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| -rw-r--r-- | Documentation/virtual/kvm/cpuid.txt | 83 |
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diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt new file mode 100644 index 000000000..97ca1940a --- /dev/null +++ b/Documentation/virtual/kvm/cpuid.txt @@ -0,0 +1,83 @@ +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_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 +---------------------------------------------------------------------------------- |