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Documentation: kvm: Convert cpuid.txt to .rst

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Convert cpuid.txt to .rst format to be parsable by sphinx.

Change format and spacing to make function definitions and return values
much more clear. Also added a table that is parsable by sphinx and makes
the information much more clean. Updated Author email to their new
active email address. Added license identifier with the consent of the
author.

Signed-off-by: Luke Nowakowski-Krijger <lnowakow@eng.ucsd.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Luke Nowakowski-Krijger 2019-07-10 08:30:53 -07:00 committed by Paolo Bonzini
parent 8373bc4f1b
commit e287d6de62
2 changed files with 107 additions and 91 deletions
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Documentation/virtual/kvm/cpuid.rst Normal file
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.. SPDX-License-Identifier: GPL-2.0
==============
KVM CPUID bits
==============
:Author: Glauber Costa <glommer@gmail.com>
A guest running on a kvm host, can check some of its features using
cpuid. This is not always guaranteed to work, since userspace can
mask-out some, or even all KVM-related cpuid features before launching
a guest.
KVM cpuid functions are:
function: KVM_CPUID_SIGNATURE (0x40000000)
returns::
eax = 0x40000001
ebx = 0x4b4d564b
ecx = 0x564b4d56
edx = 0x4d
Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
The value in eax corresponds to the maximum cpuid function present in this leaf,
and will be updated if more functions are added in the future.
Note also that old hosts set eax value to 0x0. This should
be interpreted as if the value was 0x40000001.
This function queries the presence of KVM cpuid leafs.
function: define KVM_CPUID_FEATURES (0x40000001)
returns::
ebx, ecx
eax = an OR'ed group of (1 << flag)
where ``flag`` is defined as below:
================================= =========== ================================
flag value meaning
================================= =========== ================================
KVM_FEATURE_CLOCKSOURCE 0 kvmclock available at msrs
0x11 and 0x12
KVM_FEATURE_NOP_IO_DELAY 1 not necessary to perform delays
on PIO operations
KVM_FEATURE_MMU_OP 2 deprecated
KVM_FEATURE_CLOCKSOURCE2 3 kvmclock available at msrs
0x4b564d00 and 0x4b564d01
KVM_FEATURE_ASYNC_PF 4 async pf can be enabled by
writing to msr 0x4b564d02
KVM_FEATURE_STEAL_TIME 5 steal time can be enabled by
writing to msr 0x4b564d03
KVM_FEATURE_PV_EOI 6 paravirtualized end of interrupt
handler can be enabled by
writing to msr 0x4b564d04
KVM_FEATURE_PV_UNHAULT 7 guest checks this feature bit
before enabling paravirtualized
spinlock support
KVM_FEATURE_PV_TLB_FLUSH 9 guest checks this feature bit
before enabling paravirtualized
tlb flush
KVM_FEATURE_ASYNC_PF_VMEXIT 10 paravirtualized async PF VM EXIT
can be enabled by setting bit 2
when writing to msr 0x4b564d02
KVM_FEATURE_PV_SEND_IPI 11 guest checks this feature bit
before enabling paravirtualized
sebd IPIs
KVM_FEATURE_PV_POLL_CONTROL 12 host-side polling on HLT can
be disabled by writing
to msr 0x4b564d05.
KVM_FEATURE_PV_SCHED_YIELD 13 guest checks this feature bit
before using paravirtualized
sched yield.
KVM_FEATURE_CLOCSOURCE_STABLE_BIT 24 host will warn if no guest-side
per-cpu warps are expeced in
kvmclock
================================= =========== ================================
::
edx = an OR'ed group of (1 << flag)
Where ``flag`` here is defined as below:
================== ============ =================================
flag value meaning
================== ============ =================================
KVM_HINTS_REALTIME 0 guest checks this feature bit to
determine that vCPUs are never
preempted for an unlimited time
allowing optimizations
================== ============ =================================

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Documentation/virtual/kvm/cpuid.txt
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KVM CPUID bits
Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
=====================================================
A guest running on a kvm host, can check some of its features using
cpuid. This is not always guaranteed to work, since userspace can
mask-out some, or even all KVM-related cpuid features before launching
a guest.
KVM cpuid functions are:
function: KVM_CPUID_SIGNATURE (0x40000000)
returns : eax = 0x40000001,
ebx = 0x4b4d564b,
ecx = 0x564b4d56,
edx = 0x4d.
Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
The value in eax corresponds to the maximum cpuid function present in this leaf,
and will be updated if more functions are added in the future.
Note also that old hosts set eax value to 0x0. This should
be interpreted as if the value was 0x40000001.
This function queries the presence of KVM cpuid leafs.
function: define KVM_CPUID_FEATURES (0x40000001)
returns : ebx, ecx
eax = an OR'ed group of (1 << flag), where each flags is:
flag || value || meaning
=============================================================================
KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs
|| || 0x11 and 0x12.
------------------------------------------------------------------------------
KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays
|| || on PIO operations.
------------------------------------------------------------------------------
KVM_FEATURE_MMU_OP || 2 || deprecated.
------------------------------------------------------------------------------
KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
|| || 0x4b564d00 and 0x4b564d01
------------------------------------------------------------------------------
KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by
|| || writing to msr 0x4b564d02
------------------------------------------------------------------------------
KVM_FEATURE_STEAL_TIME || 5 || steal time can be enabled by
|| || writing to msr 0x4b564d03.
------------------------------------------------------------------------------
KVM_FEATURE_PV_EOI || 6 || paravirtualized end of interrupt
|| || handler can be enabled by writing
|| || to msr 0x4b564d04.
------------------------------------------------------------------------------
KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit
|| || before enabling paravirtualized
|| || spinlock support.
------------------------------------------------------------------------------
KVM_FEATURE_PV_TLB_FLUSH || 9 || guest checks this feature bit
|| || before enabling paravirtualized
|| || tlb flush.
------------------------------------------------------------------------------
KVM_FEATURE_ASYNC_PF_VMEXIT || 10 || paravirtualized async PF VM exit
|| || can be enabled by setting bit 2
|| || when writing to msr 0x4b564d02
------------------------------------------------------------------------------
KVM_FEATURE_PV_SEND_IPI || 11 || guest checks this feature bit
|| || before using paravirtualized
|| || send IPIs.
------------------------------------------------------------------------------
KVM_FEATURE_PV_POLL_CONTROL || 12 || host-side polling on HLT can
|| || be disabled by writing
|| || to msr 0x4b564d05.
------------------------------------------------------------------------------
KVM_FEATURE_PV_SCHED_YIELD || 13 || guest checks this feature bit
|| || before using paravirtualized
|| || sched yield.
------------------------------------------------------------------------------
KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
|| || per-cpu warps are expected in
|| || kvmclock.
------------------------------------------------------------------------------
edx = an OR'ed group of (1 << flag), where each flags is:
flag || value || meaning
==================================================================================
KVM_HINTS_REALTIME || 0 || guest checks this feature bit to
|| || determine that vCPUs are never
|| || preempted for an unlimited time,
|| || allowing optimizations
----------------------------------------------------------------------------------