJUST MSR changes only in response to WRMSR (either to the MSR
itself, or to the IA32_TIME_STAMP_COUNTER MSR). Its value does not otherwise change as time elapses. Software
seeking to adjust the TSC can do so by using WRMSR to write the same value to the IA32_TSC_ADJUST MSR on
each logical processor.
Processor support for the IA32_TSC_ADJUST MSR is indicated by CPUID.(EAX=07H, ECX=0H):EBX.TSC_ADJUST
(bit 1).

17.17.4

Invariant Time-Keeping

The invariant TSC is based on the invariant timekeeping hardware (called Always Running Timer or ART), that runs
at the core crystal clock frequency. The ratio defined by CPUID leaf 15H expresses the frequency relationship
between the ART hardware and TSC.
If CPUID.15H:EBX[31:0] != 0 and CPUID.80000007H:EDX[InvariantTSC] = 1, the following linearity relationship
holds between TSC and the ART hardware:
TSC_Value = (ART_Value * CPUID.15H:EBX[31:0] )/ CPUID.15H:EAX[31:0] + K
Where 'K' is an offset that can be adjusted by a privileged agent2.
When ART hardware is reset, both invariant TSC and K are also reset.

17.18

INTEL® RESOURCE DIRECTOR TECHNOLOGY (INTEL® RDT) MONITORING
FEATURES

The Intel Resource Director Technology (Intel RDT) feature set provides a set of monitoring capabilities including
Cache Monitoring Technology (CMT) and Memory Bandwidth Monitoring (MBM). The Intel® Xeon® processor E5 v3
family introduced resource monitoring capability in each logical processor to measure specific platform shared
resource metrics, for example, L3 cache occupancy. The programming interface for these monitoring features is
described in this section. Two features within the monitoring feature set provided are described - Cache Monitoring
Technology (CMT) and Memory Bandwidth Monitoring.
Cache Monitoring Technology (CMT) allows an Operating System, Hypervisor or similar system management agent
to determine the usage of cache by applications running on the platform. The initial implementation is directed at
L3 cache monitoring (currently the last level cache in most server platforms).
Memory Bandwidth Monitoring (MBM), introduced in the Intel® Xeon® processor E5 v4 family, builds on the CMT
infrastructure to allow monitoring of bandwidth from one level of the cache hierarchy to the next - in this case
2. IA32_TSC_ADJUST MSR and the TSC-offset field in the VM execution controls of VMCS are some of the common interfaces that privileged software can use to manage the time stamp counter for keeping time
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focusing on the L3 cache, which is typically backed directly by system memory. As a result of this implementation,
memory bandwidth can be monitored.
The monitoring mechanisms described provide the following key shared infrastructure features:

•

A mechanism to enumerate the presence of the monitoring capabilities within the platform (via a CPUID feature
bit).

•

A framework to enumerate the details of each sub-feature (including CMT and MBM, as discussed later, via
CPUID leaves and sub-leaves).

•

A mechanism for the OS or Hypervisor to indicate a software-defined ID for each of the software threads (applications, virtual machines, etc.) that are scheduled to run on a logical processor. These identifiers are known as
Resource Monitoring IDs (RMIDs).

•

Mechanisms in hardware to monitor cache occupancy and bandwidth statistics as applicable to a given product
generation on a per software-id basis.

•

Mechanisms for the OS or Hypervisor to read back the collected metrics such as L3 occupancy or Memory
Bandwidth for a given software ID at any point during runtime.

17.18.1

Overview of Cache Monitoring Technology and Memory Bandwidth Monitoring

The shared resource monitoring features described in this chapter provide a layer of abstraction between applications and logical processors through the use of Resource Monitoring IDs (RMIDs). Each logical processor in the
system can be assigned an RMID independently, or multiple logical processors can be assigned to the same RMID
value (e.g., to track an application with multiple threads). For each logical processor, only one RMID value is active
at a time. This is enforced by the IA32_PQR_ASSOC MSR, which specifies the active RMID of a logical processor.
Writing to this MSR by software changes the active RMID of the logical processor from an old value to a new value.
The underlying platform shared resource monitoring hardware tracks cache metrics such as cache utilization and
misses as a result of memory accesses according to the RMIDs and reports monitored data via a counter register
(IA32_QM_CTR). The specific event types supported vary by generation and can be enumerated via CPUID. Before
reading back monitored data software must configure an event selection MSR (IA32_QM_EVTSEL) to specify which
metric is to be reported, and the specific RMID for which the data should be returned.
Processor support of the monitoring framework and sub-features such as CMT is reported via the CPUID instruction. The resource type available to the monitoring framework is enumerated via a new leaf function in CPUID.
Reading and writing to the monitoring MSRs requires the RDMSR and WRMSR instructions.
The Cache Monitoring Technology feature set provides the following unique mechanisms:

•

A mechanism to enumerate the presence and details of the CMT feature as applicable to a given level of the
cache hierarchy, independent of other monitoring features.

•

CMT-specific event codes to read occupancy for a given level of the cache hierarchy.

The Memory Bandwidth Monitoring feature provides the following unique mechanisms:

•

A mechanism to enumerate the presence and details of the MBM feature as applicable to a given level of the
cache hierarchy, independent of other monitoring features.

•

MBM-specific event codes to read bandwidth out to the next level of the hierarchy and various sub-event codes
to read more specific metrics as discussed later (e.g., total bandwidth vs. bandwidth only from local memory
controllers on the same package).

17.18.2

Enabling Monitoring: Usage Flow

Figure 17-19 illustrates the key steps for OS/VMM to detect support of shared resource monitoring features such as
CMT and enable resource monitoring for available resource types and monitoring events.

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On OS/VMM Initialization
PQM Capability
Enumeration
CPUID[
CPUID.(7,0):EBX.12
CPUID.(0FH,0):EDX[31:1]
CPUID.(0FH,1):ECX[31:0]
CPUID.(0FH,1):EDX[31:0]
CPUID.(0FH,1):EBX[31:0]
CPUID.(0FH,0):EBX[31:0]

On Context Switch
Set RMID to monitor
the scheduled app

Periodical Resource
Selection/Reporting
Configure event type
Read monitored data

WRMSR
IA32_PQR_ASSOC.RMID

RDMSR/WRMSR

IA32_QM_EVTSEL
IA32_QM_CTR

Figure 17-19. Platform Shared Resource Monitoring Usage Flow

17.18.3

Enumeration and Detecting Support of Cache Monitoring Technology and Memory
Bandwidth Monitoring

Software can query processor support of shared resource monitoring features capabilities by executing CPUID
instruction with EAX = 07H, ECX = 0H as input. If CPUID.(EAX=07H, ECX=0):EBX.PQM[bit 12] reports 1, the
processor provides the following programming interfaces for shared resource monitoring, including Cache Monitoring Technology:

•

CPUID leaf function 0FH (Shared Resource Monitoring Enumeration leaf) provides information on available
resource types (see Section 17.18.4), and monitoring capabilities for each resource type (see Section
17.18.5). Note CMT and MBM capabilities are enumerated as separate event vectors using shared enumeration
infrastructure under a given resource type.

•

IA32_PQR_ASSOC.RMID: The per-logical-processor MSR, IA32_PQR_ASSOC, that OS/VMM can use to assign
an RMID to each logical processor, see Section 17.18.6.

•

IA32_QM_EVTSEL: This MSR specifies an Event ID (EvtID) and an RMID which the platform uses to look up and
provide monitoring data in the monitoring counter, IA32_QM_CTR, see Section 17.18.7.

•

IA32_QM_CTR: This MSR reports monitored resource data when available along with bits to allow software to
check for error conditions and verify data validity.

Software must follow the following sequence of enumeration to discover Cache Monitoring Technology capabilities:
1. Execute CPUID with EAX=0 to discover the “cpuid_maxLeaf” supported in the processor;
2. If cpuid_maxLeaf >= 7, then execute CPUID with EAX=7, ECX= 0 to verify CPUID.(EAX=07H,
ECX=0):EBX.PQM[bit 12] is set;
3. If CPUID.(EAX=07H, ECX=0):EBX.PQM[bit 12] = 1, then execute CPUID with EAX=0FH, ECX= 0 to query
available resource types that support monitoring;
4. If CPUID.(EAX=0FH, ECX=0):EDX.L3[bit 1] = 1, then execute CPUID with EAX=0FH, ECX= 1 to query the
specific capabilities of L3 Cache Monitoring Technology (CMT) and Memory Bandwidth Monitoring.
5. If CPUID.(EAX=0FH, ECX=0):EDX reports additional resource types supporting monitoring, then execute
CPUID with EAX=0FH, ECX set to a corresponding resource type ID (ResID) as enumerated by the bit position
of CPUID.(EAX=0FH, ECX=0):EDX.

17.18.4

Monitoring Resource Type and Capability Enumeration

CPUID leaf function 0FH (Shared Resource Monitoring Enumeration leaf) provides one sub-leaf (sub-function 0)
that reports shared enumeration infrastructure, and one or more sub-functions that report feature-specific
enumeration data:

•

Monitoring leaf sub-function 0 enumerates available resources that support monitoring, i.e. executing CPUID
with EAX=0FH and ECX=0H. In the initial implementation, L3 cache is the only resource type available. Each
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DEBUG, BRANCH PROFILE, TSC, AND RESOURCE MONITORING FEATURES

supported resource type is represented by a bit in CPUID.(EAX=0FH, ECX=0):EDX[31:1]. The bit position
corresponds to the sub-leaf index (ResID) that software must use to query details of the monitoring capability
of that resource type (see Figure 17-21 and Figure 17-22). Reserved bits of CPUID.(EAX=0FH,
ECX=0):EDX[31:2] correspond to unsupported sub-leaves of the CPUID.0FH leaf. Additionally,
CPUID.(EAX=0FH, ECX=0H):EBX reports the highest RMID value of any resource type that supports monitoring
in the processor.

CPUID.(EAX=0FH, ECX=0H) Output: (EAX: Reserved; ECX: Reserved)
31

EDX

Reserved

2 1
L
3

31

EBX

0

0
Highest RMID Value of Any Resource Type (Zero-Based)

Figure 17-20. CPUID.(EAX=0FH, ECX=0H) Monitoring Resource Type Enumeration

17.18.5

Feature-Specific Enumeration

Each additional sub-leaf of CPUID.(EAX=0FH, ECX=ResID) enumerates the specific details for software to program
Monitoring MSRs using the resource type associated with the given ResID.
Note that in future Monitoring implementations the meanings of the returned registers may vary in other subleaves that are not yet defined. The registers will be specified and defined on a per-ResID basis.

CPUID.(EAX=0FH, ECX=1H) Output: (EAX: Reserved)
31

EBX

0

31

ECX

Upscaling Factor

Upscaling Factor to Total Occupancy (Bytes)
0
Highest RMID Value of This Resource Type (Zero-Based)

MaxRMID

Figure 17-21. L3 Cache Monitoring Capability Enumeration Data (CPUID.(EAX=0FH, ECX=1H) )
For each supported Cache Monitoring resource type, hardware supports only a finite number of RMIDs.
CPUID.(EAX=0FH, ECX=1H).ECX enumerates the highest RMID value that can be monitored with this resource
type, see Figure 17-21.
CPUID.(EAX=0FH, ECX=1H).EDX specifies a bit vector that is used to look up the EventID (See Figure 17-22 and
Table 17-18) that software must program with IA32_QM_EVTSEL in order to retrieve event data. After software
configures IA32_QMEVTSEL with the desired RMID and EventID, it can read the resulting data from IA32_QM_CTR.
The raw numerical value reported from IA32_QM_CTR can be converted to the final value (occupancy in bytes or
bandwidth in bytes per sampled time period) by multiplying the counter value by the value from CPUID.(EAX=0FH,
ECX=1H).EBX, see Figure 17-21.

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EventTypeBitMask

31

EDX

3 2 1

0

Reserved

L3 Occupancy
L3 Total BW
L3 Local BW

Figure 17-22. L3 Cache Monitoring Capability Enumeration Event Type Bit Vector (CPUID.(EAX=0FH, ECX=1H) )

17.18.5.1 Cache Monitoring Technology
On processors for which Cache Monitoring Technology supports the L3 cache occupancy event, CPUID.(EAX=0FH,
ECX=1H).EDX would return with only bit 0 set. The corresponding event ID can be looked up from Table 17-18. The
L3 occupancy data accumulated in IA32_QM_CTR can be converted to total occupancy (in bytes) by multiplying
with CPUID.(EAX=0FH, ECX=1H).EBX.
Event codes for Cache Monitoring Technology are discussed in the next section.

17.18.5.2 Memory Bandwidth Monitoring
On processors that monitoring supports Memory Bandwidth Monitoring using ResID=1 (L3), two additional bits will
be set in the vector at CPUID.(EAX=0FH, ECX=1H).EDX:

•

CPUID.(EAX=0FH, ECX=1H).EDX[bit 1]: indicates the L3 total external bandwidth monitoring event is
supported if set. This event monitors the L3 total external bandwidth to the next level of the cache hierarchy,
including all demand and prefetch misses from the L3 to the next hierarchy of the memory system. In most
platforms, this represents memory bandwidth.

•

CPUID.(EAX=0FH, ECX=1H).EDX[bit 2]: indicates L3 local memory bandwidth monitoring event is supported if
set. This event monitors the L3 external bandwidth satisfied by the local memory. In most platforms that
support this event, L3 requests are likely serviced by a memory system with non-uniform memory architecture. This allows bandwidth to off-package memory resources to be tracked by subtracting local from total
bandwidth (for instance, bandwidth over QPI to a memory controller on another physical processor could be
tracked by subtraction).

The corresponding Event ID can be looked up from Table 17-18. The L3 bandwidth data accumulated in
IA32_QM_CTR can be converted to total bandwidth (in bytes) using CPUID.(EAX=0FH, ECX=1H).EBX.

Table 17-18. Monitoring Supported Event IDs
Event Type

Event ID

Context

L3 Cache Occupancy

01H

Cache Monitoring Technology

L3 Total External Bandwidth

02H

MBM

L3 Local External Bandwidth

03H

MBM

Reserved

All other event codes

N/A

17.18.6

Monitoring Resource RMID Association

After Monitoring and sub-features has been enumerated, software can begin using the monitoring features. The
first step is to associate a given software thread (or multiple threads as part of an application, VM, group of applications or other abstraction) with an RMID.
Note that the process of associating an RMID with a given software thread is the same for all shared resource monitoring features (CMT, MBM), and a given RMID number has the same meaning from the viewpoint of any logical
processors in a package. Stated another way, a thread may be associated in a 1:1 mapping with an RMID, and that

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RMID may allow cache occupancy, memory bandwidth information or other monitoring data to be read back later
with monitoring event codes (retrieving data is discussed in a previous section).
The association of an application thread with an RMID requires an OS to program the per-logical-processor MSR
IA32_PQR_ASSOC at context swap time (updates may also be made at any other arbitrary points during program
execution such as application phase changes). The IA32_PQR_ASSOC MSR specifies the active RMID that monitoring hardware will use to tag internal operations, such as L3 cache requests. The layout of the MSR is shown in
Figure 17-23. Software specifies the active RMID to monitor in the IA32_PQR_ASSOC.RMID field. The width of the
RMID field can vary from one implementation to another, and is derived from Ceil (LOG2 ( 1 + CPUID.(EAX=0FH,
ECX=0):EBX[31:0])). The value of IA32_PQR_ASSOC after power-on is 0.

Width of IA32_PQR_ASSOC.RMID field: Log2 ( CPUID.(EAX=0FH, ECX=0H).EBX[31:0] +1)
32 31

63
Reserved for CLOS*

0

10 9
Reserved

RMID

IA32_PQR_ASSOC

*See Section 17.18

Figure 17-23. IA32_PQR_ASSOC MSR
In the initial implementation, the width of the RMID field is up to 10 bits wide, zero-referenced and fully encoded.
However, software must use CPUID to query the maximum RMID supported by the processor. If a value larger than
the maximum RMID is written to IA32_PQR_ASSOC.RMID, a #GP(0) fault will be generated.
RMIDs have a global scope within the physical package- if an RMID is assigned to one logical processor then the
same RMID can be used to read multiple thread attributes later (for example, L3 cache occupancy or external
bandwidth from the L3 to the next level of the cache hierarchy). In a multiple LLC platform the RMIDs are to be
reassigned by the OS or VMM scheduler when an application is migrated across LLCs.
Note that in a situation where Monitoring supports multiple resource types, some upper range of RMIDs (e.g. RMID
31) may only be supported by one resource type but not by another resource type.

17.18.7

Monitoring Resource Selection and Reporting Infrastructure

The reporting mechanism for Cache Monitoring Technology and other related features is architecturally exposed as
an MSR pair that can be programmed and read to measure various metrics such as the L3 cache occupancy (CMT)
and bandwidths (MBM) depending on the level of Monitoring support provided by the platform. Data is reported
back on a per-RMID basis. These events do not trigger based on event counts or trigger APIC interrupts (e.g. no
Performance Monitoring Interrupt occurs based on counts). Rather, they are used to sample counts explicitly.
The MSR pair for the shared resource monitoring features (CMT, MBM) is separate from and not shared with architectural Perfmon counters, meaning software can use these monitoring features simultaneously with the Perfmon
counters.
Access to the aggregated monitoring information is accomplished through the following programmable monitoring
MSRs:

•

IA32_QM_EVTSEL: This MSR provides a role similar to the event select MSRs for programmable performance
monitoring described in Chapter 18. The simplified layout of the MSR is shown in Figure 17-24. Bits
IA32_QM_EVTSEL.EvtID (bits 7:0) specify an event code of a supported resource type for hardware to report
monitored data associated with IA32_QM_EVTSEL.RMID (bits 41:32). Software can configure
IA32_QM_EVTSEL.RMID with any RMID that is active within the physical processor. The width of
IA32_QM_EVTSEL.RMID matches that of IA32_PQR_ASSOC.RMID. Supported event codes for the
IA32_QM_EVTSEL register are shown in Table 17-18. Note that valid event codes may not necessarily map
directly to the bit position used to enumerate support for the resource via CPUID.
Software can program an RMID / Event ID pair into the IA32_QM_EVTSEL MSR bit field to select an RMID to
read a particular counter for a given resource. The currently supported list of Monitoring Event IDs is discussed
in Section 17.18.5, which covers feature-specific details.

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Thread access to the IA32_QM_EVTSEL and IA32_QM_CTR MSR pair should be serialized to avoid situations
where one thread changes the RMID/EvtID just before another thread reads monitoring data from
IA32_QM_CTR.

•

IA32_QM_CTR: This MSR reports monitored data when available. It contains three bit fields. If software
configures an unsupported RMID or event type in IA32_QM_EVTSEL, then IA32_QM_CTR.Error (bit 63) will be
set, indicating there is no valid data to report. If IA32_QM_CTR.Unavailable (bit 62) is set, it indicates
monitored data for the RMID is not available, and IA32_QM_CTR.data (bits 61:0) should be ignored. Therefore,
IA32_QM_CTR.data (bits 61:0) is valid only if bit 63 and 62 are both clear. For Cache Monitoring Technology,
software can convert IA32_QM_CTR.data into cache occupancy or bandwidth metrics expressed in bytes by
multiplying with the conversion factor from CPUID.(EAX=0FH, ECX=1H).EBX.

42 41

63
Reserved

32 31

8 7
Reserved

RMID

61

63

0
IA32_QM_EVTSEL

EvtID

0

E U

IA32_QM_CTR

Resource Monitoring Data

Figure 17-24. IA32_QM_EVTSEL and IA32_QM_CTR MSRs

17.18.8

Monitoring Programming Considerations

Figure 17-23 illustrates how system software can program IA32_QOSEVTSEL and IA32_QM_CTR to perform
resource monitoring.

System Software
RMID

Event ID

IA32_QOSEVTSEL MSR
63
Reserved

32

41

RMID

7
Reserved

Counter Data

IA32_QM_CTR MSR
63 62

0

Event ID
Resource Monitoring ID

0
Monitoring Data

EvtID

Availability
Error

Figure 17-25. Software Usage of Cache Monitoring Resources
Though the field provided in IA32_QM_CTR allows for up to 62 bits of data to be returned, often a subset of bits are
used. With Cache Monitoring Technology for instance, the number of bits used will be proportional to the base-two
logarithm of the total cache size divided by the Upscaling Factor from CPUID.
In Memory Bandwidth Monitoring the initial counter size is 24 bits, and retrieving the value at 1Hz or faster is sufficient to ensure at most one rollover per sampling period. Any future changes to counter width will be enumerated
to software.

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17.18.8.1 Monitoring Dynamic Configuration
Both the IA32_QM_EVTSEL and IA32_PQR_ASSOC registers are accessible and modifiable at any time during
execution using RDMSR/WRMSR unless otherwise noted. When writing to these MSRs a #GP(0) will be generated
if any of the following conditions occur:

•
•

A reserved bit is modified,
An RMID exceeding the maxRMID is used.

17.18.8.2 Monitoring Operation With Power Saving Features
Note that some advanced power management features such as deep package C-states may shrink the L3 cache
and cause CMT occupancy count to be reduced. MBM bandwidth counts may increase due to flushing cached data
out of L3.

17.18.8.3 Monitoring Operation with Other Operating Modes
The states in IA32_PQR_ASSOC and monitoring counter are unmodified across an SMI delivery. Thus, the execution of SMM handler code and SMM handler’s data can manifest as spurious contribution in the monitored data.
It is possible for an SMM handler to minimize the impact on of spurious contribution in the QOS monitoring counters
by reserving a dedicated RMID for monitoring the SMM handler. Such an SMM handler can save the previously
configured QOS Monitoring state immediately upon entering SMM, and restoring the QOS monitoring state back to
the prev-SMM RMID upon exit.

17.18.8.4 Monitoring Operation with RAS Features
In general the Reliability, Availability and Serviceability (RAS) features present in Intel Platforms are not expected
to significantly affect shared resource monitoring counts. In cases where software RAS features cause memory
copies or cache accesses these may be tracked and may influence the shared resource monitoring counter values.

17.19

INTEL® RESOURCE DIRECTOR TECHNOLOGY (INTEL® RDT) ALLOCATION
FEATURES

The Intel Resource Director Technology (Intel RDT) feature set provides a set of allocation (resource control) capabilities including Cache Allocation Technology (CAT) and Code and Data Prioritization (CDP). The Intel Xeon
processor E5 v4 family (and subset of communication-focused Intel Xeon processors E5 v3 family) introduce capabilities to configure and make use of the Cache Allocation Technology (CAT) mechanisms on the L3 cache. Some
future Intel platforms may also provide support for control over the L2 cache, with capabilities as described below.
The programming interface for Cache Allocation Technology and for the more general allocation capabilities are
described in the rest of this chapter.
Future Intel processors introduce the Memory Bandwidth Allocation (MBA) feature which provides indirect control
over the memory bandwidth available to CPU cores, and is discussed later in this chapter.

17.19.1

Introduction to Cache Allocation Technology (CAT)

Cache Allocation Technology enables an Operating System (OS), Hypervisor /Virtual Machine Manager (VMM) or
similar system service management agent to specify the amount of cache space into which an application can fill
(as a hint to hardware - certain features such as power management may override CAT settings). Specialized userlevel implementations with minimal OS support are also possible, though not necessarily recommended (see notes
below for OS/Hypervisor with respect to ring 3 software and virtual guests). Depending on the processor family, L2
or L3 cache allocation capability may be provided, and the technology is designed to scale across multiple cache
levels and technology generations.
Software can determine which levels are supported in a give platform programmatically using CPUID as described
in the following sections.
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The CAT mechanisms defined in this document provide the following key features:

•

A mechanism to enumerate platform Cache Allocation Technology capabilities and available resource types that
provides CAT control capabilities. For implementations that support Cache Allocation Technology, CPUID
provides enumeration support to query which levels of the cache hierarchy are supported and specific CAT
capabilities, such as the max allocation bitmask size,

•

A mechanism for the OS or Hypervisor to configure the amount of a resource available to a particular Class of
Service via a list of allocation bitmasks,

•
•

Mechanisms for the OS or Hypervisor to signal the Class of Service to which an application belongs, and
Hardware mechanisms to guide the LLC fill policy when an application has been designated to belong to a
specific Class of Service.

Note that for many usages, an OS or Hypervisor may not want to expose Cache Allocation Technology mechanisms
to Ring3 software or virtualized guests.
The Cache Allocation Technology feature enables more cache resources (i.e. cache space) to be made available for
high priority applications based on guidance from the execution environment as shown in Figure 17-26. The architecture also allows dynamic resource reassignment during runtime to further optimize the performance of the high
priority application with minimal degradation to the low priority app. Additionally, resources can be rebalanced for
system throughput benefit across uses cases of OSes, VMMs, containers and other scenarios by managing the
CPUID and MSR interfaces. This section describes the hardware and software support required in the platform
including what is required of the execution environment (i.e. OS/VMM) to support such resource control. Note that
in Figure 17-26 the L3 Cache is shown as an example resource.

With CAT

Without CAT
Hi Pri App

Lo Pri App

Hi Pri App

Lo Pri App

Core 0

Core 1

Core 0

Core 1

Shared LLC, Low priority got more cache

Shared LLC, High priority got more cache

Figure 17-26. Cache Allocation Technology Allocates More Resource to High Priority Applications

17.19.2

Cache Allocation Technology Architecture

The fundamental goal of Cache Allocation Technology is to enable resource allocation based on application priority
or Class of Service (COS or CLOS). The processor exposes a set of Classes of Service into which applications (or
individual threads) can be assigned. Cache allocation for the respective applications or threads is then restricted
based on the class with which they are associated. Each Class of Service can be configured using capacity bitmasks
(CBMs) which represent capacity and indicate the degree of overlap and isolation between classes. For each logical
processor there is a register exposed (referred to here as the IA32_PQR_ASSOC MSR or PQR) to allow the OS/VMM
to specify a COS when an application, thread or VM is scheduled.
The usage of Classes of Service (COS) are consistent across resources - and a COS may have multiple re-source
control attributes attached, which reduces software overhead at context swap time. Rather than adding new types
of COS tags per resource for instance, the COS management overhead is constant. Cache allocation for the indicated application/thread/VM is then controlled automatically by the hardware based on the class and the bitmask
associated with that class. Bitmasks are configured via the IA32_resourceType_MASK_n MSRs, where
resourceType indicates a resource type (e.g. “L3” for the L3 cache) and n indicates a COS number.
The basic ingredients of Cache Allocation Technology are as follows:

•

An architecturally exposed mechanism using CPUID to indicate whether CAT is supported, and what resource
types are available which can be controlled,
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•

For each available resourceType, CPUID also enumerates the total number of Classes of Services and the length
of the capacity bitmasks that can be used to enforce cache allocation to applications on the platform,

•

An architecturally exposed mechanism to allow the execution environment (OS/VMM) to configure the behavior
of different classes of service using the bitmasks available,

•

An architecturally exposed mechanism to allow the execution environment (OS/VMM) to assign a COS to an
executing software thread (i.e. associating the active CR3 of a logical processor with the COS in
IA32_PQR_ASSOC),

•

Implementation-dependent mechanisms to indicate which COS is associated with a memory access and to
enforce the cache allocation on a per COS basis.

A capacity bitmask (CBM) provides a hint to the hardware indicating the cache space an application should be
limited to as well as providing an indication of overlap and isolation in the CAT-capable cache from other applications contending for the cache. The bitlength of the capacity mask available generally depends on the configuration
of the cache and is specified in the enumeration process for CAT in CPUID (this may vary between models in a
processor family as well). Similarly, other parameters such as the number of supported COS may vary for each
resource type, and these details can be enumerated via CPUID.

M7

M6

M5

M4

M3

M2

M1

M0

COS0

A

A

A

A

A

A

A

A

COS1

A

A

A

A

A

A

A

A

COS2

A

A

A

A

A

A

A

A

COS3

A

A

A

A

A

A

A

A

M7

M6
A

COS0

M5
A

M4
A

M3
A

COS1

M2

M1

M0

A

A

A

A

A

A

A

A

A

A

COS2

M7

COS1
COS2
COS3

Overlapped Bitmask

A

COS3

COS0

Default Bitmask

M6
A

M5
A

M4
A

M3

M2

M1

M0

A

Isolated Bitmask
A

A
A
A

Figure 17-27. Examples of Cache Capacity Bitmasks
Sample cache capacity bitmasks for a bitlength of 8 are shown in Figure 17-27. Please note that all (and only)
contiguous '1' combinations are allowed (e.g. FFFFH, 0FF0H, 003CH, etc.). Attempts to program a value without
contiguous '1's (including zero) will result in a general protection fault (#GP(0)). It is generally expected that in
way-based implementations, one capacity mask bit corresponds to some number of ways in cache, but the specific
mapping is implementation-dependent. In all cases, a mask bit set to '1' specifies that a particular Class of Service
can allocate into the cache subset represented by that bit. A value of '0' in a mask bit specifies that a Class of
Service cannot allocate into the given cache subset. In general, allocating more cache to a given application is
usually beneficial to its performance.

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Figure 17-27 also shows three examples of sets of Cache Capacity Bitmasks. For simplicity these are represented
as 8-bit vectors, though this may vary depending on the implementation and how the mask is mapped to the available cache capacity. The first example shows the default case where all 4 Classes of Service (the total number of
COS are implementation-dependent) have full access to the cache. The second case shows an overlapped case,
which would allow some lower-priority threads share cache space with the highest priority threads. The third case
shows various non-overlapped partitioning schemes. As a matter of software policy for extensibility COS0 should
typically be considered and configured as the highest priority COS, followed by COS1, and so on, though there is
no hardware restriction enforcing this mapping. When the system boots all threads are initialized to COS0, which
has full access to the cache by default.
Though the representation of the CBMs looks similar to a way-based mapping they are independent of any specific
enforcement implementation (e.g. way partitioning.) Rather, this is a convenient manner to represent capacity,
overlap and isolation of cache space. For example, executing a POPCNT instruction (population count of set bits) on
the capacity bitmask can provide the fraction of cache space that a class of service can allocate into. In addition to
the fraction, the exact location of the bits also shows whether the class of service overlaps with other classes of
service or is entirely isolated in terms of cache space used.

Enum/Confg

Association

Enforcement

Enumerate
Enforcement

OS Context
Switch

Application
Memory Request

Configure CBM for
each Class of Service

Set Class of Service
in IA32_PQR

Tag with Cache
Class of Service

Config

COS = 2

Mem Request

COS

Transaction

Cache Subsystem

Enforce Mask

Cache Allocation
Set 1
Set 2
COS 0

Capacity bitmask 3

COS 1

Capacity bitmask 3

COS 2

Capacity bitmask 3

COS 3

Capacity bitmask 3

....
Set n
way 1
......
way 16

Figure 17-28. Class of Service and Cache Capacity Bitmasks
Figure 17-28 shows how the Cache Capacity Bitmasks and the per-logical-processor Class of Service are logically
used to enable Cache Allocation Technology. All (and only) contiguous 1's in the CBM are permitted. The length of
CBM may vary from resource to resource or between processor generations and can be enumerated using CPUID.
From the available mask set and based on the goals of the OS/VMM (shared or isolated cache, etc.) bitmasks are
selected and associated with different classes of service. For the available Classes of Service the associated CBMs
can be programmed via the global set of CAT configuration registers (in the case of L3 CAT, via the
IA32_L3_MASK_n MSRs, where “n” is the Class of Service, starting from zero). In all architectural implementations
supporting CPUID it is possible to change the CBMs dynamically, during program execution, unless stated otherwise by Intel.
The currently running application's Class of Service is communicated to the hardware through the per-logicalprocessor PQR MSR (IA32_PQR_ASSOC MSR). When the OS schedules an application thread on a logical processor,
the application thread is associated with a specific COS (i.e. the corresponding COS in the PQR) and all requests to
the CAT-capable resource from that logical processor are tagged with that COS (in other words, the application

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thread is configured to belong to a specific COS). The cache subsystem uses this tagged request information to
enforce QoS. The capacity bitmask may be mapped into a way bitmask (or a similar enforcement entity based on
the implementation) at the cache before it is applied to the allocation policy. For example, the capacity bitmask can
be an 8-bit mask and the enforcement may be accomplished using a 16-way bitmask for a cache enforcement
implementation based on way partitioning.
The following sections describe extensions of CAT such as Code and Data Prioritization (CDP), followed by details
on specific features such as L3 CAT, L3 CDP, and L2 CAT. Depending on the specific processor a mix of features may
be supported, and CPUID provides enumeration capabilities to enable software to detect the set of supported
features.

17.19.3

Code and Data Prioritization (CDP) Technology

Code and Data Prioritization Technology is an extension of CAT. CDP enables isolation and separate prioritization of
code and data fetches to the L3 cache in a software configurable manner, which can enable workload prioritization
and tuning of cache capacity to the characteristics of the workload. CDP extends Cache Allocation Technology (CAT)
by providing separate code and data masks per Class of Service (COS).
By default, CDP is disabled on the processor. If the CAT MSRs are used without enabling CDP, the processor operates in a traditional CAT-only mode. When CDP is enabled,

•

the CAT mask MSRs are re-mapped into interleaved pairs of mask MSRs for data or code fetches (see
Figure 17-29),

•

the range of COS for CAT is re-indexed, with the lower-half of the COS range available for CDP.

Using the CDP feature, virtual isolation between code and data can be configured on the L3 cache if desired, similar
to how some processor cache levels provide separate L1 data and L1 instruction caches.
Like the CAT feature, CDP may be dynamically configured by privileged software at any point during normal system
operation, including dynamically enabling or disabling the feature provided that certain software configuration
requirements are met (see Section 17.19.5).
An example of the operating mode of CDP is shown in Figure 17-29. Shown at the top are traditional CAT usage
models where capacity masks map 1:1 with a COS number to enable control over the cache space which a given
COS (and thus applications, threads or VMs) may occupy. Shown at the bottom are example mask configurations
where CDP is enabled, and each COS number maps 1:2 to two masks, one for code and one for data. This enables
code and data to be either overlapped or isolated to varying degrees either globally or on a per-COS basis,
depending on application and system needs.

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Example of CAT-Only Usage - 16 bit Capacity Masks
COS0

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

COS1

0

0

0

0

1

1

1

1

0

0

0

0

0

0

0

0

COS2

0

0

0

0

0

0

0

0

1

1

0

0

0

0

0

0

COS3

0

0

0

0

0

0

0

0

1

1

1

1

1

1

1

1

Traditional
CAT

Example of Code/Data Prioritization Usage - 16 bit Capacity Masks
COS0.Data

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

COS0.Code

0

0

0

0

1

1

0

0

0

0

0

0

0

0

0

0

COS1.Data

0

0

0

0

0

0

1

1

1

1

1

0

0

0

0

0

COS1.Code

0

0

0

0

0

0

0

0

0

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

1

1

1

1

Other COS.Data
Other COS.Code

CAT with
CDP

Figure 17-29. Code and Data Capacity Bitmasks of CDP
When CDP is enabled, the existing mask space for CAT-only operation is split. As an example if the system supports
16 CAT-only COS, when CDP is enabled the same MSR interfaces are used, however half of the masks correspond
to code, half correspond to data, and the effective number2of COS is reduced by half. Code/Data masks are defined
per-COS and interleaved in the MSR space as described in subsequent sections.
In cases where CPUID exposes a non-even number of supported Classes of Service for the CAT or CDP features,
software using CDP should use the lower matched pairs of code/data masks, and any upper unpaired masks should
not be used. As an example, if CPUID exposes 5 CLOS, when CDP is enabled then two code/data pairs are available
(masks 0/1 for CLOS[0] data/code and masks 2/3 for CLOS[1] data/code), however the upper un-paired mask
should not be used (mask 4 in this case).

17.19.4

Enabling Cache Allocation Technology Usage Flow

Figure 17-30 illustrates the key steps for OS/VMM to detect support of Cache Allocation Technology and enable
priority-based resource allocation for a CAT-capable resource.

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On OS/VMM Initialization
CQE Capability
Enumeration

Cache Allocation Configuration

Set COS for scheduled
thread context

Configure CBM
per COS
WRMSR

CPUID[
CPUID.(7,0):EBX.15
CPUID.(10H,0):EBX[31:1]
CPUID.(10H,1):EAX[4:0]
CPUID.(10H,1):EDX[15:0]
CPUID.(10H,1):EBX[

On Context Switch

IA32_L3_QOS_MASK_0
...

WRMSR

IA32_PQR_ASSOC

A32_L3_QOS_MASK_n

Figure 17-30. Cache Allocation Technology Usage Flow
Enumeration and configuration of L2 CAT is similar to L3 CAT, however CPUID details and MSR addresses differ.
Common CLOS are used across the features.

17.19.4.1 Enumeration and Detection Support of Cache Allocation Technology
Software can query processor support of CAT capabilities by executing CPUID instruction with EAX = 07H, ECX =
0H as input. If CPUID.(EAX=07H, ECX=0):EBX.PQE[bit 15] reports 1, the processor supports software control over
shared processor resources. Software must use CPUID leaf 10H to enumerate additional details of available
resource types, classes of services and capability bitmasks. The programming interfaces provided by Cache Allocation Technology include:

•

CPUID leaf function 10H (Cache Allocation Technology Enumeration leaf) and its sub-functions provide
information on available resource types, and CAT capability for each resource type (see Section 17.19.4.2).

•

IA32_L3_MASK_n: A range of MSRs is provided for each resource type, each MSR within that range specifying
a software-configured capacity bitmask for each class of service. For L3 with Cache Allocation support, the CBM
is specified using one of the IA32_L3_QOS_MASK_n MSR, where 'n' corresponds to a number within the
supported range of COS, i.e. the range between 0 and CPUID.(EAX=10H, ECX=ResID):EDX[15:0], inclusive.
See Section 17.19.4.3 for details.

•

IA32_L2_MASK_n: A range of MSRs is provided for L2 Cache Allocation Technology, enabling software control
over the amount of L2 cache available for each CLOS. Similar to L3 CAT, a CBM is specified for each CLOS using
the set of registers, IA32_L2_QOS_MASK_n MSR, where 'n' ranges from zero to the maximum CLOS number
reported for L2 CAT in CPUID. See Section 17.19.4.3 for details.
The L2 mask MSRs are scoped at the same level as the L2 cache (similarly, the L3 mask MSRs are scoped at the
same level as the L3 cache). Software may determine which logical processors share an MSR (for instance local
to a core, or shared across multiple cores) by performing a write to one of these MSRs and noting which logical
threads observe the change. Example flows for a similar method to determine register scope are described in
Section 15.5.2, “System Software Recommendation for Managing CMCI and Machine Check Resources”.
Software may also use CPUID leaf 4 to determine the maximum number of logical processor IDs that may share
a given level of the cache.

•

IA32_PQR_ASSOC.CLOS: The IA32_PQR_ASSOC MSR provides a COS field that OS/VMM can use to assign a
logical processor to an available COS. The set of COS are common across all allocation features, meaning that
multiple features may be supported in the same processor without additional software COS management
overhead at context swap time. See Section 17.19.4.4 for details.

17.19.4.2 Cache Allocation Technology: Resource Type and Capability Enumeration
CPUID leaf function 10H (Cache Allocation Technology Enumeration leaf) provides two or more sub-functions:

•

CAT Enumeration leaf sub-function 0 enumerates available resource types that support allocation control, i.e.
by executing CPUID with EAX=10H and ECX=0H. Each supported resource type is represented by a bit field in

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CPUID.(EAX=10H, ECX=0):EBX[31:1]. The bit position of each set bit corresponds to a Resource ID (ResID),
for instance ResID=1 is used to indicate L3 CAT support, and ResID=2 indicates L2 CAT support. The ResID is
also the sub-leaf index that software must use to query details of the CAT capability of that resource type (see
Figure 17-31).

CPUID.(EAX=10H, ECX=0) Output: (EAX: Reserved; ECX: Reserved; EDX: Reserved)
31

4

EBX

Reserved

3

2

1

M
B
A

L
2

L
3

0

Figure 17-31. CPUID.(EAX=10H, ECX=0H) Available Resource Type Identification
— For ECX>0, EAX[4:0] reports the length of the capacity bitmask length (ECX=1 or 2 for L2 CAT or L3 CAT
respectively) using minus-one notation, e.g., a value of 15 corresponds to the capacity bitmask having
length of 16 bits. Bits 31:5 of EAX are reserved.

•

Sub-functions of CPUID.EAX=10H with a non-zero ECX input matching a supported ResID enumerate the
specific enforcement details of the corresponding ResID. The capabilities enumerated include the length of the
capacity bitmasks and the number of Classes of Service for a given ResID. Software should query the capability
of each available ResID that supports CAT from a sub-leaf of leaf 10H using the sub-leaf index reported by the
corresponding non-zero bit in CPUID.(EAX=10H, ECX=0):EBX[31:1] in order to obtain additional feature
details.

•

CAT capability for L3 is enumerated by CPUID.(EAX=10H, ECX=1H), see Figure 17-32. The specific CAT
capabilities reported by CPUID.(EAX=10H, ECX=1) are:

CPUID.(EAX=10H, ECX=ResID=1) Output:
5 4

31

EAX

Reserved

0

CBM_LEN

31

EBX

0
Bitmask of Shareable Resource with Other executing entities

31

ECX

2 1

0

Reserved
CDP

16 15

31

EDX

Reserved

0

COS_MAX

Figure 17-32. L3 Cache Allocation Technology and CDP Enumeration
— CPUID.(EAX=10H, ECX=ResID=1):EAX[4:0] reports the length of the capacity bitmask length using
minus-one notation, i.e. a value of 15 corresponds to the capability bitmask having length of 16 bits. Bits
31:5 of EAX are reserved.
— CPUID.(EAX=10H, ECX=1):EBX[31:0] reports a bit mask. Each set bit within the length of the CBM
indicates the corresponding unit of the L3 allocation may be used by other entities in the platform (e.g. an

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integrated graphics engine or hardware units outside the processor core and have direct access to L3). Each
cleared bit within the length of the CBM indicates the corresponding allocation unit can be configured to
implement a priority-based allocation scheme chosen by an OS/VMM without interference with other
hardware agents in the system. Bits outside the length of the CBM are reserved.
— CPUID.(EAX=10H, ECX=1):ECX.CDP[bit 2]: If 1, indicates Code and Data Prioritization Technology is
supported (see Section 17.19.5). Other bits of CPUID.(EAX=10H, ECX=1):ECX are reserved.
— CPUID.(EAX=10H, ECX=1):EDX[15:0] reports the maximum COS supported for the resource (COS are
zero-referenced, meaning a reported value of '15' would indicate 16 total supported COS). Bits 31:16 are
reserved.

•

CAT capability for L2 is enumerated by CPUID.(EAX=10H, ECX=2H), see Figure 17-33. The specific CAT
capabilities reported by CPUID.(EAX=10H, ECX=2) are:

CPUID.(EAX=10H, ECX=ResID=2) Output:
5 4

31

EAX

Reserved

0

CBM_LEN

31

EBX

0
Bitmask of Shareable Resource with Other executing entities

31

ECX

0
Reserved

16 15

31

EDX

Reserved

0

COS_MAX

Figure 17-33. L2 Cache Allocation Technology
— CPUID.(EAX=10H, ECX=ResID=2):EAX[4:0] reports the length of the capacity bitmask length using
minus-one notation, i.e. a value of 15 corresponds to the capability bitmask having length of 16 bits. Bits
31:5 of EAX are reserved.
— CPUID.(EAX=10H, ECX=2):EBX[31:0] reports a bit mask. Each set bit within the length of the CBM
indicates the corresponding unit of the L2 allocation may be used by other entities in the platform. Each
cleared bit within the length of the CBM indicates the corresponding allocation unit can be configured to
implement a priority-based allocation scheme chosen by an OS/VMM without interference with other
hardware agents in the system. Bits outside the length of the CBM are reserved.
— CPUID.(EAX=10H, ECX=2):ECX: reserved.
— CPUID.(EAX=10H, ECX=2):EDX[15:0] reports the maximum COS supported for the resource (COS are
zero-referenced, meaning a reported value of '15' would indicate 16 total supported COS). Bits 31:16 are
reserved.
A note on migration of Classes of Service (COS): Software should minimize migrations of COS across logical
processors (across threads or cores), as a reduction in the performance of the Cache Allocation Technology feature
may result if COS are migrated frequently. This is aligned with the industry-standard practice of minimizing unnecessary thread migrations across processor cores in order to avoid excessive time spent warming up processor
caches after a migration. In general, for best performance, minimize thread migration and COS migration across
processor logical threads and processor cores.

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17.19.4.3 Cache Allocation Technology: Cache Mask Configuration
After determining the length of the capacity bitmasks (CBM) and number of COS supported using CPUID (see
Section 17.19.4.2), each COS needs to be programmed with a CBM to dictate its available cache via a write to the
corresponding IA32_resourceType_MASK_n register, where 'n' corresponds to a number within the supported
range of COS, i.e. the range between 0 and CPUID.(EAX=10H, ECX=ResID):EDX[15:0], inclusive, and
'resourceType' corresponds to a specific resource as enumerated by the set bits of CPUID.(EAX=10H,
ECX=0):EAX[31:1], for instance, ‘L2’ or ‘L3’ cache.
A hierarchy of MSRs is reserved for Cache Allocation Technology registers of the form
IA32_resourceType_MASK_n:

•

From 0C90H through 0D8FH (inclusive), providing support for multiple sub-ranges to support varying resource
types. The first supported resourceType is 'L3', corresponding to the L3 cache in a platform. The MSRs range
from 0C90H through 0D0FH (inclusive), enables support for up to 128 L3 CAT Classes of Service.

31

63

63

0

10 9

32 31
Reserved

IA32_PQR_ASSOC

RMID

Reserved

COS

0
IA32_L3_MASK_0

Bit_Mask
....

63

32 31
Reserved

0
Bit_Mask

IA32_L3_MASK_n

Figure 17-34. IA32_PQR_ASSOC, IA32_L3_MASK_n MSRs

•

Within the same CAT range hierarchy, another set of registers is defined for resourceType 'L2', corresponding
to the L2 cache in a platform, and MSRs IA32_L2_MASK_n are defined for n=[0,63] at addresses 0D10H
through 0D4FH (inclusive).

Figure 17-34 and Figure 17-35 provide an overview of the relevant registers.

63

32 31
Reserved

0
IA32_L2_MASK_0

Bit_Mask
....

63

32 31
Reserved

0
Bit_Mask

IA32_L2_MASK_n

Figure 17-35. IA32_L2_MASK_n MSRs
All CAT configuration registers can be accessed using the standard RDMSR / WRMSR instructions.
Note that once L3 or L2 CAT masks are configured, threads can be grouped into Classes of Service (COS) using the
IA32_PQR_ASSOC MSR as described in Chapter 17, “Class of Service to Cache Mask Association: Common Across
Allocation Features”.

17.19.4.4 Class of Service to Cache Mask Association: Common Across Allocation Features
After configuring the available classes of service with the preferred set of capacity bitmasks, the OS/VMM can set
the IA32_PQR_ASSOC.COS of a logical processor to the class of service with the desired CBM when a thread
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context switch occurs. This allows the OS/VMM to indicate which class of service an executing thread/VM belongs
within. Each logical processor contains an instance of the IA32_PQR_ASSOC register at MSR location 0C8FH, and
Figure 17-34 shows the bit field layout for this register. Bits[63:32] contain the COS field for each logical processor.
Note that placing the RMID field within the same PQR register enables both RMID and CLOS to be swapped at
context swap time for simultaneous use of monitoring and allocation features with a single register write for efficiency.
When CDP is enabled, Specifying a COS value in IA32_PQR_ASSOC.COS greater than MAX_COS_CDP =(
CPUID.(EAX=10H, ECX=1):EDX[15:0] >> 1) will cause undefined performance impact to code and data fetches.
Note that if the IA32_PQR_ASSOC.COS is never written then the CAT capability defaults to using COS 0, which in
turn is set to the default mask in IA32_L3_MASK_0 - which is all “1”s (on reset). This essentially disables the
enforcement feature by default or for legacy operating systems and software.
See Section 17.19.6, “Cache Allocation Technology Programming Considerations” for important COS programming
considerations including maximum values when using CAT and CDP.

17.19.5

Code and Data Prioritization (CDP): Enumerating and Enabling L3 CDP Technology

CDP is an extension of CAT. The presence of the CDP feature is enumerated via CPUID.(EAX=10H,
ECX=1):ECX.CDP[bit 2] (see Figure 17-32). Most of the CPUID.(EAX=10H, ECX=1) sub-leaf data that applies to
CAT also apply to CDP. However, CPUID.(EAX=10H, ECX=1):EDX.COS_MAX_CAT specifies the maximum COS
applicable to CAT-only operation. For CDP operations, COS_MAX_CDP is equal to (CPUID.(EAX=10H,
ECX=1):EDX.COS_MAX_CAT >>1).
If CPUID.(EAX=10H, ECX=1):ECX.CDP[bit 2] =1, the processor supports CDP and provides a new MSR
IA32_L3_QOS_CFG at address 0C81H. The layout of IA32_L3_QOS_CFG is shown in Figure 17-36. The bit field
definition of IA32_L3_QOS_CFG are:

•

Bit 0: L3 CDP Enable. If set, enables CDP, maps CAT mask MSRs into pairs of Data Mask and Code Mask MSRs.
The maximum allowed value to write into IA32_PQR_ASSOC.COS is COS_MAX_CDP.

•

Bits 63:1: Reserved. Attempts to write to reserved bits result in a #GP(0).

63

IA32_L3_QOS_CFG

3 2 1

0

Reserved

L3 CDP Enable

Figure 17-36. Layout of IA32_L3_QOS_CFG
IA32_L3_QOS_CFG default values are all 0s at RESET, the mask MSRs are all 1s. Hence. all logical processors are
initialized in COS0 allocated with the entire L3 with CDP disabled, until software programs CAT and CDP.
Before enabling or disabling CDP, software should write all 1's to all of the CAT/CDP masks to ensure proper
behavior (e.g., the IA32_L3_QOS_Mask_n set of MSRs). When enabling CDP, software should also ensure that only
COS number which are valid in CDP operation is used, otherwise undefined behavior may result. For instance in a
case with 16 CAT COS, since COS are reduced by half when CDP is enabled, software should ensure that only COS
0-7 are in use before enabling CDP (along with writing 1's to all mask bits before enabling or disabling CDP).
Software should also account for the fact that mask interpretations change when CDP is enabled or disabled,
meaning for instance that a CAT mask for a given COS may become a code mask for a different Class of Service
when CDP is enabled. In order to simplify this behavior and prevent unintended remapping software should
consider resetting all threads to COS[0] before enabling or disabling CDP.

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17.19.5.1 Mapping Between L3 CDP Masks and CAT Masks
When CDP is enabled, the existing CAT mask MSR space is re-mapped to provide a code mask and a data mask per
COS. The re-mapping is shown in Table 17-19.

Table 17-19. Re-indexing of COS Numbers and Mapping to CAT/CDP Mask MSRs
Mask MSR

CAT-only Operation

CDP Operation

IA32_L3_QOS_Mask_0

COS0

COS0.Data

IA32_L3_QOS_Mask_1

COS1

COS0.Code

IA32_L3_QOS_Mask_2

COS2

COS1.Data

IA32_L3_QOS_Mask_3

COS3

COS1.Code

IA32_L3_QOS_Mask_4

COS4

COS2.Data

IA32_L3_QOS_Mask_5

COS5

COS2.Code

....

....

....

IA32_L3_QOS_Mask_’2n’

COS’2n’

COS’n’.Data

IA32_L3_QOS_Mask_’2n+1’

COS’2n+1’

COS’n’.Code

One can derive the MSR address for the data mask or code mask for a given COS number ‘n’ by:

•
•

data_mask_address (n) = base + (n <<1), where base is the address of IA32_L3_QOS_MASK_0.
code_mask_address (n) = base + (n <<1) +1.

When CDP is enabled, each COS is mapped 1:2 with mask MSRs, with one mask enabling programmatic control
over data fill location and one mask enabling control over data placement. A variety of overlapped and isolated
mask configurations are possible (see the example in Figure 17-29).
Mask MSR field definitions remain the same. Capacity masks must be formed of contiguous set bits, with a length
of 1 bit or longer and should not exceed the maximum mask length specified in CPUID. As examples, valid masks
on a cache with max bitmask length of 16b (from CPUID) include 0xFFFF, 0xFF00, 0x00FF, 0x00F0, 0x0001,
0x0003 and so on. Maximum valid mask lengths are unchanged whether CDP is enabled or disabled, and writes of
invalid mask values may lead to undefined behavior. Writes to reserved bits will generate #GP(0).

17.19.5.2 L3 CAT: Disabling CDP
Before enabling or disabling CDP, software should write all 1's to all of the CAT/CDP masks to ensure proper
behavior (e.g., the IA32_L3_QOS_Mask_n set of MSRs).
Software should also account for the fact that mask interpretations change when CDP is enabled or disabled,
meaning for instance that a CAT mask for a given COS may become a code mask for a different Class of Service
when CDP is enabled. In order to simplify this behavior and prevent unintended remapping software should
consider resetting all threads to COS[0] before enabling or disabling CDP.

17.19.6

Cache Allocation Technology Programming Considerations

17.19.6.1 Cache Allocation Technology Dynamic Configuration
Both the CAT masks and CQM registers are accessible and modifiable at any time during execution using
RDMSR/WRMSR unless otherwise noted. When writing to these MSRs a #GP(0) will be generated if any of the
following conditions occur:

•
•

A reserved bit is modified,
Accessing a QOS mask register outside the supported COS (the max COS number is specified in
CPUID.(EAX=10H, ECX=ResID):EDX[15:0]), or

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•

Writing a COS greater than the supported maximum (specified as the maximum value of CPUID.(EAX=10H,
ECX=ResID):EDX[15:0] for all valid ResID values) is written to the IA32_PQR_ASSOC.CLOS field.

When CDP is enabled, specifying a COS value in IA32_PQR_ASSOC.COS outside of the lower half of the COS space
will cause undefined performance impact to code and data fetches due to MSR space re-indexing into code/data
masks when CDP is enabled.
When reading the IA32_PQR_ASSOC register the currently programmed COS on the core will be returned.
When reading an IA32_resourceType_MASK_n register the current capacity bit mask for COS 'n' will be returned.
As noted previously, software should minimize migrations of COS across logical processors (across threads or
cores), as a reduction in the accuracy of the Cache Allocation feature may result if COS are migrated frequently.
This is aligned with the industry standard practice of minimizing unnecessary thread migrations across processor
cores in order to avoid excessive time spent warming up processor caches after a migration. In general, for best
performance, minimize thread migration and COS migration across processor logical threads and processor cores.

17.19.6.2 Cache Allocation Technology Operation With Power Saving Features
Note that the Cache Allocation Technology feature cannot be used to enforce cache coherency, and that some
advanced power management features such as C-states which may shrink or power off various caches within the
system may interfere with CAT hints - in such cases the CAT bitmasks are ignored and the other features take
precedence. If the highest possible level of CAT differentiation or determinism is required, disable any powersaving features which shrink the caches or power off caches. The details of the power management interfaces are
typically implementation-specific, but can be found at Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3C.
If software requires differentiation between threads but not absolute determinism then in many cases it is possible
to leave power-saving cache shrink features enabled, which can provide substantial power savings and increase
battery life in mobile platforms. In such cases when the caches are powered off (e.g., package C-states) the entire
cache of a portion thereof may be powered off. Upon resuming an active state any new incoming data to the cache
will be filled subject to the cache capacity bitmasks. Any data in the cache prior to the cache shrink or power off
may have been flushed to memory during the process of entering the idle state, however, and is not guaranteed to
remain in the cache. If differentiation between threads is the goal of system software then this model allows
substantial power savings while continuing to deliver performance differentiation. If system software needs optimal
determinism then power saving modes which flush portions of the caches and power them off should be disabled.

NOTE
IA32_PQR_ASSOC is saved and restored across C6 entry/exit. Similarly, the mask register contents
are saved across package C-state entry/exit and are not lost.

17.19.6.3 Cache Allocation Technology Operation with Other Operating Modes
The states in IA32_PQR_ASSOC and mask registers are unmodified across an SMI delivery. Thus, the execution of
SMM handler code can interact with the Cache Allocation Technology resource and manifest some degree of nondeterminism to the non-SMM software stack. An SMM handler may also perform certain system-level or power
management practices that affect CAT operation.
It is possible for an SMM handler to minimize the impact on data determinism in the cache by reserving a COS with
a dedicated partition in the cache. Such an SMM handler can switch to the dedicated COS immediately upon
entering SMM, and switching back to the previously running COS upon exit.

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17.19.6.4 Associating Threads with CAT/CDP Classes of Service
Threads are associated with Classes of Service (CLOS) via the per-logical-processor IA32_PQR_ASSOC MSR. The
same COS concept applies to both CAT and CDP (for instance, COS[5] means the same thing whether CAT or CDP
is in use, and the COS has associated resource usage constraint attributes including cache capacity masks). The
mapping of COS to mask MSRs does change when CDP is enabled, according to the following guidelines:

•

In CAT-only Mode - one set of bitmasks in one mask MSR control both code and data.
— Each COS number map 1:1 with a capacity mask on the applicable resource (e.g., L3 cache).

•

When CDP is enabled,
— Two mask sets exist for each COS number, one for code, one for data.
— Masks for code/data are interleaved in the MSR address space (see Table 17-19).

17.19.7

Introduction to Memory Bandwidth Allocation

The Memory Bandwidth Allocation (MBA) feature provides indirect and approximate control over memory bandwidth available per-core, and is introduced on future Intel processors. This feature provides a method to control
applications which may be over-utilizing bandwidth relative to their priority in environments such as the datacenter.
The MBA feature uses existing constructs from the Resource Director Technology (RDT) feature set including
Classes of Service (CLOS). A given CLOS used for L3 CAT for instance means the same thing as a CLOS used for
MBA. Infrastructure such as the MSR used to associate a thread with a CLOS (the IA32_PQR_ASSOC_MSR) and
some elements of the CPUID enumeration (such as CPUID leaf 10H) are shared.

•

The high-level implementation of Memory Bandwidth Allocation is shown in Figure 17-37.

Chip Multiprocessor Platform
Core[0]
Private L2
Programmable
Request Rate
Controller

Core[n]

..
.

Private L2
Programmable
Request Rate
Controller

High-Speed Interconnect

Shared L3 Cache – With CAT

New MBA Feature

Memory
Controller

Cache space available to
high-priority application
Cache space available to
low-priority application

Figure 17-37. A High-Level Overview of the MBA Feature

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As shown in Figure 17-37 the MBA feature introduces a programmable request rate controller between the cores
and the high-speed interconnect, enabling indirect control over memory bandwidth for cores over-utilizing bandwidth relative to their priority. For instance, high-priority cores may be run un-throttled, but lower priority cores
generating an excessive amount of traffic may be throttled to enable more bandwidth availability for the highpriority cores.
Since MBA uses a programmable rate controller between the cores and the interconnect, higher-level shared
caches and memory controller, bandwidth to these caches may also be reduced, so care should be taken to throttle
only bandwidth-intense applications which do not use the off-core caches effectively.
The throttling values exposed by MBA are approximate, and are calibrated to specific traffic patterns. As work-load
characteristics vary, the throttling values provided may affect each workload differently. In cases where precise
control is needed, the Memory Bandwidth Monitoring (MBM) feature can be used as input to a software controller
which makes decisions about the MBA throttling level to apply.
Enumeration and configuration details are discussed below followed by usage model considerations.

17.19.7.1 Memory Bandwidth Allocation Enumeration
Similar to other RDT features, enumeration of the presence and details of the MBA feature is provided via a subleaf of the CPUID instruction.
Key components of the enumeration are as follows.

•

Support for the MBA feature on the processor, and if MBA is supported, the following details:
— Number of supported Classes of Service (CLOS) for the processor.
— The maximum MBA delay value supported (which also implicitly provides a definition of the granularity).
— An indication of whether the delay values which can be programmed are linearly spaced or not.

The presence of any of the RDT features which enable control over shared platform resources is enumerated by
executing CPUID instruction with EAX = 07H, ECX = 0H as input. If CPUID.(EAX=07H, ECX=0):EBX.PQE[bit 15]
reports 1, the processor supports software control over shared processor resources. Software may then use CPUID
leaf 10H to enumerate additional details on the specific controls provided.
Through CPUID leaf 10H software may determine whether MBA is supported on the platform. Specifically, as shown
in Figure 17-31, bit 3 of the EBX register indicates whether MBA is supported on the processor, and the bit position
(3) constitutes a Resource ID (ResID) which allows enumeration of MBA details. For instance, if bit 3 is supported
this implies the presence of CPUID.10H.[ResID=3] as shown in Figure 17-38 which provides the following details.

•

CPUID.(EAX=10H, ECX=ResID=3):EAX[11:0] reports the maximum MBA throttling value supported, minus
one. For instance, a value of 89 indicates that a maximum throttling value of 90 is supported. Additionally, in
cases where a linear interface (see below) is supported then one hundred minus the maximum throttling value
indicates the granularity, 10% in this example.

•
•

CPUID.(EAX=10H, ECX=ResID=3):EBX is reserved.

•

CPUID.(EAX=10H, ECX=ResID=3):EDX[15:0] reports the number of Classes of Service (CLOS) supported for
the feature (minus one). For instance, a reported value of 15 implies a maximum of 16 supported MBA CLOS.

CPUID.(EAX=10H, ECX=ResID=3):ECX[2] reports whether the response of the delay values is linear (see
text).

The number of CLOS supported for the MBA feature may or may not align with other resources such as L3 CAT. In
cases where the RDT features support different numbers of CLOS the lowest numerical CLOS support the common
set of features, while higher CLOS may support a subset. For instance, if L3 CAT supports 8 CLOS while MBA
supports 4 CLOS, all 8 CLOS would have L3 CAT masks available for cache control, but the upper 4 CLOS would not
offer MBA support. In this case the upper 4 CLOS would not be subject to any throttling control. Software can
manage supported resources / CLOS in order to either have consistent capabilities across CLOS by using the
common subset or enable more flexibility by selectively applying resource control where needed based on careful
CLOS and thread mapping. In all cases, CLOS[0] supports all RDT resource control features present on the platform.
Discussion on the interpretation and usage of the MBA delay values is provided in Section 17.19.7.2 on MBA configuration.

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CPUID.(EAX = 10H, ECX = ResID = 3) Output:
31

11

EAX

Reserved

0
MBA_MAX-1

31

0

EBX

Reserved

31

2

ECX

1

0

Reserved
MBA_Lin_Rsp
31

EDX

16 15
Reserved

0
COS_MAX

Figure 17-38. CPUID.(EAX=10H, ECX=3H) MBA Feature Details Identification

17.19.7.2 Memory Bandwidth Allocation Configuration
The configuration of MBA takes consists of two processes once enumeration is complete.

•

Association of threads to Classes of Service (CLOS) - accomplished in a common fashion across RDT features
as described in Section 17.19.7.1 via the IA32_PQR_ASSOC MSR. As with features such as L3 CAT, software
may update the CLOS field of the PQR MSR at context swap time in order to maintain the proper association of
software threads to Classes of Service on the hardware. While logical processors may each be associated with
independent CLOS, see Section 17.19.7.3 for important usage model considerations (initial versions of the MBA
feature select the maximum delay value across threads).

•

Configuration of the per-CLOS delay values, accomplished via the IA32_L2_QoS_Ext_BW_Thrtl_n MSR set
shown in Table 17-20.

The MBA delay values which may be programmed range from zero (implying zero delay, and full bandwidth available) to the maximum (MBA_MAX) specified in CPUID as discussed in Section 17.19.7.1.
Software may select an MBA delay value then write the value into one or more of the
IA32_L2_QoS_Ext_BW_Thrtl_n MSRs to update the delay values applied for a specific CLOS. As shown in Table
17.20 the base address of the MSRs is at D50H, and the range corresponds to the maximum supported CLOS from
CPUID.(EAX=10H, ECX=ResID=1):EDX[15:0] as described in Section 17.19.7.1. For instance, if 16 CLOS are
supported then the valid MSR range will extend from D50H through D5F inclusive.

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Table 17-20. MBA Delay Value MSRs
Delay Value MSR

Address

IA32_L2_QoS_Ext_BW_Thrtl_0

D50H

IA32_L2_QoS_Ext_BW_Thrtl_1

D51H

IA32_L2_QoS_Ext_BW_Thrtl_2

D52H

....

....

IA32_L2_QoS_Ext_BW_Thrtl_'COS_MAX'

D50H + COS_MAX from CPUID.10H.3

The definition for the MBA delay value MSRs is provided in Figure 17.39. The lower 16 bits are used for MBA delay
values, and values from zero to the maximum from the CPUID MBA_MAX-1 value are supported. Values outside this
range will generate #GP(0).
If linear input throttling values are indicated by CPUID.(EAX=10H, ECX=ResID=3):ECX[bit 2] then values from
zero through the MBA_MAX field from CPUID.(EAX=10H, ECX=ResID=3):EAX[11:0] are supported as inputs. In
the linear mode the input precision is defined as 100-(MBA_MAX). For instance, if the MBA_MAX value is 90, the
input precision is 10%. Values not an even multiple of the precision (e.g., 12%) will be rounded down (e.g., to 10%
delay applied).

•

If linear values are not supported (CPUID.(EAX=10H, ECX=ResID=3):ECX[bit 2] = 0) then input delay values
are powers-of-two from zero to the MBA_MAX value from CPUID. In this case any values not a power of two will
be rounded down the next nearest power of two.

Base MSR Address = 0xD50
63

16 15

0

IA32_L2_QOS_Ext_BW_Thrtl_n MSR
Reserved

MBA Delay Value

Figure 17-39. IA32_L2_QoS_Ext_BW_Thrtl_n MSR Definition
Note that the throttling values provided to software are calibrated through specific traffic patterns, however as
workload characteristics may vary the response precision and linearity of the delay values will vary across
products, and should be treated as approximate values only.

17.19.7.3 Memory Bandwidth Allocation Usage Considerations
As the memory bandwidth control that MBA provides is indirect, using the feature with a closed-loop controller to
also monitor memory bandwidth and how effectively the applications use the cache (via the Cache Monitoring Technology feature) may provide additional value. This approach also allows administrators to provide a band-width
target or set-point which a controller could use to guide MBA throttling values applied, and this allows bandwidth
control independent of the execution characteristics of the application.
As control is provided per processor core (the max of the delay values of the per-thread CLOS applied to the core)
care should be taking in scheduling threads so as to not inadvertently place a high-priority thread (with zero
intended MBA throttling) next to a low-priority thread (with MBA throttling intended), which would lead to inadvertent throttling of the high-priority thread.

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CHAPTER 18
PERFORMANCE MONITORING
Intel 64 and IA-32 architectures provide facilities for monitoring performance via a PMU (Performance Monitoring
Unit).

18.1

PERFORMANCE MONITORING OVERVIEW

Performance monitoring was introduced in the Pentium processor with a set of model-specific performance-monitoring counter MSRs. These counters permit selection of processor performance parameters to be monitored and
measured. The information obtained from these counters can be used for tuning system and compiler performance.
In Intel P6 family of processors, the performance monitoring mechanism was enhanced to permit a wider selection
of events to be monitored and to allow greater control events to be monitored. Next, Intel processors based on
Intel NetBurst microarchitecture introduced a distributed style of performance monitoring mechanism and performance events.
The performance monitoring mechanisms and performance events defined for the Pentium, P6 family, and Intel
processors based on Intel NetBurst microarchitecture are not architectural. They are all model specific (not
compatible among processor families). Intel Core Solo and Intel Core Duo processors support a set of architectural
performance events and a set of non-architectural performance events. Newer Intel processor generations support
enhanced architectural performance events and non-architectural performance events.
Starting with Intel Core Solo and Intel Core Duo processors, there are two classes of performance monitoring capabilities. The first class supports events for monitoring performance using counting or interrupt-based event
sampling usage. These events are non-architectural and vary from one processor model to another. They are
similar to those available in Pentium M processors. These non-architectural performance monitoring events are
specific to the microarchitecture and may change with enhancements. They are discussed in Section 18.6.3,
“Performance Monitoring (Processors Based on Intel NetBurst® Microarchitecture).” Non-architectural events for a
given microarchitecture cannot be enumerated using CPUID; and they are listed in Chapter 19, “Performance
Monitoring Events.”
The second class of performance monitoring capabilities is referred to as architectural performance monitoring.
This class supports the same counting and Interrupt-based event sampling usages, with a smaller set of available
events. The visible behavior of architectural performance events is consistent across processor implementations.
Availability of architectural performance monitoring capabilities is enumerated using the CPUID.0AH. These events
are discussed in Section 18.2.
See also:
— Section 18.2, “Architectural Performance Monitoring”
— Section 18.3, “Performance Monitoring (Intel® Core™ Processors and Intel® Xeon® Processors)”

•

Section 18.3.1, “Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name
Nehalem”

•

Section 18.3.2, “Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name
Westmere”

•
•

Section 18.3.3, “Intel® Xeon® Processor E7 Family Performance Monitoring Facility”

•
•
•

Section 18.3.4, “Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name
Sandy Bridge”
Section 18.3.5, “3rd Generation Intel® Core™ Processor Performance Monitoring Facility”
Section 18.3.6, “4th Generation Intel® Core™ Processor Performance Monitoring Facility”
Section 18.3.7, “5th Generation Intel® Core™ Processor and Intel® Core™ M Processor Performance
Monitoring Facility”

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PERFORMANCE MONITORING

•

Section 18.3.8, “6th Generation Intel® Core™ Processor and 7th Generation Intel® Core™ Processor
Performance Monitoring Facility”

— Section 18.4, “Performance monitoring (Intel® Xeon™ Phi Processors)”

•

Section 18.4.1, “Intel® Xeon Phi™ Processor 7200/5200/3200 Performance Monitoring”

— Section 18.5, “Performance Monitoring (Intel® Atom™ Processors)”

•
•
•
•

Section 18.5.1, “Performance Monitoring (45 nm and 32 nm Intel® Atom™ Processors)”
Section 18.5.2, “Performance Monitoring for Silvermont Microarchitecture”
Section 18.5.3, “Performance Monitoring for Goldmont Microarchitecture”
Section 18.5.4, “Performance Monitoring for Goldmont Plus Microarchitecture”

— Section 18.6, “Performance Monitoring (Legacy Intel Processors)”

•
•
•
•

Section 18.6.1, “Performance Monitoring (Intel® Core™ Solo and Intel® Core™ Duo Processors)”
Section 18.6.2, “Performance Monitoring (Processors Based on Intel® Core™ Microarchitecture)”
Section 18.6.3, “Performance Monitoring (Processors Based on Intel NetBurst® Microarchitecture)”
Section 18.6.4, “Performance Monitoring and Intel Hyper-Threading Technology in Processors Based on
Intel NetBurst® Microarchitecture”

•
•
•
•
•
•

Section 18.6.4.5, “Counting Clocks on systems with Intel Hyper-Threading Technology in
Processors Based on Intel NetBurst® Microarchitecture”

Section 18.6.5, “Performance Monitoring and Dual-Core Technology”
Section 18.6.6, “Performance Monitoring on 64-bit Intel Xeon Processor MP with Up to 8-MByte L3
Cache”
Section 18.6.7, “Performance Monitoring on L3 and Caching Bus Controller Sub-Systems”
Section 18.6.8, “Performance Monitoring (P6 Family Processor)”
Section 18.6.9, “Performance Monitoring (Pentium Processors)”

— Section 18.7, “Counting Clocks”
— Section 18.8, “IA32_PERF_CAPABILITIES MSR Enumeration”

18.2

ARCHITECTURAL PERFORMANCE MONITORING

Performance monitoring events are architectural when they behave consistently across microarchitectures. Intel
Core Solo and Intel Core Duo processors introduced architectural performance monitoring. The feature provides a
mechanism for software to enumerate performance events and provides configuration and counting facilities for
events.
Architectural performance monitoring does allow for enhancement across processor implementations. The
CPUID.0AH leaf provides version ID for each enhancement. Intel Core Solo and Intel Core Duo processors support
base level functionality identified by version ID of 1. Processors based on Intel Core microarchitecture support, at
a minimum, the base level functionality of architectural performance monitoring. Intel Core 2 Duo processor T
7700 and newer processors based on Intel Core microarchitecture support both the base level functionality and
enhanced architectural performance monitoring identified by version ID of 2.
45 nm and 32 nm Intel Atom processors and Intel Atom processors based on the Silvermont microarchitecture
support the functionality provided by versionID 1, 2, and 3; CPUID.0AH:EAX[7:0] reports versionID = 3 to indicate
the aggregate of architectural performance monitoring capabilities. Intel Atom processors based on the Airmont
microarchitecture support the same performance monitoring capabilities as those based on the Silvermont microarchitecture.
Intel Core processors and related Intel Xeon processor families based on the Nehalem through Broadwell microarchitectures support version ID 1, 2, and 3. Intel processors based on the Skylake and Kaby Lake microarchitectures
support versionID 4.

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PERFORMANCE MONITORING

Next generation Intel Atom processors are based on the Goldmont microarchitecture. Intel processors based on
the Goldmont microarchitecture support versionID 4.

18.2.1

Architectural Performance Monitoring Version 1

Configuring an architectural performance monitoring event involves programming performance event select registers. There are a finite number of performance event select MSRs (IA32_PERFEVTSELx MSRs). The result of a
performance monitoring event is reported in a performance monitoring counter (IA32_PMCx MSR). Performance
monitoring counters are paired with performance monitoring select registers.
Performance monitoring select registers and counters are architectural in the following respects:

•
•
•
•

Bit field layout of IA32_PERFEVTSELx is consistent across microarchitectures.
Addresses of IA32_PERFEVTSELx MSRs remain the same across microarchitectures.
Addresses of IA32_PMC MSRs remain the same across microarchitectures.
Each logical processor has its own set of IA32_PERFEVTSELx and IA32_PMCx MSRs. Configuration facilities and
counters are not shared between logical processors sharing a processor core.

Architectural performance monitoring provides a CPUID mechanism for enumerating the following information:

•

Number of performance monitoring counters available in a logical processor (each IA32_PERFEVTSELx MSR is
paired to the corresponding IA32_PMCx MSR)

•
•

Number of bits supported in each IA32_PMCx
Number of architectural performance monitoring events supported in a logical processor

Software can use CPUID to discover architectural performance monitoring availability (CPUID.0AH). The architectural performance monitoring leaf provides an identifier corresponding to the version number of architectural
performance monitoring available in the processor.
The version identifier is retrieved by querying CPUID.0AH:EAX[bits 7:0] (see Chapter 3, “Instruction Set Reference, A-L,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A). If the version identifier is greater than zero, architectural performance monitoring capability is supported. Software queries the
CPUID.0AH for the version identifier first; it then analyzes the value returned in CPUID.0AH.EAX, CPUID.0AH.EBX
to determine the facilities available.
In the initial implementation of architectural performance monitoring; software can determine how many
IA32_PERFEVTSELx/ IA32_PMCx MSR pairs are supported per core, the bit-width of PMC, and the number of architectural performance monitoring events available.

18.2.1.1

Architectural Performance Monitoring Version 1 Facilities

Architectural performance monitoring facilities include a set of performance monitoring counters and performance
event select registers. These MSRs have the following properties:

•

IA32_PMCx MSRs start at address 0C1H and occupy a contiguous block of MSR address space; the number of
MSRs per logical processor is reported using CPUID.0AH:EAX[15:8].

•

IA32_PERFEVTSELx MSRs start at address 186H and occupy a contiguous block of MSR address space. Each
performance event select register is paired with a corresponding performance counter in the 0C1H address
block.

•

The bit width of an IA32_PMCx MSR is reported using the CPUID.0AH:EAX[23:16]. This the number of valid bits
for read operation. On write operations, the lower-order 32 bits of the MSR may be written with any value, and
the high-order bits are sign-extended from the value of bit 31.

•

Bit field layout of IA32_PERFEVTSELx MSRs is defined architecturally.

Vol. 3B 18-3

PERFORMANCE MONITORING

See Figure 18-1 for the bit field layout of IA32_PERFEVTSELx MSRs. The bit fields are:

•

Event select field (bits 0 through 7) — Selects the event logic unit used to detect microarchitectural
conditions (see Table 18-1, for a list of architectural events and their 8-bit codes). The set of values for this field
is defined architecturally; each value corresponds to an event logic unit for use with an architectural
performance event. The number of architectural events is queried using CPUID.0AH:EAX. A processor may
support only a subset of pre-defined values.

63

31

24 23 22 21 20 19 18 17 16 15

Counter Mask I E
N
(CMASK)
V N

INV—Invert counter mask
EN—Enable counters
INT—APIC interrupt enable
PC—Pin control
E—Edge detect
OS—Operating system mode
USR—User Mode

0

8 7

I
U
N P E O S Unit Mask (UMASK)
S R
T C

Event Select

Reserved

Figure 18-1. Layout of IA32_PERFEVTSELx MSRs

•

Unit mask (UMASK) field (bits 8 through 15) — These bits qualify the condition that the selected event
logic unit detects. Valid UMASK values for each event logic unit are specific to the unit. For each architectural
performance event, its corresponding UMASK value defines a specific microarchitectural condition.
A pre-defined microarchitectural condition associated with an architectural event may not be applicable to a
given processor. The processor then reports only a subset of pre-defined architectural events. Pre-defined
architectural events are listed in Table 18-1; support for pre-defined architectural events is enumerated using
CPUID.0AH:EBX. Architectural performance events available in the initial implementation are listed in Table
19-1.

•

USR (user mode) flag (bit 16) — Specifies that the selected microarchitectural condition is counted when
the logical processor is operating at privilege levels 1, 2 or 3. This flag can be used with the OS flag.

•

OS (operating system mode) flag (bit 17) — Specifies that the selected microarchitectural condition is
counted when the logical processor is operating at privilege level 0. This flag can be used with the USR flag.

•

E (edge detect) flag (bit 18) — Enables (when set) edge detection of the selected microarchitectural
condition. The logical processor counts the number of deasserted to asserted transitions for any condition that
can be expressed by the other fields. The mechanism does not permit back-to-back assertions to be distinguished.
This mechanism allows software to measure not only the fraction of time spent in a particular state, but also the
average length of time spent in such a state (for example, the time spent waiting for an interrupt to be
serviced).

•

PC (pin control) flag (bit 19) — When set, the logical processor toggles the PMi pins and increments the
counter when performance-monitoring events occur; when clear, the processor toggles the PMi pins when the
counter overflows. The toggling of a pin is defined as assertion of the pin for a single bus clock followed by
deassertion.

•

INT (APIC interrupt enable) flag (bit 20) — When set, the logical processor generates an exception
through its local APIC on counter overflow.

•

EN (Enable Counters) Flag (bit 22) — When set, performance counting is enabled in the corresponding
performance-monitoring counter; when clear, the corresponding counter is disabled. The event logic unit for a
UMASK must be disabled by setting IA32_PERFEVTSELx[bit 22] = 0, before writing to IA32_PMCx.

•

INV (invert) flag (bit 23) — When set, inverts the counter-mask (CMASK) comparison, so that both greater
than or equal to and less than comparisons can be made (0: greater than or equal; 1: less than). Note if
counter-mask is programmed to zero, INV flag is ignored.

18-4 Vol. 3B

PERFORMANCE MONITORING

•

Counter mask (CMASK) field (bits 24 through 31) — When this field is not zero, a logical processor
compares this mask to the events count of the detected microarchitectural condition during a single cycle. If
the event count is greater than or equal to this mask, the counter is incremented by one. Otherwise the counter
is not incremented.
This mask is intended for software to characterize microarchitectural conditions that can count multiple
occurrences per cycle (for example, two or more instructions retired per clock; or bus queue occupations). If
the counter-mask field is 0, then the counter is incremented each cycle by the event count associated with
multiple occurrences.

18.2.1.2

Pre-defined Architectural Performance Events

Table 18-1 lists architecturally defined events.

Table 18-1. UMask and Event Select Encodings for Pre-Defined Architectural Performance Events
Bit Position
CPUID.AH.EBX

Event Name

UMask

Event Select

0

UnHalted Core Cycles

00H

3CH

1

Instruction Retired

00H

C0H

2

UnHalted Reference Cycles

01H

3CH

3

LLC Reference

4FH

2EH

4

LLC Misses

41H

2EH

5

Branch Instruction Retired

00H

C4H

6

Branch Misses Retired

00H

C5H

A processor that supports architectural performance monitoring may not support all the predefined architectural
performance events (Table 18-1). The non-zero bits in CPUID.0AH:EBX indicate the events that are not available.
The behavior of each architectural performance event is expected to be consistent on all processors that support
that event. Minor variations between microarchitectures are noted below:

•

UnHalted Core Cycles — Event select 3CH, Umask 00H
This event counts core clock cycles when the clock signal on a specific core is running (not halted). The counter
does not advance in the following conditions:
— an ACPI C-state other than C0 for normal operation
— HLT
— STPCLK# pin asserted
— being throttled by TM1
— during the frequency switching phase of a performance state transition (see Chapter 14, “Power and
Thermal Management”)
The performance counter for this event counts across performance state transitions using different core clock
frequencies

•

Instructions Retired — Event select C0H, Umask 00H
This event counts the number of instructions at retirement. For instructions that consist of multiple micro-ops,
this event counts the retirement of the last micro-op of the instruction. An instruction with a REP prefix counts
as one instruction (not per iteration). Faults before the retirement of the last micro-op of a multi-ops instruction
are not counted.
This event does not increment under VM-exit conditions. Counters continue counting during hardware
interrupts, traps, and inside interrupt handlers.

Vol. 3B 18-5

PERFORMANCE MONITORING

•

UnHalted Reference Cycles — Event select 3CH, Umask 01H
This event counts reference clock cycles at a fixed frequency while the clock signal on the core is running. The
event counts at a fixed frequency, irrespective of core frequency changes due to performance state transitions.
Processors may implement this behavior differently. Current implementations use the core crystal clock, TSC or
the bus clock. Because the rate may differ between implementations, software should calibrate it to a time
source with known frequency.

•

Last Level Cache References — Event select 2EH, Umask 4FH
This event counts requests originating from the core that reference a cache line in the last level on-die cache.
The event count includes speculation and cache line fills due to the first-level cache hardware prefetcher, but
may exclude cache line fills due to other hardware-prefetchers.
Because cache hierarchy, cache sizes and other implementation-specific characteristics; value comparison to
estimate performance differences is not recommended.

•

Last Level Cache Misses — Event select 2EH, Umask 41H
This event counts each cache miss condition for references to the last level on-die cache. The event count may
include speculation and cache line fills due to the first-level cache hardware prefetcher, but may exclude cache
line fills due to other hardware-prefetchers.
Because cache hierarchy, cache sizes and other implementation-specific characteristics; value comparison to
estimate performance differences is not recommended.

•

Branch Instructions Retired — Event select C4H, Umask 00H
This event counts branch instructions at retirement. It counts the retirement of the last micro-op of a branch
instruction.

•

All Branch Mispredict Retired — Event select C5H, Umask 00H
This event counts mispredicted branch instructions at retirement. It counts the retirement of the last micro-op
of a branch instruction in the architectural path of execution and experienced misprediction in the branch
prediction hardware.
Branch prediction hardware is implementation-specific across microarchitectures; value comparison to
estimate performance differences is not recommended.

NOTE
Programming decisions or software precisians on functionality should not be based on the event
values or dependent on the existence of performance monitoring events.

18.2.2

Architectural Performance Monitoring Version 2

The enhanced features provided by architectural performance monitoring version 2 include the following:

•

Fixed-function performance counter register and associated control register — Three of the architectural performance events are counted using three fixed-function MSRs (IA32_FIXED_CTR0 through
IA32_FIXED_CTR2). Each of the fixed-function PMC can count only one architectural performance event.
Configuring the fixed-function PMCs is done by writing to bit fields in the MSR (IA32_FIXED_CTR_CTRL) located
at address 38DH. Unlike configuring performance events for general-purpose PMCs (IA32_PMCx) via UMASK
field in (IA32_PERFEVTSELx), configuring, programming IA32_FIXED_CTR_CTRL for fixed-function PMCs do
not require any UMASK.

18-6 Vol. 3B

PERFORMANCE MONITORING

•

Simplified event programming — Most frequent operation in programming performance events are
enabling/disabling event counting and checking the status of counter overflows. Architectural performance
event version 2 provides three architectural MSRs:
— IA32_PERF_GLOBAL_CTRL allows software to enable/disable event counting of all or any combination of
fixed-function PMCs (IA32_FIXED_CTRx) or any general-purpose PMCs via a single WRMSR.
— IA32_PERF_GLOBAL_STATUS allows software to query counter overflow conditions on any combination of
fixed-function PMCs or general-purpose PMCs via a single RDMSR.
— IA32_PERF_GLOBAL_OVF_CTRL allows software to clear counter overflow conditions on any combination of
fixed-function PMCs or general-purpose PMCs via a single WRMSR.

•

PMI Overhead Mitigation — Architectural performance monitoring version 2 introduces two bit field interface
in IA32_DEBUGCTL for PMI service routine to accumulate performance monitoring data and LBR records with
reduced perturbation from servicing the PMI. The two bit fields are:
— IA32_DEBUGCTL.Freeze_LBR_On_PMI(bit 11). In architectural performance monitoring version 2, only the
legacy semantic behavior is supported. See Section 17.4.7 for details of the legacy Freeze LBRs on PMI
control.
— IA32_DEBUGCTL.Freeze_PerfMon_On_PMI(bit 12). In architectural performance monitoring version 2,
only the legacy semantic behavior is supported. See Section 17.4.7 for details of the legacy Freeze LBRs on
PMI control.

The facilities provided by architectural performance monitoring version 2 can be queried from CPUID leaf 0AH by
examining the content of register EDX:

•

Bits 0 through 4 of CPUID.0AH.EDX indicates the number of fixed-function performance counters available per
core,

•

Bits 5 through 12 of CPUID.0AH.EDX indicates the bit-width of fixed-function performance counters. Bits
beyond the width of the fixed-function counter are reserved and must be written as zeros.
NOTE
Early generation of processors based on Intel Core microarchitecture may report in
CPUID.0AH:EDX of support for version 2 but indicating incorrect information of version 2 facilities.
The IA32_FIXED_CTR_CTRL MSR include multiple sets of 4-bit field, each 4 bit field controls the operation of a
fixed-function performance counter. Figure 18-2 shows the layout of 4-bit controls for each fixed-function PMC.
Two sub-fields are currently defined within each control. The definitions of the bit fields are:

63

12 11

9 8 7

P
M
I

P
M
I

E
N

5 43 2 1 0
E
N

P
M
I

E
N

Cntr2 — Controls for IA32_FIXED_CTR2
Cntr1 — Controls for IA32_FIXED_CTR1
PMI — Enable PMI on overflow
Cntr0 — Controls for IA32_FIXED_CTR0
ENABLE — 0: disable; 1: OS; 2: User; 3: All ring levels

Reserved

Figure 18-2. Layout of IA32_FIXED_CTR_CTRL MSR

Vol. 3B 18-7

PERFORMANCE MONITORING

•

Enable field (lowest 2 bits within each 4-bit control) — When bit 0 is set, performance counting is
enabled in the corresponding fixed-function performance counter to increment while the target condition
associated with the architecture performance event occurred at ring 0. When bit 1 is set, performance counting
is enabled in the corresponding fixed-function performance counter to increment while the target condition
associated with the architecture performance event occurred at ring greater than 0. Writing 0 to both bits stops
the performance counter. Writing a value of 11B enables the counter to increment irrespective of privilege
levels.

•

PMI field (the fourth bit within each 4-bit control) — When set, the logical processor generates an
exception through its local APIC on overflow condition of the respective fixed-function counter.

IA32_PERF_GLOBAL_CTRL MSR provides single-bit controls to enable counting of each performance counter.
Figure 18-3 shows the layout of IA32_PERF_GLOBAL_CTRL. Each enable bit in IA32_PERF_GLOBAL_CTRL is
AND’ed with the enable bits for all privilege levels in the respective IA32_PERFEVTSELx or
IA32_PERF_FIXED_CTR_CTRL MSRs to start/stop the counting of respective counters. Counting is enabled if the
AND’ed results is true; counting is disabled when the result is false.

63

35 34 33 32 31

2 1 0

IA32_FIXED_CTR2 enable
IA32_FIXED_CTR1 enable
IA32_FIXED_CTR0 enable
IA32_PMC1 enable
IA32_PMC0 enable

Reserved

Figure 18-3. Layout of IA32_PERF_GLOBAL_CTRL MSR
The behavior of the fixed function performance counters supported by architectural performance version 2 is
expected to be consistent on all processors that support those counters, and is defined as follows.

18-8 Vol. 3B

PERFORMANCE MONITORING

Table 18-2. Association of Fixed-Function Performance Counters with Architectural Performance Events
Fixed-Function Performance Counter

Address

Event Mask Mnemonic

Description

MSR_PERF_FIXED_CTR0/IA32_FIXED_CTR0

309H

INST_RETIRED.ANY

This event counts the number of
instructions that retire execution. For
instructions that consist of multiple
uops, this event counts the
retirement of the last uop of the
instruction. The counter continues
counting during hardware interrupts,
traps, and in-side interrupt handlers.

MSR_PERF_FIXED_CTR1//IA32_FIXED_CTR1

30AH

CPU_CLK_UNHALTED.THREAD

The CPU_CLK_UNHALTED.THREAD
event counts the number of core
cycles while the logical processor is
not in a halt state.

CPU_CLK_UNHALTED.CORE

If there is only one logical processor
in a processor core,
CPU_CLK_UNHALTED.CORE counts
the unhalted cycles of the processor
core.
The core frequency may change from
time to time due to transitions
associated with Enhanced Intel
SpeedStep Technology or TM2. For
this reason this event may have a
changing ratio with regards to time.
MSR_PERF_FIXED_CTR2//IA32_FIXED_CTR2

30BH

CPU_CLK_UNHALTED.REF_TSC

This event counts the number of
reference cycles at the TSC rate
when the core is not in a halt state
and not in a TM stop-clock state. The
core enters the halt state when it is
running the HLT instruction or the
MWAIT instruction. This event is not
affected by core frequency changes
(e.g., P states) but counts at the same
frequency as the time stamp counter.
This event can approximate elapsed
time while the core was not in a halt
state and not in a TM stopclock state.

IA32_PERF_GLOBAL_STATUS MSR provides single-bit status for software to query the overflow condition of each
performance counter. IA32_PERF_GLOBAL_STATUS[bit 62] indicates overflow conditions of the DS area data
buffer. IA32_PERF_GLOBAL_STATUS[bit 63] provides a CondChgd bit to indicate changes to the state of performance monitoring hardware. Figure 18-4 shows the layout of IA32_PERF_GLOBAL_STATUS. A value of 1 in bits 0,
1, 32 through 34 indicates a counter overflow condition has occurred in the associated counter.
When a performance counter is configured for PEBS, overflow condition in the counter generates a performancemonitoring interrupt signaling a PEBS event. On a PEBS event, the processor stores data records into the buffer
area (see Section 18.15.5), clears the counter overflow status., and sets the “OvfBuffer” bit in
IA32_PERF_GLOBAL_STATUS.

Vol. 3B 18-9

PERFORMANCE MONITORING

63 62

35 34 33 32 31

2 1 0

CondChgd
OvfDSBuffer
IA32_FIXED_CTR2 Overflow
IA32_FIXED_CTR1 Overflow
IA32_FIXED_CTR0 Overflow
IA32_PMC1 Overflow
IA32_PMC0 Overflow

Reserved

Figure 18-4. Layout of IA32_PERF_GLOBAL_STATUS MSR
IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of any general-purpose or fixedfunction counters via a single WRMSR. Software should clear overflow indications when

•
•
•

Setting up new values in the event select and/or UMASK field for counting or interrupt-based event sampling.
Reloading counter values to continue collecting next sample.
Disabling event counting or interrupt-based event sampling.

The layout of IA32_PERF_GLOBAL_OVF_CTL is shown in Figure 18-5.

63 62

35 34 33 32 31

2 1 0

ClrCondChgd
ClrOvfDSBuffer
IA32_FIXED_CTR2 ClrOverflow
IA32_FIXED_CTR1 ClrOverflow
IA32_FIXED_CTR0 ClrOverflow
IA32_PMC1 ClrOverflow
IA32_PMC0 ClrOverflow

Reserved

Figure 18-5. Layout of IA32_PERF_GLOBAL_OVF_CTRL MSR

18.2.3

Architectural Performance Monitoring Version 3

Processors supporting architectural performance monitoring version 3 also supports version 1 and 2, as well as
capability enumerated by CPUID leaf 0AH. Specifically, version 3 provides the following enhancement in performance monitoring facilities if a processor core comprising of more than one logical processor, i.e. a processor core
supporting Intel Hyper-Threading Technology or simultaneous multi-threading capability:

•

AnyThread counting for processor core supporting two or more logical processors. The interface that supports
AnyThread counting include:
— Each IA32_PERFEVTSELx MSR (starting at MSR address 186H) support the bit field layout defined in Figure
18-6.

18-10 Vol. 3B

PERFORMANCE MONITORING

63

31

24 23 22 21 20 19 18 17 16 15

0

8 7

A I
U
Counter Mask I E N
N
N P E O S Unit Mask (UMASK)
(CMASK)
S R
V N Y T C

INV—Invert counter mask
EN—Enable counters
ANY—Any Thread
INT—APIC interrupt enable
PC—Pin control
E—Edge detect
OS—Operating system mode
USR—User Mode

Event Select

Reserved

Figure 18-6. Layout of IA32_PERFEVTSELx MSRs Supporting Architectural Performance Monitoring Version 3
Bit 21 (AnyThread) of IA32_PERFEVTSELx is supported in architectural performance monitoring version 3 for
processor core comprising of two or more logical processors. When set to 1, it enables counting the associated
event conditions (including matching the thread’s CPL with the OS/USR setting of IA32_PERFEVTSELx)
occurring across all logical processors sharing a processor core. When bit 21 is 0, the counter only increments
the associated event conditions (including matching the thread’s CPL with the OS/USR setting of
IA32_PERFEVTSELx) occurring in the logical processor which programmed the IA32_PERFEVTSELx MSR.
— Each fixed-function performance counter IA32_FIXED_CTRx (starting at MSR address 309H) is configured
by a 4-bit control block in the IA32_PERF_FIXED_CTR_CTRL MSR. The control block also allow threadspecificity configuration using an AnyThread bit. The layout of IA32_PERF_FIXED_CTR_CTRL MSR is
shown.

63

12 11
P A
M N
I Y

9 8 7
E
N

P A
M N
I Y

5 43 2 1 0
E
N

P A
M N
I Y

E
N

Cntr2 — Controls for IA32_FIXED_CTR2
Cntr1 — Controls for IA32_FIXED_CTR1
PMI — Enable PMI on overflow on IA32_FIXED_CTR0
AnyThread — AnyThread for IA32_FIXED_CTR0
ENABLE — IA32_FIXED_CTR0. 0: disable; 1: OS; 2: User; 3: All ring levels

Reserved

Figure 18-7. IA32_FIXED_CTR_CTRL MSR Supporting Architectural Performance Monitoring Version 3
Each control block for a fixed-function performance counter provides a AnyThread (bit position 2 + 4*N, N=
0, 1, etc.) bit. When set to 1, it enables counting the associated event conditions (including matching the
thread’s CPL with the ENABLE setting of the corresponding control block of IA32_PERF_FIXED_CTR_CTRL)
occurring across all logical processors sharing a processor core. When an AnyThread bit is 0 in
IA32_PERF_FIXED_CTR_CTRL, the corresponding fixed counter only increments the associated event
conditions occurring in the logical processor which programmed the IA32_PERF_FIXED_CTR_CTRL MSR.

•

The IA32_PERF_GLOBAL_CTRL, IA32_PERF_GLOBAL_STATUS, IA32_PERF_GLOBAL_OVF_CTRL MSRs provide
single-bit controls/status for each general-purpose and fixed-function performance counter. Figure 18-8 and
Figure 18-9 show the layout of these MSRs for N general-purpose performance counters (where N is reported
by CPUID.0AH:EAX[15:8]) and three fixed-function counters.

Vol. 3B 18-11

PERFORMANCE MONITORING

Note: The number of general-purpose performance monitoring counters (i.e. N in Figure 18-9) can vary across
processor generations within a processor family, across processor families, or could be different depending on
the configuration chosen at boot time in the BIOS regarding Intel Hyper Threading Technology, (e.g. N=2 for 45
nm Intel Atom processors; N =4 for processors based on the Nehalem microarchitecture; for processors based
on the Sandy Bridge microarchitecture, N = 4 if Intel Hyper Threading Technology is active and N=8 if not
active).

Global Enable Controls IA32_PERF_GLOBAL_CTRL
35 34 33 32 31

63

IA32_FIXED_CTR2 enable
IA32_FIXED_CTR1 enable
IA32_FIXED_CTR0 enable
IA32_PMC(N-1) enable
.................... enable
IA32_PMC1 enable
IA32_PMC0 enable

N .. .. 1 0

Reserved

Figure 18-8. Layout of Global Performance Monitoring Control MSR

63 62 61

CondChgd
OvfDSBuffer
OvfUncore
IA32_FIXED_CTR2 Overflow
IA32_FIXED_CTR1 Overflow
IA32_FIXED_CTR0 Overflow
IA32_PMC1 Overflow
IA32_PMC0 Overflow

63 62

ClrCondChgd
ClrOvfDSBuffer
ClrOvfUncore
IA32_FIXED_CTR2 ClrOverflow
IA32_FIXED_CTR1 ClrOverflow
IA32_FIXED_CTR0 ClrOverflow
IA32_PMC1 ClrOverflow
IA32_PMC0 ClrOverflow

Global Overflow Status IA32_PERF_GLOBAL_STATUS
35 34 33 32 31

N .. .. 1 0

IA32_PMC(N-1) Overflow
...................... Overflow

Global Overflow Status IA32_PERF_GLOBAL_OVF_CTRL
35 34 33 32 31

N .. .. 1 0

IA32_PMC(N-1) ClrOverflow
........................ ClrOverflow

Figure 18-9. Global Performance Monitoring Overflow Status and Control MSRs

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PERFORMANCE MONITORING

18.2.3.1

AnyThread Counting and Software Evolution

The motivation for characterizing software workload over multiple software threads running on multiple logical
processors of the same processor core originates from a time earlier than the introduction of the AnyThread interface in IA32_PERFEVTSELx and IA32_FIXED_CTR_CTRL. While AnyThread counting provides some benefits in
simple software environments of an earlier era, the evolution contemporary software environments introduce
certain concepts and pre-requisites that AnyThread counting does not comply with.
One example is the proliferation of software environments that support multiple virtual machines (VM) under VMX
(see Chapter 23, “Introduction to Virtual-Machine Extensions”) where each VM represents a domain separated
from one another.
A Virtual Machine Monitor (VMM) that manages the VMs may allow individual VM to employ performance monitoring facilities to profiles the performance characteristics of a workload. The use of the Anythread interface in
IA32_PERFEVTSELx and IA32_FIXED_CTR_CTRL is discouraged with software environments supporting virtualization or requiring domain separation.
Specifically, Intel recommends VMM:

•

configure the MSR bitmap to cause VM-exits for WRMSR to IA32_PERFEVTSELx and IA32_FIXED_CTR_CTRL in
VMX non-Root operation (see CHAPTER 24 for additional information),

•

clear the AnyThread bit of IA32_PERFEVTSELx and IA32_FIXED_CTR_CTRL in the MSR-load lists for VM exits
and VM entries (see CHAPTER 24, CHAPTER 26, and CHAPTER 27).

Even when operating in simpler legacy software environments which might not emphasize the pre-requisites of a
virtualized software environment, the use of the AnyThread interface should be moderated and follow any eventspecific guidance where explicitly noted (see relevant sections of Chapter 19, “Performance Monitoring Events”).

18.2.4

Architectural Performance Monitoring Version 4

Processors supporting architectural performance monitoring version 4 also supports version 1, 2, and 3, as well as
capability enumerated by CPUID leaf 0AH. Version 4 introduced a streamlined PMI overhead mitigation interface
that replaces the legacy semantic behavior but retains the same control interface in
IA32_DEBUGCTL.Freeze_LBRs_On_PMI and Freeze_PerfMon_On_PMI. Specifically version 4 provides the following
enhancement:

•
•

New indicators (LBR_FRZ, CTR_FRZ) in IA32_PERF_GLOBAL_STATUS, see Section 18.2.4.1.

•

Fine-grain separation of control interface to manage overflow/status of IA32_PERF_GLOBAL_STATUS and
read-only performance counter enabling interface in IA32_PERF_GLOBAL_STATUS: see Section 18.2.4.2.

•

Performance monitoring resource in-use MSR to facilitate cooperative sharing protocol between perfmonmanaging privilege agents.

Streamlined Freeze/PMI Overhead management interfaces to use IA32_DEBUGCTL.Freeze_LBRs_On_PMI and
IA32_DEBUGCTL.Freeze_PerfMon_On_PMI: see Section 18.2.4.1. Legacy semantics of Freeze_LBRs_On_PMI
and Freeze_PerfMon_On_PMI (applicable to version 2 and 3) are not supported with version 4 or higher.

18.2.4.1

Enhancement in IA32_PERF_GLOBAL_STATUS

The IA32_PERF_GLOBAL_STATUS MSR provides the following indicators with architectural performance monitoring
version 4:

•

IA32_PERF_GLOBAL_STATUS.LBR_FRZ[bit 58]: This bit is set due to the following conditions:
— IA32_DEBUGCTL.FREEZE_LBR_ON_PMI has been set by the profiling agent, and
— A performance counter, configured to generate PMI, has overflowed to signal a PMI. Consequently the LBR
stack is frozen.
Effectively, the IA32_PERF_GLOBAL_STATUS.LBR_FRZ bit also serve as an read-only control to enable
capturing data in the LBR stack. To enable capturing LBR records, the following expression must hold with
architectural perfmon version 4 or higher:
— (IA32_DEBUGCTL.LBR & (!IA32_PERF_GLOBAL_STATUS.LBR_FRZ) ) =1

Vol. 3B 18-13

PERFORMANCE MONITORING

•

IA32_PERF_GLOBAL_STATUS.CTR_FRZ[bit 59]: This bit is set due to the following conditions:
— IA32_DEBUGCTL.FREEZE_PERFMON_ON_PMI has been set by the profiling agent, and
— A performance counter, configured to generate PMI, has overflowed to signal a PMI. Consequently, all the
performance counters are frozen.
Effectively, the IA32_PERF_GLOBAL_STATUS.CTR_FRZ bit also serve as an read-only control to enable
programmable performance counters and fixed counters in the core PMU. To enable counting with the
performance counters, the following expression must hold with architectural perfmon version 4 or higher:

•

(IA32_PERFEVTSELn.EN & IA32_PERF_GLOBAL_CTRL.PMCn &
(!IA32_PERF_GLOBAL_STATUS.CTR_FRZ) ) = 1 for programmable counter ‘n’, or

•

(IA32_PERF_FIXED_CRTL.ENi & IA32_PERF_GLOBAL_CTRL.FCi &
(!IA32_PERF_GLOBAL_STATUS.CTR_FRZ) ) = 1 for fixed counter ‘i’

The read-only enable interface IA32_PERF_GLOBAL_STATUS.CTR_FRZ provides a more efficient flow for a PMI
handler to use IA32_DEBUGCTL.Freeza_Perfmon_On_PMI to filter out data that may distort target workload analysis, see Table 17-3. It should be noted the IA32_PERF_GLOBAL_CTRL register continue to serve as the primary
interface to control all performance counters of the logical processor.
For example, when the Freeze-On-PMI mode is not being used, a PMI handler would be setting
IA32_PERF_GLOBAL_CTRL as the very last step to commence the overall operation after configuring the individual
counter registers, controls and PEBS facility. This does not only assure atomic monitoring but also avoids unnecessary complications (e.g. race conditions) when software attempts to change the core PMU configuration while some
counters are kept enabled.
Additionally, IA32_PERF_GLOBAL_STATUS.TraceToPAPMI[bit 55]: On processors that support Intel Processor Trace
and configured to store trace output packets to physical memory using the ToPA scheme, bit 55 is set when a PMI
occurred due to a ToPA entry memory buffer was completely filled.
IA32_PERF_GLOBAL_STATUS also provides an indicator to distinguish interaction of performance monitoring operations with other side-band activities, which apply Intel SGX on processors that support SGX (For additional information about Intel SGX, see “Intel® Software Guard Extensions Programming Reference”.):

•

IA32_PERF_GLOBAL_STATUS.ASCI[bit 60]: This bit is set when data accumulated in any of the configured
performance counters (i.e. IA32_PMCx or IA32_FIXED_CTRx) may include contributions from direct or indirect
operation of Intel SGX to protect an enclave (since the last time IA32_PERF_GLOBAL_STATUS.ASCI was
cleared).

63 62 61 60 59 58

CondChgd
OvfDSBuffer
OvfUncore
ASCI
CTR_Frz
LBR_Frz
TraceToPAPMI
IA32_FIXED_CTR2 Overflow
IA32_FIXED_CTR1 Overflow
IA32_FIXED_CTR0 Overflow

55

35 34 33 32 31

N .. .. 1 0

IA32_PMC(N-1) Overflow
...................... Overflow
IA32_PMC1 Overflow
IA32_PMC0 Overflow

Reserved

Figure 18-10. IA32_PERF_GLOBAL_STATUS MSR and Architectural Perfmon Version 4
Note, a processor’s support for IA32_PERF_GLOBAL_STATUS.TraceToPAPMI[bit 55] is enumerated as a result of
CPUID enumerated capability of Intel Processor Trace and the use of the ToPA buffer scheme. Support of
IA32_PERF_GLOBAL_STATUS.ASCI[bit 60] is enumerated by the CPUID enumeration of Intel SGX.

18-14 Vol. 3B

PERFORMANCE MONITORING

18.2.4.2

IA32_PERF_GLOBAL_STATUS_RESET and IA32_PERF_GLOBAL_STATUS_SET MSRS

With architectural performance monitoring version 3 and lower, clearing of the set bits in
IA32_PERF_GLOBAL_STATUS MSR by software is done via IA32_PERF_GLOBAL_OVF_CTRL MSR. Starting with
architectural performance monitoring version 4, software can manage the overflow and other indicators in
IA32_PERF_GLOBAL_STATUS using separate interfaces to set or clear individual bits.
The address and the architecturally-defined bits of IA32_PERF_GLOBAL_OVF_CTRL is inherited by
IA32_PERF_GLOBAL_STATUS_RESET (see Figure 18-11). Further, IA32_PERF_GLOBAL_STATUS_RESET provides
additional bit fields to clear the new indicators in IA32_PERF_GLOBAL_STATUS described in Section 18.2.4.1.

63 62 61 60 59 58

55

Clr CondChgd
Clr OvfDSBuffer
Clr OvfUncore
Clr ASCI
Clr CTR_Frz
Clr LBR_Frz
Clr TraceToPAPMI
Clr IA32_FIXED_CTR2 Ovf
Clr IA32_FIXED_CTR1 Ovf
Clr IA32_FIXED_CTR0 Ovf

35 34 33 32 31

N .. .. 1 0

Clr IA32_PMC(N-1) Ovf
Clr ...................... Ovf
Clr IA32_PMC1 Ovf
Clr IA32_PMC0 Ovf

Reserved

Figure 18-11. IA32_PERF_GLOBAL_STATUS_RESET MSR and Architectural Perfmon Version 4
The IA32_PERF_GLOBAL_STATUS_SET MSR is introduced with architectural performance monitoring version 4. It
allows software to set individual bits in IA32_PERF_GLOBAL_STATUS. The IA32_PERF_GLOBAL_STATUS_SET
interface can be used by a VMM to virtualize the state of IA32_PERF_GLOBAL_STATUS across VMs.

63 62 61 60 59 58

Set CondChgd
Set OvfDSBuffer
Set OvfUncore
Set ASCI
Set CTR_Frz
Set LBR_Frz
Set TraceToPAPMI
Set IA32_FIXED_CTR2 Ovf
Set IA32_FIXED_CTR1 Ovf
Set IA32_FIXED_CTR0 Ovf

55

35 34 33 32 31

N .. .. 1 0

Set IA32_PMC(N-1) Ovf
Set ...................... Ovf
Set IA32_PMC1 Ovf
Set IA32_PMC0 Ovf

Reserved

Figure 18-12. IA32_PERF_GLOBAL_STATUS_SET MSR and Architectural Perfmon Version 4

18.2.4.3

IA32_PERF_GLOBAL_INUSE MSR

In a contemporary software environment, multiple privileged service agents may wish to employ the processor’s
performance monitoring facilities. The IA32_MISC_ENABLE.PERFMON_AVAILABLE[bit 7] interface could not serve

Vol. 3B 18-15

PERFORMANCE MONITORING
the need of multiple agent adequately. A white paper, “Performance Monitoring Unit Sharing Guideline”1, proposed
a cooperative sharing protocol that is voluntary for participating software agents.
Architectural performance monitoring version 4 introduces a new MSR, IA32_PERF_GLOBAL_INUSE, that simplifies
the task of multiple cooperating agents to implement the sharing protocol.
The layout of IA32_PERF_GLOBAL_INUSE is shown in Figure 18-13.

63

35 34 33 32 31

PMI InUse
FIXED_CTR2 InUse
FIXED_CTR1 InUse
FIXED_CTR0 InUse

N .. .. 1 0

PERFEVTSEL(N-1) InUse
....................... InUse
PERFEVTSEL1 InUse
PERFEVTSEL0 InUse
N = CPUID.0AH:EAX[15:8]

Reserved

Figure 18-13. IA32_PERF_GLOBAL_INUSE MSR and Architectural Perfmon Version 4
The IA32_PERF_GLOBAL_INUSE MSR provides an “InUse” bit for each programmable performance counter and
fixed counter in the processor. Additionally, it includes an indicator if the PMI mechanism has been configured by a
profiling agent.

•

IA32_PERF_GLOBAL_INUSE.PERFEVTSEL0_InUse[bit 0]: This bit reflects the logical state of
(IA32_PERFEVTSEL0[7:0] != 0).

•

IA32_PERF_GLOBAL_INUSE.PERFEVTSEL1_InUse[bit 1]: This bit reflects the logical state of
(IA32_PERFEVTSEL1[7:0] != 0).

•

IA32_PERF_GLOBAL_INUSE.PERFEVTSEL2_InUse[bit 2]: This bit reflects the logical state of
(IA32_PERFEVTSEL2[7:0] != 0).

•

IA32_PERF_GLOBAL_INUSE.PERFEVTSELn_InUse[bit n]: This bit reflects the logical state of
(IA32_PERFEVTSELn[7:0] != 0), n < CPUID.0AH:EAX[15:8].

•

IA32_PERF_GLOBAL_INUSE.FC0_InUse[bit 32]: This bit reflects the logical state of
(IA32_FIXED_CTR_CTRL[1:0] != 0).

•

IA32_PERF_GLOBAL_INUSE.FC1_InUse[bit 33]: This bit reflects the logical state of
(IA32_FIXED_CTR_CTRL[5:4] != 0).

•

IA32_PERF_GLOBAL_INUSE.FC2_InUse[bit 34]: This bit reflects the logical state of
(IA32_FIXED_CTR_CTRL[9:8] != 0).

•

IA32_PERF_GLOBAL_INUSE.PMI_InUse[bit 63]: This bit is set if any one of the following bit is set:
— IA32_PERFEVTSELn.INT[bit 20], n < CPUID.0AH:EAX[15:8].
— IA32_FIXED_CTR_CTRL.ENi_PMI, i = 0, 1, 2.
— Any IA32_PEBS_ENABLES bit which enables PEBS for a general-purpose or fixed-function performance
counter.

1. Available at http://www.intel.com/sdm
18-16 Vol. 3B

PERFORMANCE MONITORING

18.2.5

Full-Width Writes to Performance Counter Registers

The general-purpose performance counter registers IA32_PMCx are writable via WRMSR instruction. However, the
value written into IA32_PMCx by WRMSR is the signed extended 64-bit value of the EAX[31:0] input of WRMSR.
A processor that supports full-width writes to the general-purpose performance counters enumerated by
CPUID.0AH:EAX[15:8] will set IA32_PERF_CAPABILITIES[13] to enumerate its full-width-write capability See
Figure 18-63.
If IA32_PERF_CAPABILITIES.FW_WRITE[bit 13] =1, each IA32_PMCi is accompanied by a corresponding alias
address starting at 4C1H for IA32_A_PMC0.
The bit width of the performance monitoring counters is specified in CPUID.0AH:EAX[23:16].
If IA32_A_PMCi is present, the 64-bit input value (EDX:EAX) of WRMSR to IA32_A_PMCi will cause IA32_PMCi to
be updated by:
COUNTERWIDTH = CPUID.0AH:EAX[23:16] bit width of the performance monitoring counter
IA32_PMCi[COUNTERWIDTH-1:32] ← EDX[COUNTERWIDTH-33:0]);
IA32_PMCi[31:0] ← EAX[31:0];
EDX[63:COUNTERWIDTH] are reserved

18.3

PERFORMANCE MONITORING (INTEL® CORE™ PROCESSORS AND INTEL®
XEON® PROCESSORS)

18.3.1

Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name
Nehalem

Intel Core i7 processor family2 supports architectural performance monitoring capability with version ID 3 (see
Section 18.2.3) and a host of non-architectural monitoring capabilities. The Intel Core i7 processor family is based
on Intel® microarchitecture code name Nehalem, and provides four general-purpose performance counters
(IA32_PMC0, IA32_PMC1, IA32_PMC2, IA32_PMC3) and three fixed-function performance counters
(IA32_FIXED_CTR0, IA32_FIXED_CTR1, IA32_FIXED_CTR2) in the processor core.
Non-architectural performance monitoring in Intel Core i7 processor family uses the IA32_PERFEVTSELx MSR to
configure a set of non-architecture performance monitoring events to be counted by the corresponding generalpurpose performance counter. The list of non-architectural performance monitoring events is listed in Table 19-29.
Non-architectural performance monitoring events fall into two broad categories:

•

Performance monitoring events in the processor core: These include many events that are similar to
performance monitoring events available to processor based on Intel Core microarchitecture. Additionally,
there are several enhancements in the performance monitoring capability for detecting microarchitectural
conditions in the processor core or in the interaction of the processor core to the off-core sub-systems in the
physical processor package. The off-core sub-systems in the physical processor package is loosely referred to
as “uncore“.

•

Performance monitoring events in the uncore: The uncore sub-system is shared by more than one processor
cores in the physical processor package. It provides additional performance monitoring facility outside of
IA32_PMCx and performance monitoring events that are specific to the uncore sub-system.

Architectural and non-architectural performance monitoring events in Intel Core i7 processor family support thread
qualification using bit 21 of IA32_PERFEVTSELx MSR.
The bit fields within each IA32_PERFEVTSELx MSR are defined in Figure 18-6 and described in Section 18.2.1.1 and
Section 18.2.3.

2. Intel Xeon processor 5500 series and 3400 series are also based on Intel microarchitecture code name Nehalem; the performance
monitoring facilities described in this section generally also apply.
Vol. 3B 18-17

PERFORMANCE MONITORING

63 62 61 60

353433 3231

8 7 6 5 43 2 1 0

CHG (R/W)
OVF_PMI (R/W)
OVF_FC2 (R/O)
OVF_FC1 (R/O)
OVF_FC0 (R/O)
OVF_PC7 (R/O), if CCNT>7
OVF_PC6 (R/O), if CCNT>6
OVF_PC5 (R/O), if CCNT>5
OVF_PC4 (R/O), if CCNT>4
OVF_PC3 (R/O)
OVF_PC2 (R/O)
OVF_PC1 (R/O)
OVF_PC0 (R/O)

Reserved

RESET Value — 00000000_00000000H

CCNT: CPUID.AH:EAX[15:8]

Figure 18-14. IA32_PERF_GLOBAL_STATUS MSR

18.3.1.1

Enhancements of Performance Monitoring in the Processor Core

The notable enhancements in the monitoring of performance events in the processor core include:

•

Four general purpose performance counters, IA32_PMCx, associated counter configuration MSRs,
IA32_PERFEVTSELx, and global counter control MSR supporting simplified control of four counters. Each of the
four performance counter can support processor event based sampling (PEBS) and thread-qualification of
architectural and non-architectural performance events. Width of IA32_PMCx supported by hardware has been
increased. The width of counter reported by CPUID.0AH:EAX[23:16] is 48 bits. The PEBS facility in Intel microarchitecture code name Nehalem has been enhanced to include new data format to capture additional information, such as load latency.

•

Load latency sampling facility. Average latency of memory load operation can be sampled using load-latency
facility in processors based on Intel microarchitecture code name Nehalem. This field measures the load latency
from load's first dispatch of till final data writeback from the memory subsystem. The latency is reported for
retired demand load operations and in core cycles (it accounts for re-dispatches). This facility is used in
conjunction with the PEBS facility.

•

Off-core response counting facility. This facility in the processor core allows software to count certain
transaction responses between the processor core to sub-systems outside the processor core (uncore).
Counting off-core response requires additional event qualification configuration facility in conjunction with
IA32_PERFEVTSELx. Two off-core response MSRs are provided to use in conjunction with specific event codes
that must be specified with IA32_PERFEVTSELx.

18.3.1.1.1 Processor Event Based Sampling (PEBS)
All four general-purpose performance counters, IA32_PMCx, can be used for PEBS if the performance event
supports PEBS. Software uses IA32_MISC_ENABLE[7] and IA32_MISC_ENABLE[12] to detect whether the performance monitoring facility and PEBS functionality are supported in the processor. The MSR IA32_PEBS_ENABLE
provides 4 bits that software must use to enable which IA32_PMCx overflow condition will cause the PEBS record to
be captured.
Additionally, the PEBS record is expanded to allow latency information to be captured. The MSR
IA32_PEBS_ENABLE provides 4 additional bits that software must use to enable latency data recording in the PEBS
record upon the respective IA32_PMCx overflow condition. The layout of IA32_PEBS_ENABLE for processors based
on Intel microarchitecture code name Nehalem is shown in Figure 18-15.

18-18 Vol. 3B

PERFORMANCE MONITORING

When a counter is enabled to capture machine state (PEBS_EN_PMCx = 1), the processor will write machine state
information to a memory buffer specified by software as detailed below. When the counter IA32_PMCx overflows
from maximum count to zero, the PEBS hardware is armed.

36 3534 33 32 31

63

8 7 6 5 43 2 1 0

LL_EN_PMC3 (R/W)
LL_EN_PMC2 (R/W)
LL_EN_PMC1 (R/W)
LL_EN_PMC0 (R/W)
PEBS_EN_PMC3 (R/W)
PEBS_EN_PMC2 (R/W)
PEBS_EN_PMC1 (R/W)
PEBS_EN_PMC0 (R/W)

Reserved

RESET Value — 00000000_00000000H

Figure 18-15. Layout of IA32_PEBS_ENABLE MSR
Upon occurrence of the next PEBS event, the PEBS hardware triggers an assist and causes a PEBS record to be
written. The format of the PEBS record is indicated by the bit field IA32_PERF_CAPABILITIES[11:8] (see
Figure 18-63).
The behavior of PEBS assists is reported by IA32_PERF_CAPABILITIES[6] (see Figure 18-63). The return instruction pointer (RIP) reported in the PEBS record will point to the instruction after (+1) the instruction that causes the
PEBS assist. The machine state reported in the PEBS record is the machine state after the instruction that causes
the PEBS assist is retired. For instance, if the instructions:
mov eax, [eax] ; causes PEBS assist
nop
are executed, the PEBS record will report the address of the nop, and the value of EAX in the PEBS record will show
the value read from memory, not the target address of the read operation.
The PEBS record format is shown in Table 18-3, and each field in the PEBS record is 64 bits long. The PEBS record
format, along with debug/store area storage format, does not change regardless of IA-32e mode is active or not.
CPUID.01H:ECX.DTES64[bit 2] reports whether the processor's DS storage format support is mode-independent.
When set, it uses 64-bit DS storage format.

Table 18-3. PEBS Record Format for Intel Core i7 Processor Family
Byte Offset

Field

Byte Offset

Field

00H

R/EFLAGS

58H

R9

08H

R/EIP

60H

R10

10H

R/EAX

68H

R11

18H

R/EBX

70H

R12

20H

R/ECX

78H

R13

28H

R/EDX

80H

R14

30H

R/ESI

88H

R15

38H

R/EDI

90H

IA32_PERF_GLOBAL_STATUS

40H

R/EBP

98H

Data Linear Address

48H

R/ESP

A0H

Data Source Encoding

Vol. 3B 18-19

PERFORMANCE MONITORING

Table 18-3. PEBS Record Format for Intel Core i7 Processor Family
Byte Offset

Field

Byte Offset

Field

50H

R8

A8H

Latency value (core cycles)

In IA-32e mode, the full 64-bit value is written to the register. If the processor is not operating in IA-32e mode, 32bit value is written to registers with bits 63:32 zeroed. Registers not defined when the processor is not in IA-32e
mode are written to zero.
Bytes AFH:90H are enhancement to the PEBS record format. Support for this enhanced PEBS record format is indicated by IA32_PERF_CAPABILITIES[11:8] encoding of 0001B.
The value written to bytes 97H:90H is the state of the IA32_PERF_GLOBAL_STATUS register before the PEBS assist
occurred. This value is written so software can determine which counters overflowed when this PEBS record was
written. Note that this field indicates the overflow status for all counters, regardless of whether they were
programmed for PEBS or not.
Programming PEBS Facility
Only a subset of non-architectural performance events in the processor support PEBS. The subset of precise events
are listed in Table 18-68. In addition to using IA32_PERFEVTSELx to specify event unit/mask settings and setting
the EN_PMCx bit in the IA32_PEBS_ENABLE register for the respective counter, the software must also initialize the
DS_BUFFER_MANAGEMENT_AREA data structure in memory to support capturing PEBS records for precise events.

NOTE
PEBS events are only valid when the following fields of IA32_PERFEVTSELx are all zero: AnyThread,
Edge, Invert, CMask.
The beginning linear address of the DS_BUFFER_MANAGEMENT_AREA data structure must be programmed into
the IA32_DS_AREA register. The layout of the DS_BUFFER_MANAGEMENT_AREA is shown in Figure 18-16.

•

PEBS Buffer Base: This field is programmed with the linear address of the first byte of the PEBS buffer
allocated by software. The processor reads this field to determine the base address of the PEBS buffer. Software
should allocate this memory from the non-paged pool.

•

PEBS Index: This field is initially programmed with the same value as the PEBS Buffer Base field, or the
beginning linear address of the PEBS buffer. The processor reads this field to determine the location of the next
PEBS record to write to. After a PEBS record has been written, the processor also updates this field with the
address of the next PEBS record to be written. The figure above illustrates the state of PEBS Index after the first
PEBS record is written.

•

PEBS Absolute Maximum: This field represents the absolute address of the maximum length of the allocated
PEBS buffer plus the starting address of the PEBS buffer. The processor will not write any PEBS record beyond
the end of PEBS buffer, when PEBS Index equals PEBS Absolute Maximum. No signaling is generated when
PEBS buffer is full. Software must reset the PEBS Index field to the beginning of the PEBS buffer address to
continue capturing PEBS records.

18-20 Vol. 3B

PERFORMANCE MONITORING

IA32_DS_AREA MSR
DS Buffer Management Area
BTS Buffer Base

0H

BTS Index

8H

BTS Absolute
Maximum
BTS Interrupt
Threshold

BTS Buffer
Branch Record 0

10H
Branch Record 1
18H

PEBS Buffer Base 20H
PEBS Index
PEBS Absolute
Maximum
PEBS Interrupt
Threshold
PEBS
Counter0 Reset
PEBS
Counter1 Reset
PEBS
Counter2 Reset
PEBS
Counter3 Reset
Reserved

28H
30H
38H

Branch Record n

40H
48H

PEBS Buffer
PEBS Record 0

50H

58H

PEBS Record 1

60H

PEBS Record n

Figure 18-16. PEBS Programming Environment

•

PEBS Interrupt Threshold: This field specifies the threshold value to trigger a performance interrupt and
notify software that the PEBS buffer is nearly full. This field is programmed with the linear address of the first
byte of the PEBS record within the PEBS buffer that represents the threshold record. After the processor writes
a PEBS record and updates PEBS Index, if the PEBS Index reaches the threshold value of this field, the
processor will generate a performance interrupt. This is the same interrupt that is generated by a performance
counter overflow, as programmed in the Performance Monitoring Counters vector in the Local Vector Table of
the Local APIC. When a performance interrupt due to PEBS buffer full is generated, the
IA32_PERF_GLOBAL_STATUS.PEBS_Ovf bit will be set.

•

PEBS CounterX Reset: This field allows software to set up PEBS counter overflow condition to occur at a rate
useful for profiling workload, thereby generating multiple PEBS records to facilitate characterizing the profile
the execution of test code. After each PEBS record is written, the processor checks each counter to see if it
overflowed and was enabled for PEBS (the corresponding bit in IA32_PEBS_ENABLED was set). If these
conditions are met, then the reset value for each overflowed counter is loaded from the DS Buffer Management
Area. For example, if counter IA32_PMC0 caused a PEBS record to be written, then the value of “PEBS Counter
0 Reset” would be written to counter IA32_PMC0. If a counter is not enabled for PEBS, its value will not be
modified by the PEBS assist.

Performance Counter Prioritization
Performance monitoring interrupts are triggered by a counter transitioning from maximum count to zero
(assuming IA32_PerfEvtSelX.INT is set). This same transition will cause PEBS hardware to arm, but not trigger.
PEBS hardware triggers upon detection of the first PEBS event after the PEBS hardware has been armed (a 0 to 1
transition of the counter). At this point, a PEBS assist will be undertaken by the processor.

Vol. 3B 18-21

PERFORMANCE MONITORING

Performance counters (fixed and general-purpose) are prioritized in index order. That is, counter IA32_PMC0 takes
precedence over all other counters. Counter IA32_PMC1 takes precedence over counters IA32_PMC2 and
IA32_PMC3, and so on. This means that if simultaneous overflows or PEBS assists occur, the appropriate action will
be taken for the highest priority performance counter. For example, if IA32_PMC1 cause an overflow interrupt and
IA32_PMC2 causes an PEBS assist simultaneously, then the overflow interrupt will be serviced first.
The PEBS threshold interrupt is triggered by the PEBS assist, and is by definition prioritized lower than the PEBS
assist. Hardware will not generate separate interrupts for each counter that simultaneously overflows. Generalpurpose performance counters are prioritized over fixed counters.
If a counter is programmed with a precise (PEBS-enabled) event and programmed to generate a counter overflow
interrupt, the PEBS assist is serviced before the counter overflow interrupt is serviced. If in addition the PEBS interrupt threshold is met, the
threshold interrupt is generated after the PEBS assist completes, followed by the counter overflow interrupt (two
separate interrupts are generated).
Uncore counters may be programmed to interrupt one or more processor cores (see Section 18.3.1.2). It is
possible for interrupts posted from the uncore facility to occur coincident with counter overflow interrupts from the
processor core. Software must check core and uncore status registers to determine the exact origin of counter
overflow interrupts.

18.3.1.1.2 Load Latency Performance Monitoring Facility
The load latency facility provides software a means to characterize the average load latency to different levels of
cache/memory hierarchy. This facility requires processor supporting enhanced PEBS record format in the PEBS
buffer, see Table 18-3. This field measures the load latency from load's first dispatch of till final data writeback from
the memory subsystem. The latency is reported for retired demand load operations and in core cycles (it accounts
for re-dispatches).
To use this feature software must assure:

•

One of the IA32_PERFEVTSELx MSR is programmed to specify the event unit MEM_INST_RETIRED, and the
LATENCY_ABOVE_THRESHOLD event mask must be specified (IA32_PerfEvtSelX[15:0] = 100H). The corresponding counter IA32_PMCx will accumulate event counts for architecturally visible loads which exceed the
programmed latency threshold specified separately in a MSR. Stores are ignored when this event is
programmed. The CMASK or INV fields of the IA32_PerfEvtSelX register used for counting load latency must be
0. Writing other values will result in undefined behavior.

•

The MSR_PEBS_LD_LAT_THRESHOLD MSR is programmed with the desired latency threshold in core clock
cycles. Loads with latencies greater than this value are eligible for counting and latency data reporting. The
minimum value that may be programmed in this register is 3 (the minimum detectable load latency is 4 core
clock cycles).

•

The PEBS enable bit in the IA32_PEBS_ENABLE register is set for the corresponding IA32_PMCx counter
register. This means that both the PEBS_EN_CTRX and LL_EN_CTRX bits must be set for the counter(s) of
interest. For example, to enable load latency on counter IA32_PMC0, the IA32_PEBS_ENABLE register must be
programmed with the 64-bit value 00000001_00000001H.

When the load-latency facility is enabled, load operations are randomly selected by hardware and tagged to carry
information related to data source locality and latency. Latency and data source information of tagged loads are
updated internally.
When a PEBS assist occurs, the last update of latency and data source information are captured by the assist and
written as part of the PEBS record. The PEBS sample after value (SAV), specified in PEBS CounterX Reset, operates
orthogonally to the tagging mechanism. Loads are randomly tagged to collect latency data. The SAV controls the
number of tagged loads with latency information that will be written into the PEBS record field by the PEBS assists.
The load latency data written to the PEBS record will be for the last tagged load operation which retired just before
the PEBS assist was invoked.
The load-latency information written into a PEBS record (see Table 18-3, bytes AFH:98H) consists of:

•
•

Data Linear Address: This is the linear address of the target of the load operation.
Latency Value: This is the elapsed cycles of the tagged load operation between dispatch to GO, measured in
processor core clock domain.

18-22 Vol. 3B

PERFORMANCE MONITORING

•

Data Source: The encoded value indicates the origin of the data obtained by the load instruction. The
encoding is shown in Table 18-4. In the descriptions local memory refers to system memory physically
attached to a processor package, and remote memory referrals to system memory physically attached to
another processor package.

Table 18-4. Data Source Encoding for Load Latency Record
Encoding

Description

00H

Unknown L3 cache miss

01H

Minimal latency core cache hit. This request was satisfied by the L1 data cache.

02H

Pending core cache HIT. Outstanding core cache miss to same cache-line address was already underway.

03H

This data request was satisfied by the L2.

04H

L3 HIT. Local or Remote home requests that hit L3 cache in the uncore with no coherency actions required (snooping).

05H

L3 HIT. Local or Remote home requests that hit the L3 cache and was serviced by another processor core with a cross
core snoop where no modified copies were found. (clean).

06H

L3 HIT. Local or Remote home requests that hit the L3 cache and was serviced by another processor core with a cross
core snoop where modified copies were found. (HITM).

07H1

Reserved/LLC Snoop HitM. Local or Remote home requests that hit the last level cache and was serviced by another
core with a cross core snoop where modified copies found

08H

L3 MISS. Local homed requests that missed the L3 cache and was serviced by forwarded data following a cross
package snoop where no modified copies found. (Remote home requests are not counted).

09H

Reserved

0AH

L3 MISS. Local home requests that missed the L3 cache and was serviced by local DRAM (go to shared state).

0BH

L3 MISS. Remote home requests that missed the L3 cache and was serviced by remote DRAM (go to shared state).

0CH

L3 MISS. Local home requests that missed the L3 cache and was serviced by local DRAM (go to exclusive state).

0DH

L3 MISS. Remote home requests that missed the L3 cache and was serviced by remote DRAM (go to exclusive state).

0EH

I/O, Request of input/output operation

0FH

The request was to un-cacheable memory.

NOTES:
1. Bit 7 is supported only for processor with CPUID DisplayFamily_DisplayModel signature of 06_2A, and 06_2E; otherwise it is
reserved.
The layout of MSR_PEBS_LD_LAT_THRESHOLD is shown in Figure 18-17.
63

1615

0

THRHLD - Load latency threshold

Reserved

RESET Value — 00000000_00000000H

Figure 18-17. Layout of MSR_PEBS_LD_LAT MSR
Bits 15:0 specifies the threshold load latency in core clock cycles. Performance events with latencies greater than
this value are counted in IA32_PMCx and their latency information is reported in the PEBS record. Otherwise, they
are ignored. The minimum value that may be programmed in this field is 3.

Vol. 3B 18-23

PERFORMANCE MONITORING

18.3.1.1.3 Off-core Response Performance Monitoring in the Processor Core
Programming a performance event using the off-core response facility can choose any of the four
IA32_PERFEVTSELx MSR with specific event codes and predefine mask bit value. Each event code for off-core
response monitoring requires programming an associated configuration MSR, MSR_OFFCORE_RSP_0. There is only
one off-core response configuration MSR. Table 18-5 lists the event code, mask value and additional off-core
configuration MSR that must be programmed to count off-core response events using IA32_PMCx.

Table 18-5. Off-Core Response Event Encoding
Event code in
IA32_PERFEVTSELx

Mask Value in
IA32_PERFEVTSELx

Required Off-core Response MSR

B7H

01H

MSR_OFFCORE_RSP_0 (address 1A6H)

The layout of MSR_OFFCORE_RSP_0 is shown in Figure 18-18. Bits 7:0 specifies the request type of a transaction
request to the uncore. Bits 15:8 specifies the response of the uncore subsystem.

63

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

RESPONSE TYPE — NON_DRAM (R/W)
RESPONSE TYPE — LOCAL_DRAM (R/W)
RESPONSE TYPE — REMOTE_DRAM (R/W)
RESPONSE TYPE — REMOTE_CACHE_FWD (R/W)
RESPONSE TYPE — RESERVED
RESPONSE TYPE — OTHER_CORE_HITM (R/W)
RESPONSE TYPE — OTHER_CORE_HIT_SNP (R/W)
RESPONSE TYPE — UNCORE_HIT (R/W)
REQUEST TYPE — OTHER (R/W)
REQUEST TYPE — PF_IFETCH (R/W)
REQUEST TYPE — PF_RFO (R/W)
REQUEST TYPE — PF_DATA_RD (R/W)
REQUEST TYPE — WB (R/W)
REQUEST TYPE — DMND_IFETCH (R/W)
REQUEST TYPE — DMND_RFO (R/W)
REQUEST TYPE — DMND_DATA_RD (R/W)

Reserved

RESET Value — 00000000_00000000H

Figure 18-18. Layout of MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 to Configure Off-core Response Events

Table 18-6. MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 Bit Field Definition
Bit Name

Offset

Description

DMND_DATA_RD

0

(R/W). Counts the number of demand and DCU prefetch data reads of full and partial cachelines as well
as demand data page table entry cacheline reads. Does not count L2 data read prefetches or
instruction fetches.

DMND_RFO

1

(R/W). Counts the number of demand and DCU prefetch reads for ownership (RFO) requests generated
by a write to data cacheline. Does not count L2 RFO.

DMND_IFETCH

2

(R/W). Counts the number of demand and DCU prefetch instruction cacheline reads. Does not count L2
code read prefetches.

WB

3

(R/W). Counts the number of writeback (modified to exclusive) transactions.

PF_DATA_RD

4

(R/W). Counts the number of data cacheline reads generated by L2 prefetchers.

PF_RFO

5

(R/W). Counts the number of RFO requests generated by L2 prefetchers.

18-24 Vol. 3B

PERFORMANCE MONITORING

Table 18-6. MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 Bit Field Definition (Contd.)
Bit Name

Offset

Description

PF_IFETCH

6

(R/W). Counts the number of code reads generated by L2 prefetchers.

OTHER

7

(R/W). Counts one of the following transaction types, including L3 invalidate, I/O, full or partial writes,
WC or non-temporal stores, CLFLUSH, Fences, lock, unlock, split lock.

UNCORE_HIT

8

(R/W). L3 Hit: local or remote home requests that hit L3 cache in the uncore with no coherency actions
required (snooping).

OTHER_CORE_HI
T_SNP

9

(R/W). L3 Hit: local or remote home requests that hit L3 cache in the uncore and was serviced by
another core with a cross core snoop where no modified copies were found (clean).

OTHER_CORE_HI
TM

10

(R/W). L3 Hit: local or remote home requests that hit L3 cache in the uncore and was serviced by
another core with a cross core snoop where modified copies were found (HITM).

Reserved

11

Reserved

REMOTE_CACHE_ 12
FWD

(R/W). L3 Miss: local homed requests that missed the L3 cache and was serviced by forwarded data
following a cross package snoop where no modified copies found. (Remote home requests are not
counted)

REMOTE_DRAM

13

(R/W). L3 Miss: remote home requests that missed the L3 cache and were serviced by remote DRAM.

LOCAL_DRAM

14

(R/W). L3 Miss: local home requests that missed the L3 cache and were serviced by local DRAM.

NON_DRAM

15

(R/W). Non-DRAM requests that were serviced by IOH.

18.3.1.2

Performance Monitoring Facility in the Uncore

The “uncore” in Intel microarchitecture code name Nehalem refers to subsystems in the physical processor
package that are shared by multiple processor cores. Some of the sub-systems in the uncore include the L3 cache,
Intel QuickPath Interconnect link logic, and integrated memory controller. The performance monitoring facilities
inside the uncore operates in the same clock domain as the uncore (U-clock domain), which is usually different
from the processor core clock domain. The uncore performance monitoring facilities described in this section apply
to Intel Xeon processor 5500 series and processors with the following CPUID signatures: 06_1AH, 06_1EH, 06_1FH
(see Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 4). An overview of the uncore performance monitoring facilities is described separately.
The performance monitoring facilities available in the U-clock domain consist of:

•

Eight General-purpose counters (MSR_UNCORE_PerfCntr0 through MSR_UNCORE_PerfCntr7). The counters
are 48 bits wide. Each counter is associated with a configuration MSR, MSR_UNCORE_PerfEvtSelx, to specify
event code, event mask and other event qualification fields. A set of global uncore performance counter
enabling/overflow/status control MSRs are also provided for software.

•

Performance monitoring in the uncore provides an address/opcode match MSR that provides event qualification
control based on address value or QPI command opcode.

•

One fixed-function counter, MSR_UNCORE_FixedCntr0. The fixed-function uncore counter increments at the
rate of the U-clock when enabled.
The frequency of the uncore clock domain can be determined from the uncore clock ratio which is available in
the PCI configuration space register at offset C0H under device number 0 and Function 0.

18.3.1.2.1 Uncore Performance Monitoring Management Facility
MSR_UNCORE_PERF_GLOBAL_CTRL provides bit fields to enable/disable general-purpose and fixed-function counters in the uncore. Figure 18-19 shows the layout of MSR_UNCORE_PERF_GLOBAL_CTRL for an uncore that is
shared by four processor cores in a physical package.

•

EN_PCn (bit n, n = 0, 7): When set, enables counting for the general-purpose uncore counter
MSR_UNCORE_PerfCntr n.

•

EN_FC0 (bit 32): When set, enables counting for the fixed-function uncore counter MSR_UNCORE_FixedCntr0.

Vol. 3B 18-25

PERFORMANCE MONITORING

•

EN_PMI_COREn (bit n, n = 0, 3 if four cores are present): When set, processor core n is programmed to receive
an interrupt signal from any interrupt enabled uncore counter. PMI delivery due to an uncore counter overflow
is enabled by setting IA32_DEBUGCTL.Offcore_PMI_EN to 1.

•

PMI_FRZ (bit 63): When set, all U-clock uncore counters are disabled when any one of them signals a
performance interrupt. Software must explicitly re-enable the counter by setting the enable bits in
MSR_UNCORE_PERF_GLOBAL_CTRL upon exit from the ISR.

63 62

51 50 49 48

32 31

8 7 6 5 43 2 1 0

PMI_FRZ (R/W)
EN_PMI_CORE3 (R/W)
EN_PMI_CORE2 (R/W)
EN_PMI_CORE1 (R/W)
EN_PMI_CORE0 (R/W)
EN_FC0 (R/W)
EN_PC7 (R/W)
EN_PC6 (R/W)
EN_PC5 (R/W)
EN_PC4 (R/W)
EN_PC3 (R/W)
EN_PC2 (R/W)
EN_PC1 (R/W)
EN_PC0 (R/W)

Reserved

RESET Value — 00000000_00000000H

Figure 18-19. Layout of MSR_UNCORE_PERF_GLOBAL_CTRL MSR
MSR_UNCORE_PERF_GLOBAL_STATUS provides overflow status of the U-clock performance counters in the
uncore. This is a read-only register. If an overflow status bit is set the corresponding counter has overflowed. The
register provides a condition change bit (bit 63) which can be quickly checked by software to determine if a significant change has occurred since the last time the condition change status was cleared. Figure 18-20 shows the
layout of MSR_UNCORE_PERF_GLOBAL_STATUS.

•

OVF_PCn (bit n, n = 0, 7): When set, indicates general-purpose uncore counter MSR_UNCORE_PerfCntr n has
overflowed.

•

OVF_FC0 (bit 32): When set, indicates the fixed-function uncore counter MSR_UNCORE_FixedCntr0 has
overflowed.

•
•

OVF_PMI (bit 61): When set indicates that an uncore counter overflowed and generated an interrupt request.
CHG (bit 63): When set indicates that at least one status bit in MSR_UNCORE_PERF_GLOBAL_STATUS register
has changed state.

18-26 Vol. 3B

PERFORMANCE MONITORING

MSR_UNCORE_PERF_GLOBAL_OVF_CTRL allows software to clear the status bits in the
UNCORE_PERF_GLOBAL_STATUS register. This is a write-only register, and individual status bits in the global
status register are cleared by writing a binary one to the corresponding bit in this register. Writing zero to any bit
position in this register has no effect on the uncore PMU hardware.

63 62 61 60

32 31

8 7 6 5 43 2 1 0

CHG (R/W)
OVF_PMI (R/W)
OVF_FC0 (R/O)
OVF_PC7 (R/O)
OVF_PC6 (R/O)
OVF_PC5 (R/O)
OVF_PC4 (R/O)
OVF_PC3 (R/O)
OVF_PC2 (R/O)
OVF_PC1 (R/O)
OVF_PC0 (R/O)

Reserved

RESET Value — 00000000_00000000H

Figure 18-20. Layout of MSR_UNCORE_PERF_GLOBAL_STATUS MSR
Figure 18-21 shows the layout of MSR_UNCORE_PERF_GLOBAL_OVF_CTRL.

63 62 61 60

32 31

8 7 6 5 43 2 1 0

CLR_CHG (WO1)
CLR_OVF_PMI (WO1)
CLR_OVF_FC0 (WO1)
CLR_OVF_PC7 (WO1)
CLR_OVF_PC6 (WO1)
CLR_OVF_PC5 (WO1)
CLR_OVF_PC4 (WO1)
CLR_OVF_PC3 (WO1)
CLR_OVF_PC2 (WO1)
CLR_OVF_PC1 (WO1)
CLR_OVF_PC0 (WO1)

Reserved

RESET Value — 00000000_00000000H

Figure 18-21. Layout of MSR_UNCORE_PERF_GLOBAL_OVF_CTRL MSR

•

CLR_OVF_PCn (bit n, n = 0, 7): Set this bit to clear the overflow status for general-purpose uncore counter
MSR_UNCORE_PerfCntr n. Writing a value other than 1 is ignored.

•

CLR_OVF_FC0 (bit 32): Set this bit to clear the overflow status for the fixed-function uncore counter
MSR_UNCORE_FixedCntr0. Writing a value other than 1 is ignored.

•

CLR_OVF_PMI (bit 61): Set this bit to clear the OVF_PMI flag in MSR_UNCORE_PERF_GLOBAL_STATUS. Writing
a value other than 1 is ignored.

•

CLR_CHG (bit 63): Set this bit to clear the CHG flag in MSR_UNCORE_PERF_GLOBAL_STATUS register. Writing
a value other than 1 is ignored.

Vol. 3B 18-27

PERFORMANCE MONITORING

18.3.1.2.2 Uncore Performance Event Configuration Facility
MSR_UNCORE_PerfEvtSel0 through MSR_UNCORE_PerfEvtSel7 are used to select performance event and
configure the counting behavior of the respective uncore performance counter. Each uncore PerfEvtSel MSR is
paired with an uncore performance counter. Each uncore counter must be locally configured using the corresponding MSR_UNCORE_PerfEvtSelx and counting must be enabled using the respective EN_PCx bit in
MSR_UNCORE_PERF_GLOBAL_CTRL. Figure 18-22 shows the layout of MSR_UNCORE_PERFEVTSELx.

63

31

24 23 22 21 20 19 18 17 16 15

Counter Mask
(CMASK)

Unit Mask (UMASK)

INV—Invert counter mask
EN—Enable counters
PMI—Enable PMI on overflow
E—Edge detect
OCC_CTR_RST—Rest Queue Occ

0

8 7
Event Select

Reserved
RESET Value — 00000000_00000000H

Figure 18-22. Layout of MSR_UNCORE_PERFEVTSELx MSRs

•
•
•

Event Select (bits 7:0): Selects the event logic unit used to detect uncore events.

•

Edge Detect (bit 18): When set causes the counter to increment when a deasserted to asserted transition
occurs for the conditions that can be expressed by any of the fields in this register.

•

PMI (bit 20): When set, the uncore will generate an interrupt request when this counter overflowed. This
request will be routed to the logical processors as enabled in the PMI enable bits (EN_PMI_COREx) in the
register MSR_UNCORE_PERF_GLOBAL_CTRL.

•

EN (bit 22): When clear, this counter is locally disabled. When set, this counter is locally enabled and counting
starts when the corresponding EN_PCx bit in MSR_UNCORE_PERF_GLOBAL_CTRL is set.

•

INV (bit 23): When clear, the Counter Mask field is interpreted as greater than or equal to. When set, the
Counter Mask field is interpreted as less than.

•

Counter Mask (bits 31:24): When this field is clear, it has no effect on counting. When set to a value other than
zero, the logical processor compares this field to the event counts on each core clock cycle. If INV is clear and
the event counts are greater than or equal to this field, the counter is incremented by one. If INV is set and the
event counts are less than this field, the counter is incremented by one. Otherwise the counter is not incremented.

Unit Mask (bits 15:8) : Condition qualifiers for the event selection logic specified in the Event Select field.
OCC_CTR_RST (bit17): When set causes the queue occupancy counter associated with this event to be cleared
(zeroed). Writing a zero to this bit will be ignored. It will always read as a zero.

Figure 18-23 shows the layout of MSR_UNCORE_FIXED_CTR_CTRL.
63

8 7 6 5 43 2 1 0

PMI - Generate PMI on overflow
EN - Enable

Reserved

RESET Value — 00000000_00000000H

Figure 18-23. Layout of MSR_UNCORE_FIXED_CTR_CTRL MSR

18-28 Vol. 3B

PERFORMANCE MONITORING

•

EN (bit 0): When clear, the uncore fixed-function counter is locally disabled. When set, it is locally enabled and
counting starts when the EN_FC0 bit in MSR_UNCORE_PERF_GLOBAL_CTRL is set.

•

PMI (bit 2): When set, the uncore will generate an interrupt request when the uncore fixed-function counter
overflowed. This request will be routed to the logical processors as enabled in the PMI enable bits
(EN_PMI_COREx) in the register MSR_UNCORE_PERF_GLOBAL_CTRL.

Both the general-purpose counters (MSR_UNCORE_PerfCntr) and the fixed-function counter
(MSR_UNCORE_FixedCntr0) are 48 bits wide. They support both counting and interrupt based sampling usages.
The event logic unit can filter event counts to specific regions of code or transaction types incoming to the home
node logic.

18.3.1.2.3 Uncore Address/Opcode Match MSR
The Event Select field [7:0] of MSR_UNCORE_PERFEVTSELx is used to select different uncore event logic unit.
When the event “ADDR_OPCODE_MATCH” is selected in the Event Select field, software can filter uncore performance events according to transaction address and certain transaction responses. The address filter and transaction response filtering requires the use of MSR_UNCORE_ADDR_OPCODE_MATCH register. The layout is shown in
Figure 18-24.

63

60

48 47

40 39
Opcode

3 2 0
ADDR

MatchSel—Select addr/Opcode
Opcode—Opcode and Message
ADDR—Bits 39:4 of physical address
Reserved

RESET Value — 00000000_00000000H

Figure 18-24. Layout of MSR_UNCORE_ADDR_OPCODE_MATCH MSR

•

Addr (bits 39:3): The physical address to match if “MatchSel“ field is set to select address match. The uncore
performance counter will increment if the lowest 40-bit incoming physical address (excluding bits 2:0) for a
transaction request matches bits 39:3.

•

Opcode (bits 47:40) : Bits 47:40 allow software to filter uncore transactions based on QPI link message
class/packed header opcode. These bits are consists two sub-fields:
— Bits 43:40 specify the QPI packet header opcode.
— Bits 47:44 specify the QPI message classes.
Table 18-7 lists the encodings supported in the opcode field.

Vol. 3B 18-29

PERFORMANCE MONITORING

Table 18-7. Opcode Field Encoding for MSR_UNCORE_ADDR_OPCODE_MATCH
Opcode [43:40]

QPI Message Class
Home Request

Snoop Response

Data Response

[47:44] = 0000B

[47:44] = 0001B

[47:44] = 1110B

1
DMND_IFETCH

2

2

WB

3

3

PF_DATA_RD

4

4

PF_RFO

5

5

PF_IFETCH

6

6

OTHER

7

7

NON_DRAM

15

15

•

MatchSel (bits 63:61): Software specifies the match criteria according to the following encoding:
— 000B: Disable addr_opcode match hardware.
— 100B: Count if only the address field matches.
— 010B: Count if only the opcode field matches.
— 110B: Count if either opcode field matches or the address field matches.
— 001B: Count only if both opcode and address field match.
— Other encoding are reserved.

18.3.1.3

Intel® Xeon® Processor 7500 Series Performance Monitoring Facility

The performance monitoring facility in the processor core of Intel® Xeon® processor 7500 series are the same as
those supported in Intel Xeon processor 5500 series. The uncore subsystem in Intel Xeon processor 7500 series are
significantly different The uncore performance monitoring facility consist of many distributed units associated with
individual logic control units (referred to as boxes) within the uncore subsystem. A high level block diagram of the
various box units of the uncore is shown in Figure 18-25.
Uncore PMUs are programmed via MSR interfaces. Each of the distributed uncore PMU units have several generalpurpose counters. Each counter requires an associated event select MSR, and may require additional MSRs to
configure sub-event conditions. The uncore PMU MSRs associated with each box can be categorized based on its
functional scope: per-counter, per-box, or global across the uncore. The number counters available in each box
type are different. Each box generally provides a set of MSRs to enable/disable, check status/overflow of multiple
counters within each box.

18-30 Vol. 3B

PERFORMANCE MONITORING

L3 Cache

CBox

CBox

CBox

CBox

CBox

SBox

CBox

CBox

CBox

SBox

SMI Channels

PBox

MBox

BBox

RBox

BBox

MBox

PBox
SMI Channels

WBox

PBox

PBox

PBox

PBox

UBox

4 Intel QPI Links

Figure 18-25. Distributed Units of the Uncore of Intel® Xeon® Processor 7500 Series
Table 18-8 summarizes the number MSRs for uncore PMU for each box.

Table 18-8. Uncore PMU MSR Summary
Box

# of Boxes

Counters per Box

Counter
Width

General
Purpose

Global
Enable

Sub-control MSRs

C-Box

8

6

48

Yes

per-box

None

S-Box

2

4

48

Yes

per-box

Match/Mask

B-Box

2

4

48

Yes

per-box

Match/Mask

M-Box

2

6

48

Yes

per-box

Yes

R-Box

1

16 ( 2 port, 8 per port)

48

Yes

per-box

Yes

W-Box

1

4

48

Yes

per-box

None

1

48

No

per-box

None

1

48

Yes

uncore

None

U-Box

1

The W-Box provides 4 general-purpose counters, each requiring an event select configuration MSR, similar to the
general-purpose counters in other boxes. There is also a fixed-function counter that increments clockticks in the
uncore clock domain.
For C,S,B,M,R, and W boxes, each box provides an MSR to enable/disable counting, configuring PMI of multiple
counters within the same box, this is somewhat similar the “global control“ programming interface,
IA32_PERF_GLOBAL_CTRL, offered in the core PMU. Similarly status information and counter overflow control for
multiple counters within the same box are also provided in C,S,B,M,R, and W boxes.
In the U-Box, MSR_U_PMON_GLOBAL_CTL provides overall uncore PMU enable/disable and PMI configuration
control. The scope of status information in the U-box is at per-box granularity, in contrast to the per-box status
information MSR (in the C,S,B,M,R, and W boxes) providing status information of individual counter overflow. The
difference in scope also apply to the overflow control MSR in the U-Box versus those in the other Boxes.
Vol. 3B 18-31

PERFORMANCE MONITORING

The individual MSRs that provide uncore PMU interfaces are listed in Chapter 2, “Model-Specific Registers (MSRs)”
in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4, Table 2-16 under the general
naming style of MSR_%box#%_PMON_%scope_function%, where %box#% designates the type of box and zerobased index if there are more the one box of the same type, %scope_function% follows the examples below:

•

Multi-counter enabling MSRs: MSR_U_PMON_GLOBAL_CTL, MSR_S0_PMON_BOX_CTL,
MSR_C7_PMON_BOX_CTL, etc.

•

Multi-counter status MSRs: MSR_U_PMON_GLOBAL_STATUS, MSR_S0_PMON_BOX_STATUS,
MSR_C7_PMON_BOX_STATUS, etc.

•

Multi-counter overflow control MSRs: MSR_U_PMON_GLOBAL_OVF_CTL, MSR_S0_PMON_BOX_OVF_CTL,
MSR_C7_PMON_BOX_OVF_CTL, etc.

•

Performance counters MSRs: the scope is implicitly per counter, e.g. MSR_U_PMON_CTR,
MSR_S0_PMON_CTR0, MSR_C7_PMON_CTR5, etc.

•

Event select MSRs: the scope is implicitly per counter, e.g. MSR_U_PMON_EVNT_SEL,
MSR_S0_PMON_EVNT_SEL0, MSR_C7_PMON_EVNT_SEL5, etc

•

Sub-control MSRs: the scope is implicitly per-box granularity, e.g. MSR_M0_PMON_TIMESTAMP,
MSR_R0_PMON_IPERF0_P1, MSR_S1_PMON_MATCH.

Details of uncore PMU MSR bit field definitions can be found in a separate document “Intel Xeon Processor 7500
Series Uncore Performance Monitoring Guide“.

18.3.2

Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name
Westmere

All of the performance monitoring programming interfaces (architectural and non-architectural core PMU facilities,
and uncore PMU) described in Section 18.6.3 also apply to processors based on Intel® microarchitecture code
name Westmere.
Table 18-5 describes a non-architectural performance monitoring event (event code 0B7H) and associated
MSR_OFFCORE_RSP_0 (address 1A6H) in the core PMU. This event and a second functionally equivalent offcore
response event using event code 0BBH and MSR_OFFCORE_RSP_1 (address 1A7H) are supported in processors
based on Intel microarchitecture code name Westmere. The event code and event mask definitions of Non-architectural performance monitoring events are listed in Table 19-29.
The load latency facility is the same as described in Section 18.3.1.1.2, but added enhancement to provide more
information in the data source encoding field of each load latency record. The additional information relates to
STLB_MISS and LOCK, see Table 18-13.

18.3.3

Intel® Xeon® Processor E7 Family Performance Monitoring Facility

The performance monitoring facility in the processor core of the Intel® Xeon® processor E7 family is the same as
those supported in the Intel Xeon processor 5600 series3. The uncore subsystem in the Intel Xeon processor E7
family is similar to those of the Intel Xeon processor 7500 series. The high level construction of the uncore subsystem is similar to that shown in Figure 18-25, with the additional capability that up to 10 C-Box units are
supported.

3. Exceptions are indicated for event code 0FH in Table 19-21; and valid bits of data source encoding field of each load
latency record is limited to bits 5:4 of Table 18-13.
18-32 Vol. 3B

PERFORMANCE MONITORING

Table 18-9 summarizes the number MSRs for uncore PMU for each box.

Table 18-9. Uncore PMU MSR Summary for Intel® Xeon® Processor E7 Family
Box

# of Boxes

Counters per Box

Counter
Width

General
Purpose

Global
Enable

Sub-control MSRs

C-Box

10

6

48

Yes

per-box

None

S-Box

2

4

48

Yes

per-box

Match/Mask

B-Box

2

4

48

Yes

per-box

Match/Mask

M-Box

2

6

48

Yes

per-box

Yes

R-Box

1

16 ( 2 port, 8 per port)

48

Yes

per-box

Yes

W-Box

1

4

48

Yes

per-box

None

1

48

No

per-box

None

1

48

Yes

uncore

None

U-Box

1

Details of the uncore performance monitoring facility of Intel Xeon Processor E7 family is available in the “Intel®
Xeon® Processor E7 Uncore Performance Monitoring Programming Reference Manual”.

18.3.4

Performance Monitoring for Processors Based on Intel® Microarchitecture Code Name
Sandy Bridge

Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx processor series, and Intel® Xeon® processor
E3-1200 family are based on Intel microarchitecture code name Sandy Bridge; this section describes the performance monitoring facilities provided in the processor core. The core PMU supports architectural performance monitoring capability with version ID 3 (see Section 18.2.3) and a host of non-architectural monitoring capabilities.
Architectural performance monitoring version 3 capabilities are described in Section 18.2.3.
The core PMU’s capability is similar to those described in Section 18.3.1.1 and Section 18.6.3, with some differences and enhancements relative to Intel microarchitecture code name Westmere summarized in Table 18-10.

Table 18-10. Core PMU Comparison
Intel® microarchitecture code
name Sandy Bridge

Intel® microarchitecture code
name Westmere

# of Fixed counters per
thread

3

3

# of general-purpose
counters per core

8

8

Counter width (R,W)

R:48, W: 32/48

R:48, W:32

See Section 18.2.2.

# of programmable counters
per thread

4 or (8 if a core not shared by two
threads)

4

Use CPUID to enumerate # of
counters.

PMI Overhead Mitigation

• Freeze_Perfmon_on_PMI with
legacy semantics.
• Freeze_on_LBR with legacy
semantics for branch profiling.
• Freeze_while_SMM.

• Freeze_Perfmon_on_PMI
with legacy semantics.
• Freeze_on_LBR with legacy
semantics for branch
profiling.
• Freeze_while_SMM.

See Section 17.4.7.

Processor Event Based
Sampling (PEBS) Events

See Table 18-12.

See Table 18-68.

IA32_PMC4-IA32_PMC7 do
not support PEBS.

Box

Comment
Use CPUID to enumerate # of
counters.

Vol. 3B 18-33

PERFORMANCE MONITORING

Table 18-10. Core PMU Comparison (Contd.)
Box

Intel® microarchitecture code
name Sandy Bridge

Intel® microarchitecture code
name Westmere

PEBS-Load Latency

See Section 18.3.4.4.2;

Data source encoding

Comment

• Data source encoding
• STLB miss encoding
• Lock transaction encoding
PEBS-Precise Store

Section 18.3.4.4.3

No

PEBS-PDIR

Yes (using precise
INST_RETIRED.ALL).

No

Off-core Response Event

MSR 1A6H and 1A7H, extended
request and response types.

MSR 1A6H and 1A7H, limited
response types.

18.3.4.1

Nehalem supports 1A6H
only.

Global Counter Control Facilities In Intel® Microarchitecture Code Name Sandy Bridge

The number of general-purpose performance counters visible to a logical processor can vary across Processors
based on Intel microarchitecture code name Sandy Bridge. Software must use CPUID to determine the number
performance counters/event select registers (See Section 18.2.1.1).

63

35 34 33 32 31

8 7 6 5 4 3 2 1 0

FIXED_CTR2 enable
FIXED_CTR1 enable
FIXED_CTR0 enable
PMC7_EN (if PMC7 present)
PMC6_EN (if PMC6 present)
PMC5_EN (if PMC5 present)
PMC4_EN (if PMC4 present)
PMC3_EN
PMC2_EN
PMC1_EN
PMC0_EN

Reserved

Valid if CPUID.0AH:EAX[15:8] = 8, else reserved.

Figure 18-26. IA32_PERF_GLOBAL_CTRL MSR in Intel® Microarchitecture Code Name Sandy Bridge
Figure 18-42 depicts the layout of IA32_PERF_GLOBAL_CTRL MSR. The enable bits (PMC4_EN, PMC5_EN,
PMC6_EN, PMC7_EN) corresponding to IA32_PMC4-IA32_PMC7 are valid only if CPUID.0AH:EAX[15:8] reports a
value of ‘8’. If CPUID.0AH:EAX[15:8] = 4, attempts to set the invalid bits will cause #GP.
Each enable bit in IA32_PERF_GLOBAL_CTRL is AND’ed with the enable bits for all privilege levels in the respective
IA32_PERFEVTSELx or IA32_PERF_FIXED_CTR_CTRL MSRs to start/stop the counting of respective counters.
Counting is enabled if the AND’ed results is true; counting is disabled when the result is false.
IA32_PERF_GLOBAL_STATUS MSR provides single-bit status used by software to query the overflow condition of
each performance counter. IA32_PERF_GLOBAL_STATUS[bit 62] indicates overflow conditions of the DS area data
buffer (see Figure 18-27). A value of 1 in each bit of the PMCx_OVF field indicates an overflow condition has
occurred in the associated counter.

18-34 Vol. 3B

PERFORMANCE MONITORING

63 62 61

35 34 33 32 31

8 7 6 5 4 3 2 1 0

CondChgd
Ovf_DSBuffer
Ovf_UncorePMU
FIXED_CTR2 Overflow (RO)
FIXED_CTR1 Overflow (RO)
FIXED_CTR0 Overflow (RO)
PMC7_OVF (RO, If PMC7 present)
PMC6_OVF (RO, If PMC6 present)
PMC5_OVF (RO, If PMC5 present)
PMC4_OVF (RO, If PMC4 present)
PMC3_OVF (RO)
PMC2_OVF (RO)
PMC1_OVF (RO)
PMC0_OVF (RO)

Valid if CPUID.0AH:EAX[15:8] = 8; else reserved

Reserved

Figure 18-27. IA32_PERF_GLOBAL_STATUS MSR in Intel® Microarchitecture Code Name Sandy Bridge
When a performance counter is configured for PEBS, an overflow condition in the counter will arm PEBS. On the
subsequent event following overflow, the processor will generate a PEBS event. On a PEBS event, the processor will
perform bounds checks based on the parameters defined in the DS Save Area (see Section 17.4.9). Upon
successful bounds checks, the processor will store the data record in the defined buffer area, clear the counter
overflow status, and reload the counter. If the bounds checks fail, the PEBS will be skipped entirely. In the event
that the PEBS buffer fills up, the processor will set the OvfBuffer bit in MSR_PERF_GLOBAL_STATUS.
IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow the indicators for general-purpose or fixedfunction counters via a single WRMSR (see Figure 18-28). Clear overflow indications when:

•
•
•

Setting up new values in the event select and/or UMASK field for counting or interrupt based sampling.
Reloading counter values to continue sampling.
Disabling event counting or interrupt based sampling.

63 62

35 34 33 32 31

8 7 6 5 4 3

2 1 0

ClrCondChgd
ClrOvfDSBuffer
ClrOvfUncore
FIXED_CTR2 ClrOverflow
FIXED_CTR1 ClrOverflow
FIXED_CTR0 ClrOverflow
PMC7_ClrOvf (if PMC7 present)
PMC6_ClrOvf (if PMC6 present)
PMC5_ClrOvf (if PMC5 present)
PMC4_ClrOvf (if PMC4 present)
PMC3_ClrOvf
PMC2_ClrOvf
PMC1_ClrOvf
PMC0_ClrOvf

Reserved

Valid if CPUID.0AH:EAX[15:8] = 8; else reserved

Figure 18-28. IA32_PERF_GLOBAL_OVF_CTRL MSR in Intel microarchitecture code name Sandy Bridge

Vol. 3B 18-35

PERFORMANCE MONITORING

18.3.4.2

Counter Coalescence

In processors based on Intel microarchitecture code name Sandy Bridge, each processor core implements eight
general-purpose counters. CPUID.0AH:EAX[15:8] will report either 4 or 8 depending specific processor’s product
features.
If a processor core is shared by two logical processors, each logical processors can access 4 counters (IA32_PMC0IA32_PMC3). This is the same as in the prior generation for processors based on Intel microarchitecture code name
Nehalem.
If a processor core is not shared by two logical processors, all eight general-purpose counters are visible, and
CPUID.0AH:EAX[15:8] reports 8. IA32_PMC4-IA32_PMC7 occupy MSR addresses 0C5H through 0C8H. Each
counter is accompanied by an event select MSR (IA32_PERFEVTSEL4-IA32_PERFEVTSEL7).
If CPUID.0AH:EAX[15:8] report 4, access to IA32_PMC4-IA32_PMC7, IA32_PMC4-IA32_PMC7 will cause #GP.
Writing 1’s to bit position 7:4 of IA32_PERF_GLOBAL_CTRL, IA32_PERF_GLOBAL_STATUS, or
IA32_PERF_GLOBAL_OVF_CTL will also cause #GP.

18.3.4.3

Full Width Writes to Performance Counters

Processors based on Intel microarchitecture code name Sandy Bridge support full-width writes to the generalpurpose counters, IA32_PMCx. Support of full-width writes are enumerated by
IA32_PERF_CAPABILITIES.FW_WRITES[13] (see Section 18.2.4).
The default behavior of IA32_PMCx is unchanged, i.e. WRMSR to IA32_PMCx results in a sign-extended 32-bit
value of the input EAX written into IA32_PMCx. Full-width writes must issue WRMSR to a dedicated alias MSR
address for each IA32_PMCx.
Software must check the presence of full-width write capability and the presence of the alias address IA32_A_PMCx
by testing IA32_PERF_CAPABILITIES[13].

18.3.4.4

PEBS Support in Intel® Microarchitecture Code Name Sandy Bridge

Processors based on Intel microarchitecture code name Sandy Bridge support PEBS, similar to those offered in
prior generation, with several enhanced features. The key components and differences of PEBS facility relative to
Intel microarchitecture code name Westmere is summarized in Table 18-11.

Table 18-11. PEBS Facility Comparison
Box

Intel® microarchitecture code name
Sandy Bridge

Intel® microarchitecture
code name Westmere

Comment

Valid IA32_PMCx

PMC0-PMC3

PMC0-PMC3

No PEBS on PMC4-PMC7.

PEBS Buffer Programming

Section 18.3.1.1.1

Section 18.3.1.1.1

Unchanged

IA32_PEBS_ENABLE
Layout

Figure 18-29

Figure 18-15

PEBS record layout

Physical Layout same as Table 18-3.

Table 18-3

Enhanced fields at offsets 98H,
A0H, A8H.

PEBS Events

See Table 18-12.

See Table 18-68.

IA32_PMC4-IA32_PMC7 do not
support PEBS.

PEBS-Load Latency

See Table 18-13.

Table 18-4

PEBS-Precise Store

Yes; see Section 18.3.4.4.3.

No

IA32_PMC3 only

PEBS-PDIR

Yes

No

IA32_PMC1 only

PEBS skid from EventingIP

1 (or 2 if micro+macro fusion)

1

SAMPLING Restriction

Small SAV(CountDown) value incur higher overhead than prior
generation.

18-36 Vol. 3B

PERFORMANCE MONITORING

Only IA32_PMC0 through IA32_PMC3 support PEBS.

NOTE
PEBS events are only valid when the following fields of IA32_PERFEVTSELx are all zero: AnyThread,
Edge, Invert, CMask.
In a PMU with PDIR capability, PEBS behavior is unpredictable if IA32_PERFEVTSELx or IA32_PMCx
is changed for a PEBS-enabled counter while an event is being counted. To avoid this, changes to
the programming or value of a PEBS-enabled counter should be performed when the counter is
disabled.
In IA32_PEBS_ENABLE MSR, bit 63 is defined as PS_ENABLE: When set, this enables IA32_PMC3 to capture
precise store information. Only IA32_PMC3 supports the precise store facility. In typical usage of PEBS, the bit
fields in IA32_PEBS_ENABLE are written to when the agent software starts PEBS operation; the enabled bit fields
should be modified only when re-programming another PEBS event or cleared when the agent uses the performance counters for non-PEBS operations.

36 3534 33 32 31

63 62

8 7 6 5 43 2 1 0

PS_EN (R/W)
LL_EN_PMC3 (R/W)
LL_EN_PMC2 (R/W)
LL_EN_PMC1 (R/W)
LL_EN_PMC0 (R/W)
PEBS_EN_PMC3 (R/W)
PEBS_EN_PMC2 (R/W)
PEBS_EN_PMC1 (R/W)
PEBS_EN_PMC0 (R/W)

Reserved

RESET Value — 00000000_00000000H

Figure 18-29. Layout of IA32_PEBS_ENABLE MSR
18.3.4.4.1 PEBS Record Format
The layout of PEBS records physically identical to those shown in Table 18-3, but the fields at offset 98H, A0H and
A8H have been enhanced to support additional PEBS capabilities.

•

Load/Store Data Linear Address (Offset 98H): This field will contain the linear address of the source of the load,
or linear address of the destination of the store.

•

Data Source /Store Status (Offset A0H):When load latency is enabled, this field will contain three piece of
information (including an encoded value indicating the source which satisfied the load operation). The source
field encodings are detailed in Table 18-4. When precise store is enabled, this field will contain information
indicating the status of the store, as detailed in Table 19.

•

Latency Value/0 (Offset A8H): When load latency is enabled, this field contains the latency in cycles to service
the load. This field is not meaningful when precise store is enabled and will be written to zero in that case. Upon
writing the PEBS record, microcode clears the overflow status bits in the IA32_PERF_GLOBAL_STATUS corresponding to those counters that both overflowed and were enabled in the IA32_PEBS_ENABLE register. The
status bits of other counters remain unaffected.

The number PEBS events has expanded. The list of PEBS events supported in Intel microarchitecture code name
Sandy Bridge is shown in Table 18-12.

Vol. 3B 18-37

PERFORMANCE MONITORING

Table 18-12. PEBS Performance Events for Intel® Microarchitecture Code Name Sandy Bridge
Event Name

Event Select

Sub-event

UMask

INST_RETIRED

C0H

PREC_DIST

01H1

UOPS_RETIRED

C2H

BR_INST_RETIRED

BR_MISP_RETIRED

MEM_UOPS_RETIRED

MEM_LOAD_UOPS_RETIRED

MEM_LOAD_UOPS_LLC_HIT_RETIRED

C4H

C5H

D0H

D1H

D2H

All

01H

Retire_Slots

02H

Conditional

01H

Near_Call

02H

All_branches

04H

Near_Return

08H

Near_Taken

20H

Conditional

01H

Near_Call

02H

All_branches

04H

Not_Taken

10H

Taken

20H

STLB_MISS_LOADS

11H

STLB_MISS_STORE

12H

LOCK_LOADS

21H

SPLIT_LOADS

41H

SPLIT_STORES

42H

ALL_LOADS

81H

ALL_STORES

82H

L1_Hit

01H

L2_Hit

02H

L3_Hit

04H

Hit_LFB

40H

XSNP_Miss

01H

XSNP_Hit

02H

XSNP_Hitm

04H

XSNP_None

08H

NOTES:
1. Only available on IA32_PMC1.

18.3.4.4.2 Load Latency Performance Monitoring Facility
The load latency facility in Intel microarchitecture code name Sandy Bridge is similar to that in prior microarchitecture. It provides software a means to characterize the average load latency to different levels of cache/memory
hierarchy. This facility requires processor supporting enhanced PEBS record format in the PEBS buffer, see
Table 18-3 and Section 18.3.4.4.1. This field measures the load latency from load's first dispatch of till final data
writeback from the memory subsystem. The latency is reported for retired demand load operations and in core
cycles (it accounts for re-dispatches).
To use this feature software must assure:

•

One of the IA32_PERFEVTSELx MSR is programmed to specify the event unit MEM_TRANS_RETIRED, and the
LATENCY_ABOVE_THRESHOLD event mask must be specified (IA32_PerfEvtSelX[15:0] = 1CDH). The corresponding counter IA32_PMCx will accumulate event counts for architecturally visible loads which exceed the
programmed latency threshold specified separately in a MSR. Stores are ignored when this event is

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PERFORMANCE MONITORING

programmed. The CMASK or INV fields of the IA32_PerfEvtSelX register used for counting load latency must be
0. Writing other values will result in undefined behavior.

•

The MSR_PEBS_LD_LAT_THRESHOLD MSR is programmed with the desired latency threshold in core clock
cycles. Loads with latencies greater than this value are eligible for counting and latency data reporting. The
minimum value that may be programmed in this register is 3 (the minimum detectable load latency is 4 core
clock cycles).

•

The PEBS enable bit in the IA32_PEBS_ENABLE register is set for the corresponding IA32_PMCx counter
register. This means that both the PEBS_EN_CTRX and LL_EN_CTRX bits must be set for the counter(s) of
interest. For example, to enable load latency on counter IA32_PMC0, the IA32_PEBS_ENABLE register must be
programmed with the 64-bit value 00000001.00000001H.

•

When Load latency event is enabled, no other PEBS event can be configured with other counters.

When the load-latency facility is enabled, load operations are randomly selected by hardware and tagged to carry
information related to data source locality and latency. Latency and data source information of tagged loads are
updated internally. The MEM_TRANS_RETIRED event for load latency counts only tagged retired loads. If a load is
cancelled it will not be counted and the internal state of the load latency facility will not be updated. In this case the
hardware will tag the next available load.
When a PEBS assist occurs, the last update of latency and data source information are captured by the assist and
written as part of the PEBS record. The PEBS sample after value (SAV), specified in PEBS CounterX Reset, operates
orthogonally to the tagging mechanism. Loads are randomly tagged to collect latency data. The SAV controls the
number of tagged loads with latency information that will be written into the PEBS record field by the PEBS assists.
The load latency data written to the PEBS record will be for the last tagged load operation which retired just before
the PEBS assist was invoked.
The physical layout of the PEBS records is the same as shown in Table 18-3. The specificity of Data Source entry at
offset A0H has been enhanced to report three pieces of information.

Table 18-13. Layout of Data Source Field of Load Latency Record
Field

Position

Description

Source

3:0

See Table 18-4

STLB_MISS

4

0: The load did not miss the STLB (hit the DTLB or STLB).
1: The load missed the STLB.

Lock

5

Reserved

63:6

0: The load was not part of a locked transaction.
1: The load was part of a locked transaction.
Reserved

The layout of MSR_PEBS_LD_LAT_THRESHOLD is the same as shown in Figure 18-17.

18.3.4.4.3 Precise Store Facility
Processors based on Intel microarchitecture code name Sandy Bridge offer a precise store capability that complements the load latency facility. It provides a means to profile store memory references in the system.
Precise stores leverage the PEBS facility and provide additional information about sampled stores. Having precise
memory reference events with linear address information for both loads and stores can help programmers improve
data structure layout, eliminate remote node references, and identify cache-line conflicts in NUMA systems.
Only IA32_PMC3 can be used to capture precise store information. After enabling this facility, counter overflows
will initiate the generation of PEBS records as previously described in PEBS. Upon counter overflow hardware
captures the linear address and other status information of the next store that retires. This information is then
written to the PEBS record.
To enable the precise store facility, software must complete the following steps. Please note that the precise store
facility relies on the PEBS facility, so the PEBS configuration requirements must be completed before attempting to
capture precise store information.

•

Complete the PEBS configuration steps.
Vol. 3B 18-39

PERFORMANCE MONITORING

•

Program the MEM_TRANS_RETIRED.PRECISE_STORE event in IA32_PERFEVTSEL3. Only counter 3
(IA32_PMC3) supports collection of precise store information.

•

Set IA32_PEBS_ENABLE[3] and IA32_PEBS_ENABLE[63]. This enables IA32_PMC3 as a PEBS counter and
enables the precise store facility, respectively.

The precise store information written into a PEBS record affects entries at offset 98H, A0H and A8H of Table 18-3.
The specificity of Data Source entry at offset A0H has been enhanced to report three piece of information.

Table 18-14. Layout of Precise Store Information In PEBS Record
Field

Offset Description

Store Data
98H
Linear Address

The linear address of the destination of the store.

Store Status

L1D Hit (Bit 0): The store hit the data cache closest to the core (lowest latency cache) if this bit is set,
otherwise the store missed the data cache.

A0H

STLB Miss (bit 4): The store missed the STLB if set, otherwise the store hit the STLB
Locked Access (bit 5): The store was part of a locked access if set, otherwise the store was not part of a
locked access.
Reserved

A8H

Reserved

18.3.4.4.4 Precise Distribution of Instructions Retired (PDIR)
Upon triggering a PEBS assist, there will be a finite delay between the time the counter overflows and when the
microcode starts to carry out its data collection obligations. INST_RETIRED is a very common event that is used to
sample where performance bottleneck happened and to help identify its location in instruction address space. Even
if the delay is constant in core clock space, it invariably manifest as variable “skids” in instruction address space.
This creates a challenge for programmers to profile a workload and pinpoint the location of bottlenecks.
The core PMU in processors based on Intel microarchitecture code name Sandy Bridge include a facility referred to
as precise distribution of Instruction Retired (PDIR).
The PDIR facility mitigates the “skid” problem by providing an early indication of when the INST_RETIRED counter
is about to overflow, allowing the machine to more precisely trap on the instruction that actually caused the counter
overflow thus eliminating skid.
PDIR applies only to the INST_RETIRED.ALL precise event, and must use IA32_PMC1 with PerfEvtSel1 property
configured and bit 1 in the IA32_PEBS_ENABLE set to 1. INST_RETIRED.ALL is a non-architectural performance
event, it is not supported in prior generation microarchitectures. Additionally, on processors with CPUID
DisplayFamily_DisplayModel signatures of 06_2A and 06_2D, the tool that programs PDIR should quiesce the rest
of the programmable counters in the core when PDIR is active.

18.3.4.5

Off-core Response Performance Monitoring

The core PMU in processors based on Intel microarchitecture code name Sandy Bridge provides off-core response
facility similar to prior generation. Off-core response can be programmed only with a specific pair of event select
and counter MSR, and with specific event codes and predefine mask bit value in a dedicated MSR to specify attributes of the off-core transaction. Two event codes are dedicated for off-core response event programming. Each
event code for off-core response monitoring requires programming an associated configuration MSR,
MSR_OFFCORE_RSP_x. Table 18-15 lists the event code, mask value and additional off-core configuration MSR that
must be programmed to count off-core response events using IA32_PMCx.

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PERFORMANCE MONITORING

Table 18-15. Off-Core Response Event Encoding
Counter

Event code

UMask

Required Off-core Response MSR

PMC0-3

B7H

01H

MSR_OFFCORE_RSP_0 (address 1A6H)

PMC0-3

BBH

01H

MSR_OFFCORE_RSP_1 (address 1A7H)

The layout of MSR_OFFCORE_RSP_0 and MSR_OFFCORE_RSP_1 are shown in Figure 18-30 and Figure 18-31. Bits
15:0 specifies the request type of a transaction request to the uncore. Bits 30:16 specifies supplier information,
bits 37:31 specifies snoop response information.
63

37

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

See Figure 18-30

RESPONSE TYPE — Other (R/W)
RESERVED
REQUEST TYPE — STRM_ST (R/W)
REQUEST TYPE — BUS_LOCKS (R/W)
REQUEST TYPE — PF_LLC_IFETCH (R/W)
REQUEST TYPE — PF_LLC_RFO (R/W)
REQUEST TYPE — PF_LLC_DATA_RD (R/W)
REQUEST TYPE — PF_IFETCH (R/W)
REQUEST TYPE — PF_RFO (R/W)
REQUEST TYPE — PF_DATA_RD (R/W)
REQUEST TYPE — WB (R/W)
REQUEST TYPE — DMND_IFETCH (R/W)
REQUEST TYPE — DMND_RFO (R/W)
REQUEST TYPE — DMND_DATA_RD (R/W)

Reserved

RESET Value — 00000000_00000000H

Figure 18-30. Request_Type Fields for MSR_OFFCORE_RSP_x

Table 18-16. MSR_OFFCORE_RSP_x Request_Type Field Definition
Bit Name

Offset Description

DMND_DATA_RD

0

(R/W). Counts the number of demand data reads of full and partial cachelines as well as demand data
page table entry cacheline reads. Does not count L2 data read prefetches or instruction fetches.

DMND_RFO

1

(R/W). Counts the number of demand and DCU prefetch reads for ownership (RFO) requests generated
by a write to data cacheline. Does not count L2 RFO prefetches.

DMND_IFETCH

2

(R/W). Counts the number of demand and DCU prefetch instruction cacheline reads. Does not count L2
code read prefetches.

WB

3

(R/W). Counts the number of writeback (modified to exclusive) transactions.

PF_DATA_RD

4

(R/W). Counts the number of data cacheline reads generated by L2 prefetchers.

PF_RFO

5

(R/W). Counts the number of RFO requests generated by L2 prefetchers.

PF_IFETCH

6

(R/W). Counts the number of code reads generated by L2 prefetchers.

PF_LLC_DATA_RD

7

(R/W). L2 prefetcher to L3 for loads.

PF_LLC_RFO

8

(R/W). RFO requests generated by L2 prefetcher

PF_LLC_IFETCH

9

(R/W). L2 prefetcher to L3 for instruction fetches.

BUS_LOCKS

10

(R/W). Bus lock and split lock requests

STRM_ST

11

(R/W). Streaming store requests

OTHER

15

(R/W). Any other request that crosses IDI, including I/O.

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PERFORMANCE MONITORING

63

37 36 35 34 33 32 31

22 21 20 19 18 17 16

RESPONSE TYPE — NON_DRAM (R/W)
RSPNS_SNOOP — HITM (R/W)
RSPNS_SNOOP — HIT_FWD
RSPNS_SNOOP — HIT_NO_FWD (R/W)
RSPNS_SNOOP — SNP_MISS (R/W)
RSPNS_SNOOP — SNP_NOT_NEEDED (R/W)
RSPNS_SNOOP — SNPl_NONE (R/W)
RSPNS_SUPPLIER — RESERVED
RSPNS_SUPPLIER — Local
RSPNS_SUPPLIER — LLC_HITF (R/W)
RSPNS_SUPPLIER — LLC_HITS (R/W)
RSPNS_SUPPLIER — LLC_HITE (R/W)
RSPNS_SUPPLIER — LLC_HITM (R/W)
RSPNS_SUPPLIER — No_SUPP (R/W)
RSPNS_SUPPLIER — ANY (R/W)

Reserved

RESET Value — 00000000_00000000H

Figure 18-31. Response_Supplier and Snoop Info Fields for MSR_OFFCORE_RSP_x
To properly program this extra register, software must set at least one request type bit and a valid response type
pattern. Otherwise, the event count reported will be zero. It is permissible and useful to set multiple request and
response type bits in order to obtain various classes of off-core response events. Although MSR_OFFCORE_RSP_x
allow an agent software to program numerous combinations that meet the above guideline, not all combinations
produce meaningful data.

Table 18-17. MSR_OFFCORE_RSP_x Response Supplier Info Field Definition
Subtype

Bit Name

Offset

Description

Common

Any

16

(R/W). Catch all value for any response types.

Supplier
Info

NO_SUPP

17

(R/W). No Supplier Information available

LLC_HITM

18

(R/W). M-state initial lookup stat in L3.

LLC_HITE

19

(R/W). E-state

LLC_HITS

20

(R/W). S-state

LLC_HITF

21

(R/W). F-state

LOCAL

22

(R/W). Local DRAM Controller

Reserved

30:23

Reserved

To specify a complete offcore response filter, software must properly program bits in the request and response type
fields. A valid request type must have at least one bit set in the non-reserved bits of 15:0. A valid response type
must be a non-zero value of the following expression:
ANY | [(‘OR’ of Supplier Info Bits) & (‘OR’ of Snoop Info Bits)]
If “ANY“ bit is set, the supplier and snoop info bits are ignored.

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PERFORMANCE MONITORING

Table 18-18. MSR_OFFCORE_RSP_x Snoop Info Field Definition
Subtype

Bit Name

Offset

Description

Snoop
Info

SNP_NONE

31

(R/W). No details on snoop-related information

SNP_NOT_NEEDED 32

(R/W). No snoop was needed to satisfy the request.

SNP_MISS

(R/W). A snoop was needed and it missed all snooped caches:

33

-For LLC Hit, ReslHitl was returned by all cores
-For LLC Miss, Rspl was returned by all sockets and data was returned from DRAM.
SNP_NO_FWD

34

(R/W). A snoop was needed and it hits in at least one snooped cache. Hit denotes a cacheline was valid before snoop effect. This includes:
-Snoop Hit w/ Invalidation (LLC Hit, RFO)
-Snoop Hit, Left Shared (LLC Hit/Miss, IFetch/Data_RD)
-Snoop Hit w/ Invalidation and No Forward (LLC Miss, RFO Hit S)
In the LLC Miss case, data is returned from DRAM.

SNP_FWD

35

(R/W). A snoop was needed and data was forwarded from a remote socket. This includes:
-Snoop Forward Clean, Left Shared (LLC Hit/Miss, IFetch/Data_RD/RFT).

HITM

36

(R/W). A snoop was needed and it HitM-ed in local or remote cache. HitM denotes a cacheline was in modified state before effect as a results of snoop. This includes:
-Snoop HitM w/ WB (LLC miss, IFetch/Data_RD)
-Snoop Forward Modified w/ Invalidation (LLC Hit/Miss, RFO)
-Snoop MtoS (LLC Hit, IFetch/Data_RD).

NON_DRAM

18.3.4.6

37

(R/W). Target was non-DRAM system address. This includes MMIO transactions.

Uncore Performance Monitoring Facilities In Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx,
Intel® Core™ i3-2xxx Processor Series

The uncore sub-system in Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx processor series
provides a unified L3 that can support up to four processor cores. The L3 cache consists multiple slices, each slice
interface with a processor via a coherence engine, referred to as a C-Box. Each C-Box provides dedicated facility of
MSRs to select uncore performance monitoring events and each C-Box event select MSR is paired with a counter
register, similar in style as those described in Section 18.3.1.2.2. The ARB unit in the uncore also provides its local
performance counters and event select MSRs. The layout of the event select MSRs in the C-Boxes and the ARB unit
are shown in Figure 18-32.

63

28

24 23 22 21 20 19 18 17 16 15

Counter Mask
(CMASK)

0

8 7

Unit Mask (UMASK)

Event Select

INV—Invert counter mask
EN—Enable counter
OVF_EN—Overflow forwarding
E—Edge detect
Reserved

RESET Value — 00000000_00000000H

Figure 18-32. Layout of Uncore PERFEVTSEL MSR for a C-Box Unit or the ARB Unit

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PERFORMANCE MONITORING

The bit fields of the uncore event select MSRs for a C-box unit or the ARB unit are summarized below:

•

Event_Select (bits 7:0) and UMASK (bits 15:8): Specifies the microarchitectural condition to count in a local
uncore PMU counter, see Table 19-18.

•
•

E (bit 18): Enables edge detection filtering, if 1.

•
•
•

EN (bit 22): Enables the local counter associated with this event select MSR.

OVF_EN (bit 20): Enables the overflow indicator from the uncore counter forwarded to
MSR_UNC_PERF_GLOBAL_CTRL, if 1.
INV (bit 23): Event count increments with non-negative value if 0, with negated value if 1.
CMASK (bits 28:24): Specifies a positive threshold value to filter raw event count input.

At the uncore domain level, there is a master set of control MSRs that centrally manages all the performance monitoring facility of uncore units. Figure 18-33 shows the layout of the uncore domain global control.
When an uncore counter overflows, a PMI can be routed to a processor core. Bits 3:0 of
MSR_UNC_PERF_GLOBAL_CTRL can be used to select which processor core to handle the uncore PMI. Software
must then write to bit 13 of IA32_DEBUGCTL (at address 1D9H) to enable this capability.

•

PMI_SEL_Core#: Enables the forwarding of an uncore PMI request to a processor core, if 1. If bit 30 (WakePMI)
is ‘1’, a wake request is sent to the respective processor core prior to sending the PMI.

•

EN: Enables the fixed uncore counter, the ARB counters, and the CBO counters in the uncore PMU, if 1. This bit
is cleared if bit 31 (FREEZE) is set and any enabled uncore counters overflow.

•

WakePMI: Controls sending a wake request to any halted processor core before issuing the uncore PMI request.
If a processor core was halted and not sent a wake request, the uncore PMI will not be serviced by the
processor core.

•

FREEZE: Provides the capability to freeze all uncore counters when an overflow condition occurs in a unit
counter. When this bit is set, and a counter overflow occurs, the uncore PMU logic will clear the global enable bit
(bit 29).
63

32 31 30 29 28

4 3 2 1

0

FREEZE—Freeze counters
WakePMI—Wake cores on PMI
EN—Enable all uncore counters
PMI_Sel_Core3 — Uncore PMI to core 3
PMI_Sel_Core2 — Uncore PMI to core 2
PMI_Sel_Core1 — Uncore PMI to core 1
PMI_Sel_Core0 — Uncore PMI to core 0
Reserved

RESET Value — 00000000_00000000H

Figure 18-33. Layout of MSR_UNC_PERF_GLOBAL_CTRL MSR for Uncore

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PERFORMANCE MONITORING

Additionally, there is also a fixed counter, counting uncore clockticks, for the uncore domain. Table 18-19 summarizes the number MSRs for uncore PMU for each box.

Table 18-19. Uncore PMU MSR Summary
Box

# of Boxes

Counters per
Box

Counter
Width

General
Purpose

Global
Enable

C-Box

SKU specific

2

44

Yes

Per-box

ARB

1

2

44

Yes

Uncore

Fixed
Counter

N.A.

N.A.

48

No

Uncore

Comment
Up to 4, seeTable 2-20
MSR_UNC_CBO_CONFIG

18.3.4.6.1 Uncore Performance Monitoring Events
There are certain restrictions on the uncore performance counters in each C-Box. Specifically,

•

Occupancy events are supported only with counter 0 but not counter 1.

Other uncore C-Box events can be programmed with either counter 0 or 1.
The C-Box uncore performance events described in Table 19-18 can collect performance characteristics of transactions initiated by processor core. In that respect, they are similar to various sub-events in the
OFFCORE_RESPONSE family of performance events in the core PMU. Information such as data supplier locality
(LLC HIT/MISS) and snoop responses can be collected via OFFCORE_RESPONSE and qualified on a per-thread
basis.
On the other hand, uncore performance event logic can not associate its counts with the same level of per-thread
qualification attributes as the core PMU events can. Therefore, whenever similar event programming capabilities
are available from both core PMU and uncore PMU, the recommendation is that utilizing the core PMU events may
be less affected by artifacts, complex interactions and other factors.

18.3.4.7

Intel® Xeon® Processor E5 Family Performance Monitoring Facility

The Intel® Xeon® Processor E5 Family (and Intel® Core™ i7-3930K Processor) are based on Intel microarchitecture code name Sandy Bridge-E. While the processor cores share the same microarchitecture as those of the Intel®
Xeon® Processor E3 Family and 2nd generation Intel Core i7-2xxx, Intel Core i5-2xxx, Intel Core i3-2xxx processor
series, the uncore subsystems are different. An overview of the uncore performance monitoring facilities of the
Intel Xeon processor E5 family (and Intel Core i7-3930K processor) is described in Section 18.3.4.8.
Thus, the performance monitoring facilities in the processor core generally are the same as those described in
Section 18.6.3 through Section 18.3.4.5. However, the MSR_OFFCORE_RSP_0/MSR_OFFCORE_RSP_1 Response
Supplier Info field shown in Table 18-17 applies to Intel Core Processors with CPUID signature of
DisplayFamily_DisplayModel encoding of 06_2AH; Intel Xeon processor with CPUID signature of
DisplayFamily_DisplayModel encoding of 06_2DH supports an additional field for remote DRAM controller shown in
Table 18-20. Additionally, the are some small differences in the non-architectural performance monitoring events
(see Table 19-16).

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PERFORMANCE MONITORING

Table 18-20. MSR_OFFCORE_RSP_x Supplier Info Field Definitions
Subtype

Bit Name

Offset

Description

Common

Any

16

(R/W). Catch all value for any response types.

Supplier Info

18.3.4.8

NO_SUPP

17

(R/W). No Supplier Information available

LLC_HITM

18

(R/W). M-state initial lookup stat in L3.

LLC_HITE

19

(R/W). E-state

LLC_HITS

20

(R/W). S-state

LLC_HITF

21

(R/W). F-state

LOCAL

22

(R/W). Local DRAM Controller

Remote

30:23

(R/W): Remote DRAM Controller (either all 0s or all 1s)

Intel® Xeon® Processor E5 Family Uncore Performance Monitoring Facility

The uncore subsystem in the Intel Xeon processor E5-2600 product family has some similarities with those of the
Intel Xeon processor E7 family. Within the uncore subsystem, localized performance counter sets are provided at
logic control unit scope. For example, each Cbox caching agent has a set of local performance counters, and the
power controller unit (PCU) has its own local performance counters. Up to 8 C-Box units are supported in the
uncore sub-system.
Table 18-21 summarizes the uncore PMU facilities providing MSR interfaces.

Table 18-21. Uncore PMU MSR Summary for Intel® Xeon® Processor E5 Family
Box

# of Boxes

Counters per Box

Counter
Width

General
Purpose

Global
Enable

Sub-control MSRs

C-Box

8

4

44

Yes

per-box

None

PCU

1

4

48

Yes

per-box

Match/Mask

U-Box

1

2

44

Yes

uncore

None

Details of the uncore performance monitoring facility of Intel Xeon Processor E5 family is available in “Intel®
Xeon® Processor E5 Uncore Performance Monitoring Programming Reference Manual”. The MSR-based uncore PMU
interfaces are listed in Table 2-23.

18.3.5

3rd Generation Intel® Core™ Processor Performance Monitoring Facility

The 3rd generation Intel® Core™ processor family and Intel® Xeon® processor E3-1200v2 product family are
based on the Ivy Bridge microarchitecture. The performance monitoring facilities in the processor core generally
are the same as those described in Section 18.6.3 through Section 18.3.4.5. The non-architectural performance
monitoring events supported by the processor core are listed in Table 19-16.

18.3.5.1

Intel® Xeon® Processor E5 v2 and E7 v2 Family Uncore Performance Monitoring Facility

The uncore subsystem in the Intel Xeon processor E5 v2 and Intel Xeon Processor E7 v2 product families are based
on the Ivy Bridge-E microarchitecture. There are some similarities with those of the Intel Xeon processor E5 family
based on the Sandy Bridge microarchitecture. Within the uncore subsystem, localized performance counter sets
are provided at logic control unit scope.
Details of the uncore performance monitoring facility of Intel Xeon Processor E5 v2 and Intel Xeon Processor E7 v2
families are available in “Intel® Xeon® Processor E5 v2 and E7 v2 Uncore Performance Monitoring Programming
Reference Manual”. The MSR-based uncore PMU interfaces are listed in Table 2-27.

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PERFORMANCE MONITORING

18.3.6

4th Generation Intel® Core™ Processor Performance Monitoring Facility

The 4th generation Intel® Core™ processor and Intel® Xeon® processor E3-1200 v3 product family are based on
the Haswell microarchitecture. The core PMU supports architectural performance monitoring capability with version
ID 3 (see Section 18.2.3) and a host of non-architectural monitoring capabilities.
Architectural performance monitoring version 3 capabilities are described in Section 18.2.3.
The core PMU’s capability is similar to those described in Section 18.6.3 through Section 18.3.4.5, with some differences and enhancements summarized in Table 18-22. Additionally, the core PMU provides some enhancement to
support performance monitoring when the target workload contains instruction streams using Intel® Transactional
Synchronization Extensions (TSX), see Section 18.3.6.5. For details of Intel TSX, see Chapter 16, “Programming with
Intel® Transactional Synchronization Extensions” of Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1.

Table 18-22. Core PMU Comparison
Box

Intel® microarchitecture code
name Haswell

Intel® microarchitecture code
name Sandy Bridge

# of Fixed counters per thread

3

3

# of general-purpose counters
per core

8

8

Counter width (R,W)

R:48, W: 32/48

R:48, W: 32/48

See Section 18.2.2.

# of programmable counters per
thread

4 or (8 if a core not shared by two
threads)

4 or (8 if a core not shared by
two threads)

Use CPUID to enumerate
# of counters.

PMI Overhead Mitigation

• Freeze_Perfmon_on_PMI with
legacy semantics.
• Freeze_on_LBR with legacy
semantics for branch profiling.
• Freeze_while_SMM.

• Freeze_Perfmon_on_PMI
with legacy semantics.
• Freeze_on_LBR with legacy
semantics for branch
profiling.
• Freeze_while_SMM.

See Section 17.4.7.

Processor Event Based Sampling
(PEBS) Events

See Table 18-12 and Section
18.3.6.5.1.

See Table 18-12.

IA32_PMC4-IA32_PMC7
do not support PEBS.

PEBS-Load Latency

See Section 18.3.4.4.2.

See Section 18.3.4.4.2.

PEBS-Precise Store

No, replaced by Data Address
profiling.

Section 18.3.4.4.3

PEBS-PDIR

Yes (using precise
INST_RETIRED.ALL)

Yes (using precise
INST_RETIRED.ALL)

PEBS-EventingIP

Yes

No

Data Address Profiling

Yes

No

LBR Profiling

Yes

Yes

Call Stack Profiling

Yes, see Section 17.11.

No

Off-core Response Event

MSR 1A6H and 1A7H; extended
request and response types.

MSR 1A6H and 1A7H; extended
request and response types.

Intel TSX support for Perfmon

See Section 18.3.6.5.

No

18.3.6.1

Comment

Use LBR facility.

Processor Event Based Sampling (PEBS) Facility

The PEBS facility in the 4th Generation Intel Core processor is similar to those in processors based on Intel microarchitecture code name Sandy Bridge, with several enhanced features. The key components and differences of
PEBS facility relative to Intel microarchitecture code name Sandy Bridge is summarized in Table 18-23.

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PERFORMANCE MONITORING

Table 18-23. PEBS Facility Comparison
Box

Intel® microarchitecture code
name Haswell

Intel® microarchitecture code
name Sandy Bridge

Comment

Valid IA32_PMCx

PMC0-PMC3

PMC0-PMC3

No PEBS on PMC4-PMC7

PEBS Buffer Programming

Section 18.3.1.1.1

Section 18.3.1.1.1

Unchanged

IA32_PEBS_ENABLE Layout

Figure 18-15

Figure 18-29

PEBS record layout

Table 18-24; enhanced fields at
offsets 98H, A0H, A8H, B0H.

Table 18-3; enhanced fields at
offsets 98H, A0H, A8H.

Precise Events

See Table 18-12.

See Table 18-12.

PEBS-Load Latency

See Table 18-13.

Table 18-13

PEBS-Precise Store

No, replaced by data address
profiling.

Yes; see Section 18.3.4.4.3.

PEBS-PDIR

Yes

Yes

PEBS skid from EventingIP

1 (or 2 if micro+macro fusion)

1

SAMPLING Restriction

Small SAV(CountDown) value incur higher overhead than prior
generation.

IA32_PMC4-IA32_PMC7 do not
support PEBS.

IA32_PMC1 only.

Only IA32_PMC0 through IA32_PMC3 support PEBS.

NOTE
PEBS events are only valid when the following fields of IA32_PERFEVTSELx are all zero: AnyThread,
Edge, Invert, CMask.
In a PMU with PDIR capability, PEBS behavior is unpredictable if IA32_PERFEVTSELx or IA32_PMCx
is changed for a PEBS-enabled counter while an event is being counted. To avoid this, changes to
the programming or value of a PEBS-enabled counter should be performed when the counter is
disabled.

18.3.6.2

PEBS Data Format

The PEBS record format for the 4th Generation Intel Core processor is shown in Table 18-24. The PEBS record
format, along with debug/store area storage format, does not change regardless of whether IA-32e mode is active
or not. CPUID.01H:ECX.DTES64[bit 2] reports whether the processor's DS storage format support is mode-independent. When set, it uses 64-bit DS storage format.

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PERFORMANCE MONITORING

Table 18-24. PEBS Record Format for 4th Generation Intel Core Processor Family
Byte Offset

Field

Byte Offset

Field

00H

R/EFLAGS

60H

R10

08H

R/EIP

68H

R11

10H

R/EAX

70H

R12

18H

R/EBX

78H

R13

20H

R/ECX

80H

R14

28H

R/EDX

88H

R15

30H

R/ESI

90H

IA32_PERF_GLOBAL_STATUS

38H

R/EDI

98H

Data Linear Address

40H

R/EBP

A0H

Data Source Encoding

48H

R/ESP

A8H

Latency value (core cycles)

50H

R8

B0H

EventingIP

58H

R9

B8H

TX Abort Information (Section
18.3.6.5.1)

The layout of PEBS records are almost identical to those shown in Table 18-3. Offset B0H is a new field that records
the eventing IP address of the retired instruction that triggered the PEBS assist.
The PEBS records at offsets 98H, A0H, and ABH record data gathered from three of the PEBS capabilities in prior
processor generations: load latency facility (Section 18.3.4.4.2), PDIR (Section 18.3.4.4.4), and the equivalent
capability of precise store in prior generation (see Section 18.3.6.3).
In the core PMU of the 4th generation Intel Core processor, load latency facility and PDIR capabilities are
unchanged. However, precise store is replaced by an enhanced capability, data address profiling, that is not
restricted to store address. Data address profiling also records information in PEBS records at offsets 98H, A0H,
and ABH.

18.3.6.3

PEBS Data Address Profiling

The Data Linear Address facility is also abbreviated as DataLA. The facility is a replacement or extension of the
precise store facility in previous processor generations. The DataLA facility complements the load latency facility by
providing a means to profile load and store memory references in the system, leverages the PEBS facility, and
provides additional information about sampled loads and stores. Having precise memory reference events with
linear address information for both loads and stores provides information to improve data structure layout, eliminate remote node references, and identify cache-line conflicts in NUMA systems.
The DataLA facility in the 4th generation processor supports the following events configured to use PEBS:

Table 18-25. Precise Events That Supports Data Linear Address Profiling
Event Name

Event Name

MEM_UOPS_RETIRED.STLB_MISS_LOADS

MEM_UOPS_RETIRED.STLB_MISS_STORES

MEM_UOPS_RETIRED.LOCK_LOADS

MEM_UOPS_RETIRED.SPLIT_STORES

MEM_UOPS_RETIRED.SPLIT_LOADS

MEM_UOPS_RETIRED.ALL_STORES

MEM_UOPS_RETIRED.ALL_LOADS

MEM_LOAD_UOPS_LLC_MISS_RETIRED.LOCAL_DRAM

MEM_LOAD_UOPS_RETIRED.L1_HIT

MEM_LOAD_UOPS_RETIRED.L2_HIT

MEM_LOAD_UOPS_RETIRED.L3_HIT

MEM_LOAD_UOPS_RETIRED.L1_MISS

MEM_LOAD_UOPS_RETIRED.L2_MISS

MEM_LOAD_UOPS_RETIRED.L3_MISS

MEM_LOAD_UOPS_RETIRED.HIT_LFB

MEM_LOAD_UOPS_L3_HIT_RETIRED.XSNP_MISS

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PERFORMANCE MONITORING

Table 18-25. Precise Events That Supports Data Linear Address Profiling (Contd.)
Event Name

Event Name

MEM_LOAD_UOPS_L3_HIT_RETIRED.XSNP_HIT

MEM_LOAD_UOPS_L3_HIT_RETIRED.XSNP_HITM

UOPS_RETIRED.ALL (if load or store is tagged)

MEM_LOAD_UOPS_LLC_HIT_RETIRED.XSNP_NONE

DataLA can use any one of the IA32_PMC0-IA32_PMC3 counters. Counter overflows will initiate the generation of
PEBS records. Upon counter overflow, hardware captures the linear address and possible other status information
of the retiring memory uop. This information is then written to the PEBS record that is subsequently generated.
To enable the DataLA facility, software must complete the following steps. Please note that the DataLA facility relies
on the PEBS facility, so the PEBS configuration requirements must be completed before attempting to capture
DataLA information.

•
•
•

Complete the PEBS configuration steps.
Program the an event listed in Table 18-25 using any one of IA32_PERFEVTSEL0-IA32_PERFEVTSEL3.
Set the corresponding IA32_PEBS_ENABLE.PEBS_EN_CTRx bit. This enables the corresponding IA32_PMCx as
a PEBS counter and enables the DataLA facility.

When the DataLA facility is enabled, the relevant information written into a PEBS record affects entries at offsets
98H, A0H and A8H, as shown in Table 18-26.

Table 18-26. Layout of Data Linear Address Information In PEBS Record
Field

Offset

Description

Data Linear
Address

98H

The linear address of the load or the destination of the store.

Store Status

A0H

• DCU Hit (Bit 0): The store hit the data cache closest to the core (L1 cache) if this bit is set, otherwise
the store missed the data cache. This information is valid only for the following store events:
UOPS_RETIRED.ALL (if store is tagged),
MEM_UOPS_RETIRED.STLB_MISS_STORES,
MEM_UOPS_RETIRED.SPLIT_STORES, MEM_UOPS_RETIRED.ALL_STORES
• Other bits are zero, The STLB_MISS, LOCK bit information can be obtained by programming the
corresponding store event in Table 18-25.

Reserved

A8H

Always zero.

18.3.6.3.1 EventingIP Record
The PEBS record layout for processors based on Intel microarchitecture code name Haswell adds a new field at
offset 0B0H. This is the eventingIP field that records the IP address of the retired instruction that triggered the
PEBS assist. The EIP/RIP field at offset 08H records the IP address of the next instruction to be executed following
the PEBS assist.

18.3.6.4

Off-core Response Performance Monitoring

The core PMU facility to collect off-core response events are similar to those described in Section 18.3.4.5. The
event codes are listed in Table 18-15. Each event code for off-core response monitoring requires programming an
associated configuration MSR, MSR_OFFCORE_RSP_x. Software must program MSR_OFFCORE_RSP_x according
to:

•
•
•

Transaction request type encoding (bits 15:0): see Table 18-27.
Supplier information (bits 30:16): see Table 18-28.
Snoop response information (bits 37:31): see Table 18-18.

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PERFORMANCE MONITORING

Table 18-27. MSR_OFFCORE_RSP_x Request_Type Definition (Haswell microarchitecture)
Bit Name

Offset Description

DMND_DATA_RD

0

(R/W). Counts the number of demand data reads of full and partial cachelines as well as demand data
page table entry cacheline reads. Does not count L2 data read prefetches or instruction fetches.

DMND_RFO

1

(R/W). Counts the number of demand and DCU prefetch reads for ownership (RFO) requests generated
by a write to data cacheline. Does not count L2 RFO prefetches.

DMND_IFETCH

2

(R/W). Counts the number of demand and DCU prefetch instruction cacheline reads. Does not count L2
code read prefetches.

COREWB

3

(R/W). Counts the number of modified cachelines written back.

PF_DATA_RD

4

(R/W). Counts the number of data cacheline reads generated by L2 prefetchers.

PF_RFO

5

(R/W). Counts the number of RFO requests generated by L2 prefetchers.

PF_IFETCH

6

(R/W). Counts the number of code reads generated by L2 prefetchers.

PF_L3_DATA_RD

7

(R/W). Counts the number of data cacheline reads generated by L3 prefetchers.

PF_L3_RFO

8

(R/W). Counts the number of RFO requests generated by L3 prefetchers.

PF_L3_CODE_RD

9

(R/W). Counts the number of code reads generated by L3 prefetchers.

SPLIT_LOCK_UC_
LOCK

10

(R/W). Counts the number of lock requests that split across two cachelines or are to UC memory.

STRM_ST

11

(R/W). Counts the number of streaming store requests electronically.

Reserved

12-14

Reserved

OTHER

15

(R/W). Any other request that crosses IDI, including I/O.

The supplier information field listed in Table 18-28. The fields vary across products (according to CPUID signatures)
and is noted in the description.

Table 18-28. MSR_OFFCORE_RSP_x Supplier Info Field Definition (CPUID Signature 06_3CH, 06_46H)
Subtype

Bit Name

Offset

Description

Common

Any

16

(R/W). Catch all value for any response types.

Supplier
Info

NO_SUPP

17

(R/W). No Supplier Information available

L3_HITM

18

(R/W). M-state initial lookup stat in L3.

L3_HITE

19

(R/W). E-state

L3_HITS

20

(R/W). S-state

Reserved

21

Reserved

LOCAL

22

(R/W). Local DRAM Controller

Reserved

30:23

Reserved

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Table 18-29. MSR_OFFCORE_RSP_x Supplier Info Field Definition (CPUID Signature 06_45H)
Subtype

Bit Name

Offset

Description

Common

Any

16

(R/W). Catch all value for any response types.

Supplier
Info

NO_SUPP

17

(R/W). No Supplier Information available

L3_HITM

18

(R/W). M-state initial lookup stat in L3.

L3_HITE

19

(R/W). E-state

L3_HITS

20

(R/W). S-state

Reserved

21

Reserved

L4_HIT_LOCAL_L4

22

(R/W). L4 Cache

L4_HIT_REMOTE_HOP0_L4

23

(R/W). L4 Cache

L4_HIT_REMOTE_HOP1_L4

24

(R/W). L4 Cache

L4_HIT_REMOTE_HOP2P_L4

25

(R/W). L4 Cache

Reserved

30:26

Reserved

18.3.6.4.1 Off-core Response Performance Monitoring in Intel Xeon Processors E5 v3 Series
Table 18-28 lists the supplier information field that apply to Intel Xeon processor E5 v3 series (CPUID signature
06_3FH).

Table 18-30. MSR_OFFCORE_RSP_x Supplier Info Field Definition
Subtype

Bit Name

Offset

Description

Common

Any

16

(R/W). Catch all value for any response types.

Supplier
Info

NO_SUPP

17

(R/W). No Supplier Information available

L3_HITM

18

(R/W). M-state initial lookup stat in L3.

L3_HITE

19

(R/W). E-state

L3_HITS

20

(R/W). S-state

L3_HITF

21

(R/W). F-state

LOCAL

22

(R/W). Local DRAM Controller

Reserved

26:23

Reserved

L3_MISS_REMOTE_HOP0

27

(R/W). Hop 0 Remote supplier

L3_MISS_REMOTE_HOP1

28

(R/W). Hop 1 Remote supplier

L3_MISS_REMOTE_HOP2P

29

(R/W). Hop 2 or more Remote supplier

Reserved

30

Reserved

18.3.6.5

Performance Monitoring and Intel® TSX

Chapter 16 of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1 describes the details of
Intel® Transactional Synchronization Extensions (Intel TSX). This section describes performance monitoring
support for Intel TSX.
If a processor supports Intel TSX, the core PMU enhances it’s IA32_PERFEVTSELx MSR with two additional bit fields
for event filtering. Support for Intel TSX is indicated by either (a) CPUID.(EAX=7, ECX=0):RTM[bit 11]=1, or (b) if
CPUID.07H.EBX.HLE [bit 4] = 1. The TSX-enhanced layout of IA32_PERFEVTSELx is shown in Figure 18-34. The
two additional bit fields are:

18-52 Vol. 3B

PERFORMANCE MONITORING

•

IN_TX (bit 32): When set, the counter will only include counts that occurred inside a transactional region,
regardless of whether that region was aborted or committed. This bit may only be set if the processor supports
HLE or RTM.

•

IN_TXCP (bit 33): When set, the counter will not include counts that occurred inside of an aborted transactional region. This bit may only be set if the processor supports HLE or RTM. This bit may only be set for
IA32_PERFEVTSEL2.

When the IA32_PERFEVTSELx MSR is programmed with both IN_TX=0 and IN_TXCP=0 on a processor that
supports Intel TSX, the result in a counter may include detectable conditions associated with a transaction code
region for its aborted execution (if any) and completed execution.
In the initial implementation, software may need to take pre-caution when using the IN_TXCP bit. see Table 2-28.

63

34

Reserved

31

24 23 22 21 20 19 18 17 16 15

8 7

A I
U
Counter Mask I E N
N
N P E O S Unit Mask (UMASK)
(CMASK)
S R
V N Y T C

0
Event Select

USR—User Mode
OS—Operating system mode
E—Edge detect
PC—Pin control
INT—APIC interrupt enable
ANY—Any Thread
EN—Enable counters
INV—Invert counter mask
IN_TX—In Trans. Rgn
IN_TXCP—In Tx exclude abort (PERFEVTSEL2 Only)

Figure 18-34. Layout of IA32_PERFEVTSELx MSRs Supporting Intel TSX
A common usage of setting IN_TXCP=1 is to capture the number of events that were discarded due to a transactional abort. With IA32_PMC2 configured to count in such a manner, then when a transactional region aborts, the
value for that counter is restored to the value it had prior to the aborted transactional region. As a result, any
updates performed to the counter during the aborted transactional region are discarded.
On the other hand, setting IN_TX=1 can be used to drill down on the performance characteristics of transactional
code regions. When a PMCx is configured with the corresponding IA32_PERFEVTSELx.IN_TX=1, only eventing
conditions that occur inside transactional code regions are propagated to the event logic and reflected in the
counter result. Eventing conditions specified by IA32_PERFEVTSELx but occurring outside a transactional region
are discarded. The following example illustrates using three counters to drill down cycles spent inside and outside
of transactional regions:

•

Program IA32_PERFEVTSEL2 to count Unhalted_Core_Cycles with (IN_TXCP=1, IN_TX=0), such that
IA32_PMC2 will count cycles spent due to aborted TSX transactions;

•

Program IA32_PERFEVTSEL0 to count Unhalted_Core_Cycles with (IN_TXCP=0, IN_TX=1), such that
IA32_PMC0 will count cycles spent by the transactional code regions;

•

Program IA32_PERFEVTSEL1 to count Unhalted_Core_Cycles with (IN_TXCP=0, IN_TX=0), such that
IA32_PMC1 will count total cycles spent by the non-transactional code and transactional code regions.

Additionally, a number of performance events are solely focused on characterizing the execution of Intel TSX transactional code, they are listed in Table 19-10.

18.3.6.5.1 Intel TSX and PEBS Support
If a PEBS event would have occurred inside a transactional region, then the transactional region first aborts, and
then the PEBS event is processed.

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PERFORMANCE MONITORING

Two of the TSX performance monitoring events in Table 19-10 also support using PEBS facility to capture additional
information. They are:

•
•

HLE_RETIRED.ABORT ED (encoding C8H mask 04H),
RTM_RETIRED.ABORTED (encoding C9H mask 04H).

A transactional abort (HLE_RETIRED.ABORTED,RTM_RETIRED.ABORTED) can also be programmed to cause PEBS
events. In this scenario, a PEBS event is processed following the abort.
Pending a PEBS record inside of a transactional region will cause a transactional abort. If a PEBS record was pended
at the time of the abort or on an overflow of the TSX PEBS events listed above, only the following PEBS entries will
be valid (enumerated by PEBS entry offset B8H bits[33:32] to indicate an HLE abort or an RTM abort):

•
•

Offset B0H: EventingIP,
Offset B8H: TX Abort Information

These fields are set for all PEBS events.

•

Offset 08H (RIP/EIP) corresponds to the instruction following the outermost XACQUIRE in HLE or the first
instruction of the fallback handler of the outermost XBEGIN instruction in RTM. This is useful to identify the
aborted transactional region.

In the case of HLE, an aborted transaction will restart execution deterministically at the start of the HLE region. In
the case of RTM, an aborted transaction will transfer execution to the RTM fallback handler.
The layout of the TX Abort Information field is given in Table 18-31.

Table 18-31. TX Abort Information Field Definition
Bit Name

Offset

Description

Cycles_Last_TX

31:0

The number of cycles in the last TSX region, regardless of whether that region had aborted or
committed.

HLE_Abort

32

If set, the abort information corresponds to an aborted HLE execution

RTM_Abort

33

If set, the abort information corresponds to an aborted RTM execution

Instruction_Abort

34

If set, the abort was associated with the instruction corresponding to the eventing IP (offset
0B0H) within the transactional region.

Non_Instruction_Abort

35

If set, the instruction corresponding to the eventing IP may not necessarily be related to the
transactional abort.

Retry

36

If set, retrying the transactional execution may have succeeded.

Data_Conflict

37

If set, another logical processor conflicted with a memory address that was part of the
transactional region that aborted.

Capacity Writes

38

If set, the transactional region aborted due to exceeding resources for transactional writes.

Capacity Reads

39

If set, the transactional region aborted due to exceeding resources for transactional reads.

Reserved

63:40

Reserved

18.3.6.6

Uncore Performance Monitoring Facilities in the 4th Generation Intel® Core™ Processors

The uncore sub-system in the 4th Generation Intel® Core™ processors provides its own performance monitoring
facility. The uncore PMU facility provides dedicated MSRs to select uncore performance monitoring events in a
similar manner as those described in Section 18.3.4.6.
The ARB unit and each C-Box provide local pairs of event select MSR and counter register. The layout of the event
select MSRs in the C-Boxes are identical as shown in Figure 18-32.
At the uncore domain level, there is a master set of control MSRs that centrally manages all the performance monitoring facility of uncore units. Figure 18-33 shows the layout of the uncore domain global control.
Additionally, there is also a fixed counter, counting uncore clockticks, for the uncore domain. Table 18-19 summarizes the number MSRs for uncore PMU for each box.

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PERFORMANCE MONITORING

Table 18-32. Uncore PMU MSR Summary
Box

# of Boxes

Counters per
Box

Counter
Width

General
Purpose

Global
Enable

C-Box

SKU specific

2

44

Yes

Per-box

ARB

1

2

44

Yes

Uncore

Fixed Counter

N.A.

N.A.

48

No

Uncore

Comment
Up to 4, seeTable 2-20
MSR_UNC_CBO_CONFIG

The uncore performance events for the C-Box and ARB units are listed in Table 19-11.

18.3.6.7

Intel® Xeon® Processor E5 v3 Family Uncore Performance Monitoring Facility

Details of the uncore performance monitoring facility of Intel Xeon Processor E5 v3 families are available in “Intel®
Xeon® Processor E5 v3 Uncore Performance Monitoring Programming Reference Manual”. The MSR-based uncore
PMU interfaces are listed in Table 2-32.

18.3.7

5th Generation Intel® Core™ Processor and Intel® Core™ M Processor Performance
Monitoring Facility

The 5th Generation Intel® Core™ processor and the Intel® Core™ M processor families are based on the Broadwell
microarchitecture. The core PMU supports architectural performance monitoring capability with version ID 3 (see
Section 18.2.3) and a host of non-architectural monitoring capabilities.
Architectural performance monitoring version 3 capabilities are described in Section 18.2.3.
The core PMU has the same capability as those described in Section 18.3.6. IA32_PERF_GLOBAL_STATUS provide
a bit indicator (bit 55) for PMI handler to distinguish PMI due to output buffer overflow condition due to accumulating packet data from Intel Processor Trace.

63 62 61

55

35 34 33 32 31

8 7 6 5 4 3 2 1 0

CondChgd
Ovf_Buffer
Ovf_UncorePMU
Trace_ToPA_PMI
FIXED_CTR2 Overflow (RO)
FIXED_CTR1 Overflow (RO)
FIXED_CTR0 Overflow (RO)
PMC7_OVF (RO, If PMC7 present)
PMC6_OVF (RO, If PMC6 present)
PMC5_OVF (RO, If PMC5 present)
PMC4_OVF (RO, If PMC4 present)
PMC3_OVF (RO)
PMC2_OVF (RO)
PMC1_OVF (RO)
PMC0_OVF (RO)

Reserved

Valid if CPUID.0AH:EAX[15:8] = 8; else reserved

Figure 18-35. IA32_PERF_GLOBAL_STATUS MSR in Broadwell Microarchitecture
Details of Intel Processor Trace is described in Chapter 35, “Intel® Processor Trace”.
IA32_PERF_GLOBAL_OVF_CTRL MSR provide a corresponding reset control bit.

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PERFORMANCE MONITORING

63 62 61

55

35 34 33 32 31

8 7 6 5 4 3

2 1 0

ClrCondChgd
ClrOvfDSBuffer
ClrOvfUncore
ClrTraceToPA_PMI
FIXED_CTR2 ClrOverflow
FIXED_CTR1 ClrOverflow
FIXED_CTR0 ClrOverflow
PMC7_ClrOvf (if PMC7 present)
PMC6_ClrOvf (if PMC6 present)
PMC5_ClrOvf (if PMC5 present)
PMC4_ClrOvf (if PMC4 present)
PMC3_ClrOvf
PMC2_ClrOvf
PMC1_ClrOvf
PMC0_ClrOvf

Reserved

Valid if CPUID.0AH:EAX[15:8] = 8; else reserved

Figure 18-36. IA32_PERF_GLOBAL_OVF_CTRL MSR in Broadwell microarchitecture
The specifics of non-architectural performance events are listed in Chapter 19, “Performance Monitoring Events”.

18.3.8

6th Generation Intel® Core™ Processor and 7th Generation Intel® Core™ Processor
Performance Monitoring Facility

The 6th generation Intel® Core™ processor is based on the Skylake microarchitecture. The 7th generation Intel®
Core™ processor is based on the Kaby Lake microarchitecture. The core PMU supports architectural performance
monitoring capability with version ID 4 (see Section 18.2.4) and a host of non-architectural monitoring capabilities.
Architectural performance monitoring version 4 capabilities are described in Section 18.2.4.
The core PMU’s capability is similar to those described in Section 18.6.3 through Section 18.3.4.5, with some differences and enhancements summarized in Table 18-22. Additionally, the core PMU provides some enhancement to
support performance monitoring when the target workload contains instruction streams using Intel® Transactional
Synchronization Extensions (TSX), see Section 18.3.6.5. For details of Intel TSX, see Chapter 16, “Programming with
Intel® Transactional Synchronization Extensions” of Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1.
Performance monitoring result may be affected by side-band activity on processors that support Intel SGX, details
are described in Chapter 42, “Enclave Code Debug and Profiling”.

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Table 18-33. Core PMU Comparison
Box

Intel® microarchitecture code name
Skylake and Kaby Lake

Intel® microarchitecture code
name Haswell and Broadwell

# of Fixed counters per thread

3

3

# of general-purpose counters
per core

8

8

Counter width (R,W)

R:48, W: 32/48

R:48, W: 32/48

See Section 18.2.2.

# of programmable counters
per thread

4 or (8 if a core not shared by two
threads)

4 or (8 if a core not shared by two
threads)

CPUID enumerates
# of counters.

Architectural Perfmon version

4

3

See Section 18.2.4

PMI Overhead Mitigation

• Freeze_Perfmon_on_PMI with
streamlined semantics.
• Freeze_on_LBR with streamlined
semantics.
• Freeze_while_SMM.

• Freeze_Perfmon_on_PMI with
legacy semantics.
• Freeze_on_LBR with legacy
semantics for branch profiling.
• Freeze_while_SMM.

See Section 17.4.7.

Comment

Legacy semantics
not supported with
version 4 or higher.

Counter and Buffer Overflow
Status Management

• Query via
• Query via
IA32_PERF_GLOBAL_STATUS
IA32_PERF_GLOBAL_STATUS
• Reset via
• Reset via
IA32_PERF_GLOBAL_OVF_CTRL
IA32_PERF_GLOBAL_STATUS_RESET
• Set via
IA32_PERF_GLOBAL_STATUS_SET

See Section 18.2.4.

IA32_PERF_GLOBAL_STATUS
Indicators of
Overflow/Overhead/Interferen
ce

•
•
•
•

• Individual counter overflow
• PEBS buffer overflow
• ToPA buffer overflow (applicable
to Broadwell microarchitecture)

See Section 18.2.4.

Enable control in
IA32_PERF_GLOBAL_STATUS

• CTR_Frz
• LBR_Frz

NA

See Section
18.2.4.1.

Perfmon Counter In-Use
Indicator

Query IA32_PERF_GLOBAL_INUSE

NA

See Section
18.2.4.3.

Precise Events

See Table 18-36.

See Table 18-12.

IA32_PMC4-PMC7
do not support
PEBS.

PEBS for front end events

See Section 18.3.8.1.4.

No

LBR Record Format Encoding

000101b

000100b

LBR Size

32 entries

16 entries

LBR Entry

From_IP/To_IP/LBR_Info triplet

From_IP/To_IP pair

Section 17.12

LBR Timing

Yes

No

Section 17.12.1

Call Stack Profiling

Yes, see Section 17.11

Yes, see Section 17.11

Use LBR facility

Off-core Response Event

MSR 1A6H and 1A7H; Extended request
and response types.

MSR 1A6H and 1A7H; Extended
request and response types.

Intel TSX support for Perfmon

See Section 18.3.6.5.

See Section 18.3.6.5.

18.3.8.1

Individual counter overflow
PEBS buffer overflow
ToPA buffer overflow
CTR_Frz, LBR_Frz, ASCI

Section 17.4.8.1

Processor Event Based Sampling (PEBS) Facility

The PEBS facility in the 6th and 7th generation Intel Core processors provides a number enhancement relative to
PEBS in processors based on Haswell/Broadwell microarchitectures. The key components and differences of PEBS
facility relative to Haswell/Broadwell microarchitecture is summarized in Table 18-34.

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PERFORMANCE MONITORING

Table 18-34. PEBS Facility Comparison
Box

Intel® microarchitecture code Intel® microarchitecture code
name Skylake and Kaby Lake name Haswell and Broadwell

Comment

Valid IA32_PMCx

PMC0-PMC3

PMC0-PMC3

No PEBS on PMC4-PMC7.

PEBS Buffer Programming

Section 18.3.1.1.1

Section 18.3.1.1.1

Unchanged

IA32_PEBS_ENABLE Layout

Figure 18-15

Figure 18-15

PEBS-EventingIP

Yes

Yes

PEBS record format encoding 0011b

0010b

PEBS record layout

Table 18-35; enhanced fields
at offsets 98H- B8H; and TSC
record field at C0H.

Table 18-24; enhanced fields at
offsets 98H, A0H, A8H, B0H.

Multi-counter PEBS
resolution

PEBS record 90H resolves the
eventing counter overflow.

PEBS record 90H reflects
IA32_PERF_GLOBAL_STATUS.

Precise Events

See Table 18-36.

See Table 18-12.

IA32_PMC4-IA32_PMC7 do not
support PEBS.

PEBS-PDIR

Yes

Yes

IA32_PMC1 only.

PEBS-Load Latency

See Section 18.3.4.4.2.

See Section 18.3.4.4.2.

Data Address Profiling

Yes

Yes

FrontEnd event support

FrontEnd_Retried event and
MSR_PEBS_FRONTEND.

No

IA32_PMC0-PMC3 only.

Only IA32_PMC0 through IA32_PMC3 support PEBS.

NOTES
Precise events are only valid when the following fields of IA32_PERFEVTSELx are all zero:
AnyThread, Edge, Invert, CMask.
In a PMU with PDIR capability, PEBS behavior is unpredictable if IA32_PERFEVTSELx or IA32_PMCx
is changed for a PEBS-enabled counter while an event is being counted. To avoid this, changes to
the programming or value of a PEBS-enabled counter should be performed when the counter is
disabled.

18.3.8.1.1 PEBS Data Format
The PEBS record format for the 6th and 7th generation Intel Core processors is reporting with encoding 0011b in
IA32_PERF_CAPABILITIES[11:8]. The lay out is shown in Table 18-35. The PEBS record format, along with
debug/store area storage format, does not change regardless of whether IA-32e mode is active or not.
CPUID.01H:ECX.DTES64[bit 2] reports whether the processor's DS storage format support is mode-independent.
When set, it uses 64-bit DS storage format.

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PERFORMANCE MONITORING

Table 18-35. PEBS Record Format for 6th Generation Intel Core Processor
and 7th Generation Intel Core Processor Families
Byte Offset

Field

Byte Offset

Field

00H

R/EFLAGS

68H

R11

08H

R/EIP

70H

R12

10H

R/EAX

78H

R13

18H

R/EBX

80H

R14

20H

R/ECX

88H

R15

28H

R/EDX

90H

Applicable Counter

30H

R/ESI

98H

Data Linear Address

38H

R/EDI

A0H

Data Source Encoding

40H

R/EBP

A8H

Latency value (core cycles)

48H

R/ESP

B0H

EventingIP

50H

R8

B8H

TX Abort Information (Section 18.3.6.5.1)

58H

R9

C0H

TSC

60H

R10

The layout of PEBS records are largely identical to those shown in Table 18-24.
The PEBS records at offsets 98H, A0H, and ABH record data gathered from three of the PEBS capabilities in prior
processor generations: load latency facility (Section 18.3.4.4.2), PDIR (Section 18.3.4.4.4), and data address
profiling (Section 18.3.6.3).
In the core PMU of the 6th and 7th generation Intel Core processors, load latency facility and PDIR capabilities and
data address profiling are unchanged relative to the 4th and 5th generation Intel Core processors. Similarly,
precise store is replaced by data address profiling.
With format 0010b, a snapshot of the IA32_PERF_GLOBAL_STATUS may be useful to resolve the situations when
more than one of IA32_PMICx have been configured to collect PEBS data and two consecutive overflows of the
PEBS-enabled counters are sufficiently far apart in time. It is also possible for the image at 90H to indicate multiple
PEBS-enabled counters have overflowed. In the latter scenario, software cannot to correlate the PEBS record entry
to the multiple overflowed bits.
With PEBS record format encoding 0011b, offset 90H reports the “applicable counter” field, which is a multicounter PEBS resolution index allowing software to correlate the PEBS record entry with the eventing PEBS overflow when multiple counters are configured to record PEBS records. Additionally, offset C0H captures a snapshot of
the TSC that provides a time line annotation for each PEBS record entry.

18.3.8.1.2 PEBS Events
The list of precise events supported for PEBS in the Skylake and Kaby Lake microarchitectures is shown in
Table 18-36.

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PERFORMANCE MONITORING

Table 18-36. Precise Events for the Skylake and Kaby Lake Microarchitectures
Event Name

Event Select

INST_RETIRED

C0H

Sub-event

UMask
1

01H

PREC_DIST
2

ALL_CYCLES

01H

OTHER_ASSISTS

C1H

ANY

3FH

BR_INST_RETIRED

C4H

CONDITIONAL

01H

NEAR_CALL

02H

BR_MISP_RETIRED

C5H

FRONTEND_RETIRED

C6H

ALL_BRANCHES

04H

NEAR_RETURN

08H

NEAR_TAKEN

20H

FAR_BRACHES

40H

CONDITIONAL

01H

ALL_BRANCHES

04H

NEAR_TAKEN

20H
3>

 PEBS_Absolute_Maximum. Note that when an out of bound
condition is encountered, the overflow bits in IA32_PERF_GLOBAL_STATUS will be cleared according to Applicable
Counters, however the IA32_PMCx values will not be reloaded with the Reset values stored in the DS_AREA.

18.5.3.2

Offcore Response Event

Event number 0B7H support offcore response monitoring using an associated configuration MSR,
MSR_OFFCORE_RSP0 (address 1A6H) in conjunction with umask value 01H or MSR_OFFCORE_RSP1 (address
1A7H) in conjunction with umask value 02H. Table 18-51 lists the event code, mask value and additional off-core
configuration MSR that must be programmed to count off-core response events using IA32_PMCx.
The Goldmont microarchitecture provides unique pairs of MSR_OFFCORE_RSPx registers per core.
The layout of MSR_OFFCORE_RSP0 and MSR_OFFCORE_RSP1 are organized as follows:

•
•
•

Bits 15:0 specifies the request type of a transaction request to the uncore. This is described in Table 18-58.

•

For outstanding requests, bit 38 can enable measurement of average latency of specific type of offcore
transaction requests using two programmable counter simultaneously; see Section 18.5.2.3 for details.

Bits 30:16 specifies common supplier information or an L2 Hit, and is described in Table 18-53.
If L2 misses, then Bits 37:31 can be used to specify snoop response information and is described in
Table 18-59.

Table 18-58. MSR_OFFCORE_RSPx Request_Type Field Definition
Bit Name

Offset

Description

DEMAND_DATA_RD

0

(R/W) Counts cacheline read requests due to demand reads (excludes prefetches).

DEMAND_RFO

1

(R/W) Counts cacheline read for ownership (RFO) requests due to demand writes
(excludes prefetches).

DEMAND_CODE_RD

2

(R/W) Counts demand instruction cacheline and I-side prefetch requests that miss the
instruction cache.

COREWB

3

(R/W) Counts writeback transactions caused by L1 or L2 cache evictions.

PF_L2_DATA_RD

4

(R/W) Counts data cacheline reads generated by hardware L2 cache prefetcher.

PF_L2_RFO

5

(R/W) Counts reads for ownership (RFO) requests generated by L2 prefetcher.

Reserved

6

Reserved.

PARTIAL_READS

7

(R/W) Counts demand data partial reads, including data in uncacheable (UC) or
uncacheable (WC) write combining memory types.

PARTIAL_WRITES

8

(R/W) Counts partial writes, including uncacheable (UC), write through (WT) and write
protected (WP) memory type writes.

UC_CODE_READS

9

(R/W) Counts code reads in uncacheable (UC) memory region.

BUS_LOCKS

10

(R/W) Counts bus lock and split lock requests.

FULL_STREAMING_STORES

11

(R/W) Counts full cacheline writes due to streaming stores.

SW_PREFETCH

12

(R/W) Counts cacheline requests due to software prefetch instructions.

PF_L1_DATA_RD

13

(R/W) Counts data cacheline reads generated by hardware L1 data cache prefetcher.

PARTIAL_STREAMING_STORES

14

(R/W) Counts partial cacheline writes due to streaming stores.
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Table 18-58. MSR_OFFCORE_RSPx Request_Type Field Definition (Contd.)
Bit Name

Offset

Description

ANY_REQUEST

15

(R/W) Counts requests to the uncore subsystem.

To properly program this extra register, software must set at least one request type bit (Table 18-52) and a valid
response type pattern (either Table 18-53 or Table 18-59). Otherwise, the event count reported will be zero. It is
permissible and useful to set multiple request and response type bits in order to obtain various classes of off-core
response events. Although MSR_OFFCORE_RSPx allow an agent software to program numerous combinations that
meet the above guideline, not all combinations produce meaningful data.

Table 18-59. MSR_OFFCORE_RSPx For L2 Miss and Outstanding Requests
Subtype

Bit Name

Offset

Description

L2_MISS
(Snoop Info)

Reserved

32:31

Reserved

L2_MISS.SNOOP_MISS_O 33
R_NO_SNOOP_NEEDED

(R/W). A true miss to this module, for which a snoop request missed the other
module or no snoop was performed/needed.

L2_MISS.HIT_OTHER_CO
RE_NO_FWD

34

(R/W) A snoop hit in the other processor module, but no data forwarding is
required.

Reserved

35

Reserved

L2_MISS.HITM_OTHER_C 36
ORE

(R/W) Counts the number of snoops hit in the other module or other core's L1
where modified copies were found.

L2_MISS.NON_DRAM

37

(R/W) Target was a non-DRAM system address. This includes MMIO transactions.

38

(R/W) Counts weighted cycles of outstanding offcore requests of the request type
specified in bits 15:0, from the time the XQ receives the request and any
response is received. Bits 37:16 must be set to 0. This bit is only available in
MSR_OFFCORE_RESP0.

Outstanding OUTSTANDING
requests1

NOTES:
1. See Section 18.5.2.3, “Average Offcore Request Latency Measurement” for details on how to use this bit to extract average latency.
To specify a complete offcore response filter, software must properly program bits in the request and response type
fields. A valid request type must have at least one bit set in the non-reserved bits of 15:0. A valid response type
must be a non-zero value of the following expression:
[ANY ‘OR’ (L2 Hit) ] ‘XOR’ ( Snoop Info Bits) ‘XOR’ (Avg Latency)

18.5.3.3

Average Offcore Request Latency Measurement

In Goldmont microarchitecture, measurement of average latency of offcore transaction requests is the same as
described in Section 18.5.2.3.

18.5.4

Performance Monitoring for Goldmont Plus Microarchitecture

Intel Atom processors based on the Goldmont Plus microarchitecture report architectural performance monitoring
versionID = 4 and support non-architectural monitoring capabilities described in this section.
Architectural performance monitoring version 4 capabilities are described in Section 18.2.4.
Goldmont Plus performance monitoring capabilities are similar to Goldmont capabilities. The differences are in
specific events and in which counters support PEBS. Goldmont Plus introduces the ability for fixed performance
monitoring counters to generate PEBS records.
Goldmont Plus will set the AnyThread deprecation CPUID bit (CPUID.0AH:EDX[15]) to indicate that the Any-Thread
bits in IA32_PERFEVTSELx and IA32_FIXED_CTR_CTRL have no effect.

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The core PMU's capability is similar to that of the Goldmont microarchitecture described in Section 18.6.3, with
some differences and enhancements summarized in Table 18-60.

Table 18-60. Core PMU Comparison Between the Goldmont Plus and Goldmont Microarchitectures
Box

Goldmont Plus Microarchitecture

Goldmont Microarchitecture

Comment

# of Fixed counters per core

3

3

No change.

# of general-purpose
counters per core

4

4

No change.

Counter width (R,W)

R:48, W: 32/48

R:48, W: 32/48

No change.

Architectural Performance
Monitoring version ID

4

4

No change.

Processor Event Based
Sampling (PEBS) Events

All General-Purpose and Fixed
counters. Each General-Purpose
counter supports all events (precise
and non-precise).

General-Purpose Counter 0 only.
Supports all events (precise and
non-precise). Precise events are
listed in Table 18-56.

Goldmont Plus supports
PEBS on all counters.

PEBS record format
encoding

0011b

0011b

No change.

18.5.4.1

Extended PEBS

The Extended PEBS feature, introduced in Goldmont Plus microarchitecture, supports PEBS (Processor Event
Based Sampling) on a fixed-function performance counters as well as all four general purpose counters (PMC0-3).
PEBS can be enabled for the four general purpose counters using PEBS_EN_PMCi bits of IA32_PEBS_ENABLE (i =
0, 1, 2, 3). PEBS can be enabled for the 3 fixed function counters using the PEBS_EN_FIXEDi bits of
IA32_PEBS_ENABLE (I = 0, 1, 2).

35 34 33 32 31

63

8 7 6 5 43 2 1 0

PEBS_EN_FIXED2 (R/W)
PEBS_EN_FIXED1 (R/W)
PEBS_EN_FIXED0 (R/W)
PEBS_EN_PMC3 (R/W)
PEBS_EN_PMC2 (R/W)
PEBS_EN_PMC1 (R/W)
PEBS_EN_PMC0 (R/W)

Reserved

RESET Value — 00000000_00000000H

Figure 18-39. Layout of IA32_PEBS_ENABLE MSR
Similar to Goldmont microarchitecture, Goldmont Plus microarchitecture processors can generate PEBS record
events on both precise as well as non-precise events.
A PEBS record due to a precise event will be generated after an instruction that causes the event when the counter
has already overflowed. A PEBS record due to a non-precise event will occur at the next opportunity after the
counter has overflowed, including immediately after an overflow is set by an MSR write.
IA32_FIXED_CTR0 counts instructions retired and is a precise event. IA32_FIXED_CTR1 counts unhalted core
cycles and is a non-precise event. IA32_FIXED_CTR2 counts unhalted reference cycles and is a non-precise event.
The Applicable Counter field at offset 90H of the PEBS record indicates which counters caused the PEBS record to
be generated. It is in the same format as the enable bits for each counter in IA32_PEBS_ENABLE. As an example,
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an Applicable Counter field with bits 2 and 32 set would indicate that both general purpose counter 2 and fixed
function counter 0 generated the PEBS record.

•

To properly use PEBS for the additional counters, software will need to set up the counter reset values in PEBS
portion of the DS_BUFFER_MANAGEMENT_AREA data structure that is indicated by the IA32_DS_AREA
register. The layout of the DS_BUFFER_MANAGEMENT_AREA for Goldmont Plus is shown in Figure 18-40. When
a counter generates a PEBS records, the appropriate counter reset values will be loaded into that counter. In
the above example where general purpose counter 2 and fixed function counter 0 generated the PEBS record,
general purpose counter 2 would be reloaded with the value contained in PEBS GP Counter 2 Reset (offset 50H)
and fixed function counter 0 would be reloaded with the value contained in PEBS Fixed Counter 0 Reset (offset
80H).

IA32_DS_AREA MSR

BTS Buffer

DS Buffer Management
63

BTS Buffer Base

0

00H
08H

BTS Absolute Maximum

10H

BTS Interrupt Threshold

18H

PEBS Buffer Base

20H

PEBS Index

28H

PEBS Absolute Maximum

30H

PEBS Interrupt Threshold

38H

PEBS GP Counter 0 Reset

40H

PEBS GP Counter 1 Reset

48H

PEBS GP Counter 2 Reset

50H

PEBS GP Counter 3 Reset

58H

Reserved

60H

Reserved

68H

Reserved

70H

Reserved

78H

PEBS Fixed Counter 0 Reset

80H

PEBS Fixed Counter 1 Reset

88H

PEBS Fixed Counter 2 Reset

90H

Branch Record 0

Branch Record 1

Branch Record n

PEBS Config Buffer

BTS Index

PEBS Buffer
PEBS Record 0

PEBS Record 1

PEBS Record n

Figure 18-40. PEBS Programming Environment

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18.5.4.2

Reduced Skid PEBS

Goldmont Plus microarchitecture processors supports the Reduced Skid PEBS feature described in Section
18.5.3.1.2 on the IA32_PMC0 counter. Although Goldmont Plus adds support for generating PEBS records for
precise events on the other general-purpose and fixed-function performance counters, those counters do not
support the Reduced Skid PEBS feature.

18.6

PERFORMANCE MONITORING (LEGACY INTEL PROCESSORS)

18.6.1

Performance Monitoring (Intel® Core™ Solo and Intel® Core™ Duo Processors)

In Intel Core Solo and Intel Core Duo processors, non-architectural performance monitoring events are
programmed using the same facilities (see Figure 18-1) used for architectural performance events.
Non-architectural performance events use event select values that are model-specific. Event mask (Umask) values
are also specific to event logic units. Some microarchitectural conditions detectable by a Umask value may have
specificity related to processor topology (see Section 8.6, “Detecting Hardware Multi-Threading Support and
Topology,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A). As a result, the unit
mask field (for example, IA32_PERFEVTSELx[bits 15:8]) may contain sub-fields that specify topology information
of processor cores.
The sub-field layout within the Umask field may support two-bit encoding that qualifies the relationship between a
microarchitectural condition and the originating core. This data is shown in Table 18-61. The two-bit encoding for
core-specificity is only supported for a subset of Umask values (see Chapter 19, “Performance Monitoring Events”)
and for Intel Core Duo processors. Such events are referred to as core-specific events.

Table 18-61. Core Specificity Encoding within a Non-Architectural Umask
IA32_PERFEVTSELx MSRs
Bit 15:14 Encoding

Description

11B

All cores

10B

Reserved

01B

This core

00B

Reserved

Some microarchitectural conditions allow detection specificity only at the boundary of physical processors. Some
bus events belong to this category, providing specificity between the originating physical processor (a bus agent)
versus other agents on the bus. Sub-field encoding for agent specificity is shown in Table 18-62.

Table 18-62. Agent Specificity Encoding within a Non-Architectural Umask
IA32_PERFEVTSELx MSRs
Bit 13 Encoding

Description

0

This agent

1

Include all agents

Some microarchitectural conditions are detectable only from the originating core. In such cases, unit mask does
not support core-specificity or agent-specificity encodings. These are referred to as core-only conditions.
Some microarchitectural conditions allow detection specificity that includes or excludes the action of hardware
prefetches. A two-bit encoding may be supported to qualify hardware prefetch actions. Typically, this applies only
to some L2 or bus events. The sub-field encoding for hardware prefetch qualification is shown in Table 18-63.

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Table 18-63. HW Prefetch Qualification Encoding within a Non-Architectural Umask
IA32_PERFEVTSELx MSRs
Bit 13:12 Encoding

Description

11B

All inclusive

10B

Reserved

01B

Hardware prefetch only

00B

Exclude hardware prefetch

Some performance events may (a) support none of the three event-specific qualification encodings (b) may
support core-specificity and agent specificity simultaneously (c) or may support core-specificity and hardware
prefetch qualification simultaneously. Agent-specificity and hardware prefetch qualification are mutually exclusive.
In addition, some L2 events permit qualifications that distinguish cache coherent states. The sub-field definition for
cache coherency state qualification is shown in Table 18-64. If no bits in the MESI qualification sub-field are set for
an event that requires setting MESI qualification bits, the event count will not increment.

Table 18-64. MESI Qualification Definitions within a Non-Architectural Umask
IA32_PERFEVTSELx MSRs
Bit Position 11:8

Description

Bit 11

Counts modified state

Bit 10

Counts exclusive state

Bit 9

Counts shared state

Bit 8

Counts Invalid state

18.6.2

Performance Monitoring (Processors Based on Intel® Core™ Microarchitecture)

In addition to architectural performance monitoring, processors based on the Intel Core microarchitecture support
non-architectural performance monitoring events.
Architectural performance events can be collected using general-purpose performance counters. Non-architectural
performance events can be collected using general-purpose performance counters (coupled with two
IA32_PERFEVTSELx MSRs for detailed event configurations), or fixed-function performance counters (see Section
18.6.2.1). IA32_PERFEVTSELx MSRs are architectural; their layout is shown in Figure 18-1. Starting with Intel
Core 2 processor T 7700, fixed-function performance counters and associated counter control and status MSR
becomes part of architectural performance monitoring version 2 facilities (see also Section 18.2.2).
Non-architectural performance events in processors based on Intel Core microarchitecture use event select values
that are model-specific. Valid event mask (Umask) bits are listed in Chapter 19. The UMASK field may contain subfields identical to those listed in Table 18-61, Table 18-62, Table 18-63, and Table 18-64. One or more of these subfields may apply to specific events on an event-by-event basis. Details are listed in Table 19-25 in Chapter 19,
“Performance Monitoring Events.”
In addition, the UMASK filed may also contain a sub-field that allows detection specificity related to snoop
responses. Bits of the snoop response qualification sub-field are defined in Table 18-65.

Table 18-65. Bus Snoop Qualification Definitions within a Non-Architectural Umask
IA32_PERFEVTSELx MSRs
Bit Position 11:8

Description

Bit 11

HITM response

Bit 10

Reserved

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Table 18-65. Bus Snoop Qualification Definitions within a Non-Architectural Umask
IA32_PERFEVTSELx MSRs
Bit Position 11:8

Description

Bit 9

HIT response

Bit 8

CLEAN response

There are also non-architectural events that support qualification of different types of snoop operation. The corresponding bit field for snoop type qualification are listed in Table 18-66.

Table 18-66. Snoop Type Qualification Definitions within a Non-Architectural Umask
IA32_PERFEVTSELx MSRs
Bit Position 9:8

Description

Bit 9

CMP2I snoops

Bit 8

CMP2S snoops

No more than one sub-field of MESI, snoop response, and snoop type qualification sub-fields can be supported in a
performance event.

NOTE
Software must write known values to the performance counters prior to enabling the counters. The
content of general-purpose counters and fixed-function counters are undefined after INIT or
RESET.

18.6.2.1

Fixed-function Performance Counters

Processors based on Intel Core microarchitecture provide three fixed-function performance counters. Bits beyond
the width of the fixed counter are reserved and must be written as zeros. Model-specific fixed-function performance counters on processors that support Architectural Perfmon version 1 are 40 bits wide.
Each of the fixed-function counter is dedicated to count a pre-defined performance monitoring events. See Table
18-2 for details of the PMC addresses and what these events count.
Programming the fixed-function performance counters does not involve any of the IA32_PERFEVTSELx MSRs, and
does not require specifying any event masks. Instead, the MSR MSR_PERF_FIXED_CTR_CTRL provides multiple
sets of 4-bit fields; each 4-bit field controls the operation of a fixed-function performance counter (PMC). See
Figures 18-41. Two sub-fields are defined for each control. See Figure 18-41; bit fields are:

•

Enable field (low 2 bits in each 4-bit control) — When bit 0 is set, performance counting is enabled in the
corresponding fixed-function performance counter to increment when the target condition associated with the
architecture performance event occurs at ring 0.
When bit 1 is set, performance counting is enabled in the corresponding fixed-function performance counter to
increment when the target condition associated with the architecture performance event occurs at ring greater
than 0.
Writing 0 to both bits stops the performance counter. Writing 11B causes the counter to increment irrespective
of privilege levels.

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PERFORMANCE MONITORING

63

12 11

9 8 7

P
M
I

P
M
I

E
N

5 43 2 1 0
E
N

P
M
I

E
N

Cntr2 — Controls for MSR_PERF_FIXED_CTR2
Cntr1 — Controls for MSR_PERF_FIXED_CTR1
PMI — Enable PMI on overflow
Cntr0 — Controls for MSR_PERF_FIXED_CTR0
ENABLE — 0: disable; 1: OS; 2: User; 3: All ring levels

Reserved

Figure 18-41. Layout of MSR_PERF_FIXED_CTR_CTRL MSR

•

PMI field (fourth bit in each 4-bit control) — When set, the logical processor generates an exception
through its local APIC on overflow condition of the respective fixed-function counter.

18.6.2.2

Global Counter Control Facilities

Processors based on Intel Core microarchitecture provides simplified performance counter control that simplifies
the most frequent operations in programming performance events, i.e. enabling/disabling event counting and
checking the status of counter overflows. This is done by the following three MSRs:

•

MSR_PERF_GLOBAL_CTRL enables/disables event counting for all or any combination of fixed-function PMCs
(MSR_PERF_FIXED_CTRx) or general-purpose PMCs via a single WRMSR.

•

MSR_PERF_GLOBAL_STATUS allows software to query counter overflow conditions on any combination of
fixed-function PMCs (MSR_PERF_FIXED_CTRx) or general-purpose PMCs via a single RDMSR.

•

MSR_PERF_GLOBAL_OVF_CTRL allows software to clear counter overflow conditions on any combination of
fixed-function PMCs (MSR_PERF_FIXED_CTRx) or general-purpose PMCs via a single WRMSR.

MSR_PERF_GLOBAL_CTRL MSR provides single-bit controls to enable counting in each performance counter (see
Figure 18-42). Each enable bit in MSR_PERF_GLOBAL_CTRL is AND’ed with the enable bits for all privilege levels in
the respective IA32_PERFEVTSELx or MSR_PERF_FIXED_CTR_CTRL MSRs to start/stop the counting of respective
counters. Counting is enabled if the AND’ed results is true; counting is disabled when the result is false.

63

35 34 33 32 31

2 10

FIXED_CTR2 enable
FIXED_CTR1 enable
FIXED_CTR0 enable
PMC1 enable
PMC0 enable

Reserved

Figure 18-42. Layout of MSR_PERF_GLOBAL_CTRL MSR
MSR_PERF_GLOBAL_STATUS MSR provides single-bit status used by software to query the overflow condition of
each performance counter. MSR_PERF_GLOBAL_STATUS[bit 62] indicates overflow conditions of the DS area data
buffer. MSR_PERF_GLOBAL_STATUS[bit 63] provides a CondChgd bit to indicate changes to the state of performance monitoring hardware (see Figure 18-43). A value of 1 in bits 34:32, 1, 0 indicates an overflow condition has

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PERFORMANCE MONITORING

occurred in the associated counter.

63 62

35 34 33 32 31

2 10

CondChgd
OvfBuffer
FIXED_CTR2 Overflow
FIXED_CTR1 Overflow
FIXED_CTR0 Overflow
PMC1 Overflow
PMC0 Overflow

Reserved

Figure 18-43. Layout of MSR_PERF_GLOBAL_STATUS MSR
When a performance counter is configured for PEBS, an overflow condition in the counter will arm PEBS. On the
subsequent event following overflow, the processor will generate a PEBS event. On a PEBS event, the processor will
perform bounds checks based on the parameters defined in the DS Save Area (see Section 17.4.9). Upon
successful bounds checks, the processor will store the data record in the defined buffer area, clear the counter
overflow status, and reload the counter. If the bounds checks fail, the PEBS will be skipped entirely. In the event
that the PEBS buffer fills up, the processor will set the OvfBuffer bit in MSR_PERF_GLOBAL_STATUS.
MSR_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow the indicators for general-purpose or fixedfunction counters via a single WRMSR (see Figure 18-44). Clear overflow indications when:

•
•
•

Setting up new values in the event select and/or UMASK field for counting or interrupt-based event sampling.
Reloading counter values to continue collecting next sample.
Disabling event counting or interrupt-based event sampling.

63 62

35 34 33 32 31

2 1 0

ClrCondChgd
ClrOvfBuffer
FIXED_CTR2 ClrOverflow
FIXED_CTR1 ClrOverflow
FIXED_CTR0 ClrOverflow
PMC1 ClrOverflow
PMC0 ClrOverflow

Reserved

Figure 18-44. Layout of MSR_PERF_GLOBAL_OVF_CTRL MSR

18.6.2.3

At-Retirement Events

Many non-architectural performance events are impacted by the speculative nature of out-of-order execution. A
subset of non-architectural performance events on processors based on Intel Core microarchitecture are enhanced
with a tagging mechanism (similar to that found in Intel NetBurst® microarchitecture) that exclude contributions
that arise from speculative execution. The at-retirement events available in processors based on Intel Core microarchitecture does not require special MSR programming control (see Section 18.6.3.6, “At-Retirement Counting”),
but is limited to IA32_PMC0. See Table 18-67 for a list of events available to processors based on Intel Core microarchitecture.

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Table 18-67. At-Retirement Performance Events for Intel Core Microarchitecture
Event Name

UMask

Event Select

ITLB_MISS_RETIRED

00H

C9H

MEM_LOAD_RETIRED.L1D_MISS

01H

CBH

MEM_LOAD_RETIRED.L1D_LINE_MISS

02H

CBH

MEM_LOAD_RETIRED.L2_MISS

04H

CBH

MEM_LOAD_RETIRED.L2_LINE_MISS

08H

CBH

MEM_LOAD_RETIRED.DTLB_MISS

10H

CBH

18.6.2.4

Processor Event Based Sampling (PEBS)

Processors based on Intel Core microarchitecture also support processor event based sampling (PEBS). This
feature was introduced by processors based on Intel NetBurst microarchitecture.
PEBS uses a debug store mechanism and a performance monitoring interrupt to store a set of architectural state
information for the processor. The information provides architectural state of the instruction executed after the
instruction that caused the event (See Section 18.6.2.4.2 and Section 17.4.9).
In cases where the same instruction causes BTS and PEBS to be activated, PEBS is processed before BTS are
processed. The PMI request is held until the processor completes processing of PEBS and BTS.
For processors based on Intel Core microarchitecture, precise events that can be used with PEBS are listed in
Table 18-68. The procedure for detecting availability of PEBS is the same as described in Section 18.6.3.8.1.

Table 18-68. PEBS Performance Events for Intel Core Microarchitecture
Event Name

UMask

Event Select

INSTR_RETIRED.ANY_P

00H

C0H

X87_OPS_RETIRED.ANY

FEH

C1H

BR_INST_RETIRED.MISPRED

00H

C5H

SIMD_INST_RETIRED.ANY

1FH

C7H

MEM_LOAD_RETIRED.L1D_MISS

01H

CBH

MEM_LOAD_RETIRED.L1D_LINE_MISS

02H

CBH

MEM_LOAD_RETIRED.L2_MISS

04H

CBH

MEM_LOAD_RETIRED.L2_LINE_MISS

08H

CBH

MEM_LOAD_RETIRED.DTLB_MISS

10H

CBH

18.6.2.4.1 Setting up the PEBS Buffer
For processors based on Intel Core microarchitecture, PEBS is available using IA32_PMC0 only. Use the following
procedure to set up the processor and IA32_PMC0 counter for PEBS:
1. Set up the precise event buffering facilities. Place values in the precise event buffer base, precise event index,
precise event absolute maximum, precise event interrupt threshold, and precise event counter reset fields of
the DS buffer management area. In processors based on Intel Core microarchitecture, PEBS records consist of
64-bit address entries. See Figure 17-8 to set up the precise event records buffer in memory.
2. Enable PEBS. Set the Enable PEBS on PMC0 flag (bit 0) in IA32_PEBS_ENABLE MSR.
3. Set up the IA32_PMC0 performance counter and IA32_PERFEVTSEL0 for an event listed in Table 18-68.

18.6.2.4.2 PEBS Record Format
The PEBS record format may be extended across different processor implementations. The
IA32_PERF_CAPABILITES MSR defines a mechanism for software to handle the evolution of PEBS record format in
processors that support architectural performance monitoring with version id equals 2 or higher. The bit fields of
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IA32_PERF_CAPABILITES are defined in Table 2-2 of Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64
and IA-32 Architectures Software Developer’s Manual, Volume 4. The relevant bit fields that governs PEBS are:

•

PEBSTrap [bit 6]: When set, PEBS recording is trap-like. After the PEBS-enabled counter has overflowed, PEBS
record is recorded for the next PEBS-able event at the completion of the sampled instruction causing the PEBS
event. When clear, PEBS recording is fault-like. The PEBS record is recorded before the sampled instruction
causing the PEBS event.

•

PEBSSaveArchRegs [bit 7]: When set, PEBS will save architectural register and state information according to
the encoded value of the PEBSRecordFormat field. When clear, only the return instruction pointer and flags are
recorded. On processors based on Intel Core microarchitecture, this bit is always 1

•

PEBSRecordFormat [bits 11:8]: Valid encodings are:
— 0000B: Only general-purpose registers, instruction pointer and RFLAGS registers are saved in each PEBS
record (seeSection 18.6.3.8).
— 0001B: PEBS record includes additional information of IA32_PERF_GLOBAL_STATUS and load latency data.
(seeSection 18.3.1.1.1).
— 0010B: PEBS record includes additional information of IA32_PERF_GLOBAL_STATUS, load latency data,
and TSX tuning information. (seeSection 18.3.6.2).
— 0011B: PEBS record includes additional information of load latency data, TSX tuning information, TSC data,
and the applicable counter field replaces IA32_PERF_GLOBAL_STATUS at offset 90H. (see Section
18.3.8.1.1).

18.6.2.4.3 Writing a PEBS Interrupt Service Routine
The PEBS facilities share the same interrupt vector and interrupt service routine (called the DS ISR) with the Interrupt-based event sampling and BTS facilities. To handle PEBS interrupts, PEBS handler code must be included in
the DS ISR. See Section 17.4.9.1, “64 Bit Format of the DS Save Area,” for guidelines when writing the DS ISR.
The service routine can query MSR_PERF_GLOBAL_STATUS to determine which counter(s) caused of overflow
condition. The service routine should clear overflow indicator by writing to MSR_PERF_GLOBAL_OVF_CTL.
A comparison of the sequence of requirements to program PEBS for processors based on Intel Core and Intel
NetBurst microarchitectures is listed in Table 18-69.

Table 18-69. Requirements to Program PEBS
For Processors based on Intel Core
microarchitecture

For Processors based on Intel NetBurst
microarchitecture

Verify PEBS support of
processor/OS.

• IA32_MISC_ENABLE.EMON_AVAILABE (bit 7) is set.
• IA32_MISC_ENABLE.PEBS_UNAVAILABE (bit 12) is clear.

Ensure counters are in disabled.

On initial set up or changing event configurations,
write MSR_PERF_GLOBAL_CTRL MSR (38FH) with 0.

Optional

On subsequent entries:
• Clear all counters if “Counter Freeze on PMI“ is not
enabled.
• If IA32_DebugCTL.Freeze is enabled, counters are
automatically disabled.
Counters MUST be stopped before writing.1
Disable PEBS.

Clear ENABLE PMC0 bit in IA32_PEBS_ENABLE MSR
(3F1H).

Optional

Check overflow conditions.

Check MSR_PERF_GLOBAL_STATUS MSR (38EH)
handle any overflow conditions.

Check OVF flag of each CCCR for overflow
condition

Clear overflow status.

Clear MSR_PERF_GLOBAL_STATUS MSR (38EH)
using IA32_PERF_GLOBAL_OVF_CTRL MSR (390H).

Clear OVF flag of each CCCR.

Write “sample-after“ values.

Configure the counter(s) with the sample after value.

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Table 18-69. Requirements to Program PEBS (Contd.)
For Processors based on Intel Core
microarchitecture

For Processors based on Intel NetBurst
microarchitecture

Configure specific counter
configuration MSR.

• Set local enable bit 22 - 1.
• Do NOT set local counter PMI/INT bit, bit 20 - 0.
• Event programmed must be PEBS capable.

• Set appropriate OVF_PMI bits - 1.
• Only CCCR for MSR_IQ_COUNTER4
support PEBS.

Allocate buffer for PEBS states.

Allocate a buffer in memory for the precise information.

Program the IA32_DS_AREA MSR. Program the IA32_DS_AREA MSR.
Configure the PEBS buffer
management records.

Configure the PEBS buffer management records in the DS buffer management area.

Configure/Enable PEBS.

Set Enable PMC0 bit in IA32_PEBS_ENABLE MSR
(3F1H).

Configure MSR_PEBS_ENABLE,
MSR_PEBS_MATRIX_VERT and
MSR_PEBS_MATRIX_HORZ as needed.

Enable counters.

Set Enable bits in MSR_PERF_GLOBAL_CTRL MSR
(38FH).

Set each CCCR enable bit 12 - 1.

NOTES:
1. Counters read while enabled are not guaranteed to be precise with event counts that occur in timing proximity to the RDMSR.

18.6.2.4.4 Re-configuring PEBS Facilities
When software needs to reconfigure PEBS facilities, it should allow a quiescent period between stopping the prior
event counting and setting up a new PEBS event. The quiescent period is to allow any latent residual PEBS records
to complete its capture at their previously specified buffer address (provided by IA32_DS_AREA).

18.6.3

Performance Monitoring (Processors Based on Intel NetBurst® Microarchitecture)

The performance monitoring mechanism provided in processors based on Intel NetBurst microarchitecture is
different from that provided in the P6 family and Pentium processors. While the general concept of selecting,
filtering, counting, and reading performance events through the WRMSR, RDMSR, and RDPMC instructions is
unchanged, the setup mechanism and MSR layouts are incompatible with the P6 family and Pentium processor
mechanisms. Also, the RDPMC instruction has been extended to support faster reading of counters and to read all
performance counters available in processors based on Intel NetBurst microarchitecture.
The event monitoring mechanism consists of the following facilities:

•

The IA32_MISC_ENABLE MSR, which indicates the availability in an Intel 64 or IA-32 processor of the
performance monitoring and processor event-based sampling (PEBS) facilities.

•

Event selection control (ESCR) MSRs for selecting events to be monitored with specific performance counters.
The number available differs by family and model (43 to 45).

•
•

18 performance counter MSRs for counting events.

•
•
•

A debug store (DS) save area in memory for storing PEBS records.

•

The MSR_PEBS_ENABLE MSR, which enables the PEBS facilities and replay tagging used in at-retirement event
counting.

•

A set of predefined events and event metrics that simplify the setting up of the performance counters to count
specific events.

18 counter configuration control (CCCR) MSRs, with one CCCR associated with each performance counter.
CCCRs sets up an associated performance counter for a specific method of counting.
The IA32_DS_AREA MSR, which establishes the location of the DS save area.
The debug store (DS) feature flag (bit 21) returned by the CPUID instruction, which indicates the availability of
the DS mechanism.

Table 18-70 lists the performance counters and their associated CCCRs, along with the ESCRs that select events to
be counted for each performance counter. Predefined event metrics and events are listed in Chapter 19, “Perfor18-90 Vol. 3B

PERFORMANCE MONITORING

mance Monitoring Events.”

Table 18-70. Performance Counter MSRs and Associated CCCR and
ESCR MSRs (Processors Based on Intel NetBurst Microarchitecture)
Counter

CCCR

ESCR

Name

No.

Addr

Name

Addr

Name

No.

Addr

MSR_BPU_COUNTER0

0

300H

MSR_BPU_CCCR0

360H

MSR_BSU_ESCR0
MSR_FSB_ESCR0
MSR_MOB_ESCR0
MSR_PMH_ESCR0
MSR_BPU_ESCR0
MSR_IS_ESCR0
MSR_ITLB_ESCR0
MSR_IX_ESCR0

7
6
2
4
0
1
3
5

3A0H
3A2H
3AAH
3ACH
3B2H
3B4H
3B6H
3C8H

MSR_BPU_COUNTER1

1

301H

MSR_BPU_CCCR1

361H

MSR_BSU_ESCR0
MSR_FSB_ESCR0
MSR_MOB_ESCR0
MSR_PMH_ESCR0
MSR_BPU_ESCR0
MSR_IS_ESCR0
MSR_ITLB_ESCR0
MSR_IX_ESCR0

7
6
2
4
0
1
3
5

3A0H
3A2H
3AAH
3ACH
3B2H
3B4H
3B6H
3C8H

MSR_BPU_COUNTER2

2

302H

MSR_BPU_CCCR2

362H

MSR_BSU_ESCR1
MSR_FSB_ESCR1
MSR_MOB_ESCR1
MSR_PMH_ESCR1
MSR_BPU_ESCR1
MSR_IS_ESCR1
MSR_ITLB_ESCR1
MSR_IX_ESCR1

7
6
2
4
0
1
3
5

3A1H
3A3H
3ABH
3ADH
3B3H
3B5H
3B7H
3C9H

MSR_BPU_COUNTER3

3

303H

MSR_BPU_CCCR3

363H

MSR_BSU_ESCR1
MSR_FSB_ESCR1
MSR_MOB_ESCR1
MSR_PMH_ESCR1
MSR_BPU_ESCR1
MSR_IS_ESCR1
MSR_ITLB_ESCR1
MSR_IX_ESCR1

7
6
2
4
0
1
3
5

3A1H
3A3H
3ABH
3ADH
3B3H
3B5H
3B7H
3C9H

MSR_MS_COUNTER0

4

304H

MSR_MS_CCCR0

364H

MSR_MS_ESCR0
MSR_TBPU_ESCR0
MSR_TC_ESCR0

0
2
1

3C0H
3C2H
3C4H

MSR_MS_COUNTER1

5

305H

MSR_MS_CCCR1

365H

MSR_MS_ESCR0
MSR_TBPU_ESCR0
MSR_TC_ESCR0

0
2
1

3C0H
3C2H
3C4H

MSR_MS_COUNTER2

6

306H

MSR_MS_CCCR2

366H

MSR_MS_ESCR1
MSR_TBPU_ESCR1
MSR_TC_ESCR1

0
2
1

3C1H
3C3H
3C5H

MSR_MS_COUNTER3

7

307H

MSR_MS_CCCR3

367H

MSR_MS_ESCR1
MSR_TBPU_ESCR1
MSR_TC_ESCR1

0
2
1

3C1H
3C3H
3C5H

MSR_FLAME_COUNTER0

8

308H

MSR_FLAME_CCCR0

368H

MSR_FIRM_ESCR0
MSR_FLAME_ESCR0
MSR_DAC_ESCR0
MSR_SAAT_ESCR0
MSR_U2L_ESCR0

1
0
5
2
3

3A4H
3A6H
3A8H
3AEH
3B0H

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PERFORMANCE MONITORING

Table 18-70. Performance Counter MSRs and Associated CCCR and
ESCR MSRs (Processors Based on Intel NetBurst Microarchitecture) (Contd.)
Counter

CCCR

ESCR

Name

No.

Addr

Name

Addr

Name

No.

Addr

MSR_FLAME_COUNTER1

9

309H

MSR_FLAME_CCCR1

369H

MSR_FIRM_ESCR0
MSR_FLAME_ESCR0
MSR_DAC_ESCR0
MSR_SAAT_ESCR0
MSR_U2L_ESCR0

1
0
5
2
3

3A4H
3A6H
3A8H
3AEH
3B0H

MSR_FLAME_COUNTER2

10

30AH

MSR_FLAME_CCCR2

36AH

MSR_FIRM_ESCR1
MSR_FLAME_ESCR1
MSR_DAC_ESCR1
MSR_SAAT_ESCR1
MSR_U2L_ESCR1

1
0
5
2
3

3A5H
3A7H
3A9H
3AFH
3B1H

MSR_FLAME_COUNTER3

11

30BH

MSR_FLAME_CCCR3

36BH

MSR_FIRM_ESCR1
MSR_FLAME_ESCR1
MSR_DAC_ESCR1
MSR_SAAT_ESCR1
MSR_U2L_ESCR1

1
0
5
2
3

3A5H
3A7H
3A9H
3AFH
3B1H

MSR_IQ_COUNTER0

12

30CH

MSR_IQ_CCCR0

36CH

MSR_CRU_ESCR0
MSR_CRU_ESCR2
MSR_CRU_ESCR4
MSR_IQ_ESCR01
MSR_RAT_ESCR0
MSR_SSU_ESCR0
MSR_ALF_ESCR0

4
5
6
0
2
3
1

3B8H
3CCH
3E0H
3BAH
3BCH
3BEH
3CAH

MSR_IQ_COUNTER1

13

30DH

MSR_IQ_CCCR1

36DH

MSR_CRU_ESCR0
MSR_CRU_ESCR2
MSR_CRU_ESCR4
MSR_IQ_ESCR01
MSR_RAT_ESCR0
MSR_SSU_ESCR0
MSR_ALF_ESCR0

4
5
6
0
2
3
1

3B8H
3CCH
3E0H
3BAH
3BCH
3BEH
3CAH

MSR_IQ_COUNTER2

14

30EH

MSR_IQ_CCCR2

36EH

MSR_CRU_ESCR1
MSR_CRU_ESCR3
MSR_CRU_ESCR5
MSR_IQ_ESCR11
MSR_RAT_ESCR1
MSR_ALF_ESCR1

4
5
6
0
2
1

3B9H
3CDH
3E1H
3BBH
3BDH
3CBH

MSR_IQ_COUNTER3

15

30FH

MSR_IQ_CCCR3

36FH

MSR_CRU_ESCR1
MSR_CRU_ESCR3
MSR_CRU_ESCR5
MSR_IQ_ESCR11
MSR_RAT_ESCR1
MSR_ALF_ESCR1

4
5
6

3B9H
3CDH
3E1H
3BBH
3BDH
3CBH

2
1

0

MSR_IQ_COUNTER4

16

310H

MSR_IQ_CCCR4

370H

MSR_CRU_ESCR0
MSR_CRU_ESCR2
MSR_CRU_ESCR4
MSR_IQ_ESCR01
MSR_RAT_ESCR0
MSR_SSU_ESCR0
MSR_ALF_ESCR0

4
5
6
0
2
3
1

3B8H
3CCH
3E0H
3BAH
3BCH
3BEH
3CAH

MSR_IQ_COUNTER5

17

311H

MSR_IQ_CCCR5

371H

MSR_CRU_ESCR1
MSR_CRU_ESCR3
MSR_CRU_ESCR5
MSR_IQ_ESCR11
MSR_RAT_ESCR1
MSR_ALF_ESCR1

4
5
6
0
2
1

3B9H
3CDH
3E1H
3BBH
3BDH
3CBH

NOTES:
1. MSR_IQ_ESCR0 and MSR_IQ_ESCR1 are available only on early processor builds (family 0FH, models 01H-02H). These MSRs are not
available on later versions.

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PERFORMANCE MONITORING

The types of events that can be counted with these performance monitoring facilities are divided into two classes:
non-retirement events and at-retirement events.

•

Non-retirement events (see Table 19-31) are events that occur any time during instruction execution (such as
bus transactions or cache transactions).

•

At-retirement events (see Table 19-32) are events that are counted at the retirement stage of instruction
execution, which allows finer granularity in counting events and capturing machine state.
The at-retirement counting mechanism includes facilities for tagging μops that have encountered a particular
performance event during instruction execution. Tagging allows events to be sorted between those that
occurred on an execution path that resulted in architectural state being committed at retirement as well as
events that occurred on an execution path where the results were eventually cancelled and never committed to
architectural state (such as, the execution of a mispredicted branch).

The Pentium 4 and Intel Xeon processor performance monitoring facilities support the three usage models
described below. The first two models can be used to count both non-retirement and at-retirement events; the
third model is used to count a subset of at-retirement events:

•

Event counting — A performance counter is configured to count one or more types of events. While the
counter is counting, software reads the counter at selected intervals to determine the number of events that
have been counted between the intervals.

•

Interrupt-based event sampling — A performance counter is configured to count one or more types of
events and to generate an interrupt when it overflows. To trigger an overflow, the counter is preset to a
modulus value that will cause the counter to overflow after a specific number of events have been counted.
When the counter overflows, the processor generates a performance monitoring interrupt (PMI). The interrupt
service routine for the PMI then records the return instruction pointer (RIP), resets the modulus, and restarts
the counter. Code performance can be analyzed by examining the distribution of RIPs with a tool like the
VTune™ Performance Analyzer.

•

Processor event-based sampling (PEBS) — In PEBS, the processor writes a record of the architectural
state of the processor to a memory buffer after the counter overflows. The records of architectural state
provide additional information for use in performance tuning. Processor-based event sampling can be used to
count only a subset of at-retirement events. PEBS captures more precise processor state information compared
to interrupt based event sampling, because the latter need to use the interrupt service routine to re-construct
the architectural states of processor.

The following sections describe the MSRs and data structures used for performance monitoring in the Pentium 4
and Intel Xeon processors.

18.6.3.1

ESCR MSRs

The 45 ESCR MSRs (see Table 18-70) allow software to select specific events to be countered. Each ESCR is usually
associated with a pair of performance counters (see Table 18-70) and each performance counter has several ESCRs
associated with it (allowing the events counted to be selected from a variety of events).
Figure 18-45 shows the layout of an ESCR MSR. The functions of the flags and fields are:

•

USR flag, bit 2 — When set, events are counted when the processor is operating at a current privilege level
(CPL) of 1, 2, or 3. These privilege levels are generally used by application code and unprotected operating
system code.

•

OS flag, bit 3 — When set, events are counted when the processor is operating at CPL of 0. This privilege level
is generally reserved for protected operating system code. (When both the OS and USR flags are set, events
are counted at all privilege levels.)

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PERFORMANCE MONITORING

31 30

25 24

Event
Select

5 4 3 2 1 0

9 8

Tag
Value

Event Mask

Tag Enable
OS
USR

Reserved
63

32

Reserved

Figure 18-45. Event Selection Control Register (ESCR) for Pentium 4
and Intel Xeon Processors without Intel HT Technology Support

•

Tag enable, bit 4 — When set, enables tagging of μops to assist in at-retirement event counting; when clear,
disables tagging. See Section 18.6.3.6, “At-Retirement Counting.”

•

Tag value field, bits 5 through 8 — Selects a tag value to associate with a μop to assist in at-retirement
event counting.

•

Event mask field, bits 9 through 24 — Selects events to be counted from the event class selected with the
event select field.

•

Event select field, bits 25 through 30) — Selects a class of events to be counted. The events within this
class that are counted are selected with the event mask field.

When setting up an ESCR, the event select field is used to select a specific class of events to count, such as retired
branches. The event mask field is then used to select one or more of the specific events within the class to be
counted. For example, when counting retired branches, four different events can be counted: branch not taken
predicted, branch not taken mispredicted, branch taken predicted, and branch taken mispredicted. The OS and
USR flags allow counts to be enabled for events that occur when operating system code and/or application code are
being executed. If neither the OS nor USR flag is set, no events will be counted.
The ESCRs are initialized to all 0s on reset. The flags and fields of an ESCR are configured by writing to the ESCR
using the WRMSR instruction. Table 18-70 gives the addresses of the ESCR MSRs.
Writing to an ESCR MSR does not enable counting with its associated performance counter; it only selects the event
or events to be counted. The CCCR for the selected performance counter must also be configured. Configuration of
the CCCR includes selecting the ESCR and enabling the counter.

18.6.3.2

Performance Counters

The performance counters in conjunction with the counter configuration control registers (CCCRs) are used for
filtering and counting the events selected by the ESCRs. Processors based on Intel NetBurst microarchitecture
provide 18 performance counters organized into 9 pairs. A pair of performance counters is associated with a particular subset of events and ESCR’s (see Table 18-70). The counter pairs are partitioned into four groups:

•

The BPU group, includes two performance counter pairs:
— MSR_BPU_COUNTER0 and MSR_BPU_COUNTER1.
— MSR_BPU_COUNTER2 and MSR_BPU_COUNTER3.

•

The MS group, includes two performance counter pairs:
— MSR_MS_COUNTER0 and MSR_MS_COUNTER1.
— MSR_MS_COUNTER2 and MSR_MS_COUNTER3.

•

The FLAME group, includes two performance counter pairs:
— MSR_FLAME_COUNTER0 and MSR_FLAME_COUNTER1.

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PERFORMANCE MONITORING

— MSR_FLAME_COUNTER2 and MSR_FLAME_COUNTER3.

•

The IQ group, includes three performance counter pairs:
— MSR_IQ_COUNTER0 and MSR_IQ_COUNTER1.
— MSR_IQ_COUNTER2 and MSR_IQ_COUNTER3.
— MSR_IQ_COUNTER4 and MSR_IQ_COUNTER5.

The MSR_IQ_COUNTER4 counter in the IQ group provides support for the PEBS.
Alternate counters in each group can be cascaded: the first counter in one pair can start the first counter in the
second pair and vice versa. A similar cascading is possible for the second counters in each pair. For example, within
the BPU group of counters, MSR_BPU_COUNTER0 can start MSR_BPU_COUNTER2 and vice versa, and
MSR_BPU_COUNTER1 can start MSR_BPU_COUNTER3 and vice versa (see Section 18.6.3.5.6, “Cascading Counters”). The cascade flag in the CCCR register for the performance counter enables the cascading of counters.
Each performance counter is 40-bits wide (see Figure 18-46). The RDPMC instruction is intended to allow reading
of either the full counter-width (40-bits) or the low 32-bits of the counter. Reading the low 32-bits is faster than
reading the full counter width and is appropriate in situations where the count is small enough to be contained in
32 bits.
The RDPMC instruction can be used by programs or procedures running at any privilege level and in virtual-8086
mode to read these counters. The PCE flag in control register CR4 (bit 8) allows the use of this instruction to be
restricted to only programs and procedures running at privilege level 0.
31

0

Counter
63

32

39

Reserved

Counter

Figure 18-46. Performance Counter (Pentium 4 and Intel Xeon Processors)
The RDPMC instruction is not serializing or ordered with other instructions. Thus, it does not necessarily wait until
all previous instructions have been executed before reading the counter. Similarly, subsequent instructions may
begin execution before the RDPMC instruction operation is performed.
Only the operating system, executing at privilege level 0, can directly manipulate the performance counters, using
the RDMSR and WRMSR instructions. A secure operating system would clear the PCE flag during system initialization to disable direct user access to the performance-monitoring counters, but provide a user-accessible programming interface that emulates the RDPMC instruction.
Some uses of the performance counters require the counters to be preset before counting begins (that is, before
the counter is enabled). This can be accomplished by writing to the counter using the WRMSR instruction. To set a
counter to a specified number of counts before overflow, enter a 2s complement negative integer in the counter.
The counter will then count from the preset value up to -1 and overflow. Writing to a performance counter in a
Pentium 4 or Intel Xeon processor with the WRMSR instruction causes all 40 bits of the counter to be written.

18.6.3.3

CCCR MSRs

Each of the 18 performance counters has one CCCR MSR associated with it (see Table 18-70). The CCCRs control
the filtering and counting of events as well as interrupt generation. Figure 18-47 shows the layout of an CCCR MSR.
The functions of the flags and fields are as follows:

•

Enable flag, bit 12 — When set, enables counting; when clear, the counter is disabled. This flag is cleared on
reset.

•

ESCR select field, bits 13 through 15 — Identifies the ESCR to be used to select events to be counted with
the counter associated with the CCCR.

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PERFORMANCE MONITORING

•

Compare flag, bit 18 — When set, enables filtering of the event count; when clear, disables filtering. The
filtering method is selected with the threshold, complement, and edge flags.

•

Complement flag, bit 19 — Selects how the incoming event count is compared with the threshold value.
When set, event counts that are less than or equal to the threshold value result in a single count being delivered
to the performance counter; when clear, counts greater than the threshold value result in a count being
delivered to the performance counter (see Section 18.6.3.5.2, “Filtering Events”). The complement flag is not
active unless the compare flag is set.

•

Threshold field, bits 20 through 23 — Selects the threshold value to be used for comparisons. The
processor examines this field only when the compare flag is set, and uses the complement flag setting to
determine the type of threshold comparison to be made. The useful range of values that can be entered in this
field depend on the type of event being counted (see Section 18.6.3.5.2, “Filtering Events”).

•

Edge flag, bit 24 — When set, enables rising edge (false-to-true) edge detection of the threshold comparison
output for filtering event counts; when clear, rising edge detection is disabled. This flag is active only when the
compare flag is set.

Reserved
31 30 29

27 26 25 24 23

20 19 18 17 16 15

Threshold

13 12 11

ESCR
Select

0
Reserved
Reserved

Enable
Reserved: Must be set to 11B
Compare
Complement
Edge
FORCE_OVF
OVF_PMI
Cascade
OVF
63

32

Reserved

Figure 18-47. Counter Configuration Control Register (CCCR)

•

FORCE_OVF flag, bit 25 — When set, forces a counter overflow on every counter increment; when clear,
overflow only occurs when the counter actually overflows.

•

OVF_PMI flag, bit 26 — When set, causes a performance monitor interrupt (PMI) to be generated when the
counter overflows occurs; when clear, disables PMI generation. Note that the PMI is generated on the next
event count after the counter has overflowed.

•

Cascade flag, bit 30 — When set, enables counting on one counter of a counter pair when its alternate
counter in the other the counter pair in the same counter group overflows (see Section 18.6.3.2, “Performance
Counters,” for further details); when clear, disables cascading of counters.

•

OVF flag, bit 31 — Indicates that the counter has overflowed when set. This flag is a sticky flag that must be
explicitly cleared by software.

The CCCRs are initialized to all 0s on reset.
The events that an enabled performance counter actually counts are selected and filtered by the following flags and
fields in the ESCR and CCCR registers and in the qualification order given:
1. The event select and event mask fields in the ESCR select a class of events to be counted and one or more event
types within the class, respectively.

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PERFORMANCE MONITORING

2. The OS and USR flags in the ESCR selected the privilege levels at which events will be counted.
3. The ESCR select field of the CCCR selects the ESCR. Since each counter has several ESCRs associated with it,
one ESCR must be chosen to select the classes of events that may be counted.
4. The compare and complement flags and the threshold field of the CCCR select an optional threshold to be used
in qualifying an event count.
5. The edge flag in the CCCR allows events to be counted only on rising-edge transitions.
The qualification order in the above list implies that the filtered output of one “stage” forms the input for the next.
For instance, events filtered using the privilege level flags can be further qualified by the compare and complement
flags and the threshold field, and an event that matched the threshold criteria, can be further qualified by edge
detection.
The uses of the flags and fields in the CCCRs are discussed in greater detail in Section 18.6.3.5, “Programming the
Performance Counters for Non-Retirement Events.”

18.6.3.4

Debug Store (DS) Mechanism

The debug store (DS) mechanism was introduced with processors based on Intel NetBurst microarchitecture to
allow various types of information to be collected in memory-resident buffers for use in debugging and tuning
programs. The DS mechanism can be used to collect two types of information: branch records and processor
event-based sampling (PEBS) records. The availability of the DS mechanism in a processor is indicated with the DS
feature flag (bit 21) returned by the CPUID instruction.
See Section 17.4.5, “Branch Trace Store (BTS),” and Section 18.6.3.8, “Processor Event-Based Sampling (PEBS),”
for a description of these facilities. Records collected with the DS mechanism are saved in the DS save area. See
Section 17.4.9, “BTS and DS Save Area.”

18.6.3.5

Programming the Performance Counters for Non-Retirement Events

The basic steps to program a performance counter and to count events include the following:
1. Select the event or events to be counted.
2. For each event, select an ESCR that supports the event using the values in the ESCR restrictions row in Table
19-31, Chapter 19.
3. Match the CCCR Select value and ESCR name in Table 19-31 to a value listed in Table 18-70; select a CCCR and
performance counter.
4. Set up an ESCR for the specific event or events to be counted and the privilege levels at which the are to be
counted.
5. Set up the CCCR for the performance counter by selecting the ESCR and the desired event filters.
6. Set up the CCCR for optional cascading of event counts, so that when the selected counter overflows its
alternate counter starts.
7. Set up the CCCR to generate an optional performance monitor interrupt (PMI) when the counter overflows. If
PMI generation is enabled, the local APIC must be set up to deliver the interrupt to the processor and a handler
for the interrupt must be in place.
8. Enable the counter to begin counting.

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18.6.3.5.1 Selecting Events to Count
Table 19-32 in Chapter 19 lists a set of at-retirement events for processors based on Intel NetBurst microarchitecture. For each event listed in Table 19-32, setup information is provided. Table 18-71 gives an example of one of
the events.

Table 18-71. Event Example
Event Name

Event Parameters

Parameter Value Description

branch_retired

Counts the retirement of a branch. Specify one or more mask bits to select
any combination of branch taken, not-taken, predicted and mispredicted.
ESCR restrictions

MSR_CRU_ESCR2
MSR_CRU_ESCR3

See Table 15-3 for the addresses of the ESCR MSRs.

Counter numbers per ESCR2: 12, 13, 16 The counter numbers associated with each ESCR are provided. The
ESCR
ESCR3: 14, 15, 17 performance counters and corresponding CCCRs can be obtained from
Table 15-3.
ESCR Event Select

06H

ESCR[24:9]

ESCR Event Mask
Bit 0: MMNP

CCCR Select

ESCR[31:25]

1: MMNM

Branch Not-taken Mispredicted

2: MMTP

Branch Taken Predicted

3: MMTM

Branch Taken Mispredicted

05H

Event Specific Notes

Branch Not-taken Predicted

CCCR[15:13]
P6: EMON_BR_INST_RETIRED

Can Support PEBS

No

Requires Additional
MSRs for Tagging

No

For Table 19-31 and Table 19-32, Chapter 19, the name of the event is listed in the Event Name column and parameters that define the event and other information are listed in the Event Parameters column. The Parameter Value
and Description columns give specific parameters for the event and additional description information. Entries in
the Event Parameters column are described below.

•

ESCR restrictions — Lists the ESCRs that can be used to program the event. Typically only one ESCR is
needed to count an event.

•

Counter numbers per ESCR — Lists which performance counters are associated with each ESCR. Table 18-70
gives the name of the counter and CCCR for each counter number. Typically only one counter is needed to count
the event.

•
•

ESCR event select — Gives the value to be placed in the event select field of the ESCR to select the event.
ESCR event mask — Gives the value to be placed in the Event Mask field of the ESCR to select sub-events to
be counted. The parameter value column defines the documented bits with relative bit position offset starting
from 0, where the absolute bit position of relative offset 0 is bit 9 of the ESCR. All undocumented bits are
reserved and should be set to 0.

•

CCCR select — Gives the value to be placed in the ESCR select field of the CCCR associated with the counter
to select the ESCR to be used to define the event. This value is not the address of the ESCR; it is the number of
the ESCR from the Number column in Table 18-70.

•

Event specific notes — Gives additional information about the event, such as the name of the same or a
similar event defined for the P6 family processors.

•

Can support PEBS — Indicates if PEBS is supported for the event (only supplied for at-retirement events listed
in Table 19-32.)

•

Requires additional MSR for tagging — Indicates which if any additional MSRs must be programmed to
count the events (only supplied for the at-retirement events listed in Table 19-32.)

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NOTE
The performance-monitoring events listed in Chapter 19, “Performance Monitoring Events,” are
intended to be used as guides for performance tuning. The counter values reported are not
guaranteed to be absolutely accurate and should be used as a relative guide for tuning. Known
discrepancies are documented where applicable.
The following procedure shows how to set up a performance counter for basic counting; that is, the counter is set
up to count a specified event indefinitely, wrapping around whenever it reaches its maximum count. This procedure
is continued through the following four sections.
Using information in Table 19-31, Chapter 19, an event to be counted can be selected as follows:
1. Select the event to be counted.
2. Select the ESCR to be used to select events to be counted from the ESCRs field.
3. Select the number of the counter to be used to count the event from the Counter Numbers Per ESCR field.
4. Determine the name of the counter and the CCCR associated with the counter, and determine the MSR
addresses of the counter, CCCR, and ESCR from Table 18-70.
5. Use the WRMSR instruction to write the ESCR Event Select and ESCR Event Mask values into the appropriate
fields in the ESCR. At the same time set or clear the USR and OS flags in the ESCR as desired.
6. Use the WRMSR instruction to write the CCCR Select value into the appropriate field in the CCCR.

NOTE
Typically all the fields and flags of the CCCR will be written with one WRMSR instruction; however,
in this procedure, several WRMSR writes are used to more clearly demonstrate the uses of the
various CCCR fields and flags.
This setup procedure is continued in the next section, Section 18.6.3.5.2, “Filtering Events.”

18.6.3.5.2 Filtering Events
Each counter receives up to 4 input lines from the processor hardware from which it is counting events. The
counter treats these inputs as binary inputs (input 0 has a value of 1, input 1 has a value of 2, input 3 has a value
of 4, and input 3 has a value of 8). When a counter is enabled, it adds this binary input value to the counter value
on each clock cycle. For each clock cycle, the value added to the counter can then range from 0 (no event) to 15.
For many events, only the 0 input line is active, so the counter is merely counting the clock cycles during which the
0 input is asserted. However, for some events two or more input lines are used. Here, the counters threshold
setting can be used to filter events. The compare, complement, threshold, and edge fields control the filtering of
counter increments by input value.
If the compare flag is set, then a “greater than” or a “less than or equal to” comparison of the input value vs. a
threshold value can be made. The complement flag selects “less than or equal to” (flag set) or “greater than” (flag
clear). The threshold field selects a threshold value of from 0 to 15. For example, if the complement flag is cleared
and the threshold field is set to 6, than any input value of 7 or greater on the 4 inputs to the counter will cause the
counter to be incremented by 1, and any value less than 7 will cause an increment of 0 (or no increment) of the
counter. Conversely, if the complement flag is set, any value from 0 to 6 will increment the counter and any value
from 7 to 15 will not increment the counter. Note that when a threshold condition has been satisfied, the input to
the counter is always 1, not the input value that is presented to the threshold filter.
The edge flag provides further filtering of the counter inputs when a threshold comparison is being made. The edge
flag is only active when the compare flag is set. When the edge flag is set, the resulting output from the threshold
filter (a value of 0 or 1) is used as an input to the edge filter. Each clock cycle, the edge filter examines the last and
current input values and sends a count to the counter only when it detects a “rising edge” event; that is, a falseto-true transition. Figure 18-48 illustrates rising edge filtering.

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The following procedure shows how to configure a CCCR to filter events using the threshold filter and the edge filter.
This procedure is a continuation of the setup procedure introduced in Section 18.6.3.5.1, “Selecting Events to
Count.”
7. (Optional) To set up the counter for threshold filtering, use the WRMSR instruction to write values in the CCCR
compare and complement flags and the threshold field:
— Set the compare flag.
— Set or clear the complement flag for less than or equal to or greater than comparisons, respectively.
— Enter a value from 0 to 15 in the threshold field.
8. (Optional) Select rising edge filtering by setting the CCCR edge flag.
This setup procedure is continued in the next section, Section 18.6.3.5.3, “Starting Event Counting.”

Processor Clock
Output from
Threshold Filter
Counter Increments
On Rising Edge
(False-to-True)

Figure 18-48. Effects of Edge Filtering
18.6.3.5.3 Starting Event Counting
Event counting by a performance counter can be initiated in either of two ways. The typical way is to set the enable
flag in the counter’s CCCR. Following the instruction to set the enable flag, event counting begins and continues
until it is stopped (see Section 18.6.3.5.5, “Halting Event Counting”).
The following procedural step shows how to start event counting. This step is a continuation of the setup procedure
introduced in Section 18.6.3.5.2, “Filtering Events.”
9. To start event counting, use the WRMSR instruction to set the CCCR enable flag for the performance counter.
This setup procedure is continued in the next section, Section 18.6.3.5.4, “Reading a Performance Counter’s
Count.”
The second way that a counter can be started by using the cascade feature. Here, the overflow of one counter automatically starts its alternate counter (see Section 18.6.3.5.6, “Cascading Counters”).

18.6.3.5.4 Reading a Performance Counter’s Count
Performance counters can be read using either the RDPMC or RDMSR instructions. The enhanced functions of the
RDPMC instruction (including fast read) are described in Section 18.6.3.2, “Performance Counters.” These instructions can be used to read a performance counter while it is counting or when it is stopped.
The following procedural step shows how to read the event counter. This step is a continuation of the setup procedure introduced in Section 18.6.3.5.3, “Starting Event Counting.”
10. To read a performance counters current event count, execute the RDPMC instruction with the counter number
obtained from Table 18-70 used as an operand.
This setup procedure is continued in the next section, Section 18.6.3.5.5, “Halting Event Counting.”

18.6.3.5.5 Halting Event Counting
After a performance counter has been started (enabled), it continues counting indefinitely. If the counter overflows
(goes one count past its maximum count), it wraps around and continues counting. When the counter wraps

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around, it sets its OVF flag to indicate that the counter has overflowed. The OVF flag is a sticky flag that indicates
that the counter has overflowed at least once since the OVF bit was last cleared.
To halt counting, the CCCR enable flag for the counter must be cleared.
The following procedural step shows how to stop event counting. This step is a continuation of the setup procedure
introduced in Section 18.6.3.5.4, “Reading a Performance Counter’s Count.”
11. To stop event counting, execute a WRMSR instruction to clear the CCCR enable flag for the performance
counter.
To halt a cascaded counter (a counter that was started when its alternate counter overflowed), either clear the
Cascade flag in the cascaded counter’s CCCR MSR or clear the OVF flag in the alternate counter’s CCCR MSR.

18.6.3.5.6 Cascading Counters
As described in Section 18.6.3.2, “Performance Counters,” eighteen performance counters are implemented in
pairs. Nine pairs of counters and associated CCCRs are further organized as four blocks: BPU, MS, FLAME, and IQ
(see Table 18-70). The first three blocks contain two pairs each. The IQ block contains three pairs of counters (12
through 17) with associated CCCRs (MSR_IQ_CCCR0 through MSR_IQ_CCCR5).
The first 8 counter pairs (0 through 15) can be programmed using ESCRs to detect performance monitoring events.
Pairs of ESCRs in each of the four blocks allow many different types of events to be counted. The cascade flag in
the CCCR MSR allows nested monitoring of events to be performed by cascading one counter to a second counter
located in another pair in the same block (see Figure 18-47 for the location of the flag).
Counters 0 and 1 form the first pair in the BPU block. Either counter 0 or 1 can be programmed to detect an event
via MSR_MO B_ESCR0. Counters 0 and 2 can be cascaded in any order, as can counters 1 and 3. It’s possible to set
up 4 counters in the same block to cascade on two pairs of independent events. The pairing described also applies
to subsequent blocks. Since the IQ PUB has two extra counters, cascading operates somewhat differently if 16 and
17 are involved. In the IQ block, counter 16 can only be cascaded from counter 14 (not from 12); counter 14
cannot be cascaded from counter 16 using the CCCR cascade bit mechanism. Similar restrictions apply to counter
17.
Example 18-1. Counting Events
Assume a scenario where counter X is set up to count 200 occurrences of event A; then counter Y is set up to count
400 occurrences of event B. Each counter is set up to count a specific event and overflow to the next counter. In
the above example, counter X is preset for a count of -200 and counter Y for a count of -400; this setup causes the
counters to overflow on the 200th and 400th counts respectively.
Continuing this scenario, counter X is set up to count indefinitely and wraparound on overflow. This is described in
the basic performance counter setup procedure that begins in Section 18.6.3.5.1, “Selecting Events to Count.”
Counter Y is set up with the cascade flag in its associated CCCR MSR set to 1 and its enable flag set to 0.
To begin the nested counting, the enable bit for the counter X is set. Once enabled, counter X counts until it overflows. At this point, counter Y is automatically enabled and begins counting. Thus counter X overflows after 200
occurrences of event A. Counter Y then starts, counting 400 occurrences of event B before overflowing. When
performance counters are cascaded, the counter Y would typically be set up to generate an interrupt on overflow.
This is described in Section 18.6.3.5.8, “Generating an Interrupt on Overflow.”
The cascading counters mechanism can be used to count a single event. The counting begins on one counter then
continues on the second counter after the first counter overflows. This technique doubles the number of event
counts that can be recorded, since the contents of the two counters can be added together.

18.6.3.5.7 EXTENDED CASCADING
Extended cascading is a model-specific feature in the Intel NetBurst microarchitecture with CPUID
DisplayFamily_DisplayModel 0F_02, 0F_03, 0F_04, 0F_06. This feature uses bit 11 in CCCRs associated with the IQ

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block. See Table 18-72.

Table 18-72. CCR Names and Bit Positions
CCCR Name:Bit Position

Bit Name

Description

MSR_IQ_CCCR1|2:11

Reserved

MSR_IQ_CCCR0:11

CASCNT4INTO0

Allow counter 4 to cascade into counter 0

MSR_IQ_CCCR3:11

CASCNT5INTO3

Allow counter 5 to cascade into counter 3

MSR_IQ_CCCR4:11

CASCNT5INTO4

Allow counter 5 to cascade into counter 4

MSR_IQ_CCCR5:11

CASCNT4INTO5

Allow counter 4 to cascade into counter 5

The extended cascading feature can be adapted to the Interrupt based sampling usage model for performance
monitoring. However, it is known that performance counters do not generate PMI in cascade mode or extended
cascade mode due to an erratum. This erratum applies to processors with CPUID DisplayFamily_DisplayModel
signature of 0F_02. For processors with CPUID DisplayFamily_DisplayModel signature of 0F_00 and 0F_01, the
erratum applies to processors with stepping encoding greater than 09H.
Counters 16 and 17 in the IQ block are frequently used in processor event-based sampling or at-retirement
counting of events indicating a stalled condition in the pipeline. Neither counter 16 or 17 can initiate the cascading
of counter pairs using the cascade bit in a CCCR.
Extended cascading permits performance monitoring tools to use counters 16 and 17 to initiate cascading of two
counters in the IQ block. Extended cascading from counter 16 and 17 is conceptually similar to cascading other
counters, but instead of using CASCADE bit of a CCCR, one of the four CASCNTxINTOy bits is used.
Example 18-2. Scenario for Extended Cascading
A usage scenario for extended cascading is to sample instructions retired on logical processor 1 after the first 4096
instructions retired on logical processor 0. A procedure to program extended cascading in this scenario is outlined
below:
1. Write the value 0 to counter 12.
2. Write the value 04000603H to MSR_CRU_ESCR0 (corresponding to selecting the NBOGNTAG and NBOGTAG
event masks with qualification restricted to logical processor 1).
3. Write the value 04038800H to MSR_IQ_CCCR0. This enables CASCNT4INTO0 and OVF_PMI. An ISR can sample
on instruction addresses in this case (do not set ENABLE, or CASCADE).
4. Write the value FFFFF000H into counter 16.1.
5. Write the value 0400060CH to MSR_CRU_ESCR2 (corresponding to selecting the NBOGNTAG and NBOGTAG
event masks with qualification restricted to logical processor 0).
6. Write the value 00039000H to MSR_IQ_CCCR4 (set ENABLE bit, but not OVF_PMI).
Another use for cascading is to locate stalled execution in a multithreaded application. Assume MOB replays in
thread B cause thread A to stall. Getting a sample of the stalled execution in this scenario could be accomplished
by:
1. Set up counter B to count MOB replays on thread B.
2. Set up counter A to count resource stalls on thread A; set its force overflow bit and the appropriate CASCNTxINTOy bit.
3. Use the performance monitoring interrupt to capture the program execution data of the stalled thread.

18.6.3.5.8 Generating an Interrupt on Overflow
Any performance counter can be configured to generate a performance monitor interrupt (PMI) if the counter overflows. The PMI interrupt service routine can then collect information about the state of the processor or program

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when overflow occurred. This information can then be used with a tool like the Intel® VTune™ Performance
Analyzer to analyze and tune program performance.
To enable an interrupt on counter overflow, the OVR_PMI flag in the counter’s associated CCCR MSR must be set.
When overflow occurs, a PMI is generated through the local APIC. (Here, the performance counter entry in the local
vector table [LVT] is set up to deliver the interrupt generated by the PMI to the processor.)
The PMI service routine can use the OVF flag to determine which counter overflowed when multiple counters have
been configured to generate PMIs. Also, note that these processors mask PMIs upon receiving an interrupt. Clear
this condition before leaving the interrupt handler.
When generating interrupts on overflow, the performance counter being used should be preset to value that will
cause an overflow after a specified number of events are counted plus 1. The simplest way to select the preset
value is to write a negative number into the counter, as described in Section 18.6.3.5.6, “Cascading Counters.”
Here, however, if an interrupt is to be generated after 100 event counts, the counter should be preset to minus 100
plus 1 (-100 + 1), or -99. The counter will then overflow after it counts 99 events and generate an interrupt on the
next (100th) event counted. The difference of 1 for this count enables the interrupt to be generated immediately
after the selected event count has been reached, instead of waiting for the overflow to be propagation through the
counter.
Because of latency in the microarchitecture between the generation of events and the generation of interrupts on
overflow, it is sometimes difficult to generate an interrupt close to an event that caused it. In these situations, the
FORCE_OVF flag in the CCCR can be used to improve reporting. Setting this flag causes the counter to overflow on
every counter increment, which in turn triggers an interrupt after every counter increment.

18.6.3.5.9 Counter Usage Guideline
There are some instances where the user must take care to configure counting logic properly, so that it is not
powered down. To use any ESCR, even when it is being used just for tagging, (any) one of the counters that the
particular ESCR (or its paired ESCR) can be connected to should be enabled. If this is not done, 0 counts may
result. Likewise, to use any counter, there must be some event selected in a corresponding ESCR (other than
no_event, which generally has a select value of 0).

18.6.3.6

At-Retirement Counting

At-retirement counting provides a means counting only events that represent work committed to architectural
state and ignoring work that was performed speculatively and later discarded.
One example of this speculative activity is branch prediction. When a branch misprediction occurs, the results of
instructions that were decoded and executed down the mispredicted path are canceled. If a performance counter
was set up to count all executed instructions, the count would include instructions whose results were canceled as
well as those whose results committed to architectural state.
To provide finer granularity in event counting in these situations, the performance monitoring facilities provided in
the Pentium 4 and Intel Xeon processors provide a mechanism for tagging events and then counting only those
tagged events that represent committed results. This mechanism is called “at-retirement counting.”
Tables 19-32 through 19-36 list predefined at-retirement events and event metrics that can be used to for tagging
events when using at retirement counting. The following terminology is used in describing at-retirement counting:

•

Bogus, non-bogus, retire — In at-retirement event descriptions, the term “bogus” refers to instructions or
μops that must be canceled because they are on a path taken from a mispredicted branch. The terms “retired”
and “non-bogus” refer to instructions or μops along the path that results in committed architectural state
changes as required by the program being executed. Thus instructions and μops are either bogus or nonbogus, but not both. Several of the Pentium 4 and Intel Xeon processors’ performance monitoring events (such
as, Instruction_Retired and Uops_Retired in Table 19-32) can count instructions or μops that are retired based
on the characterization of bogus” versus non-bogus.

•

Tagging — Tagging is a means of marking μops that have encountered a particular performance event so they
can be counted at retirement. During the course of execution, the same event can happen more than once per
μop and a direct count of the event would not provide an indication of how many μops encountered that event.
The tagging mechanisms allow a μop to be tagged once during its lifetime and thus counted once at retirement.
The retired suffix is used for performance metrics that increment a count once per μop, rather than once per
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event. For example, a μop may encounter a cache miss more than once during its life time, but a “Miss Retired”
metric (that counts the number of retired μops that encountered a cache miss) will increment only once for that
μop. A “Miss Retired” metric would be useful for characterizing the performance of the cache hierarchy for a
particular instruction sequence. Details of various performance metrics and how these can be constructed using
the Pentium 4 and Intel Xeon processors performance events are provided in the Intel Pentium 4 Processor
Optimization Reference Manual (see Section 1.4, “Related Literature”).

•

Replay — To maximize performance for the common case, the Intel NetBurst microarchitecture aggressively
schedules μops for execution before all the conditions for correct execution are guaranteed to be satisfied. In
the event that all of these conditions are not satisfied, μops must be reissued. The mechanism that the Pentium
4 and Intel Xeon processors use for this reissuing of μops is called replay. Some examples of replay causes are
cache misses, dependence violations, and unforeseen resource constraints. In normal operation, some number
of replays is common and unavoidable. An excessive number of replays is an indication of a performance
problem.

•

Assist — When the hardware needs the assistance of microcode to deal with some event, the machine takes
an assist. One example of this is an underflow condition in the input operands of a floating-point operation. The
hardware must internally modify the format of the operands in order to perform the computation. Assists clear
the entire machine of μops before they begin and are costly.

18.6.3.6.1 Using At-Retirement Counting
Processors based on Intel NetBurst microarchitecture allow counting both events and μops that encountered a
specified event. For a subset of the at-retirement events listed in Table 19-32, a μop may be tagged when it
encounters that event. The tagging mechanisms can be used in Interrupt-based event sampling, and a subset of
these mechanisms can be used in PEBS. There are four independent tagging mechanisms, and each mechanism
uses a different event to count μops tagged with that mechanism:

•

Front-end tagging — This mechanism pertains to the tagging of μops that encountered front-end events (for
example, trace cache and instruction counts) and are counted with the Front_end_event event.

•

Execution tagging — This mechanism pertains to the tagging of μops that encountered execution events (for
example, instruction types) and are counted with the Execution_Event event.

•

Replay tagging — This mechanism pertains to tagging of μops whose retirement is replayed (for example, a
cache miss) and are counted with the Replay_event event. Branch mispredictions are also tagged with this
mechanism.

•

No tags — This mechanism does not use tags. It uses the Instr_retired and the Uops_ retired events.

Each tagging mechanism is independent from all others; that is, a μop that has been tagged using one mechanism
will not be detected with another mechanism’s tagged-μop detector. For example, if μops are tagged using the
front-end tagging mechanisms, the Replay_event will not count those as tagged μops unless they are also tagged
using the replay tagging mechanism. However, execution tags allow up to four different types of μops to be counted
at retirement through execution tagging.
The independence of tagging mechanisms does not hold when using PEBS. When using PEBS, only one tagging
mechanism should be used at a time.
Certain kinds of μops that cannot be tagged, including I/O, uncacheable and locked accesses, returns, and far
transfers.
Table 19-32 lists the performance monitoring events that support at-retirement counting: specifically the
Front_end_event, Execution_event, Replay_event, Inst_retired and Uops_retired events. The following sections
describe the tagging mechanisms for using these events to tag μop and count tagged μops.

18.6.3.6.2 Tagging Mechanism for Front_end_event
The Front_end_event counts μops that have been tagged as encountering any of the following events:

•

μop decode events — Tagging μops for μop decode events requires specifying bits in the ESCR associated with
the performance-monitoring event, Uop_type.

•

Trace cache events — Tagging μops for trace cache events may require specifying certain bits in the
MSR_TC_PRECISE_EVENT MSR (see Table 19-34).

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Table 19-32 describes the Front_end_event and Table 19-34 describes metrics that are used to set up a
Front_end_event count.
The MSRs specified in the Table 19-32 that are supported by the front-end tagging mechanism must be set and one
or both of the NBOGUS and BOGUS bits in the Front_end_event event mask must be set to count events. None of
the events currently supported requires the use of the MSR_TC_PRECISE_EVENT MSR.

18.6.3.6.3 Tagging Mechanism For Execution_event
Table 19-32 describes the Execution_event and Table 19-35 describes metrics that are used to set up an
Execution_event count.
The execution tagging mechanism differs from other tagging mechanisms in how it causes tagging. One upstream
ESCR is used to specify an event to detect and to specify a tag value (bits 5 through 8) to identify that event. A
second downstream ESCR is used to detect μops that have been tagged with that tag value identifier using
Execution_event for the event selection.
The upstream ESCR that counts the event must have its tag enable flag (bit 4) set and must have an appropriate
tag value mask entered in its tag value field. The 4-bit tag value mask specifies which of tag bits should be set for
a particular μop. The value selected for the tag value should coincide with the event mask selected in the downstream ESCR. For example, if a tag value of 1 is set, then the event mask of NBOGUS0 should be enabled, correspondingly in the downstream ESCR. The downstream ESCR detects and counts tagged μops. The normal (not tag
value) mask bits in the downstream ESCR specify which tag bits to count. If any one of the tag bits selected by the
mask is set, the related counter is incremented by one. This mechanism is summarized in the Table 19-35 metrics
that are supported by the execution tagging mechanism. The tag enable and tag value bits are irrelevant for the
downstream ESCR used to select the Execution_event.
The four separate tag bits allow the user to simultaneously but distinctly count up to four execution events at
retirement. (This applies for interrupt-based event sampling. There are additional restrictions for PEBS as noted in
Section 18.6.3.8.3, “Setting Up the PEBS Buffer.”) It is also possible to detect or count combinations of events by
setting multiple tag value bits in the upstream ESCR or multiple mask bits in the downstream ESCR. For example,
use a tag value of 3H in the upstream ESCR and use NBOGUS0/NBOGUS1 in the downstream ESCR event mask.

18.6.3.7

Tagging Mechanism for Replay_event

Table 19-32 describes the Replay_event and Table 19-36 describes metrics that are used to set up an Replay_event
count.
The replay mechanism enables tagging of μops for a subset of all replays before retirement. Use of the replay
mechanism requires selecting the type of μop that may experience the replay in the MSR_PEBS_MATRIX_VERT
MSR and selecting the type of event in the MSR_PEBS_ENABLE MSR. Replay tagging must also be enabled with the
UOP_Tag flag (bit 24) in the MSR_PEBS_ENABLE MSR.
The Table 19-36 lists the metrics that are support the replay tagging mechanism and the at-retirement events that
use the replay tagging mechanism, and specifies how the appropriate MSRs need to be configured. The replay tags
defined in Table A-5 also enable Processor Event-Based Sampling (PEBS, see Section 17.4.9). Each of these replay
tags can also be used in normal sampling by not setting Bit 24 nor Bit 25 in IA_32_PEBS_ENABLE_MSR. Each of
these metrics requires that the Replay_Event (see Table 19-32) be used to count the tagged μops.

18.6.3.8

Processor Event-Based Sampling (PEBS)

The debug store (DS) mechanism in processors based on Intel NetBurst microarchitecture allow two types of information to be collected for use in debugging and tuning programs: PEBS records and BTS records. See Section
17.4.5, “Branch Trace Store (BTS),” for a description of the BTS mechanism.
PEBS permits the saving of precise architectural information associated with one or more performance events in
the precise event records buffer, which is part of the DS save area (see Section 17.4.9, “BTS and DS Save Area”).
To use this mechanism, a counter is configured to overflow after it has counted a preset number of events. After
the counter overflows, the processor copies the current state of the general-purpose and EFLAGS registers and
instruction pointer into a record in the precise event records buffer. The processor then resets the count in the
performance counter and restarts the counter. When the precise event records buffer is nearly full, an interrupt is

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generated, allowing the precise event records to be saved. A circular buffer is not supported for precise event
records.
PEBS is supported only for a subset of the at-retirement events: Execution_event, Front_end_event, and
Replay_event. Also, PEBS can only be carried out using the one performance counter, the MSR_IQ_COUNTER4
MSR.
In processors based on Intel Core microarchitecture, a similar PEBS mechanism is also supported using IA32_PMC0
and IA32_PERFEVTSEL0 MSRs (See Section 18.6.2.4).

18.6.3.8.1 Detection of the Availability of the PEBS Facilities
The DS feature flag (bit 21) returned by the CPUID instruction indicates (when set) the availability of the DS mechanism in the processor, which supports the PEBS (and BTS) facilities. When this bit is set, the following PEBS facilities are available:

•

The PEBS_UNAVAILABLE flag in the IA32_MISC_ENABLE MSR indicates (when clear) the availability of the
PEBS facilities, including the MSR_PEBS_ENABLE MSR.

•

The enable PEBS flag (bit 24) in the MSR_PEBS_ENABLE MSR allows PEBS to be enabled (set) or disabled
(clear).

•

The IA32_DS_AREA MSR can be programmed to point to the DS save area.

18.6.3.8.2 Setting Up the DS Save Area
Section 17.4.9.2, “Setting Up the DS Save Area,” describes how to set up and enable the DS save area. This procedure is common for PEBS and BTS.

18.6.3.8.3 Setting Up the PEBS Buffer
Only the MSR_IQ_COUNTER4 performance counter can be used for PEBS. Use the following procedure to set up the
processor and this counter for PEBS:
1. Set up the precise event buffering facilities. Place values in the precise event buffer base, precise event index,
precise event absolute maximum, and precise event interrupt threshold, and precise event counter reset fields
of the DS buffer management area (see Figure 17-5) to set up the precise event records buffer in memory.
2. Enable PEBS. Set the Enable PEBS flag (bit 24) in MSR_PEBS_ENABLE MSR.
3. Set up the MSR_IQ_COUNTER4 performance counter and its associated CCCR and one or more ESCRs for PEBS
as described in Tables 19-32 through 19-36.

18.6.3.8.4 Writing a PEBS Interrupt Service Routine
The PEBS facilities share the same interrupt vector and interrupt service routine (called the DS ISR) with the nonprecise event-based sampling and BTS facilities. To handle PEBS interrupts, PEBS handler code must be included in
the DS ISR. See Section 17.4.9.5, “Writing the DS Interrupt Service Routine,” for guidelines for writing the DS ISR.

18.6.3.8.5 Other DS Mechanism Implications
The DS mechanism is not available in the SMM. It is disabled on transition to the SMM mode. Similarly the DS
mechanism is disabled on the generation of a machine check exception and is cleared on processor RESET and INIT.
The DS mechanism is available in real address mode.

18.6.3.9

Operating System Implications

The DS mechanism can be used by the operating system as a debugging extension to facilitate failure analysis.
When using this facility, a 25 to 30 times slowdown can be expected due to the effects of the trace store occurring
on every taken branch.

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Depending upon intended usage, the instruction pointers that are part of the branch records or the PEBS records
need to have an association with the corresponding process. One solution requires the ability for the DS specific
operating system module to be chained to the context switch. A separate buffer can then be maintained for each
process of interest and the MSR pointing to the configuration area saved and setup appropriately on each context
switch.
If the BTS facility has been enabled, then it must be disabled and state stored on transition of the system to a sleep
state in which processor context is lost. The state must be restored on return from the sleep state.
It is required that an interrupt gate be used for the DS interrupt as opposed to a trap gate to prevent the generation
of an endless interrupt loop.
Pages that contain buffers must have mappings to the same physical address for all processes/logical processors,
such that any change to CR3 will not change DS addresses. If this requirement cannot be satisfied (that is, the
feature is enabled on a per thread/process basis), then the operating system must ensure that the feature is
enabled/disabled appropriately in the context switch code.

18.6.4

Performance Monitoring and Intel Hyper-Threading Technology in Processors Based
on Intel NetBurst® Microarchitecture

The performance monitoring capability of processors based on Intel NetBurst microarchitecture and supporting
Intel Hyper-Threading Technology is similar to that described in Section 18.6.3. However, the capability is extended
so that:

•
•

Performance counters can be programmed to select events qualified by logical processor IDs.
Performance monitoring interrupts can be directed to a specific logical processor within the physical processor.

The sections below describe performance counters, event qualification by logical processor ID, and special purpose
bits in ESCRs/CCCRs. They also describe MSR_PEBS_ENABLE, MSR_PEBS_MATRIX_VERT, and
MSR_TC_PRECISE_EVENT.

18.6.4.1

ESCR MSRs

Figure 18-49 shows the layout of an ESCR MSR in processors supporting Intel Hyper-Threading Technology.
The functions of the flags and fields are as follows:

•

T1_USR flag, bit 0 — When set, events are counted when thread 1 (logical processor 1) is executing at a
current privilege level (CPL) of 1, 2, or 3. These privilege levels are generally used by application code and
unprotected operating system code.

31 30

25 24

Event
Select

5 4 3 2 1 0

9 8

Tag
Value

Event Mask

Tag Enable
T0_OS
T0_USR
T1_OS
T1_USR

Reserved

63

32

Reserved

Figure 18-49. Event Selection Control Register (ESCR) for the Pentium 4 Processor, Intel Xeon Processor and Intel
Xeon Processor MP Supporting Hyper-Threading Technology

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PERFORMANCE MONITORING

•

T1_OS flag, bit 1 — When set, events are counted when thread 1 (logical processor 1) is executing at CPL of
0. This privilege level is generally reserved for protected operating system code. (When both the T1_OS and
T1_USR flags are set, thread 1 events are counted at all privilege levels.)

•

T0_USR flag, bit 2 — When set, events are counted when thread 0 (logical processor 0) is executing at a CPL
of 1, 2, or 3.

•

T0_OS flag, bit 3 — When set, events are counted when thread 0 (logical processor 0) is executing at CPL of
0. (When both the T0_OS and T0_USR flags are set, thread 0 events are counted at all privilege levels.)

•

Tag enable, bit 4 — When set, enables tagging of μops to assist in at-retirement event counting; when clear,
disables tagging. See Section 18.6.3.6, “At-Retirement Counting.”

•

Tag value field, bits 5 through 8 — Selects a tag value to associate with a μop to assist in at-retirement
event counting.

•

Event mask field, bits 9 through 24 — Selects events to be counted from the event class selected with the
event select field.

•

Event select field, bits 25 through 30) — Selects a class of events to be counted. The events within this
class that are counted are selected with the event mask field.

The T0_OS and T0_USR flags and the T1_OS and T1_USR flags allow event counting and sampling to be specified
for a specific logical processor (0 or 1) within an Intel Xeon processor MP (See also: Section 8.4.5, “Identifying
Logical Processors in an MP System,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 3A).
Not all performance monitoring events can be detected within an Intel Xeon processor MP on a per logical processor
basis (see Section 18.6.4.4, “Performance Monitoring Events”). Some sub-events (specified by an event mask bits)
are counted or sampled without regard to which logical processor is associated with the detected event.

18.6.4.2

CCCR MSRs

Figure 18-50 shows the layout of a CCCR MSR in processors supporting Intel Hyper-Threading Technology. The
functions of the flags and fields are as follows:

•

Enable flag, bit 12 — When set, enables counting; when clear, the counter is disabled. This flag is cleared on
reset

•

ESCR select field, bits 13 through 15 — Identifies the ESCR to be used to select events to be counted with
the counter associated with the CCCR.

•

Active thread field, bits 16 and 17 — Enables counting depending on which logical processors are active
(executing a thread). This field enables filtering of events based on the state (active or inactive) of the logical
processors. The encodings of this field are as follows:
00 — None. Count only when neither logical processor is active.
01 — Single. Count only when one logical processor is active (either 0 or 1).
10 — Both. Count only when both logical processors are active.
11 — Any. Count when either logical processor is active.
A halted logical processor or a logical processor in the “wait for SIPI” state is considered inactive.

•

Compare flag, bit 18 — When set, enables filtering of the event count; when clear, disables filtering. The
filtering method is selected with the threshold, complement, and edge flags.

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Reserved
31 30 29

27 26 25 24 23

20 19 18 17 16 15

Threshold

13 12 11

ESCR
Select

0
Reserved
Reserved

Enable
Active Thread
Compare
Complement
Edge
FORCE_OVF
OVF_PMI_T0
OVF_PMI_T1
Cascade
OVF
63

32

Reserved

Figure 18-50. Counter Configuration Control Register (CCCR)

•

Complement flag, bit 19 — Selects how the incoming event count is compared with the threshold value.
When set, event counts that are less than or equal to the threshold value result in a single count being
delivered to the performance counter; when clear, counts greater than the threshold value result in a count
being delivered to the performance counter (see Section 18.6.3.5.2, “Filtering Events”). The compare flag is
not active unless the compare flag is set.

•

Threshold field, bits 20 through 23 — Selects the threshold value to be used for comparisons. The
processor examines this field only when the compare flag is set, and uses the complement flag setting to
determine the type of threshold comparison to be made. The useful range of values that can be entered in this
field depend on the type of event being counted (see Section 18.6.3.5.2, “Filtering Events”).

•

Edge flag, bit 24 — When set, enables rising edge (false-to-true) edge detection of the threshold comparison
output for filtering event counts; when clear, rising edge detection is disabled. This flag is active only when the
compare flag is set.

•

FORCE_OVF flag, bit 25 — When set, forces a counter overflow on every counter increment; when clear,
overflow only occurs when the counter actually overflows.

•

OVF_PMI_T0 flag, bit 26 — When set, causes a performance monitor interrupt (PMI) to be sent to logical
processor 0 when the counter overflows occurs; when clear, disables PMI generation for logical processor 0.
Note that the PMI is generate on the next event count after the counter has overflowed.

•

OVF_PMI_T1 flag, bit 27 — When set, causes a performance monitor interrupt (PMI) to be sent to logical
processor 1 when the counter overflows occurs; when clear, disables PMI generation for logical processor 1.
Note that the PMI is generate on the next event count after the counter has overflowed.

•

Cascade flag, bit 30 — When set, enables counting on one counter of a counter pair when its alternate
counter in the other the counter pair in the same counter group overflows (see Section 18.6.3.2, “Performance
Counters,” for further details); when clear, disables cascading of counters.

•

OVF flag, bit 31 — Indicates that the counter has overflowed when set. This flag is a sticky flag that must be
explicitly cleared by software.

18.6.4.3

IA32_PEBS_ENABLE MSR

In a processor supporting Intel Hyper-Threading Technology and based on the Intel NetBurst microarchitecture,
PEBS is enabled and qualified with two bits in the MSR_PEBS_ENABLE MSR: bit 25 (ENABLE_PEBS_MY_THR) and
26 (ENABLE_PEBS_OTH_THR) respectively. These bits do not explicitly identify a specific logical processor by logic

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PERFORMANCE MONITORING

processor ID(T0 or T1); instead, they allow a software agent to enable PEBS for subsequent threads of execution
on the same logical processor on which the agent is running (“my thread”) or for the other logical processor in the
physical package on which the agent is not running (“other thread”).
PEBS is supported for only a subset of the at-retirement events: Execution_event, Front_end_event, and
Replay_event. Also, PEBS can be carried out only with two performance counters: MSR_IQ_CCCR4 (MSR address
370H) for logical processor 0 and MSR_IQ_CCCR5 (MSR address 371H) for logical processor 1.
Performance monitoring tools should use a processor affinity mask to bind the kernel mode components that need
to modify the ENABLE_PEBS_MY_THR and ENABLE_PEBS_OTH_THR bits in the MSR_PEBS_ENABLE MSR to a
specific logical processor. This is to prevent these kernel mode components from migrating between different
logical processors due to OS scheduling.

18.6.4.4

Performance Monitoring Events

All of the events listed in Table 19-31 and 19-32 are available in an Intel Xeon processor MP. When Intel HyperThreading Technology is active, many performance monitoring events can be can be qualified by the logical
processor ID, which corresponds to bit 0 of the initial APIC ID. This allows for counting an event in any or all of the
logical processors. However, not all the events have this logic processor specificity, or thread specificity.
Here, each event falls into one of two categories:

•
•

Thread specific (TS) — The event can be qualified as occurring on a specific logical processor.
Thread independent (TI) — The event cannot be qualified as being associated with a specific logical
processor.

Table 19-37 gives logical processor specific information (TS or TI) for each of the events described in Tables 19-31
and 19-32. If for example, a TS event occurred in logical processor T0, the counting of the event (as shown in Table
18-73) depends only on the setting of the T0_USR and T0_OS flags in the ESCR being used to set up the event
counter. The T1_USR and T1_OS flags have no effect on the count.

Table 18-73. Effect of Logical Processor and CPL Qualification
for Logical-Processor-Specific (TS) Events
T1_OS/T1_USR = 00

T1_OS/T1_USR = 01

T1_OS/T1_USR = 11

T1_OS/T1_USR = 10

T0_OS/T0_USR = 00

Zero count

Counts while T1 in USR

Counts while T1 in OS or
USR

Counts while T1 in OS

T0_OS/T0_USR = 01

Counts while T0 in USR

Counts while T0 in USR
or T1 in USR

Counts while (a) T0 in
USR or (b) T1 in OS or (c)
T1 in USR

Counts while (a) T0 in OS
or (b) T1 in OS

T0_OS/T0_USR = 11

Counts while T0 in OS or
USR

Counts while (a) T0 in OS
or (b) T0 in USR or (c) T1
in USR

Counts irrespective of
CPL, T0, T1

Counts while (a) T0 in OS
or (b) or T0 in USR or (c)
T1 in OS

T0_OS/T0_USR = 10

Counts T0 in OS

Counts T0 in OS or T1 in
USR

Counts while (a)T0 in Os
or (b) T1 in OS or (c) T1
in USR

Counts while (a) T0 in OS
or (b) T1 in OS

When a bit in the event mask field is TI, the effect of specifying bit-0-3 of the associated ESCR are described in
Table 15-6. For events that are marked as TI in Chapter 19, the effect of selectively specifying T0_USR, T0_OS,
T1_USR, T1_OS bits is shown in Table 18-74.

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Table 18-74. Effect of Logical Processor and CPL Qualification
for Non-logical-Processor-specific (TI) Events
T1_OS/T1_USR = 00

T1_OS/T1_USR = 01

T1_OS/T1_USR = 11

T1_OS/T1_USR = 10

T0_OS/T0_USR = 00

Zero count

Counts while (a) T0 in
USR or (b) T1 in USR

Counts irrespective of
CPL, T0, T1

Counts while (a) T0 in OS
or (b) T1 in OS

T0_OS/T0_USR = 01

Counts while (a) T0 in
USR or (b) T1 in USR

Counts while (a) T0 in
USR or (b) T1 in USR

Counts irrespective of
CPL, T0, T1

Counts irrespective of
CPL, T0, T1

T0_OS/T0_USR = 11

Counts irrespective of
CPL, T0, T1

Counts irrespective of
CPL, T0, T1

Counts irrespective of
CPL, T0, T1

Counts irrespective of
CPL, T0, T1

T0_OS/T0_USR = 0

Counts while (a) T0 in OS
or (b) T1 in OS

Counts irrespective of
CPL, T0, T1

Counts irrespective of
CPL, T0, T1

Counts while (a) T0 in OS
or (b) T1 in OS

18.6.4.5

Counting Clocks on systems with Intel Hyper-Threading Technology in Processors Based on
Intel NetBurst® Microarchitecture

18.6.4.5.1 Non-Halted Clockticks
Use the following procedure to program ESCRs and CCCRs to obtain non-halted clockticks on processors based on
Intel NetBurst microarchitecture:
1. Select an ESCR for the global_power_events and specify the RUNNING sub-event mask and the desired
T0_OS/T0_USR/T1_OS/T1_USR bits for the targeted processor.
2. Select an appropriate counter.
3. Enable counting in the CCCR for that counter by setting the enable bit.

18.6.4.5.2 Non-Sleep Clockticks
Performance monitoring counters can be configured to count clockticks whenever the performance monitoring
hardware is not powered-down. To count Non-sleep Clockticks with a performance-monitoring counter, do the
following:
1. Select one of the 18 counters.
2. Select any of the ESCRs whose events the selected counter can count. Set its event select to anything other
than “no_event”; the counter may be disabled if this is not done.
3. Turn threshold comparison on in the CCCR by setting the compare bit to “1”.
4. Set the threshold to “15” and the complement to “1” in the CCCR. Since no event can exceed this threshold, the
threshold condition is met every cycle and the counter counts every cycle. Note that this overrides any qualification (e.g. by CPL) specified in the ESCR.
5. Enable counting in the CCCR for the counter by setting the enable bit.
In most cases, the counts produced by the non-halted and non-sleep metrics are equivalent if the physical package
supports one logical processor and is not placed in a power-saving state. Operating systems may execute an HLT
instruction and place a physical processor in a power-saving state.
On processors that support Intel Hyper-Threading Technology (Intel HT Technology), each physical package can
support two or more logical processors. Current implementation of Intel HT Technology provides two logical
processors for each physical processor. While both logical processors can execute two threads simultaneously, one
logical processor may halt to allow the other logical processor to execute without sharing execution resources
between two logical processors.
Non-halted Clockticks can be set up to count the number of processor clock cycles for each logical processor whenever the logical processor is not halted (the count may include some portion of the clock cycles for that logical
processor to complete a transition to a halted state). Physical processors that support Intel HT Technology enter
into a power-saving state if all logical processors halt.

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PERFORMANCE MONITORING

The Non-sleep Clockticks mechanism uses a filtering mechanism in CCCRs. The mechanism will continue to increment as long as one logical processor is not halted or in a power-saving state. Applications may cause a processor
to enter into a power-saving state by using an OS service that transfers control to an OS's idle loop. The idle loop
then may place the processor into a power-saving state after an implementation-dependent period if there is no
work for the processor.

18.6.5

Performance Monitoring and Dual-Core Technology

The performance monitoring capability of dual-core processors duplicates the microarchitectural resources of a
single-core processor implementation. Each processor core has dedicated performance monitoring resources.
In the case of Pentium D processor, each logical processor is associated with dedicated resources for performance
monitoring. In the case of Pentium processor Extreme edition, each processor core has dedicated resources, but
two logical processors in the same core share performance monitoring resources (see Section 18.6.4, “Performance Monitoring and Intel Hyper-Threading Technology in Processors Based on Intel NetBurst® Microarchitecture”).

18.6.6

Performance Monitoring on 64-bit Intel Xeon Processor MP with Up to 8-MByte L3
Cache

The 64-bit Intel Xeon processor MP with up to 8-MByte L3 cache has a CPUID signature of family [0FH], model [03H
or 04H]. Performance monitoring capabilities available to Pentium 4 and Intel Xeon processors with the same
values (see Section 18.1 and Section 18.6.4) apply to the 64-bit Intel Xeon processor MP with an L3 cache.
The level 3 cache is connected between the system bus and IOQ through additional control logic. See Figure 18-51.

System Bus

iBUSQ and iSNPQ

3rd Level Cache
8 or 4 -way

iFSB

IOQ

Processor Core
(Front end, Execution,
Retirement, L1, L2

Figure 18-51. Block Diagram of 64-bit Intel Xeon Processor MP with 8-MByte L3
Additional performance monitoring capabilities and facilities unique to 64-bit Intel Xeon processor MP with an L3
cache are described in this section. The facility for monitoring events consists of a set of dedicated model-specific
registers (MSRs), each dedicated to a specific event. Programming of these MSRs requires using RDMSR/WRMSR
instructions with 64-bit values.
The lower 32-bits of the MSRs at addresses 107CC through 107D3 are treated as 32 bit performance counter registers. These performance counters can be accessed using RDPMC instruction with the index starting from 18
through 25. The EDX register returns zero when reading these 8 PMCs.
The performance monitoring capabilities consist of four events. These are:

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PERFORMANCE MONITORING

•

IBUSQ event — This event detects the occurrence of micro-architectural conditions related to the iBUSQ unit.
It provides two MSRs: MSR_IFSB_IBUSQ0 and MSR_IFSB_IBUSQ1. Configure sub-event qualification and
enable/disable functions using the high 32 bits of these MSRs. The low 32 bits act as a 32-bit event counter.
Counting starts after software writes a non-zero value to one or more of the upper 32 bits. See Figure 18-52.

MSR_IFSB_IBUSQx, Addresses: 107CCH and 107CDH
63

49 48

60 59 58 57 56 55

0

38 37 36 35 34 33 32 31

46 45

1 1

Saturate
Fill_match
Eviction_match
L3_state_match
Snoop_match
Type_match
T1_match
T0_match

32 bit event count

Reserved

Figure 18-52. MSR_IFSB_IBUSQx, Addresses: 107CCH and 107CDH

•

ISNPQ event — This event detects the occurrence of microarchitectural conditions related to the iSNPQ unit.
It provides two MSRs: MSR_IFSB_ISNPQ0 and MSR_IFSB_ISNPQ1. Configure sub-event qualifications and
enable/disable functions using the high 32 bits of the MSRs. The low 32-bits act as a 32-bit event counter.
Counting starts after software writes a non-zero value to one or more of the upper 32-bits. See Figure 18-53.

MSR_IFSB_ISNPQx, Addresses: 107CEH and 107CFH
63

60 59 58 57 56 55

48

46 45

Reserved
39 38 37 36 35 34 33 32

Saturate
L3_state_match
Snoop_match
Type_match
Agent_match
T1_match
T0_match
31

0

32 bit event count

Figure 18-53. MSR_IFSB_ISNPQx, Addresses: 107CEH and 107CFH

•

EFSB event — This event can detect the occurrence of micro-architectural conditions related to the iFSB unit
or system bus. It provides two MSRs: MSR_EFSB_DRDY0 and MSR_EFSB_DRDY1. Configure sub-event qualifications and enable/disable functions using the high 32 bits of the 64-bit MSR. The low 32-bit act as a 32-bit
event counter. Counting starts after software writes a non-zero value to one or more of the qualification bits in
the upper 32-bits of the MSR. See Figure 18-54.

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PERFORMANCE MONITORING

MSR_EFSB_DRDYx, Addresses: 107D0H and 107D1H
63

60 59 58 57 56 55

50 49 48

39 38 37 36 35 34 33 32

Saturate
Other
Own

Reserved

31

0

32 bit event count

Figure 18-54. MSR_EFSB_DRDYx, Addresses: 107D0H and 107D1H

•

IBUSQ Latency event — This event accumulates weighted cycle counts for latency measurement of transactions in the iBUSQ unit. The count is enabled by setting MSR_IFSB_CTRL6[bit 26] to 1; the count freezes after
software sets MSR_IFSB_CTRL6[bit 26] to 0. MSR_IFSB_CNTR7 acts as a 64-bit event counter for this event.
See Figure 18-55.

MSR_IFSB_CTL6 Address: 107D2H
63

59

0

57

Enable
MSR_IFSB_CNTR7 Address: 107D3H

Reserved
0

63

64 bit event count

Figure 18-55. MSR_IFSB_CTL6, Address: 107D2H;
MSR_IFSB_CNTR7, Address: 107D3H

18.6.7

Performance Monitoring on L3 and Caching Bus Controller Sub-Systems

The Intel Xeon processor 7400 series and Dual-Core Intel Xeon processor 7100 series employ a distinct L3/caching
bus controller sub-system. These sub-system have a unique set of performance monitoring capability and
programming interfaces that are largely common between these two processor families.
Intel Xeon processor 7400 series are based on 45 nm enhanced Intel Core microarchitecture. The CPUID signature
is indicated by DisplayFamily_DisplayModel value of 06_1DH (see CPUID instruction in Chapter 3, “Instruction Set
Reference, A-L” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A). Intel Xeon
processor 7400 series have six processor cores that share an L3 cache.
Dual-Core Intel Xeon processor 7100 series are based on Intel NetBurst microarchitecture, have a CPUID signature
of family [0FH], model [06H] and a unified L3 cache shared between two cores. Each core in an Intel Xeon
processor 7100 series supports Intel Hyper-Threading Technology, providing two logical processors per core.
Both Intel Xeon processor 7400 series and Intel Xeon processor 7100 series support multi-processor configurations
using system bus interfaces. In Intel Xeon processor 7400 series, the L3/caching bus controller sub-system
provides three Simple Direct Interface (SDI) to service transactions originated the XQ-replacement SDI logic in
each dual-core modules. In Intel Xeon processor 7100 series, the IOQ logic in each processor core is replaced with
a Simple Direct Interface (SDI) logic. The L3 cache is connected between the system bus and the SDI through addi18-114 Vol. 3B

PERFORMANCE MONITORING

tional control logic. See Figure 18-56 for the block configuration of six processor cores and the L3/Caching bus
controller sub-system in Intel Xeon processor 7400 series. Figure 18-56 shows the block configuration of two
processor cores (four logical processors) and the L3/Caching bus controller sub-system in Intel Xeon processor
7100 series.

FSB

GBSQ, GSNPQ,
GINTQ, ...

L3

SDI

SDI interface
L2
Core

SDI interface
L2

Core

Core

SDI interface
L2

Core

Core

Core

Figure 18-56. Block Diagram of Intel Xeon Processor 7400 Series
Almost all of the performance monitoring capabilities available to processor cores with the same CPUID signatures
(see Section 18.1 and Section 18.6.4) apply to Intel Xeon processor 7100 series. The MSRs used by performance
monitoring interface are shared between two logical processors in the same processor core.
The performance monitoring capabilities available to processor with DisplayFamily_DisplayModel signature 06_17H
also apply to Intel Xeon processor 7400 series. Each processor core provides its own set of MSRs for performance
monitoring interface.
The IOQ_allocation and IOQ_active_entries events are not supported in Intel Xeon processor 7100 series and 7400
series. Additional performance monitoring capabilities applicable to the L3/caching bus controller sub-system are
described in this section.

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PERFORMANCE MONITORING

FSB

GBSQ, GSNPQ,
GINTQ, ...

L3

SDI

SDI interface

SDI interface

Processor core

Processor core

Logical

processor

Logical

processor

Logical

processor

Logical

processor

Figure 18-57. Block Diagram of Intel Xeon Processor 7100 Series

18.6.7.1

Overview of Performance Monitoring with L3/Caching Bus Controller

The facility for monitoring events consists of a set of dedicated model-specific registers (MSRs). There are eight
event select/counting MSRs that are dedicated to counting events associated with specified microarchitectural
conditions. Programming of these MSRs requires using RDMSR/WRMSR instructions with 64-bit values. In addition,
an MSR MSR_EMON_L3_GL_CTL provides simplified interface to control freezing, resetting, re-enabling operation
of any combination of these event select/counting MSRs.
The eight MSRs dedicated to count occurrences of specific conditions are further divided to count three sub-classes
of microarchitectural conditions:

•

Two MSRs (MSR_EMON_L3_CTR_CTL0 and MSR_EMON_L3_CTR_CTL1) are dedicated to counting GBSQ
events. Up to two GBSQ events can be programmed and counted simultaneously.

•

Two MSRs (MSR_EMON_L3_CTR_CTL2 and MSR_EMON_L3_CTR_CTL3) are dedicated to counting GSNPQ
events. Up to two GBSQ events can be programmed and counted simultaneously.

•

Four MSRs (MSR_EMON_L3_CTR_CTL4, MSR_EMON_L3_CTR_CTL5, MSR_EMON_L3_CTR_CTL6, and
MSR_EMON_L3_CTR_CTL7) are dedicated to counting external bus operations.

The bit fields in each of eight MSRs share the following common characteristics:

•

Bits 63:32 is the event control field that includes an event mask and other bit fields that control counter
operation. The event mask field specifies details of the microarchitectural condition, and its definition differs
across GBSQ, GSNPQ, FSB.

•

Bits 31:0 is the event count field. If the specified condition is met during each relevant clock domain of the
event logic, the matched condition signals the counter logic to increment the associated event count field. The
lower 32-bits of these 8 MSRs at addresses 107CC through 107D3 are treated as 32 bit performance counter
registers.

In Dual-Core Intel Xeon processor 7100 series, the uncore performance counters can be accessed using RDPMC
instruction with the index starting from 18 through 25. The EDX register returns zero when reading these 8 PMCs.
In Intel Xeon processor 7400 series, RDPMC with ECX between 2 and 9 can be used to access the eight uncore
performance counter/control registers.

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18.6.7.2

GBSQ Event Interface

The layout of MSR_EMON_L3_CTR_CTL0 and MSR_EMON_L3_CTR_CTL1 is given in Figure 18-58. Counting starts
after software writes a non-zero value to one or more of the upper 32 bits.
The event mask field (bits 58:32) consists of the following eight attributes:

•

Agent_Select (bits 35:32): The definition of this field differs slightly between Intel Xeon processor 7100 and
7400.
For Intel Xeon processor 7100 series, each bit specifies a logical processor in the physical package. The lower
two bits corresponds to two logical processors in the first processor core, the upper two bits corresponds to two
logical processors in the second processor core. 0FH encoding matches transactions from any logical processor.
For Intel Xeon processor 7400 series, each bit of [34:32] specifies the SDI logic of a dual-core module as the
originator of the transaction. A value of 0111B in bits [35:32] specifies transaction from any processor core.

MSR_EMON_L3_CTR_CTL0/1, Addresses: 107CCH/107CDH
63

60 59 58 57 56 55 54 53

47 46

44 43

Reserved
38 37 36 35

32

Saturate
Cross_snoop
Fill_eviction
Core_module_select
L3_state
Snoop_match
Type_match
Data_flow
Agent_select
31

0

32 bit event count

Figure 18-58. MSR_EMON_L3_CTR_CTL0/1, Addresses: 107CCH/107CDH

•
•

Data_Flow (bits 37:36): Bit 36 specifies demand transactions, bit 37 specifies prefetch transactions.

•

Snoop_Match: (bits 46:44): The three bits specify (in ascending bit position) clean snoop result, HIT snoop
result, and HITM snoop results respectively.

•
•

L3_State (bits 53:47): Each bit specifies an L2 coherency state.

Type_Match (bits 43:38): Specifies transaction types. If all six bits are set, event count will include all
transaction types.

Core_Module_Select (bits 55:54): The valid encodings for L3 lookup differ slightly between Intel Xeon
processor 7100 and 7400.
For Intel Xeon processor 7100 series,
— 00B: Match transactions from any core in the physical package
— 01B: Match transactions from this core only
— 10B: Match transactions from the other core in the physical package
— 11B: Match transaction from both cores in the physical package
For Intel Xeon processor 7400 series,
— 00B: Match transactions from any dual-core module in the physical package
— 01B: Match transactions from this dual-core module only
— 10B: Match transactions from either one of the other two dual-core modules in the physical package
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PERFORMANCE MONITORING

— 11B: Match transaction from more than one dual-core modules in the physical package

•

Fill_Eviction (bits 57:56): The valid encodings are
— 00B: Match any transactions
— 01B: Match transactions that fill L3
— 10B: Match transactions that fill L3 without an eviction
— 11B: Match transaction fill L3 with an eviction

•

Cross_Snoop (bit 58): The encodings are

\

— 0B: Match any transactions
— 1B: Match cross snoop transactions
For each counting clock domain, if all eight attributes match, event logic signals to increment the event count field.

18.6.7.3

GSNPQ Event Interface

The layout of MSR_EMON_L3_CTR_CTL2 and MSR_EMON_L3_CTR_CTL3 is given in Figure 18-59. Counting starts
after software writes a non-zero value to one or more of the upper 32 bits.
The event mask field (bits 58:32) consists of the following six attributes:

•

Agent_Select (bits 37:32): The definition of this field differs slightly between Intel Xeon processor 7100 and
7400.

•

For Intel Xeon processor 7100 series, each of the lowest 4 bits specifies a logical processor in the physical
package. The lowest two bits corresponds to two logical processors in the first processor core, the next two bits
corresponds to two logical processors in the second processor core. Bit 36 specifies other symmetric agent
transactions. Bit 37 specifies central agent transactions. 3FH encoding matches transactions from any logical
processor.
For Intel Xeon processor 7400 series, each of the lowest 3 bits specifies a dual-core module in the physical
package. Bit 37 specifies central agent transactions.

•

Type_Match (bits 43:38): Specifies transaction types. If all six bits are set, event count will include any
transaction types.

•

Snoop_Match: (bits 46:44): The three bits specify (in ascending bit position) clean snoop result, HIT snoop
result, and HITM snoop results respectively.

•
•

L2_State (bits 53:47): Each bit specifies an L3 coherency state.
Core_Module_Select (bits 56:54): Bit 56 enables Core_Module_Select matching. If bit 56 is clear,
Core_Module_Select encoding is ignored. The valid encodings for the lower two bits (bit 55, 54) differ slightly
between Intel Xeon processor 7100 and 7400.
For Intel Xeon processor 7100 series, if bit 56 is set, the valid encodings for the lower two bits (bit 55, 54) are
— 00B: Match transactions from only one core (irrespective which core) in the physical package
— 01B: Match transactions from this core and not the other core
— 10B: Match transactions from the other core in the physical package, but not this core
— 11B: Match transaction from both cores in the physical package
For Intel Xeon processor 7400 series, if bit 56 is set, the valid encodings for the lower two bits (bit 55, 54) are
— 00B: Match transactions from only one dual-core module (irrespective which module) in the physical
package.
— 01B: Match transactions from one or more dual-core modules.
— 10B: Match transactions from two or more dual-core modules.
— 11B: Match transaction from all three dual-core modules in the physical package.

•

Block_Snoop (bit 57): specifies blocked snoop.

For each counting clock domain, if all six attributes match, event logic signals to increment the event count field.

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MSR_EMON_L3_CTR_CTL2/3, Addresses: 107CEH/107CFH
63

60 59 58 57 56 55 54 53

47 46

44 43

Reserved
32

39 38 37 36

Saturate
Block_snoop
Core_select
L2_state
Snoop_match
Type_match
Agent_match
31

0

32 bit event count

Figure 18-59. MSR_EMON_L3_CTR_CTL2/3, Addresses: 107CEH/107CFH

18.6.7.4

FSB Event Interface

The layout of MSR_EMON_L3_CTR_CTL4 through MSR_EMON_L3_CTR_CTL7 is given in Figure 18-60. Counting
starts after software writes a non-zero value to one or more of the upper 32 bits.
The event mask field (bits 58:32) is organized as follows:

•
•

Bit 58: must set to 1.
FSB_Submask (bits 57:32): Specifies FSB-specific sub-event mask.

The FSB sub-event mask defines a set of independent attributes. The event logic signals to increment the associated event count field if one of the attribute matches. Some of the sub-event mask bit counts durations. A duration
event increments at most once per cycle.

MSR_EMON_L3_CTR_CTL4/5/6/7, Addresses: 107D0H-107D3H
63

60 59 58 57 56 55

50 49 48

39 38 37 36 35 34 33 32

1

Reserved

Saturate
FSB submask
31

0

32 bit event count

Figure 18-60. MSR_EMON_L3_CTR_CTL4/5/6/7, Addresses: 107D0H-107D3H
18.6.7.4.1

FSB Sub-Event Mask Interface

•
•

FSB_type (bit 37:32): Specifies different FSB transaction types originated from this physical package.

•

FSB_L_hit (bit 39): Count HIT snoop results from any source for transaction originated from this physical
package.

FSB_L_clear (bit 38): Count clean snoop results from any source for transaction originated from this physical
package.

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PERFORMANCE MONITORING

•

FSB_L_hitm (bit 40): Count HITM snoop results from any source for transaction originated from this physical
package.

•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

FSB_L_defer (bit 41): Count DEFER responses to this processor’s transactions.
FSB_L_retry (bit 42): Count RETRY responses to this processor’s transactions.
FSB_L_snoop_stall (bit 43): Count snoop stalls to this processor’s transactions.
FSB_DBSY (bit 44): Count DBSY assertions by this processor (without a concurrent DRDY).
FSB_DRDY (bit 45): Count DRDY assertions by this processor.
FSB_BNR (bit 46): Count BNR assertions by this processor.
FSB_IOQ_empty (bit 47): Counts each bus clocks when the IOQ is empty.
FSB_IOQ_full (bit 48): Counts each bus clocks when the IOQ is full.
FSB_IOQ_active (bit 49): Counts each bus clocks when there is at least one entry in the IOQ.
FSB_WW_data (bit 50): Counts back-to-back write transaction’s data phase.
FSB_WW_issue (bit 51): Counts back-to-back write transaction request pairs issued by this processor.
FSB_WR_issue (bit 52): Counts back-to-back write-read transaction request pairs issued by this processor.
FSB_RW_issue (bit 53): Counts back-to-back read-write transaction request pairs issued by this processor.
FSB_other_DBSY (bit 54): Count DBSY assertions by another agent (without a concurrent DRDY).
FSB_other_DRDY (bit 55): Count DRDY assertions by another agent.
FSB_other_snoop_stall (bit 56): Count snoop stalls on the FSB due to another agent.
FSB_other_BNR (bit 57): Count BNR assertions from another agent.

18.6.7.5

Common Event Control Interface

The MSR_EMON_L3_GL_CTL MSR provides simplified access to query overflow status of the GBSQ, GSNPQ, FSB
event counters. It also provides control bit fields to freeze, unfreeze, or reset those counters. The following bit
fields are supported:

•
•
•

GL_freeze_cmd (bit 0): Freeze the event counters specified by the GL_event_select field.

•

GL_event_select (bit 23:16): Selects one or more event counters to subject to specified command operations
indicated by bits 2:0. Bit 16 corresponds to MSR_EMON_L3_CTR_CTL0, bit 23 corresponds to
MSR_EMON_L3_CTR_CTL7.

•

GL_event_status (bit 55:48): Indicates the overflow status of each event counters. Bit 48 corresponds to
MSR_EMON_L3_CTR_CTL0, bit 55 corresponds to MSR_EMON_L3_CTR_CTL7.

GL_unfreeze_cmd (bit 1): Unfreeze the event counters specified by the GL_event_select field.
GL_reset_cmd (bit 2): Clear the event count field of the event counters specified by the GL_event_select field.
The event select field is not affected.

In the event control field (bits 63:32) of each MSR, if the saturate control (bit 59, see Figure 18-58 for example) is
set, the event logic forces the value FFFF_FFFFH into the event count field instead of incrementing it.

18.6.8

Performance Monitoring (P6 Family Processor)

The P6 family processors provide two 40-bit performance counters, allowing two types of events to be monitored
simultaneously. These can either count events or measure duration. When counting events, a counter increments
each time a specified event takes place or a specified number of events takes place. When measuring duration, it
counts the number of processor clocks that occur while a specified condition is true. The counters can count events
or measure durations that occur at any privilege level.
Table 19-40, Chapter 19, lists the events that can be counted with the P6 family performance monitoring counters.

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PERFORMANCE MONITORING

NOTE
The performance-monitoring events listed in Chapter 19 are intended to be used as guides for
performance tuning. Counter values reported are not guaranteed to be accurate and should be
used as a relative guide for tuning. Known discrepancies are documented where applicable.
The performance-monitoring counters are supported by four MSRs: the performance event select MSRs
(PerfEvtSel0 and PerfEvtSel1) and the performance counter MSRs (PerfCtr0 and PerfCtr1). These registers can be
read from and written to using the RDMSR and WRMSR instructions, respectively. They can be accessed using
these instructions only when operating at privilege level 0. The PerfCtr0 and PerfCtr1 MSRs can be read from any
privilege level using the RDPMC (read performance-monitoring counters) instruction.

NOTE
The PerfEvtSel0, PerfEvtSel1, PerfCtr0, and PerfCtr1 MSRs and the events listed in Table 19-40 are
model-specific for P6 family processors. They are not guaranteed to be available in other IA-32
processors.

18.6.8.1

PerfEvtSel0 and PerfEvtSel1 MSRs

The PerfEvtSel0 and PerfEvtSel1 MSRs control the operation of the performance-monitoring counters, with one
register used to set up each counter. They specify the events to be counted, how they should be counted, and the
privilege levels at which counting should take place. Figure 18-61 shows the flags and fields in these MSRs.
The functions of the flags and fields in the PerfEvtSel0 and PerfEvtSel1 MSRs are as follows:

•

Event select field (bits 0 through 7) — Selects the event logic unit to detect certain microarchitectural
conditions (see Table 19-40, for a list of events and their 8-bit codes).

•

Unit mask (UMASK) field (bits 8 through 15) — Further qualifies the event logic unit selected in the event
select field to detect a specific microarchitectural condition. For example, for some cache events, the mask is
used as a MESI-protocol qualifier of cache states (see Table 19-40).

31

24 23 22 21 20 19 18 17 16 15
Counter Mask
(CMASK)

INV—Invert counter mask
EN—Enable counters*
INT—APIC interrupt enable
PC—Pin control
E—Edge detect
OS—Operating system mode
USR—User Mode

I
N E
V N

0

8 7

I
U
N P E O S Unit Mask (UMASK)
S R
T C

Event Select

Reserved

* Only available in PerfEvtSel0.

Figure 18-61. PerfEvtSel0 and PerfEvtSel1 MSRs

•

USR (user mode) flag (bit 16) — Specifies that events are counted only when the processor is operating at
privilege levels 1, 2 or 3. This flag can be used in conjunction with the OS flag.

•

OS (operating system mode) flag (bit 17) — Specifies that events are counted only when the processor is
operating at privilege level 0. This flag can be used in conjunction with the USR flag.

•

E (edge detect) flag (bit 18) — Enables (when set) edge detection of events. The processor counts the
number of deasserted to asserted transitions of any condition that can be expressed by the other fields. The
mechanism is limited in that it does not permit back-to-back assertions to be distinguished. This mechanism
allows software to measure not only the fraction of time spent in a particular state, but also the average length
of time spent in such a state (for example, the time spent waiting for an interrupt to be serviced).

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PERFORMANCE MONITORING

•

PC (pin control) flag (bit 19) — When set, the processor toggles the PMi pins and increments the counter
when performance-monitoring events occur; when clear, the processor toggles the PMi pins when the counter
overflows. The toggling of a pin is defined as assertion of the pin for a single bus clock followed by deassertion.

•

INT (APIC interrupt enable) flag (bit 20) — When set, the processor generates an exception through its
local APIC on counter overflow.

•

EN (Enable Counters) Flag (bit 22) — This flag is only present in the PerfEvtSel0 MSR. When set,
performance counting is enabled in both performance-monitoring counters; when clear, both counters are
disabled.

•

INV (invert) flag (bit 23) — When set, inverts the counter-mask (CMASK) comparison, so that both greater
than or equal to and less than comparisons can be made (0: greater than or equal; 1: less than). Note if
counter-mask is programmed to zero, INV flag is ignored.

•

Counter mask (CMASK) field (bits 24 through 31) — When nonzero, the processor compares this mask to
the number of events counted during a single cycle. If the event count is greater than or equal to this mask, the
counter is incremented by one. Otherwise the counter is not incremented. This mask can be used to count
events only if multiple occurrences happen per clock (for example, two or more instructions retired per clock).
If the counter-mask field is 0, then the counter is incremented each cycle by the number of events that
occurred that cycle.

18.6.8.2

PerfCtr0 and PerfCtr1 MSRs

The performance-counter MSRs (PerfCtr0 and PerfCtr1) contain the event or duration counts for the selected
events being counted. The RDPMC instruction can be used by programs or procedures running at any privilege level
and in virtual-8086 mode to read these counters. The PCE flag in control register CR4 (bit 8) allows the use of this
instruction to be restricted to only programs and procedures running at privilege level 0.
The RDPMC instruction is not serializing or ordered with other instructions. Thus, it does not necessarily wait until
all previous instructions have been executed before reading the counter. Similarly, subsequent instructions may
begin execution before the RDPMC instruction operation is performed.
Only the operating system, executing at privilege level 0, can directly manipulate the performance counters, using
the RDMSR and WRMSR instructions. A secure operating system would clear the PCE flag during system initialization to disable direct user access to the performance-monitoring counters, but provide a user-accessible programming interface that emulates the RDPMC instruction.
The WRMSR instruction cannot arbitrarily write to the performance-monitoring counter MSRs (PerfCtr0 and
PerfCtr1). Instead, the lower-order 32 bits of each MSR may be written with any value, and the high-order 8 bits
are sign-extended according to the value of bit 31. This operation allows writing both positive and negative values
to the performance counters.

18.6.8.3

Starting and Stopping the Performance-Monitoring Counters

The performance-monitoring counters are started by writing valid setup information in the PerfEvtSel0 and/or
PerfEvtSel1 MSRs and setting the enable counters flag in the PerfEvtSel0 MSR. If the setup is valid, the counters
begin counting following the execution of a WRMSR instruction that sets the enable counter flag. The counters can
be stopped by clearing the enable counters flag or by clearing all the bits in the PerfEvtSel0 and PerfEvtSel1 MSRs.
Counter 1 alone can be stopped by clearing the PerfEvtSel1 MSR.

18.6.8.4

Event and Time-Stamp Monitoring Software

To use the performance-monitoring counters and time-stamp counter, the operating system needs to provide an
event-monitoring device driver. This driver should include procedures for handling the following operations:

•
•
•
•
•

Feature checking.
Initialize and start counters.
Stop counters.
Read the event counters.
Read the time-stamp counter.

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PERFORMANCE MONITORING

The event monitor feature determination procedure must check whether the current processor supports the
performance-monitoring counters and time-stamp counter. This procedure compares the family and model of the
processor returned by the CPUID instruction with those of processors known to support performance monitoring.
(The Pentium and P6 family processors support performance counters.) The procedure also checks the MSR and
TSC flags returned to register EDX by the CPUID instruction to determine if the MSRs and the RDTSC instruction
are supported.
The initialize and start counters procedure sets the PerfEvtSel0 and/or PerfEvtSel1 MSRs for the events to be
counted and the method used to count them and initializes the counter MSRs (PerfCtr0 and PerfCtr1) to starting
counts. The stop counters procedure stops the performance counters (see Section 18.6.8.3, “Starting and Stopping the Performance-Monitoring Counters”).
The read counters procedure reads the values in the PerfCtr0 and PerfCtr1 MSRs, and a read time-stamp counter
procedure reads the time-stamp counter. These procedures would be provided in lieu of enabling the RDTSC and
RDPMC instructions that allow application code to read the counters.

18.6.8.5

Monitoring Counter Overflow

The P6 family processors provide the option of generating a local APIC interrupt when a performance-monitoring
counter overflows. This mechanism is enabled by setting the interrupt enable flag in either the PerfEvtSel0 or the
PerfEvtSel1 MSR. The primary use of this option is for statistical performance sampling.
To use this option, the operating system should do the following things on the processor for which performance
events are required to be monitored:

•
•
•

Provide an interrupt vector for handling the counter-overflow interrupt.

•

Provide an event monitor driver that provides the actual interrupt handler and modifies the reserved IDT entry
to point to its interrupt routine.

Initialize the APIC PERF local vector entry to enable handling of performance-monitor counter overflow events.
Provide an entry in the IDT that points to a stub exception handler that returns without executing any instructions.

When interrupted by a counter overflow, the interrupt handler needs to perform the following actions:

•

Save the instruction pointer (EIP register), code-segment selector, TSS segment selector, counter values and
other relevant information at the time of the interrupt.

•

Reset the counter to its initial setting and return from the interrupt.

An event monitor application utility or another application program can read the information collected for analysis
of the performance of the profiled application.

18.6.9

Performance Monitoring (Pentium Processors)

The Pentium processor provides two 40-bit performance counters, which can be used to count events or measure
duration. The counters are supported by three MSRs: the control and event select MSR (CESR) and the performance counter MSRs (CTR0 and CTR1). These can be read from and written to using the RDMSR and WRMSR
instructions, respectively. They can be accessed using these instructions only when operating at privilege level 0.
Each counter has an associated external pin (PM0/BP0 and PM1/BP1), which can be used to indicate the state of
the counter to external hardware.

NOTES
The CESR, CTR0, and CTR1 MSRs and the events listed in Table 19-41 are model-specific for the
Pentium processor.
The performance-monitoring events listed in Chapter 19 are intended to be used as guides for
performance tuning. Counter values reported are not guaranteed to be accurate and should be
used as a relative guide for tuning. Known discrepancies are documented where applicable.

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PERFORMANCE MONITORING

18.6.9.1

Control and Event Select Register (CESR)

The 32-bit control and event select MSR (CESR) controls the operation of performance-monitoring counters CTR0
and CTR1 and the associated pins (see Figure 18-62). To control each counter, the CESR register contains a 6-bit
event select field (ES0 and ES1), a pin control flag (PC0 and PC1), and a 3-bit counter control field (CC0 and CC1).
The functions of these fields are as follows:

•

ES0 and ES1 (event select) fields (bits 0-5, bits 16-21) — Selects (by entering an event code in the field)
up to two events to be monitored. See Table 19-41 for a list of available event codes.

31

26 25 24
P
C
1

22 21

CC1

16 15
ES1

10 9 8
P
C
0

6 5
CC0

0
ESO

PC1—Pin control 1
CC1—Counter control 1
ES1—Event select 1
PC0—Pin control 0
CC0—Counter control 0
ES0—Event select 0
Reserved

Figure 18-62. CESR MSR (Pentium Processor Only)

•

CC0 and CC1 (counter control) fields (bits 6-8, bits 22-24) — Controls the operation of the counter.
Control codes are as follows:
000 — Count nothing (counter disabled).
001 — Count the selected event while CPL is 0, 1, or 2.
010 — Count the selected event while CPL is 3.
011 — Count the selected event regardless of CPL.
100 — Count nothing (counter disabled).
101 — Count clocks (duration) while CPL is 0, 1, or 2.
110 — Count clocks (duration) while CPL is 3.
111 — Count clocks (duration) regardless of CPL.
The highest order bit selects between counting events and counting clocks (duration); the middle bit enables
counting when the CPL is 3; and the low-order bit enables counting when the CPL is 0, 1, or 2.

•

PC0 and PC1 (pin control) flags (bits 9, 25) — Selects the function of the external performance-monitoring
counter pin (PM0/BP0 and PM1/BP1). Setting one of these flags to 1 causes the processor to assert its
associated pin when the counter has overflowed; setting the flag to 0 causes the pin to be asserted when the
counter has been incremented. These flags permit the pins to be individually programmed to indicate the
overflow or incremented condition. The external signalling of the event on the pins will lag the internal event by
a few clocks as the signals are latched and buffered.

While a counter need not be stopped to sample its contents, it must be stopped and cleared or preset before
switching to a new event. It is not possible to set one counter separately. If only one event needs to be changed,
the CESR register must be read, the appropriate bits modified, and all bits must then be written back to CESR. At
reset, all bits in the CESR register are cleared.

18.6.9.2

Use of the Performance-Monitoring Pins

When performance-monitor pins PM0/BP0 and/or PM1/BP1 are configured to indicate when the performancemonitor counter has incremented and an “occurrence event” is being counted, the associated pin is asserted (high)
each time the event occurs. When a “duration event” is being counted, the associated PM pin is asserted for the

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PERFORMANCE MONITORING

entire duration of the event. When the performance-monitor pins are configured to indicate when the counter has
overflowed, the associated PM pin is asserted when the counter has overflowed.
When the PM0/BP0 and/or PM1/BP1 pins are configured to signal that a counter has incremented, it should be
noted that although the counters may increment by 1 or 2 in a single clock, the pins can only indicate that the event
occurred. Moreover, since the internal clock frequency may be higher than the external clock frequency, a single
external clock may correspond to multiple internal clocks.
A “count up to” function may be provided when the event pin is programmed to signal an overflow of the counter.
Because the counters are 40 bits, a carry out of bit 39 indicates an overflow. A counter may be preset to a specific
value less then 240 − 1. After the counter has been enabled and the prescribed number of events has transpired,
the counter will overflow.
Approximately 5 clocks later, the overflow is indicated externally and appropriate action, such as signaling an interrupt, may then be taken.
The PM0/BP0 and PM1/BP1 pins also serve to indicate breakpoint matches during in-circuit emulation, during which
time the counter increment or overflow function of these pins is not available. After RESET, the PM0/BP0 and
PM1/BP1 pins are configured for performance monitoring, however a hardware debugger may reconfigure these
pins to indicate breakpoint matches.

18.6.9.3

Events Counted

Events that performance-monitoring counters can be set to count and record (using CTR0 and CTR1) are divided in
two categories: occurrence and duration:

•

Occurrence events — Counts are incremented each time an event takes place. If PM0/BP0 or PM1/BP1 pins
are used to indicate when a counter increments, the pins are asserted each clock counters increment. But if an
event happens twice in one clock, the counter increments by 2 (the pins are asserted only once).

•

Duration events — Counters increment the total number of clocks that the condition is true. When used to
indicate when counters increment, PM0/BP0 and/or PM1/BP1 pins are asserted for the duration.

18.7

COUNTING CLOCKS

The count of cycles, also known as clockticks, forms the basis for measuring how long a program takes to execute.
Clockticks are also used as part of efficiency ratios like cycles per instruction (CPI). Processor clocks may stop
ticking under circumstances like the following:

•

The processor is halted when there is nothing for the CPU to do. For example, the processor may halt to save
power while the computer is servicing an I/O request. When Intel Hyper-Threading Technology is enabled, both
logical processors must be halted for performance-monitoring counters to be powered down.

•

The processor is asleep as a result of being halted or because of a power-management scheme. There are
different levels of sleep. In the some deep sleep levels, the time-stamp counter stops counting.

In addition, processor core clocks may undergo transitions at different ratios relative to the processor’s bus clock
frequency. Some of the situations that can cause processor core clock to undergo frequency transitions include:

•
•

TM2 transitions.
Enhanced Intel SpeedStep Technology transitions (P-state transitions).

For Intel processors that support TM2, the processor core clocks may operate at a frequency that differs from the
Processor Base frequency (as indicated by processor frequency information reported by CPUID instruction). See
Section 18.7.2 for more detail.
Due to the above considerations there are several important clocks referenced in this manual:

•

Base Clock — The frequency of this clock is the frequency of the processor when the processor is not in turbo
mode, and not being throttled via Intel SpeedStep.

•
•

Maximum Clock — This is the maximum frequency of the processor when turbo mode is at the highest point.
Bus Clock — These clockticks increment at a fixed frequency and help coordinate the bus on some systems.

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PERFORMANCE MONITORING

•

Core Crystal Clock — This is a clock that runs at fixed frequency; it coordinates the clocks on all packages
across the system.

•

Non-halted Clockticks — Measures clock cycles in which the specified logical processor is not halted and is
not in any power-saving state. When Intel Hyper-Threading Technology is enabled, ticks can be measured on a
per-logical-processor basis. There are also performance events on dual-core processors that measure
clockticks per logical processor when the processor is not halted.

•

Non-sleep Clockticks — Measures clock cycles in which the specified physical processor is not in a sleep mode
or in a power-saving state. These ticks cannot be measured on a logical-processor basis.

•
•

Time-stamp Counter — See Section 17.17, “Time-Stamp Counter”.
Reference Clockticks — TM2 or Enhanced Intel SpeedStep technology are two examples of processor
features that can cause processor core clockticks to represent non-uniform tick intervals due to change of bus
ratios. Performance events that counts clockticks of a constant reference frequency was introduced Intel Core
Duo and Intel Core Solo processors. The mechanism is further enhanced on processors based on Intel Core
microarchitecture.

Some processor models permit clock cycles to be measured when the physical processor is not in deep sleep (by
using the time-stamp counter and the RDTSC instruction). Note that such ticks cannot be measured on a perlogical-processor basis. See Section 17.17, “Time-Stamp Counter,” for detail on processor capabilities.
The first two methods use performance counters and can be set up to cause an interrupt upon overflow (for
sampling). They may also be useful where it is easier for a tool to read a performance counter than to use a time
stamp counter (the timestamp counter is accessed using the RDTSC instruction).
For applications with a significant amount of I/O, there are two ratios of interest:

•

Non-halted CPI — Non-halted clockticks/instructions retired measures the CPI for phases where the CPU was
being used. This ratio can be measured on a logical-processor basis when Intel Hyper-Threading Technology is
enabled.

•

Nominal CPI — Time-stamp counter ticks/instructions retired measures the CPI over the duration of a
program, including those periods when the machine halts while waiting for I/O.

18.7.1

Non-Halted Reference Clockticks

Software can use UnHalted Reference Cycles on either a general purpose performance counter using event mask
0x3C and umask 0x01 or on fixed function performance counter 2 to count at a constant rate. These events count
at a consistent rate irrespective of P-state, TM2, or frequency transitions that may occur to the processor. The
UnHalted Reference Cycles event may count differently on the general purpose event and fixed counter.

18.7.2

Cycle Counting and Opportunistic Processor Operation

As a result of the state transitions due to opportunistic processor performance operation (see Chapter 14, “Power
and Thermal Management”), a logical processor or a processor core can operate at frequency different from the
Processor Base frequency.
The following items are expected to hold true irrespective of when opportunistic processor operation causes state
transitions:

•
•

The time stamp counter operates at a fixed-rate frequency of the processor.

•

The IA32_FIXED_CTR2 counter increments at the same TSC frequency irrespective of any transitions caused by
opportunistic processor operation.

•
•

The Local APIC timer operation is unaffected by opportunistic processor operation.

The IA32_MPERF counter increments at a fixed frequency irrespective of any transitions caused by opportunistic processor operation.

The TSC, IA32_MPERF, and IA32_FIXED_CTR2 operate at close to the maximum non-turbo frequency, which is
equal to the product of scalable bus frequency and maximum non-turbo ratio.

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PERFORMANCE MONITORING

18.7.3

Determining the Processor Base Frequency

For Intel processors in which the nominal core crystal clock frequency is enumerated in CPUID.15H.ECX and the
core crystal clock ratio is encoded in CPUID.15H (see Table 3-8 “Information Returned by CPUID Instruction”), the
nominal TSC frequency can be determined by using the following equation:
Nominal TSC frequency = ( CPUID.15H.ECX[31:0] * CPUID.15H.EBX[31:0] ) ÷ CPUID.15H.EAX[31:0]
For Intel processors in which CPUID.15H.EBX[31:0] ÷ CPUID.0x15.EAX[31:0] is enumerated but CPUID.15H.ECX
is not enumerated, Table 18-75 can be used to look up the nominal core crystal clock frequency.

Table 18-75. Nominal Core Crystal Clock Frequency
Processor Families/Processor Number Series1

Nominal Core Crystal Clock Frequency

Future Intel® Xeon® processors with CPUID signature 06_55H.

25 MHz

6th and 7th generation Intel® Core™ processors (does not include Intel® Xeon®
processors).

24 MHz

Next Generation Intel® Atom™ processors based on Goldmont Microarchitecture with
CPUID signature 06_5CH (does not include Intel Xeon processors).

19.2 MHz

NOTES:
1. For any processor in which CPUID.15H is enumerated and MSR_PLATFORM_INFO[15:8] (which gives the scalable bus frequency) is
available, a more accurate frequency can be obtained by using CPUID.15H.

18.7.3.1

For Intel® Processors Based on Microarchitecture Code Name Sandy Bridge, Ivy Bridge,
Haswell and Broadwell

The scalable bus frequency is encoded in the bit field MSR_PLATFORM_INFO[15:8] and the nominal TSC frequency
can be determined by multiplying this number by a bus speed of 100 MHz.

18.7.3.2

For Intel® Processors Based on Microarchitecture Code Name Nehalem

The scalable bus frequency is encoded in the bit field MSR_PLATFORM_INFO[15:8] and the nominal TSC frequency
can be determined by multiplying this number by a bus speed of 133.33 MHz.

18.7.3.3

For Intel® Atom™ Processors Based on the Silvermont Microarchitecture (Including Intel
Processors Based on Airmont Microarchitecture)

The scalable bus frequency is encoded in the bit field MSR_PLATFORM_INFO[15:8] and the nominal TSC frequency
can be determined by multiplying this number by the scalable bus frequency. The scalable bus frequency is
encoded in the bit field MSR_FSB_FREQ[2:0] for Intel Atom processors based on the Silvermont microarchitecture,
and in bit field MSR_FSB_FREQ[3:0] for processors based on the Airmont microarchitecture; see Chapter 2,
“Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
4.

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PERFORMANCE MONITORING

18.7.3.4

For Intel® Core™ 2 Processor Family and for Intel® Xeon® Processors Based on Intel Core
Microarchitecture

For processors based on Intel Core microarchitecture, the scalable bus frequency is encoded in the bit field
MSR_FSB_FREQ[2:0] at (0CDH), see Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 4. The maximum resolved bus ratio can be read from the
following bit field:

•

If XE operation is disabled, the maximum resolved bus ratio can be read in MSR_PLATFORM_ID[12:8]. It
corresponds to the Processor Base frequency.

•

IF XE operation is enabled, the maximum resolved bus ratio is given in MSR_PERF_STATUS[44:40], it
corresponds to the maximum XE operation frequency configured by BIOS.

XE operation of an Intel 64 processor is implementation specific. XE operation can be enabled only by BIOS. If
MSR_PERF_STATUS[31] is set, XE operation is enabled. The MSR_PERF_STATUS[31] field is read-only.

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PERFORMANCE MONITORING

18.8

IA32_PERF_CAPABILITIES MSR ENUMERATION

The layout of IA32_PERF_CAPABILITIES MSR is shown in Figure 18-63, it provides enumeration of a variety of
interfaces:

•

IA32_PERF_CAPABILITIES.LBR_FMT[bits 5:0]: encodes the LBR format, details are described in Section
17.4.8.1.

•

IA32_PERF_CAPABILITIES.PEBSTrap[6]: Trap/Fault-like indicator of PEBS recording assist, see Section
18.6.2.4.2.

•

IA32_PERF_CAPABILITIES.PEBSArchRegs[7]: Indicator of PEBS assist save architectural registers, see Section
18.6.2.4.2.

•

IA32_PERF_CAPABILITIES.PEBS_FMT[bits 11:8]: Specifies the encoding of the layout of PEBS records, see
Section 18.6.2.4.2.

•

IA32_PERF_CAPABILITIES.SMM_FRZ[12]: Indicates IA32_DEBUGCTL.FREEZE_WHILE_SMM is supported if 1,
see Section 18.8.1.

•

IA32_PERF_CAPABILITIES.FULL_WRITE[13]: Indicates the processor supports IA32_A_PMCx interface for
updating bits 32 and above of IA32_PMCx, see Section 18.2.5.

63

13 12 11

8 7 6 5 43 2 1 0

FW_WRITE (R/O)
SMM_FREEZE (R/O)
PEBS_REC_FMT (R/O)
PEBS_ARCH_REG (R/O)
PEBS_TRAP (R/O)
LBR_FMT (R/O)

Reserved

Figure 18-63. Layout of IA32_PERF_CAPABILITIES MSR

18.8.1

Filtering of SMM Handler Overhead

When performance monitoring facilities and/or branch profiling facilities (see Section 17.5, “Last Branch, Interrupt,
and Exception Recording (Intel® Core™ 2 Duo and Intel® Atom™ Processors)”) are enabled, these facilities
capture event counts, branch records and branch trace messages occurring in a logical processor. The occurrence
of interrupts, instruction streams due to various interrupt handlers all contribute to the results recorded by these
facilities.
If CPUID.01H:ECX.PDCM[bit 15] is 1, the processor supports the IA32_PERF_CAPABILITIES MSR. If
IA32_PERF_CAPABILITIES.FREEZE_WHILE_SMM[Bit 12] is 1, the processor supports the ability for system software using performance monitoring and/or branch profiling facilities to filter out the effects of servicing system
management interrupts.
If the FREEZE_WHILE_SMM capability is enabled on a logical processor and after an SMI is delivered, the processor
will clear all the enable bits of IA32_PERF_GLOBAL_CTRL, save a copy of the content of IA32_DEBUGCTL and
disable LBR, BTF, TR, and BTS fields of IA32_DEBUGCTL before transferring control to the SMI handler.
The enable bits of IA32_PERF_GLOBAL_CTRL will be set to 1, the saved copy of IA32_DEBUGCTL prior to SMI
delivery will be restored , after the SMI handler issues RSM to complete its servicing.
It is the responsibility of the SMM code to ensure the state of the performance monitoring and branch profiling facilities are preserved upon entry or until prior to exiting the SMM. If any of this state is modified due to actions by the
SMM code, the SMM code is required to restore such state to the values present at entry to the SMM handler.
System software is allowed to set IA32_DEBUGCTL.FREEZE_WHILE_SMM_EN[bit 14] to 1 only supported as indicated by IA32_PERF_CAPABILITIES.FREEZE_WHILE_SMM[Bit 12] reporting 1.

Vol. 3B 18-129

PERFORMANCE MONITORING

18-130 Vol. 3B

CHAPTER 19
PERFORMANCE MONITORING EVENTS
This chapter lists the performance monitoring events that can be monitored with the Intel 64 or IA-32 processors.
The ability to monitor performance events and the events that can be monitored in these processors are mostly
model-specific, except for architectural performance events, described in Section 19.1.
Model-specific performance events are listed for each generation of microarchitecture:

•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

Section 19.2 - Processors based on Skylake microarchitecture
Section 19.3 - Processors based on Skylake and Kaby Lake microarchitectures
Section 19.4 - Processors based on Knights Landing microarchitecture
Section 19.5 - Processors based on Broadwell microarchitecture
Section 19.6 - Processors based on Haswell microarchitecture
Section 19.6.1 - Processors based on Haswell-E microarchitecture
Section 19.7 - Processors based on Ivy Bridge microarchitecture
Section 19.7.1 - Processors based on Ivy Bridge-E microarchitecture
Section 19.8 - Processors based on Sandy Bridge microarchitecture
Section 19.9 - Processors based on Intel® microarchitecture code name Nehalem
Section 19.10 - Processors based on Intel® microarchitecture code name Westmere
Section 19.11 - Processors based on Enhanced Intel® Core™ microarchitecture
Section 19.12 - Processors based on Intel® Core™ microarchitecture
Section 19.13 - Processors based on the Goldmont microarchitecture
Section 19.15 - Processors based on the Silvermont microarchitecture
Section 19.15.1 - Processors based on the Airmont microarchitecture
Section 19.16 - 45 nm and 32 nm Intel® Atom™ Processors
Section 19.17 - Intel® Core™ Solo and Intel® Core™ Duo processors
Section 19.18 - Processors based on Intel NetBurst® microarchitecture
Section 19.19 - Pentium® M family processors
Section 19.20 - P6 family processors
Section 19.21 - Pentium® processors

NOTE
These performance monitoring events are intended to be used as guides for performance tuning.
The counter values reported by the performance monitoring events are approximate and believed
to be useful as relative guides for tuning software. Known discrepancies are documented where
applicable.
All performance event encodings not documented in the appropriate tables for the given processor
are considered reserved, and their use will result in undefined counter updates with associated
overflow actions.
The event tables listed this chapter provide information for tool developers to support architectural
and model-specific performance monitoring events. The tables are up to date at processor launch,
but are subject to changes. The most up to date event tables and additional details of performance
event implementation for end-user (including additional details beyond event code/umask) can
found at the “perfmon” repository provided by The Intel Open Source Technology Center
(https://download.01.org/perfmon/).

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PERFORMANCE MONITORING EVENTS

19.1

ARCHITECTURAL PERFORMANCE MONITORING EVENTS

Architectural performance events are introduced in Intel Core Solo and Intel Core Duo processors. They are also
supported on processors based on Intel Core microarchitecture. Table 19-1 lists pre-defined architectural performance events that can be configured using general-purpose performance counters and associated event-select
registers.

Table 19-1. Architectural Performance Events
Event
Num.

Event Mask Name

Umask
Value

3CH

UnHalted Core Cycles

00H

Counts core clock cycles whenever the logical processor is in C0 state
(not halted). The frequency of this event varies with state transitions in
the core.

3CH

UnHalted Reference Cycles1

01H

Counts at a fixed frequency whenever the logical processor is in C0
state (not halted).

C0H

Instructions Retired

00H

Counts when the last uop of an instruction retires.

2EH

LLC Reference

4FH

Counts requests originating from the core that reference a cache line in
the last level on-die cache.

2EH

LLC Misses

41H

Counts each cache miss condition for references to the last level on-die
cache.

C4H

Branch Instruction Retired

00H

Counts when the last uop of a branch instruction retires.

C5H

Branch Misses Retired

00H

Counts when the last uop of a branch instruction retires which
corrected misprediction of the branch prediction hardware at execution
time.

Description

NOTES:
1. Current implementations count at core crystal clock, TSC, or bus clock frequency.
Fixed-function performance counters count only events defined in Table 19-2.

Table 19-2. Fixed-Function Performance Counter and Pre-defined Performance Events
Fixed-Function Performance
Counter

Address

Event Mask Mnemonic

Description

IA32_PERF_FIXED_CTR0

309H

Inst_Retired.Any

This event counts the number of instructions that retire
execution. For instructions that consist of multiple microops, this event counts the retirement of the last micro-op
of the instruction. The counter continues counting during
hardware interrupts, traps, and inside interrupt handlers.

IA32_PERF_FIXED_CTR1

30AH

CPU_CLK_UNHALTED.THRE
AD/CPU_CLK_UNHALTED.C
ORE/CPU_CLK_UNHALTED.
THREAD_ANY

The CPU_CLK_UNHALTED.THREAD event counts the
number of core cycles while the logical processor is not in
a halt state.
If there is only one logical processor in a processor core,
CPU_CLK_UNHALTED.CORE counts the unhalted cycles of
the processor core.
If there are more than one logical processor in a processor
core, CPU_CLK_UNHALTED.THREAD_ANY is supported by
programming IA32_FIXED_CTR_CTRL[bit 6]AnyThread =
1.
The core frequency may change from time to time due to
transitions associated with Enhanced Intel SpeedStep
Technology or TM2. For this reason this event may have a
changing ratio with regards to time.

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PERFORMANCE MONITORING EVENTS

Table 19-2. Fixed-Function Performance Counter and Pre-defined Performance Events (Contd.)
Fixed-Function Performance
Counter

Address

Event Mask Mnemonic

Description

IA32_PERF_FIXED_CTR2

30BH

CPU_CLK_UNHALTED.REF_
TSC

This event counts the number of reference cycles at the
TSC rate when the core is not in a halt state and not in a
TM stop-clock state. The core enters the halt state when
it is running the HLT instruction or the MWAIT instruction.
This event is not affected by core frequency changes (e.g.,
P states) but counts at the same frequency as the time
stamp counter. This event can approximate elapsed time
while the core was not in a halt state and not in a TM
stopclock state.

19.2

PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR
SCALABLE FAMILY

The Intel® Xeon® Processor Scalable Family is based on the Skylake microarchitecture. These processors support
the architectural performance monitoring events listed in Table 19-1. Fixed counters in the core PMU support the
architecture events defined in Table 19-2. Model-specific performance monitoring events in the processor core are
listed in Table 19-4. The events in Table 19-4 apply to processors with CPUID signature of
DisplayFamily_DisplayModel encoding with the following value: 06_55H .
The comment column in Table 19-4 uses abbreviated letters to indicate additional conditions applicable to the
Event Mask Mnemonic. For event umasks listed in Table 19-4 that do not show “AnyT”, users should refrain from
programming “AnyThread =1” in IA32_PERF_EVTSELx.

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

00H

01H

INST_RETIRED.ANY

Counts the number of instructions retired from
execution. For instructions that consist of multiple
micro-ops, Counts the retirement of the last micro-op of
the instruction. Counting continues during hardware
interrupts, traps, and inside interrupt handlers. Notes:
INST_RETIRED.ANY is counted by a designated fixed
counter, leaving the four (eight when Hyperthreading is
disabled) programmable counters available for other
events. INST_RETIRED.ANY_P is counted by a
programmable counter and it is an architectural
performance event. Counting: Faulting executions of
GETSEC/VM entry/VM Exit/MWait will not count as
retired instructions.

Fixed Counter

00H

02H

CPU_CLK_UNHALTED.THREAD

Counts the number of core cycles while the thread is
Fixed Counter
not in a halt state. The thread enters the halt state
when it is running the HLT instruction. This event is a
component in many key event ratios. The core
frequency may change from time to time due to
transitions associated with Enhanced Intel SpeedStep
Technology or TM2. For this reason this event may
have a changing ratio with regards to time. When the
core frequency is constant, this event can approximate
elapsed time while the core was not in the halt state. It
is counted on a dedicated fixed counter, leaving the
four (eight when Hyperthreading is disabled)
programmable counters available for other events.
Vol. 3B 19-3

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

00H

02H

CPU_CLK_UNHALTED.THREAD_
ANY

Core cycles when at least one thread on the physical
core is not in halt state.

AnyThread=1

00H

03H

CPU_CLK_UNHALTED.REF_TSC

Counts the number of reference cycles when the core is Fixed Counter
not in a halt state. The core enters the halt state when
it is running the HLT instruction or the MWAIT
instruction. This event is not affected by core
frequency changes (for example, P states, TM2
transitions) but has the same incrementing frequency
as the time stamp counter. This event can approximate
elapsed time while the core was not in a halt state. This
event has a constant ratio with the
CPU_CLK_UNHALTED.REF_XCLK event. It is counted on
a dedicated fixed counter, leaving the four (eight when
Hyperthreading is disabled) programmable counters
available for other events. Note: On all current
platforms this event stops counting during ‘throttling
(TM)’ states duty off periods the processor is ‘halted’.
The counter update is done at a lower clock rate then
the core clock the overflow status bit for this counter
may appear ‘sticky’. After the counter has overflowed
and software clears the overflow status bit and resets
the counter to less than MAX. The reset value to the
counter is not clocked immediately so the overflow
status bit will flip “high (1)” and generate another PMI
(if enabled) after which the reset value gets clocked
into the counter. Therefore, software will get the
interrupt, read the overflow status bit ‘1 for bit 34
while the counter value is less than MAX. Software
should ignore this case.

03H

02H

LD_BLOCKS.STORE_FORWARD

Counts how many times the load operation got the true
Block-on-Store blocking code preventing store
forwarding. This includes cases when: a. preceding
store conflicts with the load (incomplete overlap), b.
store forwarding is impossible due to u-arch limitations,
c. preceding lock RMW operations are not forwarded, d.
store has the no-forward bit set (uncacheable/pagesplit/masked stores), e. all-blocking stores are used
(mostly, fences and port I/O), and others. The most
common case is a load blocked due to its address range
overlapping with a preceding smaller uncompleted
store. Note: This event does not take into account cases
of out-of-SW-control (for example, SbTailHit), unknown
physical STA, and cases of blocking loads on store due
to being non-WB memory type or a lock. These cases
are covered by other events. See the table of not
supported store forwards in the Optimization Guide.

03H

08H

LD_BLOCKS.NO_SR

The number of times that split load operations are
temporarily blocked because all resources for handling
the split accesses are in use.

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PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

07H

01H

LD_BLOCKS_PARTIAL.ADDRESS
_ALIAS

Counts false dependencies in MOB when the partial
comparison upon loose net check and dependency was
resolved by the Enhanced Loose net mechanism. This
may not result in high performance penalties. Loose net
checks can fail when loads and stores are 4k aliased.

08H

01H

DTLB_LOAD_MISSES.MISS_CAUS Counts demand data loads that caused a page walk of
ES_A_WALK
any page size (4K/2M/4M/1G). This implies it missed in
all TLB levels, but the walk need not have completed.

08H

02H

DTLB_LOAD_MISSES.WALK_COM Counts demand data loads that caused a completed
PLETED_4K
page walk (4K page size). This implies it missed in all
TLB levels. The page walk can end with or without a
fault.

08H

04H

DTLB_LOAD_MISSES.WALK_COM Counts demand data loads that caused a completed
PLETED_2M_4M
page walk (2M and 4M page sizes). This implies it
missed in all TLB levels. The page walk can end with or
without a fault.

08H

08H

DTLB_LOAD_MISSES.WALK_COM Counts load misses in all DTLB levels that cause a
PLETED_1G
completed page walk (1G page size). The page walk can
end with or without a fault.

08H

0EH

DTLB_LOAD_MISSES.WALK_COM Counts demand data loads that caused a completed
PLETED
page walk of any page size (4K/2M/4M/1G). This implies
it missed in all TLB levels. The page walk can end with
or without a fault.

08H

10H

DTLB_LOAD_MISSES.WALK_PEN Counts 1 per cycle for each PMH that is busy with a
DING
page walk for a load. EPT page walk duration are
excluded in Skylake microarchitecture.

08H

10H

DTLB_LOAD_MISSES.WALK_ACT Counts cycles when at least one PMH (Page Miss
IVE
Handler) is busy with a page walk for a load.

08H

20H

DTLB_LOAD_MISSES.STLB_HIT

Counts loads that miss the DTLB (Data TLB) and hit the
STLB (Second level TLB).

0DH

01H

INT_MISC.RECOVERY_CYCLES

Core cycles the Resource allocator was stalled due to
recovery from an earlier branch misprediction or
machine clear event.

0DH

01H

INT_MISC.RECOVERY_CYCLES_A Core cycles the allocator was stalled due to recovery
NY
from earlier clear event for any thread running on the
physical core (e.g. misprediction or memory nuke).

0DH

80H

INT_MISC.CLEAR_RESTEER_CYC
LES

Cycles the issue-stage is waiting for front-end to fetch
from resteered path following branch misprediction or
machine clear events.

0EH

01H

UOPS_ISSUED.ANY

Counts the number of uops that the Resource
Allocation Table (RAT) issues to the Reservation Station
(RS).

0EH

01H

UOPS_ISSUED.STALL_CYCLES

Counts cycles during which the Resource Allocation
CounterMask=1
Table (RAT) does not issue any uops to the reservation Invert=1 CMSK1, INV
station (RS) for the current thread.

CounterMask=1
CMSK1

AnyThread=1 AnyT

Vol. 3B 19-5

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

0EH

02H

UOPS_ISSUED.VECTOR_WIDTH_ Counts the number of Blend Uops issued by the
MISMATCH
Resource Allocation Table (RAT) to the reservation
station (RS) in order to preserve upper bits of vector
registers. Starting with the Skylake microarchitecture,
these Blend uops are needed since every Intel SSE
instruction executed in Dirty Upper State needs to
preserve bits 128-255 of the destination register. For
more information, refer to Mixing Intel AVX and Intel
SSE Code section of the Optimization Guide.

0EH

20H

UOPS_ISSUED.SLOW_LEA

Number of slow LEA uops being allocated. A uop is
generally considered SlowLea if it has 3 sources (e.g. 2
sources + immediate) regardless if as a result of LEA
instruction or not.

14H

01H

ARITH.DIVIDER_ACTIVE

Cycles when divide unit is busy executing divide or
square root operations. Accounts for integer and
floating-point operations.

24H

21H

L2_RQSTS.DEMAND_DATA_RD_ Counts the number of demand Data Read requests that
MISS
miss L2 cache. Only not rejected loads are counted.

24H

22H

L2_RQSTS.RFO_MISS

Counts the RFO (Read-for-Ownership) requests that
miss L2 cache.

24H

24H

L2_RQSTS.CODE_RD_MISS

Counts L2 cache misses when fetching instructions.

24H

27H

L2_RQSTS.ALL_DEMAND_MISS

Demand requests that miss L2 cache.

24H

38H

L2_RQSTS.PF_MISS

Counts requests from the L1/L2/L3 hardware
prefetchers or Load software prefetches that miss L2
cache.

24H

3FH

L2_RQSTS.MISS

All requests that miss L2 cache.

24H

41H

L2_RQSTS.DEMAND_DATA_RD_ Counts the number of demand Data Read requests that
HIT
hit L2 cache. Only non rejected loads are counted.

24H

42H

L2_RQSTS.RFO_HIT

Counts the RFO (Read-for-Ownership) requests that hit
L2 cache.

24H

44H

L2_RQSTS.CODE_RD_HIT

Counts L2 cache hits when fetching instructions, code
reads.

24H

D8H

L2_RQSTS.PF_HIT

Counts requests from the L1/L2/L3 hardware
prefetchers or Load software prefetches that hit L2
cache.

24H

E1H

L2_RQSTS.ALL_DEMAND_DATA
_RD

Counts the number of demand Data Read requests
(including requests from L1D hardware prefetchers).
These loads may hit or miss L2 cache. Only non rejected
loads are counted.

24H

E2H

L2_RQSTS.ALL_RFO

Counts the total number of RFO (read for ownership)
requests to L2 cache. L2 RFO requests include both
L1D demand RFO misses as well as L1D RFO
prefetches.

24H

E4H

L2_RQSTS.ALL_CODE_RD

Counts the total number of L2 code requests.

24H

E7H

L2_RQSTS.ALL_DEMAND_REFE
RENCES

Demand requests to L2 cache.

24H

F8H

L2_RQSTS.ALL_PF

Counts the total number of requests from the L2
hardware prefetchers.

19-6 Vol. 3B

Description

Comment

CounterMask=1

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

24H

FFH

L2_RQSTS.REFERENCES

All L2 requests.

28H

07H

CORE_POWER.LVL0_TURBO_LIC Core cycles where the core was running with powerENSE
delivery for baseline license level 0. This includes nonAVX codes, SSE, AVX 128-bit, and low-current AVX
256-bit codes.

28H

18H

CORE_POWER.LVL1_TURBO_LIC Core cycles where the core was running with powerENSE
delivery for license level 1. This includes high current
AVX 256-bit instructions as well as low current AVX
512-bit instructions.

28H

20H

CORE_POWER.LVL2_TURBO_LIC Core cycles where the core was running with powerENSE
delivery for license level 2 (introduced in Skylake
Server microarchitecture). This includes high current
AVX 512-bit instructions.

28H

40H

CORE_POWER.THROTTLE

Core cycles the out-of-order engine was throttled due
to a pending power level request.

2EH

41H

LONGEST_LAT_CACHE.MISS

Counts core-originated cacheable requests that miss
See Table 19-1.
the L3 cache (Longest Latency cache). Requests include
data and code reads, Reads-for-Ownership (RFOs),
speculative accesses and hardware prefetches from L1
and L2. It does not include all misses to the L3.

2EH

4FH

LONGEST_LAT_CACHE.REFEREN Counts core-originated cacheable requests to the L3
See Table 19-1.
CE
cache (Longest Latency cache). Requests include data
and code reads, Reads-for-Ownership (RFOs),
speculative accesses and hardware prefetches from L1
and L2. It does not include all accesses to the L3.

3CH

00H

CPU_CLK_UNHALTED.THREAD_
P

This is an architectural event that counts the number of See Table 19-1.
thread cycles while the thread is not in a halt state. The
thread enters the halt state when it is running the HLT
instruction. The core frequency may change from time
to time due to power or thermal throttling. For this
reason, this event may have a changing ratio with
regards to wall clock time.

3CH

00H

CPU_CLK_UNHALTED.THREAD_
P_ANY

Core cycles when at least one thread on the physical
core is not in halt state.

3CH

00H

CPU_CLK_UNHALTED.RING0_TR Counts when the Current Privilege Level (CPL)
ANS
transitions from ring 1, 2 or 3 to ring 0 (Kernel).

EdgeDetect=1
CounterMask=1

3CH

01H

CPU_CLK_THREAD_UNHALTED.
REF_XCLK

Core crystal clock cycles when the thread is unhalted.

See Table 19-1.

3CH

01H

CPU_CLK_THREAD_UNHALTED.
REF_XCLK_ANY

Core crystal clock cycles when at least one thread on
the physical core is unhalted.

AnyThread=1 AnyT

3CH

01H

CPU_CLK_UNHALTED.REF_XCLK Core crystal clock cycles when the thread is unhalted.

See Table 19-1.

3CH

01H

CPU_CLK_UNHALTED.REF_XCLK Core crystal clock cycles when at least one thread on
_ANY
the physical core is unhalted.

AnyThread=1 AnyT

3CH

02H

CPU_CLK_THREAD_UNHALTED.
ONE_THREAD_ACTIVE

Core crystal clock cycles when this thread is unhalted
and the other thread is halted.

3CH

02H

CPU_CLK_UNHALTED.ONE_THR
EAD_ACTIVE

Core crystal clock cycles when this thread is unhalted
and the other thread is halted.

AnyThread=1 AnyT

Vol. 3B 19-7

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

48H

01H

L1D_PEND_MISS.PENDING

Counts duration of L1D miss outstanding, that is each
cycle number of Fill Buffers (FB) outstanding required
by Demand Reads. FB either is held by demand loads, or
it is held by non-demand loads and gets hit at least
once by demand. The valid outstanding interval is
defined until the FB deallocation by one of the
following ways: from FB allocation, if FB is allocated by
demand from the demand Hit FB, if it is allocated by
hardware or software prefetch.Note: In the L1D, a
Demand Read contains cacheable or noncacheable
demand loads, including ones causing cache-line splits
and reads due to page walks resulted from any request
type.

48H

01H

L1D_PEND_MISS.PENDING_CYCL Counts duration of L1D miss outstanding in cycles.
ES

CounterMask=1
CMSK1

48H

01H

L1D_PEND_MISS.PENDING_CYCL Cycles with L1D load Misses outstanding from any
ES_ANY
thread on physical core.

CounterMask=1
AnyThread=1
CMSK1, AnyT

48H

02H

L1D_PEND_MISS.FB_FULL

49H

01H

DTLB_STORE_MISSES.MISS_CAU Counts demand data stores that caused a page walk of
SES_A_WALK
any page size (4K/2M/4M/1G). This implies it missed in
all TLB levels, but the walk need not have completed.

49H

02H

DTLB_STORE_MISSES.WALK_CO Counts demand data stores that caused a completed
MPLETED_4K
page walk (4K page size). This implies it missed in all
TLB levels. The page walk can end with or without a
fault.

49H

04H

DTLB_STORE_MISSES.WALK_CO Counts demand data stores that caused a completed
MPLETED_2M_4M
page walk (2M and 4M page sizes). This implies it
missed in all TLB levels. The page walk can end with or
without a fault.

49H

08H

DTLB_STORE_MISSES.WALK_CO Counts store misses in all DTLB levels that cause a
MPLETED_1G
completed page walk (1G page size). The page walk can
end with or without a fault.

49H

0EH

DTLB_STORE_MISSES.WALK_CO Counts demand data stores that caused a completed
MPLETED
page walk of any page size (4K/2M/4M/1G). This implies
it missed in all TLB levels. The page walk can end with
or without a fault.

49H

10H

DTLB_STORE_MISSES.WALK_PE Counts 1 per cycle for each PMH that is busy with a
NDING
page walk for a store. EPT page walk duration are
excluded in Skylake microarchitecture.

49H

10H

DTLB_STORE_MISSES.WALK_AC Counts cycles when at least one PMH (Page Miss
TIVE
Handler) is busy with a page walk for a store.

49H

20H

DTLB_STORE_MISSES.STLB_HIT Stores that miss the DTLB (Data TLB) and hit the STLB
(2nd Level TLB).

19-8 Vol. 3B

Comment

Number of times a request needed a FB (Fill Buffer)
entry but there was no entry available for it. A request
includes cacheable/uncacheable demands that are load,
store or SW prefetch instructions.

CounterMask=1
CMSK1

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

4CH

01H

LOAD_HIT_PRE.SW_PF

Counts all not software-prefetch load dispatches that
hit the fill buffer (FB) allocated for the software
prefetch. It can also be incremented by some lock
instructions. So it should only be used with profiling so
that the locks can be excluded by ASM (Assembly File)
inspection of the nearby instructions.

4FH

10H

EPT.WALK_PENDING

Counts cycles for each PMH (Page Miss Handler) that is
busy with an EPT (Extended Page Table) walk for any
request type.

51H

01H

L1D.REPLACEMENT

Counts L1D data line replacements including
opportunistic replacements, and replacements that
require stall-for-replace or block-for-replace.

54H

01H

TX_MEM.ABORT_CONFLICT

Number of times a TSX line had a cache conflict.

54H

02H

TX_MEM.ABORT_CAPACITY

Number of times a transactional abort was signaled due
to a data capacity limitation for transactional reads or
writes.

54H

04H

TX_MEM.ABORT_HLE_STORE_T Number of times a TSX Abort was triggered due to a
O_ELIDED_LOCK
non-release/commit store to lock.

54H

08H

TX_MEM.ABORT_HLE_ELISION_
BUFFER_NOT_EMPTY

Number of times a TSX Abort was triggered due to
commit but Lock Buffer not empty.

54H

10H

TX_MEM.ABORT_HLE_ELISION_
BUFFER_MISMATCH

Number of times a TSX Abort was triggered due to
release/commit but data and address mismatch.

54H

20H

TX_MEM.ABORT_HLE_ELISION_ Number of times a TSX Abort was triggered due to
BUFFER_UNSUPPORTED_ALIGN attempting an unsupported alignment from Lock
MENT
Buffer.

54H

40H

TX_MEM.HLE_ELISION_BUFFER
_FULL

Number of times we could not allocate Lock Buffer.

5DH

01H

TX_EXEC.MISC1

Unfriendly TSX abort triggered by a flowmarker.

5DH

02H

TX_EXEC.MISC2

Unfriendly TSX abort triggered by a vzeroupper
instruction.

5DH

04H

TX_EXEC.MISC3

Unfriendly TSX abort triggered by a nest count that is
too deep.

5DH

08H

TX_EXEC.MISC4

RTM region detected inside HLE.

5DH

10H

TX_EXEC.MISC5

Counts the number of times an HLE XACQUIRE
instruction was executed inside an RTM transactional
region.

5EH

01H

RS_EVENTS.EMPTY_CYCLES

Counts cycles during which the reservation station (RS)
is empty for the thread.; Note: In ST-mode, not active
thread should drive 0. This is usually caused by
severely costly branch mispredictions, or allocator/FE
issues.

5EH

01H

RS_EVENTS.EMPTY_END

Counts end of periods where the Reservation Station
(RS) was empty. Could be useful to precisely locate
front-end Latency Bound issues.

Comment

EdgeDetect=1
CounterMask=1
Invert=1 CMSK1, INV

Vol. 3B 19-9

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

60H

01H

OFFCORE_REQUESTS_OUTSTAN Counts the number of offcore outstanding Demand
DING.DEMAND_DATA_RD
Data Read transactions in the super queue (SQ) every
cycle. A transaction is considered to be in the Offcore
outstanding state between L2 miss and transaction
completion sent to requestor. See the corresponding
Umask under OFFCORE_REQUESTS. Note: A prefetch
promoted to Demand is counted from the promotion
point.

60H

01H

OFFCORE_REQUESTS_OUTSTAN Counts cycles when offcore outstanding Demand Data CounterMask=1
DING.CYCLES_WITH_DEMAND_D Read transactions are present in the super queue (SQ). CMSK1
ATA_RD
A transaction is considered to be in the Offcore
outstanding state between L2 miss and transaction
completion sent to requestor (SQ de-allocation).

60H

01H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least 6 offcore outstanding Demand Data CounterMask=6
DING.DEMAND_DATA_RD_GE_6 Read transactions in uncore queue.
CMSK6

60H

02H

OFFCORE_REQUESTS_OUTSTAN Counts the number of offcore outstanding Code Reads
DING.DEMAND_CODE_RD
transactions in the super queue every cycle. The
'Offcore outstanding' state of the transaction lasts
from the L2 miss until the sending transaction
completion to requestor (SQ deallocation). See the
corresponding Umask under OFFCORE_REQUESTS.

CounterMask=1
CMSK1

60H

02H

OFFCORE_REQUESTS_OUTSTAN Counts the number of offcore outstanding Code Reads
DING.CYCLES_WITH_DEMAND_C transactions in the super queue every cycle. The
ODE_RD
'Offcore outstanding' state of the transaction lasts
from the L2 miss until the sending transaction
completion to requestor (SQ deallocation). See the
corresponding Umask under OFFCORE_REQUESTS.

CMSK1

60H

04H

OFFCORE_REQUESTS_OUTSTAN Counts the number of offcore outstanding RFO (store)
DING.DEMAND_RFO
transactions in the super queue (SQ) every cycle. A
transaction is considered to be in the Offcore
outstanding state between L2 miss and transaction
completion sent to requestor (SQ de-allocation). See
corresponding Umask under OFFCORE_REQUESTS.

CounterMask=1
CMSK1

60H

04H

OFFCORE_REQUESTS_OUTSTAN Counts the number of offcore outstanding demand rfo CMSK1
DING.CYCLES_WITH_DEMAND_R Reads transactions in the super queue every cycle. The
FO
'Offcore outstanding' state of the transaction lasts
from the L2 miss until the sending transaction
completion to requestor (SQ deallocation). See the
corresponding Umask under OFFCORE_REQUESTS.

60H

08H

OFFCORE_REQUESTS_OUTSTAN Counts the number of offcore outstanding cacheable
DING.ALL_DATA_RD
Core Data Read transactions in the super queue every
cycle. A transaction is considered to be in the Offcore
outstanding state between L2 miss and transaction
completion sent to requestor (SQ de-allocation). See
corresponding Umask under OFFCORE_REQUESTS.

60H

08H

OFFCORE_REQUESTS_OUTSTAN Counts cycles when offcore outstanding cacheable Core CounterMask=1
DING.CYCLES_WITH_DATA_RD
Data Read transactions are present in the super queue. CMSK1
A transaction is considered to be in the Offcore
outstanding state between L2 miss and transaction
completion sent to requestor (SQ de-allocation). See
corresponding Umask under OFFCORE_REQUESTS.

19-10 Vol. 3B

Description

Comment

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

60H

10H

OFFCORE_REQUESTS_OUTSTAN Counts number of Offcore outstanding Demand Data
DING.L3_MISS_DEMAND_DATA_ Read requests that miss L3 cache in the superQ every
RD
cycle.

60H

10H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least 1 Demand Data Read requests who CounterMask=1
DING.CYCLES_WITH_L3_MISS_D miss L3 cache in the superQ.
CMSK1
EMAND_DATA_RD

60H

10H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least 6 Demand Data Read requests that CounterMask=6
DING.L3_MISS_DEMAND_DATA_ miss L3 cache in the superQ.
CMSK6
RD_GE_6

79H

04H

IDQ.MITE_UOPS

Counts the number of uops delivered to Instruction
Decode Queue (IDQ) from the MITE path. Counting
includes uops that may 'bypass' the IDQ. This also
means that uops are not being delivered from the
Decode Stream Buffer (DSB).

79H

04H

IDQ.MITE_CYCLES

Counts cycles during which uops are being delivered to CounterMask=1
Instruction Decode Queue (IDQ) from the MITE path.
CMSK1
Counting includes uops that may 'bypass' the IDQ.

79H

08H

IDQ.DSB_UOPS

Counts the number of uops delivered to Instruction
Decode Queue (IDQ) from the Decode Stream Buffer
(DSB) path. Counting includes uops that may ‘bypass’
the IDQ.

79H

08H

IDQ.DSB_CYCLES

Counts cycles during which uops are being delivered to CounterMask=1
Instruction Decode Queue (IDQ) from the Decode
CMSK1
Stream Buffer (DSB) path. Counting includes uops that
may 'bypass' the IDQ.

79H

10H

IDQ.MS_DSB_CYCLES

Counts cycles during which uops initiated by Decode
Stream Buffer (DSB) are being delivered to Instruction
Decode Queue (IDQ) while the Microcode Sequencer
(MS) is busy. Counting includes uops that may 'bypass'
the IDQ.

79H

18H

IDQ.ALL_DSB_CYCLES_4_UOPS

Counts the number of cycles 4 uops were delivered to CounterMask=4
Instruction Decode Queue (IDQ) from the Decode
CMSK4
Stream Buffer (DSB) path. Count includes uops that may
'bypass' the IDQ.

79H

18H

IDQ.ALL_DSB_CYCLES_ANY_UO
PS

Counts the number of cycles uops were delivered to
CounterMask=1
Instruction Decode Queue (IDQ) from the Decode
CMSK1
Stream Buffer (DSB) path. Count includes uops that may
'bypass' the IDQ.

79H

20H

IDQ.MS_MITE_UOPS

Counts the number of uops initiated by MITE and
delivered to Instruction Decode Queue (IDQ) while the
Microcode Sequencer (MS) is busy. Counting includes
uops that may 'bypass' the IDQ.

79H

24H

IDQ.ALL_MITE_CYCLES_4_UOPS Counts the number of cycles 4 uops were delivered to CounterMask=4
the Instruction Decode Queue (IDQ) from the MITE
CMSK4
(legacy decode pipeline) path. Counting includes uops
that may 'bypass' the IDQ. During these cycles uops are
not being delivered from the Decode Stream Buffer
(DSB).

CounterMask=1

Vol. 3B 19-11

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

79H

24H

IDQ.ALL_MITE_CYCLES_ANY_UO Counts the number of cycles uops were delivered to
CounterMask=1
PS
the Instruction Decode Queue (IDQ) from the MITE
CMSK1
(legacy decode pipeline) path. Counting includes uops
that may 'bypass' the IDQ. During these cycles uops are
not being delivered from the Decode Stream Buffer
(DSB).

79H

30H

IDQ.MS_CYCLES

Counts cycles during which uops are being delivered to CounterMask=1
Instruction Decode Queue (IDQ) while the Microcode
CMSK1
Sequencer (MS) is busy. Counting includes uops that
may 'bypass' the IDQ. Uops maybe initiated by Decode
Stream Buffer (DSB) or MITE.

79H

30H

IDQ.MS_SWITCHES

Number of switches from DSB (Decode Stream Buffer)
or MITE (legacy decode pipeline) to the Microcode
Sequencer.

79H

30H

IDQ.MS_UOPS

Counts the total number of uops delivered by the
Microcode Sequencer (MS). Any instruction over 4 uops
will be delivered by the MS. Some instructions such as
transcendentals may additionally generate uops from
the MS.

80H

04H

ICACHE_16B.IFDATA_STALL

Cycles where a code line fetch is stalled due to an L1
instruction cache miss. The legacy decode pipeline
works at a 16 Byte granularity.

83H

01H

ICACHE_64B.IFTAG_HIT

Instruction fetch tag lookups that hit in the instruction
cache (L1I). Counts at 64-byte cache-line granularity.

83H

02H

ICACHE_64B.IFTAG_MISS

Instruction fetch tag lookups that miss in the
instruction cache (L1I). Counts at 64-byte cache-line
granularity.

83H

04H

ICACHE_64B.IFTAG_STALL

Cycles where a code fetch is stalled due to L1
instruction cache tag miss.

85H

01H

ITLB_MISSES.MISS_CAUSES_A_
WALK

Counts page walks of any page size (4K/2M/4M/1G)
caused by a code fetch. This implies it missed in the
ITLB and further levels of TLB, but the walk need not
have completed.

85H

02H

ITLB_MISSES.WALK_COMPLETE
D_4K

Counts completed page walks (4K page size) caused by
a code fetch. This implies it missed in the ITLB and
further levels of TLB. The page walk can end with or
without a fault.

85H

04H

ITLB_MISSES.WALK_COMPLETE
D_2M_4M

Counts completed page walks of any page size
(4K/2M/4M/1G) caused by a code fetch. This implies it
missed in the ITLB and further levels of TLB. The page
walk can end with or without a fault.

85H

08H

ITLB_MISSES.WALK_COMPLETE
D_1G

Counts store misses in all DTLB levels that cause a
completed page walk (1G page size). The page walk can
end with or without a fault.

85H

0EH

ITLB_MISSES.WALK_COMPLETE
D

Counts completed page walks (2M and 4M page sizes)
caused by a code fetch. This implies it missed in the
ITLB and further levels of TLB. The page walk can end
with or without a fault.

19-12 Vol. 3B

Description

Comment

EdgeDetect=1
CounterMask=1
EDGE

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

85H

10H

ITLB_MISSES.WALK_PENDING

Counts 1 per cycle for each PMH that is busy with a
page walk for an instruction fetch request. EPT page
walk duration are excluded in Skylake
microarchitecture.

85H

10H

ITLB_MISSES.WALK_ACTIVE

Cycles when at least one PMH is busy with a page walk CounterMask=1
for code (instruction fetch) request. EPT page walk
duration are excluded in Skylake microarchitecture.

85H

20H

ITLB_MISSES.STLB_HIT

Instruction fetch requests that miss the ITLB and hit
the STLB.

87H

01H

ILD_STALL.LCP

Counts cycles that the Instruction Length decoder (ILD)
stalls occurred due to dynamically changing prefix
length of the decoded instruction (by operand size
prefix instruction 0x66, address size prefix instruction
0x67 or REX.W for Intel64). Count is proportional to the
number of prefixes in a 16B-line. This may result in a
three-cycle penalty for each LCP (Length changing
prefix) in a 16-byte chunk.

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CO
RE

Counts the number of uops not delivered to Resource
Allocation Table (RAT) per thread adding “4 – x” ? when
Resource Allocation Table (RAT) is not stalled and
Instruction Decode Queue (IDQ) delivers x uops to
Resource Allocation Table (RAT) (where x belongs to
{0,1,2,3}). Counting does not cover cases when: a. IDQResource Allocation Table (RAT) pipe serves the other
thread. b. Resource Allocation Table (RAT) is stalled for
the thread (including uop drops and clear BE
conditions). c. Instruction Decode Queue (IDQ) delivers
four uops.

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Counts, on the per-thread basis, cycles when no uops
LES_0_UOPS_DELIV.CORE
are delivered to Resource Allocation Table (RAT).
IDQ_Uops_Not_Delivered.core =4.

CounterMask=4
CMSK4

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Counts, on the per-thread basis, cycles when less than
LES_LE_1_UOP_DELIV.CORE
1 uop is delivered to Resource Allocation Table (RAT).
IDQ_Uops_Not_Delivered.core >= 3.

CounterMask=3
CMSK3

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Cycles with less than 2 uops delivered by the front end. CounterMask=2
LES_LE_2_UOP_DELIV.CORE
CMSK2

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Cycles with less than 3 uops delivered by the front end. CounterMask=1
LES_LE_3_UOP_DELIV.CORE
CMSK1

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Counts cycles FE delivered 4 uops or Resource
LES_FE_WAS_OK
Allocation Table (RAT) was stalling FE.

A1H

01H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_0
least one uop is dispatched from the Reservation
Station (RS) to port 0.

A1H

02H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_1
least one uop is dispatched from the Reservation
Station (RS) to port 1.

A1H

04H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_2
least one uop is dispatched from the Reservation
Station (RS) to port 2.

CounterMask=1
Invert=1 CMSK, INV

Vol. 3B 19-13

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

A1H

08H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_3
least one uop is dispatched from the Reservation
Station (RS) to port 3.

A1H

10H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_4
least one uop is dispatched from the Reservation
Station (RS) to port 4.

A1H

20H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_5
least one uop is dispatched from the Reservation
Station (RS) to port 5.

A1H

40H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_6
least one uop is dispatched from the Reservation
Station (RS) to port 6.

A1H

80H

UOPS_DISPATCHED_PORT.PORT Counts, on the per-thread basis, cycles during which at
_7
least one uop is dispatched from the Reservation
Station (RS) to port 7.

A2H

01H

RESOURCE_STALLS.ANY

Counts resource-related stall cycles. Reasons for stalls
can be as follows: a. *any* u-arch structure got full (LB,
SB, RS, ROB, BOB, LM, Physical Register Reclaim Table
(PRRT), or Physical History Table (PHT) slots). b. *any*
u-arch structure got empty (like INT/SIMD FreeLists). c.
FPU control word (FPCW), MXCSR.and others. This
counts cycles that the pipeline back end blocked uop
delivery from the front end.

A2H

08H

RESOURCE_STALLS.SB

Counts allocation stall cycles caused by the store buffer
(SB) being full. This counts cycles that the pipeline back
end blocked uop delivery from the front end.

A3H

01H

CYCLE_ACTIVITY.CYCLES_L2_MI
SS

Cycles while L2 cache miss demand load is outstanding. CounterMask=1
CMSK1

A3H

02H

CYCLE_ACTIVITY.CYCLES_L3_MI
SS

Cycles while L3 cache miss demand load is outstanding. CounterMask=2
CMSK2

A3H

04H

CYCLE_ACTIVITY.STALLS_TOTAL Total execution stalls.

CounterMask=4
CMSK4

A3H

05H

CYCLE_ACTIVITY.STALLS_L2_MI
SS

Execution stalls while L2 cache miss demand load is
outstanding.

CounterMask=5
CMSK5

A3H

06H

CYCLE_ACTIVITY.STALLS_L3_MI
SS

Execution stalls while L3 cache miss demand load is
outstanding.

CounterMask=6
CMSK6

A3H

08H

CYCLE_ACTIVITY.CYCLES_L1D_M Cycles while L1 cache miss demand load is outstanding. CounterMask=8
ISS
CMSK8

A3H

0CH

CYCLE_ACTIVITY.STALLS_L1D_M Execution stalls while L1 cache miss demand load is
ISS
outstanding.

CounterMask=12
CMSK12

A3H

10H

CYCLE_ACTIVITY.CYCLES_MEM_
ANY

Cycles while memory subsystem has an outstanding
load.

CounterMask=16
CMSK16

A3H

14H

CYCLE_ACTIVITY.STALLS_MEM_
ANY

Execution stalls while memory subsystem has an
outstanding load.

CounterMask=20
CMSK20

A6H

01H

EXE_ACTIVITY.EXE_BOUND_0_P Counts cycles during which no uops were executed on
ORTS
all ports and Reservation Station (RS) was not empty.

19-14 Vol. 3B

Description

Comment

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

A6H

02H

EXE_ACTIVITY.1_PORTS_UTIL

Counts cycles during which a total of 1 uop was
executed on all ports and Reservation Station (RS) was
not empty.

A6H

04H

EXE_ACTIVITY.2_PORTS_UTIL

Counts cycles during which a total of 2 uops were
executed on all ports and Reservation Station (RS) was
not empty.

A6H

08H

EXE_ACTIVITY.3_PORTS_UTIL

Cycles total of 3 uops are executed on all ports and
Reservation Station (RS) was not empty.

A6H

10H

EXE_ACTIVITY.4_PORTS_UTIL

Cycles total of 4 uops are executed on all ports and
Reservation Station (RS) was not empty.

A6H

40H

EXE_ACTIVITY.BOUND_ON_STO
RES

Cycles where the Store Buffer was full and no
outstanding load.

A8H

01H

LSD.UOPS

Number of uops delivered to the back-end by the LSD
(Loop Stream Detector).

A8H

01H

LSD.CYCLES_ACTIVE

Counts the cycles when at least one uop is delivered by CounterMask=1
the LSD (Loop-stream detector).
CMSK1

A8H

01H

LSD.CYCLES_4_UOPS

Counts the cycles when 4 uops are delivered by the
LSD (Loop-stream detector).

ABH

02H

DSB2MITE_SWITCHES.PENALTY
_CYCLES

Counts Decode Stream Buffer (DSB)-to-MITE switch
true penalty cycles. These cycles do not include uops
routed through because of the switch itself, for
example, when Instruction Decode Queue (IDQ) preallocation is unavailable, or Instruction Decode Queue
(IDQ) is full. SBD-to-MITE switch true penalty cycles
happen after the merge mux (MM) receives Decode
Stream Buffer (DSB) Sync-indication until receiving the
first MITE uop. MM is placed before Instruction Decode
Queue (IDQ) to merge uops being fed from the MITE
and Decode Stream Buffer (DSB) paths. Decode Stream
Buffer (DSB) inserts the Sync-indication whenever a
Decode Stream Buffer (DSB)-to-MITE switch
occurs.Penalty: A Decode Stream Buffer (DSB) hit
followed by a Decode Stream Buffer (DSB) miss can
cost up to six cycles in which no uops are delivered to
the IDQ. Most often, such switches from the Decode
Stream Buffer (DSB) to the legacy pipeline cost 0 to 2
cycles.

AEH

01H

ITLB.ITLB_FLUSH

Counts the number of flushes of the big or small ITLB
pages. Counting include both TLB Flush (covering all
sets) and TLB Set Clear (set-specific).

B0H

01H

OFFCORE_REQUESTS.DEMAND_ Counts the Demand Data Read requests sent to uncore.
DATA_RD
Use it in conjunction with
OFFCORE_REQUESTS_OUTSTANDING to determine
average latency in the uncore.

B0H

02H

OFFCORE_REQUESTS.DEMAND_ Counts both cacheable and non-cacheable code read
CODE_RD
requests.

B0H

04H

OFFCORE_REQUESTS.DEMAND_ Counts the demand RFO (read for ownership) requests
RFO
including regular RFOs, locks, ItoM.

CounterMask=4
CMSK4

Vol. 3B 19-15

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

B0H

08H

OFFCORE_REQUESTS.ALL_DATA Counts the demand and prefetch data reads. All Core
_RD
Data Reads include cacheable 'Demands' and L2
prefetchers (not L3 prefetchers). Counting also covers
reads due to page walks resulted from any request
type.

B0H

10H

OFFCORE_REQUESTS.L3_MISS_
DEMAND_DATA_RD

B0H

80H

OFFCORE_REQUESTS.ALL_REQU Counts memory transactions reached the super queue
ESTS
including requests initiated by the core, all L3
prefetches, page walks, etc.

B1H

01H

UOPS_EXECUTED.THREAD

Number of uops to be executed per-thread each cycle.

B1H

01H

UOPS_EXECUTED.STALL_CYCLE
S

Counts cycles during which no uops were dispatched
from the Reservation Station (RS) per thread.

B1H

01H

UOPS_EXECUTED.CYCLES_GE_1 Cycles where at least 1 uop was executed per-thread.
_UOP_EXEC

B1H

01H

UOPS_EXECUTED.CYCLES_GE_2 Cycles where at least 2 uops were executed per-thread. CounterMask=2
_UOPS_EXEC
CMSK2

B1H

01H

UOPS_EXECUTED.CYCLES_GE_3 Cycles where at least 3 uops were executed per-thread. CounterMask=3
_UOPS_EXEC
CMSK3

B1H

01H

UOPS_EXECUTED.CYCLES_GE_4 Cycles where at least 4 uops were executed per-thread. CounterMask=4
_UOPS_EXEC
CMSK4

B1H

02H

UOPS_EXECUTED.CORE

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles at least 1 micro-op is executed from any thread
_GE_1
on physical core.

CounterMask=1
CMSK1

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles at least 2 micro-op is executed from any thread
_GE_2
on physical core.

CounterMask=2
CMSK2

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles at least 3 micro-op is executed from any thread
_GE_3
on physical core.

CounterMask=3
CMSK3

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles at least 4 micro-op is executed from any thread
_GE_4
on physical core.

CounterMask=4
CMSK4

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles with no micro-ops executed from any thread on
_NONE
physical core.

CounterMask=1
Invert=1 CMSK1, INV

B1H

10H

UOPS_EXECUTED.X87

B2H

01H

OFFCORE_REQUESTS_BUFFER.S Counts the number of cases when the offcore requests
Q_FULL
buffer cannot take more entries for the core. This can
happen when the superqueue does not contain eligible
entries, or when L1D writeback pending FIFO requests
is full. Note: Writeback pending FIFO has six entries.

BDH

01H

TLB_FLUSH.DTLB_THREAD

Counts the number of DTLB flush attempts of the
thread-specific entries.

BDH

20H

TLB_FLUSH.STLB_ANY

Counts the number of any STLB flush attempts (such as
entire, VPID, PCID, InvPage, CR3 write, etc.).

C0H

00H

INST_RETIRED.ANY_P

Counts the number of instructions (EOMs) retired.
Counting covers macro-fused instructions individually
(that is, increments by two).

19-16 Vol. 3B

Description

Comment

Demand Data Read requests who miss L3 cache.

CounterMask=1
Invert=1 CMSK, INV
CounterMask=1
CMSK1

Number of uops executed from any thread.

Counts the number of x87 uops executed.

See Table 19-1.

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

C0H

01H

INST_RETIRED.PREC_DIST

A version of INST_RETIRED that allows for a more
unbiased distribution of samples across instructions
retired. It utilizes the Precise Distribution of
Instructions Retired (PDIR) feature to mitigate some
bias in how retired instructions get sampled.

Precise event capable
Requires PEBS on
General Counter
1(PDIR).

C1H

3FH

OTHER_ASSISTS.ANY

Number of times a microcode assist is invoked by HW
other than FP-assist. Examples include AD (page Access
Dirty) and AVX* related assists.

C2H

01H

UOPS_RETIRED.STALL_CYCLES

This is a non-precise version (that is, does not use
PEBS) of the event that counts cycles without actually
retired uops.

C2H

01H

UOPS_RETIRED.TOTAL_CYCLES

Number of cycles using always true condition (uops_ret CounterMask=10
< 16) applied to non PEBS uops retired event.
Invert=1 CMSK10,
INV

C2H

02H

UOPS_RETIRED.RETIRE_SLOTS

Counts the retirement slots used.

C3H

01H

MACHINE_CLEARS.COUNT

Number of machine clears (nukes) of any type.

C3H

02H

MACHINE_CLEARS.MEMORY_OR
DERING

Counts the number of memory ordering Machine Clears
detected. Memory Ordering Machine Clears can result
from one of the following: a. memory disambiguation, b.
external snoop, or c. cross SMT-HW-thread snoop
(stores) hitting load buffer.

C3H

04H

MACHINE_CLEARS.SMC

Counts self-modifying code (SMC) detected, which
causes a machine clear.

C4H

00H

BR_INST_RETIRED.ALL_BRANC
HES

Counts all (macro) branch instructions retired.

C4H

01H

BR_INST_RETIRED.CONDITIONA This is a non-precise version (that is, does not use
L
PEBS) of the event that counts conditional branch
instructions retired.

C4H

02H

BR_INST_RETIRED.NEAR_CALL

This is a non-precise version (that is, does not use
Precise event capable.
PEBS) of the event that counts both direct and indirect PS
near call instructions retired.

C4H

08H

BR_INST_RETIRED.NEAR_RETU
RN

This is a non-precise version (that is, does not use
PEBS) of the event that counts return instructions
retired.

C4H

10H

BR_INST_RETIRED.NOT_TAKEN

This is a non-precise version (that is, does not use
PEBS) of the event that counts not taken branch
instructions retired.

C4H

20H

BR_INST_RETIRED.NEAR_TAKE
N

This is a non-precise version (that is, does not use
PEBS) of the event that counts taken branch
instructions retired.

Precise event capable.
PS

C4H

40H

BR_INST_RETIRED.FAR_BRANC
H

This is a non-precise version (that is, does not use
PEBS) of the event that counts far branch instructions
retired.

Precise event capable.
PS

CounterMask=1
Invert=1 CMSK1, INV

EdgeDetect=1
CounterMask=1
CMSK1, EDG

Precise event capable.
See Table 19-1.
Precise event capable.
PS

Precise event capable.
PS

Vol. 3B 19-17

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

C5H

00H

BR_MISP_RETIRED.ALL_BRANC
HES

Counts all the retired branch instructions that were
Precise event capable.
mispredicted by the processor. A branch misprediction See Table 19-1.
occurs when the processor incorrectly predicts the
destination of the branch. When the misprediction is
discovered at execution, all the instructions executed in
the wrong (speculative) path must be discarded, and
the processor must start fetching from the correct
path.

C5H

01H

BR_MISP_RETIRED.CONDITIONA This is a non-precise version (that is, does not use
Precise event capable.
L
PEBS) of the event that counts mispredicted conditional PS
branch instructions retired.

C5H

02H

BR_MISP_RETIRED.NEAR_CALL

Counts both taken and not taken retired mispredicted
Precise event capable.
direct and indirect near calls, including both register and
memory indirect.

C5H

20H

BR_MISP_RETIRED.NEAR_TAKE
N

Number of near branch instructions retired that were
mispredicted and taken.

Precise event capable.
PS

C6H

01H

FRONTEND_RETIRED.DSB_MISS

Counts retired Instructions that experienced DSB
(Decode stream buffer, i.e. the decoded instructioncache) miss.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.L1I_MISS

Retired Instructions who experienced Instruction L1
Cache true miss.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.L2_MISS

Retired Instructions who experienced Instruction L2
Cache true miss.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.ITLB_MISS Counts retired Instructions that experienced iTLB
(Instruction TLB) true miss.

C6H

01H

FRONTEND_RETIRED.STLB_MIS
S

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
Precise event capable.
GE_2
where the front end delivered no uops for a period of 2
cycles which was not interrupted by a back-end stall.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
Precise event capable.
GE_4
where the front end delivered no uops for a period of 4
cycles which was not interrupted by a back-end stall.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Counts retired instructions that are delivered to the
GE_8
back end after a front-end stall of at least 8 cycles.
During this period the front end delivered no uops.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Counts retired instructions that are delivered to the
GE_16
back end after a front-end stall of at least 16 cycles.
During this period the front end delivered no uops.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Counts retired instructions that are delivered to the
GE_32
back end after a front-end stall of at least 32 cycles.
During this period the front end delivered no uops.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
GE_64
where the front end delivered no uops for a period of
64 cycles which was not interrupted by a back-end
stall.

Precise event capable.

19-18 Vol. 3B

Comment

Precise event capable.

Counts retired Instructions that experienced STLB (2nd Precise event capable.
level TLB) true miss.

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
GE_128
where the front end delivered no uops for a period of
128 cycles which was not interrupted by a back-end
stall.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
GE_256
where the front end delivered no uops for a period of
256 cycles which was not interrupted by a back-end
stall.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
GE_512
where the front end delivered no uops for a period of
512 cycles which was not interrupted by a back-end
stall.

Precise event capable.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Counts retired instructions that are delivered to the
Precise event capable.
GE_2_BUBBLES_GE_1
back end after the front end had at least 1 bubble-slot
for a period of 2 cycles. A bubble-slot is an empty issuepipeline slot while there was no RAT stall.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
Precise event capable.
GE_2_BUBBLES_GE_2
where the front end had at least 2 bubble-slots for a
period of 2 cycles which was not interrupted by a backend stall.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
Precise event capable.
GE_2_BUBBLES_GE_3
where the front end had at least 3 bubble-slots for a
period of 2 cycles which was not interrupted by a backend stall.

C7H

01H

FP_ARITH_INST_RETIRED.SCAL
AR_DOUBLE

Number of SSE/AVX computational scalar double
precision floating-point instructions retired. Each count
represents 1 computation. Applies to SSE* and AVX*
scalar double precision floating-point instructions: ADD
SUB MUL DIV MIN MAX SQRT FM(N)ADD/SUB.
FM(N)ADD/SUB instructions count twice as they
perform multiple calculations per element.

Software may treat
each count as one DP
FLOP.

C7H

02H

FP_ARITH_INST_RETIRED.SCAL
AR_SINGLE

Number of SSE/AVX computational scalar single
precision floating-point instructions retired. Each count
represents 1 computation. Applies to SSE* and AVX*
scalar single precision floating-point instructions: ADD
SUB MUL DIV MIN MAX RCP RSQRT SQRT
FM(N)ADD/SUB. FM(N)ADD/SUB instructions count
twice as they perform multiple calculations per
element.

Software may treat
each count as one SP
FLOP.

C7H

04H

FP_ARITH_INST_RETIRED.128B Number of SSE/AVX computational 128-bit packed
Software may treat
_PACKED_DOUBLE
double precision floating-point instructions retired.
each count as two DP
Each count represents 2 computations. Applies to SSE* FLOPs.
and AVX* packed double precision floating-point
instructions: ADD SUB MUL DIV MIN MAX SQRT DPP
FM(N)ADD/SUB. DPP and FM(N)ADD/SUB instructions
count twice as they perform multiple calculations per
element.

Vol. 3B 19-19

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

C7H

08H

FP_ARITH_INST_RETIRED.128B Number of SSE/AVX computational 128-bit packed
Software may treat
_PACKED_SINGLE
single precision floating-point instructions retired. Each each count as four SP
count represents 4 computations. Applies to SSE* and FLOPs.
AVX* packed single precision floating-point
instructions: ADD SUB MUL DIV MIN MAX RCP RSQRT
SQRT DPP FM(N)ADD/SUB. DPP and FM(N)ADD/SUB
instructions count twice as they perform multiple
calculations per element.

C7H

10H

FP_ARITH_INST_RETIRED.256B Number of SSE/AVX computational 256-bit packed
Software may treat
_PACKED_DOUBLE
double precision floating-point instructions retired.
each count as four DP
Each count represents 4 computations. Applies to SSE* FLOPs.
and AVX* packed double precision floating-point
instructions: ADD SUB MUL DIV MIN MAX SQRT DPP
FM(N)ADD/SUB. DPP and FM(N)ADD/SUB instructions
count twice as they perform multiple calculations per
element.

C7H

20H

FP_ARITH_INST_RETIRED.256B Number of SSE/AVX computational 256-bit packed
Software may treat
_PACKED_SINGLE
single precision floating-point instructions retired. Each each count as eight
count represents 8 computations. Applies to SSE* and SP FLOPs.
AVX* packed single precision floating-point
instructions: ADD SUB MUL DIV MIN MAX RCP RSQRT
SQRT DPP FM(N)ADD/SUB. DPP and FM(N)ADD/SUB
instructions count twice as they perform multiple
calculations per element.

C7H

40H

FP_ARITH_INST_RETIRED.512B Number of Packed Double-Precision FP arithmetic
_PACKED_DOUBLE
instructions (use operation multiplier of 8).

Only applicable when
AVX-512 is enabled.

C7H

80H

FP_ARITH_INST_RETIRED.512B Number of Packed Single-Precision FP arithmetic
_PACKED_SINGLE
instructions (use operation multiplier of 16).

Only applicable when
AVX-512 is enabled.

C8H

01H

HLE_RETIRED.START

Number of times we entered an HLE region. Does not
count nested transactions.

C8H

02H

HLE_RETIRED.COMMIT

Number of times HLE commit succeeded.

C8H

04H

HLE_RETIRED.ABORTED

Number of times HLE abort was triggered.

C8H

08H

HLE_RETIRED.ABORTED_MEM

Number of times an HLE execution aborted due to
various memory events (e.g., read/write capacity and
conflicts).

C8H

10H

HLE_RETIRED.ABORTED_TIMER

Number of times an HLE execution aborted due to
hardware timer expiration.

C8H

20H

HLE_RETIRED.ABORTED_UNFRI
ENDLY

Number of times an HLE execution aborted due to HLEunfriendly instructions and certain unfriendly events
(such as AD assists etc.).

C8H

40H

HLE_RETIRED.ABORTED_MEMT
YPE

Number of times an HLE execution aborted due to
incompatible memory type.

C8H

80H

HLE_RETIRED.ABORTED_EVENT Number of times an HLE execution aborted due to
S
unfriendly events (such as interrupts).

C9H

01H

RTM_RETIRED.START

Number of times we entered an RTM region. Does not
count nested transactions.

C9H

02H

RTM_RETIRED.COMMIT

Number of times RTM commit succeeded.

C9H

04H

RTM_RETIRED.ABORTED

Number of times RTM abort was triggered.

19-20 Vol. 3B

Comment

Precise event capable.

Precise event capable.

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

C9H

08H

RTM_RETIRED.ABORTED_MEM

Number of times an RTM execution aborted due to
various memory events (e.g. read/write capacity and
conflicts).

C9H

10H

RTM_RETIRED.ABORTED_TIMER Number of times an RTM execution aborted due to
uncommon conditions.

C9H

20H

RTM_RETIRED.ABORTED_UNFRI Number of times an RTM execution aborted due to
ENDLY
HLE-unfriendly instructions.

C9H

40H

RTM_RETIRED.ABORTED_MEMT Number of times an RTM execution aborted due to
YPE
incompatible memory type.

C9H

80H

RTM_RETIRED.ABORTED_EVENT Number of times an RTM execution aborted due to
S
none of the previous 4 categories (e.g. interrupt).

CAH

1EH

FP_ASSIST.ANY

Counts cycles with any input and output SSE or x87 FP CounterMask=1
assist. If an input and output assist are detected on the CMSK1
same cycle the event increments by 1.

CBH

01H

HW_INTERRUPTS.RECEIVED

Counts the number of hardware interruptions received
by the processor.

CCH

20H

ROB_MISC_EVENTS.LBR_INSERT Increments when an entry is added to the Last Branch
S
Record (LBR) array (or removed from the array in case
of RETURNs in call stack mode). The event requires LBR
enable via IA32_DEBUGCTL MSR and branch type
selection via MSR_LBR_SELECT.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_4

Counts loads when the latency from first dispatch to
completion is greater than 4 cycles. Reported latency
may be longer than just the memory latency.

Precise event capable.
Specify threshold in
MSR 3F6H.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_8

Counts loads when the latency from first dispatch to
completion is greater than 8 cycles. Reported latency
may be longer than just the memory latency.

Precise event capable.
Specify threshold in
MSR 3F6H.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_16

Counts loads when the latency from first dispatch to
completion is greater than 16 cycles. Reported latency
may be longer than just the memory latency.

Precise event capable.
Specify threshold in
MSR 3F6H.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_32

Counts loads when the latency from first dispatch to
completion is greater than 32 cycles. Reported latency
may be longer than just the memory latency.

Precise event capable.
Specify threshold in
MSR 3F6H.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_64

Counts loads when the latency from first dispatch to
completion is greater than 64 cycles. Reported latency
may be longer than just the memory latency.

Precise event capable.
Specify threshold in
MSR 3F6H.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_128

Counts loads when the latency from first dispatch to
Precise event capable.
completion is greater than 128 cycles. Reported latency Specify threshold in
may be longer than just the memory latency.
MSR 3F6H.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_256

Counts loads when the latency from first dispatch to
Precise event capable.
completion is greater than 256 cycles. Reported latency Specify threshold in
may be longer than just the memory latency.
MSR 3F6H.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY_GT_512

Precise event capable.
Counts loads when the latency from first dispatch to
completion is greater than 512 cycles. Reported latency Specify threshold in
MSR 3F6H.
may be longer than just the memory latency.

D0H

11H

MEM_INST_RETIRED.STLB_MISS Retired load instructions that miss the STLB.
_LOADS

Precise event capable.
PSDLA

Vol. 3B 19-21

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

D0H

12H

MEM_INST_RETIRED.STLB_MISS Retired store instructions that miss the STLB.
_STORES

Precise event capable.
PSDLA

D0H

21H

MEM_INST_RETIRED.LOCK_LOA
DS

Precise event capable.
PSDLA

D0H

41H

MEM_INST_RETIRED.SPLIT_LOA Counts retired load instructions that split across a
DS
cacheline boundary.

Precise event capable.
PSDLA

D0H

42H

MEM_INST_RETIRED.SPLIT_STO Counts retired store instructions that split across a
RES
cacheline boundary.

Precise event capable.
PSDLA

D0H

81H

MEM_INST_RETIRED.ALL_LOAD
S

All retired load instructions.

Precise event capable.
PSDLA

D0H

82H

MEM_INST_RETIRED.ALL_STOR
ES

All retired store instructions.

Precise event capable.
PSDLA

D1H

01H

MEM_LOAD_RETIRED.L1_HIT

Counts retired load instructions with at least one uop
Precise event capable.
that hit in the L1 data cache. This event includes all SW PSDLA
prefetches and lock instructions regardless of the data
source.

D1H

02H

MEM_LOAD_RETIRED.L2_HIT

Retired load instructions with L2 cache hits as data
sources.

Precise event capable.
PSDLA

D1H

04H

MEM_LOAD_RETIRED.L3_HIT

Counts retired load instructions with at least one uop
that hit in the L3 cache.

Precise event capable.
PSDLA

D1H

08H

MEM_LOAD_RETIRED.L1_MISS

Counts retired load instructions with at least one uop
that missed in the L1 cache.

Precise event capable.
PSDLA

D1H

10H

MEM_LOAD_RETIRED.L2_MISS

Retired load instructions missed L2 cache as data
sources.

Precise event capable.
PSDLA

D1H

20H

MEM_LOAD_RETIRED.L3_MISS

Counts retired load instructions with at least one uop
that missed in the L3 cache.

Precise event capable.
PSDLA

D1H

40H

MEM_LOAD_RETIRED.FB_HIT

Counts retired load instructions with at least one uop
was load missed in L1 but hit FB (Fill Buffers) due to
preceding miss to the same cache line with data not
ready.

Precise event capable.
PSDLA

D2H

01H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_MISS

Retired load instructions which data sources were L3
hit and cross-core snoop missed in on-pkg core cache.

Precise event capable.
PSDLA

D2H

02H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_HIT

Retired load instructions which data sources were L3
and cross-core snoop hits in on-pkg core cache.

Precise event capable.
PSDLA

D2H

04H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_HITM

Retired load instructions which data sources were HitM Precise event capable.
responses from shared L3.
PSDLA

D2H

08H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_NONE

Retired load instructions which data sources were hits
in L3 without snoops required.

D3H

01H

MEM_LOAD_L3_MISS_RETIRED.
LOCAL_DRAM

Retired load instructions which data sources missed L3 Precise event capable.
but serviced from local DRAM.

D3H

02H

MEM_LOAD_L3_MISS_RETIRED.
REMOTE_DRAM

Retired load instructions which data sources missed L3 Precise event capable.
but serviced from remote dram.

D3H

04H

MEM_LOAD_L3_MISS_RETIRED.
REMOTE_HITM

Retired load instructions whose data sources was
remote HITM.

D3H

08H

MEM_LOAD_L3_MISS_RETIRED.
REMOTE_FWD

Retired load instructions whose data sources was
forwarded from a remote cache.

19-22 Vol. 3B

Description

Retired load instructions with locked access.

Comment

Precise event capable.
PSDLA

Precise event capable.

PERFORMANCE MONITORING EVENTS

Table 19-3. Performance Events of the Processor Core Supported in
Intel® Xeon® Processor Scalable Family with Skylake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

D4H

04H

MEM_LOAD_MISC_RETIRED.UC

Retired instructions with at least 1 uncacheable load or Precise event capable.
lock.

E6H

01H

BACLEARS.ANY

Counts the number of times the front-end is resteered
when it finds a branch instruction in a fetch line. This
occurs for the first time a branch instruction is fetched
or when the branch is not tracked by the BPU (Branch
Prediction Unit) anymore.

F0H

40H

L2_TRANS.L2_WB

Counts L2 writebacks that access L2 cache.

F1H

1FH

L2_LINES_IN.ALL

Counts the number of L2 cache lines filling the L2.
Counting does not cover rejects.

F2H

01H

L2_LINES_OUT.SILENT

Counts the number of lines that are silently dropped by
L2 cache when triggered by an L2 cache fill. These lines
are typically in Shared state. A non-threaded event.

F2H

02H

L2_LINES_OUT.NON_SILENT

Counts the number of lines that are evicted by L2 cache
when triggered by an L2 cache fill. Those lines can be
either in modified state or clean state. Modified lines
may either be written back to L3 or directly written to
memory and not allocated in L3. Clean lines may either
be allocated in L3 or dropped.

F2H

04H

L2_LINES_OUT.USELESS_PREF

Counts the number of lines that have been hardware
prefetched but not used and now evicted by L2 cache.

F2H

04H

L2_LINES_OUT.USELESS_HWPF

Counts the number of lines that have been hardware
prefetched but not used and now evicted by L2 cache.

F4H

10H

SQ_MISC.SPLIT_LOCK

Counts the number of cache line split locks sent to the
uncore.

FEH

02H

IDI_MISC.WB_UPGRADE

Counts number of cache lines that are allocated and
written back to L3 with the intention that they are
more likely to be reused shortly.

FEH

04H

IDI_MISC.WB_DOWNGRADE

Counts number of cache lines that are dropped and not
written back to L3 as they are deemed to be less likely
to be reused shortly.

19.3

Comment

PERFORMANCE MONITORING EVENTS FOR 6TH GENERATION INTEL®
CORE™ PROCESSOR AND 7TH GENERATION INTEL® CORE™ PROCESSOR

6th Generation Intel® Core™ processors are based on the Skylake microarchitecture. They support the architectural performance monitoring events listed in Table 19-1. Fixed counters in the core PMU support the architecture
events defined in Table 19-2. Model-specific performance monitoring events in the processor core are listed in
Table 19-4. The events in Table 19-4 apply to processors with CPUID signature of DisplayFamily_DisplayModel
encoding with the following values: 06_4EH and 06_5EH. Table 19-10 lists performance events supporting Intel
TSX (see Section 18.3.6.5) and the events are applicable to processors based on Skylake microarchitecture. Where
Skylake microarchitecture implements TSX-related event semantics that differ from Table 19-10, they are listed in
Table 19-5.
7th Generation Intel® Core™ processors are based on the Kaby Lake microarchitecture. Model-specific performance monitoring events in the processor core are listed in Table 19-4. The events in Table 19-4 apply to processors with CPUID signature of DisplayFamily_DisplayModel encoding with the following values: 06_8EH and
06_9EH.

Vol. 3B 19-23

PERFORMANCE MONITORING EVENTS

The comment column in Table 19-4 uses abbreviated letters to indicate additional conditions applicable to the Event
Mask Mnemonic. For event umasks listed in Table 19-4 that do not show “AnyT”, users should refrain from programming “AnyThread =1” in IA32_PERF_EVTSELx.

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

03H

02H

LD_BLOCKS.STORE_FORWARD

Loads blocked by overlapping with store buffer that
cannot be forwarded.

03H

08H

LD_BLOCKS.NO_SR

The number of times that split load operations are
temporarily blocked because all resources for handling
the split accesses are in use.

07H

01H

LD_BLOCKS_PARTIAL.ADDRESS
_ALIAS

False dependencies in MOB due to partial compare on
address.

08H

01H

DTLB_LOAD_MISSES.MISS_CAUS Load misses in all TLB levels that cause a page walk of
ES_A_WALK
any page size.

08H

0EH

DTLB_LOAD_MISSES.WALK_COM Load misses in all TLB levels causes a page walk that
PLETED
completes. (All page sizes.)

08H

10H

DTLB_LOAD_MISSES.WALK_PEN Counts 1 per cycle for each PMH that is busy with a
DING
page walk for a load.

08H

10H

DTLB_LOAD_MISSES.WALK_ACT Cycles when at least one PMH is busy with a walk for a CMSK1
IVE
load.

08H

20H

DTLB_LOAD_MISSES.STLB_HIT

Loads that miss the DTLB but hit STLB.

0DH

01H

INT_MISC.RECOVERY_CYCLES

Core cycles the allocator was stalled due to recovery
from earlier machine clear event for this thread (for
example, misprediction or memory order conflict).

0DH

01H

INT_MISC.RECOVERY_CYCLES_A Core cycles the allocator was stalled due to recovery
NY
from earlier machine clear event for any logical thread
in this processor core.

0DH

80H

INT_MISC.CLEAR_RESTEER_CYC
LES

Cycles the issue-stage is waiting for front end to fetch
from resteered path following branch misprediction or
machine clear events.

Comment

AnyT

0EH

01H

UOPS_ISSUED.ANY

The number of uops issued by the RAT to RS.

0EH

01H

UOPS_ISSUED.STALL_CYCLES

Cycles when the RAT does not issue uops to RS for the CMSK1, INV
thread.

0EH

02H

UOPS_ISSUED.VECTOR_WIDTH_ Uops inserted at issue-stage in order to preserve upper
MISMATCH
bits of vector registers.

0EH

20H

UOPS_ISSUED.SLOW_LEA

Number of slow LEA or similar uops allocated. Such uop
has 3 sources (for example, 2 sources + immediate)
regardless of whether it is a result of LEA instruction or
not.

14H

01H

ARITH.FPU_DIVIDER_ACTIVE

Cycles when divider is busy executing divide or square
root operations. Accounts for FP operations including
integer divides.

24H

21H

L2_RQSTS.DEMAND_DATA_RD_ Demand Data Read requests that missed L2, no rejects.
MISS

24H

22H

L2_RQSTS.RFO_MISS

RFO requests that missed L2.

24H

24H

L2_RQSTS.CODE_RD_MISS

L2 cache misses when fetching instructions.

24H

27H

L2_RQSTS.ALL_DEMAND_MISS

Demand requests that missed L2.

19-24 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

24H

38H

L2_RQSTS.PF_MISS

Requests from the L1/L2/L3 hardware prefetchers or
load software prefetches that miss L2 cache.

24H

3FH

L2_RQSTS.MISS

All requests that missed L2.

24H

41H

L2_RQSTS.DEMAND_DATA_RD_
HIT

Demand Data Read requests that hit L2 cache.

24H

42H

L2_RQSTS.RFO_HIT

RFO requests that hit L2 cache.

24H

44H

L2_RQSTS.CODE_RD_HIT

L2 cache hits when fetching instructions.

24H

D8H

L2_RQSTS.PF_HIT

Prefetches that hit L2.

24H

E1H

L2_RQSTS.ALL_DEMAND_DATA
_RD

All demand data read requests to L2.

24H

E2H

L2_RQSTS.ALL_RFO

All L RFO requests to L2.

24H

E4H

L2_RQSTS.ALL_CODE_RD

All L2 code requests.

24H

E7H

L2_RQSTS.ALL_DEMAND_REFE
RENCES

All demand requests to L2.

24H

F8H

L2_RQSTS.ALL_PF

All requests from the L1/L2/L3 hardware prefetchers
or load software prefetches.
All requests to L2.

Comment

24H

EFH

L2_RQSTS.REFERENCES

2EH

4FH

LONGEST_LAT_CACHE.REFEREN This event counts requests originating from the core
CE
that reference a cache line in the L3 cache.

See Table 19-1.

2EH

41H

LONGEST_LAT_CACHE.MISS

This event counts each cache miss condition for
references to the L3 cache.

See Table 19-1.

3CH

00H

CPU_CLK_UNHALTED.THREAD_
P

Cycles while the logical processor is not in a halt state.

See Table 19-1.

3CH

00H

CPU_CLK_UNHALTED.THREAD_
P_ANY

Cycles while at least one logical processor is not in a
halt state.

AnyT

3CH

01H

CPU_CLK_THREAD_UNHALTED.
REF_XCLK

Core crystal clock cycles when the thread is unhalted.

See Table 19-1.

3CH

01H

CPU_CLK_THREAD_UNHALTED.
REF_XCLK_ANY

Core crystal clock cycles when at least one thread on
the physical core is unhalted.

AnyT

3CH

02H

CPU_CLK_THREAD_UNHALTED.
ONE_THREAD_ACTIVE

Core crystal clock cycles when this thread is unhalted
and the other thread is halted.

48H

01H

L1D_PEND_MISS.PENDING

Increments the number of outstanding L1D misses
every cycle.

48H

01H

L1D_PEND_MISS.PENDING_CYCL Cycles with at least one outstanding L1D misses from
ES
this logical processor.

CMSK1

48H

01H

L1D_PEND_MISS.PENDING_CYCL Cycles with at least one outstanding L1D misses from
ES_ANY
any logical processor in this core.

CMSK1, AnyT

48H

02H

L1D_PEND_MISS.FB_FULL

49H

01H

DTLB_STORE_MISSES.MISS_CAU Store misses in all TLB levels that cause page walks.
SES_A_WALK

Number of times a request needed a FB entry but there
was no entry available for it. That is, the FB
unavailability was the dominant reason for blocking the
request. A request includes cacheable/uncacheable
demand that is load, store or SW prefetch. HWP are
excluded.

Vol. 3B 19-25

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

49H

0EH

DTLB_STORE_MISSES.WALK_CO Counts completed page walks in any TLB levels due to
MPLETED
store misses (all page sizes).

49H

10H

DTLB_STORE_MISSES.WALK_PE Counts 1 per cycle for each PMH that is busy with a
NDING
page walk for a store.

49H

10H

DTLB_STORE_MISSES.WALK_AC Cycles when at least one PMH is busy with a page walk CMSK1
TIVE
for a store.

49H

20H

DTLB_STORE_MISSES.STLB_HIT Store misses that missed DTLB but hit STLB.

4CH

01H

LOAD_HIT_PRE.HW_PF

Demand load dispatches that hit fill buffer allocated for
software prefetch.

4FH

10H

EPT.WALK_PENDING

Counts 1 per cycle for each PMH that is busy with an
EPT walk for any request type.

51H

01H

L1D.REPLACEMENT

Counts the number of lines brought into the L1 data
cache.

5EH

01H

RS_EVENTS.EMPTY_CYCLES

Cycles the RS is empty for the thread.

5EH

01H

RS_EVENTS.EMPTY_END

Counts end of periods where the Reservation Station
(RS) was empty. Could be useful to precisely locate
Front-end Latency Bound issues.

60H

01H

OFFCORE_REQUESTS_OUTSTAN Increment each cycle of the number of offcore
DING.DEMAND_DATA_RD
outstanding Demand Data Read transactions in SQ to
uncore.

60H

01H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least one offcore outstanding Demand
DING.CYCLES_WITH_DEMAND_D Data Read transactions in SQ to uncore.
ATA_RD

60H

01H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least 6 offcore outstanding Demand Data CMSK6
DING.DEMAND_DATA_RD_GE_6 Read transactions in SQ to uncore.

60H

02H

OFFCORE_REQUESTS_OUTSTAN Increment each cycle of the number of offcore
DING.DEMAND_CODE_RD
outstanding demand code read transactions in SQ to
uncore.

60H

02H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least one offcore outstanding demand
DING.CYCLES_WITH_DEMAND_C code read transactions in SQ to uncore.
ODE_RD

60H

04H

OFFCORE_REQUESTS_OUTSTAN Increment each cycle of the number of offcore
DING.DEMAND_RFO
outstanding RFO store transactions in SQ to uncore. Set
Cmask=1 to count cycles.

60H

04H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least one offcore outstanding RFO
DING.CYCLES_WITH_DEMAND_R transactions in SQ to uncore.
FO

60H

08H

OFFCORE_REQUESTS_OUTSTAN Increment each cycle of the number of offcore
DING.ALL_DATA_RD
outstanding cacheable data read transactions in SQ to
uncore. Set Cmask=1 to count cycles.

60H

08H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least one offcore outstanding data read
DING.CYCLES_WITH_DATA_RD
transactions in SQ to uncore.

60H

10H

OFFCORE_REQUESTS_OUTSTAN Increment each cycle of the number of offcore
DING.L3_MISS_DEMAND_DATA_ outstanding demand data read requests from SQ that
RD
missed L3.

19-26 Vol. 3B

Event Mask Mnemonic

Description

Comment

CMSK1, INV

CMSK1

CMSK1

CMSK1

CMSK1

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

60H

10H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least one offcore outstanding demand
DING.CYCLES_WITH_L3_MISS_D data read requests from SQ that missed L3.
EMAND_DATA_RD

CMSK1

60H

10H

OFFCORE_REQUESTS_OUTSTAN Cycles with at least one offcore outstanding demand
DING.L3_MISS_DEMAND_DATA_ data read requests from SQ that missed L3.
RD_GE_6

CMSK6

63H

02H

LOCK_CYCLES.CACHE_LOCK_DU
RATION

Cycles in which the L1D is locked.

79H

04H

IDQ.MITE_UOPS

Increment each cycle # of uops delivered to IDQ from
MITE path.

79H

04H

IDQ.MITE_CYCLES

Cycles when uops are being delivered to IDQ from MITE CMSK1
path.

79H

08H

IDQ.DSB_UOPS

Increment each cycle. # of uops delivered to IDQ from
DSB path.

79H

08H

IDQ.DSB_CYCLES

Cycles when uops are being delivered to IDQ from DSB
path.

79H

10H

IDQ.MS_DSB_UOPS

Increment each cycle # of uops delivered to IDQ by DSB
when MS_busy.

79H

18H

IDQ.ALL_DSB_CYCLES_ANY_UO
PS

Cycles DSB is delivered at least one uops.

CMSK1
CMSK4

Event Mask Mnemonic

Description

Comment

CMSK1

79H

18H

IDQ.ALL_DSB_CYCLES_4_UOPS

Cycles DSB is delivered four uops.

79H

20H

IDQ.MS_MITE_UOPS

Increment each cycle # of uops delivered to IDQ by
MITE when MS_busy.

79H

24H

IDQ.ALL_MITE_CYCLES_ANY_UO Counts cycles MITE is delivered at least one uops.
PS

CMSK1

79H

24H

IDQ.ALL_MITE_CYCLES_4_UOPS Counts cycles MITE is delivered four uops.

CMSK4

79H

30H

IDQ.MS_UOPS

Increment each cycle # of uops delivered to IDQ while
MS is busy.

79H

30H

IDQ.MS_SWITCHES

Number of switches from DSB or MITE to MS.

EDG

79H

30H

IDQ.MS_CYCLES

Cycles MS is delivered at least one uops.

CMSK1

80H

04H

ICACHE_16B.IFDATA_STALL

Cycles where a code fetch is stalled due to L1
instruction cache miss.

80H

04H

ICACHE_64B.IFDATA_STALL

Cycles where a code fetch is stalled due to L1
instruction cache tag miss.

83H

01H

ICACHE_64B.IFTAG_HIT

Instruction fetch tag lookups that hit in the instruction
cache (L1I). Counts at 64-byte cache-line granularity.

83H

02H

ICACHE_64B.IFTAG_MISS

Instruction fetch tag lookups that miss in the
instruction cache (L1I). Counts at 64-byte cache-line
granularity.

85H

01H

ITLB_MISSES.MISS_CAUSES_A_
WALK

Misses at all ITLB levels that cause page walks.

85H

0EH

ITLB_MISSES.WALK_COMPLETE
D

Counts completed page walks in any TLB level due to
code fetch misses (all page sizes).

85H

10H

ITLB_MISSES.WALK_PENDING

Counts 1 per cycle for each PMH that is busy with a
page walk for an instruction fetch request.

Vol. 3B 19-27

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

85H

20H

ITLB_MISSES.STLB_HIT

ITLB misses that hit STLB.

87H

01H

ILD_STALL.LCP

Stalls caused by changing prefix length of the
instruction.

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CO
RE

Count issue pipeline slots where no uop was delivered
from the front end to the back end when there is no
back-end stall.

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Cycles which 4 issue pipeline slots had no uop delivered CMSK4
LES_0_UOP_DELIV.CORE
from the front end to the back end when there is no
back-end stall.

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Cycles which “4-n” issue pipeline slots had no uop
LES_LE_n_UOP_DELIV.CORE
delivered from the front end to the back end when
there is no back-end stall.

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CYC Cycles which front end delivered 4 uops or the RAT was CMSK, INV
LES_FE_WAS_OK
stalling FE.

A1H

01H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_0
dispatched to port 0.

A1H

02H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_1
dispatched to port 1.

A1H

04H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_2
dispatched to port 2.

A1H

08H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_3
dispatched to port 3.

A1H

10H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_4
dispatched to port 4.

A1H

20H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_5
dispatched to port 5.

A1H

40H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_6
dispatched to port 6.

A1H

80H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_7
dispatched to port 7.

A2H

01H

RESOURCE_STALLS.ANY

Resource-related stall cycles.

A2H

08H

RESOURCE_STALLS.SB

Cycles stalled due to no store buffers available (not
including draining form sync).

A3H

01H

CYCLE_ACTIVITY.CYCLES_L2_MI
SS

Cycles while L2 cache miss demand load is outstanding. CMSK1

A3H

02H

CYCLE_ACTIVITY.CYCLES_L3_MI
SS

Cycles while L3 cache miss demand load is outstanding. CMSK2

A3H

04H

CYCLE_ACTIVITY.STALLS_TOTAL Total execution stalls.

CMSK4

A3H

05H

CYCLE_ACTIVITY.STALLS_L2_MI
SS

Execution stalls while L2 cache miss demand load is
outstanding.

CMSK5

A3H

06H

CYCLE_ACTIVITY.STALLS_L3_MI
SS

Execution stalls while L3 cache miss demand load is
outstanding.

CMSK6

A3H

08H

CYCLE_ACTIVITY.CYCLES_L1D_M Cycles while L1 data cache miss demand load is
ISS
outstanding.

CMSK8

A3H

0CH

CYCLE_ACTIVITY.STALLS_L1D_M Execution stalls while L1 data cache miss demand load
ISS
is outstanding.

CMSK12

19-28 Vol. 3B

Comment

Set CMSK = 4-n; n = 1,
2, 3

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

A3H

10H

CYCLE_ACTIVITY.CYCLES_MEM_
ANY

Cycles while memory subsystem has an outstanding
load.

CMSK16

A3H

14H

CYCLE_ACTIVITY.STALLS_MEM_
ANY

Execution stalls while memory subsystem has an
outstanding load.

CMSK20

A6H

01H

EXE_ACTIVITY.EXE_BOUND_0_P Cycles for which no uops began execution, the
ORTS
Reservation Station was not empty, the Store Buffer
was full and there was no outstanding load.

A6H

02H

EXE_ACTIVITY.1_PORTS_UTIL

Cycles for which one uop began execution on any port,
and the Reservation Station was not empty.

A6H

04H

EXE_ACTIVITY.2_PORTS_UTIL

Cycles for which two uops began execution, and the
Reservation Station was not empty.

A6H

08H

EXE_ACTIVITY.3_PORTS_UTIL

Cycles for which three uops began execution, and the
Reservation Station was not empty.

A6H

04H

EXE_ACTIVITY.4_PORTS_UTIL

Cycles for which four uops began execution, and the
Reservation Station was not empty.

A6H

40H

EXE_ACTIVITY.BOUND_ON_STO
RES

Cycles where the Store Buffer was full and no
outstanding load.

A8H

01H

LSD.UOPS

Number of uops delivered by the LSD.

A8H

01H

LSD.CYCLES_ACTIVE

Cycles with at least one uop delivered by the LSD and
none from the decoder.

A8H

01H

LSD.CYCLES_4_UOPS

Cycles with 4 uops delivered by the LSD and none from CMSK4
the decoder.

ABH

02H

DSB2MITE_SWITCHES.PENALTY
_CYCLES

DSB-to-MITE switch true penalty cycles.

AEH

01H

ITLB.ITLB_FLUSH

Flushing of the Instruction TLB (ITLB) pages, includes
4k/2M/4M pages.

B0H

01H

OFFCORE_REQUESTS.DEMAND_ Demand data read requests sent to uncore.
DATA_RD

B0H

02H

OFFCORE_REQUESTS.DEMAND_ Demand code read requests sent to uncore.
CODE_RD

B0H

04H

OFFCORE_REQUESTS.DEMAND_ Demand RFO read requests sent to uncore, including
RFO
regular RFOs, locks, ItoM.

B0H

08H

OFFCORE_REQUESTS.ALL_DATA Data read requests sent to uncore (demand and
_RD
prefetch).

B0H

10H

OFFCORE_REQUESTS.L3_MISS_
DEMAND_DATA_RD

B0H

80H

OFFCORE_REQUESTS.ALL_REQU Any memory transaction that reached the SQ.
ESTS

B1H

01H

UOPS_EXECUTED.THREAD

Counts the number of uops that begin execution across
all ports.

B1H

01H

UOPS_EXECUTED.STALL_CYCLE
S

Cycles where there were no uops that began execution. CMSK, INV

B1H

01H

UOPS_EXECUTED.CYCLES_GE_1 Cycles where there was at least one uop that began
_UOP_EXEC
execution.

CMSK1

B1H

01H

UOPS_EXECUTED.CYCLES_GE_2 Cycles where there were at least two uops that began
_UOP_EXEC
execution.

CMSK2

CMSK1

Demand data read requests that missed L3.

Vol. 3B 19-29

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

B1H

01H

UOPS_EXECUTED.CYCLES_GE_3 Cycles where there were at least three uops that began CMSK3
_UOP_EXEC
execution.

B1H

01H

UOPS_EXECUTED.CYCLES_GE_4 Cycles where there were at least four uops that began CMSK4
_UOP_EXEC
execution.

B1H

02H

UOPS_EXECUTED.CORE

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles where there was at least one uop, from any
_GE_1
logical processor in this core, that began execution.

CMSK1

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles where there were at least two uops, from any
_GE_2
logical processor in this core, that began execution.

CMSK2

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles where there were at least three uops, from any
_GE_3
logical processor in this core, that began execution.

CMSK3

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles where there were at least four uops, from any
_GE_4
logical processor in this core, that began execution.

CMSK4

B1H

02H

UOPS_EXECUTED.CORE_CYCLES Cycles where there were no uops from any logical
_NONE
processor in this core that began execution.

CMSK1, INV

Event Mask Mnemonic

Description

Comment

Counts the number of uops from any logical processor
in this core that begin execution.

B1H

10H

UOPS_EXECUTED.X87

B2H

01H

OFF_CORE_REQUEST_BUFFER.S Offcore requests buffer cannot take more entries for
Q_FULL
this core.

Counts the number of X87 uops that begin execution.

B7H

01H

OFF_CORE_RESPONSE_0

See Section 18.3.4.5, “Off-core Response Performance
Monitoring”.

Requires MSR 01A6H

BBH

01H

OFF_CORE_RESPONSE_1

See Section 18.3.4.5, “Off-core Response Performance
Monitoring”.

Requires MSR 01A7H

BDH

01H

TLB_FLUSH.DTLB_THREAD

DTLB flush attempts of the thread-specific entries.

BDH

01H

TLB_FLUSH.STLB_ANY

STLB flush attempts.

C0H

00H

INST_RETIRED.ANY_P

Number of instructions at retirement.

See Table 19-1.

C0H

01H

INST_RETIRED.PREC_DIST

Precise instruction retired event with HW to reduce
effect of PEBS shadow in IP distribution.

PMC1 only;

C0H

01H

INST_RETIRED.TOTAL_CYCLES

Number of cycles using always true condition applied to CMSK10, PS
PEBS instructions retired event.

C1H

3FH

OTHER_ASSISTS.ANY

Number of times a microcode assist is invoked by HW
other than FP-assist. Examples include AD (page Access
Dirty) and AVX* related assists.

C2H

01H

UOPS_RETIRED.STALL_CYCLES

Cycles without actually retired uops.

CMSK1, INV

C2H

01H

UOPS_RETIRED.TOTAL_CYCLES

Cycles with less than 10 actually retired uops.

CMSK10, INV

C2H

02H

UOPS_RETIRED.RETIRE_SLOTS

Retirement slots used.

C3H

01H

MACHINE_CLEARS.COUNT

Number of machine clears of any type.

C3H

02H

MACHINE_CLEARS.MEMORY_OR
DERING

Counts the number of machine clears due to memory
order conflicts.

C3H

04H

MACHINE_CLEARS.SMC

Number of self-modifying-code machine clears
detected.

C4H

00H

BR_INST_RETIRED.ALL_BRANC
HES

Branch instructions that retired.

See Table 19-1.

C4H

01H

BR_INST_RETIRED.CONDITIONA
L

Counts the number of conditional branch instructions
retired.

PS

19-30 Vol. 3B

CMSK1, EDG

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

C4H

02H

BR_INST_RETIRED.NEAR_CALL

Direct and indirect near call instructions retired.

PS

C4H

04H

BR_INST_RETIRED.ALL_BRANC
HES

Counts the number of branch instructions retired.

PS

C4H

08H

BR_INST_RETIRED.NEAR_RETU
RN

Counts the number of near return instructions retired.

PS

C4H

10H

BR_INST_RETIRED.NOT_TAKEN

Counts the number of not taken branch instructions
retired.

C4H

20H

BR_INST_RETIRED.NEAR_TAKE
N

Number of near taken branches retired.

PS

C4H

40H

BR_INST_RETIRED.FAR_BRANC
H

Number of far branches retired.

PS

C5H

00H

BR_MISP_RETIRED.ALL_BRANC
HES

Mispredicted branch instructions at retirement.

See Table 19-1.

C5H

01H

BR_MISP_RETIRED.CONDITIONA Mispredicted conditional branch instructions retired.
L

PS

C5H

04H

BR_MISP_RETIRED.ALL_BRANC
HES

Mispredicted macro branch instructions retired.

PS

C5H

20H

BR_MISP_RETIRED.NEAR_TAKE
N

Number of near branch instructions retired that were
mispredicted and taken.

PS

C6H

01H

FRONTEND_RETIRED.DSB_MISS

Retired instructions which experienced DSB miss.
Specify MSR_PEBS_FRONTEND.EVTSEL=11H.

PS

C6H

01H

FRONTEND_RETIRED.L1I_MISS

Retired instructions which experienced instruction L1
cache true miss. Specify
MSR_PEBS_FRONTEND.EVTSEL=12H.

PS

C6H

01H

FRONTEND_RETIRED.L2_MISS

Retired instructions which experienced L2 cache true
miss. Specify MSR_PEBS_FRONTEND.EVTSEL=13H.

PS

C6H

01H

FRONTEND_RETIRED.ITLB_MISS Retired instructions which experienced ITLB true miss.
Specify MSR_PEBS_FRONTEND.EVTSEL=14H.

C6H

01H

FRONTEND_RETIRED.STLB_MIS
S

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
GE_16
where the front end delivered no uops for at least 16
cycles. Specify the following fields in
MSR_PEBS_FRONTEND: EVTSEL=16H,
IDQ_Bubble_Length =16, IDQ_Bubble_Width = 4.

C6H

01H

FRONTEND_RETIRED.LATENCY_ Retired instructions that are fetched after an interval
PS, m = 1, 2, 3
GE_2_BUBBLES_GE_m
where the front end had ‘m’ IDQ slots delivered, no uops
for at least 2 cycles. Specify the following fields in
MSR_PEBS_FRONTEND: EVTSEL=16H,
IDQ_Bubble_Length =2, IDQ_Bubble_Width = m.

C7H

01H

FP_ARITH_INST_RETIRED.SCAL
AR_DOUBLE

Number of double-precision, floating-point, scalar
SSE/AVX computational instructions that are retired.
Each scalar FMA instruction counts as 2.

Software may treat
each count as one DP
FLOP.

C7H

02H

FP_ARITH_INST_RETIRED.SCAL
AR_SINGLE

Number of single-precision, floating-point, scalar
SSE/AVX computational instructions that are retired.
Each scalar FMA instruction counts as 2.

Software may treat
each count as one SP
FLOP.

PS

Retired instructions which experienced STLB true miss. PS
Specify MSR_PEBS_FRONTEND.EVTSEL=15H.
PS

Vol. 3B 19-31

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

C7H

04H

FP_ARITH_INST_RETIRED.128B Number of double-precision, floating-point, 128-bit
_PACKED_DOUBLE
SSE/AVX computational instructions that are retired.
Each 128-bit FMA or (V)DPPD instruction counts as 2.

Software may treat
each count as two DP
FLOPs.

C7H

08H

FP_ARITH_INST_RETIRED.128B Number of single-precision, floating-point, 128-bit
_PACKED_SINGLE
SSE/AVX computational instructions that are retired.
Each 128-bit FMA or (V)DPPS instruction counts as 2.

Software may treat
each count as four SP
FLOPs.

C7H

10H

FP_ARITH_INST_RETIRED.256B Number of double-precision, floating-point, 256-bit
_PACKED_DOUBLE
SSE/AVX computational instructions that are retired.
Each 256-bit FMA instruction counts as 2.

Software may treat
each count as four DP
FLOPs.

C7H

20H

FP_ARITH_INST_RETIRED.256B Number of single-precision, floating-point, 256-bit
_PACKED_SINGLE
SSE/AVX computational instructions that are retired.
Each 256-bit FMA or VDPPS instruction counts as 2.

Software may treat
each count as eight
SP FLOPs.
CMSK1

Event Mask Mnemonic

Description

Comment

CAH

1EH

FP_ASSIST.ANY

Cycles with any input/output SSE* or FP assists.

CBH

01H

HW_INTERRUPTS.RECEIVED

Number of hardware interrupts received by the
processor.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY

Randomly sampled loads whose latency is above a user Specify threshold in
defined threshold. A small fraction of the overall loads MSR 3F6H.
are sampled due to randomization.
PSDLA

D0H

11H

MEM_INST_RETIRED.STLB_MISS Retired load instructions that miss the STLB.
_LOADS

PSDLA

D0H

12H

MEM_INST_RETIRED.STLB_MISS Retired store instructions that miss the STLB.
_STORES

PSDLA

D0H

21H

MEM_INST_RETIRED.LOCK_LOA
DS

PSDLA

D0H

41H

MEM_INST_RETIRED.SPLIT_LOA Number of load instructions retired with cache-line
DS
splits that may impact performance.

PSDLA

D0H

42H

MEM_INST_RETIRED.SPLIT_STO Number of store instructions retired with line-split.
RES

PSDLA

D0H

81H

MEM_INST_RETIRED.ALL_LOAD
S

All retired load instructions.

PSDLA

D0H

82H

MEM_INST_RETIRED.ALL_STOR
ES

All retired store instructions.

PSDLA

D1H

01H

MEM_LOAD_RETIRED.L1_HIT

Retired load instructions with L1 cache hits as data
sources.

PSDLA

D1H

02H

MEM_LOAD_RETIRED.L2_HIT

Retired load instructions with L2 cache hits as data
sources.

PSDLA

D1H

04H

MEM_LOAD_RETIRED.L3_HIT

Retired load instructions with L3 cache hits as data
sources.

PSDLA

D1H

08H

MEM_LOAD_RETIRED.L1_MISS

Retired load instructions missed L1 cache as data
sources.

PSDLA

D1H

10H

MEM_LOAD_RETIRED.L2_MISS

Retired load instructions missed L2. Unknown data
source excluded.

PSDLA

D1H

20H

MEM_LOAD_RETIRED.L3_MISS

Retired load instructions missed L3. Excludes unknown PSDLA
data source.

19-32 Vol. 3B

Retired load instructions with locked access.

PERFORMANCE MONITORING EVENTS

Table 19-4. Performance Events of the Processor Core Supported by
Skylake Microarchitecture and Kaby Lake Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

D1H

40H

MEM_LOAD_RETIRED.FB_HIT

Retired load instructions where data sources were load PSDLA
uops missed L1 but hit FB due to preceding miss to the
same cache line with data not ready.

D2H

01H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_MISS

Retired load instructions where data sources were L3
hit and cross-core snoop missed in on-pkg core cache.

PSDLA

D2H

02H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_HIT

Retired load Instructions where data sources were L3
and cross-core snoop hits in on-pkg core cache.

PSDLA

D2H

04H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_HITM

Retired load instructions where data sources were HitM PSDLA
responses from shared L3.

D2H

08H

MEM_LOAD_L3_HIT_RETIRED.X
SNP_NONE

Retired load instructions where data sources were hits PSDLA
in L3 without snoops required.

E6H

01H

BACLEARS.ANY

Number of front end re-steers due to BPU
misprediction.

F0H

40H

L2_TRANS.L2_WB

L2 writebacks that access L2 cache.

F1H

07H

L2_LINES_IN.ALL

L2 cache lines filling L2.

Comment

CMSK1: Counter Mask = 1 required; CMSK4: CounterMask = 4 required; CMSK6: CounterMask = 6 required; CMSK8: CounterMask = 8
required; CMSK10: CounterMask = 10 required; CMSK12: CounterMask = 12 required; CMSK16: CounterMask = 16 required; CMSK20:
CounterMask = 20 required.
AnyT: AnyThread = 1 required.
INV: Invert = 1 required.
EDG: EDGE = 1 required.
PSDLA: Also supports PEBS and DataLA.
PS: Also supports PEBS.

Table 19-10 lists performance events supporting Intel TSX (see Section 18.3.6.5) and the events are applicable to
processors based on Skylake microarchitecture. Where Skylake microarchitecture implements TSX-related event
semantics that differ from Table 19-10, they are listed in Table 19-5.

Table 19-5. Intel® TSX Performance Event Addendum in Processors based on Skylake Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

54H

02H

TX_MEM.ABORT_CAPACITY

Number of times a transactional abort was signaled due
to a data capacity limitation for transactional reads or
writes.

19.4

Comment

PERFORMANCE MONITORING EVENTS FOR INTEL® XEON PHI™ PROCESSOR
3200, 5200, 7200 SERIES

Intel® Xeon Phi™ processors 3200/5200/7200 series are based on the Knights Landing microarchitecture. Modelspecific performance monitoring events in the processor core are listed in Table 19-6. The events in Table 19-6
apply to processors with CPUID signature of DisplayFamily_DisplayModel encoding with the following value
06_57H.

Vol. 3B 19-33

PERFORMANCE MONITORING EVENTS

Table 19-6. Performance Events of the Processor Core Supported by
Knights Landing Microarchitecture
Event
Num.

Umask
Value

03H

01H

RECYCLEQ.LD_BLOCK_ST_FORW Counts the number of occurrences a retired load gets
ARD
blocked because its address partially overlaps with a
store.

03H

02H

RECYCLEQ.LD_BLOCK_STD_NOT Counts the number of occurrences a retired load gets
READY
blocked because its address overlaps with a store
whose data is not ready.

03H

04H

RECYCLEQ.ST_SPLITS

Counts the number of occurrences a retired store that
is a cache line split. Each split should be counted only
once.

03H

08H

RECYCLEQ.LD_SPLITS

Counts the number of occurrences a retired load that is PSDLA
a cache line split. Each split should be counted only
once.

03H

10H

RECYCLEQ.LOCK

Counts all the retired locked loads. It does not include
stores because we would double count if we count
stores.

03H

20H

RECYCLEQ.STA_FULL

Counts the store micro-ops retired that were pushed in
the recycle queue because the store address buffer is
full.

03H

40H

RECYCLEQ.ANY_LD

Counts any retired load that was pushed into the
recycle queue for any reason.

03H

80H

RECYCLEQ.ANY_ST

Counts any retired store that was pushed into the
recycle queue for any reason.

04H

01H

MEM_UOPS_RETIRED.L1_MISS_
LOADS

Counts the number of load micro-ops retired that miss
in L1 D cache.

04H

02H

MEM_UOPS_RETIRED.L2_HIT_L
OADS

Counts the number of load micro-ops retired that hit in
the L2.

PSDLA

04H

04H

MEM_UOPS_RETIRED.L2_MISS_
LOADS

Counts the number of load micro-ops retired that miss
in the L2.

PSDLA

04H

08H

MEM_UOPS_RETIRED.DTLB_MIS Counts the number of load micro-ops retired that cause PSDLA
S_LOADS
a DTLB miss.

04H

10H

MEM_UOPS_RETIRED.UTLB_MIS Counts the number of load micro-ops retired that
S_LOADS
caused micro TLB miss.

04H

20H

MEM_UOPS_RETIRED.HITM

04H

40H

MEM_UOPS_RETIRED.ALL_LOAD Counts all the load micro-ops retired.
S

04H

80H

MEM_UOPS_RETIRED.ALL_STOR Counts all the store micro-ops retired.
ES

05H

01H

PAGE_WALKS.D_SIDE_WALKS

Counts the total D-side page walks that are completed
or started. The page walks started in the speculative
path will also be counted.

05H

01H

PAGE_WALKS.D_SIDE_CYCLES

Counts the total number of core cycles for all the D-side
page walks. The cycles for page walks started in
speculative path will also be included.

05H

02H

PAGE_WALKS.I_SIDE_WALKS

Counts the total I-side page walks that are completed.

19-34 Vol. 3B

Event Mask Mnemonic

Description

Comment
PSDLA

Counts the loads retired that get the data from the
other core in the same tile in M state.

EdgeDetect=1

EdgeDetect=1

PERFORMANCE MONITORING EVENTS

Table 19-6. Performance Events of the Processor Core Supported by
Knights Landing Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

05H

02H

PAGE_WALKS.I_SIDE_CYCLES

Counts the total number of core cycles for all the I-side
page walks. The cycles for page walks started in
speculative path will also be included.

05H

03H

PAGE_WALKS.WALKS

Counts the total page walks that are completed (I-side
and D-side).

05H

03H

PAGE_WALKS.CYCLES

Counts the total number of core cycles for all the page
walks. The cycles for page walks started in speculative
path will also be included.

2EH

41H

LONGEST_LAT_CACHE.MISS

Counts the number of L2 cache misses. Also called
L2_REQUESTS_MISS.

2EH

4FH

LONGEST_LAT_CACHE.REFEREN Counts the total number of L2 cache references. Also
CE
called L2_REQUESTS_REFERENCE.

30H

00H

L2_REQUESTS_REJECT.ALL

Counts the number of MEC requests from the L2Q that
reference a cache line (cacheable requests) excluding
SW prefetches filling only to L2 cache and L1 evictions
(automatically excludes L2HWP, UC, WC) that were
rejected - Multiple repeated rejects should be counted
multiple times.

31H

00H

CORE_REJECT_L2Q.ALL

Counts the number of MEC requests that were not
accepted into the L2Q because of any L2 queue reject
condition. There is no concept of at-ret here. It might
include requests due to instructions in the speculative
path.

3CH

00H

CPU_CLK_UNHALTED.THREAD_
P

Counts the number of unhalted core clock cycles.

3CH

01H

CPU_CLK_UNHALTED.REF

Counts the number of unhalted reference clock cycles.

3EH

04H

L2_PREFETCHER.ALLOC_XQ

Counts the number of L2HWP allocated into XQ GP.

80H

01H

ICACHE.HIT

Counts all instruction fetches that hit the instruction
cache.

80H

02H

ICACHE.MISSES

Counts all instruction fetches that miss the instruction
cache or produce memory requests. An instruction
fetch miss is counted only once and not once for every
cycle it is outstanding.

80H

03H

ICACHE.ACCESSES

Counts all instruction fetches, including uncacheable
fetches.

86H

04H

FETCH_STALL.ICACHE_FILL_PEN Counts the number of core cycles the fetch stalls
DING_CYCLES
because of an icache miss. This is a cumulative count of
core cycles the fetch stalled for all icache misses.

B7H

01H

OFFCORE_RESPONSE_0

See Section 18.4.1.1.2.

Requires
MSR_OFFCORE_RESP
0 to specify request
type and response.

B7H

02H

OFFCORE_RESPONSE_1

See Section 18.4.1.1.2.

Requires
MSR_OFFCORE_RESP
1 to specify request
type and response.

C0H

00H

INST_RETIRED.ANY_P

Counts the total number of instructions retired.

PS

Comment

EdgeDetect=1

Vol. 3B 19-35

PERFORMANCE MONITORING EVENTS

Table 19-6. Performance Events of the Processor Core Supported by
Knights Landing Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

C2H

01H

UOPS_RETIRED.MS

Counts the number of micro-ops retired that are from
the complex flows issued by the micro-sequencer (MS).

C2H

10H

UOPS_RETIRED.ALL

Counts the number of micro-ops retired.

C2H

20H

UOPS_RETIRED.SCALAR_SIMD

Counts the number of scalar SSE, AVX, AVX2, and AVX512 micro-ops except for loads (memory-to-register
mov-type micro ops), division and sqrt.

C2H

40H

UOPS_RETIRED.PACKED_SIMD

Counts the number of packed SSE, AVX, AVX2, and
AVX-512 micro-ops (both floating point and integer)
except for loads (memory-to-register mov-type microops), packed byte and word multiplies.

C3H

01H

MACHINE_CLEARS.SMC

Counts the number of times that the machine clears
due to program modifying data within 1K of a recently
fetched code page.

C3H

02H

MACHINE_CLEARS.MEMORY_OR
DERING

Counts the number of times the machine clears due to
memory ordering hazards.

C3H

04H

MACHINE_CLEARS.FP_ASSIST

Counts the number of floating operations retired that
required microcode assists.

C3H

08H

MACHINE_CLEARS.ALL

Counts all machine clears.

C4H

00H

BR_INST_RETIRED.ALL_BRANC
HES

Counts the number of branch instructions retired.

C4H

7EH

BR_INST_RETIRED.JCC

Counts the number of JCC branch instructions retired.

PS

C4H

BFH

BR_INST_RETIRED.FAR_BRANC
H

Counts the number of far branch instructions retired.

PS

C4H

EBH

BR_INST_RETIRED.NON_RETUR Counts the number of branch instructions retired that
N_IND
were near indirect CALL or near indirect JMP.

PS

C4H

F7H

BR_INST_RETIRED.RETURN

Counts the number of near RET branch instructions
retired.

PS

C4H

F9H

BR_INST_RETIRED.CALL

Counts the number of near CALL branch instructions
retired.

PS

C4H

FBH

BR_INST_RETIRED.IND_CALL

Counts the number of near indirect CALL branch
instructions retired.

PS

C4H

FDH

BR_INST_RETIRED.REL_CALL

Counts the number of near relative CALL branch
instructions retired.

PS

C4H

FEH

BR_INST_RETIRED.TAKEN_JCC

Counts the number of branch instructions retired that
were taken conditional jumps.

PS

C5H

00H

BR_MISP_RETIRED.ALL_BRANC
HES

Counts the number of mispredicted branch instructions PS
retired.

C5H

7EH

BR_MISP_RETIRED.JCC

Counts the number of mispredicted JCC branch
instructions retired.

PS

C5H

BFH

BR_MISP_RETIRED.FAR_BRANC
H

Counts the number of mispredicted far branch
instructions retired.

PS

C5H

EBH

BR_MISP_RETIRED.NON_RETUR Counts the number of mispredicted branch instructions PS
N_IND
retired that were near indirect CALL or near indirect
JMP.

C5H

F7H

BR_MISP_RETIRED.RETURN

19-36 Vol. 3B

Counts the number of mispredicted near RET branch
instructions retired.

Comment

PS

PS

PERFORMANCE MONITORING EVENTS

Table 19-6. Performance Events of the Processor Core Supported by
Knights Landing Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

C5H

F9H

BR_MISP_RETIRED.CALL

Counts the number of mispredicted near CALL branch
instructions retired.

PS

C5H

FBH

BR_MISP_RETIRED.IND_CALL

Counts the number of mispredicted near indirect CALL
branch instructions retired.

PS

C5H

FDH

BR_MISP_RETIRED.REL_CALL

Counts the number of mispredicted near relative CALL
branch instructions retired.

PS

C5H

FEH

BR_MISP_RETIRED.TAKEN_JCC

Counts the number of mispredicted branch instructions PS
retired that were taken conditional jumps.

CAH

01H

NO_ALLOC_CYCLES.ROB_FULL

Counts the number of core cycles when no micro-ops
are allocated and the ROB is full.

CAH

04H

NO_ALLOC_CYCLES.MISPREDICT Counts the number of core cycles when no micro-ops
S
are allocated and the alloc pipe is stalled waiting for a
mispredicted branch to retire.

CAH

20H

NO_ALLOC_CYCLES.RAT_STALL

CAH

90H

NO_ALLOC_CYCLES.NOT_DELIVE Counts the number of core cycles when no micro-ops
RED
are allocated, the IQ is empty, and no other condition is
blocking allocation.

CAH

7FH

NO_ALLOC_CYCLES.ALL

Counts the total number of core cycles when no microops are allocated for any reason.

CBH

01H

RS_FULL_STALL.MEC

Counts the number of core cycles when allocation
pipeline is stalled and is waiting for a free MEC
reservation station entry.

CBH

1FH

RS_FULL_STALL.ALL

Counts the total number of core cycles the allocation
pipeline is stalled when any one of the reservation
stations is full.

CDH

01H

CYCLES_DIV_BUSY.ALL

Cycles the number of core cycles when divider is busy.
Does not imply a stall waiting for the divider.

E6H

01H

BACLEARS.ALL

Counts the number of times the front end resteers for
any branch as a result of another branch handling
mechanism in the front end.

E6H

08H

BACLEARS.RETURN

Counts the number of times the front end resteers for
RET branches as a result of another branch handling
mechanism in the front end.

E6H

10H

BACLEARS.COND

Counts the number of times the front end resteers for
conditional branches as a result of another branch
handling mechanism in the front end.

E7H

01H

MS_DECODED.MS_ENTRY

Counts the number of times the MSROM starts a flow
of uops.

Counts the number of core cycles when no micro-ops
are allocated and a RATstall (caused by reservation
station full) is asserted.

PS: Also supports PEBS.
PSDLA: Also supports PEBS and DataLA.

Vol. 3B 19-37

PERFORMANCE MONITORING EVENTS

19.5

PERFORMANCE MONITORING EVENTS FOR THE INTEL® CORE™ M AND 5TH
GENERATION INTEL® CORE™ PROCESSORS

The Intel® Core™ M processors, the 5th generation Intel® Core™ processors and the Intel Xeon processor E3 1200
v4 product family are based on the Broadwell microarchitecture. They support the architectural performance monitoring events listed in Table 19-1. Model-specific performance monitoring events in the processor core are listed in
Table 19-7. The events in Table 19-7 apply to processors with CPUID signature of DisplayFamily_DisplayModel
encoding with the following values: 06_3DH and 06_47H. Table 19-10 lists performance events supporting Intel
TSX (see Section 18.3.6.5) and the events are available on processors based on Broadwell microarchitecture. Fixed
counters in the core PMU support the architecture events defined in Table 19-2.
Model-specific performance monitoring events that are located in the uncore sub-system are implementation
specific between different platforms using processors based on Broadwell microarchitecture and with different
DisplayFamily_DisplayModel signatures. Processors with CPUID signature of DisplayFamily_DisplayModel 06_3DH
and 06_47H support uncore performance events listed in Table 19-11.

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

03H

02H

LD_BLOCKS.STORE_FORWARD

Loads blocked by overlapping with store buffer that
cannot be forwarded.

03H

08H

LD_BLOCKS.NO_SR

The number of times that split load operations are
temporarily blocked because all resources for
handling the split accesses are in use.

05H

01H

MISALIGN_MEM_REF.LOADS

Speculative cache-line split load uops dispatched to
L1D.

05H

02H

MISALIGN_MEM_REF.STORES

Speculative cache-line split store-address uops
dispatched to L1D.

07H

01H

LD_BLOCKS_PARTIAL.ADDRESS
_ALIAS

False dependencies in MOB due to partial compare
on address.

08H

01H

DTLB_LOAD_MISSES.MISS_CAUS Load misses in all TLB levels that cause a page walk
ES_A_WALK
of any page size.

08H

02H

DTLB_LOAD_MISSES.WALK_COM Completed page walks due to demand load misses
PLETED_4K
that caused 4K page walks in any TLB levels.

08H

10H

DTLB_LOAD_MISSES.WALK_DUR Cycle PMH is busy with a walk.
ATION

08H

20H

DTLB_LOAD_MISSES.STLB_HIT_ Load misses that missed DTLB but hit STLB (4K).
4K

0DH

03H

INT_MISC.RECOVERY_CYCLES

Cycles waiting to recover after Machine Clears
except JEClear. Set Cmask= 1.

Set Edge to count
occurrences.

0EH

01H

UOPS_ISSUED.ANY

Increments each cycle the # of uops issued by the
RAT to RS. Set Cmask = 1, Inv = 1, Any= 1to count
stalled cycles of this core.

Set Cmask = 1, Inv = 1to
count stalled cycles.

0EH

10H

UOPS_ISSUED.FLAGS_MERGE

Number of flags-merge uops allocated. Such uops
add delay.

0EH

20H

UOPS_ISSUED.SLOW_LEA

Number of slow LEA or similar uops allocated. Such
uop has 3 sources (for example, 2 sources +
immediate) regardless of whether it is a result of
LEA instruction or not.

0EH

40H

UOPS_ISSUED.SiNGLE_MUL

Number of multiply packed/scalar single precision
uops allocated.

19-38 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

14H

01H

ARITH.FPU_DIV_ACTIVE

Cycles when divider is busy executing divide
operations.

24H

21H

L2_RQSTS.DEMAND_DATA_RD_ Demand data read requests that missed L2, no
MISS
rejects.

24H

41H

L2_RQSTS.DEMAND_DATA_RD_ Demand data read requests that hit L2 cache.
HIT

24H

50H

L2_RQSTS.L2_PF_HIT

Counts all L2 HW prefetcher requests that hit L2.

24H

30H

L2_RQSTS.L2_PF_MISS

Counts all L2 HW prefetcher requests that missed
L2.

24H

E1H

L2_RQSTS.ALL_DEMAND_DATA
_RD

Counts any demand and L1 HW prefetch data load
requests to L2.

24H

E2H

L2_RQSTS.ALL_RFO

Counts all L2 store RFO requests.

24H

E4H

L2_RQSTS.ALL_CODE_RD

Counts all L2 code requests.

24H

F8H

L2_RQSTS.ALL_PF

Counts all L2 HW prefetcher requests.

27H

50H

L2_DEMAND_RQSTS.WB_HIT

Not rejected writebacks that hit L2 cache.

2EH

4FH

LONGEST_LAT_CACHE.REFEREN This event counts requests originating from the core See Table 19-1.
CE
that reference a cache line in the last level cache.

2EH

41H

LONGEST_LAT_CACHE.MISS

This event counts each cache miss condition for
references to the last level cache.

3CH

00H

CPU_CLK_UNHALTED.THREAD_
P

Counts the number of thread cycles while the thread See Table 19-1.
is not in a halt state. The thread enters the halt state
when it is running the HLT instruction. The core
frequency may change from time to time due to
power or thermal throttling.

3CH

01H

CPU_CLK_THREAD_UNHALTED.
REF_XCLK

Increments at the frequency of XCLK (100 MHz)
when not halted.

See Table 19-1.

48H

01H

L1D_PEND_MISS.PENDING

Increments the number of outstanding L1D misses
every cycle. Set Cmask = 1 and Edge =1 to count
occurrences.

Counter 2 only.

49H

01H

DTLB_STORE_MISSES.MISS_CAU Miss in all TLB levels causes a page walk of any page
SES_A_WALK
size (4K/2M/4M/1G).

49H

02H

DTLB_STORE_MISSES.WALK_CO Completed page walks due to store misses in one or
MPLETED_4K
more TLB levels of 4K page structure.

49H

10H

DTLB_STORE_MISSES.WALK_DU Cycles PMH is busy with this walk.
RATION

49H

20H

DTLB_STORE_MISSES.STLB_HIT Store misses that missed DTLB but hit STLB (4K).
_4K

4CH

02H

LOAD_HIT_PRE.HW_PF

4FH

10H

EPT.WALK_CYCLES

Cycles of Extended Page Table walks.

51H

01H

L1D.REPLACEMENT

Counts the number of lines brought into the L1 data
cache.

58H

04H

MOVE_ELIMINATION.INT_NOT_E Number of integer move elimination candidate uops
LIMINATED
that were not eliminated.

Comment

See Table 19-1.

Set Cmask = 1 to count
cycles.

Non-SW-prefetch load dispatches that hit fill buffer
allocated for H/W prefetch.

Vol. 3B 19-39

PERFORMANCE MONITORING EVENTS

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture (Contd.)
Event
Num.

Umask
Value

58H

08H

MOVE_ELIMINATION.SIMD_NOT_ Number of SIMD move elimination candidate uops
ELIMINATED
that were not eliminated.

58H

01H

MOVE_ELIMINATION.INT_ELIMIN Number of integer move elimination candidate uops
ATED
that were eliminated.

58H

02H

MOVE_ELIMINATION.SIMD_ELIMI Number of SIMD move elimination candidate uops
NATED
that were eliminated.

5CH

01H

CPL_CYCLES.RING0

Unhalted core cycles when the thread is in ring 0.

Event Mask Mnemonic

Description

Comment

Use Edge to count
transition.

5CH

02H

CPL_CYCLES.RING123

Unhalted core cycles when the thread is not in ring 0.

5EH

01H

RS_EVENTS.EMPTY_CYCLES

Cycles the RS is empty for the thread.

60H

01H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding demand data read transactions
DING.DEMAND_DATA_RD
in SQ to uncore. Set Cmask=1 to count cycles.

60H

02H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding demand code read transactions Use only when HTT is off.
DING.DEMAND_CODE_RD
in SQ to uncore. Set Cmask=1 to count cycles.

60H

04H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding RFO store transactions in SQ to Use only when HTT is off.
DING.DEMAND_RFO
uncore. Set Cmask=1 to count cycles.

60H

08H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding cacheable data read
DING.ALL_DATA_RD
transactions in SQ to uncore. Set Cmask=1 to count
cycles.

63H

01H

LOCK_CYCLES.SPLIT_LOCK_UC_
LOCK_DURATION

Cycles in which the L1D and L2 are locked, due to a
UC lock or split lock.

63H

02H

LOCK_CYCLES.CACHE_LOCK_DU
RATION

Cycles in which the L1D is locked.

79H

02H

IDQ.EMPTY

Counts cycles the IDQ is empty.

79H

04H

IDQ.MITE_UOPS

Increment each cycle # of uops delivered to IDQ from Can combine Umask 04H
MITE path. Set Cmask = 1 to count cycles.
and 20H.

79H

08H

IDQ.DSB_UOPS

Increment each cycle # of uops delivered to IDQ from Can combine Umask 08H
DSB path. Set Cmask = 1 to count cycles.
and 10H.

79H

10H

IDQ.MS_DSB_UOPS

Increment each cycle # of uops delivered to IDQ
when MS_busy by DSB. Set Cmask = 1 to count
cycles. Add Edge=1 to count # of delivery.

Can combine Umask 04H,
08H.

79H

20H

IDQ.MS_MITE_UOPS

Increment each cycle # of uops delivered to IDQ
when MS_busy by MITE. Set Cmask = 1 to count
cycles.

Can combine Umask 04H,
08H.

79H

30H

IDQ.MS_UOPS

Increment each cycle # of uops delivered to IDQ from Can combine Umask 04H,
MS by either DSB or MITE. Set Cmask = 1 to count
08H.
cycles.

79H

18H

IDQ.ALL_DSB_CYCLES_ANY_UO
PS

Counts cycles DSB is delivered at least one uops. Set
Cmask = 1.

79H

18H

IDQ.ALL_DSB_CYCLES_4_UOPS

Counts cycles DSB is delivered four uops. Set Cmask
= 4.

79H

24H

IDQ.ALL_MITE_CYCLES_ANY_UO Counts cycles MITE is delivered at least one uop. Set
PS
Cmask = 1.

79H

24H

IDQ.ALL_MITE_CYCLES_4_UOPS Counts cycles MITE is delivered four uops. Set Cmask
= 4.

79H

3CH

IDQ.MITE_ALL_UOPS

19-40 Vol. 3B

Number of uops delivered to IDQ from any path.

Use only when HTT is off.

Use only when HTT is off.

PERFORMANCE MONITORING EVENTS

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

80H

02H

ICACHE.MISSES

Number of Instruction Cache, Streaming Buffer and
Victim Cache Misses. Includes UC accesses.

85H

01H

ITLB_MISSES.MISS_CAUSES_A_
WALK

Misses in ITLB that cause a page walk of any page
size.

85H

02H

ITLB_MISSES.WALK_COMPLETE
D_4K

Completed page walks due to misses in ITLB 4K page
entries.

85H

10H

ITLB_MISSES.WALK_DURATION

Cycle PMH is busy with a walk.

85H

20H

ITLB_MISSES.STLB_HIT_4K

ITLB misses that hit STLB (4K).

87H

01H

ILD_STALL.LCP

Stalls caused by changing prefix length of the
instruction.

88H

01H

BR_INST_EXEC.COND

Qualify conditional near branch instructions
executed, but not necessarily retired.

Must combine with
umask 40H, 80H.

88H

02H

BR_INST_EXEC.DIRECT_JMP

Qualify all unconditional near branch instructions
excluding calls and indirect branches.

Must combine with
umask 80H.

88H

04H

BR_INST_EXEC.INDIRECT_JMP_
NON_CALL_RET

Qualify executed indirect near branch instructions
that are not calls or returns.

Must combine with
umask 80H.

88H

08H

BR_INST_EXEC.RETURN_NEAR

Qualify indirect near branches that have a return
mnemonic.

Must combine with
umask 80H.

88H

10H

BR_INST_EXEC.DIRECT_NEAR_C Qualify unconditional near call branch instructions,
ALL
excluding non-call branch, executed.

88H

20H

BR_INST_EXEC.INDIRECT_NEAR Qualify indirect near calls, including both register and Must combine with
_CALL
memory indirect, executed.
umask 80H.

88H

40H

BR_INST_EXEC.NONTAKEN

Qualify non-taken near branches executed.

88H

80H

BR_INST_EXEC.TAKEN

Qualify taken near branches executed. Must combine
with 01H,02H, 04H, 08H, 10H, 20H.

88H

FFH

BR_INST_EXEC.ALL_BRANCHES Counts all near executed branches (not necessarily
retired).

89H

01H

BR_MISP_EXEC.COND

Qualify conditional near branch instructions
mispredicted.

Must combine with
umask 40H, 80H.

89H

04H

BR_MISP_EXEC.INDIRECT_JMP_
NON_CALL_RET

Qualify mispredicted indirect near branch
instructions that are not calls or returns.

Must combine with
umask 80H.

89H

08H

BR_MISP_EXEC.RETURN_NEAR

Qualify mispredicted indirect near branches that
have a return mnemonic.

Must combine with
umask 80H.

89H

10H

BR_MISP_EXEC.DIRECT_NEAR_C Qualify mispredicted unconditional near call branch
ALL
instructions, excluding non-call branch, executed.

Must combine with
umask 80H.

89H

20H

BR_MISP_EXEC.INDIRECT_NEAR Qualify mispredicted indirect near calls, including
_CALL
both register and memory indirect, executed.

Must combine with
umask 80H.

89H

40H

BR_MISP_EXEC.NONTAKEN

Qualify mispredicted non-taken near branches
executed.

Applicable to umask 01H
only.

89H

80H

BR_MISP_EXEC.TAKEN

Qualify mispredicted taken near branches executed.
Must combine with 01H,02H, 04H, 08H, 10H, 20H.

89H

FFH

BR_MISP_EXEC.ALL_BRANCHES Counts all near executed branches (not necessarily
retired).

Comment

Must combine with
umask 80H.

Applicable to umask 01H
only.

Vol. 3B 19-41

PERFORMANCE MONITORING EVENTS

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CO
RE

Count issue pipeline slots where no uop was
delivered from the front end to the back end when
there is no back end stall.

Use Cmask to qualify uop
b/w.

A1H

01H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_0
dispatched to port 0.

Set AnyThread to count
per core.

A1H

02H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_1
dispatched to port 1.

Set AnyThread to count
per core.

A1H

04H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_2
dispatched to port 2.

Set AnyThread to count
per core.

A1H

08H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_3
dispatched to port 3.

Set AnyThread to count
per core.

A1H

10H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_4
dispatched to port 4.

Set AnyThread to count
per core.

A1H

20H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_5
dispatched to port 5.

Set AnyThread to count
per core.

A1H

40H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_6
dispatched to port 6.

Set AnyThread to count
per core.

A1H

80H

UOPS_DISPATCHED_PORT.PORT Counts the number of cycles in which a uop is
_7
dispatched to port 7.

Set AnyThread to count
per core.

A2H

01H

RESOURCE_STALLS.ANY

Cycles Allocation is stalled due to resource related
reason.

A2H

04H

RESOURCE_STALLS.RS

Cycles stalled due to no eligible RS entry available.

A2H

08H

RESOURCE_STALLS.SB

Cycles stalled due to no store buffers available (not
including draining form sync).

A2H

10H

RESOURCE_STALLS.ROB

Cycles stalled due to re-order buffer full.

A8H

01H

LSD.UOPS

Number of uops delivered by the LSD.

ABH

02H

DSB2MITE_SWITCHES.PENALTY
_CYCLES

Cycles of delay due to Decode Stream Buffer to MITE
switches.

AEH

01H

ITLB.ITLB_FLUSH

Counts the number of ITLB flushes; includes
4k/2M/4M pages.

B0H

01H

OFFCORE_REQUESTS.DEMAND_ Demand data read requests sent to uncore.
DATA_RD

Use only when HTT is off.

B0H

02H

OFFCORE_REQUESTS.DEMAND_ Demand code read requests sent to uncore.
CODE_RD

Use only when HTT is off.

B0H

04H

OFFCORE_REQUESTS.DEMAND_ Demand RFO read requests sent to uncore, including Use only when HTT is off.
RFO
regular RFOs, locks, ItoM.

B0H

08H

OFFCORE_REQUESTS.ALL_DATA Data read requests sent to uncore (demand and
_RD
prefetch).

Use only when HTT is off.

B1H

01H

UOPS_EXECUTED.THREAD

Counts total number of uops to be executed perlogical-processor each cycle.

Use Cmask to count stall
cycles.

B1H

02H

UOPS_EXECUTED.CORE

Counts total number of uops to be executed per-core Do not need to set ANY.
each cycle.

B7H

01H

OFF_CORE_RESPONSE_0

See Section 18.3.4.5, “Off-core Response
Performance Monitoring”.

19-42 Vol. 3B

Requires MSR 01A6H.

PERFORMANCE MONITORING EVENTS

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

BBH

01H

OFF_CORE_RESPONSE_1

See Section 18.3.4.5, “Off-core Response
Performance Monitoring”.

Requires MSR 01A7H.

BCH

11H

PAGE_WALKER_LOADS.DTLB_L1 Number of DTLB page walker loads that hit in the
L1+FB.

BCH

21H

PAGE_WALKER_LOADS.ITLB_L1

BCH

12H

PAGE_WALKER_LOADS.DTLB_L2 Number of DTLB page walker loads that hit in the L2.

Number of ITLB page walker loads that hit in the
L1+FB.

BCH

22H

PAGE_WALKER_LOADS.ITLB_L2

BCH

14H

PAGE_WALKER_LOADS.DTLB_L3 Number of DTLB page walker loads that hit in the L3.

Number of ITLB page walker loads that hit in the L2.

BCH

24H

PAGE_WALKER_LOADS.ITLB_L3

Number of ITLB page walker loads that hit in the L3.

BCH

18H

PAGE_WALKER_LOADS.DTLB_M
EMORY

Number of DTLB page walker loads from memory.

C0H

00H

INST_RETIRED.ANY_P

Number of instructions at retirement.

See Table 19-1.

C0H

01H

INST_RETIRED.PREC_DIST

Precise instruction retired event with HW to reduce
effect of PEBS shadow in IP distribution.

PMC1 only.

C0H

02H

INST_RETIRED.X87

FP operations retired. X87 FP operations that have
no exceptions.

C1H

08H

OTHER_ASSISTS.AVX_TO_SSE

Number of transitions from AVX-256 to legacy SSE
when penalty applicable.

C1H

10H

OTHER_ASSISTS.SSE_TO_AVX

Number of transitions from SSE to AVX-256 when
penalty applicable.

C1H

40H

OTHER_ASSISTS.ANY_WB_ASSI
ST

Number of microcode assists invoked by HW upon
uop writeback.

C2H

01H

UOPS_RETIRED.ALL

Counts the number of micro-ops retired.
Use cmask=1 and invert to count active cycles or
stalled cycles.

Supports PEBS and
DataLA, use Any=1 for
core granular.

C2H

02H

UOPS_RETIRED.RETIRE_SLOTS

Counts the number of retirement slots used each
cycle.

Supports PEBS.

C3H

01H

MACHINE_CLEARS.CYCLES

Counts cycles while a machine clears stalled forward
progress of a logical processor or a processor core.

C3H

02H

MACHINE_CLEARS.MEMORY_OR Counts the number of machine clears due to memory
DERING
order conflicts.

C3H

04H

MACHINE_CLEARS.SMC

Number of self-modifying-code machine clears
detected.

C3H

20H

MACHINE_CLEARS.MASKMOV

Counts the number of executed AVX masked load
operations that refer to an illegal address range with
the mask bits set to 0.

C4H

00H

BR_INST_RETIRED.ALL_BRANC
HES

Branch instructions at retirement.

C4H

01H

BR_INST_RETIRED.CONDITIONA Counts the number of conditional branch instructions Supports PEBS.
L
retired.

C4H

02H

BR_INST_RETIRED.NEAR_CALL

Direct and indirect near call instructions retired.

Supports PEBS.

C4H

04H

BR_INST_RETIRED.ALL_BRANC
HES

Counts the number of branch instructions retired.

Supports PEBS.

See Table 19-1.

Vol. 3B 19-43

PERFORMANCE MONITORING EVENTS

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

C4H

08H

BR_INST_RETIRED.NEAR_RETU
RN

Counts the number of near return instructions
retired.

Supports PEBS.

C4H

10H

BR_INST_RETIRED.NOT_TAKEN

Counts the number of not taken branch instructions
retired.

C4H

20H

BR_INST_RETIRED.NEAR_TAKE
N

Number of near taken branches retired.

C4H

40H

BR_INST_RETIRED.FAR_BRANC
H

Number of far branches retired.

C5H

00H

BR_MISP_RETIRED.ALL_BRANC
HES

Mispredicted branch instructions at retirement.

C5H

01H

BR_MISP_RETIRED.CONDITIONA Mispredicted conditional branch instructions retired.
L

Supports PEBS.

C5H

04H

BR_MISP_RETIRED.ALL_BRANC
HES

Mispredicted macro branch instructions retired.

Supports PEBS.

CAH

02H

FP_ASSIST.X87_OUTPUT

Number of X87 FP assists due to output values.

CAH

04H

FP_ASSIST.X87_INPUT

Number of X87 FP assists due to input values.

CAH

08H

FP_ASSIST.SIMD_OUTPUT

Number of SIMD FP assists due to output values.

CAH

10H

FP_ASSIST.SIMD_INPUT

Number of SIMD FP assists due to input values.

CAH

1EH

FP_ASSIST.ANY

Cycles with any input/output SSE* or FP assists.

CCH

20H

ROB_MISC_EVENTS.LBR_INSER
TS

Count cases of saving new LBR records by hardware.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY

Randomly sampled loads whose latency is above a
Specify threshold in MSR
user defined threshold. A small fraction of the overall 3F6H.
loads are sampled due to randomization.

D0H

11H

MEM_UOPS_RETIRED.STLB_MIS Retired load uops that miss the STLB.
S_LOADS

Supports PEBS and
DataLA.

D0H

12H

MEM_UOPS_RETIRED.STLB_MIS Retired store uops that miss the STLB.
S_STORES

Supports PEBS and
DataLA.

D0H

21H

MEM_UOPS_RETIRED.LOCK_LOA Retired load uops with locked access.
DS

Supports PEBS and
DataLA.

D0H

41H

MEM_UOPS_RETIRED.SPLIT_LO
ADS

Retired load uops that split across a cacheline
boundary.

Supports PEBS and
DataLA.

D0H

42H

MEM_UOPS_RETIRED.SPLIT_ST
ORES

Retired store uops that split across a cacheline
boundary.

Supports PEBS and
DataLA.

D0H

81H

MEM_UOPS_RETIRED.ALL_LOAD All retired load uops.
S

Supports PEBS and
DataLA.

D0H

82H

MEM_UOPS_RETIRED.ALL_STOR All retired store uops.
ES

Supports PEBS and
DataLA.

D1H

01H

MEM_LOAD_UOPS_RETIRED.L1_ Retired load uops with L1 cache hits as data sources. Supports PEBS and
HIT
DataLA.

D1H

02H

MEM_LOAD_UOPS_RETIRED.L2_ Retired load uops with L2 cache hits as data sources. Supports PEBS and
HIT
DataLA.

D1H

04H

MEM_LOAD_UOPS_RETIRED.L3_ Retired load uops with L3 cache hits as data sources. Supports PEBS and
HIT
DataLA.

D1H

08H

MEM_LOAD_UOPS_RETIRED.L1_ Retired load uops missed L1 cache as data sources.
MISS

19-44 Vol. 3B

Supports PEBS.

See Table 19-1.

Supports PEBS and
DataLA.

PERFORMANCE MONITORING EVENTS

Table 19-7. Performance Events of the Processor Core Supported by Broadwell Microarchitecture (Contd.)
Event
Num.

Umask
Value

D1H

10H

MEM_LOAD_UOPS_RETIRED.L2_ Retired load uops missed L2. Unknown data source
MISS
excluded.

D1H

20H

MEM_LOAD_UOPS_RETIRED.L3_ Retired load uops missed L3. Excludes unknown data Supports PEBS and
MISS
source.
DataLA.

D1H

40H

MEM_LOAD_UOPS_RETIRED.HIT Retired load uops where data sources were load
_LFB
uops missed L1 but hit FB due to preceding miss to
the same cache line with data not ready.

Supports PEBS and
DataLA.

D2H

01H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops where data sources were L3 hit
RED.XSNP_MISS
and cross-core snoop missed in on-pkg core cache.

Supports PEBS and
DataLA.

D2H

02H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops where data sources were L3 and
RED.XSNP_HIT
cross-core snoop hits in on-pkg core cache.

Supports PEBS and
DataLA.

D2H

04H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops where data sources were HitM
RED.XSNP_HITM
responses from shared L3.

Supports PEBS and
DataLA.

D2H

08H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops where data sources were hits in
RED.XSNP_NONE
L3 without snoops required.

Supports PEBS and
DataLA.

D3H

01H

MEM_LOAD_UOPS_L3_MISS_RE Retired load uops where data sources missed L3 but Supports PEBS and
TIRED.LOCAL_DRAM
serviced from local dram.
DataLA.

F0H

01H

L2_TRANS.DEMAND_DATA_RD

Demand data read requests that access L2 cache.

F0H

02H

L2_TRANS.RFO

RFO requests that access L2 cache.

F0H

04H

L2_TRANS.CODE_RD

L2 cache accesses when fetching instructions.

F0H

08H

L2_TRANS.ALL_PF

Any MLC or L3 HW prefetch accessing L2, including
rejects.

F0H

10H

L2_TRANS.L1D_WB

L1D writebacks that access L2 cache.

F0H

20H

L2_TRANS.L2_FILL

L2 fill requests that access L2 cache.

Event Mask Mnemonic

Description

Comment
Supports PEBS and
DataLA.

F0H

40H

L2_TRANS.L2_WB

L2 writebacks that access L2 cache.

F0H

80H

L2_TRANS.ALL_REQUESTS

Transactions accessing L2 pipe.

F1H

01H

L2_LINES_IN.I

L2 cache lines in I state filling L2.

Counting does not cover
rejects.

F1H

02H

L2_LINES_IN.S

L2 cache lines in S state filling L2.

Counting does not cover
rejects.

F1H

04H

L2_LINES_IN.E

L2 cache lines in E state filling L2.

Counting does not cover
rejects.

F1H

07H

L2_LINES_IN.ALL

L2 cache lines filling L2.

Counting does not cover
rejects.

F2H

05H

L2_LINES_OUT.DEMAND_CLEAN Clean L2 cache lines evicted by demand.

Table 19-10 lists performance events supporting Intel TSX (see Section 18.3.6.5) and the events are applicable to
processors based on Broadwell microarchitecture. Where Broadwell microarchitecture implements TSX-related
event semantics that differ from Table 19-10, they are listed in Table 19-8.

Table 19-8. Intel® TSX Performance Event Addendum in Processors Based on Broadwell Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

54H

02H

TX_MEM.ABORT_CAPACITY

Number of times a transactional abort was signaled due
to a data capacity limitation for transactional reads or
writes.

Comment

Vol. 3B 19-45

PERFORMANCE MONITORING EVENTS

19.6

PERFORMANCE MONITORING EVENTS FOR THE 4TH GENERATION
INTEL® CORE™ PROCESSORS

4th generation Intel® Core™ processors and Intel Xeon processor E3-1200 v3 product family are based on the
Haswell microarchitecture. They support the architectural performance monitoring events listed in Table 19-1.
Model-specific performance monitoring events in the processor core are listed in Table 19-9. The events in Table
19-9 apply to processors with CPUID signature of DisplayFamily_DisplayModel encoding with the following values:
06_3CH, 06_45H and 06_46H. Table 19-10 lists performance events focused on supporting Intel TSX (see Section
18.3.6.5). Fixed counters in the core PMU support the architecture events defined in Table 19-2.
Additional information on event specifics (e.g., derivative events using specific IA32_PERFEVTSELx modifiers, limitations, special notes and recommendations) can be found at https://software.intel.com/en-us/forums/softwaretuning-performance-optimization-platform-monitoring.

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

03H

02H

LD_BLOCKS.STORE_FORWARD

Loads blocked by overlapping with store buffer that
cannot be forwarded.

03H

08H

LD_BLOCKS.NO_SR

The number of times that split load operations are
temporarily blocked because all resources for
handling the split accesses are in use.

05H

01H

MISALIGN_MEM_REF.LOADS

Speculative cache-line split load uops dispatched to
L1D.

05H

02H

MISALIGN_MEM_REF.STORES

Speculative cache-line split store-address uops
dispatched to L1D.

07H

01H

LD_BLOCKS_PARTIAL.ADDRESS
_ALIAS

False dependencies in MOB due to partial compare
on address.

08H

01H

DTLB_LOAD_MISSES.MISS_CAUS Misses in all TLB levels that cause a page walk of any
ES_A_WALK
page size.

08H

02H

DTLB_LOAD_MISSES.WALK_COM Completed page walks due to demand load misses
PLETED_4K
that caused 4K page walks in any TLB levels.

08H

04H

DTLB_LOAD_MISSES.WALK_COM Completed page walks due to demand load misses
PLETED_2M_4M
that caused 2M/4M page walks in any TLB levels.

08H

0EH

DTLB_LOAD_MISSES.WALK_COM Completed page walks in any TLB of any page size
PLETED
due to demand load misses.

08H

10H

DTLB_LOAD_MISSES.WALK_DUR Cycle PMH is busy with a walk.
ATION

08H

20H

DTLB_LOAD_MISSES.STLB_HIT_ Load misses that missed DTLB but hit STLB (4K).
4K

08H

40H

DTLB_LOAD_MISSES.STLB_HIT_ Load misses that missed DTLB but hit STLB (2M).
2M

08H

60H

DTLB_LOAD_MISSES.STLB_HIT

08H

80H

DTLB_LOAD_MISSES.PDE_CACH DTLB demand load misses with low part of linear-toE_MISS
physical address translation missed.

0DH

03H

INT_MISC.RECOVERY_CYCLES

Cycles waiting to recover after Machine Clears
except JEClear. Set Cmask= 1.

Set Edge to count
occurrences.

0EH

01H

UOPS_ISSUED.ANY

Increments each cycle the # of uops issued by the
RAT to RS. Set Cmask = 1, Inv = 1, Any= 1 to count
stalled cycles of this core.

Set Cmask = 1, Inv = 1to
count stalled cycles.

0EH

10H

UOPS_ISSUED.FLAGS_MERGE

Number of flags-merge uops allocated. Such uops
add delay.

19-46 Vol. 3B

Comment

Number of cache load STLB hits. No page walk.

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

0EH

20H

UOPS_ISSUED.SLOW_LEA

Number of slow LEA or similar uops allocated. Such
uop has 3 sources (for example, 2 sources +
immediate) regardless of whether it is a result of
LEA instruction or not.

0EH

40H

UOPS_ISSUED.SiNGLE_MUL

Number of multiply packed/scalar single precision
uops allocated.

24H

21H

L2_RQSTS.DEMAND_DATA_RD_ Demand data read requests that missed L2, no
MISS
rejects.

24H

41H

L2_RQSTS.DEMAND_DATA_RD_ Demand data read requests that hit L2 cache.
HIT

24H

E1H

L2_RQSTS.ALL_DEMAND_DATA
_RD

Counts any demand and L1 HW prefetch data load
requests to L2.

24H

42H

L2_RQSTS.RFO_HIT

Counts the number of store RFO requests that hit
the L2 cache.

24H

22H

L2_RQSTS.RFO_MISS

Counts the number of store RFO requests that miss
the L2 cache.

24H

E2H

L2_RQSTS.ALL_RFO

Counts all L2 store RFO requests.

24H

44H

L2_RQSTS.CODE_RD_HIT

Number of instruction fetches that hit the L2 cache.

24H

24H

L2_RQSTS.CODE_RD_MISS

Number of instruction fetches that missed the L2
cache.

24H

27H

L2_RQSTS.ALL_DEMAND_MISS

Demand requests that miss L2 cache.

24H

E7H

L2_RQSTS.ALL_DEMAND_REFE
RENCES

Demand requests to L2 cache.

24H

E4H

L2_RQSTS.ALL_CODE_RD

Counts all L2 code requests.

24H

50H

L2_RQSTS.L2_PF_HIT

Counts all L2 HW prefetcher requests that hit L2.

24H

30H

L2_RQSTS.L2_PF_MISS

Counts all L2 HW prefetcher requests that missed
L2.

24H

F8H

L2_RQSTS.ALL_PF

Counts all L2 HW prefetcher requests.

24H

3FH

L2_RQSTS.MISS

All requests that missed L2.

24H

FFH

L2_RQSTS.REFERENCES

All requests to L2 cache.

27H

50H

L2_DEMAND_RQSTS.WB_HIT

Not rejected writebacks that hit L2 cache.

2EH

4FH

LONGEST_LAT_CACHE.REFEREN This event counts requests originating from the core See Table 19-1.
CE
that reference a cache line in the last level cache.

2EH

41H

LONGEST_LAT_CACHE.MISS

This event counts each cache miss condition for
references to the last level cache.

3CH

00H

CPU_CLK_UNHALTED.THREAD_
P

Counts the number of thread cycles while the thread See Table 19-1.
is not in a halt state. The thread enters the halt state
when it is running the HLT instruction. The core
frequency may change from time to time due to
power or thermal throttling.

3CH

01H

CPU_CLK_THREAD_UNHALTED.
REF_XCLK

Increments at the frequency of XCLK (100 MHz)
when not halted.

See Table 19-1.

48H

01H

L1D_PEND_MISS.PENDING

Increments the number of outstanding L1D misses
every cycle. Set Cmask = 1 and Edge =1 to count
occurrences.

Counter 2 only.

Comment

See Table 19-1.

Set Cmask = 1 to count
cycles.

Vol. 3B 19-47

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

49H

01H

DTLB_STORE_MISSES.MISS_CAU Miss in all TLB levels causes a page walk of any page
SES_A_WALK
size (4K/2M/4M/1G).

49H

02H

DTLB_STORE_MISSES.WALK_CO Completed page walks due to store misses in one or
MPLETED_4K
more TLB levels of 4K page structure.

49H

04H

DTLB_STORE_MISSES.WALK_CO Completed page walks due to store misses in one or
MPLETED_2M_4M
more TLB levels of 2M/4M page structure.

49H

0EH

DTLB_STORE_MISSES.WALK_CO Completed page walks due to store miss in any TLB
MPLETED
levels of any page size (4K/2M/4M/1G).

49H

10H

DTLB_STORE_MISSES.WALK_DU Cycles PMH is busy with this walk.
RATION

49H

20H

DTLB_STORE_MISSES.STLB_HIT Store misses that missed DTLB but hit STLB (4K).
_4K

49H

40H

DTLB_STORE_MISSES.STLB_HIT Store misses that missed DTLB but hit STLB (2M).
_2M

49H

60H

DTLB_STORE_MISSES.STLB_HIT Store operations that miss the first TLB level but hit
the second and do not cause page walks.

49H

80H

DTLB_STORE_MISSES.PDE_CAC
HE_MISS

DTLB store misses with low part of linear-to-physical
address translation missed.

4CH

01H

LOAD_HIT_PRE.SW_PF

Non-SW-prefetch load dispatches that hit fill buffer
allocated for S/W prefetch.

4CH

02H

LOAD_HIT_PRE.HW_PF

Non-SW-prefetch load dispatches that hit fill buffer
allocated for H/W prefetch.

51H

01H

L1D.REPLACEMENT

Counts the number of lines brought into the L1 data
cache.

58H

04H

MOVE_ELIMINATION.INT_NOT_E Number of integer move elimination candidate uops
LIMINATED
that were not eliminated.

58H

08H

MOVE_ELIMINATION.SIMD_NOT_ Number of SIMD move elimination candidate uops
ELIMINATED
that were not eliminated.

58H

01H

MOVE_ELIMINATION.INT_ELIMIN Number of integer move elimination candidate uops
ATED
that were eliminated.

58H

02H

MOVE_ELIMINATION.SIMD_ELIMI Number of SIMD move elimination candidate uops
NATED
that were eliminated.

5CH

01H

CPL_CYCLES.RING0

Unhalted core cycles when the thread is in ring 0.

5CH

02H

CPL_CYCLES.RING123

Unhalted core cycles when the thread is not in ring 0.

5EH

01H

RS_EVENTS.EMPTY_CYCLES

Cycles the RS is empty for the thread.

60H

01H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding demand data read transactions
DING.DEMAND_DATA_RD
in SQ to uncore. Set Cmask=1 to count cycles.

60H

02H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding Demand code Read transactions Use only when HTT is off.
DING.DEMAND_CODE_RD
in SQ to uncore. Set Cmask=1 to count cycles.

60H

04H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding RFO store transactions in SQ to Use only when HTT is off.
DING.DEMAND_RFO
uncore. Set Cmask=1 to count cycles.

60H

08H

OFFCORE_REQUESTS_OUTSTAN Offcore outstanding cacheable data read
DING.ALL_DATA_RD
transactions in SQ to uncore. Set Cmask=1 to count
cycles.

63H

01H

LOCK_CYCLES.SPLIT_LOCK_UC_
LOCK_DURATION

19-48 Vol. 3B

Event Mask Mnemonic

Description

Cycles in which the L1D and L2 are locked, due to a
UC lock or split lock.

Comment

Use Edge to count
transition.

Use only when HTT is off.

Use only when HTT is off.

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

63H

02H

LOCK_CYCLES.CACHE_LOCK_DU
RATION

Cycles in which the L1D is locked.

79H

02H

IDQ.EMPTY

Counts cycles the IDQ is empty.

79H

04H

IDQ.MITE_UOPS

Increment each cycle # of uops delivered to IDQ from Can combine Umask 04H
MITE path. Set Cmask = 1 to count cycles.
and 20H.

79H

08H

IDQ.DSB_UOPS

Increment each cycle. # of uops delivered to IDQ
from DSB path. Set Cmask = 1 to count cycles.

Can combine Umask 08H
and 10H.

79H

10H

IDQ.MS_DSB_UOPS

Increment each cycle # of uops delivered to IDQ
when MS_busy by DSB. Set Cmask = 1 to count
cycles. Add Edge=1 to count # of delivery.

Can combine Umask 04H,
08H.

79H

20H

IDQ.MS_MITE_UOPS

Increment each cycle # of uops delivered to IDQ
when MS_busy by MITE. Set Cmask = 1 to count
cycles.

Can combine Umask 04H,
08H.

79H

30H

IDQ.MS_UOPS

Increment each cycle # of uops delivered to IDQ from Can combine Umask 04H,
MS by either DSB or MITE. Set Cmask = 1 to count
08H.
cycles.

79H

18H

IDQ.ALL_DSB_CYCLES_ANY_UO
PS

Counts cycles DSB is delivered at least one uops. Set
Cmask = 1.

79H

18H

IDQ.ALL_DSB_CYCLES_4_UOPS

Counts cycles DSB is delivered four uops. Set Cmask
= 4.

79H

24H

IDQ.ALL_MITE_CYCLES_ANY_UO Counts cycles MITE is delivered at least one uop. Set
PS
Cmask = 1.

79H

24H

IDQ.ALL_MITE_CYCLES_4_UOPS Counts cycles MITE is delivered four uops. Set Cmask
= 4.

Comment

79H

3CH

IDQ.MITE_ALL_UOPS

# of uops delivered to IDQ from any path.

80H

02H

ICACHE.MISSES

Number of Instruction Cache, Streaming Buffer and
Victim Cache Misses. Includes UC accesses.

85H

01H

ITLB_MISSES.MISS_CAUSES_A_
WALK

Misses in ITLB that causes a page walk of any page
size.

85H

02H

ITLB_MISSES.WALK_COMPLETE
D_4K

Completed page walks due to misses in ITLB 4K page
entries.

85H

04H

ITLB_MISSES.WALK_COMPLETE
D_2M_4M

Completed page walks due to misses in ITLB 2M/4M
page entries.

85H

0EH

ITLB_MISSES.WALK_COMPLETE
D

Completed page walks in ITLB of any page size.

85H

10H

ITLB_MISSES.WALK_DURATION

Cycle PMH is busy with a walk.

85H

20H

ITLB_MISSES.STLB_HIT_4K

ITLB misses that hit STLB (4K).

85H

40H

ITLB_MISSES.STLB_HIT_2M

ITLB misses that hit STLB (2M).

85H

60H

ITLB_MISSES.STLB_HIT

ITLB misses that hit STLB. No page walk.

87H

01H

ILD_STALL.LCP

Stalls caused by changing prefix length of the
instruction.

87H

04H

ILD_STALL.IQ_FULL

Stall cycles due to IQ is full.

88H

01H

BR_INST_EXEC.COND

Qualify conditional near branch instructions
executed, but not necessarily retired.

Must combine with
umask 40H, 80H.

88H

02H

BR_INST_EXEC.DIRECT_JMP

Qualify all unconditional near branch instructions
excluding calls and indirect branches.

Must combine with
umask 80H.

Vol. 3B 19-49

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

88H

04H

BR_INST_EXEC.INDIRECT_JMP_
NON_CALL_RET

Qualify executed indirect near branch instructions
that are not calls or returns.

Must combine with
umask 80H.

88H

08H

BR_INST_EXEC.RETURN_NEAR

Qualify indirect near branches that have a return
mnemonic.

Must combine with
umask 80H.

88H

10H

BR_INST_EXEC.DIRECT_NEAR_C Qualify unconditional near call branch instructions,
ALL
excluding non-call branch, executed.

88H

20H

BR_INST_EXEC.INDIRECT_NEAR Qualify indirect near calls, including both register and Must combine with
_CALL
memory indirect, executed.
umask 80H.

88H

40H

BR_INST_EXEC.NONTAKEN

Qualify non-taken near branches executed.

88H

80H

BR_INST_EXEC.TAKEN

Qualify taken near branches executed. Must combine
with 01H,02H, 04H, 08H, 10H, 20H.

88H

FFH

BR_INST_EXEC.ALL_BRANCHES Counts all near executed branches (not necessarily
retired).

89H

01H

BR_MISP_EXEC.COND

Qualify conditional near branch instructions
mispredicted.

Must combine with
umask 40H, 80H.

89H

04H

BR_MISP_EXEC.INDIRECT_JMP_
NON_CALL_RET

Qualify mispredicted indirect near branch
instructions that are not calls or returns.

Must combine with
umask 80H.

89H

08H

BR_MISP_EXEC.RETURN_NEAR

Qualify mispredicted indirect near branches that
have a return mnemonic.

Must combine with
umask 80H.

89H

10H

BR_MISP_EXEC.DIRECT_NEAR_C Qualify mispredicted unconditional near call branch
ALL
instructions, excluding non-call branch, executed.

Must combine with
umask 80H.

89H

20H

BR_MISP_EXEC.INDIRECT_NEAR Qualify mispredicted indirect near calls, including
_CALL
both register and memory indirect, executed.

Must combine with
umask 80H.

89H

40H

BR_MISP_EXEC.NONTAKEN

Qualify mispredicted non-taken near branches
executed.

Applicable to umask 01H
only.

89H

80H

BR_MISP_EXEC.TAKEN

Qualify mispredicted taken near branches executed.
Must combine with 01H,02H, 04H, 08H, 10H, 20H.

89H

FFH

BR_MISP_EXEC.ALL_BRANCHES Counts all near executed branches (not necessarily
retired).

9CH

01H

IDQ_UOPS_NOT_DELIVERED.CO
RE

Count issue pipeline slots where no uop was
delivered from the front end to the back end when
there is no back-end stall.

Use Cmask to qualify uop
b/w.

A1H

01H

UOPS_EXECUTED_PORT.PORT_
0

Cycles which a uop is dispatched on port 0 in this
thread.

Set AnyThread to count
per core.

A1H

02H

UOPS_EXECUTED_PORT.PORT_
1

Cycles which a uop is dispatched on port 1 in this
thread.

Set AnyThread to count
per core.

A1H

04H

UOPS_EXECUTED_PORT.PORT_
2

Cycles which a uop is dispatched on port 2 in this
thread.

Set AnyThread to count
per core.

A1H

08H

UOPS_EXECUTED_PORT.PORT_
3

Cycles which a uop is dispatched on port 3 in this
thread.

Set AnyThread to count
per core.

A1H

10H

UOPS_EXECUTED_PORT.PORT_
4

Cycles which a uop is dispatched on port 4 in this
thread.

Set AnyThread to count
per core.

A1H

20H

UOPS_EXECUTED_PORT.PORT_
5

Cycles which a uop is dispatched on port 5 in this
thread.

Set AnyThread to count
per core.

A1H

40H

UOPS_EXECUTED_PORT.PORT_
6

Cycles which a uop is dispatched on port 6 in this
thread.

Set AnyThread to count
per core.

19-50 Vol. 3B

Must combine with
umask 80H.

Applicable to umask 01H
only.

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

A1H

80H

UOPS_EXECUTED_PORT.PORT_
7

Cycles which a uop is dispatched on port 7 in this
thread

Set AnyThread to count
per core.

A2H

01H

RESOURCE_STALLS.ANY

Cycles allocation is stalled due to resource related
reason.

A2H

04H

RESOURCE_STALLS.RS

Cycles stalled due to no eligible RS entry available.

A2H

08H

RESOURCE_STALLS.SB

Cycles stalled due to no store buffers available (not
including draining form sync).
Cycles stalled due to re-order buffer full.

A2H

10H

RESOURCE_STALLS.ROB

A3H

01H

CYCLE_ACTIVITY.CYCLES_L2_PE Cycles with pending L2 miss loads. Set Cmask=2 to
NDING
count cycle.

A3H

02H

CYCLE_ACTIVITY.CYCLES_LDM_
PENDING

A3H

05H

CYCLE_ACTIVITY.STALLS_L2_PE Number of loads missed L2.
NDING

Use only when HTT is off.

A3H

08H

CYCLE_ACTIVITY.CYCLES_L1D_P Cycles with pending L1 data cache miss loads. Set
ENDING
Cmask=8 to count cycle.

PMC2 only.

A3H

0CH

CYCLE_ACTIVITY.STALLS_L1D_P Execution stalls due to L1 data cache miss loads. Set PMC2 only.
ENDING
Cmask=0CH.

A8H

01H

LSD.UOPS

Number of uops delivered by the LSD.

AEH

01H

ITLB.ITLB_FLUSH

Counts the number of ITLB flushes, includes
4k/2M/4M pages.

B0H

01H

OFFCORE_REQUESTS.DEMAND_ Demand data read requests sent to uncore.
DATA_RD

Use only when HTT is off.

B0H

02H

OFFCORE_REQUESTS.DEMAND_ Demand code read requests sent to uncore.
CODE_RD

Use only when HTT is off.

B0H

04H

OFFCORE_REQUESTS.DEMAND_ Demand RFO read requests sent to uncore, including Use only when HTT is off.
RFO
regular RFOs, locks, ItoM.

B0H

08H

OFFCORE_REQUESTS.ALL_DATA Data read requests sent to uncore (demand and
_RD
prefetch).

B1H

02H

UOPS_EXECUTED.CORE

Counts total number of uops to be executed per-core Do not need to set ANY.
each cycle.

B7H

01H

OFF_CORE_RESPONSE_0

See Table 18-28 or Table 18-29.

Requires MSR 01A6H.

See Table 18-28 or Table 18-29.

Requires MSR 01A7H.

Use only when HTT is off.

Cycles with pending memory loads. Set Cmask=2 to
count cycle.

BBH

01H

OFF_CORE_RESPONSE_1

BCH

11H

PAGE_WALKER_LOADS.DTLB_L1 Number of DTLB page walker loads that hit in the
L1+FB.

BCH

21H

PAGE_WALKER_LOADS.ITLB_L1

BCH

12H

PAGE_WALKER_LOADS.DTLB_L2 Number of DTLB page walker loads that hit in the L2.

BCH

22H

PAGE_WALKER_LOADS.ITLB_L2

BCH

14H

PAGE_WALKER_LOADS.DTLB_L3 Number of DTLB page walker loads that hit in the L3.

BCH

24H

PAGE_WALKER_LOADS.ITLB_L3

Number of ITLB page walker loads that hit in the L3.

BCH

18H

PAGE_WALKER_LOADS.DTLB_M
EMORY

Number of DTLB page walker loads from memory.

BCH

28H

PAGE_WALKER_LOADS.ITLB_ME Number of ITLB page walker loads from memory.
MORY

Use only when HTT is off.

Number of ITLB page walker loads that hit in the
L1+FB.
Number of ITLB page walker loads that hit in the L2.

Vol. 3B 19-51

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

BDH

01H

TLB_FLUSH.DTLB_THREAD

DTLB flush attempts of the thread-specific entries.

BDH

20H

TLB_FLUSH.STLB_ANY

Count number of STLB flush attempts.

C0H

00H

INST_RETIRED.ANY_P

Number of instructions at retirement.

See Table 19-1.

C0H

01H

INST_RETIRED.PREC_DIST

Precise instruction retired event with HW to reduce
effect of PEBS shadow in IP distribution.

PMC1 only.

C1H

08H

OTHER_ASSISTS.AVX_TO_SSE

Number of transitions from AVX-256 to legacy SSE
when penalty applicable.

C1H

10H

OTHER_ASSISTS.SSE_TO_AVX

Number of transitions from SSE to AVX-256 when
penalty applicable.

C1H

40H

OTHER_ASSISTS.ANY_WB_ASSI
ST

Number of microcode assists invoked by HW upon
uop writeback.

C2H

01H

UOPS_RETIRED.ALL

Counts the number of micro-ops retired. Use
Supports PEBS and
Cmask=1 and invert to count active cycles or stalled DataLA; use Any=1 for
cycles.
core granular.

C2H

02H

UOPS_RETIRED.RETIRE_SLOTS

Counts the number of retirement slots used each
cycle.

C3H

02H

MACHINE_CLEARS.MEMORY_OR Counts the number of machine clears due to memory
DERING
order conflicts.

C3H

04H

MACHINE_CLEARS.SMC

Number of self-modifying-code machine clears
detected.

C3H

20H

MACHINE_CLEARS.MASKMOV

Counts the number of executed AVX masked load
operations that refer to an illegal address range with
the mask bits set to 0.

C4H

00H

BR_INST_RETIRED.ALL_BRANC
HES

Branch instructions at retirement.

C4H

01H

BR_INST_RETIRED.CONDITIONA Counts the number of conditional branch instructions Supports PEBS.
L
retired.

C4H

02H

BR_INST_RETIRED.NEAR_CALL

Direct and indirect near call instructions retired.

Supports PEBS.

C4H

04H

BR_INST_RETIRED.ALL_BRANC
HES

Counts the number of branch instructions retired.

Supports PEBS.

C4H

08H

BR_INST_RETIRED.NEAR_RETU
RN

Counts the number of near return instructions
retired.

Supports PEBS.

C4H

10H

BR_INST_RETIRED.NOT_TAKEN

Counts the number of not taken branch instructions
retired.

C4H

20H

BR_INST_RETIRED.NEAR_TAKE
N

Number of near taken branches retired.

C4H

40H

BR_INST_RETIRED.FAR_BRANC
H

Number of far branches retired.

C5H

00H

BR_MISP_RETIRED.ALL_BRANC
HES

Mispredicted branch instructions at retirement.

C5H

01H

BR_MISP_RETIRED.CONDITIONA Mispredicted conditional branch instructions retired.
L

Supports PEBS.

C5H

04H

BR_MISP_RETIRED.ALL_BRANC
HES

Mispredicted macro branch instructions retired.

Supports PEBS.

C5H

20H

BR_MISP_RETIRED.NEAR_TAKE
N

Number of near branch instructions retired that
were taken but mispredicted.

19-52 Vol. 3B

Comment

Supports PEBS.

See Table 19-1.

Supports PEBS.

See Table 19-1.

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

CAH

02H

FP_ASSIST.X87_OUTPUT

Number of X87 FP assists due to output values.

CAH

04H

FP_ASSIST.X87_INPUT

Number of X87 FP assists due to input values.

CAH

08H

FP_ASSIST.SIMD_OUTPUT

Number of SIMD FP assists due to output values.

CAH

10H

FP_ASSIST.SIMD_INPUT

Number of SIMD FP assists due to input values.

CAH

1EH

FP_ASSIST.ANY

Cycles with any input/output SSE* or FP assists.

CCH

20H

ROB_MISC_EVENTS.LBR_INSER
TS

Count cases of saving new LBR records by hardware.

CDH

01H

MEM_TRANS_RETIRED.LOAD_L
ATENCY

Randomly sampled loads whose latency is above a
Specify threshold in MSR
user defined threshold. A small fraction of the overall 3F6H.
loads are sampled due to randomization.

D0H

11H

MEM_UOPS_RETIRED.STLB_MIS Retired load uops that miss the STLB.
S_LOADS

Supports PEBS and
DataLA.

D0H

12H

MEM_UOPS_RETIRED.STLB_MIS Retired store uops that miss the STLB.
S_STORES

Supports PEBS and
DataLA.

D0H

21H

MEM_UOPS_RETIRED.LOCK_LOA Retired load uops with locked access.
DS

Supports PEBS and
DataLA.

D0H

41H

MEM_UOPS_RETIRED.SPLIT_LO
ADS

Retired load uops that split across a cacheline
boundary.

Supports PEBS and
DataLA.

D0H

42H

MEM_UOPS_RETIRED.SPLIT_ST
ORES

Retired store uops that split across a cacheline
boundary.

Supports PEBS and
DataLA.

D0H

81H

MEM_UOPS_RETIRED.ALL_LOAD All retired load uops.
S

Supports PEBS and
DataLA.

D0H

82H

MEM_UOPS_RETIRED.ALL_STOR All retired store uops.
ES

Supports PEBS and
DataLA.

D1H

01H

MEM_LOAD_UOPS_RETIRED.L1_ Retired load uops with L1 cache hits as data sources. Supports PEBS and
HIT
DataLA.

D1H

02H

MEM_LOAD_UOPS_RETIRED.L2_ Retired load uops with L2 cache hits as data sources. Supports PEBS and
HIT
DataLA.

D1H

04H

MEM_LOAD_UOPS_RETIRED.L3_ Retired load uops with L3 cache hits as data sources. Supports PEBS and
HIT
DataLA.

D1H

08H

MEM_LOAD_UOPS_RETIRED.L1_ Retired load uops missed L1 cache as data sources.
MISS

Supports PEBS and
DataLA.

D1H

10H

MEM_LOAD_UOPS_RETIRED.L2_ Retired load uops missed L2. Unknown data source
MISS
excluded.

Supports PEBS and
DataLA.

D1H

20H

MEM_LOAD_UOPS_RETIRED.L3_ Retired load uops missed L3. Excludes unknown data Supports PEBS and
MISS
source .
DataLA.

D1H

40H

MEM_LOAD_UOPS_RETIRED.HIT Retired load uops which data sources were load uops Supports PEBS and
_LFB
missed L1 but hit FB due to preceding miss to the
DataLA.
same cache line with data not ready.

D2H

01H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops which data sources were L3 hit
RED.XSNP_MISS
and cross-core snoop missed in on-pkg core cache.

Supports PEBS and
DataLA.

D2H

02H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops which data sources were L3 and
RED.XSNP_HIT
cross-core snoop hits in on-pkg core cache.

Supports PEBS and
DataLA.

D2H

04H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops which data sources were HitM
RED.XSNP_HITM
responses from shared L3.

Supports PEBS and
DataLA.

Comment

Vol. 3B 19-53

PERFORMANCE MONITORING EVENTS

Table 19-9. Performance Events in the Processor Core of 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.

Umask
Value

D2H

08H

MEM_LOAD_UOPS_L3_HIT_RETI Retired load uops which data sources were hits in L3 Supports PEBS and
RED.XSNP_NONE
without snoops required.
DataLA.

D3H

01H

MEM_LOAD_UOPS_L3_MISS_RE Retired load uops which data sources missed L3 but
TIRED.LOCAL_DRAM
serviced from local dram.

E6H

1FH

BACLEARS.ANY

Number of front end re-steers due to BPU
misprediction.

F0H

01H

L2_TRANS.DEMAND_DATA_RD

Demand data read requests that access L2 cache.

Event Mask Mnemonic

Description

Comment

Supports PEBS and
DataLA.

F0H

02H

L2_TRANS.RFO

RFO requests that access L2 cache.

F0H

04H

L2_TRANS.CODE_RD

L2 cache accesses when fetching instructions.

F0H

08H

L2_TRANS.ALL_PF

Any MLC or L3 HW prefetch accessing L2, including
rejects.

F0H

10H

L2_TRANS.L1D_WB

L1D writebacks that access L2 cache.

F0H

20H

L2_TRANS.L2_FILL

L2 fill requests that access L2 cache.

F0H

40H

L2_TRANS.L2_WB

L2 writebacks that access L2 cache.

F0H

80H

L2_TRANS.ALL_REQUESTS

Transactions accessing L2 pipe.

F1H

01H

L2_LINES_IN.I

L2 cache lines in I state filling L2.

Counting does not cover
rejects.

F1H

02H

L2_LINES_IN.S

L2 cache lines in S state filling L2.

Counting does not cover
rejects.

F1H

04H

L2_LINES_IN.E

L2 cache lines in E state filling L2.

Counting does not cover
rejects.

F1H

07H

L2_LINES_IN.ALL

L2 cache lines filling L2.

Counting does not cover
rejects.

F2H

05H

L2_LINES_OUT.DEMAND_CLEAN Clean L2 cache lines evicted by demand.

F2H

06H

L2_LINES_OUT.DEMAND_DIRTY

Event
Num.

Umask
Value

Event Mask Mnemonic

Description

54H

01H

TX_MEM.ABORT_CONFLICT

Number of times a transactional abort was signaled due
to a data conflict on a transactionally accessed address.

54H

02H

TX_MEM.ABORT_CAPACITY_W Number of times a transactional abort was signaled due
RITE
to a data capacity limitation for transactional writes.

54H

04H

TX_MEM.ABORT_HLE_STORE_ Number of times a HLE transactional region aborted due
TO_ELIDED_LOCK
to a non XRELEASE prefixed instruction writing to an
elided lock in the elision buffer.

54H

08H

TX_MEM.ABORT_HLE_ELISION Number of times an HLE transactional execution aborted
_BUFFER_NOT_EMPTY
due to NoAllocatedElisionBuffer being non-zero.

54H

10H

TX_MEM.ABORT_HLE_ELISION Number of times an HLE transactional execution aborted
_BUFFER_MISMATCH
due to XRELEASE lock not satisfying the address and
value requirements in the elision buffer.

54H

20H

TX_MEM.ABORT_HLE_ELISION Number of times an HLE transactional execution aborted
_BUFFER_UNSUPPORTED_ALI due to an unsupported read alignment from the elision
GNMENT
buffer.

Dirty L2 cache lines evicted by demand.

Table 19-10. Intel TSX Performance Events in Processors Based on Haswell Microarchitecture

19-54 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-10. Intel TSX Performance Events in Processors Based on Haswell Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

54H

40H

TX_MEM.HLE_ELISION_BUFFE
R_FULL

Number of times HLE lock could not be elided due to
ElisionBufferAvailable being zero.

5DH

01H

TX_EXEC.MISC1

Counts the number of times a class of instructions that
may cause a transactional abort was executed. Since this
is the count of execution, it may not always cause a
transactional abort.

5DH

02H

TX_EXEC.MISC2

Counts the number of times a class of instructions (for
example, vzeroupper) that may cause a transactional
abort was executed inside a transactional region.

5DH

04H

TX_EXEC.MISC3

Counts the number of times an instruction execution
caused the transactional nest count supported to be
exceeded.

5DH

08H

TX_EXEC.MISC4

Counts the number of times an XBEGIN instruction was
executed inside an HLE transactional region.

5DH

10H

TX_EXEC.MISC5

Counts the number of times an instruction with HLEXACQUIRE semantic was executed inside an RTM
transactional region.

C8H

01H

HLE_RETIRED.START

Number of times an HLE execution started.

C8H

02H

HLE_RETIRED.COMMIT

Number of times an HLE execution successfully
committed.

C8H

04H

HLE_RETIRED.ABORTED

Number of times an HLE execution aborted due to any
reasons (multiple categories may count as one). Supports
PEBS.

C8H

08H

HLE_RETIRED.ABORTED_MEM

Number of times an HLE execution aborted due to
various memory events (for example, read/write
capacity and conflicts).

C8H

10H

HLE_RETIRED.ABORTED_TIME
R

Number of times an HLE execution aborted due to
uncommon conditions.

C8H

20H

HLE_RETIRED.ABORTED_UNFR Number of times an HLE execution aborted due to HLEIENDLY
unfriendly instructions.

C8H

40H

HLE_RETIRED.ABORTED_MEM
TYPE

C8H

80H

HLE_RETIRED.ABORTED_EVEN Number of times an HLE execution aborted due to none
TS
of the previous 4 categories (for example, interrupts).

C9H

01H

RTM_RETIRED.START

Number of times an RTM execution started.

C9H

02H

RTM_RETIRED.COMMIT

Number of times an RTM execution successfully
committed.

C9H

04H

RTM_RETIRED.ABORTED

Number of times an RTM execution aborted due to any
reasons (multiple categories may count as one). Supports
PEBS.

Comment

IF HLE is supported.

Number of times an HLE execution aborted due to
incompatible memory type.

IF RTM is supported.

Vol. 3B 19-55

PERFORMANCE MONITORING EVENTS

Table 19-10. Intel TSX Performance Events in Processors Based on Haswell Microarchitecture
Event
Num.

Umask
Value

C9H

08H

RTM_RETIRED.ABORTED_MEM Number of times an RTM execution aborted due to
various memory events (for example, read/write
capacity and conflicts).

C9H

10H

RTM_RETIRED.ABORTED_TIME Number of times an RTM execution aborted due to
R
uncommon conditions.

C9H

20H

RTM_RETIRED.ABORTED_UNF
RIENDLY

C9H

40H

RTM_RETIRED.ABORTED_MEM Number of times an RTM execution aborted due to
TYPE
incompatible memory type.

C9H

80H

RTM_RETIRED.ABORTED_EVE
NTS

Event Mask Mnemonic

Description

Comment
IF RTM is supported.

Number of times an RTM execution aborted due to HLEunfriendly instructions.

Number of times an RTM execution aborted due to none
of the previous 4 categories (for example, interrupt).

Model-specific performance monitoring events that are located in the uncore sub-system are implementation
specific between different platforms using processors based on Haswell microarchitecture and with different
DisplayFamily_DisplayModel signatures. Processors with CPUID signature of DisplayFamily_DisplayModel 06_3CH
and 06_45H support performance events listed in Table 19-11.

Table 19-11. Uncore Performance Events in the 4th Generation Intel® Core™ Processors
Event
Num.1

Umask
Value

22H

01H

UNC_CBO_XSNP_RESPONSE.M A snoop misses in some processor core.
ISS

22H

02H

UNC_CBO_XSNP_RESPONSE.I
NVAL

22H

04H

UNC_CBO_XSNP_RESPONSE.H A snoop hits a non-modified line in some processor
IT
core.

22H

08H

UNC_CBO_XSNP_RESPONSE.H A snoop hits a modified line in some processor core.
ITM

22H

10H

UNC_CBO_XSNP_RESPONSE.I
NVAL_M

A snoop invalidates a modified line in some processor
core.

22H

20H

UNC_CBO_XSNP_RESPONSE.E
XTERNAL_FILTER

Filter on cross-core snoops initiated by this Cbox due
to external snoop request.

22H

40H

UNC_CBO_XSNP_RESPONSE.X Filter on cross-core snoops initiated by this Cbox due
CORE_FILTER
to processor core memory request.

22H

80H

UNC_CBO_XSNP_RESPONSE.E
VICTION_FILTER

Filter on cross-core snoops initiated by this Cbox due
to L3 eviction.

34H

01H

UNC_CBO_CACHE_LOOKUP.M

L3 lookup request that access cache and found line in
M-state.

34H

06H

UNC_CBO_CACHE_LOOKUP.ES

34H

08H

UNC_CBO_CACHE_LOOKUP.I

L3 lookup request that access cache and found line in Istate.

34H

10H

UNC_CBO_CACHE_LOOKUP.RE
AD_FILTER

Filter on processor core initiated cacheable read
requests. Must combine with at least one of 01H, 02H,
04H, 08H.

19-56 Vol. 3B

Event Mask Mnemonic

Description

A snoop invalidates a non-modified line in some
processor core.

Comment
Must combine with
one of the umask
values of 20H, 40H,
80H.

Must combine with at
least one of 01H, 02H,
04H, 08H, 10H.

Must combine with
one of the umask
L3 lookup request that access cache and found line in E values of 10H, 20H,
40H, 80H.
or S state.

PERFORMANCE MONITORING EVENTS

Table 19-11. Uncore Performance Events in the 4th Generation Intel® Core™ Processors (Contd.)
Event
Num.1

Umask
Value

34H

20H

UNC_CBO_CACHE_LOOKUP.WR Filter on processor core initiated cacheable write
ITE_FILTER
requests. Must combine with at least one of 01H, 02H,
04H, 08H.

34H

40H

UNC_CBO_CACHE_LOOKUP.EX
TSNP_FILTER

34H

80H

UNC_CBO_CACHE_LOOKUP.AN Filter on any IRQ or IPQ initiated requests including
Y_REQUEST_FILTER
uncacheable, non-coherent requests. Must combine
with at least one of 01H, 02H, 04H, 08H.

80H

01H

UNC_ARB_TRK_OCCUPANCY.A Counts cycles weighted by the number of requests
Counter 0 only.
LL
waiting for data returning from the memory controller.
Accounts for coherent and non-coherent requests
initiated by IA cores, processor graphic units, or L3.

81H

01H

UNC_ARB_TRK_REQUEST.ALL

Counts the number of coherent and in-coherent
requests initiated by IA cores, processor graphic units,
or L3.

81H

20H

UNC_ARB_TRK_REQUEST.WRI
TES

Counts the number of allocated write entries, include
full, partial, and L3 evictions.

81H

80H

UNC_ARB_TRK_REQUEST.EVIC Counts the number of L3 evictions allocated.
TIONS

83H

01H

UNC_ARB_COH_TRK_OCCUPA
NCY.ALL

Cycles weighted by number of requests pending in
Coherency Tracker.

84H

01H

UNC_ARB_COH_TRK_REQUES
T.ALL

Number of requests allocated in Coherency Tracker.

Event Mask Mnemonic

Description

Comment

Filter on external snoop requests. Must combine with
at least one of 01H, 02H, 04H, 08H.

Counter 0 only.

NOTES:
1. The uncore events must be programmed using MSRs located in specific performance monitoring units in the uncore. UNC_CBO*
events are supported using MSR_UNC_CBO* MSRs; UNC_ARB* events are supported using MSR_UNC_ARB*MSRs.

19.6.1

Performance Monitoring Events in the Processor Core of Intel Xeon Processor E5 v3
Family

Model-specific performance monitoring events in the processor core that are applicable only to Intel Xeon
processor E5 v3 family based on the Haswell-E microarchitecture, with CPUID signature of
DisplayFamily_DisplayModel 06_3FH, are listed in Table 19-12. The performance events listed in Table 19-9 and
Table 19-10 also apply Intel Xeon processor E5 v3 family, except that the OFF_CORE_RESPONSE_x event listed in
Table 19-9 should reference Table 18-30.
Uncore performance monitoring events for Intel Xeon Processor E5 v3 families are described in “Intel® Xeon®
Processor E5 v3 Uncore Performance Monitoring Programming Reference Manual”.

Table 19-12. Performance Events Applicable only to the Processor Core of Intel® Xeon® Processor E5 v3 Family
Event
Num.

Umask
Value

D3H

04H

MEM_LOAD_UOPS_L3_MISS_RE Retired load uops whose data sources were remote
TIRED.REMOTE_DRAM
DRAM (snoop not needed, Snoop Miss).

Supports PEBS.

D3H

10H

MEM_LOAD_UOPS_L3_MISS_RE Retired load uops whose data sources were remote
TIRED.REMOTE_HITM
cache HITM.

Supports PEBS.

D3H

20H

MEM_LOAD_UOPS_L3_MISS_RE Retired load uops whose data sources were forwards
TIRED.REMOTE_FWD
from a remote cache.

Supports PEBS.

Event Mask Mnemonic

Description

Comment

Vol. 3B 19-57

PERFORMANCE MONITORING EVENTS

19.7

PERFORMANCE MONITORING EVENTS FOR 3RD GENERATION
INTEL® CORE™ PROCESSORS

3rd generation Intel® Core™ processors and Intel Xeon processor E3-1200 v2 product family are based on Intel
microarchitecture code name Ivy Bridge. They support architectural performance monitoring events listed in Table
19-1. Model-specific performance monitoring events in the processor core are listed in Table 19-13. The events in
Table 19-13 apply to processors with CPUID signature of DisplayFamily_DisplayModel encoding with the following
values: 06_3AH. Fixed counters in the core PMU support the architecture events defined in Table 19-24.
Additional information on event specifics (e.g. derivative events using specific IA32_PERFEVTSELx modifiers, limitations, special notes and recommendations) can be found at found at https://software.intel.com/enus/forums/software-tuning-performance-optimization-platform-monitoring.

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

03H

02H

LD_BLOCKS.STORE_FORWARD

Loads blocked by overlapping with store buffer that
cannot be forwarded.

03H

08H

LD_BLOCKS.NO_SR

The number of times that split load operations are
temporarily blocked because all resources for
handling the split accesses are in use.

05H

01H

MISALIGN_MEM_REF.LOADS

Speculative cache-line split load uops dispatched to
L1D.

05H

02H

MISALIGN_MEM_REF.STORES

Speculative cache-line split Store-address uops
dispatched to L1D.

07H

01H

LD_BLOCKS_PARTIAL.ADDRESS_
ALIAS

False dependencies in MOB due to partial compare
on address.

08H

81H

DTLB_LOAD_MISSES.MISS_CAUSE Misses in all TLB levels that cause a page walk of
S_A_WALK
any page size from demand loads.

08H

82H

DTLB_LOAD_MISSES.WALK_COM
PLETED

Misses in all TLB levels that caused page walk
completed of any size by demand loads.

08H

84H

DTLB_LOAD_MISSES.WALK_DUR
ATION

Cycle PMH is busy with a walk due to demand loads.

08H

88H

DTLB_LOAD_MISSES.LARGE_PAG Page walk for a large page completed for Demand
E_WALK_DURATION
load.

0EH

01H

UOPS_ISSUED.ANY

Increments each cycle the # of Uops issued by the
RAT to RS. Set Cmask = 1, Inv = 1, Any= 1to count
stalled cycles of this core.

0EH

10H

UOPS_ISSUED.FLAGS_MERGE

Number of flags-merge uops allocated. Such uops
adds delay.

0EH

20H

UOPS_ISSUED.SLOW_LEA

Number of slow LEA or similar uops allocated. Such
uop has 3 sources (e.g. 2 sources + immediate)
regardless if as a result of LEA instruction or not.

0EH

40H

UOPS_ISSUED.SiNGLE_MUL

Number of multiply packed/scalar single precision
uops allocated.
Counts number of X87 uops executed.

10H

01H

FP_COMP_OPS_EXE.X87

10H

10H

FP_COMP_OPS_EXE.SSE_FP_PAC Counts number of SSE* or AVX-128 double
KED_DOUBLE
precision FP packed uops executed.

10H

20H

FP_COMP_OPS_EXE.SSE_FP_SCA Counts number of SSE* or AVX-128 single precision
LAR_SINGLE
FP scalar uops executed.

10H

40H

FP_COMP_OPS_EXE.SSE_PACKED Counts number of SSE* or AVX-128 single precision
SINGLE
FP packed uops executed.

19-58 Vol. 3B

Comment

Set Cmask = 1, Inv = 1to
count stalled cycles.

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

10H

80H

FP_COMP_OPS_EXE.SSE_SCALAR Counts number of SSE* or AVX-128 double
_DOUBLE
precision FP scalar uops executed.

11H

01H

SIMD_FP_256.PACKED_SINGLE

Counts 256-bit packed single-precision floatingpoint instructions.

11H

02H

SIMD_FP_256.PACKED_DOUBLE

Counts 256-bit packed double-precision floatingpoint instructions.

14H

01H

ARITH.FPU_DIV_ACTIVE

Cycles that the divider is active, includes INT and FP.
Set 'edge =1, cmask=1' to count the number of
divides.

24H

01H

L2_RQSTS.DEMAND_DATA_RD_H Demand Data Read requests that hit L2 cache.
IT

24H

03H

L2_RQSTS.ALL_DEMAND_DATA_
RD

Counts any demand and L1 HW prefetch data load
requests to L2.

24H

04H

L2_RQSTS.RFO_HITS

Counts the number of store RFO requests that hit
the L2 cache.

24H

08H

L2_RQSTS.RFO_MISS

Counts the number of store RFO requests that miss
the L2 cache.

24H

0CH

L2_RQSTS.ALL_RFO

Counts all L2 store RFO requests.

24H

10H

L2_RQSTS.CODE_RD_HIT

Number of instruction fetches that hit the L2 cache.

24H

20H

L2_RQSTS.CODE_RD_MISS

Number of instruction fetches that missed the L2
cache.

24H

30H

L2_RQSTS.ALL_CODE_RD

Counts all L2 code requests.

24H

40H

L2_RQSTS.PF_HIT

Counts all L2 HW prefetcher requests that hit L2.

24H

80H

L2_RQSTS.PF_MISS

Counts all L2 HW prefetcher requests that missed
L2.

24H

C0H

L2_RQSTS.ALL_PF

Counts all L2 HW prefetcher requests.

27H

01H

L2_STORE_LOCK_RQSTS.MISS

RFOs that miss cache lines.

27H

08H

L2_STORE_LOCK_RQSTS.HIT_M

RFOs that hit cache lines in M state.

27H

0FH

L2_STORE_LOCK_RQSTS.ALL

RFOs that access cache lines in any state.

28H

01H

L2_L1D_WB_RQSTS.MISS

Not rejected writebacks that missed LLC.

28H

04H

L2_L1D_WB_RQSTS.HIT_E

Not rejected writebacks from L1D to L2 cache lines
in E state.

28H

08H

L2_L1D_WB_RQSTS.HIT_M

Not rejected writebacks from L1D to L2 cache lines
in M state.

28H

0FH

L2_L1D_WB_RQSTS.ALL

Not rejected writebacks from L1D to L2 cache lines
in any state.

2EH

4FH

LONGEST_LAT_CACHE.REFERENC This event counts requests originating from the
E
core that reference a cache line in the last level
cache.

See Table 19-1

2EH

41H

LONGEST_LAT_CACHE.MISS

This event counts each cache miss condition for
references to the last level cache.

See Table 19-1

3CH

00H

CPU_CLK_UNHALTED.THREAD_P

Counts the number of thread cycles while the
thread is not in a halt state. The thread enters the
halt state when it is running the HLT instruction.
The core frequency may change from time to time
due to power or thermal throttling.

See Table 19-1.

Event Mask Mnemonic

Description

Comment

Vol. 3B 19-59

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

3CH

01H

CPU_CLK_THREAD_UNHALTED.R Increments at the frequency of XCLK (100 MHz)
EF_XCLK
when not halted.

See Table 19-1.

48H

01H

L1D_PEND_MISS.PENDING

PMC2 only;

Event Mask Mnemonic

Description

Increments the number of outstanding L1D misses
every cycle. Set Cmask = 1 and Edge =1 to count
occurrences.

49H

01H

DTLB_STORE_MISSES.MISS_CAUS Miss in all TLB levels causes a page walk of any
ES_A_WALK
page size (4K/2M/4M/1G).

49H

02H

DTLB_STORE_MISSES.WALK_CO
MPLETED

49H

04H

DTLB_STORE_MISSES.WALK_DUR Cycles PMH is busy with this walk.
ATION

49H

10H

DTLB_STORE_MISSES.STLB_HIT

Store operations that miss the first TLB level but hit
the second and do not cause page walks.

4CH

01H

LOAD_HIT_PRE.SW_PF

Non-SW-prefetch load dispatches that hit fill buffer
allocated for S/W prefetch.

4CH

02H

LOAD_HIT_PRE.HW_PF

Non-SW-prefetch load dispatches that hit fill buffer
allocated for H/W prefetch.

51H

01H

L1D.REPLACEMENT

Counts the number of lines brought into the L1 data
cache.

58H

04H

MOVE_ELIMINATION.INT_NOT_EL Number of integer Move Elimination candidate uops
IMINATED
that were not eliminated.

58H

08H

MOVE_ELIMINATION.SIMD_NOT_E Number of SIMD Move Elimination candidate uops
LIMINATED
that were not eliminated.

58H

01H

MOVE_ELIMINATION.INT_ELIMINA Number of integer Move Elimination candidate uops
TED
that were eliminated.

58H

02H

MOVE_ELIMINATION.SIMD_ELIMIN Number of SIMD Move Elimination candidate uops
ATED
that were eliminated.

5CH

01H

CPL_CYCLES.RING0

Unhalted core cycles when the thread is in ring 0.

5CH

02H

CPL_CYCLES.RING123

Unhalted core cycles when the thread is not in ring
0.

5EH

01H

RS_EVENTS.EMPTY_CYCLES

Cycles the RS is empty for the thread.

5FH

04H

DTLB_LOAD_MISSES.STLB_HIT

Counts load operations that missed 1st level DTLB
but hit the 2nd level.

60H

01H

OFFCORE_REQUESTS_OUTSTAN
DING.DEMAND_DATA_RD

Offcore outstanding Demand Data Read
transactions in SQ to uncore. Set Cmask=1 to count
cycles.

60H

02H

OFFCORE_REQUESTS_OUTSTAN
DING.DEMAND_CODE_RD

Offcore outstanding Demand Code Read
transactions in SQ to uncore. Set Cmask=1 to count
cycles.

60H

04H

OFFCORE_REQUESTS_OUTSTAN
DING.DEMAND_RFO

Offcore outstanding RFO store transactions in SQ to
uncore. Set Cmask=1 to count cycles.

60H

08H

OFFCORE_REQUESTS_OUTSTAN
DING.ALL_DATA_RD

Offcore outstanding cacheable data read
transactions in SQ to uncore. Set Cmask=1 to count
cycles.

63H

01H

LOCK_CYCLES.SPLIT_LOCK_UC_L
OCK_DURATION

Cycles in which the L1D and L2 are locked, due to a
UC lock or split lock.

19-60 Vol. 3B

Comment

Set Cmask = 1 to count
cycles.

Miss in all TLB levels causes a page walk that
completes of any page size (4K/2M/4M/1G).

Use Edge to count
transition.

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

63H

02H

LOCK_CYCLES.CACHE_LOCK_DUR Cycles in which the L1D is locked.
ATION

79H

02H

IDQ.EMPTY

Counts cycles the IDQ is empty.

79H

04H

IDQ.MITE_UOPS

Increment each cycle # of uops delivered to IDQ
from MITE path. Set Cmask = 1 to count cycles.

Can combine Umask 04H
and 20H.

79H

08H

IDQ.DSB_UOPS

Increment each cycle. # of uops delivered to IDQ
from DSB path. Set Cmask = 1 to count cycles.

Can combine Umask 08H
and 10H.

79H

10H

IDQ.MS_DSB_UOPS

Increment each cycle # of uops delivered to IDQ
when MS_busy by DSB. Set Cmask = 1 to count
cycles. Add Edge=1 to count # of delivery.

Can combine Umask 04H,
08H.

79H

20H

IDQ.MS_MITE_UOPS

Increment each cycle # of uops delivered to IDQ
when MS_busy by MITE. Set Cmask = 1 to count
cycles.

Can combine Umask 04H,
08H.

79H

30H

IDQ.MS_UOPS

Increment each cycle # of uops delivered to IDQ
from MS by either DSB or MITE. Set Cmask = 1 to
count cycles.

Can combine Umask 04H,
08H.

79H

18H

IDQ.ALL_DSB_CYCLES_ANY_UOP
S

Counts cycles DSB is delivered at least one uops.
Set Cmask = 1.

79H

18H

IDQ.ALL_DSB_CYCLES_4_UOPS

Counts cycles DSB is delivered four uops. Set Cmask
= 4.

79H

24H

IDQ.ALL_MITE_CYCLES_ANY_UOP Counts cycles MITE is delivered at least one uops.
S
Set Cmask = 1.

79H

24H

IDQ.ALL_MITE_CYCLES_4_UOPS

79H

3CH

IDQ.MITE_ALL_UOPS

# of uops delivered to IDQ from any path.

80H

04H

ICACHE.IFETCH_STALL

Cycles where a code-fetch stalled due to L1
instruction-cache miss or an iTLB miss.

80H

02H

ICACHE.MISSES

Number of Instruction Cache, Streaming Buffer and
Victim Cache Misses. Includes UC accesses.

85H

01H

ITLB_MISSES.MISS_CAUSES_A_W Misses in all ITLB levels that cause page walks.
ALK

85H

02H

ITLB_MISSES.WALK_COMPLETED

Misses in all ITLB levels that cause completed page
walks.

85H

04H

ITLB_MISSES.WALK_DURATION

Cycle PMH is busy with a walk.

85H

10H

ITLB_MISSES.STLB_HIT

Number of cache load STLB hits. No page walk.

87H

01H

ILD_STALL.LCP

Stalls caused by changing prefix length of the
instruction.

87H

04H

ILD_STALL.IQ_FULL

Stall cycles due to IQ is full.

88H

01H

BR_INST_EXEC.COND

Qualify conditional near branch instructions
executed, but not necessarily retired.

Must combine with
umask 40H, 80H.

88H

02H

BR_INST_EXEC.DIRECT_JMP

Qualify all unconditional near branch instructions
excluding calls and indirect branches.

Must combine with
umask 80H.

88H

04H

BR_INST_EXEC.INDIRECT_JMP_N
ON_CALL_RET

Qualify executed indirect near branch instructions
that are not calls or returns.

Must combine with
umask 80H.

88H

08H

BR_INST_EXEC.RETURN_NEAR

Qualify indirect near branches that have a return
mnemonic.

Must combine with
umask 80H.

Event Mask Mnemonic

Description

Comment

Counts cycles MITE is delivered four uops. Set
Cmask = 4.

Vol. 3B 19-61

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

88H

10H

BR_INST_EXEC.DIRECT_NEAR_C
ALL

Qualify unconditional near call branch instructions,
excluding non-call branch, executed.

Must combine with
umask 80H.

88H

20H

BR_INST_EXEC.INDIRECT_NEAR_ Qualify indirect near calls, including both register
CALL
and memory indirect, executed.

Must combine with
umask 80H.

88H

40H

BR_INST_EXEC.NONTAKEN

Qualify non-taken near branches executed.

Applicable to umask 01H
only.

88H

80H

BR_INST_EXEC.TAKEN

Qualify taken near branches executed. Must
combine with 01H,02H, 04H, 08H, 10H, 20H.

88H

FFH

BR_INST_EXEC.ALL_BRANCHES

Counts all near executed branches (not necessarily
retired).

89H

01H

BR_MISP_EXEC.COND

Qualify conditional near branch instructions
mispredicted.

Must combine with
umask 40H, 80H.

89H

04H

BR_MISP_EXEC.INDIRECT_JMP_N
ON_CALL_RET

Qualify mispredicted indirect near branch
instructions that are not calls or returns.

Must combine with
umask 80H.

89H

08H

BR_MISP_EXEC.RETURN_NEAR

Qualify mispredicted indirect near branches that
have a return mnemonic.

Must combine with
umask 80H.

89H

10H

BR_MISP_EXEC.DIRECT_NEAR_C
ALL

Qualify mispredicted unconditional near call branch
instructions, excluding non-call branch, executed.

Must combine with
umask 80H.

89H

20H

BR_MISP_EXEC.INDIRECT_NEAR_ Qualify mispredicted indirect near calls, including
CALL
both register and memory indirect, executed.

Must combine with
umask 80H.

89H

40H

BR_MISP_EXEC.NONTAKEN

Qualify mispredicted non-taken near branches
executed.

Applicable to umask 01H
only.

89H

80H

BR_MISP_EXEC.TAKEN

Qualify mispredicted taken near branches executed.
Must combine with 01H,02H, 04H, 08H, 10H, 20H.

89H

FFH

BR_MISP_EXEC.ALL_BRANCHES

Counts all near executed branches (not necessarily
retired).

9CH

01H

IDQ_UOPS_NOT_DELIVERED.COR Count issue pipeline slots where no uop was
E
delivered from the front end to the back end when
there is no back-end stall.

A1H

01H

UOPS_DISPATCHED_PORT.PORT_ Cycles which a Uop is dispatched on port 0.
0

A1H

02H

UOPS_DISPATCHED_PORT.PORT_ Cycles which a Uop is dispatched on port 1.
1

A1H

0CH

UOPS_DISPATCHED_PORT.PORT_ Cycles which a Uop is dispatched on port 2.
2

A1H

30H

UOPS_DISPATCHED_PORT.PORT_ Cycles which a Uop is dispatched on port 3.
3

A1H

40H

UOPS_DISPATCHED_PORT.PORT_ Cycles which a Uop is dispatched on port 4.
4

A1H

80H

UOPS_DISPATCHED_PORT.PORT_ Cycles which a Uop is dispatched on port 5.
5

A2H

01H

RESOURCE_STALLS.ANY

Cycles Allocation is stalled due to Resource Related
reason.

A2H

04H

RESOURCE_STALLS.RS

Cycles stalled due to no eligible RS entry available.

A2H

08H

RESOURCE_STALLS.SB

Cycles stalled due to no store buffers available (not
including draining form sync).

A2H

10H

RESOURCE_STALLS.ROB

Cycles stalled due to re-order buffer full.

19-62 Vol. 3B

Use Cmask to qualify uop
b/w.

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

A3H

01H

CYCLE_ACTIVITY.CYCLES_L2_PEN Cycles with pending L2 miss loads. Set AnyThread
DING
to count per core.

A3H

02H

CYCLE_ACTIVITY.CYCLES_LDM_P
ENDING

Cycles with pending memory loads. Set AnyThread
to count per core.

Restricted to counters 03 when HTT is disabled.

A3H

04H

CYCLE_ACTIVITY.CYCLES_NO_EX
ECUTE

Cycles of dispatch stalls. Set AnyThread to count
per core.

Restricted to counters 03 when HTT is disabled.

A3H

05H

CYCLE_ACTIVITY.STALLS_L2_PEN Number of loads missed L2.
DING

Restricted to counters 03 when HTT is disabled.

A3H

06H

CYCLE_ACTIVITY.STALLS_LDM_P
ENDING

Restricted to counters 03 when HTT is disabled.

A3H

08H

CYCLE_ACTIVITY.CYCLES_L1D_PE Cycles with pending L1 cache miss loads. Set
NDING
AnyThread to count per core.

PMC2 only.

A3H

0CH

CYCLE_ACTIVITY.STALLS_L1D_PE Execution stalls due to L1 data cache miss loads.
NDING
Set Cmask=0CH.

PMC2 only.

A8H

01H

LSD.UOPS

Number of Uops delivered by the LSD.

ABH

01H

DSB2MITE_SWITCHES.COUNT

Number of DSB to MITE switches.

ABH

02H

DSB2MITE_SWITCHES.PENALTY_
CYCLES

Cycles DSB to MITE switches caused delay.

ACH

08H

DSB_FILL.EXCEED_DSB_LINES

DSB Fill encountered > 3 DSB lines.

AEH

01H

ITLB.ITLB_FLUSH

Counts the number of ITLB flushes, includes
4k/2M/4M pages.

B0H

01H

OFFCORE_REQUESTS.DEMAND_D Demand data read requests sent to uncore.
ATA_RD

B0H

02H

OFFCORE_REQUESTS.DEMAND_C Demand code read requests sent to uncore.
ODE_RD

B0H

04H

OFFCORE_REQUESTS.DEMAND_R Demand RFO read requests sent to uncore,
FO
including regular RFOs, locks, ItoM.

B0H

08H

OFFCORE_REQUESTS.ALL_DATA_ Data read requests sent to uncore (demand and
RD
prefetch).

B1H

01H

UOPS_EXECUTED.THREAD

Counts total number of uops to be executed perthread each cycle. Set Cmask = 1, INV =1 to count
stall cycles.

B1H

02H

UOPS_EXECUTED.CORE

Counts total number of uops to be executed percore each cycle.

Do not need to set ANY.

B7H

01H

OFFCORE_RESPONSE_0

See Section 18.3.4.5, “Off-core Response
Performance Monitoring”.

Requires MSR 01A6H.

BBH

01H

OFFCORE_RESPONSE_1

See Section 18.3.4.5, “Off-core Response
Performance Monitoring”.

Requires MSR 01A7H.

BDH

01H

TLB_FLUSH.DTLB_THREAD

DTLB flush attempts of the thread-specific entries.

BDH

20H

TLB_FLUSH.STLB_ANY

Count number of STLB flush attempts.

C0H

00H

INST_RETIRED.ANY_P

Number of instructions at retirement.

C0H

01H

INST_RETIRED.PREC_DIST

Precise instruction retired event with HW to reduce PMC1 only.
effect of PEBS shadow in IP distribution.

C1H

08H

OTHER_ASSISTS.AVX_STORE

Number of assists associated with 256-bit AVX
store operations.

Event Mask Mnemonic

Description

Comment

See Table 19-1.

Vol. 3B 19-63

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

C1H

10H

OTHER_ASSISTS.AVX_TO_SSE

Number of transitions from AVX-256 to legacy SSE
when penalty applicable.

C1H

20H

OTHER_ASSISTS.SSE_TO_AVX

Number of transitions from SSE to AVX-256 when
penalty applicable.

C1H

80H

OTHER_ASSISTS.WB

Number of times microcode assist is invoked by
hardware upon uop writeback.

C2H

01H

UOPS_RETIRED.ALL

Counts the number of micro-ops retired, Use
Supports PEBS, use
cmask=1 and invert to count active cycles or stalled Any=1 for core granular.
cycles.

C2H

02H

UOPS_RETIRED.RETIRE_SLOTS

Counts the number of retirement slots used each
cycle.

C3H

02H

MACHINE_CLEARS.MEMORY_ORD Counts the number of machine clears due to
ERING
memory order conflicts.

C3H

04H

MACHINE_CLEARS.SMC

Number of self-modifying-code machine clears
detected.

C3H

20H

MACHINE_CLEARS.MASKMOV

Counts the number of executed AVX masked load
operations that refer to an illegal address range
with the mask bits set to 0.

C4H

00H

BR_INST_RETIRED.ALL_BRANCH
ES

Branch instructions at retirement.

C4H

01H

BR_INST_RETIRED.CONDITIONAL Counts the number of conditional branch
instructions retired.

Supports PEBS.

C4H

02H

BR_INST_RETIRED.NEAR_CALL

Direct and indirect near call instructions retired.

Supports PEBS.

C4H

04H

BR_INST_RETIRED.ALL_BRANCH
ES

Counts the number of branch instructions retired.

Supports PEBS.

C4H

08H

BR_INST_RETIRED.NEAR_RETUR Counts the number of near return instructions
N
retired.

C4H

10H

BR_INST_RETIRED.NOT_TAKEN

Counts the number of not taken branch instructions Supports PEBS.
retired.

C4H

20H

BR_INST_RETIRED.NEAR_TAKEN

Number of near taken branches retired.

C4H

40H

BR_INST_RETIRED.FAR_BRANCH Number of far branches retired.

Supports PEBS.

C5H

00H

BR_MISP_RETIRED.ALL_BRANCH Mispredicted branch instructions at retirement.
ES

See Table 19-1.

C5H

01H

BR_MISP_RETIRED.CONDITIONAL Mispredicted conditional branch instructions retired. Supports PEBS.

C5H

04H

BR_MISP_RETIRED.ALL_BRANCH Mispredicted macro branch instructions retired.
ES

Supports PEBS.

C5H

20H

BR_MISP_RETIRED.NEAR_TAKEN Mispredicted taken branch instructions retired.

Supports PEBS.

CAH

02H

FP_ASSIST.X87_OUTPUT

Number of X87 FP assists due to output values.

Supports PEBS.

CAH

04H

FP_ASSIST.X87_INPUT

Number of X87 FP assists due to input values.

Supports PEBS.

CAH

08H

FP_ASSIST.SIMD_OUTPUT

Number of SIMD FP assists due to output values.

Supports PEBS.

CAH

10H

FP_ASSIST.SIMD_INPUT

Number of SIMD FP assists due to input values.

CAH

1EH

FP_ASSIST.ANY

Cycles with any input/output SSE* or FP assists.

CCH

20H

ROB_MISC_EVENTS.LBR_INSERT
S

Count cases of saving new LBR records by
hardware.

19-64 Vol. 3B

Comment

Supports PEBS.

See Table 19-1.

Supports PEBS.

Supports PEBS.

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

CDH

01H

MEM_TRANS_RETIRED.LOAD_LA
TENCY

Randomly sampled loads whose latency is above a
user defined threshold. A small fraction of the
overall loads are sampled due to randomization.

Specify threshold in MSR
3F6H. PMC 3 only.

CDH

02H

MEM_TRANS_RETIRED.PRECISE_
STORE

Sample stores and collect precise store operation
via PEBS record. PMC3 only.

See Section 18.3.4.4.3.

D0H

11H

MEM_UOPS_RETIRED.STLB_MISS Retired load uops that miss the STLB.
_LOADS

Supports PEBS.

D0H

12H

MEM_UOPS_RETIRED.STLB_MISS Retired store uops that miss the STLB.
_STORES

Supports PEBS.

D0H

21H

MEM_UOPS_RETIRED.LOCK_LOA
DS

Retired load uops with locked access.

Supports PEBS.

D0H

41H

MEM_UOPS_RETIRED.SPLIT_LOA
DS

Retired load uops that split across a cacheline
boundary.

Supports PEBS.

D0H

42H

MEM_UOPS_RETIRED.SPLIT_STO
RES

Retired store uops that split across a cacheline
boundary.

Supports PEBS.

D0H

81H

MEM_UOPS_RETIRED.ALL_LOADS All retired load uops.

Supports PEBS.

D0H

82H

MEM_UOPS_RETIRED.ALL_STORE All retired store uops.
S

Supports PEBS.

D1H

01H

MEM_LOAD_UOPS_RETIRED.L1_
HIT

Retired load uops with L1 cache hits as data
sources.

Supports PEBS.

D1H

02H

MEM_LOAD_UOPS_RETIRED.L2_
HIT

Retired load uops with L2 cache hits as data
sources.

Supports PEBS.

D1H

04H

MEM_LOAD_UOPS_RETIRED.LLC_ Retired load uops whose data source was LLC hit
HIT
with no snoop required.

Supports PEBS.

D1H

08H

MEM_LOAD_UOPS_RETIRED.L1_
MISS

Retired load uops whose data source followed an
L1 miss.

Supports PEBS.

D1H

10H

MEM_LOAD_UOPS_RETIRED.L2_
MISS

Retired load uops that missed L2, excluding
unknown sources.

Supports PEBS.

D1H

20H

MEM_LOAD_UOPS_RETIRED.LLC_ Retired load uops whose data source is LLC miss.
MISS

D1H

40H

MEM_LOAD_UOPS_RETIRED.HIT_ Retired load uops which data sources were load
Supports PEBS.
LFB
uops missed L1 but hit FB due to preceding miss to
the same cache line with data not ready.

D2H

01H

MEM_LOAD_UOPS_LLC_HIT_RETI Retired load uops whose data source was an onRED.XSNP_MISS
package core cache LLC hit and cross-core snoop
missed.

Supports PEBS.

D2H

02H

MEM_LOAD_UOPS_LLC_HIT_RETI Retired load uops whose data source was an onRED.XSNP_HIT
package LLC hit and cross-core snoop hits.

Supports PEBS.

D2H

04H

MEM_LOAD_UOPS_LLC_HIT_RETI Retired load uops whose data source was an onRED.XSNP_HITM
package core cache with HitM responses.

Supports PEBS.

D2H

08H

MEM_LOAD_UOPS_LLC_HIT_RETI Retired load uops whose data source was LLC hit
with no snoop required.
RED.XSNP_NONE

Supports PEBS.

D3H

01H

MEM_LOAD_UOPS_LLC_MISS_RE
TIRED.LOCAL_DRAM

Retired load uops whose data source was local
Supports PEBS.
memory (cross-socket snoop not needed or missed).

E6H

1FH

BACLEARS.ANY

Number of front end re-steers due to BPU
misprediction.

Supports PEBS.
Restricted to counters 03 when HTT is disabled.

Vol. 3B 19-65

PERFORMANCE MONITORING EVENTS

Table 19-13. Performance Events In the Processor Core of 3rd Generation Intel® Core™ i7, i5, i3 Processors (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

F0H

01H

L2_TRANS.DEMAND_DATA_RD

Demand Data Read requests that access L2 cache.

F0H

02H

L2_TRANS.RFO

RFO requests that access L2 cache.

F0H

04H

L2_TRANS.CODE_RD

L2 cache accesses when fetching instructions.

F0H

08H

L2_TRANS.ALL_PF

Any MLC or LLC HW prefetch accessing L2, including
rejects.

F0H

10H

L2_TRANS.L1D_WB

L1D writebacks that access L2 cache.

F0H

20H

L2_TRANS.L2_FILL

L2 fill requests that access L2 cache.

F0H

40H

L2_TRANS.L2_WB

L2 writebacks that access L2 cache.

F0H

80H

L2_TRANS.ALL_REQUESTS

Transactions accessing L2 pipe.

F1H

01H

L2_LINES_IN.I

L2 cache lines in I state filling L2.

Counting does not cover
rejects.

F1H

02H

L2_LINES_IN.S

L2 cache lines in S state filling L2.

Counting does not cover
rejects.

F1H

04H

L2_LINES_IN.E

L2 cache lines in E state filling L2.

Counting does not cover
rejects.

F1H

07H

L2_LINES_IN.ALL

L2 cache lines filling L2.

Counting does not cover
rejects.

F2H

01H

L2_LINES_OUT.DEMAND_CLEAN

Clean L2 cache lines evicted by demand.

F2H

02H

L2_LINES_OUT.DEMAND_DIRTY

Dirty L2 cache lines evicted by demand.

F2H

04H

L2_LINES_OUT.PF_CLEAN

Clean L2 cache lines evicted by the MLC prefetcher.

F2H

08H

L2_LINES_OUT.PF_DIRTY

Dirty L2 cache lines evicted by the MLC prefetcher.

F2H

0AH

L2_LINES_OUT.DIRTY_ALL

Dirty L2 cache lines filling the L2.

19.7.1

Comment

Counting does not cover
rejects.

Performance Monitoring Events in the Processor Core of Intel Xeon Processor E5 v2
Family and Intel Xeon Processor E7 v2 Family

Model-specific performance monitoring events in the processor core that are applicable only to Intel Xeon
processor E5 v2 family and Intel Xeon processor E7 v2 family based on the Ivy Bridge-E microarchitecture, with
CPUID signature of DisplayFamily_DisplayModel 06_3EH, are listed in Table 19-14.

Table 19-14. Performance Events Applicable Only to the Processor Core of
Intel® Xeon® Processor E5 v2 Family and Intel® Xeon® Processor E7 v2 Family
Event
Num.

Umask
Value

D3H

Event Mask Mnemonic

Description

Comment

03H

MEM_LOAD_UOPS_LLC_MISS_R
ETIRED.LOCAL_DRAM

Retired load uops whose data sources were local
DRAM (snoop not needed, Snoop Miss, or Snoop Hit
data not forwarded).

Supports PEBS.

D3H

0CH

MEM_LOAD_UOPS_LLC_MISS_R
ETIRED.REMOTE_DRAM

Retired load uops whose data source was remote
DRAM (snoop not needed, Snoop Miss, or Snoop Hit
data not forwarded).

Supports PEBS.

D3H

10H

MEM_LOAD_UOPS_LLC_MISS_R
ETIRED.REMOTE_HITM

Retired load uops whose data sources were remote
HITM.

Supports PEBS.

D3H

20H

MEM_LOAD_UOPS_LLC_MISS_R
ETIRED.REMOTE_FWD

Retired load uops whose data sources were forwards
from a remote cache.

Supports PEBS.

19-66 Vol. 3B

PERFORMANCE MONITORING EVENTS

19.8

PERFORMANCE MONITORING EVENTS FOR 2ND GENERATION
INTEL® CORE™ I7-2XXX, INTEL® CORE™ I5-2XXX, INTEL® CORE™ I3-2XXX
PROCESSOR SERIES

2nd generation Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx processor series, and Intel
Xeon processor E3-1200 product family are based on the Intel microarchitecture code name Sandy Bridge. They
support architectural performance monitoring events listed in Table 19-1. Model-specific performance monitoring
events in the processor core are listed in Table 19-15, Table 19-16, and Table 19-17. The events in Table 19-15
apply to processors with CPUID signature of DisplayFamily_DisplayModel encoding with the following values:
06_2AH and 06_2DH. The events in Table 19-16 apply to processors with CPUID signature 06_2AH. The events in
Table 19-17 apply to processors with CPUID signature 06_2DH. Fixed counters in the core PMU support the architecture events defined in Table 19-2.
Additional information on event specifics (e.g. derivative events using specific IA32_PERFEVTSELx modifiers, limitations, special notes and recommendations) can be found at found at https://software.intel.com/enus/forums/software-tuning-performance-optimization-platform-monitoring.

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

03H

01H

LD_BLOCKS.DATA_UNKNOWN

Blocked loads due to store buffer blocks with
unknown data.

03H

02H

LD_BLOCKS.STORE_FORWARD Loads blocked by overlapping with store buffer that
cannot be forwarded.

03H

08H

LD_BLOCKS.NO_SR

# of Split loads blocked due to resource not
available.

03H

10H

LD_BLOCKS.ALL_BLOCK

Number of cases where any load is blocked but has
no DCU miss.

05H

01H

MISALIGN_MEM_REF.LOADS

Speculative cache-line split load uops dispatched to
L1D.

05H

02H

MISALIGN_MEM_REF.STORES

Speculative cache-line split Store-address uops
dispatched to L1D.

07H

01H

LD_BLOCKS_PARTIAL.ADDRES False dependencies in MOB due to partial compare
S_ALIAS
on address.

07H

08H

LD_BLOCKS_PARTIAL.ALL_STA The number of times that load operations are
_BLOCK
temporarily blocked because of older stores, with
addresses that are not yet known. A load operation
may incur more than one block of this type.

08H

01H

DTLB_LOAD_MISSES.MISS_CA
USES_A_WALK

08H

02H

DTLB_LOAD_MISSES.WALK_CO Misses in all TLB levels that caused page walk
MPLETED
completed of any size.

08H

04H

DTLB_LOAD_MISSES.WALK_DU Cycle PMH is busy with a walk.
RATION

08H

10H

DTLB_LOAD_MISSES.STLB_HIT Number of cache load STLB hits. No page walk.

0DH

03H

INT_MISC.RECOVERY_CYCLES

Cycles waiting to recover after Machine Clears or
JEClear. Set Cmask= 1.

0DH

40H

INT_MISC.RAT_STALL_CYCLES

Cycles RAT external stall is sent to IDQ for this
thread.

Comment

Misses in all TLB levels that cause a page walk of
any page size.

Set Edge to count
occurrences.

Vol. 3B 19-67

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

0EH

01H

UOPS_ISSUED.ANY

Increments each cycle the # of Uops issued by the
RAT to RS. Set Cmask = 1, Inv = 1, Any= 1to count
stalled cycles of this core.

Set Cmask = 1, Inv = 1to
count stalled cycles.

10H

01H

FP_COMP_OPS_EXE.X87

Counts number of X87 uops executed.

10H

10H

FP_COMP_OPS_EXE.SSE_FP_P Counts number of SSE* double precision FP packed
ACKED_DOUBLE
uops executed.

10H

20H

FP_COMP_OPS_EXE.SSE_FP_S Counts number of SSE* single precision FP scalar
CALAR_SINGLE
uops executed.

10H

40H

FP_COMP_OPS_EXE.SSE_PACK Counts number of SSE* single precision FP packed
ED SINGLE
uops executed.

10H

80H

FP_COMP_OPS_EXE.SSE_SCAL Counts number of SSE* double precision FP scalar
AR_DOUBLE
uops executed.

11H

01H

SIMD_FP_256.PACKED_SINGLE Counts 256-bit packed single-precision floatingpoint instructions.

11H

02H

SIMD_FP_256.PACKED_DOUBL Counts 256-bit packed double-precision floatingE
point instructions.

14H

01H

ARITH.FPU_DIV_ACTIVE

Cycles that the divider is active, includes INT and FP.
Set 'edge =1, cmask=1' to count the number of
divides.

17H

01H

INSTS_WRITTEN_TO_IQ.INSTS

Counts the number of instructions written into the
IQ every cycle.

24H

01H

L2_RQSTS.DEMAND_DATA_RD Demand Data Read requests that hit L2 cache.
_HIT

24H

03H

L2_RQSTS.ALL_DEMAND_DAT
A_RD

Counts any demand and L1 HW prefetch data load
requests to L2.

24H

04H

L2_RQSTS.RFO_HITS

Counts the number of store RFO requests that hit
the L2 cache.

24H

08H

L2_RQSTS.RFO_MISS

Counts the number of store RFO requests that miss
the L2 cache.

24H

0CH

L2_RQSTS.ALL_RFO

Counts all L2 store RFO requests.

24H

10H

L2_RQSTS.CODE_RD_HIT

Number of instruction fetches that hit the L2 cache.

24H

20H

L2_RQSTS.CODE_RD_MISS

Number of instruction fetches that missed the L2
cache.

24H

30H

L2_RQSTS.ALL_CODE_RD

Counts all L2 code requests.

24H

40H

L2_RQSTS.PF_HIT

Requests from L2 Hardware prefetcher that hit L2.

24H

80H

L2_RQSTS.PF_MISS

Requests from L2 Hardware prefetcher that missed
L2.

24H

C0H

L2_RQSTS.ALL_PF

Any requests from L2 Hardware prefetchers.

27H

01H

L2_STORE_LOCK_RQSTS.MISS

RFOs that miss cache lines.

27H

04H

L2_STORE_LOCK_RQSTS.HIT_
E

RFOs that hit cache lines in E state.

27H

08H

L2_STORE_LOCK_RQSTS.HIT_
M

RFOs that hit cache lines in M state.

27H

0FH

L2_STORE_LOCK_RQSTS.ALL

RFOs that access cache lines in any state.

19-68 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

28H

01H

L2_L1D_WB_RQSTS.MISS

Not rejected writebacks from L1D to L2 cache lines
that missed L2.

28H

02H

L2_L1D_WB_RQSTS.HIT_S

Not rejected writebacks from L1D to L2 cache lines
in S state.

28H

04H

L2_L1D_WB_RQSTS.HIT_E

Not rejected writebacks from L1D to L2 cache lines
in E state.

28H

08H

L2_L1D_WB_RQSTS.HIT_M

Not rejected writebacks from L1D to L2 cache lines
in M state.
Not rejected writebacks from L1D to L2 cache.

Comment

28H

0FH

L2_L1D_WB_RQSTS.ALL

2EH

4FH

LONGEST_LAT_CACHE.REFERE This event counts requests originating from the
NCE
core that reference a cache line in the last level
cache.

See Table 19-1.

2EH

41H

LONGEST_LAT_CACHE.MISS

See Table 19-1.

3CH

00H

CPU_CLK_UNHALTED.THREAD Counts the number of thread cycles while the
_P
thread is not in a halt state. The thread enters the
halt state when it is running the HLT instruction.
The core frequency may change from time to time
due to power or thermal throttling.

See Table 19-1.

3CH

01H

CPU_CLK_THREAD_UNHALTED Increments at the frequency of XCLK (100 MHz)
.REF_XCLK
when not halted.

See Table 19-1.

48H

01H

L1D_PEND_MISS.PENDING

PMC2 only;

This event counts each cache miss condition for
references to the last level cache.

Increments the number of outstanding L1D misses
every cycle. Set Cmask = 1 and Edge =1 to count
occurrences.

49H

01H

DTLB_STORE_MISSES.MISS_CA Miss in all TLB levels causes a page walk of any page
USES_A_WALK
size (4K/2M/4M/1G).

49H

02H

DTLB_STORE_MISSES.WALK_C Miss in all TLB levels causes a page walk that
OMPLETED
completes of any page size (4K/2M/4M/1G).

49H

04H

DTLB_STORE_MISSES.WALK_D Cycles PMH is busy with this walk.
URATION

49H

10H

DTLB_STORE_MISSES.STLB_HI Store operations that miss the first TLB level but hit
T
the second and do not cause page walks.

4CH

01H

LOAD_HIT_PRE.SW_PF

Not SW-prefetch load dispatches that hit fill buffer
allocated for S/W prefetch.

4CH

02H

LOAD_HIT_PRE.HW_PF

Not SW-prefetch load dispatches that hit fill buffer
allocated for H/W prefetch.

4EH

02H

HW_PRE_REQ.DL1_MISS

Hardware Prefetch requests that miss the L1D
cache. A request is being counted each time it
access the cache & miss it, including if a block is
applicable or if hit the Fill Buffer for example.

51H

01H

L1D.REPLACEMENT

Counts the number of lines brought into the L1 data
cache.

51H

02H

L1D.ALLOCATED_IN_M

Counts the number of allocations of modified L1D
cache lines.

51H

04H

L1D.EVICTION

Counts the number of modified lines evicted from
the L1 data cache due to replacement.

Set Cmask = 1 to count
cycles.

This accounts for both L1
streamer and IP-based
(IPP) HW prefetchers.

Vol. 3B 19-69

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

51H

08H

L1D.ALL_M_REPLACEMENT

Cache lines in M state evicted out of L1D due to
Snoop HitM or dirty line replacement.

59H

20H

PARTIAL_RAT_STALLS.FLAGS_ Increments the number of flags-merge uops in flight
MERGE_UOP
each cycle. Set Cmask = 1 to count cycles.

59H

40H

PARTIAL_RAT_STALLS.SLOW_
LEA_WINDOW

59H

80H

PARTIAL_RAT_STALLS.MUL_SI Number of Multiply packed/scalar single precision
NGLE_UOP
uops allocated.

5BH

0CH

RESOURCE_STALLS2.ALL_FL_
EMPTY

5BH

0FH

RESOURCE_STALLS2.ALL_PRF Cycles stalled due to control structures full for
_CONTROL
physical registers.

5BH

40H

RESOURCE_STALLS2.BOB_FUL Cycles Allocator is stalled due Branch Order Buffer.
L

5BH

4FH

RESOURCE_STALLS2.OOO_RS
RC

Cycles stalled due to out of order resources full.

5CH

01H

CPL_CYCLES.RING0

Unhalted core cycles when the thread is in ring 0.

5CH

02H

CPL_CYCLES.RING123

Unhalted core cycles when the thread is not in ring
0.

5EH

01H

RS_EVENTS.EMPTY_CYCLES

Cycles the RS is empty for the thread.

60H

01H

OFFCORE_REQUESTS_OUTSTA Offcore outstanding Demand Data Read
NDING.DEMAND_DATA_RD
transactions in SQ to uncore. Set Cmask=1 to count
cycles.

60H

04H

OFFCORE_REQUESTS_OUTSTA Offcore outstanding RFO store transactions in SQ to
NDING.DEMAND_RFO
uncore. Set Cmask=1 to count cycles.

60H

08H

OFFCORE_REQUESTS_OUTSTA Offcore outstanding cacheable data read
NDING.ALL_DATA_RD
transactions in SQ to uncore. Set Cmask=1 to count
cycles.

63H

01H

LOCK_CYCLES.SPLIT_LOCK_UC Cycles in which the L1D and L2 are locked, due to a
_LOCK_DURATION
UC lock or split lock.

63H

02H

LOCK_CYCLES.CACHE_LOCK_D
URATION

Cycles in which the L1D is locked.

79H

02H

IDQ.EMPTY

Counts cycles the IDQ is empty.

79H

04H

IDQ.MITE_UOPS

Increment each cycle # of uops delivered to IDQ
from MITE path. Set Cmask = 1 to count cycles.

Can combine Umask 04H
and 20H.

79H

08H

IDQ.DSB_UOPS

Increment each cycle. # of uops delivered to IDQ
from DSB path. Set Cmask = 1 to count cycles.

Can combine Umask 08H
and 10H.

79H

10H

IDQ.MS_DSB_UOPS

Increment each cycle # of uops delivered to IDQ
when MS busy by DSB. Set Cmask = 1 to count
cycles MS is busy. Set Cmask=1 and Edge =1 to
count MS activations.

Can combine Umask 08H
and 10H.

79H

20H

IDQ.MS_MITE_UOPS

Increment each cycle # of uops delivered to IDQ
when MS is busy by MITE. Set Cmask = 1 to count
cycles.

Can combine Umask 04H
and 20H.

19-70 Vol. 3B

Comment

Cycles with at least one slow LEA uop allocated.

Cycles stalled due to free list empty.

PMC0-3 only regardless
HTT.

Use Edge to count
transition.

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

79H

30H

IDQ.MS_UOPS

Increment each cycle # of uops delivered to IDQ
from MS by either DSB or MITE. Set Cmask = 1 to
count cycles.

Can combine Umask 04H,
08H and 30H.

80H

02H

ICACHE.MISSES

Number of Instruction Cache, Streaming Buffer and
Victim Cache Misses. Includes UC accesses.

85H

01H

ITLB_MISSES.MISS_CAUSES_A
_WALK

Misses in all ITLB levels that cause page walks.

85H

02H

ITLB_MISSES.WALK_COMPLET
ED

Misses in all ITLB levels that cause completed page
walks.

85H

04H

ITLB_MISSES.WALK_DURATIO
N

Cycle PMH is busy with a walk.

85H

10H

ITLB_MISSES.STLB_HIT

Number of cache load STLB hits. No page walk.

87H

01H

ILD_STALL.LCP

Stalls caused by changing prefix length of the
instruction.

87H

04H

ILD_STALL.IQ_FULL

Stall cycles due to IQ is full.

88H

41H

BR_INST_EXEC.NONTAKEN_CO Not-taken macro conditional branches.
NDITIONAL

88H

81H

BR_INST_EXEC.TAKEN_CONDI
TIONAL

88H

82H

BR_INST_EXEC.TAKEN_DIRECT Taken speculative and retired conditional branches
_JUMP
excluding calls and indirects.

88H

84H

BR_INST_EXEC.TAKEN_INDIRE Taken speculative and retired indirect branches
CT_JUMP_NON_CALL_RET
excluding calls and returns.

88H

88H

BR_INST_EXEC.TAKEN_INDIRE Taken speculative and retired indirect branches that
CT_NEAR_RETURN
are returns.

88H

90H

BR_INST_EXEC.TAKEN_DIRECT Taken speculative and retired direct near calls.
_NEAR_CALL

88H

A0H

BR_INST_EXEC.TAKEN_INDIRE Taken speculative and retired indirect near calls.
CT_NEAR_CALL

88H

C1H

BR_INST_EXEC.ALL_CONDITIO Speculative and retired conditional branches.
NAL

88H

C2H

BR_INST_EXEC.ALL_DIRECT_J
UMP

Speculative and retired conditional branches
excluding calls and indirects.

88H

C4H

BR_INST_EXEC.ALL_INDIRECT
_JUMP_NON_CALL_RET

Speculative and retired indirect branches excluding
calls and returns.

88H

C8H

BR_INST_EXEC.ALL_INDIRECT
_NEAR_RETURN

Speculative and retired indirect branches that are
returns.

88H

D0H

BR_INST_EXEC.ALL_NEAR_CA
LL

Speculative and retired direct near calls.

88H

FFH

BR_INST_EXEC.ALL_BRANCHE Speculative and retired branches.
S

89H

41H

BR_MISP_EXEC.NONTAKEN_CO Not-taken mispredicted macro conditional branches.
NDITIONAL

89H

81H

BR_MISP_EXEC.TAKEN_CONDI
TIONAL

Taken speculative and retired conditional branches.

Taken speculative and retired mispredicted
conditional branches.

Vol. 3B 19-71

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

89H

84H

BR_MISP_EXEC.TAKEN_INDIRE Taken speculative and retired mispredicted indirect
CT_JUMP_NON_CALL_RET
branches excluding calls and returns.

89H

88H

BR_MISP_EXEC.TAKEN_RETUR Taken speculative and retired mispredicted indirect
N_NEAR
branches that are returns.

89H

90H

BR_MISP_EXEC.TAKEN_DIRECT Taken speculative and retired mispredicted direct
_NEAR_CALL
near calls.

89H

A0H

BR_MISP_EXEC.TAKEN_INDIRE Taken speculative and retired mispredicted indirect
CT_NEAR_CALL
near calls.

89H

C1H

BR_MISP_EXEC.ALL_CONDITIO Speculative and retired mispredicted conditional
NAL
branches.

89H

C4H

BR_MISP_EXEC.ALL_INDIRECT
_JUMP_NON_CALL_RET

89H

D0H

BR_MISP_EXEC.ALL_NEAR_CA Speculative and retired mispredicted direct near
LL
calls.

89H

FFH

BR_MISP_EXEC.ALL_BRANCHE Speculative and retired mispredicted branches.
S

9CH

01H

IDQ_UOPS_NOT_DELIVERED.C
ORE

A1H

01H

UOPS_DISPATCHED_PORT.POR Cycles which a Uop is dispatched on port 0.
T_0

A1H

02H

UOPS_DISPATCHED_PORT.POR Cycles which a Uop is dispatched on port 1.
T_1

A1H

0CH

UOPS_DISPATCHED_PORT.POR Cycles which a Uop is dispatched on port 2.
T_2

A1H

30H

UOPS_DISPATCHED_PORT.POR Cycles which a Uop is dispatched on port 3.
T_3

A1H

40H

UOPS_DISPATCHED_PORT.POR Cycles which a Uop is dispatched on port 4.
T_4

A1H

80H

UOPS_DISPATCHED_PORT.POR Cycles which a Uop is dispatched on port 5.
T_5

A2H

01H

RESOURCE_STALLS.ANY

Cycles Allocation is stalled due to Resource Related
reason.

A2H

02H

RESOURCE_STALLS.LB

Counts the cycles of stall due to lack of load buffers.

A2H

04H

RESOURCE_STALLS.RS

Cycles stalled due to no eligible RS entry available.

A2H

08H

RESOURCE_STALLS.SB

Cycles stalled due to no store buffers available (not
including draining form sync).

A2H

10H

RESOURCE_STALLS.ROB

Cycles stalled due to re-order buffer full.

A2H

20H

RESOURCE_STALLS.FCSW

Cycles stalled due to writing the FPU control word.

A3H

01H

CYCLE_ACTIVITY.CYCLES_L2_P Cycles with pending L2 miss loads. Set AnyThread
ENDING
to count per core.

A3H

02H

CYCLE_ACTIVITY.CYCLES_L1D_ Cycles with pending L1 cache miss loads. Set
PENDING
AnyThread to count per core.

A3H

04H

CYCLE_ACTIVITY.CYCLES_NO_
DISPATCH

19-72 Vol. 3B

Event Mask Mnemonic

Description

Comment

Speculative and retired mispredicted indirect
branches excluding calls and returns.

Count issue pipeline slots where no uop was
delivered from the front end to the back end when
there is no back-end stall.

Use Cmask to qualify uop
b/w.

PMC2 only.

Cycles of dispatch stalls. Set AnyThread to count per PMC0-3 only.
core.

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

A3H

05H

CYCLE_ACTIVITY.STALL_CYCLE
S_L2_PENDING

PMC0-3 only.

A3H

06H

CYCLE_ACTIVITY.STALL_CYCLE
S_L1D_PENDING

PMC2 only.

A8H

01H

LSD.UOPS

Number of Uops delivered by the LSD.

ABH

01H

DSB2MITE_SWITCHES.COUNT

Number of DSB to MITE switches.

ABH

02H

DSB2MITE_SWITCHES.PENALT
Y_CYCLES

Cycles DSB to MITE switches caused delay.

ACH

02H

DSB_FILL.OTHER_CANCEL

Cases of cancelling valid DSB fill not because of
exceeding way limit.

ACH

08H

DSB_FILL.EXCEED_DSB_LINES

DSB Fill encountered > 3 DSB lines.

AEH

01H

ITLB.ITLB_FLUSH

Counts the number of ITLB flushes; includes
4k/2M/4M pages.

B0H

01H

OFFCORE_REQUESTS.DEMAND Demand data read requests sent to uncore.
_DATA_RD

B0H

04H

OFFCORE_REQUESTS.DEMAND Demand RFO read requests sent to uncore, including
_RFO
regular RFOs, locks, ItoM.

B0H

08H

OFFCORE_REQUESTS.ALL_DAT Data read requests sent to uncore (demand and
A_RD
prefetch).

B1H

01H

UOPS_DISPATCHED.THREAD

Counts total number of uops to be dispatched perthread each cycle. Set Cmask = 1, INV =1 to count
stall cycles.

PMC0-3 only regardless
HTT.

B1H

02H

UOPS_DISPATCHED.CORE

Counts total number of uops to be dispatched percore each cycle.

Do not need to set ANY.

B2H

01H

OFFCORE_REQUESTS_BUFFER Offcore requests buffer cannot take more entries
.SQ_FULL
for this thread core.

B6H

01H

AGU_BYPASS_CANCEL.COUNT

Counts executed load operations with all the
following traits: 1. Addressing of the format [base +
offset], 2. The offset is between 1 and 2047, 3. The
address specified in the base register is in one page
and the address [base+offset] is in another page.

B7H

01H

OFF_CORE_RESPONSE_0

See Section 18.3.4.5, “Off-core Response
Performance Monitoring”.

Requires MSR 01A6H.

BBH

01H

OFF_CORE_RESPONSE_1

See Section 18.3.4.5, “Off-core Response
Performance Monitoring”.

Requires MSR 01A7H.

BDH

01H

TLB_FLUSH.DTLB_THREAD

DTLB flush attempts of the thread-specific entries.

BDH

20H

TLB_FLUSH.STLB_ANY

Count number of STLB flush attempts.

BFH

05H

L1D_BLOCKS.BANK_CONFLICT Cycles when dispatched loads are cancelled due to
_CYCLES
L1D bank conflicts with other load ports.

Cmask=1.

C0H

00H

INST_RETIRED.ANY_P

Number of instructions at retirement.

See Table 19-1.

C0H

01H

INST_RETIRED.PREC_DIST

Precise instruction retired event with HW to reduce PMC1 only; must quiesce
effect of PEBS shadow in IP distribution.
other PMCs.

C1H

02H

OTHER_ASSISTS.ITLB_MISS_R
ETIRED

Instructions that experienced an ITLB miss.

Event Mask Mnemonic

Description

Comment

Vol. 3B 19-73

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

C1H

08H

OTHER_ASSISTS.AVX_STORE

Number of assists associated with 256-bit AVX
store operations.

C1H

10H

OTHER_ASSISTS.AVX_TO_SSE Number of transitions from AVX-256 to legacy SSE
when penalty applicable.

C1H

20H

OTHER_ASSISTS.SSE_TO_AVX Number of transitions from SSE to AVX-256 when
penalty applicable.

C2H

01H

UOPS_RETIRED.ALL

C2H

02H

UOPS_RETIRED.RETIRE_SLOTS Counts the number of retirement slots used each
cycle.

C3H

02H

MACHINE_CLEARS.MEMORY_O Counts the number of machine clears due to
RDERING
memory order conflicts.

C3H

04H

MACHINE_CLEARS.SMC

Counts the number of times that a program writes
to a code section.

C3H

20H

MACHINE_CLEARS.MASKMOV

Counts the number of executed AVX masked load
operations that refer to an illegal address range
with the mask bits set to 0.

C4H

00H

BR_INST_RETIRED.ALL_BRAN
CHES

Branch instructions at retirement.

C4H

01H

BR_INST_RETIRED.CONDITION Counts the number of conditional branch
AL
instructions retired.

Supports PEBS.

C4H

02H

BR_INST_RETIRED.NEAR_CALL Direct and indirect near call instructions retired.

Supports PEBS.

C4H

04H

BR_INST_RETIRED.ALL_BRAN
CHES

Counts the number of branch instructions retired.

Supports PEBS.

C4H

08H

BR_INST_RETIRED.NEAR_RET
URN

Counts the number of near return instructions
retired.

Supports PEBS.

C4H

10H

BR_INST_RETIRED.NOT_TAKE
N

Counts the number of not taken branch instructions
retired.

C4H

20H

BR_INST_RETIRED.NEAR_TAK
EN

Number of near taken branches retired.

C4H

40H

BR_INST_RETIRED.FAR_BRAN
CH

Number of far branches retired.

C5H

00H

BR_MISP_RETIRED.ALL_BRAN
CHES

Mispredicted branch instructions at retirement.

C5H

01H

BR_MISP_RETIRED.CONDITION Mispredicted conditional branch instructions retired. Supports PEBS.
AL

C5H

02H

BR_MISP_RETIRED.NEAR_CAL
L

Direct and indirect mispredicted near call
instructions retired.

Supports PEBS.

C5H

04H

BR_MISP_RETIRED.ALL_BRAN
CHES

Mispredicted macro branch instructions retired.

Supports PEBS.

C5H

10H

BR_MISP_RETIRED.NOT_TAKE
N

Mispredicted not taken branch instructions retired.

Supports PEBS.

C5H

20H

BR_MISP_RETIRED.TAKEN

Mispredicted taken branch instructions retired.

Supports PEBS.

CAH

02H

FP_ASSIST.X87_OUTPUT

Number of X87 assists due to output value.

19-74 Vol. 3B

Comment

Counts the number of micro-ops retired, Use
Supports PEBS.
cmask=1 and invert to count active cycles or stalled
cycles.
Supports PEBS.

See Table 19-1.

Supports PEBS.

See Table 19-1.

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

CAH

04H

FP_ASSIST.X87_INPUT

Number of X87 assists due to input value.

CAH

08H

FP_ASSIST.SIMD_OUTPUT

Number of SIMD FP assists due to output values.

CAH

10H

FP_ASSIST.SIMD_INPUT

Number of SIMD FP assists due to input values.

Comment

CAH

1EH

FP_ASSIST.ANY

Cycles with any input/output SSE* or FP assists.

CCH

20H

ROB_MISC_EVENTS.LBR_INSE
RTS

Count cases of saving new LBR records by
hardware.

CDH

01H

MEM_TRANS_RETIRED.LOAD_
LATENCY

Randomly sampled loads whose latency is above a
user defined threshold. A small fraction of the
overall loads are sampled due to randomization.
PMC3 only.

CDH

02H

MEM_TRANS_RETIRED.PRECIS Sample stores and collect precise store operation
E_STORE
via PEBS record. PMC3 only.

See Section 18.3.4.4.3.

D0H

11H

MEM_UOPS_RETIRED.STLB_MI Retired load uops that miss the STLB.
SS_LOADS

Supports PEBS. PMC0-3
only regardless HTT.

D0H

12H

MEM_UOPS_RETIRED.STLB_MI Retired store uops that miss the STLB.
SS_STORES

Supports PEBS. PMC0-3
only regardless HTT.

D0H

21H

MEM_UOPS_RETIRED.LOCK_LO Retired load uops with locked access.
ADS

Supports PEBS. PMC0-3
only regardless HTT.

D0H

41H

MEM_UOPS_RETIRED.SPLIT_L
OADS

Retired load uops that split across a cacheline
boundary.

Supports PEBS. PMC0-3
only regardless HTT.

D0H

42H

MEM_UOPS_RETIRED.SPLIT_S
TORES

Retired store uops that split across a cacheline
boundary.

Supports PEBS. PMC0-3
only regardless HTT.

D0H

81H

MEM_UOPS_RETIRED.ALL_LOA All retired load uops.
DS

Supports PEBS. PMC0-3
only regardless HTT.

D0H

82H

MEM_UOPS_RETIRED.ALL_STO All retired store uops.
RES

Supports PEBS. PMC0-3
only regardless HTT.

D1H

01H

MEM_LOAD_UOPS_RETIRED.L
1_HIT

Retired load uops with L1 cache hits as data
sources.

Supports PEBS. PMC0-3
only regardless HTT.

D1H

02H

MEM_LOAD_UOPS_RETIRED.L
2_HIT

Retired load uops with L2 cache hits as data
sources.

Supports PEBS.

D1H

04H

MEM_LOAD_UOPS_RETIRED.LL Retired load uops which data sources were data hits Supports PEBS.
C_HIT
in LLC without snoops required.

D1H

20H

MEM_LOAD_UOPS_RETIRED.LL Retired load uops which data sources were data
C_MISS
missed LLC (excluding unknown data source).

Supports PEBS.

D1H

40H

MEM_LOAD_UOPS_RETIRED.HI Retired load uops which data sources were load
T_LFB
uops missed L1 but hit FB due to preceding miss to
the same cache line with data not ready.

Supports PEBS.

D2H

01H

MEM_LOAD_UOPS_LLC_HIT_R
ETIRED.XSNP_MISS

Retired load uops whose data source was an onpackage core cache LLC hit and cross-core snoop
missed.

Supports PEBS.

D2H

02H

MEM_LOAD_UOPS_LLC_HIT_R
ETIRED.XSNP_HIT

Retired load uops whose data source was an onpackage LLC hit and cross-core snoop hits.

Supports PEBS.

D2H

04H

MEM_LOAD_UOPS_LLC_HIT_R
ETIRED.XSNP_HITM

Retired load uops whose data source was an onpackage core cache with HitM responses.

Supports PEBS.

D2H

08H

MEM_LOAD_UOPS_LLC_HIT_R
ETIRED.XSNP_NONE

Retired load uops whose data source was LLC hit
with no snoop required.

Supports PEBS.

Specify threshold in MSR
3F6H.

Vol. 3B 19-75

PERFORMANCE MONITORING EVENTS

Table 19-15. Performance Events In the Processor Core Common to 2nd Generation Intel® Core™ i7-2xxx, Intel®
Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series and Intel® Xeon® Processors E3 and E5 Family (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

E6H

01H

BACLEARS.ANY

Counts the number of times the front end is resteered, mainly when the BPU cannot provide a
correct prediction and this is corrected by other
branch handling mechanisms at the front end.

F0H

01H

L2_TRANS.DEMAND_DATA_RD Demand Data Read requests that access L2 cache.

F0H

02H

L2_TRANS.RFO

RFO requests that access L2 cache.

F0H

04H

L2_TRANS.CODE_RD

L2 cache accesses when fetching instructions.

Comment

F0H

08H

L2_TRANS.ALL_PF

L2 or LLC HW prefetches that access L2 cache.

F0H

10H

L2_TRANS.L1D_WB

L1D writebacks that access L2 cache.

Including rejects.

F0H

20H

L2_TRANS.L2_FILL

L2 fill requests that access L2 cache.

F0H

40H

L2_TRANS.L2_WB

L2 writebacks that access L2 cache.

F0H

80H

L2_TRANS.ALL_REQUESTS

Transactions accessing L2 pipe.

F1H

01H

L2_LINES_IN.I

L2 cache lines in I state filling L2.

Counting does not cover
rejects.

F1H

02H

L2_LINES_IN.S

L2 cache lines in S state filling L2.

Counting does not cover
rejects.

F1H

04H

L2_LINES_IN.E

L2 cache lines in E state filling L2.

Counting does not cover
rejects.

F1H

07H

L2_LINES_IN.ALL

L2 cache lines filling L2.

Counting does not cover
rejects.

F2H

01H

L2_LINES_OUT.DEMAND_CLEA Clean L2 cache lines evicted by demand.
N

F2H

02H

L2_LINES_OUT.DEMAND_DIRT
Y

F2H

04H

L2_LINES_OUT.PF_CLEAN

Clean L2 cache lines evicted by L2 prefetch.

F2H

08H

L2_LINES_OUT.PF_DIRTY

Dirty L2 cache lines evicted by L2 prefetch.

F2H

0AH

L2_LINES_OUT.DIRTY_ALL

Dirty L2 cache lines filling the L2.

F4H

10H

SQ_MISC.SPLIT_LOCK

Split locks in SQ.

Dirty L2 cache lines evicted by demand.

Counting does not cover
rejects.

Non-architecture performance monitoring events in the processor core that are applicable only to Intel processors
with CPUID signature of DisplayFamily_DisplayModel 06_2AH are listed in Table 19-16.

Table 19-16. Performance Events applicable only to the Processor core for 2nd Generation Intel® Core™ i7-2xxx,
Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series
Event
Num.

Umask
Value

D2H

01H

MEM_LOAD_UOPS_LLC_HIT_R Retired load uops which data sources were LLC hit and Supports PEBS. PMC0ETIRED.XSNP_MISS
cross-core snoop missed in on-pkg core cache.
3 only regardless HTT.

D2H

02H

MEM_LOAD_UOPS_LLC_HIT_R Retired load uops which data sources were LLC and
ETIRED.XSNP_HIT
cross-core snoop hits in on-pkg core cache.

Supports PEBS.

D2H

04H

MEM_LOAD_UOPS_LLC_HIT_R Retired load uops which data sources were HitM
ETIRED.XSNP_HITM
responses from shared LLC.

Supports PEBS.

D2H

08H

MEM_LOAD_UOPS_LLC_HIT_R Retired load uops which data sources were hits in LLC
ETIRED.XSNP_NONE
without snoops required.

Supports PEBS.

19-76 Vol. 3B

Event Mask Mnemonic

Description

Comment

PERFORMANCE MONITORING EVENTS

Table 19-16. Performance Events applicable only to the Processor core for 2nd Generation Intel® Core™ i7-2xxx,
Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series (Contd.)
Event
Num.

Umask
Value

D4H

02H

B7H/BBH 01H

Event Mask Mnemonic

Description

Comment

MEM_LOAD_UOPS_MISC_RETI
RED.LLC_MISS

Retired load uops with unknown information as data
source in cache serviced the load.

Supports PEBS. PMC03 only regardless HTT.

OFF_CORE_RESPONSE_N

Sub-events of OFF_CORE_RESPONSE_N (suffix N = 0,
1) programmed using MSR 01A6H/01A7H with values
shown in the comment column.

OFFCORE_RESPONSE.ALL_CODE_RD.LLC_HIT_N

10003C0244H

OFFCORE_RESPONSE.ALL_CODE_RD.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0244H

OFFCORE_RESPONSE.ALL_CODE_RD.LLC_HIT.SNOOP_MISS_N

2003C0244H

OFFCORE_RESPONSE.ALL_CODE_RD.LLC_HIT.MISS_DRAM_N

300400244H

OFFCORE_RESPONSE.ALL_DATA_RD.LLC_HIT.ANY_RESPONSE_N

3F803C0091H

OFFCORE_RESPONSE.ALL_DATA_RD.LLC_MISS.DRAM_N

300400091H

OFFCORE_RESPONSE.ALL_PF_CODE_RD.LLC_HIT.ANY_RESPONSE_N

3F803C0240H

OFFCORE_RESPONSE.ALL_PF_CODE_RD.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0240H

OFFCORE_RESPONSE.ALL_PF_CODE_RD.LLC_HIT.HITM_OTHER_CORE_N

10003C0240H

OFFCORE_RESPONSE.ALL_PF_CODE_RD.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0240H

OFFCORE_RESPONSE.ALL_PF_CODE_RD.LLC_HIT.SNOOP_MISS_N

2003C0240H

OFFCORE_RESPONSE.ALL_PF_CODE_RD.LLC_MISS.DRAM_N

300400240H

OFFCORE_RESPONSE.ALL_PF_DATA_RD.LLC_MISS.DRAM_N

300400090H

OFFCORE_RESPONSE.ALL_PF_RFO.LLC_HIT.ANY_RESPONSE_N

3F803C0120H

OFFCORE_RESPONSE.ALL_PF_RFO.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0120H

OFFCORE_RESPONSE.ALL_PF_RFO.LLC_HIT.HITM_OTHER_CORE_N

10003C0120H

OFFCORE_RESPONSE.ALL_PF_RfO.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0120H

OFFCORE_RESPONSE.ALL_PF_RFO.LLC_HIT.SNOOP_MISS_N

2003C0120H

OFFCORE_RESPONSE.ALL_PF_RFO.LLC_MISS.DRAM_N

300400120H

OFFCORE_RESPONSE.ALL_READS.LLC_MISS.DRAM_N

3004003F7H

OFFCORE_RESPONSE.ALL_RFO.LLC_HIT.ANY_RESPONSE_N

3F803C0122H

OFFCORE_RESPONSE.ALL_RFO.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0122H

OFFCORE_RESPONSE.ALL_RFO.LLC_HIT.HITM_OTHER_CORE_N

10003C0122H

OFFCORE_RESPONSE.ALL_RFO.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0122H

OFFCORE_RESPONSE.ALL_RFO.LLC_HIT.SNOOP_MISS_N

2003C0122H

OFFCORE_RESPONSE.ALL_RFO.LLC_MISS.DRAM_N

300400122H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_HIT.HITM_OTHER_CORE_N

10003C0004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_HIT.SNOOP_MISS_N

2003C0004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_MISS.DRAM_N

300400004H

OFFCORE_RESPONSE.DEMAND_DATA_RD.LLC_MISS.DRAM_N

300400001H

OFFCORE_RESPONSE.DEMAND_RFO.LLC_HIT.ANY_RESPONSE_N

3F803C0002H

OFFCORE_RESPONSE.DEMAND_RFO.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0002H

OFFCORE_RESPONSE.DEMAND_RFO.LLC_HIT.HITM_OTHER_CORE_N

10003C0002H

Vol. 3B 19-77

PERFORMANCE MONITORING EVENTS

Table 19-16. Performance Events applicable only to the Processor core for 2nd Generation Intel® Core™ i7-2xxx,
Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

OFFCORE_RESPONSE.DEMAND_RFO.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0002H

OFFCORE_RESPONSE.DEMAND_RFO.LLC_HIT.SNOOP_MISS_N

2003C0002H

OFFCORE_RESPONSE.DEMAND_RFO.LLC_MISS.DRAM_N

300400002H

OFFCORE_RESPONSE.OTHER.ANY_RESPONSE_N

18000H

OFFCORE_RESPONSE.PF_L2_CODE_RD.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0040H

OFFCORE_RESPONSE.PF_L2_CODE_RD.LLC_HIT.HITM_OTHER_CORE_N

10003C0040H

OFFCORE_RESPONSE.PF_L2_CODE_RD.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0040H

OFFCORE_RESPONSE.PF_L2_CODE_RD.LLC_HIT.SNOOP_MISS_N

2003C0040H

OFFCORE_RESPONSE.PF_L2_CODE_RD.LLC_MISS.DRAM_N

300400040H

OFFCORE_RESPONSE.PF_L2_DATA_RD.LLC_MISS.DRAM_N

300400010H

OFFCORE_RESPONSE.PF_L2_RFO.LLC_HIT.ANY_RESPONSE_N

3F803C0020H

OFFCORE_RESPONSE.PF_L2_RFO.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0020H

OFFCORE_RESPONSE.PF_L2_RFO.LLC_HIT.HITM_OTHER_CORE_N

10003C0020H

OFFCORE_RESPONSE.PF_L2_RFO.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0020H

OFFCORE_RESPONSE.PF_L2_RFO.LLC_HIT.SNOOP_MISS_N

2003C0020H

OFFCORE_RESPONSE.PF_L2_RFO.LLC_MISS.DRAM_N

300400020H

OFFCORE_RESPONSE.PF_LLC_CODE_RD.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0200H

OFFCORE_RESPONSE.PF_LLC_CODE_RD.LLC_HIT.HITM_OTHER_CORE_N

10003C0200H

OFFCORE_RESPONSE.PF_LLC_CODE_RD.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0200H

OFFCORE_RESPONSE.PF_LLC_CODE_RD.LLC_HIT.SNOOP_MISS_N

2003C0200H

OFFCORE_RESPONSE.PF_LLC_CODE_RD.LLC_MISS.DRAM_N

300400200H

OFFCORE_RESPONSE.PF_LLC_DATA_RD.LLC_MISS.DRAM_N

300400080H

OFFCORE_RESPONSE.PF_LLC_RFO.LLC_HIT.ANY_RESPONSE_N

3F803C0100H

OFFCORE_RESPONSE.PF_LLC_RFO.LLC_HIT.HIT_OTHER_CORE_NO_FWD_N

4003C0100H

OFFCORE_RESPONSE.PF_LLC_RFO.LLC_HIT.HITM_OTHER_CORE_N

10003C0100H

OFFCORE_RESPONSE.PF_LLC_RFO.LLC_HIT.NO_SNOOP_NEEDED_N

1003C0100H

OFFCORE_RESPONSE.PF_LLC_RFO.LLC_HIT.SNOOP_MISS_N

2003C0100H

OFFCORE_RESPONSE.PF_LLC_RFO.LLC_MISS.DRAM_N

300400100H

Non-architecture performance monitoring events in the processor core that are applicable only to Intel Xeon
processor E5 family (and Intel Core i7-3930 processor) based on Intel microarchitecture code name Sandy Bridge,
with CPUID signature of DisplayFamily_DisplayModel 06_2DH, are listed in Table 19-17.

Table 19-17. Performance Events Applicable only to the Processor Core of
Intel® Xeon® Processor E5 Family
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

CDH

01H

MEM_TRANS_RETIRED.LOAD_
LATENCY

Additional Configuration: Disable BL bypass and direct2core, and if the memory
is remotely homed. The count is not reliable If the memory is locally homed.

D1H

04H

MEM_LOAD_UOPS_RETIRED.LL Additional Configuration: Disable BL bypass. Supports PEBS.
C_HIT

19-78 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-17. Performance Events Applicable only to the Processor Core of
Intel® Xeon® Processor E5 Family
Event
Num.

Umask
Value

D1H

20H

MEM_LOAD_UOPS_RETIRED.LL Additional Configuration: Disable BL bypass and direct2core. Supports PEBS.
C_MISS

D2H

01H

MEM_LOAD_UOPS_LLC_HIT_R Additional Configuration: Disable bypass. Supports PEBS.
ETIRED.XSNP_MISS

D2H

02H

MEM_LOAD_UOPS_LLC_HIT_R Additional Configuration: Disable bypass. Supports PEBS.
ETIRED.XSNP_HIT

D2H

04H

MEM_LOAD_UOPS_LLC_HIT_R Additional Configuration: Disable bypass. Supports PEBS.
ETIRED.XSNP_HITM

D2H

08H

MEM_LOAD_UOPS_LLC_HIT_R Additional Configuration: Disable bypass. Supports PEBS.
ETIRED.XSNP_NONE

D3H

01H

MEM_LOAD_UOPS_LLC_MISS_
RETIRED.LOCAL_DRAM

Retired load uops which data sources were data
missed LLC but serviced by local DRAM. Supports
PEBS.

Disable BL bypass and
direct2core (see MSR
3C9H).

D3H

04H

MEM_LOAD_UOPS_LLC_MISS_
RETIRED.REMOTE_DRAM

Retired load uops which data sources were data
missed LLC but serviced by remote DRAM. Supports
PEBS.

Disable BL bypass and
direct2core (see MSR
3C9H).

OFF_CORE_RESPONSE_N

Sub-events of OFF_CORE_RESPONSE_N (suffix N = 0,
1) programmed using MSR 01A6H/01A7H with values
shown in the comment column.

B7H/BB 01H
H

Event Mask Mnemonic

Description

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_MISS.ANY_RESPONSE_N

Comment

3FFFC00004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_MISS.LOCAL_DRAM_N

600400004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_MISS.REMOTE_DRAM_N

67F800004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_MISS.REMOTE_HIT_FWD_N

87F800004H

OFFCORE_RESPONSE.DEMAND_CODE_RD.LLC_MISS.REMOTE_HITM_N

107FC00004H

OFFCORE_RESPONSE.DEMAND_DATA_RD.LLC_MISS.ANY_DRAM_N

67FC00001H

OFFCORE_RESPONSE.DEMAND_DATA_RD.LLC_MISS.ANY_RESPONSE_N

3F803C0001H

OFFCORE_RESPONSE.DEMAND_DATA_RD.LLC_MISS.LOCAL_DRAM_N

600400001H

OFFCORE_RESPONSE.DEMAND_DATA_RD.LLC_MISS.REMOTE_DRAM_N

67F800001H

OFFCORE_RESPONSE.DEMAND_DATA_RD.LLC_MISS.REMOTE_HIT_FWD_N

87F800001H

OFFCORE_RESPONSE.DEMAND_DATA_RD.LLC_MISS.REMOTE_HITM_N

107FC00001H

OFFCORE_RESPONSE.PF_L2_CODE_RD.LLC_MISS.ANY_RESPONSE_N

3F803C0040H

OFFCORE_RESPONSE.PF_L2_DATA_RD.LLC_MISS.ANY_DRAM_N

67FC00010H

OFFCORE_RESPONSE.PF_L2_DATA_RD.LLC_MISS.ANY_RESPONSE_N

3F803C0010H

OFFCORE_RESPONSE.PF_L2_DATA_RD.LLC_MISS.LOCAL_DRAM_N

600400010H

OFFCORE_RESPONSE.PF_L2_DATA_RD.LLC_MISS.REMOTE_DRAM_N

67F800010H

OFFCORE_RESPONSE.PF_L2_DATA_RD.LLC_MISS.REMOTE_HIT_FWD_N

87F800010H

OFFCORE_RESPONSE.PF_L2_DATA_RD.LLC_MISS.REMOTE_HITM_N

107FC00010H

OFFCORE_RESPONSE.PF_LLC_CODE_RD.LLC_MISS.ANY_RESPONSE_N

3FFFC00200H

OFFCORE_RESPONSE.PF_LLC_DATA_RD.LLC_MISS.ANY_RESPONSE_N

3FFFC00080H

Model-specific performance monitoring events that are located in the uncore sub-system are implementation
specific between different platforms using processors based on Intel microarchitecture code name Sandy Bridge.
Processors with CPUID signature of DisplayFamily_DisplayModel 06_2AH support performance events listed in
Table 19-18.
Vol. 3B 19-79

PERFORMANCE MONITORING EVENTS

Table 19-18. Performance Events In the Processor Uncore for 2nd Generation
Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series
Event
Num.1

Umask
Value

22H

01H

UNC_CBO_XSNP_RESPONSE.M A snoop misses in some processor core.
ISS

22H

02H

UNC_CBO_XSNP_RESPONSE.I
NVAL

22H

04H

UNC_CBO_XSNP_RESPONSE.H A snoop hits a non-modified line in some processor
IT
core.

22H

08H

UNC_CBO_XSNP_RESPONSE.H A snoop hits a modified line in some processor core.
ITM

22H

10H

UNC_CBO_XSNP_RESPONSE.I
NVAL_M

A snoop invalidates a modified line in some processor
core.

22H

20H

UNC_CBO_XSNP_RESPONSE.E
XTERNAL_FILTER

Filter on cross-core snoops initiated by this Cbox due
to external snoop request.

22H

40H

UNC_CBO_XSNP_RESPONSE.X Filter on cross-core snoops initiated by this Cbox due
CORE_FILTER
to processor core memory request.

22H

80H

UNC_CBO_XSNP_RESPONSE.E
VICTION_FILTER

Filter on cross-core snoops initiated by this Cbox due
to LLC eviction.

34H

01H

UNC_CBO_CACHE_LOOKUP.M

34H

02H

UNC_CBO_CACHE_LOOKUP.E

LLC lookup request that access cache and found line in Must combine with
M-state.
one of the umask
LLC lookup request that access cache and found line in values of 10H, 20H,
40H, 80H.
E-state.

34H

04H

UNC_CBO_CACHE_LOOKUP.S

LLC lookup request that access cache and found line in
S-state.

34H

08H

UNC_CBO_CACHE_LOOKUP.I

LLC lookup request that access cache and found line in
I-state.

34H

10H

UNC_CBO_CACHE_LOOKUP.RE
AD_FILTER

Filter on processor core initiated cacheable read
requests. Must combine with at least one of 01H, 02H,
04H, 08H.

34H

20H

UNC_CBO_CACHE_LOOKUP.WR Filter on processor core initiated cacheable write
ITE_FILTER
requests. Must combine with at least one of 01H, 02H,
04H, 08H.

34H

40H

UNC_CBO_CACHE_LOOKUP.EX
TSNP_FILTER

34H

80H

UNC_CBO_CACHE_LOOKUP.AN Filter on any IRQ or IPQ initiated requests including
Y_REQUEST_FILTER
uncacheable, non-coherent requests. Must combine
with at least one of 01H, 02H, 04H, 08H.

80H

01H

UNC_ARB_TRK_OCCUPANCY.A Counts cycles weighted by the number of requests
Counter 0 only.
LL
waiting for data returning from the memory controller.
Accounts for coherent and non-coherent requests
initiated by IA cores, processor graphic units, or LLC.

81H

01H

UNC_ARB_TRK_REQUEST.ALL

Counts the number of coherent and in-coherent
requests initiated by IA cores, processor graphic units,
or LLC.

81H

20H

UNC_ARB_TRK_REQUEST.WRI
TES

Counts the number of allocated write entries, include
full, partial, and LLC evictions.

81H

80H

UNC_ARB_TRK_REQUEST.EVIC Counts the number of LLC evictions allocated.
TIONS

19-80 Vol. 3B

Event Mask Mnemonic

Description

A snoop invalidates a non-modified line in some
processor core.

Comment
Must combine with
one of the umask
values of 20H, 40H,
80H.

Must combine with at
least one of 01H, 02H,
04H, 08H, 10H.

Filter on external snoop requests. Must combine with
at least one of 01H, 02H, 04H, 08H.

PERFORMANCE MONITORING EVENTS

Table 19-18. Performance Events In the Processor Uncore for 2nd Generation
Intel® Core™ i7-2xxx, Intel® Core™ i5-2xxx, Intel® Core™ i3-2xxx Processor Series (Contd.)
Event
Num.1

Umask
Value

Event Mask Mnemonic

Description

Comment

83H

01H

UNC_ARB_COH_TRK_OCCUPA
NCY.ALL

Cycles weighted by number of requests pending in
Coherency Tracker.

Counter 0 only.

84H

01H

UNC_ARB_COH_TRK_REQUES
T.ALL

Number of requests allocated in Coherency Tracker.

NOTES:
1. The uncore events must be programmed using MSRs located in specific performance monitoring units in the uncore. UNC_CBO*
events are supported using MSR_UNC_CBO* MSRs; UNC_ARB* events are supported using MSR_UNC_ARB*MSRs.

19.9

PERFORMANCE MONITORING EVENTS FOR INTEL® CORE™ I7 PROCESSOR
FAMILY AND INTEL® XEON® PROCESSOR FAMILY

Processors based on the Intel microarchitecture code name Nehalem support the architectural and model-specific
performance monitoring events listed in Table 19-1 and Table 19-19. The events in Table 19-19 generally applies to
processors with CPUID signature of DisplayFamily_DisplayModel encoding with the following values: 06_1AH,
06_1EH, 06_1FH, and 06_2EH. However, Intel Xeon processors with CPUID signature of
DisplayFamily_DisplayModel 06_2EH have a small number of events that are not supported in processors with
CPUID signature 06_1AH, 06_1EH, and 06_1FH. These events are noted in the comment column.
In addition, these processors (CPUID signature of DisplayFamily_DisplayModel 06_1AH, 06_1EH, 06_1FH) also
support the following model-specific, product-specific uncore performance monitoring events listed in Table 19-20.
Fixed counters in the core PMU support the architecture events defined in Table 19-2.

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

04H

07H

SB_DRAIN.ANY

Counts the number of store buffer drains.

06H

04H

STORE_BLOCKS.AT_RET

Counts number of loads delayed with at-Retirement
block code. The following loads need to be executed
at retirement and wait for all senior stores on the
same thread to be drained: load splitting across 4K
boundary (page split), load accessing uncacheable
(UC or WC) memory, load lock, and load with page
table in UC or WC memory region.

06H

08H

STORE_BLOCKS.L1D_BLOCK

Cacheable loads delayed with L1D block code.

07H

01H

PARTIAL_ADDRESS_ALIAS

Counts false dependency due to partial address
aliasing.

08H

01H

DTLB_LOAD_MISSES.ANY

Counts all load misses that cause a page walk.

08H

02H

DTLB_LOAD_MISSES.WALK_CO Counts number of completed page walks due to load
MPLETED
miss in the STLB.

08H

10H

DTLB_LOAD_MISSES.STLB_HIT Number of cache load STLB hits.

08H

20H

DTLB_LOAD_MISSES.PDE_MIS
S

08H

80H

DTLB_LOAD_MISSES.LARGE_W Counts number of completed large page walks due
ALK_COMPLETED
to load miss in the STLB.

Comment

Number of DTLB cache load misses where the low
part of the linear to physical address translation
was missed.

Vol. 3B 19-81

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

0BH

01H

MEM_INST_RETIRED.LOADS

Counts the number of instructions with an
architecturally-visible load retired on the
architected path.

0BH

02H

MEM_INST_RETIRED.STORES

Counts the number of instructions with an
architecturally-visible store retired on the
architected path.

0BH

10H

MEM_INST_RETIRED.LATENCY
_ABOVE_THRESHOLD

Counts the number of instructions exceeding the
latency specified with ld_lat facility.

0CH

01H

MEM_STORE_RETIRED.DTLB_
MISS

The event counts the number of retired stores that
missed the DTLB. The DTLB miss is not counted if
the store operation causes a fault. Does not counter
prefetches. Counts both primary and secondary
misses to the TLB.

0EH

01H

UOPS_ISSUED.ANY

Counts the number of Uops issued by the Register
Allocation Table to the Reservation Station, i.e. the
UOPs issued from the front end to the back end.

0EH

01H

UOPS_ISSUED.STALLED_CYCLE Counts the number of cycles no Uops issued by the Set “invert=1, cmask =
S
Register Allocation Table to the Reservation
1“.
Station, i.e. the UOPs issued from the front end to
the back end.

0EH

02H

UOPS_ISSUED.FUSED

Counts the number of fused Uops that were issued
from the Register Allocation Table to the
Reservation Station.

0FH

01H

MEM_UNCORE_RETIRED.L3_D
ATA_MISS_UNKNOWN

Counts number of memory load instructions retired Available only for CPUID
where the memory reference missed L3 and data
signature 06_2EH.
source is unknown.

0FH

02H

MEM_UNCORE_RETIRED.OTHE Counts number of memory load instructions retired
R_CORE_L2_HITM
where the memory reference hit modified data in a
sibling core residing on the same socket.

0FH

08H

MEM_UNCORE_RETIRED.REMO Counts number of memory load instructions retired
TE_CACHE_LOCAL_HOME_HIT where the memory reference missed the L1, L2 and
L3 caches and HIT in a remote socket's cache. Only
counts locally homed lines.

0FH

10H

MEM_UNCORE_RETIRED.REMO Counts number of memory load instructions retired
TE_DRAM
where the memory reference missed the L1, L2 and
L3 caches and was remotely homed. This includes
both DRAM access and HITM in a remote socket's
cache for remotely homed lines.

0FH

20H

MEM_UNCORE_RETIRED.LOCA
L_DRAM

0FH

80H

MEM_UNCORE_RETIRED.UNCA Counts number of memory load instructions retired Available only for CPUID
CHEABLE
where the memory reference missed the L1, L2 and signature 06_2EH.
L3 caches and to perform I/O.

19-82 Vol. 3B

Comment

In conjunction with ld_lat
facility.

Counts number of memory load instructions retired
where the memory reference missed the L1, L2 and
L3 caches and required a local socket memory
reference. This includes locally homed cachelines
that were in a modified state in another socket.

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

10H

01H

FP_COMP_OPS_EXE.X87

Counts the number of FP Computational Uops
Executed. The number of FADD, FSUB, FCOM,
FMULs, integer MULs and IMULs, FDIVs, FPREMs,
FSQRTS, integer DIVs, and IDIVs. This event does
not distinguish an FADD used in the middle of a
transcendental flow from a separate FADD
instruction.

10H

02H

FP_COMP_OPS_EXE.MMX

Counts number of MMX Uops executed.

10H

04H

FP_COMP_OPS_EXE.SSE_FP

Counts number of SSE and SSE2 FP uops executed.

10H

08H

FP_COMP_OPS_EXE.SSE2_INT Counts number of SSE2 integer uops executed.
EGER

10H

10H

FP_COMP_OPS_EXE.SSE_FP_P Counts number of SSE FP packed uops executed.
ACKED

10H

20H

FP_COMP_OPS_EXE.SSE_FP_S Counts number of SSE FP scalar uops executed.
CALAR

10H

40H

FP_COMP_OPS_EXE.SSE_SING Counts number of SSE* FP single precision uops
LE_PRECISION
executed.

10H

80H

FP_COMP_OPS_EXE.SSE_DOU
BLE_PRECISION

Counts number of SSE* FP double precision uops
executed.

12H

01H

SIMD_INT_128.PACKED_MPY

Counts number of 128 bit SIMD integer multiply
operations.

12H

02H

SIMD_INT_128.PACKED_SHIFT Counts number of 128 bit SIMD integer shift
operations.

12H

04H

SIMD_INT_128.PACK

Counts number of 128 bit SIMD integer pack
operations.

12H

08H

SIMD_INT_128.UNPACK

Counts number of 128 bit SIMD integer unpack
operations.

12H

10H

SIMD_INT_128.PACKED_LOGIC Counts number of 128 bit SIMD integer logical
AL
operations.

12H

20H

SIMD_INT_128.PACKED_ARITH Counts number of 128 bit SIMD integer arithmetic
operations.

12H

40H

SIMD_INT_128.SHUFFLE_MOV Counts number of 128 bit SIMD integer shuffle and
E
move operations.

13H

01H

LOAD_DISPATCH.RS

Counts number of loads dispatched from the
Reservation Station that bypass the Memory Order
Buffer.

13H

02H

LOAD_DISPATCH.RS_DELAYED

Counts the number of delayed RS dispatches at the
stage latch. If an RS dispatch cannot bypass to LB, it
has another chance to dispatch from the one-cycle
delayed staging latch before it is written into the
LB.

13H

04H

LOAD_DISPATCH.MOB

Counts the number of loads dispatched from the
Reservation Station to the Memory Order Buffer.

13H

07H

LOAD_DISPATCH.ANY

Counts all loads dispatched from the Reservation
Station.

Comment

Vol. 3B 19-83

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

14H

01H

ARITH.CYCLES_DIV_BUSY

Counts the number of cycles the divider is busy
executing divide or square root operations. The
divide can be integer, X87 or Streaming SIMD
Extensions (SSE). The square root operation can be
either X87 or SSE.

Count may be incorrect
When SMT is on.

Set 'edge =1, invert=1, cmask=1' to count the
number of divides.
14H

02H

ARITH.MUL

Counts the number of multiply operations executed. Count may be incorrect
This includes integer as well as floating point
When SMT is on.
multiply operations but excludes DPPS mul and
MPSAD.

17H

01H

INST_QUEUE_WRITES

Counts the number of instructions written into the
instruction queue every cycle.

18H

01H

INST_DECODED.DEC0

Counts number of instructions that require decoder
0 to be decoded. Usually, this means that the
instruction maps to more than 1 uop.

19H

01H

TWO_UOP_INSTS_DECODED

An instruction that generates two uops was
decoded.

1EH

01H

INST_QUEUE_WRITE_CYCLES

This event counts the number of cycles during
which instructions are written to the instruction
queue. Dividing this counter by the number of
instructions written to the instruction queue
(INST_QUEUE_WRITES) yields the average number
of instructions decoded each cycle. If this number is
less than four and the pipe stalls, this indicates that
the decoder is failing to decode enough instructions
per cycle to sustain the 4-wide pipeline.

20H

01H

LSD_OVERFLOW

Counts number of loops that can’t stream from the
instruction queue.

24H

01H

L2_RQSTS.LD_HIT

Counts number of loads that hit the L2 cache. L2
loads include both L1D demand misses as well as
L1D prefetches. L2 loads can be rejected for various
reasons. Only non rejected loads are counted.

24H

02H

L2_RQSTS.LD_MISS

Counts the number of loads that miss the L2 cache.
L2 loads include both L1D demand misses as well as
L1D prefetches.

24H

03H

L2_RQSTS.LOADS

Counts all L2 load requests. L2 loads include both
L1D demand misses as well as L1D prefetches.

24H

04H

L2_RQSTS.RFO_HIT

Counts the number of store RFO requests that hit
the L2 cache. L2 RFO requests include both L1D
demand RFO misses as well as L1D RFO prefetches.
Count includes WC memory requests, where the
data is not fetched but the permission to write the
line is required.

24H

08H

L2_RQSTS.RFO_MISS

Counts the number of store RFO requests that miss
the L2 cache. L2 RFO requests include both L1D
demand RFO misses as well as L1D RFO prefetches.

19-84 Vol. 3B

If SSE* instructions that
are 6 bytes or longer
arrive one after another,
then front end
throughput may limit
execution speed.

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

24H

0CH

L2_RQSTS.RFOS

Counts all L2 store RFO requests. L2 RFO requests
include both L1D demand RFO misses as well as
L1D RFO prefetches.

24H

10H

L2_RQSTS.IFETCH_HIT

Counts number of instruction fetches that hit the
L2 cache. L2 instruction fetches include both L1I
demand misses as well as L1I instruction
prefetches.

24H

20H

L2_RQSTS.IFETCH_MISS

Counts number of instruction fetches that miss the
L2 cache. L2 instruction fetches include both L1I
demand misses as well as L1I instruction
prefetches.

24H

30H

L2_RQSTS.IFETCHES

Counts all instruction fetches. L2 instruction fetches
include both L1I demand misses as well as L1I
instruction prefetches.

24H

40H

L2_RQSTS.PREFETCH_HIT

Counts L2 prefetch hits for both code and data.

24H

80H

L2_RQSTS.PREFETCH_MISS

Counts L2 prefetch misses for both code and data.

24H

C0H

L2_RQSTS.PREFETCHES

Counts all L2 prefetches for both code and data.

24H

AAH

L2_RQSTS.MISS

Counts all L2 misses for both code and data.

24H

FFH

L2_RQSTS.REFERENCES

Counts all L2 requests for both code and data.

26H

01H

L2_DATA_RQSTS.DEMAND.I_S
TATE

Counts number of L2 data demand loads where the
cache line to be loaded is in the I (invalid) state, i.e., a
cache miss. L2 demand loads are both L1D demand
misses and L1D prefetches.

26H

02H

L2_DATA_RQSTS.DEMAND.S_S Counts number of L2 data demand loads where the
TATE
cache line to be loaded is in the S (shared) state. L2
demand loads are both L1D demand misses and L1D
prefetches.

26H

04H

L2_DATA_RQSTS.DEMAND.E_S Counts number of L2 data demand loads where the
TATE
cache line to be loaded is in the E (exclusive) state.
L2 demand loads are both L1D demand misses and
L1D prefetches.

26H

08H

L2_DATA_RQSTS.DEMAND.M_
STATE

Counts number of L2 data demand loads where the
cache line to be loaded is in the M (modified) state.
L2 demand loads are both L1D demand misses and
L1D prefetches.

26H

0FH

L2_DATA_RQSTS.DEMAND.ME
SI

Counts all L2 data demand requests. L2 demand
loads are both L1D demand misses and L1D
prefetches.

26H

10H

L2_DATA_RQSTS.PREFETCH.I_ Counts number of L2 prefetch data loads where the
STATE
cache line to be loaded is in the I (invalid) state, i.e., a
cache miss.

26H

20H

L2_DATA_RQSTS.PREFETCH.S
_STATE

Counts number of L2 prefetch data loads where the
cache line to be loaded is in the S (shared) state. A
prefetch RFO will miss on an S state line, while a
prefetch read will hit on an S state line.

26H

40H

L2_DATA_RQSTS.PREFETCH.E
_STATE

Counts number of L2 prefetch data loads where the
cache line to be loaded is in the E (exclusive) state.

Comment

Vol. 3B 19-85

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

26H

80H

L2_DATA_RQSTS.PREFETCH.M Counts number of L2 prefetch data loads where the
_STATE
cache line to be loaded is in the M (modified) state.

26H

F0H

L2_DATA_RQSTS.PREFETCH.M Counts all L2 prefetch requests.
ESI

26H

FFH

L2_DATA_RQSTS.ANY

Counts all L2 data requests.

27H

01H

L2_WRITE.RFO.I_STATE

Counts number of L2 demand store RFO requests
This is a demand RFO
where the cache line to be loaded is in the I (invalid) request.
state, i.e., a cache miss. The L1D prefetcher does
not issue a RFO prefetch.

27H

02H

L2_WRITE.RFO.S_STATE

Counts number of L2 store RFO requests where the This is a demand RFO
cache line to be loaded is in the S (shared) state.
request.
The L1D prefetcher does not issue a RFO prefetch.

27H

08H

L2_WRITE.RFO.M_STATE

Counts number of L2 store RFO requests where the This is a demand RFO
cache line to be loaded is in the M (modified) state. request.
The L1D prefetcher does not issue a RFO prefetch.

27H

0EH

L2_WRITE.RFO.HIT

Counts number of L2 store RFO requests where the This is a demand RFO
cache line to be loaded is in either the S, E or M
request.
states. The L1D prefetcher does not issue a RFO
prefetch.

27H

0FH

L2_WRITE.RFO.MESI

Counts all L2 store RFO requests. The L1D
prefetcher does not issue a RFO prefetch.

27H

10H

L2_WRITE.LOCK.I_STATE

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in the I (invalid)
state, for example, a cache miss.

27H

20H

L2_WRITE.LOCK.S_STATE

Counts number of L2 lock RFO requests where the
cache line to be loaded is in the S (shared) state.

27H

40H

L2_WRITE.LOCK.E_STATE

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in the E
(exclusive) state.

27H

80H

L2_WRITE.LOCK.M_STATE

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in the M
(modified) state.

27H

E0H

L2_WRITE.LOCK.HIT

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in either the S,
E, or M state.

27H

F0H

L2_WRITE.LOCK.MESI

Counts all L2 demand lock RFO requests.

28H

01H

L1D_WB_L2.I_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the I (invalid) state,
i.e., a cache miss.

28H

02H

L1D_WB_L2.S_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the S state.

28H

04H

L1D_WB_L2.E_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the E (exclusive)
state.

28H

08H

L1D_WB_L2.M_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the M (modified)
state.

19-86 Vol. 3B

Event Mask Mnemonic

Description

Comment

This is a demand RFO
request.

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

28H

0FH

L1D_WB_L2.MESI

Counts all L1 writebacks to the L2 .

2EH

4FH

L3_LAT_CACHE.REFERENCE

This event counts requests originating from the
See Table 19-1.
core that reference a cache line in the last level
cache. The event count includes speculative traffic
but excludes cache line fills due to a L2 hardwareprefetch. Because cache hierarchy, cache sizes and
other implementation-specific characteristics; value
comparison to estimate performance differences is
not recommended.

2EH

41H

L3_LAT_CACHE.MISS

This event counts each cache miss condition for
references to the last level cache. The event count
may include speculative traffic but excludes cache
line fills due to L2 hardware-prefetches. Because
cache hierarchy, cache sizes and other
implementation-specific characteristics; value
comparison to estimate performance differences is
not recommended.

See Table 19-1.

3CH

00H

CPU_CLK_UNHALTED.THREAD Counts the number of thread cycles while the
_P
thread is not in a halt state. The thread enters the
halt state when it is running the HLT instruction.
The core frequency may change from time to time
due to power or thermal throttling.

See Table 19-1.

3CH

01H

CPU_CLK_UNHALTED.REF_P

Increments at the frequency of TSC when not
halted.

See Table 19-1.

40H

01H

L1D_CACHE_LD.I_STATE

Counts L1 data cache read requests where the
cache line to be loaded is in the I (invalid) state, i.e.
the read request missed the cache.

Counter 0, 1 only.

40H

02H

L1D_CACHE_LD.S_STATE

Counts L1 data cache read requests where the
cache line to be loaded is in the S (shared) state.

Counter 0, 1 only.

40H

04H

L1D_CACHE_LD.E_STATE

Counts L1 data cache read requests where the
cache line to be loaded is in the E (exclusive) state.

Counter 0, 1 only.

40H

08H

L1D_CACHE_LD.M_STATE

Counts L1 data cache read requests where the
cache line to be loaded is in the M (modified) state.

Counter 0, 1 only.

40H

0FH

L1D_CACHE_LD.MESI

Counts L1 data cache read requests.

Counter 0, 1 only.

41H

02H

L1D_CACHE_ST.S_STATE

Counts L1 data cache store RFO requests where the Counter 0, 1 only.
cache line to be loaded is in the S (shared) state.

41H

04H

L1D_CACHE_ST.E_STATE

Counts L1 data cache store RFO requests where the Counter 0, 1 only.
cache line to be loaded is in the E (exclusive) state.

41H

08H

L1D_CACHE_ST.M_STATE

Counts L1 data cache store RFO requests where
cache line to be loaded is in the M (modified) state.

Counter 0, 1 only.

42H

01H

L1D_CACHE_LOCK.HIT

Counts retired load locks that hit in the L1 data
cache or hit in an already allocated fill buffer. The
lock portion of the load lock transaction must hit in
the L1D.

The initial load will pull
the lock into the L1 data
cache. Counter 0, 1 only.

42H

02H

L1D_CACHE_LOCK.S_STATE

Counts L1 data cache retired load locks that hit the
target cache line in the shared state.

Counter 0, 1 only.

42H

04H

L1D_CACHE_LOCK.E_STATE

Counts L1 data cache retired load locks that hit the
target cache line in the exclusive state.

Counter 0, 1 only.

Comment

Vol. 3B 19-87

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

42H

08H

L1D_CACHE_LOCK.M_STATE

Counts L1 data cache retired load locks that hit the
target cache line in the modified state.

Counter 0, 1 only.

43H

01H

L1D_ALL_REF.ANY

Counts all references (uncached, speculated and
retired) to the L1 data cache, including all loads and
stores with any memory types. The event counts
memory accesses only when they are actually
performed. For example, a load blocked by unknown
store address and later performed is only counted
once.

The event does not
include non-memory
accesses, such as I/O
accesses. Counter 0, 1
only.

43H

02H

L1D_ALL_REF.CACHEABLE

Counts all data reads and writes (speculated and
retired) from cacheable memory, including locked
operations.

Counter 0, 1 only.

49H

01H

DTLB_MISSES.ANY

Counts the number of misses in the STLB which
causes a page walk.

49H

02H

DTLB_MISSES.WALK_COMPLET Counts number of misses in the STLB which
ED
resulted in a completed page walk.

49H

10H

DTLB_MISSES.STLB_HIT

Counts the number of DTLB first level misses that
hit in the second level TLB. This event is only
relevant if the core contains multiple DTLB levels.

49H

20H

DTLB_MISSES.PDE_MISS

Number of DTLB misses caused by low part of
address, includes references to 2M pages because
2M pages do not use the PDE.

49H

80H

DTLB_MISSES.LARGE_WALK_C Counts number of misses in the STLB which
OMPLETED
resulted in a completed page walk for large pages.

4CH

01H

LOAD_HIT_PRE

Counts load operations sent to the L1 data cache
while a previous SSE prefetch instruction to the
same cache line has started prefetching but has not
yet finished.

4EH

01H

L1D_PREFETCH.REQUESTS

Counts number of hardware prefetch requests
dispatched out of the prefetch FIFO.

4EH

02H

L1D_PREFETCH.MISS

Counts number of hardware prefetch requests that
miss the L1D. There are two prefetchers in the L1D.
A streamer, which predicts lines sequentially after
this one should be fetched, and the IP prefetcher
that remembers access patterns for the current
instruction. The streamer prefetcher stops on an
L1D hit, while the IP prefetcher does not.

4EH

04H

L1D_PREFETCH.TRIGGERS

Counts number of prefetch requests triggered by
the Finite State Machine and pushed into the
prefetch FIFO. Some of the prefetch requests are
dropped due to overwrites or competition between
the IP index prefetcher and streamer prefetcher.
The prefetch FIFO contains 4 entries.

51H

01H

L1D.REPL

Counts the number of lines brought into the L1 data Counter 0, 1 only.
cache.

51H

02H

L1D.M_REPL

Counts the number of modified lines brought into
the L1 data cache.

Counter 0, 1 only.

51H

04H

L1D.M_EVICT

Counts the number of modified lines evicted from
the L1 data cache due to replacement.

Counter 0, 1 only.

19-88 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

51H

08H

L1D.M_SNOOP_EVICT

Counts the number of modified lines evicted from
the L1 data cache due to snoop HITM intervention.

Counter 0, 1 only.

52H

01H

L1D_CACHE_PREFETCH_LOCK
_FB_HIT

Counts the number of cacheable load lock
speculated instructions accepted into the fill buffer.

53H

01H

L1D_CACHE_LOCK_FB_HIT

Counts the number of cacheable load lock
speculated or retired instructions accepted into the
fill buffer.

63H

01H

CACHE_LOCK_CYCLES.L1D_L2

Cycle count during which the L1D and L2 are locked.
A lock is asserted when there is a locked memory
access, due to uncacheable memory, a locked
operation that spans two cache lines, or a page walk
from an uncacheable page table.

Counter 0, 1 only. L1D
and L2 locks have a very
high performance
penalty and it is highly
recommended to avoid
such accesses.

63H

02H

CACHE_LOCK_CYCLES.L1D

Counts the number of cycles that cacheline in the
L1 data cache unit is locked.

Counter 0, 1 only.

6CH

01H

IO_TRANSACTIONS

Counts the number of completed I/O transactions.

80H

01H

L1I.HITS

Counts all instruction fetches that hit the L1
instruction cache.

80H

02H

L1I.MISSES

Counts all instruction fetches that miss the L1I
cache. This includes instruction cache misses,
streaming buffer misses, victim cache misses and
uncacheable fetches. An instruction fetch miss is
counted only once and not once for every cycle it is
outstanding.

80H

03H

L1I.READS

Counts all instruction fetches, including uncacheable
fetches that bypass the L1I.

80H

04H

L1I.CYCLES_STALLED

Cycle counts for which an instruction fetch stalls
due to a L1I cache miss, ITLB miss or ITLB fault.

82H

01H

LARGE_ITLB.HIT

Counts number of large ITLB hits.

85H

01H

ITLB_MISSES.ANY

Counts the number of misses in all levels of the ITLB
which causes a page walk.

85H

02H

ITLB_MISSES.WALK_COMPLET
ED

Counts number of misses in all levels of the ITLB
which resulted in a completed page walk.

87H

01H

ILD_STALL.LCP

Cycles Instruction Length Decoder stalls due to
length changing prefixes: 66, 67 or REX.W (for Intel
64) instructions which change the length of the
decoded instruction.

87H

02H

ILD_STALL.MRU

Instruction Length Decoder stall cycles due to Brand
Prediction Unit (PBU) Most Recently Used (MRU)
bypass.

87H

04H

ILD_STALL.IQ_FULL

Stall cycles due to a full instruction queue.

87H

08H

ILD_STALL.REGEN

Counts the number of regen stalls.

87H

0FH

ILD_STALL.ANY

Counts any cycles the Instruction Length Decoder is
stalled.

88H

01H

BR_INST_EXEC.COND

Counts the number of conditional near branch
instructions executed, but not necessarily retired.

Vol. 3B 19-89

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

88H

02H

BR_INST_EXEC.DIRECT

Counts all unconditional near branch instructions
excluding calls and indirect branches.

88H

04H

BR_INST_EXEC.INDIRECT_NON Counts the number of executed indirect near
_CALL
branch instructions that are not calls.

88H

07H

BR_INST_EXEC.NON_CALLS

Counts all non-call near branch instructions
executed, but not necessarily retired.

88H

08H

BR_INST_EXEC.RETURN_NEA
R

Counts indirect near branches that have a return
mnemonic.

88H

10H

BR_INST_EXEC.DIRECT_NEAR
_CALL

Counts unconditional near call branch instructions,
excluding non-call branch, executed.

88H

20H

BR_INST_EXEC.INDIRECT_NEA Counts indirect near calls, including both register
R_CALL
and memory indirect, executed.

88H

30H

BR_INST_EXEC.NEAR_CALLS

Counts all near call branches executed, but not
necessarily retired.

88H

40H

BR_INST_EXEC.TAKEN

Counts taken near branches executed, but not
necessarily retired.

88H

7FH

BR_INST_EXEC.ANY

Counts all near executed branches (not necessarily
retired). This includes only instructions and not
micro-op branches. Frequent branching is not
necessarily a major performance issue. However
frequent branch mispredictions may be a problem.

89H

01H

BR_MISP_EXEC.COND

Counts the number of mispredicted conditional near
branch instructions executed, but not necessarily
retired.

89H

02H

BR_MISP_EXEC.DIRECT

Counts mispredicted macro unconditional near
branch instructions, excluding calls and indirect
branches (should always be 0).

89H

04H

BR_MISP_EXEC.INDIRECT_NO
N_CALL

Counts the number of executed mispredicted
indirect near branch instructions that are not calls.

89H

07H

BR_MISP_EXEC.NON_CALLS

Counts mispredicted non-call near branches
executed, but not necessarily retired.

89H

08H

BR_MISP_EXEC.RETURN_NEA
R

Counts mispredicted indirect branches that have a
rear return mnemonic.

89H

10H

BR_MISP_EXEC.DIRECT_NEAR
_CALL

Counts mispredicted non-indirect near calls
executed, (should always be 0).

89H

20H

BR_MISP_EXEC.INDIRECT_NEA Counts mispredicted indirect near calls executed,
R_CALL
including both register and memory indirect.

89H

30H

BR_MISP_EXEC.NEAR_CALLS

Counts all mispredicted near call branches executed,
but not necessarily retired.

89H

40H

BR_MISP_EXEC.TAKEN

Counts executed mispredicted near branches that
are taken, but not necessarily retired.

89H

7FH

BR_MISP_EXEC.ANY

Counts the number of mispredicted near branch
instructions that were executed, but not
necessarily retired.

19-90 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

A2H

01H

RESOURCE_STALLS.ANY

Counts the number of Allocator resource related
stalls. Includes register renaming buffer entries,
memory buffer entries. In addition to resource
related stalls, this event counts some other events.
Includes stalls arising during branch misprediction
recovery, such as if retirement of the mispredicted
branch is delayed and stalls arising while store
buffer is draining from synchronizing operations.

Does not include stalls
due to SuperQ (off core)
queue full, too many
cache misses, etc.

A2H

02H

RESOURCE_STALLS.LOAD

Counts the cycles of stall due to lack of load buffer
for load operation.

A2H

04H

RESOURCE_STALLS.RS_FULL

This event counts the number of cycles when the
number of instructions in the pipeline waiting for
execution reaches the limit the processor can
handle. A high count of this event indicates that
there are long latency operations in the pipe
(possibly load and store operations that miss the L2
cache, or instructions dependent upon instructions
further down the pipeline that have yet to retire.

A2H

08H

RESOURCE_STALLS.STORE

This event counts the number of cycles that a
resource related stall will occur due to the number
of store instructions reaching the limit of the
pipeline, (i.e. all store buffers are used). The stall
ends when a store instruction commits its data to
the cache or memory.

A2H

10H

RESOURCE_STALLS.ROB_FULL Counts the cycles of stall due to re-order buffer full.

A2H

20H

RESOURCE_STALLS.FPCW

Counts the number of cycles while execution was
stalled due to writing the floating-point unit (FPU)
control word.

A2H

40H

RESOURCE_STALLS.MXCSR

Stalls due to the MXCSR register rename occurring
to close to a previous MXCSR rename. The MXCSR
provides control and status for the MMX registers.

A2H

80H

RESOURCE_STALLS.OTHER

Counts the number of cycles while execution was
stalled due to other resource issues.

A6H

01H

MACRO_INSTS.FUSIONS_DECO Counts the number of instructions decoded that are
DED
macro-fused but not necessarily executed or
retired.

A7H

01H

BACLEAR_FORCE_IQ

Counts number of times a BACLEAR was forced by
the Instruction Queue. The IQ is also responsible for
providing conditional branch prediction direction
based on a static scheme and dynamic data
provided by the L2 Branch Prediction Unit. If the
conditional branch target is not found in the Target
Array and the IQ predicts that the branch is taken,
then the IQ will force the Branch Address Calculator
to issue a BACLEAR. Each BACLEAR asserted by the
BAC generates approximately an 8 cycle bubble in
the instruction fetch pipeline.

A8H

01H

LSD.UOPS

Counts the number of micro-ops delivered by loop
stream detector.

AEH

01H

ITLB_FLUSH

Counts the number of ITLB flushes.

When RS is full, new
instructions cannot enter
the reservation station
and start execution.

Use cmask=1 and invert
to count cycles.

Vol. 3B 19-91

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

B0H

40H

OFFCORE_REQUESTS.L1D_WR Counts number of L1D writebacks to the uncore.
ITEBACK

B1H

01H

UOPS_EXECUTED.PORT0

Counts number of uops executed that were issued
on port 0. Port 0 handles integer arithmetic, SIMD
and FP add uops.

B1H

02H

UOPS_EXECUTED.PORT1

Counts number of uops executed that were issued
on port 1. Port 1 handles integer arithmetic, SIMD,
integer shift, FP multiply and FP divide uops.

B1H

04H

UOPS_EXECUTED.PORT2_COR Counts number of uops executed that were issued
E
on port 2. Port 2 handles the load uops. This is a
core count only and cannot be collected per thread.

B1H

08H

UOPS_EXECUTED.PORT3_COR Counts number of uops executed that were issued
E
on port 3. Port 3 handles store uops. This is a core
count only and cannot be collected per thread.

B1H

10H

UOPS_EXECUTED.PORT4_COR Counts number of uops executed that where issued
E
on port 4. Port 4 handles the value to be stored for
the store uops issued on port 3. This is a core count
only and cannot be collected per thread.

B1H

1FH

UOPS_EXECUTED.CORE_ACTIV Counts cycles when the uops executed were issued
E_CYCLES_NO_PORT5
from any ports except port 5. Use Cmask=1 for
active cycles; Cmask=0 for weighted cycles. Use
CMask=1, Invert=1 to count P0-4 stalled cycles. Use
Cmask=1, Edge=1, Invert=1 to count P0-4 stalls.

B1H

20H

UOPS_EXECUTED.PORT5

B1H

3FH

UOPS_EXECUTED.CORE_ACTIV Counts cycles when the uops are executing. Use
E_CYCLES
Cmask=1 for active cycles; Cmask=0 for weighted
cycles. Use CMask=1, Invert=1 to count P0-4 stalled
cycles. Use Cmask=1, Edge=1, Invert=1 to count P04 stalls.

B1H

40H

UOPS_EXECUTED.PORT015

Counts number of uops executed that where issued Use cmask=1, invert=1
on port 0, 1, or 5.
to count stall cycles.

B1H

80H

UOPS_EXECUTED.PORT234

Counts number of uops executed that where issued
on port 2, 3, or 4.

B2H

01H

OFFCORE_REQUESTS_SQ_FUL Counts number of cycles the SQ is full to handle offL
core requests.

B7H

01H

OFF_CORE_RESPONSE_0

See Section 18.3.1.1.3, “Off-core Response
Performance Monitoring in the Processor Core”.

B8H

01H

SNOOP_RESPONSE.HIT

Counts HIT snoop response sent by this thread in
response to a snoop request.

B8H

02H

SNOOP_RESPONSE.HITE

Counts HIT E snoop response sent by this thread in
response to a snoop request.

B8H

04H

SNOOP_RESPONSE.HITM

Counts HIT M snoop response sent by this thread in
response to a snoop request.

BBH

01H

OFF_CORE_RESPONSE_1

See Section 18.6.3, “Performance Monitoring
(Processors Based on Intel NetBurst®
Microarchitecture)”.

19-92 Vol. 3B

Event Mask Mnemonic

Description

Comment

Counts number of uops executed that where issued
on port 5.

Requires programming
MSR 01A6H.

Requires programming
MSR 01A7H.

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

C0H

00H

INST_RETIRED.ANY_P

See Table 19-1.

Counting: Faulting
executions of
GETSEC/VM entry/VM
Exit/MWait will not count
as retired instructions.

Notes: INST_RETIRED.ANY is counted by a
designated fixed counter. INST_RETIRED.ANY_P is
counted by a programmable counter and is an
architectural performance event. Event is
supported if CPUID.A.EBX[1] = 0.
C0H

02H

INST_RETIRED.X87

Counts the number of MMX instructions retired.

C0H

04H

INST_RETIRED.MMX

Counts the number of floating point computational
operations retired: floating point computational
operations executed by the assist handler and suboperations of complex floating point instructions
like transcendental instructions.

C2H

01H

UOPS_RETIRED.ANY

Counts the number of micro-ops retired, (macroUse cmask=1 and invert
fused=1, micro-fused=2, others=1; maximum count to count active cycles or
of 8 per cycle). Most instructions are composed of
stalled cycles.
one or two micro-ops. Some instructions are
decoded into longer sequences such as repeat
instructions, floating point transcendental
instructions, and assists.

C2H

02H

UOPS_RETIRED.RETIRE_SLOTS Counts the number of retirement slots used each
cycle.

C2H

04H

UOPS_RETIRED.MACRO_FUSE
D

Counts number of macro-fused uops retired.

C3H

01H

MACHINE_CLEARS.CYCLES

Counts the cycles machine clear is asserted.

C3H

02H

MACHINE_CLEARS.MEM_ORDE Counts the number of machine clears due to
R
memory order conflicts.

C3H

04H

MACHINE_CLEARS.SMC

Counts the number of times that a program writes
to a code section. Self-modifying code causes a
severe penalty in all Intel 64 and IA-32 processors.
The modified cache line is written back to the L2
and L3caches.

C4H

00H

BR_INST_RETIRED.ALL_BRAN
CHES

Branch instructions at retirement.

C4H

01H

BR_INST_RETIRED.CONDITION Counts the number of conditional branch
AL
instructions retired.

C4H

02H

BR_INST_RETIRED.NEAR_CAL
L

Counts the number of direct & indirect near
unconditional calls retired.

C5H

00H

BR_MISP_RETIRED.ALL_BRAN
CHES

Mispredicted branch instructions at retirement.

C5H

02H

BR_MISP_RETIRED.NEAR_CAL
L

Counts mispredicted direct & indirect near
unconditional retired calls.

C7H

01H

SSEX_UOPS_RETIRED.PACKED Counts SIMD packed single-precision floating point
_SINGLE
Uops retired.

C7H

02H

SSEX_UOPS_RETIRED.SCALAR Counts SIMD scalar single-precision floating point
_SINGLE
Uops retired.

C7H

04H

SSEX_UOPS_RETIRED.PACKED Counts SIMD packed double-precision floating point
_DOUBLE
Uops retired.

See Table 19-1.

See Table 19-1.

Vol. 3B 19-93

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

C7H

08H

SSEX_UOPS_RETIRED.SCALAR Counts SIMD scalar double-precision floating point
_DOUBLE
Uops retired.

C7H

10H

SSEX_UOPS_RETIRED.VECTOR Counts 128-bit SIMD vector integer Uops retired.
_INTEGER

C8H

20H

ITLB_MISS_RETIRED

CBH

01H

MEM_LOAD_RETIRED.L1D_HIT Counts number of retired loads that hit the L1 data
cache.

CBH

02H

MEM_LOAD_RETIRED.L2_HIT

Counts number of retired loads that hit the L2 data
cache.

CBH

04H

MEM_LOAD_RETIRED.L3_UNS
HARED_HIT

Counts number of retired loads that hit their own,
unshared lines in the L3 cache.

CBH

08H

MEM_LOAD_RETIRED.OTHER_
CORE_L2_HIT_HITM

Counts number of retired loads that hit in a sibling
core's L2 (on die core). Since the L3 is inclusive of all
cores on the package, this is an L3 hit. This counts
both clean and modified hits.

CBH

10H

MEM_LOAD_RETIRED.L3_MISS Counts number of retired loads that miss the L3
cache. The load was satisfied by a remote socket,
local memory or an IOH.

CBH

40H

MEM_LOAD_RETIRED.HIT_LFB Counts number of retired loads that miss the L1D
and the address is located in an allocated line fill
buffer and will soon be committed to cache. This is
counting secondary L1D misses.

CBH

80H

MEM_LOAD_RETIRED.DTLB_MI Counts the number of retired loads that missed the
SS
DTLB. The DTLB miss is not counted if the load
operation causes a fault. This event counts loads
from cacheable memory only. The event does not
count loads by software prefetches. Counts both
primary and secondary misses to the TLB.

CCH

01H

FP_MMX_TRANS.TO_FP

Counts the first floating-point instruction following
any MMX instruction. You can use this event to
estimate the penalties for the transitions between
floating-point and MMX technology states.

CCH

02H

FP_MMX_TRANS.TO_MMX

Counts the first MMX instruction following a
floating-point instruction. You can use this event to
estimate the penalties for the transitions between
floating-point and MMX technology states.

CCH

03H

FP_MMX_TRANS.ANY

Counts all transitions from floating point to MMX
instructions and from MMX instructions to floating
point instructions. You can use this event to
estimate the penalties for the transitions between
floating-point and MMX technology states.

D0H

01H

MACRO_INSTS.DECODED

Counts the number of instructions decoded, (but
not necessarily executed or retired).

D1H

02H

UOPS_DECODED.MS

Counts the number of Uops decoded by the
Microcode Sequencer, MS. The MS delivers uops
when the instruction is more than 4 uops long or a
microcode assist is occurring.

19-94 Vol. 3B

Event Mask Mnemonic

Description

Counts the number of retired instructions that
missed the ITLB when the instruction was fetched.

Comment

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

D1H

04H

UOPS_DECODED.ESP_FOLDING Counts number of stack pointer (ESP) instructions
decoded: push, pop, call, ret, etc. ESP instructions do
not generate a Uop to increment or decrement ESP.
Instead, they update an ESP_Offset register that
keeps track of the delta to the current value of the
ESP register.

D1H

08H

UOPS_DECODED.ESP_SYNC

Counts number of stack pointer (ESP) sync
operations where an ESP instruction is corrected by
adding the ESP offset register to the current value
of the ESP register.

D2H

01H

RAT_STALLS.FLAGS

Counts the number of cycles during which
execution stalled due to several reasons, one of
which is a partial flag register stall. A partial register
stall may occur when two conditions are met: 1) an
instruction modifies some, but not all, of the flags in
the flag register and 2) the next instruction, which
depends on flags, depends on flags that were not
modified by this instruction.

