Normally, genuine Hyper-V doesn't expose architectural invariant TSC (CPUID.80000007H:EDX[8]) to its guests by default. A special PV MSR (HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x40000118) and corresponding CPUID feature bit (CPUID.0x40000003.EAX[15]) were introduced. When bit 0 of the PV MSR is set, invariant TSC bit starts to show up in CPUID. When the feature is exposed to Hyper-V guests, reenlightenment becomes unneeded. Note: strictly speaking, KVM doesn't have to have the feature as exposing raw invariant TSC bit (CPUID.80000007H:EDX[8]) also seems to work for modern Windows versions. The feature is, however, tiny and straitforward and gives additional flexibility so why not. Vitaly Kuznetsov (3): KVM: x86: Hyper-V invariant TSC control KVM: selftests: Fix wrmsr_safe() KVM: selftests: Test Hyper-V invariant TSC control arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/cpuid.c | 7 ++ arch/x86/kvm/hyperv.c | 19 +++++ arch/x86/kvm/hyperv.h | 15 ++++ arch/x86/kvm/x86.c | 4 +- .../selftests/kvm/include/x86_64/processor.h | 2 +- .../selftests/kvm/x86_64/hyperv_features.c | 73 ++++++++++++++++++- 7 files changed, 115 insertions(+), 6 deletions(-) -- 2.35.3
