Intel 64 and IA-32 Architectures Software Developers Manual Volume 3B, System Programming Guide Part 2

Table Of Contents
Vol. 3 20-7
VIRTUAL-MACHINE CONTROL STRUCTURES
Table 20-3. 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.
1Blocking by
MOV SS
See the “MOV—Move a Value from the Stack” and “POP—Pop
a Value from the Stack” sections in Chapter 3 and Chapter 4
of the Intel® 64 and IA-32 Architectures Software
Developer’s Manual, Volumes 2A & 2B, and Section 5.8.3 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 25.2. 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 5.7.1 in the Intel® 64 and IA-32 Architectures
Software Developer’s Manual, Volume 3A and Section 25.8.
Delivery of a non-maskable interrupt (NMI) or a system-
management interrupt (SMI) blocks subsequent NMIs until the
next execution of IRET. See Section 21.4 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
20.6.1) 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).
31:4 Reserved VM entry will fail if these bits are not 0. See Section 22.3.1.5.