On Fri, 2024-05-17 at 10:38 -0700, Sean Christopherson wrote:
> Refresh selftests' CPUID cache in the vCPU structure when querying a CPUID
> entry so that tests don't consume stale data when KVM modifies CPUID as a
> side effect to a completely unrelated change. E.g. KVM adjusts OSXSAVE in
> response to CR4.OSXSAVE changes.
>
> Unnecessarily invoking KVM_GET_CPUID is suboptimal, but vcpu->cpuid exists
> to simplify selftests development, not for performance reasons. And,
> unfortunately, trying to handle the side effects in tests or other flows
> is unpleasant, e.g. selftests could manually refresh if KVM_SET_SREGS is
> successful, but that would still leave a gap with respect to guest CR4
> changes.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> .../testing/selftests/kvm/include/x86_64/processor.h | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
> index 8eb57de0b587..99aa3dfca16c 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/processor.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
> @@ -992,10 +992,17 @@ static inline struct kvm_cpuid2 *allocate_kvm_cpuid2(int nr_entries)
> void vcpu_init_cpuid(struct kvm_vcpu *vcpu, const struct kvm_cpuid2 *cpuid);
> void vcpu_set_hv_cpuid(struct kvm_vcpu *vcpu);
>
> +static inline void vcpu_get_cpuid(struct kvm_vcpu *vcpu)
> +{
> + vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
> +}
> +
> static inline struct kvm_cpuid_entry2 *__vcpu_get_cpuid_entry(struct kvm_vcpu *vcpu,
> uint32_t function,
> uint32_t index)
> {
> + vcpu_get_cpuid(vcpu);
> +
> return (struct kvm_cpuid_entry2 *)get_cpuid_entry(vcpu->cpuid,
> function, index);
> }
> @@ -1016,7 +1023,7 @@ static inline int __vcpu_set_cpuid(struct kvm_vcpu *vcpu)
> return r;
>
> /* On success, refresh the cache to pick up adjustments made by KVM. */
> - vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
> + vcpu_get_cpuid(vcpu);
> return 0;
> }
>
> @@ -1026,7 +1033,7 @@ static inline void vcpu_set_cpuid(struct kvm_vcpu *vcpu)
> vcpu_ioctl(vcpu, KVM_SET_CPUID2, vcpu->cpuid);
>
> /* Refresh the cache to pick up adjustments made by KVM. */
> - vcpu_ioctl(vcpu, KVM_GET_CPUID2, vcpu->cpuid);
> + vcpu_get_cpuid(vcpu);
> }
>
> void vcpu_set_cpuid_property(struct kvm_vcpu *vcpu,
Hi,
Indeed - fully agree with this, and again very sad that Intel
made their CPUID dynamic - what a hack :(
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Best regards,
Maxim Levitsky