D2H

02H

RAT_STALLS.REGISTERS

This event counts the number of cycles instruction
execution latency became longer than the defined
latency because the instruction used a register that
was partially written by previous instruction.

D2H

04H

RAT_STALLS.ROB_READ_POR
T

Counts the number of cycles when ROB read port
stalls occurred, which did not allow new micro-ops
to enter the out-of-order pipeline. Note that, at this
stage in the pipeline, additional stalls may occur at
the same cycle and prevent the stalled micro-ops
from entering the pipe. In such a case, micro-ops
retry entering the execution pipe in the next cycle
and the ROB-read port stall is counted again.

D2H

08H

RAT_STALLS.SCOREBOARD

Counts the cycles where we stall due to
microarchitecturally required serialization.
Microcode scoreboarding stalls.

D2H

0FH

RAT_STALLS.ANY

Counts all Register Allocation Table stall cycles due
to: Cycles when ROB read port stalls occurred,
which did not allow new micro-ops to enter the
execution pipe. Cycles when partial register stalls
occurred. Cycles when flag stalls occurred. Cycles
floating-point unit (FPU) status word stalls occurred.
To count each of these conditions separately use
the events: RAT_STALLS.ROB_READ_PORT,
RAT_STALLS.PARTIAL, RAT_STALLS.FLAGS, and
RAT_STALLS.FPSW.

D4H

01H

SEG_RENAME_STALLS

Counts the number of stall cycles due to the lack of
renaming resources for the ES, DS, FS, and GS
segment registers. If a segment is renamed but not
retired and a second update to the same segment
occurs, a stall occurs in the front end of the pipeline
until the renamed segment retires.

D5H

01H

ES_REG_RENAMES

Counts the number of times the ES segment
register is renamed.

Event Mask Mnemonic

Description

Comment

Vol. 3B 19-95

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

DBH

01H

UOP_UNFUSION

Counts unfusion events due to floating-point
exception to a fused uop.

E0H

01H

BR_INST_DECODED

Counts the number of branch instructions decoded.

E5H

01H

BPU_MISSED_CALL_RET

Counts number of times the Branch Prediction Unit
missed predicting a call or return branch.

E6H

01H

BACLEAR.CLEAR

Counts the number of times the front end is
resteered, mainly when the Branch Prediction Unit
cannot provide a correct prediction and this is
corrected by the Branch Address Calculator at the
front end. This can occur if the code has many
branches such that they cannot be consumed by
the BPU. Each BACLEAR asserted by the BAC
generates approximately an 8 cycle bubble in the
instruction fetch pipeline. The effect on total
execution time depends on the surrounding code.

E6H

02H

BACLEAR.BAD_TARGET

Counts number of Branch Address Calculator clears
(BACLEAR) asserted due to conditional branch
instructions in which there was a target hit but the
direction was wrong. Each BACLEAR asserted by
the BAC generates approximately an 8 cycle bubble
in the instruction fetch pipeline.

E8H

01H

BPU_CLEARS.EARLY

Counts early (normal) Branch Prediction Unit clears: The BPU clear leads to 2
BPU predicted a taken branch after incorrectly
cycle bubble in the front
assuming that it was not taken.
end.

E8H

02H

BPU_CLEARS.LATE

Counts late Branch Prediction Unit clears due to
Most Recently Used conflicts. The PBU clear leads
to a 3 cycle bubble in the front end.

F0H

01H

L2_TRANSACTIONS.LOAD

Counts L2 load operations due to HW prefetch or
demand loads.

F0H

02H

L2_TRANSACTIONS.RFO

Counts L2 RFO operations due to HW prefetch or
demand RFOs.

F0H

04H

L2_TRANSACTIONS.IFETCH

Counts L2 instruction fetch operations due to HW
prefetch or demand ifetch.

F0H

08H

L2_TRANSACTIONS.PREFETCH Counts L2 prefetch operations.

F0H

10H

L2_TRANSACTIONS.L1D_WB

Counts L1D writeback operations to the L2.

F0H

20H

L2_TRANSACTIONS.FILL

Counts L2 cache line fill operations due to load, RFO,
L1D writeback or prefetch.

F0H

40H

L2_TRANSACTIONS.WB

Counts L2 writeback operations to the L3.

F0H

80H

L2_TRANSACTIONS.ANY

Counts all L2 cache operations.

F1H

02H

L2_LINES_IN.S_STATE

Counts the number of cache lines allocated in the
L2 cache in the S (shared) state.

F1H

04H

L2_LINES_IN.E_STATE

Counts the number of cache lines allocated in the
L2 cache in the E (exclusive) state.

F1H

07H

L2_LINES_IN.ANY

Counts the number of cache lines allocated in the
L2 cache.

F2H

01H

L2_LINES_OUT.DEMAND_CLEA Counts L2 clean cache lines evicted by a demand
N
request.

19-96 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-19. Performance Events In the Processor Core for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

F2H

02H

L2_LINES_OUT.DEMAND_DIRT Counts L2 dirty (modified) cache lines evicted by a
Y
demand request.

F2H

04H

L2_LINES_OUT.PREFETCH_CLE Counts L2 clean cache line evicted by a prefetch
AN
request.

F2H

08H

L2_LINES_OUT.PREFETCH_DIR Counts L2 modified cache line evicted by a prefetch
TY
request.

F2H

0FH

L2_LINES_OUT.ANY

Counts all L2 cache lines evicted for any reason.

F4H

10H

SQ_MISC.SPLIT_LOCK

Counts the number of SQ lock splits across a cache
line.

F6H

01H

SQ_FULL_STALL_CYCLES

Counts cycles the Super Queue is full. Neither of the
threads on this core will be able to access the
uncore.

F7H

01H

FP_ASSIST.ALL

Counts the number of floating point operations
executed that required micro-code assist
intervention. Assists are required in the following
cases: SSE instructions (denormal input when the
DAZ flag is off or underflow result when the FTZ
flag is off); x87 instructions (NaN or denormal are
loaded to a register or used as input from memory,
division by 0 or underflow output).

F7H

02H

FP_ASSIST.OUTPUT

Counts number of floating point micro-code assist
when the output value (destination register) is
invalid.

F7H

04H

FP_ASSIST.INPUT

Counts number of floating point micro-code assist
when the input value (one of the source operands
to an FP instruction) is invalid.

FDH

01H

SIMD_INT_64.PACKED_MPY

Counts number of SID integer 64 bit packed multiply
operations.

FDH

02H

SIMD_INT_64.PACKED_SHIFT

Counts number of SID integer 64 bit packed shift
operations.

FDH

04H

SIMD_INT_64.PACK

Counts number of SID integer 64 bit pack
operations.

FDH

08H

SIMD_INT_64.UNPACK

Counts number of SID integer 64 bit unpack
operations.

FDH

10H

SIMD_INT_64.PACKED_LOGICA Counts number of SID integer 64 bit logical
L
operations.

FDH

20H

SIMD_INT_64.PACKED_ARITH

FDH

40H

SIMD_INT_64.SHUFFLE_MOVE Counts number of SID integer 64 bit shift or move
operations.

Event Mask Mnemonic

Description

Comment

Counts number of SID integer 64 bit arithmetic
operations.

Model-specific performance monitoring events that are located in the uncore sub-system are implementation
specific between different platforms using processors based on Intel microarchitecture code name Nehalem.
Processors with CPUID signature of DisplayFamily_DisplayModel 06_1AH, 06_1EH, and 06_1FH support performance events listed in Table 19-20.

Vol. 3B 19-97

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series
Event
Num.

Umask
Value

00H

01H

UNC_GQ_CYCLES_FULL.READ_ Uncore cycles Global Queue read tracker is full.
TRACKER

00H

02H

UNC_GQ_CYCLES_FULL.WRITE Uncore cycles Global Queue write tracker is full.
_TRACKER

00H

04H

UNC_GQ_CYCLES_FULL.PEER_ Uncore cycles Global Queue peer probe tracker is full.
PROBE_TRACKER
The peer probe tracker queue tracks snoops from the
IOH and remote sockets.

01H

01H

UNC_GQ_CYCLES_NOT_EMPTY Uncore cycles were Global Queue read tracker has at
.READ_TRACKER
least one valid entry.

01H

02H

UNC_GQ_CYCLES_NOT_EMPTY Uncore cycles were Global Queue write tracker has at
.WRITE_TRACKER
least one valid entry.

01H

04H

UNC_GQ_CYCLES_NOT_EMPTY Uncore cycles were Global Queue peer probe tracker
.PEER_PROBE_TRACKER
has at least one valid entry. The peer probe tracker
queue tracks IOH and remote socket snoops.

03H

01H

UNC_GQ_ALLOC.READ_TRACK Counts the number of tread tracker allocate to
ER
deallocate entries. The GQ read tracker allocate to
deallocate occupancy count is divided by the count to
obtain the average read tracker latency.

03H

02H

UNC_GQ_ALLOC.RT_L3_MISS

03H

04H

UNC_GQ_ALLOC.RT_TO_L3_RE Counts the number of GQ read tracker entries that are
SP
allocated in the read tracker queue that hit or miss the
L3. The GQ read tracker L3 hit occupancy count is
divided by this count to obtain the average L3 hit
latency.

03H

08H

UNC_GQ_ALLOC.RT_TO_RTID_ Counts the number of GQ read tracker entries that are
ACQUIRED
allocated in the read tracker, have missed in the L3
and have not acquired a Request Transaction ID. The
GQ read tracker L3 miss to RTID acquired occupancy
count is divided by this count to obtain the average
latency for a read L3 miss to acquire an RTID.

03H

10H

UNC_GQ_ALLOC.WT_TO_RTID
_ACQUIRED

Counts the number of GQ write tracker entries that
are allocated in the write tracker, have missed in the
L3 and have not acquired a Request Transaction ID.
The GQ write tracker L3 miss to RTID occupancy count
is divided by this count to obtain the average latency
for a write L3 miss to acquire an RTID.

03H

20H

UNC_GQ_ALLOC.WRITE_TRAC
KER

Counts the number of GQ write tracker entries that
are allocated in the write tracker queue that miss the
L3. The GQ write tracker occupancy count is divided by
this count to obtain the average L3 write miss latency.

19-98 Vol. 3B

Event Mask Mnemonic

Description

Counts the number GQ read tracker entries for which a
full cache line read has missed the L3. The GQ read
tracker L3 miss to fill occupancy count is divided by
this count to obtain the average cache line read L3
miss latency. The latency represents the time after
which the L3 has determined that the cache line has
missed. The time between a GQ read tracker allocation
and the L3 determining that the cache line has missed
is the average L3 hit latency. The total L3 cache line
read miss latency is the hit latency + L3 miss latency.

Comment

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

03H

40H

UNC_GQ_ALLOC.PEER_PROBE
_TRACKER

Counts the number of GQ peer probe tracker (snoop)
entries that are allocated in the peer probe tracker
queue that miss the L3. The GQ peer probe occupancy
count is divided by this count to obtain the average L3
peer probe miss latency.

04H

01H

UNC_GQ_DATA.FROM_QPI

Cycles Global Queue Quickpath Interface input data
port is busy importing data from the Quickpath
Interface. Each cycle the input port can transfer 8 or
16 bytes of data.

04H

02H

UNC_GQ_DATA.FROM_QMC

Cycles Global Queue Quickpath Memory Interface input
data port is busy importing data from the Quickpath
Memory Interface. Each cycle the input port can
transfer 8 or 16 bytes of data.

04H

04H

UNC_GQ_DATA.FROM_L3

Cycles GQ L3 input data port is busy importing data
from the Last Level Cache. Each cycle the input port
can transfer 32 bytes of data.

04H

08H

UNC_GQ_DATA.FROM_CORES_ Cycles GQ Core 0 and 2 input data port is busy
02
importing data from processor cores 0 and 2. Each
cycle the input port can transfer 32 bytes of data.

04H

10H

UNC_GQ_DATA.FROM_CORES_ Cycles GQ Core 1 and 3 input data port is busy
13
importing data from processor cores 1 and 3. Each
cycle the input port can transfer 32 bytes of data.

05H

01H

UNC_GQ_DATA.TO_QPI_QMC

Cycles GQ QPI and QMC output data port is busy
sending data to the Quickpath Interface or Quickpath
Memory Interface. Each cycle the output port can
transfer 32 bytes of data.

05H

02H

UNC_GQ_DATA.TO_L3

Cycles GQ L3 output data port is busy sending data to
the Last Level Cache. Each cycle the output port can
transfer 32 bytes of data.

05H

04H

UNC_GQ_DATA.TO_CORES

Cycles GQ Core output data port is busy sending data
to the Cores. Each cycle the output port can transfer
32 bytes of data.

06H

01H

UNC_SNP_RESP_TO_LOCAL_H Number of snoop responses to the local home that L3
OME.I_STATE
does not have the referenced cache line.

06H

02H

UNC_SNP_RESP_TO_LOCAL_H Number of snoop responses to the local home that L3
OME.S_STATE
has the referenced line cached in the S state.

06H

04H

UNC_SNP_RESP_TO_LOCAL_H Number of responses to code or data read snoops to
OME.FWD_S_STATE
the local home that the L3 has the referenced cache
line in the E state. The L3 cache line state is changed
to the S state and the line is forwarded to the local
home in the S state.

06H

08H

UNC_SNP_RESP_TO_LOCAL_H Number of responses to read invalidate snoops to the
OME.FWD_I_STATE
local home that the L3 has the referenced cache line in
the M state. The L3 cache line state is invalidated and
the line is forwarded to the local home in the M state.

06H

10H

UNC_SNP_RESP_TO_LOCAL_H Number of conflict snoop responses sent to the local
OME.CONFLICT
home.

Comment

Vol. 3B 19-99

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

06H

20H

UNC_SNP_RESP_TO_LOCAL_H Number of responses to code or data read snoops to
OME.WB
the local home that the L3 has the referenced line
cached in the M state.

07H

01H

UNC_SNP_RESP_TO_REMOTE
_HOME.I_STATE

Number of snoop responses to a remote home that L3
does not have the referenced cache line.

07H

02H

UNC_SNP_RESP_TO_REMOTE
_HOME.S_STATE

Number of snoop responses to a remote home that L3
has the referenced line cached in the S state.

07H

04H

UNC_SNP_RESP_TO_REMOTE
_HOME.FWD_S_STATE

Number of responses to code or data read snoops to a
remote home that the L3 has the referenced cache
line in the E state. The L3 cache line state is changed
to the S state and the line is forwarded to the remote
home in the S state.

07H

08H

UNC_SNP_RESP_TO_REMOTE
_HOME.FWD_I_STATE

Number of responses to read invalidate snoops to a
remote home that the L3 has the referenced cache
line in the M state. The L3 cache line state is
invalidated and the line is forwarded to the remote
home in the M state.

07H

10H

UNC_SNP_RESP_TO_REMOTE
_HOME.CONFLICT

Number of conflict snoop responses sent to the local
home.

07H

20H

UNC_SNP_RESP_TO_REMOTE
_HOME.WB

Number of responses to code or data read snoops to a
remote home that the L3 has the referenced line
cached in the M state.

07H

24H

UNC_SNP_RESP_TO_REMOTE
_HOME.HITM

Number of HITM snoop responses to a remote home.

08H

01H

UNC_L3_HITS.READ

Number of code read, data read and RFO requests that
hit in the L3.

08H

02H

UNC_L3_HITS.WRITE

Number of writeback requests that hit in the L3.
Writebacks from the cores will always result in L3 hits
due to the inclusive property of the L3.

08H

04H

UNC_L3_HITS.PROBE

Number of snoops from IOH or remote sockets that hit
in the L3.

08H

03H

UNC_L3_HITS.ANY

Number of reads and writes that hit the L3.

09H

01H

UNC_L3_MISS.READ

Number of code read, data read and RFO requests that
miss the L3.

09H

02H

UNC_L3_MISS.WRITE

Number of writeback requests that miss the L3.
Should always be zero as writebacks from the cores
will always result in L3 hits due to the inclusive
property of the L3.

09H

04H

UNC_L3_MISS.PROBE

Number of snoops from IOH or remote sockets that
miss the L3.

Event Mask Mnemonic

Description

09H

03H

UNC_L3_MISS.ANY

Number of reads and writes that miss the L3.

0AH

01H

UNC_L3_LINES_IN.M_STATE

Counts the number of L3 lines allocated in M state. The
only time a cache line is allocated in the M state is
when the line was forwarded in M state is forwarded
due to a Snoop Read Invalidate Own request.

0AH

02H

UNC_L3_LINES_IN.E_STATE

Counts the number of L3 lines allocated in E state.

0AH

04H

UNC_L3_LINES_IN.S_STATE

Counts the number of L3 lines allocated in S state.

19-100 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

0AH

08H

UNC_L3_LINES_IN.F_STATE

Counts the number of L3 lines allocated in F state.

0AH

0FH

UNC_L3_LINES_IN.ANY

Counts the number of L3 lines allocated in any state.

0BH

01H

UNC_L3_LINES_OUT.M_STATE Counts the number of L3 lines victimized that were in
the M state. When the victim cache line is in M state,
the line is written to its home cache agent which can
be either local or remote.

0BH

02H

UNC_L3_LINES_OUT.E_STATE

Counts the number of L3 lines victimized that were in
the E state.

0BH

04H

UNC_L3_LINES_OUT.S_STATE

Counts the number of L3 lines victimized that were in
the S state.

0BH

08H

UNC_L3_LINES_OUT.I_STATE

Counts the number of L3 lines victimized that were in
the I state.

0BH

10H

UNC_L3_LINES_OUT.F_STATE

Counts the number of L3 lines victimized that were in
the F state.

0BH

1FH

UNC_L3_LINES_OUT.ANY

Counts the number of L3 lines victimized in any state.

20H

01H

UNC_QHL_REQUESTS.IOH_RE
ADS

Counts number of Quickpath Home Logic read
requests from the IOH.

20H

02H

UNC_QHL_REQUESTS.IOH_WR Counts number of Quickpath Home Logic write
ITES
requests from the IOH.

20H

04H

UNC_QHL_REQUESTS.REMOTE Counts number of Quickpath Home Logic read
_READS
requests from a remote socket.

20H

08H

UNC_QHL_REQUESTS.REMOTE Counts number of Quickpath Home Logic write
_WRITES
requests from a remote socket.

20H

10H

UNC_QHL_REQUESTS.LOCAL_
READS

Counts number of Quickpath Home Logic read
requests from the local socket.

20H

20H

UNC_QHL_REQUESTS.LOCAL_
WRITES

Counts number of Quickpath Home Logic write
requests from the local socket.

21H

01H

UNC_QHL_CYCLES_FULL.IOH

Counts uclk cycles all entries in the Quickpath Home
Logic IOH are full.

21H

02H

UNC_QHL_CYCLES_FULL.REM
OTE

Counts uclk cycles all entries in the Quickpath Home
Logic remote tracker are full.

21H

04H

UNC_QHL_CYCLES_FULL.LOCA Counts uclk cycles all entries in the Quickpath Home
L
Logic local tracker are full.

22H

01H

UNC_QHL_CYCLES_NOT_EMPT Counts uclk cycles all entries in the Quickpath Home
Y.IOH
Logic IOH is busy.

22H

02H

UNC_QHL_CYCLES_NOT_EMPT Counts uclk cycles all entries in the Quickpath Home
Y.REMOTE
Logic remote tracker is busy.

22H

04H

UNC_QHL_CYCLES_NOT_EMPT Counts uclk cycles all entries in the Quickpath Home
Y.LOCAL
Logic local tracker is busy.

23H

01H

UNC_QHL_OCCUPANCY.IOH

23H

02H

UNC_QHL_OCCUPANCY.REMOT QHL remote tracker allocate to deallocate read
E
occupancy.

23H

04H

UNC_QHL_OCCUPANCY.LOCAL

Comment

QHL IOH tracker allocate to deallocate read occupancy.

QHL local tracker allocate to deallocate read
occupancy.

Vol. 3B 19-101

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

24H

02H

UNC_QHL_ADDRESS_CONFLIC Counts number of QHL Active Address Table (AAT)
TS.2WAY
entries that saw a max of 2 conflicts. The AAT is a
structure that tracks requests that are in conflict. The
requests themselves are in the home tracker entries.
The count is reported when an AAT entry deallocates.

24H

04H

UNC_QHL_ADDRESS_CONFLIC Counts number of QHL Active Address Table (AAT)
TS.3WAY
entries that saw a max of 3 conflicts. The AAT is a
structure that tracks requests that are in conflict. The
requests themselves are in the home tracker entries.
The count is reported when an AAT entry deallocates.

25H

01H

UNC_QHL_CONFLICT_CYCLES.I Counts cycles the Quickpath Home Logic IOH Tracker
OH
contains two or more requests with an address
conflict. A max of 3 requests can be in conflict.

25H

02H

UNC_QHL_CONFLICT_CYCLES.
REMOTE

Counts cycles the Quickpath Home Logic Remote
Tracker contains two or more requests with an
address conflict. A max of 3 requests can be in conflict.

25H

04H

UNC_QHL_CONFLICT_CYCLES.
LOCAL

Counts cycles the Quickpath Home Logic Local Tracker
contains two or more requests with an address
conflict. A max of 3 requests can be in conflict.

26H

01H

UNC_QHL_TO_QMC_BYPASS

Counts number or requests to the Quickpath Memory
Controller that bypass the Quickpath Home Logic. All
local accesses can be bypassed. For remote requests,
only read requests can be bypassed.

27H

01H

UNC_QMC_NORMAL_FULL.RE
AD.CH0

Uncore cycles all the entries in the DRAM channel 0
medium or low priority queue are occupied with read
requests.

27H

02H

UNC_QMC_NORMAL_FULL.RE
AD.CH1

Uncore cycles all the entries in the DRAM channel 1
medium or low priority queue are occupied with read
requests.

27H

04H

UNC_QMC_NORMAL_FULL.RE
AD.CH2

Uncore cycles all the entries in the DRAM channel 2
medium or low priority queue are occupied with read
requests.

27H

08H

UNC_QMC_NORMAL_FULL.WRI Uncore cycles all the entries in the DRAM channel 0
TE.CH0
medium or low priority queue are occupied with write
requests.

27H

10H

UNC_QMC_NORMAL_FULL.WRI Counts cycles all the entries in the DRAM channel 1
TE.CH1
medium or low priority queue are occupied with write
requests.

27H

20H

UNC_QMC_NORMAL_FULL.WRI Uncore cycles all the entries in the DRAM channel 2
TE.CH2
medium or low priority queue are occupied with write
requests.

28H

01H

UNC_QMC_ISOC_FULL.READ.C
H0

Counts cycles all the entries in the DRAM channel 0
high priority queue are occupied with isochronous
read requests.

28H

02H

UNC_QMC_ISOC_FULL.READ.C
H1

Counts cycles all the entries in the DRAM channel
1high priority queue are occupied with isochronous
read requests.

19-102 Vol. 3B

Event Mask Mnemonic

Description

Comment

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

28H

04H

UNC_QMC_ISOC_FULL.READ.C
H2

Counts cycles all the entries in the DRAM channel 2
high priority queue are occupied with isochronous
read requests.

28H

08H

UNC_QMC_ISOC_FULL.WRITE.C Counts cycles all the entries in the DRAM channel 0
H0
high priority queue are occupied with isochronous
write requests.

28H

10H

UNC_QMC_ISOC_FULL.WRITE.C Counts cycles all the entries in the DRAM channel 1
H1
high priority queue are occupied with isochronous
write requests.

28H

20H

UNC_QMC_ISOC_FULL.WRITE.C Counts cycles all the entries in the DRAM channel 2
H2
high priority queue are occupied with isochronous
write requests.

29H

01H

UNC_QMC_BUSY.READ.CH0

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding read request to DRAM channel
0.

29H

02H

UNC_QMC_BUSY.READ.CH1

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding read request to DRAM channel
1.

29H

04H

UNC_QMC_BUSY.READ.CH2

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding read request to DRAM channel
2.

29H

08H

UNC_QMC_BUSY.WRITE.CH0

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding write request to DRAM channel
0.

29H

10H

UNC_QMC_BUSY.WRITE.CH1

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding write request to DRAM channel
1.

29H

20H

UNC_QMC_BUSY.WRITE.CH2

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding write request to DRAM channel
2.

2AH

01H

UNC_QMC_OCCUPANCY.CH0

IMC channel 0 normal read request occupancy.

2AH

02H

UNC_QMC_OCCUPANCY.CH1

IMC channel 1 normal read request occupancy.

2AH

04H

UNC_QMC_OCCUPANCY.CH2

IMC channel 2 normal read request occupancy.

2BH

01H

UNC_QMC_ISSOC_OCCUPANCY. IMC channel 0 issoc read request occupancy.
CH0

2BH

02H

UNC_QMC_ISSOC_OCCUPANCY. IMC channel 1 issoc read request occupancy.
CH1

2BH

04H

UNC_QMC_ISSOC_OCCUPANCY. IMC channel 2 issoc read request occupancy.
CH2

2BH

07H

UNC_QMC_ISSOC_READS.ANY

IMC issoc read request occupancy.

2CH

01H

UNC_QMC_NORMAL_READS.C
H0

Counts the number of Quickpath Memory Controller
channel 0 medium and low priority read requests. The
QMC channel 0 normal read occupancy divided by this
count provides the average QMC channel 0 read
latency.

Comment

Vol. 3B 19-103

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

2CH

02H

UNC_QMC_NORMAL_READS.C
H1

Counts the number of Quickpath Memory Controller
channel 1 medium and low priority read requests. The
QMC channel 1 normal read occupancy divided by this
count provides the average QMC channel 1 read
latency.

2CH

04H

UNC_QMC_NORMAL_READS.C
H2

Counts the number of Quickpath Memory Controller
channel 2 medium and low priority read requests. The
QMC channel 2 normal read occupancy divided by this
count provides the average QMC channel 2 read
latency.

2CH

07H

UNC_QMC_NORMAL_READS.A
NY

Counts the number of Quickpath Memory Controller
medium and low priority read requests. The QMC
normal read occupancy divided by this count provides
the average QMC read latency.

2DH

01H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.CH0
channel 0 high priority isochronous read requests.

2DH

02H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.CH1
channel 1 high priority isochronous read requests.

2DH

04H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.CH2
channel 2 high priority isochronous read requests.

2DH

07H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.ANY
high priority isochronous read requests.

2EH

01H

UNC_QMC_CRITICAL_PRIORIT
Y_READS.CH0

Counts the number of Quickpath Memory Controller
channel 0 critical priority isochronous read requests.

2EH

02H

UNC_QMC_CRITICAL_PRIORIT
Y_READS.CH1

Counts the number of Quickpath Memory Controller
channel 1 critical priority isochronous read requests.

2EH

04H

UNC_QMC_CRITICAL_PRIORIT
Y_READS.CH2

Counts the number of Quickpath Memory Controller
channel 2 critical priority isochronous read requests.

2EH

07H

UNC_QMC_CRITICAL_PRIORIT
Y_READS.ANY

Counts the number of Quickpath Memory Controller
critical priority isochronous read requests.

2FH

01H

UNC_QMC_WRITES.FULL.CH0

Counts number of full cache line writes to DRAM
channel 0.

2FH

02H

UNC_QMC_WRITES.FULL.CH1

Counts number of full cache line writes to DRAM
channel 1.

2FH

04H

UNC_QMC_WRITES.FULL.CH2

Counts number of full cache line writes to DRAM
channel 2.

2FH

07H

UNC_QMC_WRITES.FULL.ANY

Counts number of full cache line writes to DRAM.

2FH

08H

UNC_QMC_WRITES.PARTIAL.C
H0

Counts number of partial cache line writes to DRAM
channel 0.

2FH

10H

UNC_QMC_WRITES.PARTIAL.C
H1

Counts number of partial cache line writes to DRAM
channel 1.

2FH

20H

UNC_QMC_WRITES.PARTIAL.C
H2

Counts number of partial cache line writes to DRAM
channel 2.

2FH

38H

UNC_QMC_WRITES.PARTIAL.A
NY

Counts number of partial cache line writes to DRAM.

30H

01H

UNC_QMC_CANCEL.CH0

Counts number of DRAM channel 0 cancel requests.

30H

02H

UNC_QMC_CANCEL.CH1

Counts number of DRAM channel 1 cancel requests.

19-104 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

30H

04H

UNC_QMC_CANCEL.CH2

Counts number of DRAM channel 2 cancel requests.

30H

07H

UNC_QMC_CANCEL.ANY

Counts number of DRAM cancel requests.

31H

01H

UNC_QMC_PRIORITY_UPDATE
S.CH0

Counts number of DRAM channel 0 priority updates. A
priority update occurs when an ISOC high or critical
request is received by the QHL and there is a matching
request with normal priority that has already been
issued to the QMC. In this instance, the QHL will send
a priority update to QMC to expedite the request.

31H

02H

UNC_QMC_PRIORITY_UPDATE
S.CH1

Counts number of DRAM channel 1 priority updates. A
priority update occurs when an ISOC high or critical
request is received by the QHL and there is a matching
request with normal priority that has already been
issued to the QMC. In this instance, the QHL will send a
priority update to QMC to expedite the request.

31H

04H

UNC_QMC_PRIORITY_UPDATE
S.CH2

Counts number of DRAM channel 2 priority updates. A
priority update occurs when an ISOC high or critical
request is received by the QHL and there is a matching
request with normal priority that has already been
issued to the QMC. In this instance, the QHL will send
a priority update to QMC to expedite the request.

31H

07H

UNC_QMC_PRIORITY_UPDATE
S.ANY

Counts number of DRAM priority updates. A priority
update occurs when an ISOC high or critical request is
received by the QHL and there is a matching request
with normal priority that has already been issued to
the QMC. In this instance, the QHL will send a priority
update to QMC to expedite the request.

33H

04H

UNC_QHL_FRC_ACK_CNFLTS.L Counts number of Force Acknowledge Conflict
OCAL
messages sent by the Quickpath Home Logic to the
local home.

40H

01H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 0 HOME
E_FLIT.HOME.LINK_0
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

02H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 0 SNOOP
E_FLIT.SNOOP.LINK_0
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

04H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 0 non-data
E_FLIT.NDR.LINK_0
response virtual channel is stalled due to lack of a VNA
and VN0 credit. Note that this event does not filter out
when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

40H

08H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 1 HOME
E_FLIT.HOME.LINK_1
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

Comment

Vol. 3B 19-105

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

40H

10H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 1 SNOOP
E_FLIT.SNOOP.LINK_1
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

20H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 1 non-data
E_FLIT.NDR.LINK_1
response virtual channel is stalled due to lack of a VNA
and VN0 credit. Note that this event does not filter out
when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

40H

07H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 0 virtual
E_FLIT.LINK_0
channels are stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

38H

UNC_QPI_TX_STALLED_SINGL Counts cycles the Quickpath outbound link 1 virtual
E_FLIT.LINK_1
channels are stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

41H

01H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 Data
_FLIT.DRS.LINK_0
Response virtual channel is stalled due to lack of VNA
and VN0 credits. Note that this event does not filter
out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

02H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 Non_FLIT.NCB.LINK_0
Coherent Bypass virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

04H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 Non_FLIT.NCS.LINK_0
Coherent Standard virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

08H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 Data
_FLIT.DRS.LINK_1
Response virtual channel is stalled due to lack of VNA
and VN0 credits. Note that this event does not filter
out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

10H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 Non_FLIT.NCB.LINK_1
Coherent Bypass virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

19-106 Vol. 3B

Event Mask Mnemonic

Description

Comment

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

41H

20H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 Non_FLIT.NCS.LINK_1
Coherent Standard virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

07H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 virtual
_FLIT.LINK_0
channels are stalled due to lack of VNA and VN0
credits. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

41H

38H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 virtual
_FLIT.LINK_1
channels are stalled due to lack of VNA and VN0
credits. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

42H

02H

UNC_QPI_TX_HEADER.BUSY.LI Number of cycles that the header buffer in the
NK_0
Quickpath Interface outbound link 0 is busy.

42H

08H

UNC_QPI_TX_HEADER.BUSY.LI Number of cycles that the header buffer in the
NK_1
Quickpath Interface outbound link 1 is busy.

43H

01H

UNC_QPI_RX_NO_PPT_CREDI
T.STALLS.LINK_0

Number of cycles that snoop packets incoming to the
Quickpath Interface link 0 are stalled and not sent to
the GQ because the GQ Peer Probe Tracker (PPT) does
not have any available entries.

43H

02H

UNC_QPI_RX_NO_PPT_CREDI
T.STALLS.LINK_1

Number of cycles that snoop packets incoming to the
Quickpath Interface link 1 are stalled and not sent to
the GQ because the GQ Peer Probe Tracker (PPT) does
not have any available entries.

60H

01H

UNC_DRAM_OPEN.CH0

Counts number of DRAM Channel 0 open commands
issued either for read or write. To read or write data,
the referenced DRAM page must first be opened.

60H

02H

UNC_DRAM_OPEN.CH1

Counts number of DRAM Channel 1 open commands
issued either for read or write. To read or write data,
the referenced DRAM page must first be opened.

60H

04H

UNC_DRAM_OPEN.CH2

Counts number of DRAM Channel 2 open commands
issued either for read or write. To read or write data,
the referenced DRAM page must first be opened.

61H

01H

UNC_DRAM_PAGE_CLOSE.CH0 DRAM channel 0 command issued to CLOSE a page due
to page idle timer expiration. Closing a page is done by
issuing a precharge.

61H

02H

UNC_DRAM_PAGE_CLOSE.CH1 DRAM channel 1 command issued to CLOSE a page due
to page idle timer expiration. Closing a page is done by
issuing a precharge.

61H

04H

UNC_DRAM_PAGE_CLOSE.CH2 DRAM channel 2 command issued to CLOSE a page due
to page idle timer expiration. Closing a page is done by
issuing a precharge.

Event Mask Mnemonic

Description

Comment

Vol. 3B 19-107

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

62H

01H

UNC_DRAM_PAGE_MISS.CH0

Counts the number of precharges (PRE) that were
issued to DRAM channel 0 because there was a page
miss. A page miss refers to a situation in which a page
is currently open and another page from the same
bank needs to be opened. The new page experiences a
page miss. Closing of the old page is done by issuing a
precharge.

62H

02H

UNC_DRAM_PAGE_MISS.CH1

Counts the number of precharges (PRE) that were
issued to DRAM channel 1 because there was a page
miss. A page miss refers to a situation in which a page
is currently open and another page from the same
bank needs to be opened. The new page experiences a
page miss. Closing of the old page is done by issuing a
precharge.

62H

04H

UNC_DRAM_PAGE_MISS.CH2

Counts the number of precharges (PRE) that were
issued to DRAM channel 2 because there was a page
miss. A page miss refers to a situation in which a page
is currently open and another page from the same
bank needs to be opened. The new page experiences a
page miss. Closing of the old page is done by issuing a
precharge.

63H

01H

UNC_DRAM_READ_CAS.CH0

Counts the number of times a read CAS command was
issued on DRAM channel 0.

63H

02H

UNC_DRAM_READ_CAS.AUTO
PRE_CH0

Counts the number of times a read CAS command was
issued on DRAM channel 0 where the command issued
used the auto-precharge (auto page close) mode.

63H

04H

UNC_DRAM_READ_CAS.CH1

Counts the number of times a read CAS command was
issued on DRAM channel 1.

63H

08H

UNC_DRAM_READ_CAS.AUTO
PRE_CH1

Counts the number of times a read CAS command was
issued on DRAM channel 1 where the command issued
used the auto-precharge (auto page close) mode.

63H

10H

UNC_DRAM_READ_CAS.CH2

Counts the number of times a read CAS command was
issued on DRAM channel 2.

63H

20H

UNC_DRAM_READ_CAS.AUTO
PRE_CH2

Counts the number of times a read CAS command was
issued on DRAM channel 2 where the command issued
used the auto-precharge (auto page close) mode.

64H

01H

UNC_DRAM_WRITE_CAS.CH0

Counts the number of times a write CAS command was
issued on DRAM channel 0.

64H

02H

UNC_DRAM_WRITE_CAS.AUTO Counts the number of times a write CAS command was
PRE_CH0
issued on DRAM channel 0 where the command issued
used the auto-precharge (auto page close) mode.

64H

04H

UNC_DRAM_WRITE_CAS.CH1

64H

08H

UNC_DRAM_WRITE_CAS.AUTO Counts the number of times a write CAS command was
PRE_CH1
issued on DRAM channel 1 where the command issued
used the auto-precharge (auto page close) mode.

64H

10H

UNC_DRAM_WRITE_CAS.CH2

19-108 Vol. 3B

Counts the number of times a write CAS command was
issued on DRAM channel 1.

Counts the number of times a write CAS command was
issued on DRAM channel 2.

Comment

PERFORMANCE MONITORING EVENTS

Table 19-20. Performance Events In the Processor Uncore for
Intel® Core™ i7 Processor and Intel® Xeon® Processor 5500 Series (Contd.)
Event
Num.

Umask
Value

64H

20H

UNC_DRAM_WRITE_CAS.AUTO Counts the number of times a write CAS command was
PRE_CH2
issued on DRAM channel 2 where the command issued
used the auto-precharge (auto page close) mode.

65H

01H

UNC_DRAM_REFRESH.CH0

Counts number of DRAM channel 0 refresh commands.
DRAM loses data content over time. In order to keep
correct data content, the data values have to be
refreshed periodically.

65H

02H

UNC_DRAM_REFRESH.CH1

Counts number of DRAM channel 1 refresh commands.
DRAM loses data content over time. In order to keep
correct data content, the data values have to be
refreshed periodically.

65H

04H

UNC_DRAM_REFRESH.CH2

Counts number of DRAM channel 2 refresh commands.
DRAM loses data content over time. In order to keep
correct data content, the data values have to be
refreshed periodically.

66H

01H

UNC_DRAM_PRE_ALL.CH0

Counts number of DRAM Channel 0 precharge-all
(PREALL) commands that close all open pages in a
rank. PREALL is issued when the DRAM needs to be
refreshed or needs to go into a power down mode.

66H

02H

UNC_DRAM_PRE_ALL.CH1

Counts number of DRAM Channel 1 precharge-all
(PREALL) commands that close all open pages in a
rank. PREALL is issued when the DRAM needs to be
refreshed or needs to go into a power down mode.

66H

04H

UNC_DRAM_PRE_ALL.CH2

Counts number of DRAM Channel 2 precharge-all
(PREALL) commands that close all open pages in a
rank. PREALL is issued when the DRAM needs to be
refreshed or needs to go into a power down mode.

Event Mask Mnemonic

Description

Comment

Intel Xeon processors with CPUID signature of DisplayFamily_DisplayModel 06_2EH have a distinct uncore subsystem that is significantly different from the uncore found in processors with CPUID signature 06_1AH, 06_1EH,
and 06_1FH. Model-specific performance monitoring events for its uncore will be available in future documentation.

19.10

PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON
INTEL® MICROARCHITECTURE CODE NAME WESTMERE

Intel 64 processors based on Intel® microarchitecture code name Westmere support the architectural and modelspecific performance monitoring events listed in Table 19-1 and Table 19-21. Table 19-21 applies to processors with
CPUID signature of DisplayFamily_DisplayModel encoding with the following values: 06_25H, 06_2CH. In addition,
these processors (CPUID signature of DisplayFamily_DisplayModel 06_25H, 06_2CH) also support the following
model-specific, product-specific uncore performance monitoring events listed in Table 19-22. Fixed counters
support the architecture events defined in Table 19-2.

Vol. 3B 19-109

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere
Event
Num.

Umask
Value

03H

02H

LOAD_BLOCK.OVERLAP_STOR Loads that partially overlap an earlier store.
E

04H

07H

SB_DRAIN.ANY

All Store buffer stall cycles.

05H

02H

MISALIGN_MEMORY.STORE

All store referenced with misaligned address.

06H

04H

STORE_BLOCKS.AT_RET

Counts number of loads delayed with at-Retirement
block code. The following loads need to be executed
at retirement and wait for all senior stores on the
same thread to be drained: load splitting across 4K
boundary (page split), load accessing uncacheable
(UC or WC) memory, load lock, and load with page
table in UC or WC memory region.

06H

08H

STORE_BLOCKS.L1D_BLOCK

Cacheable loads delayed with L1D block code.

07H

01H

PARTIAL_ADDRESS_ALIAS

Counts false dependency due to partial address
aliasing.

08H

01H

DTLB_LOAD_MISSES.ANY

Counts all load misses that cause a page walk.

08H

02H

DTLB_LOAD_MISSES.WALK_C
OMPLETED

Counts number of completed page walks due to load
miss in the STLB.

08H

04H

DTLB_LOAD_MISSES.WALK_CY Cycles PMH is busy with a page walk due to a load
CLES
miss in the STLB.

08H

10H

DTLB_LOAD_MISSES.STLB_HI
T

Number of cache load STLB hits.

08H

20H

DTLB_LOAD_MISSES.PDE_MIS
S

Number of DTLB cache load misses where the low
part of the linear to physical address translation
was missed.

0BH

01H

MEM_INST_RETIRED.LOADS

Counts the number of instructions with an
architecturally-visible load retired on the
architected path.

0BH

02H

MEM_INST_RETIRED.STORES

Counts the number of instructions with an
architecturally-visible store retired on the
architected path.

0BH

10H

MEM_INST_RETIRED.LATENCY Counts the number of instructions exceeding the
_ABOVE_THRESHOLD
latency specified with ld_lat facility.

0CH

01H

MEM_STORE_RETIRED.DTLB_
MISS

The event counts the number of retired stores that
missed the DTLB. The DTLB miss is not counted if
the store operation causes a fault. Does not counter
prefetches. Counts both primary and secondary
misses to the TLB.

0EH

01H

UOPS_ISSUED.ANY

Counts the number of Uops issued by the Register
Allocation Table to the Reservation Station, i.e. the
UOPs issued from the front end to the back end.

0EH

01H

UOPS_ISSUED.STALLED_CYCL
ES

Counts the number of cycles no uops issued by the
Register Allocation Table to the Reservation
Station, i.e. the UOPs issued from the front end to
the back end.

0EH

02H

UOPS_ISSUED.FUSED

Counts the number of fused Uops that were issued
from the Register Allocation Table to the
Reservation Station.

19-110 Vol. 3B

Event Mask Mnemonic

Description

Comment

In conjunction with ld_lat
facility.

Set “invert=1, cmask =
1“.

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

0FH

01H

MEM_UNCORE_RETIRED.UNK
NOWN_SOURCE

Load instructions retired with unknown LLC miss
(Precise Event).

Applicable to one and
two sockets.

0FH

02H

MEM_UNCORE_RETIRED.OHTE Load instructions retired that HIT modified data in
R_CORE_L2_HIT
sibling core (Precise Event).

Applicable to one and
two sockets.

0FH

04H

MEM_UNCORE_RETIRED.REMO Load instructions retired that HIT modified data in
TE_HITM
remote socket (Precise Event).

Applicable to two
sockets only.

0FH

08H

MEM_UNCORE_RETIRED.LOCA Load instructions retired local dram and remote
L_DRAM_AND_REMOTE_CACH cache HIT data sources (Precise Event).
E_HIT

Applicable to one and
two sockets.

0FH

10H

MEM_UNCORE_RETIRED.REMO Load instructions retired remote DRAM and remote
TE_DRAM
home-remote cache HITM (Precise Event).

Applicable to two
sockets only.

0FH

20H

MEM_UNCORE_RETIRED.OTHE Load instructions retired other LLC miss (Precise
R_LLC_MISS
Event).

Applicable to two
sockets only.

0FH

80H

MEM_UNCORE_RETIRED.UNCA Load instructions retired I/O (Precise Event).
CHEABLE

Applicable to one and
two sockets.

10H

01H

FP_COMP_OPS_EXE.X87

Counts the number of FP Computational Uops
Executed. The number of FADD, FSUB, FCOM,
FMULs, integer MULs and IMULs, FDIVs, FPREMs,
FSQRTS, integer DIVs, and IDIVs. This event does
not distinguish an FADD used in the middle of a
transcendental flow from a separate FADD
instruction.

10H

02H

FP_COMP_OPS_EXE.MMX

Counts number of MMX Uops executed.
Counts number of SSE and SSE2 FP uops executed.

10H

04H

FP_COMP_OPS_EXE.SSE_FP

10H

08H

FP_COMP_OPS_EXE.SSE2_INT Counts number of SSE2 integer uops executed.
EGER

10H

10H

FP_COMP_OPS_EXE.SSE_FP_P Counts number of SSE FP packed uops executed.
ACKED

10H

20H

FP_COMP_OPS_EXE.SSE_FP_S Counts number of SSE FP scalar uops executed.
CALAR

10H

40H

FP_COMP_OPS_EXE.SSE_SING Counts number of SSE* FP single precision uops
LE_PRECISION
executed.

10H

80H

FP_COMP_OPS_EXE.SSE_DOU Counts number of SSE* FP double precision uops
BLE_PRECISION
executed.

12H

01H

SIMD_INT_128.PACKED_MPY

12H

02H

SIMD_INT_128.PACKED_SHIFT Counts number of 128 bit SIMD integer shift
operations.

12H

04H

SIMD_INT_128.PACK

Counts number of 128 bit SIMD integer pack
operations.

12H

08H

SIMD_INT_128.UNPACK

Counts number of 128 bit SIMD integer unpack
operations.

12H

10H

SIMD_INT_128.PACKED_LOGIC Counts number of 128 bit SIMD integer logical
AL
operations.

12H

20H

SIMD_INT_128.PACKED_ARIT
H

Counts number of 128 bit SIMD integer multiply
operations.

Counts number of 128 bit SIMD integer arithmetic
operations.

Vol. 3B 19-111

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

12H

40H

SIMD_INT_128.SHUFFLE_MOV Counts number of 128 bit SIMD integer shuffle and
E
move operations.

13H

01H

LOAD_DISPATCH.RS

13H

02H

LOAD_DISPATCH.RS_DELAYED Counts the number of delayed RS dispatches at the
stage latch. If an RS dispatch cannot bypass to LB, it
has another chance to dispatch from the one-cycle
delayed staging latch before it is written into the
LB.

13H

04H

LOAD_DISPATCH.MOB

Counts the number of loads dispatched from the
Reservation Station to the Memory Order Buffer.

13H

07H

LOAD_DISPATCH.ANY

Counts all loads dispatched from the Reservation
Station.

14H

01H

ARITH.CYCLES_DIV_BUSY

Count may be incorrect
Counts the number of cycles the divider is busy
executing divide or square root operations. The
When SMT is on.
divide can be integer, X87 or Streaming SIMD
Extensions (SSE). The square root operation can be
either X87 or SSE. Set 'edge =1, invert=1, cmask=1'
to count the number of divides.

14H

02H

ARITH.MUL

Counts the number of multiply operations executed. Count may be incorrect
This includes integer as well as floating point
When SMT is on.
multiply operations but excludes DPPS mul and
MPSAD.

17H

01H

INST_QUEUE_WRITES

Counts the number of instructions written into the
instruction queue every cycle.

18H

01H

INST_DECODED.DEC0

Counts number of instructions that require decoder
0 to be decoded. Usually, this means that the
instruction maps to more than 1 uop.

19H

01H

TWO_UOP_INSTS_DECODED

An instruction that generates two uops was
decoded.

1EH

01H

INST_QUEUE_WRITE_CYCLES

This event counts the number of cycles during
which instructions are written to the instruction
queue. Dividing this counter by the number of
instructions written to the instruction queue
(INST_QUEUE_WRITES) yields the average number
of instructions decoded each cycle. If this number is
less than four and the pipe stalls, this indicates that
the decoder is failing to decode enough instructions
per cycle to sustain the 4-wide pipeline.

20H

01H

LSD_OVERFLOW

Number of loops that cannot stream from the
instruction queue.

24H

01H

L2_RQSTS.LD_HIT

Counts number of loads that hit the L2 cache. L2
loads include both L1D demand misses as well as
L1D prefetches. L2 loads can be rejected for various
reasons. Only non rejected loads are counted.

24H

02H

L2_RQSTS.LD_MISS

Counts the number of loads that miss the L2 cache.
L2 loads include both L1D demand misses as well as
L1D prefetches.

19-112 Vol. 3B

Event Mask Mnemonic

Description

Comment

Counts number of loads dispatched from the
Reservation Station that bypass the Memory Order
Buffer.

If SSE* instructions that
are 6 bytes or longer
arrive one after another,
then front end
throughput may limit
execution speed.

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

24H

03H

L2_RQSTS.LOADS

Counts all L2 load requests. L2 loads include both
L1D demand misses as well as L1D prefetches.

24H

04H

L2_RQSTS.RFO_HIT

Counts the number of store RFO requests that hit
the L2 cache. L2 RFO requests include both L1D
demand RFO misses as well as L1D RFO prefetches.
Count includes WC memory requests, where the
data is not fetched but the permission to write the
line is required.

24H

08H

L2_RQSTS.RFO_MISS

Counts the number of store RFO requests that miss
the L2 cache. L2 RFO requests include both L1D
demand RFO misses as well as L1D RFO prefetches.

24H

0CH

L2_RQSTS.RFOS

Counts all L2 store RFO requests. L2 RFO requests
include both L1D demand RFO misses as well as L1D
RFO prefetches.

24H

10H

L2_RQSTS.IFETCH_HIT

Counts number of instruction fetches that hit the
L2 cache. L2 instruction fetches include both L1I
demand misses as well as L1I instruction
prefetches.

24H

20H

L2_RQSTS.IFETCH_MISS

Counts number of instruction fetches that miss the
L2 cache. L2 instruction fetches include both L1I
demand misses as well as L1I instruction
prefetches.

24H

30H

L2_RQSTS.IFETCHES

Counts all instruction fetches. L2 instruction fetches
include both L1I demand misses as well as L1I
instruction prefetches.

24H

40H

L2_RQSTS.PREFETCH_HIT

Counts L2 prefetch hits for both code and data.

24H

80H

L2_RQSTS.PREFETCH_MISS

Counts L2 prefetch misses for both code and data.

24H

C0H

L2_RQSTS.PREFETCHES

Counts all L2 prefetches for both code and data.

24H

AAH

L2_RQSTS.MISS

Counts all L2 misses for both code and data.

24H

FFH

L2_RQSTS.REFERENCES

Counts all L2 requests for both code and data.

26H

01H

L2_DATA_RQSTS.DEMAND.I_S Counts number of L2 data demand loads where the
TATE
cache line to be loaded is in the I (invalid) state, i.e., a
cache miss. L2 demand loads are both L1D demand
misses and L1D prefetches.

26H

02H

L2_DATA_RQSTS.DEMAND.S_
STATE

Counts number of L2 data demand loads where the
cache line to be loaded is in the S (shared) state. L2
demand loads are both L1D demand misses and L1D
prefetches.

26H

04H

L2_DATA_RQSTS.DEMAND.E_
STATE

Counts number of L2 data demand loads where the
cache line to be loaded is in the E (exclusive) state.
L2 demand loads are both L1D demand misses and
L1D prefetches.

26H

08H

L2_DATA_RQSTS.DEMAND.M_ Counts number of L2 data demand loads where the
STATE
cache line to be loaded is in the M (modified) state.
L2 demand loads are both L1D demand misses and
L1D prefetches.

Comment

Vol. 3B 19-113

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

26H

0FH

L2_DATA_RQSTS.DEMAND.ME Counts all L2 data demand requests. L2 demand
SI
loads are both L1D demand misses and L1D
prefetches.

26H

10H

L2_DATA_RQSTS.PREFETCH.I_ Counts number of L2 prefetch data loads where the
STATE
cache line to be loaded is in the I (invalid) state, i.e., a
cache miss.

26H

20H

L2_DATA_RQSTS.PREFETCH.S Counts number of L2 prefetch data loads where the
_STATE
cache line to be loaded is in the S (shared) state. A
prefetch RFO will miss on an S state line, while a
prefetch read will hit on an S state line.

26H

40H

L2_DATA_RQSTS.PREFETCH.E Counts number of L2 prefetch data loads where the
_STATE
cache line to be loaded is in the E (exclusive) state.

26H

80H

L2_DATA_RQSTS.PREFETCH.M Counts number of L2 prefetch data loads where the
_STATE
cache line to be loaded is in the M (modified) state.

26H

F0H

L2_DATA_RQSTS.PREFETCH.M Counts all L2 prefetch requests.
ESI

Event Mask Mnemonic

Description

Comment

26H

FFH

L2_DATA_RQSTS.ANY

Counts all L2 data requests.

27H

01H

L2_WRITE.RFO.I_STATE

Counts number of L2 demand store RFO requests
This is a demand RFO
where the cache line to be loaded is in the I (invalid) request.
state, i.e., a cache miss. The L1D prefetcher does
not issue a RFO prefetch.

27H

02H

L2_WRITE.RFO.S_STATE

Counts number of L2 store RFO requests where the This is a demand RFO
cache line to be loaded is in the S (shared) state.
request.
The L1D prefetcher does not issue a RFO prefetch.

27H

08H

L2_WRITE.RFO.M_STATE

Counts number of L2 store RFO requests where the This is a demand RFO
cache line to be loaded is in the M (modified) state. request.
The L1D prefetcher does not issue a RFO prefetch.

27H

0EH

L2_WRITE.RFO.HIT

Counts number of L2 store RFO requests where the This is a demand RFO
cache line to be loaded is in either the S, E or M
request.
states. The L1D prefetcher does not issue a RFO
prefetch.

27H

0FH

L2_WRITE.RFO.MESI

Counts all L2 store RFO requests. The L1D
prefetcher does not issue a RFO prefetch.

27H

10H

L2_WRITE.LOCK.I_STATE

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in the I (invalid)
state, i.e., a cache miss.

27H

20H

L2_WRITE.LOCK.S_STATE

Counts number of L2 lock RFO requests where the
cache line to be loaded is in the S (shared) state.

27H

40H

L2_WRITE.LOCK.E_STATE

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in the E
(exclusive) state.

27H

80H

L2_WRITE.LOCK.M_STATE

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in the M
(modified) state.

27H

E0H

L2_WRITE.LOCK.HIT

Counts number of L2 demand lock RFO requests
where the cache line to be loaded is in either the S,
E, or M state.

19-114 Vol. 3B

This is a demand RFO
request.

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

27H

F0H

L2_WRITE.LOCK.MESI

Counts all L2 demand lock RFO requests.

28H

01H

L1D_WB_L2.I_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the I (invalid) state,
i.e., a cache miss.

28H

02H

L1D_WB_L2.S_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the S state.

28H

04H

L1D_WB_L2.E_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the E (exclusive)
state.

28H

08H

L1D_WB_L2.M_STATE

Counts number of L1 writebacks to the L2 where
the cache line to be written is in the M (modified)
state.

Comment

28H

0FH

L1D_WB_L2.MESI

Counts all L1 writebacks to the L2 .

2EH

41H

L3_LAT_CACHE.MISS

Counts uncore Last Level Cache misses. Because
cache hierarchy, cache sizes and other
implementation-specific characteristics; value
comparison to estimate performance differences is
not recommended.

See Table 19-1.

2EH

4FH

L3_LAT_CACHE.REFERENCE

Counts uncore Last Level Cache references.
Because cache hierarchy, cache sizes and other
implementation-specific characteristics; value
comparison to estimate performance differences is
not recommended.

See Table 19-1.

3CH

00H

CPU_CLK_UNHALTED.THREAD Counts the number of thread cycles while the
_P
thread is not in a halt state. The thread enters the
halt state when it is running the HLT instruction.
The core frequency may change from time to time
due to power or thermal throttling.

See Table 19-1.

3CH

01H

CPU_CLK_UNHALTED.REF_P

Increments at the frequency of TSC when not
halted.

See Table 19-1.

49H

01H

DTLB_MISSES.ANY

Counts the number of misses in the STLB which
causes a page walk.

49H

02H

DTLB_MISSES.WALK_COMPLE
TED

Counts number of misses in the STLB which
resulted in a completed page walk.

49H

04H

DTLB_MISSES.WALK_CYCLES

Counts cycles of page walk due to misses in the
STLB.

49H

10H

DTLB_MISSES.STLB_HIT

Counts the number of DTLB first level misses that
hit in the second level TLB. This event is only
relevant if the core contains multiple DTLB levels.

49H

20H

DTLB_MISSES.PDE_MISS

Number of DTLB misses caused by low part of
address, includes references to 2M pages because
2M pages do not use the PDE.

49H

80H

DTLB_MISSES.LARGE_WALK_C Counts number of completed large page walks due
OMPLETED
to misses in the STLB.

4CH

01H

LOAD_HIT_PRE

Counter 0, 1 only.
Counts load operations sent to the L1 data cache
while a previous SSE prefetch instruction to the
same cache line has started prefetching but has not
yet finished.

Vol. 3B 19-115

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

4EH

01H

L1D_PREFETCH.REQUESTS

Counts number of hardware prefetch requests
dispatched out of the prefetch FIFO.

Counter 0, 1 only.

4EH

02H

L1D_PREFETCH.MISS

Counts number of hardware prefetch requests that Counter 0, 1 only.
miss the L1D. There are two prefetchers in the L1D.
A streamer, which predicts lines sequentially after
this one should be fetched, and the IP prefetcher
that remembers access patterns for the current
instruction. The streamer prefetcher stops on an
L1D hit, while the IP prefetcher does not.

4EH

04H

L1D_PREFETCH.TRIGGERS

Counts number of prefetch requests triggered by
Counter 0, 1 only.
the Finite State Machine and pushed into the
prefetch FIFO. Some of the prefetch requests are
dropped due to overwrites or competition between
the IP index prefetcher and streamer prefetcher.
The prefetch FIFO contains 4 entries.

4FH

10H

EPT.WALK_CYCLES

Counts Extended Page walk cycles.

51H

01H

L1D.REPL

Counts the number of lines brought into the L1 data Counter 0, 1 only.
cache.

51H

02H

L1D.M_REPL

Counts the number of modified lines brought into
the L1 data cache.

Counter 0, 1 only.

51H

04H

L1D.M_EVICT

Counts the number of modified lines evicted from
the L1 data cache due to replacement.

Counter 0, 1 only.

51H

08H

L1D.M_SNOOP_EVICT

Counts the number of modified lines evicted from
the L1 data cache due to snoop HITM intervention.

Counter 0, 1 only.

52H

01H

L1D_CACHE_PREFETCH_LOCK Counts the number of cacheable load lock
_FB_HIT
speculated instructions accepted into the fill buffer.

60H

01H

OFFCORE_REQUESTS_OUTST Counts weighted cycles of offcore demand data
ANDING.DEMAND.READ_DATA read requests. Does not include L2 prefetch
requests.

Counter 0.

60H

02H

OFFCORE_REQUESTS_OUTST Counts weighted cycles of offcore demand code
ANDING.DEMAND.READ_CODE read requests. Does not include L2 prefetch
requests.

Counter 0.

60H

04H

OFFCORE_REQUESTS_OUTST
ANDING.DEMAND.RFO

Counts weighted cycles of offcore demand RFO
requests. Does not include L2 prefetch requests.

Counter 0.

60H

08H

OFFCORE_REQUESTS_OUTST
ANDING.ANY.READ

Counts weighted cycles of offcore read requests of
any kind. Include L2 prefetch requests.

Counter 0.

63H

01H

CACHE_LOCK_CYCLES.L1D_L2 Cycle count during which the L1D and L2 are locked.
A lock is asserted when there is a locked memory
access, due to uncacheable memory, a locked
operation that spans two cache lines, or a page walk
from an uncacheable page table. This event does
not cause locks, it merely detects them.

Counter 0, 1 only. L1D
and L2 locks have a very
high performance
penalty and it is highly
recommended to avoid
such accesses.

63H

02H

CACHE_LOCK_CYCLES.L1D

Counter 0, 1 only.

Counts the number of cycles that cacheline in the
L1 data cache unit is locked.

6CH

01H

IO_TRANSACTIONS

Counts the number of completed I/O transactions.

80H

01H

L1I.HITS

Counts all instruction fetches that hit the L1
instruction cache.

19-116 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

80H

02H

L1I.MISSES

Counts all instruction fetches that miss the L1I
cache. This includes instruction cache misses,
streaming buffer misses, victim cache misses and
uncacheable fetches. An instruction fetch miss is
counted only once and not once for every cycle it is
outstanding.

80H

03H

L1I.READS

Counts all instruction fetches, including uncacheable
fetches that bypass the L1I.

80H

04H

L1I.CYCLES_STALLED

Cycle counts for which an instruction fetch stalls
due to a L1I cache miss, ITLB miss or ITLB fault.

82H

01H

LARGE_ITLB.HIT

Counts number of large ITLB hits.

85H

01H

ITLB_MISSES.ANY

Counts the number of misses in all levels of the ITLB
which causes a page walk.

85H

02H

ITLB_MISSES.WALK_COMPLET Counts number of misses in all levels of the ITLB
ED
which resulted in a completed page walk.

85H

04H

ITLB_MISSES.WALK_CYCLES

Counts ITLB miss page walk cycles.

85H

10H

ITLB_MISSES.STLB_HIT

Counts number of ITLB first level miss but second
level hits.

85H

80H

ITLB_MISSES.LARGE_WALK_C
OMPLETED

Counts number of completed large page walks due
to misses in the STLB.

87H

01H

ILD_STALL.LCP

Cycles Instruction Length Decoder stalls due to
length changing prefixes: 66, 67 or REX.W (for Intel
64) instructions which change the length of the
decoded instruction.

87H

02H

ILD_STALL.MRU

Instruction Length Decoder stall cycles due to Brand
Prediction Unit (PBU) Most Recently Used (MRU)
bypass.

87H

04H

ILD_STALL.IQ_FULL

Stall cycles due to a full instruction queue.

87H

08H

ILD_STALL.REGEN

Counts the number of regen stalls.

87H

0FH

ILD_STALL.ANY

Counts any cycles the Instruction Length Decoder is
stalled.

88H

01H

BR_INST_EXEC.COND

Counts the number of conditional near branch
instructions executed, but not necessarily retired.

88H

02H

BR_INST_EXEC.DIRECT

Counts all unconditional near branch instructions
excluding calls and indirect branches.

88H

04H

BR_INST_EXEC.INDIRECT_NO
N_CALL

Counts the number of executed indirect near branch
instructions that are not calls.

88H

07H

BR_INST_EXEC.NON_CALLS

Counts all non-call near branch instructions
executed, but not necessarily retired.

88H

08H

BR_INST_EXEC.RETURN_NEA
R

Counts indirect near branches that have a return
mnemonic.

88H

10H

BR_INST_EXEC.DIRECT_NEAR
_CALL

Counts unconditional near call branch instructions,
excluding non-call branch, executed.

88H

20H

BR_INST_EXEC.INDIRECT_NEA Counts indirect near calls, including both register
R_CALL
and memory indirect, executed.

Comment

Vol. 3B 19-117

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

88H

30H

BR_INST_EXEC.NEAR_CALLS

Counts all near call branches executed, but not
necessarily retired.

88H

40H

BR_INST_EXEC.TAKEN

Counts taken near branches executed, but not
necessarily retired.

88H

7FH

BR_INST_EXEC.ANY

Counts all near executed branches (not necessarily
retired). This includes only instructions and not
micro-op branches. Frequent branching is not
necessarily a major performance issue. However
frequent branch mispredictions may be a problem.

89H

01H

BR_MISP_EXEC.COND

Counts the number of mispredicted conditional near
branch instructions executed, but not necessarily
retired.

89H

02H

BR_MISP_EXEC.DIRECT

Counts mispredicted macro unconditional near
branch instructions, excluding calls and indirect
branches (should always be 0).

89H

04H

BR_MISP_EXEC.INDIRECT_NO
N_CALL

Counts the number of executed mispredicted
indirect near branch instructions that are not calls.

89H

07H

BR_MISP_EXEC.NON_CALLS

Counts mispredicted non-call near branches
executed, but not necessarily retired.

89H

08H

BR_MISP_EXEC.RETURN_NEA
R

Counts mispredicted indirect branches that have a
rear return mnemonic.

89H

10H

BR_MISP_EXEC.DIRECT_NEAR Counts mispredicted non-indirect near calls
_CALL
executed, (should always be 0).

89H

20H

BR_MISP_EXEC.INDIRECT_NE
AR_CALL

Counts mispredicted indirect near calls executed,
including both register and memory indirect.

89H

30H

BR_MISP_EXEC.NEAR_CALLS

Counts all mispredicted near call branches executed,
but not necessarily retired.

89H

40H

BR_MISP_EXEC.TAKEN

Counts executed mispredicted near branches that
are taken, but not necessarily retired.

89H

7FH

BR_MISP_EXEC.ANY

Counts the number of mispredicted near branch
instructions that were executed, but not
necessarily retired.

A2H

01H

RESOURCE_STALLS.ANY

Counts the number of Allocator resource related
stalls. Includes register renaming buffer entries,
memory buffer entries. In addition to resource
related stalls, this event counts some other events.
Includes stalls arising during branch misprediction
recovery, such as if retirement of the mispredicted
branch is delayed and stalls arising while store
buffer is draining from synchronizing operations.

A2H

02H

RESOURCE_STALLS.LOAD

Counts the cycles of stall due to lack of load buffer
for load operation.

19-118 Vol. 3B

Comment

Does not include stalls
due to SuperQ (off core)
queue full, too many
cache misses, etc.

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

A2H

04H

RESOURCE_STALLS.RS_FULL

This event counts the number of cycles when the
number of instructions in the pipeline waiting for
execution reaches the limit the processor can
handle. A high count of this event indicates that
there are long latency operations in the pipe
(possibly load and store operations that miss the L2
cache, or instructions dependent upon instructions
further down the pipeline that have yet to retire.

When RS is full, new
instructions cannot enter
the reservation station
and start execution.

A2H

08H

RESOURCE_STALLS.STORE

This event counts the number of cycles that a
resource related stall will occur due to the number
of store instructions reaching the limit of the
pipeline, (i.e. all store buffers are used). The stall
ends when a store instruction commits its data to
the cache or memory.

A2H

10H

RESOURCE_STALLS.ROB_FULL Counts the cycles of stall due to re-order buffer full.

A2H

20H

RESOURCE_STALLS.FPCW

Counts the number of cycles while execution was
stalled due to writing the floating-point unit (FPU)
control word.

A2H

40H

RESOURCE_STALLS.MXCSR

Stalls due to the MXCSR register rename occurring
to close to a previous MXCSR rename. The MXCSR
provides control and status for the MMX registers.

A2H

80H

RESOURCE_STALLS.OTHER

Counts the number of cycles while execution was
stalled due to other resource issues.

A6H

01H

MACRO_INSTS.FUSIONS_DECO Counts the number of instructions decoded that are
DED
macro-fused but not necessarily executed or
retired.

A7H

01H

BACLEAR_FORCE_IQ

Counts number of times a BACLEAR was forced by
the Instruction Queue. The IQ is also responsible for
providing conditional branch prediction direction
based on a static scheme and dynamic data
provided by the L2 Branch Prediction Unit. If the
conditional branch target is not found in the Target
Array and the IQ predicts that the branch is taken,
then the IQ will force the Branch Address Calculator
to issue a BACLEAR. Each BACLEAR asserted by the
BAC generates approximately an 8 cycle bubble in
the instruction fetch pipeline.

A8H

01H

LSD.UOPS

Counts the number of micro-ops delivered by loop
stream detector.

AEH

01H

ITLB_FLUSH

Counts the number of ITLB flushes.

B0H

01H

OFFCORE_REQUESTS.DEMAN
D.READ_DATA

Counts number of offcore demand data read
requests. Does not count L2 prefetch requests.

B0H

02H

OFFCORE_REQUESTS.DEMAN
D.READ_CODE

Counts number of offcore demand code read
requests. Does not count L2 prefetch requests.

B0H

04H

OFFCORE_REQUESTS.DEMAN
D.RFO

Counts number of offcore demand RFO requests.
Does not count L2 prefetch requests.

B0H

08H

OFFCORE_REQUESTS.ANY.REA Counts number of offcore read requests. Includes
D
L2 prefetch requests.

Use cmask=1 and invert
to count cycles.

Vol. 3B 19-119

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

B0H

10H

OFFCORE_REQUESTS.ANY.RFO Counts number of offcore RFO requests. Includes L2
prefetch requests.

B0H

40H

OFFCORE_REQUESTS.L1D_WR Counts number of L1D writebacks to the uncore.
ITEBACK

B0H

80H

OFFCORE_REQUESTS.ANY

Counts all offcore requests.

B1H

01H

UOPS_EXECUTED.PORT0

Counts number of uops executed that were issued
on port 0. Port 0 handles integer arithmetic, SIMD
and FP add uops.

B1H

02H

UOPS_EXECUTED.PORT1

Counts number of uops executed that were issued
on port 1. Port 1 handles integer arithmetic, SIMD,
integer shift, FP multiply and FP divide uops.

B1H

04H

UOPS_EXECUTED.PORT2_COR Counts number of uops executed that were issued
E
on port 2. Port 2 handles the load uops. This is a
core count only and cannot be collected per thread.

B1H

08H

UOPS_EXECUTED.PORT3_COR Counts number of uops executed that were issued
E
on port 3. Port 3 handles store uops. This is a core
count only and cannot be collected per thread.

B1H

10H

UOPS_EXECUTED.PORT4_COR Counts number of uops executed that where issued
E
on port 4. Port 4 handles the value to be stored for
the store uops issued on port 3. This is a core count
only and cannot be collected per thread.

B1H

1FH

UOPS_EXECUTED.CORE_ACTI
VE_CYCLES_NO_PORT5

Counts number of cycles there are one or more
uops being executed and were issued on ports 0-4.
This is a core count only and cannot be collected per
thread.

B1H

20H

UOPS_EXECUTED.PORT5

Counts number of uops executed that where issued
on port 5.

B1H

3FH

UOPS_EXECUTED.CORE_ACTI
VE_CYCLES

Counts number of cycles there are one or more
uops being executed on any ports. This is a core
count only and cannot be collected per thread.

B1H

40H

UOPS_EXECUTED.PORT015

Counts number of uops executed that where issued Use cmask=1, invert=1
on port 0, 1, or 5.
to count stall cycles.

B1H

80H

UOPS_EXECUTED.PORT234

Counts number of uops executed that where issued
on port 2, 3, or 4.

B2H

01H

OFFCORE_REQUESTS_SQ_FUL Counts number of cycles the SQ is full to handle offL
core requests.

B3H

01H

SNOOPQ_REQUESTS_OUTSTA Counts weighted cycles of snoopq requests for
NDING.DATA
data. Counter 0 only.

Use cmask=1 to count
cycles not empty.

B3H

02H

SNOOPQ_REQUESTS_OUTSTA Counts weighted cycles of snoopq invalidate
NDING.INVALIDATE
requests. Counter 0 only.

Use cmask=1 to count
cycles not empty.

B3H

04H

SNOOPQ_REQUESTS_OUTSTA Counts weighted cycles of snoopq requests for
NDING.CODE
code. Counter 0 only.

Use cmask=1 to count
cycles not empty.

B4H

01H

SNOOPQ_REQUESTS.CODE

Counts the number of snoop code requests.

B4H

02H

SNOOPQ_REQUESTS.DATA

Counts the number of snoop data requests.

B4H

04H

SNOOPQ_REQUESTS.INVALID
ATE

Counts the number of snoop invalidate requests.

19-120 Vol. 3B

Event Mask Mnemonic

Description

Comment

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

Comment

B7H

01H

OFF_CORE_RESPONSE_0

See Section 18.3.1.1.3, “Off-core Response
Performance Monitoring in the Processor Core”.

Requires programming
MSR 01A6H.

B8H

01H

SNOOP_RESPONSE.HIT

Counts HIT snoop response sent by this thread in
response to a snoop request.

B8H

02H

SNOOP_RESPONSE.HITE

Counts HIT E snoop response sent by this thread in
response to a snoop request.

B8H

04H

SNOOP_RESPONSE.HITM

Counts HIT M snoop response sent by this thread in
response to a snoop request.

BBH

01H

OFF_CORE_RESPONSE_1

See Section 18.3.1.1.3, “Off-core Response
Performance Monitoring in the Processor Core”.

Use MSR 01A7H.

C0H

00H

INST_RETIRED.ANY_P

See Table 19-1.

Counting: Faulting
executions of
GETSEC/VM entry/VM
Exit/MWait will not count
as retired instructions.

Notes: INST_RETIRED.ANY is counted by a
designated fixed counter. INST_RETIRED.ANY_P is
counted by a programmable counter and is an
architectural performance event. Event is
supported if CPUID.A.EBX[1] = 0.
C0H

02H

INST_RETIRED.X87

Counts the number of floating point computational
operations retired: floating point computational
operations executed by the assist handler and suboperations of complex floating point instructions
like transcendental instructions.

C0H

04H

INST_RETIRED.MMX

Counts the number of retired: MMX instructions.

C2H

01H

UOPS_RETIRED.ANY

Counts the number of micro-ops retired, (macroUse cmask=1 and invert
fused=1, micro-fused=2, others=1; maximum count to count active cycles or
of 8 per cycle). Most instructions are composed of
stalled cycles.
one or two micro-ops. Some instructions are
decoded into longer sequences such as repeat
instructions, floating point transcendental
instructions, and assists.

C2H

02H

UOPS_RETIRED.RETIRE_SLOT
S

Counts the number of retirement slots used each
cycle.

C2H

04H

UOPS_RETIRED.MACRO_FUSE
D

Counts number of macro-fused uops retired.

C3H

01H

MACHINE_CLEARS.CYCLES

Counts the cycles machine clear is asserted.

C3H

02H

MACHINE_CLEARS.MEM_ORDE Counts the number of machine clears due to
R
memory order conflicts.

C3H

04H

MACHINE_CLEARS.SMC

C4H

00H

BR_INST_RETIRED.ALL_BRAN Branch instructions at retirement.
CHES

C4H

01H

BR_INST_RETIRED.CONDITION Counts the number of conditional branch
AL
instructions retired.

C4H

02H

BR_INST_RETIRED.NEAR_CAL Counts the number of direct & indirect near
L
unconditional calls retired.

Counts the number of times that a program writes
to a code section. Self-modifying code causes a
severe penalty in all Intel 64 and IA-32 processors.
The modified cache line is written back to the L2
and L3caches.
See Table 19-1.

Vol. 3B 19-121

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

C5H

00H

BR_MISP_RETIRED.ALL_BRAN Mispredicted branch instructions at retirement.
CHES

C5H

01H

BR_MISP_RETIRED.CONDITION Counts mispredicted conditional retired calls.
AL

C5H

02H

BR_MISP_RETIRED.NEAR_CAL Counts mispredicted direct & indirect near
L
unconditional retired calls.

C5H

04H

BR_MISP_RETIRED.ALL_BRAN Counts all mispredicted retired calls.
CHES

C7H

01H

SSEX_UOPS_RETIRED.PACKED Counts SIMD packed single-precision floating-point
_SINGLE
uops retired.

C7H

02H

SSEX_UOPS_RETIRED.SCALAR Counts SIMD scalar single-precision floating-point
_SINGLE
uops retired.

C7H

04H

SSEX_UOPS_RETIRED.PACKED Counts SIMD packed double-precision floating-point
_DOUBLE
uops retired.

C7H

08H

SSEX_UOPS_RETIRED.SCALAR Counts SIMD scalar double-precision floating-point
_DOUBLE
uops retired.

C7H

10H

SSEX_UOPS_RETIRED.VECTOR Counts 128-bit SIMD vector integer uops retired.
_INTEGER

C8H

20H

ITLB_MISS_RETIRED

CBH

01H

MEM_LOAD_RETIRED.L1D_HIT Counts number of retired loads that hit the L1 data
cache.

CBH

02H

MEM_LOAD_RETIRED.L2_HIT

Counts number of retired loads that hit the L2 data
cache.

CBH

04H

MEM_LOAD_RETIRED.L3_UNS
HARED_HIT

Counts number of retired loads that hit their own,
unshared lines in the L3 cache.

CBH

08H

MEM_LOAD_RETIRED.OTHER_ Counts number of retired loads that hit in a sibling
CORE_L2_HIT_HITM
core's L2 (on die core). Since the L3 is inclusive of all
cores on the package, this is an L3 hit. This counts
both clean and modified hits.

CBH

10H

MEM_LOAD_RETIRED.L3_MISS Counts number of retired loads that miss the L3
cache. The load was satisfied by a remote socket,
local memory or an IOH.

CBH

40H

MEM_LOAD_RETIRED.HIT_LFB Counts number of retired loads that miss the L1D
and the address is located in an allocated line fill
buffer and will soon be committed to cache. This is
counting secondary L1D misses.

CBH

80H

MEM_LOAD_RETIRED.DTLB_MI Counts the number of retired loads that missed the
SS
DTLB. The DTLB miss is not counted if the load
operation causes a fault. This event counts loads
from cacheable memory only. The event does not
count loads by software prefetches. Counts both
primary and secondary misses to the TLB.

CCH

01H

FP_MMX_TRANS.TO_FP

19-122 Vol. 3B

Event Mask Mnemonic

Description

Counts the number of retired instructions that
missed the ITLB when the instruction was fetched.

Counts the first floating-point instruction following
any MMX instruction. You can use this event to
estimate the penalties for the transitions between
floating-point and MMX technology states.

Comment
See Table 19-1.

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

CCH

02H

FP_MMX_TRANS.TO_MMX

Counts the first MMX instruction following a
floating-point instruction. You can use this event to
estimate the penalties for the transitions between
floating-point and MMX technology states.

CCH

03H

FP_MMX_TRANS.ANY

Counts all transitions from floating point to MMX
instructions and from MMX instructions to floating
point instructions. You can use this event to
estimate the penalties for the transitions between
floating-point and MMX technology states.

D0H

01H

MACRO_INSTS.DECODED

Counts the number of instructions decoded, (but not
necessarily executed or retired).

D1H

01H

UOPS_DECODED.STALL_CYCLE Counts the cycles of decoder stalls. INV=1, Cmask=
S
1.

D1H

02H

UOPS_DECODED.MS

Counts the number of Uops decoded by the
Microcode Sequencer, MS. The MS delivers uops
when the instruction is more than 4 uops long or a
microcode assist is occurring.

D1H

04H

UOPS_DECODED.ESP_FOLDIN
G

Counts number of stack pointer (ESP) instructions
decoded: push, pop, call, ret, etc. ESP instructions do
not generate a Uop to increment or decrement ESP.
Instead, they update an ESP_Offset register that
keeps track of the delta to the current value of the
ESP register.

D1H

08H

UOPS_DECODED.ESP_SYNC

Counts number of stack pointer (ESP) sync
operations where an ESP instruction is corrected by
adding the ESP offset register to the current value
of the ESP register.

D2H

01H

RAT_STALLS.FLAGS

Counts the number of cycles during which
execution stalled due to several reasons, one of
which is a partial flag register stall. A partial register
stall may occur when two conditions are met: 1) an
instruction modifies some, but not all, of the flags in
the flag register and 2) the next instruction, which
depends on flags, depends on flags that were not
modified by this instruction.

D2H

02H

RAT_STALLS.REGISTERS

This event counts the number of cycles instruction
execution latency became longer than the defined
latency because the instruction used a register that
was partially written by previous instruction.

D2H

04H

RAT_STALLS.ROB_READ_POR
T

Counts the number of cycles when ROB read port
stalls occurred, which did not allow new micro-ops
to enter the out-of-order pipeline. Note that, at this
stage in the pipeline, additional stalls may occur at
the same cycle and prevent the stalled micro-ops
from entering the pipe. In such a case, micro-ops
retry entering the execution pipe in the next cycle
and the ROB-read port stall is counted again.

D2H

08H

RAT_STALLS.SCOREBOARD

Counts the cycles where we stall due to
microarchitecturally required serialization.
Microcode scoreboarding stalls.

Comment

Vol. 3B 19-123

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

D2H

0FH

RAT_STALLS.ANY

Counts all Register Allocation Table stall cycles due
to: Cycles when ROB read port stalls occurred,
which did not allow new micro-ops to enter the
execution pipe, Cycles when partial register stalls
occurred, Cycles when flag stalls occurred, Cycles
floating-point unit (FPU) status word stalls occurred.
To count each of these conditions separately use
the events: RAT_STALLS.ROB_READ_PORT,
RAT_STALLS.PARTIAL, RAT_STALLS.FLAGS, and
RAT_STALLS.FPSW.

D4H

01H

SEG_RENAME_STALLS

Counts the number of stall cycles due to the lack of
renaming resources for the ES, DS, FS, and GS
segment registers. If a segment is renamed but not
retired and a second update to the same segment
occurs, a stall occurs in the front end of the pipeline
until the renamed segment retires.

D5H

01H

ES_REG_RENAMES

Counts the number of times the ES segment
register is renamed.

DBH

01H

UOP_UNFUSION

Counts unfusion events due to floating point
exception to a fused uop.

E0H

01H

BR_INST_DECODED

Counts the number of branch instructions decoded.

E5H

01H

BPU_MISSED_CALL_RET

Counts number of times the Branch Prediction Unit
missed predicting a call or return branch.

E6H

01H

BACLEAR.CLEAR

Counts the number of times the front end is
resteered, mainly when the Branch Prediction Unit
cannot provide a correct prediction and this is
corrected by the Branch Address Calculator at the
front end. This can occur if the code has many
branches such that they cannot be consumed by
the BPU. Each BACLEAR asserted by the BAC
generates approximately an 8 cycle bubble in the
instruction fetch pipeline. The effect on total
execution time depends on the surrounding code.

E6H

02H

BACLEAR.BAD_TARGET

Counts number of Branch Address Calculator clears
(BACLEAR) asserted due to conditional branch
instructions in which there was a target hit but the
direction was wrong. Each BACLEAR asserted by
the BAC generates approximately an 8 cycle bubble
in the instruction fetch pipeline.

E8H

01H

BPU_CLEARS.EARLY

Counts early (normal) Branch Prediction Unit clears: The BPU clear leads to 2
BPU predicted a taken branch after incorrectly
cycle bubble in the front
assuming that it was not taken.
end.

E8H

02H

BPU_CLEARS.LATE

Counts late Branch Prediction Unit clears due to
Most Recently Used conflicts. The PBU clear leads
to a 3 cycle bubble in the front end.

ECH

01H

THREAD_ACTIVE

Counts cycles threads are active.

F0H

01H

L2_TRANSACTIONS.LOAD

Counts L2 load operations due to HW prefetch or
demand loads.

19-124 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

F0H

02H

L2_TRANSACTIONS.RFO

Counts L2 RFO operations due to HW prefetch or
demand RFOs.

F0H

04H

L2_TRANSACTIONS.IFETCH

Counts L2 instruction fetch operations due to HW
prefetch or demand ifetch.

F0H

08H

L2_TRANSACTIONS.PREFETC
H

Counts L2 prefetch operations.

F0H

10H

L2_TRANSACTIONS.L1D_WB

Counts L1D writeback operations to the L2.

F0H

20H

L2_TRANSACTIONS.FILL

Counts L2 cache line fill operations due to load, RFO,
L1D writeback or prefetch.

F0H

40H

L2_TRANSACTIONS.WB

Counts L2 writeback operations to the L3.

F0H

80H

L2_TRANSACTIONS.ANY

Counts all L2 cache operations.

F1H

02H

L2_LINES_IN.S_STATE

Counts the number of cache lines allocated in the L2
cache in the S (shared) state.

F1H

04H

L2_LINES_IN.E_STATE

Counts the number of cache lines allocated in the L2
cache in the E (exclusive) state.

F1H

07H

L2_LINES_IN.ANY

Counts the number of cache lines allocated in the L2
cache.

F2H

01H

L2_LINES_OUT.DEMAND_CLEA Counts L2 clean cache lines evicted by a demand
N
request.

F2H

02H

L2_LINES_OUT.DEMAND_DIRT Counts L2 dirty (modified) cache lines evicted by a
Y
demand request.

F2H

04H

L2_LINES_OUT.PREFETCH_CL
EAN

F2H

08H

L2_LINES_OUT.PREFETCH_DIR Counts L2 modified cache line evicted by a prefetch
TY
request.

F2H

0FH

L2_LINES_OUT.ANY

Counts all L2 cache lines evicted for any reason.

F4H

04H

SQ_MISC.LRU_HINTS

Counts number of Super Queue LRU hints sent to
L3.

F4H

10H

SQ_MISC.SPLIT_LOCK

Counts the number of SQ lock splits across a cache
line.

F6H

01H

SQ_FULL_STALL_CYCLES

Counts cycles the Super Queue is full. Neither of the
threads on this core will be able to access the
uncore.

F7H

01H

FP_ASSIST.ALL

Counts the number of floating point operations
executed that required micro-code assist
intervention. Assists are required in the following
cases: SSE instructions, (Denormal input when the
DAZ flag is off or Underflow result when the FTZ
flag is off): x87 instructions, (NaN or denormal are
loaded to a register or used as input from memory,
Division by 0 or Underflow output).

F7H

02H

FP_ASSIST.OUTPUT

Counts number of floating point micro-code assist
when the output value (destination register) is
invalid.

F7H

04H

FP_ASSIST.INPUT

Counts number of floating point micro-code assist
when the input value (one of the source operands
to an FP instruction) is invalid.

Comment

Counts L2 clean cache line evicted by a prefetch
request.

Vol. 3B 19-125

PERFORMANCE MONITORING EVENTS

Table 19-21. Performance Events In the Processor Core for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

FDH

01H

SIMD_INT_64.PACKED_MPY

Counts number of SID integer 64 bit packed multiply
operations.

FDH

02H

SIMD_INT_64.PACKED_SHIFT

Counts number of SID integer 64 bit packed shift
operations.

FDH

04H

SIMD_INT_64.PACK

Counts number of SID integer 64 bit pack
operations.

FDH

08H

SIMD_INT_64.UNPACK

Counts number of SID integer 64 bit unpack
operations.

FDH

10H

SIMD_INT_64.PACKED_LOGICA Counts number of SID integer 64 bit logical
L
operations.

FDH

20H

SIMD_INT_64.PACKED_ARITH

FDH

40H

SIMD_INT_64.SHUFFLE_MOVE Counts number of SID integer 64 bit shift or move
operations.

Comment

Counts number of SID integer 64 bit arithmetic
operations.

Model-specific performance monitoring events of the uncore sub-system for processors with CPUID signature of
DisplayFamily_DisplayModel 06_25H, 06_2CH, and 06_1FH support performance events listed in Table 19-22.

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere
Event
Num.

Umask
Value

00H

01H

UNC_GQ_CYCLES_FULL.READ_ Uncore cycles Global Queue read tracker is full.
TRACKER

00H

02H

UNC_GQ_CYCLES_FULL.WRITE Uncore cycles Global Queue write tracker is full.
_TRACKER

00H

04H

UNC_GQ_CYCLES_FULL.PEER_ Uncore cycles Global Queue peer probe tracker is full.
PROBE_TRACKER
The peer probe tracker queue tracks snoops from the
IOH and remote sockets.

01H

01H

UNC_GQ_CYCLES_NOT_EMPTY Uncore cycles were Global Queue read tracker has at
.READ_TRACKER
least one valid entry.

01H

02H

UNC_GQ_CYCLES_NOT_EMPTY Uncore cycles were Global Queue write tracker has at
.WRITE_TRACKER
least one valid entry.

01H

04H

UNC_GQ_CYCLES_NOT_EMPTY Uncore cycles were Global Queue peer probe tracker
.PEER_PROBE_TRACKER
has at least one valid entry. The peer probe tracker
queue tracks IOH and remote socket snoops.

02H

01H

UNC_GQ_OCCUPANCY.READ_T Increments the number of queue entries (code read,
RACKER
data read, and RFOs) in the tread tracker. The GQ read
tracker allocate to deallocate occupancy count is
divided by the count to obtain the average read tracker
latency.

03H

01H

UNC_GQ_ALLOC.READ_TRACK
ER

19-126 Vol. 3B

Event Mask Mnemonic

Description

Counts the number of tread tracker allocate to
deallocate entries. The GQ read tracker allocate to
deallocate occupancy count is divided by the count to
obtain the average read tracker latency.

Comment

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

03H

02H

UNC_GQ_ALLOC.RT_L3_MISS

Counts the number GQ read tracker entries for which a
full cache line read has missed the L3. The GQ read
tracker L3 miss to fill occupancy count is divided by
this count to obtain the average cache line read L3
miss latency. The latency represents the time after
which the L3 has determined that the cache line has
missed. The time between a GQ read tracker allocation
and the L3 determining that the cache line has missed
is the average L3 hit latency. The total L3 cache line
read miss latency is the hit latency + L3 miss latency.

03H

04H

UNC_GQ_ALLOC.RT_TO_L3_RE Counts the number of GQ read tracker entries that are
SP
allocated in the read tracker queue that hit or miss the
L3. The GQ read tracker L3 hit occupancy count is
divided by this count to obtain the average L3 hit
latency.

03H

08H

UNC_GQ_ALLOC.RT_TO_RTID_ Counts the number of GQ read tracker entries that are
ACQUIRED
allocated in the read tracker, have missed in the L3 and
have not acquired a Request Transaction ID. The GQ
read tracker L3 miss to RTID acquired occupancy count
is divided by this count to obtain the average latency
for a read L3 miss to acquire an RTID.

03H

10H

UNC_GQ_ALLOC.WT_TO_RTID_ Counts the number of GQ write tracker entries that are
ACQUIRED
allocated in the write tracker, have missed in the L3
and have not acquired a Request Transaction ID. The
GQ write tracker L3 miss to RTID occupancy count is
divided by this count to obtain the average latency for
a write L3 miss to acquire an RTID.

03H

20H

UNC_GQ_ALLOC.WRITE_TRAC
KER

Counts the number of GQ write tracker entries that are
allocated in the write tracker queue that miss the L3.
The GQ write tracker occupancy count is divided by
this count to obtain the average L3 write miss latency.

03H

40H

UNC_GQ_ALLOC.PEER_PROBE
_TRACKER

Counts the number of GQ peer probe tracker (snoop)
entries that are allocated in the peer probe tracker
queue that miss the L3. The GQ peer probe occupancy
count is divided by this count to obtain the average L3
peer probe miss latency.

04H

01H

UNC_GQ_DATA.FROM_QPI

Cycles Global Queue Quickpath Interface input data
port is busy importing data from the Quickpath
Interface. Each cycle the input port can transfer 8 or
16 bytes of data.

04H

02H

UNC_GQ_DATA.FROM_QMC

Cycles Global Queue Quickpath Memory Interface input
data port is busy importing data from the Quickpath
Memory Interface. Each cycle the input port can
transfer 8 or 16 bytes of data.

04H

04H

UNC_GQ_DATA.FROM_L3

Cycles GQ L3 input data port is busy importing data
from the Last Level Cache. Each cycle the input port
can transfer 32 bytes of data.

04H

08H

UNC_GQ_DATA.FROM_CORES_ Cycles GQ Core 0 and 2 input data port is busy
02
importing data from processor cores 0 and 2. Each
cycle the input port can transfer 32 bytes of data.

Comment

Vol. 3B 19-127

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

04H

10H

UNC_GQ_DATA.FROM_CORES_ Cycles GQ Core 1 and 3 input data port is busy
13
importing data from processor cores 1 and 3. Each
cycle the input port can transfer 32 bytes of data.

05H

01H

UNC_GQ_DATA.TO_QPI_QMC

Cycles GQ QPI and QMC output data port is busy
sending data to the Quickpath Interface or Quickpath
Memory Interface. Each cycle the output port can
transfer 32 bytes of data.

05H

02H

UNC_GQ_DATA.TO_L3

Cycles GQ L3 output data port is busy sending data to
the Last Level Cache. Each cycle the output port can
transfer 32 bytes of data.

05H

04H

UNC_GQ_DATA.TO_CORES

Cycles GQ Core output data port is busy sending data
to the Cores. Each cycle the output port can transfer
32 bytes of data.

06H

01H

UNC_SNP_RESP_TO_LOCAL_H Number of snoop responses to the local home that L3
OME.I_STATE
does not have the referenced cache line.

06H

02H

UNC_SNP_RESP_TO_LOCAL_H Number of snoop responses to the local home that L3
OME.S_STATE
has the referenced line cached in the S state.

06H

04H

UNC_SNP_RESP_TO_LOCAL_H Number of responses to code or data read snoops to
OME.FWD_S_STATE
the local home that the L3 has the referenced cache
line in the E state. The L3 cache line state is changed
to the S state and the line is forwarded to the local
home in the S state.

06H

08H

UNC_SNP_RESP_TO_LOCAL_H Number of responses to read invalidate snoops to the
OME.FWD_I_STATE
local home that the L3 has the referenced cache line in
the M state. The L3 cache line state is invalidated and
the line is forwarded to the local home in the M state.

06H

10H

UNC_SNP_RESP_TO_LOCAL_H Number of conflict snoop responses sent to the local
OME.CONFLICT
home.

06H

20H

UNC_SNP_RESP_TO_LOCAL_H Number of responses to code or data read snoops to
OME.WB
the local home that the L3 has the referenced line
cached in the M state.

07H

01H

UNC_SNP_RESP_TO_REMOTE_ Number of snoop responses to a remote home that L3
HOME.I_STATE
does not have the referenced cache line.

07H

02H

UNC_SNP_RESP_TO_REMOTE_ Number of snoop responses to a remote home that L3
HOME.S_STATE
has the referenced line cached in the S state.

07H

04H

UNC_SNP_RESP_TO_REMOTE_ Number of responses to code or data read snoops to a
HOME.FWD_S_STATE
remote home that the L3 has the referenced cache
line in the E state. The L3 cache line state is changed
to the S state and the line is forwarded to the remote
home in the S state.

07H

08H

UNC_SNP_RESP_TO_REMOTE_ Number of responses to read invalidate snoops to a
HOME.FWD_I_STATE
remote home that the L3 has the referenced cache
line in the M state. The L3 cache line state is
invalidated and the line is forwarded to the remote
home in the M state.

07H

10H

UNC_SNP_RESP_TO_REMOTE_ Number of conflict snoop responses sent to the local
HOME.CONFLICT
home.

19-128 Vol. 3B

Event Mask Mnemonic

Description

Comment

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

07H

20H

UNC_SNP_RESP_TO_REMOTE_ Number of responses to code or data read snoops to a
HOME.WB
remote home that the L3 has the referenced line
cached in the M state.

07H

24H

UNC_SNP_RESP_TO_REMOTE_ Number of HITM snoop responses to a remote home.
HOME.HITM

08H

01H

UNC_L3_HITS.READ

Number of code read, data read and RFO requests that
hit in the L3.

08H

02H

UNC_L3_HITS.WRITE

Number of writeback requests that hit in the L3.
Writebacks from the cores will always result in L3 hits
due to the inclusive property of the L3.

08H

04H

UNC_L3_HITS.PROBE

Number of snoops from IOH or remote sockets that hit
in the L3.

08H

03H

UNC_L3_HITS.ANY

Number of reads and writes that hit the L3.

09H

01H

UNC_L3_MISS.READ

Number of code read, data read and RFO requests that
miss the L3.

09H

02H

UNC_L3_MISS.WRITE

Number of writeback requests that miss the L3.
Should always be zero as writebacks from the cores
will always result in L3 hits due to the inclusive
property of the L3.

09H

04H

UNC_L3_MISS.PROBE

Number of snoops from IOH or remote sockets that
miss the L3.

09H

03H

UNC_L3_MISS.ANY

Number of reads and writes that miss the L3.

0AH

01H

UNC_L3_LINES_IN.M_STATE

Counts the number of L3 lines allocated in M state. The
only time a cache line is allocated in the M state is
when the line was forwarded in M state is forwarded
due to a Snoop Read Invalidate Own request.

0AH

02H

UNC_L3_LINES_IN.E_STATE

Counts the number of L3 lines allocated in E state.

0AH

04H

UNC_L3_LINES_IN.S_STATE

Counts the number of L3 lines allocated in S state.

Event Mask Mnemonic

Description

0AH

08H

UNC_L3_LINES_IN.F_STATE

Counts the number of L3 lines allocated in F state.

0AH

0FH

UNC_L3_LINES_IN.ANY

Counts the number of L3 lines allocated in any state.

0BH

01H

UNC_L3_LINES_OUT.M_STATE

Counts the number of L3 lines victimized that were in
the M state. When the victim cache line is in M state,
the line is written to its home cache agent which can
be either local or remote.

0BH

02H

UNC_L3_LINES_OUT.E_STATE

Counts the number of L3 lines victimized that were in
the E state.

0BH

04H

UNC_L3_LINES_OUT.S_STATE

Counts the number of L3 lines victimized that were in
the S state.

0BH

08H

UNC_L3_LINES_OUT.I_STATE

Counts the number of L3 lines victimized that were in
the I state.

0BH

10H

UNC_L3_LINES_OUT.F_STATE

Counts the number of L3 lines victimized that were in
the F state.

0BH

1FH

UNC_L3_LINES_OUT.ANY

Counts the number of L3 lines victimized in any state.

0CH

01H

UNC_GQ_SNOOP.GOTO_S

Counts the number of remote snoops that have
requested a cache line be set to the S state.

Comment

Vol. 3B 19-129

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

0CH

02H

UNC_GQ_SNOOP.GOTO_I

Counts the number of remote snoops that have
requested a cache line be set to the I state.

0CH

04H

UNC_GQ_SNOOP.GOTO_S_HIT_ Counts the number of remote snoops that have
E
requested a cache line be set to the S state from E
state.

Requires writing MSR
301H with mask = 2H.

0CH

04H

UNC_GQ_SNOOP.GOTO_S_HIT_ Counts the number of remote snoops that have
F
requested a cache line be set to the S state from F
(forward) state.

Requires writing MSR
301H with mask = 8H.

0CH

04H

UNC_GQ_SNOOP.GOTO_S_HIT_ Counts the number of remote snoops that have
M
requested a cache line be set to the S state from M
state.

Requires writing MSR
301H with mask = 1H.

0CH

04H

UNC_GQ_SNOOP.GOTO_S_HIT_ Counts the number of remote snoops that have
S
requested a cache line be set to the S state from S
state.

Requires writing MSR
301H with mask = 4H.

0CH

08H

UNC_GQ_SNOOP.GOTO_I_HIT_ Counts the number of remote snoops that have
E
requested a cache line be set to the I state from E
state.

Requires writing MSR
301H with mask = 2H.

0CH

08H

UNC_GQ_SNOOP.GOTO_I_HIT_ Counts the number of remote snoops that have
F
requested a cache line be set to the I state from F
(forward) state.

Requires writing MSR
301H with mask = 8H.

0CH

08H

UNC_GQ_SNOOP.GOTO_I_HIT_ Counts the number of remote snoops that have
M
requested a cache line be set to the I state from M
state.

Requires writing MSR
301H with mask = 1H.

0CH

08H

UNC_GQ_SNOOP.GOTO_I_HIT_ Counts the number of remote snoops that have
S
requested a cache line be set to the I state from S
state.

Requires writing MSR
301H with mask = 4H.

20H

01H

UNC_QHL_REQUESTS.IOH_RE
ADS

20H

02H

UNC_QHL_REQUESTS.IOH_WRI Counts number of Quickpath Home Logic write
TES
requests from the IOH.

20H

04H

UNC_QHL_REQUESTS.REMOTE Counts number of Quickpath Home Logic read requests
_READS
from a remote socket.

20H

08H

UNC_QHL_REQUESTS.REMOTE Counts number of Quickpath Home Logic write
_WRITES
requests from a remote socket.

20H

10H

UNC_QHL_REQUESTS.LOCAL_
READS

Counts number of Quickpath Home Logic read requests
from the local socket.

20H

20H

UNC_QHL_REQUESTS.LOCAL_
WRITES

Counts number of Quickpath Home Logic write
requests from the local socket.

21H

01H

UNC_QHL_CYCLES_FULL.IOH

Counts uclk cycles all entries in the Quickpath Home
Logic IOH are full.

21H

02H

UNC_QHL_CYCLES_FULL.REMO Counts uclk cycles all entries in the Quickpath Home
TE
Logic remote tracker are full.

21H

04H

UNC_QHL_CYCLES_FULL.LOCA Counts uclk cycles all entries in the Quickpath Home
L
Logic local tracker are full.

22H

01H

UNC_QHL_CYCLES_NOT_EMPT Counts uclk cycles all entries in the Quickpath Home
Logic IOH is busy.
Y.IOH

19-130 Vol. 3B

Counts number of Quickpath Home Logic read requests
from the IOH.

Comment

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

22H

02H

UNC_QHL_CYCLES_NOT_EMPT Counts uclk cycles all entries in the Quickpath Home
Y.REMOTE
Logic remote tracker is busy.

22H

04H

UNC_QHL_CYCLES_NOT_EMPT Counts uclk cycles all entries in the Quickpath Home
Y.LOCAL
Logic local tracker is busy.

Event Mask Mnemonic

Description

23H

01H

UNC_QHL_OCCUPANCY.IOH

23H

02H

UNC_QHL_OCCUPANCY.REMOT QHL remote tracker allocate to deallocate read
E
occupancy.

23H

04H

UNC_QHL_OCCUPANCY.LOCAL

QHL local tracker allocate to deallocate read
occupancy.

24H

02H

UNC_QHL_ADDRESS_CONFLIC
TS.2WAY

Counts number of QHL Active Address Table (AAT)
entries that saw a max of 2 conflicts. The AAT is a
structure that tracks requests that are in conflict. The
requests themselves are in the home tracker entries.
The count is reported when an AAT entry deallocates.

24H

04H

UNC_QHL_ADDRESS_CONFLIC
TS.3WAY

Counts number of QHL Active Address Table (AAT)
entries that saw a max of 3 conflicts. The AAT is a
structure that tracks requests that are in conflict. The
requests themselves are in the home tracker entries.
The count is reported when an AAT entry deallocates.

25H

01H

UNC_QHL_CONFLICT_CYCLES.I Counts cycles the Quickpath Home Logic IOH Tracker
OH
contains two or more requests with an address
conflict. A max of 3 requests can be in conflict.

25H

02H

UNC_QHL_CONFLICT_CYCLES.
REMOTE

25H

04H

UNC_QHL_CONFLICT_CYCLES.L Counts cycles the Quickpath Home Logic Local Tracker
OCAL
contains two or more requests with an address
conflict. A max of 3 requests can be in conflict.

26H

01H

UNC_QHL_TO_QMC_BYPASS

Counts number or requests to the Quickpath Memory
Controller that bypass the Quickpath Home Logic. All
local accesses can be bypassed. For remote requests,
only read requests can be bypassed.

28H

01H

UNC_QMC_ISOC_FULL.READ.C
H0

Counts cycles all the entries in the DRAM channel 0
high priority queue are occupied with isochronous read
requests.

28H

02H

UNC_QMC_ISOC_FULL.READ.C
H1

Counts cycles all the entries in the DRAM channel
1high priority queue are occupied with isochronous
read requests.

28H

04H

UNC_QMC_ISOC_FULL.READ.C
H2

Counts cycles all the entries in the DRAM channel 2
high priority queue are occupied with isochronous read
requests.

28H

08H

UNC_QMC_ISOC_FULL.WRITE.C Counts cycles all the entries in the DRAM channel 0
H0
high priority queue are occupied with isochronous
write requests.

28H

10H

UNC_QMC_ISOC_FULL.WRITE.C Counts cycles all the entries in the DRAM channel 1
H1
high priority queue are occupied with isochronous
write requests.

Comment

QHL IOH tracker allocate to deallocate read occupancy.

Counts cycles the Quickpath Home Logic Remote
Tracker contains two or more requests with an
address conflict. A max of 3 requests can be in conflict.

Vol. 3B 19-131

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

28H

20H

UNC_QMC_ISOC_FULL.WRITE.C Counts cycles all the entries in the DRAM channel 2
H2
high priority queue are occupied with isochronous
write requests.

29H

01H

UNC_QMC_BUSY.READ.CH0

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding read request to DRAM channel
0.

29H

02H

UNC_QMC_BUSY.READ.CH1

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding read request to DRAM channel
1.

29H

04H

UNC_QMC_BUSY.READ.CH2

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding read request to DRAM channel
2.

29H

08H

UNC_QMC_BUSY.WRITE.CH0

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding write request to DRAM channel
0.

29H

10H

UNC_QMC_BUSY.WRITE.CH1

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding write request to DRAM channel
1.

29H

20H

UNC_QMC_BUSY.WRITE.CH2

Counts cycles where Quickpath Memory Controller has
at least 1 outstanding write request to DRAM channel
2.

2AH

01H

UNC_QMC_OCCUPANCY.CH0

IMC channel 0 normal read request occupancy.

2AH

02H

UNC_QMC_OCCUPANCY.CH1

IMC channel 1 normal read request occupancy.

2AH

04H

UNC_QMC_OCCUPANCY.CH2

IMC channel 2 normal read request occupancy.
Normal read request occupancy for any channel.

Event Mask Mnemonic

Description

2AH

07H

UNC_QMC_OCCUPANCY.ANY

2BH

01H

UNC_QMC_ISSOC_OCCUPANCY. IMC channel 0 issoc read request occupancy.
CH0

2BH

02H

UNC_QMC_ISSOC_OCCUPANCY. IMC channel 1 issoc read request occupancy.
CH1

2BH

04H

UNC_QMC_ISSOC_OCCUPANCY. IMC channel 2 issoc read request occupancy.
CH2

2BH

07H

UNC_QMC_ISSOC_READS.ANY

IMC issoc read request occupancy.

2CH

01H

UNC_QMC_NORMAL_READS.C
H0

Counts the number of Quickpath Memory Controller
channel 0 medium and low priority read requests. The
QMC channel 0 normal read occupancy divided by this
count provides the average QMC channel 0 read
latency.

2CH

02H

UNC_QMC_NORMAL_READS.C
H1

Counts the number of Quickpath Memory Controller
channel 1 medium and low priority read requests. The
QMC channel 1 normal read occupancy divided by this
count provides the average QMC channel 1 read
latency.

2CH

04H

UNC_QMC_NORMAL_READS.C
H2

Counts the number of Quickpath Memory Controller
channel 2 medium and low priority read requests. The
QMC channel 2 normal read occupancy divided by this
count provides the average QMC channel 2 read
latency.

19-132 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

2CH

07H

UNC_QMC_NORMAL_READS.A
NY

Counts the number of Quickpath Memory Controller
medium and low priority read requests. The QMC
normal read occupancy divided by this count provides
the average QMC read latency.

2DH

01H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.CH0
channel 0 high priority isochronous read requests.

2DH

02H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.CH1
channel 1 high priority isochronous read requests.

2DH

04H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.CH2
channel 2 high priority isochronous read requests.

2DH

07H

UNC_QMC_HIGH_PRIORITY_RE Counts the number of Quickpath Memory Controller
ADS.ANY
high priority isochronous read requests.

2EH

01H

UNC_QMC_CRITICAL_PRIORITY Counts the number of Quickpath Memory Controller
_READS.CH0
channel 0 critical priority isochronous read requests.

2EH

02H

UNC_QMC_CRITICAL_PRIORITY Counts the number of Quickpath Memory Controller
_READS.CH1
channel 1 critical priority isochronous read requests.

2EH

04H

UNC_QMC_CRITICAL_PRIORITY Counts the number of Quickpath Memory Controller
_READS.CH2
channel 2 critical priority isochronous read requests.

2EH

07H

UNC_QMC_CRITICAL_PRIORITY Counts the number of Quickpath Memory Controller
_READS.ANY
critical priority isochronous read requests.

2FH

01H

UNC_QMC_WRITES.FULL.CH0

Counts number of full cache line writes to DRAM
channel 0.

2FH

02H

UNC_QMC_WRITES.FULL.CH1

Counts number of full cache line writes to DRAM
channel 1.

2FH

04H

UNC_QMC_WRITES.FULL.CH2

Counts number of full cache line writes to DRAM
channel 2.

2FH

07H

UNC_QMC_WRITES.FULL.ANY

Counts number of full cache line writes to DRAM.

2FH

08H

UNC_QMC_WRITES.PARTIAL.C
H0

Counts number of partial cache line writes to DRAM
channel 0.

2FH

10H

UNC_QMC_WRITES.PARTIAL.C
H1

Counts number of partial cache line writes to DRAM
channel 1.

2FH

20H

UNC_QMC_WRITES.PARTIAL.C
H2

Counts number of partial cache line writes to DRAM
channel 2.

2FH

38H

UNC_QMC_WRITES.PARTIAL.A
NY

Counts number of partial cache line writes to DRAM.

30H

01H

UNC_QMC_CANCEL.CH0

Counts number of DRAM channel 0 cancel requests.

30H

02H

UNC_QMC_CANCEL.CH1

Counts number of DRAM channel 1 cancel requests.

30H

04H

UNC_QMC_CANCEL.CH2

Counts number of DRAM channel 2 cancel requests.

30H

07H

UNC_QMC_CANCEL.ANY

Counts number of DRAM cancel requests.

31H

01H

UNC_QMC_PRIORITY_UPDATE
S.CH0

Counts number of DRAM channel 0 priority updates. A
priority update occurs when an ISOC high or critical
request is received by the QHL and there is a matching
request with normal priority that has already been
issued to the QMC. In this instance, the QHL will send a
priority update to QMC to expedite the request.

Comment

Vol. 3B 19-133

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

31H

02H

UNC_QMC_PRIORITY_UPDATE
S.CH1

Counts number of DRAM channel 1 priority updates. A
priority update occurs when an ISOC high or critical
request is received by the QHL and there is a matching
request with normal priority that has already been
issued to the QMC. In this instance, the QHL will send a
priority update to QMC to expedite the request.

31H

04H

UNC_QMC_PRIORITY_UPDATE
S.CH2

Counts number of DRAM channel 2 priority updates. A
priority update occurs when an ISOC high or critical
request is received by the QHL and there is a matching
request with normal priority that has already been
issued to the QMC. In this instance, the QHL will send a
priority update to QMC to expedite the request.

31H

07H

UNC_QMC_PRIORITY_UPDATE
S.ANY

Counts number of DRAM priority updates. A priority
update occurs when an ISOC high or critical request is
received by the QHL and there is a matching request
with normal priority that has already been issued to
the QMC. In this instance, the QHL will send a priority
update to QMC to expedite the request.

32H

01H

UNC_IMC_RETRY.CH0

Counts number of IMC DRAM channel 0 retries. DRAM
retry only occurs when configured in RAS mode.

32H

02H

UNC_IMC_RETRY.CH1

Counts number of IMC DRAM channel 1 retries. DRAM
retry only occurs when configured in RAS mode.

32H

04H

UNC_IMC_RETRY.CH2

Counts number of IMC DRAM channel 2 retries. DRAM
retry only occurs when configured in RAS mode.

32H

07H

UNC_IMC_RETRY.ANY

Counts number of IMC DRAM retries from any channel.
DRAM retry only occurs when configured in RAS mode.

33H

01H

UNC_QHL_FRC_ACK_CNFLTS.I
OH

Counts number of Force Acknowledge Conflict
messages sent by the Quickpath Home Logic to the
IOH.

33H

02H

UNC_QHL_FRC_ACK_CNFLTS.R Counts number of Force Acknowledge Conflict
EMOTE
messages sent by the Quickpath Home Logic to the
remote home.

33H

04H

UNC_QHL_FRC_ACK_CNFLTS.L Counts number of Force Acknowledge Conflict
OCAL
messages sent by the Quickpath Home Logic to the
local home.

33H

07H

UNC_QHL_FRC_ACK_CNFLTS.A Counts number of Force Acknowledge Conflict
NY
messages sent by the Quickpath Home Logic.

34H

01H

UNC_QHL_SLEEPS.IOH_ORDER Counts number of occurrences a request was put to
sleep due to IOH ordering (write after read) conflicts.
While in the sleep state, the request is not eligible to
be scheduled to the QMC.

34H

02H

UNC_QHL_SLEEPS.REMOTE_O
RDER

34H

04H

UNC_QHL_SLEEPS.LOCAL_ORD Counts number of occurrences a request was put to
ER
sleep due to local socket ordering (write after read)
conflicts. While in the sleep state, the request is not
eligible to be scheduled to the QMC.

19-134 Vol. 3B

Counts number of occurrences a request was put to
sleep due to remote socket ordering (write after read)
conflicts. While in the sleep state, the request is not
eligible to be scheduled to the QMC.

Comment

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

34H

08H

UNC_QHL_SLEEPS.IOH_CONFLI Counts number of occurrences a request was put to
CT
sleep due to IOH address conflicts. While in the sleep
state, the request is not eligible to be scheduled to the
QMC.

34H

10H

UNC_QHL_SLEEPS.REMOTE_C
ONFLICT

34H

20H

UNC_QHL_SLEEPS.LOCAL_CON Counts number of occurrences a request was put to
FLICT
sleep due to local socket address conflicts. While in the
sleep state, the request is not eligible to be scheduled
to the QMC.

35H

01H

UNC_ADDR_OPCODE_MATCH.I
OH

Event Mask Mnemonic

Description

Comment

Counts number of occurrences a request was put to
sleep due to remote socket address conflicts. While in
the sleep state, the request is not eligible to be
scheduled to the QMC.

Counts number of requests from the IOH,
address/opcode of request is qualified by mask value
written to MSR 396H. The following mask values are
supported:

Match opcode/address
by writing MSR 396H
with mask supported
mask value.

0: NONE
40000000_00000000H:RSPFWDI
40001A00_00000000H:RSPFWDS
40001D00_00000000H:RSPIWB
35H

02H

UNC_ADDR_OPCODE_MATCH.R Counts number of requests from the remote socket,
EMOTE
address/opcode of request is qualified by mask value
written to MSR 396H. The following mask values are
supported:

Match opcode/address
by writing MSR 396H
with mask supported
mask value.

0: NONE
40000000_00000000H:RSPFWDI
40001A00_00000000H:RSPFWDS
40001D00_00000000H:RSPIWB
35H

04H

UNC_ADDR_OPCODE_MATCH.L Counts number of requests from the local socket,
OCAL
address/opcode of request is qualified by mask value
written to MSR 396H. The following mask values are
supported:

Match opcode/address
by writing MSR 396H
with mask supported
mask value.

0: NONE
40000000_00000000H:RSPFWDI
40001A00_00000000H:RSPFWDS
40001D00_00000000H:RSPIWB
40H

01H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.HOME.LINK_0

Counts cycles the Quickpath outbound link 0 HOME
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

02H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.SNOOP.LINK_0

Counts cycles the Quickpath outbound link 0 SNOOP
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

Vol. 3B 19-135

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

40H

04H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.NDR.LINK_0

Counts cycles the Quickpath outbound link 0 non-data
response virtual channel is stalled due to lack of a VNA
and VN0 credit. Note that this event does not filter out
when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

40H

08H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.HOME.LINK_1

Counts cycles the Quickpath outbound link 1 HOME
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

10H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.SNOOP.LINK_1

Counts cycles the Quickpath outbound link 1 SNOOP
virtual channel is stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

20H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.NDR.LINK_1

Counts cycles the Quickpath outbound link 1 non-data
response virtual channel is stalled due to lack of a VNA
and VN0 credit. Note that this event does not filter out
when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

40H

07H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.LINK_0

Counts cycles the Quickpath outbound link 0 virtual
channels are stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

40H

38H

UNC_QPI_TX_STALLED_SINGL
E_FLIT.LINK_1

Counts cycles the Quickpath outbound link 1 virtual
channels are stalled due to lack of a VNA and VN0
credit. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

41H

01H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 Data
_FLIT.DRS.LINK_0
Response virtual channel is stalled due to lack of VNA
and VN0 credits. Note that this event does not filter
out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

02H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 Non_FLIT.NCB.LINK_0
Coherent Bypass virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

04H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 Non_FLIT.NCS.LINK_0
Coherent Standard virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

19-136 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

41H

08H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 Data
_FLIT.DRS.LINK_1
Response virtual channel is stalled due to lack of VNA
and VN0 credits. Note that this event does not filter
out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

10H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 Non_FLIT.NCB.LINK_1
Coherent Bypass virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

20H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 Non_FLIT.NCS.LINK_1
Coherent Standard virtual channel is stalled due to lack
of VNA and VN0 credits. Note that this event does not
filter out when a flit would not have been selected for
arbitration because another virtual channel is getting
arbitrated.

41H

07H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 0 virtual
_FLIT.LINK_0
channels are stalled due to lack of VNA and VN0
credits. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

41H

38H

UNC_QPI_TX_STALLED_MULTI Counts cycles the Quickpath outbound link 1 virtual
_FLIT.LINK_1
channels are stalled due to lack of VNA and VN0
credits. Note that this event does not filter out when a
flit would not have been selected for arbitration
because another virtual channel is getting arbitrated.

42H

01H

UNC_QPI_TX_HEADER.FULL.LI Number of cycles that the header buffer in the
NK_0
Quickpath Interface outbound link 0 is full.

42H

02H

UNC_QPI_TX_HEADER.BUSY.LI Number of cycles that the header buffer in the
NK_0
Quickpath Interface outbound link 0 is busy.

42H

04H

UNC_QPI_TX_HEADER.FULL.LI Number of cycles that the header buffer in the
NK_1
Quickpath Interface outbound link 1 is full.

42H

08H

UNC_QPI_TX_HEADER.BUSY.LI Number of cycles that the header buffer in the
NK_1
Quickpath Interface outbound link 1 is busy.

43H

01H

UNC_QPI_RX_NO_PPT_CREDI
T.STALLS.LINK_0

Number of cycles that snoop packets incoming to the
Quickpath Interface link 0 are stalled and not sent to
the GQ because the GQ Peer Probe Tracker (PPT) does
not have any available entries.

43H

02H

UNC_QPI_RX_NO_PPT_CREDI
T.STALLS.LINK_1

Number of cycles that snoop packets incoming to the
Quickpath Interface link 1 are stalled and not sent to
the GQ because the GQ Peer Probe Tracker (PPT) does
not have any available entries.

60H

01H

UNC_DRAM_OPEN.CH0

Counts number of DRAM Channel 0 open commands
issued either for read or write. To read or write data,
the referenced DRAM page must first be opened.

Event Mask Mnemonic

Description

Comment

Vol. 3B 19-137

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

60H

02H

UNC_DRAM_OPEN.CH1

Counts number of DRAM Channel 1 open commands
issued either for read or write. To read or write data,
the referenced DRAM page must first be opened.

60H

04H

UNC_DRAM_OPEN.CH2

Counts number of DRAM Channel 2 open commands
issued either for read or write. To read or write data,
the referenced DRAM page must first be opened.

61H

01H

UNC_DRAM_PAGE_CLOSE.CH0 DRAM channel 0 command issued to CLOSE a page due
to page idle timer expiration. Closing a page is done by
issuing a precharge.

61H

02H

UNC_DRAM_PAGE_CLOSE.CH1 DRAM channel 1 command issued to CLOSE a page due
to page idle timer expiration. Closing a page is done by
issuing a precharge.

61H

04H

UNC_DRAM_PAGE_CLOSE.CH2 DRAM channel 2 command issued to CLOSE a page due
to page idle timer expiration. Closing a page is done by
issuing a precharge.

62H

01H

UNC_DRAM_PAGE_MISS.CH0

Counts the number of precharges (PRE) that were
issued to DRAM channel 0 because there was a page
miss. A page miss refers to a situation in which a page
is currently open and another page from the same
bank needs to be opened. The new page experiences a
page miss. Closing of the old page is done by issuing a
precharge.

62H

02H

UNC_DRAM_PAGE_MISS.CH1

Counts the number of precharges (PRE) that were
issued to DRAM channel 1 because there was a page
miss. A page miss refers to a situation in which a page
is currently open and another page from the same
bank needs to be opened. The new page experiences a
page miss. Closing of the old page is done by issuing a
precharge.

62H

04H

UNC_DRAM_PAGE_MISS.CH2

Counts the number of precharges (PRE) that were
issued to DRAM channel 2 because there was a page
miss. A page miss refers to a situation in which a page
is currently open and another page from the same
bank needs to be opened. The new page experiences a
page miss. Closing of the old page is done by issuing a
precharge.

63H

01H

UNC_DRAM_READ_CAS.CH0

Counts the number of times a read CAS command was
issued on DRAM channel 0.

63H

02H

UNC_DRAM_READ_CAS.AUTO
PRE_CH0

Counts the number of times a read CAS command was
issued on DRAM channel 0 where the command issued
used the auto-precharge (auto page close) mode.

63H

04H

UNC_DRAM_READ_CAS.CH1

Counts the number of times a read CAS command was
issued on DRAM channel 1.

63H

08H

UNC_DRAM_READ_CAS.AUTO
PRE_CH1

Counts the number of times a read CAS command was
issued on DRAM channel 1 where the command issued
used the auto-precharge (auto page close) mode.

63H

10H

UNC_DRAM_READ_CAS.CH2

Counts the number of times a read CAS command was
issued on DRAM channel 2.

19-138 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

63H

20H

UNC_DRAM_READ_CAS.AUTO
PRE_CH2

Counts the number of times a read CAS command was
issued on DRAM channel 2 where the command issued
used the auto-precharge (auto page close) mode.

64H

01H

UNC_DRAM_WRITE_CAS.CH0

Counts the number of times a write CAS command was
issued on DRAM channel 0.

64H

02H

UNC_DRAM_WRITE_CAS.AUTO Counts the number of times a write CAS command was
PRE_CH0
issued on DRAM channel 0 where the command issued
used the auto-precharge (auto page close) mode.

64H

04H

UNC_DRAM_WRITE_CAS.CH1

64H

08H

UNC_DRAM_WRITE_CAS.AUTO Counts the number of times a write CAS command was
PRE_CH1
issued on DRAM channel 1 where the command issued
used the auto-precharge (auto page close) mode.

64H

10H

UNC_DRAM_WRITE_CAS.CH2

64H

20H

UNC_DRAM_WRITE_CAS.AUTO Counts the number of times a write CAS command was
PRE_CH2
issued on DRAM channel 2 where the command issued
used the auto-precharge (auto page close) mode.

65H

01H

UNC_DRAM_REFRESH.CH0

Counts number of DRAM channel 0 refresh commands.
DRAM loses data content over time. In order to keep
correct data content, the data values have to be
refreshed periodically.

65H

02H

UNC_DRAM_REFRESH.CH1

Counts number of DRAM channel 1 refresh commands.
DRAM loses data content over time. In order to keep
correct data content, the data values have to be
refreshed periodically.

65H

04H

UNC_DRAM_REFRESH.CH2

Counts number of DRAM channel 2 refresh commands.
DRAM loses data content over time. In order to keep
correct data content, the data values have to be
refreshed periodically.

66H

01H

UNC_DRAM_PRE_ALL.CH0

Counts number of DRAM Channel 0 precharge-all
(PREALL) commands that close all open pages in a rank.
PREALL is issued when the DRAM needs to be
refreshed or needs to go into a power down mode.

66H

02H

UNC_DRAM_PRE_ALL.CH1

Counts number of DRAM Channel 1 precharge-all
(PREALL) commands that close all open pages in a rank.
PREALL is issued when the DRAM needs to be
refreshed or needs to go into a power down mode.

66H

04H

UNC_DRAM_PRE_ALL.CH2

Counts number of DRAM Channel 2 precharge-all
(PREALL) commands that close all open pages in a rank.
PREALL is issued when the DRAM needs to be
refreshed or needs to go into a power down mode.

67H

01H

UNC_DRAM_THERMAL_THROT Uncore cycles DRAM was throttled due to its
TLED
temperature being above the thermal throttling
threshold.

80H

01H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 0 is above the
TEMP.CORE_0
thermal throttling threshold temperature.

Comment

Counts the number of times a write CAS command was
issued on DRAM channel 1.

Counts the number of times a write CAS command was
issued on DRAM channel 2.

Vol. 3B 19-139

PERFORMANCE MONITORING EVENTS

Table 19-22. Performance Events In the Processor Uncore for
Processors Based on Intel® Microarchitecture Code Name Westmere (Contd.)
Event
Num.

Umask
Value

80H

02H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 1 is above the
TEMP.CORE_1
thermal throttling threshold temperature.

80H

04H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 2 is above the
TEMP.CORE_2
thermal throttling threshold temperature.

80H

08H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 3 is above the
TEMP.CORE_3
thermal throttling threshold temperature.

81H

01H

UNC_THERMAL_THROTTLED_
TEMP.CORE_0

Cycles that the PCU records that core 0 is in the power
throttled state due to core’s temperature being above
the thermal throttling threshold.

81H

02H

UNC_THERMAL_THROTTLED_
TEMP.CORE_1

Cycles that the PCU records that core 1 is in the power
throttled state due to core’s temperature being above
the thermal throttling threshold.

81H

04H

UNC_THERMAL_THROTTLED_
TEMP.CORE_2

Cycles that the PCU records that core 2 is in the power
throttled state due to core’s temperature being above
the thermal throttling threshold.

81H

08H

UNC_THERMAL_THROTTLED_
TEMP.CORE_3

Cycles that the PCU records that core 3 is in the power
throttled state due to core’s temperature being above
the thermal throttling threshold.

82H

01H

UNC_PROCHOT_ASSERTION

Number of system assertions of PROCHOT indicating
the entire processor has exceeded the thermal limit.

83H

01H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 0 is a low power
PROCHOT.CORE_0
state due to the system asserting PROCHOT the entire
processor has exceeded the thermal limit.

83H

02H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 1 is a low power
PROCHOT.CORE_1
state due to the system asserting PROCHOT the entire
processor has exceeded the thermal limit.

83H

04H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 2 is a low power
PROCHOT.CORE_2
state due to the system asserting PROCHOT the entire
processor has exceeded the thermal limit.

83H

08H

UNC_THERMAL_THROTTLING_ Cycles that the PCU records that core 3 is a low power
PROCHOT.CORE_3
state due to the system asserting PROCHOT the entire
processor has exceeded the thermal limit.

84H

01H

UNC_TURBO_MODE.CORE_0

Uncore cycles that core 0 is operating in turbo mode.

84H

02H

UNC_TURBO_MODE.CORE_1

Uncore cycles that core 1 is operating in turbo mode.

84H

04H

UNC_TURBO_MODE.CORE_2

Uncore cycles that core 2 is operating in turbo mode.

84H

08H

UNC_TURBO_MODE.CORE_3

Uncore cycles that core 3 is operating in turbo mode.

85H

02H

UNC_CYCLES_UNHALTED_L3_
FLL_ENABLE

Uncore cycles that at least one core is unhalted and all
L3 ways are enabled.

86H

01H

UNC_CYCLES_UNHALTED_L3_
FLL_DISABLE

Uncore cycles that at least one core is unhalted and all
L3 ways are disabled.

19-140 Vol. 3B

Event Mask Mnemonic

Description

Comment

PERFORMANCE MONITORING EVENTS

19.11

PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR
5200, 5400 SERIES AND INTEL® CORE™2 EXTREME PROCESSORS QX
9000 SERIES

Processors based on the Enhanced Intel Core microarchitecture support the architectural and model-specific
performance monitoring events listed in Table 19-1 and Table 19-25. In addition, they also support the following
model-specific performance monitoring events listed in Table 19-23. Fixed counters support the architecture
events defined in Table 19-24.

Table 19-23. Performance Events for Processors Based on Enhanced Intel Core Microarchitecture
Event
Num.

Umask
Value

Event Mask Mnemonic

Description

C0H

08H

INST_RETIRED.VM_HOST

Instruction retired while in VMX root operations.

D2H

10H

RAT_STAALS.OTHER_SERIALIZ
ATION_STALLS

This event counts the number of stalls due to other
RAT resource serialization not counted by Umask
value 0FH.

19.12

Comment

PERFORMANCE MONITORING EVENTS FOR INTEL® XEON® PROCESSOR
3000, 3200, 5100, 5300 SERIES AND INTEL® CORE™2 DUO PROCESSORS

Processors based on the Intel® Core™ microarchitecture support architectural and model-specific performance
monitoring events.
Fixed-function performance counters are introduced first on processors based on Intel Core microarchitecture.
Table 19-24 lists pre-defined performance events that can be counted using fixed-function performance counters.

Table 19-24. Fixed-Function Performance Counter and Pre-defined Performance Events
Fixed-Function Performance
Counter

Address

Event Mask Mnemonic

Description

MSR_PERF_FIXED_
CTR0/IA32_PERF_FIXED_CTR0

309H

Inst_Retired.Any

This event counts the number of instructions that
retire execution. For instructions that consist of
multiple micro-ops, this event counts the retirement
of the last micro-op of the instruction. The counter
continues counting during hardware interrupts, traps,
and inside interrupt handlers.

MSR_PERF_FIXED_
CTR1/IA32_PERF_FIXED_CTR1

30AH

CPU_CLK_UNHALTED.CORE This event counts the number of core cycles while the
core is not in a halt state. The core enters the halt
state when it is running the HLT instruction. This
event is a component in many key event ratios.
The core frequency may change from time to time
due to transitions associated with Enhanced Intel
SpeedStep Technology or TM2. For this reason this
event may have a changing ratio with regards to time.
When the core frequency is constant, this event can
approximate elapsed time while the core was not in
halt state.

MSR_PERF_FIXED_
CTR2/IA32_PERF_FIXED_CTR2

30BH

CPU_CLK_UNHALTED.REF

This event counts the number of reference cycles
when the core is not in a halt state and not in a TM
stop-clock state. The core enters the halt state when
it is running the HLT instruction or the MWAIT
instruction.

Vol. 3B 19-141

PERFORMANCE MONITORING EVENTS

Table 19-24. Fixed-Function Performance Counter and Pre-defined Performance Events (Contd.)
Fixed-Function Performance
Counter

Address

Event Mask Mnemonic

Description
This event is not affected by core frequency changes
(e.g., P states) but counts at the same frequency as
the time stamp counter. This event can approximate
elapsed time while the core was not in halt state and
not in a TM stop-clock state.
This event has a constant ratio with the
CPU_CLK_UNHALTED.BUS event.

Table 19-25 lists general-purpose model-specific performance monitoring events supported in processors based on
Intel® Core™ microarchitecture. For convenience, Table 19-25 also includes architectural events and describes
minor model-specific behavior where applicable. Software must use a general-purpose performance counter to
count events listed in Table 19-25.

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture
Event
Num

Umask
Value

Event Name

Definition

03H

02H

LOAD_BLOCK.STA

Loads blocked by a
preceding store with
unknown address.

Description and
Comment
This event indicates that loads are blocked by preceding
stores. A load is blocked when there is a preceding store to
an address that is not yet calculated. The number of events
is greater or equal to the number of load operations that
were blocked.
If the load and the store are always to different addresses,
check why the memory disambiguation mechanism is not
working. To avoid such blocks, increase the distance
between the store and the following load so that the store
address is known at the time the load is dispatched.

03H

04H

LOAD_BLOCK.STD

Loads blocked by a
preceding store with
unknown data.

This event indicates that loads are blocked by preceding
stores. A load is blocked when there is a preceding store to
the same address and the stored data value is not yet
known. The number of events is greater or equal to the
number of load operations that were blocked.
To avoid such blocks, increase the distance between the
store and the dependent load, so that the store data is
known at the time the load is dispatched.

03H

08H

LOAD_BLOCK.
OVERLAP_STORE

Loads that partially
overlap an earlier
store, or 4-Kbyte
aliased with a previous
store.

This event indicates that loads are blocked due to a variety
of reasons. Some of the triggers for this event are when a
load is blocked by a preceding store, in one of the following:
• Some of the loaded byte locations are written by the
preceding store and some are not.
• The load is from bytes written by the preceding store,
the store is aligned to its size and either:
• The load’s data size is one or two bytes and it is not
aligned to the store.
• The load’s data size is of four or eight bytes and the load
is misaligned.

19-142 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

Description and
Comment
• The load is from bytes written by the preceding store,
the store is misaligned and the load is not aligned on the
beginning of the store.
• The load is split over an eight byte boundary (excluding
16-byte loads).
• The load and store have the same offset relative to the
beginning of different 4-KByte pages. This case is also
called 4-KByte aliasing.
• In all these cases the load is blocked until after the
blocking store retires and the stored data is committed to
the cache hierarchy.

03H

10H

LOAD_BLOCK.
UNTIL_RETIRE

Loads blocked until
retirement.

This event indicates that load operations were blocked until
retirement. The number of events is greater or equal to the
number of load operations that were blocked.
This includes mainly uncacheable loads and split loads (loads
that cross the cache line boundary) but may include other
cases where loads are blocked until retirement.

03H

20H

LOAD_BLOCK.L1D

Loads blocked by the
L1 data cache.

This event indicates that loads are blocked due to one or
more reasons. Some triggers for this event are:
• The number of L1 data cache misses exceeds the
maximum number of outstanding misses supported by
the processor. This includes misses generated as result of
demand fetches, software prefetches or hardware
prefetches.
• Cache line split loads.
• Partial reads, such as reads to un-cacheable memory, I/O
instructions and more.
• A locked load operation is in progress. The number of
events is greater or equal to the number of load
operations that were blocked.

04H

01H

SB_DRAIN_
CYCLES

Cycles while stores are This event counts every cycle during which the store buffer
blocked due to store
is draining. This includes:
buffer drain.
• Serializing operations such as CPUID
• Synchronizing operations such as XCHG
• Interrupt acknowledgment
• Other conditions, such as cache flushing

04H

02H

STORE_BLOCK.
ORDER

Cycles while store is
waiting for a
preceding store to be
globally observed.

This event counts the total duration, in number of cycles,
which stores are waiting for a preceding stored cache line to
be observed by other cores.
This situation happens as a result of the strong store
ordering behavior, as defined in “Memory Ordering,” Chapter
8, Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3A.
The stall may occur and be noticeable if there are many
cases when a store either misses the L1 data cache or hits a
cache line in the Shared state. If the store requires a bus
transaction to read the cache line then the stall ends when
snoop response for the bus transaction arrives.

04H

08H

STORE_BLOCK.
SNOOP

A store is blocked due
to a conflict with an
external or internal
snoop.

This event counts the number of cycles the store port was
used for snooping the L1 data cache and a store was stalled
by the snoop. The store is typically resubmitted one cycle
later.

Vol. 3B 19-143

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

06H

00H

Event Name

Definition

SEGMENT_REG_
LOADS

Number of segment
register loads.

Description and
Comment
This event counts the number of segment register load
operations. Instructions that load new values into segment
registers cause a penalty.
This event indicates performance issues in 16-bit code. If
this event occurs frequently, it may be useful to calculate
the number of instructions retired per segment register
load. If the resulting calculation is low (on average a small
number of instructions are executed between segment
register loads), then the code’s segment register usage
should be optimized.
As a result of branch misprediction, this event is speculative
and may include segment register loads that do not actually
occur. However, most segment register loads are internally
serialized and such speculative effects are minimized.

07H

00H

SSE_PRE_EXEC.
NTA

Streaming SIMD
This event counts the number of times the SSE instruction
Extensions (SSE)
prefetchNTA is executed.
Prefetch NTA
This instruction prefetches the data to the L1 data cache.
instructions executed.

07H

01H

SSE_PRE_EXEC.L1

Streaming SIMD
This event counts the number of times the SSE instruction
Extensions (SSE)
prefetchT0 is executed. This instruction prefetches the data
PrefetchT0
to the L1 data cache and L2 cache.
instructions executed.

07H

02H

SSE_PRE_EXEC.L2

Streaming SIMD
This event counts the number of times the SSE instructions
Extensions (SSE)
prefetchT1 and prefetchT2 are executed. These
PrefetchT1 and
instructions prefetch the data to the L2 cache.
PrefetchT2
instructions executed.

07H

03H

SSE_PRE_
EXEC.STORES

Streaming SIMD
This event counts the number of times SSE non-temporal
Extensions (SSE)
store instructions are executed.
Weakly-ordered store
instructions executed.

08H

01H

DTLB_MISSES.
ANY

Memory accesses that This event counts the number of Data Table Lookaside
missed the DTLB.
Buffer (DTLB) misses. The count includes misses detected
as a result of speculative accesses.
Typically a high count for this event indicates that the code
accesses a large number of data pages.

08H

02H

DTLB_MISSES
.MISS_LD

DTLB misses due to
load operations.

This event counts the number of Data Table Lookaside
Buffer (DTLB) misses due to load operations.
This count includes misses detected as a result of
speculative accesses.

08H

04H

DTLB_MISSES.L0_MISS_LD

L0 DTLB misses due to This event counts the number of level 0 Data Table
load operations.
Lookaside Buffer (DTLB0) misses due to load operations.
This count includes misses detected as a result of
speculative accesses. Loads that miss that DTLB0 and hit
the DTLB1 can incur two-cycle penalty.

19-144 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

08H

08H

Event Name

Definition

Description and
Comment

DTLB_MISSES.
MISS_ST

TLB misses due to
store operations.

This event counts the number of Data Table Lookaside
Buffer (DTLB) misses due to store operations.
This count includes misses detected as a result of
speculative accesses. Address translation for store
operations is performed in the DTLB1.

09H

01H

MEMORY_
DISAMBIGUATION.RESET

Memory
disambiguation reset
cycles.

This event counts the number of cycles during which
memory disambiguation misprediction occurs. As a result
the execution pipeline is cleaned and execution of the
mispredicted load instruction and all succeeding instructions
restarts.
This event occurs when the data address accessed by a load
instruction, collides infrequently with preceding stores, but
usually there is no collision. It happens rarely, and may have
a penalty of about 20 cycles.

09H

02H

MEMORY_DISAMBIGUATIO
N.SUCCESS

Number of loads
successfully
disambiguated.

This event counts the number of load operations that were
successfully disambiguated. Loads are preceded by a store
with an unknown address, but they are not blocked.

0CH

01H

PAGE_WALKS
.COUNT

Number of page-walks This event counts the number of page-walks executed due
executed.
to either a DTLB or ITLB miss.
The page walk duration, PAGE_WALKS.CYCLES, divided by
number of page walks is the average duration of a page
walk. The average can hint whether most of the page-walks
are satisfied by the caches or cause an L2 cache miss.

0CH

02H

PAGE_WALKS.
CYCLES

Duration of pagewalks in core cycles.

This event counts the duration of page-walks in core cycles.
The paging mode in use typically affects the duration of
page walks.
Page walk duration divided by number of page walks is the
average duration of page-walks. The average can hint at
whether most of the page-walks are satisfied by the caches
or cause an L2 cache miss.

10H

11H

00H

00H

FP_COMP_OPS
_EXE
FP_ASSIST

Floating point
computational microops executed.

This event counts the number of floating point
computational micro-ops executed.

Floating point assists.

This event counts the number of floating point operations
executed that required micro-code assist intervention.
Assists are required in the following cases:

Use IA32_PMC0 only.

• Streaming SIMD Extensions (SSE) instructions:
• Denormal input when the DAZ (Denormals Are Zeros) flag
is off
• Underflow result when the FTZ (Flush To Zero) flag is off
• X87 instructions:
• NaN or denormal are loaded to a register or used as input
from memory
• Division by 0
• Underflow output
Use IA32_PMC1 only.
12H

00H

MUL

Multiply operations
executed.

This event counts the number of multiply operations
executed. This includes integer as well as floating point
multiply operations.
Use IA32_PMC1 only.
Vol. 3B 19-145

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

13H

00H

DIV

Divide operations
executed.

Description and
Comment
This event counts the number of divide operations
executed. This includes integer divides, floating point
divides and square-root operations executed.
Use IA32_PMC1 only.

14H

00H

CYCLES_DIV
_BUSY

Cycles the divider
busy.

This event counts the number of cycles the divider is busy
executing divide or square root operations. The divide can
be integer, X87 or Streaming SIMD Extensions (SSE). The
square root operation can be either X87 or SSE.
Use IA32_PMC0 only.

18H

00H

IDLE_DURING
_DIV

Cycles the divider is
busy and all other
execution units are
idle.

This event counts the number of cycles the divider is busy
(with a divide or a square root operation) and no other
execution unit or load operation is in progress.
Load operations are assumed to hit the L1 data cache. This
event considers only micro-ops dispatched after the divider
started operating.
Use IA32_PMC0 only.

19H

00H

DELAYED_
BYPASS.FP

Delayed bypass to FP
operation.

This event counts the number of times floating point
operations use data immediately after the data was
generated by a non-floating point execution unit. Such cases
result in one penalty cycle due to data bypass between the
units.
Use IA32_PMC1 only.

19H

01H

DELAYED_
BYPASS.SIMD

Delayed bypass to
SIMD operation.

19H

02H

DELAYED_
BYPASS.LOAD

Delayed bypass to
load operation.

This event counts the number of times SIMD operations use
data immediately after the data was generated by a nonSIMD execution unit. Such cases result in one penalty cycle
due to data bypass between the units.
Use IA32_PMC1 only.
This event counts the number of delayed bypass penalty
cycles that a load operation incurred.
When load operations use data immediately after the data
was generated by an integer execution unit, they may
(pending on certain dynamic internal conditions) incur one
penalty cycle due to delayed data bypass between the units.
Use IA32_PMC1 only.

21H

See
Table
18-61

L2_ADS.(Core)

Cycles L2 address bus
is in use.

This event counts the number of cycles the L2 address bus
is being used for accesses to the L2 cache or bus queue. It
can count occurrences for this core or both cores.

23H

See
Table
18-61

L2_DBUS_BUSY
_RD.(Core)

Cycles the L2
transfers data to the
core.

This event counts the number of cycles during which the L2
data bus is busy transferring data from the L2 cache to the
core. It counts for all L1 cache misses (data and instruction)
that hit the L2 cache.
This event can count occurrences for this core or both cores.

19-146 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

24H

Combin L2_LINES_IN.
ed mask (Core, Prefetch)
from
Table
18-61
and
Table
18-63

25H

26H

27H

28H

29H

2AH

Event Name

Definition
L2 cache misses.

Description and
Comment
This event counts the number of cache lines allocated in the
L2 cache. Cache lines are allocated in the L2 cache as a
result of requests from the L1 data and instruction caches
and the L2 hardware prefetchers to cache lines that are
missing in the L2 cache.
This event can count occurrences for this core or both cores.
It can also count demand requests and L2 hardware
prefetch requests together or separately.

See
Table
18-61

L2_M_LINES_IN.
(Core)

L2 cache line
modifications.

This event counts whenever a modified cache line is written
back from the L1 data cache to the L2 cache.

See
Table
18-61
and
Table
18-63

L2_LINES_OUT.
(Core, Prefetch)

L2 cache lines evicted. This event counts the number of L2 cache lines evicted.

See
Table
18-61
and
Table
18-63

L2_M_LINES_OUT.(Core,
Prefetch)

Modified lines evicted
from the L2 cache.

Combined
mask
from
Table
18-61
and
Table
18-64

L2_IFETCH.(Core, Cache
Line State)

This event can count occurrences for this core or both cores.
This event can count occurrences for this core or both cores.
It can also count evictions due to demand requests and L2
hardware prefetch requests together or separately.

This event counts the number of L2 modified cache lines
evicted. These lines are written back to memory unless they
also exist in a modified-state in one of the L1 data caches.
This event can count occurrences for this core or both cores.
It can also count evictions due to demand requests and L2
hardware prefetch requests together or separately.

L2 cacheable
instruction fetch
requests.

This event counts the number of instruction cache line
requests from the IFU. It does not include fetch requests
from uncacheable memory. It does not include ITLB miss
accesses.
This event can count occurrences for this core or both cores.
It can also count accesses to cache lines at different MESI
states.

Combin L2_LD.(Core, Prefetch,
ed mask Cache Line State)
from
Table
18-61,
Table
18-63,
and
Table
18-64

L2 cache reads.

See
Table
18-61
and
Table
18-64

L2 store requests.

L2_ST.(Core, Cache Line
State)

This event counts L2 cache read requests coming from the
L1 data cache and L2 prefetchers.
The event can count occurrences:
• For this core or both cores.
• Due to demand requests and L2 hardware prefetch
requests together or separately.
• Of accesses to cache lines at different MESI states.

This event counts all store operations that miss the L1 data
cache and request the data from the L2 cache.
The event can count occurrences for this core or both cores.
It can also count accesses to cache lines at different MESI
states.

Vol. 3B 19-147

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

2BH

2EH

2EH

Event Name

Definition

See
Table
18-61
and
Table
18-64

L2_LOCK.(Core, Cache Line
State)

L2 locked accesses.

See
Table
18-61,
Table
18-63,
and
Table
18-64

L2_RQSTS.(Core, Prefetch,
Cache Line State)

41H

L2_RQSTS.SELF.
DEMAND.I_STATE

Description and
Comment
This event counts all locked accesses to cache lines that
miss the L1 data cache.
The event can count occurrences for this core or both cores.
It can also count accesses to cache lines at different MESI
states.

L2 cache requests.

This event counts all completed L2 cache requests. This
includes L1 data cache reads, writes, and locked accesses,
L1 data prefetch requests, instruction fetches, and all L2
hardware prefetch requests.
This event can count occurrences:
• For this core or both cores.
• Due to demand requests and L2 hardware prefetch
requests together, or separately.
• Of accesses to cache lines at different MESI states.

L2 cache demand
requests from this
core that missed the
L2.

This event counts all completed L2 cache demand requests
from this core that miss the L2 cache. This includes L1 data
cache reads, writes, and locked accesses, L1 data prefetch
requests, and instruction fetches.
This is an architectural performance event.

2EH

4FH

L2_RQSTS.SELF.
DEMAND.MESI

L2 cache demand
requests from this
core.

This event counts all completed L2 cache demand requests
from this core. This includes L1 data cache reads, writes,
and locked accesses, L1 data prefetch requests, and
instruction fetches.
This is an architectural performance event.

30H

See
Table
18-61,
Table
18-63,
and
Table
18-64

L2_REJECT_BUSQ.(Core,
Rejected L2 cache
Prefetch, Cache Line State) requests.

This event indicates that a pending L2 cache request that
requires a bus transaction is delayed from moving to the bus
queue. Some of the reasons for this event are:
• The bus queue is full.
• The bus queue already holds an entry for a cache line in
the same set.
The number of events is greater or equal to the number of
requests that were rejected.
• For this core or both cores.
• Due to demand requests and L2 hardware prefetch
requests together, or separately.
• Of accesses to cache lines at different MESI states.

32H

See
Table
18-61

L2_NO_REQ.(Core)

Cycles no L2 cache
requests are pending.

This event counts the number of cycles that no L2 cache
requests were pending from a core. When using the
BOTH_CORE modifier, the event counts only if none of the
cores have a pending request. The event counts also when
one core is halted and the other is not halted.
The event can count occurrences for this core or both cores.

3AH

00H

EIST_TRANS

Number of Enhanced
Intel SpeedStep
Technology (EIST)
transitions.

This event counts the number of transitions that include a
frequency change, either with or without voltage change.
This includes Enhanced Intel SpeedStep Technology (EIST)
and TM2 transitions.
The event is incremented only while the counting core is in
C0 state. Since transitions to higher-numbered CxE states
and TM2 transitions include a frequency change or voltage
transition, the event is incremented accordingly.

19-148 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

3BH

C0H

THERMAL_TRIP

Number of thermal
trips.

Description and
Comment
This event counts the number of thermal trips. A thermal
trip occurs whenever the processor temperature exceeds
the thermal trip threshold temperature.
Following a thermal trip, the processor automatically
reduces frequency and voltage. The processor checks the
temperature every millisecond and returns to normal when
the temperature falls below the thermal trip threshold
temperature.

3CH

00H

CPU_CLK_
UNHALTED.
CORE_P

Core cycles when core This event counts the number of core cycles while the core
is not halted.
is not in a halt state. The core enters the halt state when it
is running the HLT instruction. This event is a component in
many key event ratios.
The core frequency may change due to transitions
associated with Enhanced Intel SpeedStep Technology or
TM2. For this reason, this event may have a changing ratio in
regard to time.
When the core frequency is constant, this event can give
approximate elapsed time while the core not in halt state.
This is an architectural performance event.

3CH

01H

CPU_CLK_
UNHALTED.BUS

Bus cycles when core
is not halted.

This event counts the number of bus cycles while the core is
not in the halt state. This event can give a measurement of
the elapsed time while the core was not in the halt state.
The core enters the halt state when it is running the HLT
instruction.
The event also has a constant ratio with
CPU_CLK_UNHALTED.REF event, which is the maximum bus
to processor frequency ratio.
Non-halted bus cycles are a component in many key event
ratios.

3CH

02H

CPU_CLK_
UNHALTED.NO
_OTHER

Bus cycles when core This event counts the number of bus cycles during which
is active and the other the core remains non-halted and the other core on the
is halted.
processor is halted.
This event can be used to determine the amount of
parallelism exploited by an application or a system. Divide
this event count by the bus frequency to determine the
amount of time that only one core was in use.

40H

See
Table
18-64

L1D_CACHE_LD.
(Cache Line State)

L1 cacheable data
reads.

This event counts the number of data reads from cacheable
memory. Locked reads are not counted.

41H

See
Table
18-64

L1D_CACHE_ST.
(Cache Line State)

L1 cacheable data
writes.

This event counts the number of data writes to cacheable
memory. Locked writes are not counted.

42H

See
Table
18-64

L1D_CACHE_
LOCK.(Cache Line State)

L1 data cacheable
locked reads.

This event counts the number of locked data reads from
cacheable memory.

Vol. 3B 19-149

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

42H

10H

43H

01H

Event Name

Definition

L1D_CACHE_
LOCK_DURATION

Duration of L1 data
cacheable locked
operation.

L1D_ALL_REF

All references to the
L1 data cache.

Description and
Comment
This event counts the number of cycles during which any
cache line is locked by any locking instruction.
Locking happens at retirement and therefore the event does
not occur for instructions that are speculatively executed.
Locking duration is shorter than locked instruction execution
duration.
This event counts all references to the L1 data cache,
including all loads and stores with any memory types.
The event counts memory accesses only when they are
actually performed. For example, a load blocked by unknown
store address and later performed is only counted once.
The event includes non-cacheable accesses, such as I/O
accesses.

43H

02H

L1D_ALL_
CACHE_REF

L1 Data cacheable
reads and writes.

This event counts the number of data reads and writes from
cacheable memory, including locked operations.
This event is a sum of:
• L1D_CACHE_LD.MESI
• L1D_CACHE_ST.MESI
• L1D_CACHE_LOCK.MESI

45H

0FH

L1D_REPL

Cache lines allocated
in the L1 data cache.

This event counts the number of lines brought into the L1
data cache.

46H

00H

L1D_M_REPL

Modified cache lines
allocated in the L1
data cache.

This event counts the number of modified lines brought into
the L1 data cache.

47H

00H

L1D_M_EVICT

Modified cache lines
evicted from the L1
data cache.

This event counts the number of modified lines evicted from
the L1 data cache, whether due to replacement or by snoop
HITM intervention.

48H

00H

L1D_PEND_
MISS

Total number of
outstanding L1 data
cache misses at any
cycle.

This event counts the number of outstanding L1 data cache
misses at any cycle. An L1 data cache miss is outstanding
from the cycle on which the miss is determined until the
first chunk of data is available. This event counts:
• All cacheable demand requests.
• L1 data cache hardware prefetch requests.
• Requests to write through memory.
• Requests to write combine memory.
Uncacheable requests are not counted. The count of this
event divided by the number of L1 data cache misses,
L1D_REPL, is the average duration in core cycles of an L1
data cache miss.

49H

01H

L1D_SPLIT.LOADS

Cache line split loads
from the L1 data
cache.

This event counts the number of load operations that span
two cache lines. Such load operations are also called split
loads. Split load operations are executed at retirement.

49H

02H

L1D_SPLIT.
STORES

Cache line split stores
to the L1 data cache.

This event counts the number of store operations that span
two cache lines.

4BH

00H

SSE_PRE_
MISS.NTA

Streaming SIMD
Extensions (SSE)
Prefetch NTA
instructions missing all
cache levels.

This event counts the number of times the SSE instructions
prefetchNTA were executed and missed all cache levels.

19-150 Vol. 3B

Due to speculation an executed instruction might not retire.
This instruction prefetches the data to the L1 data cache.

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

4BH

01H

4BH

02H

Description and
Comment

Event Name

Definition

SSE_PRE_
MISS.L1

Streaming SIMD
Extensions (SSE)
PrefetchT0
instructions missing all
cache levels.

This event counts the number of times the SSE instructions
prefetchT0 were executed and missed all cache levels.

Streaming SIMD
Extensions (SSE)
PrefetchT1 and
PrefetchT2
instructions missing all
cache levels.

This event counts the number of times the SSE instructions
prefetchT1 and prefetchT2 were executed and missed all
cache levels.

This event counts load operations sent to the L1 data cache
while a previous Streaming SIMD Extensions (SSE) prefetch
instruction to the same cache line has started prefetching
but has not yet finished.

SSE_PRE_
MISS.L2

Due to speculation executed instruction might not retire.
The prefetchT0 instruction prefetches data to the L2 cache
and L1 data cache.

Due to speculation, an executed instruction might not retire.
The prefetchT1 and PrefetchNT2 instructions prefetch data
to the L2 cache.

4CH

00H

LOAD_HIT_PRE

Load operations
conflicting with a
software prefetch to
the same address.

4EH

10H

L1D_PREFETCH.
REQUESTS

L1 data cache prefetch This event counts the number of times the L1 data cache
requests.
requested to prefetch a data cache line. Requests can be
rejected when the L2 cache is busy and resubmitted later or
lost.
All requests are counted, including those that are rejected.

60H

61H

See
Table
18-61
and
Table
18-62.

BUS_REQUEST_
OUTSTANDING.
(Core and Bus Agents)

See
Table
18-62.

BUS_BNR_DRV.
(Bus Agents)

Outstanding cacheable This event counts the number of pending full cache line read
data read bus
transactions on the bus occurring in each cycle. A read
requests duration.
transaction is pending from the cycle it is sent on the bus
until the full cache line is received by the processor.
The event counts only full-line cacheable read requests from
either the L1 data cache or the L2 prefetchers. It does not
count Read for Ownership transactions, instruction byte
fetch transactions, or any other bus transaction.
Number of Bus Not
Ready signals
asserted.

This event counts the number of Bus Not Ready (BNR)
signals that the processor asserts on the bus to suspend
additional bus requests by other bus agents.
A bus agent asserts the BNR signal when the number of
data and snoop transactions is close to the maximum that
the bus can handle. To obtain the number of bus cycles
during which the BNR signal is asserted, multiply the event
count by two.
While this signal is asserted, new transactions cannot be
submitted on the bus. As a result, transaction latency may
have higher impact on program performance.

62H

See
Table
18-62.

BUS_DRDY_
CLOCKS.(Bus Agents)

Bus cycles when data
is sent on the bus.

This event counts the number of bus cycles during which
the DRDY (Data Ready) signal is asserted on the bus. The
DRDY signal is asserted when data is sent on the bus. With
the 'THIS_AGENT' mask this event counts the number of bus
cycles during which this agent (the processor) writes data
on the bus back to memory or to other bus agents. This
includes all explicit and implicit data writebacks, as well as
partial writes.
With the 'ALL_AGENTS' mask, this event counts the number
of bus cycles during which any bus agent sends data on the
bus. This includes all data reads and writes on the bus.

Vol. 3B 19-151

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

63H

Description and
Comment

Event Name

Definition

See
Table
18-61
and
Table
18-62.

BUS_LOCK_
CLOCKS.(Core and Bus
Agents)

Bus cycles when a
LOCK signal asserted.

64H

See
Table
18-61.

BUS_DATA_
RCV.(Core)

Bus cycles while
processor receives
data.

This event counts the number of bus cycles during which
the processor is busy receiving data.

65H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_BRD.(Core
and Bus Agents)

Burst read bus
transactions.

This event counts the number of burst read transactions
including:

66H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_RFO.(Core
and Bus Agents)

RFO bus transactions.

This event counts the number of Read For Ownership (RFO)
bus transactions, due to store operations that miss the L1
data cache and the L2 cache. It also counts RFO bus
transactions due to locked operations.

67H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_WB.
(Core and Bus Agents)

Explicit writeback bus
transactions.

This event counts all explicit writeback bus transactions due
to dirty line evictions. It does not count implicit writebacks
due to invalidation by a snoop request.

68H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_
IFETCH.(Core and Bus
Agents)

Instruction-fetch bus
transactions.

This event counts all instruction fetch full cache line bus
transactions.

69H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_
INVAL.(Core and Bus
Agents)

Invalidate bus
transactions.

This event counts all invalidate transactions. Invalidate
transactions are generated when:

See
Table
18-61
and
Table
18-62.

BUS_TRANS_
Partial write bus
PWR.(Core and Bus Agents) transaction.

6AH

19-152 Vol. 3B

This event counts the number of bus cycles, during which
the LOCK signal is asserted on the bus. A LOCK signal is
asserted when there is a locked memory access, due to:
• Uncacheable memory.
• Locked operation that spans two cache lines.
• Page-walk from an uncacheable page table.
Bus locks have a very high performance penalty and it is
highly recommended to avoid such accesses.

• L1 data cache read misses (and L1 data cache hardware
prefetches).
• L2 hardware prefetches by the DPL and L2 streamer.
• IFU read misses of cacheable lines.
It does not include RFO transactions.

• A store operation hits a shared line in the L2 cache.
• A full cache line write misses the L2 cache or hits a
shared line in the L2 cache.
This event counts partial write bus transactions.

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

Description and
Comment

6BH

See
Table
18-61
and
Table
18-62.

BUS_TRANS
_P.(Core and Bus Agents)

Partial bus
transactions.

This event counts all (read and write) partial bus
transactions.

6CH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_IO.(Core and
Bus Agents)

IO bus transactions.

This event counts the number of completed I/O bus
transactions as a result of IN and OUT instructions. The
count does not include memory mapped IO.

6DH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_
DEF.(Core and Bus Agents)

Deferred bus
transactions.

This event counts the number of deferred transactions.

6EH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_
BURST.(Core and Bus
Agents)

Burst (full cache-line)
bus transactions.

This event counts burst (full cache line) transactions
including:

See
Table
18-61
and
Table
18-62.

BUS_TRANS_
Memory bus
MEM.(Core and Bus Agents) transactions.

This event counts all memory bus transactions including:

See
Table
18-61
and
Table
18-62.

BUS_TRANS_
ANY.(Core and Bus Agents)

All bus transactions.

This event counts all bus transactions. This includes:

See
Table
18-61
and
Table
18-65.

EXT_SNOOP.
(Bus Agents, Snoop
Response)

External snoops.

See
Table
18-61
and
Table
18-66.

CMP_SNOOP.(Core, Snoop
Type)

6FH

70H

77H

78H

•
•
•
•

Burst reads.
RFOs.
Explicit writebacks.
Write combine lines.

• Burst transactions.
• Partial reads and writes - invalidate transactions.
The BUS_TRANS_MEM count is the sum of
BUS_TRANS_BURST, BUS_TRANS_P and BUS_TRANS_IVAL.

•
•
•
•

Memory transactions.
IO transactions (non memory-mapped).
Deferred transaction completion.
Other less frequent transactions, such as interrupts.

This event counts the snoop responses to bus transactions.
Responses can be counted separately by type and by bus
agent.
With the 'THIS_AGENT' mask, the event counts snoop
responses from this processor to bus transactions sent by
this processor. With the 'ALL_AGENTS' mask the event
counts all snoop responses seen on the bus.

L1 data cache
This event counts the number of times the L1 data cache is
snooped by other core. snooped for a cache line that is needed by the other core in
the same processor. The cache line is either missing in the
L1 instruction or data caches of the other core, or is
available for reading only and the other core wishes to write
the cache line.

Vol. 3B 19-153

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

Description and
Comment
The snoop operation may change the cache line state. If the
other core issued a read request that hit this core in E state,
typically the state changes to S state in this core. If the
other core issued a read for ownership request (due a write
miss or hit to S state) that hits this core's cache line in E or S
state, this typically results in invalidation of the cache line in
this core. If the snoop hits a line in M state, the state is
changed at a later opportunity.
These snoops are performed through the L1 data cache
store port. Therefore, frequent snoops may conflict with
extensive stores to the L1 data cache, which may increase
store latency and impact performance.

7AH

7BH

7DH

See
Table
18-62.

BUS_HIT_DRV.

See
Table
18-62.

BUS_HITM_DRV.

See
Table
18-61.

BUSQ_EMPTY.

HIT signal asserted.

This event counts the number of bus cycles during which
the processor drives the HIT# pin to signal HIT snoop
response.

HITM signal asserted.

This event counts the number of bus cycles during which
the processor drives the HITM# pin to signal HITM snoop
response.

Bus queue empty.

This event counts the number of cycles during which the
core did not have any pending transactions in the bus queue.
It also counts when the core is halted and the other core is
not halted.

(Bus Agents)

(Bus Agents)

(Core)

This event can count occurrences for this core or both cores.
7EH

7FH

See
Table
18-61
and
Table
18-62.

SNOOP_STALL_
Bus stalled for snoops. This event counts the number of times that the bus snoop
DRV.(Core and Bus Agents)
stall signal is asserted. To obtain the number of bus cycles
during which snoops on the bus are prohibited, multiply the
event count by two.

See
Table
18-61.

BUS_IO_WAIT.
(Core)

During the snoop stall cycles, no new bus transactions
requiring a snoop response can be initiated on the bus. A
bus agent asserts a snoop stall signal if it cannot response
to a snoop request within three bus cycles.
IO requests waiting in
the bus queue.

This event counts the number of core cycles during which IO
requests wait in the bus queue. With the SELF modifier this
event counts IO requests per core.
With the BOTH_CORE modifier, this event increments by one
for any cycle for which there is a request from either core.

80H

00H

L1I_READS

Instruction fetches.

This event counts all instruction fetches, including
uncacheable fetches that bypass the Instruction Fetch Unit
(IFU).

81H

00H

L1I_MISSES

Instruction Fetch Unit
misses.

This event counts all instruction fetches that miss the
Instruction Fetch Unit (IFU) or produce memory requests.
This includes uncacheable fetches.
An instruction fetch miss is counted only once and not once
for every cycle it is outstanding.

82H

02H

ITLB.SMALL_MISS

ITLB small page
misses.

This event counts the number of instruction fetches from
small pages that miss the ITLB.

82H

10H

ITLB.LARGE_MISS

ITLB large page
misses.

This event counts the number of instruction fetches from
large pages that miss the ITLB.

19-154 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

Description and
Comment

82H

40H

ITLB.FLUSH

ITLB flushes.

This event counts the number of ITLB flushes. This usually
happens upon CR3 or CR0 writes, which are executed by
the operating system during process switches.

82H

12H

ITLB.MISSES

ITLB misses.

This event counts the number of instruction fetches from
either small or large pages that miss the ITLB.

83H

02H

INST_QUEUE.FULL

Cycles during which
the instruction queue
is full.

This event counts the number of cycles during which the
instruction queue is full. In this situation, the core front end
stops fetching more instructions. This is an indication of
very long stalls in the back-end pipeline stages.

86H

00H

CYCLES_L1I_
MEM_STALLED

Cycles during which
instruction fetches
stalled.

This event counts the number of cycles for which an
instruction fetch stalls, including stalls due to any of the
following reasons:
• Instruction Fetch Unit cache misses.
• Instruction TLB misses.
• Instruction TLB faults.

87H

00H

ILD_STALL

Instruction Length
Decoder stall cycles
due to a length
changing prefix.

This event counts the number of cycles during which the
instruction length decoder uses the slow length decoder.
Usually, instruction length decoding is done in one cycle.
When the slow decoder is used, instruction decoding
requires 6 cycles.
The slow decoder is used in the following cases:
• Operand override prefix (66H) preceding an instruction
with immediate data.
• Address override prefix (67H) preceding an instruction
with a modr/m in real, big real, 16-bit protected or 32-bit
protected modes.
To avoid instruction length decoding stalls, generate code
using imm8 or imm32 values instead of imm16 values. If
you must use an imm16 value, store the value in a register
using “mov reg, imm32” and use the register format of the
instruction.

88H

00H

BR_INST_EXEC

Branch instructions
executed.

This event counts all executed branches (not necessarily
retired). This includes only instructions and not micro-op
branches.
Frequent branching is not necessarily a major performance
issue. However frequent branch mispredictions may be a
problem.

89H

00H

BR_MISSP_EXEC

Mispredicted branch
This event counts the number of mispredicted branch
instructions executed. instructions that were executed.

8AH

00H

BR_BAC_
MISSP_EXEC

Branch instructions
mispredicted at
decoding.

8BH

00H

BR_CND_EXEC

Conditional branch
This event counts the number of conditional branch
instructions executed. instructions executed, but not necessarily retired.

8CH

00H

BR_CND_
MISSP_EXEC

Mispredicted
This event counts the number of mispredicted conditional
conditional branch
branch instructions that were executed.
instructions executed.

8DH

00H

BR_IND_EXEC

Indirect branch
This event counts the number of indirect branch instructions
instructions executed. that were executed.

This event counts the number of branch instructions that
were mispredicted at decoding.

Vol. 3B 19-155

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

8EH

Description and
Comment

Event Name

Definition

00H

BR_IND_MISSP
_EXEC

Mispredicted indirect
branch instructions
executed.

This event counts the number of mispredicted indirect
branch instructions that were executed.

8FH

00H

BR_RET_EXEC

RET instructions
executed.

This event counts the number of RET instructions that were
executed.

90H

00H

BR_RET_
MISSP_EXEC

Mispredicted RET
This event counts the number of mispredicted RET
instructions executed. instructions that were executed.

91H

00H

BR_RET_BAC_
MISSP_EXEC

This event counts the number of RET instructions that were
RET instructions
executed mispredicted executed and were mispredicted at decoding.
at decoding.

92H

00H

BR_CALL_EXEC

CALL instructions
executed.

93H

00H

BR_CALL_
MISSP_EXEC

Mispredicted CALL
This event counts the number of mispredicted CALL
instructions executed. instructions that were executed.

94H

00H

BR_IND_CALL_
EXEC

Indirect CALL
This event counts the number of indirect CALL instructions
instructions executed. that were executed.

97H

00H

BR_TKN_
BUBBLE_1

Branch predicted
taken with bubble 1.

This event counts the number of CALL instructions
executed.

The events BR_TKN_BUBBLE_1 and BR_TKN_BUBBLE_2
together count the number of times a taken branch
prediction incurred a one-cycle penalty. The penalty incurs
when:
• Too many taken branches are placed together. To avoid
this, unroll loops and add a non-taken branch in the
middle of the taken sequence.
• The branch target is unaligned. To avoid this, align the
branch target.

98H

00H

BR_TKN_
BUBBLE_2

Branch predicted
taken with bubble 2.

The events BR_TKN_BUBBLE_1 and BR_TKN_BUBBLE_2
together count the number of times a taken branch
prediction incurred a one-cycle penalty. The penalty incurs
when:
• Too many taken branches are placed together. To avoid
this, unroll loops and add a non-taken branch in the
middle of the taken sequence.
• The branch target is unaligned. To avoid this, align the
branch target.

A0H

00H

RS_UOPS_
DISPATCHED

Micro-ops dispatched
for execution.

This event counts the number of micro-ops dispatched for
execution. Up to six micro-ops can be dispatched in each
cycle.

A1H

01H

RS_UOPS_
DISPATCHED.PORT0

Cycles micro-ops
dispatched for
execution on port 0.

This event counts the number of cycles for which micro-ops
dispatched for execution. Each cycle, at most one micro-op
can be dispatched on the port. Issue Ports are described in
Intel® 64 and IA-32 Architectures Optimization Reference
Manual. Use IA32_PMC0 only.

A1H

02H

RS_UOPS_
DISPATCHED.PORT1

Cycles micro-ops
dispatched for
execution on port 1.

This event counts the number of cycles for which micro-ops
dispatched for execution. Each cycle, at most one micro-op
can be dispatched on the port. Use IA32_PMC0 only.

A1H

04H

RS_UOPS_
DISPATCHED.PORT2

Cycles micro-ops
dispatched for
execution on port 2.

This event counts the number of cycles for which micro-ops
dispatched for execution. Each cycle, at most one micro-op
can be dispatched on the port. Use IA32_PMC0 only.

19-156 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

Description and
Comment

A1H

08H

RS_UOPS_
DISPATCHED.PORT3

Cycles micro-ops
dispatched for
execution on port 3.

This event counts the number of cycles for which micro-ops
dispatched for execution. Each cycle, at most one micro-op
can be dispatched on the port. Use IA32_PMC0 only.

A1H

10H

RS_UOPS_
DISPATCHED.PORT4

Cycles micro-ops
dispatched for
execution on port 4.

This event counts the number of cycles for which micro-ops
dispatched for execution. Each cycle, at most one micro-op
can be dispatched on the port. Use IA32_PMC0 only.

A1H

20H

RS_UOPS_
DISPATCHED.PORT5

Cycles micro-ops
dispatched for
execution on port 5.

This event counts the number of cycles for which micro-ops
dispatched for execution. Each cycle, at most one micro-op
can be dispatched on the port. Use IA32_PMC0 only.

AAH

01H

MACRO_INSTS.
DECODED

Instructions decoded.

This event counts the number of instructions decoded (but
not necessarily executed or retired).

AAH

08H

MACRO_INSTS.
CISC_DECODED

CISC Instructions
decoded.

This event counts the number of complex instructions
decoded. Complex instructions usually have more than four
micro-ops. Only one complex instruction can be decoded at a
time.

ABH

01H

ESP.SYNCH

ESP register content
synchron-ization.

This event counts the number of times that the ESP register
is explicitly used in the address expression of a load or store
operation, after it is implicitly used, for example by a push or
a pop instruction.
ESP synch micro-op uses resources from the rename pipestage and up to retirement. The expected ratio of this event
divided by the number of ESP implicit changes is 0,2. If the
ratio is higher, consider rearranging your code to avoid ESP
synchronization events.

ABH

02H

ESP.ADDITIONS

ESP register automatic This event counts the number of ESP additions performed
additions.
automatically by the decoder. A high count of this event is
good, since each automatic addition performed by the
decoder saves a micro-op from the execution units.
To maximize the number of ESP additions performed
automatically by the decoder, choose instructions that
implicitly use the ESP, such as PUSH, POP, CALL, and RET
instructions whenever possible.

B0H

00H

SIMD_UOPS_EXEC

SIMD micro-ops
executed (excluding
stores).

This event counts all the SIMD micro-ops executed. It does
not count MOVQ and MOVD stores from register to memory.

B1H

00H

SIMD_SAT_UOP_
EXEC

SIMD saturated
arithmetic micro-ops
executed.

This event counts the number of SIMD saturated arithmetic
micro-ops executed.

B3H

01H

SIMD_UOP_
TYPE_EXEC.MUL

SIMD packed multiply
micro-ops executed.

This event counts the number of SIMD packed multiply
micro-ops executed.

B3H

02H

SIMD_UOP_TYPE_EXEC.SHI SIMD packed shift
FT
micro-ops executed.

This event counts the number of SIMD packed shift microops executed.

B3H

04H

SIMD_UOP_TYPE_EXEC.PA
CK

This event counts the number of SIMD pack micro-ops
executed.

B3H

08H

SIMD_UOP_TYPE_EXEC.UN SIMD unpack microPACK
ops executed.

This event counts the number of SIMD unpack micro-ops
executed.

B3H

10H

SIMD_UOP_TYPE_EXEC.LO
GICAL

This event counts the number of SIMD packed logical microops executed.

SIMD pack micro-ops
executed.

SIMD packed logical
micro-ops executed.

Vol. 3B 19-157

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

B3H

20H

SIMD_UOP_TYPE_EXEC.ARI SIMD packed
THMETIC
arithmetic micro-ops
executed.

This event counts the number of SIMD packed arithmetic
micro-ops executed.

C0H

00H

INST_RETIRED.
ANY_P

This event counts the number of instructions that retire
execution. For instructions that consist of multiple microops, this event counts the retirement of the last micro-op of
the instruction. The counter continues counting during
hardware interrupts, traps, and inside interrupt handlers.

Event Name

Definition

Instructions retired.

Description and
Comment

INST_RETIRED.ANY_P is an architectural performance
event.
C0H

01H

INST_RETIRED.
LOADS

Instructions retired,
which contain a load.

This event counts the number of instructions retired that
contain a load operation.

C0H

02H

INST_RETIRED.
STORES

Instructions retired,
which contain a store.

This event counts the number of instructions retired that
contain a store operation.

C0H

04H

INST_RETIRED.
OTHER

Instructions retired,
with no load or store
operation.

This event counts the number of instructions retired that do
not contain a load or a store operation.

C1H

01H

X87_OPS_
RETIRED.FXCH

FXCH instructions
retired.

This event counts the number of FXCH instructions retired.
Modern compilers generate more efficient code and are less
likely to use this instruction. If you obtain a high count for
this event consider recompiling the code.

C1H

FEH

X87_OPS_
RETIRED.ANY

Retired floating-point
computational
operations (precise
event).

This event counts the number of floating-point
computational operations retired. It counts:
• Floating point computational operations executed by the
assist handler.
• Sub-operations of complex floating-point instructions like
transcendental instructions.
This event does not count:
• Floating-point computational operations that cause traps
or assists.
• Floating-point loads and stores.
When this event is captured with the precise event
mechanism, the collected samples contain the address of
the instruction that was executed immediately after the
instruction that caused the event.

C2H

01H

UOPS_RETIRED.
LD_IND_BR

Fused load+op or
load+indirect branch
retired.

This event counts the number of retired micro-ops that
fused a load with another operation. This includes:
• Fusion of a load and an arithmetic operation, such as with
the following instruction: ADD EAX, [EBX] where the
content of the memory location specified by EBX register
is loaded, added to EXA register, and the result is stored
in EAX.
• Fusion of a load and a branch in an indirect branch
operation, such as with the following instructions:
• JMP [RDI+200]
• RET
• Fusion decreases the number of micro-ops in the
processor pipeline. A high value for this event count
indicates that the code is using the processor resources
effectively.

19-158 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

C2H

02H

Description and
Comment

Event Name

Definition

UOPS_RETIRED.
STD_STA

Fused store address + This event counts the number of store address calculations
data retired.
that are fused with store data emission into one micro-op.
Traditionally, each store operation required two micro-ops.
This event counts fusion of retired micro-ops only. Fusion
decreases the number of micro-ops in the processor
pipeline. A high value for this event count indicates that the
code is using the processor resources effectively.

C2H

04H

UOPS_RETIRED.
MACRO_FUSION

Retired instruction
pairs fused into one
micro-op.

This event counts the number of times CMP or TEST
instructions were fused with a conditional branch
instruction into one micro-op. It counts fusion by retired
micro-ops only.
Fusion decreases the number of micro-ops in the processor
pipeline. A high value for this event count indicates that the
code uses the processor resources more effectively.

C2H

07H

UOPS_RETIRED.
FUSED

Fused micro-ops
retired.

This event counts the total number of retired fused microops. The counts include the following fusion types:
• Fusion of load operation with an arithmetic operation or
with an indirect branch (counted by event
UOPS_RETIRED.LD_IND_BR)
• Fusion of store address and data (counted by event
UOPS_RETIRED.STD_STA)
• Fusion of CMP or TEST instruction with a conditional
branch instruction (counted by event
UOPS_RETIRED.MACRO_FUSION)
Fusion decreases the number of micro-ops in the processor
pipeline. A high value for this event count indicates that the
code is using the processor resources effectively.

C2H

08H

UOPS_RETIRED.
NON_FUSED

Non-fused micro-ops
retired.

This event counts the number of micro-ops retired that
were not fused.

C2H

0FH

UOPS_RETIRED.
ANY

Micro-ops retired.

This event counts the number of micro-ops retired. The
processor decodes complex macro instructions into a
sequence of simpler micro-ops. Most instructions are
composed of one or two micro-ops.
Some instructions are decoded into longer sequences such
as repeat instructions, floating point transcendental
instructions, and assists. In some cases micro-op sequences
are fused or whole instructions are fused into one micro-op.
See other UOPS_RETIRED events for differentiating retired
fused and non-fused micro-ops.

C3H

01H

MACHINE_
NUKES.SMC

Self-Modifying Code
detected.

This event counts the number of times that a program
writes to a code section. Self-modifying code causes a
severe penalty in all Intel 64 and IA-32 processors.

Vol. 3B 19-159

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

C3H

04H

Event Name

Definition

MACHINE_NUKES.MEM_OR
DER

Execution pipeline
restart due to memory
ordering conflict or
memory
disambiguation
misprediction.

Description and
Comment
This event counts the number of times the pipeline is
restarted due to either multi-threaded memory ordering
conflicts or memory disambiguation misprediction.
A multi-threaded memory ordering conflict occurs when a
store, which is executed in another core, hits a load that is
executed out of order in this core but not yet retired. As a
result, the load needs to be restarted to satisfy the memory
ordering model.
See Chapter 8, “Multiple-Processor Management” in the
Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3A.
To count memory disambiguation mispredictions, use the
event MEMORY_DISAMBIGUATION.RESET.

C4H

00H

BR_INST_RETIRED.ANY

Retired branch
instructions.

This event counts the number of branch instructions retired.
This is an architectural performance event.

C4H

01H

BR_INST_RETIRED.PRED_N Retired branch
This event counts the number of branch instructions retired
OT_
instructions that were that were correctly predicted to be not-taken.
TAKEN
predicted not-taken.

C4H

02H

BR_INST_RETIRED.MISPRE
D_NOT_
TAKEN

C4H

04H

BR_INST_RETIRED.PRED_T Retired branch
This event counts the number of branch instructions retired
AKEN
instructions that were that were correctly predicted to be taken.
predicted taken.

C4H

08H

BR_INST_RETIRED.MISPRE
D_TAKEN

Retired branch
This event counts the number of branch instructions retired
instructions that were that were mispredicted and taken.
mispredicted taken.

C4H

0CH

BR_INST_RETIRED.TAKEN

Retired taken branch
instructions.

This event counts the number of branches retired that were
taken.

C5H

00H

BR_INST_RETIRED.MISPRE
D

Retired mispredicted
branch instructions.
(precise event)

This event counts the number of retired branch instructions
that were mispredicted by the processor. A branch
misprediction occurs when the processor predicts that the
branch would be taken, but it is not, or vice-versa.

Retired branch
This event counts the number of branch instructions retired
instructions that were that were mispredicted and not-taken.
mispredicted nottaken.

This is an architectural performance event.
C6H

01H

CYCLES_INT_
MASKED

Cycles during which
interrupts are
disabled.

C6H

02H

CYCLES_INT_
PENDING_AND
_MASKED

Cycles during which
This event counts the number of cycles during which there
interrupts are pending are pending interrupts but interrupts are disabled.
and disabled.

C7H

01H

SIMD_INST_
RETIRED.PACKED_SINGLE

Retired SSE packedsingle instructions.

This event counts the number of SSE packed-single
instructions retired.

C7H

02H

SIMD_INST_
RETIRED.SCALAR_SINGLE

Retired SSE scalarsingle instructions.

This event counts the number of SSE scalar-single
instructions retired.

C7H

04H

SIMD_INST_
RETIRED.PACKED_DOUBLE

Retired SSE2 packeddouble instructions.

This event counts the number of SSE2 packed-double
instructions retired.

C7H

08H

SIMD_INST_
RETIRED.SCALAR_DOUBLE

Retired SSE2 scalardouble instructions.

This event counts the number of SSE2 scalar-double
instructions retired.

19-160 Vol. 3B

This event counts the number of cycles during which
interrupts are disabled.

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

Description and
Comment

C7H

10H

SIMD_INST_
RETIRED.VECTOR

Retired SSE2 vector
integer instructions.

This event counts the number of SSE2 vector integer
instructions retired.

C7H

1FH

SIMD_INST_
RETIRED.ANY

Retired Streaming
SIMD instructions
(precise event).

This event counts the overall number of retired SIMD
instructions that use XMM registers. To count each type of
SIMD instruction separately, use the following events:
• SIMD_INST_RETIRED.PACKED_SINGLE
• SIMD_INST_RETIRED.SCALAR_SINGLE
• SIMD_INST_RETIRED.PACKED_DOUBLE
• SIMD_INST_RETIRED.SCALAR_DOUBLE
• and SIMD_INST_RETIRED.VECTOR
When this event is captured with the precise event
mechanism, the collected samples contain the address of
the instruction that was executed immediately after the
instruction that caused the event.

C8H

00H

HW_INT_RCV

Hardware interrupts
received.

This event counts the number of hardware interrupts
received by the processor.

C9H

00H

ITLB_MISS_
RETIRED

Retired instructions
that missed the ITLB.

This event counts the number of retired instructions that
missed the ITLB when they were fetched.

CAH

01H

SIMD_COMP_
INST_RETIRED.
PACKED_SINGLE

Retired computational This event counts the number of computational SSE packedSSE packed-single
single instructions retired. Computational instructions
instructions.
perform arithmetic computations (for example: add, multiply
and divide).
Instructions that perform load and store operations or
logical operations, like XOR, OR, and AND are not counted by
this event.

CAH

02H

SIMD_COMP_
INST_RETIRED.
SCALAR_SINGLE

Retired computational This event counts the number of computational SSE scalarSSE scalar-single
single instructions retired. Computational instructions
instructions.
perform arithmetic computations (for example: add, multiply
and divide).
Instructions that perform load and store operations or
logical operations, like XOR, OR, and AND are not counted by
this event.

CAH

04H

SIMD_COMP_
INST_RETIRED.
PACKED_DOUBLE

Retired computational This event counts the number of computational SSE2
SSE2 packed-double
packed-double instructions retired. Computational
instructions.
instructions perform arithmetic computations (for example:
add, multiply and divide).
Instructions that perform load and store operations or
logical operations, like XOR, OR, and AND are not counted by
this event.

CAH

08H

SIMD_COMP_INST_RETIRE
D.SCALAR_DOUBLE

Retired computational This event counts the number of computational SSE2 scalarSSE2 scalar-double
double instructions retired. Computational instructions
instructions.
perform arithmetic computations (for example: add, multiply
and divide).
Instructions that perform load and store operations or
logical operations, like XOR, OR, and AND are not counted by
this event.

Vol. 3B 19-161

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

CBH

01H

Description and
Comment

Event Name

Definition

MEM_LOAD_
RETIRED.L1D
_MISS

Retired loads that miss This event counts the number of retired load operations
the L1 data cache
that missed the L1 data cache. This includes loads from
(precise event).
cache lines that are currently being fetched, due to a
previous L1 data cache miss to the same cache line.
This event counts loads from cacheable memory only. The
event does not count loads by software prefetches.
When this event is captured with the precise event
mechanism, the collected samples contain the address of
the instruction that was executed immediately after the
instruction that caused the event.
Use IA32_PMC0 only.

CBH

02H

MEM_LOAD_
RETIRED.L1D_
LINE_MISS

L1 data cache line
missed by retired
loads (precise event).

This event counts the number of load operations that miss
the L1 data cache and send a request to the L2 cache to
fetch the missing cache line. That is the missing cache line
fetching has not yet started.
The event count is equal to the number of cache lines
fetched from the L2 cache by retired loads.
This event counts loads from cacheable memory only. The
event does not count loads by software prefetches.
The event might not be counted if the load is blocked (see
LOAD_BLOCK events).
When this event is captured with the precise event
mechanism, the collected samples contain the address of
the instruction that was executed immediately after the
instruction that caused the event.
Use IA32_PMC0 only.

CBH

04H

MEM_LOAD_
RETIRED.L2_MISS

Retired loads that miss This event counts the number of retired load operations
the L2 cache (precise that missed the L2 cache.
event).
This event counts loads from cacheable memory only. It
does not count loads by software prefetches.
When this event is captured with the precise event
mechanism, the collected samples contain the address of
the instruction that was executed immediately after the
instruction that caused the event.
Use IA32_PMC0 only.

19-162 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

CBH

08H

Event Name

Definition

MEM_LOAD_
RETIRED.L2_LINE_MISS

L2 cache line missed
by retired loads
(precise event).

Description and
Comment
This event counts the number of load operations that miss
the L2 cache and result in a bus request to fetch the missing
cache line. That is the missing cache line fetching has not
yet started.
This event count is equal to the number of cache lines
fetched from memory by retired loads.
This event counts loads from cacheable memory only. The
event does not count loads by software prefetches.
The event might not be counted if the load is blocked (see
LOAD_BLOCK events).
When this event is captured with the precise event
mechanism, the collected samples contain the address of
the instruction that was executed immediately after the
instruction that caused the event.
Use IA32_PMC0 only.

CBH

10H

MEM_LOAD_
RETIRED.DTLB_
MISS

Retired loads that miss This event counts the number of retired loads that missed
the DTLB (precise
the DTLB. The DTLB miss is not counted if the load
event).
operation causes a fault.
This event counts loads from cacheable memory only. The
event does not count loads by software prefetches.
When this event is captured with the precise event
mechanism, the collected samples contain the address of
the instruction that was executed immediately after the
instruction that caused the event.
Use IA32_PMC0 only.

CCH

01H

FP_MMX_TRANS_TO_MMX Transitions from
This event counts the first MMX instructions following a
Floating Point to MMX floating-point instruction. Use this event to estimate the
Instructions.
penalties for the transitions between floating-point and
MMX states.

CCH

02H

FP_MMX_TRANS_TO_FP

Transitions from MMX
Instructions to
Floating Point
Instructions.

This event counts the first floating-point instructions
following any MMX instruction. Use this event to estimate
the penalties for the transitions between floating-point and
MMX states.

CDH

00H

SIMD_ASSIST

SIMD assists invoked.

This event counts the number of SIMD assists invoked. SIMD
assists are invoked when an EMMS instruction is executed,
changing the MMX state in the floating point stack.

CEH

00H

SIMD_INSTR_
RETIRED

SIMD Instructions
retired.

This event counts the number of retired SIMD instructions
that use MMX registers.

CFH

00H

SIMD_SAT_INSTR_RETIRED Saturated arithmetic
instructions retired.

This event counts the number of saturated arithmetic SIMD
instructions that retired.

D2H

01H

RAT_STALLS.
ROB_READ_PORT

This event counts the number of cycles when ROB read port
stalls occurred, which did not allow new micro-ops to enter
the out-of-order pipeline.

ROB read port stalls
cycles.

Note that, at this stage in the pipeline, additional stalls may
occur at the same cycle and prevent the stalled micro-ops
from entering the pipe. In such a case, micro-ops retry
entering the execution pipe in the next cycle and the ROBread-port stall is counted again.

Vol. 3B 19-163

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

D2H

D2H

Description and
Comment

Event Name

Definition

02H

RAT_STALLS.
PARTIAL_CYCLES

Partial register stall
cycles.

This event counts the number of cycles instruction
execution latency became longer than the defined latency
because the instruction uses a register that was partially
written by previous instructions.

04H

RAT_STALLS.
FLAGS

Flag stall cycles.

This event counts the number of cycles during which
execution stalled due to several reasons, one of which is a
partial flag register stall.
A partial register stall may occur when two conditions are
met:
• An instruction modifies some, but not all, of the flags in
the flag register.
• The next instruction, which depends on flags, depends on
flags that were not modified by this instruction.

D2H

08H

RAT_STALLS.
FPSW

FPU status word stall.

This event indicates that the FPU status word (FPSW) is
written. To obtain the number of times the FPSW is written
divide the event count by 2.
The FPSW is written by instructions with long latency; a
small count may indicate a high penalty.

D2H

0FH

RAT_STALLS.
ANY

All RAT stall cycles.

This event counts the number of stall cycles due to
conditions described by:
•
•
•
•

RAT_STALLS.ROB_READ_PORT
RAT_STALLS.PARTIAL
RAT_STALLS.FLAGS
RAT_STALLS.FPSW.

D4H

01H

SEG_RENAME_
STALLS.ES

Segment rename stalls This event counts the number of stalls due to the lack of
- ES.
renaming resources for the ES segment register. If a
segment is renamed, but not retired and a second update to
the same segment occurs, a stall occurs in the front end of
the pipeline until the renamed segment retires.

D4H

02H

SEG_RENAME_
STALLS.DS

Segment rename stalls This event counts the number of stalls due to the lack of
- DS.
renaming resources for the DS segment register. If a
segment is renamed, but not retired and a second update to
the same segment occurs, a stall occurs in the front end of
the pipeline until the renamed segment retires.

D4H

04H

SEG_RENAME_
STALLS.FS

Segment rename stalls This event counts the number of stalls due to the lack of
- FS.
renaming resources for the FS segment register.
If a segment is renamed, but not retired and a second
update to the same segment occurs, a stall occurs in the
front end of the pipeline until the renamed segment retires.

D4H

08H

SEG_RENAME_
STALLS.GS

Segment rename stalls This event counts the number of stalls due to the lack of
- GS.
renaming resources for the GS segment register.
If a segment is renamed, but not retired and a second
update to the same segment occurs, a stall occurs in the
front end of the pipeline until the renamed segment retires.

D4H

0FH

SEG_RENAME_
STALLS.ANY

Any (ES/DS/FS/GS)
This event counts the number of stalls due to the lack of
segment rename stall. renaming resources for the ES, DS, FS, and GS segment
registers.
If a segment is renamed but not retired and a second update
to the same segment occurs, a stall occurs in the front end
of the pipeline until the renamed segment retires.

19-164 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

Event Name

Definition

Description and
Comment

D5H

01H

SEG_REG_
RENAMES.ES

Segment renames ES.

This event counts the number of times the ES segment
register is renamed.

D5H

02H

SEG_REG_
RENAMES.DS

Segment renames DS.

This event counts the number of times the DS segment
register is renamed.

D5H

04H

SEG_REG_
RENAMES.FS

Segment renames FS.

This event counts the number of times the FS segment
register is renamed.

D5H

08H

SEG_REG_
RENAMES.GS

Segment renames GS.

This event counts the number of times the GS segment
register is renamed.

D5H

0FH

SEG_REG_
RENAMES.ANY

Any (ES/DS/FS/GS)
segment rename.

This event counts the number of times any of the four
segment registers (ES/DS/FS/GS) is renamed.

DCH

01H

RESOURCE_
STALLS.ROB_FULL

Cycles during which
the ROB full.

This event counts the number of cycles when the number of
instructions in the pipeline waiting for retirement reaches
the limit the processor can handle.
A high count for this event indicates that there are long
latency operations in the pipe (possibly load and store
operations that miss the L2 cache, and other instructions
that depend on these cannot execute until the former
instructions complete execution). In this situation new
instructions cannot enter the pipe and start execution.

DCH

02H

RESOURCE_
STALLS.RS_FULL

Cycles during which
the RS full.

This event counts the number of cycles when the number of
instructions in the pipeline waiting for execution reaches
the limit the processor can handle.
A high count of this event indicates that there are long
latency operations in the pipe (possibly load and store
operations that miss the L2 cache, and other instructions
that depend on these cannot execute until the former
instructions complete execution). In this situation new
instructions cannot enter the pipe and start execution.

DCH

04

RESOURCE_
STALLS.LD_ST

Cycles during which
This event counts the number of cycles while resourcethe pipeline has
related stalls occur due to:
exceeded load or store • The number of load instructions in the pipeline reached
limit or waiting to
the limit the processor can handle. The stall ends when a
commit all stores.
loading instruction retires.
• The number of store instructions in the pipeline reached
the limit the processor can handle. The stall ends when a
storing instruction commits its data to the cache or
memory.
• There is an instruction in the pipe that can be executed
only when all previous stores complete and their data is
committed in the caches or memory. For example, the
SFENCE and MFENCE instructions require this behavior.

DCH

08H

RESOURCE_
STALLS.FPCW

Cycles stalled due to
FPU control word
write.

This event counts the number of cycles while execution was
stalled due to writing the floating-point unit (FPU) control
word.

DCH

10H

RESOURCE_
STALLS.BR_MISS_CLEAR

Cycles stalled due to
branch misprediction.

This event counts the number of cycles after a branch
misprediction is detected at execution until the branch and
all older micro-ops retire. During this time new micro-ops
cannot enter the out-of-order pipeline.

Vol. 3B 19-165

PERFORMANCE MONITORING EVENTS

Table 19-25. Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)
Event
Num

Umask
Value

DCH

1FH

Event Name

Definition

RESOURCE_
STALLS.ANY

Resource related
stalls.

Description and
Comment
This event counts the number of cycles while resourcerelated stalls occurs for any conditions described by the
following events:
•
•
•
•
•

RESOURCE_STALLS.ROB_FULL
RESOURCE_STALLS.RS_FULL
RESOURCE_STALLS.LD_ST
RESOURCE_STALLS.FPCW
RESOURCE_STALLS.BR_MISS_CLEAR

E0H

00H

BR_INST_
DECODED

Branch instructions
decoded.

This event counts the number of branch instructions
decoded.

E4H

00H

BOGUS_BR

Bogus branches.

This event counts the number of byte sequences that were
mistakenly detected as taken branch instructions.
This results in a BACLEAR event. This occurs mainly after
task switches.

E6H

00H

BACLEARS

BACLEARS asserted.

This event counts the number of times the front end is
resteered, mainly when the BPU cannot provide a correct
prediction and this is corrected by other branch handling
mechanisms at the front and. This can occur if the code has
many branches such that they cannot be consumed by the
BPU.
Each BACLEAR asserted costs approximately 7 cycles of
instruction fetch. The effect on total execution time
depends on the surrounding code.

F0H

00H

PREF_RQSTS_UP

Upward prefetches
issued from DPL.

F8H

00H

PREF_RQSTS_DN

Downward prefetches This event counts the number of downward prefetches
issued from DPL.
issued from the Data Prefetch Logic (DPL) to the L2 cache. A
prefetch request issued to the L2 cache cannot be cancelled
and the requested cache line is fetched to the L2 cache.

19-166 Vol. 3B

This event counts the number of upward prefetches issued
from the Data Prefetch Logic (DPL) to the L2 cache. A
prefetch request issued to the L2 cache cannot be cancelled
and the requested cache line is fetched to the L2 cache.

PERFORMANCE MONITORING EVENTS

19.13

PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON THE
GOLDMONT PLUS MICROARCHITECTURE

Intel Atom processors based on the Goldmont Plus microarchitecture support the architectural performance monitoring events listed in Table 19-1 and fixed-function performance events using a fixed counter. They also support
the following performance monitoring events listed in Table 19-27. These events apply to processors with CPUID
signature of 06_7AH. In addition, processors based on the Goldmont Plus microarchitecture also support the
events listed in Table 19-27 (see Section 19.14, “Performance Monitoring Events for Processors Based on the Goldmont Microarchitecture”). For an event listed in Table 19-27 that also appears in the model-specific tables of prior
generations, Table 19-27 supersedes prior generation tables.
Performance monitoring event descriptions may refer to terminology described in Section B.2, “Intel® Xeon®
processor 5500 Series,” in Appendix B of the Intel® 64 and IA-32 Architectures Optimization Reference Manual.
In Goldmont Plus microarchitecture, performance monitoring events that support Processor Event Based Sampling
(PEBS) and PEBS records that contain processor state information that are associated with at-retirement tagging
are marked by “Precise Event”.

Table 19-26. Performance Events for the Goldmont Plus Microarchitecture
Event
Num.

Umask
Value

Event Name

Description

Comment

00H

01H

INST_RETIRED.ANY

Counts the number of instructions that retire execution. For
instructions that consist of multiple uops, this event counts the
retirement of the last uop of the instruction. The counter continues
counting during hardware interrupts, traps, and inside interrupt
handlers. This event uses fixed counter 0. You cannot collect a PEBS
record for this event.

Fixed Event,
Precise Event,
Not Reduced
Skid

08H

02H

DTLB_LOAD_MISSES.W
ALK_COMPLETED_4K

Counts page walks completed due to demand data loads (including SW
prefetches) whose address translations missed in all TLB levels and
were mapped to 4K pages. The page walks can end with or without a
page fault.

08H

04H

DTLB_LOAD_MISSES.W
ALK_COMPLETED_2M_
4M

Counts page walks completed due to demand data loads (including SW
prefetches) whose address translations missed in all TLB levels and
were mapped to 2M or 4M pages. The page walks can end with or
without a page fault.

08H

08H

DTLB_LOAD_MISSES.W
ALK_COMPLETED_1GB

Counts page walks completed due to demand data loads (including SW
prefetches) whose address translations missed in all TLB levels and
were mapped to 1GB pages. The page walks can end with or without a
page fault.

08H

10H

DTLB_LOAD_MISSES.W
ALK_PENDING

Counts once per cycle for each page walk occurring due to a load
(demand data loads or SW prefetches). Includes cycles spent traversing
the Extended Page Table (EPT). Average cycles per walk can be
calculated by dividing by the number of walks.

49H

02H

DTLB_STORE_MISSES.W Counts page walks completed due to demand data stores whose
ALK_COMPLETED_4K
address translations missed in the TLB and were mapped to 4K pages.
The page walks can end with or without a page fault.

49H

04H

DTLB_STORE_MISSES.W Counts page walks completed due to demand data stores whose
ALK_COMPLETED_2M_ address translations missed in the TLB and were mapped to 2M or 4M
4M
pages. The page walks can end with or without a page fault.

49H

08H

DTLB_STORE_MISSES.W Counts page walks completed due to demand data stores whose
ALK_COMPLETED_1GB address translations missed in the TLB and were mapped to 1GB pages.
The page walks can end with or without a page fault.

49H

10H

DTLB_STORE_MISSES.W Counts once per cycle for each page walk occurring due to a demand
ALK_PENDING
data store. Includes cycles spent traversing the Extended Page Table
(EPT). Average cycles per walk can be calculated by dividing by the
number of walks.
Vol. 3B 19-167

PERFORMANCE MONITORING EVENTS

Table 19-26. Performance Events for the Goldmont Plus Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Name

Description

4FH

10H

EPT.WALK_PENDING

Counts once per cycle for each page walk only while traversing the
Extended Page Table (EPT), and does not count during the rest of the
translation. The EPT is used for translating Guest-Physical Addresses to
Physical Addresses for Virtual Machine Monitors (VMMs). Average
cycles per walk can be calculated by dividing the count by number of
walks.

85H

02H

ITLB_MISSES.WALK_CO
MPLETED_4K

Counts page walks completed due to instruction fetches whose address
translations missed in the TLB and were mapped to 4K pages. The page
walks can end with or without a page fault.

85H

04H

ITLB_MISSES.WALK_CO
MPLETED_2M_4M

Counts page walks completed due to instruction fetches whose address
translations missed in the TLB and were mapped to 2M or 4M pages.
The page walks can end with or without a page fault.

85H

08H

ITLB_MISSES.WALK_CO
MPLETED_1GB

Counts page walks completed due to instruction fetches whose address
translations missed in the TLB and were mapped to 1GB pages. The
page walks can end with or without a page fault.

85H

10H

ITLB_MISSES.WALK_PE
NDING

Counts once per cycle for each page walk occurring due to an
instruction fetch. Includes cycles spent traversing the Extended Page
Table (EPT). Average cycles per walk can be calculated by dividing by
the number of walks.

BDH

20H

TLB_FLUSHES.STLB_AN Counts STLB flushes. The TLBs are flushed on instructions like INVLPG
Y
and MOV to CR3.

C3H

20H

MACHINE_CLEARS.PAGE Counts the number of times that the machines clears due to a page
_FAULT
fault. Covers both I-side and D-side (Loads/Stores) page faults. A page
fault occurs when either page is not present, or an access violation.

19.14

Comment

PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON THE
GOLDMONT MICROARCHITECTURE

Intel Atom processors based on the Goldmont microarchitecture support the architectural performance monitoring
events listed in Table 19-1 and fixed-function performance events using a fixed counter. In addition, they also
support the following model-specific performance monitoring events listed in Table 19-27. These events apply to
processors with CPUID signatures of 06_5CH, 06_5FH, and 06_7AH.
Performance monitoring event descriptions may refer to terminology described in Section B.2, “Intel® Xeon®
processor 5500 Series,” in Appendix B of the Intel® 64 and IA-32 Architectures Optimization Reference Manual.
In Goldmont microarchitecture, performance monitoring events that support Processor Event Based Sampling
(PEBS) and PEBS records that contain processor state information that are associated with at-retirement tagging
are marked by “Precise Event”.

Table 19-27. Performance Events for the Goldmont Microarchitecture
Event
Num.

Umask
Value

Event Name

03H

10H

LD_BLOCKS.ALL_BLOCK Counts anytime a load that retires is blocked for any reason.

Precise Event

03H

08H

LD_BLOCKS.UTLB_MISS Counts loads blocked because they are unable to find their physical
address in the micro TLB (UTLB).

Precise Event

03H

02H

LD_BLOCKS.STORE_FO
RWARD

Precise Event

19-168 Vol. 3B

Description

Counts a load blocked from using a store forward because of an
address/size mismatch; only one of the loads blocked from each store
will be counted.

Comment

PERFORMANCE MONITORING EVENTS

Table 19-27. Performance Events for the Goldmont Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Name

Description

03H

01H

LD_BLOCKS.DATA_UNK
NOWN

Counts a load blocked from using a store forward, but did not occur
Precise Event
because the store data was not available at the right time. The forward
might occur subsequently when the data is available.

03H

04H

LD_BLOCKS.4K_ALIAS

Counts loads that block because their address modulo 4K matches a
pending store.

05H

01H

PAGE_WALKS.D_SIDE_C Counts every core cycle when a Data-side (walks due to data operation)
YCLES
page walk is in progress.

05H

02H

PAGE_WALKS.I_SIDE_CY Counts every core cycle when an Instruction-side (walks due to an
CLES
instruction fetch) page walk is in progress.

05H

03H

PAGE_WALKS.CYCLES

Counts every core cycle a page-walk is in progress due to either a data
memory operation, or an instruction fetch.

0EH

00H

UOPS_ISSUED.ANY

Counts uops issued by the front end and allocated into the back end of
the machine. This event counts uops that retire as well as uops that
were speculatively executed but didn't retire. The sort of speculative
uops that might be counted includes, but is not limited to those uops
issued in the shadow of a mispredicted branch, those uops that are
inserted during an assist (such as for a denormal floating-point result),
and (previously allocated) uops that might be canceled during a
machine clear.

13H

02H

MISALIGN_MEM_REF.LO Counts when a memory load of a uop that spans a page boundary (a
AD_PAGE_SPLIT
split) is retired.

Precise Event

13H

04H

MISALIGN_MEM_REF.ST Counts when a memory store of a uop that spans a page boundary (a
ORE_PAGE_SPLIT
split) is retired.

Precise Event

2EH

4FH

LONGEST_LAT_CACHE.
REFERENCE

Counts memory requests originating from the core that reference a
cache line in the L2 cache.

2EH

41H

LONGEST_LAT_CACHE.
MISS

Counts memory requests originating from the core that miss in the L2
cache.

30H

00H

L2_REJECT_XQ.ALL

Counts the number of demand and prefetch transactions that the L2
XQ rejects due to a full or near full condition which likely indicates back
pressure from the intra-die interconnect (IDI) fabric. The XQ may reject
transactions from the L2Q (non-cacheable requests), L2 misses and L2
write-back victims.

31H

00H

CORE_REJECT_L2Q.ALL

Counts the number of demand and L1 prefetcher requests rejected by
the L2Q due to a full or nearly full condition which likely indicates back
pressure from L2Q. It also counts requests that would have gone
directly to the XQ, but are rejected due to a full or nearly full condition,
indicating back pressure from the IDI link. The L2Q may also reject
transactions from a core to ensure fairness between cores, or to delay
a core's dirty eviction when the address conflicts with incoming
external snoops.

3CH

00H

CPU_CLK_UNHALTED.C
ORE_P

Core cycles when core is not halted. This event uses a programmable
general purpose performance counter.

3CH

01H

CPU_CLK_UNHALTED.R
EF

Reference cycles when core is not halted. This event uses a
programmable general purpose performance counter.

51H

01H

DL1.DIRTY_EVICTION

Counts when a modified (dirty) cache line is evicted from the data L1
cache and needs to be written back to memory. No count will occur if
the evicted line is clean, and hence does not require a writeback.

Comment

Precise Event

Vol. 3B 19-169

PERFORMANCE MONITORING EVENTS

Table 19-27. Performance Events for the Goldmont Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Name

Description

80H

01H

ICACHE.HIT

Counts requests to the Instruction Cache (ICache) for one or more
bytes in an ICache Line and that cache line is in the Icache (hit). The
event strives to count on a cache line basis, so that multiple accesses
which hit in a single cache line count as one ICACHE.HIT. Specifically, the
event counts when straight line code crosses the cache line boundary,
or when a branch target is to a new line, and that cache line is in the
ICache. This event counts differently than Intel processors based on
the Silvermont microarchitecture.

80H

02H

ICACHE.MISSES

Counts requests to the Instruction Cache (ICache) for one or more
bytes in an ICache Line and that cache line is not in the Icache (miss).
The event strives to count on a cache line basis, so that multiple
accesses which miss in a single cache line count as one ICACHE.MISS.
Specifically, the event counts when straight line code crosses the cache
line boundary, or when a branch target is to a new line, and that cache
line is not in the ICache. This event counts differently than Intel
processors based on the Silvermont microarchitecture.

80H

03H

ICACHE.ACCESSES

Counts requests to the Instruction Cache (ICache) for one or more
bytes in an ICache Line. The event strives to count on a cache line basis,
so that multiple fetches to a single cache line count as one
ICACHE.ACCESS. Specifically, the event counts when accesses from
straight line code crosses the cache line boundary, or when a branch
target is to a new line. This event counts differently than Intel
processors based on the Silvermont microarchitecture.

81H

04H

ITLB.MISS

Counts the number of times the machine was unable to find a
translation in the Instruction Translation Lookaside Buffer (ITLB) for a
linear address of an instruction fetch. It counts when new translations
are filled into the ITLB. The event is speculative in nature, but will not
count translations (page walks) that are begun and not finished, or
translations that are finished but not filled into the ITLB.

86H

00H

FETCH_STALL.ALL

Counts cycles that fetch is stalled due to any reason. That is, the
decoder queue is able to accept bytes, but the fetch unit is unable to
provide bytes. This will include cycles due to an ITLB miss, ICache miss
and other events.

86H

01H

FETCH_STALL.ITLB_FIL
L_PENDING_CYCLES

Counts cycles that fetch is stalled due to an outstanding ITLB miss.
That is, the decoder queue is able to accept bytes, but the fetch unit is
unable to provide bytes due to an ITLB miss. Note: this event is not the
same as page walk cycles to retrieve an instruction translation.

86H

02H

FETCH_STALL.ICACHE_F Counts cycles that an ICache miss is outstanding, and instruction fetch
ILL_PENDING_CYCLES
is stalled. That is, the decoder queue is able to accept bytes, but the
fetch unit is unable to provide bytes, while an Icache miss is
outstanding. Note this event is not the same as cycles to retrieve an
instruction due to an Icache miss. Rather, it is the part of the
Instruction Cache (ICache) miss time where no bytes are available for
the decoder.

19-170 Vol. 3B

Comment

PERFORMANCE MONITORING EVENTS

Table 19-27. Performance Events for the Goldmont Microarchitecture (Contd.)
Event
Num.

Umask
Value

9CH

00H

Event Name

Description

Comment

UOPS_NOT_DELIVERED. This event is used to measure front-end inefficiencies, i.e., when the
ANY
front end of the machine is not delivering uops to the back end and the
back end has not stalled. This event can be used to identify if the
machine is truly front-end bound. When this event occurs, it is an
indication that the front end of the machine is operating at less than its
theoretical peak performance.
Background: We can think of the processor pipeline as being divided
into 2 broader parts: the front end and the back end. The front end is
responsible for fetching the instruction, decoding into uops in machine
understandable format and putting them into a uop queue to be
consumed by the back end. The back end then takes these uops and
allocates the required resources. When all resources are ready, uops are
executed. If the back end is not ready to accept uops from the front
end, then we do not want to count these as front-end bottlenecks.
However, whenever we have bottlenecks in the back end, we will have
allocation unit stalls and eventually force the front end to wait until the
back end is ready to receive more uops. This event counts only when
the back end is requesting more micro-uops and the front end is not
able to provide them. When 3 uops are requested and no uops are
delivered, the event counts 3. When 3 are requested, and only 1 is
delivered, the event counts 2. When only 2 are delivered, the event
counts 1. Alternatively stated, the event will not count if 3 uops are
delivered, or if the back end is stalled and not requesting any uops at
all. Counts indicate missed opportunities for the front end to deliver a
uop to the back end. Some examples of conditions that cause front-end
efficiencies are: Icache misses, ITLB misses, and decoder restrictions
that limit the front-end bandwidth.
Known Issues: Some uops require multiple allocation slots. These uops
will not be charged as a front end 'not delivered' opportunity, and will
be regarded as a back-end problem. For example, the INC instruction
has one uop that requires 2 issue slots. A stream of INC instructions will
not count as UOPS_NOT_DELIVERED, even though only one instruction
can be issued per clock. The low uop issue rate for a stream of INC
instructions is considered to be a back-end issue.

B7H

01H,
02H

OFFCORE_RESPONSE

Requires MSR_OFFCORE_RESP[0,1] to specify request type and
response. (Duplicated for both MSRs.)

C0H

00H

INST_RETIRED.ANY_P

Counts the number of instructions that retire execution. For
Precise Event
instructions that consist of multiple uops, this event counts the
retirement of the last uop of the instruction. The event continues
counting during hardware interrupts, traps, and inside interrupt
handlers. This is an architectural performance event. This event uses a
programmable general purpose performance counter. *This event is a
Precise Event: the EventingRIP field in the PEBS record is precise to the
address of the instruction which caused the event.
Note: Because PEBS records can be collected only on IA32_PMC0, only
one event can use the PEBS facility at a time.

C2H

00H

UOPS_RETIRED.ANY

Counts uops which have retired.

Precise Event,
Not Reduced
Skid

Vol. 3B 19-171

PERFORMANCE MONITORING EVENTS

Table 19-27. Performance Events for the Goldmont Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Name

Description

Comment

C2H

01H

UOPS_RETIRED.MS

Counts uops retired that are from the complex flows issued by the
micro-sequencer (MS). Counts both the uops from a micro-coded
instruction, and the uops that might be generated from a micro-coded
assist.

Precise Event,
Not Reduced
Skid

C2H

08H

UOPS_RETIRED.FPDIV

Counts the number of floating point divide uops retired.

Precise Event

C2H

10H

UOPS_RETIRED.IDIV

Counts the number of integer divide uops retired.

Precise Event

C3H

01H

MACHINE_CLEARS.SMC

Counts the number of times that the processor detects that a program
is writing to a code section and has to perform a machine clear because
of that modification. Self-modifying code (SMC) causes a severe penalty
in all Intel architecture processors.

C3H

02H

MACHINE_CLEARS.MEM Counts machine clears due to memory ordering issues. This occurs
ORY_ORDERING
when a snoop request happens and the machine is uncertain if memory
ordering will be preserved as another core is in the process of
modifying the data.

C3H

04H

MACHINE_CLEARS.FP_A Counts machine clears due to floating-point (FP) operations needing
SSIST
assists. For instance, if the result was a floating-point denormal, the
hardware clears the pipeline and reissues uops to produce the correct
IEEE compliant denormal result.

C3H

08H

MACHINE_CLEARS.DISA Counts machine clears due to memory disambiguation. Memory
MBIGUATION
disambiguation happens when a load which has been issued conflicts
with a previous un-retired store in the pipeline whose address was not
known at issue time, but is later resolved to be the same as the load
address.

C3H

00H

MACHINE_CLEARS.ALL

C4H

00H

BR_INST_RETIRED.ALL_ Counts branch instructions retired for all branch types. This is an
BRANCHES
architectural performance event.

Precise Event

C4H

7EH

BR_INST_RETIRED.JCC

Precise Event

C4H

80H

BR_INST_RETIRED.ALL_ Counts the number of taken branch instructions retired.
TAKEN_BRANCHES

Precise Event

C4H

FEH

BR_INST_RETIRED.TAK
EN_JCC

Precise Event

C4H

F9H

BR_INST_RETIRED.CALL Counts near CALL branch instructions retired.

Precise Event

C4H

FDH

BR_INST_RETIRED.REL_ Counts near relative CALL branch instructions retired.
CALL

Precise Event

C4H

FBH

BR_INST_RETIRED.IND_ Counts near indirect CALL branch instructions retired.
CALL

Precise Event

C4H

F7H

BR_INST_RETIRED.RET
URN

Precise Event

C4H

EBH

BR_INST_RETIRED.NON Counts near indirect call or near indirect jmp branch instructions retired. Precise Event
_RETURN_IND

C4H

BFH

BR_INST_RETIRED.FAR
_BRANCH

Counts far branch instructions retired. This includes far jump, far call
and return, and Interrupt call and return.

Precise Event

C5H

00H

BR_MISP_RETIRED.ALL
_BRANCHES

Counts mispredicted branch instructions retired including all branch
types.

Precise Event

19-172 Vol. 3B

Counts machine clears for any reason.

Counts retired Jcc (Jump on Conditional Code/Jump if Condition is Met)
branch instructions retired, including both when the branch was taken
and when it was not taken.

Counts Jcc (Jump on Conditional Code/Jump if Condition is Met) branch
instructions retired that were taken and does not count when the Jcc
branch instruction were not taken.

Counts near return branch instructions retired.

PERFORMANCE MONITORING EVENTS

Table 19-27. Performance Events for the Goldmont Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Name

Description

C5H

7EH

BR_MISP_RETIRED.JCC

Counts mispredicted retired Jcc (Jump on Conditional Code/Jump if
Precise Event
Condition is Met) branch instructions retired, including both when the
branch was supposed to be taken and when it was not supposed to be
taken (but the processor predicted the opposite condition).

C5H

FEH

BR_MISP_RETIRED.TAK
EN_JCC

Counts mispredicted retired Jcc (Jump on Conditional Code/Jump if
Condition is Met) branch instructions retired that were supposed to be
taken but the processor predicted that it would not be taken.

C5H

FBH

BR_MISP_RETIRED.IND_ Counts mispredicted near indirect CALL branch instructions retired,
Precise Event
CALL
where the target address taken was not what the processor predicted.

C5H

F7H

BR_MISP_RETIRED.RET
URN

C5H

EBH

BR_MISP_RETIRED.NON Counts mispredicted branch instructions retired that were near indirect Precise Event
_RETURN_IND
call or near indirect jmp, where the target address taken was not what
the processor predicted.

CAH

01H

ISSUE_SLOTS_NOT_CO Counts the number of issue slots per core cycle that were not
NSUMED.RESOURCE_FU consumed because of a full resource in the back end. Including but not
LL
limited to resources include the Re-order Buffer (ROB), reservation
stations (RS), load/store buffers, physical registers, or any other
needed machine resource that is currently unavailable. Note that uops
must be available for consumption in order for this event to fire. If a
uop is not available (Instruction Queue is empty), this event will not
count.

CAH

02H

ISSUE_SLOTS_NOT_CO
NSUMED.RECOVERY

Counts the number of issue slots per core cycle that were not
consumed by the back end because allocation is stalled waiting for a
mispredicted jump to retire or other branch-like conditions (e.g. the
event is relevant during certain microcode flows). Counts all issue slots
blocked while within this window, including slots where uops were not
available in the Instruction Queue.

CAH

00H

ISSUE_SLOTS_NOT_CO
NSUMED.ANY

Counts the number of issue slots per core cycle that were not
consumed by the back end due to either a full resource in the back end
(RESOURCE_FULL), or due to the processor recovering from some
event (RECOVERY).

CBH

01H

HW_INTERRUPTS.RECEI Counts hardware interrupts received by the processor.
VED

CBH

02H

HW_INTERRUPTS.MASK Counts the number of core cycles during which interrupts are masked
ED
(disabled). Increments by 1 each core cycle that EFLAGS.IF is 0,
regardless of whether interrupts are pending or not.

CBH

04H

HW_INTERRUPTS.PENDI Counts core cycles during which there are pending interrupts, but
NG_AND_MASKED
interrupts are masked (EFLAGS.IF = 0).

CDH

00H

CYCLES_DIV_BUSY.ALL

Counts core cycles if either divide unit is busy.

CDH

01H

CYCLES_DIV_BUSY.IDIV

Counts core cycles if the integer divide unit is busy.

CDH

02H

CYCLES_DIV_BUSY.FPDI Counts core cycles if the floating point divide unit is busy.
V

D0H

81H

MEM_UOPS_RETIRED.A
LL_LOADS

Counts the number of load uops retired.

Precise Event

D0H

82H

MEM_UOPS_RETIRED.A
LL_STORES

Counts the number of store uops retired.

Precise Event

Counts mispredicted near RET branch instructions retired, where the
return address taken was not what the processor predicted.

Comment

Precise Event

Precise Event

Vol. 3B 19-173

PERFORMANCE MONITORING EVENTS

Table 19-27. Performance Events for the Goldmont Microarchitecture (Contd.)
Event
Num.

Umask
Value

Event Name

Description

Comment

D0H

83H

MEM_UOPS_RETIRED.A
LL

Counts the number of memory uops retired that are either a load or a
store or both.

Precise Event

D0H

11H

MEM_UOPS_RETIRED.D
TLB_MISS_LOADS

Counts load uops retired that caused a DTLB miss.

Precise Event

D0H

12H

MEM_UOPS_RETIRED.D
TLB_MISS_STORES

Counts store uops retired that caused a DTLB miss.

Precise Event

D0H

13H

MEM_UOPS_RETIRED.D
TLB_MISS

Counts uops retired that had a DTLB miss on load, store or either.

Precise Event

Note that when two distinct memory operations to the same page miss
the DTLB, only one of them will be recorded as a DTLB miss.

D0H

21H

MEM_UOPS_RETIRED.L
OCK_LOADS

Counts locked memory uops retired. This includes 'regular' locks and
Precise Event
bus locks. To specifically count bus locks only, see the offcore response
event. A locked access is one with a lock prefix, or an exchange to
memory.

D0H

41H

MEM_UOPS_RETIRED.S
PLIT_LOADS

Counts load uops retired where the data requested spans a 64 byte
cache line boundary.

Precise Event

D0H

42H

MEM_UOPS_RETIRED.S
PLIT_STORES

Counts store uops retired where the data requested spans a 64 byte
cache line boundary.

Precise Event

D0H

43H

MEM_UOPS_RETIRED.S
PLIT

Counts memory uops retired where the data requested spans a 64
byte cache line boundary.

Precise Event

D1H

01H

MEM_LOAD_UOPS_RETI Counts load uops retired that hit the L1 data cache.
RED.L1_HIT

Precise Event

D1H

08H

MEM_LOAD_UOPS_RETI Counts load uops retired that miss the L1 data cache.
RED.L1_MISS

Precise Event

D1H

02H

MEM_LOAD_UOPS_RETI Counts load uops retired that hit in the L2 cache.
RED.L2_HIT

Precise Event

0xD1H

10H

MEM_LOAD_UOPS_RETI Counts load uops retired that miss in the L2 cache.
RED.L2_MISS

Precise Event

D1H

20H

MEM_LOAD_UOPS_RETI Counts load uops retired where the cache line containing the data was Precise Event
RED.HITM
in the modified state of another core or modules cache (HITM). More
specifically, this means that when the load address was checked by
other caching agents (typically another processor) in the system, one
of those caching agents indicated that they had a dirty copy of the
data. Loads that obtain a HITM response incur greater latency than
most that is typical for a load. In addition, since HITM indicates that
some other processor had this data in its cache, it implies that the data
was shared between processors, or potentially was a lock or
semaphore value. This event is useful for locating sharing, false
sharing, and contended locks.

19-174 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-27. Performance Events for the Goldmont Microarchitecture (Contd.)
Event
Num.

Umask
Value

D1H

40H

MEM_LOAD_UOPS_RETI Counts memory load uops retired where the data is retrieved from the Precise Event
RED.WCB_HIT
WCB (or fill buffer), indicating that the load found its data while that
data was in the process of being brought into the L1 cache. Typically a
load will receive this indication when some other load or prefetch
missed the L1 cache and was in the process of retrieving the cache line
containing the data, but that process had not yet finished (and written
the data back to the cache). For example, consider load X and Y, both
referencing the same cache line that is not in the L1 cache. If load X
misses cache first, it obtains and WCB (or fill buffer) begins the process
of requesting the data. When load Y requests the data, it will either hit
the WCB, or the L1 cache, depending on exactly what time the request
to Y occurs.

D1H

80H

MEM_LOAD_UOPS_RETI Counts memory load uops retired where the data is retrieved from
Precise Event
RED.DRAM_HIT
DRAM. Event is counted at retirement, so the speculative loads are
ignored. A memory load can hit (or miss) the L1 cache, hit (or miss) the
L2 cache, hit DRAM, hit in the WCB or receive a HITM response.

E6H

01H

BACLEARS.ALL

E6H

08H

BACLEARS.RETURN

Counts BACLEARS on return instructions.

E6H

10H

BACLEARS.COND

Counts BACLEARS on Jcc (Jump on Conditional Code/Jump if Condition is
Met) branches.

E7H

01H

MS_DECODED.MS_ENTR Counts the number of times the Microcode Sequencer (MS) starts a
Y
flow of uops from the MSROM. It does not count every time a uop is
read from the MSROM. The most common case that this counts is when
a micro-coded instruction is encountered by the front end of the
machine. Other cases include when an instruction encounters a fault,
trap, or microcode assist of any sort that initiates a flow of uops. The
event will count MS startups for uops that are speculative, and
subsequently cleared by branch mispredict or a machine clear.

E9H

01H

DECODE_RESTRICTION.
PREDECODE_WRONG

19.15

Event Name

Description

Comment

Counts the number of times a BACLEAR is signaled for any reason,
including, but not limited to indirect branch/call, Jcc (Jump on Conditional
Code/Jump if Condition is Met) branch, unconditional branch/call, and
returns.

Counts the number of times the prediction (from the pre-decode cache)
for instruction length is incorrect.

PERFORMANCE MONITORING EVENTS FOR PROCESSORS BASED ON THE
SILVERMONT MICROARCHITECTURE

Processors based on the Silvermont microarchitecture support the architectural performance monitoring events
listed in Table 19-1 and fixed-function performance events using fixed counter. In addition, they also support the
following model-specific performance monitoring events listed in Table 19-28. These processors have the CPUID
signatures of 06_37H, 06_4AH, 06_4DH, 06_5AH, and 06_5DH.
Performance monitoring event descriptions may refer to terminology described in Section B.2, “Intel® Xeon®
processor 5500 Series,” in Appendix B of the Intel® 64 and IA-32 Architectures Optimization Reference Manual.

Vol. 3B 19-175

PERFORMANCE MONITORING EVENTS

Table 19-28. Performance Events for Silvermont Microarchitecture
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

03H

01H

REHABQ.LD_BLOCK_S
T_FORWARD

Loads blocked due to
store forward
restriction.

This event counts the number of retired loads that were
prohibited from receiving forwarded data from the store
because of address mismatch.

03H

02H

REHABQ.LD_BLOCK_S
TD_NOTREADY

Loads blocked due to
store data not ready.

This event counts the cases where a forward was technically
possible, but did not occur because the store data was not
available at the right time.

03H

04H

REHABQ.ST_SPLITS

Store uops that split
cache line boundary.

This event counts the number of retire stores that experienced
cache line boundary splits.

03H

08H

REHABQ.LD_SPLITS

Load uops that split
cache line boundary.

This event counts the number of retire loads that experienced
cache line boundary splits.

03H

10H

REHABQ.LOCK

Uops with lock
semantics.

This event counts the number of retired memory operations
with lock semantics. These are either implicit locked instructions
such as the XCHG instruction or instructions with an explicit
LOCK prefix (F0H).

03H

20H

REHABQ.STA_FULL

Store address buffer
full.

This event counts the number of retired stores that are delayed
because there is not a store address buffer available.

03H

40H

REHABQ.ANY_LD

Any reissued load uops. This event counts the number of load uops reissued from
Rehabq.

03H

80H

REHABQ.ANY_ST

Any reissued store
uops.

04H

01H

MEM_UOPS_RETIRED.L Loads retired that
1_MISS_LOADS
missed L1 data cache.

This event counts the number of load ops retired that miss in L1
Data cache. Note that prefetch misses will not be counted.

04H

02H

MEM_UOPS_RETIRED.L Loads retired that hit
2_HIT_LOADS
L2.

This event counts the number of load micro-ops retired that hit
L2.

04H

04H

MEM_UOPS_RETIRED.L Loads retired that
2_MISS_LOADS
missed L2.

This event counts the number of load micro-ops retired that
missed L2.

04H

08H

MEM_UOPS_RETIRED.
DTLB_MISS_LOADS

Loads missed DTLB.

This event counts the number of load ops retired that had DTLB
miss.

04H

10H

MEM_UOPS_RETIRED.
UTLB_MISS

Loads missed UTLB.

This event counts the number of load ops retired that had UTLB
miss.

04H

20H

MEM_UOPS_RETIRED.
HITM

Cross core or cross
module hitm.

This event counts the number of load ops retired that got data
from the other core or from the other module.

04H

40H

MEM_UOPS_RETIRED.
ALL_LOADS

All Loads.

This event counts the number of load ops retired.

04H

80H

MEM_UOP_RETIRED.A
LL_STORES

All Stores.

This event counts the number of store ops retired.

05H

01H

PAGE_WALKS.D_SIDE_
CYCLES

Duration of D-side
page-walks in core
cycles.

This event counts every cycle when a D-side (walks due to a
load) page walk is in progress. Page walk duration divided by
number of page walks is the average duration of page-walks.

This event counts the number of store uops reissued from
Rehabq.

Edge trigger bit must be cleared. Set Edge to count the number
of page walks.
05H

02H

PAGE_WALKS.I_SIDE_C Duration of I-side page- This event counts every cycle when an I-side (walks due to an
YCLES
walks in core cycles.
instruction fetch) page walk is in progress. Page walk duration
divided by number of page walks is the average duration of
page-walks.
Edge trigger bit must be cleared. Set Edge to count the number
of page walks.

19-176 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-28. Performance Events for Silvermont Microarchitecture
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

05H

03H

PAGE_WALKS.WALKS

Total number of pagewalks that are
completed (I-side and
D-side).

This event counts when a data (D) page walk or an instruction (I)
page walk is completed or started. Since a page walk implies a
TLB miss, the number of TLB misses can be counted by counting
the number of pagewalks.
Edge trigger bit must be set. Clear Edge to count the number of
cycles.

2EH

41H

LONGEST_LAT_CACHE. L2 cache request
MISS
misses.

This event counts the total number of L2 cache references and
the number of L2 cache misses respectively.
L3 is not supported in Silvermont microarchitecture.

2EH

4FH

LONGEST_LAT_CACHE. L2 cache requests
REFERENCE
from this core.

This event counts requests originating from the core that
references a cache line in the L2 cache.
L3 is not supported in Silvermont microarchitecture.

30H

00H

L2_REJECT_XQ.ALL

Counts the number of
request from the L2
that were not accepted
into the XQ.

This event counts the number of demand and prefetch
transactions that the L2 XQ rejects due to a full or near full
condition which likely indicates back pressure from the IDI link.
The XQ may reject transactions from the L2Q (non-cacheable
requests), BBS (L2 misses) and WOB (L2 write-back victims).

31H

00H

CORE_REJECT_L2Q.ALL Counts the number of
request that were not
accepted into the L2Q
because the L2Q is
FULL.

This event counts the number of demand and L1 prefetcher
requests rejected by the L2Q due to a full or nearly full condition
which likely indicates back pressure from L2Q. It also counts
requests that would have gone directly to the XQ, but are
rejected due to a full or nearly full condition, indicating back
pressure from the IDI link. The L2Q may also reject transactions
from a core to insure fairness between cores, or to delay a core's
dirty eviction when the address conflicts incoming external
snoops. (Note that L2 prefetcher requests that are dropped are
not counted by this event.).

3CH

00H

CPU_CLK_UNHALTED.C Core cycles when core
ORE_P
is not halted.

This event counts the number of core cycles while the core is not
in a halt state. The core enters the halt state when it is running
the HLT instruction. In mobile systems the core frequency may
change from time to time. For this reason this event may have a
changing ratio with regards to time.

N/A

N/A

CPU_CLK_UNHALTED.C Core cycles when core
ORE
is not halted.

This uses the fixed counter 1 to count the same condition as
CPU_CLK_UNHALTED.CORE_P does.

3CH

01H

CPU_CLK_UNHALTED.R Bus cycles when core is This event counts the number of bus cycles that the core is not
EF_P
not halted.
in a halt state. The core enters the halt state when it is running
the HLT instruction.
In mobile systems the core frequency may change from time.
This event is not affected by core frequency changes.

N/A

N/A

CPU_CLK_UNHALTED.R Reference cycles when This event counts the number of reference cycles at a TSC rate
EF_TSC
core is not halted.
that the core is not in a halt state. The core enters the halt state
when it is running the HLT instruction.
In mobile systems the core frequency may change from time.
This event is not affected by core frequency changes.

80H

01H

ICACHE.HIT

Instruction fetches
from Icache.

This event counts all instruction fetches from the instruction
cache.

80H

02H

ICACHE.MISSES

Icache miss.

This event counts all instruction fetches that miss the
Instruction cache or produce memory requests. This includes
uncacheable fetches. An instruction fetch miss is counted only
once and not once for every cycle it is outstanding.
Vol. 3B 19-177

PERFORMANCE MONITORING EVENTS

Table 19-28. Performance Events for Silvermont Microarchitecture
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

80H

03H

ICACHE.ACCESSES

Instruction fetches.

This event counts all instruction fetches, including uncacheable
fetches.

B7H

01H

OFFCORE_RESPONSE_ See Section 18.5.2.2.
0

Requires MSR_OFFCORE_RESP0 to specify request type and
response.

B7H

02H

OFFCORE_RESPONSE_ See Section 18.5.2.2.
1

Requires MSR_OFFCORE_RESP1 to specify request type and
response.

C0H

00H

INST_RETIRED.ANY_P

Instructions retired
(PEBS supported with
IA32_PMC0).

This event counts the number of instructions that retire
execution. For instructions that consist of multiple micro-ops,
this event counts the retirement of the last micro-op of the
instruction. The counter continues counting during hardware
interrupts, traps, and inside interrupt handlers.

N/A

N/A

INST_RETIRED.ANY

Instructions retired.

This uses the fixed counter 0 to count the same condition as
INST_RETIRED.ANY_P does.

C2H

01H

UOPS_RETIRED.MS

MSROM micro-ops
retired.

This event counts the number of micro-ops retired that were
supplied from MSROM.

C2H

10H

UOPS_RETIRED.ALL

Micro-ops retired.

This event counts the number of micro-ops retired.

C3H

01H

MACHINE_CLEARS.SMC Self-Modifying Code
detected.

This event counts the number of times that a program writes to
a code section. Self-modifying code causes a severe penalty in all
Intel® architecture processors.

C3H

02H

MACHINE_CLEARS.ME
MORY_ORDERING

This event counts the number of times that pipeline was cleared
due to memory ordering issues.

C3H

04H

MACHINE_CLEARS.FP_ Stalls due to FP assists. This event counts the number of times that pipeline stalled due
ASSIST
to FP operations needing assists.

C3H

08H

MACHINE_CLEARS.ALL Stalls due to any
causes.

This event counts the number of times that pipeline stalled due
to due to any causes (including SMC, MO, FP assist, etc.).

C4H

00H

BR_INST_RETIRED.ALL Retired branch
_BRANCHES
instructions.

This event counts the number of branch instructions retired.

C4H

7EH

BR_INST_RETIRED.JCC

This event counts the number of branch instructions retired that
were conditional jumps.

C4H

BFH

BR_INST_RETIRED.FAR Retired far branch
_BRANCH
instructions.

This event counts the number of far branch instructions retired.

C4H

EBH

BR_INST_RETIRED.NO
N_RETURN_IND

This event counts the number of branch instructions retired that
were near indirect call or near indirect jmp.

C4H

F7H

BR_INST_RETIRED.RET Retired near return
URN
instructions.

This event counts the number of near RET branch instructions
retired.

C4H

F9H

BR_INST_RETIRED.CAL Retired near call
L
instructions.

This event counts the number of near CALL branch instructions
retired.

C4H

FBH

BR_INST_RETIRED.IND Retired near indirect
_CALL
call instructions.

This event counts the number of near indirect CALL branch
instructions retired.

C4H

FDH

BR_INST_RETIRED.REL Retired near relative
_CALL
call instructions.

This event counts the number of near relative CALL branch
instructions retired.

C4H

FEH

BR_INST_RETIRED.TAK Retired conditional
This event counts the number of branch instructions retired that
EN_JCC
jumps that were taken. were conditional jumps and taken.

C5H

00H

BR_MISP_RETIRED.ALL Retired mispredicted
_BRANCHES
branch instructions.

19-178 Vol. 3B

Stalls due to Memory
ordering.

Retired branch
instructions that were
conditional jumps.

Retired instructions of
near indirect Jmp or
call.

This event counts the number of mispredicted branch
instructions retired.

PERFORMANCE MONITORING EVENTS

Table 19-28. Performance Events for Silvermont Microarchitecture
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

C5H

7EH

BR_MISP_RETIRED.JCC

Retired mispredicted
conditional jumps.

This event counts the number of mispredicted branch
instructions retired that were conditional jumps.

C5H

BFH

BR_MISP_RETIRED.FA
R

Retired mispredicted
This event counts the number of mispredicted far branch
far branch instructions. instructions retired.

C5H

EBH

BR_MISP_RETIRED.NO
N_RETURN_IND

Retired mispredicted
instructions of near
indirect Jmp or call.

This event counts the number of mispredicted branch
instructions retired that were near indirect call or near indirect
jmp.

C5H

F7H

BR_MISP_RETIRED.RE
TURN

Retired mispredicted
near return
instructions.

This event counts the number of mispredicted near RET branch
instructions retired.

C5H

F9H

BR_MISP_RETIRED.CAL Retired mispredicted
L
near call instructions.

This event counts the number of mispredicted near CALL branch
instructions retired.

C5H

FBH

BR_MISP_RETIRED.IND Retired mispredicted
_CALL
near indirect call
instructions.

This event counts the number of mispredicted near indirect CALL
branch instructions retired.

C5H

FDH

BR_MISP_RETIRED.REL Retired mispredicted
_CALL
near relative call
instructions

This event counts the number of mispredicted near relative CALL
branch instructions retired.

C5H

FEH

BR_MISP_RETIRED.TA
KEN_JCC

This event counts the number of mispredicted branch
instructions retired that were conditional jumps and taken.

CAH

01H

NO_ALLOC_CYCLES.RO Counts the number of
B_FULL
cycles when no uops
are allocated and the
ROB is full (less than 2
entries available).

Counts the number of cycles when no uops are allocated and the
ROB is full (less than 2 entries available).

CAH

20H

NO_ALLOC_CYCLES.RA Counts the number of
T_STALL
cycles when no uops
are allocated and a
RATstall is asserted.

Counts the number of cycles when no uops are allocated and a
RATstall is asserted.

CAH

3FH

NO_ALLOC_CYCLES.AL
L

This event counts the number of cycles when the front end does
not provide any instructions to be allocated for any reason.

CAH

50H

NO_ALLOC_CYCLES.NO Front end not
This event counts the number of cycles when the front end does
T_DELIVERED
delivering back end not not provide any instructions to be allocated but the back end is
stalled.
not stalled.

CBH

01H

RS_FULL_STALL.MEC

MEC RS full.

This event counts the number of cycles the allocation pipe line
stalled due to the RS for the MEC cluster is full.

CBH

1FH

RS_FULL_STALL.ALL

Any RS full.

This event counts the number of cycles that the allocation pipe
line stalled due to any one of the RS is full.

CDH

01H

CYCLES_DIV_BUSY.AN
Y

Divider Busy.

This event counts the number of cycles the divider is busy.

E6H

01H

BACLEARS.ALL

BACLEARS asserted for This event counts the number of baclears for any type of branch.
any branch.

E6H

08H

BACLEARS.RETURN

BACLEARS asserted for This event counts the number of baclears for return branches.
return branch.

Retired mispredicted
conditional jumps that
were taken.

Front end not
delivering.

Vol. 3B 19-179

PERFORMANCE MONITORING EVENTS

Table 19-28. Performance Events for Silvermont Microarchitecture
Event
Num.

Umask
Value

Event Name

Definition

E6H

10H

BACLEARS.COND

BACLEARS asserted for This event counts the number of baclears for conditional
conditional branch.
branches.

E7H

01H

MS_DECODED.MS_ENT MS Decode starts.
RY

Description and Comment

This event counts the number of times the MSROM starts a flow
of UOPS.

19.15.1 Performance Monitoring Events for Processors Based on the Airmont
Microarchitecture
Intel processors based on the Airmont microarchitecture support the same architectural and the model-specific
performance monitoring events as processors based on the Silvermont microarchitecture. All of the events listed
in Table 19-28 apply. These processors have the CPUID signatures that include 06_4CH.

19.16

PERFORMANCE MONITORING EVENTS FOR 45 NM AND 32 NM
INTEL® ATOM™ PROCESSORS

45 nm and 32 nm processors based on the Intel® Atom™ microarchitecture support the architectural performance
monitoring events listed in Table 19-1 and fixed-function performance events using fixed counter listed in Table
19-24. In addition, they also support the following model-specific performance monitoring events listed in Table
19-29.

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors
Event
Num.

Umask
Value

02H

81H

STORe_FORWARDS.GO Good store forwards.
OD

This event counts the number of times store data was
forwarded directly to a load.

06H

00H

SEGMENT_REG_
LOADS.ANY

This event counts the number of segment register load
operations. Instructions that load new values into segment
registers cause a penalty. This event indicates performance
issues in 16-bit code. If this event occurs frequently, it may be
useful to calculate the number of instructions retired per
segment register load. If the resulting calculation is low (on
average a small number of instructions are executed between
segment register loads), then the code’s segment register
usage should be optimized.

Event Name

Definition

Number of segment
register loads.

Description and Comment

As a result of branch misprediction, this event is speculative and
may include segment register loads that do not actually occur.
However, most segment register loads are internally serialized
and such speculative effects are minimized.
07H

01H

PREFETCH.PREFETCHT Streaming SIMD
0
Extensions (SSE)
PrefetchT0
instructions executed.

This event counts the number of times the SSE instruction
prefetchT0 is executed. This instruction prefetches the data to
the L1 data cache and L2 cache.

07H

06H

PREFETCH.SW_L2

This event counts the number of times the SSE instructions
prefetchT1 and prefetchT2 are executed. These instructions
prefetch the data to the L2 cache.

19-180 Vol. 3B

Streaming SIMD
Extensions (SSE)
PrefetchT1 and
PrefetchT2
instructions executed.

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

07H

08H

PREFETCH.PREFETCHN Streaming SIMD
TA
Extensions (SSE)
Prefetch NTA
instructions executed.

This event counts the number of times the SSE instruction
prefetchNTA is executed. This instruction prefetches the data
to the L1 data cache.

08H

07H

DATA_TLB_MISSES.DT
LB_MISS

Memory accesses that
missed the DTLB.

This event counts the number of Data Table Lookaside Buffer
(DTLB) misses. The count includes misses detected as a result
of speculative accesses. Typically a high count for this event
indicates that the code accesses a large number of data pages.

08H

05H

DATA_TLB_MISSES.DT
LB_MISS_LD

DTLB misses due to
load operations.

This event counts the number of Data Table Lookaside Buffer
(DTLB) misses due to load operations. This count includes
misses detected as a result of speculative accesses.

08H

09H

DATA_TLB_MISSES.L0
_DTLB_MISS_LD

L0_DTLB misses due to This event counts the number of L0_DTLB misses due to load
load operations.
operations. This count includes misses detected as a result of
speculative accesses.

08H

06H

DATA_TLB_MISSES.DT
LB_MISS_ST

DTLB misses due to
store operations.

This event counts the number of Data Table Lookaside Buffer
(DTLB) misses due to store operations. This count includes
misses detected as a result of speculative accesses.

0CH

03H

PAGE_WALKS.WALKS

Number of page-walks
executed.

This event counts the number of page-walks executed due to
either a DTLB or ITLB miss. The page walk duration,
PAGE_WALKS.CYCLES, divided by number of page walks is the
average duration of a page walk. This can hint to whether most
of the page-walks are satisfied by the caches or cause an L2
cache miss.

0CH

03H

PAGE_WALKS.CYCLES

Duration of page-walks This event counts the duration of page-walks in core cycles. The
in core cycles.
paging mode in use typically affects the duration of page walks.
Page walk duration divided by number of page walks is the
average duration of page-walks. This can hint at whether most
of the page-walks are satisfied by the caches or cause an L2
cache miss.

10H

01H

X87_COMP_OPS_EXE.
ANY.S

Floating point
computational microops executed.

This event counts the number of x87 floating point
computational micro-ops executed.

10H

81H

X87_COMP_OPS_EXE.
ANY.AR

Floating point
computational microops retired.

This event counts the number of x87 floating point
computational micro-ops retired.

11H

01H

FP_ASSIST

Floating point assists.

This event counts the number of floating point operations
executed that required micro-code assist intervention. These
assists are required in the following cases.

Event Name

Definition

Description and Comment

Edge trigger bit must be set.

Edge trigger bit must be cleared.

X87 instructions:
1. NaN or denormal are loaded to a register or used as input
from memory.
2. Division by 0.
3. Underflow output.

Vol. 3B 19-181

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

11H

81H

FP_ASSIST.AR

Floating point assists.

This event counts the number of floating point operations
executed that required micro-code assist intervention. These
assists are required in the following cases.
X87 instructions:
1. NaN or denormal are loaded to a register or used as input
from memory.
2. Division by 0.
3. Underflow output.

12H

01H

MUL.S

Multiply operations
executed.

This event counts the number of multiply operations executed.
This includes integer as well as floating point multiply
operations.

12H

81H

MUL.AR

Multiply operations
retired.

This event counts the number of multiply operations retired.
This includes integer as well as floating point multiply
operations.

13H

01H

DIV.S

Divide operations
executed.

This event counts the number of divide operations executed.
This includes integer divides, floating point divides and squareroot operations executed.

13H

81H

DIV.AR

Divide operations
retired.

This event counts the number of divide operations retired. This
includes integer divides, floating point divides and square-root
operations executed.

14H

01H

CYCLES_DIV_BUSY

Cycles the driver is
busy.

This event counts the number of cycles the divider is busy
executing divide or square root operations. The divide can be
integer, X87 or Streaming SIMD Extensions (SSE). The square
root operation can be either X87 or SSE.

21H

See
Table
18-61

L2_ADS

Cycles L2 address bus
is in use.

This event counts the number of cycles the L2 address bus is
being used for accesses to the L2 cache or bus queue.

22H

See
Table
18-61

L2_DBUS_BUSY

Cycles the L2 cache
data bus is busy.

This event counts core cycles during which the L2 cache data
bus is busy transferring data from the L2 cache to the core. It
counts for all L1 cache misses (data and instruction) that hit the
L2 cache. The count will increment by two for a full cache-line
request.

24H

See
Table
18-61
and
Table
18-63

L2_LINES_IN

L2 cache misses.

This event counts the number of cache lines allocated in the L2
cache. Cache lines are allocated in the L2 cache as a result of
requests from the L1 data and instruction caches and the L2
hardware prefetchers to cache lines that are missing in the L2
cache.

See
Table
18-61

L2_M_LINES_IN

25H

19-182 Vol. 3B

This event can count occurrences for this core or both cores.

This event can count occurrences for this core or both cores.
This event can also count demand requests and L2 hardware
prefetch requests together or separately.
L2 cache line
modifications.

This event counts whenever a modified cache line is written
back from the L1 data cache to the L2 cache.
This event can count occurrences for this core or both cores.

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

26H

See
Table
18-61
and
Table
18-63

L2_LINES_OUT

L2 cache lines evicted.

This event counts the number of L2 cache lines evicted.

See
Table
18-61
and
Table
18-63

L2_M_LINES_OUT

See
Table
18-61
and
Table
18-64

L2_IFETCH

See
Table
18-61,
Table
18-63
and
Table
18-64

L2_LD

27H

28H

29H

This event can count occurrences for this core or both cores.
This event can also count evictions due to demand requests and
L2 hardware prefetch requests together or separately.

Modified lines evicted
from the L2 cache.

This event counts the number of L2 modified cache lines
evicted. These lines are written back to memory unless they
also exist in a shared-state in one of the L1 data caches.
This event can count occurrences for this core or both cores.
This event can also count evictions due to demand requests and
L2 hardware prefetch requests together or separately.

L2 cacheable
instruction fetch
requests.

This event counts the number of instruction cache line requests
from the ICache. It does not include fetch requests from
uncacheable memory. It does not include ITLB miss accesses.
This event can count occurrences for this core or both cores.
This event can also count accesses to cache lines at different
MESI states.

L2 cache reads.

This event counts L2 cache read requests coming from the L1
data cache and L2 prefetchers.
This event can count occurrences for this core or both cores.
This event can count occurrences
- for this core or both cores.
- due to demand requests and L2 hardware prefetch requests
together or separately.
- of accesses to cache lines at different MESI states.

2AH

2BH

2EH

See
Table
18-61
and
Table
18-64

L2_ST

See
Table
18-61
and
Table
18-64

L2_LOCK

See
Table
18-61,
Table
18-63
and
Table
18-64

L2_RQSTS

L2 store requests.

This event counts all store operations that miss the L1 data
cache and request the data from the L2 cache.
This event can count occurrences for this core or both cores.
This event can also count accesses to cache lines at different
MESI states.

L2 locked accesses.

This event counts all locked accesses to cache lines that miss
the L1 data cache.
This event can count occurrences for this core or both cores.
This event can also count accesses to cache lines at different
MESI states.

L2 cache requests.

This event counts all completed L2 cache requests. This
includes L1 data cache reads, writes, and locked accesses, L1
data prefetch requests, instruction fetches, and all L2 hardware
prefetch requests.
This event can count occurrences
- for this core or both cores.
- due to demand requests and L2 hardware prefetch requests
together, or separately.
- of accesses to cache lines at different MESI states.

Vol. 3B 19-183

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

2EH

41H

Event Name

Definition

L2_RQSTS.SELF.DEMA
ND.I_STATE

L2 cache demand
This event counts all completed L2 cache demand requests
requests from this core from this core that miss the L2 cache. This includes L1 data
that missed the L2.
cache reads, writes, and locked accesses, L1 data prefetch
requests, and instruction fetches.

Description and Comment

This is an architectural performance event.
2EH

4FH

L2_RQSTS.SELF.DEMA
ND.MESI

L2 cache demand
requests from this
core.

This event counts all completed L2 cache demand requests
from this core. This includes L1 data cache reads, writes, and
locked accesses, L1 data prefetch requests, and instruction
fetches.
This is an architectural performance event.

30H

See
Table
18-61,
Table
18-63
and
Table
18-64

L2_REJECT_BUSQ

Rejected L2 cache
requests.

This event indicates that a pending L2 cache request that
requires a bus transaction is delayed from moving to the bus
queue. Some of the reasons for this event are:
- The bus queue is full.
- The bus queue already holds an entry for a cache line in the
same set.
The number of events is greater or equal to the number of
requests that were rejected.
- For this core or both cores.
- Due to demand requests and L2 hardware prefetch requests
together, or separately.
- Of accesses to cache lines at different MESI states.

32H

See
Table
18-61

L2_NO_REQ

Cycles no L2 cache
requests are pending.

This event counts the number of cycles that no L2 cache
requests are pending.

3AH

00H

EIST_TRANS

Number of Enhanced
Intel SpeedStep(R)
Technology (EIST)
transitions.

This event counts the number of Enhanced Intel SpeedStep(R)
Technology (EIST) transitions that include a frequency change,
either with or without VID change. This event is incremented
only while the counting core is in C0 state. In situations where
an EIST transition was caused by hardware as a result of CxE
state transitions, those EIST transitions will also be registered
in this event.
Enhanced Intel Speedstep Technology transitions are commonly
initiated by OS, but can be initiated by HW internally. For
example: CxE states are C-states (C1,C2,C3…) which not only
place the CPU into a sleep state by turning off the clock and
other components, but also lower the voltage (which reduces
the leakage power consumption). The same is true for thermal
throttling transition which uses Enhanced Intel Speedstep
Technology internally.

3BH

C0H

19-184 Vol. 3B

THERMAL_TRIP

Number of thermal
trips.

This event counts the number of thermal trips. A thermal trip
occurs whenever the processor temperature exceeds the
thermal trip threshold temperature. Following a thermal trip,
the processor automatically reduces frequency and voltage.
The processor checks the temperature every millisecond, and
returns to normal when the temperature falls below the
thermal trip threshold temperature.

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

3CH

00H

Event Name

Definition

CPU_CLK_UNHALTED.C Core cycles when core
ORE_P
is not halted.

Description and Comment
This event counts the number of core cycles while the core is
not in a halt state. The core enters the halt state when it is
running the HLT instruction. This event is a component in many
key event ratios.
In mobile systems the core frequency may change from time to
time. For this reason this event may have a changing ratio with
regards to time. In systems with a constant core frequency, this
event can give you a measurement of the elapsed time while
the core was not in halt state by dividing the event count by the
core frequency.
-This is an architectural performance event.
- The event CPU_CLK_UNHALTED.CORE_P is counted by a
programmable counter.
- The event CPU_CLK_UNHALTED.CORE is counted by a
designated fixed counter, leaving the two programmable
counters available for other events.

3CH

01H

CPU_CLK_UNHALTED.B Bus cycles when core is This event counts the number of bus cycles while the core is not
US
not halted.
in the halt state. This event can give you a measurement of the
elapsed time while the core was not in the halt state, by
dividing the event count by the bus frequency. The core enters
the halt state when it is running the HLT instruction.
The event also has a constant ratio with
CPU_CLK_UNHALTED.REF event, which is the maximum bus to
processor frequency ratio.
Non-halted bus cycles are a component in many key event
ratios.

3CH

02H

CPU_CLK_UNHALTED.
NO_OTHER

Bus cycles when core is This event counts the number of bus cycles during which the
active and the other is core remains non-halted, and the other core on the processor is
halted.
halted.
This event can be used to determine the amount of parallelism
exploited by an application or a system. Divide this event count
by the bus frequency to determine the amount of time that
only one core was in use.

40H

21H

L1D_CACHE.LD

L1 Cacheable Data
Reads.

This event counts the number of data reads from cacheable
memory.

40H

22H

L1D_CACHE.ST

L1 Cacheable Data
Writes.

This event counts the number of data writes to cacheable
memory.

60H

See
Table
18-61
and
Table
18-62.

BUS_REQUEST_OUTST Outstanding cacheable This event counts the number of pending full cache line read
ANDING
data read bus requests transactions on the bus occurring in each cycle. A read
duration.
transaction is pending from the cycle it is sent on the bus until
the full cache line is received by the processor. NOTE: This
event is thread-independent and will not provide a count per
logical processor when AnyThr is disabled.

Vol. 3B 19-185

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

61H

See
Table
18-62.

Event Name

Definition

BUS_BNR_DRV

Number of Bus Not
This event counts the number of Bus Not Ready (BNR) signals
Ready signals asserted. that the processor asserts on the bus to suspend additional bus
requests by other bus agents. A bus agent asserts the BNR
signal when the number of data and snoop transactions is close
to the maximum that the bus can handle.

Description and Comment

While this signal is asserted, new transactions cannot be
submitted on the bus. As a result, transaction latency may have
higher impact on program performance. NOTE: This event is
thread-independent and will not provide a count per logical
processor when AnyThr is disabled.
62H

See
Table
18-62.

BUS_DRDY_CLOCKS

Bus cycles when data
is sent on the bus.

This event counts the number of bus cycles during which the
DRDY (Data Ready) signal is asserted on the bus. The DRDY
signal is asserted when data is sent on the bus.
This event counts the number of bus cycles during which this
agent (the processor) writes data on the bus back to memory or
to other bus agents. This includes all explicit and implicit data
writebacks, as well as partial writes.
Note: This event is thread-independent and will not provide a
count per logical processor when AnyThr is disabled.

63H

See
Table
18-61
and
Table
18-62.

BUS_LOCK_CLOCKS

Bus cycles when a
This event counts the number of bus cycles, during which the
LOCK signal is asserted. LOCK signal is asserted on the bus. A LOCK signal is asserted
when there is a locked memory access, due to:
- Uncacheable memory.
- Locked operation that spans two cache lines.
- Page-walk from an uncacheable page table.
Bus locks have a very high performance penalty and it is highly
recommended to avoid such accesses. NOTE: This event is
thread-independent and will not provide a count per logical
processor when AnyThr is disabled.

64H

See
Table
18-61.

BUS_DATA_RCV

Bus cycles while
processor receives
data.

This event counts the number of cycles during which the
processor is busy receiving data. NOTE: This event is threadindependent and will not provide a count per logical processor
when AnyThr is disabled.

65H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_BRD

Burst read bus
transactions.

This event counts the number of burst read transactions
including:
- L1 data cache read misses (and L1 data cache hardware
prefetches).
- L2 hardware prefetches by the DPL and L2 streamer.
- IFU read misses of cacheable lines.
It does not include RFO transactions.

66H

See
Table
18-61
and
Table
18-62.

19-186 Vol. 3B

BUS_TRANS_RFO

RFO bus transactions.

This event counts the number of Read For Ownership (RFO) bus
transactions, due to store operations that miss the L1 data
cache and the L2 cache. This event also counts RFO bus
transactions due to locked operations.

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

67H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_WB

Explicit writeback bus
transactions.

This event counts all explicit writeback bus transactions due to
dirty line evictions. It does not count implicit writebacks due to
invalidation by a snoop request.

68H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_IFETCH

Instruction-fetch bus
transactions.

This event counts all instruction fetch full cache line bus
transactions.

69H

See
Table
18-61
and
Table
18-62.

BUS_TRANS_INVAL

Invalidate bus
transactions.

This event counts all invalidate transactions. Invalidate
transactions are generated when:

6AH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_PWR

Partial write bus
transaction.

This event counts partial write bus transactions.

6BH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_P

Partial bus
transactions.

This event counts all (read and write) partial bus transactions.

6CH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_IO

IO bus transactions.

This event counts the number of completed I/O bus
transactions as a result of IN and OUT instructions. The count
does not include memory mapped IO.

6DH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_DEF

Deferred bus
transactions.

This event counts the number of deferred transactions.

6EH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_BURST

Burst (full cache-line)
bus transactions.

This event counts burst (full cache line) transactions including:

- A store operation hits a shared line in the L2 cache.
- A full cache line write misses the L2 cache or hits a shared line
in the L2 cache.

- Burst reads.
- RFOs.
- Explicit writebacks.
- Write combine lines.

Vol. 3B 19-187

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

6FH

See
Table
18-61
and
Table
18-62.

BUS_TRANS_MEM

Memory bus
transactions.

This event counts all memory bus transactions including:

See
Table
18-61
and
Table
18-62.

BUS_TRANS_ANY

See
Table
18-61
and
Table
18-64.

EXT_SNOOP

See
Table
18-62.

BUS_HIT_DRV

7BH

See
Table
18-62.

BUS_HITM_DRV

HITM signal asserted.

This event counts the number of bus cycles during which the
processor drives the HITM# pin to signal HITM snoop response.
NOTE: This event is thread-independent and will not provide a
count per logical processor when AnyThr is disabled.

7DH

See
Table
18-61.

BUSQ_EMPTY

Bus queue is empty.

This event counts the number of cycles during which the core
did not have any pending transactions in the bus queue.

See
Table
18-61
and
Table
18-62.

SNOOP_STALL_DRV

7FH

See
Table
18-61.

BUS_IO_WAIT

IO requests waiting in
the bus queue.

This event counts the number of core cycles during which IO
requests wait in the bus queue. This event counts IO requests
from the core.

80H

03H

ICACHE.ACCESSES

Instruction fetches.

This event counts all instruction fetches, including uncacheable
fetches.

80H

02H

ICACHE.MISSES

Icache miss.

This event counts all instruction fetches that miss the
Instruction cache or produce memory requests. This includes
uncacheable fetches. An instruction fetch miss is counted only
once and not once for every cycle it is outstanding.

82H

04H

ITLB.FLUSH

ITLB flushes.

This event counts the number of ITLB flushes.

82H

02H

ITLB.MISSES

ITLB misses.

This event counts the number of instruction fetches that miss
the ITLB.

70H

77H

7AH

7EH

19-188 Vol. 3B

- Burst transactions.
- Partial reads and writes.
- Invalidate transactions.
The BUS_TRANS_MEM count is the sum of
BUS_TRANS_BURST, BUS_TRANS_P and BUS_TRANS_INVAL.

All bus transactions.

This event counts all bus transactions. This includes:
- Memory transactions.
- IO transactions (non memory-mapped).
- Deferred transaction completion.
- Other less frequent transactions, such as interrupts.

External snoops.

This event counts the snoop responses to bus transactions.
Responses can be counted separately by type and by bus agent.
Note: This event is thread-independent and will not provide a
count per logical processor when AnyThr is disabled.

HIT signal asserted.

This event counts the number of bus cycles during which the
processor drives the HIT# pin to signal HIT snoop response.
Note: This event is thread-independent and will not provide a
count per logical processor when AnyThr is disabled.

Note: This event is thread-independent and will not provide a
count per logical processor when AnyThr is disabled.
Bus stalled for snoops.

This event counts the number of times that the bus snoop stall
signal is asserted. During the snoop stall cycles no new bus
transactions requiring a snoop response can be initiated on the
bus.
Note: This event is thread-independent and will not provide a
count per logical processor when AnyThr is disabled.

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

AAH

02H

MACRO_INSTS.CISC_DE CISC macro instructions This event counts the number of complex instructions decoded,
CODED
decoded.
but not necessarily executed or retired. Only one complex
instruction can be decoded at a time.

AAH

03H

MACRO_INSTS.ALL_DE All Instructions
CODED
decoded.

This event counts the number of instructions decoded.

B0H

00H

SIMD_UOPS_EXEC.S

SIMD micro-ops
executed (excluding
stores).

This event counts all the SIMD micro-ops executed. This event
does not count MOVQ and MOVD stores from register to
memory.

B0H

80H

SIMD_UOPS_EXEC.AR

SIMD micro-ops retired This event counts the number of SIMD saturated arithmetic
(excluding stores).
micro-ops executed.

B1H

00H

SIMD_SAT_UOP_EXEC. SIMD saturated
S
arithmetic micro-ops
executed.

This event counts the number of SIMD saturated arithmetic
micro-ops executed.

B1H

80H

SIMD_SAT_UOP_EXEC. SIMD saturated
AR
arithmetic micro-ops
retired.

This event counts the number of SIMD saturated arithmetic
micro-ops retired.

B3H

01H

SIMD_UOP_TYPE_EXE
C.MUL.S

SIMD packed multiply
micro-ops executed.

This event counts the number of SIMD packed multiply microops executed.

B3H

81H

SIMD_UOP_TYPE_EXE
C.MUL.AR

SIMD packed multiply
micro-ops retired.

This event counts the number of SIMD packed multiply microops retired.

B3H

02H

SIMD_UOP_TYPE_EXE
C.SHIFT.S

SIMD packed shift
micro-ops executed.

This event counts the number of SIMD packed shift micro-ops
executed.

B3H

82H

SIMD_UOP_TYPE_EXE
C.SHIFT.AR

SIMD packed shift
micro-ops retired.

This event counts the number of SIMD packed shift micro-ops
retired.

B3H

04H

SIMD_UOP_TYPE_EXE
C.PACK.S

SIMD pack micro-ops
executed.

This event counts the number of SIMD pack micro-ops executed.

B3H

84H

SIMD_UOP_TYPE_EXE
C.PACK.AR

SIMD pack micro-ops
retired.

This event counts the number of SIMD pack micro-ops retired.

B3H

08H

SIMD_UOP_TYPE_EXE
C.UNPACK.S

SIMD unpack micro-ops This event counts the number of SIMD unpack micro-ops
executed.
executed.

B3H

88H

SIMD_UOP_TYPE_EXE
C.UNPACK.AR

SIMD unpack micro-ops This event counts the number of SIMD unpack micro-ops retired.
retired.

B3H

10H

SIMD_UOP_TYPE_EXE
C.LOGICAL.S

SIMD packed logical
micro-ops executed.

This event counts the number of SIMD packed logical micro-ops
executed.

B3H

90H

SIMD_UOP_TYPE_EXE
C.LOGICAL.AR

SIMD packed logical
micro-ops retired.

This event counts the number of SIMD packed logical micro-ops
retired.

B3H

20H

SIMD_UOP_TYPE_EXE
C.ARITHMETIC.S

SIMD packed arithmetic This event counts the number of SIMD packed arithmetic micromicro-ops executed.
ops executed.

B3H

A0H

SIMD_UOP_TYPE_EXE
C.ARITHMETIC.AR

SIMD packed arithmetic This event counts the number of SIMD packed arithmetic micromicro-ops retired.
ops retired.

C0H

00H

INST_RETIRED.ANY_P

Instructions retired
(precise event).

Event Name

Definition

Description and Comment

This event counts the number of instructions that retire
execution. For instructions that consist of multiple micro-ops,
this event counts the retirement of the last micro-op of the
instruction. The counter continues counting during hardware
interrupts, traps, and inside interrupt handlers.

Vol. 3B 19-189

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment

N/A

00H

INST_RETIRED.ANY

Instructions retired.

This event counts the number of instructions that retire
execution. For instructions that consist of multiple micro-ops,
this event counts the retirement of the last micro-op of the
instruction. The counter continues counting during hardware
interrupts, traps, and inside interrupt handlers.

C2H

10H

UOPS_RETIRED.ANY

Micro-ops retired.

This event counts the number of micro-ops retired. The
processor decodes complex macro instructions into a sequence
of simpler micro-ops. Most instructions are composed of one or
two micro-ops. Some instructions are decoded into longer
sequences such as repeat instructions, floating point
transcendental instructions, and assists. In some cases micro-op
sequences are fused or whole instructions are fused into one
micro-op. See other UOPS_RETIRED events for differentiating
retired fused and non-fused micro-ops.

C3H

01H

MACHINE_CLEARS.SMC Self-Modifying Code
detected.

This event counts the number of times that a program writes to
a code section. Self-modifying code causes a severe penalty in
all Intel® architecture processors.

C4H

00H

BR_INST_RETIRED.AN
Y

This event counts the number of branch instructions retired.

Retired branch
instructions.

This is an architectural performance event.

C4H

01H

BR_INST_RETIRED.PRE Retired branch
D_NOT_TAKEN
instructions that were
predicted not-taken.

This event counts the number of branch instructions retired
that were correctly predicted to be not-taken.

C4H

02H

BR_INST_RETIRED.MIS Retired branch
PRED_NOT_TAKEN
instructions that were
mispredicted nottaken.

This event counts the number of branch instructions retired
that were mispredicted and not-taken.

C4H

04H

BR_INST_RETIRED.PRE Retired branch
D_TAKEN
instructions that were
predicted taken.

This event counts the number of branch instructions retired
that were correctly predicted to be taken.

C4H

08H

BR_INST_RETIRED.MIS Retired branch
PRED_TAKEN
instructions that were
mispredicted taken.

This event counts the number of branch instructions retired
that were mispredicted and taken.

C4H

0AH

BR_INST_RETIRED.MIS Retired mispredicted
PRED
branch instructions
(precise event).

This event counts the number of retired branch instructions
that were mispredicted by the processor. A branch
misprediction occurs when the processor predicts that the
branch would be taken, but it is not, or vice-versa. Mispredicted
branches degrade the performance because the processor
starts executing instructions along a wrong path it predicts.
When the misprediction is discovered, all the instructions
executed in the wrong path must be discarded, and the
processor must start again on the correct path.
Using the Profile-Guided Optimization (PGO) features of the
Intel® C++ compiler may help reduce branch mispredictions. See
the compiler documentation for more information on this
feature.

19-190 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

Event Name

Definition

Description and Comment
To determine the branch misprediction ratio, divide the
BR_INST_RETIRED.MISPRED event count by the number of
BR_INST_RETIRED.ANY event count. To determine the number
of mispredicted branches per instruction, divide the number of
mispredicted branches by the INST_RETIRED.ANY event count.
To measure the impact of the branch mispredictions use the
event RESOURCE_STALLS.BR_MISS_CLEAR.
Tips:
- See the optimization guide for tips on reducing branch
mispredictions.
- PGO's purpose is to have straight line code for the most
frequent execution paths, reducing branches taken and
increasing the “basic block” size, possibly also reducing the code
footprint or working-set.

C4H

0CH

BR_INST_RETIRED.TAK Retired taken branch
EN
instructions.

This event counts the number of branches retired that were
taken.

C4H

0FH

BR_INST_RETIRED.AN
Y1

This event counts the number of branch instructions retired
that were mispredicted. This event is a duplicate of
BR_INST_RETIRED.MISPRED.

C5H

00H

BR_INST_RETIRED.MIS Retired mispredicted
PRED
branch instructions
(precise event).

Retired branch
instructions.

This event counts the number of retired branch instructions
that were mispredicted by the processor. A branch
misprediction occurs when the processor predicts that the
branch would be taken, but it is not, or vice-versa. Mispredicted
branches degrade the performance because the processor
starts executing instructions along a wrong path it predicts.
When the misprediction is discovered, all the instructions
executed in the wrong path must be discarded, and the
processor must start again on the correct path.
Using the Profile-Guided Optimization (PGO) features of the
Intel® C++ compiler may help reduce branch mispredictions. See
the compiler documentation for more information on this
feature.
To determine the branch misprediction ratio, divide the
BR_INST_RETIRED.MISPRED event count by the number of
BR_INST_RETIRED.ANY event count. To determine the number
of mispredicted branches per instruction, divide the number of
mispredicted branches by the INST_RETIRED.ANY event count.
To measure the impact of the branch mispredictions use the
event RESOURCE_STALLS.BR_MISS_CLEAR.
Tips:
- See the optimization guide for tips on reducing branch
mispredictions.
- PGO's purpose is to have straight line code for the most
frequent execution paths, reducing branches taken and
increasing the “basic block” size, possibly also reducing the code
footprint or working-set.

C6H

01H

CYCLES_INT_MASKED.
CYCLES_INT_MASKED

Cycles during which
This event counts the number of cycles during which interrupts
interrupts are disabled. are disabled.

C6H

02H

CYCLES_INT_MASKED.
CYCLES_INT_PENDING
_AND_MASKED

Cycles during which
interrupts are pending
and disabled.

This event counts the number of cycles during which there are
pending interrupts but interrupts are disabled.

Vol. 3B 19-191

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

C7H

01H

SIMD_INST_RETIRED.P Retired Streaming
ACKED_SINGLE
SIMD Extensions (SSE)
packed-single
instructions.

This event counts the number of SSE packed-single instructions
retired.

C7H

02H

SIMD_INST_RETIRED.S Retired Streaming
CALAR_SINGLE
SIMD Extensions (SSE)
scalar-single
instructions.

This event counts the number of SSE scalar-single instructions
retired.

C7H

04H

SIMD_INST_RETIRED.P Retired Streaming
ACKED_DOUBLE
SIMD Extensions 2
(SSE2) packed-double
instructions.

This event counts the number of SSE2 packed-double
instructions retired.

C7H

08H

SIMD_INST_RETIRED.S Retired Streaming
CALAR_DOUBLE
SIMD Extensions 2
(SSE2) scalar-double
instructions.

This event counts the number of SSE2 scalar-double
instructions retired.

C7H

10H

SIMD_INST_RETIRED.V Retired Streaming
ECTOR
SIMD Extensions 2
(SSE2) vector
instructions.

This event counts the number of SSE2 vector instructions
retired.

C7H

1FH

SIMD_INST_RETIRED.A Retired Streaming
NY
SIMD instructions.

This event counts the overall number of SIMD instructions
retired. To count each type of SIMD instruction separately, use
the following events:

Event Name

Definition

Description and Comment

SIMD_INST_RETIRED.PACKED_SINGLE
SIMD_INST_RETIRED.SCALAR_SINGLE
SIMD_INST_RETIRED.PACKED_DOUBLE
SIMD_INST_RETIRED.SCALAR_DOUBLE
SIMD_INST_RETIRED.VECTOR.
C8H

00H

HW_INT_RCV

CAH

01H

SIMD_COMP_INST_RET Retired computational
IRED.PACKED_SINGLE Streaming SIMD
Extensions (SSE)
packed-single
instructions.

This event counts the number of computational SSE packedsingle instructions retired. Computational instructions perform
arithmetic computations, like add, multiply and divide.
Instructions that perform load and store operations or logical
operations, like XOR, OR, and AND are not counted by this
event.

CAH

02H

SIMD_COMP_INST_RET Retired computational
IRED.SCALAR_SINGLE Streaming SIMD
Extensions (SSE)
scalar-single
instructions.

This event counts the number of computational SSE scalarsingle instructions retired. Computational instructions perform
arithmetic computations, like add, multiply and divide.
Instructions that perform load and store operations or logical
operations, like XOR, OR, and AND are not counted by this
event.

CAH

04H

SIMD_COMP_INST_RET Retired computational
IRED.PACKED_DOUBLE Streaming SIMD
Extensions 2 (SSE2)
packed-double
instructions.

This event counts the number of computational SSE2 packeddouble instructions retired. Computational instructions perform
arithmetic computations, like add, multiply and divide.
Instructions that perform load and store operations or logical
operations, like XOR, OR, and AND are not counted by this
event.

19-192 Vol. 3B

Hardware interrupts
received.

This event counts the number of hardware interrupts received
by the processor. This event will count twice for dual-pipe
micro-ops.

PERFORMANCE MONITORING EVENTS

Table 19-29. Performance Events for 45 nm, 32 nm Intel® Atom™ Processors (Contd.)
Event
Num.

Umask
Value

CAH

08H

SIMD_COMP_INST_RET Retired computational
IRED.SCALAR_DOUBLE Streaming SIMD
Extensions 2 (SSE2)
scalar-double
instructions.

This event counts the number of computational SSE2 scalardouble instructions retired. Computational instructions perform
arithmetic computations, like add, multiply and divide.
Instructions that perform load and store operations or logical
operations, like XOR, OR, and AND are not counted by this
event.

CBH

01H

MEM_LOAD_RETIRED.L Retired loads that hit
2_HIT
the L2 cache (precise
event).

This event counts the number of retired load operations that
missed the L1 data cache and hit the L2 cache.

CBH

02H

MEM_LOAD_RETIRED.L Retired loads that miss This event counts the number of retired load operations that
2_MISS
the L2 cache (precise
missed the L2 cache.
event).

CBH

04H

MEM_LOAD_RETIRED.D Retired loads that miss This event counts the number of retired loads that missed the
DTLB. The DTLB miss is not counted if the load operation causes
TLB_MISS
the DTLB (precise
a fault.
event).

CDH

00H

SIMD_ASSIST

Event Name

Definition

SIMD assists invoked.

Description and Comment

This event counts the number of SIMD assists invoked. SIMD
assists are invoked when an EMMS instruction is executed after
MMX™ technology code has changed the MMX state in the
floating point stack. For example, these assists are required in
the following cases.
Streaming SIMD Extensions (SSE) instructions:
1. Denormal input when the DAZ (Denormals Are Zeros) flag is
off.
2. Underflow result when the FTZ (Flush To Zero) flag is off.

CEH

00H

SIMD_INSTR_RETIRED

SIMD Instructions
retired.

This event counts the number of SIMD instructions that retired.

CFH

00H

SIMD_SAT_INSTR_RETI Saturated arithmetic
RED
instructions retired.

This event counts the number of saturated arithmetic SIMD
instructions that retired.

E0H

01H

BR_INST_DECODED

Branch instructions
decoded.

This event counts the number of branch instructions decoded.

E4H

01H

BOGUS_BR

Bogus branches.

This event counts the number of byte sequences that were
mistakenly detected as taken branch instructions. This results
in a BACLEAR event and the BTB is flushed. This occurs mainly
after task switches.

E6H

01H

BACLEARS.ANY

BACLEARS asserted.

This event counts the number of times the front end is
redirected for a branch prediction, mainly when an early branch
prediction is corrected by other branch handling mechanisms in
the front end. This can occur if the code has many branches
such that they cannot be consumed by the branch predictor.
Each Baclear asserted costs approximately 7 cycles. The effect
on total execution time depends on the surrounding code.

Vol. 3B 19-193

PERFORMANCE MONITORING EVENTS

19.17

PERFORMANCE MONITORING EVENTS FOR INTEL® CORE™ SOLO AND
INTEL® CORE™ DUO PROCESSORS

Table 19-30 lists model-specific performance events for Intel® Core™ Duo processors. If a model-specific event
requires qualification in core specificity, it is indicated in the comment column. Table 19-30 also applies to Intel®
Core™ Solo processors; bits in the unit mask corresponding to core-specificity are reserved and should be 00B.

Table 19-30. Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors
Event
Num.

Event Mask
Mnemonic

Umask
Value

Description

03H

LD_Blocks

00H

Load operations delayed due to store buffer blocks.

Comment

The preceding store may be blocked due to
unknown address, unknown data, or conflict due to
partial overlap between the load and store.
04H

SD_Drains

00H

Cycles while draining store buffers.

05H

Misalign_Mem_Ref

00H

Misaligned data memory references (MOB splits of
loads and stores).

06H

Seg_Reg_Loads

00H

Segment register loads.

07H

SSE_PrefNta_Ret

00H

SSE software prefetch instruction PREFETCHNTA
retired.

07H

SSE_PrefT1_Ret

01H

SSE software prefetch instruction PREFETCHT1
retired.

07H

SSE_PrefT2_Ret

02H

SSE software prefetch instruction PREFETCHT2
retired.

07H

SSE_NTStores_Ret

03H

SSE streaming store instruction retired.

10H

FP_Comps_Op_Exe

00H

FP computational Instruction executed. FADD,
FSUB, FCOM, FMULs, MUL, IMUL, FDIVs, DIV, IDIV,
FPREMs, FSQRT are included; but exclude FADD or
FMUL used in the middle of a transcendental
instruction.

11H

FP_Assist

00H

FP exceptions experienced microcode assists.

IA32_PMC1 only.

12H

Mul

00H

Multiply operations (a speculative count, including
FP and integer multiplies).

IA32_PMC1 only.

13H

Div

00H

Divide operations (a speculative count, including FP IA32_PMC1 only.
and integer divisions).

14H

Cycles_Div_Busy

00H

Cycles the divider is busy.

IA32_PMC0 only.

21H

L2_ADS

00H

L2 Address strobes.

Requires corespecificity.

22H

Dbus_Busy

00H

Core cycle during which data bus was busy
(increments by 4).

Requires corespecificity.

23H

Dbus_Busy_Rd

00H

Cycles data bus is busy transferring data to a core
(increments by 4).

Requires corespecificity.

24H

L2_Lines_In

00H

L2 cache lines allocated.

Requires core-specificity
and HW prefetch
qualification.

25H

L2_M_Lines_In

00H

L2 Modified-state cache lines allocated.

Requires corespecificity.

26H

L2_Lines_Out

00H

L2 cache lines evicted.

27H

L2_M_Lines_Out

00H

L2 Modified-state cache lines evicted.

Requires core-specificity
and HW prefetch
qualification.

19-194 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-30. Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors (Contd.)
Event
Num.

Event Mask
Mnemonic

Umask
Value

Description

Comment

28H

L2_IFetch

Requires MESI
qualification

L2 instruction fetches from instruction fetch unit
(includes speculative fetches).

Requires corespecificity.

29H

L2_LD

Requires MESI
qualification

L2 cache reads.

Requires corespecificity.

2AH

L2_ST

Requires MESI
qualification

L2 cache writes (includes speculation).

Requires corespecificity.

2EH

L2_Rqsts

Requires MESI
qualification

L2 cache reference requests.

30H

L2_Reject_Cycles

Requires MESI
qualification

Cycles L2 is busy and rejecting new requests.

Requires corespecificity, HW prefetch
qualification.

32H

L2_No_Request_
Cycles

Requires MESI
qualification

Cycles there is no request to access L2.

3AH

EST_Trans_All

00H

Any Intel Enhanced SpeedStep(R) Technology
transitions.

3AH

EST_Trans_All

10H

Intel Enhanced SpeedStep Technology frequency
transitions.

3BH

Thermal_Trip

C0H

Duration in a thermal trip based on the current core Use edge trigger to
clock.
count occurrence.

3CH

NonHlt_Ref_Cycles

01H

Non-halted bus cycles.

3CH

Serial_Execution_
Cycles

02H

Non-halted bus cycles of this core executing code
while the other core is halted.

40H

DCache_Cache_LD

Requires MESI
qualification

L1 cacheable data read operations.

41H

DCache_Cache_ST

Requires MESI
qualification

L1 cacheable data write operations.

42H

DCache_Cache_
Lock

Requires MESI
qualification

L1 cacheable lock read operations to invalid state.

43H

Data_Mem_Ref

01H

L1 data read and writes of cacheable and noncacheable types.

44H

Data_Mem_Cache_
Ref

02H

L1 data cacheable read and write operations.

45H

DCache_Repl

0FH

L1 data cache line replacements.

46H

DCache_M_Repl

00H

L1 data M-state cache line allocated.

47H

DCache_M_Evict

00H

L1 data M-state cache line evicted.

48H

DCache_Pend_Miss

00H

Weighted cycles of L1 miss outstanding.

49H

Dtlb_Miss

00H

Data references that missed TLB.

4BH

SSE_PrefNta_Miss

00H

PREFETCHNTA missed all caches.

4BH

SSE_PrefT1_Miss

01H

PREFETCHT1 missed all caches.

4BH

SSE_PrefT2_Miss

02H

PREFETCHT2 missed all caches.

4BH

SSE_NTStores_
Miss

03H

SSE streaming store instruction missed all caches.

4FH

L1_Pref_Req

00H

L1 prefetch requests due to DCU cache misses.

Use Cmask =1 to count
duration.

May overcount if
request re-submitted.

Vol. 3B 19-195

PERFORMANCE MONITORING EVENTS

Table 19-30. Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors (Contd.)
Event
Num.

Event Mask
Mnemonic

Umask
Value

60H

Bus_Req_
Outstanding

00; Requires coreWeighted cycles of cacheable bus data read
specificity, and agent requests. This event counts full-line read request
specificity
from DCU or HW prefetcher, but not RFO, write,
instruction fetches, or others.

Description

Comment
Use Cmask =1 to count
duration.
Use Umask bit 12 to
include HWP or exclude
HWP separately.

61H

Bus_BNR_Clocks

00H

External bus cycles while BNR asserted.

62H

Bus_DRDY_Clocks

00H

External bus cycles while DRDY asserted.

Requires agent
specificity.

63H

Bus_Locks_Clocks

00H

External bus cycles while bus lock signal asserted.

Requires core
specificity.

64H

Bus_Data_Rcv

40H

Number of data chunks received by this processor.

65H

Bus_Trans_Brd

See comment.

Burst read bus transactions (data or code).

Requires core
specificity.

66H

Bus_Trans_RFO

See comment.

Completed read for ownership (RFO) transactions.

68H

Bus_Trans_Ifetch

See comment.

Completed instruction fetch transactions.

Requires agent
specificity.

69H

Bus_Trans_Inval

See comment.

Completed invalidate transactions.

6AH

Bus_Trans_Pwr

See comment.

Completed partial write transactions.

6BH

Bus_Trans_P

See comment.

6CH

Bus_Trans_IO

See comment.

6DH

Bus_Trans_Def

20H

Requires core
specificity.

Each transaction counts
Completed partial transactions (include partial read its address strobe.
+ partial write + line write).
Retried transaction may
be counted more than
Completed I/O transactions (read and write).
once.
Completed defer transactions.

Requires core
specificity.
Retried transaction may
be counted more than
once.

67H

Bus_Trans_WB

C0H

Completed writeback transactions from DCU (does
not include L2 writebacks).

Requires agent
specificity.

6EH

Bus_Trans_Burst

C0H

6FH

Bus_Trans_Mem

C0H

70H

Bus_Trans_Any

C0H

Completed burst transactions (full line transactions Each transaction counts
its address strobe.
include reads, write, RFO, and writebacks).
Retried transaction may
Completed memory transactions. This includes
Bus_Trans_Burst + Bus_Trans_P+Bus_Trans_Inval. be counted more than
once.
Any completed bus transactions.

77H

Bus_Snoops

00H

Counts any snoop on the bus.

Requires MESI
qualification.
Requires agent
specificity.

78H

DCU_Snoop_To_
Share

01H

DCU snoops to share-state L1 cache line due to L1
misses.

Requires core
specificity.

7DH

Bus_Not_In_Use

00H

Number of cycles there is no transaction from the
core.

Requires core
specificity.

7EH

Bus_Snoop_Stall

00H

Number of bus cycles while bus snoop is stalled.

80H

ICache_Reads

00H

Number of instruction fetches from ICache,
streaming buffers (both cacheable and uncacheable
fetches).

19-196 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-30. Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors (Contd.)
Event
Num.

Event Mask
Mnemonic

Umask
Value

81H

ICache_Misses

00H

Number of instruction fetch misses from ICache,
streaming buffers.

85H

ITLB_Misses

00H

Number of iITLB misses.

86H

IFU_Mem_Stall

00H

Cycles IFU is stalled while waiting for data from
memory.

87H

ILD_Stall

00H

Number of instruction length decoder stalls (Counts
number of LCP stalls).

88H

Br_Inst_Exec

00H

Branch instruction executed (includes speculation).

89H

Br_Missp_Exec

00H

Branch instructions executed and mispredicted at
execution (includes branches that do not have
prediction or mispredicted).

8AH

Br_BAC_Missp_
Exec

00H

Branch instructions executed that were
mispredicted at front end.

8BH

Br_Cnd_Exec

00H

Conditional branch instructions executed.

8CH

Br_Cnd_Missp_
Exec

00H

Conditional branch instructions executed that were
mispredicted.

8DH

Br_Ind_Exec

00H

Indirect branch instructions executed.

8EH

Br_Ind_Missp_Exec

00H

Indirect branch instructions executed that were
mispredicted.

8FH

Br_Ret_Exec

00H

Return branch instructions executed.

90H

Br_Ret_Missp_Exec

00H

Return branch instructions executed that were
mispredicted.

91H

Br_Ret_BAC_Missp_
Exec

00H

Return branch instructions executed that were
mispredicted at the front end.

Description

92H

Br_Call_Exec

00H

Return call instructions executed.

93H

Br_Call_Missp_Exec

00H

Return call instructions executed that were
mispredicted.

94H

Br_Ind_Call_Exec

00H

Indirect call branch instructions executed.

A2H

Resource_Stall

00H

Cycles while there is a resource related stall
(renaming, buffer entries) as seen by allocator.

B0H

MMX_Instr_Exec

00H

Number of MMX instructions executed (does not
include MOVQ and MOVD stores).

B1H

SIMD_Int_Sat_Exec

00H

Number of SIMD Integer saturating instructions
executed.

B3H

SIMD_Int_Pmul_
Exec

01H

Number of SIMD Integer packed multiply
instructions executed.

B3H

SIMD_Int_Psft_Exec

02H

Number of SIMD Integer packed shift instructions
executed.

B3H

SIMD_Int_Pck_Exec

04H

Number of SIMD Integer pack operations instruction
executed.

B3H

SIMD_Int_Upck_
Exec

08H

Number of SIMD Integer unpack instructions
executed.

B3H

SIMD_Int_Plog_
Exec

10H

Number of SIMD Integer packed logical instructions
executed.

B3H

SIMD_Int_Pari_Exec

20H

Number of SIMD Integer packed arithmetic
instructions executed.

Comment

Vol. 3B 19-197

PERFORMANCE MONITORING EVENTS

Table 19-30. Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors (Contd.)
Event
Num.

Event Mask
Mnemonic

Umask
Value

C0H

Instr_Ret

00H

Number of instruction retired (Macro fused
instruction count as 2).

C1H

FP_Comp_Instr_Ret

00H

Number of FP compute instructions retired (X87
instruction or instruction that contains X87
operations).

C2H

Uops_Ret

00H

Number of micro-ops retired (include fused uops).

C3H

SMC_Detected

00H

Number of times self-modifying code condition
detected.

C4H

Br_Instr_Ret

00H

Number of branch instructions retired.

C5H

Br_MisPred_Ret

00H

Number of mispredicted branch instructions retired.

C6H

Cycles_Int_Masked

00H

Cycles while interrupt is disabled.

C7H

Cycles_Int_Pedning_ 00H
Masked

Cycles while interrupt is disabled and interrupts are
pending.

C8H

HW_Int_Rx

00H

Number of hardware interrupts received.

C9H

Br_Taken_Ret

00H

Number of taken branch instruction retired.

CAH

Br_MisPred_Taken_
Ret

00H

Number of taken and mispredicted branch
instructions retired.

CCH

MMX_FP_Trans

00H

Number of transitions from MMX to X87.

CCH

FP_MMX_Trans

01H

Number of transitions from X87 to MMX.

CDH

MMX_Assist

00H

Number of EMMS executed.

CEH

MMX_Instr_Ret

00H

Number of MMX instruction retired.

D0H

Instr_Decoded

00H

Number of instruction decoded.

D7H

ESP_Uops

00H

Number of ESP folding instruction decoded.

D8H

SIMD_FP_SP_Ret

00H

Number of SSE/SSE2 single precision instructions
retired (packed and scalar).

D8H

SIMD_FP_SP_S_
Ret

01H

Number of SSE/SSE2 scalar single precision
instructions retired.

D8H

SIMD_FP_DP_P_
Ret

02H

Number of SSE/SSE2 packed double precision
instructions retired.

D8H

SIMD_FP_DP_S_
Ret

03H

Number of SSE/SSE2 scalar double precision
instructions retired.

D8H

SIMD_Int_128_Ret

04H

Number of SSE2 128 bit integer instructions
retired.

D9H

SIMD_FP_SP_P_
Comp_Ret

00H

Number of SSE/SSE2 packed single precision
compute instructions retired (does not include AND,
OR, XOR).

D9H

SIMD_FP_SP_S_
Comp_Ret

01H

Number of SSE/SSE2 scalar single precision
compute instructions retired (does not include AND,
OR, XOR).

D9H

SIMD_FP_DP_P_
Comp_Ret

02H

Number of SSE/SSE2 packed double precision
compute instructions retired (does not include AND,
OR, XOR).

D9H

SIMD_FP_DP_S_
Comp_Ret

03H

Number of SSE/SSE2 scalar double precision
compute instructions retired (does not include AND,
OR, XOR).

19-198 Vol. 3B

Description

Comment

Use IA32_PMC0 only.

PERFORMANCE MONITORING EVENTS

Table 19-30. Performance Events in Intel® Core™ Solo and Intel® Core™ Duo Processors (Contd.)
Event
Num.

Event Mask
Mnemonic

Umask
Value

Description

DAH

Fused_Uops_Ret

00H

All fused uops retired.

DAH

Fused_Ld_Uops_
Ret

01H

Fused load uops retired.

DAH

Fused_St_Uops_Ret

02H

Fused store uops retired.

DBH

Unfusion

00H

Number of unfusion events in the ROB (due to
exception).

E0H

Br_Instr_Decoded

00H

Branch instructions decoded.

E2H

BTB_Misses

00H

Number of branches the BTB did not produce a
prediction.

E4H

Br_Bogus

00H

Number of bogus branches.

E6H

BAClears

00H

Number of BAClears asserted.

F0H

Pref_Rqsts_Up

00H

Number of hardware prefetch requests issued in
forward streams.

F8H

Pref_Rqsts_Dn

00H

Number of hardware prefetch requests issued in
backward streams.

19.18

Comment

PENTIUM® 4 AND INTEL® XEON® PROCESSOR PERFORMANCE
MONITORING EVENTS

Tables 19-31, 19-32 and 19-33 list performance monitoring events that can be counted or sampled on processors
based on Intel NetBurst® microarchitecture. Table 19-31 lists the non-retirement events, and Table 19-32 lists the
at-retirement events. Tables 19-34, 19-35, and 19-36 describes three sets of parameters that are available for
three of the at-retirement counting events defined in Table 19-32. Table 19-37 shows which of the non-retirement
and at retirement events are logical processor specific (TS) (see Section 18.6.4.4, “Performance Monitoring
Events”) and which are non-logical processor specific (TI).
Some of the Pentium 4 and Intel Xeon processor performance monitoring events may be available only to specific
models. The performance monitoring events listed in Tables 19-31 and 19-32 apply to processors with CPUID
signature that matches family encoding 15, model encoding 0, 1, 2 3, 4, or 6. Table applies to processors with a
CPUID signature that matches family encoding 15, model encoding 3, 4 or 6.
The functionality of performance monitoring events in Pentium 4 and Intel Xeon processors is also available when
IA-32e mode is enabled.

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting
Event Name

Event Parameters

Parameter Value

TC_deliver_mode

Description
This event counts the duration (in clock cycles) of the operating
modes of the trace cache and decode engine in the processor
package. The mode is specified by one or more of the event mask
bits.

ESCR restrictions

MSR_TC_ESCR0
MSR_TC_ESCR1

Counter numbers
per ESCR

ESCR0: 4, 5

ESCR Event Select

01H

ESCR1: 6, 7
ESCR[31:25]

Vol. 3B 19-199

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

ESCR Event Mask

Description
ESCR[24:9]

Bit

CCCR Select

0: DD

Both logical processors are in deliver mode.

1: DB

Logical processor 0 is in deliver mode and logical processor 1 is in
build mode.

2: DI

Logical processor 0 is in deliver mode and logical processor 1 is
either halted, under a machine clear condition or transitioning to a
long microcode flow.

3: BD

Logical processor 0 is in build mode and logical processor 1 is in
deliver mode.

4: BB

Both logical processors are in build mode.

5: BI

Logical processor 0 is in build mode and logical processor 1 is either
halted, under a machine clear condition or transitioning to a long
microcode flow.

6: ID

Logical processor 0 is either halted, under a machine clear condition
or transitioning to a long microcode flow. Logical processor 1 is in
deliver mode.

7: IB

Logical processor 0 is either halted, under a machine clear condition
or transitioning to a long microcode flow. Logical processor 1 is in
build mode.

01H

CCCR[15:13]

Event Specific
Notes

If only one logical processor is available from a physical processor
package, the event mask should be interpreted as logical processor 1
is halted. Event mask bit 2 was previously known as “DELIVER”, bit 5
was previously known as “BUILD”.

BPU_fetch_
request

This event counts instruction fetch requests of specified request
type by the Branch Prediction unit. Specify one or more mask bits to
qualify the request type(s).
ESCR restrictions

MSR_BPU_ESCR0
MSR_BPU_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

03H

ESCR1: 2, 3

ESCR Event Mask

CCCR Select

19-200 Vol. 3B

ESCR[31:25]
ESCR[24:9]

Bit 0: TCMISS

Trace cache lookup miss

00H

CCCR[15:13]

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

ITLB_reference

Description
This event counts translations using the Instruction Translation
Look-aside Buffer (ITLB).

ESCR restrictions

MSR_ITLB_ESCR0
MSR_ITLB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

18H

ESCR1: 2, 3
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

0: HIT

ITLB hit

1: MISS

ITLB miss

2: HIT_UC

Uncacheable ITLB hit

03H

CCCR[15:13]

Event Specific
Notes

All page references regardless of the page size are looked up as
actual 4-KByte pages. Use the page_walk_type event with the
ITMISS mask for a more conservative count.

memory_cancel

This event counts the canceling of various type of request in the
Data cache Address Control unit (DAC). Specify one or more mask
bits to select the type of requests that are canceled.
ESCR restrictions

MSR_DAC_ESCR0
MSR_DAC_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

02H

ESCR1: 10, 11
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit
2: ST_RB_FULL
3: 64K_CONF
CCCR Select

05H

Event Specific
Notes

Replayed because no store request buffer is available.
Conflicts due to 64-KByte aliasing.
CCCR[15:13]
All_CACHE_MISS includes uncacheable memory in count.

memory_
complete

This event counts the completion of a load split, store split,
uncacheable (UC) split, or UC load. Specify one or more mask bits to
select the operations to be counted.
ESCR restrictions

MSR_SAAT_ESCR0
MSR_SAAT_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

08H

ESCR1: 10, 11
ESCR[31:25]

Vol. 3B 19-201

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

ESCR Event Mask

Description
ESCR[24:9]

Bit
0: LSC

Load split completed, excluding UC/WC loads.
Any split stores completed.

1: SSC
CCCR Select

02H

load_port_replay

CCCR[15:13]
This event counts replayed events at the load port. Specify one or
more mask bits to select the cause of the replay.

ESCR restrictions

MSR_SAAT_ESCR0
MSR_SAAT_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

04H

ESCR1: 10, 11

ESCR Event Mask
CCCR Select

ESCR[31:25]
ESCR[24:9]

Bit 1: SPLIT_LD

Split load.

02H

CCCR[15:13]

Event Specific
Notes

Must use ESCR1 for at-retirement counting.

store_port_replay

This event counts replayed events at the store port. Specify one or
more mask bits to select the cause of the replay.
ESCR restrictions

MSR_SAAT_ESCR0
MSR_SAAT_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

05H

ESCR1: 10, 11

ESCR Event Mask
CCCR Select

ESCR[31:25]
ESCR[24:9]

Bit 1: SPLIT_ST

Split store

02H

CCCR[15:13]

Event Specific
Notes

Must use ESCR1 for at-retirement counting.

MOB_load_replay

This event triggers if the memory order buffer (MOB) caused a load
operation to be replayed. Specify one or more mask bits to select the
cause of the replay.
ESCR restrictions

MSR_MOB_ESCR0
MSR_MOB_ESCR1

19-202 Vol. 3B

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

03H

ESCR1: 2, 3
ESCR[31:25]

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

ESCR Event Mask

Description
ESCR[24:9]

Bit
1: NO_STA

Replayed because of unknown store address.
Replayed because of unknown store data.

3: NO_STD
4: PARTIAL_DATA

CCCR Select

Replayed because of partially overlapped data access between the
load and store operations.

5: UNALGN_ADDR

Replayed because the lower 4 bits of the linear address do not
match between the load and store operations.

02H

CCCR[15:13]

page_walk_type

This event counts various types of page walks that the page miss
handler (PMH) performs.
ESCR restrictions

MSR_PMH_
ESCR0
MSR_PMH_
ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

01H

ESCR1: 2, 3

ESCR Event Mask

ESCR[31:25]
ESCR[24:9]

Bit
0: DTMISS

Page walk for a data TLB miss (either load or store).
Page walk for an instruction TLB miss.

1: ITMISS
CCCR Select

04H

BSQ_cache
_reference

CCCR[15:13]
This event counts cache references (2nd level cache or 3rd level
cache) as seen by the bus unit.
Specify one or more mask bit to select an access according to the
access type (read type includes both load and RFO, write type
includes writebacks and evictions) and the access result (hit, misses).

ESCR restrictions

MSR_BSU_
ESCR0
MSR_BSU_
ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

0CH

ESCR1: 2, 3
ESCR[31:25]

Vol. 3B 19-203

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description
ESCR[24:9]

Bit
0: RD_2ndL_HITS

Read 2nd level cache hit Shared (includes load and RFO).

1: RD_2ndL_HITE

Read 2nd level cache hit Exclusive (includes load and RFO).

2: RD_2ndL_HITM

Read 2nd level cache hit Modified (includes load and RFO).

3: RD_3rdL_HITS

Read 3rd level cache hit Shared (includes load and RFO).

4: RD_3rdL_HITE

Read 3rd level cache hit Exclusive (includes load and RFO).

5: RD_3rdL_HITM
ESCR Event Mask

CCCR Select
Event Specific
Notes

Read 3rd level cache hit Modified (includes load and RFO).

8: RD_2ndL_MISS

Read 2nd level cache miss (includes load and RFO).

9: RD_3rdL_MISS

Read 3rd level cache miss (includes load and RFO).

10: WR_2ndL_MISS

A Writeback lookup from DAC misses the 2nd level cache (unlikely to
happen).

07H

CCCR[15:13]
1: The implementation of this event in current Pentium 4 and Xeon
processors treats either a load operation or a request for
ownership (RFO) request as a “read” type operation.
2: Currently this event causes both over and undercounting by as
much as a factor of two due to an erratum.
3: It is possible for a transaction that is started as a prefetch to
change the transaction's internal status, making it no longer a
prefetch. or change the access result status (hit, miss) as seen by
this event.

IOQ_allocation

This event counts the various types of transactions on the bus. A
count is generated each time a transaction is allocated into the IOQ
that matches the specified mask bits. An allocated entry can be a
sector (64 bytes) or a chunks of 8 bytes.
Requests are counted once per retry. The event mask bits constitute
4 bit fields. A transaction type is specified by interpreting the values
of each bit field.
Specify one or more event mask bits in a bit field to select the value
of the bit field.
Each field (bits 0-4 are one field) are independent of and can be
ORed with the others. The request type field is further combined
with bit 5 and 6 to form a binary expression. Bits 7 and 8 form a bit
field to specify the memory type of the target address.
Bits 13 and 14 form a bit field to specify the source agent of the
request. Bit 15 affects read operation only. The event is triggered by
evaluating the logical expression: (((Request type) OR Bit 5 OR Bit 6)
OR (Memory type)) AND (Source agent).

19-204 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

ESCR restrictions

MSR_FSB_ESCR0,
MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1;

ESCR Event Select

03H

Description

ESCR1: 2, 3
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bits

CCCR Select
Event Specific
Notes

0-4 (single field)

Bus request type (use 00001 for invalid or default).

5: ALL_READ

Count read entries.

6: ALL_WRITE

Count write entries.

7: MEM_UC

Count UC memory access entries.

8: MEM_WC

Count WC memory access entries.

9: MEM_WT

Count write-through (WT) memory access entries.

10: MEM_WP

Count write-protected (WP) memory access entries.

11: MEM_WB

Count WB memory access entries.

13: OWN

Count all store requests driven by processor, as opposed to other
processor or DMA.

14: OTHER

Count all requests driven by other processors or DMA.

15: PREFETCH

Include HW and SW prefetch requests in the count.

06H

CCCR[15:13]
1: If PREFETCH bit is cleared, sectors fetched using prefetch are
excluded in the counts. If PREFETCH bit is set, all sectors or chunks
read are counted.
2: Specify the edge trigger in CCCR to avoid double counting.
3: The mapping of interpreted bit field values to transaction types
may differ with different processor model implementations of the
Pentium 4 processor family. Applications that program
performance monitoring events should use CPUID to determine
processor models when using this event. The logic equations that
trigger the event are model-specific (see 4a and 4b below).
4a:For Pentium 4 and Xeon Processors starting with CPUID Model
field encoding equal to 2 or greater, this event is triggered by
evaluating the logical expression ((Request type) and (Bit 5 or Bit
6) and (Memory type) and (Source agent)).
4b:For Pentium 4 and Xeon Processors with CPUID Model field
encoding less than 2, this event is triggered by evaluating the
logical expression [((Request type) or Bit 5 or Bit 6) or (Memory
type)] and (Source agent). Note that event mask bits for memory
type are ignored if either ALL_READ or ALL_WRITE is specified.
5: This event is known to ignore CPL in early implementations of
Pentium 4 and Xeon Processors. Both user requests and OS
requests are included in the count. This behavior is fixed starting
with Pentium 4 and Xeon Processors with CPUID signature F27H
(Family 15, Model 2, Stepping 7).

Vol. 3B 19-205

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description
6: For write-through (WT) and write-protected (WP) memory types,
this event counts reads as the number of 64-byte sectors. Writes
are counted by individual chunks.
7: For uncacheable (UC) memory types, this event counts the
number of 8-byte chunks allocated.
8: For Pentium 4 and Xeon Processors with CPUID Signature less
than F27H, only MSR_FSB_ESCR0 is available.

IOQ_active_
entries

This event counts the number of entries (clipped at 15) in the IOQ
that are active. An allocated entry can be a sector (64 bytes) or a
chunks of 8 bytes.
The event must be programmed in conjunction with IOQ_allocation.
Specify one or more event mask bits to select the transactions that
is counted.
ESCR restrictions

MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR1: 2, 3

ESCR Event Select

01AH

ESCR[30:25]
ESCR[24:9]

ESCR Event Mask
Bits

CCCR Select
Event Specific
Notes

0-4 (single field)

Bus request type (use 00001 for invalid or default).

5: ALL_READ

Count read entries.

6: ALL_WRITE

Count write entries.

7: MEM_UC

Count UC memory access entries.

8: MEM_WC

Count WC memory access entries.

9: MEM_WT

Count write-through (WT) memory access entries.

10: MEM_WP

Count write-protected (WP) memory access entries.

11: MEM_WB

Count WB memory access entries.

13: OWN

Count all store requests driven by processor, as opposed to other
processor or DMA.

14: OTHER

Count all requests driven by other processors or DMA.

15: PREFETCH

Include HW and SW prefetch requests in the count.

06H

CCCR[15:13]
1: Specified desired mask bits in ESCR0 and ESCR1.
2: See the ioq_allocation event for descriptions of the mask bits.
3: Edge triggering should not be used when counting cycles.
4: The mapping of interpreted bit field values to transaction types
may differ across different processor model implementations of
the Pentium 4 processor family. Applications that programs
performance monitoring events should use the CPUID instruction
to detect processor models when using this event. The logical
expression that triggers this event as describe below:
5a:For Pentium 4 and Xeon Processors starting with CPUID MODEL
field encoding equal to 2 or greater, this event is triggered by
evaluating the logical expression ((Request type) and (Bit 5 or Bit
6) and (Memory type) and (Source agent)).

19-206 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description
5b:For Pentium 4 and Xeon Processors starting with CPUID MODEL
field encoding less than 2, this event is triggered by evaluating
the logical expression [((Request type) or Bit 5 or Bit 6) or
(Memory type)] and (Source agent). Event mask bits for memory
type are ignored if either ALL_READ or ALL_WRITE is specified.
5c: This event is known to ignore CPL in the current implementations
of Pentium 4 and Xeon Processors Both user requests and OS
requests are included in the count.
6: An allocated entry can be a full line (64 bytes) or in individual
chunks of 8 bytes.

FSB_data_
activity

This event increments once for each DRDY or DBSY event that
occurs on the front side bus. The event allows selection of a specific
DRDY or DBSY event.
ESCR restrictions

MSR_FSB_ESCR0
MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

17H

ESCR1: 2, 3

ESCR Event Mask

ESCR[31:25]
ESCR[24:9]

Bit 0:
DRDY_DRV

Count when this processor drives data onto the bus - includes writes
and implicit writebacks.
Asserted two processor clock cycles for partial writes and 4
processor clocks (usually in consecutive bus clocks) for full line
writes.

1: DRDY_OWN

Count when this processor reads data from the bus - includes loads
and some PIC transactions. Asserted two processor clock cycles for
partial reads and 4 processor clocks (usually in consecutive bus
clocks) for full line reads.
Count DRDY events that we drive.
Count DRDY events sampled that we own.

2: DRDY_OTHER

Count when data is on the bus but not being sampled by the
processor. It may or may not be being driven by this processor.
Asserted two processor clock cycles for partial transactions and 4
processor clocks (usually in consecutive bus clocks) for full line
transactions.

3: DBSY_DRV

Count when this processor reserves the bus for use in the next bus
cycle in order to drive data. Asserted for two processor clock cycles
for full line writes and not at all for partial line writes.
May be asserted multiple times (in consecutive bus clocks) if we stall
the bus waiting for a cache lock to complete.

4: DBSY_OWN

Count when some agent reserves the bus for use in the next bus
cycle to drive data that this processor will sample.
Asserted for two processor clock cycles for full line writes and not at
all for partial line writes. May be asserted multiple times (all one bus
clock apart) if we stall the bus for some reason.

Vol. 3B 19-207

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description

5:DBSY_OTHER

Count when some agent reserves the bus for use in the next bus
cycle to drive data that this processor will NOT sample. It may or may
not be being driven by this processor.
Asserted two processor clock cycles for partial transactions and 4
processor clocks (usually in consecutive bus clocks) for full line
transactions.

CCCR Select

06H

Event Specific
Notes

CCCR[15:13]
Specify edge trigger in the CCCR MSR to avoid double counting.
DRDY_OWN and DRDY_OTHER are mutually exclusive; similarly for
DBSY_OWN and DBSY_OTHER.

BSQ_allocation

This event counts allocations in the Bus Sequence Unit (BSQ)
according to the specified mask bit encoding. The event mask bits
consist of four sub-groups:
•
•
•
•

Request type.
Request length.
Memory type.
Sub-group consisting mostly of independent bits (bits 5, 6, 7, 8, 9,
and 10).
Specify an encoding for each sub-group.
ESCR restrictions

MSR_BSU_ESCR0

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

05H

ESCR[31:25]

ESCR Event Mask

19-208 Vol. 3B

Bit

ESCR[24:9]

0: REQ_TYPE0
1: REQ_TYPE1

Request type encoding (bit 0 and 1) are:

2: REQ_LEN0
3: REQ_LEN1

Request length encoding (bit 2, 3) are:

5: REQ_IO_TYPE

Request type is input or output.

6: REQ_LOCK_
TYPE

Request type is bus lock.

7: REQ_CACHE_
TYPE

Request type is cacheable.

8: REQ_SPLIT_
TYPE
9: REQ_DEM_TYPE

Request type is a bus 8-byte chunk split across 8-byte boundary.

10: REQ_ORD_
TYPE

Request is an ordered type.

0 – Read (excludes read invalidate).
1 – Read invalidate.
2 – Write (other than writebacks).
3 – Writeback (evicted from cache). (public)
0 – 0 chunks
1 – 1 chunks
3 – 8 chunks

Request type is a demand if set. Request type is HW.SW prefetch
if 0.

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

CCCR Select

Parameter Value

Description

11: MEM_TYPE0
12: MEM_TYPE1
13: MEM_TYPE2

Memory type encodings (bit 11-13) are:

07H

CCCR[15:13]

Event Specific
Notes

0 – UC
1 – WC
4 – WT
5 – WP
6 – WB
1: Specify edge trigger in CCCR to avoid double counting.
2: A writebacks to 3rd level cache from 2nd level cache counts as a
separate entry, this is in additional to the entry allocated for a
request to the bus.
3: A read request to WB memory type results in a request to the
64-byte sector, containing the target address, followed by a
prefetch request to an adjacent sector.
4: For Pentium 4 and Xeon processors with CPUID model encoding
value equals to 0 and 1, an allocated BSQ entry includes both the
demand sector and prefetched 2nd sector.
5: An allocated BSQ entry for a data chunk is any request less than
64 bytes.
6a:This event may undercount for requests of split type transactions
if the data address straddled across modulo-64 byte boundary.
6b:This event may undercount for requests of read request of
16-byte operands from WC or UC address.
6c: This event may undercount WC partial requests originated from
store operands that are
dwords.

bsq_active_
entries

This event represents the number of BSQ entries (clipped at 15)
currently active (valid) which meet the subevent mask criteria during
allocation in the BSQ. Active request entries are allocated on the BSQ
until de-allocated.
De-allocation of an entry does not necessarily imply the request is
filled. This event must be programmed in conjunction with
BSQ_allocation. Specify one or more event mask bits to select the
transactions that is counted.
ESCR restrictions

ESCR1

Counter numbers
per ESCR

ESCR1: 2, 3

ESCR Event Select

06H

ESCR Event Mask
CCCR Select
Event Specific
Notes

ESCR[30:25]
ESCR[24:9]

07H

CCCR[15:13]
1: Specified desired mask bits in ESCR0 and ESCR1.
2: See the BSQ_allocation event for descriptions of the mask bits.
3: Edge triggering should not be used when counting cycles.
4: This event can be used to estimate the latency of a transaction
from allocation to de-allocation in the BSQ. The latency observed
by BSQ_allocation includes the latency of FSB, plus additional
overhead.

Vol. 3B 19-209

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description
5: Additional overhead may include the time it takes to issue two
requests (the sector by demand and the adjacent sector via
prefetch). Since adjacent sector prefetches have lower priority
that demand fetches, on a heavily used system there is a high
probability that the adjacent sector prefetch will have to wait
until the next bus arbitration.
6: For Pentium 4 and Xeon processors with CPUID model encoding
value less than 3, this event is updated every clock.
7: For Pentium 4 and Xeon processors with CPUID model encoding
value equals to 3 or 4, this event is updated every other clock.

SSE_input_assist

This event counts the number of times an assist is requested to
handle problems with input operands for SSE/SSE2/SSE3 operations;
most notably denormal source operands when the DAZ bit is not set.
Set bit 15 of the event mask to use this event.
ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

34H

ESCR1: 10, 11

ESCR Event Mask
CCCR Select

ESCR[31:25]
ESCR[24:9]

15: ALL

Count assists for SSE/SSE2/SSE3 μops.

01H

CCCR[15:13]

Event Specific
Notes

1: Not all requests for assists are actually taken. This event is known
to overcount in that it counts requests for assists from
instructions on the non-retired path that do not incur a
performance penalty. An assist is actually taken only for nonbogus μops. Any appreciable counts for this event are an
indication that the DAZ or FTZ bit should be set and/or the source
code should be changed to eliminate the condition.
2: Two common situations for an SSE/SSE2/SSE3 operation needing
an assist are: (1) when a denormal constant is used as an input and
the Denormals-Are-Zero (DAZ) mode is not set, (2) when the input
operand uses the underflowed result of a previous
SSE/SSE2/SSE3 operation and neither the DAZ nor Flush-To-Zero
(FTZ) modes are set.
3: Enabling the DAZ mode prevents SSE/SSE2/SSE3 operations from
needing assists in the first situation. Enabling the FTZ mode
prevents SSE/SSE2/SSE3 operations from needing assists in the
second situation.

packed_SP_uop

19-210 Vol. 3B

This event increments for each packed single-precision μop,
specified through the event mask for detection.
ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

08H

ESCR1: 10, 11
ESCR[31:25]

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

ESCR Event Mask
CCCR Select

Description
ESCR[24:9]

Bit 15: ALL

Count all μops operating on packed single-precision operands.

01H

CCCR[15:13]

Event Specific
Notes

1: If an instruction contains more than one packed SP μops, each
packed SP μop that is specified by the event mask will be counted.
2: This metric counts instances of packed memory μops in a repeat
move string.

packed_DP_uop

This event increments for each packed double-precision μop,
specified through the event mask for detection.
ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

0CH

ESCR1: 10, 11

ESCR Event Mask
CCCR Select

ESCR[31:25]
ESCR[24:9]

Bit 15: ALL

Count all μops operating on packed double-precision operands.

01H

CCCR[15:13]

Event Specific
Notes

If an instruction contains more than one packed DP μops, each
packed DP μop that is specified by the event mask will be counted.

scalar_SP_uop

This event increments for each scalar single-precision μop, specified
through the event mask for detection.
ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

0AH

ESCR1: 10, 11

ESCR Event Mask

ESCR[24:9]
Bit 15: ALL

CCCR Select

ESCR[31:25]

01H

Event Specific
Notes

Count all μops operating on scalar single-precision operands.
CCCR[15:13]
If an instruction contains more than one scalar SP μops, each scalar
SP μop that is specified by the event mask will be counted.

scalar_DP_uop

This event increments for each scalar double-precision μop, specified
through the event mask for detection.
ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

0EH

ESCR1: 10, 11

ESCR Event Mask
CCCR Select

ESCR[31:25]
ESCR[24:9]

Bit 15: ALL

Count all μops operating on scalar double-precision operands.

01H

CCCR[15:13]

Vol. 3B 19-211

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Event Specific
Notes

Description
If an instruction contains more than one scalar DP μops, each scalar
DP μop that is specified by the event mask is counted.

64bit_MMX_uop

This event increments for each MMX instruction, which operate on
64-bit SIMD operands.
ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

02H

ESCR1: 10, 11

ESCR Event Mask

CCCR Select

ESCR[31:25]
ESCR[24:9]

Bit 15: ALL

Count all μops operating on 64- bit SIMD integer operands in memory
or MMX registers.

01H

CCCR[15:13]

Event Specific
Notes

If an instruction contains more than one 64-bit MMX μops, each 64bit MMX μop that is specified by the event mask will be counted.

128bit_MMX_uop

This event increments for each integer SIMD SSE2 instruction, which
operate on 128-bit SIMD operands.

ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

1AH

ESCR1: 10, 11

ESCR Event Mask

CCCR Select

ESCR[24:9]
Bit 15: ALL

Count all μops operating on 128-bit SIMD integer operands in
memory or XMM registers.

01H

CCCR[15:13]

Event Specific
Notes

If an instruction contains more than one 128-bit MMX μops, each
128-bit MMX μop that is specified by the event mask will be counted.

x87_FP_uop

This event increments for each x87 floating-point μop, specified
through the event mask for detection.
ESCR restrictions

MSR_FIRM_ESCR0
MSR_FIRM_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

04H

ESCR1: 10, 11

ESCR Event Mask
CCCR Select

19-212 Vol. 3B

ESCR[31:25]

ESCR[31:25]
ESCR[24:9]

Bit 15: ALL

Count all x87 FP μops.

01H

CCCR[15:13]

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Event Specific
Notes

Description
1: If an instruction contains more than one x87 FP μops, each x87
FP μop that is specified by the event mask will be counted.
2: This event does not count x87 FP μop for load, store, move
between registers.

TC_misc

This event counts miscellaneous events detected by the TC. The
counter will count twice for each occurrence.
ESCR restrictions

MSR_TC_ESCR0
MSR_TC_ESCR1

Counter numbers
per ESCR

ESCR0: 4, 5

ESCR Event Select

06H

ESCR[31:25]

CCCR Select

01H

CCCR[15:13]

ESCR1: 6, 7

ESCR Event Mask

ESCR[24:9]
Bit 4: FLUSH

global_power
_events

Number of flushes
This event accumulates the time during which a processor is not
stopped.

ESCR restrictions

MSR_FSB_ESCR0
MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

013H

ESCR Event Mask

Bit 0: Running

ESCR1: 2, 3
ESCR[31:25]
ESCR[24:9]
The processor is active (includes the handling of HLT STPCLK and
throttling.

CCCR Select

06H

tc_ms_xfer

CCCR[15:13]
This event counts the number of times that uop delivery changed
from TC to MS ROM.

ESCR restrictions

MSR_MS_ESCR0
MSR_MS_ESCR1

Counter numbers
per ESCR

ESCR0: 4, 5

ESCR Event Select

05H

ESCR1: 6, 7

ESCR Event Mask
CCCR Select

ESCR[31:25]
ESCR[24:9]

Bit 0: CISC

A TC to MS transfer occurred.

0H

CCCR[15:13]

uop_queue_
writes

This event counts the number of valid uops written to the uop
queue. Specify one or more mask bits to select the source type of
writes.
ESCR restrictions

MSR_MS_ESCR0
MSR_MS_ESCR1

Counter numbers
per ESCR

ESCR0: 4, 5
ESCR1: 6, 7

Vol. 3B 19-213

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description

ESCR Event Select

09H

ESCR[31:25]

ESCR Event Mask

ESCR[24:9]
Bit
0: FROM_TC_
BUILD

The uops being written are from TC build mode.

1: FROM_TC_
DELIVER

The uops being written are from TC deliver mode.

2: FROM_ROM
CCCR Select

0H

retired_mispred

The uops being written are from microcode ROM.
CCCR[15:13]
This event counts retiring mispredicted branches by type.

_branch_type
ESCR restrictions

MSR_TBPU_ESCR0
MSR_TBPU_ESCR1

Counter numbers
per ESCR

ESCR0: 4, 5

ESCR Event Select

05H

ESCR1: 6, 7
ESCR[30:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

1: CONDITIONAL

Conditional jumps.

2: CALL

Indirect call branches.

3: RETURN

Return branches.

4: INDIRECT

Returns, indirect calls, or indirect jumps.

02H

CCCR[15:13]

Event Specific
Notes

This event may overcount conditional branches if:
• Mispredictions cause the trace cache and delivery engine to build
new traces.
• When the processor's pipeline is being cleared.

retired_branch

This event counts retiring branches by type. Specify one or more
mask bits to qualify the branch by its type.

_type
ESCR restrictions

MSR_TBPU_ESCR0
MSR_TBPU_ESCR1

Counter numbers
per ESCR

ESCR0: 4, 5

ESCR Event Select

04H

ESCR1: 6, 7
ESCR[30:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

19-214 Vol. 3B

1: CONDITIONAL

Conditional jumps.

2: CALL

Direct or indirect calls.

3: RETURN

Return branches.

4: INDIRECT

Returns, indirect calls, or indirect jumps.

02H

CCCR[15:13]

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Event Specific
Notes

Description
This event may overcount conditional branches if :
• Mispredictions cause the trace cache and delivery engine to build
new traces.
• When the processor's pipeline is being cleared.

resource_stall

This event monitors the occurrence or latency of stalls in the
Allocator.
ESCR restrictions

MSR_ALF_ESCR0
MSR_ALF_ESCR1

Counter numbers
per ESCR

ESCR0: 12, 13, 16
ESCR1: 14, 15, 17

ESCR Event Select

01H

Event Masks

ESCR[30:25]
ESCR[24:9]

Bit
CCCR Select

5: SBFULL

A Stall due to lack of store buffers.

01H

CCCR[15:13]

Event Specific
Notes

This event may not be supported in all models of the processor
family.

WC_Buffer

This event counts Write Combining Buffer operations that are
selected by the event mask.
ESCR restrictions

MSR_DAC_ESCR0
MSR_DAC_ESCR1

Counter numbers
per ESCR

ESCR0: 8, 9

ESCR Event Select

05H

ESCR1: 10, 11

Event Masks

ESCR[30:25]
ESCR[24:9]

Bit

CCCR Select

0: WCB_EVICTS

WC Buffer evictions of all causes.

1: WCB_FULL_
EVICT

WC Buffer eviction: no WC buffer is available.

05H

CCCR[15:13]

Event Specific
Notes

This event is useful for detecting the subset of 64K aliasing cases
that are more costly (i.e. 64K aliasing cases involving stores) as long
as there are no significant contributions due to write combining
buffer full or hit-modified conditions.

b2b_cycles

This event can be configured to count the number back-to-back bus
cycles using sub-event mask bits 1 through 6.
ESCR restrictions

MSR_FSB_ESCR0
MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

016H

ESCR[30:25]

Event Masks

Bit

ESCR[24:9]

ESCR1: 2, 3

Vol. 3B 19-215

PERFORMANCE MONITORING EVENTS

Table 19-31. Performance Monitoring Events Supported by Intel NetBurst® Microarchitecture
for Non-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description

CCCR Select

03H

CCCR[15:13]

Event Specific
Notes

This event may not be supported in all models of the processor
family.

bnr

This event can be configured to count bus not ready conditions using
sub-event mask bits 0 through 2.
ESCR restrictions

MSR_FSB_ESCR0
MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

08H

ESCR[30:25]

Event Masks

Bit

ESCR[24:9]

CCCR Select

03H

CCCR[15:13]

ESCR1: 2, 3

Event Specific
Notes

This event may not be supported in all models of the processor
family.

snoop

This event can be configured to count snoop hit modified bus traffic
using sub-event mask bits 2, 6 and 7.
ESCR restrictions

MSR_FSB_ESCR0
MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

06H

ESCR[30:25]

Event Masks

Bit

ESCR[24:9]

CCCR Select

03H

CCCR[15:13]

ESCR1: 2, 3

Event Specific
Notes

This event may not be supported in all models of the processor
family.

Response

This event can be configured to count different types of responses
using sub-event mask bits 1,2, 8, and 9.
ESCR restrictions

MSR_FSB_ESCR0
MSR_FSB_ESCR1

Counter numbers
per ESCR

ESCR0: 0, 1

ESCR Event Select

04H

ESCR[30:25]

Event Masks

Bit

ESCR[24:9]

CCCR Select

03H

CCCR[15:13]

Event Specific
Notes

19-216 Vol. 3B

ESCR1: 2, 3

This event may not be supported in all models of the processor
family.

PERFORMANCE MONITORING EVENTS

Table 19-32. Performance Monitoring Events For Intel NetBurst® Microarchitecture
for At-Retirement Counting
Event Name

Event Parameters

Parameter Value

front_end_event

Description
This event counts the retirement of tagged μops, which are specified
through the front-end tagging mechanism. The event mask specifies
bogus or non-bogus μops.

ESCR restrictions

MSR_CRU_ESCR2
MSR_CRU_ESCR3

Counter numbers
per ESCR

ESCR2: 12, 13, 16

ESCR Event Select

08H

ESCR3: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit
0: NBOGUS

The marked μops are not bogus.

1: BOGUS

The marked μops are bogus.

CCCR Select

05H

CCCR[15:13]

Can Support PEBS

Yes

Require Additional
MSRs for tagging

Selected ESCRs
and/or MSR_TC_
PRECISE_EVENT

execution_event

See list of metrics supported by Front_end tagging in Table A-3

This event counts the retirement of tagged μops, which are specified
through the execution tagging mechanism.
The event mask allows from one to four types of μops to be
specified as either bogus or non-bogus μops to be tagged.
ESCR restrictions

MSR_CRU_ESCR2
MSR_CRU_ESCR3

Counter numbers
per ESCR

ESCR2: 12, 13, 16

ESCR Event Select

0CH

ESCR3: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

0: NBOGUS0

The marked μops are not bogus.

1: NBOGUS1

The marked μops are not bogus.

2: NBOGUS2

The marked μops are not bogus.

3: NBOGUS3

The marked μops are not bogus.

4: BOGUS0

The marked μops are bogus.

5: BOGUS1

The marked μops are bogus.

6: BOGUS2

The marked μops are bogus.

7: BOGUS3

The marked μops are bogus.

05H

CCCR[15:13]

Event Specific
Notes

Can Support PEBS

Each of the 4 slots to specify the bogus/non-bogus μops must be
coordinated with the 4 TagValue bits in the ESCR (for example,
NBOGUS0 must accompany a ‘1’ in the lowest bit of the TagValue
field in ESCR, NBOGUS1 must accompany a ‘1’ in the next but lowest
bit of the TagValue field).
Yes

Vol. 3B 19-217

PERFORMANCE MONITORING EVENTS

Table 19-32. Performance Monitoring Events For Intel NetBurst® Microarchitecture
for At-Retirement Counting (Contd.)
Event Name

Event Parameters
Require Additional
MSRs for tagging

Parameter Value
An ESCR for an
upstream event

replay_event

Description
See list of metrics supported by execution tagging in Table A-4.
This event counts the retirement of tagged μops, which are specified
through the replay tagging mechanism. The event mask specifies
bogus or non-bogus μops.

ESCR restrictions

MSR_CRU_ESCR2
MSR_CRU_ESCR3

Counter numbers
per ESCR

ESCR2: 12, 13, 16

ESCR Event Select

09H

ESCR3: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

0: NBOGUS

The marked μops are not bogus.

1: BOGUS

The marked μops are bogus.

05H

CCCR[15:13]

Event Specific
Notes

Supports counting tagged μops with additional MSRs.

Can Support PEBS

Yes

Require Additional
MSRs for tagging

IA32_PEBS_
ENABLE

See list of metrics supported by replay tagging in Table A-5.

MSR_PEBS_
MATRIX_VERT
Selected ESCR
instr_retired

This event counts instructions that are retired during a clock cycle.
Mask bits specify bogus or non-bogus (and whether they are tagged
using the front-end tagging mechanism).
ESCR restrictions

MSR_CRU_ESCR0
MSR_CRU_ESCR1

Counter numbers
per ESCR

ESCR0: 12, 13, 16

ESCR Event Select

02H

ESCR1: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit
0: NBOGUSNTAG
1: NBOGUSTAG
2: BOGUSNTAG
3: BOGUSTAG
CCCR Select
Event Specific
Notes

04H

Non-bogus instructions that are not tagged.
Non-bogus instructions that are tagged.
Bogus instructions that are not tagged.
Bogus instructions that are tagged.
CCCR[15:13]
1: The event count may vary depending on the microarchitectural
states of the processor when the event detection is enabled.
2: The event may count more than once for some instructions with
complex uop flows and were interrupted before retirement.

19-218 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-32. Performance Monitoring Events For Intel NetBurst® Microarchitecture
for At-Retirement Counting (Contd.)
Event Name

Event Parameters
Can Support PEBS

Parameter Value

Description

No

uops_retired

This event counts μops that are retired during a clock cycle. Mask bits
specify bogus or non-bogus.
ESCR restrictions

MSR_CRU_ESCR0
MSR_CRU_ESCR1

Counter numbers
per ESCR

ESCR0: 12, 13, 16

ESCR Event Select

01H

ESCR1: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

0: NBOGUS

The marked μops are not bogus.

1: BOGUS

The marked μops are bogus.

04H

CCCR[15:13]

Event Specific
Notes
Can Support PEBS

P6: EMON_UOPS_RETIRED
No

uop_type

This event is used in conjunction with the front-end at-retirement
mechanism to tag load and store μops.
ESCR restrictions

MSR_RAT_ESCR0
MSR_RAT_ESCR1

Counter numbers
per ESCR

ESCR0: 12, 13, 16

ESCR Event Select

02H

ESCR1: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

1: TAGLOADS

The μop is a load operation.

2: TAGSTORES

The μop is a store operation.

02H

CCCR[15:13]

Event Specific
Notes
Can Support PEBS

Setting the TAGLOADS and TAGSTORES mask bits does not cause a
counter to increment. They are only used to tag uops.
No

branch_retired

This event counts the retirement of a branch. Specify one or more
mask bits to select any combination of taken, not-taken, predicted
and mispredicted.
ESCR restrictions

MSR_CRU_ESCR2
MSR_CRU_ESCR3

See Table 18-70 for the addresses of the ESCR MSRs

Counter numbers
per ESCR

ESCR2: 12, 13, 16
ESCR3: 14, 15, 17

The counter numbers associated with each ESCR are provided. The
performance counters and corresponding CCCRs can be obtained
from Table 18-70.

ESCR Event Select

06H

ESCR[31:25]

Vol. 3B 19-219

PERFORMANCE MONITORING EVENTS

Table 19-32. Performance Monitoring Events For Intel NetBurst® Microarchitecture
for At-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

Description
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

0: MMNP

Branch not-taken predicted

1: MMNM

Branch not-taken mispredicted

2: MMTP

Branch taken predicted

3: MMTM

Branch taken mispredicted

05H

CCCR[15:13]

Event Specific
Notes
Can Support PEBS

P6: EMON_BR_INST_RETIRED
No

mispred_branch_
retired

This event represents the retirement of mispredicted branch
instructions.
ESCR restrictions

MSR_CRU_ESCR0
MSR_CRU_ESCR1

Counter numbers
per ESCR

ESCR0: 12, 13, 16

ESCR Event Select

03H

ESCR1: 14, 15, 17

ESCR Event Mask

ESCR[31:25]
ESCR[24:9]

Bit 0: NBOGUS

The retired instruction is not bogus.

CCCR Select

04H

CCCR[15:13]

Can Support PEBS

No

x87_assist

This event counts the retirement of x87 instructions that required
special handling.
Specifies one or more event mask bits to select the type of
assistance.
ESCR restrictions

MSR_CRU_ESCR2
MSR_CRU_ESCR3

Counter numbers
per ESCR

ESCR2: 12, 13, 16

ESCR Event Select

03H

ESCR3: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit

19-220 Vol. 3B

0: FPSU

Handle FP stack underflow.

1: FPSO

Handle FP stack overflow.

2: POAO

Handle x87 output overflow.

3: POAU

Handle x87 output underflow.

4: PREA

Handle x87 input assist.

CCCR Select

05H

CCCR[15:13]

Can Support PEBS

No

PERFORMANCE MONITORING EVENTS

Table 19-32. Performance Monitoring Events For Intel NetBurst® Microarchitecture
for At-Retirement Counting (Contd.)
Event Name

Event Parameters

Parameter Value

machine_clear

Description
This event increments according to the mask bit specified while the
entire pipeline of the machine is cleared. Specify one of the mask bit
to select the cause.

ESCR restrictions

MSR_CRU_ESCR2
MSR_CRU_ESCR3

Counter numbers
per ESCR

ESCR2: 12, 13, 16

ESCR Event Select

02H

ESCR3: 14, 15, 17

ESCR Event Mask

ESCR[31:25]
ESCR[24:9]

Bit
0: CLEAR

Counts for a portion of the many cycles while the machine is cleared
for any cause. Use Edge triggering for this bit only to get a count of
occurrence versus a duration.

2: MOCLEAR

Increments each time the machine is cleared due to memory ordering
issues.

6: SMCLEAR

Increments each time the machine is cleared due to self-modifying
code issues.

CCCR Select

05H

CCCR[15:13]

Can Support PEBS

No

Table 19-33. Intel NetBurst® Microarchitecture Model-Specific Performance Monitoring Events
(For Model Encoding 3, 4 or 6)
Event Name

Event Parameters

Parameter Value

instr_completed

Description
This event counts instructions that have completed and retired
during a clock cycle. Mask bits specify whether the instruction is
bogus or non-bogus and whether they are:

ESCR restrictions

MSR_CRU_ESCR0
MSR_CRU_ESCR1

Counter numbers
per ESCR

ESCR0: 12, 13, 16

ESCR Event Select

07H

ESCR1: 14, 15, 17
ESCR[31:25]
ESCR[24:9]

ESCR Event Mask
Bit

CCCR Select

0: NBOGUS

Non-bogus instructions

1: BOGUS

Bogus instructions

04H

CCCR[15:13]

Event Specific
Notes
Can Support PEBS

This metric differs from instr_retired, since it counts instructions
completed, rather than the number of times that instructions started.
No

Vol. 3B 19-221

PERFORMANCE MONITORING EVENTS

Table 19-34. List of Metrics Available for Front_end Tagging (For Front_end Event Only)
Front-end metric1

MSR_
TC_PRECISE_EVENT
MSR Bit field

Additional MSR

Event mask value for
Front_end_event

memory_loads

None

Set TAGLOADS bit in ESCR corresponding to
event Uop_Type.

NBOGUS

memory_stores

None

Set TAGSTORES bit in the ESCR corresponding
to event Uop_Type.

NBOGUS

NOTES:
1. There may be some undercounting of front end events when there is an overflow or underflow of the floating point stack.

Table 19-35. List of Metrics Available for Execution Tagging (For Execution Event Only)
Execution metric

Upstream ESCR

TagValue in
Upstream ESCR

Event mask value for
execution_event

packed_SP_retired

Set ALL bit in event mask, TagUop bit in ESCR of
packed_SP_uop.

1

NBOGUS0

packed_DP_retired

Set ALL bit in event mask, TagUop bit in ESCR of
packed_DP_uop.

1

NBOGUS0

scalar_SP_retired

Set ALL bit in event mask, TagUop bit in ESCR of
scalar_SP_uop.

1

NBOGUS0

scalar_DP_retired

Set ALL bit in event mask, TagUop bit in ESCR of
scalar_DP_uop.

1

NBOGUS0

128_bit_MMX_retired

Set ALL bit in event mask, TagUop bit in ESCR of
128_bit_MMX_uop.

1

NBOGUS0

64_bit_MMX_retired

Set ALL bit in event mask, TagUop bit in ESCR of
64_bit_MMX_uop.

1

NBOGUS0

X87_FP_retired

Set ALL bit in event mask, TagUop bit in ESCR of
x87_FP_uop.

1

NBOGUS0

1

NBOGUS0

X87_SIMD_memory_m Set ALLP0, ALLP2 bits in event mask, TagUop bit in
oves_retired
ESCR of X87_SIMD_ moves_uop.

Table 19-36. List of Metrics Available for Replay Tagging (For Replay Event Only)
Replay metric1

IA32_PEBS_
ENABLE Field
to Set

MSR_PEBS_
MATRIX_VERT Bit
Field to Set

Additional MSR/ Event

Event Mask Value for
Replay_event

1stL_cache_load
_miss_retired

Bit 0, Bit 24,
Bit 25

Bit 0

None

NBOGUS

2ndL_cache_load
_miss_retired2

Bit 1, Bit 24,
Bit 25

Bit 0

None

NBOGUS

DTLB_load_miss
_retired

Bit 2, Bit 24,
Bit 25

Bit 0

None

NBOGUS

DTLB_store_miss
_retired

Bit 2, Bit 24,
Bit 25

Bit 1

None

NBOGUS

DTLB_all_miss
_retired

Bit 2, Bit 24,
Bit 25

Bit 0, Bit 1

None

NBOGUS

Tagged_mispred_
branch

Bit 15, Bit 16, Bit 24,
Bit 25

Bit 4

None

NBOGUS

19-222 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-36. List of Metrics Available for Replay Tagging (For Replay Event Only) (Contd.)
Replay metric1

IA32_PEBS_
ENABLE Field
to Set

MSR_PEBS_
MATRIX_VERT Bit
Field to Set

MOB_load
_replay_retired3

Bit 9, Bit 24,
Bit 25

Bit 0

Select MOB_load_replay
event and set
PARTIAL_DATA and
UNALGN_ADDR bit.

NBOGUS

split_load_retired

Bit 10, Bit 24,
Bit 25

Bit 0

Select load_port_replay
event with the
MSR_SAAT_ESCR1 MSR
and set the SPLIT_LD mask
bit.

NBOGUS

split_store_retired

Bit 10, Bit 24,
Bit 25

Bit 1

Select store_port_replay
event with the
MSR_SAAT_ESCR0 MSR
and set the SPLIT_ST mask
bit.

NBOGUS

Additional MSR/ Event

Event Mask Value for
Replay_event

NOTES:
1. Certain kinds of μops cannot be tagged. These include I/O operations, UC and locked accesses, returns, and far transfers.
2. 2nd-level misses retired does not count all 2nd-level misses. It only includes those references that are found to be misses by the fast
detection logic and not those that are later found to be misses.
3. While there are several causes for a MOB replay, the event counted with this event mask setting is the case where the data from a
load that would otherwise be forwarded is not an aligned subset of the data from a preceding store.

Vol. 3B 19-223

PERFORMANCE MONITORING EVENTS

Table 19-37. Event Mask Qualification for Logical Processors
Event Type

Event Name

Event Masks, ESCR[24:9]

Non-Retirement

BPU_fetch_request

Bit 0: TCMISS

Non-Retirement

BSQ_allocation

Bit

Non-Retirement

Non-Retirement

BSQ_cache_reference

memory_cancel

TS or TI
TS

0: REQ_TYPE0

TS

1: REQ_TYPE1

TS

2: REQ_LEN0

TS

3: REQ_LEN1

TS

5: REQ_IO_TYPE

TS

6: REQ_LOCK_TYPE

TS

7: REQ_CACHE_TYPE

TS

8: REQ_SPLIT_TYPE

TS

9: REQ_DEM_TYPE

TS

10: REQ_ORD_TYPE

TS

11: MEM_TYPE0

TS

12: MEM_TYPE1

TS

13: MEM_TYPE2

TS

Bit
0: RD_2ndL_HITS

TS

1: RD_2ndL_HITE

TS

2: RD_2ndL_HITM

TS

3: RD_3rdL_HITS

TS

4: RD_3rdL_HITE

TS

5: RD_3rdL_HITM

TS

6: WR_2ndL_HIT

TS

7: WR_3rdL_HIT

TS

8: RD_2ndL_MISS

TS

9: RD_3rdL_MISS

TS

10: WR_2ndL_MISS

TS

11: WR_3rdL_MISS

TS

Bit
2: ST_RB_FULL

TS

3: 64K_CONF

TS

Non-Retirement

SSE_input_assist

Bit 15: ALL

TI

Non-Retirement

64bit_MMX_uop

Bit 15: ALL

TI

Non-Retirement

packed_DP_uop

Bit 15: ALL

TI

Non-Retirement

packed_SP_uop

Bit 15: ALL

TI

Non-Retirement

scalar_DP_uop

Bit 15: ALL

TI

Non-Retirement

scalar_SP_uop

Bit 15: ALL

TI

Non-Retirement

128bit_MMX_uop

Bit 15: ALL

TI

Non-Retirement

x87_FP_uop

Bit 15: ALL

TI

19-224 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-37. Event Mask Qualification for Logical Processors (Contd.)
Event Type

Event Name

Non-Retirement

x87_SIMD_moves_uop

Non-Retirement

FSB_data_activity

Event Masks, ESCR[24:9]
Bit
3: ALLP0

TI

4: ALLP2

TI

Bit
0: DRDY_DRV

Non-Retirement

Non-Retirement

IOQ_allocation

IOQ_active_entries

TS or TI

TI

1: DRDY_OWN

TI

2: DRDY_OTHER

TI

3: DBSY_DRV

TI

4: DBSY_OWN

TI

5: DBSY_OTHER

TI

Bit
0: ReqA0

TS

1: ReqA1

TS

2: ReqA2

TS

3: ReqA3

TS

4: ReqA4

TS

5: ALL_READ

TS

6: ALL_WRITE

TS

7: MEM_UC

TS

8: MEM_WC

TS

9: MEM_WT

TS

10: MEM_WP

TS

11: MEM_WB

TS

13: OWN

TS

14: OTHER

TS

15: PREFETCH

TS

Bit

TS

0: ReqA0
1:ReqA1

TS

2: ReqA2

TS

3: ReqA3

TS

4: ReqA4

TS

5: ALL_READ

TS

6: ALL_WRITE

TS

7: MEM_UC

TS

8: MEM_WC

TS

9: MEM_WT

TS

10: MEM_WP

TS

11: MEM_WB

TS

Vol. 3B 19-225

PERFORMANCE MONITORING EVENTS

Table 19-37. Event Mask Qualification for Logical Processors (Contd.)
Event Type

Event Name

Event Masks, ESCR[24:9]
13: OWN

TS

14: OTHER

TS

15: PREFETCH

TS
TS

Non-Retirement

global_power_events

Bit 0: RUNNING

Non-Retirement

ITLB_reference

Bit

Non-Retirement

Non-Retirement

Non-Retirement

MOB_load_replay

page_walk_type

uop_type

TS or TI

0: HIT

TS

1: MISS

TS

2: HIT_UC

TS

Bit
1: NO_STA

TS

3: NO_STD

TS

4: PARTIAL_DATA

TS

5: UNALGN_ADDR

TS

Bit
0: DTMISS

TI

1: ITMISS

TI

Bit
1: TAGLOADS

TS

2: TAGSTORES

TS

Non-Retirement

load_port_replay

Bit 1: SPLIT_LD

TS

Non-Retirement

store_port_replay

Bit 1: SPLIT_ST

TS

Non-Retirement

memory_complete

Non-Retirement

Non-Retirement

19-226 Vol. 3B

retired_mispred_branch_
type

retired_branch_type

Bit
0: LSC

TS

1: SSC

TS

2: USC

TS

3: ULC

TS

Bit
0: UNCONDITIONAL

TS

1: CONDITIONAL

TS

2: CALL

TS

3: RETURN

TS

4: INDIRECT

TS

Bit
0: UNCONDITIONAL

TS

1: CONDITIONAL

TS

2: CALL

TS

3: RETURN

TS

4: INDIRECT

TS

PERFORMANCE MONITORING EVENTS

Table 19-37. Event Mask Qualification for Logical Processors (Contd.)
Event Type

Event Name

Event Masks, ESCR[24:9]

Non-Retirement

tc_ms_xfer

Bit
0: CISC

Non-Retirement

tc_misc

Bit
4: FLUSH

Non-Retirement

Non-Retirement

TC_deliver_mode

uop_queue_writes

Bit

TS or TI
TS
TS

0: DD

TI

1: DB

TI

2: DI

TI

3: BD

TI

4: BB

TI

5: BI

TI

6: ID

TI

7: IB

TI

Bit
0: FROM_TC_BUILD

TS

1: FROM_TC_DELIVER

TS

2: FROM_ROM

TS

Non-Retirement

resource_stall

Bit 5: SBFULL

TS

Non-Retirement

WC_Buffer

Bit

TI

At Retirement

At Retirement

At Retirement

At Retirement

At Retirement

instr_retired

machine_clear

front_end_event

replay_event

execution_event

0: WCB_EVICTS

TI

1: WCB_FULL_EVICT

TI

2: WCB_HITM_EVICT

TI

Bit
0: NBOGUSNTAG

TS

1: NBOGUSTAG

TS

2: BOGUSNTAG

TS

3: BOGUSTAG

TS

Bit
0: CLEAR

TS

2: MOCLEAR

TS

6: SMCCLEAR

TS

Bit
0: NBOGUS

TS

1: BOGUS

TS

Bit
0: NBOGUS

TS

1: BOGUS

TS

Bit
0: NONBOGUS0

TS

1: NONBOGUS1

TS
Vol. 3B 19-227

PERFORMANCE MONITORING EVENTS

Table 19-37. Event Mask Qualification for Logical Processors (Contd.)
Event Type

Event Name

At Retirement

At Retirement

x87_assist

branch_retired

At Retirement

mispred_branch_retired

At Retirement

uops_retired

At Retirement

19.19

instr_completed

Event Masks, ESCR[24:9]

TS or TI

2: NONBOGUS2

TS

3: NONBOGUS3

TS

4: BOGUS0

TS

5: BOGUS1

TS

6: BOGUS2

TS

7: BOGUS3

TS

Bit
0: FPSU

TS

1: FPSO

TS

2: POAO

TS

3: POAU

TS

4: PREA

TS

Bit
0: MMNP

TS

1: MMNM

TS

2: MMTP

TS

3: MMTM

TS

Bit 0: NBOGUS

TS

Bit
0: NBOGUS

TS

1: BOGUS

TS

Bit
0: NBOGUS

TS

1: BOGUS

TS

PERFORMANCE MONITORING EVENTS FOR INTEL® PENTIUM® M
PROCESSORS

The Pentium M processor’s performance monitoring events are based on monitoring events for the P6 family of
processors. All of these performance events are model specific for the Pentium M processor and are not available in
this form in other processors. Table 19-38 lists the performance monitoring events that were added in the Pentium
M processor.

