Documentation/kvm/cpuid.txt

   1 KVM CPUID bits
   2 Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
   3 =====================================================
   4
   5 A guest running on a kvm host, can check some of its features using
   6 cpuid. This is not always guaranteed to work, since userspace can
   7 mask-out some, or even all KVM-related cpuid features before launching
   8 a guest.
   9
  10 KVM cpuid functions are:
  11
  12 function: KVM_CPUID_SIGNATURE (0x40000000)
  13 returns : eax = 0,
  14           ebx = 0x4b4d564b,
  15           ecx = 0x564b4d56,
  16           edx = 0x4d.
  17 Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
  18 This function queries the presence of KVM cpuid leafs.
  19
  20
  21 function: define KVM_CPUID_FEATURES (0x40000001)
  22 returns : ebx, ecx, edx = 0
  23           eax = and OR'ed group of (1 << flag), where each flags is:
  24
  25
  26 flag                               || value || meaning
  27 =============================================================================
  28 KVM_FEATURE_CLOCKSOURCE            ||     0 || kvmclock available at msrs
  29                                    ||       || 0x11 and 0x12.
  30 ------------------------------------------------------------------------------
  31 KVM_FEATURE_NOP_IO_DELAY           ||     1 || not necessary to perform delays
  32                                    ||       || on PIO operations.
  33 ------------------------------------------------------------------------------
  34 KVM_FEATURE_MMU_OP                 ||     2 || deprecated.
  35 ------------------------------------------------------------------------------
  36 KVM_FEATURE_CLOCKSOURCE2           ||     3 || kvmclock available at msrs
  37                                    ||       || 0x4b564d00 and 0x4b564d01
  38 ------------------------------------------------------------------------------
  39 KVM_FEATURE_ASYNC_PF               ||     4 || async pf can be enabled by
  40                                    ||       || writing to msr 0x4b564d02
  41 ------------------------------------------------------------------------------
  42 KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no guest-side
  43                                    ||       || per-cpu warps are expected in
  44                                    ||       || kvmclock.
  45 ------------------------------------------------------------------------------