Re: [RFC PATCH 27/41] KVM: x86/pmu: Clear PERF_METRICS MSR for guest

[Mi, Dapeng]

On 4/12/2024 5:50 AM, Sean Christopherson wrote:
> On Fri, Jan 26, 2024, Xiong Zhang wrote:
> > From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> >
> > Since perf topdown metrics feature is not supported yet, clear
> > PERF_METRICS MSR for guest.
> Please rewrite with --verbose, I have no idea what MSR_PERF_METRICS, and thus no
> clue why it needs to be zeroed when loading guest context, e.g. it's not passed
> through, so why does it matter?

Sure. MSR_PERF_METRICS actually reports the perf topdown metrics 
portion. I would add more details.


> > Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/kvm/vmx/pmu_intel.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> > index 4b4da7f17895..ad0434646a29 100644
> > --- a/arch/x86/kvm/vmx/pmu_intel.c
> > +++ b/arch/x86/kvm/vmx/pmu_intel.c
> > @@ -916,6 +916,10 @@ static void intel_restore_pmu_context(struct kvm_vcpu *vcpu)
> >   	 */
> >   	for (i = pmu->nr_arch_fixed_counters; i < kvm_pmu_cap.num_counters_fixed; i++)
> >   		wrmsrl(MSR_CORE_PERF_FIXED_CTR0 + i, 0);
> > +
> > +	/* Clear PERF_METRICS MSR since guest topdown metrics is not supported yet. */
> > +	if (kvm_caps.host_perf_cap & PMU_CAP_PERF_METRICS)
> > +		wrmsrl(MSR_PERF_METRICS, 0);
> >   }
> >   
> >   struct kvm_pmu_ops intel_pmu_ops __initdata = {
> > --
> > 2.34.1