From 09c9e81366b9167b88ff05cf29fa94dc3553eb3d Mon Sep 17 00:00:00 2001 From: Glauber Costa Date: Tue, 11 May 2010 12:17:47 -0400 Subject: [PATCH] KVM: Add cpuid.txt file This file documents cpuid bits used by KVM. Signed-off-by: Glauber Costa Acked-by: Zachary Amsden Signed-off-by: Marcelo Tosatti --- Documentation/kvm/cpuid.txt | 42 +++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) create mode 100644 Documentation/kvm/cpuid.txt diff --git a/Documentation/kvm/cpuid.txt b/Documentation/kvm/cpuid.txt new file mode 100644 index 000000000000..14a12ea92b7f --- /dev/null +++ b/Documentation/kvm/cpuid.txt @@ -0,0 +1,42 @@ +KVM CPUID bits +Glauber Costa , 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_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side + || || per-cpu warps are expected in + || || kvmclock. +------------------------------------------------------------------------------ -- 2.20.1