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authorGlauber Costa <glommer@redhat.com>2010-05-11 12:17:47 -0400
committerAvi Kivity <avi@redhat.com>2010-05-19 04:41:07 -0400
commit09c9e81366b9167b88ff05cf29fa94dc3553eb3d (patch)
treeb2555594894cbd5768ee01331fb3a3a7686e6481 /Documentation
parent371bcf646d170ee1325abaf4f3e73485b4fd4d2d (diff)
KVM: Add cpuid.txt file
This file documents cpuid bits used by KVM. Signed-off-by: Glauber Costa <glommer@redhat.com> Acked-by: Zachary Amsden <zamsden@redhat.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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1KVM CPUID bits
2Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
3=====================================================
4
5A guest running on a kvm host, can check some of its features using
6cpuid. This is not always guaranteed to work, since userspace can
7mask-out some, or even all KVM-related cpuid features before launching
8a guest.
9
10KVM cpuid functions are:
11
12function: KVM_CPUID_SIGNATURE (0x40000000)
13returns : eax = 0,
14 ebx = 0x4b4d564b,
15 ecx = 0x564b4d56,
16 edx = 0x4d.
17Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
18This function queries the presence of KVM cpuid leafs.
19
20
21function: define KVM_CPUID_FEATURES (0x40000001)
22returns : ebx, ecx, edx = 0
23 eax = and OR'ed group of (1 << flag), where each flags is:
24
25
26flag || value || meaning
27=============================================================================
28KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs
29 || || 0x11 and 0x12.
30------------------------------------------------------------------------------
31KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays
32 || || on PIO operations.
33------------------------------------------------------------------------------
34KVM_FEATURE_MMU_OP || 2 || deprecated.
35------------------------------------------------------------------------------
36KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
37 || || 0x4b564d00 and 0x4b564d01
38------------------------------------------------------------------------------
39KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
40 || || per-cpu warps are expected in
41 || || kvmclock.
42------------------------------------------------------------------------------