Re: [PATCH V4 3/4] KVM: x86/pmu: Support PERF_METRICS MSR in mediated vPMU

[Sean Christopherson <seanjc@google.com>]

On Tue, Jun 23, 2026, Zide Chen wrote:
> On 6/22/2026 11:48 PM, sashiko-bot@kernel.org wrote:
> >> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> >> index 59b7a90c79e12..2c3367f5e2dfb 100644
> >> --- a/arch/x86/kvm/vmx/pmu_intel.c
> >> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> > [ ... ]
> >> @@ -345,6 +347,11 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >>  	case MSR_CORE_PERF_FIXED_CTR_CTRL:
> >>  		msr_info->data = pmu->fixed_ctr_ctrl;
> >>  		break;
> >> +	case MSR_PERF_METRICS:
> >> +		if (!msr_info->host_initiated)
> >> +			return 1;
> > 
> > [Severity: High]
> > If KVM needs to emulate a guest RDMSR instruction targeting MSR_PERF_METRICS,
> > won't this unconditional return inject a #GP fault into the guest?
> 
> I can't think of a case that KVM needs to emulate RDMSR/WRMSR on
> MSR_PERF_METRICS.

If the literal emulator happens to emulate a RDMSR/WRMSR, KVM should behave
correctly.  Even if that weren't the case, KVM's implementation should adhere to
the architecture.  Assuming MSR_PERF_METRICS is read/write, KVM should emulate
it as such.