19-228 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-38. Performance Monitoring Events on Intel® Pentium® M Processors
Name

Hex Values

Descriptions

Power Management
EMON_EST_TRANS

58H

Number of Enhanced Intel SpeedStep technology transitions:
Mask = 00H - All transitions
Mask = 02H - Only Frequency transitions

EMON_THERMAL_TRIP

59H

Duration/Occurrences in thermal trip; to count number of thermal trips: bit
22 in PerfEvtSel0/1 needs to be set to enable edge detect.

BR_INST_EXEC

88H

Branch instructions that were executed (not necessarily retired).

BR_MISSP_EXEC

89H

Branch instructions executed that were mispredicted at execution.

BR_BAC_MISSP_EXEC

8AH

Branch instructions executed that were mispredicted at front end (BAC).

BR_CND_EXEC

8BH

Conditional branch instructions that were executed.

BR_CND_MISSP_EXEC

8CH

Conditional branch instructions executed that were mispredicted.

BR_IND_EXEC

8DH

Indirect branch instructions executed.

BR_IND_MISSP_EXEC

8EH

Indirect branch instructions executed that were mispredicted.

BR_RET_EXEC

8FH

Return branch instructions executed.

BR_RET_MISSP_EXEC

90H

Return branch instructions executed that were mispredicted at execution.

BR_RET_BAC_MISSP_EXEC

91H

Return branch instructions executed that were mispredicted at front end
(BAC).

BR_CALL_EXEC

92H

CALL instruction executed.

BR_CALL_MISSP_EXEC

93H

CALL instruction executed and miss predicted.

BR_IND_CALL_EXEC

94H

Indirect CALL instructions executed.

EMON_SIMD_INSTR_RETIRED

CEH

Number of retired MMX instructions.

EMON_SYNCH_UOPS

D3H

Sync micro-ops

EMON_ESP_UOPS

D7H

Total number of micro-ops

EMON_FUSED_UOPS_RET

DAH

Number of retired fused micro-ops:

BPU

Decoder

Mask = 0 - Fused micro-ops
Mask = 1 - Only load+Op micro-ops
Mask = 2 - Only std+sta micro-ops
EMON_UNFUSION

DBH

Number of unfusion events in the ROB, happened on a FP exception to a
fused µop.

EMON_PREF_RQSTS_UP

F0H

Number of upward prefetches issued.

EMON_PREF_RQSTS_DN

F8H

Number of downward prefetches issued.

Prefetcher

Vol. 3B 19-229

PERFORMANCE MONITORING EVENTS

A number of P6 family processor performance monitoring events are modified for the Pentium M processor. Table
19-39 lists the performance monitoring events that were changed in the Pentium M processor, and differ from
performance monitoring events for the P6 family of processors.

Table 19-39. Performance Monitoring Events Modified on Intel® Pentium® M Processors
Name

Hex
Values

Descriptions

CPU_CLK_UNHALTED

79H

Number of cycles during which the processor is not halted, and not in a thermal trip.

EMON_SSE_SSE2_INST_
RETIRED

D8H

Streaming SIMD Extensions Instructions Retired:
Mask = 0 – SSE packed single and scalar single
Mask = 1 – SSE scalar-single
Mask = 2 – SSE2 packed-double
Mask = 3 – SSE2 scalar-double

EMON_SSE_SSE2_COMP_INST_
RETIRED

D9H

Computational SSE Instructions Retired:
Mask = 0 – SSE packed single
Mask = 1 – SSE Scalar-single
Mask = 2 – SSE2 packed-double
Mask = 3 – SSE2 scalar-double

L2_LD

29H

L2 data loads

Mask[0] = 1 – count I state lines

L2_LINES_IN

24H

L2 lines allocated

Mask[1] = 1 – count S state lines

L2_LINES_OUT

26H

L2 lines evicted

Mask[2] = 1 – count E state lines

L2_M_LINES_OUT

27H

Lw M-state lines evicted

Mask[3] = 1 – count M state lines
Mask[5:4]:
00H – Excluding hardware-prefetched lines
01H - Hardware-prefetched lines only
02H/03H – All (HW-prefetched lines and non HW -Prefetched lines)

19.20

P6 FAMILY PROCESSOR PERFORMANCE MONITORING EVENTS

Table 19-40 lists the events that can be counted with the performance monitoring counters and read with the
RDPMC instruction for the P6 family processors. The unit column gives the microarchitecture or bus unit that
produces the event; the event number column gives the hexadecimal number identifying the event; the mnemonic
event name column gives the name of the event; the unit mask column gives the unit mask required (if any); the
description column describes the event; and the comments column gives additional information about the event.
All of these performance events are model specific for the P6 family processors and are not available in this form in
the Pentium 4 processors or the Pentium processors. Some events (such as those added in later generations of the
P6 family processors) are only available in specific processors in the P6 family. All performance event encodings not
listed in Table 19-40 are reserved and their use will result in undefined counter results.
See the end of the table for notes related to certain entries in the table.

19-230 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters
Unit
Data Cache
Unit (DCU)

Event Mnemonic Event
Num. Name

Unit
Mask

43H

00H

DATA_MEM_REFS

Description

Comments

All loads from any memory type. All stores
to any memory type. Each part of a split is
counted separately. The internal logic counts
not only memory loads and stores, but also
internal retries.
80-bit floating-point accesses are double
counted, since they are decomposed into a
16-bit exponent load and a 64-bit mantissa
load. Memory accesses are only counted
when they are actually performed (such as a
load that gets squashed because a previous
cache miss is outstanding to the same
address, and which finally gets performed, is
only counted once).
Does not include I/O accesses, or other
nonmemory accesses.

45H

DCU_LINES_IN

00H

Total lines allocated in DCU.

46H

DCU_M_LINES_IN

00H

Number of M state lines allocated in DCU.

47H

DCU_M_LINES_
OUT

00H

DCU_MISS_
OUTSTANDING

00H

48H

Number of M state lines evicted from DCU.
This includes evictions via snoop HITM,
intervention or replacement.
Weighted number of cycles while a DCU miss
is outstanding, incremented by the number
of outstanding cache misses at any
particular time.

An access that also misses the L2
is short-changed by 2 cycles (i.e., if
counts N cycles, should be N+2
cycles).

Cacheable read requests only are
considered.

Subsequent loads to the same
cache line will not result in any
additional counts.

Uncacheable requests are excluded.
Read-for-ownerships are counted, as well as
line fills, invalidates, and stores.
Instruction
Fetch Unit
(IFU)

80H

IFU_IFETCH

00H

Number of instruction fetches, both
cacheable and noncacheable, including UC
fetches.

81H

IFU_IFETCH_
MISS

00H

Number of instruction fetch misses

85H

ITLB_MISS

00H

Number of ITLB misses.

86H

IFU_MEM_STALL

00H

Number of cycles instruction fetch is stalled,
for any reason.

Count value not precise, but still
useful.

All instruction fetches that do not hit the IFU
(i.e., that produce memory requests). This
includes UC accesses.

Includes IFU cache misses, ITLB misses, ITLB
faults, and other minor stalls.

L2 Cache1

87H

ILD_STALL

00H

Number of cycles that the instruction length
decoder is stalled.

28H

L2_IFETCH

MESI
0FH

Number of L2 instruction fetches.
This event indicates that a normal
instruction fetch was received by the L2.

Vol. 3B 19-231

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Unit

Event Mnemonic Event
Num. Name

Unit
Mask

Description

Comments

The count includes only L2 cacheable
instruction fetches; it does not include UC
instruction fetches.
It does not include ITLB miss accesses.
29H

L2_LD

MESI
0FH

Number of L2 data loads.
This event indicates that a normal, unlocked,
load memory access was received by the L2.
It includes only L2 cacheable memory
accesses; it does not include I/O accesses,
other nonmemory accesses, or memory
accesses such as UC/WT memory accesses.
It does include L2 cacheable TLB miss
memory accesses.

2AH

L2_ST

MESI
0FH

Number of L2 data stores.
This event indicates that a normal, unlocked,
store memory access was received by the
L2.
it indicates that the DCU sent a read-forownership request to the L2. It also includes
Invalid to Modified requests sent by the DCU
to the L2.
It includes only L2 cacheable memory
accesses; it does not include I/O accesses,
other nonmemory accesses, or memory
accesses such as UC/WT memory accesses.
It includes TLB miss memory accesses.

External
Bus Logic
(EBL)2

19-232 Vol. 3B

24H

L2_LINES_IN

00H

Number of lines allocated in the L2.

26H

L2_LINES_OUT

00H

Number of lines removed from the L2 for
any reason.

25H

L2_M_LINES_INM

00H

Number of modified lines allocated in the L2.

27H

L2_M_LINES_
OUTM

00H

Number of modified lines removed from the
L2 for any reason.

2EH

L2_RQSTS

MESI
0FH

Total number of L2 requests.

21H

L2_ADS

00H

Number of L2 address strobes.

22H

L2_DBUS_BUSY

00H

Number of cycles during which the L2 cache
data bus was busy.

23H

L2_DBUS_BUSY_
RD

00H

Number of cycles during which the data bus
was busy transferring read data from L2 to
the processor.

62H

BUS_DRDY_
CLOCKS

00H
(Self)

Number of clocks during which DRDY# is
asserted.

20H
(Any)

Utilization of the external system data bus
during data transfers.

Unit Mask = 00H counts bus clocks
when the processor is driving
DRDY#.
Unit Mask = 20H counts in
processor clocks when any agent is
driving DRDY#.

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Unit

Event Mnemonic Event
Num. Name

Unit
Mask

Description

Comments

63H

00H
(Self)

Number of clocks during which LOCK# is
asserted on the external system bus.3

Always counts in processor clocks.

Counts only DCU full-line cacheable
reads, not RFOs, writes, instruction
fetches, or anything else. Counts
“waiting for bus to complete” (last
data chunk received).

BUS_LOCK_
CLOCKS

20H
(Any)
60H

65H

BUS_REQ_
OUTSTANDING

00H
(Self)

Number of bus requests outstanding.

BUS_TRAN_BRD

00H
(Self)

Number of burst read transactions.

This counter is incremented by the number
of cacheable read bus requests outstanding
in any given cycle.

20H
(Any)
66H

BUS_TRAN_RFO

00H
(Self)

Number of completed read for ownership
transactions.

20H
(Any)

67H

BUS_TRANS_WB

00H
(Self)

Number of completed write back
transactions.

20H
(Any)
68H

BUS_TRAN_
IFETCH

00H
(Self)

Number of completed instruction fetch
transactions.

20H
(Any)
69H

BUS_TRAN_INVA
L

00H
(Self)

Number of completed invalidate
transactions.

20H
(Any)
6AH

BUS_TRAN_PWR

00H
(Self)

Number of completed partial write
transactions.

20H
(Any)
6BH

BUS_TRANS_P

00H
(Self)

Number of completed partial transactions.

20H
(Any)
6CH

BUS_TRANS_IO

00H
(Self)

Number of completed I/O transactions.

20H
(Any)
6DH

BUS_TRAN_DEF

00H
(Self)

Number of completed deferred transactions.

20H
(Any)

Vol. 3B 19-233

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Unit

Event Mnemonic Event
Num. Name

Unit
Mask

6EH

00H
(Self)

BUS_TRAN_
BURST

Description

Comments

Number of completed burst transactions.

20H
(Any)
70H

BUS_TRAN_ANY

00H
(Self)
20H
(Any)

Number of all completed bus transactions.
Address bus utilization can be calculated
knowing the minimum address bus
occupancy.
Includes special cycles, etc.

6FH

BUS_TRAN_MEM

00H
(Self)

Number of completed memory transactions.

20H
(Any)
64H

BUS_DATA_RCV

00H
(Self)

Number of bus clock cycles during which this
processor is receiving data.

61H

BUS_BNR_DRV

00H
(Self)

Number of bus clock cycles during which this
processor is driving the BNR# pin.

7AH

BUS_HIT_DRV

00H
(Self)

Number of bus clock cycles during which this
processor is driving the HIT# pin.

Includes cycles due to snoop stalls.
The event counts correctly, but
BPMi (breakpoint monitor) pins
function as follows based on the
setting of the PC bits (bit 19 in the
PerfEvtSel0 and PerfEvtSel1
registers):
• If the core-clock-to- bus-clock
ratio is 2:1 or 3:1, and a PC bit is
set, the BPMi pins will be
asserted for a single clock when
the counters overflow.
• If the PC bit is clear, the
processor toggles the BPMi pins
when the counter overflows.
• If the clock ratio is not 2:1 or 3:1,
the BPMi pins will not function
for these performance
monitoring counter events.

7BH

BUS_HITM_DRV

00H
(Self)

Number of bus clock cycles during which this
processor is driving the HITM# pin.

Includes cycles due to snoop stalls.
The event counts correctly, but
BPMi (breakpoint monitor) pins
function as follows based on the
setting of the PC bits (bit 19 in the
PerfEvtSel0 and PerfEvtSel1
registers):
• If the core-clock-to- bus-clock
ratio is 2:1 or 3:1, and a PC bit is
set, the BPMi pins will be
asserted for a single clock when
the counters overflow.

19-234 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Unit

Event Mnemonic Event
Num. Name

Unit
Mask

Description

Comments
• If the PC bit is clear, the
processor toggles the BPMipins
when the counter overflows.
• If the clock ratio is not 2:1 or 3:1,
the BPMi pins will not function
for these performance
monitoring counter events.

FloatingPoint Unit

7EH

BUS_SNOOP_
STALL

00H
(Self)

Number of clock cycles during which the bus
is snoop stalled.

C1H

FLOPS

00H

Number of computational floating-point
operations retired.

Counter 0 only.

Excludes floating-point computational
operations that cause traps or assists.
Includes floating-point computational
operations executed by the assist handler.
Includes internal sub-operations for complex
floating-point instructions like
transcendentals.
Excludes floating-point loads and stores.
10H

FP_COMP_OPS_
EXE

00H

Number of computational floating-point
operations executed.

Counter 0 only.

The number of FADD, FSUB, FCOM, FMULs,
integer MULs and IMULs, FDIVs, FPREMs,
FSQRTS, integer DIVs, and IDIVs.
This number does not include the number of
cycles, but the number of operations.
This event does not distinguish an FADD
used in the middle of a transcendental flow
from a separate FADD instruction.
11H

12H

FP_ASSIST

MUL

00H

00H

Number of floating-point exception cases
handled by microcode.

Counter 1 only.

Number of multiplies.

Counter 1 only.

This event includes counts due to
speculative execution.

This count includes integer as well as FP
multiplies and is speculative.
13H

DIV

00H

Number of divides.

Counter 1 only.

This count includes integer as well as FP
divides and is speculative.
14H

CYCLES_DIV_
BUSY

00H

Number of cycles during which the divider is
busy, and cannot accept new divides.

Counter 0 only.

This includes integer and FP divides, FPREM,
FPSQRT, etc. and is speculative.

Vol. 3B 19-235

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Unit
Memory
Ordering

Event Mnemonic Event
Num. Name

Unit
Mask

03H

00H

LD_BLOCKS

Description

Comments

Number of load operations delayed due to
store buffer blocks.
Includes counts caused by preceding stores
whose addresses are unknown, preceding
stores whose addresses are known but
whose data is unknown, and preceding
stores that conflicts with the load but which
incompletely overlap the load.

04H

SB_DRAINS

00H

Number of store buffer drain cycles.
Incremented every cycle the store buffer is
draining.
Draining is caused by serializing operations
like CPUID, synchronizing operations like
XCHG, interrupt acknowledgment, as well as
other conditions (such as cache flushing).

05H

MISALIGN_
MEM_REF

00H

Number of misaligned data memory
references.
Incremented by 1 every cycle, during which
either the processor’s load or store pipeline
dispatches a misaligned μop.
Counting is performed if it is the first or
second half, or if it is blocked, squashed, or
missed.

MISALIGN_MEM_
REF is only an approximation to the
true number of misaligned memory
references.
The value returned is roughly
proportional to the number of
misaligned memory accesses (the
size of the problem).

In this context, misaligned means crossing a
64-bit boundary.
07H

EMON_KNI_PREF
_DISPATCHED

Number of Streaming SIMD extensions
prefetch/weakly-ordered instructions
dispatched (speculative prefetches are
included in counting):
00H

0: prefetch NTA

01H

1: prefetch T1

02H

2: prefetch T2

03H
4BH

Instruction
Decoding
and
Retirement

C0H

EMON_KNI_PREF
_MISS

INST_RETIRED

Counters 0 and 1. Pentium III
processor only.

3: weakly ordered stores
Number of prefetch/weakly-ordered
instructions that miss all caches:

00H

0: prefetch NTA

01H

1: prefetch T1

02H

2: prefetch T2

03H

3: weakly ordered stores

00H

Number of instructions retired.

Counters 0 and 1. Pentium III
processor only.

A hardware interrupt received
during/after the last iteration of
the REP STOS flow causes the
counter to undercount by 1
instruction.
An SMI received while executing a
HLT instruction will cause the
performance counter to not count
the RSM instruction and
undercount by 1.

19-236 Vol. 3B

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Unit

Event Mnemonic Event
Num. Name

Unit
Mask

Description

C2H

UOPS_RETIRED

00H

Number of μops retired.

D0H

INST_DECODED

00H

D8H

EMON_KNI_INST_
RETIRED

D9H

Number of instructions decoded.
Number of Streaming SIMD extensions
retired:

00H

0: packed & scalar

01H

1: scalar

EMON_KNI_
COMP_
INST_RET

Comments

Number of Streaming SIMD extensions
computation instructions retired:

Counters 0 and 1. Pentium III
processor only.

Counters 0 and 1. Pentium III
processor only.

0: packed and scalar
00H

1: scalar

01H

Interrupts

Branches

C8H

HW_INT_RX

00H

Number of hardware interrupts received.

C6H

CYCLES_INT_
MASKED

00H

Number of processor cycles for which
interrupts are disabled.

C7H

CYCLES_INT_
PENDING_
AND_MASKED

00H

Number of processor cycles for which
interrupts are disabled and interrupts are
pending.

C4H

BR_INST_
RETIRED

00H

Number of branch instructions retired.

C5H

BR_MISS_PRED_
RETIRED

00H

Number of mispredicted branches retired.

C9H

BR_TAKEN_
RETIRED

00H

Number of taken branches retired.

CAH

BR_MISS_PRED_
TAKEN_RET

00H

Number of taken mispredictions branches
retired.

E0H

BR_INST_
DECODED

00H

Number of branch instructions decoded.

E2H

BTB_MISSES

00H

Number of branches for which the BTB did
not produce a prediction.

E4H

BR_BOGUS

00H

Number of bogus branches.

E6H

BACLEARS

00H

Number of times BACLEAR is asserted.
This is the number of times that a static
branch prediction was made, in which the
branch decoder decided to make a branch
prediction because the BTB did not.

Stalls

A2H

RESOURCE_
STALLS

00H

Incremented by 1 during every cycle for
which there is a resource related stall.
Includes register renaming buffer entries,
memory buffer entries.

Vol. 3B 19-237

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Unit

Event Mnemonic Event
Num. Name

Unit
Mask

Description

Comments

Does not include stalls due to bus queue full,
too many cache misses, etc.
In addition to resource related stalls, this
event counts some other events.
Includes stalls arising during branch
misprediction recovery, such as if retirement
of the mispredicted branch is delayed and
stalls arising while store buffer is draining
from synchronizing operations.
D2H

PARTIAL_RAT_
STALLS

00H

Number of cycles or events for partial stalls.
This includes flag partial stalls.

Segment
Register
Loads

06H

SEGMENT_REG_
LOADS

00H

Number of segment register loads.

Clocks

79H

CPU_CLK_
UNHALTED

00H

Number of cycles during which the
processor is not halted.

MMX Unit

B0H

MMX_INSTR_
EXEC

00H

Number of MMX Instructions Executed.

Available in Intel Celeron, Pentium II
and Pentium II Xeon processors
only.
Does not account for MOVQ and
MOVD stores from register to
memory.

B1H

MMX_SAT_
INSTR_EXEC

00H

Number of MMX Saturating Instructions
Executed.

Available in Pentium II and Pentium
III processors only.

B2H

MMX_UOPS_
EXEC

0FH

Number of MMX μops Executed.

Available in Pentium II and Pentium
III processors only.

B3H

MMX_INSTR_
TYPE_EXEC

01H

MMX packed multiply instructions executed.

Available in Pentium II and Pentium
III processors only.

02H

MMX packed shift instructions executed.
MMX pack operation instructions executed.

04H

CCH

FP_MMX_TRANS

08H

MMX unpack operation instructions
executed.

10H

MMX packed logical instructions executed.

20H

MMX packed arithmetic instructions
executed.

00H

01H

Segment
Register
Renaming

19-238 Vol. 3B

Transitions from MMX instruction to
floating-point instructions.

Available in Pentium II and Pentium
III processors only.

Transitions from floating-point instructions
to MMX instructions.

CDH

MMX_ASSIST

00H

Number of MMX Assists (that is, the number
of EMMS instructions executed).

Available in Pentium II and Pentium
III processors only.

CEH

MMX_INSTR_RET

00H

Number of MMX Instructions Retired.

Available in Pentium II processors
only.

D4H

SEG_RENAME_
STALLS

Number of Segment Register Renaming
Stalls:

Available in Pentium II and Pentium
III processors only.

PERFORMANCE MONITORING EVENTS

Table 19-40. Events That Can Be Counted with the P6 Family Performance Monitoring Counters (Contd.)
Event Mnemonic Event
Num. Name

Unit

Unit
Mask

Description

02H

Segment register ES

04H

Segment register DS

08H

Segment register FS

0FH

Segment register FS

Comments

Segment registers
ES + DS + FS + GS
D5H

D6H

SEG_REG_
RENAMES

RET_SEG_
RENAMES

Number of Segment Register Renames:
01H

Segment register ES

02H

Segment register DS

04H

Segment register FS

08H

Segment register FS

0FH

Segment registers
ES + DS + FS + GS

00H

Number of segment register rename events
retired.

Available in Pentium II and Pentium
III processors only.

Available in Pentium II and Pentium
III processors only.

NOTES:
1. Several L2 cache events, where noted, can be further qualified using the Unit Mask (UMSK) field in the PerfEvtSel0 and
PerfEvtSel1 registers. The lower 4 bits of the Unit Mask field are used in conjunction with L2 events to indicate the cache state or
cache states involved.
The P6 family processors identify cache states using the “MESI” protocol and consequently each bit in the Unit Mask field represents one of the four states: UMSK[3] = M (8H) state, UMSK[2] = E (4H) state, UMSK[1] = S (2H) state, and UMSK[0] = I (1H) state.
UMSK[3:0] = MESI” (FH) should be used to collect data for all states; UMSK = 0H, for the applicable events, will result in nothing
being counted.
2. All of the external bus logic (EBL) events, except where noted, can be further qualified using the Unit Mask (UMSK) field in the
PerfEvtSel0 and PerfEvtSel1 registers.
Bit 5 of the UMSK field is used in conjunction with the EBL events to indicate whether the processor should count transactions that
are self- generated (UMSK[5] = 0) or transactions that result from any processor on the bus (UMSK[5] = 1).
3. L2 cache locks, so it is possible to have a zero count.

19.21

PENTIUM PROCESSOR PERFORMANCE MONITORING EVENTS

Table 19-41 lists the events that can be counted with the performance monitoring counters for the Pentium
processor. The Event Number column gives the hexadecimal code that identifies the event and that is entered in
the ES0 or ES1 (event select) fields of the CESR MSR. The Mnemonic Event Name column gives the name of the
event, and the Description and Comments columns give detailed descriptions of the events. Most events can be
counted with either counter 0 or counter 1; however, some events can only be counted with only counter 0 or only
counter 1 (as noted).

NOTE
The events in the table that are shaded are implemented only in the Pentium processor with MMX
technology.

Vol. 3B 19-239

PERFORMANCE MONITORING EVENTS

Table 19-41. Events That Can Be Counted with Pentium Processor Performance Monitoring Counters
Event
Num.

Mnemonic Event
Name

Description

Comments

00H

DATA_READ

Number of memory data reads
(internal data cache hit and miss
combined).

Split cycle reads are counted individually. Data Memory
Reads that are part of TLB miss processing are not
included. These events may occur at a maximum of two
per clock. I/O is not included.

01H

DATA_WRITE

Number of memory data writes
(internal data cache hit and miss
combined); I/O not included.

Split cycle writes are counted individually. These events
may occur at a maximum of two per clock. I/O is not
included.

0H2

DATA_TLB_MISS

Number of misses to the data cache
translation look-aside buffer.

03H

DATA_READ_MISS

Number of memory read accesses that
miss the internal data cache whether
or not the access is cacheable or
noncacheable.

Additional reads to the same cache line after the first
BRDY# of the burst line fill is returned but before the final
(fourth) BRDY# has been returned, will not cause the
counter to be incremented additional times.
Data accesses that are part of TLB miss processing are
not included. Accesses directed to I/O space are not
included.

04H

DATA WRITE MISS

Number of memory write accesses
that miss the internal data cache
whether or not the access is cacheable
or noncacheable.

Data accesses that are part of TLB miss processing are
not included. Accesses directed to I/O space are not
included.

05H

WRITE_HIT_TO_
M-_OR_ESTATE_LINES

Number of write hits to exclusive or
modified lines in the data cache.

These are the writes that may be held up if EWBE# is
inactive. These events may occur a maximum of two per
clock.

06H

DATA_CACHE_
LINES_
WRITTEN_BACK

Number of dirty lines (all) that are
written back, regardless of the cause.

Replacements and internal and external snoops can all
cause writeback and are counted.

07H

EXTERNAL_
SNOOPS

Number of accepted external snoops
whether they hit in the code cache or
data cache or neither.

Assertions of EADS# outside of the sampling interval are
not counted, and no internal snoops are counted.

08H

EXTERNAL_DATA_
CACHE_SNOOP_
HITS

Number of external snoops to the data
cache.

Snoop hits to a valid line in either the data cache, the data
line fill buffer, or one of the write back buffers are all
counted as hits.

09H

MEMORY ACCESSES
IN BOTH PIPES

Number of data memory reads or
writes that are paired in both pipes of
the pipeline.

These accesses are not necessarily run in parallel due to
cache misses, bank conflicts, etc.

0AH

BANK CONFLICTS

Number of actual bank conflicts.

0BH

MISALIGNED DATA
MEMORY OR I/O
REFERENCES

Number of memory or I/O reads or
writes that are misaligned.

0CH

CODE READ

Number of instruction reads; whether Individual 8-byte noncacheable instruction reads are
the read is cacheable or noncacheable. counted.

0DH

CODE TLB MISS

Number of instruction reads that miss
the code TLB whether the read is
cacheable or noncacheable.

Individual 8-byte noncacheable instruction reads are
counted.

0EH

CODE CACHE MISS

Number of instruction reads that miss
the internal code cache; whether the
read is cacheable or noncacheable.

Individual 8-byte noncacheable instruction reads are
counted.

19-240 Vol. 3B

A 2- or 4-byte access is misaligned when it crosses a 4byte boundary; an 8-byte access is misaligned when it
crosses an 8-byte boundary. Ten byte accesses are
treated as two separate accesses of 8 and 2 bytes each.

PERFORMANCE MONITORING EVENTS

Table 19-41. Events That Can Be Counted with Pentium Processor Performance Monitoring Counters (Contd.)
Event
Num.

Mnemonic Event
Name

0FH

ANY SEGMENT
REGISTER LOADED

10H

Reserved

11H

Reserved

12H

Branches

Description

Comments

Number of writes into any segment
register in real or protected mode
including the LDTR, GDTR, IDTR, and
TR.

Segment loads are caused by explicit segment register
load instructions, far control transfers, and task switches.
Far control transfers and task switches causing a privilege
level change will signal this event twice. Interrupts and
exceptions may initiate a far control transfer.

Number of taken and not taken
branches, including: conditional
branches, jumps, calls, returns,
software interrupts, and interrupt
returns.

Also counted as taken branches are serializing
instructions, VERR and VERW instructions, some segment
descriptor loads, hardware interrupts (including FLUSH#),
and programmatic exceptions that invoke a trap or fault
handler. The pipe is not necessarily flushed.
The number of branches actually executed is measured,
not the number of predicted branches.

13H

BTB_HITS

Number of BTB hits that occur.

Hits are counted only for those instructions that are
actually executed.

14H

TAKEN_BRANCH_
OR_BTB_HIT

Number of taken branches or BTB hits
that occur.

This event type is a logical OR of taken branches and BTB
hits. It represents an event that may cause a hit in the
BTB. Specifically, it is either a candidate for a space in the
BTB or it is already in the BTB.

15H

PIPELINE FLUSHES

Number of pipeline flushes that occur

The counter will not be incremented for serializing
instructions (serializing instructions cause the prefetch
queue to be flushed but will not trigger the Pipeline
Flushed event counter) and software interrupts (software
interrupts do not flush the pipeline).

Pipeline flushes are caused by BTB
misses on taken branches,
mispredictions, exceptions, interrupts,
and some segment descriptor loads.
16H

INSTRUCTIONS_
EXECUTED

Number of instructions executed (up
to two per clock).

Invocations of a fault handler are considered instructions.
All hardware and software interrupts and exceptions will
also cause the count to be incremented. Repeat prefixed
string instructions will only increment this counter once
despite the fact that the repeat loop executes the same
instruction multiple times until the loop criteria is
satisfied.
This applies to all the Repeat string instruction prefixes
(i.e., REP, REPE, REPZ, REPNE, and REPNZ). This counter
will also only increment once per each HLT instruction
executed regardless of how many cycles the processor
remains in the HALT state.

17H

INSTRUCTIONS_
EXECUTED_ V PIPE

Number of instructions executed in
the V_pipe.
The event indicates the number of
instructions that were paired.

18H

BUS_CYCLE_
DURATION

Number of clocks while a bus cycle is in
progress.

This event is the same as the 16H event except it only
counts the number of instructions actually executed in
the V-pipe.
The count includes HLDA, AHOLD, and BOFF# clocks.

This event measures bus use.
19H

WRITE_BUFFER_
FULL_STALL_
DURATION

Number of clocks while the pipeline is
stalled due to full write buffers.

Full write buffers stall data memory read misses, data
memory write misses, and data memory write hits to Sstate lines. Stalls on I/O accesses are not included.

Vol. 3B 19-241

PERFORMANCE MONITORING EVENTS

Table 19-41. Events That Can Be Counted with Pentium Processor Performance Monitoring Counters (Contd.)
Event
Num.

Mnemonic Event
Name

Description

Comments
Data TLB Miss processing is also included in the count. The
pipeline stalls while a data memory read is in progress
including attempts to read that are not bypassed while a
line is being filled.

1AH

WAITING_FOR_
DATA_MEMORY_
READ_STALL_
DURATION

Number of clocks while the pipeline is
stalled while waiting for data memory
reads.

1BH

STALL ON WRITE
TO AN E- OR MSTATE LINE

Number of stalls on writes to E- or Mstate lines.

1CH

LOCKED BUS CYCLE

Number of locked bus cycles that occur
as the result of the LOCK prefix or
LOCK instruction, page-table updates,
and descriptor table updates.

Only the read portion of the locked read-modify-write is
counted. Split locked cycles (SCYC active) count as two
separate accesses. Cycles restarted due to BOFF# are not
re-counted.

1DH

I/O READ OR WRITE
CYCLE

Number of bus cycles directed to I/O
space.

Misaligned I/O accesses will generate two bus cycles. Bus
cycles restarted due to BOFF# are not re-counted.

1EH

NONCACHEABLE_
MEMORY_READS

Number of noncacheable instruction or
data memory read bus cycles.

Cycles restarted due to BOFF# are not re-counted.

The count includes read cycles caused
by TLB misses, but does not include
read cycles to I/O space.
1FH

PIPELINE_AGI_
STALLS

Number of address generation
interlock (AGI) stalls.
An AGI occurring in both the U- and Vpipelines in the same clock signals this
event twice.

20H

Reserved

21H

Reserved

22H

FLOPS

Number of floating-point operations
that occur.

An AGI occurs when the instruction in the execute stage
of either of U- or V-pipelines is writing to either the index
or base address register of an instruction in the D2
(address generation) stage of either the U- or V- pipelines.

Number of floating-point adds, subtracts, multiplies,
divides, remainders, and square roots are counted. The
transcendental instructions consist of multiple adds and
multiplies and will signal this event multiple times.
Instructions generating the divide-by-zero, negative
square root, special operand, or stack exceptions will not
be counted.
Instructions generating all other floating-point exceptions
will be counted. The integer multiply instructions and
other instructions which use the x87 FPU will be counted.

23H

BREAKPOINT
MATCH ON DR0
REGISTER

Number of matches on register DR0
breakpoint.

The counters is incremented regardless if the breakpoints
are enabled or not. However, if breakpoints are not
enabled, code breakpoint matches will not be checked for
instructions executed in the V-pipe and will not cause this
counter to be incremented. (They are checked on
instruction executed in the U-pipe only when breakpoints
are not enabled.)
These events correspond to the signals driven on the
BP[3:0] pins. Refer to Chapter 17, “Debug, Branch Profile,
TSC, and Resource Monitoring Features” for more
information.

24H

BREAKPOINT
MATCH ON DR1
REGISTER

19-242 Vol. 3B

Number of matches on register DR1
breakpoint.

See comment for 23H event.

PERFORMANCE MONITORING EVENTS

Table 19-41. Events That Can Be Counted with Pentium Processor Performance Monitoring Counters (Contd.)
Event
Num.

Mnemonic Event
Name

Description

Comments

25H

BREAKPOINT
MATCH ON DR2
REGISTER

Number of matches on register DR2
breakpoint.

See comment for 23H event.

26H

BREAKPOINT
MATCH ON DR3
REGISTER

Number of matches on register DR3
breakpoint.

See comment for 23H event.

27H

HARDWARE
INTERRUPTS

Number of taken INTR and NMI
interrupts.

28H

DATA_READ_OR_
WRITE

Number of memory data reads and/or
writes (internal data cache hit and
miss combined).

Split cycle reads and writes are counted individually. Data
Memory Reads that are part of TLB miss processing are
not included. These events may occur at a maximum of
two per clock. I/O is not included.

29H

DATA_READ_MISS
OR_WRITE MISS

Number of memory read and/or write
accesses that miss the internal data
cache, whether or not the access is
cacheable or noncacheable.

Additional reads to the same cache line after the first
BRDY# of the burst line fill is returned but before the final
(fourth) BRDY# has been returned, will not cause the
counter to be incremented additional times.
Data accesses that are part of TLB miss processing are
not included. Accesses directed to I/O space are not
included.

2AH

BUS_OWNERSHIP_
LATENCY
(Counter 0)

The time from LRM bus ownership
request to bus ownership granted
(that is, the time from the earlier of a
PBREQ (0), PHITM# or HITM#
assertion to a PBGNT assertion)

The ratio of the 2AH events counted on counter 0 and
counter 1 is the average stall time due to bus ownership
conflict.

2AH

BUS OWNERSHIP
TRANSFERS
(Counter 1)

The number of buss ownership
transfers (that is, the number of
PBREQ (0) assertions

The ratio of the 2AH events counted on counter 0 and
counter 1 is the average stall time due to bus ownership
conflict.

2BH

MMX_
INSTRUCTIONS_
EXECUTED_
U-PIPE (Counter 0)

Number of MMX instructions executed
in the U-pipe

2BH

MMX_
INSTRUCTIONS_
EXECUTED_
V-PIPE (Counter 1)

Number of MMX instructions executed
in the V-pipe

2CH

CACHE_MSTATE_LINE_
SHARING
(Counter 0)

Number of times a processor identified
a hit to a modified line due to a
memory access in the other processor
(PHITM (O))

2CH

CACHE_LINE_
SHARING
(Counter 1)

Number of shared data lines in the L1
cache (PHIT (O))

2DH

EMMS_
INSTRUCTIONS_
EXECUTED (Counter
0)

Number of EMMS instructions
executed

If the average memory latencies of the system are known,
this event enables the user to count the Write Backs on
PHITM(O) penalty and the Latency on Hit Modified(I)
penalty.

Vol. 3B 19-243

PERFORMANCE MONITORING EVENTS

Table 19-41. Events That Can Be Counted with Pentium Processor Performance Monitoring Counters (Contd.)
Event
Num.
2DH

Mnemonic Event
Name

Description

Comments

TRANSITIONS_
BETWEEN_MMX_
AND_FP_
INSTRUCTIONS
(Counter 1)

Number of transitions between MMX
and floating-point instructions or vice
versa

This event counts the first floating-point instruction
following an MMX instruction or first MMX instruction
following a floating-point instruction.

An even count indicates the processor
is in MMX state. an odd count indicates
it is in FP state.

The count may be used to estimate the penalty in
transitions between floating-point state and MMX state.

2EH

BUS_UTILIZATION_
DUE_TO_
PROCESSOR_
ACTIVITY
(Counter 0)

Number of clocks the bus is busy due
to the processor’s own activity (the
bus activity that is caused by the
processor)

2EH

WRITES_TO_
NONCACHEABLE_
MEMORY
(Counter 1)

Number of write accesses to
noncacheable memory

2FH

SATURATING_
MMX_
INSTRUCTIONS_
EXECUTED (Counter
0)

Number of saturating MMX
instructions executed, independently
of whether they actually saturated.

2FH

SATURATIONS_
PERFORMED
(Counter 1)

Number of MMX instructions that used
saturating arithmetic when at least
one of its results actually saturated

If an MMX instruction operating on 4 doublewords
saturated in three out of the four results, the counter will
be incremented by one only.

30H

NUMBER_OF_
CYCLES_NOT_IN_
HALT_STATE
(Counter 0)

Number of cycles the processor is not
idle due to HLT instruction

This event will enable the user to calculate “net CPI”. Note
that during the time that the processor is executing the
HLT instruction, the Time-Stamp Counter is not disabled.
Since this event is controlled by the Counter Controls CC0,
CC1 it can be used to calculate the CPI at CPL=3, which
the TSC cannot provide.

30H

DATA_CACHE_
TLB_MISS_
STALL_DURATION
(Counter 1)

Number of clocks the pipeline is stalled
due to a data cache translation lookaside buffer (TLB) miss

31H

MMX_
INSTRUCTION_
DATA_READS
(Counter 0)

Number of MMX instruction data reads

31H

MMX_
INSTRUCTION_
DATA_READ_
MISSES
(Counter 1)

Number of MMX instruction data read
misses

32H

FLOATING_POINT_S Number of clocks while pipe is stalled
TALLS_DURATION
due to a floating-point freeze
(Counter 0)

32H

TAKEN_BRANCHES
(Counter 1)

19-244 Vol. 3B

The count includes write cycles caused by TLB misses and
I/O write cycles.
Cycles restarted due to BOFF# are not re-counted.

Number of taken branches

PERFORMANCE MONITORING EVENTS

Table 19-41. Events That Can Be Counted with Pentium Processor Performance Monitoring Counters (Contd.)
Event
Num.

Mnemonic Event
Name

Description

Comments

33H

D1_STARVATION_
AND_FIFO_IS_
EMPTY
(Counter 0)

Number of times D1 stage cannot
issue ANY instructions since the FIFO
buffer is empty

The D1 stage can issue 0, 1, or 2 instructions per clock if
those are available in an instructions FIFO buffer.

33H

D1_STARVATION_
AND_ONLY_ONE_
INSTRUCTION_IN_
FIFO
(Counter 1)

Number of times the D1 stage issues a
single instruction (since the FIFO
buffer had just one instruction ready)

The D1 stage can issue 0, 1, or 2 instructions per clock if
those are available in an instructions FIFO buffer.

34H

MMX_
INSTRUCTION_
DATA_WRITES
(Counter 0)

Number of data writes caused by MMX
instructions

34H

MMX_
INSTRUCTION_
DATA_WRITE_
MISSES
(Counter 1)

Number of data write misses caused
by MMX instructions

35H

PIPELINE_
FLUSHES_DUE_
TO_WRONG_
BRANCH_
PREDICTIONS
(Counter 0)

Number of pipeline flushes due to
wrong branch predictions resolved in
either the E-stage or the WB-stage

35H

PIPELINE_
FLUSHES_DUE_
TO_WRONG_
BRANCH_
PREDICTIONS_
RESOLVED_IN_
WB-STAGE
(Counter 1)

Number of pipeline flushes due to
wrong branch predictions resolved in
the WB-stage

36H

MISALIGNED_
DATA_MEMORY_
REFERENCE_ON_
MMX_
INSTRUCTIONS
(Counter 0)

Number of misaligned data memory
references when executing MMX
instructions

36H

PIPELINE_
ISTALL_FOR_MMX_
INSTRUCTION_
DATA_MEMORY_
READS
(Counter 1)

Number clocks during pipeline stalls
caused by waits form MMX instruction
data memory reads

When combined with the previously defined events,
Instruction Executed (16H) and Instruction Executed in
the V-pipe (17H), this event enables the user to calculate
the numbers of time pairing rules prevented issuing of
two instructions.

The count includes any pipeline flush due to a branch that
the pipeline did not follow correctly. It includes cases
where a branch was not in the BTB, cases where a branch
was in the BTB but was mispredicted, and cases where a
branch was correctly predicted but to the wrong address.
Branches are resolved in either the Execute stage
(E-stage) or the Writeback stage (WB-stage). In the later
case, the misprediction penalty is larger by one clock. The
difference between the 35H event count in counter 0 and
counter 1 is the number of E-stage resolved branches.
See note for event 35H (Counter 0).

T3:

Vol. 3B 19-245

PERFORMANCE MONITORING EVENTS

Table 19-41. Events That Can Be Counted with Pentium Processor Performance Monitoring Counters (Contd.)
Event
Num.

Mnemonic Event
Name

Description

Comments

37H

MISPREDICTED_
OR_
UNPREDICTED_
RETURNS
(Counter 1)

Number of returns predicted
incorrectly or not predicted at all

The count is the difference between the total number of
executed returns and the number of returns that were
correctly predicted. Only RET instructions are counted (for
example, IRET instructions are not counted).

37H

PREDICTED_
RETURNS
(Counter 1)

Number of predicted returns (whether
they are predicted correctly and
incorrectly

Only RET instructions are counted (for example, IRET
instructions are not counted).

38H

MMX_MULTIPLY_
UNIT_INTERLOCK
(Counter 0)

Number of clocks the pipe is stalled
since the destination of previous MMX
multiply instruction is not ready yet

The counter will not be incremented if there is another
cause for a stall. For each occurrence of a multiply
interlock, this event will be counted twice (if the stalled
instruction comes on the next clock after the multiply) or
by once (if the stalled instruction comes two clocks after
the multiply).

38H

MOVD/MOVQ_
STORE_STALL_
DUE_TO_
PREVIOUS_MMX_
OPERATION
(Counter 1)

Number of clocks a MOVD/MOVQ
instruction store is stalled in D2 stage
due to a previous MMX operation with
a destination to be used in the store
instruction.

39H

RETURNS
(Counter 0)

Number or returns executed.

Only RET instructions are counted; IRET instructions are
not counted. Any exception taken on a RET instruction
and any interrupt recognized by the processor on the
instruction boundary prior to the execution of the RET
instruction will also cause this counter to be incremented.

39H

Reserved

3AH

BTB_FALSE_
ENTRIES
(Counter 0)

Number of false entries in the Branch
Target Buffer

False entries are causes for misprediction other than a
wrong prediction.

3AH

BTB_MISS_
PREDICTION_ON_
NOT-TAKEN_
BRANCH
(Counter 1)

Number of times the BTB predicted a
not-taken branch as taken

3BH

FULL_WRITE_
BUFFER_STALL_
DURATION_
WHILE_
EXECUTING_MMX_I
NSTRUCTIONS
(Counter 0)

Number of clocks while the pipeline is
stalled due to full write buffers while
executing MMX instructions

3BH

STALL_ON_MMX_
INSTRUCTION_
WRITE_TO E-_OR_
M-STATE_LINE
(Counter 1)

Number of clocks during stalls on MMX
instructions writing to E- or M-state
lines

19-246 Vol. 3B

CHAPTER 20
8086 EMULATION
IA-32 processors (beginning with the Intel386 processor) provide two ways to execute new or legacy programs
that are assembled and/or compiled to run on an Intel 8086 processor:

•
•

Real-address mode.
Virtual-8086 mode.

Figure 2-3 shows the relationship of these operating modes to protected mode and system management mode
(SMM).
When the processor is powered up or reset, it is placed in the real-address mode. This operating mode almost
exactly duplicates the execution environment of the Intel 8086 processor, with some extensions. Virtually any
program assembled and/or compiled to run on an Intel 8086 processor will run on an IA-32 processor in this mode.
When running in protected mode, the processor can be switched to virtual-8086 mode to run 8086 programs. This
mode also duplicates the execution environment of the Intel 8086 processor, with extensions. In virtual-8086
mode, an 8086 program runs as a separate protected-mode task. Legacy 8086 programs are thus able to run
under an operating system (such as Microsoft Windows*) that takes advantage of protected mode and to use
protected-mode facilities, such as the protected-mode interrupt- and exception-handling facilities. Protected-mode
multitasking permits multiple virtual-8086 mode tasks (with each task running a separate 8086 program) to be run
on the processor along with other non-virtual-8086 mode tasks.
This section describes both the basic real-address mode execution environment and the virtual-8086-mode execution environment, available on the IA-32 processors beginning with the Intel386 processor.

20.1

REAL-ADDRESS MODE

The IA-32 architecture’s real-address mode runs programs written for the Intel 8086, Intel 8088, Intel 80186, and
Intel 80188 processors, or for the real-address mode of the Intel 286, Intel386, Intel486, Pentium, P6 family,
Pentium 4, and Intel Xeon processors.
The execution environment of the processor in real-address mode is designed to duplicate the execution environment of the Intel 8086 processor. To an 8086 program, a processor operating in real-address mode behaves like a
high-speed 8086 processor. The principal features of this architecture are defined in Chapter 3, “Basic Execution
Environment”, of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.
The following is a summary of the core features of the real-address mode execution environment as would be seen
by a program written for the 8086:

•

The processor supports a nominal 1-MByte physical address space (see Section 20.1.1, “Address Translation in
Real-Address Mode”, for specific details). This address space is divided into segments, each of which can be up
to 64 KBytes in length. The base of a segment is specified with a 16-bit segment selector, which is shifted left
by 4 bits to form a 20-bit offset from address 0 in the address space. An operand within a segment is addressed
with a 16-bit offset from the base of the segment. A physical address is thus formed by adding the offset to the
20-bit segment base (see Section 20.1.1, “Address Translation in Real-Address Mode”).

•

All operands in “native 8086 code” are 8-bit or 16-bit values. (Operand size override prefixes can be used to
access 32-bit operands.)

•

Eight 16-bit general-purpose registers are provided: AX, BX, CX, DX, SP, BP, SI, and DI. The extended 32 bit
registers (EAX, EBX, ECX, EDX, ESP, EBP, ESI, and EDI) are accessible to programs that explicitly perform a size
override operation.

•

Four segment registers are provided: CS, DS, SS, and ES. (The FS and GS registers are accessible to programs
that explicitly access them.) The CS register contains the segment selector for the code segment; the DS and
ES registers contain segment selectors for data segments; and the SS register contains the segment selector
for the stack segment.

•

The 8086 16-bit instruction pointer (IP) is mapped to the lower 16-bits of the EIP register. Note this register is
a 32-bit register and unintentional address wrapping may occur.
Vol. 3B 20-1

8086 EMULATION

•

The 16-bit FLAGS register contains status and control flags. (This register is mapped to the 16 least significant
bits of the 32-bit EFLAGS register.)

•

All of the Intel 8086 instructions are supported (see Section 20.1.3, “Instructions Supported in Real-Address
Mode”).

•

A single, 16-bit-wide stack is provided for handling procedure calls and invocations of interrupt and exception
handlers. This stack is contained in the stack segment identified with the SS register. The SP (stack pointer)
register contains an offset into the stack segment. The stack grows down (toward lower segment offsets) from
the stack pointer. The BP (base pointer) register also contains an offset into the stack segment that can be used
as a pointer to a parameter list. When a CALL instruction is executed, the processor pushes the current
instruction pointer (the 16 least-significant bits of the EIP register and, on far calls, the current value of the CS
register) onto the stack. On a return, initiated with a RET instruction, the processor pops the saved instruction
pointer from the stack into the EIP register (and CS register on far returns). When an implicit call to an interrupt
or exception handler is executed, the processor pushes the EIP, CS, and EFLAGS (low-order 16-bits only)
registers onto the stack. On a return from an interrupt or exception handler, initiated with an IRET instruction,
the processor pops the saved instruction pointer and EFLAGS image from the stack into the EIP, CS, and
EFLAGS registers.

•

A single interrupt table, called the “interrupt vector table” or “interrupt table,” is provided for handling
interrupts and exceptions (see Figure 20-2). The interrupt table (which has 4-byte entries) takes the place of
the interrupt descriptor table (IDT, with 8-byte entries) used when handling protected-mode interrupts and
exceptions. Interrupt and exception vector numbers provide an index to entries in the interrupt table. Each
entry provides a pointer (called a “vector”) to an interrupt- or exception-handling procedure. See Section
20.1.4, “Interrupt and Exception Handling”, for more details. It is possible for software to relocate the IDT by
means of the LIDT instruction on IA-32 processors beginning with the Intel386 processor.

•

The x87 FPU is active and available to execute x87 FPU instructions in real-address mode. Programs written to
run on the Intel 8087 and Intel 287 math coprocessors can be run in real-address mode without modification.

The following extensions to the Intel 8086 execution environment are available in the IA-32 architecture’s realaddress mode. If backwards compatibility to Intel 286 and Intel 8086 processors is required, these features should
not be used in new programs written to run in real-address mode.

•
•

Two additional segment registers (FS and GS) are available.

•

The 32-bit operand prefix can be used in real-address mode programs to execute the 32-bit forms of instructions. This prefix also allows real-address mode programs to use the processor’s 32-bit general-purpose
registers.

•

The 32-bit address prefix can be used in real-address mode programs, allowing 32-bit offsets.

Many of the integer and system instructions that have been added to later IA-32 processors can be executed in
real-address mode (see Section 20.1.3, “Instructions Supported in Real-Address Mode”).

The following sections describe address formation, registers, available instructions, and interrupt and exception
handling in real-address mode. For information on I/O in real-address mode, see Chapter 18, “Input/Output”, of
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1.

20.1.1

Address Translation in Real-Address Mode

In real-address mode, the processor does not interpret segment selectors as indexes into a descriptor table;
instead, it uses them directly to form linear addresses as the 8086 processor does. It shifts the segment selector
left by 4 bits to form a 20-bit base address (see Figure 20-1). The offset into a segment is added to the base
address to create a linear address that maps directly to the physical address space.
When using 8086-style address translation, it is possible to specify addresses larger than 1 MByte. For example,
with a segment selector value of FFFFH and an offset of FFFFH, the linear (and physical) address would be 10FFEFH
(1 megabyte plus 64 KBytes). The 8086 processor, which can form addresses only up to 20 bits long, truncates the
high-order bit, thereby “wrapping” this address to FFEFH. When operating in real-address mode, however, the
processor does not truncate such an address and uses it as a physical address. (Note, however, that for IA-32
processors beginning with the Intel486 processor, the A20M# signal can be used in real-address mode to mask
address line A20, thereby mimicking the 20-bit wrap-around behavior of the 8086 processor.) Care should be take
to ensure that A20M# based address wrapping is handled correctly in multiprocessor based system.

20-2 Vol. 3B

8086 EMULATION

19

4 3

Base

+
Offset

=

16-bit Segment Selector
19

0

0 0 0 0

16 15

0 0 0 0

0

16-bit Effective Address

19

Linear
Address

0

20-bit Linear Address

Figure 20-1. Real-Address Mode Address Translation
The IA-32 processors beginning with the Intel386 processor can generate 32-bit offsets using an address override
prefix; however, in real-address mode, the value of a 32-bit offset may not exceed FFFFH without causing an
exception.
For full compatibility with Intel 286 real-address mode, pseudo-protection faults (interrupt 12 or 13) occur if a 32bit offset is generated outside the range 0 through FFFFH.

20.1.2

Registers Supported in Real-Address Mode

The register set available in real-address mode includes all the registers defined for the 8086 processor plus the
new registers introduced in later IA-32 processors, such as the FS and GS segment registers, the debug registers,
the control registers, and the floating-point unit registers. The 32-bit operand prefix allows a real-address mode
program to use the 32-bit general-purpose registers (EAX, EBX, ECX, EDX, ESP, EBP, ESI, and EDI).

20.1.3

Instructions Supported in Real-Address Mode

The following instructions make up the core instruction set for the 8086 processor. If backwards compatibility to
the Intel 286 and Intel 8086 processors is required, only these instructions should be used in a new program
written to run in real-address mode.

•

Move (MOV) instructions that move operands between general-purpose registers, segment registers, and
between memory and general-purpose registers.

•
•
•
•
•
•
•
•
•
•
•
•
•
•

The exchange (XCHG) instruction.
Load segment register instructions LDS and LES.
Arithmetic instructions ADD, ADC, SUB, SBB, MUL, IMUL, DIV, IDIV, INC, DEC, CMP, and NEG.
Logical instructions AND, OR, XOR, and NOT.
Decimal instructions DAA, DAS, AAA, AAS, AAM, and AAD.
Stack instructions PUSH and POP (to general-purpose registers and segment registers).
Type conversion instructions CWD, CDQ, CBW, and CWDE.
Shift and rotate instructions SAL, SHL, SHR, SAR, ROL, ROR, RCL, and RCR.
TEST instruction.
Control instructions JMP, Jcc, CALL, RET, LOOP, LOOPE, and LOOPNE.
Interrupt instructions INT n, INTO, and IRET.
EFLAGS control instructions STC, CLC, CMC, CLD, STD, LAHF, SAHF, PUSHF, and POPF.
I/O instructions IN, INS, OUT, and OUTS.
Load effective address (LEA) instruction, and translate (XLATB) instruction.

Vol. 3B 20-3

8086 EMULATION

•
•
•
•

LOCK prefix.
Repeat prefixes REP, REPE, REPZ, REPNE, and REPNZ.
Processor halt (HLT) instruction.
No operation (NOP) instruction.

The following instructions, added to later IA-32 processors (some in the Intel 286 processor and the remainder in
the Intel386 processor), can be executed in real-address mode, if backwards compatibility to the Intel 8086
processor is not required.

•
•
•
•
•
•
•
•
•
•

Move (MOV) instructions that operate on the control and debug registers.

•
•
•
•
•
•

Double shift instructions SHLD and SHRD.

Load segment register instructions LSS, LFS, and LGS.
Generalized multiply instructions and multiply immediate data.
Shift and rotate by immediate counts.
Stack instructions PUSHA, PUSHAD, POPA and POPAD, and PUSH immediate data.
Move with sign extension instructions MOVSX and MOVZX.
Long-displacement Jcc instructions.
Exchange instructions CMPXCHG, CMPXCHG8B, and XADD.
String instructions MOVS, CMPS, SCAS, LODS, and STOS.
Bit test and bit scan instructions BT, BTS, BTR, BTC, BSF, and BSR; the byte-set-on condition instruction SETcc;
and the byte swap (BSWAP) instruction.
EFLAGS control instructions PUSHF and POPF.
ENTER and LEAVE control instructions.
BOUND instruction.
CPU identification (CPUID) instruction.
System instructions CLTS, INVD, WINVD, INVLPG, LGDT, SGDT, LIDT, SIDT, LMSW, SMSW, RDMSR, WRMSR,
RDTSC, and RDPMC.

Execution of any of the other IA-32 architecture instructions (not given in the previous two lists) in real-address
mode result in an invalid-opcode exception (#UD) being generated.

20.1.4

Interrupt and Exception Handling

When operating in real-address mode, software must provide interrupt and exception-handling facilities that are
separate from those provided in protected mode. Even during the early stages of processor initialization when the
processor is still in real-address mode, elementary real-address mode interrupt and exception-handling facilities
must be provided to insure reliable operation of the processor, or the initialization code must insure that no interrupts or exceptions will occur.
The IA-32 processors handle interrupts and exceptions in real-address mode similar to the way they handle them
in protected mode. When a processor receives an interrupt or generates an exception, it uses the vector number of
the interrupt or exception as an index into the interrupt table. (In protected mode, the interrupt table is called the
interrupt descriptor table (IDT), but in real-address mode, the table is usually called the interrupt vector
table, or simply the interrupt table.) The entry in the interrupt vector table provides a pointer to an interrupt- or
exception-handler procedure. (The pointer consists of a segment selector for a code segment and a 16-bit offset
into the segment.) The processor performs the following actions to make an implicit call to the selected handler:
1. Pushes the current values of the CS and EIP registers onto the stack. (Only the 16 least-significant bits of the
EIP register are pushed.)
2. Pushes the low-order 16 bits of the EFLAGS register onto the stack.
3. Clears the IF flag in the EFLAGS register to disable interrupts.
4. Clears the TF, RF, and AC flags, in the EFLAGS register.

20-4 Vol. 3B

8086 EMULATION

5. Transfers program control to the location specified in the interrupt vector table.
An IRET instruction at the end of the handler procedure reverses these steps to return program control to the interrupted program. Exceptions do not return error codes in real-address mode.
The interrupt vector table is an array of 4-byte entries (see Figure 20-2). Each entry consists of a far pointer to a
handler procedure, made up of a segment selector and an offset. The processor scales the interrupt or exception
vector by 4 to obtain an offset into the interrupt table. Following reset, the base of the interrupt vector table is
located at physical address 0 and its limit is set to 3FFH. In the Intel 8086 processor, the base address and limit of
the interrupt vector table cannot be changed. In the later IA-32 processors, the base address and limit of the interrupt vector table are contained in the IDTR register and can be changed using the LIDT instruction.
(For backward compatibility to Intel 8086 processors, the default base address and limit of the interrupt vector
table should not be changed.)

Up to Entry 255
Entry 3
12
Entry 2

8

Entry 1
4
Interrupt Vector 0*

Segment Selector

2

Offset

0

15
* Interrupt vector number 0 selects entry 0
(called “interrupt vector 0”) in the interrupt
vector table. Interrupt vector 0 in turn
points to the start of the interrupt handler
for interrupt 0.

0
IDTR

Figure 20-2. Interrupt Vector Table in Real-Address Mode
Table 20-1 shows the interrupt and exception vectors that can be generated in real-address mode and virtual-8086
mode, and in the Intel 8086 processor. See Chapter 6, “Interrupt and Exception Handling”, for a description of the
exception conditions.

20.2

VIRTUAL-8086 MODE

Virtual-8086 mode is actually a special type of a task that runs in protected mode. When the operating-system or
executive switches to a virtual-8086-mode task, the processor emulates an Intel 8086 processor. The execution
environment of the processor while in the 8086-emulation state is the same as is described in Section 20.1, “RealAddress Mode” for real-address mode, including the extensions. The major difference between the two modes is
that in virtual-8086 mode the 8086 emulator uses some protected-mode services (such as the protected-mode
interrupt and exception-handling and paging facilities).

Vol. 3B 20-5

8086 EMULATION

As in real-address mode, any new or legacy program that has been assembled and/or compiled to run on an Intel
8086 processor will run in a virtual-8086-mode task. And several 8086 programs can be run as virtual-8086-mode
tasks concurrently with normal protected-mode tasks, using the processor’s multitasking facilities.

Table 20-1. Real-Address Mode Exceptions and Interrupts
Vector
No.

Description

Real-Address Mode

Virtual-8086 Mode

Intel 8086 Processor

0

Divide Error (#DE)

Yes

Yes

Yes

1

Debug Exception (#DB)

Yes

Yes

No

2

NMI Interrupt

Yes

Yes

Yes

3

Breakpoint (#BP)

Yes

Yes

Yes

4

Overflow (#OF)

Yes

Yes

Yes

5

BOUND Range Exceeded (#BR)

Yes

Yes

Reserved

6

Invalid Opcode (#UD)

Yes

Yes

Reserved

7

Device Not Available (#NM)

Yes

Yes

Reserved

8

Double Fault (#DF)

Yes

Yes

Reserved

9

(Intel reserved. Do not use.)

Reserved

Reserved

Reserved

10

Invalid TSS (#TS)

Reserved

Yes

Reserved

11

Segment Not Present (#NP)

Reserved

Yes

Reserved

12

Stack Fault (#SS)

Yes

Yes

Reserved

13

General Protection (#GP)*

Yes

Yes

Reserved

14

Page Fault (#PF)

Reserved

Yes

Reserved

15

(Intel reserved. Do not use.)

Reserved

Reserved

Reserved

16

Floating-Point Error (#MF)

Yes

Yes

Reserved

17

Alignment Check (#AC)

Reserved

Yes

Reserved

18

Machine Check (#MC)

Yes

Yes

Reserved

19-31

(Intel reserved. Do not use.)

Reserved

Reserved

Reserved

32-255

User Defined Interrupts

Yes

Yes

Yes

NOTE:
* In the real-address mode, vector 13 is the segment overrun exception. In protected and virtual-8086 modes, this exception covers all general-protection error conditions, including traps to the virtual-8086 monitor from virtual-8086 mode.

20.2.1

Enabling Virtual-8086 Mode

The processor runs in virtual-8086 mode when the VM (virtual machine) flag in the EFLAGS register is set. This flag
can only be set when the processor switches to a new protected-mode task or resumes virtual-8086 mode via an
IRET instruction.
System software cannot change the state of the VM flag directly in the EFLAGS register (for example, by using the
POPFD instruction). Instead it changes the flag in the image of the EFLAGS register stored in the TSS or on the
stack following a call to an interrupt- or exception-handler procedure. For example, software sets the VM flag in the
EFLAGS image in the TSS when first creating a virtual-8086 task.
The processor tests the VM flag under three general conditions:

•
•

When loading segment registers, to determine whether to use 8086-style address translation.
When decoding instructions, to determine which instructions are not supported in virtual-8086 mode and which
instructions are sensitive to IOPL.

20-6 Vol. 3B

8086 EMULATION

•

When checking privileged instructions, on page accesses, or when performing other permission checks.
(Virtual-8086 mode always executes at CPL 3.)

20.2.2

Structure of a Virtual-8086 Task

A virtual-8086-mode task consists of the following items:

•
•
•
•

A 32-bit TSS for the task.
The 8086 program.
A virtual-8086 monitor.
8086 operating-system services.

The TSS of the new task must be a 32-bit TSS, not a 16-bit TSS, because the 16-bit TSS does not load the mostsignificant word of the EFLAGS register, which contains the VM flag. All TSS’s, stacks, data, and code used to handle
exceptions when in virtual-8086 mode must also be 32-bit segments.
The processor enters virtual-8086 mode to run the 8086 program and returns to protected mode to run the virtual8086 monitor.
The virtual-8086 monitor is a 32-bit protected-mode code module that runs at a CPL of 0. The monitor consists of
initialization, interrupt- and exception-handling, and I/O emulation procedures that emulate a personal computer
or other 8086-based platform. Typically, the monitor is either part of or closely associated with the protected-mode
general-protection (#GP) exception handler, which also runs at a CPL of 0. As with any protected-mode code
module, code-segment descriptors for the virtual-8086 monitor must exist in the GDT or in the task’s LDT. The
virtual-8086 monitor also may need data-segment descriptors so it can examine the IDT or other parts of the 8086
program in the first 1 MByte of the address space. The linear addresses above 10FFEFH are available for the
monitor, the operating system, and other system software.
The 8086 operating-system services consists of a kernel and/or operating-system procedures that the 8086
program makes calls to. These services can be implemented in either of the following two ways:

•

They can be included in the 8086 program. This approach is desirable for either of the following reasons:
— The 8086 program code modifies the 8086 operating-system services.
— There is not sufficient development time to merge the 8086 operating-system services into main operating
system or executive.

•

They can be implemented or emulated in the virtual-8086 monitor. This approach is desirable for any of the
following reasons:
— The 8086 operating-system procedures can be more easily coordinated among several virtual-8086 tasks.
— Memory can be saved by not duplicating 8086 operating-system procedure code for several virtual-8086
tasks.
— The 8086 operating-system procedures can be easily emulated by calls to the main operating system or
executive.

The approach chosen for implementing the 8086 operating-system services may result in different virtual-8086mode tasks using different 8086 operating-system services.

20.2.3

Paging of Virtual-8086 Tasks

Even though a program running in virtual-8086 mode can use only 20-bit linear addresses, the processor converts
these addresses into 32-bit linear addresses before mapping them to the physical address space. If paging is being
used, the 8086 address space for a program running in virtual-8086 mode can be paged and located in a set of
pages in physical address space. If paging is used, it is transparent to the program running in virtual-8086 mode
just as it is for any task running on the processor.
Paging is not necessary for a single virtual-8086-mode task, but paging is useful or necessary in the following situations:

Vol. 3B 20-7

8086 EMULATION

•

When running multiple virtual-8086-mode tasks. Here, paging allows the lower 1 MByte of the linear address
space for each virtual-8086-mode task to be mapped to a different physical address location.

•

When emulating the 8086 address-wraparound that occurs at 1 MByte. When using 8086-style address translation, it is possible to specify addresses larger than 1 MByte. These addresses automatically wraparound in the
Intel 8086 processor (see Section 20.1.1, “Address Translation in Real-Address Mode”). If any 8086 programs
depend on address wraparound, the same effect can be achieved in a virtual-8086-mode task by mapping the
linear addresses between 100000H and 110000H and linear addresses between 0 and 10000H to the same
physical addresses.

•

When sharing the 8086 operating-system services or ROM code that is common to several 8086 programs
running as different 8086-mode tasks.

•

When redirecting or trapping references to memory-mapped I/O devices.

20.2.4

Protection within a Virtual-8086 Task

Protection is not enforced between the segments of an 8086 program. Either of the following techniques can be
used to protect the system software running in a virtual-8086-mode task from the 8086 program:

•

Reserve the first 1 MByte plus 64 KBytes of each task’s linear address space for the 8086 program. An 8086
processor task cannot generate addresses outside this range.

•

Use the U/S flag of page-table entries to protect the virtual-8086 monitor and other system software in the
virtual-8086 mode task space. When the processor is in virtual-8086 mode, the CPL is 3. Therefore, an 8086
processor program has only user privileges. If the pages of the virtual-8086 monitor have supervisor privilege,
they cannot be accessed by the 8086 program.

20.2.5

Entering Virtual-8086 Mode

Figure 20-3 summarizes the methods of entering and leaving virtual-8086 mode. The processor switches to
virtual-8086 mode in either of the following situations:

•

Task switch when the VM flag is set to 1 in the EFLAGS register image stored in the TSS for the task. Here the
task switch can be initiated in either of two ways:
— A CALL or JMP instruction.
— An IRET instruction, where the NT flag in the EFLAGS image is set to 1.

•

Return from a protected-mode interrupt or exception handler when the VM flag is set to 1 in the EFLAGS
register image on the stack.

When a task switch is used to enter virtual-8086 mode, the TSS for the virtual-8086-mode task must be a 32-bit
TSS. (If the new TSS is a 16-bit TSS, the upper word of the EFLAGS register is not in the TSS, causing the processor
to clear the VM flag when it loads the EFLAGS register.) The processor updates the VM flag prior to loading the
segment registers from their images in the new TSS. The new setting of the VM flag determines whether the
processor interprets the contents of the segment registers as 8086-style segment selectors or protected-mode
segment selectors. When the VM flag is set, the segment registers are loaded from the TSS, using 8086-style
address translation to form base addresses.
See Section 20.3, “Interrupt and Exception Handling in Virtual-8086 Mode”, for information on entering virtual8086 mode on a return from an interrupt or exception handler.

20-8 Vol. 3B

8086 EMULATION

Real Mode
Code

Real-Address
Mode

PE=0 or
RESET

PE=1

Protected
Mode

ProtectedMode Tasks

Task Switch1

Task Switch
VM=0

ProtectedMode Interrupt
and Exception
Handlers

CALL
Virtual-8086
Monitor
RET

VM = 0
VM = 1

Virtual-8086
Mode

Interrupt or
Exception2
RESET

Virtual-8086
Mode Tasks
(8086
Programs)

#GP Exception3
IRET4
IRET5
Redirect Interrupt to 8086 Program
Interrupt or Exception Handler6

NOTES:
1. Task switch carried out in either of two ways:
- CALL or JMP where the VM flag in the EFLAGS image is 1.
- IRET where VM is 1 and NT is 1.
2. Hardware interrupt or exception; software interrupt (INT n) when IOPL is 3.
3. General-protection exception caused by software interrupt (INT n), IRET,
POPF, PUSHF, IN, or OUT when IOPL is less than 3.
4. Normal return from protected-mode interrupt or exception handler.
5. A return from the 8086 monitor to redirect an interrupt or exception back
to an interrupt or exception handler in the 8086 program running in virtual8086 mode.
6. Internal redirection of a software interrupt (INT n) when VME is 1,
IOPL is <3, and the redirection bit is 1.

Figure 20-3. Entering and Leaving Virtual-8086 Mode

20.2.6

Leaving Virtual-8086 Mode

The processor can leave the virtual-8086 mode only through an interrupt or exception. The following are situations
where an interrupt or exception will lead to the processor leaving virtual-8086 mode (see Figure 20-3):

•

The processor services a hardware interrupt generated to signal the suspension of execution of the virtual8086 application. This hardware interrupt may be generated by a timer or other external mechanism. Upon
receiving the hardware interrupt, the processor enters protected mode and switches to a protected-mode (or
another virtual-8086 mode) task either through a task gate in the protected-mode IDT or through a trap or
interrupt gate that points to a handler that initiates a task switch. A task switch from a virtual-8086 task to
another task loads the EFLAGS register from the TSS of the new task. The value of the VM flag in the new
EFLAGS determines if the new task executes in virtual-8086 mode or not.

•

The processor services an exception caused by code executing the virtual-8086 task or services a hardware
interrupt that “belongs to” the virtual-8086 task. Here, the processor enters protected mode and services the

Vol. 3B 20-9

8086 EMULATION

exception or hardware interrupt through the protected-mode IDT (normally through an interrupt or trap gate)
and the protected-mode exception- and interrupt-handlers. The processor may handle the exception or
interrupt within the context of the virtual 8086 task and return to virtual-8086 mode on a return from the
handler procedure. The processor may also execute a task switch and handle the exception or interrupt in the
context of another task.

•

The processor services a software interrupt generated by code executing in the virtual-8086 task (such as a
software interrupt to call a MS-DOS* operating system routine). The processor provides several methods of
handling these software interrupts, which are discussed in detail in Section 20.3.3, “Class 3—Software
Interrupt Handling in Virtual-8086 Mode”. Most of them involve the processor entering protected mode, often
by means of a general-protection (#GP) exception. In protected mode, the processor can send the interrupt to
the virtual-8086 monitor for handling and/or redirect the interrupt back to the application program running in
virtual-8086 mode task for handling.
IA-32 processors that incorporate the virtual mode extension (enabled with the VME flag in control register
CR4) are capable of redirecting software-generated interrupts back to the program’s interrupt handlers without
leaving virtual-8086 mode. See Section 20.3.3.4, “Method 5: Software Interrupt Handling”, for more
information on this mechanism.

•

A hardware reset initiated by asserting the RESET or INIT pin is a special kind of interrupt. When a RESET or
INIT is signaled while the processor is in virtual-8086 mode, the processor leaves virtual-8086 mode and enters
real-address mode.

•

Execution of the HLT instruction in virtual-8086 mode will cause a general-protection (GP#) fault, which the
protected-mode handler generally sends to the virtual-8086 monitor. The virtual-8086 monitor then
determines the correct execution sequence after verifying that it was entered as a result of a HLT execution.

See Section 20.3, “Interrupt and Exception Handling in Virtual-8086 Mode”, for information on leaving virtual-8086
mode to handle an interrupt or exception generated in virtual-8086 mode.

20.2.7

Sensitive Instructions

When an IA-32 processor is running in virtual-8086 mode, the CLI, STI, PUSHF, POPF, INT n, and IRET instructions
are sensitive to IOPL. The IN, INS, OUT, and OUTS instructions, which are sensitive to IOPL in protected mode, are
not sensitive in virtual-8086 mode.
The CPL is always 3 while running in virtual-8086 mode; if the IOPL is less than 3, an attempt to use the IOPL-sensitive instructions listed above triggers a general-protection exception (#GP). These instructions are sensitive to
IOPL to give the virtual-8086 monitor a chance to emulate the facilities they affect.

20.2.8

Virtual-8086 Mode I/O

Many 8086 programs written for non-multitasking systems directly access I/O ports. This practice may cause problems in a multitasking environment. If more than one program accesses the same port, they may interfere with
each other. Most multitasking systems require application programs to access I/O ports through the operating
system. This results in simplified, centralized control.
The processor provides I/O protection for creating I/O that is compatible with the environment and transparent to
8086 programs. Designers may take any of several possible approaches to protecting I/O ports:

•
•
•
•

Protect the I/O address space and generate exceptions for all attempts to perform I/O directly.
Let the 8086 program perform I/O directly.
Generate exceptions on attempts to access specific I/O ports.
Generate exceptions on attempts to access specific memory-mapped I/O ports.

The method of controlling access to I/O ports depends upon whether they are I/O-port mapped or memory
mapped.

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8086 EMULATION

20.2.8.1

I/O-Port-Mapped I/O

The I/O permission bit map in the TSS can be used to generate exceptions on attempts to access specific I/O port
addresses. The I/O permission bit map of each virtual-8086-mode task determines which I/O addresses generate
exceptions for that task. Because each task may have a different I/O permission bit map, the addresses that
generate exceptions for one task may be different from the addresses for another task. This differs from protected
mode in which, if the CPL is less than or equal to the IOPL, I/O access is allowed without checking the I/O permission bit map. See Chapter 18, “Input/Output”, in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1, for more information about the I/O permission bit map.

20.2.8.2

Memory-Mapped I/O

In systems which use memory-mapped I/O, the paging facilities of the processor can be used to generate exceptions for attempts to access I/O ports. The virtual-8086 monitor may use paging to control memory-mapped I/O in
these ways:

•

Map part of the linear address space of each task that needs to perform I/O to the physical address space
where I/O ports are placed. By putting the I/O ports at different addresses (in different pages), the paging
mechanism can enforce isolation between tasks.

•

Map part of the linear address space to pages that are not-present. This generates an exception whenever a
task attempts to perform I/O to those pages. System software then can interpret the I/O operation being
attempted.

Software emulation of the I/O space may require too much operating system intervention under some conditions.
In these cases, it may be possible to generate an exception for only the first attempt to access I/O. The system
software then may determine whether a program can be given exclusive control of I/O temporarily, the protection
of the I/O space may be lifted, and the program allowed to run at full speed.

20.2.8.3

Special I/O Buffers

Buffers of intelligent controllers (for example, a bit-mapped frame buffer) also can be emulated using page
mapping. The linear space for the buffer can be mapped to a different physical space for each virtual-8086-mode
task. The virtual-8086 monitor then can control which virtual buffer to copy onto the real buffer in the physical
address space.

20.3

INTERRUPT AND EXCEPTION HANDLING IN VIRTUAL-8086 MODE

When the processor receives an interrupt or detects an exception condition while in virtual-8086 mode, it invokes
an interrupt or exception handler, just as it does in protected or real-address mode. The interrupt or exception
handler that is invoked and the mechanism used to invoke it depends on the class of interrupt or exception that has
been detected or generated and the state of various system flags and fields.
In virtual-8086 mode, the interrupts and exceptions are divided into three classes for the purposes of handling:

•

Class 1 — All processor-generated exceptions and all hardware interrupts, including the NMI interrupt and the
hardware interrupts sent to the processor’s external interrupt delivery pins. All class 1 exceptions and
interrupts are handled by the protected-mode exception and interrupt handlers.

•

Class 2 — Special case for maskable hardware interrupts (Section 6.3.2, “Maskable Hardware Interrupts”)
when the virtual mode extensions are enabled.

•

Class 3 — All software-generated interrupts, that is interrupts generated with the INT n instruction1.

The method the processor uses to handle class 2 and 3 interrupts depends on the setting of the following flags and
fields:

•

IOPL field (bits 12 and 13 in the EFLAGS register) — Controls how class 3 software interrupts are handled
when the processor is in virtual-8086 mode (see Section 2.3, “System Flags and Fields in the EFLAGS

1. The INT 3 instruction is a special case (see the description of the INT n instruction in Chapter 3, “Instruction Set Reference, A-L”, of
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A).
Vol. 3B 20-11

8086 EMULATION

Register”). This field also controls the enabling of the VIF and VIP flags in the EFLAGS register when the VME
flag is set. The VIF and VIP flags are provided to assist in the handling of class 2 maskable hardware interrupts.

•

VME flag (bit 0 in control register CR4) — Enables the virtual mode extension for the processor when set
(see Section 2.5, “Control Registers”).

•

Software interrupt redirection bit map (32 bytes in the TSS, see Figure 20-5) — Contains 256 flags
that indicates how class 3 software interrupts should be handled when they occur in virtual-8086 mode. A
software interrupt can be directed either to the interrupt and exception handlers in the currently running 8086
program or to the protected-mode interrupt and exception handlers.

•

The virtual interrupt flag (VIF) and virtual interrupt pending flag (VIP) in the EFLAGS register —
Provides virtual interrupt support for the handling of class 2 maskable hardware interrupts (see Section
20.3.2, “Class 2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the Virtual Interrupt
Mechanism”).

NOTE
The VME flag, software interrupt redirection bit map, and VIF and VIP flags are only available in
IA-32 processors that support the virtual mode extensions. These extensions were introduced in
the IA-32 architecture with the Pentium processor.
The following sections describe the actions that processor takes and the possible actions of interrupt and exception
handlers for the two classes of interrupts described in the previous paragraphs. These sections describe three
possible types of interrupt and exception handlers:

•

Protected-mode interrupt and exceptions handlers — These are the standard handlers that the processor
calls through the protected-mode IDT.

•

Virtual-8086 monitor interrupt and exception handlers — These handlers are resident in the virtual-8086
monitor, and they are commonly accessed through a general-protection exception (#GP, interrupt 13) that is
directed to the protected-mode general-protection exception handler.

•

8086 program interrupt and exception handlers — These handlers are part of the 8086 program that is
running in virtual-8086 mode.

The following sections describe how these handlers are used, depending on the selected class and method of interrupt and exception handling.

20.3.1

Class 1—Hardware Interrupt and Exception Handling in Virtual-8086 Mode

In virtual-8086 mode, the Pentium, P6 family, Pentium 4, and Intel Xeon processors handle hardware interrupts
and exceptions in the same manner as they are handled by the Intel486 and Intel386 processors. They invoke the
protected-mode interrupt or exception handler that the interrupt or exception vector points to in the IDT. Here, the
IDT entry must contain either a 32-bit trap or interrupt gate or a task gate. The following sections describe various
ways that a virtual-8086 mode interrupt or exception can be handled after the protected-mode handler has been
invoked.
See Section 20.3.2, “Class 2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the Virtual Interrupt Mechanism”, for a description of the virtual interrupt mechanism that is available for handling maskable hardware interrupts while in virtual-8086 mode. When this mechanism is either not available or not enabled, maskable
hardware interrupts are handled in the same manner as exceptions, as described in the following sections.

20.3.1.1

Handling an Interrupt or Exception Through a Protected-Mode Trap or Interrupt Gate

When an interrupt or exception vector points to a 32-bit trap or interrupt gate in the IDT, the gate must in turn point
to a nonconforming, privilege-level 0, code segment. When accessing this code segment, processor performs the
following steps.
1. Switches to 32-bit protected mode and privilege level 0.
2. Saves the state of the processor on the privilege-level 0 stack. The states of the EIP, CS, EFLAGS, ESP, SS, ES,
DS, FS, and GS registers are saved (see Figure 20-4).

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8086 EMULATION

3. Clears the segment registers. Saving the DS, ES, FS, and GS registers on the stack and then clearing the
registers lets the interrupt or exception handler safely save and restore these registers regardless of the type
segment selectors they contain (protected-mode or 8086-style). The interrupt and exception handlers, which
may be called in the context of either a protected-mode task or a virtual-8086-mode task, can use the same
code sequences for saving and restoring the registers for any task. Clearing these registers before execution of
the IRET instruction does not cause a trap in the interrupt handler. Interrupt procedures that expect values in
the segment registers or that return values in the segment registers must use the register images saved on the
stack for privilege level 0.
4. Clears VM, NT, RF and TF flags (in the EFLAGS register). If the gate is an interrupt gate, clears the IF flag.
5. Begins executing the selected interrupt or exception handler.
If the trap or interrupt gate references a procedure in a conforming segment or in a segment at a privilege level
other than 0, the processor generates a general-protection exception (#GP). Here, the error code is the segment
selector of the code segment to which a call was attempted.

Without Error Code

Unused

With Error Code

ESP from
TSS

Unused

Old GS

Old GS

Old FS

Old FS

Old DS

Old DS

Old ES

Old ES

Old SS

Old SS

Old ESP

Old ESP

Old EFLAGS

Old EFLAGS

Old CS
Old EIP

ESP from
TSS

Old CS
New ESP

Old EIP
Error Code

New ESP

Figure 20-4. Privilege Level 0 Stack After Interrupt or
Exception in Virtual-8086 Mode
Interrupt and exception handlers can examine the VM flag on the stack to determine if the interrupted procedure
was running in virtual-8086 mode. If so, the interrupt or exception can be handled in one of three ways:

•
•

The protected-mode interrupt or exception handler that was called can handle the interrupt or exception.

•

The virtual-8086 monitor (if called) can in turn pass control back to the 8086 program’s interrupt and exception
handler.

The protected-mode interrupt or exception handler can call the virtual-8086 monitor to handle the interrupt or
exception.

If the interrupt or exception is handled with a protected-mode handler, the handler can return to the interrupted
program in virtual-8086 mode by executing an IRET instruction. This instruction loads the EFLAGS and segment
registers from the images saved in the privilege level 0 stack (see Figure 20-4). A set VM flag in the EFLAGS image
causes the processor to switch back to virtual-8086 mode. The CPL at the time the IRET instruction is executed
must be 0, otherwise the processor does not change the state of the VM flag.

Vol. 3B 20-13

8086 EMULATION

The virtual-8086 monitor runs at privilege level 0, like the protected-mode interrupt and exception handlers. It is
commonly closely tied to the protected-mode general-protection exception (#GP, vector 13) handler. If the
protected-mode interrupt or exception handler calls the virtual-8086 monitor to handle the interrupt or exception,
the return from the virtual-8086 monitor to the interrupted virtual-8086 mode program requires two return
instructions: a RET instruction to return to the protected-mode handler and an IRET instruction to return to the
interrupted program.
The virtual-8086 monitor has the option of directing the interrupt and exception back to an interrupt or exception
handler that is part of the interrupted 8086 program, as described in Section 20.3.1.2, “Handling an Interrupt or
Exception With an 8086 Program Interrupt or Exception Handler”.

20.3.1.2

Handling an Interrupt or Exception With an 8086 Program Interrupt or Exception Handler

Because it was designed to run on an 8086 processor, an 8086 program running in a virtual-8086-mode task
contains an 8086-style interrupt vector table, which starts at linear address 0. If the virtual-8086 monitor correctly
directs an interrupt or exception vector back to the virtual-8086-mode task it came from, the handlers in the 8086
program can handle the interrupt or exception. The virtual-8086 monitor must carry out the following steps to send
an interrupt or exception back to the 8086 program:
1. Use the 8086 interrupt vector to locate the appropriate handler procedure in the 8086 program interrupt table.
2. Store the EFLAGS (low-order 16 bits only), CS and EIP values of the 8086 program on the privilege-level 3
stack. This is the stack that the virtual-8086-mode task is using. (The 8086 handler may use or modify this
information.)
3. Change the return link on the privilege-level 0 stack to point to the privilege-level 3 handler procedure.
4. Execute an IRET instruction to pass control to the 8086 program handler.
5. When the IRET instruction from the privilege-level 3 handler triggers a general-protection exception (#GP) and
thus effectively again calls the virtual-8086 monitor, restore the return link on the privilege-level 0 stack to
point to the original, interrupted, privilege-level 3 procedure.
6. Copy the low order 16 bits of the EFLAGS image from the privilege-level 3 stack to the privilege-level 0 stack
(because some 8086 handlers modify these flags to return information to the code that caused the interrupt).
7. Execute an IRET instruction to pass control back to the interrupted 8086 program.
Note that if an operating system intends to support all 8086 MS-DOS-based programs, it is necessary to use the
actual 8086 interrupt and exception handlers supplied with the program. The reason for this is that some programs
modify their own interrupt vector table to substitute (or hook in series) their own specialized interrupt and exception handlers.

20.3.1.3

Handling an Interrupt or Exception Through a Task Gate

When an interrupt or exception vector points to a task gate in the IDT, the processor performs a task switch to the
selected interrupt- or exception-handling task. The following actions are carried out as part of this task switch:
1. The EFLAGS register with the VM flag set is saved in the current TSS.
2. The link field in the TSS of the called task is loaded with the segment selector of the TSS for the interrupted
virtual-8086-mode task.
3. The EFLAGS register is loaded from the image in the new TSS, which clears the VM flag and causes the
processor to switch to protected mode.
4. The NT flag in the EFLAGS register is set.
5. The processor begins executing the selected interrupt- or exception-handler task.
When an IRET instruction is executed in the handler task and the NT flag in the EFLAGS register is set, the processors switches from a protected-mode interrupt- or exception-handler task back to a virtual-8086-mode task. Here,
the EFLAGS and segment registers are loaded from images saved in the TSS for the virtual-8086-mode task. If the
VM flag is set in the EFLAGS image, the processor switches back to virtual-8086 mode on the task switch. The CPL
at the time the IRET instruction is executed must be 0, otherwise the processor does not change the state of the
VM flag.

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8086 EMULATION

20.3.2

Class 2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the
Virtual Interrupt Mechanism

Maskable hardware interrupts are those interrupts that are delivered through the INTR# pin or through an interrupt request to the local APIC (see Section 6.3.2, “Maskable Hardware Interrupts”). These interrupts can be inhibited (masked) from interrupting an executing program or task by clearing the IF flag in the EFLAGS register.
When the VME flag in control register CR4 is set and the IOPL field in the EFLAGS register is less than 3, two additional flags are activated in the EFLAGS register:

•
•

VIF (virtual interrupt) flag, bit 19 of the EFLAGS register.
VIP (virtual interrupt pending) flag, bit 20 of the EFLAGS register.

These flags provide the virtual-8086 monitor with more efficient control over handling maskable hardware interrupts that occur during virtual-8086 mode tasks. They also reduce interrupt-handling overhead, by eliminating the
need for all IF related operations (such as PUSHF, POPF, CLI, and STI instructions) to trap to the virtual-8086
monitor. The purpose and use of these flags are as follows.

NOTE
The VIF and VIP flags are only available in IA-32 processors that support the virtual mode
extensions. These extensions were introduced in the IA-32 architecture with the Pentium
processor. When this mechanism is either not available or not enabled, maskable hardware
interrupts are handled as class 1 interrupts. Here, if VIF and VIP flags are needed, the virtual-8086
monitor can implement them in software.
Existing 8086 programs commonly set and clear the IF flag in the EFLAGS register to enable and disable maskable
hardware interrupts, respectively; for example, to disable interrupts while handling another interrupt or an exception. This practice works well in single task environments, but can cause problems in multitasking and multipleprocessor environments, where it is often desirable to prevent an application program from having direct control
over the handling of hardware interrupts. When using earlier IA-32 processors, this problem was often solved by
creating a virtual IF flag in software. The IA-32 processors (beginning with the Pentium processor) provide hardware support for this virtual IF flag through the VIF and VIP flags.
The VIF flag is a virtualized version of the IF flag, which an application program running from within a virtual-8086
task can used to control the handling of maskable hardware interrupts. When the VIF flag is enabled, the CLI and
STI instructions operate on the VIF flag instead of the IF flag. When an 8086 program executes the CLI instruction,
the processor clears the VIF flag to request that the virtual-8086 monitor inhibit maskable hardware interrupts
from interrupting program execution; when it executes the STI instruction, the processor sets the VIF flag
requesting that the virtual-8086 monitor enable maskable hardware interrupts for the 8086 program. But actually
the IF flag, managed by the operating system, always controls whether maskable hardware interrupts are enabled.
Also, if under these circumstances an 8086 program tries to read or change the IF flag using the PUSHF or POPF
instructions, the processor will change the VIF flag instead, leaving IF unchanged.
The VIP flag provides software a means of recording the existence of a deferred (or pending) maskable hardware
interrupt. This flag is read by the processor but never explicitly written by the processor; it can only be written by
software.
If the IF flag is set and the VIF and VIP flags are enabled, and the processor receives a maskable hardware interrupt (interrupt vector 0 through 255), the processor performs and the interrupt handler software should perform
the following operations:
1. The processor invokes the protected-mode interrupt handler for the interrupt received, as described in the
following steps. These steps are almost identical to those described for method 1 interrupt and exception
handling in Section 20.3.1.1, “Handling an Interrupt or Exception Through a Protected-Mode Trap or Interrupt
Gate”:
a. Switches to 32-bit protected mode and privilege level 0.
b. Saves the state of the processor on the privilege-level 0 stack. The states of the EIP, CS, EFLAGS, ESP, SS,
ES, DS, FS, and GS registers are saved (see Figure 20-4).
c.

Clears the segment registers.

Vol. 3B 20-15

8086 EMULATION

d. Clears the VM flag in the EFLAGS register.
e. Begins executing the selected protected-mode interrupt handler.
2. The recommended action of the protected-mode interrupt handler is to read the VM flag from the EFLAGS
image on the stack. If this flag is set, the handler makes a call to the virtual-8086 monitor.
3. The virtual-8086 monitor should read the VIF flag in the EFLAGS register.
— If the VIF flag is clear, the virtual-8086 monitor sets the VIP flag in the EFLAGS image on the stack to
indicate that there is a deferred interrupt pending and returns to the protected-mode handler.
— If the VIF flag is set, the virtual-8086 monitor can handle the interrupt if it “belongs” to the 8086 program
running in the interrupted virtual-8086 task; otherwise, it can call the protected-mode interrupt handler to
handle the interrupt.
4. The protected-mode handler executes a return to the program executing in virtual-8086 mode.
5. Upon returning to virtual-8086 mode, the processor continues execution of the 8086 program.
When the 8086 program is ready to receive maskable hardware interrupts, it executes the STI instruction to set the
VIF flag (enabling maskable hardware interrupts). Prior to setting the VIF flag, the processor automatically checks
the VIP flag and does one of the following, depending on the state of the flag:

•
•

If the VIP flag is clear (indicating no pending interrupts), the processor sets the VIF flag.
If the VIP flag is set (indicating a pending interrupt), the processor generates a general-protection exception
(#GP).

The recommended action of the protected-mode general-protection exception handler is to then call the virtual8086 monitor and let it handle the pending interrupt. After handling the pending interrupt, the typical action of the
virtual-8086 monitor is to clear the VIP flag and set the VIF flag in the EFLAGS image on the stack, and then
execute a return to the virtual-8086 mode. The next time the processor receives a maskable hardware interrupt, it
will then handle it as described in steps 1 through 5 earlier in this section.
If the processor finds that both the VIF and VIP flags are set at the beginning of an instruction, it generates a
general-protection exception. This action allows the virtual-8086 monitor to handle the pending interrupt for the
virtual-8086 mode task for which the VIF flag is enabled. Note that this situation can only occur immediately
following execution of a POPF or IRET instruction or upon entering a virtual-8086 mode task through a task switch.
Note that the states of the VIF and VIP flags are not modified in real-address mode or during transitions between
real-address and protected modes.

NOTE
The virtual interrupt mechanism described in this section is also available for use in protected
mode, see Section 20.4, “Protected-Mode Virtual Interrupts”.

20.3.3

Class 3—Software Interrupt Handling in Virtual-8086 Mode

When the processor receives a software interrupt (an interrupt generated with the INT n instruction) while in
virtual-8086 mode, it can use any of six different methods to handle the interrupt. The method selected depends
on the settings of the VME flag in control register CR4, the IOPL field in the EFLAGS register, and the software interrupt redirection bit map in the TSS. Table 20-2 lists the six methods of handling software interrupts in virtual-8086
mode and the respective settings of the VME flag, IOPL field, and the bits in the interrupt redirection bit map for
each method. The table also summarizes the various actions the processor takes for each method.
The VME flag enables the virtual mode extensions for the Pentium and later IA-32 processors. When this flag is
clear, the processor responds to interrupts and exceptions in virtual-8086 mode in the same manner as an Intel386
or Intel486 processor does. When this flag is set, the virtual mode extension provides the following enhancements
to virtual-8086 mode:

•

Speeds up the handling of software-generated interrupts in virtual-8086 mode by allowing the processor to
bypass the virtual-8086 monitor and redirect software interrupts back to the interrupt handlers that are part of
the currently running 8086 program.

•

Supports virtual interrupts for software written to run on the 8086 processor.

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8086 EMULATION

The IOPL value interacts with the VME flag and the bits in the interrupt redirection bit map to determine how
specific software interrupts should be handled.
The software interrupt redirection bit map (see Figure 20-5) is a 32-byte field in the TSS. This map is located
directly below the I/O permission bit map in the TSS. Each bit in the interrupt redirection bit map is mapped to an
interrupt vector. Bit 0 in the interrupt redirection bit map (which maps to vector zero in the interrupt table) is
located at the I/O base map address in the TSS minus 32 bytes. When a bit in this bit map is set, it indicates that
the associated software interrupt (interrupt generated with an INT n instruction) should be handled through the
protected-mode IDT and interrupt and exception handlers. When a bit in this bit map is clear, the processor redirects the associated software interrupt back to the interrupt table in the 8086 program (located at linear address 0
in the program’s address space).

NOTE
The software interrupt redirection bit map does not affect hardware generated interrupts and
exceptions. Hardware generated interrupts and exceptions are always handled by the protectedmode interrupt and exception handlers.

Table 20-2. Software Interrupt Handling Methods While in Virtual-8086 Mode
Method VME
1

0

Bit in
Redir.
IOPL Bitmap*
3

X

Processor Action
Interrupt directed to a protected-mode interrupt handler:
•
•
•
•
•
•
•

Switches to privilege-level 0 stack
Pushes GS, FS, DS and ES onto privilege-level 0 stack
Pushes SS, ESP, EFLAGS, CS and EIP of interrupted task onto privilege-level 0 stack
Clears VM, RF, NT, and TF flags
If serviced through interrupt gate, clears IF flag
Clears GS, FS, DS and ES to 0
Sets CS and EIP from interrupt gate

2

0

<3

X

Interrupt directed to protected-mode general-protection exception (#GP) handler.

3

1

<3

1

Interrupt directed to a protected-mode general-protection exception (#GP) handler; VIF and VIP
flag support for handling class 2 maskable hardware interrupts.

4

1

3

1

Interrupt directed to protected-mode interrupt handler: (see method 1 processor action).

5

1

3

0

Interrupt redirected to 8086 program interrupt handler:
•
•
•
•
•

6

1

<3

0

Pushes EFLAGS
Pushes CS and EIP (lower 16 bits only)
Clears IF flag
Clears TF flag
Loads CS and EIP (lower 16 bits only) from selected entry in the interrupt vector table of the
current virtual-8086 task

Interrupt redirected to 8086 program interrupt handler; VIF and VIP flag support for handling class
2 maskable hardware interrupts:
•
•
•
•
•

Pushes EFLAGS with IOPL set to 3 and VIF copied to IF
Pushes CS and EIP (lower 16 bits only)
Clears the VIF flag
Clears TF flag
Loads CS and EIP (lower 16 bits only) from selected entry in the interrupt vector table of the
current virtual-8086 task

NOTE:
* When set to 0, software interrupt is redirected back to the 8086 program interrupt handler; when set to 1, interrupt is directed to
protected-mode handler.

Vol. 3B 20-17

8086 EMULATION

Last byte of
bit

31

24 23

Task-State Segment (TSS)

0

1 1 1 1 1 1 1 1

map must be
I/O Permission Bit Map

Software Interrupt Redirection Bit Map (32 Bytes)

I/O map
base must
not exceed
DFFFH.

I/O Map Base

64H

0

Figure 20-5. Software Interrupt Redirection Bit Map in TSS
Redirecting software interrupts back to the 8086 program potentially speeds up interrupt handling because a
switch back and forth between virtual-8086 mode and protected mode is not required. This latter interrupthandling technique is particularly useful for 8086 operating systems (such as MS-DOS) that use the INT n instruction to call operating system procedures.
The CPUID instruction can be used to verify that the virtual mode extension is implemented on the processor. Bit 1
of the feature flags register (EDX) indicates the availability of the virtual mode extension (see “CPUID—CPU Identification” in Chapter 3, “Instruction Set Reference, A-L”, of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A).
The following sections describe the six methods (or mechanisms) for handling software interrupts in virtual-8086
mode. See Section 20.3.2, “Class 2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the Virtual
Interrupt Mechanism”, for a description of the use of the VIF and VIP flags in the EFLAGS register for handling
maskable hardware interrupts.

20.3.3.1

Method 1: Software Interrupt Handling

When the VME flag in control register CR4 is clear and the IOPL field is 3, a Pentium or later IA-32 processor
handles software interrupts in the same manner as they are handled by an Intel386 or Intel486 processor. It
executes an implicit call to the interrupt handler in the protected-mode IDT pointed to by the interrupt vector. See
Section 20.3.1, “Class 1—Hardware Interrupt and Exception Handling in Virtual-8086 Mode”, for a complete
description of this mechanism and its possible uses.

20.3.3.2

Methods 2 and 3: Software Interrupt Handling

When a software interrupt occurs in virtual-8086 mode and the method 2 or 3 conditions are present, the processor
generates a general-protection exception (#GP). Method 2 is enabled when the VME flag is set to 0 and the IOPL
value is less than 3. Here the IOPL value is used to bypass the protected-mode interrupt handlers and cause any
software interrupt that occurs in virtual-8086 mode to be treated as a protected-mode general-protection exception (#GP). The general-protection exception handler calls the virtual-8086 monitor, which can then emulate an
8086-program interrupt handler or pass control back to the 8086 program’s handler, as described in Section
20.3.1.2, “Handling an Interrupt or Exception With an 8086 Program Interrupt or Exception Handler”.
Method 3 is enabled when the VME flag is set to 1, the IOPL value is less than 3, and the corresponding bit for the
software interrupt in the software interrupt redirection bit map is set to 1. Here, the processor performs the same
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8086 EMULATION

operation as it does for method 2 software interrupt handling. If the corresponding bit for the software interrupt in
the software interrupt redirection bit map is set to 0, the interrupt is handled using method 6 (see Section 20.3.3.5,
“Method 6: Software Interrupt Handling”).

20.3.3.3

Method 4: Software Interrupt Handling

Method 4 handling is enabled when the VME flag is set to 1, the IOPL value is 3, and the bit for the interrupt vector
in the redirection bit map is set to 1. Method 4 software interrupt handling allows method 1 style handling when the
virtual mode extension is enabled; that is, the interrupt is directed to a protected-mode handler (see Section
20.3.3.1, “Method 1: Software Interrupt Handling”).

20.3.3.4

Method 5: Software Interrupt Handling

Method 5 software interrupt handling provides a streamlined method of redirecting software interrupts (invoked
with the INT n instruction) that occur in virtual 8086 mode back to the 8086 program’s interrupt vector table and
its interrupt handlers. Method 5 handling is enabled when the VME flag is set to 1, the IOPL value is 3, and the bit
for the interrupt vector in the redirection bit map is set to 0. The processor performs the following actions to make
an implicit call to the selected 8086 program interrupt handler:
1. Pushes the low-order 16 bits of the EFLAGS register onto the stack.
2. Pushes the current values of the CS and EIP registers onto the current stack. (Only the 16 least-significant bits
of the EIP register are pushed and no stack switch occurs.)
3. Clears the IF flag in the EFLAGS register to disable interrupts.
4. Clears the TF flag, in the EFLAGS register.
5. Locates the 8086 program interrupt vector table at linear address 0 for the 8086-mode task.
6. Loads the CS and EIP registers with values from the interrupt vector table entry pointed to by the interrupt
vector number. Only the 16 low-order bits of the EIP are loaded and the 16 high-order bits are set to 0. The
interrupt vector table is assumed to be at linear address 0 of the current virtual-8086 task.
7. Begins executing the selected interrupt handler.
An IRET instruction at the end of the handler procedure reverses these steps to return program control to the interrupted 8086 program.
Note that with method 5 handling, a mode switch from virtual-8086 mode to protected mode does not occur. The
processor remains in virtual-8086 mode throughout the interrupt-handling operation.
The method 5 handling actions are virtually identical to the actions the processor takes when handling software
interrupts in real-address mode. The benefit of using method 5 handling to access the 8086 program handlers is
that it avoids the overhead of methods 2 and 3 handling, which requires first going to the virtual-8086 monitor,
then to the 8086 program handler, then back again to the virtual-8086 monitor, before returning to the interrupted
8086 program (see Section 20.3.1.2, “Handling an Interrupt or Exception With an 8086 Program Interrupt or
Exception Handler”).

NOTE
Methods 1 and 4 handling can handle a software interrupt in a virtual-8086 task with a regular
protected-mode handler, but this approach requires all virtual-8086 tasks to use the same software
interrupt handlers, which generally does not give sufficient latitude to the programs running in the
virtual-8086 tasks, particularly MS-DOS programs.

20.3.3.5

Method 6: Software Interrupt Handling

Method 6 handling is enabled when the VME flag is set to 1, the IOPL value is less than 3, and the bit for the interrupt or exception vector in the redirection bit map is set to 0. With method 6 interrupt handling, software interrupts
are handled in the same manner as was described for method 5 handling (see Section 20.3.3.4, “Method 5: Software Interrupt Handling”).

Vol. 3B 20-19

8086 EMULATION

Method 6 differs from method 5 in that with the IOPL value set to less than 3, the VIF and VIP flags in the EFLAGS
register are enabled, providing virtual interrupt support for handling class 2 maskable hardware interrupts (see
Section 20.3.2, “Class 2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the Virtual Interrupt
Mechanism”). These flags provide the virtual-8086 monitor with an efficient means of handling maskable hardware
interrupts that occur during a virtual-8086 mode task. Also, because the IOPL value is less than 3 and the VIF flag
is enabled, the information pushed on the stack by the processor when invoking the interrupt handler is slightly
different between methods 5 and 6 (see Table 20-2).

20.4

PROTECTED-MODE VIRTUAL INTERRUPTS

The IA-32 processors (beginning with the Pentium processor) also support the VIF and VIP flags in the EFLAGS
register in protected mode by setting the PVI (protected-mode virtual interrupt) flag in the CR4 register. Setting the
PVI flag allows applications running at privilege level 3 to execute the CLI and STI instructions without causing a
general-protection exception (#GP) or affecting hardware interrupts.
When the PVI flag is set to 1, the CPL is 3, and the IOPL is less than 3, the STI and CLI instructions set and clear
the VIF flag in the EFLAGS register, leaving IF unaffected. In this mode of operation, an application running in
protected mode and at a CPL of 3 can inhibit interrupts in the same manner as is described in Section 20.3.2, “Class
2—Maskable Hardware Interrupt Handling in Virtual-8086 Mode Using the Virtual Interrupt Mechanism”, for a
virtual-8086 mode task. When the application executes the CLI instruction, the processor clears the VIF flag. If the
processor receives a maskable hardware interrupt, the processor invokes the protected-mode interrupt handler.
This handler checks the state of the VIF flag in the EFLAGS register. If the VIF flag is clear (indicating that the active
task does not want to have interrupts handled now), the handler sets the VIP flag in the EFLAGS image on the stack
and returns to the privilege-level 3 application, which continues program execution. When the application executes
a STI instruction to set the VIF flag, the processor automatically invokes the general-protection exception handler,
which can then handle the pending interrupt. After handing the pending interrupt, the handler typically sets the VIF
flag and clears the VIP flag in the EFLAGS image on the stack and executes a return to the application program. The
next time the processor receives a maskable hardware interrupt, the processor will handle it in the normal manner
for interrupts received while the processor is operating at a CPL of 3.
If the protected-mode virtual interrupt extension is enabled, CPL = 3, and the processor finds that both the VIF and
VIP flags are set at the beginning of an instruction, a general-protection exception is generated.
Because the protected-mode virtual interrupt extension changes only the treatment of EFLAGS.IF (by having CLI
and STI update EFLAGS.VIF instead), it affects only the masking of maskable hardware interrupts (interrupt
vectors 32 through 255). NMI interrupts and exceptions are handled in the normal manner.
(When protected-mode virtual interrupts are disabled (that is, when the PVI flag in control register CR4 is set to 0,
the CPL is less than 3, or the IOPL value is 3), then the CLI and STI instructions execute in a manner compatible
with the Intel486 processor. That is, if the CPL is greater (less privileged) than the I/O privilege level (IOPL), a
general-protection exception occurs. If the IOPL value is 3, CLI and STI clear or set the IF flag, respectively.)
PUSHF, POPF, IRET and INT are executed like in the Intel486 processor, regardless of whether protected-mode
virtual interrupts are enabled.
It is only possible to enter virtual-8086 mode through a task switch or the execution of an IRET instruction, and it
is only possible to leave virtual-8086 mode by faulting to a protected-mode interrupt handler (typically the generalprotection exception handler, which in turn calls the virtual 8086-mode monitor). In both cases, the EFLAGS
register is saved and restored. This is not true, however, in protected mode when the PVI flag is set and the
processor is not in virtual-8086 mode. Here, it is possible to call a procedure at a different privilege level, in which
case the EFLAGS register is not saved or modified. However, the states of VIF and VIP flags are never examined by
the processor when the CPL is not 3.

20-20 Vol. 3B

CHAPTER 21
MIXING 16-BIT AND 32-BIT CODE
Program modules written to run on IA-32 processors can be either 16-bit modules or 32-bit modules. Table 21-1
shows the characteristic of 16-bit and 32-bit modules.

Table 21-1. Characteristics of 16-Bit and 32-Bit Program Modules
Characteristic

16-Bit Program Modules

32-Bit Program Modules

Segment Size

0 to 64 KBytes

0 to 4 GBytes

Operand Sizes

8 bits and 16 bits

8 bits and 32 bits

Pointer Offset Size (Address Size)

16 bits

32 bits

Stack Pointer Size

16 Bits

32 Bits

Control Transfers Allowed to Code Segments
of This Size

16 Bits

32 Bits

The IA-32 processors function most efficiently when executing 32-bit program modules. They can, however, also
execute 16-bit program modules, in any of the following ways:

•
•
•
•

In real-address mode.

•
•

By integrating 16-bit and 32-bit segments into a single protected-mode task.

In virtual-8086 mode.
System management mode (SMM).
As a protected-mode task, when the code, data, and stack segments for the task are all configured as a 16-bit
segments.
By integrating 16-bit operations into 32-bit code segments.

Real-address mode, virtual-8086 mode, and SMM are native 16-bit modes. A legacy program assembled and/or
compiled to run on an Intel 8086 or Intel 286 processor should run in real-address mode or virtual-8086 mode
without modification. Sixteen-bit program modules can also be written to run in real-address mode for handling
system initialization or to run in SMM for handling system management functions. See Chapter 20, “8086 Emulation,” for detailed information on real-address mode and virtual-8086 mode; see Chapter 34, “System Management Mode,” for information on SMM.
This chapter describes how to integrate 16-bit program modules with 32-bit program modules when operating in
protected mode and how to mix 16-bit and 32-bit code within 32-bit code segments.

21.1

DEFINING 16-BIT AND 32-BIT PROGRAM MODULES

The following IA-32 architecture mechanisms are used to distinguish between and support 16-bit and 32-bit
segments and operations:

•
•
•
•
•

The D (default operand and address size) flag in code-segment descriptors.
The B (default stack size) flag in stack-segment descriptors.
16-bit and 32-bit call gates, interrupt gates, and trap gates.
Operand-size and address-size instruction prefixes.
16-bit and 32-bit general-purpose registers.

The D flag in a code-segment descriptor determines the default operand-size and address-size for the instructions
of a code segment. (In real-address mode and virtual-8086 mode, which do not use segment descriptors, the
default is 16 bits.) A code segment with its D flag set is a 32-bit segment; a code segment with its D flag clear is a
16-bit segment.
Vol. 3B 21-1

MIXING 16-BIT AND 32-BIT CODE

The B flag in the stack-segment descriptor specifies the size of stack pointer (the 32-bit ESP register or the 16-bit
SP register) used by the processor for implicit stack references. The B flag for all data descriptors also controls
upper address range for expand down segments.
When transferring program control to another code segment through a call gate, interrupt gate, or trap gate, the
operand size used during the transfer is determined by the type of gate used (16-bit or 32-bit), (not by the D-flag
or prefix of the transfer instruction). The gate type determines how return information is saved on the stack (or
stacks).
For most efficient and trouble-free operation of the processor, 32-bit programs or tasks should have the D flag in
the code-segment descriptor and the B flag in the stack-segment descriptor set, and 16-bit programs or tasks
should have these flags clear. Program control transfers from 16-bit segments to 32-bit segments (and vice versa)
are handled most efficiently through call, interrupt, or trap gates.
Instruction prefixes can be used to override the default operand size and address size of a code segment. These
prefixes can be used in real-address mode as well as in protected mode and virtual-8086 mode. An operand-size or
address-size prefix only changes the size for the duration of the instruction.

21.2

MIXING 16-BIT AND 32-BIT OPERATIONS WITHIN A CODE SEGMENT

The following two instruction prefixes allow mixing of 32-bit and 16-bit operations within one segment:

•
•

The operand-size prefix (66H)
The address-size prefix (67H)

These prefixes reverse the default size selected by the D flag in the code-segment descriptor. For example, the
processor can interpret the (MOV mem, reg) instruction in any of four ways:

•

In a 32-bit code segment:
— Moves 32 bits from a 32-bit register to memory using a 32-bit effective address.
— If preceded by an operand-size prefix, moves 16 bits from a 16-bit register to memory using a 32-bit
effective address.
— If preceded by an address-size prefix, moves 32 bits from a 32-bit register to memory using a 16-bit
effective address.
— If preceded by both an address-size prefix and an operand-size prefix, moves 16 bits from a 16-bit register
to memory using a 16-bit effective address.

•

In a 16-bit code segment:
— Moves 16 bits from a 16-bit register to memory using a 16-bit effective address.
— If preceded by an operand-size prefix, moves 32 bits from a 32-bit register to memory using a 16-bit
effective address.
— If preceded by an address-size prefix, moves 16 bits from a 16-bit register to memory using a 32-bit
effective address.
— If preceded by both an address-size prefix and an operand-size prefix, moves 32 bits from a 32-bit register
to memory using a 32-bit effective address.

The previous examples show that any instruction can generate any combination of operand size and address size
regardless of whether the instruction is in a 16- or 32-bit segment. The choice of the 16- or 32-bit default for a code
segment is normally based on the following criteria:

•

Performance — Always use 32-bit code segments when possible. They run much faster than 16-bit code
segments on P6 family processors, and somewhat faster on earlier IA-32 processors.

•

The operating system the code segment will be running on — If the operating system is a 16-bit
operating system, it may not support 32-bit program modules.

•

Mode of operation — If the code segment is being designed to run in real-address mode, virtual-8086 mode,
or SMM, it must be a 16-bit code segment.

21-2 Vol. 3B

MIXING 16-BIT AND 32-BIT CODE

•

Backward compatibility to earlier IA-32 processors — If a code segment must be able to run on an Intel
8086 or Intel 286 processor, it must be a 16-bit code segment.

21.3

SHARING DATA AMONG MIXED-SIZE CODE SEGMENTS

Data segments can be accessed from both 16-bit and 32-bit code segments. When a data segment that is larger
than 64 KBytes is to be shared among 16- and 32-bit code segments, the data that is to be accessed from the 16bit code segments must be located within the first 64 KBytes of the data segment. The reason for this is that 16bit pointers by definition can only point to the first 64 KBytes of a segment.
A stack that spans less than 64 KBytes can be shared by both 16- and 32-bit code segments. This class of stacks
includes:

•
•
•

Stacks in expand-up segments with the G (granularity) and B (big) flags in the stack-segment descriptor clear.
Stacks in expand-down segments with the G and B flags clear.
Stacks in expand-up segments with the G flag set and the B flag clear and where the stack is contained
completely within the lower 64 KBytes. (Offsets greater than FFFFH can be used for data, other than the stack,
which is not shared.)

See Section 3.4.5, “Segment Descriptors,” for a description of the G and B flags and the expand-down stack type.
The B flag cannot, in general, be used to change the size of stack used by a 16-bit code segment. This flag controls
the size of the stack pointer only for implicit stack references such as those caused by interrupts, exceptions, and
the PUSH, POP, CALL, and RET instructions. It does not control explicit stack references, such as accesses to
parameters or local variables. A 16-bit code segment can use a 32-bit stack only if the code is modified so that all
explicit references to the stack are preceded by the 32-bit address-size prefix, causing those references to use 32bit addressing and explicit writes to the stack pointer are preceded by a 32-bit operand-size prefix.
In 32-bit, expand-down segments, all offsets may be greater than 64 KBytes; therefore, 16-bit code cannot use
this kind of stack segment unless the code segment is modified to use 32-bit addressing.

21.4

TRANSFERRING CONTROL AMONG MIXED-SIZE CODE SEGMENTS

There are three ways for a procedure in a 16-bit code segment to safely make a call to a 32-bit code segment:

•
•

Make the call through a 32-bit call gate.

•

Modify the 16-bit procedure, inserting an operand-size prefix before the call, to change it to a 32-bit call.

Make a 16-bit call to a 32-bit interface procedure. The interface procedure then makes a 32-bit call to the
intended destination.

Likewise, there are three ways for procedure in a 32-bit code segment to safely make a call to a 16-bit code
segment:

•
•

Make the call through a 16-bit call gate. Here, the EIP value at the CALL instruction cannot exceed FFFFH.

•

Modify the 32-bit procedure, inserting an operand-size prefix before the call, changing it to a 16-bit call. Be
certain that the return offset does not exceed FFFFH.

Make a 32-bit call to a 16-bit interface procedure. The interface procedure then makes a 16-bit call to the
intended destination.

These methods of transferring program control overcome the following architectural limitations imposed on calls
between 16-bit and 32-bit code segments:

•

Pointers from 16-bit code segments (which by default can only be 16 bits) cannot be used to address data or
code located beyond FFFFH in a 32-bit segment.

•

The operand-size attributes for a CALL and its companion RETURN instruction must be the same to maintain
stack coherency. This is also true for implicit calls to interrupt and exception handlers and their companion IRET
instructions.

•

A 32-bit parameters (particularly a pointer parameter) greater than FFFFH cannot be squeezed into a 16-bit
parameter location on a stack.
Vol. 3B 21-3

MIXING 16-BIT AND 32-BIT CODE

•

The size of the stack pointer (SP or ESP) changes when switching between 16-bit and 32-bit code segments.

These limitations are discussed in greater detail in the following sections.

21.4.1

Code-Segment Pointer Size

For control-transfer instructions that use a pointer to identify the next instruction (that is, those that do not use
gates), the operand-size attribute determines the size of the offset portion of the pointer. The implications of this
rule are as follows:

•

A JMP, CALL, or RET instruction from a 32-bit segment to a 16-bit segment is always possible using a 32-bit
operand size, providing the 32-bit pointer does not exceed FFFFH.

•

A JMP, CALL, or RET instruction from a 16-bit segment to a 32-bit segment cannot address a destination greater
than FFFFH, unless the instruction is given an operand-size prefix.

See Section 21.4.5, “Writing Interface Procedures,” for an interface procedure that can transfer program control
from 16-bit segments to destinations in 32-bit segments beyond FFFFH.

21.4.2

Stack Management for Control Transfer

Because the stack is managed differently for 16-bit procedure calls than for 32-bit calls, the operand-size attribute
of the RET instruction must match that of the CALL instruction (see Figure 21-1). On a 16-bit call, the processor
pushes the contents of the 16-bit IP register and (for calls between privilege levels) the 16-bit SP register. The
matching RET instruction must also use a 16-bit operand size to pop these 16-bit values from the stack into the 16bit registers.
A 32-bit CALL instruction pushes the contents of the 32-bit EIP register and (for inter-privilege-level calls) the 32bit ESP register. Here, the matching RET instruction must use a 32-bit operand size to pop these 32-bit values from
the stack into the 32-bit registers. If the two parts of a CALL/RET instruction pair do not have matching operand
sizes, the stack will not be managed correctly and the values of the instruction pointer and stack pointer will not be
restored to correct values.

21-4 Vol. 3B

MIXING 16-BIT AND 32-BIT CODE

Without Privilege Transition
After 16-bit Call
31

Stack
Growth

After 32-bit Call
0

31

PARM 2 PARM 1
CS

PARM 2
SP

IP

0

PARM 1
CS
EIP

ESP

With Privilege Transition
After 16-bit Call
31

SS
Stack
Growth

After 32-bit Call
0

31

0

SP

SS

PARM 2 PARM 1
CS

IP

ESP
SP

PARM 2
PARM 1
CS
EIP

ESP

Undefined

Figure 21-1. Stack after Far 16- and 32-Bit Calls
While executing 32-bit code, if a call is made to a 16-bit code segment which is at the same or a more privileged
level (that is, the DPL of the called code segment is less than or equal to the CPL of the calling code segment)
through a 16-bit call gate, then the upper 16-bits of the ESP register may be unreliable upon returning to the 32bit code segment (that is, after executing a RET in the 16-bit code segment).
When the CALL instruction and its matching RET instruction are in code segments that have D flags with the same
values (that is, both are 32-bit code segments or both are 16-bit code segments), the default settings may be
used. When the CALL instruction and its matching RET instruction are in segments which have different D-flag
settings, an operand-size prefix must be used.

21.4.2.1

Controlling the Operand-Size Attribute For a Call

Three things can determine the operand-size of a call:

•
•
•

The D flag in the segment descriptor for the calling code segment.
An operand-size instruction prefix.
The type of call gate (16-bit or 32-bit), if a call is made through a call gate.

When a call is made with a pointer (rather than a call gate), the D flag for the calling code segment determines the
operand-size for the CALL instruction. This operand-size attribute can be overridden by prepending an operandsize prefix to the CALL instruction. So, for example, if the D flag for a code segment is set for 16 bits and the
operand-size prefix is used with a CALL instruction, the processor will cause the information stored on the stack to

Vol. 3B 21-5

MIXING 16-BIT AND 32-BIT CODE

be stored in 32-bit format. If the call is to a 32-bit code segment, the instructions in that code segment will be able
to read the stack coherently. Also, a RET instruction from the 32-bit code segment without an operand-size prefix
will maintain stack coherency with the 16-bit code segment being returned to.
When a CALL instruction references a call-gate descriptor, the type of call is determined by the type of call gate (16bit or 32-bit). The offset to the destination in the code segment being called is taken from the gate descriptor;
therefore, if a 32-bit call gate is used, a procedure in a 16-bit code segment can call a procedure located more than
64 KBytes from the base of a 32-bit code segment, because a 32-bit call gate uses a 32-bit offset.
Note that regardless of the operand size of the call and how it is determined, the size of the stack pointer used (SP
or ESP) is always controlled by the B flag in the stack-segment descriptor currently in use (that is, when B is clear,
SP is used, and when B is set, ESP is used).
An unmodified 16-bit code segment that has run successfully on an 8086 processor or in real-mode on a later IA32 architecture processor will have its D flag clear and will not use operand-size override prefixes. As a result, all
CALL instructions in this code segment will use the 16-bit operand-size attribute. Procedures in these code
segments can be modified to safely call procedures to 32-bit code segments in either of two ways:

•

Relink the CALL instruction to point to 32-bit call gates (see Section 21.4.2.2, “Passing Parameters With a
Gate”).

•

Add a 32-bit operand-size prefix to each CALL instruction.

21.4.2.2

Passing Parameters With a Gate

When referencing 32-bit gates with 16-bit procedures, it is important to consider the number of parameters passed
in each procedure call. The count field of the gate descriptor specifies the size of the parameter string to copy from
the current stack to the stack of a more privileged (numerically lower privilege level) procedure. The count field of
a 16-bit gate specifies the number of 16-bit words to be copied, whereas the count field of a 32-bit gate specifies
the number of 32-bit doublewords to be copied. The count field for a 32-bit gate must thus be half the size of the
number of words being placed on the stack by a 16-bit procedure. Also, the 16-bit procedure must use an even
number of words as parameters.

21.4.3

Interrupt Control Transfers

A program-control transfer caused by an exception or interrupt is always carried out through an interrupt or trap
gate (located in the IDT). Here, the type of the gate (16-bit or 32-bit) determines the operand-size attribute used
in the implicit call to the exception or interrupt handler procedure in another code segment.
A 32-bit interrupt or trap gate provides a safe interface to a 32-bit exception or interrupt handler when the exception or interrupt occurs in either a 32-bit or a 16-bit code segment. It is sometimes impractical, however, to place
exception or interrupt handlers in 16-bit code segments, because only 16-bit return addresses are saved on the
stack. If an exception or interrupt occurs in a 32-bit code segment when the EIP was greater than FFFFH, the 16bit handler procedure cannot provide the correct return address.

21.4.4

Parameter Translation

When segment offsets or pointers (which contain segment offsets) are passed as parameters between 16-bit and
32-bit procedures, some translation is required. If a 32-bit procedure passes a pointer to data located beyond 64
KBytes to a 16-bit procedure, the 16-bit procedure cannot use it. Except for this limitation, interface code can
perform any format conversion between 32-bit and 16-bit pointers that may be needed.
Parameters passed by value between 32-bit and 16-bit code also may require translation between 32-bit and 16bit formats. The form of the translation is application-dependent.

21.4.5

Writing Interface Procedures

Placing interface code between 32-bit and 16-bit procedures can be the solution to the following interface problems:

21-6 Vol. 3B

MIXING 16-BIT AND 32-BIT CODE

•

Allowing procedures in 16-bit code segments to call procedures with offsets greater than FFFFH in 32-bit code
segments.

•
•

Matching operand-size attributes between companion CALL and RET instructions.

•

The possible invalidation of the upper bits of the ESP register.

Translating parameters (data), including managing parameter strings with a variable count or an odd number
of 16-bit words.

The interface procedure is simplified where these rules are followed.
1. The interface procedure must reside in a 32-bit code segment (the D flag for the code-segment descriptor is
set).
2. All procedures that may be called by 16-bit procedures must have offsets not greater than FFFFH.
3. All return addresses saved by 16-bit procedures must have offsets not greater than FFFFH.
The interface procedure becomes more complex if any of these rules are violated. For example, if a 16-bit procedure calls a 32-bit procedure with an entry point beyond FFFFH, the interface procedure will need to provide the
offset to the entry point. The mapping between 16- and 32-bit addresses is only performed automatically when a
call gate is used, because the gate descriptor for a call gate contains a 32-bit address. When a call gate is not used,
the interface code must provide the 32-bit address.
The structure of the interface procedure depends on the types of calls it is going to support, as follows:

•

Calls from 16-bit procedures to 32-bit procedures — Calls to the interface procedure from a 16-bit code
segment are made with 16-bit CALL instructions (by default, because the D flag for the calling code-segment
descriptor is clear), and 16-bit operand-size prefixes are used with RET instructions to return from the interface
procedure to the calling procedure. Calls from the interface procedure to 32-bit procedures are performed with
32-bit CALL instructions (by default, because the D flag for the interface procedure’s code segment is set), and
returns from the called procedures to the interface procedure are performed with 32-bit RET instructions (also
by default).

•

Calls from 32-bit procedures to 16-bit procedures — Calls to the interface procedure from a 32-bit code
segment are made with 32-bit CALL instructions (by default), and returns to the calling procedure from the
interface procedure are made with 32-bit RET instructions (also by default). Calls from the interface procedure
to 16-bit procedures require the CALL instructions to have the operand-size prefixes, and returns from the
called procedures to the interface procedure are performed with 16-bit RET instructions (by default).

Vol. 3B 21-7

MIXING 16-BIT AND 32-BIT CODE

21-8 Vol. 3B

CHAPTER 22
ARCHITECTURE COMPATIBILITY
Intel 64 and IA-32 processors are binary compatible. Compatibility means that, within limited constraints,
programs that execute on previous generations of processors will produce identical results when executed on later
processors. The compatibility constraints and any implementation differences between the Intel 64 and IA-32
processors are described in this chapter.
Each new processor has enhanced the software visible architecture from that found in earlier Intel 64 and IA-32
processors. Those enhancements have been defined with consideration for compatibility with previous and future
processors. This chapter also summarizes the compatibility considerations for those extensions.

22.1

PROCESSOR FAMILIES AND CATEGORIES

IA-32 processors are referred to in several different ways in this chapter, depending on the type of compatibility
information being related, as described in the following:

•

IA-32 Processors — All the Intel processors based on the Intel IA-32 Architecture, which include the
8086/88, Intel 286, Intel386, Intel486, Pentium, Pentium Pro, Pentium II, Pentium III, Pentium 4, and Intel
Xeon processors.

•

32-bit Processors — All the IA-32 processors that use a 32-bit architecture, which include the Intel386,
Intel486, Pentium, Pentium Pro, Pentium II, Pentium III, Pentium 4, and Intel Xeon processors.

•

16-bit Processors — All the IA-32 processors that use a 16-bit architecture, which include the 8086/88 and
Intel 286 processors.

•

P6 Family Processors — All the IA-32 processors that are based on the P6 microarchitecture, which include
the Pentium Pro, Pentium II, and Pentium III processors.

•

Pentium® 4 Processors — A family of IA-32 and Intel 64 processors that are based on the Intel NetBurst®
microarchitecture.

•

Intel® Pentium® M Processors — A family of IA-32 processors that are based on the Intel Pentium M
processor microarchitecture.

•

Intel® Core™ Duo and Solo Processors — Families of IA-32 processors that are based on an improved Intel
Pentium M processor microarchitecture.

•

Intel® Xeon® Processors — A family of IA-32 and Intel 64 processors that are based on the Intel NetBurst
microarchitecture. This family includes the Intel Xeon processor and the Intel Xeon processor MP based on the
Intel NetBurst microarchitecture. Intel Xeon processors 3000, 3100, 3200, 3300, 3200, 5100, 5200, 5300,
5400, 7200, 7300 series are based on Intel Core microarchitectures and support Intel 64 architecture.

•

Pentium® D Processors — A family of dual-core Intel 64 processors that provides two processor cores in a
physical package. Each core is based on the Intel NetBurst microarchitecture.

•

Pentium® Processor Extreme Editions — A family of dual-core Intel 64 processors that provides two
processor cores in a physical package. Each core is based on the Intel NetBurst microarchitecture and supports
Intel Hyper-Threading Technology.

•

Intel® Core™ 2 Processor family— A family of Intel 64 processors that are based on the Intel Core microarchitecture. Intel Pentium Dual-Core processors are also based on the Intel Core microarchitecture.

•

Intel® Atom™ Processors — A family of IA-32 and Intel 64 processors. 45 nm Intel Atom processors are
based on the Intel Atom microarchitecture. 32 nm Intel Atom processors are based on newer microarchitectures including the Silvermont microarchitecture and the Airmont microarchitecture. Each generation of Intel
Atom processors can be identified by the CPUID’s DisplayFamily_DisplayModel signature; see Table 2-1 “CPUID
Signature Values of DisplayFamily_DisplayModel” in Chapter 2, “Model-Specific Registers (MSRs)” of the Intel®
64 and IA-32 Architectures Software Developer’s Manual, Volume 4.

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22.2

RESERVED BITS

Throughout this manual, certain bits are marked as reserved in many register and memory layout descriptions.
When bits are marked as undefined or reserved, it is essential for compatibility with future processors that software
treat these bits as having a future, though unknown effect. Software should follow these guidelines in dealing with
reserved bits:

•

Do not depend on the states of any reserved bits when testing the values of registers or memory locations that
contain such bits. Mask out the reserved bits before testing.

•
•
•

Do not depend on the states of any reserved bits when storing them to memory or to a register.
Do not depend on the ability to retain information written into any reserved bits.
When loading a register, always load the reserved bits with the values indicated in the documentation, if any, or
reload them with values previously read from the same register.

Software written for existing IA-32 processor that handles reserved bits correctly will port to future IA-32 processors without generating protection exceptions.

22.3

ENABLING NEW FUNCTIONS AND MODES

Most of the new control functions defined for the P6 family and Pentium processors are enabled by new mode flags
in the control registers (primarily register CR4). This register is undefined for IA-32 processors earlier than the
Pentium processor. Attempting to access this register with an Intel486 or earlier IA-32 processor results in an
invalid-opcode exception (#UD). Consequently, programs that execute correctly on the Intel486 or earlier IA-32
processor cannot erroneously enable these functions. Attempting to set a reserved bit in register CR4 to a value
other than its original value results in a general-protection exception (#GP). So, programs that execute on the P6
family and Pentium processors cannot erroneously enable functions that may be implemented in future IA-32
processors.
The P6 family and Pentium processors do not check for attempts to set reserved bits in model-specific registers;
however these bits may be checked on more recent processors. It is the obligation of the software writer to enforce
this discipline. These reserved bits may be used in future Intel processors.

22.4

DETECTING THE PRESENCE OF NEW FEATURES THROUGH SOFTWARE

Software can check for the presence of new architectural features and extensions in either of two ways:
1. Test for the presence of the feature or extension. Software can test for the presence of new flags in the EFLAGS
register and control registers. If these flags are reserved (meaning not present in the processor executing the
test), an exception is generated. Likewise, software can attempt to execute a new instruction, which results in
an invalid-opcode exception (#UD) being generated if it is not supported.
2. Execute the CPUID instruction. The CPUID instruction (added to the IA-32 in the Pentium processor) indicates
the presence of new features directly.
See Chapter 19, “Processor Identification and Feature Determination,” in the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1, for detailed information on detecting new processor features and extensions.

22.5

INTEL MMX TECHNOLOGY

The Pentium processor with MMX technology introduced the MMX technology and a set of MMX instructions to the
IA-32. The MMX instructions are described in Chapter 9, “Programming with Intel® MMX™ Technology,” in the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, and in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C & 2D. The MMX technology and MMX instructions are
also included in the Pentium II, Pentium III, Pentium 4, and Intel Xeon processors.

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ARCHITECTURE COMPATIBILITY

22.6

STREAMING SIMD EXTENSIONS (SSE)

The Streaming SIMD Extensions (SSE) were introduced in the Pentium III processor. The SSE extensions consist of
a new set of instructions and a new set of registers. The new registers include the eight 128-bit XMM registers and
the 32-bit MXCSR control and status register. These instructions and registers are designed to allow SIMD computations to be made on single-precision floating-point numbers. Several of these new instructions also operate in the
MMX registers. SSE instructions and registers are described in Section 10, “Programming with Streaming SIMD
Extensions (SSE),” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, and in the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C & 2D.

22.7

STREAMING SIMD EXTENSIONS 2 (SSE2)

The Streaming SIMD Extensions 2 (SSE2) were introduced in the Pentium 4 and Intel Xeon processors. They
consist of a new set of instructions that operate on the XMM and MXCSR registers and perform SIMD operations on
double-precision floating-point values and on integer values. Several of these new instructions also operate in the
MMX registers. SSE2 instructions and registers are described in Chapter 11, “Programming with Streaming SIMD
Extensions 2 (SSE2),” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, and in the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C & 2D.

22.8

STREAMING SIMD EXTENSIONS 3 (SSE3)

The Streaming SIMD Extensions 3 (SSE3) were introduced in Pentium 4 processors supporting Intel HyperThreading Technology and Intel Xeon processors. SSE3 extensions include 13 instructions. Ten of these 13 instructions support the single instruction multiple data (SIMD) execution model used with SSE/SSE2 extensions. One
SSE3 instruction accelerates x87 style programming for conversion to integer. The remaining two instructions
(MONITOR and MWAIT) accelerate synchronization of threads. SSE3 instructions are described in Chapter 12,
“Programming with SSE3, SSSE3 and SSE4,” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1, and in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C
& 2D.

22.9

ADDITIONAL STREAMING SIMD EXTENSIONS

The Supplemental Streaming SIMD Extensions 3 (SSSE3) were introduced in the Intel Core 2 processor and Intel
Xeon processor 5100 series. Streaming SIMD Extensions 4 provided 54 new instructions introduced in 45 nm Intel
Xeon processors and Intel Core 2 processors. SSSE3, SSE4.1 and SSE4.2 instructions are described in Chapter 12,
“Programming with SSE3, SSSE3 and SSE4,” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1, and in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C
& 2D.

22.10

INTEL HYPER-THREADING TECHNOLOGY

Intel Hyper-Threading Technology provides two logical processors that can execute two separate code streams
(called threads) concurrently by using shared resources in a single processor core or in a physical package.
This feature was introduced in the Intel Xeon processor MP and later steppings of the Intel Xeon processor, and
Pentium 4 processors supporting Intel Hyper-Threading Technology. The feature is also found in the Pentium
processor Extreme Edition. See also: Section 8.7, “Intel® Hyper-Threading Technology Architecture.”
45 nm and 32 nm Intel Atom processors support Intel Hyper-Threading Technology.
Intel Atom processors based on Silvermont and Airmont microarchitectures do not support Intel Hyper-Threading
Technology

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22.11

MULTI-CORE TECHNOLOGY

The Pentium D processor and Pentium processor Extreme Edition provide two processor cores in each physical
processor package. See also: Section 8.5, “Intel® Hyper-Threading Technology and Intel® Multi-Core Technology,”
and Section 8.8, “Multi-Core Architecture.” Intel Core 2 Duo, Intel Pentium Dual-Core processors, Intel Xeon
processors 3000, 3100, 5100, 5200 series provide two processor cores in each physical processor package. Intel
Core 2 Extreme, Intel Core 2 Quad processors, Intel Xeon processors 3200, 3300, 5300, 5400, 7300 series provide
two processor cores in each physical processor package.

22.12

SPECIFIC FEATURES OF DUAL-CORE PROCESSOR

Dual-core processors may have some processor-specific features. Use CPUID feature flags to detect the availability
features. Note the following:

•

CPUID Brand String — On Pentium processor Extreme Edition, the process will report the correct brand string
only after the correct microcode updates are loaded.

•

Enhanced Intel SpeedStep Technology — This feature is supported in Pentium D processor but not in
Pentium processor Extreme Edition.

22.13

NEW INSTRUCTIONS IN THE PENTIUM AND LATER IA-32 PROCESSORS

Table 22-1 identifies the instructions introduced into the IA-32 in the Pentium processor and later IA-32 processors.

22.13.1 Instructions Added Prior to the Pentium Processor
The following instructions were added in the Intel486 processor:

•
•
•
•
•
•

BSWAP (byte swap) instruction.
XADD (exchange and add) instruction.
CMPXCHG (compare and exchange) instruction.
ΙNVD (invalidate cache) instruction.
WBINVD (write-back and invalidate cache) instruction.
INVLPG (invalidate TLB entry) instruction.

Table 22-1. New Instruction in the Pentium Processor and Later IA-32 Processors
Instruction

CPUID Identification Bits

CMOVcc (conditional move)

EDX, Bit 15

FCMOVcc (floating-point conditional move)

EDX, Bits 0 and 15

FCOMI (floating-point compare and set EFLAGS)

EDX, Bits 0 and 15

RDPMC (read performance monitoring counters)

EAX, Bits 8-11, set to 6H;
see Note 1

UD2 (undefined)

EAX, Bits 8-11, set to 6H

CMPXCHG8B (compare and exchange 8 bytes)

EDX, Bit 8

CPUID (CPU identification)

None; see Note 2

RDTSC (read time-stamp counter)

EDX, Bit 4

RDMSR (read model-specific register)

EDX, Bit 5

WRMSR (write model-specific register)

EDX, Bit 5

MMX Instructions

EDX, Bit 23

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Pentium processor

ARCHITECTURE COMPATIBILITY

Table 22-1. New Instruction in the Pentium Processor and Later IA-32 Processors (Contd.)
Instruction

CPUID Identification Bits

Introduced In

NOTES:
1. The RDPMC instruction was introduced in the P6 family of processors and added to later model Pentium processors. This instruction is model specific in nature and not architectural.
2. The CPUID instruction is available in all Pentium and P6 family processors and in later models of the Intel486 processors. The ability
to set and clear the ID flag (bit 21) in the EFLAGS register indicates the availability of the CPUID instruction.
The following instructions were added in the Intel386 processor:

•
•
•
•
•
•
•
•
•
•
•
•

LSS, LFS, and LGS (load SS, FS, and GS registers).
Long-displacement conditional jumps.
Single-bit instructions.
Bit scan instructions.
Double-shift instructions.
Byte set on condition instruction.
Move with sign/zero extension.
Generalized multiply instruction.
MOV to and from control registers.
MOV to and from test registers (now obsolete).
MOV to and from debug registers.
RSM (resume from SMM). This instruction was introduced in the Intel386 SL and Intel486 SL processors.

The following instructions were added in the Intel 387 math coprocessor:

•
•

FPREM1.
FUCOM, FUCOMP, and FUCOMPP.

22.14

OBSOLETE INSTRUCTIONS

The MOV to and from test registers instructions were removed from the Pentium processor and future IA-32
processors. Execution of these instructions generates an invalid-opcode exception (#UD).

22.15

UNDEFINED OPCODES

All new instructions defined for Intel 64 and IA-32 processors use binary encodings that were reserved on earliergeneration processors. Generally, attempting to execute a reserved opcode results in an invalid-opcode (#UD)
exception being generated. Consequently, programs that execute correctly on earlier-generation processors
cannot erroneously execute these instructions and thereby produce unexpected results when executed on later
Intel 64 processors.
For compatibility with prior generations, there are a few reserved opcodes which do not result in a #UD but rather
result in the same behavior as certain defined instructions. In the interest of standardization, it is recommended
that software not use the opcodes given below but instead use those defined in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C & 2D.
The following items enumerate those reserved opcodes (referring in some cases to opcode groups as defined in
Appendix A, “Opcode Map” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2D).

•

Immediate Group 1 - When not in 64-bit mode, instructions encoded with opcode 82H result in the behavior
of the corresponding instructions encoded with opcode 80H. Depending on the Op/Reg field of the ModR/M
Byte, these opcodes are the byte forms of ADD, OR, ADC, SBB, AND, SUB, XOR, CMP. (In 64-bit mode, these
opcodes cause a #UD.)

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ARCHITECTURE COMPATIBILITY

•

Shift Group 2 /6 - Instructions encoded with opcodes C0H, C1H, D0H, D1H, D2H, and D3H with value 110B in
the Op/Reg field (/6) of the ModR/M Byte result in the behavior of the corresponding instructions with value
100B in the Op/Reg field (/4). These are various forms of the SAL/SHL instruction.

•

Unary Group 3 /1 - Instructions encoded with opcodes F6H and F7H with value 001B in the Op/Reg field (/01)
of the ModR/M Byte result in the behavior of the corresponding instructions with value 000B in the Op/Reg field
(/0). These are various forms of the TEST instruction.

•

Reserved NOP - Instructions encoded with the opcode 0F0DH or with the opcodes 0F18H through 0F1FH
result in the behavior of the NOP (No Operation) instruction, except for those opcodes defined in the the Intel®
64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C & 2D. The opcodes not so
defined are considered "Reserved NOP" and may be used for future instructions which have no defined impact
on existing architectural state. These reserved NOP opcodes are decoded with a ModR/M byte and typical
instruction prefix options but still result in the behavior of the NOP instruction.

•

x87 Opcodes - There are several groups of x87 opcodes which provide the same behavior as other x87
instructions. See Section 22.18.9 for the complete list.

There are a few reserved opcodes that provide unique behavior but do not provide capabilities that are not already
available in the main instructions defined in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volumes 2A, 2B, 2C & 2D.

•
•

F1H - INT1 has subtly different behavior from CD01H, Interrupt with vector 01.

•

x87 Opcodes - There are a few x87 opcodes with subtly different behavior from existing x87 instructions. See
Section 22.18.9 for details.

D6H - When not in 64-bit mode SALC - Set AL to Cary flag. IF (CF=1), AL=FF, ELSE, AL=0 (#UD in 64-bit
mode)

22.16

NEW FLAGS IN THE EFLAGS REGISTER

The section titled “EFLAGS Register” in Chapter 3, “Basic Execution Environment,” of the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 1, shows the configuration of flags in the EFLAGS register for
the P6 family processors. No new flags have been added to this register in the P6 family processors. The flags
added to this register in the Pentium and Intel486 processors are described in the following sections.
The following flags were added to the EFLAGS register in the Pentium processor:

•
•
•

VIF (virtual interrupt flag), bit 19.
VIP (virtual interrupt pending), bit 20.
ID (identification flag), bit 21.

The AC flag (bit 18) was added to the EFLAGS register in the Intel486 processor.

22.16.1 Using EFLAGS Flags to Distinguish Between 32-Bit IA-32 Processors
The following bits in the EFLAGS register that can be used to differentiate between the 32-bit IA-32 processors:

•

Bit 18 (the AC flag) can be used to distinguish an Intel386 processor from the P6 family, Pentium, and Intel486
processors. Since it is not implemented on the Intel386 processor, it will always be clear.

•

Bit 21 (the ID flag) indicates whether an application can execute the CPUID instruction. The ability to set and
clear this bit indicates that the processor is a P6 family or Pentium processor. The CPUID instruction can then
be used to determine which processor.

•

Bits 19 (the VIF flag) and 20 (the VIP flag) will always be zero on processors that do not support virtual mode
extensions, which includes all 32-bit processors prior to the Pentium processor.

See Chapter 19, “Processor Identification and Feature Determination,” in the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 1, for more information on identifying processors.

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22.17

STACK OPERATIONS AND USER SOFTWARE

This section identifies the differences in stack implementation between the various IA-32 processors.

22.17.1

PUSH SP

The P6 family, Pentium, Intel486, Intel386, and Intel 286 processors push a different value on the stack for a PUSH
SP instruction than the 8086 processor. The 32-bit processors push the value of the SP register before it is decremented as part of the push operation; the 8086 processor pushes the value of the SP register after it is decremented. If the value pushed is important, replace PUSH SP instructions with the following three instructions:
PUSH BP
MOV BP, SP
XCHG BP, [BP]
This code functions as the 8086 processor PUSH SP instruction on the P6 family, Pentium, Intel486, Intel386, and
Intel 286 processors.

22.17.2

EFLAGS Pushed on the Stack

The setting of the stored values of bits 12 through 15 (which includes the IOPL field and the NT flag) in the EFLAGS
register by the PUSHF instruction, by interrupts, and by exceptions is different with the 32-bit IA-32 processors
than with the 8086 and Intel 286 processors. The differences are as follows:

•
•
•

8086 processor—bits 12 through 15 are always set.
Intel 286 processor—bits 12 through 15 are always cleared in real-address mode.
32-bit processors in real-address mode—bit 15 (reserved) is always cleared, and bits 12 through 14 have the
last value loaded into them.

22.18

X87 FPU

This section addresses the issues that must be faced when porting floating-point software designed to run on
earlier IA-32 processors and math coprocessors to a Pentium 4, Intel Xeon, P6 family, or Pentium processor with
integrated x87 FPU. To software, a Pentium 4, Intel Xeon, or P6 family processor looks very much like a Pentium
processor. Floating-point software which runs on a Pentium or Intel486 DX processor, or on an Intel486 SX
processor/Intel 487 SX math coprocessor system or an Intel386 processor/Intel 387 math coprocessor system,
will run with at most minor modifications on a Pentium 4, Intel Xeon, or P6 family processor. To port code directly
from an Intel 286 processor/Intel 287 math coprocessor system or an Intel 8086 processor/8087 math coprocessor system to a Pentium 4, Intel Xeon, P6 family, or Pentium processor, certain additional issues must be
addressed.
In the following sections, the term “32-bit x87 FPUs” refers to the P6 family, Pentium, and Intel486 DX processors,
and to the Intel 487 SX and Intel 387 math coprocessors; the term “16-bit IA-32 math coprocessors” refers to the
Intel 287 and 8087 math coprocessors.

22.18.1 Control Register CR0 Flags
The ET, NE, and MP flags in control register CR0 control the interface between the integer unit of an IA-32 processor
and either its internal x87 FPU or an external math coprocessor. The effect of these flags in the various IA-32
processors are described in the following paragraphs.
The ET (extension type) flag (bit 4 of the CR0 register) is used in the Intel386 processor to indicate whether the
math coprocessor in the system is an Intel 287 math coprocessor (flag is clear) or an Intel 387 DX math coprocessor (flag is set). This bit is hardwired to 1 in the P6 family, Pentium, and Intel486 processors.
The NE (Numeric Exception) flag (bit 5 of the CR0 register) is used in the P6 family, Pentium, and Intel486 processors to determine whether unmasked floating-point exceptions are reported internally through interrupt vector 16
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ARCHITECTURE COMPATIBILITY

(flag is set) or externally through an external interrupt (flag is clear). On a hardware reset, the NE flag is initialized
to 0, so software using the automatic internal error-reporting mechanism must set this flag to 1. This flag is nonexistent on the Intel386 processor.
As on the Intel 286 and Intel386 processors, the MP (monitor coprocessor) flag (bit 1 of register CR0) determines
whether the WAIT/FWAIT instructions or waiting-type floating-point instructions trap when the context of the x87
FPU is different from that of the currently-executing task. If the MP and TS flag are set, then a WAIT/FWAIT instruction and waiting instructions will cause a device-not-available exception (interrupt vector 7). The MP flag is used on
the Intel 286 and Intel386 processors to support the use of a WAIT/FWAIT instruction to wait on a device other
than a math coprocessor. The device reports its status through the BUSY# pin. Since the P6 family, Pentium, and
Intel486 processors do not have such a pin, the MP flag has no relevant use and should be set to 1 for normal operation.

22.18.2 x87 FPU Status Word
This section identifies differences to the x87 FPU status word for the different IA-32 processors and math coprocessors, the reason for the differences, and their impact on software.

22.18.2.1 Condition Code Flags (C0 through C3)
The following information pertains to differences in the use of the condition code flags (C0 through C3) located in
bits 8, 9, 10, and 14 of the x87 FPU status word.
After execution of an FINIT instruction or a hardware reset on a 32-bit x87 FPU, the condition code flags are set to
0. The same operations on a 16-bit IA-32 math coprocessor leave these flags intact (they contain their prior value).
This difference in operation has no impact on software and provides a consistent state after reset.
Transcendental instruction results in the core range of the P6 family and Pentium processors may differ from the
Intel486 DX processor and Intel 487 SX math coprocessor by 2 to 3 units in the last place (ulps)—(see “Transcendental Instruction Accuracy” in Chapter 8, “Programming with the x87 FPU,” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1). As a result, the value saved in the C1 flag may also differ.
After an incomplete FPREM/FPREM1 instruction, the C0, C1, and C3 flags are set to 0 on the 32-bit x87 FPUs. After
the same operation on a 16-bit IA-32 math coprocessor, these flags are left intact.
On the 32-bit x87 FPUs, the C2 flag serves as an incomplete flag for the FTAN instruction. On the 16-bit IA-32 math
coprocessors, the C2 flag is undefined for the FPTAN instruction. This difference has no impact on software,
because Intel 287 or 8087 programs do not check C2 after an FPTAN instruction. The use of this flag on later
processors allows fast checking of operand range.

22.18.2.2 Stack Fault Flag
When unmasked stack overflow or underflow occurs on a 32-bit x87 FPU, the IE flag (bit 0) and the SF flag (bit 6)
of the x87 FPU status word are set to indicate a stack fault and condition code flag C1 is set or cleared to indicate
overflow or underflow, respectively. When unmasked stack overflow or underflow occurs on a 16-bit IA-32 math
coprocessor, only the IE flag is set. Bit 6 is reserved on these processors. The addition of the SF flag on a 32-bit x87
FPU has no impact on software. Existing exception handlers need not change, but may be upgraded to take advantage of the additional information.

22.18.3 x87 FPU Control Word
Only affine closure is supported for infinity control on a 32-bit x87 FPU. The infinity control flag (bit 12 of the x87
FPU control word) remains programmable on these processors, but has no effect. This change was made to
conform to the IEEE Standard 754 for Binary Floating-Point Arithmetic. On a 16-bit IA-32 math coprocessor, both
affine and projective closures are supported, as determined by the setting of bit 12. After a hardware reset, the
default value of bit 12 is projective. Software that requires projective infinity arithmetic may give different results.

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22.18.4 x87 FPU Tag Word
When loading the tag word of a 32-bit x87 FPU, using an FLDENV, FRSTOR, or FXRSTOR (Pentium III processor only)
instruction, the processor examines the incoming tag and classifies the location only as empty or non-empty. Thus,
tag values of 00, 01, and 10 are interpreted by the processor to indicate a non-empty location. The tag value of 11
is interpreted by the processor to indicate an empty location. Subsequent operations on a non-empty register
always examine the value in the register, not the value in its tag. The FSTENV, FSAVE, and FXSAVE (Pentium III
processor only) instructions examine the non-empty registers and put the correct values in the tags before storing
the tag word.
The corresponding tag for a 16-bit IA-32 math coprocessor is checked before each register access to determine the
class of operand in the register; the tag is updated after every change to a register so that the tag always reflects
the most recent status of the register. Software can load a tag with a value that disagrees with the contents of a
register (for example, the register contains a valid value, but the tag says special). Here, the 16-bit IA-32 math
coprocessors honor the tag and do not examine the register.
Software written to run on a 16-bit IA-32 math coprocessor may not operate correctly on a 16-bit x87 FPU, if it
uses the FLDENV, FRSTOR, or FXRSTOR instructions to change tags to values (other than to empty) that are
different from actual register contents.
The encoding in the tag word for the 32-bit x87 FPUs for unsupported data formats (including pseudo-zero and
unnormal) is special (10B), to comply with IEEE Standard 754. The encoding in the 16-bit IA-32 math coprocessors
for pseudo-zero and unnormal is valid (00B) and the encoding for other unsupported data formats is special (10B).
Code that recognizes the pseudo-zero or unnormal format as valid must therefore be changed if it is ported to a 32bit x87 FPU.

22.18.5 Data Types
This section discusses the differences of data types for the various x87 FPUs and math coprocessors.

22.18.5.1 NaNs
The 32-bit x87 FPUs distinguish between signaling NaNs (SNaNs) and quiet NaNs (QNaNs). These x87 FPUs only
generate QNaNs and normally do not generate an exception upon encountering a QNaN. An invalid-operation
exception (#I) is generated only upon encountering a SNaN, except for the FCOM, FIST, and FBSTP instructions,
which also generates an invalid-operation exceptions for a QNaNs. This behavior matches IEEE Standard 754.
The 16-bit IA-32 math coprocessors only generate one kind of NaN (the equivalent of a QNaN), but the raise an
invalid-operation exception upon encountering any kind of NaN.
When porting software written to run on a 16-bit IA-32 math coprocessor to a 32-bit x87 FPU, uninitialized memory
locations that contain QNaNs should be changed to SNaNs to cause the x87 FPU or math coprocessor to fault when
uninitialized memory locations are referenced.

22.18.5.2 Pseudo-zero, Pseudo-NaN, Pseudo-infinity, and Unnormal Formats
The 32-bit x87 FPUs neither generate nor support the pseudo-zero, pseudo-NaN, pseudo-infinity, and unnormal
formats. Whenever they encounter them in an arithmetic operation, they raise an invalid-operation exception. The
16-bit IA-32 math coprocessors define and support special handling for these formats. Support for these formats
was dropped to conform with IEEE Standard 754 for Binary Floating-Point Arithmetic.
This change should not impact software ported from 16-bit IA-32 math coprocessors to 32-bit x87 FPUs. The 32bit x87 FPUs do not generate these formats, and therefore will not encounter them unless software explicitly loads
them in the data registers. The only affect may be in how software handles the tags in the tag word (see also:
Section 22.18.4, “x87 FPU Tag Word”).

22.18.6 Floating-Point Exceptions
This section identifies the implementation differences in exception handling for floating-point instructions in the
various x87 FPUs and math coprocessors.
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22.18.6.1 Denormal Operand Exception (#D)
When the denormal operand exception is masked, the 32-bit x87 FPUs automatically normalize denormalized
numbers when possible; whereas, the 16-bit IA-32 math coprocessors return a denormal result. A program written
to run on a 16-bit IA-32 math coprocessor that uses the denormal exception solely to normalize denormalized
operands is redundant when run on the 32-bit x87 FPUs. If such a program is run on 32-bit x87 FPUs, performance
can be improved by masking the denormal exception. Floating-point programs run faster when the FPU performs
normalization of denormalized operands.
The denormal operand exception is not raised for transcendental instructions and the FXTRACT instruction on the
16-bit IA-32 math coprocessors. This exception is raised for these instructions on the 32-bit x87 FPUs. The exception handlers ported to these latter processors need to be changed only if the handlers gives special treatment to
different opcodes.

22.18.6.2 Numeric Overflow Exception (#O)
On the 32-bit x87 FPUs, when the numeric overflow exception is masked and the rounding mode is set to chop
(toward 0), the result is the largest positive or smallest negative number. The 16-bit IA-32 math coprocessors do
not signal the overflow exception when the masked response is not ∞; that is, they signal overflow only when the
rounding control is not set to round to 0. If rounding is set to chop (toward 0), the result is positive or negative ∞.
Under the most common rounding modes, this difference has no impact on existing software.
If rounding is toward 0 (chop), a program on a 32-bit x87 FPU produces, under overflow conditions, a result that is
different in the least significant bit of the significand, compared to the result on a 16-bit IA-32 math coprocessor.
The reason for this difference is IEEE Standard 754 compatibility.
When the overflow exception is not masked, the precision exception is flagged on the 32-bit x87 FPUs. When the
result is stored in the stack, the significand is rounded according to the precision control (PC) field of the FPU
control word or according to the opcode. On the 16-bit IA-32 math coprocessors, the precision exception is not
flagged and the significand is not rounded. The impact on existing software is that if the result is stored on the
stack, a program running on a 32-bit x87 FPU produces a different result under overflow conditions than on a 16bit IA-32 math coprocessor. The difference is apparent only to the exception handler. This difference is for IEEE
Standard 754 compatibility.

22.18.6.3 Numeric Underflow Exception (#U)
When the underflow exception is masked on the 32-bit x87 FPUs, the underflow exception is signaled when the
result is tiny and inexact (see Section 4.9.1.5, “Numeric Underflow Exception (#U)” in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1). When the underflow exception is unmasked and the instruction
is supposed to store the result on the stack, the significand is rounded to the appropriate precision (according to
the PC flag in the FPU control word, for those instructions controlled by PC, otherwise to extended precision), after
adjusting the exponent.

22.18.6.4 Exception Precedence
There is no difference in the precedence of the denormal-operand exception on the 32-bit x87 FPUs, whether it be
masked or not. When the denormal-operand exception is not masked on the 16-bit IA-32 math coprocessors, it
takes precedence over all other exceptions. This difference causes no impact on existing software, but some
unneeded normalization of denormalized operands is prevented on the Intel486 processor and Intel 387 math
coprocessor.

22.18.6.5 CS and EIP For FPU Exceptions
On the Intel 32-bit x87 FPUs, the values from the CS and EIP registers saved for floating-point exceptions point to
any prefixes that come before the floating-point instruction. On the 8087 math coprocessor, the saved CS and IP
registers points to the floating-point instruction.

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ARCHITECTURE COMPATIBILITY

22.18.6.6 FPU Error Signals
The floating-point error signals to the P6 family, Pentium, and Intel486 processors do not pass through an interrupt
controller; an INT# signal from an Intel 387, Intel 287 or 8087 math coprocessors does. If an 8086 processor uses
another exception for the 8087 interrupt, both exception vectors should call the floating-point-error exception
handler. Some instructions in a floating-point-error exception handler may need to be deleted if they use the interrupt controller. The P6 family, Pentium, and Intel486 processors have signals that, with the addition of external
logic, support reporting for emulation of the interrupt mechanism used in many personal computers.
On the P6 family, Pentium, and Intel486 processors, an undefined floating-point opcode will cause an invalidopcode exception (#UD, interrupt vector 6). Undefined floating-point opcodes, like legal floating-point opcodes,
cause a device not available exception (#NM, interrupt vector 7) when either the TS or EM flag in control register
CR0 is set. The P6 family, Pentium, and Intel486 processors do not check for floating-point error conditions on
encountering an undefined floating-point opcode.

22.18.6.7 Assertion of the FERR# Pin
When using the MS-DOS compatibility mode for handing floating-point exceptions, the FERR# pin must be
connected to an input to an external interrupt controller. An external interrupt is then generated when the FERR#
output drives the input to the interrupt controller and the interrupt controller in turn drives the INTR pin on the
processor.
For the P6 family and Intel386 processors, an unmasked floating-point exception always causes the FERR# pin to
be asserted upon completion of the instruction that caused the exception. For the Pentium and Intel486 processors, an unmasked floating-point exception may cause the FERR# pin to be asserted either at the end of the
instruction causing the exception or immediately before execution of the next floating-point instruction. (Note that
the next floating-point instruction would not be executed until the pending unmasked exception has been
handled.) See Appendix D, “Guidelines for Writing x87 FPU Extension Handlers,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for a complete description of the required mechanism for
handling floating-point exceptions using the MS-DOS compatibility mode.
Using FERR# and IGNNE# to handle floating-point exception is deprecated by modern operating systems; this
approach also limits newer processors to operate with one logical processor active.

22.18.6.8 Invalid Operation Exception On Denormals
An invalid-operation exception is not generated on the 32-bit x87 FPUs upon encountering a denormal value when
executing a FSQRT, FDIV, or FPREM instruction or upon conversion to BCD or to integer. The operation proceeds by
first normalizing the value. On the 16-bit IA-32 math coprocessors, upon encountering this situation, the invalidoperation exception is generated. This difference has no impact on existing software. Software running on the 32bit x87 FPUs continues to execute in cases where the 16-bit IA-32 math coprocessors trap. The reason for this
change was to eliminate an exception from being raised.

22.18.6.9 Alignment Check Exceptions (#AC)
If alignment checking is enabled, a misaligned data operand on the P6 family, Pentium, and Intel486 processors
causes an alignment check exception (#AC) when a program or procedure is running at privilege-level 3, except
for the stack portion of the FSAVE/FNSAVE, FXSAVE, FRSTOR, and FXRSTOR instructions.

22.18.6.10 Segment Not Present Exception During FLDENV
On the Intel486 processor, when a segment not present exception (#NP) occurs in the middle of an FLDENV
instruction, it can happen that part of the environment is loaded and part not. In such cases, the FPU control word
is left with a value of 007FH. The P6 family and Pentium processors ensure the internal state is correct at all times
by attempting to read the first and last bytes of the environment before updating the internal state.

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22.18.6.11 Device Not Available Exception (#NM)
The device-not-available exception (#NM, interrupt 7) will occur in the P6 family, Pentium, and Intel486 processors
as described in Section 2.5, “Control Registers,” Table 2-2, and Chapter 6, “Interrupt 7—Device Not Available
Exception (#NM).”

22.18.6.12 Coprocessor Segment Overrun Exception
The coprocessor segment overrun exception (interrupt 9) does not occur in the P6 family, Pentium, and Intel486
processors. In situations where the Intel 387 math coprocessor would cause an interrupt 9, the P6 family, Pentium,
and Intel486 processors simply abort the instruction. To avoid undetected segment overruns, it is recommended
that the floating-point save area be placed in the same page as the TSS. This placement will prevent the FPU environment from being lost if a page fault occurs during the execution of an FLDENV, FRSTOR, or FXRSTOR instruction
while the operating system is performing a task switch.

22.18.6.13 General Protection Exception (#GP)
A general-protection exception (#GP, interrupt 13) occurs if the starting address of a floating-point operand falls
outside a segment’s size. An exception handler should be included to report these programming errors.

22.18.6.14 Floating-Point Error Exception (#MF)
In real mode and protected mode (not including virtual-8086 mode), interrupt vector 16 must point to the floatingpoint exception handler. In virtual-8086 mode, the virtual-8086 monitor can be programmed to accommodate a
different location of the interrupt vector for floating-point exceptions.

22.18.7 Changes to Floating-Point Instructions
This section identifies the differences in floating-point instructions for the various Intel FPU and math coprocessor
architectures, the reason for the differences, and their impact on software.

22.18.7.1 FDIV, FPREM, and FSQRT Instructions
The 32-bit x87 FPUs support operations on denormalized operands and, when detected, an underflow exception
can occur, for compatibility with the IEEE Standard 754. The 16-bit IA-32 math coprocessors do not operate on
denormalized operands or return underflow results. Instead, they generate an invalid-operation exception when
they detect an underflow condition. An existing underflow exception handler will require change only if it gives
different treatment to different opcodes. Also, it is possible that fewer invalid-operation exceptions will occur.

22.18.7.2 FSCALE Instruction
With the 32-bit x87 FPUs, the range of the scaling operand is not restricted. If (0 < | ST(1) < 1), the scaling factor
is 0; therefore, ST(0) remains unchanged. If the rounded result is not exact or if there was a loss of accuracy
(masked underflow), the precision exception is signaled. With the 16-bit IA-32 math coprocessors, the range of the
scaling operand is restricted. If (0 < | ST(1) | < 1), the result is undefined and no exception is signaled. The
impact of this difference on exiting software is that different results are delivered on the 32-bit and 16-bit FPUs and
math coprocessors when (0 < | ST(1) | < 1).

22.18.7.3 FPREM1 Instruction
The 32-bit x87 FPUs compute a partial remainder according to IEEE Standard 754. This instruction does not exist
on the 16-bit IA-32 math coprocessors. The availability of the FPREM1 instruction has is no impact on existing software.

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ARCHITECTURE COMPATIBILITY

22.18.7.4 FPREM Instruction
On the 32-bit x87 FPUs, the condition code flags C0, C3, C1 in the status word correctly reflect the three low-order
bits of the quotient following execution of the FPREM instruction. On the 16-bit IA-32 math coprocessors, the
quotient bits are incorrect when performing a reduction of (64N + M) when (N ≥ 1) and M is 1 or 2. This difference
does not affect existing software; software that works around the bug should not be affected.

22.18.7.5 FUCOM, FUCOMP, and FUCOMPP Instructions
When executing the FUCOM, FUCOMP, and FUCOMPP instructions, the 32-bit x87 FPUs perform unordered compare
according to IEEE Standard 754. These instructions do not exist on the 16-bit IA-32 math coprocessors. The availability of these new instructions has no impact on existing software.

22.18.7.6 FPTAN Instruction
On the 32-bit x87 FPUs, the range of the operand for the FPTAN instruction is much less restricted (| ST(0) | < 263)
than on earlier math coprocessors. The instruction reduces the operand internally using an internal π/4 constant
that is more accurate. The range of the operand is restricted to (| ST(0) | < π/4) on the 16-bit IA-32 math coprocessors; the operand must be reduced to this range using FPREM. This change has no impact on existing software.
See also sections 8.3.8 and section 8.3.10 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 1 for more information on the accuracy of the FPTAN instruction.

22.18.7.7 Stack Overflow
On the 32-bit x87 FPUs, if an FPU stack overflow occurs when the invalid-operation exception is masked, the FPU
returns the real, integer, or BCD-integer indefinite value to the destination operand, depending on the instruction
being executed. On the 16-bit IA-32 math coprocessors, the original operand remains unchanged following a stack
overflow, but it is loaded into register ST(1). This difference has no impact on existing software.

22.18.7.8 FSIN, FCOS, and FSINCOS Instructions
On the 32-bit x87 FPUs, these instructions perform three common trigonometric functions. These instructions do
not exist on the 16-bit IA-32 math coprocessors. The availability of these instructions has no impact on existing
software, but using them provides a performance upgrade. See also sections 8.3.8 and section 8.3.10 of the Intel®
64 and IA-32 Architectures Software Developer’s Manual, Volume 1 for more information on the accuracy of the
FSIN, FCOS, and FSINCOS instructions.

22.18.7.9 FPATAN Instruction
On the 32-bit x87 FPUs, the range of operands for the FPATAN instruction is unrestricted. On the 16-bit IA-32 math
coprocessors, the absolute value of the operand in register ST(0) must be smaller than the absolute value of the
operand in register ST(1). This difference has impact on existing software.

22.18.7.10 F2XM1 Instruction
The 32-bit x87 FPUs support a wider range of operands (–1 < ST (0) < + 1) for the F2XM1 instruction. The
supported operand range for the 16-bit IA-32 math coprocessors is (0 ≤ ST(0) ≤ 0.5). This difference has no impact
on existing software.

22.18.7.11 FLD Instruction
On the 32-bit x87 FPUs, when using the FLD instruction to load an extended-real value, a denormal-operand
exception is not generated because the instruction is not arithmetic. The 16-bit IA-32 math coprocessors do report
a denormal-operand exception in this situation. This difference does not affect existing software.
On the 32-bit x87 FPUs, loading a denormal value that is in single- or double-real format causes the value to be
converted to extended-real format. Loading a denormal value on the 16-bit IA-32 math coprocessors causes the
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ARCHITECTURE COMPATIBILITY

value to be converted to an unnormal. If the next instruction is FXTRACT or FXAM, the 32-bit x87 FPUs will give a
different result than the 16-bit IA-32 math coprocessors. This change was made for IEEE Standard 754 compatibility.
On the 32-bit x87 FPUs, loading an SNaN that is in single- or double-real format causes the FPU to generate an
invalid-operation exception. The 16-bit IA-32 math coprocessors do not raise an exception when loading a signaling
NaN. The invalid-operation exception handler for 16-bit math coprocessor software needs to be updated to handle
this condition when porting software to 32-bit FPUs. This change was made for IEEE Standard 754 compatibility.

22.18.7.12 FXTRACT Instruction
On the 32-bit x87 FPUs, if the operand is 0 for the FXTRACT instruction, the divide-by-zero exception is reported
and –∞ is delivered to register ST(1). If the operand is +∞, no exception is reported. If the operand is 0 on the 16bit IA-32 math coprocessors, 0 is delivered to register ST(1) and no exception is reported. If the operand is +∞, the
invalid-operation exception is reported. These differences have no impact on existing software. Software usually
bypasses 0 and ∞. This change is due to the IEEE Standard 754 recommendation to fully support the “logb” function.

22.18.7.13 Load Constant Instructions
On 32-bit x87 FPUs, rounding control is in effect for the load constant instructions. Rounding control is not in effect
for the 16-bit IA-32 math coprocessors. Results for the FLDPI, FLDLN2, FLDLG2, and FLDL2E instructions are the
same as for the 16-bit IA-32 math coprocessors when rounding control is set to round to nearest or round to +∞.
They are the same for the FLDL2T instruction when rounding control is set to round to nearest, round to –∞, or
round to zero. Results are different from the 16-bit IA-32 math coprocessors in the least significant bit of the
mantissa if rounding control is set to round to –∞ or round to 0 for the FLDPI, FLDLN2, FLDLG2, and FLDL2E instructions; they are different for the FLDL2T instruction if round to +∞ is specified. These changes were implemented for
compatibility with IEEE Standard 754 for Floating-Point Arithmetic recommendations.

22.18.7.14 FXAM Instruction
With the 32-bit x87 FPUs, if the FPU encounters an empty register when executing the FXAM instruction, it not
generate combinations of C0 through C3 equal to 1101 or 1111. The 16-bit IA-32 math coprocessors may generate
these combinations, among others. This difference has no impact on existing software; it provides a performance
upgrade to provide repeatable results.

22.18.7.15 FSAVE and FSTENV Instructions
With the 32-bit x87 FPUs, the address of a memory operand pointer stored by FSAVE or FSTENV is undefined if the
previous floating-point instruction did not refer to memory

22.18.8 Transcendental Instructions
The floating-point results of the P6 family and Pentium processors for transcendental instructions in the core range
may differ from the Intel486 processors by about 2 or 3 ulps (see “Transcendental Instruction Accuracy” in Chapter
8, “Programming with the x87 FPU,” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 1). Condition code flag C1 of the status word may differ as a result. The exact threshold for underflow and
overflow will vary by a few ulps. The P6 family and Pentium processors’ results will have a worst case error of less
than 1 ulp when rounding to the nearest-even and less than 1.5 ulps when rounding in other modes. The transcendental instructions are guaranteed to be monotonic, with respect to the input operands, throughout the domain
supported by the instruction.
Transcendental instructions may generate different results in the round-up flag (C1) on the 32-bit x87 FPUs. The
round-up flag is undefined for these instructions on the 16-bit IA-32 math coprocessors. This difference has no
impact on existing software.

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ARCHITECTURE COMPATIBILITY

22.18.9 Obsolete Instructions and Undefined Opcodes
The 8087 math coprocessor instructions FENI and FDISI, and the Intel 287 math coprocessor instruction FSETPM
are treated as integer NOP instructions in the 32-bit x87 FPUs. If these opcodes are detected in the instruction
stream, no specific operation is performed and no internal states are affected. FSETPM informed the Intel 287 math
coprocessor that the processor was in protected mode. The 32-bit x87 FPUs handle all addressing and exceptionpointer information, whether in protected mode or not.
For compatibility with prior generations there are a few reserved x87 opcodes which do not result in an invalidopcode (#UD) exception, but rather result in the same behavior as existing defined x87 instructions. In the interest
of standardization, it is recommended that the opcodes defined in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volumes 2A, 2B, 2C & 2D be used for these operations for standardization.

•
•
•
•
•
•
•

DCD0H through DCD7H - Behaves the same as FCOM, D8D0H through D8D7H.
DCD8H through DCDFH - Behaves the same as FCOMP, D8D8H through D8DFH.
D0C8H through D0CFH - Behaves the same as FXCH, D9C8H through D9CFH.
DED0H through DED7H - Behaves the same as FCOMP, D8D8H through D8DFH.
DFD0H through DFD7H - Behaves the same as FSTP, DDD8H through DDDFH.
DFC8H through DFCFH - Behaves the same as FXCH, D9C8H through D9CFH.
DFD8H through DFDFH - Behaves the same as FSTP, DDD8H through DDDFH.

There are a few reserved x87 opcodes which provide unique behavior but do not provide capabilities which are not
already available in the main instructions defined in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volumes 2A, 2B, 2C & 2D.

•

D9D8H through D9DFH - Behaves the same as FSTP (DDD8H through DDDFH) but won't cause a stack
underflow exception.

•

DFC0H through DFC7H - Behaves the same as FFREE (DDC0H through DDD7H) with the addition of an x87
stack POP.

22.18.10 WAIT/FWAIT Prefix Differences
On the Intel486 processor, when a WAIT/FWAIT instruction precedes a floating-point instruction (one which itself
automatically synchronizes with the previous floating-point instruction), the WAIT/FWAIT instruction is treated as
a no-op. Pending floating-point exceptions from a previous floating-point instruction are processed not on the
WAIT/FWAIT instruction but on the floating-point instruction following the WAIT/FWAIT instruction. In such a case,
the report of a floating-point exception may appear one instruction later on the Intel486 processor than on a P6
family or Pentium FPU, or on Intel 387 math coprocessor.

22.18.11 Operands Split Across Segments and/or Pages
On the P6 family, Pentium, and Intel486 processor FPUs, when the first half of an operand to be written is inside a
page or segment and the second half is outside, a memory fault can cause the first half to be stored but not the
second half. In this situation, the Intel 387 math coprocessor stores nothing.

22.18.12 FPU Instruction Synchronization
On the 32-bit x87 FPUs, all floating-point instructions are automatically synchronized; that is, the processor automatically waits until the previous floating-point instruction has completed before completing the next floating-point
instruction. No explicit WAIT/FWAIT instructions are required to assure this synchronization. For the 8087 math
coprocessors, explicit waits are required before each floating-point instruction to ensure synchronization. Although
8087 programs having explicit WAIT instructions execute perfectly on the 32-bit IA-32 processors without reassembly, these WAIT instructions are unnecessary.

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ARCHITECTURE COMPATIBILITY

22.19

SERIALIZING INSTRUCTIONS

Certain instructions have been defined to serialize instruction execution to ensure that modifications to flags, registers and memory are completed before the next instruction is executed (or in P6 family processor terminology
“committed to machine state”). Because the P6 family processors use branch-prediction and out-of-order execution techniques to improve performance, instruction execution is not generally serialized until the results of an
executed instruction are committed to machine state (see Chapter 2, “Intel® 64 and IA-32 Architectures,” in the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1).
As a result, at places in a program or task where it is critical to have execution completed for all previous instructions before executing the next instruction (for example, at a branch, at the end of a procedure, or in multiprocessor dependent code), it is useful to add a serializing instruction. See Section 8.3, “Serializing Instructions,” for
more information on serializing instructions.

22.20

FPU AND MATH COPROCESSOR INITIALIZATION

Table 9-1 shows the states of the FPUs in the P6 family, Pentium, Intel486 processors and of the Intel 387 math
coprocessor and Intel 287 coprocessor following a power-up, reset, or INIT, or following the execution of an
FINIT/FNINIT instruction. The following is some additional compatibility information concerning the initialization of
x87 FPUs and math coprocessors.

22.20.1 Intel® 387 and Intel® 287 Math Coprocessor Initialization
Following an Intel386 processor reset, the processor identifies its coprocessor type (Intel® 287 or Intel® 387 DX
math coprocessor) by sampling its ERROR# input some time after the falling edge of RESET# signal and before
execution of the first floating-point instruction. The Intel 287 coprocessor keeps its ERROR# output in inactive
state after hardware reset; the Intel 387 coprocessor keeps its ERROR# output in active state after hardware
reset.
Upon hardware reset or execution of the FINIT/FNINIT instruction, the Intel 387 math coprocessor signals an error
condition. The P6 family, Pentium, and Intel486 processors, like the Intel 287 coprocessor, do not.

22.20.2 Intel486 SX Processor and Intel 487 SX Math Coprocessor Initialization
When initializing an Intel486 SX processor and an Intel 487 SX math coprocessor, the initialization routine should
check the presence of the math coprocessor and should set the FPU related flags (EM, MP, and NE) in control
register CR0 accordingly (see Section 2.5, “Control Registers,” for a complete description of these flags). Table 22-2
gives the recommended settings for these flags when the math coprocessor is present. The FSTCW instruction will
give a value of FFFFH for the Intel486 SX microprocessor and 037FH for the Intel 487 SX math coprocessor.

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ARCHITECTURE COMPATIBILITY

Table 22-2. Recommended Values of the EM, MP, and NE Flags for Intel486 SX Microprocessor/Intel 487 SX Math
Coprocessor System
CR0 Flags

Intel486 SX Processor Only

Intel 487 SX Math Coprocessor Present

EM

1

0

MP

0

1

NE

1

0, for MS-DOS* systems
1, for user-defined exception handler

The EM and MP flags in register CR0 are interpreted as shown in Table 22-3.

Table 22-3. EM and MP Flag Interpretation
EM

MP

Interpretation

0

0

Floating-point instructions are passed to FPU; WAIT/FWAIT and other waiting-type instructions
ignore TS.

0

1

Floating-point instructions are passed to FPU; WAIT/FWAIT and other waiting-type instructions
test TS.

1

0

Floating-point instructions trap to emulator; WAIT/FWAIT and other waiting-type instructions
ignore TS.

1

1

Floating-point instructions trap to emulator; WAIT/FWAIT and other waiting-type instructions
test TS.

Following is an example code sequence to initialize the system and check for the presence of Intel486 SX
processor/Intel 487 SX math coprocessor.
fninit
fstcw mem_loc
mov ax, mem_loc
cmp ax, 037fh
jz Intel487_SX_Math_CoProcessor_present
jmp Intel486_SX_microprocessor_present

;ax=037fh
;ax=ffffh

If the Intel 487 SX math coprocessor is not present, the following code can be run to set the CR0 register for the
Intel486 SX processor.
mov eax, cr0
and eax, fffffffdh ;make MP=0
or eax, 0024h
;make EM=1, NE=1
mov cr0, eax
This initialization will cause any floating-point instruction to generate a device not available exception (#NH), interrupt 7. The software emulation will then take control to execute these instructions. This code is not required if an
Intel 487 SX math coprocessor is present in the system. In that case, the typical initialization routine for the
Intel486 SX microprocessor will be adequate.
Also, when designing an Intel486 SX processor based system with an Intel 487 SX math coprocessor, timing loops
should be independent of frequency and clocks per instruction. One way to attain this is to implement these loops
in hardware and not in software (for example, BIOS).

22.21

CONTROL REGISTERS

The following sections identify the new control registers and control register flags and fields that were introduced
to the 32-bit IA-32 in various processor families. See Figure 2-7 for the location of these flags and fields in the
control registers.
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ARCHITECTURE COMPATIBILITY

The Pentium III processor introduced one new control flag in control register CR4:

•

OSXMMEXCPT (bit 10) — The OS will set this bit if it supports unmasked SIMD floating-point exceptions.

The Pentium II processor introduced one new control flag in control register CR4:

•

OSFXSR (bit 9) — The OS supports saving and restoring the Pentium III processor state during context
switches.

The Pentium Pro processor introduced three new control flags in control register CR4:

•

PAE (bit 5) — Physical address extension. Enables paging mechanism to reference extended physical addresses
when set; restricts physical addresses to 32 bits when clear (see also: Section 22.22.1.1, “Physical Memory
Addressing Extension”).

•

PGE (bit 7) — Page global enable. Inhibits flushing of frequently-used or shared pages on CR3 writes (see also:
Section 22.22.1.2, “Global Pages”).

•

PCE (bit 8) — Performance-monitoring counter enable. Enables execution of the RDPMC instruction at any
protection level.

The content of CR4 is 0H following a hardware reset.
Control register CR4 was introduced in the Pentium processor. This register contains flags that enable certain new
extensions provided in the Pentium processor:

•

VME — Virtual-8086 mode extensions. Enables support for a virtual interrupt flag in virtual-8086 mode (see
Section 20.3, “Interrupt and Exception Handling in Virtual-8086 Mode”).

•

PVI — Protected-mode virtual interrupts. Enables support for a virtual interrupt flag in protected mode (see
Section 20.4, “Protected-Mode Virtual Interrupts”).

•

TSD — Time-stamp disable. Restricts the execution of the RDTSC instruction to procedures running at
privileged level 0.

•

DE — Debugging extensions. Causes an undefined opcode (#UD) exception to be generated when debug
registers DR4 and DR5 are references for improved performance (see Section 22.23.3, “Debug Registers DR4
and DR5”).

•

PSE — Page size extensions. Enables 4-MByte pages with 32-bit paging when set (see Section 4.3, “32-Bit
Paging”).

•

MCE — Machine-check enable. Enables the machine-check exception, allowing exception handling for certain
hardware error conditions (see Chapter 15, “Machine-Check Architecture”).

The Intel486 processor introduced five new flags in control register CR0:

•
•
•

NE — Numeric error. Enables the normal mechanism for reporting floating-point numeric errors.

•

NW — Not write-through. Enables write-throughs and cache invalidation cycles when clear and disables invalidation cycles and write-throughs that hit in the cache when set.

•

CD — Cache disable. Enables the internal cache when clear and disables the cache when set.

WP — Write protect. Write-protects read-only pages against supervisor-mode accesses.
AM — Alignment mask. Controls whether alignment checking is performed. Operates in conjunction with the AC
(Alignment Check) flag.

The Intel486 processor introduced two new flags in control register CR3:

•

PCD — Page-level cache disable. The state of this flag is driven on the PCD# pin during bus cycles that are not
paged, such as interrupt acknowledge cycles, when paging is enabled. The PCD# pin is used to control caching
in an external cache on a cycle-by-cycle basis.

•

PWT — Page-level write-through. The state of this flag is driven on the PWT# pin during bus cycles that are not
paged, such as interrupt acknowledge cycles, when paging is enabled. The PWT# pin is used to control write
through in an external cache on a cycle-by-cycle basis.

22-18 Vol. 3B

ARCHITECTURE COMPATIBILITY

22.22

MEMORY MANAGEMENT FACILITIES

The following sections describe the new memory management facilities available in the various IA-32 processors
and some compatibility differences.

22.22.1 New Memory Management Control Flags
The Pentium Pro processor introduced three new memory management features: physical memory addressing
extension, the global bit in page-table entries, and general support for larger page sizes. These features are only
available when operating in protected mode.

22.22.1.1 Physical Memory Addressing Extension
The new PAE (physical address extension) flag in control register CR4, bit 5, may enable additional address lines
on the processor, allowing extended physical addresses. This option can only be used when paging is enabled,
using a new page-table mechanism provided to support the larger physical address range (see Section 4.1, “Paging
Modes and Control Bits”).

22.22.1.2 Global Pages
The new PGE (page global enable) flag in control register CR4, bit 7, provides a mechanism for preventing
frequently used pages from being flushed from the translation lookaside buffer (TLB). When this flag is set,
frequently used pages (such as pages containing kernel procedures or common data tables) can be marked global
by setting the global flag in a page-directory or page-table entry.
On a task switch or a write to control register CR3 (which normally causes the TLBs to be flushed), the entries in
the TLB marked global are not flushed. Marking pages global in this manner prevents unnecessary reloading of the
TLB due to TLB misses on frequently used pages. See Section 4.10, “Caching Translation Information” for a
detailed description of this mechanism.

22.22.1.3 Larger Page Sizes
The P6 family processors support large page sizes. For 32-bit paging, this facility is enabled with the PSE (page size
extension) flag in control register CR4, bit 4. When this flag is set, the processor supports either 4-KByte or 4MByte page sizes. PAE paging and 4-level paging1 support 2-MByte pages regardless of the value of CR4.PSE (see
Section 4.4, “PAE Paging” and Section 4.5, “4-Level Paging”). See Chapter 4, “Paging,” for more information about
large page sizes.

22.22.2 CD and NW Cache Control Flags
The CD and NW flags in control register CR0 were introduced in the Intel486 processor. In the P6 family and
Pentium processors, these flags are used to implement a writeback strategy for the data cache; in the Intel486
processor, they implement a write-through strategy. See Table 11-5 for a comparison of these bits on the P6 family,
Pentium, and Intel486 processors. For complete information on caching, see Chapter 11, “Memory Cache Control.”

22.22.3 Descriptor Types and Contents
Operating-system code that manages space in descriptor tables often contains an invalid value in the access-rights
field of descriptor-table entries to identify unused entries. Access rights values of 80H and 00H remain invalid for
the P6 family, Pentium, Intel486, Intel386, and Intel 286 processors. Other values that were invalid on the Intel
286 processor may be valid on the 32-bit processors because uses for these bits have been defined.

1. Earlier versions of this manual used the term “IA-32e paging” to identify 4-level paging.
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ARCHITECTURE COMPATIBILITY

22.22.4 Changes in Segment Descriptor Loads
On the Intel386 processor, loading a segment descriptor always causes a locked read and write to set the accessed
bit of the descriptor. On the P6 family, Pentium, and Intel486 processors, the locked read and write occur only if the
bit is not already set.

22.23

DEBUG FACILITIES

The P6 family and Pentium processors include extensions to the Intel486 processor debugging support for breakpoints. To use the new breakpoint features, it is necessary to set the DE flag in control register CR4.

22.23.1 Differences in Debug Register DR6
It is not possible to write a 1 to reserved bit 12 in debug status register DR6 on the P6 family and Pentium processors; however, it is possible to write a 1 in this bit on the Intel486 processor. See Table 9-1 for the different setting
of this register following a power-up or hardware reset.

22.23.2 Differences in Debug Register DR7
The P6 family and Pentium processors determines the type of breakpoint access by the R/W0 through R/W3 fields
in debug control register DR7 as follows:
00

Break on instruction execution only.

01

Break on data writes only.

10

Undefined if the DE flag in control register CR4 is cleared; break on I/O reads or writes but not instruction
fetches if the DE flag in control register CR4 is set.

11

Break on data reads or writes but not instruction fetches.

On the P6 family and Pentium processors, reserved bits 11, 12, 14 and 15 are hard-wired to 0. On the Intel486
processor, however, bit 12 can be set. See Table 9-1 for the different settings of this register following a power-up
or hardware reset.

22.23.3 Debug Registers DR4 and DR5
Although the DR4 and DR5 registers are documented as reserved, previous generations of processors aliased references to these registers to debug registers DR6 and DR7, respectively. When debug extensions are not enabled
(the DE flag in control register CR4 is cleared), the P6 family and Pentium processors remain compatible with
existing software by allowing these aliased references. When debug extensions are enabled (the DE flag is set),
attempts to reference registers DR4 or DR5 will result in an invalid-opcode exception (#UD).

22.24

RECOGNITION OF BREAKPOINTS

For the Pentium processor, it is recommended that debuggers execute the LGDT instruction before returning to the
program being debugged to ensure that breakpoints are detected. This operation does not need to be performed
on the P6 family, Intel486, or Intel386 processors.
The implementation of test registers on the Intel486 processor used for testing the cache and TLB has been redesigned using MSRs on the P6 family and Pentium processors. (Note that MSRs used for this function are different
on the P6 family and Pentium processors.) The MOV to and from test register instructions generate invalid-opcode
exceptions (#UD) on the P6 family processors.

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ARCHITECTURE COMPATIBILITY

22.25

EXCEPTIONS AND/OR EXCEPTION CONDITIONS

This section describes the new exceptions and exception conditions added to the 32-bit IA-32 processors and
implementation differences in existing exception handling. See Chapter 6, “Interrupt and Exception Handling,” for
a detailed description of the IA-32 exceptions.
The Pentium III processor introduced new state with the XMM registers. Computations involving data in these registers can produce exceptions. A new MXCSR control/status register is used to determine which exception or exceptions have occurred. When an exception associated with the XMM registers occurs, an interrupt is generated.

•

SIMD floating-point exception (#XM, interrupt 19) — New exceptions associated with the SIMD floating-point
registers and resulting computations.

No new exceptions were added with the Pentium Pro and Pentium II processors. The set of available exceptions is
the same as for the Pentium processor. However, the following exception condition was added to the IA-32 with the
Pentium Pro processor:

•

Machine-check exception (#MC, interrupt 18) — New exception conditions. Many exception conditions have
been added to the machine-check exception and a new architecture has been added for handling and reporting
on hardware errors. See Chapter 15, “Machine-Check Architecture,” for a detailed description of the new
conditions.

The following exceptions and/or exception conditions were added to the IA-32 with the Pentium processor:

•

Machine-check exception (#MC, interrupt 18) — New exception. This exception reports parity and other
hardware errors. It is a model-specific exception and may not be implemented or implemented differently in
future processors. The MCE flag in control register CR4 enables the machine-check exception. When this bit is
clear (which it is at reset), the processor inhibits generation of the machine-check exception.

•

General-protection exception (#GP, interrupt 13) — New exception condition added. An attempt to write a 1 to
a reserved bit position of a special register causes a general-protection exception to be generated.

•

Page-fault exception (#PF, interrupt 14) — New exception condition added. When a 1 is detected in any of the
reserved bit positions of a page-table entry, page-directory entry, or page-directory pointer during address
translation, a page-fault exception is generated.

The following exception was added to the Intel486 processor:

•

Alignment-check exception (#AC, interrupt 17) — New exception. Reports unaligned memory references when
alignment checking is being performed.

The following exceptions and/or exception conditions were added to the Intel386 processor:

•

Divide-error exception (#DE, interrupt 0)
— Change in exception handling. Divide-error exceptions on the Intel386 processors always leave the saved
CS:IP value pointing to the instruction that failed. On the 8086 processor, the CS:IP value points to the next
instruction.
— Change in exception handling. The Intel386 processors can generate the largest negative number as a
quotient for the IDIV instruction (80H and 8000H). The 8086 processor generates a divide-error exception
instead.

•

Invalid-opcode exception (#UD, interrupt 6) — New exception condition added. Improper use of the LOCK
instruction prefix can generate an invalid-opcode exception.

•

Page-fault exception (#PF, interrupt 14) — New exception condition added. If paging is enabled in a 16-bit
program, a page-fault exception can be generated as follows. Paging can be used in a system with 16-bit tasks
if all tasks use the same page directory. Because there is no place in a 16-bit TSS to store the PDBR register,
switching to a 16-bit task does not change the value of the PDBR register. Tasks ported from the Intel 286
processor should be given 32-bit TSSs so they can make full use of paging.

•

General-protection exception (#GP, interrupt 13) — New exception condition added. The Intel386 processor
sets a limit of 15 bytes on instruction length. The only way to violate this limit is by putting redundant prefixes
before an instruction. A general-protection exception is generated if the limit on instruction length is violated.
The 8086 processor has no instruction length limit.

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ARCHITECTURE COMPATIBILITY

22.25.1 Machine-Check Architecture
The Pentium Pro processor introduced a new architecture to the IA-32 for handling and reporting on machine-check
exceptions. This machine-check architecture (described in detail in Chapter 15, “Machine-Check Architecture”)
greatly expands the ability of the processor to report on internal hardware errors.

22.25.2 Priority of Exceptions
The priority of exceptions are broken down into several major categories:
1. Traps on the previous instruction
2. External interrupts
3. Faults on fetching the next instruction
4. Faults in decoding the next instruction
5. Faults on executing an instruction
There are no changes in the priority of these major categories between the different processors, however, exceptions within these categories are implementation dependent and may change from processor to processor.

22.25.3 Exception Conditions of Legacy SIMD Instructions Operating on MMX Registers
MMX instructions and a subset of SSE, SSE2, SSSE3 instructions operate on MMX registers. The exception conditions of these instructions are described in the following tables.

Real

Virtual-8086

Protected and
Compatibility

64-bit

Table 22-4. Exception Conditions for Legacy SIMD/MMX Instructions with FP Exception and 16-Byte Alignment

X

X

X

X

If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 0.

X

X

X

X

If CR0.EM[bit 2] = 1.
If CR4.OSFXSR[bit 9] = 0.

X

X

X

X

If preceded by a LOCK prefix (F0H)

X

X

X

X

If any corresponding CPUID feature flag is ‘0’

#MF

X

X

X

X

If there is a pending X87 FPU exception

#NM

X

X

X

X

If CR0.TS[bit 3]=1

Exception

Invalid Opcode,
#UD

X

Stack, SS(0)
X

X

#PF(fault-code)

22-22 Vol. 3B

If a memory address referencing the SS segment is in a non-canonical form

X

Legacy SSE: Memory operand is not 16-byte aligned
For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments.

X
X

Applicable
Instructions

For an illegal address in the SS segment
X

X

General Protection, #GP(0)

#XM

X

X

Cause of Exception

X

If the memory address is in a non-canonical form.
If any part of the operand lies outside the effective address space from 0 to FFFFH

X

X

X

For a page fault

X

X

X

If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 1

CVTPD2PI, CVTTPD2PI

ARCHITECTURE COMPATIBILITY

Virtual-8086

Protected and
Compatibility

64-bit

Exception

Real

Table 22-5. Exception Conditions for Legacy SIMD/MMX Instructions with XMM and FP Exception

X

X

X

X

Cause of Exception

If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 0.

X

X

X

X

If CR0.EM[bit 2] = 1.
If CR4.OSFXSR[bit 9] = 0.

X

X

X

X

If preceded by a LOCK prefix (F0H)

X

X

X

X

If any corresponding CPUID feature flag is ‘0’

#MF

X

X

X

X

If there is a pending X87 FPU exception

#NM

X

X

X

X

If CR0.TS[bit 3]=1

Invalid Opcode, #UD

X

Stack, SS(0)

For an illegal address in the SS segment
X

For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments.

X
General Protection,
#GP(0)

X
X

If a memory address referencing the SS segment is in a non-canonical form

If the memory address is in a non-canonical form.
If any part of the operand lies outside the effective address space from 0 to
FFFFH

X

#PF(fault-code)

X

X

X

For a page fault

Alignment Check
#AC(0)

X

X

X

If alignment checking is enabled and an unaligned memory reference is made while
the current privilege level is 3.

X

X

X

If an unmasked SIMD floating-point exception and CR4.OSXMMEXCPT[bit 10] = 1

SIMD Floating-point
Exception, #XM
Applicable Instructions

X

CVTPI2PS, CVTPS2PI, CVTTPS2PI

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ARCHITECTURE COMPATIBILITY

Real

Virtual-8086

Protected and
Compatibility

64-bit

Table 22-6. Exception Conditions for Legacy SIMD/MMX Instructions with XMM and without FP Exception

X

X

X

X

If CR0.EM[bit 2] = 1.
If CR4.OSFXSR[bit 9] = 0.

X

X

X

X

If preceded by a LOCK prefix (F0H)

X

X

X

X

If any corresponding CPUID feature flag is ‘0’

#MF1

X

X

X

X

If there is a pending X87 FPU exception

#NM

X

X

X

X

If CR0.TS[bit 3]=1

Exception

Invalid Opcode, #UD

X

Stack, SS(0)

For an illegal address in the SS segment
X

X
X

If a memory address referencing the SS segment is in a non-canonical form
For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments.

X
General Protection,
#GP(0)

Cause of Exception

If the memory address is in a non-canonical form.
If any part of the operand lies outside the effective address space from 0 to
FFFFH

X

#PF(fault-code)

X

X

X

For a page fault

Alignment Check
#AC(0)

X

X

X

If alignment checking is enabled and an unaligned memory reference is made
while the current privilege level is 3.

Applicable Instructions

CVTPI2PD

NOTES:
1. Applies to “CVTPI2PD xmm, mm” but not “CVTPI2PD xmm, m64”.

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ARCHITECTURE COMPATIBILITY

Virtual-8086

X

X

X

X

If CR0.EM[bit 2] = 1.

X

X

X

X

If preceded by a LOCK prefix (F0H)

X

X

X

X

If any corresponding CPUID feature flag is ‘0’

#MF

X

X

X

X

If there is a pending X87 FPU exception

#NM

X

X

X

X

If CR0.TS[bit 3]=1

Exception

Invalid Opcode, #UD

64-bit

Real

Protected and
Compatibility

Table 22-7. Exception Conditions for SIMD/MMX Instructions with Memory Reference

X

Stack, SS(0)

For an illegal address in the SS segment
X

X
X

If a memory address referencing the SS segment is in a non-canonical form
For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments.

X

General Protection,
#GP(0)

Cause of Exception

X

If the memory address is in a non-canonical form.
If any part of the operand lies outside the effective address space from 0 to FFFFH

#PF(fault-code)

X

X

X

For a page fault

Alignment Check
#AC(0)

X

X

X

If alignment checking is enabled and an unaligned memory reference is made while
the current privilege level is 3.

Applicable Instructions

PABSB, PABSD, PABSW, PACKSSWB, PACKSSDW, PACKUSWB, PADDB, PADDD, PADDQ, PADDW, PADDSB,
PADDSW, PADDUSB, PADDUSW, PALIGNR, PAND, PANDN, PAVGB, PAVGW, PCMPEQB, PCMPEQD, PCMPEQW,
PCMPGTB, PCMPGTD, PCMPGTW, PHADDD, PHADDW, PHADDSW, PHSUBD, PHSUBW, PHSUBSW, PINSRW,
PMADDUBSW, PMADDWD, PMAXSW, PMAXUB, PMINSW, PMINUB, PMULHRSW, PMULHUW, PMULHW, PMULLW,
PMULUDQ, PSADBW, PSHUFB, PSHUFW, PSIGNB PSIGND PSIGNW, PSLLW, PSLLD, PSLLQ, PSRAD, PSRAW,
PSRLW, PSRLD, PSRLQ, PSUBB, PSUBD, PSUBQ, PSUBW, PSUBSB, PSUBSW, PSUBUSB, PSUBUSW,
PUNPCKHBW, PUNPCKHWD, PUNPCKHDQ, PUNPCKLBW, PUNPCKLWD, PUNPCKLDQ, PXOR

Vol. 3B 22-25

ARCHITECTURE COMPATIBILITY

Real

Virtual-8086

Protected and
Compatibility

64-bit

Table 22-8. Exception Conditions for Legacy SIMD/MMX Instructions without FP Exception

X

X

X

X

If CR0.EM[bit 2] = 1.
If ModR/M.mod ≠ 11b1

X

X

X

X

If preceded by a LOCK prefix (F0H)

X

X

X

X

If any corresponding CPUID feature flag is ‘0’

#MF

X

X

X

X

If there is a pending X87 FPU exception

#NM

X

X

X

X

If CR0.TS[bit 3]=1

Exception

Invalid Opcode, #UD

X

Stack, SS(0)

For an illegal address in the SS segment
X

If a memory address referencing the SS segment is in a non-canonical form
For an illegal memory operand effective address in the CS, DS, ES, FS or GS segments.
If the destination operand is in a non-writable segment.2
If the DS, ES, FS, or GS register contains a NULL segment selector.3

X
#GP(0)
X
X

Cause of Exception

X

If the memory address is in a non-canonical form.
If any part of the operand lies outside the effective address space from 0 to FFFFH

#PF(fault-code)

X

X

X

For a page fault

#AC(0)

X

X

X

If alignment checking is enabled and an unaligned memory reference is made while
the current privilege level is 3.

Applicable Instructions

MASKMOVQ, MOVNTQ, “MOVQ (mmreg)”

NOTES:
1. Applies to MASKMOVQ only.
2. Applies to MASKMOVQ and MOVQ (mmreg) only.
3. Applies to MASKMOVQ only.

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ARCHITECTURE COMPATIBILITY

#MF

X

X

X

X

If CR0.EM[bit 2] = 1.

X

X

X

X

If preceded by a LOCK prefix (F0H)

X

X

X

X

If any corresponding CPUID feature flag is ‘0’

X

X

X

X

If there is a pending X87 FPU exception

X

X

If CR0.TS[bit 3]=1

#NM
Applicable Instructions

22.26

64-bit

Virtual-8086

Invalid Opcode, #UD

Real

Exception

Protected and
Compatibility

Table 22-9. Exception Conditions for Legacy SIMD/MMX Instructions without Memory Reference

Cause of Exception

PEXTRW, PMOVMSKB

INTERRUPTS

The following differences in handling interrupts are found among the IA-32
processors.

22.26.1 Interrupt Propagation Delay
External hardware interrupts may be recognized on different instruction boundaries on the P6 family, Pentium,
Intel486, and Intel386 processors, due to the superscaler designs of the P6 family and Pentium processors. Therefore, the EIP pushed onto the stack when servicing an interrupt may be different for the P6 family, Pentium,
Intel486, and Intel386 processors.

22.26.2 NMI Interrupts
After an NMI interrupt is recognized by the P6 family, Pentium, Intel486, Intel386, and Intel 286 processors, the
NMI interrupt is masked until the first IRET instruction is executed, unlike the 8086 processor.

22.26.3 IDT Limit
The LIDT instruction can be used to set a limit on the size of the IDT. A double-fault exception (#DF) is generated
if an interrupt or exception attempts to read a vector beyond the limit. Shutdown then occurs on the 32-bit IA-32
processors if the double-fault handler vector is beyond the limit. (The 8086 processor does not have a shutdown
mode nor a limit.)

22.27

ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)

The Advanced Programmable Interrupt Controller (APIC), referred to in this book as the local APIC, was introduced into the IA-32 processors with the Pentium processor (beginning with the 735/90 and 815/100 models) and
is included in the Pentium 4, Intel Xeon, and P6 family processors. The features and functions of the local APIC are
derived from the Intel 82489DX external APIC, which was used with the Intel486 and early Pentium processors.
Additional refinements of the local APIC architecture were incorporated in the Pentium 4 and Intel Xeon processors.

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ARCHITECTURE COMPATIBILITY

22.27.1

Software Visible Differences Between the Local APIC and the 82489DX

The following features in the local APIC features differ from those found in the 82489DX external APIC:

•

When the local APIC is disabled by clearing the APIC software enable/disable flag in the spurious-interrupt
vector MSR, the state of its internal registers are unaffected, except that the mask bits in the LVT are all set to
block local interrupts to the processor. Also, the local APIC ceases accepting IPIs except for INIT, SMI, NMI, and
start-up IPIs. In the 82489DX, when the local unit is disabled, all the internal registers including the IRR, ISR
and TMR are cleared and the mask bits in the LVT are set. In this state, the 82489DX local unit will accept only
the reset deassert message.

•

In the local APIC, NMI and INIT (except for INIT deassert) are always treated as edge triggered interrupts, even
if programmed otherwise. In the 82489DX, these interrupts are always level triggered.

•

In the local APIC, IPIs generated through the ICR are always treated as edge triggered (except INIT Deassert).
In the 82489DX, the ICR can be used to generate either edge or level triggered IPIs.

•
•
•

In the local APIC, the logical destination register supports 8 bits; in the 82489DX, it supports 32 bits.

•

For the 82489DX, in the lowest priority delivery mode, all the target local APICs specified by the destination
field participate in the lowest priority arbitration. For the local APIC, only those local APICs which have free
interrupt slots will participate in the lowest priority arbitration.

In the local APIC, the APIC ID register is 4 bits wide; in the 82489DX, it is 8 bits wide.
The remote read delivery mode provided in the 82489DX and local APIC for Pentium processors is not
supported in the local APIC in the Pentium 4, Intel Xeon, and P6 family processors.

22.27.2

New Features Incorporated in the Local APIC for the P6 Family and Pentium
Processors

The local APIC in the Pentium and P6 family processors have the following new features not found in the 82489DX
external APIC.

•
•
•
•
•

Cluster addressing is supported in logical destination mode.
Focus processor checking can be enabled/disabled.
Interrupt input signal polarity can be programmed for the LINT0 and LINT1 pins.
An SMI IPI is supported through the ICR and I/O redirection table.
An error status register is incorporated into the LVT to log and report APIC errors.

In the P6 family processors, the local APIC incorporates an additional LVT register to handle performance monitoring counter interrupts.

22.27.3

New Features Incorporated in the Local APIC of the Pentium 4 and Intel Xeon
Processors

The local APIC in the Pentium 4 and Intel Xeon processors has the following new features not found in the P6 family
and Pentium processors and in the 82489DX.

•
•
•
•

The local APIC ID is extended to 8 bits.
An thermal sensor register is incorporated into the LVT to handle thermal sensor interrupts.
The the ability to deliver lowest-priority interrupts to a focus processor is no longer supported.
The flat cluster logical destination mode is not supported.

22.28

TASK SWITCHING AND TSS

This section identifies the implementation differences of task switching, additions to the TSS and the handling of
TSSs and TSS segment selectors.

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ARCHITECTURE COMPATIBILITY

22.28.1 P6 Family and Pentium Processor TSS
When the virtual mode extensions are enabled (by setting the VME flag in control register CR4), the TSS in the P6
family and Pentium processors contain an interrupt redirection bit map, which is used in virtual-8086 mode to redirect interrupts back to an 8086 program.

22.28.2 TSS Selector Writes
During task state saves, the Intel486 processor writes 2-byte segment selectors into a 32-bit TSS, leaving the
upper 16 bits undefined. For performance reasons, the P6 family and Pentium processors write 4-byte segment
selectors into the TSS, with the upper 2 bytes being 0. For compatibility reasons, code should not depend on the
value of the upper 16 bits of the selector in the TSS.

22.28.3 Order of Reads/Writes to the TSS
The order of reads and writes into the TSS is processor dependent. The P6 family and Pentium processors may
generate different page-fault addresses in control register CR2 in the same TSS area than the Intel486 and
Intel386 processors, if a TSS crosses a page boundary (which is not recommended).

22.28.4 Using A 16-Bit TSS with 32-Bit Constructs
Task switches using 16-bit TSSs should be used only for pure 16-bit code. Any new code written using 32-bit
constructs (operands, addressing, or the upper word of the EFLAGS register) should use only 32-bit TSSs. This is
due to the fact that the 32-bit processors do not save the upper 16 bits of EFLAGS to a 16-bit TSS. A task switch
back to a 16-bit task that was executing in virtual mode will never re-enable the virtual mode, as this flag was not
saved in the upper half of the EFLAGS value in the TSS. Therefore, it is strongly recommended that any code using
32-bit constructs use a 32-bit TSS to ensure correct behavior in a multitasking environment.

22.28.5 Differences in I/O Map Base Addresses
The Intel486 processor considers the TSS segment to be a 16-bit segment and wraps around the 64K boundary.
Any I/O accesses check for permission to access this I/O address at the I/O base address plus the I/O offset. If the
I/O map base address exceeds the specified limit of 0DFFFH, an I/O access will wrap around and obtain the permission for the I/O address at an incorrect location within the TSS. A TSS limit violation does not occur in this situation
on the Intel486 processor. However, the P6 family and Pentium processors consider the TSS to be a 32-bit segment
and a limit violation occurs when the I/O base address plus the I/O offset is greater than the TSS limit. By following
the recommended specification for the I/O base address to be less than 0DFFFH, the Intel486 processor will not
wrap around and access incorrect locations within the TSS for I/O port validation and the P6 family and Pentium
processors will not experience general-protection exceptions (#GP). Figure 22-1 demonstrates the different areas
accessed by the Intel486 and the P6 family and Pentium processors.

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ARCHITECTURE COMPATIBILITY

Intel486 Processor

P6 family and Pentium Processors
FFFFH + 10H = Outside Segment
for I/O Validation

FFFFH
I/O Map
Base Addres

FFFFH

FFFFH

I/O Map
Base Addres

FFFFH

FFFFH + 10H = FH
for I/O Validation

0H
I/O access at port 10H checks
bitmap at I/O map base address
FFFFH + 10H = offset 10H.
Offset FH from beginning of
TSS segment results because
wraparound occurs.

0H
I/O access at port 10H checks
bitmap at I/O address FFFFH + 10H,
which exceeds segment limit.
Wrap around does not occur,
general-protection exception (#GP)
occurs.

Figure 22-1. I/O Map Base Address Differences

22.29

CACHE MANAGEMENT

The P6 family processors include two levels of internal caches: L1 (level 1) and L2 (level 2). The L1 cache is divided
into an instruction cache and a data cache; the L2 cache is a general-purpose cache. See Section 11.1, “Internal
Caches, TLBs, and Buffers,” for a description of these caches. (Note that although the Pentium II processor L2
cache is physically located on a separate chip in the cassette, it is considered an internal cache.)
The Pentium processor includes separate level 1 instruction and data caches. The data cache supports a writeback
(or alternatively write-through, on a line by line basis) policy for memory updates.
The Intel486 processor includes a single level 1 cache for both instructions and data.
The meaning of the CD and NW flags in control register CR0 have been redefined for the P6 family and Pentium
processors. For these processors, the recommended value (00B) enables writeback for the data cache of the
Pentium processor and for the L1 data cache and L2 cache of the P6 family processors. In the Intel486 processor,
setting these flags to (00B) enables write-through for the cache.
External system hardware can force the Pentium processor to disable caching or to use the write-through cache
policy should that be required. In the P6 family processors, the MTRRs can be used to override the CD and NW flags
(see Table 11-6).
The P6 family and Pentium processors support page-level cache management in the same manner as the Intel486
processor by using the PCD and PWT flags in control register CR3, the page-directory entries, and the page-table
entries. The Intel486 processor, however, is not affected by the state of the PWT flag since the internal cache of the
Intel486 processor is a write-through cache.

22.29.1 Self-Modifying Code with Cache Enabled
On the Intel486 processor, a write to an instruction in the cache will modify it in both the cache and memory. If the
instruction was prefetched before the write, however, the old version of the instruction could be the one executed.
To prevent this problem, it is necessary to flush the instruction prefetch unit of the Intel486 processor by coding a
jump instruction immediately after any write that modifies an instruction. The P6 family and Pentium processors,
however, check whether a write may modify an instruction that has been prefetched for execution. This check is
based on the linear address of the instruction. If the linear address of an instruction is found to be present in the

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prefetch queue, the P6 family and Pentium processors flush the prefetch queue, eliminating the need to code a
jump instruction after any writes that modify an instruction.
Because the linear address of the write is checked against the linear address of the instructions that have been
prefetched, special care must be taken for self-modifying code to work correctly when the physical addresses of the
instruction and the written data are the same, but the linear addresses differ. In such cases, it is necessary to
execute a serializing operation to flush the prefetch queue after the write and before executing the modified
instruction. See Section 8.3, “Serializing Instructions,” for more information on serializing instructions.

NOTE
The check on linear addresses described above is not in practice a concern for compatibility. Applications that include self-modifying code use the same linear address for modifying and fetching the
instruction. System software, such as a debugger, that might possibly modify an instruction using
a different linear address than that used to fetch the instruction must execute a serializing
operation, such as IRET, before the modified instruction is executed.

22.29.2 Disabling the L3 Cache
A unified third-level (L3) cache in processors based on Intel NetBurst microarchitecture (see Section 11.1,
“Internal Caches, TLBs, and Buffers”) provides the third-level cache disable flag, bit 6 of the IA32_MISC_ENABLE
MSR. The third-level cache disable flag allows the L3 cache to be disabled and enabled, independently of the L1 and
L2 caches (see Section 11.5.4, “Disabling and Enabling the L3 Cache”). The third-level cache disable flag applies
only to processors based on Intel NetBurst microarchitecture. Processors with L3 and based on other microarchitectures do not support the third-level cache disable flag.

22.30

PAGING

This section identifies enhancements made to the paging mechanism and implementation differences in the paging
mechanism for various IA-32 processors.

22.30.1 Large Pages
The Pentium processor extended the memory management/paging facilities of the IA-32 to allow large (4 MBytes)
pages sizes (see Section 4.3, “32-Bit Paging”). The first P6 family processor (the Pentium Pro processor) added a
2 MByte page size to the IA-32 in conjunction with the physical address extension (PAE) feature (see Section 4.4,
“PAE Paging”).
The availability of large pages with 32-bit paging on any IA-32 processor can be determined via feature bit 3 (PSE)
of register EDX after the CPUID instruction has been execution with an argument of 1. (Large pages are always
available with PAE paging and 4-level paging.) Intel processors that do not support the CPUID instruction support
only 32-bit paging and do not support page size enhancements. (See “CPUID—CPU Identification” in Chapter 3,
“Instruction Set Reference, A-L,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
2A for more information on the CPUID instruction.)

22.30.2 PCD and PWT Flags
The PCD and PWT flags were introduced to the IA-32 in the Intel486 processor to control the caching of pages:

•
•

PCD (page-level cache disable) flag—Controls caching on a page-by-page basis.
PWT (page-level write-through) flag—Controls the write-through/writeback caching policy on a page-by-page
basis. Since the internal cache of the Intel486 processor is a write-through cache, it is not affected by the state
of the PWT flag.

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22.30.3 Enabling and Disabling Paging
Paging is enabled and disabled by loading a value into control register CR0 that modifies the PG flag. For backward
and forward compatibility with all IA-32 processors, Intel recommends that the following operations be performed
when enabling or disabling paging:
1. Execute a MOV CR0, REG instruction to either set (enable paging) or clear (disable paging) the PG flag.
2. Execute a near JMP instruction.
The sequence bounded by the MOV and JMP instructions should be identity mapped (that is, the instructions should
reside on a page whose linear and physical addresses are identical).
For the P6 family processors, the MOV CR0, REG instruction is serializing, so the jump operation is not required.
However, for backwards compatibility, the JMP instruction should still be included.

22.31

STACK OPERATIONS AND SUPERVISOR SOFTWARE

This section identifies the differences in the stack mechanism for the various IA-32 processors.

22.31.1 Selector Pushes and Pops
When pushing a segment selector onto the stack, the Pentium 4, Intel Xeon, P6 family, and Intel486 processors
decrement the ESP register by the operand size and then write 2 bytes. If the operand size is 32-bits, the upper two
bytes of the write are not modified. The Pentium processor decrements the ESP register by the operand size and
determines the size of the write by the operand size. If the operand size is 32-bits, the upper two bytes are written
as 0s.
When popping a segment selector from the stack, the Pentium 4, Intel Xeon, P6 family, and Intel486 processors
read 2 bytes and increment the ESP register by the operand size of the instruction. The Pentium processor determines the size of the read from the operand size and increments the ESP register by the operand size.
It is possible to align a 32-bit selector push or pop such that the operation generates an exception on a Pentium
processor and not on an Pentium 4, Intel Xeon, P6 family, or Intel486 processor. This could occur if the third and/or
fourth byte of the operation lies beyond the limit of the segment or if the third and/or fourth byte of the operation
is locate on a non-present or inaccessible page.
For a POP-to-memory instruction that meets the following conditions:

•
•
•

The stack segment size is 16-bit.
Any 32-bit addressing form with the SIB byte specifying ESP as the base register.
The initial stack pointer is FFFCH (32-bit operand) or FFFEH (16-bit operand) and will wrap around to 0H as a
result of the POP operation.

The result of the memory write is implementation-specific. For example, in P6 family processors, the result of the
memory write is SS:0H plus any scaled index and displacement. In Pentium processors, the result of the memory
write may be either a stack fault (real mode or protected mode with stack segment size of 64 KByte), or write to
SS:10000H plus any scaled index and displacement (protected mode and stack segment size exceeds 64 KByte).

22.31.2 Error Code Pushes
The Intel486 processor implements the error code pushed on the stack as a 16-bit value. When pushed onto a 32bit stack, the Intel486 processor only pushes 2 bytes and updates ESP by 4. The P6 family and Pentium processors’
error code is a full 32 bits with the upper 16 bits set to zero. The P6 family and Pentium processors, therefore, push
4 bytes and update ESP by 4. Any code that relies on the state of the upper 16 bits may produce inconsistent
results.

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22.31.3 Fault Handling Effects on the Stack
During the handling of certain instructions, such as CALL and PUSHA, faults may occur in different sequences for
the different processors. For example, during far calls, the Intel486 processor pushes the old CS and EIP before a
possible branch fault is resolved. A branch fault is a fault from a branch instruction occurring from a segment limit
or access rights violation. If a branch fault is taken, the Intel486 and P6 family processors will have corrupted
memory below the stack pointer. However, the ESP register is backed up to make the instruction restartable. The
P6 family processors issue the branch before the pushes. Therefore, if a branch fault does occur, these processors
do not corrupt memory below the stack pointer. This implementation difference, however, does not constitute a
compatibility problem, as only values at or above the stack pointer are considered to be valid. Other operations
that encounter faults may also corrupt memory below the stack pointer and this behavior may vary on different
implementations.

22.31.4 Interlevel RET/IRET From a 16-Bit Interrupt or Call Gate
If a call or interrupt is made from a 32-bit stack environment through a 16-bit gate, only 16 bits of the old ESP can
be pushed onto the stack. On the subsequent RET/IRET, the 16-bit ESP is popped but the full 32-bit ESP is updated
since control is being resumed in a 32-bit stack environment. The Intel486 processor writes the SS selector into the
upper 16 bits of ESP. The P6 family and Pentium processors write zeros into the upper 16 bits.

22.32

MIXING 16- AND 32-BIT SEGMENTS

The features of the 16-bit Intel 286 processor are an object-code compatible subset of those of the 32-bit IA-32
processors. The D (default operation size) flag in segment descriptors indicates whether the processor treats a
code or data segment as a 16-bit or 32-bit segment; the B (default stack size) flag in segment descriptors indicates
whether the processor treats a stack segment as a 16-bit or 32-bit segment.
The segment descriptors used by the Intel 286 processor are supported by the 32-bit IA-32 processors if the Intelreserved word (highest word) of the descriptor is clear. On the 32-bit IA-32 processors, this word includes the
upper bits of the base address and the segment limit.
The segment descriptors for data segments, code segments, local descriptor tables (there are no descriptors for
global descriptor tables), and task gates are the same for the 16- and 32-bit processors. Other 16-bit descriptors
(TSS segment, call gate, interrupt gate, and trap gate) are supported by the 32-bit processors.
The 32-bit processors also have descriptors for TSS segments, call gates, interrupt gates, and trap gates that
support the 32-bit architecture. Both kinds of descriptors can be used in the same system.
For those segment descriptors common to both 16- and 32-bit processors, clear bits in the reserved word cause the
32-bit processors to interpret these descriptors exactly as an Intel 286 processor does, that is:

•
•
•

Base Address — The upper 8 bits of the 32-bit base address are clear, which limits base addresses to 24 bits.

•

Big bit — In a data-segment descriptor, the B flag is clear in the segment descriptor used by the 32-bit
processors, indicating the segment is no larger than 64 KBytes.

•

Default bit — In a code-segment descriptor, the D flag is clear, indicating 16-bit addressing and operands are
the default. In a stack-segment descriptor, the D flag is clear, indicating use of the SP register (instead of the
ESP register) and a 64-KByte maximum segment limit.

Limit — The upper 4 bits of the limit field are clear, restricting the value of the limit field to 64 KBytes.
Granularity bit — The G (granularity) flag is clear, indicating the value of the 16-bit limit is interpreted in units
of 1 byte.

For information on mixing 16- and 32-bit code in applications, see Chapter 21, “Mixing 16-Bit and 32-Bit Code.”

22.33

SEGMENT AND ADDRESS WRAPAROUND

This section discusses differences in segment and address wraparound between the P6 family, Pentium, Intel486,
Intel386, Intel 286, and 8086 processors.
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ARCHITECTURE COMPATIBILITY

22.33.1 Segment Wraparound
On the 8086 processor, an attempt to access a memory operand that crosses offset 65,535 or 0FFFFH or offset 0
(for example, moving a word to offset 65,535 or pushing a word when the stack pointer is set to 1) causes the
offset to wrap around modulo 65,536 or 010000H. With the Intel 286 processor, any base and offset combination
that addresses beyond 16 MBytes wraps around to the 1 MByte of the address space. The P6 family, Pentium,
Intel486, and Intel386 processors in real-address mode generate an exception in these cases:

•

A general-protection exception (#GP) if the segment is a data segment (that is, if the CS, DS, ES, FS, or GS
register is being used to address the segment).

•

A stack-fault exception (#SS) if the segment is a stack segment (that is, if the SS register is being used).

An exception to this behavior occurs when a stack access is data aligned, and the stack pointer is pointing to the
last aligned piece of data that size at the top of the stack (ESP is FFFFFFFCH). When this data is popped, no
segment limit violation occurs and the stack pointer will wrap around to 0.
The address space of the P6 family, Pentium, and Intel486 processors may wraparound at 1 MByte in real-address
mode. An external A20M# pin forces wraparound if enabled. On Intel 8086 processors, it is possible to specify
addresses greater than 1 MByte. For example, with a selector value FFFFH and an offset of FFFFH, the effective
address would be 10FFEFH (1 MByte plus 65519 bytes). The 8086 processor, which can form addresses up to 20
bits long, truncates the uppermost bit, which “wraps” this address to FFEFH. However, the P6 family, Pentium, and
Intel486 processors do not truncate this bit if A20M# is not enabled.
If a stack operation wraps around the address limit, shutdown occurs. (The 8086 processor does not have a shutdown mode or a limit.)
The behavior when executing near the limit of a 4-GByte selector (limit = FFFFFFFFH) is different between the
Pentium Pro and the Pentium 4 family of processors. On the Pentium Pro, instructions which cross the limit -- for
example, a two byte instruction such as INC EAX that is encoded as FFH C0H starting exactly at the limit faults for
a segment violation (a one byte instruction at FFFFFFFFH does not cause an exception). Using the Pentium 4 microprocessor family, neither of these situations causes a fault.
Segment wraparound and the functionality of A20M# is used primarily by older operating systems and not used by
modern operating systems. On newer Intel 64 processors, A20M# may be absent.

22.34

STORE BUFFERS AND MEMORY ORDERING

The Pentium 4, Intel Xeon, and P6 family processors provide a store buffer for temporary storage of writes (stores)
to memory (see Section 11.10, “Store Buffer”). Writes stored in the store buffer(s) are always written to memory
in program order, with the exception of “fast string” store operations (see Section 8.2.4, “Fast-String Operation and
Out-of-Order Stores”).
The Pentium processor has two store buffers, one corresponding to each of the pipelines. Writes in these buffers
are always written to memory in the order they were generated by the processor core.
It should be noted that only memory writes are buffered and I/O writes are not. The Pentium 4, Intel Xeon, P6
family, Pentium, and Intel486 processors do not synchronize the completion of memory writes on the bus and
instruction execution after a write. An I/O, locked, or serializing instruction needs to be executed to synchronize
writes with the next instruction (see Section 8.3, “Serializing Instructions”).
The Pentium 4, Intel Xeon, and P6 family processors use processor ordering to maintain consistency in the order
that data is read (loaded) and written (stored) in a program and the order the processor actually carries out the
reads and writes. With this type of ordering, reads can be carried out speculatively and in any order, reads can pass
buffered writes, and writes to memory are always carried out in program order. (See Section 8.2, “Memory
Ordering,” for more information about processor ordering.) The Pentium III processor introduced a new instruction
to serialize writes and make them globally visible. Memory ordering issues can arise between a producer and a
consumer of data. The SFENCE instruction provides a performance-efficient way of ensuring ordering between
routines that produce weakly-ordered results and routines that consume this data.
No re-ordering of reads occurs on the Pentium processor, except under the condition noted in Section 8.2.1,
“Memory Ordering in the Intel® Pentium® and Intel486™ Processors,” and in the following paragraph describing the
Intel486 processor.

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ARCHITECTURE COMPATIBILITY

Specifically, the store buffers are flushed before the IN instruction is executed. No reads (as a result of cache miss)
are reordered around previously generated writes sitting in the store buffers. The implication of this is that the
store buffers will be flushed or emptied before a subsequent bus cycle is run on the external bus.
On both the Intel486 and Pentium processors, under certain conditions, a memory read will go onto the external
bus before the pending memory writes in the buffer even though the writes occurred earlier in the program execution. A memory read will only be reordered in front of all writes pending in the buffers if all writes pending in the
buffers are cache hits and the read is a cache miss. Under these conditions, the Intel486 and Pentium processors
will not read from an external memory location that needs to be updated by one of the pending writes.
During a locked bus cycle, the Intel486 processor will always access external memory, it will never look for the
location in the on-chip cache. All data pending in the Intel486 processor's store buffers will be written to memory
before a locked cycle is allowed to proceed to the external bus. Thus, the locked bus cycle can be used for eliminating the possibility of reordering read cycles on the Intel486 processor. The Pentium processor does check its
cache on a read-modify-write access and, if the cache line has been modified, writes the contents back to memory
before locking the bus. The P6 family processors write to their cache on a read-modify-write operation (if the
access does not split across a cache line) and does not write back to system memory. If the access does split across
a cache line, it locks the bus and accesses system memory.
I/O reads are never reordered in front of buffered memory writes on an IA-32 processor. This ensures an update of
all memory locations before reading the status from an I/O device.

22.35

BUS LOCKING

The Intel 286 processor performs the bus locking differently than the Intel P6 family, Pentium, Intel486, and
Intel386 processors. Programs that use forms of memory locking specific to the Intel 286 processor may not run
properly when run on later processors.
A locked instruction is guaranteed to lock only the area of memory defined by the destination operand, but may
lock a larger memory area. For example, typical 8086 and Intel 286 configurations lock the entire physical memory
space. Programmers should not depend on this.
On the Intel 286 processor, the LOCK prefix is sensitive to IOPL. If the CPL is greater than the IOPL, a generalprotection exception (#GP) is generated. On the Intel386 DX, Intel486, and Pentium, and P6 family processors, no
check against IOPL is performed.
The Pentium processor automatically asserts the LOCK# signal when acknowledging external interrupts. After
signaling an interrupt request, an external interrupt controller may use the data bus to send the interrupt vector to
the processor. After receiving the interrupt request signal, the processor asserts LOCK# to insure that no other
data appears on the data bus until the interrupt vector is received. This bus locking does not occur on the P6 family
processors.

22.36

BUS HOLD

Unlike the 8086 and Intel 286 processors, but like the Intel386 and Intel486 processors, the P6 family and Pentium
processors respond to requests for control of the bus from other potential bus masters, such as DMA controllers,
between transfers of parts of an unaligned operand, such as two words which form a doubleword. Unlike the
Intel386 processor, the P6 family, Pentium and Intel486 processors respond to bus hold during reset initialization.

22.37

MODEL-SPECIFIC EXTENSIONS TO THE IA-32

Certain extensions to the IA-32 are specific to a processor or family of IA-32 processors and may not be implemented or implemented in the same way in future processors. The following sections describe these model-specific
extensions. The CPUID instruction indicates the availability of some of the model-specific features.

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ARCHITECTURE COMPATIBILITY

22.37.1

Model-Specific Registers

The Pentium processor introduced a set of model-specific registers (MSRs) for use in controlling hardware functions
and performance monitoring. To access these MSRs, two new instructions were added to the IA-32 architecture:
read MSR (RDMSR) and write MSR (WRMSR). The MSRs in the Pentium processor are not guaranteed to be duplicated or provided in the next generation IA-32 processors.
The P6 family processors greatly increased the number of MSRs available to software. See Chapter 2, “ModelSpecific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4 for a
complete list of the available MSRs. The new registers control the debug extensions, the performance counters, the
machine-check exception capability, the machine-check architecture, and the MTRRs. These registers are accessible using the RDMSR and WRMSR instructions. Specific information on some of these new MSRs is provided in the
following sections. As with the Pentium processor MSR, the P6 family processor MSRs are not guaranteed to be
duplicated or provided in the next generation IA-32 processors.

22.37.2

RDMSR and WRMSR Instructions

The RDMSR (read model-specific register) and WRMSR (write model-specific register) instructions recognize a
much larger number of model-specific registers in the P6 family processors. (See “RDMSR—Read from Model
Specific Register” and “WRMSR—Write to Model Specific Register” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volumes 2A, 2B, 2C & 2D for more information.)

22.37.3

Memory Type Range Registers

Memory type range registers (MTRRs) are a new feature introduced into the IA-32 in the Pentium Pro processor.
MTRRs allow the processor to optimize memory operations for different types of memory, such as RAM, ROM, frame
buffer memory, and memory-mapped I/O.
MTRRs are MSRs that contain an internal map of how physical address ranges are mapped to various types of
memory. The processor uses this internal memory map to determine the cacheability of various physical memory
locations and the optimal method of accessing memory locations. For example, if a memory location is specified in
an MTRR as write-through memory, the processor handles accesses to this location as follows. It reads data from
that location in lines and caches the read data or maps all writes to that location to the bus and updates the cache
to maintain cache coherency. In mapping the physical address space with MTRRs, the processor recognizes five
types of memory: uncacheable (UC), uncacheable, speculatable, write-combining (WC), write-through (WT),
write-protected (WP), and writeback (WB).
Earlier IA-32 processors (such as the Intel486 and Pentium processors) used the KEN# (cache enable) pin and
external logic to maintain an external memory map and signal cacheable accesses to the processor. The MTRR
mechanism simplifies hardware designs by eliminating the KEN# pin and the external logic required to drive it.
See Chapter 9, “Processor Management and Initialization,” and Chapter 2, “Model-Specific Registers (MSRs)” in the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4 for more information on the MTRRs.

22.37.4

Machine-Check Exception and Architecture

The Pentium processor introduced a new exception called the machine-check exception (#MC, interrupt 18). This
exception is used to detect hardware-related errors, such as a parity error on a read cycle.
The P6 family processors extend the types of errors that can be detected and that generate a machine-check
exception. It also provides a new machine-check architecture for recording information about a machine-check
error and provides extended recovery capability.
The machine-check architecture provides several banks of reporting registers for recording machine-check errors.
Each bank of registers is associated with a specific hardware unit in the processor. The primary focus of the
machine checks is on bus and interconnect operations; however, checks are also made of translation lookaside
buffer (TLB) and cache operations.

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The machine-check architecture can correct some errors automatically and allow for reliable restart of instruction
execution. It also collects sufficient information for software to use in correcting other machine errors not corrected
by hardware.
See Chapter 15, “Machine-Check Architecture,” for more information on the machine-check exception and the
machine-check architecture.

22.37.5

Performance-Monitoring Counters

The P6 family and Pentium processors provide two performance-monitoring counters for use in monitoring internal
hardware operations. The number of performance monitoring counters and associated programming interfaces
may be implementation specific for Pentium 4 processors, Pentium M processors. Later processors may have
implemented these as part of an architectural performance monitoring feature. The architectural and non-architectural performance monitoring interfaces for different processor families are described in Chapter 18, “Performance
Monitoring,”. Chapter 19, “Performance Monitoring Events.” lists all the events that can be counted for architectural
performance monitoring events and non-architectural events. The counters are set up, started, and stopped using
two MSRs and the RDMSR and WRMSR instructions. For the P6 family processors, the current count for a particular
counter can be read using the new RDPMC instruction.
The performance-monitoring counters are useful for debugging programs, optimizing code, diagnosing system failures, or refining hardware designs. See Chapter 18, “Performance Monitoring,” for more information on these
counters.

22.38

TWO WAYS TO RUN INTEL 286 PROCESSOR TASKS

When porting 16-bit programs to run on 32-bit IA-32 processors, there are two approaches to consider:

•

Porting an entire 16-bit software system to a 32-bit processor, complete with the old operating system, loader,
and system builder. Here, all tasks will have 16-bit TSSs. The 32-bit processor is being used as if it were a faster
version of the 16-bit processor.

•

Porting selected 16-bit applications to run in a 32-bit processor environment with a 32-bit operating system,
loader, and system builder. Here, the TSSs used to represent 286 tasks should be changed to 32-bit TSSs. It is
possible to mix 16 and 32-bit TSSs, but the benefits are small and the problems are great. All tasks in a 32-bit
software system should have 32-bit TSSs. It is not necessary to change the 16-bit object modules themselves;
TSSs are usually constructed by the operating system, by the loader, or by the system builder. See Chapter 21,
“Mixing 16-Bit and 32-Bit Code,” for more detailed information about mixing 16-bit and 32-bit code.

Because the 32-bit processors use the contents of the reserved word of 16-bit segment descriptors, 16-bit
programs that place values in this word may not run correctly on the 32-bit processors.

22.39

INITIAL STATE OF PENTIUM, PENTIUM PRO AND PENTIUM 4 PROCESSORS

Table 22-10 shows the state of the flags and other registers following power-up for the Pentium, Pentium Pro and
Pentium 4 processors. The state of control register CR0 is 60000010H (see Figure 9-1 “Contents of CR0 Register
after Reset” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A). This places the
processor in real-address mode with paging disabled.

Table 22-10. Processor State Following Power-up/Reset/INIT for Pentium, Pentium Pro and Pentium 4 Processors
Register

Pentium 4 Processor

Pentium Pro Processor

Pentium Processor

EFLAGS1

00000002H

00000002H

00000002H

EIP

0000FFF0H

0000FFF0H

0000FFF0H

CR0

60000010H2

60000010H2

60000010H2

CR2, CR3, CR4

00000000H

00000000H

00000000H
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Table 22-10. Processor State Following Power-up/Reset/INIT for Pentium, Pentium Pro and Pentium 4 Processors
Register

Pentium 4 Processor

Pentium Pro Processor

CS

Selector = F000H
Base = FFFF0000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = F000H
Base = FFFF0000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = F000H
Base = FFFF0000H
Limit = FFFFH
AR = Present, R/W, Accessed

SS, DS, ES, FS, GS

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W, Accessed

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W, Accessed

EDX

00000FxxH

000n06xxH3

000005xxH

4

04

EAX

0

EBX, ECX, ESI, EDI, EBP,
ESP

00000000H

00000000H

00000000H

ST0 through ST75

Pwr up or Reset: +0.0
FINIT/FNINIT: Unchanged

Pwr up or Reset: +0.0
FINIT/FNINIT: Unchanged

Pwr up or Reset: +0.0
FINIT/FNINIT: Unchanged

x87 FPU Control
Word5

Pwr up or Reset: 0040H
FINIT/FNINIT: 037FH

Pwr up or Reset: 0040H
FINIT/FNINIT: 037FH

Pwr up or Reset: 0040H
FINIT/FNINIT: 037FH

x87 FPU Status Word5 Pwr up or Reset: 0000H
FINIT/FNINIT: 0000H

Pwr up or Reset: 0000H
FINIT/FNINIT: 0000H

Pwr up or Reset: 0000H
FINIT/FNINIT: 0000H

x87 FPU Tag Word5

Pwr up or Reset: 5555H
FINIT/FNINIT: FFFFH

Pwr up or Reset: 5555H
FINIT/FNINIT: FFFFH

Pwr up or Reset: 5555H
FINIT/FNINIT: FFFFH

x87 FPU Data
Operand and CS Seg.
Selectors5

Pwr up or Reset: 0000H
FINIT/FNINIT: 0000H

Pwr up or Reset: 0000H
FINIT/FNINIT: 0000H

Pwr up or Reset: 0000H
FINIT/FNINIT: 0000H

x87 FPU Data
Operand and Inst.
Pointers5

Pwr up or Reset:
00000000H
FINIT/FNINIT: 00000000H

Pwr up or Reset:
00000000H
FINIT/FNINIT: 00000000H

Pwr up or Reset:
00000000H
FINIT/FNINIT: 00000000H

MM0 through MM75

Pwr up or Reset:
0000000000000000H
INIT or FINIT/FNINIT:
Unchanged

Pentium II and Pentium III
Processors Only—

Pentium with MMX Technology
Only—

Pwr up or Reset:
0000000000000000H
INIT or FINIT/FNINIT:
Unchanged

Pwr up or Reset:
0000000000000000H
INIT or FINIT/FNINIT:
Unchanged

Pwr up or Reset: 0H
INIT: Unchanged

If CPUID.01H:SSE is 1 —

NA

Pwr up or Reset: 1F80H
INIT: Unchanged

Pentium III processor only-

GDTR, IDTR

Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Base = 00000000H
Limit = FFFFH
AR = Present, R/W

LDTR, Task Register

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W

Selector = 0000H
Base = 00000000H
Limit = FFFFH
AR = Present, R/W

DR0, DR1, DR2, DR3

00000000H

00000000H

00000000H

DR6

FFFF0FF0H

FFFF0FF0H

FFFF0FF0H

XMM0 through XMM7

MXCSR

22-38 Vol. 3B

0

4

Pentium Processor

Pwr up or Reset: 0H
INIT: Unchanged
NA

Pwr up or Reset: 1F80H
INIT: Unchanged

ARCHITECTURE COMPATIBILITY

Table 22-10. Processor State Following Power-up/Reset/INIT for Pentium, Pentium Pro and Pentium 4 Processors
Register

Pentium 4 Processor

Pentium Pro Processor

Pentium Processor

DR7

00000400H

00000400H

00000400H

Time-Stamp Counter

Power up or Reset: 0H
INIT: Unchanged

Power up or Reset: 0H
INIT: Unchanged

Power up or Reset: 0H
INIT: Unchanged

Perf. Counters and
Event Select

Power up or Reset: 0H
INIT: Unchanged

Power up or Reset: 0H
INIT: Unchanged

Power up or Reset: 0H
INIT: Unchanged

All Other MSRs

Pwr up or Reset:
Undefined
INIT: Unchanged

Pwr up or Reset:
Undefined
INIT: Unchanged

Pwr up or Reset:
Undefined
INIT: Unchanged

Data and Code Cache,
TLBs

Invalid6

Invalid6

Invalid6

Fixed MTRRs

Pwr up or Reset: Disabled
INIT: Unchanged

Pwr up or Reset: Disabled
INIT: Unchanged

Not Implemented

Variable MTRRs

Pwr up or Reset: Disabled
INIT: Unchanged

Pwr up or Reset: Disabled
INIT: Unchanged

Not Implemented

Machine-Check
Architecture

Pwr up or Reset:
Undefined
INIT: Unchanged

Pwr up or Reset:
Undefined
INIT: Unchanged

Not Implemented

APIC

Pwr up or Reset: Enabled
INIT: Unchanged

Pwr up or Reset: Enabled
INIT: Unchanged

Pwr up or Reset: Enabled
INIT: Unchanged

R8-R157

0000000000000000H

0000000000000000H

N.A.

XMM8-XMM157

Pwr up or Reset: 0H
INIT: Unchanged

Pwr up or Reset: 0H
INIT: Unchanged

N.A.

NOTES:
1. The 10 most-significant bits of the EFLAGS register are undefined following a reset. Software should not depend on the states of
any of these bits.
2. The CD and NW flags are unchanged, bit 4 is set to 1, all other bits are cleared.
3. Where “n” is the Extended Model Value for the respective processor.
4. If Built-In Self-Test (BIST) is invoked on power up or reset, EAX is 0 only if all tests passed. (BIST cannot be invoked during an INIT.)
5. The state of the x87 FPU and MMX registers is not changed by the execution of an INIT.
6. Internal caches are invalid after power-up and RESET, but left unchanged with an INIT.
7. If the processor supports IA-32e mode.

Vol. 3B 22-39

ARCHITECTURE COMPATIBILITY

22-40 Vol. 3B

CHAPTER 23
INTRODUCTION TO VIRTUAL MACHINE EXTENSIONS
23.1

OVERVIEW

This chapter describes the basics of virtual machine architecture and an overview of the virtual-machine extensions
(VMX) that support virtualization of processor hardware for multiple software environments.
Information about VMX instructions is provided in Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 2B. Other aspects of VMX and system programming considerations are described in chapters of Intel® 64
and IA-32 Architectures Software Developer’s Manual, Volume 3B.

23.2

VIRTUAL MACHINE ARCHITECTURE

Virtual-machine extensions define processor-level support for virtual machines on IA-32 processors. Two principal
classes of software are supported:

•

Virtual-machine monitors (VMM) — A VMM acts as a host and has full control of the processor(s) and other
platform hardware. A VMM presents guest software (see next paragraph) with an abstraction of a virtual
processor and allows it to execute directly on a logical processor. A VMM is able to retain selective control of
processor resources, physical memory, interrupt management, and I/O.

•

Guest software — Each virtual machine (VM) is a guest software environment that supports a stack consisting
of operating system (OS) and application software. Each operates independently of other virtual machines and
uses on the same interface to processor(s), memory, storage, graphics, and I/O provided by a physical
platform. The software stack acts as if it were running on a platform with no VMM. Software executing in a
virtual machine must operate with reduced privilege so that the VMM can retain control of platform resources.

23.3

INTRODUCTION TO VMX OPERATION

Processor support for virtualization is provided by a form of processor operation called VMX operation. There are
two kinds of VMX operation: VMX root operation and VMX non-root operation. In general, a VMM will run in VMX
root operation and guest software will run in VMX non-root operation. Transitions between VMX root operation and
VMX non-root operation are called VMX transitions. There are two kinds of VMX transitions. Transitions into VMX
non-root operation are called VM entries. Transitions from VMX non-root operation to VMX root operation are called
VM exits.
Processor behavior in VMX root operation is very much as it is outside VMX operation. The principal differences are
that a set of new instructions (the VMX instructions) is available and that the values that can be loaded into certain
control registers are limited (see Section 23.8).
Processor behavior in VMX non-root operation is restricted and modified to facilitate virtualization. Instead of their
ordinary operation, certain instructions (including the new VMCALL instruction) and events cause VM exits to the
VMM. Because these VM exits replace ordinary behavior, the functionality of software in VMX non-root operation is
limited. It is this limitation that allows the VMM to retain control of processor resources.
There is no software-visible bit whose setting indicates whether a logical processor is in VMX non-root operation.
This fact may allow a VMM to prevent guest software from determining that it is running in a virtual machine.
Because VMX operation places restrictions even on software running with current privilege level (CPL) 0, guest
software can run at the privilege level for which it was originally designed. This capability may simplify the development of a VMM.

Vol. 3C 23-1

INTRODUCTION TO VIRTUAL MACHINE EXTENSIONS

23.4

LIFE CYCLE OF VMM SOFTWARE

Figure 23-1 illustrates the life cycle of a VMM and its guest software as well as the interactions between them. The
following items summarize that life cycle:

•
•

Software enters VMX operation by executing a VMXON instruction.

•

VM exits transfer control to an entry point specified by the VMM. The VMM can take action appropriate to the
cause of the VM exit and can then return to the virtual machine using a VM entry.

•

Eventually, the VMM may decide to shut itself down and leave VMX operation. It does so by executing the
VMXOFF instruction.

Using VM entries, a VMM can then enter guests into virtual machines (one at a time). The VMM effects a
VM entry using instructions VMLAUNCH and VMRESUME; it regains control using VM exits.

Guest 0

VM Exit
VMXON

Guest 1

VM Entry

VM Monitor

VM Exit
VMXOFF

Figure 23-1. Interaction of a Virtual-Machine Monitor and Guests

23.5

VIRTUAL-MACHINE CONTROL STRUCTURE

VMX non-root operation and VMX transitions are controlled by a data structure called a virtual-machine control
structure (VMCS).
Access to the VMCS is managed through a component of processor state called the VMCS pointer (one per logical
processor). The value of the VMCS pointer is the 64-bit address of the VMCS. The VMCS pointer is read and written
using the instructions VMPTRST and VMPTRLD. The VMM configures a VMCS using the VMREAD, VMWRITE, and
VMCLEAR instructions.
A VMM could use a different VMCS for each virtual machine that it supports. For a virtual machine with multiple
logical processors (virtual processors), the VMM could use a different VMCS for each virtual processor.

23.6

DISCOVERING SUPPORT FOR VMX

Before system software enters into VMX operation, it must discover the presence of VMX support in the processor.
System software can determine whether a processor supports VMX operation using CPUID. If
CPUID.1:ECX.VMX[bit 5] = 1, then VMX operation is supported. See Chapter 3, “Instruction Set Reference, A-L” of
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A.
The VMX architecture is designed to be extensible so that future processors in VMX operation can support additional features not present in first-generation implementations of the VMX architecture. The availability of extensible VMX features is reported to software using a set of VMX capability MSRs (see Appendix A, “VMX Capability
Reporting Facility”).

23-2 Vol. 3C

INTRODUCTION TO VIRTUAL MACHINE EXTENSIONS

23.7

ENABLING AND ENTERING VMX OPERATION

Before system software can enter VMX operation, it enables VMX by setting CR4.VMXE[bit 13] = 1. VMX operation
is then entered by executing the VMXON instruction. VMXON causes an invalid-opcode exception (#UD) if executed
with CR4.VMXE = 0. Once in VMX operation, it is not possible to clear CR4.VMXE (see Section 23.8). System software leaves VMX operation by executing the VMXOFF instruction. CR4.VMXE can be cleared outside of VMX operation after executing of VMXOFF.
VMXON is also controlled by the IA32_FEATURE_CONTROL MSR (MSR address 3AH). This MSR is cleared to zero
when a logical processor is reset. The relevant bits of the MSR are:

•

Bit 0 is the lock bit. If this bit is clear, VMXON causes a general-protection exception. If the lock bit is set,
WRMSR to this MSR causes a general-protection exception; the MSR cannot be modified until a power-up reset
condition. System BIOS can use this bit to provide a setup option for BIOS to disable support for VMX. To
enable VMX support in a platform, BIOS must set bit 1, bit 2, or both (see below), as well as the lock bit.

•

Bit 1 enables VMXON in SMX operation. If this bit is clear, execution of VMXON in SMX operation causes a
general-protection exception. Attempts to set this bit on logical processors that do not support both VMX
operation (see Section 23.6) and SMX operation (see Chapter 6, “Safer Mode Extensions Reference,” in Intel®
64 and IA-32 Architectures Software Developer’s Manual, Volume 2D) cause general-protection exceptions.

•

Bit 2 enables VMXON outside SMX operation. If this bit is clear, execution of VMXON outside SMX
operation causes a general-protection exception. Attempts to set this bit on logical processors that do not
support VMX operation (see Section 23.6) cause general-protection exceptions.

NOTE
A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last
execution of GETSEC[SENTER]. A logical processor is outside SMX operation if GETSEC[SENTER]
has not been executed or if GETSEC[SEXIT] was executed after the last execution of
GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference,” in Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 2D.
Before executing VMXON, software should allocate a naturally aligned 4-KByte region of memory that a logical
processor may use to support VMX operation.1 This region is called the VMXON region. The address of the VMXON
region (the VMXON pointer) is provided in an operand to VMXON. Section 24.11.5, “VMXON Region,” details how
software should initialize and access the VMXON region.

23.8

RESTRICTIONS ON VMX OPERATION

VMX operation places restrictions on processor operation. These are detailed below:

•

In VMX operation, processors may fix certain bits in CR0 and CR4 to specific values and not support other
values. VMXON fails if any of these bits contains an unsupported value (see “VMXON—Enter VMX Operation” in
Chapter 30). Any attempt to set one of these bits to an unsupported value while in VMX operation (including
VMX root operation) using any of the CLTS, LMSW, or MOV CR instructions causes a general-protection
exception. VM entry or VM exit cannot set any of these bits to an unsupported value. Software should consult
the VMX capability MSRs IA32_VMX_CR0_FIXED0 and IA32_VMX_CR0_FIXED1 to determine how bits in CR0
are fixed (see Appendix A.7). For CR4, software should consult the VMX capability MSRs
IA32_VMX_CR4_FIXED0 and IA32_VMX_CR4_FIXED1 (see Appendix A.8).

NOTES
The first processors to support VMX operation require that the following bits be 1 in VMX operation:
CR0.PE, CR0.NE, CR0.PG, and CR4.VMXE. The restrictions on CR0.PE and CR0.PG imply that VMX
operation is supported only in paged protected mode (including IA-32e mode). Therefore, guest
software cannot be run in unpaged protected mode or in real-address mode. See Section 31.2,
1. Future processors may require that a different amount of memory be reserved. If so, this fact is reported to software using the
VMX capability-reporting mechanism.
Vol. 3C 23-3

INTRODUCTION TO VIRTUAL MACHINE EXTENSIONS

“Supporting Processor Operating Modes in Guest Environments,” for a discussion of how a VMM
might support guest software that expects to run in unpaged protected mode or in real-address
mode.
Later processors support a VM-execution control called “unrestricted guest” (see Section 24.6.2).
If this control is 1, CR0.PE and CR0.PG may be 0 in VMX non-root operation (even if the capability
MSR IA32_VMX_CR0_FIXED0 reports otherwise).1 Such processors allow guest software to run in
unpaged protected mode or in real-address mode.

•

VMXON fails if a logical processor is in A20M mode (see “VMXON—Enter VMX Operation” in Chapter 30). Once
the processor is in VMX operation, A20M interrupts are blocked. Thus, it is impossible to be in A20M mode in
VMX operation.

•

The INIT signal is blocked whenever a logical processor is in VMX root operation. It is not blocked in VMX nonroot operation. Instead, INITs cause VM exits (see Section 25.2, “Other Causes of VM Exits”).

•

Intel® Processor Trace (Intel PT) can be used in VMX operation only if IA32_VMX_MISC[14] is read as 1 (see
Appendix A.6). On processors that support Intel PT but which do not allow it to be used in VMX operation,
execution of VMXON clears IA32_RTIT_CTL.TraceEn (see “VMXON—Enter VMX Operation” in Chapter 30); any
attempt to write IA32_RTIT_CTL while in VMX operation (including VMX root operation) causes a generalprotection exception.

1. “Unrestricted guest” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VMX non-root operation functions as if the “unrestricted guest” VM-execution control were 0. See Section 24.6.2.
23-4 Vol. 3C

CHAPTER 24
VIRTUAL MACHINE CONTROL STRUCTURES
24.1

OVERVIEW

A logical processor uses virtual-machine control data structures (VMCSs) while it is in VMX operation. These
manage transitions into and out of VMX non-root operation (VM entries and VM exits) as well as processor behavior
in VMX non-root operation. This structure is manipulated by the new instructions VMCLEAR, VMPTRLD, VMREAD,
and VMWRITE.
A VMM can use a different VMCS for each virtual machine that it supports. For a virtual machine with multiple
logical processors (virtual processors), the VMM can use a different VMCS for each virtual processor.
A logical processor associates a region in memory with each VMCS. This region is called the VMCS region.1 Software references a specific VMCS using the 64-bit physical address of the region (a VMCS pointer). VMCS pointers
must be aligned on a 4-KByte boundary (bits 11:0 must be zero). These pointers must not set bits beyond the
processor’s physical-address width.2,3
A logical processor may maintain a number of VMCSs that are active. The processor may optimize VMX operation
by maintaining the state of an active VMCS in memory, on the processor, or both. At any given time, at most one
of the active VMCSs is the current VMCS. (This document frequently uses the term “the VMCS” to refer to the
current VMCS.) The VMLAUNCH, VMREAD, VMRESUME, and VMWRITE instructions operate only on the current
VMCS.
The following items describe how a logical processor determines which VMCSs are active and which is current:

•

The memory operand of the VMPTRLD instruction is the address of a VMCS. After execution of the instruction,
that VMCS is both active and current on the logical processor. Any other VMCS that had been active remains so,
but no other VMCS is current.

•

The VMCS link pointer field in the current VMCS (see Section 24.4.2) is itself the address of a VMCS. If VM entry
is performed successfully with the 1-setting of the “VMCS shadowing” VM-execution control, the VMCS
referenced by the VMCS link pointer field becomes active on the logical processor. The identity of the current
VMCS does not change.

•

The memory operand of the VMCLEAR instruction is also the address of a VMCS. After execution of the
instruction, that VMCS is neither active nor current on the logical processor. If the VMCS had been current on
the logical processor, the logical processor no longer has a current VMCS.

The VMPTRST instruction stores the address of the logical processor’s current VMCS into a specified memory location (it stores the value FFFFFFFF_FFFFFFFFH if there is no current VMCS).
The launch state of a VMCS determines which VM-entry instruction should be used with that VMCS: the
VMLAUNCH instruction requires a VMCS whose launch state is “clear”; the VMRESUME instruction requires a VMCS
whose launch state is “launched”. A logical processor maintains a VMCS’s launch state in the corresponding VMCS
region. The following items describe how a logical processor manages the launch state of a VMCS:

•

If the launch state of the current VMCS is “clear”, successful execution of the VMLAUNCH instruction changes
the launch state to “launched”.

•

The memory operand of the VMCLEAR instruction is the address of a VMCS. After execution of the instruction,
the launch state of that VMCS is “clear”.

•

There are no other ways to modify the launch state of a VMCS (it cannot be modified using VMWRITE) and there
is no direct way to discover it (it cannot be read using VMREAD).

1. The amount of memory required for a VMCS region is at most 4 KBytes. The exact size is implementation specific and can be determined by consulting the VMX capability MSR IA32_VMX_BASIC to determine the size of the VMCS region (see Appendix A.1).
2. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
3. If IA32_VMX_BASIC[48] is read as 1, these pointers must not set any bits in the range 63:32; see Appendix A.1.
Vol. 3C 24-1

VIRTUAL MACHINE CONTROL STRUCTURES

Figure 24-1 illustrates the different states of a VMCS. It uses “X” to refer to the VMCS and “Y” to refer to any other
VMCS. Thus: “VMPTRLD X” always makes X current and active; “VMPTRLD Y” always makes X not current (because
it makes Y current); VMLAUNCH makes the launch state of X “launched” if X was current and its launch state was
“clear”; and VMCLEAR X always makes X inactive and not current and makes its launch state “clear”.
The figure does not illustrate operations that do not modify the VMCS state relative to these parameters (e.g.,
execution of VMPTRLD X when X is already current). Note that VMCLEAR X makes X “inactive, not current, and
clear,” even if X’s current state is not defined (e.g., even if X has not yet been initialized). See Section 24.11.3.

VMCLEAR X

VMCLEAR X

X

VMLAUNCH

VMPTRLD Y

R

Anything
Else

Active
Not Current
Launched

VMPTRLD X

VMCLEAR X
A
LE

Active
Current
Clear

Inactive
Not Current
Clear

C
VM

VMPTRLD Y

VMPTRLD X

V
VM M P
CL TR
EA LD
R X
X

Active
Not Current
Clear

Active
Current
Launched

Figure 24-1. States of VMCS X
Because a shadow VMCS (see Section 24.10) cannot be used for VM entry, the launch state of a shadow VMCS is
not meaningful. Figure 24-1 does not illustrate all the ways in which a shadow VMCS may be made active.

24.2

FORMAT OF THE VMCS REGION

A VMCS region comprises up to 4-KBytes.1 The format of a VMCS region is given in Table 24-1.

Table 24-1. Format of the VMCS Region
Byte Offset
0

Contents
Bits 30:0: VMCS revision identifier
Bit 31: shadow-VMCS indicator (see Section 24.10)

4

VMX-abort indicator

8

VMCS data (implementation-specific format)

The first 4 bytes of the VMCS region contain the VMCS revision identifier at bits 30:0.2 Processors that maintain
VMCS data in different formats (see below) use different VMCS revision identifiers. These identifiers enable soft-

1. The exact size is implementation specific and can be determined by consulting the VMX capability MSR IA32_VMX_BASIC to determine the size of the VMCS region (see Appendix A.1).
24-2 Vol. 3C

VIRTUAL MACHINE CONTROL STRUCTURES
ware to avoid using a VMCS region formatted for one processor on a processor that uses a different format.1 Bit 31
of this 4-byte region indicates whether the VMCS is a shadow VMCS (see Section 24.10).
Software should write the VMCS revision identifier to the VMCS region before using that region for a VMCS. The
VMCS revision identifier is never written by the processor; VMPTRLD fails if its operand references a VMCS region
whose VMCS revision identifier differs from that used by the processor. (VMPTRLD also fails if the shadow-VMCS
indicator is 1 and the processor does not support the 1-setting of the “VMCS shadowing” VM-execution control; see
Section 24.6.2) Software can discover the VMCS revision identifier that a processor uses by reading the VMX capability MSR IA32_VMX_BASIC (see Appendix A.1).
Software should clear or set the shadow-VMCS indicator depending on whether the VMCS is to be an ordinary
VMCS or a shadow VMCS (see Section 24.10). VMPTRLD fails if the shadow-VMCS indicator is set and the processor
does not support the 1-setting of the “VMCS shadowing” VM-execution control. Software can discover support for
this setting by reading the VMX capability MSR IA32_VMX_PROCBASED_CTLS2 (see Appendix A.3.3).
The next 4 bytes of the VMCS region are used for the VMX-abort indicator. The contents of these bits do not
control processor operation in any way. A logical processor writes a non-zero value into these bits if a VMX abort
occurs (see Section 27.7). Software may also write into this field.
The remainder of the VMCS region is used for VMCS data (those parts of the VMCS that control VMX non-root
operation and the VMX transitions). The format of these data is implementation-specific. VMCS data are discussed
in Section 24.3 through Section 24.9. To ensure proper behavior in VMX operation, software should maintain the
VMCS region and related structures (enumerated in Section 24.11.4) in writeback cacheable memory. Future
implementations may allow or require a different memory type2. Software should consult the VMX capability MSR
IA32_VMX_BASIC (see Appendix A.1).

24.3

ORGANIZATION OF VMCS DATA

The VMCS data are organized into six logical groups:

•

Guest-state area. Processor state is saved into the guest-state area on VM exits and loaded from there on
VM entries.

•
•

Host-state area. Processor state is loaded from the host-state area on VM exits.

•
•
•

VM-execution control fields. These fields control processor behavior in VMX non-root operation. They
determine in part the causes of VM exits.
VM-exit control fields. These fields control VM exits.
VM-entry control fields. These fields control VM entries.
VM-exit information fields. These fields receive information on VM exits and describe the cause and the
nature of VM exits. On some processors, these fields are read-only.3

The VM-execution control fields, the VM-exit control fields, and the VM-entry control fields are sometimes referred
to collectively as VMX controls.

2. Earlier versions of this manual specified that the VMCS revision identifier was a 32-bit field. For all processors produced prior to this
change, bit 31 of the VMCS revision identifier was 0.
1. Logical processors that use the same VMCS revision identifier use the same size for VMCS regions.
2. Alternatively, software may map any of these regions or structures with the UC memory type. Doing so is strongly discouraged
unless necessary as it will cause the performance of transitions using those structures to suffer significantly. In addition, the processor will continue to use the memory type reported in the VMX capability MSR IA32_VMX_BASIC with exceptions noted in Appendix A.1.
3.

Software can discover whether these fields can be written by reading the VMX capability MSR IA32_VMX_MISC (see Appendix A.6).
Vol. 3C 24-3

VIRTUAL MACHINE CONTROL STRUCTURES

24.4

GUEST-STATE AREA

This section describes fields contained in the guest-state area of the VMCS. As noted earlier, processor state is
loaded from these fields on every VM entry (see Section 26.3.2) and stored into these fields on every VM exit (see
Section 27.3).

24.4.1

Guest Register State

The following fields in the guest-state area correspond to processor registers:

•

Control registers CR0, CR3, and CR4 (64 bits each; 32 bits on processors that do not support Intel 64 architecture).

•
•
•

Debug register DR7 (64 bits; 32 bits on processors that do not support Intel 64 architecture).
RSP, RIP, and RFLAGS (64 bits each; 32 bits on processors that do not support Intel 64 architecture).1
The following fields for each of the registers CS, SS, DS, ES, FS, GS, LDTR, and TR:
— Selector (16 bits).
— Base address (64 bits; 32 bits on processors that do not support Intel 64 architecture). The base-address
fields for CS, SS, DS, and ES have only 32 architecturally-defined bits; nevertheless, the corresponding
VMCS fields have 64 bits on processors that support Intel 64 architecture.
— Segment limit (32 bits). The limit field is always a measure in bytes.
— Access rights (32 bits). The format of this field is given in Table 24-2 and detailed as follows:

•

The low 16 bits correspond to bits 23:8 of the upper 32 bits of a 64-bit segment descriptor. While bits
19:16 of code-segment and data-segment descriptors correspond to the upper 4 bits of the segment
limit, the corresponding bits (bits 11:8) are reserved in this VMCS field.

•

Bit 16 indicates an unusable segment. Attempts to use such a segment fault except in 64-bit mode.
In general, a segment register is unusable if it has been loaded with a null selector.2

•

Bits 31:17 are reserved.

Table 24-2. Format of Access Rights
Bit Position(s)

Field

3:0

Segment type

4

S — Descriptor type (0 = system; 1 = code or data)

6:5

DPL — Descriptor privilege level

7

P — Segment present

11:8

Reserved

12

AVL — Available for use by system software

1. This chapter uses the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that support VMX operation also support Intel 64 architecture. For processors that do not support Intel 64 architecture, this notation refers to the 32-bit
forms of those registers (EAX, EIP, ESP, EFLAGS, etc.). In a few places, notation such as EAX is used to refer specifically to lower 32
bits of the indicated register.
2. There are a few exceptions to this statement. For example, a segment with a non-null selector may be unusable following a task
switch that fails after its commit point; see “Interrupt 10—Invalid TSS Exception (#TS)” in Section 6.14, “Exception and Interrupt
Handling in 64-bit Mode,” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A. In contrast, the TR register is usable after processor reset despite having a null selector; see Table 10-1 in the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 3A.
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Table 24-2. Format of Access Rights (Contd.)
Bit Position(s)

Field

13

Reserved (except for CS)
L — 64-bit mode active (for CS only)

14

D/B — Default operation size (0 = 16-bit segment; 1 = 32-bit segment)

15

G — Granularity

16

Segment unusable (0 = usable; 1 = unusable)

31:17

Reserved

The base address, segment limit, and access rights compose the “hidden” part (or “descriptor cache”) of each
segment register. These data are included in the VMCS because it is possible for a segment register’s descriptor
cache to be inconsistent with the segment descriptor in memory (in the GDT or the LDT) referenced by the
segment register’s selector.
The value of the DPL field for SS is always equal to the logical processor’s current privilege level (CPL).1

•

The following fields for each of the registers GDTR and IDTR:
— Base address (64 bits; 32 bits on processors that do not support Intel 64 architecture).
— Limit (32 bits). The limit fields contain 32 bits even though these fields are specified as only 16 bits in the
architecture.

•

The following MSRs:
— IA32_DEBUGCTL (64 bits)
— IA32_SYSENTER_CS (32 bits)
— IA32_SYSENTER_ESP and IA32_SYSENTER_EIP (64 bits; 32 bits on processors that do not support Intel 64
architecture)
— IA32_PERF_GLOBAL_CTRL (64 bits). This field is supported only on processors that support the 1-setting
of the “load IA32_PERF_GLOBAL_CTRL” VM-entry control.
— IA32_PAT (64 bits). This field is supported only on processors that support either the 1-setting of the “load
IA32_PAT” VM-entry control or that of the “save IA32_PAT” VM-exit control.
— IA32_EFER (64 bits). This field is supported only on processors that support either the 1-setting of the “load
IA32_EFER” VM-entry control or that of the “save IA32_EFER” VM-exit control.
— IA32_BNDCFGS (64 bits). This field is supported only on processors that support either the 1-setting of the
“load IA32_BNDCFGS” VM-entry control or that of the “clear IA32_BNDCFGS” VM-exit control.

•

The register SMBASE (32 bits). This register contains the base address of the logical processor’s SMRAM image.

24.4.2

Guest Non-Register State

In addition to the register state described in Section 24.4.1, the guest-state area includes the following fields that
characterize guest state but which do not correspond to processor registers:

•

Activity state (32 bits). This field identifies the logical processor’s activity state. When a logical processor is
executing instructions normally, it is in the active state. Execution of certain instructions and the occurrence
of certain events may cause a logical processor to transition to an inactive state in which it ceases to execute
instructions.
The following activity states are defined:2
— 0: Active. The logical processor is executing instructions normally.

1. In protected mode, CPL is also associated with the RPL field in the CS selector. However, the RPL fields are not meaningful in realaddress mode or in virtual-8086 mode.
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— 1: HLT. The logical processor is inactive because it executed the HLT instruction.
— 2: Shutdown. The logical processor is inactive because it incurred a triple fault1 or some other serious
error.
— 3: Wait-for-SIPI. The logical processor is inactive because it is waiting for a startup-IPI (SIPI).
Future processors may include support for other activity states. Software should read the VMX capability MSR
IA32_VMX_MISC (see Appendix A.6) to determine what activity states are supported.

•

Interruptibility state (32 bits). The IA-32 architecture includes features that permit certain events to be
blocked for a period of time. This field contains information about such blocking. Details and the format of this
field are given in Table 24-3.

Table 24-3. Format of Interruptibility State
Bit
Position(s)

Bit Name

Notes

0

Blocking by STI

See the “STI—Set Interrupt Flag” section in Chapter 4 of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 2B.
Execution of STI with RFLAGS.IF = 0 blocks interrupts (and, optionally, other events) for one
instruction after its execution. Setting this bit indicates that this blocking is in effect.

1

Blocking by
MOV SS

See the “MOV—Move a Value from the Stack” from Chapter 4 of the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 2B, and “POP—Pop a Value from the
Stack” from Chapter 4 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 2B, and Section 6.8.3 in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3A.
Execution of a MOV to SS or a POP to SS blocks interrupts for one instruction after its
execution. In addition, certain debug exceptions are inhibited between a MOV to SS or a POP to
SS and a subsequent instruction. Setting this bit indicates that the blocking of all these events
is in effect. This document uses the term “blocking by MOV SS,” but it applies equally to POP SS.

2

Blocking by SMI

See Section 34.2. System-management interrupts (SMIs) are disabled while the processor is in
system-management mode (SMM). Setting this bit indicates that blocking of SMIs is in effect.

3

Blocking by NMI

See Section 6.7.1 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 3A and Section 34.8.
Delivery of a non-maskable interrupt (NMI) or a system-management interrupt (SMI) blocks
subsequent NMIs until the next execution of IRET. See Section 25.3 for how this behavior of
IRET may change in VMX non-root operation. Setting this bit indicates that blocking of NMIs is
in effect. Clearing this bit does not imply that NMIs are not (temporarily) blocked for other
reasons.
If the “virtual NMIs” VM-execution control (see Section 24.6.1) is 1, this bit does not control the
blocking of NMIs. Instead, it refers to “virtual-NMI blocking” (the fact that guest software is not
ready for an NMI).

•

4

Enclave
interruption

A VM exit saves this bit as 1 to indicate that the VM exit was incident to enclave mode.

31:5

Reserved

VM entry will fail if these bits are not 0. See Section 26.3.1.5.

Pending debug exceptions (64 bits; 32 bits on processors that do not support Intel 64 architecture). IA-32
processors may recognize one or more debug exceptions without immediately delivering them.2 This field
contains information about such exceptions. This field is described in Table 24-4.

2. Execution of the MWAIT instruction may put a logical processor into an inactive state. However, this VMCS field never reflects this
state. See Section 27.1.
1. A triple fault occurs when a logical processor encounters an exception while attempting to deliver a double fault.
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Table 24-4. Format of Pending-Debug-Exceptions
Bit
Position(s)

Bit Name

Notes

3:0

B3 – B0

When set, each of these bits indicates that the corresponding breakpoint condition was met.
Any of these bits may be set even if the corresponding enabling bit in DR7 is not set.

11:4

Reserved

VM entry fails if these bits are not 0. See Section 26.3.1.5.

12

Enabled
breakpoint

When set, this bit indicates that at least one data or I/O breakpoint was met and was enabled in
DR7.

13

Reserved

VM entry fails if this bit is not 0. See Section 26.3.1.5.

14

BS

When set, this bit indicates that a debug exception would have been triggered by single-step
execution mode.

15

Reserved

VM entry fails if this bit is not 0. See Section 26.3.1.5.

16

RTM

When set, this bit indicates that a debug exception (#DB) or a breakpoint exception (#BP)
occurred inside an RTM region while advanced debugging of RTM transactional regions was
enabled (see Section 16.3.7, “RTM-Enabled Debugger Support,” of Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 1).1

63:17

Reserved

VM entry fails if these bits are not 0. See Section 26.3.1.5. Bits 63:32 exist only on processors
that support Intel 64 architecture.

NOTES:
1. In general, the format of this field matches that of DR6. However, DR6 clears bit 16 to indicate an RTM-related exception, while this
field sets the bit to indicate that condition.

•

VMCS link pointer (64 bits). If the “VMCS shadowing” VM-execution control is 1, the VMREAD and VMWRITE
instructions access the VMCS referenced by this pointer (see Section 24.10). Otherwise, software should set
this field to FFFFFFFF_FFFFFFFFH to avoid VM-entry failures (see Section 26.3.1.5).

•

VMX-preemption timer value (32 bits). This field is supported only on processors that support the 1-setting
of the “activate VMX-preemption timer” VM-execution control. This field contains the value that the VMXpreemption timer will use following the next VM entry with that setting. See Section 25.5.1 and Section 26.6.4.

•

Page-directory-pointer-table entries (PDPTEs; 64 bits each). These four (4) fields (PDPTE0, PDPTE1,
PDPTE2, and PDPTE3) are supported only on processors that support the 1-setting of the “enable EPT” VMexecution control. They correspond to the PDPTEs referenced by CR3 when PAE paging is in use (see Section
4.4 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A). They are used only if
the “enable EPT” VM-execution control is 1.

•

Guest interrupt status (16 bits). This field is supported only on processors that support the 1-setting of the
“virtual-interrupt delivery” VM-execution control. It characterizes part of the guest’s virtual-APIC state and
does not correspond to any processor or APIC registers. It comprises two 8-bit subfields:
— Requesting virtual interrupt (RVI). This is the low byte of the guest interrupt status. The processor
treats this value as the vector of the highest priority virtual interrupt that is requesting service. (The value
0 implies that there is no such interrupt.)
— Servicing virtual interrupt (SVI). This is the high byte of the guest interrupt status. The processor
treats this value as the vector of the highest priority virtual interrupt that is in service. (The value 0 implies
that there is no such interrupt.)

2. For example, execution of a MOV to SS or a POP to SS may inhibit some debug exceptions for one instruction. See Section 6.8.3 of
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A. In addition, certain events incident to an instruction
(for example, an INIT signal) may take priority over debug traps generated by that instruction. See Table 6-2 in the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 3A.

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See Chapter 29 for more information on the use of this field.

•

PML index (16 bits). This field is supported only on processors that support the 1-setting of the “enable PML”
VM-execution control. It contains the logical index of the next entry in the page-modification log. Because the
page-modification log comprises 512 entries, the PML index is typically a value in the range 0–511. Details of
the page-modification log and use of the PML index are given in Section 28.2.5.

24.5

HOST-STATE AREA

This section describes fields contained in the host-state area of the VMCS. As noted earlier, processor state is
loaded from these fields on every VM exit (see Section 27.5).
All fields in the host-state area correspond to processor registers:

•
•
•

CR0, CR3, and CR4 (64 bits each; 32 bits on processors that do not support Intel 64 architecture).

•

Base-address fields for FS, GS, TR, GDTR, and IDTR (64 bits each; 32 bits on processors that do not support
Intel 64 architecture).

•

The following MSRs:

RSP and RIP (64 bits each; 32 bits on processors that do not support Intel 64 architecture).
Selector fields (16 bits each) for the segment registers CS, SS, DS, ES, FS, GS, and TR. There is no field in the
host-state area for the LDTR selector.

— IA32_SYSENTER_CS (32 bits)
— IA32_SYSENTER_ESP and IA32_SYSENTER_EIP (64 bits; 32 bits on processors that do not support Intel 64
architecture).
— IA32_PERF_GLOBAL_CTRL (64 bits). This field is supported only on processors that support the 1-setting of
the “load IA32_PERF_GLOBAL_CTRL” VM-exit control.
— IA32_PAT (64 bits). This field is supported only on processors that support the 1-setting of the “load
IA32_PAT” VM-exit control.
— IA32_EFER (64 bits). This field is supported only on processors that support the 1-setting of the “load
IA32_EFER” VM-exit control.
In addition to the state identified here, some processor state components are loaded with fixed values on every
VM exit; there are no fields corresponding to these components in the host-state area. See Section 27.5 for details
of how state is loaded on VM exits.

24.6

VM-EXECUTION CONTROL FIELDS

The VM-execution control fields govern VMX non-root operation. These are described in Section 24.6.1 through
Section 24.6.8.

24.6.1

Pin-Based VM-Execution Controls

The pin-based VM-execution controls constitute a 32-bit vector that governs the handling of asynchronous events
(for example: interrupts).1 Table 24-5 lists the controls. See Chapter 27 for how these controls affect processor
behavior in VMX non-root operation.

1. Some asynchronous events cause VM exits regardless of the settings of the pin-based VM-execution controls (see Section 25.2).
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Table 24-5. Definitions of Pin-Based VM-Execution Controls
Bit Position(s) Name

Description

0

External-interrupt
exiting

If this control is 1, external interrupts cause VM exits. Otherwise, they are delivered normally
through the guest interrupt-descriptor table (IDT). If this control is 1, the value of RFLAGS.IF
does not affect interrupt blocking.

3

NMI exiting

If this control is 1, non-maskable interrupts (NMIs) cause VM exits. Otherwise, they are
delivered normally using descriptor 2 of the IDT. This control also determines interactions
between IRET and blocking by NMI (see Section 25.3).

5

Virtual NMIs

If this control is 1, NMIs are never blocked and the “blocking by NMI” bit (bit 3) in the
interruptibility-state field indicates “virtual-NMI blocking” (see Table 24-3). This control also
interacts with the “NMI-window exiting” VM-execution control (see Section 24.6.2).

6

Activate VMXpreemption timer

If this control is 1, the VMX-preemption timer counts down in VMX non-root operation; see
Section 25.5.1. A VM exit occurs when the timer counts down to zero; see Section 25.2.

7

Process posted
interrupts

If this control is 1, the processor treats interrupts with the posted-interrupt notification vector
(see Section 24.6.8) specially, updating the virtual-APIC page with posted-interrupt requests
(see Section 29.6).

All other bits in this field are reserved, some to 0 and some to 1. Software should consult the VMX capability MSRs
IA32_VMX_PINBASED_CTLS and IA32_VMX_TRUE_PINBASED_CTLS (see Appendix A.3.1) to determine how to
set reserved bits. Failure to set reserved bits properly causes subsequent VM entries to fail (see Section 26.2.1.1).
The first processors to support the virtual-machine extensions supported only the 1-settings of bits 1, 2, and 4.
The VMX capability MSR IA32_VMX_PINBASED_CTLS will always report that these bits must be 1. Logical processors that support the 0-settings of any of these bits will support the VMX capability MSR
IA32_VMX_TRUE_PINBASED_CTLS MSR, and software should consult this MSR to discover support for the 0settings of these bits. Software that is not aware of the functionality of any one of these bits should set that bit to 1.

24.6.2

Processor-Based VM-Execution Controls

The processor-based VM-execution controls constitute two 32-bit vectors that govern the handling of synchronous
events, mainly those caused by the execution of specific instructions.1 These are the primary processor-based
VM-execution controls and the secondary processor-based VM-execution controls.
Table 24-6 lists the primary processor-based VM-execution controls. See Chapter 25 for more details of how these
controls affect processor behavior in VMX non-root operation.

Table 24-6. Definitions of Primary Processor-Based VM-Execution Controls
Bit Position(s) Name

Description

2

Interrupt-window
exiting

If this control is 1, a VM exit occurs at the beginning of any instruction if RFLAGS.IF = 1 and
there are no other blocking of interrupts (see Section 24.4.2).

3

Use TSC offsetting

This control determines whether executions of RDTSC, executions of RDTSCP, and executions
of RDMSR that read from the IA32_TIME_STAMP_COUNTER MSR return a value modified by
the TSC offset field (see Section 24.6.5 and Section 25.3).

7

HLT exiting

This control determines whether executions of HLT cause VM exits.

9

INVLPG exiting

This determines whether executions of INVLPG cause VM exits.

10

MWAIT exiting

This control determines whether executions of MWAIT cause VM exits.

11

RDPMC exiting

This control determines whether executions of RDPMC cause VM exits.

12

RDTSC exiting

This control determines whether executions of RDTSC and RDTSCP cause VM exits.

1. Some instructions cause VM exits regardless of the settings of the processor-based VM-execution controls (see Section 25.1.2), as
do task switches (see Section 25.2).
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Table 24-6. Definitions of Primary Processor-Based VM-Execution Controls (Contd.)
Bit Position(s) Name

Description

15

In conjunction with the CR3-target controls (see Section 24.6.7), this control determines
whether executions of MOV to CR3 cause VM exits. See Section 25.1.3.

CR3-load exiting

The first processors to support the virtual-machine extensions supported only the 1-setting
of this control.
16

CR3-store exiting

This control determines whether executions of MOV from CR3 cause VM exits.
The first processors to support the virtual-machine extensions supported only the 1-setting
of this control.

19

CR8-load exiting

This control determines whether executions of MOV to CR8 cause VM exits.

20

CR8-store exiting

This control determines whether executions of MOV from CR8 cause VM exits.

21

Use TPR shadow

Setting this control to 1 enables TPR virtualization and other APIC-virtualization features. See
Chapter 29.

22

NMI-window
exiting

If this control is 1, a VM exit occurs at the beginning of any instruction if there is no virtualNMI blocking (see Section 24.4.2).

23

MOV-DR exiting

This control determines whether executions of MOV DR cause VM exits.

24

Unconditional I/O
exiting

This control determines whether executions of I/O instructions (IN, INS/INSB/INSW/INSD, OUT,
and OUTS/OUTSB/OUTSW/OUTSD) cause VM exits.

25

Use I/O bitmaps

This control determines whether I/O bitmaps are used to restrict executions of I/O instructions
(see Section 24.6.4 and Section 25.1.3).
For this control, “0” means “do not use I/O bitmaps” and “1” means “use I/O bitmaps.” If the I/O
bitmaps are used, the setting of the “unconditional I/O exiting” control is ignored.

27

Monitor trap flag

If this control is 1, the monitor trap flag debugging feature is enabled. See Section 25.5.2.

28

Use MSR bitmaps

This control determines whether MSR bitmaps are used to control execution of the RDMSR
and WRMSR instructions (see Section 24.6.9 and Section 25.1.3).
For this control, “0” means “do not use MSR bitmaps” and “1” means “use MSR bitmaps.” If the
MSR bitmaps are not used, all executions of the RDMSR and WRMSR instructions cause
VM exits.

29

MONITOR exiting

This control determines whether executions of MONITOR cause VM exits.

30

PAUSE exiting

This control determines whether executions of PAUSE cause VM exits.

31

Activate secondary This control determines whether the secondary processor-based VM-execution controls are
controls
used. If this control is 0, the logical processor operates as if all the secondary processor-based
VM-execution controls were also 0.

All other bits in this field are reserved, some to 0 and some to 1. Software should consult the VMX capability MSRs
IA32_VMX_PROCBASED_CTLS and IA32_VMX_TRUE_PROCBASED_CTLS (see Appendix A.3.2) to determine how
to set reserved bits. Failure to set reserved bits properly causes subsequent VM entries to fail (see Section
26.2.1.1).
The first processors to support the virtual-machine extensions supported only the 1-settings of bits 1, 4–6, 8, 13–
16, and 26. The VMX capability MSR IA32_VMX_PROCBASED_CTLS will always report that these bits must be 1.
Logical processors that support the 0-settings of any of these bits will support the VMX capability MSR
IA32_VMX_TRUE_PROCBASED_CTLS MSR, and software should consult this MSR to discover support for the 0settings of these bits. Software that is not aware of the functionality of any one of these bits should set that bit to 1.
Bit 31 of the primary processor-based VM-execution controls determines whether the secondary processor-based
VM-execution controls are used. If that bit is 0, VM entry and VMX non-root operation function as if all the
secondary processor-based VM-execution controls were 0. Processors that support only the 0-setting of bit 31 of
the primary processor-based VM-execution controls do not support the secondary processor-based VM-execution
controls.

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Table 24-7 lists the secondary processor-based VM-execution controls. See Chapter 25 for more details of how
these controls affect processor behavior in VMX non-root operation.

Table 24-7. Definitions of Secondary Processor-Based VM-Execution Controls
Bit Position(s) Name

Description

0

Virtualize APIC
accesses

If this control is 1, the logical processor treats specially accesses to the page with the APICaccess address. See Section 29.4.

1

Enable EPT

If this control is 1, extended page tables (EPT) are enabled. See Section 28.2.

2

Descriptor-table
exiting

This control determines whether executions of LGDT, LIDT, LLDT, LTR, SGDT, SIDT, SLDT, and
STR cause VM exits.

3

Enable RDTSCP

If this control is 0, any execution of RDTSCP causes an invalid-opcode exception (#UD).

4

Virtualize x2APIC
mode

If this control is 1, the logical processor treats specially RDMSR and WRMSR to APIC MSRs (in
the range 800H–8FFH). See Section 29.5.

5

Enable VPID

If this control is 1, cached translations of linear addresses are associated with a virtualprocessor identifier (VPID). See Section 28.1.

6

WBINVD exiting

This control determines whether executions of WBINVD cause VM exits.

7

Unrestricted guest

This control determines whether guest software may run in unpaged protected mode or in realaddress mode.

8

APIC-register
virtualization

If this control is 1, the logical processor virtualizes certain APIC accesses. See Section 29.4 and
Section 29.5.

9

Virtual-interrupt
delivery

This controls enables the evaluation and delivery of pending virtual interrupts as well as the
emulation of writes to the APIC registers that control interrupt prioritization.

10

PAUSE-loop exiting This control determines whether a series of executions of PAUSE can cause a VM exit (see
Section 24.6.13 and Section 25.1.3).

11

RDRAND exiting

This control determines whether executions of RDRAND cause VM exits.

12

Enable INVPCID

If this control is 0, any execution of INVPCID causes a #UD.

13

Enable
VM functions

Setting this control to 1 enables use of the VMFUNC instruction in VMX non-root operation. See
Section 25.5.5.

14

VMCS shadowing

If this control is 1, executions of VMREAD and VMWRITE in VMX non-root operation may access
a shadow VMCS (instead of causing VM exits). See Section 24.10 and Section 30.3.

15

Enable ENCLS
exiting

If this control is 1, executions of ENCLS consult the ENCLS-exiting bitmap to determine whether
the instruction causes a VM exit. See Section 24.6.16 and Section 25.1.3.

16

RDSEED exiting

This control determines whether executions of RDSEED cause VM exits.

17

Enable PML

If this control is 1, an access to a guest-physical address that sets an EPT dirty bit first adds an
entry to the page-modification log. See Section 28.2.5.

18

EPT-violation #VE

If this control is 1, EPT violations may cause virtualization exceptions (#VE) instead of VM exits.
See Section 25.5.6.

19

Conceal VMX non- If this control is 1, Intel Processor Trace suppresses data packets that indicate the use of
root operation from virtualization (see Chapter 35).
Intel PT

20

Enable
XSAVES/XRSTORS

22

Mode-based
If this control is 1, EPT execute permissions are based on whether the linear address being
execute control for accessed is supervisor mode or user mode. See Chapter 28.
EPT

25

Use TSC scaling

If this control is 0, any execution of XSAVES or XRSTORS causes a #UD.

This control determines whether executions of RDTSC, executions of RDTSCP, and executions
of RDMSR that read from the IA32_TIME_STAMP_COUNTER MSR return a value modified by the
TSC multiplier field (see Section 24.6.5 and Section 25.3).

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All other bits in this field are reserved to 0. Software should consult the VMX capability MSR
IA32_VMX_PROCBASED_CTLS2 (see Appendix A.3.3) to determine which bits may be set to 1. Failure to clear
reserved bits causes subsequent VM entries to fail (see Section 26.2.1.1).

24.6.3

Exception Bitmap

The exception bitmap is a 32-bit field that contains one bit for each exception. When an exception occurs, its
vector is used to select a bit in this field. If the bit is 1, the exception causes a VM exit. If the bit is 0, the exception
is delivered normally through the IDT, using the descriptor corresponding to the exception’s vector.
Whether a page fault (exception with vector 14) causes a VM exit is determined by bit 14 in the exception bitmap
as well as the error code produced by the page fault and two 32-bit fields in the VMCS (the page-fault error-code
mask and page-fault error-code match). See Section 25.2 for details.

24.6.4

I/O-Bitmap Addresses

The VM-execution control fields include the 64-bit physical addresses of I/O bitmaps A and B (each of which are
4 KBytes in size). I/O bitmap A contains one bit for each I/O port in the range 0000H through 7FFFH; I/O bitmap B
contains bits for ports in the range 8000H through FFFFH.
A logical processor uses these bitmaps if and only if the “use I/O bitmaps” control is 1. If the bitmaps are used,
execution of an I/O instruction causes a VM exit if any bit in the I/O bitmaps corresponding to a port it accesses is
1. See Section 25.1.3 for details. If the bitmaps are used, their addresses must be 4-KByte aligned.

24.6.5

Time-Stamp Counter Offset and Multiplier

The VM-execution control fields include a 64-bit TSC-offset field. If the “RDTSC exiting” control is 0 and the “use
TSC offsetting” control is 1, this field controls executions of the RDTSC and RDTSCP instructions. It also controls
executions of the RDMSR instruction that read from the IA32_TIME_STAMP_COUNTER MSR. For all of these, the
value of the TSC offset is added to the value of the time-stamp counter, and the sum is returned to guest software
in EDX:EAX.
Processors that support the 1-setting of the “use TSC scaling” control also support a 64-bit TSC-multiplier field.
If this control is 1 (and the “RDTSC exiting” control is 0 and the “use TSC offsetting” control is 1), this field also
affects the executions of the RDTSC, RDTSCP, and RDMSR instructions identified above. Specifically, the contents
of the time-stamp counter is first multiplied by the TSC multiplier before adding the TSC offset.
See Chapter 27 for a detailed treatment of the behavior of RDTSC, RDTSCP, and RDMSR in VMX non-root operation.

24.6.6

Guest/Host Masks and Read Shadows for CR0 and CR4

VM-execution control fields include guest/host masks and read shadows for the CR0 and CR4 registers. These
fields control executions of instructions that access those registers (including CLTS, LMSW, MOV CR, and SMSW).
They are 64 bits on processors that support Intel 64 architecture and 32 bits on processors that do not.
In general, bits set to 1 in a guest/host mask correspond to bits “owned” by the host:

•

Guest attempts to set them (using CLTS, LMSW, or MOV to CR) to values differing from the corresponding bits
in the corresponding read shadow cause VM exits.

•

Guest reads (using MOV from CR or SMSW) return values for these bits from the corresponding read shadow.

Bits cleared to 0 correspond to bits “owned” by the guest; guest attempts to modify them succeed and guest reads
return values for these bits from the control register itself.
See Chapter 27 for details regarding how these fields affect VMX non-root operation.

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24.6.7

CR3-Target Controls

The VM-execution control fields include a set of 4 CR3-target values and a CR3-target count. The CR3-target
values each have 64 bits on processors that support Intel 64 architecture and 32 bits on processors that do not.
The CR3-target count has 32 bits on all processors.
An execution of MOV to CR3 in VMX non-root operation does not cause a VM exit if its source operand matches one
of these values. If the CR3-target count is n, only the first n CR3-target values are considered; if the CR3-target
count is 0, MOV to CR3 always causes a VM exit
There are no limitations on the values that can be written for the CR3-target values. VM entry fails (see Section
26.2) if the CR3-target count is greater than 4.
Future processors may support a different number of CR3-target values. Software should read the VMX capability
MSR IA32_VMX_MISC (see Appendix A.6) to determine the number of values supported.

24.6.8

Controls for APIC Virtualization

There are three mechanisms by which software accesses registers of the logical processor’s local APIC:

•

If the local APIC is in xAPIC mode, it can perform memory-mapped accesses to addresses in the 4-KByte page
referenced by the physical address in the IA32_APIC_BASE MSR (see Section 10.4.4, “Local APIC Status and
Location” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A and Intel® 64
Architecture Processor Topology Enumeration).1

•

If the local APIC is in x2APIC mode, it can accesses the local APIC’s registers using the RDMSR and WRMSR
instructions (see Intel® 64 Architecture Processor Topology Enumeration).

•

In 64-bit mode, it can access the local APIC’s task-priority register (TPR) using the MOV CR8 instruction.

There are five processor-based VM-execution controls (see Section 24.6.2) that control such accesses. There are
“use TPR shadow”, “virtualize APIC accesses”, “virtualize x2APIC mode”, “virtual-interrupt delivery”, and “APICregister virtualization”. These controls interact with the following fields:

•

APIC-access address (64 bits). This field contains the physical address of the 4-KByte APIC-access page.
If the “virtualize APIC accesses” VM-execution control is 1, access to this page may cause VM exits or be
virtualized by the processor. See Section 29.4.
The APIC-access address exists only on processors that support the 1-setting of the “virtualize APIC accesses”
VM-execution control.

•

Virtual-APIC address (64 bits). This field contains the physical address of the 4-KByte virtual-APIC page.
The processor uses the virtual-APIC page to virtualize certain accesses to APIC registers and to manage virtual
interrupts; see Chapter 29.
Depending on the setting of the controls indicated earlier, the virtual-APIC page may be accessed by the
following operations:
— The MOV CR8 instructions (see Section 29.3).
— Accesses to the APIC-access page if, in addition, the “virtualize APIC accesses” VM-execution control is 1
(see Section 29.4).
— The RDMSR and WRMSR instructions if, in addition, the value of ECX is in the range 800H–8FFH (indicating
an APIC MSR) and the “virtualize x2APIC mode” VM-execution control is 1 (see Section 29.5).
If the “use TPR shadow” VM-execution control is 1, VM entry ensures that the virtual-APIC address is 4-KByte
aligned. The virtual-APIC address exists only on processors that support the 1-setting of the “use TPR shadow”
VM-execution control.

•

TPR threshold (32 bits). Bits 3:0 of this field determine the threshold below which bits 7:4 of VTPR (see
Section 29.1.1) cannot fall. If the “virtual-interrupt delivery” VM-execution control is 0, a VM exit occurs after
an operation (e.g., an execution of MOV to CR8) that reduces the value of those bits below the TPR threshold.
See Section 29.1.2.

1. If the local APIC does not support x2APIC mode, it is always in xAPIC mode.
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The TPR threshold exists only on processors that support the 1-setting of the “use TPR shadow” VM-execution
control.

•

EOI-exit bitmap (4 fields; 64 bits each). These fields are supported only on processors that support the 1setting of the “virtual-interrupt delivery” VM-execution control. They are used to determine which virtualized
writes to the APIC’s EOI register cause VM exits:
— EOI_EXIT0 contains bits for vectors from 0 (bit 0) to 63 (bit 63).
— EOI_EXIT1 contains bits for vectors from 64 (bit 0) to 127 (bit 63).
— EOI_EXIT2 contains bits for vectors from 128 (bit 0) to 191 (bit 63).
— EOI_EXIT3 contains bits for vectors from 192 (bit 0) to 255 (bit 63).
See Section 29.1.4 for more information on the use of this field.

•

Posted-interrupt notification vector (16 bits). This field is supported only on processors that support the 1setting of the “process posted interrupts” VM-execution control. Its low 8 bits contain the interrupt vector that
is used to notify a logical processor that virtual interrupts have been posted. See Section 29.6 for more
information on the use of this field.

•

Posted-interrupt descriptor address (64 bits). This field is supported only on processors that support the 1setting of the “process posted interrupts” VM-execution control. It is the physical address of a 64-byte aligned
posted interrupt descriptor. See Section 29.6 for more information on the use of this field.

24.6.9

MSR-Bitmap Address

On processors that support the 1-setting of the “use MSR bitmaps” VM-execution control, the VM-execution control
fields include the 64-bit physical address of four contiguous MSR bitmaps, which are each 1-KByte in size. This
field does not exist on processors that do not support the 1-setting of that control. The four bitmaps are:

•

Read bitmap for low MSRs (located at the MSR-bitmap address). This contains one bit for each MSR address
in the range 00000000H to 00001FFFH. The bit determines whether an execution of RDMSR applied to that
MSR causes a VM exit.

•

Read bitmap for high MSRs (located at the MSR-bitmap address plus 1024). This contains one bit for each
MSR address in the range C0000000H toC0001FFFH. The bit determines whether an execution of RDMSR
applied to that MSR causes a VM exit.

•

Write bitmap for low MSRs (located at the MSR-bitmap address plus 2048). This contains one bit for each
MSR address in the range 00000000H to 00001FFFH. The bit determines whether an execution of WRMSR
applied to that MSR causes a VM exit.

•

Write bitmap for high MSRs (located at the MSR-bitmap address plus 3072). This contains one bit for each
MSR address in the range C0000000H toC0001FFFH. The bit determines whether an execution of WRMSR
applied to that MSR causes a VM exit.

A logical processor uses these bitmaps if and only if the “use MSR bitmaps” control is 1. If the bitmaps are used, an
execution of RDMSR or WRMSR causes a VM exit if the value of RCX is in neither of the ranges covered by the
bitmaps or if the appropriate bit in the MSR bitmaps (corresponding to the instruction and the RCX value) is 1. See
Section 25.1.3 for details. If the bitmaps are used, their address must be 4-KByte aligned.

24.6.10 Executive-VMCS Pointer
The executive-VMCS pointer is a 64-bit field used in the dual-monitor treatment of system-management interrupts
(SMIs) and system-management mode (SMM). SMM VM exits save this field as described in Section 34.15.2.
VM entries that return from SMM use this field as described in Section 34.15.4.

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24.6.11 Extended-Page-Table Pointer (EPTP)
The extended-page-table pointer (EPTP) contains the address of the base of EPT PML4 table (see Section
28.2.2), as well as other EPT configuration information. The format of this field is shown in Table 24-8.

Table 24-8. Format of Extended-Page-Table Pointer
Bit
Position(s)

Field

2:0

EPT paging-structure memory type (see Section 28.2.6):
0 = Uncacheable (UC)
6 = Write-back (WB)
Other values are reserved.1

5:3

This value is 1 less than the EPT page-walk length (see Section 28.2.2)

6

Setting this control to 1 enables accessed and dirty flags for EPT (see Section 28.2.4)2

11:7

Reserved

N–1:12

Bits N–1:12 of the physical address of the 4-KByte aligned EPT PML4 table3

63:N

Reserved

NOTES:
1. Software should read the VMX capability MSR IA32_VMX_EPT_VPID_CAP (see Appendix A.10) to determine what EPT paging-structure memory types are supported.
2. Not all processors support accessed and dirty flags for EPT. Software should read the VMX capability MSR
IA32_VMX_EPT_VPID_CAP (see Appendix A.10) to determine whether the processor supports this feature.
3. N is the physical-address width supported by the logical processor. Software can determine a processor’s physical-address width by
executing CPUID with 80000008H in EAX. The physical-address width is returned in bits 7:0 of EAX.
The EPTP exists only on processors that support the 1-setting of the “enable EPT” VM-execution control.

24.6.12 Virtual-Processor Identifier (VPID)
The virtual-processor identifier (VPID) is a 16-bit field. It exists only on processors that support the 1-setting
of the “enable VPID” VM-execution control. See Section 28.1 for details regarding the use of this field.

24.6.13 Controls for PAUSE-Loop Exiting
On processors that support the 1-setting of the “PAUSE-loop exiting” VM-execution control, the VM-execution
control fields include the following 32-bit fields:

•

PLE_Gap. Software can configure this field as an upper bound on the amount of time between two successive
executions of PAUSE in a loop.

•

PLE_Window. Software can configure this field as an upper bound on the amount of time a guest is allowed to
execute in a PAUSE loop.

These fields measure time based on a counter that runs at the same rate as the timestamp counter (TSC). See
Section 25.1.3 for more details regarding PAUSE-loop exiting.

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24.6.14 VM-Function Controls
The VM-function controls constitute a 64-bit vector that governs use of the VMFUNC instruction in VMX non-root
operation. This field is supported only on processors that support the 1-settings of both the “activate secondary
controls” primary processor-based VM-execution control and the “enable VM functions” secondary processorbased VM-execution control.
Table 24-9 lists the VM-function controls. See Section 25.5.5 for more details of how these controls affect processor
behavior in VMX non-root operation.

Table 24-9. Definitions of VM-Function Controls
Bit Position(s) Name

Description

0

The EPTP-switching VM function changes the EPT pointer to a value chosen from the EPTP list.
See Section 25.5.5.3.

EPTP switching

All other bits in this field are reserved to 0. Software should consult the VMX capability MSR IA32_VMX_VMFUNC
(see Appendix A.11) to determine which bits are reserved. Failure to clear reserved bits causes subsequent
VM entries to fail (see Section 26.2.1.1).
Processors that support the 1-setting of the “EPTP switching” VM-function control also support a 64-bit field called
the EPTP-list address. This field contains the physical address of the 4-KByte EPTP list. The EPTP list comprises
512 8-Byte entries (each an EPTP value) and is used by the EPTP-switching VM function (see Section 25.5.5.3).

24.6.15 VMCS Shadowing Bitmap Addresses
On processors that support the 1-setting of the “VMCS shadowing” VM-execution control, the VM-execution control
fields include the 64-bit physical addresses of the VMREAD bitmap and the VMWRITE bitmap. Each bitmap is 4
KBytes in size and thus contains 32 KBits. The addresses are the VMREAD-bitmap address and the VMWRITEbitmap address.
If the “VMCS shadowing” VM-execution control is 1, executions of VMREAD and VMWRITE may consult these
bitmaps (see Section 24.10 and Section 30.3).

24.6.16 ENCLS-Exiting Bitmap
The ENCLS-exiting bitmap is a 64-bit field. If the “enable ENCLS exiting” VM-execution control is 1, execution of
ENCLS causes a VM exit if the bit in this field corresponding to the value of EAX is 1. If the bit is 0, the instruction
executes normally. See Section 25.1.3 for more information.

24.6.17 Control Field for Page-Modification Logging
The PML address is a 64-bit field. It is the 4-KByte aligned address of the page-modification log. The pagemodification log consists of 512 64-bit entries. It is used for the page-modification logging feature. Details of the
page-modification logging are given in Section 28.2.5.
If the “enable PML” VM-execution control is 1, VM entry ensures that the PML address is 4-KByte aligned. The PML
address exists only on processors that support the 1-setting of the “enable PML” VM-execution control.

24.6.18 Controls for Virtualization Exceptions
On processors that support the 1-setting of the “EPT-violation #VE” VM-execution control, the VM-execution
control fields include the following:

•

Virtualization-exception information address (64 bits). This field contains the physical address of the
virtualization-exception information area. When a logical processor encounters a virtualization exception,
it saves virtualization-exception information at the virtualization-exception information address; see Section
25.5.6.2.

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•

EPTP index (16 bits). When an EPT violation causes a virtualization exception, the processor writes the value
of this field to the virtualization-exception information area. The EPTP-switching VM function updates this field
(see Section 25.5.5.3).

24.6.19 XSS-Exiting Bitmap
On processors that support the 1-setting of the “enable XSAVES/XRSTORS” VM-execution control, the VM-execution control fields include a 64-bit XSS-exiting bitmap. If the “enable XSAVES/XRSTORS” VM-execution control is
1, executions of XSAVES and XRSTORS may consult this bitmap (see Section 25.1.3 and Section 25.3).

24.7

VM-EXIT CONTROL FIELDS

The VM-exit control fields govern the behavior of VM exits. They are discussed in Section 24.7.1 and Section
24.7.2.

24.7.1

VM-Exit Controls

The VM-exit controls constitute a 32-bit vector that governs the basic operation of VM exits. Table 24-10 lists the
controls supported. See Chapter 27 for complete details of how these controls affect VM exits.

Table 24-10. Definitions of VM-Exit Controls
Bit Position(s) Name

Description

2

Save debug
controls

This control determines whether DR7 and the IA32_DEBUGCTL MSR are saved on VM exit.

9

Host addressspace size

On processors that support Intel 64 architecture, this control determines whether a logical
processor is in 64-bit mode after the next VM exit. Its value is loaded into CS.L,
IA32_EFER.LME, and IA32_EFER.LMA on every VM exit.1

12

Load
IA32_PERF_GLOB
AL_CTRL

This control determines whether the IA32_PERF_GLOBAL_CTRL MSR is loaded on VM exit.

15

Acknowledge
interrupt on exit

This control affects VM exits due to external interrupts:

18

Save IA32_PAT

This control determines whether the IA32_PAT MSR is saved on VM exit.

19

Load IA32_PAT

This control determines whether the IA32_PAT MSR is loaded on VM exit.

The first processors to support the virtual-machine extensions supported only the 1-setting
of this control.

This control must be 0 on processors that do not support Intel 64 architecture.

• If such a VM exit occurs and this control is 1, the logical processor acknowledges the
interrupt controller, acquiring the interrupt’s vector. The vector is stored in the VM-exit
interruption-information field, which is marked valid.
• If such a VM exit occurs and this control is 0, the interrupt is not acknowledged and the
VM-exit interruption-information field is marked invalid.

20

Save IA32_EFER

This control determines whether the IA32_EFER MSR is saved on VM exit.

21

Load IA32_EFER

This control determines whether the IA32_EFER MSR is loaded on VM exit.

22

Save VMXpreemption timer
value

This control determines whether the value of the VMX-preemption timer is saved on VM exit.

23

Clear
IA32_BNDCFGS

This control determines whether the IA32_BNDCFGS MSR is cleared on VM exit.

24

Conceal VM exits
from Intel PT

If this control is 1, Intel Processor Trace does not produce a paging information packet (PIP) on
a VM exit (see Chapter 35).

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NOTES:
1. Since Intel 64 architecture specifies that IA32_EFER.LMA is always set to the logical-AND of CR0.PG and IA32_EFER.LME, and since
CR0.PG is always 1 in VMX operation, IA32_EFER.LMA is always identical to IA32_EFER.LME in VMX operation.
All other bits in this field are reserved, some to 0 and some to 1. Software should consult the VMX capability MSRs
IA32_VMX_EXIT_CTLS and IA32_VMX_TRUE_EXIT_CTLS (see Appendix A.4) to determine how it should set the
reserved bits. Failure to set reserved bits properly causes subsequent VM entries to fail (see Section 26.2.1.2).
The first processors to support the virtual-machine extensions supported only the 1-settings of bits 0–8, 10, 11,
13, 14, 16, and 17. The VMX capability MSR IA32_VMX_EXIT_CTLS always reports that these bits must be 1.
Logical processors that support the 0-settings of any of these bits will support the VMX capability MSR
IA32_VMX_TRUE_EXIT_CTLS MSR, and software should consult this MSR to discover support for the 0-settings of
these bits. Software that is not aware of the functionality of any one of these bits should set that bit to 1.

24.7.2

VM-Exit Controls for MSRs

A VMM may specify lists of MSRs to be stored and loaded on VM exits. The following VM-exit control fields determine how MSRs are stored on VM exits:

•

VM-exit MSR-store count (32 bits). This field specifies the number of MSRs to be stored on VM exit. It is
recommended that this count not exceed 512 bytes.1 Otherwise, unpredictable processor behavior (including a
machine check) may result during VM exit.

•

VM-exit MSR-store address (64 bits). This field contains the physical address of the VM-exit MSR-store area.
The area is a table of entries, 16 bytes per entry, where the number of entries is given by the VM-exit MSR-store
count. The format of each entry is given in Table 24-11. If the VM-exit MSR-store count is not zero, the address
must be 16-byte aligned.

Table 24-11. Format of an MSR Entry
Bit Position(s)

Contents

31:0

MSR index

63:32

Reserved

127:64

MSR data

See Section 27.4 for how this area is used on VM exits.
The following VM-exit control fields determine how MSRs are loaded on VM exits:

•

VM-exit MSR-load count (32 bits). This field contains the number of MSRs to be loaded on VM exit. It is
recommended that this count not exceed 512 bytes. Otherwise, unpredictable processor behavior (including a
machine check) may result during VM exit.2

•

VM-exit MSR-load address (64 bits). This field contains the physical address of the VM-exit MSR-load area.
The area is a table of entries, 16 bytes per entry, where the number of entries is given by the VM-exit MSR-load
count (see Table 24-11). If the VM-exit MSR-load count is not zero, the address must be 16-byte aligned.

See Section 27.6 for how this area is used on VM exits.

24.8

VM-ENTRY CONTROL FIELDS

The VM-entry control fields govern the behavior of VM entries. They are discussed in Sections 24.8.1 through
24.8.3.
1. Future implementations may allow more MSRs to be stored reliably. Software should consult the VMX capability MSR
IA32_VMX_MISC to determine the number supported (see Appendix A.6).
2. Future implementations may allow more MSRs to be loaded reliably. Software should consult the VMX capability MSR
IA32_VMX_MISC to determine the number supported (see Appendix A.6).
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24.8.1

VM-Entry Controls

The VM-entry controls constitute a 32-bit vector that governs the basic operation of VM entries. Table 24-12 lists
the controls supported. See Chapter 24 for how these controls affect VM entries.

Table 24-12. Definitions of VM-Entry Controls
Bit Position(s) Name

Description

2

This control determines whether DR7 and the IA32_DEBUGCTL MSR are loaded on VM entry.

Load debug
controls

9

The first processors to support the virtual-machine extensions supported only the 1-setting of
this control.

IA-32e mode guest On processors that support Intel 64 architecture, this control determines whether the logical
processor is in IA-32e mode after VM entry. Its value is loaded into IA32_EFER.LMA as part of
VM entry.1
This control must be 0 on processors that do not support Intel 64 architecture.

10

Entry to SMM

This control determines whether the logical processor is in system-management mode (SMM)
after VM entry. This control must be 0 for any VM entry from outside SMM.

11

Deactivate dualmonitor treatment

If set to 1, the default treatment of SMIs and SMM is in effect after the VM entry (see Section
34.15.7). This control must be 0 for any VM entry from outside SMM.

13

Load
This control determines whether the IA32_PERF_GLOBAL_CTRL MSR is loaded on VM entry.
IA32_PERF_GLOBA
L_CTRL

14

Load IA32_PAT

This control determines whether the IA32_PAT MSR is loaded on VM entry.

15

Load IA32_EFER

This control determines whether the IA32_EFER MSR is loaded on VM entry.

16

Load
IA32_BNDCFGS

This control determines whether the IA32_BNDCFGS MSR is loaded on VM entry.

17

Conceal VM entries If this control is 1, Intel Processor Trace does not produce a paging information packet (PIP) on
from Intel PT
a VM entry (see Chapter 35).

NOTES:
1. Bit 5 of the IA32_VMX_MISC MSR is read as 1 on any logical processor that supports the 1-setting of the “unrestricted guest” VMexecution control. If it is read as 1, every VM exit stores the value of IA32_EFER.LMA into the “IA-32e mode guest” VM-entry control
(see Section 27.2).
All other bits in this field are reserved, some to 0 and some to 1. Software should consult the VMX capability MSRs
IA32_VMX_ENTRY_CTLS and IA32_VMX_TRUE_ENTRY_CTLS (see Appendix A.5) to determine how it should set
the reserved bits. Failure to set reserved bits properly causes subsequent VM entries to fail (see Section 26.2.1.3).
The first processors to support the virtual-machine extensions supported only the 1-settings of bits 0–8 and 12.
The VMX capability MSR IA32_VMX_ENTRY_CTLS always reports that these bits must be 1. Logical processors that
support the 0-settings of any of these bits will support the VMX capability MSR IA32_VMX_TRUE_ENTRY_CTLS
MSR, and software should consult this MSR to discover support for the 0-settings of these bits. Software that is not
aware of the functionality of any one of these bits should set that bit to 1.

24.8.2

VM-Entry Controls for MSRs

A VMM may specify a list of MSRs to be loaded on VM entries. The following VM-entry control fields manage this
functionality:

•

VM-entry MSR-load count (32 bits). This field contains the number of MSRs to be loaded on VM entry. It is
recommended that this count not exceed 512 bytes. Otherwise, unpredictable processor behavior (including a
machine check) may result during VM entry.1

1. Future implementations may allow more MSRs to be loaded reliably. Software should consult the VMX capability MSR
IA32_VMX_MISC to determine the number supported (see Appendix A.6).
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•

VM-entry MSR-load address (64 bits). This field contains the physical address of the VM-entry MSR-load
area. The area is a table of entries, 16 bytes per entry, where the number of entries is given by the VM-entry
MSR-load count. The format of entries is described in Table 24-11. If the VM-entry MSR-load count is not zero,
the address must be 16-byte aligned.

See Section 26.4 for details of how this area is used on VM entries.

24.8.3

VM-Entry Controls for Event Injection

VM entry can be configured to conclude by delivering an event through the IDT (after all guest state and MSRs have
been loaded). This process is called event injection and is controlled by the following three VM-entry control
fields:

•

VM-entry interruption-information field (32 bits). This field provides details about the event to be injected.
Table 24-13 describes the field.

Table 24-13. Format of the VM-Entry Interruption-Information Field
Bit Position(s)

Content

7:0

Vector of interrupt or exception

10:8

Interruption type:
0: External interrupt
1: Reserved
2: Non-maskable interrupt (NMI)
3: Hardware exception
4: Software interrupt
5: Privileged software exception
6: Software exception
7: Other event

11

Deliver error code (0 = do not deliver; 1 = deliver)

30:12

Reserved

31

Valid
— The vector (bits 7:0) determines which entry in the IDT is used or which other event is injected.
— The interruption type (bits 10:8) determines details of how the injection is performed. In general, a VMM
should use the type hardware exception for all exceptions other than breakpoint exceptions (#BP;
generated by INT3) and overflow exceptions (#OF; generated by INTO); it should use the type software
exception for #BP and #OF. The type other event is used for injection of events that are not delivered
through the IDT.
— For exceptions, the deliver-error-code bit (bit 11) determines whether delivery pushes an error code on
the guest stack.
— VM entry injects an event if and only if the valid bit (bit 31) is 1. The valid bit in this field is cleared on every
VM exit (see Section 27.2).

•

VM-entry exception error code (32 bits). This field is used if and only if the valid bit (bit 31) and the delivererror-code bit (bit 11) are both set in the VM-entry interruption-information field.

•

VM-entry instruction length (32 bits). For injection of events whose type is software interrupt, software
exception, or privileged software exception, this field is used to determine the value of RIP that is pushed on
the stack.

See Section 26.5 for details regarding the mechanics of event injection, including the use of the interruption type
and the VM-entry instruction length.
VM exits clear the valid bit (bit 31) in the VM-entry interruption-information field.

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24.9

VM-EXIT INFORMATION FIELDS

The VMCS contains a section of fields that contain information about the most recent VM exit.
On some processors, attempts to write to these fields with VMWRITE fail (see “VMWRITE—Write Field to VirtualMachine Control Structure” in Chapter 30).1

24.9.1

Basic VM-Exit Information

The following VM-exit information fields provide basic information about a VM exit:

•

Exit reason (32 bits). This field encodes the reason for the VM exit and has the structure given in Table 24-14.

Table 24-14. Format of Exit Reason
Bit Position(s)

Contents

15:0

Basic exit reason

26:16

Reserved (cleared to 0)

27

A VM exit saves this bit as 1 to indicate that the VM exit was incident to enclave mode.

28

Pending MTF VM exit

29

VM exit from VMX root operation

30

Reserved (cleared to 0)

31

VM-entry failure (0 = true VM exit; 1 = VM-entry failure)

— Bits 15:0 provide basic information about the cause of the VM exit (if bit 31 is clear) or of the VM-entry
failure (if bit 31 is set). Appendix C enumerates the basic exit reasons.
— Bit 28 is set only by an SMM VM exit (see Section 34.15.2) that took priority over an MTF VM exit (see
Section 25.5.2) that would have occurred had the SMM VM exit not occurred. See Section 34.15.2.3.
— Bit 29 is set if and only if the processor was in VMX root operation at the time the VM exit occurred. This can
happen only for SMM VM exits. See Section 34.15.2.
— Because some VM-entry failures load processor state from the host-state area (see Section 26.7), software
must be able to distinguish such cases from true VM exits. Bit 31 is used for that purpose.

•

Exit qualification (64 bits; 32 bits on processors that do not support Intel 64 architecture). This field contains
additional information about the cause of VM exits due to the following: debug exceptions; page-fault
exceptions; start-up IPIs (SIPIs); task switches; INVEPT; INVLPG;INVVPID; LGDT; LIDT; LLDT; LTR; SGDT;
SIDT; SLDT; STR; VMCLEAR; VMPTRLD; VMPTRST; VMREAD; VMWRITE; VMXON; control-register accesses;
MOV DR; I/O instructions; and MWAIT. The format of the field depends on the cause of the VM exit. See Section
27.2.1 for details.

•

Guest-linear address (64 bits; 32 bits on processors that do not support Intel 64 architecture). This field is
used in the following cases:
— VM exits due to attempts to execute LMSW with a memory operand.
— VM exits due to attempts to execute INS or OUTS.
— VM exits due to system-management interrupts (SMIs) that arrive immediately after retirement of I/O
instructions.
— Certain VM exits due to EPT violations
See Section 27.2.1 and Section 34.15.2.3 for details of when and how this field is used.

1.

Software can discover whether these fields can be written by reading the VMX capability MSR IA32_VMX_MISC (see Appendix A.6).
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•

Guest-physical address (64 bits). This field is used VM exits due to EPT violations and EPT misconfigurations.
See Section 27.2.1 for details of when and how this field is used.

24.9.2

Information for VM Exits Due to Vectored Events

Event-specific information is provided for VM exits due to the following vectored events: exceptions (including
those generated by the instructions INT3, INTO, BOUND, and UD); external interrupts that occur while the
“acknowledge interrupt on exit” VM-exit control is 1; and non-maskable interrupts (NMIs). This information is
provided in the following fields:

•

VM-exit interruption information (32 bits). This field receives basic information associated with the event
causing the VM exit. Table 24-15 describes this field.

Table 24-15. Format of the VM-Exit Interruption-Information Field
Bit Position(s)

Content

7:0

Vector of interrupt or exception

10:8

Interruption type:
0: External interrupt
1: Not used
2: Non-maskable interrupt (NMI)
3: Hardware exception
4 – 5: Not used
6: Software exception
7: Not used

11

Error code valid (0 = invalid; 1 = valid)

12

NMI unblocking due to IRET

30:13

Reserved (cleared to 0)

31

Valid

•

VM-exit interruption error code (32 bits). For VM exits caused by hardware exceptions that would have
delivered an error code on the stack, this field receives that error code.

Section 27.2.2 provides details of how these fields are saved on VM exits.

24.9.3

Information for VM Exits That Occur During Event Delivery

Additional information is provided for VM exits that occur during event delivery in VMX non-root operation.1 This
information is provided in the following fields:

•

IDT-vectoring information (32 bits). This field receives basic information associated with the event that was
being delivered when the VM exit occurred. Table 24-16 describes this field.

1. This includes cases in which the event delivery was caused by event injection as part of VM entry; see Section 26.5.1.2.
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Table 24-16. Format of the IDT-Vectoring Information Field
Bit Position(s)

Content

7:0

Vector of interrupt or exception

10:8

Interruption type:
0: External interrupt
1: Not used
2: Non-maskable interrupt (NMI)
3: Hardware exception
4: Software interrupt
5: Privileged software exception
6: Software exception
7: Not used

11

Error code valid (0 = invalid; 1 = valid)

12

Undefined

30:13

Reserved (cleared to 0)

31

Valid

•

IDT-vectoring error code (32 bits). For VM exits the occur during delivery of hardware exceptions that would
have delivered an error code on the stack, this field receives that error code.

See Section 27.2.3 provides details of how these fields are saved on VM exits.

24.9.4

Information for VM Exits Due to Instruction Execution

The following fields are used for VM exits caused by attempts to execute certain instructions in VMX non-root operation:

•

VM-exit instruction length (32 bits). For VM exits resulting from instruction execution, this field receives the
length in bytes of the instruction whose execution led to the VM exit.1 See Section 27.2.4 for details of when
and how this field is used.

•

VM-exit instruction information (32 bits). This field is used for VM exits due to attempts to execute INS,
INVEPT, INVVPID, LIDT, LGDT, LLDT, LTR, OUTS, SIDT, SGDT, SLDT, STR, VMCLEAR, VMPTRLD, VMPTRST,
VMREAD, VMWRITE, or VMXON.2 The format of the field depends on the cause of the VM exit. See Section
27.2.4 for details.

The following fields (64 bits each; 32 bits on processors that do not support Intel 64 architecture) are used only for
VM exits due to SMIs that arrive immediately after retirement of I/O instructions. They provide information about
that I/O instruction:

•
•
•
•

I/O RCX. The value of RCX before the I/O instruction started.
I/O RSI. The value of RSI before the I/O instruction started.
I/O RDI. The value of RDI before the I/O instruction started.
I/O RIP. The value of RIP before the I/O instruction started (the RIP that addressed the I/O instruction).

24.9.5

VM-Instruction Error Field

The 32-bit VM-instruction error field does not provide information about the most recent VM exit. In fact, it is
not modified on VM exits. Instead, it provides information about errors encountered by a non-faulting execution of
one of the VMX instructions.

1. This field is also used for VM exits that occur during the delivery of a software interrupt or software exception.
2. Whether the processor provides this information on VM exits due to attempts to execute INS or OUTS can be determined by consulting the VMX capability MSR IA32_VMX_BASIC (see Appendix A.1).
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24.10

VMCS TYPES: ORDINARY AND SHADOW

Every VMCS is either an ordinary VMCS or a shadow VMCS. A VMCS’s type is determined by the shadow-VMCS
indicator in the VMCS region (this is the value of bit 31 of the first 4 bytes of the VMCS region; see Table 24-1): 0
indicates an ordinary VMCS, while 1 indicates a shadow VMCS. Shadow VMCSs are supported only on processors
that support the 1-setting of the “VMCS shadowing” VM-execution control (see Section 24.6.2).
A shadow VMCS differs from an ordinary VMCS in two ways:

•

An ordinary VMCS can be used for VM entry but a shadow VMCS cannot. Attempts to perform VM entry when
the current VMCS is a shadow VMCS fail (see Section 26.1).

•

The VMREAD and VMWRITE instructions can be used in VMX non-root operation to access a shadow VMCS but
not an ordinary VMCS. This fact results from the following:
— If the “VMCS shadowing” VM-execution control is 0, execution of the VMREAD and VMWRITE instructions in
VMX non-root operation always cause VM exits (see Section 25.1.3).
— If the “VMCS shadowing” VM-execution control is 1, execution of the VMREAD and VMWRITE instructions in
VMX non-root operation can access the VMCS referenced by the VMCS link pointer (see Section 30.3).
— If the “VMCS shadowing” VM-execution control is 1, VM entry ensures that any VMCS referenced by the
VMCS link pointer is a shadow VMCS (see Section 26.3.1.5).

In VMX root operation, both types of VMCSs can be accessed with the VMREAD and VMWRITE instructions.
Software should not modify the shadow-VMCS indicator in the VMCS region of a VMCS that is active. Doing so may
cause the VMCS to become corrupted (see Section 24.11.1). Before modifying the shadow-VMCS indicator, software should execute VMCLEAR for the VMCS to ensure that it is not active.

24.11

SOFTWARE USE OF THE VMCS AND RELATED STRUCTURES

This section details guidelines that software should observe when using a VMCS and related structures. It also
provides descriptions of consequences for failing to follow guidelines.

24.11.1 Software Use of Virtual-Machine Control Structures
To ensure proper processor behavior, software should observe certain guidelines when using an active VMCS.
No VMCS should ever be active on more than one logical processor. If a VMCS is to be “migrated” from one logical
processor to another, the first logical processor should execute VMCLEAR for the VMCS (to make it inactive on that
logical processor and to ensure that all VMCS data are in memory) before the other logical processor executes
VMPTRLD for the VMCS (to make it active on the second logical processor).1 A VMCS that is made active on more
than one logical processor may become corrupted (see below).
Software should not modify the shadow-VMCS indicator (see Table 24-1) in the VMCS region of a VMCS that is
active. Doing so may cause the VMCS to become corrupted. Before modifying the shadow-VMCS indicator, software
should execute VMCLEAR for the VMCS to ensure that it is not active.
Software should use the VMREAD and VMWRITE instructions to access the different fields in the current VMCS (see
Section 24.11.2). Software should never access or modify the VMCS data of an active VMCS using ordinary
memory operations, in part because the format used to store the VMCS data is implementation-specific and not
architecturally defined, and also because a logical processor may maintain some VMCS data of an active VMCS on
the processor and not in the VMCS region. The following items detail some of the hazards of accessing VMCS data
using ordinary memory operations:

•

Any data read from a VMCS with an ordinary memory read does not reliably reflect the state of the VMCS.
Results may vary from time to time or from logical processor to logical processor.

1. As noted in Section 24.1, execution of the VMPTRLD instruction makes a VMCS is active. In addition, VM entry makes active any
shadow VMCS referenced by the VMCS link pointer in the current VMCS. If a shadow VMCS is made active by VM entry, it is necessary to execute VMCLEAR for that VMCS before allowing that VMCS to become active on another logical processor.
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•

Writing to a VMCS with an ordinary memory write is not guaranteed to have a deterministic effect on the VMCS.
Doing so may cause the VMCS to become corrupted (see below).

(Software can avoid these hazards by removing any linear-address mappings to a VMCS region before executing a
VMPTRLD for that region and by not remapping it until after executing VMCLEAR for that region.)
If a logical processor leaves VMX operation, any VMCSs active on that logical processor may be corrupted (see
below). To prevent such corruption of a VMCS that may be used either after a return to VMX operation or on
another logical processor, software should execute VMCLEAR for that VMCS before executing the VMXOFF instruction or removing power from the processor (e.g., as part of a transition to the S3 and S4 power states).
This section has identified operations that may cause a VMCS to become corrupted. These operations may cause
the VMCS’s data to become undefined. Behavior may be unpredictable if that VMCS used subsequently on any
logical processor. The following items detail some hazards of VMCS corruption:

•
•

VM entries may fail for unexplained reasons or may load undesired processor state.

•

VM exits may load undesired processor state, save incorrect state into the VMCS, or cause the logical processor
to transition to a shutdown state.

The processor may not correctly support VMX non-root operation as documented in Chapter 27 and may
generate unexpected VM exits.

24.11.2 VMREAD, VMWRITE, and Encodings of VMCS Fields
Every field of the VMCS is associated with a 32-bit value that is its encoding. The encoding is provided in an
operand to VMREAD and VMWRITE when software wishes to read or write that field. These instructions fail if given,
in 64-bit mode, an operand that sets an encoding bit beyond bit 32. See Chapter 30 for a description of these
instructions.
The structure of the 32-bit encodings of the VMCS components is determined principally by the width of the fields
and their function in the VMCS. See Table 24-17.

Table 24-17. Structure of VMCS Component Encoding
Bit Position(s)

Contents

0

Access type (0 = full; 1 = high); must be full for 16-bit, 32-bit, and natural-width fields

9:1

Index

11:10

Type:
0: control
1: VM-exit information
2: guest state
3: host state

12

Reserved (must be 0)

14:13

Width:
0: 16-bit
1: 64-bit
2: 32-bit
3: natural-width

31:15

Reserved (must be 0)

The following items detail the meaning of the bits in each encoding:

•

Field width. Bits 14:13 encode the width of the field.
— A value of 0 indicates a 16-bit field.
— A value of 1 indicates a 64-bit field.

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— A value of 2 indicates a 32-bit field.
— A value of 3 indicates a natural-width field. Such fields have 64 bits on processors that support Intel 64
architecture and 32 bits on processors that do not.
Fields whose encodings use value 1 are specially treated to allow 32-bit software access to all 64 bits of the
field. Such access is allowed by defining, for each such field, an encoding that allows direct access to the high
32 bits of the field. See below.

•

Field type. Bits 11:10 encode the type of VMCS field: control, guest-state, host-state, or VM-exit information.
(The last category also includes the VM-instruction error field.)

•
•

Index. Bits 9:1 distinguish components with the same field width and type.
Access type. Bit 0 must be 0 for all fields except for 64-bit fields (those with field-width 1; see above). A
VMREAD or VMWRITE using an encoding with this bit cleared to 0 accesses the entire field. For a 64-bit field
with field-width 1, a VMREAD or VMWRITE using an encoding with this bit set to 1 accesses only the high 32 bits
of the field.

Appendix B gives the encodings of all fields in the VMCS.
The following describes the operation of VMREAD and VMWRITE based on processor mode, VMCS-field width, and
access type:

•

16-bit fields:
— A VMREAD returns the value of the field in bits 15:0 of the destination operand; other bits of the destination
operand are cleared to 0.
— A VMWRITE writes the value of bits 15:0 of the source operand into the VMCS field; other bits of the source
operand are not used.

•

32-bit fields:
— A VMREAD returns the value of the field in bits 31:0 of the destination operand; in 64-bit mode, bits 63:32
of the destination operand are cleared to 0.
— A VMWRITE writes the value of bits 31:0 of the source operand into the VMCS field; in 64-bit mode,
bits 63:32 of the source operand are not used.

•

64-bit fields and natural-width fields using the full access type outside IA-32e mode.
— A VMREAD returns the value of bits 31:0 of the field in its destination operand; bits 63:32 of the field are
ignored.
— A VMWRITE writes the value of its source operand to bits 31:0 of the field and clears bits 63:32 of the field.

•

64-bit fields and natural-width fields using the full access type in 64-bit mode (only on processors that support
Intel 64 architecture).
— A VMREAD returns the value of the field in bits 63:0 of the destination operand
— A VMWRITE writes the value of bits 63:0 of the source operand into the VMCS field.

•

64-bit fields using the high access type.
— A VMREAD returns the value of bits 63:32 of the field in bits 31:0 of the destination operand; in 64-bit
mode, bits 63:32 of the destination operand are cleared to 0.
— A VMWRITE writes the value of bits 31:0 of the source operand to bits 63:32 of the field; in 64-bit mode,
bits 63:32 of the source operand are not used.

Software seeking to read a 64-bit field outside IA-32e mode can use VMREAD with the full access type (reading
bits 31:0 of the field) and VMREAD with the high access type (reading bits 63:32 of the field); the order of the two
VMREAD executions is not important. Software seeking to modify a 64-bit field outside IA-32e mode should first
use VMWRITE with the full access type (establishing bits 31:0 of the field while clearing bits 63:32) and then use
VMWRITE with the high access type (establishing bits 63:32 of the field).

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24.11.3 Initializing a VMCS
Software should initialize fields in a VMCS (using VMWRITE) before using the VMCS for VM entry. Failure to do so
may result in unpredictable behavior; for example, a VM entry may fail for unexplained reasons, or a successful
transition (VM entry or VM exit) may load processor state with unexpected values.
It is not necessary to initialize fields that the logical processor will not use. (For example, it is not necessary to
unitize the MSR-bitmap address if the “use MSR bitmaps” VM-execution control is 0.)
A processor maintains some VMCS information that cannot be modified with the VMWRITE instruction; this
includes a VMCS’s launch state (see Section 24.1). Such information may be stored in the VMCS data portion of a
VMCS region. Because the format of this information is implementation-specific, there is no way for software to
know, when it first allocates a region of memory for use as a VMCS region, how the processor will determine this
information from the contents of the memory region.
In addition to its other functions, the VMCLEAR instruction initializes any implementation-specific information in
the VMCS region referenced by its operand. To avoid the uncertainties of implementation-specific behavior, software should execute VMCLEAR on a VMCS region before making the corresponding VMCS active with VMPTRLD for
the first time. (Figure 24-1 illustrates how execution of VMCLEAR puts a VMCS into a well-defined state.)
The following software usage is consistent with these limitations:

•
•

VMCLEAR should be executed for a VMCS before it is used for VM entry for the first time.

•

VMRESUME should be used for any subsequent VM entry using a VMCS (until the next execution of VMCLEAR
for the VMCS).

VMLAUNCH should be used for the first VM entry using a VMCS after VMCLEAR has been executed for that
VMCS.

It is expected that, in general, VMRESUME will have lower latency than VMLAUNCH. Since “migrating” a VMCS from
one logical processor to another requires use of VMCLEAR (see Section 24.11.1), which sets the launch state of the
VMCS to “clear”, such migration requires the next VM entry to be performed using VMLAUNCH. Software developers can avoid the performance cost of increased VM-entry latency by avoiding unnecessary migration of a VMCS
from one logical processor to another.

24.11.4 Software Access to Related Structures
In addition to data in the VMCS region itself, VMX non-root operation can be controlled by data structures that are
referenced by pointers in a VMCS (for example, the I/O bitmaps). While the pointers to these data structures are
parts of the VMCS, the data structures themselves are not. They are not accessible using VMREAD and VMWRITE
but by ordinary memory writes.
Software should ensure that each such data structure is modified only when no logical processor with a current
VMCS that references it is in VMX non-root operation. Doing otherwise may lead to unpredictable behavior
(including behaviors identified in Section 24.11.1).

24.11.5 VMXON Region
Before executing VMXON, software allocates a region of memory (called the VMXON region)1 that the logical
processor uses to support VMX operation. The physical address of this region (the VMXON pointer) is provided in
an operand to VMXON. The VMXON pointer is subject to the limitations that apply to VMCS pointers:

•
•

The VMXON pointer must be 4-KByte aligned (bits 11:0 must be zero).
The VMXON pointer must not set any bits beyond the processor’s physical-address width.2,3

1. The amount of memory required for the VMXON region is the same as that required for a VMCS region. This size is implementation
specific and can be determined by consulting the VMX capability MSR IA32_VMX_BASIC (see Appendix A.1).
2. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
3. If IA32_VMX_BASIC[48] is read as 1, the VMXON pointer must not set any bits in the range 63:32; see Appendix A.1.
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Before executing VMXON, software should write the VMCS revision identifier (see Section 24.2) to the VMXON
region. (Specifically, it should write the 31-bit VMCS revision identifier to bits 30:0 of the first 4 bytes of the VMXON
region; bit 31 should be cleared to 0.) It need not initialize the VMXON region in any other way. Software should
use a separate region for each logical processor and should not access or modify the VMXON region of a logical
processor between execution of VMXON and VMXOFF on that logical processor. Doing otherwise may lead to unpredictable behavior (including behaviors identified in Section 24.11.1).

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CHAPTER 25
VMX NON-ROOT OPERATION
In a virtualized environment using VMX, the guest software stack typically runs on a logical processor in VMX nonroot operation. This mode of operation is similar to that of ordinary processor operation outside of the virtualized
environment. This chapter describes the differences between VMX non-root operation and ordinary processor operation with special attention to causes of VM exits (which bring a logical processor from VMX non-root operation to
root operation). The differences between VMX non-root operation and ordinary processor operation are described
in the following sections:

•
•
•
•
•
•

Section 25.1, “Instructions That Cause VM Exits”
Section 25.2, “Other Causes of VM Exits”
Section 25.3, “Changes to Instruction Behavior in VMX Non-Root Operation”
Section 25.4, “Other Changes in VMX Non-Root Operation”
Section 25.5, “Features Specific to VMX Non-Root Operation”
Section 25.6, “Unrestricted Guests”

Chapter 26, “VM Entries,” describes the data control structures that govern VMX non-root operation. Chapter 26,
“VM Entries,” describes the operation of VM entries by which the processor transitions from VMX root operation to
VMX non-root operation. Chapter 25, “VMX Non-Root Operation,” describes the operation of VM exits by which the
processor transitions from VMX non-root operation to VMX root operation.
Chapter 28, “VMX Support for Address Translation,” describes two features that support address translation in VMX
non-root operation. Chapter 29, “APIC Virtualization and Virtual Interrupts,” describes features that support virtualization of interrupts and the Advanced Programmable Interrupt Controller (APIC) in VMX non-root operation.

25.1

INSTRUCTIONS THAT CAUSE VM EXITS

Certain instructions may cause VM exits if executed in VMX non-root operation. Unless otherwise specified, such
VM exits are “fault-like,” meaning that the instruction causing the VM exit does not execute and no processor state
is updated by the instruction. Section 27.1 details architectural state in the context of a VM exit.
Section 25.1.1 defines the prioritization between faults and VM exits for instructions subject to both. Section
25.1.2 identifies instructions that cause VM exits whenever they are executed in VMX non-root operation (and thus
can never be executed in VMX non-root operation). Section 25.1.3 identifies instructions that cause VM exits
depending on the settings of certain VM-execution control fields (see Section 24.6).

25.1.1

Relative Priority of Faults and VM Exits

The following principles describe the ordering between existing faults and VM exits:

•

Certain exceptions have priority over VM exits. These include invalid-opcode exceptions, faults based on
privilege level,1 and general-protection exceptions that are based on checking I/O permission bits in the taskstate segment (TSS). For example, execution of RDMSR with CPL = 3 generates a general-protection exception
and not a VM exit.2

•

Faults incurred while fetching instruction operands have priority over VM exits that are conditioned based on
the contents of those operands (see LMSW in Section 25.1.3).

•

VM exits caused by execution of the INS and OUTS instructions (resulting either because the “unconditional I/O
exiting” VM-execution control is 1 or because the “use I/O bitmaps control is 1) have priority over the following
faults:

1. These include faults generated by attempts to execute, in virtual-8086 mode, privileged instructions that are not recognized in that
mode.
2. MOV DR is an exception to this rule; see Section 25.1.3.
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VMX NON-ROOT OPERATION

— A general-protection fault due to the relevant segment (ES for INS; DS for OUTS unless overridden by an
instruction prefix) being unusable
— A general-protection fault due to an offset beyond the limit of the relevant segment
— An alignment-check exception

•

Fault-like VM exits have priority over exceptions other than those mentioned above. For example, RDMSR of a
non-existent MSR with CPL = 0 generates a VM exit and not a general-protection exception.

When Section 25.1.2 or Section 25.1.3 (below) identify an instruction execution that may lead to a VM exit, it is
assumed that the instruction does not incur a fault that takes priority over a VM exit.

25.1.2

Instructions That Cause VM Exits Unconditionally

The following instructions cause VM exits when they are executed in VMX non-root operation: CPUID, GETSEC,1
INVD, and XSETBV. This is also true of instructions introduced with VMX, which include: INVEPT, INVVPID,
VMCALL,2 VMCLEAR, VMLAUNCH, VMPTRLD, VMPTRST, VMRESUME, VMXOFF, and VMXON.

25.1.3

Instructions That Cause VM Exits Conditionally

Certain instructions cause VM exits in VMX non-root operation depending on the setting of the VM-execution
controls. The following instructions can cause “fault-like” VM exits based on the conditions described:3

•

CLTS. The CLTS instruction causes a VM exit if the bits in position 3 (corresponding to CR0.TS) are set in both
the CR0 guest/host mask and the CR0 read shadow.

•

ENCLS. The ENCLS instruction causes a VM exit if the “enable ENCLS exiting” VM-execution control is 1 and
one of the following is true:
— The value of EAX is less than 63 and the corresponding bit in the ENCLS-exiting bitmap is 1 (see Section
24.6.16).
— The value of EAX is greater than or equal to 63 and bit 63 in the ENCLS-exiting bitmap is 1.

•
•

HLT. The HLT instruction causes a VM exit if the “HLT exiting” VM-execution control is 1.
IN, INS/INSB/INSW/INSD, OUT, OUTS/OUTSB/OUTSW/OUTSD. The behavior of each of these instructions is determined by the settings of the “unconditional I/O exiting” and “use I/O bitmaps” VM-execution
controls:
— If both controls are 0, the instruction executes normally.
— If the “unconditional I/O exiting” VM-execution control is 1 and the “use I/O bitmaps” VM-execution control
is 0, the instruction causes a VM exit.
— If the “use I/O bitmaps” VM-execution control is 1, the instruction causes a VM exit if it attempts to access
an I/O port corresponding to a bit set to 1 in the appropriate I/O bitmap (see Section 24.6.4). If an I/O
operation “wraps around” the 16-bit I/O-port space (accesses ports FFFFH and 0000H), the I/O instruction
causes a VM exit (the “unconditional I/O exiting” VM-execution control is ignored if the “use I/O bitmaps”
VM-execution control is 1).
See Section 25.1.1 for information regarding the priority of VM exits relative to faults that may be caused by
the INS and OUTS instructions.

•
•

INVLPG. The INVLPG instruction causes a VM exit if the “INVLPG exiting” VM-execution control is 1.
INVPCID. The INVPCID instruction causes a VM exit if the “INVLPG exiting” and “enable INVPCID”
VM-execution controls are both 1.

1. An execution of GETSEC in VMX non-root operation causes a VM exit if CR4.SMXE[Bit 14] = 1 regardless of the value of CPL or RAX.
An execution of GETSEC causes an invalid-opcode exception (#UD) if CR4.SMXE[Bit 14] = 0.
2. Under the dual-monitor treatment of SMIs and SMM, executions of VMCALL cause SMM VM exits in VMX root operation outside SMM.
See Section 34.15.2.
3. Many of the items in this section refer to secondary processor-based VM-execution controls. If bit 31 of the primary processorbased VM-execution controls is 0, VMX non-root operation functions as if these controls were all 0. See Section 24.6.2.
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VMX NON-ROOT OPERATION

•

LGDT, LIDT, LLDT, LTR, SGDT, SIDT, SLDT, STR. These instructions cause VM exits if the “descriptor-table
exiting” VM-execution control is 1.

•

LMSW. In general, the LMSW instruction causes a VM exit if it would write, for any bit set in the low 4 bits of
the CR0 guest/host mask, a value different than the corresponding bit in the CR0 read shadow. LMSW never
clears bit 0 of CR0 (CR0.PE); thus, LMSW causes a VM exit if either of the following are true:
— The bits in position 0 (corresponding to CR0.PE) are set in both the CR0 guest/host mask and the source
operand, and the bit in position 0 is clear in the CR0 read shadow.
— For any bit position in the range 3:1, the bit in that position is set in the CR0 guest/host mask and the
values of the corresponding bits in the source operand and the CR0 read shadow differ.

•
•

MONITOR. The MONITOR instruction causes a VM exit if the “MONITOR exiting” VM-execution control is 1.

•

MOV from CR8. The MOV from CR8 instruction causes a VM exit if the “CR8-store exiting” VM-execution
control is 1.

•

MOV to CR0. The MOV to CR0 instruction causes a VM exit unless the value of its source operand matches, for
the position of each bit set in the CR0 guest/host mask, the corresponding bit in the CR0 read shadow. (If every
bit is clear in the CR0 guest/host mask, MOV to CR0 cannot cause a VM exit.)

