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Documentation/virtual/kvm/cpuid.txt 2.19 KB
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09c9e8136   Glauber Costa   KVM: Add cpuid.tx... 
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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 = 0,
            ebx = 0x4b4d564b,
            ecx = 0x564b4d56,
            edx = 0x4d.
  Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
  This function queries the presence of KVM cpuid leafs.
  
  
  function: define KVM_CPUID_FEATURES (0x40000001)
  returns : ebx, ecx, edx = 0
            eax = and 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
  ------------------------------------------------------------------------------
344d9588a   Gleb Natapov   KVM: Add PV MSR t... 
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  KVM_FEATURE_ASYNC_PF               ||     4 || async pf can be enabled by
                                     ||       || writing to msr 0x4b564d02
  ------------------------------------------------------------------------------
09c9e8136   Glauber Costa   KVM: Add cpuid.tx... 
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  KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no guest-side
                                     ||       || per-cpu warps are expected in
                                     ||       || kvmclock.
  ------------------------------------------------------------------------------