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
------------------------------------------------------------------------------
KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by
|| || writing to msr 0x4b564d02
------------------------------------------------------------------------------
KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
|| || per-cpu warps are expected in
|| || kvmclock.
------------------------------------------------------------------------------