•

MOV to CR3. The MOV to CR3 instruction causes a VM exit unless the “CR3-load exiting” VM-execution control
is 0 or the value of its source operand is equal to one of the CR3-target values specified in the VMCS. Only the
first n CR3-target values are considered, where n is the CR3-target count. If the “CR3-load exiting” VMexecution control is 1 and the CR3-target count is 0, MOV to CR3 always causes a VM exit.

MOV from CR3. The MOV from CR3 instruction causes a VM exit if the “CR3-store exiting” VM-execution
control is 1. The first processors to support the virtual-machine extensions supported only the 1-setting of this
control.

The first processors to support the virtual-machine extensions supported only the 1-setting of the “CR3-load
exiting” VM-execution control. These processors always consult the CR3-target controls to determine whether
an execution of MOV to CR3 causes a VM exit.

•

MOV to CR4. The MOV to CR4 instruction causes a VM exit unless the value of its source operand matches, for
the position of each bit set in the CR4 guest/host mask, the corresponding bit in the CR4 read shadow.

•
•

MOV to CR8. The MOV to CR8 instruction causes a VM exit if the “CR8-load exiting” VM-execution control is 1.

•

MWAIT. The MWAIT instruction causes a VM exit if the “MWAIT exiting” VM-execution control is 1. If this
control is 0, the behavior of the MWAIT instruction may be modified (see Section 25.3).

•

PAUSE. The behavior of each of this instruction depends on CPL and the settings of the “PAUSE exiting” and
“PAUSE-loop exiting” VM-execution controls:

MOV DR. The MOV DR instruction causes a VM exit if the “MOV-DR exiting” VM-execution control is 1. Such
VM exits represent an exception to the principles identified in Section 25.1.1 in that they take priority over the
following: general-protection exceptions based on privilege level; and invalid-opcode exceptions that occur
because CR4.DE=1 and the instruction specified access to DR4 or DR5.

— CPL = 0.

•

If the “PAUSE exiting” and “PAUSE-loop exiting” VM-execution controls are both 0, the PAUSE
instruction executes normally.

•

If the “PAUSE exiting” VM-execution control is 1, the PAUSE instruction causes a VM exit (the “PAUSEloop exiting” VM-execution control is ignored if CPL = 0 and the “PAUSE exiting” VM-execution control
is 1).

•

If the “PAUSE exiting” VM-execution control is 0 and the “PAUSE-loop exiting” VM-execution control is
1, the following treatment applies.
The processor determines the amount of time between this execution of PAUSE and the previous
execution of PAUSE at CPL 0. If this amount of time exceeds the value of the VM-execution control field
PLE_Gap, the processor considers this execution to be the first execution of PAUSE in a loop. (It also
does so for the first execution of PAUSE at CPL 0 after VM entry.)
Otherwise, the processor determines the amount of time since the most recent execution of PAUSE that
was considered to be the first in a loop. If this amount of time exceeds the value of the VM-execution
control field PLE_Window, a VM exit occurs.
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VMX NON-ROOT OPERATION

For purposes of these computations, time is measured based on a counter that runs at the same rate as
the timestamp counter (TSC).
— CPL > 0.

•
•

If the “PAUSE exiting” VM-execution control is 0, the PAUSE instruction executes normally.
If the “PAUSE exiting” VM-execution control is 1, the PAUSE instruction causes a VM exit.

The “PAUSE-loop exiting” VM-execution control is ignored if CPL > 0.

•

RDMSR. The RDMSR instruction causes a VM exit if any of the following are true:
— The “use MSR bitmaps” VM-execution control is 0.
— The value of ECX is not in the ranges 00000000H – 00001FFFH and C0000000H – C0001FFFH.
— The value of ECX is in the range 00000000H – 00001FFFH and bit n in read bitmap for low MSRs is 1, where
n is the value of ECX.
— The value of ECX is in the range C0000000H – C0001FFFH and bit n in read bitmap for high MSRs is 1,
where n is the value of ECX & 00001FFFH.
See Section 24.6.9 for details regarding how these bitmaps are identified.

•
•
•
•
•

RDPMC. The RDPMC instruction causes a VM exit if the “RDPMC exiting” VM-execution control is 1.

•
•

RSM. The RSM instruction causes a VM exit if executed in system-management mode (SMM).1

RDRAND. The RDRAND instruction causes a VM exit if the “RDRAND exiting” VM-execution control is 1.
RDSEED. The RDSEED instruction causes a VM exit if the “RDSEED exiting” VM-execution control is 1.
RDTSC. The RDTSC instruction causes a VM exit if the “RDTSC exiting” VM-execution control is 1.
RDTSCP. The RDTSCP instruction causes a VM exit if the “RDTSC exiting” and “enable RDTSCP” VM-execution
controls are both 1.
VMREAD. The VMREAD instruction causes a VM exit if any of the following are true:
— The “VMCS shadowing” VM-execution control is 0.
— Bits 63:15 (bits 31:15 outside 64-bit mode) of the register source operand are not all 0.
— Bit n in VMREAD bitmap is 1, where n is the value of bits 14:0 of the register source operand. See Section
24.6.15 for details regarding how the VMREAD bitmap is identified.
If the VMREAD instruction does not cause a VM exit, it reads from the VMCS referenced by the VMCS link
pointer. See Chapter 30, “VMREAD—Read Field from Virtual-Machine Control Structure” for details of the
operation of the VMREAD instruction.

•

VMWRITE. The VMWRITE instruction causes a VM exit if any of the following are true:
— The “VMCS shadowing” VM-execution control is 0.
— Bits 63:15 (bits 31:15 outside 64-bit mode) of the register source operand are not all 0.
— Bit n in VMWRITE bitmap is 1, where n is the value of bits 14:0 of the register source operand. See Section
24.6.15 for details regarding how the VMWRITE bitmap is identified.
If the VMWRITE instruction does not cause a VM exit, it writes to the VMCS referenced by the VMCS link
pointer. See Chapter 30, “VMWRITE—Write Field to Virtual-Machine Control Structure” for details of the
operation of the VMWRITE instruction.

•
•

WBINVD. The WBINVD instruction causes a VM exit if the “WBINVD exiting” VM-execution control is 1.
WRMSR. The WRMSR instruction causes a VM exit if any of the following are true:
— The “use MSR bitmaps” VM-execution control is 0.
— The value of ECX is not in the ranges 00000000H – 00001FFFH and C0000000H – C0001FFFH.
— The value of ECX is in the range 00000000H – 00001FFFH and bit n in write bitmap for low MSRs is 1, where
n is the value of ECX.

1. Execution of the RSM instruction outside SMM causes an invalid-opcode exception regardless of whether the processor is in VMX
operation. It also does so in VMX root operation in SMM; see Section 34.15.3.
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VMX NON-ROOT OPERATION

— The value of ECX is in the range C0000000H – C0001FFFH and bit n in write bitmap for high MSRs is 1,
where n is the value of ECX & 00001FFFH.
See Section 24.6.9 for details regarding how these bitmaps are identified.

•

XRSTORS. The XRSTORS instruction causes a VM exit if the “enable XSAVES/XRSTORS” VM-execution control
is 1and any bit is set in the logical-AND of the following three values: EDX:EAX, the IA32_XSS MSR, and the
XSS-exiting bitmap (see Section 24.6.19).

•

XSAVES. The XSAVES instruction causes a VM exit if the “enable XSAVES/XRSTORS” VM-execution control is
1 and any bit is set in the logical-AND of the following three values: EDX:EAX, the IA32_XSS MSR, and the XSSexiting bitmap (see Section 24.6.19).

25.2

OTHER CAUSES OF VM EXITS

In addition to VM exits caused by instruction execution, the following events can cause VM exits:

•

Exceptions. Exceptions (faults, traps, and aborts) cause VM exits based on the exception bitmap (see Section
24.6.3). If an exception occurs, its vector (in the range 0–31) is used to select a bit in the exception bitmap. If
the bit is 1, a VM exit occurs; if the bit is 0, the exception is delivered normally through the guest IDT. This use
of the exception bitmap applies also to exceptions generated by the instructions INT3, INTO, BOUND, and UD.
Page faults (exceptions with vector 14) are specially treated. When a page fault occurs, a processor consults
(1) bit 14 of the exception bitmap; (2) the error code produced with the page fault [PFEC]; (3) the page-fault
error-code mask field [PFEC_MASK]; and (4) the page-fault error-code match field [PFEC_MATCH]. It checks if
PFEC & PFEC_MASK = PFEC_MATCH. If there is equality, the specification of bit 14 in the exception bitmap is
followed (for example, a VM exit occurs if that bit is set). If there is inequality, the meaning of that bit is
reversed (for example, a VM exit occurs if that bit is clear).
Thus, if software desires VM exits on all page faults, it can set bit 14 in the exception bitmap to 1 and set the
page-fault error-code mask and match fields each to 00000000H. If software desires VM exits on no page
faults, it can set bit 14 in the exception bitmap to 1, the page-fault error-code mask field to 00000000H, and
the page-fault error-code match field to FFFFFFFFH.

•

Triple fault. A VM exit occurs if the logical processor encounters an exception while attempting to call the
double-fault handler and that exception itself does not cause a VM exit due to the exception bitmap. This
applies to the case in which the double-fault exception was generated within VMX non-root operation, the case
in which the double-fault exception was generated during event injection by VM entry, and to the case in which
VM entry is injecting a double-fault exception.

•

External interrupts. An external interrupt causes a VM exit if the “external-interrupt exiting” VM-execution
control is 1. (See Section 25.6 for an exception.) Otherwise, the interrupt is delivered normally through the
IDT. (If a logical processor is in the shutdown state or the wait-for-SIPI state, external interrupts are blocked.
The interrupt is not delivered through the IDT and no VM exit occurs.)

•

Non-maskable interrupts (NMIs). An NMI causes a VM exit if the “NMI exiting” VM-execution control is 1.
Otherwise, it is delivered using descriptor 2 of the IDT. (If a logical processor is in the wait-for-SIPI state, NMIs
are blocked. The NMI is not delivered through the IDT and no VM exit occurs.)

•

INIT signals. INIT signals cause VM exits. A logical processor performs none of the operations normally
associated with these events. Such exits do not modify register state or clear pending events as they would
outside of VMX operation. (If a logical processor is in the wait-for-SIPI state, INIT signals are blocked. They do
not cause VM exits in this case.)

•

Start-up IPIs (SIPIs). SIPIs cause VM exits. If a logical processor is not in the wait-for-SIPI activity state
when a SIPI arrives, no VM exit occurs and the SIPI is discarded. VM exits due to SIPIs do not perform any of
the normal operations associated with those events: they do not modify register state as they would outside of
VMX operation. (If a logical processor is not in the wait-for-SIPI state, SIPIs are blocked. They do not cause
VM exits in this case.)

•

Task switches. Task switches are not allowed in VMX non-root operation. Any attempt to effect a task switch
in VMX non-root operation causes a VM exit. See Section 25.4.2.

•

System-management interrupts (SMIs). If the logical processor is using the dual-monitor treatment of
SMIs and system-management mode (SMM), SMIs cause SMM VM exits. See Section 34.15.2.1

Vol. 3C 25-5

VMX NON-ROOT OPERATION

•

VMX-preemption timer. A VM exit occurs when the timer counts down to zero. See Section 25.5.1 for details
of operation of the VMX-preemption timer.
Debug-trap exceptions and higher priority events take priority over VM exits caused by the VMX-preemption
timer. VM exits caused by the VMX-preemption timer take priority over VM exits caused by the “NMI-window
exiting” VM-execution control and lower priority events.
These VM exits wake a logical processor from the same inactive states as would a non-maskable interrupt.
Specifically, they wake a logical processor from the shutdown state and from the states entered using the HLT
and MWAIT instructions. These VM exits do not occur if the logical processor is in the wait-for-SIPI state.

In addition, there are controls that cause VM exits based on the readiness of guest software to receive interrupts:

•

If the “interrupt-window exiting” VM-execution control is 1, a VM exit occurs before execution of any instruction
if RFLAGS.IF = 1 and there is no blocking of events by STI or by MOV SS (see Table 24-3). Such a VM exit
occurs immediately after VM entry if the above conditions are true (see Section 26.6.5).
Non-maskable interrupts (NMIs) and higher priority events take priority over VM exits caused by this control.
VM exits caused by this control take priority over external interrupts and lower priority events.
These VM exits wake a logical processor from the same inactive states as would an external interrupt. Specifically, they wake a logical processor from the states entered using the HLT and MWAIT instructions. These
VM exits do not occur if the logical processor is in the shutdown state or the wait-for-SIPI state.

•

If the “NMI-window exiting” VM-execution control is 1, a VM exit occurs before execution of any instruction if
there is no virtual-NMI blocking and there is no blocking of events by MOV SS (see Table 24-3). (A logical
processor may also prevent such a VM exit if there is blocking of events by STI.) Such a VM exit occurs
immediately after VM entry if the above conditions are true (see Section 26.6.6).
VM exits caused by the VMX-preemption timer and higher priority events take priority over VM exits caused by
this control. VM exits caused by this control take priority over non-maskable interrupts (NMIs) and lower
priority events.
These VM exits wake a logical processor from the same inactive states as would an NMI. Specifically, they wake
a logical processor from the shutdown state and from the states entered using the HLT and MWAIT instructions.
These VM exits do not occur if the logical processor is in the wait-for-SIPI state.

25.3

CHANGES TO INSTRUCTION BEHAVIOR IN VMX NON-ROOT OPERATION

The behavior of some instructions is changed in VMX non-root operation. Some of these changes are determined
by the settings of certain VM-execution control fields. The following items detail such changes:1

•

CLTS. Behavior of the CLTS instruction is determined by the bits in position 3 (corresponding to CR0.TS) in the
CR0 guest/host mask and the CR0 read shadow:
— If bit 3 in the CR0 guest/host mask is 0, CLTS clears CR0.TS normally (the value of bit 3 in the CR0 read
shadow is irrelevant in this case), unless CR0.TS is fixed to 1 in VMX operation (see Section 23.8), in which
case CLTS causes a general-protection exception.
— If bit 3 in the CR0 guest/host mask is 1 and bit 3 in the CR0 read shadow is 0, CLTS completes but does not
change the contents of CR0.TS.
— If the bits in position 3 in the CR0 guest/host mask and the CR0 read shadow are both 1, CLTS causes a
VM exit.

•

INVPCID. Behavior of the INVPCID instruction is determined first by the setting of the “enable INVPCID”
VM-execution control:
— If the “enable INVPCID” VM-execution control is 0, INVPCID causes an invalid-opcode exception (#UD).
This exception takes priority over any other exception the instruction may incur.

1. Under the dual-monitor treatment of SMIs and SMM, SMIs also cause SMM VM exits if they occur in VMX root operation outside SMM.
If the processor is using the default treatment of SMIs and SMM, SMIs are delivered as described in Section 34.14.1.
1. Some of the items in this section refer to secondary processor-based VM-execution controls. If bit 31 of the primary processorbased VM-execution controls is 0, VMX non-root operation functions as if these controls were all 0. See Section 24.6.2.
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VMX NON-ROOT OPERATION

— If the “enable INVPCID” VM-execution control is 1, treatment is based on the setting of the “INVLPG
exiting” VM-execution control:

•

•
•

If the “INVLPG exiting” VM-execution control is 0, INVPCID operates normally.
If the “INVLPG exiting” VM-execution control is 1, INVPCID causes a VM exit.

IRET. Behavior of IRET with regard to NMI blocking (see Table 24-3) is determined by the settings of the “NMI
exiting” and “virtual NMIs” VM-execution controls:
— If the “NMI exiting” VM-execution control is 0, IRET operates normally and unblocks NMIs. (If the “NMI
exiting” VM-execution control is 0, the “virtual NMIs” control must be 0; see Section 26.2.1.1.)
— If the “NMI exiting” VM-execution control is 1, IRET does not affect blocking of NMIs. If, in addition, the
“virtual NMIs” VM-execution control is 1, the logical processor tracks virtual-NMI blocking. In this case,
IRET removes any virtual-NMI blocking.
The unblocking of NMIs or virtual NMIs specified above occurs even if IRET causes a fault.

•

LMSW. Outside of VMX non-root operation, LMSW loads its source operand into CR0[3:0], but it does not clear
CR0.PE if that bit is set. In VMX non-root operation, an execution of LMSW that does not cause a VM exit (see
Section 25.1.3) leaves unmodified any bit in CR0[3:0] corresponding to a bit set in the CR0 guest/host mask.
An attempt to set any other bit in CR0[3:0] to a value not supported in VMX operation (see Section 23.8)
causes a general-protection exception. Attempts to clear CR0.PE are ignored without fault.

•

MOV from CR0. The behavior of MOV from CR0 is determined by the CR0 guest/host mask and the CR0 read
shadow. For each position corresponding to a bit clear in the CR0 guest/host mask, the destination operand is
loaded with the value of the corresponding bit in CR0. For each position corresponding to a bit set in the CR0
guest/host mask, the destination operand is loaded with the value of the corresponding bit in the CR0 read
shadow. Thus, if every bit is cleared in the CR0 guest/host mask, MOV from CR0 reads normally from CR0; if
every bit is set in the CR0 guest/host mask, MOV from CR0 returns the value of the CR0 read shadow.
Depending on the contents of the CR0 guest/host mask and the CR0 read shadow, bits may be set in the
destination that would never be set when reading directly from CR0.

•

MOV from CR3. If the “enable EPT” VM-execution control is 1 and an execution of MOV from CR3 does not
cause a VM exit (see Section 25.1.3), the value loaded from CR3 is a guest-physical address; see Section
28.2.1.

•

MOV from CR4. The behavior of MOV from CR4 is determined by the CR4 guest/host mask and the CR4 read
shadow. For each position corresponding to a bit clear in the CR4 guest/host mask, the destination operand is
loaded with the value of the corresponding bit in CR4. For each position corresponding to a bit set in the CR4
guest/host mask, the destination operand is loaded with the value of the corresponding bit in the CR4 read
shadow. Thus, if every bit is cleared in the CR4 guest/host mask, MOV from CR4 reads normally from CR4; if
every bit is set in the CR4 guest/host mask, MOV from CR4 returns the value of the CR4 read shadow.
Depending on the contents of the CR4 guest/host mask and the CR4 read shadow, bits may be set in the
destination that would never be set when reading directly from CR4.

•

MOV from CR8. If the MOV from CR8 instruction does not cause a VM exit (see Section 25.1.3), its behavior
is modified if the “use TPR shadow” VM-execution control is 1; see Section 29.3.

•

MOV to CR0. An execution of MOV to CR0 that does not cause a VM exit (see Section 25.1.3) leaves
unmodified any bit in CR0 corresponding to a bit set in the CR0 guest/host mask. Treatment of attempts to
modify other bits in CR0 depends on the setting of the “unrestricted guest” VM-execution control:
— If the control is 0, MOV to CR0 causes a general-protection exception if it attempts to set any bit in CR0 to
a value not supported in VMX operation (see Section 23.8).
— If the control is 1, MOV to CR0 causes a general-protection exception if it attempts to set any bit in CR0
other than bit 0 (PE) or bit 31 (PG) to a value not supported in VMX operation. It remains the case,
however, that MOV to CR0 causes a general-protection exception if it would result in CR0.PE = 0 and
CR0.PG = 1 or if it would result in CR0.PG = 1, CR4.PAE = 0, and IA32_EFER.LME = 1.

•

MOV to CR3. If the “enable EPT” VM-execution control is 1 and an execution of MOV to CR3 does not cause a
VM exit (see Section 25.1.3), the value loaded into CR3 is treated as a guest-physical address; see Section
28.2.1.
— If PAE paging is not being used, the instruction does not use the guest-physical address to access memory
and it does not cause it to be translated through EPT.1
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VMX NON-ROOT OPERATION

— If PAE paging is being used, the instruction translates the guest-physical address through EPT and uses the
result to load the four (4) page-directory-pointer-table entries (PDPTEs). The instruction does not use the
guest-physical addresses the PDPTEs to access memory and it does not cause them to be translated
through EPT.

•

MOV to CR4. An execution of MOV to CR4 that does not cause a VM exit (see Section 25.1.3) leaves
unmodified any bit in CR4 corresponding to a bit set in the CR4 guest/host mask. Such an execution causes a
general-protection exception if it attempts to set any bit in CR4 (not corresponding to a bit set in the CR4
guest/host mask) to a value not supported in VMX operation (see Section 23.8).

•

MOV to CR8. If the MOV to CR8 instruction does not cause a VM exit (see Section 25.1.3), its behavior is
modified if the “use TPR shadow” VM-execution control is 1; see Section 29.3.

•

MWAIT. Behavior of the MWAIT instruction (which always causes an invalid-opcode exception—#UD—if
CPL > 0) is determined by the setting of the “MWAIT exiting” VM-execution control:
— If the “MWAIT exiting” VM-execution control is 1, MWAIT causes a VM exit.
— If the “MWAIT exiting” VM-execution control is 0, MWAIT operates normally if one of the following are true:
(1) ECX[0] is 0; (2) RFLAGS.IF = 1; or both of the following are true: (a) the “interrupt-window exiting” VMexecution control is 0; and (b) the logical processor has not recognized a pending virtual interrupt (see
Section 29.2.1).
— If the “MWAIT exiting” VM-execution control is 0, ECX[0] = 1, and RFLAGS.IF = 0, MWAIT does not cause
the processor to enter an implementation-dependent optimized state if either the “interrupt-window
exiting” VM-execution control is 1 or the logical processor has recognized a pending virtual interrupt;
instead, control passes to the instruction following the MWAIT instruction.

•

RDMSR. Section 25.1.3 identifies when executions of the RDMSR instruction cause VM exits. If such an
execution causes neither a fault due to CPL > 0 nor a VM exit, the instruction’s behavior may be modified for
certain values of ECX:
— If ECX contains 10H (indicating the IA32_TIME_STAMP_COUNTER MSR), the value returned by the
instruction is determined by the setting of the “use TSC offsetting” VM-execution control:

•

If the control is 0, RDMSR operates normally, loading EAX:EDX with the value of the
IA32_TIME_STAMP_COUNTER MSR.

•

If the control is 1, the value returned is determined by the setting of the “use TSC scaling” VM-execution
control:
—

If the control is 0, RDMSR loads EAX:EDX with the sum of the value of the
IA32_TIME_STAMP_COUNTER MSR and the value of the TSC offset.

—

If the control is 1, RDMSR first computes the product of the value of the
IA32_TIME_STAMP_COUNTER MSR and the value of the TSC multiplier. It then shifts the value of
the product right 48 bits and loads EAX:EDX with the sum of that shifted value and the value of the
TSC offset.

The 1-setting of the “use TSC-offsetting” VM-execution control does not affect executions of RDMSR if ECX
contains 6E0H (indicating the IA32_TSC_DEADLINE MSR). Such executions return the APIC-timer deadline
relative to the actual timestamp counter without regard to the TSC offset.
— If ECX is in the range 800H–8FFH (indicating an APIC MSR), instruction behavior may be modified if the
“virtualize x2APIC mode” VM-execution control is 1; see Section 29.5.

•

RDPID. Behavior of the RDPID instruction is determined first by the setting of the “enable RDTSCP”
VM-execution control:
— If the “enable RDTSCP” VM-execution control is 0, RDPID causes an invalid-opcode exception (#UD).
— If the “enable RDTSCP” VM-execution control is 1, RDPID operates normally.

•

RDTSC. Behavior of the RDTSC instruction is determined by the settings of the “RDTSC exiting” and “use TSC
offsetting” VM-execution controls:

1. A logical processor uses PAE paging if CR0.PG = 1, CR4.PAE = 1 and IA32_EFER.LMA = 0. See Section 4.4 in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 3A.
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VMX NON-ROOT OPERATION

— If both controls are 0, RDTSC operates normally.
— If the “RDTSC exiting” VM-execution control is 0 and the “use TSC offsetting” VM-execution control is 1, the
value returned is determined by the setting of the “use TSC scaling” VM-execution control:

•

If the control is 0, RDTSC loads EAX:EDX with the sum of the value of the IA32_TIME_STAMP_COUNTER
MSR and the value of the TSC offset.

•

If the control is 1, RDTSC first computes the product of the value of the IA32_TIME_STAMP_COUNTER
MSR and the value of the TSC multiplier. It then shifts the value of the product right 48 bits and loads
EAX:EDX with the sum of that shifted value and the value of the TSC offset.

— If the “RDTSC exiting” VM-execution control is 1, RDTSC causes a VM exit.

•

RDTSCP. Behavior of the RDTSCP instruction is determined first by the setting of the “enable RDTSCP”
VM-execution control:
— If the “enable RDTSCP” VM-execution control is 0, RDTSCP causes an invalid-opcode exception (#UD). This
exception takes priority over any other exception the instruction may incur.
— If the “enable RDTSCP” VM-execution control is 1, treatment is based on the settings of the “RDTSC exiting”
and “use TSC offsetting” VM-execution controls:

•
•

If both controls are 0, RDTSCP operates normally.
If the “RDTSC exiting” VM-execution control is 0 and the “use TSC offsetting” VM-execution control is 1,
the value returned is determined by the setting of the “use TSC scaling” VM-execution control:
—

If the control is 0, RDTSCP loads EAX:EDX with the sum of the value of the
IA32_TIME_STAMP_COUNTER MSR and the value of the TSC offset.

—

If the control is 1, RDTSCP first computes the product of the value of the
IA32_TIME_STAMP_COUNTER MSR and the value of the TSC multiplier. It then shifts the value of
the product right 48 bits and loads EAX:EDX with the sum of that shifted value and the value of the
TSC offset.

In either case, RDTSCP also loads ECX with the value of bits 31:0 of the IA32_TSC_AUX MSR.

•

•

If the “RDTSC exiting” VM-execution control is 1, RDTSCP causes a VM exit.

SMSW. The behavior of SMSW is determined by the CR0 guest/host mask and the CR0 read shadow. For each
position corresponding to a bit clear in the CR0 guest/host mask, the destination operand is loaded with the
value of the corresponding bit in CR0. For each position corresponding to a bit set in the CR0 guest/host mask,
the destination operand is loaded with the value of the corresponding bit in the CR0 read shadow. Thus, if every
bit is cleared in the CR0 guest/host mask, SMSW reads normally from CR0; if every bit is set in the CR0
guest/host mask, SMSW returns the value of the CR0 read shadow.
Note the following: (1) for any memory destination or for a 16-bit register destination, only the low 16 bits of
the CR0 guest/host mask and the CR0 read shadow are used (bits 63:16 of a register destination are left
unchanged); (2) for a 32-bit register destination, only the low 32 bits of the CR0 guest/host mask and the CR0
read shadow are used (bits 63:32 of the destination are cleared); and (3) depending on the contents of the
CR0 guest/host mask and the CR0 read shadow, bits may be set in the destination that would never be set
when reading directly from CR0.

•

WRMSR. Section 25.1.3 identifies when executions of the WRMSR instruction cause VM exits. If such an
execution neither a fault due to CPL > 0 nor a VM exit, the instruction’s behavior may be modified for certain
values of ECX:
— If ECX contains 79H (indicating IA32_BIOS_UPDT_TRIG MSR), no microcode update is loaded, and control
passes to the next instruction. This implies that microcode updates cannot be loaded in VMX non-root
operation.
— On processors that support Intel PT but which do not allow it to be used in VMX operation, if ECX contains
570H (indicating the IA32_RTIT_CTL MSR), the instruction causes a general-protection exception.1

1. Software should read the VMX capability MSR IA32_VMX_MISC to determine whether the processor allows Intel PT to be used in
VMX operation (see Appendix A.6).
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VMX NON-ROOT OPERATION

— If ECX contains 808H (indicating the TPR MSR), 80BH (the EOI MSR), or 83FH (self-IPI MSR), instruction
behavior may modified if the “virtualize x2APIC mode” VM-execution control is 1; see Section 29.5.

•

XRSTORS. Behavior of the XRSTORS instruction is determined first by the setting of the “enable
XSAVES/XRSTORS” VM-execution control:
— If the “enable XSAVES/XRSTORS” VM-execution control is 0, XRSTORS causes an invalid-opcode exception
(#UD).
— If the “enable XSAVES/XRSTORS” VM-execution control is 1, treatment is based on the value of the XSSexiting bitmap (see Section 24.6.19):

•

•

XRSTORS causes a VM exit if any bit is set in the logical-AND of the following three values: EDX:EAX,
the IA32_XSS MSR, and the XSS-exiting bitmap.

•

Otherwise, XRSTORS operates normally.

XSAVES. Behavior of the XSAVES instruction is determined first by the setting of the “enable
XSAVES/XRSTORS” VM-execution control:
— If the “enable XSAVES/XRSTORS” VM-execution control is 0, XSAVES causes an invalid-opcode exception
(#UD).
— If the “enable XSAVES/XRSTORS” VM-execution control is 1, treatment is based on the value of the XSSexiting bitmap (see Section 24.6.19):

•

XSAVES causes a VM exit if any bit is set in the logical-AND of the following three values: EDX:EAX, the
IA32_XSS MSR, and the XSS-exiting bitmap.

•

Otherwise, XSAVES operates normally.

25.4

OTHER CHANGES IN VMX NON-ROOT OPERATION

Treatments of event blocking and of task switches differ in VMX non-root operation as described in the following
sections.

25.4.1

Event Blocking

Event blocking is modified in VMX non-root operation as follows:

•

If the “external-interrupt exiting” VM-execution control is 1, RFLAGS.IF does not control the blocking of
external interrupts. In this case, an external interrupt that is not blocked for other reasons causes a VM exit
(even if RFLAGS.IF = 0).

•

If the “external-interrupt exiting” VM-execution control is 1, external interrupts may or may not be blocked by
STI or by MOV SS (behavior is implementation-specific).

•

If the “NMI exiting” VM-execution control is 1, non-maskable interrupts (NMIs) may or may not be blocked by
STI or by MOV SS (behavior is implementation-specific).

25.4.2

Treatment of Task Switches

Task switches are not allowed in VMX non-root operation. Any attempt to effect a task switch in VMX non-root operation causes a VM exit. However, the following checks are performed (in the order indicated), possibly resulting in
a fault, before there is any possibility of a VM exit due to task switch:
1. If a task gate is being used, appropriate checks are made on its P bit and on the proper values of the relevant
privilege fields. The following cases detail the privilege checks performed:
a. If CALL, INT n, or JMP accesses a task gate in IA-32e mode, a general-protection exception occurs.
b. If CALL, INT n, INT3, INTO, or JMP accesses a task gate outside IA-32e mode, privilege-levels checks are
performed on the task gate but, if they pass, privilege levels are not checked on the referenced task-state
segment (TSS) descriptor.

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c.

If CALL or JMP accesses a TSS descriptor directly in IA-32e mode, a general-protection exception occurs.

d. If CALL or JMP accesses a TSS descriptor directly outside IA-32e mode, privilege levels are checked on the
TSS descriptor.
e. If a non-maskable interrupt (NMI), an exception, or an external interrupt accesses a task gate in the IDT in
IA-32e mode, a general-protection exception occurs.
f.

If a non-maskable interrupt (NMI), an exception other than breakpoint exceptions (#BP) and overflow
exceptions (#OF), or an external interrupt accesses a task gate in the IDT outside IA-32e mode, no
privilege checks are performed.

g. If IRET is executed with RFLAGS.NT = 1 in IA-32e mode, a general-protection exception occurs.
h. If IRET is executed with RFLAGS.NT = 1 outside IA-32e mode, a TSS descriptor is accessed directly and no
privilege checks are made.
2. Checks are made on the new TSS selector (for example, that is within GDT limits).
3. The new TSS descriptor is read. (A page fault results if a relevant GDT page is not present).
4. The TSS descriptor is checked for proper values of type (depends on type of task switch), P bit, S bit, and limit.
Only if checks 1–4 all pass (do not generate faults) might a VM exit occur. However, the ordering between a VM exit
due to a task switch and a page fault resulting from accessing the old TSS or the new TSS is implementationspecific. Some processors may generate a page fault (instead of a VM exit due to a task switch) if accessing either
TSS would cause a page fault. Other processors may generate a VM exit due to a task switch even if accessing
either TSS would cause a page fault.
If an attempt at a task switch through a task gate in the IDT causes an exception (before generating a VM exit due
to the task switch) and that exception causes a VM exit, information about the event whose delivery that accessed
the task gate is recorded in the IDT-vectoring information fields and information about the exception that caused
the VM exit is recorded in the VM-exit interruption-information fields. See Section 27.2. The fact that a task gate
was being accessed is not recorded in the VMCS.
If an attempt at a task switch through a task gate in the IDT causes VM exit due to the task switch, information
about the event whose delivery accessed the task gate is recorded in the IDT-vectoring fields of the VMCS. Since
the cause of such a VM exit is a task switch and not an interruption, the valid bit for the VM-exit interruption information field is 0. See Section 27.2.

25.5

FEATURES SPECIFIC TO VMX NON-ROOT OPERATION

Some VM-execution controls support features that are specific to VMX non-root operation. These are the VMXpreemption timer (Section 25.5.1) and the monitor trap flag (Section 25.5.2), translation of guest-physical
addresses (Section 25.5.3), VM functions (Section 25.5.5), and virtualization exceptions (Section 25.5.6).

25.5.1

VMX-Preemption Timer

If the last VM entry was performed with the 1-setting of “activate VMX-preemption timer” VM-execution control,
the VMX-preemption timer counts down (from the value loaded by VM entry; see Section 26.6.4) in VMX nonroot operation. When the timer counts down to zero, it stops counting down and a VM exit occurs (see Section
25.2).
The VMX-preemption timer counts down at rate proportional to that of the timestamp counter (TSC). Specifically,
the timer counts down by 1 every time bit X in the TSC changes due to a TSC increment. The value of X is in the
range 0–31 and can be determined by consulting the VMX capability MSR IA32_VMX_MISC (see Appendix A.6).
The VMX-preemption timer operates in the C-states C0, C1, and C2; it also operates in the shutdown and wait-forSIPI states. If the timer counts down to zero in any state other than the wait-for SIPI state, the logical processor
transitions to the C0 C-state and causes a VM exit; the timer does not cause a VM exit if it counts down to zero in
the wait-for-SIPI state. The timer is not decremented in C-states deeper than C2.
Treatment of the timer in the case of system management interrupts (SMIs) and system-management mode
(SMM) depends on whether the treatment of SMIs and SMM:
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•

If the default treatment of SMIs and SMM (see Section 34.14) is active, the VMX-preemption timer counts
across an SMI to VMX non-root operation, subsequent execution in SMM, and the return from SMM via the RSM
instruction. However, the timer can cause a VM exit only from VMX non-root operation. If the timer expires
during SMI, in SMM, or during RSM, a timer-induced VM exit occurs immediately after RSM with its normal
priority unless it is blocked based on activity state (Section 25.2).

•

If the dual-monitor treatment of SMIs and SMM (see Section 34.15) is active, transitions into and out of SMM
are VM exits and VM entries, respectively. The treatment of the VMX-preemption timer by those transitions is
mostly the same as for ordinary VM exits and VM entries; Section 34.15.2 and Section 34.15.4 detail some
differences.

25.5.2

Monitor Trap Flag

The monitor trap flag is a debugging feature that causes VM exits to occur on certain instruction boundaries in
VMX non-root operation. Such VM exits are called MTF VM exits. An MTF VM exit may occur on an instruction
boundary in VMX non-root operation as follows:

•

If the “monitor trap flag” VM-execution control is 1 and VM entry is injecting a vectored event (see Section
26.5.1), an MTF VM exit is pending on the instruction boundary before the first instruction following the
VM entry.

•

If VM entry is injecting a pending MTF VM exit (see Section 26.5.2), an MTF VM exit is pending on the
instruction boundary before the first instruction following the VM entry. This is the case even if the “monitor
trap flag” VM-execution control is 0.

•

If the “monitor trap flag” VM-execution control is 1, VM entry is not injecting an event, and a pending event
(e.g., debug exception or interrupt) is delivered before an instruction can execute, an MTF VM exit is pending
on the instruction boundary following delivery of the event (or any nested exception).

•

Suppose that the “monitor trap flag” VM-execution control is 1, VM entry is not injecting an event, and the first
instruction following VM entry is a REP-prefixed string instruction:
— If the first iteration of the instruction causes a fault, an MTF VM exit is pending on the instruction boundary
following delivery of the fault (or any nested exception).
— If the first iteration of the instruction does not cause a fault, an MTF VM exit is pending on the instruction
boundary after that iteration.

•

Suppose that the “monitor trap flag” VM-execution control is 1, VM entry is not injecting an event, and the first
instruction following VM entry is the XBEGIN instruction. In this case, an MTF VM exit is pending at the fallback
instruction address of the XBEGIN instruction. This behavior applies regardless of whether advanced debugging
of RTM transactional regions has been enabled (see Section 16.3.7, “RTM-Enabled Debugger Support,” of
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1).

•

Suppose that the “monitor trap flag” VM-execution control is 1, VM entry is not injecting an event, and the first
instruction following VM entry is neither a REP-prefixed string instruction or the XBEGIN instruction:
— If the instruction causes a fault, an MTF VM exit is pending on the instruction boundary following delivery of
the fault (or any nested exception).1
— If the instruction does not cause a fault, an MTF VM exit is pending on the instruction boundary following
execution of that instruction. If the instruction is INT3 or INTO, this boundary follows delivery of any
software exception. If the instruction is INT n, this boundary follows delivery of a software interrupt. If the
instruction is HLT, the MTF VM exit will be from the HLT activity state.

No MTF VM exit occurs if another VM exit occurs before reaching the instruction boundary on which an MTF VM exit
would be pending (e.g., due to an exception or triple fault).
An MTF VM exit occurs on the instruction boundary on which it is pending unless a higher priority event takes
precedence or the MTF VM exit is blocked due to the activity state:

•

System-management interrupts (SMIs), INIT signals, and higher priority events take priority over MTF
VM exits. MTF VM exits take priority over debug-trap exceptions and lower priority events.

1. This item includes the cases of an invalid opcode exception—#UD— generated by the UD instruction and a BOUND-range exceeded
exception—#BR—generated by the BOUND instruction.
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•

No MTF VM exit occurs if the processor is in either the shutdown activity state or wait-for-SIPI activity state. If
a non-maskable interrupt subsequently takes the logical processor out of the shutdown activity state without
causing a VM exit, an MTF VM exit is pending after delivery of that interrupt.

Special treatment may apply to Intel SGX instructions or if the logical processor is in enclave mode. See Section
42.2 for details.

25.5.3

Translation of Guest-Physical Addresses Using EPT

The extended page-table mechanism (EPT) is a feature that can be used to support the virtualization of physical
memory. When EPT is in use, certain physical addresses are treated as guest-physical addresses and are not used
to access memory directly. Instead, guest-physical addresses are translated by traversing a set of EPT paging
structures to produce physical addresses that are used to access memory.
Details of the EPT mechanism are given in Section 28.2.

25.5.4

APIC Virtualization

APIC virtualization is a collection of features that can be used to support the virtualization of interrupts and the
Advanced Programmable Interrupt Controller (APIC). When APIC virtualization is enabled, the processor emulates
many accesses to the APIC, tracks the state of the virtual APIC, and delivers virtual interrupts — all in VMX nonroot operation without a VM exit.
Details of the APIC virtualization are given in Chapter 29.

25.5.5

VM Functions

A VM function is an operation provided by the processor that can be invoked from VMX non-root operation
without a VM exit. VM functions are enabled and configured by the settings of different fields in the VMCS. Software in VMX non-root operation invokes a VM function with the VMFUNC instruction; the value of EAX selects the
specific VM function being invoked.
Section 25.5.5.1 explains how VM functions are enabled. Section 25.5.5.2 specifies the behavior of the VMFUNC
instruction. Section 25.5.5.3 describes a specific VM function called EPTP switching.

25.5.5.1

Enabling VM Functions

Software enables VM functions generally by setting the “enable VM functions” VM-execution control. A specific
VM function is enabled by setting the corresponding VM-function control.
Suppose, for example, that software wants to enable EPTP switching (VM function 0; see Section 24.6.14).To do
so, it must set the “activate secondary controls” VM-execution control (bit 31 of the primary processor-based VMexecution controls), the “enable VM functions” VM-execution control (bit 13 of the secondary processor-based VMexecution controls) and the “EPTP switching” VM-function control (bit 0 of the VM-function controls).

25.5.5.2

General Operation of the VMFUNC Instruction

The VMFUNC instruction causes an invalid-opcode exception (#UD) if the “enable VM functions” VM-execution
controls is 01 or the value of EAX is greater than 63 (only VM functions 0–63 can be enable). Otherwise, the
instruction causes a VM exit if the bit at position EAX is 0 in the VM-function controls (the selected VM function is
not enabled). If such a VM exit occurs, the basic exit reason used is 59 (3BH), indicating “VMFUNC”, and the length
of the VMFUNC instruction is saved into the VM-exit instruction-length field. If the instruction causes neither an
invalid-opcode exception nor a VM exit due to a disabled VM function, it performs the functionality of the
VM function specified by the value in EAX.
1. “Enable VM functions” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VMX non-root operation functions as if the “enable VM functions” VM-execution control were 0. See Section 24.6.2.
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Individual VM functions may perform additional fault checking (e.g., one might cause a general-protection exception if CPL > 0). In addition, specific VM functions may include checks that might result in a VM exit. If such a
VM exit occurs, VM-exit information is saved as described in the previous paragraph. The specification of a
VM function may indicate that additional VM-exit information is provided.
The specific behavior of the EPTP-switching VM function (including checks that result in VM exits) is given in
Section 25.5.5.3.

25.5.5.3

EPTP Switching

EPTP switching is VM function 0. This VM function allows software in VMX non-root operation to load a new value
for the EPT pointer (EPTP), thereby establishing a different EPT paging-structure hierarchy (see Section 28.2 for
details of the operation of EPT). Software is limited to selecting from a list of potential EPTP values configured in
advance by software in VMX root operation.
Specifically, the value of ECX is used to select an entry from the EPTP list, the 4-KByte structure referenced by the
EPTP-list address (see Section 24.6.14; because this structure contains 512 8-Byte entries, VMFUNC causes a
VM exit if ECX ≥ 512). If the selected entry is a valid EPTP value (it would not cause VM entry to fail; see Section
26.2.1.1), it is stored in the EPTP field of the current VMCS and is used for subsequent accesses using guest-physical addresses. The following pseudocode provides details:
IF ECX ≥ 512
THEN VM exit;
ELSE
tent_EPTP ← 8 bytes from EPTP-list address + 8 * ECX;
IF tent_EPTP is not a valid EPTP value (would cause VM entry to fail if in EPTP)
THEN VMexit;
ELSE
write tent_EPTP to the EPTP field in the current VMCS;
use tent_EPTP as the new EPTP value for address translation;
IF processor supports the 1-setting of the “EPT-violation #VE” VM-execution control
THEN
write ECX[15:0] to EPTP-index field in current VMCS;
use ECX[15:0] as EPTP index for subsequent EPT-violation virtualization exceptions (see Section 25.5.6.2);
FI;
FI;
FI;
Execution of the EPTP-switching VM function does not modify the state of any registers; no flags are modified.
As noted in Section 25.5.5.2, an execution of the EPTP-switching VM function that causes a VM exit (as specified
above), uses the basic exit reason 59, indicating “VMFUNC”. The length of the VMFUNC instruction is saved into the
VM-exit instruction-length field. No additional VM-exit information is provided.
An execution of VMFUNC loads EPTP from the EPTP list (and thus does not cause a fault or VM exit) is called an
EPTP-switching VMFUNC. After an EPTP-switching VMFUNC, control passes to the next instruction. The logical
processor starts creating and using guest-physical and combined mappings associated with the new value of bits
51:12 of EPTP; the combined mappings created and used are associated with the current VPID and PCID (these are
not changed by VMFUNC).1 If the “enable VPID” VM-execution control is 0, an EPTP-switching VMFUNC invalidates
combined mappings associated with VPID 0000H (for all PCIDs and for all EP4TA values, where EP4TA is the value
of bits 51:12 of EPTP).
Because an EPTP-switching VMFUNC may change the translation of guest-physical addresses, it may affect use of
the guest-physical address in CR3. The EPTP-switching VMFUNC cannot itself cause a VM exit due to an EPT violation or an EPT misconfiguration due to the translation of that guest-physical address through the new EPT paging
structures. The following items provide details that apply if CR0.PG = 1:

1. If the “enable VPID” VM-execution control is 0, the current VPID is 0000H; if CR4.PCIDE = 0, the current PCID is 000H.
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•

If 32-bit paging or 4-level paging1 is in use (either CR4.PAE = 0 or IA32_EFER.LMA = 1), the next memory
access with a linear address uses the translation of the guest-physical address in CR3 through the new EPT
paging structures. As a result, this access may cause a VM exit due to an EPT violation or an EPT misconfiguration encountered during that translation.

•

If PAE paging is in use (CR4.PAE = 1 and IA32_EFER.LMA = 0), an EPTP-switching VMFUNC does not load the
four page-directory-pointer-table entries (PDPTEs) from the guest-physical address in CR3. The logical
processor continues to use the four guest-physical addresses already present in the PDPTEs. The guestphysical address in CR3 is not translated through the new EPT paging structures (until some operation that
would load the PDPTEs).
The EPTP-switching VMFUNC cannot itself cause a VM exit due to an EPT violation or an EPT misconfiguration
encountered during the translation of a guest-physical address in any of the PDPTEs. A subsequent memory
access with a linear address uses the translation of the guest-physical address in the appropriate PDPTE
through the new EPT paging structures. As a result, such an access may cause a VM exit due to an EPT
violation or an EPT misconfiguration encountered during that translation.

If an EPTP-switching VMFUNC establishes an EPTP value that enables accessed and dirty flags for EPT (by setting
bit 6), subsequent memory accesses may fail to set those flags as specified if there has been no appropriate execution of INVEPT since the last use of an EPTP value that does not enable accessed and dirty flags for EPT (because
bit 6 is clear) and that is identical to the new value on bits 51:12.
IF the processor supports the 1-setting of the “EPT-violation #VE” VM-execution control, an EPTP-switching
VMFUNC loads the value in ECX[15:0] into to EPTP-index field in current VMCS. Subsequent EPT-violation virtualization exceptions will save this value into the virtualization-exception information area (see Section 25.5.6.2);

25.5.6

Virtualization Exceptions

A virtualization exception is a new processor exception. It uses vector 20 and is abbreviated #VE.
A virtualization exception can occur only in VMX non-root operation. Virtualization exceptions occur only with
certain settings of certain VM-execution controls. Generally, these settings imply that certain conditions that would
normally cause VM exits instead cause virtualization exceptions
In particular, the 1-setting of the “EPT-violation #VE” VM-execution control causes some EPT violations to generate
virtualization exceptions instead of VM exits. Section 25.5.6.1 provides the details of how the processor determines whether an EPT violation causes a virtualization exception or a VM exit.
When the processor encounters a virtualization exception, it saves information about the exception to the virtualization-exception information area; see Section 25.5.6.2.
After saving virtualization-exception information, the processor delivers a virtualization exception as it would any
other exception; see Section 25.5.6.3 for details.

25.5.6.1

Convertible EPT Violations

If the “EPT-violation #VE” VM-execution control is 0 (e.g., on processors that do not support this feature), EPT
violations always cause VM exits. If instead the control is 1, certain EPT violations may be converted to cause virtualization exceptions instead; such EPT violations are convertible.
The values of certain EPT paging-structure entries determine which EPT violations are convertible. Specifically,
bit 63 of certain EPT paging-structure entries may be defined to mean suppress #VE:

•

If bits 2:0 of an EPT paging-structure entry are all 0, the entry is not present.2 If the processor encounters
such an entry while translating a guest-physical address, it causes an EPT violation. The EPT violation is
convertible if and only if bit 63 of the entry is 0.

•

If an EPT paging-structure entry is present, the following cases apply:

1. Earlier versions of this manual used the term “IA-32e paging” to identify 4-level paging.
2. If the “mode-based execute control for EPT” VM-execution control is 1, an EPT paging-structure entry is present if any of bits 2:0 or
bit 10 is 1.
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VMX NON-ROOT OPERATION

— If the value of the EPT paging-structure entry is not supported, the entry is misconfigured. If the
processor encounters such an entry while translating a guest-physical address, it causes an EPT misconfiguration (not an EPT violation). EPT misconfigurations always cause VM exits.
— If the value of the EPT paging-structure entry is supported, the following cases apply:

•

If bit 7 of the entry is 1, or if the entry is an EPT PTE, the entry maps a page. If the processor uses such
an entry to translate a guest-physical address, and if an access to that address causes an EPT violation,
the EPT violation is convertible if and only if bit 63 of the entry is 0.

•

If bit 7 of the entry is 0 and the entry is not an EPT PTE, the entry references another EPT paging
structure. The processor does not use the value of bit 63 of the entry to determine whether any
subsequent EPT violation is convertible.

If an access to a guest-physical address causes an EPT violation, bit 63 of exactly one of the EPT paging-structure
entries used to translate that address is used to determine whether the EPT violation is convertible: either a entry
that is not present (if the guest-physical address does not translate to a physical address) or an entry that maps a
page (if it does).
A convertible EPT violation instead causes a virtualization exception if the following all hold:

•
•
•

CR0.PE = 1;
the logical processor is not in the process of delivering an event through the IDT; and
the 32 bits at offset 4 in the virtualization-exception information area are all 0.

Delivery of virtualization exceptions writes the value FFFFFFFFH to offset 4 in the virtualization-exception information area (see Section 25.5.6.2). Thus, once a virtualization exception occurs, another can occur only if software
clears this field.

25.5.6.2

Virtualization-Exception Information

Virtualization exceptions save data into the virtualization-exception information area (see Section 24.6.18).
Table 25-1 enumerates the data saved and the format of the area.

Table 25-1. Format of the Virtualization-Exception Information Area
Byte Offset

Contents

0

The 32-bit value that would have been saved into the VMCS as an exit reason had a VM exit occurred
instead of the virtualization exception. For EPT violations, this value is 48 (00000030H)

4

FFFFFFFFH

8

The 64-bit value that would have been saved into the VMCS as an exit qualification had a VM exit
occurred instead of the virtualization exception

16

The 64-bit value that would have been saved into the VMCS as a guest-linear address had a VM exit
occurred instead of the virtualization exception

24

The 64-bit value that would have been saved into the VMCS as a guest-physical address had a VM
exit occurred instead of the virtualization exception

32

The current 16-bit value of the EPTP index VM-execution control (see Section 24.6.18 and Section
25.5.5.3)

25.5.6.3

Delivery of Virtualization Exceptions

After saving virtualization-exception information, the processor treats a virtualization exception as it does other
exceptions:

•

If bit 20 (#VE) is 1 in the exception bitmap in the VMCS, a virtualization exception causes a VM exit (see
below). If the bit is 0, the virtualization exception is delivered using gate descriptor 20 in the IDT.

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•

Virtualization exceptions produce no error code. Delivery of a virtualization exception pushes no error code on
the stack.

•

With respect to double faults, virtualization exceptions have the same severity as page faults. If delivery of a
virtualization exception encounters a nested fault that is either contributory or a page fault, a double fault
(#DF) is generated. See Chapter 6, “Interrupt 8—Double Fault Exception (#DF)” in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.
It is not possible for a virtualization exception to be encountered while delivering another exception (see
Section 25.5.6.1).

If a virtualization exception causes a VM exit directly (because bit 20 is 1 in the exception bitmap), information
about the exception is saved normally in the VM-exit interruption information field in the VMCS (see Section
27.2.2). Specifically, the event is reported as a hardware exception with vector 20 and no error code. Bit 12 of the
field (NMI unblocking due to IRET) is set normally.
If a virtualization exception causes a VM exit indirectly (because bit 20 is 0 in the exception bitmap and delivery of
the exception generates an event that causes a VM exit), information about the exception is saved normally in the
IDT-vectoring information field in the VMCS (see Section 27.2.3). Specifically, the event is reported as a hardware
exception with vector 20 and no error code.

25.6

UNRESTRICTED GUESTS

The first processors to support VMX operation require CR0.PE and CR0.PG to be 1 in VMX operation (see Section
23.8). This restriction implies that guest software cannot be run in unpaged protected mode or in real-address
mode. Later processors support a VM-execution control called “unrestricted guest”.1 If this control is 1, CR0.PE and
CR0.PG may be 0 in VMX non-root operation. Such processors allow guest software to run in unpaged protected
mode or in real-address mode. The following items describe the behavior of such software:

•

The MOV CR0 instructions does not cause a general-protection exception simply because it would set either
CR0.PE and CR0.PG to 0. See Section 25.3 for details.

•

A logical processor treats the values of CR0.PE and CR0.PG in VMX non-root operation just as it does outside
VMX operation. Thus, if CR0.PE = 0, the processor operates as it does normally in real-address mode (for
example, it uses the 16-bit interrupt table to deliver interrupts and exceptions). If CR0.PG = 0, the processor
operates as it does normally when paging is disabled.

•

Processor operation is modified by the fact that the processor is in VMX non-root operation and by the settings
of the VM-execution controls just as it is in protected mode or when paging is enabled. Instructions, interrupts,
and exceptions that cause VM exits in protected mode or when paging is enabled also do so in real-address
mode or when paging is disabled. The following examples should be noted:
— If CR0.PG = 0, page faults do not occur and thus cannot cause VM exits.
— If CR0.PE = 0, invalid-TSS exceptions do not occur and thus cannot cause VM exits.
— If CR0.PE = 0, the following instructions cause invalid-opcode exceptions and do not cause VM exits:
INVEPT, INVVPID, LLDT, LTR, SLDT, STR, VMCLEAR, VMLAUNCH, VMPTRLD, VMPTRST, VMREAD,
VMRESUME, VMWRITE, VMXOFF, and VMXON.

•

If CR0.PG = 0, each linear address is passed directly to the EPT mechanism for translation to a physical
address.2 The guest memory type passed on to the EPT mechanism is WB (writeback).

1. “Unrestricted guest” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VMX non-root operation functions as if the “unrestricted guest” VM-execution control were 0. See Section 24.6.2.
2. As noted in Section 26.2.1.1, the “enable EPT” VM-execution control must be 1 if the “unrestricted guest” VM-execution control is 1.
Vol. 3C 25-17

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CHAPTER 26
VM ENTRIES
Software can enter VMX non-root operation using either of the VM-entry instructions VMLAUNCH and VMRESUME.
VMLAUNCH can be used only with a VMCS whose launch state is clear and VMRESUME can be used only with a
VMCS whose the launch state is launched. VMLAUNCH should be used for the first VM entry after VMCLEAR; VMRESUME should be used for subsequent VM entries with the same VMCS.
Each VM entry performs the following steps in the order indicated:
1. Basic checks are performed to ensure that VM entry can commence
(Section 26.1).
2. The control and host-state areas of the VMCS are checked to ensure that they are proper for supporting VMX
non-root operation and that the VMCS is correctly configured to support the next VM exit (Section 26.2).
3. The following may be performed in parallel or in any order (Section 26.3):

•

The guest-state area of the VMCS is checked to ensure that, after the VM entry completes, the state of the
logical processor is consistent with IA-32 and Intel 64 architectures.

•
•

Processor state is loaded from the guest-state area and based on controls in the VMCS.
Address-range monitoring is cleared.

4. MSRs are loaded from the VM-entry MSR-load area (Section 26.4).
5. If VMLAUNCH is being executed, the launch state of the VMCS is set to “launched.”
6. An event may be injected in the guest context (Section 26.5).
Steps 1–4 above perform checks that may cause VM entry to fail. Such failures occur in one of the following three
ways:

•

Some of the checks in Section 26.1 may generate ordinary faults (for example, an invalid-opcode exception).
Such faults are delivered normally.

•

Some of the checks in Section 26.1 and all the checks in Section 26.2 cause control to pass to the instruction
following the VM-entry instruction. The failure is indicated by setting RFLAGS.ZF1 (if there is a current VMCS)
or RFLAGS.CF (if there is no current VMCS). If there is a current VMCS, an error number indicating the cause of
the failure is stored in the VM-instruction error field. See Chapter 30 for the error numbers.

•

The checks in Section 26.3 and Section 26.4 cause processor state to be loaded from the host-state area of the
VMCS (as would be done on a VM exit). Information about the failure is stored in the VM-exit information fields.
See Section 26.7 for details.

EFLAGS.TF = 1 causes a VM-entry instruction to generate a single-step debug exception only if failure of one of the
checks in Section 26.1 and Section 26.2 causes control to pass to the following instruction. A VM-entry does not
generate a single-step debug exception in any of the following cases: (1) the instruction generates a fault; (2)
failure of one of the checks in Section 26.3 or in loading MSRs causes processor state to be loaded from the hoststate area of the VMCS; or (3) the instruction passes all checks in Section 26.1, Section 26.2, and Section 26.3 and
there is no failure in loading MSRs.
Section 34.15 describes the dual-monitor treatment of system-management interrupts (SMIs) and systemmanagement mode (SMM). Under this treatment, code running in SMM returns using VM entries instead of the RSM
instruction. A VM entry returns from SMM if it is executed in SMM and the “entry to SMM” VM-entry control is 0.
VM entries that return from SMM differ from ordinary VM entries in ways that are detailed in Section 34.15.4.

1. This chapter uses the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that support VMX operation also support Intel 64 architecture. For IA-32 processors, this notation refers to the 32-bit forms of those registers (EAX, EIP,
ESP, EFLAGS, etc.). In a few places, notation such as EAX is used to refer specifically to lower 32 bits of the indicated register.
Vol. 3C 26-1

VM ENTRIES

26.1

BASIC VM-ENTRY CHECKS

Before a VM entry commences, the current state of the logical processor is checked in the following order:
1. If the logical processor is in virtual-8086 mode or compatibility mode, an invalid-opcode exception is
generated.
2. If the current privilege level (CPL) is not zero, a general-protection exception is generated.
3. If there is no current VMCS, RFLAGS.CF is set to 1 and control passes to the next instruction.
4. If there is a current VMCS but the current VMCS is a shadow VMCS (see Section 24.10), RFLAGS.CF is set to 1
and control passes to the next instruction.
5. If there is a current VMCS that is not a shadow VMCS, the following conditions are evaluated in order; any of
these cause VM entry to fail:
a. if there is MOV-SS blocking (see Table 24-3)
b. if the VM entry is invoked by VMLAUNCH and the VMCS launch state is not clear
c.

if the VM entry is invoked by VMRESUME and the VMCS launch state is not launched

If any of these checks fail, RFLAGS.ZF is set to 1 and control passes to the next instruction. An error number
indicating the cause of the failure is stored in the VM-instruction error field. See Chapter 30 for the error
numbers.

26.2

CHECKS ON VMX CONTROLS AND HOST-STATE AREA

If the checks in Section 26.1 do not cause VM entry to fail, the control and host-state areas of the VMCS are
checked to ensure that they are proper for supporting VMX non-root operation, that the VMCS is correctly configured to support the next VM exit, and that, after the next VM exit, the processor’s state is consistent with the Intel
64 and IA-32 architectures.
VM entry fails if any of these checks fail. When such failures occur, control is passed to the next instruction,
RFLAGS.ZF is set to 1 to indicate the failure, and the VM-instruction error field is loaded with an error number that
indicates whether the failure was due to the controls or the host-state area (see Chapter 30).
These checks may be performed in any order. Thus, an indication by error number of one cause (for example, host
state) does not imply that there are not also other errors. Different processors may thus give different error
numbers for the same VMCS. Some checks prevent establishment of settings (or combinations of settings) that are
currently reserved. Future processors may allow such settings (or combinations) and may not perform the corresponding checks. The correctness of software should not rely on VM-entry failures resulting from the checks documented in this section.
The checks on the controls and the host-state area are presented in Section 26.2.1 through Section 26.2.4. These
sections reference VMCS fields that correspond to processor state. Unless otherwise stated, these references are to
fields in the host-state area.

26.2.1

Checks on VMX Controls

This section identifies VM-entry checks on the VMX control fields.

26.2.1.1

VM-Execution Control Fields

VM entries perform the following checks on the VM-execution control fields:1

•

Reserved bits in the pin-based VM-execution controls must be set properly. Software may consult the VMX
capability MSRs to determine the proper settings (see Appendix A.3.1).

1. If the “activate secondary controls” primary processor-based VM-execution control is 0, VM entry operates as if each secondary processor-based VM-execution control were 0.
26-2 Vol. 3C

VM ENTRIES

•

Reserved bits in the primary processor-based VM-execution controls must be set properly. Software may
consult the VMX capability MSRs to determine the proper settings (see Appendix A.3.2).

•

If the “activate secondary controls” primary processor-based VM-execution control is 1, reserved bits in the
secondary processor-based VM-execution controls must be cleared. Software may consult the VMX capability
MSRs to determine which bits are reserved (see Appendix A.3.3).
If the “activate secondary controls” primary processor-based VM-execution control is 0 (or if the processor
does not support the 1-setting of that control), no checks are performed on the secondary processor-based
VM-execution controls. The logical processor operates as if all the secondary processor-based VM-execution
controls were 0.

•

The CR3-target count must not be greater than 4. Future processors may support a different number of CR3target values. Software should read the VMX capability MSR IA32_VMX_MISC to determine the number of
values supported (see Appendix A.6).

•

If the “use I/O bitmaps” VM-execution control is 1, bits 11:0 of each I/O-bitmap address must be 0. Neither
address should set any bits beyond the processor’s physical-address width.1,2

•

If the “use MSR bitmaps” VM-execution control is 1, bits 11:0 of the MSR-bitmap address must be 0. The
address should not set any bits beyond the processor’s physical-address width.3

•

If the “use TPR shadow” VM-execution control is 1, the virtual-APIC address must satisfy the following checks:
— Bits 11:0 of the address must be 0.
— The address should not set any bits beyond the processor’s physical-address width.4
If all of the above checks are satisfied and the “use TPR shadow” VM-execution control is 1, bytes 3:1 of VTPR
(see Section 29.1.1) may be cleared (behavior may be implementation-specific).
The clearing of these bytes may occur even if the VM entry fails. This is true either if the failure causes control
to pass to the instruction following the VM-entry instruction or if it causes processor state to be loaded from
the host-state area of the VMCS.

•

If the “use TPR shadow” VM-execution control is 1 and the “virtual-interrupt delivery” VM-execution control is
0, bits 31:4 of the TPR threshold VM-execution control field must be 0.5

•

The following check is performed if the “use TPR shadow” VM-execution control is 1 and the “virtualize APIC
accesses” and “virtual-interrupt delivery” VM-execution controls are both 0: the value of bits 3:0 of the TPR
threshold VM-execution control field should not be greater than the value of bits 7:4 of VTPR (see Section
29.1.1).

•
•
•

If the “NMI exiting” VM-execution control is 0, the “virtual NMIs” VM-execution control must be 0.
If the “virtual NMIs” VM-execution control is 0, the “NMI-window exiting” VM-execution control must be 0.
If the “virtualize APIC-accesses” VM-execution control is 1, the APIC-access address must satisfy the following
checks:
— Bits 11:0 of the address must be 0.
— The address should not set any bits beyond the processor’s physical-address width.6

•

If the “use TPR shadow” VM-execution control is 0, the following VM-execution controls must also be 0:
“virtualize x2APIC mode”, “APIC-register virtualization”, and “virtual-interrupt delivery”.7

1. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
2. If IA32_VMX_BASIC[48] is read as 1, these addresses must not set any bits in the range 63:32; see Appendix A.1.
3. If IA32_VMX_BASIC[48] is read as 1, this address must not set any bits in the range 63:32; see Appendix A.1.
4. If IA32_VMX_BASIC[48] is read as 1, this address must not set any bits in the range 63:32; see Appendix A.1.
5. “Virtual-interrupt delivery” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls is 0, VM entry functions as if the “virtual-interrupt delivery” VM-execution control were 0. See Section 24.6.2.
6. If IA32_VMX_BASIC[48] is read as 1, this address must not set any bits in the range 63:32; see Appendix A.1.
7. “Virtualize x2APIC mode” and “APIC-register virtualization” are secondary processor-based VM-execution controls. If bit 31 of the
primary processor-based VM-execution controls is 0, VM entry functions as if these controls were 0. See Section 24.6.2.
Vol. 3C 26-3

VM ENTRIES

•

If the “virtualize x2APIC mode” VM-execution control is 1, the “virtualize APIC accesses” VM-execution control
must be 0.

•

If the “virtual-interrupt delivery” VM-execution control is 1, the “external-interrupt exiting” VM-execution
control must be 1.

•

If the “process posted interrupts” VM-execution control is 1, the following must be true:1
— The “virtual-interrupt delivery” VM-execution control is 1.
— The “acknowledge interrupt on exit” VM-exit control is 1.
— The posted-interrupt notification vector has a value in the range 0–255 (bits 15:8 are all 0).
— Bits 5:0 of the posted-interrupt descriptor address are all 0.
— The posted-interrupt descriptor address does not set any bits beyond the processor's physical-address
width.2

•

If the “enable VPID” VM-execution control is 1, the value of the VPID VM-execution control field must not be
0000H.3

•

If the “enable EPT” VM-execution control is 1, the EPTP VM-execution control field (see Table 24-8 in Section
24.6.11) must satisfy the following checks:4
— The EPT memory type (bits 2:0) must be a value supported by the processor as indicated in the
IA32_VMX_EPT_VPID_CAP MSR (see Appendix A.10).
— Bits 5:3 (1 less than the EPT page-walk length) must be 3, indicating an EPT page-walk length of 4; see
Section 28.2.2.
— Bit 6 (enable bit for accessed and dirty flags for EPT) must be 0 if bit 21 of the IA32_VMX_EPT_VPID_CAP
MSR (see Appendix A.10) is read as 0, indicating that the processor does not support accessed and dirty
flags for EPT.
— Reserved bits 11:7 and 63:N (where N is the processor’s physical-address width) must all be 0.

•

If the “enable PML” VM-execution control is 1, the “enable EPT” VM-execution control must also be 1.5 In
addition, the PML address must satisfy the following checks:
— Bits 11:0 of the address must be 0.
— The address should not set any bits beyond the processor’s physical-address width.6

•

If either the “unrestricted guest” VM-execution control or the “mode-based execute control for EPT” VMexecution control is 1, the “enable EPT” VM-execution control must also be 1.7

•

If the “enable VM functions” processor-based VM-execution control is 1, reserved bits in the VM-function
controls must be clear.8 Software may consult the VMX capability MSRs to determine which bits are reserved
(see Appendix A.11). In addition, the following check is performed based on the setting of bits in the VMfunction controls (see Section 24.6.14):

1. “Process posted interrupts” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls is 0, VM entry functions as if the “process posted interrupts” VM-execution control were 0. See Section 24.6.2.
2. If IA32_VMX_BASIC[48] is read as 1, this address must not set any bits in the range 63:32; see Appendix A.1.
3. “Enable VPID” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls
is 0, VM entry functions as if the “enable VPID” VM-execution control were 0. See Section 24.6.2.
4. “Enable EPT” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls
is 0, VM entry functions as if the “enable EPT” VM-execution control were 0. See Section 24.6.2.
5. “Enable PML” and “enable EPT” are both secondary processor-based VM-execution controls. If bit 31 of the primary processor-based
VM-execution controls is 0, VM entry functions as if both these controls were 0. See Section 24.6.2.
6. If IA32_VMX_BASIC[48] is read as 1, this address must not set any bits in the range 63:32; see Appendix A.1.
7. All these controls are secondary processor-based VM-execution controls. If bit 31 of the primary processor-based VM-execution controls is 0, VM entry functions as if all these controls were 0. See Section 24.6.2.
8. “Enable VM functions” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VM entry functions as if the “enable VM functions” VM-execution control were 0. See Section 24.6.2.
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VM ENTRIES

— If “EPTP switching” VM-function control is 1, the “enable EPT” VM-execution control must also be 1. In
addition, the EPTP-list address must satisfy the following checks:

•
•

Bits 11:0 of the address must be 0.
The address must not set any bits beyond the processor’s physical-address width.

If the “enable VM functions” processor-based VM-execution control is 0, no checks are performed on the VMfunction controls.

•

If the “VMCS shadowing” VM-execution control is 1, the VMREAD-bitmap and VMWRITE-bitmap addresses
must each satisfy the following checks:1
— Bits 11:0 of the address must be 0.
— The address must not set any bits beyond the processor’s physical-address width.

•

If the “EPT-violation #VE” VM-execution control is 1, the virtualization-exception information address must
satisfy the following checks:2
— Bits 11:0 of the address must be 0.
— The address must not set any bits beyond the processor’s physical-address width.

26.2.1.2

VM-Exit Control Fields

VM entries perform the following checks on the VM-exit control fields.

•

Reserved bits in the VM-exit controls must be set properly. Software may consult the VMX capability MSRs to
determine the proper settings (see Appendix A.4).

•

If the “activate VMX-preemption timer” VM-execution control is 0, the “save VMX-preemption timer value” VMexit control must also be 0.

•

The following checks are performed for the VM-exit MSR-store address if the VM-exit MSR-store count field is
non-zero:
— The lower 4 bits of the VM-exit MSR-store address must be 0. The address should not set any bits beyond
the processor’s physical-address width.3
— The address of the last byte in the VM-exit MSR-store area should not set any bits beyond the processor’s
physical-address width. The address of this last byte is VM-exit MSR-store address + (MSR count * 16) –
1. (The arithmetic used for the computation uses more bits than the processor’s physical-address width.)
If IA32_VMX_BASIC[48] is read as 1, neither address should set any bits in the range 63:32; see Appendix
A.1.

•

The following checks are performed for the VM-exit MSR-load address if the VM-exit MSR-load count field is
non-zero:
— The lower 4 bits of the VM-exit MSR-load address must be 0. The address should not set any bits beyond
the processor’s physical-address width.
— The address of the last byte in the VM-exit MSR-load area should not set any bits beyond the processor’s
physical-address width. The address of this last byte is VM-exit MSR-load address + (MSR count * 16) – 1.
(The arithmetic used for the computation uses more bits than the processor’s physical-address width.)
If IA32_VMX_BASIC[48] is read as 1, neither address should set any bits in the range 63:32; see Appendix
A.1.

1. “VMCS shadowing” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VM entry functions as if the “VMCS shadowing” VM-execution control were 0. See Section 24.6.2.
2. “EPT-violation #VE” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VM entry functions as if the “EPT-violation #VE” VM-execution control were 0. See Section 24.6.2.
3. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
Vol. 3C 26-5

VM ENTRIES

26.2.1.3

VM-Entry Control Fields

VM entries perform the following checks on the VM-entry control fields.

•

Reserved bits in the VM-entry controls must be set properly. Software may consult the VMX capability MSRs to
determine the proper settings (see Appendix A.5).

•

Fields relevant to VM-entry event injection must be set properly. These fields are the VM-entry interruptioninformation field (see Table 24-13 in Section 24.8.3), the VM-entry exception error code, and the VM-entry
instruction length. If the valid bit (bit 31) in the VM-entry interruption-information field is 1, the following must
hold:
— The field’s interruption type (bits 10:8) is not set to a reserved value. Value 1 is reserved on all logical
processors; value 7 (other event) is reserved on logical processors that do not support the 1-setting of the
“monitor trap flag” VM-execution control.
— The field’s vector (bits 7:0) is consistent with the interruption type:

•
•
•

If the interruption type is non-maskable interrupt (NMI), the vector is 2.
If the interruption type is hardware exception, the vector is at most 31.
If the interruption type is other event, the vector is 0 (pending MTF VM exit).

— The field's deliver-error-code bit (bit 11) is 1 if and only if (1) either (a) the "unrestricted guest" VMexecution control is 0; or (b) bit 0 (corresponding to CR0.PE) is set in the CR0 field in the guest-state area;
(2) the interruption type is hardware exception; and (3) the vector indicates an exception that would
normally deliver an error code (8 = #DF; 10 = TS; 11 = #NP; 12 = #SS; 13 = #GP; 14 = #PF; or 17 =
#AC).
— Reserved bits in the field (30:12) are 0.
— If the deliver-error-code bit (bit 11) is 1, bits 31:15 of the VM-entry exception error-code field are 0.
— If the interruption type is software interrupt, software exception, or privileged software exception, the
VM-entry instruction-length field is in the range 0–15. A VM-entry instruction length of 0 is allowed only if
IA32_VMX_MISC[30] is read as 1; see Appendix A.6.

•

The following checks are performed for the VM-entry MSR-load address if the VM-entry MSR-load count field is
non-zero:
— The lower 4 bits of the VM-entry MSR-load address must be 0. The address should not set any bits beyond
the processor’s physical-address width.1
— The address of the last byte in the VM-entry MSR-load area should not set any bits beyond the processor’s
physical-address width. The address of this last byte is VM-entry MSR-load address + (MSR count * 16) –
1. (The arithmetic used for the computation uses more bits than the processor’s physical-address width.)
If IA32_VMX_BASIC[48] is read as 1, neither address should set any bits in the range 63:32; see Appendix
A.1.

•

If the processor is not in SMM, the “entry to SMM” and “deactivate dual-monitor treatment” VM-entry controls
must be 0.

•

The “entry to SMM” and “deactivate dual-monitor treatment” VM-entry controls cannot both be 1.

26.2.2

Checks on Host Control Registers and MSRs

The following checks are performed on fields in the host-state area that correspond to control registers and MSRs:

•
•

The CR0 field must not set any bit to a value not supported in VMX operation (see Section 23.8).2
The CR4 field must not set any bit to a value not supported in VMX operation (see Section 23.8).

1. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
2. The bits corresponding to CR0.NW (bit 29) and CR0.CD (bit 30) are never checked because the values of these bits are not changed
by VM exit; see Section 27.5.1.
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VM ENTRIES

•

On processors that support Intel 64 architecture, the CR3 field must be such that bits 63:52 and bits in the
range 51:32 beyond the processor’s physical-address width must be 0.1,2

•

On processors that support Intel 64 architecture, the IA32_SYSENTER_ESP field and the IA32_SYSENTER_EIP
field must each contain a canonical address.

•

If the “load IA32_PERF_GLOBAL_CTRL” VM-exit control is 1, bits reserved in the IA32_PERF_GLOBAL_CTRL
MSR must be 0 in the field for that register (see Figure 18-3).

•

If the “load IA32_PAT” VM-exit control is 1, the value of the field for the IA32_PAT MSR must be one that could
be written by WRMSR without fault at CPL 0. Specifically, each of the 8 bytes in the field must have one of the
values 0 (UC), 1 (WC), 4 (WT), 5 (WP), 6 (WB), or 7 (UC-).

•

If the “load IA32_EFER” VM-exit control is 1, bits reserved in the IA32_EFER MSR must be 0 in the field for that
register. In addition, the values of the LMA and LME bits in the field must each be that of the “host addressspace size” VM-exit control.

26.2.3

Checks on Host Segment and Descriptor-Table Registers

The following checks are performed on fields in the host-state area that correspond to segment and descriptortable registers:

•

In the selector field for each of CS, SS, DS, ES, FS, GS and TR, the RPL (bits 1:0) and the TI flag (bit 2) must
be 0.

•
•
•

The selector fields for CS and TR cannot be 0000H.
The selector field for SS cannot be 0000H if the “host address-space size” VM-exit control is 0.
On processors that support Intel 64 architecture, the base-address fields for FS, GS, GDTR, IDTR, and TR must
contain canonical addresses.

26.2.4

Checks Related to Address-Space Size

On processors that support Intel 64 architecture, the following checks related to address-space size are performed
on VMX controls and fields in the host-state area:

•

If the logical processor is outside IA-32e mode (if IA32_EFER.LMA = 0) at the time of VM entry, the following
must hold:
— The “IA-32e mode guest” VM-entry control is 0.
— The “host address-space size” VM-exit control is 0.

•

If the logical processor is in IA-32e mode (if IA32_EFER.LMA = 1) at the time of VM entry, the “host addressspace size” VM-exit control must be 1.

•

If the “host address-space size” VM-exit control is 0, the following must hold:
— The “IA-32e mode guest” VM-entry control is 0.
— Bit 17 of the CR4 field (corresponding to CR4.PCIDE) is 0.
— Bits 63:32 in the RIP field is 0.

•

If the “host address-space size” VM-exit control is 1, the following must hold:
— Bit 5 of the CR4 field (corresponding to CR4.PAE) is 1.
— The RIP field contains a canonical address.

On processors that do not support Intel 64 architecture, checks are performed to ensure that the “IA-32e mode
guest” VM-entry control and the “host address-space size” VM-exit control are both 0.
1. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
2. Bit 63 of the CR3 field in the host-state area must be 0. This is true even though, If CR4.PCIDE = 1, bit 63 of the source operand to
MOV to CR3 is used to determine whether cached translation information is invalidated.
Vol. 3C 26-7

VM ENTRIES

26.3 CHECKING AND LOADING GUEST STATE
If all checks on the VMX controls and the host-state area pass (see Section 26.2), the following operations take
place concurrently: (1) the guest-state area of the VMCS is checked to ensure that, after the VM entry completes,
the state of the logical processor is consistent with IA-32 and Intel 64 architectures; (2) processor state is loaded
from the guest-state area or as specified by the VM-entry control fields; and (3) address-range monitoring is
cleared.
Because the checking and the loading occur concurrently, a failure may be discovered only after some state has
been loaded. For this reason, the logical processor responds to such failures by loading state from the host-state
area, as it would for a VM exit. See Section 26.7.

26.3.1

Checks on the Guest State Area

This section describes checks performed on fields in the guest-state area. These checks may be performed in any
order. Some checks prevent establishment of settings (or combinations of settings) that are currently reserved.
Future processors may allow such settings (or combinations) and may not perform the corresponding checks. The
correctness of software should not rely on VM-entry failures resulting from the checks documented in this section.
The following subsections reference fields that correspond to processor state. Unless otherwise stated, these references are to fields in the guest-state area.

26.3.1.1

Checks on Guest Control Registers, Debug Registers, and MSRs

The following checks are performed on fields in the guest-state area corresponding to control registers, debug
registers, and MSRs:

•

The CR0 field must not set any bit to a value not supported in VMX operation (see Section 23.8). The following
are exceptions:
— Bit 0 (corresponding to CR0.PE) and bit 31 (PG) are not checked if the “unrestricted guest” VM-execution
control is 1.1
— Bit 29 (corresponding to CR0.NW) and bit 30 (CD) are never checked because the values of these bits are
not changed by VM entry; see Section 26.3.2.1.

•
•
•

If bit 31 in the CR0 field (corresponding to PG) is 1, bit 0 in that field (PE) must also be 1.2

•

The following checks are performed on processors that support Intel 64 architecture:

The CR4 field must not set any bit to a value not supported in VMX operation (see Section 23.8).
If the “load debug controls” VM-entry control is 1, bits reserved in the IA32_DEBUGCTL MSR must be 0 in the
field for that register. The first processors to support the virtual-machine extensions supported only the 1setting of this control and thus performed this check unconditionally.
— If the “IA-32e mode guest” VM-entry control is 1, bit 31 in the CR0 field (corresponding to CR0.PG) and
bit 5 in the CR4 field (corresponding to CR4.PAE) must each be 1.3
— If the “IA-32e mode guest” VM-entry control is 0, bit 17 in the CR4 field (corresponding to CR4.PCIDE)
must be 0.
— The CR3 field must be such that bits 63:52 and bits in the range 51:32 beyond the processor’s physicaladdress width are 0.4,5

1. “Unrestricted guest” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VM entry functions as if the “unrestricted guest” VM-execution control were 0. See Section 24.6.2.
2. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PE must be 1 in VMX operation, bit 0 in the CR0 field must be 1
unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
3. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PG must be 1 in VMX operation, bit 31 in the CR0 field must be 1
unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
4. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
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VM ENTRIES

— If the “load debug controls” VM-entry control is 1, bits 63:32 in the DR7 field must be 0. The first
processors to support the virtual-machine extensions supported only the 1-setting of this control and thus
performed this check unconditionally (if they supported Intel 64 architecture).
— The IA32_SYSENTER_ESP field and the IA32_SYSENTER_EIP field must each contain a canonical address.

•

If the “load IA32_PERF_GLOBAL_CTRL” VM-entry control is 1, bits reserved in the IA32_PERF_GLOBAL_CTRL
MSR must be 0 in the field for that register (see Figure 18-3).

•

If the “load IA32_PAT” VM-entry control is 1, the value of the field for the IA32_PAT MSR must be one that could
be written by WRMSR without fault at CPL 0. Specifically, each of the 8 bytes in the field must have one of the
values 0 (UC), 1 (WC), 4 (WT), 5 (WP), 6 (WB), or 7 (UC-).

•

If the “load IA32_EFER” VM-entry control is 1, the following checks are performed on the field for the
IA32_EFER MSR:
— Bits reserved in the IA32_EFER MSR must be 0.
— Bit 10 (corresponding to IA32_EFER.LMA) must equal the value of the “IA-32e mode guest” VM-entry
control. It must also be identical to bit 8 (LME) if bit 31 in the CR0 field (corresponding to CR0.PG) is 1.1

•

If the “load IA32_BNDCFGS” VM-entry control is 1, the following checks are performed on the field for the
IA32_BNDCFGS MSR:
— Bits reserved in the IA32_BNDCFGS MSR must be 0.
— The linear address in bits 63:12 must be canonical.

26.3.1.2

Checks on Guest Segment Registers

This section specifies the checks on the fields for CS, SS, DS, ES, FS, GS, TR, and LDTR. The following terms are
used in defining these checks:

•
•

The guest will be virtual-8086 if the VM flag (bit 17) is 1 in the RFLAGS field in the guest-state area.

•

Any one of these registers is said to be usable if the unusable bit (bit 16) is 0 in the access-rights field for that
register.

The guest will be IA-32e mode if the “IA-32e mode guest” VM-entry control is 1. (This is possible only on
processors that support Intel 64 architecture.)

The following are the checks on these fields:

•

Selector fields.
— TR. The TI flag (bit 2) must be 0.
— LDTR. If LDTR is usable, the TI flag (bit 2) must be 0.
— SS. If the guest will not be virtual-8086 and the “unrestricted guest” VM-execution control is 0, the RPL
(bits 1:0) must equal the RPL of the selector field for CS.2

•

Base-address fields.
— CS, SS, DS, ES, FS, GS. If the guest will be virtual-8086, the address must be the selector field shifted left
4 bits (multiplied by 16).
— The following checks are performed on processors that support Intel 64 architecture:

•
•
•

TR, FS, GS. The address must be canonical.
LDTR. If LDTR is usable, the address must be canonical.
CS. Bits 63:32 of the address must be zero.

5. Bit 63 of the CR3 field in the guest-state area must be 0. This is true even though, If CR4.PCIDE = 1, bit 63 of the source operand to
MOV to CR3 is used to determine whether cached translation information is invalidated.
1. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PG must be 1 in VMX operation, bit 31 in the CR0 field must be 1
unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
2. “Unrestricted guest” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VM entry functions as if the “unrestricted guest” VM-execution control were 0. See Section 24.6.2.
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VM ENTRIES

•
•

•

SS, DS, ES. If the register is usable, bits 63:32 of the address must be zero.

Limit fields for CS, SS, DS, ES, FS, GS. If the guest will be virtual-8086, the field must be 0000FFFFH.
Access-rights fields.
— CS, SS, DS, ES, FS, GS.

•

If the guest will be virtual-8086, the field must be 000000F3H. This implies the following:
— Bits 3:0 (Type) must be 3, indicating an expand-up read/write accessed data segment.
— Bit 4 (S) must be 1.
— Bits 6:5 (DPL) must be 3.
— Bit 7 (P) must be 1.
— Bits 11:8 (reserved), bit 12 (software available), bit 13 (reserved/L), bit 14 (D/B), bit 15 (G),
bit 16 (unusable), and bits 31:17 (reserved) must all be 0.

•

If the guest will not be virtual-8086, the different sub-fields are considered separately:
— Bits 3:0 (Type).

•

CS. The values allowed depend on the setting of the “unrestricted guest” VM-execution
control:
— If the control is 0, the Type must be 9, 11, 13, or 15 (accessed code segment).
— If the control is 1, the Type must be either 3 (read/write accessed expand-up data
segment) or one of 9, 11, 13, and 15 (accessed code segment).

•
•

SS. If SS is usable, the Type must be 3 or 7 (read/write, accessed data segment).
DS, ES, FS, GS. The following checks apply if the register is usable:
— Bit 0 of the Type must be 1 (accessed).
— If bit 3 of the Type is 1 (code segment), then bit 1 of the Type must be 1 (readable).

— Bit 4 (S). If the register is CS or if the register is usable, S must be 1.
— Bits 6:5 (DPL).

•

CS.
— If the Type is 3 (read/write accessed expand-up data segment), the DPL must be 0. The
Type can be 3 only if the “unrestricted guest” VM-execution control is 1.
— If the Type is 9 or 11 (non-conforming code segment), the DPL must equal the DPL in the
access-rights field for SS.
— If the Type is 13 or 15 (conforming code segment), the DPL cannot be greater than the
DPL in the access-rights field for SS.

•

SS.
— If the “unrestricted guest” VM-execution control is 0, the DPL must equal the RPL from the
selector field.
— The DPL must be 0 either if the Type in the access-rights field for CS is 3 (read/write
accessed expand-up data segment) or if bit 0 in the CR0 field (corresponding to CR0.PE) is
0.1

•

DS, ES, FS, GS. The DPL cannot be less than the RPL in the selector field if (1) the
“unrestricted guest” VM-execution control is 0; (2) the register is usable; and (3) the Type in
the access-rights field is in the range 0 – 11 (data segment or non-conforming code segment).

— Bit 7 (P). If the register is CS or if the register is usable, P must be 1.
1. The following apply if either the “unrestricted guest” VM-execution control or bit 31 of the primary processor-based VM-execution
controls is 0: (1) bit 0 in the CR0 field must be 1 if the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PE must be 1 in
VMX operation; and (2) the Type in the access-rights field for CS cannot be 3.
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— Bits 11:8 (reserved). If the register is CS or if the register is usable, these bits must all be 0.
— Bit 14 (D/B). For CS, D/B must be 0 if the guest will be IA-32e mode and the L bit (bit 13) in the
access-rights field is 1.
— Bit 15 (G). The following checks apply if the register is CS or if the register is usable:

•
•

If any bit in the limit field in the range 11:0 is 0, G must be 0.
If any bit in the limit field in the range 31:20 is 1, G must be 1.

— Bits 31:17 (reserved). If the register is CS or if the register is usable, these bits must all be 0.
— TR. The different sub-fields are considered separately:

•

Bits 3:0 (Type).
— If the guest will not be IA-32e mode, the Type must be 3 (16-bit busy TSS) or 11 (32-bit busy
TSS).
— If the guest will be IA-32e mode, the Type must be 11 (64-bit busy TSS).

•
•
•
•

Bit 4 (S). S must be 0.
Bit 7 (P). P must be 1.
Bits 11:8 (reserved). These bits must all be 0.
Bit 15 (G).
— If any bit in the limit field in the range 11:0 is 0, G must be 0.
— If any bit in the limit field in the range 31:20 is 1, G must be 1.

•
•

Bit 16 (Unusable). The unusable bit must be 0.
Bits 31:17 (reserved). These bits must all be 0.

— LDTR. The following checks on the different sub-fields apply only if LDTR is usable:

•
•
•
•
•

Bits 3:0 (Type). The Type must be 2 (LDT).
Bit 4 (S). S must be 0.
Bit 7 (P). P must be 1.
Bits 11:8 (reserved). These bits must all be 0.
Bit 15 (G).
— If any bit in the limit field in the range 11:0 is 0, G must be 0.
— If any bit in the limit field in the range 31:20 is 1, G must be 1.

•
26.3.1.3

Bits 31:17 (reserved). These bits must all be 0.

Checks on Guest Descriptor-Table Registers

The following checks are performed on the fields for GDTR and IDTR:

•
•

On processors that support Intel 64 architecture, the base-address fields must contain canonical addresses.
Bits 31:16 of each limit field must be 0.

26.3.1.4

Checks on Guest RIP and RFLAGS

The following checks are performed on fields in the guest-state area corresponding to RIP and RFLAGS:

•

RIP. The following checks are performed on processors that support Intel 64 architecture:
— Bits 63:32 must be 0 if the “IA-32e mode guest” VM-entry control is 0 or if the L bit (bit 13) in the accessrights field for CS is 0.
— If the processor supports N < 64 linear-address bits, bits 63:N must be identical if the “IA-32e mode guest”
VM-entry control is 1 and the L bit in the access-rights field for CS is 1.1 (No check applies if the processor
supports 64 linear-address bits.)
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VM ENTRIES

•

RFLAGS.
— Reserved bits 63:22 (bits 31:22 on processors that do not support Intel 64 architecture), bit 15, bit 5 and
bit 3 must be 0 in the field, and reserved bit 1 must be 1.
— The VM flag (bit 17) must be 0 either if the “IA-32e mode guest” VM-entry control is 1 or if bit 0 in the CR0
field (corresponding to CR0.PE) is 0.1
— The IF flag (RFLAGS[bit 9]) must be 1 if the valid bit (bit 31) in the VM-entry interruption-information field
is 1 and the interruption type (bits 10:8) is external interrupt.

26.3.1.5

Checks on Guest Non-Register State

The following checks are performed on fields in the guest-state area corresponding to non-register state:

•

Activity state.
— The activity-state field must contain a value in the range 0 – 3, indicating an activity state supported by the
implementation (see Section 24.4.2). Future processors may include support for other activity states.
Software should read the VMX capability MSR IA32_VMX_MISC (see Appendix A.6) to determine what
activity states are supported.
— The activity-state field must not indicate the HLT state if the DPL (bits 6:5) in the access-rights field for SS
is not 0.2
— The activity-state field must indicate the active state if the interruptibility-state field indicates blocking by
either MOV-SS or by STI (if either bit 0 or bit 1 in that field is 1).
— If the valid bit (bit 31) in the VM-entry interruption-information field is 1, the interruption to be delivered
(as defined by interruption type and vector) must not be one that would normally be blocked while a logical
processor is in the activity state corresponding to the contents of the activity-state field. The following
items enumerate the interruptions (as specified in the VM-entry interruption-information field) whose
injection is allowed for the different activity states:

•
•

Active. Any interruption is allowed.
HLT. The only events allowed are the following:
— Those with interruption type external interrupt or non-maskable interrupt (NMI).
— Those with interruption type hardware exception and vector 1 (debug exception) or vector 18
(machine-check exception).
— Those with interruption type other event and vector 0 (pending MTF VM exit).
See Table 24-13 in Section 24.8.3 for details regarding the format of the VM-entry interruptioninformation field.

•
•

Shutdown. Only NMIs and machine-check exceptions are allowed.
Wait-for-SIPI. No interruptions are allowed.

— The activity-state field must not indicate the wait-for-SIPI state if the “entry to SMM” VM-entry control is 1.

•

Interruptibility state.
— The reserved bits (bits 31:5) must be 0.
— The field cannot indicate blocking by both STI and MOV SS (bits 0 and 1 cannot both be 1).
— Bit 0 (blocking by STI) must be 0 if the IF flag (bit 9) is 0 in the RFLAGS field.

1. Software can determine the number N by executing CPUID with 80000008H in EAX. The number of linear-address bits supported is
returned in bits 15:8 of EAX.
1. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PE must be 1 in VMX operation, bit 0 in the CR0 field must be 1
unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
2. As noted in Section 24.4.1, SS.DPL corresponds to the logical processor’s current privilege level (CPL).
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— Bit 0 (blocking by STI) and bit 1 (blocking by MOV-SS) must both be 0 if the valid bit (bit 31) in the
VM-entry interruption-information field is 1 and the interruption type (bits 10:8) in that field has value 0,
indicating external interrupt.
— Bit 1 (blocking by MOV-SS) must be 0 if the valid bit (bit 31) in the VM-entry interruption-information field
is 1 and the interruption type (bits 10:8) in that field has value 2, indicating non-maskable interrupt (NMI).
— Bit 2 (blocking by SMI) must be 0 if the processor is not in SMM.
— Bit 2 (blocking by SMI) must be 1 if the “entry to SMM” VM-entry control is 1.
— A processor may require bit 0 (blocking by STI) to be 0 if the valid bit (bit 31) in the VM-entry interruptioninformation field is 1 and the interruption type (bits 10:8) in that field has value 2, indicating NMI. Other
processors may not make this requirement.
— Bit 3 (blocking by NMI) must be 0 if the “virtual NMIs” VM-execution control is 1, the valid bit (bit 31) in the
VM-entry interruption-information field is 1, and the interruption type (bits 10:8) in that field has value 2
(indicating NMI).
— If bit 4 (enclave interruption) is 1, bit 1 (blocking by MOV-SS) must be 0 and the processor must support
for SGX by enumerating CPUID.(EAX=07H,ECX=0):EBX.SGX[bit 2] as 1.

NOTE
If the “virtual NMIs” VM-execution control is 0, there is no requirement that bit 3 be 0 if the valid
bit in the VM-entry interruption-information field is 1 and the interruption type in that field has
value 2.

•

Pending debug exceptions.
— Bits 11:4, bit 13, bit 15, and bits 63:17 (bits 31:17 on processors that do not support Intel 64 architecture) must be 0.
— The following checks are performed if any of the following holds: (1) the interruptibility-state field indicates
blocking by STI (bit 0 in that field is 1); (2) the interruptibility-state field indicates blocking by MOV SS
(bit 1 in that field is 1); or (3) the activity-state field indicates HLT:

•

Bit 14 (BS) must be 1 if the TF flag (bit 8) in the RFLAGS field is 1 and the BTF flag (bit 1) in the
IA32_DEBUGCTL field is 0.

•

Bit 14 (BS) must be 0 if the TF flag (bit 8) in the RFLAGS field is 0 or the BTF flag (bit 1) in the
IA32_DEBUGCTL field is 1.

— The following checks are performed if bit 16 (RTM) is 1:

•

•

Bits 11:0, bits 15:13, and bits 63:17 (bits 31:17 on processors that do not support Intel 64 architecture) must be 0; bit 12 must be 1.

•
•

The processor must support for RTM by enumerating CPUID.(EAX=07H,ECX=0):EBX[bit 11] as 1.
The interruptibility-state field must not indicate blocking by MOV SS (bit 1 in that field must be 0).

VMCS link pointer. The following checks apply if the field contains a value other than FFFFFFFF_FFFFFFFFH:
— Bits 11:0 must be 0.
— Bits beyond the processor’s physical-address width must be 0.1,2
— The 4 bytes located in memory referenced by the value of the field (as a physical address) must satisfy the
following:

•

Bits 30:0 must contain the processor’s VMCS revision identifier (see Section 24.2).3

1. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
2. If IA32_VMX_BASIC[48] is read as 1, this field must not set any bits in the range 63:32; see Appendix A.1.
3. Earlier versions of this manual specified that the VMCS revision identifier was a 32-bit field. For all processors produced prior to this
change, bit 31 of the VMCS revision identifier was 0.
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VM ENTRIES

•

Bit 31 must contain the setting of the “VMCS shadowing” VM-execution control.1 This implies that the
referenced VMCS is a shadow VMCS (see Section 24.10) if and only if the “VMCS shadowing” VMexecution control is 1.

— If the processor is not in SMM or the “entry to SMM” VM-entry control is 1, the field must not contain the
current VMCS pointer.
— If the processor is in SMM and the “entry to SMM” VM-entry control is 0, the field must differ from the
executive-VMCS pointer.

26.3.1.6

Checks on Guest Page-Directory-Pointer-Table Entries

If CR0.PG =1, CR4.PAE = 1, and IA32_EFER.LME = 0, the logical processor uses PAE paging (see Section 4.4 in
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A).2 When PAE paging is in use, the
physical address in CR3 references a table of page-directory-pointer-table entries (PDPTEs). A MOV to CR3
when PAE paging is in use checks the validity of the PDPTEs.
A VM entry is to a guest that uses PAE paging if (1) bit 31 (corresponding to CR0.PG) is set in the CR0 field in the
guest-state area; (2) bit 5 (corresponding to CR4.PAE) is set in the CR4 field; and (3) the “IA-32e mode guest”
VM-entry control is 0. Such a VM entry checks the validity of the PDPTEs:

•

If the “enable EPT” VM-execution control is 0, VM entry checks the validity of the PDPTEs referenced by the CR3
field in the guest-state area if either (1) PAE paging was not in use before the VM entry; or (2) the value of CR3
is changing as a result of the VM entry. VM entry may check their validity even if neither (1) nor (2) hold.3

•

If the “enable EPT” VM-execution control is 1, VM entry checks the validity of the PDPTE fields in the guest-state
area (see Section 24.4.2).

A VM entry to a guest that does not use PAE paging does not check the validity of any PDPTEs.
A VM entry that checks the validity of the PDPTEs uses the same checks that are used when CR3 is loaded with
MOV to CR3 when PAE paging is in use.4 If MOV to CR3 would cause a general-protection exception due to the
PDPTEs that would be loaded (e.g., because a reserved bit is set), the VM entry fails.

26.3.2 Loading Guest State
Processor state is updated on VM entries in the following ways:

•
•
•

Some state is loaded from the guest-state area.
Some state is determined by VM-entry controls.
The page-directory pointers are loaded based on the values of certain control registers.

This loading may be performed in any order and in parallel with the checking of VMCS contents (see Section
26.3.1).
The loading of guest state is detailed in Section 26.3.2.1 to Section 26.3.2.4. These sections reference VMCS fields
that correspond to processor state. Unless otherwise stated, these references are to fields in the guest-state area.
In addition to the state loading described in this section, VM entries may load MSRs from the VM-entry MSR-load
area (see Section 26.4). This loading occurs only after the state loading described in this section and the checking
of VMCS contents described in Section 26.3.1.

1. “VMCS shadowing” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VM entry functions as if the “VMCS shadowing” VM-execution control were 0. See Section 24.6.2.
2. On processors that support Intel 64 architecture, the physical-address extension may support more than 36 physical-address bits.
Software can determine the number physical-address bits supported by executing CPUID with 80000008H in EAX. The physicaladdress width is returned in bits 7:0 of EAX.
3. “Enable EPT” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls
is 0, VM entry functions as if the “enable EPT” VM-execution control were 0. See Section 24.6.2.
4. This implies that (1) bits 11:9 in each PDPTE are ignored; and (2) if bit 0 (present) is clear in one of the PDPTEs, bits 63:1 of that
PDPTE are ignored.
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26.3.2.1

Loading Guest Control Registers, Debug Registers, and MSRs

The following items describe how guest control registers, debug registers, and MSRs are loaded on VM entry:

•

CR0 is loaded from the CR0 field with the exception of the following bits, which are never modified on VM entry:
ET (bit 4); reserved bits 15:6, 17, and 28:19; NW (bit 29) and CD (bit 30).1 The values of these bits in the CR0
field are ignored.

•
•

CR3 and CR4 are loaded from the CR3 field and the CR4 field, respectively.
If the “load debug controls” VM-entry control is 1, DR7 is loaded from the DR7 field with the exception that
bit 12 and bits 15:14 are always 0 and bit 10 is always 1. The values of these bits in the DR7 field are ignored.
The first processors to support the virtual-machine extensions supported only the 1-setting of the “load
debug controls” VM-entry control and thus always loaded DR7 from the DR7 field.

•

The following describes how certain MSRs are loaded using fields in the guest-state area:
— If the “load debug controls” VM-entry control is 1, the IA32_DEBUGCTL MSR is loaded from the
IA32_DEBUGCTL field. The first processors to support the virtual-machine extensions supported only the 1setting of this control and thus always loaded the IA32_DEBUGCTL MSR from the IA32_DEBUGCTL field.
— The IA32_SYSENTER_CS MSR is loaded from the IA32_SYSENTER_CS field. Since this field has only 32
bits, bits 63:32 of the MSR are cleared to 0.
— The IA32_SYSENTER_ESP and IA32_SYSENTER_EIP MSRs are loaded from the IA32_SYSENTER_ESP field
and the IA32_SYSENTER_EIP field, respectively. On processors that do not support Intel 64 architecture,
these fields have only 32 bits; bits 63:32 of the MSRs are cleared to 0.
— The following are performed on processors that support Intel 64 architecture:

•

The MSRs FS.base and GS.base are loaded from the base-address fields for FS and GS, respectively
(see Section 26.3.2.2).

•

If the “load IA32_EFER” VM-entry control is 0, bits in the IA32_EFER MSR are modified as follows:
— IA32_EFER.LMA is loaded with the setting of the “IA-32e mode guest” VM-entry control.
— If CR0 is being loaded so that CR0.PG = 1, IA32_EFER.LME is also loaded with the setting of the
“IA-32e mode guest” VM-entry control.2 Otherwise, IA32_EFER.LME is unmodified.
See below for the case in which the “load IA32_EFER” VM-entry control is 1

— If the “load IA32_PERF_GLOBAL_CTRL” VM-entry control is 1, the IA32_PERF_GLOBAL_CTRL MSR is loaded
from the IA32_PERF_GLOBAL_CTRL field.
— If the “load IA32_PAT” VM-entry control is 1, the IA32_PAT MSR is loaded from the IA32_PAT field.
— If the “load IA32_EFER” VM-entry control is 1, the IA32_EFER MSR is loaded from the IA32_EFER field.
— If the “load IA32_BNDCFGS” VM-entry control is 1, the IA32_BNDCFGS MSR is loaded from the
IA32_BNDCFGS field.
With the exception of FS.base and GS.base, any of these MSRs is subsequently overwritten if it appears in the
VM-entry MSR-load area. See Section 26.4.

•

The SMBASE register is unmodified by all VM entries except those that return from SMM.

1. Bits 15:6, bit 17, and bit 28:19 of CR0 and CR0.ET are unchanged by executions of MOV to CR0. Bits 15:6, bit 17, and bit 28:19 of
CR0 are always 0 and CR0.ET is always 1.
2. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PG must be 1 in VMX operation, VM entry must be loading CR0 so
that CR0.PG = 1 unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
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26.3.2.2

Loading Guest Segment Registers and Descriptor-Table Registers

For each of CS, SS, DS, ES, FS, GS, TR, and LDTR, fields are loaded from the guest-state area as follows:

•

The unusable bit is loaded from the access-rights field. This bit can never be set for TR (see Section 26.3.1.2).
If it is set for one of the other registers, the following apply:
— For each of CS, SS, DS, ES, FS, and GS, uses of the segment cause faults (general-protection exception or
stack-fault exception) outside 64-bit mode, just as they would had the segment been loaded using a null
selector. This bit does not cause accesses to fault in 64-bit mode.
— If this bit is set for LDTR, uses of LDTR cause general-protection exceptions in all modes, just as they would
had LDTR been loaded using a null selector.
If this bit is clear for any of CS, SS, DS, ES, FS, GS, TR, and LDTR, a null selector value does not cause a fault
(general-protection exception or stack-fault exception).

•
•

TR. The selector, base, limit, and access-rights fields are loaded.
CS.
— The following fields are always loaded: selector, base address, limit, and (from the access-rights field) the
L, D, and G bits.
— For the other fields, the unusable bit of the access-rights field is consulted:

•

•
•

If the unusable bit is 0, all of the access-rights field is loaded.
If the unusable bit is 1, the remainder of CS access rights are undefined after VM entry.

SS, DS, ES, FS, GS, and LDTR.
— The selector fields are loaded.
— For the other fields, the unusable bit of the corresponding access-rights field is consulted:

•
•

If the unusable bit is 0, the base-address, limit, and access-rights fields are loaded.
If the unusable bit is 1, the base address, the segment limit, and the remainder of the access rights are
undefined after VM entry with the following exceptions:
— Bits 3:0 of the base address for SS are cleared to 0.
— SS.DPL is always loaded from the SS access-rights field. This will be the current privilege level
(CPL) after the VM entry completes.
— SS.B is always set to 1.
— The base addresses for FS and GS are loaded from the corresponding fields in the VMCS. On
processors that support Intel 64 architecture, the values loaded for base addresses for FS and GS
are also manifest in the FS.base and GS.base MSRs.
— On processors that support Intel 64 architecture, the base address for LDTR is set to an undefined
but canonical value.
— On processors that support Intel 64 architecture, bits 63:32 of the base addresses for SS, DS, and
ES are cleared to 0.

GDTR and IDTR are loaded using the base and limit fields.

26.3.2.3

Loading Guest RIP, RSP, and RFLAGS

RSP, RIP, and RFLAGS are loaded from the RSP field, the RIP field, and the RFLAGS field, respectively. The following
items regard the upper 32 bits of these fields on VM entries that are not to 64-bit mode:

•

Bits 63:32 of RSP are undefined outside 64-bit mode. Thus, a logical processor may ignore the contents of
bits 63:32 of the RSP field on VM entries that are not to 64-bit mode.

•

As noted in Section 26.3.1.4, bits 63:32 of the RIP and RFLAGS fields must be 0 on VM entries that are not to
64-bit mode.

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26.3.2.4

Loading Page-Directory-Pointer-Table Entries

As noted in Section 26.3.1.6, the logical processor uses PAE paging if CR0.PG = 1, CR4.PAE = 1, and
IA32_EFER.LME = 0. A VM entry to a guest that uses PAE paging loads the PDPTEs into internal, non-architectural
registers based on the setting of the “enable EPT” VM-execution control:

•

If the control is 0, the PDPTEs are loaded from the page-directory-pointer table referenced by the physical
address in the value of CR3 being loaded by the VM entry (see Section 26.3.2.1). The values loaded are treated
as physical addresses in VMX non-root operation.

•

If the control is 1, the PDPTEs are loaded from corresponding fields in the guest-state area (see Section
24.4.2). The values loaded are treated as guest-physical addresses in VMX non-root operation.

26.3.2.5

Updating Non-Register State

Section 28.3 describes how the VMX architecture controls how a logical processor manages information in the TLBs
and paging-structure caches. The following items detail how VM entries invalidate cached mappings:

•

If the “enable VPID” VM-execution control is 0, the logical processor invalidates linear mappings and combined
mappings associated with VPID 0000H (for all PCIDs); combined mappings for VPID 0000H are invalidated for
all EP4TA values (EP4TA is the value of bits 51:12 of EPTP).

•

VM entries are not required to invalidate any guest-physical mappings, nor are they required to invalidate any
linear mappings or combined mappings if the “enable VPID” VM-execution control is 1.

If the “virtual-interrupt delivery” VM-execution control is 1, VM entry loads the values of RVI and SVI from the
guest interrupt-status field in the VMCS (see Section 24.4.2). After doing so, the logical processor first causes PPR
virtualization (Section 29.1.3) and then evaluates pending virtual interrupts (Section 29.2.1).
If a virtual interrupt is recognized, it may be delivered in VMX non-root operation immediately after VM entry
(including any specified event injection) completes; see Section 26.6.5. See Section 29.2.2 for details regarding
the delivery of virtual interrupts.

26.3.3

Clearing Address-Range Monitoring

The Intel 64 and IA-32 architectures allow software to monitor a specified address range using the MONITOR and
MWAIT instructions. See Section 8.10.4 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 3A. VM entries clear any address-range monitoring that may be in effect.

26.4

LOADING MSRS

VM entries may load MSRs from the VM-entry MSR-load area (see Section 24.8.2). Specifically each entry in that
area (up to the number specified in the VM-entry MSR-load count) is processed in order by loading the MSR
indexed by bits 31:0 with the contents of bits 127:64 as they would be written by WRMSR.1
Processing of an entry fails in any of the following cases:

•
•

The value of bits 31:0 is either C0000100H (the IA32_FS_BASE MSR) or C0000101 (the IA32_GS_BASE MSR).

•

The value of bits 31:0 indicates an MSR that can be written only in system-management mode (SMM) and the
VM entry did not commence in SMM. (IA32_SMM_MONITOR_CTL is an MSR that can be written only in SMM.)

•

The value of bits 31:0 indicates an MSR that cannot be loaded on VM entries for model-specific reasons. A
processor may prevent loading of certain MSRs even if they can normally be written by WRMSR. Such modelspecific behavior is documented in Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 4.

The value of bits 31:8 is 000008H, meaning that the indexed MSR is one that allows access to an APIC register
when the local APIC is in x2APIC mode.

1. Because attempts to modify the value of IA32_EFER.LMA by WRMSR are ignored, attempts to modify it using the VM-entry MSRload area are also ignored.
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•
•

Bits 63:32 are not all 0.
An attempt to write bits 127:64 to the MSR indexed by bits 31:0 of the entry would cause a general-protection
exception if executed via WRMSR with CPL = 0.1

The VM entry fails if processing fails for any entry. The logical processor responds to such failures by loading state
from the host-state area, as it would for a VM exit. See Section 26.7.
If any MSR is being loaded in such a way that would architecturally require a TLB flush, the TLBs are updated so
that, after VM entry, the logical processor will not use any translations that were cached before the transition.

26.5

EVENT INJECTION

If the valid bit in the VM-entry interruption-information field (see Section 24.8.3) is 1, VM entry causes an event to
be delivered (or made pending) after all components of guest state have been loaded (including MSRs) and after
the VM-execution control fields have been established.

•

If the interruption type in the field is 0 (external interrupt), 2 (non-maskable interrupt); 3 (hardware
exception), 4 (software interrupt), 5 (privileged software exception), or 6 (software exception), the event is
delivered as described in Section 26.5.1.

•

If the interruption type in the field is 7 (other event) and the vector field is 0, an MTF VM exit is pending after
VM entry. See Section 26.5.2.

26.5.1

Vectored-Event Injection

VM entry delivers an injected vectored event within the guest context established by VM entry. This means that
delivery occurs after all components of guest state have been loaded (including MSRs) and after the VM-execution
control fields have been established.2 The event is delivered using the vector in that field to select a descriptor in
the IDT. Since event injection occurs after loading IDTR from the guest-state area, this is the guest IDT.
Section 26.5.1.1 provides details of vectored-event injection. In general, the event is delivered exactly as if it had
been generated normally.
If event delivery encounters a nested exception (for example, a general-protection exception because the vector
indicates a descriptor beyond the IDT limit), the exception bitmap is consulted using the vector of that exception:

•

If the bit for the nested exception is 0, the nested exception is delivered normally. If the nested exception is
benign, it is delivered through the IDT. If it is contributory or a page fault, a double fault may be generated,
depending on the nature of the event whose delivery encountered the nested exception. See Chapter 6,
“Interrupt 8—Double Fault Exception (#DF)” in Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3A.3

•

If the bit for the nested exception is 1, a VM exit occurs. Section 26.5.1.2 details cases in which event injection
causes a VM exit.

1. If CR0.PG = 1, WRMSR to the IA32_EFER MSR causes a general-protection exception if it would modify the LME bit. If VM entry has
established CR0.PG = 1, the IA32_EFER MSR should not be included in the VM-entry MSR-load area for the purpose of modifying the
LME bit.
2. This does not imply that injection of an exception or interrupt will cause a VM exit due to the settings of VM-execution control fields
(such as the exception bitmap) that would cause a VM exit if the event had occurred in VMX non-root operation. In contrast, a nested
exception encountered during event delivery may cause a VM exit; see Section 26.5.1.1.
3. Hardware exceptions with the following unused vectors are considered benign: 15 and 21–31. A hardware exception with vector 20
is considered benign unless the processor supports the 1-setting of the “EPT-violation #VE” VM-execution control; in that case, it
has the same severity as page faults.
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26.5.1.1

Details of Vectored-Event Injection

The event-injection process is controlled by the contents of the VM-entry interruption information field (format
given in Table 24-13), the VM-entry exception error-code field, and the VM-entry instruction-length field. The
following items provide details of the process:

•

The value pushed on the stack for RFLAGS is generally that which was loaded from the guest-state area. The
value pushed for the RF flag is not modified based on the type of event being delivered. However, the pushed
value of RFLAGS may be modified if a software interrupt is being injected into a guest that will be in virtual8086 mode (see below). After RFLAGS is pushed on the stack, the value in the RFLAGS register is modified as
is done normally when delivering an event through the IDT.

•

The instruction pointer that is pushed on the stack depends on the type of event and whether nested
exceptions occur during its delivery. The term current guest RIP refers to the value to be loaded from the
guest-state area. The value pushed is determined as follows:1
— If VM entry successfully injects (with no nested exception) an event with interruption type external
interrupt, NMI, or hardware exception, the current guest RIP is pushed on the stack.
— If VM entry successfully injects (with no nested exception) an event with interruption type software
interrupt, privileged software exception, or software exception, the current guest RIP is incremented by the
VM-entry instruction length before being pushed on the stack.
— If VM entry encounters an exception while injecting an event and that exception does not cause a VM exit,
the current guest RIP is pushed on the stack regardless of event type or VM-entry instruction length. If the
encountered exception does cause a VM exit that saves RIP, the saved RIP is current guest RIP.

•

If the deliver-error-code bit (bit 11) is set in the VM-entry interruption-information field, the contents of the
VM-entry exception error-code field is pushed on the stack as an error code would be pushed during delivery of
an exception.

•

DR6, DR7, and the IA32_DEBUGCTL MSR are not modified by event injection, even if the event has vector 1
(normal deliveries of debug exceptions, which have vector 1, do update these registers).

•

If VM entry is injecting a software interrupt and the guest will be in virtual-8086 mode (RFLAGS.VM = 1), no
general-protection exception can occur due to RFLAGS.IOPL < 3. A VM monitor should check RFLAGS.IOPL
before injecting such an event and, if desired, inject a general-protection exception instead of a software
interrupt.

•

If VM entry is injecting a software interrupt and the guest will be in virtual-8086 mode with virtual-8086 mode
extensions (RFLAGS.VM = CR4.VME = 1), event delivery is subject to VME-based interrupt redirection based
on the software interrupt redirection bitmap in the task-state segment (TSS) as follows:
— If bit n in the bitmap is clear (where n is the number of the software interrupt), the interrupt is directed to
an 8086 program interrupt handler: the processor uses a 16-bit interrupt-vector table (IVT) located at
linear address zero. If the value of RFLAGS.IOPL is less than 3, the following modifications are made to the
value of RFLAGS that is pushed on the stack: IOPL is set to 3, and IF is set to the value of VIF.
— If bit n in the bitmap is set (where n is the number of the software interrupt), the interrupt is directed to a
protected-mode interrupt handler. (In other words, the injection is treated as described in the next item.)
In this case, the software interrupt does not invoke such a handler if RFLAGS.IOPL < 3 (a generalprotection exception occurs instead). However, as noted above, RFLAGS.IOPL cannot cause an injected
software interrupt to cause such a exception. Thus, in this case, the injection invokes a protected-mode
interrupt handler independent of the value of RFLAGS.IOPL.
Injection of events of other types are not subject to this redirection.

•

If VM entry is injecting a software interrupt (not redirected as described above) or software exception, privilege
checking is performed on the IDT descriptor being accessed as would be the case for executions of INT n, INT3,
or INTO (the descriptor’s DPL cannot be less than CPL). There is no checking of RFLAGS.IOPL, even if the guest
will be in virtual-8086 mode. Failure of this check may lead to a nested exception. Injection of an event with
interruption type external interrupt, NMI, hardware exception, and privileged software exception, or with interruption type software interrupt and being redirected as described above, do not perform these checks.

1. While these items refer to RIP, the width of the value pushed (16 bits, 32 bits, or 64 bits) is determined normally.
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VM ENTRIES

•

If VM entry is injecting a non-maskable interrupt (NMI) and the “virtual NMIs” VM-execution control is 1,
virtual-NMI blocking is in effect after VM entry.

•

The transition causes a last-branch record to be logged if the LBR bit is set in the IA32_DEBUGCTL MSR. This is
true even for events such as debug exceptions, which normally clear the LBR bit before delivery.

•

The last-exception record MSRs (LERs) may be updated based on the setting of the LBR bit in the
IA32_DEBUGCTL MSR. Events such as debug exceptions, which normally clear the LBR bit before they are
delivered, and therefore do not normally update the LERs, may do so as part of VM-entry event injection.

•

If injection of an event encounters a nested exception that does not itself cause a VM exit, the value of the EXT
bit (bit 0) in any error code pushed on the stack is determined as follows:
— If event being injected has interruption type external interrupt, NMI, hardware exception, or privileged
software exception and encounters a nested exception (but does not produce a double fault), the error code
for the first such exception encountered sets the EXT bit.
— If event being injected is a software interrupt or an software exception and encounters a nested exception
(but does not produce a double fault), the error code for the first such exception encountered clears the EXT
bit.
— If event delivery encounters a nested exception and delivery of that exception encounters another
exception (but does not produce a double fault), the error code for that exception sets the EXT bit. If a
double fault is produced, the error code for the double fault is 0000H (the EXT bit is clear).

26.5.1.2

VM Exits During Event Injection

An event being injected never causes a VM exit directly regardless of the settings of the VM-execution controls. For
example, setting the “NMI exiting” VM-execution control to 1 does not cause a VM exit due to injection of an NMI.
However, the event-delivery process may lead to a VM exit:

•

If the vector in the VM-entry interruption-information field identifies a task gate in the IDT, the attempted task
switch may cause a VM exit just as it would had the injected event occurred during normal execution in VMX
non-root operation (see Section 25.4.2).

•

If event delivery encounters a nested exception, a VM exit may occur depending on the contents of the
exception bitmap (see Section 25.2).

•

If event delivery generates a double-fault exception (due to a nested exception); the logical processor
encounters another nested exception while attempting to call the double-fault handler; and that exception does
not cause a VM exit due to the exception bitmap; then a VM exit occurs due to triple fault (see Section 25.2).

•

If event delivery injects a double-fault exception and encounters a nested exception that does not cause a
VM exit due to the exception bitmap, then a VM exit occurs due to triple fault (see Section 25.2).

•

If the “virtualize APIC accesses” VM-execution control is 1 and event delivery generates an access to the APICaccess page, that access is treated as described in Section 29.4 and may cause a VM exit.1

If the event-delivery process does cause a VM exit, the processor state before the VM exit is determined just as it
would be had the injected event occurred during normal execution in VMX non-root operation. If the injected event
directly accesses a task gate that cause a VM exit or if the first nested exception encountered causes a VM exit,
information about the injected event is saved in the IDT-vectoring information field (see Section 27.2.3).

26.5.1.3

Event Injection for VM Entries to Real-Address Mode

If VM entry is loading CR0.PE with 0, any injected vectored event is delivered as would normally be done in realaddress mode.2 Specifically, VM entry uses the vector provided in the VM-entry interruption-information field to

1. “Virtualize APIC accesses” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls is 0, VM entry functions as if the “virtualize APIC accesses” VM-execution control were 0. See Section 24.6.2.
2. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PE must be 1 in VMX operation, VM entry must be loading CR0.PE
with 1 unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are
both 1.
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select a 4-byte entry from an interrupt-vector table at the linear address in IDTR.base. Further details are provided
in Section 15.1.4 in Volume 3A of the IA-32 Intel® Architecture Software Developer’s Manual.
Because bit 11 (deliver error code) in the VM-entry interruption-information field must be 0 if CR0.PE will be 0 after
VM entry (see Section 26.2.1.3), vectored events injected with CR0.PE = 0 do not push an error code on the stack.
This is consistent with event delivery in real-address mode.
If event delivery encounters a fault (due to a violation of IDTR.limit or of SS.limit), the fault is treated as if it had
occurred during event delivery in VMX non-root operation. Such a fault may lead to a VM exit as discussed in
Section 26.5.1.2.

26.5.2

Injection of Pending MTF VM Exits

If the interruption type in the VM-entry interruption-information field is 7 (other event) and the vector field is 0,
VM entry causes an MTF VM exit to be pending on the instruction boundary following VM entry. This is the case
even if the “monitor trap flag” VM-execution control is 0. See Section 25.5.2 for the treatment of pending MTF
VM exits.

26.6

SPECIAL FEATURES OF VM ENTRY

This section details a variety of features of VM entry. It uses the following terminology: a VM entry is vectoring if
the valid bit (bit 31) of the VM-entry interruption information field is 1 and the interruption type in the field is 0
(external interrupt), 2 (non-maskable interrupt); 3 (hardware exception), 4 (software interrupt), 5 (privileged
software exception), or 6 (software exception).

26.6.1

Interruptibility State

The interruptibility-state field in the guest-state area (see Table 24-3) contains bits that control blocking by STI,
blocking by MOV SS, and blocking by NMI. This field impacts event blocking after VM entry as follows:

•

If the VM entry is vectoring, there is no blocking by STI or by MOV SS following the VM entry, regardless of the
contents of the interruptibility-state field.

•

If the VM entry is not vectoring, the following apply:
— Events are blocked by STI if and only if bit 0 in the interruptibility-state field is 1. This blocking is cleared
after the guest executes one instruction or incurs an exception (including a debug exception made pending
by VM entry; see Section 26.6.3).
— Events are blocked by MOV SS if and only if bit 1 in the interruptibility-state field is 1. This may affect the
treatment of pending debug exceptions; see Section 26.6.3. This blocking is cleared after the guest
executes one instruction or incurs an exception (including a debug exception made pending by VM entry).

•

The blocking of non-maskable interrupts (NMIs) is determined as follows:
— If the “virtual NMIs” VM-execution control is 0, NMIs are blocked if and only if bit 3 (blocking by NMI) in the
interruptibility-state field is 1. If the “NMI exiting” VM-execution control is 0, execution of the IRET
instruction removes this blocking (even if the instruction generates a fault). If the “NMI exiting” control is
1, IRET does not affect this blocking.
— The following items describe the use of bit 3 (blocking by NMI) in the interruptibility-state field if the
“virtual NMIs” VM-execution control is 1:

•

The bit’s value does not affect the blocking of NMIs after VM entry. NMIs are not blocked in VMX nonroot operation (except for ordinary blocking for other reasons, such as by the MOV SS instruction, the
wait-for-SIPI state, etc.)

•

The bit’s value determines whether there is virtual-NMI blocking after VM entry. If the bit is 1, virtualNMI blocking is in effect after VM entry. If the bit is 0, there is no virtual-NMI blocking after VM entry
unless the VM entry is injecting an NMI (see Section 26.5.1.1). Execution of IRET removes virtual-NMI
blocking (even if the instruction generates a fault).

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VM ENTRIES

If the “NMI exiting” VM-execution control is 0, the “virtual NMIs” control must be 0; see Section 26.2.1.1.

•

Blocking of system-management interrupts (SMIs) is determined as follows:
— If the VM entry was not executed in system-management mode (SMM), SMI blocking is unchanged by
VM entry.
— If the VM entry was executed in SMM, SMIs are blocked after VM entry if and only if the bit 2 in the interruptibility-state field is 1.

26.6.2

Activity State

The activity-state field in the guest-state area controls whether, after VM entry, the logical processor is active or in
one of the inactive states identified in Section 24.4.2. The use of this field is determined as follows:

•

If the VM entry is vectoring, the logical processor is in the active state after VM entry. While the consistency
checks described in Section 26.3.1.5 on the activity-state field do apply in this case, the contents of the
activity-state field do not determine the activity state after VM entry.

•

If the VM entry is not vectoring, the logical processor ends VM entry in the activity state specified in the gueststate area. If VM entry ends with the logical processor in an inactive activity state, the VM entry generates any
special bus cycle that is normally generated when that activity state is entered from the active state. If
VM entry would end with the logical processor in the shutdown state and the logical processor is in SMX
operation,1 an Intel® TXT shutdown condition occurs. The error code used is 0000H, indicating “legacy
shutdown.” See Intel® Trusted Execution Technology Preliminary Architecture Specification.

•

Some activity states unconditionally block certain events. The following blocking is in effect after any VM entry
that puts the processor in the indicated state:
— The active state blocks start-up IPIs (SIPIs). SIPIs that arrive while a logical processor is in the active state
and in VMX non-root operation are discarded and do not cause VM exits.
— The HLT state blocks start-up IPIs (SIPIs). SIPIs that arrive while a logical processor is in the HLT state and
in VMX non-root operation are discarded and do not cause VM exits.
— The shutdown state blocks external interrupts and SIPIs. External interrupts that arrive while a logical
processor is in the shutdown state and in VMX non-root operation do not cause VM exits even if the
“external-interrupt exiting” VM-execution control is 1. SIPIs that arrive while a logical processor is in the
shutdown state and in VMX non-root operation are discarded and do not cause VM exits.
— The wait-for-SIPI state blocks external interrupts, non-maskable interrupts (NMIs), INIT signals, and
system-management interrupts (SMIs). Such events do not cause VM exits if they arrive while a logical
processor is in the wait-for-SIPI state and in VMX non-root operation.

26.6.3

Delivery of Pending Debug Exceptions after VM Entry

The pending debug exceptions field in the guest-state area indicates whether there are debug exceptions that have
not yet been delivered (see Section 24.4.2). This section describes how these are treated on VM entry.
There are no pending debug exceptions after VM entry if any of the following are true:

•

The VM entry is vectoring with one of the following interruption types: external interrupt, non-maskable
interrupt (NMI), hardware exception, or privileged software exception.

•

The interruptibility-state field does not indicate blocking by MOV SS and the VM entry is vectoring with either of
the following interruption type: software interrupt or software exception.

•

The VM entry is not vectoring and the activity-state field indicates either shutdown or wait-for-SIPI.

If none of the above hold, the pending debug exceptions field specifies the debug exceptions that are pending for
the guest. There are valid pending debug exceptions if either the BS bit (bit 14) or the enable-breakpoint bit
(bit 12) is 1. If there are valid pending debug exceptions, they are handled as follows:
1. A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last execution of GETSEC[SENTER]. See
Chapter 6, “Safer Mode Extensions Reference,” in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B.
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VM ENTRIES

•

If the VM entry is not vectoring, the pending debug exceptions are treated as they would had they been
encountered normally in guest execution:
— If the logical processor is not blocking such exceptions (the interruptibility-state field indicates no blocking
by MOV SS), a debug exception is delivered after VM entry (see below).
— If the logical processor is blocking such exceptions (due to blocking by MOV SS), the pending debug
exceptions are held pending or lost as would normally be the case.

•

If the VM entry is vectoring (with interruption type software interrupt or software exception and with blocking
by MOV SS), the following items apply:
— For injection of a software interrupt or of a software exception with vector 3 (#BP) or vector 4 (#OF), the
pending debug exceptions are treated as they would had they been encountered normally in guest
execution if the corresponding instruction (INT3 or INTO) were executed after a MOV SS that encountered
a debug trap.
— For injection of a software exception with a vector other than 3 and 4, the pending debug exceptions may
be lost or they may be delivered after injection (see below).

If there are no valid pending debug exceptions (as defined above), no pending debug exceptions are delivered after
VM entry.
If a pending debug exception is delivered after VM entry, it has the priority of “traps on the previous instruction”
(see Section 6.9 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A). Thus, INIT
signals and system-management interrupts (SMIs) take priority of such an exception, as do VM exits induced by
the TPR threshold (see Section 26.6.7) and pending MTF VM exits (see Section 26.6.8. The exception takes priority
over any pending non-maskable interrupt (NMI) or external interrupt and also over VM exits due to the 1-settings
of the “interrupt-window exiting” and “NMI-window exiting” VM-execution controls.
A pending debug exception delivered after VM entry causes a VM exit if the bit 1 (#DB) is 1 in the exception
bitmap. If it does not cause a VM exit, it updates DR6 normally.

26.6.4

VMX-Preemption Timer

If the “activate VMX-preemption timer” VM-execution control is 1, VM entry starts the VMX-preemption timer with
the unsigned value in the VMX-preemption timer-value field.
It is possible for the VMX-preemption timer to expire during VM entry (e.g., if the value in the VMX-preemption
timer-value field is zero). If this happens (and if the VM entry was not to the wait-for-SIPI state), a VM exit occurs
with its normal priority after any event injection and before execution of any instruction following VM entry. For
example, any pending debug exceptions established by VM entry (see Section 26.6.3) take priority over a timerinduced VM exit. (The timer-induced VM exit will occur after delivery of the debug exception, unless that exception
or its delivery causes a different VM exit.)
See Section 25.5.1 for details of the operation of the VMX-preemption timer in VMX non-root operation, including
the blocking and priority of the VM exits that it causes.

26.6.5

Interrupt-Window Exiting and Virtual-Interrupt Delivery

If “interrupt-window exiting” VM-execution control is 1, an open interrupt window may cause a VM exit immediately after VM entry (see Section 25.2 for details). If the “interrupt-window exiting” VM-execution control is 0 but
the “virtual-interrupt delivery” VM-execution control is 1, a virtual interrupt may be delivered immediately after
VM entry (see Section 26.3.2.5 and Section 29.2.1).
The following items detail the treatment of these events:

•
•
•

These events occur after any event injection specified for VM entry.
Non-maskable interrupts (NMIs) and higher priority events take priority over these events. These events take
priority over external interrupts and lower priority events.
These events wake the logical processor if it just entered the HLT state because of a VM entry (see Section
26.6.2). They do not occur if the logical processor just entered the shutdown state or the wait-for-SIPI state.

Vol. 3C 26-23

VM ENTRIES

26.6.6

NMI-Window Exiting

The “NMI-window exiting” VM-execution control may cause a VM exit to occur immediately after VM entry (see
Section 25.2 for details).
The following items detail the treatment of these VM exits:

•
•

These VM exits follow event injection if such injection is specified for VM entry.

•

VM exits caused by this control wake the logical processor if it just entered either the HLT state or the shutdown
state because of a VM entry (see Section 26.6.2). They do not occur if the logical processor just entered the
wait-for-SIPI state.

Debug-trap exceptions (see Section 26.6.3) and higher priority events take priority over VM exits caused by
this control. VM exits caused by this control take priority over non-maskable interrupts (NMIs) and lower
priority events.

26.6.7

VM Exits Induced by the TPR Threshold

If the “use TPR shadow” and “virtualize APIC accesses” VM-execution controls are both 1 and the “virtual-interrupt
delivery” VM-execution control is 0, a VM exit occurs immediately after VM entry if the value of bits 3:0 of the TPR
threshold VM-execution control field is greater than the value of bits 7:4 of VTPR (see Section 29.1.1).1
The following items detail the treatment of these VM exits:

•

The VM exits are not blocked if RFLAGS.IF = 0 or by the setting of bits in the interruptibility-state field in gueststate area.

•
•

The VM exits follow event injection if such injection is specified for VM entry.

•

These VM exits wake the logical processor if it just entered the HLT state as part of a VM entry (see Section
26.6.2). They do not occur if the logical processor just entered the shutdown state or the wait-for-SIPI state.

VM exits caused by this control take priority over system-management interrupts (SMIs), INIT signals, and
lower priority events. They thus have priority over the VM exits described in Section 26.6.5, Section 26.6.6,
and Section 26.6.8, as well as any interrupts or debug exceptions that may be pending at the time of VM entry.

If such a VM exit is suppressed because the processor just entered the shutdown state, it occurs after the
delivery of any event that cause the logical processor to leave the shutdown state while remaining in VMX
non-root operation (e.g., due to an NMI that occurs while the “NMI-exiting” VM-execution control is 0).

•

The basic exit reason is “TPR below threshold.”

26.6.8

Pending MTF VM Exits

As noted in Section 26.5.2, VM entry may cause an MTF VM exit to be pending immediately after VM entry. The
following items detail the treatment of these VM exits:

•

System-management interrupts (SMIs), INIT signals, and higher priority events take priority over these
VM exits. These VM exits take priority over debug-trap exceptions and lower priority events.

•

These VM exits wake the logical processor if it just entered the HLT state because of a VM entry (see Section
26.6.2). They do not occur if the logical processor just entered the shutdown state or the wait-for-SIPI state.

26.6.9

VM Entries and Advanced Debugging Features

VM entries are not logged with last-branch records, do not produce branch-trace messages, and do not update the
branch-trace store.

1. “Virtualize APIC accesses” and “virtual-interrupt delivery” are secondary processor-based VM-execution controls. If bit 31 of the primary processor-based VM-execution controls is 0, VM entry functions as if these controls were 0. See Section 24.6.2.
26-24 Vol. 3C

VM ENTRIES

26.7

VM-ENTRY FAILURES DURING OR AFTER LOADING GUEST STATE

VM-entry failures due to the checks identified in Section 26.3.1 and failures during the MSR loading identified in
Section 26.4 are treated differently from those that occur earlier in VM entry. In these cases, the following steps
take place:
1. Information about the VM-entry failure is recorded in the VM-exit information fields:
— Exit reason.

•

Bits 15:0 of this field contain the basic exit reason. It is loaded with a number indicating the general
cause of the VM-entry failure. The following numbers are used:
33. VM-entry failure due to invalid guest state. A VM entry failed one of the checks identified in Section
26.3.1.
34. VM-entry failure due to MSR loading. A VM entry failed in an attempt to load MSRs (see Section
26.4).
41. VM-entry failure due to machine-check event. A machine-check event occurred during VM entry
(see Section 26.8).

•
•

Bit 31 is set to 1 to indicate a VM-entry failure.
The remainder of the field (bits 30:16) is cleared.

— Exit qualification. This field is set based on the exit reason.

•

VM-entry failure due to invalid guest state. In most cases, the exit qualification is cleared to 0. The
following non-zero values are used in the cases indicated:
1. Not used.
2. Failure was due to a problem loading the PDPTEs (see Section 26.3.1.6).
3. Failure was due to an attempt to inject a non-maskable interrupt (NMI) into a guest that is blocking
events through the STI blocking bit in the interruptibility-state field. Such failures are implementation-specific (see Section 26.3.1.5).
4. Failure was due to an invalid VMCS link pointer (see Section 26.3.1.5).
VM-entry checks on guest-state fields may be performed in any order. Thus, an indication by exit
qualification of one cause does not imply that there are not also other errors. Different processors
may give different exit qualifications for the same VMCS.

•

VM-entry failure due to MSR loading. The exit qualification is loaded to indicate which entry in the
VM-entry MSR-load area caused the problem (1 for the first entry, 2 for the second, etc.).

— All other VM-exit information fields are unmodified.
2. Processor state is loaded as would be done on a VM exit (see Section 27.5). If this results in
[CR4.PAE & CR0.PG & ~IA32_EFER.LMA] = 1, page-directory-pointer-table entries (PDPTEs) may be checked
and loaded (see Section 27.5.4).
3. The state of blocking by NMI is what it was before VM entry.
4. MSRs are loaded as specified in the VM-exit MSR-load area (see Section 27.6).
Although this process resembles that of a VM exit, many steps taken during a VM exit do not occur for these
VM-entry failures:

•
•
•
•

Most VM-exit information fields are not updated (see step 1 above).
The valid bit in the VM-entry interruption-information field is not cleared.
The guest-state area is not modified.
No MSRs are saved into the VM-exit MSR-store area.

26.8

MACHINE-CHECK EVENTS DURING VM ENTRY

If a machine-check event occurs during a VM entry, one of the following occurs:
Vol. 3C 26-25

VM ENTRIES

•

The machine-check event is handled as if it occurred before the VM entry:
— If CR4.MCE = 0, operation of the logical processor depends on whether the logical processor is in SMX
operation:1

•

If the logical processor is in SMX operation, an Intel® TXT shutdown condition occurs. The error code
used is 000CH, indicating “unrecoverable machine-check condition.”

•

If the logical processor is outside SMX operation, it goes to the shutdown state.

— If CR4.MCE = 1, a machine-check exception (#MC) is delivered through the IDT.

•

The machine-check event is handled after VM entry completes:
— If the VM entry ends with CR4.MCE = 0, operation of the logical processor depends on whether the logical
processor is in SMX operation:

•

If the logical processor is in SMX operation, an Intel® TXT shutdown condition occurs with error code
000CH (unrecoverable machine-check condition).

•

If the logical processor is outside SMX operation, it goes to the shutdown state.

— If the VM entry ends with CR4.MCE = 1, a machine-check exception (#MC) is generated:

•

•
•

If bit 18 (#MC) of the exception bitmap is 0, the exception is delivered through the guest IDT.
If bit 18 of the exception bitmap is 1, the exception causes a VM exit.

A VM-entry failure occurs as described in Section 26.7. The basic exit reason is 41, for “VM-entry failure due to
machine-check event.”

The first option is not used if the machine-check event occurs after any guest state has been loaded. The second
option is used only if VM entry is able to load all guest state.

1. A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last execution of GETSEC[SENTER]. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the last
execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference,” in Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 2B.
26-26 Vol. 3C

CHAPTER 27
VM EXITS
VM exits occur in response to certain instructions and events in VMX non-root operation as detailed in Section 25.1
through Section 25.2. VM exits perform the following operations:
1. Information about the cause of the VM exit is recorded in the VM-exit information fields and VM-entry control
fields are modified as described in Section 27.2.
2. Processor state is saved in the guest-state area (Section 27.3).
3. MSRs may be saved in the VM-exit MSR-store area (Section 27.4). This step is not performed for SMM VM exits
that activate the dual-monitor treatment of SMIs and SMM.
4. The following may be performed in parallel and in any order (Section 27.5):
— Processor state is loaded based in part on the host-state area and some VM-exit controls. This step is not
performed for SMM VM exits that activate the dual-monitor treatment of SMIs and SMM. See Section
34.15.6 for information on how processor state is loaded by such VM exits.
— Address-range monitoring is cleared.
5. MSRs may be loaded from the VM-exit MSR-load area (Section 27.6). This step is not performed for SMM
VM exits that activate the dual-monitor treatment of SMIs and SMM.
VM exits are not logged with last-branch records, do not produce branch-trace messages, and do not update the
branch-trace store.
Section 27.1 clarifies the nature of the architectural state before a VM exit begins. The steps described above are
detailed in Section 27.2 through Section 27.6.
Section 34.15 describes the dual-monitor treatment of system-management interrupts (SMIs) and systemmanagement mode (SMM). Under this treatment, ordinary transitions to SMM are replaced by VM exits to a separate SMM monitor. Called SMM VM exits, these are caused by the arrival of an SMI or the execution of VMCALL in
VMX root operation. SMM VM exits differ from other VM exits in ways that are detailed in Section 34.15.2.

27.1

ARCHITECTURAL STATE BEFORE A VM EXIT

This section describes the architectural state that exists before a VM exit, especially for VM exits caused by events
that would normally be delivered through the IDT. Note the following:

•

An exception causes a VM exit directly if the bit corresponding to that exception is set in the exception bitmap.
A non-maskable interrupt (NMI) causes a VM exit directly if the “NMI exiting” VM-execution control is 1. An
external interrupt causes a VM exit directly if the “external-interrupt exiting” VM-execution control is 1. A startup IPI (SIPI) that arrives while a logical processor is in the wait-for-SIPI activity state causes a VM exit directly.
INIT signals that arrive while the processor is not in the wait-for-SIPI activity state cause VM exits directly.

•

An exception, NMI, external interrupt, or software interrupt causes a VM exit indirectly if it does not do so
directly but delivery of the event causes a nested exception, double fault, task switch, APIC access (see Section
27.4), EPT violation, EPT misconfiguration, or page-modification log-full event that causes a VM exit.

•

An event results in a VM exit if it causes a VM exit (directly or indirectly).

The following bullets detail when architectural state is and is not updated in response to VM exits:

•

If an event causes a VM exit directly, it does not update architectural state as it would have if it had it not
caused the VM exit:
— A debug exception does not update DR6, DR7.GD, or IA32_DEBUGCTL.LBR. (Information about the nature
of the debug exception is saved in the exit qualification field.)
— A page fault does not update CR2. (The linear address causing the page fault is saved in the exit-qualification field.)
— An NMI causes subsequent NMIs to be blocked, but only after the VM exit completes.
Vol. 3C 27-1

VM EXITS

— An external interrupt does not acknowledge the interrupt controller and the interrupt remains pending,
unless the “acknowledge interrupt on exit” VM-exit control is 1. In such a case, the interrupt controller is
acknowledged and the interrupt is no longer pending.
— The flags L0 – L3 in DR7 (bit 0, bit 2, bit 4, and bit 6) are not cleared when a task switch causes a VM exit.
— If a task switch causes a VM exit, none of the following are modified by the task switch: old task-state
segment (TSS); new TSS; old TSS descriptor; new TSS descriptor; RFLAGS.NT1; or the TR register.
— No last-exception record is made if the event that would do so directly causes a VM exit.
— If a machine-check exception causes a VM exit directly, this does not prevent machine-check MSRs from
being updated. These are updated by the machine-check event itself and not the resulting machine-check
exception.
— If the logical processor is in an inactive state (see Section 24.4.2) and not executing instructions, some
events may be blocked but others may return the logical processor to the active state. Unblocked events
may cause VM exits.2 If an unblocked event causes a VM exit directly, a return to the active state occurs
only after the VM exit completes.3 The VM exit generates any special bus cycle that is normally generated
when the active state is entered from that activity state.
MTF VM exits (see Section 25.5.2 and Section 26.6.8) are not blocked in the HLT activity state. If an MTF
VM exit occurs in the HLT activity state, the logical processor returns to the active state only after the
VM exit completes. MTF VM exits are blocked the shutdown state and the wait-for-SIPI state.

•

If an event causes a VM exit indirectly, the event does update architectural state:
— A debug exception updates DR6, DR7, and the IA32_DEBUGCTL MSR. No debug exceptions are considered
pending.
— A page fault updates CR2.
— An NMI causes subsequent NMIs to be blocked before the VM exit commences.
— An external interrupt acknowledges the interrupt controller and the interrupt is no longer pending.
— If the logical processor had been in an inactive state, it enters the active state and, before the VM exit
commences, generates any special bus cycle that is normally generated when the active state is entered
from that activity state.
— There is no blocking by STI or by MOV SS when the VM exit commences.
— Processor state that is normally updated as part of delivery through the IDT (CS, RIP, SS, RSP, RFLAGS) is
not modified. However, the incomplete delivery of the event may write to the stack.
— The treatment of last-exception records is implementation dependent:

•

•

Some processors make a last-exception record when beginning the delivery of an event through the IDT
(before it can encounter a nested exception). Such processors perform this update even if the event
encounters a nested exception that causes a VM exit (including the case where nested exceptions lead
to a triple fault).

•

Other processors delay making a last-exception record until event delivery has reached some event
handler successfully (perhaps after one or more nested exceptions). Such processors do not update the
last-exception record if a VM exit or triple fault occurs before an event handler is reached.

If the “virtual NMIs” VM-execution control is 1, VM entry injects an NMI, and delivery of the NMI causes a
nested exception, double fault, task switch, or APIC access that causes a VM exit, virtual-NMI blocking is in
effect before the VM exit commences.

1. This chapter uses the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that support VMX operation also support Intel 64 architecture. For processors that do not support Intel 64 architecture, this notation refers to the 32-bit
forms of those registers (EAX, EIP, ESP, EFLAGS, etc.). In a few places, notation such as EAX is used to refer specifically to lower 32
bits of the indicated register.
2. If a VM exit takes the processor from an inactive state resulting from execution of a specific instruction (HLT or MWAIT), the value
saved for RIP by that VM exit will reference the following instruction.
3. An exception is made if the logical processor had been inactive due to execution of MWAIT; in this case, it is considered to have
become active before the VM exit.
27-2 Vol. 3C

VM EXITS

•

If a VM exit results from a fault, EPT violation, EPT misconfiguration, or page-modification log-full event is
encountered during execution of IRET and the “NMI exiting” VM-execution control is 0, any blocking by NMI is
cleared before the VM exit commences. However, the previous state of blocking by NMI may be recorded in the
exit qualification or in the VM-exit interruption-information field; see Section 27.2.1 and Section 27.2.2.

•

If a VM exit results from a fault, EPT violation, EPT misconfiguration, or page-modification log-full event is
encountered during execution of IRET and the “virtual NMIs” VM-execution control is 1, virtual-NMI blocking is
cleared before the VM exit commences. However, the previous state of blocking by NMI may be recorded in the
exit qualification or in the VM-exit interruption-information field; see Section 27.2.1 and Section 27.2.2.

•

Suppose that a VM exit is caused directly by an x87 FPU Floating-Point Error (#MF) or by any of the following
events if the event was unblocked due to (and given priority over) an x87 FPU Floating-Point Error: an INIT
signal, an external interrupt, an NMI, an SMI; or a machine-check exception. In these cases, there is no
blocking by STI or by MOV SS when the VM exit commences.

•

Normally, a last-branch record may be made when an event is delivered through the IDT. However, if such an
event results in a VM exit before delivery is complete, no last-branch record is made.

•

If machine-check exception results in a VM exit, processor state is suspect and may result in suspect state
being saved to the guest-state area. A VM monitor should consult the RIPV and EIPV bits in the
IA32_MCG_STATUS MSR before resuming a guest that caused a VM exit resulting from a machine-check
exception.

•

If a VM exit results from a fault, APIC access (see Section 29.4), EPT violation, EPT misconfiguration, or pagemodification log-full event is encountered while executing an instruction, data breakpoints due to that
instruction may have been recognized and information about them may be saved in the pending debug
exceptions field (unless the VM exit clears that field; see Section 27.3.4).

•

The following VM exits are considered to happen after an instruction is executed:
— VM exits resulting from debug traps (single-step, I/O breakpoints, and data breakpoints).
— VM exits resulting from debug exceptions whose recognition was delayed by blocking by MOV SS.
— VM exits resulting from some machine-check exceptions.
— Trap-like VM exits due to execution of MOV to CR8 when the “CR8-load exiting” VM-execution control is 0
and the “use TPR shadow” VM-execution control is 1 (see Section 29.3). (Such VM exits can occur only from
64-bit mode and thus only on processors that support Intel 64 architecture.)
— Trap-like VM exits due to execution of WRMSR when the “use MSR bitmaps” VM-execution control is 1; the
value of ECX is in the range 800H–8FFH; and the bit corresponding to the ECX value in write bitmap for low
MSRs is 0; and the “virtualize x2APIC mode” VM-execution control is 1. See Section 29.5.
— VM exits caused by APIC-write emulation (see Section 29.4.3.2) that result from APIC accesses as part of
instruction execution.
For these VM exits, the instruction’s modifications to architectural state complete before the VM exit occurs.
Such modifications include those to the logical processor’s interruptibility state (see Table 24-3). If there had
been blocking by MOV SS, POP SS, or STI before the instruction executed, such blocking is no longer in effect.

A VM exit that occurs in enclave mode sets bit 27 of the exit-reason field and bit 4 of the guest interruptibility-state
field. Before such a VM exit is delivered, an Asynchronous Enclave Exit (AEX) occurs (see Chapter 39, “Enclave
Exiting Events”). An AEX modifies architectural state (Section 39.3). In particular, the processor establishes the
following architectural state as indicated:

•
•
•
•

The following bits in RFLAGS are cleared: CF, PF, AF, ZF, SF, OF, and RF.
FS and GS are restored to the values they had prior to the most recent enclave entry.
RIP is loaded with the AEP of interrupted enclave thread.
RSP is loaded from the URSP field in the enclave’s state-save area (SSA).

Vol. 3C 27-3

VM EXITS

27.2

RECORDING VM-EXIT INFORMATION AND UPDATING VM-ENTRY CONTROL
FIELDS

VM exits begin by recording information about the nature of and reason for the VM exit in the VM-exit information
fields. Section 27.2.1 to Section 27.2.4 detail the use of these fields.
In addition to updating the VM-exit information fields, the valid bit (bit 31) is cleared in the VM-entry interruptioninformation field. If bit 5 of the IA32_VMX_MISC MSR (index 485H) is read as 1 (see Appendix A.6), the value of
IA32_EFER.LMA is stored into the “IA-32e mode guest” VM-entry control.1

27.2.1

Basic VM-Exit Information

Section 24.9.1 defines the basic VM-exit information fields. The following items detail their use.

•

Exit reason.
— Bits 15:0 of this field contain the basic exit reason. It is loaded with a number indicating the general cause
of the VM exit. Appendix C lists the numbers used and their meaning.
— Bit 27 of this field is set to 1 if the VM exit occurred while the logical processor was in enclave mode.
Such VM exits includes those caused by interrupts, non-maskable interrupts, system-management
interrupts, INIT signals, and exceptions occurring in enclave mode as well as exceptions encountered
during the delivery of such events incident to enclave mode.
A VM exit also sets this bit if it is incident to delivery of an event injected by VM entry and the guest interruptibility-state field indicates an enclave interrupt (bit 4 of the field is 1).
— The remainder of the field (bits 31:28 and bits 26:16) is cleared to 0 (certain SMM VM exits may set some
of these bits; see Section 34.15.2.3).2

•

Exit qualification. This field is saved for VM exits due to the following causes: debug exceptions; page-fault
exceptions; start-up IPIs (SIPIs); system-management interrupts (SMIs) that arrive immediately after the
retirement of I/O instructions; task switches; INVEPT; INVLPG; INVPCID; INVVPID; LGDT; LIDT; LLDT; LTR;
SGDT; SIDT; SLDT; STR; VMCLEAR; VMPTRLD; VMPTRST; VMREAD; VMWRITE; VMXON; XRSTORS; XSAVES;
control-register accesses; MOV DR; I/O instructions; MWAIT; accesses to the APIC-access page (see Section
29.4); EPT violations; EOI virtualization (see Section 29.1.4); APIC-write emulation (see Section 29.4.3.3);
and page-modification log full (see Section 28.2.5). For all other VM exits, this field is cleared. The following
items provide details:
— For a debug exception, the exit qualification contains information about the debug exception. The
information has the format given in Table 27-1.

Table 27-1. Exit Qualification for Debug Exceptions
Bit Position(s)

Contents

3:0

B3 – B0. When set, each of these bits indicates that the corresponding breakpoint condition was met. Any of
these bits may be set even if its corresponding enabling bit in DR7 is not set.

12:4

Reserved (cleared to 0).

13

BD. When set, this bit indicates that the cause of the debug exception is “debug register access detected.”

14

BS. When set, this bit indicates that the cause of the debug exception is either the execution of a single
instruction (if RFLAGS.TF = 1 and IA32_DEBUGCTL.BTF = 0) or a taken branch (if
RFLAGS.TF = DEBUGCTL.BTF = 1).

63:15

Reserved (cleared to 0). Bits 63:32 exist only on processors that support Intel 64 architecture.

1. Bit 5 of the IA32_VMX_MISC MSR is read as 1 on any logical processor that supports the 1-setting of the “unrestricted guest” VMexecution control.
2. Bit 31 of this field is set on certain VM-entry failures; see Section 26.7.
27-4 Vol. 3C

VM EXITS

— For a page-fault exception, the exit qualification contains the linear address that caused the page fault. On
processors that support Intel 64 architecture, bits 63:32 are cleared if the logical processor was not in 64bit mode before the VM exit.
If the page-fault exception occurred during execution of an instruction in enclave mode (and not during
delivery of an event incident to enclave mode), bits 11:0 of the exit qualification are cleared.
— For a start-up IPI (SIPI), the exit qualification contains the SIPI vector information in bits 7:0. Bits 63:8 of
the exit qualification are cleared to 0.
— For a task switch, the exit qualification contains details about the task switch, encoded as shown in
Table 27-2.
— For INVLPG, the exit qualification contains the linear-address operand of the instruction.

•

On processors that support Intel 64 architecture, bits 63:32 are cleared if the logical processor was not
in 64-bit mode before the VM exit.

•

If the INVLPG source operand specifies an unusable segment, the linear address specified in the exit
qualification will match the linear address that the INVLPG would have used if no VM exit occurred. This
address is not architecturally defined and may be implementation-specific.

Table 27-2. Exit Qualification for Task Switch
Bit Position(s)

Contents

15:0

Selector of task-state segment (TSS) to which the guest attempted to switch

29:16

Reserved (cleared to 0)

31:30

Source of task switch initiation:
0: CALL instruction
1: IRET instruction
2: JMP instruction
3: Task gate in IDT

63:32

Reserved (cleared to 0). These bits exist only on processors that support Intel 64 architecture.

— For INVEPT, INVPCID, INVVPID, LGDT, LIDT, LLDT, LTR, SGDT, SIDT, SLDT, STR, VMCLEAR, VMPTRLD,
VMPTRST, VMREAD, VMWRITE, VMXON, XRSTORS, and XSAVES, the exit qualification receives the value of
the instruction’s displacement field, which is sign-extended to 64 bits if necessary (32 bits on processors
that do not support Intel 64 architecture). If the instruction has no displacement (for example, has a
register operand), zero is stored into the exit qualification.
On processors that support Intel 64 architecture, an exception is made for RIP-relative addressing (used
only in 64-bit mode). Such addressing causes an instruction to use an address that is the sum of the
displacement field and the value of RIP that references the following instruction. In this case, the exit
qualification is loaded with the sum of the displacement field and the appropriate RIP value.
In all cases, bits of this field beyond the instruction’s address size are undefined. For example, suppose
that the address-size field in the VM-exit instruction-information field (see Section 24.9.4 and Section
27.2.4) reports an n-bit address size. Then bits 63:n (bits 31:n on processors that do not support Intel 64
architecture) of the instruction displacement are undefined.
— For a control-register access, the exit qualification contains information about the access and has the
format given in Table 27-3.
— For MOV DR, the exit qualification contains information about the instruction and has the format given in
Table 27-4.
— For an I/O instruction, the exit qualification contains information about the instruction and has the format
given in Table 27-5.

Vol. 3C 27-5

VM EXITS

— For MWAIT, the exit qualification contains a value that indicates whether address-range monitoring
hardware was armed. The exit qualification is set either to 0 (if address-range monitoring hardware is not
armed) or to 1 (if address-range monitoring hardware is armed).
— For an APIC-access VM exit resulting from a linear access or a guest-physical access to the APIC-access
page (see Section 29.4), the exit qualification contains information about the access and has the format
given in Table 27-6.1
If the access to the APIC-access page occurred during execution of an instruction in enclave mode (and not
during delivery of an event incident to enclave mode), bits 11:0 of the exit qualification are cleared.
Such a VM exit that set bits 15:12 of the exit qualification to 0000b (data read during instruction execution)
or 0001b (data write during instruction execution) set bit 12—which distinguishes data read from data
write—to that which would have been stored in bit 1—W/R—of the page-fault error code had the access
caused a page fault instead of an APIC-access VM exit. This implies the following:

•

For an APIC-access VM exit caused by the CLFLUSH and CLFLUSHOPT instructions, the access type is
“data read during instruction execution.”

•

For an APIC-access VM exit caused by the ENTER instruction, the access type is “data write during
instruction execution.”

Table 27-3. Exit Qualification for Control-Register Accesses
Bit Positions

Contents

3:0

Number of control register (0 for CLTS and LMSW). Bit 3 is always 0 on processors that do not support Intel 64
architecture as they do not support CR8.

5:4

Access type:
0 = MOV to CR
1 = MOV from CR
2 = CLTS
3 = LMSW

6

LMSW operand type:
0 = register
1 = memory
For CLTS and MOV CR, cleared to 0

7

Reserved (cleared to 0)

11:8

For MOV CR, the general-purpose register:
0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8–15 represent R8–R15, respectively (used only on processors that support Intel 64 architecture)
For CLTS and LMSW, cleared to 0

15:12

Reserved (cleared to 0)

1. The exit qualification is undefined if the access was part of the logging of a branch record or a processor-event-based-sampling
(PEBS) record to the DS save area. It is recommended that software configure the paging structures so that no address in the DS
save area translates to an address on the APIC-access page.
27-6 Vol. 3C

VM EXITS

Table 27-3. Exit Qualification for Control-Register Accesses (Contd.)
Bit Positions
31:16

Contents
For LMSW, the LMSW source data
For CLTS and MOV CR, cleared to 0

63:32

Reserved (cleared to 0). These bits exist only on processors that support Intel 64 architecture.

•

For an APIC-access VM exit caused by the MASKMOVQ instruction or the MASKMOVDQU instruction, the
access type is “data write during instruction execution.”

•

For an APIC-access VM exit caused by the MONITOR instruction, the access type is “data read during
instruction execution.”

Such a VM exit stores 1 for bit 31 for IDT-vectoring information field (see Section 27.2.3) if and only if it
sets bits 15:12 of the exit qualification to 0011b (linear access during event delivery) or 1010b (guestphysical access during event delivery).
See Section 29.4.4 for further discussion of these instructions and APIC-access VM exits.
For APIC-access VM exits resulting from physical accesses to the APIC-access page (see Section 29.4.6),
the exit qualification is undefined.
— For an EPT violation, the exit qualification contains information about the access causing the EPT violation
and has the format given in Table 27-7.
As noted in that table, the format and meaning of the exit qualification depends on the setting of the
“mode-based execute control for EPT” VM-execution control and whether the processor supports advanced
VM-exit information for EPT violations.1
An EPT violation that occurs during as a result of execution of a read-modify-write operation sets bit 1 (data
write). Whether it also sets bit 0 (data read) is implementation-specific and, for a given implementation,
may differ for different kinds of read-modify-write operations.

Table 27-4. Exit Qualification for MOV DR
Bit Position(s)

Contents

2:0

Number of debug register

3

Reserved (cleared to 0)

4

Direction of access (0

7:5

Reserved (cleared to 0)

11:8

General-purpose register:

= MOV to DR; 1 = MOV from DR)

0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8 –15 = R8 – R15, respectively
63:12

Reserved (cleared to 0)

1. Software can determine whether advanced VM-exit information for EPT violations is supported by consulting the VMX capability
MSR IA32_VMX_EPT_VPID_CAP (see Appendix A.10).
Vol. 3C 27-7

VM EXITS

Table 27-5. Exit Qualification for I/O Instructions
Bit Position(s)

Contents

2:0

Size of access:
0 = 1-byte
1 = 2-byte
3 = 4-byte
Other values not used

3

Direction of the attempted access (0 = OUT, 1

= IN)

4

String instruction (0 = not string; 1 = string)

5

REP prefixed (0 = not REP; 1 = REP)

6

Operand encoding (0 = DX, 1 = immediate)

15:7

Reserved (cleared to 0)

31:16

Port number (as specified in DX or in an immediate operand)

63:32

Reserved (cleared to 0). These bits exist only on processors that support Intel 64 architecture.
Bit 12 is undefined in any of the following cases:

•
•

If the “NMI exiting” VM-execution control is 1 and the “virtual NMIs” VM-execution control is 0.
If the VM exit sets the valid bit in the IDT-vectoring information field (see Section 27.2.3).

Otherwise, bit 12 is defined as follows:

•

If the “virtual NMIs” VM-execution control is 0, the EPT violation was caused by a memory access as
part of execution of the IRET instruction, and blocking by NMI (see Table 24-3) was in effect before
execution of IRET, bit 12 is set to 1.

Table 27-6. Exit Qualification for APIC-Access VM Exits from Linear Accesses and Guest-Physical Accesses
Bit Position(s)

Contents

11:0

• If the APIC-access VM exit is due to a linear access, the offset of access within the APIC page.
• Undefined if the APIC-access VM exit is due a guest-physical access

15:12

Access type:
0 = linear access for a data read during instruction execution
1 = linear access for a data write during instruction execution
2 = linear access for an instruction fetch
3 = linear access (read or write) during event delivery
10 = guest-physical access during event delivery
15 = guest-physical access for an instruction fetch or during instruction execution
Other values not used

63:16

27-8 Vol. 3C

Reserved (cleared to 0). Bits 63:32 exist only on processors that support Intel 64 architecture.

VM EXITS

•

If the “virtual NMIs” VM-execution control is 1,the EPT violation was caused by a memory access as part
of execution of the IRET instruction, and virtual-NMI blocking was in effect before execution of IRET,
bit 12 is set to 1.

•

For all other relevant VM exits, bit 12 is cleared to 0.

— For VM exits caused as part of EOI virtualization (Section 29.1.4), bits 7:0 of the exit qualification are set
to vector of the virtual interrupt that was dismissed by the EOI virtualization. Bits above bit 7 are cleared.
— For APIC-write VM exits (Section 29.4.3.3), bits 11:0 of the exit qualification are set to the page offset of
the write access that caused the VM exit.1 Bits above bit 11 are cleared.
— For a VM exit due to a page-modification log-full event (Section 28.2.5), only bit 12 of the exit qualification
is defined, and only in some cases. It is undefined in the following cases:

•
•

If the “NMI exiting” VM-execution control is 1 and the “virtual NMIs” VM-execution control is 0.
If the VM exit sets the valid bit in the IDT-vectoring information field (see Section 27.2.3).

Otherwise, it is defined as follows:

•

If the “virtual NMIs” VM-execution control is 0, the page-modification log-full event was caused by a
memory access as part of execution of the IRET instruction, and blocking by NMI (see Table 24-3) was
in effect before execution of IRET, bit 12 is set to 1.

•

If the “virtual NMIs” VM-execution control is 1,the page-modification log-full event was caused by a
memory access as part of execution of the IRET instruction, and virtual-NMI blocking was in effect
before execution of IRET, bit 12 is set to 1.

•

For all other relevant VM exits, bit 12 is cleared to 0.

For these VM exits, all bits other than bit 12 are undefined.

•

Guest-linear address. For some VM exits, this field receives a linear address that pertains to the VM exit. The
field is set for different VM exits as follows:
— VM exits due to attempts to execute LMSW with a memory operand. In these cases, this field receives the
linear address of that operand. Bits 63:32 are cleared if the logical processor was not in 64-bit mode before
the VM exit.
— VM exits due to attempts to execute INS or OUTS for which the relevant segment is usable (if the relevant
segment is not usable, the value is undefined). (ES is always the relevant segment for INS; for OUTS, the
relevant segment is DS unless overridden by an instruction prefix.) The linear address is the base address
of relevant segment plus (E)DI (for INS) or (E)SI (for OUTS). Bits 63:32 are cleared if the logical processor
was not in 64-bit mode before the VM exit.

Table 27-7. Exit Qualification for EPT Violations
Bit Position(s)

Contents

0

Set if the access causing the EPT violation was a data read.1

1

Set if the access causing the EPT violation was a data write.1

2

Set if the access causing the EPT violation was an instruction fetch.

3

The logical-AND of bit 0 in the EPT paging-structure entries used to translate the guest-physical address of the
access causing the EPT violation (indicates whether the guest-physical address was readable).2

4

The logical-AND of bit 1 in the EPT paging-structure entries used to translate the guest-physical address of the
access causing the EPT violation (indicates whether the guest-physical address was writeable).

1. Execution of WRMSR with ECX = 83FH (self-IPI MSR) can lead to an APIC-write VM exit; the exit qualification for such an APIC-write
VM exit is 3F0H.
Vol. 3C 27-9

VM EXITS

Table 27-7. Exit Qualification for EPT Violations (Contd.)
Bit Position(s)

Contents

5

The logical-AND of bit 2 in the EPT paging-structure entries used to translate the guest-physical address of the
access causing the EPT violation.
If the “mode-based execute control for EPT” VM-execution control is 0, this indicates whether the guest-physical
address was executable. If that control is 1, this indicates whether the guest-physical address was executable
for supervisor-mode linear addresses.

6

If the “mode-based execute control” VM-execution control is 0, the value of this bit is undefined. If that control is
1, this bit is the logical-AND of bit 10 in the EPT paging-structures entries used to translate the guest-physical
address of the access causing the EPT violation. In this case, it indicates whether the guest-physical address was
executable for user-mode linear addresses.

7

Set if the guest linear-address field is valid.
The guest linear-address field is valid for all EPT violations except those resulting from an attempt to load the
guest PDPTEs as part of the execution of the MOV CR instruction.

8

If bit 7 is 1:
• Set if the access causing the EPT violation is to a guest-physical address that is the translation of a linear
address.
• Clear if the access causing the EPT violation is to a paging-structure entry as part of a page walk or the
update of an accessed or dirty bit.
Reserved if bit 7 is 0 (cleared to 0).

9

If bit 7 is 1, bit 8 is 1, and the processor supports advanced VM-exit information for EPT violations,3 this bit is 0
if the linear address is a supervisor-mode linear address and 1 if it is a user-mode linear address. (If CR0.PG = 0,
the translation of every linear address is a user-mode linear address and thus this bit will be 1.) Otherwise, this
bit is undefined.

10

If bit 7 is 1, bit 8 is 1, and the processor supports advanced VM-exit information for EPT violations,3 this bit is 0
if paging translates the linear address to a read-only page and 1 if it translates to a read/write page. (If CR0.PG =
0, every linear address is read/write and thus this bit will be 1.) Otherwise, this bit is undefined.

11

If bit 7 is 1, bit 8 is 1, and the processor supports advanced VM-exit information for EPT violations,3 this bit is 0
if paging translates the linear address to an executable page and 1 if it translates to an execute-disable page. (If
CR0.PG = 0, CR4.PAE = 0, or IA32_EFER.NXE = 0, every linear address is executable and thus this bit will be 0.)
Otherwise, this bit is undefined.

12

NMI unblocking due to IRET

63:13

Reserved (cleared to 0).

NOTES:
1. If accessed and dirty flags for EPT are enabled, processor accesses to guest paging-structure entries are treated as writes with
regard to EPT violations (see Section 28.2.3.2). If such an access causes an EPT violation, the processor sets both bit 0 and bit 1 of
the exit qualification.
2. Bits 5:3 are cleared to 0 if any of EPT paging-structure entries used to translate the guest-physical address of the access causing the
EPT violation is not present (see Section 28.2.2).
3. Software can determine whether advanced VM-exit information for EPT violations is supported by consulting the VMX capability
MSR IA32_VMX_EPT_VPID_CAP (see Appendix A.10).
— VM exits due to EPT violations that set bit 7 of the exit qualification (see Table 27-7; these are all EPT
violations except those resulting from an attempt to load the PDPTEs as of execution of the MOV CR
instruction). The linear address may translate to the guest-physical address whose access caused the EPT
violation. Alternatively, translation of the linear address may reference a paging-structure entry whose
access caused the EPT violation. Bits 63:32 are cleared if the logical processor was not in 64-bit mode
before the VM exit.

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VM EXITS

If the EPT violation occurred during execution of an instruction in enclave mode (and not during delivery of
an event incident to enclave mode), bits 11:0 of this field are cleared.
— For all other VM exits, the field is undefined.

•

Guest-physical address. For a VM exit due to an EPT violation or an EPT misconfiguration, this field receives
the guest-physical address that caused the EPT violation or EPT misconfiguration. For all other VM exits, the
field is undefined.
If the EPT violation or EPT misconfiguration occurred during execution of an instruction in enclave mode (and
not during delivery of an event incident to enclave mode), bits 11:0 of this field are cleared.

27.2.2

Information for VM Exits Due to Vectored Events

Section 24.9.2 defines fields containing information for VM exits due to the following events: exceptions (including
those generated by the instructions INT3, INTO, BOUND, and UD); external interrupts that occur while the
“acknowledge interrupt on exit” VM-exit control is 1; and non-maskable interrupts (NMIs). Such VM exits include
those that occur on an attempt at a task switch that causes an exception before generating the VM exit due to the
task switch that causes the VM exit.
The following items detail the use of these fields:

•

VM-exit interruption information (format given in Table 24-15). The following items detail how this field is
established for VM exits due to these events:
— For an exception, bits 7:0 receive the exception vector (at most 31). For an NMI, bits 7:0 are set to 2. For
an external interrupt, bits 7:0 receive the vector.
— Bits 10:8 are set to 0 (external interrupt), 2 (non-maskable interrupt), 3 (hardware exception), or 6
(software exception). Hardware exceptions comprise all exceptions except breakpoint exceptions (#BP;
generated by INT3) and overflow exceptions (#OF; generated by INTO); these are software exceptions. (A
#BP that occurs in enclave mode is considered a hardware exception.) BOUND-range exceeded exceptions
(#BR; generated by BOUND) and invalid opcode exceptions (#UD) generated by UD are hardware
exceptions.
— Bit 11 is set to 1 if the VM exit is caused by a hardware exception that would have delivered an error code
on the stack. This bit is always 0 if the VM exit occurred while the logical processor was in real-address
mode (CR0.PE=0).1 If bit 11 is set to 1, the error code is placed in the VM-exit interruption error code (see
below).
— Bit 12 is undefined in any of the following cases:

•
•
•

If the “NMI exiting” VM-execution control is 1 and the “virtual NMIs” VM-execution control is 0.
If the VM exit sets the valid bit in the IDT-vectoring information field (see Section 27.2.3).
If the VM exit is due to a double fault (the interruption type is hardware exception and the vector is 8).

Otherwise, bit 12 is defined as follows:

•

If the “virtual NMIs” VM-execution control is 0, the VM exit is due to a fault on the IRET instruction
(other than a debug exception for an instruction breakpoint), and blocking by NMI (see Table 24-3) was
in effect before execution of IRET, bit 12 is set to 1.

•

If the “virtual NMIs” VM-execution control is 1, the VM exit is due to a fault on the IRET instruction
(other than a debug exception for an instruction breakpoint), and virtual-NMI blocking was in effect
before execution of IRET, bit 12 is set to 1.

•

For all other relevant VM exits, bit 12 is cleared to 0.2

— Bits 30:13 are always set to 0.
1. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PE must be 1 in VMX operation, a logical processor cannot be in realaddress mode unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
2. The conditions imply that, if the “NMI exiting” VM-execution control is 0 or the “virtual NMIs” VM-execution control is 1, bit 12 is
always cleared to 0 by VM exits due to debug exceptions.
Vol. 3C 27-11

VM EXITS

— Bit 31 is always set to 1.
For other VM exits (including those due to external interrupts when the “acknowledge interrupt on exit” VM-exit
control is 0), the field is marked invalid (by clearing bit 31) and the remainder of the field is undefined.

•

VM-exit interruption error code.
— For VM exits that set both bit 31 (valid) and bit 11 (error code valid) in the VM-exit interruption-information
field, this field receives the error code that would have been pushed on the stack had the event causing the
VM exit been delivered normally through the IDT. The EXT bit is set in this field exactly when it would be set
normally. For exceptions that occur during the delivery of double fault (if the IDT-vectoring information field
indicates a double fault), the EXT bit is set to 1, assuming that (1) that the exception would produce an
error code normally (if not incident to double-fault delivery) and (2) that the error code uses the EXT bit
(not for page faults, which use a different format).
— For other VM exits, the value of this field is undefined.

27.2.3

Information for VM Exits During Event Delivery

Section 24.9.3 defined fields containing information for VM exits that occur while delivering an event through the
IDT and as a result of any of the following cases:1

•

A fault occurs during event delivery and causes a VM exit (because the bit associated with the fault is set to 1
in the exception bitmap).

•

A task switch is invoked through a task gate in the IDT. The VM exit occurs due to the task switch only after the
initial checks of the task switch pass (see Section 25.4.2).

•
•

Event delivery causes an APIC-access VM exit (see Section 29.4).
An EPT violation, EPT misconfiguration, or page-modification log-full event that occurs during event delivery.

These fields are used for VM exits that occur during delivery of events injected as part of VM entry (see Section
26.5.1.2).
A VM exit is not considered to occur during event delivery in any of the following circumstances:

•

The original event causes the VM exit directly (for example, because the original event is a non-maskable
interrupt (NMI) and the “NMI exiting” VM-execution control is 1).

•
•
•

The original event results in a double-fault exception that causes the VM exit directly.
The VM exit occurred as a result of fetching the first instruction of the handler invoked by the event delivery.
The VM exit is caused by a triple fault.

The following items detail the use of these fields:

•

IDT-vectoring information (format given in Table 24-16). The following items detail how this field is established
for VM exits that occur during event delivery:
— If the VM exit occurred during delivery of an exception, bits 7:0 receive the exception vector (at most 31).
If the VM exit occurred during delivery of an NMI, bits 7:0 are set to 2. If the VM exit occurred during
delivery of an external interrupt, bits 7:0 receive the vector.
— Bits 10:8 are set to indicate the type of event that was being delivered when the VM exit occurred: 0
(external interrupt), 2 (non-maskable interrupt), 3 (hardware exception), 4 (software interrupt), 5
(privileged software interrupt), or 6 (software exception).
Hardware exceptions comprise all exceptions except breakpoint exceptions (#BP; generated by INT3) and
overflow exceptions (#OF; generated by INTO); these are software exceptions. (A #BP that occurs in
enclave mode is considered a hardware exception.) BOUND-range exceeded exceptions (#BR; generated
by BOUND) and invalid opcode exceptions (#UD) generated by UD are hardware exceptions.
Bits 10:8 may indicate privileged software interrupt if such an event was injected as part of VM entry.

1. This includes the case in which a VM exit occurs while delivering a software interrupt (INT n) through the 16-bit IVT (interrupt vector table) that is used in virtual-8086 mode with virtual-machine extensions (if RFLAGS.VM = CR4.VME = 1).
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VM EXITS

— Bit 11 is set to 1 if the VM exit occurred during delivery of a hardware exception that would have delivered
an error code on the stack. This bit is always 0 if the VM exit occurred while the logical processor was in
real-address mode (CR0.PE=0).1 If bit 11 is set to 1, the error code is placed in the IDT-vectoring error
code (see below).
— Bit 12 is undefined.
— Bits 30:13 are always set to 0.
— Bit 31 is always set to 1.
For other VM exits, the field is marked invalid (by clearing bit 31) and the remainder of the field is undefined.

•

IDT-vectoring error code.
— For VM exits that set both bit 31 (valid) and bit 11 (error code valid) in the IDT-vectoring information field,
this field receives the error code that would have been pushed on the stack by the event that was being
delivered through the IDT at the time of the VM exit. The EXT bit is set in this field when it would be set
normally.
— For other VM exits, the value of this field is undefined.

27.2.4

Information for VM Exits Due to Instruction Execution

Section 24.9.4 defined fields containing information for VM exits that occur due to instruction execution. (The VMexit instruction length is also used for VM exits that occur during the delivery of a software interrupt or software
exception.) The following items detail their use.

•

VM-exit instruction length. This field is used in the following cases:
— For fault-like VM exits due to attempts to execute one of the following instructions that cause VM exits
unconditionally (see Section 25.1.2) or based on the settings of VM-execution controls (see Section
25.1.3): CLTS, CPUID, ENCLS, GETSEC, HLT, IN, INS, INVD, INVEPT, INVLPG, INVPCID, INVVPID, LGDT,
LIDT, LLDT, LMSW, LTR, MONITOR, MOV CR, MOV DR, MWAIT, OUT, OUTS, PAUSE, RDMSR, RDPMC,
RDRAND, RDSEED, RDTSC, RDTSCP, RSM, SGDT, SIDT, SLDT, STR, VMCALL, VMCLEAR, VMLAUNCH,
VMPTRLD, VMPTRST, VMREAD, VMRESUME, VMWRITE, VMXOFF, VMXON, WBINVD, WRMSR, XRSTORS,
XSETBV, and XSAVES.2
— For VM exits due to software exceptions (those generated by executions of INT3 or INTO).
— For VM exits due to faults encountered during delivery of a software interrupt, privileged software
exception, or software exception.
— For VM exits due to attempts to effect a task switch via instruction execution. These are VM exits that
produce an exit reason indicating task switch and either of the following:

•
•

An exit qualification indicating execution of CALL, IRET, or JMP instruction.
An exit qualification indicating a task gate in the IDT and an IDT-vectoring information field indicating
that the task gate was encountered during delivery of a software interrupt, privileged software
exception, or software exception.

— For APIC-access VM exits and for VM exits caused by EPT violations and page-modification log-full events
encountered during delivery of a software interrupt, privileged software exception, or software exception.3
— For VM exits due executions of VMFUNC that fail because one of the following is true:

1. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PE must be 1 in VMX operation, a logical processor cannot be in realaddress mode unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
2. This item applies only to fault-like VM exits. It does not apply to trap-like VM exits following executions of the MOV to CR8 instruction when the “use TPR shadow” VM-execution control is 1 or to those following executions of the WRMSR instruction when the
“virtualize x2APIC mode” VM-execution control is 1.
3. The VM-exit instruction-length field is not defined following APIC-access VM exits resulting from physical accesses (see Section
29.4.6) even if encountered during delivery of a software interrupt, privileged software exception, or software exception.
Vol. 3C 27-13

VM EXITS

•

EAX indicates a VM function that is not enabled (the bit at position EAX is 0 in the VM-function controls;
see Section 25.5.5.2).

•

EAX = 0 and either ECX ≥ 512 or the value of ECX selects an invalid tentative EPTP value (see Section
25.5.5.3).

In all the above cases, this field receives the length in bytes (1–15) of the instruction (including any instruction
prefixes) whose execution led to the VM exit (see the next paragraph for one exception).
The cases of VM exits encountered during delivery of a software interrupt, privileged software exception, or
software exception include those encountered during delivery of events injected as part of VM entry (see
Section 26.5.1.2). If the original event was injected as part of VM entry, this field receives the value of the VMentry instruction length.
All VM exits other than those listed in the above items leave this field undefined.
If the VM exit occurred in enclave mode, this field is cleared (none of the previous items apply).

Table 27-8. Format of the VM-Exit Instruction-Information Field as Used for INS and OUTS
Bit Position(s) Content
6:0

Undefined.

9:7

Address size:
0: 16-bit
1: 32-bit
2: 64-bit (used only on processors that support Intel 64 architecture)
Other values not used.

14:10

Undefined.

17:15

Segment register:
0: ES
1: CS
2: SS
3: DS
4: FS
5: GS
Other values not used. Undefined for VM exits due to execution of INS.

31:18

•

Undefined.

VM-exit instruction information. For VM exits due to attempts to execute INS, INVEPT, INVPCID, INVVPID,
LIDT, LGDT, LLDT, LTR, OUTS, RDRAND, RDSEED, SIDT, SGDT, SLDT, STR, VMCLEAR, VMPTRLD, VMPTRST,
VMREAD, VMWRITE, VMXON, XRSTORS, or XSAVES, this field receives information about the instruction that
caused the VM exit. The format of the field depends on the identity of the instruction causing the VM exit:
— For VM exits due to attempts to execute INS or OUTS, the field has the format is given in Table 27-8.1
— For VM exits due to attempts to execute INVEPT, INVPCID, or INVVPID, the field has the format is given in
Table 27-9.
— For VM exits due to attempts to execute LIDT, LGDT, SIDT, or SGDT, the field has the format is given in
Table 27-10.
— For VM exits due to attempts to execute LLDT, LTR, SLDT, or STR, the field has the format is given in
Table 27-11.
— For VM exits due to attempts to execute RDRAND or RDSEED, the field has the format is given in
Table 27-12.

1. The format of the field was undefined for these VM exits on the first processors to support the virtual-machine extensions. Software can determine whether the format specified in Table 27-8 is used by consulting the VMX capability MSR IA32_VMX_BASIC
(see Appendix A.1).
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VM EXITS

— For VM exits due to attempts to execute VMCLEAR, VMPTRLD, VMPTRST, VMXON, XRSTORS, or XSAVES,
the field has the format is given in Table 27-13.
— For VM exits due to attempts to execute VMREAD or VMWRITE, the field has the format is given in
Table 27-14.
For all other VM exits, the field is undefined, unless the VM exit occurred in enclave mode, in which case the
field is cleared.

•

I/O RCX, I/O RSI, I/O RDI, I/O RIP. These fields are undefined except for SMM VM exits due to systemmanagement interrupts (SMIs) that arrive immediately after retirement of I/O instructions. See Section
34.15.2.3. Note that, if the VM exit occurred in enclave mode, these fields are all cleared.

Table 27-9. Format of the VM-Exit Instruction-Information Field as Used for INVEPT, INVPCID, and INVVPID
Bit Position(s) Content
1:0

Scaling:
0: no scaling
1: scale by 2
2: scale by 4
3: scale by 8 (used only on processors that support Intel 64 architecture)
Undefined for instructions with no index register (bit 22 is set).

6:2

Undefined.

9:7

Address size:
0: 16-bit
1: 32-bit
2: 64-bit (used only on processors that support Intel 64 architecture)
Other values not used.

10

Cleared to 0.

14:11

Undefined.

17:15

Segment register:
0: ES
1: CS
2: SS
3: DS
4: FS
5: GS
Other values not used.

21:18

IndexReg:
0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8–15 represent R8–R15, respectively (used only on processors that support Intel 64 architecture)
Undefined for instructions with no index register (bit 22 is set).

22

IndexReg invalid (0 = valid; 1 = invalid)

26:23

BaseReg (encoded as IndexReg above)
Undefined for memory instructions with no base register (bit 27 is set).

27

BaseReg invalid (0 = valid; 1 = invalid)

31:28

Reg2 (same encoding as IndexReg above)

Vol. 3C 27-15

VM EXITS

Table 27-10. Format of the VM-Exit Instruction-Information Field as Used for LIDT, LGDT, SIDT, or SGDT
Bit Position(s) Content
1:0

Scaling:
0: no scaling
1: scale by 2
2: scale by 4
3: scale by 8 (used only on processors that support Intel 64 architecture)
Undefined for instructions with no index register (bit 22 is set).

6:2

Undefined.

9:7

Address size:
0: 16-bit
1: 32-bit
2: 64-bit (used only on processors that support Intel 64 architecture)
Other values not used.

10

Cleared to 0.

11

Operand size:
0: 16-bit
1: 32-bit
Undefined for VM exits from 64-bit mode.

14:12

Undefined.

17:15

Segment register:
0: ES
1: CS
2: SS
3: DS
4: FS
5: GS
Other values not used.

21:18

IndexReg:
0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8–15 represent R8–R15, respectively (used only on processors that support Intel 64 architecture)
Undefined for instructions with no index register (bit 22 is set).

22

IndexReg invalid (0 = valid; 1 = invalid)

26:23

BaseReg (encoded as IndexReg above)

27

BaseReg invalid (0 = valid; 1 = invalid)

29:28

Instruction identity:

Undefined for instructions with no base register (bit 27 is set).

0: SGDT
1: SIDT
2: LGDT
3: LIDT

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VM EXITS

Table 27-10. Format of the VM-Exit Instruction-Information Field as Used for LIDT, LGDT, SIDT, or SGDT (Contd.)
Bit Position(s) Content
31:30

Undefined.

Table 27-11. Format of the VM-Exit Instruction-Information Field as Used for LLDT, LTR, SLDT, and STR
Bit Position(s) Content
1:0

Scaling:
0: no scaling
1: scale by 2
2: scale by 4
3: scale by 8 (used only on processors that support Intel 64 architecture)
Undefined for register instructions (bit 10 is set) and for memory instructions with no index register (bit 10 is clear
and bit 22 is set).

2

Undefined.

6:3

Reg1:
0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8–15 represent R8–R15, respectively (used only on processors that support Intel 64 architecture)
Undefined for memory instructions (bit 10 is clear).

9:7

Address size:
0: 16-bit
1: 32-bit
2: 64-bit (used only on processors that support Intel 64 architecture)
Other values not used. Undefined for register instructions (bit 10 is set).

10

Mem/Reg (0 = memory; 1 = register).

14:11

Undefined.

17:15

Segment register:
0: ES
1: CS
2: SS
3: DS
4: FS
5: GS
Other values not used. Undefined for register instructions (bit 10 is set).

21:18

IndexReg (encoded as Reg1 above)
Undefined for register instructions (bit 10 is set) and for memory instructions with no index register (bit 10 is clear
and bit 22 is set).

22

IndexReg invalid (0 = valid; 1 = invalid)
Undefined for register instructions (bit 10 is set).

26:23

BaseReg (encoded as Reg1 above)
Undefined for register instructions (bit 10 is set) and for memory instructions with no base register (bit 10 is clear
and bit 27 is set).

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VM EXITS

Table 27-11. Format of the VM-Exit Instruction-Information Field as Used for LLDT, LTR, SLDT, and STR (Contd.)
Bit Position(s) Content
27

BaseReg invalid (0 = valid; 1 = invalid)
Undefined for register instructions (bit 10 is set).

29:28

Instruction identity:
0: SLDT
1: STR
2: LLDT
3: LTR

31:30

Undefined.

Table 27-12. Format of the VM-Exit Instruction-Information Field as Used for RDRAND and RDSEED
Bit Position(s) Content
2:0

Undefined.

6:3

Destination register:
0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8–15 represent R8–R15, respectively (used only on processors that support Intel 64 architecture)

10:7

Undefined.

12:11

Operand size:
0: 16-bit
1: 32-bit
2: 64-bit
The value 3 is not used.

31:13

Undefined.

Table 27-13. Format of the VM-Exit Instruction-Information Field as Used for VMCLEAR, VMPTRLD, VMPTRST,
VMXON, XRSTORS, and XSAVES
Bit Position(s) Content
1:0

Scaling:
0: no scaling
1: scale by 2
2: scale by 4
3: scale by 8 (used only on processors that support Intel 64 architecture)
Undefined for instructions with no index register (bit 22 is set).

6:2

Undefined.

9:7

Address size:
0: 16-bit
1: 32-bit
2: 64-bit (used only on processors that support Intel 64 architecture)
Other values not used.

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VM EXITS

Table 27-13. Format of the VM-Exit Instruction-Information Field as Used for VMCLEAR, VMPTRLD, VMPTRST,
VMXON, XRSTORS, and XSAVES (Contd.)
Bit Position(s) Content
10

Cleared to 0.

14:11

Undefined.

17:15

Segment register:
0: ES
1: CS
2: SS
3: DS
4: FS
5: GS
Other values not used.

21:18

IndexReg:
0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8–15 represent R8–R15, respectively (used only on processors that support Intel 64 architecture)
Undefined for instructions with no index register (bit 22 is set).

22

IndexReg invalid (0 = valid; 1 = invalid)

26:23

BaseReg (encoded as IndexReg above)
Undefined for instructions with no base register (bit 27 is set).

27

BaseReg invalid (0 = valid; 1 = invalid)

31:28

Undefined.

Table 27-14. Format of the VM-Exit Instruction-Information Field as Used for VMREAD and VMWRITE
Bit Position(s) Content
1:0

Scaling:
0: no scaling
1: scale by 2
2: scale by 4
3: scale by 8 (used only on processors that support Intel 64 architecture)
Undefined for register instructions (bit 10 is set) and for memory instructions with no index register (bit 10 is clear
and bit 22 is set).

2

Undefined.

Vol. 3C 27-19

VM EXITS

Table 27-14. Format of the VM-Exit Instruction-Information Field as Used for VMREAD and VMWRITE (Contd.)
Bit Position(s) Content
6:3

Reg1:
0 = RAX
1 = RCX
2 = RDX
3 = RBX
4 = RSP
5 = RBP
6 = RSI
7 = RDI
8–15 represent R8–R15, respectively (used only on processors that support Intel 64 architecture)
Undefined for memory instructions (bit 10 is clear).

9:7

Address size:
0: 16-bit
1: 32-bit
2: 64-bit (used only on processors that support Intel 64 architecture)
Other values not used. Undefined for register instructions (bit 10 is set).

10

Mem/Reg (0 = memory; 1 = register).

14:11

Undefined.

17:15

Segment register:
0: ES
1: CS
2: SS
3: DS
4: FS
5: GS
Other values not used. Undefined for register instructions (bit 10 is set).

21:18

IndexReg (encoded as Reg1 above)
Undefined for register instructions (bit 10 is set) and for memory instructions with no index register (bit 10 is clear
and bit 22 is set).

22

IndexReg invalid (0 = valid; 1 = invalid)
Undefined for register instructions (bit 10 is set).

26:23

BaseReg (encoded as Reg1 above)
Undefined for register instructions (bit 10 is set) and for memory instructions with no base register (bit 10 is clear
and bit 27 is set).

27

BaseReg invalid (0 = valid; 1 = invalid)

31:28

Reg2 (same encoding as Reg1 above)

Undefined for register instructions (bit 10 is set).

27.3

SAVING GUEST STATE

Each field in the guest-state area of the VMCS (see Section 24.4) is written with the corresponding component of
processor state. On processors that support Intel 64 architecture, the full values of each natural-width field (see
Section 24.11.2) is saved regardless of the mode of the logical processor before and after the VM exit.
In general, the state saved is that which was in the logical processor at the time the VM exit commences. See
Section 27.1 for a discussion of which architectural updates occur at that time.
Section 27.3.1 through Section 27.3.4 provide details for how certain components of processor state are saved.
These sections reference VMCS fields that correspond to processor state. Unless otherwise stated, these references
are to fields in the guest-state area.
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27.3.1

Saving Control Registers, Debug Registers, and MSRs

Contents of certain control registers, debug registers, and MSRs is saved as follows:

•

The contents of CR0, CR3, CR4, and the IA32_SYSENTER_CS, IA32_SYSENTER_ESP, and IA32_SYSENTER_EIP
MSRs are saved into the corresponding fields. Bits 63:32 of the IA32_SYSENTER_CS MSR are not saved. On
processors that do not support Intel 64 architecture, bits 63:32 of the IA32_SYSENTER_ESP and
IA32_SYSENTER_EIP MSRs are not saved.

•

If the “save debug controls” VM-exit control is 1, the contents of DR7 and the IA32_DEBUGCTL MSR are saved
into the corresponding fields. The first processors to support the virtual-machine extensions supported only the
1-setting of this control and thus always saved data into these fields.

•

If the “save IA32_PAT” VM-exit control is 1, the contents of the IA32_PAT MSR are saved into the corresponding
field.

•

If the “save IA32_EFER” VM-exit control is 1, the contents of the IA32_EFER MSR are saved into the corresponding field.

•

If the processor supports either the 1-setting of the “load IA32_BNDCFGS” VM-entry control or that of the
“clear IA32_BNDCFGS” VM-exit control, the contents of the IA32_BNDCFGS MSR are saved into the corresponding field.

•

The value of the SMBASE field is undefined after all VM exits except SMM VM exits. See Section 34.15.2.

27.3.2

Saving Segment Registers and Descriptor-Table Registers

For each segment register (CS, SS, DS, ES, FS, GS, LDTR, or TR), the values saved for the base-address, segmentlimit, and access rights are based on whether the register was unusable (see Section 24.4.1) before the VM exit:

•

If the register was unusable, the values saved into the following fields are undefined: (1) base address;
(2) segment limit; and (3) bits 7:0 and bits 15:12 in the access-rights field. The following exceptions apply:
— CS.

•
•

The base-address and segment-limit fields are saved.
The L, D, and G bits are saved in the access-rights field.

— SS.

•
•

DPL is saved in the access-rights field.
On processors that support Intel 64 architecture, bits 63:32 of the value saved for the base address are
always zero.

— DS and ES. On processors that support Intel 64 architecture, bits 63:32 of the values saved for the base
addresses are always zero.
— FS and GS. The base-address field is saved.
— LDTR. The value saved for the base address is always canonical.

•

If the register was not unusable, the values saved into the following fields are those which were in the register
before the VM exit: (1) base address; (2) segment limit; and (3) bits 7:0 and bits 15:12 in access rights.

•

Bits 31:17 and 11:8 in the access-rights field are always cleared. Bit 16 is set to 1 if and only if the segment is
unusable.

The contents of the GDTR and IDTR registers are saved into the corresponding base-address and limit fields.

27.3.3

Saving RIP, RSP, and RFLAGS

The contents of the RIP, RSP, and RFLAGS registers are saved as follows:

•

The value saved in the RIP field is determined by the nature and cause of the VM exit:
— If the VM exit occurred in enclave mode, the value saved is the AEP of interrupted enclave thread (the
remaining items do not apply).

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VM EXITS

— If the VM exit occurs due to by an attempt to execute an instruction that causes VM exits unconditionally or
that has been configured to cause a VM exit via the VM-execution controls, the value saved references that
instruction.
— If the VM exit is caused by an occurrence of an INIT signal, a start-up IPI (SIPI), or system-management
interrupt (SMI), the value saved is that which was in RIP before the event occurred.
— If the VM exit occurs due to the 1-setting of either the “interrupt-window exiting” VM-execution control or
the “NMI-window exiting” VM-execution control, the value saved is that which would be in the register had
the VM exit not occurred.
— If the VM exit is due to an external interrupt, non-maskable interrupt (NMI), or hardware exception (as
defined in Section 27.2.2), the value saved is the return pointer that would have been saved (either on the
stack had the event been delivered through a trap or interrupt gate,1 or into the old task-state segment had
the event been delivered through a task gate).
— If the VM exit is due to a triple fault, the value saved is the return pointer that would have been saved
(either on the stack had the event been delivered through a trap or interrupt gate, or into the old task-state
segment had the event been delivered through a task gate) had delivery of the double fault not
encountered the nested exception that caused the triple fault.
— If the VM exit is due to a software exception (due to an execution of INT3 or INTO), the value saved
references the INT3 or INTO instruction that caused that exception.
— Suppose that the VM exit is due to a task switch that was caused by execution of CALL, IRET, or JMP or by
execution of a software interrupt (INT n) or software exception (due to execution of INT3 or INTO) that
encountered a task gate in the IDT. The value saved references the instruction that caused the task switch
(CALL, IRET, JMP, INT n, INT3, or INTO).
— Suppose that the VM exit is due to a task switch that was caused by a task gate in the IDT that was
encountered for any reason except the direct access by a software interrupt or software exception. The
value saved is that which would have been saved in the old task-state segment had the task switch
completed normally.
— If the VM exit is due to an execution of MOV to CR8 or WRMSR that reduced the value of bits 7:4 of VTPR
(see Section 29.1.1) below that of TPR threshold VM-execution control field (see Section 29.1.2), the value
saved references the instruction following the MOV to CR8 or WRMSR.
— If the VM exit was caused by APIC-write emulation (see Section 29.4.3.2) that results from an APIC access
as part of instruction execution, the value saved references the instruction following the one whose
execution caused the APIC-write emulation.

•
•

The contents of the RSP register are saved into the RSP field.
With the exception of the resume flag (RF; bit 16), the contents of the RFLAGS register is saved into the
RFLAGS field. RFLAGS.RF is saved as follows:
— If the VM exit occurred in enclave mode, the value saved is 0 (the remaining items do not apply).
— If the VM exit is caused directly by an event that would normally be delivered through the IDT, the value
saved is that which would appear in the saved RFLAGS image (either that which would be saved on the
stack had the event been delivered through a trap or interrupt gate2 or into the old task-state segment had
the event been delivered through a task gate) had the event been delivered through the IDT. See below for
VM exits due to task switches caused by task gates in the IDT.
— If the VM exit is caused by a triple fault, the value saved is that which the logical processor would have in
RF in the RFLAGS register had the triple fault taken the logical processor to the shutdown state.
— If the VM exit is caused by a task switch (including one caused by a task gate in the IDT), the value saved
is that which would have been saved in the RFLAGS image in the old task-state segment (TSS) had the task
switch completed normally without exception.

1. The reference here is to the full value of RIP before any truncation that would occur had the stack width been only 32 bits or 16
bits.
2. The reference here is to the full value of RFLAGS before any truncation that would occur had the stack width been only 32 bits or
16 bits.
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VM EXITS

— If the VM exit is caused by an attempt to execute an instruction that unconditionally causes VM exits or one
that was configured to do with a VM-execution control, the value saved is 0.1
— For APIC-access VM exits and for VM exits caused by EPT violations, EPT misconfigurations, and pagemodification log-full events, the value saved depends on whether the VM exit occurred during delivery of an
event through the IDT:

•

If the VM exit stored 0 for bit 31 for IDT-vectoring information field (because the VM exit did not occur
during delivery of an event through the IDT; see Section 27.2.3), the value saved is 1.

•

If the VM exit stored 1 for bit 31 for IDT-vectoring information field (because the VM exit did occur
during delivery of an event through the IDT), the value saved is the value that would have appeared in
the saved RFLAGS image had the event been delivered through the IDT (see above).

— For all other VM exits, the value saved is the value RFLAGS.RF had before the VM exit occurred.

27.3.4

Saving Non-Register State

Information corresponding to guest non-register state is saved as follows:

•

The activity-state field is saved with the logical processor’s activity state before the VM exit.2 See Section 27.1
for details of how events leading to a VM exit may affect the activity state.

•

The interruptibility-state field is saved to reflect the logical processor’s interruptibility before the VM exit.
— See Section 27.1 for details of how events leading to a VM exit may affect this state.
— VM exits that end outside system-management mode (SMM) save bit 2 (blocking by SMI) as 0 regardless
of the state of such blocking before the VM exit.
— Bit 3 (blocking by NMI) is treated specially if the “virtual NMIs” VM-execution control is 1. In this case, the
value saved for this field does not indicate the blocking of NMIs but rather the state of virtual-NMI blocking.
— Bit 4 (enclave interruption) is set to 1 if the VM exit occurred while the logical processor was in enclave
mode.
Such VM exits includes those caused by interrupts, non-maskable interrupts, system-management
interrupts, INIT signals, and exceptions occurring in enclave mode as well as exceptions encountered
during the delivery of such events incident to enclave mode.
A VM exit that is incident to delivery of an event injected by VM entry leaves this bit unmodified.

•

The pending debug exceptions field is saved as clear for all VM exits except the following:
— A VM exit caused by an INIT signal, a machine-check exception, or a system-management interrupt (SMI).
— A VM exit with basic exit reason “TPR below threshold”,3 “virtualized EOI”, “APIC write”, or “monitor trap
flag.”
— VM exits that are not caused by debug exceptions and that occur while there is MOV-SS blocking of debug
exceptions.
For VM exits that do not clear the field, the value saved is determined as follows:
— Each of bits 3:0 may be set if it corresponds to a matched breakpoint. This may be true even if the corresponding breakpoint is not enabled in DR7.
— Suppose that a VM exit is due to an INIT signal, a machine-check exception, or an SMI; or that a VM exit
has basic exit reason “TPR below threshold” or “monitor trap flag.” In this case, the value saved sets bits
corresponding to the causes of any debug exceptions that were pending at the time of the VM exit.

1. This is true even if RFLAGS.RF was 1 before the instruction was executed. If, in response to such a VM exit, a VM monitor re-enters
the guest to re-execute the instruction that caused the VM exit (for example, after clearing the VM-execution control that caused
the VM exit), the instruction may encounter a code breakpoint that has already been processed. A VM monitor can avoid this by setting the guest value of RFLAGS.RF to 1 before resuming guest software.
2. If this activity state was an inactive state resulting from execution of a specific instruction (HLT or MWAIT), the value saved for RIP
by that VM exit will reference the following instruction.
3. This item includes VM exits that occur as a result of certain VM entries (Section 26.6.7).
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VM EXITS

If the VM exit occurs immediately after VM entry, the value saved may match that which was loaded on
VM entry (see Section 26.6.3). Otherwise, the following items apply:

•

Bit 12 (enabled breakpoint) is set to 1 in any of the following cases:
— If there was at least one matched data or I/O breakpoint that was enabled in DR7.
— If it had been set on VM entry, causing there to be valid pending debug exceptions (see Section
26.6.3) and the VM exit occurred before those exceptions were either delivered or lost.
— If the XBEGIN instruction was executed immediately before the VM exit and advanced debugging of
RTM transactional regions had been enabled (see Section 16.3.7, “RTM-Enabled Debugger
Support,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1). (This does
not apply to VM exits with basic exit reason “monitor trap flag.”)
In other cases, bit 12 is cleared to 0.

•

Bit 14 (BS) is set if RFLAGS.TF = 1 in either of the following cases:
— IA32_DEBUGCTL.BTF = 0 and the cause of a pending debug exception was the execution of a single
instruction.
— IA32_DEBUGCTL.BTF = 1 and the cause of a pending debug exception was a taken branch.

•

Bit 16 (RTM) is set if a debug exception (#DB) or a breakpoint exception (#BP) occurred inside an RTM
region while advanced debugging of RTM transactional regions had been enabled. (This does not apply
to VM exits with basic exit reason “monitor trap flag.”)

— Suppose that a VM exit is due to another reason (but not a debug exception) and occurs while there is MOVSS blocking of debug exceptions. In this case, the value saved sets bits corresponding to the causes of any
debug exceptions that were pending at the time of the VM exit. If the VM exit occurs immediately after
VM entry (no instructions were executed in VMX non-root operation), the value saved may match that
which was loaded on VM entry (see Section 26.6.3). Otherwise, the following items apply:

•

Bit 12 (enabled breakpoint) is set to 1 if there was at least one matched data or I/O breakpoint that was
enabled in DR7. Bit 12 is also set if it had been set on VM entry, causing there to be valid pending debug
exceptions (see Section 26.6.3) and the VM exit occurred before those exceptions were either delivered
or lost. In other cases, bit 12 is cleared to 0.

•

The setting of bit 14 (BS) is implementation-specific. However, it is not set if RFLAGS.TF = 0 or
IA32_DEBUGCTL.BTF = 1.

— The reserved bits in the field are cleared.

•

If the “save VMX-preemption timer value” VM-exit control is 1, the value of timer is saved into the VMXpreemption timer-value field. This is the value loaded from this field on VM entry as subsequently decremented
(see Section 25.5.1). VM exits due to timer expiration save the value 0. Other VM exits may also save the value
0 if the timer expired during VM exit. (If the “save VMX-preemption timer value” VM-exit control is 0, VM exit
does not modify the value of the VMX-preemption timer-value field.)

•

If the logical processor supports the 1-setting of the “enable EPT” VM-execution control, values are saved into
the four (4) PDPTE fields as follows:
— If the “enable EPT” VM-execution control is 1 and the logical processor was using PAE paging at the time of
the VM exit, the PDPTE values currently in use are saved:1

•
•

The values saved into bits 11:9 of each of the fields is undefined.

•

If the value saved into one of the fields has bit 0 (present) set, the value saved into bits 63:12 of the
field is a guest-physical address.

If the value saved into one of the fields has bit 0 (present) clear, the value saved into bits 63:1 of that
field is undefined. That value need not correspond to the value that was loaded by VM entry or to any
value that might have been loaded in VMX non-root operation.

1. A logical processor uses PAE paging if CR0.PG = 1, CR4.PAE = 1 and IA32_EFER.LMA = 0. See Section 4.4 in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 3A. “Enable EPT” is a secondary processor-based VM-execution control. If bit 31
of the primary processor-based VM-execution controls is 0, VM exit functions as if the “enable EPT” VM-execution control were 0.
See Section 24.6.2.
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VM EXITS

— If the “enable EPT” VM-execution control is 0 or the logical processor was not using PAE paging at the time
of the VM exit, the values saved are undefined.

27.4

SAVING MSRS

After processor state is saved to the guest-state area, values of MSRs may be stored into the VM-exit MSR-store
area (see Section 24.7.2). Specifically each entry in that area (up to the number specified in the VM-exit MSR-store
count) is processed in order by storing the value of the MSR indexed by bits 31:0 (as they would be read by
RDMSR) into bits 127:64. Processing of an entry fails in either of the following cases:

•

The value of bits 31:8 is 000008H, meaning that the indexed MSR is one that allows access to an APIC register
when the local APIC is in x2APIC mode.

•

The value of bits 31:0 indicates an MSR that can be read only in system-management mode (SMM) and the
VM exit will not end in SMM. (IA32_SMBASE is an MSR that can be read only in SMM.)

•

The value of bits 31:0 indicates an MSR that cannot be saved on VM exits for model-specific reasons. A
processor may prevent certain MSRs (based on the value of bits 31:0) from being stored on VM exits, even if
they can normally be read by RDMSR. Such model-specific behavior is documented in Chapter 2, “ModelSpecific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4.

•
•

Bits 63:32 of the entry are not all 0.
An attempt to read the MSR indexed by bits 31:0 would cause a general-protection exception if executed via
RDMSR with CPL = 0.

A VMX abort occurs if processing fails for any entry. See Section 27.7.

27.5

LOADING HOST STATE

Processor state is updated on VM exits in the following ways:

•
•
•
•

Some state is loaded from or otherwise determined by the contents of the host-state area.
Some state is determined by VM-exit controls.
Some state is established in the same way on every VM exit.
The page-directory pointers are loaded based on the values of certain control registers.

This loading may be performed in any order.
On processors that support Intel 64 architecture, the full values of each 64-bit field loaded (for example, the base
address for GDTR) is loaded regardless of the mode of the logical processor before and after the VM exit.
The loading of host state is detailed in Section 27.5.1 to Section 27.5.5. These sections reference VMCS fields that
correspond to processor state. Unless otherwise stated, these references are to fields in the host-state area.
A logical processor is in IA-32e mode after a VM exit only if the “host address-space size” VM-exit control is 1. If
the logical processor was in IA-32e mode before the VM exit and this control is 0, a VMX abort occurs. See Section
27.7.
In addition to loading host state, VM exits clear address-range monitoring (Section 27.5.6).
After the state loading described in this section, VM exits may load MSRs from the VM-exit MSR-load area (see
Section 27.6). This loading occurs only after the state loading described in this section.

27.5.1

Loading Host Control Registers, Debug Registers, MSRs

VM exits load new values for controls registers, debug registers, and some MSRs:

•

CR0, CR3, and CR4 are loaded from the CR0 field, the CR3 field, and the CR4 field, respectively, with the
following exceptions:
— The following bits are not modified:

Vol. 3C 27-25

VM EXITS

•

For CR0, ET, CD, NW; bits 63:32 (on processors that support Intel 64 architecture), 28:19, 17, and
15:6; and any bits that are fixed in VMX operation (see Section 23.8).1

•

For CR3, bits 63:52 and bits in the range 51:32 beyond the processor’s physical-address width (they
are cleared to 0).2 (This item applies only to processors that support Intel 64 architecture.)

•

For CR4, any bits that are fixed in VMX operation (see Section 23.8).

— CR4.PAE is set to 1 if the “host address-space size” VM-exit control is 1.
— CR4.PCIDE is set to 0 if the “host address-space size” VM-exit control is 0.

•
•

DR7 is set to 400H.
The following MSRs are established as follows:
— The IA32_DEBUGCTL MSR is cleared to 00000000_00000000H.
— The IA32_SYSENTER_CS MSR is loaded from the IA32_SYSENTER_CS field. Since that field has only 32
bits, bits 63:32 of the MSR are cleared to 0.
— IA32_SYSENTER_ESP MSR and IA32_SYSENTER_EIP MSR are loaded from the IA32_SYSENTER_ESP field
and the IA32_SYSENTER_EIP field, respectively.
If the processor does not support the Intel 64 architecture, these fields have only 32 bits; bits 63:32 of the
MSRs are cleared to 0.
If the processor does support the Intel 64 architecture and the processor supports N < 64 linear-address
bits, each of bits 63:N is set to the value of bit N–1.3
— The following steps are performed on processors that support Intel 64 architecture:

•

The MSRs FS.base and GS.base are loaded from the base-address fields for FS and GS, respectively
(see Section 27.5.2).

•

The LMA and LME bits in the IA32_EFER MSR are each loaded with the setting of the “host addressspace size” VM-exit control.

— If the “load IA32_PERF_GLOBAL_CTRL” VM-exit control is 1, the IA32_PERF_GLOBAL_CTRL MSR is loaded
from the IA32_PERF_GLOBAL_CTRL field. Bits that are reserved in that MSR are maintained with their
reserved values.
— If the “load IA32_PAT” VM-exit control is 1, the IA32_PAT MSR is loaded from the IA32_PAT field. Bits that
are reserved in that MSR are maintained with their reserved values.
— If the “load IA32_EFER” VM-exit control is 1, the IA32_EFER MSR is loaded from the IA32_EFER field. Bits
that are reserved in that MSR are maintained with their reserved values.
— If the “clear IA32_BNDCFGS” VM-exit control is 1, the IA32_BNDCFGS MSR is cleared to
00000000_00000000H; otherwise, it is not modified.
With the exception of FS.base and GS.base, any of these MSRs is subsequently overwritten if it appears in the
VM-exit MSR-load area. See Section 27.6.

27.5.2

Loading Host Segment and Descriptor-Table Registers

Each of the registers CS, SS, DS, ES, FS, GS, and TR is loaded as follows (see below for the treatment of LDTR):

•

The selector is loaded from the selector field. The segment is unusable if its selector is loaded with zero. The
checks specified Section 26.3.1.2 limit the selector values that may be loaded. In particular, CS and TR are
never loaded with zero and are thus never unusable. SS can be loaded with zero only on processors that

1. Bits 28:19, 17, and 15:6 of CR0 and CR0.ET are unchanged by executions of MOV to CR0. CR0.ET is always 1 and the other bits are
always 0.
2. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
3. Software can determine the number N by executing CPUID with 80000008H in EAX. The number of linear-address bits supported is
returned in bits 15:8 of EAX.
27-26 Vol. 3C

VM EXITS

support Intel 64 architecture and only if the VM exit is to 64-bit mode (64-bit mode allows use of segments
marked unusable).

•

The base address is set as follows:
— CS. Cleared to zero.
— SS, DS, and ES. Undefined if the segment is unusable; otherwise, cleared to zero.
— FS and GS. Undefined (but, on processors that support Intel 64 architecture, canonical) if the segment is
unusable and the VM exit is not to 64-bit mode; otherwise, loaded from the base-address field.
If the processor supports the Intel 64 architecture and the processor supports N < 64 linear-address bits,
each of bits 63:N is set to the value of bit N–1.1 The values loaded for base addresses for FS and GS are
also manifest in the FS.base and GS.base MSRs.
— TR. Loaded from the host-state area. If the processor supports the Intel 64 architecture and the processor
supports N < 64 linear-address bits, each of bits 63:N is set to the value of bit N–1.

•

The segment limit is set as follows:
— CS. Set to FFFFFFFFH (corresponding to a descriptor limit of FFFFFH and a G-bit setting of 1).
— SS, DS, ES, FS, and GS. Undefined if the segment is unusable; otherwise, set to FFFFFFFFH.
— TR. Set to 00000067H.

•

The type field and S bit are set as follows:
— CS. Type set to 11 and S set to 1 (execute/read, accessed, non-conforming code segment).
— SS, DS, ES, FS, and GS. Undefined if the segment is unusable; otherwise, type set to 3 and S set to 1
(read/write, accessed, expand-up data segment).
— TR. Type set to 11 and S set to 0 (busy 32-bit task-state segment).

•

The DPL is set as follows:
— CS, SS, and TR. Set to 0. The current privilege level (CPL) will be 0 after the VM exit completes.
— DS, ES, FS, and GS. Undefined if the segment is unusable; otherwise, set to 0.

•

The P bit is set as follows:
— CS, TR. Set to 1.
— SS, DS, ES, FS, and GS. Undefined if the segment is unusable; otherwise, set to 1.

•

On processors that support Intel 64 architecture, CS.L is loaded with the setting of the “host address-space
size” VM-exit control. Because the value of this control is also loaded into IA32_EFER.LMA (see Section 27.5.1),
no VM exit is ever to compatibility mode (which requires IA32_EFER.LMA = 1 and CS.L = 0).

•

D/B.
— CS. Loaded with the inverse of the setting of the “host address-space size” VM-exit control. For example, if
that control is 0, indicating a 32-bit guest, CS.D/B is set to 1.
— SS. Set to 1.
— DS, ES, FS, and GS. Undefined if the segment is unusable; otherwise, set to 1.
— TR. Set to 0.

•

G.
— CS. Set to 1.
— SS, DS, ES, FS, and GS. Undefined if the segment is unusable; otherwise, set to 1.
— TR. Set to 0.

1. Software can determine the number N by executing CPUID with 80000008H in EAX. The number of linear-address bits supported is
returned in bits 15:8 of EAX.
Vol. 3C 27-27

VM EXITS

The host-state area does not contain a selector field for LDTR. LDTR is established as follows on all VM exits: the
selector is cleared to 0000H, the segment is marked unusable and is otherwise undefined (although the base
address is always canonical).
The base addresses for GDTR and IDTR are loaded from the GDTR base-address field and the IDTR base-address
field, respectively. If the processor supports the Intel 64 architecture and the processor supports N < 64 linearaddress bits, each of bits 63:N of each base address is set to the value of bit N–1 of that base address. The GDTR
and IDTR limits are each set to FFFFH.

27.5.3

Loading Host RIP, RSP, and RFLAGS

RIP and RSP are loaded from the RIP field and the RSP field, respectively. RFLAGS is cleared, except bit 1, which is
always set.

27.5.4

Checking and Loading Host Page-Directory-Pointer-Table Entries

If CR0.PG = 1, CR4.PAE = 1, and IA32_EFER.LMA = 0, the logical processor uses PAE paging. See Section 4.4 of
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.1 When in PAE paging is in use, the
physical address in CR3 references a table of page-directory-pointer-table entries (PDPTEs). A MOV to CR3
when PAE paging is in use checks the validity of the PDPTEs and, if they are valid, loads them into the processor
(into internal, non-architectural registers).
A VM exit is to a VMM that uses PAE paging if (1) bit 5 (corresponding to CR4.PAE) is set in the CR4 field in the hoststate area of the VMCS; and (2) the “host address-space size” VM-exit control is 0. Such a VM exit may check the
validity of the PDPTEs referenced by the CR3 field in the host-state area of the VMCS. Such a VM exit must check
their validity if either (1) PAE paging was not in use before the VM exit; or (2) the value of CR3 is changing as a
result of the VM exit. A VM exit to a VMM that does not use PAE paging must not check the validity of the PDPTEs.
A VM exit that checks the validity of the PDPTEs uses the same checks that are used when CR3 is loaded with
MOV to CR3 when PAE paging is in use. If MOV to CR3 would cause a general-protection exception due to the
PDPTEs that would be loaded (e.g., because a reserved bit is set), a VMX abort occurs (see Section 27.7). If a
VM exit to a VMM that uses PAE does not cause a VMX abort, the PDPTEs are loaded into the processor as would
MOV to CR3, using the value of CR3 being load by the VM exit.

27.5.5

Updating Non-Register State

VM exits affect the non-register state of a logical processor as follows:

•
•

A logical processor is always in the active state after a VM exit.
Event blocking is affected as follows:
— There is no blocking by STI or by MOV SS after a VM exit.
— VM exits caused directly by non-maskable interrupts (NMIs) cause blocking by NMI (see Table 24-3). Other
VM exits do not affect blocking by NMI. (See Section 27.1 for the case in which an NMI causes a VM exit
indirectly.)

•

There are no pending debug exceptions after a VM exit.

Section 28.3 describes how the VMX architecture controls how a logical processor manages information in the TLBs
and paging-structure caches. The following items detail how VM exits invalidate cached mappings:

•

If the “enable VPID” VM-execution control is 0, the logical processor invalidates linear mappings and combined
mappings associated with VPID 0000H (for all PCIDs); combined mappings for VPID 0000H are invalidated for
all EP4TA values (EP4TA is the value of bits 51:12 of EPTP).

1. On processors that support Intel 64 architecture, the physical-address extension may support more than 36 physical-address bits.
Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
27-28 Vol. 3C

VM EXITS

•

VM exits are not required to invalidate any guest-physical mappings, nor are they required to invalidate any
linear mappings or combined mappings if the “enable VPID” VM-execution control is 1.

27.5.6

Clearing Address-Range Monitoring

The Intel 64 and IA-32 architectures allow software to monitor a specified address range using the MONITOR and
MWAIT instructions. See Section 8.10.4 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 3A. VM exits clear any address-range monitoring that may be in effect.

27.6

LOADING MSRS

VM exits may load MSRs from the VM-exit MSR-load area (see Section 24.7.2). Specifically each entry in that area
(up to the number specified in the VM-exit MSR-load count) is processed in order by loading the MSR indexed by
bits 31:0 with the contents of bits 127:64 as they would be written by WRMSR.
Processing of an entry fails in any of the following cases:

•

The value of bits 31:0 is either C0000100H (the IA32_FS_BASE MSR) or C0000101H (the IA32_GS_BASE
MSR).

•

The value of bits 31:8 is 000008H, meaning that the indexed MSR is one that allows access to an APIC register
when the local APIC is in x2APIC mode.

•

The value of bits 31:0 indicates an MSR that can be written only in system-management mode (SMM) and the
VM exit will not end in SMM. (IA32_SMM_MONITOR_CTL is an MSR that can be written only in SMM.)

•

The value of bits 31:0 indicates an MSR that cannot be loaded on VM exits for model-specific reasons. A
processor may prevent loading of certain MSRs even if they can normally be written by WRMSR. Such modelspecific behavior is documented in Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 4.

•
•

Bits 63:32 are not all 0.
An attempt to write bits 127:64 to the MSR indexed by bits 31:0 of the entry would cause a general-protection
exception if executed via WRMSR with CPL = 0.1

If processing fails for any entry, a VMX abort occurs. See Section 27.7.
If any MSR is being loaded in such a way that would architecturally require a TLB flush, the TLBs are updated so
that, after VM exit, the logical processor does not use any translations that were cached before the transition.

27.7

VMX ABORTS

A problem encountered during a VM exit leads to a VMX abort. A VMX abort takes a logical processor into a shutdown state as described below.
A VMX abort does not modify the VMCS data in the VMCS region of any active VMCS. The contents of these data
are thus suspect after the VMX abort.
On a VMX abort, a logical processor saves a nonzero 32-bit VMX-abort indicator field at byte offset 4 in the VMCS
region of the VMCS whose misconfiguration caused the failure (see Section 24.2). The following values are used:
1. There was a failure in saving guest MSRs (see Section 27.4).
2. Host checking of the page-directory-pointer-table entries (PDPTEs) failed (see Section 27.5.4).
3. The current VMCS has been corrupted (through writes to the corresponding VMCS region) in such a way that
the logical processor cannot complete the VM exit properly.
1. Note the following about processors that support Intel 64 architecture. If CR0.PG = 1, WRMSR to the IA32_EFER MSR causes a general-protection exception if it would modify the LME bit. Since CR0.PG is always 1 in VMX operation, the IA32_EFER MSR should not
be included in the VM-exit MSR-load area for the purpose of modifying the LME bit.
Vol. 3C 27-29

VM EXITS

4. There was a failure on loading host MSRs (see Section 27.6).
5. There was a machine-check event during VM exit (see Section 27.8).
6. The logical processor was in IA-32e mode before the VM exit and the “host address-space size” VM-entry
control was 0 (see Section 27.5).
Some of these causes correspond to failures during the loading of state from the host-state area. Because the
loading of such state may be done in any order (see Section 27.5) a VM exit that might lead to a VMX abort for
multiple reasons (for example, the current VMCS may be corrupt and the host PDPTEs might not be properly
configured). In such cases, the VMX-abort indicator could correspond to any one of those reasons.
A logical processor never reads the VMX-abort indicator in a VMCS region and writes it only with one of the nonzero values mentioned above. The VMX-abort indicator allows software on one logical processor to diagnose the
VMX-abort on another. For this reason, it is recommended that software running in VMX root operation zero the
VMX-abort indicator in the VMCS region of any VMCS that it uses.
After saving the VMX-abort indicator, operation of a logical processor experiencing a VMX abort depends on
whether the logical processor is in SMX operation:1

•

If the logical processor is in SMX operation, an Intel® TXT shutdown condition occurs. The error code used is
000DH, indicating “VMX abort.” See Intel® Trusted Execution Technology Measured Launched Environment
Programming Guide.

•

If the logical processor is outside SMX operation, it issues a special bus cycle (to notify the chipset) and enters
the VMX-abort shutdown state. RESET is the only event that wakes a logical processor from the VMX-abort
shutdown state. The following events do not affect a logical processor in this state: machine-check events; INIT
signals; external interrupts; non-maskable interrupts (NMIs); start-up IPIs (SIPIs); and system-management
interrupts (SMIs).

27.8

MACHINE-CHECK EVENTS DURING VM EXIT

If a machine-check event occurs during VM exit, one of the following occurs:

•

The machine-check event is handled as if it occurred before the VM exit:
— If CR4.MCE = 0, operation of the logical processor depends on whether the logical processor is in SMX
operation:2

•

If the logical processor is in SMX operation, an Intel® TXT shutdown condition occurs. The error code
used is 000CH, indicating “unrecoverable machine-check condition.”

•

If the logical processor is outside SMX operation, it goes to the shutdown state.

— If CR4.MCE = 1, a machine-check exception (#MC) is generated:

•

•
•

If bit 18 (#MC) of the exception bitmap is 0, the exception is delivered through the guest IDT.
If bit 18 of the exception bitmap is 1, the exception causes a VM exit.

The machine-check event is handled after VM exit completes:
— If the VM exit ends with CR4.MCE = 0, operation of the logical processor depends on whether the logical
processor is in SMX operation:

•

If the logical processor is in SMX operation, an Intel® TXT shutdown condition occurs with error code
000CH (unrecoverable machine-check condition).

1. A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last execution of GETSEC[SENTER]. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the last
execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference,” in Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 2B.
2. A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last execution of GETSEC[SENTER]. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the last
execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference,” in Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 2B.
27-30 Vol. 3C

VM EXITS

•

If the logical processor is outside SMX operation, it goes to the shutdown state.

— If the VM exit ends with CR4.MCE = 1, a machine-check exception (#MC) is delivered through the host IDT.

•

A VMX abort is generated (see Section 27.7). The logical processor blocks events as done normally in
VMX abort. The VMX abort indicator is 5, for “machine-check event during VM exit.”

The first option is not used if the machine-check event occurs after any host state has been loaded. The second
option is used only if VM entry is able to load all host state.

Vol. 3C 27-31

VM EXITS

27-32 Vol. 3C

CHAPTER 28
VMX SUPPORT FOR ADDRESS TRANSLATION
The architecture for VMX operation includes two features that support address translation: virtual-processor identifiers (VPIDs) and the extended page-table mechanism (EPT). VPIDs are a mechanism for managing translations
of linear addresses. EPT defines a layer of address translation that augments the translation of linear addresses.
Section 28.1 details the architecture of VPIDs. Section 28.2 provides the details of EPT. Section 28.3 explains how
a logical processor may cache information from the paging structures, how it may use that cached information, and
how software can managed the cached information.

28.1

VIRTUAL PROCESSOR IDENTIFIERS (VPIDS)

The original architecture for VMX operation required VMX transitions to flush the TLBs and paging-structure caches.
This ensured that translations cached for the old linear-address space would not be used after the transition.
Virtual-processor identifiers (VPIDs) introduce to VMX operation a facility by which a logical processor may cache
information for multiple linear-address spaces. When VPIDs are used, VMX transitions may retain cached information and the logical processor switches to a different linear-address space.
Section 28.3 details the mechanisms by which a logical processor manages information cached for multiple address
spaces. A logical processor may tag some cached information with a 16-bit VPID. This section specifies how the
current VPID is determined at any point in time:

•

The current VPID is 0000H in the following situations:
— Outside VMX operation. (This includes operation in system-management mode under the default treatment
of SMIs and SMM with VMX operation; see Section 34.14.)
— In VMX root operation.
— In VMX non-root operation when the “enable VPID” VM-execution control is 0.

•

If the logical processor is in VMX non-root operation and the “enable VPID” VM-execution control is 1, the
current VPID is the value of the VPID VM-execution control field in the VMCS. (VM entry ensures that this value
is never 0000H; see Section 26.2.1.1.)

VPIDs and PCIDs (see Section 4.10.1) can be used concurrently. When this is done, the processor associates
cached information with both a VPID and a PCID. Such information is used only if the current VPID and PCID both
match those associated with the cached information.

28.2

THE EXTENDED PAGE TABLE MECHANISM (EPT)

The extended page-table mechanism (EPT) is a feature that can be used to support the virtualization of physical
memory. When EPT is in use, certain addresses that would normally be treated as physical addresses (and used to
access memory) are instead treated as guest-physical addresses. Guest-physical addresses are translated by
traversing a set of EPT paging structures to produce physical addresses that are used to access memory.

•
•
•
•

Section 28.2.1 gives an overview of EPT.
Section 28.2.2 describes operation of EPT-based address translation.
Section 28.2.3 discusses VM exits that may be caused by EPT.
Section 28.2.6 describes interactions between EPT and memory typing.

28.2.1

EPT Overview

EPT is used when the “enable EPT” VM-execution control is 1.1 It translates the guest-physical addresses used in
VMX non-root operation and those used by VM entry for event injection.
Vol. 3C 28-1

VMX SUPPORT FOR ADDRESS TRANSLATION

The translation from guest-physical addresses to physical addresses is determined by a set of EPT paging structures. The EPT paging structures are similar to those used to translate linear addresses while the processor is in
IA-32e mode. Section 28.2.2 gives the details of the EPT paging structures.
If CR0.PG = 1, linear addresses are translated through paging structures referenced through control register CR3.
While the “enable EPT” VM-execution control is 1, these are called guest paging structures. There are no guest
paging structures if CR0.PG = 0.1
When the “enable EPT” VM-execution control is 1, the identity of guest-physical addresses depends on the value
of CR0.PG:

•
•

If CR0.PG = 0, each linear address is treated as a guest-physical address.
If CR0.PG = 1, guest-physical addresses are those derived from the contents of control register CR3 and the
guest paging structures. (This includes the values of the PDPTEs, which logical processors store in internal,
non-architectural registers.) The latter includes (in page-table entries and in other paging-structure entries for
which bit 7—PS—is 1) the addresses to which linear addresses are translated by the guest paging structures.

If CR0.PG = 1, the translation of a linear address to a physical address requires multiple translations of guest-physical addresses using EPT. Assume, for example, that CR4.PAE = CR4.PSE = 0. The translation of a 32-bit linear
address then operates as follows:

•

Bits 31:22 of the linear address select an entry in the guest page directory located at the guest-physical
address in CR3. The guest-physical address of the guest page-directory entry (PDE) is translated through EPT
to determine the guest PDE’s physical address.

•

Bits 21:12 of the linear address select an entry in the guest page table located at the guest-physical address in
the guest PDE. The guest-physical address of the guest page-table entry (PTE) is translated through EPT to
determine the guest PTE’s physical address.

•

Bits 11:0 of the linear address is the offset in the page frame located at the guest-physical address in the guest
PTE. The guest-physical address determined by this offset is translated through EPT to determine the physical
address to which the original linear address translates.

In addition to translating a guest-physical address to a physical address, EPT specifies the privileges that software
is allowed when accessing the address. Attempts at disallowed accesses are called EPT violations and cause
VM exits. See Section 28.2.3.
A processor uses EPT to translate guest-physical addresses only when those addresses are used to access memory.
This principle implies the following:

•

The MOV to CR3 instruction loads CR3 with a guest-physical address. Whether that address is translated
through EPT depends on whether PAE paging is being used.2
— If PAE paging is not being used, the instruction does not use that address to access memory and does not
cause it to be translated through EPT. (If CR0.PG = 1, the address will be translated through EPT on the
next memory accessing using a linear address.)
— If PAE paging is being used, the instruction loads the four (4) page-directory-pointer-table entries (PDPTEs)
from that address and it does cause the address to be translated through EPT.

•

Section 4.4.1 identifies executions of MOV to CR0 and MOV to CR4 that load the PDPTEs from the guestphysical address in CR3. Such executions cause that address to be translated through EPT.

•

The PDPTEs contain guest-physical addresses. The instructions that load the PDPTEs (see above) do not use
those addresses to access memory and do not cause them to be translated through EPT. The address in a
PDPTE will be translated through EPT on the next memory accessing using a linear address that uses that
PDPTE.

1. “Enable EPT” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls
is 0, the logical processor operates as if the “enable EPT” VM-execution control were 0. See Section 24.6.2.
1. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PG must be 1 in VMX operation, CR0.PG can be 0 in VMX non-root
operation only if the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are
both 1.
2. A logical processor uses PAE paging if CR0.PG = 1, CR4.PAE = 1 and IA32_EFER.LMA = 0. See Section 4.4 in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 3A.
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VMX SUPPORT FOR ADDRESS TRANSLATION

28.2.2

EPT Translation Mechanism

The EPT translation mechanism uses only bits 47:0 of each guest-physical address.1 It uses a page-walk length of
4, meaning that at most 4 EPT paging-structure entries are accessed to translate a guest-physical address.2
These 48 bits are partitioned by the logical processor to traverse the EPT paging structures:

•

A 4-KByte naturally aligned EPT PML4 table is located at the physical address specified in bits 51:12 of the
extended-page-table pointer (EPTP), a VM-execution control field (see Table 24-8 in Section 24.6.11). An EPT
PML4 table comprises 512 64-bit entries (EPT PML4Es). An EPT PML4E is selected using the physical address
defined as follows:
— Bits 63:52 are all 0.
— Bits 51:12 are from the EPTP.
— Bits 11:3 are bits 47:39 of the guest-physical address.
— Bits 2:0 are all 0.
Because an EPT PML4E is identified using bits 47:39 of the guest-physical address, it controls access to a 512GByte region of the guest-physical-address space. The format of an EPT PML4E is given in Table 28-1.

Table 28-1. Format of an EPT PML4 Entry (PML4E) that References an EPT Page-Directory-Pointer Table
Bit
Position(s)

Contents

0

Read access; indicates whether reads are allowed from the 512-GByte region controlled by this entry

1

Write access; indicates whether writes are allowed from the 512-GByte region controlled by this entry

2

If the “mode-based execute control for EPT” VM-execution control is 0, execute access; indicates whether instruction
fetches are allowed from the 512-GByte region controlled by this entry
If that control is 1, execute access for supervisor-mode linear addresses; indicates whether instruction fetches are
allowed from supervisor-mode linear addresses in the 512-GByte region controlled by this entry

7:3

Reserved (must be 0)

8

If bit 6 of EPTP is 1, accessed flag for EPT; indicates whether software has accessed the 512-GByte region
controlled by this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

9

Ignored

10

Execute access for user-mode linear addresses. If the “mode-based execute control for EPT” VM-execution control is
1, indicates whether instruction fetches are allowed from user-mode linear addresses in the 512-GByte region
controlled by this entry. If that control is 0, this bit is ignored.

11

Ignored

(N–1):12

Physical address of 4-KByte aligned EPT page-directory-pointer table referenced by this entry1

51:N

Reserved (must be 0)

63:52

Ignored

1. No processors supporting the Intel 64 architecture support more than 48 physical-address bits. Thus, no such processor can produce a guest-physical address with more than 48 bits. An attempt to use such an address causes a page fault. An attempt to load
CR3 with such an address causes a general-protection fault. If PAE paging is being used, an attempt to load CR3 that would load a
PDPTE with such an address causes a general-protection fault.
2. Future processors may include support for other EPT page-walk lengths. Software should read the VMX capability MSR
IA32_VMX_EPT_VPID_CAP (see Appendix A.10) to determine what EPT page-walk lengths are supported.
Vol. 3C 28-3

VMX SUPPORT FOR ADDRESS TRANSLATION

NOTES:
1. N is the physical-address width supported by the processor. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address width is returned in bits 7:0 of EAX.

•

A 4-KByte naturally aligned EPT page-directory-pointer table is located at the physical address specified in
bits 51:12 of the EPT PML4E. An EPT page-directory-pointer table comprises 512 64-bit entries (EPT PDPTEs).
An EPT PDPTE is selected using the physical address defined as follows:
— Bits 63:52 are all 0.
— Bits 51:12 are from the EPT PML4E.
— Bits 11:3 are bits 38:30 of the guest-physical address.
— Bits 2:0 are all 0.

Because an EPT PDPTE is identified using bits 47:30 of the guest-physical address, it controls access to a 1-GByte
region of the guest-physical-address space. Use of the EPT PDPTE depends on the value of bit 7 in that entry:1

•

If bit 7 of the EPT PDPTE is 1, the EPT PDPTE maps a 1-GByte page. The final physical address is computed as
follows:
— Bits 63:52 are all 0.
— Bits 51:30 are from the EPT PDPTE.
— Bits 29:0 are from the original guest-physical address.
The format of an EPT PDPTE that maps a 1-GByte page is given in Table 28-2.

•

If bit 7 of the EPT PDPTE is 0, a 4-KByte naturally aligned EPT page directory is located at the physical address
specified in bits 51:12 of the EPT PDPTE. The format of an EPT PDPTE that references an EPT page directory is
given in Table 28-3.

1. Not all processors allow bit 7 of an EPT PDPTE to be set to 1. Software should read the VMX capability MSR
IA32_VMX_EPT_VPID_CAP (see Appendix A.10) to determine whether this is allowed.
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VMX SUPPORT FOR ADDRESS TRANSLATION

Table 28-2. Format of an EPT Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page
Bit
Position(s)

Contents

0

Read access; indicates whether reads are allowed from the 1-GByte page referenced by this entry

1

Write access; indicates whether writes are allowed from the 1-GByte page referenced by this entry

2

If the “mode-based execute control for EPT” VM-execution control is 0, execute access; indicates whether
instruction fetches are allowed from the 1-GByte page controlled by this entry
If that control is 1, execute access for supervisor-mode linear addresses; indicates whether instruction fetches are
allowed from supervisor-mode linear addresses in the 1-GByte page controlled by this entry

5:3

EPT memory type for this 1-GByte page (see Section 28.2.6)

6

Ignore PAT memory type for this 1-GByte page (see Section 28.2.6)

7

Must be 1 (otherwise, this entry references an EPT page directory)

8

If bit 6 of EPTP is 1, accessed flag for EPT; indicates whether software has accessed the 1-GByte page referenced
by this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

9

If bit 6 of EPTP is 1, dirty flag for EPT; indicates whether software has written to the 1-GByte page referenced by
this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

10

Execute access for user-mode linear addresses. If the “mode-based execute control for EPT” VM-execution control is
1, indicates whether instruction fetches are allowed from user-mode linear addresses in the 1-GByte page controlled
by this entry. If that control is 0, this bit is ignored.

11

Ignored

29:12

Reserved (must be 0)

(N–1):30

Physical address of the 1-GByte page referenced by this entry1

51:N

Reserved (must be 0)

62:52

Ignored

63

Suppress #VE. If the “EPT-violation #VE” VM-execution control is 1, EPT violations caused by accesses to this page
are convertible to virtualization exceptions only if this bit is 0 (see Section 25.5.6.1). If “EPT-violation #VE” VMexecution control is 0, this bit is ignored.

NOTES:
1. N is the physical-address width supported by the logical processor.

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Table 28-3. Format of an EPT Page-Directory-Pointer-Table Entry (PDPTE) that References an EPT Page Directory
Bit
Position(s)

Contents

0

Read access; indicates whether reads are allowed from the 1-GByte region controlled by this entry

1

Write access; indicates whether writes are allowed from the 1-GByte region controlled by this entry

2

If the “mode-based execute control for EPT” VM-execution control is 0, execute access; indicates whether instruction
fetches are allowed from the 1-GByte region controlled by this entry
If that control is 1, execute access for supervisor-mode linear addresses; indicates whether instruction fetches are
allowed from supervisor-mode linear addresses in the 1-GByte region controlled by this entry

7:3

Reserved (must be 0)

8

If bit 6 of EPTP is 1, accessed flag for EPT; indicates whether software has accessed the 1-GByte region controlled
by this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

9

Ignored

10

Execute access for user-mode linear addresses. If the “mode-based execute control for EPT” VM-execution control is
1, indicates whether instruction fetches are allowed from user-mode linear addresses in the 1-GByte region
controlled by this entry. If that control is 0, this bit is ignored.

11

Ignored

(N–1):12

Physical address of 4-KByte aligned EPT page directory referenced by this entry1

51:N

Reserved (must be 0)

63:52

Ignored

NOTES:
1. N is the physical-address width supported by the logical processor.
An EPT page-directory comprises 512 64-bit entries (PDEs). An EPT PDE is selected using the physical address
defined as follows:
— Bits 63:52 are all 0.
— Bits 51:12 are from the EPT PDPTE.
— Bits 11:3 are bits 29:21 of the guest-physical address.
— Bits 2:0 are all 0.
Because an EPT PDE is identified using bits 47:21 of the guest-physical address, it controls access to a 2-MByte
region of the guest-physical-address space. Use of the EPT PDE depends on the value of bit 7 in that entry:

•

If bit 7 of the EPT PDE is 1, the EPT PDE maps a 2-MByte page. The final physical address is computed as
follows:
— Bits 63:52 are all 0.
— Bits 51:21 are from the EPT PDE.
— Bits 20:0 are from the original guest-physical address.
The format of an EPT PDE that maps a 2-MByte page is given in Table 28-4.

•

If bit 7 of the EPT PDE is 0, a 4-KByte naturally aligned EPT page table is located at the physical address
specified in bits 51:12 of the EPT PDE. The format of an EPT PDE that references an EPT page table is given in
Table 28-5.
An EPT page table comprises 512 64-bit entries (PTEs). An EPT PTE is selected using a physical address defined
as follows:
— Bits 63:52 are all 0.

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Table 28-4. Format of an EPT Page-Directory Entry (PDE) that Maps a 2-MByte Page
Bit
Position(s)

Contents

0

Read access; indicates whether reads are allowed from the 2-MByte page referenced by this entry

1

Write access; indicates whether writes are allowed from the 2-MByte page referenced by this entry

2

If the “mode-based execute control for EPT” VM-execution control is 0, execute access; indicates whether instruction
fetches are allowed from the 2-MByte page controlled by this entry
If that control is 1, execute access for supervisor-mode linear addresses; indicates whether instruction fetches are
allowed from supervisor-mode linear addresses in the 2-MByte page controlled by this entry

5:3

EPT memory type for this 2-MByte page (see Section 28.2.6)

6

Ignore PAT memory type for this 2-MByte page (see Section 28.2.6)

7

Must be 1 (otherwise, this entry references an EPT page table)

8

If bit 6 of EPTP is 1, accessed flag for EPT; indicates whether software has accessed the 2-MByte page referenced
by this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

9

If bit 6 of EPTP is 1, dirty flag for EPT; indicates whether software has written to the 2-MByte page referenced by
this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

10

Execute access for user-mode linear addresses. If the “mode-based execute control for EPT” VM-execution control is
1, indicates whether instruction fetches are allowed from user-mode linear addresses in the 2-MByte page controlled
by this entry. If that control is 0, this bit is ignored.

11

Ignored

20:12

Reserved (must be 0)

(N–1):21

Physical address of the 2-MByte page referenced by this entry1

51:N

Reserved (must be 0)

62:52

Ignored

63

Suppress #VE. If the “EPT-violation #VE” VM-execution control is 1, EPT violations caused by accesses to this page
are convertible to virtualization exceptions only if this bit is 0 (see Section 25.5.6.1). If “EPT-violation #VE” VMexecution control is 0, this bit is ignored.

NOTES:
1. N is the physical-address width supported by the logical processor.
— Bits 51:12 are from the EPT PDE.
— Bits 11:3 are bits 20:12 of the guest-physical address.
— Bits 2:0 are all 0.

•

Because an EPT PTE is identified using bits 47:12 of the guest-physical address, every EPT PTE maps a 4-KByte
page. The final physical address is computed as follows:
— Bits 63:52 are all 0.
— Bits 51:12 are from the EPT PTE.
— Bits 11:0 are from the original guest-physical address.
The format of an EPT PTE is given in Table 28-6.

An EPT paging-structure entry is present if any of bits 2:0 is 1; otherwise, the entry is not present. The processor
ignores bits 62:3 and uses the entry neither to reference another EPT paging-structure entry nor to produce a
physical address. A reference using a guest-physical address whose translation encounters an EPT paging-strucVol. 3C 28-7

VMX SUPPORT FOR ADDRESS TRANSLATION

ture that is not present causes an EPT violation (see Section 28.2.3.2). (If the “EPT-violation #VE” VM-execution
control is 1, the EPT violation is convertible to a virtualization exception only if bit 63 is 0; see Section 25.5.6.1. If
the “EPT-violation #VE” VM-execution control is 0, this bit is ignored.)

Table 28-5. Format of an EPT Page-Directory Entry (PDE) that References an EPT Page Table
Bit
Position(s)

Contents

0

Read access; indicates whether reads are allowed from the 2-MByte region controlled by this entry

1

Write access; indicates whether writes are allowed from the 2-MByte region controlled by this entry

2

If the “mode-based execute control for EPT” VM-execution control is 0, execute access; indicates whether instruction
fetches are allowed from the 2-MByte region controlled by this entry
If that control is 1, execute access for supervisor-mode linear addresses; indicates whether instruction fetches are
allowed from supervisor-mode linear addresses in the 2-MByte region controlled by this entry

6:3

Reserved (must be 0)

7

Must be 0 (otherwise, this entry maps a 2-MByte page)

8

If bit 6 of EPTP is 1, accessed flag for EPT; indicates whether software has accessed the 2-MByte region controlled
by this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

9

Ignored

10

Execute access for user-mode linear addresses. If the “mode-based execute control for EPT” VM-execution control is
1, indicates whether instruction fetches are allowed from user-mode linear addresses in the 2-MByte region
controlled by this entry. If that control is 0, this bit is ignored.

11

Ignored

(N–1):12

Physical address of 4-KByte aligned EPT page table referenced by this entry1

51:N

Reserved (must be 0)

63:52

Ignored

NOTES:
1. N is the physical-address width supported by the logical processor.

NOTE
If the “mode-based execute control for EPT” VM-execution control is 1, an EPT paging-structure
entry is present if any of bits 2:0 or bit 10 is 1. If bits 2:0 are all 0 but bit 10 is 1, the entry is used
normally to reference another EPT paging-structure entry or to produce a physical address.
The discussion above describes how the EPT paging structures reference each other and how the logical processor
traverses those structures when translating a guest-physical address. It does not cover all details of the translation
process. Additional details are provided as follows:

•

Situations in which the translation process may lead to VM exits (sometimes before the process completes) are
described in Section 28.2.3.

•

Interactions between the EPT translation mechanism and memory typing are described in Section 28.2.6.

Figure 28-1 gives a summary of the formats of the EPTP and the EPT paging-structure entries. For the EPT paging
structure entries, it identifies separately the format of entries that map pages, those that reference other EPT
paging structures, and those that do neither because they are not present; bits 2:0 and bit 7 are highlighted
because they determine how a paging-structure entry is used. (Figure 28-1 does not comprehend the fact that, if
the “mode-based execute control for EPT” VM-execution control is 1, an entry is present if any of bits 2:0 or bit 10
is 1.)

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28.2.3

EPT-Induced VM Exits

Accesses using guest-physical addresses may cause VM exits due to EPT misconfigurations, EPT violations, and
page-modification log-full events. An EPT misconfiguration occurs when, in the course of translating a guestphysical address, the logical processor encounters an EPT paging-structure entry that contains an unsupported
value (see Section 28.2.3.1). An EPT violation occurs when there is no EPT misconfiguration but the EPT pagingstructure entries disallow an access using the guest-physical address (see Section 28.2.3.2). A page-modifica-

Table 28-6. Format of an EPT Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)

Contents

0

Read access; indicates whether reads are allowed from the 4-KByte page referenced by this entry

1

Write access; indicates whether writes are allowed from the 4-KByte page referenced by this entry

2

If the “mode-based execute control for EPT” VM-execution control is 0, execute access; indicates whether
instruction fetches are allowed from the 4-KByte page controlled by this entry
If that control is 1, execute access for supervisor-mode linear addresses; indicates whether instruction fetches are
allowed from supervisor-mode linear addresses in the 4-KByte page controlled by this entry

5:3

EPT memory type for this 4-KByte page (see Section 28.2.6)

6

Ignore PAT memory type for this 4-KByte page (see Section 28.2.6)

7

Ignored

8

If bit 6 of EPTP is 1, accessed flag for EPT; indicates whether software has accessed the 4-KByte page referenced
by this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

9

If bit 6 of EPTP is 1, dirty flag for EPT; indicates whether software has written to the 4-KByte page referenced by
this entry (see Section 28.2.4). Ignored if bit 6 of EPTP is 0

10

Execute access for user-mode linear addresses. If the “mode-based execute control for EPT” VM-execution control is
1, indicates whether instruction fetches are allowed from user-mode linear addresses in the 4-KByte page controlled
by this entry. If that control is 0, this bit is ignored.

11

Ignored

(N–1):12

Physical address of the 4-KByte page referenced by this entry1

51:N

Reserved (must be 0)

62:52

Ignored

63

Suppress #VE. If the “EPT-violation #VE” VM-execution control is 1, EPT violations caused by accesses to this page
are convertible to virtualization exceptions only if this bit is 0 (see Section 25.5.6.1). If “EPT-violation #VE” VMexecution control is 0, this bit is ignored.

NOTES:
1. N is the physical-address width supported by the logical processor.
tion log-full event occurs when the logical processor determines a need to create a page-modification log entry
and the current log is full (see Section 28.2.5).
These events occur only due to an attempt to access memory with a guest-physical address. Loading CR3 with a
guest-physical address with the MOV to CR3 instruction can cause neither an EPT configuration nor an EPT violation
until that address is used to access a paging structure.1
If the “EPT-violation #VE” VM-execution control is 1, certain EPT violations may cause virtualization exceptions
instead of VM exits. See Section 25.5.6.1.

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28.2.3.1

EPT Misconfigurations

An EPT misconfiguration occurs if translation of a guest-physical address encounters an EPT paging-structure that
meets any of the following conditions:

•

Bit 0 of the entry is clear (indicating that data reads are not allowed) and bit 1 is set (indicating that data writes
are allowed).

•

Either of the following if the processor does not support execute-only translations:
— Bit 0 of the entry is clear (indicating that data reads are not allowed) and bit 2 is set (indicating that
instruction fetches are allowed).1
— The “mode-based execute control for EPT” VM-execution control is 1, bit 0 of the entry is clear (indicating
that data reads are not allowed), and bit 10 is set (indicating that instruction fetches are allowed from usermode linear addresses).
Software should read the VMX capability MSR IA32_VMX_EPT_VPID_CAP to determine whether execute-only
translations are supported (see Appendix A.10).

•

The entry is present (see Section 28.2.2) and one of the following holds:
— A reserved bit is set. This includes the setting of a bit in the range 51:12 that is beyond the logical
processor’s physical-address width.2 See Section 28.2.2 for details of which bits are reserved in which EPT
paging-structure entries.
— The entry is the last one used to translate a guest physical address (either an EPT PDE with bit 7 set to 1 or
an EPT PTE) and the value of bits 5:3 (EPT memory type) is 2, 3, or 7 (these values are reserved).

EPT misconfigurations result when an EPT paging-structure entry is configured with settings reserved for future
functionality. Software developers should be aware that such settings may be used in the future and that an EPT
paging-structure entry that causes an EPT misconfiguration on one processor might not do so in the future.

28.2.3.2

EPT Violations

An EPT violation may occur during an access using a guest-physical address whose translation does not cause an
EPT misconfiguration. An EPT violation occurs in any of the following situations:

•

Translation of the guest-physical address encounters an EPT paging-structure entry that is not present (see
Section 28.2.2).

•

The access is a data read and, for any byte to be read, bit 0 (read access) was clear in any of the EPT pagingstructure entries used to translate the guest-physical address of the byte. Reads by the logical processor of
guest paging structures to translate a linear address are considered to be data reads.

1. If the logical processor is using PAE paging—because CR0.PG = CR4.PAE = 1 and IA32_EFER.LMA = 0—the MOV to CR3 instruction
loads the PDPTEs from memory using the guest-physical address being loaded into CR3. In this case, therefore, the MOV to CR3
instruction may cause an EPT misconfiguration, an EPT violation, or a page-modification log-full event.
1. If the “mode-based execute control for EPT” VM-execution control is 1, setting bit 2 indicates that instruction fetches are allowed
from supervisor-mode linear addresses.
2. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
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VMX SUPPORT FOR ADDRESS TRANSLATION

6666555555555
3210987654321

M1 M-1

Reserved

Ignored

Rsvd.

33322222222221111111111
210987654321098765432109876543210
A EPT EPT
Address of EPT PML4 table
Rsvd.
/ PWL– PS
D 1
MT
Address of EPT page-directory-pointer table

S
V
E6

S
V
E

Ignored

Rsvd.

Rsvd.

S
V
E
S
V
E

Ignored

Rsvd.

Rsvd.

S
V
E

S
V
E

000

PML4E:
not
present

Physical
address of
1GB page

Reserved

I
Ig X D A 1 P EPT X W R
n. U
A MT
T

PDPTE:
1GB
page

Address of EPT page directory

Ig X Ig A 0 Rsvd. X W R PDPTE:
page
n. U n.
directory

Ignored

Ignored

S
V
E

Ig X
Ig A Reserved X W R PML4E:
4
n. U
present5
3 n.

Ignored

Ignored

Physical address
of 2MB page

000

Reserved

Address of EPT page table

Rsvd.

Physical address of 4KB page

PDTPE:
not
present

I
Ig X D A 1 P EPT X W R
n. U
A MT
T

PDE:
2MB
page

Ig X Ig A 0 Rsvd. X W R
n. U n.

PDE:
page
table

Ignored

Ignored

EPTP2

000
I
Ig X D A gI P EPT X W R
n. U
MT
n A
T

Ignored

000

PDE:
not
present
PTE:
4KB
page
PTE:
not
present

Figure 28-1. Formats of EPTP and EPT Paging-Structure Entries
NOTES:
1. M is an abbreviation for MAXPHYADDR.
2. See Section 24.6.11 for details of the EPTP.
3. Execute access for user-mode linear addresses. If the “mode-based execute control for EPT” VM-execution control is 0, this bit is
ignored.
4. Execute access. If the “mode-based execute control for EPT” VM-execution control is 1, this bit controls execute access for supervisor-mode linear addresses.
5. If the “mode-based execute control for EPT” VM-execution control is 1, an EPT paging-structure entry is present if any of bits 2:0 or
bit 10 is 1. This table does not comprehend that fact.
6. Suppress #VE. If the “EPT-violation #VE” VM-execution control is 0, this bit is ignored.

•

The access is a data write, for any byte to be written, bit 1 (write access) was clear in any of the EPT pagingstructure entries used to translate the guest-physical address of the byte. Writes by the logical processor to
guest paging structures to update accessed and dirty flags are considered to be data writes.
If bit 6 of the EPT pointer (EPTP) is 1 (enabling accessed and dirty flags for EPT), processor accesses to guest
paging-structure entries are treated as writes with regard to EPT violations. Thus, if bit 1 is clear in any of the

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VMX SUPPORT FOR ADDRESS TRANSLATION

EPT paging-structure entries used to translate the guest-physical address of a guest paging-structure entry, an
attempt to use that entry to translate a linear address causes an EPT violation.
(This does not apply to loads of the PDPTE registers by the MOV to CR instruction for PAE paging; see Section
4.4.1. Those loads of guest PDPTEs are treated as reads and do not cause EPT violations due to a guest-physical
address not being writable.)

•

The access is an instruction fetch and the EPT paging structures prevent execute access to any of the bytes
being fetched. Whether this occurs depends upon the setting of the “mode-based execute control for EPT” VMexecution control:
— If the control is 0, an instruction fetch from a byte is prevented if bit 2 (execute access) was clear in any of
the EPT paging-structure entries used to translate the guest-physical address of the byte.
— If the control is 1, an instruction fetch from a byte is prevented in either of the following cases:

•

Paging maps the linear address of the byte as a supervisor-mode address and bit 2 (execute access for
supervisor-mode linear addresses) was clear in any of the EPT paging-structure entries used to
translate the guest-physical address of the byte.
Paging maps a linear address as a supervisor-mode address if the U/S flag (bit 2) is 0 in at least one of
the paging-structure entries controlling the translation of the linear address.

•

Paging maps the linear address of the byte as a user-mode address and bit 10 (execute access for usermode linear addresses) was clear in any of the EPT paging-structure entries used to translate the guestphysical address of the byte.
Paging maps a linear address as a user-mode address if the U/S flag is 1 in all of the paging-structure
entries controlling the translation of the linear address. If paging is disabled (CR0.PG = 0), every linear
address is a user-mode address.

28.2.3.3

Prioritization of EPT Misconfigurations and EPT Violations

The translation of a linear address to a physical address requires one or more translations of guest-physical
addresses using EPT (see Section 28.2.1). This section specifies the relative priority of EPT-induced VM exits with
respect to each other and to other events that may be encountered when accessing memory using a linear address.
For an access to a guest-physical address, determination of whether an EPT misconfiguration or an EPT violation
occurs is based on an iterative process:1
1. An EPT paging-structure entry is read (initially, this is an EPT PML4 entry):
a. If the entry is not present (see Section 28.2.2), an EPT violation occurs.
b. If the entry is present but its contents are not configured properly (see Section 28.2.3.1), an EPT misconfiguration occurs.
c.

If the entry is present and its contents are configured properly, operation depends on whether the entry
references another EPT paging structure (whether it is an EPT PDE with bit 7 set to 1 or an EPT PTE):
i)

If the entry does reference another EPT paging structure, an entry from that structure is accessed;
step 1 is executed for that other entry.

ii) Otherwise, the entry is used to produce the ultimate physical address (the translation of the original
guest-physical address); step 2 is executed.
2. Once the ultimate physical address is determined, the privileges determined by the EPT paging-structure
entries are evaluated:
a. If the access to the guest-physical address is not allowed by these privileges (see Section 28.2.3.2), an EPT
violation occurs.
b. If the access to the guest-physical address is allowed by these privileges, memory is accessed using the
ultimate physical address.
If CR0.PG = 1, the translation of a linear address is also an iterative process, with the processor first accessing an
entry in the guest paging structure referenced by the guest-physical address in CR3 (or, if PAE paging is in use, the
1. This is a simplification of the more detailed description given in Section 28.2.2.
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VMX SUPPORT FOR ADDRESS TRANSLATION

guest-physical address in the appropriate PDPTE register), then accessing an entry in another guest paging structure referenced by the guest-physical address in the first guest paging-structure entry, etc. Each guest-physical
address is itself translated using EPT and may cause an EPT-induced VM exit. The following items detail how page
faults and EPT-induced VM exits are recognized during this iterative process:
1. An attempt is made to access a guest paging-structure entry with a guest-physical address (initially, the
address in CR3 or PDPTE register).
a. If the access fails because of an EPT misconfiguration or an EPT violation (see above), an EPT-induced
VM exit occurs.
b. If the access does not cause an EPT-induced VM exit, bit 0 (the present flag) of the entry is consulted:
i)

If the present flag is 0 or any reserved bit is set, a page fault occurs.

ii) If the present flag is 1, no reserved bit is set, operation depends on whether the entry references
another guest paging structure (whether it is a guest PDE with PS = 1 or a guest PTE):

•

If the entry does reference another guest paging structure, an entry from that structure is
accessed; step 1 is executed for that other entry.

•

Otherwise, the entry is used to produce the ultimate guest-physical address (the translation of the
original linear address); step 2 is executed.

2. Once the ultimate guest-physical address is determined, the privileges determined by the guest pagingstructure entries are evaluated:
a. If the access to the linear address is not allowed by these privileges (e.g., it was a write to a read-only
page), a page fault occurs.
b. If the access to the linear address is allowed by these privileges, an attempt is made to access memory at
the ultimate guest-physical address:
i)

If the access fails because of an EPT misconfiguration or an EPT violation (see above), an EPT-induced
VM exit occurs.

ii) If the access does not cause an EPT-induced VM exit, memory is accessed using the ultimate physical
address (the translation, using EPT, of the ultimate guest-physical address).
If CR0.PG = 0, a linear address is treated as a guest-physical address and is translated using EPT (see above). This
process, if it completes without an EPT violation or EPT misconfiguration, produces a physical address and determines the privileges allowed by the EPT paging-structure entries. If these privileges do not allow the access to the
physical address (see Section 28.2.3.2), an EPT violation occurs. Otherwise, memory is accessed using the physical address.

28.2.4

Accessed and Dirty Flags for EPT

The Intel 64 architecture supports accessed and dirty flags in ordinary paging-structure entries (see Section
4.8). Some processors also support corresponding flags in EPT paging-structure entries. Software should read the
VMX capability MSR IA32_VMX_EPT_VPID_CAP (see Appendix A.10) to determine whether the processor supports
this feature.
Software can enable accessed and dirty flags for EPT using bit 6 of the extended-page-table pointer (EPTP), a VMexecution control field (see Table 24-8 in Section 24.6.11). If this bit is 1, the processor will set the accessed and
dirty flags for EPT as described below. In addition, setting this flag causes processor accesses to guest pagingstructure entries to be treated as writes (see below and Section 28.2.3.2).
For any EPT paging-structure entry that is used during guest-physical-address translation, bit 8 is the accessed
flag. For a EPT paging-structure entry that maps a page (as opposed to referencing another EPT paging structure),
bit 9 is the dirty flag.
Whenever the processor uses an EPT paging-structure entry as part of guest-physical-address translation, it sets
the accessed flag in that entry (if it is not already set).
Whenever there is a write to a guest-physical address, the processor sets the dirty flag (if it is not already set) in
the EPT paging-structure entry that identifies the final physical address for the guest-physical address (either an
EPT PTE or an EPT paging-structure entry in which bit 7 is 1).

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When accessed and dirty flags for EPT are enabled, processor accesses to guest paging-structure entries are
treated as writes (see Section 28.2.3.2). Thus, such an access will cause the processor to set the dirty flag in the
EPT paging-structure entry that identifies the final physical address of the guest paging-structure entry.
(This does not apply to loads of the PDPTE registers for PAE paging by the MOV to CR instruction; see Section 4.4.1.
Those loads of guest PDPTEs are treated as reads and do not cause the processor to set the dirty flag in any EPT
paging-structure entry.)
These flags are “sticky,” meaning that, once set, the processor does not clear them; only software can clear them.
A processor may cache information from the EPT paging-structure entries in TLBs and paging-structure caches (see
Section 28.3). This fact implies that, if software changes an accessed flag or a dirty flag from 1 to 0, the processor
might not set the corresponding bit in memory on a subsequent access using an affected guest-physical address.

28.2.5

Page-Modification Logging

When accessed and dirty flags for EPT are enabled, software can track writes to guest-physical addresses using a
feature called page-modification logging.
Software can enable page-modification logging by setting the “enable PML” VM-execution control (see Table 24-7
in Section 24.6.2). When this control is 1, the processor adds entries to the page-modification log as described
below. The page-modification log is a 4-KByte region of memory located at the physical address in the PML address
VM-execution control field. The page-modification log consists of 512 64-bit entries; the PML index VM-execution
control field indicates the next entry to use.
Before allowing a guest-physical access, the processor may determine that it first needs to set an accessed or dirty
flag for EPT (see Section 28.2.4). When this happens, the processor examines the PML index. If the PML index is
not in the range 0–511, there is a page-modification log-full event and a VM exit occurs. In this case, the
accessed or dirty flag is not set, and the guest-physical access that triggered the event does not occur.
If instead the PML index is in the range 0–511, the processor proceeds to update accessed or dirty flags for EPT as
described in Section 28.2.4. If the processor updated a dirty flag for EPT (changing it from 0 to 1), it then operates
as follows:
1. The guest-physical address of the access is written to the page-modification log. Specifically, the guest-physical
address is written to physical address determined by adding 8 times the PML index to the PML address.
Bits 11:0 of the value written are always 0 (the guest-physical address written is thus 4-KByte aligned).
2. The PML index is decremented by 1 (this may cause the value to transition from 0 to FFFFH).
Because the processor decrements the PML index with each log entry, the value may transition from 0 to FFFFH. At
that point, no further logging will occur, as the processor will determine that the PML index is not in the range 0–
511 and will generate a page-modification log-full event (see above).

28.2.6

EPT and Memory Typing

This section specifies how a logical processor determines the memory type use for a memory access while EPT is in
use. (See Chapter 11, “Memory Cache Control” of Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 3A for details of memory typing in the Intel 64 architecture.) Section 28.2.6.1 explains how the memory
type is determined for accesses to the EPT paging structures. Section 28.2.6.2 explains how the memory type is
determined for an access using a guest-physical address that is translated using EPT.

28.2.6.1

Memory Type Used for Accessing EPT Paging Structures

This section explains how the memory type is determined for accesses to the EPT paging structures. The determination is based first on the value of bit 30 (cache disable—CD) in control register CR0:

•

If CR0.CD = 0, the memory type used for any such reference is the EPT paging-structure memory type, which
is specified in bits 2:0 of the extended-page-table pointer (EPTP), a VM-execution control field (see Section
24.6.11). A value of 0 indicates the uncacheable type (UC), while a value of 6 indicates the write-back type
(WB). Other values are reserved.

•

If CR0.CD = 1, the memory type used for any such reference is uncacheable (UC).

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The MTRRs have no effect on the memory type used for an access to an EPT paging structure.

28.2.6.2

Memory Type Used for Translated Guest-Physical Addresses

The effective memory type of a memory access using a guest-physical address (an access that is translated
using EPT) is the memory type that is used to access memory. The effective memory type is based on the value of
bit 30 (cache disable—CD) in control register CR0; the last EPT paging-structure entry used to translate the guestphysical address (either an EPT PDE with bit 7 set to 1 or an EPT PTE); and the PAT memory type (see below):

•

The PAT memory type depends on the value of CR0.PG:
— If CR0.PG = 0, the PAT memory type is WB (writeback).1
— If CR0.PG = 1, the PAT memory type is the memory type selected from the IA32_PAT MSR as specified in
Section 11.12.3, “Selecting a Memory Type from the PAT”.2

•

The EPT memory type is specified in bits 5:3 of the last EPT paging-structure entry: 0 = UC; 1 = WC; 4 =
WT; 5 = WP; and 6 = WB. Other values are reserved and cause EPT misconfigurations (see Section 28.2.3).

•

If CR0.CD = 0, the effective memory type depends upon the value of bit 6 of the last EPT paging-structure
entry:
— If the value is 0, the effective memory type is the combination of the EPT memory type and the PAT
memory type specified in Table 11-7 in Section 11.5.2.2, using the EPT memory type in place of the MTRR
memory type.
— If the value is 1, the memory type used for the access is the EPT memory type. The PAT memory type is
ignored.

•

If CR0.CD = 1, the effective memory type is UC.

The MTRRs have no effect on the memory type used for an access to a guest-physical address.

28.3

CACHING TRANSLATION INFORMATION

Processors supporting Intel® 64 and IA-32 architectures may accelerate the address-translation process by
caching on the processor data from the structures in memory that control that process. Such caching is discussed
in Section 4.10, “Caching Translation Information” in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3A. The current section describes how this caching interacts with the VMX architecture.
The VPID and EPT features of the architecture for VMX operation augment this caching architecture. EPT defines
the guest-physical address space and defines translations to that address space (from the linear-address space)
and from that address space (to the physical-address space). Both features control the ways in which a logical
processor may create and use information cached from the paging structures.
Section 28.3.1 describes the different kinds of information that may be cached. Section 28.3.2 specifies when such
information may be cached and how it may be used. Section 28.3.3 details how software can invalidate cached
information.

28.3.1

Information That May Be Cached

Section 4.10, “Caching Translation Information” in Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 3A identifies two kinds of translation-related information that may be cached by a logical
1. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PG must be 1 in VMX operation, CR0.PG can be 0 in VMX non-root
operation only if the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls
are both 1.
2. Table 11-11 in Section 11.12.3, “Selecting a Memory Type from the PAT” illustrates how the PAT memory type is selected based on
the values of the PAT, PCD, and PWT bits in a page-table entry (or page-directory entry with PS = 1). For accesses to a guest pagingstructure entry X, the PAT memory type is selected from the table by using a value of 0 for the PAT bit with the values of PCD and
PWT from the paging-structure entry Y that references X (or from CR3 if X is in the root paging structure). With PAE paging, the PAT
memory type for accesses to the PDPTEs is WB.
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processor: translations, which are mappings from linear page numbers to physical page frames, and pagingstructure caches, which map the upper bits of a linear page number to information from the paging-structure
entries used to translate linear addresses matching those upper bits.
The same kinds of information may be cached when VPIDs and EPT are in use. A logical processor may cache and
use such information based on its function. Information with different functionality is identified as follows:

•

Linear mappings.1 There are two kinds:
— Linear translations. Each of these is a mapping from a linear page number to the physical page frame to
which it translates, along with information about access privileges and memory typing.
— Linear paging-structure-cache entries. Each of these is a mapping from the upper portion of a linear
address to the physical address of the paging structure used to translate the corresponding region of the
linear-address space, along with information about access privileges. For example, bits 47:39 of a linear
address would map to the address of the relevant page-directory-pointer table.
Linear mappings do not contain information from any EPT paging structure.

•

Guest-physical mappings.2 There are two kinds:
— Guest-physical translations. Each of these is a mapping from a guest-physical page number to the physical
page frame to which it translates, along with information about access privileges and memory typing.
— Guest-physical paging-structure-cache entries. Each of these is a mapping from the upper portion of a
guest-physical address to the physical address of the EPT paging structure used to translate the corresponding region of the guest-physical address space, along with information about access privileges.
The information in guest-physical mappings about access privileges and memory typing is derived from EPT
paging structures.

•

Combined mappings.3 There are two kinds:
— Combined translations. Each of these is a mapping from a linear page number to the physical page frame to
which it translates, along with information about access privileges and memory typing.
— Combined paging-structure-cache entries. Each of these is a mapping from the upper portion of a linear
address to the physical address of the paging structure used to translate the corresponding region of the
linear-address space, along with information about access privileges.
The information in combined mappings about access privileges and memory typing is derived from both guest
paging structures and EPT paging structures.

28.3.2

Creating and Using Cached Translation Information

The following items detail the creation of the mappings described in the previous section:4

•

The following items describe the creation of mappings while EPT is not in use (including execution outside VMX
non-root operation):
— Linear mappings may be created. They are derived from the paging structures referenced (directly or
indirectly) by the current value of CR3 and are associated with the current VPID and the current PCID.
— No linear mappings are created with information derived from paging-structure entries that are not present
(bit 0 is 0) or that set reserved bits. For example, if a PTE is not present, no linear mapping are created for
any linear page number whose translation would use that PTE.
— No guest-physical or combined mappings are created while EPT is not in use.

•

The following items describe the creation of mappings while EPT is in use:

1. Earlier versions of this manual used the term “VPID-tagged” to identify linear mappings.
2. Earlier versions of this manual used the term “EPTP-tagged” to identify guest-physical mappings.
3. Earlier versions of this manual used the term “dual-tagged” to identify combined mappings.
4. This section associated cached information with the current VPID and PCID. If PCIDs are not supported or are not being used (e.g.,
because CR4.PCIDE = 0), all the information is implicitly associated with PCID 000H; see Section 4.10.1, “Process-Context Identifiers
(PCIDs),” in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.
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— Guest-physical mappings may be created. They are derived from the EPT paging structures referenced
(directly or indirectly) by bits 51:12 of the current EPTP. These 40 bits contain the address of the EPT-PML4table. (the notation EP4TA refers to those 40 bits). Newly created guest-physical mappings are associated
with the current EP4TA.
— Combined mappings may be created. They are derived from the EPT paging structures referenced (directly
or indirectly) by the current EP4TA. If CR0.PG = 1, they are also derived from the paging structures
referenced (directly or indirectly) by the current value of CR3. They are associated with the current VPID,
the current PCID, and the current EP4TA.1 No combined paging-structure-cache entries are created if
CR0.PG = 0.2
— No guest-physical mappings or combined mappings are created with information derived from EPT pagingstructure entries that are not present (see Section 28.2.2) or that are misconfigured (see Section
28.2.3.1).
— No combined mappings are created with information derived from guest paging-structure entries that are
not present or that set reserved bits.
— No linear mappings are created while EPT is in use.
The following items detail the use of the various mappings:

•

If EPT is not in use (e.g., when outside VMX non-root operation), a logical processor may use cached mappings
as follows:
— For accesses using linear addresses, it may use linear mappings associated with the current VPID and the
current PCID. It may also use global TLB entries (linear mappings) associated with the current VPID and
any PCID.
— No guest-physical or combined mappings are used while EPT is not in use.

•

If EPT is in use, a logical processor may use cached mappings as follows:
— For accesses using linear addresses, it may use combined mappings associated with the current VPID, the
current PCID, and the current EP4TA. It may also use global TLB entries (combined mappings) associated
with the current VPID, the current EP4TA, and any PCID.
— For accesses using guest-physical addresses, it may use guest-physical mappings associated with the
current EP4TA.
— No linear mappings are used while EPT is in use.

28.3.3

Invalidating Cached Translation Information

Software modifications of paging structures (including EPT paging structures) may result in inconsistencies
between those structures and the mappings cached by a logical processor. Certain operations invalidate information cached by a logical processor and can be used to eliminate such inconsistencies.

28.3.3.1

Operations that Invalidate Cached Mappings

The following operations invalidate cached mappings as indicated:

•

Operations that architecturally invalidate entries in the TLBs or paging-structure caches independent of VMX
operation (e.g., the INVLPG and INVPCID instructions) invalidate linear mappings and combined mappings.3
They are required to do so only for the current VPID (but, for combined mappings, all EP4TAs). Linear

1. At any given time, a logical processor may be caching combined mappings for a VPID and a PCID that are associated with different
EP4TAs. Similarly, it may be caching combined mappings for an EP4TA that are associated with different VPIDs and PCIDs.
2. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PG must be 1 in VMX operation, CR0.PG can be 0 in VMX non-root
operation only if the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls
are both 1.
3. See Section 4.10.4, “Invalidation of TLBs and Paging-Structure Caches,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A for an enumeration of operations that architecturally invalidate entries in the TLBs and paging-structure
caches independent of VMX operation.
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mappings for the current VPID are invalidated even if EPT is in use.1 Combined mappings for the current
VPID are invalidated even if EPT is not in use.2

•

An EPT violation invalidates any guest-physical mappings (associated with the current EP4TA) that would be
used to translate the guest-physical address that caused the EPT violation. If that guest-physical address was
the translation of a linear address, the EPT violation also invalidates any combined mappings for that linear
address associated with the current PCID, the current VPID and the current EP4TA.

•

If the “enable VPID” VM-execution control is 0, VM entries and VM exits invalidate linear mappings and
combined mappings associated with VPID 0000H (for all PCIDs). Combined mappings for VPID 0000H are
invalidated for all EP4TAs.

•

Execution of the INVVPID instruction invalidates linear mappings and combined mappings. Invalidation is based
on instruction operands, called the INVVPID type and the INVVPID descriptor. Four INVVPID types are currently
defined:
— Individual-address. If the INVVPID type is 0, the logical processor invalidates linear mappings and
combined mappings associated with the VPID specified in the INVVPID descriptor and that would be used
to translate the linear address specified in of the INVVPID descriptor. Linear mappings and combined
mappings for that VPID and linear address are invalidated for all PCIDs and, for combined mappings, all
EP4TAs. (The instruction may also invalidate mappings associated with other VPIDs and for other linear
addresses.)
— Single-context. If the INVVPID type is 1, the logical processor invalidates all linear mappings and
combined mappings associated with the VPID specified in the INVVPID descriptor. Linear mappings and
combined mappings for that VPID are invalidated for all PCIDs and, for combined mappings, all EP4TAs.
(The instruction may also invalidate mappings associated with other VPIDs.)
— All-context. If the INVVPID type is 2, the logical processor invalidates linear mappings and combined
mappings associated with all VPIDs except VPID 0000H and with all PCIDs. (The instruction may also
invalidate linear mappings with VPID 0000H.) Combined mappings are invalidated for all EP4TAs.
— Single-context-retaining-globals. If the INVVPID type is 3, the logical processor invalidates linear
mappings and combined mappings associated with the VPID specified in the INVVPID descriptor. Linear
mappings and combined mappings for that VPID are invalidated for all PCIDs and, for combined mappings,
all EP4TAs. The logical processor is not required to invalidate information that was used for global translations (although it may do so). See Section 4.10, “Caching Translation Information” for details regarding
global translations. (The instruction may also invalidate mappings associated with other VPIDs.)
See Chapter 30 for details of the INVVPID instruction. See Section 28.3.3.3 for guidelines regarding use of this
instruction.

•

Execution of the INVEPT instruction invalidates guest-physical mappings and combined mappings. Invalidation
is based on instruction operands, called the INVEPT type and the INVEPT descriptor. Two INVEPT types are
currently defined:
— Single-context. If the INVEPT type is 1, the logical processor invalidates all guest-physical mappings and
combined mappings associated with the EP4TA specified in the INVEPT descriptor. Combined mappings for
that EP4TA are invalidated for all VPIDs and all PCIDs. (The instruction may invalidate mappings associated
with other EP4TAs.)
— All-context. If the INVEPT type is 2, the logical processor invalidates guest-physical mappings and
combined mappings associated with all EP4TAs (and, for combined mappings, for all VPIDs and PCIDs).
See Chapter 30 for details of the INVEPT instruction. See Section 28.3.3.4 for guidelines regarding use of this
instruction.

•

A power-up or a reset invalidates all linear mappings, guest-physical mappings, and combined mappings.

1. While no linear mappings are created while EPT is in use, a logical processor may retain, while EPT is in use, linear mappings (for the
same VPID as the current one) there were created earlier, when EPT was not in use.
2. While no combined mappings are created while EPT is not in use, a logical processor may retain, while EPT is in not use, combined
mappings (for the same VPID as the current one) there were created earlier, when EPT was in use.
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28.3.3.2

Operations that Need Not Invalidate Cached Mappings

The following items detail cases of operations that are not required to invalidate certain cached mappings:

•

Operations that architecturally invalidate entries in the TLBs or paging-structure caches independent of VMX
operation are not required to invalidate any guest-physical mappings.

•
•
•

The INVVPID instruction is not required to invalidate any guest-physical mappings.

•

The VMXOFF and VMXON instructions are not required to invalidate any linear mappings, guest-physical
mappings, or combined mappings.

The INVEPT instruction is not required to invalidate any linear mappings.
VMX transitions are not required to invalidate any guest-physical mappings. If the “enable VPID” VM-execution
control is 1, VMX transitions are not required to invalidate any linear mappings or combined mappings.

A logical processor may invalidate any cached mappings at any time. For this reason, the operations identified
above may invalidate the indicated mappings despite the fact that doing so is not required.

28.3.3.3

Guidelines for Use of the INVVPID Instruction

The need for VMM software to use the INVVPID instruction depends on how that software is virtualizing memory
(e.g., see Section 32.3, “Memory Virtualization”).
If EPT is not in use, it is likely that the VMM is virtualizing the guest paging structures. Such a VMM may configure
the VMCS so that all or some of the operations that invalidate entries the TLBs and the paging-structure caches
(e.g., the INVLPG instruction) cause VM exits. If VMM software is emulating these operations, it may be necessary
to use the INVVPID instruction to ensure that the logical processor’s TLBs and the paging-structure caches are
appropriately invalidated.
Requirements of when software should use the INVVPID instruction depend on the specific algorithm being used for
page-table virtualization. The following items provide guidelines for software developers:

•

Emulation of the INVLPG instruction may require execution of the INVVPID instruction as follows:
— The INVVPID type is individual-address (0).
— The VPID in the INVVPID descriptor is the one assigned to the virtual processor whose execution is being
emulated.
— The linear address in the INVVPID descriptor is that of the operand of the INVLPG instruction being
emulated.

•

Some instructions invalidate all entries in the TLBs and paging-structure caches—except for global translations.
An example is the MOV to CR3 instruction. (See Section 4.10, “Caching Translation Information” in the Intel®
64 and IA-32 Architectures Software Developer’s Manual, Volume 3A for details regarding global translations.)
Emulation of such an instruction may require execution of the INVVPID instruction as follows:
— The INVVPID type is single-context-retaining-globals (3).
— The VPID in the INVVPID descriptor is the one assigned to the virtual processor whose execution is being
emulated.

•

Some instructions invalidate all entries in the TLBs and paging-structure caches—including for global translations. An example is the MOV to CR4 instruction if the value of value of bit 4 (page global enable—PGE) is
changing. Emulation of such an instruction may require execution of the INVVPID instruction as follows:
— The INVVPID type is single-context (1).
— The VPID in the INVVPID descriptor is the one assigned to the virtual processor whose execution is being
emulated.

If EPT is not in use, the logical processor associates all mappings it creates with the current VPID, and it will use
such mappings to translate linear addresses. For that reason, a VMM should not use the same VPID for different
non-EPT guests that use different page tables. Doing so may result in one guest using translations that pertain to
the other.
If EPT is in use, the instructions enumerated above might not be configured to cause VM exits and the VMM might
not be emulating them. In that case, executions of the instructions by guest software properly invalidate the

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required entries in the TLBs and paging-structure caches (see Section 28.3.3.1); execution of the INVVPID instruction is not required.
If EPT is in use, the logical processor associates all mappings it creates with the value of bits 51:12 of current EPTP.
If a VMM uses different EPTP values for different guests, it may use the same VPID for those guests. Doing so
cannot result in one guest using translations that pertain to the other.
The following guidelines apply more generally and are appropriate even if EPT is in use:

•

As detailed in Section 29.4.5, an access to the APIC-access page might not cause an APIC-access VM exit if
software does not properly invalidate information that may be cached from the paging structures. If, at one
time, the current VPID on a logical processor was a non-zero value X, it is recommended that software use the
INVVPID instruction with the “single-context” INVVPID type and with VPID X in the INVVPID descriptor before
a VM entry on the same logical processor that establishes VPID X and either (a) the “virtualize APIC accesses”
VM-execution control was changed from 0 to 1; or (b) the value of the APIC-access address was changed.

•

Software can use the INVVPID instruction with the “all-context” INVVPID type immediately after execution of
the VMXON instruction or immediately prior to execution of the VMXOFF instruction. Either prevents potentially
undesired retention of information cached from paging structures between separate uses of VMX operation.

28.3.3.4

Guidelines for Use of the INVEPT Instruction

The following items provide guidelines for use of the INVEPT instruction to invalidate information cached from the
EPT paging structures.

•

Software should use the INVEPT instruction with the “single-context” INVEPT type after making any of the
following changes to an EPT paging-structure entry (the INVEPT descriptor should contain an EPTP value that
references — directly or indirectly — the modified EPT paging structure):
— Changing any of the privilege bits 2:0 from 1 to 0.1
— Changing the physical address in bits 51:12.
— Clearing bit 8 (the accessed flag) if accessed and dirty flags for EPT will be enabled.
— For an EPT PDPTE or an EPT PDE, changing bit 7 (which determines whether the entry maps a page).
— For the last EPT paging-structure entry used to translate a guest-physical address (an EPT PDPTE with bit 7
set to 1, an EPT PDE with bit 7 set to 1, or an EPT PTE), changing either bits 5:3 or bit 6. (These bits
determine the effective memory type of accesses using that EPT paging-structure entry; see Section
28.2.6.)
— For the last EPT paging-structure entry used to translate a guest-physical address (an EPT PDPTE with bit 7
set to 1, an EPT PDE with bit 7 set to 1, or an EPT PTE), clearing bit 9 (the dirty flag) if accessed and dirty
flags for EPT will be enabled.

•

Software should use the INVEPT instruction with the “single-context” INVEPT type before a VM entry with an
EPTP value X such that X[6] = 1 (accessed and dirty flags for EPT are enabled) if the logical processor had
earlier been in VMX non-root operation with an EPTP value Y such that Y[6] = 0 (accessed and dirty flags for
EPT are not enabled) and Y[51:12] = X[51:12].

•

Software may use the INVEPT instruction after modifying a present EPT paging-structure entry (see Section
28.2.2) to change any of the privilege bits 2:0 from 0 to 1.2 Failure to do so may cause an EPT violation that
would not otherwise occur. Because an EPT violation invalidates any mappings that would be used by the access
that caused the EPT violation (see Section 28.3.3.1), an EPT violation will not recur if the original access is
performed again, even if the INVEPT instruction is not executed.

•

Because a logical processor does not cache any information derived from EPT paging-structure entries that are
not present (see Section 28.2.2) or misconfigured (see Section 28.2.3.1), it is not necessary to execute INVEPT
following modification of an EPT paging-structure entry that had been not present or misconfigured.

1. If the “mode-based execute control for EPT” VM-execution control is 1, software should use the INVEPT instruction changing privilege bit 10 from 1 to 0.
2. If the “mode-based execute control for EPT” VM-execution control is 1, software may use the INVEPT instruction after modifying a
present EPT paging-structure entry to change privilege bit 10 from 0 to 1.
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•

As detailed in Section 29.4.5, an access to the APIC-access page might not cause an APIC-access VM exit if
software does not properly invalidate information that may be cached from the EPT paging structures. If EPT
was in use on a logical processor at one time with EPTP X, it is recommended that software use the INVEPT
instruction with the “single-context” INVEPT type and with EPTP X in the INVEPT descriptor before a VM entry
on the same logical processor that enables EPT with EPTP X and either (a) the “virtualize APIC accesses” VMexecution control was changed from 0 to 1; or (b) the value of the APIC-access address was changed.

•

Software can use the INVEPT instruction with the “all-context” INVEPT type immediately after execution of the
VMXON instruction or immediately prior to execution of the VMXOFF instruction. Either prevents potentially
undesired retention of information cached from EPT paging structures between separate uses of VMX
operation.

In a system containing more than one logical processor, software must account for the fact that information from
an EPT paging-structure entry may be cached on logical processors other than the one that modifies that entry. The
process of propagating the changes to a paging-structure entry is commonly referred to as “TLB shootdown.” A
discussion of TLB shootdown appears in Section 4.10.5, “Propagation of Paging-Structure Changes to Multiple
Processors,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.

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CHAPTER 29
APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS
The VMCS includes controls that enable the virtualization of interrupts and the Advanced Programmable Interrupt
Controller (APIC).
When these controls are used, the processor will emulate many accesses to the APIC, track the state of the virtual
APIC, and deliver virtual interrupts — all in VMX non-root operation with out a VM exit.1
The processor tracks the state of the virtual APIC using a virtual-APIC page identified by the virtual-machine
monitor (VMM). Section 29.1 discusses the virtual-APIC page and how the processor uses it to track the state of the
virtual APIC.
The following are the VM-execution controls relevant to APIC virtualization and virtual interrupts (see Section 24.6
for information about the locations of these controls):

•

Virtual-interrupt delivery. This controls enables the evaluation and delivery of pending virtual interrupts
(Section 29.2). It also enables the emulation of writes (memory-mapped or MSR-based, as enabled) to the
APIC registers that control interrupt prioritization.

•

Use TPR shadow. This control enables emulation of accesses to the APIC’s task-priority register (TPR) via CR8
(Section 29.3) and, if enabled, via the memory-mapped or MSR-based interfaces.

•

Virtualize APIC accesses. This control enables virtualization of memory-mapped accesses to the APIC
(Section 29.4) by causing VM exits on accesses to a VMM-specified APIC-access page. Some of the other
controls, if set, may cause some of these accesses to be emulated rather than causing VM exits.

•

Virtualize x2APIC mode. This control enables virtualization of MSR-based accesses to the APIC (Section
29.5).

•

APIC-register virtualization. This control allows memory-mapped and MSR-based reads of most APIC
registers (as enabled) by satisfying them from the virtual-APIC page. It directs memory-mapped writes to the
APIC-access page to the virtual-APIC page, following them by VM exits for VMM emulation.

•

Process posted interrupts. This control allows software to post virtual interrupts in a data structure and send
a notification to another logical processor; upon receipt of the notification, the target processor will process the
posted interrupts by copying them into the virtual-APIC page (Section 29.6).

“Virtualize APIC accesses”, “virtualize x2APIC mode”, “virtual-interrupt delivery”, and “APIC-register virtualization”
are all secondary processor-based VM-execution controls. If bit 31 of the primary processor-based VM-execution
controls is 0, the processor operates as if these controls were all 0. See Section 24.6.2.

29.1

VIRTUAL APIC STATE

The virtual-APIC page is a 4-KByte region of memory that the processor uses to virtualize certain accesses to
APIC registers and to manage virtual interrupts. The physical address of the virtual-APIC page is the virtual-APIC
address, a 64-bit VM-execution control field in the VMCS (see Section 24.6.8).
Depending on the settings of certain VM-execution controls, the processor may virtualize certain fields on the
virtual-APIC page with functionality analogous to that performed by the local APIC. Section 29.1.1 identifies and
defines these fields. Section 29.1.2, Section 29.1.3, Section 29.1.4, and Section 29.1.5 detail the actions taken to
virtualize updates to some of these fields.

29.1.1

Virtualized APIC Registers

Depending on the setting of certain VM-execution controls, a logical processor may virtualize certain accesses to
APIC registers using the following fields on the virtual-APIC page:

•

Virtual task-priority register (VTPR): the 32-bit field located at offset 080H on the virtual-APIC page.

1. In most cases, it is not necessary for a virtual-machine monitor (VMM) to inject virtual interrupts as part of VM entry.
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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

•

Virtual processor-priority register (VPPR): the 32-bit field located at offset 0A0H on the virtual-APIC
page.

•
•

Virtual end-of-interrupt register (VEOI): the 32-bit field located at offset 0B0H on the virtual-APIC page.

•

Virtual interrupt-request register (VIRR): the 256-bit value comprising eight non-contiguous 32-bit fields
at offsets 200H, 210H, 220H, 230H, 240H, 250H, 260H, and 270H on the virtual-APIC page. Bit x of the VIRR
is at bit position (x & 1FH) at offset (200H | ((x & E0H) » 1)). The processor uses only the low 4 bytes of each
of the 16-Byte fields at offsets 200H, 210H, 220H, 230H, 240H, 250H, 260H, and 270H.

•

Virtual interrupt-command register (VICR_LO): the 32-bit field located at offset 300H on the virtual-APIC
page

•

Virtual interrupt-command register (VICR_HI): the 32-bit field located at offset 310H on the virtual-APIC
page.

Virtual interrupt-service register (VISR): the 256-bit value comprising eight non-contiguous 32-bit fields
at offsets 100H, 110H, 120H, 130H, 140H, 150H, 160H, and 170H on the virtual-APIC page. Bit x of the VISR
is at bit position (x & 1FH) at offset (100H | ((x & E0H) » 1)). The processor uses only the low 4 bytes of each
of the 16-byte fields at offsets 100H, 110H, 120H, 130H, 140H, 150H, 160H, and 170H.

29.1.2

TPR Virtualization

The processor performs TPR virtualization in response to the following operations: (1) virtualization of the MOV
to CR8 instruction; (2) virtualization of a write to offset 080H on the APIC-access page; and (3) virtualization of the
WRMSR instruction with ECX = 808H. See Section 29.3, Section 29.4.3, and Section 29.5 for details of when TPR
virtualization is performed.
The following pseudocode details the behavior of TPR virtualization:
IF “virtual-interrupt delivery” is 0
THEN
IF VTPR[7:4] < TPR threshold (see Section 24.6.8)
THEN cause VM exit due to TPR below threshold;
FI;
ELSE
perform PPR virtualization (see Section 29.1.3);
evaluate pending virtual interrupts (see Section 29.2.1);
FI;
Any VM exit caused by TPR virtualization is trap-like: the instruction causing TPR virtualization completes before
the VM exit occurs (for example, the value of CS:RIP saved in the guest-state area of the VMCS references the next
instruction).

29.1.3

PPR Virtualization

The processor performs PPR virtualization in response to the following operations: (1) VM entry; (2) TPR virtualization; and (3) EOI virtualization. See Section 26.3.2.5, Section 29.1.2, and Section 29.1.4 for details of when
PPR virtualization is performed.
PPR virtualization uses the guest interrupt status (specifically, SVI; see Section 24.4.2) and VTPR. The following
pseudocode details the behavior of PPR virtualization:
IF VTPR[7:4] ≥ SVI[7:4]
THEN VPPR ← VTPR & FFH;
ELSE VPPR ← SVI & F0H;
FI;
PPR virtualization always clears bytes 3:1 of VPPR.
PPR virtualization is caused only by TPR virtualization, EOI virtualization, and VM entry. Delivery of a virtual interrupt also modifies VPPR, but in a different way (see Section 29.2.2). No other operations modify VPPR, even if they
modify SVI, VISR, or VTPR.

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29.1.4

EOI Virtualization

The processor performs EOI virtualization in response to the following operations: (1) virtualization of a write to
offset 0B0H on the APIC-access page; and (2) virtualization of the WRMSR instruction with ECX = 80BH. See
Section 29.4.3 and Section 29.5 for details of when EOI virtualization is performed. EOI virtualization occurs only
if the “virtual-interrupt delivery” VM-execution control is 1.
EOI virtualization uses and updates the guest interrupt status (specifically, SVI; see Section 24.4.2). The following
pseudocode details the behavior of EOI virtualization:
Vector ← SVI;
VISR[Vector] ← 0; (see Section 29.1.1 for definition of VISR)
IF any bits set in VISR
THEN SVI ← highest index of bit set in VISR
ELSE SVI ← 0;
FI;
perform PPR virtualiation (see Section 29.1.3);
IF EOI_exit_bitmap[Vector] = 1 (see Section 24.6.8 for definition of EOI_exit_bitmap)
THEN cause EOI-induced VM exit with Vector as exit qualification;
ELSE evaluate pending virtual interrupts; (see Section 29.2.1)
FI;
Any VM exit caused by EOI virtualization is trap-like: the instruction causing EOI virtualization completes before
the VM exit occurs (for example, the value of CS:RIP saved in the guest-state area of the VMCS references the next
instruction).

29.1.5

Self-IPI Virtualization

The processor performs self-IPI virtualization in response to the following operations: (1) virtualization of a
write to offset 300H on the APIC-access page; and (2) virtualization of the WRMSR instruction with ECX = 83FH.
See Section 29.4.3 and Section 29.5 for details of when self-IPI virtualization is performed. Self-IPI virtualization
occurs only if the “virtual-interrupt delivery” VM-execution control is 1.
Each operation that leads to self-IPI virtualization provides an 8-bit vector (see Section 29.4.3 and Section 29.5).
Self-IPI virtualization updates the guest interrupt status (specifically, RVI; see Section 24.4.2). The following
pseudocode details the behavior of self-IPI virtualization:
VIRR[Vector] ← 1; (see Section 29.1.1 for definition of VIRR)
RVI ← max{RVI,Vector};
evaluate pending virtual interrupts; (see Section 29.2.1)

29.2

EVALUATION AND DELIVERY OF VIRTUAL INTERRUPTS

If the “virtual-interrupt delivery” VM-execution control is 1, certain actions in VMX non-root operation or during
VM entry cause the processor to evaluate and deliver virtual interrupts.
Evaluation of virtual interrupts is triggered by certain actions change the state of the virtual-APIC page and is
described in Section 29.2.1. This evaluation may result in recognition of a virtual interrupt. Once a virtual interrupt
is recognized, the processor may deliver it within VMX non-root operation without a VM exit. Virtual-interrupt
delivery is described in Section 29.2.2.

29.2.1

Evaluation of Pending Virtual Interrupts

If the “virtual-interrupt delivery” VM-execution control is 1, certain actions cause a logical processor to evaluate
pending virtual interrupts.
The following actions cause the evaluation of pending virtual interrupts: VM entry; TPR virtualization; EOI virtualization; self-IPI virtualization; and posted-interrupt processing. See Section 26.3.2.5, Section 29.1.2, Section

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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

29.1.4, Section 29.1.5, and Section 29.6 for details of when evaluation of pending virtual interrupts is performed.
No other operations cause the evaluation of pending virtual interrupts, even if they modify RVI or VPPR.
Evaluation of pending virtual interrupts uses the guest interrupt status (specifically, RVI; see Section 24.4.2). The
following pseudocode details the evaluation of pending virtual interrupts:
IF “interrupt-window exiting” is 0 AND
RVI[7:4] > VPPR[7:4] (see Section 29.1.1 for definition of VPPR)
THEN recognize a pending virtual interrupt;
ELSE
do not recognize a pending virtual interrupt;
FI;
Once recognized, a virtual interrupt may be delivered in VMX non-root operation; see Section 29.2.2.
Evaluation of pending virtual interrupts is caused only by VM entry, TPR virtualization, EOI virtualization, self-IPI
virtualization, and posted-interrupt processing. No other operations do so, even if they modify RVI or VPPR. The
logical processor ceases recognition of a pending virtual interrupt following the delivery of a virtual interrupt.

29.2.2

Virtual-Interrupt Delivery

If a virtual interrupt has been recognized (see Section 29.2.1), it is delivered at an instruction boundary when the
following conditions all hold: (1) RFLAGS.IF = 1; (2) there is no blocking by STI; (3) there is no blocking by MOV
SS or by POP SS; and (4) the “interrupt-window exiting” VM-execution control is 0.
Virtual-interrupt delivery has the same priority as that of VM exits due to the 1-setting of the “interrupt-window
exiting” VM-execution control.2 Thus, non-maskable interrupts (NMIs) and higher priority events take priority over
delivery of a virtual interrupt; delivery of a virtual interrupt takes priority over external interrupts and lower priority
events.
Virtual-interrupt delivery wakes a logical processor from the same inactive activity states as would an external
interrupt. Specifically, it wakes a logical processor from the states entered using the HLT and MWAIT instructions.
It does not wake a logical processor in the shutdown state or in the wait-for-SIPI state.
Virtual-interrupt delivery updates the guest interrupt status (both RVI and SVI; see Section 24.4.2) and delivers an
event within VMX non-root operation without a VM exit. The following pseudocode details the behavior of virtualinterrupt delivery (see Section 29.1.1 for definition of VISR, VIRR, and VPPR):
Vector ← RVI;
VISR[Vector] ← 1;
SVI ← Vector;
VPPR ← Vector & F0H;
VIRR[Vector] ← 0;
IF any bits set in VIRR
THEN RVI ← highest index of bit set in VIRR
ELSE RVI ← 0;
FI;
deliver interrupt with Vector through IDT;
cease recognition of any pending virtual interrupt;
If a logical processor is in enclave mode, an Asynchronous Enclave Exit (AEX) occurs before delivery of a virtual
interrupt (see Chapter 39, “Enclave Exiting Events”).

2. A logical processor never recognizes or delivers a virtual interrupt if the “interrupt-window exiting” VM-execution control is 1.
Because of this, the relative priority of virtual-interrupt delivery and VM exits due to the 1-setting of that control is not defined.
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29.3

VIRTUALIZING CR8-BASED TPR ACCESSES

In 64-bit mode, software can access the local APIC’s task-priority register (TPR) through CR8. Specifically, software
uses the MOV from CR8 and MOV to CR8 instructions (see Section 10.8.6, “Task Priority in IA-32e Mode”). This
section describes how these accesses can be virtualized.
A virtual-machine monitor can virtualize these CR8-based APIC accesses by setting the “CR8-load exiting” and
“CR8-store exiting” VM-execution controls, ensuring that the accesses cause VM exits (see Section 25.1.3). Alternatively, there are methods for virtualizing some CR8-based APIC accesses without VM exits.
Normally, an execution of MOV from CR8 or MOV to CR8 that does not fault or cause a VM exit accesses the APIC’s
TPR. However, such an execution are treated specially if the “use TPR shadow” VM-execution control is 1. The
following items provide details:

•

MOV from CR8. The instruction loads bits 3:0 of its destination operand with bits 7:4 of VTPR (see Section
29.1.1). Bits 63:4 of the destination operand are cleared.

•

MOV to CR8. The instruction stores bits 3:0 of its source operand into bits 7:4 of VTPR; the remainder of VTPR
(bits 3:0 and bits 31:8) are cleared. Following this, the processor performs TPR virtualization (see Section
29.1.2).

29.4

VIRTUALIZING MEMORY-MAPPED APIC ACCESSES

When the local APIC is in xAPIC mode, software accesses the local APIC’s control registers using a memorymapped interface. Specifically, software uses linear addresses that translate to physical addresses on page frame
indicated by the base address in the IA32_APIC_BASE MSR (see Section 10.4.4, “Local APIC Status and Location”).
This section describes how these accesses can be virtualized.
A virtual-machine monitor (VMM) can virtualize these memory-mapped APIC accesses by ensuring that any access
to a linear address that would access the local APIC instead causes a VM exit. This could be done using paging or
the extended page-table mechanism (EPT). Another way is by using the 1-setting of the “virtualize APIC accesses”
VM-execution control.
If the “virtualize APIC accesses” VM-execution control is 1, the logical processor treats specially memory accesses
using linear addresses that translate to physical addresses in the 4-KByte APIC-access page.3 (The APIC-access
page is identified by the APIC-access address, a field in the VMCS; see Section 24.6.8.)
In general, an access to the APIC-access page causes an APIC-access VM exit. APIC-access VM exits provide a
VMM with information about the access causing the VM exit. Section 29.4.1 discusses the priority of APIC-access
VM exits.
Certain VM-execution controls enable the processor to virtualize certain accesses to the APIC-access page without
a VM exit. In general, this virtualization causes these accesses to be made to the virtual-APIC page instead of the
APIC-access page.

NOTES
Unless stated otherwise, this section characterizes only linear accesses to the APIC-access page;
an access to the APIC-access page is a linear access if (1) it results from a memory access using a
linear address; and (2) the access’s physical address is the translation of that linear address.
Section 29.4.6 discusses accesses to the APIC-access page that are not linear accesses.
The distinction between the APIC-access page and the virtual-APIC page allows a VMM to share
paging structures or EPT paging structures among the virtual processors of a virtual machine (the
shared paging structures referencing the same APIC-access address, which appears in the VMCS of

3. Even when addresses are translated using EPT (see Section 28.2), the determination of whether an APIC-access VM exit occurs
depends on an access’s physical address, not its guest-physical address. Even when CR0.PG = 0, ordinary memory accesses by software use linear addresses; the fact that CR0.PG = 0 means only that the identity translation is used to convert linear addresses to
physical (or guest-physical) addresses.
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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

all the virtual processors) while giving each virtual processor its own virtual APIC (the VMCS of each
virtual processor will have a unique virtual-APIC address).
Section 29.4.2 discusses when and how the processor may virtualize read accesses from the APIC-access page.
Section 29.4.3 does the same for write accesses. When virtualizing a write to the APIC-access page, the processor
typically takes actions in addition to passing the write through to the virtual-APIC page.
The discussion in those sections uses the concept of an operation within which these memory accesses may occur.
For those discussions, an “operation” can be an iteration of a REP-prefixed string instruction, an execution of any
other instruction, or delivery of an event through the IDT.
The 1-setting of the “virtualize APIC accesses” VM-execution control may also affect accesses to the APIC-access
page that do not result directly from linear addresses. This is discussed in Section 29.4.6.
Special treatment may apply to Intel SGX instructions or if the logical processor is in enclave mode. See Section
41.5.3 for details.

29.4.1

Priority of APIC-Access VM Exits

The following items specify the priority of APIC-access VM exits relative to other events.

•

The priority of an APIC-access VM exit due to a memory access is below that of any page fault or EPT violation
that that access may incur. That is, an access does not cause an APIC-access VM exit if it would cause a page
fault or an EPT violation.

•

A memory access does not cause an APIC-access VM exit until after the accessed flags are set in the paging
structures (including EPT paging structures, if enabled).

•

A write access does not cause an APIC-access VM exit until after the dirty flags are set in the appropriate paging
structure and EPT paging structure (if enabled).

•

With respect to all other events, any APIC-access VM exit due to a memory access has the same priority as any
page fault or EPT violation that the access could cause. (This item applies to other events that the access may
generate as well as events that may be generated by other accesses by the same operation.)

These principles imply, among other things, that an APIC-access VM exit may occur during the execution of a
repeated string instruction (including INS and OUTS). Suppose, for example, that the first n iterations (n may be
0) of such an instruction do not access the APIC-access page and that the next iteration does access that page. As
a result, the first n iterations may complete and be followed by an APIC-access VM exit. The instruction pointer
saved in the VMCS references the repeated string instruction and the values of the general-purpose registers
reflect the completion of n iterations.

29.4.2

Virtualizing Reads from the APIC-Access Page

A read access from the APIC-access page causes an APIC-access VM exit if any of the following are true:

•
•
•
•

The “use TPR shadow” VM-execution control is 0.

•

The access is not entirely contained within the low 4 bytes of a naturally aligned 16-byte region. That is, bits
3:2 of the access’s address are 0, and the same is true of the address of the highest byte accessed.

The access is for an instruction fetch.
The access is more than 32 bits in size.
The access is part of an operation for which the processor has already virtualized a write to the APIC-access
page.

If none of the above are true, whether a read access is virtualized depends on the setting of the “APIC-register
virtualization” VM-execution control:

•

If “APIC-register virtualization” is 0, a read access is virtualized if its page offset is 080H (task priority);
otherwise, the access causes an APIC-access VM exit.

•

If “APIC-register virtualization” is 1, a read access is virtualized if it is entirely within one the following ranges
of offsets:

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— 020H–023H (local APIC ID);
— 030H–033H (local APIC version);
— 080H–083H (task priority);
— 0B0H–0B3H (end of interrupt);
— 0D0H–0D3H (logical destination);
— 0E0H–0E3H (destination format);
— 0F0H–0F3H (spurious-interrupt vector);
— 100H–103H, 110H–113H, 120H–123H, 130H–133H, 140H–143H, 150H–153H, 160H–163H, or 170H–
173H (in-service);
— 180H–183H, 190H–193H, 1A0H–1A3H, 1B0H–1B3H, 1C0H–1C3H, 1D0H–1D3H, 1E0H–1E3H, or 1F0H–
1F3H (trigger mode);
— 200H–203H, 210H–213H, 220H–223H, 230H–233H, 240H–243H, 250H–253H, 260H–263H, or 270H–
273H (interrupt request);
— 280H–283H (error status);
— 300H–303H or 310H–313H (interrupt command);
— 320H–323H, 330H–333H, 340H–343H, 350H–353H, 360H–363H, or 370H–373H (LVT entries);
— 380H–383H (initial count); or
— 3E0H–3E3H (divide configuration).
In all other cases, the access causes an APIC-access VM exit.
A read access from the APIC-access page that is virtualized returns data from the corresponding page offset on the
virtual-APIC page.4

29.4.3

Virtualizing Writes to the APIC-Access Page

Whether a write access to the APIC-access page is virtualized depends on the settings of the VM-execution controls
and the page offset of the access. Section 29.4.3.1 details when APIC-write virtualization occurs.
Unlike reads, writes to the local APIC have side effects; because of this, virtualization of writes to the APIC-access
page may require emulation specific to the access’s page offset (which identifies the APIC register being accessed).
Section 29.4.3.2 describes this APIC-write emulation.
For some page offsets, it is necessary for software to complete the virtualization after a write completes. In these
cases, the processor causes an APIC-write VM exit to invoke VMM software. Section 29.4.3.3 discusses APICwrite VM exits.

29.4.3.1

Determining Whether a Write Access is Virtualized

A write access to the APIC-access page causes an APIC-access VM exit if any of the following are true:

•
•
•

The “use TPR shadow” VM-execution control is 0.

•

The access is not entirely contained within the low 4 bytes of a naturally aligned 16-byte region. That is, bits
3:2 of the access’s address are 0, and the same is true of the address of the highest byte accessed.

The access is more than 32 bits in size.
The access is part of an operation for which the processor has already virtualized a write (with a different page
offset or a different size) to the APIC-access page.

If none of the above are true, whether a write access is virtualized depends on the settings of the “APIC-register
virtualization” and “virtual-interrupt delivery” VM-execution controls:
4. The memory type used for accesses that read from the virtual-APIC page is reported in bits 53:50 of the IA32_VMX_BASIC MSR
(see Appendix A.1).
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•

If the “APIC-register virtualization” and “virtual-interrupt delivery” VM-execution controls are both 0, a write
access is virtualized if its page offset is 080H; otherwise, the access causes an APIC-access VM exit.

•

If the “APIC-register virtualization” VM-execution control is 0 and the “virtual-interrupt delivery” VM-execution
control is 1, a write access is virtualized if its page offset is 080H (task priority), 0B0H (end of interrupt), and
300H (interrupt command — low); otherwise, the access causes an APIC-access VM exit.

•

If “APIC-register virtualization is 1, a write access is virtualized if it is entirely within one the following ranges of
offsets:
— 020H–023H (local APIC ID);
— 080H–083H (task priority);
— 0B0H–0B3H (end of interrupt);
— 0D0H–0D3H (logical destination);
— 0E0H–0E3H (destination format);
— 0F0H–0F3H (spurious-interrupt vector);
— 280H–283H (error status);
— 300H–303H or 310H–313H (interrupt command);
— 320H–323H, 330H–333H, 340H–343H, 350H–353H, 360H–363H, or 370H–373H (LVT entries);
— 380H–383H (initial count); or
— 3E0H–3E3H (divide configuration).
In all other cases, the access causes an APIC-access VM exit.

The processor virtualizes a write access to the APIC-access page by writing data to the corresponding page offset
on the virtual-APIC page.5 Following this, the processor performs certain actions after completion of the operation
of which the access was a part.6 APIC-write emulation is described in Section 29.4.3.2.

29.4.3.2

APIC-Write Emulation

If the processor virtualizes a write access to the APIC-access page, it performs additional actions after completion
of an operation of which the access was a part. These actions are called APIC-write emulation.
The details of APIC-write emulation depend upon the page offset of the virtualized write access:7

•

080H (task priority). The processor clears bytes 3:1 of VTPR and then causes TPR virtualization (Section
29.1.2).

•

0B0H (end of interrupt). If the “virtual-interrupt delivery” VM-execution control is 1, the processor clears VEOI
and then causes EOI virtualization (Section 29.1.4); otherwise, the processor causes an APIC-write VM exit
(Section 29.4.3.3).

•

300H (interrupt command — low). If the “virtual-interrupt delivery” VM-execution control is 1, the processor
checks the value of VICR_LO to determine whether the following are all true:
— Reserved bits (31:20, 17:16, 13) and bit 12 (delivery status) are all 0.
— Bits 19:18 (destination shorthand) are 01B (self).
— Bit 15 (trigger mode) is 0 (edge).
— Bits 10:8 (delivery mode) are 000B (fixed).
— Bits 7:4 (the upper half of the vector) are not 0000B.

5. The memory type used for accesses that write to the virtual-APIC page is reported in bits 53:50 of the IA32_VMX_BASIC MSR (see
Appendix A.1).
6. Recall that, for the purposes of this discussion, an operation is an iteration of a REP-prefixed string instruction, an execution of any
other instruction, or delivery of an event through the IDT.
7. For any operation, there can be only one page offset for which a write access was virtualized. This is because a write access is not
virtualized if the processor has already virtualized a write access for the same operation with a different page offset.
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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

If all of the items above are true, the processor performs self-IPI virtualization using the 8-bit vector in byte 0
of VICR_LO (Section 29.1.5).
If the “virtual-interrupt delivery” VM-execution control is 0, or if any of the items above are false, the
processor causes an APIC-write VM exit (Section 29.4.3.3).

•

310H–313H (interrupt command — high). The processor clears bytes 2:0 of VICR_HI. No other virtualization or
VM exit occurs.

•

Any other page offset. The processor causes an APIC-write VM exit (Section 29.4.3.3).

APIC-write emulation takes priority over system-management interrupts (SMIs), INIT signals, and lower priority
events. APIC-write emulation is not blocked if RFLAGS.IF = 0 or by the MOV SS, POP SS, or STI instructions.
If an operation causes a fault after a write access to the APIC-access page and before APIC-write emulation, and
that fault is delivered without a VM exit, APIC-write emulation occurs after the fault is delivered and before the fault
handler can execute. If an operation causes a VM exit (perhaps due to a fault) after a write access to the APICaccess page and before APIC-write emulation, the APIC-write emulation does not occur.

29.4.3.3

APIC-Write VM Exits

In certain cases, VMM software must be invoked to complete the virtualization of a write access to the APIC-access
page. In this case, APIC-write emulation causes an APIC-write VM exit. (Section 29.4.3.2 details the cases that
causes APIC-write VM exits.)
APIC-write VM exits are invoked by APIC-write emulation, and APIC-write emulation occurs after an operation that
performs a write access to the APIC-access page. Because of this, every APIC-write VM exit is trap-like: it occurs
after completion of the operation containing the write access that caused the VM exit (for example, the value of
CS:RIP saved in the guest-state area of the VMCS references the next instruction).
The basic exit reason for an APIC-write VM exit is “APIC write.” The exit qualification is the page offset of the write
access that led to the VM exit.
As noted in Section 29.5, execution of WRMSR with ECX = 83FH (self-IPI MSR) can lead to an APIC-write VM exit if
the “virtual-interrupt delivery” VM-execution control is 1. The exit qualification for such an APIC-write VM exit is
3F0H.

29.4.4

Instruction-Specific Considerations

Certain instructions that use linear address may cause page faults even though they do not use those addresses to
access memory. The APIC-virtualization features may affect these instructions as well:

•

CLFLUSH, CLFLUSHOPT. With regard to faulting, the processor operates as if each of these instructions reads
from the linear address in its source operand. If that address translates to one on the APIC-access page, the
instruction may cause an APIC-access VM exit. If it does not, it will flush the corresponding cache line on the
virtual-APIC page instead of the APIC-access page.

•

ENTER. With regard to faulting, the processor operates if ENTER writes to the byte referenced by the final
value of the stack pointer (even though it does not if its size operand is non-zero). If that value translates to an
address on the APIC-access page, the instruction may cause an APIC-access VM exit. If it does not, it will cause
the APIC-write emulation appropriate to the address’s page offset.

•

MASKMOVQ and MAKSMOVDQU. Even if the instruction’s mask is zero, the processor may operate with
regard to faulting as if MASKMOVQ or MASKMOVDQU writes to memory (the behavior is implementationspecific). In such a situation, an APIC-access VM exit may occur.

•

MONITOR. With regard to faulting, the processor operates as if MONITOR reads from the effective address in
RAX. If the resulting linear address translates to one on the APIC-access page, the instruction may cause an
APIC-access VM exit.8 If it does not, it will monitor the corresponding address on the virtual-APIC page instead
of the APIC-access page.

8. This chapter uses the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that support VMX operation also support Intel 64 architecture. For IA-32 processors, this notation refers to the 32-bit forms of those registers (EAX, EIP,
ESP, EFLAGS, etc.). In a few places, notation such as EAX is used to refer specifically to lower 32 bits of the indicated register.
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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

•

PREFETCH. An execution of the PREFETCH instruction that would result in an access to the APIC-access page
does not cause an APIC-access VM exit. Such an access may prefetch data; if so, it is from the corresponding
address on the virtual-APIC page.

Virtualization of accesses to the APIC-access page is principally intended for basic instructions such as AND, MOV,
OR, TEST, XCHG, and XOR. Use of an instruction that normally operates on floating-point, SSE, AVX, or AVX-512
registers may cause an APIC-access VM exit unconditionally regardless of the page offset it accesses on the APICaccess page.

29.4.5

Issues Pertaining to Page Size and TLB Management

The 1-setting of the “virtualize APIC accesses” VM-execution is guaranteed to apply only if translations to the APICaccess address use a 4-KByte page. The following items provide details:

•

If EPT is not in use, any linear address that translates to an address on the APIC-access page should use a 4KByte page. Any access to a linear address that translates to the APIC-access page using a larger page may
operate as if the “virtualize APIC accesses” VM-execution control were 0.

•

If EPT is in use, any guest-physical address that translates to an address on the APIC-access page should use a
4-KByte page. Any access to a linear address that translates to a guest-physical address that in turn translates
to the APIC-access page using a larger page may operate as if the “virtualize APIC accesses” VM-execution
control were 0. (This is true also for guest-physical accesses to the APIC-access page; see Section 29.4.6.1.)

In addition, software should perform appropriate TLB invalidation when making changes that may affect APICvirtualization. The specifics depend on whether VPIDs or EPT is being used:

•

VPIDs being used but EPT not being used. Suppose that there is a VPID that has been used before and that
software has since made either of the following changes: (1) set the “virtualize APIC accesses” VM-execution
control when it had previously been 0; or (2) changed the paging structures so that some linear address
translates to the APIC-access address when it previously did not. In that case, software should execute
INVVPID (see “INVVPID— Invalidate Translations Based on VPID” in Section 30.3) before performing on the
same logical processor and with the same VPID.9

•

EPT being used. Suppose that there is an EPTP value that has been used before and that software has since
made either of the following changes: (1) set the “virtualize APIC accesses” VM-execution control when it had
previously been 0; or (2) changed the EPT paging structures so that some guest-physical address translates to
the APIC-access address when it previously did not. In that case, software should execute INVEPT (see
“INVEPT— Invalidate Translations Derived from EPT” in Section 30.3) before performing on the same logical
processor and with the same EPTP value.10

•

Neither VPIDs nor EPT being used. No invalidation is required.

Failure to perform the appropriate TLB invalidation may result in the logical processor operating as if the “virtualize
APIC accesses” VM-execution control were 0 in responses to accesses to the affected address. (No invalidation is
necessary if neither VPIDs nor EPT is being used.)

29.4.6

APIC Accesses Not Directly Resulting From Linear Addresses

Section 29.4 has described the treatment of accesses that use linear addresses that translate to addresses on the
APIC-access page. This section considers memory accesses that do not result directly from linear addresses.

•

An access is called a guest-physical access if (1) CR0.PG = 1;11 (2) the “enable EPT” VM-execution control
is 1;12 (3) the access’s physical address is the result of an EPT translation; and (4) either (a) the access was
not generated by a linear address; or (b) the access’s guest-physical address is not the translation of the

9. INVVPID should use either (1) the all-contexts INVVPID type; (2) the single-context INVVPID type with the VPID in the INVVPID
descriptor; or (3) the individual-address INVVPID type with the linear address and the VPID in the INVVPID descriptor.
10. INVEPT should use either (1) the global INVEPT type; or (2) the single-context INVEPT type with the EPTP value in the INVEPT
descriptor.
11. If the capability MSR IA32_VMX_CR0_FIXED0 reports that CR0.PG must be 1 in VMX operation, CR0.PG must be 1 unless the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls are both 1.
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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

access’s linear address. Section 29.4.6.1 discusses the treatment of guest-physical accesses to the APICaccess page.

•

An access is called a physical access if (1) either (a) the “enable EPT” VM-execution control is 0; or (b) the
access’s physical address is not the result of a translation through the EPT paging structures; and (2) either
(a) the access is not generated by a linear address; or (b) the access’s physical address is not the translation
of its linear address. Section 29.4.6.2 discusses the treatment of physical accesses to the APIC-access page.

29.4.6.1

Guest-Physical Accesses to the APIC-Access Page

Guest-physical accesses include the following when guest-physical addresses are being translated using EPT:

•

Reads from the guest paging structures when translating a linear address (such an access uses a guestphysical address that is not the translation of that linear address).

•

Loads of the page-directory-pointer-table entries by MOV to CR when the logical processor is using (or that
causes the logical processor to use) PAE paging (see Section 4.4).

•

Updates to the accessed and dirty flags in the guest paging structures when using a linear address (such an
access uses a guest-physical address that is not the translation of that linear address).

Every guest-physical access to an address on the APIC-access page causes an APIC-access VM exit. Such accesses
are never virtualized regardless of the page offset.
The following items specify the priority relative to other events of APIC-access VM exits caused by guest-physical
accesses to the APIC-access page.

•

The priority of an APIC-access VM exit caused by a guest-physical access to memory is below that of any EPT
violation that that access may incur. That is, a guest-physical access does not cause an APIC-access VM exit if
it would cause an EPT violation.

•

With respect to all other events, any APIC-access VM exit caused by a guest-physical access has the same
priority as any EPT violation that the guest-physical access could cause.

29.4.6.2

Physical Accesses to the APIC-Access Page

Physical accesses include the following:

•

If the “enable EPT” VM-execution control is 0:
— Reads from the paging structures when translating a linear address.
— Loads of the page-directory-pointer-table entries by MOV to CR when the logical processor is using (or that
causes the logical processor to use) PAE paging (see Section 4.4).
— Updates to the accessed and dirty flags in the paging structures.

•

If the “enable EPT” VM-execution control is 1, accesses to the EPT paging structures (including updates to the
accessed and dirty flags for EPT).

•

Any of the following accesses made by the processor to support VMX non-root operation:
— Accesses to the VMCS region.
— Accesses to data structures referenced (directly or indirectly) by physical addresses in VM-execution
control fields in the VMCS. These include the I/O bitmaps, the MSR bitmaps, and the virtual-APIC page.

•

Accesses that effect transitions into and out of SMM.13 These include the following:
— Accesses to SMRAM during SMI delivery and during execution of RSM.
— Accesses during SMM VM exits (including accesses to MSEG) and during VM entries that return from SMM.

12. “Enable EPT” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls
is 0, VMX non-root operation functions as if the “enable EPT” VM-execution control were 0. See Section 24.6.2.
13. Technically, these accesses do not occur in VMX non-root operation. They are included here for clarity.
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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

A physical access to the APIC-access page may or may not cause an APIC-access VM exit. If it does not cause an
APIC-access VM exit, it may access the APIC-access page or the virtual-APIC page. Physical write accesses to the
APIC-access page may or may not cause APIC-write emulation or APIC-write VM exits.
The priority of an APIC-access VM exit caused by physical access is not defined relative to other events that the
access may cause.
It is recommended that software not set the APIC-access address to any of the addresses used by physical memory
accesses (identified above). For example, it should not set the APIC-access address to the physical address of any
of the active paging structures if the “enable EPT” VM-execution control is 0.

29.5

VIRTUALIZING MSR-BASED APIC ACCESSES

When the local APIC is in x2APIC mode, software accesses the local APIC’s control registers using the MSR interface. Specifically, software uses the RDMSR and WRMSR instructions, setting ECX (identifying the MSR being
accessed) to values in the range 800H–8FFH (see Section 10.12, “Extended XAPIC (x2APIC)”). This section
describes how these accesses can be virtualized.
A virtual-machine monitor can virtualize these MSR-based APIC accesses by configuring the MSR bitmaps (see
Section 24.6.9) to ensure that the accesses cause VM exits (see Section 25.1.3). Alternatively, there are methods
for virtualizing some MSR-based APIC accesses without VM exits.
Normally, an execution of RDMSR or WRMSR that does not fault or cause a VM exit accesses the MSR indicated in
ECX. However, such an execution treats some values of ECX in the range 800H–8FFH specially if the “virtualize
x2APIC mode” VM-execution control is 1. The following items provide details:

•

RDMSR. The instruction’s behavior depends on the setting of the “APIC-register virtualization” VM-execution
control.
— If the “APIC-register virtualization” VM-execution control is 0, behavior depends upon the value of ECX.

•

If ECX contains 808H (indicating the TPR MSR), the instruction reads the 8 bytes from offset 080H on
the virtual-APIC page (VTPR and the 4 bytes above it) into EDX:EAX. This occurs even if the local APIC
is not in x2APIC mode (no general-protection fault occurs because the local APIC is not x2APIC mode).

•

If ECX contains any other value in the range 800H–8FFH, the instruction operates normally. If the local
APIC is in x2APIC mode and ECX indicates a readable APIC register, EDX and EAX are loaded with the
value of that register. If the local APIC is not in x2APIC mode or ECX does not indicate a readable APIC
register, a general-protection fault occurs.

— If “APIC-register virtualization” is 1 and ECX contains a value in the range 800H–8FFH, the instruction reads
the 8 bytes from offset X on the virtual-APIC page into EDX:EAX, where X = (ECX & FFH) « 4. This occurs
even if the local APIC is not in x2APIC mode (no general-protection fault occurs because the local APIC is
not in x2APIC mode).

•

WRMSR. The instruction’s behavior depends on the value of ECX and the setting of the “virtual-interrupt
delivery” VM-execution control.
Special processing applies in the following cases: (1) ECX contains 808H (indicating the TPR MSR); (2) ECX
contains 80BH (indicating the EOI MSR) and the “virtual-interrupt delivery” VM-execution control is 1; and
(3) ECX contains 83FH (indicating the self-IPI MSR) and the “virtual-interrupt delivery” VM-execution control
is 1.
If special processing applies, no general-protection exception is produced due to the fact that the local APIC is
in xAPIC mode. However, WRMSR does perform the normal reserved-bit checking:
— If ECX contains 808H or 83FH, a general-protection fault occurs if either EDX or EAX[31:8] is non-zero.
— If ECX contains 80BH, a general-protection fault occurs if either EDX or EAX is non-zero.
If there is no fault, WRMSR stores EDX:EAX at offset X on the virtual-APIC page, where X = (ECX & FFH) « 4.
Following this, the processor performs an operation depending on the value of ECX:
— If ECX contains 808H, the processor performs TPR virtualization (see Section 29.1.2).
— If ECX contains 80BH, the processor performs EOI virtualization (see Section 29.1.4).
— If ECX contains 83FH, the processor then checks the value of EAX[7:4] and proceeds as follows:

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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

•

If the value is non-zero, the logical processor performs self-IPI virtualization with the 8-bit vector in
EAX[7:0] (see Section 29.1.5).

•

If the value is zero, the logical processor causes an APIC-write VM exit as if there had been a write
access to page offset 3F0H on the APIC-access page (see Section 29.4.3.3).

If special processing does not apply, the instruction operates normally. If the local APIC is in x2APIC mode
and ECX indicates a writable APIC register, the value in EDX:EAX is written to that register. If the local APIC is
not in x2APIC mode or ECX does not indicate a writable APIC register, a general-protection fault occurs.

29.6

POSTED-INTERRUPT PROCESSING

Posted-interrupt processing is a feature by which a processor processes the virtual interrupts by recording them as
pending on the virtual-APIC page.
Posted-interrupt processing is enabled by setting the “process posted interrupts” VM-execution control. The
processing is performed in response to the arrival of an interrupt with the posted-interrupt notification vector.
In response to such an interrupt, the processor processes virtual interrupts recorded in a data structure called a
posted-interrupt descriptor. The posted-interrupt notification vector and the address of the posted-interrupt
descriptor are fields in the VMCS; see Section 24.6.8.
If the “process posted interrupts” VM-execution control is 1, a logical processor uses a 64-byte posted-interrupt
descriptor located at the posted-interrupt descriptor address. The posted-interrupt descriptor has the following
format:

Table 29-1. Format of Posted-Interrupt Descriptor
Bit
Position(s)

Name

Description

255:0

Posted-interrupt requests

One bit for each interrupt vector. There is a posted-interrupt request for a vector if
the corresponding bit is 1

256

Outstanding notification

If this bit is set, there is a notification outstanding for one or more posted interrupts
in bits 255:0

511:257

Reserved for software and
other agents

These bits may be used by software and by other agents in the system (e.g.,
chipset). The processor does not modify these bits.

The notation PIR (posted-interrupt requests) refers to the 256 posted-interrupt bits in the posted-interrupt
descriptor.
Use of the posted-interrupt descriptor differs from that of other data structures that are referenced by pointers in
a VMCS. There is a general requirement that software ensure that each such data structure is modified only when
no logical processor with a current VMCS that references it is in VMX non-root operation. That requirement does
not apply to the posted-interrupt descriptor. There is a requirement, however, that such modifications be done
using locked read-modify-write instructions.
If the “external-interrupt exiting” VM-execution control is 1, any unmasked external interrupt causes a VM exit
(see Section 25.2). If the “process posted interrupts” VM-execution control is also 1, this behavior is changed and
the processor handles an external interrupt as follows:14
1. The local APIC is acknowledged; this provides the processor core with an interrupt vector, called here the
physical vector.
2. If the physical vector equals the posted-interrupt notification vector, the logical processor continues to the next
step. Otherwise, a VM exit occurs as it would normally due to an external interrupt; the vector is saved in the
VM-exit interruption-information field.
3. The processor clears the outstanding-notification bit in the posted-interrupt descriptor. This is done atomically
so as to leave the remainder of the descriptor unmodified (e.g., with a locked AND operation).
14. VM entry ensures that the “process posted interrupts” VM-execution control is 1 only if the “external-interrupt exiting” VM-execution control is also 1. SeeSection 26.2.1.1.
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APIC VIRTUALIZATION AND VIRTUAL INTERRUPTS

4. The processor writes zero to the EOI register in the local APIC; this dismisses the interrupt with the postedinterrupt notification vector from the local APIC.
5. The logical processor performs a logical-OR of PIR into VIRR and clears PIR. No other agent can read or write a
PIR bit (or group of bits) between the time it is read (to determine what to OR into VIRR) and when it is cleared.
6. The logical processor sets RVI to be the maximum of the old value of RVI and the highest index of all bits that
were set in PIR; if no bit was set in PIR, RVI is left unmodified.
7. The logical processor evaluates pending virtual interrupts as described in Section 29.2.1.
The logical processor performs the steps above in an uninterruptible manner. If step #7 leads to recognition of a
virtual interrupt, the processor may deliver that interrupt immediately.
Steps #1 to #7 above occur when the interrupt controller delivers an unmasked external interrupt to the CPU core.
The following items consider certain cases of interrupt delivery:

•

Interrupt delivery can occur between iterations of a REP-prefixed instruction (after at least one iteration has
completed but before all iterations have completed). If this occurs, the following items characterize processor
state after posted-interrupt processing completes and before guest execution resumes:
— RIP references the REP-prefixed instruction;
— RCX, RSI, and RDI are updated to reflect the iterations completed; and
— RFLAGS.RF = 1.

•

Interrupt delivery can occur when the logical processor is in the active, HLT, or MWAIT states. If the logical
processor had been in the active or MWAIT state before the arrival of the interrupt, it is in the active state
following completion of step #7; if it had been in the HLT state, it returns to the HLT state after step #7 (if a
pending virtual interrupt was recognized, the logical processor may immediately wake from the HLT state).

•

Interrupt delivery can occur while the logical processor is in enclave mode. If the logical processor had been in
enclave mode before the arrival of the interrupt, an Asynchronous Enclave Exit (AEX) may occur before the
steps #1 to #7 (see Chapter 39, “Enclave Exiting Events”). If no AEX occurs before step #1 and a VM exit
occurs at step #2, an AEX occurs before the VM exit is delivered.

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CHAPTER 30
VMX INSTRUCTION REFERENCE
NOTE
This chapter was previously located in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 2B as chapter 5.

30.1

OVERVIEW

This chapter describes the virtual-machine extensions (VMX) for the Intel 64 and IA-32 architectures. VMX is
intended to support virtualization of processor hardware and a system software layer acting as a host to multiple
guest software environments. The virtual-machine extensions (VMX) includes five instructions that manage the
virtual-machine control structure (VMCS), four instructions that manage VMX operation, two TLB-management
instructions, and two instructions for use by guest software. Additional details of VMX are described in Chapter 23
through Chapter 29.
The behavior of the VMCS-maintenance instructions is summarized below:

•

VMPTRLD — This instruction takes a single 64-bit source operand that is in memory. It makes the referenced
VMCS active and current, loading the current-VMCS pointer with this operand and establishes the current VMCS
based on the contents of VMCS-data area in the referenced VMCS region. Because this makes the referenced
VMCS active, a logical processor may start maintaining on the processor some of the VMCS data for the VMCS.

•

VMPTRST — This instruction takes a single 64-bit destination operand that is in memory. The current-VMCS
pointer is stored into the destination operand.

•

VMCLEAR — This instruction takes a single 64-bit operand that is in memory. The instruction sets the launch
state of the VMCS referenced by the operand to “clear”, renders that VMCS inactive, and ensures that data for
the VMCS have been written to the VMCS-data area in the referenced VMCS region. If the operand is the same
as the current-VMCS pointer, that pointer is made invalid.

•

VMREAD — This instruction reads a component from a VMCS (the encoding of that field is given in a register
operand) and stores it into a destination operand that may be a register or in memory.

•

VMWRITE — This instruction writes a component to a VMCS (the encoding of that field is given in a register
operand) from a source operand that may be a register or in memory.

The behavior of the VMX management instructions is summarized below:

•

VMLAUNCH — This instruction launches a virtual machine managed by the VMCS. A VM entry occurs, transferring control to the VM.

•

VMRESUME — This instruction resumes a virtual machine managed by the VMCS. A VM entry occurs, transferring control to the VM.

•
•

VMXOFF — This instruction causes the processor to leave VMX operation.
VMXON — This instruction takes a single 64-bit source operand that is in memory. It causes a logical processor
to enter VMX root operation and to use the memory referenced by the operand to support VMX operation.

The behavior of the VMX-specific TLB-management instructions is summarized below:

•

INVEPT — This instruction invalidates entries in the TLBs and paging-structure caches that were derived from
extended page tables (EPT).

•

INVVPID — This instruction invalidates entries in the TLBs and paging-structure caches based on a VirtualProcessor Identifier (VPID).

None of the instructions above can be executed in compatibility mode; they generate invalid-opcode exceptions if
executed in compatibility mode.
The behavior of the guest-available instructions is summarized below:

•

VMCALL — This instruction allows software in VMX non-root operation to call the VMM for service. A VM exit
occurs, transferring control to the VMM.
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VMX INSTRUCTION REFERENCE

•

VMFUNC — This instruction allows software in VMX non-root operation to invoke a VM function (processor
functionality enabled and configured by software in VMX root operation) without a VM exit.

30.2

CONVENTIONS

The operation sections for the VMX instructions in Section 30.3 use the pseudo-function VMexit, which indicates
that the logical processor performs a VM exit.
The operation sections also use the pseudo-functions VMsucceed, VMfail, VMfailInvalid, and VMfailValid. These
pseudo-functions signal instruction success or failure by setting or clearing bits in RFLAGS and, in some cases, by
writing the VM-instruction error field. The following pseudocode fragments detail these functions:
VMsucceed:
CF ← 0;
PF ← 0;
AF ← 0;
ZF ← 0;
SF ← 0;
OF ← 0;
VMfail(ErrorNumber):
IF VMCS pointer is valid
THEN VMfailValid(ErrorNumber);
ELSE VMfailInvalid;
FI;
VMfailInvalid:
CF ← 1;
PF ← 0;
AF ← 0;
ZF ← 0;
SF ← 0;
OF ← 0;
VMfailValid(ErrorNumber):// executed only if there is a current VMCS
CF ← 0;
PF ← 0;
AF ← 0;
ZF ← 1;
SF ← 0;
OF ← 0;
Set the VM-instruction error field to ErrorNumber;
The different VM-instruction error numbers are enumerated in Section 30.4, “VM Instruction Error Numbers”.

30.3

VMX INSTRUCTIONS

This section provides detailed descriptions of the VMX instructions.

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VMX INSTRUCTION REFERENCE

INVEPT— Invalidate Translations Derived from EPT
Opcode

Instruction

Description

66 0F 38 80

INVEPT r64, m128

Invalidates EPT-derived entries in the TLBs and paging-structure caches (in 64bit mode)

66 0F 38 80

INVEPT r32, m128

Invalidates EPT-derived entries in the TLBs and paging-structure caches (outside
64-bit mode)

Description
Invalidates mappings in the translation lookaside buffers (TLBs) and paging-structure caches that were derived
from extended page tables (EPT). (See Chapter 28, “VMX Support for Address Translation”.) Invalidation is based
on the INVEPT type specified in the register operand and the INVEPT descriptor specified in the memory
operand.
Outside IA-32e mode, the register operand is always 32 bits, regardless of the value of CS.D; in 64-bit mode, the
register operand has 64 bits (the instruction cannot be executed in compatibility mode).
The INVEPT types supported by a logical processors are reported in the IA32_VMX_EPT_VPID_CAP MSR (see
Appendix A, “VMX Capability Reporting Facility”). There are two INVEPT types currently defined:

•

Single-context invalidation. If the INVEPT type is 1, the logical processor invalidates all mappings associated
with bits 51:12 of the EPT pointer (EPTP) specified in the INVEPT descriptor. It may invalidate other mappings
as well.

•

Global invalidation: If the INVEPT type is 2, the logical processor invalidates mappings associated with all
EPTPs.

If an unsupported INVEPT type is specified, the instruction fails.
INVEPT invalidates all the specified mappings for the indicated EPTP(s) regardless of the VPID and PCID values with
which those mappings may be associated.
The INVEPT descriptor comprises 128 bits and contains a 64-bit EPTP value in bits 63:0 (see Figure 30-1).

127

64 63
Reserved (must be zero)

0
EPT pointer (EPTP)

Figure 30-1. INVEPT Descriptor
Operation
IF (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
THEN VM exit;
ELSIF CPL > 0
THEN #GP(0);
ELSE
INVEPT_TYPE ← value of register operand;
IF IA32_VMX_EPT_VPID_CAP MSR indicates that processor does not support INVEPT_TYPE
THEN VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
// INVEPT_TYPE must be 1 or 2
INVEPT_DESC ← value of memory operand;
EPTP ← INVEPT_DESC[63:0];
Vol. 3C 30-3

VMX INSTRUCTION REFERENCE

CASE INVEPT_TYPE OF
1:
// single-context invalidation
IF VM entry with the “enable EPT“ VM execution control set to 1
would fail due to the EPTP value
THEN VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
Invalidate mappings associated with EPTP[51:12];
VMsucceed;
FI;
BREAK;
2:
// global invalidation
Invalidate mappings associated with all EPTPs;
VMsucceed;
BREAK;
ESAC;
FI;
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
If the DS, ES, FS, or GS register contains an unusable segment.
If the source operand is located in an execute-only code segment.

#PF(fault-code)

If a page fault occurs in accessing the memory operand.

#SS(0)

If the memory operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If not in VMX operation.
If the logical processor does not support EPT (IA32_VMX_PROCBASED_CTLS2[33]=0).
If the logical processor supports EPT (IA32_VMX_PROCBASED_CTLS2[33]=1) but does not
support the INVEPT instruction (IA32_VMX_EPT_VPID_CAP[20]=0).

Real-Address Mode Exceptions
#UD

The INVEPT instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The INVEPT instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The INVEPT instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory operand is in the CS, DS, ES, FS, or GS segments and the memory address is
in a non-canonical form.

#PF(fault-code)

If a page fault occurs in accessing the memory operand.

#SS(0)

If the memory operand is in the SS segment and the memory address is in a non-canonical
form.

30-4 Vol. 3C

VMX INSTRUCTION REFERENCE

#UD

If not in VMX operation.
If the logical processor does not support EPT (IA32_VMX_PROCBASED_CTLS2[33]=0).
If the logical processor supports EPT (IA32_VMX_PROCBASED_CTLS2[33]=1) but does not
support the INVEPT instruction (IA32_VMX_EPT_VPID_CAP[20]=0).

Vol. 3C 30-5

VMX INSTRUCTION REFERENCE

INVVPID— Invalidate Translations Based on VPID
Opcode

Instruction

Description

66 0F 38 81

INVVPID r64, m128

Invalidates entries in the TLBs and paging-structure caches based on VPID (in
64-bit mode)

66 0F 38 81

INVVPID r32, m128

Invalidates entries in the TLBs and paging-structure caches based on VPID
(outside 64-bit mode)

Description
Invalidates mappings in the translation lookaside buffers (TLBs) and paging-structure caches based on virtualprocessor identifier (VPID). (See Chapter 28, “VMX Support for Address Translation”.) Invalidation is based on
the INVVPID type specified in the register operand and the INVVPID descriptor specified in the memory
operand.
Outside IA-32e mode, the register operand is always 32 bits, regardless of the value of CS.D; in 64-bit mode, the
register operand has 64 bits (the instruction cannot be executed in compatibility mode).
The INVVPID types supported by a logical processors are reported in the IA32_VMX_EPT_VPID_CAP MSR (see
Appendix A, “VMX Capability Reporting Facility”). There are four INVVPID types currently defined:

•

Individual-address invalidation: If the INVVPID type is 0, the logical processor invalidates mappings for the
linear address and VPID specified in the INVVPID descriptor. In some cases, it may invalidate mappings for
other linear addresses (or other VPIDs) as well.

•

Single-context invalidation: If the INVVPID type is 1, the logical processor invalidates all mappings tagged with
the VPID specified in the INVVPID descriptor. In some cases, it may invalidate mappings for other VPIDs as
well.

•

All-contexts invalidation: If the INVVPID type is 2, the logical processor invalidates all mappings tagged with all
VPIDs except VPID 0000H. In some cases, it may invalidate translations with VPID 0000H as well.

•

Single-context invalidation, retaining global translations: If the INVVPID type is 3, the logical processor
invalidates all mappings tagged with the VPID specified in the INVVPID descriptor except global translations. In
some cases, it may invalidate global translations (and mappings with other VPIDs) as well. See the “Caching
Translation Information” section in Chapter 4 of the IA-32 Intel Architecture Software Developer’s Manual,
Volumes 3A for information about global translations.

If an unsupported INVVPID type is specified, the instruction fails.
INVVPID invalidates all the specified mappings for the indicated VPID(s) regardless of the EPTP and PCID values
with which those mappings may be associated.
The INVVPID descriptor comprises 128 bits and consists of a VPID and a linear address as shown in Figure 30-2.

127

64 63
Linear Address

Reserved (must be zero)

Figure 30-2. INVVPID Descriptor

30-6 Vol. 3C

16 15
VPID

0

VMX INSTRUCTION REFERENCE

Operation
IF (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
THEN VM exit;
ELSIF CPL > 0
THEN #GP(0);
ELSE
INVVPID_TYPE ← value of register operand;
IF IA32_VMX_EPT_VPID_CAP MSR indicates that processor does not support
INVVPID_TYPE
THEN VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
// INVVPID_TYPE must be in the range 0–3
INVVPID_DESC ← value of memory operand;
IF INVVPID_DESC[63:16] ≠ 0
THEN VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
CASE INVVPID_TYPE OF
0:
// individual-address invalidation
VPID ← INVVPID_DESC[15:0];
IF VPID = 0
THEN VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
GL_ADDR ← INVVPID_DESC[127:64];
IF (GL_ADDR is not in a canonical form)
THEN
VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
Invalidate mappings for GL_ADDR tagged with VPID;
VMsucceed;
FI;
FI;
BREAK;
1:
// single-context invalidation
VPID ← INVVPID_DESC[15:0];
IF VPID = 0
THEN VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
Invalidate all mappings tagged with VPID;
VMsucceed;
FI;
BREAK;
2:
// all-context invalidation
Invalidate all mappings tagged with all non-zero VPIDs;
VMsucceed;
BREAK;
3:
// single-context invalidation retaining globals
VPID ← INVVPID_DESC[15:0];
IF VPID = 0
THEN VMfail(Invalid operand to INVEPT/INVVPID);
ELSE
Invalidate all mappings tagged with VPID except global translations;
VMsucceed;

Vol. 3C 30-7

VMX INSTRUCTION REFERENCE

FI;
BREAK;
ESAC;
FI;
FI;
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
If the DS, ES, FS, or GS register contains an unusable segment.
If the source operand is located in an execute-only code segment.

#PF(fault-code)

If a page fault occurs in accessing the memory operand.

#SS(0)

If the memory operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If not in VMX operation.
If the logical processor does not support VPIDs (IA32_VMX_PROCBASED_CTLS2[37]=0).
If the logical processor supports VPIDs (IA32_VMX_PROCBASED_CTLS2[37]=1) but does not
support the INVVPID instruction (IA32_VMX_EPT_VPID_CAP[32]=0).

Real-Address Mode Exceptions
#UD

The INVVPID instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The INVVPID instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The INVVPID instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory operand is in the CS, DS, ES, FS, or GS segments and the memory address is
in a non-canonical form.

#PF(fault-code)

If a page fault occurs in accessing the memory operand.

#SS(0)

If the memory destination operand is in the SS segment and the memory address is in a noncanonical form.

#UD

If not in VMX operation.
If the logical processor does not support VPIDs (IA32_VMX_PROCBASED_CTLS2[37]=0).
If the logical processor supports VPIDs (IA32_VMX_PROCBASED_CTLS2[37]=1) but does not
support the INVVPID instruction (IA32_VMX_EPT_VPID_CAP[32]=0).

