Re: [PATCH 3/3] KVM: selftests: Test Hyper-V invariant TSC control

[Maxim Levitsky]

On Wed, 2022-07-13 at 17:05 +0200, Vitaly Kuznetsov wrote:
> Add a test for the newly introduced Hyper-V invariant TSC control feature:
> - HV_X64_MSR_TSC_INVARIANT_CONTROL is not available without
>  HV_ACCESS_TSC_INVARIANT CPUID bit set and available with it.
> - BIT(0) of HV_X64_MSR_TSC_INVARIANT_CONTROL controls the filtering of
> architectural invariant TSC (CPUID.80000007H:EDX[8]) bit.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  .../selftests/kvm/x86_64/hyperv_features.c    | 73 ++++++++++++++++++-
>  1 file changed, 69 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/hyperv_features.c b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
> index c05acd78548f..9599eecdedff 100644
> --- a/tools/testing/selftests/kvm/x86_64/hyperv_features.c
> +++ b/tools/testing/selftests/kvm/x86_64/hyperv_features.c
> @@ -15,6 +15,9 @@
>  
>  #define LINUX_OS_ID ((u64)0x8100 << 48)
>  
> +/* CPUID.80000007H:EDX */
> +#define X86_FEATURE_INVTSC (1 << 8)
> +
>  static inline uint8_t hypercall(u64 control, vm_vaddr_t input_address,
>                                 vm_vaddr_t output_address, uint64_t *hv_status)
>  {
> @@ -60,6 +63,24 @@ static void guest_msr(struct msr_data *msr)
>                 GUEST_ASSERT_2(!vector, msr->idx, vector);
>         else
>                 GUEST_ASSERT_2(vector == GP_VECTOR, msr->idx, vector);
> +
> +       /* Invariant TSC bit appears when TSC invariant control MSR is written to */
> +       if (msr->idx == HV_X64_MSR_TSC_INVARIANT_CONTROL) {
> +               u32 eax = 0x80000007, ebx = 0, ecx = 0, edx = 0;
> +
> +               cpuid(&eax, &ebx, &ecx, &edx);
> +
> +               /*
> +                * TSC invariant bit is present without the feature (legacy) or
> +                * when the feature is present and enabled.
> +                */
> +               if ((!msr->available && !msr->write) || (msr->write && msr->write_val == 1))
> +                       GUEST_ASSERT(edx & X86_FEATURE_INVTSC);
> +               else
> +                       GUEST_ASSERT(!(edx & X86_FEATURE_INVTSC));
> +       }
> +
> +
>         GUEST_DONE();
>  }
>  
> @@ -105,6 +126,15 @@ static void hv_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>         vcpu_set_cpuid(vcpu, cpuid);
>  }
>  
> +static bool guest_has_invtsc(void)
> +{
> +       struct kvm_cpuid_entry2 *cpuid;
> +
> +       cpuid = kvm_get_supported_cpuid_entry(0x80000007);
> +
> +       return cpuid->edx & X86_FEATURE_INVTSC;
> +}
> +
>  static void guest_test_msrs_access(void)
>  {
>         struct kvm_vcpu *vcpu;
> @@ -124,6 +154,7 @@ static void guest_test_msrs_access(void)
>         struct kvm_cpuid2 *best;
>         vm_vaddr_t msr_gva;
>         struct msr_data *msr;
> +       bool has_invtsc = guest_has_invtsc();
>  
>         while (true) {
>                 vm = vm_create_with_one_vcpu(&vcpu, guest_msr);
> @@ -136,8 +167,7 @@ static void guest_test_msrs_access(void)
>                 vcpu_enable_cap(vcpu, KVM_CAP_HYPERV_ENFORCE_CPUID, 1);
>  
>                 vcpu_set_hv_cpuid(vcpu);
> -
> -               best = kvm_get_supported_hv_cpuid();
> +               best = vcpu_get_cpuid(vcpu);
>  
>                 vm_init_descriptor_tables(vm);
>                 vcpu_init_descriptor_tables(vcpu);
> @@ -431,6 +461,42 @@ static void guest_test_msrs_access(void)
>                         break;
>  
>                 case 44:
> +                       /* MSR is not available when CPUID feature bit is unset */
> +                       if (!has_invtsc)
> +                               continue;
> +                       msr->idx = HV_X64_MSR_TSC_INVARIANT_CONTROL;
> +                       msr->write = 0;
> +                       msr->available = 0;
> +                       break;
> +               case 45:
> +                       /* MSR is vailable when CPUID feature bit is set */
> +                       if (!has_invtsc)
> +                               continue;
> +                       feat.eax |= HV_ACCESS_TSC_INVARIANT;
> +                       msr->idx = HV_X64_MSR_TSC_INVARIANT_CONTROL;
> +                       msr->write = 0;
> +                       msr->available = 1;
> +                       break;
> +               case 46:
> +                       /* Writing bits other than 0 is forbidden */
> +                       if (!has_invtsc)
> +                               continue;
> +                       msr->idx = HV_X64_MSR_TSC_INVARIANT_CONTROL;
> +                       msr->write = 1;
> +                       msr->write_val = 0xdeadbeef;
> +                       msr->available = 0;
> +                       break;
> +               case 47:
> +                       /* Setting bit 0 enables the feature */
> +                       if (!has_invtsc)
> +                               continue;
> +                       msr->idx = HV_X64_MSR_TSC_INVARIANT_CONTROL;
> +                       msr->write = 1;
> +                       msr->write_val = 1;
> +                       msr->available = 1;
> +                       break;
> +
> +               default:
>                         kvm_vm_free(vm);
>                         return;
>                 }
> @@ -502,8 +568,7 @@ static void guest_test_hcalls_access(void)
>                 vcpu_enable_cap(vcpu, KVM_CAP_HYPERV_ENFORCE_CPUID, 1);
>  
>                 vcpu_set_hv_cpuid(vcpu);
> -
> -               best = kvm_get_supported_hv_cpuid();
> +               best = vcpu_get_cpuid(vcpu);
>  
>                 run = vcpu->run;
>  

Tiny unrelated nitpick: 'msr->available' is misleading, it is more like
'msr->should_not_gp' or something  - might be worth it to refactor in the future.


Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky