forked from Minki/linux
Documentation: kvm: Convert cpuid.txt to .rst
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
Paolo Bonzini
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107
Documentation/virtual/kvm/cpuid.rst
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Documentation/virtual/kvm/cpuid.rst
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.. SPDX-License-Identifier: GPL-2.0
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==============
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KVM CPUID bits
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==============
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:Author: Glauber Costa <glommer@gmail.com>
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A guest running on a kvm host, can check some of its features using
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cpuid. This is not always guaranteed to work, since userspace can
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mask-out some, or even all KVM-related cpuid features before launching
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a guest.
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KVM cpuid functions are:
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function: KVM_CPUID_SIGNATURE (0x40000000)
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returns::
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eax = 0x40000001
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ebx = 0x4b4d564b
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ecx = 0x564b4d56
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edx = 0x4d
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Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
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The value in eax corresponds to the maximum cpuid function present in this leaf,
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and will be updated if more functions are added in the future.
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Note also that old hosts set eax value to 0x0. This should
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be interpreted as if the value was 0x40000001.
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This function queries the presence of KVM cpuid leafs.
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function: define KVM_CPUID_FEATURES (0x40000001)
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returns::
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ebx, ecx
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eax = an OR'ed group of (1 << flag)
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where ``flag`` is defined as below:
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================================= =========== ================================
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flag value meaning
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================================= =========== ================================
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KVM_FEATURE_CLOCKSOURCE 0 kvmclock available at msrs
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0x11 and 0x12
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KVM_FEATURE_NOP_IO_DELAY 1 not necessary to perform delays
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on PIO operations
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KVM_FEATURE_MMU_OP 2 deprecated
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KVM_FEATURE_CLOCKSOURCE2 3 kvmclock available at msrs
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0x4b564d00 and 0x4b564d01
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KVM_FEATURE_ASYNC_PF 4 async pf can be enabled by
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writing to msr 0x4b564d02
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KVM_FEATURE_STEAL_TIME 5 steal time can be enabled by
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writing to msr 0x4b564d03
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KVM_FEATURE_PV_EOI 6 paravirtualized end of interrupt
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handler can be enabled by
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writing to msr 0x4b564d04
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KVM_FEATURE_PV_UNHAULT 7 guest checks this feature bit
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before enabling paravirtualized
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spinlock support
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KVM_FEATURE_PV_TLB_FLUSH 9 guest checks this feature bit
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before enabling paravirtualized
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tlb flush
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KVM_FEATURE_ASYNC_PF_VMEXIT 10 paravirtualized async PF VM EXIT
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can be enabled by setting bit 2
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when writing to msr 0x4b564d02
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KVM_FEATURE_PV_SEND_IPI 11 guest checks this feature bit
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before enabling paravirtualized
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sebd IPIs
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KVM_FEATURE_PV_POLL_CONTROL 12 host-side polling on HLT can
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be disabled by writing
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to msr 0x4b564d05.
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KVM_FEATURE_PV_SCHED_YIELD 13 guest checks this feature bit
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before using paravirtualized
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sched yield.
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KVM_FEATURE_CLOCSOURCE_STABLE_BIT 24 host will warn if no guest-side
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per-cpu warps are expeced in
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kvmclock
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================================= =========== ================================
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::
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edx = an OR'ed group of (1 << flag)
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Where ``flag`` here is defined as below:
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================== ============ =================================
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flag value meaning
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================== ============ =================================
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KVM_HINTS_REALTIME 0 guest checks this feature bit to
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determine that vCPUs are never
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preempted for an unlimited time
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allowing optimizations
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================== ============ =================================
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@ -1,91 +0,0 @@
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KVM CPUID bits
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Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
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=====================================================
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A guest running on a kvm host, can check some of its features using
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cpuid. This is not always guaranteed to work, since userspace can
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mask-out some, or even all KVM-related cpuid features before launching
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a guest.
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KVM cpuid functions are:
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function: KVM_CPUID_SIGNATURE (0x40000000)
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returns : eax = 0x40000001,
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ebx = 0x4b4d564b,
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ecx = 0x564b4d56,
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edx = 0x4d.
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Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
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The value in eax corresponds to the maximum cpuid function present in this leaf,
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and will be updated if more functions are added in the future.
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Note also that old hosts set eax value to 0x0. This should
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be interpreted as if the value was 0x40000001.
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This function queries the presence of KVM cpuid leafs.
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function: define KVM_CPUID_FEATURES (0x40000001)
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returns : ebx, ecx
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eax = an OR'ed group of (1 << flag), where each flags is:
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flag || value || meaning
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=============================================================================
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KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs
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|| || 0x11 and 0x12.
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------------------------------------------------------------------------------
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KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays
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|| || on PIO operations.
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------------------------------------------------------------------------------
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KVM_FEATURE_MMU_OP || 2 || deprecated.
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------------------------------------------------------------------------------
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KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
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|| || 0x4b564d00 and 0x4b564d01
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------------------------------------------------------------------------------
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KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by
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|| || writing to msr 0x4b564d02
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------------------------------------------------------------------------------
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KVM_FEATURE_STEAL_TIME || 5 || steal time can be enabled by
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|| || writing to msr 0x4b564d03.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_EOI || 6 || paravirtualized end of interrupt
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|| || handler can be enabled by writing
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|| || to msr 0x4b564d04.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit
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|| || before enabling paravirtualized
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|| || spinlock support.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_TLB_FLUSH || 9 || guest checks this feature bit
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|| || before enabling paravirtualized
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|| || tlb flush.
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------------------------------------------------------------------------------
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KVM_FEATURE_ASYNC_PF_VMEXIT || 10 || paravirtualized async PF VM exit
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|| || can be enabled by setting bit 2
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|| || when writing to msr 0x4b564d02
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_SEND_IPI || 11 || guest checks this feature bit
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|| || before using paravirtualized
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|| || send IPIs.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_POLL_CONTROL || 12 || host-side polling on HLT can
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|| || be disabled by writing
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|| || to msr 0x4b564d05.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_SCHED_YIELD || 13 || guest checks this feature bit
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|| || before using paravirtualized
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|| || sched yield.
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------------------------------------------------------------------------------
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KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
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|| || per-cpu warps are expected in
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|| || kvmclock.
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------------------------------------------------------------------------------
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edx = an OR'ed group of (1 << flag), where each flags is:
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flag || value || meaning
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==================================================================================
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KVM_HINTS_REALTIME || 0 || guest checks this feature bit to
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|| || determine that vCPUs are never
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|| || preempted for an unlimited time,
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|| || allowing optimizations
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----------------------------------------------------------------------------------
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