30-8 Vol. 3C

VMX INSTRUCTION REFERENCE

VMCALL—Call to VM Monitor
Opcode

Instruction

Description

0F 01 C1

VMCALL

Call to VM monitor by causing VM exit.

Description
This instruction allows guest software can make a call for service into an underlying VM monitor. The details of the
programming interface for such calls are VMM-specific; this instruction does nothing more than cause a VM exit,
registering the appropriate exit reason.
Use of this instruction in VMX root operation invokes an SMM monitor (see Section 34.15.2). This invocation will activate the dual-monitor treatment of system-management interrupts (SMIs) and system-management mode (SMM)
if it is not already active (see Section 34.15.6).

Operation
IF not in VMX operation
THEN #UD;
ELSIF in VMX non-root operation
THEN VM exit;
ELSIF (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF CPL > 0
THEN #GP(0);
ELSIF in SMM or the logical processor does not support the dual-monitor treatment of SMIs and SMM or the valid bit in the
IA32_SMM_MONITOR_CTL MSR is clear
THEN VMfail (VMCALL executed in VMX root operation);
ELSIF dual-monitor treatment of SMIs and SMM is active
THEN perform an SMM VM exit (see Section 34.15.2);
ELSIF current-VMCS pointer is not valid
THEN VMfailInvalid;
ELSIF launch state of current VMCS is not clear
THEN VMfailValid(VMCALL with non-clear VMCS);
ELSIF VM-exit control fields are not valid (see Section 34.15.6.1)
THEN VMfailValid (VMCALL with invalid VM-exit control fields);
ELSE
enter SMM;
read revision identifier in MSEG;
IF revision identifier does not match that supported by processor
THEN
leave SMM;
VMfailValid(VMCALL with incorrect MSEG revision identifier);
ELSE
read SMM-monitor features field in MSEG (see Section 34.15.6.1);
IF features field is invalid
THEN
leave SMM;
VMfailValid(VMCALL with invalid SMM-monitor features);
ELSE activate dual-monitor treatment of SMIs and SMM (see Section 34.15.6);
FI;
FI;
FI;

Vol. 3C 30-9

VMX INSTRUCTION REFERENCE

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0 and the logical processor is in VMX root operation.

#UD

If executed outside VMX operation.

Real-Address Mode Exceptions
#UD

If executed outside VMX operation.

Virtual-8086 Mode Exceptions
#UD

If executed outside VMX non-root operation.

Compatibility Mode Exceptions
#UD

If executed outside VMX non-root operation.

64-Bit Mode Exceptions
#UD

30-10 Vol. 3C

If executed outside VMX operation.

VMX INSTRUCTION REFERENCE

VMCLEAR—Clear Virtual-Machine Control Structure
Opcode

Instruction

Description

66 0F C7 /6

VMCLEAR m64

Copy VMCS data to VMCS region in memory.

Description
This instruction applies to the VMCS whose VMCS region resides at the physical address contained in the instruction
operand. The instruction ensures that VMCS data for that VMCS (some of these data may be currently maintained
on the processor) are copied to the VMCS region in memory. It also initializes parts of the VMCS region (for
example, it sets the launch state of that VMCS to clear). See Chapter 24, “Virtual-Machine Control Structures”.
The operand of this instruction is always 64 bits and is always in memory. If the operand is the current-VMCS
pointer, then that pointer is made invalid (set to FFFFFFFF_FFFFFFFFH).
Note that the VMCLEAR instruction might not explicitly write any VMCS data to memory; the data may be already
resident in memory before the VMCLEAR is executed.

Operation
IF (register operand) or (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
THEN VM exit;
ELSIF CPL > 0
THEN #GP(0);
ELSE
addr ← contents of 64-bit in-memory operand;
IF addr is not 4KB-aligned OR
addr sets any bits beyond the physical-address width1
THEN VMfail(VMCLEAR with invalid physical address);
ELSIF addr = VMXON pointer
THEN VMfail(VMCLEAR with VMXON pointer);
ELSE
ensure that data for VMCS referenced by the operand is in memory;
initialize implementation-specific data in VMCS region;
launch state of VMCS referenced by the operand ← “clear”
IF operand addr = current-VMCS pointer
THEN current-VMCS pointer ← FFFFFFFF_FFFFFFFFH;
FI;
VMsucceed;
FI;
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
If the DS, ES, FS, or GS register contains an unusable segment.
If the operand is located in an execute-only code segment.

1. If IA32_VMX_BASIC[48] is read as 1, VMfail occurs if addr sets any bits in the range 63:32; see Appendix A.1.
Vol. 3C 30-11

VMX INSTRUCTION REFERENCE

#PF(fault-code)
#SS(0)

If a page fault occurs in accessing the memory operand.
If the memory operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If operand is a register.
If not in VMX operation.

Real-Address Mode Exceptions
#UD

The VMCLEAR instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMCLEAR instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The VMCLEAR instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the source operand is in the CS, DS, ES, FS, or GS segments and the memory address is in
a non-canonical form.

#PF(fault-code)

If a page fault occurs in accessing the memory operand.

#SS(0)

If the source operand is in the SS segment and the memory address is in a non-canonical
form.

#UD

If operand is a register.
If not in VMX operation.

30-12 Vol. 3C

VMX INSTRUCTION REFERENCE

VMFUNC—Invoke VM function
Opcode

Instruction

Description

NP 0F 01 D4

VMFUNC

Invoke VM function specified in EAX.

Description
This instruction allows software in VMX non-root operation to invoke a VM function, which is processor functionality
enabled and configured by software in VMX root operation. The value of EAX selects the specific VM function being
invoked.
The behavior of each VM function (including any additional fault checking) is specified in Section 25.5.5,
“VM Functions”.

Operation
Perform functionality of the VM function specified in EAX;

Flags Affected
Depends on the VM function specified in EAX. See Section 25.5.5, “VM Functions”.

Protected Mode Exceptions (not including those defined by specific VM functions)
#UD

If executed outside VMX non-root operation.
If “enable VM functions” VM-execution control is 0.
If EAX ≥ 64.

Real-Address Mode Exceptions
Same exceptions as in protected mode.

Virtual-8086 Exceptions
Same exceptions as in protected mode.

Compatibility Mode Exceptions
Same exceptions as in protected mode.

64-Bit Mode Exceptions
Same exceptions as in protected mode.

Vol. 3C 30-13

VMX INSTRUCTION REFERENCE

VMLAUNCH/VMRESUME—Launch/Resume Virtual Machine
Opcode

Instruction

Description

0F 01 C2

VMLAUNCH

Launch virtual machine managed by current VMCS.

0F 01 C3

VMRESUME

Resume virtual machine managed by current VMCS.

Description
Effects a VM entry managed by the current VMCS.

•

VMLAUNCH fails if the launch state of current VMCS is not “clear”. If the instruction is successful, it sets the
launch state to “launched.”

•

VMRESUME fails if the launch state of the current VMCS is not “launched.”

If VM entry is attempted, the logical processor performs a series of consistency checks as detailed in Chapter 26,
“VM Entries”. Failure to pass checks on the VMX controls or on the host-state area passes control to the instruction
following the VMLAUNCH or VMRESUME instruction. If these pass but checks on the guest-state area fail, the logical
processor loads state from the host-state area of the VMCS, passing control to the instruction referenced by the RIP
field in the host-state area.
VM entry is not allowed when events are blocked by MOV SS or POP SS. Neither VMLAUNCH nor VMRESUME should
be used immediately after either MOV to SS or POP to SS.

Operation
IF (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSIF current-VMCS pointer is not valid
THEN VMfailInvalid;
ELSIF events are being blocked by MOV SS
THEN VMfailValid(VM entry with events blocked by MOV SS);
ELSIF (VMLAUNCH and launch state of current VMCS is not “clear”)
THEN VMfailValid(VMLAUNCH with non-clear VMCS);
ELSIF (VMRESUME and launch state of current VMCS is not “launched”)
THEN VMfailValid(VMRESUME with non-launched VMCS);
ELSE
Check settings of VMX controls and host-state area;
IF invalid settings
THEN VMfailValid(VM entry with invalid VMX-control field(s)) or
VMfailValid(VM entry with invalid host-state field(s)) or
VMfailValid(VM entry with invalid executive-VMCS pointer)) or
VMfailValid(VM entry with non-launched executive VMCS) or
VMfailValid(VM entry with executive-VMCS pointer not VMXON pointer) or
VMfailValid(VM entry with invalid VM-execution control fields in executive
VMCS)
as appropriate;
ELSE
Attempt to load guest state and PDPTRs as appropriate;
clear address-range monitoring;
IF failure in checking guest state or PDPTRs
THEN VM entry fails (see Section 26.7);

30-14 Vol. 3C

VMX INSTRUCTION REFERENCE

ELSE
Attempt to load MSRs from VM-entry MSR-load area;
IF failure
THEN VM entry fails
(see Section 26.7);
ELSE
IF VMLAUNCH
THEN launch state of VMCS ← “launched”;
FI;
IF in SMM and “entry to SMM” VM-entry control is 0
THEN
IF “deactivate dual-monitor treatment” VM-entry
control is 0
THEN SMM-transfer VMCS pointer ←
current-VMCS pointer;
FI;
IF executive-VMCS pointer is VMXON pointer
THEN current-VMCS pointer ←
VMCS-link pointer;
ELSE current-VMCS pointer ←
executive-VMCS pointer;
FI;
leave SMM;
FI;
VM entry succeeds;
FI;
FI;
FI;
FI;
Further details of the operation of the VM-entry appear in Chapter 26.

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.

#UD

If executed outside VMX operation.

Real-Address Mode Exceptions
#UD

The VMLAUNCH and VMRESUME instructions are not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMLAUNCH and VMRESUME instructions are not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The VMLAUNCH and VMRESUME instructions are not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.

#UD

If executed outside VMX operation.

Vol. 3C 30-15

VMX INSTRUCTION REFERENCE

VMPTRLD—Load Pointer to Virtual-Machine Control Structure
Opcode

Instruction

Description

NP 0F C7 /6

VMPTRLD m64

Loads the current VMCS pointer from memory.

Description
Marks the current-VMCS pointer valid and loads it with the physical address in the instruction operand. The instruction fails if its operand is not properly aligned, sets unsupported physical-address bits, or is equal to the VMXON
pointer. In addition, the instruction fails if the 32 bits in memory referenced by the operand do not match the VMCS
revision identifier supported by this processor.1
The operand of this instruction is always 64 bits and is always in memory.

Operation
IF (register operand) or (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSE
addr ← contents of 64-bit in-memory source operand;
IF addr is not 4KB-aligned OR
addr sets any bits beyond the physical-address width2
THEN VMfail(VMPTRLD with invalid physical address);
ELSIF addr = VMXON pointer
THEN VMfail(VMPTRLD with VMXON pointer);
ELSE
rev ← 32 bits located at physical address addr;
IF rev[30:0] ≠ VMCS revision identifier supported by processor OR
rev[31] = 1 AND processor does not support 1-setting of “VMCS shadowing”
THEN VMfail(VMPTRLD with incorrect VMCS revision identifier);
ELSE
current-VMCS pointer ← addr;
VMsucceed;
FI;
FI;
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory source operand effective address is outside the CS, DS, ES, FS, or GS segment
limit.
If the DS, ES, FS, or GS register contains an unusable segment.

1. Software should consult the VMX capability MSR VMX_BASIC to discover the VMCS revision identifier supported by this processor
(see Appendix A, “VMX Capability Reporting Facility”).
2. If IA32_VMX_BASIC[48] is read as 1, VMfail occurs if addr sets any bits in the range 63:32; see Appendix A.1.
30-16 Vol. 3C

VMX INSTRUCTION REFERENCE

If the source operand is located in an execute-only code segment.
#PF(fault-code)

If a page fault occurs in accessing the memory source operand.

#SS(0)

If the memory source operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If operand is a register.
If not in VMX operation.

Real-Address Mode Exceptions
#UD

The VMPTRLD instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMPTRLD instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The VMPTRLD instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the source operand is in the CS, DS, ES, FS, or GS segments and the memory address is in
a non-canonical form.

#PF(fault-code)

If a page fault occurs in accessing the memory source operand.

#SS(0)

If the source operand is in the SS segment and the memory address is in a non-canonical
form.

#UD

If operand is a register.
If not in VMX operation.

Vol. 3C 30-17

VMX INSTRUCTION REFERENCE

VMPTRST—Store Pointer to Virtual-Machine Control Structure
Opcode

Instruction

Description

NP 0F C7 /7

VMPTRST m64

Stores the current VMCS pointer into memory.

Description
Stores the current-VMCS pointer into a specified memory address. The operand of this instruction is always 64 bits
and is always in memory.

Operation
IF (register operand) or (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSE
64-bit in-memory destination operand ← current-VMCS pointer;
VMsucceed;
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory destination operand effective address is outside the CS, DS, ES, FS, or GS
segment limit.
If the DS, ES, FS, or GS register contains an unusable segment.
If the destination operand is located in a read-only data segment or any code segment.

#PF(fault-code)

If a page fault occurs in accessing the memory destination operand.

#SS(0)

If the memory destination operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If operand is a register.
If not in VMX operation.

Real-Address Mode Exceptions
#UD

The VMPTRST instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMPTRST instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

30-18 Vol. 3C

The VMPTRST instruction is not recognized in compatibility mode.

VMX INSTRUCTION REFERENCE

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the destination operand is in the CS, DS, ES, FS, or GS segments and the memory address
is in a non-canonical form.

#PF(fault-code)

If a page fault occurs in accessing the memory destination operand.

#SS(0)

If the destination operand is in the SS segment and the memory address is in a non-canonical
form.

#UD

If operand is a register.
If not in VMX operation.

Vol. 3C 30-19

VMX INSTRUCTION REFERENCE

VMREAD—Read Field from Virtual-Machine Control Structure
Opcode

Instruction

Description

NP 0F 78

VMREAD r/m64, r64

Reads a specified VMCS field (in 64-bit mode).

NP 0F 78

VMREAD r/m32, r32

Reads a specified VMCS field (outside 64-bit mode).

Description
Reads a specified field from a VMCS and stores it into a specified destination operand (register or memory). In VMX
root operation, the instruction reads from the current VMCS. If executed in VMX non-root operation, the instruction
reads from the VMCS referenced by the VMCS link pointer field in the current VMCS.
The VMCS field is specified by the VMCS-field encoding contained in the register source operand. Outside IA-32e
mode, the source operand has 32 bits, regardless of the value of CS.D. In 64-bit mode, the source operand has 64
bits.
The effective size of the destination operand, which may be a register or in memory, is always 32 bits outside IA32e mode (the setting of CS.D is ignored with respect to operand size) and 64 bits in 64-bit mode. If the VMCS field
specified by the source operand is shorter than this effective operand size, the high bits of the destination operand
are cleared to 0. If the VMCS field is longer, then the high bits of the field are not read.
Note that any faults resulting from accessing a memory destination operand can occur only after determining, in
the operation section below, that the relevant VMCS pointer is valid and that the specified VMCS field is supported.

Operation
IF (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation AND (“VMCS shadowing” is 0 OR source operand sets bits in range 63:15 OR
VMREAD bit corresponding to bits 14:0 of source operand is 1)1
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSIF (in VMX root operation AND current-VMCS pointer is not valid) OR
(in VMX non-root operation AND VMCS link pointer is not valid)
THEN VMfailInvalid;
ELSIF source operand does not correspond to any VMCS field
THEN VMfailValid(VMREAD/VMWRITE from/to unsupported VMCS component);
ELSE
IF in VMX root operation
THEN destination operand ← contents of field indexed by source operand in current VMCS;
ELSE destination operand ← contents of field indexed by source operand in VMCS referenced by VMCS link pointer;
FI;
VMsucceed;
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.

1. The VMREAD bit for a source operand is defined as follows. Let x be the value of bits 14:0 of the source operand and let addr be the
VMREAD-bitmap address. The corresponding VMREAD bit is in bit position x & 7 of the byte at physical address addr | (x » 3).
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VMX INSTRUCTION REFERENCE

If a memory destination operand effective address is outside the CS, DS, ES, FS, or GS
segment limit.
If the DS, ES, FS, or GS register contains an unusable segment.
If the destination operand is located in a read-only data segment or any code segment.
#PF(fault-code)

If a page fault occurs in accessing a memory destination operand.

#SS(0)

If a memory destination operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If not in VMX operation.

Real-Address Mode Exceptions
#UD

The VMREAD instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMREAD instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The VMREAD instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory destination operand is in the CS, DS, ES, FS, or GS segments and the memory
address is in a non-canonical form.

#PF(fault-code)

If a page fault occurs in accessing a memory destination operand.

#SS(0)

If the memory destination operand is in the SS segment and the memory address is in a noncanonical form.

#UD

If not in VMX operation.

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VMX INSTRUCTION REFERENCE

VMRESUME—Resume Virtual Machine
See VMLAUNCH/VMRESUME—Launch/Resume Virtual Machine.

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VMX INSTRUCTION REFERENCE

VMWRITE—Write Field to Virtual-Machine Control Structure
Opcode

Instruction

Description

NP 0F 79

VMWRITE r64, r/m64

Writes a specified VMCS field (in 64-bit mode)

NP 0F 79

VMWRITE r32, r/m32

Writes a specified VMCS field (outside 64-bit mode)

Description
Writes the contents of a primary source operand (register or memory) to a specified field in a VMCS. In VMX root
operation, the instruction writes to the current VMCS. If executed in VMX non-root operation, the instruction writes
to the VMCS referenced by the VMCS link pointer field in the current VMCS.
The VMCS field is specified by the VMCS-field encoding contained in the register secondary source operand.
Outside IA-32e mode, the secondary source operand is always 32 bits, regardless of the value of CS.D. In 64-bit
mode, the secondary source operand has 64 bits.
The effective size of the primary source operand, which may be a register or in memory, is always 32 bits outside
IA-32e mode (the setting of CS.D is ignored with respect to operand size) and 64 bits in 64-bit mode. If the VMCS
field specified by the secondary source operand is shorter than this effective operand size, the high bits of the
primary source operand are ignored. If the VMCS field is longer, then the high bits of the field are cleared to 0.
Note that any faults resulting from accessing a memory source operand occur after determining, in the operation
section below, that the relevant VMCS pointer is valid but before determining if the destination VMCS field is
supported.

Operation
IF (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation AND (“VMCS shadowing” is 0 OR secondary source operand sets bits in range 63:15 OR
VMWRITE bit corresponding to bits 14:0 of secondary source operand is 1)1
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSIF (in VMX root operation AND current-VMCS pointer is not valid) OR
(in VMX non-root operation AND VMCS-link pointer is not valid)
THEN VMfailInvalid;
ELSIF secondary source operand does not correspond to any VMCS field
THEN VMfailValid(VMREAD/VMWRITE from/to unsupported VMCS component);
ELSIF VMCS field indexed by secondary source operand is a VM-exit information field AND
processor does not support writing to such fields2
THEN VMfailValid(VMWRITE to read-only VMCS component);
ELSE
IF in VMX root operation
THEN field indexed by secondary source operand in current VMCS ← primary source operand;
ELSE field indexed by secondary source operand in VMCS referenced by VMCS link pointer ← primary source operand;

FI;
VMsucceed;
FI;

1. The VMWRITE bit for a secondary source operand is defined as follows. Let x be the value of bits 14:0 of the secondary source operand and let addr be the VMWRITE-bitmap address. The corresponding VMWRITE bit is in bit position x & 7 of the byte at physical
address addr | (x » 3).
2. Software can discover whether these fields can be written by reading the VMX capability MSR IA32_VMX_MISC (see Appendix A.6).
Vol. 3C 30-23

VMX INSTRUCTION REFERENCE

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If a memory source operand effective address is outside the CS, DS, ES, FS, or GS segment
limit.
If the DS, ES, FS, or GS register contains an unusable segment.
If the source operand is located in an execute-only code segment.

#PF(fault-code)

If a page fault occurs in accessing a memory source operand.

#SS(0)

If a memory source operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If not in VMX operation.

Real-Address Mode Exceptions
#UD

The VMWRITE instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMWRITE instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The VMWRITE instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If the current privilege level is not 0.
If the memory source operand is in the CS, DS, ES, FS, or GS segments and the memory
address is in a non-canonical form.

#PF(fault-code)

If a page fault occurs in accessing a memory source operand.

#SS(0)

If the memory source operand is in the SS segment and the memory address is in a noncanonical form.

#UD

If not in VMX operation.

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VMX INSTRUCTION REFERENCE

VMXOFF—Leave VMX Operation
Opcode

Instruction

Description

0F 01 C4

VMXOFF

Leaves VMX operation.

Description
Takes the logical processor out of VMX operation, unblocks INIT signals, conditionally re-enables A20M, and clears
any address-range monitoring.1

Operation
IF (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF in VMX non-root operation
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSIF dual-monitor treatment of SMIs and SMM is active
THEN VMfail(VMXOFF under dual-monitor treatment of SMIs and SMM);
ELSE
leave VMX operation;
unblock INIT;
IF IA32_SMM_MONITOR_CTL[2] = 02
THEN unblock SMIs;
IF outside SMX operation3
THEN unblock and enable A20M;
FI;
clear address-range monitoring;
VMsucceed;
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If executed in VMX root operation with CPL > 0.

#UD

If executed outside VMX operation.

Real-Address Mode Exceptions
#UD

The VMXOFF instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMXOFF instruction is not recognized in virtual-8086 mode.

1. See the information on MONITOR/MWAIT in Chapter 8, “Multiple-Processor Management,” of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 3A.
2. Setting IA32_SMM_MONITOR_CTL[bit 2] to 1 prevents VMXOFF from unblocking SMIs regardless of the value of the register’s value
bit (bit 0). Not all processors allow this bit to be set to 1. Software should consult the VMX capability MSR IA32_VMX_MISC (see
Appendix A.6) to determine whether this is allowed.
3. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the
last execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference.”
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VMX INSTRUCTION REFERENCE

Compatibility Mode Exceptions
#UD

The VMXOFF instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If executed in VMX root operation with CPL > 0.

#UD

If executed outside VMX operation.

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VMX INSTRUCTION REFERENCE

VMXON—Enter VMX Operation
Opcode

Instruction

Description

F3 0F C7 /6

VMXON m64

Enter VMX root operation.

Description
Puts the logical processor in VMX operation with no current VMCS, blocks INIT signals, disables A20M, and clears
any address-range monitoring established by the MONITOR instruction.1
The operand of this instruction is a 4KB-aligned physical address (the VMXON pointer) that references the VMXON
region, which the logical processor may use to support VMX operation. This operand is always 64 bits and is always
in memory.

Operation
IF (register operand) or (CR0.PE = 0) or (CR4.VMXE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
THEN #UD;
ELSIF not in VMX operation
THEN
IF (CPL > 0) or (in A20M mode) or
(the values of CR0 and CR4 are not supported in VMX operation; see Section 23.8) or
(bit 0 (lock bit) of IA32_FEATURE_CONTROL MSR is clear) or
(in SMX operation2 and bit 1 of IA32_FEATURE_CONTROL MSR is clear) or
(outside SMX operation and bit 2 of IA32_FEATURE_CONTROL MSR is clear)
THEN #GP(0);
ELSE
addr ← contents of 64-bit in-memory source operand;
IF addr is not 4KB-aligned or
addr sets any bits beyond the physical-address width3
THEN VMfailInvalid;
ELSE
rev ← 32 bits located at physical address addr;
IF rev[30:0] ≠ VMCS revision identifier supported by processor OR rev[31] = 1
THEN VMfailInvalid;
ELSE
current-VMCS pointer ← FFFFFFFF_FFFFFFFFH;
enter VMX operation;
block INIT signals;
block and disable A20M;
clear address-range monitoring;
IF the processor supports Intel PT but does not allow it to be used in VMX operation4
THEN IA32_RTIT_CTL.TraceEn ← 0;
FI;
VMsucceed;
1. See the information on MONITOR/MWAIT in Chapter 8, “Multiple-Processor Management,” of the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 3A.
2. A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last execution of GETSEC[SENTER]. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the last
execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference.”
3. If IA32_VMX_BASIC[48] is read as 1, VMfailInvalid occurs if addr sets any bits in the range 63:32; see Appendix A.1.
4. Software should read the VMX capability MSR IA32_VMX_MISC to determine whether the processor allows Intel PT to be used in
VMX operation (see Appendix A.6).
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VMX INSTRUCTION REFERENCE

FI;
FI;

FI;
ELSIF in VMX non-root operation
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSE VMfail(“VMXON executed in VMX root operation”);
FI;

Flags Affected
See the operation section and Section 30.2.

Protected Mode Exceptions
#GP(0)

If executed outside VMX operation with CPL>0 or with invalid CR0 or CR4 fixed bits.
If executed in A20M mode.
If the memory source operand effective address is outside the CS, DS, ES, FS, or GS segment
limit.
If the DS, ES, FS, or GS register contains an unusable segment.
If the source operand is located in an execute-only code segment.
If the value of the IA32_FEATURE_CONTROL MSR does not support entry to VMX operation in
the current processor mode.

#PF(fault-code)

If a page fault occurs in accessing the memory source operand.

#SS(0)

If the memory source operand effective address is outside the SS segment limit.
If the SS register contains an unusable segment.

#UD

If operand is a register.
If executed with CR4.VMXE = 0.

Real-Address Mode Exceptions
#UD

The VMXON instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions
#UD

The VMXON instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
#UD

The VMXON instruction is not recognized in compatibility mode.

64-Bit Mode Exceptions
#GP(0)

If executed outside VMX operation with CPL > 0 or with invalid CR0 or CR4 fixed bits.
If executed in A20M mode.
If the source operand is in the CS, DS, ES, FS, or GS segments and the memory address is in
a non-canonical form.
If the value of the IA32_FEATURE_CONTROL MSR does not support entry to VMX operation in
the current processor mode.

#PF(fault-code)

If a page fault occurs in accessing the memory source operand.

#SS(0)

If the source operand is in the SS segment and the memory address is in a non-canonical
form.

#UD

If operand is a register.
If executed with CR4.VMXE = 0.

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VMX INSTRUCTION REFERENCE

30.4

VM INSTRUCTION ERROR NUMBERS

For certain error conditions, the VM-instruction error field is loaded with an error number to indicate the source of
the error. Table 30-1 lists VM-instruction error numbers.

Table 30-1. VM-Instruction Error Numbers
Error
Description
Number
1

VMCALL executed in VMX root operation

2

VMCLEAR with invalid physical address

3

VMCLEAR with VMXON pointer

4

VMLAUNCH with non-clear VMCS

5

VMRESUME with non-launched VMCS

6

VMRESUME after VMXOFF (VMXOFF and VMXON between VMLAUNCH and VMRESUME)a

7

VM entry with invalid control field(s)b,c

8

VM entry with invalid host-state field(s)b

9

VMPTRLD with invalid physical address

10

VMPTRLD with VMXON pointer

11

VMPTRLD with incorrect VMCS revision identifier

12

VMREAD/VMWRITE from/to unsupported VMCS component

13

VMWRITE to read-only VMCS component

15

VMXON executed in VMX root operation

16

VM entry with invalid executive-VMCS pointerb

17

VM entry with non-launched executive VMCSb

18

VM entry with executive-VMCS pointer not VMXON pointer (when attempting to deactivate the dual-monitor treatment of
SMIs and SMM)b

19

VMCALL with non-clear VMCS (when attempting to activate the dual-monitor treatment of SMIs and SMM)

20

VMCALL with invalid VM-exit control fields

22

VMCALL with incorrect MSEG revision identifier (when attempting to activate the dual-monitor treatment of SMIs and SMM)

23

VMXOFF under dual-monitor treatment of SMIs and SMM

24

VMCALL with invalid SMM-monitor features (when attempting to activate the dual-monitor treatment of SMIs and SMM)

25

VM entry with invalid VM-execution control fields in executive VMCS (when attempting to return from SMM)b,c

26

VM entry with events blocked by MOV SS.

28

Invalid operand to INVEPT/INVVPID.

NOTES:
a. Earlier versions of this manual described this error as “VMRESUME with a corrupted VMCS”.
b. VM-entry checks on control fields and host-state fields may be performed in any order. Thus, an indication by error number of one
cause does not imply that there are not also other errors. Different processors may give different error numbers for the same VMCS.
c. Error number 7 is not used for VM entries that return from SMM that fail due to invalid VM-execution control fields in the executive
VMCS. Error number 25 is used for these cases.

Vol. 3C 30-29

VMX INSTRUCTION REFERENCE

30-30 Vol. 3C

CHAPTER 31
VIRTUAL-MACHINE MONITOR PROGRAMMING CONSIDERATIONS
31.1

VMX SYSTEM PROGRAMMING OVERVIEW

The Virtual Machine Monitor (VMM) is a software class used to manage virtual machines (VM). This chapter
describes programming considerations for VMMs.
Each VM behaves like a complete physical machine and can run operating system (OS) and applications. The VMM
software layer runs at the most privileged level and has complete ownership of the underlying system hardware.
The VMM controls creation of a VM, transfers control to a VM, and manages situations that can cause transitions
between the guest VMs and host VMM. The VMM allows the VMs to share the underlying hardware and yet provides
isolation between the VMs. The guest software executing in a VM is unaware of any transitions that might have
occurred between the VM and its host.

31.2

SUPPORTING PROCESSOR OPERATING MODES IN GUEST ENVIRONMENTS

Typically, VMMs transfer control to a VM using VMX transitions referred to as VM entries. The boundary conditions
that define what a VM is allowed to execute in isolation are specified in a virtual-machine control structure (VMCS).
As noted in Section 23.8, processors may fix certain bits in CR0 and CR4 to specific values and not support other
values. The first processors to support VMX operation require that CR0.PE and CR0.PG be 1 in VMX operation. Thus,
a VM entry is allowed only to guests with paging enabled that are in protected mode or in virtual-8086 mode. Guest
execution in other processor operating modes need to be specially handled by the VMM.
One example of such a condition is guest execution in real-mode. A VMM could support guest real-mode execution
using at least two approaches:

•
•

By using a fast instruction set emulator in the VMM.
By using the similarity between real-mode and virtual-8086 mode to support real-mode guest execution in a
virtual-8086 container. The virtual-8086 container may be implemented as a virtual-8086 container task within
a monitor that emulates real-mode guest state and instructions, or by running the guest VM as the virtual-8086
container (by entering the guest with RFLAGS.VM1 set). Attempts by real-mode code to access privileged state
outside the virtual-8086 container would trap to the VMM and would also need to be emulated.

Another example of such a condition is guest execution in protected mode with paging disabled. A VMM could
support such guest execution by using “identity” page tables to emulate unpaged protected mode.

31.2.1

Using Unrestricted Guest Mode

Processors which support the “unrestricted guest” VM-execution control allow VM software to run in real-address
mode and unpaged protected mode. Since these modes do not use paging, VMM software must virtualize guest
memory using EPT.
Special notes for 64-bit VMM software using the 1-setting of the “unrestricted guest” VM-execution control:

•

It is recommended that 64-bit VMM software use the 1-settings of the "load IA32_EFER" VM entry control and
the "save IA32_EFER" VM-exit control. If VM entry is establishing CR0.PG=0 and if the "IA-32e mode guest"
and "load IA32_EFER" VM entry controls are both 0, VM entry leaves IA32_EFER.LME unmodified (i.e., the host
value will persist in the guest).

•

It is not necessary for VMM software to track guest transitions into and out of IA-32e mode for the purpose of
maintaining the correct setting of the "IA-32e mode guest" VM entry control. This is because VM exits on

1. This chapter uses the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that support VMX operation also support Intel 64 architecture. For processors that do not support Intel 64 architecture, this notation refers to the 32-bit
forms of those registers (EAX, EIP, ESP, EFLAGS, etc.).
Vol. 3C 31-1

VIRTUAL-MACHINE MONITOR PROGRAMMING CONSIDERATIONS

processors supporting the 1-setting of the "unrestricted guest" VM-execution control save the (guest) value of
IA32_EFER.LMA into the "IA-32e mode guest" VM entry control.

31.3

MANAGING VMCS REGIONS AND POINTERS

A VMM must observe necessary procedures when working with a VMCS, the associated VMCS pointer, and the
VMCS region. It must also not assume the state of persistency for VMCS regions in memory or cache.
Before entering VMX operation, the host VMM allocates a VMXON region. A VMM can host several virtual machines
and have many VMCSs active under its management. A unique VMCS region is required for each virtual machine;
a VMXON region is required for the VMM itself.
A VMM determines the VMCS region size by reading IA32_VMX_BASIC MSR; it creates VMCS regions of this size
using a 4-KByte-aligned area of physical memory. Each VMCS region needs to be initialized with a VMCS revision
identifier (at byte offset 0) identical to the revision reported by the processor in the VMX capability MSR.

NOTE
Software must not read or write directly to the VMCS data region as the format is not architecturally
defined. Consequently, Intel recommends that the VMM remove any linear-address mappings to
VMCS regions before loading.
System software does not need to do special preparation to the VMXON region before entering into VMX operation.
The address of the VMXON region for the VMM is provided as an operand to VMXON instruction. Once in VMX root
operation, the VMM needs to prepare data fields in the VMCS that control the execution of a VM upon a VM entry.
The VMM can make a VMCS the current VMCS by using the VMPTRLD instruction. VMCS data fields must be read or
written only through VMREAD and VMWRITE commands respectively.
Every component of the VMCS is identified by a 32-bit encoding that is provided as an operand to VMREAD and
VMWRITE. Appendix B provides the encodings. A VMM must properly initialize all fields in a VMCS before using the
current VMCS for VM entry.
A VMCS is referred to as a controlling VMCS if it is the current VMCS on a logical processor in VMX non-root operation. A current VMCS for controlling a logical processor in VMX non-root operation may be referred to as a working
VMCS if the logical processor is not in VMX non-root operation. The relationship of active, current (i.e. working) and
controlling VMCS during VMX operation is shown in Figure 31-1.

NOTE
As noted in Section 24.1, the processor may optimize VMX operation by maintaining the state of an
active VMCS (one for which VMPTRLD has been executed) on the processor. Before relinquishing
control to other system software that may, without informing the VMM, remove power from the
processor (e.g., for transitions to S3 or S4) or leave VMX operation, a VMM must VMCLEAR all active
VMCSs. This ensures that all VMCS data cached by the processor are flushed to memory and that
no other software can corrupt the current VMM’s VMCS data. It is also recommended that the VMM
execute VMXOFF after such executions of VMCLEAR.
The VMX capability MSR IA32_VMX_BASIC reports the memory type used by the processor for accessing a VMCS
or any data structures referenced through pointers in the VMCS. Software must maintain the VMCS structures in
cache-coherent memory. Software must always map the regions hosting the I/O bitmaps, MSR bitmaps, VM-exit
MSR-store area, VM-exit MSR-load area, and VM-entry MSR-load area to the write-back (WB) memory type.
Mapping these regions to uncacheable (UC) memory type is supported, but strongly discouraged due to negative
impact on performance.

31.4

USING VMX INSTRUCTIONS

VMX instructions are allowed only in VMX root operation. An attempt to execute a VMX instruction in VMX non-root
operation causes a VM exit.

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VIRTUAL-MACHINE MONITOR PROGRAMMING CONSIDERATIONS

(a) VMX Operation and VMX Transitions
VM Entry

VM Entry

VM Entry

VM Entry

VMXOFF

Processor
Operation

VMXON

VM Exit

VM Exit

VM Exit
VM Exit

Legend:
VMX Root
Operation

Outside
VMX
Operation

VMX
Non-Root
Operation

(b) State of VMCS and VMX Operation
VMLAUNCH
VMPTRLD B

VMRESUME

VMCLEAR B

VM Exit

VM Exit

VMCS B
VMCS A
VMPTRLD A

VMPTRLD A

VM Exit

VMLAUNCH
Legend:

Inactive
VMCS

Current VMCS
(working)

Active VMCS
(not current)

VM Exit

VMRESUME

VMCLEAR A

Current VMCS
(controlling)

Figure 31-1. VMX Transitions and States of VMCS in a Logical Processor
Processors perform various checks while executing any VMX instruction. They follow well-defined error handling on
failures. VMX instruction execution failures detected before loading of a guest state are handled by the processor
as follows:

•
•

If the working-VMCS pointer is not valid, the instruction fails by setting RFLAGS.CF to 1.
If the working-VMCS pointer is valid, RFLAGS.ZF is set to 1 and the proper error-code is saved in the VMinstruction error field of the working-VMCS.

Software is required to check RFLAGS.CF and RFLAGS.ZF to determine the success or failure of VMX instruction
executions.
The following items provide details regarding use of the VM-entry instructions (VMLAUNCH and VMRESUME):

•

If the working-VMCS pointer is valid, the state of the working VMCS may cause the VM-entry instruction to fail.
RFLAGS.ZF is set to 1 and one of the following values is saved in the VM-instruction error field:
— 4: VMLAUNCH with non-clear VMCS.
If this error occurs, software can avoid the error by executing VMRESUME.
— 5: VMRESUME with non-launched VMCS.
If this error occurs, software can avoid the error by executing VMLAUNCH.

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VIRTUAL-MACHINE MONITOR PROGRAMMING CONSIDERATIONS
— 6: VMRESUME after VMXOFF.1
If this error occurs, software can avoid the error by executing the following sequence of instructions:
VMPTRST working-VMCS pointer
VMCLEAR working-VMCS pointer
VMPTRLD working-VMCS pointer
VMLAUNCH
(VMPTRST may not be necessary is software already knows the working-VMCS pointer.)

•

If none of the above errors occur, the processor checks on the VMX controls and host-state area. If any of these
checks fail, the VM-entry instruction fails. RFLAGS.ZF is set to 1 and either 7 (VM entry with invalid control
field(s)) or 8 (VM entry with invalid host-state field(s)) is saved in the VM-instruction error field.

•

After a VM-entry instruction (VMRESUME or VMLAUNCH) successfully completes the general checks and checks
on VMX controls and the host-state area (see Section 26.2), any errors encountered while loading of gueststate (due to bad guest-state or bad MSR loading) causes the processor to load state from the host-state area
of the working VMCS as if a VM exit had occurred (see Section 31.7).
This failure behavior differs from that of VM exits in that no guest-state is saved to the guest-state area. A VMM
can detect its VM-exit handler was invoked by such a failure by checking bit 31 (for 1) in the exit reason field of
the working VMCS and further identify the failure by using the exit qualification field.

See Chapter 26 for more details about the VM-entry instructions.

31.5

VMM SETUP & TEAR DOWN

VMMs need to ensure that the processor is running in protected mode with paging before entering VMX operation.
The following list describes the minimal steps required to enter VMX root operation with a VMM running at CPL = 0.

•
•

Check VMX support in processor using CPUID.

•

Create a VMXON region in non-pageable memory of a size specified by IA32_VMX_BASIC MSR and aligned to a
4-KByte boundary. Software should read the capability MSRs to determine width of the physical addresses that
may be used for the VMXON region and ensure the entire VMXON region can be addressed by addresses with
that width. Also, software must ensure that the VMXON region is hosted in cache-coherent memory.

•

Initialize the version identifier in the VMXON region (the first 31 bits) with the VMCS revision identifier reported
by capability MSRs. Clear bit 31 of the first 4 bytes of the VMXON region.

•

Ensure the current processor operating mode meets the required CR0 fixed bits (CR0.PE = 1, CR0.PG = 1).
Other required CR0 fixed bits can be detected through the IA32_VMX_CR0_FIXED0 and
IA32_VMX_CR0_FIXED1 MSRs.

•

Enable VMX operation by setting CR4.VMXE = 1. Ensure the resultant CR4 value supports all the CR4 fixed bits
reported in the IA32_VMX_CR4_FIXED0 and IA32_VMX_CR4_FIXED1 MSRs.

•

Ensure that the IA32_FEATURE_CONTROL MSR (MSR index 3AH) has been properly programmed and that its
lock bit is set (Bit 0 = 1). This MSR is generally configured by the BIOS using WRMSR.

•

Execute VMXON with the physical address of the VMXON region as the operand. Check successful execution of
VMXON by checking if RFLAGS.CF = 0.

Determine the VMX capabilities supported by the processor through the VMX capability MSRs. See Section
31.5.1 and Appendix A.

Upon successful execution of the steps above, the processor is in VMX root operation.
A VMM executing in VMX root operation and CPL = 0 leaves VMX operation by executing VMXOFF and verifies
successful execution by checking if RFLAGS.CF = 0 and RFLAGS.ZF = 0.
If an SMM monitor has been configured to service SMIs while in VMX operation (see Section 34.15), the SMM
monitor needs to be torn down before the executive monitor can leave VMX operation (see Section 34.15.7).
VMXOFF fails for the executive monitor (a VMM that entered VMX operation by way of issuing VMXON) if SMM
monitor is configured.
1. Earlier versions of this manual described this error as “VMRESUME with a corrupted VMCS”.
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31.5.1

Algorithms for Determining VMX Capabilities

As noted earlier, a VMM should determine the VMX capabilities supported by the processor by reading the VMX
capability MSRs. The architecture for these MSRs is detailed in Appendix A.
As noted in Chapter 26, “VM Entries”, certain VMX controls are reserved and must be set to a specific value (0 or
1) determined by the processor. The specific value to which a reserved control must be set is its default setting.
Most controls have a default setting of 0; Appendix A.2 identifies those controls that have a default setting of 1. The
term default1 describes the class of controls whose default setting is 1. The are controls in this class from the pinbased VM-execution controls, the primary processor-based VM-execution controls, the VM-exit controls, and the
VM-entry controls. There are no secondary processor-based VM-execution controls in the default1 class.
Future processors may define new functionality for one or more reserved controls. Such processors would allow
each newly defined control to be set either to 0 or to 1. Software that does not desire a control’s new functionality
should set the control to its default setting.
The capability MSRs IA32_VMX_PINBASED_CTLS, IA32_VMX_PROCBASED_CTLS, IA32_VMX_EXIT_CTLS, and
IA32_VMX_ENTRY_CTLS report, respectively, on the allowed settings of most of the pin-based VM-execution
controls, the primary processor-based VM-execution controls, the VM-exit controls, and the VM-entry controls.
However, they will always report that any control in the default1 class must be 1. If a logical processor allows any
control in the default1 class to be 0, it indicates this fact by returning 1 for the value of bit 55 of the
IA32_VMX_BASIC MSR. If this bit is 1, the logical processor supports the capability MSRs
IA32_VMX_TRUE_PINBASED_CTLS, IA32_VMX_TRUE_PROCBASED_CTLS, IA32_VMX_TRUE_EXIT_CTLS, and
IA32_VMX_TRUE_ENTRY_CTLS. These capability MSRs report, respectively, on the allowed settings of all of the
pin-based VM-execution controls, the primary processor-based VM-execution controls, the VM-exit controls, and
the VM-entry controls.
Software may use one of the following high-level algorithms to determine the correct default control settings:1
1. The following algorithm does not use the details given in Appendix A.2:
a. Ignore bit 55 of the IA32_VMX_BASIC MSR.
b. Using RDMSR, read the VMX capability MSRs IA32_VMX_PINBASED_CTLS, IA32_VMX_PROCBASED_CTLS,
IA32_VMX_EXIT_CTLS, and IA32_VMX_ENTRY_CTLS.
c.

Set the VMX controls as follows:
i)

If the relevant VMX capability MSR reports that a control has a single setting, use that setting.

ii) If (1) the relevant VMX capability MSR reports that a control can be set to 0 or 1; and (2) the control’s
meaning is known to the VMM; then set the control based on functionality desired.
iii) If (1) the relevant VMX capability MSR reports that a control can be set to 0 or 1; and (2) the control’s
meaning is not known to the VMM; then set the control to 0.
A VMM using this algorithm will set to 1 all controls in the default1 class (in step (c)(i)). It will operate
correctly even on processors that allow some controls in the default1 class to be 0. However, such a VMM will
not be able to use the new features enabled by the 0-setting of such controls. For that reason, this algorithm
is not recommended.
2. The following algorithm uses the details given in Appendix A.2. This algorithm requires software to know the
identity of the controls in the default1 class:
a. Using RDMSR, read the IA32_VMX_BASIC MSR.
b. Use bit 55 of that MSR as follows:
i)

If bit 55 is 0, use RDMSR to read the VMX capability MSRs IA32_VMX_PINBASED_CTLS,
IA32_VMX_PROCBASED_CTLS, IA32_VMX_EXIT_CTLS, and IA32_VMX_ENTRY_CTLS.

ii) If bit 55 is 1, use RDMSR to read the VMX capability MSRs IA32_VMX_TRUE_PINBASED_CTLS,
IA32_VMX_TRUE_PROCBASED_CTLS, IA32_VMX_TRUE_EXIT_CTLS, and
IA32_VMX_TRUE_ENTRY_CTLS.
1. These algorithms apply only to the pin-based VM-execution controls, the primary processor-based VM-execution controls, the VMexit controls, and the VM-entry controls. Because there are no secondary processor-based VM-execution controls in the default1
class, a VMM can always set to 0 any such control whose meaning is unknown to it.
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c.

Set the VMX controls as follows:
i)

If the relevant VMX capability MSR reports that a control has a single setting, use that setting.

ii) If (1) the relevant VMX capability MSR reports that a control can be set to 0 or 1; and (2) the control’s
meaning is known to the VMM; then set the control based on functionality desired.
iii) If (1) the relevant VMX capability MSR reports that a control can be set to 0 or 1; (2) the control’s
meaning is not known to the VMM; and (3) the control is not in the default1 class; then set the control
to 0.
iv) If (1) the relevant VMX capability MSR reports that a control can be set to 0 or 1; (2) the control’s
meaning is not known to the VMM; and (3) the control is in the default1 class; then set the control to 1.
A VMM using this algorithm will set to 1 all controls in default1 class whose meaning it does not know (either
in step (c)(i) or step (c)(iv)). It will operate correctly even on processors that allow some controls in the
default1 class to be 0. Unlike a VMM using Algorithm 1, a VMM using Algorithm 2 will be able to use the new
features enabled by the 0-setting of such controls.
3. The following algorithm uses the details given in Appendix A.2. This algorithm does not require software to
know the identity of the controls in the default1 class:
a. Using RDMSR, read the VMX capability MSRs IA32_VMX_BASIC, IA32_VMX_PINBASED_CTLS,
IA32_VMX_PROCBASED_CTLS, IA32_VMX_EXIT_CTLS, and IA32_VMX_ENTRY_CTLS.
b. If bit 55 of the IA32_VMX_BASIC MSR is 0, set the VMX controls as follows:
i)

If the relevant VMX capability MSR reports that a control has a single setting, use that setting.

ii) If (1) the relevant VMX capability MSR reports that a control can be set to 0 or 1; and (2) the control’s
meaning is known to the VMM; then set the control based on functionality desired.
iii) If (1) the relevant VMX capability MSR reports that a control can be set to 0 or 1; and (2) the control’s
meaning is not known to the VMM; then set the control to 0.
c.

If bit 55 of the IA32_VMX_BASIC MSR is 1, use RDMSR to read the VMX capability MSRs
IA32_VMX_TRUE_PINBASED_CTLS, IA32_VMX_TRUE_PROCBASED_CTLS, IA32_VMX_TRUE_EXIT_CTLS,
and IA32_VMX_TRUE_ENTRY_CTLS. Set the VMX controls as follows:
i)

If the relevant VMX capability MSR just read reports that a control has a single setting, use that
setting.

ii) If (1) the relevant VMX capability MSR just read reports that a control can be set to 0 or 1; and (2) the
control’s meaning is known to the VMM; then set the control based on functionality desired.
iii) If (1) the relevant VMX capability MSR just read reports that a control can be set to 0 or 1; (2) the
control’s meaning is not known to the VMM; and (3) the relevant VMX capability MSR as read in step (a)
reports that a control can be set to 0; then set the control to 0.
iv) If (1) the relevant VMX capability MSR just read reports that a control can be set to 0 or 1; (2) the
control’s meaning is not known to the VMM; and (3) the relevant VMX capability MSR as read in step (a)
reports that a control must be 1; then set the control to 1.
A VMM using this algorithm will set to 1 all controls in the default1 class whose meaning it does not know (in
step (b)(i), step (c)(i), or step (c)(iv)). It will operate correctly even on processors that allow some controls in
the default1 class to be 0. Unlike a VMM using Algorithm 1, a VMM using Algorithm 3 will be able to use the
new features enabled by the 0-setting of such controls. Unlike a VMM using Algorithm 2, a VMM using
Algorithm 3 need not know the identities of the controls in the default1 class.

31.6

PREPARATION AND LAUNCHING A VIRTUAL MACHINE

The following list describes the minimal steps required by the VMM to set up and launch a guest VM.

•

Create a VMCS region in non-pageable memory of size specified by the VMX capability MSR IA32_VMX_BASIC
and aligned to 4-KBytes. Software should read the capability MSRs to determine width of the physical
addresses that may be used for a VMCS region and ensure the entire VMCS region can be addressed by

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addresses with that width. The term “guest-VMCS address” refers to the physical address of the new VMCS
region for the following steps.

•

Initialize the version identifier in the VMCS (first 31 bits) with the VMCS revision identifier reported by the VMX
capability MSR IA32_VMX_BASIC. Clear bit 31 of the first 4 bytes of the VMCS region.

•

Execute the VMCLEAR instruction by supplying the guest-VMCS address. This will initialize the new VMCS
region in memory and set the launch state of the VMCS to “clear”. This action also invalidates the workingVMCS pointer register to FFFFFFFF_FFFFFFFFH. Software should verify successful execution of VMCLEAR by
checking if RFLAGS.CF = 0 and RFLAGS.ZF = 0.

•

Execute the VMPTRLD instruction by supplying the guest-VMCS address. This initializes the working-VMCS
pointer with the new VMCS region’s physical address.

•

Issue a sequence of VMWRITEs to initialize various host-state area fields in the working VMCS. The initialization
sets up the context and entry-points to the VMM upon subsequent VM exits from the guest. Host-state fields
include control registers (CR0, CR3 and CR4), selector fields for the segment registers (CS, SS, DS, ES, FS, GS
and TR), and base-address fields (for FS, GS, TR, GDTR and IDTR; RSP, RIP and the MSRs that control fast
system calls).
Chapter 27 describes the host-state consistency checking done by the processor for VM entries. The VMM is
required to set up host-state that comply with these consistency checks. For example, VMX requires the hostarea to have a task register (TR) selector with TI and RPL fields set to 0 and pointing to a valid TSS.

•

Use VMWRITEs to set up the various VM-exit control fields, VM-entry control fields, and VM-execution control
fields in the VMCS. Care should be taken to make sure the settings of individual fields match the allowed 0 and
1 settings for the respective controls as reported by the VMX capability MSRs (see Appendix A). Any settings
inconsistent with the settings reported by the capability MSRs will cause VM entries to fail.

•

Use VMWRITE to initialize various guest-state area fields in the working VMCS. This sets up the context and
entry-point for guest execution upon VM entry. Chapter 27 describes the guest-state loading and checking
done by the processor for VM entries to protected and virtual-8086 guest execution.

•

The VMM is required to set up guest-state that complies with these consistency checks:
— If the VMM design requires the initial VM launch to cause guest software (typically the guest virtual BIOS)
execution from the guest’s reset vector, it may need to initialize the guest execution state to reflect the
state of a physical processor at power-on reset (described in Chapter 9, Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 3A).
— The VMM may need to initialize additional guest execution state that is not captured in the VMCS gueststate area by loading them directly on the respective processor registers. Examples include general
purpose registers, the CR2 control register, debug registers, floating point registers and so forth. VMM may
support lazy loading of FPU, MMX, SSE, and SSE2 states with CR0.TS = 1 (described in Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 3A).

•

Execute VMLAUNCH to launch the guest VM. If VMLAUNCH fails due to any consistency checks before gueststate loading, RFLAGS.CF or RFLAGS.ZF will be set and the VM-instruction error field (see Section 24.9.5) will
contain the error-code. If guest-state consistency checks fail upon guest-state loading, the processor loads
state from the host-state area as if a VM exit had occurred (see Section 31.6).

VMLAUNCH updates the controlling-VMCS pointer with the working-VMCS pointer and saves the old value of
controlling-VMCS as the parent pointer. In addition, the launch state of the guest VMCS is changed to “launched”
from “clear”. Any programmed exit conditions will cause the guest to VM exit to the VMM. The VMM should execute
VMRESUME instruction for subsequent VM entries to guests in a “launched” state.

31.7

HANDLING OF VM EXITS

This section provides examples of software steps involved in a VMM’s handling of VM-exit conditions:

•

Determine the exit reason through a VMREAD of the exit-reason field in the working-VMCS. Appendix C
describes exit reasons and their encodings.

•

VMREAD the exit-qualification from the VMCS if the exit-reason field provides a valid qualification. The exitqualification field provides additional details on the VM-exit condition. For example, in case of page faults, the
exit-qualification field provides the guest linear address that caused the page fault.
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•

Depending on the exit reason, fetch other relevant fields from the VMCS. Appendix C lists the various exit
reasons.

•

Handle the VM-exit condition appropriately in the VMM. This may involve the VMM emulating one or more guest
instructions, programming the underlying host hardware resources, and then re-entering the VM to continue
execution.

31.7.1

Handling VM Exits Due to Exceptions

As noted in Section 25.2, an exception causes a VM exit if the bit corresponding to the exception’s vector is set in
the exception bitmap. (For page faults, the error code also determines whether a VM exit occurs.) This section
provide some guidelines of how a VMM might handle such exceptions.
Exceptions result when a logical processor encounters an unusual condition that software may not have expected.
When guest software encounters an exception, it may be the case that the condition was caused by the guest software. For example, a guest application may attempt to access a page that is restricted to supervisor access. Alternatively, the condition causing the exception may have been established by the VMM. For example, a guest OS may
attempt to access a page that the VMM has chosen to make not present.
When the condition causing an exception was established by guest software, the VMM may choose to reflect the
exception to guest software. When the condition was established by the VMM itself, the VMM may choose to
resume guest software after removing the condition.

31.7.1.1

Reflecting Exceptions to Guest Software

If the VMM determines that a VM exit was caused by an exception due to a condition established by guest software,
it may reflect that exception to guest software. The VMM would cause the exception to be delivered to guest software, where it can be handled as it would be if the guest were running on a physical machine. This section describes
how that may be done.
In general, the VMM can deliver the exception to guest software using VM-entry event injection as described in
Section 26.5. The VMM can copy (using VMREAD and VMWRITE) the contents of the VM-exit interruption-information field (which is valid, since the VM exit was caused by an exception) to the VM-entry interruption-information
field (which, if valid, will cause the exception to be delivered as part of the next VM entry). The VMM would also
copy the contents of the VM-exit interruption error-code field to the VM-entry exception error-code field; this need
not be done if bit 11 (error code valid) is clear in the VM-exit interruption-information field. After this, the VMM can
execute VMRESUME.
The following items provide details that may qualify the general approach:

•

Care should be taken to ensure that reserved bits 30:12 in the VM-entry interruption-information field are 0. In
particular, some VM exits may set bit 12 in the VM-exit interruption-information field to indicate NMI
unblocking due to IRET. If this bit is copied as 1 into the VM-entry interruption-information field, the next
VM entry will fail because that bit should be 0.

•

Bit 31 (valid) of the IDT-vectoring information field indicates, if set, that the exception causing the VM exit
occurred while another event was being delivered to guest software. If this is the case, it may not be
appropriate simply to reflect that exception to guest software. To provide proper virtualization of the exception
architecture, a VMM should handle nested events as a physical processor would. Processor handling is
described in Chapter 6, “Interrupt 8—Double Fault Exception (#DF)” in Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 3A.
— The VMM should reflect the exception causing the VM exit to guest software in any of the following cases:

•

The value of bits 10:8 (interruption type) of the IDT-vectoring information field is anything other than 3
(hardware exception).

•

The value of bits 7:0 (vector) of the IDT-vectoring information field indicates a benign exception (1, 2,
3, 4, 5, 6, 7, 9, 16, 17, 18, or 19).

•

The value of bits 7:0 (vector) of the VM-exit interruption-information field indicates a benign exception.

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•

The value of bits 7:0 of the IDT-vectoring information field indicates a contributory exception (0, 10,
11, 12, or 13) and the value of bits 7:0 of the VM-exit interruption-information field indicates a page
fault (14).

— If the value of bits 10:8 of the IDT-vectoring information field is 3 (hardware exception), the VMM should
reflect a double-fault exception to guest software in any of the following cases:

•

The value of bits 7:0 of the IDT-vectoring information field and the value of bits 7:0 of the VM-exit
interruption-information field each indicates a contributory exception.

•

The value of bits 7:0 of the IDT-vectoring information field indicates a page fault and the value of
bits 7:0 of the VM-exit interruption-information field indicates either a contributory exception or a page
fault.

A VMM can reflect a double-fault exception to guest software by setting the VM-entry interruptioninformation and VM-entry exception error-code fields as follows:

•
•
•
•
•
•

Set bits 7:0 (vector) of the VM-entry interruption-information field to 8 (#DF).
Set bits 10:8 (interruption type) of the VM-entry interruption-information field to 3 (hardware
exception).
Set bit 11 (deliver error code) of the VM-entry interruption-information field to 1.
Clear bits 30:12 (reserved) of VM-entry interruption-information field.
Set bit 31 (valid) of VM-entry interruption-information field.
Set the VM-entry exception error-code field to zero.

— If the value of bits 10:8 of the IDT-vectoring information field is 3 (hardware exception) and the value of
bits 7:0 is 8 (#DF), guest software would have encountered a triple fault. Event injection should not be
used in this case. The VMM may choose to terminate the guest, or it might choose to enter the guest in the
shutdown activity state.

31.7.1.2

Resuming Guest Software after Handling an Exception

If the VMM determines that a VM exit was caused by an exception due to a condition established by the VMM itself,
it may choose to resume guest software after removing the condition. The approach for removing the condition
may be specific to the VMM’s software architecture. and algorithms This section describes how guest software may
be resumed after removing the condition.
In general, the VMM can resume guest software simply by executing VMRESUME. The following items provide
details of cases that may require special handling:

•

If the “NMI exiting” VM-execution control is 0, bit 12 of the VM-exit interruption-information field indicates that
the VM exit was due to a fault encountered during an execution of the IRET instruction that unblocked nonmaskable interrupts (NMIs). In particular, it provides this indication if the following are both true:
— Bit 31 (valid) in the IDT-vectoring information field is 0.
— The value of bits 7:0 (vector) of the VM-exit interruption-information field is not 8 (the VM exit is not due
to a double-fault exception).
If both are true and bit 12 of the VM-exit interruption-information field is 1, NMIs were blocked before guest
software executed the IRET instruction that caused the fault that caused the VM exit. The VMM should set bit 3
(blocking by NMI) in the interruptibility-state field (using VMREAD and VMWRITE) before resuming guest
software.

•

If the “virtual NMIs” VM-execution control is 1, bit 12 of the VM-exit interruption-information field indicates
that the VM exit was due to a fault encountered during an execution of the IRET instruction that removed
virtual-NMI blocking. In particular, it provides this indication if the following are both true:
— Bit 31 (valid) in the IDT-vectoring information field is 0.
— The value of bits 7:0 (vector) of the VM-exit interruption-information field is not 8 (the VM exit is not due
to a double-fault exception).
If both are true and bit 12 of the VM-exit interruption-information field is 1, there was virtual-NMI blocking
before guest software executed the IRET instruction that caused the fault that caused the VM exit. The VMM
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should set bit 3 (blocking by NMI) in the interruptibility-state field (using VMREAD and VMWRITE) before
resuming guest software.

•

Bit 31 (valid) of the IDT-vectoring information field indicates, if set, that the exception causing the VM exit
occurred while another event was being delivered to guest software. The VMM should ensure that the other
event is delivered when guest software is resumed. It can do so using the VM-entry event injection described
in Section 26.5 and detailed in the following paragraphs:
— The VMM can copy (using VMREAD and VMWRITE) the contents of the IDT-vectoring information field
(which is presumed valid) to the VM-entry interruption-information field (which, if valid, will cause the
exception to be delivered as part of the next VM entry).

•

The VMM should ensure that reserved bits 30:12 in the VM-entry interruption-information field are 0. In
particular, the value of bit 12 in the IDT-vectoring information field is undefined after all VM exits. If this
bit is copied as 1 into the VM-entry interruption-information field, the next VM entry will fail because the
bit should be 0.

•

If the “virtual NMIs” VM-execution control is 1 and the value of bits 10:8 (interruption type) in the IDTvectoring information field is 2 (indicating NMI), the VM exit occurred during delivery of an NMI that had
been injected as part of the previous VM entry. In this case, bit 3 (blocking by NMI) will be 1 in the interruptibility-state field in the VMCS. The VMM should clear this bit; otherwise, the next VM entry will fail
(see Section 26.3.1.5).

— The VMM can also copy the contents of the IDT-vectoring error-code field to the VM-entry exception errorcode field. This need not be done if bit 11 (error code valid) is clear in the IDT-vectoring information field.
— The VMM can also copy the contents of the VM-exit instruction-length field to the VM-entry instructionlength field. This need be done only if bits 10:8 (interruption type) in the IDT-vectoring information field
indicate either software interrupt, privileged software exception, or software exception.

31.8

MULTI-PROCESSOR CONSIDERATIONS

The most common VMM design will be the symmetric VMM. This type of VMM runs the same VMM binary on all
logical processors. Like a symmetric operating system, the symmetric VMM is written to ensure all critical data is
updated by only one processor at a time, IO devices are accessed sequentially, and so forth. Asymmetric VMM
designs are possible. For example, an asymmetric VMM may run its scheduler on one processor and run just
enough of the VMM on other processors to allow the correct execution of guest VMs. The remainder of this section
focuses on the multi-processor considerations for a symmetric VMM.
A symmetric VMM design does not preclude asymmetry in its operations. For example, a symmetric VMM can
support asymmetric allocation of logical processor resources to guests. Multiple logical processors can be brought
into a single guest environment to support an MP-aware guest OS. Because an active VMCS can not control more
than one logical processor simultaneously, a symmetric VMM must make copies of its VMCS to control the VM allocated to support an MP-aware guest OS. Care must be taken when accessing data structures shared between these
VMCSs. See Section 31.8.4.
Although it may be easier to develop a VMM that assumes a fully-symmetric view of hardware capabilities (with all
processors supporting the same processor feature sets, including the same revision of VMX), there are advantages
in developing a VMM that comprehends different levels of VMX capability (reported by VMX capability MSRs). One
possible advantage of such an approach could be that an existing software installation (VMM and guest software
stack) could continue to run without requiring software upgrades to the VMM, when the software installation is
upgraded to run on hardware with enhancements in the processor’s VMX capabilities. Another advantage could be
that a single software installation image, consisting of a VMM and guests, could be deployed to multiple hardware
platforms with varying VMX capabilities. In such cases, the VMM could fall back to a common subset of VMX
features supported by all VMX revisions, or choose to understand the asymmetry of the VMX capabilities and assign
VMs accordingly.
This section outlines some of the considerations to keep in mind when developing an MP-aware VMM.

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31.8.1

Initialization

Before enabling VMX, an MP-aware VMM must check to make sure that all processors in the system are compatible
and support features required. This can be done by:

•

Checking the CPUID on each logical processor to ensure VMX is supported and that the overall feature set of
each logical processor is compatible.

•
•

Checking VMCS revision identifiers on each logical processor.
Checking each of the “allowed-1” or “allowed-0” fields of the VMX capability MSR’s on each processor.

31.8.2

Moving a VMCS Between Processors

An MP-aware VMM is free to assign any logical processor to a VM. But for performance considerations, moving a
guest VMCS to another logical processor is slower than resuming that guest VMCS on the same logical processor.
Certain VMX performance features (such as caching of portions of the VMCS in the processor) are optimized for a
guest VMCS that runs on the same logical processor.
The reasons are:

•

To restart a guest on the same logical processor, a VMM can use VMRESUME. VMRESUME is expected to be
faster than VMLAUNCH in general.

•

To migrate a VMCS to another logical processor, a VMM must use the sequence of VMCLEAR, VMPTRLD and
VMLAUNCH.

•

Operations involving VMCLEAR can impact performance negatively. See
Section 24.11.3.

A VMM scheduler should make an effort to schedule a guest VMCS to run on the logical processor where it last ran.
Such a scheduler might also benefit from doing lazy VMCLEARs (that is: performing a VMCLEAR on a VMCS only
when the scheduler knows the VMCS is being moved to a new logical processor). The remainder of this section
describes the steps a VMM must take to move a VMCS from one processor to another.
A VMM must check the VMCS revision identifier in the VMX capability MSR IA32_VMX_BASIC to determine if the
VMCS regions are identical between all logical processors. If the VMCS regions are identical (same revision ID) the
following sequence can be used to move or copy the VMCS from one logical processor to another:

•

Perform a VMCLEAR operation on the source logical processor. This ensures that all VMCS data that may be
cached by the processor are flushed to memory.

•

Copy the VMCS region from one memory location to another location. This is an optional step assuming the
VMM wishes to relocate the VMCS or move the VMCS to another system.

•

Perform a VMPTRLD of the physical address of VMCS region on the destination processor to establish its current
VMCS pointer.

If the revision identifiers are different, each field must be copied to an intermediate structure using individual reads
(VMREAD) from the source fields and writes (VMWRITE) to destination fields. Care must be taken on fields that are
hard-wired to certain values on some processor implementations.

31.8.3

Paired Index-Data Registers

A VMM may need to virtualize hardware that is visible to software using paired index-data registers. Paired indexdata register interfaces, such as those used in PCI (CF8, CFC), require special treatment in cases where a VM
performing writes to these pairs can be moved during execution. In this case, the index (e.g. CF8) should be part
of the virtualized state. If the VM is moved during execution, writes to the index should be redone so subsequent
data reads/writes go to the right location.

31.8.4

External Data Structures

Certain fields in the VMCS point to external data structures (for example: the MSR bitmap, the I/O bitmaps). If a
logical processor is in VMX non-root operation, none of the external structures referenced by that logical

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processor's current VMCS should be modified by any logical processor or DMA. Before updating one of these structures, the VMM must ensure that no logical processor whose current VMCS references the structure is in VMX nonroot operation.
If a VMM uses multiple VMCS with each VMCS using separate external structures, and these structures must be
kept synchronized, the VMM must apply the same care to updating these structures.

31.8.5

CPUID Emulation

CPUID reports information that is used by OS and applications to detect hardware features. It also provides multithreading/multi-core configuration information. For example, MP-aware OSs rely on data reported by CPUID to
discover the topology of logical processors in a platform (see Section 8.9, “Programming Considerations for Hardware Multi-Threading Capable Processors,” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual,
Volume 3A).
If a VMM is to support asymmetric allocation of logical processor resources to guest OSs that are MP aware, then
the VMM must emulate CPUID for its guests. The emulation of CPUID by the VMM must ensure the guest’s view of
CPUID leaves are consistent with the logical processor allocation committed by the VMM to each guest OS.

31.9

32-BIT AND 64-BIT GUEST ENVIRONMENTS

For the most part, extensions provided by VMX to support virtualization are orthogonal to the extensions provided
by Intel 64 architecture. There are considerations that impact VMM designs. These are described in the following
subsections.

31.9.1

Operating Modes of Guest Environments

For Intel 64 processors, VMX operation supports host and guest environments that run in IA-32e mode or without
IA-32e mode. VMX operation also supports host and guest environments on IA-32 processors.
A VMM entering VMX operation while IA-32e mode is active is considered to be an IA-32e mode host. A VMM
entering VMX operation while IA-32e mode is not activated or not available is referred to as a 32-bit VMM. The type
of guest operations such VMMs support are summarized in Table 31-1.

Table 31-1. Operating Modes for Host and Guest Environments
Capability

Guest Operation
in IA-32e mode

Guest Operation
Not Requiring IA-32e Mode

IA-32e mode VMM

Yes

Yes

32-bit VMM

Not supported

Yes

A VM exit may occur to an IA-32e mode guest in either 64-bit sub-mode or compatibility sub-mode of IA-32e
mode. VMMs may resume guests in either mode. The sub-mode in which an IA-32e mode guest resumes VMX nonroot operation is determined by the attributes of the code segment which experienced the VM exit. If CS.L = 1, the
guest is executing in 64-bit mode; if CS.L = 0, the guest is executing in compatibility mode (see Section 31.9.5).
Not all of an IA-32e mode VMM must run in 64-bit mode. While some parts of an IA-32e mode VMM must run in 64bit mode, there are only a few restrictions preventing a VMM from executing in compatibility mode. The most
notable restriction is that most VMX instructions cause exceptions when executed in compatibility mode.

31.9.2

Handling Widths of VMCS Fields

Individual VMCS control fields must be accessed using VMREAD or VMWRITE instructions. Outside of 64-Bit mode,
VMREAD and VMWRITE operate on 32 bits of data. The widths of VMCS control fields may vary depending on
whether a processor supports Intel 64 architecture.

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Many VMCS fields are architected to extend transparently on processors supporting Intel 64 architecture (64 bits
on processors that support Intel 64 architecture, 32 bits on processors that do not). Some VMCS fields are 64-bits
wide regardless of whether the processor supports Intel 64 architecture or is in IA-32e mode.

31.9.2.1

Natural-Width VMCS Fields

Many VMCS fields operate using natural width. Such fields return (on reads) and set (on writes) 32-bits when operating in 32-bit mode and 64-bits when operating in 64-bit mode. For the most part, these fields return the naturally
expected data widths. The “Guest RIP” field in the VMCS guest-state area is an example of this type of field.

31.9.2.2

64-Bit VMCS Fields

Unlike natural width fields, these fields are fixed to 64-bit width on all processors. When in 64-bit mode, reads of
these fields return 64-bit wide data and writes to these fields write 64-bits. When outside of 64-bit mode, reads of
these fields return the low 32-bits and writes to these fields write the low 32-bits and zero the upper 32-bits.
Should a non-IA-32e mode host require access to the upper 32-bits of these fields, a separate VMCS encoding is
used when issuing VMREAD/VMWRITE instructions.
The VMCS control field “MSR bitmap address” (which contains the physical address of a region of memory which
specifies which MSR accesses should generate VM-exits) is an example of this type of field. Specifying encoding
00002004H to VMREAD returns the lower 32-bits to non-IA-32e mode hosts and returns 64-bits to 64-bit hosts.
The separate encoding 00002005H returns only the upper 32-bits.

31.9.3

IA-32e Mode Hosts

An IA-32e mode host is required to support 64-bit guest environments. Because activating IA-32e mode currently
requires that paging be disabled temporarily and VMX entry requires paging to be enabled, IA-32e mode must be
enabled before entering VMX operation. For this reason, it is not possible to toggle in and out of IA-32e mode in a
VMM.
Section 31.5 describes the steps required to launch a VMM. An IA-32e mode host is also required to set the “host
address-space size” VMCS VM-exit control to 1. The value of this control is then loaded in the IA32_EFER.LME/LMA
and CS.L bits on each VM exit. This establishes a 64-bit host environment as execution transfers to the VMM entry
point. At a minimum, the entry point is required to be in a 64-bit code segment. Subsequently, the VMM can, if it
chooses, switch to 32-bit compatibility mode on a code-segment basis (see Section 31.9.1). Note, however, that
VMX instructions other than VMCALL and VMFUNC are not supported in compatibility mode; they generate an
invalid opcode exception if used.
The following VMCS controls determine the value of IA32_EFER when a VM exit occurs: the “host address-space
size” control (described above), the “load IA32_EFER” VM-exit control, the “VM-exit MSR-load count,” and the “VMexit MSR-load address” (see Section 27.3).
If the “load IA32_EFER” VM-exit control is 1, the value of the LME and LMA bits in the IA32_EFER field in the hoststate area must be the value of the “host address-space size” VM-exit control.
The loading of IA32_EFER.LME/LMA and CS.L bits established by the “host address-space size” control precede any
loading of the IA32_EFER MSR due from the VM-exit MSR-load area. If IA32_EFER is specified in the VM-exit MSRload area, the value of the LME bit in the load image of IA32_EFER should match the setting of the “host addressspace size” control. Otherwise the attempt to modify the LME bit (while paging is enabled) will lead to a VMX-abort.
However, IA32_EFER.LMA is always set by the processor to equal IA32_EFER.LME & CR0.PG; the value specified
for LMA in the load image of the IA32_EFER MSR is ignored. For these and performance reasons, VMM writers may
choose to not use the VM-exit/entry MSR-load/save areas for IA32_EFER.
On a VMM teardown, VMX operation should be exited before deactivating IA-32e mode if the latter is required.

31.9.4

IA-32e Mode Guests

A 32-bit guest can be launched by either IA-32e-mode hosts or non-IA-32e-mode hosts. A 64-bit guests can only
be launched by a IA-32e-mode host.

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In addition to the steps outlined in Section 31.6, VMM writers need to:

•

Set the “IA-32e-mode guest” VM-entry control to 1 in the VMCS to assure VM-entry (VMLAUNCH or
VMRESUME) will establish a 64-bit (or 32-bit compatible) guest operating environment.

•
•

Enable paging (CR0.PG) and PAE mode (CR4.PAE) to assure VM-entry to a 64-bit guest will succeed.
Ensure that the host to be in IA-32e mode (the IA32_EFER.LMA must be set to 1) and the setting of the VM-exit
“host address-space size” control bit in the VMCS must also be set to 1.

If each of the above conditions holds true, then VM-entry will copy the value of the VM-entry “IA-32e-mode guest”
control bit into the guests IA32_EFER.LME bit, which will result in subsequent activation of IA-32e mode. If any of
the above conditions is false, the VM-entry will fail and load state from the host-state area of the working VMCS as
if a VM exit had occurred (see Section 26.7).
The following VMCS controls determine the value of IA32_EFER on a VM entry: the “IA-32e-mode guest” VM-entry
control (described above), the “load IA32_EFER” VM-entry control, the “VM-entry MSR-load count,” and the “VMentry MSR-load address” (see Section 26.4).
If the “load IA32_EFER” VM-entry control is 1, the value of the LME and LMA bits in the IA32_EFER field in the
guest-state area must be the value of the “IA-32e-mode guest” VM-entry control. Otherwise, the VM entry fails.
The loading of IA32_EFER.LME bit (described above) precedes any loading of the IA32_EFER MSR from the VMentry MSR-load area of the VMCS. If loading of IA32_EFER is specified in the VM-entry MSR-load area, the value of
the LME bit in the load image should be match the setting of the “IA-32e-mode guest” VM-entry control. Otherwise,
the attempt to modify the LME bit (while paging is enabled) results in a failed VM entry. However, IA32_EFER.LMA
is always set by the processor to equal IA32_EFER.LME & CR0.PG; the value specified for LMA in the load image of
the IA32_EFER MSR is ignored. For these and performance reasons, VMM writers may choose to not use the VMexit/entry MSR-load/save areas for IA32_EFER MSR.
Note that the VMM can control the processor’s architectural state when transferring control to a VM. VMM writers
may choose to launch guests in protected mode and subsequently allow the guest to activate IA-32e mode or they
may allow guests to toggle in and out of IA-32e mode. In this case, the VMM should require VM exit on accesses to
the IA32_EFER MSR to detect changes in the operating mode and modify the VM-entry “IA-32e-mode guest”
control accordingly.
A VMM should save/restore the extended (full 64-bit) contents of the guest general-purpose registers, the new
general-purpose registers (R8-R15) and the SIMD registers introduced in 64-bit mode should it need to modify
these upon VM exit.

31.9.5

32-Bit Guests

To launch or resume a 32-bit guest, VMM writers can follow the steps outlined in Section 31.6, making sure that the
“IA-32e-mode guest” VM-entry control bit is set to 0. Then the “IA-32e-mode guest” control bit is copied into the
guest IA32_EFER.LME bit, establishing IA32_EFER.LMA as 0.

31.10

HANDLING MODEL SPECIFIC REGISTERS

Model specific registers (MSR) provide a wide range of functionality. They affect processor features, control the
programming interfaces, or are used in conjunction with specific instructions. As part of processor virtualization, a
VMM may wish to protect some or all MSR resources from direct guest access.
VMX operation provides the following features to virtualize processor MSRs.

31.10.1 Using VM-Execution Controls
Processor-based VM-execution controls provide two levels of support for handling guest access to processor MSRs
using RDMSR and WRMSR:

•

MSR bitmaps: In VMX implementations that support a 1-setting (see Appendix A) of the user-MSR-bitmaps
execution control bit, MSR bitmaps can be used to provide flexibility in managing guest MSR accesses. The

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MSR-bitmap-address in the guest VMCS can be programmed by VMM to point to a bitmap region which
specifies VM-exit behavior when reading and writing individual MSRs.
MSR bitmaps form a 4-KByte region in physical memory and are required to be aligned to a 4-KByte boundary.
The first 1-KByte region manages read control of MSRs in the range 00000000H-00001FFFH; the second 1KByte region covers read control of MSR addresses in the range C0000000H-C0001FFFH. The bitmaps for write
control of these MSRs are located in the 2-KByte region immediately following the read control bitmaps. While
the MSR bitmap address is part of VMCS, the MSR bitmaps themselves are not. This implies MSR bitmaps are
not accessible through VMREAD and VMWRITE instructions but rather by using ordinary memory writes. Also,
they are not specially cached by the processor and may be placed in normal cache-coherent memory by the
VMM.
When MSR bitmap addresses are properly programmed and the use-MSR-bitmap control (see Section 24.6.2)
is set, the processor consults the associated bit in the appropriate bitmap on guest MSR accesses to the corresponding MSR and causes a VM exit if the bit in the bitmap is set. Otherwise, the access is permitted to
proceed. This level of protection may be utilized by VMMs to selectively allow guest access to some MSRs while
virtualizing others.

•

Default MSR protection: If the use-MSR-bitmap control is not set, an attempt by a guest to access any MSR
causes a VM exit. This also occurs for any attempt to access an MSR outside the ranges identified above (even
if the use-MSR-bitmap control is set).

VM exits due to guest MSR accesses may be identified by the VMM through VM-exit reason codes. The MSR-read
exit reason implies guest software attempted to read an MSR protected either by default or through MSR bitmaps.
The MSR-write exit reason implies guest software attempting to write a MSR protected through the VM-execution
controls. Upon VM exits caused by MSR accesses, the VMM may virtualize the guest MSR access through emulation
of RDMSR/WRMSR.

31.10.2 Using VM-Exit Controls for MSRs
If a VMM allows its guest to access MSRs directly, the VMM may need to store guest MSR values and load host MSR
values for these MSRs on VM exits. This is especially true if the VMM uses the same MSRs while in VMX root operation.
A VMM can use the VM-exit MSR-store-address and the VM-exit MSR-store-count exit control fields (see Section
24.7.2) to manage how MSRs are stored on VM exits. The VM-exit MSR-store-address field contains the physical
address (16-byte aligned) of the VM-exit MSR-store area (a table of entries with 16 bytes per entry). Each table
entry specifies an MSR whose value needs to be stored on VM exits. The VM-exit MSR-store-count contains the
number of entries in the table.
Similarly the VM-exit MSR-load-address and VM-exit MSR-load-count fields point to the location and size of the VMexit MSR load area. The entries in the VM-exit MSR-load area contain the host expected values of specific MSRs
when a VM exit occurs.
Upon VM-exit, bits 127:64 of each entry in the VM-exit MSR-store area is updated with the contents of the MSR
indexed by bits 31:0. Also, bits 127:64 of each entry in the VM-exit MSR-load area is updated by loading with
values from bits 127:64 the contents of the MSR indexed by bits 31:0.

31.10.3 Using VM-Entry Controls for MSRs
A VMM may require specific MSRs to be loaded explicitly on VM entries while launching or resuming guest execution. The VM-entry MSR-load-address and VM-entry MSR-load-count entry control fields determine how MSRs are
loaded on VM-entries. The VM-entry MSR-load-address and count fields are similar in structure and function to the
VM-exit MSR-load address and count fields, except the MSR loading is done on VM-entries.

31.10.4 Handling Special-Case MSRs and Instructions
A number of instructions make use of designated MSRs in their operation. The VMM may need to consider saving
the states of those MSRs. Instructions that merit such consideration include SYSENTER/SYSEXIT,
SYSCALL/SYSRET, SWAPGS.

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31.10.4.1 Handling IA32_EFER MSR
The IA32_EFER MSR includes bit fields that allow system software to enable processor features. For example: the
SCE bit enables SYSCALL/SYSRET and the NXE bit enables the execute-disable bits in the paging-structure entries.
VMX provides hardware support to load the IA32_EFER MSR on VMX transitions and to save it on VM exits. Because
of this, VMM software need not use the RDMSR and WRMSR instruction to give the register different values during
host and guest execution.

31.10.4.2 Handling the SYSENTER and SYSEXIT Instructions
The SYSENTER and SYSEXIT instructions use three dedicated MSRs (IA32_SYSENTER_CS, IA32_SYSENTER_ESP
and IA32_SYSENTER_EIP) to manage fast system calls. These MSRs may be utilized by both the VMM and the
guest OS to manage system calls in VMX root operation and VMX non-root operation respectively.
VM entries load these MSRs from fields in the guest-state area of the VMCS. VM exits save the values of these MSRs
into those fields and loads the MSRs from fields in the host-state area.

31.10.4.3 Handling the SYSCALL and SYSRET Instructions
The SYSCALL/SYSRET instructions are similar to SYSENTER/SYSEXIT but are designed to operate within the
context of a 64-bit flat code segment. They are available only in 64-bit mode and only when the SCE bit of the
IA32_EFER MSR is set. SYSCALL/SYSRET invocations can occur from either 32-bit compatibility mode application
code or from 64-bit application code. Three related MSR registers (IA32_STAR, IA32_LSTAR, IA32_FMASK) are
used in conjunction with fast system calls/returns that use these instructions.
64-Bit hosts which make use of these instructions in the VMM environment will need to save the guest state of the
above registers on VM exit, load the host state, and restore the guest state on VM entry. One possible approach is
to use the VM-exit MSR-save and MSR-load areas and the VM-entry MSR-load area defined by controls in the VMCS.
A disadvantage to this approach, however, is that the approach results in the unconditional saving, loading, and
restoring of MSR registers on each VM exit or VM entry.
Depending on the design of the VMM, it is likely that many VM-exits will require no fast system call support but the
VMM will be burdened with the additional overhead of saving and restoring MSRs if the VMM chooses to support fast
system call uniformly. Further, even if the host intends to support fast system calls during a VM-exit, some of the
MSR values (such as the setting of the SCE bit in IA32_EFER) may not require modification as they may already be
set to the appropriate value in the guest.
For performance reasons, a VMM may perform lazy save, load, and restore of these MSR values on certain VM exits
when it is determined that this is acceptable. The lazy-save-load-restore operation can be carried out “manually”
using RDMSR and WRMSR.

31.10.4.4 Handling the SWAPGS Instruction
The SWAPGS instruction is available only in 64-bit mode. It swaps the contents of two specific MSRs
(IA32_GS_BASE and IA32_KERNEL_GS_BASE). The IA32_GS_BASE MSR shadows the base address portion of the
GS descriptor register; the IA32_KERNEL_GS_BASE MSR holds the base address of the GS segment used by the
kernel (typically it houses kernel structures). SWAPGS is intended for use with fast system calls when in 64-bit
mode to allow immediate access to kernel structures on transition to kernel mode.
Similar to SYSCALL/SYSRET, IA-32e mode hosts which use fast system calls may need to save, load, and restore
these MSR registers on VM exit and VM entry using the guidelines discussed in previous paragraphs.

31.10.4.5 Implementation Specific Behavior on Writing to Certain MSRs
As noted in Section 26.4 and Section 27.4, a processor may prevent writing to certain MSRs when loading guest
states on VM entries or storing guest states on VM exits. This is done to ensure consistent operation. The subset
and number of MSRs subject to restrictions are implementation specific. For initial VMX implementations, there are
two MSRs: IA32_BIOS_UPDT_TRIG and IA32_BIOS_SIGN_ID (see Chapter 2, “Model-Specific Registers (MSRs)” in
the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4).

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31.10.5 Handling Accesses to Reserved MSR Addresses
Privileged software (either a VMM or a guest OS) can access a model specific register by specifying addresses in
MSR address space. VMMs, however, must prevent a guest from accessing reserved MSR addresses in MSR address
space.
Consult Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4 for lists of supported MSRs and their usage. Use the MSR bitmap control to cause a VM
exit when a guest attempts to access a reserved MSR address. The response to such a VM exit should be to reflect
#GP(0) back to the guest.

31.11

HANDLING ACCESSES TO CONTROL REGISTERS

Bit fields in control registers (CR0, CR4) control various aspects of processor operation. The VMM must prevent
guests from modifying bits in CR0 or CR4 that are reserved at the time the VMM is written.
Guest/host masks should be used by the VMM to cause VM exits when a guest attempts to modify reserved bits.
Read shadows should be used to ensure that the guest always reads the reserved value (usually 0) for such bits.
The VMM response to VM exits due to attempts from a guest to modify reserved bits should be to emulate the
response which the processor would have normally produced (usually a #GP(0)).

31.12

PERFORMANCE CONSIDERATIONS

VMX provides hardware features that may be used for improving processor virtualization performance. VMMs must
be designed to use this support properly. The basic idea behind most of these performance optimizations of the
VMM is to reduce the number of VM exits while executing a guest VM.
This section lists ways that VMMs can take advantage of the performance enhancing features in VMX.

•

Read Access to Control Registers. Analysis of common client workloads with common PC operating systems
in a virtual machine shows a large number of VM-exits are caused by control register read accesses (particularly CR0). Reads of CR0 and CR4 does not cause VM exits. Instead, they return values from the CR0/CR4 readshadows configured by the VMM in the guest controlling-VMCS with the guest-expected values.

•

Write Access to Control Registers. Most VMM designs require only certain bits of the control registers to be
protected from direct guest access. Write access to CR0/CR4 registers can be reduced by defining the hostowned and guest-owned bits in them through the CR0/CR4 host/guest masks in the VMCS. CR0/CR4 write
values by the guest are qualified with the mask bits. If they change only guest-owned bits, they are allowed
without causing VM exits. Any write that cause changes to host-owned bits cause VM exits and need to be
handled by the VMM.

•

Access Rights based Page Table protection. For VMM that implement access-rights-based page table
protection, the VMCS provides a CR3 target value list that can be consulted by the processor to determine if a
VM exit is required. Loading of CR3 with a value matching an entry in the CR3 target-list are allowed to proceed
without VM exits. The VMM can utilize the CR3 target-list to save page-table hierarchies whose state is
previously verified by the VMM.

•

Page-fault handling. Another common cause for a VM exit is due to page-faults induced by guest address
remapping done through virtual memory virtualization. VMX provides page-fault error-code mask and match
fields in the VMCS to filter VM exits due to page-faults based on their cause (reflected in the error-code).

31.13

USE OF THE VMX-PREEMPTION TIMER

The VMX-preemption timer allows VMM software to preempt guest VM execution after a specified amount of time.
Typical VMX-preemption timer usage is to program the initial VM quantum into the timer, save the timer value on
each successive VM-exit (using the VM-exit control “save preemption timer value”) and run the VM until the timer
expires.

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In an alternative scenario, the VMM may use another timer (e.g. the TSC) to track the amount of time the VM has
run while still using the VMX-preemption timer for VM preemption. In this scenario the VMM would not save the
VMX-preemption timer on each VM-exit but instead would reload the VMX-preemption timer with initial VM
quantum less the time the VM has already run. This scenario includes all the VM-entry and VM-exit latencies in the
VM run time.
In both scenarios, on each successive VM-entry the VMX-preemption timer contains a smaller value until the VM
quantum ends. If the VMX-preemption timer is loaded with a value smaller than the VM-entry latency then the VM
will not execute any instructions before the timer expires. The VMM must ensure the initial VM quantum is greater
than the VM-entry latency; otherwise the VM will make no forward progress.

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VIRTUALIZATION OF SYSTEM RESOURCES
32.1

OVERVIEW

When a VMM is hosting multiple guest environments (VMs), it must monitor potential interactions between software components using the same system resources. These interactions can require the virtualization of resources.
This chapter describes the virtualization of system resources. These include: debugging facilities, address translation, physical memory, and microcode update facilities.

32.2

VIRTUALIZATION SUPPORT FOR DEBUGGING FACILITIES

The Intel 64 and IA-32 debugging facilities (see Chapter 17) provide breakpoint instructions, exception conditions,
register flags, debug registers, control registers and storage buffers for functions related to debugging system and
application software. In VMX operation, a VMM can support debugging system and application software from within
virtual machines if the VMM properly virtualizes debugging facilities. The following list describes features relevant
to virtualizing these facilities.

•

The VMM can program the exception-bitmap (see Section 24.6.3) to ensure it gets control on debug functions
(like breakpoint exceptions occurring while executing guest code such as INT3 instructions). Normally, debug
exceptions modify debug registers (such as DR6, DR7, IA32_DEBUGCTL). However, if debug exceptions cause
VM exits, exiting occurs before register modification.

•

The VMM may utilize the VM-entry event injection facilities described in Section 26.5 to inject debug or
breakpoint exceptions to the guest. See Section 32.2.1 for a more detailed discussion.

•

The MOV-DR exiting control bit in the processor-based VM-execution control field (see Section 24.6.2) can be
enabled by the VMM to cause VM exits on explicit guest access of various processor debug registers (for
example, MOV to/from DR0-DR7). These exits would always occur on guest access of DR0-DR7 registers
regardless of the values in CPL, DR4.DE or DR7.GD. Since all guest task switches cause VM exits, a VMM can
control any indirect guest access or modification of debug registers during guest task switches.

•

Guest software access to debug-related model-specific registers (such as IA32_DEBUGCTL MSR) can be
trapped by the VMM through MSR access control features (such as the MSR-bitmaps that are part of processorbased VM-execution controls). See Section 31.10 for details on MSR virtualization.

•

Debug registers such as DR7 and the IA32_DEBUGCTL MSR may be explicitly modified by the guest (through
MOV-DR or WRMSR instructions) or modified implicitly by the processor as part of generating debug
exceptions. The current values of DR7 and the IA32_DEBUGCTL MSR are saved to guest-state area of VMCS on
every VM exit. Pending debug exceptions are debug exceptions that are recognized by the processor but not yet
delivered. See Section 26.6.3 for details on pending debug exceptions.

•

DR7 and the IA32-DEBUGCTL MSR are loaded from values in the guest-state area of the VMCS on every VM
entry. This allows the VMM to properly virtualize debug registers when injecting debug exceptions to guest.
Similarly, the RFLAGS1 register is loaded on every VM entry (or pushed to stack if injecting a virtual event) from
guest-state area of the VMCS. Pending debug exceptions are also loaded from guest-state area of VMCS so that
they may be delivered after VM entry is completed.

32.2.1

Debug Exceptions

If a VMM emulates a guest instruction that would encounter a debug trap (single step or data or I/O breakpoint), it
should cause that trap to be delivered. The VMM should not inject the debug exception using VM-entry event injection, but should set the appropriate bits in the pending debug exceptions field. This method will give the trap the
1. This chapter uses the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that support VMX operation also support Intel 64 architecture. For processors that do not support Intel 64 architecture, this notation refers to the 32-bit
forms of those registers (EAX, EIP, ESP, EFLAGS, etc.).
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right priority with respect to other events. (If the exception bitmap was programmed to cause VM exits on debug
exceptions, the debug trap will cause a VM exit. At this point, the trap can be injected during VM entry with the
proper priority.)
There is a valid pending debug exception if the BS bit (see Table 24-4) is set, regardless of the values of RFLAGS.TF
or IA32_DEBUGCTL.BTF. The values of these bits do not impact the delivery of pending debug exceptions.
VMMs should exercise care when emulating a guest write (attempted using WRMSR) to IA32_DEBUGCTL to modify
BTF if this is occurring with RFLAGS.TF = 1 and after a MOV SS or POP SS instruction (for example: while debug
exceptions are blocked). Note the following:

•

Normally, if WRMSR clears BTF while RFLAGS.TF = 1 and with debug exceptions blocked, a single-step trap will
occur after WRMSR. A VMM emulating such an instruction should set the BS bit (see Table 24-4) in the pending
debug exceptions field before VM entry.

•

Normally, if WRMSR sets BTF while RFLAGS.TF = 1 and with debug exceptions blocked, neither a single-step
trap nor a taken-branch trap can occur after WRMSR. A VMM emulating such an instruction should clear the BS
bit (see Table 24-4) in the pending debug exceptions field before VM entry.

32.3

MEMORY VIRTUALIZATION

VMMs must control physical memory to ensure VM isolation and to remap guest physical addresses in host physical
address space for virtualization. Memory virtualization allows the VMM to enforce control of physical memory and
yet support guest OSs’ expectation to manage memory address translation.

32.3.1

Processor Operating Modes & Memory Virtualization

Memory virtualization is required to support guest execution in various processor operating modes. This includes:
protected mode with paging, protected mode with no paging, real-mode and any other transient execution modes.
VMX allows guest operation in protected-mode with paging enabled and in virtual-8086 mode (with paging
enabled) to support guest real-mode execution. Guest execution in transient operating modes (such as in real
mode with one or more segment limits greater than 64-KByte) must be emulated by the VMM.
Since VMX operation requires processor execution in protected mode with paging (through CR0 and CR4 fixed bits),
the VMM may utilize paging structures to support memory virtualization. To support guest real-mode execution,
the VMM may establish a simple flat page table for guest linear to host physical address mapping. Memory virtualization algorithms may also need to capture other guest operating conditions (such as guest performing A20M#
address masking) to map the resulting 20-bit effective guest physical addresses.

32.3.2

Guest & Host Physical Address Spaces

Memory virtualization provides guest software with contiguous guest physical address space starting zero and
extending to the maximum address supported by the guest virtual processor’s physical address width. The VMM
utilizes guest physical to host physical address mapping to locate all or portions of the guest physical address space
in host memory. The VMM is responsible for the policies and algorithms for this mapping which may take into
account the host system physical memory map and the virtualized physical memory map exposed to a guest by the
VMM. The memory virtualization algorithm needs to accommodate various guest memory uses (such as: accessing
DRAM, accessing memory-mapped registers of virtual devices or core logic functions and so forth). For example:

•

To support guest DRAM access, the VMM needs to map DRAM-backed guest physical addresses to host-DRAM
regions. The VMM also requires the guest to host memory mapping to be at page granularity.

•

Virtual devices (I/O devices or platform core logic) emulated by the VMM may claim specific regions in the guest
physical address space to locate memory-mapped registers. Guest access to these virtual registers may be
configured to cause page-fault induced VM-exits by marking these regions as always not present. The VMM
may handle these VM exits by invoking appropriate virtual device emulation code.

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32.3.3

Virtualizing Virtual Memory by Brute Force

VMX provides the hardware features required to fully virtualize guest virtual memory accesses. VMX allows the
VMM to trap guest accesses to the PAT (Page Attribute Table) MSR and the MTRR (Memory Type Range Registers).
This control allows the VMM to virtualize the specific memory type of a guest memory. The VMM may control
caching by controlling the guest CR0.CRD and CR0.NW bits, as well as by trapping guest execution of the INVD
instruction. The VMM can trap guest CR3 loads and stores, and it may trap guest execution of INVLPG.
Because a VMM must retain control of physical memory, it must also retain control over the processor’s addresstranslation mechanisms. Specifically, this means that only the VMM can access CR3 (which contains the base of the
page directory) and can execute INVLPG (the only other instruction that directly manipulates the TLB).
At the same time that the VMM controls address translation, a guest operating system will also expect to perform
normal memory management functions. It will access CR3, execute INVLPG, and modify (what it believes to be)
page directories and page tables. Virtualization of address translation must tolerate and support guest attempts to
control address translation.
A simple-minded way to do this would be to ensure that all guest attempts to access address-translation hardware
trap to the VMM where such operations can be properly emulated. It must ensure that accesses to page directories
and page tables also get trapped. This may be done by protecting these in-memory structures with conventional
page-based protection. The VMM can do this because it can locate the page directory because its base address is
in CR3 and the VMM receives control on any change to CR3; it can locate the page tables because their base
addresses are in the page directory.
Such a straightforward approach is not necessarily desirable. Protection of the in-memory translation structures
may be cumbersome. The VMM may maintain these structures with different values (e.g., different page base
addresses) than guest software. This means that there must be traps on guest attempt to read these structures
and that the VMM must maintain, in auxiliary data structures, the values to return to these reads. There must also
be traps on modifications to these structures even if the translations they effect are never used. All this implies
considerable overhead that should be avoided.

32.3.4

Alternate Approach to Memory Virtualization

Guest software is allowed to freely modify the guest page-table hierarchy without causing traps to the VMM.
Because of this, the active page-table hierarchy might not always be consistent with the guest hierarchy. Any
potential problems arising from inconsistencies can be solved using techniques analogous to those used by the
processor and its TLB.
This section describes an alternative approach that allows guest software to freely access page directories and
page tables. Traps occur on CR3 accesses and executions of INVLPG. They also occur when necessary to ensure
that guest modifications to the translation structures actually take effect. The software mechanisms to support this
approach are collectively called virtual TLB. This is because they emulate the functionality of the processor’s physical translation look-aside buffer (TLB).
The basic idea behind the virtual TLB is similar to that behind the processor TLB. While the page-table hierarchy
defines the relationship between physical to linear address, it does not directly control the address translation of
each memory access. Instead, translation is controlled by the TLB, which is occasionally filled by the processor with
translations derived from the page-table hierarchy. With a virtual TLB, the page-table hierarchy established by
guest software (specifically, the guest operating system) does not control translation, either directly or indirectly.
Instead, translation is controlled by the processor (through its TLB) and by the VMM (through a page-table hierarchy that it maintains).
Specifically, the VMM maintains an alternative page-table hierarchy that effectively caches translations derived
from the hierarchy maintained by guest software. The remainder of this document refers to the former as the
active page-table hierarchy (because it is referenced by CR3 and may be used by the processor to load its TLB) and
the latter as the guest page-table hierarchy (because it is maintained by guest software). The entries in the active
hierarchy may resemble the corresponding entries in the guest hierarchy in some ways and may differ in others.
Guest software is allowed to freely modify the guest page-table hierarchy without causing VM exits to the VMM.
Because of this, the active page-table hierarchy might not always be consistent with the guest hierarchy. Any
potential problems arising from any inconsistencies can be solved using techniques analogous to those used by the
processor and its TLB. Note the following:

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VIRTUALIZATION OF SYSTEM RESOURCES

•

Suppose the guest page-table hierarchy allows more access than active hierarchy (for example: there is a
translation for a linear address in the guest hierarchy but not in the active hierarchy); this is analogous to a
situation in which the TLB allows less access than the page-table hierarchy. If an access occurs that would be
allowed by the guest hierarchy but not the active one, a page fault occurs; this is analogous to a TLB miss. The
VMM gains control (as it handles all page faults) and can update the active page-table hierarchy appropriately;
this corresponds to a TLB fill.

•

Suppose the guest page-table hierarchy allows less access than the active hierarchy; this is analogous to a
situation in which the TLB allows more access than the page-table hierarchy. This situation can occur only if the
guest operating system has modified a page-table entry to reduce access (for example: by marking it notpresent). Because the older, more permissive translation may have been cached in the TLB, the processor is
architecturally permitted to use the older translation and allow more access. Thus, the VMM may (through the
active page-table hierarchy) also allow greater access. For the new, less permissive translation to take effect,
guest software should flush any older translations from the TLB either by executing INVLPG or by loading CR3.
Because both these operations will cause a trap to the VMM, the VMM will gain control and can remove from the
active page-table hierarchy the translations indicated by guest software (the translation of a specific linear
address for INVLPG or all translations for a load of CR3).

As noted previously, the processor reads the page-table hierarchy to cache translations in the TLB. It also writes to
the hierarchy to main the accessed (A) and dirty (D) bits in the PDEs and PTEs. The virtual TLB emulates this
behavior as follows:

•

When a page is accessed by guest software, the A bit in the corresponding PTE (or PDE for a 4-MByte page) in
the active page-table hierarchy will be set by the processor (the same is true for PDEs when active page tables
are accessed by the processor). For guest software to operate properly, the VMM should update the A bit in the
guest entry at this time. It can do this reliably if it keeps the active PTE (or PDE) marked not-present until it has
set the A bit in the guest entry.

•

When a page is written by guest software, the D bit in the corresponding PTE (or PDE for a 4-MByte page) in
the active page-table hierarchy will be set by the processor. For guest software to operate properly, the VMM
should update the D bit in the guest entry at this time. It can do this reliably if it keeps the active PTE (or PDE)
marked read-only until it has set the D bit in the guest entry. This solution is valid for guest software running at
privilege level 3; support for more privileged guest software is described in Section 32.3.5.

32.3.5

Details of Virtual TLB Operation

This section describes in more detail how a VMM could support a virtual TLB. It explains how an active page-table
hierarchy is initialized and how it is maintained in response to page faults, uses of INVLPG, and accesses to CR3.
The mechanisms described here are the minimum necessary. They may not result in the best performance.

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VIRTUALIZATION OF SYSTEM RESOURCES

"Virtual TLB"
Active Page-Table Hierarchy

Guest Page-Table Hierarchy
Guest

Active
F

CR3

TLB

refill on
TLB miss
set dirty
accessed

PT
F

PD

F

F

CR3
refill on
page fault
set accessed
and dirty bits

PT

PT
INVLPG
MOV to
CR3
task switch

F

PD

F
PT

F

F

INVLPG
MOV to CR3
task switch

PD = page directory
PT = page table
F = page frame

OM19040

Figure 32-1. Virtual TLB Scheme
As noted above, the VMM maintains an active page-table hierarchy for each virtual machine that it supports. It also
maintains, for each machine, values that the machine expects for control registers CR0, CR2, CR3, and CR4 (they
control address translation). These values are called the guest control registers.
In general, the VMM selects the physical-address space that is allocated to guest software. The term guest address
refers to an address installed by guest software in the guest CR3, in a guest PDE (as a page table base address or
a page base address), or in a guest PTE (as a page base address). While guest software considers these to be
specific physical addresses, the VMM may map them differently.

32.3.5.1

Initialization of Virtual TLB

To enable the Virtual TLB scheme, the VMCS must be set up to trigger VM exits on:

•

All writes to CR3 (the CR3-target count should be 0) or the paging-mode bits in CR0 and CR4 (using the CR0
and CR4 guest/host masks)

•
•

Page-fault (#PF) exceptions
Execution of INVLPG

When guest software first enables paging, the VMM creates an aligned 4-KByte active page directory that is invalid
(all entries marked not-present). This invalid directory is analogous to an empty TLB.

32.3.5.2

Response to Page Faults

Page faults can occur for a variety of reasons. In some cases, the page fault alerts the VMM to an inconsistency
between the active and guest page-table hierarchy. In such cases, the VMM can update the former and re-execute
the faulting instruction. In other cases, the hierarchies are already consistent and the fault should be handled by
the guest operating system. The VMM can detect this and use an established mechanism for raising a page fault to
guest software.
The VMM can handle a page fault by following these steps (The steps below assume the guest is operating in a
paging mode without PAE. Analogous steps to handle address translation using PAE or four-level paging mechaVol. 3C 32-5

VIRTUALIZATION OF SYSTEM RESOURCES

nisms can be derived by VMM developers according to the paging behavior defined in Chapter 3 of the Intel® 64
and IA-32 Architectures Software Developer’s Manual, Volume 3A):
1. First consult the active PDE, which can be located using the upper 10 bits of the faulting address and the current
value of CR3. The active PDE is the source of the fault if it is marked not present or if its R/W bit and U/S bits
are inconsistent with the attempted guest access (the guest privilege level and the values of CR0.WP and
CR4.SMEP should also be taken into account).
2. If the active PDE is the source of the fault, consult the corresponding guest PDE using the same 10 bits from the
faulting address and the physical address that corresponds to the guest address in the guest CR3. If the guest
PDE would cause a page fault (for example: it is marked not present), then raise a page fault to the guest
operating system.
The following steps assume that the guest PDE would not have caused a page fault.
3. If the active PDE is the source of the fault and the guest PDE contains, as page-table base address (if PS = 0)
or page base address (PS = 1), a guest address that the VMM has chosen not to support; then raise a machine
check (or some other abort) to the guest operating system.
The following steps assume that the guest address in the guest PDE is supported for the virtual machine.
4. If the active PDE is marked not-present, then set the active PDE to correspond to guest PDE as follows:
a. If the active PDE contains a page-table base address (if PS = 0), then allocate an aligned 4-KByte active
page table marked completely invalid and set the page-table base address in the active PDE to be the
physical address of the newly allocated page table.
b. If the active PDE contains a page base address (if PS = 1), then set the page base address in the active PDE
to be the physical page base address that corresponds to the guest address in the guest PDE.
c.

Set the P, U/S, and PS bits in the active PDE to be identical to those in the guest PDE.

d. Set the PWT, PCD, and G bits according to the policy of the VMM.
e. Set A = 1 in the guest PDE.
f.

If D = 1 in the guest PDE or PS = 0 (meaning that this PDE refers to a page table), then set the R/W bit in
the active PDE as in the guest PDE.

g. If D = 0 in the guest PDE, PS = 1 (this is a 4-MByte page), and the attempted access is a write; then set
R/W in the active PDE as in the guest PDE and set D = 1 in the guest PDE.
h. If D = 0 in the guest PDE, PS = 1, and the attempted access is not a write; then set R/W = 0 in the active
PDE.
i.

After modifying the active PDE, re-execute the faulting instruction.

The remaining steps assume that the active PDE is already marked present.
5. If the active PDE is the source of the fault, the active PDE refers to a 4-MByte page (PS = 1), the attempted
access is a write; D = 0 in the guest PDE, and the active PDE has caused a fault solely because it has R/W = 0;
then set R/W in the active PDE as in the guest PDE; set D = 1 in the guest PDE, and re-execute the faulting
instruction.
6. If the active PDE is the source of the fault and none of the above cases apply, then raise a page fault of the
guest operating system.
The remaining steps assume that the source of the original page fault is not the active PDE.

NOTE
It is possible that the active PDE might be causing a fault even though the guest PDE would not.
However, this can happen only if the guest operating system increased access in the guest PDE and
did not take action to ensure that older translations were flushed from the TLB. Such translations
might have caused a page fault if the guest software were running on bare hardware.
7. If the active PDE refers to a 4-MByte page (PS = 1) but is not the source of the fault, then the fault resulted
from an inconsistency between the active page-table hierarchy and the processor’s TLB. Since the transition to

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the VMM caused an address-space change and flushed the processor’s TLB, the VMM can simply re-execute the
faulting instruction.
The remaining steps assume that PS = 0 in the active and guest PDEs.
8. Consult the active PTE, which can be located using the next 10 bits of the faulting address (bits 21–12) and the
physical page-table base address in the active PDE. The active PTE is the source of the fault if it is marked notpresent or if its R/W bit and U/S bits are inconsistent with the attempted guest access (the guest privilege level
and the values of CR0.WP and CR4.SMEP should also be taken into account).
9. If the active PTE is not the source of the fault, then the fault has resulted from an inconsistency between the
active page-table hierarchy and the processor’s TLB. Since the transition to the VMM caused an address-space
change and flushed the processor’s TLB, the VMM simply re-executes the faulting instruction.
The remaining steps assume that the active PTE is the source of the fault.
10. Consult the corresponding guest PTE using the same 10 bits from the faulting address and the physical address
that correspond to the guest page-table base address in the guest PDE. If the guest PTE would cause a page
fault (it is marked not-present), the raise a page fault to the guest operating system.
The following steps assume that the guest PTE would not have caused a page fault.
11. If the guest PTE contains, as page base address, a physical address that is not valid for the virtual machine
being supported; then raise a machine check (or some other abort) to the guest operating system.
The following steps assume that the address in the guest PTE is valid for the virtual machine.
12. If the active PTE is marked not-present, then set the active PTE to correspond to guest PTE:
a. Set the page base address in the active PTE to be the physical address that corresponds to the guest page
base address in the guest PTE.
b. Set the P, U/S, and PS bits in the active PTE to be identical to those in the guest PTE.
c.

Set the PWT, PCD, and G bits according to the policy of the VMM.

d. Set A = 1 in the guest PTE.
e. If D = 1 in the guest PTE, then set the R/W bit in the active PTE as in the guest PTE.
f.

If D = 0 in the guest PTE and the attempted access is a write, then set R/W in the active PTE as in the guest
PTE and set D = 1 in the guest PTE.

g. If D = 0 in the guest PTE and the attempted access is not a write, then set R/W = 0 in the active PTE.
h. After modifying the active PTE, re-execute the faulting instruction.
The remaining steps assume that the active PTE is already marked present.
13. If the attempted access is a write, D = 0 (not dirty) in the guest PTE and the active PTE has caused a fault
solely because it has R/W = 0 (read-only); then set R/W in the active PTE as in the guest PTE, set D = 1 in the
guest PTE and re-execute the faulting instruction.
14. If none of the above cases apply, then raise a page fault of the guest operating system.

32.3.5.3

Response to Uses of INVLPG

Operating-systems can use INVLPG to flush entries from the TLB. This instruction takes a linear address as an
operand and software expects any cached translations for the address to be flushed. A VMM should set the
processor-based VM-execution control “INVLPG exiting” to 1 so that any attempts by a privileged guest to execute
INVLPG will trap to the VMM. The VMM can then modify the active page-table hierarchy to emulate the desired
effect of the INVLPG.
The following steps are performed. Note that these steps are performed only if the guest invocation of INVLPG
would not fault and only if the guest software is running at privilege level 0:
1. Locate the relevant active PDE using the upper 10 bits of the operand address and the current value of CR3. If
the PDE refers to a 4-MByte page (PS = 1), then set P = 0 in the PDE.
2. If the PDE is marked present and refers to a page table (PS = 0), locate the relevant active PTE using the next
10 bits of the operand address (bits 21–12) and the page-table base address in the PDE. Set P = 0 in the PTE.

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VIRTUALIZATION OF SYSTEM RESOURCES

Examine all PTEs in the page table; if they are now all marked not-present, de-allocate the page table and set
P = 0 in the PDE (this step may be optional).

32.3.5.4

Response to CR3 Writes

A guest operating system may attempt to write to CR3. Any write to CR3 implies a TLB flush and a possible page
table change. The following steps are performed:
1. The VMM notes the new CR3 value (used later to walk guest page tables) and emulates the write.
2. The VMM allocates a new PD page, with all invalid entries.
3. The VMM sets actual processor CR3 register to point to the new PD page.
The VMM may, at this point, speculatively fill in VTLB mappings for performance reasons.

32.4

MICROCODE UPDATE FACILITY

The microcode code update facility may be invoked at various points during the operation of a platform. Typically,
the BIOS invokes the facility on all processors during the BIOS boot process. This is sufficient to boot the BIOS and
operating system. As a microcode update more current than the system BIOS may be available, system software
should provide another mechanism for invoking the microcode update facility. The implications of the microcode
update mechanism on the design of the VMM are described in this section.

NOTE
Microcode updates must not be performed during VMX non-root operation. Updates performed in
VMX non-root operation may result in unpredictable system behavior.

32.4.1

Early Load of Microcode Updates

The microcode update facility may be invoked early in the VMM or guest OS boot process. Loading the microcode
update early provides the opportunity to correct errata affecting the boot process but the technique generally
requires a reboot of the software.
A microcode update may be loaded from the OS or VMM image loader. Typically, such image loaders do not run on
every logical processor, so this method effects only one logical processor. Later in the VMM or OS boot process,
after bringing all application processors on-line, the VMM or OS needs to invoke the microcode update facility for all
application processors.
Depending on the order of the VMM and the guest OS boot, the microcode update facility may be invoked by the
VMM or the guest OS. For example, if the guest OS boots first and then loads the VMM, the guest OS may invoke
the microcode update facility on all the logical processors. If a VMM boots before its guests, then the VMM may
invoke the microcode update facility during its boot process. In both cases, the VMM or OS should invoke the microcode update facilities soon after performing the multiprocessor startup.
In the early load scenario, microcode updates may be contained in the VMM or OS image or, the VMM or OS may
manage a separate database or file of microcode updates. Maintaining a separate microcode update image database has the advantage of reducing the number of required VMM or OS releases as a result of microcode update
releases.

32.4.2

Late Load of Microcode Updates

A microcode update may be loaded during normal system operation. This allows system software to activate the
microcode update at anytime without requiring a system reboot. This scenario does not allow the microcode update
to correct errata which affect the processor’s boot process but does allow high-availability systems to activate
microcode updates without interrupting the availability of the system. In this late load scenario, either the VMM or
a designated guest may load the microcode update. If the guest is loading the microcode update, the VMM must

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make sure that the entire guest memory buffer (which contains the microcode update image) will not cause a page
fault when accessed.
If the VMM loads the microcode update, then the VMM must have access to the current set of microcode updates.
These updates could be part of the VMM image or could be contained in a separate microcode update image database (for example: a database file on disk or in memory). Again, maintaining a separate microcode update image
database has the advantage of reducing the number of required VMM or OS releases as a result of microcode
update releases.
The VMM may wish to prevent a guest from loading a microcode update or may wish to support the microcode
update requested by a guest using emulation (without actually loading the microcode update). To prevent microcode update loading, the VMM may return a microcode update signature value greater than the value of
IA32_BIOS_SIGN_ID MSR. A well behaved guest will not attempt to load an older microcode update. The VMM may
also drop the guest attempts to write to IA32_BIOS_UPDT_TRIG MSR, preventing the guest from loading any
microcode updates. Later, when the guest queries IA32_BIOS_SIGN_ID MSR, the VMM could emulate the microcode update signature that the guest expects.
In general, loading a microcode update later will limit guest software’s visibility of features that may be enhanced
by a microcode update.

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32-10 Vol. 3C

CHAPTER 33
HANDLING BOUNDARY CONDITIONS IN A VIRTUAL MACHINE MONITOR
33.1

OVERVIEW

This chapter describes what a VMM must consider when handling exceptions, interrupts, error conditions, and transitions between activity states.

33.2

INTERRUPT HANDLING IN VMX OPERATION

The following bullets summarize VMX support for handling interrupts:

•

Control of processor exceptions. The VMM can get control on specific guest exceptions through the
exception-bitmap in the guest controlling VMCS. The exception bitmap is a 32-bit field that allows the VMM to
specify processor behavior on specific exceptions (including traps, faults, and aborts). Setting a specific bit in
the exception bitmap implies VM exits will be generated when the corresponding exception occurs. Any
exceptions that are programmed not to cause VM exits are delivered directly to the guest through the guest
IDT. The exception bitmap also controls execution of relevant instructions such as BOUND, INTO and INT3. VM
exits on page-faults are treated in such a way the page-fault error code is qualified through the page-faulterror-code mask and match fields in the VMCS.

•

Control over triple faults. If a fault occurs while attempting to call a double-fault handler in the guest and
that fault is not configured to cause a VM exit in the exception bitmap, the resulting triple fault causes a
VM exit.

•

Control of external interrupts. VMX allows both host and guest control of external interrupts through the
“external-interrupt exiting” VM execution control. If the control is 0, external-interrupts do not cause VM exits
and the interrupt delivery is masked by the guest programmed RFLAGS.IF value.1 If the control is 1, externalinterrupts causes VM exits and are not masked by RFLAGS.IF. The VMM can identify VM exits due to external
interrupts by checking the exit reason for an “external interrupt” (value = 1).

•

Control of other events. There is a pin-based VM-execution control that controls system behavior (exit or noexit) for NMI events. Most VMM usages will need handling of NMI external events in the VMM and hence will
specify host control of these events.
Some processors also support a pin-based VM-execution control called “virtual NMIs.” When this control is set,
NMIs cause VM exits, but the processor tracks guest readiness for virtual NMIs. This control interacts with the
“NMI-window exiting” VM-execution control (see below).
INIT and SIPI events always cause VM exits.

•

Acknowledge interrupt on exit. The “acknowledge interrupt on exit” VM-exit control in the controlling VMCS
controls processor behavior for external interrupt acknowledgement. If the control is 1, the processor acknowledges the interrupt controller to acquire the interrupt vector upon VM exit, and stores the vector in the VM-exit
interruption-information field. If the control is 0, the external interrupt is not acknowledged during VM exit.
Since RFLAGS.IF is automatically cleared on VM exits due to external interrupts, VMM re-enabling of interrupts
(setting RFLAGS.IF = 1) initiates the external interrupt acknowledgement and vectoring of the external
interrupt through the monitor/host IDT.

•

Event-masking Support. VMX captures the masking conditions of specific events while in VMX non-root
operation through the interruptibility-state field in the guest-state area of the VMCS.
This feature allows proper virtualization of various interrupt blocking states, such as: (a) blocking of external
interrupts for the instruction following STI; (b) blocking of interrupts for the instruction following a MOV-SS or
POP-SS instruction; (c) SMI blocking of subsequent SMIs until the next execution of RSM; and (d) NMI/SMI
blocking of NMIs until the next execution of IRET or RSM.

1. This chapter uses the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that support VMX operation also support Intel 64 architecture. For processors that do not support Intel 64 architecture, this notation refers to the 32-bit
forms of those registers (EAX, EIP, ESP, EFLAGS, etc.).
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INIT and SIPI events are treated specially. INIT assertions are always blocked in VMX root operation and while
in SMM, and unblocked otherwise. SIPI events are always blocked in VMX root operation.
The interruptibility state is loaded from the VMCS guest-state area on every VM entry and saved into the VMCS
on every VM exit.

•

Event injection. VMX operation allows injecting interruptions to a guest virtual machine through the use of
VM-entry interrupt-information field in VMCS. Injectable interruptions include external interrupts, NMI,
processor exceptions, software generated interrupts, and software traps. If the interrupt-information field
indicates a valid interrupt, exception or trap event upon the next VM entry; the processor will use the
information in the field to vector a virtual interruption through the guest IDT after all guest state and MSRs are
loaded. Delivery through the guest IDT emulates vectoring in non-VMX operation by doing the normal privilege
checks and pushing appropriate entries to the guest stack (entries may include RFLAGS, EIP and exception
error code). A VMM with host control of NMI and external interrupts can use the event-injection facility to
forward virtual interruptions to various guest virtual machines.

•

Interrupt-window exiting. When set to 1, the “interrupt-window exiting” VM-execution control (Section
24.6.2) causes VM exits when guest RFLAGS.IF is 1 and no other conditions block external interrupts. A VM exit
occurs at the beginning of any instruction at which RFLAGS.IF = 1 and on which the interruptibility state of the
guest would allow delivery of an interrupt. For example: when the guest executes an STI instruction,
RFLAGS = 1, and if at the completion of next instruction the interruptibility state masking due to STI is
removed; a VM exit occurs if the “interrupt-window exiting” VM-execution control is 1. This feature allows a
VMM to queue a virtual interrupt to the guest when the guest is not in an interruptible state. The VMM can set
the “interrupt-window exiting” VM-execution control for the guest and depend on a VM exit to know when the
guest becomes interruptible (and, therefore, when it can inject a virtual interrupt). The VMM can detect such
VM exits by checking for the basic exit reason “interrupt-window” (value = 7). If this feature is not used, the
VMM will need to poll and check the interruptibility state of the guest to deliver virtual interrupts.

•

NMI-window exiting. If the “virtual NMIs” VM-execution is set, the processor tracks virtual-NMI blocking.
The “NMI-window exiting” VM-execution control (Section 24.6.2) causes VM exits when there is no virtual-NMI
blocking. For example, after execution of the IRET instruction, a VM exit occurs if the “NMI-window exiting” VMexecution control is 1. This feature allows a VMM to queue a virtual NMI to a guest when the guest is not ready
to receive NMIs. The VMM can set the “NMI-window exiting” VM-execution control for the guest and depend on
a VM exit to know when the guest becomes ready for NMIs (and, therefore, when it can inject a virtual NMI).
The VMM can detect such VM exits by checking for the basic exit reason “NMI window” (value = 8). If this
feature is not used, the VMM will need to poll and check the interruptibility state of the guest to deliver virtual
NMIs.

•

VM-exit information. The VM-exit information fields provide details on VM exits due to exceptions and
interrupts. This information is provided through the exit-qualification, VM-exit-interruption-information,
instruction-length and interruption-error-code fields. Also, for VM exits that occur in the course of vectoring
through the guest IDT, information about the event that was being vectored through the guest IDT is provided
in the IDT-vectoring-information and IDT-vectoring-error-code fields. These information fields allow the VMM to
identify the exception cause and to handle it properly.

33.3

EXTERNAL INTERRUPT VIRTUALIZATION

VMX operation allows both host and guest control of external interrupts. While guest control of external interrupts
might be suitable for partitioned usages (different CPU cores/threads and I/O devices partitioned to independent
virtual machines), most VMMs built upon VMX are expected to utilize host control of external interrupts. The rest of
this section describes a general host-controlled interrupt virtualization architecture for standard PC platforms
through the use of VMX supported features.
With host control of external interrupts, the VMM (or the host OS in a hosted VMM model) manages the physical
interrupt controllers in the platform and the interrupts generated through them. The VMM exposes softwareemulated virtual interrupt controller devices (such as PIC and APIC) to each guest virtual machine instance.

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33.3.1

Virtualization of Interrupt Vector Space

The Intel 64 and IA-32 architectures use 8-bit vectors of which 224 (20H – FFH) are available for external interrupts. Vectors are used to select the appropriate entry in the interrupt descriptor table (IDT). VMX operation allows
each guest to control its own IDT. Host vectors refer to vectors delivered by the platform to the processor during
the interrupt acknowledgement cycle. Guest vectors refer to vectors programmed by a guest to select an entry in
its guest IDT. Depending on the I/O resource management models supported by the VMM design, the guest vector
space may or may not overlap with the underlying host vector space.

•

Interrupts from virtual devices: Guest vector numbers for virtual interrupts delivered to guests on behalf of
emulated virtual devices have no direct relation to the host vector numbers of interrupts from physical devices
on which they are emulated. A guest-vector assigned for a virtual device by the guest operating environment
is saved by the VMM and utilized when injecting virtual interrupts on behalf of the virtual device.

•

Interrupts from assigned physical devices: Hardware support for I/O device assignment allows physical I/O
devices in the host platform to be assigned (direct-mapped) to VMs. Guest vectors for interrupts from directmapped physical devices take up equivalent space from the host vector space, and require the VMM to perform
host-vector to guest-vector mapping for interrupts.

Figure 33-1 illustrates the functional relationship between host external interrupts and guest virtual external interrupts. Device A is owned by the host and generates external interrupts with host vector X. The host IDT is set up
such that the interrupt service routine (ISR) for device driver A is hooked to host vector X as normal. VMM
emulates (over device A) virtual device C in software which generates virtual interrupts to the VM with guest
expected vector P. Device B is assigned to a VM and generates external interrupts with host vector Y. The host IDT
is programmed to hook the VMM interrupt service routine (ISR) for assigned devices for vector Y, and the VMM
handler injects virtual interrupt with guest vector Q to the VM. The guest operating system programs the guest to
hook appropriate guest driver’s ISR to vectors P and Q.

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VM
Device Driver C

Guest IDT
Device Driver B

Guest
Vector P

Guest
Vector Q

Guest IDTR
Virtual Interrupt

Virtual Interrupt

Virtual Device C
Emulation

Host IDT
Monitor Handler

Platform Interrupt

Vector Y

Host

Virtual Machine Monitor (VMM)

Host

Host IDTR

Vector X

Device Driver A

Platform Interrupt

Hardware
Device A

Device B
OM19041

Figure 33-1. Host External Interrupts and Guest Virtual Interrupts

33.3.2

Control of Platform Interrupts

To meet the interrupt virtualization requirements, the VMM needs to take ownership of the physical interrupts and
the various interrupt controllers in the platform. VMM control of physical interrupts may be enabled through the
host-control settings of the “external-interrupt exiting” VM-execution control. To take ownership of the platform
interrupt controllers, the VMM needs to expose the virtual interrupt controller devices to the virtual machines and
restrict guest access to the platform interrupt controllers.
Intel 64 and IA-32 platforms can support three types of external interrupt control mechanisms: Programmable
Interrupt Controllers (PIC), Advanced Programmable Interrupt Controllers (APIC), and Message Signaled Interrupts (MSI). The following sections provide information on the virtualization of each of these mechanisms.

33.3.2.1

PIC Virtualization

Typical PIC-enabled platform implementations support dual 8259 interrupt controllers cascaded as master and
slave controllers. They supporting up to 15 possible interrupt inputs. The 8259 controllers are programmed
through initialization command words (ICWx) and operation command words (OCWx) accessed through specific
I/O ports. The various interrupt line states are captured in the PIC through interrupt requests, interrupt service
routines and interrupt mask registers.
Guest access to the PIC I/O ports can be restricted by activating I/O bitmaps in the guest controlling-VMCS (activate-I/O-bitmap bit in VM-execution control field set to 1) and pointing the I/O-bitmap physical addresses to valid

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bitmap regions. Bits corresponding to the PIC I/O ports can be cleared to cause a VM exit on guest access to these
ports.
If the VMM is not supporting direct access to any I/O ports from a guest, it can set the unconditional-I/O-exiting in
the VM-execution control field instead of activating I/O bitmaps. The exit-reason field in VM-exit information allows
identification of VM exits due to I/O access and can provide an exit-qualification to identify details about the guest
I/O operation that caused the VM exit.
The VMM PIC virtualization needs to emulate the platform PIC functionality including interrupt priority, mask,
request and service states, and specific guest programmed modes of PIC operation.

33.3.2.2

xAPIC Virtualization

Most modern Intel 64 and IA-32 platforms include support for an APIC. While the standard PIC is intended for use
on uniprocessor systems, APIC can be used in either uniprocessor or multi-processor systems.
APIC based interrupt control consists of two physical components: the interrupt acceptance unit (Local APIC) which
is integrated with the processor, and the interrupt delivery unit (I/O APIC) which is part of the I/O subsystem. APIC
virtualization involves protecting the platform’s local and I/O APICs and emulating them for the guest.

33.3.2.3

Local APIC Virtualization

The local APIC is responsible for the local interrupt sources, interrupt acceptance, dispensing interrupts to the
logical processor, and generating inter-processor interrupts. Software interacts with the local APIC by reading and
writing its memory-mapped registers residing within a 4-KByte uncached memory region with base address stored
in the IA32_APIC_BASE MSR. Since the local APIC registers are memory-mapped, the VMM can utilize memory
virtualization techniques (such as page-table virtualization) to trap guest accesses to the page frame hosting the
virtual local APIC registers.
Local APIC virtualization in the VMM needs to emulate the various local APIC operations and registers, such as:
APIC identification/format registers, the local vector table (LVT), the interrupt command register (ICR), interrupt
capture registers (TMR, IRR and ISR), task and processor priority registers (TPR, PPR), the EOI register and the
APIC-timer register. Since local APICs are designed to operate with non-specific EOI, local APIC emulation also
needs to emulate broadcast of EOI to the guest’s virtual I/O APICs for level triggered virtual interrupts.
A local APIC allows interrupt masking at two levels: (1) mask bit in the local vector table entry for local interrupts
and (2) raising processor priority through the TPR registers for masking lower priority external interrupts. The VMM
needs to comprehend these virtual local APIC mask settings as programmed by the guest in addition to the guest
virtual processor interruptibility state (when injecting APIC routed external virtual interrupts to a guest VM).
VMX provides several features which help the VMM to virtualize the local APIC. These features allow many of guest
TPR accesses (using CR8 only) to occur without VM exits to the VMM:

•

The VMCS contains a “virtual-APIC address” field. This 64-bit field is the physical address of the 4-KByte virtual
APIC page (4-KByte aligned). The virtual-APIC page contains a TPR shadow, which is accessed by the MOV CR8
instruction. The TPR shadow comprises bits 7:4 in byte 80H of the virtual-APIC page.

•

The TPR threshold: bits 3:0 of this 32-bit field determine the threshold below which the TPR shadow cannot fall.
A VM exit will occur after an execution of MOV CR8 that reduces the TPR shadow below this value.

•

The processor-based VM-execution controls field contains a “use TPR shadow” bit and a “CR8-store exiting” bit.
If the “use TPR shadow” VM-execution control is 1 and the “CR8-store exiting” VM-execution control is 0, then
a MOV from CR8 reads from the TPR shadow. If the “CR8-store exiting” VM-execution control is 1, then MOV
from CR8 causes a VM exit; the “use TPR shadow” VM-execution control is ignored in this case.

•

The processor-based VM-execution controls field contains a “CR8-load exiting” bit. If the “use TPR shadow” VMexecution control is set and the “CR8-load exiting” VM-execution control is clear, then MOV to CR8 writes to the
“TPR shadow”. A VM exit will occur after this write if the value written is below the TPR threshold. If the “CR8load exiting” VM-execution control is set, then MOV to CR8 causes a VM exit; the “use TPR shadow” VMexecution control is ignored in this case.

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33.3.2.4

I/O APIC Virtualization

The I/O APIC registers are typically mapped to a 1 MByte region where each I/O APIC is allocated a 4K address
window within this range. The VMM may utilize physical memory virtualization to trap guest accesses to the virtual
I/O APIC memory-mapped registers. The I/O APIC virtualization needs to emulate the various I/O APIC operations
and registers such as identification/version registers, indirect-I/O-access registers, EOI register, and the I/O redirection table. I/O APIC virtualization also need to emulate various redirection table entry settings such as delivery
mode, destination mode, delivery status, polarity, masking, and trigger mode programmed by the guest and track
remote-IRR state on guest EOI writes to various virtual local APICs.

33.3.2.5

Virtualization of Message Signaled Interrupts

The PCI Local Bus Specification (Rev. 2.2) introduces the concept of message signaled interrupts (MSI). MSI enable
PCI devices to request service by writing a system-specified message to a system specified address. The transaction address specifies the message destination while the transaction data specifies the interrupt vector, trigger
mode and delivery mode. System software is expected to configure the message data and address during MSI
device configuration, allocating one or more no-shared messages to MSI capable devices. Chapter 10, “Advanced
Programmable Interrupt Controller (APIC),” specifies the MSI message address and data register formats to be
followed on Intel 64 and IA-32 platforms. While MSI is optional for conventional PCI devices, it is the preferred
interrupt mechanism for PCI-Express devices.
Since the MSI address and data are configured through PCI configuration space, to control these physical interrupts
the VMM needs to assume ownership of PCI configuration space. This allows the VMM to capture the guest configuration of message address and data for MSI-capable virtual and assigned guest devices. PCI configuration transactions on PC-compatible systems are generated by software through two different methods:
1. The standard CONFIG_ADDRESS/CONFIG_DATA register mechanism (CFCH/CF8H ports) as defined in the PCI
Local Bus Specification.
2. The enhanced flat memory-mapped (MEMCFG) configuration mechanism as defined in the PCI-Express Base
Specification (Rev. 1.0a.).
The CFCH/CF8H configuration access from guests can be trapped by the VMM through use of I/O-bitmap VMexecution controls. The memory-mapped PCI-Express MEMCFG guest configuration accesses can be trapped by
VMM through physical memory virtualization.

33.3.3

Examples of Handling of External Interrupts

The following sections illustrate interrupt processing in a VMM (when used to support the external interrupt virtualization requirements).

33.3.3.1

Guest Setup

The VMM sets up the guest to cause a VM exit to the VMM on external interrupts. This is done by setting the
“external-interrupt exiting” VM-execution control in the guest controlling-VMCS.

33.3.3.2

Processor Treatment of External Interrupt

Interrupts are automatically masked by hardware in the processor on VM exit by clearing RFLAGS.IF. The exitreason field in VMCS is set to 1 to indicate an external interrupt as the exit reason.
If the VMM is utilizing the acknowledge-on-exit feature (by setting the “acknowledge interrupt on exit” VM-exit
control), the processor acknowledges the interrupt, retrieves the host vector, and saves the interrupt in the VMexit-interruption-information field (in the VM-exit information region of the VMCS) before transitioning control to
the VMM.

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33.3.3.3

Processing of External Interrupts by VMM

Upon VM exit, the VMM can determine the exit cause of an external interrupt by checking the exit-reason field
(value = 1) in VMCS. If the acknowledge-interrupt-on-exit control (see Section 24.7.1) is enabled, the VMM can
use the saved host vector (in the exit-interruption-information field) to switch to the appropriate interrupt handler.
If the “acknowledge interrupt on exit” VM-exit control is 0, the VMM may re-enable interrupts (by setting
RFLAGS.IF) to allow vectoring of external interrupts through the monitor/host IDT.
The following steps may need to be performed by the VMM to process an external interrupt:

•

Host Owned I/O Devices: For host-owned I/O devices, the interrupting device is owned by the VMM (or
hosting OS in a hosted VMM). In this model, the interrupt service routine in the VMM/host driver is invoked and,
upon ISR completion, the appropriate write sequences (TPR updates, EOI etc.) to respective interrupt
controllers are performed as normal. If the work completion indicated by the driver implies virtual device
activity, the VMM runs the virtual device emulation. Depending on the device class, physical device activity
could imply activity by multiple virtual devices mapped over the device. For each affected virtual device, the
VMM injects a virtual external interrupt event to respective guest virtual machines. The guest driver interacts
with the emulated virtual device to process the virtual interrupt. The interrupt controller emulation in the VMM
supports various guest accesses to the VMM’s virtual interrupt controller.

•

Guest Assigned I/O Devices: For assigned I/O devices, either the VMM uses a software proxy or it can
directly map the physical device to the assigned VM. In both cases, servicing of the interrupt condition on the
physical device is initiated by the driver running inside the guest VM. With host control of external interrupts,
interrupts from assigned physical devices cause VM exits to the VMM and vectoring through the host IDT to the
registered VMM interrupt handler. To unblock delivery of other low priority platform interrupts, the VMM
interrupt handler must mask the interrupt source (for level triggered interrupts) and issue the appropriate EOI
write sequences.

Once the physical interrupt source is masked and the platform EOI generated, the VMM can map the host vector to
its corresponding guest vector to inject the virtual interrupt into the assigned VM. The guest software does EOI
write sequences to its virtual interrupt controller after completing interrupt processing. For level triggered interrupts, these EOI writes to the virtual interrupt controller may be trapped by the VMM which may in turn unmask
the previously masked interrupt source.

33.3.3.4

Generation of Virtual Interrupt Events by VMM

The following provides some of the general steps that need to be taken by VMM designs when generating virtual
interrupts:
1. Check virtual processor interruptibility state. The virtual processor interruptibility state is reflected in the guest
RFLAGS.IF flag and the processor interruptibility-state saved in the guest state area of the controlling-VMCS. If
RFLAGS.IF is set and the interruptibility state indicates readiness to take external interrupts (STI-masking and
MOV-SS/POP-SS-masking bits are clear), the guest virtual processor is ready to take external interrupts. If the
VMM design supports non-active guest sleep states, the VMM needs to make sure the current guest sleep state
allows injection of external interrupt events.
2. If the guest virtual processor state is currently not interruptible, a VMM may utilize the “interrupt-window
exiting” VM-execution to notify the VMM (through a VM exit) when the virtual processor state changes to interruptible state.
3. Check the virtual interrupt controller state. If the guest VM exposes a virtual local APIC, the current value of its
processor priority register specifies if guest software allows dispensing an external virtual interrupt with a
specific priority to the virtual processor. If the virtual interrupt is routed through the local vector table (LVT)
entry of the local APIC, the mask bits in the corresponding LVT entry specifies if the interrupt is currently
masked. Similarly, the virtual interrupt controller’s current mask (IO-APIC or PIC) and priority settings reflect
guest state to accept specific external interrupts. The VMM needs to check both the virtual processor and
interrupt controller states to verify its guest interruptibility state. If the guest is currently interruptible, the
VMM can inject the virtual interrupt. If the current guest state does not allow injecting a virtual interrupt, the
interrupt needs to be queued by the VMM until it can be delivered.
4. Prioritize the use of VM-entry event injection. A VMM may use VM-entry event injection to deliver various
virtual events (such as external interrupts, exceptions, traps, and so forth). VMM designs may prioritize use of
virtual-interrupt injection between these event types. Since each VM entry allows injection of one event,

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depending on the VMM event priority policies, the VMM may need to queue the external virtual interrupt if a
higher priority event is to be delivered on the next VM entry. Since the VMM has masked this particular interrupt
source (if it was level triggered) and done EOI to the platform interrupt controller, other platform interrupts can
be serviced while this virtual interrupt event is queued for later delivery to the VM.
5. Update the virtual interrupt controller state. When the above checks have passed, before generating the virtual
interrupt to the guest, the VMM updates the virtual interrupt controller state (Local-APIC, IO-APIC and/or PIC)
to reflect assertion of the virtual interrupt. This involves updating the various interrupt capture registers, and
priority registers as done by the respective hardware interrupt controllers. Updating the virtual interrupt
controller state is required for proper interrupt event processing by guest software.
6. Inject the virtual interrupt on VM entry. To inject an external virtual interrupt to a guest VM, the VMM sets up
the VM-entry interruption-information field in the guest controlling-VMCS before entry to guest using
VMRESUME. Upon VM entry, the processor will use this vector to access the gate in guest’s IDT and the value of
RFLAGS and EIP in guest-state area of controlling-VMCS is pushed on the guest stack. If the guest RFLAGS.IF
is clear, the STI-masking bit is set, or the MOV- SS/POP-SS-masking bit is set, the VM entry will fail and the
processor will load state from the host-state area of the working VMCS as if a VM exit had occurred (see Section
26.7).

33.4

ERROR HANDLING BY VMM

Error conditions may occur during VM entries and VM exits and a few other situations. This section describes how
VMM should handle these error conditions, including triple faults and machine-check exceptions.

33.4.1

VM-Exit Failures

All VM exits load processor state from the host-state area of the VMCS that was the controlling VMCS before the VM
exit. This state is checked for consistency while being loaded. Because the host-state is checked on VM entry, these
checks will generally succeed. Failure is possible only if host software is incorrect or if VMCS data in the VMCS
region in memory has been written by guest software (or by I/O DMA) since the last VM entry. VM exits may fail for
the following reasons:

•
•
•

There was a failure on storing guest MSRs.

•
•

There was a failure on loading host MSRs.

There was failure in loading a PDPTR.
The controlling VMCS has been corrupted (through writes to the corresponding VMCS region) in such a way that
the implementation cannot complete the VM exit.
A machine-check event occurred.

If one of these problems occurs on a VM exit, a VMX abort results.

33.4.2

Machine-Check Considerations

The following sequence determine how machine-check events are handled during VMXON, VMXOFF, VM entries,
and VM exits:

•

VMXOFF and VMXON:
If a machine-check event occurs during VMXOFF or VMXON and CR4.MCE = 1, a machine-check exception
(#MC) is generated. If CR4.MCE = 0, the processor goes to shutdown state.

•

VM entry:
If a machine-check event occurs during VM entry, one of the following three treatments must occur:
a. Normal delivery before VM entry. If CR4.MCE = 1 before VM entry, delivery of a machine-check exception
(#MC) through the host IDT occurs. If CR4.MCE = 0, the processor goes to shutdown state.

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b. Normal delivery after VM entry. If CR4.MCE = 1 after VM entry, delivery of a machine-check exception
(#MC) through the guest IDT occurs (alternatively, this exception may cause a VM exit). If CR4.MCE = 0,
the processor goes to shutdown state.
c.

Load state from the host-state area of the working VMCS as if a VM exit had occurred (see Section 26.7).
The basic exit reason will be “VM-entry failure due to machine-check event.”

If the machine-check event occurs after any guest state has been loaded, option a above will not be used; it
may be used if the machine-check event occurs while checking host state and VMX controls (or while reporting
a failure due to such checks). An implementation may use option b only if all guest state has been loaded
properly.

•

VM exit:
If a machine-check event occurs during VM exit, one of the following three treatments must occur:
a. Normal delivery before VM exit. If CR4.MCE = 1 before the VM exit, delivery of a machine-check exception
(#MC) through the guest IDT (alternatively, this may cause a VM exit). If CR4.MCE = 0, the processor goes
to shutdown state.
b. Normal delivery after VM exit. If CR4.MCE = 1 after the VM exit, delivery of a machine-check exception
(#MC) through the host IDT. If CR4.MCE = 0, the processor goes to shutdown state.
c.

Fail the VM exit. If the VM exit is to VMX root operation, a VMX abort will result; it will block events as done
normally in VMX abort. The VMX abort indicator will show that a machine-check event induced the abort
operation.

If a machine-check event is induced by an action in VMX non-root operation before any determination is made
that the inducing action may cause a VM exit, that machine-check event should be considered as happening
during guest execution in VMX non-root operation. This is the case even if the part of the action that caused the
machine-check event was VMX-specific (for example, the processor’s consulting an I/O bitmap). If a machinecheck exception occurs and if bit 12H of the exception bitmap is cleared to 0, the exception is delivered to the
guest through gate 12H of its IDT; if the bit is set to 1, the machine-check exception causes a VM exit.

NOTE
The state saved in the guest-state area on VM exits due to machine-check exceptions should be
considered suspect. A VMM should consult the RIPV and EIPV bits in the IA32_MCG_STATUS MSR
before resuming a guest that caused a VM exit due to a machine-check exception.

33.4.3

MCA Error Handling Guidelines for VMM

Section 33.4.2 covers general requirements for VMMs to handle machine-check exceptions, when normal operation
of the guest machine and/or the VMM is no longer possible. enhancements of machine-check architecture in newer
processors may support software recovery of uncorrected MC errors (UCR) signaled through either machine-check
exceptions or corrected machine-check interrupt (CMCI). Section 15.5 and Section 15.6 describes details of these
more recent enhancements of machine-check architecture.
In general, Virtual Machine Monitor (VMM) error handling should follow the recommendations for OS error handling
described in Section 15.3, Section 15.6, Section 15.9, and Section 15.10. This section describes additional guidelines for hosted and native hypervisor-based VMM implementations to support corrected MC errors and recoverable
uncorrected MC errors.
Because a hosted VMM provides virtualization services in the context of an existing standard host OS, the host OS
controls platform hardware through the host OS services such as the standard OS device drivers. In hosted VMMs.
MCA errors will be handled by the host OS error handling software.
In native VMMs, the hypervisor runs on the hardware directly, and may provide only a limited set of platform
services for guest VMs. Most platform services may instead be provided by a “control OS”. In hypervisor-based
VMMs, MCA errors will either be delivered directly to the VMM MCA handler (when the error is signaled while in the
VMM context) or cause by a VM exit from a guest VM or be delivered to the MCA intercept handler. There are two
general approaches the hypervisor can use to handle the MCA error: either within the hypervisor itself or by
forwarding the error to the control OS.

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33.4.3.1

VMM Error Handling Strategies

Broadly speaking, there are two strategies that VMMs may take for error handling:

•

Basic error handling: in this approach the guest VM is treated as any other thread of execution. If the error
recovery action does not support restarting the thread after handling the error, the guest VM should be
terminated.

•

MCA virtualization: in this approach, the VMM virtualizes the MCA events and hardware. This enables the VMM
to intercept MCA events and inject an MCA into the guest VM. The guest VM then has the opportunity to attempt
error recovery actions, rather than being terminated by the VMM.

Details of these approaches and implementation considerations for hosted and native VMMs are discussed below.

33.4.3.2

Basic VMM MCA error recovery handling

The simplest approach is for the VMM to treat the guest VM as any other thread of execution:

•

MCE's that occur outside the stream of execution of a virtual machine guest will cause an MCE abort and may
be handled by the MCA error handler following the recovery actions and guidelines described in Section 15.9,
and Section 15.10. This includes logging the error and taking appropriate recovery actions when necessary. The
VMM must not resume the interrupted thread of execution or another VM until it has taken the appropriate
recovery action or, in the case of fatal MCAs, reset the system.

•

MCE's that occur while executing in the context of a virtual machine will be intercepted by the VMM. The MCA
intercept handler may follow the error handling guidelines listed in Section 15.9 and Section 15.10 for SRAO
and SRAR errors. For SRAR errors, terminating the thread of execution will involve terminating the affected
guest VM. For fatal errors the MCA handler should log the error and reset the system -- the VMM should not
resume execution of the interrupted VM.

33.4.3.3

Implementation Considerations for the Basic Model

For hosted VMMs, the host OS MCA error handling code will perform error analysis and initiate the appropriate
recovery actions. For the basic model this flow does not change when terminating a guest VM although the specific
actions needed to terminate a guest VM may be different than terminating an application or user process.
For native, hypervisor-based VMMs, MCA errors will either be delivered directly to the VMM MCA handler (when the
error is signaled while in the VMM context) or cause a VM exit from a guest VM or be delivered to the MCA intercept
handler. There are two general approaches the hypervisor can use to handle the MCA error: either by forwarding
the error to the control OS or within the hypervisor itself. These approaches are described in the following paragraphs.
The hypervisor may forward the error to the control OS for handling errors. This approach simplifies the hypervisor
error handling since it relies on the control OS to implement the basic error handling model. The control OS error
handling code will be similar to the error handling code in the hosted VMM. Errors can be forwarded to the control
OS via an OS callback or by injecting an MCE event into the control OS. Injecting an MCE will cause the control OS
MCA error handler to be invoked. The control OS is responsible for terminating the affected guest VM, if necessary,
which may require cooperation from the hypervisor.
Alternatively, the error may be handled completely in the hypervisor. The hypervisor error handler is enhanced to
implement the basic error handling model and the hypervisor error handler has the capability to fully analyze the
error information and take recovery actions based on the guidelines. In this case error handling steps in the hypervisor are similar to those for the hosted VMM described above (where the hypervisor replaces the host OS actions).
The hypervisor is responsible for terminating the affected guest VM, if necessary.
In all cases, if a fatal error is detected the VMM error handler should log the error and reset the system. The VMM
error handler must ensure that guest VMs are not resumed after a fatal error is detected to ensure error containment is maintained.

33.4.3.4

MCA Virtualization

A more sophisticated approach for handling errors is to virtualize the MCA. This involves virtualizing the MCA hardware and intercepting the MCA event in the VMM when a guest VM is interrupted by an MCA. After analyzing the

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HANDLING BOUNDARY CONDITIONS IN A VIRTUAL MACHINE MONITOR

error, the VMM error handler may then decide to inject an MCE abort into the guest VM for attempted guest VM
error recovery. This would enable the guest OS the opportunity to take recovery actions specific to that guest.
For MCA virtualization, the VMM must provide the guest physical address for memory errors instead of the system
physical address when reporting the errors to the guest VM. To compute the guest physical address, the VMM
needs to maintain a reverse mapping of system physical page addresses to guest physical page addresses.
When the MCE is injected into the guest VM, the guest OS MCA handler would be invoked. The guest OS implements the MCA handling guidelines and it could potentially terminate the interrupted thread of execution within the
guest instead of terminating the VM. The guest OS may also disable use of the affected page by the guest. When
disabling the page the VMM error handler may handle the case where a page is shared by the VMM and a guest or
by two guests. In these cases the page use must be disabled in both contexts to ensure no subsequent consumption errors are generated.

33.4.3.5

Implementation Considerations for the MCA Virtualization Model

MCA virtualization may be done in either hosted VMMs or hypervisor-based VMMs. The error handling flow is
similar to the flow described in the basic handling case. The major difference is that the recovery action includes
injecting the MCE abort into the guest VM to enable recovery by the guest OS when the MCA interrupts the execution of a guest VM.

33.5

HANDLING ACTIVITY STATES BY VMM

A VMM might place a logic processor in the wait-for-SIPI activity state if supporting certain guest operating system
using the multi-processor (MP) start-up algorithm. A guest with direct access to the physical local APIC and using
the MP start-up algorithm sends an INIT-SIPI-SIPI IPI sequence to start the application processor. In order to trap
the SIPIs, the VMM must start the logic processor which is the target of the SIPIs in wait-for-SIPI mode.

Vol. 3C 33-11

HANDLING BOUNDARY CONDITIONS IN A VIRTUAL MACHINE MONITOR

33-12 Vol. 3C

CHAPTER 34
SYSTEM MANAGEMENT MODE
This chapter describes aspects of IA-64 and IA-32 architecture used in system management mode (SMM).
SMM provides an alternate operating environment that can be used to monitor and manage various system
resources for more efficient energy usage, to control system hardware, and/or to run proprietary code. It was
introduced into the IA-32 architecture in the Intel386 SL processor (a mobile specialized version of the Intel386
processor). It is also available in the Pentium M, Pentium 4, Intel Xeon, P6 family, and Pentium and Intel486
processors (beginning with the enhanced versions of the Intel486 SL and Intel486 processors).

34.1

SYSTEM MANAGEMENT MODE OVERVIEW

SMM is a special-purpose operating mode provided for handling system-wide functions like power management,
system hardware control, or proprietary OEM-designed code. It is intended for use only by system firmware, not by
applications software or general-purpose systems software. The main benefit of SMM is that it offers a distinct and
easily isolated processor environment that operates transparently to the operating system or executive and software applications.
When SMM is invoked through a system management interrupt (SMI), the processor saves the current state of the
processor (the processor’s context), then switches to a separate operating environment defined by a new address
space. The system management software executive (SMI handler) starts execution in that environment, and the
critical code and data of the SMI handler reside in a physical memory region (SMRAM) within that address space.
While in SMM, the processor executes SMI handler code to perform operations such as powering down unused disk
drives or monitors, executing proprietary code, or placing the whole system in a suspended state. When the SMI
handler has completed its operations, it executes a resume (RSM) instruction. This instruction causes the processor
to reload the saved context of the processor, switch back to protected or real mode, and resume executing the
interrupted application or operating-system program or task.
The following SMM mechanisms make it transparent to applications programs and operating systems:

•
•

The only way to enter SMM is by means of an SMI.

•
•
•

Upon entering SMM, the processor saves the context of the interrupted program or task.

The processor executes SMM code in a separate address space that can be made inaccessible from the other
operating modes.
All interrupts normally handled by the operating system are disabled upon entry into SMM.
The RSM instruction can be executed only in SMM.

Section 34.3 describes transitions into and out of SMM. The execution environment after entering SMM is in realaddress mode with paging disabled (CR0.PE = CR0.PG = 0). In this initial execution environment, the SMI handler
can address up to 4 GBytes of memory and can execute all I/O and system instructions. Section 34.5 describes in
detail the initial SMM execution environment for an SMI handler and operation within that environment. The SMI
handler may subsequently switch to other operating modes while remaining in SMM.

NOTES
Software developers should be aware that, even if a logical processor was using the physicaladdress extension (PAE) mechanism (introduced in the P6 family processors) or was in IA-32e
mode before an SMI, this will not be the case after the SMI is delivered. This is because delivery of
an SMI disables paging (see Table 34-4). (This does not apply if the dual-monitor treatment of SMIs
and SMM is active; see Section 34.15.)

34.1.1

System Management Mode and VMX Operation

Traditionally, SMM services system management interrupts and then resumes program execution (back to the software stack consisting of executive and application software; see Section 34.2 through Section 34.13).
Vol. 3C 34-1

SYSTEM MANAGEMENT MODE

A virtual machine monitor (VMM) using VMX can act as a host to multiple virtual machines and each virtual machine
can support its own software stack of executive and application software. On processors that support VMX, virtualmachine extensions may use system-management interrupts (SMIs) and system-management mode (SMM) in one
of two ways:

•

Default treatment. System firmware handles SMIs. The processor saves architectural states and critical
states relevant to VMX operation upon entering SMM. When the firmware completes servicing SMIs, it uses
RSM to resume VMX operation.

•

Dual-monitor treatment. Two VM monitors collaborate to control the servicing of SMIs: one VMM operates
outside of SMM to provide basic virtualization in support for guests; the other VMM operates inside SMM (while
in VMX operation) to support system-management functions. The former is referred to as executive monitor,
the latter SMM-transfer monitor (STM).1

The default treatment is described in Section 34.14, “Default Treatment of SMIs and SMM with VMX Operation and
SMX Operation”. Dual-monitor treatment of SMM is described in Section 34.15, “Dual-Monitor Treatment of SMIs
and SMM”.

34.2

SYSTEM MANAGEMENT INTERRUPT (SMI)

The only way to enter SMM is by signaling an SMI through the SMI# pin on the processor or through an SMI
message received through the APIC bus. The SMI is a nonmaskable external interrupt that operates independently
from the processor’s interrupt- and exception-handling mechanism and the local APIC. The SMI takes precedence
over an NMI and a maskable interrupt. SMM is non-reentrant; that is, the SMI is disabled while the processor is in
SMM.

NOTES
In the Pentium 4, Intel Xeon, and P6 family processors, when a processor that is designated as an
application processor during an MP initialization sequence is waiting for a startup IPI (SIPI), it is in
a mode where SMIs are masked. However if a SMI is received while an application processor is in
the wait for SIPI mode, the SMI will be pended. The processor then responds on receipt of a SIPI by
immediately servicing the pended SMI and going into SMM before handling the SIPI.
An SMI may be blocked for one instruction following execution of STI, MOV to SS, or POP into SS.

34.3

SWITCHING BETWEEN SMM AND THE OTHER
PROCESSOR OPERATING MODES

Figure 2-3 shows how the processor moves between SMM and the other processor operating modes (protected,
real-address, and virtual-8086). Signaling an SMI while the processor is in real-address, protected, or virtual-8086
modes always causes the processor to switch to SMM. Upon execution of the RSM instruction, the processor always
returns to the mode it was in when the SMI occurred.

34.3.1

Entering SMM

The processor always handles an SMI on an architecturally defined “interruptible” point in program execution
(which is commonly at an IA-32 architecture instruction boundary). When the processor receives an SMI, it waits
for all instructions to retire and for all stores to complete. The processor then saves its current context in SMRAM
(see Section 34.4), enters SMM, and begins to execute the SMI handler.
Upon entering SMM, the processor signals external hardware that SMI handling has begun. The signaling mechanism used is implementation dependent. For the P6 family processors, an SMI acknowledge transaction is gener-

1. The dual-monitor treatment may not be supported by all processors. Software should consult the VMX capability MSR
IA32_VMX_BASIC (see Appendix A.1) to determine whether it is supported.
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SYSTEM MANAGEMENT MODE

ated on the system bus and the multiplexed status signal EXF4 is asserted each time a bus transaction is generated
while the processor is in SMM. For the Pentium and Intel486 processors, the SMIACT# pin is asserted.
An SMI has a greater priority than debug exceptions and external interrupts. Thus, if an NMI, maskable hardware
interrupt, or a debug exception occurs at an instruction boundary along with an SMI, only the SMI is handled.
Subsequent SMI requests are not acknowledged while the processor is in SMM. The first SMI interrupt request that
occurs while the processor is in SMM (that is, after SMM has been acknowledged to external hardware) is latched
and serviced when the processor exits SMM with the RSM instruction. The processor will latch only one SMI while
in SMM.
See Section 34.5 for a detailed description of the execution environment when in SMM.

34.3.2

Exiting From SMM

The only way to exit SMM is to execute the RSM instruction. The RSM instruction is only available to the SMI
handler; if the processor is not in SMM, attempts to execute the RSM instruction result in an invalid-opcode exception (#UD) being generated.
The RSM instruction restores the processor’s context by loading the state save image from SMRAM back into the
processor’s registers. The processor then returns an SMIACK transaction on the system bus and returns program
control back to the interrupted program.
Upon successful completion of the RSM instruction, the processor signals external hardware that SMM has been
exited. For the P6 family processors, an SMI acknowledge transaction is generated on the system bus and the
multiplexed status signal EXF4 is no longer generated on bus cycles. For the Pentium and Intel486 processors, the
SMIACT# pin is deserted.
If the processor detects invalid state information saved in the SMRAM, it enters the shutdown state and generates
a special bus cycle to indicate it has entered shutdown state. Shutdown happens only in the following situations:

•

A reserved bit in control register CR4 is set to 1 on a write to CR4. This error should not happen unless SMI
handler code modifies reserved areas of the SMRAM saved state map (see Section 34.4.1). CR4 is saved in the
state map in a reserved location and cannot be read or modified in its saved state.

•

An illegal combination of bits is written to control register CR0, in particular PG set to 1 and PE set to 0, or NW
set to 1 and CD set to 0.

•
•

CR4.PCIDE would be set to 1 and IA32_EFER.LMA to 0.
(For the Pentium and Intel486 processors only.) If the address stored in the SMBASE register when an RSM
instruction is executed is not aligned on a 32-KByte boundary. This restriction does not apply to the P6 family
processors.

In the shutdown state, Intel processors stop executing instructions until a RESET#, INIT# or NMI# is asserted.
While Pentium family processors recognize the SMI# signal in shutdown state, P6 family and Intel486 processors
do not. Intel does not support using SMI# to recover from shutdown states for any processor family; the response
of processors in this circumstance is not well defined. On Pentium 4 and later processors, shutdown will inhibit INTR
and A20M but will not change any of the other inhibits. On these processors, NMIs will be inhibited if no action is
taken in the SMI handler to uninhibit them (see Section 34.8).
If the processor is in the HALT state when the SMI is received, the processor handles the return from SMM slightly
differently (see Section 34.10). Also, the SMBASE address can be changed on a return from SMM (see Section
34.11).

34.4

SMRAM

Upon entering SMM, the processor switches to a new address space. Because paging is disabled upon entering
SMM, this initial address space maps all memory accesses to the low 4 GBytes of the processor's physical address
space. The SMI handler's critical code and data reside in a memory region referred to as system-management RAM
(SMRAM). The processor uses a pre-defined region within SMRAM to save the processor's pre-SMI context. SMRAM
can also be used to store system management information (such as the system configuration and specific information about powered-down devices) and OEM-specific information.

Vol. 3C 34-3

SYSTEM MANAGEMENT MODE

The default SMRAM size is 64 KBytes beginning at a base physical address in physical memory called the SMBASE
(see Figure 34-1). The SMBASE default value following a hardware reset is 30000H. The processor looks for the
first instruction of the SMI handler at the address [SMBASE + 8000H]. It stores the processor’s state in the area
from [SMBASE + FE00H] to [SMBASE + FFFFH]. See Section 34.4.1 for a description of the mapping of the state
save area.
The system logic is minimally required to decode the physical address range for the SMRAM from [SMBASE +
8000H] to [SMBASE + FFFFH]. A larger area can be decoded if needed. The size of this SMRAM can be between 32
KBytes and 4 GBytes.
The location of the SMRAM can be changed by changing the SMBASE value (see Section 34.11). It should be noted
that all processors in a multiple-processor system are initialized with the same SMBASE value (30000H). Initialization software must sequentially place each processor in SMM and change its SMBASE so that it does not overlap
those of other processors.
The actual physical location of the SMRAM can be in system memory or in a separate RAM memory. The processor
generates an SMI acknowledge transaction (P6 family processors) or asserts the SMIACT# pin (Pentium and
Intel486 processors) when the processor receives an SMI (see Section 34.3.1).
System logic can use the SMI acknowledge transaction or the assertion of the SMIACT# pin to decode accesses to
the SMRAM and redirect them (if desired) to specific SMRAM memory. If a separate RAM memory is used for
SMRAM, system logic should provide a programmable method of mapping the SMRAM into system memory space
when the processor is not in SMM. This mechanism will enable start-up procedures to initialize the SMRAM space
(that is, load the SMI handler) before executing the SMI handler during SMM.

34.4.1

SMRAM State Save Map

When an IA-32 processor that does not support Intel 64 architecture initially enters SMM, it writes its state to the
state save area of the SMRAM. The state save area begins at [SMBASE + 8000H + 7FFFH] and extends down to
[SMBASE + 8000H + 7E00H]. Table 34-1 shows the state save map. The offset in column 1 is relative to the
SMBASE value plus 8000H. Reserved spaces should not be used by software.
Some of the registers in the SMRAM state save area (marked YES in column 3) may be read and changed by the
SMI handler, with the changed values restored to the processor registers by the RSM instruction. Some register
images are read-only, and must not be modified (modifying these registers will result in unpredictable behavior).
An SMI handler should not rely on any values stored in an area that is marked as reserved.
SMRAM
SMBASE + FFFFH

SMBASE + 8000H

Start of State Save Area

SMI Handler Entry Point

SMBASE

Figure 34-1. SMRAM Usage

34-4 Vol. 3C

SYSTEM MANAGEMENT MODE

Table 34-1. SMRAM State Save Map
Offset
(Added to SMBASE + 8000H)

Register

Writable?

7FFCH

CR0

No

7FF8H

CR3

No

7FF4H

EFLAGS

Yes

7FF0H

EIP

Yes

7FECH

EDI

Yes

7FE8H

ESI

Yes

7FE4H

EBP

Yes

7FE0H

ESP

Yes

7FDCH

EBX

Yes

7FD8H

EDX

Yes

7FD4H

ECX

Yes

7FD0H

EAX

Yes

7FCCH

DR6

No

7FC8H

DR7

No

7FC4H

TR

1

No

7FC0H

Reserved

No

7FBCH

GS1

No

7FB8H

1

No

7FB4H

DS

1

No

7FB0H

SS1

No

7FACH

1

No

1

FS

CS

7FA8H

ES

No

7FA4H

I/O State Field, see Section 34.7

No

7FA0H

I/O Memory Address Field, see Section 34.7

No

7F9FH-7F03H

Reserved

No

7F02H

Auto HALT Restart Field (Word)

Yes

7F00H

I/O Instruction Restart Field (Word)

Yes

7EFCH

SMM Revision Identifier Field (Doubleword)

No

7EF8H

SMBASE Field (Doubleword)

Yes

7EF7H - 7E00H

Reserved

No

NOTE:
1. The two most significant bytes are reserved.
The following registers are saved (but not readable) and restored upon exiting SMM:

•
•

Control register CR4. (This register is cleared to all 0s when entering SMM).
The hidden segment descriptor information stored in segment registers CS, DS, ES, FS, GS, and SS.

If an SMI request is issued for the purpose of powering down the processor, the values of all reserved locations in
the SMM state save must be saved to nonvolatile memory.
The following state is not automatically saved and restored following an SMI and the RSM instruction, respectively:
Vol. 3C 34-5

SYSTEM MANAGEMENT MODE

•
•
•
•
•

Debug registers DR0 through DR3.

•
•
•
•

The state of the trap controller.

The x87 FPU registers.
The MTRRs.
Control register CR2.
The model-specific registers (for the P6 family and Pentium processors) or test registers TR3 through TR7 (for
the Pentium and Intel486 processors).
The machine-check architecture registers.
The APIC internal interrupt state (ISR, IRR, etc.).
The microcode update state.

If an SMI is used to power down the processor, a power-on reset will be required before returning to SMM, which
will reset much of this state back to its default values. So an SMI handler that is going to trigger power down should
first read these registers listed above directly, and save them (along with the rest of RAM) to nonvolatile storage.
After the power-on reset, the continuation of the SMI handler should restore these values, along with the rest of
the system's state. Anytime the SMI handler changes these registers in the processor, it must also save and restore
them.

NOTES
A small subset of the MSRs (such as, the time-stamp counter and performance-monitoring
counters) are not arbitrarily writable and therefore cannot be saved and restored. SMM-based
power-down and restoration should only be performed with operating systems that do not use or
rely on the values of these registers.
Operating system developers should be aware of this fact and insure that their operating-system
assisted power-down and restoration software is immune to unexpected changes in these register
values.

34.4.1.1

SMRAM State Save Map and Intel 64 Architecture

When the processor initially enters SMM, it writes its state to the state save area of the SMRAM. The state save area
on an Intel 64 processor at [SMBASE + 8000H + 7FFFH] and extends to [SMBASE + 8000H + 7C00H].
Support for Intel 64 architecture is reported by CPUID.80000001:EDX[29] = 1. The layout of the SMRAM state save
map is shown in Table 34-3.
Additionally, the SMRAM state save map shown in Table 34-3 also applies to processors with the following CPUID
signatures listed in Table 34-2, irrespective of the value in CPUID.80000001:EDX[29].

Table 34-2. Processor Signatures and 64-bit SMRAM State Save Map Format
DisplayFamily_DisplayModel Processor Families/Processor Number Series
06_17H

Intel Xeon Processor 5200, 5400 series, Intel Core 2 Quad processor Q9xxx, Intel Core 2 Duo
processors E8000, T9000,

06_0FH

Intel Xeon Processor 3000, 3200, 5100, 5300, 7300 series, Intel Core 2 Quad, Intel Core 2 Extreme,
Intel Core 2 Duo processors, Intel Pentium dual-core processors

06_1CH

45 nm Intel® Atom™ processors

34-6 Vol. 3C

SYSTEM MANAGEMENT MODE

Table 34-3. SMRAM State Save Map for Intel 64 Architecture
Offset
(Added to SMBASE + 8000H)

Register

Writable?

7FF8H

CR0

No

7FF0H

CR3

No

7FE8H

RFLAGS

Yes

7FE0H

IA32_EFER

Yes

7FD8H

RIP

Yes

7FD0H

DR6

No

7FC8H

DR7

7FC4H

No

TR SEL

1

No
1

7FC0H

LDTR SEL

7FBCH

1

GS SEL

No

7FB8H

FS SEL1

No

7FB4H

1

No

7FB0H

SS SEL

1

No

7FACH

CS SEL1

No

7FA8H

1

ES SEL

No

7FA4H

IO_MISC

No

7F9CH

IO_MEM_ADDR

No

7F94H

RDI

Yes

7F8CH

RSI

Yes

7F84H

RBP

Yes

7F7CH

RSP

Yes

7F74H

RBX

Yes

7F6CH

RDX

Yes

7F64H

RCX

Yes

7F5CH

RAX

Yes

7F54H

R8

Yes

7F4CH

R9

Yes

7F44H

R10

Yes

7F3CH

R11

Yes

7F34H

R12

Yes

7F2CH

R13

Yes

7F24H

R14

Yes

7F1CH

R15

Yes

7F1BH-7F04H

Reserved

No

7F02H

Auto HALT Restart Field (Word)

Yes

7F00H

I/O Instruction Restart Field (Word)

Yes

7EFCH

SMM Revision Identifier Field (Doubleword)

No

7EF8H

SMBASE Field (Doubleword)

Yes

DS SEL

No

Vol. 3C 34-7

SYSTEM MANAGEMENT MODE

Table 34-3. SMRAM State Save Map for Intel 64 Architecture (Contd.)
Offset
(Added to SMBASE + 8000H)

Register

Writable?

7EF7H - 7EE4H

Reserved

No

7EE0H

Setting of “enable EPT” VM-execution control

No

7ED8H

Value of EPTP VM-execution control field

No

7ED7H - 7EA0H

Reserved

No

7E9CH

LDT Base (lower 32 bits)

No

7E98H

Reserved

No

7E94H

IDT Base (lower 32 bits)

No

7E90H

Reserved

No

7E8CH

GDT Base (lower 32 bits)

No

7E8BH - 7E44H

Reserved

No

7E40H

CR4

No

7E3FH - 7DF0H

Reserved

No

7DE8H

IO_RIP

Yes

7DE7H - 7DDCH

Reserved

No

7DD8H

IDT Base (Upper 32 bits)

No

7DD4H

LDT Base (Upper 32 bits)

No

7DD0H

GDT Base (Upper 32 bits)

No

7DCFH - 7C00H

Reserved

No

NOTE:
1. The two most significant bytes are reserved.

34.4.2

SMRAM Caching

An IA-32 processor does not automatically write back and invalidate its caches before entering SMM or before
exiting SMM. Because of this behavior, care must be taken in the placement of the SMRAM in system memory and
in the caching of the SMRAM to prevent cache incoherence when switching back and forth between SMM and
protected mode operation. Any of the following three methods of locating the SMRAM in system memory will guarantee cache coherency.

•

Place the SMRAM in a dedicated section of system memory that the operating system and applications are
prevented from accessing. Here, the SMRAM can be designated as cacheable (WB, WT, or WC) for optimum
processor performance, without risking cache incoherence when entering or exiting SMM.

•

Place the SMRAM in a section of memory that overlaps an area used by the operating system (such as the video
memory), but designate the SMRAM as uncacheable (UC). This method prevents cache access when in SMM to
maintain cache coherency, but the use of uncacheable memory reduces the performance of SMM code.

•

Place the SMRAM in a section of system memory that overlaps an area used by the operating system and/or
application code, but explicitly flush (write back and invalidate) the caches upon entering and exiting SMM
mode. This method maintains cache coherency, but incurs the overhead of two complete cache flushes.

For Pentium 4, Intel Xeon, and P6 family processors, a combination of the first two methods of locating the SMRAM
is recommended. Here the SMRAM is split between an overlapping and a dedicated region of memory. Upon
entering SMM, the SMRAM space that is accessed overlaps video memory (typically located in low memory). This
SMRAM section is designated as UC memory. The initial SMM code then jumps to a second SMRAM section that is
located in a dedicated region of system memory (typically in high memory). This SMRAM section can be cached for
optimum processor performance.

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SYSTEM MANAGEMENT MODE

For systems that explicitly flush the caches upon entering SMM (the third method described above), the cache flush
can be accomplished by asserting the FLUSH# pin at the same time as the request to enter SMM (generally initiated by asserting the SMI# pin). The priorities of the FLUSH# and SMI# pins are such that the FLUSH# is serviced
first. To guarantee this behavior, the processor requires that the following constraints on the interaction of FLUSH#
and SMI# be met. In a system where the FLUSH# and SMI# pins are synchronous and the set up and hold times
are met, then the FLUSH# and SMI# pins may be asserted in the same clock. In asynchronous systems, the
FLUSH# pin must be asserted at least one clock before the SMI# pin to guarantee that the FLUSH# pin is serviced
first.
Upon leaving SMM (for systems that explicitly flush the caches), the WBINVD instruction should be executed prior
to leaving SMM to flush the caches.

NOTES
In systems based on the Pentium processor that use the FLUSH# pin to write back and invalidate
cache contents before entering SMM, the processor will prefetch at least one cache line in between
when the Flush Acknowledge cycle is run and the subsequent recognition of SMI# and the assertion
of SMIACT#.
It is the obligation of the system to ensure that these lines are not cached by returning KEN#
inactive to the Pentium processor.

34.4.2.1

System Management Range Registers (SMRR)

SMI handler code and data stored by SMM code resides in SMRAM. The SMRR interface is an enhancement in Intel
64 architecture to limit cacheable reference of addresses in SMRAM to code running in SMM. The SMRR interface
can be configured only by code running in SMM. Details of SMRR is described in Section 11.11.2.4.

34.5

SMI HANDLER EXECUTION ENVIRONMENT

Section 34.5.1 describes the initial execution environment for an SMI handler. An SMI handler may re-configure its
execution environment to other supported operating modes. Section 34.5.2 discusses modifications an SMI
handler can make to its execution environment.

34.5.1

Initial SMM Execution Environment

After saving the current context of the processor, the processor initializes its core registers to the values shown in
Table 34-4. Upon entering SMM, the PE and PG flags in control register CR0 are cleared, which places the processor
in an environment similar to real-address mode. The differences between the SMM execution environment and the
real-address mode execution environment are as follows:

•
•
•

The addressable address space ranges from 0 to FFFFFFFFH (4 GBytes).
The normal 64-KByte segment limit for real-address mode is increased to 4 GBytes.
The default operand and address sizes are set to 16 bits, which restricts the addressable SMRAM address space
to the 1-MByte real-address mode limit for native real-address-mode code. However, operand-size and
address-size override prefixes can be used to access the address space beyond the 1-MByte.

Table 34-4. Processor Register Initialization in SMM
Register

Contents

General-purpose registers

Undefined

EFLAGS

00000002H

EIP

00008000H

CS selector

SMM Base shifted right 4 bits (default 3000H)

CS base

SMM Base (default 30000H)

DS, ES, FS, GS, SS Selectors

0000H

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Table 34-4. Processor Register Initialization in SMM
DS, ES, FS, GS, SS Bases

000000000H

DS, ES, FS, GS, SS Limits

0FFFFFFFFH

CR0

PE, EM, TS, and PG flags set to 0; others unmodified

CR4

Cleared to zero

DR6

Undefined

DR7

00000400H

•

Near jumps and calls can be made to anywhere in the 4-GByte address space if a 32-bit operand-size override
prefix is used. Due to the real-address-mode style of base-address formation, a far call or jump cannot transfer
control to a segment with a base address of more than 20 bits (1 MByte). However, since the segment limit in
SMM is 4 GBytes, offsets into a segment that go beyond the 1-MByte limit are allowed when using 32-bit
operand-size override prefixes. Any program control transfer that does not have a 32-bit operand-size override
prefix truncates the EIP value to the 16 low-order bits.

•

Data and the stack can be located anywhere in the 4-GByte address space, but can be accessed only with a 32bit address-size override if they are located above 1 MByte. As with the code segment, the base address for a
data or stack segment cannot be more than 20 bits.

The value in segment register CS is automatically set to the default of 30000H for the SMBASE shifted 4 bits to the
right; that is, 3000H. The EIP register is set to 8000H. When the EIP value is added to shifted CS value (the
SMBASE), the resulting linear address points to the first instruction of the SMI handler.
The other segment registers (DS, SS, ES, FS, and GS) are cleared to 0 and their segment limits are set to 4 GBytes.
In this state, the SMRAM address space may be treated as a single flat 4-GByte linear address space. If a segment
register is loaded with a 16-bit value, that value is then shifted left by 4 bits and loaded into the segment base
(hidden part of the segment register). The limits and attributes are not modified.
Maskable hardware interrupts, exceptions, NMI interrupts, SMI interrupts, A20M interrupts, single-step traps,
breakpoint traps, and INIT operations are inhibited when the processor enters SMM. Maskable hardware interrupts,
exceptions, single-step traps, and breakpoint traps can be enabled in SMM if the SMM execution environment
provides and initializes an interrupt table and the necessary interrupt and exception handlers (see Section 34.6).

34.5.2

SMI Handler Operating Mode Switching

Within SMM, an SMI handler may change the processor's operating mode (e.g., to enable PAE paging, enter 64-bit
mode, etc.) after it has made proper preparation and initialization to do so. For example, if switching to 32-bit
protected mode, the SMI handler should follow the guidelines provided in Chapter 9, “Processor Management and
Initialization”. If the SMI handler does wish to change operating mode, it is responsible for executing the appropriate mode-transition code after each SMI.
It is recommended that the SMI handler make use of all means available to protect the integrity of its critical code
and data. In particular, it should use the system-management range register (SMRR) interface if it is available (see
Section 11.11.2.4). The SMRR interface can protect only the first 4 GBytes of the physical address space. The SMI
handler should take that fact into account if it uses operating modes that allow access to physical addresses beyond
that 4-GByte limit (e.g. PAE paging or 64-bit mode).
Execution of the RSM instruction restores the pre-SMI processor state from the SMRAM state-state map (see
Section 34.4.1) into which it was stored when the processor entered SMM. (The SMBASE field in the SMRAM statesave map does not determine the state following RSM but rather the initial environment following the next entry to
SMM.) Any required change to operating mode is performed by the RSM instruction; there is no need for the SMI
handler to change modes explicitly prior to executing RSM.

34.6

EXCEPTIONS AND INTERRUPTS WITHIN SMM

When the processor enters SMM, all hardware interrupts are disabled in the following manner:

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•

The IF flag in the EFLAGS register is cleared, which inhibits maskable hardware interrupts from being
generated.

•
•

The TF flag in the EFLAGS register is cleared, which disables single-step traps.

•

NMI, SMI, and A20M interrupts are blocked by internal SMM logic. (See Section 34.8 for more information
about how NMIs are handled in SMM.)

Debug register DR7 is cleared, which disables breakpoint traps. (This action prevents a debugger from accidentally breaking into an SMI handler if a debug breakpoint is set in normal address space that overlays code or
data in SMRAM.)

Software-invoked interrupts and exceptions can still occur, and maskable hardware interrupts can be enabled by
setting the IF flag. Intel recommends that SMM code be written in so that it does not invoke software interrupts
(with the INT n, INTO, INT 3, or BOUND instructions) or generate exceptions.
If the SMI handler requires interrupt and exception handling, an SMM interrupt table and the necessary exception
and interrupt handlers must be created and initialized from within SMM. Until the interrupt table is correctly initialized (using the LIDT instruction), exceptions and software interrupts will result in unpredictable processor
behavior.
The following restrictions apply when designing SMM interrupt and exception-handling facilities:

•

The interrupt table should be located at linear address 0 and must contain real-address mode style interrupt
vectors (4 bytes containing CS and IP).

•

Due to the real-address mode style of base address formation, an interrupt or exception cannot transfer control
to a segment with a base address of more that 20 bits.

•
•

An interrupt or exception cannot transfer control to a segment offset of more than 16 bits (64 KBytes).

•

The SMBASE relocation feature affects the way the processor will return from an interrupt or exception
generated while the SMI handler is executing. For example, if the SMBASE is relocated to above 1 MByte, but
the exception handlers are below 1 MByte, a normal return to the SMI handler is not possible. One solution is
to provide the exception handler with a mechanism for calculating a return address above 1 MByte from the 16bit return address on the stack, then use a 32-bit far call to return to the interrupted procedure.

•

If an SMI handler needs access to the debug trap facilities, it must insure that an SMM accessible debug handler
is available and save the current contents of debug registers DR0 through DR3 (for later restoration). Debug
registers DR0 through DR3 and DR7 must then be initialized with the appropriate values.

•

If an SMI handler needs access to the single-step mechanism, it must insure that an SMM accessible singlestep handler is available, and then set the TF flag in the EFLAGS register.

•

If the SMI design requires the processor to respond to maskable hardware interrupts or software-generated
interrupts while in SMM, it must ensure that SMM accessible interrupt handlers are available and then set the
IF flag in the EFLAGS register (using the STI instruction). Software interrupts are not blocked upon entry to
SMM, so they do not need to be enabled.

When an exception or interrupt occurs, only the 16 least-significant bits of the return address (EIP) are pushed
onto the stack. If the offset of the interrupted procedure is greater than 64 KBytes, it is not possible for the
interrupt/exception handler to return control to that procedure. (One solution to this problem is for a handler
to adjust the return address on the stack.)

34.7

MANAGING SYNCHRONOUS AND ASYNCHRONOUS
SYSTEM MANAGEMENT INTERRUPTS

When coding for a multiprocessor system or a system with Intel HT Technology, it was not always possible for an
SMI handler to distinguish between a synchronous SMI (triggered during an I/O instruction) and an asynchronous
SMI. To facilitate the discrimination of these two events, incremental state information has been added to the SMM
state save map.
Processors that have an SMM revision ID of 30004H or higher have the incremental state information described
below.

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34.7.1

I/O State Implementation

Within the extended SMM state save map, a bit (IO_SMI) is provided that is set only when an SMI is either taken
immediately after a successful I/O instruction or is taken after a successful iteration of a REP I/O instruction (the
successful notion pertains to the processor point of view; not necessarily to the corresponding platform function).
When set, the IO_SMI bit provides a strong indication that the corresponding SMI was synchronous. In this case,
the SMM State Save Map also supplies the port address of the I/O operation. The IO_SMI bit and the I/O Port
Address may be used in conjunction with the information logged by the platform to confirm that the SMI was
indeed synchronous.
The IO_SMI bit by itself is a strong indication, not a guarantee, that the SMI is synchronous. This is because an
asynchronous SMI might coincidentally be taken after an I/O instruction. In such a case, the IO_SMI bit would still
be set in the SMM state save map.
Information characterizing the I/O instruction is saved in two locations in the SMM State Save Map (Table 34-5).
The IO_SMI bit also serves as a valid bit for the rest of the I/O information fields. The contents of these I/O information fields are not defined when the IO_SMI bit is not set.

Table 34-5. I/O Instruction Information in the SMM State Save Map
State (SMM Rev. ID: 30004H or higher)

Format
31

15

8

I/O Memory Address

When IO_SMI is set, the other fields may be interpreted as follows:

•

I/O length:

•
•
•

001 – Byte
010 – Word
100 – Dword

I/O instruction type (Table 34-6)

Table 34-6. I/O Instruction Type Encodings
Instruction

Encoding

IN Immediate

1001

IN DX

0001

OUT Immediate

1000

OUT DX

0000

INS

0011

OUTS

0010

REP INS

0111

REP OUTS

0110

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0

0

SMRAM offset 7FA0

•

1

IO_SMI

I/O Memory Address Field

3

I/O Length

31

4
I/O Type

SMRAM offset 7FA4

7
Reserved

I/O Port

I/0 State Field

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SYSTEM MANAGEMENT MODE

34.8

NMI HANDLING WHILE IN SMM

NMI interrupts are blocked upon entry to the SMI handler. If an NMI request occurs during the SMI handler, it is
latched and serviced after the processor exits SMM. Only one NMI request will be latched during the SMI handler.
If an NMI request is pending when the processor executes the RSM instruction, the NMI is serviced before the next
instruction of the interrupted code sequence. This assumes that NMIs were not blocked before the SMI occurred. If
NMIs were blocked before the SMI occurred, they are blocked after execution of RSM.
Although NMI requests are blocked when the processor enters SMM, they may be enabled through software by
executing an IRET instruction. If the SMI handler requires the use of NMI interrupts, it should invoke a dummy
interrupt service routine for the purpose of executing an IRET instruction. Once an IRET instruction is executed,
NMI interrupt requests are serviced in the same “real mode” manner in which they are handled outside of SMM.
A special case can occur if an SMI handler nests inside an NMI handler and then another NMI occurs. During NMI
interrupt handling, NMI interrupts are disabled, so normally NMI interrupts are serviced and completed with an
IRET instruction one at a time. When the processor enters SMM while executing an NMI handler, the processor
saves the SMRAM state save map but does not save the attribute to keep NMI interrupts disabled. Potentially, an
NMI could be latched (while in SMM or upon exit) and serviced upon exit of SMM even though the previous NMI
handler has still not completed. One or more NMIs could thus be nested inside the first NMI handler. The NMI interrupt handler should take this possibility into consideration.
Also, for the Pentium processor, exceptions that invoke a trap or fault handler will enable NMI interrupts from inside
of SMM. This behavior is implementation specific for the Pentium processor and is not part of the IA-32 architecture.

34.9

SMM REVISION IDENTIFIER

The SMM revision identifier field is used to indicate the version of SMM and the SMM extensions that are supported
by the processor (see Figure 34-2). The SMM revision identifier is written during SMM entry and can be examined
in SMRAM space at offset 7EFCH. The lower word of the SMM revision identifier refers to the version of the base
SMM architecture.
Register Offset
7EFCH
31

0

18 17 16 15
Reserved

SMM Revision Identifier

SMBASE Relocation
I/O Instruction Restart

Figure 34-2. SMM Revision Identifier
The upper word of the SMM revision identifier refers to the extensions available. If the I/O instruction restart flag
(bit 16) is set, the processor supports the I/O instruction restart (see Section 34.12); if the SMBASE relocation flag
(bit 17) is set, SMRAM base address relocation is supported (see Section 34.11).

34.10

AUTO HALT RESTART

If the processor is in a HALT state (due to the prior execution of a HLT instruction) when it receives an SMI, the
processor records the fact in the auto HALT restart flag in the saved processor state (see Figure 34-3). (This flag is
located at offset 7F02H and bit 0 in the state save area of the SMRAM.)
If the processor sets the auto HALT restart flag upon entering SMM (indicating that the SMI occurred when the
processor was in the HALT state), the SMI handler has two options:

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SYSTEM MANAGEMENT MODE

•

It can leave the auto HALT restart flag set, which instructs the RSM instruction to return program control to the
HLT instruction. This option in effect causes the processor to re-enter the HALT state after handling the SMI.
(This is the default operation.)

•

It can clear the auto HALT restart flag, which instructs the RSM instruction to return program control to the
instruction following the HLT instruction.
15

1 0
Reserved

Register Offset
7F02H

Auto HALT Restart

Figure 34-3. Auto HALT Restart Field
These options are summarized in Table 34-7. If the processor was not in a HALT state when the SMI was received
(the auto HALT restart flag is cleared), setting the flag to 1 will cause unpredictable behavior when the RSM instruction is executed.

Table 34-7. Auto HALT Restart Flag Values
Value of Flag After
Entry to SMM

Value of Flag When
Exiting SMM

Action of Processor When Exiting SMM

0

0

Returns to next instruction in interrupted program or task.

0

1

Unpredictable.

1

0

Returns to next instruction after HLT instruction.

1

1

Returns to HALT state.

If the HLT instruction is restarted, the processor will generate a memory access to fetch the HLT instruction (if it is
not in the internal cache), and execute a HLT bus transaction. This behavior results in multiple HLT bus transactions
for the same HLT instruction.

34.10.1 Executing the HLT Instruction in SMM
The HLT instruction should not be executed during SMM, unless interrupts have been enabled by setting the IF flag
in the EFLAGS register. If the processor is halted in SMM, the only event that can remove the processor from this
state is a maskable hardware interrupt or a hardware reset.

34.11

SMBASE RELOCATION

The default base address for the SMRAM is 30000H. This value is contained in an internal processor register called
the SMBASE register. The operating system or executive can relocate the SMRAM by setting the SMBASE field in the
saved state map (at offset 7EF8H) to a new value (see Figure 34-4). The RSM instruction reloads the internal
SMBASE register with the value in the SMBASE field each time it exits SMM. All subsequent SMI requests will use
the new SMBASE value to find the starting address for the SMI handler (at SMBASE + 8000H) and the SMRAM state
save area (from SMBASE + FE00H to SMBASE + FFFFH). (The processor resets the value in its internal SMBASE
register to 30000H on a RESET, but does not change it on an INIT.)

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31

0
Register Offset
7EF8H

SMM Base

Figure 34-4. SMBASE Relocation Field
In multiple-processor systems, initialization software must adjust the SMBASE value for each processor so that the
SMRAM state save areas for each processor do not overlap. (For Pentium and Intel486 processors, the SMBASE
values must be aligned on a 32-KByte boundary or the processor will enter shutdown state during the execution of
a RSM instruction.)
If the SMBASE relocation flag in the SMM revision identifier field is set, it indicates the ability to relocate the
SMBASE (see Section 34.9).

34.12

I/O INSTRUCTION RESTART

If the I/O instruction restart flag in the SMM revision identifier field is set (see Section 34.9), the I/O instruction
restart mechanism is present on the processor. This mechanism allows an interrupted I/O instruction to be reexecuted upon returning from SMM mode. For example, if an I/O instruction is used to access a powered-down I/O
device, a chip set supporting this device can intercept the access and respond by asserting SMI#. This action
invokes the SMI handler to power-up the device. Upon returning from the SMI handler, the I/O instruction restart
mechanism can be used to re-execute the I/O instruction that caused the SMI.
The I/O instruction restart field (at offset 7F00H in the SMM state-save area, see Figure 34-5) controls I/O instruction restart. When an RSM instruction is executed, if this field contains the value FFH, then the EIP register is modified to point to the I/O instruction that received the SMI request. The processor will then automatically re-execute
the I/O instruction that the SMI trapped. (The processor saves the necessary machine state to insure that reexecution of the instruction is handled coherently.)
15

0
I/O Instruction Restart Field

Register Offset
7F00H

Figure 34-5. I/O Instruction Restart Field
If the I/O instruction restart field contains the value 00H when the RSM instruction is executed, then the processor
begins program execution with the instruction following the I/O instruction. (When a repeat prefix is being used,
the next instruction may be the next I/O instruction in the repeat loop.) Not re-executing the interrupted I/O
instruction is the default behavior; the processor automatically initializes the I/O instruction restart field to 00H
upon entering SMM. Table 34-8 summarizes the states of the I/O instruction restart field.

Table 34-8. I/O Instruction Restart Field Values
Value of Flag After
Entry to SMM

Value of Flag When
Exiting SMM

Action of Processor When Exiting SMM

00H

00H

Does not re-execute trapped I/O instruction.

00H

FFH

Re-executes trapped I/O instruction.

The I/O instruction restart mechanism does not indicate the cause of the SMI. It is the responsibility of the SMI
handler to examine the state of the processor to determine the cause of the SMI and to determine if an I/O instruction was interrupted and should be restarted upon exiting SMM. If an SMI interrupt is signaled on a non-I/O
instruction boundary, setting the I/O instruction restart field to FFH prior to executing the RSM instruction will likely
result in a program error.
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34.12.1 Back-to-Back SMI Interrupts When I/O Instruction Restart Is Being Used
If an SMI interrupt is signaled while the processor is servicing an SMI interrupt that occurred on an I/O instruction
boundary, the processor will service the new SMI request before restarting the originally interrupted I/O instruction. If the I/O instruction restart field is set to FFH prior to returning from the second SMI handler, the EIP will point
to an address different from the originally interrupted I/O instruction, which will likely lead to a program error. To
avoid this situation, the SMI handler must be able to recognize the occurrence of back-to-back SMI interrupts when
I/O instruction restart is being used and insure that the handler sets the I/O instruction restart field to 00H prior to
returning from the second invocation of the SMI handler.

34.13

SMM MULTIPLE-PROCESSOR CONSIDERATIONS

The following should be noted when designing multiple-processor systems:

•
•
•

Any processor in a multiprocessor system can respond to an SMM.

•
•

The SMI handler will need to initialize the SMBASE for each processor.

•
•

Each processor needs its own SMRAM space. This space can be in system memory or in a separate RAM.
The SMRAMs for different processors can be overlapped in the same memory space. The only stipulation is that
each processor needs its own state save area and its own dynamic data storage area. (Also, for the Pentium
and Intel486 processors, the SMBASE address must be located on a 32-KByte boundary.) Code and static data
can be shared among processors. Overlapping SMRAM spaces can be done more efficiently with the P6 family
processors because they do not require that the SMBASE address be on a 32-KByte boundary.
Processors can respond to local SMIs through their SMI# pins or to SMIs received through the APIC interface.
The APIC interface can distribute SMIs to different processors.
Two or more processors can be executing in SMM at the same time.
When operating Pentium processors in dual processing (DP) mode, the SMIACT# pin is driven only by the MRM
processor and should be sampled with ADS#. For additional details, see Chapter 14 of the Pentium Processor
Family User’s Manual, Volume 1.

SMM is not re-entrant, because the SMRAM State Save Map is fixed relative to the SMBASE. If there is a need to
support two or more processors in SMM mode at the same time then each processor should have dedicated SMRAM
spaces. This can be done by using the SMBASE Relocation feature (see Section 34.11).

34.14

DEFAULT TREATMENT OF SMIS AND SMM WITH VMX OPERATION AND
SMX OPERATION

Under the default treatment, the interactions of SMIs and SMM with VMX operation are few. This section details
those interactions. It also explains how this treatment affects SMX operation.

34.14.1 Default Treatment of SMI Delivery
Ordinary SMI delivery saves processor state into SMRAM and then loads state based on architectural definitions.
Under the default treatment, processors that support VMX operation perform SMI delivery as follows:
enter SMM;
save the following internal to the processor:
CR4.VMXE
an indication of whether the logical processor was in VMX operation (root or non-root)
IF the logical processor is in VMX operation
THEN
save current VMCS pointer internal to the processor;
leave VMX operation;
save VMX-critical state defined below;
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FI;
IF the logical processor supports SMX operation
THEN
save internal to the logical processor an indication of whether the Intel® TXT private space is locked;
IF the TXT private space is unlocked
THEN lock the TXT private space;
FI;
FI;
CR4.VMXE ← 0;
perform ordinary SMI delivery:
save processor state in SMRAM;
set processor state to standard SMM values;1
invalidate linear mappings and combined mappings associated with VPID 0000H (for all PCIDs); combined mappings for VPID 0000H
are invalidated for all EP4TA values (EP4TA is the value of bits 51:12 of EPTP; see Section 28.3);
The pseudocode above makes reference to the saving of VMX-critical state. This state consists of the following:
(1) SS.DPL (the current privilege level); (2) RFLAGS.VM2; (3) the state of blocking by STI and by MOV SS (see
Table 24-3 in Section 24.4.2); (4) the state of virtual-NMI blocking (only if the processor is in VMX non-root operation and the “virtual NMIs” VM-execution control is 1); and (5) an indication of whether an MTF VM exit is pending
(see Section 25.5.2). These data may be saved internal to the processor or in the VMCS region of the current
VMCS. Processors that do not support SMI recognition while there is blocking by STI or by MOV SS need not save
the state of such blocking.
If the logical processor supports the 1-setting of the “enable EPT” VM-execution control and the logical processor
was in VMX non-root operation at the time of an SMI, it saves the value of that control into bit 0 of the 32-bit field
at offset SMBASE + 8000H + 7EE0H (SMBASE + FEE0H; see Table 34-3).3 If the logical processor was not in VMX
non-root operation at the time of the SMI, it saves 0 into that bit. If the logical processor saves 1 into that bit (it
was in VMX non-root operation and the “enable EPT” VM-execution control was 1), it saves the value of the EPT
pointer (EPTP) into the 64-bit field at offset SMBASE + 8000H + 7ED8H (SMBASE + FED8H).
Because SMI delivery causes a logical processor to leave VMX operation, all the controls associated with VMX nonroot operation are disabled in SMM and thus cannot cause VM exits while the logical processor in SMM.

34.14.2 Default Treatment of RSM
Ordinary execution of RSM restores processor state from SMRAM. Under the default treatment, processors that
support VMX operation perform RSM as follows:
IF VMXE = 1 in CR4 image in SMRAM
THEN fail and enter shutdown state;
ELSE
restore state normally from SMRAM;
invalidate linear mappings and combined mappings associated with all VPIDs and all PCIDs; combined mappings are invalidated
for all EP4TA values (EP4TA is the value of bits 51:12 of EPTP; see Section 28.3);
IF the logical processor supports SMX operation andthe Intel® TXT private space was unlocked at the time of the last SMI (as
saved)
THEN unlock the TXT private space;
FI;
CR4.VMXE ← value stored internally;
1. This causes the logical processor to block INIT signals, NMIs, and SMIs.
2. Section 34.14 and Section 34.15 use the notation RAX, RIP, RSP, RFLAGS, etc. for processor registers because most processors that
support VMX operation also support Intel 64 architecture. For processors that do not support Intel 64 architecture, this notation
refers to the 32-bit forms of these registers (EAX, EIP, ESP, EFLAGS, etc.). In a few places, notation such as EAX is used to refer specifically to the lower 32 bits of the register.
3. “Enable EPT” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution controls
is 0, SMI functions as the “enable EPT” VM-execution control were 0. See Section 24.6.2.
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IF internal storage indicates that the logical processor
had been in VMX operation (root or non-root)
THEN
enter VMX operation (root or non-root);
restore VMX-critical state as defined in Section 34.14.1;
set to their fixed values any bits in CR0 and CR4 whose values must be fixed in VMX operation (see Section 23.8);1
IF RFLAGS.VM = 0 AND (in VMX root operation OR the “unrestricted guest” VM-execution control is 0)2
THEN
CS.RPL ← SS.DPL;
SS.RPL ← SS.DPL;
FI;
restore current VMCS pointer;
FI;
leave SMM;
IF logical processor will be in VMX operation or in SMX operation after RSM
THEN block A20M and leave A20M mode;
FI;
FI;
RSM unblocks SMIs. It restores the state of blocking by NMI (see Table 24-3 in Section 24.4.2) as follows:

•

If the RSM is not to VMX non-root operation or if the “virtual NMIs” VM-execution control will be 0, the state of
NMI blocking is restored normally.

•

If the RSM is to VMX non-root operation and the “virtual NMIs” VM-execution control will be 1, NMIs are not
blocked after RSM. The state of virtual-NMI blocking is restored as part of VMX-critical state.

INIT signals are blocked after RSM if and only if the logical processor will be in VMX root operation.
If RSM returns a logical processor to VMX non-root operation, it re-establishes the controls associated with the
current VMCS. If the “interrupt-window exiting” VM-execution control is 1, a VM exit occurs immediately after RSM
if the enabling conditions apply. The same is true for the “NMI-window exiting” VM-execution control. Such
VM exits occur with their normal priority. See Section 25.2.
If an MTF VM exit was pending at the time of the previous SMI, an MTF VM exit is pending on the instruction
boundary following execution of RSM. The following items detail the treatment of MTF VM exits that may be
pending following RSM:

•

System-management interrupts (SMIs), INIT signals, and higher priority events take priority over these MTF
VM exits. These MTF VM exits take priority over debug-trap exceptions and lower priority events.

•

These MTF VM exits wake the logical processor if RSM caused the logical processor to enter the HLT state (see
Section 34.10). They do not occur if the logical processor just entered the shutdown state.

34.14.3 Protection of CR4.VMXE in SMM
Under the default treatment, CR4.VMXE is treated as a reserved bit while a logical processor is in SMM. Any
attempt by software running in SMM to set this bit causes a general-protection exception. In addition, software
cannot use VMX instructions or enter VMX operation while in SMM.

34.14.4 VMXOFF and SMI Unblocking
The VMXOFF instruction can be executed only with the default treatment (see Section 34.15.1) and only outside
SMM. If SMIs are blocked when VMXOFF is executed, VMXOFF unblocks them unless
1. If the RSM is to VMX non-root operation and both the “unrestricted guest” VM-execution control and bit 31 of the primary processor-based VM-execution controls will be 1, CR0.PE and CR0.PG retain the values that were loaded from SMRAM regardless of what is
reported in the capability MSR IA32_VMX_CR0_FIXED0.
2. “Unrestricted guest” is a secondary processor-based VM-execution control. If bit 31 of the primary processor-based VM-execution
controls is 0, VM entry functions as if the “unrestricted guest” VM-execution control were 0. See Section 24.6.2.
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SYSTEM MANAGEMENT MODE
IA32_SMM_MONITOR_CTL[bit 2] is 1 (see Section 34.15.5 for details regarding this MSR).1 Section 34.15.7 identifies a case in which SMIs may be blocked when VMXOFF is executed.
Not all processors allow this bit to be set to 1. Software should consult the VMX capability MSR IA32_VMX_MISC
(see Appendix A.6) to determine whether this is allowed.

34.15

DUAL-MONITOR TREATMENT OF SMIs AND SMM

Dual-monitor treatment is activated through the cooperation of the executive monitor (the VMM that operates
outside of SMM to provide basic virtualization) and the SMM-transfer monitor (STM; the VMM that operates
inside SMM—while in VMX operation—to support system-management functions). Control is transferred to the STM
through VM exits; VM entries are used to return from SMM.
The dual-monitor treatment may not be supported by all processors. Software should consult the VMX capability
MSR IA32_VMX_BASIC (see Appendix A.1) to determine whether it is supported.

34.15.1 Dual-Monitor Treatment Overview
The dual-monitor treatment uses an executive monitor and an SMM-transfer monitor (STM). Transitions from the
executive monitor or its guests to the STM are called SMM VM exits and are discussed in Section 34.15.2. SMM
VM exits are caused by SMIs as well as executions of VMCALL in VMX root operation. The latter allow the executive
monitor to call the STM for service.
The STM runs in VMX root operation and uses VMX instructions to establish a VMCS and perform VM entries to its
own guests. This is done all inside SMM (see Section 34.15.3). The STM returns from SMM, not by using the RSM
instruction, but by using a VM entry that returns from SMM. Such VM entries are described in Section 34.15.4.
Initially, there is no STM and the default treatment (Section 34.14) is used. The dual-monitor treatment is not used
until it is enabled and activated. The steps to do this are described in Section 34.15.5 and Section 34.15.6.
It is not possible to leave VMX operation under the dual-monitor treatment; VMXOFF will fail if executed. The dualmonitor treatment must be deactivated first. The STM deactivates dual-monitor treatment using a VM entry that
returns from SMM with the “deactivate dual-monitor treatment” VM-entry control set to 1 (see Section 34.15.7).
The executive monitor configures any VMCS that it uses for VM exits to the executive monitor. SMM VM exits, which
transfer control to the STM, use a different VMCS. Under the dual-monitor treatment, each logical processor uses
a separate VMCS called the SMM-transfer VMCS. When the dual-monitor treatment is active, the logical
processor maintains another VMCS pointer called the SMM-transfer VMCS pointer. The SMM-transfer VMCS
pointer is established when the dual-monitor treatment is activated.

34.15.2 SMM VM Exits
An SMM VM exit is a VM exit that begins outside SMM and that ends in SMM.
Unlike other VM exits, SMM VM exits can begin in VMX root operation. SMM VM exits result from the arrival of an
SMI outside SMM or from execution of VMCALL in VMX root operation outside SMM. Execution of VMCALL in VMX
root operation causes an SMM VM exit only if the valid bit is set in the IA32_SMM_MONITOR_CTL MSR (see Section
34.15.5).
Execution of VMCALL in VMX root operation causes an SMM VM exit even under the default treatment. This SMM
VM exit activates the dual-monitor treatment (see Section 34.15.6).
Differences between SMM VM exits and other VM exits are detailed in Sections 34.15.2.1 through 34.15.2.5.
Differences between SMM VM exits that activate the dual-monitor treatment and other SMM VM exits are described
in Section 34.15.6.

1. Setting IA32_SMM_MONITOR_CTL[bit 2] to 1 prevents VMXOFF from unblocking SMIs regardless of the value of the register’s valid
bit (bit 0).
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34.15.2.1 Architectural State Before a VM Exit
System-management interrupts (SMIs) that cause SMM VM exits always do so directly. They do not save state to
SMRAM as they do under the default treatment.

34.15.2.2 Updating the Current-VMCS and Executive-VMCS Pointers
SMM VM exits begin by performing the following steps:
1. The executive-VMCS pointer field in the SMM-transfer VMCS is loaded as follows:
— If the SMM VM exit commenced in VMX non-root operation, it receives the current-VMCS pointer.
— If the SMM VM exit commenced in VMX root operation, it receives the VMXON pointer.
2. The current-VMCS pointer is loaded with the value of the SMM-transfer VMCS pointer.
The last step ensures that the current VMCS is the SMM-transfer VMCS. VM-exit information is recorded in that
VMCS, and VM-entry control fields in that VMCS are updated. State is saved into the guest-state area of that VMCS.
The VM-exit controls and host-state area of that VMCS determine how the VM exit operates.

34.15.2.3 Recording VM-Exit Information
SMM VM exits differ from other VM exit with regard to the way they record VM-exit information. The differences
follow.

•

Exit reason.
— Bits 15:0 of this field contain the basic exit reason. The field is loaded with the reason for the SMM VM exit:
I/O SMI (an SMI arrived immediately after retirement of an I/O instruction), other SMI, or VMCALL. See
Appendix C, “VMX Basic Exit Reasons”.
— SMM VM exits are the only VM exits that may occur in VMX root operation. Because the SMM-transfer
monitor may need to know whether it was invoked from VMX root or VMX non-root operation, this
information is stored in bit 29 of the exit-reason field (see Table 24-14 in Section 24.9.1). The bit is set by
SMM VM exits from VMX root operation.
— If the SMM VM exit occurred in VMX non-root operation and an MTF VM exit was pending, bit 28 of the exitreason field is set; otherwise, it is cleared.
— Bits 27:16 and bits 31:30 are cleared.

•

Exit qualification. For an SMM VM exit due an SMI that arrives immediately after the retirement of an I/O
instruction, the exit qualification contains information about the I/O instruction that retired immediately before
the SMI. It has the format given in Table 34-9.

Table 34-9. Exit Qualification for SMIs That Arrive Immediately After the Retirement of an I/O Instruction
Bit Position(s)

Contents

2:0

Size of access:
0 = 1-byte
1 = 2-byte
3 = 4-byte
Other values not used.

3

Direction of the attempted access (0 = OUT, 1 = IN)

4

String instruction (0 = not string; 1 = string)

5

REP prefixed (0 = not REP; 1 = REP)

6

Operand encoding (0 = DX, 1 = immediate)

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Table 34-9. Exit Qualification for SMIs That Arrive Immediately After the Retirement of an I/O Instruction (Contd.)
Bit Position(s)

Contents

15:7

Reserved (cleared to 0)

31:16

Port number (as specified in the I/O instruction)

63:32

Reserved (cleared to 0). These bits exist only on processors
that support Intel 64 architecture.

•

Guest linear address. This field is used for VM exits due to SMIs that arrive immediately after the retirement
of an INS or OUTS instruction for which the relevant segment (ES for INS; DS for OUTS unless overridden by
an instruction prefix) is usable. The field receives the value of the linear address generated by ES:(E)DI (for
INS) or segment:(E)SI (for OUTS; the default segment is DS but can be overridden by a segment override
prefix) at the time the instruction started. If the relevant segment is not usable, the value is undefined. On
processors that support Intel 64 architecture, bits 63:32 are clear if the logical processor was not in 64-bit
mode before the VM exit.

•

I/O RCX, I/O RSI, I/O RDI, and I/O RIP. For an SMM VM exit due an SMI that arrives immediately after
the retirement of an I/O instruction, these fields receive the values that were in RCX, RSI, RDI, and RIP, respectively, before the I/O instruction executed. Thus, the value saved for I/O RIP addresses the I/O instruction.

34.15.2.4 Saving Guest State
SMM VM exits save the contents of the SMBASE register into the corresponding field in the guest-state area.
The value of the VMX-preemption timer is saved into the corresponding field in the guest-state area if the “save
VMX-preemption timer value” VM-exit control is 1. That field becomes undefined if, in addition, either the SMM
VM exit is from VMX root operation or the SMM VM exit is from VMX non-root operation and the “activate VMXpreemption timer” VM-execution control is 0.

34.15.2.5 Updating Non-Register State
SMM VM exits affect the non-register state of a logical processor as follows:

•

SMM VM exits cause non-maskable interrupts (NMIs) to be blocked; they may be unblocked through execution
of IRET or through a VM entry (depending on the value loaded for the interruptibility state and the setting of
the “virtual NMIs” VM-execution control).

•

SMM VM exits cause SMIs to be blocked; they may be unblocked by a VM entry that returns from SMM (see
Section 34.15.4).

SMM VM exits invalidate linear mappings and combined mappings associated with VPID 0000H for all PCIDs.
Combined mappings for VPID 0000H are invalidated for all EP4TA values (EP4TA is the value of bits 51:12 of EPTP;
see Section 28.3). (Ordinary VM exits are not required to perform such invalidation if the “enable VPID” VM-execution control is 1; see Section 27.5.5.)

34.15.3 Operation of the SMM-Transfer Monitor
Once invoked, the SMM-transfer monitor (STM) is in VMX root operation and can use VMX instructions to configure
VMCSs and to cause VM entries to virtual machines supported by those structures. As noted in Section 34.15.1, the
VMXOFF instruction cannot be used under the dual-monitor treatment and thus cannot be used by the STM.
The RSM instruction also cannot be used under the dual-monitor treatment. As noted in Section 25.1.3, it causes
a VM exit if executed in SMM in VMX non-root operation. If executed in VMX root operation, it causes an invalidopcode exception. The STM uses VM entries to return from SMM (see Section 34.15.4).

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34.15.4 VM Entries that Return from SMM
The SMM-transfer monitor (STM) returns from SMM using a VM entry with the “entry to SMM” VM-entry control
clear. VM entries that return from SMM reverse the effects of an SMM VM exit (see Section 34.15.2).
VM entries that return from SMM may differ from other VM entries in that they do not necessarily enter VMX nonroot operation. If the executive-VMCS pointer field in the current VMCS contains the VMXON pointer, the logical
processor remains in VMX root operation after VM entry.
For differences between VM entries that return from SMM and other VM entries see Sections 34.15.4.1 through
34.15.4.10.

34.15.4.1 Checks on the Executive-VMCS Pointer Field
VM entries that return from SMM perform the following checks on the executive-VMCS pointer field in the current
VMCS:

•
•
•

Bits 11:0 must be 0.
The pointer must not set any bits beyond the processor’s physical-address width.1,2
The 32 bits located in memory referenced by the physical address in the pointer must contain the processor’s
VMCS revision identifier (see Section 24.2).

The checks above are performed before the checks described in Section 34.15.4.2 and before any of the following
checks:

•

'If the “deactivate dual-monitor treatment” VM-entry control is 0 and the executive-VMCS pointer field does not
contain the VMXON pointer, the launch state of the executive VMCS (the VMCS referenced by the executiveVMCS pointer field) must be launched (see Section 24.11.3).

•

If the “deactivate dual-monitor treatment” VM-entry control is 1, the executive-VMCS pointer field must
contain the VMXON pointer (see Section 34.15.7).3

34.15.4.2 Checks on VM-Execution Control Fields
VM entries that return from SMM differ from other VM entries with regard to the checks performed on the VMexecution control fields specified in Section 26.2.1.1. They do not apply the checks to the current VMCS. Instead,
VM-entry behavior depends on whether the executive-VMCS pointer field contains the VMXON pointer:

•

If the executive-VMCS pointer field contains the VMXON pointer (the VM entry remains in VMX root operation),
the checks are not performed at all.

•

If the executive-VMCS pointer field does not contain the VMXON pointer (the VM entry enters VMX non-root
operation), the checks are performed on the VM-execution control fields in the executive VMCS (the VMCS
referenced by the executive-VMCS pointer field in the current VMCS). These checks are performed after
checking the executive-VMCS pointer field itself (for proper alignment).

Other VM entries ensure that, if “activate VMX-preemption timer” VM-execution control is 0, the “save VMXpreemption timer value” VM-exit control is also 0. This check is not performed by VM entries that return from SMM.

34.15.4.3 Checks on VM-Entry Control Fields
VM entries that return from SMM differ from other VM entries with regard to the checks performed on the VM-entry
control fields specified in Section 26.2.1.3.

1. Software can determine a processor’s physical-address width by executing CPUID with 80000008H in EAX. The physical-address
width is returned in bits 7:0 of EAX.
2. If IA32_VMX_BASIC[48] is read as 1, this pointer must not set any bits in the range 63:32; see Appendix A.1.
3. The STM can determine the VMXON pointer by reading the executive-VMCS pointer field in the current VMCS after the SMM VM exit
that activates the dual-monitor treatment.
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Specifically, if the executive-VMCS pointer field contains the VMXON pointer (the VM entry remains in VMX root
operation), the VM-entry interruption-information field must not indicate injection of a pending MTF VM exit (see
Section 26.5.2). Specifically, the following cannot all be true for that field:

•
•
•

the valid bit (bit 31) is 1
the interruption type (bits 10:8) is 7 (other event); and
the vector (bits 7:0) is 0 (pending MTF VM exit).

34.15.4.4 Checks on the Guest State Area
Section 26.3.1 specifies checks performed on fields in the guest-state area of the VMCS. Some of these checks are
conditioned on the settings of certain VM-execution controls (e.g., “virtual NMIs” or “unrestricted guest”).
VM entries that return from SMM modify these checks based on whether the executive-VMCS pointer field contains
the VMXON pointer:1

•

If the executive-VMCS pointer field contains the VMXON pointer (the VM entry remains in VMX root operation),
the checks are performed as all relevant VM-execution controls were 0. (As a result, some checks may not be
performed at all.)

•

If the executive-VMCS pointer field does not contain the VMXON pointer (the VM entry enters VMX non-root
operation), this check is performed based on the settings of the VM-execution controls in the executive VMCS
(the VMCS referenced by the executive-VMCS pointer field in the current VMCS).

For VM entries that return from SMM, the activity-state field must not indicate the wait-for-SIPI state if the executive-VMCS pointer field contains the VMXON pointer (the VM entry is to VMX root operation).

34.15.4.5 Loading Guest State
VM entries that return from SMM load the SMBASE register from the SMBASE field.
VM entries that return from SMM invalidate linear mappings and combined mappings associated with all VPIDs.
Combined mappings are invalidated for all EP4TA values (EP4TA is the value of bits 51:12 of EPTP; see Section
28.3). (Ordinary VM entries are required to perform such invalidation only for VPID 0000H and are not required to
do even that if the “enable VPID” VM-execution control is 1; see Section 26.3.2.5.)

34.15.4.6 VMX-Preemption Timer
A VM entry that returns from SMM activates the VMX-preemption timer only if the executive-VMCS pointer field
does not contain the VMXON pointer (the VM entry enters VMX non-root operation) and the “activate VMX-preemption timer” VM-execution control is 1 in the executive VMCS (the VMCS referenced by the executive-VMCS pointer
field). In this case, VM entry starts the VMX-preemption timer with the value in the VMX-preemption timer-value
field in the current VMCS.

34.15.4.7 Updating the Current-VMCS and SMM-Transfer VMCS Pointers
Successful VM entries (returning from SMM) load the SMM-transfer VMCS pointer with the current-VMCS pointer.
Following this, they load the current-VMCS pointer from a field in the current VMCS:

•

If the executive-VMCS pointer field contains the VMXON pointer (the VM entry remains in VMX root operation),
the current-VMCS pointer is loaded from the VMCS-link pointer field.

•

If the executive-VMCS pointer field does not contain the VMXON pointer (the VM entry enters VMX non-root
operation), the current-VMCS pointer is loaded with the value of the executive-VMCS pointer field.

If the VM entry successfully enters VMX non-root operation, the VM-execution controls in effect after the VM entry
are those from the new current VMCS. This includes any structures external to the VMCS referenced by VM-execution control fields.

1. The STM can determine the VMXON pointer by reading the executive-VMCS pointer field in the current VMCS after the SMM VM exit
that activates the dual-monitor treatment.
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The updating of these VMCS pointers occurs before event injection. Event injection is determined, however, by the
VM-entry control fields in the VMCS that was current when the VM entry commenced.

34.15.4.8 VM Exits Induced by VM Entry
Section 26.5.1.2 describes how the event-delivery process invoked by event injection may lead to a VM exit.
Section 26.6.3 to Section 26.6.7 describe other situations that may cause a VM exit to occur immediately after a
VM entry.
Whether these VM exits occur is determined by the VM-execution control fields in the current VMCS. For VM entries
that return from SMM, they can occur only if the executive-VMCS pointer field does not contain the VMXON pointer
(the VM entry enters VMX non-root operation).
In this case, determination is based on the VM-execution control fields in the VMCS that is current after the
VM entry. This is the VMCS referenced by the value of the executive-VMCS pointer field at the time of the VM entry
(see Section 34.15.4.7). This VMCS also controls the delivery of such VM exits. Thus, VM exits induced by a
VM entry returning from SMM are to the executive monitor and not to the STM.

34.15.4.9 SMI Blocking
VM entries that return from SMM determine the blocking of system-management interrupts (SMIs) as follows:

•

If the “deactivate dual-monitor treatment” VM-entry control is 0, SMIs are blocked after VM entry if and only if
the bit 2 in the interruptibility-state field is 1.

•

If the “deactivate dual-monitor treatment” VM-entry control is 1, the blocking of SMIs depends on whether the
logical processor is in SMX operation:1
— If the logical processor is in SMX operation, SMIs are blocked after VM entry.
— If the logical processor is outside SMX operation, SMIs are unblocked after VM entry.

VM entries that return from SMM and that do not deactivate the dual-monitor treatment may leave SMIs blocked.
This feature exists to allow the STM to invoke functionality outside of SMM without unblocking SMIs.

34.15.4.10 Failures of VM Entries That Return from SMM
Section 26.7 describes the treatment of VM entries that fail during or after loading guest state. Such failures record
information in the VM-exit information fields and load processor state as would be done on a VM exit. The VMCS
used is the one that was current before the VM entry commenced. Control is thus transferred to the STM and the
logical processor remains in SMM.

34.15.5 Enabling the Dual-Monitor Treatment
Code and data for the SMM-transfer monitor (STM) reside in a region of SMRAM called the monitor segment
(MSEG). Code running in SMM determines the location of MSEG and establishes its content. This code is also
responsible for enabling the dual-monitor treatment.
SMM code enables the dual-monitor treatment and specifies the location of MSEG by writing to the
IA32_SMM_MONITOR_CTL MSR (index 9BH). The MSR has the following format:

•

Bit 0 is the register’s valid bit. The STM may be invoked using VMCALL only if this bit is 1. Because VMCALL is
used to activate the dual-monitor treatment (see Section 34.15.6), the dual-monitor treatment cannot be
activated if the bit is 0. This bit is cleared when the logical processor is reset.

•

Bit 1 is reserved.

1. A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last execution of GETSEC[SENTER]. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the last
execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference‚” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2D.
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•

Bit 2 determines whether executions of VMXOFF unblock SMIs under the default treatment of SMIs and SMM.
Executions of VMXOFF unblock SMIs unless bit 2 is 1 (the value of bit 0 is irrelevant). See Section 34.14.4.
Certain leaf functions of the GETSEC instruction clear this bit (see Chapter 6, “Safer Mode Extensions
Reference,” in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2D).

•
•

Bits 11:3 are reserved.

•

Bits 63:32 are reserved.

Bits 31:12 contain a value that, when shifted left 12 bits, is the physical address of MSEG (the MSEG base
address).

The following items detail use of this MSR:

•

The IA32_SMM_MONITOR_CTL MSR is supported only on processors that support the dual-monitor treatment.1
On other processors, accesses to the MSR using RDMSR or WRMSR generate a general-protection fault
(#GP(0)).

•

A write to the IA32_SMM_MONITOR_CTL MSR using WRMSR generates a general-protection fault (#GP(0)) if
executed outside of SMM or if an attempt is made to set any reserved bit. An attempt to write to the
IA32_SMM_MONITOR_CTL MSR fails if made as part of a VM exit that does not end in SMM or part of a
VM entry that does not begin in SMM.

•

Reads from the IA32_SMM_MONITOR_CTL MSR using RDMSR are allowed any time RDMSR is allowed. The
MSR may be read as part of any VM exit.

•

The dual-monitor treatment can be activated only if the valid bit in the MSR is set to 1.

The 32 bytes located at the MSEG base address are called the MSEG header. The format of the MSEG header is
given in Table 34-10 (each field is 32 bits).

Table 34-10. Format of MSEG Header
Byte Offset

Field

0

MSEG-header revision identifier

4

SMM-transfer monitor features

8

GDTR limit

12

GDTR base offset

16

CS selector

20

EIP offset

24

ESP offset

28

CR3 offset

To ensure proper behavior in VMX operation, software should maintain the MSEG header in writeback cacheable
memory. Future implementations may allow or require a different memory type.2 Software should consult the VMX
capability MSR IA32_VMX_BASIC (see Appendix A.1).
SMM code should enable the dual-monitor treatment (by setting the valid bit in IA32_SMM_MONITOR_CTL MSR)
only after establishing the content of the MSEG header as follows:

1. Software should consult the VMX capability MSR IA32_VMX_BASIC (see Appendix A.1) to determine whether the dual-monitor
treatment is supported.
2. Alternatively, software may map the MSEG header with the UC memory type; this may be necessary, depending on how memory is
organized. Doing so is strongly discouraged unless necessary as it will cause the performance of transitions using those structures
to suffer significantly. In addition, the processor will continue to use the memory type reported in the VMX capability MSR
IA32_VMX_BASIC with exceptions noted in Appendix A.1.
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•

Bytes 3:0 contain the MSEG revision identifier. Different processors may use different MSEG revision identifiers. These identifiers enable software to avoid using an MSEG header formatted for one processor on a
processor that uses a different format. Software can discover the MSEG revision identifier that a processor uses
by reading the VMX capability MSR IA32_VMX_MISC (see Appendix A.6).

•

Bytes 7:4 contain the SMM-transfer monitor features field. Bits 31:1 of this field are reserved and must be
zero. Bit 0 of the field is the IA-32e mode SMM feature bit. It indicates whether the logical processor will be
in IA-32e mode after the STM is activated (see Section 34.15.6).

•

Bytes 31:8 contain fields that determine how processor state is loaded when the STM is activated (see Section
34.15.6.5). SMM code should establish these fields so that activating of the STM invokes the STM’s initialization
code.

34.15.6 Activating the Dual-Monitor Treatment
The dual-monitor treatment may be enabled by SMM code as described in Section 34.15.5. The dual-monitor treatment is activated only if it is enabled and only by the executive monitor. The executive monitor activates the dualmonitor treatment by executing VMCALL in VMX root operation.
When VMCALL activates the dual-monitor treatment, it causes an SMM VM exit. Differences between this SMM
VM exit and other SMM VM exits are discussed in Sections 34.15.6.1 through 34.15.6.6. See also “VMCALL—Call to
VM Monitor” in Chapter 30.

34.15.6.1 Initial Checks
An execution of VMCALL attempts to activate the dual-monitor treatment if (1) the processor supports the dualmonitor treatment;1 (2) the logical processor is in VMX root operation; (3) the logical processor is outside SMM and
the valid bit is set in the IA32_SMM_MONITOR_CTL MSR; (4) the logical processor is not in virtual-8086 mode and
not in compatibility mode; (5) CPL = 0; and (6) the dual-monitor treatment is not active.
Such an execution of VMCALL begins with some initial checks. These checks are performed before updating the
current-VMCS pointer and the executive-VMCS pointer field (see Section 34.15.2.2).
The VMCS that manages SMM VM exit caused by this VMCALL is the current VMCS established by the executive
monitor. The VMCALL performs the following checks on the current VMCS in the order indicated:
1. There must be a current VMCS pointer.
2. The launch state of the current VMCS must be clear.
3. Reserved bits in the VM-exit controls in the current VMCS must be set properly. Software may consult the VMX
capability MSR IA32_VMX_EXIT_CTLS to determine the proper settings (see Appendix A.4).
If any of these checks fail, subsequent checks are skipped and VMCALL fails. If all these checks succeed, the logical
processor uses the IA32_SMM_MONITOR_CTL MSR to determine the base address of MSEG. The following checks
are performed in the order indicated:
1. The logical processor reads the 32 bits at the base of MSEG and compares them to the processor’s MSEG
revision identifier.
2. The logical processor reads the SMM-transfer monitor features field:
— Bit 0 of the field is the IA-32e mode SMM feature bit, and it indicates whether the logical processor will be
in IA-32e mode after the SMM-transfer monitor (STM) is activated.

•

If the VMCALL is executed on a processor that does not support Intel 64 architecture, the IA-32e mode
SMM feature bit must be 0.

•

If the VMCALL is executed in 64-bit mode, the IA-32e mode SMM feature bit must be 1.

— Bits 31:1 of this field are currently reserved and must be zero.
If any of these checks fail, subsequent checks are skipped and the VMCALL fails.
1. Software should consult the VMX capability MSR IA32_VMX_BASIC (see Appendix A.1) to determine whether the dual-monitor
treatment is supported.
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34.15.6.2 Updating the Current-VMCS and Executive-VMCS Pointers
Before performing the steps in Section 34.15.2.2, SMM VM exits that activate the dual-monitor treatment begin by
loading the SMM-transfer VMCS pointer with the value of the current-VMCS pointer.

34.15.6.3 Saving Guest State
As noted in Section 34.15.2.4, SMM VM exits save the contents of the SMBASE register into the corresponding field
in the guest-state area. While this is true also for SMM VM exits that activate the dual-monitor treatment, the
VMCS used for those VM exits exists outside SMRAM.
The SMM-transfer monitor (STM) can also discover the current value of the SMBASE register by using the RDMSR
instruction to read the IA32_SMBASE MSR (MSR address 9EH). The following items detail use of this MSR:

•
•

The MSR is supported only if IA32_VMX_MISC[15] = 1 (see Appendix A.6).

•

A read from the IA32_SMBASE MSR using RDMSR generates a general-protection fault (#GP(0)) if executed
outside of SMM. An attempt to read from the IA32_SMBASE MSR fails if made as part of a VM exit that does not
end in SMM.

A write to the IA32_SMBASE MSR using WRMSR generates a general-protection fault (#GP(0)). An attempt to
write to the IA32_SMBASE MSR fails if made as part of a VM exit or part of a VM entry.

34.15.6.4 Saving MSRs
The VM-exit MSR-store area is not used by SMM VM exits that activate the dual-monitor treatment. No MSRs are
saved into that area.

34.15.6.5 Loading Host State
The VMCS that is current during an SMM VM exit that activates the dual-monitor treatment was established by the
executive monitor. It does not contain the VM-exit controls and host state required to initialize the STM. For this
reason, such SMM VM exits do not load processor state as described in Section 27.5. Instead, state is set to fixed
values or loaded based on the content of the MSEG header (see Table 34-10):

•

CR0 is set to as follows:
— PG, NE, ET, MP, and PE are all set to 1.
— CD and NW are left unchanged.
— All other bits are cleared to 0.

•

CR3 is set as follows:
— Bits 63:32 are cleared on processors that support IA-32e mode.
— Bits 31:12 are set to bits 31:12 of the sum of the MSEG base address and the CR3-offset field in the MSEG
header.
— Bits 11:5 and bits 2:0 are cleared (the corresponding bits in the CR3-offset field in the MSEG header are
ignored).
— Bits 4:3 are set to bits 4:3 of the CR3-offset field in the MSEG header.

•

CR4 is set as follows:
— MCE, PGE, and PCIDE are cleared.
— PAE is set to the value of the IA-32e mode SMM feature bit.
— If the IA-32e mode SMM feature bit is clear, PSE is set to 1 if supported by the processor; if the bit is set,
PSE is cleared.
— All other bits are unchanged.

•
•

DR7 is set to 400H.
The IA32_DEBUGCTL MSR is cleared to 00000000_00000000H.

Vol. 3C 34-27

SYSTEM MANAGEMENT MODE

•

The registers CS, SS, DS, ES, FS, and GS are loaded as follows:
— All registers are usable.
— CS.selector is loaded from the corresponding field in the MSEG header (the high 16 bits are ignored), with
bits 2:0 cleared to 0. If the result is 0000H, CS.selector is set to 0008H.
— The selectors for SS, DS, ES, FS, and GS are set to CS.selector+0008H. If the result is 0000H (if the CS
selector was FFF8H), these selectors are instead set to 0008H.
— The base addresses of all registers are cleared to zero.
— The segment limits for all registers are set to FFFFFFFFH.
— The AR bytes for the registers are set as follows:

•
•
•
•
•
•
•
•
•

CS.Type is set to 11 (execute/read, accessed, non-conforming code segment).
For SS, DS, ES, FS, and GS, the Type is set to 3 (read/write, accessed, expand-up data segment).
The S bits for all registers are set to 1.
The DPL for each register is set to 0.
The P bits for all registers are set to 1.
On processors that support Intel 64 architecture, CS.L is loaded with the value of the IA-32e mode SMM
feature bit.
CS.D is loaded with the inverse of the value of the IA-32e mode SMM feature bit.
For each of SS, DS, ES, FS, and GS, the D/B bit is set to 1.
The G bits for all registers are set to 1.

•

LDTR is unusable. The LDTR selector is cleared to 0000H, and the register is otherwise undefined (although the
base address is always canonical)

•

GDTR.base is set to the sum of the MSEG base address and the GDTR base-offset field in the MSEG header
(bits 63:32 are always cleared on processors that support IA-32e mode). GDTR.limit is set to the corresponding
field in the MSEG header (the high 16 bits are ignored).

•
•

IDTR.base is unchanged. IDTR.limit is cleared to 0000H.

•

RSP is set to the sum of the MSEG base address and the value of the RSP-offset field in the MSEG header
(bits 63:32 are always cleared on logical processor that supports IA-32e mode).

•
•
•

RFLAGS is cleared, except bit 1, which is always set.

RIP is set to the sum of the MSEG base address and the value of the RIP-offset field in the MSEG header
(bits 63:32 are always cleared on logical processors that support IA-32e mode).

The logical processor is left in the active state.
Event blocking after the SMM VM exit is as follows:
— There is no blocking by STI or by MOV SS.
— There is blocking by non-maskable interrupts (NMIs) and by SMIs.

•
•

There are no pending debug exceptions after the SMM VM exit.
For processors that support IA-32e mode, the IA32_EFER MSR is modified so that LME and LMA both contain
the value of the IA-32e mode SMM feature bit.

If any of CR3[63:5], CR4.PAE, CR4.PSE, or IA32_EFER.LMA is changing, the TLBs are updated so that, after
VM exit, the logical processor does not use translations that were cached before the transition. This is not necessary for changes that would not affect paging due to the settings of other bits (for example, changes to CR4.PSE if
IA32_EFER.LMA was 1 before and after the transition).

34.15.6.6 Loading MSRs
The VM-exit MSR-load area is not used by SMM VM exits that activate the dual-monitor treatment. No MSRs are
loaded from that area.

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SYSTEM MANAGEMENT MODE

34.15.7 Deactivating the Dual-Monitor Treatment
The SMM-transfer monitor may deactivate the dual-monitor treatment and return the processor to default treatment of SMIs and SMM (see Section 34.14). It does this by executing a VM entry with the “deactivate dual-monitor
treatment” VM-entry control set to 1.
As noted in Section 26.2.1.3 and Section 34.15.4.1, an attempt to deactivate the dual-monitor treatment fails in
the following situations: (1) the processor is not in SMM; (2) the “entry to SMM” VM-entry control is 1; or (3) the
executive-VMCS pointer does not contain the VMXON pointer (the VM entry is to VMX non-root operation).
As noted in Section 34.15.4.9, VM entries that deactivate the dual-monitor treatment ignore the SMI bit in the
interruptibility-state field of the guest-state area. Instead, the blocking of SMIs following such a VM entry depends
on whether the logical processor is in SMX operation:1

•

If the logical processor is in SMX operation, SMIs are blocked after VM entry. SMIs may later be unblocked by
the VMXOFF instruction (see Section 34.14.4) or by certain leaf functions of the GETSEC instruction (see
Chapter 6, “Safer Mode Extensions Reference,” in Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 2D).

•

If the logical processor is outside SMX operation, SMIs are unblocked after VM entry.

34.16

SMI AND PROCESSOR EXTENDED STATE MANAGEMENT

On processors that support processor extended states using XSAVE/XRSTOR (see Chapter 13, “Managing State
Using the XSAVE Feature Set” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1),
the processor does not save any XSAVE/XRSTOR related state on an SMI. It is the responsibility of the SMI handler
code to properly preserve the state information (including CR4.OSXSAVE, XCR0, and possibly processor extended
states using XSAVE/XRSTOR). Therefore, the SMI handler must follow the rules described in Chapter 13,
“Managing State Using the XSAVE Feature Set” of the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 1.

34.17

MODEL-SPECIFIC SYSTEM MANAGEMENT ENHANCEMENT

This section describes enhancement of system management features that apply only to the 4th generation Intel
Core processors. These features are model-specific. BIOS and SMM handler must use CPUID to enumerate
DisplayFamily_DisplayModel signature when programming with these interfaces.

34.17.1

SMM Handler Code Access Control

The BIOS may choose to restrict the address ranges of code that SMM handler executes. When SMM handler code
execution check is enabled, an attempt by the SMM handler to execute outside the ranges specified by SMRR (see
Section 34.4.2.1) will cause the assertion of an unrecoverable machine check exception (MCE).
The interface to enable SMM handler code access check resides in a per-package scope model-specific register
MSR_SMM_FEATURE_CONTROL at address 4E0H. An attempt to access MSR_SMM_FEATURE_CONTROL outside of
SMM will cause a #GP. Writes to MSR_SMM_FEATURE_CONTROL is further protected by configuration interface of
MSR_SMM_MCA_CAP at address 17DH.
Details of the interface of MSR_SMM_FEATURE_CONTROL and MSR_SMM_MCA_CAP are described in Table 2-28 in
Chapter 2, “Model-Specific Registers (MSRs)” of the Intel® 64 and IA-32 Architectures Software Developer’s
Manual, Volume 4.

1. A logical processor is in SMX operation if GETSEC[SEXIT] has not been executed since the last execution of GETSEC[SENTER]. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the last
execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference,” in Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 2B.
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SYSTEM MANAGEMENT MODE

34.17.2

SMI Delivery Delay Reporting

Entry into the system management mode occurs at instruction boundary. In situations where a logical processor is
executing an instruction involving a long flow of internal operations, servicing an SMI by that logical processor will
be delayed. Delayed servicing of SMI of each logical processor due to executing long flows of internal operation in
a physical processor can be queried via a package-scope register MSR_SMM_DELAYED at address 4E2H.
The interface to enable reporting of SMI delivery delay due to long internal flows resides in a per-package scope
model-specific register MSR_SMM_DELAYED. An attempt to access MSR_SMM_DELAYED outside of SMM will cause
a #GP. Availability to MSR_SMM_DELAYED is protected by configuration interface of MSR_SMM_MCA_CAP at
address 17DH.
Details of the interface of MSR_SMM_DELAYED and MSR_SMM_MCA_CAP are described in Table 2-28 in Chapter 2,
“Model-Specific Registers (MSRs)” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
4.

34.17.3

Blocked SMI Reporting

A logical processor may have entered into a state and blocked from servicing other interrupts (including SMI).
Logical processors in a physical processor that are blocked in serving SMI can be queried in a package-scope
register MSR_SMM_BLOCKED at address 4E3H. An attempt to access MSR_SMM_BLOCKED outside of SMM will
cause a #GP.
Details of the interface of MSR_SMM_BLOCKED is described in Table 2-28 in Chapter 2, “Model-Specific Registers
(MSRs)” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 4.

34-30 Vol. 3C

INTEL® PROCESSOR TRACE

CHAPTER 35
INTEL® PROCESSOR TRACE
35.1

OVERVIEW

®

Intel Processor Trace (Intel PT) is an extension of Intel® Architecture that captures information about software
execution using dedicated hardware facilities that cause only minimal performance perturbation to the software
being traced. This information is collected in data packets. The initial implementations of Intel PT offer control
flow tracing, which generates a variety of packets to be processed by a software decoder. The packets include
timing, program flow information (e.g. branch targets, branch taken/not taken indications) and program-induced
mode related information (e.g. Intel TSX state transitions, CR3 changes). These packets may be buffered internally
before being sent to the memory subsystem or other output mechanism available in the platform. Debug software
can process the trace data and reconstruct the program flow.
Later generations include additional trace sources, including software trace instrumentation using PTWRITE, and
Power Event tracing.

35.1.1

Features and Capabilities

Intel PT’s control flow trace generates a variety of packets that, when combined with the binaries of a program by
a post-processing tool, can be used to produce an exact execution trace. The packets record flow information such
as instruction pointers (IP), indirect branch targets, and directions of conditional branches within contiguous code
regions (basic blocks).
Intel PT can also be configured to log software-generated packets using PTWRITE, and packets describing
processor power management events.
In addition, the packets record other contextual, timing, and bookkeeping information that enables both functional
and performance debugging of applications. Intel PT has several control and filtering capabilities available to
customize the tracing information collected and to append other processor state and timing information to enable
debugging. For example, there are modes that allow packets to be filtered based on the current privilege level
(CPL) or the value of CR3.
Configuration of the packet generation and filtering capabilities are programmed via a set of MSRs. The MSRs
generally follow the naming convention of IA32_RTIT_*. The capability provided by these configuration MSRs are
enumerated by CPUID, see Section 35.3. Details of the MSRs for configuring Intel PT are described in Section
35.2.7.

35.1.1.1

Packet Summary

After a tracing tool has enabled and configured the appropriate MSRs, the processor will collect and generate trace
information in the following categories of packets (for more details on the packets, see Section 35.4):

•

Packets about basic information on program execution: These include:
— Packet Stream Boundary (PSB) packets: PSB packets act as ‘heartbeats’ that are generated at regular
intervals (e.g., every 4K trace packet bytes). These packets allow the packet decoder to find the packet
boundaries within the output data stream; a PSB packet should be the first packet that a decoder looks for
when beginning to decode a trace.
— Paging Information Packet (PIP): PIPs record modifications made to the CR3 register. This information,
along with information from the operating system on the CR3 value of each process, allows the debugger
to attribute linear addresses to their correct application source.
— Time-Stamp Counter (TSC) packets: TSC packets aid in tracking wall-clock time, and contain some portion
of the software-visible time-stamp counter.
— Core Bus Ratio (CBR) packets: CBR packets contain the core:bus clock ratio.

Vol. 3C 35-1

INTEL® PROCESSOR TRACE

— Overflow (OVF) packets: OVF packets are sent when the processor experiences an internal buffer overflow,
resulting in packets being dropped. This packet notifies the decoder of the loss and can help the decoder to
respond to this situation.

•

Packets about control flow information:
— Taken Not-Taken (TNT) packets: TNT packets track the “direction” of direct conditional branches (taken or
not taken).
— Target IP (TIP) packets: TIP packets record the target IP of indirect branches, exceptions, interrupts, and
other branches or events. These packets can contain the IP, although that IP value may be compressed by
eliminating upper bytes that match the last IP. There are various types of TIP packets; they are covered in
more detail in Section 35.4.2.2.
— Flow Update Packets (FUP): FUPs provide the source IP addresses for asynchronous events (interrupt and
exceptions), as well as other cases where the source address cannot be determined from the binary.
— MODE packets: These packets provide the decoder with important processor execution information so that
it can properly interpret the dis-assembled binary and trace log. MODE packets have a variety of formats
that indicate details such as the execution mode (16-bit, 32-bit, or 64-bit).

•

Packets inserted by software:
— PTWRITE (PTW) packets: includes the value of the operand passed to the PTWRITE instruction (see
“PTWRITE - Write Data to a Processor Trace Packet” in Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volume 2B).

•

Packets about processor power management events:
— MWAIT packets: Indicate successful completion of an MWAIT operation to a C-state deeper than C0.0.
— Power State Entry (PWRE) packets: Indicate entry to a C-state deeper than C0.0.
— Power State Exit (PWRX) packets: Indicate exit from a C-state deeper than C0.0, returning to C0.
— Execution Stopped (EXSTOP) packets: Indicate that software execution has stopped, due to events such as
P-state change, C-state change, or thermal throttling.

35.2

INTEL® PROCESSOR TRACE OPERATIONAL MODEL

This section describes the overall Intel Processor Trace mechanism and the essential concepts relevant to how it
operates.

35.2.1

Change of Flow Instruction (COFI) Tracing

A basic program block is a section of code where no jumps or branches occur. The instruction pointers (IPs) in this
block of code need not be traced, as the processor will execute them from start to end without redirecting code
flow. Instructions such as branches, and events such as exceptions or interrupts, can change the program flow.
These instructions and events that change program flow are called Change of Flow Instructions (COFI). There are
three categories of COFI:

•
•
•

Direct transfer COFI.
Indirect transfer COFI.
Far transfer COFI.

The following subsections describe the COFI events that result in trace packet generation. Table 35-1 lists branch
instruction by COFI types. For detailed description of specific instructions, see Intel® 64 and IA-32 Architectures
Software Developer’s Manual.

Table 35-1. COFI Type for Branch Instructions
COFI Type
Conditional Branch

35-2 Vol. 3C

Instructions
JA, JAE, JB, JBE, JC, JCXZ< JECXZ, JRCXZ, JE, JG, JGE, JL, JLE, JNA, JNAE, JNB, JNBE, JNC, JNE, JNG, JNGE,
JNL, JNLE, JNO, JNP, JNS, JNZ, JO, JP, JPE, JPO, JS, JZ, LOOP, LOOPE, LOOPNE, LOOPNZ, LOOPZ

INTEL® PROCESSOR TRACE

Table 35-1. COFI Type for Branch Instructions
COFI Type
Unconditional Direct Branch

Instructions
JMP (E9 xx, EB xx), CALL (E8 xx)

Indirect Branch

JMP (FF /4), CALL (FF /2)

Near Ret

RET (C3, C2 xx)

Far Transfers

INT3, INTn, INTO, IRET, IRETD, IRETQ, JMP (EA xx, FF /5), CALL (9A xx, FF /3), RET (CB, CA xx), SYSCALL, SYSRET, SYSENTER, SYSEXIT, VMLAUNCH, VMRESUME

35.2.1.1

Direct Transfer COFI

Direct Transfer COFI are relative branches. This means that their target is an IP whose offset from the current IP is
embedded in the instruction bytes. It is not necessary to indicate target of these instructions in the trace output
since it can be obtained through the source disassembly. Conditional branches need to indicate only whether the
branch is taken or not. Unconditional branches do not need any recording in the trace output. There are two subcategories:

•

Conditional Branch (Jcc, J*CXZ) and LOOP
To track this type of instruction, the processor encodes a single bit (taken or not taken — TNT) to indicate the
program flow after the instruction.
Jcc, J*CXZ, and LOOP can be traced with TNT bits. To improve the trace packet output efficiency, the processor
will compact several TNT bits into a single packet.

•

Unconditional Direct Jumps
There is no trace output required for direct unconditional jumps (like JMP near relative or CALL near relative)
since they can be directly inferred from the application assembly. Direct unconditional jumps do not generate a
TNT bit or a Target IP packet, though TIP.PGD and TIP.PGE packets can be generated by unconditional direct
jumps that toggle Intel PT enables (see Section 35.2.5).

35.2.1.2

Indirect Transfer COFI

Indirect transfer instructions involve updating the IP from a register or memory location. Since the register or
memory contents can vary at any time during execution, there is no way to know the target of the indirect transfer
until the register or memory contents are read. As a result, the disassembled code is not sufficient to determine the
target of this type of COFI. Therefore, tracing hardware must send out the destination IP in the trace packet for
debug software to determine the target address of the COFI. Note that this IP may be a linear or effective address
(see Section 35.3.1.1).
An indirect transfer instruction generates a Target IP Packet (TIP) that contains the target address of the branch.
There are two sub-categories:

•

Near JMP Indirect and Near Call Indirect
As previously mentioned, the target of an indirect COFI resides in the contents of either a register or memory
location. Therefore, the processor must generate a packet that includes this target address to allow the
decoder to determine the program flow.

•

Near RET
When a CALL instruction executes, it pushes onto the stack the address of the next instruction following the
CALL. Upon completion of the call procedure, the RET instruction is often used to pop the return address off of
the call stack and redirect code flow back to the instruction following the CALL.
A RET instruction simply transfers program flow to the address it popped off the stack. Because a called
procedure may change the return address on the stack before executing the RET instruction, debug software
can be misled if it assumes that code flow will return to the instruction following the last CALL. Therefore,
even for near RET, a Target IP Packet may be sent.
— RET Compression
A special case is applied if the target of the RET is consistent with what would be expected from tracking the
CALL stack. If it is assured that the decoder has seen the corresponding CALL (with “corresponding” defined
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INTEL® PROCESSOR TRACE

as the CALL with matching stack depth), and the RET target is the instruction after that CALL, the RET
target may be “compressed”. In this case, only a single TNT bit of “taken” is generated instead of a Target
IP Packet. To ensure that the decoder will not be confused in cases of RET compression, only RETs that
correspond to CALLs which have been seen since the last PSB packet may be compressed in a given logical
processor. For details, see “Indirect Transfer Compression for Returns (RET)” in Section 35.4.2.2.

35.2.1.3

Far Transfer COFI

All operations that change the instruction pointer and are not near jumps are “far transfers”. This includes exceptions, interrupts, traps, TSX aborts, and instructions that do far transfers.
All far transfers will produce a Target IP (TIP) packet, which provides the destination IP address. For those far
transfers that cannot be inferred from the binary source (e.g., asynchronous events such as exceptions and interrupts), the TIP will be preceded by a Flow Update packet (FUP), which provides the source IP address at which the
event was taken. Table 35-23 indicates exactly which IP will be included in the FUP generated by a far transfer.

35.2.2

Software Trace Instrumentation with PTWRITE

PTWRITE provides a mechanism by which software can instrument the Intel PT trace. PTWRITE is a ring3-accessible instruction that can be passed a register or memory variable, see “PTWRITE - Write Data to a Processor Trace
Packet” in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B for details. The contents of
that variable will be used as the payload for the PTW packet (see Table 35-40 “PTW Packet Definition”), inserted at
the time of PTWRITE retirement, assuming PTWRITE is enabled and all other filtering conditions are met. Decode
and analysis software will then be able to determine the meaning of the PTWRITE packet based on the IP of the
associated PTWRITE instruction.
PTWRITE is enabled via IA32_RTIT_CTL.PTWEn[12] (see Table 35-6). Optionally, the user can use
IA32_RTIT_CTL.FUPonPTW[5] to enable PTW packets to be followed by FUP packets containing the IP of the associated PTWRITE instruction.

35.2.3

Power Event Tracing

Power Event Trace is a capability that exposes core- and thread-level sleep state and power down transition information. When this capability is enabled, the trace will expose information about:
— Scenarios where software execution stops.

•
•

Due to sleep state entry, frequency change, or other powerdown.
Includes the IP, when in the tracing context.

— The requested and resolved hardware thread C-state.

•

Including indication of hardware autonomous C-state entry.

— The last and deepest core C-state achieved during a sleep session.
— The reason for C-state wake.
This information is in addition to the bus ratio (CBR) information provided by default after any powerdown, and the
timing information (TSC, TMA, MTC, CYC) provided during or after a powerdown state.
Power Event Trace is enabled via IA32_RTIT_CTL.PwrEvtEn[4].

35.2.4

Trace Filtering

Intel Processor Trace provides filtering capabilities, by which the debug/profile tool can control what code is traced.

35.2.4.1

Filtering by Current Privilege Level (CPL)

Intel PT provides the ability to configure a logical processor to generate trace packets only when CPL = 0, when
CPL > 0, or regardless of CPL.
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INTEL® PROCESSOR TRACE

CPL filtering ensures that no IPs or other architectural state information associated with the filtered CPL can be
seen in the log. For example, if the processor is configured to trace only when CPL > 0, and software executes
SYSCALL (changing the CPL to 0), the destination IP of the SYSCALL will be suppressed from the generated packet
(see the discussion of TIP.PGD in Section 35.4.2.5).
It should be noted that CPL is always 0 in real-address mode and that CPL is always 3 in virtual-8086 mode. To
trace code in these modes, filtering should be configured accordingly.
When software is executing in a non-enabled CPL, ContextEn is cleared. See Section 35.2.5.1 for details.

35.2.4.2

Filtering by CR3

Intel PT supports a CR3-filtering mechanism by which the generation of packets containing architectural states can
be enabled or disabled based on the value of CR3. A debugger can use CR3 filtering to trace only a single application without context switching the state of the RTIT MSRs. For the reconstruction of traces from software with
multiple threads, debug software may wish to context-switch for the state of the RTIT MSRs (if the operating
system does not provide context-switch support) to separate the output for the different threads (see Section
35.3.5, “Context Switch Consideration”).
To trace for only a single CR3 value, software can write that value to the IA32_RTIT_CR3_MATCH MSR, and set
IA32_RTIT_CTL.CR3Filter. When CR3 value does not match IA32_RTIT_CR3_MATCH and IA32_RTIT_CTL.CR3Filter
is 1, ContextEn is forced to 0, and packets containing architectural states will not be generated. Some other
packets can be generated when ContextEn is 0; see Section 35.2.5.3 for details. When CR3 does match
IA32_RTIT_CR3_MATCH (or when IA32_RTIT_CTL.CR3Filter is 0), CR3 filtering does not force ContextEn to 0
(although it could be 0 due to other filters or modes).
CR3 matches IA32_RTIT_CR3_MATCH if the two registers are identical for bits 63:12, or 63:5 when in PAE paging
mode; the lower 5 bits of CR3 and IA32_RTIT_CR3_MATCH are ignored. CR3 filtering is independent of the value
of CR0.PG.
When CR3 filtering is in use, PIP packets may still be seen in the log if the processor is configured to trace when
CPL = 0 (IA32_RTIT_CTL.OS = 1). If not, no PIP packets will be seen.

35.2.4.3

Filtering by IP

Trace packet generation with configurable filtering by IP is supported if CPUID.(EAX=14H, ECX=0):EBX[bit 2] = 1.
Intel PT can be configured to enable the generation of packets containing architectural states only when the
processor is executing code within certain IP ranges. If the IP is outside of these ranges, generation of some
packets is blocked.
IP filtering is enabled using the ADDRn_CFG fields in the IA32_RTIT_CTL MSR (Section 35.2.7.2), where the digit
'n' is a zero-based number that selects which address range is being configured. Each ADDRn_CFG field configures
the use of the register pair IA32_RTIT_ADDRn_A and IA32_RTIT_ADDRn_B (Section 35.2.7.5).
IA32_RTIT_ADDRn_A defines the base and IA32_RTIT_ADDRn_B specifies the limit of the range in which tracing is
enabled. Thus each range, referred to as the ADDRn range, is defined by [IA32_RTIT_ADDRn_A.
IA32_RTIT_ADDRn_B]. There can be multiple such ranges, software can query CPUID (Section 35.3.1) for the
number of ranges supported on a processor.
Default behavior (ADDRn_CFG=0) defines no IP filter range, meaning FilterEn is always set. In this case code at
any IP can be traced, though other filters, such as CR3 or CPL, could limit tracing. When ADDRn_CFG is set to
enable IP filtering (see Section 35.3.1), tracing will commence when a taken branch or event is seen whose target
address is in the ADDRn range.
While inside a tracing region and with FilterEn is set, leaving the tracing region may only be detected once a taken
branch or event with a target outside the range is retired. If an ADDRn range is entered or exited by executing the
next sequential instruction, rather than by a control flow transfer, FilterEn may not toggle immediately. See Section
35.2.5.5 for more details on FilterEn.
Note that these address range base and limit values are inclusive, such that the range includes the first and last
instruction whose first instruction byte is in the ADDRn range.
Depending upon processor implementation, IP filtering may be based on linear or effective address. This can cause
different behavior between implementations if CSbase is not equal to zero or in real mode. See Section 35.3.1.1 for
details. Software can query CPUID to determine filters are based on linear or effective address (Section 35.3.1).

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Note that some packets, such as MTC (Section 35.3.7) and other timing packets, do not depend on FilterEn. For
details on which packets depend on FilterEn, and hence are impacted by IP filtering, see Section 35.4.1.

TraceStop
The ADDRn ranges can also be configured to cause tracing to be disabled upon entry to the specified region. This is
intended for cases where unexpected code is executed, and the user wishes to immediately stop generating
packets in order to avoid overwriting previously written packets.
The TraceStop mechanism works much the same way that IP filtering does, and uses the same address comparison
logic. The TraceStop region base and limit values are programmed into one or more ADDRn ranges, but
IA32_RTIT_CTL.ADDRn_CFG is configured with the TraceStop encoding. Like FilterEn, TraceStop is detected when
a taken branch or event lands in a TraceStop region.
Further, TraceStop requires that TriggerEn=1 at the beginning of the branch/event, and ContextEn=1 upon
completion of the branch/event. When this happens, the CPU will set IA32_RTIT_STATUS.Stopped, thereby
clearing TriggerEn and hence disabling packet generation. This may generate a TIP.PGD packet with the target IP
of the branch or event that entered the TraceStop region. Finally, a TraceStop packet will be inserted, to indicate
that the condition was hit.
If a TraceStop condition is encountered during buffer overflow (Section 35.3.8), it will not be dropped, but will
instead be signaled once the overflow has resolved.
Note that a TraceStop event does not guarantee that all internally buffered packets are flushed out of internal
buffers. To ensure that this has occurred, the user should clear TraceEn.
To resume tracing after a TraceStop event, the user must first disable Intel PT by clearing IA32_RTIT_CTL.TraceEn
before the IA32_RTIT_STATUS.Stopped bit can be cleared. At this point Intel PT can be reconfigured, and tracing
resumed.
Note that the IA32_RTIT_STATUS.Stopped bit can also be set using the ToPA STOP bit. See Section 35.2.6.2.

IP Filtering Example
The following table gives an example of IP filtering behavior. Assume that IA32_RTIT_ADDRn_A = the IP of RangeBase, and that IA32_RTIT_ADDRn_B = the IP of RangeLimit, while IA32_RTIT_CTL.ADDRn_CFG = 0x1 (enable
ADDRn range as a FilterEn range).

Table 35-2. IP Filtering Packet Example
Code Flow
Bar:
jmp RangeBase // jump into filter range
RangeBase:
jcc Foo // not taken
add eax, 1
Foo:
jmp RangeLimit+1 // jump out of filter range
RangeLimit:
nop
jcc Bar

Packets
TIP.PGE(RangeBase)
TNT(0)
TIP.PGD(RangeLimit+1)

IP Filtering and TraceStop
It is possible for the user to configure IP filter range(s) and TraceStop range(s) that overlap. In this case, code
executing in the non-overlapping portion of either range will behave as would be expected from that range. Code
executing in the overlapping range will get TraceStop behavior.

35.2.5

Packet Generation Enable Controls

Intel Processor Trace includes a variety of controls that determine whether a packet is generated. In general, most
packets are sent only if Packet Enable (PacketEn) is set. PacketEn is an internal state maintained in hardware in

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response to software configurable enable controls, PacketEn is not visible to software directly. The relationship of
PacketEn to the software-visible controls in the configuration MSRs is described in this section.

35.2.5.1

Packet Enable (PacketEn)

When PacketEn is set, the processor is in the mode that Intel PT is monitoring and all packets can be generated to
log what is being executed. PacketEn is composed of other states according to this relationship:
PacketEn  TriggerEn AND ContextEn AND FilterEn AND BranchEn
These constituent controls are detailed in the following subsections.
PacketEn ultimately determines when the processor is tracing. When PacketEn is set, all control flow packets are
enabled. When PacketEn is clear, no control flow packets are generated, though other packets (timing and bookkeeping packets) may still be sent. See Section 35.2.6 for details of PacketEn and packet generation.
Note that, on processors that do not support IP filtering (i.e., CPUID.(EAX=14H,
ECX=0):EBX.IPFILT_WRSTPRSV[bit 2] = 0), FilterEn is treated as always set.

35.2.5.2

Trigger Enable (TriggerEn)

Trigger Enable (TriggerEn) is the primary indicator that trace packet generation is active. TriggerEn is set when
IA32_RTIT_CTL.TraceEn is set, and cleared by any of the following conditions:

•
•
•

TraceEn is cleared by software.
A TraceStop condition is encountered and IA32_RTIT_STATUS.Stopped is set.
IA32_RTIT_STATUS.Error is set due to an operational error (see Section 35.3.9).

Software can discover the current TriggerEn value by reading the IA32_RTIT_STATUS.TriggerEn bit. When TriggerEn is clear, tracing is inactive and no packets are generated.

35.2.5.3

Context Enable (ContextEn)

Context Enable (ContextEn) indicates whether the processor is in the state or mode that software configured
hardware to trace. For example, if execution with CPL = 0 code is not being traced (IA32_RTIT_CTL.OS = 0), then
ContextEn will be 0 when the processor is in CPL0.
Software can discover the current ContextEn value by reading the IA32_RTIT_STATUS.ContextEn bit. ContextEn is
defined as follows:
ContextEn = !((IA32_RTIT_CTL.OS = 0 AND CPL = 0) OR
(IA32_RTIT_CTL.USER = 0 AND CPL > 0) OR (IS_IN_A_PRODUCTION_ENCLAVE1) OR
(IA32_RTIT_CTL.CR3Filter = 1 AND IA32_RTIT_CR3_MATCH does not match CR3)
If the clearing of ContextEn causes PacketEn to be cleared, a Packet Generation Disable (TIP.PGD) packet is generated, but its IP payload is suppressed. If the setting of ContextEn causes PacketEn to be set, a Packet Generation
Enable (TIP.PGE) packet is generated.
When ContextEn is 0, control flow packets (TNT, FUP, TIP.*, MODE.*) are not generated, and no Linear Instruction
Pointers (LIPs) are exposed. However, some packets, such as MTC and PSB (see Section 35.4.2.16 and Section
35.4.2.17), may still be generated while ContextEn is 0. For details of which packets are generated only when
ContextEn is set, see Section 35.4.1.
The processor does not update ContextEn when TriggerEn = 0.
The value of ContextEn will toggle only when TriggerEn = 1.

35.2.5.4

Branch Enable (BranchEn)

This value is based purely on the IA32_RTIT_CTL.BranchEn value. If BranchEn is not set, then relevant COFI
packets (TNT, TIP*, FUP, MODE.*) are suppressed. Other packets related to timing (TSC, TMA, MTC, CYC), as well
1. Trace packets generation is disabled in a production enclave, see Section 35.2.8.3. See Intel® Software Guard
Extensions Programming Reference about differences between a production enclave and a debug enclave.
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INTEL® PROCESSOR TRACE

as PSB, will be generated normally regardless. Further, PIP and VMCS continue to be generated, as indicators of
what software is running.

35.2.5.5

Filter Enable (FilterEn)

Filter Enable indicates that the Instruction Pointer (IP) is within the range of IPs that Intel PT is configured to watch.
Software can get the state of Filter Enable by a RDMSR of IA32_RTIT_STATUS.FilterEn. For details on configuration
and use of IP filtering, see Section 35.2.4.3.
On clearing of FilterEn that also clears PacketEn, a Packet Generation Disable (TIP.PGD) will be generated, but
unlike the ContextEn case, the IP payload may not be suppressed. For direct, unconditional branches, as well as for
indirect branches (including RETs), the PGD generated by leaving the tracing region and clearing FilterEn will
contain the target IP. This means that IPs from outside the configured range can be exposed in the trace, as long
as they are within context.
When FilterEn is 0, control flow packets are not generated (e.g., TNT, TIP). However, some packets, such as PIP,
MTC, and PSB, may still be generated while FilterEn is clear. For details on packet enable dependencies, see Section
35.4.1.
After TraceEn is set, FilterEn is set to 1 at all times if there is no IP filter range configured by software
(IA32_RTIT_CTL.ADDRn_CFG != 1, for all n), or if the processor does not support IP filtering (i.e.,
CPUID.(EAX=14H, ECX=0):EBX.IPFILT_WRSTPRSV[bit 2] = 0). FilterEn will toggle only when TraceEn=1 and
ContextEn=1, and when at least one range is configured for IP filtering.

35.2.6

Trace Output

Intel PT output should be viewed independently from trace content and filtering mechanisms. The options available
for trace output can vary across processor generations and platforms.
Trace output is written out using one of the following output schemes, as configured by the ToPA and FabricEn bit
fields of IA32_RTIT_CTL (see Section 35.2.7.2):

•
•
•

A single, contiguous region of physical address space.
A collection of variable-sized regions of physical memory. These regions are linked together by tables of
pointers to those regions, referred to as Table of Physical Addresses (ToPA). The trace output stores bypass
the caches and the TLBs, but are not serializing. This is intended to minimize the performance impact of the
output.
A platform-specific trace transport subsystem.

Regardless of the output scheme chosen, Intel PT stores bypass the processor caches by default. This ensures that
they don't consume precious cache space, but they do not have the serializing aspects associated with un-cacheable (UC) stores. Software should avoid using MTRRs to mark any portion of the Intel PT output region as UC, as
this may override the behavior described above and force Intel PT stores to UC, thereby incurring severe performance impact.
There is no guarantee that a packet will be written to memory or other trace endpoint after some fixed number of
cycles after a packet-producing instruction executes. The only way to assure that all packets generated have
reached their endpoint is to clear TraceEn and follow that with a store, fence, or serializing instruction; doing so
ensures that all buffered packets are flushed out of the processor.

35.2.6.1

Single Range Output

When IA32_RTIT_CTL.ToPA and IA32_RTIT_CTL.FabricEn bits are clear, trace packet output is sent to a single,
contiguous memory (or MMIO if DRAM is not available) range defined by a base address in
IA32_RTIT_OUTPUT_BASE (Section 35.2.7.7) and mask value in IA32_RTIT_OUTPUT_MASK_PTRS (Section
35.2.7.8). The current write pointer in this range is also stored in IA32_RTIT_OUTPUT_MASK_PTRS. This output
range is circular, meaning that when the writes wrap around the end of the buffer they begin again at the base
address.
This output method is best suited for cases where Intel PT output is either:

•

Configured to be directed to a sufficiently large contiguous region of DRAM.

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INTEL® PROCESSOR TRACE

•

Configured to go to an MMIO debug port, in order to route Intel PT output to a platform-specific trace endpoint
(e.g., JTAG). In this scenario, a specific range of addresses is written in a circular manner, and SoC will intercept
these writes and direct them to the proper device. Repeated writes to the same address do not overwrite each
other, but are accumulated by the debugger, and hence no data is lost by the circular nature of the buffer.

The processor will determine the address to which to write the next trace packet output byte as follows:
OutputBase[63:0]  IA32_RTIT_OUTPUT_BASE[63:0]
OutputMask[63:0]  ZeroExtend64(IA32_RTIT_OUTPUT_MASK_PTRS[31:0])
OutputOffset[63:0]  ZeroExtend64(IA32_RTIT_OUTPUT_MASK_PTRS[63:32])
trace_store_phys_addr  (OutputBase & ~OutputMask) + (OutputOffset & OutputMask)

Single-Range Output Errors
If the output base and mask are not properly configured by software, an operational error (see Section 35.3.9) will
be signaled, and tracing disabled. Error scenarios with single-range output are:

•

Mask value is non-contiguous.
IA32_RTIT_OUTPUT_MASK_PTRS.MaskOrTablePointer value has a 0 in a less significant bit position than the
most significant bit containing a 1.

•

Base address and Mask are mis-aligned, and have overlapping bits set.
IA32_RTIT_OUTPUT_BASE && IA32_RTIT_OUTPUT_MASK_PTRS.MaskOrTableOffset > 0.

•

Illegal Output Offset
IA32_RTIT_OUTPUT_MASK_PTRS.OutputOffset
is
(IA32_RTIT_OUTPUT_MASK_PTRS.MaskOrTableOffset).

greater

than

the

mask

value

Also note that errors can be signaled due to trace packet output overlapping with restricted memory, see Section
35.2.6.4.

35.2.6.2

Table of Physical Addresses (ToPA)

When IA32_RTIT_CTL.ToPA is set and IA32_RTIT_CTL.FabricEn is clear, the ToPA output mechanism is utilized. The
ToPA mechanism uses a linked list of tables; see Figure 35-1 for an illustrative example. Each entry in the table
contains some attribute bits, a pointer to an output region, and the size of the region. The last entry in the table
may hold a pointer to the next table. This pointer can either point to the top of the current table (for circular array)
or to the base of another table. The table size is not fixed, since the link to the next table can exist at any entry.
The processor treats the various output regions referenced by the ToPA table(s) as a unified buffer. This means that
a single packet may span the boundary between one output region and the next.
The ToPA mechanism is controlled by three values maintained by the processor:

•

proc_trace_table_base.
This is the physical address of the base of the current ToPA table. When tracing is enabled, the processor loads
this value from the IA32_RTIT_OUTPUT_BASE MSR. While tracing is enabled, the processor updates the
IA32_RTIT_OUTPUT_BASE MSR with changes to proc_trace_table_base, but these updates may not be
synchronous to software execution. When tracing is disabled, the processor ensures that the MSR contains the
latest value of proc_trace_table_base.

•

proc_trace_table_offset.
This indicates the entry of the current table that is currently in use. (This entry contains the address of the
current output region.) When tracing is enabled, the processor loads this value from bits 31:7 (MaskOrTableOffset) of the IA32_RTIT_OUTPUT_MASK_PTRS. While tracing is enabled, the processor updates
IA32_RTIT_OUTPUT_MASK_PTRS.MaskOrTableOffset with changes to proc_trace_table_offset, but these
updates may not be synchronous to software execution. When tracing is disabled, the processor ensures that
the MSR contains the latest value of proc_trace_table_offset.

•

proc_trace_output_offset.
This a pointer into the current output region and indicates the location of the next write. When tracing is
enabled, the processor loads this value from bits 63:32 (OutputOffset) of the
IA32_RTIT_OUTPUT_MASK_PTRS. While tracing is enabled, the processor updates

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INTEL® PROCESSOR TRACE

IA32_RTIT_OUTPUT_MASK_PTRS.OutputOffset with changes to proc_trace_output_offset, but these updates
may not be synchronous to software execution. When tracing is disabled, the processor ensures that the MSR
contains the latest value of proc_trace_output_offset.
Figure 35-1 provides an illustration (not to scale) of the table and associated pointers.

0FF_FFFF _FFFFH

Physical Memory
proc_trace_output_offset: IA32_RTIT_OUTPUT_MASK_PTRS.OutputOffset

OutputRegionX

END=1
4K

TableBaseB
OutputBaseY

64K

OutputBaseX

proc_trace_table_offset: IA32_RTIT_OUTPUT_MASK_PTRS.TableOffset

ToPA Table A

proc_trace_table_base: IA32_RTIT_OUTPUT_BASE
OutputRegionY
STOP=1
ToPA Table B

0

Figure 35-1. ToPA Memory Illustration
With the ToPA mechanism, the processor writes packets to the current output region (identified by
proc_trace_table_base and the proc_trace_table_offset). The offset within that region to which the next byte will
be written is identified by proc_trace_output_offset. When that region is filled with packet output (thus
proc_trace_output_offset = RegionSize–1), proc_trace_table_offset is moved to the next ToPA entry,
proc_trace_output_offset is set to 0, and packet writes begin filling the new output region specified by
proc_trace_table_offset.
As packets are written out, each store derives its physical address as follows:
trace_store_phys_addr  Base address from current ToPA table entry +
proc_trace_output_offset
Eventually, the regions represented by all entries in the table may become full, and the final entry of the table is
reached. An entry can be identified as the final entry because it has either the END or STOP attribute. The END
attribute indicates that the address in the entry does not point to another output region, but rather to another ToPA
table. The STOP attribute indicates that tracing will be disabled once the corresponding region is filled. See Section
35.2.6.2 for details on STOP.
When an END entry is reached, the processor loads proc_trace_table_base with the base address held in this END
entry, thereby moving the current table pointer to this new table. The proc_trace_table_offset is reset to 0, as is
the proc_trace_output_offset, and packet writes will resume at the base address indicated in the first entry.
If the table has no STOP or END entry, and trace-packet generation remains enabled, eventually the maximum
table size will be reached (proc_trace_table_offset = 01FFFFFH). In this case, the proc_trace_table_offset and
proc_trace_output_offset are reset to 0 (wrapping back to the beginning of the current table) once the last output
region is filled.
It is important to note that processor updates to the IA32_RTIT_OUTPUT_BASE and
IA32_RTIT_OUTPUT_MASK_PTRS MSRs are asynchronous to instruction execution. Thus, reads of these MSRs

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INTEL® PROCESSOR TRACE

while Intel PT is enabled may return stale values. Like all IA32_RTIT_* MSRs, the values of these MSRs should not
be trusted or saved unless trace packet generation is first disabled by clearing IA32_RTIT_CTL.TraceEn. This
ensures that he output MSR values account for all packets generated to that point, after which the output MSR
values will be frozen until tracing resumes. 1
The processor may cache internally any number of entries from the current table or from tables that it references
(directly or indirectly). If tracing is enabled, the processor may ignore or delay detection of modifications to these
tables. To ensure that table changes are detected by the processor in a predictable manner, software should clear
TraceEn before modifying the current table (or tables that it references) and only then re-enable packet generation.

Single Output Region ToPA Implementation
The first processor generation to implement Intel PT supports only ToPA configurations with a single ToPA entry
followed by an END entry that points back to the first entry (creating one circular output buffer). Such processors
enumerate CPUID.(EAX=14H,ECX=0):ECX.MENTRY[bit 1] = 0 and CPUID.(EAX=14H,ECX=0):ECX.TOPAOUT[bit
0] = 1.
If CPUID.(EAX=14H,ECX=0):ECX.MENTRY[bit 1] = 0, ToPA tables can hold only one output entry, which must be
followed by an END=1 entry which points back to the base of the table. Hence only one contiguous block can be
used as output.
The lone output entry can have INT or STOP set, but nonetheless must be followed by an END entry as described
above. Note that, if INT=1, the PMI will actually be delivered before the region is filled.

ToPA Table Entry Format
The format of ToPA table entries is shown in Figure 35-2. The size of the address field is determined by the
processor’s physical-address width (MAXPHYADDR) in bits, as reported in CPUID.80000008H:EAX[7:0].

63

12 11 10 9

MAXPHYADDR–1

6 5

4

3

2 1 0

Output Region Base Physical Address

9:6 Size
4 : STOP
2 : INT
0 : END

Reserved

Figure 35-2. Layout of ToPA Table Entry
Table 35-3 describes the details of the ToPA table entry fields. If reserved bits are set to 1, an error is signaled.

Table 35-3. ToPA Table Entry Fields
ToPA Entry Field

Description

Output Region
Base Physical
Address

If END=0, this is the base physical address of the output region specified by this entry. Note that all regions
must be aligned based on their size. Thus a 2M region must have bits 20:12 clear. If the region is not properly
aligned, an operational error will be signaled when the entry is reached.
If END=1, this is the 4K-aligned base physical address of the next ToPA table (which may be the base of the current table, or the first table in the linked list if a circular buffer is desired). If the processor supports only a single
ToPA output region (see above), this address must be the value currently in the IA32_RTIT_OUTPUT_BASE
MSR.

Size

Indicates the size of the associated output region. Encodings are:
0: 4K, 1: 8K,
2: 16K,
3: 32K,
4: 64K,
5: 128K,
6: 256K,
8: 1M, 9: 2M,
10: 4M,
11: 8M,
12: 16M, 13: 32M, 14: 64M,
This field is ignored if END=1.

7: 512K,
15: 128M

1. Although WRMSR is a serializing instruction, the execution of WRMSR that forces packet writes by clearing TraceEn does not itself
cause these writes to be globally observed.
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INTEL® PROCESSOR TRACE

Table 35-3. ToPA Table Entry Fields (Contd.)
ToPA Entry Field

Description

STOP

When the output region indicated by this entry is filled, software should disable packet generation. This will be
accomplished by setting IA32_RTIT_STATUS.Stopped, which clears TriggerEn. This bit must be 0 if END=1; otherwise it is treated as reserved bit violation (see ToPA Errors).

INT

When the output region indicated by this entry is filled, signal Perfmon LVT interrupt.
Note that if both INT and STOP are set in the same entry, the STOP will happen before the INT. Thus the interrupt handler should expect that the IA32_RTIT_STATUS.Stopped bit will be set, and will need to be reset before
tracing can be resumed.
This bit must be 0 if END=1; otherwise it is treated as reserved bit violation (see ToPA Errors).

END

If set, indicates that this is an END entry, and thus the address field points to a table base rather than an output
region base.
If END=1, INT and STOP must be set to 0; otherwise it is treated as reserved bit violation (see ToPA Errors). The
Size field is ignored in this case.
If the processor supports only a single ToPA output region (see above), END must be set in the second table
entry.

ToPA STOP
Each ToPA entry has a STOP bit. If this bit is set, the processor will set the IA32_RTIT_STATUS.Stopped bit when
the corresponding trace output region is filled. This will clear TriggerEn and thereby cease packet generation. See
Section 35.2.7.4 for details on IA32_RTIT_STATUS.Stopped. This sequence is known as “ToPA Stop”.
No TIP.PGD packet will be seen in the output when the ToPA stop occurs, since the disable happens only when the
region is already full. When this occurs, output ceases after the last byte of the region is filled, which may mean
that a packet is cut off in the middle. Any packets remaining in internal buffers are lost and cannot be recovered.
When ToPA stop occurs, the IA32_RTIT_OUTPUT_BASE MSR will hold the base address of the table whose entry
had STOP=1. IA32_RTIT_OUTPUT_MASK_PTRS.MaskOrTableOffset will hold the index value for that entry, and the
IA32_RTIT_OUTPUT_MASK_PTRS.OutputOffset should be set to the size of the region.
Note that this means the offset pointer is pointing to the next byte after the end of the region, a configuration that
would produce an operational error if the configuration remained when tracing is re-enabled with
IA32_RTIT_STATUS.Stopped cleared.

ToPA PMI
Each ToPA entry has an INT bit. If this bit is set, the processor will signal a performance-monitoring interrupt (PMI)
when the corresponding trace output region is filled. This interrupt is not precise, and it is thus likely that writes to
the next region will occur by the time the interrupt is taken.
The following steps should be taken to configure this interrupt:
1. Enable PMI via the LVT Performance Monitor register (at MMIO offset 340H in xAPIC mode; via MSR 834H in
x2APIC mode). See Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3B for more
details on this register. For ToPA PMI, set all fields to 0, save for the interrupt vector, which can be selected by
software.
2. Set up an interrupt handler to service the interrupt vector that a ToPA PMI can raise.
3. Set the interrupt flag by executing STI.
4. Set the INT bit in the ToPA entry of interest and enable packet generation, using the ToPA output option. Thus,
TraceEn=ToPA=1 in the IA32_RTIT_CTL MSR.
Once the INT region has been filled with packet output data, the interrupt will be signaled. This PMI can be distinguished from others by checking bit 55 (Trace_ToPA_PMI) of the IA32_PERF_GLOBAL_STATUS MSR (MSR 38EH).
Once the ToPA PMI handler has serviced the relevant buffer, writing 1 to bit 55 of the MSR at 390H
(IA32_GLOBAL_STATUS_RESET) clears IA32_PERF_GLOBAL_STATUS.Trace_ToPA_PMI.
Intel PT is not frozen on PMI, and thus the interrupt handler will be traced (though filtering can prevent this). The
Freeze_Perfmon_on_PMI and Freeze_LBRs_on_PMI settings in IA32_DEBUGCTL will be applied on ToPA PMI just as
on other PMIs, and hence Perfmon counters are frozen.

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Assuming the PMI handler wishes to read any buffered packets for persistent output, or wishes to modify any Intel
PT MSRs, software should first disable packet generation by clearing TraceEn. This ensures that all buffered packets
are written to memory and avoids tracing of the PMI handler. The configuration MSRs can then be used to determine where tracing has stopped. If packet generation is disabled by the handler, it should then be manually reenabled before the IRET if continued tracing is desired.
In rare cases, it may be possible to trigger a second ToPA PMI before the first is handled. This can happen if another
ToPA region with INT=1 is filled before, or shortly after, the first PMI is taken, perhaps due to EFLAGS.IF being
cleared for an extended period of time. This can manifest in two ways: either the second PMI is triggered before the
first is taken, and hence only one PMI is taken, or the second is triggered after the first is taken, and thus will be
taken when the handler for the first completes. Software can minimize the likelihood of the second case by clearing
TraceEn at the beginning of the PMI handler. Further, it can detect such cases by then checking the Interrupt
Request Register (IRR) for PMI pending, and checking the ToPA table base and off-set pointers (in
IA32_RTIT_OUTPUT_BASE and IA32_RTIT_OUTPUT_MASK_PTRS) to see if multiple entries with INT=1 have been
filled.

ToPA PMI and Single Output Region ToPA Implementation
A processor that supports only a single ToPA output region implementation (such that only one output region is
supported; see above) will attempt to signal a ToPA PMI interrupt before the output wraps and overwrites the top
of the buffer. To support this functionality, the PMI handler should disable packet generation as soon as possible.
Due to PMI skid, it is possible that, in rare cases, the wrap will have occurred before the PMI is delivered. Software
can avoid this by setting the STOP bit in the ToPA entry (see Table 35-3); this will disable tracing once the region is
filled, and no wrap will occur. This approach has the downside of disabling packet generation so that some of the
instructions that led up to the PMI will not be traced. If the PMI skid is significant enough to cause the region to fill
and tracing to be disabled, the PMI handler will need to clear the IA32_RTIT_STATUS.Stopped indication before
tracing can resume.

ToPA PMI and XSAVES/XRSTORS State Handling
In some cases the ToPA PMI may be taken after completion of an XSAVES instruction that switches Intel PT state,
and in such cases any modification of Intel PT MSRs within the PMI handler will not persist when the saved Intel PT
context is later restored with XRSTORS. To account for such a scenario, it is recommended that the Intel PT output
configuration be modified by altering the ToPA tables themselves, rather than the Intel PT output MSRs.
Table 35-4 depicts a recommended PMI handler algorithm for managing multi-region ToPA output and handling
ToPA PMIs that may arrive between XSAVES and XRSTORS. This algorithm is flexible to allow software to choose
between adding entries to the current ToPA table, adding a new ToPA table, or using the current ToPA table as a
circular buffer. It assumes that the ToPA entry that triggers the PMI is not the last entry in the table, which is the
recommended treatment.

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INTEL® PROCESSOR TRACE

Table 35-4. Algorithm to Manage Intel PT ToPA PMI and XSAVES/XRSTORS
Pseudo Code Flow
IF (IA32_PERF_GLOBAL_STATUS.ToPA)
Save IA32_RTIT_CTL value;
IF ( IA32_RTIT_CTL.TraceEN )
Disable Intel PT by clearing TraceEn;
FI;
IF ( there is space available to grow the current ToPA table )
Add one or more ToPA entries after the last entry in the ToPA table;
Point new ToPA entry address field(s) to new output region base(s);
ELSE
Modify an upcoming ToPA entry in the current table to have END=1;
IF (output should transition to a new ToPA table )
Point the address of the “END=1” entry of the current table to the new table base;
ELSE
/* Continue to use the current ToPA table, make a circular. */
Point the address of the “END=1”l entry to the base of the current table;
Modify the ToPA entry address fields for filled output regions to point to new, unused output regions;
/* Filled regions are those with index in the range of 0 to (IA32_RTIT_MASK_PTRS.MaskOrTableOffset -1). */
FI;
FI;
Restore saved IA32_RTIT_CTL.value;
FI;

ToPA Errors
When a malformed ToPA entry is found, an operation error results (see Section 35.3.9). A malformed entry can
be any of the following:
1. ToPA entry reserved bit violation.
This describes cases where a bit marked as reserved in Section 35.2.6.2 above is set to 1.
2. ToPA alignment violation.
This includes cases where illegal ToPA entry base address bits are set to 1:
a. ToPA table base address is not 4KB-aligned. The table base can be from a WRMSR to
IA32_RTIT_OUTPUT_BASE, or from a ToPA entry with END=1.
b. ToPA entry base address is not aligned to the ToPA entry size (e.g., a 2MB region with base address[20:12]
not equal to 0).
c.

ToPA entry base address sets upper physical address bits not supported by the processor.

3. Illegal ToPA Output Offset (if IA32_RTIT_STATUS.Stopped=0).
IA32_RTIT_OUTPUT_MASK_PTRS.OutputOffset is greater than or equal to the size of the current ToPA output
region size.
4. ToPA rules violations.
These are similar to ToPA entry reserved bit violations; they are cases when a ToPA entry is encountered with
illegal field combinations. They include the following:
a. Setting the STOP or INT bit on an entry with END=1.
b. Setting the END bit in entry 0 of a ToPA table.
c.

On processors that support only a single ToPA entry (see above), two additional illegal settings apply:
i)

ToPA table entry 1 with END=0.

ii) ToPA table entry 1 with base address not matching the table base.

35-14 Vol. 3C

INTEL® PROCESSOR TRACE

In all cases, the error will be logged by setting IA32_RTIT_STATUS.Error, thereby disabling tracing when the problematic ToPA entry is reached (when proc_trace_table_offset points to the entry containing the error). Any packet
bytes that are internally buffered when the error is detected may be lost.
Note that operational errors may also be signaled due to attempts to access restricted memory. See Section
35.2.6.4 for details.
A tracing software have a range of flexibility using ToPA to manage the interaction of Intel PT with application
buffers, see Section 35.5.

35.2.6.3

Trace Transport Subsystem

When IA32_RTIT_CTL.FabricEn is set, the IA32_RTIT_CTL.ToPA bit is ignored, and trace output is written to the
trace transport subsystem. The endpoints of this transport are platform-specific, and details of configuration
options should refer to the specific platform documentation. The FabricEn bit is available to be set if
CPUID(EAX=14H,ECX=0):EBX[bit 3] = 1.

35.2.6.4

Restricted Memory Access

Packet output cannot be directed to any regions of memory that are restricted by the platform. In particular, all
memory accesses on behalf of packet output are checked against the SMRR regions. If there is any overlap with
these regions, trace data collection will not function properly. Exact processor behavior is implementation-dependent; Table 35-5 summarizes several scenarios.

Table 35-5. Behavior on Restricted Memory Access
Scenario

Description

ToPA output region
overlaps with
SMRR

Stores to the restricted memory region will be dropped, and that packet data will be lost. Any attempt to read
from that restricted region will return all 1s. The processor also may signal an error (Section 35.3.9) and disable
tracing when the output pointer reaches the restricted region. If packet generation remains enabled, then
packet output may continue once stores are no longer directed to restricted memory (on wrap, or if the output
region is larger than the restricted memory region).

ToPA table overlaps
with SMRR

The processor will signal an error (Section 35.3.9) and disable tracing when the ToPA read pointer
(IA32_RTIT_OUTPUT_BASE + (proc_trace_table_offset « 3)) enters the restricted region.

It should also be noted that packet output should not be routed to the 4KB APIC MMIO region, as defined by the
IA32_APIC_BASE MSR. For details about the APIC, refer to Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A. No error is signaled for this case.

Modifications to Restricted Memory Regions
It is recommended that software disable packet generation before modifying the SMRRs to change the scope of the
SMRR regions. This is because the processor reserves the right to cache any number of ToPA table entries internally, after checking them against restricted memory ranges. Once cached, the entries will not be checked again,
meaning one could potentially route packet output to a newly restricted region. Software can ensure that any
cached entries are written to memory by clearing IA32_RTIT_CTL.TraceEn.

35.2.7

Enabling and Configuration MSRs

35.2.7.1

General Considerations

Trace packet generation is enabled and configured by a collection of model-specific registers (MSRs), which are
detailed below. Some notes on the configuration MSR behavior:

•

If Intel Processor Trace is not supported by the processor (see Section 35.3.1), RDMSR or WRMSR of the
IA32_RTIT_* MSRs will cause #GP.

•

A WRMSR to any of these configuration MSRs that begins and ends with IA32_RTIT_CTL.TraceEn set will #GP
fault. Packet generation must be disabled before the configuration MSRs can be changed.

Vol. 3C 35-15

INTEL® PROCESSOR TRACE

Note: Software may write the same value back to IA32_RTIT_CTL without #GP, even if TraceEn=1.

•
•

All configuration MSRs for Intel PT are duplicated per logical processor

•

All configuration MSRs for Intel PT are cleared on a cold RESET.

For each configuration MSR, any MSR write that attempts to change bits marked reserved, or utilize encodings
marked reserved, will cause a #GP fault.
— If CPUID.(EAX=14H, ECX=0):EBX.IPFILT_WRSTPRSV[bit 2] = 1, only the TraceEn bit is cleared on warm
RESET; though this may have the impact of clearing other bits in IA32_RTIT_STATUS. Other MSR values of
the trace configuration MSRs are preserved on warm RESET.

•

The semantics of MSR writes to trace configuration MSRs in this chapter generally apply to explicit WRMSR to
these registers, using VM-exit or VM-entry MSR load list to these MSRs, XRSTORS with requested feature bit
map including XSAVE map component of state_8 (corresponding to IA32_XSS[bit 8]), and the write to
IA32_RTIT_CTL.TraceEn by XSAVES (Section 35.3.5.2).

35.2.7.2

IA32_RTIT_CTL MSR

IA32_RTIT_CTL, at address 570H, is the primary enable and control MSR for trace packet generation. Bit positions
are listed in Table 35-6.

Table 35-6. IA32_RTIT_CTL MSR
Position
0

Bit Name
TraceEn

At Reset
0

Bit Description
If 1, enables tracing; else tracing is disabled if 0.
When this bit transitions from 1 to 0, all buffered packets are flushed out of internal buffers.
A further store, fence, or architecturally serializing instruction may be required to ensure that
packet data can be observed at the trace endpoint. See Section 35.2.7.3 for details of
enabling and disabling packet generation.
Note that the processor will clear this bit on #SMI (Section ) and warm reset. Other MSR bits
of IA32_RTIT_CTL (and other trace configuration MSRs) are not impacted by these events.

1

CYCEn

0

0: Disables CYC Packet (see Section 35.4.2.14).
1: Enables CYC Packet.
This bit is reserved if CPUID.(EAX=14H, ECX=0):EBX.CPSB_CAM[bit 1] = 0.

2

OS

0

0: Packet generation is disabled when CPL = 0.
1: Packet generation may be enabled when CPL = 0.

3

User

0

0: Packet generation is disabled when CPL > 0.
1: Packet generation may be enabled when CPL > 0.

4

PwrEvtEn

0

0: Power Event Trace packets are disabled.
1: Power Event Trace packets are enabled (see Section 35.2.3, “Power Event Tracing”).

5

FUPonPTW

0

0: PTW packets are not followed by FUPs.
1: PTW packets are followed by FUPs.

6

FabricEn

0

0: Trace output is directed to the memory subsystem, mechanism depends on
IA32_RTIT_CTL.ToPA.
1: Trace output is directed to the trace transport subsystem, IA32_RTIT_CTL.ToPA is ignored.
This bit is reserved if CPUID.(EAX=14H, ECX=0):ECX[bit 3] = 0.

7

CR3Filter

0

0: Disables CR3 filtering.
1: Enables CR3 filtering.

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INTEL® PROCESSOR TRACE

Table 35-6. IA32_RTIT_CTL MSR (Contd.)
Position
8

Bit Name
ToPA

At Reset
0

Bit Description
0: Single-range output scheme enabled if CPUID.(EAX=14H, ECX=0):ECX.SNGLRGNOUT[bit 2]
= 1 and IA32_RTIT_CTL.FabricEn=0.
1: ToPA output scheme enabled (see Section 35.2.6.2) if CPUID.(EAX=14H,
ECX=0):ECX.TOPA[bit 0] = 1, and IA32_RTIT_CTL.FabricEn=0.
Note: WRMSR to IA32_RTIT_CTL that sets TraceEn but clears this bit and FabricEn would
cause #GP, if CPUID.(EAX=14H, ECX=0):ECX.SNGLRGNOUT[bit 2] = 0.
WRMSR to IA32_RTIT_CTL that sets this bit causes #GP, if CPUID.(EAX=14H,
ECX=0):ECX.TOPA[bit 0] = 0.

9

MTCEn

0

0: Disables MTC Packet (see Section 35.4.2.16).
1: Enables MTC Packet.
This bit is reserved if CPUID.(EAX=14H, ECX=0):EBX.MTC[bit 3] = 0.

10

TSCEn

0

0: Disable TSC packets.
1: Enable TSC packets (see Section 35.4.2.11).

11

DisRETC

0

0: Enable RET compression.
1: Disable RET compression (see Section 35.2.1.2).

12

PTWEn

0

0: PTWRITE packet generation disabled.
1: PTWRITE packet generation enabled (see Table 35-40 “PTW Packet Definition”).

13

BranchEn

0

0: Disable COFI-based packets.
1: Enable COFI-based packets: FUP, TIP, TIP.PGE, TIP.PGD, TNT, MODE.Exec, MODE.TSX.
see Section 35.2.6 for details on BranchEn.

17:14

MTCFreq

0

Defines MTC packet Frequency, which is based on the core crystal clock, or Always Running
Timer (ART). MTC will be sent each time the selected ART bit toggles. The following Encodings
are defined:
0: ART(0), 1: ART(1), 2: ART(2), 3: ART(3), 4: ART(4), 5: ART(5), 6: ART(6), 7: ART(7),
8: ART(8), 9: ART(9), 10: ART(10), 11: ART(11), 12: ART(12), 13: ART(13), 14: ART(14), 15:
ART(15)
Software must use CPUID to query the supported encodings in the processor, see Section
35.3.1. Use of unsupported encodings will result in a #GP fault. This field is reserved if
CPUID.(EAX=14H, ECX=0):EBX.MTC[bit 3] = 0.

18

Reserved

0

Must be 0.

22:19

CycThresh

0

CYC packet threshold, see Section 35.3.6 for details. CYC packets will be sent with the first
eligible packet after N cycles have passed since the last CYC packet. If CycThresh is 0 then
N=0, otherwise N is defined as 2(CycThresh-1). The following Encodings are defined:
0: 0, 1: 1,
2: 2,
3: 4,
4: 8,
5: 16,
6: 32,
7: 64,
8: 128, 9: 256, 10: 512,
11: 1024, 12: 2048, 13: 4096, 14: 8192, 15: 16384
Software must use CPUID to query the supported encodings in the processor, see Section
35.3.1. Use of unsupported encodings will result in a #GP fault. This field is reserved if
CPUID.(EAX=14H, ECX=0):EBX.CPSB_CAM[bit 1] = 0.

23

Reserved

0

Must be 0.

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INTEL® PROCESSOR TRACE

Table 35-6. IA32_RTIT_CTL MSR (Contd.)
Position
27:24

Bit Name
PSBFreq

At Reset
0

Bit Description
Indicates the frequency of PSB packets. PSB packet frequency is based on the number of Intel
PT packet bytes output, so this field allows the user to determine the increment of
IA32_IA32_RTIT_STATUS.PacketByteCnt that should cause a PSB to be generated. Note that
PSB insertion is not precise, but the average output bytes per PSB should approximate the
SW selected period. The following Encodings are defined:
0: 2K, 1: 4K,
2: 8K,
3: 16K,
4: 32K,
5: 64K,
6: 128K,
7: 256K,
8: 512K, 9: 1M, 10: 2M,
11: 4M,
12: 8M,
13: 16M, 14: 32M, 15: 64M
Software must use CPUID to query the supported encodings in the processor, see Section
35.3.1. Use of unsupported encodings will result in a #GP fault. This field is reserved if
CPUID.(EAX=14H, ECX=0):EBX.CPSB_CAM[bit 1] = 0.

31:28

Reserved

0

Must be 0.

35:32

ADDR0_CFG

0

Configures the base/limit register pair IA32_RTIT_ADDR0_A/B based on the following
encodings:
0: ADDR0 range unused.
1: The [IA32_RTIT_ADDR0_A..IA32_RTIT_ADDR0_B] range defines a FilterEn range. FilterEn
will only be set when the IP is within this range, though other FilterEn ranges can additionally
be used. See Section 35.2.4.3 for details on IP filtering.
2: The [IA32_RTIT_ADDR0_A..IA32_RTIT_ADDR0_B] range defines a TraceStop range.
TraceStop will be asserted if code branches into this range. See 4.2.8 for details on TraceStop.
3..15: Reserved (#GP).
This field is reserved if CPUID.(EAX=14H, ECX=1):EBX.RANGECNT[2:0] >= 0.

39:36

ADDR1_CFG

0

Configures the base/limit register pair IA32_RTIT_ADDR1_A/B based on the following
encodings:
0: ADDR1 range unused.
1: The [IA32_RTIT_ADDR1_A..IA32_RTIT_ADDR1_B] range defines a FilterEn range. FilterEn
will only be set when the IP is within this range, though other FilterEn ranges can additionally
be used. See Section 35.2.4.3 for details on IP filtering.
2: The [IA32_RTIT_ADDR1_A..IA32_RTIT_ADDR1_B] range defines a TraceStop range.
TraceStop will be asserted if code branches into this range. See Section 35.4.2.10 for details
on TraceStop.
3..15: Reserved (#GP).
This field is reserved if CPUID.(EAX=14H, ECX=1):EBX.RANGECNT[2:0] < 2.

43:40

ADDR2_CFG

0

Configures the base/limit register pair IA32_RTIT_ADDR2_A/B based on the following
encodings:
0: ADDR2 range unused.
1: The [IA32_RTIT_ADDR2_A..IA32_RTIT_ADDR2_B] range defines a FilterEn range. FilterEn
will only be set when the IP is within this range, though other FilterEn ranges can additionally
be used. See Section 35.2.4.3 for details on IP filtering.
2: The [IA32_RTIT_ADDR2_A..IA32_RTIT_ADDR2_B] range defines a TraceStop range.
TraceStop will be asserted if code branches into this range. See Section 35.4.2.10 for details
on TraceStop.
3..15: Reserved (#GP).
This field is reserved if CPUID.(EAX=14H, ECX=1):EBX.RANGECNT[2:0] < 3.

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INTEL® PROCESSOR TRACE

Table 35-6. IA32_RTIT_CTL MSR (Contd.)
Position
47:44

Bit Name
ADDR3_CFG

At Reset
0

Bit Description
Configures the base/limit register pair IA32_RTIT_ADDR3_A/B based on the following
encodings:
0: ADDR3 range unused.
1: The [IA32_RTIT_ADDR3_A..IA32_RTIT_ADDR3_B] range defines a FilterEn range. FilterEn
will only be set when the IP is within this range, though other FilterEn ranges can additionally
be used. See Section 35.2.4.3 for details on IP filtering.
2: The [IA32_RTIT_ADDR3_A..IA32_RTIT_ADDR3_B] range defines a TraceStop range.
TraceStop will be asserted if code branches into this range. See Section 35.4.2.10 for details
on TraceStop.
3..15: Reserved (#GP).
This field is reserved if CPUID.(EAX=14H, ECX=1):EBX.RANGECNT[2:0] < 4.

59:48

Reserved

0

Reserved only for future trace content enables, or address filtering configuration enables.
Must be 0.

63:60

Reserved

0

Must be 0.

35.2.7.3

Enabling and Disabling Packet Generation with TraceEn

When TraceEn transitions from 0 to 1, Intel Processor Trace is enabled, and a series of packets may be generated.
These packets help ensure that the decoder is aware of the state of the processor when the trace begins, and that
it can keep track of any timing or state changes that may have occurred while packet generation was disabled. A
full PSB+ (see Section 35.4.2.17) will be generated if IA32_RTIT_STATUS.PacketByteCnt=0, and may be generated in other cases as well. Otherwise, timing packets will be generated, including TSC, TMA, and CBR (see Section
35.4.2).
In addition to the packets discussed above, if and when PacketEn (Section 35.2.5.1) transitions from 0 to 1 (which
may happen immediately, depending on filtering settings), a TIP.PGE packet (Section 35.4.2.3) will be generated.
When TraceEn is set, the processor may read ToPA entries from memory and cache them internally. For this reason,
software should disable packet generation before making modifications to the ToPA tables (or changing the configuration of restricted memory regions). See Section 35.7 for more details of packets that may be generated with
modifications to TraceEn.

Disabling Packet Generation
Clearing TraceEn causes any packet data buffered within the logical processor to be flushed out, after which the
output MSRs (IA32_RTIT_OUTPUT_BASE and IA32_RTIT_OUTPUT_MASK_PTRS) will have stable values. When
output is directed to memory, a store, fence, or architecturally serializing instruction may be required to ensure
that the packet data is globally observed. No special packets are generated by disabling packet generation, though
a TIP.PGD may result if PacketEn=1 at the time of disable.

Other Writes to IA32_RTIT_CTL
Any attempt to modify IA32_RTIT_CTL while TraceEn is set will result in a general-protection fault (#GP) unless the
same write also clears TraceEn. However, writes to IA32_RTIT_CTL that do not modify any bits will not cause a
#GP, even if TraceEn remains set.

35.2.7.4

IA32_RTIT_STATUS MSR

The IA32_RTIT_STATUS MSR is readable and writable by software, but some bits (ContextEn, TriggerEn) are readonly and cannot be directly modified. The WRMSR instruction ignores these bits in the source operand (attempts to
modify these bits are ignored and do not cause WRMSR to fault).
This MSR can only be written when IA32_RTIT_CTL.TraceEn is 0; otherwise WRMSR causes a general-protection
fault (#GP). The processor does not modify the value of this MSR while TraceEn is 0 (software can modify it with
WRMSR).

Vol. 3C 35-19

INTEL® PROCESSOR TRACE

Table 35-7. IA32_RTIT_STATUS MSR
Position

Bit Name

At Reset

Bit Description

0

FilterEn

0

This bit is written by the processor, and indicates that tracing is allowed for the current IP,
see Section 35.2.5.5. Writes are ignored.

1

ContextEn

0

The processor sets this bit to indicate that tracing is allowed for the current context. See
Section 35.2.5.3. Writes are ignored.

2

TriggerEn

0

The processor sets this bit to indicate that tracing is enabled. See Section 35.2.5.2. Writes are
ignored.

3

Reserved

0

Must be 0.

4

Error

0

The processor sets this bit to indicate that an operational error has been encountered. When
this bit is set, TriggerEn is cleared to 0 and packet generation is disabled. For details, see
“ToPA Errors” in Section 35.2.6.2.
When TraceEn is cleared, software can write this bit. Once it is set, only software can clear it.
It is not recommended that software ever set this bit, except in cases where it is restoring a
prior saved state.

5

Stopped

0

The processor sets this bit to indicate that a ToPA Stop condition has been encountered.
When this bit is set, TriggerEn is cleared to 0 and packet generation is disabled. For details,
see “ToPA STOP” in Section 35.2.6.2.
When TraceEn is cleared, software can write this bit. Once it is set, only software can clear it.
It is not recommended that software ever set this bit, except in cases where it is restoring a
prior saved state.

31:6

Reserved

0

48:32

PacketByteCnt 0

Must be 0.
This field is written by the processor, and holds a count of packet bytes that have been sent
out. The processor also uses this field to determine when the next PSB packet should be
inserted. Note that the processor may clear or modify this field at any time while
IA32_RTIT_CTL.TraceEn=1. It will have a stable value when IA32_RTIT_CTL.TraceEn=0.
See Section 35.4.2.17 for details.

63:49

Reserved

35.2.7.5

0

Must be 0.

IA32_RTIT_ADDRn_A and IA32_RTIT_ADDRn_B MSRs

The role of the IA32_RTIT_ADDRn_A/B register pairs, for each n, is determined by the corresponding ADDRn_CFG
fields in IA32_RTIT_CTL (see Section 35.2.7.2). The number of these register pairs is enumerated by
CPUID.(EAX=14H, ECX=1):EAX.RANGECNT[2:0].

•

Processors that enumerate support for 1 range support:
IA32_RTIT_ADDR0_A, IA32_RTIT_ADDR0_B

35-20 Vol. 3C

INTEL® PROCESSOR TRACE

•

Processors that enumerate support for 2 ranges support:
IA32_RTIT_ADDR0_A, IA32_RTIT_ADDR0_B

•

IA32_RTIT_ADDR1_A, IA32_RTIT_ADDR1_B
Processors that enumerate support for 3 ranges support:
IA32_RTIT_ADDR0_A, IA32_RTIT_ADDR0_B
IA32_RTIT_ADDR1_A, IA32_RTIT_ADDR1_B

•

IA32_RTIT_ADDR2_A, IA32_RTIT_ADDR2_B
Processors that enumerate support for 4 ranges support:
IA32_RTIT_ADDR0_A, IA32_RTIT_ADDR0_B
IA32_RTIT_ADDR1_A, IA32_RTIT_ADDR1_B
IA32_RTIT_ADDR2_A, IA32_RTIT_ADDR2_B

IA32_RTIT_ADDR3_A, IA32_RTIT_ADDR3_B
Each register has a single 64-bit field that holds a linear address value. Writes must ensure that the address is
properly sign-extended, otherwise a #GP fault will result.

35.2.7.6

IA32_RTIT_CR3_MATCH MSR

The IA32_RTIT_CR3_MATCH register is compared against CR3 when IA32_RTIT_CTL.CR3Filter is 1. Bits 63:5 hold
the CR3 address value to match, bits 4:0 are reserved to 0. For more details on CR3 filtering and the treatment of
this register, see Section 35.2.4.2.
This MSR can be written only when IA32_RTIT_CTL.TraceEn is 0; otherwise WRMSR causes a general-protection
fault (#GP). IA32_RTIT_CR3_MATCH[4:0] are reserved and must be 0; an attempt to set those bits using WRMSR
causes a #GP.

35.2.7.7

IA32_RTIT_OUTPUT_BASE MSR

This MSR is used to configure the trace output destination, when output is directed to memory
(IA32_RTIT_CTL.FabricEn = 0). The size of the address field is determined by the maximum physical address width
(MAXPHYADDR), as reported by CPUID.80000008H:EAX[7:0].
When the ToPA output scheme is used, the processor may update this MSR when packet generation is enabled, and
those updates are asynchronous to instruction execution. Therefore, the values in this MSR should be considered
unreliable unless packet generation is disabled (IA32_RTIT_CTL.TraceEn = 0).
Accesses to this MSR are supported only if Intel PT output to memory is supported, hence when either
CPUID.(EAX=14H, ECX=0):ECX[bit 0] or CPUID.(EAX=14H, ECX=0):ECX[bit 2] are set. Otherwise WRMSR or
RDMSR cause a general-protection fault (#GP). If supported, this MSR can be written only when
IA32_RTIT_CTL.TraceEn is 0; otherwise WRMSR causes a general-protection fault (#GP).

Vol. 3C 35-21

INTEL® PROCESSOR TRACE

Table 35-8. IA32_RTIT_OUTPUT_BASE MSR
Position
6:0

Bit Name

At Reset

Reserved

MAXPHYADDR-1:7

0

BasePhysAddr 0

Bit Description
Must be 0.
The base physical address. How this address is used depends on the value of
IA32_RTIT_CTL.ToPA:
0: This is the base physical address of a single, contiguous physical output region.
This could be mapped to DRAM or to MMIO, depending on the value.
The base address should be aligned with the size of the region, such that none of
the 1s in the mask value(Section 35.2.7.8) overlap with 1s in the base address. If
the base is not aligned, an operational error will result (see Section 35.3.9).
1: The base physical address of the current ToPA table. The address must be 4K
aligned. Writing an address in which bits 11:7 are non-zero will not cause a #GP, but
an operational error will be signaled once TraceEn is set. See “ToPA Errors” in
Section 35.2.6.2 as well as Section 35.3.9.

63:MAXPHYADDR

35.2.7.8

Reserved

0

Must be 0.

IA32_RTIT_OUTPUT_MASK_PTRS MSR

This MSR holds any mask or pointer values needed to indicate where the next byte of trace output should be
written. The meaning of the values held in this MSR depend on whether the ToPA output mechanism is in use. See
Section 35.2.6.2 for details.
The processor updates this MSR while when packet generation is enabled, and those updates are asynchronous to
instruction execution. Therefore, the values in this MSR should be considered unreliable unless packet generation
is disabled (IA32_RTIT_CTL.TraceEn = 0).
Accesses to this MSR are supported only if Intel PT output to memory is supported, hence when either
CPUID.(EAX=14H, ECX=0):ECX[bit 0] or CPUID.(EAX=14H, ECX=0):ECX[bit 2] are set. Otherwise WRMSR or
RDMSR cause a general-protection fault (#GP). If supported, this MSR can be written only when
IA32_RTIT_CTL.TraceEn is 0; otherwise WRMSR causes a general-protection fault (#GP).

Table 35-9. IA32_RTIT_OUTPUT_MASK_PTRS MSR
Position

Bit Name

At Reset

Bit Description

6:0

LowerMask

7FH

Forced to 1, writes are ignored.

31:7

MaskOrTableO
ffset

0

The use of this field depends on the value of IA32_RTIT_CTL.ToPA:
0: This field holds bits 31:7 of the mask value for the single, contiguous physical output
region. The size of this field indicates that regions can be of size 128B up to 4GB. This value
(combined with the lower 7 bits, which are reserved to 1) will be ANDed with the
OutputOffset field to determine the next write address. All 1s in this field should be
consecutive and starting at bit 7, otherwise the region will not be contiguous, and an
operational error (Section 35.3.9) will be signaled when TraceEn is set.
1: This field holds bits 27:3 of the offset pointer into the current ToPA table. This value can
be added to the IA32_RTIT_OUTPUT_BASE value to produce a pointer to the current ToPA
table entry, which itself is a pointer to the current output region. In this scenario, the lower 7
reserved bits are ignored. This field supports tables up to 256 MBytes in size.

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INTEL® PROCESSOR TRACE

Table 35-9. IA32_RTIT_OUTPUT_MASK_PTRS MSR (Contd.)
Position

Bit Name

63:32

OutputOffset

At Reset
0

Bit Description
The use of this field depends on the value of IA32_RTIT_CTL.ToPA:
0: This is bits 31:0 of the offset pointer into the single, contiguous physical output region.
This value will be added to the IA32_RTIT_OUTPUT_BASE value to form the physical address
at which the next byte of packet output data will be written. This value must be less than or
equal to the MaskOrTableOffset field, otherwise an operational error (Section 35.3.9) will be
signaled when TraceEn is set.
1: This field holds bits 31:0 of the offset pointer into the current ToPA output region. This
value will be added to the output region base field, found in the current ToPA table entry, to
form the physical address at which the next byte of trace output data will be written.
This value must be less than the ToPA entry size, otherwise an operational error (Section
35.3.9) will be signaled when TraceEn is set.

35.2.8

Interaction of Intel® Processor Trace and Other Processor Features

35.2.8.1

Intel® Transactional Synchronization Extensions (Intel® TSX)

The operation of Intel TSX is described in Chapter 14 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1. For tracing purpose, packet generation does not distinguish between hardware lock
elision (HLE) and restricted transactional memory (RTM), but speculative execution does have impacts on the trace
output. Specifically, packets are generated as instructions complete, even for instructions in a transactional region
that is later aborted. For this reason, debugging software will need indication of the beginning and end of a transactional region; this will allow software to understand when instructions are part of a transactional region and
whether that region has been committed.
To enable this, TSX information is included in a MODE packet leaf. The mode bits in the leaf are:

•
•

InTX: Set to 1 on an TSX transaction begin, and cleared on transaction commit or abort.
TXAbort: Set to 1 only when InTX transitions from 1 to 0 on an abort. Cleared otherwise.

If BranchEn=1, this MODE packet will be sent each time the transaction status changes. See Table 35-10 for
details.

Table 35-10. TSX Packet Scenarios
TSX Event
Transaction Begin
Transaction
Commit
Transaction Abort
Other

Instruction

Packets

Either XBEGIN or XACQUIRE lock (the latter if executed
transactionally)

MODE(TXAbort=0, InTX=1), FUP(CurrentIP)

Either XEND or XRELEASE lock, if transactional execution
ends. This happens only on the outermost commit

MODE(TXAbort=0, InTX=0), FUP(CurrentIP)

XABORT or other transactional abort

MODE(TXAbort=1, InTX=0), FUP(CurrentIP),
TIP(TargetIP)

One of the following:
• Nested XBEGIN or XACQUIRE lock
• An outer XACQUIRE lock that doesn’t begin a transaction
(InTX not set)
• Non-outermost XEND or XRELEASE lock

None. No change to TSX mode bits for these
cases.

The CurrentIP listed above is the IP of the associated instruction. The TargetIP is the IP of the next instruction to
be executed; for HLE, this is the XACQUIRE lock; for RTM, this is the fallback handler.
Intel PT stores are non-transactional, and thus packet writes are not rolled back on TSX abort.

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INTEL® PROCESSOR TRACE

TSX and IP Filtering
A complication with tracking transactions is handling transactions that start or end outside of the tracing region.
Transactions can’t span across a change in ContextEn, because CPL changes and CR3 changes each cause aborts.
But a transaction can start within the IP filter region and end outside it.
To assist the decoder handling this situation, MODE.TSX packets can be sent even if FilterEn=0, though there will
be no FUP attached. Instead, they will merely serve to indicate to the decoder when transactions are active and
when they are not. When tracing resumes (due to PacketEn=1), the last MODE.TSX preceding the TIP.PGE will indicate the current transaction status.

System Management Mode (SMM)
SMM code has special privileges that non-SMM code does not have. Intel Processor Trace can be used to trace SMM
code, but special care is taken to ensure that SMM handler context is not exposed in any non-SMM trace collection.
Additionally, packet output from tracing non-SMM code cannot be written into memory space that is either
protected by SMRR or used by the SMM handler.
SMM is entered via a system management interrupt (SMI). SMI delivery saves the value of IA32_RTIT_CTL.TraceEn
into SMRAM and then clears it, thereby disabling packet generation.
The saving and clearing of IA32_RTIT_CTL.TraceEn ensures two things:
1. All internally buffered packet data is flushed before entering SMM (see Section 35.2.7.2).
2. Packet generation ceases before entering SMM, so any tracing that was configured outside SMM does not
continue into SMM. No SMM instruction pointers or other state will be exposed in the non-SMM trace.
When the RSM instruction is executed to return from SMM, the TraceEn value that was saved by SMI delivery is
restored, allowing tracing to be resumed. As is done any time packet generation is enabled, ContextEn is re-evaluated, based on the values of CPL, CR3, etc., established by RSM.
Like other interrupts, delivery of an SMI produces a FUP containing the IP of the next instruction to execute. By
toggling TraceEn, SMI and RSM can produce TIP.PGD and TIP.PGE packets, respectively, indicating that tracing was
disabled or re-enabled. See Table 35.7 for more information about packets entering and leaving SMM.
Although #SMI and RSM change CR3, PIP packets are not generated in these cases. With #SMI tracing is disabled
before the CR3 change; with RSM TraceEn is restored after CR3 is written.
TraceEn must be cleared before executing RSM, otherwise it will cause a shutdown. Further, on processors that
restrict use of Intel PT with LBRs (see Section 35.3.1.2), any RSM that results in enabling of both will cause a shutdown.
Intel PT can support tracing of System Transfer Monitor operating in SMM, see Section 35.6.

35.2.8.2

Virtual-Machine Extensions (VMX)

Initial implementations of Intel Processor Trace do not support tracing in VMX operation. Such processors indicate
this by returning 0 for IA32_VMX_MISC[bit 14]. On these processors, execution of the VMXON instruction clears
IA32_RTIT_CTL.TraceEn and any attempt to write IA32_RTIT_CTL causes a general-protection exception (#GP).
Processors that support Intel Processor Trace in VMX operation return 1 for IA32_VMX_MISC[bit 14]. Details of
tracing in VMX operation are described in Section 35.5.

35.2.8.3

Intel Software Guard Extensions (SGX)

SGX provides an application with ability to instantiate a protective container (an enclave) with confidentiality and
integrity (see Intel® Software Guard Extensions Programming Reference). On a processor with both Intel PT and
SGX enabled, when executing code within a production enclave, no control flow packets are produced by Intel PT.
Enclave entry will clear ContextEn, thereby blocking control flow packet generation. A TIP.PGD packet will be generated if PacketEn=1 at the time of the entry.
Upon enclave exit, ContextEn will no longer be forced to 0. If other enables are set at the time, a TIP.PGE may be
generated to indicate that tracing is resumed.
During the enclave execution, Intel PT remains enabled, and periodic or timing packets such as PSB, TSC, MTC, or
CBR can still be generated. No IPs or other architectural state will be exposed.

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INTEL® PROCESSOR TRACE

For packet generation examples on enclave entry or exit, see Section 35.7.

Debug Enclaves
SGX allows an enclave to be configured with relaxed protection of confidentiality for debug purposes, see Intel®
Software Guard Extensions Programming Reference. In a debug enclave, Intel PT continues to function normally.
Specifically, ContextEn is not impacted by enclave entry or exit. Hence the generation of ContextEn-dependent
packets within a debug enclave is allowed.

35.2.8.4

SENTER/ENTERACCS and ACM

GETSEC[SENTER] and GETSEC[ENTERACCS] instructions clear TraceEn, and it is not restored when those instruction complete. SENTER also causes TraceEn to be cleared on other logical processors when they rendezvous and
enter the SENTER sleep state. In these two cases, the disabling of packet generation is not guaranteed to flush
internally buffered packets. Some packets may be dropped.
When executing an authenticated code module (ACM), packet generation is silently disabled during ACRAM setup.
TraceEn will be cleared, but no TIP.PGD packet is generated. After completion of the module, the TraceEn value will
be restored. There will be no TIP.PGE packet, but timing packets, like TSC and CBR, may be produced.

35.2.8.5

Intel® Memory Protection Extensions (Intel® MPX)

Bounds exceptions (#BR) caused by Intel MPX are treated like other exceptions, producing FUP and TIP packets
that indicate the source and destination IPs.

35.3

CONFIGURATION AND PROGRAMMING GUIDELINE

35.3.1

Detection of Intel Processor Trace and Capability Enumeration

Processor support for Intel Processor Trace is indicated by CPUID.(EAX=07H,ECX=0H):EBX[bit 25] = 1. CPUID
function 14H is dedicated to enumerate the resource and capability of processors that report
CPUID.(EAX=07H,ECX=0H):EBX[bit 25] = 1. Different processor generations may have architecturally-defined
variation in capabilities. Table 35-11 describes details of the enumerable capabilities that software must use across
generations of processors that support Intel Processor Trace.

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INTEL® PROCESSOR TRACE

Table 35-11. CPUID Leaf 14H Enumeration of Intel Processor Trace Capabilities
CPUID.(EAX=14H,ECX=0)
Register
EAX

Name

Description Behavior

Bits
31:0

Maximum valid sub-leaf Index

Specifies the index of the maximum valid sub-leaf for this CPUID leaf

0

CR3 Filtering Support

1: Indicates that IA32_RTIT_CTL.CR3Filter can be set to 1, and that
IA32_RTIT_CR3_MATCH MSR can be accessed. See Section 35.2.7.

EBX

0: Indicates that writes that set IA32_RTIT_CTL.CR3Filter to 1, or any
access to IA32_RTIT_CR3_MATCH, will #GP fault.
1

Configurable PSB and CycleAccurate Mode Supported

1: (a) IA32_RTIT_CTL.PSBFreq can be set to a non-zero value, in order to
select the preferred PSB frequency (see below for allowed values). (b)
IA32_RTIT_STATUS.PacketByteCnt can be set to a non-zero value, and
will be incremented by the processor when tracing to indicate progress
towards the next PSB. If trace packet generation is enabled by setting
TraceEn, a PSB will only be generated if PacketByteCnt=0. (c)
IA32_RTIT_CTL.CYCEn can be set to 1 to enable Cycle-Accurate Mode.
See Section 35.2.7.
0: (a) Any attempt to set IA32_RTIT_CTL.PSBFreq, to set
IA32_RTIT_CTL.CYCEn, or write a non-zero value to
IA32_RTIT_STATUS.PacketByteCnt any access to
IA32_RTIT_CR3_MATCH, will #GP fault. (b) If trace packet generation is
enabled by setting TraceEn, a PSB is always generated. (c) Any attempt
to set IA32_RTIT_CTL.CYCEn will #GP fault.

2

IP Filtering and TraceStop
supported, and Preserve Intel
PT MSRs across warm reset

1: (a) IA32_RTIT_CTL provides at one or more ADDRn_CFG field to
configure the corresponding address range MSRs for IP Filtering or IP
TraceStop. Each ADDRn_CFG field accepts a value in the range of 0:2
inclusive. The number of ADDRn_CFG fields is reported by
CPUID.(EAX=14H, ECX=1):EAX.RANGECNT[2:0]. (b) At least one register
pair IA32_RTIT_ADDRn_A and IA32_RTIT_ADDRn_B are provided to
configure address ranges for IP filtering or IP TraceStop. (c) On warm
reset, all Intel PT MSRs will retain their pre-reset values, though
IA32_RTIT_CTL.TraceEn will be cleared. The Intel PT MSRs are listed in
Section 35.2.7.
0: (a) An Attempt to write IA32_RTIT_CTL.ADDRn_CFG with non-zero
encoding values will cause #GP. (b) Any access to IA32_RTIT_ADDRn_A
and IA32_RTIT_ADDRn_B, will #GP fault. (c) On warm reset, all Intel PT
MSRs will be cleared.

3

MTC Supported

1: IA32_RTIT_CTL.MTCEn can be set to 1, and MTC packets will be
generated. See Section 35.2.7.
0: An attempt to set IA32_RTIT_CTL.MTCEn or IA32_RTIT_CTL.MTCFreq
to a non-zero value will #GP fault.

4

PTWRITE Supported

1: Writes can set IA32_RTIT_CTL[12] (PTWEn) and IA32_RTIT_CTL[5]
(FUPonPTW), and PTWRITE can generate packets.
0: Writes that set IA32_RTIT_CTL[12] or IA32_RTIT_CTL[5] will #GP,
and PTWRITE will #UD fault.

5

Power Event Trace Supported 1: Writes can set IA32_RTIT_CTL[4] (PwrEvtEn), enabling Power Event
Trace packet generation.
0: Writes that set IA32_RTIT_CTL[4] will #GP.

31:6

35-26 Vol. 3C

Reserved

INTEL® PROCESSOR TRACE

Table 35-11. CPUID Leaf 14H Enumeration of Intel Processor Trace Capabilities (Contd.)
CPUID.(EAX=14H,ECX=0)
Register

Name

Description Behavior

Bits
0

ToPA Output Supported

ECX

1: Tracing can be enabled with IA32_RTIT_CTL.ToPA = 1, hence utilizing
the ToPA output scheme (Section 35.2.6.2) IA32_RTIT_OUTPUT_BASE
and IA32_RTIT_OUTPUT_MASK_PTRS MSRs can be accessed.
0: Unless CPUID.(EAX=14H, ECX=0):ECX.SNGLRNGOUT[bit 2] = 1. writes
to IA32_RTIT_OUTPUT_BASE or IA32_RTIT_OUTPUT_MASK_PTRS.
MSRs will #GP fault.

1

ToPA Tables Allow Multiple
Output Entries

1: ToPA tables can hold any number of output entries, up to the
maximum allowed by the MaskOrTableOffset field of
IA32_RTIT_OUTPUT_MASK_PTRS.
0: ToPA tables can hold only one output entry, which must be followed
by an END=1 entry which points back to the base of the table.
Further, ToPA PMIs will be delivered before the region is filled. See ToPA
PMI in Section 35.2.6.2.
If there is more than one output entry before the END entry, or if the
END entry has the wrong base address, an operational error will be
signaled (see “ToPA Errors” in Section 35.2.6.2).

2

Single-Range Output
Supported

1: Enabling tracing (TraceEn=1) with IA32_RTIT_CTL.ToPA=0 is
supported.
0: Unless CPUID.(EAX=14H, ECX=0):ECX.TOPAOUT[bit 0] = 1. writes to
IA32_RTIT_OUTPUT_BASE or IA32_RTIT_OUTPUT_MASK_PTRS. MSRs
will #GP fault.

3

Output to Trace Transport
Subsystem Supported

30:4

Reserved

31

IP Payloads are LIP

1: Setting IA32_RTIT_CTL.FabricEn to 1 is supported.
0: IA32_RTIT_CTL.FabricEn is reserved. Write 1 to
IA32_RTIT_CTL.FabricEn will #GP fault.
1: Generated packets which contain IP payloads have LIP values, which
include the CS base component.
0: Generated packets which contain IP payloads have RIP values, which
are the offset from CS base.

EDX

31:0

Reserved

If CPUID.(EAX=14H, ECX=0):EAX reports a non-zero value, additional capabilities of Intel Processor Trace are
described in the sub-leaves of CPUID leaf 14H.

Vol. 3C 35-27

INTEL® PROCESSOR TRACE

Table 35-12. CPUID Leaf 14H, sub-leaf 1H Enumeration of Intel Processor Trace Capabilities
CPUID.(EAX=14H,ECX=1)
Register
EAX

Name

Description Behavior

Bits
2:0

Number of Address Ranges

A non-zero value specifies the number ADDRn_CFG field supported in
IA32_RTIT_CTL and the number of register pair
IA32_RTIT_ADDRn_A/IA32_RTIT_ADDRn_B supported for IP filtering
and IP TraceStop.
NOTE: Currently, no processors support more than 4 address ranges.

15:3

Reserved

31:16

Bitmap of supported MTC
Period Encodings

The non-zero bit positions indicate the map of supported encoding
values for the IA32_RTIT_CTL.MTCFreq field. This applies only if
CPUID.(EAX=14H, ECX=0):EBX.MTC[bit 3] = 1 (MTC Packet generation is
supported), otherwise the MTCFreq field is reserved to 0.
Each bit position in this field represents 1 encoding value in the 4-bit
MTCFreq field (ie, bit 0 is associated with encoding value 0). For each
bit:
1: MTCFreq can be assigned the associated encoding value.
0: MTCFreq cannot be assigned to the associated encoding value. A
write to IA32_RTIT_CTLMTCFreq with unsupported encoding will cause
#GP fault.

EBX

15:0

Bitmap of supported Cycle
Threshold values

The non-zero bit positions indicate the map of supported encoding for
the IA32_RTIT_CTL.CycThresh field. This applies only if
CPUID.(EAX=14H, ECX=0):EBX.CPSB_CAM[bit 1] = 1 (Cycle-Accurate
Mode is Supported), otherwise the CycThresh field is reserved to 0. See
Section 35.2.7.
Each bit position in this field represents 1 encoding value in the 4-bit
CycThresh field (ie, bit 0 is associated with encoding value 0). For each
bit:
1: CycThresh can be assigned the associated encoding value.
0: CycThresh cannot be assigned to the associated encoding value. A
write to CycThresh with unsupported encoding will cause #GP fault.

31:16

Bitmap of supported
Configurable PSB Frequency
encoding

The non-zero bit positions indicate the map of supported encoding for
the IA32_RTIT_CTL.PSBFreq field. This applies only if
CPUID.(EAX=14H, ECX=0):EBX.CPSB_CAM[bit 1] = 1 (Configurable PSB
is supported), otherwise the PSBFreq field is reserved to 0. See
Section 35.2.7.
Each bit position in this field represents 1 encoding value in the 4-bit
PSBFreq field (ie, bit 0 is associated with encoding value 0). For each
bit:
1: PSBFreq can be assigned the associated encoding value.
0: PSBFreq cannot be assigned to the associated encoding value. A
write to PSBFreq with unsupported encoding will cause #GP fault.

ECX

31:0

Reserved

EDX

31:0

Reserved

35-28 Vol. 3C

INTEL® PROCESSOR TRACE

35.3.1.1

Packet Decoding of RIP versus LIP

FUP, TIP, TIP.PGE, and TIP.PGE packets can contain an instruction pointer (IP) payload. On some processor generations, this payload will be an effective address (RIP), while on others this will be a linear address (LIP). In the
former case, the payload is the offset from the current CS base address, while in the latter it is the sum of the offset
and the CS base address (Note that in real mode, the CS base address is the value of CS<<4, while in protected
mode the CS base address is the base linear address of the segment indicated by the CS register.). Which IP type
is in use is indicated by enumeration (see CPUID.(EAX=14H, ECX=0):ECX.LIP[bit 31] in Table 35-11).
For software that executes while the CS base address is 0 (including all software executing in 64-bit mode), the
difference is indistinguishable. A trace decoder must account for cases where the CS base address is not 0 and the
resolved LIP will not be evident in a trace generated on a CPU that enumerates use of RIP. This is likely to cause
problems when attempting to link the trace with the associated binaries.
Note that IP comparison logic, for IP filtering and TraceStop range calculation, is based on the same IP type as
these IP packets. For processors that output RIP, the IP comparison mechanism is also based on RIP, and hence on
those processors RIP values should be written to IA32_RTIT_ADDRn_[AB] MSRs. This can produce differing
behavior if the same trace configuration setting is run on processors reporting different IP types, i.e.
CPUID.(EAX=14H, ECX=0):ECX.LIP[bit 31]. Care should be taken to check CPUID when configuring IP filters.

35.3.1.2

Model Specific Capability Restrictions

Some processor generations impose restrictions that prevent use of LBRs/BTS/BTM/LERs when software has
enabled tracing with Intel Processor Trace. On these processors, when TraceEn is set, updates of LBR, BTS, BTM,
LERs are suspended but the states of the corresponding IA32_DEBUGCTL control fields remained unchanged as if
it were still enabled. When TraceEn is cleared, the LBR array is reset, and LBR/BTS/BTM/LERs updates will resume.
Further, reads of these registers will return 0, and writes will be dropped.
The list of MSRs whose updates/accesses are restricted follows.

•
•
•

MSR_LASTBRANCH_x_TO_IP, MSR_LASTBRANCH_x_FROM_IP, MSR_LBR_INFO_x, MSR_LASTBRANCH_TOS
MSR_LER_FROM_IP, MSR_LER_TO_IP
MSR_LBR_SELECT

For processor with CPUID DisplayFamily_DisplayModel signature of 06_3DH, 06_47H, 06_4EH, 06_4FH, 06_56H
and 06_5EH, the use of Intel PT and LBRs are mutually exclusive.

35.3.2

Enabling and Configuration of Trace Packet Generation

To configure trace packets, enable packet generation, and capture packets, software starts with using CPUID
instruction to detect its feature flag, CPUID.(EAX=07H,ECX=0H):EBX[bit 25] = 1; followed by enumerating the
capabilities described in Section 35.3.1.
Based on the capability queried from Section 35.3.1, software must configure a number of model-specific registers. This section describes programming considerations related to those MSRs.

35.3.2.1

Enabling Packet Generation

When configuring and enabling packet generation, the IA32_RTIT_CTL MSR should be written after any other Intel
PT MSRs have been written, since writes to the other configuration MSRs cause a general-protection fault (#GP) if
TraceEn = 1. If a prior trace collection context is not being restored, then software should first clear
IA32_RTIT_STATUS. This is important since the Stopped, and Error fields are writable; clearing the MSR clears any
values that may have persisted from prior trace packet collection contexts. See Section 35.2.7.2 for details of
packets generated by setting TraceEn to 1.
If setting TraceEn to 1 causes an operational error (see Section 35.3.9), there may be a delay after the WRMSR
completes before the error is signaled in the IA32_RTIT_STATUS MSR.
While packet generation is enabled, the values of some configuration MSRs (e.g., IA32_RTIT_STATUS and
IA32_RTIT_OUTPUT_*) are transient, and reads may return values that are out of date. Only after packet generation is disabled (by clearing TraceEn) do reads of these MSRs return reliable values.

Vol. 3C 35-29

INTEL® PROCESSOR TRACE

35.3.2.2

Disabling Packet Generation

After disabling packet generation by clearing IA32_RTIT_CTL, it is advisable to read the IA32_RTIT_STATUS MSR
(Section 35.2.7.4):

•

If the Error bit is set, an operational error was encountered, and the trace is most likely compromised. Software
should check the source of the error (by examining the output MSR values), correct the source of the problem,
and then attempt to gather the trace again. For details on operational errors, see Section 35.3.9. Software
should clear IA32_RTIT_STATUS.Error before re-enabling packet generation.

•

If the Stopped bit is set, software execution encountered an IP TraceStop (see Section 35.2.4.3) or the ToPA
Stop condition (see “ToPA STOP” in Section 35.2.6.2) before packet generation was disabled.

35.3.3

Flushing Trace Output

Packets are first buffered internally and then written out asynchronously. To collect packet output for postprocessing, a collector needs first to ensure that all packet data has been flushed from internal buffers. Software
can ensure this by stopping packet generation by clearing IA32_RTIT_CTL.TraceEn (see “Disabling Packet Generation” in Section 35.2.7.2).
When software clears IA32_RTIT_CTL.TraceEn to flush out internally buffered packets, the logical processor issues
an SFENCE operation which ensures that WC trace output stores will be ordered with respect to the next store, or
serializing operation. A subsequent read from the same logical processor will see the flushed trace data, while a
read from another logical processor should be preceded by a store, fence, or architecturally serializing operation on
the tracing logical processor.
When the flush operations complete, the IA32_RTIT_OUTPUT_* MSR values indicate where the trace ended. While
TraceEn is set, these MSRs may hold stale values. Further, if a ToPA region with INT=1 is filled, meaning a ToPA PMI
has been triggered, IA32_PERF_GLOBAL_STATUS.Trace_ToPA_PMI[55] will be set by the time the flush completes.

35.3.4

Warm Reset

The MSRs software uses to program Intel Processor Trace are cleared after a power-on RESET (or cold RESET). On
a warm RESET, the contents of those MSRs can retain their values from before the warm RESET with the exception
that IA32_RTIT_CTL.TraceEn will be cleared (which may have the side effect of clearing some bits in
IA32_RTIT_STATUS).

35.3.5

Context Switch Consideration

To facilitate construction of instruction execution traces at the granularity of a software process or thread context,
software can save and restore the states of the trace configuration MSRs across the process or thread context
switch boundary. The principle is the same as saving and restoring the typical architectural processor states across
context switches.

35.3.5.1

Manual Trace Configuration Context Switch

The configuration can be saved and restored through a sequence of instructions of RDMSR, management of MSR
content and WRMSR. To stop tracing and to ensure that all configuration MSRs contain stable values, software must
clear IA32_RTIT_CTL.TraceEn before reading any other trace configuration MSRs. The recommended method for
saving trace configuration context manually follows:
1. RDMSR IA32_RTIT_CTL, save value to memory
2. WRMSR IA32_RTIT_CTL with saved value from RDMSR above and TraceEn cleared
3. RDMSR all other configuration MSRs whose values had changed from previous saved value, save changed
values to memory

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INTEL® PROCESSOR TRACE

When restoring the trace configuration context, IA32_RTIT_CTL should be restored last:
1. Read saved configuration MSR values, aside from IA32_RTIT_CTL, from memory, and restore them with
WRMSR
2. Read saved IA32_RTIT_CTL value from memory, and restore with WRMSR.

35.3.5.2

Trace Configuration Context Switch Using XSAVES/XRSTORS

On processors whose XSAVE feature set supports XSAVES and XRSTORS, the Trace configuration state can be
saved using XSAVES and restored by XRSTORS, in conjunction with the bit field associated with supervisory state
component in IA32_XSS. See Chapter 13, “Managing State Using the XSAVE Feature Set” of Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 1.
The layout of the trace configuration component state in the XSAVE area is shown in Table 35-13.1

Table 35-13. Memory Layout of the Trace Configuration State Component
Offset within
Component Area

Field

Offset within
Component Area

Field

0H

IA32_RTIT_CTL

08H

IA32_RTIT_OUTPUT_BASE

10H

IA32_RTIT_OUTPUT_MASK_PTRS

18H

IA32_RTIT_STATUS

20H

IA32_RTIT_CR3_MATCH

28H

IA32_RTIT_ADDR0_A

30H

IA32_RTIT_ADDR0_B

38H

IA32_RTIT_ADDR1_A

40H

IA32_RTIT_ADDR1_B

48H–End

Reserved

The IA32_XSS MSR is zero coming out of RESET. Once IA32_XSS[bit 8] is set, system software operating at CPL=
0 can use XSAVES/XRSTORS with the appropriate requested-feature bitmap (RFBM) to manage supervisor state
components in the XSAVE map. See Chapter 13, “Managing State Using the XSAVE Feature Set” of Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 1.

35.3.6

Cycle-Accurate Mode

Intel PT can be run in a cycle-accurate mode which enables CYC packets (see Section 35.4.2.14) that provide lowlevel information in the processor core clock domain. This cycle counter data in CYC packets can be used to
compute IPC (Instructions Per Cycle), or to track wall-clock time on a fine-grain level.
To enable cycle-accurate mode packet generation, software should set IA32_RTIT_CTL.CYCEn=1. It is recommended that software also set TSCEn=1 anytime cycle-accurate mode is in use. With this, all CYC-eligible packets
will be preceded by a CYC packet, the payload of which indicates the number of core clock cycles since the last CYC
packet. In cases where multiple CYC-eligible packets are generated in a single cycle, only a single CYC will be
generated before the CYC-eligible packets, otherwise each CYC-eligible packet will be preceded by its own CYC. The
CYC-eligible packets are:

•

TNT, TIP, TIP.PGE, TIP.PGD, MODE.EXEC, MODE.TSX, PIP, VMCS, OVF, MTC, TSC, PTWRITE, EXSTOP

TSC packets are generated when there is insufficient information to reconstruct wall-clock time, due to tracing
being disabled (TriggerEn=0), or power down scenarios like a transition to a deep-sleep MWAIT C-state. In this
case, the CYC that is generated along with the TSC will indicate the number of cycles actively tracing (those
powered up, with TriggerEn=1) executed between the last CYC packet and the TSC packet. And hence the amount
of time spent while tracing is inactive can be inferred from the difference in time between that expected based on
the CYC value, and the actual time indicated by the TSC.
Additional CYC packets may be sent stand-alone, so that the processor can ensure that the decoder is aware of the
number of cycles that have passed before the internal hardware counter wraps, or is reset due to other microarchitectural condition. There is no guarantee at what intervals these standalone CYC packets will be sent, except
that they will be sent before the wrap occurs. An illustration is given below.
1. Table 35-13 documents support for the MSRs defining address ranges 0 and 1. Processors that provide XSAVE support for Intel Processor
Trace support only those address ranges.
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INTEL® PROCESSOR TRACE

Example 35-1. An Illustrative CYC Packet Example
Time (cycles)

Instruction Snapshot

Generated Packets

Comment

x

call %eax

CYC(?), TIP

?Elapsed cycles from the previous CYC unknown

x+2

call %ebx

CYC(2), TIP

1 byte CYC packet; 2 cycles elapsed from the previous CYC

x+8

jnz Foo (not taken)

CYC(6)

1 byte CYC packet

x+9

ret (compressed)

x + 12

jnz Bar (taken)

x + 16

ret (uncompressed)

TNT, CYC(8), TIP

1 byte CYC packet

x + 4111

CYC(4095)

2 byte CYC packet

x + 12305

CYC(8194)

3 byte CYC packet

CYC(4027), PIP

2 byte CYC packet

x + 16332

35.3.6.1

mov cr3, %ebx

Cycle Counter

The cycle counter is implemented in hardware (independent of the time stamp counter or performance monitoring
counters), and is a simple incrementing counter that does not saturate, but rather wraps. The size of the counter is
implementation specific.
The cycle counter is reset to zero any time that TriggerEn is cleared, and when a CYC packet is sent. The cycle
counter will continue to count when ContextEn or FilterEn are cleared, and cycle packets will still be generated. It
will not count during sleep states that result in Intel PT logic being powered-down, but will count up to the point
where clocks are disabled, and resume counting once they are re-enabled.

35.3.6.2

Cycle Packet Semantics

Cycle-accurate mode adheres to the following protocol:

•
•

All packets that precede a CYC packet represent instructions or events that took place before the CYC time.

•

The CYC-eligible packet that immediately follows a CYC packet represents an instruction or event that took
place at the same time as the CYC time.

All packets that follow a CYC packet represent instructions or events that took place at the same time as, or
after, the CYC time.

These items above give the decoder a means to apply CYC packets to a specific instruction in the assembly stream.
Most packets represent a single instruction or event, and hence the CYC packet that precedes each of those packets
represents the retirement time of that instruction or event. In the case of TNT packets, up to 6 conditional branches
and/or compressed RETs may be contained in the packet. In this case, the preceding CYC packet provides the
retirement time of the first branch in the packet. It is possible that multiple branches retired in the same cycle as
that first branch in the TNT, but the protocol will not make that obvious. Also note that a MTC packet could be
generated in the same cycle as the first JCC in the TNT packet. In this case, the CYC would precede both the MTC
and the TNT, and apply to both.
Note that there are times when the cycle counter will stop counting, though cycle-accurate mode is enabled. After
any such scenario, a CYC packet followed by TSC packet will be sent. See Section 35.8.3.2 to understand how to
interpret the payload values

Multi-packet Instructions or Events
Some operations, such as interrupts or task switches, generate multiple packets. In these cases, multiple CYC
packets may be sent for the operation, preceding each CYC-eligible packet in the operation. An example, using a
task switch on a software interrupt, is shown below.

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INTEL® PROCESSOR TRACE

Example 35-2. An Example of CYC in the Presence of Multi-Packet Operations
Time (cycles)

Instruction Snapshot

Generated Packets

x

jnz Foo (not taken)

x+2

ret (compressed)

x+8

jnz Bar (taken)

x+9

jmp %eax

TNT, CYC(9), TIP

x + 12

jnz Bar (not taken)

CYC(3)

x + 32

int3 (task gate)

TNT, FUP, CYC(10), PIP, CYC(20), MODE.Exec, TIP

35.3.6.3

CYC(?),

Cycle Thresholds

Software can opt to reduce the frequency of cycle packets, a trade-off to save bandwidth and intrusion at the
expense of precision. This is done by utilizing a cycle threshold (see Section 35.2.7.2).
IA32_RTIT_CTL.CycThresh indicates to the processor the minimum number of cycles that must pass before the
next CYC packet should be sent. If this value is 0, no threshold is used, and CYC packets can be sent every cycle in
which a CYC-eligible packet is generated. If this value is greater than 0, the hardware will wait until the associated
number of cycles have passed since the last CYC packet before sending another. CPUID provides the threshold
options for CycThresh, see Section 35.3.1.
Note that the cycle threshold does not dictate how frequently a CYC packet will be posted, it merely assigns the
maximum frequency. If the cycle threshold is 16, a CYC packet can be posted no more frequently than every 16
cycles. However, once that threshold of 16 cycles has passed, it still requires a new CYC-eligible packet to be generated before a CYC will be inserted. Table 35-14 illustrates the threshold behavior.

Table 35-14. An Illustrative CYC Packet Example
Time (cycles)

Instruction Snapshot

Threshold
0

16

32

64

x

jmp %eax

CYC, TIP

CYC, TIP

CYC, TIP

CYC, TIP

x+9

call %ebx

CYC, TIP

TIP

TIP

TIP

x + 15

call %ecx

CYC, TIP

TIP

TIP

TIP

x + 30

jmp %edx

CYC, TIP

CYC, TIP

TIP

TIP

x + 38

mov cr3, %eax

CYC, PIP

PIP

CYC, PIP

PIP

x + 46

jmp [%eax]

CYC, TIP

CYC, TIP

TIP

TIP

x + 64

call %edx

CYC, TIP

CYC, TIP

TIP

CYC,TIP

x + 71

jmp %edx

CYC, TIP

TIP

CYC,TIP

TIP

35.3.7

Decoder Synchronization (PSB+)

The PSB packet (Section 35.4.2.17) serves as a synchronization point for a trace-packet decoder. It is a pattern in
the trace log for which the decoder can quickly scan to align packet boundaries. No legal packet combination can
result in such a byte sequence. As such, it serves as the starting point for packet decode. To decode a trace log
properly, the decoder needs more than simply to be aligned: it needs to know some state and potentially some
timing information as well. The decoder should never need to retain any information (e.g., LastIP, call stack,
compound packet event) across a PSB; all compound packet events will be completed before a PSB, and any
compression state will be reset.
When a PSB packet is generated, it is followed by a PSBEND packet (Section 35.4.2.18). One or more packets may
be generated in between those two packets, and these inform the decoder of the current state of the processor.
These packets, known collectively as PSB+, should be interpreted as “status only”, since they do not imply any
change of state at the time of the PSB, nor are they associated directly with any instruction or event. Thus, the

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INTEL® PROCESSOR TRACE

normal binding and ordering rules that apply to these packets outside of PSB+ can be ignored when these packets
are between a PSB and PSBEND. They inform the decoder of the state of the processor at the time of the PSB.
PSB+ can include:

•
•
•

Timestamp (TSC), if IA32_RTIT_CTL.TSCEn=1.

•

VMCS packet, if either the logical is in VMX root operation or the logical processor is in VMX non-root operation
and the “conceal VMX non-root operation from Intel PT” VM-execution control is 0.

•
•
•
•

Core Bus Ratio (CBR).

Timestamp-MTC Align (TMA), if IA32_RTIT_CTL.TSCEn=1 && IA32_RTIT_CTL.MTCEn=1.
Paging Info Packet (PIP), if ContextEn=1 and IA32_RTIT_CTL.OS=1. The non-root bit (NR) is set if the logical
processor is in VMX non-root operation and the “conceal VMX non-root operation from Intel PT”. VM-execution
control is 0.

