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| author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2022-10-13 12:58:45 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-12-29 23:33:29 +0300 |
| commit | 2be1bd3a70c81835b8969216ceedbd017fea732d (patch) | |
| tree | 31f44149290304d750087309a3d0782f2f0fe29b /arch/x86/kvm/hyperv.h | |
| parent | 0fcf86f05af208e4e6c62cf1a7e7e28bc6c9d9f9 (diff) | |
| download | linux-2be1bd3a70c81835b8969216ceedbd017fea732d.tar.xz | |
KVM: x86: Hyper-V invariant TSC control
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.
Add the feature to KVM. Keep CPUID output intact when the feature
wasn't exposed to L1 and implement the required logic for hiding
invariant TSC when the feature was exposed and invariant TSC control
MSR wasn't written to. Copy genuine Hyper-V behavior and forbid to
disable the feature once it was enabled.
For the reference, for linux guests, support for the feature was added
in commit dce7cd62754b ("x86/hyperv: Allow guests to enable InvariantTSC").
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221013095849.705943-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/hyperv.h')
| -rw-r--r-- | arch/x86/kvm/hyperv.h | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h index 9f96414a31c5..f83b8db72b11 100644 --- a/arch/x86/kvm/hyperv.h +++ b/arch/x86/kvm/hyperv.h @@ -136,6 +136,33 @@ static inline bool kvm_hv_has_stimer_pending(struct kvm_vcpu *vcpu) HV_SYNIC_STIMER_COUNT); } +/* + * With HV_ACCESS_TSC_INVARIANT feature, invariant TSC (CPUID.80000007H:EDX[8]) + * is only observed after HV_X64_MSR_TSC_INVARIANT_CONTROL was written to. + */ +static inline bool kvm_hv_invtsc_suppressed(struct kvm_vcpu *vcpu) +{ + struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu); + + /* + * If Hyper-V's invariant TSC control is not exposed to the guest, + * the invariant TSC CPUID flag is not suppressed, Windows guests were + * observed to be able to handle it correctly. Going forward, VMMs are + * encouraged to enable Hyper-V's invariant TSC control when invariant + * TSC CPUID flag is set to make KVM's behavior match genuine Hyper-V. + */ + if (!hv_vcpu || + !(hv_vcpu->cpuid_cache.features_eax & HV_ACCESS_TSC_INVARIANT)) + return false; + + /* + * If Hyper-V's invariant TSC control is exposed to the guest, KVM is + * responsible for suppressing the invariant TSC CPUID flag if the + * Hyper-V control is not enabled. + */ + return !(to_kvm_hv(vcpu->kvm)->hv_invtsc_control & HV_EXPOSE_INVARIANT_TSC); +} + void kvm_hv_process_stimers(struct kvm_vcpu *vcpu); void kvm_hv_setup_tsc_page(struct kvm *kvm, |