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SubjectRe: [PATCH] KVM: selftests: Avoid KVM_SET_CPUID2 after KVM_RUN in vmx_pmu_msrs_test
On Thu, Dec 16, 2021, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 85127b3e3690..65e297875405 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -3424,7 +3424,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >
> > if (!msr_info->host_initiated)
> > return 1;
> > - if (guest_cpuid_has(vcpu, X86_FEATURE_PDCM) && kvm_get_msr_feature(&msr_ent))
> > + if (kvm_get_msr_feature(&msr_ent))
> > return 1;
> > if (data & ~msr_ent.data)
> > return 1;
>
> This looks OK.
>
> > @@ -3779,14 +3779,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > msr_info->data = vcpu->arch.microcode_version;
> > break;
> > case MSR_IA32_ARCH_CAPABILITIES:
> > - if (!msr_info->host_initiated &&
> > - !guest_cpuid_has(vcpu, X86_FEATURE_ARCH_CAPABILITIES))
> > + if (!msr_info->host_initiated)
> > return 1;
> > msr_info->data = vcpu->arch.arch_capabilities;
> > break;
> > case MSR_IA32_PERF_CAPABILITIES:
> > - if (!msr_info->host_initiated &&
> > - !guest_cpuid_has(vcpu, X86_FEATURE_PDCM))
> > + if (!msr_info->host_initiated)
> > return 1;
> > msr_info->data = vcpu->arch.perf_capabilities;
> > break;
> >
>
> Hm, this change will unconditionally forbid reading
> MSR_IA32_ARCH_CAPABILITIES/MSR_IA32_PERF_CAPABILITIES from the guest. Is
> this what we want?

No, I completely misread the code. The kvm_set_msr_common() goof seems to be
the only bug, and that would also explain the selftest's bad testcase.

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