MODE.TSX, if ContextEn=1 and BranchEn = 1.
MODE.Exec, if PacketEn=1.
Flow Update Packet (FUP), if PacketEn=1.

PSB is generated only when TriggerEn=1; hence PSB+ has the same dependencies. The ordering of packets within
PSB+ is not fixed. Timing packets such as CYC and MTC may be generated between PSB and PSBEND, and their
meanings are the same as outside PSB+.
A PSB+ can be lost in some scenarios. If IA32_RTIT_STATUS.TriggerEn is cleared just as the PSB threshold is
reached, the PSB+ may not be generated. TriggerEn can be cleared by a WRMSR that clears
IA32_RTIT_CTL.TraceEn, a VM-exit that clears IA32_RTIT_CTL.TraceEn, an #SMI, or any time that either
IA32_RTIT_STATUS.Stopped is set (e.g., by a TraceStop or ToPA stop condition) or IA32_RTIT_STATUS.Error is set
(e.g., by an Intel PT output error).
Note that an overflow can occur during PSB+, and this could cause the PSBEND packet to be lost. For this reason,
the OVF packet should also be viewed as terminating PSB+.

35.3.8

Internal Buffer Overflow

In the rare circumstances when new packets need to be generated but the processor’s dedicated internal buffers
are all full, an “internal buffer overflow” occurs. On such an overflow packet generation ceases (as packets would
need to enter the processor’s internal buffer) until the overflow resolves. Once resolved, packet generation
resumes.
When the buffer overflow is cleared, an OVF packet (Section 35.4.2.16) is generated, and the processor ensures
that packets which follow the OVF are not compressed (IP compression or RET compression) against packets that
were lost.
If IA32_RTIT_CTL.BranchEn = 1, the OVF packet will be followed by a FUP if the overflow resolves while PacketEn=1. If the overflow resolves while PacketEn = 0 no packet is generated, but a TIP.PGE will naturally be generated later, once PacketEn = 1. The payload of the FUP or TIP.PGE will be the Current IP of the first instruction upon
which tracing resumes after the overflow is cleared. If the overflow resolves while PacketEn=1, only timing packets
may come between the OVF and the FUP. If the overflow resolves while PacketEn=0, any other packets that are not
dependent on PacketEn may come between the OVF and the TIP.PGE.

35.3.8.1

Overflow Impact on Enables

The address comparisons to ADDRn ranges, for IP filtering and TraceStop (Section 35.2.4.3), continue during a
buffer overflow, and TriggerEn, ContextEn, and FilterEn may change during a buffer overflow. Like other packets,
however, any TIP.PGE or TIP.PGD packets that would have been generated will be lost. Further,
IA32_RTIT_STATUS.PacketByteCnt will not increment, since it is only incremented when packets are generated.
If a TraceStop event occurs during the buffer overflow, IA32_RTIT_STATUS.Stopped will still be set, tracing will
cease as a result. However, the TraceStop packet, and any TIP.PGD that result from the TraceStop, may be
dropped.

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INTEL® PROCESSOR TRACE

35.3.8.2

Overflow Impact on Timing Packets

Any timing packets that are generated during a buffer overflow will be dropped. If only a few MTC packets are
dropped, a decoder should be able to detect this by noticing that the time value in the first MTC packet after the
buffer overflow incremented by more than one. If the buffer overflow lasted long enough that 256 MTC packets are
lost (and thus the MTC packet ‘wraps’ its 8-bit CTC value), then the decoder may be unable to properly understand
the trace. This is not an expected scenario. No CYC packets are generated during overflow, even if the cycle counter
wraps.
Note that, if cycle-accurate mode is enabled, the OVF packet will generate a CYC packet. Because the cycle counter
counts during overflows, this CYC packet can provide the duration of the overflow. However, there is a risk that the
cycle counter wrapped during the overflow, which could render this CYC misleading.

35.3.9

Operational Errors

Errors are detected as a result of packet output configuration problems, which can include output alignment issues,
ToPA reserved bit violations, or overlapping packet output with restricted memory. See “ToPA Errors” in Section
35.2.6.2 for details on ToPA errors, and Section 35.2.6.4 for details on restricted memory errors. Operational
errors are only detected and signaled when TraceEn=1.
When an operational error is detected, tracing is disabled and the error is logged. Specifically,
IA32_RTIT_STATUS.Error is set, which will cause IA32_RTIT_STATUS.TriggerEn to be 0. This will disable generation of all packets. Some causes of operational errors may lead to packet bytes being dropped.
It should be noted that the timing of error detection may not be predictable. Errors are signaled when the
processor encounters the problematic configuration. This could be as soon as packet generation is enabled but
could also be later when the problematic entry or field needs to be used.
Once an error is signaled, software should disable packet generation by clearing TraceEn, diagnose and fix the error
condition, and clear IA32_RTIT_STATUS.Error. At this point, packet generation can be re-enabled.

35.4

TRACE PACKETS AND DATA TYPES

This section details the data packets generated by Intel Processor Trace. It is useful for developers writing the
interpretation code that will decode the data packets and apply it to the traced source code.

35.4.1

Packet Relationships and Ordering

This section introduces the concept of packet “binding”, which involves determining the IP in a binary disassembly
at which the change indicated by a given packet applies. Some packets have the associated IP as the payload (FUP,
TIP), while for others the decoder need only search for the next instance of a particular instruction (or instructions)
to bind the packet (TNT). However, in many cases, the decoder will need to consider the relationship between
packets, and to use this packet context to determine how to bind the packet.
Section 35.4.2 below provides detailed descriptions of the packets, including how packets bind to IPs in the disassembly, to other packets, or to nothing at all. Many packets listed are simple to bind, because they are generated
in only a few scenarios. Those that require more consideration are typically part of “compound packet events”, such
as interrupts, exceptions, and some instructions, where multiple packets are generated by a single operation
(instruction or event). These compound packet events frequently begin with a FUP to indicate the source address
(if it is not clear from the disassembly), and are concluded by a TIP or TIP.PGD packet that indicates the destination
address (if one is provided). In this scenario, the FUP is said to be “coupled” with the TIP packet.
Other packets could be in between the coupled FUP and TIP packet. Timing packets, such as TSC, MTC, CYC, or
CBR, could arrive at any time, and hence could intercede in a compound packet event. If an operation changes CR3
or the processor’s mode of execution, a state update packet (i.e., PIP or MODE) is generated. The state changes
indicated by these intermediate packets should be applied at the IP of the TIP* packet. A summary of compound
packet events is provided in Table 35-15; see Section 35.4.2 for more per-packet details and Section 35.7 for more
detailed packet generation examples.

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INTEL® PROCESSOR TRACE

Table 35-15. Compound Packet Event Summary
Event Type

Beginning

Unconditional,
uncompressed
control-flow
transfer
TSX Update
Overflow

35.4.2

End

Comment

Any combination
of PIP, VMCS,
MODE.Exec, or
none

TIP or TIP.PGD

FUP only for asynchronous events. Order of middle packets
may vary.

MODE.TSX, and
(FUP or none)

None

TIP, TIP.PGD, or
none

FUP

OVF

PSB, PSBEND, or
none

FUP or TIP.PGE

FUP if overflow resolves while ContextEn=1, else TIP.PGE.

FUP or none

Middle

PIP/VMCS/MODE only if the operation modifies the state
tracked by these respective packets.
TIP/TIP.PGD only for TSX abort cases.

Packet Definitions

The following description of packet definitions are in tabular format. Figure 35-3 explains how to interpret them.
Packet bits listed as “RSVD” are not guaranteed to be 0.

Byte Number

Name

Header bits
in Green

Bit Number

Payload in White

Packet name

Packet Format
7

6

5

4

3

2

1

0

0

0

1

0

1

0

1

0

1

1

1

1

0

0

0

1

1

0

2

0

1

0

0

0

1

1

0

Description of fields
Dependencies

Depends on packet generation configuration enable controls or other
bits (Section 35.2.5).

Generation Scenario

Which instructions, events, or other
scenarios can cause this packet to be
generated.

Description

Description of the packet, including the purpose it serves, meaning of the information or payload, etc

Application

How a decoder should apply this packet. It may bind to a specific instruction from the binary, or to
another packet in the stream, or have other implications on decode

Figure 35-3. Interpreting Tabular Definition of Packet Format

35.4.2.1

Taken/Not-taken (TNT) Packet
Table 35-16. TNT Packet Definition

Name

Taken/Not-taken (TNT) Packet

Packet Format
0

35-36 Vol. 3C

7

6

5

4

3

2

1

0

1

B1

B2

B3

B4

B5

B6

0

Short TNT

INTEL® PROCESSOR TRACE

Table 35-16. TNT Packet Definition (Contd.)
B1…BN represent the last N conditional branch or compressed RET (Section 35.4.2.2) results, such that B1 is oldest
and BN is youngest. The short TNT packet can contain from 1 to 6 TNT bits. The long TNT packet can contain up
from 1 to 47 TNT bits.
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

0

1

0

0

0

1

1

2

B40

B41

B42

B43

B44

B45

B46

B47

3

B32

B33

B34

B35

B36

B37

B38

B39

4

B24

B25

B26

B27

B28

B29

B30

B31

5

B16

B17

B18

B19

B20

B21

B22

B23

6

B8

B9

B10

B11

B12

B13

B14

B15

7

1

B1

B2

B3

B4

B5

B6

B7

Long TNT

Irrespective of how many TNT bits is in a packet, the last valid TNT bit is followed by a trailing 1, or Stop bit, as
shown above. If the TNT packet is not full (fewer than 6 TNT bits for the Short TNT, or fewer than 47 TNT bits for
the Long TNT), the Stop bit moves up, and the trailing bits of the packet are filled with 0s. Examples of these
“partial TNTs” are shown below.

0

7

6

5

4

3

2

1

0

0

0

1

B1

B2

B3

B4

0

7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

0

1

0

0

0

1

1

2

B24

B25

B26

B27

B28

B29

B30

B31

3

B16

B17

B18

B19

B20

B21

B22

B23

4

B8

B9

B10

B11

B12

B13

B14

B15

5

1

B1

B2

B3

B4

B5

B6

B7

6

0

0

0

0

0

0

0

0

7

0

0

0

0

0

0

0

0

Generation
Scenario

Short TNT

Long TNT

Dependencies

PacketEn

On a conditional branch or compressed RET, if it fills the TNT.
Also, partial TNTs may be generated at any time, as a result of
other packets being generated,
or certain micro-architectural conditions occurring, before the
TNT is full.

Description

Provides the taken/not-taken results for the last 1–N conditional branches (Jcc, J*CXZ, or LOOP) or compressed RETs
(Section 35.4.2.2). The TNT payload bits should be interpreted as follows:
• 1 indicates a taken conditional branch, or a compressed RET
• 0 indicates a not-taken conditional branch

Application

Each valid payload bit (that is, bits between the header bits and the trailing Stop bit) applies to an upcoming conditional branch or RET instruction. Once a decoder consumes a TNT packet with N valid payload bits, these bits should
be applied to (and hence provide the destination for) the next N conditional branches or RETs

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INTEL® PROCESSOR TRACE

35.4.2.2

Target IP (TIP) Packet
Table 35-17. IP Packet Definition

Name

Target IP (TIP) Packet

Packet Format
7

6

0

IPBytes

1

TargetIP[7:0]

2

TargetIP[15:8]

3

TargetIP[23:16]

4

TargetIP[31:24]

5

TargetIP[39:32]

6

TargetIP[47:40]

7

TargetIP[55:48]

8

TargetIP[63:56]

5

Generation Scenario

4

3

2

1

0

0

1

1

0

1

Dependencies

PacketEn

Indirect branch (including un-compressed RET), far branch, interrupt,
exception, INIT, SIPI, (VM exit, VM entry,)1 TSX abort, (EENTER, EEXIT,
ERESUME, AEX)2.

Description

Provides the target for some control flow transfers

Application

Anytime a TIP is encountered, it indicates that control was transferred to the IP provided in the payload.
The source of this control flow change, and hence the IP or instruction to which it binds, depends on the packets
that precede the TIP. If a TIP is encountered and all preceding packets have already been bound, then the TIP will
apply to the upcoming indirect branch, far branch, or VMRESUME. However, if there was a preceding FUP that
remains unbound, it will bind to the TIP. Here, the TIP provides the target of an asynchronous event or TSX abort
that occurred at the IP given in the FUP payload. Note that there may be other packets, in addition to the FUP, which
will bind to the TIP packet. See the packet application descriptions for other packets for details.

NOTES:
1. If IA32_VMX_MISC[bit 14] reports 1.
2. In a debug enclave.

IP Compression
The IP payload in a TIP. FUP, TIP.PGE, or TIP.PGD packet can vary in size, based on the mode of execution, and the
use of IP compression. IP compression is an optional compression technique the processor may choose to employ
to reduce bandwidth. With IP compression, the IP to be represented in the payload is compared with the last IP sent
out, via any of FUP, TIP, TIP.PGE, or TIP.PGD. If that previous IP had the same upper (most significant) address
bytes, those matching bytes may be suppressed in the current packet. The processor maintains an internal state of
the “Last IP” that was encoded in trace packets, thus the decoder will need to keep track of the “Last IP” state in
software, to match fidelity with packets generated by hardware. “Last IP” is initialized to zero, hence if the first IP
in the trace may be compressed if the upper bytes are zeroes.
The “IPBytes” field of the IP packets (FUP, TIP, TIP.PGE, TIP.PGD) serves to indicate how many bytes of payload are
provided, and how the decoder should fill in any suppressed bytes. The algorithm for reconstructing the IP for a
TIP/FUP packet is shown in the table below.

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INTEL® PROCESSOR TRACE

Table 35-18. FUP/TIP IP Reconstruction
IPBytes

Uncompressed IP Value
63:56

55:48

000b

None, IP is out of context

001b

Last IP[63:16]

010b

Last IP[63:32]

47:40

39:32

31:24

23:16

15:8

7:0

IP Payload[15:0]
IP Payload[31:0]

011b

IP Payload[47] extended

IP Payload[47:0]

100b

Last IP [63:48]

IP Payload[47:0]

101b

Reserved

110b

IP Payload[63:0]

111b

Reserved

The processor-internal Last IP state is guaranteed to be reset to zero when a PSB is sent out. This means that the
IP that follows the PSB with either be un-compressed (011b or 110b, see Table 35-18), or compressed against
zero.
At times, “IPbytes” will have a value of 0. As shown above, this does not mean that the IP payload matches the full
address of the last IP, but rather that the IP for this packet was suppressed. This is used for cases where the IP that
applies to the packet is out of context. An example is the TIP.PGD sent on a SYSCALL, when tracing only USR code.
In that case, no TargetIP will be included in the packet, since that would expose an instruction point at CPL = 0.
When the IP payload is suppressed in this manner, Last IP is not cleared, and instead refers to the last IP packet
with a non-zero IPBytes field.
On processors that support a maximum linear address size of 32 bits, IP payloads may never exceed 32 bits
(IPBytes <= 010b).

Indirect Transfer Compression for Returns (RET)
In addition to IP compression, TIP packets for near return (RET) instructions can also be compressed. If the RET
target matches the next IP of the corresponding CALL, then the TIP packet is unneeded, since the decoder can
deduce the target IP by maintaining a CALL/RET stack of its own.
A CALL/RET stack can be maintained by the decoder by doing the following:
1. Allocate space to store 64 RET targets.
2. For near CALLs, push the Next IP onto the stack. Once the stack is full, new CALLs will force the oldest entry off
the end of the stack, such that only the youngest 64 entries are stored. Note that this excludes zero-length
CALLs, which are direct near CALLs with displacement zero (to the next IP). These CALLs typically don’t have
matching RETs.
3. For near RETs, pop the top (youngest) entry off the stack. This will be the target of the RET.
In cases where the RET is compressed, the target is guaranteed to match the value produced in 2) above. If the
target is not compressed, a TIP packet will be generated with the RET target, which may differ from 2).
The hardware ensure that packets read by the decoder will always have seen the CALL that corresponds to any
compressed RET. The processor will never compress a RET across a PSB, a buffer overflow, or scenario where PacketEn=0. This means that a RET whose corresponding CALL executed while PacketEn=0, or before the last PSB, etc.,
will not be compressed.
If the CALL/RET stack is manipulated or corrupted by software, and thereby causes a RET to transfer control to a
target that is inconsistent with the CALL/RET stack, then the RET will not be compressed, and will produce a TIP
packet. This can happen, for example, if software executes a PUSH instruction to push a target onto the stack, and
a later RET uses this target.
When a RET is compressed, a Taken indication is added to the TNT buffer. Because it sends no TIP packet, it also
does not update the internal Last IP value, and thus the decoder should treat it the same way. If the RET is not
compressed, it will generate a TIP packet (just like when RET compression is disabled, via
IA32_RTIT_CTL.DisRETC). For processors that employ deferred TIPs (Section 35.4.2.3), an uncompressed RET will
not be deferred, and hence will force out any accumulated TNTs or TIPs. This serves to avoid ambiguity, and make
Vol. 3C 35-39

INTEL® PROCESSOR TRACE

clear to the decoder whether the near RET was compressed, and hence a bit in the in-progress TNT should be
consumed, or uncompressed, in which case there will be no in-progress TNT and thus a TIP should be consumed.
Note that in the unlikely case that a RET executes in a different execution mode than the associated CALL, the
decoder will need to model the same behavior with its CALL stack. For instance, if a CALL executes in 64-bit mode,
a 64-bit IP value will be pushed onto the software stack. If the corresponding RET executes in 32-bit mode, then
only the lower 32 target bits will be popped off of the stack, which may mean that the RET does not go to the CALL’s
Next IP. This is architecturally correct behavior, and this RET could be compressed, thus the decoder should match
this behavior

35.4.2.3

Deferred TIPs

The processor may opt to defer sending out the TNT when TIPs are generated. Thus, rather than sending a partial
TNT followed by a TIP, both packets will be deferred while the TNT accumulates more Jcc/RET results. Any number
of TIP packets may be accumulated this way, such that only once the TNT is filled, or once another packet (e.g.,
FUP) is generated, the TNT will be sent, followed by all the deferred TIP packets, and finally terminated by the other
packet(s) that forced out the TNT and TIP packets. Generation of many other packets (see list below) will force out
the TNT and any accumulated TIP packets. This is an optional optimization in hardware to reduce the bandwidth
consumption, and hence the performance impact, incurred by tracing.

Table 35-19. TNT Examples with Deferred TIPs
Code Flow

Packets, Non-Deferred TIPS

Packets, Deferred TIPS

0x1000 cmp %rcx, 0
0x1004 jnz Foo // not-taken
0x1008 jmp %rdx

TNT(0b0), TIP(0x1308)

0x1308 cmp %rcx, 1
0x130c jnz Bar // not-taken
0x1310 cmp %rcx, 2
0x1314 jnz Baz // taken
0x1500 cmp %eax, 7
0x1504 jg Exit // not-taken

TNT(0b010), TIP(0x1100)

0x1508 jmp %r15
0x1100 cmp %rbx, 1
0x1104 jg Start // not-taken
0x1108 add %rcx, %eax
0x110c … // an asynchronous Interrupt arrives
INThandler:
0xcc00 pop %rdx

35-40 Vol. 3C

TNT(0b0), FUP(0x110c),
TIP(0xcc00)
TNT(0b00100), TIP(0x1308),
TIP(0x1100), FUP(0x110c),
TIP(0xcc00)

INTEL® PROCESSOR TRACE

35.4.2.4

Packet Generation Enable (TIP.PGE)
Table 35-20. TIP.PGE Packet Definition

Name

Target IP - Packet Generation Enable (TIP.PGE)

Packet Format
7

6

0

IPBytes

1

TargetIP[7:0]

2

TargetIP[15:8]

3

TargetIP[23:16]

4

TargetIP[31:24]

5

TargetIP[39:32]

6

TargetIP[47:40]

7

TargetIP[55:48]

8

TargetIP[63:56]

5

4

3

2

1

0

1

0

0

0

1

Dependencies

PacketEn transitions to 1

Generation
Scenario

Any branch instruction, control flow transfer, or MOV
CR3 that sets PacketEn, a WRMSR that enables
packet generation and sets PacketEn

Description

Indicates that PacketEn has transitioned to 1. It provides the IP at which the tracing begins.
This can occur due to any of the enables that comprise PacketEn transitioning from 0 to 1, as long as all the others
are asserted. Examples:
• TriggerEn: This is set on software write to set IA32_RTIT_CTL.TraceEn as long as the Stopped and Error bits in
IA32_RTIT_STATUS are clear. The IP payload will be the Next IP of the WRMSR.
• FilterEn: This is set when software jumps into the tracing region. This region is defined by enabling IP filtering in
IA32_RTIT_CTL.ADDRn_CFG, and defining the range in IA32_RTIT_ADDRn_[AB], see. Section 35.2.4.3. The
IP payload will be the target of the branch.
• ContextEn: This is set on a CPL change, a CR3 write or any other means of changing ContextEn. The IP payload
will be the Next IP of the instruction that changes context if it is not a branch, otherwise it will be the target of
the branch.

Application

TIP.PGE packets bind to the instruction at the IP given in the payload.

Vol. 3C 35-41

INTEL® PROCESSOR TRACE

35.4.2.5

Packet Generation Disable (TIP.PGD)
Table 35-21. TIP.PGD Packet Definition

Name

Target IP - Packet Generation Disable (TIP.PGD)

Packet Format
7

6

5

0

IPBytes

1

TargetIP[7:0]

2

TargetIP[15:8]

3

TargetIP[23:16]

4

TargetIP[31:24]

5

TargetIP[39:32]

6

TargetIP[47:40]

7

TargetIP[55:48]

8

TargetIP[63:56]

3

2

1

0

0

0

0

0

1

Dependencies

PacketEn transitions to
0

Description

Indicates that PacketEn has transitioned to 0. It will include the IP at which the tracing ends, unless ContextEn= 0 or
TraceEn=0 at the conclusion of the instruction or event that cleared PacketEn.
PacketEn can be cleared due to any of the enables that comprise PacketEn transitioning from 1 to 0. Examples:
• TriggerEn: This is cleared on software write to clear IA32_RTIT_CTL.TraceEn, or when
IA32_RTIT_STATUS.Stopped is set, or on operational error. The IP payload will be suppressed in this case, and the
“IPBytes” field will have the value 0.
• FilterEn: This is set when software jumps out of the tracing region. This region is defined by enabling IP filtering
in IA32_RTIT_CTL.ADDRn_CFG, and defining the range in IA32_RTIT_ADDRn_[AB], see. Section 35.2.4.3.
The IP payload will depend on the type of the branch. For conditional branches, the payload is
suppressed (IPBytes = 0), and in this case the destination can be inferred from the disassembly. For any other
type of branch, the IP payload will be the target of the branch.
• ContextEn: This can happen on a CPL change, a CR3 write or any other means of changing ContextEn. See
Section 35.2.4.3 for details. In this case, when ContextEn is cleared, there will be no IP payload. The “IPBytes”
field will have value 0.
Note that, in cases where a branch that would normally produce a TIP packet (i.e., far transfer, indirect branch, interrupt, etc) or TNT update (conditional branch or compressed RT) causes PacketEn to transition from 1 to 0, the TIP or
TNI bit will be replaced with TIP.PGD. The payload of the TIP.PGD will be the target of the branch, unless the result
of the instruction causes TraceEn or ContextEn to be cleared (ie, SYSCALL when IA32_RTIT_CTL.OS=0, In the case
where a conditional branch clears FilterEn and hence PacketEn, there will be no TNT bit for this branch, replaced
instead by the TIP.PGD.

Application

TIP.PGD can be produced by any branch instructions, as well as some non-branch instructions, that clear PacketEn.
When produced by a branch, it replaces any TIP or TNT update that the branch would normally produce.
In cases where there is an unbound FUP preceding the TIP.PGD, then the TIP.PGD is part of compound operation (i.e.,
asynchronous event or TSX abort) which cleared PacketEn. For most such cases, the TIP.PGD is simply replacing a
TIP, and should be treated the same way. The TIP.PGD may or may not have an IP payload, depending on whether
the operation cleared ContextEn.
If there is not an associated FUP, the binding will depend on whether there is an IP payload. If there is an IP payload,
then the TIP.PGD should be applied to either the next direct branch whose target matches the TIP.PGD payload, or
the next branch that would normally generate a TIP or TNT packet. If there is no IP payload, then the TIP.PGD should
apply to the next branch or MOV CR3 instruction.

35-42 Vol. 3C

Generation
Scenario

4

Any branch instruction, control flow transfer, or MOV CR3 that clears
PacketEn, a WRMSR that disables packet generation and clears PacketEn

INTEL® PROCESSOR TRACE

35.4.2.6

Flow Update (FUP) Packet
Table 35-22. FUP Packet Definition

Name

Flow Update (FUP) Packet

Packet Format
7
0

IPBytes

1

IP[7:0]

2

IP[15:8]

3

IP[23:16]

4

IP[31:24]

5

IP[39:32]

6

IP[47:40]

7

IP[55:48]

8

IP[63:56]

6

5

Generation
Scenario

4

3

2

1

0

1

1

1

0

1

Dependencies

TriggerEn & ContextEn.
(Typically depends on
BranchEn and FilterEn as well,
see Section 35.2.4 for details.)

Asynchronous Events (interrupts, exceptions, INIT, SIPI, SMI, VM
exit1, #MC), XBEGIN, XEND, XABORT, XACQUIRE, XRELEASE, (EENTRY, EEXIT, ERESUME, EEE, AEX,)2, INT 0, INT 3, INT n, a WRMSR that
disables packet generation.

Description

Provides the source address for asynchronous events, and some other instructions. Is never sent alone, always sent
with an associated TIP or MODE packet, and potentially others.

Application

FUP packets provide the IP to which they bind. However, they are never standalone, but are coupled with other
packets.
In TSX cases, the FUP is immediately preceded by a MODE.TSX, which binds to the same IP. A TIP will follow only in
the case of TSX aborts, see Section 35.4.2.8 for details.
Otherwise, FUPs are part of compound packet events (see Section 35.4.1). In these compound cases, the FUP provides the source IP for an instruction or event, while a following TIP (or TIP.PGD) uop will provide any destination IP.
Other packets may be included in the compound event between the FUP and TIP.

NOTES:
1. If IA32_VMX_MISC[bit 14] reports 1.
2. If Intel Software Guard Extensions is supported.

Vol. 3C 35-43

INTEL® PROCESSOR TRACE

FUP IP Payload
Flow Update Packet gives the source address of an instruction when it is needed. In general, branch instructions do
not need a FUP, because the source address is clear from the disassembly. For asynchronous events, however, the
source address cannot be inferred from the source, and hence a FUP will be sent. Table 35-23 illustrates cases
where FUPs are sent, and which IP can be expected in those cases.

Table 35-23. FUP Cases and IP Payload
Event

Flow Update IP

Comment

External Interrupt, NMI/SMI, Traps,
Machine Check (trap-like), INIT/SIPI

Address of next instruction (Next IP) that
would have been executed

Functionally, this matches the LBR FROM field
value and also the EIP value which is saved onto
the stack.

Exceptions/Faults, Machine check
(fault-like)

Address of the instruction which took the

This matches the similar functionality of LBR
FROM field value and also the EIP value which is
saved onto the stack.

Software Interrupt

Address of the software interrupt instruction
(Current IP)

This matches the similar functionality of LBR
FROM field value, but does not match the EIP
value which is saved onto the stack (Next
Linear Instruction Pointer - NLIP).

EENTER, EEXIT, ERESUME, Enclave
Exiting Event (EEE), AEX1

Current IP of the instruction

This matches the LBR FROM field value and also
the EIP value which is saved onto the stack.

XACQUIRE

Address of the X* instruction

XRELEASE, XBEGIN, XEND,
XABORT, other transactional abort

Current IP

#SMI

IP that is saved into SMRAM

WRMSR that clears TraceEn

Current IP

exception/fault (Current IP)

NOTES:
1. Information on EENTER, EEXIT, ERESUME, EEE, Asynchronous Enclave eXit (AEX) can be found in Intel® Software Guard Extensions Programming Reference.
On a canonical fault due to sequentially fetching an instruction in non-canonical space (as opposed to jumping to
non-canonical space), the IP of the fault (and thus the payload of the FUP) will be a non-canonical address. This is
consistent with what is pushed on the stack for such faulting cases.
If there are post-commit task switch faults, the IP value of the FUP will be the original IP when the task switch
started. This is the same value as would be seen in the LBR_FROM field. But it is a different value as is saved on the
stack or VMCS.

35-44 Vol. 3C

INTEL® PROCESSOR TRACE

35.4.2.7

Paging Information (PIP) Packet
Table 35-24. PIP Packet Definition

Name

Paging Information (PIP) Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

1

0

1

0

1

0

0

0

0

1

2

CR3[11:5] or 0

3

CR3[19:12]

4

CR3[27:20]

5

CR3[35:28]

6

CR3[43:36]

7

CR3[51:44]

0

1
RSVD/NR

Dependencies

TriggerEn && ContextEn &&
IA32_RTIT_CTL.OS

Generation
Scenario

MOV CR3, Task switch, INIT, SIPI, PSB+;
If IA32_VMX_MISC[bit 14] reports 1: VM exit, VM entry

Description

The CR3 payload shown includes only the address portion of the CR3 value. For PAE paging, CR3[11:5] are thus
included. For other page modes (32-bit and 4-level paging1), these bits are 0.
This packet holds the CR3 address value. It will be generated on operations that modify CR3:
• MOV CR3 operation
• Task Switch
• INIT and SIPI
• VM exit and VM entry, if appropriate controls in the VMCS are clear (see Section 35.5.1)
PIPs are not generated, despite changes to CR3, on SMI and RSM. This is due to the special behavior on these operations, see Section for details. Note that, for some cases of task switch where CR3 is not modified, no PIP will be
produced.
The purpose of the PIP is to indicate to the decoder which application is running, so that it can apply the proper
binaries to the linear addresses that are being traced.
The PIP packet contains the new CR3 value when CR3 is written.
PIPs generated by VM entries set the NR bit. PIPs generated in VMX non-root operation set the NR bit if the “conceal VMX non-root operation from Intel PT” VM-execution control is 0. All other PIPs clear the NR bit.

Application

The purpose of the PIP packet is to help the decoder uniquely identify what software is running at any given time.
When a PIP is encountered, a decoder should do the following:
1) If there was a prior unbound FUP (that is, a FUP not preceded by a packet such as MODE.TSX that consumes it,
and it hence pairs with a TIP that has not yet been seen), then this PIP is part of a compound packet event (Section
35.4.1). Find the ending TIP and apply the new CR3/NR values to the TIP payload IP.
2) Otherwise, look for the next MOV CR3, far branch, or VMRESUME/VMLAUNCH in the disassembly, and apply the
new CR3 to the next (or target) IP.
For examples of the packets generated by these flows, see Section 35.7.

NOTES:
1. Earlier versions of this manual used the term “IA-32e paging” to identify 4-level paging.

Vol. 3C 35-45

INTEL® PROCESSOR TRACE

35.4.2.8

MODE Packets

MODE packets keep the decoder informed of various processor modes about which it needs to know in order to
properly manage the packet output, or to properly disassemble the associated binaries. MODE packets include a
header and a mode byte, as shown below.

Table 35-25. General Form of MODE Packets
7

6

5

4

3

2

1

0

0

1

0

0

1

1

0

0

1

1

Leaf ID

Mode

The MODE Leaf ID indicates which set of mode bits are held in the lower bits.

MODE.Exec Packet
Table 35-26. MODE.Exec Packet Definition
Name

MODE.Exec Packet

Packet Format
7

6

5

4

3

2

1

0

0

1

0

0

1

1

0

0

1

1

0

0

0

0

0

0

CS.D

(CS.L & LMA)

Dependencies

PacketEn

Generation
Scenario

Description

Indicates whether software is in 16, 32, or 64-bit mode, by providing the CS.D and (CS.L & IA32_EFER.LMA) values.
Essential for the decoder to properly disassemble the associated binary.

Far branch, interrupt, exception, (VM exit, VM entry,)1 if the mode changes.
PSB+, and any scenario that can generate a TIP.PGE, such that the mode may have
changed since the last MODE.Exec.

CS.D

(CS.L & IA32_EFER.LMA)

Addressing Mode

1

1

N/A

0

1

64-bit mode

1

0

32-bit mode

0

0

16-bit mode

MODE.Exec is sent at the time of a mode change, if PacketEn=1 at the time, or when tracing resumes, if necessary.
In the former case, the MODE.Exec packet is generated along with other packets that result from the far transfer
operation that changes the mode. In cases where the mode changes while PacketEn=0, the processor will send out
a MODE.Exec along with the TIP.PGE when tracing resumes. The processor may opt to suppress the MODE.Exec
when tracing resumes if the mode matches that from the last MODE.Exec packet, if there was no PSB in between.
Application

MODE.Exec always immediately precedes a TIP or TIP.PGE. The mode change applies to the IP address in the payload
of the next TIP or TIP.PGE.

NOTES:
1. If IA32_VMX_MISC[bit 14] reports 1.

35-46 Vol. 3C

INTEL® PROCESSOR TRACE

MODE.TSX Packet
Table 35-27. MODE.TSX Packet Definition
Name

MODE.TSX Packet

Packet Format
7

6

5

4

3

0

1

0

0

1

1

1

0

0

1

0

0

1

0

0

0

1

0

TXAbort

InTX

Dependencies

TriggerEn and ContextEn

Description

Indicates when a TSX transaction (either HLE or RTM) begins, commits, or aborts. Instructions executed transactionally will be “rolled back” if the transaction is aborted.

TXAbort

Application

InTX

Generation
Scenario

2

XBEGIN, XEND, XABORT, XACQUIRE, XRELEASE, if INTX
changes, Asynchronous TSX Abort, PSB+

Implication

1

1

N/A

0

1

Transaction begins, or executing transactionally

1

0

Transaction aborted

0

0

Transaction committed, or not executing transactionally

If PacketEn=1, MODE.TSX always immediately precedes a FUP. If the TXAbort bit is zero, then the mode change
applies to the IP address in the payload of the FUP. If TXAbort=1, then the FUP will be followed by a TIP, and the
mode change will apply to the IP address in the payload of the TIP.
MODE.TSX packets may be generated when PacketEn=0, due to FilterEn=0. In this case, only the last MODE.TSX
generated before TIP.PGE need be applied.

Vol. 3C 35-47

INTEL® PROCESSOR TRACE

35.4.2.9

TraceStop Packet
Table 35-28. TraceStop Packet Definition

Name

TraceStop Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

0

0

0

0

0

1

1

Dependencies

TriggerEn && ContextEn

Generation
Scenario

Taken branch with target in TraceStop IP region, MOV CR3 in TraceStop IP region, or WRMSR that sets TraceEn in TraceStop IP region.

Description

Indicates when software has entered a user-configured TraceStop region.
When the IP matches a TraceStop range while ContextEn and TriggerEn are set, a TraceStop action occurs. This disables tracing by setting IA32_RTIT_STATUS.Stopped, thereby clearing TriggerEn, and causes a TraceStop
packet to be generated.
The TraceStop action also forces FilterEn to 0. Note that TraceStop may not force a flush of internally buffered
packets, and thus trace packet generation should still be manually disabled by clearing IA32_RTIT_CTL.TraceEn
before examining output. See Section 35.2.4.3 for more details.

Application

.If TraceStop follows a TIP.PGD (before the next TIP.PGE), then it was triggered either by the instruction that cleared
PacketEn, or it was triggered by some later instruction that executed while FilterEn=0. In either case, the TraceStop
can be applied at the IP of the TIP.PGD (if any).
If TraceStop follows a TIP.PGE (before the next TIP.PGD), it should be applied at the last known IP.

35.4.2.10 Core:Bus Ratio (CBR) Packet
Table 35-29. CBR Packet Definition
Name

Core:Bus Ratio (CBR) Packet

Packet Format

7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

0

0

0

0

0

0

1

1

2

Core:Bus Ratio

3

Reserved

Dependencies

TriggerEn

Description

Indicates the core:bus ratio of the processor core. Useful for correlating wall-clock time and cycle time.

Application

All packets following the CBR represent instructions that executed with the new core:bus ratio, while all preceding
packets (aside from timing packets) represent instructions that executed with the prior ratio. There is not a precise
IP provided, to which to bind the CBR packet.

35-48 Vol. 3C

Generation
Scenario

After any frequency change, on C-state wake up, PSB+, and after
enabling trace packet generation.

INTEL® PROCESSOR TRACE

35.4.2.11 Timestamp Counter (TSC) Packet
Table 35-30. TSC Packet Definition
Name

Timestamp Counter (TSC) Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

1

1

0

0

1

1

SW TSC[7:0]

2

SW TSC[15:8]

3

SW TSC[23:16]

4

SW TSC[31:24]

5

SW TSC[39:32]

6

SW TSC[47:40]

7

SW TSC[55:48]

Dependencies

IA32_RTIT_CTL.TSCEn &&
TriggerEn

Generation
Scenario

Sent after any event that causes the processor clocks or Intel PT timing
packets (such as MTC or CYC) to stop, This may include P-state changes,
wake from C-state, or clock modulation. Also on transition of TraceEn
from 0 to 1.

Description

When enabled by software, a TSC packet provides the lower 7 bytes of the current TSC value, as returned by the
RDTSC instruction. This may be useful for tracking wall-clock time, and synchronizing the packets in the log with
other timestamped logs.

Application

TSC packet provides a wall-clock proxy of the event which generated it (packet generation enable, sleep state wake,
etc). In all cases, TSC does not precisely indicate the time of any control flow packets; however, all preceding packets
represent instructions that executed before the indicated TSC time, and all subsequent packets represent instructions that executed after it. There is not a precise IP to which to bind the TSC packet.

Vol. 3C 35-49

INTEL® PROCESSOR TRACE

35.4.2.12 Mini Time Counter (MTC) Packet
Table 35-31. MTC Packet Definition
Name

Mini time Counter (MTC) Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

1

0

1

1

0

0

1

1

CTC[N+7:N]

Dependencies

IA32_RTIT_CTL.MTCEn &&
TriggerEn

Description

When enabled by software, an MTC packet provides a periodic indication of wall-clock time. The 8-bit CTC (Common
Timestamp Copy) payload value is set to (ART >> N) & 0xFF. The frequency of the ART is related to the Maximum
Non-Turbo frequency, and the ratio can be determined from CPUID leaf 15H, as described in Section 35.8.3.
Software can select the threshold N, which determines the MTC frequency by setting the IA32_RTIT_CTL.MTCFreq
field (see Section 35.2.7.2) to a supported value using the lookup enumerated by CPUID (see Section 35.3.1).
See Section 35.8.3 for details on how to use the MTC payload to track TSC time.
MTC provides 8 bits from the ART, starting with the bit selected by MTCFreq to dictate the frequency of the packet.
Whenever that 8-bit range being watched changes, an MTC packet will be sent out with the new value of that 8-bit
range. This allows the decoder to keep track of how much wall-clock time has elapsed since the last TSC packet was
sent, by keeping track of how many MTC packets were sent and what their value was. The decoder can infer the
truncated bits, CTC[N-1:0], are 0 at the time of the MTC packet.
There are cases in which MTC packet can be dropped, due to overflow or other micro-architectural conditions. The
decoder should be able to recover from such cases by checking the 8-bit payload of the next MTC packet, to determine how many MTC packets were dropped. It is not expected that >256 consecutive MTC packets should ever be
dropped.

Application

MTC does not precisely indicate the time of any other packet, nor does it bind to any IP. However, all preceding packets represent instructions or events that executed before the indicated ART time, and all subsequent packets represent instructions that executed after, or at the same time as, the ART time.

35-50 Vol. 3C

Generation
Scenario

Periodic, based on the core crystal clock, or Always Running Timer
(ART).

INTEL® PROCESSOR TRACE

35.4.2.13 TSC/MTC Alignment (TMA) Packet
Table 35-32. TMA Packet Definition
Name

TSC/MTC Alignment (TMA) Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

0

1

1

1

0

0

1

1

2

CTC[7:0]

3

CTC[15:8]

4

Reserved

5

FastCounter[7:0]

6

Reserved

0
FC[8]

Dependencies

IA32_RTIT_CTL.MTCEn &&
IA32_RTIT_CTL.TSCEn && TriggerEn

Generation Scenario

Sent with any TSC packet.

Description

The TMA packet serves to provide the information needed to allow the decoder to correlate MTC packets with TSC
packets. With this packet, when a MTC packet is encountered, the decoder can determine how many timestamp
counter ticks have passed since the last TSC or MTC packet. See Section 35.8.3.2 for details on how to make this calculation.

Application

TMA is always sent immediately following a TSC packet, and the payload values are consistent with the TSC payload
value. Thus the application of TMA matches that of TSC.

Vol. 3C 35-51

INTEL® PROCESSOR TRACE

35.4.2.14 Cycle Count Packet (CYC) Packet
Table 35-33. Cycle Count Packet Definition
Name

Cycle Count (CYC) Packet

Packet Format
7

6

5

4

3

2

1

0

Exp

1

1

0

Cycle Counter[4:0]

1

Cycle Counter[11:5]

Exp

2

Cycle Counter[18:12]

Exp

...

... (if Exp = 1 in the previous byte)

Dependencies

IA32_RTIT_CTL.CYCEn &&
TriggerEn

Description

The Cycle Counter field increments at the same rate as the processor core clock ticks, but with a variable length format (using a trailing EXP bit field) and a range-capped byte length.
If the CYC value is less than 32, a 1-byte CYC will be generated, with Exp=0. If the CYC value is between 32 and
4095 inclusive, a 2-byte CYC will be generated, with byte 0 Exp=1 and byte 1 Exp=0. And so on.
CYC provides the number of core clocks that have passed since the last CYC packet. CYC can be configured to be
sent in every cycle in which an eligible packet is generated, or software can opt to use a threshold to limit the number of CYC packets, at the expense of some precision. These settings are configured using the
IA32_RTIT_CTL.CycThresh field (see Section 35.2.7.2). For details on Cycle-Accurate Mode, IPC calculation, etc, see
Section 35.3.6.
When CycThresh=0, and hence no threshold is in use, then a CYC packet will be generated in any cycle in which any
CYC-eligible packet is generated. The CYC packet will precede the other packets generated in the cycle, and provides
the precise cycle time of the packets that follow.
In addition to these CYC packets generated with other packets, CYC packets can be sent stand-alone. These packets
serve simply to update the decoder with the number of cycles passed, and are used to ensure that a wrap of the
processor’s internal cycle counter doesn’t cause cycle information to be lost. These stand-alone CYC packets do not
indicate the cycle time of any other packet or operation, and will be followed by another CYC packet before any
other CYC-eligible packet is seen.
When CycThresh>0, CYC packets are generated only after a minimum number of cycles have passed since the last
CYC packet. Once this threshold has passed, the behavior above resumes, where CYC will either be sent in the next
cycle that produces other CYC-eligible packets, or could be sent stand-alone.
When using CYC thresholds, only the cycle time of the operation (instruction or event) that generates the CYC
packet is truly known. Other operations simply have their execution time bounded: they completed at or after the
last CYC time, and before the next CYC time.

Application

CYC provides the offset cycle time (since the last CYC packet) for the CYC-eligible packet that follows. If another CYC
is encountered before the next CYC-eligible packet, the cycle values should be accumulated and applied to the next
CYC-eligible packet.
If a CYC packet is generated by a TNT, note that the cycle time provided by the CYC packet applies to the first
branch in the TNT packet.

35-52 Vol. 3C

Generation Sce- Can be sent at any time, though a maximum of one CYC packet is
nario
sent per core clock cycle. See Section 35.3.6 for CYC-eligible packets.

INTEL® PROCESSOR TRACE

35.4.2.15 VMCS Packet
Table 35-34. VMCS Packet Definition
Name

VMCS Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

1

0

0

1

0

0

0

2

VMCS Base Address [19:12]

3

VMCS Base Address [27:20]

4

VMCS Base Address [35:28]

5

VMCS Base Address [43:36]

6

VMCS Base Address [51:44]

Dependencies

TriggerEn && ContextEn;
Also in VMX operation.

Generation Scenario

Generated on successful VMPTRLD, and optionally on SMM VM
exits and VM entries that return from SMM (see Section 35.5).

Description

The VMCS packet provides an address related to a VMCS pointer for a decoder to determine the transition of code
contexts:

•

On a successful VMPTRLD (i.e., a VMPTRLD that doesn’t fault, fail, or VM exit), the VMCS packet contains the
address of the current working VMCS pointer of the logical processor that will execute a VM guest context.

•

On SMM VM exits, the VMCS packet provides the STM VMCS base address (SMM Transfer VMCS pointer), if VMCSbased controls are clear (see Section 35.5.1). See Section 35.6 on tracing inside and outside STM.

•

On VM entries that return from SMM, the VMCS packet provides the current working VMCS pointer of the guest
VM (see Section 35.6), if VMCS-based controls are clear (see Section 35.5.1). Root versus Non-Root operation can
be distinguished from the PIP.NR bit.
If a VMCS packet is generated before a VMCS has been loaded, or after it has been cleared, the base address value
will be all 1s.
VMCS packets will not be seen on processors with IA32_VMX_MISC[bit 14]=0, as these processors do not allow
TraceEn to be set in VMX operation.
Application

The purpose of the VMCS packet is to help the decoder uniquely identify changes in the executing software context
in situations that CR3 may not be unique.
When a VMCS is encountered, a decoder should do the following:
• If there was a prior unbound FUP (that is, a FUP not preceded by a packet such as MODE.TSX that consumes it, and
it hence pairs with a TIP that has not yet been seen), then this VMCS is part of a compound packet event (Section
35.4.1). Find the ending TIP and apply the new VMCS base pointer value to the TIP payload IP.
• Otherwise, look for the next VMPTRLD, VMRESUME, or VMLAUNCH in the disassembly, and apply the new VMCS
base pointer on the next VM entry.
For examples of the packets generated by these flows, see Section 35.7.

Vol. 3C 35-53

INTEL® PROCESSOR TRACE

35.4.2.16 Overflow (OVF) Packet
Table 35-35. OVF Packet Definition
Name

Overflow (OVF) Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

1

1

1

0

0

1

1

Dependencies

TriggerEn

Generation
Scenario

On resolution of internal buffer overflow

Description

OVF simply indicates to the decoder that an internal buffer overflow occurred, and packets were likely lost. If
BranchEN= 1, OVF is followed by a FUP or TIP.PGE which will provide the IP at which packet generation resumes. See
Section 35.3.8.

Application

When an OVF packet is encountered, the decoder should skip to the IP given in the subsequent FUP or TIP.PGE. The
cycle counter for the CYC packet will be reset at the time the OVF packet is sent.
Software should reset its call stack depth on overflow, since no RET compression is allowed across an overflow. Similarly, any IP compression that follows the OVF is guaranteed to use as a reference LastIP the IP payload of an IP
packet that preceded the overflow.

35.4.2.17 Packet Stream Boundary (PSB) Packet
Table 35-36. PSB Packet Definition
Name

Packet Stream Boundary (PSB) Packet

Packet Format

35-54 Vol. 3C

7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

0

0

0

0

0

1

0

2

0

0

0

0

0

0

1

0

3

1

0

0

0

0

0

1

0

4

0

0

0

0

0

0

1

0

5

1

0

0

0

0

0

1

0

6

0

0

0

0

0

0

1

0

7

1

0

0

0

0

0

1

0

8

0

0

0

0

0

0

1

0

9

1

0

0

0

0

0

1

0

10

0

0

0

0

0

0

1

0

11

1

0

0

0

0

0

1

0

12

0

0

0

0

0

0

1

0

13

1

0

0

0

0

0

1

0

14

0

0

0

0

0

0

1

0

15

1

0

0

0

0

0

1

0

INTEL® PROCESSOR TRACE

Table 35-36. PSB Packet Definition (Contd.)
Dependencies

TriggerEn

Generation
Scenario

Periodic, based on the number of output bytes generated while tracing. PSB is sent
when IA32_RTIT_STATUS.PacketByteCnt=0, and each time it crosses the software
selected threshold after that. May be sent for other micro-architectural conditions
as well.

Description

PSB is a unique pattern in the packet output log, and hence serves as a sync point for the decoder. It is a pattern
that the decoder can search for in order to get aligned on packet boundaries. This packet is periodic, based on the
number of output bytes, as indicated by IA32_RTIT_STATUS.PacketByteCnt. The period is chosen by software, via
IA32_RTIT_CTL.PSBFreq (see Section 35.2.7.2). Note, however, that the PSB period is not precise, it simply reflects
the average number of output bytes that should pass between PSBs. The processor will make a best effort to
insert PSB as quickly after the selected threshold is reached as possible. The processor also may send extra
PSB packets for some micro-architectural conditions.
PSB also serves as the leading packet for a set of “status-only” packets collectively known as PSB+ (Section 35.3.7).

Application

When a PSB is seen, the decoder should interpret all following packets as “status only”, until either a PSBEND or
OVF packet is encountered. “Status only” implies that the binding and ordering rules to which these packets normally adhere are ignored, and the state they carry can instead be applied to the IP payload in the FUP packet that is
included.

35.4.2.18 PSBEND Packet
Table 35-37. PSBEND Packet Definition
Name

PSBEND Packet

Packet Format

7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

0

0

1

0

0

0

1

1

Dependencies

TriggerEn

Generation
Scenario

Always follows PSB packet, separated by PSB+ packets

Description

PSBEND is simply a terminator for the series of “status only” (PSB+) packets that follow PSB (Section 35.3.7).

Application

When a PSBEND packet is seen, the decoder should cease to treat packets as “status only”.

Vol. 3C 35-55

INTEL® PROCESSOR TRACE

35.4.2.19 Maintenance (MNT) Packet
Table 35-38. MNT Packet Definition
Name

Maintenance (MNT) Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

1

0

0

0

0

1

1

2

1

0

0

0

1

0

0

0

3

Payload[7:0]

4

Payload[15:8]

5

Payload[23:16]

6

Payload[31:24]

7

Payload[39:32]

8

Payload[47:40]

9

Payload[55:48]

10

Payload[63:56]

Dependencies

TriggerEn

Generation Scenario

Implementation specific.

Description

This packet is generated by hardware, the payload meaning is model-specific.

Application

Unless a decoder has been extended for a particular family/model/stepping to interpret MNT packet payloads, this
packet should simply be ignored. It does not bind to any IP.

35.4.2.20 PAD Packet
Table 35-39. PAD Packet Definition
Name

PAD Packet

Packet Format
0

7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

0

Dependencies

TriggerEn

Description

PAD is simply a NOP packet. Processor implementations may choose to add pad packets to improve packet alignment or for implementation-specific reasons.

Application

Ignore PAD packets.

35-56 Vol. 3C

Generation
Scenario

Implementation specific

INTEL® PROCESSOR TRACE

35.4.2.21 PTWRITE Packet
Table 35-40. PTW Packet Definition
Name

PTW Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

IP

PayloadBytes

1

0

0

1

0

2

Payload[7:0]

3

Payload[15:8]

4

Payload[23:16]

5

Payload[31:24]

6

Payload[39:32]

7

Payload[47:40]

8

Payload[55:48]

9

Payload[63:56]

The PayloadBytes field indicates the number of bytes of payload that follow the header bytes. Encodings are as follows:
PayloadBytes

Bytes of Payload

‘00

4

‘01

8

‘10

Reserved

‘11

Reserved

IP bit indicates if a FUP, whose payload will be the IP of the PTWRITE instruction, will follow.
Dependencies

TriggerEn & ContextEn & FilterEn
& PTWEn

Generation
Scenario

PTWRITE Instruction

Description

Contains the value held in the PTWRITE operand.
This packet is CYC-eligible, and hence will generate a CYC packet if IA32_RTIT_CTL.CYCEn=1 and any CYC Threshold
has been reached.

Application

Binds to the associated PTWRITE instruction. The IP of the PTWRITE will be provided by a following FUP, when
PTW.IP=1.

Vol. 3C 35-57

INTEL® PROCESSOR TRACE

35.4.2.22 Execution Stop (EXSTOP) Packet
Table 35-41. EXSTOP Packet Definition
Name

EXSTOP Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

IP

1

1

0

0

0

1

0

IP bit indicates if a FUP will follow.
Dependencies

TriggerEn & PwrEvtEn

Description

This packet indicates that software execution has stopped due to processor clock powerdown. Later packets will
indicate when execution resumes.
If EXSTOP is generated while ContextEn is set, the IP bit will be set, and EXSTOP will be followed by a FUP packet
containing the IP at which execution stopped. More precisely, this will be the IP of the oldest instruction that has
not yet completed.
This packet is CYC-eligible, and hence will generate a CYC packet if IA32_RTIT_CTL.CYCEn=1 and any CYC Threshold
has been reached.

Application

If a FUP follows EXSTOP (hence IP bit set), the EXSTOP can be bound to the FUP IP. Otherwise the IP is not known.
Time of powerdown can be inferred from the preceding CYC, if CYCEn=1. Combined with the TSC at the time of
wake (if TSCEn=1), this can be used to determine the duration of the powerdown.

35-58 Vol. 3C

Generation
Scenario

C-state entry, P-state change, or other processor clock powerdown. Includes :
• Entry to C-state deeper than C0.0
• TM1/2
• STPCLK#
• Frequency change due to IA32_CLOCK_MODULATION, Turbo

INTEL® PROCESSOR TRACE

35.4.2.23 MWAIT Packet
Table 35-42. MWAIT Packet Definition
Name

MWAIT Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

1

0

0

0

0

1

0

2

MWAIT Hints[7:0]

3

Reserved

4

Reserved

5

Reserved

6

Reserved

7

Reserved

8

Reserved

9

Reserved

EXT[1:0]

Dependencies

TriggerEn & PwrEvtEn & ContextEn

Generation
Scenario

MWAIT instruction, or I/O redirection to MWAIT, that complete
without fault or VMexit.

Description

Indicates that an MWAIT operation to C-state deeper than C0.0 completed. The MWAIT hints and extensions passed
in by software are exposed in the payload.
This packet is CYC-eligible, and hence will generate a CYC packet if IA32_RTIT_CTL.CYCEn=1 and any CYC Threshold
has been reached.

Application

The MWAIT packet should bind to the IP of the next FUP, which will be the IP of the instruction that caused the
MWAIT. This FUP will be shared with EXSTOP.

Vol. 3C 35-59

INTEL® PROCESSOR TRACE

35.4.2.24 Power Entry (PWRE) Packet
Table 35-43. PWRE Packet Definition
Name

PWRE Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

0

0

1

0

0

0

1

0

2

HW

Reserved

3

Resolved Thread C-State

Dependencies

TriggerEn & PwrEvtEn

Description

Indicates processor entry to the resolved thread C-state and sub C-state indicated. The processor will remain in this
C-state until either another PWRE indicates the processor has moved to a C-state deeper than C0.0, or a PWRX
packet indicates a return to C0.
Note that some CPUs may allow MWAIT to request a deeper C-state than is supported by the core. These deeper Cstates may have platform-level implications that differentiate them. However, the PWRE packet will provide only
the resolved thread C-state, which will not exceed that supported by the core.
If the C-state entry was initiated by hardware, rather than a direct software request (such as MWAIT, HLT, or shutdown), the HW bit will be set to indicate this. Hardware Duty Cycling (see Section 14.5, “Hardware Duty Cycling
(HDC)” in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3B) is an example of such a
case.

Application

When transitioning from C0.0 to a deeper C-state, the PWRE packet will be followed by an EXSTOP. If that EXSTOP
packet has the IP bit set, then the following FUP will provide the IP at which the C-state entry occurred. Subsequent
PWRE packets generated before the next PWRX should bind to the same IP.

35-60 Vol. 3C

Generation
Scenario

Resolved Thread Sub C-State
Transition to a C-state deeper than C0.0.

INTEL® PROCESSOR TRACE

35.4.2.25 Power Exit (PWRX) Packet
Table 35-44. PWRX Packet Definition
Name

PWRX Packet

Packet Format
7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

1

0

1

1

0

1

0

0

0

1

0

2

Last Core C-State

Deepest Core C-State

3

Reserved

Wake Reason

4

Reserved

5

Reserved

6

Reserved

Dependencies

TriggerEn & PwrEvtEn

Description

Indicates processor return to thread C0 from a C-state deeper than C0.0.
The Last Core C-State field provides the MWAIT encoding for the core C-state at the time of the wake. The Deepest
Core C-State provides the MWAIT encoding for the deepest core C-state achieved during the sleep session, or since
leaving thread C0. MWAIT encodings for C-states can be found in Table 4-11 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2B. Note that these values reflect only the core C-state, and hence will
not exceed the maximum supported core C-state, even if deeper C-states can be requested.
The Wake Reason field is one-hot, encoded as follows:

Application

35.5

Generation
Scenario

Transition from a C-state deeper than C0.0 to C0.

Bit

Field

Meaning

0

Interrupt

Wake due to external interrupt received.

1

Reserved

2

Store to Monitored Address

Wake due to store to monitored address.

3

HW Wake

Wake due to hardware autonomous condition,
such as HDC.

PWRX will always apply to the same IP as the PWRE. The time of wake can be discerned from (optional) timing packets that precede PWRX.

TRACING IN VMX OPERATION

On processors that IA32_VMX_MISC[bit 14] reports 1, TraceEn can be set in VMX operation. A series of mechanisms exist to allow the VMM to configure tracing based on the desired trace domain, and on the consumer of the
trace output. The VMM can configure specific VM-execution controls to control what virtualization-specific data are
included within the trace packets (see Section 35.5.1 for details). MSR save and load lists can be employed by the
VMM to restrict tracing to the desired context (see Section 35.5.2 for details). These configuration options are
summarized in Table 35-45. Table 35-45 covers common Intel PT usages while SMIs are handled by the default
SMM treatment. Tracing with SMM Transfer Monitor is described in Section 35.6.

Vol. 3C 35-61

INTEL® PROCESSOR TRACE

Table 35-45. Common Usages of Intel PT and VMX
Target Domain

Output
Consumer

Virtualize
Output

Configure VMCS
Controls

TraceEN Configuration

Save/Restore MSR states
of Trace Configuration

System-Wide
(VMM + VMs)

Host

NA

Default Setting
(no suppression)

WRMSR or XRSTORS by Host

NA

VMM Only

Intel PT Aware
VMM

NA

Enable
suppression

MSR load list to disable tracing in
VM, enable tracing on VM exits

NA

VM Only

Intel PT Aware
VMM

NA

Enable
suppression

MSR load list to enable tracing in
VM, disable tracing on VM exits

NA

Intel PT Aware
Guest(s)

Per Guest

VMM adds
trace output
virtualization

Enable
suppression

MSR load list to enable tracing in
VM, disable tracing on VM exits

VMM Update guest state
on XRSTORS-exiting VM
exits

35.5.1

VMX-Specific Packets and VMCS Controls

In all of the usages of VMX and Intel PT, the decoder in the host or VMM context can identify the occurrences of VMX
transitions with the aid of VMX-specific packets. Packets relevant to VMX fall into the follow two kinds:

•

VMCS Packet: The VMX transitions of individual VM can be distinguished by a decoder using the base address
field in a VMCS packet. The base address field stores the VMCS pointer address of a successful VMPTRLD. A
VMCS packet is sent on a successful execution of VMPTRLD. See Section 35.4.2.15 for details.

•

NonRoot (NR) bit field in PIP packet: PIP packets are generated with each VM entry/exit. The NR bit in a PIP
packet is set when in VMX non-Root operation. Thus a transition of the NR bit from 0 to 1 indicates the
occurrence of a VM entry, and a transition of 1 to 0 indicates the occurrence of a VM exit.

Processors with IA32_VMX_MISC[bit 14]= 1 also provides VMCS controls that a VMM can configure to prevent
VMX-specific information from leaking across virtualization boundaries.

Table 35-46. VMCS Controls For Intel Processor Trace
Name
Conceal VMX
non-root
operation from
Intel PT

Type
VM-execution
control

Bit
Position
19

Value
0

Behavior
PIPs generated in VM non-root operation will set the PIP.NR bit.
PSB+ in VMX non-root operation will include the VMCS packet, to ensure
that the decoder knows which guest is currently in use.

1

PIPs generated in VMX non-root operation will not set the PIP.NR bit.
PSB+ in VMX non-root operation will not include the VMCS packet.

Conceal VM
exits from Intel
PT

VM-exit control

Conceal VM
entries from
Intel PT

VM-entry control

24

0

PIPs are generated on VM exit, with NonRoot=0.
On VM exit to SMM, VMCS packets are additionally generated.

17

1

No PIP is generated on VM exit, and no VMCS packet is generated on
VM exit to SMM.

0

PIPs are generated on VM entry, with NonRoot=1 if the destination of
the VM entry is VMX non-root operation.
On VM entry to SMM, VMCS packets are additionally generated.

1

No PIP is generated on VM entry, and no VMCS packet is generated on
VM entry to SMM.

The default setting for the VMCS controls that interacts with Intel PT is to enable all VMX-specific packet information. The scenarios that would use the default setting also do not require the VMM to use MSR load list to manage
the configuration of turning-on/off of trace packet generation across VM exits.
If IA32_VMX_MISC[bit 14] reports 0, any attempt to set the VMCS control bits in Table 35-46 will result in a failure
on guest entry.

35-62 Vol. 3C

INTEL® PROCESSOR TRACE

35.5.2

Managing Trace Packet Generation Across VMX Transitions

In tracing scenarios that collect packets for both VMX root operation and VMX non-root operation, a host executive
can manage the MSRs associated with trace packet generation directly. The states of these MSRs need not be
modified using MSR load list or MSR save list across VMX transitions.
For tracing scenarios that collect only packets within either VMX root operation or VMX non-root operation, the
VMM can use the MSR load list and/or MSR save list to toggle IA32_RTIT_CTL.TraceEn.

35.5.2.1

System-Wide Tracing

When a host or VMM configures Intel PT to collect trace packets of the entire system, it can leave the VMCS controls
clear to allow VMX-specific packets to provide information across VMX transitions. MSR load list is not used across
VM exits or VM entries, nor is VM-exit MSR save list.
The decoder will desire to identify the occurrence of VMX transitions. The packets of interests to a decoder are
shown in Table 35-47.

Table 35-47. Packets on VMX Transitions (System-Wide Tracing)
Event
VM exit

Packets

Description

FUP(GuestIP)

The FUP indicates at which point in the guest flow the VM exit occurred. This is important,
since VM exit can be an asynchronous event. The IP will match that written into the VMCS.

PIP(HostCR3, NR=0)

The PIP packet provides the new host CR3 value, as well as indication that the logical processor
is entering VMX root operation. This allows the decoder to identify the change of executing
context from guest to host and load the appropriate set of binaries to continue decode.

TIP(HostIP)

The TIP indicates the destination IP, the IP of the first instruction to be executed in VMX root
operation.
Note, this packet could be preceded by a MODE.Exec packet (Section 35.4.2.8). This is
generated only in cases where CS.D or (CS.L & EFER.LMA) change during the transition.

VM entry

PIP(GuestCR3, NR=1)

The PIP packet provides the new guest CR3 value, as well as indication that the logical
processor is entering VMX non-root operation. This allows the decoder to identify the change
of executing context from host to guest and load the appropriate set of binaries to continue
decode.

TIP(GuestIP)

The TIP indicates the destination IP, the IP of the first instruction to be executed in VMX nonroot operation. This should match the IP value read out from the VMCS.
Note, this packet could be preceded by a MODE.Exec packet (Section 35.4.2.8). This is
generated only in cases where CS.D or (CS.L & EFER.LMA) change during the transition.

Since the packet suppression controls are cleared, the VMCS packet will be included in all PSB+ for this usage
scenario. Thus the decoder can distinguish the execution context of different VMs. Additionally, it will be generated
on VMPTRLD. Thus the decoder can distinguish the execution context of different VMs.
When the host VMM configures a system to collect trace packets in this scenario, it should emulate CPUID to report
CPUID.(EAX=07H, ECX=0):EBX[bit 26] with 0 to guests, indicating to guests that Intel PT is not available.

VMX TSC Manipulation
The TSC packets generated while in VMX non-root operation will include any changes resulting from the use of a
VMM’s use of the TSC offsetting or TSC scaling VMCS control (see Chapter 25, “VMX Non-Root Operation”). In this
system-wide usage model, the decoder may need to account for the effect of per-VM adjustments in the TSC
packets generated in VMX non-root operation and the absence of TSC adjustments in TSC packets generated in
VMX root operation. The VMM can supply this information to the decoder.

35.5.2.2

Host-Only Tracing

When trace packets in VMX non-root operation are not desired, the VMM can use VM-entry MSR load list with
IA32_RTIT_CTL.TraceEn=0 to disable trace packet generation in guests, set IA32_RTIT_CTL.TraceEn=1 via VMexit MSR load list.
Vol. 3C 35-63

INTEL® PROCESSOR TRACE

When tracing only the host, the decoder does not need information about the guests, the VMCS controls for
suppressing VMX-specific packets can be set to reduce the packets generated. VMCS packets will still be generated
on successful VMPTRLD and in PSB+ generated in the Host, but these will be unused by the decoder.
The packets of interests to a decoder when trace packets are collected for host-only tracing are shown in Table 3548.

Table 35-48. Packets on VMX Transitions (Host-Only Tracing)
Event
VM exit

Packets
TIP.PGE(HostIP)

Description
The TIP.PGE indicates that trace packet generation is enabled and gives the IP of the first
instruction to be executed in VMX root operation.
Note, this packet could be preceded by a MODE.Exec packet (Section 35.4.2.8). This is
generated only in cases where CS.D or (CS.L & EFER.LMA) change during the transition.

VM entry

35.5.2.3

TIP.PGD()

The TIP indicates that trace packet generation was disabled. This ensure that all buffered
packets are flushed out.

Guest-Only Tracing

A VMM can configure trace packet generation while in non-root operation for guests executing normally. This is
accomplished by utilizing the MSR load lists across VM exit and VM entry to confine trace packet generation to
stay within the guest environment.
For this usage, the VM-entry MSR load list is programmed to turn on trace packet generation. The VM-exit MSR
load list is used to clear TraceEn=0 to disable trace packet generation in the host. Further, if it is preferred that
the guest packet stream contain no indication that execution was in VMX non-root operation, the VMM should set
the VMCS controls described in Table 35-46.

35.5.2.4

Virtualization of Guest Output Packet Streams

Each Intel PT aware guest OS can produce one or more output packet streams to destination addresses specified
as guest physical address (GPA) using context-switched IA32_RTIT_OUTPUT_BASE within the guest. The processor
generates trace packets to the platform physical address specified in IA32_RTIT_OUTPUT_BASE, and those specified in the ToPA tables. Thus, a VMM that supports Intel PT aware guest OS may wish to virtualize the output configurations of IA32_RTIT_OUTPUT_BASE and ToPA for each trace configuration state of all the guests.

35.5.2.5

Emulation of Intel PT Traced State

If a VMM emulates an element of processor state by taking a VM exit on reads and/or writes to that piece of state,
and the state element impacts Intel PT packet generation or values, it may be incumbent upon the VMM to insert
or modify the output trace data.
If a VM exit is taken on a guest write to CR3 (including “MOV CR3” as well as task switches), the PIP packet
normally generated on the CR3 write will be missing.
To avoid decoder confusion when the guest trace is decoded, the VMM should emulate the missing PIP by writing it
into the guest output buffer. If the guest CR3 value is manipulated, the VMM may also need to manipulate the
IA32_RTIT_CR3_MATCH value, in order to ensure the trace behavior matches the guest's expectation.
Similarly, if a VMM emulates the TSC value by taking a VM exit on RDTSC, the TSC packets generated in the trace
may mismatch the TSC values returned by the VMM on RDTSC. To ensure that the trace can be properly aligned
with software logs based on RDTSC, the VMM should either make corresponding modifications to the TSC packet
values in the guest trace, or use mechanisms such as TSC offsetting or TSC scaling in place of exiting.

35.5.2.6

TSC Scaling

When TSC scaling is enabled for a guest using Intel PT, the VMM should ensure that the value of Maximum NonTurbo Ratio[15:8] in MSR_PLATFORM_INFO (MSR 0CEH) and the TSC/”core crystal clock” ratio (EBX/EAX) in CPUID
leaf 15H are set in a manner consistent with the resulting TSC rate that will be visible to the VM. This will allow the
decoder to properly apply TSC packets, MTC packets (based on the core crystal clock or ART, whose frequency is
indicated by CPUID leaf 15H), and CBR packets (which indicate the ratio of the processor frequency to the Max
35-64 Vol. 3C

INTEL® PROCESSOR TRACE

Non-Turbo frequency). Absent this, or separate indication of the scaling factor, the decoder will be unable to properly track time in the trace. See Section 35.8.3 for details on tracking time within an Intel PT trace.

35.5.2.7

Failed VM Entry

The packets generated by a failed VM entry depend both on the VMCS configuration, as well as on the type of
failure. The results to expect are summarized in the table below. Note that packets in italics may or may not be
generated, depending on implementation choice, and the point of failure.

Table 35-49. Packets on a Failed VM Entry
Usage Model

Entry Configuration

Early Failure (fall
through to Next IP)

Late Failure (VM exit)

System-Wide

No MSR load list

TIP (NextIP)

PIP(Guest CR3, NR=1), TraceEn 0->1 Packets (See Section
35.2.7.3), PIP(HostCR3, NR=0), TIP(HostIP)

VMM Only

MSR load list
disables TraceEn

TIP (NextIP)

TraceEn 0->1 Packets (See Section 35.2.7.3), TIP(HostIP)

VM Only

MSR load list
Enables TraceEn

None

None

35.5.2.8

VMX Abort

VMX abort conditions take the processor into a shutdown state. On a VM exit that leads to VMX abort, some packets
(FUP, PIP) may be generated, but any expected TIP, TIP.PGE, or TIP.PGD may be dropped.

35.6

TRACING AND SMM TRANSFER MONITOR (STM)

SMM Transfer Monitor is a VMM that operates inside SMM while in VMX root operation. An STM operates in conjunction with an executive monitor. The latter operates outside SMM and in VMX root operation. Transitions from the
executive monitor or its VMs to the STM are called SMM VM exits. The STM returns from SMM via a VM entry to the
VM in VMX non-root operation or the executive monitor in VMX root operation.
Intel PT supports tracing in an STM similar to tracing support for VMX operation as described above in Section 35.7.
As a result, on a SMM VM exit resulting from #SMI, TraceEn is not saved and then cleared. Software can save the
state of the trace configuration MSRs and clear TraceEn using the MSR load/save lists.

35.7

PACKET GENERATION SCENARIOS

Table 35-50 and Table 35-52 illustrate the packets generated in various scenarios. In the heading row, PacketEn is
abbreviated as PktEn, ContextEn as CntxEn. Note that this assumes that TraceEn=1 in IA32_RTIT_CTL, while TriggerEn=1 and Error=0 in IA32_RTIT_STATUS, unless otherwise specified. Entries that do not matter in packet
generation are marked “D.C.” Packets followed by a “?” imply that these packets depend on additional factors,
which are listed in the “Other Dependencies” column.
In Table 35-50, PktEn is evaluated based on TiggerEn & ContextEn & FilterEn & BranchEn.

Table 35-50. Packet Generation under Different Enable Conditions
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

1a

Normal non-jump operation

0

0

D.C.

None

1b

Normal non-jump operation

1

1

1

None

2a

WRMSR/XRSTORS/RSM that changes
0
TraceEn 0 -> 1, with PacketByteCnt >0

0

D.C.

*TSC if TSCEn=1;
*TMA if TSCEn=MTCEn=1

TSC?, TMA?, CBR

Vol. 3C 35-65

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

2b

WRMSR/XRSTORS/RSM that changes
0
TraceEn 0 -> 1, with PacketByteCnt =0

0

D.C.

*TSC if TSCEn=1;
*TMA if TSCEn=MTCEn=1

PSB, PSBEND (see Section 35.4.2.17)

2d

WRMSR/XRSTORS/RSM that changes
0
TraceEn 0 -> 1, with PacketByteCnt >0

1

1

TSC if TSCEn=1;
TMA if TSCEn=MTCEn=1

TSC?, TMA?, CBR,
MODE.Exec, TIP.PGE(NLIP)

2e

WRMSR/XRSTORS/RSM that changes
0
TraceEn 0 -> 1, with PacketByteCnt =0

1

1

MODE.Exec,
TIP.PGE(NLIP), PSB,
PSBEND (see Section
35.4.2.8, 35.4.2.7,
35.4.2.13,35.4.2.15,
35.4.2.17)

3a

WRMSR that changes TraceEn 1 -> 0

0

0

D.C.

None

3b

WRMSR that changes TraceEn 1 -> 0

1

0

D.C.

FUP(CLIP), TIP.PGD()

5a

MOV to CR3

0

0

0

None

5f

MOV to CR3

0

0

1

TraceStop if executed in a
TraceStop region

PIP(NewCR3,NR?), TraceStop?

5b

MOV to CR3

0

1

1

*PIP.NR=1 if not in root
operation, and “Conceal
VMX non-root operation
from Intel PT” execution
control = 0
*MODE.Exec if the mode has
changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

PIP(NewCR3, NR?),
MODE.Exec?,
TIP.PGE(NLIP)

5c

MOV to CR3

1

0

0

5e

MOV to CR3

1

0

1

*PIP.NR=1 if not in root
operation, and “Conceal
VMX non-root operation
from Intel PT” execution
control = 0
*TraceStop if executed in a
TraceStop region

PIP(NewCR3, NR?),
TIP.PGE(NLIP), TraceStop?

5d

MOV to CR3

1

1

1

*PIP.NR=1 if not in root
operation, and “Conceal
VMX non-root operation
from Intel PT” execution
control = 0

PIP(NewCR3, NR?)

6a

Unconditional direct near jump

0

0

D.C.

6b

Unconditional direct near jump

1

0

1

TraceStop if BLIP is in a
TraceStop region

TIP.PGD(BLIP), TraceStop?

6c

Unconditional direct near jump

0

1

1

MODE.Exec if the mode has
changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

MODE.Exec?,
TIP.PGE(BLIP)

6d

Unconditional direct near jump

1

1

1

None

7a

Conditional taken jump or compressed
RET that does not fill up the internal
TNT buffer

0

0

D.C.

None

35-66 Vol. 3C

TIP.PGD()

None

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

7b

Conditional taken jump or compressed
RET

0

1

1

MODE.Exec if the mode has
changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

MODE.Exec?,
TIP.PGE(BLIP)

7e

Conditional taken jump or compressed
RET, with empty TNT buffer

1

0

1

TraceStop if BLIP is in a
TraceStop region

TIP.PGD(), TraceStop?

7f

Conditional taken jump or compressed
RET, with non-empty TNT buffer

1

0

1

TraceStop if BLIP is in a
TraceStop region

TNT, TIP.PGD(), TraceStop?

7d

Conditional taken jump or compressed
RET that fills up the internal TNT buffer

1

1

1

TNT

8a

Conditional non-taken jump

0

0

D.C.

None

8d

Conditional not-taken jump that fills up
the internal TNT buffer

1

1

1

TNT

9a

Near indirect jump (JMP, CALL, or
uncompressed RET)

0

0

D.C.

None

9b

Near indirect jump (JMP, CALL, or
uncompressed RET)

0

1

1

MODE.Exec if the mode has
changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

MODE.Exec?,
TIP.PGE(BLIP)

9c

Near indirect jump (JMP, CALL, or
uncompressed RET)

1

0

1

TraceStop if BLIP is in a
TraceStop region

TIP.PGD(BLIP), TraceStop?

9d

Near indirect jump (JMP, CALL, or
uncompressed RET)

1

1

1

TIP(BLIP)

10a

Far Branch (CALL/JMP/RET)

0

0

0

None

10f

Far Branch (CALL/JMP/RET)

0

0

1

*PIP if CR3 is updated (i.e.,
task switch), and OS=1;
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

PIP(new CR3, NR?), TraceStop?

10b

Far Branch (CALL/JMP/RET)

0

1

1

*PIP if CR3 is updated (i.e.,
task switch), and OS=1;
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*MODE.Exec if the mode has
changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

PIP(new CR3, NR?),
MODE.Exec?,
TIP.PGE(BLIP)

10c

Far Branch (CALL/JMP/RET)

1

0

0

TIP.PGD()

Vol. 3C 35-67

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

10d

Far Branch (CALL/JMP/RET)

1

0

1

*PIP if CR3 is updated (i.e.,
task switch), and OS=1;
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

PIP(new CR3, NR?),
TIP.PGD(BLIP), TraceStop?

10e

Far Branch (CALL/JMP/RET)

1

1

1

*PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
* MODE.Exec if the operation changes CS.L/D or
IA32_EFER.LMA

PIP(NewCR3, NR?)?,
MODE.Exec?, TIP(BLIP)

11a

HW Interrupt

0

0

0

11f

HW Interrupt

0

0

1

*PIP if CR3 is updated (i.e.,
task switch), and OS=1;
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

PIP(new CR3, NR?), TraceStop?

11b

HW Interrupt

0

1

1

*PIP if CR3 is updated (i.e.,
task switch), and OS=1;
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
* MODE.Exec if the mode
has changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

PIP(new CR3, NR?),
MODE.Exec?,
TIP.PGE(BLIP)

11c

HW Interrupt

1

0

0

11d

HW Interrupt

1

0

1

35-68 Vol. 3C

None

FUP(NLIP), TIP.PGD()
* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

FUP(NLIP), PIP(NewCR3,
NR?)?, TIP.PGD(BLIP),
TraceStop

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies
* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
* MODE.Exec if the operation changes CS.L/D or
IA32_EFER.LMA

Packets Output

11e

HW Interrupt

1

1

1

12a

SW Interrupt

0

0

0

12f

SW Interrupt

0

0

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

PIP(NewCR3, NR?)?,
TraceStop?

12b

SW Interrupt

0

1

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*MODE.Exec if the mode has
changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

PIP(NewCR3, NR?)?,
MODE.Exec?,
TIP.PGE(BLIP)

12c

SW Interrupt

1

0

0

12d

SW Interrupt

1

0

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

FUP(CLIP), PIP(NewCR3,
NR?)?, TIP.PGD(BLIP),
TraceStop?

12e

SW Interrupt

1

1

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
* MODE.Exec if the operation changes CS.L/D or
IA32_EFER.LMA

FUP(CLIP), PIP(NewCR3,
NR?)?, MODE.Exec?,
TIP(BLIP)

13a

Exception/Fault

0

0

0

FUP(NLIP), PIP(NewCR3,
NR?)?, MODE.Exec?,
TIP(BLIP)

None

FUP(CLIP), TIP.PGD()

None
Vol. 3C 35-69

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

13f

Exception/Fault

0

0

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

PIP(NewCR3, NR?)?,
TraceStop?

13b

Exception/Fault

0

1

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*MODE.Exec if the mode has
changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

PIP(NewCR3, NR?)?,
MODE.Exec?,
TIP.PGE(BLIP)

13c

Exception/Fault

1

0

0

13d

Exception/Fault

1

0

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
*TraceStop if BLIP is in a
TraceStop region

FUP(CLIP), PIP(NewCR3,
NR?)?, TIP.PGD(BLIP),
TraceStop?

13e

Exception/Fault

1

1

1

* PIP if CR3 is updated (i.e.,
task switch), and OS=1
*PIP.NR=1 if destination is
not root operation, and
“Conceal VMX non-root
operation from Intel PT”
execution control = 0;
* MODE.Exec if the operation changes CS.L/D or
IA32_EFER.LMA

FUP(CLIP), PIP(NewCR3,
NR?)?, MODE.Exec?,
TIP(BLIP)

14a

SMI (TraceEn cleared)

0

0

D.C.

None

14b

SMI (TraceEn cleared)

1

0

0

FUP(SMRAM,LIP),
TIP.PGD()

14f

SMI (TraceEn cleared)

1

0

1

NA

14c

SMI (TraceEn cleared)

1

1

1

NA

15a

RSM, TraceEn restored to 0

0

0

0

None

15b

RSM, TraceEn restored to 1

0

0

D.C.

See WRMSR cases for
packets on enable

35-70 Vol. 3C

FUP(CLIP), TIP.PGD()

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

15c

RSM, TraceEn restored to 1

0

1

1

See WRMSR cases for
packets on enable.
FUP/TIP.PGE IP is
SMRAM.LIP

15e

RSM (TraceEn=1, goes to shutdown)

1

0

0

None

15f

RSM (TraceEn=1, goes to shutdown)

1

0

1

None

15d

RSM (TraceEn=1, goes to shutdown)

1

1

1

None

16i

Vmext

0

0

0

None

16a

Vmext

0

0

1

16b

VM exit, MSR list sets TraceEn=1

0

0

0

See WRMSR cases for
packets on enable. FUP IP
is VMCSh.LIP

16c

VM exit, MSR list sets TraceEn=1

0

1

1

See WRMSR cases for
packets on enable.
FUP/TIP.PGE IP is
VMCSh.LIP

16e

VM exit

0

1

1

*PIP if OF=1, and “Conceal
PIP(HostCR3, NR=0)?,
VM exits from Intel PT” exe- MODE.Exec?,
cution control = 0;
TIP.PGE(VMCSh.LIP)
*MODE.Exec if the value is
different, since last TIP.PGD

16f

VM exit, MSR list clears TraceEn=0

1

0

0

*PIP if OF=1, and “Conceal
FUP(VMCSg.LIP),
VM exits from Intel PT” exe- PIP(HostCR3, NR=0)?,
cution control = 0;
TIP.PGD

16j

VM exit, ContextEN 1->0

1

0

0

16g

VM exit

1

0

1

*PIP if OF=1, and “Conceal
VM exits from Intel PT” execution control = 0;
*TraceStop if VMCSh.LIP is
in a TraceStop region

FUP(VMCSg.LIP),
PIP(HostCR3, NR=0)?,
TIP.PGD(VMCSh.LIP),
TraceStop?

16h

VM exit

1

1

1

*PIP if OF=1, and “Conceal
VM exits from Intel PT” execution control = 0;
*MODE.Exec if the value is
different, since last TIP.PGD

FUP(VMCSg.LIP),
PIP(HostCR3, NR=0)?,
MODE.Exec,
TIP(VMCSh.LIP)

17a

VM entry

0

0

0

17b

VM entry

0

0

1

17c

VM entry, MSR load list sets TraceEn=1 0

0

1

*PIP if OF=1, and “Conceal
PIP(HostCR3, NR=0)?,
VM exits from Intel PT” exe- TraceStop?
cution control = 0;
*TraceStop if VMCSh.LIP is
in a TraceStop region

FUP(VMCSg.LIP), TIP.PGD

None
*PIP if OF=1, and “Conceal
VM entries from Intel PT”
execution control = 0;
*TraceStop if VMCSg.LIP is
in a TraceStop region

PIP(GuestCR3, NR=1)?,
TraceStop?

See WRMSR cases for
packets on enable. FUP IP
is VMCSg.LIP
Vol. 3C 35-71

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

17d

VM entry, MSR load list sets TraceEn=1 0

1

1

17f

VM entry, FilterEN 0->1

0

1

1

*PIP if OF=1, and “Conceal
VM entries from Intel PT”
execution control = 0;
*MODE.Exec if the value is
different, since last TIP.PGD

PIP(GuestCR3, NR=1)?,
MODE.Exec?,
TIP.PGE(VMCSg.LIP)

17j

VM entry, ContextEN 0->1

0

1

1

*MODE.Exec if the value is
different, since last TIP.PGD

MODE.Exec,
TIP.PGE(VMCSg.LIP)

17g

VM entry, MSR list clears TraceEn=0

1

0

0

*PIP if OF=1, and “Conceal
VM entries from Intel PT”
execution control = 0;

PIP(GuestCR3, NR=1)?,
TIP.PGD

17h

VM entry

1

0

1

*PIP if OF=1, and “Conceal
VM entries from Intel PT”
execution control = 0;
*TraceStop if VMCSg.LIP is
in a TraceStop region

PIP(GuestCR3, NR=1)?,
TIP.PGD(VMCSg.LIP),
TraceStop?

17i

VM entry

1

1

1

*PIP if OF=1, and “Conceal
VM entries from Intel PT”
execution control = 0;
*MODE.Exec if the value is
different, since last TIP.PGD

PIP(GuestCR3, NR=1)?,
MODE.Exec,
TIP(VMCSg.LIP)

20a

EENTER/ERESUME to non-debug
enclave

0

0

0

None

20c

EENTER/ERESUME to non-debug
enclave

1

0

0

FUP(CLIP), TIP.PGD()

21a

EEXIT from non-debug enclave

0

0

D.C.

None

21b

EEXIT from non-debug enclave

0

1

1

22a

AEX/EEE from non-debug enclave

0

0

D.C.

22b

AEX/EEE from non-debug enclave

0

1

1

23a

EENTER/ERESUME to debug enclave

0

0

D.C.

23b

EENTER/ERESUME to debug enclave

0

1

1

23c

EENTER/ERESUME to debug enclave

1

0

0

23d

EENTER/ERESUME to debug enclave

0

0

1

23e

EENTER/ERESUME to debug enclave

1

1

1

FUP(CLIP), TIP(BLIP)

24f

EEXIT from debug enclave

0

0

D.C.

None

24b

EEXIT from debug enclave

0

1

1

*MODE.Exec if the value is
different, since last TIP.PGD

MODE.Exec?,
TIP.PGE(BLIP)

24d

EEXIT from debug enclave

1

0

1

*TraceStop if BLIP is in a
TraceStop region

FUP(CLIP), TIP.PGD(BLIP),
TraceStop?

35-72 Vol. 3C

See WRMSR cases for
packets on enable.
FUP/TIP.PGE IP is
VMCSg.LIP

*MODE.Exec if the value is
different, since last TIP.PGD

MODE.Exec?,
TIP.PGE(BLIP)
None

*MODE.Exec if the value is
different, since last TIP.PGD

MODE.Exec?,
TIP.PGE(AEP.LIP)
None

*MODE.Exec if the value is
different, since last TIP.PGD

MODE.Exec?,
TIP.PGE(BLIP)
FUP(CLIP), TIP.PGD()

*TraceStop if BLIP is in a
TraceStop region

FUP(CLIP), TIP.PGD(BLIP),
TraceStop?

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

24e

EEXIT from debug enclave

1

1

1

FUP(CLIP), TIP(BLIP)

25a

AEX/EEE from debug enclave

0

0

D.C.

None

25b

AEX/EEE from debug enclave

0

1

1

*MODE.Exec if the value is
different, since last TIP.PGD

MODE.Exec?,
TIP.PGE(AEP.LIP)

25d

AEX/EEE from debug enclave

1

0

1

*For AEX, FUP IP could be
NLIP, for trap-like events

FUP(CLIP),
TIP.PGD(AEP.LIP)

25e

AEX/EEE from debug enclave

1

1

1

*MODE.Exec if the value is
different, since last TIP.PGD
*For AEX, FUP IP could be
NLIP, for trap-like events

FUP(CLIP), MODE.Exec?,
TIP(AEP.LIP)

26a

XBEGIN/XACQUIRE

0

0

D.C.

None

26d

XBEGIN/XACQUIRE that does not set
InTX

1

1

1

None

26e

XBEGIN/XACQUIRE that sets InTX

1

1

1

MODE(InTX=1,
TXAbort=0), FUP(CLIP)

27a

XEND/XRELEASE

0

0

D.C.

None

27d

XEND/XRELEASE that does not clear
InTX

1

1

1

None

27e

XEND/XRELEASE that clears InTX

1

1

1

MODE(InTX=0,
TXAbort=0), FUP(CLIP)

28a

XABORT(Async XAbort, or other)

0

0

0

None

28e

XABORT(Async XAbort, or other)

0

0

1

28b

XABORT(Async XAbort, or other)

0

1

1

28c

XABORT(Async XAbort, or other)

1

0

1

28d

XABORT(Async XAbort, or other)

1

1

1

MODE(InTX=0,
TXAbort=1), FUP(CLIP),
TIP(BLIP)

30a

INIT (BSP)

0

0

0

None

30b

INIT (BSP)

0

0

1

*TraceStop if RESET.LIP is in
a TraceStop region

BIP(0), TraceStop?

30c

INIT (BSP)

0

1

1

* MODE.Exec if the value is
different, since last TIP.PGD

MODE.Exec?, PIP(0),
TIP.PGE(ResetLIP)

30d

INIT (BSP)

1

0

0

30e

INIT (BSP)

1

0

1

*TraceStop if BLIP is in a
TraceStop region

MODE(InTX=0,
TXAbort=1), TraceStop?
MODE(InTX=0,
TXAbort=1),
TIP.PGE(BLIP)

*TraceStop if BLIP is in a
TraceStop region

MODE(InTX=0,
TXAbort=1), TIP.PGD
(BLIP), TraceStop?

FUP(NLIP), TIP.PGD()
* PIP if OS=1
*TraceStop if RESET.LIP is in
a TraceStop region

FUP(NLIP), PIP(0),
TIP.PGD, TraceStop?

Vol. 3C 35-73

INTEL® PROCESSOR TRACE

Table 35-50. Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies
* MODE.Exec if the mode
has changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB
* PIP if OS=1

Packets Output

30f

INIT (BSP)

1

1

1

31a

INIT (AP, goes to wait-for-SIPI)

0

D.C.

D.C.

31b

INIT (AP, goes to wait-for-SIPI)

1

D.C.

D.C.

32a

SIPI

0

0

0

32c

SIPI

0

1

1

32d

SIPI

1

0

0

32e

SIPI

1

0

1

*TraceStop if SIPI LIP is in a
TraceStop region

TIP.PGD(SIPILIP); TraceStop?

32f

SIPI

1

1

1

* MODE.Exec if the mode
has changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

MODE.Exec?, TIP(SIPILIP)

33a

MWAIT (to C0)

D.C.

D.C.

D.C.

33b

MWAIT (to higher-numbered C-State,
packet sent on wake)

D.C.

D.C.

D.C.

FUP(NLIP), PIP(0)?,
MODE.Exec?,
TIP(ResetLIP)

None
* PIP if OS=1

FUP(NLIP), PIP(0)
None

* MODE.Exec if the mode
has changed since the last
MODE.Exec, or if no
MODE.Exec since last PSB

MODE.Exec?, TIP.PGE(SIPILIP)

TIP.PGD

None
*TSC if TSCEn=1
*TMA if TSCEn=MTCEn=1

TSC?, TMA?, CBR

In Table 35-52, PktEn is evaluated based on (TiggerEn & ContextEn & FilterEn & BranchEn & PwrEvtEn).

Table 35-51. PwrEvtEn and PTWEn Packet Generation under Different Enable Conditions
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

16.1

MWAIT or I/O redir to MWAIT, gets
#UD or #GP fault

dc

dc

dc

None

16.2

MWAIT or I/O redir to MWAIT, VM
exits

dc

dc

dc

See VM exit examples
(16[a-z] in Table 35-50)
for BranchEn packets.

16.3

MWAIT or I/O redir to MWAIT,
requests C0, or monitor not armed,
or VMX virtual-interrupt delivery

dc

dc

dc

None

16.4a

MWAIT(X) or I/O redir to MWAIT,
goes to C-state Y (Y>0)

dc

0

0

PWRE(Cx), EXSTOP

16.4b

MWAIT(X) or I/O redir to MWAIT,
goes to C-state Y (Y>0)

dc

dc

1

MWAIT(Cy), PWRE(Cx),
EXSTOP(IP), FUP(CLIP)

16.5a

MWAIT(X) or I/O redir to MWAIT,
Pending event after resolving to go
to C-state Y (Y>0)

dc

0

0

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

PWRE(Cx), EXSTOP, TSC?,
TMA?, CBR, PWRX(LCC,
DCC, 0)

16.5b

MWAIT(X) or I/O redir to MWAIT,
Pending event after resolving to go
to C-state Y (Y>0)

dc

dc

1

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

PWRE(Cx), EXSTOP(IP),
FUP(CLIP), TSC?, TMA?,
CBR, PWRX(LCC, DCC, 0)

35-74 Vol. 3C

INTEL® PROCESSOR TRACE

Table 35-51. PwrEvtEn and PTWEn Packet Generation under Different Enable Conditions (Contd.)
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

16.6a

MWAIT(5) or I/O redir to MWAIT,
other thread(s) in core in C0/C1

dc

0

0

PWRE(C1), EXSTOP

16.6b

MWAIT(5) or I/O redir to MWAIT,
other thread(s) in core in C0/C1

dc

dc

1

MWAIT(5), PWRE(C1),
EXSTOP(IP), FUP(CLIP)

16.9a

HLT, Triple-fault shutdown, #MC
with CR4.MCE=0, RSM to Cx (x>0)

dc

0

0

PWRE(C1), EXSTOP

16.9b

HLT, Triple-fault shutdown, #MC
with CR4.MCE=1, RSM to Cx (x>0)

dc

dc

16.10a

VMX abort

dc

0

PWRE(C1), EXSTOP(IP),
FUP(CLIP)
0

See “VMX Abort” (cases
16* and 18* in Table 3550) for BranchEn packets
that precede
PWRE(C1), EXSTOP

16.10b

VMX abort

dc

dc

1

See “VMX Abort” (cases
16* and 18* in Table 3550) for BranchEn packets
that precede
PWRE(C1), EXSTOP(IP),
FUP(CLIP)

16.11a

RSM to Shutdown

dc

0

0

See “RSM to Shutdown”
(cases 15[def] in Table
35-50) for BranchEn
packets that precede
PWRE(C1), EXSTOP

16.11b

RSM to Shutdown

dc

dc

1

See “RSM to Shutdown”
(cases 15[def] in Table
35-50) for BranchEn
packets that precede
PWRE(C1), EXSTOP(IP),
FUP(CLIP)

16.12a

INIT (BSP)

dc

0

0

See “INIT (BSP)” (cases
30[a-z] in Table 35-50)
for packets that BranchEn
precede
PWRE(C1), EXSTOP

16.12b

INIT (BSP)

dc

dc

1

See “INIT (BSP)” (cases
30[a-z] in Table 35-50)
for packets that BranchEn
precede
PWRE(C1), EXSTOP(IP),
FUP(NLIP)

Vol. 3C 35-75

INTEL® PROCESSOR TRACE

Table 35-51. PwrEvtEn and PTWEn Packet Generation under Different Enable Conditions (Contd.)
Case
16.13a

Operation
INIT (AP, goes to Wait-for-SIPI)

PktEn
Before

PktEn CntxEn
After
After

dc

0

Other Dependencies

0

Packets Output
See “INIT (AP, goes to
Wait-for-SIPI)” (cases
31[a-z] in Table 35-50)
for BranchEn packets that
precede
PWRE(C1), EXSTOP

16.13b

INIT (AP, goes to Wait-for-SIPI)

dc

dc

1

See “INIT (AP, goes to
Wait-for-SIPI)” (cases
31[a-z] in Table 35-50)
for BranchEn packets that
precede
PWRE(C1), EXSTOP(IP),
FUP(NLIP)

16.14a

Hardware Duty Cycling (HDC)

dc

0

0

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

PWRE(HW, C6), EXSTOP,
TSC?, TMA?, CBR,
PWRX(CC6, CC6, 0x8)

16.14b

Hardware Duty Cycling (HDC)

dc

dc

1

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

PWRE(HW, C6), EXSTOP(IP), FUP(NLIP), TSC?,
TMA?, CBR, PWRX(CC6,
CC6, 0x8)

16.15a

VM entry to HLT or Shutdown

dc

0

0

See “VM entry” (cases
17[a-z] in Table 35-50)
for BranchEn packets that
precede.
PWRE(C1), EXSTOP

16.15b

VM entry to HLT or Shutdown

dc

dc

1

See “VM entry” (cases
17[a-z] in Table 35-50)
for BranchEn packets that
precede.
PWRE(C1), EXSTOP(IP),
FUP(CLIP)

16.16a

EIST in C0, S1/TM1/TM2, or STPCLK#

dc

0

0

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

EXSTOP, TSC?, TMA?, CBR

16.16b

EIST in C0, S1/TM1/TM2, or STPCLK#

dc

dc

1

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

EXSTOP(IP), FUP(NLIP),
TSC?, TMA?, CBR

16.17

EIST in Cx (x>0)

dc

dc

dc

16.18

INTR during Cx (x>0)

dc

dc

dc

None
* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

TSC?, TMA?, CBR,
PWRX(LCC, DCC, 0x1)
See “HW Interrupt” (cases
11[a-z] in Table 35-50)
for BranchEn packets that
follow.

35-76 Vol. 3C

INTEL® PROCESSOR TRACE

Table 35-51. PwrEvtEn and PTWEn Packet Generation under Different Enable Conditions (Contd.)
Case
16.18

Operation
SMI during Cx (x>0)

PktEn
Before

PktEn CntxEn
After
After

dc

dc

dc

Other Dependencies
* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

Packets Output
TSC?, TMA?, CBR,
PWRX(LCC, DCC, 0)
See “HW Interrupt” (cases
14[a-z] in Table 35-50)
for BranchEn packets that
follow.

16.19

NMI during Cx (x>0)

dc

dc

dc

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

TSC?, TMA?, CBR,
PWRX(LCC, DCC, 0)
See “HW Interrupt” (cases
11[a-z] in Table 35-50)
for BranchEn packets that
follow.

16.2

Store to monitored address during
Cx (x>0)

dc

dc

dc

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

TSC?, TMA?, CBR,
PWRX(LCC, DCC, 0x4)

16.22

#MC, IERR, TSC deadline timer
expiration, or APIC counter underflow during Cx (x>0)

dc

dc

dc

* TSC if TSCEn=1
* TMA if TSCEn=MTCEn=1

TSC?, TMA?, CBR,
PWRX(LCC, DCC, 0)

Vol. 3C 35-77

INTEL® PROCESSOR TRACE

In Table 35-52, PktEn is evaluated based on (TiggerEn & ContextEn & FilterEn & BranchEn & PTWEn).

Table 35-52. PwrEvtEn and PTWEn Packet Generation under Different Enable Conditions
Case

Operation

PktEn
Before

PktEn CntxEn
After
After

Other Dependencies

Packets Output

16.24a

PTWRITE rm32/64, no fault

dc

dc

dc

None

16.24b

PTWRITE rm32/64, no fault

dc

0

0

None

16.24d

PTWRITE rm32, no fault

dc

1

1

* FUP, IP=1 if FUPonPTW=1

PTW(IP=1?, 4B,
rm32_value), FUP(CLIP)?

16.24e

PTWRITE rm64, no fault

dc

1

1

* FUP, IP=1 if FUPonPTW=1

PTW(IP=1?, 8B,
rm64_value), FUP(CLIP)?

16.25a

PTWRITE mem32/64, fault

dc

dc

dc

35.8

SOFTWARE CONSIDERATIONS

35.8.1

Tracing SMM Code

See “Exception/fault”
(cases 13[a-z] in Table
35-50) for BranchEn
packets.

Nothing prevents an SMM handler from configuring and enabling packet generation for its own use. As described in
Section , SMI will always clear TraceEn, so the SMM handler would have to set TraceEn in order to enable tracing.
There are some unique aspects and guidelines involved with tracing SMM code, which follows:
1. SMM should save away the existing values of any configuration MSRs that SMM intends to modify for tracing.
This will allow the non-SMM tracing context to be restored before RSM.
2. It is recommended that SMM wait until it sets CSbase to 0 before enabling packet generation, to avoid possible
LIP vs RIP confusion.
3. Packet output cannot be directed to SMRR memory, even while tracing in SMM.
4. Before performing RSM, SMM should take care to restore modified configuration MSRs to the values they had
immediately after #SMI. This involves first disabling packet generation by clearing TraceEn, then restoring any
other configuration MSRs that were modified.
5. RSM
— Software must ensure that TraceEn=0 at the time of RSM. Tracing RSM is not a supported usage model, and
the packets generated by RSM are undefined.
— For processors on which Intel PT and LBR use are mutually exclusive (see Section 35.3.1.2), any RSM
during which TraceEn is restored to 1 will suspend any LBR or BTS logging.

35.8.2

Cooperative Transition of Multiple Trace Collection Agents

A third-party trace-collection tool should take into consideration the fact that it may be deployed on a processor
that supports Intel PT but may run under any operating system.
In such a deployment scenario, Intel recommends that tool agents follow similar principles of cooperative transition
of single-use hardware resources, similar to how performance monitoring tools handle performance monitoring
hardware:

•

Respect the “in-use” ownership of an agent who already configured the trace configuration MSRs, see architectural MSRs with the prefix “IA32_RTIT_” in Chapter 2, “Model-Specific Registers (MSRs)” in the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 4, where “in-use” can be determined by reading the
“enable bits” in the configuration MSRs.

35-78 Vol. 3C

INTEL® PROCESSOR TRACE

•

Relinquish ownership of the trace configuration MSRs by clearing the “enabled bits” of those configuration
MSRs.

35.8.3

Tracking Time

This section describes the relationships of several clock counters whose update frequencies reside in different
domains that feed into the timing packets. To track time, the decoder also needs to know the regularity or irregularity of the occurrences of various timing packets that store those clock counters.
Intel PT provides time information for three different but related domains:

•

Processor timestamp counter

•

This counter increments at the max non-turbo or P1 frequency, and its value is returned on a RDTSC. Its
frequency is fixed. The TSC packet holds the lower 7 bytes of the timestamp counter value. The TSC packet
occurs occasionally and are much less frequent than the frequency of the time stamp counter. The timestamp
counter will continue to increment when the processor is in deep C-States, with the exception of processors
reporting CPUID.80000007H:EDX.InvariantTSC[bit 8] =0.
Core crystal clock
The ratio of the core crystal clock to timestamp counter frequency is known as P, and can calculating
CPUID.15H:EBX[31:0] / CPUID.15H:EAX[31:0]. The frequency of the core crystal clock is fixed and lower than
that of the timestamp counter. The periodic MTC packet is generated based on software-selected multiples of
the crystal clock frequency. The MTC packet is expected to occur more frequently than the TSC packet.

•

Processor core clock
The processor core clock frequency can vary due to P-state and thermal conditions. The CYC packet provides
elapsed time as measured in processor core clock cycles relative to the last CYC packet.

A decoder can use all or some combination of these packets to track time at different resolutions throughout the
trace packets.

35.8.3.1

Time Domain Relationships

The three domains are related by the following formula:
TimeStampValue = (CoreCrystalClockValue * P) + AdjustedProcessorCycles + Software_Offset;
The CoreCrystalClockValue can provide the coarse-grained component of the TSC value. P, or the TSC/”core crystal
clock” ratio, can be derived from CPUID leaf 15H, as described in Section 35.8.3.
The AdjustedProcessorCycles component provides the fine-grained distance from the rising edge of the last core
crystal clock. Specifically, it is a cycle count in the same frequency as the timestamp counter from the last crystal
clock rising edge. The value is adjusted based on the ratio of the processor core clock frequency to the Maximum
Non-Turbo (or P1) frequency.
The Software_Offsets component includes software offsets that are factored into the timestamp value, such as
IA32_TSC_ADJUST.

35.8.3.2

Estimating TSC within Intel PT

For many usages, it may be useful to have an estimated timestamp value for all points in the trace. The formula
provided in Section 35.8.3.1 above provides the framework for how such an estimate can be calculated from the
various timing packets present in the trace.
The TSC packet provides the precise timestamp value at the time it is generated; however, TSC packets are infrequent, and estimates of the current timestamp value based purely on TSC packets are likely to be very inaccurate
for this reason. In order to get more precise timing information between TSC packets, CYC packets and/or MTC
packets should be enabled.
MTC packets provide incremental updates of the CoreCrystalClockValue. On processors that support CPUID leaf
15H, the frequency of the timestamp counter and the core crystal clock is fixed, thus MTC packets provide a means
to update the running timestamp estimate. Between two MTC packets A and B, the number of crystal clock cycles
passed is calculated from the 8-bit payloads of respective MTC packets:

Vol. 3C 35-79

INTEL® PROCESSOR TRACE

(CTCB - CTCA), where CTCi = MTCi[15:8] << IA32_RTIT_CTL.MTCFreq and i = A, B.
The time from a TSC packet to the subsequent MTC packet can be calculated using the TMA packet that follows the
TSC packet. The TMA packet provides both the crystal clock value (lower 16 bits, in the CTC field) and the AdjustedProcessorCycles value (in the FastCounter field) that can be used in the calculation of the corresponding core
crystal clock value of the TSC packet.
When the next MTC after a pair of TSC/TMA is seen, the number of crystal clocks passed since the TSC packet can
be calculated by subtracting the TMA.CTC value from the time indicated by the MTCNext packet by
CTCDelta[15:0] = (CTCNext[15:0] - TMA.CTC[15:0]), where CTCNext = MTCPayload << IA32_RTIT_CTL.MTCFreq.
The TMA.FastCounter field provides the fractional component of the TSC packet into the next crystal clock cycle.
CYC packets can provide further precision of an estimated timestamp value to many non-timing packets, by
providing an indication of the time passed between other timing packets (MTCs or TSCs).
When enabled, CYC packets are sent preceding each CYC-eligible packet, and provide the number of processor core
clock cycles that have passed since the last CYC packet. Thus between MTCs and TSCs, the accumulated CYC
values can be used to estimate the adjusted_processor_cycles component of the timestamp value. The accumulated CPU cycles will have to be adjusted to account for the difference in frequency between the processor core
clock and the P1 frequency. The necessary adjustment can be estimated using the core:bus ratio value given in the
CBR packet, by multiplying the accumulated cycle count value by P1/CBRpayload.
Note that stand-alone TSC packets (that is, TSC packets that are not a part of a PSB+) are typically generated only
when generation of other timing packets (MTCs and CYCs) has ceased for a period of time. Example scenarios
include when Intel PT is re-enabled, or on wake after a sleep state. Thus any calculation of ART or cycle time
leading up to a TSC packet will likely result in a discrepancy, which the TSC packet serves to correct.
A greater level of precision may be achieved by calculating the CPU clock frequency, see Section 35.8.3.4 below for
a method to do so using Intel PT packets.
CYCs can be used to estimate time between TSCs even without MTCs, though this will likely result in a reduction in
estimated TSC precision.

35.8.3.3

VMX TSC Manipulation

When software executes in non-Root operation, additional offset and scaling factors may be applied to the TSC
value. These are optional, but may be enabled via VMCS controls on a per-VM basis. See Chapter 25, “VMX NonRoot Operation” for details on VMX TSC offsetting and TSC scaling.
Like the value returned by RDTSC, TSC packets will include these adjustments, but other timing packets (such as
MTC, CYC, and CBR) are not impacted. In order to use the algorithm above to estimate the TSC value when TSC
scaling is in use, it will be necessary for software to account for the scaling factor. See Section 35.5.2.6 for details.

35.8.3.4

Calculating Frequency with Intel PT

Because Intel PT can provide both wall-clock time and processor clock cycle time, it can be used to measure the
processor core clock frequency. Either TSC or MTC packets can be used to track the wall-clock time. By using CYC
packets to count the number of processor core cycles that pass in between a pair of wall-clock time packets, the
ratio between processor core clock frequency and TSC frequency can be derived. If the P1 frequency is known, it
can be applied to determine the CPU frequency. See Section 35.8.3.1 above for details on the relationship between
TSC, MTC, and CYC.

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INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS

CHAPTER 36
INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS
36.1

OVERVIEW

®

Intel Software Guard Extensions (Intel® SGX) is a set of instructions and mechanisms for memory accesses
added to Intel® Architecture processors. Intel SGX can encompass two collections of instruction extensions,
referred to as SGX1 and SGX2, see Table 36-1 and Table 36-2. The SGX1 extensions allow an application to instantiate a protected container, referred to as an enclave. An enclave is a protected area in the application’s address
space (see Figure 36-1), which provides confidentiality and integrity even in the presence of privileged malware.
Accesses to the enclave memory area from any software not resident in the enclave are prevented. The SGX2
extensions allow additional flexibility in runtime management of enclave resources and thread execution within an
enclave.
Chapter 37 covers main concepts, objects and data structure formats that interact within the Intel SGX architecture. Chapter 38 covers operational aspects ranging from preparing an enclave, transferring control to enclave
code, and programming considerations for the enclave code and system software providing support for enclave
execution. Chapter 39 describes the behavior of Asynchronous Enclave Exit (AEX) caused by events while
executing enclave code. Chapter 40 covers the syntax and operational details of the instruction and associated leaf
functions available in Intel SGX. Chapter 41 describes interaction of various aspects of IA32 and Intel® 64 architectures with Intel SGX. Chapter 42 covers Intel SGX support for application debug, profiling and performance
monitoring.

OS

Enclave

Entry Table
Enclave Heap

App Code

Enclave Stack
Enclave Code

App Code

Figure 36-1. An Enclave Within the Application’s Virtual Address Space

36.2

ENCLAVE INTERACTION AND PROTECTION

Intel SGX allows the protected portion of an application to be distributed in the clear. Before the enclave is built, the
enclave code and data are free for inspection and analysis. The protected portion is loaded into an enclave where
its code and data is measured. Once the application’s protected portion of the code and data are loaded into an
enclave, it is protected against external software access. An enclave can prove its identity to a remote party and
provide the necessary building-blocks for secure provisioning of keys and credentials. The application can also
request an enclave-specific and platform-specific key that it can use to protect keys and data that it wishes to store
outside the enclave.1
1. For additional information, see white papers on Intel SGX at http://software.intel.com/en-us/intel-isa-extensions.
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INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS

Intel SGX introduces two significant capabilities to the Intel Architecture. First is the change in enclave memory
access semantics. The second is protection of the address mappings of the application.

36.3

ENCLAVE LIFE CYCLE

Enclave memory management is divided into two parts: address space allocation and memory commitment.
Address space allocation is the specification of the range of logical addresses that the enclave may use. This range
is called the ELRANGE. No actual resources are committed to this region. Memory commitment is the assignment
of actual memory resources (as pages) within the allocated address space. This two-phase technique allows flexibility for enclaves to control their memory usage and to adjust dynamically without overusing memory resources
when enclave needs are low. Commitment adds physical pages to the enclave. An operating system may support
separate allocate and commit operations.
During enclave creation, code and data for an enclave are loaded from a clear-text source, i.e. from non-enclave
memory.
Untrusted application code starts using an initialized enclave typically by using the EENTER leaf function provided
by Intel SGX to transfer control to the enclave code residing in the protected Enclave Page Cache (EPC). The
enclave code returns to the caller via the EEXIT leaf function. Upon enclave entry, control is transferred by hardware to software inside the enclave. The software inside the enclave switches the stack pointer to one inside the
enclave. When returning back from the enclave, the software swaps back the stack pointer then executes the
EEXIT leaf function.
On processors that support the SGX2 extensions, an enclave writer may add memory to an enclave using the SGX2
instruction set, after the enclave is built and running. These instructions allow adding additional memory resources
to the enclave for use in such areas as the heap. In addition, SGX2 instructions allow the enclave to add new
threads to the enclave. The SGX2 features provide additional capabilities to the software model without changing
the security properties of the Intel SGX architecture.
Calling an external procedure from an enclave could be done using the EEXIT leaf function. Software would use
EEXIT and a software convention between the trusted section and the untrusted section.
An active enclave consumes resources from the Enclave Page Cache (EPC, see Section 36.5). Intel SGX provides
the EREMOVE instruction that an EPC manager can use to reclaim EPC pages committed to an enclave. The EPC
manager uses EREMOVE on every enclave page when the enclave is torn down. After successful execution of
EREMOVE the EPC page is available for allocation to another enclave.

36.4

DATA STRUCTURES AND ENCLAVE OPERATION

There are 2 main data structures associated with operating an enclave, the SGX Enclave Control Structure (SECS,
see Section 37.7) and the Thread Control Structure (TCS, see Section 37.8).
There is one SECS for each enclave. The SECS contains meta-data about the enclave which is used by the hardware
and cannot be directly accessed by software. Included in the SECS is a field that stores the enclave build measurement value. This field, MRENCLAVE, is initialized by the ECREATE instruction and updated by every EADD and
EEXTEND. It is locked by EINIT.
Every enclave contains one or more TCS structures. The TCS contains meta-data used by the hardware to save and
restore thread specific information when entering/exiting the enclave. There is one field, FLAGS, that may be
accessed by software. This field can only be accessed by debug enclaves. The flag bit, DBGOPTIN, allows to single
step into the thread associated with the TCS. (see Section 37.8.1)
The SECS is created when ECREATE (see Table 36-1) is executed. The TCS can be created using the EADD instruction or the SGX2 instructions (see Table 36-2).

36.5

ENCLAVE PAGE CACHE

The Enclave Page Cache (EPC) is the secure storage used to store enclave pages when they are a part of an
executing enclave. For an EPC page, hardware performs additional access control checks to restrict access to the
page. After the current page access checks and translations are performed, the hardware checks that the EPC page
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INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS

is accessible to the program currently executing. Generally an EPC page is only accessed by the owner of the
executing enclave or an instruction which is setting up an EPC page
The EPC is divided into EPC pages. An EPC page is 4KB in size and always aligned on a 4KB boundary.
Pages in the EPC can either be valid or invalid. Every valid page in the EPC belongs to one enclave instance. Each
enclave instance has an EPC page that holds its SECS. The security metadata for each EPC page is held in an
internal micro-architectural structure called Enclave Page Cache Map (EPCM, see Section 36.5.1).
The EPC is managed by privileged software. Intel SGX provides a set of instructions for adding and removing
content to and from the EPC. The EPC may be configured by BIOS at boot time. On implementations in which EPC
memory is part of system DRAM, the contents of the EPC are protected by an encryption engine.

36.5.1

Enclave Page Cache Map (EPCM)

The EPCM is a secure structure used by the processor to track the contents of the EPC. The EPCM holds one entry
for each page in the EPC. The format of the EPCM is micro-architectural, and consequently is implementation
dependent. However, the EPCM contains the following architectural information:

•
•
•
•
•

The status of EPC page with respect to validity and accessibility.
An SECS identifier (see Section 37.19) of the enclave to which the page belongs.
The type of page: regular, SECS, TCS or VA.
The linear address through which the enclave is allowed to access the page.
The specified read/write/execute permissions on that page.

The EPCM structure is used by the CPU in the address-translation flow to enforce access-control on the EPC pages.
The EPCM structure is described in Table 37-27, and the conceptual access-control flow is described in Section
37.5.
The EPCM entries are managed by the processor as part of various instruction flows.

36.6

ENCLAVE INSTRUCTIONS AND INTEL® SGX

The enclave instructions available with Intel SGX are organized as leaf functions under two instruction mnemonics:
ENCLS (ring 0) and ENCLU (ring 3). Each leaf function uses EAX to specify the leaf function index, and may require
additional implicit input registers as parameters. The use of EAX is implied implicitly by the ENCLS and ENCLU
instructions, ModR/M byte encoding is not used with ENCLS and ENCLU. The use of additional registers does not
use ModR/M encoding and is implied implicitly by the respective leaf function index.
Each leaf function index is also associated with a unique, leaf-specific mnemonic. A long-form expression of Intel
SGX instruction takes the form of ENCLx[LEAF_MNEMONIC], where ‘x’ is either ‘S’ or ‘U’. The long-form expression
provides clear association of the privilege-level requirement of a given “leaf mnemonic”. For simplicity, the unique
“Leaf_Mnemonic” name is used (omitting the ENCLx for convenience) throughout in this document.
Details of individual SGX leaf functions are described in Chapter 40. Table 36-1 provides a summary of the instruction leaves that are available in the initial implementation of Intel SGX, which is introduced in the 6th generation
Intel Core processors. Table 36-2 summarizes enhancement of Intel SGX for future Intel processors.

Table 36-1. Supervisor and User Mode Enclave Instruction Leaf Functions in Long-Form of SGX1
Supervisor Instruction

Description

User Instruction

Description

ENCLS[EADD]

Add an EPC page to an enclave.

ENCLU[EENTER]

Enter an enclave.

ENCLS[EBLOCK]

Block an EPC page.

ENCLU[EEXIT]

Exit an enclave.

ENCLS[ECREATE]

Create an enclave.

ENCLU[EGETKEY]

Create a cryptographic key.

ENCLS[EDBGRD]

Read data from a debug enclave by debug- ENCLU[EREPORT]
ger.

Create a cryptographic report.

ENCLS[EDBGWR]

Write data into a debug enclave by debug- ENCLU[ERESUME]
ger.

Re-enter an enclave.

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INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS

Table 36-1. Supervisor and User Mode Enclave Instruction Leaf Functions in Long-Form of SGX1
Supervisor Instruction

Description

ENCLS[EEXTEND]

Extend EPC page measurement.

ENCLS[EINIT]

Initialize an enclave.

ENCLS[ELDB]

Load an EPC page in blocked state.

ENCLS[ELDU]

Load an EPC page in unblocked state.

ENCLS[EPA]

Add an EPC page to create a version array.

ENCLS[EREMOVE]

Remove an EPC page from an enclave.

ENCLS[ETRACK]

Activate EBLOCK checks.

ENCLS[EWB]

Write back/invalidate an EPC page.

User Instruction

Description

Table 36-2. Supervisor and User Mode Enclave Instruction Leaf Functions in Long-Form of SGX2
Supervisor Instruction

Description

User Instruction

Description

ENCLS[EAUG]

Allocate EPC page to an existing enclave.

ENCLU[EACCEPT]

Accept EPC page into the enclave.

ENCLS[EMODPR]

Restrict page permissions.

ENCLU[EMODPE]

Enhance page permissions.

ENCLS[EMODT]

Modify EPC page type.

ENCLU[EACCEPTCOPY] Copy contents to an augmented EPC
page and accept the EPC page into
the enclave.

36.7

DISCOVERING SUPPORT FOR INTEL® SGX AND ENABLING ENCLAVE
INSTRUCTIONS

Detection of support of Intel SGX and enumeration of available and enabled Intel SGX resources are queried using
the CPUID instruction. The enumeration interface comprises the following:

•

Processor support of Intel SGX is enumerated by a feature flag in CPUID leaf 07H: CPUID.(EAX=07H,
ECX=0H):EBX.SGX[bit 2]. If CPUID.(EAX=07H, ECX=0H):EBX.SGX = 1, the processor has support for Intel
SGX, and requires opt-in enabling by BIOS via IA32_FEATURE_CONTROL MSR.
If CPUID.(EAX=07H, ECX=0H):EBX.SGX = 1, CPUID will report via the available sub-leaves of
CPUID.(EAX=12H) on available and/or configured Intel SGX resources.
The available and configured Intel SGX resources enumerated by the sub-leaves of CPUID.(EAX=12H) depend
on the state of BIOS configuration.

•

36.7.1

Intel® SGX Opt-In Configuration

On processors that support Intel SGX, IA32_FEATURE_CONTROL provides the SGX_ENABLE field (bit 18). Before
system software can configure and enable Intel SGX resources, BIOS is required to set
IA32_FEATURE_CONTROL.SGX_ENABLE = 1 to opt-in the use of Intel SGX by system software.
The semantics of setting SGX_ENABLE follows the rules of IA32_FEATURE_CONTROL.LOCK (bit 0). Software is
considered to have opted into Intel SGX if and only if IA32_FEATURE_CONTROL.SGX_ENABLE and
IA32_FEATURE_CONTROL.LOCK are set to 1. The setting of IA32_FEATURE_CONTROL.SGX_ENABLE (bit 18) is not
reflected by CPUID.

Table 36-3. Intel® SGX Opt-in and Enabling Behavior
CPUID.(07H,0H):EBX.
SGX

CPUID.(12H)

FEATURE_CONTROL. FEATURE_CONTROL.
LOCK
SGX_ENABLE

Enclave Instruction

0

Invalid

X

X

#UD

1

Valid*

X

X

#UD**

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INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS

Table 36-3. Intel® SGX Opt-in and Enabling Behavior
CPUID.(07H,0H):EBX.
SGX

CPUID.(12H)

FEATURE_CONTROL. FEATURE_CONTROL.
LOCK
SGX_ENABLE

Enclave Instruction

1

Valid*

0

X

#GP

1

Valid*

1

0

#GP

1

Valid*

1

1

Available (see Table 36-4 for details
of SGX1 and SGX2).

* Leaf 12H enumeration results are dependent on enablement.
** See list of conditions in the #UD section of the reference pages of ENCLS and ENCLU

36.7.2

Intel® SGX Resource Enumeration Leaves

If CPUID.(EAX=07H, ECX=0H):EBX.SGX = 1, the processor also supports querying CPUID with EAX=12H on Intel
SGX resource capability and configuration. The number of available sub-leaves in leaf 12H depends on the Opt-in
and system software configuration. Information returned by CPUID.12H is thread specific; software should not
assume that if Intel SGX instructions are supported on one hardware thread, they are also supported elsewhere.
A properly configured processor exposes Intel SGX functionality with CPUID.EAX=12H reporting valid information
(non-zero content) in three or more sub-leaves, see Table 36-4.

•
•

CPUID.(EAX=12H, ECX=0H) enumerates Intel SGX capability, including enclave instruction opcode support.

•

CPUID.(EAX=12H, ECX >1) enumerates available EPC resources.

CPUID.(EAX=12H, ECX=1H) enumerates Intel SGX capability of processor state configuration and enclave
configuration in the SECS structure (see Table 37-3).

Table 36-4. CPUID Leaf 12H, Sub-Leaf 0 Enumeration of Intel® SGX Capabilities
CPUID.(EAX=12H,ECX=0)
Register
EAX

EBX
ECX

EDX

Description Behavior

Bits
0

SGX1: If 1, indicates leaf functions of SGX1 instruction listed in Table 36-1 are supported.

1

SGX2: If 1, indicates leaf functions of SGX2 instruction listed in Table 36-2 are supported.

31:2

Reserved (0)

31:0

MISCSELECT: Reports the bit vector of supported extended features that can be written to the MISC
region of the SSA.

31:0

Reserved (0).

7:0

MaxEnclaveSize_Not64: the maximum supported enclave size is 2^(EDX[7:0]) bytes when not in 64-bit
mode.

15:8

MaxEnclaveSize_64: the maximum supported enclave size is 2^(EDX[15:8]) bytes when operating in 64bit mode.

31:16

Reserved (0).

Table 36-5. CPUID Leaf 12H, Sub-Leaf 1 Enumeration of Intel® SGX Capabilities
CPUID.(EAX=12H,ECX=1)
Register

Description Behavior

Bits

EAX

31:0

Report the valid bits of SECS.ATTRIBUTES[31:0] that software can set with ECREATE.
SECS.ATTRIBUTES[n] can be set to 1 using ECREATE only if EAX[n] is 1, where n < 32.

EBX

31:0

Report the valid bits of SECS.ATTRIBUTES[63:32] that software can set with ECREATE.
SECS.ATTRIBUTES[n+32] can be set to 1 using ECREATE only if EBX[n] is 1, where n < 32.

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INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS

Table 36-5. CPUID Leaf 12H, Sub-Leaf 1 Enumeration of Intel® SGX Capabilities
CPUID.(EAX=12H,ECX=1)
Register

Description Behavior

Bits

ECX

31:0

Report the valid bits of SECS.ATTRIBUTES[95:64] that software can set with ECREATE.
SECS.ATTRIBUTES[n+64] can be set to 1 using ECREATE only if ECX[n] is 1, where n < 32.

EDX

31:0

Report the valid bits of SECS.ATTRIBUTES[127:96] that software can set with ECREATE.
SECS.ATTRIBUTES[n+96] can be set to 1 using ECREATE only if EDX[n] is 1, where n < 32.

On processors that support Intel SGX1 and SGX2, CPUID leaf 12H sub-leaf 2 report physical memory resources
available for use with Intel SGX. These physical memory sections are typically allocated by BIOS as Processor
Reserved Memory, and available to the OS to manage as EPC.
To enumerate how many EPC sections are available to the EPC manager, software can enumerate CPUID leaf 12H
with sub-leaf index starting from 2, and decode the sub-leaf-type encoding (returned in EAX[3:0]) until the subleaf type is invalid. All invalid sub-leaves of CPUID leaf 12H return EAX/EBX/ECX/EDX with 0.

Table 36-6. CPUID Leaf 12H, Sub-Leaf Index 2 or Higher Enumeration of Intel® SGX Resources
CPUID.(EAX=12H,ECX > 1)
Register
EAX

Description Behavior

Bits
3:0

0000b: This sub-leaf is invalid; EDX:ECX:EBX:EAX return 0.
0001b: This sub-leaf enumerates an EPC section. EBX:EAX and EDX:ECX provide information on the
Enclave Page Cache (EPC) section.
All other encoding are reserved.

EBX

11:4

Reserved (enumerate 0).

31:12

If EAX[3:0] = 0001b, these are bits 31:12 of the physical address of the base of the EPC section.

19:0

If EAX[3:0] = 0001b, these are bits 51:32 of the physical address of the base of the EPC section.

31:20

Reserved.

3: 0

If EAX[3:0] 0000b, then all bits of the EDX:ECX pair are enumerated as 0.
If EAX[3:0] 0001b, then this section has confidentiality and integrity protection.

ECX

EDX

36-6 Vol. 3D

All other encoding are reserved.
11:4

Reserved (enumerate 0).

31:12

If EAX[3:0] = 0001b, these are bits 31:12 of the size of the corresponding EPC section within the
Processor Reserved Memory.

19: 0

If EAX[3:0] = 0001b, these are bits 51:32 of the size of the corresponding EPC section within the
Processor Reserved Memory.

31:20

Reserved.

ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

CHAPTER 37
ENCLAVE ACCESS CONTROL AND DATA STRUCTURES
37.1

OVERVIEW OF ENCLAVE EXECUTION ENVIRONMENT

When an enclave is created, it has a range of linear addresses that the processor applies enhanced access control.
This ranged is called the ELRANGE (see Section 36.3). When an enclave generates a memory access, the existing
IA32 segmentation and paging architecture are applied. Additionally, linear addresses inside the ELRANGE must
map to an EPC page otherwise when an enclave attempts to access that linear address a fault is generated.
The EPC pages need not be physically contiguous. System software allocates EPC pages to various enclaves.
Enclaves must abide by OS/VMM imposed segmentation and paging policies. OS/VMM-managed page tables and
extended page tables provide address translation for the enclave pages. Hardware requires that these pages are
properly mapped to EPC (any failure generates an exception).
Enclave entry must happen through specific enclave instructions:

•

ENCLU[EENTER], ENCLU[ERESUME].

Enclave exit must happen through specific enclave instructions or events:

•

ENCLU[EEXIT], Asynchronous Enclave Exit (AEX).

Attempts to execute, read, or write to linear addresses mapped to EPC pages when not inside an enclave will result
in the processor altering the access to preserve the confidentiality and integrity of the enclave. The exact behavior
may be different between implementations. As an example a read of an enclave page may result in the return of all
one's or return of cyphertext of the cache line. Writing to an enclave page may result in a dropped write or a
machine check at a later time. The processor will provide the protections as described in Section 37.4 and Section
37.5 on such accesses.

37.2

TERMINOLOGY

A memory access to the ELRANGE and initiated by an instruction executed by an enclave is called a Direct Enclave
Access (Direct EA).
Memory accesses initiated by certain Intel® SGX instruction leaf functions such as ECREATE, EADD, EDBGRD,
EDBGWR, ELDU/ELDB, EWB, EREMOVE, EENTER, and ERESUME to EPC pages are called Indirect Enclave Accesses
(Indirect EA). Table 37-1 lists additional details of the indirect EA of SGX1 and SGX2 extensions.
Direct EAs and Indirect EAs together are called Enclave Accesses (EAs).
Any memory access that is not an Enclave Access is called a non-enclave access.

37.3

ACCESS-CONTROL REQUIREMENTS

Enclave accesses have the following access-control attributes:

•
•
•

All memory accesses must conform to segmentation and paging protection mechanisms.

•

EPC pages of page types PT_REG, PT_TCS and PT_TRIM must be mapped to ELRANGE at the linear address
specified when the EPC page was allocated to the enclave using ENCLS[EADD] or ENCLS[EAUG] leaf functions.
Enclave accesses through other linear address result in a #PF with the PFEC.SGX bit set.

•

Direct EAs to any EPC pages must conform to the currently defined security attributes for that EPC page in the
EPCM. These attributes may be defined at enclave creation time (EADD) or when the enclave sets them using
SGX2 instructions. The failure of these checks results in a #PF with the PFEC.SGX bit set.

Code fetches from inside an enclave to a linear address outside that enclave result in a #GP(0) exception.
Non-enclave accesses to EPC memory result in undefined behavior. EPC memory is protected as described in
Section 37.4 and Section 37.5 on such accesses.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

— Target page must belong to the currently executing enclave.
— Data may be written to an EPC page if the EPCM allow write access.
— Data may be read from an EPC page if the EPCM allow read access.
— Instruction fetches from an EPC page are allowed if the EPCM allows execute access.
— Target page must not have a restricted page type1 (PT_SECS, PT_TCS, PT_VA, or PT_TRIM).
— The EPC page must not be BLOCKED.
— The EPC page must not be PENDING.
— The EPC page must not be MODIFIED.

37.4

SEGMENT-BASED ACCESS CONTROL

Intel SGX architecture does not modify the segment checks performed by a logical processor. All memory accesses
arising from a logical processor in protected mode (including enclave access) are subject to segmentation checks
with the applicable segment register.
To ensure that outside entities do not modify the enclave's logical-to-linear address translation in an unexpected
fashion, ENCLU[EENTER] and ENCLU[ERESUME] check that CS, DS, ES, and SS, if usable (i.e., not null), have
segment base value of zero. A non-zero segment base value for these registers results in a #GP(0).
On enclave entry either via EENTER or ERESUME, the processor saves the contents of the external FS and GS registers, and loads these registers with values stored in the TCS at build time to enable the enclave’s use of these registers for accessing the thread-local storage inside the enclave. On EEXIT and AEX, the contents at time of entry are
restored. On AEX, the values of FS and GS are saved in the SSA frame. On ERESUME, FS and GS are restored from
the SSA frame. The details of these operations can be found in the descriptions of EENTER, ERESUME, EEXIT, and
AEX flows.

37.5

PAGE-BASED ACCESS CONTROL

37.5.1

Access-control for Accesses that Originate from non-SGX Instructions

Intel SGX builds on the processor's paging mechanism to provide page-granular access-control for enclave pages.
Enclave pages are only accessible from inside the currently executing enclave if they belong to that enclave. In
addition, enclave accesses must conform to the access control requirements described in Section 37.3. or through
certain Intel SGX instructions. Attempts to execute, read, or write to linear addresses mapped to EPC pages when
not inside an enclave will result in the processor altering the access to preserve the confidentiality and integrity of
the enclave. The exact behavior may be different between implementations.

37.5.2

Memory Accesses that Split across ELRANGE

Memory data accesses are allowed to split across ELRANGE (i.e., a part of the access is inside ELRANGE and a part
of the access is outside ELRANGE) while the processor is inside an enclave. If an access splits across ELRANGE, the
processor splits the access into two sub-accesses (one inside ELRANGE and the other outside ELRANGE), and each
access is evaluated. A code-fetch access that splits across ELRANGE results in a #GP due to the portion that lies
outside of the ELRANGE.

37.5.3

Implicit vs. Explicit Accesses

Memory accesses originating from Intel SGX instruction leaf functions are categorized as either explicit accesses or
implicit accesses. Table 37-1 lists the implicit and explicit memory accesses made by Intel SGX leaf functions.
1. EPCM may allow write, read or execute access only for pages with page type PT_REG.
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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

37.5.3.1

Explicit Accesses

Accesses to memory locations provided as explicit operands to Intel SGX instruction leaf functions, or their linked
data structures are called explicit accesses.
Explicit accesses are always made using logical addresses. These accesses are subject to segmentation, paging,
extended paging, and APIC-virtualization checks, and trigger any faults/exit associated with these checks when the
access is made.
The interaction of explicit memory accesses with data breakpoints is leaf-function-specific, and is documented in
Section 42.3.4.

37.5.3.2

Implicit Accesses

Accesses to data structures whose physical addresses are cached by the processor are called implicit accesses.
These addresses are not passed as operands of the instruction but are implied by use of the instruction.
These accesses do not trigger any access-control faults/exits or data breakpoints. Table 37-1 lists memory objects
that Intel SGX instruction leaf functions access either by explicit access or implicit access. The addresses of explicit
access objects are passed via register operands with the second through fourth column of Table 37-1 matching
implicitly encoded registers RBX, RCX, RDX.
Physical addresses used in different implicit accesses are cached via different instructions and for different durations. The physical address of SECS associated with each EPC page is cached at the time the page is added to the
enclave via ENCLS[EADD] or ENCLS[EAUG], or when the page is loaded to EPC via ENCLS[ELDB] or ENCLS[ELDU].
This binding is severed when the corresponding page is removed from the EPC via ENCLS[EREMOVE] or
ENCLS[EWB]. Physical addresses of TCS and SSA pages are cached at the time of most-recent enclave entry. Exit
from an enclave (ENCLU[EEXIT] or AEX) flushes this caching. Details of Asynchronous Enclave Exit is described in
Chapter 39.
The physical addresses that are cached for use by implicit accesses are derived from logical (or linear) addresses
after checks such as segmentation, paging, EPT, and APIC virtualization checks. These checks may trigger exceptions or VM exits. Note, however, that such exception or VM exits may not occur after a physical address is cached
and used for an implicit access.

Table 37-1. List of Implicit and Explicit Memory Access by Intel® SGX Enclave Instructions
Instr. Leaf

Enum.

Explicit 1

Explicit 2

EACCEPT

SGX2

SECINFO

EPCPAGE

EACCEPTCOPY

SGX2

SECINFO

EPCPAGE (Src)

EADD

SGX1

PAGEINFO and linked structures

EPCPAGE
EPCPAGE

Explicit 3

Implicit
SECS

EPCPAGE (Dst)

EAUG

SGX2

PAGEINFO and linked structures

EBLOCK

SGX1

EPCPAGE

SECS

ECREATE

SGX1

PAGEINFO and linked structures

EPCPAGE

EDBGRD

SGX1

EPCADDR

Destination

EDBGWR

SGX1

EPCADDR

Source

EENTER

SGX1

TCS and linked SSA

EEXIT

SGX1

EEXTEND

SGX1

SECS

EPCPAGE

EGETKEY

SGX1

KEYREQUEST

KEY

EINIT

SGX1

SIGSTRUCT

SECS

EINITTOKEN

ELDB/ELDU

SGX1

PAGEINFO and linked structures, PCMD

EPCPAGE

VAPAGE

EMODPE

SGX2

SECINFO

EPCPAGE

EMODPR

SGX2

SECINFO

EPCPAGE

SECS

EMODT

SGX2

SECINFO

EPCPAGE

SECS

SECS
SECS
SECS
SECS
SECS, TCS
SECS

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

Table 37-1. List of Implicit and Explicit Memory Access by Intel® SGX Enclave Instructions (Contd.)
Instr. Leaf

Enum.

EPA

SGX1

Explicit 1

Explicit 2

Explicit 3

REPORTDATA

OUTPUTDATA

Implicit

EPCADDR

EREMOVE

SGX1

EPCPAGE

EREPORT

SGX1

TARGETINFO

SECS

ERESUME

SGX1

TCS and linked SSA

ETRACK

SGX1

EPCPAGE

EWB

SGX1

PAGEINFO and linked structures, PCMD

SECS
SECS

EPCPAGE

VAPAGE

Asynchronous Enclave Exit*

SECS
SECS, TCS,
SSA

*Details of Asynchronous Enclave Exit (AEX) is described in Section 39.4

37.6

INTEL® SGX DATA STRUCTURES OVERVIEW

Enclave operation is managed via a collection of data structures. Many of the top-level data structures contain substructures. The top-level data structures relate to parameters that may be used in enclave setup/maintenance, by
Intel SGX instructions, or AEX event. The top-level data structures are:

•
•
•
•
•
•
•
•
•
•
•
•
•

SGX Enclave Control Structure (SECS)
Thread Control Structure (TCS)
State Save Area (SSA)
Page Information (PAGEINFO)
Security Information (SECINFO)
Paging Crypto MetaData (PCMD)
Enclave Signature Structure (SIGSTRUCT)
EINIT Token Structure (EINITTOKEN)
Report Structure (REPORT)
Report Target Info (TARGETINFO)
Key Request (KEYREQUEST)
Version Array (VA)
Enclave Page Cache Map (EPCM)

Details of the top-level data structures and associated sub-structures are listed in Section 37.7 through Section
37.19.

37.7

SGX ENCLAVE CONTROL STRUCTURE (SECS)

The SECS data structure requires 4K-Bytes alignment.

Table 37-2. Layout of SGX Enclave Control Structure (SECS)
Field

OFFSET (Bytes)

Size (Bytes)

Description

SIZE

0

8

Size of enclave in bytes; must be power of 2.

BASEADDR

8

8

Enclave Base Linear Address must be naturally aligned to size.

SSAFRAMESIZE

16

4

Size of one SSA frame in pages, including XSAVE, pad, GPR, and MISC (if
CPUID.(EAX=12H, ECX=0):.EBX != 0).

MISCSELECT

20

4

Bit vector specifying which extended features are saved to the MISC region
(see Section 37.7.2) of the SSA frame when an AEX occurs.

37-4 Vol. 3D

ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

Table 37-2. Layout of SGX Enclave Control Structure (SECS) (Contd.)
Field

OFFSET (Bytes)

Size (Bytes)

Description

RESERVED

24

24

ATTRIBUTES

48

16

Attributes of the Enclave, see Table 37-3.

MRENCLAVE

64

32

Measurement Register of enclave build process. See SIGSTRUCT for format.

RESERVED

96

32

MRSIGNER

128

32

RESERVED

160

96

ISVPRODID

256

2

Measurement Register extended with the public key that verified the
enclave. See SIGSTRUCT for format.
Product ID of enclave.

ISVSVN

258

2

Security version number (SVN) of the enclave.

RESERVED

260

3836

The RESERVED field consists of the following:
• EID: An 8 byte Enclave Identifier. Its location is implementation specific.
• PAD: A 352 bytes padding pattern from the Signature (used for key
derivation strings). It’s location is implementation specific.
• The remaining 3476 bytes are reserved area.
The entire 3836 byte field must be cleared prior to executing ECREATE or
EREPORT.

37.7.1

ATTRIBUTES

The ATTRIBUTES data structure is comprised of bit-granular fields that are used in the SECS, the REPORT and the
KEYREQUEST structures. CPUID.(EAX=12H, ECX=1) enumerates a bitmap of permitted 1-setting of bits in ATTRIBUTES.

Table 37-3. Layout of ATTRIBUTES Structure
Field

Bit Position

INIT

0

Description
This bit indicates if the enclave has been initialized by EINIT. It must be cleared when loaded as
part of ECREATE. For EREPORT instruction, TARGET_INFO.ATTRIBUTES[ENIT] must always be 1 to
match the state after EINIT has initialized the enclave.

DEBUG

1

If 1, the enclave permit debugger to read and write enclave data using EDBGRD and EDBGWR.

MODE64BIT

2

Enclave runs in 64-bit mode.

RESERVED

3

Must be Zero.

PROVISIONKEY

4

Provisioning Key is available from EGETKEY.

EINITTOKEN_KEY

5

EINIT token key is available from EGETKEY.

RESERVED

63:6

XFRM

127:64

37.7.2

XSAVE Feature Request Mask. See Section 41.7.

SECS.MISCSELECT Field

CPUID.(EAX=12H, ECX=0):EBX[31:0] enumerates which extended information that the processor can save into
the MISC region of SSA when an AEX occurs. An enclave writer can specify via SIGSTRUCT how to set the
SECS.MISCSELECT field. The bit vector of MISCSELECT selects which extended information is to be saved in the
MISC region of the SSA frame when an AEX is generated. The bit vector definition of extended information is listed
in Table 37-4.
If CPUID.(EAX=12H, ECX=0):EBX[31:0] = 0, SECS.MISCSELECT field must be all zeros.
The SECS.MISCSELECT field determines the size of MISC region of the SSA frame, see Section 37.9.2.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

Table 37-4. Bit Vector Layout of MISCSELECT Field of Extended Information
Field

Bit Position

Description

EXINFO

0

Report information about page fault and general protection exception that occurred inside an
enclave.

Reserved

31:1

Reserved (0).

37.8

THREAD CONTROL STRUCTURE (TCS)

Each executing thread in the enclave is associated with a Thread Control Structure. It requires 4K-Bytes alignment.

Table 37-5. Layout of Thread Control Structure (TCS)
Field
STAGE

OFFSET (Bytes)
0

Size (Bytes)
8

Description
Enclave execution state of the thread controlled by this TCS. A value of 0 indicates that this TCS is available for enclave entry. A value of 1 indicates that a
processer is currently executing an enclave in the context of this TCS.

FLAGS

8

8

The thread’s execution flags (see Section 37.8.1).

OSSA

16

8

Offset of the base of the State Save Area stack, relative to the enclave base.
Must be page aligned.

CSSA

24

4

Current slot index of an SSA frame, cleared by EADD and EACCEPT.

NSSA

28

4

Number of available slots for SSA frames.

OENTRY

32

8

Offset in enclave to which control is transferred on EENTER relative to the
base of the enclave.

AEP

40

8

The value of the Asynchronous Exit Pointer that was saved at EENTER time.

OFSBASGX

48

8

Offset to add to the base address of the enclave for producing the base
address of FS segment inside the enclave. Must be page aligned.

OGSBASGX

56

8

Offset to add to the base address of the enclave for producing the base
address of GS segment inside the enclave. Must be page aligned.

FSLIMIT

64

4

Size to become the new FS limit in 32-bit mode.

GSLIMIT

68

4

Size to become the new GS limit in 32-bit mode.

RESERVED

72

4024

Must be zero.

37.8.1

TCS.FLAGS
Table 37-6. Layout of TCS.FLAGS Field

Field

Bit Position

DBGOPTIN

0

RESERVED

63:1

37.8.2

Description
If set, allows debugging features (single-stepping, breakpoints, etc.) to be enabled and active while
executing in the enclave on this TCS. Hardware clears this bit on EADD. A debugger may later modify it if the enclave’s ATTRIBUTES.DEBUG is set.

State Save Area Offset (OSSA)

The OSSA points to a stack of State Save Area (SSA) frames (see Section 37.9) used to save the processor state
when an interrupt or exception occurs while executing in the enclave.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

37.8.3

Current State Save Area Frame (CSSA)

CSSA is the index of the current SSA frame that will be used by the processor to determine where to save the
processor state on an interrupt or exception that occurs while executing in the enclave. It is an index into the array
of frames addressed by OSSA. CSSA is incremented on an AEX and decremented on an ERESUME.

37.8.4

Number of State Save Area Frames (NSSA)

NSSA specifies the number of SSA frames available for this TCS. There must be at least one available SSA frame
when EENTER-ing the enclave or the EENTER will fail.

37.9

STATE SAVE AREA (SSA) FRAME

When an AEX occurs while running in an enclave, the architectural state is saved in the thread’s current SSA frame,
which is pointed to by TCS.CSSA. An SSA frame must be page aligned, and contains the following regions:

•

The XSAVE region starts at the base of the SSA frame, this region contains extended feature register state in
an XSAVE/FXSAVE-compatible non-compacted format.

•

A Pad region: software may choose to maintain a pad region separating the XSAVE region and the MISC region.
Software choose the size of the pad region according to the sizes of the MISC and GPRSGX regions.

•

The GPRSGX region. The GPRSGX region is the last region of an SSA frame (see Table 37-7). This is used to
hold the processor general purpose registers (RAX … R15), the RIP, the outside RSP and RBP, RFLAGS and the
AEX information.

•

The MISC region (If CPUIDEAX=12H, ECX=0):EBX[31:0] != 0). The MISC region is adjacent to the GRPSGX
region, and may contain zero or more components of extended information that would be saved when an AEX
occurs. If the MISC region is absent, the region between the GPRSGX and XSAVE regions is the pad region that
software can use. If the MISC region is present, the region between the MISC and XSAVE regions is the pad
region that software can use. See additional details in Section 37.9.2.

Table 37-7. Top-to-Bottom Layout of an SSA Frame
Region

Offset (Byte)

Size (Bytes)

Description

XSAVE

0

Calculate using CPUID The size of XSAVE region in SSA is derived from the enclave’s support of the colleaf 0DH information lection of processor extended states that would be managed by XSAVE. The
enablement of those processor extended state components in conjunction with
CPUID leaf 0DH information determines the XSAVE region size in SSA.

Pad

End of XSAVE
region

Chosen by enclave
writer

MISC

base of GPRSGX Calculate from high– sizeof(MISC)
est set bit of
SECS.MISCSELECT

See Section 37.9.2.

GPRSGX

SSAFRAMESIZE 176
– 176

See Table 37-8 for layout of the GPRSGX region.

Ensure the end of GPRSGX region is aligned to the end of a 4KB page.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

37.9.1

GPRSGX Region

The layout of the GPRSGX region is shown in Table 37-8.

Table 37-8. Layout of GPRSGX Portion of the State Save Area
Field

OFFSET (Bytes)

Size (Bytes)

Description

RAX

0

8

RCX

8

8

RDX

16

8

RBX

24

8

RSP

32

8

RBP

40

8

RSI

48

8

RDI

56

8

R8

64

8

R9

72

8

R10

80

8

R11

88

8

R12

96

8

R13

104

8

R14

112

8

R15

120

8

RFLAGS

128

8

Flag register.

RIP

136

8

Instruction pointer.

URSP

144

8

Non-Enclave (outside) stack pointer. Saved by EENTER, restored on AEX.

URBP

152

8

Non-Enclave (outside) RBP pointer. Saved by EENTER, restored on AEX.

EXITINFO

160

4

Contains information about exceptions that cause AEXs, which might be
needed by enclave software (see Section 37.9.1.1).

RESERVED

164

4

FSBASE

168

8

FS BASE.

GSBASE

176

8

GS BASE.

37.9.1.1

EXITINFO

EXITINFO contains the information used to report exit reasons to software inside the enclave. It is a 4 byte field laid
out as in Table 37-9. The VALID bit is set only for the exceptions conditions which are reported inside an enclave.
See Table 37-10 for which exceptions are reported inside the enclave. If the exception condition is not one reported
inside the enclave then VECTOR and EXIT_TYPE are cleared.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

Table 37-9. Layout of EXITINFO Field
Field

Bit Position

Description

VECTOR

7:0

Exception number of exceptions reported inside enclave.

EXIT_TYPE

10:8

011b: Hardware exceptions.
110b: Software exceptions.
Other values: Reserved.

RESERVED

30:11

Reserved as zero.

VALID

31

0: unsupported exceptions.
1: Supported exceptions. Includes two categories:

•
•

Unconditionally supported exceptions: #DE, #DB, #BP, #BR, #UD, #MF, #AC, #XM.
Conditionally supported exception:
—

37.9.1.2

#PF, #GP if SECS.MISCSELECT.EXINFO = 1.

VECTOR Field Definition

Table 37-10 contains the VECTOR field. This field contains information about some exceptions which occur inside
the enclave. These vector values are the same as the values that would be used when vectoring into regular exception handlers. All values not shown are not reported inside an enclave.

Table 37-10. Exception Vectors
Name

Vector #

Description

#DE

0

Divider exception.

#DB

1

Debug exception.

#BP

3

Breakpoint exception.

#BR

5

Bound range exceeded exception.

#UD

6

Invalid opcode exception.

#GP

13

General protection exception. Only reported if SECS.MISCSELECT.EXINFO = 1.

#PF

14

Page fault exception. Only reported if SECS.MISCSELECT.EXINFO = 1.

#MF

16

x87 FPU floating-point error.

#AC

17

Alignment check exceptions.

#XM

19

SIMD floating-point exceptions.

37.9.2

MISC Region

The layout of the MISC region is shown in Table 37-11. The number of components that the processor supports in
the MISC region corresponds to the set bits of CPUID.(EAX=12H, ECX=0):EBX[31:0] set to 1. Each set bit in
CPUID.(EAX=12H, ECX=0):EBX[31:0] has a defined size for the corresponding component, as shown in Table
37-11. Enclave writers needs to do the following:

•
•
•

Decide which MISC region components will be supported for the enclave.
Allocate an SSA frame large enough to hold the components chosen above.
Instruct each enclave builder software to set the appropriate bits in SECS.MISCSELECT.

The first component, EXINFO, starts next to the GPRSGX region. Additional components in the MISC region grow
in ascending order within the MISC region towards the XSAVE region.
The size of the MISC region is calculated as follows:

•
•

If CPUID.(EAX=12H, ECX=0):EBX[31:0] = 0, MISC region is not supported.
If CPUID.(EAX=12H, ECX=0):EBX[31:0] != 0, the size of MISC region is derived from sum of the highest bit set
in SECS.MISCSELECT and the size of the MISC component corresponding to that bit. Offset and size

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

information of currently defined MISC components are listed in Table 37-11. For example, if the highest bit set
in SECS.MISCSELECT is bit 0, the MISC region offset is OFFSET(GPRSGX)-16 and size is 16 bytes.

•

The processor saves a MISC component i in the MISC region if and only if SECS.MISCSELECT[i] is 1.

Table 37-11. Layout of MISC region of the State Save Area
MISC Components

OFFSET (Bytes)

Size (Bytes)

Description

EXINFO

Offset(GPRSGX) –16 16

if CPUID.(EAX=12H, ECX=0):EBX[0] = 1, exception information on #GP or
#PF that occurred inside an enclave can be written to the EXINFO structure
if specified by SECS.MISCSELECT[0] = 1.

Future Extension

Below EXINFO

Reserved. (Zero size if CPUID.(EAX=12H, ECX=0):EBX[31:1] =0).

37.9.2.1

TBD

EXINFO Structure

Table 37-12 contains the layout of the EXINFO structure that provides additional information.

Table 37-12. Layout of EXINFO Structure
Field

OFFSET (Bytes)

Size (Bytes)

Description

MADDR

0

8

If #PF: contains the page fault linear address that caused a page fault.
If #GP: the field is cleared.

ERRCD

8

4

Exception error code for either #GP or #PF.

RESERVED

12

4

37.9.2.2

Page Fault Error Codes

Table 37-13 contains page fault error code that may be reported in EXINFO.ERRCD.

Table 37-13. Page Fault Error Codes
Name
P

Bit Position

Description

0

Same as non-SGX page fault exception P flag.

W/R

1

Same as non-SGX page fault exception W/R flag.

1

2

Always set to 1 (user mode reference).

RSVD

3

Same as non-SGX page fault exception RSVD flag.

I/D

4

Same as non-SGX page fault exception I/D flag.

PK

5

Protection Key induced fault.

RSVD

14:6

Reserved.

SGX

15

EPCM induced fault.

RSVD

31:5

Reserved.

U/S

NOTES:
1. Page faults incident to enclave mode that report U/S=0 are not reported in EXINFO

37.10

PAGE INFORMATION (PAGEINFO)

PAGEINFO is an architectural data structure that is used as a parameter to the EPC-management instructions. It
requires 32-Byte alignment.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

Table 37-14. Layout of PAGEINFO Data Structure
Field

OFFSET (Bytes)

LINADDR

0

Size (Bytes)
8

Description
Enclave linear address.

SRCPGE

8

8

Effective address of the page where contents are located.

SECINFO/PCMD

16

8

Effective address of the SECINFO or PCMD (for ELDU, ELDB, EWB) structure for
the page.

SECS

24

8

Effective address of EPC slot that currently contains the SECS.

37.11

SECURITY INFORMATION (SECINFO)

The SECINFO data structure holds meta-data about an enclave page.

Table 37-15. Layout of SECINFO Data Structure
Field

OFFSET (Bytes)

Size (Bytes)

Description

FLAGS

0

8

Flags describing the state of the enclave page.

RESERVED

8

56

Must be zero.

37.11.1

SECINFO.FLAGS

The SECINFO.FLAGS are a set of fields describing the properties of an enclave page.

Table 37-16. Layout of SECINFO.FLAGS Field
Field

Bit Position

Description

R

0

If 1 indicates that the page can be read from inside the enclave; otherwise the page cannot be read
from inside the enclave.

W

1

If 1 indicates that the page can be written from inside the enclave; otherwise the page cannot be written from inside the enclave.

X

2

If 1 indicates that the page can be executed from inside the enclave; otherwise the page cannot be
executed from inside the enclave.

PENDING

3

If 1 indicates that the page is in the PENDING state; otherwise the page is not in the PENDING state.

MODIFIED

4

If 1 indicates that the page is in the MODIFIED state; otherwise the page is not in the MODIFIED state.

PR

5

If 1 indicates that a permission restriction operation on the page is in progress, otherwise a permission
restriction operation is not in progress.

RESERVED

7:6

Must be zero.

PAGE_TYPE

15:8

The type of page that the SECINFO is associated with.

RESERVED

63:16

Must be zero.

Vol. 3D 37-11

ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

37.11.2

PAGE_TYPE Field Definition

The SECINFO flags and EPC flags contain bits indicating the type of page.

Table 37-17. Supported PAGE_TYPE
TYPE

Value

Description

PT_SECS

0

Page is an SECS.

PT_TCS

1

Page is a TCS.

PT_REG

2

Page is a regular page.

PT_VA

3

Page is a Version Array.

PT_TRIM

4

Page is in trimmed state.

All other

Reserved.

37.12

PAGING CRYPTO METADATA (PCMD)

The PCMD structure is used to keep track of crypto meta-data associated with a paged-out page. Combined with
PAGEINFO, it provides enough information for the processor to verify, decrypt, and reload a paged-out EPC page.
The size of the PCMD structure (128 bytes) is architectural.
EWB calculates the Message Authentication Code (MAC) value and writes out the PCMD. ELDB/U reads the fields
and checks the MAC.
The format of PCMD is as follows:

Table 37-18. Layout of PCMD Data Structure
Field

OFFSET (Bytes)

Size (Bytes)

Description

SECINFO

0

64

Flags describing the state of the enclave page; R/W by software.

ENCLAVEID

64

8

Enclave Identifier used to establish a cryptographic binding between paged-out
page and the enclave.

RESERVED

72

40

Must be zero.

MAC

112

16

Message Authentication Code for the page, page meta-data and reserved
field.

37.13

ENCLAVE SIGNATURE STRUCTURE (SIGSTRUCT)

SIGSTRUCT is a structure created and signed by the enclave developer that contains information about the
enclave. SIGSTRUCT is processed by the EINIT leaf function to verify that the enclave was properly built.
SIGSTRUCT includes ENCLAVEHASH as SHA256 digest, as defined in FIPS PUB 180-4. The digests are byte strings
of length 32. Each of the 8 HASH dwords is stored in little-endian order.
SIGSTRUCT includes four 3072-bit integers (MODULUS, SIGNATURE, Q1, Q2). Each such integer is represented as
a byte strings of length 384, with the most significant byte at the position “offset + 383”, and the least significant
byte at position “offset”.
The (3072-bit integer) SIGNATURE should be an RSA signature, where: a) the RSA modulus (MODULUS) is a 3072bit integer; b) the public exponent is set to 3; c) the signing procedure uses the EMSA-PKCS1-v1.5 format with DER
encoding of the “DigestInfo” value as specified in of PKCS#1 v2.1/RFC 3447.
The 3072-bit integers Q1 and Q2 are defined by:
q1 = floor(Signature^2 / Modulus);
q2 = floor((Signature^3 - q1 * Signature * Modulus) / Modulus);
SIGSTRUCT must be page aligned

37-12 Vol. 3D

ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

In column 5 of Table 37-19, ‘Y’ indicates that this field should be included in the signature generated by the developer.

Table 37-19. Layout of Enclave Signature Structure (SIGSTRUCT)
Field

OFFSET (Bytes)

Size (Bytes)

Description

Signed

HEADER

0

16

Must be byte stream
06000000E10000000000010000000000H

Y

VENDOR

16

4

Intel Enclave: 00008086H
Non-Intel Enclave: 00000000H

Y

DATE

20

4

Build date is yyyymmdd in hex:
yyyy=4 digit year, mm=1-12, dd=1-31

Y

HEADER2

24

16

Must be byte stream
01010000600000006000000001000000H

Y

SWDEFINED

40

4

Available for software use.

Y

RESERVED

44

84

Must be zero.

Y

MODULUS

128

384

Module Public Key (keylength=3072 bits).

N

EXPONENT

512

4

RSA Exponent = 3.

N

SIGNATURE

516

384

Signature over Header and Body.

N

MISCSELECT*

900

4

Bit vector specifying Extended SSA frame feature set to be
used.

Y

MISCMASK*

904

4

Bit vector mask of MISCSELECT to enforce.

Y

RESERVED

908

20

Must be zero.

Y

ATTRIBUTES

928

16

Enclave Attributes that must be set.

Y

ATTRIBUTEMASK

944

16

Mask of Attributes to enforce.

Y

ENCLAVEHASH

960

32

MRENCLAVE of enclave this structure applies to.

Y

RESERVED

992

32

Must be zero.

Y

ISVPRODID

1024

2

ISV assigned Product ID.

Y

ISVSVN

1026

2

ISV assigned SVN (security version number).

Y

RESERVED

1028

12

Must be zero.

N

Q1

1040

384

Q1 value for RSA Signature Verification.

N

Q2

1424

384

Q2 value for RSA Signature Verification.

N

* If CPUID.(EAX=12H, ECX=0):EBX[31:0] = 0, MISCSELECT must be 0.
If CPUID.(EAX=12H, ECX=0):EBX[31:0] !=0, enclave writers must specify MISCSELECT such that each cleared
bit in MISCMASK must also specify the corresponding bit as 0 in MISCSELECT.

37.14

EINIT TOKEN STRUCTURE (EINITTOKEN)

The EINIT token is used by EINIT to verify that the enclave is permitted to launch. EINIT token is generated by an
enclave in possession of the EINITTOKEN key (the Launch Enclave).
EINIT token must be 512-Byte aligned.

Vol. 3D 37-13

ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

Table 37-20. Layout of EINIT Token (EINITTOKEN)
Field

OFFSET (Bytes)

Size (Bytes) MACed

Description

Valid

0

4

Y

Bit 0: 1: Valid; 0: Invalid.
All other bits reserved.

RESERVED

4

44

Y

Must be zero.

ATTRIBUTES

48

16

Y

ATTRIBUTES of the Enclave.

MRENCLAVE

64

32

Y

MRENCLAVE of the Enclave.

RESERVED

96

32

Y

Reserved.

MRSIGNER

128

32

Y

MRSIGNER of the Enclave.

RESERVED

160

32

Y

Reserved.

CPUSVNLE

192

16

N

Launch Enclave’s CPUSVN.

ISVPRODIDLE

208

02

N

Launch Enclave’s ISVPRODID.

ISVSVNLE

210

02

N

Launch Enclave’s ISVSVN.

RESERVED

212

24

N

Reserved.

MASKEDMISCSEL
ECTLE

236

4

Launch Enclave’s MASKEDMISCSELECT: set by the LE to the resolved
MISCSELECT value, used by EGETKEY (after applying KEYREQUEST’s
masking).

MASKEDATTRIBU 240
TESLE

16

N

Launch Enclave’s MASKEDATTRIBUTES: This should be set to the LE’s
ATTRIBUTES masked with ATTRIBUTEMASK of the LE’s KEYREQUEST.

KEYID

256

32

N

Value for key wear-out protection.

MAC

288

16

N

Message Authentication Code on EINITTOKEN using EINITTOKEN_KEY.

37.15

REPORT (REPORT)

The REPORT structure is the output of the EREPORT instruction, and must be 512-Byte aligned.

Table 37-21. Layout of REPORT
Field

OFFSET (Bytes) Size (Bytes)

Description

CPUSVN

0

16

The security version number of the processor.

MISCSELECT

16

4

Bit vector specifying which extended features are saved to the MISC region of the
SSA frame when an AEX occurs.

RESERVED

20

28

Must be zero.

ATTRIBUTES

48

16

ATTRIBUTES of the Enclave. See Section 37.7.1.

MRENCLAVE

64

32

The value of SECS.MRENCLAVE.

RESERVED

96

32

Reserved.

MRSIGNER

128

32

The value of SECS.MRSIGNER.

RESERVED

160

96

Zero.

ISVPRODID

256

02

Product ID of enclave.

ISVSVN

258

02

Security version number (SVN) of the enclave.

RESERVED

260

60

Zero.

REPORTDATA

320

64

Data provided by the user and protected by the REPORT's MAC, see Section
37.15.1.

KEYID

384

32

Value for key wear-out protection.

MAC

416

16

Message Authentication Code on the report using report key.

37-14 Vol. 3D

ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

37.15.1

REPORTDATA

REPORTDATA is a 64-Byte data structure that is provided by the enclave and included in the REPORT. It can be used
to securely pass information from the enclave to the target enclave.

37.16

REPORT TARGET INFO (TARGETINFO)

This structure is an input parameter to the EREPORT leaf function. The address of TARGETINFO is specified as an
effective address in RBX. It is used to identify the target enclave which will be able to cryptographically verify the
REPORT structure returned by EREPORT. TARGETINFO must be 512-Byte aligned.

Table 37-22. Layout of TARGETINFO Data Structure
Field

OFFSET (Bytes)

Size (Bytes)

Description

MEASUREMENT

0

32

The MRENCLAVE of the target enclave.

ATTRIBUTES

32

16

The ATTRIBUTES field of the target enclave.

RESERVED

48

4

MISCSELECT

52

4

RESERVED

56

456

37.17

The MISCSELECT of the target enclave.

KEY REQUEST (KEYREQUEST)

This structure is an input parameter to the EGETKEY leaf function. It is passed in as an effective address in RBX and
must be 512-Byte aligned. It is used for selecting the appropriate key and any additional parameters required in
the derivation of that key.

Table 37-23. Layout of KEYREQUEST Data Structure
Field

OFFSET (Bytes)

Size (Bytes)

Description

KEYNAME

0

02

Identifies the Key Required.

KEYPOLICY

02

02

Identifies which inputs are required to be used in the key derivation.

ISVSVN

04

02

The ISV security version number that will be used in the key derivation.

RESERVED

06

02

Must be zero.

CPUSVN

08

16

The security version number of the processor used in the key derivation.

ATTRIBUTEMASK 24

16

A mask defining which ATTRIBUTES bits will be included in key derivation.

KEYID

40

32

Value for key wear-out protection.

MISCMASK

72

4

A mask defining which MISCSELECT bits will be included in key derivation.

RESERVED

76

436

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

37.17.1

KEY REQUEST KeyNames
Table 37-24. Supported KEYName Values

Key Name

Value

Description

EINITTOKEN_KEY

0

EINIT_TOKEN key

PROVISION_KEY

1

Provisioning Key

PROVISION_SEAL_KEY

2

Provisioning Seal Key

REPORT_KEY

3

Report Key

SEAL_KEY

4

Seal Key

All other

Reserved

37.17.2

Key Request Policy Structure
Table 37-25. Layout of KEYPOLICY Field

Field
MRENCLAVE

Bit Position
0

Description
If 1, derive key using the enclave's MRENCLAVE measurement register.

MRSIGNER

1

If 1, derive key using the enclave's MRSIGNER measurement register.

RESERVED

15:2

Must be zero.

37.18

VERSION ARRAY (VA)

In order to securely store the versions of evicted EPC pages, Intel SGX defines a special EPC page type called a
Version Array (VA). Each VA page contains 512 slots, each of which can contain an 8-byte version number for a
page evicted from the EPC. When an EPC page is evicted, software chooses an empty slot in a VA page; this slot
receives the unique version number of the page being evicted. When the EPC page is reloaded, there must be a VA
slot that must hold the version of the page. If the page is successfully reloaded, the version in the VA slot is cleared.
VA pages can be evicted, just like any other EPC page. When evicting a VA page, a version slot in some other VA
page must be used to hold the version for the VA being evicted. A Version Array Page must be 4K-Bytes aligned.

Table 37-26. Layout of Version Array Data Structure
Field

OFFSET (Bytes)

Size (Bytes)

Description

Slot 0

0

08

Version Slot 0

Slot 1

8

08

Version Slot 1

4088

08

Version Slot 511

...
Slot 511

37.19

ENCLAVE PAGE CACHE MAP (EPCM)

EPCM is a secure structure used by the processor to track the contents of the EPC. The EPCM holds exactly one
entry for each page that is currently loaded into the EPC. EPCM is not accessible by software, and the layout of
EPCM fields is implementation specific.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

Table 37-27. Content of an Enclave Page Cache Map Entry
Field

Description

VALID

Indicates whether the EPCM entry is valid.

R

Read access; indicates whether enclave accesses for reads are allowed from the EPC page referenced by this
entry.

W

Write access; indicates whether enclave accesses for writes are allowed to the EPC page referenced by this
entry.

X

Execute access; indicates whether enclave accesses for instruction fetches are allowed from the EPC page
referenced by this entry.

PT

EPCM page type (PT_SECS, PT_TCS, PT_REG, PT_VA, PT_TRIM).

ENCLAVESECS

SECS identifier of the enclave to which the EPC page belongs.

ENCLAVEADDRESS

Linear enclave address of the EPC page.

BLOCKED

Indicates whether the EPC page is in the blocked state.

PENDING

Indicates whether the EPC page is in the pending state.

MODIFIED

Indicates whether the EPC page is in the modified state.

PR

Indicates whether the EPC page is in a permission restriction state.

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ENCLAVE ACCESS CONTROL AND DATA STRUCTURES

37-18 Vol. 3D

ENCLAVE OPERATION

CHAPTER 38
ENCLAVE OPERATION
The following aspects of enclave operation are described in this chapter:

•

Enclave creation: Includes loading code and data from outside of enclave into the EPC and establishing the
enclave entity.

•
•

Adding pages and measuring the enclave.

•

Enclave entry and exiting including:

Initialization of an enclave: Finalizes the cryptographic log and establishes the enclave identity and sealing
identity.
— Controlled entry and exit.
— Asynchronous Enclave Exit (AEX) and resuming execution after an AEX.

38.1

CONSTRUCTING AN ENCLAVE

Figure 38-1 illustrates a typical Enclave memory layout.

SECS

Base + Size

Replicated once
per thread

OS Context

Enclave Memory
Thread Data
TCS

Application Context
Global Data

Code

Base
Enclave {Base, Size}
Figure 38-1. Enclave Memory Layout
The enclave creation, commitment of memory resources, and finalizing the enclave’s identity with measurement
comprises multiple phases. This process can be illustrated by the following exemplary steps:
1. The application hands over the enclave content along with additional information required by the enclave
creation API to the enclave creation service running at privilege level 0.
2. The enclave creation service running at privilege level 0 uses the ECREATE leaf function to set up the initial
environment, specifying base address and size of the enclave. This address range, the ELRANGE, is part of the
application's address space. This reserves the memory range. The enclave will now reside in this address

Vol. 3D 38-1

ENCLAVE OPERATION

region. ECREATE also allocates an Enclave Page Cache (EPC) page for the SGX Enclave Control Structure
(SECS). Note that this page is not required to be a part of the enclave linear address space and is not required
to be mapped into the process.
3. The enclave creation service uses the EADD leaf function to commit EPC pages to the enclave, and use
EEXTEND to measure the committed memory content of the enclave. For each page to be added to the enclave:
— Use EADD to add the new page to the enclave.
— If the enclave developer requires measurement of the page as a proof for the content, use EEXTEND to add
a measurement for 256 bytes of the page. Repeat this operation until the entire page is measured.
4. The enclave creation service uses the EINIT leaf function to complete the enclave creation process and finalize
the enclave measurement to establish the enclave identity. Until an EINIT is executed, the enclave is not
permitted to execute any enclave code (i.e. entering the enclave by executing EENTER would result in a fault).

38.1.1

ECREATE

The ECREATE leaf function sets up the initial environment for the enclave by reading an SGX Enclave Control Structure (SECS) that contains the enclave's address range (ELRANGE) as defined by BASEADDR and SIZE, the ATTRIBUTES and MISCSELECT bitmaps, and the SSAFRAMESIZE. It then securely stores this information in an Enclave
Page Cache (EPC) page. ELRANGE is part of the application's address space. ECREATE also initializes a cryptographic log of the enclave's build process.

38.1.2

EADD and EEXTEND Interaction

Once the SECS has been created, enclave pages can be added to the enclave via EADD. This involves converting a
free EPC page into either a PT_REG or a PT_TCS page.
When EADD is invoked, the processor will update the EPCM entry with the type of page (PT_REG or PT_TCS), the
linear address used by the enclave to access the page, and the enclave access permissions for the page. It associates the page to the SECS provided as input. The EPCM entry information is used by hardware to manage access
control to the page. EADD records EPCM information in the cryptographic log stored in the SECS and copies 4
KBytes of data from unprotected memory outside the EPC to the allocated EPC page.
System software is responsible for selecting a free EPC page. System software is also responsible for providing the
type of page to be added, the attributes of the page, the contents of the page, and the SECS (enclave) to which the
page is to be added as requested by the application. Incorrect data would lead to a failure of EADD or to an incorrect cryptographic log and a failure at EINIT time.
After a page has been added to an enclave, software can measure a 256 byte region as determined by the developer by invoking EEXTEND. Thus to measure an entire 4KB page, system software must execute EEXTEND 16
times. Each invocation of EEXTEND adds to the cryptographic log information about which region is being measured
and the measurement of the section.
Entries in the cryptographic log define the measurement of the enclave and are critical in gaining assurance that
the enclave was correctly constructed by the untrusted system software.

38.1.3

EINIT Interaction

Once system software has completed the process of adding and measuring pages, the enclave needs to be initialized by the EINIT leaf function. After an enclave is initialized, EADD and EEXTEND are disabled for that enclave (An
attempt to execute EADD/EEXTEND to enclave after enclave initialization will result in a fault). The initialization
process finalizes the cryptographic log and establishes the enclave identity and sealing identity used by
EGETKEY and EREPORT.
A cryptographic hash of the log is stored as the enclave identity. Correct construction of the enclave results in the
cryptographic hash matching the one built by the enclave owner and included as the ENCLAVEHASH field of
SIGSTRUCT. The enclave identity provided by the EREPORT leaf function can be verified by a remote party.

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ENCLAVE OPERATION

The EINIT leaf function checks the EINIT token to validate that the enclave has been enabled on this platform. If
the enclave is not correctly constructed, or the EINIT token is not valid for the platform, or SIGSTRUCT isn't properly signed, then EINIT will fail. See the EINIT leaf function for details on the error reporting.
The enclave identity is a cryptographic hash that reflects the enclave attributes and MISCSELECT value, content
of the enclave, the order in which it was built, the addresses it occupies in memory, the security attributes, and
access right permissions of each page. The enclave identity is established by the EINIT leaf function.
The sealing identity is managed by a sealing authority represented by the hash of the public key used to sign the
SIGSTRUCT structure processed by EINIT. The sealing authority assigns a product ID (ISVPRODID) and security
version number (ISVSVN) to a particular enclave identity.
EINIT establishes the sealing identity using the following steps:
1. Verifies that SIGSTRUCT is properly signed using the public key enclosed in the SIGSTRUCT.
2. Checks that the measurement of the enclave matches the measurement of the enclave specified in SIGSTRUCT.
3. Checks that the enclave’s attributes and MISCSELECT values are compatible with those specified in SIGSTRUCT.
4. Finalizes the measurement of the enclave and records the sealing identity (the sealing authority, product id
and security version number) and enclave identity in the SECS.
5. Sets the ATTRIBUTES.INIT bit for the enclave.

38.1.4

Intel® SGX Launch Control Configuration

Intel®

SGX Launch Control is a set of controls that govern the creation of enclaves. Before the EINIT leaf function
will successfully initialize an enclave, a designated Launch Enclave must create an EINITTOKEN for that enclave.
Launch Enclaves have SECS.ATTRIBUTES.EINITTOKEN_KEY = 1, granting them access to the EINITTOKEN_KEY
from the EGETKEY leaf function. EINITTOKEN_KEY must be used by the Launch Enclave when computing EINITTOKEN.MAC, the Message Authentication Code of the EINITTOKEN.
The hash of the public key used to sign the SIGSTRUCT of the Launch Enclave must equal the value in the
IA32_SGXLEPUBKEYHASH MSRs. Only Launch Enclaves are allowed to launch without a valid token.
The IA32_SGXLEPUBKEYHASH MSRs are provided to designate the platform’s Launch Enclave.
IA32_SGXLEPUBKEYHASH defaults to digest of Intel’s launch enclave signing key after reset.
IA32_FEATURE_CONTROL bit 17 controls the permissions on the IA32_SGXLEPUBKEYHASH MSRs when
CPUID.(EAX=12H, ECX=00H):EAX[0] = 1. If IA32_FEATURE_CONTROL is locked with bit 17 set,
IA32_SGXLEPUBKEYHASH MSRs are reconfigurable (writeable). If either IA32_FEATURE_CONTROL is not locked or
bit 17 is clear, the MSRs are read only. By leaving these MSRs writable, system SW or a VMM can support a plurality
of Launch Enclaves for hosting multiple execution environments. See Table 42.2.2 for more details.

38.2

ENCLAVE ENTRY AND EXITING

38.2.1

Controlled Entry and Exit

The EENTER leaf function is the method to enter the enclave under program control. To execute EENTER, software
must supply an address of a TCS that is part of the enclave to be entered. The TCS holds the location inside the
enclave to transfer control to and a pointer to the SSA frame inside the enclave that an AEX should store the
register state to.
When a logical processor enters an enclave, the TCS is considered busy until the logical processors exits the
enclave. An attempt to enter an enclave through a busy TCS results in a fault. Intel® SGX allows an enclave builder
to define multiple TCSs, thereby providing support for multithreaded enclaves.
Software must also supply to EENTER the Asynchronous Exit Pointer (AEP) parameter. AEP is an address external
to the enclave which an exception handler will return to using IRET. Typically the location would contain the
ERESUME instruction. ERESUME transfers control back to the enclave, to the address retrieved from the enclave
thread’s saved state.
EENTER performs the following operations:
Vol. 3D 38-3

ENCLAVE OPERATION

1. Check that TCS is not busy and flush all cached linear-to-physical mappings.
2. Change the mode of operation to be in enclave mode.
3. Save the old RSP, RBP for later restore on AEX (Software is responsible for setting up the new RSP, RBP to be
used inside enclave).
4. Save XCR0 and replace it with the XFRM value for the enclave.
5. Check if software wishes to debug (applicable to a debuggable enclave):
— If not debugging, then configure hardware so the enclave appears as a single instruction.
— If debugging, then configure hardware to allow traps, breakpoints, and single steps inside the enclave.
6. Set the TCS as busy.
7. Transfer control from outside enclave to predetermined location inside the enclave specified by the TCS.
The EEXIT leaf function is the method of leaving the enclave under program control. EEXIT receives the target
address outside of the enclave that the enclave wishes to transfer control to. It is the responsibility of enclave software to erase any secret from the registers prior to invoking EEXIT. To allow enclave software to easily perform an
external function call and re-enter the enclave (using EEXIT and EENTER leaf functions), EEXIT returns the value of
the AEP that was used when the enclave was entered.
EEXIT performs the following operations:
1. Clear enclave mode and flush all cached linear-to-physical mappings.
2. Mark TCS as not busy.
3. Transfer control from inside the enclave to a location on the outside specified as parameter to the EEXIT leaf
function.

38.2.2

Asynchronous Enclave Exit (AEX)

Asynchronous and synchronous events, such as exceptions, interrupts, traps, SMIs, and VM exits may occur while
executing inside an enclave. These events are referred to as Enclave Exiting Events (EEE). Upon an EEE, the
processor state is securely saved inside the enclave (in the thread’s current SSA frame) and then replaced by a
synthetic state to prevent leakage of secrets. The process of securely saving state and establishing the synthetic
state is called an Asynchronous Enclave Exit (AEX). Details of AEX is described in Chapter 39, “Enclave Exiting
Events”.
As part of most EEEs, the AEP is pushed onto the stack as the location of the eventing address. This is the location
where control will return to after executing the IRET. The ERESUME leaf function can be executed from that point
to reenter the enclave and resume execution from the interrupted point.
After AEX has completed, the logical processor is no longer in enclave mode and the exiting event is processed
normally. Any new events that occur after the AEX has completed are treated as having occurred outside the
enclave (e.g. a #PF in dispatching to an interrupt handler).

38.2.3

Resuming Execution after AEX

After system software has serviced the event that caused the logical processor to exit an enclave, the logical
processor can continue enclave execution using ERESUME. ERESUME restores processor state and returns control
to where execution was interrupted.
If the cause of the exit was an exception or a fault and was not resolved, the event will be triggered again if the
enclave is re-entered using ERESUME. For example, if an enclave performs a divide by 0 operation, executing
ERESUME will cause the enclave to attempt to re-execute the faulting instruction and result in another divide by 0
exception. Intel® SGX provides the means for an enclave developer to handle enclave exceptions from within the
enclave. Software can enter the enclave at a different location and invoke the exception handler within the enclave
by executing the EENTER leaf function. The exception handler within the enclave can read the fault information
from the SSA frame and attempt to resolve the faulting condition or simply return and indicate to software that the
enclave should be terminated (e.g. using EEXIT).

38-4 Vol. 3D

ENCLAVE OPERATION

38.2.3.1

ERESUME Interaction

ERESUME restores registers depending on the mode of the enclave (32 or 64 bit).

•

In 32-bit mode (IA32_EFER.LMA = 0 || CS.L = 0), the low 32-bits of the legacy registers (EAX, EBX, ECX, EDX,
ESP, EBP, ESI, EDI, EIP and EFLAGS) are restored from the thread’s GPR area of the current SSA frame. Neither
the upper 32 bits of the legacy registers nor the 64-bit registers (R8 … R15) are loaded.

•

In 64-bit mode (IA32_EFER.LMA = 1 && CS.L = 1), all 64 bits of the general processor registers (RAX, RBX,
RCX, RDX, RSP, RBP, RSI, RDI, R8 … R15, RIP and RFLAGS) are loaded.

Extended features specified by SECS.ATTRIBUTES.XFRM are restored from the XSAVE area of the current SSA
frame. The layout of the x87 area depends on the current values of IA32_EFER.LMA and CS.L:

•

IA32_EFER.LMA = 0 || CS.L = 0
— 32-bit load in the same format that XSAVE/FXSAVE uses with these values.

•

IA32_EFER.LMA = 1 && CS.L = 1
— 64-bit load in the same format that XSAVE/FXSAVE uses with these values as if REX.W = 1.

38.3

CALLING ENCLAVE PROCEDURES

38.3.1

Calling Convention

In standard call conventions subroutine parameters are generally pushed onto the stack. The called routine, being
aware of its own stack layout, knows how to find parameters based on compile-time-computable offsets from the
SP or BP register (depending on runtime conventions used by the compiler).
Because of the stack switch when calling an enclave, stack-located parameters cannot be found in this manner.
Entering the enclave requires a modified parameter passing convention.
For example, the caller might push parameters onto the untrusted stack and then pass a pointer to those parameters in RAX to the enclave software. The exact choice of calling conventions is up to the writer of the edge routines;
be those routines hand-coded or compiler generated.

38.3.2

Register Preservation

As with most systems, it is the responsibility of the callee to preserve all registers except that used for returning a
value. This is consistent with conventional usage and tends to optimize the number of register save/restore operations that need be performed. It has the additional security result that it ensures that data is scrubbed from any
registers that were used by enclave to temporarily contain secrets.

38.3.3

Returning to Caller

No registers are modified during EEXIT. It is the responsibility of software to remove secrets in registers before
executing EEXIT.

38.4

INTEL® SGX KEY AND ATTESTATION

38.4.1

Enclave Measurement

During the enclave build process, two “measurements” are taken of each enclave and are stored in two 256-bit
Measurement Registers (MR): MRENCLAVE and MRSIGNER. MRENCLAVE represents the enclave's contents and
build process. MRSIGNER represents the entity that signed the enclave's SIGSTRUCT.

Vol. 3D 38-5

ENCLAVE OPERATION

The values of the Measurement Registers are included in attestations to identify the enclave to remote parties. The
MRs are also included in most keys, binding keys to enclaves with specific MRs.

38.4.1.1

MRENCLAVE

MRENCLAVE is a unique 256 bit value that identifies the code and data that was loaded into the enclave during the
initial launch. It is computed as a SHA256 hash that is initialized by the ECREATE leaf function. EADD and EEXTEND
leaf functions record information about each page and the content of those pages. The EINIT leaf function finalizes
the hash, which is stored in SECS.MRENCLAVE. Any tampering with the build process, contents of a page, page
permissions, etc will result in a different MRENCLAVE value.
Figure 38-2 illustrates a simplified flow of changes to the MRENCLAVE register when building an enclave:

•
•
•
•

Enclave creation with ECREATE.
Copying a non-enclave source page into the EPC of an un-initialized enclave with EADD.
Updating twice of the MRENCLAVE after modifying the enclave’s page content, i.e. EEXTEND twice.
Finalizing the enclave build with EINIT.

Details on specific values inserted in the hash are available in the individual instruction definitions.

Page
Metadata

Data
Chunk 1

Chunk 1
Metadata

Data
Chunk 2

Chunk 2
Metadata

SHA_INIT

SHA_UPDATE

SHA_UPDATE

SHA_UPDATE

SHA_FINAL

MRENCLAVE

MRENCLAVE

MRENCLAVE

MRENCLAVE

MRENCLAVE

ECREATE

EADD

EEXTEND

EEXTEND

EINIT

Figure 38-2. Measurement Flow of Enclave Build Process

38.4.1.2

MRSIGNER

Each enclave is signed using a 3072 bit RSA key. The signature is stored in the SIGSTRUCT. In the SIGSTRUCT, the
enclave's signer also assigns a product ID (ISVPRODID) and a security version (ISVSVN) to the enclave.
MRSIGNER is the SHA-256 hash of the signer's public key.
In attestation, MRSIGNER can be used to allow software to approve of an enclave based on the author rather than
maintaining a list of MRENCLAVEs. It is used in key derivation to allow software to create a lineage of an application. By signing multiple enclaves with the same key, the enclaves will share the same keys and data. Combined
with security version numbering, the author can release multiple versions of an application which can access keys
for previous versions, but not future versions of that application.

38-6 Vol. 3D

ENCLAVE OPERATION

38.4.2

Security Version Numbers (SVN)

Intel® SGX supports a versioning system that allows the signer to identify different versions of the same software
released by an author. The security version is independent of the functional version an author uses and is intended
to specify security equivalence. Multiple releases with functional enhancements may all share the same SVN if they
all have the same security properties or posture. Each enclave has an SVN and the underlying hardware has an
SVN.
The SVNs are attested to in EREPORT and are included in the derivation of most keys, thus providing separation
between data for older/newer versions.

38.4.2.1

Enclave Security Version

In the SIGSTRUCT, the MRSIGNER is associated with a 16-bit Product ID (ISVPRODID) and a 16 bit integer SVN
(ISVSVN). Together they define a specific group of versions of a specific product. Most keys, including the Seal Key,
can be bound to this pair.
To support upgrading from one release to another, EGETKEY will return keys corresponding to any value less than
or equal to the software's ISVSVN.

38.4.2.2

Hardware Security Version

CPUSVN is a 128 bit value that reflects the microcode update version and authenticated code modules supported
by the processor. Unlike ISVSVN, CPUSVN is not an integer and cannot be compared mathematically. Not all values
are valid CPUSVNs.
Software must ensure that the CPUSVN provided to EGETKEY is valid. EREPORT will return the CPUSVN of the
current environment. Software can execute EREPORT with TARGETINFO set to zeros to retrieve a CPUSVN from
REPORTDATA. Software can access keys for a CPUSVN recorded previously, provided that each of the elements
reflected in CPUSVN are the same or have been upgraded.

38.4.3

Keys

Intel®

SGX provides software with access to keys unique to each processor and rooted in HW keys inserted into the
processor during manufacturing.

Each enclave requests keys using the EGETKEY leaf function. The key is based on enclave parameters such as
measurement, the enclave signing key, security attributes of the enclave, and the Hardware Security version of the
processor itself. A full list of parameter options is specified in the KEYREQUEST structure, see details in Section
37.17.
By deriving keys using enclave properties, SGX guarantees that if two enclaves call EGETKEY, they will receive a
unique key only accessible by the respective enclave. It also guarantees that the enclave will receive the same key
on every future execution of EGETKEY. Some parameters are optional or configurable by software. For example, a
Seal key can be based on the signer of the enclave, resulting in a key available to multiple enclaves signed by the
same party.
The EGETKEY leaf function provides several key types. Each key is specific to the processor, CPUSVN, and the
enclave that executed EGETKEY. The EGETKEY instruction definition details how each of these keys is derived, see
Table 40-56. Additionally,

•

SEAL Key: The Seal key is a general purpose key for the enclave to use to protect secrets. Typical uses of the
Seal key are encrypting and calculating MAC of secrets on disk. There are 2 types of Seal Key described in
Section 38.4.3.1.

•

REPORT Key: This key is used to compute the MAC on the REPORT structure. The EREPORT leaf function is used
to compute this MAC, and destination enclave uses the Report key to verify the MAC. The software usage flow
is detailed in Section 38.4.3.2.

•

EINITTOKEN_KEY: This key is used by Launch Enclaves to compute the MAC on EINITTOKENs. These tokens are
then verified in the EINIT leaf function. The key is only available to enclaves with ATTRIBUTE.EINITTOKEN_KEY set
to 1.

Vol. 3D 38-7

ENCLAVE OPERATION

•

PROVISIONING Key and PROVISIONING SEAL Key: These keys are used by attestation key provisioning
software to prove to remote parties that the processor is genuine and identify the currently executing TCB.
These keys are only available to enclaves with ATTRIBUTE.PROVISIONKEY set to 1.

38.4.3.1

Sealing Enclave Data

Enclaves can protect persistent data using Seal keys to provide encryption and/or integrity protection. EGETKEY
provides two types of Seal keys specified in KEYREQUEST.KEYPOLICY field: MRENCLAVE-based key and
MRSIGNER-based key.
The MRENCLAVE-based keys are available only to enclave instances sharing the same MRENCLAVE. If a new
version of the enclave is released, the Seal keys will be different. Retrieving previous data requires additional software support.
The MRSIGNER-based keys are bound to the 3 tuple (MRSIGNER, ISVPRODID, ISVSVN). These keys are available
to any enclave with the same MRSIGNER and ISVPRODID and an ISVSVN equal to or greater than the key in questions. This is valuable for allowing new versions of the same software to retrieve keys created before an upgrade.

38.4.3.2

Using REPORTs for Local Attestation

SGX provides a means for enclaves to securely identify one another, this is referred to as “Local Attestation”. SGX
provides a hardware assertion, REPORT that contains calling enclaves Attributes, Measurements and User supplied
data (described in detail in Section 37.15). Figure 38-3 shows the basic flow of information.
1. The source enclave determines the identity of the target enclave to populate TARGETINFO.
2. The source enclave calls EREPORT instruction to generate a REPORT structure. The EREPORT instruction
conducts the following:
— Populates the REPORT with identify information about the calling enclave.
— Derives the Report Key that is returned when the target enclave executes the EGETKEY. TARGETINFO
provides information about the target.
— Computes a MAC over the REPORT using derived target enclave Report Key.
3. Non-enclave software copies the REPORT from source to destination.
4. The target enclave executes the EGETKEY instruction to request its REPORT key, which is the same key used by
EREPORT at the source.
5. The target enclave verifies the MAC and can then inspect the REPORT to identify the source.

Source Enclave
TARGETINFO

Destination Enclave

EREPORT
(Symmetric Key)

REPORT

Legend:
Hardware

EGETKEY
REPORT KEY

Verify REPORT
(Symmetric Key)

Software

Figure 38-3. SGX Local Attestation

38-8 Vol. 3D

ENCLAVE OPERATION

38.5

EPC AND MANAGEMENT OF EPC PAGES

EPC layout is implementation specific, and is enumerated through CPUID (see Table 36-6 for EPC layout). EPC is
typically configured by BIOS at system boot time.

38.5.1

EPC Implementation

EPC must be properly protected against attacks. One example of EPC implementation could use a Memory Encryption Engine (MEE). An MEE provides a cost-effective mechanism of creating cryptographically protected volatile
storage using platform DRAM. These units provide integrity, replay, and confidentiality protection. Details are
implementation specific.

38.5.2

OS Management of EPC Pages

The EPC is a finite resource. SGX1 (i.e. CPUID.(EAX=12H, ECX=0):EAX.SGX1 = 1 but CPUID.(EAX=12H,
ECX=0):EAX.SGX2 = 0) provides the EPC manager with leaf functions to manage this resource and properly swap
pages out of and into the EPC. For that, the EPC manager would need to keep track of all EPC entries, type and
state, context affiliation, and SECS affiliation.
Enclave pages that are candidates for eviction should be moved to BLOCKED state using EBLOCK instruction that
ensures no new cached virtual to physical address mappings can be created by attempts to reference a BLOCKED
page.
Before evicting blocked pages, EPC manager should execute ETRACK leaf function on that enclave and ensure that
there are no stale cached virtual to physical address mappings for the blocked pages remain on any thread on the
platform.
After removing all stale translations from blocked pages, system software should use the EWB leaf function for
securely evicting pages out of the EPC. EWB encrypts a page in the EPC, writes it to unprotected memory, and
invalidates the copy in EPC. In addition, EWB also creates a cryptographic MAC (PCMD.MAC) of the page and stores
it in unprotected memory. A page can be reloaded back to the processor only if the data and MAC match. To ensure
that only the latest version of the evicted page can be loaded back, the version of the evicted page is stored
securely in a Version Array (VA) in EPC.
SGX1 includes two instructions for reloading pages that have been evicted by system software: ELDU and ELDB.
The difference between the two instructions is the value of the paging state at the end of the instruction. ELDU
results in a page being reloaded and set to an UNBLOCKED state, while ELDB results in a page loaded to a
BLOCKED state.
ELDB is intended for use by a Virtual Machine Monitor (VMM). When a VMM reloads an evicted page, it needs to
restore it to the correct state of the page (BLOCKED vs. UNBLOCKED) as it existed at the time the page was
evicted. Based on the state of the page at eviction, the VMM chooses either ELDB or ELDU.

38.5.2.1

Enhancement to Managing EPC Pages

On processors supporting SGX2 (i.e. CPUID.(EAX=12H, ECX=0):EAX.SGX2 = 1), the EPC manager can manage
EPC resources (while enclave is running) with more flexibility provided by the SGX2 leaf functions. The additional
flexibility is described in Section 38.5.7 through Section 38.5.11.

38.5.3

Eviction of Enclave Pages

Intel SGX paging is optimized to allow the Operating System (OS) to evict multiple pages out of the EPC under a
single synchronization.
The suggested flow for evicting a list of pages from the EPC is:
1. For each page to be evicted from the EPC:
a. Select an empty slot in a Version Array (VA) page.

•

If no empty VA page slots exist, create a new VA page using the EPA leaf function.

Vol. 3D 38-9

ENCLAVE OPERATION

b. Remove linear-address to physical-address mapping from the enclave context’s mapping tables (page table
and EPT tables).
c.

Execute the EBLOCK leaf function for the target page. This sets the target page state to BLOCKED. At this
point no new mappings of the page will be created. So any access which does not have the mapping cached
in the TLB will generate a #PF.

2. For each enclave containing pages selected in step 1:
— Execute an ETRACK leaf function pointing to that enclave’s SECS. This initiates the tracking process that
ensures that all caching of linear-address to physical-address translations for the blocked pages is cleared.
3. For all logical processors executing in processes (OS) or guests (VMM) that contain the enclaves selected in
step 1:
— Issue an IPI (inter-processor interrupt) to those threads. This causes those logical processors to asynchronously exit any enclaves they might be in, and as a result flush cached linear-address to physical-address
translations that might hold stale translations to blocked pages. There is no need for additional measures
such as performing a “TLB shootdown”.
4. After enclaves exit, allow logical processors to resume normal operation, including enclave re-entry as the
tracking logic keeps track of the activity.
5. For each page to be evicted:
— Evict the page using the EWB leaf function with parameters include the effective-address pointer to the EPC
page, the VA slot, a 4K byte buffer to hold the encrypted page contents, and a 128 byte buffer to hold page
metadata. The last three elements are tied together cryptographically and must be used to later reload the
page.
At this point, system software has the only copy of each page data encrypted with its page metadata in main
memory.

38.5.4

Loading an Enclave Page

To reload a previously evicted page, system software needs four elements: the VA slot used when the page was
evicted, a buffer containing the encrypted page contents, a buffer containing the page metadata, and the parent
SECS to associate this page with. If the VA page or the parent SECS are not already in the EPC, they must be
reloaded first.
1. Execute ELDB/ELDU (depending on the desired BLOCKED state for the page), passing as parameters: the EPC
page linear address, the VA slot, the encrypted page, and the page metadata.
2. Create a mapping in the enclave context’s mapping tables (page tables and EPT tables) to allow the application
to access that page (OS: system page table; VMM: EPT).
The ELDB/ELDU instruction marks the VA slot empty so that the page cannot be replayed at a later date.

38.5.5

Eviction of an SECS Page

The eviction of an SECS page is similar to the eviction of an enclave page. The only difference is that an SECS page
cannot be evicted until all other pages belonging to the enclave have been evicted. Since all other pages have been
evicted, there will be no threads executing inside the enclave and tracking with ETRACK isn’t necessary. When
reloading an enclave, the SECS page must be reloaded before all other constituent pages.
1. Ensure all pages are evicted from enclave.
2. Select an empty slot in a Version Array page.
— If no VA page exists with an empty slot, create a new one using the EPA function leaf.
3. Evict the page using the EWB leaf function with parameters include the effective-address pointer to the EPC
page, the VA slot, a 4K byte buffer to hold the encrypted page contents and a 128 byte buffer to hold page
metadata. The last three elements are tied together cryptographically and must be used to later reload the
page.

38-10 Vol. 3D

ENCLAVE OPERATION

38.5.6

Eviction of a Version Array Page

VA pages do not belong to any enclave and tracking with ETRACK isn’t necessary. When evicting the VA page, a slot
in a different VA page must be specified in order to provide versioning of the evicted VA page.
1. Select a slot in a Version Array page other than the page being evicted.
— If no VA page exists with an empty slot, create a new one using the EPA leaf function.
2. Evict the page using the EWB leaf function with parameters include the effective-address pointer to the EPC
page, the VA slot, a 4K byte buffer to hold the encrypted page contents, and a 128 byte buffer to hold page
metadata. The last three elements are tied together cryptographically and must be used to later reload the
page.

38.5.7

Allocating a Regular Page

On processors that support SGX2, allocating a new page to an already initialized enclave is accomplished by
invoking the EAUG leaf function. Typically, the enclave requests that the OS allocate a new page at a particular
location within the enclave’s address space. Once allocated, the page remains in a pending state until the enclave
executes the corresponding EACCEPT leaf function to accept the new page into the enclave. Page allocation operations may be batched to improve efficiency.
The typical process for allocating a regular page is as follows:
1. Enclave requests additional memory from OS when the current allocation becomes insufficient.
2. The OS invokes the EAUG leaf function to add a new memory page to the enclave.
a. EAUG may only be called on a free EPC page.
b. Successful completion of the EAUG instruction places the target page in the VALID and PENDING state.
c.

All dynamically created pages have the type PT_REG and content of all zeros.

3. The OS maps the page in the enclave context's mapping tables.
4. The enclave issues an EACCEPT instruction, which verifies the page’s attributes and clears the PENDING state.
At that point the page becomes accessible for normal enclave use.

38.5.8

Allocating a TCS Page

On processors that support SGX2, allocating a new TCS page to an already initialized enclave is a two-step process.
First the OS allocates a regular page with a call to EAUG. This page must then be accepted and initialized by the
enclave to which it belongs. Once the page has been initialized with appropriate values for a TCS page, the enclave
requests the OS to change the page’s type to PT_TCS. This change must also be accepted. As with allocating a
regular page, TCS allocation operations may be batched.
A typical process for allocating a TCS page is as follows:
1. Enclave requests an additional page from the OS.
2. The OS invokes EAUG to add a new regular memory page to the enclave.
a. EAUG may only be called on a free EPC page.
b. Successful completion of the EAUG instruction places the target page in the VALID and PENDING state.
3. The OS maps the page in the enclave context's mapping tables.
4. The enclave issues an EACCEPT instruction, at which point the page becomes accessible for normal enclave
use.
5. The enclave initializes the contents of the new page.
6. The enclave requests that the OS convert the page from type PT_REG to PT_TCS.
7. OS issues an EMODT instruction on the page.
a. The parameters to EMODT indicate that the regular page should be converted into a TCS.

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ENCLAVE OPERATION

b. EMODT forces all access rights to a page to be removed because TCS pages may not be accessed by enclave
code.
8. The enclave issues an EACCEPT instruction to confirm the requested modification.

38.5.9

Trimming a Page

On processors that support SGX2, Intel SGX supports the trimming of an enclave page as a special case of EMODT.
Trimming allows an enclave to actively participate in the process of removing a page from the enclave (deallocation) by splitting the process into first removing it from the enclave's access and then removing it from the EPC
using the EREMOVE leaf function. The page type PT_TRIM indicates that a page has been trimmed from the
enclave’s address space and that the page is no longer accessible to enclave software. Modifications to a page in
the PT_TRIM state are not permitted; the page must be removed and then reallocated by the OS before the enclave
may use the page again. Page deallocation operations may be batched to improve efficiency.
The typical process for trimming a page from an enclave is as follows:
1. Enclave signals OS that a particular page is no longer in use.
2. OS invokes the EMODT leaf function on the page, requesting that the page’s type be changed to PT_TRIM.
a. SECS and VA pages cannot be trimmed in this way, so the initial type of the page must be PT_REG or
PT_TCS.
b. EMODT may only be called on valid enclave pages.
3. OS invokes the ETRACK leaf function on the enclave containing the page to track removal the TLB addresses
from all the processors.
4. Issue an IPI (inter-processor interrupt) to flush the stale linear-address to physical-address translations for all
logical processors executing in processes that contain the enclave.
5. Enclave issues an EACCEPT leaf function.
6. The OS may now permanently remove the page from the EPC (by issuing EREMOVE).

38.5.10 Restricting the EPCM Permissions of a Page
On processors that support SGX2, restricting the EPCM permissions associated with an enclave page is accomplished using the EMODPR leaf function. This operation requires the cooperation of the OS to flush stale entries to
the page and to update the page-table permissions of the page to match. Permissions restriction operations may
be batched.
The typical process for restricting the permissions of an enclave page is as follows:
1. Enclave requests that the OS to restrict the permissions of an EPC page.
2. OS performs permission restriction, flushing cached linear-address to physical-address translations, and pagetable modifications.
a. Invokes the EMODPR leaf function to restrict permissions (EMODPR may only be called on VALID pages).
b. Invokes the ETRACK leaf function on the enclave containing the page to track removal of the TLB addresses
from all the processor.
c.

Issue an IPI (inter-processor interrupt) to flush the stale linear-address to physical-address translations for
all logical processors executing in processes that contain the enclave.

d. Sends IPIs to trigger enclave thread exit and TLB shootdown.
e. OS informs the Enclave that all logical processors should now see the new restricted permissions.
3. Enclave invokes the EACCEPT leaf function.
a. Enclave may access the page throughout the entire process.
b. Successful call to EACCEPT guarantees that no stale cached linear-address to physical-address translations
are present.

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ENCLAVE OPERATION

38.5.11 Extending the EPCM Permissions of a Page
On processors that support SGX2, extending the EPCM permissions associated with an enclave page is accomplished directly be the enclave using the EMODPE leaf function. After performing the EPCM permission extension,
the enclave requests the OS to update the page table permissions to match the extended permission. Security
wise, permission extension does not require enclave threads to leave the enclave as TLBs with stale references to
the more restrictive permissions will be flushed on demand, but to allow forward progress, an OS needs to be
aware that an application might signal a page fault.
The typical process for extending the permissions of an enclave page is as follows:
1. Enclave invokes EMODPE to extend the EPCM permissions associated with an EPC page (EMODPE may only be
called on VALID pages).
2. Enclave requests that OS update the page tables to match the new EPCM permissions.
3. Enclave code resumes.
a. If cached linear-address to physical-address translations are present to the more restrictive permissions,
the enclave thread will page fault. The SGX2-aware OS will see that the page tables permit the access and
resume the thread, which can now successfully access the page because exiting cleared the TLB.
b. If cached linear-address to physical-address translations are not present, access to the page with the new
permissions will succeed without an enclave exit.

38.6

CHANGES TO INSTRUCTION BEHAVIOR INSIDE AN ENCLAVE

This section covers instructions whose behavior changes when executed in enclave mode.

38.6.1

Illegal Instructions

The instructions listed in Table 38-1 are ring 3 instructions which become illegal when executed inside an enclave.
Executing these instructions inside an enclave will generate an exception.
The first row of Table 38-1 enumerates instructions that may cause a VM exit for VMM emulation. Since a VMM
cannot emulate enclave execution, execution of any these instructions inside an enclave results in an invalidopcode exception (#UD) and no VM exit.
The second row of Table 38-1 enumerates I/O instructions that may cause a fault or a VM exit for emulation. Again,
enclave execution cannot be emulated, so execution of any these instructions inside an enclave results in #UD.
The third row of Table 38-1 enumerates instructions that load descriptors from the GDT or the LDT or that change
privilege level. The former class is disallowed because enclave software should not depend on the contents of the
descriptor tables and the latter because enclave execution must be entirely with CPL = 3. Again, execution of any
these instructions inside an enclave results in #UD.
The fourth row of Table 38-1 enumerates instructions that provide access to kernel information from user mode
and can be used to aid kernel exploits from within enclave. Execution of any these instructions inside an enclave
results in #UD

Table 38-1. Illegal Instructions Inside an Enclave
Instructions

Result

CPUID, GETSEC, RDPMC, SGDT, SIDT, SLDT, STR, VMCALL, VMFUNC #UD
IN, INS/INSB/INSW/INSD, OUT, OUTS/OUTSB/OUTSW/OUTSD

#UD

Comment
Might cause VM exit.
I/O fault may not safely recover. May require emulation.

Far call, Far jump, Far Ret, INT n/INTO, IRET, LDS/LES/LFS/LGS/LSS, #UD
MOV to DS/ES/SS/FS/GS, POP DS/ES/SS/FS/GS, SYSCALL,
SYSENTER

Access segment register could change privilege level.

SMSW

#UD

Might provide access to kernel information.

ENCLU[EENTER], ENCLU[ERESUME]

#GP

Cannot enter an enclave from within an enclave.

Vol. 3D 38-13

ENCLAVE OPERATION

RDTSC and RDTSCP are legal inside an enclave for processors that support SGX2 (subject to the value of CR4.TSD).
For processors which support SGX1 but not SGX2, RDTSC and RDTSCP will cause #UD.
RDTSC and RDTSCP instructions may cause a VM exit when inside an enclave.
Software developers must take into account that the RDTSC/RDTSCP results are not immune to influences by other
software, e.g. the TSC can be manipulated by software outside the enclave.

38.6.2

RDRAND and RDSEED Instructions

These instructions may cause a VM exit if the “RDRAND exiting” VM-execution control is 1. Unlike other instructions
that can cause VM exits, these instructions are legal inside an enclave. As noted in Section 6.5.5, any VM exit originating on an instruction boundary inside an enclave sets bit 27 of the exit-reason field of the VMCS. If a VMM
receives a VM exit due to an attempt to execute either of these instructions determines (by that bit) that the execution was inside an enclave, it can do either of two things. It can clear the “RDRAND exiting” VM-execution control
and execute VMRESUME; this will result in the enclave executing RDRAND or RDSEED again, and this time a VM exit
will not occur. Alternatively, the VMM might choose to discontinue execution of this virtual machine.

NOTE
It is expected that VMMs that virtualize Intel SGX will not set “RDRAND exiting” to 1.

38.6.3

PAUSE Instruction

The PAUSE instruction may cause a VM exit if either of the “PAUSE exiting” and “PAUSE-loop exiting” VM-execution
controls is 1. Unlike other instructions that can cause VM exits, the PAUSE instruction is legal inside an enclave.
If a VMM receives a VM exit due to the 1-setting of “PAUSE-loop exiting”, it may take action to prevent recurrence
of the PAUSE loop (e.g., by scheduling another virtual CPU of this virtual machine) and then execute VMRESUME;
this will result in the enclave executing PAUSE again, but this time the PAUSE loop (and resulting VM exit) will not
occur.
If a VMM receives a VM exit due to the 1-setting of “PAUSE exiting”, it can do either of two things. It can clear the
“PAUSE exiting” VM-execution control and execute VMRESUME; this will result in the enclave executing PAUSE
again, but this time a VM exit will not occur. Alternatively, the VMM might choose to discontinue execution of this
virtual machine.

NOTE
It is expected that VMMs that virtualize Intel SGX will not set “PAUSE exiting” to 1.

38.6.4

INT 3 Behavior Inside an Enclave

INT3 is legal inside an enclave, however, the behavior inside an enclave is different from its behavior outside an
enclave. See Section 42.4.1 for details.

38.6.5

INVD Handling when Enclaves Are Enabled

Once processor reserved memory protections are activated (see Section 38.5), any execution of INVD will result in
a #GP(0).

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ENCLAVE EXITING EVENTS

CHAPTER 39
ENCLAVE EXITING EVENTS
Certain events, such as exceptions and interrupts, incident to (but asynchronous with) enclave execution may
cause control to transition outside of enclave mode. (Most of these also cause a change of privilege level.) To
protect the integrity and security of the enclave, the processor will exit the enclave (and enclave mode) before
invoking the handler for such an event. For that reason, such events are called enclave-exiting events (EEE);
EEEs include external interrupts, non-maskable interrupts, system-management interrupts, exceptions, and VM
exits.
The process of leaving an enclave in response to an EEE is called an asynchronous enclave exit (AEX). To protect
the secrecy of the enclave, an AEX saves the state of certain registers within enclave memory and then loads those
registers with fixed values called synthetic state.

39.1

COMPATIBLE SWITCH TO THE EXITING STACK OF AEX

AEXs load registers with a pre-determined synthetic state. These register may be later pushed onto the appropriate stack in a form as defined by the enclave-exiting event. To allow enclave execution to resume after the
invoking handler has process the enclave exiting event, the asynchronous enclave exit loads the address of trampoline code outside of the enclave into RIP. This trampoline code eventually returns to the enclave by means of an
ENCLU(ERESUME) leaf function. Prior to exiting the enclave the RSP and RBP registers are restored to their values
prior to enclave entry.
The stack to be used is chosen using the same rules as for non-SGX mode:

•
•
•

If there is a privilege level change, the stack will be the one associated with the new ring.
If there is no privilege level change, the current application stack is used.
If the IA-32e IST mechanism is used, the exit stack is chosen using that method.

TCS

Next SSA Frame
CSSA

Current SSA Frame

uRSP

AEP

Per-Thread
Trampoline in uRTS

Exit Stack

uRSP

ENCLU[ERESUME]

SS
RSP

TCS LA

RAX
RBX

RFLAGS

AEP

RCX

CS

ENCLU[ERESUME]

RIP
Error Code (optional)

RSP after pushes

RSP

Figure 39-1. Exit Stack Just After Interrupt with Stack Switch

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ENCLAVE EXITING EVENTS

In all cases, the choice of exit stack and the information pushed onto it is consistent with non-SGX operation.
Figure 39-1 shows the Application and Exiting Stacks after an exit with a stack switch. An exit without a stack
switch uses the Application Stack. The ERESUME leaf index value is placed into RAX, the TCS pointer is placed in
RBX and the AEP (see below) is placed into RCX to facilitate resuming the enclave after the exit.
Upon an AEX, the AEP (Asynchronous Exit Pointer) is loaded into the RIP. The AEP points to a trampoline code
sequence which includes the ERESUME instruction that is later used to reenter the enclave.
The following bits of RFLAGS are cleared before RFLAGS is pushed onto the exit stack: CF, PF, AF, ZF, SF, OF, RF. The
remaining bits are left unchanged.

39.2

STATE SAVING BY AEX

The State Save Area holds the processor state at the time of an AEX. To allow handling events within the enclave
and re-entering it after an AEX, the SSA can be a stack of multiple SSA frames as illustrated in Figure 39-2.

SSA Stack

TCS

GRP_N-1

NSSA

MISC_N-1

CSSA

XSAVE_N-1

OSSA

GPR_1
MISC_1
XSAVE_1

SECS.SSAFRAMESIZE
(in pages)

Current
SSA Fram

GRP_0
MISC_0
XAVE_0

Figure 39-2. The SSA Stack
The location of the SSA frames to be used is controlled by the following variables in the TCS and the SECS:

•

Size of a frame in the State Save Area (SECS.SSAFRAMESIZE): This defines the number of 4K Byte pages in a
single frame in the State Save Area. The SSA frame size must be large enough to hold the GPR state, the XSAVE
state, and the MISC state.

•

Base address of the enclave (SECS.BASEADDR): This defines the enclave's base linear address from which the
offset to the base of the SSA stack is calculated.

•

Number of State Save Area Slots (TCS.NSSA): This defines the total number of slots (frames) in the State Save
Area stack.

•
•

Current State Save Area Slot (TCS.CSSA): This defines the slot to use on the next exit.
State Save Area (TCS.OSSA): This defines the offset of the base address of a set of State Save Area slots from
the enclave’s base address.

When an AEX occurs, hardware selects the SSA frame to use by examining TCS.CSSA. Processor state is saved into
the SSA frame (see Section 39.4) and loaded with a synthetic state (as described in Section 39.3.1) to avoid
leaking secrets, RSP and RBP are restored to their values prior to enclave entry, and TCS.CSSA is incremented. As
will be described later, if an exception takes the last slot, it will not be possible to reenter the enclave to handle the

39-2 Vol. 3D

ENCLAVE EXITING EVENTS

exception from within the enclave. A subsequent ERESUME restores the processor state from the current SSA
frame and frees the SSA frame.
The format of the XSAVE section of SSA is identical to the format used by the XSAVE/XRSTOR instructions. On
EENTER, CSSA must be less than NSSA, ensuring that there is at least one State Save Area slot available for exits.
If there is no free SSA frame when executing EENTER, the entry will fail.

39.3

SYNTHETIC STATE ON ASYNCHRONOUS ENCLAVE EXIT

39.3.1

Processor Synthetic State on Asynchronous Enclave Exit

Table 39-1 shows the synthetic state loaded on AEX. The values shown are the lower 32 bits when the processor is
in 32 bit mode and 64 bits when the processor is in 64 bit mode.

Table 39-1. GPR, x87 Synthetic States on Asynchronous Enclave Exit
Register

Value

RAX

3 (ENCLU[3] is ERESUME).

RBX

Pointer to TCS of interrupted enclave thread.

RCX

AEP of interrupted enclave thread.

RDX, RSI, RDI

0.

RSP

Restored from SSA.uRSP.

RBP

Restored from SSA.uRBP.

R8-R15

0 in 64-bit mode; unchanged in 32-bit mode.

RIP

AEP of interrupted enclave thread.

RFLAGS

CF, PF, AF, ZF, SF, OF, RF bits are cleared. All other bits are left unchanged.

x87/SSE State

Unless otherwise listed here, all x87 and SSE state are set to the INIT state. The INIT state is the state
that would be loaded by the XRSTOR instruction with bits 1:0 both set in the requested feature bitmask
(RFBM), and both clear in XSTATE_BV the XSAVE header.

FCW

On #MF exception: set to 037EH. On all other exits: set to 037FH.

FSW

On #MF exception: set to 8081H. On all other exits: set to 0H.

MXCSR

On #XM exception: set to 1F01H. On all other exits: set to 1FB0H.

CR2

If the event that caused the AEX is a #PF, and the #PF does not directly cause a VM exit, then the low
12 bits are cleared.
If the #PF leads directly to a VM exit, CR2 is not updated (usual IA behavior).
Note: The low 12 bits are not cleared if a #PF is encountered during the delivery of the EEE that caused
the AEX. This is because the #PF was not the EEE.

FS, GS

Restored to values as of most recent EENTER/ERESUME.

39.3.2

Synthetic State for Extended Features

When CR4.OSXSAVE = 1, extended features (those controlled by XCR0[63:2]) are set to their respective INIT
states when this corresponding bit of SECS.XFRM is set. The INIT state is the state that would be loaded by the
XRSTOR instruction had the instruction mask and the XSTATE_BV field of the XSAVE header each contained the
value XFRM. (When the AEX occurs in 32-bit mode, those features that do not exist in 32-bit mode are unchanged.)

Vol. 3D 39-3

ENCLAVE EXITING EVENTS

39.3.3

Synthetic State for MISC Features

State represented by SECS.MISCSELECT might also be overridden by synthetic state after it has been saved into
the SSA. State represented by MISCSELECT[0] is not overridden but if the exiting event is a page fault then lower
12 bits of CR2 are cleared.

39.4

AEX FLOW

On Enclave Exiting Events (interrupts, exceptions, VM exits or SMIs), the processor state is securely saved inside
the enclave, a synthetic state is loaded and the enclave is exited. The EEE then proceeds in the usual exit-defined
fashion. The following sections describes the details of an AEX:
1. The exact processor state saved into the current SSA frame depends on whether the enclave is a 32-bit or a 64bit enclave. In 32-bit mode (IA32_EFER.LMA = 0 || CS.L = 0), the low 32 bits of the legacy registers (EAX, EBX,
ECX, EDX, ESP, EBP, ESI, EDI, EIP and EFLAGS) are stored. The upper 32 bits of the legacy registers and the
64-bit registers (R8 … R15) are not stored.
In 64-bit mode (IA32_EFER.LMA = 1 && CS.L = 1), all 64 bits of the general processor registers (RAX, RBX,
RCX, RDX, RSP, RBP, RSI, RDI, R8 … R15, RIP and RFLAGS) are stored.
The state of those extended features specified by SECS.ATTRIBUTES.XFRM are stored into the XSAVE area of
the current SSA frame. The layout of the x87 and XMM portions (the 1st 512 bytes) depends on the current
values of IA32_EFER.LMA and CS.L:
If IA32_EFER.LMA = 0 || CS.L = 0, the same format (32-bit) that XSAVE/FXSAVE uses with these values.
If IA32_EFER.LMA = 1 && CS.L = 1, the same format (64-bit) that XSAVE/FXSAVE uses with these values
when REX.W = 1.
The cause of the AEX is saved in the EXITINFO field. See Table 37-9 for details and values of the various
fields.
The state of those miscellaneous features (see Section 37.7.2) specified by SECS.MISCSELECT are stored into
the MISC area of the current SSA frame.
2. Synthetic state is created for a number of processor registers to present an opaque view of the enclave state.
Table 39-1 shows the values for GPRs, x87, SSE, FS, GS, Debug and performance monitoring on AEX. The
synthetic state for other extended features (those controlled by XCR0[62:2]) is set to their respective INIT
states when their corresponding bit of SECS.ATTRIBUTES.XFRM is set. The INIT state is that state as defined by
the behavior of the XRSTOR instruction when HEADER.XSTATE_BV[n] is 0. Synthetic state of those miscellaneous features specified by SECS.MISCSELECT depends on the miscellaneous feature. There is no synthetic
state required for the miscellaneous state controlled by SECS.MISCSELECT[0].
3. Any code and data breakpoints that were suppressed at the time of enclave entry are unsuppressed when
exiting the enclave.
4. RFLAGS.TF is set to the value that it had at the time of the most recent enclave entry (except for the situation
that the entry was opt-in for debug; see Section 42.2). In the SSA, RFLAGS.TF is set to 0.
5. RFLAGS.RF is set to 0 in the synthetic state. In the SSA, the value saved is the same as what would have been
saved on stack in the non-SGX case (architectural value of RF). Thus, AEXs due to interrupts, traps, and code
breakpoints save RF unmodified into SSA, while AEXs due to other faults save RF as 1 in the SSA.
If the event causing AEX happened on intermediate iteration of a REP-prefixed instruction, then RF=1 is
saved on SSA, irrespective of its priority.
6. Any performance monitoring activity (including PEBS) or profiling activity (LBR, Tracing using Intel PT) on the
exiting thread that was suppressed due to the enclave entry on that thread is unsuppressed. Any counting that
had been demoted from AnyThread counting to MyThread counting (on one logical processor) is promoted back
to AnyThread counting.

39-4 Vol. 3D

ENCLAVE EXITING EVENTS

39.4.1

AEX Operational Detail
Temp Variables in AEX Operational Flow

Name

Type

Size (bits)

Description

TMP_RIP

Effective Address

32/64

Address of instruction at which to resume execution on ERESUME.

TMP_MODE64

binary

1

((IA32_EFER.LMA = 1) && (CS.L = 1)).

TMP_BRANCH_RECORD

LBR Record

2x64

From/To address to be pushed onto LBR stack.

The pseudo code in this section describes the internal operations that are executed when an AEX occurs in enclave
mode. These operations occur just before the normal interrupt or exception processing occurs.
(* Save RIP for later use *)
TMP_RIP = Linear Address of Resume RIP
(* Is the processor in 64-bit mode? *)
TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));
(* Save all registers, When saving EFLAGS, the TF bit is set to 0 and
the RF bit is set to what would have been saved on stack in the non-SGX case *)
IF (TMP_MODE64 = 0)
THEN
Save EAX, EBX, ECX, EDX, ESP, EBP, ESI, EDI, EFLAGS, EIP into the current SSA frame using
CR_GPR_PA; (* see Table 40-4 for list of CREGs used to describe internal operation within Intel SGX *)
SSA.RFLAGS.TF  0;
ELSE (* TMP_MODE64 = 1 *)
Save RAX, RBX, RCX, RDX, RSP, RBP, RSI, RDI, R8-R15, RFLAGS, RIP into the current SSA frame using
CR_GPR_PA;
SSA.RFLAGS.TF  0;
FI;
Save FS and GS BASE into SSA using CR_GPR_PA;
(* store XSAVE state into the current SSA frame's XSAVE area using the physical addresses
that were determined and cached at enclave entry time with CR_XSAVE_PAGE_i. *)
For each XSAVE state i defined by (SECS.ATTRIBUTES.XFRM[i] = 1, destination address cached in
CR_XSAVE_PAGE_i)
SSA.XSAVE.i  XSAVE_STATE_i;
(* Clear bytes 8 to 23 of XSAVE_HEADER, i.e. the next 16 bytes after XHEADER_BV *)
CR_XSAVE_PAGE_0.XHEADER_BV[191:64]  0;
(* Clear bits in XHEADER_BV[63:0] that are not enabled in ATTRIBUTES.XFRM *)
CR_XSAVE_PAGE_0.XHEADER_BV[63:0] 
CR_XSAVE_PAGE_0.XHEADER_BV[63:0] & SECS(CR_ACTIVE_SECS).ATTRIBUTES.XFRM;
Apply synthetic state to GPRs, RFLAGS, extended features, etc.
(* Restore the RSP and RBP from the current SSA frame's GPR area using the physical address
that was determined and cached at enclave entry time with CR_GPR_PA. *)
RSP  CR_GPR_PA.URSP;
RBP  CR_GPR_PA.URBP;
Vol. 3D 39-5

ENCLAVE EXITING EVENTS

(* Restore the FS and GS *)
FS.selector  CR_SAVE_FS.selector;
FS.base  CR_SAVE_FS.base;
FS.limit  CR_SAVE_FS.limit;
FS.access_rights  CR_SAVE_FS.access_rights;
GS.selector  CR_SAVE_GS.selector;
GS.base  CR_SAVE_GS.base;
GS.limit  CR_SAVE_GS.limit;
GS.access_rights  CR_SAVE_GS.access_rights;
(* Examine exception code and update enclave internal states*)
exception_code  Exception or interrupt vector;
(* Indicate the exit reason in SSA *)
IF (exception_code = (#DE OR #DB OR #BP OR #BR OR #UD OR #MF OR #AC OR #XM ))
THEN
CR_GPR_PA.EXITINFO.VECTOR  exception_code;
IF (exception code = #BP)
THEN CR_GPR_PA.EXITINFO.EXIT_TYPE  6;
ELSE CR_GPR_PA.EXITINFO.EXIT_TYPE  3;
FI;
CR_GPR_PA.EXITINFO.VALID  1;
ELSE IF (exception_code is #PF or #GP )
THEN
(* Check SECS.MISCSELECT using CR_ACTIVE_SECS *)
IF (SECS.MISCSELECT[0] is set)
THEN
CR_GPR_PA.EXITINFO.VECTOR  exception_code;
CR_GPR_PA.EXITINFO.EXIT_TYPE  3;
IF (exception_code is #PF)
THEN
SSA.MISC.EXINFO. MADDR  CR2;
SSA.MISC.EXINFO.ERRCD  PFEC;
SSA.MISC.EXINFO.RESERVED  0;
ELSE
SSA.MISC.EXINFO. MADDR  0;
SSA.MISC.EXINFO.ERRCD  GPEC;
SSA.MISC.EXINFO.RESERVED  0;
FI;
CR_GPR_PA.EXITINFO.VALID  1;
FI;
ELSE
CR_GPR_PA.EXITINFO.VECTOR  0;
CR_GPR_PA.EXITINFO.EXIT_TYPE  0
CR_GPR_PA.REASON.VALID  0;
FI;
(* Execution will resume at the AEP *)
RIP  CR_TCS_PA.AEP;
(* Set EAX to the ERESUME leaf index *)
EAX  3;

39-6 Vol. 3D

ENCLAVE EXITING EVENTS

(* Put the TCS LA into RBX for later use by ERESUME *)
RBX  CR_TCS_LA;
(* Put the AEP into RCX for later use by ERESUME *)
RCX  CR_TCS_PA.AEP;
(* Increment the SSA frame # *)
CR_TCS_PA.CSSA  CR_TCS_PA.CSSA + 1;
(* Restore XCR0 if needed *)
IF (CR4.OSXSAVE = 1)
THEN XCR0  CR_SAVE_XCR0; FI;
Un-suppress all code breakpoints that are outside ELRANGE
(* Update the thread context to show not in enclave mode *)
CR_ENCLAVE_MODE  0;
(* Assure consistent translations. *)
Flush linear context including TLBs and paging-structure caches
IF (CR_DBGOPTIN = 0)
THEN
Un-suppress all breakpoints that overlap ELRANGE
(* Clear suppressed breakpoint matches *)
Restore suppressed breakpoint matches
(* Restore TF *)
RFLAGS.TF  CR_SAVE_TF;
Un-suppress monitor trap flag;
Un-suppress branch recording facilities;
Un-suppress all suppressed performance monitoring activity;
Promote any sibling-thread counters that were demoted from AnyThread to MyThread during enclave
entry back to AnyThread;
FI;
IF the “monitor trap flag” VM-execution control is 1
THEN Pend MTF VM Exit at the end of exit; FI;
(* Clear low 12 bits of CR2 on #PF *)
IF (Exception code is #PF)
THEN CR2  CR2 & ~0xFFF; FI;
(* end_of_flow *)
(* Execution continues with normal event processing. *)

Vol. 3D 39-7

ENCLAVE EXITING EVENTS

39-8 Vol. 3D

SGX INSTRUCTION REFERENCES

CHAPTER 40
SGX INSTRUCTION REFERENCES
This chapter describes the supervisor and user level instructions provided by Intel® Software Guard Extensions
(Intel® SGX). In general, various functionality is encoded as leaf functions within the ENCLS (supervisor) and
ENCLU (user) instruction mnemonics. Different leaf functions are encoded by specifying an input value in the EAX
register of the respective instruction mnemonic.

40.1

INTEL® SGX INSTRUCTION SYNTAX AND OPERATION

ENCLS and ENCLU instruction mnemonics for all leaf functions are covered in this section.
For all instructions, the value of CS.D is ignored; addresses and operands are 64 bits in 64-bit mode and are otherwise 32 bits. Aside from EAX specifying the leaf number as input, each instruction leaf may require all or some
subset of the RBX/RCX/RDX as input parameters. Some leaf functions may return data or status information in one
or more of the general purpose registers.

40.1.1

ENCLS Register Usage Summary

Table 40-1 summarizes the implicit register usage of supervisor mode enclave instructions.

Table 40-1. Register Usage of Privileged Enclave Instruction Leaf Functions
Instr. Leaf

EAX

RBX

RCX

ECREATE

00H (In)

PAGEINFO (In, EA)

EPCPAGE (In, EA)

EADD

01H (In)

PAGEINFO (In, EA)

EPCPAGE (In, EA)

EINIT

02H (In)

SIGSTRUCT (In, EA)

SECS (In, EA)

RDX

EINITTOKEN (In, EA)

EREMOVE

03H (In)

EDBGRD

04H (In)

Result Data (Out)

EPCPAGE (In, EA)

EPCPAGE (In, EA)

EDBGWR

05H (In)

Source Data (In)

EPCPAGE (In, EA)

EEXTEND

06H (In)

SECS (In, EA)

EPCPAGE (In, EA)

ELDB

07H (In)

PAGEINFO (In, EA)

EPCPAGE (In, EA)

VERSION (In, EA)

ELDU

08H (In)

PAGEINFO (In, EA)

EPCPAGE (In, EA)

VERSION (In, EA)

EBLOCK

09H (In)

EPA

0AH (In)

PT_VA (In)

EWB

0BH (In)

PAGEINFO (In, EA)

ETRACK

0CH (In)

EAUG

0DH (In)

PAGEINFO (In, EA)

EPCPAGE (In, EA)

EMODPR

0EH (In)

SECINFO (In, EA)

EPCPAGE (In, EA)

EMODT

0FH (In)

SECINFO (In, EA)

EPCPAGE (In, EA)

EPCPAGE (In, EA)
EPCPAGE (In, EA)
EPCPAGE (In, EA)

VERSION (In, EA)

EPCPAGE (In, EA)

EA: Effective Address

40.1.2

ENCLU Register Usage Summary

Table 40-2 Summarized the implicit register usage of user mode enclave instructions.

Vol. 3D 40-1

SGX INSTRUCTION REFERENCES

Table 40-2. Register Usage of Unprivileged Enclave Instruction Leaf Functions
Instr. Leaf

EAX

RBX

RCX

RDX

EREPORT

00H (In)

TARGETINFO (In, EA)

REPORTDATA (In, EA)

OUTPUTDATA (In, EA)

EGETKEY

01H (In)

KEYREQUEST (In, EA)

KEY (In, EA)

EENTER

02H (In)

TCS (In, EA)

AEP (In, EA)

RBX.CSSA (Out)

Return (Out, EA)

ERESUME

03H (In)

TCS (In, EA)

AEP (In, EA)

EEXIT

04H (In)

Target (In, EA)

Current AEP (Out)

EACCEPT

05H (In)

SECINFO (In, EA)

EPCPAGE (In, EA)

EMODPE

06H (In)

SECINFO (In, EA)

EPCPAGE (In, EA)

EACCEPTCOPY

07H (In)

SECINFO (In, EA)

EPCPAGE (In, EA)

EPCPAGE (In, EA)

EA: Effective Address

40.1.3

Information and Error Codes

Information and error codes are reported by various instruction leaf functions to show an abnormal termination of
the instruction or provide information which may be useful to the developer. Table 40-3 shows the various codes
and the instruction which generated the code. Details of the meaning of the code is provided in the individual
instruction.

Table 40-3. Error or Information Codes for Intel® SGX Instructions
Name

Value

Returned By

No Error

0

SGX_INVALID_SIG_STRUCT

1

EINIT

SGX_INVALID_ATTRIBUTE

2

EINIT, EGETKEY

SGX_BLSTATE

3

EBLOCK

SGX_INVALID_MEASUREMENT

4

EINIT

SGX_NOTBLOCKABLE

5

EBLOCK

SGX_PG_INVLD

6

EBLOCK

SGX_LOCKFAIL

7

EBLOCK, EMODPR, EMODT

SGX_INVALID_SIGNATURE

8

EINIT

SGX_MAC_COMPARE_FAIL

9

ELDB, ELDU

SGX_PAGE_NOT_BLOCKED

10

EWB

SGX_NOT_TRACKED

11

EWB, EACCEPT

SGX_VA_SLOT_OCCUPIED

12

EWB

SGX_CHILD_PRESENT

13

EWB, EREMOVE

SGX_ENCLAVE_ACT

14

EREMOVE

SGX_ENTRYEPOCH_LOCKED

15

EBLOCK

SGX_INVALID_EINITTOKEN

16

EINIT

SGX_PREV_TRK_INCMPL

17

ETRACK

SGX_PG_IS_SECS

18

EBLOCK

SGX_PAGE_ATTRIBUTES_MISMATCH

19

EACCEPT, EACCEPTCOPY

SGX_PAGE_NOT_MODIFIABLE

20

EMODPR, EMODT

SGX_PAGE_NOT_DEBUGGABLE

21

EDBGRD, EDBGWR

40-2 Vol. 3D

SGX INSTRUCTION REFERENCES

Table 40-3. Error or Information Codes for Intel® SGX Instructions
Name

Value

Returned By

SGX_INVALID_CPUSVN

32

EINIT, EGETKEY

SGX_INVALID_ISVSVN

64

EGETKEY

SGX_UNMASKED_EVENT

128

EINIT

SGX_INVALID_KEYNAME

256

EGETKEY

40.1.4

Internal CREGs

The CREGs as shown in Table 5-4 are hardware specific registers used in this document to indicate values kept by
the processor. These values are used while executing in enclave mode or while executing an Intel SGX instruction.
These registers are not software visible and are implementation specific. The values in Table 40-4 appear at various
places in the pseudo-code of this document. They are used to enhance understanding of the operations.

Table 40-4. List of Internal CREG
Name

Size (Bits)

Scope

CR_ENCLAVE_MODE

1

LP

CR_DBGOPTIN

1

LP

CR_TCS_LA

64

LP

CR_TCS_PA

64

LP

CR_ACTIVE_SECS

64

LP

CR_ELRANGE

128

LP

CR_SAVE_TF

1

LP

CR_SAVE_FS

64

LP

CR_GPR_PA

64

LP

CR_XSAVE_PAGE_n

64

LP

CR_SAVE_DR7

64

LP

CR_SAVE_PERF_GLOBAL_CTRL

64

LP

CR_SAVE_DEBUGCTL

64

LP

CR_SAVE_PEBS_ENABLE

64

LP

CR_CPUSVN

128

PACKAGE

CR_SGXOWNEREPOCH

128

PACKAGE

CR_SAVE_XCR0

64

LP

CR_SGX_ATTRIBUTES_MASK

128

LP

CR_PAGING_VERSION

64

PACKAGE

CR_VERSION_THRESHOLD

64

PACKAGE

CR_NEXT_EID

64

PACKAGE

CR_BASE_PK

128

PACKAGE

CR_SEAL_FUSES

128

PACKAGE

40.1.5

Concurrent Operation Restrictions

To protect the integrity of Intel SGX data structures, under certain conditions, Intel SGX disallows certain leaf functions from operating concurrently. Listed below are some examples of concurrency that are not allowed.

•

For example, Intel SGX disallows the following leafs to concurrently operate on the same EPC page.

Vol. 3D 40-3

SGX INSTRUCTION REFERENCES

— ECREATE, EADD, and EREMOVE are not allowed to operate on the same EPC page concurrently with
themselves.
— EADD, EEXTEND, and EINIT leafs are not allowed to operate on the same SECS concurrently.

•
•

Intel SGX disallows the EREMOVE leaf from removing pages from an enclave that is in use.
Intel SGX disallows entry (EENTER and ERESUME) to an enclave while a page from that enclave is being
removed.

When disallowed operation is detected, a leaf function causes an exception. To prevent such exceptions, software
must serialize leaf functions or prevent these leaf functions from accessing the same resource.

40.1.5.1

Concurrency Tables of Intel® SGX Instructions

Concurrent restriction of an individual leaf function (ENCLS or ENCLU) with another Intel SGX instruction leaf functions is listed under the Concurrency Restriction paragraph of the respective reference pages of the leaf function.
Each cell in the table for a given Intel SGX Instruction leaf details the concurrency restriction when that instruction
references the same EPC page (as an explicit or an implicit parameter) as referenced by a concurrent instruction
leaf executed on another logical processor. The concurrency behavior of the instruction leaf if focus shown in a
given row is denoted by the following:

•

‘N’: The instructions listed in a given row heading may not execute concurrently with the instruction leaf shown
in the respective column. Software should serialize them. For example, multiple ETRACK operations on the
same enclave are not allowed to execute concurrently on the same SECS page.

•

‘Y’: The instruction leaf listed in a given row may execute concurrently with the instruction leaf shown in the
respective column. For instance, multiple ELDB/ELDUs are allowed to execute concurrently as long as the
selected EPC page is not the same page.

•

‘C’: The instruction leaf listed in a given row heading may return an error code when executed concurrently with
the instruction leaf shown in the respective column.

•

‘U’: These two instruction leaves may complete, but the occurrence these two simultaneous flows are
considered a user program error for which the processor does not enforce any restriction.

•

A grey cell indicates the concurrency behavior of the instruction in focus (in the row header) may be different
than that of the concurrent instruction (in the column header). The concurrent instruction's behavior is detailed
in its respective concurrency table. For example, EBLOCK's SECS parameter is implicit, thus it is always shown
as 'Y' in the table. However a concurrent instruction may return an error code when accessing the same page.

For instance, multiple ELDB/ELDUs are allowed to execute as long as the selected EPC page is not the same page.
Multiple ETRACK operations are not allowed to execute concurrently.

40.2

40-4 Vol. 3D

INTEL® SGX INSTRUCTION REFERENCE

SGX INSTRUCTION REFERENCES

ENCLS—Execute an Enclave System Function of Specified Leaf Number
Opcode/
Instruction

Op/En

NP 0F 01 CF
ENCLS

NP

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This instruction is used to execute privileged Intel SGX leaf functions that are used for managing and debugging the enclaves.

Instruction Operand Encoding
Op/En

Operand 1

Operand 2

Operand 3

Implicit Register Operands

NP

NA

NA

NA

See Section 40.3

Description
The ENCLS instruction invokes the specified privileged Intel SGX leaf function for managing and debugging
enclaves. Software specifies the leaf function by setting the appropriate value in the register EAX as input. The
registers RBX, RCX, and RDX have leaf-specific purpose, and may act as input, as output, or may be unused. In 64bit mode, the instruction ignores upper 32 bits of the RAX register.
The ENCLS instruction produces an invalid-opcode exception (#UD) if CR0.PE = 0 or RFLAGS.VM = 1, or if it is
executed in system-management mode (SMM). Additionally, any attempt to execute the instruction when CPL > 0
results in #UD. The instruction produces a general-protection exception (#GP) if CR0.PG = 0 or if an attempt is
made to invoke an undefined leaf function.
In VMX non-root operation, execution of ENCLS may cause a VM exit if the “enable ENCLS exiting” VM-execution
control is 1. In this case, execution of individual leaf functions of ENCLS is governed by the ENCLS-exiting bitmap
field in the VMCS. Each bit in that field corresponds to the index of an ENCLS leaf function (as provided in EAX).
Software in VMX root operation can thus intercept the invocation of various ENCLS leaf functions in VMX non-root
operation by setting the “enable ENCLS exiting” VM-execution control and setting the corresponding bits in the
ENCLS-exiting bitmap.
Addresses and operands are 32 bits outside 64-bit mode (IA32_EFER.LMA = 0 || CS.L = 0) and are 64 bits in 64bit mode (IA32_EFER.LMA = 1 || CS.L = 1). CS.D value has no impact on address calculation. The DS segment is
used to create linear addresses.
Segment override prefixes and address-size override prefixes are ignored, and is the REX prefix in 64-bit mode.
Operation
IF TSX_ACTIVE
THEN GOTO TSX_ABORT_PROCESSING; FI;
IF CR0.PE = 0 or RFLAGS.VM = 1 or in SMM or CPUID.SGX_LEAF.0:EAX.SE1 = 0
THEN #UD; FI;
IF (CPL > 0)
THEN #UD; FI;
IF in VMX non-root operation and the “enable ENCLS exiting“ VM-execution control is 1
THEN
IF EAX < 63 and ENCLS_exiting_bitmap[EAX] = 1 or EAX> 62 and ENCLS_exiting_bitmap[63] = 1
THEN VM exit;
FI;
FI;
IF IA32_FEATURE_CONTROL.LOCK = 0 or IA32_FEATURE_CONTROL.SGX_ENABLE = 0
THEN #GP(0); FI;
IF EAX is invalid leaf number)

Vol. 3D 40-5

SGX INSTRUCTION REFERENCES

THEN #GP(0); FI;
IF CR0.PG = 0
THEN #GP(0); FI;
(* DS must not be an expanded down segment *)
IF not in 64-bit mode and DS.Type is expand-down data
THEN #GP(0); FI;
Jump to leaf specific flow
Flags Affected
See individual leaf functions
Protected Mode Exceptions
#UD

If any of the LOCK/OSIZE/REP/VEX prefix is used.
If current privilege level is not 0.
If CPUID.(EAX=12H,ECX=0):EAX.SGX1 [bit 0] = 0.
If logical processor is in SMM.

#GP(0)

If IA32_FEATURE_CONTROL.LOCK = 0.
If IA32_FEATURE_CONTROL.SGX_ENABLE = 0.
If input value in EAX encodes an unsupported leaf.
If data segment expand down.
If CR0.PG=0.

Real-Address Mode Exceptions
#UD

ENCLS is not recognized in real mode.

Virtual-8086 Mode Exceptions
#UD

ENCLS is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
Same exceptions as in protected mode.
64-Bit Mode Exceptions
#UD

If any of the LOCK/OSIZE/REP/VEX prefix is used.
If current privilege level is not 0.
If CPUID.(EAX=12H,ECX=0):EAX.SGX1 [bit 0] = 0.
If logical processor is in SMM.

#GP(0)

If IA32_FEATURE_CONTROL.LOCK = 0.
If IA32_FEATURE_CONTROL.SGX_ENABLE = 0.
If input value in EAX encodes an unsupported leaf.

40-6 Vol. 3D

SGX INSTRUCTION REFERENCES

ENCLU—Execute an Enclave User Function of Specified Leaf Number
Opcode/
Instruction

Op/En

NP 0F 01 D7
ENCLU

NP

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This instruction is used to execute non-privileged Intel SGX leaf
functions.

Instruction Operand Encoding
Op/En

Operand 1

Operand 2

Operand 3

Implicit Register Operands

NP

NA

NA

NA

See Section 40.4

Description
The ENCLU instruction invokes the specified non-privileged Intel SGX leaf functions. Software specifies the leaf
function by setting the appropriate value in the register EAX as input. The registers RBX, RCX, and RDX have leafspecific purpose, and may act as input, as output, or may be unused. In 64-bit mode, the instruction ignores upper
32 bits of the RAX register.
The ENCLU instruction produces an invalid-opcode exception (#UD) if CR0.PE = 0 or RFLAGS.VM = 1, or if it is
executed in system-management mode (SMM). Additionally, any attempt to execute this instruction when CPL < 3
results in #UD. The instruction produces a general-protection exception (#GP) if either CR0.PG or CR0.NE is 0, or
if an attempt is made to invoke an undefined leaf function. The ENCLU instruction produces a device not available
exception (#NM) if CR0.TS = 1.
Addresses and operands are 32 bits outside 64-bit mode (IA32_EFER.LMA = 0 or CS.L = 0) and are 64 bits in 64bit mode (IA32_EFER.LMA = 1 and CS.L = 1). CS.D value has no impact on address calculation. The DS segment
is used to create linear addresses.
Segment override prefixes and address-size override prefixes are ignored, as is the REX prefix in 64-bit mode.
Operation
IN_64BIT_MODE 0;
IF TSX_ACTIVE
THEN GOTO TSX_ABORT_PROCESSING; FI;
IF CR0.PE= 0 or RFLAGS.VM = 1 or in SMM or CPUID.SGX_LEAF.0:EAX.SE1 = 0
THEN #UD; FI;
IF CR0.TS = 1
THEN #NM; FI;
IF CPL < 3
THEN #UD; FI;
IF IA32_FEATURE_CONTROL.LOCK = 0 or IA32_FEATURE_CONTROL.SGX_ENABLE = 0
THEN #GP(0); FI;
IF EAX is invalid leaf number
THEN #GP(0); FI;
IF CR0.PG = 0 or CR0.NE = 0
THEN #GP(0); FI;
IN_64BIT_MODE  IA32_EFER.LMA AND CS.L ? 1 : 0;
(* Check not in 16-bit mode and DS is not a 16-bit segment *)
IF not in 64-bit mode and (CS.D = 0 or DS.B = 0)
Vol. 3D 40-7

SGX INSTRUCTION REFERENCES

THEN #GP(0); FI;
IF CR_ENCLAVE_MODE = 1 and (EAX = 2 or EAX = 3) (* EENTER or ERESUME *)
THEN #GP(0); FI;
IF CR_ENCLAVE_MODE = 0 and (EAX = 0 or EAX = 1 or EAX = 4 or EAX = 5 or EAX = 6 or EAX = 7)
(* EREPORT, EGETKEY, EEXIT, EACCEPT, EMODPE, or EACCEPTCOPY *)
THEN #GP(0); FI;
Jump to leaf specific flow
Flags Affected
See individual leaf functions
Protected Mode Exceptions
#UD

If any of the LOCK/OSIZE/REP/VEX prefix is used.
If current privilege level is not 3.
If CPUID.(EAX=12H,ECX=0):EAX.SGX1 [bit 0] = 0.
If logical processor is in SMM.

#GP(0)

If IA32_FEATURE_CONTROL.LOCK = 0.
If IA32_FEATURE_CONTROL.SGX_ENABLE = 0.
If input value in EAX encodes an unsupported leaf.
If input value in EAX encodes EENTER/ERESUME and ENCLAVE_MODE = 1.
If input value in EAX encodes EGETKEY/EREPORT/EEXIT/EACCEPT/EACCEPTCOPY/EMODPE
and ENCLAVE_MODE = 0.
If operating in 16-bit mode.
If data segment is in 16-bit mode.
If CR0.PG = 0 or CR0.NE= 0.

#NM

If CR0.TS = 1.

Real-Address Mode Exceptions
#UD

ENCLS is not recognized in real mode.

Virtual-8086 Mode Exceptions
#UD

ENCLS is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions
Same exceptions as in protected mode.
64-Bit Mode Exceptions
#UD

If any of the LOCK/OSIZE/REP/VEX prefix is used.
If current privilege level is not 3.
If CPUID.(EAX=12H,ECX=0):EAX.SGX1 [bit 0] = 0.
If logical processor is in SMM.

#GP(0)

If IA32_FEATURE_CONTROL.LOCK = 0.
If IA32_FEATURE_CONTROL.SGX_ENABLE = 0.
If input value in EAX encodes an unsupported leaf.
If input value in EAX encodes EENTER/ERESUME and ENCLAVE_MODE = 1.
If input value in EAX encodes EGETKEY/EREPORT/EEXIT/EACCEPT/EACCEPTCOPY/EMODPE
and ENCLAVE_MODE = 0.

40-8 Vol. 3D

SGX INSTRUCTION REFERENCES

If CR0.NE= 0.
#NM

If CR0.TS = 1.

Vol. 3D 40-9

SGX INSTRUCTION REFERENCES

40.3

INTEL® SGX SYSTEM LEAF FUNCTION REFERENCE

Leaf functions available with the ENCLS instruction mnemonic are covered in this section. In general, each instruction leaf requires EAX to specify the leaf function index and/or additional implicit registers specifying leaf-specific
input parameters. An instruction operand encoding table provides details of each implicit register usage and associated input/output semantics.
In many cases, an input parameter specifies an effective address associated with a memory object inside or outside
the EPC, the memory addressing semantics of these memory objects are also summarized in a separate table.

40-10 Vol. 3D

SGX INSTRUCTION REFERENCES

EADD—Add a Page to an Uninitialized Enclave
Opcode/
Instruction

Op/En

EAX = 01H
ENCLS[EADD]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function adds a page to an uninitialized enclave.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EADD (In)

Address of a PAGEINFO (In)

Address of the destination EPC page (In)

Description
This leaf function copies a source page from non-enclave memory into the EPC, associates the EPC page with an
SECS page residing in the EPC, and stores the linear address and security attributes in EPCM. As part of the association, the enclave offset and the security attributes are measured and extended into the SECS.MRENCLAVE. This
instruction can only be executed when current privilege level is 0.
RBX contains the effective address of a PAGEINFO structure while RCX contains the effective address of an EPC
page. The table below provides additional information on the memory parameter of EADD leaf function.

EADD Memory Parameter Semantics
PAGEINFO

PAGEINFO.SECS

PAGEINFO.SRCPGE

PAGEINFO.SECINFO

EPCPAGE

Read access permitted
by Non Enclave

Read/Write access permitted by Enclave

Read access permitted
by Non Enclave

Read access permitted
by Non Enclave

Write access permitted
by Enclave

The instruction faults if any of the following:

EADD Faulting Conditions
The operands are not properly aligned.

Unsupported security attributes are set.

Refers to an invalid SECS.

Reference is made to an SECS that is locked by another thread.

The EPC page is locked by another thread.

RCX does not contain an effective address of an EPC page.

The EPC page is already valid.

If security attributes specifies a TCS and the source page specifies unsupported
TCS values or fields.

The SECS has been initialized.

The specified enclave offset is outside of the enclave address space.

Concurrency Restrictions

Table 40-5. Concurrency Restrictions of EADD with Other Intel® SGX Operations 1 of 2
Operation
Param
EADD

EEXIT
TCS SSA

EADD
SECS Targ SECS
N

Targ
SECS

N

N

EBLOCK

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

EPA

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

SECS VA

N

N

N

N

N

N

N

N

Y

N

Y

Y

N

Y

N
N

N

N

N

N

Vol. 3D 40-11

SGX INSTRUCTION REFERENCES

Table 40-6. Concurrency Restrictions of EADD with Other Intel® SGX Operations 2 of 2
Operation

EADD

EREMOVE

EREPORT

Param

Targ SECS Para
m

Targ

N

SECS

N

Y

SECS

N

ETRACK

EWB

SECS

SRC

VA

N

N

N

Y

N

EAUG

EMODPE

EMODPR

SECS Targ SECS Targ SECI Targ SEC
NFO
S
Y

N

N

N

N

N

EMODT
Targ SEC
S

EACCEPT
Targ SECI
NFO

EACCEPTCOPY

SECS Targ SR
C

SECI
NFO

N
N

N

N

N

Operation

Temp Variables in EADD Operational Flow
Name

Type

Size (bits)

Description

TMP_SRCPGE

Effective Address

32/64

Effective address of the source page.

TMP_SECS

Effective Address

32/64

Effective address of the SECS destination page.

TMP_SECINFO

Effective Address

32/64

Effective address of an SECINFO structure which contains security
attributes of the page to be added.

SCRATCH_SECINFO

SECINFO

512

Scratch storage for holding the contents of DS:TMP_SECINFO.

TMP_LINADDR

Unsigned Integer

64

Holds the linear address to be stored in the EPCM and used to
calculate TMP_ENCLAVEOFFSET.

TMP_ENCLAVEOFFSET

Enclave Offset

64

The page displacement from the enclave base address.

TMPUPDATEFIELD

SHA256 Buffer

512

Buffer used to hold data being added to TMP_SECS.MRENCLAVE.

IF (DS:RBX is not 32Byte Aligned)
THEN #GP(0); FI;
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
TMP_SRCPGE  DS:RBX.SRCPGE;
TMP_SECS  DS:RBX.SECS;
TMP_SECINFO  DS:RBX.SECINFO;
TMP_LINADDR  DS:RBX.LINADDR;
IF (DS:TMP_SRCPGE is not 4KByte aligned or DS:TMP_SECS is not 4KByte aligned or
DS:TMP_SECINFO is not 64Byte aligned or TMP_LINADDR is not 4KByte aligned)
THEN #GP(0); FI;
IF (DS:TMP_SECS does not resolve within an EPC)
THEN #PF(DS:TMP_SECS); FI;
SCRATCH_SECINFO  DS:TMP_SECINFO;
(* Check for mis-configured SECINFO flags*)
IF (SCRATCH_SECINFO reserved fields are not zero or
! (SCRATCH_SECINFO.FLAGS.PT is PT_REG or SCRATCH_SECINFO.FLAGS.PT is PT_TCS) )
THEN #GP(0); FI;

40-12 Vol. 3D

SGX INSTRUCTION REFERENCES

(* Check the EPC page for concurrency *)
IF (EPC page in use)
THEN #GP(0); FI;
IF (EPCM(DS:RCX).VALID ≠ 0)
THEN #PF(DS:RCX); FI;
(* Check the SECS for concurrency *)
IF (SECS is not available for EADD)
THEN #GP(0); FI;
IF (EPCM(DS:TMP_SECS).VALID = 0 or EPCM(DS:TMP_SECS).PT ≠ PT_SECS)
THEN #PF(DS:TMP_SECS); FI;
(* Copy 4KBytes from source page to EPC page*)
DS:RCX[32767:0]  DS:TMP_SRCPGE[32767:0];
CASE (SCRATCH_SECINFO.FLAGS.PT)
{
PT_TCS:
IF (DS:RCX.RESERVED ≠ 0) #GP(0); FI;
IF ( (DS:TMP_SECS.ATTIBUTES.MODE64BIT = 0) and
((DS:TCS.FSLIMIT & 0FFFH ≠ 0FFFH) or (DS:TCS.GSLIMIT & 0FFFH ≠ 0FFFH) )) #GP(0); FI;
BREAK;
PT_REG:
IF (SCRATCH_SECINFO.FLAGS.W = 1 and SCRATCH_SECINFO.FLAGS.R = 0) #GP(0); FI;
BREAK;
ESAC;
(* Check the enclave offset is within the enclave linear address space *)
IF (TMP_LINADDR < DS:TMP_SECS.BASEADDR or TMP_LINADDR ≥ DS:TMP_SECS.BASEADDR + DS:TMP_SECS.SIZE)
THEN #GP(0); FI;
(* Check concurrency of measurement resource*)
IF (Measurement being updated)
THEN #GP(0); FI;
(* Check if the enclave to which the page will be added is already in Initialized state *)
IF (DS:TMP_SECS already initialized)
THEN #GP(0); FI;
(* For TCS pages, force EPCM.rwx bits to 0 and no debug access *)
IF (SCRATCH_SECINFO.FLAGS.PT = PT_TCS)
THEN
SCRATCH_SECINFO.FLAGS.R  0;
SCRATCH_SECINFO.FLAGS.W  0;
SCRATCH_SECINFO.FLAGS.X  0;
(DS:RCX).FLAGS.DBGOPTIN  0; // force TCS.FLAGS.DBGOPTIN off
DS:RCX.CSSA  0;
DS:RCX.AEP  0;
DS:RCX.STATE  0;
FI;
(* Add enclave offset and security attributes to MRENCLAVE *)
Vol. 3D 40-13

SGX INSTRUCTION REFERENCES

TMP_ENCLAVEOFFSET  TMP_LINADDR - DS:TMP_SECS.BASEADDR;
TMPUPDATEFIELD[63:0]  0000000044444145H; // “EADD”
TMPUPDATEFIELD[127:64]  TMP_ENCLAVEOFFSET;
TMPUPDATEFIELD[511:128]  SCRATCH_SECINFO[375:0]; // 48 bytes
DS:TMP_SECS.MRENCLAVE  SHA256UPDATE(DS:TMP_SECS.MRENCLAVE, TMPUPDATEFIELD)
INC enclave’s MRENCLAVE update counter;
(* Add enclave offset and security attributes to MRENCLAVE *)
EPCM(DS:RCX).R  SCRATCH_SECINFO.FLAGS.R;
EPCM(DS:RCX).W  SCRATCH_SECINFO.FLAGS.W;
EPCM(DS:RCX).X  SCRATCH_SECINFO.FLAGS.X;
EPCM(DS:RCX).PT  SCRATCH_SECINFO.FLAGS.PT;
EPCM(DS:RCX).ENCLAVEADDRESS  TMP_LINADDR;
(* associate the EPCPAGE with the SECS by storing the SECS identifier of DS:TMP_SECS *)
Update EPCM(DS:RCX) SECS identifier to reference DS:TMP_SECS identifier;
(* Set EPCM entry fields *)
EPCM(DS:RCX).BLOCKED  0;
EPCM(DS:RCX).PENDING  0;
EPCM(DS:RCX).MODIFIED  0;
EPCM(DS:RCX).VALID  1;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If an enclave memory operand is outside of the EPC.
If an enclave memory operand is the wrong type.
If a memory operand is locked.
If the enclave is initialized.
If the enclave's MRENCLAVE is locked.
If the TCS page reserved bits are set.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the EPC page is valid.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If an enclave memory operand is outside of the EPC.
If an enclave memory operand is the wrong type.
If a memory operand is locked.
If the enclave is initialized.
If the enclave's MRENCLAVE is locked.
If the TCS page reserved bits are set.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the EPC page is valid.

40-14 Vol. 3D

SGX INSTRUCTION REFERENCES

EAUG—Add a Page to an Initialized Enclave
Opcode/
Instruction

Op/En

EAX = 0DH
ENCLS[EAUG]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX2

Description

This leaf function adds a page to an initialized enclave.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EAUG (In)

Address of a SECINFO (In)

Address of the destination EPC page (In)

Description
This leaf function zeroes a page of EPC memory, associates the EPC page with an SECS page residing in the EPC,
and stores the linear address and security attributes in the EPCM. As part of the association, the security attributes
are configured to prevent access to the EPC page until a corresponding invocation of the EACCEPT leaf or EACCEPTCOPY leaf confirms the addition of the new page into the enclave. This instruction can only be executed when
current privilege level is 0.
RBX contains the effective address of a PAGEINFO structure while RCX contains the effective address of an EPC
page. The table below provides additional information on the memory parameter of the EAUG leaf function.

EAUG Memory Parameter Semantics
PAGEINFO

PAGEINFO.SECS

PAGEINFO.SRCPGE

PAGEINFO.SECINFO

EPCPAGE

Read access permitted by Non Enclave

Read/Write access permitted by Enclave

Must be zero

Read access permitted by
Non Enclave

Write access permitted by
Enclave

The instruction faults if any of the following:

EAUG Faulting Conditions
The operands are not properly aligned.

Unsupported security attributes are set.

Refers to an invalid SECS.

Reference is made to an SECS that is locked by another thread.

The EPC page is locked by another thread.

RCX does not contain an effective address of an EPC page.

The EPC page is already valid.

The specified enclave offset is outside of the enclave address space.

The SECS has been initialized.
Concurrency Restrictions

Table 40-7. Concurrency Restrictions of EAUG with Other Intel® SGX Operations 1 of 2
Operation
Param
EAUG

EEXIT
TCS SSA

SECS

Targ
SECS

Y

EADD

EBLOCK

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

EP
A

Targ SECS

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

SECS VA

N

N

N

N

N

N

N

N

N

N

N

N

N

N

Y

N

Y

N

Y

N
Y

N

Y

N

Vol. 3D 40-15

SGX INSTRUCTION REFERENCES

Table 40-8. Concurrency Restrictions of EAUG with Other Intel® SGX Operations 2 of 2
Operation

EAUG

EREMOVE

EREPORT

ETRACK

EWB

Param

Targ SECS Param SECS

SECS

SRC

VA

Targ

N

N

N

N

SECS

N

Y

N

Y

Y

EAUG

EMODPE

EMODPR

SECS Targ SECS Targ SECI Targ SEC
NFO
S
Y

N

N

N

Y

N

EMODT
Targ SEC
S

EACCEPT
Targ SECI
NFO

EACCEPTCOPY

SECS Targ SR
C

SECI
NFO

N
Y

N

Y

Y

Operation

Temp Variables in EAUG Operational Flow
Name

Type

Size (bits)

Description

TMP_SECS

Effective Address

32/64

Effective address of the SECS destination page.

TMP_SECINFO

Effective Address

32/64

Effective address of an SECINFO structure which contains security
attributes of the page to be added.

SCRATCH_SECINFO

SECINFO

512

Scratch storage for holding the contents of DS:TMP_SECINFO.

TMP_LINADDR

Unsigned Integer

64

Holds the linear address to be stored in the EPCM and used to
calculate TMP_ENCLAVEOFFSET.

IF (DS:RBX is not 32Byte Aligned)
THEN #GP(0); FI;
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
TMP_SECS  DS:RBX.SECS;
TMP_LINADDR  DS:RBX.LINADDR;
IF ( DS:TMP_SECS is not 4KByte aligned or TMP_LINADDR is not 4KByte aligned )
THEN #GP(0); FI;
IF ( (DS:RBX.SRCPAGE is not 0) or (DS:RBX.SECINFO is not 0) )
THEN #GP(0); FI;
IF (DS:TMP_SECS does not resolve within an EPC)
THEN #PF(DS:TMP_SECS); FI;
(* Check the EPC page for concurrency *)
IF (EPC page in use)
THEN #GP(0); FI;
IF (EPCM(DS:RCX).VALID ≠ 0)
THEN #PF(DS:RCX); FI;
(* Check the SECS for concurrency *)
IF (SECS is not available for EAUG)
THEN #GP(0); FI;

40-16 Vol. 3D

SGX INSTRUCTION REFERENCES

IF (EPCM(DS:TMP_SECS).VALID = 0 or EPCM(DS:TMP_SECS).PT ≠ PT_SECS)
THEN #PF(DS:TMP_SECS); FI;
(* Check if the enclave to which the page will be added is in the Initialized state *)
IF (DS:TMP_SECS is not initialized)
THEN #GP(0); FI;
(* Check the enclave offset is within the enclave linear address space *)
IF ( (TMP_LINADDR < DS:TMP_SECS.BASEADDR) or (TMP_LINADDR ≥ DS:TMP_SECS.BASEADDR + DS:TMP_SECS.SIZE) )
THEN #GP(0); FI;
(* Clear the content of EPC page*)
DS:RCX[32767:0]  0;
(* Set EPCM security attributes *)
EPCM(DS:RCX).R  1;
EPCM(DS:RCX).W  1;
EPCM(DS:RCX).X  0;
EPCM(DS:RCX).PT  PT_REG;
EPCM(DS:RCX).ENCLAVEADDRESS  TMP_LINADDR;
EPCM(DS:RCX).BLOCKED  0;
EPCM(DS:RCX).PENDING  1;
EPCM(DS:RCX).MODIFIED  0;
EPCM(DS:RCX).PR  0;
(* associate the EPCPAGE with the SECS by storing the SECS identifier of DS:TMP_SECS *)
Update EPCM(DS:RCX) SECS identifier to reference DS:TMP_SECS identifier;
(* Set EPCM valid fields *)
EPCM(DS:RCX).VALID  1;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If a memory operand is locked.
If the enclave is not initialized.

#PF(error code)

If a page fault occurs in accessing memory operands.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If a memory operand is locked.
If the enclave is not initialized.

#PF(error code)

If a page fault occurs in accessing memory operands.

Vol. 3D 40-17

SGX INSTRUCTION REFERENCES

EBLOCK—Mark a page in EPC as Blocked
Opcode/
Instruction

Op/En

EAX = 09H
ENCLS[EBLOCK]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function marks a page in the EPC as blocked.

Instruction Operand Encoding
Op/En

EAX

IR

EBLOCK (In)

RCX
Return error code (Out)

Effective address of the EPC page (In)

Description
This leaf function causes an EPC page to be marked as BLOCKED. This instruction can only be executed when
current privilege level is 0.
The content of RCX is an effective address of an EPC page. The DS segment is used to create linear address.
Segment override is not supported.
An error code is returned in RAX.
The table below provides additional information on the memory parameter of EBLOCK leaf function.

EBLOCK Memory Parameter Semantics
EPCPAGE
Read/Write access permitted by Enclave
The error codes are:

Table 40-9. EBLOCK Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EBLOCK successful

SGX_BLKSTATE

Page already blocked. This value is used to indicate to a VMM that the page was already in
BLOCKED state as a result of EBLOCK and thus will need to be restored to this state when it is
eventually reloaded (using ELDB).

SGX_ENTRYEPOCH_LOCKED

SECS locked for Entry Epoch update. This value indicates that an ETRACK is
currently executing on the SECS. The EBLOCK should be reattempted.

SGX_NOTBLOCKABLE

Page type is not one which can be blocked

SGX_PG_INVLD

Page is not valid and cannot be blocked

SGX_LOCKFAIL

Page is being written by EADD, EAUG, ECREATE, ELDU/B, EMODT, or EWB

Concurrency Restrictions

Table 40-10. Concurrency Restrictions of EBLOCK with Other Intel® SGX Operations 1 of 2
Operation

EBLOCK

EEXIT

EADD

EBLOCK

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

EPA

Param

TCS SSA

SECS Targ SECS

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

SECS VA

Targ

Y

Y

N

C

C

C

N

Y

C

Y

Y

C

Y

C

Y

C

Y

N

C

C

N

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

SECS

40-18 Vol. 3D

Y

SGX INSTRUCTION REFERENCES

Table 40-11. Concurrency Restrictions of EBLOCK with Other Intel® SGX Operations 2 of 2
Operation

EBLOCK

EREMOVE

EREPORT

ETRACK

EWB

EAUG

EMODPE

EMODPR

EMODT

EACCEPT

EACCEPTCOPY

Param

Targ SECS Param SECS

SECS

SRC

VA

SECS Targ SECS Targ SECI Targ SEC
NFO
S

Targ SEC
S

Targ SECI
NFO

SECS Targ SR
C

SECI
NFO

Targ

N

C

Y

C

C

N

C

C

N

C

Y

Y

Y

C

N

C

Y

Y

C

Y

Y

Y

SECS

Y

Y

Y

Y

U

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Operation

Temp Variables in EBLOCK Operational Flow
Name

Type

Size (Bits)

Description

TMP_BLKSTATE

Integer

64

Page is already blocked.

IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
RFLAGS.ZF,CF,PF,AF,OF,SF  0;
RAX 0;
(* Check the EPC page for concurrency*)
IF (EPC page in use)
THEN
RFLAGS.ZF  1;
RAX SGX_LOCKFAIL;
GOTO DONE;
FI;
IF (EPCM(DS:RCX). VALID = 0)
THEN
RFLAGS.ZF  1;
RAX SGX_PG_INVLD;
GOTO DONE;
FI;
IF ( (EPCM(DS:RCX).PT ≠ PT_REG) and (EPCM(DS:RCX).PT ≠ PT_TCS) and (EPCM(DS:RCX).PT ≠ PT_TRIM) )
THEN
RFLAGS.CF  1;
IF (EPCM(DS:RCX).PT = PT_SECS)
THEN RAX SGX_PG_IS_SECS;
ELSE RAX SGX_NOTBLOCKABLE;
FI;
GOTO DONE;
FI;
(* Check if the page is already blocked and report blocked state *)
TMP_BLKSTATE  EPCM(DS:RCX).BLOCKED;
(* at this point, the page must be valid and PT_TCS or PT_REG or PT_TRIM*)
Vol. 3D 40-19

SGX INSTRUCTION REFERENCES

IF (TMP_BLKSTATE = 1) )
THEN
RFLAGS.CF  1;
RAX SGX_BLKSTATE;
ELSE
EPCM(DS:RCX).BLOCKED  1
FI;
DONE:
Flags Affected
Sets ZF if SECS is in use or invalid, otherwise cleared. Sets CF if page is BLOCKED or not blockable, otherwise
cleared. Clears PF, AF, OF, SF.
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If the specified EPC resource is in use.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If the specified EPC resource is in use.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

40-20 Vol. 3D

SGX INSTRUCTION REFERENCES

ECREATE—Create an SECS page in the Enclave Page Cache
Opcode/
Instruction

Op/En

EAX = 00H
ENCLS[ECREATE]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function begins an enclave build by creating an SECS
page in EPC.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

ECREATE (In)

Address of a PAGEINFO (In)

Address of the destination SECS page (In)

Description
ENCLS[ECREATE] is the first instruction executed in the enclave build process. ECREATE copies an SECS structure
outside the EPC into an SECS page inside the EPC. The internal structure of SECS is not accessible to software.
ECREATE will set up fields in the protected SECS and mark the page as valid inside the EPC. ECREATE initializes or
checks unused fields.
Software sets the following fields in the source structure: SECS:BASEADDR, SECS:SIZE in bytes, and ATTRIBUTES.
SECS:BASEADDR must be naturally aligned on an SECS.SIZE boundary. SECS.SIZE must be at least 2 pages
(8192).
The source operand RBX contains an effective address of a PAGEINFO structure. PAGEINFO contains an effective
address of a source SECS and an effective address of an SECINFO. The SECS field in PAGEINFO is not used.
The RCX register is the effective address of the destination SECS. It is an address of an empty slot in the EPC. The
SECS structure must be page aligned. SECINFO flags must specify the page as an SECS page.

ECREATE Memory Parameter Semantics
PAGEINFO

PAGEINFO.SRCPGE

PAGEINFO.SECINFO

EPCPAGE

Read access permitted by
Non Enclave

Read access permitted by
Non Enclave

Read access permitted by Non
Enclave

Write access permitted by
Enclave

ECREATE will fault if the SECS target page is in use; already valid; outside the EPC. It will also fault if addresses are
not aligned; unused PAGEINFO fields are not zero.
If the amount of space needed to store the SSA frame is greater than the amount specified in SECS.SSAFRAMESIZE, a #GP(0) results. The amount of space needed for an SSA frame is computed based on
DS:TMP_SECS.ATTRIBUTES.XFRM size. Details of computing the size can be found Section 41.7.
Concurrency Restrictions

Table 40-12. Concurrency Restrictions of ECREATE with Other Intel® SGX Operations 1 of 2
Operation

EEXIT

Param
ECREATE

TCS SSA

EADD
SECS Targ SECS
N

SECS

ECRE
ATE

EBLOCK

N

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

EPA

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

SECS VA

N

N

N

N

N

N

N

N

N

N

Table 40-13. Concurrency Restrictions of ECREATE with Other Intel® SGX Operations 2 of 2
Operation

ECREATE

EREMOVE

Param

Tar
g

SECS

N

EREPORT

SECS Param SECS

ETRACK

EWB

SECS

SRC

VA

N

N

N

EAUG

EMODPE

SECS Targ SECS Targ SECI
NFO
N

N

EMODPR

EMODT

EACCEPT

EACCEPTCOPY

Targ SECS Targ SECS Targ SECI SECS Targ SR
NFO
C
N

SECI
NFO

N

Vol. 3D 40-21

SGX INSTRUCTION REFERENCES

Operation

Temp Variables in ECREATE Operational Flow
Name

Type

Size (Bits)

Description

TMP_SRCPGE

Effective Address

32/64

Effective address of the SECS source page.

TMP_SECS

Effective Address

32/64

Effective address of the SECS destination page.

TMP_SECINFO

Effective Address

32/64

Effective address of an SECINFO structure which contains security
attributes of the SECS page to be added.

TMP_XSIZE

SSA Size

64

The size calculation of SSA frame.

TMP_MISC_SIZE

MISC Field Size

64

Size of the selected MISC field components.

TMPUPDATEFIELD

SHA256 Buffer

512

Buffer used to hold data being added to TMP_SECS.MRENCLAVE.

IF (DS:RBX is not 32Byte Aligned)
THEN #GP(0); FI;
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
TMP_SRCPGE  DS:RBX.SRCPGE;
TMP_SECINFO  DS:RBX.SECINFO;
IF (DS:TMP_SRCPGE is not 4KByte aligned or DS:TMP_SECINFO is not 64Byte aligned)
THEN #GP(0); FI;
IF (DS:RBX.LINADDR ! = 0 or DS:RBX.SECS ≠ 0)
THEN #GP(0); FI;
(* Check for misconfigured SECINFO flags*)
IF (DS:TMP_SECINFO reserved fields are not zero or DS:TMP_SECINFO.FLAGS.PT ≠ PT_SECS) )
THEN #GP(0); FI;
TMP_SECS  RCX;
IF (EPC entry in use)
THEN #GP(0); FI;
IF (EPCM(DS:RCX).VALID = 1)
THEN #PF(DS:RCX); FI;
(* Copy 4KBytes from source page to EPC page*)
DS:RCX[32767:0]  DS:TMP_SRCPGE[32767:0];
(* Check lower 2 bits of XFRM are set *)
IF ( ( DS:TMP_SECS.ATTRIBUTES.XFRM BitwiseAND 03H) ≠ 03H)
THEN #GP(0); FI;
IF (XFRM is illegal)

40-22 Vol. 3D

SGX INSTRUCTION REFERENCES

THEN #GP(0); FI;
(* Make sure that the SECS does not have any unsupported MISCSELECT options*)
IF ( !(CPUID.(EAX=12H, ECX=0):EBX[31:0] & DS:TMP_SECS.MISCSELECT[31:0]) )
THEN
EPCM(DS:TMP_SECS).EntryLock.Release();
#GP(0);
FI;
( * Compute size of MISC area *)
TMP_MISC_SIZE  compute_misc_region_size();
(* Compute the size required to save state of the enclave on async exit, see Section 41.7.2.2*)
TMP_XSIZE  compute_xsave_size(DS:TMP_SECS.ATTRIBUTES.XFRM) + GPR_SIZE + TMP_MISC_SIZE;
(* Ensure that the declared area is large enough to hold XSAVE and GPR stat *)
IF ( ( DS:TMP_SECS.SSAFRAMESIZE*4096 < TMP_XSIZE)
THEN #GP(0); FI;
IF ( (DS:TMP_SECS.ATTRIBUTES.MODE64BIT = 1) and (DS:TMP_SECS.BASEADDR is not canonical) )
THEN #GP(0); FI;
IF ( (DS:TMP_SECS.ATTRIBUTES.MODE64BIT = 0) and (DS:TMP_SECS.BASEADDR and 0FFFFFFFF00000000H) )
THEN #GP(0); FI;
IF ( (DS:TMP_SECS.ATTRIBUTES.MODE64BIT = 0) and (DS:TMP_SECS.SIZE ≥ 2 ^ (CPUID.(EAX=12H, ECX=0):.EDX[7:0]) ) )
THEN #GP(0); FI;
IF ( (DS:TMP_SECS.ATTRIBUTES.MODE64BIT = 1) and (DS:TMP_SECS.SIZE ≥ 2 ^ (CPUID.(EAX=12H, ECX=0):.EDX[15:8]) ) )
THEN #GP(0); FI;
(* Enclave size must be at least 8192 bytes and must be power of 2 in bytes*)
IF (DS:TMP_SECS.SIZE < 8192 or popcnt(DS:TMP_SECS.SIZE) > 1)
THEN #GP(0); FI;
(* Ensure base address of an enclave is aligned on size*)
IF ( ( DS:TMP_SECS.BASEADDR and (DS:TMP_SECS.SIZE-1) )
THEN #GP(0); FI;
* Ensure the SECS does not have any unsupported attributes*)
IF ( ( DS:TMP_SECS.ATTRIBUTES and (~CR_SGX_ATTRIBUTES_MASK) )
THEN #GP(0); FI;
IF ( ( DS:TMP_SECS reserved fields are not zero)
THEN #GP(0); FI;
Clear DS:TMP_SECS to Uninitialized;
DS:TMP_SECS.MRENCLAVE  SHA256INITIALIZE(DS:TMP_SECS.MRENCLAVE);
DS:TMP_SECS.ISVSVN  0;
DS:TMP_SECS.ISVPRODID  0;
(* Initialize hash updates etc*)
Initialize enclave’s MRENCLAVE update counter;

Vol. 3D 40-23

SGX INSTRUCTION REFERENCES

(* Add “ECREATE” string and SECS fields to MRENCLAVE *)
TMPUPDATEFIELD[63:0]  0045544145524345H; // “ECREATE”
TMPUPDATEFIELD[95:64]  DS:TMP_SECS.SSAFRAMESIZE;
TMPUPDATEFIELD[159:96]  DS:TMP_SECS.SIZE;
TMPUPDATEFIELD[511:160]  0;
DS:TMP_SECS.MRENCLAVE  SHA256UPDATE(DS:TMP_SECS.MRENCLAVE, TMPUPDATEFIELD)
INC enclave’s MRENCLAVE update counter;
(* Set EID *)
DS:TMP_SECS.EID  LockedXAdd(CR_NEXT_EID, 1);
(* Set the EPCM entry, first create SECS identifier and store the identifier in EPCM *)
EPCM(DS:TMP_SECS).PT  PT_SECS;
EPCM(DS:TMP_SECS).ENCLAVEADDRESS  0;
EPCM(DS:TMP_SECS).R  0;
EPCM(DS:TMP_SECS).W  0;
EPCM(DS:TMP_SECS).X  0;
(* Set EPCM entry fields *)
EPCM(DS:RCX).BLOCKED  0;
EPCM(DS:RCX).PENDING  0;
EPCM(DS:RCX).MODIFIED  0;
EPCM(DS:RCX).PR  0;
EPCM(DS:RCX).VALID  1;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If the reserved fields are not zero.
If PAGEINFO.SECS is not zero.
If PAGEINFO.LINADDR is not zero.
If the SECS destination is locked.
If SECS.SSAFRAMESIZE is insufficient.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the SECS destination is outside the EPC.

64-Bit Mode Exceptions
#GP(0)

If a memory address is non-canonical form.
If a memory operand is not properly aligned.
If the reserved fields are not zero.
If PAGEINFO.SECS is not zero.
If PAGEINFO.LINADDR is not zero.
If the SECS destination is locked.
If SECS.SSAFRAMESIZE is insufficient.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the SECS destination is outside the EPC.

40-24 Vol. 3D

SGX INSTRUCTION REFERENCES

EDBGRD—Read From a Debug Enclave
Opcode/
Instruction

Op/En

EAX = 04H
ENCLS[EDBGRD]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function reads a dword/quadword from a debug enclave.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EDBGRD (In)

Data read from a debug enclave (Out)

Address of source memory in the EPC (In)

Description
This leaf function copies a quadword/doubleword from an EPC page belonging to a debug enclave into the RBX
register. Eight bytes are read in 64-bit mode, four bytes are read in non-64-bit modes. The size of data read cannot
be overridden.
The effective address of the source location inside the EPC is provided in the register RCX.

EDBGRD Memory Parameter Semantics
EPCQW
Read access permitted by Enclave
The error codes are:

Table 40-14. EDBGRD Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EDBGRD successful

SGX_PAGE_NOT_DEBUGGABLE

The EPC page cannot be accessed because it is in the PENDING or MODIFIED state

The instruction faults if any of the following:

EDBGRD Faulting Conditions
RCX points into a page that is an SECS.

RCX does not resolve to a naturally aligned linear address.

RCX points to a page that does not belong to an
enclave that is in debug mode.

RCX points to a location inside a TCS that is beyond the architectural size of the
TCS (SGX_TCS_LIMIT).

An operand causing any segment violation.

May page fault.

CPL > 0.
This instruction ignores the EPCM RWX attributes on the enclave page. Consequently, violation of EPCM RWX attributes via EDBGRD does not result in a #GP.

Vol. 3D 40-25

SGX INSTRUCTION REFERENCES

Concurrency Restrictions

Table 40-15. Concurrency Restrictions of EDBGRD with Other Intel® SGX Operations 1 of 2
Operation

EDBGRD

EEXIT

Param

TCS SSA

Targ

Y

EADD

EBLOCK

SECS Targ SECS
N

Y
Y

SECS

Y

Y

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

Y

N

Y

Y

Y

N

N

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y
Y

Y

Y

Y

Y

Y

EPA

SECS VA
N
Y

Y

Table 40-16. Concurrency Restrictions of EDBGRD with Other Intel® SGX Operations 2 of 2
Operation

EDBGRD

EREMOVE

EREPORT

Param

Targ SECS Param SECS

Targ

N

SECS

Y

Y
Y

Y

Y

ETRACK

EWB

SECS

SRC

VA

N

N

Y

Y

Y

Y

EAUG

EMODPE

EMODPR

SECS Targ SECS Targ SECI Targ SEC
NFO
S
N
Y

Y

Y

Y

Y

Y

Y

Y

Y

EMODT
Targ SEC
S

EACCEPT
Targ SECI
NFO

N
Y

Y

EACCEPTCOPY

SECS Targ SR
C

Y
Y

Y

Y

Y

Y

Y

Y

Y

Y

Operation

Temp Variables in EDBGRD Operational Flow
Name

Type

Size (Bits)

Description

TMP_MODE64

Binary

1

((IA32_EFER.LMA = 1) && (CS.L = 1))

64

Physical address of SECS of the enclave to which source operand belongs

TMP_SECS

TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));
IF ( (TMP_MODE64 = 1) and (DS:RCX is not 8Byte Aligned) )
THEN #GP(0); FI;
IF ( (TMP_MODE64 = 0) and (DS:RCX is not 4Byte Aligned) )
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
(* make sure no other Intel SGX instruction is accessing EPCM *)
IF (Other EPCM modifying instructions executing)
THEN #GP(0); FI;
IF (EPCM(DS:RCX). VALID = 0)
THEN #PF(DS:RCX); FI;
(* make sure that DS:RCX (SOURCE) is pointing to a PT_REG or PT_TCS or PT_VA *)
IF ( (EPCM(DS:RCX).PT ≠ PT_REG) and (EPCM(DS:RCX).PT ≠ PT_TCS) and (EPCM(DS:RCX).PT ≠ PT_VA))
THEN #PF(DS:RCX); FI;
(* make sure that DS:RCX points to an accessible EPC page *)
IF ( (EPCM(DS:RCX).PENDING is not 0 or (EPCM(DS:RCX).MODIFIED is not 0) )
THEN
RFLAGS.ZF  1;

40-26 Vol. 3D

SECI
NFO

SGX INSTRUCTION REFERENCES

RAX  SGX_PAGE_NOT_DEBUGGABLE;
GOTO DONE;
FI;
(* If source is a TCS, then make sure that the offset into the page is not beyond the TCS size*)
IF ( ( EPCM(DS:RCX). PT = PT_TCS) and ((DS:RCX) & FFFH ≥ SGX_TCS_LIMIT) )
THEN #GP(0); FI;
(* make sure the enclave owning the PT_REG or PT_TCS page allow debug *)
IF ( (EPCM(DS:RCX).PT = PT_REG) or (EPCM(DS:RCX).PT = PT_TCS) )
THEN
TMP_SECS  GET_SECS_ADDRESS;
IF (TMP_SECS.ATTRIBUTES.DEBUG = 0)
THEN #GP(0); FI;
IF ( (TMP_MODE64 = 1) )
THEN RBX[63:0]  (DS:RCX)[63:0];
ELSE EBX[31:0]  (DS:RCX)[31:0];
FI;
ELSE
TMP_64BIT_VAL[63:0]  (DS:RCX)[63:0] & (~07H); // Read contents from VA slot
IF (TMP_MODE64 = 1)
THEN
IF (TMP_64BIT_VAL ≠ 0H)
THEN RBX[63:0]  0FFFFFFFFFFFFFFFFH;
ELSE RBX[63:0]  0H;
FI;
ELSE
IF (TMP_64BIT_VAL ≠ 0H)
THEN EBX[31:0]  0FFFFFFFFH;
ELSE EBX[31:0]  0H;
FI;
FI;
(* clear EAX and ZF to indicate successful completion *)
RAX  0;
RFLAGS.ZF  0;
DONE:
(* clear flags *)
RFLAGS.CF,PF,AF,OF,SF  0;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If the address in RCS violates DS limit or access rights.
If DS segment is unusable.
If RCX points to a memory location not 4Byte-aligned.
If the address in RCX points to a page belonging to a non-debug enclave.
If the address in RCX points to a page which is not PT_TCS, PT_REG or PT_VA.
If the address in RCX points to a location inside TCS that is beyond SGX_TCS_LIMIT.

#PF(error code)

If a page fault occurs in accessing memory operands.

Vol. 3D 40-27

SGX INSTRUCTION REFERENCES

If the address in RCX points to a non-EPC page.
If the address in RCX points to an invalid EPC page.
64-Bit Mode Exceptions
#GP(0)

If RCX is non-canonical form.
If RCX points to a memory location not 8Byte-aligned.
If the address in RCX points to a page belonging to a non-debug enclave.
If the address in RCX points to a page which is not PT_TCS, PT_REG or PT_VA.
If the address in RCX points to a location inside TCS that is beyond SGX_TCS_LIMIT.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the address in RCX points to a non-EPC page.
If the address in RCX points to an invalid EPC page.

40-28 Vol. 3D

SGX INSTRUCTION REFERENCES

EDBGWR—Write to a Debug Enclave
Opcode/
Instruction

Op/En

EAX = 05H
ENCLS[EDBGWR]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function writes a dword/quadword to a debug enclave.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EDBGWR (In)

Data to be written to a debug enclave (In)

Address of Target memory in the EPC (In)

Description
This leaf function copies the content in EBX/RBX to an EPC page belonging to a debug enclave. Eight bytes are
written in 64-bit mode, four bytes are written in non-64-bit modes. The size of data cannot be overridden.
The effective address of the source location inside the EPC is provided in the register RCX.

EDBGWR Memory Parameter Semantics
EPCQW
Write access permitted by Enclave
The instruction faults if any of the following:

EDBGWR Faulting Conditions
RCX points into a page that is an SECS.

RCX does not resolve to a naturally aligned linear address.

RCX points to a page that does not belong to an
enclave that is in debug mode.

RCX points to a location inside a TCS that is not the FLAGS word.

An operand causing any segment violation.

May page fault.

CPL > 0.
The error codes are:

Table 40-17. EDBGWR Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EDBGWR successful

SGX_PAGE_NOT_DEBUGGABLE

The EPC page cannot be accessed because it is in the PENDING or MODIFIED
state

This instruction ignores the EPCM RWX attributes on the enclave page. Consequently, violation of EPCM RWX attributes via EDBGRD does not result in a #GP.

Vol. 3D 40-29

SGX INSTRUCTION REFERENCES

Concurrency Restrictions

Table 40-18. Concurrency Restrictions of EDBGWR with Other Intel® SGX Operations 1 of 2
Operation

EDBGWR

EEXIT

Param

TCS SSA

Targ

Y

EADD

EBLOCK

SECS Targ SECS
N

Y
Y

SECS

Y

Y

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

Y

N

Y

Y

Y

N

N

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y
Y

Y

Y

Y

Y

Y

EPA

SECS VA
N
Y

Y

Table 40-19. Concurrency Restrictions of EDBGWR with Other Intel® SGX Operations 2 of 2
Operation

EDBGWR

EREMOVE

EREPORT

Param

Targ SECS Param SECS

Targ

N

SECS

Y

Y
Y

Y

Y

ETRACK

EWB

SECS

SRC

VA

N

N

Y

Y

Y

Y

EAUG

EMODPE

EMODPR

SECS Targ SECS Targ SECI Targ SEC
NFO
S
N
Y

Y

Y

Y

Y

Y

Y

Y

Y

EMODT
Targ SEC
S

EACCEPT
Targ SECI
NFO

N
Y

Y

EACCEPTCOPY

SECS Targ SR
C

Y
Y

Y

Y

Y

Y

Y

Y

Y

Y

Operation

Temp Variables in EDBGWR Operational Flow
Name

Type

Size (Bits)

Description

TMP_MODE64

Binary

1

((IA32_EFER.LMA = 1) && (CS.L = 1)).

64

Physical address of SECS of the enclave to which source operand belongs.

TMP_SECS

TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));
IF ( (TMP_MODE64 = 1) and (DS:RCX is not 8Byte Aligned) )
THEN #GP(0); FI;
IF ( (TMP_MODE64 = 0) and (DS:RCX is not 4Byte Aligned) )
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
(* make sure no other Intel SGX instruction is accessing EPCM *)
IF (Other EPCM modifying instructions executing)
THEN #GP(0); FI;
IF (EPCM(DS:RCX). VALID = 0)
THEN #PF(DS:RCX); FI;
(* make sure that DS:RCX (DST) is pointing to a PT_REG or PT_TCS *)
IF ( (EPCM(DS:RCX).PT ≠ PT_REG) and (EPCM(DS:RCX).PT ≠ PT_TCS) )
THEN #PF(DS:RCX); FI;
(* make sure that DS:RCX points to an accessible EPC page *)
IF ( (EPCM(DS:RCX).PENDING is not 0) or (EPCM(DS:RCS).MODIFIED is not 0) )
THEN
RFLAGS.ZF  1;
RAX  SGX_PAGE_NOT_DEBUGGABLE;
GOTO DONE;

40-30 Vol. 3D

SECI
NFO

SGX INSTRUCTION REFERENCES

FI;
(* If destination is a TCS, then make sure that the offset into the page can only point to the FLAGS field*)
IF ( ( EPCM(DS:RCX). PT = PT_TCS) and ((DS:RCX) & FF8H ≠ offset_of_FLAGS & 0FF8H) )
THEN #GP(0); FI;
(* Locate the SECS for the enclave to which the DS:RCX page belongs *)
TMP_SECS  GET_SECS_PHYS_ADDRESS(EPCM(DS:RCX).ENCLAVESECS);
(* make sure the enclave owning the PT_REG or PT_TCS page allow debug *)
IF (TMP_SECS.ATTRIBUTES.DEBUG = 0)
THEN #GP(0); FI;
IF ( (TMP_MODE64 = 1) )
THEN (DS:RCX)[63:0]  RBX[63:0];
ELSE (DS:RCX)[31:0]  EBX[31:0];
FI;
(* clear EAX and ZF to indicate successful completion *)
RAX  0;
RFLAGS.ZF  0;
DONE:
(* clear flags *)
RFLAGS.CF,PF,AF,OF,SF  0
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If the address in RCS violates DS limit or access rights.
If DS segment is unusable.
If RCX points to a memory location not 4Byte-aligned.
If the address in RCX points to a page belonging to a non-debug enclave.
If the address in RCX points to a page which is not PT_TCS or PT_REG.
If the address in RCX points to a location inside TCS that is not the FLAGS word.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the address in RCX points to a non-EPC page.
If the address in RCX points to an invalid EPC page.

64-Bit Mode Exceptions
#GP(0)

If RCX is non-canonical form.
If RCX points to a memory location not 8Byte-aligned.
If the address in RCX points to a page belonging to a non-debug enclave.
If the address in RCX points to a page which is not PT_TCS or PT_REG.
If the address in RCX points to a location inside TCS that is not the FLAGS word.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the address in RCX points to a non-EPC page.
If the address in RCX points to an invalid EPC page.

Vol. 3D 40-31

SGX INSTRUCTION REFERENCES

EEXTEND—Extend Uninitialized Enclave Measurement by 256 Bytes
Opcode/
Instruction

Op/En

EAX = 06H
ENCLS[EEXTEND]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function measures 256 bytes of an uninitialized enclave
page.

Instruction Operand Encoding
Op/En

EAX

EBX

RCX

IR

EEXTEND (In)

Effective address of the SECS of the
data chunk (In)

Effective address of a 256-byte chunk in the EPC (In)

Description
This leaf function updates the MRENCLAVE measurement register of an SECS with the measurement of an EXTEND
string compromising of “EEXTEND” || ENCLAVEOFFSET || PADDING || 256 bytes of the enclave page. This instruction can only be executed when current privilege level is 0 and the enclave is uninitialized.
RBX contains the effective address of the SECS of the region to be measured. The address must be the same as the
one used to add the page into the enclave.
RCX contains the effective address of the 256 byte region of an EPC page to be measured. The DS segment is used
to create linear addresses. Segment override is not supported.

EEXTEND Memory Parameter Semantics
EPC[RCX]
Read access by Enclave
The instruction faults if any of the following:

EEXTEND Faulting Conditions
RBX points to an address not 4KBytes aligned.

RBX does not resolve to an SECS.

RBX does not point to an SECS page.

RBX does not point to the SECS page of the data chunk.

RCX points to an address not 256B aligned.

RCX points to an unused page or a SECS.

RCX does not resolve in an EPC page.

If SECS is locked.

If the SECS is already initialized.

May page fault.

CPL > 0.
Concurrency Restrictions

Table 40-20. Concurrency Restrictions of EEXTEND with Other Intel® SGX Operations 1 of 2
Operation
Param
EEXTEND

EEXIT
TCS SSA

Targ

N

N

SECS

Y

Y

40-32 Vol. 3D

EADD
SECS Targ SECS
N
Y

Y

N

EBLOCK

ECRE
ATE

EDBGRD/
WR

Targ SECS

SECS

Targ SECS

Y

N

Y

Y

Y

Y

Y

EENTER/
ERESUME

EEXTEND

EGETKEY

TCS SSA SECS Targ SECS Param SECS
Y

Y

Y

Y

N

Y

N

Y

N

EINIT

ELDB/ELDU

SECS

Targ VA

N

N

N

Y

EPA

SECS VA
N

Y

Y

Y

SGX INSTRUCTION REFERENCES

Table 40-21. Concurrency Restrictions of EEXTEND with Other Intel® SGX Operations 2 of 2
Operation

EEXTEND

EREMOVE

EREPORT

Param

Targ SECS Param SECS

Targ

N

SECS

Y

ETRACK
SECS

EWB
SRC

EAUG

Y

N

Y

Y

EMODPR

VA

SECS Targ SECS Targ SECI Targ SEC
NFO
S

Y

Y

N
Y

EMODPE

N
Y

N
N

Y

Y

Y

EMODT
Targ SEC
S

EACCEPT

EACCEPTCOPY

Targ SECI
NFO

SECS Targ SR
C

SECI
NFO

Y

N

Y

N
N

Y

N

Y

Y

Y

Operation

Temp Variables in EEXTEND Operational Flow
Name

Type

TMP_SECS

Size (Bits)

Description

64

Physical address of SECS of the enclave to which source operand belongs.

TMP_ENCLAVEOFFS
ET

Enclave Offset

64

The page displacement from the enclave base address.

TMPUPDATEFIELD

SHA256 Buffer

512

Buffer used to hold data being added to TMP_SECS.MRENCLAVE.

TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));
IF (DS:RBX is not 4096 Byte Aligned)
THEN #GP(0); FI;
IF (DS:RBX does resolve to an EPC page)
THEN #PF(DS:RBX); FI;
IF (DS:RCX is not 256Byte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
(* make sure no other Intel SGX instruction is accessing EPCM *)
IF (Other instructions accessing EPCM)
THEN #GP(0); FI;
IF (EPCM(DS:RCX). VALID = 0)
THEN #PF(DS:RCX); FI;
(* make sure that DS:RCX (DST) is pointing to a PT_REG or PT_TCS *)
IF ( (EPCM(DS:RCX).PT ≠ PT_REG) and (EPCM(DS:RCX).PT ≠ PT_TCS) )
THEN #PF(DS:RCX); FI;
TMP_SECS  Get_SECS_ADDRESS();
IF (DS:RBX does not resolve to TMP_SECS)
THEN #GP(0); FI;
(* make sure no other instruction is accessing MRENCLAVE or ATTRIBUETS.INIT *)
IF ( (Other instruction accessing MRENCLAVE) or (Other instructions checking or updating the initialized state of the SECS))
THEN #GP(0); FI;
(* Calculate enclave offset *)

Vol. 3D 40-33

SGX INSTRUCTION REFERENCES

TMP_ENCLAVEOFFSET EPCM(DS:RCX).ENCLAVEADDRESS - TMP_SECS.BASEADDR;
TMP_ENCLAVEOFFSET TMP_ENCLAVEOFFSET + (DS:RCX & 0FFFH)
(* Add EEXTEND message and offset to MRENCLAVE *)
TMPUPDATEFIELD[63:0]  00444E4554584545H; // “EEXTEND”
TMPUPDATEFIELD[127:64]  TMP_ENCLAVEOFFSET;
TMPUPDATEFIELD[511:128]  0; // 48 bytes
TMP_SECS.MRENCLAVE  SHA256UPDATE(TMP_SECS.MRENCLAVE, TMPUPDATEFIELD)
INC enclave’s MRENCLAVE update counter;
(*Add 256 bytes to MRENCLAVE, 64 byte at a time *)
TMP_SECS.MRENCLAVE  SHA256UPDATE(TMP_SECS.MRENCLAVE, DS:RCX[511:0] );
TMP_SECS.MRENCLAVE  SHA256UPDATE(TMP_SECS.MRENCLAVE, DS:RCX[1023: 512] );
TMP_SECS.MRENCLAVE  SHA256UPDATE(TMP_SECS.MRENCLAVE, DS:RCX[1535: 1024] );
TMP_SECS.MRENCLAVE  SHA256UPDATE(TMP_SECS.MRENCLAVE, DS:RCX[2047: 1536] );
INC enclave’s MRENCLAVE update counter by 4;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If the address in RBX is outside the DS segment limit.
If RBX points to an SECS page which is not the SECS of the data chunk.
If the address in RCX is outside the DS segment limit.
If RCX points to a memory location not 256Byte-aligned.
If another instruction is accessing MRENCLAVE.
If another instruction is checking or updating the SECS.
If the enclave is already initialized.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the address in RBX points to a non-EPC page.
If the address in RCX points to a page which is not PT_TCS or PT_REG.
If the address in RCX points to a non-EPC page.
If the address in RCX points to an invalid EPC page.

64-Bit Mode Exceptions
#GP(0)

If RBX is non-canonical form.
If RBX points to an SECS page which is not the SECS of the data chunk.
If RCX is non-canonical form.
If RCX points to a memory location not 256 Byte-aligned.
If another instruction is accessing MRENCLAVE.
If another instruction is checking or updating the SECS.
If the enclave is already initialized.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the address in RBX points to a non-EPC page.
If the address in RCX points to a page which is not PT_TCS or PT_REG.
If the address in RCX points to a non-EPC page.
If the address in RCX points to an invalid EPC page.

40-34 Vol. 3D

SGX INSTRUCTION REFERENCES

EINIT—Initialize an Enclave for Execution
Opcode/
Instruction

Op/En

EAX = 02H
ENCLS[EINIT]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function initializes the enclave and makes it ready to
execute enclave code.

Instruction Operand Encoding
Op/En
IR

EAX
EINIT (In)

Error code (Out)

RBX

RCX

RDX

Address of SIGSTRUCT (In)

Address of SECS (In)

Address of EINITTOKEN (In)

Description
This leaf function is the final instruction executed in the enclave build process. After EINIT, the MRENCLAVE
measurement is complete, and the enclave is ready to start user code execution using the EENTER instruction.
EINIT takes the effective address of a SIGSTRUCT and EINITTOKEN. The SIGSTRUCT describes the enclave
including MRENCLAVE, ATTRIBUTES, ISVSVN, a 3072 bit RSA key, and a signature using the included key.
SIGSTRUCT must be populated with two values, q1 and q2. These are calculated using the formulas shown below:
q1 = floor(Signature2 / Modulus);
q2 = floor((Signature3 - q1 * Signature * Modulus) / Modulus);
The EINITTOKEN contains the MRENCLAVE, MRSIGNER, and ATTRIBUTES. These values must match the corresponding values in the SECS. If the EINITTOKEN was created with a debug launch key, the enclave must be in
debug mode as well.

Verify

Signature
Hashed

PubKey
ATTRIBUTES
ATTRIBUTEMASK
MRENCLAVE

Check

MRSIGNER

SIGSTRUCT
DS:RBX
DS:RDX

ATTRIBUTES
MRENCLAVE

If VALID=1, Check
MRSIGNER
If VALID=1,
Check

EINITTOKEN

EINIT

Copy

DS:RCX

SECS
Check

ATTRIBUTES
MRENCLAVE

ENCLAVE
EPC

Figure 40-1. Relationships Between SECS, SIGSTRUCT and EINITTOKEN

Vol. 3D 40-35

SGX INSTRUCTION REFERENCES

EINIT Memory Parameter Semantics
SIGSTRUCT

SECS

EINITTOKEN

Access by non-Enclave

Read/Write access by Enclave

Access by non-Enclave

EINIT performs the following steps, which can be seen in Figure 40-1:
Validates that SIGSTRUCT is signed using the enclosed public key.
Checks that the completed computation of SECS.MRENCLAVE equals SIGSTRUCT.HASHENCLAVE.
Checks that no reserved bits are set to 1 in SIGSTRUCT.ATTRIBUTES and no reserved bits in SIGSTRUCT.ATTRIBUTESMASK are set to 0.
Checks that no controlled ATTRIBUTES bits are set in SIGSTRUCT.ATTRIBUTES unless the SHA256 digest of
SIGSTRUCT.MODULUS equals IA32_SGX_LEPUBKEYHASH.
Checks that SIGSTRUCT.ATTRIBUTES equals the result of logically and-ing SIGSTRUCT.ATTRIBUTEMASK with
SECS.ATTRIBUTES.
If EINITTOKEN.VALID is 0, checks that the SHA256 digest of SIGSTRUCT.MODULUS equals
IA32_SGX_LEPUBKEYHASH.
If EINITTOKEN.VALID is 1, checks the validity of EINITTOKEN.
If EINITTOKEN.VALID is 1, checks that EINITTOKEN.MRENCLAVE equals SECS.MRENCLAVE.
If EINITTOKEN.VALID is 1 and EINITTOKEN.ATTRIBUTES.DEBUG is 1, SECS.ATTRIBUTES.DEBUG must be 1.
Commits SECS.MRENCLAVE, and sets SECS.MRSIGNER, SECS.ISVSVN, and SECS.ISVPRODID based on
SIGSTRUCT.
Update the SECS as Initialized.
Periodically, EINIT polls for certain asynchronous events. If such an event is detected, it completes with failure code
(ZF=1 and RAX = SGX_UNMASKED_EVENT), and RIP is incremented to point to the next instruction. These events
includes external interrupts, non-maskable interrupts, system-management interrupts, machine checks, INIT
signals, and the VMX-preemption timer. EINIT does not fail if the pending event is inhibited (e.g., external interrupts could be inhibited due to blocking by MOV SS blocking or by STI).
The following bits in RFLAGS are cleared: CF, PF, AF, OF, and SF. When the instruction completes with an error,
RFLAGS.ZF is set to 1, and the corresponding error bit is set in RAX. If no error occurs, RFLAGS.ZF is cleared and
RAX is set to 0.
The error codes are:

Table 40-22. EINIT Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EINIT successful

SGX_INVALID_SIG_STRUCT

If SIGSTRUCT contained an invalid value

SGX_INVALID_ATTRIBUTE

If SIGSTRUCT contains an unauthorized attributes mask

SGX_INVALID_MEASUREMENT

If SIGSTRUCT contains an incorrect measurement
If EINITTOKEN contains an incorrect measurement

SGX_INVALID_SIGNATURE

If signature does not validate with enclosed public key

SGX_INVALID_LICENSE

If license is invalid

SGX_INVALID_CPUSVN

If license SVN is unsupported

SGX_UNMASKED_EVENT

If an unmasked event is received before the instruction completes its
operation

40-36 Vol. 3D

SGX INSTRUCTION REFERENCES

Concurrency Restrictions

Table 40-23. Concurrency Restrictions of EINIT with Other Intel® SGX Operations 1 of 2
Operation
Param
EINIT

EEXIT
TCS SSA

SECS

EADD

EBLOCK

ECRE
ATE

EDBGRD/
WR

SECS Targ SECS

Targ SECS

SECS

Targ SECS

N

Y

N

N

N

N

Y

EENTER/
ERESUME

EEXTEND

EGETKEY

TCS SSA SECS Targ SECS Param SECS

Y

N

N

N

N

EINIT

ELDB/ELDU

EPA

SECS

Targ VA

SECS VA

N

N

Y

N

Table 40-24. Concurrency Restrictions of EINIT with Other Intel® SGX Operations 2 of 2
Operation

EINIT

EREMOVE

EREPORT

Param

Targ SECS Param SECS

SECS

N

N

Y

ETRACK

EWB

SECS

SRC

Y

N

VA

EAUG

EMODPE

SECS Targ SECS Targ SECI
NFO
Y

N

EMODPR

EMODT

EACCEPT

EACCEPTCOPY

Targ SECS Targ SECS Targ SECI SECS Targ SR
NFO
C

N

N

N

N

SECI
NFO

N

Operation

Temp Variables in EINIT Operational Flow
Name

Type

Size

Description

TMP_SIG

SIGSTRUCT

1808Bytes

Temp space for SIGSTRUCT.

TMP_TOKEN

EINITTOKEN

304Bytes

Temp space for EINITTOKEN.

TMP_MRENCLAVE

32Bytes

Temp space for calculating MRENCLAVE.

TMP_MRSIGNER

32Bytes

Temp space for calculating MRSIGNER.

CONTROLLED_ATTRIBU
TES

ATTRIBUTES

16Bytes

Constant mask of all ATTRIBUTE bits that can only be set for authorized
enclaves.

TMP_KEYDEPENDENCIE
S

Buffer

224Bytes

Temp space for key derivation.

16Bytes

Temp space for the derived EINITTOKEN Key.

352Bytes

The value of the top 352 bytes from the computation of Signature3
modulo MRSIGNER.

TMP_EINITTOKENKEY
TMP_SIG_PADDING

PKCS Padding
Buffer

(* make sure SIGSTRUCT and SECS are aligned *)
IF ( (DS:RBX is not 4KByte Aligned) or (DS:RCX is not 4KByte Aligned) )
THEN #GP(0); FI;
(* make sure the EINITTOKEN is aligned *)
IF (DS:RDX is not 512Byte Aligned)
THEN #GP(0); FI;
(* make sure the SECS is inside the EPC *)
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
TMP_SIG[14463:0]  DS:RBX[14463:0]; // 1808 bytes
TMP_TOKEN[2423:0]  DS:RDX[2423:0]; // 304 bytes
(* Verify SIGSTRUCT Header. *)
IF ( (TMP_SIG.HEADER ≠ 06000000E10000000000010000000000h) or
((TMP_SIG.VENDOR ≠ 0) and (TMP_SIG.VENDOR ≠ 00008086h) ) or
(TMP_SIG HEADER2 ≠ 01010000600000006000000001000000h) or
Vol. 3D 40-37

SGX INSTRUCTION REFERENCES

(TMP_SIG.EXPONENT ≠ 00000003h) or (Reserved space is not 0’s) )
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_SIG_STRUCT;
GOTO EXIT;
FI;
(* Open “Event Window” Check for Interrupts. Verify signature using embedded public key, q1, and q2. Save upper 352 bytes of the
PKCS1.5 encoded message into the TMP_SIG_PADDING*)
IF (interrupt was pending) THEN
RFLAGS.ZF  1;
RAX  SGX_UNMASKED_EVENT;
GOTO EXIT;
FI
IF (signature failed to verify) THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_SIGNATURE;
GOTO EXIT;
FI;
(*Close “Event Window” *)
(* make sure no other Intel SGX instruction is modifying SECS*)
IF (Other instructions modifying SECS)
THEN #GP(0); FI;
IF ( (EPCM(DS:RCX). VALID = 0) or (EPCM(DS:RCX).PT ≠ PT_SECS) )
THEN #PF(DS:RCX); FI;
(* make sure no other instruction is accessing MRENCLAVE or ATTRIBUETS.INIT *)
IF ( (Other instruction modifying MRENCLAVE) or (Other instructions modifying the SECS’s Initialized state))
THEN #GP(0); FI;
(* Calculate finalized version of MRENCLAVE *)
(* SHA256 algorithm requires one last update that compresses the length of the hashed message into the output SHA256 digest *)
TMP_ENCLAVE SHA256FINAL( (DS:RCX).MRENCLAVE, enclave’s MRENCLAVE update count *512);
(* Verify MRENCLAVE from SIGSTRUCT *)
IF (TMP_SIG.ENCLAVEHASH ≠ TMP_MRENCLAVE)
RFLAGS.ZF  1;
RAX  SGX_INVALID_MEASUREMENT;
GOTO EXIT;
FI;
TMP_MRSIGNER  SHA256(TMP_SIG.MODULUS)
(* if controlled ATTRIBUTES are set, SIGSTRUCT must be signed using an authorized key *)
CONTROLLED_ATTRIBUTES  0000000000000020H;
IF ( ( (DS:RCX.ATTRIBUTES & CONTROLLED_ATTRIBUTES) ≠ 0) and (TMP_MRSIGNER ≠ IA32_SGXLEPUBKEYHASH) )
RFLAGS.ZF  1;
RAX  SGX_INVALID_ATTRIBUTE;
GOTO EXIT;
FI;
(* Verify SIGSTRUCT.ATTRIBUTE requirements are met *)
40-38 Vol. 3D

SGX INSTRUCTION REFERENCES

IF ( (DS:RCX.ATTRIBUTES & TMP_SIG.ATTRIBUTEMASK) ≠ (TMP_SIG.ATTRIBUTE & TMP_SIG.ATTRIBUTEMASK) )
RFLAGS.ZF  1;
RAX  SGX_INVALID_ATTRIBUTE;
GOTO EXIT;
FI;
( *Verify SIGSTRUCT.MISCSELECT requirements are met *)
IF ( (DS:RCX.MISCSELECT & TMP_SIG.MISCMASK) ≠ (TMP_SIG.MISCSELECT & TMP_SIG.MISCMASK) )
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ATTRIBUTE;
GOTO EXIT
FI;
(* if EINITTOKEN.VALID[0] is 0, verify the enclave is signed by an authorized key *)
IF (TMP_TOKEN.VALID[0] = 0)
IF (TMP_MRSIGNER ≠ IA32_SGXLEPUBKEYHASH)
RFLAGS.ZF  1;
RAX  SGX_INVALID_EINITTOKEN;
GOTO EXIT;
FI;
GOTO COMMIT;
FI;
(* Debug Launch Enclave cannot launch Production Enclaves *)
IF ( (DS:RDX.MASKEDATTRIBUTESLE.DEBUG = 1) and (DS:RCX.ATTRIBUTES.DEBUG = 0) )
RFLAGS.ZF  1;
RAX  SGX_INVALID_EINITTOKEN;
GOTO EXIT;
FI;
(* Check reserve space in EINIT token includes reserved regions and upper bits in valid field *)
IF (TMP_TOKEN reserved space is not clear)
RFLAGS.ZF  1;
RAX  SGX_INVALID_EINITTOKEN;
GOTO EXIT;
FI;
(* EINIT token must be ≤ CR_CPUSVN *)
IF (TMP_TOKEN.CPUSVN > CR_CPUSVN)
RFLAGS.ZF  1;
RAX  SGX_INVALID_CPUSVN;
GOTO EXIT;
FI;
(* Derive Launch key used to calculate EINITTOKEN.MAC *)
HARDCODED_PKCS1_5_PADDING[15:0]  0100H;
HARDCODED_PKCS1_5_PADDING[2655:16]  SignExtend330Byte(-1); // 330 bytes of 0FFH
HARDCODED_PKCS1_5_PADDING[2815:2656]  2004000501020403650148866009060D30313000H;
TMP_KEYDEPENDENCIES.KEYNAME  EINITTOKEN_KEY;
TMP_KEYDEPENDENCIES.ISVPRODID  TMP_TOKEN.ISVPRODIDLE;
TMP_KEYDEPENDENCIES.ISVSVN  TMP_TOKEN.ISVSVN;
TMP_KEYDEPENDENCIES.SGXOWNEREPOCH  CR_SGXOWNEREPOCH;
Vol. 3D 40-39

SGX INSTRUCTION REFERENCES

TMP_KEYDEPENDENCIES.ATTRIBUTES  TMP_TOKEN.MASKEDATTRIBUTESLE;
TMP_KEYDEPENDENCIES.ATTRIBUTESMASK  0;
TMP_KEYDEPENDENCIES.MRENCLAVE  0;
TMP_KEYDEPENDENCIES.MRSIGNER  IA32_SGXLEPUBKEYHASH;
TMP_KEYDEPENDENCIES.KEYID  TMP_TOKEN.KEYID;
TMP_KEYDEPENDENCIES.SEAL_KEY_FUSES  CR_SEAL_FUSES;
TMP_KEYDEPENDENCIES.CPUSVN  TMP_TOKEN.CPUSVN;
TMP_KEYDEPENDENCIES.MISCSELECT  TMP_TOKEN.MASKEDMISCSELECTLE;
TMP_KEYDEPENDENCIES.MISCMASK  0;
TMP_KEYDEPENDENCIES.PADDING  HARDCODED_PKCS1_5_PADDING;
(* Calculate the derived key*)
TMP_EINITTOKENKEY  derivekey(TMP_KEYDEPENDENCIES);
(* Verify EINITTOKEN was generated using this CPU's Launch key and that it has not been modified since issuing by the Launch
Enclave. Only 192 bytes of EINITTOKEN are CMACed *)
IF (TMP_TOKEN.MAC ≠ CMAC(TMP_EINITTOKENKEY, TMP_TOKEN[1535:0] ) )
RFLAGS.ZF  1;
RAX  SGX_INVALID_EINITTOKEN;
GOTO EXIT;
FI;
(* Verify EINITTOKEN (RDX) is for this enclave *)
IF (TMP_TOKEN.MRENCLAVE ≠ TMP_MRENCLAVE) or (TMP_TOKEN.MRSIGNER ≠ TMP_MRSIGNER) )
RFLAGS.ZF  1;
RAX  SGX_INVALID_MEASUREMENT;
GOTO EXIT;
FI;
(* Verify ATTRIBUTES in EINITTOKEN are the same as the enclave’s *)
IF (TMP_TOKEN.ATTRIBUTES ≠ DS:RCX.ATTRIBUTES)
RFLAGS.ZF  1;
RAX  SGX_INVALID_EINIT_ATTRIBUTE;
GOTO EXIT;
FI;
COMMIT:
(* Commit changes to the SECS; Set ISVPRODID, ISVSVN, MRSIGNER, INIT ATTRIBUTE fields in SECS (RCX) *)
DS:RCX.MRENCLAVE  TMP_MRENCLAVE;
(* MRSIGNER stores a SHA256 in little endian implemented natively on x86 *)
DS:RCX.MRSIGNER  TMP_MRSIGNER;
DS:RCX.ISVPRODID  TMP_SIG.ISVPRODID;
DS:RCX.ISVSVN  TMP_SIG.ISVSVN;
DS:RCX.PADDING  TMP_SIG_PADDING;
(* Mark the SECS as initialized *)
Update DS:RCX to initialized;
(* Set RAX and ZF for success*)
RFLAGS.ZF  0;
RAX  0;
EXIT:
RFLAGS.CF,PF,AF,OF,SF  0;

40-40 Vol. 3D

SGX INSTRUCTION REFERENCES

Flags Affected
ZF is cleared if successful, otherwise ZF is set and RAX contains the error code. CF, PF, AF, OF, SF are cleared.
Protected Mode Exceptions
#GP(0)

If a memory operand is not properly aligned.
If another instruction is modifying the SECS.
If the enclave is already initialized.
If the SECS.MRENCLAVE is in use.

#PF(error code)

If a page fault occurs in accessing memory operands.
If RCX does not resolve in an EPC page.
If the memory address is not a valid, uninitialized SECS.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is not properly aligned.
If another instruction is modifying the SECS.
If the enclave is already initialized.
If the SECS.MRENCLAVE is in use.

#PF(error code)

If a page fault occurs in accessing memory operands.
If RCX does not resolve in an EPC page.
If the memory address is not a valid, uninitialized SECS.

Vol. 3D 40-41

SGX INSTRUCTION REFERENCES

ELDB/ELDU—Load an EPC page and Marked its State
Opcode/
Instruction

Op/En

CPUID
Feature
Flag
SGX1

Description

IR

64/32
bit Mode
Support
V/V

EAX = 07H
ENCLS[ELDB]
EAX = 08H
ENCLS[ELDU]

IR

V/V

SGX1

This leaf function loads, verifies an EPC page and marks the page
as unblocked.

This leaf function loads, verifies an EPC page and marks the page
as blocked.

Instruction Operand Encoding
Op/En

EAX
ELDB/ELDU
(In)

IR

Return error
code (Out)

RBX

RCX

RDX

Address of the PAGEINFO
(In)

Address of the EPC page
(In)

Address of the versionarray slot (In)

Description
This leaf function copies a page from regular main memory to the EPC. As part of the copying process, the page is
cryptographically authenticated and decrypted. This instruction can only be executed when current privilege level
is 0.
The ELDB leaf function sets the BLOCK bit in the EPCM entry for the destination page in the EPC after copying. The
ELDU leaf function clears the BLOCK bit in the EPCM entry for the destination page in the EPC after copying.
RBX contains the effective address of a PAGEINFO structure; RCX contains the effective address of the destination
EPC page; RDX holds the effective address of the version array slot that holds the version of the page.
The table below provides additional information on the memory parameter of ELDB/ELDU leaf functions.

EBLDB/ELDBU Memory Parameter Semantics
PAGEINFO

PAGEINFO.SRCPGE

PAGEINFO.PCMD

PAGEINFO.SECS

EPCPAGE

Version-Array Slot

Non-enclave
read access

Non-enclave read
access

Non-enclave read
access

Enclave read/write
access

Read/Write access
permitted by Enclave

Read/Write access permitted by Enclave

The error codes are:

Table 40-25. ELDB/ELDU Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

ELDB/ELDU successful

SGX_MAC_COMPARE_FAIL

If the MAC check fails

Concurrency Restrictions

Table 40-26. Concurrency Restrictions of ELDB/ELDU with Intel® SGX Instructions - 1of 2
Operation
Param
ELDB/E
LDU

EEXIT
Targ VA

EADD

SECS Targ SECS Targ SECS

Targ

N

VA

N

SECS

40-42 Vol. 3D

EBLOCK

Y

N

N
Y

Y

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

N

N

N

N

N

Y

N

Y

N
Y

Y

Y

Y

ELDB/ELDU

EPA

Targ VA

SECS VA

N

N

N

N

Y

N

N
N

Y

SGX INSTRUCTION REFERENCES

Table 40-27. Concurrency Restrictions of ELDB/ELDU with Intel® SGX Instructions - 2 of 2
Operation

ELDB/E
LDU

EREMOVE

ETRA
CK

EREPORT

Param

Targ SECS Param SECS SECS

Targ

N

VA

N

SECS

N

N
Y

Y

Y

EWB
SRC VA

EAUG

EMODPE

SECS Targ SECS

N

N

N

N

Y

N
Y

N

Targ

SECI
NFO

N

EMODPR
Targ

SECS

N

EMODT
Targ

SECS

EACCEPT
Targ SECI
NFO

EACCEPTCOPY

SECS Targ SRC

SECI
NFO

N
N

Y

Y

Y

Y

Operation

Temp Variables in ELDB/ELDU Operational Flow
Name

Type

Size (Bits)

TMP_SRCPGE

Memory page

4KBytes

TMP_SECS

Memory page

4KBytes

TMP_PCMD

PCMD

128 Bytes

TMP_HEADER

MACHEADER

128 Bytes

TMP_VER

UINT64

64

TMP_MAC

UINT128

128

TMP_PK

UINT128

128

SCRATCH_PCMD

PCMD

128 Bytes

Description

Page encryption/MAC key.

(* Check PAGEINFO and EPCPAGE alignment *)
IF ( (DS:RBX is not 32Byte Aligned) or (DS:RCX is not 4KByte Aligned) )
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
(* Check VASLOT alignment *)
IF (DS:RDX is not 8Byte aligned)
THEN #GP(0); FI;
IF (DS:RDX does not resolve within an EPC)
THEN #PF(DS:RDX); FI;
TMP_SRCPGE  DS:RBX.SRCPGE;
TMP_SECS  DS:RBX.SECS;
TMP_PCMD  DS:RBX.PCMD;
(* Check alignment of PAGEINFO (RBX)linked parameters. Note: PCMD pointer is overlaid on top of PAGEINFO.SECINFO field *)
IF ( (DS:TMP_PCMD is not 128Byte aligned) or (DS:TMP_SRCPGE is not 4KByte aligned) )
THEN #GP(0); FI;
(* Check concurrency of EPC and VASLOT by other Intel SGX instructions *)
IF ( (other instructions accessing EPC) or (Other instructions modifying VA slot) )
THEN #GP(0); FI;
(* Verify EPCM attributes of EPC page, VA, and SECS *)
Vol. 3D 40-43

SGX INSTRUCTION REFERENCES

IF (EPCM(DS:RCX).VALID = 1)
THEN #PF(DS:RCX); FI;
IF ( (EPCM(DS:RDX & ~0FFFH).VALID = 0) or (EPCM(DS:RDX & ~0FFFH).PT ≠ PT_VA) )
THEN #PF(DS:RDX); FI;
(* Copy PCMD into scratch buffer *)
SCRATCH_PCMD[1023: 0] DS:TMP_PCMD[1023:0];
(* Zero out TMP_HEADER*)
TMP_HEADER[sizeof(TMP_HEADER)-1: 0] 0;
TMP_HEADER.SECINFO  SCRATCH_PCMD.SECINFO;
TMP_HEADER.RSVD  SCRATCH_PCMD.RSVD;
TMP_HEADER.LINADDR  DS:RBX.LINADDR;
(* Verify various attributes of SECS parameter *)
IF ( (TMP_HEADER.SECINFO.FLAGS.PT = PT_REG) or (TMP_HEADER.SECINFO.FLAGS.PT = PT_TCS) or
(TMP_HEADER.SECINFO.FLAGS.PT = PT_TRIM) )
THEN
IF ( DS:TMP_SECS is not 4KByte aligned)
THEN #GP(0) FI;
IF (DS:TMP_SECS does not resolve within an EPC)
THEN #PF(DS:TMP_SECS) FI;
IF ( Other instructions modifying SECS)
THEN #GP(0) FI;
IF ( (EPCM(DS:TMP_SECS).VALID = 0) or (EPCM(DS:TMP_SECS).PT ≠ PT_SECS) )
THEN #PF(DS:TMP_SECS) FI;
ELSIF ( (TMP_HEADER.SECINFO.FLAGS.PT = PT_SECS) or (TMP_HEADER.SECINFO.FLAGS.PT = PT_VA) )
IF ( ( TMP_SECS ≠ 0) )
THEN #GP(0) FI;
ELSE
#GP(0)
FI;
IF ( (TMP_HEADER.SECINFO.FLAGS.PT = PT_REG) or (TMP_HEADER.SECINFO.FLAGS.PT = PT_TCS) or
(TMP_HEADER.SECINFO.FLAGS.PT = PT_TRIM) )
THEN
TMP_HEADER.EID  DS:TMP_SECS.EID;
ELSE
(* These pages do not have any parent, and hence no EID binding *)
TMP_HEADER.EID  0;
FI;
(* Copy 4KBytes SRCPGE to secure location *)
DS:RCX[32767: 0] DS:TMP_SRCPGE[32767: 0];
TMP_VER  DS:RDX[63:0];
(* Decrypt and MAC page. AES_GCM_DEC has 2 outputs, {plain text, MAC} *)
(* Parameters for AES_GCM_DEC {Key, Counter, ..} *)
{DS:RCX, TMP_MAC}  AES_GCM_DEC(CR_BASE_PK, TMP_VER << 32, TMP_HEADER, 128, DS:RCX, 4096);
IF ( (TMP_MAC ≠ DS:TMP_PCMD.MAC) )
THEN
40-44 Vol. 3D

SGX INSTRUCTION REFERENCES

RFLAGS.ZF  1;
RAX SGX_MAC_COMPARE_FAIL;
GOTO ERROR_EXIT;
FI;
(* Check version before committing *)
IF (DS:RDX ≠ 0)
THEN #GP(0);
ELSE
DS:RDX TMP_VER;
FI;
(* Commit EPCM changes *)
EPCM(DS:RCX).PT  TMP_HEADER.SECINFO.FLAGS.PT;
EPCM(DS:RCX).RWX  TMP_HEADER.SECINFO.FLAGS.RWX;
EPCM(DS:RCX).PENDING  TMP_HEADER.SECINFO.FLAGS.PENDING;
EPCM(DS:RCX).MODIFIED  TMP_HEADER.SECINFO.FLAGS.MODIFIED;
EPCM(DS:RCX).PR  TMP_HEADER.SECINFO.FLAGS.PR;
EPCM(DS:RCX).ENCLAVEADDRESS  TMP_HEADER.LINADDR;
IF ( (EAX = 07H) and (TMP_HEADER.SECINFO.FLAGS.PT is NOT PT_SECS or PT_VA))
THEN
EPCM(DS:RCX).BLOCKED  1;
ELSE
EPCM(DS:RCX).BLOCKED  0;
FI;
EPCM(DS:RCX). VALID  1;
RAX 0;
RFLAGS.ZF  0;
ERROR_EXIT:
RFLAGS.CF,PF,AF,OF,SF  0;
Flags Affected
Sets ZF if unsuccessful, otherwise cleared and RAX returns error code. Clears CF, PF, AF, OF, SF.
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If the instruction’s EPC resource is in use by others.
If the instruction fails to verify MAC.
If the version-array slot is in use.
If the parameters fail consistency checks.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand expected to be in EPC does not resolve to an EPC page.
If one of the EPC memory operands has incorrect page type.
If the destination EPC page is already valid.

Vol. 3D 40-45

SGX INSTRUCTION REFERENCES

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If the instruction’s EPC resource is in use by others.
If the instruction fails to verify MAC.
If the version-array slot is in use.
If the parameters fail consistency checks.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand expected to be in EPC does not resolve to an EPC page.
If one of the EPC memory operands has incorrect page type.
If the destination EPC page is already valid.

40-46 Vol. 3D

SGX INSTRUCTION REFERENCES

EMODPR—Restrict the Permissions of an EPC Page
Opcode/
Instruction

Op/En

EAX = 0EH
ENCLS[EMODPR]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX2

Description

This leaf function restricts the access rights associated with a
EPC page in an initialized enclave.

Instruction Operand Encoding
Op/En

EAX

IR

EMODPR (In)

Return Error Code (Out)

RBX

RCX

Address of a SECINFO (In)

Address of the destination EPC page (In)

Description
This leaf function restricts the access rights associated with an EPC page in an initialized enclave. THE RWX bits of
the SECINFO parameter are treated as a permissions mask; supplying a value that does not restrict the page
permissions will have no effect. This instruction can only be executed when current privilege level is 0.
RBX contains the effective address of a SECINFO structure while RCX contains the effective address of an EPC
page. The table below provides additional information on the memory parameter of the EMODPR leaf function.

EMODPR Memory Parameter Semantics
SECINFO

EPCPAGE

Read access permitted by Non Enclave

Read/Write access permitted by Enclave

The instruction faults if any of the following:

EMODPR Faulting Conditions
The operands are not properly aligned.

If unsupported security attributes are set.

The Enclave is not initialized.

SECS is locked by another thread.

The EPC page is locked by another thread.

RCX does not contain an effective address of an EPC page in the running enclave.

The EPC page is not valid.
The error codes are:

Table 40-28. EMODPR Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EMODPR successful

SGX_PAGE_NOT_MODIFIABLE

The EPC page cannot be modified because it is in the PENDING or MODIFIED
state

SGX_LOCKFAIL

Page is being written by EADD, EAUG, ECREATE, ELDU/B, EMODT, or EWB

Concurrency Restrictions

Table 40-29. Concurrency Restrictions of EMODPR with Other Intel® SGX Operations 1 of 2
Operation
Param
EMODPR

Targ
SECS

EEXIT
TCS SSA

SECS

Y
Y

ECRE
ATE

EDBGRD/
WR

EADD

EBLOCK

Targ SECS

Targ SECS

SECS

Targ SECS

N

Y

N

Y

Y

Y

Y

N

Y

Y

EENTER/
ERESUME

EGETKEY

TCS SSA SECS Targ SECS Param SECS
Y

Y

EEXTEND

Y

Y

N
Y

Y

EINIT
SECS

Y
N

Y

ELDB/ELDU
Targ VA

SECS VA

N
Y

N

Y

EP
A
N

Y

Y

Y

Vol. 3D 40-47

SGX INSTRUCTION REFERENCES

Table 40-30. Concurrency Restrictions of EMODPR with Other Intel® SGX Operations 2 of 2
Operation

EMODP
R

EREMOVE

EREPORT

Param

Targ SECS Param SECS

Targ

N

SECS

Y

Y

ETRACK
SECS

Y
Y

Y

EWB
SRC

EAUG

Y

EMODPR

VA

SECS Targ SECS Targ SECI Targ SEC
NFO
S

Y

Y

N
Y

EMODPE

N
Y

Y

C

Y

C

Y

Y

Y

Y

EMODT

EACCEPT

Targ SEC
S

Targ SECI
NFO

C

C

Y

Y

Y

Y

Y

EACCEPTCOPY

SECS Targ SR
C
Y

C

Y

Y

Y

Y

Y

Operation

Temp Variables in EMODPR Operational Flow
Name

Type

Size (bits)

Description

TMP_SECS

Effective Address

32/64

Physical address of SECS to which EPC operand belongs.

SCRATCH_SECINFO

SECINFO

512

Scratch storage for holding the contents of DS:RBX.

IF (DS:RBX is not 64Byte Aligned)
THEN #GP(0); FI;
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
SCRATCH_SECINFO  DS:RBX;
(* Check for mis-configured SECINFO flags*)
IF ( (SCRATCH_SECINFO reserved fields are not zero ) or
( (SCRATCH_SECINFO.FLAGS.R is 0 and SCRATCH_SECINFO.FLAGS.W is not 0) )
THEN #GP(0); FI;
(* Check concurrency with SGX1 or SGX2 instructions on the EPC page *)
IF (SGX1 or other SGX2 instructions accessing EPC page)
THEN #GP(0); FI;
IF (EPCM(DS:RCX).VALID is 0 )
THEN #PF(DS:RCX); FI;
(* Check the EPC page for concurrency *)
IF (EPC page in use by another SGX2 instruction)
THEN
RFLAGS.ZF  1;
RAX  SGX_LOCKFAIL;
GOTO DONE;
FI;
IF ( (EPCM(DS:RCX).PENDING is not 0 or (EPCM(DS:RCX).MODIFIED is not 0) )
THEN
RFLAGS.ZF  1;
RAX  SGX_PAGE_NOT_MODIFIABLE;
GOTO DONE;

40-48 Vol. 3D

SECI
NFO

SGX INSTRUCTION REFERENCES

FI;
IF (EPCM(DS:RCX).PT is not PT_REG)
THEN #PF(DS:RCX); FI;
TMP_SECS  GET_SECS_ADDRESS
IF (TMP_SECS.ATTRIBUTES.INIT = 0)
THEN #GP(0); FI;
(* Set the PR bit to indicate that permission restriction is in progress *)
EPCM(DS:RCX).PR  1;
(* Update EPCM permissions *)
EPCM(DS:RCX).R  EPCM(DS:RCX).R & SCRATCH_SECINFO.FLAGS.R;
EPCM(DS:RCX).W  EPCM(DS:RCX).W & SCRATCH_SECINFO.FLAGS.W;
EPCM(DS:RCX).X  EPCM(DS:RCX).X & SCRATCH_SECINFO.FLAGS.X;
RFLAGS.ZF  0;
RAX  0;
DONE:
RFLAGS.CF,PF,AF,OF,SF  0;

Flags Affected
Sets ZF if page is not modifiable or if other SGX2 instructions are executing concurrently, otherwise cleared. Clears
CF, PF, AF, OF, SF.
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

Vol. 3D 40-49

SGX INSTRUCTION REFERENCES

EMODT—Change the Type of an EPC Page
Opcode/
Instruction

Op/En

EAX = 0FH
ENCLS[EMODT]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX2

Description

This leaf function changes the type of an existing EPC page.

Instruction Operand Encoding
Op/En

EAX

IR

EMODT (In)

Return Error Code (Out)

RBX

RCX

Address of a SECINFO (In)

Address of the destination EPC page (In)

Description
This leaf function modifies the type of an EPC page. The security attributes are configured to prevent access to the
EPC page at its new type until a corresponding invocation of the EACCEPT leaf confirms the modification. This
instruction can only be executed when current privilege level is 0.
RBX contains the effective address of a SECINFO structure while RCX contains the effective address of an EPC page.
The table below provides additional information on the memory parameter of the EMODT leaf function.

EMODT Memory Parameter Semantics
SECINFO

EPCPAGE

Read access permitted by Non Enclave

Read/Write access permitted by Enclave

The instruction faults if any of the following:

EMODT Faulting Conditions
The operands are not properly aligned.

If unsupported security attributes are set.

The Enclave is not initialized.

SECS is locked by another thread.

The EPC page is locked by another thread.

RCX does not contain an effective address of an EPC page in the running enclave.

The EPC page is not valid.
The error codes are:

Table 40-31. EMODT Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EMODT successful

SGX_PAGE_NOT_MODIFIABLE

The EPC page cannot be modified because it is in the PENDING or MODIFIED state

SGX_LOCKFAIL

Page is being written by EADD, EAUG, ECREATE, ELDU/B, EMODPR, or EWB

Concurrency Restrictions

Table 40-32. Concurrency Restrictions of EMODT with Other Intel® SGX Operations 1 of 2
Operation

EMODT

EEXIT

Param

TCS SSA

Targ

Y

SECS

40-50 Vol. 3D

EADD
SECS

Y
Y

EBLOCK

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

Targ SECS

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

C

C

C

C

C

C

Y

N

C

C

Y

N

Y

Y

Y

Y

Y

N

Y

Y

Y

Y

C
Y

Y

Y
N

Y

Y

EP
A

SECS VA
C
Y

Y

SGX INSTRUCTION REFERENCES

Table 40-33. Concurrency Restrictions of EMODT with Other Intel® SGX Operations 2 of 2
Operation

EMODT

EREMOVE

EREPORT

Param

Targ SECS Param SECS

Targ

C

SECS

Y

ETRACK
SECS

Y
Y

Y

Y

Y

EWB
SRC

VA

C

C

Y

Y

EAUG

EMODPE

EMODPR

SECS Targ SECS Targ SECI Targ SEC
NFO
S
Y

C

C

C

Y

C

Y

Y

Y

Y

Y

EMODT
Targ SEC
S
C

Y

EACCEPT
Targ SECI
NFO

Y

C

Y

Y

Y

Y

EACCEPTCOPY

SECS Targ SR
C
Y

SECI
NFO

C

Y

Y

Y

Y

Y

Operation

Temp Variables in EMODT Operational Flow
Name

Type

Size (bits)

Description

TMP_SECS

Effective Address

32/64

Physical address of SECS to which EPC operand belongs.

SCRATCH_SECINFO

SECINFO

512

Scratch storage for holding the contents of DS:RBX.

IF (DS:RBX is not 64Byte Aligned)
THEN #GP(0); FI;
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
SCRATCH_SECINFO  DS:RBX;
(* Check for mis-configured SECINFO flags*)
IF ( (SCRATCH_SECINFO reserved fields are not zero ) or
!(SCRATCH_SECINFO.FLAGS.PT is PT_TCS or SCRATCH_SECINFO.FLAGS.PT is PT_TRIM) )
THEN #GP(0); FI;
(* Check concurrency with SGX1 instructions on the EPC page *)
IF (other SGX1 instructions accessing EPC page)
THEN THEN
RFLAGS  1;
RAX  SGX_LOCKFAIL;
GOTO DONE;
FI;
IF (EPCM(DS:RCX).VALID is 0)
THEN #PF(DS:RCX); FI;
(* Check the EPC page for concurrency *)
IF (EPC page in use by another SGX2 instruction)
THEN
RFLAGS  1;
RAX  SGX_LOCKFAIL;
GOTO DONE;
FI;
IF (!(EPCM(DS:RCX).PT is PT_REG or

Vol. 3D 40-51

SGX INSTRUCTION REFERENCES

(EPCM(DS:RCX).PT is PT_TCS and SCRATCH_SECINFO.FLAGS.PT is PT_TRIM)))
THEN #PF(DS:RCX); FI;
IF ( (EPCM(DS:RCX).PENDING is not 0 or (EPCM(DS:RCX).MODIFIED is not 0) )
THEN
RFLAGS  1;
RAX  SGX_PAGE_NOT_MODIFIABLE;
GOTO DONE;
FI;
TMP_SECS  GET_SECS_ADDRESS
IF (TMP_SECS.ATTRIBUTES.INIT = 0)
THEN #GP(0); FI;
(* Update EPCM fields *)
EPCM(DS:RCX).PR  0;
EPCM(DS:RCX).MODIFIED  1;
EPCM(DS:RCX).R  0;
EPCM(DS:RCX).W  0;
EPCM(DS:RCX).X  0;
EPCM(DS:RCX).PT  SCRATCH_SECINFO.FLAGS.PT;
RFLAGS.ZF  0;
RAX  0;
DONE:
RFLAGS.CF,PF,AF,OF,SF  0;
Flags Affected
Sets ZF if page is not modifiable or if other SGX2 instructions are executing concurrently, otherwise cleared. Clears
CF, PF, AF, OF, SF.
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

40-52 Vol. 3D

SGX INSTRUCTION REFERENCES

EPA—Add Version Array
Opcode/
Instruction

Op/En

EAX = 0AH
ENCLS[EPA]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function adds a Version Array to the EPC.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EPA (In)

PT_VA (In, Constant)

Effective address of the EPC page (In)

Description
This leaf function creates an empty version array in the EPC page whose logical address is given by DS:RCX, and

sets up EPCM attributes for that page. At the time of execution of this instruction, the register RBX must be set to
PT_VA.

The table below provides additional information on the memory parameter of EPA leaf function.

EPA Memory Parameter Semantics
EPCPAGE
Write access permitted by Enclave
Concurrency Restrictions

Table 40-34. Concurrency Restrictions of EPA with Other Intel® SGX Operations 1 of 2
Operation
Param
EPA

EEXIT
TCS SSA

EADD
SECS Targ SECS
N

VA

EBLOCK

N

ECRE
ATE

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

N

N

N

N

N

N

N

EPA

SECS VA

N

N

Table 40-35. Concurrency Restrictions of EPA with Other Intel® SGX Operations 2 of 2
Operation

EPA

EREMOVE

EREPORT

ETRACK

EWB

Param

Targ SECS Param SECS

SECS

SRC

VA

VA

N

N

N

N

EAUG

EMODPE

SECS Targ SECS Targ SECI
NFO
N

N

EMODPR

EMODT

EACCEPT

EACCEPTCOPY

Targ SECS Targ SECS Targ SECI SECS Targ SR
NFO
C
N

SECI
NFO

N

Operation
IF (RBX ≠ PT_VA or DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
(* Check concurrency with other Intel SGX instructions *)
IF (Other Intel SGX instructions accessing the page)
THEN #GP(0); FI;

Vol. 3D 40-53

SGX INSTRUCTION REFERENCES

(* Check EPC page must be empty *)
IF (EPCM(DS:RCX). VALID ≠ 0)
THEN #PF(DS:RCX); FI;
(* Clears EPC page *)
DS:RCX[32767:0]  0;
EPCM(DS:RCX).PT  PT_VA;
EPCM(DS:RCX).ENCLAVEADDRESS  0;
EPCM(DS:RCX).BLOCKED  0;
EPCM(DS:RCX).PENDING  0;
EPCM(DS:RCX).MODIFIED  0;
EPCM(DS:RCX).PR  0;
EPCM(DS:RCX).RWX  0;
EPCM(DS:RCX).VALID  1;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If another Intel SGX instruction is accessing the EPC page.
If RBX is not set to PT_VA.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If the EPC page is valid.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If another Intel SGX instruction is accessing the EPC page.
If RBX is not set to PT_VA.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If the EPC page is valid.

40-54 Vol. 3D

SGX INSTRUCTION REFERENCES

EREMOVE—Remove a page from the EPC
Opcode/
Instruction

Op/En

EAX = 03H
ENCLS[EREMOVE]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function removes a page from the EPC.

Instruction Operand Encoding
Op/En

EAX

RCX

IR

EREMOVE (In)

Effective address of the EPC page (In)

Description
This leaf function causes an EPC page to be un-associated with its SECS and be marked as unused. This instruction
leaf can only be executed when the current privilege level is 0.
The content of RCX is an effective address of an EPC page. The DS segment is used to create linear address.
Segment override is not supported.
The instruction fails if the operand is not properly aligned or does not refer to an EPC page or the page is in use by
another thread, or other threads are running in the enclave to which the page belongs. In addition the instruction
fails if the operand refers to an SECS with associations.

EREMOVE Memory Parameter Semantics
EPCPAGE
Write access permitted by Enclave
The instruction faults if any of the following:

EREMOVE Faulting Conditions
The memory operand is not properly aligned.

The memory operand does not resolve in an EPC page.

Refers to an invalid SECS.

Refers to an EPC page that is locked by another thread.

Another Intel SGX instruction is accessing the EPC page.

RCX does not contain an effective address of an EPC page.

the EPC page refers to an SECS with associations.
The error codes are:

Table 40-36. EREMOVE Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EREMOVE successful

SGX_CHILD_PRESENT

If the SECS still have enclave pages loaded into EPC

SGX_ENCLAVE_ACT

If there are still logical processors executing inside the enclave

Vol. 3D 40-55

SGX INSTRUCTION REFERENCES

Concurrency Restrictions

Table 40-37. Concurrency Restrictions of EREMOVE with Other Intel® SGX Operations 1 of 2
Operation

EREMOVE

EEXIT

Param

TCS SSA

Targ

C

C

SECS

EADD

EBLOCK

SECS Targ SECS

Targ SECS

ECRE
ATE
SECS

EDBGRD/
WR
Targ SECS

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

EPA

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

SECS VA

C

N

N

N

C

N

N

C

N

C

C

N

C

C

C

N

N

N

N

N

C

Y

Y

Y

Y

Y

Y

Y

Y

Y

C

Y

Y

Y

C

Y

Y

Y

Y

Y

Table 40-38. Concurrency Restrictions of EREMOVE with Other Intel® SGX Operations 2 of 2
Operation
Param
EREMOVE

EREMOVE

EREPORT

Targ SECS Param SECS

ETRACK
SECS

EWB
SRC

VA

EAUG

EMODPE

EMODPR

EMODT

EACCEPT

EACCEPTCOPY

SECS Targ SECS Targ SECI Targ SEC
NFO
S

Targ SEC
S

Targ SECI
NFO

SECS Targ SR
C

SECI
NFO

Targ

N

C

C

C

N

N

N

C

N

N

C

C

N

C

N

C

C

C

C

C

C

C

SECS

Y

Y

Y

C

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

C

C

C

Y

Y

Y

Operation

Temp Variables in EREMOVE Operational Flow
Name

Type

Size (Bits)

Description

TMP_SECS

Effective Address

32/64

Effective address of the SECS destination page.

IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve to an EPC page)
THEN #PF(DS:RCX); FI;
TMP_SECS  Get_SECS_ADDRESS();
(* Check the EPC page for concurrency *)
IF (EPC page being referenced by another Intel SGX instruction)
THEN #GP(0); FI;
(* if DS:RCX is already unused, nothing to do*)
IF ( (EPCM(DS:RCX).VALID = 0) or (EPCM(DS:RCX).PT = PT_TRIM AND EPCM(DS:RCX).MODIFIED = 0))
THEN GOTO DONE;
FI;
IF ( (EPCM(DS:RCX).PT = PT_VA) OR
((EPCM(DS:RCX).PT = PT_TRIM) AND (EPCM(DS:RCX).MODIFIED = 0)) )
THEN
EPCM(DS:RCX).VALID  0;
GOTO DONE;
FI;
IF (EPCM(DS:RCX).PT = PT_SECS)
THEN
IF (DS:RCX has an EPC page associated with it)
THEN

40-56 Vol. 3D

SGX INSTRUCTION REFERENCES

RFLAGS.ZF  1;
RAX SGX_CHILD_PRESENT;
GOTO ERROR_EXIT;
FI;
EPCM(DS:RCX).VALID  0;
GOTO DONE;
FI;
IF (Other threads active using SECS)
THEN
RFLAGS.ZF  1;
RAX SGX_ENCLAVE_ACT;
GOTO ERROR_EXIT;
FI;
IF ( (EPCM(DS:RCX).PT is PT_REG) or (EPCM(DS:RCX).PT is PT_TCS) or (EPCM(DS:RCX).PT is PT_TRIM) )
THEN
EPCM(DS:RCX).VALID  0;
GOTO DONE;
FI;
DONE:
RAX 0;
RFLAGS.ZF  0;
ERROR_EXIT:
RFLAGS.CF,PF,AF,OF,SF  0;
Flags Affected
Sets ZF if unsuccessful, otherwise cleared and RAX returns error code. Clears CF, PF, AF, OF, SF
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If another Intel SGX instruction is accessing the page.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the memory operand is not an EPC page.

64-Bit Mode Exceptions
#GP(0)

If the memory operand is non-canonical form.
If a memory operand is not properly aligned.
If another Intel SGX instruction is accessing the page.

#PF(error code)

If a page fault occurs in accessing memory operands.
If the memory operand is not an EPC page.

Vol. 3D 40-57

SGX INSTRUCTION REFERENCES

ETRACK—Activates EBLOCK Checks
Opcode/
Instruction

Op/En

EAX = 0CH
ENCLS[ETRACK]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function activates EBLOCK checks.

Instruction Operand Encoding
Op/En

EAX

IR

ETRACK (In)

RCX
Return error code (Out)

Pointer to the SECS of the EPC page (In)

Description
This leaf function provides the mechanism for hardware to track that software has completed the required TLB
address clears successfully. The instruction can only be executed when the current privilege level is 0.
The content of RCX is an effective address of an EPC page.
The table below provides additional information on the memory parameter of ETRACK leaf function.

ETRACK Memory Parameter Semantics
EPCPAGE
Read/Write access permitted by Enclave
The error codes are:

Table 40-39. ETRACK Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

ETRACK successful

SGX_PREV_TRK_INCMPL

All processors did not complete the previous shoot-down sequence

Concurrency Restrictions

Table 40-40. Concurrency Restrictions of ETRACK with Other Intel® SGX Operations 1 of 2
Operation
Param
ETRACK

EEXIT
TCS SSA

SECS

EADD

EBLOCK

SECS Targ SECS
Y

N

Targ SECS

Y

Y

ECRE
ATE

EDBGRD/
WR

SECS

Targ SECS

N

N

Y

EENTER/
ERESUME

EEXTEND

EGETKEY

TCS SSA SECS Targ SECS Param SECS
Y

Y

Y

EINIT

ELDB/ELDU

EPA

SECS

Targ VA

SECS VA

Y

N

Y

N

Table 40-41. Concurrency Restrictions of ETRACK with Other Intel® SGX Operations 2 of 2
Operation

ETRACK

EREMOVE

EREPORT

Param

Targ SECS Param SECS

SECS

N

Y

Y

ETRACK
SECS

SRC

N

N

Operation
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
40-58 Vol. 3D

EWB
VA

EAUG

EMODPE

SECS Targ SECS Targ SECI
NFO
Y

N

Y

EMODPR

EMODT

EACCEPT

EACCEPTCOPY

Targ SECS Targ SECS Targ SECI SECS Targ SR
NFO
C
Y

Y

Y

SECI
NFO

SGX INSTRUCTION REFERENCES

(* Check concurrency with other Intel SGX instructions *)
IF (Other Intel SGX instructions using tracking facility on this SECS)
THEN #GP(0); FI;
IF (EPCM(DS:RCX). VALID = 0)
THEN #PF(DS:RCX); FI;
IF (EPCM(DS:RCX).PT ≠ PT_SECS)
THEN #PF(DS:RCX); FI;
(* All processors must have completed the previous tracking cycle*)
IF ( (DS:RCX).TRACKING ≠ 0) )
THEN
RFLAGS.ZF  1;
RAX SGX_PREV_TRK_INCMPL;
GOTO DONE;
ELSE
RAX 0;
RFLAGS.ZF  0;
FI;
DONE:
RFLAGS.CF,PF,AF,OF,SF  0;
Flags Affected
Sets ZF if SECS is in use or invalid, otherwise cleared. Clears CF, PF, AF, OF, SF.
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If another thread is concurrently using the tracking facility on this SECS.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If the specified EPC resource is in use.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.

Table 40-42. ETRACK Return Value in RAX
Error Code (see Table 40-3)
No Error
SGX_PREV_TRK_INCMPL

Value
0

Description
ETRACK successful
All processors did not complete the previous shoot-down sequence

Vol. 3D 40-59

SGX INSTRUCTION REFERENCES

EWB—Invalidate an EPC Page and Write out to Main Memory
Opcode/
Instruction

Op/En

EAX = 0BH
ENCLS[EWB]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function invalidates an EPC page and writes it out to
main memory.

Instruction Operand Encoding
Op/En
IR

EAX
EWB (In)

Error code (Out)

RBX

RCX

RDX

Address of an PAGEINFO (In)

Address of the EPC page (In)

Address of a VA slot (In)

Description
This leaf function copies a page from the EPC to regular main memory. As part of the copying process, the page is

cryptographically protected. This instruction can only be executed when current privilege level is 0.

The table below provides additional information on the memory parameter of EPA leaf function.

EWB Memory Parameter Semantics
PAGEINFO

PAGEINFO.SRCPGE

PAGEINFO.PCMD

EPCPAGE

VASLOT

Non-EPC R/W access

Non-EPC R/W access

Non-EPC R/W access

EPC R/W access

EPC R/W access

The error codes are:

Table 40-43. EWB Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EWB successful

SGX_PAGE_NOT_BLOCKED

If page is not marked as blocked

SGX_NOT_TRACKED

If EWB is racing with ETRACK instruction

SGX_VA_SLOT_OCCUPIED

Version array slot contained valid entry

SGX_CHILD_PRESENT

Child page present while attempting to page out enclave

Concurrency Restrictions

Table 40-44. Concurrency Restrictions of EWB with Intel® SGX Instructions - 1of 2
Operation

EWB

EEXIT

EADD

ECRE
ATE

EBLOCK

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

EPA

Param

Targ VA

SECS Targ SECS Targ SECS

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

Src

C

C

N

N

N

N

N

N

N

N

Y

N

Y

N

Y

Y

Y

Y

C

N

N

N

C

N

VA
Y

SECS

Y

Y

Y

Y

C
Y

C

Y

C

Y

N

Y

C

Y

C

Y

C

Y

Y

Y

SECS VA

Y

Y

Table 40-45. Concurrency Restrictions of EWB with Intel® SGX Instructions - 2 of 2
Operation
Param

40-60 Vol. 3D

EREMOVE

EREPORT

ETRA
CK

Targ SECS Param SECS SECS

EWB
SRC VA

EAUG
SECS Targ SECS

EMODPE
Targ

SECI
NFO

EMODPR
Targ

SECS

EMODT
Targ

SECS

EACCEPT
Targ SECI
NFO

EACCEPTCOPY

SECS Targ SRC

SECI
NFO

SGX INSTRUCTION REFERENCES

Table 40-45. Concurrency Restrictions of EWB with Intel® SGX Instructions - 2 of 2
Operation
EWB

EREMOVE

Src

N

VA

N

SECS

Y

C
Y

EREPORT
C
Y

C
Y

ETRA
CK
N
Y

EWB
N

N

N

Y

Y

Y

EAUG
C

N

EMODPE

N

C

C

EMODPR
N

C

N
Y

Y

EMODT
N

EACCEPT

EACCEPTCOPY

C

C

C

C

C

C

C

Y

Y

Y

Y

Y

Y

Y

N
Y

Y

Y

Y

Y

Y

Operation

Temp Variables in EWB Operational Flow
Name

Type

Size (Bytes)

TMP_SRCPGE

Memory page

4096

TMP_PCMD

PCMD

128

TMP_SECS

SECS

4096

TMP_BPEPOCH

UINT64

8

TMP_BPREFCOUNT

UINT64

8

TMP_HEADER

MAC Header

128

TMP_PCMD_ENCLAVEID

UINT64

8

TMP_VER

UINT64

8

TMP_PK

UINT128

16

Description

IF ( (DS:RBX is not 32Byte Aligned) or (DS:RCX is not 4KByte Aligned) )
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
IF (DS:RDX is not 8Byte Aligned)
THEN #GP(0); FI;
IF (DS:RDX does not resolve within an EPC)
THEN #PF(DS:RDX); FI;
(* EPCPAGE and VASLOT should not resolve to the same EPC page*)
IF (DS:RCX and DS:RDX resolve to the same EPC page)
THEN #GP(0); FI;
TMP_SRCPGE  DS:RBX.SRCPGE;
(* Note PAGEINFO.PCMD is overlaid on top of PAGEINFO.SECINFO *)
TMP_PCMD  DS:RBX.PCMD;
If (DS:RBX.LINADDR ≠ 0) OR (DS:RBX.SECS ≠ 0)
THEN #GP(0); FI;
IF ( (DS:TMP_PCMD is not 128Byte Aligned) or (DSTMP_SRCPGE is not 4KByte Aligned) )
THEN #GP(0); FI;
(* Check for concurrent Intel SGX instruction access to the page *)
IF (Other Intel SGX instruction is accessing page)

Vol. 3D 40-61

SGX INSTRUCTION REFERENCES

THEN #GP(0); FI;
(*Check if the VA Page is being removed or changed*)
IF (VA Page is being modified)
THEN #GP(0); FI;
(* Verify that EPCPAGE and VASLOT page are valid EPC pages and DS:RDX is VA *)
IF (EPCM(DS:RCX).VALID = 0)
THEN #PF(DS:RCX); FI;
IF ( (EPCM(DS:RDX & ~0FFFH).VALID = 0) or (EPCM(DS:RDX & ~FFFH).PT is not PT_VA) )
THEN #PF(DS:RDX); FI;
(* Perform page-type-specific exception checks *)
IF ( (EPCM(DS:RCX).PT is PT_REG) or (EPCM(DS:RCX).PT is PT_TCS) or (EPCM(DS:RCX).PT is PT_TRIM ) )
THEN
TMP_SECS = Obtain SECS through EPCM(DS:RCX)
(* Check that EBLOCK has occurred correctly *)
IF (EBLOCK is not correct)
THEN #GP(0); FI;
FI;
RFLAGS.ZF,CF,PF,AF,OF,SF  0;
RAX  0;
(* Perform page-type-specific checks *)
IF ( (EPCM(DS:RCX).PT is PT_REG) or (EPCM(DS:RCX).PT is PT_TCS) or (EPCM(DS:RCX).PT is PT_TRIM ))
THEN
(* check to see if the page is evictable *)
IF (EPCM(DS:RCX).BLOCKED = 0)
THEN
RAX  SGX_PAGE NOT_BLOCKED;
RFLAGS.ZF  1;
GOTO ERROR_EXIT;
FI;
(* Check if tracking done correctly *)
IF (Tracking not correct)
THEN
RAX  SGX_NOT_TRACKED;
RFLAGS.ZF  1;
GOTO ERROR_EXIT;
FI;
(* Obtain EID to establish cryptographic binding between the paged-out page and the enclave *)
TMP_HEADER.EID  TMP_SECS.EID;
(* Obtain EID as an enclave handle for software *)
TMP_PCMD_ENCLAVEID  TMP_SECS.EID;
ELSE IF (EPCM(DS:RCX).PT is PT_SECS)
(*check that there are no child pages inside the enclave *)
IF (DS:RCX has an EPC page associated with it)
THEN
RAX  SGX_CHILD_PRESENT;
RFLAGS.ZF  1;
40-62 Vol. 3D

SGX INSTRUCTION REFERENCES

GOTO ERROR_EXIT;
FI:
TMP_HEADER.EID  0;
(* Obtain EID as an enclave handle for software *)
TMP_PCMD_ENCLAVEID  (DS:RCX).EID;
ELSE IF (EPCM(DS:RCX).PT is PT_VA)
TMP_HEADER.EID  0; // Zero is not a special value
(* No enclave handle for VA pages*)
TMP_PCMD_ENCLAVEID  0;
FI;
(* Zero out TMP_HEADER*)
TMP_HEADER[ sizeof(TMP_HEADER)-1 : 0]  0;
TMP_HEADER.LINADDR  EPCM(DS:RCX).ENCLAVEADDRESS;
TMP_HEADER.SECINFO.FLAGS.PT  EPCM(DS:RCX).PT;
TMP_HEADER.SECINFO.FLAGS.RWX  EPCM(DS:RCX).RWX;
TMP_HEADER.SECINFO.FLAGS.PENDING  EPCM(DS:RCX).PENDING;
TMP_HEADER.SECINFO.FLAGS.MODIFIED  EPCM(DS:RCX).MODIFIED;
TMP_HEADER.SECINFO.FLAGS.PR  EPCM(DS:RCX).PR;
(* Encrypt the page, DS:RCX could be encrypted in place. AES-GCM produces 2 values, {ciphertext, MAC}. *)
(* AES-GCM input parameters: key, GCM Counter, MAC_HDR, MAC_HDR_SIZE, SRC, SRC_SIZE)*)
{DS:TMP_SRCPGE, DS:TMP_PCMD.MAC}  AES_GCM_ENC(CR_BASE_PK), (TMP_VER << 32),
TMP_HEADER, 128, DS:RCX, 4096);
(* Write the output *)
Zero out DS:TMP_PCMD.SECINFO
DS:TMP_PCMD.SECINFO.FLAGS.PT  EPCM(DS:RCX).PT;
DS:TMP_PCMD.SECINFO.FLAGS.RWX  EPCM(DS:RCX).RWX;
DS:TMP_PCMD.SECINFO.FLAGS.PENDING  EPCM(DS:RCX).PENDING;
DS:TMP_PCMD.SECINFO.FLAGS.MODIFIED  EPCM(DS:RCX).MODIFIED;
DS:TMP_PCMD.SECINFO.FLAGS.PR  EPCM(DS:RCX).PR;
DS:TMP_PCMD.RESERVED  0;
DS:TMP_PCMD.ENCLAVEID  TMP_PCMD_ENCLAVEID;
DS:RBX.LINADDR  EPCM(DS:RCX).ENCLAVEADDRESS;
(*Check if version array slot was empty *)
IF ([DS.RDX])
THEN
RAX  SGX_VA_SLOT_OCCUPIED
RFLAGS.CF  1;
FI;
(* Write version to Version Array slot *)
[DS.RDX]  TMP_VER;
(* Free up EPCM Entry *)
EPCM.(DS:RCX).VALID  0;
ERROR_EXIT:
Flags Affected
ZF is set if page is not blocked, not tracked, or a child is present. Otherwise cleared.
CF is set if VA slot is previously occupied, Otherwise cleared.
Vol. 3D 40-63

SGX INSTRUCTION REFERENCES

Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If the EPC page and VASLOT resolve to the same EPC page.
If another Intel SGX instruction is concurrently accessing either the target EPC, VA, or SECS
pages.
If the tracking resource is in use.
If the EPC page or the version array page is invalid.
If the parameters fail consistency checks.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If one of the EPC memory operands has incorrect page type.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If the EPC page and VASLOT resolve to the same EPC page.
If another Intel SGX instruction is concurrently accessing either the target EPC, VA, or SECS
pages.
If the tracking resource is in use.
If the EPC page or the version array page in invalid.
If the parameters fail consistency checks.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If one of the EPC memory operands has incorrect page type.

40-64 Vol. 3D

SGX INSTRUCTION REFERENCES

40.4

INTEL® SGX USER LEAF FUNCTION REFERENCE

40.4.1

Instruction Column in the Instruction Summary Table

Leaf functions available with the ENCLU instruction mnemonic are covered in this section. In general, each instruction leaf requires EAX to specify the leaf function index and/or additional registers specifying leaf-specific input
parameters. An instruction operand encoding table provides details of the implicitly-encoded register usage and
associated input/output semantics.
In many cases, an input parameter specifies an effective address associated with a memory object inside or
outside the EPC, the memory addressing semantics of these memory objects are also summarized in a separate
table.

Vol. 3D 40-65

SGX INSTRUCTION REFERENCES

EACCEPT—Accept Changes to an EPC Page
Opcode/
Instruction

Op/En

EAX = 05H
ENCLU[EACCEPT]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX2

Description

This leaf function accepts changes made by system software to
an EPC page in the running enclave.

Instruction Operand Encoding
Op/En
IR

EAX
EACCEPT (In)

Return Error Code (Out)

RBX

RCX

Address of a SECINFO (In)

Address of the destination EPC page (In)

Description
This leaf function accepts changes to a page in the running enclave by verifying that the security attributes specified in the SECINFO match the security attributes of the page in the EPCM. This instruction leaf can only be
executed when inside the enclave.
RBX contains the effective address of a SECINFO structure while RCX contains the effective address of an EPC page.
The table below provides additional information on the memory parameter of the EACCEPT leaf function.

EACCEPT Memory Parameter Semantics
SECINFO

EPCPAGE (Destination)

Read access permitted by Non Enclave

Read access permitted by Enclave

The instruction faults if any of the following:

EACCEPT Faulting Conditions
The operands are not properly aligned.

If security attributes of the SECINFO page make the page inaccessible.

The EPC page is locked by another thread.

RBX does not contain an effective address in an EPC page in the running enclave.

The EPC page is not valid.

RCX does not contain an effective address of an EPC page in the running enclave.

SECINFO contains an invalid request.

Page type is PT_REG and MODIFIED bit is 0.
Page type is PT_TCS or PT_TRIM and PENDING bit is 0 and MODIFIED bit is 1.

The error codes are:

Table 40-46. EACCEPT Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EACCEPT successful

SGX_PAGE_ATTRIBUTES_MISMATCH

The attributes of the target EPC page do not match the expected values

SGX_NOT_TRACKED

The OS did not complete an ETRACK on the target page

Concurrency Restrictions

Table 40-47. Concurrency Restrictions of EACCEPT with Intel® SGX Instructions - 1of 2
Operation
Param

40-66 Vol. 3D

EEXIT
Targ VA

EADD

EBLOCK

SECS Targ SECS Targ SECS

ECRE
ATE
SECS

EDBGRD/
WR
Targ SECS

EENTER/
ERESUME

EEXTEND

EGETKEY

TCS SSA SECS Targ SECS Param SECS

EINIT
SECS

ELDB/ELDU
Targ VA

EPA

SECS VA

SGX INSTRUCTION REFERENCES

Table 40-47. Concurrency Restrictions of EACCEPT with Intel® SGX Instructions - 1of 2
Operation

EEXIT

Targ
EACCE
PT

C

SECINFO

EADD

ECRE
ATE

EBLOCK

EDBGRD/
WR

Y

Y

U

Y

SECS

Y

Y

Y

Y

Y

Y

EENTER/
ERESUME
C

EEXTEND

Y

Y

Y

Y

EINIT

ELDB/ELDU

EPA

Y

U

Y

EGETKEY

U
Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Table 40-48. Concurrency Restrictions of EACCEPT with Intel® SGX Instructions - 2 of 2
Operation
Param

EACCE
PT

EREMOVE

ETRA
CK

EREPORT

Targ SECS Param SECS SECS

EWB
SRC VA

EAUG
SECS Targ SECS

EMODPE
Targ

SECI
NFO

Targ
N

Targ

Y

N

Y

SECIN
FO

U

Y

Y

Y

Y

SECS

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

EMODPR

Y

SECS

EMODT
Targ

SECS

N

Y

Y

Y

EACCEPT
Targ SECI
NFO
N

Y

Y

Y

Y

Y

EACCEPTCOPY

SECS Targ SRC
N

Y

Y

SECI
NFO

Y

C

U

Y

Y

Y

Operation

Temp Variables in EACCEPT Operational Flow
Name

Type

Size (bits)

Description

TMP_SECS

Effective Address

32/64

Physical address of SECS to which EPC operands belongs.

SCRATCH_SECINFO

SECINFO

512

Scratch storage for holding the contents of DS:RBX.

IF (DS:RBX is not 64Byte Aligned)
THEN #GP(0); FI;
IF (DS:RBX is not within CR_ELRANGE)
THEN #GP(0); FI;
IF (DS:RBX does not resolve within an EPC)
THEN #PF(DS:RBX); FI;
IF ( (EPCM(DS:RBX &~FFFH).VALID = 0) or (EPCM(DS:RBX &~FFFH).R = 0) or (EPCM(DS:RBX &~FFFH).PENDING ≠ 0) or
(EPCM(DS:RBX &~FFFH).MODIFIED ≠ 0) or (EPCM(DS:RBX &~FFFH).BLOCKED ≠ 0) or
(EPCM(DS:RBX &~FFFH).PT ≠ PT_REG) or (EPCM(DS:RBX &~FFFH).ENCLAVESECS ≠ CR_ACTIVE_SECS) or
(EPCM(DS:RBX &~FFFH).ENCLAVEADDRESS ≠ (DS:RBX & FFFH)) )
THEN #PF(DS:RBX); FI;
(* Copy 64 bytes of contents *)
SCRATCH_SECINFO  DS:RBX;
(* Check for mis-configured SECINFO flags*)
IF (SCRATCH_SECINFO reserved fields are not zero ) )
THEN #GP(0); FI;
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RCX is not within CR_ELRANGE)
THEN #GP(0); FI;
Vol. 3D 40-67

SGX INSTRUCTION REFERENCES

IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
(* Check that the combination of requested PT, PENDING and MODIFIED is legal *)
IF (NOT (((SCRATCH_SECINFO.FLAGS.PT is PT_REG) and
((SCRATCH_SECINFO.FLAGS.PR is 1) or
(SCRATCH_SECINFO.FLAGS.PENDING is 1)) and
(SCRATCH_SECINFO.FLAGS.MODIFIED is 0)) or
((SCRATCH_SECINFO.FLAGS.PT is PT_TCS or PT_TRIM) and
(SCRATCH_SECINFO.FLAGS.PR is 0) and
(SCRATCH_SECINFO.FLAGS.PENDING is 0) and
(SCRATCH_SECINFO.FLAGS.MODIFIED is 1) )))
THEN #GP(0); FI
(* Check security attributes of the destination EPC page *)
If ( (EPCM(DS:RCX).VALID is 0) or (EPCM(DS:RCX).BLOCKED is not 0) or
((EPCM(DS:RCX).PT is not PT_REG) and (EPCM(DS:RCX).PT is not PT_TCS) and (EPCM(DS:RCX).PT is not PT_TRIM)) or
(EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS))
THEN #PF((DS:RCX); FI;
(* Check the destination EPC page for concurrency *)
IF ( EPC page in use )
THEN #GP(0); FI;
(* Re-Check security attributes of the destination EPC page *)
IF ( (EPCM(DS:RCX).VALID is 0) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) )
THEN #PF(DS:RCX); FI;
(* Verify that accept request matches current EPC page settings *)
IF ( (EPCM(DS:RCX).ENCLAVEADDRESS ≠ DS:RCX) or (EPCM(DS:RCX).PENDING ≠ SCRATCH_SECINFO.FLAGS.PENDING) or
(EPCM(DS:RCX).MODIFIED ≠ SCRATCH_SECINFO.FLAGS.MODIFIED) or (EPCM(DS:RCX).R ≠ SCRATCH_SECINFO.FLAGS.R) or
(EPCM(DS:RCX).W ≠ SCRATCH_SECINFO.FLAGS.W) or (EPCM(DS:RCX).X ≠ SCRATCH_SECINFO.FLAGS.X) or
(EPCM(DS:RCX).PT ≠ SCRATCH_SECINFO.FLAGS.PT) )
THEN
RFLAGS.ZF  1;
RAX  SGX_PAGE_ATTRIBUTES_MISMATCH;
GOTO DONE;
FI;
(* Check that all required threads have left enclave *)
IF (Tracking not correct)
THEN
RFLAGS.ZF  1;
RAX  SGX_NOT_TRACKED;
GOTO DONE;
FI;
(* Get pointer to the SECS to which the EPC page belongs *)
TMP_SECS = << Obtain physical address of SECS through EPCM(DS:RCX)>>
(* For TCS pages, perform additional checks *)
IF (SCRATCH_SECINFO.FLAGS.PT = PT_TCS)
THEN
IF (DS:RCX.RESERVED ≠ 0) #GP(0); FI;
FI;
40-68 Vol. 3D

SGX INSTRUCTION REFERENCES

(* Check that TCS.FLAGS.DBGOPTIN, TCS stack, and TCS status are correctly initialized *)
IF ( ((DS:RCX).FLAGS.DBGOPTIN is not 0) or ((DS:RCX).CSSA ≥ (DS:RCX).NSSA) or ((DS:RCX).AEP is not 0) or ((DS:RCX).STATE is not 0)
THEN #GP(0); FI;
(* Check consistency of FS & GS Limit *)
IF ( (TMP_SECS.ATTRIBUTES.MODE64BIT is 0) and ((DS:RCX.FSLIMIT & FFFH ≠ FFFH) or (DS:RCX.GSLIMIT & FFFH ≠ FFFH)) )
THEN #GP(0); FI;
(* Clear PENDING/MODIFIED flags to mark accept operation complete *)
EPCM(DS:RCX).PENDING  0;
EPCM(DS:RCX).MODIFIED  0;
EPCM(DS:RCX).PR  0;
(* Clear EAX and ZF to indicate successful completion *)
RFLAGS.ZF  0;
RAX  0;
DONE:
RFLAGS.CF,PF,AF,OF,SF  0;

Flags Affected
Sets ZF if page cannot be accepted, otherwise cleared. Clears CF, PF, AF, OF, SF
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If EPC page has incorrect page type or security attributes.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If EPC page has incorrect page type or security attributes.

Vol. 3D 40-69

SGX INSTRUCTION REFERENCES

EACCEPTCOPY—Initialize a Pending Page
Opcode/
Instruction

Op/En

EAX = 07H
ENCLU[EACCEPTCOPY]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX2

Description

This leaf function initializes a dynamically allocated EPC page
from another page in the EPC.

Instruction Operand Encoding
Op/En
IR

EAX
EACCEPTCOPY (In)

Return Error Code
(Out)

RBX

RCX

RDX

Address of a SECINFO (In)

Address of the destination EPC page (In)

Address of the
source EPC page (In)

Description
This leaf function copies the contents of an existing EPC page into an uninitialized EPC page (created by EAUG).
After initialization, the instruction may also modify the access rights associated with the destination EPC page. This
instruction leaf can only be executed when inside the enclave.
RBX contains the effective address of a SECINFO structure while RCX and RDX each contain the effective address
of an EPC page. The table below provides additional information on the memory parameter of the EACCEPTCOPY
leaf function.

EACCEPTCOPY Memory Parameter Semantics
SECINFO

EPCPAGE (Destination)

EPCPAGE (Source)

Read access permitted by Non Enclave

Read/Write access permitted by Enclave

Read access permitted by Enclave

The instruction faults if any of the following:

EACCEPTCOPY Faulting Conditions
The operands are not properly aligned.

If security attributes of the SECINFO page make the page inaccessible.

The EPC page is locked by another thread.

If security attributes of the source EPC page make the page inaccessible.

The EPC page is not valid.

RBX does not contain an effective address in an EPC page in the running enclave.

SECINFO contains an invalid request.

RCX/RDX does not contain an effective address of an EPC page in the running
enclave.

The error codes are:

Table 40-49. EACCEPTCOPY Return Value in RAX
Error Code (see Table 40-3)

Description

No Error

EACCEPTCOPY successful

SGX_PAGE_ATTRIBUTES_MISMATCH

The attributes of the target EPC page do not match the expected values

40-70 Vol. 3D

SGX INSTRUCTION REFERENCES

Concurrency Restrictions

Table 40-50. Concurrency Restrictions of EACCEPTCOPY with Intel® SGX Instructions - 1of 2
Operation
Param

EEXIT
Targ VA

EADD

ECRE
ATE

EBLOCK

SECS Targ SECS Targ SECS

SECS

EDBGRD/
WR
Targ SECS

EENTER/
ERESUME

EEXTEND

EGETKEY

TCS SSA SECS Targ SECS Param SECS

EINIT
SECS

ELDB/ELDU
Targ VA

EPA

SECS VA

Targ
EACCE
PTCOP
Y

Src

U

Y

U

Y

SECIN
FO

U

Y

U

U

Table 40-51. Concurrency Restrictions of EACCEPTCOPY with Intel® SGX Instructions - 2 of 2
Operation
Param

EREMOVE

EREPORT

ETRA
CK

Targ SECS Param SECS SECS

EWB
SRC VA

EAUG
SECS Targ SECS

EMODPE
Targ

SECI
NFO

Targ
N

Targ
EACCE
PTCOP
Y

EMODPR
SECS

EMODT
Targ
N

SECS

EACCEPT
Targ SECI
NFO

EACCEPTCOPY

SECS Targ SRC

N

SECI
NFO

N

Src

Y

Y

Y

Y

U

Y

Y

SECIN
FO

U

Y

Y

Y

Y

Y

Y

Operation

Temp Variables in EACCEPTCOPY Operational Flow
Name

Type

Size (bits)

Description

SCRATCH_SECINFO

SECINFO

512

Scratch storage for holding the contents of DS:RBX.

IF (DS:RBX is not 64Byte Aligned)
THEN #GP(0); FI;
IF ( (DS:RCX is not 4KByte Aligned) or (DS:RDX is not 4KByte Aligned) )
THEN #GP(0); FI;
IF ((DS:RBX is not within CR_ELRANGE) or (DS:RCX is not within CR_ELRANGE) or (DS:RDX is not within CR_ELRANGE))
THEN #GP(0); FI;
IF (DS:RBX does not resolve within an EPC)
THEN #PF(DS:RBX); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
IF (DS:RDX does not resolve within an EPC)
THEN #PF(DS:RDX); FI;
IF ( (EPCM(DS:RBX &~FFFH).VALID = 0) or (EPCM(DS:RBX &~FFFH).R = 0) or (EPCM(DS:RBX &~FFFH).PENDING ≠ 0) or
(EPCM(DS:RBX &~FFFH).MODIFIED ≠ 0) or (EPCM(DS:RBX &~FFFH).BLOCKED ≠ 0) or (EPCM(DS:RBX &~FFFH).PT ≠ PT_REG) or
(EPCM(DS:RBX &~FFFH).ENCLAVESECS ≠ CR_ACTIVE_SECS) or
(EPCM(DS:RBX &~FFFH).ENCLAVEADDRESS ≠ DS:RBX) )
THEN #PF(DS:RBX); FI;

Vol. 3D 40-71

SGX INSTRUCTION REFERENCES

(* Copy 64 bytes of contents *)
SCRATCH_SECINFO  DS:RBX;
(* Check for mis-configured SECINFO flags*)
IF ( (SCRATCH_SECINFO reserved fields are not zero ) or ((SCRATCH_SECINFO.FLAGS.R=0) AND(SCRATCH_SECINFO.FLAGS.W≠0 ) or
(SCRATCH_SECINFO.FLAGS.PT is not PT_REG) )
THEN #GP(0); FI;
(* Check security attributes of the source EPC page *)
IF ( (EPCM(DS:RDX).VALID = 0) or (EPCM(DS:RCX).R = 0) or (EPCM(DS:RDX).PENDING ≠ 0) or (EPCM(DS:RDX).MODIFIED ≠ 0) or
(EPCM(DS:RDX).BLOCKED ≠ 0) or (EPCM(DS:RDX).PT ≠ PT_REG) or (EPCM(DS:RDX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or
(EPCM(DS:RDX).ENCLAVEADDRESS ≠ DS:RDX))
THEN #PF(DS:RDX); FI;
(* Check security attributes of the destination EPC page *)
IF ( (EPCM(DS:RCX).VALID = 0) or (EPCM(DS:RCX).PENDING ≠ 1) or (EPCM(DS:RCX).MODIFIED ≠ 0) or
(EPCM(DS:RDX).BLOCKED ≠ 0) or (EPCM(DS:RCX).PT ≠ PT_REG) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) )
THEN
RFLAGS.ZF  1;
RAX  SGX_PAGE_ATTRIBUTES_MISMATCH;
GOTO DONE;
FI;
(* Check the destination EPC page for concurrency *)
IF (destination EPC page in use )
THEN #GP(0); FI;
(* Re-Check security attributes of the destination EPC page *)
IF ( (EPCM(DS:RCX).VALID = 0) or (EPCM(DS:RCX).PENDING ≠ 1) or (EPCM(DS:RCX).MODIFIED ≠ 0) or
(EPCM(DS:RCX).R ≠ 1) or (EPCM(DS:RCX).W ≠ 1) or (EPCM(DS:RCX).X ≠ 0) or
(EPCM(DS:RCX).PT ≠ SCRATCH_SECINFO.FLAGS.PT) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or
(EPCM(DS:RCX).ENCLAVEADDRESS ≠ DS:RCX))
THEN
RFLAGS.ZF  1;
RAX  SGX_PAGE_ATTRIBUTES_MISMATCH;
GOTO DONE;
FI;
(* Copy 4KBbytes form the source to destination EPC page*)
DS:RCX[32767:0]  DS:RDX[32767:0];
(* Update EPCM permissions *)
EPCM(DS:RCX).R  SCRATCH_SECINFO.FLAGS.R;
EPCM(DS:RCX).W  SCRATCH_SECINFO.FLAGS.W;
EPCM(DS:RCX).X  SCRATCH_SECINFO.FLAGS.X;
EPCM(DS:RCX).PENDING  0;
RFLAGS.ZF  0;
RAX  0;
DONE:
RFLAGS.CF,PF,AF,OF,SF  0;

40-72 Vol. 3D

SGX INSTRUCTION REFERENCES

Flags Affected
Sets ZF if page is not modifiable, otherwise cleared. Clears CF, PF, AF, OF, SF
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If EPC page has incorrect page type or security attributes.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.
If a memory operand is not an EPC page.
If EPC page has incorrect page type or security attributes.

Vol. 3D 40-73

SGX INSTRUCTION REFERENCES

EENTER—Enters an Enclave
Opcode/
Instruction

Op/En

EAX = 02H
ENCLU[EENTER]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function is used to enter an enclave.

Instruction Operand Encoding
Op/En
IR

EAX
EENTER (In)

RBX

Content of RBX.CSSA
(Out)

Address of a TCS (In)

RCX
Address of AEP (In)

Address of IP following
EENTER (Out)

Description
The ENCLU[EENTER] instruction transfers execution to an enclave. At the end of the instruction, the logical
processor is executing in enclave mode at the RIP computed as EnclaveBase + TCS.OENTRY. If the target address
is not within the CS segment (32-bit) or is not canonical (64-bit), a #GP(0) results.

EENTER Memory Parameter Semantics
TCS
Enclave access
EENTER is a serializing instruction. The instruction faults if any of the following occurs:

Address in RBX is not properly aligned.

Any TCS.FLAGS’s must-be-zero bit is not zero.

TCS pointed to by RBX is not valid or available or
locked.

Current 32/64 mode does not match the enclave mode in
SECS.ATTRIBUTES.MODE64.

The SECS is in use.

Either of TCS-specified FS and GS segment is not a subsets of the current DS
segment.

Any one of DS, ES, CS, SS is not zero.

If XSAVE available, CR4.OSXSAVE = 0, but SECS.ATTRIBUTES.XFRM ≠ 3.

CR4.OSFXSR ≠ 1.

If CR4.OSXSAVE = 1, SECS.ATTRIBUTES.XFRM is not a subset of XCR0.

The following operations are performed by EENTER:

•

RSP and RBP are saved in the current SSA frame on EENTER and are automatically restored on EEXIT or
interrupt.

•

The AEP contained in RCX is stored into the TCS for use by AEXs.FS and GS (including hidden portions) are
saved and new values are constructed using TCS.OFSBASE/GSBASE (32 and 64-bit mode) and
TCS.OFSLIMIT/GSLIMIT (32-bit mode only). The resulting segments must be a subset of the DS segment.

•

If CR4.OSXSAVE == 1, XCR0 is saved and replaced by SECS.ATTRIBUTES.XFRM. The effect of RFLAGS.TF
depends on whether the enclave entry is opt-in or opt-out (see Section 42.1.2):
— On opt-out entry, TF is saved and cleared (it is restored on EEXIT or AEX). Any attempt to set TF via a POPF
instruction while inside the enclave clears TF (see Section 42.2.5).
— On opt-in entry, a single-step debug exception is pended on the instruction boundary immediately after
EENTER (see Section 42.2.2).

•

All code breakpoints that do not overlap with ELRANGE are also suppressed. If the entry is an opt-out entry, all
code and data breakpoints that overlap with the ELRANGE are suppressed.

•

On opt-out entry, a number of performance monitoring counters and behaviors are modified or suppressed (see
Section 42.2.3):

40-74 Vol. 3D

SGX INSTRUCTION REFERENCES

— All performance monitoring activity on the current thread is suppressed except for incrementing and firing
of FIXED_CTR1 and FIXED_CTR2.
— PEBS is suppressed.
— AnyThread counting on other threads is demoted to MyThread mode and IA32_PERF_GLOBAL_STATUS[60]
on that thread is set
— If the opt-out entry on a hardware thread results in suppression of any performance monitoring, then the
processor sets IA32_PERF_GLOBAL_STATUS[60] and IA32_PERF_GLOBAL_STATUS[63].
Concurrency Restrictions

Table 40-52. Concurrency Restrictions of EENTER with Intel® SGX Instructions - 1of 2
Operation

EENTE
R

EEXIT

Param

Targ VA

TCS

N

EADD

ECRE
ATE

EBLOCK

SECS Targ SECS Targ SECS
N

SECS
N

U

SSA
SECS

Y

Y

N

Y

Y

Y

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

Targ SECS

TCS SSA SECS Targ SECS Param SECS

Y

N

Y

Y

U

Y

Y

Y

Y

EINIT
SECS

ELDB/ELDU
Targ VA

EPA

SECS VA

N

N

U
Y

Y

N

Y

Y

N

Y

Y

Y

Y

Table 40-53. Concurrency Restrictions of EENTER with Intel® SGX Instructions - 2 of 2
Operation

EENTE
R

EREMOVE

EREPORT

ETRA
CK

EWB

Param

Targ SECS Param SECS SECS

SRC VA

TCS

N

N

SSA
SECS

EAUG
SECS Targ SECS

Y

Y

Y

Y

Y

Targ

SECI
NFO

Y

U

Y

Y

EMODPR
Targ

SECS

N
Y

Y

Y

EMODT
Targ

SECS

EACCEPT
Targ SECI
NFO

EACCEPTCOPY

SECS Targ SRC

SECI
NFO

N

U
Y

EMODPE

Y

Y
Y

Y

Y

Y

U

Y

Y

Y

U

U

Y

Y

Operation

Temp Variables in EENTER Operational Flow
Name

Type

Size (Bits)

Description

TMP_FSBASE

Effective Address

32/64

Proposed base address for FS segment.

TMP_GSBASE

Effective Address

32/64

Proposed base address for FS segment.

TMP_FSLIMIT

Effective Address

32/64

Highest legal address in proposed FS segment.

TMP_GSLIMIT

Effective Address

32/64

Highest legal address in proposed GS segment.

TMP_XSIZE

integer

64

Size of XSAVE area based on SECS.ATTRIBUTES.XFRM.

TMP_SSA_PAGE

Effective Address

32/64

Pointer used to iterate over the SSA pages in the current frame.

TMP_GPR

Effective Address

32/64

Address of the GPR area within the current SSA frame.

TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));
(* Make sure DS is usable, expand up *)
IF (TMP_MODE64 = 0 and (DS not usable or ( ( DS[S] = 1) and (DS[bit 11] = 0) and DS[bit 10] = 1) ) ) )
THEN #GP(0); FI;
(* Check that CS, SS, DS, ES.base is 0 *)
IF (TMP_MODE64 = 0)
THEN
IF(CS.base ≠ 0 or DS.base ≠ 0) #GP(0); FI;
Vol. 3D 40-75

SGX INSTRUCTION REFERENCES

IF(ES usable and ES.base ≠ 0) #GP(0); FI;
IF(SS usable and SS.base ≠ 0) #GP(0); FI;
IF(SS usable and SS.B = 0) #GP(0); FI;
FI;
IF (DS:RBX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RBX does not resolve within an EPC)
THEN #PF(DS:RBX); FI;
(* Check AEP is canonical*)
IF (TMP_MODE64 = 1 and (CS:RCX is not canonical) )
THEN #GP(0); FI;
(* Check concurrency of TCS operation*)
IF (Other Intel SGX instructions is operating on TCS)
THEN #GP(0); FI;
(* TCS verification *)
IF (EPCM(DS:RBX).VALID = 0)
THEN #PF(DS:RBX); FI;
IF (EPCM(DS:RBX).BLOCKED = 1)
THEN #PF(DS:RBX); FI;
IF ( (EPCM(DS:RBX).ENCLAVEADDRESS ≠ DS:RBX) or (EPCM(DS:RBX).PT ≠ PT_TCS) )
THEN #PF(DS:RBX); FI;
IF ((EPCM(DS:RBX).PENDING = 1) or (EPCM(DS:RBX).MODIFIED = 1))
THEN #PF(DS:RBX); FI;
IF ( (DS:RBX).OSSA is not 4KByte Aligned)
THEN #GP(0); FI;
(* Check proposed FS and GS *)
IF ( ( (DS:RBX).OFSBASE is not 4KByte Aligned) or ( (DS:RBX).OGSBASE is not 4KByte Aligned) )
THEN #GP(0); FI;
(* Get the SECS for the enclave in which the TCS resides *)
TMP_SECS  Address of SECS for TCS;
(* Check proposed FS/GS segments fall within DS *)
IF (TMP_MODE64 = 0)
THEN
TMP_FSBASE  (DS:RBX).OFSBASE + TMP_SECS.BASEADDR;
TMP_FSLIMIT  (DS:RBX).OFSBASE + TMP_SECS.BASEADDR + (DS:RBX).FSLIMIT;
TMP_GSBASE  (DS:RBX).OGSBASE + TMP_SECS.BASEADDR;
TMP_GSLIMIT  (DS:RBX).OGSBASE + TMP_SECS.BASEADDR + (DS:RBX).GSLIMIT;
(* if FS wrap-around, make sure DS has no holes*)
IF (TMP_FSLIMIT < TMP_FSBASE)
THEN
IF (DS.limit < 4GB) THEN #GP(0); FI;
ELSE
40-76 Vol. 3D

SGX INSTRUCTION REFERENCES

IF (TMP_FSLIMIT > DS.limit) THEN #GP(0); FI;
FI;
(* if GS wrap-around, make sure DS has no holes*)
IF (TMP_GSLIMIT < TMP_GSBASE)
THEN
IF (DS.limit < 4GB) THEN #GP(0); FI;
ELSE
IF (TMP_GSLIMIT > DS.limit) THEN #GP(0); FI;
FI;
ELSE
TMP_FSBASE  (DS:RBX).OFSBASE + TMP_SECS.BASEADDR;
TMP_GSBASE  (DS:RBX).OGSBASE + TMP_SECS.BASEADDR;
IF ( (TMP_FSBASE is not canonical) or (TMP_GSBASE is not canonical))
THEN #GP(0); FI;
FI;
(* Ensure that the FLAGS field in the TCS does not have any reserved bits set *)
IF ( ( (DS:RBX).FLAGS & FFFFFFFFFFFFFFFEH) ≠ 0)
THEN #GP(0); FI;
(* SECS must exist and enclave must have previously been EINITted *)
IF (the enclave is not already initialized)
THEN #GP(0); FI;
(* make sure the logical processor’s operating mode matches the enclave *)
IF ( (TMP_MODE64 ≠ TMP_SECS.ATTRIBUTES.MODE64BIT) )
THEN #GP(0); FI;
IF (CR4.OSFXSR = 0)
THEN #GP(0); FI;
(* Check for legal values of SECS.ATTRIBUTES.XFRM *)
IF (CR4.OSXSAVE = 0)
THEN
IF (TMP_SECS.ATTRIBUTES.XFRM ≠ 03H) THEN #GP(0); FI;
ELSE
IF ( (TMP_SECS.ATTRIBUTES.XFRM & XCR0) ≠ TMP_SECS.ATTRIBUES.XFRM) THEN #GP(0); FI;
FI;
(* Make sure the SSA contains at least one more frame *)
IF ( (DS:RBX).CSSA ≥ (DS:RBX).NSSA)
THEN #GP(0); FI;
(* Compute linear address of SSA frame *)
TMP_SSA  (DS:RBX).OSSA + TMP_SECS.BASEADDR + 4096 * TMP_SECS.SSAFRAMESIZE * (DS:RBX).CSSA;
TMP_XSIZE  compute_XSAVE_frame_size(TMP_SECS.ATTRIBUTES.XFRM);
FOR EACH TMP_SSA_PAGE = TMP_SSA to TMP_SSA + TMP_XSIZE
(* Check page is read/write accessible *)
Check that DS:TMP_SSA_PAGE is read/write accessible;
If a fault occurs, release locks, abort and deliver that fault;
IF (DS:TMP_SSA_PAGE does not resolve to EPC page)
THEN #PF(DS:TMP_SSA_PAGE); FI;
Vol. 3D 40-77

SGX INSTRUCTION REFERENCES

IF (EPCM(DS:TMP_SSA_PAGE).VALID = 0)
THEN #PF(DS:TMP_SSA_PAGE); FI;
IF (EPCM(DS:TMP_SSA_PAGE).BLOCKED = 1)
THEN #PF(DS:TMP_SSA_PAGE); FI;
IF ((EPCM(DS:TMP_SSA_PAGE).PENDING = 1) or (EPCM(DS:TMP_SSA_PAGE).MODIFIED = 1))
THEN #PF(DS:TMP_SSA_PAGE); FI;
IF ( ( EPCM(DS:TMP_SSA_PAGE).ENCLAVEADDRESS ≠ DS:TMP_SSA_PAGE) or (EPCM(DS:TMP_SSA_PAGE).PT ≠ PT_REG) or
(EPCM(DS:TMP_SSA_PAGE).ENCLAVESECS ≠ EPCM(DS:RBX).ENCLAVESECS) or
(EPCM(DS:TMP_SSA_PAGE).R = 0) or (EPCM(DS:TMP_SSA_PAGE).W = 0) )
THEN #PF(DS:TMP_SSA_PAGE); FI;
CR_XSAVE_PAGE_n  Physical_Address(DS:TMP_SSA_PAGE);
ENDFOR
(* Compute address of GPR area*)
TMP_GPR  TMP_SSA + 4096 * DS:TMP_SECS.SSAFRAMESIZE -- sizeof(GPRSGX_AREA);
If a fault occurs; release locks, abort and deliver that fault;
IF (DS:TMP_GPR does not resolve to EPC page)
THEN #PF(DS:TMP_GPR); FI;
IF (EPCM(DS:TMP_GPR).VALID = 0)
THEN #PF(DS:TMP_GPR); FI;
IF (EPCM(DS:TMP_GPR).BLOCKED = 1)
THEN #PF(DS:TMP_GPR); FI;
IF ((EPCM(DS:TMP_GPR).PENDING = 1) or (EPCM(DS:TMP_GPR).MODIFIED = 1))
THEN #PF(DS:TMP_GPR); FI;
IF ( ( EPCM(DS:TMP_GPR).ENCLAVEADDRESS ≠ DS:TMP_GPR) or (EPCM(DS:TMP_GPR).PT ≠ PT_REG) or
(EPCM(DS:TMP_GPR).ENCLAVESECS EPCM(DS:RBX).ENCLAVESECS) or
(EPCM(DS:TMP_GPR).R = 0) or (EPCM(DS:TMP_GPR).W = 0) )
THEN #PF(DS:TMP_GPR); FI;
IF (TMP_MODE64 = 0)
THEN
IF (TMP_GPR + (GPR_SIZE -1) is not in DS segment) THEN #GP(0); FI;
FI;
CR_GPR_PA  Physical_Address (DS: TMP_GPR);
(* Validate TCS.OENTRY *)
TMP_TARGET  (DS:RBX).OENTRY + TMP_SECS.BASEADDR;
IF (TMP_MODE64 = 1)
THEN
IF (TMP_TARGET is not canonical) THEN #GP(0); FI;
ELSE
IF (TMP_TARGET > CS limit) THEN #GP(0); FI;
FI;
(* Ensure the enclave is not already active and this thread is the only one using the TCS*)
IF (DS:RBX.STATE = ACTIVE))
THEN #GP(0); FI;
CR_ENCLAVE_MODE  1;
CR_ACTIVE_SECS  TMP_SECS;
CR_ELRANGE  (TMPSECS.BASEADDR, TMP_SECS.SIZE);

40-78 Vol. 3D

SGX INSTRUCTION REFERENCES

(* Save state for possible AEXs *)
CR_TCS_PA  Physical_Address (DS:RBX);
CR_TCS_LA  RBX;
CR_TCS_LA.AEP  RCX;
(* Save the hidden portions of FS and GS *)
CR_SAVE_FS_selector  FS.selector;
CR_SAVE_FS_base  FS.base;
CR_SAVE_FS_limit  FS.limit;
CR_SAVE_FS_access_rights  FS.access_rights;
CR_SAVE_GS_selector  GS.selector;
CR_SAVE_GS_base  GS.base;
CR_SAVE_GS_limit  GS.limit;
CR_SAVE_GS_access_rights  GS.access_rights;
(* If XSAVE is enabled, save XCR0 and replace it with SECS.ATTRIBUTES.XFRM*)
IF (CR4.OSXSAVE = 1)
CR_SAVE_XCR0  XCR0;
XCR0  TMP_SECS.ATTRIBUTES.XFRM;
FI;
RCX  RIP;
RIP  TMP_TARGET;
RAX  (DS:RBX).CSSA;
(* Save the outside RSP and RBP so they can be restored on interrupt or EEXIT *)
DS:TMP_SSA.U_RSP  RSP;
DS:TMP_SSA.U_RBP  RBP;
(* Do the FS/GS swap *)
FS.base  TMP_FSBASE;
FS.limit  DS:RBX.FSLIMIT;
FS.type  0001b;
FS.W  DS.W;
FS.S  1;
FS.DPL  DS.DPL;
FS.G  1;
FS.B  1;
FS.P  1;
FS.AVL  DS.AVL;
FS.L  DS.L;
FS.unusable  0;
FS.selector  0BH;
GS.base  TMP_GSBASE;
GS.limit  DS:RBX.GSLIMIT;
GS.type  0001b;
GS.W  DS.W;
GS.S  1;
GS.DPL  DS.DPL;
GS.G  1;
GS.B  1;
GS.P  1;
GS.AVL  DS.AVL;
GS.L  DS.L;
Vol. 3D 40-79

SGX INSTRUCTION REFERENCES

GS.unusable  0;
GS.selector  0BH;
CR_DBGOPTIN  TCS.FLAGS.DBGOPTIN;
Suppress_all_code_breakpoints_that_are_outside_ELRANGE;
IF (CR_DBGOPTIN = 0)
THEN
Suppress_all_code_breakpoints_that_overlap_with_ELRANGE;
CR_SAVE_TF  RFLAGS.TF;
RFLAGS.TF  0;
Suppress_monitor_trap_flag for the source of the execution of the enclave;
Suppress any pending debug exceptions;
Suppress any pending MTF VM exit;
ELSE
IF RFLAGS.TF = 1
THEN pend a single-step #DB at the end of EENTER; FI;
IF the “monitor trap flag” VM-execution control is set
THEN pend an MTF VM exit at the end of EENTER; FI;
FI;
Flush_linear_context;
Allow_front_end_to_begin_fetch_at_new_RIP;
Flags Affected
RFLAGS.TF is cleared on opt-out entry
Protected Mode Exceptions
#GP(0)

If DS:RBX is not page aligned.
If the enclave is not initialized.
If part or all of the FS or GS segment specified by TCS is outside the DS segment or not properly aligned.
If the thread is not in the INACTIVE state.
If CS, DS, ES or SS bases are not all zero.
If executed in enclave mode.
If any reserved field in the TCS FLAG is set.
If the target address is not within the CS segment.
If CR4.OSFXSR = 0.
If CR4.OSXSAVE = 0 and SECS.ATTRIBUTES.XFRM ≠ 3.
If CR4.OSXSAVE = 1and SECS.ATTRIBUTES.XFRM is not a subset of XCR0.

#PF(error code)

If a page fault occurs in accessing memory.
If DS:RBX does not point to a valid TCS.
If one or more pages of the current SSA frame are not readable/writable, or do not resolve to
a valid PT_REG EPC page.

64-Bit Mode Exceptions
#GP(0)

If DS:RBX is not page aligned.
If the enclave is not initialized.
If the thread is not in the INACTIVE state.
If CS, DS, ES or SS bases are not all zero.
If executed in enclave mode.

40-80 Vol. 3D

SGX INSTRUCTION REFERENCES

If part or all of the FS or GS segment specified by TCS is outside the DS segment or not properly aligned.
If the target address is not canonical.
If CR4.OSFXSR = 0.
If CR4.OSXSAVE = 0 and SECS.ATTRIBUTES.XFRM ≠ 3.
If CR4.OSXSAVE = 1and SECS.ATTRIBUTES.XFRM is not a subset of XCR0.
#PF(error code)

If a page fault occurs in accessing memory operands.
If DS:RBX does not point to a valid TCS.
If one or more pages of the current SSA frame are not readable/writable, or do not resolve to
a valid PT_REG EPC page.

Vol. 3D 40-81

SGX INSTRUCTION REFERENCES

EEXIT—Exits an Enclave
Opcode/
Instruction

Op/En

EAX = 04H
ENCLU[EEXIT]

IR

Description

CPUID
Feature
Flag
SGX1

64/32
bit Mode
Support
V/V

This leaf function is used to exit an enclave.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EEXIT (In)

Target address outside the enclave (In)

Address of the current AEP (In)

Description
The ENCLU[EEXIT] instruction exits the currently executing enclave and branches to the location specified in RBX.
RCX receives the current AEP. If RBX is not within the CS (32-bit mode) or is not canonical (64-bit mode) a #GP(0)
results.

EEXIT Memory Parameter Semantics
Target Address
Non-Enclave read and execute access
If RBX specifies an address that is inside the enclave, the instruction will complete normally. The fetch of the next
instruction will occur in non-enclave mode, but will attempt to fetch from inside the enclave. This has the effect of
abort page semantics on the next destination.
If secrets are contained in any registers, it is responsibility of enclave software to clear those registers.
If XCR0 was modified on enclave entry, it is restored to the value it had at the time of the most recent EENTER or
ERESUME.
If the enclave is opt-out, RFLAGS.TF is loaded from the value previously saved on EENTER.
Code and data breakpoints are unsuppressed.
Performance monitoring counters are unsuppressed.
Concurrency Restrictions

Table 40-54. Concurrency Restrictions of EEXIT with Intel® SGX Instructions - 1of 2
Operation
Param
EEXIT

EEXIT
Targ VA

EADD

SECS Targ SECS Targ SECS

TCS
U

SSA

Y

SECS

ECRE
ATE

EBLOCK

EDBGRD/
WR

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

ELDB/ELDU

EPA

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

SECS

Targ VA

SECS VA

Y

Y

Y

Y

Y

N

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

U

Y

Y

U

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Y

Table 40-55. Concurrency Restrictions of EEXIT with Intel® SGX Instructions - 2 of 2
Operation

EEXIT

EREMOVE

EREPORT

ETRA
CK

Para
m

Targ SECS Param SECS SECS

TCS

Y

SSA

Y

SECS

Y

40-82 Vol. 3D

Y
Y

Y

Y

EWB
SRC VA

Y

Y

Y

Y

Y

Y

Y

Y

Y

EAUG
SECS Targ SECS

Y

EMODPE

EMODPR

Targ

SECI
NFO

Targ

Y

Y

Y

Y

Y

Y

Y

Y

U

Y

Y

Y

Y

Y

Y

SECS

EMODT
Targ

SECS

Y
Y
Y

Y

Y

EACCEPT
Targ SECI
NFO
Y

Y

Y

U

Y

Y

EACCEPTCOPY

SECS Targ SRC

Y

SECI
NFO

Y

Y

Y

Y

U

U

Y

Y

Y

SGX INSTRUCTION REFERENCES

Operation

Temp Variables in EEXIT Operational Flow
Name

Type

Size (Bits)

Description

TMP_RIP

Effective Address

32/64

Saved copy of CRIP for use when creating LBR.

TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));
IF (TMP_MODE64 = 1)
THEN
IF (RBX is not canonical) THEN #GP(0); FI;
ELSE
IF (RBX > CS limit) THEN #GP(0); FI;
FI;
TMP_RIP  CRIP;
RIP  RBX;
(* Return current AEP in RCX *)
RCX  CR_TCS_PA.AEP;
(* Do the FS/GS swap *)
FS.selector  CR_SAVE_FS.selector;
FS.base  CR_SAVE_FS.base;
FS.limit  CR_SAVE_FS.limit;
FS.access_rights  CR_SAVE_FS.access_rights;
GS.selector  CR_SAVE_GS.selector;
GS.base  CR_SAVE_GS.base;
GS.limit  CR_SAVE_GS.limit;
GS.access_rights  CR_SAVE_GS.access_rights;
(* Restore XCR0 if needed *)
IF (CR4.OSXSAVE = 1)
XCR0  CR_SAVE__XCR0;
FI;
Unsuppress_all_code_breakpoints_that_are_outside_ELRANGE;
IF (CR_DBGOPTIN = 0)
THEN
UnSuppress_all_code_breakpoints_that_overlap_with_ELRANGE;
Restore suppressed breakpoint matches;
RFLAGS.TF  CR_SAVE_TF;
UnSuppress_montior_trap_flag;
UnSuppress_LBR_Generation;
UnSuppress_performance monitoring_activity;
Restore performance monitoring counter AnyThread demotion to MyThread in enclave back to AnyThread
FI;
IF RFLAGS.TF = 1
THEN Pend Single-Step #DB at the end of EEXIT;
FI;

Vol. 3D 40-83

SGX INSTRUCTION REFERENCES

IF the “monitor trap flag” VM-execution control is set
THEN pend a MTF VM exit at the end of EEXIT;
FI;
CR_ENCLAVE_MODE  0;
CR_TCS_PA.STATE  INACTIVE;
(* Assure consistent translations *)
Flush_linear_context;
Flags Affected
RFLAGS.TF is restored from the value previously saved in EENTER or ERESUME.
Protected Mode Exceptions
#GP(0)

If executed outside an enclave.
If RBX is outside the CS segment.

#PF(error code)

If a page fault occurs in accessing memory.

64-Bit Mode Exceptions
#GP(0)

If executed outside an enclave.
If RBX is not canonical.

#PF(error code)

40-84 Vol. 3D

If a page fault occurs in accessing memory operands.

SGX INSTRUCTION REFERENCES

EGETKEY—Retrieves a Cryptographic Key
Opcode/
Instruction

Op/En

EAX = 04H
ENCLU[EGETKEY]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function retrieves a cryptographic key.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EGETKEY (In)

Address to a KEYREQUEST (In)

Address of the OUTPUTDATA (In)

Description
The ENCLU[EGETKEY] instruction returns a 128-bit secret key from the processor specific key hierarchy. The
register RBX contains the effective address of a KEYREQUEST structure, which the instruction interprets to determine the key being requested. The Requesting Keys section below provides a description of the keys that can be
requested. The RCX register contains the effective address where the key will be returned. Both the addresses in
RBX & RCX should be locations inside the enclave.
EGETKEY derives keys using a processor unique value to create a specific key based on a number of possible
inputs. This instruction leaf can only be executed inside an enclave.

EEGETKEY Memory Parameter Semantics
KEYREQUEST

OUTPUTDATA

Enclave read access

Enclave write access

After validating the operands, the instruction determines which key is to be produced and performs the following
actions:

•
•
•

The instruction assembles the derivation data for the key based on the Table 40-56
Computes derived key using the derivation data and package specific value
Outputs the calculated key to the address in RCX

The instruction fails with #GP(0) if the operands are not properly aligned. Successful completion of the instruction
will clear RFLAGS.{ZF, CF, AF, OF, SF, PF}. The instruction returns an error code if the user tries to request a key
based on an invalid CPUSVN or ISVSVN (when the user request is accepted, see the table below), requests a key
for which it has not been granted the attribute to request, or requests a key that is not supported by the hardware.
These checks may be performed in any order. Thus, an indication by error number of one cause (for example,
invalid attribute) does not imply that there are not also other errors. Different processors may thus give different
error numbers for the same Enclave. The correctness of software should not rely on the order resulting from the
checks documented in this section. In such cases the ZF flag is set and the corresponding error bit
(SGX_INVALID_SVN, SGX_INVALID_ATTRIBUTE, SGX_INVALID_KEYNAME) is set in RAX and the data at the
address specified by RCX is unmodified.
Requesting Keys
The KEYREQUEST structure (see Section 37.17.1) identifies the key to be provided. The Keyrequest.KeyName field
identifies which type of key is requested.
Deriving Keys
Key derivation is based on a combination of the enclave specific values (see Table 40-56) and a processor key.
Depending on the key being requested a field may either be included by definition or the value may be included
from the KeyRequest. A “yes” in Table 40-56 indicates the value for the field is included from its default location,
identified in the source row, and a “request” indicates the values for the field is included from its corresponding
KeyRequest field.

Vol. 3D 40-85

SGX INSTRUCTION REFERENCES

Table 40-56. Key Derivation
Owner
Epoch

Key Name Attributes

CPU SVN

ISV SVN

Key
Y
CR_SGX Y CPUSVN
Dependent SECS.ATTRIBUTES OWNER Register;
Constant
and
EPOCH
SECS.MISCSELECT;

Source

RAttribMask &
SECS.ATTRIBUTES
and
SECS.MISCSELECT;

ISV
PRODID MRENCLAVE MRSIGNER RAND

R
SECS.
Req.ISVSVN; ISVID

SECS.
SECS.
Req.
MRENCLAVE MRSIGNER KEYID

R
Req.CPUSVN;

EINITTOKEN Yes

Request

Yes

Request

Request

Yes

No

Yes

Request

Report

Yes

Yes

Yes

Yes

No

No

Yes

No

Request

Seal

Yes

Request

Yes

Request

Request

Yes

Request

Request

Request

Provisioning Yes

Request

No

Request

Request

Yes

No

Yes

Yes

Provisioning Yes
Seal

Request

No

Request

Request

Yes

No

Yes

Yes

Keys that permit the specification of a CPU or ISV's code's SVNs have additional requirements. The caller may not
request a key for an SVN beyond the current CPU or ISV SVN, respectively.
Several keys are access controlled. Access to the Provisioning Key and Provisioning Seal key requires the enclave's
ATTRIBUTES.PROVISIONKEY be set. The EINITTOKEN Key requires ATTRIBUTES.EINITTOKEN_KEY be set and
SECS.MRSIGNER equal IA32_SGXLEPUBKEYHASH.
Some keys are derived based on a hardcode PKCS padding constant (352 byte string):
HARDCODED_PKCS1_5_PADDING[15:0]  0100H;
HARDCODED_PKCS1_5_PADDING[2655:16]  SignExtend330Byte(-1); // 330 bytes of 0FFH
HARDCODED_PKCS1_5_PADDING[2815:2656]  2004000501020403650148866009060D30313000H;
The error codes are:

Table 40-57. EGETKEY Return Value in RAX
Error Code (see Table 40-3)

Value

No Error

0

Description
EGETKEY successful

SGX_INVALID_ATTRIBUTE

The KEYREQUEST contains a KEYNAME for which the enclave is not
authorized

SGX_INVALID_CPUSVN

If KEYREQUEST.CPUSVN is an unsupported platforms CPUSVN value

SGX_INVALID_ISVSVN

If KEYREQUEST.ISVSVN is greater than the enclave's ISV_SVN

SGX_INVALID_KEYNAME

If KEYREQUEST.KEYNAME is an unsupported value

Concurrency Restrictions

Table 40-58. Concurrency Restrictions of EGETKEY with Other Intel® SGX Operations 1 of 2
Operation
Param
EGETKEY

Param
SECS

40-86 Vol. 3D

EEXIT
TCS SSA

EADD
SECS Targ SECS

EBLOCK
Targ SECS

ECRE
ATE
SECS

U

EDBGRD/
WR
Targ SECS

EENTER/
ERESUME

Y

Y

Y

Y

Y

Y

U
Y

EGETKEY

TCS SSA SECS Targ SECS Param SECS

Y
Y

EEXTEND

Y

Y

EINIT

ELDB/ELDU

EPA

SECS

Targ VA

SECS VA

Y

Y

Y

U
Y

Y

Y

Y

Y

Y

Y

SGX INSTRUCTION REFERENCES

Table 40-59. Concurrency Restrictions of EGETKEY with Other Intel® SGX Operations 2 of 2
Operation
Param
EGETKEY

EREMOVE

Targ SECS Param SECS

ETRACK

EWB

EAUG

Y

Y

Y

Y

EMODPE

EMODPR

SECS

SRC

VA

SECS Targ SECS Targ SECI Targ SEC
NFO
S

Y

Y

Y

Y

U

Param
SECS

EREPORT

Y

Y

Y

U

Y

Y

Y

Y

EMODT
Targ SEC
S
Y

Y

EACCEPT
Targ SECI
NFO
Y

U

Y

Y

EACCEPTCOPY

SECS Targ SR
C
Y

Y

SECI
NFO

Y

U

Y

Y

Operation

Temp Variables in EGETKEY Operational Flow
Name

Type

Size (Bits)

Description

TMP_CURRENTSECS

Address of the SECS for the currently executing enclave.

TMP_KEYDEPENDENCIES

Temp space for key derivation.

TMP_ATTRIBUTES

128

Temp Space for the calculation of the sealable Attributes.

TMP_OUTPUTKEY

128

Temp Space for the calculation of the key.

(* Make sure KEYREQUEST is properly aligned and inside the current enclave *)
IF ( (DS:RBX is not 512Byte aligned) or (DS:RBX is within CR_ELRANGE) )
THEN #GP(0); FI;
(* Make sure DS:RBX is an EPC address and the EPC page is valid *)
IF ( (DS:RBX does not resolve to an EPC address) or (EPCM(DS:RBX).VALID = 0) )
THEN #PF(DS:RBX); FI;
IF (EPCM(DS:RBX).BLOCKED = 1)
THEN #PF(DS:RBX); FI;
(* Check page parameters for correctness *)
IF ( (EPCM(DS:RBX).PT ≠ PT_REG) or (EPCM(DS:RBX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or (EPCM(DS:RBX).PENDING = 1) or
(EPCM(DS:RBX).MODIFIED = 1) or (EPCM(DS:RBX).ENCLAVEADDRESS ≠ (DS:RBX & ~0FFFH) ) or (EPCM(DS:RBX).R = 0) )
THEN #PF(DS:RBX);
FI;
(* Make sure OUTPUTDATA is properly aligned and inside the current enclave *)
IF ( (DS:RCX is not 16Byte aligned) or (DS:RCX is not within CR_ELRANGE) )
THEN #GP(0); FI;
(* Make sure DS:RCX is an EPC address and the EPC page is valid *)
IF ( (DS:RCX does not resolve to an EPC address) or (EPCM(DS:RCX).VALID = 0) )
THEN #PF(DS:RCX); FI;
IF (EPCM(DS:RCX).BLOCKED = 1)
THEN #PF(DS:RCX); FI;
(* Check page parameters for correctness *)
IF ( (EPCM(DS:RCX).PT ≠ PT_REG) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or (EPCM(DS:RCX).PENDING = 1) or
(EPCM(DS:RCX).MODIFIED = 1) or (EPCM(DS:RCX).ENCLAVEADDRESS ≠ (DS:RCX & ~0FFFH) ) or (EPCM(DS:RCX).W = 0) )
THEN #PF(DS:RCX);
FI;

Vol. 3D 40-87

SGX INSTRUCTION REFERENCES

(* Verify RESERVED spaces in KEYREQUEST are valid *)
IF ( (DS:RBX).RESERVED ≠ 0) or (DS:RBX.KEYPOLICY.RESERVED ≠ 0) )
THEN #GP(0); FI;
TMP_CURRENTSECS  CR_ACTIVE_SECS;
(* Determine which enclave attributes that must be included in the key. Attributes that must always be include INIT & DEBUG *)
REQUIRED_SEALING_MASK[127:0]  00000000 00000000 00000000 00000003H;
TMP_ATTRIBUTES  (DS:RBX.ATTRIBUTEMASK | REQUIRED_SEALING_MASK) & TMP_CURRENTSECS.ATTRIBUTES;
(* Compute MISCSELECT fields to be included *)
TMP_MISCSELECT  DS:RBX.MISCMASK & TMP_CURRENTSECS.MISCSELECT
CASE (DS:RBX.KEYNAME)
SEAL_KEY:
IF (DS:RBX.CPUSVN is beyond current CPU configuration)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_CPUSVN;
GOTO EXIT;
FI;
IF (DS:RBX.ISVSVN > TMP_CURRENTSECS.ISVSVN)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ISVSVN;
GOTO EXIT;
FI;
// Include enclave identity?
TMP_MRENCLAVE  0;
IF (DS:RBX.KEYPOLICY.MRENCLAVE = 1)
THEN TMP_MRENCLAVE  TMP_CURRENTSECS.MRENCLAVE;
FI;
// Include enclave author?
TMP_MRSIGNER  0;
IF (DS:RBX.KEYPOLICY.MRSIGNER = 1)
THEN TMP_MRSIGNER  TMP_CURRENTSECS.MRSIGNER;
FI;
//Determine values key is based on
TMP_KEYDEPENDENCIES.KEYNAME  SEAL_KEY;
TMP_KEYDEPENDENCIES.ISVPRODID  TMP_CURRENTSECS.ISVPRODID;
TMP_KEYDEPENDENCIES.ISVSVN  DS:RBX.ISVSVN;
TMP_KEYDEPENDENCIES.SGXOWNEREPOCH  CR_SGXOWNEREPOCH;
TMP_KEYDEPENDENCIES.ATTRIBUTES  TMP_ATTRIBUTES;
TMP_KEYDEPENDENCIES.ATTRIBUTESMASK  DS:RBX.ATTRIBUTEMASK;
TMP_KEYDEPENDENCIES.MRENCLAVE  TMP_MRENCLAVE;
TMP_KEYDEPENDENCIES.MRSIGNER  TMP_MRSIGNER;
TMP_KEYDEPENDENCIES.KEYID  DS:RBX.KEYID;
TMP_KEYDEPENDENCIES.SEAL_KEY_FUSES  CR_SEAL_FUSES;
TMP_KEYDEPENDENCIES.CPUSVN  DS:RBX.CPUSVN;
TMP_KEYDEPENDENCIES.PADDING  TMP_CURRENTSECS.PADDING;
TMP_KEYDEPENDENCIES.MISCSELECT  TMP_MISCSELECT;
TMP_KEYDEPENDENCIES.MISCMASK  ~DS:RBX.MISCMASK;
BREAK;
REPORT_KEY:
40-88 Vol. 3D

SGX INSTRUCTION REFERENCES

//Determine values key is based on
TMP_KEYDEPENDENCIES.KEYNAME  REPORT_KEY;
TMP_KEYDEPENDENCIES.ISVPRODID  0;
TMP_KEYDEPENDENCIES.ISVSVN  0;
TMP_KEYDEPENDENCIES.SGXOWNEREPOCH  CR_SGXOWNEREPOCH;
TMP_KEYDEPENDENCIES.ATTRIBUTES  TMP_CURRENTSECS.ATTRIBUTES;
TMP_KEYDEPENDENCIES.ATTRIBUTESMASK  0;
TMP_KEYDEPENDENCIES.MRENCLAVE  TMP_CURRENTSECS.MRENCLAVE;
TMP_KEYDEPENDENCIES.MRSIGNER  0;
TMP_KEYDEPENDENCIES.KEYID  DS:RBX.KEYID;
TMP_KEYDEPENDENCIES.SEAL_KEY_FUSES  CR_SEAL_FUSES;
TMP_KEYDEPENDENCIES.CPUSVN  CR_CPUSVN;
TMP_KEYDEPENDENCIES.PADDING  HARDCODED_PKCS1_5_PADDING;
TMP_KEYDEPENDENCIES.MISCSELECT  TMP_CURRENTSECS.MISCSELECT;
TMP_KEYDEPENDENCIES.MISCMASK  0;
BREAK;
EINITTOKEN_KEY:
(* Check ENCLAVE has LAUNCH capability *)
IF (TMP_CURRENTSECS.ATTRIBUTES.LAUNCHKEY = 0)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ATTRIBUTE;
GOTO EXIT;
FI;
IF (DS:RBX.CPUSVN is beyond current CPU configuration)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_CPUSVN;
GOTO EXIT;
FI;
IF (DS:RBX.ISVSVN > TMP_CURRENTSECS.ISVSVN)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ISVSVN;
GOTO EXIT;
FI;
(* Determine values key is based on *)
TMP_KEYDEPENDENCIES.KEYNAME  EINITTOKEN_KEY;
TMP_KEYDEPENDENCIES.ISVPRODID  TMP_CURRENTSECS.ISVPRODID
TMP_KEYDEPENDENCIES.ISVSVN  DS:RBX.ISVSVN;
TMP_KEYDEPENDENCIES.SGXOWNEREPOCH  CR_SGXOWNEREPOCH;
TMP_KEYDEPENDENCIES.ATTRIBUTES  TMP_ATTRIBUTES;
TMP_KEYDEPENDENCIES.ATTRIBUTESMASK  0;
TMP_KEYDEPENDENCIES.MRENCLAVE  0;
TMP_KEYDEPENDENCIES.MRSIGNER  TMP_CURRENTSECS.MRSIGNER;
TMP_KEYDEPENDENCIES.KEYID  DS:RBX.KEYID;
TMP_KEYDEPENDENCIES.SEAL_KEY_FUSES  CR_SEAL_FUSES;
TMP_KEYDEPENDENCIES.CPUSVN  DS:RBX.CPUSVN;
TMP_KEYDEPENDENCIES.PADDING  TMP_CURRENTSECS.PADDING;
TMP_KEYDEPENDENCIES.MISCSELECT  TMP_MISCSELECT;
TMP_KEYDEPENDENCIES.MISCMASK  0;
BREAK;
PROVISION_KEY:
(* Check ENCLAVE has PROVISIONING capability *)
Vol. 3D 40-89

SGX INSTRUCTION REFERENCES

IF (TMP_CURRENTSECS.ATTRIBUTES.PROVISIONKEY = 0)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ATTRIBUTE;
GOTO EXIT;
FI;
IF (DS:RBX.CPUSVN is beyond current CPU configuration)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_CPUSVN;
GOTO EXIT;
FI;
IF (DS:RBX.ISVSVN > TMP_CURRENTSECS.ISVSVN)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ISVSVN;
GOTO EXIT;
FI;
(* Determine values key is based on *)
TMP_KEYDEPENDENCIES.KEYNAME  PROVISION_KEY;
TMP_KEYDEPENDENCIES.ISVPRODID  TMP_CURRENTSECS.ISVPRODID;
TMP_KEYDEPENDENCIES.ISVSVN  DS:RBX.ISVSVN;
TMP_KEYDEPENDENCIES.SGXOWNEREPOCH  0;
TMP_KEYDEPENDENCIES.ATTRIBUTES  TMP_ATTRIBUTES;
TMP_KEYDEPENDENCIES.ATTRIBUTESMASK  DS:RBX.ATTRIBUTEMASK;
TMP_KEYDEPENDENCIES.MRENCLAVE  0;
TMP_KEYDEPENDENCIES.MRSIGNER  TMP_CURRENTSECS.MRSIGNER;
TMP_KEYDEPENDENCIES.KEYID  0;
TMP_KEYDEPENDENCIES.SEAL_KEY_FUSES  0;
TMP_KEYDEPENDENCIES.CPUSVN  DS:RBX.CPUSVN;
TMP_KEYDEPENDENCIES.PADDING  TMP_CURRENTSECS.PADDING;
TMP_KEYDEPENDENCIES.MISCSELECT  TMP_MISCSELECT;
TMP_KEYDEPENDENCIES.MISCMASK  ~DS:RBX.MISCMASK;
BREAK;
PROVISION_SEAL_KEY:
(* Check ENCLAVE has PROVISIONING capability *)
IF (TMP_CURRENTSECS.ATTRIBUTES.PROVISIONKEY = 0)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ATTRIBUTE;
GOTO EXIT;
FI;
IF (DS:RBX.CPUSVN is beyond current CPU configuration)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_CPUSVN;
GOTO EXIT;
FI;
IF (DS:RBX.ISVSVN > TMP_CURRENTSECS.ISVSVN)
THEN
RFLAGS.ZF  1;
RAX  SGX_INVALID_ISVSVN;
GOTO EXIT;
FI;
40-90 Vol. 3D

SGX INSTRUCTION REFERENCES

(* Determine values key is based on *)
TMP_KEYDEPENDENCIES.KEYNAME  PROVISION_SEAL_KEY;
TMP_KEYDEPENDENCIES.ISVPRODID  TMP_CURRENTSECS.ISVPRODID;
TMP_KEYDEPENDENCIES.ISVSVN  DS:RBX.ISVSVN;
TMP_KEYDEPENDENCIES.SGXOWNEREPOCH  0;
TMP_KEYDEPENDENCIES.ATTRIBUTES  TMP_ATTRIBUTES;
TMP_KEYDEPENDENCIES.ATTRIBUTESMASK  DS:RBX.ATTRIBUTEMASK;
TMP_KEYDEPENDENCIES.MRENCLAVE  0;
TMP_KEYDEPENDENCIES.MRSIGNER  TMP_CURRENTSECS.MRSIGNER;
TMP_KEYDEPENDENCIES.KEYID  0;
TMP_KEYDEPENDENCIES.SEAL_KEY_FUSES  CR_SEAL_FUSES;
TMP_KEYDEPENDENCIES.CPUSVN  DS:RBX.CPUSVN;
TMP_KEYDEPENDENCIES.PADDING  TMP_CURRENTSECS.PADDING;
TMP_KEYDEPENDENCIES.MISCSELECT  TMP_MISCSELECT;
TMP_KEYDEPENDENCIES.MISCMASK  ~DS:RBX.MISCMASK;
BREAK;
DEFAULT:
(* The value of KEYNAME is invalid *)
RFLAGS.ZF  1;
RAX  SGX_INVALID_KEYNAME;
GOTO EXIT:
ESAC;
(* Calculate the final derived key and output to the address in RCX *)
TMP_OUTPUTKEY  derivekey(TMP_KEYDEPENDENCIES);
DS:RCX[15:0]  TMP_OUTPUTKEY;
RAX  0;
RFLAGS.ZF  0;
EXIT:
RFLAGS.CF  0;
RFLAGS.PF  0;
RFLAGS.AF  0;
RFLAGS.OF  0;
RFLAGS.SF  0;
Flags Affected
ZF is cleared if successful, otherwise ZF is set. CF, PF, AF, OF, SF are cleared.
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the current enclave.
If an effective address is not properly aligned.
If an effective address is outside the DS segment limit.
If KEYREQUEST format is invalid.

#PF(error code)

If a page fault occurs in accessing memory.

64-Bit Mode Exceptions
#GP(0)

If a memory operand effective address is outside the current enclave.
If an effective address is not properly aligned.
If an effective address is not canonical.
If KEYREQUEST format is invalid.

#PF(error code)

If a page fault occurs in accessing memory operands.

Vol. 3D 40-91

SGX INSTRUCTION REFERENCES

EMODPE—Extend an EPC Page Permissions
Opcode/
Instruction

Op/En

EAX = 06H
ENCLU[EMODPE]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX2

Description

This leaf function extends the access rights of an existing EPC
page.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

IR

EMODPE (In)

Address of a SECINFO (In)

Address of the destination EPC page (In)

Description
This leaf function extends the access rights associated with an existing EPC page in the running enclave. THE RWX
bits of the SECINFO parameter are treated as a permissions mask; supplying a value that does not extend the page
permissions will have no effect. This instruction leaf can only be executed when inside the enclave.
RBX contains the effective address of a SECINFO structure while RCX contains the effective address of an EPC page.
The table below provides additional information on the memory parameter of the EMODPE leaf function.

EMODPE Memory Parameter Semantics
SECINFO

EPCPAGE

Read access permitted by Non Enclave

Read access permitted by Enclave

The instruction faults if any of the following:

EMODPE Faulting Conditions
The operands are not properly aligned.

If security attributes of the SECINFO page make the page inaccessible.

The EPC page is locked by another thread.

RBX does not contain an effective address in an EPC page in the running enclave.

The EPC page is not valid.

RCX does not contain an effective address of an EPC page in the running enclave.

SECINFO contains an invalid request.
Concurrency Restrictions

Table 40-60. Concurrency Restrictions of EMODPE with Other Intel® SGX Operations 1 of 2
Operation

EEXIT

Param
EMODPE

TCS SSA

SECS

EADD

EBLOCK

Targ SECS

Targ SECS

ECRE
ATE
SECS

EDBGRD/
WR
Targ SECS

EENTER/
ERESUME

EEXTEND

EGETKEY

EINIT

TCS SSA SECS Targ SECS Param SECS

Targ

Y

Y

Y

Y

SECIN
FO

U

Y

U

U

SECS

EP
A

ELDB/ELDU
Targ VA

SECS VA

Table 40-61. Concurrency Restrictions of EMODPE with Other Intel® SGX Operations 2 of 2
Operation
Param
EMODP
E

EREMOVE

EREPORT

Targ SECS Param SECS

ETRACK
SECS

EWB
SRC

VA

EAUG

EMODPE

Targ

Y

N

Y

SECIN
FO

U

Y

Y

40-92 Vol. 3D

EMODPR

SECS Targ SECS Targ SECI Targ SEC
NFO
S
N

EMODT

EACCEPT

EACCEPTCOPY

Targ SEC
S

Targ SECI
NFO

SECS Targ SR
C

SECI
NFO

N

N

Y

Y

Y

Y

Y

Y

Y

SGX INSTRUCTION REFERENCES

Operation

Temp Variables in EMODPE Operational Flow
Name

Type

Size (bits)

Description

SCRATCH_SECINFO

SECINFO

512

Scratch storage for holding the contents of DS:RBX.

IF (DS:RBX is not 64Byte Aligned)
THEN #GP(0); FI;
IF (DS:RCX is not 4KByte Aligned)
THEN #GP(0); FI;
IF ((DS:RBX is not within CR_ELRANGE) or (DS:RCX is not within CR_ELRANGE) )
THEN #GP(0); FI;
IF (DS:RBX does not resolve within an EPC)
THEN #PF(DS:RBX); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #PF(DS:RCX); FI;
IF ( (EPCM(DS:RBX).VALID = 0) or (EPCM(DS:RBX).R = 0) or (EPCM(DS:RBX).PENDING ≠ 0) or (EPCM(DS:RBX).MODIFIED ≠ 0) or
(EPCM(DS:RBX).BLOCKED ≠ 0) or (EPCM(DS:RBX).PT ≠ PT_REG) or (EPCM(DS:RBX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or
(EPCM(DS:RBX).ENCLAVEADDRESS ≠ (DS:RBX & ~0xFFF)) )
THEN #PF(DS:RBX); FI;
SCRATCH_SECINFO  DS:RBX;
(* Check for mis-configured SECINFO flags*)
IF (SCRATCH_SECINFO reserved fields are not zero )
THEN #GP(0); FI;
(* Check security attributes of the EPC page *)
IF ( (EPCM(DS:RCX).VALID = 0) or (EPCM(DS:RCX).PENDING ≠ 0) or (EPCM(DS:RCX).MODIFIED ≠ 0) or
(EPCM(DS:RCX).BLOCKED ≠ 0) or (EPCM(DS:RCX).PT ≠ PT_REG) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) )
THEN #PF(DS:RCX); FI;
(* Check the EPC page for concurrency *)
IF (EPC page in use by another SGX2 instruction)
THEN #GP(0); FI;
(* Re-Check security attributes of the EPC page *)
IF ( (EPCM(DS:RCX).VALID = 0) or (EPCM(DS:RCX).PENDING ≠ 0) or (EPCM(DS:RCX).MODIFIED ≠ 0) or
(EPCM(DS:RCX).PT ≠ PT_REG) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or
(EPCM(DS:RCX).ENCLAVEADDRESS ≠ DS:RCX))
THEN #PF(DS:RCX); FI;
(* Check for mis-configured SECINFO flags*)
IF ( (EPCM(DS:RCX).R = 0) and (SCRATCH_SECINFO.FLAGS.R = 0) and (SCRATCH_SECINFO.FLAGS.W ≠ 0) ))
THEN #GP(0); FI;

Vol. 3D 40-93

SGX INSTRUCTION REFERENCES

(* Update EPCM permissions *)
EPCM(DS:RCX).R  EPCM(DS:RCX).R | SCRATCH_SECINFO.FLAGS.R;
EPCM(DS:RCX).W  EPCM(DS:RCX).W | SCRATCH_SECINFO.FLAGS.W;
EPCM(DS:RCX).X  EPCM(DS:RCX).X | SCRATCH_SECINFO.FLAGS.X;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If a memory operand effective address is outside the DS segment limit.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

If a page fault occurs in accessing memory operands.

64-Bit Mode Exceptions
#GP(0)

If a memory operand is non-canonical form.
If a memory operand is not properly aligned.
If a memory operand is locked.

#PF(error code)

40-94 Vol. 3D

If a page fault occurs in accessing memory operands.

SGX INSTRUCTION REFERENCES

EREPORT—Create a Cryptographic Report of the Enclave
Opcode/
Instruction

Op/En

EAX = 00H
ENCLU[EREPORT]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function creates a cryptographic report of the enclave.

Instruction Operand Encoding
Op/En

EAX

RBX

RCX

RDX

IR

EREPORT (In)

Address of TARGETINFO
(In)

Address of REPORTDATA
(In)

Address where the REPORT is
written to in an OUTPUTDATA (In)

Description
This leaf function creates a cryptographic REPORT that describes the contents of the enclave. This instruction leaf
can only be executed when inside the enclave. The cryptographic report can be used by other enclaves to determine that the enclave is running on the same platform.
RBX contains the effective address of the MRENCLAVE value of the enclave that will authenticate the REPORT
output, using the REPORT key delivered by EGETKEY command for that enclave. RCX contains the effective address
of a 64-byte REPORTDATA structure, which allows the caller of the instruction to associate data with the enclave
from which the instruction is called. RDX contains the address where the REPORT will be output by the instruction.

EREPORT Memory Parameter Semantics
TARGETINFO

REPORTDATA

OUTPUTDATA

Read access by Enclave

Read access by Enclave

Read/Write access by Enclave

This instruction leaf perform the following:
1. Validate the 3 operands (RBX, RCX, RDX) are inside the enclave.
2. Compute a report key for the target enclave, as indicated by the value located in RBX(TARGETINFO).
3. Assemble the enclave SECS data to complete the REPORT structure (including the data provided using the RCX
(REPORTDATA) operand).
4. Computes a crytpographic hash over REPORT structure.
5. Add the computed hash to the REPORT structure.
6. Output the completed REPORT structure to the address in RDX (OUTPUTDATA).
The instruction fails if the operands are not properly aligned.
CR_REPORT_KEYID, used to provide key wearout protection, is populated with a statistically unique value on boot
of the platform by a trusted entity within the SGX TCB.
The instruction faults if any of the following:

Vol. 3D 40-95

SGX INSTRUCTION REFERENCES

EREPORT Faulting Conditions
An effective address not properly aligned.

An memory address does not resolve in an EPC page.

If accessing an invalid EPC page.

If the EPC page is blocked.

May page fault.
Concurrency Restrictions

Table 40-62. Concurrency Restrictions of EREPORT with Other Intel® SGX Operations 1 of 2
Operation

EEXIT

Param
EREPORT

TCS SSA

EADD

EBLOCK

ECRE
ATE

SECS Targ SECS

Targ SECS

SECS

Y

Y

Y

Targ SECS

U

Param
SECS

EDBGRD/
WR

EENTER/
ERESUME

Y

Y

U

Y

Y

EGETKEY

TCS SSA SECS Targ SECS Param SECS

Y
Y

EEXTEND

Y

EINIT

ELDB/ELDU

EPA

SECS

Targ VA

SECS VA

Y

Y

Y

U

Y

Y

Y

Y

Y

Y

Y

Y

Table 40-63. Concurrency Restrictions of EREPORT with Other Intel® SGX Operations 2 of 2
Operation
Param
EREPORT

EREMOVE

ETRACK

EWB

EAUG

Y

Y

Y

Y

EMODPE

EMODPR

SECS

SRC

VA

SECS Targ SECS Targ SECI Targ SEC
NFO
S

Y

Y

Y

Y

U

Param
SECS

EREPORT

Targ SECS Param SECS

Y

Y

Y

U

Y

Y

Y

Y

EMODT
Targ SEC
S
Y

Y

EACCEPT
Targ SECI
NFO
Y

U

Y

Y

EACCEPTCOPY

SECS Targ SR
C
Y

Y

Y

U

Y

Y

Operation

Temp Variables in EREPORT Operational Flow
Name

Type

TMP_ATTRIBUTES

Size (bits)

Description

32

Physical address of SECS of the enclave to which source operand belongs.

TMP_CURRENTSECS

Address of the SECS for the currently executing enclave.

TMP_KEYDEPENDENCIES

Temp space for key derivation.

TMP_REPORTKEY

128

TMP_REPORT

3712

REPORTKEY generated by the instruction.

TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));
(* Address verification for TARGETINFO (RBX) *)
IF ( (DS:RBX is not 512Byte Aligned) or (DS:RBX is not within CR_ELRANGE) )
THEN #GP(0); FI;
IF (DS:RBX does not resolve within an EPC)
THEN #PF(DS:RBX); FI;
IF (EPCM(DS:RBX). VALID = 0)
THEN #PF(DS:RBX); FI;
IF (EPCM(DS:RBX).BLOCKED = 1) )
THEN #PF(DS:RBX); FI;
(* Check page parameters for correctness *)
IF ( (EPCM(DS:RBX).PT ≠ PT_REG) or (EPCM(DS:RBX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or (EPCM(DS:RBX).PENDING = 1) or
(EPCM(DS:RBX).MODIFIED = 1) or (EPCM(DS:RBX).ENCLAVEADDRESS ≠ (DS:RBX & ~0FFFH) ) or (EPCM(DS:RBX).R = 0) )

40-96 Vol. 3D

SECI
NFO

SGX INSTRUCTION REFERENCES

THEN #PF(DS:RBX);
FI;
(* Address verification for REPORTDATA (RCX) *)
IF ( (DS:RCX is not 128Byte Aligned) or (DS:RCX is not within CR_ELRANGE) )
THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
THEN #P(DS:RCX); FI;
IF (EPCM(DS:RCX). VALID = 0)
THEN #PF(DS:RCX); FI;
IF (EPCM(DS:RCX).BLOCKED = 1) )
THEN #PF(DS:RCX); FI;
(* Check page parameters for correctness *)
IF ( (EPCM(DS:RCX).PT ≠ PT_REG) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or (EPCM(DS:RCX).PENDING = 1) or
(EPCM(DS:RCX).MODIFIED = 1) or (EPCM(DS:RCX).ENCLAVEADDRESS ≠ (DS:RCX & ~0FFFH) ) or (EPCM(DS:RCX).R = 0) )
THEN #PF(DS:RCX);
FI;
(* Address verification for OUTPUTDATA (RDX) *)
IF ( (DS:RDX is not 512Byte Aligned) or (DS:RDX is not within CR_ELRANGE) )
THEN #GP(0); FI;
IF (DS:RDX does not resolve within an EPC)
THEN #PF(DS:RDX); FI;
IF (EPCM(DS:RDX). VALID = 0)
THEN #PF(DS:RDX); FI;
IF (EPCM(DS:RDX).BLOCKED = 1) )
THEN #PF(DS:RDX); FI;
(* Check page parameters for correctness *)
IF ( (EPCM(DS:RDX).PT ≠ PT_REG) or (EPCM(DS:RDX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or (EPCM(DS:RCX).PENDING = 1) or
(EPCM(DS:RCX).MODIFIED = 1) or (EPCM(DS:RDX).ENCLAVEADDRESS ≠ (DS:RDX & ~0FFFH) ) or (EPCM(DS:RDX).W = 0) )
THEN #PF(DS:RDX);
FI;
(* REPORT MAC needs to be computed over data which cannot be modified *)
TMP_REPORT.CPUSVN  CR_CPUSVN;
TMP_REPORT.ISVPRODID  TMP_CURRENTSECS.ISVPRODID;
TMP_REPORT.ISVSVN  TMP_CURRENTSECS..ISVSVN;
TMP_REPORT.ATTRIBUTES  TMP_CURRENTSECS.ATTRIBUTES;
TMP_REPORT.REPORTDATA  DS:RCX[511:0];
TMP_REPORT.MRENCLAVE  TMP_CURRENTSECS.MRENCLAVE;
TMP_REPORT.MRSIGNER  TMP_CURRENTSECS.MRSIGNER;
TMP_REPORT.MRRESERVED  0;
TMP_REPORT.KEYID[255:0]  CR_REPORT_KEYID;
TMP_REPORT.MISCSELECT  TMP_CURRENTSECS.MISCSELECT;

Vol. 3D 40-97

SGX INSTRUCTION REFERENCES

(* Derive the report key *)
TMP_KEYDEPENDENCIES.KEYNAME  REPORT_KEY;
TMP_KEYDEPENDENCIES.ISVPRODID  0;
TMP_KEYDEPENDENCIES.ISVSVN  0;
TMP_KEYDEPENDENCIES.SGXOWNEREPOCH  CR_SGXOWNEREPOCH;
TMP_KEYDEPENDENCIES.ATTRIBUTES  DS:RBX.ATTRIBUTES;
TMP_KEYDEPENDENCIES.ATTRIBUTESMASK  0;
TMP_KEYDEPENDENCIES.MRENCLAVE  DS:RBX.MEASUREMENT;
TMP_KEYDEPENDENCIES.MRSIGNER  0;
TMP_KEYDEPENDENCIES.KEYID  TMP_REPORT.KEYID;
TMP_KEYDEPENDENCIES.SEAL_KEY_FUSES  CR_SEAL_FUSES;
TMP_KEYDEPENDENCIES.CPUSVN  CR_CPUSVN;
TMP_KEYDEPENDENCIES.PADDING  TMP_CURRENTSECS.PADDING;
TMP_KEYDEPENDENCIES.MISCSELECT  DS:RBX.MISCSELECT;
TMP_KEYDEPENDENCIES.MISCMASK  0;
(* Calculate the derived key*)
TMP_REPORTKEY  derive_key(TMP_KEYDEPENDENCIES);
(* call cryptographic CMAC function, CMAC data are not including MAC&KEYID *)
TMP_REPORT.MAC  cmac(TMP_REPORTKEY, TMP_REPORT[3071:0] );
DS:RDX[3455: 0]  TMP_REPORT;
Flags Affected
None
Protected Mode Exceptions
#GP(0)

If the address in RCS is outside the DS segment limit.
If a memory operand is not properly aligned.
If a memory operand is not in the current enclave.

#PF(error code)

If a page fault occurs in accessing memory operands.

64-Bit Mode Exceptions
#GP(0)

If RCX is non-canonical form.
If a memory operand is not properly aligned.
If a memory operand is not in the current enclave.

#PF(error code)

40-98 Vol. 3D

If a page fault occurs in accessing memory operands.

SGX INSTRUCTION REFERENCES

ERESUME—Re-Enters an Enclave
Opcode/
Instruction

Op/En

EAX = 03H
ENCLU[ERESUME]

IR

64/32
bit Mode
Support
V/V

CPUID
Feature
Flag
SGX1

Description

This leaf function is used to re-enter an enclave after an interrupt.

Instruction Operand Encoding
Op/En

RAX

RBX

RCX

IR

ERESUME (In)

Address of a TCS (In)

Address of AEP (In)

Description
The ENCLU[ERESUME] instruction resumes execution of an enclave that was interrupted due to an exception or
interrupt, using the machine state previously stored in the SSA.

ERESUME Memory Parameter Semantics
TCS
Enclave read/write access
The instruction faults if any of the following:

Address in RBX is not properly aligned.

Any TCS.FLAGS’s must-be-zero bit is not zero.

TCS pointed to by RBX is not valid or available or
locked.

Current 32/64 mode does not match the enclave mode in
SECS.ATTRIBUTES.MODE64.

The SECS is in use by another enclave.

Either of TCS-specified FS and GS segment is not a subset of the current DS
segment.

Any one of DS, ES, CS, SS is not zero.

If XSAVE available, CR4.OSXSAVE = 0, but SECS.ATTRIBUTES.XFRM ≠ 3.

CR4.OSFXSR ≠ 1.

If CR4.OSXSAVE = 1, SECS.ATTRIBUTES.XFRM is not a subset of XCR0.

Offsets 520-535 of the XSAVE area not 0.

The bit vector stored at offset 512 of the XSAVE area must be a subset of
SECS.ATTRIBUTES.XFRM.

The SSA frame is not valid or in use.
The following operations are performed by ERESUME:

•

RSP and RBP are saved in the current SSA frame on EENTER and are automatically restored on EEXIT or an
asynchronous exit due to any Interrupt event.

•

The AEP contained in RCX is stored into the TCS for use by AEXs.FS and GS (including hidden portions) are
saved and new values are constructed using TCS.OFSBASE/GSBASE (32 and 64-bit mode) and
TCS.OFSLIMIT/GSLIMIT (32-bit mode only). The resulting segments must be a subset of the DS segment.

•

If CR4.OSXSAVE == 1, XCR0 is saved and replaced by SECS.ATTRIBUTES.XFRM. The effect of RFLAGS.TF
depends on whether the enclave entry is opt-in or opt-out (see Section 42.1.2):
— On opt-out entry, TF is saved and cleared (it is restored on EEXIT or AEX). Any attempt to set TF via a POPF
instruction while inside the enclave clears TF (see Section 42.2.5).
— On opt-in entry, a single-step debug exception is pended on the instruction boundary immediately after
EENTER (see Section 42.2.3).

•

All code breakpoints that do not overlap with ELRANGE are also suppressed. If the entry is an opt-out entry, all
code and data breakpoints that overlap with the ELRANGE are suppressed.

Vol. 3D 40-99

SGX INSTRUCTION REFERENCES

•

On opt-out entry, a number of performance monitoring counters and behaviors are modified or suppressed (see
Section 42.2.3):
— All performance monitoring activity on the current thread is suppressed except for incrementing and firing
of FIXED_CTR1 and FIXED_CTR2.
— PEBS is suppressed.
— AnyThread counting on other threads is demoted to MyThread mode and IA32_PERF_GLOBAL_STATUS[60]
on that thread is set.
— If the opt-out entry on a hardware thread results in suppression of any performance monitoring, then the
processor sets IA32_PERF_GLOBAL_STATUS[60] and IA32_PERF_GLOBAL_STATUS[63].

Concurrency Restrictions

Table 40-64. Concurrency Restrictions of ERESUME with Intel® SGX Instructions - 1of 2
Operation

ERESU
ME

EEXIT

Param

Targ VA

TCS

N

EADD

ECRE
ATE

EBLOCK

SECS Targ SECS Targ SECS
N
Y

N

Y

Y

EEXTEND

EGETKEY

SECS

Targ SECS

TCS SSA SECS Targ SECS Param SECS

Y

N

Y
Y

EENTER/
ERESUME

N

U

SSA
SECS

EDBGRD/
WR

Y

Y

Y

EINIT

ELDB/ELDU

SECS

Targ VA

SECS VA

N

Y

U

Y

Y

EPA

N

U
Y

Y

N

Y

Y

N

Y

Y

Y

Y

Table 40-65. Concurrency Restrictions of ERESUME with Intel® SGX Instructions - 2 of 2
Operation

ERESU
ME

EREMOVE

EREPORT

ETRA
CK

EWB

Param

Targ SECS Param SECS SECS

SRC VA

TCS

N

N

SSA
SECS

EAUG
SECS Targ SECS

Y

Y

Y

Y

Targ

SECI
NFO

Y

U

EMODPR
Targ

SECS

N
Y

Y

EMODT
Targ

SECS

EACCEPT
Targ SECI
NFO

EACCEPTCOPY

SECS Targ SRC

SECI
NFO

N

U
Y

EMODPE

Y

Y
Y

U

Y

U

U

Y

Operation

Temp Variables in ERESUME Operational Flow
Name

Type

Size

Description

TMP_FSBASE

Effective Address

32/64

Proposed base address for FS segment.

TMP_GSBASE

Effective Address

32/64

Proposed base address for FS segment.

TMP_FSLIMIT

Effective Address

32/64

Highest legal address in proposed FS segment.

TMP_GSLIMIT

Effective Address

32/64

Highest legal address in proposed GS segment.

TMP_TARGET

Effective Address

32/64

Address of first instruction inside enclave at which execution is to resume.

TMP_SECS

Effective Address

32/64

Physical address of SECS for this enclave.

TMP_SSA

Effective Address

32/64

Address of current SSA frame.

TMP_XSIZE

integer

64

Size of XSAVE area based on SECS.ATTRIBUTES.XFRM.

TMP_SSA_PAGE

Effective Address

32/64

Pointer used to iterate over the SSA pages in the current frame.

TMP_GPR

Effective Address

32/64

Address of the GPR area within the current SSA frame.

TMP_BRANCH_RECORD

LBR Record

TMP_MODE64  ((IA32_EFER.LMA = 1) && (CS.L = 1));

40-100 Vol. 3D

From/to addresses to be pushed onto the LBR stack.

SGX INSTRUCTION REFERENCES

(* Make sure DS is usable, expand up *)
IF (TMP_MODE64 = 0 and (DS not usable or ( ( DS[S] = 1) and (DS[bit 11] = 0) and DS[bit 10] = 1) ) ) )
THEN #GP(0); FI;
(* Check that CS, SS, DS, ES.base is 0 *)
IF (TMP_MODE64 = 0)
THEN
IF(CS.base ≠ 0 or DS.base ≠ 0) #GP(0); FI;
IF(ES usable and ES.base ≠ 0) #GP(0); FI;
IF(SS usable and SS.base ≠ 0) #GP(0); FI;
IF(SS usable and SS.B = 0) #GP(0); FI;
FI;
IF (DS:RBX is not 4KByte Aligned)
THEN #GP(0); FI;
IF (DS:RBX does not resolve within an EPC)
THEN #PF(DS:RBX); FI;
(* Check AEP is canonical*)
IF (TMP_MODE64 = 1 and (CS:RCX is not canonical) )
THEN #GP(0); FI;
(* Check concurrency of TCS operation*)
IF (Other Intel SGX instructions is operating on TCS)
THEN #GP(0); FI;
(* TCS verification *)
IF (EPCM(DS:RBX).VALID = 0)
THEN #PF(DS:RBX); FI;
IF (EPCM(DS:RBX).BLOCKED = 1)
THEN #PF(DS:RBX); FI;
IF ((EPCM(DS:RBX).PENDING = 1) or (EPCM(DS:RBX).MODIFIED = 1))
THEN #PF(DS:RBX); FI;
IF ( (EPCM(DS:RBX).ENCLAVEADDRESS ≠ DS:RBX) or (EPCM(DS:RBX).PT ≠ PT_TCS) )
THEN #PF(DS:RBX); FI;
IF ( (DS:RBX).OSSA is not 4KByte Aligned)
THEN #GP(0); FI;
(* Check proposed FS and GS *)
IF ( ( (DS:RBX).OFSBASE is not 4KByte Aligned) or ( (DS:RBX).OGSBASE is not 4KByte Aligned) )
THEN #GP(0); FI;
(* Get the SECS for the enclave in which the TCS resides *)
TMP_SECS  Address of SECS for TCS;
(* Make sure that the FLAGS field in the TCS does not have any reserved bits set *)
IF ( ( (DS:RBX).FLAGS & & FFFFFFFFFFFFFFFEH) ≠ 0)
THEN #GP(0); FI;

Vol. 3D 40-101

SGX INSTRUCTION REFERENCES

(* SECS must exist and enclave must have previously been EINITted *)
IF (the enclave is not already initialized)
THEN #GP(0); FI;
(* make sure the logical processor’s operating mode matches the enclave *)
IF ( (TMP_MODE64 ≠ TMP_SECS.ATTRIBUTES.MODE64BIT) )
THEN #GP(0); FI;
IF (CR4.OSFXSR = 0)
THEN #GP(0); FI;
(* Check for legal values of SECS.ATTRIBUTES.XFRM *)
IF (CR4.OSXSAVE = 0)
THEN
IF (TMP_SECS.ATTRIBUTES.XFRM ≠ 03H) THEN #GP(0); FI;
ELSE
IF ( (TMP_SECS.ATTRIBUTES.XFRM & XCR0) ≠ TMP_SECS.ATTRIBUTES.XFRM) THEN #GP(0); FI;
FI;
(* Make sure the SSA contains at least one active frame *)
IF ( (DS:RBX).CSSA = 0)
THEN #GP(0); FI;
(* Compute linear address of SSA frame *)
TMP_SSA  (DS:RBX).OSSA + TMP_SECS.BASEADDR + 4096 * TMP_SECS.SSAFRAMESIZE * ( (DS:RBX).CSSA - 1);
TMP_XSIZE  compute_XSAVE_frame_size(TMP_SECS.ATTRIBUTES.XFRM);
FOR EACH TMP_SSA_PAGE = TMP_SSA to TMP_SSA + TMP_XSIZE
(* Check page is read/write accessible *)
Check that DS:TMP_SSA_PAGE is read/write accessible;
If a fault occurs, release locks, abort and deliver that fault;
IF (DS:TMP_SSA_PAGE does not resolve to EPC page)
THEN #PF(DS:TMP_SSA_PAGE); FI;
IF (EPCM(DS:TMP_SSA_PAGE).VALID = 0)
THEN #PF(DS:TMP_SSA_PAGE); FI;
IF (EPCM(DS:TMP_SSA_PAGE).BLOCKED = 1)
THEN #PF(DS:TMP_SSA_PAGE); FI;
IF ((EPCM(DS:TMP_SSA_PAGE).PENDING = 1) or (EPCM(DS:TMP_SSA_PAGE_.MODIFIED = 1))
THEN #PF(DS:TMP_SSA_PAGE); FI;
IF ( ( EPCM(DS:TMP_SSA_PAGE).ENCLAVEADDRESS ≠ DS:TMPSSA_PAGE) or (EPCM(DS:TMP_SSA_PAGE).PT ≠ PT_REG) or
(EPCM(DS:TMP_SSA_PAGE).ENCLAVESECS ≠ EPCM(DS:RBX).ENCLAVESECS) or
(EPCM(DS:TMP_SSA_PAGE).R = 0) or (EPCM(DS:TMP_SSA_PAGE).W = 0) )
THEN #PF(DS:TMP_SSA_PAGE); FI;
CR_XSAVE_PAGE_n  Physical_Address(DS:TMP_SSA_PAGE);
ENDFOR
(* Compute address of GPR area*)
TMP_GPR  TMP_SSA + 4096 * DS:TMP_SECS.SSAFRAMESIZE -- sizeof(GPRSGX_AREA);
Check that DS:TMP_SSA_PAGE is read/write accessible;
If a fault occurs, release locks, abort and deliver that fault;
IF (DS:TMP_GPR does not resolve to EPC page)
THEN #PF(DS:TMP_GPR); FI;
IF (EPCM(DS:TMP_GPR).VALID = 0)
THEN #PF(DS:TMP_GPR); FI;
40-102 Vol. 3D

SGX INSTRUCTION REFERENCES

IF (EPCM(DS:TMP_GPR).BLOCKED = 1)
THEN #PF(DS:TMP_GPR); FI;
IF ((EPCM(DS:TMP_GPR).PENDING = 1) or (EPCM(DS:TMP_GPR).MODIFIED = 1))
THEN #PF(DS:TMP_GPR); FI;
IF ( ( EPCM(DS:TMP_GPR).ENCLAVEADDRESS ≠ DS:TMP_GPR) or (EPCM(DS:TMP_GPR).PT ≠ PT_REG) or
(EPCM(DS:TMP_GPR).ENCLAVESECS ≠ EPCM(DS:RBX).ENCLAVESECS) or
(EPCM(DS:TMP_GPR).R = 0) or (EPCM(DS:TMP_GPR).W = 0) )
THEN #PF(DS:TMP_GPR); FI;
IF (TMP_MODE64 = 0)
THEN
IF (TMP_GPR + (GPR_SIZE -1) is not in DS segment) THEN #GP(0); FI;
FI;
CR_GPR_PA  Physical_Address (DS: TMP_GPR);
TMP_TARGET  (DS:TMP_GPR).RIP;
IF (TMP_MODE64 = 1)
THEN
IF (TMP_TARGET is not canonical) THEN #GP(0); FI;
ELSE
IF (TMP_TARGET > CS limit) THEN #GP(0); FI;
FI;
(* Check proposed FS/GS segments fall within DS *)
IF (TMP_MODE64 = 0)
THEN
TMP_FSBASE  (DS:RBX).OFSBASE + TMP_SECS.BASEADDR;
TMP_FSLIMIT  (DS:RBX).OFSBASE + TMP_SECS.BASEADDR + (DS:RBX).FSLIMIT;
TMP_GSBASE  (DS:RBX).OGSBASE + TMP_SECS.BASEADDR;
TMP_GSLIMIT  (DS:RBX).OGSBASE + TMP_SECS.BASEADDR + (DS:RBX).GSLIMIT;
(* if FS wrap-around, make sure DS has no holes*)
IF (TMP_FSLIMIT < TMP_FSBASE)
THEN
IF (DS.limit < 4GB) THEN #GP(0); FI;
ELSE
IF (TMP_FSLIMIT > DS.limit) THEN #GP(0); FI;
FI;
(* if GS wrap-around, make sure DS has no holes*)
IF (TMP_GSLIMIT < TMP_GSBASE)
THEN
IF (DS.limit < 4GB) THEN #GP(0); FI;
ELSE
IF (TMP_GSLIMIT > DS.limit) THEN #GP(0); FI;
FI;
ELSE
TMP_FSBASE  (DS:RBX).OFSBASE + TMP_SECS.BASEADDR;
TMP_GSBASE  (DS:RBX).OGSBASE + TMP_SECS.BASEADDR;
IF ( (TMP_FSBASE is not canonical) or (TMP_GSBASE is not canonical))
THEN #GP(0); FI;
FI;
(* Ensure the enclave is not already active and this thread is the only one using the TCS*)
IF (DS:RBX.STATE = ACTIVE))
Vol. 3D 40-103

SGX INSTRUCTION REFERENCES

THEN #GP(0); FI;
(* SECS.ATTRIBUTES.XFRM selects the features to be saved. *)
(* CR_XSAVE_PAGE_n: A list of 1 or more physical address of pages that contain the XSAVE area. *)
XRSTOR(TMP_MODE64, SECS.ATTRIBUTES.XFRM, CR_XSAVE_PAGE_n);
IF (XRSTOR failed with #GP)
THEN
DS:RBX.STATE  INACTIVE;
#GP(0);
FI;
CR_ENCLAVE_MODE  1;
CR_ACTIVE_SECS  TMP_SECS;
CR_ELRANGE  (TMP_SECS.BASEADDR, TMP_SECS.SIZE);
(* Save sate for possible AEXs *)
CR_TCS_PA  Physical_Address (DS:RBX);
CR_TCS_LA  RBX;
CR_TCS_LA.AEP  RCX;
(* Save the hidden portions of FS and GS *)
CR_SAVE_FS_selector  FS.selector;
CR_SAVE_FS_base  FS.base;
CR_SAVE_FS_limit  FS.limit;
CR_SAVE_FS_access_rights  FS.access_rights;
CR_SAVE_GS_selector  GS.selector;
CR_SAVE_GS_base  GS.base;
CR_SAVE_GS_limit  GS.limit;
CR_SAVE_GS_access_rights  GS.access_rights;
RIP  TMP_TARGET;
Restore_GPRs from DS:TMP_GPR;
(*Restore the RFLAGS values from SSA*)
RFLAGS.CF  DS:TMP_GPR.RFLAGS.CF;
RFLAGS.PF  DS:TMP_GPR.RFLAGS.PF;
RFLAGS.AF  DS:TMP_GPR.RFLAGS.AF;
RFLAGS.ZF  DS:TMP_GPR.RFLAGS.ZF;
RFLAGS.SF  DS:TMP_GPR.RFLAGS.SF;
RFLAGS.DF  DS:TMP_GPR.RFLAGS.DF;
RFLAGS.OF  DS:TMP_GPR.RFLAGS.OF;
RFLAGS.NT  DS:TMP_GPR.RFLAGS.NT;
RFLAGS.AC  DS:TMP_GPR.RFLAGS.AC;
RFLAGS.ID  DS:TMP_GPR.RFLAGS.ID;
RFLAGS.RF  DS:TMP_GPR.RFLAGS.RF;
RFLAGS.VM  0;
IF (RFLAGS.IOPL = 3)
THEN RFLAGS.IF = DS:TMP_GPR.IF; FI;
IF (TCS.FLAGS.OPTIN = 0)
THEN RFLAGS.TF = 0; FI;

40-104 Vol. 3D

SGX INSTRUCTION REFERENCES

(* If XSAVE is enabled, save XCR0 and replace it with SECS.ATTRIBUTES.XFRM*)
IF (CR4.OSXSAVE = 1)
CR_SAVE_XCR0  XCR0;
XCR0  TMP_SECS.ATTRIBUTES.XFRM;
FI;
(* Pop the SSA stack*)
(DS:RBX).CSSA  (DS:RBX).CSSA -1;
(* Do the FS/GS swap *)
FS.base  TMP_FSBASE;
FS.limit  DS:RBX.FSLIMIT;
FS.type  0001b;
FS.W  DS.W;
FS.S  1;
FS.DPL  DS.DPL;
FS.G  1;
FS.B  1;
FS.P  1;
FS.AVL  DS.AVL;
FS.L  DS.L;
FS.unusable  0;
FS.selector  0BH;
GS.base  TMP_GSBASE;
GS.limit  DS:RBX.GSLIMIT;
GS.type  0001b;
GS.W  DS.W;
GS.S  1;
GS.DPL  DS.DPL;
GS.G  1;
GS.B  1;
GS.P  1;
GS.AVL  DS.AVL;
GS.L  DS.L;
GS.unusable  0;
GS.selector  0BH;
CR_DBGOPTIN  TCS.FLAGS.DBGOPTIN;
Suppress all code breakpoints that are outside ELRANGE;
IF (CR_DBGOPTIN = 0)
THEN
Suppress all code breakpoints that overlap with ELRANGE;
CR_SAVE_TF  RFLAGS.TF;
RFLAGS.TF  0;
Suppress any MTF VM exits during execution of the enclave;
Clear all pending debug exceptions;
Clear any pending MTF VM exit;
ELSE
Clear all pending debug exceptions;
Clear pending MTF VM exits;
FI;

Vol. 3D 40-105

SGX INSTRUCTION REFERENCES

(* Assure consistent translations *)
Flush_linear_context;
Clear_Monitor_FSM;
Allow_front_end_to_begin_fetch_at_new_RIP;
Flags Affected
RFLAGS.TF is cleared on opt-out entry
Protected Mode Exceptions
#GP(0)

If DS:RBX is not page aligned.
If the enclave is not initialized.
If the thread is not in the INACTIVE state.
If CS, DS, ES or SS bases are not all zero.
If executed in enclave mode.
If part or all of the FS or GS segment specified by TCS is outside the DS segment.
If any reserved field in the TCS FLAG is set.
If the target address is not within the CS segment.
If CR4.OSFXSR = 0.
If CR4.OSXSAVE = 0 and SECS.ATTRIBUTES.XFRM ≠ 3.
If CR4.OSXSAVE = 1and SECS.ATTRIBUTES.XFRM is not a subset of XCR0.

#PF(error code)

If a page fault occurs in accessing memory.
If DS:RBX does not point to a valid TCS.
If one or more pages of the current SSA frame are not readable/writable, or do not resolve to
a valid PT_REG EPC page.

64-Bit Mode Exceptions
#GP(0)

If DS:RBX is not page aligned.
If the enclave is not initialized.
If the thread is not in the INACTIVE state.
If CS, DS, ES or SS bases are not all zero.
If executed in enclave mode.
If part or all of the FS or GS segment specified by TCS is outside the DS segment.
If any reserved field in the TCS FLAG is set.
If the target address is not canonical.
If CR4.OSFXSR = 0.
If CR4.OSXSAVE = 0 and SECS.ATTRIBUTES.XFRM ≠ 3.
If CR4.OSXSAVE = 1and SECS.ATTRIBUTES.XFRM is not a subset of XCR0.

#PF(error code)

If a page fault occurs in accessing memory operands.
If DS:RBX does not point to a valid TCS.
If one or more pages of the current SSA frame are not readable/writable, or do not resolve to
a valid PT_REG EPC page.

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CHAPTER 41
INTEL® SGX INTERACTIONS WITH IA32 AND INTEL® 64 ARCHITECTURE
Intel® SGX provides Intel® Architecture with a collection of enclave instructions for creating protected execution
environments on processors supporting IA32 and Intel® 64 architectures. These Intel SGX instructions are
designed to work with legacy software and the various IA32 and Intel 64 modes of operation.

41.1

INTEL® SGX AVAILABILITY IN VARIOUS PROCESSOR MODES

The Intel SGX extensions (see Table 36-1) are available only when the processor is executing in protected mode of
operation. Additionally, the extensions are not available in System Management Mode (SMM) of operation or in
Virtual 8086 (VM86) mode of operation. Finally, all leaf functions of ENCLU and ENCLS require CR0.PG enabled.
The exact details of exceptions resulting from illegal modes and their priority are listed in the reference pages of
ENCLS and ENCLU.

41.2

IA32_FEATURE_CONTROL

IA32_FEATURE_CONTROL MSR provides two new bits related to two aspects of Intel SGX: using the instruction
extensions and launch control configuration.

41.2.1

Availability of Intel SGX

IA32_FEATURE_CONTROL[bit 18] allows BIOS to control the availability of Intel SGX extensions. For Intel SGX
extensions to be available on a logical processor, bit 18 in the IA32_FEATURE_CONTROL MSR on that logical
processor must be set, and IA32_FEATURE_CONTROL MSR on that logical processor must be locked (bit 0 must be
set). See Section 36.7.1 for additional details. OS is expected to examine the value of bit 18 prior to enabling Intel
SGX on the thread, as the settings of bit 18 is not reflected by CPUID.

41.2.2

Intel SGX Launch Control Configuration

The IA32_SGXLEPUBKEYHASHn MSRs used to configure authorized launch enclaves' MRSIGNER digest value. They
are present on logical processors that support the collection of SGX1 leaf functions (i.e. CPUID.(EAX=12H,
ECX=00H):EAX[0] = 1) and that CPUID.(EAX=07H, ECX=00H):ECX[30] = 1. IA32_FEATURE_CONTROL[bit 17]
allows to BIOS to enable write access to these MSRs. If IA32_FEATURE_CONTROL.LE_WR (bit 17) is set to 1 and
IA32_FEATURE_CONTROL is locked on that logical processor, IA32_SGXLEPUBKEYHASH MSRs on that logical
processor are writeable. If this bit 17 is not set or IA32_FEATURE_CONTROL is not locked,
IA32_SGXLEPUBKEYHASH MSRs are read only. See Section 38.1.4 for additional details.

41.3

INTERACTIONS WITH SEGMENTATION

41.3.1

Scope of Interaction

Intel SGX extensions are available only when the processor is executing in a protected mode operation (see Section
41.1 for Intel SGX availability in various processor modes). Enclaves abide by all the segmentation policies set up
by the OS, but they can be more restrictive than the OS.
Intel SGX interacts with segmentation at two levels:

•

The Intel SGX instruction (see the enclave instruction in Table 36-1).

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INTEL® SGX INTERACTIONS WITH IA32 AND INTEL® 64 ARCHITECTURE

•

While executing inside an enclave (legacy instructions and enclave instructions permitted inside an enclave).

41.3.2

Interactions of Intel® SGX Instructions with Segment, Operand, and Addressing
Prefixes

All the memory operands used by the Intel SGX instructions are interpreted as offsets within the data segment
(DS). The segment-override prefix on Intel SGX instructions is ignored.
Operand size is fixed for each enclave instruction. The operand-size prefix is reserved, and results in a #UD exception if used.
All address sizes are determined by the operating mode of the processor. The address-size prefix is ignored. This
implies that while operating in 64-bit mode of operation, the address size is always 64 bits, and while operating in
32-bit mode of operation, the address size is always 32 bits. Additionally, when operating in 16-bit addressing,
memory operands used by enclave instructions use 32 bit addressing; the value of CS.D is ignored.

41.3.3

Interaction of Intel® SGX Instructions with Segmentation

All leaf functions of ENCLU and ENCLS instructions require that the DS segment be usable, and be an expand-up
segment. Failing this check results in generation of a #GP(0) exception.
The Intel SGX leaf functions used for entering the enclave (ENCLU[EENTER] and ENCLU[ERESUME]) operate as
follows:

•
•
•
•

All usable segment registers except for FS and GS have a zero base.

•

The CS segment mode (64-bit, compatible, or 32 bit modes) must be consistent with the segment mode for
which the enclave was created, as indicated by the SECS.ATTRIBUTES.MODE64 bit, and that the CPL of the
logical processor is 3

The contents of the FS/GS segment registers (including the hidden portion) is saved in the processor.
New FS and GS values compatible with enclave security are loaded from the TCS
The linear ranges and access rights available under the newly-loaded FS and GS must abide to OS policies by
ensuring they are subsets of the linear-address range and access rights available for the DS segment.

An exit from the enclave either via ENCLU[EEXIT] or via an AEX restores the saved values of FS/GS segment registers.

41.3.4

Interactions of Enclave Execution with Segmentation

During the course of execution, enclave code abides by all segmentation policies as dictated by IA32 and Intel 64
Architectures, and generates appropriate exceptions on violations.
Additionally, any attempt by software executing inside an enclave to modify the processor's segmentation state
(e.g. via MOV seg register, POP seg register, LDS, far jump, etc; excluding WRFSBASE/WRGSBASE) results in the
generation of a #UD. See Section 38.6.1 for more information.
Upon enclave entry via the EENTER leaf function, FS is loaded from the (TCS.OFSBASE + SECS.BASEADDR) and
TCS.FSLIMIT fields and GS is loaded from the (TCS.OGSBASE + SECS.BASEADDR) and TCS.GSLIMIT fields.
Execution of WRFSBASE and WRGSBASE from inside a 64-bit enclave is allowed. The processor will save the new
values into the current SSA frame on an asynchronous exit (AEX) and restore them back on enclave entry via
ENCLU[ERESUME] instruction.

41.4

INTERACTIONS WITH PAGING

Intel SGX instructions are available only when the processor is executing in a protected mode of operation. Additionally, all Intel SGX leaf functions except for EDBGRD and EDBGWR are available only if paging is enabled. Any
attempt to execute these leaf functions with paging disabled results in an invalid-opcode exception (#UD). As with

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segmentation, enclaves abide by all the paging policies set up by the OS, but they can be more restrictive than the
OS.
All the memory operands passed into Intel SGX instructions are interpreted as offsets within the DS segment, and
the linear addresses generated by combining these offsets with DS segment register are subject to paging-based
access control if paging is enabled at the time of the execution of the leaf function.
Since the ENCLU[EENTER] and ENCLU[ERESUME] can only be executed when paging is enabled, and since paging
cannot be disabled by software running inside an enclave (recall that enclaves always run with CPL = 3), enclave
execution is always subject to paging-based access control. The Intel SGX access control itself is implemented as
an extension to the existing paging modes. See Section 37.5 for details.
Execution of Intel SGX instructions may set accessed and dirty flags on accesses to EPC pages that do not fault
even if the instruction later causes a fault for some other reason.

41.5

INTERACTIONS WITH VMX

Intel SGX functionality (including SGX1 and SGX2) can be made available to software running in either VMX root
operation or VMX non-root operation, as long as the processor is using a legal mode of operation (see Section
41.1).
A VMM has the flexibility to configure a VMCS to permit a guest to use any subset of the ENCLS leaf functions. Availability of the ENCLU leaf functions in VMX non-root operation has the same requirement as ENCLU leaf functions
outside of a virtualized environment.
Details of the VMCS control to allow VMM to configure support of Intel SGX in VMX non-root operation is described
in Section 41.5.1

41.5.1

VMM Controls to Configure Guest Support of Intel® SGX

Intel SGX capabilities are primarily exposed to the software via the CPUID instruction. VMMs can virtualize CPUID
instruction to expose/hide this capability to/from guests.
Some of Intel SGX resources are exposed/controlled via model-specific registers (see Section 36.7). VMMs can
virtualize these MSRs for the guests using the MSR bitmaps referenced by pointers in the VMCS.
The VMM can partition the Enclave Page Cache, and assign various partitions to (a subset of) its guests via the
usual memory-virtualization techniques such as paging or the extended page table mechanism (EPT).
The VMM can set the “enable ENCLS exiting” VM-execution controls to cause a VM exit when the ENCLS instruction
is executed in VMX non-root operation. If the “enable ENCLS exiting” control is 0, all of the ENCLS leaf functions are
permitted in VMX non-root operation. If the “enable ENCLS exiting” control is 1, execution of ENCLS leaf functions
in VMX non-root operation is governed by consulting the bits in a new 64-bit VM-execution control field called the
ENCLS-exiting bitmap (Each bit in the bitmap corresponds to an ENCLS leaf function with an EAX value that is identical to the bit’s position). When bits in the “ENCLS-exiting bitmap” are set, attempts to execute the corresponding
ENCLS leaf functions in VMX non-root operation causes VM exits. The checking for these VM exits occurs immediately after checking that CPL = 0.

41.5.2

Interactions with the Extended Page Table Mechanism (EPT)

Intel SGX instructions are fully compatible with the extended page-table mechanism (EPT; see Section 28.2).
All the memory operands passed into Intel SGX instructions are interpreted as offsets within the DS segment, and
the linear addresses generated by combining these offsets with DS segment register are subject to paging and EPT.
As with paging, enclaves abide by all the policies set up by the VMM.
The Intel SGX access control itself is implemented as an extension to paging and EPT, and may be more restrictive.
See Section 41.4 for details of this extension.
An execution of an Intel SGX instruction may set accessed and dirty flags for EPT (when enabled; see Section
28.2.4) on accesses to EPC pages that do not fault or cause VM exits even if the instruction later causes a fault or
VM exit for some other reason.

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41.5.3

Interactions with APIC Virtualization

This section applies to Intel SGX in VMX non-root operation when the “virtualize APIC accesses” VM-execution
control is 1.
A memory access by an enclave instruction that implicitly uses a cached physical address is never checked for
overlap with the APIC-access page. Such accesses never cause APIC-access VM exits and are never redirected to
the virtual-APIC page. Implicit memory accesses can only be made to the SECS, the TCS, or the SSA of an enclave
(see Section 37.5.3.2).
An explicit Enclave Access (a linear memory access which is either from within an enclave into its ELRANGE, or an
access by an Intel SGX instruction that is expected to be in the EPC) that overlaps with the APIC-access page
causes a #PF exception (APIC page is expected to be outside of EPC).
Non-Enclave accesses made either by an Intel SGX instruction or by a logical processor inside an enclave to an
address that without SGX would have caused redirection to the virtual-APIC page instead cause an APIC-access
VM exit.
Other than implicit accesses made by Intel SGX instructions, guest-physical and physical accesses are not considered “enclave accesses”; consequently, such accesses result in undefined behavior if these accesses eventually
reach EPC. This applies to any non-enclave physical accesses.
While a logical processor is executing inside an enclave, an attempt to execute an instruction outside of ELRANGE
results in a #GP(0), even if the linear address would translate to a physical address that overlaps the APIC-access
page.

41.6

INTEL® SGX INTERACTIONS WITH ARCHITECTURALLY-VISIBLE EVENTS

All architecturally visible vectored events (IA32 exceptions, interrupts, SMI, NMI, INIT, VM exit) can be detected
while inside an enclave and will cause an asynchronous enclave exit if they are not blocked. Additionally, INT3, and
the SignalTXTMsg[SENTER] (i.e. GETSEC[SENTER]’s rendezvous event message) events also cause asynchronous
enclave exits. Note that SignalTXTMsg[SEXIT] (i.e. GETSEC[SEXIT]’s teardown message) does not cause an AEX.
On an AEX, information about the event causing the AEX is stored in the SSA (see Section 39.4 for details of AEX).
The information stored in the SSA only describes the first event that triggered the AEX. If parsing/delivery of the
first event results in detection of further events (e.g. VM exit, double fault, etc.), then the event information in the
SSA is not updated to reflect these subsequently detected events.

41.7

INTERACTIONS WITH THE PROCESSOR EXTENDED STATE AND
MISCELLANEOUS STATE

41.7.1

Requirements and Architecture Overview

Processor extended states are the ISA features that are enabled by the settings of CR4.OSXSAVE and the XCR0
register. Processor extended states are normally saved/restored by software via XSAVE/XRSTOR instructions.
Details of discovery of processor extended states and management of these states are described in CHAPTER 13 of
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.
Additionally, the following requirements apply to Intel SGX:

•

On an AEX, the Intel SGX architecture must protect the processor extended state and miscellaneous state by
saving them in the enclave’s state-save area (SSA), and clear the secrets from the processor extended state
that is used by an enclave.

•

Intel SGX architecture must verify that the SSA frame size is large enough to contain all the processor extended
states and miscellaneous state used by the enclave.

•

Intel SGX architecture must ensure that enclaves can only use processor extended state that is enabled by
system software in XCR0.

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•

Enclave software should be able to discover only those processor extended state and miscellaneous state for
which such protection is enabled.

•

The processor extended states that are enabled inside the enclave must be approved by the enclave developer:
— Certain processor extended state (e.g., Memory Protection Extensions, see Chapter 17, “Intel® MPX” of
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1) modify the behavior of the
legacy ISA software. If such features are enabled for enclaves that do not understand those features, then
such a configuration could lead to a compromise of the enclave's security.

•

The processor extended states that are enabled inside the enclave must form an integral part of the enclave's
identity. This requirement has two implications:
— Service providers may decide to assign different trust level to the same enclave depending on the ISA
features the enclave is using.

To meet these requirements, the Intel SGX architecture defines a sub-field called X-Feature Request Mask (XFRM)
in the ATTRIBUTES field of the SECS. On enclave creation (ENCLS[ECREATE] leaf function), the required SSA frame
size is calculated by the processor from the list of enabled extended and miscellaneous states and verified against
the actual SSA frame size defined by SECS.SSAFRAMESIZE.
On enclave entry, after verifying that XFRM is only enabling features that are already enabled in XCR0, the value in
the XCR0 is saved internally by the processor, and is replaced by the XFRM. On enclave exit, the original value of
XCR0 is restored. Consequently, while inside the enclave, the processor extended states enabled in XFRM are in
enabled state, and those that are disabled in XFRM are in disabled state.
The entire ATTRIBUTES field, including the XFRM subfield is integral part of enclave's identity (i.e., its value is
included in reports generated by ENCLU[EREPORT], and select bits from this field can be included in key-derivation
for keys obtained via the ENCLU[EGETKEY] leaf function).
Enclave developers can create their enclave to work with certain features and fallback to another code path in case
those features aren't available (e.g. optimize for AVX and fallback to SSE). For this purpose Intel SGX provides the
following fields in SIGSTRUCT: ATTRIBUTES, ATTRIBUTESMASK, MISCSELECT, and MISCMASK. EINIT ensures that
the final SECS.ATTRIBUTES and SECS.MISCSELECT comply with the enclave developer's requirements as follows:
SIGSTRUCT.ATTRIBUTES & SIGSTRUCT.ATTRIBUTEMASK = SECS.ATTRIBUTES & SIGSTRUCT.ATTRIBUTEMASK
SIGSTRUCT.MISCSELECT & SIGSTRUCT.MISCMASK = SECS.MISCSELECT & SIGSTRUCT.MISCMASK.
On an asynchronous enclave exit, the processor extended states enabled by XFRM are saved in the current SSA
frame, and overwritten by synthetic state (see Section 39.3 for the definition of the synthetic state). When the
interrupted enclave is resumed via the ENCLU[ERESUME] leaf function, the saved state for processor extended
states enabled by XFRM is restored.

41.7.2

Relevant Fields in Various Data Structures

41.7.2.1

SECS.ATTRIBUTES.XFRM

The ATTRIBUTES field of the SECS data structure (see Section 37.7) contains a sub-field called XSAVE-Feature
Request Mask (XFRM). Software populates this field at the time of enclave creation according to the features that
are enabled by the operating system and approved by the enclave developer.
Intel SGX architecture guarantees that during enclave execution, the processor extended state configuration of the
processor is identical to what is required by the XFRM sub-field. All the processor extended states enabled in XFRM
are saved on AEX from the enclave and restored on ERESUME.
The XFRM sub-field has the same layout as XCR0, and has consistency requirements that are similar to those for
XCR0. Specifically, the consistency requirements on XFRM values depend on the processor implementation and the
set of features enabled in CR4.
Legal values for SECS.ATTRIBUTES.XFRM conform to these requirements:

•
•

XFRM[1:0] must be set to 0x3.

•

If the processor does support XSAVE, XFRM must contain a value that would be legal if loaded into XCR0.

If the processor does not support XSAVE, or if the system software has not enabled XSAVE, then XFRM[63:2]
must be zero.

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The various consistency requirements are enforced at different times in the enclave's life cycle, and the exact
enforcement mechanisms are elaborated in Section 41.7.3 through Section 41.7.6.
On processors not supporting XSAVE, software should initialize XFRM to 0x3. On processors supporting XSAVE,
software should initialize XFRM to be a subset of XCR0 that would be present at the time of enclave execution.
Because bits 0 and 1 of XFRM must always be set, the use of Intel SGX requires that SSE be enabled (CR4.OSFXSR
= 1).

41.7.2.2

SECS.SSAFRAMESIZE

The SSAFRAMESIZE field in the SECS data structure specifies the number of pages which software allocated1 for
each SSA frame, including both the GPRSGX area, MISC area, the XSAVE area (x87 and XMM states are stored in
the latter area), and optionally padding between the MISC and XSAVE area. The GPRSGX area must hold all the
general-purpose registers and additional Intel SGX specific information. The MISC area must hold the Miscellaneous state as specified by SECS.MISCSELECT, the XSAVE area holds the set of processor extended states specified
by SECS.ATTRIBUTES.XFRM (see Section 37.9 for the layout of SSA and Section 41.7.3 for ECREATE's consistency
checks). The SSA is always in non-compacted format.
If the processor does not support XSAVE, the XSAVE area will always be 576 bytes; a copy of XFRM (which will be
set to 0x3) is saved at offset 512 on an AEX.
If the processor does support XSAVE, the length of the XSAVE area depends on SECS.ATTRIBUTES.XFRM. The
length would be equal to what CPUID.(EAX=0DH, ECX= 0):EBX would return if XCR0 were set to XFRM. The
following pseudo code illustrates how software can calculate this length using XFRM as the input parameter without
modifying XCR0:
offset = 576;
size_last_x = 0;
For x=2 to 63
IF (XFRM[x] != 0) Then
tmp_offset = CPUID.(EAX=0DH, ECX= x):EBX[31:0];
IF (tmp_offset >= offset + size_last_x) Then
offset = tmp_offset;
size_last_x = CPUID.(EAX=0DH, ECX= x):EAX[31:0];
FI;
FI;
EndFor
return (offset + size_last_x); (* compute_xsave_size(XFRM), see “ECREATE—Create an SECS page in the Enclave
Page Cache”*)
Where the non-zero bits in XFRM are a subset of non-zero bit fields in XCR0.
The size of the MISC region depends on the setting of SECS.MISCSELECT and can be calculated using the layout
information described in Section 37.9.2

41.7.2.3

XSAVE Area in SSA

The XSAVE area of an SSA frame begins at offset 0 of the frame.

41.7.2.4

MISC Area in SSA

The MISC area of an SSA frame is positioned immediately before the GPRSGX region.

41.7.2.5

SIGSTRUCT Fields

Intel SGX provides the flexibility for an enclave developer to choose the enclave's code path according to the
features that are enabled on the platform (e.g. optimize for AVX and fallback to SSE). See Section 41.7.1 for
details.

1. It is the responsibility of the enclave to actually allocate this memory.
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SIGSTRUCT includes the following fields:
SIGSTRUCT.ATTRIBUTES, SIGSTRUCT.ATTRIBUTEMASK, SIGSTRUCT.MISCSELECT, SIGSTRUCT.MISCMASK.

41.7.2.6

REPORT.ATTRIBUTES.XFRM and REPORT.MISCSELECT

The processor extended states and miscellaneous states that are enabled inside the enclave form an integral part
of the enclave's identity and are therefore included in the enclave's report, as provided by the ENCLU[EREPORT]
leaf function. The REPORT structure includes the enclave's XFRM and MISCSELECT configurations.

41.7.2.7

KEYREQUEST

An enclave developer can specify which bits out of XFRM and MISCSELECT ENCLU[EGETKEY] should include in the
derivation of the sealing key by specifying ATTRIBUTESMASK and MISCMASK in the KEYREQUEST structure.

41.7.3

Processor Extended States and ENCLS[ECREATE]

The ECREATE leaf function of the ENCLS instruction enforces a number of consistency checks described earlier. The
execution of ENCLS[ECREATE] leaf function results in a #GP(0) in any of the following cases:

•
•

SECS.ATTRIBUTES.XFRM[1:0] is not 3.
The processor does not support XSAVE and any of the following is true:
— SECS.ATTRIBUTES.XFRM[63:2] is not 0.
— SECS.SSAFRAMESIZE is 0.

•

The processor supports XSAVE and any of the following is true:
— XSETBV would fault on an attempt to load XFRM into XCR0.
— XFRM[63]=1.
— The SSAFRAME is too small to hold required, enabled states (see Section 41.7.2.2).

41.7.4

Processor Extended States and ENCLU[EENTER]

41.7.4.1

Fault Checking

The EENTER leaf function of the ENCLU instruction enforces a number of consistency requirements described
earlier. The execution of the ENCLU[EENTER] leaf function results in a #GP(0) in any of the following cases:

•
•

If CR4.OSFXSR=0.
If The processor supports XSAVE and either of the following is true:
— CR4.OSXSAVE=0 and SECS.ATTRIBUTES.XFRM is not 3.
— (SECS.ATTRIBUTES.XFRM & XCR0) != SECS.ATTRIBUTES.XFRM

41.7.4.2

State Loading

If ENCLU[EENTER] is successful, the current value of XCR0 is saved internally by the processor and replaced by
SECS.ATTRIBUTES.XFRM.

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41.7.5

Processor Extended States and AEX

41.7.5.1

State Saving

On an AEX, processor extended states are saved into the XSAVE area of the SSA frame in a compatible format with
XSAVE that was executed with EDX:EAX = SECS.ATTRIBUTES.XFRM, with the memory operand being the XSAVE
area, and (for 64-bit enclaves) as if REX.W=1. The XSTATE_BV part of the XSAVE header is saved with 0 for every
bit that is 0 in XFRM. Other bits may be saved as 0 if the state saved is initialized.
Note that enclave entry ensures that if CR4.OSXSAVE is set to 0, then SECS.ATTRIBUTES.XFRM is set to 3. It
should also be noted that it is not possible to enter an enclave with FXSAVE disabled.

41.7.5.2

State Synthesis

After saving the extended state, the processor restores XCR0 to the value it held at the time of the most recent
enclave entry.
The state of features corresponding to bits set in XFRM is synthesized. In general, these states are initialized.
Details of state synthesis on AEX are documented in Section 39.3.1.

41.7.6

Processor Extended States and ENCLU[ERESUME]

41.7.6.1

Fault Checking

The ERESUME leaf function of the ENCLU instruction enforces a number of consistency requirements described
earlier. Specifically, the ENCLU[ERESUME] leaf function results in a #GP(0) in any of the following cases:

•
•

CR4.OSFXSR=0.
The processor supports XSAVE and either of the following is true:
— CR4.OSXSAVE=0 and SECS.ATTRIBUTES.XFRM is not 3.
— (SECS.ATTRIBUTES.XFRM & XCR0) != SECS.ATTRIBUTES.XFRM.

A successful execution of ENCLU[ERESUME] loads state from the XSAVE area of the SSA frame in a fashion similar
to that used by the XRSTOR instruction. Data in the XSAVE area that would cause the XRSTOR instruction to fault
will cause the ENCLU[ERESUME] leaf function to fault. Examples include, but are not restricted to the following:

•
•
•

A bit is set in the XSTATE_BV field and clear in XFRM.
The required bytes in the header are not clear.
Loading data would set a reserved bit in MXCSR.

Any of these conditions will cause ERESUME to fault, even if CR4.OSXSAVE=0.

41.7.6.2

State Loading

If ENCLU[ERESUME] is successful, the current value of XCR0 is saved internally by the processor and replaced by
SECS.ATTRIBUTES.XFRM.
State is loaded from the XSAVE area of the SSA frame as if the XRSTOR instruction were executed with
XCR0=XFRM, EDX:EAX = XFRM, with the memory operand being the XSAVE area, and (for 64-bit enclaves) as if
REX.W=1.
ENCLU[ERESUME] ensures that a subsequent execution of XSAVEOPT inside the enclave will operate properly (e.g.,
by marking all state as modified).

41.7.7

Processor Extended States and ENCLU[EEXIT]

The ENCLU[EEXIT] leaf function does not perform any X-feature specific consistency checks, nor performs any
state synthesis. It is the responsibility of enclave software to clear any sensitive data from the registers before
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executing EEXIT. However, successful execution of the ENCLU[EEXIT] leaf function restores XCR0 to the value it
held at the time of the most recent enclave entry.

41.7.8

Processor Extended States and ENCLU[EREPORT]

The ENCLU[EREPORT] leaf function creates the MAC-protected REPORT structure that reports on the enclave’s
identity. ENCLU[EREPORT] includes in the report the values of SECS.ATTRIBUTES.XFRM and SECS.MISCSELECT.

41.7.9

Processor Extended States and ENCLU[EGETKEY]

The ENCLU[EGETKEY] leaf function returns a cryptographic key based on the information provided by the KEYREQUEST structure. Intel SGX provides the means for isolation between different operating conditions by allowing an
enclave developer to select which bits out of XFRM and MISCSELECT need to be included in the derivation of the
keys.

41.8

INTERACTIONS WITH SMM

41.8.1

Availability of Intel® SGX instructions in SMM

Enclave instructions are not available in SMM, and any attempt to execute ENCLS or ENCLU instructions inside SMM
results in an invalid-opcode exception (#UD).

41.8.2

SMI while Inside an Enclave

If the logical processor executing inside an enclave receives an SMI, the logical processor exits the enclave asynchronously. The response to an SMI received while executing inside an enclave depends on whether the dualmonitor treatment is enabled. For detailed discussion of transfer to SMM, see Chapter 34, “System Management
Mode” of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C.
If the logical processor executing inside an enclave receives an SMI when dual-monitor treatment is not enabled,
the logical processor exits the enclave asynchronously, and transfers the control to the SMM handler. In addition to
saving the synthetic architectural state to the SMRAM State Save Map (SSM), the logical processor also sets the
“Enclave Interruption” bit in the SMRAM SSM (bit position 1 in SMRAM field at offset 7EE0H).
If the logical processor executing inside an enclave receives an SMI when dual-monitor treatment is enabled, the
logical processor exits the enclave asynchronously, and transfers the control to the SMM monitor via SMM VM exit.
The SMM VM exit sets the “Enclave Interruption” bit in the Exit Reason (see Table 41-1) and in the Guest Interruptibility State field (see Table 41-2) of the SMM VMCS.

41.8.3

SMRAM Synthetic State of AEX Triggered by SMI

All processor registers saved in the SMRAM have the same synthetic values listed in Section 39.3. Additional
SMRAM fields that are treated specially on SMI are:

Table 41-1. SMRAM Synthetic States on Asynchronous Enclave Exit
Position
SMRAM Offset 07EE0H.Bit 1

Field

Value

ENCLAVE_INTERRUPTION Set to 1 if exit occurred in enclave mode

Writable
No

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INTEL® SGX INTERACTIONS WITH IA32 AND INTEL® 64 ARCHITECTURE

41.9

INTERACTIONS OF INIT, SIPI, AND WAIT-FOR-SIPI WITH INTEL® SGX

INIT received inside an enclave, while the logical processor is not in VMX operation, causes the logical processor to
exit the enclave asynchronously. After the AEX, the processor's architectural state is initialized to “Power-on” state
(Table 9.1 in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A). If the logical processor
is BSP, then it proceeds to execute the BIOS initialization code. If the logical processor is an AP, it enters wait-forSIPI state.
INIT received inside an enclave, while the logical processor (LP) is in VMX root operation, follows regular Intel
Architecture behavior and is blocked.
INIT received inside an enclave, while the logical processor is in VMX non-root operation, causes an AEX. Subsequent to the AEX, the INIT causes a VM exit with the Enclave Interruption bit in the exit-reason field in the VMCS.
A processor cannot be inside an enclave in the wait-for-SIPI state. Consequently, a SIPI received while inside an
enclave is lost.
Intel SGX does not change the behavior of the processor in the wait-for-SIPI state.
The SGX-related processor states after INIT-SIPI-SIPI is as follows:

•
•
•
•
•

EPC Settings: Unchanged
EPCM: Unchanged
CPUID.LEAF_12H.*: Unchanged
ENCLAVE_MODE: 0 (LP exits enclave asynchronously)
MEE state: Unchanged

Software should be aware that following INIT-SIPI-SIPI, the EPC might contain valid pages and should take appropriate measures such as initialize the EPC with the EREMOVE leaf function.

41.10

INTERACTIONS WITH DMA

DMA is not allowed to access any Processor Reserved Memory.

41.11

INTERACTIONS WITH TXT

41.11.1 Enclaves Created Prior to Execution of GETSEC
Enclaves which have been created before the GETSEC[SENTER] leaf function are available for execution after the
successful completion of GETSEC[SENTER] and the corresponding SINIT ACM. Actions that a TXT Launched Environment performs in preparation to execute code in the Launched Environment, also applies to enclave code that
would run after GETSEC[SENTER].

41.11.2 Interaction of GETSEC with Intel® SGX
All leaf functions of the GETSEC instruction are illegal inside an enclave, and results in an invalid-opcode exception
(#UD).
Responding Logical Processors (RLP) which are executing inside an enclave at the time a GETSEC[SENTER] event
occurs perform an AEX from the enclave and then enter the Wait-for-SIPI state.
RLP executing inside an enclave at the time of GETSEC[SEXIT], behave as defined for GETSEC[SEXIT]-that is, the
RLPs pause during execution of SEXIT and resume after the completion of SEXIT.
The execution of a TXT launch does not affect Intel SGX configuration or security parameters.

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41.11.3 Interactions with Authenticated Code Modules (ACMs)
Intel SGX only allows launching ACMs with an Intel SGX SVN that is at the same level or higher than the expected
Intel SGX SVN. The expected Intel SGX SVN is specified by BIOS and locked down by the processor on the first
successful execution of an Intel SGX instruction that doesn’t return an error code. Intel SGX provides interfaces for
system software to discover whether a non faulting Intel SGX instruction has been executed, and evaluate the suitability of the Intel SGX SVN value of any ACM that is expected to be launched by the OS or the VMM.
These interfaces are provided through a read-only MSR called the IA32_SGX_SVN_STATUS MSR (MSR address
500h). The IA32_SGX_SVN_STATUS MSR has the format shown in Table 41-2.

Table 41-2. Layout of the IA32_SGX_SVN_STATUS MSR
Bit Position

Name

ACM Module ID

Value

0

Lock

N.A.

• If 1, indicates that a non-faulting Intel SGX instruction has been
executed, consequently, launching a properly signed ACM but with Intel
SGX SVN value less than the BIOS specified Intel SGX SVN threshold
would lead to an TXT shutdown.
• If 0, indicates that the processor will allow a properly signed ACM to
launch irrespective of the Intel SGX SVN value of the ACM.

15:1

RSVD

N.A.

0

23:16

SGX_SVN_SINIT

SINIT ACM

• If CPUID.01H:ECX.SMX =1, this field reflects the expected threshold of
Intel SGX SVN for the SINIT ACM.
• If CPUID.01H:ECX.SMX =0, this field is reserved (0).

63:24

RSVD

N.A.

0

OS/VMM that wishes to launch an architectural ACM such as SINIT is expected to read the IA32_SGX_SVN_STATUS
MSR to determine whether the ACM can be launched or a new ACM is needed:

•

If either the Intel SGX SVN of the ACM is greater than the value reported by IA32_SGX_SVN_STATUS, or the
lock bit in the IA32_SGX_SVN_STATUS is not set, then the OS/VMM can safely launch the ACM.

•

If the Intel SGX SVN value reported in the corresponding component of the IA32_SGX_SVN_STATUS is greater
than the Intel SGX SVN value in the ACM's header, and if bit 0 of IA32_SGX_SVN_STATUS is 1, then the
OS/VMM should not launch that version of the ACM. It should obtain an updated version of the ACM either from
the BIOS or from an external resource.

However, OSVs/VMMs are strongly advised to update their version of the ACM any time they detect that the Intel
SGX SVN of the ACM carried by the OS/VMM is lower than that reported by IA32_SGX_SVN_STATUS MSR, irrespective of the setting of the lock bit.

41.12

INTERACTIONS WITH CACHING OF LINEAR-ADDRESS TRANSLATIONS

Entering and exiting an enclave causes the logical processor to flush all the global linear-address context as well as
the linear-address context associated with the current VPID and PCID. The MONITOR FSM is also cleared.

41.13

INTERACTIONS WITH INTEL® TRANSACTIONAL SYNCHRONIZATION
EXTENSIONS (INTEL® TSX)

1. ENCLU or ENCLS instructions inside an HLE region will cause the flow to be aborted and restarted non-speculatively. ENCLU or ENCLS instructions inside an RTM region will cause the flow to be aborted and transfer control to
the fallback handler.
2. If XBEGIN is executed inside an enclave, the processor does NOT check whether the address of the fallback
handler is within the enclave.
3. If an RTM transaction is executing inside an enclave and there is an attempt to fetch an instruction outside the
enclave, the transaction is aborted and control is transferred to the fallback handler. No #GP is delivered.

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INTEL® SGX INTERACTIONS WITH IA32 AND INTEL® 64 ARCHITECTURE

4. If an RTM transaction is executing inside an enclave and there is a data access to an address within the enclave
that denied due to EPCM content (e.g., to a page belonging to a different enclave), the transaction is aborted and
control is transferred to the fallback handler. No #GP is delivered.
5. If an RTM transaction executing inside an enclave aborts and the address of the fallback handler is outside the
enclave, a #GP is delivered after the abort (EIP reported is that of the fallback handler).

41.13.1 HLE and RTM Debug
RTM debug will be suppressed on opt-out enclave entry. After opt-out entry, the logical processor will behave as if
IA32_DEBUG_CTL[15]=0. Any #DB detected inside an RTM transaction region will just cause an abort with no
exception delivered.
After opt-in entry, if either DR7[11] = 0 OR IA32_DEBUGCTL[15] = 0, any #DB or #BP detected inside an RTM
transaction region will just cause an abort with no exception delivered.
After opt-in entry, if DR7[11] = 1 AND IA32_DEBUGCTL[15] = 1, any #DB or #BP detected inside an RTM translation will

•
•
•
•

terminate speculative execution,
set RIP to the address of the XBEGIN instruction, and
be delivered as #DB (implying an Intel SGX AEX; any #BP is converted to #DB).
DR6[16] will be cleared, indicating RTM debug (if the #DB causes a VM exit, DR6 is not modified but bit 16 of
the pending debug exceptions field in the VMCS will be set).

41.14

INTEL® SGX INTERACTIONS WITH S STATES

Whenever an Intel SGX enabled processor enters S3-S5 state, enclaves are destroyed. This is due to the EPC being
destroyed when power down occurs. It is the application runtime’s responsibility to re-instantiate an enclave after
a power transition for which the enclaves were destroyed.

41.15

INTEL® SGX INTERACTIONS WITH MACHINE CHECK ARCHITECTURE (MCA)

41.15.1 Interactions with MCA Events
All architecturally visible machine check events (#MC and CMCI) that are detected while inside an enclave cause an
asynchronous enclave exit.
Any machine check exception (#MC) that occurs after Intel SGX is first enables causes Intel SGX to be disabled,
(CPUID.SGX_Leaf.0:EAX[SGX1] == 0). It cannot be enabled until after the next reset.

41.15.2 Machine Check Enables (IA32_MCi_CTL)
All supported IA32_MCi_CTL bits for all the machine check banks must be set for Intel SGX to be available
(CPUID.SGX_Leaf.0:EAX[SGX1] == 1). Any act of clearing bits from '1 to '0 in any of the IA32_MCi_CTL register
may disable Intel SGX (set CPUID.SGX_Leaf.0:EAX[SGX1] to 0) until the next reset.

41.15.3 CR4.MCE
CR4.MCE can be set or cleared with no interactions with Intel SGX.

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INTEL® SGX INTERACTIONS WITH IA32 AND INTEL® 64 ARCHITECTURE

41.16

INTEL® SGX INTERACTIONS WITH PROTECTED MODE VIRTUAL
INTERRUPTS

ENCLS[EENTER] modifies neither EFLAGS.VIP nor EFLAGS.VIF.
ENCLS[ERESUME] loads EFLAGS in a manner similar to that of an execution of IRET with CPL = 3. This means that
ERESUME modifies neither EFLAGS.VIP nor EFLAGS.VIF regardless of the value of the EFLAGS image in the SSA
frame.
AEX saves EFLAGS.VIP and EFLAGS.VIF unmodified into the EFLAGS image in the SSA frame. AEX modifies neither
EFLAGS.VIP nor EFLAGS.VIF after saving EFLAGS.
If CR4.PVI = 1, CPL = 3, EFLAGS.VM = 0, IOPL < 3, EFLAGS.VIP = 1, and EFLAGS.VIF = 0, execution of STI causes
a #GP fault. In this case, STI modifies neither EFLAGS.IF nor EFLAGS.VIF. This behavior applies without change
within an enclave (where CPL is always 3). Note that, if IOPL = 3, STI always sets EFLAGS.IF without fault;
CR4.PVI, EFLAGS.VIP, and EFLAGS.VIF are neither consulted nor modified in this case.

41.17

INTEL SGX INTERACTION WITH PROTECTION KEYS

SGX interactions with PKRU are as follows:

•

CPUID.(EAX=12H, ECX=1):ECX.PKRU indicates whether SECS.ATTRIBUTES.XFRM.PKRU can be set. If
SECS.ATTRIBUTES.XFRM.PKRU is set, then PKRU is saved and cleared as part of AEX and is restored as part of
ERESUME. If CR4.PKE is set, an enclave can execute RDPKRU and WRKRU independent of whether
SECS.ATTRIBUTES.XFRM.PKRU is set.

SGX interactions with domain permission checks are as follows:
1) If CR4.PKE is not set, then legacy and SGX permission checks are not effected.
2) If CR4.PKE is set, then domain permission checks are applied to all non-enclave access and
enclave accesses to user pages in addition to legacy and SGX permission checks at a higher
priority than SGX permission checks.
3) Implicit accesses aren't subject to domain permission checks.

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INTEL® SGX INTERACTIONS WITH IA32 AND INTEL® 64 ARCHITECTURE

41-14 Vol. 3D

ENCLAVE CODE DEBUG AND PROFILING

CHAPTER 42
ENCLAVE CODE DEBUG AND PROFILING
Intel® SGX is architected to provide protection for production enclaves and permit enclave code developers to use
an SGX-aware debugger to effectively debug a non-production enclave (debug enclave). Intel SGX also allows a
non-SGX-aware debugger to debug non-enclave portions of the application without getting confused by enclave
instructions.

42.1

CONFIGURATION AND CONTROLS

42.1.1

Debug Enclave vs. Production Enclave

The SECS of each enclave provides a bit, SECS.ATTRIBUTES.DEBUG, indicating whether the enclave is a debug
enclave (if set) or a production enclave (if 0). If this bit is set, software outside the enclave can use
EDBGRD/EDBGWR to access the EPC memory of the enclave. The value of DEBUG is not included in the measurement of the enclave and therefore doesn't require an alternate SIGSTRUCT to be generated to debug the enclave.
The ATTRIBUTES field in the SECS is reported in the enclave's attestation, and is included in the key derivation.
Enclave secrets that were protected by the enclave using Intel SGX keys when it ran as a production enclave will
not be accessible by the debug enclave. A debugger needs to be aware that special debug content might be
required for a debug enclave to run in a meaningful way.
EPC memory belonging to a debug enclave can be accessed via the EDBGRD/EDBGWR leaf functions (see Section
40.4), while that belonging to a non-debug enclave cannot be accessed by these leaf functions.

42.1.2

Tool-Chain Opt-in

The TCS.FLAGS.DBGOPTIN bit controls interactions of certain debug and profiling features with enclaves, including
code/data breakpoints, TF, RF, monitor trap flag, BTF, LBRs, BTM, BTS, Intel Processor Trace, and performance
monitoring. This bit is forced to zero when EPC pages are added via EADD. A debugger can set this bit via EDBGWR
to the TCS of a debug enclave.
An enclave entry through a TCS with the TCS.FLAGS.DBGOPTIN set to 0 is called an opt-out entry. Conversely, an
enclave entry through a TCS with TCS.FLAGS.DBGOPTIN set to 1 is called an opt-in entry.

42.2

SINGLE STEP DEBUG

42.2.1

Single Stepping ENCLS Instruction Leafs

If the RFLAGS.TF bit is set at the beginning of ENCLS, then a single-step debug exception is pending as a trap-class
exception on the instruction boundary immediately after the ENCLS instruction. Additionally, if the instruction is
executed in VMX non-root operation and the “monitor trap flag” VM-execution control is 1, an MTF VM exit is
pending on the instruction boundary immediately after the instruction if the instruction does not fault.

42.2.2

Single Stepping ENCLU Instruction Leafs

The interactions of the unprivileged Intel SGX instruction ENCLU are leaf dependent.
An enclave entry via EENTER/ERESUME leaf functions of the ENCLU, in certain cases, may mask the RFLAGS.TF bit,
and mask the setting of the “monitor trap flag” VM-execution control. In such situations, an exit from the enclave,
either via the EEXIT leaf function or via an AEX unmasks the RFLAGS.TF bit and the “monitor trap flag” VM-execu-

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ENCLAVE CODE DEBUG AND PROFILING

tion control. The details of this masking/unmasking and the pending of single stepping events across
EENTER/ERESUME/EEXIT/AEX are covered in detail in Section 42.2.3.
If the EFLAGS.TF bit is set at the beginning of EREPORT or EGETKEY leafs, and if the EFLAGS.TF is not masked by
the preceding enclave entry, then a single-step debug exception is pending on the instruction boundary immediately after the ENCLU instruction. Additionally, if the instruction is executed in VMX non-root operation and the
“monitor trap flag” VM-execution control is 1, and if the monitor trap flag is not masked by the preceding enclave
entry, then an MTF VM exit is pending on the instruction boundary immediately after the instruction.
If the instruction under consideration results in a fault, then the control flow goes to the fault handler, and no
single-step debug exception is asserted. In such a situation, if the instruction is executed in VMX non-root operation and the “monitor trap flag” VM-execution control is 1, an MTF VM exit is pending after the delivery of the fault
(or any nested exception). No MTF VM exit occurs if another VM exit occurs before reaching that boundary on which
an MTF VM exit would be pending.

42.2.3

Single-Stepping Enclave Entry with Opt-out Entry

42.2.3.1

Single Stepping without AEX

Figure 42-1 shows the most common case for single-stepping after an opt-out entry.

EENTER
ERESUME

Inst1

Inst2

Inst3

EEXIT

Inst4
TF/MTF
Handler

RFLAGS.TF

Single-Step #DB Pending

VMCS.MTF

MTF VM Exit Pending

SMI
INIT
#MC
Higher Priority
Handler

Figure 42-1. Single Stepping with Opt-out Entry - No AEX
In this scenario, if the RFLAGS.TF bit is set at the time of the enclave entry, then a single step debug exception is
pending on the instruction boundary after EEXIT. Additionally, if the enclave is executing in VMX non-root operation
and the “monitor trap flag” VM-execution control is 1, an MTF VM exit is pending on the instruction boundary after
EEXIT.
The value of the RFLAGS.TF bit at the end of EEXIT is the same as the value of RFLAGS.TF at the time of the enclave
entry.

42.2.3.2

Single Step Preempted by AEX Due to Non-SMI Event

Figure 42-2 shows the interaction of single stepping with AEX due to a non-SMI event after an opt-out entry.

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ENCLAVE CODE DEBUG AND PROFILING

EENTER
ERESUME

Inst1

Inst2

Event Inside Enclave

Inst3

EEXIT

AEX

Inst4
TF/MTF
Handler

RFLAGS.TF

Single-Step #DB Pending

Higher Priority
Handler

VMCS.MTF

MTF VM Exit Pending

AEX
Handler

Figure 42-2. Single Stepping with Opt-out Entry -AEX Due to Non-SMI Event Before Single-Step Boundary
In this scenario, if the enclave is executing in VMX non-root operation and the “monitor trap flag” VM-execution
control is 1, an MTF VM exit is pending on the instruction boundary after the AEX. No MTF VM exit occurs if another
VM exit happens before reaching that instruction boundary.
The value of the RFLAGS.TF bit at the end of AEX is the same as the value of RFLAGS.TF at the time of the enclave
entry.

42.2.4

RFLAGS.TF Treatment on AEX

The value of EFLAGS.TF at the end of AEX from an opt-out enclave is same as the value of EFLAGS.TF at the time
of the enclave entry. The value of EFLAGS.TF at the end of AEX from an opt-in enclave is unmodified. The
EFLAGS.TF saved in GPR portion of the SSA on an AEX is 0. For more detail see EENTER and ERESUME in Chapter 5.

42.2.5

Restriction on Setting of TF after an Opt-Out Entry

Enclave entered through an opt-out entry is not allowed to set EFLAGS.TF. The POPF instruction forces RFLAGS.TF
to 0 if the enclave was entered through opt-out entry.

42.2.6

Trampoline Code Considerations

Any AEX from the enclave which results in the RFLAGS.TF =1 on the reporting stack will result in a single-step #DB
after the first instruction of the trampoline code if the trampoline is entered using the IRET instruction.

42.3

CODE AND DATA BREAKPOINTS

42.3.1

Breakpoint Suppression

Following an opt-out entry:

•
•
•

Instruction breakpoints are suppressed during execution in an enclave.
Data breakpoints are not triggered on accesses to the address range defined by ELRANGE.
Data breakpoints are triggered on accesses to addresses outside the ELRANGE

Vol. 3D 42-3

ENCLAVE CODE DEBUG AND PROFILING

Following an opt-in entry instruction and data breakpoints are not suppressed.
The processor does not report any matches on debug breakpoints that are suppressed on enclave entry. However,
the processor does not clear any bits in DR6 that were already set at the time of the enclave entry.

42.3.2

Reporting of Instruction Breakpoint on Next Instruction on a Debug Trap

A debug exception caused by the single-step execution mode or when a data breakpoint condition was met causes
the processor to perform an AEX. Following such an AEX, the processor reports in the debug status register (DR6)
matches of the new instruction pointer (the AEP address) in a breakpoint address register setup to detect instruction execution.

42.3.3

RF Treatment on AEX

RF flag value saved in SSA is the same as what would have been pushed on stack if the exception or event causing
the AEX occurred when executing outside an enclave (see Section 17.3.1.1). Following an AEX, the RF flag is 0 in
the synthetic state.

42.3.4

Breakpoint Matching in Intel® SGX Instruction Flows

Implicit accesses made by Intel SGX instructions to EPC regions do not trigger data breakpoints. Explicit accesses
made by ENCLS[ECREATE], ENCLS[EADD], ENCLS[EEXTEND], ENCLS[EINIT], ENCLS[EREMOVE],
ENCLS[ETRACK], ENCLS[EBLOCK], ENCLS[EPA], ENCLS[EWB], ENCLS[ELD], ENCLS[EDBGRD], ENCLS[EDBGWR],
ENCLU[EENTER], and ENCLU[ERESUME] to the EPC operands do not trigger data breakpoints.
Explicit accesses made by the Intel SGX instructions (ENCLU[EGETKEY] and ENCLU[EREPORT]) executed by an
enclave following an opt-in entry, trigger data breakpoints on accesses to their EPC operands. All Intel SGX instructions trigger data breakpoints on accesses to their non-EPC operands.

42.4

INT3 CONSIDERATION

42.4.1

Behavior of INT3 Inside an Enclave

Inside an enclave, INT3 delivers a fault-class exception and thus does not require the CPL to be less than DPL in the
IDT gate 3. Following opt-out entry, the instruction delivers #UD. Following opt-in entry, INT3 delivers #BP.
The RIP saved in the SSA on AEX is that of the INT3 instruction. The RIP saved on the stack ( or in the TSS or VMCS)
is that of the AEP.
If execution of INT3 in an enclave causes a VM exit, the event type in the VM-exit interruption information field indicates a hardware exception (type 3; not a software exception with type 6) and the VM-exit instruction length field
is saved as zero.

42.4.2

Debugger Considerations

The INT3 is fault-like inside an enclave and the RIP saved in the SSA on AEX is that of the INT3 instruction. Consequently, the debugger must not decrement SSA.RIP for #BP coming from an enclave to re-execute the instruction
at the RIP of the INT3 instruction on a subsequent enclave entry.

42.4.3

VMM Considerations

As described above, INT3 executed by enclave delivers #BP with “interruption type” of 3. A VMM that re-injects
#BP into the guest can obtain the VM entry interruption information from appropriate VMCS fields (as recommended in Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C).

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VMMs that create the VM-entry interruption information based on the interruption vector should use event type of
3 (instead of 6) when they detect a VM exit incident to enclave mode that is due to an event with vector 3.

42.5

BRANCH TRACING

42.5.1

BTF Treatment

When software enables single-stepping on branches then:

•
•

Following an opt-in entry using EENTER the processor generates a single step debug exception.
Following an EEXIT the processor generates a single-step debug exception

Enclave entry using ERESUME (opt-in or opt-out) and an AEX from the enclave do not cause generation of the
single-step debug exception.

42.5.2

LBR Treatment

42.5.2.1

LBR Stack on Opt-in Entry

Following an opt-in entry into an enclave, last branch recording facilities if enabled continued to store branch
records in the LBR stack MSRs as follows:

•

On enclave entry using EENTER/ERESUME, the processor push the address of EENTER/ERESUME instruction
into MSR_LASTBRANCH_n_FROM_IP, and the destination address of the EENTER/ERESUME into
MSR_LASTBRANCH_n_TO_IP.

•

On EEXIT, the processor pushes the address of EEXIT instruction into MSR_LASTBRANCH_n_FROM_IP, and the
address of EEXIT destination into MSR_LASTBRANCH_n_TO_IP.

•

On AEX, the processor pushes RIP saved in the SSA into MSR_LASTBRANCH_n_FROM_IP, and the address of
AEP into MSR_LASTBRANCH_n_TO_IP.

•

For every branch inside the enclave, a branch record is pushed on the LBR stack.

Figure 42-3 shows an example of LBR stack manipulation after an opt-in entry. Every arrow in this picture indicates
a branch record pushed on the LBR stack. The “From IP” of the branch record contains the linear address of the
instruction located at the start of the arrow, while the “To IP” of the branch record contains the linear address of the
instruction at the end of the arrow.

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ENCLAVE CODE DEBUG AND PROFILING

EENTER

Inst1

BR2

Inst3

Inst4

Fault

Inst4

AEP

AEP

OS

IRET

AEP

ERESUME

Inst4

BR5

Inst6

EEXIT

Inst7

Figure 42-3. LBR Stack Interaction with Opt-in Entry

42.5.2.2

LBR Stack on Opt-out Entry

An opt-out entry into an enclave suppresses last branch recording facilities, and enclave exit after an opt-out entry
un-suppresses last branch recording facilities.
Opt-out entry into an enclave does not push any record on LBR stack.
If last branch recording facilities were enabled at the time of enclave entry, then EEXIT following such an enclave
entry pushes one record on LBR stack. The MSR_LASTBRANCH_n_FROM_IP of such record holds the linear address
of the instruction (EENTER or ERESUME) that was used to enter the enclave, while the
MSR_LASTBRANCH_n_TO_IP of such record holds linear address of the destination of EEXIT.
Additionally, if last branch recording facilities were enabled at the time of enclave entry, then an AEX after such an
entry pushes one record on LBR stack, before pushing record for the event causing the AEX if the event pushes a
record on LBR stack. The MSR_LASTBRANCH_n_FROM_IP of the new record holds linear address of the instruction
(EENTER or ERESUME) that was used to enter the enclave, while MSR_LASTBRANCH_n_TO_IP of the new record
holds linear address of the AEP. If the event causing AEX pushes a record on LBR stack, then the
MSR_LASTBRANCH_n_FROM_IP for that record holds linear address of the AEP.
Figure 42-4 shows an example of LBR stack manipulation after an opt-out entry. Every arrow in this picture indicates a branch record pushed on the LBR stack. The “From IP” of the branch record contains the linear address of
the instruction located at the start of the arrow, while the “To IP” of the branch record contains the linear address
of the instruction at the end of the arrow.

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EENTER

Inst1

BR2

Inst3

Inst4

Fault
AEP

AEP

OS

IRET

AEP

ERESUME

Inst4

BR5

Inst6

EEXIT

Inst7

Figure 42-4. LBR Stack Interaction with Opt-out Entry

42.5.2.3

Mispredict Bit, Record Type, and Filtering

All branch records resulting from Intel SGX instructions/AEXs are reported as predicted branches, and consequently, bit 63 of MSR_LASTBRANCH_n_FROM_IP for such records is set. Branch records due to these Intel SGX
operations are always non-HLE/non-RTM records.
EENTER, ERESUME, EEXIT, and AEX are considered to be far branches. Consequently, bit 8 in MSR_LBR_SELECT
controls filtering of the new records introduced by Intel SGX.

42.6

INTERACTION WITH PERFORMANCE MONITORING

42.6.1

IA32_PERF_GLOBAL_STATUS Enhancement

On processors supporting Intel SGX, the IA32_PERF_GLOBAL_STATUS MSR provides a bit indicator, known as “Anti
Side-channel Interference” (ASCI) at bit position 60. If this bit is 0, the performance monitoring data in various
performance monitoring counters are accumulated normally as defined by relevant architectural/microarchitectural conditions. If the ASCI bit is set, the contents in various performance monitoring counters can be affected by
the direct or indirect consequence of Intel SGX protection of enclave code executing in the processor.

42.6.2

Performance Monitoring with Opt-in Entry

An opt-in enclave entry allow performance monitoring logic to observe the contribution of enclave code executing
in the processor. Thus the contents of performance monitoring counters does not distinguish between contribution
originating from enclave code or otherwise. All counters, events, precise events, etc. continue to work as defined
in the IA32/Intel 64 Software Developer Manual. Consequently, bit 60 of IA32_PERF_GLOBAL_STATUS MSR is not
set.

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ENCLAVE CODE DEBUG AND PROFILING

42.6.3

Performance Monitoring with Opt-out Entry

In general, performance monitoring activities are suppressed when entering an opt-out enclave. This applies to all
thread-specific, configured performance monitoring, except for the cycle-counting fixed counter,
IA32_FIXED_CTR1 and IA32_FIXED_CTR2. Upon entering an opt-out enclave, IA32_FIXED_CTR0, IA32_PMCx will
stop accumulating counts. Additionally, if PEBS is configured to capture PEBS record for this thread, PEBS record
generation will also be suppressed. Consequently, bit 60 of IA32_PERF_GLOBAL_STATUS MSR is set.
Performance monitoring on the sibling thread may also be affected. Any one of IA32_FIXED_CTRx or IA32_PMCx
on the sibling thread configured to monitor thread-specific eventing logic with AnyThread =1 is demoted to count
only MyThread while an opt-out enclave is executing on the other thread.

42.6.4

Enclave Exit and Performance Monitoring

When a logical processor exits an enclave, either via ENCLU[EEXIT] or via AEX, all performance monitoring activity
(including PEBS) on that logical processor that was suppressed is unsuppressed.
Any counters that were demoted from AnyThread to MyThread on the sibling thread are promoted back to
AnyThread.

42.6.5

PEBS Record Generation on Intel® SGX Instructions

All leaf functions of the ENCLS instruction report “Eventing RIP” of the ENCLS instruction if a PEBS record is generated at the end of the instruction execution. Additionally, the EGETKEY and EREPORT leaf functions of the ENCLU
instruction report “Eventing RIP” of the ENCLU instruction if a PEBS record is generated at the end of the instruction
execution.
If the EENTER and ERESUME leaf functions are performing an opt-in entry report “Eventing RIP” of the ENCLU
instruction if a PEBS record is generated at the end of the instruction execution. On the other hand, if these leaf
functions are performing an opt-out entry, then these leaf functions result in PEBS being suppressed, and no PEBS
record is generated at the end of these instructions.
A PEBS record is generated if there is a PEBS event pending at the end of EEXIT (due to a counter overflowing
during enclave execution or during EEXIT execution). This PEBS record contains the architectural state of the
logical processor at the end of EEXIT. If the enclave was entered via an opt-in entry, then this record reports the
“Eventing RIP” as the linear address of the ENCLU[EEXIT] instruction. If the enclave was entered via an opt-out
entry, then the record reports the “Eventing RIP” as the linear address of the ENCLU[EENTER/ERESUME] instruction that performed the last enclave entry.
A PEBS record is generated after the AEX if there is a PEBS event pending at the end of AEX (due to a counter overflowing during enclave execution or during AEX execution). This PEBS record contains the synthetic state of the
logical processor that is established at the end of AEX. For opt-in entry, this record has the EVENTING_RIP set to
the RIP saved in the SSA. For opt-out entry, the record has the EVENTING_RIP set to the linear address of
EENTER/ERESUME used for the last enclave entry.
If the enclave was entered via an opt-in entry, then this record reports the “Eventing RIP” as the linear address in
the SSA of the enclave (a.k.a., the “Eventing LIP” inside the enclave). If the enclave was entered via an opt-out
entry, then the record reports the “Eventing RIP” as the linear address of the ENCLU[EENTER/ERESUME] instruction that performed the last enclave entry.
A second PEBS event may be pended during the Enclave Exiting Event (EEE). If the PEBS event is taken at the end
of delivery of the EEE then the “Eventing RIP” in this second PEBS record is the linear address of the AEP.

42.6.6

Exception-Handling on PEBS/BTS Loads/Stores after AEX

The operating system should allocate sections of the DS save area from a non-paged pool, and mark them as
accessed and dirty. If the loads/stores to any section of the DS save area incur faults then such faults are reported
to the OS/VMM immediately, and generation of the PEBS/BTS record is skipped and may leave the buffers in a state
where they have a partial PEBS or BTS records.
However, any events that are detected during PEBS/BTS record generation at the end of AEX and before delivering
the Enclave Exiting Event (EEE) cannot be reported immediately to the OS/VMM, as an event window is not open at
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ENCLAVE CODE DEBUG AND PROFILING

the end of AEX. Consequently, fault-like events such as page faults, EPT faults, EPT mis-configuration, and
accesses to APIC-access page detected on stores to the PEBS/BTS buffer are not reported, and generation of the
PEBS and/or BTS record at the end of AEX is aborted (this may leave the buffers in a state where they have partial
PEBS or BTS records). Trap-like events detected on stores to the PEBS/BTS buffer (such as debug traps) are
pended until the next instruction boundary, where they are handled according to the architecturally defined
priority. The processor continues the handling of the Enclave Exiting Event (SMI, NMI, interrupt, exception delivery,
VM exit, etc.) after aborting the PEBS/BTS record generation.

42.6.6.1

Other Interactions with Performance Monitoring

For opt-in entry, EENTER, ERESUME, EEXIT, and AEX are all treated as predicted far branches, and any counters
that are counting such branches are incremented by 1 as a part of retirement of these instructions. Retirement of
these instructions is also counted in any counters configured to count instructions retired.
For opt-out entry, execution inside an enclave is treated as a single predicted branch, and all branch-counting
performance monitoring counters are incremented accordingly. Additionally, such execution is also counted as a
single instruction, and all performance monitoring counters counting instructions are incremented accordingly.
Enclave entry does not affect any performance monitoring counters shared between cores.

Vol. 3D 42-9

ENCLAVE CODE DEBUG AND PROFILING

42-10 Vol. 3D

APPENDIX A
VMX CAPABILITY REPORTING FACILITY
The ability of a processor to support VMX operation and related instructions is indicated by
CPUID.1:ECX.VMX[bit 5] = 1. A value 1 in this bit indicates support for VMX features.
Support for specific features detailed in Chapter 26 and other VMX chapters is determined by reading values from
a set of capability MSRs. These MSRs are indexed starting at MSR address 480H. VMX capability MSRs are readonly; an attempt to write them (with WRMSR) produces a general-protection exception (#GP(0)). They do not exist
on processors that do not support VMX operation; an attempt to read them (with RDMSR) on such processors
produces a general-protection exception (#GP(0)).

A.1

BASIC VMX INFORMATION

The IA32_VMX_BASIC MSR (index 480H) consists of the following fields:

•

Bits 30:0 contain the 31-bit VMCS revision identifier used by the processor. Processors that use the same VMCS
revision identifier use the same size for VMCS regions (see subsequent item on bits 44:32).1

•
•

Bit 31 is always 0.

•

Bit 48 indicates the width of the physical addresses that may be used for the VMXON region, each VMCS, and
data structures referenced by pointers in a VMCS (I/O bitmaps, virtual-APIC page, MSR areas for VMX transitions). If the bit is 0, these addresses are limited to the processor’s physical-address width.2 If the bit is 1,
these addresses are limited to 32 bits. This bit is always 0 for processors that support Intel 64 architecture.

•

If bit 49 is read as 1, the logical processor supports the dual-monitor treatment of system-management
interrupts and system-management mode. See Section 34.15 for details of this treatment.

•

Bits 53:50 report the memory type that should be used for the VMCS, for data structures referenced by
pointers in the VMCS (I/O bitmaps, virtual-APIC page, MSR areas for VMX transitions), and for the MSEG
header. If software needs to access these data structures (e.g., to modify the contents of the MSR bitmaps), it
can configure the paging structures to map them into the linear-address space. If it does so, it should establish
mappings that use the memory type reported bits 53:50 in this MSR.3

Bits 44:32 report the number of bytes that software should allocate for the VMXON region and any VMCS
region. It is a value greater than 0 and at most 4096 (bit 44 is set if and only if bits 43:32 are clear).

As of this writing, all processors that support VMX operation indicate the write-back type. The values used are
given in Table A-1.

Table A-1. Memory Types Recommended for VMCS and Related Data Structures
Value(s)

Field

0

Uncacheable (UC)

1–5

Not used

6

Write Back (WB)

7–15

Not used

1. Earlier versions of this manual specified that the VMCS revision identifier was a 32-bit field in bits 31:0 of this MSR. For all processors produced prior to this change, bit 31 of this MSR was read as 0.
2. On processors that support Intel 64 architecture, the pointer must not set bits beyond the processor's physical address width.
3. Alternatively, software may map any of these regions or structures with the UC memory type. (This may be necessary for the MSEG
header.) Doing so is discouraged unless necessary as it will cause the performance of software accesses to those structures to suffer.
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VMX CAPABILITY REPORTING FACILITY

If software needs to access these data structures (e.g., to modify the contents of the MSR bitmaps), it can
configure the paging structures to map them into the linear-address space. If it does so, it should establish
mappings that use the memory type reported in this MSR.1

•

If bit 54 is read as 1, the processor reports information in the VM-exit instruction-information field on VM exits
due to execution of the INS and OUTS instructions (see Section 27.2.4). This reporting is done only if this bit is
read as 1.

•

Bit 55 is read as 1 if any VMX controls that default to 1 may be cleared to 0. See Appendix A.2 for details. It also
reports support for the VMX capability MSRs IA32_VMX_TRUE_PINBASED_CTLS,
IA32_VMX_TRUE_PROCBASED_CTLS, IA32_VMX_TRUE_EXIT_CTLS, and IA32_VMX_TRUE_ENTRY_CTLS. See
Appendix A.3.1, Appendix A.3.2, Appendix A.4, and Appendix A.5 for details.

•

The values of bits 47:45 and bits 63:56 are reserved and are read as 0.

A.2

RESERVED CONTROLS AND DEFAULT SETTINGS

As noted in Chapter 26, “VM Entries”, certain VMX controls are reserved and must be set to a specific value (0 or 1)
determined by the processor. The specific value to which a reserved control must be set is its default setting.
Software can discover the default setting of a reserved control by consulting the appropriate VMX capability MSR
(see Appendix A.3 through Appendix A.5).
Future processors may define new functionality for one or more reserved controls. Such processors would allow
each newly defined control to be set either to 0 or to 1. Software that does not desire a control’s new functionality
should set the control to its default setting. For that reason, it is useful for software to know the default settings of
the reserved controls.
Default settings partition the various controls into the following classes:

•
•
•

Always-flexible. These have never been reserved.
Default0. These are (or have been) reserved with a default setting of 0.
Default1. They are (or have been) reserved with a default setting of 1.

As noted in Appendix A.1, a logical processor uses bit 55 of the IA32_VMX_BASIC MSR to indicate whether any of
the default1 controls may be 0:

•

If bit 55 of the IA32_VMX_BASIC MSR is read as 0, all the default1 controls are reserved and must be 1.
VM entry will fail if any of these controls are 0 (see Section 26.2.1).

•

If bit 55 of the IA32_VMX_BASIC MSR is read as 1, not all the default1 controls are reserved, and some (but
not necessarily all) may be 0. The CPU supports four (4) new VMX capability MSRs:
IA32_VMX_TRUE_PINBASED_CTLS, IA32_VMX_TRUE_PROCBASED_CTLS, IA32_VMX_TRUE_EXIT_CTLS, and
IA32_VMX_TRUE_ENTRY_CTLS. See Appendix A.3 through Appendix A.5 for details. (These MSRs are not
supported if bit 55 of the IA32_VMX_BASIC MSR is read as 0.)

See Section 31.5.1 for recommended software algorithms for proper capability detection of the default1 controls.

A.3

VM-EXECUTION CONTROLS

There are separate capability MSRs for the pin-based VM-execution controls, the primary processor-based VMexecution controls, and the secondary processor-based VM-execution controls. These are described in Appendix
A.3.1, Appendix A.3.2, and Appendix A.3.3, respectively.

1. Alternatively, software may map any of these regions or structures with the UC memory type. (This may be necessary for the MSEG
header.) Doing so is discouraged unless necessary as it will cause the performance of software accesses to those structures to suffer. The processor will continue to use the memory type reported in the VMX capability MSR IA32_VMX_BASIC with the exceptions
noted.
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VMX CAPABILITY REPORTING FACILITY

A.3.1

Pin-Based VM-Execution Controls

The IA32_VMX_PINBASED_CTLS MSR (index 481H) reports on the allowed settings of most of the pin-based
VM-execution controls (see Section 24.6.1):

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X (bit X of the pin-based
VM-execution controls) to be 0 if bit X in the MSR is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if
control X is 0.
Exceptions are made for the pin-based VM-execution controls in the default1 class (see Appendix A.2). These
are bits 1, 2, and 4; the corresponding bits of the IA32_VMX_PINBASED_CTLS MSR are always read as 1. The
treatment of these controls by VM entry is determined by bit 55 in the IA32_VMX_BASIC MSR:
— If bit 55 in the IA32_VMX_BASIC MSR is read as 0, VM entry fails if any pin-based VM-execution control in
the default1 class is 0.
— If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_PINBASED_CTLS MSR (see
below) reports which of the pin-based VM-execution controls in the default1 class can be 0 on VM entry.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control X to be 1 if bit 32+X in
the MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_PINBASED_CTLS MSR (index 48DH)
reports on the allowed settings of all of the pin-based VM-execution controls:

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X to be 0 if bit X in the MSR
is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if control X is 0. There are no exceptions.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control X to be 1 if bit 32+X in the
MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

It is necessary for software to consult only one of the capability MSRs to determine the allowed settings of the pinbased VM-execution controls:

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 0, all information about the allowed settings of the pin-based
VM-execution controls is contained in the IA32_VMX_PINBASED_CTLS MSR. (The
IA32_VMX_TRUE_PINBASED_CTLS MSR is not supported.)

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, all information about the allowed settings of the pin-based
VM-execution controls is contained in the IA32_VMX_TRUE_PINBASED_CTLS MSR. Assuming that software
knows that the default1 class of pin-based VM-execution controls contains bits 1, 2, and 4, there is no need for
software to consult the IA32_VMX_PINBASED_CTLS MSR.

A.3.2

Primary Processor-Based VM-Execution Controls

The IA32_VMX_PROCBASED_CTLS MSR (index 482H) reports on the allowed settings of most of the primary
processor-based VM-execution controls (see Section 24.6.2):

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X (bit X of the primary
processor-based VM-execution controls) to be 0 if bit X in the MSR is cleared to 0; if bit X in the MSR is set to
1, VM entry fails if control X is 0.
Exceptions are made for the primary processor-based VM-execution controls in the default1 class (see
Appendix A.2). These are bits 1, 4–6, 8, 13–16, and 26; the corresponding bits of the
IA32_VMX_PROCBASED_CTLS MSR are always read as 1. The treatment of these controls by VM entry is
determined by bit 55 in the IA32_VMX_BASIC MSR:
— If bit 55 in the IA32_VMX_BASIC MSR is read as 0, VM entry fails if any of the primary processor-based VMexecution controls in the default1 class is 0.
— If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_PROCBASED_CTLS MSR (see
below) reports which of the primary processor-based VM-execution controls in the default1 class can be 0
on VM entry.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control X to be 1 if bit 32+X in the
MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

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VMX CAPABILITY REPORTING FACILITY

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_PROCBASED_CTLS MSR (index 48EH)
reports on the allowed settings of all of the primary processor-based VM-execution controls:

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X to be 0 if bit X in the MSR
is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if control X is 0. There are no exceptions.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control X to be 1 if bit 32+X in the
MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

It is necessary for software to consult only one of the capability MSRs to determine the allowed settings of the
primary processor-based VM-execution controls:

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 0, all information about the allowed settings of the primary
processor-based VM-execution controls is contained in the IA32_VMX_PROCBASED_CTLS MSR. (The
IA32_VMX_TRUE_PROCBASED_CTLS MSR is not supported.)

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, all information about the allowed settings of the processorbased VM-execution controls is contained in the IA32_VMX_TRUE_PROCBASED_CTLS MSR. Assuming that
software knows that the default1 class of processor-based VM-execution controls contains bits 1, 4–6, 8, 13–
16, and 26, there is no need for software to consult the IA32_VMX_PROCBASED_CTLS MSR.

A.3.3

Secondary Processor-Based VM-Execution Controls

The IA32_VMX_PROCBASED_CTLS2 MSR (index 48BH) reports on the allowed settings of the secondary processorbased VM-execution controls (see Section 24.6.2). VM entries perform the following checks:

•

Bits 31:0 indicate the allowed 0-settings of these controls. These bits are always 0. This fact indicates that
VM entry allows each bit of the secondary processor-based VM-execution controls to be 0 (reserved bits must
be 0)

•

Bits 63:32 indicate the allowed 1-settings of these controls; the 1-setting is not allowed for any reserved bit.
VM entry allows control X (bit X of the secondary processor-based VM-execution controls) to be 1 if bit 32+X in
the MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X and the “activate secondary
controls” primary processor-based VM-execution control are both 1.

The IA32_VMX_PROCBASED_CTLS2 MSR exists only on processors that support the 1-setting of the “activate
secondary controls” VM-execution control (only if bit 63 of the IA32_VMX_PROCBASED_CTLS MSR is 1).

A.4

VM-EXIT CONTROLS

The IA32_VMX_EXIT_CTLS MSR (index 483H) reports on the allowed settings of most of the VM-exit controls (see
Section 24.7.1):

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X (bit X of the VM-exit
controls) to be 0 if bit X in the MSR is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if control X is 0.
Exceptions are made for the VM-exit controls in the default1 class (see Appendix A.2). These are bits 0–8, 10,
11, 13, 14, 16, and 17; the corresponding bits of the IA32_VMX_EXIT_CTLS MSR are always read as 1. The
treatment of these controls by VM entry is determined by bit 55 in the IA32_VMX_BASIC MSR:
— If bit 55 in the IA32_VMX_BASIC MSR is read as 0, VM entry fails if any VM-exit control in the default1 class
is 0.
— If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_EXIT_CTLS MSR (see below)
reports which of the VM-exit controls in the default1 class can be 0 on VM entry.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control 32+X to be 1 if bit X in the
MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_EXIT_CTLS MSR (index 48FH) reports on
the allowed settings of all of the VM-exit controls:

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X to be 0 if bit X in the MSR
is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if control X is 0. There are no exceptions.

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VMX CAPABILITY REPORTING FACILITY

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control X to be 1 if bit 32+X in the
MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

It is necessary for software to consult only one of the capability MSRs to determine the allowed settings of the
VM-exit controls:

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 0, all information about the allowed settings of the VM-exit
controls is contained in the IA32_VMX_EXIT_CTLS MSR. (The IA32_VMX_TRUE_EXIT_CTLS MSR is not
supported.)

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, all information about the allowed settings of the VM-exit
controls is contained in the IA32_VMX_TRUE_EXIT_CTLS MSR. Assuming that software knows that the default1
class of VM-exit controls contains bits 0–8, 10, 11, 13, 14, 16, and 17, there is no need for software to consult
the IA32_VMX_EXIT_CTLS MSR.

A.5

VM-ENTRY CONTROLS

The IA32_VMX_ENTRY_CTLS MSR (index 484H) reports on the allowed settings of most of the VM-entry controls
(see Section 24.8.1):

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X (bit X of the VM-entry
controls) to be 0 if bit X in the MSR is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if control X is 0.
Exceptions are made for the VM-entry controls in the default1 class (see Appendix A.2). These are bits 0–8 and
12; the corresponding bits of the IA32_VMX_ENTRY_CTLS MSR are always read as 1. The treatment of these
controls by VM entry is determined by bit 55 in the IA32_VMX_BASIC MSR:
— If bit 55 in the IA32_VMX_BASIC MSR is read as 0, VM entry fails if any VM-entry control in the default1
class is 0.
— If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_ENTRY_CTLS MSR (see below)
reports which of the VM-entry controls in the default1 class can be 0 on VM entry.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry fails if bit X is 1 in the VM-entry controls
and bit 32+X is 0 in this MSR.

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, the IA32_VMX_TRUE_ENTRY_CTLS MSR (index 490H) reports
on the allowed settings of all of the VM-entry controls:

•

Bits 31:0 indicate the allowed 0-settings of these controls. VM entry allows control X to be 0 if bit X in the MSR
is cleared to 0; if bit X in the MSR is set to 1, VM entry fails if control X is 0. There are no exceptions.

•

Bits 63:32 indicate the allowed 1-settings of these controls. VM entry allows control 32+X to be 1 if bit X in the
MSR is set to 1; if bit 32+X in the MSR is cleared to 0, VM entry fails if control X is 1.

It is necessary for software to consult only one of the capability MSRs to determine the allowed settings of the
VM-entry controls:

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 0, all information about the allowed settings of the VM-entry
controls is contained in the IA32_VMX_ENTRY_CTLS MSR. (The IA32_VMX_TRUE_ENTRY_CTLS MSR is not
supported.)

•

If bit 55 in the IA32_VMX_BASIC MSR is read as 1, all information about the allowed settings of the VM-entry
controls is contained in the IA32_VMX_TRUE_ENTRY_CTLS MSR. Assuming that software knows that the
default1 class of VM-entry controls contains bits 0–8 and 12, there is no need for software to consult the
IA32_VMX_ENTRY_CTLS MSR.

A.6

MISCELLANEOUS DATA

The IA32_VMX_MISC MSR (index 485H) consists of the following fields:

•

Bits 4:0 report a value X that specifies the relationship between the rate of the VMX-preemption timer and that
of the timestamp counter (TSC). Specifically, the VMX-preemption timer (if it is active) counts down by 1 every
time bit X in the TSC changes due to a TSC increment.

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VMX CAPABILITY REPORTING FACILITY

•

If bit 5 is read as 1, VM exits store the value of IA32_EFER.LMA into the “IA-32e mode guest” VM-entry control;
see Section 27.2 for more details. This bit is read as 1 on any logical processor that supports the 1-setting of
the “unrestricted guest” VM-execution control.

•

Bits 8:6 report, as a bitmap, the activity states supported by the implementation:
— Bit 6 reports (if set) the support for activity state 1 (HLT).
— Bit 7 reports (if set) the support for activity state 2 (shutdown).
— Bit 8 reports (if set) the support for activity state 3 (wait-for-SIPI).
If an activity state is not supported, the implementation causes a VM entry to fail if it attempts to establish that
activity state. All implementations support VM entry to activity state 0 (active).

•

If bit 14 is read as 1, Intel® Processor Trace (Intel PT) can be used in VMX operation. If the processor supports
Intel PT but does not allow it to be used in VMX operation, execution of VMXON clears IA32_RTIT_CTL.TraceEn
(see “VMXON—Enter VMX Operation” in Chapter 30); any attempt to write IA32_RTIT_CTL while in VMX
operation (including VMX root operation) causes a general-protection exception.

•

If bit 15 is read as 1, the RDMSR instruction can be used in system-management mode (SMM) to read the
IA32_SMBASE MSR (MSR address 9EH). See Section 34.15.6.3.

•

Bits 24:16 indicate the number of CR3-target values supported by the processor. This number is a value
between 0 and 256, inclusive (bit 24 is set if and only if bits 23:16 are clear).

•

Bits 27:25 is used to compute the recommended maximum number of MSRs that should appear in the VM-exit
MSR-store list, the VM-exit MSR-load list, or the VM-entry MSR-load list. Specifically, if the value bits 27:25 of
IA32_VMX_MISC is N, then 512 * (N + 1) is the recommended maximum number of MSRs to be included in
each list. If the limit is exceeded, undefined processor behavior may result (including a machine check during
the VMX transition).

•

If bit 28 is read as 1, bit 2 of the IA32_SMM_MONITOR_CTL can be set to 1. VMXOFF unblocks SMIs unless
IA32_SMM_MONITOR_CTL[bit 2] is 1 (see Section 34.14.4).

•

If bit 29 is read as 1, software can use VMWRITE to write to any supported field in the VMCS; otherwise,
VMWRITE cannot be used to modify VM-exit information fields.

•

If bit 30 is read as 1, VM entry allows injection of a software interrupt, software exception, or privileged
software exception with an instruction length of 0.

•
•

Bits 63:32 report the 32-bit MSEG revision identifier used by the processor.
Bits 13:9 and bit 31 are reserved and are read as 0.

A.7

VMX-FIXED BITS IN CR0

The IA32_VMX_CR0_FIXED0 MSR (index 486H) and IA32_VMX_CR0_FIXED1 MSR (index 487H) indicate how bits
in CR0 may be set in VMX operation. They report on bits in CR0 that are allowed to be 0 and to be 1, respectively,
in VMX operation. If bit X is 1 in IA32_VMX_CR0_FIXED0, then that bit of CR0 is fixed to 1 in VMX operation. Similarly, if bit X is 0 in IA32_VMX_CR0_FIXED1, then that bit of CR0 is fixed to 0 in VMX operation. It is always the case
that, if bit X is 1 in IA32_VMX_CR0_FIXED0, then that bit is also 1 in IA32_VMX_CR0_FIXED1; if bit X is 0 in
IA32_VMX_CR0_FIXED1, then that bit is also 0 in IA32_VMX_CR0_FIXED0. Thus, each bit in CR0 is either fixed to
0 (with value 0 in both MSRs), fixed to 1 (1 in both MSRs), or flexible (0 in IA32_VMX_CR0_FIXED0 and 1 in
IA32_VMX_CR0_FIXED1).

A.8

VMX-FIXED BITS IN CR4

The IA32_VMX_CR4_FIXED0 MSR (index 488H) and IA32_VMX_CR4_FIXED1 MSR (index 489H) indicate how bits
in CR4 may be set in VMX operation. They report on bits in CR4 that are allowed to be 0 and 1, respectively, in VMX
operation. If bit X is 1 in IA32_VMX_CR4_FIXED0, then that bit of CR4 is fixed to 1 in VMX operation. Similarly, if
bit X is 0 in IA32_VMX_CR4_FIXED1, then that bit of CR4 is fixed to 0 in VMX operation. It is always the case that,
if bit X is 1 in IA32_VMX_CR4_FIXED0, then that bit is also 1 in IA32_VMX_CR4_FIXED1; if bit X is 0 in
IA32_VMX_CR4_FIXED1, then that bit is also 0 in IA32_VMX_CR4_FIXED0. Thus, each bit in CR4 is either fixed to

A-6 Vol. 3D

VMX CAPABILITY REPORTING FACILITY

0 (with value 0 in both MSRs), fixed to 1 (1 in both MSRs), or flexible (0 in IA32_VMX_CR4_FIXED0 and 1 in
IA32_VMX_CR4_FIXED1).

A.9

VMCS ENUMERATION

The IA32_VMX_VMCS_ENUM MSR (index 48AH) provides information to assist software in enumerating fields in
the VMCS.
As noted in Section 24.11.2, each field in the VMCS is associated with a 32-bit encoding which is structured as
follows:

•
•
•
•
•
•

Bits 31:15 are reserved (must be 0).
Bits 14:13 indicate the field’s width.
Bit 12 is reserved (must be 0).
Bits 11:10 indicate the field’s type.
Bits 9:1 is an index field that distinguishes different fields with the same width and type.
Bit 0 indicates access type.

IA32_VMX_VMCS_ENUM indicates to software the highest index value used in the encoding of any field supported
by the processor:

•
•

Bits 9:1 contain the highest index value used for any VMCS encoding.
Bit 0 and bits 63:10 are reserved and are read as 0.

A.10

VPID AND EPT CAPABILITIES

The IA32_VMX_EPT_VPID_CAP MSR (index 48CH) reports information about the capabilities of the logical
processor with regard to virtual-processor identifiers (VPIDs, Section 28.1) and extended page tables (EPT, Section
28.2):

•

If bit 0 is read as 1, the processor supports execute-only translations by EPT. This support allows software to
configure EPT paging-structure entries in which bits 1:0 are clear (indicating that data accesses are not
allowed) and bit 2 is set (indicating that instruction fetches are allowed).1

•
•

Bit 6 indicates support for a page-walk length of 4.

•

If bit 14 is read as 1, the logical processor allows software to configure the EPT paging-structure memory type
to be write-back (WB).

•

If bit 16 is read as 1, the logical processor allows software to configure a EPT PDE to map a 2-Mbyte page (by
setting bit 7 in the EPT PDE).

•

If bit 17 is read as 1, the logical processor allows software to configure a EPT PDPTE to map a 1-Gbyte page (by
setting bit 7 in the EPT PDPTE).

•

Support for the INVEPT instruction (see Chapter 30 and Section 28.3.3.1).

If bit 8 is read as 1, the logical processor allows software to configure the EPT paging-structure memory type
to be uncacheable (UC); see Section 24.6.11.

— If bit 20 is read as 1, the INVEPT instruction is supported.
— If bit 25 is read as 1, the single-context INVEPT type is supported.
— If bit 26 is read as 1, the all-context INVEPT type is supported.

•

If bit 21 is read as 1, accessed and dirty flags for EPT are supported (see Section 28.2.4).

1. If the “mode-based execute control for EPT” VM-execution control is 1, setting bit 0 indicates also that software may also configure
EPT paging-structure entries in which bits 1:0 are both clear and in which bit 10 is set (indicating a translation that can be used to
fetch instructions from a supervisor-mode linear address or a user-mode linear address).
Vol. 3D A-7

VMX CAPABILITY REPORTING FACILITY

•

If bit 22 is read as 1, the processor reports advanced VM-exit information for EPT violations (see Section
27.2.1). This reporting is done only if this bit is read as 1.

•

Support for the INVVPID instruction (see Chapter 30 and Section 28.3.3.1).
— If bit 32 is read as 1, the INVVPID instruction is supported.
— If bit 40 is read as 1, the individual-address INVVPID type is supported.
— If bit 41 is read as 1, the single-context INVVPID type is supported.
— If bit 42 is read as 1, the all-context INVVPID type is supported.
— If bit 43 is read as 1, the single-context-retaining-globals INVVPID type is supported.

•

Bits 5:1, bit 7, bits 13:9, bit 15, bits 19:18, bits 24:23, bits 31:27, bits 39:33, and bits 63:44 are reserved
and are read as 0.

The IA32_VMX_EPT_VPID_CAP MSR exists only on processors that support the 1-setting of the “activate secondary
controls” VM-execution control (only if bit 63 of the IA32_VMX_PROCBASED_CTLS MSR is 1) and that support
either the 1-setting of the “enable EPT” VM-execution control (only if bit 33 of the IA32_VMX_PROCBASED_CTLS2
MSR is 1) or the 1-setting of the “enable VPID” VM-execution control (only if bit 37 of the
IA32_VMX_PROCBASED_CTLS2 MSR is 1).

A.11

VM FUNCTIONS

The IA32_VMX_VMFUNC MSR (index 491H) reports on the allowed settings of the VM-function controls (see
Section 24.6.14). VM entry allows bit X of the VM-function controls to be 1 if bit X in the MSR is set to 1; if bit X in
the MSR is cleared to 0, VM entry fails if bit X of the VM-function controls, the “activate secondary controls” primary
processor-based VM-execution control, and the “enable VM functions” secondary processor-based VM-execution
control are all 1.
The IA32_VMX_VMFUNC MSR exists only on processors that support the 1-setting of the “activate secondary
controls” VM-execution control (only if bit 63 of the IA32_VMX_PROCBASED_CTLS MSR is 1) and the 1-setting of
the “enable VM functions” secondary processor-based VM-execution control (only if bit 45 of the
IA32_VMX_PROCBASED_CTLS2 MSR is 1).

A-8 Vol. 3D

APPENDIX B
FIELD ENCODING IN VMCS
Every component of the VMCS is encoded by a 32-bit field that can be used by VMREAD and VMWRITE. Section
24.11.2 describes the structure of the encoding space (the meanings of the bits in each 32-bit encoding).
This appendix enumerates all fields in the VMCS and their encodings. Fields are grouped by width (16-bit, 32-bit,
etc.) and type (guest-state, host-state, etc.)

B.1

16-BIT FIELDS

A value of 0 in bits 14:13 of an encoding indicates a 16-bit field. Only guest-state areas and the host-state area
contain 16-bit fields. As noted in Section 24.11.2, each 16-bit field allows only full access, meaning that bit 0 of its
encoding is 0. Each such encoding is thus an even number.

B.1.1

16-Bit Control Fields

A value of 0 in bits 11:10 of an encoding indicates a control field. These fields are distinguished by their index value
in bits 9:1. Table B-1 enumerates the 16-bit control fields.

Table B-1. Encoding for 16-Bit Control Fields (0000_00xx_xxxx_xxx0B)
Field Name
Virtual-processor identifier

(VPID)1
2

Posted-interrupt notification vector
EPTP

index3

Index

Encoding

000000000B

00000000H

000000001B

00000002H

000000010B

00000004H

NOTES:
1. This field exists only on processors that support the 1-setting of the “enable VPID” VM-execution control.
2. This field exists only on processors that support the 1-setting of the “process posted interrupts” VM-execution control.
3. This field exists only on processors that support the 1-setting of the “EPT-violation #VE” VM-execution control.

B.1.2

16-Bit Guest-State Fields

A value of 2 in bits 11:10 of an encoding indicates a field in the guest-state area. These fields are distinguished by
their index value in bits 9:1. Table B-2 enumerates 16-bit guest-state fields.

Table B-2. Encodings for 16-Bit Guest-State Fields (0000_10xx_xxxx_xxx0B)
Field Name

Index

Encoding

Guest ES selector

000000000B

00000800H

Guest CS selector

000000001B

00000802H

Guest SS selector

000000010B

00000804H

Guest DS selector

000000011B

00000806H

Guest FS selector

000000100B

00000808H

Guest GS selector

000000101B

0000080AH

Guest LDTR selector

000000110B

0000080CH

Guest TR selector

000000111B

0000080EH

Vol. 3D B-1

FIELD ENCODING IN VMCS

Table B-2. Encodings for 16-Bit Guest-State Fields (0000_10xx_xxxx_xxx0B) (Contd.)
Field Name

Index

Encoding

Guest interrupt status

000001000B

00000810H

2

000001001B

00000812H

1

PML index

NOTES:
1. This field exists only on processors that support the 1-setting of the “virtual-interrupt delivery” VM-execution control.
2. This field exists only on processors that support the 1-setting of the “enable PML” VM-execution control.

B.1.3

16-Bit Host-State Fields

A value of 3 in bits 11:10 of an encoding indicates a field in the host-state area. These fields are distinguished by
their index value in bits 9:1. Table B-3 enumerates the 16-bit host-state fields.

Table B-3. Encodings for 16-Bit Host-State Fields (0000_11xx_xxxx_xxx0B)
Field Name

Index

Encoding

Host ES selector

000000000B

00000C00H

Host CS selector

000000001B

00000C02H

Host SS selector

000000010B

00000C04H

Host DS selector

000000011B

00000C06H

Host FS selector

000000100B

00000C08H

Host GS selector

000000101B

00000C0AH

Host TR selector

000000110B

00000C0CH

B.2

64-BIT FIELDS

A value of 1 in bits 14:13 of an encoding indicates a 64-bit field. There are 64-bit fields only for controls and for
guest state. As noted in Section 24.11.2, every 64-bit field has two encodings, which differ on bit 0, the access
type. Thus, each such field has an even encoding for full access and an odd encoding for high access.

B.2.1

64-Bit Control Fields

A value of 0 in bits 11:10 of an encoding indicates a control field. These fields are distinguished by their index value
in bits 9:1. Table B-4 enumerates the 64-bit control fields.

Table B-4. Encodings for 64-Bit Control Fields (0010_00xx_xxxx_xxxAb)
Field Name

Index

Address of I/O bitmap A (full)

000000000B

Address of I/O bitmap A (high)
Address of I/O bitmap B (full)

000000001B

Address of I/O bitmap B (high)
Address of MSR bitmaps

(full)1
1

Address of MSR bitmaps (high)

VM-exit MSR-store address (full)
VM-exit MSR-store address (high)

B-2 Vol. 3D

000000010B
000000011B

Encoding
00002000H
00002001H
00002002H
00002003H
00002004H
00002005H
00002006H
00002007H

FIELD ENCODING IN VMCS

Table B-4. Encodings for 64-Bit Control Fields (0010_00xx_xxxx_xxxAb) (Contd.)
Field Name

Index

VM-exit MSR-load address (full)

000000100B

VM-exit MSR-load address (high)
VM-entry MSR-load address (full)

000000101B

VM-entry MSR-load address (high)
Executive-VMCS pointer (full)

000000110B

Executive-VMCS pointer (high)
PML address

(full)2

000000111B

2

PML address (high)
TSC offset (full)

000001000B

TSC offset (high)
Virtual-APIC address

(full)3

000001001B

3

Virtual-APIC address (high)
APIC-access address

(full)4

APIC-access address

(high)4

000001010B

Posted-interrupt descriptor address

(full)5

Posted-interrupt descriptor address

(high)5

VM-function controls

000001011B

(full)6

000001100B

6

VM-function controls (high)
EPT pointer (EPTP;

full)7

EPT pointer (EPTP;

high)7

000001101B

EOI-exit bitmap 0 (EOI_EXIT0;

full)8

EOI-exit bitmap 0 (EOI_EXIT0;

high)8

EOI-exit bitmap 1 (EOI_EXIT1;

full)8

000001110B
000001111B

8

EOI-exit bitmap 1 (EOI_EXIT1; high)
EOI-exit bitmap 2 (EOI_EXIT2;

full)8

EOI-exit bitmap 2 (EOI_EXIT2;

high)8

EOI-exit bitmap 3 (EOI_EXIT3;

full)8

EOI-exit bitmap 3 (EOI_EXIT3;

high)8

EPTP-list address

000010000B
000010001B

(full)9

EPTP-list address (high)

000010010B

9

VMREAD-bitmap address

(full)10

VMREAD-bitmap address

(high)10

VMWRITE-bitmap address

(full)10

VMWRITE-bitmap address

(high)10

Virtualization-exception information address

000010011B
000010100B
(full)11
11

Virtualization-exception information address (high)
XSS-exiting bitmap

(full)12

XSS-exiting bitmap

(high)12

000010101B
000010110B

Encoding
00002008H
00002009H
0000200AH
0000200BH
0000200CH
0000200DH
0000200EH
0000200FH
00002010H
00002011H
00002012H
00002013H
00002014H
00002015H
00002016H
00002017H
00002018H
00002019H
0000201AH
0000201BH
0000201CH
0000201DH
0000201EH
0000201FH
00002020H
00002021H
00002022H
00002023H
00002024H
00002025H
00002026H
00002027H
00002028H
00002029H
0000202AH
0000202BH
0000202CH
0000202DH

Vol. 3D B-3

FIELD ENCODING IN VMCS

Table B-4. Encodings for 64-Bit Control Fields (0010_00xx_xxxx_xxxAb) (Contd.)
Field Name

Index

ENCLS-exiting bitmap (full)

13

ENCLS-exiting bitmap (high)

13

000010111B

14

TSC multiplier (full)
TSC multiplier

000011001B

(high)14

Encoding
0000202EH
0000202FH
00002032H
00002033H

NOTES:
1. This field exists only on processors that support the 1-setting of the “use MSR bitmaps”
VM-execution control.
2. This field exists only on processors that support the 1-setting of the “enable PML” VM-execution control.
3. This field exists only on processors that support the 1-setting of the “use TPR shadow” VM-execution control.
4. This field exists only on processors that support the 1-setting of the “virtualize APIC accesses” VM-execution control.
5. This field exists only on processors that support the 1-setting of the “process posted interrupts” VM-execution control.
6. This field exists only on processors that support the 1-setting of the “enable VM functions” VM-execution control.
7. This field exists only on processors that support the 1-setting of the “enable EPT” VM-execution control.
8. This field exists only on processors that support the 1-setting of the “virtual-interrupt delivery” VM-execution control.
9. This field exists only on processors that support the 1-setting of the “EPTP switching” VM-function control.
10. This field exists only on processors that support the 1-setting of the “VMCS shadowing” VM-execution control.
11. This field exists only on processors that support the 1-setting of the “EPT-violation #VE” VM-execution control.
12. This field exists only on processors that support the 1-setting of the “enable XSAVES/XRSTORS” VM-execution control.
13. This field exists only on processors that support the 1-setting of the “enable ENCLS exiting” VM-execution control.
14. This field exists only on processors that support the 1-setting of the “use TSC scaling” VM-execution control.

B.2.2

64-Bit Read-Only Data Field

A value of 1 in bits 11:10 of an encoding indicates a read-only data field. These fields are distinguished by their
index value in bits 9:1. There is only one such 64-bit field as given in Table B-5.(As with other 64-bit fields, this one
has two encodings.)

Table B-5. Encodings for 64-Bit Read-Only Data Field (0010_01xx_xxxx_xxxAb)
Field Name

Index

Guest-physical address

(full)1

Guest-physical address

(high)1

000000000B

Encoding
00002400H
00002401H

NOTES:
1. This field exists only on processors that support the 1-setting of the "enable EPT” VM-execution control.

B.2.3

64-Bit Guest-State Fields

A value of 2 in bits 11:10 of an encoding indicates a field in the guest-state area. These fields are distinguished by
their index value in bits 9:1. Table B-6 enumerates the 64-bit guest-state fields.

Table B-6. Encodings for 64-Bit Guest-State Fields (0010_10xx_xxxx_xxxAb)
Field Name
VMCS link pointer (full)
VMCS link pointer (high)
Guest IA32_DEBUGCTL (full)
Guest IA32_DEBUGCTL (high)
B-4 Vol. 3D

Index
000000000B
000000001B

Encoding
00002800H
00002801H
00002802H
00002803H

FIELD ENCODING IN VMCS

Table B-6. Encodings for 64-Bit Guest-State Fields (0010_10xx_xxxx_xxxAb) (Contd.)
Field Name

Index

Encoding

1

Guest IA32_PAT (full)

00002804H

000000010B

1

Guest IA32_PAT (high)

00002805H

2

Guest IA32_EFER (full)
Guest IA32_EFER

00002806H

000000011B

(high)2

00002807H

3

Guest IA32_PERF_GLOBAL_CTRL (full)
Guest IA32_PERF_GLOBAL_CTRL
Guest PDPTE0

(high)3

(full)4

00002809H
0000280AH

000000101B

4

Guest PDPTE0 (high)
Guest PDPTE1 (full)

00002808H

000000100B

0000280BH

4

Guest PDPTE1

(high)4

Guest PDPTE2

(full)4

Guest PDPTE2 (high)
Guest PDPTE3
Guest PDPTE3

(high)4

0000280DH
0000280EH

000000111B

4

(full)4

0000280CH

000000110B

0000280FH
00002810H

000001000B

Guest IA32_BNDCFGS

(full)5

Guest IA32_BNDCFGS

(high)5

00002811H
00002812H

000001001B

00002813H

NOTES:
1. This field exists only on processors that support either the 1-setting of the "load IA32_PAT" VM-entry control or that of the "save
IA32_PAT" VM-exit control.
2. This field exists only on processors that support either the 1-setting of the "load IA32_EFER" VM-entry control or that of the "save
IA32_EFER" VM-exit control.
3. This field exists only on processors that support the 1-setting of the "load IA32_PERF_GLOBAL_CTRL" VM-entry control.
4. This field exists only on processors that support the 1-setting of the "enable EPT" VM-execution control.
5. This field exists only on processors that support either the 1-setting of the “load IA32_BNDCFGS” VM-entry control or that of the
“clear IA32_BNDCFGS” VM-exit control.

B.2.4

64-Bit Host-State Fields

A value of 3 in bits 11:10 of an encoding indicates a field in the host-state area. These fields are distinguished by
their index value in bits 9:1. Table B-7 enumerates the 64-bit control fields.

Table B-7. Encodings for 64-Bit Host-State Fields (0010_11xx_xxxx_xxxAb)
Field Name
Host IA32_PAT

Index
(full)1

000000000B

1

Host IA32_PAT (high)

2

Host IA32_EFER (full)
Host IA32_EFER

000000001B

(high)2

Host IA32_PERF_GLOBAL_CTRL

(full)3

Host IA32_PERF_GLOBAL_CTRL

(high)3

000000010B

Encoding
00002C00H
00002C01H
00002C02H
00002C03H
00002C04H
00002C05H

NOTES:
1. This field exists only on processors that support the 1-setting of the "load IA32_PAT" VM-exit control.
2. This field exists only on processors that support the 1-setting of the "load IA32_EFER" VM-exit control.

Vol. 3D B-5

FIELD ENCODING IN VMCS

3. This field exists only on processors that support the 1-setting of the "load IA32_PERF_GLOBAL_CTRL" VM-exit control.

B.3

32-BIT FIELDS

A value of 2 in bits 14:13 of an encoding indicates a 32-bit field. As noted in Section 24.11.2, each 32-bit field
allows only full access, meaning that bit 0 of its encoding is 0. Each such encoding is thus an even number.

B.3.1

32-Bit Control Fields

A value of 0 in bits 11:10 of an encoding indicates a control field. These fields are distinguished by their index value
in bits 9:1. Table B-8 enumerates the 32-bit control fields.

Table B-8. Encodings for 32-Bit Control Fields (0100_00xx_xxxx_xxx0B)
Field Name

Index

Encoding

Pin-based VM-execution controls

000000000B

00004000H

Primary processor-based VM-execution controls

000000001B

00004002H

Exception bitmap

000000010B

00004004H

Page-fault error-code mask

000000011B

00004006H

Page-fault error-code match

000000100B

00004008H

CR3-target count

000000101B

0000400AH

VM-exit controls

000000110B

0000400CH

VM-exit MSR-store count

000000111B

0000400EH

VM-exit MSR-load count

000001000B

00004010H

VM-entry controls

000001001B

00004012H

VM-entry MSR-load count

000001010B

00004014H

VM-entry interruption-information field

000001011B

00004016H

VM-entry exception error code

000001100B

00004018H

VM-entry instruction length

000001101B

0000401AH

000001110B

0000401CH

TPR

threshold1

Secondary processor-based VM-execution

controls2

000001111b

0000401EH

PLE_Gap3

000010000b

00004020H

PLE_Window3

000010001b

00004022H

NOTES:
1. This field exists only on processors that support the 1-setting of the “use TPR shadow” VM-execution control.
2. This field exists only on processors that support the 1-setting of the “activate secondary controls” VM-execution control.
3. This field exists only on processors that support the 1-setting of the “PAUSE-loop exiting” VM-execution control.

B-6 Vol. 3D

FIELD ENCODING IN VMCS

B.3.2

32-Bit Read-Only Data Fields

A value of 1 in bits 11:10 of an encoding indicates a read-only data field. These fields are distinguished by their
index value in bits 9:1. Table B-9 enumerates the 32-bit read-only data fields.

Table B-9. Encodings for 32-Bit Read-Only Data Fields (0100_01xx_xxxx_xxx0B)
Field Name

Index

Encoding

VM-instruction error

000000000B

00004400H

Exit reason

000000001B

00004402H

VM-exit interruption information

000000010B

00004404H

VM-exit interruption error code

000000011B

00004406H

IDT-vectoring information field

000000100B

00004408H

IDT-vectoring error code

000000101B

0000440AH

VM-exit instruction length

000000110B

0000440CH

VM-exit instruction information

000000111B

0000440EH

B.3.3

32-Bit Guest-State Fields

A value of 2 in bits 11:10 of an encoding indicates a field in the guest-state area. These fields are distinguished by
their index value in bits 9:1. Table B-10 enumerates the 32-bit guest-state fields.

Table B-10. Encodings for 32-Bit Guest-State Fields
(0100_10xx_xxxx_xxx0B)
Field Name

Index

Encoding

Guest ES limit

000000000B

00004800H

Guest CS limit

000000001B

00004802H

Guest SS limit

000000010B

00004804H

Guest DS limit

000000011B

00004806H

Guest FS limit

000000100B

00004808H

Guest GS limit

000000101B

0000480AH

Guest LDTR limit

000000110B

0000480CH

Guest TR limit

000000111B

0000480EH

Guest GDTR limit

000001000B

00004810H

Guest IDTR limit

000001001B

00004812H

Guest ES access rights

000001010B

00004814H

Guest CS access rights

000001011B

00004816H

Guest SS access rights

000001100B

00004818H

Guest DS access rights

000001101B

0000481AH

Guest FS access rights

000001110B

0000481CH

Guest GS access rights

000001111B

0000481EH

Guest LDTR access rights

000010000B

00004820H

Guest TR access rights

000010001B

00004822H

Guest interruptibility state

000010010B

00004824H

Guest activity state

000010011B

00004826H

Vol. 3D B-7

FIELD ENCODING IN VMCS

Table B-10. Encodings for 32-Bit Guest-State Fields
(0100_10xx_xxxx_xxx0B) (Contd.)
Field Name

Index

Encoding

Guest SMBASE

000010100B

00004828H

000010101B

0000482AH

000010111B

0000482EH

Guest IA32_SYSENTER_CS
1

VMX-preemption timer value

NOTES:
1. This field exists only on processors that support the 1-setting of the "activate VMX-preemption timer" VM-execution control.
The limit fields for GDTR and IDTR are defined to be 32 bits in width even though these fields are only 16-bits wide
in the Intel 64 and IA-32 architectures. VM entry ensures that the high 16 bits of both these fields are cleared to 0.

B.3.4

32-Bit Host-State Field

A value of 3 in bits 11:10 of an encoding indicates a field in the host-state area. There is only one such 32-bit field
as given in Table B-11.

Table B-11. Encoding for 32-Bit Host-State Field (0100_11xx_xxxx_xxx0B)
Field Name

Index

Encoding

Host IA32_SYSENTER_CS

000000000B

00004C00H

B.4

NATURAL-WIDTH FIELDS

A value of 3 in bits 14:13 of an encoding indicates a natural-width field. As noted in Section 24.11.2, each of these
fields allows only full access, meaning that bit 0 of its encoding is 0. Each such encoding is thus an even number.

B.4.1

Natural-Width Control Fields

A value of 0 in bits 11:10 of an encoding indicates a control field. These fields are distinguished by their index value
in bits 9:1. Table B-12 enumerates the natural-width control fields.

Table B-12. Encodings for Natural-Width Control Fields (0110_00xx_xxxx_xxx0B)
Field Name

Index

Encoding

CR0 guest/host mask

000000000B

00006000H

CR4 guest/host mask

000000001B

00006002H

CR0 read shadow

000000010B

00006004H

CR4 read shadow

000000011B

00006006H

CR3-target value 0

000000100B

00006008H

CR3-target value 1

000000101B

0000600AH

CR3-target value 2

000000110B

0000600CH

000000111B

0000600EH

CR3-target value

31

NOTES:
1. If a future implementation supports more than 4 CR3-target values, they will be encoded consecutively following the 4 encodings
given here.

B-8 Vol. 3D

FIELD ENCODING IN VMCS

B.4.2

Natural-Width Read-Only Data Fields

A value of 1 in bits 11:10 of an encoding indicates a read-only data field. These fields are distinguished by their
index value in bits 9:1. Table B-13 enumerates the natural-width read-only data fields.

Table B-13. Encodings for Natural-Width Read-Only Data Fields (0110_01xx_xxxx_xxx0B)
Field Name

Index

Encoding

Exit qualification

000000000B

00006400H

I/O RCX

000000001B

00006402H

I/O RSI

000000010B

00006404H

I/O RDI

000000011B

00006406H

I/O RIP

000000100B

00006408H

Guest-linear address

000000101B

0000640AH

B.4.3

Natural-Width Guest-State Fields

A value of 2 in bits 11:10 of an encoding indicates a field in the guest-state area. These fields are distinguished by
their index value in bits 9:1. Table B-14 enumerates the natural-width guest-state fields.

Table B-14. Encodings for Natural-Width Guest-State Fields (0110_10xx_xxxx_xxx0B)
Field Name

Index

Encoding

Guest CR0

000000000B

00006800H

Guest CR3

000000001B

00006802H

Guest CR4

000000010B

00006804H

Guest ES base

000000011B

00006806H

Guest CS base

000000100B

00006808H

Guest SS base

000000101B

0000680AH

Guest DS base

000000110B

0000680CH

Guest FS base

000000111B

0000680EH

Guest GS base

000001000B

00006810H

Guest LDTR base

000001001B

00006812H

Guest TR base

000001010B

00006814H

Guest GDTR base

000001011B

00006816H

Guest IDTR base

000001100B

00006818H

Guest DR7

000001101B

0000681AH

Guest RSP

000001110B

0000681CH

Guest RIP

000001111B

0000681EH

Guest RFLAGS

000010000B

00006820H

Guest pending debug exceptions

000010001B

00006822H

Guest IA32_SYSENTER_ESP

000010010B

00006824H

Guest IA32_SYSENTER_EIP

000010011B

00006826H

The base-address fields for ES, CS, SS, and DS in the guest-state area are defined to be natural-width (with 64 bits
on processors supporting Intel 64 architecture) even though these fields are only 32-bits wide in the Intel 64 architecture. VM entry ensures that the high 32 bits of these fields are cleared to 0.
Vol. 3D B-9

FIELD ENCODING IN VMCS

B.4.4

Natural-Width Host-State Fields

A value of 3 in bits 11:10 of an encoding indicates a field in the host-state area. These fields are distinguished by
their index value in bits 9:1. Table B-15 enumerates the natural-width host-state fields.

Table B-15. Encodings for Natural-Width Host-State Fields (0110_11xx_xxxx_xxx0B)
Field Name

Index

Encoding

Host CR0

000000000B

00006C00H

Host CR3

000000001B

00006C02H

Host CR4

000000010B

00006C04H

Host FS base

000000011B

00006C06H

Host GS base

000000100B

00006C08H

Host TR base

000000101B

00006C0AH

Host GDTR base

000000110B

00006C0CH

Host IDTR base

000000111B

00006C0EH

Host IA32_SYSENTER_ESP

000001000B

00006C10H

Host IA32_SYSENTER_EIP

000001001B

00006C12H

Host RSP

000001010B

00006C14H

Host RIP

000001011B

00006C16H

B-10 Vol. 3D

APPENDIX C
VMX BASIC EXIT REASONS
Every VM exit writes a 32-bit exit reason to the VMCS (see Section 24.9.1). Certain VM-entry failures also do this
(see Section 26.7). The low 16 bits of the exit-reason field form the basic exit reason which provides basic information about the cause of the VM exit or VM-entry failure.
Table C-1 lists values for basic exit reasons and explains their meaning. Entries apply to VM exits, unless otherwise
noted.

Table C-1. Basic Exit Reasons
Basic Exit
Reason

Description

0

Exception or non-maskable interrupt (NMI). Either:
1: Guest software caused an exception and the bit in the exception bitmap associated with exception’s vector was 1.
2: An NMI was delivered to the logical processor and the “NMI exiting” VM-execution control was 1. This case includes
executions of BOUND that cause #BR, executions of INT3 (they cause #BP), executions of INTO that cause #OF,
and executions of UD (they cause #UD).

1

External interrupt. An external interrupt arrived and the “external-interrupt exiting” VM-execution control was 1.

2

Triple fault. The logical processor encountered an exception while attempting to call the double-fault handler and
that exception did not itself cause a VM exit due to the exception bitmap.

3

INIT signal. An INIT signal arrived

4

Start-up IPI (SIPI). A SIPI arrived while the logical processor was in the “wait-for-SIPI” state.

5

I/O system-management interrupt (SMI). An SMI arrived immediately after retirement of an I/O instruction and
caused an SMM VM exit (see Section 34.15.2).

6

Other SMI. An SMI arrived and caused an SMM VM exit (see Section 34.15.2) but not immediately after retirement of
an I/O instruction.

7

Interrupt window. At the beginning of an instruction, RFLAGS.IF was 1; events were not blocked by STI or by MOV
SS; and the “interrupt-window exiting” VM-execution control was 1.

8

NMI window. At the beginning of an instruction, there was no virtual-NMI blocking; events were not blocked by MOV
SS; and the “NMI-window exiting” VM-execution control was 1.

9

Task switch. Guest software attempted a task switch.

10

CPUID. Guest software attempted to execute CPUID.

11

GETSEC. Guest software attempted to execute GETSEC.

12

HLT. Guest software attempted to execute HLT and the “HLT exiting” VM-execution control was 1.

13

INVD. Guest software attempted to execute INVD.

14

INVLPG. Guest software attempted to execute INVLPG and the “INVLPG exiting” VM-execution control was 1.

15

RDPMC. Guest software attempted to execute RDPMC and the “RDPMC exiting” VM-execution control was 1.

16

RDTSC. Guest software attempted to execute RDTSC and the “RDTSC exiting” VM-execution control was 1.

17

RSM. Guest software attempted to execute RSM in SMM.

18

VMCALL. VMCALL was executed either by guest software (causing an ordinary VM exit) or by the executive monitor
(causing an SMM VM exit; see Section 34.15.2).

19

VMCLEAR. Guest software attempted to execute VMCLEAR.

20

VMLAUNCH. Guest software attempted to execute VMLAUNCH.

21

VMPTRLD. Guest software attempted to execute VMPTRLD.

22

VMPTRST. Guest software attempted to execute VMPTRST.

23

VMREAD. Guest software attempted to execute VMREAD.

Vol. 3D C-1

VMX BASIC EXIT REASONS

Table C-1. Basic Exit Reasons (Contd.)
Basic Exit
Reason

Description

24

VMRESUME. Guest software attempted to execute VMRESUME.

25

VMWRITE. Guest software attempted to execute VMWRITE.

26

VMXOFF. Guest software attempted to execute VMXOFF.

27

VMXON. Guest software attempted to execute VMXON.

28

Control-register accesses. Guest software attempted to access CR0, CR3, CR4, or CR8 using CLTS, LMSW, or
MOV CR and the VM-execution control fields indicate that a VM exit should occur (see Section 25.1 for details). This
basic exit reason is not used for trap-like VM exits following executions of the MOV to CR8 instruction when the “use
TPR shadow” VM-execution control is 1. Such VM exits instead use basic exit reason 43.

29

MOV DR. Guest software attempted a MOV to or from a debug register and the “MOV-DR exiting” VM-execution
control was 1.

30

I/O instruction. Guest software attempted to execute an I/O instruction and either:
1: The “use I/O bitmaps” VM-execution control was 0 and the “unconditional I/O exiting” VM-execution control was 1.
2: The “use I/O bitmaps” VM-execution control was 1 and a bit in the I/O bitmap associated with one of the ports
accessed by the I/O instruction was 1.

31

RDMSR. Guest software attempted to execute RDMSR and either:
1: The “use MSR bitmaps” VM-execution control was 0.
2: The value of RCX is neither in the range 00000000H – 00001FFFH nor in the range C0000000H – C0001FFFH.
3: The value of RCX was in the range 00000000H – 00001FFFH and the nth bit in read bitmap for low MSRs is 1,
where n was the value of RCX.
4: The value of RCX is in the range C0000000H – C0001FFFH and the nth bit in read bitmap for high MSRs is 1, where
n is the value of RCX & 00001FFFH.

32

WRMSR. Guest software attempted to execute WRMSR and either:
1: The “use MSR bitmaps” VM-execution control was 0.
2: The value of RCX is neither in the range 00000000H – 00001FFFH nor in the range C0000000H – C0001FFFH.
3: The value of RCX was in the range 00000000H – 00001FFFH and the nth bit in write bitmap for low MSRs is 1,
where n was the value of RCX.
4: The value of RCX is in the range C0000000H – C0001FFFH and the nth bit in write bitmap for high MSRs is 1,
where n is the value of RCX & 00001FFFH.

33

VM-entry failure due to invalid guest state. A VM entry failed one of the checks identified in Section 26.3.1.

34

VM-entry failure due to MSR loading. A VM entry failed in an attempt to load MSRs. See Section 26.4.

36

MWAIT. Guest software attempted to execute MWAIT and the “MWAIT exiting” VM-execution control was 1.

37

Monitor trap flag. A VM entry occurred due to the 1-setting of the “monitor trap flag” VM-execution control and
injection of an MTF VM exit as part of VM entry. See Section 25.5.2.

39

MONITOR. Guest software attempted to execute MONITOR and the “MONITOR exiting” VM-execution control was 1.

40

PAUSE. Either guest software attempted to execute PAUSE and the “PAUSE exiting” VM-execution control was 1 or
the “PAUSE-loop exiting” VM-execution control was 1 and guest software executed a PAUSE loop with execution
time exceeding PLE_Window (see Section 25.1.3).

41

VM-entry failure due to machine-check event. A machine-check event occurred during VM entry (see Section
26.8).

43

TPR below threshold. The logical processor determined that the value of bits 7:4 of the byte at offset 080H on the
virtual-APIC page was below that of the TPR threshold VM-execution control field while the “use TPR shadow” VMexecution control was 1 either as part of TPR virtualization (Section 29.1.2) or VM entry (Section 26.6.7).

44

APIC access. Guest software attempted to access memory at a physical address on the APIC-access page and the
“virtualize APIC accesses” VM-execution control was 1 (see Section 29.4).

45

Virtualized EOI. EOI virtualization was performed for a virtual interrupt whose vector indexed a bit set in the EOIexit bitmap.

C-2 Vol. 3D

VMX BASIC EXIT REASONS

Table C-1. Basic Exit Reasons (Contd.)
Basic Exit
Reason

Description

46

Access to GDTR or IDTR. Guest software attempted to execute LGDT, LIDT, SGDT, or SIDT and the “descriptor-table
exiting” VM-execution control was 1.

47

Access to LDTR or TR. Guest software attempted to execute LLDT, LTR, SLDT, or STR and the “descriptor-table
exiting” VM-execution control was 1.

48

EPT violation. An attempt to access memory with a guest-physical address was disallowed by the configuration of
the EPT paging structures.

49

EPT misconfiguration. An attempt to access memory with a guest-physical address encountered a misconfigured
EPT paging-structure entry.

50

INVEPT. Guest software attempted to execute INVEPT.

51

RDTSCP. Guest software attempted to execute RDTSCP and the “enable RDTSCP” and “RDTSC exiting” VM-execution
controls were both 1.

52

VMX-preemption timer expired. The preemption timer counted down to zero.

53

INVVPID. Guest software attempted to execute INVVPID.

54

WBINVD. Guest software attempted to execute WBINVD and the “WBINVD exiting” VM-execution control was 1.

55

XSETBV. Guest software attempted to execute XSETBV.

56

APIC write. Guest software completed a write to the virtual-APIC page that must be virtualized by VMM software
(see Section 29.4.3.3).

57

RDRAND. Guest software attempted to execute RDRAND and the “RDRAND exiting” VM-execution control was 1.

58

INVPCID. Guest software attempted to execute INVPCID and the “enable INVPCID” and “INVLPG exiting”
VM-execution controls were both 1.

59

VMFUNC. Guest software invoked a VM function with the VMFUNC instruction and the VM function either was not
enabled or generated a function-specific condition causing a VM exit.

60

ENCLS. Guest software attempted to execute ENCLS and “enable ENCLS exiting” VM-execution control was 1 and
either (1) EAX < 63 and the corresponding bit in the ENCLS-exiting bitmap is 1; or (2) EAX ≥ 63 and bit 63 in the
ENCLS-exiting bitmap is 1.

61

RDSEED. Guest software attempted to execute RDSEED and the “RDSEED exiting” VM-execution control was 1.

62

Page-modification log full. The processor attempted to create a page-modification log entry and the value of the
PML index was not in the range 0–511.

63

XSAVES. Guest software attempted to execute XSAVES, the “enable XSAVES/XRSTORS” was 1, and a bit was set in
the logical-AND of the following three values: EDX:EAX, the IA32_XSS MSR, and the XSS-exiting bitmap.

64

XRSTORS. Guest software attempted to execute XRSTORS, the “enable XSAVES/XRSTORS” was 1, and a bit was set
in the logical-AND of the following three values: EDX:EAX, the IA32_XSS MSR, and the XSS-exiting bitmap.

Vol. 3D C-3

VMX BASIC EXIT REASONS

C-4 Vol. 3D

INDEX
Numerics
16-bit code, mixing with 32-bit code, 21-1
32-bit code, mixing with 16-bit code, 21-1
32-bit physical addressing
overview, 3-6
36-bit physical addressing
overview, 3-6
64-bit mode
call gates, 5-14
code segment descriptors, 5-3, 9-12
control registers, 2-13
CR8 register, 2-13
D flag, 5-4
debug registers, 2-7
descriptors, 5-3, 5-5
DPL field, 5-4
exception handling, 6-16
external interrupts, 10-31
fast system calls, 5-22
GDTR register, 2-12, 2-13
GP faults, causes of, 6-37
IDTR register, 2-12
initialization process, 2-8, 9-11
interrupt and trap gates, 6-16
interrupt controller, 10-31
interrupt descriptors, 2-5
interrupt handling, 6-16
interrupt stack table, 6-19
IRET instruction, 6-18
L flag, 3-12, 5-4
logical address translation, 3-7
MOV CRn, 2-13, 10-31
null segment checking, 5-6
paging, 2-6
reading counters, 2-26
reading & writing MSRs, 2-26
registers and mode changes, 9-12
RFLAGS register, 2-11
segment descriptor tables, 3-16, 5-3
segment loading instructions, 3-9
segments, 3-5
stack switching, 5-19, 6-18
SYSCALL and SYSRET, 2-7, 5-22
SYSENTER and SYSEXIT, 5-21
system registers, 2-7
task gate, 7-16
task priority, 2-19, 10-31
task register, 2-13
TSS
stack pointers, 7-17
See also: IA-32e mode, compatibility mode
8086
emulation, support for, 20-1
processor, exceptions and interrupts, 20-6
8086/8088 processor, 22-7
8087 math coprocessor, 22-7
82489DX, 22-27, 22-28
Local APIC and I/O APICs, 10-4

A
A20M# signal, 20-2, 22-34, 23-4
Aborts
description of, 6-5
restarting a program or task after, 6-5
AC (alignment check) flag, EFLAGS register, 2-11, 6-44, 22-6
Access rights
checking, 2-23

checking caller privileges, 5-26
description of, 5-24
invalid values, 22-19
ADC instruction, 8-3
ADD instruction, 8-3
Address
size prefix, 21-1
space, of task, 7-14
Address translation
in real-address mode, 20-2
logical to linear, 3-7
overview, 3-6
Addressing, segments, 1-8
Advanced power management
C-state and Sub C-state, 14-18
MWAIT extensions, 14-18
See also: thermal monitoring
Advanced programmable interrupt controller (see I/O APIC or Local APIC)
Alignment
check exception, 2-11, 6-44, 22-11, 22-21
checking, 5-27
AM (alignment mask) flag
CR0 control register, 2-15, 22-18
AND instruction, 8-3
APIC, 10-40, 10-41
APIC bus
arbitration mechanism and protocol, 10-26, 10-33
bus message format, 10-34, 10-47
diagram of, 10-2, 10-3
EOI message format, 10-15, 10-47
nonfocused lowest priority message, 10-49
short message format, 10-48
SMI message, 34-2
status cycles, 10-50
structure of, 10-4
See also
local APIC
APIC flag, CPUID instruction, 10-8
APIC ID, 10-40, 10-44, 10-46
APIC (see I/O APIC or Local APIC)
ARPL instruction, 2-24, 5-27
not supported in 64-bit mode, 2-24
Atomic operations
automatic bus locking, 8-3
effects of a locked operation on internal processor caches, 8-5
guaranteed, description of, 8-2
overview of, 8-1, 8-3
software-controlled bus locking, 8-3
At-retirement
counting, 18-87, 18-88, 18-103
events, 18-87, 18-88, 18-93, 18-94, 18-103, 18-108
Auto HALT restart
field, SMM, 34-14
SMM, 34-13
Automatic bus locking, 8-3
Automatic thermal monitoring mechanism, 14-19

B
B (busy) flag
TSS descriptor, 7-5, 7-10, 7-13, 8-3
B (default stack size) flag
segment descriptor, 21-1, 22-33
B0-B3 (BP condition detected) flags
DR6 register, 17-3
Backlink (see Previous task link)
Base address fields, segment descriptor, 3-10
BD (debug register access detected) flag, DR6 register, 17-3, 17-9
Vol. 3D INDEX-1

INDEX

Binary numbers, 1-8
BINIT# signal, 2-25
BIOS role in microcode updates, 9-38
Bit order, 1-6
BOUND instruction, 2-5, 6-4, 6-25
BOUND range exceeded exception (#BR), 6-25
BP0#, BP1#, BP2#, and BP3# pins, 17-38, 17-40
Branch record
branch trace message, 17-13
IA-32e mode, 17-21
saving, 17-15, 17-25, 17-26, 17-35
saving as a branch trace message, 17-13
structure, 17-35
structure of in BTS buffer, 17-19
Branch trace message (see BTM)
Branch trace store (see BTS)
Breakpoint exception (#BP), 6-4, 6-23, 17-10
Breakpoints
data breakpoint, 17-5
data breakpoint exception conditions, 17-9
description of, 17-1
DR0-DR3 debug registers, 17-3
example, 17-5
exception, 6-23
field recognition, 17-5, 17-6
general-detect exception condition, 17-9
instruction breakpoint, 17-5
instruction breakpoint exception condition, 17-8
I/O breakpoint exception conditions, 17-9
LEN0 - LEN3 (Length) fields
DR7 register, 17-5
R/W0-R/W3 (read/write) fields
DR7 register, 17-4
single-step exception condition, 17-9
task-switch exception condition, 17-10
BS (single step) flag, DR6 register, 17-3
BSP flag, IA32_APIC_BASE MSR, 10-8
BSWAP instruction, 22-4
BT (task switch) flag, DR6 register, 17-3, 17-10
BTC instruction, 8-3
BTF (single-step on branches) flag
DEBUGCTLMSR MSR, 17-40
BTMs (branch trace messages)
description of, 17-13
enabling, 17-11, 17-23, 17-24, 17-34, 17-37, 17-38
TR (trace message enable) flag
MSR_DEBUGCTLA MSR, 17-34
MSR_DEBUGCTLB MSR, 17-11, 17-37, 17-38
BTR instruction, 8-3
BTS buffer
description of, 17-18
introduction to, 17-11, 17-13
records in, 17-19
setting up, 17-23
structure of, 17-19, 17-21, 18-21, 18-82
BTS instruction, 8-3
BTS (branch trace store) facilities
availability of, 17-33
BTS_UNAVAILABLE flag,
IA32_MISC_ENABLE MSR, 17-18
introduction to, 17-11
setting up BTS buffer, 17-23
writing an interrupt service routine for, 17-24
BTS_UNAVAILABLE, 17-18
Built-in self-test (BIST)
description of, 9-1
performing, 9-5
Bus
errors detected with MCA, 15-27
hold, 22-35
locking, 8-3, 22-35
Byte order, 1-6
INDEX-2 Vol. 3D

C
C (conforming) flag, segment descriptor, 5-11
C1 flag, x87 FPU status word, 22-8, 22-14
C2 flag, x87 FPU status word, 22-8
Cache control, 11-20
adaptive mode, L1 Data Cache, 11-18
cache management instructions, 11-17, 11-18
cache mechanisms in IA-32 processors, 22-30
caching terminology, 11-5
CD flag, CR0 control register, 11-10, 22-19
choosing a memory type, 11-8
CPUID feature flag, 11-18
flags and fields, 11-10
flushing TLBs, 11-19
G (global) flag
page-directory entries, 11-13
page-table entries, 11-13
internal caches, 11-1
MemTypeGet() function, 11-29
MemTypeSet() function, 11-31
MESI protocol, 11-5, 11-9
methods of caching available, 11-6
MTRR initialization, 11-29
MTRR precedences, 11-28
MTRRs, description of, 11-20
multiple-processor considerations, 11-32
NW flag, CR0 control register, 11-13, 22-19
operating modes, 11-12
overview of, 11-1
page attribute table (PAT), 11-33
PCD flag
CR3 control register, 11-13
page-directory entries, 11-13, 11-33
page-table entries, 11-13, 11-33
PGE (page global enable) flag, CR4 control register, 11-13
precedence of controls, 11-13
preventing caching, 11-16
protocol, 11-9
PWT flag
CR3 control register, 11-13
page-directory entries, 11-33
page-table entries, 11-33
remapping memory types, 11-29
setting up memory ranges with MTRRs, 11-22
shared mode, L1 Data Cache, 11-18
variable-range MTRRs, 11-23, 11-25
Caches, 2-7
cache hit, 11-5
cache line, 11-5
cache line fill, 11-5
cache write hit, 11-5
description of, 11-1
effects of a locked operation on internal processor caches, 8-5
enabling, 9-7
management, instructions, 2-24, 11-17
Caching
cache control protocol, 11-9
cache line, 11-5
cache management instructions, 11-17
cache mechanisms in IA-32 processors, 22-30
caching terminology, 11-5
choosing a memory type, 11-8
flushing TLBs, 11-19
implicit caching, 11-19
internal caches, 11-1
L1 (level 1) cache, 11-4
L2 (level 2) cache, 11-4
L3 (level 3) cache, 11-4
methods of caching available, 11-6
MTRRs, description of, 11-20
operating modes, 11-12
overview of, 11-1

INDEX

self-modifying code, effect on, 11-18, 22-30
snooping, 11-6
store buffer, 11-20
TLBs, 11-5
UC (strong uncacheable) memory type, 11-6
UC- (uncacheable) memory type, 11-6
WB (write back) memory type, 11-7
WC (write combining) memory type, 11-7
WP (write protected) memory type, 11-7
write-back caching, 11-6
WT (write through) memory type, 11-7
Call gates
16-bit, interlevel return from, 22-33
accessing a code segment through, 5-15
description of, 5-13
for 16-bit and 32-bit code modules, 21-1
IA-32e mode, 5-14
introduction to, 2-4
mechanism, 5-15
privilege level checking rules, 5-16
CALL instruction, 2-5, 3-9, 5-10, 5-15, 5-20, 7-2, 7-9, 7-10, 21-5
Caller access privileges, checking, 5-26
Calls
16 and 32-bit code segments, 21-3
controlling operand-size attribute, 21-5
returning from, 5-20
Catastrophic shutdown detector
Thermal monitoring
catastrophic shutdown detector, 14-20
catastrophic shutdown detector, 14-19
CC0 and CC1 (counter control) fields, CESR MSR (Pentium processor),
18-124
CD (cache disable) flag, CR0 control register, 2-14, 9-7, 11-10, 11-12,
11-13, 11-16, 11-32, 22-18, 22-19, 22-30
CESR (control and event select) MSR (Pentium processor), 18-123, 18-124
CLFLSH feature flag, CPUID instruction, 9-8
CLFLUSH instruction, 2-15, 9-8, 11-17
CLI instruction, 6-7
Clocks
counting processor clocks, 18-125
Hyper-Threading Technology, 18-125
nominal CPI, 18-125
non-halted clockticks, 18-125
non-halted CPI, 18-125
non-sleep Clockticks, 18-125
time stamp counter, 18-125
CLTS instruction, 2-23, 5-24, 25-2, 25-6
Cluster model, local APIC, 10-24
CMOVcc instructions, 22-4
CMPXCHG instruction, 8-3, 22-4
CMPXCHG8B instruction, 8-3, 22-4
Code modules
16 bit vs. 32 bit, 21-1
mixing 16-bit and 32-bit code, 21-1
sharing data, mixed-size code segs, 21-3
transferring control, mixed-size code segs, 21-3
Code segments
accessing data in, 5-9
accessing through a call gate, 5-15
description of, 3-12
descriptor format, 5-2
descriptor layout, 5-2
direct calls or jumps to, 5-10
paging of, 2-6
pointer size, 21-4
privilege level checks
transferring control between code segs, 5-10
Compatibility
IA-32 architecture, 22-1
software, 1-7
Compatibility mode
code segment descriptor, 5-3

code segment descriptors, 9-12
control registers, 2-13
CS.L and CS.D, 9-12
debug registers, 2-24
EFLAGS register, 2-11
exception handling, 2-5
gates, 2-4
GDTR register, 2-12, 2-13
global and local descriptor tables, 2-4
IDTR register, 2-12
interrupt handling, 2-5
L flag, 3-12, 5-4
memory management, 2-6
operation, 9-12
segment loading instructions, 3-9
segments, 3-5
switching to, 9-12
SYSCALL and SYSRET, 5-22
SYSENTER and SYSEXIT, 5-21
system flags, 2-11
system registers, 2-7
task register, 2-13
See also: 64-bit mode, IA-32e mode
Condition code flags, x87 FPU status word
compatibility information, 22-8
Conforming code segments
accessing, 5-12
C (conforming) flag, 5-11
description of, 3-13
Context, task (see Task state)
Control registers
64-bit mode, 2-13
CR0, 2-13
CR1 (reserved), 2-13
CR2, 2-13
CR3 (PDBR), 2-6, 2-13
CR4, 2-13
description of, 2-13
introduction to, 2-6
VMX operation, 31-17
Coprocessor segment
overrun exception, 6-30, 22-12
Counter mask field
PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family processors), 18-5,
18-122
CPL
description of, 5-7
field, CS segment selector, 5-2
CPUID instruction
availability, 22-4
control register flags, 2-19
detecting features, 22-2
serializing instructions, 8-17
syntax for data, 1-9
CR0 control register, 22-7
description of, 2-13
introduction to, 2-6
state following processor reset, 9-2
CR1 control register (reserved), 2-13
CR2 control register
description of, 2-13
introduction to, 2-6
CR3 control register (PDBR)
associated with a task, 7-1, 7-3
description of, 2-13
in TSS, 7-4, 7-14
introduction to, 2-6
loading during initialization, 9-10
memory management, 2-6
page directory base address, 2-6
page table base address, 2-5
CR4 control register
Vol. 3D INDEX-3

INDEX

description of, 2-13
enabling control functions, 22-2
inclusion in IA-32 architecture, 22-18
introduction to, 2-6
VMX usage of, 23-3
CR8 register, 2-7
64-bit mode, 2-13
compatibility mode, 2-13
description of, 2-13
task priority level bits, 2-19
when available, 2-13
CS register, 22-10
state following initialization, 9-5
C-state, 14-18
CTR0 and CTR1 (performance counters) MSRs (Pentium processor),
18-123, 18-125
Current privilege level (see CPL)

D
D (default operation size) flag
segment descriptor, 21-1, 22-33
Data breakpoint exception conditions, 17-9
Data segments
description of, 3-12
descriptor layout, 5-2
expand-down type, 3-11
paging of, 2-6
privilege level checking when accessing, 5-8
DE (debugging extensions) flag, CR4 control register, 2-17, 22-18, 22-20
Debug exception (#DB), 6-7, 6-21, 7-5, 17-7, 17-12, 17-41
Debug store (see DS)
DEBUGCTLMSR MSR, 17-39, 17-40
Debugging facilities
breakpoint exception (#BP), 17-1
debug exception (#DB), 17-1
DR6 debug status register, 17-1
DR7 debug control register, 17-1
exceptions, 17-6
INT3 instruction, 17-1
last branch, interrupt, and exception recording, 17-1, 17-11
masking debug exceptions, 6-7
overview of, 17-1
performance-monitoring counters, 18-1
registers
description of, 17-2
introduction to, 2-6
loading, 2-24
RF (resume) flag, EFLAGS, 17-1
see DS (debug store) mechanism
T (debug trap) flag, TSS, 17-1
TF (trap) flag, EFLAGS, 17-1
virtualization, 32-1
VMX operation, 32-1
DEC instruction, 8-3
Denormal operand exception (#D), 22-10
Denormalized operand, 22-12
Device-not-available exception (#NM), 2-15, 2-23, 6-27, 9-7, 22-11,
22-12
DFR
Destination Format Register, 10-38, 10-41, 10-46
Digital readout bits, 14-26, 14-29
DIV instruction, 6-20
Divide configuration register, local APIC, 10-16
Divide-error exception (#DE), 6-20, 22-21
Double-fault exception (#DF), 6-28, 22-27
DPL (descriptor privilege level) field, segment descriptor, 3-11, 5-2, 5-4,
5-7
DR0-DR3 breakpoint-address registers, 17-1, 17-3, 17-38, 17-40, 17-41
DR4-DR5 debug registers, 17-3, 22-20
DR6 debug status register, 17-3
B0-B3 (BP detected) flags, 17-3

INDEX-4 Vol. 3D

BD (debug register access detected) flag, 17-3
BS (single step) flag, 17-3
BT (task switch) flag, 17-3
debug exception (#DB), 6-21
reserved bits, 22-20
DR7 debug control register, 17-4
G0-G3 (global breakpoint enable) flags, 17-4
GD (general detect enable) flag, 17-4
GE (global exact breakpoint enable) flag, 17-4
L0-L3 (local breakpoint enable) flags, 17-4
LE local exact breakpoint enable) flag, 17-4
LEN0-LEN3 (Length) fields, 17-4
R/W0-R/W3 (read/write) fields, 17-4, 22-20
DS feature flag, CPUID instruction, 17-17, 17-33, 17-37, 17-38
DS save area, 17-19, 17-20, 17-21
DS (debug store) mechanism
availability of, 18-97
description of, 18-97
DS feature flag, CPUID instruction, 18-97
DS save area, 17-17, 17-20
IA-32e mode, 17-20
interrupt service routine (DS ISR), 17-24
setting up, 17-22
Dual-core technology
architecture, 8-32
logical processors supported, 8-25
MTRR memory map, 8-33
multi-threading feature flag, 8-24
performance monitoring, 18-112
specific features, 22-4
Dual-monitor treatment, 34-19
D/B (default operation size/default stack pointer size and/or upper bound)
flag, segment descriptor, 3-11, 5-4

E
E (edge detect) flag
PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family), 18-4
E (edge detect) flag, PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family
processors), 18-121
E (expansion direction) flag
segment descriptor, 5-2, 5-4
E (MTRRs enabled) flag
IA32_MTRR_DEF_TYPE MSR, 11-23
EFLAGS register
identifying 32-bit processors, 22-6
introduction to, 2-6
new flags, 22-6
saved in TSS, 7-4
system flags, 2-9
VMX operation, 31-2
EIP register, 22-10
saved in TSS, 7-4
state following initialization, 9-5
EM (emulation) flag
CR0 control register, 2-15, 2-16, 6-27, 9-6, 9-7, 12-1, 13-3
EMMS instruction, 12-3
Enhanced Intel SpeedStep Technology
ACPI 3.0 specification, 14-1
IA32_APERF MSR, 14-2
IA32_MPERF MSR, 14-2
IA32_PERF_CTL MSR, 14-1
IA32_PERF_STATUS MSR, 14-1
introduction, 14-1
multiple processor cores, 14-1
performance transitions, 14-1
P-state coordination, 14-1
See also: thermal monitoring
EOI
End Of Interrupt register, 10-38
Error code, 16-3, 16-7, 16-10, 16-13, 16-15
architectural MCA, 16-1, 16-3, 16-7, 16-10, 16-13, 16-15

INDEX

decoding IA32_MCi_STATUS, 16-1, 16-3, 16-7, 16-10, 16-13, 16-15
exception, description of, 6-14
external bus, 16-1, 16-3, 16-7, 16-10, 16-13, 16-15
memory hierarchy, 16-3, 16-7, 16-10, 16-13, 16-15
pushing on stack, 22-32
watchdog timer, 16-1, 16-3, 16-7, 16-10, 16-13, 16-15
Error numbers
VM-instruction error field, 30-29
Error signals, 22-11
Error-reporting bank registers, 15-2
ERROR#
input, 22-16
output, 22-16
ES0 and ES1 (event select) fields, CESR MSR (Pentium processor), 18-124
ESR
Error Status Register, 10-39
ET (extension type) flag, CR0 control register, 2-15, 22-7
Event select field, PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family
processors), 18-4, 18-85, 18-121
Events
at-retirement, 18-103
at-retirement (Pentium 4 processor), 18-93
non-retirement (Pentium 4 processor), 18-93, 19-199
P6 family processors, 19-230
Pentium processor, 19-239
Exception handler
calling, 6-11
defined, 6-1
flag usage by handler procedure, 6-14
machine-check exception handler, 15-27
machine-check exceptions (#MC), 15-27
machine-error logging utility, 15-27
procedures, 6-11
protection of handler procedures, 6-13
task, 6-14, 7-2
Exceptions
alignment check, 22-11
classifications, 6-4
compound error codes, 15-21
conditions checked during a task switch, 7-11
coprocessor segment overrun, 22-12
description of, 2-5, 6-1
device not available, 22-12
double fault, 6-28
error code, 6-14
exception bitmap, 32-1
execute-disable bit, 5-32
floating-point error, 22-12
general protection, 22-12
handler mechanism, 6-11
handler procedures, 6-11
handling, 6-11
handling in real-address mode, 20-4
handling in SMM, 34-10
handling in virtual-8086 mode, 20-11
handling through a task gate in virtual-8086 mode, 20-14
handling through a trap or interrupt gate in virtual-8086 mode, 20-12
IA-32e mode, 2-5
IDT, 6-9
initializing for protected-mode operation, 9-10
invalid-opcode, 22-5
masking debug exceptions, 6-7
masking when switching stack segments, 6-7
MCA error codes, 15-20
MMX instructions, 12-1
notation, 1-9
overview of, 6-1
priorities among simultaneous exceptions and interrupts, 6-8
priority of, 22-22
priority of, x87 FPU exceptions, 22-10
reference information on all exceptions, 6-19
reference information, 64-bit mode, 6-16

restarting a task or program, 6-5
segment not present, 22-11
simple error codes, 15-21
sources of, 6-4
summary of, 6-2
vectors, 6-1
Executable, 3-11
Execute-disable bit capability
conditions for, 5-30
CPUID flag, 5-30
detecting and enabling, 5-30
exception handling, 5-32
page-fault exceptions, 6-39
protection matrix for IA-32e mode, 5-31
protection matrix for legacy modes, 5-31
reserved bit checking, 5-31
Execution events, 19-222
Exit-reason numbers
VM entries & exits, C-1
Expand-down data segment type, 3-11
Extended signature table, 9-31
extended signature table, 9-31
External bus errors, detected with machine-check architecture, 15-27

F
F2XM1 instruction, 22-13
Family 06H, 16-1
Family 0FH, 16-1
microcode update facilities, 9-28
Faults
description of, 6-5
restarting a program or task after, 6-5
FCMOVcc instructions, 22-4
FCOMI instruction, 22-4
FCOMIP instruction, 22-4
FCOS instruction, 22-13
FDIV instruction, 22-11, 22-12
FE (fixed MTRRs enabled) flag, IA32_MTRR_DEF_TYPE MSR, 11-23
Feature
determination, of processor, 22-2
information, processor, 22-2
FINIT/FNINIT instructions, 22-8, 22-16
FIX (fixed range registers supported) flag, IA32_MTRRCAPMSR, 11-22
Fixed-range MTRRs
description of, 11-23
Flat segmentation model, 3-3
FLD instruction, 22-13
FLDENV instruction, 22-11, 22-12
FLDL2E instruction, 22-14
FLDL2T instruction, 22-14
FLDLG2 instruction, 22-14
FLDLN2 instruction, 22-14
FLDPI instruction, 22-14
Floating-point error exception (#MF), 22-12
Floating-point exceptions
denormal operand exception (#D), 22-10
invalid operation (#I), 22-14
numeric overflow (#O), 22-10
numeric underflow (#U), 22-10
saved CS and EIP values, 22-10
FLUSH# pin, 6-3
FNSAVE instruction, 12-4
Focus processor, local APIC, 10-26
FORCEPR# log, 14-25, 14-29
FORCPR# interrupt enable bit, 14-27
FPATAN instruction, 22-13
FPREM instruction, 22-8, 22-11, 22-12, 22-13
FPREM1 instruction, 22-8, 22-12
FPTAN instruction, 22-8, 22-13
Front_end events, 19-222
FRSTOR instruction, 12-4, 22-11, 22-12

Vol. 3D INDEX-5

INDEX

FSAVE instruction, 12-3, 12-4
FSAVE/FNSAVE instructions, 22-11, 22-14
FSCALE instruction, 22-12
FSIN instruction, 22-13
FSINCOS instruction, 22-13
FSQRT instruction, 22-11, 22-12
FSTENV instruction, 12-3
FSTENV/FNSTENV instructions, 22-14
FTAN instruction, 22-8
FUCOM instruction, 22-13
FUCOMI instruction, 22-4
FUCOMIP instruction, 22-4
FUCOMP instruction, 22-13
FUCOMPP instruction, 22-13
FWAIT instruction, 6-27
FXAM instruction, 22-14
FXRSTOR instruction, 2-18, 2-19, 9-8, 12-3, 12-4, 13-2, 13-6
FXSAVE instruction, 2-18, 2-19, 9-8, 12-3, 12-4, 13-2, 13-6
FXSR feature flag, CPUID instruction, 9-8
FXTRACT instruction, 22-10, 22-14

G
G (global) flag
page-directory entries, 11-13
page-table entries, 11-13
G (granularity) flag
segment descriptor, 3-10, 3-11, 5-2, 5-4
G0-G3 (global breakpoint enable) flags
DR7 register, 17-4
Gate descriptors
call gates, 5-13
description of, 5-13
IA-32e mode, 5-14
Gates, 2-4
IA-32e mode, 2-4
GD (general detect enable) flag
DR7 register, 17-4, 17-9
GDT
description of, 2-3, 3-15
IA-32e mode, 2-4
index field of segment selector, 3-7
initializing, 9-10
paging of, 2-6
pointers to exception/interrupt handlers, 6-11
segment descriptors in, 3-9
selecting with TI flag of segment selector, 3-7
task switching, 7-9
task-gate descriptor, 7-8
TSS descriptors, 7-5
use in address translation, 3-6
GDTR register
description of, 2-3, 2-6, 2-12, 3-15
IA-32e mode, 2-4, 2-12
limit, 5-5
loading during initialization, 9-10
storing, 3-15
GE (global exact breakpoint enable) flag
DR7 register, 17-4, 17-9
General-detect exception condition, 17-9
General-protection exception (#GP), 3-12, 5-6, 5-7, 5-11, 5-12, 6-9,
6-13, 6-36, 7-5, 17-3, 22-12, 22-21, 22-34, 22-35
General-purpose registers, saved in TSS, 7-4
Global control MSRs, 15-2
Global descriptor table register (see GDTR)
Global descriptor table (see GDT)

H
HALT state
relationship to SMI interrupt, 34-3, 34-13
Hardware reset

INDEX-6 Vol. 3D

description of, 9-1
processor state after reset, 9-2
state of MTRRs following, 11-20
value of SMBASE following, 34-4
Hexadecimal numbers, 1-8
high-temperature interrupt enable bit, 14-27, 14-30
HITM# line, 11-6
HLT instruction, 2-25, 5-24, 6-29, 25-2, 34-13, 34-14
Hyper-Threading Technology
architectural state of a logical processor, 8-33
architecture description, 8-27
caches, 8-31
debug registers, 8-30
description of, 8-24, 22-3, 22-4
detecting, 8-36, 8-40, 8-41
executing multiple threads, 8-26
execution-based timing loops, 8-53
external signal compatibility, 8-32
halting logical processors, 8-51
handling interrupts, 8-26
HLT instruction, 8-47
IA32_MISC_ENABLE MSR, 8-30, 8-33
initializing IA-32 processors with, 8-25
introduction of into the IA-32 architecture, 22-3, 22-4
local a, 8-28
local APIC
functionality in logical processor, 8-29
logical processors, identifying, 8-36
machine check architecture, 8-29
managing idle and blocked conditions, 8-47
mapping resources, 8-34
memory ordering, 8-30
microcode update resources, 8-30, 8-33, 9-35
MP systems, 8-27
MTRRs, 8-29, 8-33
multi-threading feature flag, 8-24
multi-threading support, 8-24
PAT, 8-29
PAUSE instruction, 8-47, 8-48
performance monitoring, 18-107, 18-112
performance monitoring counters, 8-30, 8-33
placement of locks and semaphores, 8-53
required operating system support, 8-49
scheduling multiple threads, 8-52
self modifying code, 8-31
serializing instructions, 8-30
spin-wait loops
PAUSE instructions in, 8-50, 8-52
thermal monitor, 8-32
TLBs, 8-31

I
IA-32 Intel architecture
compatibility, 22-1
processors, 22-1
IA32e mode
registers and mode changes, 9-12
IA-32e mode
call gates, 5-14
code segment descriptor, 5-3
D flag, 5-4
data structures and initialization, 9-11
debug registers, 2-7
debug store area
descriptors, 2-4
DPL field, 5-4
exceptions during initialization, 9-12
feature-enable register, 2-7
gates, 2-4
global and local descriptor tables, 2-4
IA32_EFER MSR, 2-7, 5-30

INDEX

initialization process, 9-11
interrupt stack table, 6-19
interrupts and exceptions, 2-5
IRET instruction, 6-18
L flag, 3-12, 5-4
logical address, 3-7
MOV CRn, 9-11
MTRR calculations, 11-27
NXE bit, 5-30
page level protection, 5-30
paging, 2-6
PDE tables, 5-31
PDP tables, 5-31
PML4 tables, 5-31
PTE tables, 5-31
registers and data structures, 2-1
segment descriptor tables, 3-16, 5-3
segment descriptors, 3-9
segment loading instructions, 3-9
segmentation, 3-5
stack switching, 5-19, 6-18
SYSCALL and SYSRET, 5-22
SYSENTER and SYSEXIT, 5-21
system descriptors, 3-14
system registers, 2-7
task switching, 7-16
task-state segments, 2-5
terminating mode operation, 9-12
See also: 64-bit mode, compatibility mode
IA32_APERF MSR, 14-2
IA32_APIC_BASE MSR, 8-18, 8-19, 10-6, 10-8
IA32_BIOS_UPDT_TRIG MSR, 32-9
IA32_BISO_SIGN_ID MSR, 32-9
IA32_CLOCK_MODULATION MSR, 8-32, 14-7, 14-10, 14-11, 14-14,
14-15, 14-16, 14-17, 14-23, 14-24, 14-26, 14-34, 14-35,
14-36, 14-37, 14-38
IA32_DEBUGCTL MSR, 27-26
IA32_DS_AREA MSR, 17-17, 17-18, 17-22, 18-90, 18-106
IA32_EFER MSR, 2-7, 2-8, 5-30, 27-26, 31-16
IA32_FEATURE_CONTROL MSR, 23-3
IA32_KernelGSbase MSR, 2-7
IA32_LSTAR MSR, 2-7, 5-22
IA32_MCG_CAP MSR, 15-2, 15-28
IA32_MCG_CTL MSR, 15-2, 15-4
IA32_MCG_EAX MSR, 15-12
IA32_MCG_EBP MSR, 15-12
IA32_MCG_EBX MSR, 15-12
IA32_MCG_ECX MSR, 15-12
IA32_MCG_EDI MSR, 15-12
IA32_MCG_EDX MSR, 15-12
IA32_MCG_EFLAGS MSR, 15-12
IA32_MCG_EIP MSR, 15-12
IA32_MCG_ESI MSR, 15-12
IA32_MCG_ESP MSR, 15-12
IA32_MCG_MISC MSR, 15-12, 15-13
IA32_MCG_R10 MSR, 15-13
IA32_MCG_R11 MSR, 15-13
IA32_MCG_R12 MSR, 15-13
IA32_MCG_R13 MSR, 15-13
IA32_MCG_R14 MSR, 15-13
IA32_MCG_R15 MSR, 15-13
IA32_MCG_R8 MSR, 15-13
IA32_MCG_R9 MSR, 15-13
IA32_MCG_RAX MSR, 15-12
IA32_MCG_RBP MSR, 15-12
IA32_MCG_RBX MSR, 15-12
IA32_MCG_RCX MSR, 15-12
IA32_MCG_RDI MSR, 15-12
IA32_MCG_RDX MSR, 15-12
IA32_MCG_RESERVEDn MSR, 15-12
IA32_MCG_RFLAGS MSR, 15-12
IA32_MCG_RIP MSR, 15-12

IA32_MCG_RSI MSR, 15-12
IA32_MCG_RSP MSR, 15-12
IA32_MCG_STATUS MSR, 15-2, 15-4, 15-28, 15-30, 27-3
IA32_MCi_ADDR MSR, 15-9, 15-30
IA32_MCi_CTL, 15-5
IA32_MCi_CTL MSR, 15-5
IA32_MCi_MISC MSR, 15-9, 15-11, 15-12, 15-30
IA32_MCi_STATUS MSR, 15-6, 15-28, 15-30
decoding for Family 06H, 16-1
decoding for Family 0FH, 16-1, 16-3, 16-7, 16-10, 16-13, 16-15
IA32_MISC_ENABLE MSR, 14-1, 14-20, 17-18, 17-33, 18-90
IA32_MPERF MSR, 14-1, 14-2
IA32_MTRRCAP MSR, 11-21, 11-22
IA32_MTRR_DEF_TYPE MSR, 11-22
IA32_MTRR_FIXn, fixed ranger MTRRs, 11-23
IA32_PAT_CR MSR, 11-34
IA32_PEBS_ENABLE MSR, 18-88, 18-90, 18-106, 19-222
IA32_PERF_CTL MSR, 14-1
IA32_PERF_STATUS MSR, 14-1
IA32_STAR MSR, 5-22
IA32_STAR_CS MSR, 2-7
IA32_SYSCALL_FLAG_MASK MSR, 2-7
IA32_SYSENTER_CS MSR, 5-21, 5-22, 27-21
IA32_SYSENTER_EIP MSR, 5-21, 27-26
IA32_SYSENTER_ESP MSR, 5-21, 27-26
IA32_THERM_INTERRUPT MSR, 14-22, 14-24, 14-25, 14-27
FORCPR# interrupt enable bit, 14-27
high-temperature interrupt enable bit, 14-27, 14-30
low-temperature interrupt enable bit, 14-27, 14-30
overheat interrupt enable bit, 14-27, 14-30
THERMTRIP# interrupt enable bit, 14-27, 14-30
threshold #1 interrupt enable bit, 14-27, 14-30
threshold #1 value, 14-27, 14-30
threshold #2 interrupt enable, 14-27, 14-30
threshold #2 value, 14-27, 14-30
IA32_THERM_STATUS MSR, 14-24, 14-25
digital readout bits, 14-26, 14-29
out-of-spec status bit, 14-25, 14-29
out-of-spec status log, 14-26, 14-29
PROCHOT# or FORCEPR# event bit, 14-25, 14-29
PROCHOT# or FORCEPR# log, 14-25, 14-29
resolution in degrees, 14-26
thermal status bit, 14-25, 14-28
thermal status log, 14-25, 14-29
thermal threshold #1 log, 14-26, 14-29
thermal threshold #1 status, 14-26, 14-29
thermal threshold #2 log, 14-26, 14-29
thermal threshold #2 status, 14-26, 14-29
validation bit, 14-26
IA32_VMX_BASIC MSR, 24-3, 31-2, 31-5, 31-6, 31-11, A-1, A-2
IA32_VMX_CR0_FIXED0 MSR, 31-4, A-6
IA32_VMX_CR0_FIXED1 MSR, 31-4, A-6
IA32_VMX_CR4_FIXED0 MSR, 31-4, A-6
IA32_VMX_CR4_FIXED1 MSR, 31-4, A-6
IA32_VMX_ENTRY_CTLS MSR, 31-5, 31-6, A-2, A-5
IA32_VMX_EXIT_CTLS MSR, 31-5, 31-6, A-2, A-4, A-5
IA32_VMX_MISC MSR, 24-6, 26-3, 26-12, 34-26, A-5
IA32_VMX_PINBASED_CTLS MSR, 31-5, 31-6, A-2, A-3
IA32_VMX_PROCBASED_CTLS MSR, 24-9, 31-5, 31-6, A-2, A-3, A-4, A-8
IA32_VMX_VMCS_ENUM MSR, A-7
ICR
Interrupt Command Register, 10-38, 10-41, 10-47
ID (identification) flag
EFLAGS register, 2-11, 22-6
IDIV instruction, 6-20, 22-21
IDT
64-bit mode, 6-16
call interrupt & exception-handlers from, 6-11
change base & limit in real-address mode, 20-5
description of, 6-9
handling NMIs during initialization, 9-9
initializing protected-mode operation, 9-10
Vol. 3D INDEX-7

INDEX

initializing real-address mode operation, 9-8
introduction to, 2-5
limit, 22-27
paging of, 2-6
structure in real-address mode, 20-5
task switching, 7-10
task-gate descriptor, 7-8
types of descriptors allowed, 6-10
use in real-address mode, 20-4
IDTR register
description of, 2-12, 6-9
IA-32e mode, 2-12
introduction to, 2-5
limit, 5-5
loading in real-address mode, 20-5
storing, 3-16
IE (invalid operation exception) flag
x87 FPU status word, 22-8
IEEE Standard 754 for Binary Floating-Point Arithmetic, 22-8, 22-9,
22-10, 22-12, 22-13, 22-14
IF (interrupt enable) flag
EFLAGS register, 2-10, 2-11, 6-6, 6-10, 6-14, 20-4, 20-19, 34-11
IN instruction, 8-15, 22-35, 25-2
INC instruction, 8-3
Index field, segment selector, 3-7
INIT interrupt, 10-3
Initial-count register, local APIC, 10-16, 10-17
Initialization
built-in self-test (BIST), 9-1, 9-5
CS register state following, 9-5
EIP register state following, 9-5
example, 9-14
first instruction executed, 9-5
hardware reset, 9-1
IA-32e mode, 9-11
IDT, protected mode, 9-10
IDT, real-address mode, 9-8
Intel486 SX processor and Intel 487 SX math coprocessor, 22-16
location of software-initialization code, 9-5
machine-check initialization, 15-19
model and stepping information, 9-5
multitasking environment, 9-10, 9-11
overview, 9-1
paging, 9-10
processor state after reset, 9-2
protected mode, 9-9
real-address mode, 9-8
RESET# pin, 9-1
setting up exception- and interrupt-handling facilities, 9-10
x87 FPU, 9-5
INIT# pin, 6-3, 9-1
INIT# signal, 2-25, 23-4
INS instruction, 17-9
Instruction operands, 1-8
Instruction-breakpoint exception condition, 17-8
Instructions
new instructions, 22-4
obsolete instructions, 22-5
privileged, 5-23
serializing, 8-17, 8-30, 22-16
supported in real-address mode, 20-3
system, 2-7, 2-21
INS/INSB/INSW/INSD instruction, 25-2
INT 3 instruction, 2-5, 6-23
INT instruction, 2-5, 5-10
INT n instruction, 3-9, 6-1, 6-4, 17-10
INT (APIC interrupt enable) flag, PerfEvtSel0 and PerfEvtSel1 MSRs (P6
family processors), 18-4, 18-122
INT15 and microcode updates, 9-42
INT3 instruction, 3-9, 6-4
Intel 287 math coprocessor, 22-7
Intel 387 math coprocessor system, 22-7
INDEX-8 Vol. 3D

Intel 487 SX math coprocessor, 22-7, 22-16
Intel 64 architecture
definition of, 1-4
relation to IA-32, 1-4
Intel 8086 processor, 22-7
Intel Core Solo and Intel Core Duo processors
event mask (Umask), 18-83, 18-84
last branch, interrupt, exception recording, 17-36
notes on P-state transitions, 14-1
performance monitoring, 18-83, 18-84
performance monitoring events, 19-46, 19-58, 19-67, 19-81,
19-141, 19-175, 19-180
sub-fields layouts, 18-83, 18-84
time stamp counters, 17-41
Intel NetBurst microarchitecture, 1-3
Intel software network link, 1-10
Intel SpeedStep Technology
See: Enhanced Intel SpeedStep Technology
Intel VTune Performance Analyzer
related information, 1-10
Intel Xeon processor, 1-1
last branch, interrupt, and exception recording, 17-33
time-stamp counter, 17-41
Intel Xeon processor MP
with 8MB L3 cache, 18-112, 18-114
Intel286 processor, 22-7
Intel386 DX processor, 22-7
Intel386 SL processor, 2-7
Intel486 DX processor, 22-7
Intel486 SX processor, 22-7, 22-16
Interprivilege level calls
call mechanism, 5-15
stack switching, 5-17
Interprocessor interrupt (IPIs), 10-1
Interprocessor interrupt (IPI)
in MP systems, 10-1
interrupt, 6-12
Interrupt Command Register, 10-38
Interrupt command register (ICR), local APIC, 10-19
Interrupt gates
16-bit, interlevel return from, 22-33
clearing IF flag, 6-7, 6-14
difference between interrupt and trap gates, 6-14
for 16-bit and 32-bit code modules, 21-1
handling a virtual-8086 mode interrupt or exception through, 20-12
in IDT, 6-10
introduction to, 2-4, 2-5
layout of, 6-10
Interrupt handler
calling, 6-11
defined, 6-1
flag usage by handler procedure, 6-14
procedures, 6-11
protection of handler procedures, 6-13
task, 6-14, 7-2
Interrupts
automatic bus locking, 22-35
control transfers between 16- and 32-bit code modules, 21-6
description of, 2-5, 6-1
destination, 10-26
distribution mechanism, local APIC, 10-25
enabling and disabling, 6-6
handling, 6-11
handling in real-address mode, 20-4
handling in SMM, 34-10
handling in virtual-8086 mode, 20-11
handling multiple NMIs, 6-6
handling through a task gate in virtual-8086 mode, 20-14
handling through a trap or interrupt gate in virtual-8086 mode, 20-12
IA-32e mode, 2-5, 2-12
IDT, 6-9
IDTR, 2-12

INDEX

initializing for protected-mode operation, 9-10
interrupt descriptor table register (see IDTR)
interrupt descriptor table (see IDT)
list of, 6-2, 20-6
local APIC, 10-1
maskable hardware interrupts, 2-10
masking maskable hardware interrupts, 6-6
masking when switching stack segments, 6-7
message signalled interrupts, 10-34
on-die sensors for, 14-19
overview of, 6-1
priorities among simultaneous exceptions and interrupts, 6-8
priority, 10-28
propagation delay, 22-27
real-address mode, 20-6
restarting a task or program, 6-5
software, 6-50
sources of, 10-1
summary of, 6-2
thermal monitoring, 14-19
user defined, 6-1, 6-50
valid APIC interrupts, 10-14
vectors, 6-1
virtual-8086 mode, 20-6
INTO instruction, 2-5, 3-9, 6-4, 6-24, 17-10
INTR# pin, 6-2, 6-6
Invalid opcode exception (#UD), 2-16, 6-26, 6-47, 12-1, 17-3, 22-5,
22-11, 22-20, 22-21, 34-3
Invalid TSS exception (#TS), 6-31, 7-6
Invalid-operation exception, x87 FPU, 22-11, 22-14
INVD instruction, 2-24, 5-24, 11-17, 22-4
INVLPG instruction, 2-24, 5-24, 22-4, 25-2, 32-3, 32-4
IOPL (I/O privilege level) field, EFLAGS register
description of, 2-10
on return from exception, interrupt handler, 6-13
sensitive instructions in virtual-8086 mode, 20-10
virtual interrupt, 2-11
IPI (see interprocessor interrupt)
IRET instruction, 3-9, 6-7, 6-13, 6-14, 6-18, 7-10, 8-17, 20-5, 20-19,
25-7
IRETD instruction, 2-10, 8-17
IRR
Interrupt Request Register, 10-39, 10-41, 10-47
IRR (interrupt request register), local APIC, 10-30
ISR
In Service Register, 10-38, 10-41, 10-47
I/O
breakpoint exception conditions, 17-9
in virtual-8086 mode, 20-10
instruction restart flag
SMM revision identifier field, 34-15
instruction restart flag, SMM revision identifier field, 34-15
IO_SMI bit, 34-12
I/O permission bit map, TSS, 7-5
map base address field, TSS, 7-5
restarting following SMI interrupt, 34-15
saving I/O state, 34-12
SMM state save map, 34-12
I/O APIC, 10-26
bus arbitration, 10-26
description of, 10-1
external interrupts, 6-3
information about, 10-1
interrupt sources, 10-2
local APIC and I/O APIC, 10-2, 10-3
overview of, 10-1
valid interrupts, 10-14
See also: local APIC

J
JMP instruction, 2-5, 3-9, 5-10, 5-15, 7-2, 7-9, 7-10

K
KEN# pin, 11-13, 22-36

L
L0-L3 (local breakpoint enable) flags
DR7 register, 17-4
L1 (level 1) cache
caching methods, 11-6
CPUID feature flag, 11-18
description of, 11-4
effect of using write-through memory, 11-8
introduction of, 22-30
invalidating and flushing, 11-17
MESI cache protocol, 11-9
shared and adaptive mode, 11-18
L2 (level 2) cache
caching methods, 11-6
description of, 11-4
disabling, 11-17
effect of using write-through memory, 11-8
introduction of, 22-30
invalidating and flushing, 11-17
MESI cache protocol, 11-9
L3 (level 3) cache
caching methods, 11-6
description of, 11-4
disabling and enabling, 11-13, 11-17
effect of using write-through memory, 11-8
introduction of, 22-31
invalidating and flushing, 11-17
MESI cache protocol, 11-9
LAR instruction, 2-24, 5-24
Larger page sizes
introduction of, 22-31
support for, 22-19
Last branch
interrupt & exception recording
description of, 17-11, 17-25, 17-27, 17-30, 17-32, 17-34, 17-36,
17-38, 17-39
record stack, 17-16, 17-17, 17-25, 17-26, 17-33, 17-35, 17-37,
17-39
record top-of-stack pointer, 17-16, 17-26, 17-33, 17-37, 17-39
LastBranchFromIP MSR, 17-40
LastBranchToIP MSR, 17-40
LastExceptionFromIP MSR, 17-36, 17-37, 17-40
LastExceptionToIP MSR, 17-36, 17-37, 17-40
LBR (last branch/interrupt/exception) flag, DEBUGCTLMSR MSR, 17-12,
17-34, 17-39, 17-40
LDR
Logical Destination Register, 10-41, 10-45, 10-46
LDS instruction, 3-8, 5-8
LDT
associated with a task, 7-3
description of, 2-3, 2-5, 3-15
index into with index field of segment selector, 3-7
pointer to in TSS, 7-4
pointers to exception and interrupt handlers, 6-11
segment descriptors in, 3-9
segment selector field, TSS, 7-14
selecting with TI (table indicator) flag of segment selector, 3-7
setting up during initialization, 9-10
task switching, 7-9
task-gate descriptor, 7-8
use in address translation, 3-6
LDTR register
description of, 2-3, 2-5, 2-6, 2-12, 3-15
IA-32e mode, 2-12
limit, 5-5
storing, 3-16
LE (local exact breakpoint enable) flag, DR7 register, 17-4, 17-9
LEN0-LEN3 (Length) fields, DR7 register, 17-4, 17-5
Vol. 3D INDEX-9

INDEX

LES instruction, 3-8, 5-8, 6-26
LFENCE instruction, 2-15, 8-6, 8-15, 8-16, 8-17
LFS instruction, 3-8, 5-8
LGDT instruction, 2-23, 5-23, 8-17, 9-10, 22-20
LGS instruction, 3-8, 5-8
LIDT instruction, 2-23, 5-24, 6-9, 8-17, 9-9, 20-5, 22-27
Limit checking
description of, 5-4
pointer offsets are within limits, 5-25
Limit field, segment descriptor, 5-2, 5-4
Linear address
description of, 3-6
IA-32e mode, 3-7
introduction to, 2-6
Linear address space, 3-6
defined, 3-1
of task, 7-14
Link (to previous task) field, TSS, 6-14
Linking tasks
mechanism, 7-12
modifying task linkages, 7-13
LINT pins
function of, 6-2
LLDT instruction, 2-23, 5-23, 8-17
LMSW instruction, 2-23, 5-24, 25-3, 25-7
Local APIC, 10-38
64-bit mode, 10-32
APIC_ID value, 8-34
arbitration over the APIC bus, 10-26
arbitration over the system bus, 10-26
block diagram, 10-4
cluster model, 10-24
CR8 usage, 10-32
current-count register, 10-17
description of, 10-1
detecting with CPUID, 10-8
DFR (destination format register), 10-24
divide configuration register, 10-16
enabling and disabling, 10-8
external interrupts, 6-2
features
Pentium 4 and Intel Xeon, 22-28
Pentium and P6, 22-28
focus processor, 10-26
global enable flag, 10-8
IA32_APIC_BASE MSR, 10-8
initial-count register, 10-16, 10-17
internal error interrupts, 10-2
interrupt command register (ICR), 10-19
interrupt destination, 10-26
interrupt distribution mechanism, 10-25
interrupt sources, 10-2
IRR (interrupt request register), 10-30
I/O APIC, 10-1
local APIC and 82489DX, 22-28
local APIC and I/O APIC, 10-2, 10-3
local vector table (LVT), 10-12
logical destination mode, 10-23
LVT (local-APIC version register), 10-11
mapping of resources, 8-34
MDA (message destination address), 10-23
overview of, 10-1
performance-monitoring counter, 18-123
physical destination mode, 10-23
receiving external interrupts, 6-2
register address map, 10-6, 10-38
shared resources, 8-34
SMI interrupt, 34-2
spurious interrupt, 10-32
spurious-interrupt vector register, 10-8
state after a software (INIT) reset, 10-11
state after INIT-deassert message, 10-11
INDEX-10 Vol. 3D

state after power-up reset, 10-10
state of, 10-33
SVR (spurious-interrupt vector register), 10-8
timer, 10-16
timer generated interrupts, 10-1
TMR (trigger mode register), 10-30
valid interrupts, 10-14
version register, 10-11
Local descriptor table register (see LDTR)
Local descriptor table (see LDT)
Local vector table (LVT)
description of, 10-12
thermal entry, 14-22
Local x2APIC, 10-31, 10-41, 10-46
Local xAPIC ID, 10-41
LOCK prefix, 2-25, 6-26, 8-1, 8-3, 8-15, 22-35
Locked (atomic) operations
automatic bus locking, 8-3
bus locking, 8-3
effects on caches, 8-5
loading a segment descriptor, 22-20
on IA-32 processors, 22-35
overview of, 8-1
software-controlled bus locking, 8-3
LOCK# signal, 2-25, 8-1, 8-3, 8-4, 8-5
Logical address
description of, 3-6
IA-32e mode, 3-7
Logical address space, of task, 7-15
Logical destination mode, local APIC, 10-23
Logical processors
per physical package, 8-25
Logical x2APIC ID, 10-46
low-temperature interrupt enable bit, 14-27, 14-30
LSL instruction, 2-24, 5-25
LSS instruction, 3-8, 5-8
LTR instruction, 2-23, 5-24, 7-7, 8-17, 9-11
LVT (see Local vector table)

M
Machine check architecture
VMX considerations, 33-11
Machine-check architecture
availability of MCA and exception, 15-19
compatibility with Pentium processor, 15-1
compound error codes, 15-21
CPUID flags, 15-19
error codes, 15-20, 15-21
error-reporting bank registers, 15-2
error-reporting MSRs, 15-5
extended machine check state MSRs, 15-12
external bus errors, 15-27
first introduced, 22-22
global MSRs, 15-2
initialization of, 15-19
introduction of in IA-32 processors, 22-36
logging correctable errors, 15-29, 15-31, 15-35
machine-check exception handler, 15-27
machine-check exception (#MC), 15-1
MSRs, 15-2
overview of MCA, 15-1
Pentium processor exception handling, 15-29
Pentium processor style error reporting, 15-13
simple error codes, 15-21
VMX considerations, 33-8, 33-9
writing machine-check software, 15-27
Machine-check exception (#MC), 6-46, 15-1, 15-19, 15-27, 22-21, 22-36
Mapping of shared resources, 8-34
Maskable hardware interrupts
description of, 6-3
handling with virtual interrupt mechanism, 20-15

INDEX

masking, 2-10, 6-6
MCA flag, CPUID instruction, 15-19
MCE flag, CPUID instruction, 15-19
MCE (machine-check enable) flag
CR4 control register, 2-17, 22-18
MDA (message destination address)
local APIC, 10-23
Memory, 11-1
Memory management
introduction to, 2-6
overview, 3-1
paging, 3-1, 3-2
registers, 2-11
segments, 3-1, 3-2, 3-7
virtualization of, 32-2
Memory ordering
in IA-32 processors, 22-34
overview, 8-5
processor ordering, 8-5
strengthening or weakening, 8-15
write ordering, 8-5
Memory type range registers (see MTRRs)
Memory types
caching methods, defined, 11-6
choosing, 11-8
MTRR types, 11-21
selecting for Pentium III and Pentium 4 processors, 11-15
selecting for Pentium Pro and Pentium II processors, 11-14
UC (strong uncacheable), 11-6
UC- (uncacheable), 11-6
WB (write back), 11-7
WC (write combining), 11-7
WP (write protected), 11-7
writing values across pages with different memory types, 11-16
WT (write through), 11-7
MemTypeGet() function, 11-29
MemTypeSet() function, 11-31
MESI cache protocol, 11-5, 11-9
Message address register, 10-34
Message data register format, 10-35
Message signalled interrupts
message address register, 10-34
message data register format, 10-34
MFENCE instruction, 2-15, 8-6, 8-15, 8-16, 8-17
Microcode update facilities
authenticating an update, 9-37
BIOS responsibilities, 9-38
calling program responsibilities, 9-39
checksum, 9-33
extended signature table, 9-31
family 0FH processors, 9-28
field definitions, 9-28
format of update, 9-28
function 00H presence test, 9-42
function 01H write microcode update data, 9-43
function 02H microcode update control, 9-46
function 03H read microcode update data, 9-47
general description, 9-28
HT Technology, 9-35
INT 15H-based interface, 9-42
overview, 9-27
process description, 9-28
processor identification, 9-32
processor signature, 9-32
return codes, 9-48
update loader, 9-34
update signature and verification, 9-36
update specifications, 9-37
VMX non-root operation, 25-9, 32-8
VMX support
early loading, 32-8
late loading, 32-8

virtualization issues, 32-8
Mixing 16-bit and 32-bit code
in IA-32 processors, 22-33
overview, 21-1
MMX technology
debugging MMX code, 12-5
effect of MMX instructions on pending x87 floating-point exceptions,
12-5
emulation of the MMX instruction set, 12-1
exceptions that can occur when executing MMX instructions, 12-1
introduction of into the IA-32 architecture, 22-2
register aliasing, 12-1
state, 12-1
state, saving and restoring, 12-3
system programming, 12-1
task or context switches, 12-4
using TS flag to control saving of MMX state, 13-7
Mode switching
example, 9-14
real-address and protected mode, 9-13
to SMM, 34-2
Model and stepping information, following processor initialization or reset
, 9-5
Model-specific registers (see MSRs)
Modes of operation (see Operating modes)
MONITOR instruction, 25-3
MOV instruction, 3-8, 5-8
MOV (control registers) instructions, 2-23, 5-24, 8-17, 9-13
MOV (debug registers) instructions, 2-24, 5-24, 8-17, 17-9
MOVNTDQ instruction, 8-6, 11-17
MOVNTI instruction, 2-15, 8-6, 11-17
MOVNTPD instruction, 8-6, 11-17
MOVNTPS instruction, 8-6, 11-17
MOVNTQ instruction, 8-6, 11-17
MP (monitor coprocessor) flag
CR0 control register, 2-15, 2-16, 6-27, 9-6, 9-7, 12-1, 22-8
MSR
Model Specific Register, 10-37, 10-38
MSRs
description of, 9-7
introduction of in IA-32 processors, 22-36
introduction to, 2-6
machine-check architecture, 15-2
reading and writing, 2-19, 2-21, 2-26
reading & writing in 64-bit mode, 2-26
virtualization support, 31-14
VMX support, 31-14
MSR_ TC_PRECISE_EVENT MSR, 19-222
MSR_DEBUBCTLB MSR, 17-12, 17-28, 17-37, 17-38
MSR_DEBUGCTLA MSR, 17-11, 17-17, 17-23, 17-24, 17-33, 17-34, 18-5,
18-9, 18-38, 18-49, 18-67, 18-71, 18-77, 18-88
MSR_DEBUGCTLB MSR, 17-11, 17-36, 17-38
MSR_IFSB_CNTR7 MSR, 18-114
MSR_IFSB_CTRL6 MSR, 18-114
MSR_IFSB_DRDY0 MSR, 18-113
MSR_IFSB_DRDY1 MSR, 18-113
MSR_IFSB_IBUSQ0 MSR, 18-113
MSR_IFSB_IBUSQ1 MSR, 18-113
MSR_IFSB_ISNPQ0 MSR, 18-113
MSR_IFSB_ISNPQ1 MSR, 18-113
MSR_LASTBRANCH_n MSR, 17-17, 17-35
MSR_LASTBRANCH_n_FROM_IP MSR, 17-16, 17-17, 17-35, 17-36
MSR_LASTBRANCH_n_TO_IP MSR, 17-16, 17-17, 17-35, 17-36
MSR_LASTBRANCH_TOS MSR, 17-35
MSR_LER_FROM_LIP MSR, 17-36, 17-37
MSR_LER_TO_LIP MSR, 17-36, 17-37
MSR_PEBS_ MATRIX_VERT MSR, 19-222
MTRR feature flag, CPUID instruction, 11-21
MTRRcap MSR, 11-21
MTRRfix MSR, 11-23
MTRRs, 8-15
base & mask calculations, 11-26, 11-27
Vol. 3D INDEX-11

INDEX

cache control, 11-13
description of, 9-8, 11-20
dual-core processors, 8-33
enabling caching, 9-7
feature identification, 11-21
fixed-range registers, 11-23
IA32_MTRRCAP MSR, 11-21
IA32_MTRR_DEF_TYPE MSR, 11-22
initialization of, 11-29
introduction of in IA-32 processors, 22-36
introduction to, 2-6
large page size considerations, 11-33
logical processors, 8-33
mapping physical memory with, 11-21
memory types and their properties, 11-21
MemTypeGet() function, 11-29
MemTypeSet() function, 11-31
multiple-processor considerations, 11-32
precedence of cache controls, 11-13
precedences, 11-28
programming interface, 11-29
remapping memory types, 11-29
state of following a hardware reset, 11-20
variable-range registers, 11-23, 11-25
Multi-core technology
See multi-threading support
Multiple-processor management
bus locking, 8-3
guaranteed atomic operations, 8-2
initialization
MP protocol, 8-18
procedure, 8-54
local APIC, 10-1
memory ordering, 8-5
MP protocol, 8-18
overview of, 8-1
SMM considerations, 34-16
VMM design, 31-10
asymmetric, 31-10
CPUID emulation, 31-12
external data structures, 31-11
index-data registers, 31-11
initialization, 31-11
moving between processors, 31-11
symmetric, 31-10
Multiple-processor system
local APIC and I/O APICs, Pentium 4, 10-3
local APIC and I/O APIC, P6 family, 10-3
Multisegment model, 3-4
Multitasking
initialization for, 9-10, 9-11
initializing IA-32e mode, 9-11
linking tasks, 7-12
mechanism, description of, 7-2
overview, 7-1
setting up TSS, 9-10
setting up TSS descriptor, 9-10
Multi-threading support
executing multiple threads, 8-26
handling interrupts, 8-26
logical processors per package, 8-25
mapping resources, 8-34
microcode updates, 8-33
performance monitoring counters, 8-33
programming considerations, 8-34
See also: Hyper-Threading Technology and dual-core technology
MWAIT instruction, 25-3
power management extensions, 14-18
MXCSR register, 6-47, 9-8, 13-6

INDEX-12 Vol. 3D

N
NaN, compatibility, IA-32 processors, 22-9
NE (numeric error) flag
CR0 control register, 2-15, 6-42, 9-6, 9-7, 22-7, 22-18
NEG instruction, 8-3
NetBurst microarchitecture (see Intel NetBurst microarchitecture)
NMI interrupt, 2-25, 10-3
description of, 6-2
handling during initialization, 9-9
handling in SMM, 34-11
handling multiple NMIs, 6-6
masking, 22-27
receiving when processor is shutdown, 6-29
reference information, 6-22
vector, 6-2
NMI# pin, 6-2, 6-22
Nominal CPI method, 18-126
Nonconforming code segments
accessing, 5-11
C (conforming) flag, 5-11
description of, 3-13
Non-halted clockticks, 18-126
setting up counters, 18-126
Non-Halted CPI method, 18-126
Nonmaskable interrupt (see NMI)
Non-precise event-based sampling
defined, 18-93
used for at-retirement counting, 18-104
writing an interrupt service routine for, 17-24
Non-retirement events, 18-93, 19-199
Non-sleep clockticks, 18-126
NOT instruction, 8-3
Notation
bit and byte order, 1-6
conventions, 1-6
exceptions, 1-9
hexadecimal and binary numbers, 1-8
Instructions
operands, 1-8
reserved bits, 1-7
segmented addressing, 1-8
NT (nested task) flag
EFLAGS register, 2-10, 7-10, 7-12
Null segment selector, checking for, 5-6
Numeric overflow exception (#O), 22-10
Numeric underflow exception (#U), 22-10
NV (invert) flag, PerfEvtSel0 MSR
(P6 family processors), 18-4, 18-122
NW (not write-through) flag
CR0 control register, 2-14, 9-7, 11-12, 11-13, 11-16, 11-32, 22-18,
22-19, 22-30
NXE bit, 5-30

O
Obsolete instructions, 22-5, 22-15
OF flag, EFLAGS register, 6-24
On die digital thermal sensor, 14-25
relevant MSRs, 14-25
sensor enumeration, 14-25
On-Demand
clock modulation enable bits, 14-23
On-demand
clock modulation duty cycle bits, 14-23
On-die sensors, 14-19
Opcodes
undefined, 22-5
Operands
instruction, 1-8
operand-size prefix, 21-1
Operating modes
64-bit mode, 2-7

INDEX

compatibility mode, 2-7
IA-32e mode, 2-7, 2-8
introduction to, 2-7
protected mode, 2-7
SMM (system management mode), 2-7
transitions between, 2-8
virtual-8086 mode, 2-7
VMX operation
enabling and entering, 23-3
guest environments, 31-1
OR instruction, 8-3
OS (operating system mode) flag
PerfEvtSel0 and PerfEvtSel1 MSRs (P6 only), 18-4, 18-121
OSFXSR (FXSAVE/FXRSTOR support) flag
CR4 control register, 2-18, 9-8, 13-2
OSXMMEXCPT (SIMD floating-point exception support) flag, CR4 control
register, 2-18, 6-47, 9-8, 13-3
OUT instruction, 8-15, 25-2
Out-of-spec status bit, 14-25, 14-29
Out-of-spec status log, 14-26, 14-29
OUTS/OUTSB/OUTSW/OUTSD instruction, 17-9, 25-2
Overflow exception (#OF), 6-24
Overheat interrupt enable bit, 14-27, 14-30

P
P (present) flag
page-directory entry, 6-39
page-table entry, 6-39
segment descriptor, 3-11
P5_MC_ADDR MSR, 15-13, 15-29
P5_MC_TYPE MSR, 15-13, 15-29
P6 family processors
compatibility with FP software, 22-7
description of, 1-1
last branch, interrupt, and exception recording, 17-39
list of performance-monitoring events, 19-230
PAE paging
feature flag, CR4 register, 2-17
flag, CR4 control register, 3-6, 22-18, 22-19
Page attribute table (PAT)
compatibility with earlier IA-32 processors, 11-36
detecting support for, 11-34
IA32_PAT MSR, 11-34
introduction to, 11-33
memory types that can be encoded with, 11-34
MSR, 11-13
precedence of cache controls, 11-14
programming, 11-35
selecting a memory type with, 11-35
Page directories, 2-6
Page directory
base address (PDBR), 7-5
introduction to, 2-6
overview, 3-2
setting up during initialization, 9-10
Page directory pointers, 2-6
Page frame (see Page)
Page tables, 2-6
introduction to, 2-6
overview, 3-2
setting up during initialization, 9-10
Page-directory entries, 8-3, 11-5
Page-fault exception (#PF), 4-47, 6-39, 22-21
Pages
disabling protection of, 5-1
enabling protection of, 5-1
introduction to, 2-6
overview, 3-2
PG flag, CR0 control register, 5-1
split, 22-15
Page-table entries, 8-3, 11-5, 11-19

Paging
combining segment and page-level protection, 5-29
combining with segmentation, 3-5
defined, 3-1
IA-32e mode, 2-6
initializing, 9-10
introduction to, 2-6
large page size MTRR considerations, 11-33
mapping segments to pages, 4-48
page boundaries regarding TSS, 7-5
page-fault exception, 6-39, 6-49
page-level protection, 5-2, 5-3, 5-27
page-level protection flags, 5-28
virtual-8086 tasks, 20-7
Parameter
passing, between 16- and 32-bit call gates, 21-6
translation, between 16- and 32-bit code segments, 21-6
PAUSE instruction, 2-15, 25-3
PBi (performance monitoring/breakpoint pins) flags, DEBUGCTLMSR MSR,
17-38, 17-40
PC (pin control) flag, PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family
processors), 18-4, 18-122
PC0 and PC1 (pin control) fields, CESR MSR (Pentium processor), 18-124
PCD pin (Pentium processor), 11-13
PCD (page-level cache disable) flag
CR3 control register, 2-16, 11-13, 22-18, 22-30
page-directory entries, 9-7, 11-13, 11-33
page-table entries, 9-7, 11-13, 11-33, 22-31
PCE (performance monitoring counter enable) flag, CR4 control register,
2-18, 5-24, 18-95, 18-122
PCE (performance-monitoring counter enable) flag, CR4 control register,
22-18
PDBR (see CR3 control register)
PE (protection enable) flag, CR0 control register, 2-16, 5-1, 9-10, 9-13,
34-9
PEBS records, 17-21
PEBS (precise event-based sampling) facilities
availability of, 18-106
description of, 18-93, 18-105
DS save area, 17-17
IA-32e mode, 17-21
PEBS buffer, 17-18, 18-106
PEBS records, 17-17, 17-20
writing a PEBS interrupt service routine, 18-106
writing interrupt service routine, 17-24
PEBS_UNAVAILABLE flag
IA32_MISC_ENABLE MSR, 17-18
Pentium 4 processor, 1-1
compatibility with FP software, 22-7
last branch, interrupt, and exception recording, 17-33
list of performance-monitoring events, 19-2, 19-199
time-stamp counter, 17-41
Pentium M processor
last branch, interrupt, and exception recording, 17-38
time-stamp counter, 17-41
Pentium processor, 1-1, 22-7
compatibility with MCA, 15-1
list of performance-monitoring events, 19-239
performance-monitoring counters, 18-123
PerfCtr0 and PerfCtr1 MSRs
(P6 family processors), 18-121, 18-122
PerfEvtSel0 and PerfEvtSel1 MSRs
(P6 family processors), 18-121
PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family processors), 18-121
Performance events
architectural, 18-1
Intel Core Solo and Intel Core Duo processors, 18-1
non-architectural, 18-1
non-retirement events (Pentium 4 processor), 19-199
P6 family processors, 19-230
Pentium 4 and Intel Xeon processors, 17-33
Pentium M processors, 17-38
Vol. 3D INDEX-13

INDEX

Pentium processor, 19-239
Performance state, 14-1
Performance-monitoring counters
counted events (P6 family processors), 19-230
counted events (Pentium 4 processor), 19-2, 19-199
counted events (Pentium processors), 18-125
description of, 18-1, 18-2
events that can be counted (Pentium processors), 19-239
interrupt, 10-1
introduction of in IA-32 processors, 22-37
monitoring counter overflow (P6 family processors), 18-123
overflow, monitoring (P6 family processors), 18-123
overview of, 2-7
P6 family processors, 18-120
Pentium II processor, 18-120
Pentium Pro processor, 18-120
Pentium processor, 18-123
reading, 2-25, 18-122
setting up (P6 family processors), 18-121
software drivers for, 18-122
starting and stopping, 18-122
PG (paging) flag
CR0 control register, 2-14, 5-1
PG (paging) flag, CR0 control register, 9-10, 9-13, 22-32, 34-9
PGE (page global enable) flag, CR4 control register, 2-17, 11-13, 22-18,
22-19
PhysBase field, IA32_MTRR_PHYSBASEn MTRR, 11-24, 11-26
Physical address extension
introduction to, 3-6
Physical address space
4 GBytes, 3-6
64 GBytes, 3-6
addressing, 2-6
defined, 3-1
description of, 3-6
guest and host spaces, 32-2
IA-32e mode, 3-6
mapped to a task, 7-14
mapping with variable-range MTRRs, 11-23, 11-25
memory virtualization, 32-2
See also: VMM, VMX
Physical destination mode, local APIC, 10-23
PhysMask
IA32_MTRR_PHYSMASKn MTRR, 11-24, 11-26
PM0/BP0 and PM1/BP1 (performance-monitor) pins (Pentium processor),
18-123, 18-124, 18-125
PML4 tables, 2-6
Pointers
code-segment pointer size, 21-4
limit checking, 5-25
validation, 5-24
POP instruction, 3-8
POPF instruction, 6-7, 17-9
Power consumption
software controlled clock, 14-19, 14-23
Precise event-based sampling (see PEBS)
PREFETCHh instruction, 2-15, 11-17
Previous task link field, TSS, 7-4, 7-12, 7-13
Privilege levels
checking when accessing data segments, 5-8
checking, for call gates, 5-15
checking, when transferring program control between code segments,
5-10
description of, 5-6
protection rings, 5-8
Privileged instructions, 5-23
Processor families
06H, 16-1
0FH, 16-1
Processor management
initialization, 9-1
local APIC, 10-1
INDEX-14 Vol. 3D

microcode update facilities, 9-27
overview of, 8-1
See also: multiple-processor management
Processor ordering, description of, 8-5
PROCHOT# log, 14-25, 14-29
PROCHOT# or FORCEPR# event bit, 14-25, 14-29
Protected mode
IDT initialization, 9-10
initialization for, 9-9
mixing 16-bit and 32-bit code modules, 21-1
mode switching, 9-13
PE flag, CR0 register, 5-1
switching to, 5-1, 9-13
system data structures required during initialization, 9-9
Protection
combining segment & page-level, 5-29
disabling, 5-1
enabling, 5-1
flags used for page-level protection, 5-2, 5-3
flags used for segment-level protection, 5-2
IA-32e mode, 5-3
of exception, interrupt-handler procedures, 6-13
overview of, 5-1
page level, 5-1, 5-27, 5-28, 5-30
page level, overriding, 5-29
page-level protection flags, 5-28
read/write, page level, 5-28
segment level, 5-1
user/supervisor type, 5-28
Protection rings, 5-8
PSE (page size extension) flag
CR4 control register, 2-17, 11-20, 22-18, 22-19
PSE-36 page size extension, 3-6
Pseudo-functions
VMfail, 30-2
VMfailInvalid, 30-2
VMfailValid, 30-2
VMsucceed, 30-2
Pseudo-infinity, 22-9
Pseudo-NaN, 22-9
Pseudo-zero, 22-9
P-state, 14-1
PUSH instruction, 22-7
PUSHF instruction, 6-7, 22-7
PVI (protected-mode virtual interrupts) flag
CR4 control register, 2-11, 2-17, 22-18
PWT pin (Pentium processor), 11-13
PWT (page-level write-through) flag
CR3 control register, 2-17, 11-13, 22-18, 22-30
page-directory entries, 9-7, 11-13, 11-33
page-table entries, 9-7, 11-33, 22-31

Q
QNaN, compatibility, IA-32 processors, 22-9

R
RDMSR instruction, 2-19, 2-21, 2-26, 5-24, 17-35, 17-40, 17-42, 18-95,
18-121, 18-122, 18-123, 22-4, 22-36, 25-4, 25-8
RDPMC instruction, 2-25, 5-24, 18-95, 18-121, 18-122, 22-4, 22-18,
22-37, 25-4
in 64-bit mode, 2-26
RDTSC instruction, 2-25, 5-24, 17-42, 22-4, 25-4, 25-9
in 64-bit mode, 2-26
reading sensors, 14-25
Read/write
protection, page level, 5-28
rights, checking, 5-25
Real-address mode
8086 emulation, 20-1
address translation in, 20-2

INDEX

description of, 20-1
exceptions and interrupts, 20-6
IDT initialization, 9-8
IDT, changing base and limit of, 20-5
IDT, structure of, 20-5
IDT, use of, 20-4
initialization, 9-8
instructions supported, 20-3
interrupt and exception handling, 20-4
interrupts, 20-6
introduction to, 2-7
mode switching, 9-13
native 16-bit mode, 21-1
overview of, 20-1
registers supported, 20-3
switching to, 9-14
Recursive task switching, 7-13
Related literature, 1-10
Replay events, 19-222
Requested privilege level (see RPL)
Reserved bits, 1-7, 22-2
RESET# pin, 6-3, 22-16
RESET# signal, 2-25
Resolution in degrees, 14-26
Restarting program or task, following an exception or interrupt, 6-5
Restricting addressable domain, 5-28
RET instruction, 5-10, 5-20, 21-6
Returning
from a called procedure, 5-20
from an interrupt or exception handler, 6-13
RF (resume) flag
EFLAGS register, 2-10, 6-7
RPL
description of, 3-8, 5-8
field, segment selector, 5-2
RSM instruction, 2-25, 8-17, 22-5, 25-4, 34-1, 34-2, 34-3, 34-13, 34-15,
34-18
RsvdZ, 10-40
R/S# pin, 6-3
R/W (read/write) flag
page-directory entry, 5-1, 5-2, 5-28
page-table entry, 5-1, 5-2, 5-28
R/W0-R/W3 (read/write) fields
DR7 register, 17-4, 22-20

S
S (descriptor type) flag
segment descriptor, 3-11, 3-12, 5-2, 5-5
SBB instruction, 8-3
Segment descriptors
access rights, 5-24
access rights, invalid values, 22-19
automatic bus locking while updating, 8-3
base address fields, 3-10
code type, 5-2
data type, 5-2
description of, 2-4, 3-9
DPL (descriptor privilege level) field, 3-11, 5-2
D/B (default operation size/default stack pointer size and/or upper
bound) flag, 3-11, 5-4
E (expansion direction) flag, 5-2, 5-4
G (granularity) flag, 3-11, 5-2, 5-4
limit field, 5-2, 5-4
loading, 22-20
P (segment-present) flag, 3-11
S (descriptor type) flag, 3-11, 3-12, 5-2, 5-5
segment limit field, 3-10
system type, 5-2
tables, 3-14
TSS descriptor, 7-5, 7-6
type field, 3-10, 3-12, 5-2, 5-5

type field, encoding, 3-14
when P (segment-present) flag is clear, 3-11
Segment limit
checking, 2-23
field, segment descriptor, 3-10
Segment not present exception (#NP), 3-11
Segment registers
description of, 3-8
IA-32e mode, 3-9
saved in TSS, 7-4
Segment selectors
description of, 3-7
index field, 3-7
null, 5-6
null in 64-bit mode, 5-6
RPL field, 3-8, 5-2
TI (table indicator) flag, 3-7
Segmented addressing, 1-8
Segment-not-present exception (#NP), 6-33
Segments
64-bit mode, 3-5
basic flat model, 3-3
code type, 3-12
combining segment, page-level protection, 5-29
combining with paging, 3-5
compatibility mode, 3-5
data type, 3-12
defined, 3-1
disabling protection of, 5-1
enabling protection of, 5-1
mapping to pages, 4-48
multisegment usage model, 3-4
protected flat model, 3-3
segment-level protection, 5-2, 5-3
segment-not-present exception, 6-33
system, 2-4
types, checking access rights, 5-24
typing, 5-5
using, 3-2
wraparound, 22-34
SELF IPI register, 10-38
Self-modifying code, effect on caches, 11-18
Serializing, 8-17
Serializing instructions
CPUID, 8-17
HT technology, 8-30
non-privileged, 8-17
privileged, 8-17
SF (stack fault) flag, x87 FPU status word, 22-8
SFENCE instruction, 2-15, 8-6, 8-15, 8-16, 8-17
SGDT instruction, 2-23, 3-15
Shared resources
mapping of, 8-34
Shutdown
resulting from double fault, 6-29
resulting from out of IDT limit condition, 6-29
SIDT instruction, 2-23, 3-16, 6-9
SIMD floating-point exception (#XM), 2-18, 6-47, 9-8
SIMD floating-point exceptions
description of, 6-47, 13-5
handler, 13-3
support for, 2-18
Single-stepping
breakpoint exception condition, 17-9
on branches, 17-13
on exceptions, 17-13
on interrupts, 17-13
TF (trap) flag, EFLAGS register, 17-9
SLDT instruction, 2-23
SLTR instruction, 3-16
SMBASE
default value, 34-4
Vol. 3D INDEX-15

INDEX

relocation of, 34-14
SMI handler
description of, 34-1
execution environment for, 34-9
exiting from, 34-3
VMX treatment of, 34-16
SMI interrupt, 2-25, 10-3
description of, 34-1, 34-2
IO_SMI bit, 34-11
priority, 34-3
switching to SMM, 34-2
synchronous and asynchronous, 34-11
VMX treatment of, 34-16
SMI# pin, 6-3, 34-2, 34-15
SMM
asynchronous SMI, 34-11
auto halt restart, 34-13
executing the HLT instruction in, 34-14
exiting from, 34-3
handling exceptions and interrupts, 34-10
introduction to, 2-7
I/O instruction restart, 34-15
I/O state implementation, 34-12
native 16-bit mode, 21-1
overview of, 34-1
revision identifier, 34-13
revision identifier field, 34-13
switching to, 34-2
switching to from other operating modes, 34-2
synchronous SMI, 34-11
VMX operation
default RSM treatment, 34-17
default SMI delivery, 34-16
dual-monitor treatment, 34-19
overview, 34-1
protecting CR4.VMXE, 34-18
RSM instruction, 34-18
SMM monitor, 34-1
SMM VM exits, 27-1, 34-19
SMM-transfer VMCS, 34-19
SMM-transfer VMCS pointer, 34-19
VMCS pointer preservation, 34-17
VMX-critical state, 34-17
SMRAM
caching, 34-8
state save map, 34-4
structure of, 34-3
SMSW instruction, 2-23, 25-9
SNaN, compatibility, IA-32 processors, 22-9, 22-14
Snooping mechanism, 11-6
Software controlled clock
modulation control bits, 14-23
power consumption, 14-19, 14-23
Software interrupts, 6-4
Software-controlled bus locking, 8-3
Split pages, 22-15
Spurious interrupt, local APIC, 10-32
SSE extensions
checking for with CPUID, 13-2
checking support for FXSAVE/FXRSTOR, 13-2
CPUID feature flag, 9-8
EM flag, 2-16
emulation of, 13-6
facilities for automatic saving of state, 13-6, 13-7
initialization, 9-8
introduction of into the IA-32 architecture, 22-3
providing exception handlers for, 13-4, 13-5
providing operating system support for, 13-1
saving and restoring state, 13-6
saving state on task, context switches, 13-6
SIMD Floating-point exception (#XM), 6-47
using TS flag to control saving of state, 13-7
INDEX-16 Vol. 3D

SSE feature flag
CPUID instruction, 13-2
SSE2 extensions
checking for with CPUID, 13-2
checking support for FXSAVE/FXRSTOR, 13-2
CPUID feature flag, 9-8
EM flag, 2-16
emulation of, 13-6
facilities for automatic saving of state, 13-6, 13-7
initialization, 9-8
introduction of into the IA-32 architecture, 22-3
providing exception handlers for, 13-4, 13-5
providing operating system support for, 13-1
saving and restoring state, 13-6
saving state on task, context switches, 13-6
SIMD Floating-point exception (#XM), 6-47
using TS flag to control saving state, 13-7
SSE2 feature flag
CPUID instruction, 13-2
SSE3 extensions
checking for with CPUID, 13-2
CPUID feature flag, 9-8
EM flag, 2-16
emulation of, 13-6
example verifying SS3 support, 8-44, 8-48, 14-2
facilities for automatic saving of state, 13-6, 13-7
initialization, 9-8
introduction of into the IA-32 architecture, 22-3
providing exception handlers for, 13-4, 13-5
providing operating system support for, 13-1
saving and restoring state, 13-6
saving state on task, context switches, 13-6
using TS flag to control saving of state, 13-7
SSE3 feature flag
CPUID instruction, 13-2
Stack fault exception (#SS), 6-35
Stack fault, x87 FPU, 22-8, 22-13
Stack pointers
privilege level 0, 1, and 2 stacks, 7-5
size of, 3-11
Stack segments
paging of, 2-6
privilege level check when loading SS register, 5-10
size of stack pointer, 3-11
Stack switching
exceptions/interrupts when switching stacks, 6-7
IA-32e mode, 6-18
inter-privilege level calls, 5-17
Stack-fault exception (#SS), 22-34
Stacks
error code pushes, 22-32
faults, 6-35
for privilege levels 0, 1, and 2, 5-17
interlevel RET/IRET
from a 16-bit interrupt or call gate, 22-33
interrupt stack table, 64-bit mode, 6-19
management of control transfers for
16- and 32-bit procedure calls, 21-4
operation on pushes and pops, 22-32
pointers to in TSS, 7-5
stack switching, 5-17, 6-18
usage on call to exception
or interrupt handler, 22-33
Stepping information, following processor initialization or reset, 9-5
STI instruction, 6-7
Store buffer
caching terminology, 11-5
characteristics of, 11-4
description of, 11-5, 11-20
in IA-32 processors, 22-34
location of, 11-1
operation of, 11-20

INDEX

STPCLK# pin, 6-3
STR instruction, 2-23, 3-16, 7-7
Strong uncached (UC) memory type
description of, 11-6
effect on memory ordering, 8-16
use of, 9-8, 11-8
Sub C-state, 14-18
SUB instruction, 8-3
Supervisor mode
description of, 5-28
U/S (user/supervisor) flag, 5-28
SVR (spurious-interrupt vector register), local APIC, 10-8, 22-28
SWAPGS instruction, 2-7, 31-15
SYSCALL instruction, 2-7, 5-22, 31-15
SYSENTER instruction, 3-9, 5-10, 5-20, 5-21, 31-15, 31-16
SYSENTER_CS_MSR, 5-21
SYSENTER_EIP_MSR, 5-21
SYSENTER_ESP_MSR, 5-21
SYSEXIT instruction, 3-9, 5-10, 5-20, 5-21, 31-15, 31-16
SYSRET instruction, 2-7, 5-22, 31-15
System
architecture, 2-1, 2-2
data structures, 2-2
instructions, 2-7, 2-21
registers in IA-32e mode, 2-7
registers, introduction to, 2-6
segment descriptor, layout of, 5-2
segments, paging of, 2-6
System programming
MMX technology, 12-1
virtualization of resources, 32-1
System-management mode (see SMM)

T
T (debug trap) flag, TSS, 7-5
Task gates
descriptor, 7-8
executing a task, 7-2
handling a virtual-8086 mode interrupt or exception through, 20-14
IA-32e mode, 2-5
in IDT, 6-10
introduction for IA-32e, 2-4
introduction to, 2-4, 2-5
layout of, 6-10
referencing of TSS descriptor, 6-14
Task management, 7-1
data structures, 7-3
mechanism, description of, 7-2
Task register, 3-16
description of, 2-13, 7-1, 7-7
IA-32e mode, 2-13
initializing, 9-11
introduction to, 2-6
Task switching
description of, 7-3
exception condition, 17-10
operation, 7-10
preventing recursive task switching, 7-13
saving MMX state on, 12-4
saving SSE/SSE2/SSE3 state
on task or context switches, 13-6
T (debug trap) flag, 7-5
Tasks
address space, 7-14
description of, 7-1
exception-handler task, 6-11
executing, 7-2
Intel 286 processor tasks, 22-37
interrupt-handler task, 6-11
interrupts and exceptions, 6-14
linking, 7-12

logical address space, 7-15
management, 7-1
mapping linear and physical address space, 7-14
restart following an exception or interrupt, 6-5
state (context), 7-2, 7-3
structure, 7-1
switching, 7-3
task management data structures, 7-3
TF (trap) flag, EFLAGS register, 2-9, 6-14, 17-9, 17-11, 17-34, 17-36,
17-38, 17-40, 20-4, 20-19, 34-11
Thermal monitoring
advanced power management, 14-18
automatic, 14-20
automatic thermal monitoring, 14-19
catastrophic shutdown detector, 14-19, 14-20
clock-modulation bits, 14-23
C-state, 14-18
detection of facilities, 14-24
Enhanced Intel SpeedStep Technology, 14-1
IA32_APERF MSR, 14-2
IA32_MPERF MSR, 14-1
IA32_THERM_INTERRUPT MSR, 14-25
IA32_THERM_STATUS MSR, 14-25
interrupt enable/disable flags, 14-22
interrupt mechanisms, 14-19
MWAIT extensions for, 14-18
on die sensors, 14-19, 14-24
overview of, 14-1, 14-19
performance state transitions, 14-21
sensor interrupt, 10-1
setting thermal thresholds, 14-25
software controlled clock modulation, 14-19, 14-23
status flags, 14-21
status information, 14-21, 14-22
stop clock mechanism, 14-19
thermal monitor 1 (TM1), 14-20
thermal monitor 2 (TM2), 14-20
TM flag, CPUID instruction, 14-24
Thermal status bit, 14-25, 14-28
Thermal status log bit, 14-25, 14-29
Thermal threshold #1 log, 14-26, 14-29
Thermal threshold #1 status, 14-26, 14-29
Thermal threshold #2 log, 14-26, 14-29
Thermal threshold #2 status, 14-26, 14-29
THERMTRIP# interrupt enable bit, 14-27, 14-30
thread timeout indicator, 16-3, 16-7, 16-10, 16-13, 16-15
Threshold #1 interrupt enable bit, 14-27, 14-30
Threshold #1 value, 14-27, 14-30
Threshold #2 interrupt enable, 14-27, 14-30
Threshold #2 value, 14-27, 14-30
TI (table indicator) flag, segment selector, 3-7
Timer, local APIC, 10-16
Time-stamp counter
counting clockticks, 18-126
description of, 17-41
IA32_TIME_STAMP_COUNTER MSR, 17-41
RDTSC instruction, 17-41
reading, 2-25
software drivers for, 18-122
TSC flag, 17-41
TSD flag, 17-41
TLBs
description of, 11-1, 11-5
flushing, 11-19
invalidating (flushing), 2-24
relationship to PGE flag, 22-19
relationship to PSE flag, 11-20
virtual TLBs, 32-3
TM1 and TM2
See: thermal monitoring, 14-20
TMR
Trigger Mode Register, 10-31, 10-39, 10-41, 10-47
Vol. 3D INDEX-17

INDEX

TMR (Trigger Mode Register), local APIC, 10-30
TPR
Task Priority Register, 10-38, 10-41
TR (trace message enable) flag
DEBUGCTLMSR MSR, 17-11, 17-34, 17-37, 17-38, 17-40
Trace cache, 11-4, 11-5
Transcendental instruction accuracy, 22-8, 22-14
Translation lookaside buffer (see TLB)
Trap gates
difference between interrupt and trap gates, 6-14
for 16-bit and 32-bit code modules, 21-1
handling a virtual-8086 mode interrupt or exception through, 20-12
in IDT, 6-10
introduction for IA-32e, 2-4
introduction to, 2-4, 2-5
layout of, 6-10
Traps
description of, 6-5
restarting a program or task after, 6-5
TS (task switched) flag
CR0 control register, 2-15, 2-23, 6-27, 12-1, 13-3, 13-7
TSD (time-stamp counter disable) flag
CR4 control register, 2-17, 5-24, 17-42, 22-18
TSS
16-bit TSS, structure of, 7-15
32-bit TSS, structure of, 7-3
64-bit mode, 7-16
CR3 control register (PDBR), 7-4, 7-14
description of, 2-4, 2-5, 7-1, 7-3
EFLAGS register, 7-4
EFLAGS.NT, 7-12
EIP, 7-4
executing a task, 7-2
floating-point save area, 22-12
format in 64-bit mode, 7-16
general-purpose registers, 7-4
IA-32e mode, 2-5
initialization for multitasking, 9-10
interrupt stack table, 7-17
invalid TSS exception, 6-31
IRET instruction, 7-12
I/O map base address field, 7-5, 22-29
I/O permission bit map, 7-5, 7-17
LDT segment selector field, 7-4, 7-14
link field, 6-14
order of reads/writes to, 22-29
pointed to by task-gate descriptor, 7-8
previous task link field, 7-4, 7-12, 7-13
privilege-level 0, 1, and 2 stacks, 5-17
referenced by task gate, 6-14
segment registers, 7-4
T (debug trap) flag, 7-5
task register, 7-7
using 16-bit TSSs in a 32-bit environment, 22-29
virtual-mode extensions, 22-29
TSS descriptor
B (busy) flag, 7-5
busy flag, 7-13
initialization for multitasking, 9-10
structure of, 7-5, 7-6
TSS segment selector
field, task-gate descriptor, 7-8
writes, 22-29
Type
checking, 5-5
field, IA32_MTRR_DEF_TYPE MSR, 11-22
field, IA32_MTRR_PHYSBASEn MTRR, 11-24, 11-26
field, segment descriptor, 3-10, 3-12, 3-14, 5-2, 5-5
of segment, 5-5

INDEX-18 Vol. 3D

U
UC- (uncacheable) memory type, 11-6
UD2 instruction, 22-4
Uncached (UC-) memory type, 11-8
Uncached (UC) memory type (see Strong uncached (UC) memory type)
Undefined opcodes, 22-5
Unit mask field, PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family processors)
, 18-4, 18-7, 18-8, 18-10, 18-11, 18-12, 18-14, 18-24, 18-26,
18-34, 18-35, 18-53, 18-55, 18-56, 18-86, 18-87, 18-121
Un-normal number, 22-9
User mode
description of, 5-28
U/S (user/supervisor) flag, 5-28
User-defined interrupts, 6-1, 6-50
USR (user mode) flag, PerfEvtSel0 and PerfEvtSel1 MSRs (P6 family
processors), 18-4, 18-7, 18-8, 18-10, 18-11, 18-12, 18-24,
18-26, 18-34, 18-35, 18-53, 18-55, 18-56, 18-86, 18-87,
18-121
U/S (user/supervisor) flag
page-directory entry, 5-1, 5-2, 5-28
page-table entries, 20-8
page-table entry, 5-1, 5-2, 5-28

V
V (valid) flag
IA32_MTRR_PHYSMASKn MTRR, 11-24, 11-26
Variable-range MTRRs, description of, 11-23, 11-25
VCNT (variable range registers count) field, IA32_MTRRCAP MSR, 11-22
Vectors
exceptions, 6-1
interrupts, 6-1
VERR instruction, 2-24, 5-25
VERW instruction, 2-24, 5-25
VIF (virtual interrupt) flag
EFLAGS register, 2-11, 22-6
VIP (virtual interrupt pending) flag
EFLAGS register, 2-11, 22-6
Virtual memory, 2-6, 3-1, 3-2
Virtual-8086 mode
8086 emulation, 20-1
description of, 20-5
emulating 8086 operating system calls, 20-18
enabling, 20-6
entering, 20-8
exception and interrupt handling overview, 20-11
exceptions and interrupts, handling through a task gate, 20-14
exceptions and interrupts, handling through a trap or interrupt gate,
20-12
handling exceptions and interrupts through a task gate, 20-14
interrupts, 20-6
introduction to, 2-7
IOPL sensitive instructions, 20-10
I/O-port-mapped I/O, 20-11
leaving, 20-9
memory mapped I/O, 20-11
native 16-bit mode, 21-1
overview of, 20-1
paging of virtual-8086 tasks, 20-7
protection within a virtual-8086 task, 20-8
special I/O buffers, 20-11
structure of a virtual-8086 task, 20-7
virtual I/O, 20-10
VM flag, EFLAGS register, 2-10
Virtual-8086 tasks
paging of, 20-7
protection within, 20-8
structure of, 20-7
Virtualization
debugging facilities, 32-1
interrupt vector space, 33-3
memory, 32-2

INDEX

VM

microcode update facilities, 32-8
operating modes, 32-2
page faults, 32-5
system resources, 32-1
TLBs, 32-3

OSs and application software, 31-1
programming considerations, 31-1
VM entries
basic VM-entry checks, 26-2
checking guest state
control registers, 26-8
debug registers, 26-8
descriptor-table registers, 26-11
MSRs, 26-8
non-register state, 26-12
RIP and RFLAGS, 26-11
segment registers, 26-9
checks on controls, host-state area, 26-2
registers and MSRs, 26-6
segment and descriptor-table registers, 26-7
VMX control checks, 26-2
exit-reason numbers, C-1
loading guest state, 26-14
control and debug registers, MSRs, 26-15
RIP, RSP, RFLAGS, 26-16
segment & descriptor-table registers, 26-16
loading MSRs, 26-17
failure cases, 26-17
VM-entry MSR-load area, 26-17
overview of failure conditions, 26-1
overview of steps, 26-1
VMLAUNCH and VMRESUME, 26-1
See also: VMCS, VMM, VM exits
VM exits
architectural state
existing before exit, 27-1
updating state before exit, 27-1
basic VM-exit information fields, 27-4
basic exit reasons, 27-4
exit qualification, 27-4
exception bitmap, 27-1
exceptions (faults, traps, and aborts), 25-5
exit-reason numbers, C-1
external interrupts, 25-5
handling of exits due to exceptions, 31-8
IA-32 faults and VM exits, 25-1
INITs, 25-5
instructions that cause:
conditional exits, 25-2
unconditional exits, 25-2
interrupt-window exiting, 25-6
non-maskable interrupts (NMIs), 25-5
page faults, 25-5
reflecting exceptions to guest, 31-8
resuming guest after exception handling, 31-9
start-up IPIs (SIPIs), 25-5
task switches, 25-5
See also: VMCS, VMM, VM entries
VM (virtual-8086 mode) flag
EFLAGS register, 2-8, 2-10
VMCALL instruction, 30-1
VMCLEAR instruction, 30-1, 31-7
VMCS
error numbers, 30-29
field encodings, 1-6, B-1
16-bit guest-state fields, B-1
16-bit host-state fields, B-2
32-bit control fields, B-1, B-6
32-bit guest-state fields, B-7
32-bit read-only data fields, B-7
64-bit control fields, B-2

64-bit guest-state fields, B-4, B-5
natural-width control fields, B-8
natural-width guest-state fields, B-9
natural-width host-state fields, B-10
natural-width read-only data fields, B-9
format of VMCS region, 24-2
guest-state area, 24-3, 24-4
guest non-register state, 24-5
guest register state, 24-4
host-state area, 24-3, 24-8
introduction, 24-1
migrating between processors, 24-24
software access to, 24-24
VMCS data, 24-2, 25-16
VMCS pointer, 24-1, 31-2
VMCS region, 24-1, 31-2
VMCS revision identifier, 24-2, 25-16
VM-entry control fields, 24-3, 24-18
entry controls, 24-19
entry controls for event injection, 24-20
entry controls for MSRs, 24-19
VM-execution control fields, 24-3, 24-8
controls for CR8 accesses, 24-13
CR3-target controls, 24-13
exception bitmap, 24-12
I/O bitmaps, 24-12
masks & read shadows CR0 & CR4, 24-12
pin-based controls, 24-8
processor-based controls, 24-9
time-stamp counter offset, 24-12
VM-exit control fields, 24-3, 24-17
exit controls, 24-17
exit controls for MSRs, 24-18
VM-exit information fields, 24-3, 24-21
basic exit information, 24-21, C-1
basic VM-exit information, 24-21
exits due to instruction execution, 24-23
exits due to vectored events, 24-22
exits occurring during event delivery, 24-22
VM-instruction error field, 24-23
VM-instruction error field, 26-1, 30-29
VMREAD instruction, 31-2
field encodings, 1-6, B-1
VMWRITE instruction, 31-2
field encodings, 1-6, B-1
VMX-abort indicator, 24-2, 25-16
See also: VM entries, VM exits, VMM, VMX
VME (virtual-8086 mode extensions) flag, CR4 control register, 2-11,
2-17, 22-18
VMLAUNCH instruction, 30-1, 31-7
VMM
asymmetric design, 31-10
control registers, 31-17
CPUID instruction emulation, 31-12
debug exceptions, 32-1
debugging facilities, 32-1
entering VMX root operation, 31-4
error handling, 31-2
exception bitmap, 32-1
external interrupts, 33-1
fast instruction set emulator, 31-1
index data pairs, usage of, 31-11
interrupt handling, 33-1
interrupt vectors, 33-3
leaving VMX operation, 31-4
machine checks, 33-8, 33-9, 33-11
memory virtualization, 32-2
microcode update facilities, 32-8
multi-processor considerations, 31-10
operating modes, 31-12
programming considerations, 31-1
response to page faults, 32-5
Vol. 3D INDEX-19

INDEX

root VMCS, 31-2
SMI transfer monitor, 31-4
steps for launching VMs, 31-6
SWAPGS instruction, 31-15
symmetric design, 31-10
SYSCALL/SYSRET instructions, 31-15
SYSENTER/SYSEXIT instructions, 31-15
triple faults, 33-1
virtual TLBs, 32-3
virtual-8086 container, 31-1
virtualization of system resources, 32-1
VM exits, 27-1
VM exits, handling of, 31-7
VMCLEAR instruction, 31-7
VMCS field width, 31-12
VMCS pointer, 31-2
VMCS region, 31-2
VMCS revision identifier, 31-2
VMCS, writing/reading fields, 31-2
VM-exit failures, 33-8
VMLAUNCH instruction, 31-7
VMREAD instruction, 31-2
VMRESUME instruction, 31-7
VMWRITE instruction, 31-2, 31-7
VMXOFF instruction, 31-4
See also: VMCS, VM entries, VM exits, VMX
VMM software interrupts, 33-1
VMPTRLD instruction, 30-1
VMPTRST instruction, 30-1
VMREAD instruction, 30-1, 31-2
field encodings, B-1
VMRESUME instruction, 30-1, 31-7
VMWRITE instruction, 30-1, 31-2, 31-7
field encodings, B-1
VMX
A20M# signal, 23-4
capability MSRs
overview, 23-2, A-1
IA32_VMX_BASIC MSR, 24-3, 31-2, 31-5, 31-6, 31-11, A-1, A-2
IA32_VMX_CR0_FIXED0 MSR, 31-4, A-6
IA32_VMX_CR0_FIXED1 MSR, 31-4, A-6
IA32_VMX_CR4_FIXED0 MSR, 31-4
IA32_VMX_CR4_FIXED1 MSR, 31-4
IA32_VMX_ENTRY_CTLS MSR, 31-5, 31-6, A-2, A-5
IA32_VMX_EXIT_CTLS MSR, 31-5, 31-6, A-2, A-4, A-5
IA32_VMX_MISC MSR, 24-6, 26-3, 26-12, 34-26, A-5
IA32_VMX_PINBASED_CTLS MSR, 31-5, 31-6, A-2, A-3
IA32_VMX_PROCBASED_CTLS MSR, 24-9, 31-5, 31-6, A-2, A-3,
A-4, A-8
CPUID instruction, 23-2, A-1
CR4 control register, 23-3
CR4 fixed bits, A-6
debugging facilities, 32-1
EFLAGS, 31-2
entering operation, 23-3
entering root operation, 31-4
error handling, 31-2
guest software, 23-1
IA32_FEATURE_CONTROL MSR, 23-3
INIT# signal, 23-4
instruction set, 23-2
introduction, 23-1
memory virtualization, 32-2
microcode update facilities, 25-9, 32-8
non-root operation, 23-1
event blocking, 25-10
instruction changes, 25-6
overview, 25-1
task switches not allowed, 25-10
see VM exits
operation restrictions, 23-3
root operation, 23-1
INDEX-20 Vol. 3D

SMM
CR4.VMXE reserved, 34-18
overview, 34-1
RSM instruction, 34-18
VMCS pointer, 34-17
VMX-critical state, 34-17
testing for support, 23-2
virtual TLBs, 32-3
virtual-machine control structure (VMCS), 23-2
virtual-machine monitor (VMM), 23-1
vitualization of system resources, 32-1
VM entries and exits, 23-1
VM exits, 27-1
VMCS pointer, 23-2
VMM life cycle, 23-2
VMXOFF instruction, 23-3
VMXON instruction, 23-3
VMXON pointer, 23-3
VMXON region, 23-3
See also:VMM, VMCS, VM entries, VM exits
VMXOFF instruction, 23-3, 30-1
VMXON instruction, 23-3, 30-1

W
WAIT/FWAIT instructions, 6-27, 22-8, 22-15
WB (write back) memory type, 8-16, 11-7, 11-8
WB (write-back) pin (Pentium processor), 11-13
WBINVD instruction, 2-24, 5-24, 11-16, 11-17, 22-4
WB/WT# pins, 11-13
WC buffer (see Write combining (WC) buffer)
WC (write combining)
flag, IA32_MTRRCAP MSR, 11-22
memory type, 11-7, 11-8
WP (write protected) memory type, 11-7
WP (write protect) flag
CR0 control register, 2-15, 5-28, 22-18
Write
hit, 11-5
Write combining (WC) buffer, 11-4, 11-7
Write-back caching, 11-6
WRMSR instruction, 2-19, 2-21, 2-26, 5-24, 8-17, 17-34, 17-39, 17-42,
18-95, 18-121, 18-122, 18-123, 22-4, 22-36, 25-9
WT (write through) memory type, 11-7, 11-8
WT# (write-through) pin (Pentium processor), 11-13

X
x2APIC ID, 10-40, 10-41, 10-44, 10-46
x2APIC Mode, 10-31, 10-37, 10-38, 10-40, 10-41, 10-44, 10-45, 10-46
x87 FPU
compatibility with IA-32 x87 FPUs and math coprocessors, 22-7
configuring the x87 FPU environment, 9-6
device-not-available exception, 6-27
effect of MMX instructions on pending x87 floating-point exceptions,
12-5
effects of MMX instructions on x87 FPU state, 12-3
effects of MMX, x87 FPU, FXSAVE, and FXRSTOR instructions on x87
FPU tag word, 12-3
error signals, 22-11
initialization, 9-5
instruction synchronization, 22-15
register stack, aliasing with MMX registers, 12-2
setting up for software emulation of x87 FPU functions, 9-6
using TS flag to control saving of x87 FPU state, 13-7
x87 floating-point error exception (#MF), 6-42
x87 FPU control word
compatibility, IA-32 processors, 22-8
x87 FPU floating-point error exception (#MF), 6-42
x87 FPU status word
condition code flags, 22-8
x87 FPU tag word, 22-9

INDEX

XADD instruction, 8-3, 22-4
xAPIC, 10-38, 10-40
determining lowest priority processor, 10-25
interrupt control register, 10-21
introduction to, 10-4
message passing protocol on system bus, 10-33
new features, 22-28
spurious vector, 10-32
using system bus, 10-4
xAPIC Mode, 10-31, 10-37, 10-41, 10-44, 10-46
XCHG instruction, 8-3, 8-16
XCR0, 2-19
XGETBV, 2-19, 2-23
XMM registers, saving, 13-6
XOR instruction, 8-3
XSAVE, 2-19, 13-7, 13-8, 13-9, 13-10
XSETBV, 2-19, 2-20, 2-23, 2-26

Z
ZF flag, EFLAGS register, 5-25

Vol. 3D INDEX-21

INDEX

INDEX-22 Vol. 3D



---

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Title                           : Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3 (3A, 3B, 3C & 3D): System Programming Guide
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