Re: [PATCH 1/1] KVM: x86/vPMU: Check PMU is enabled for vCPU before searching for PMC

[Sean Christopherson]

On Thu, Nov 09, 2023, Jim Mattson wrote:
> On Thu, Nov 9, 2023 at 10:24 AM Konstantin Khorenko <khorenko@xxxxxxxxxxxxx> wrote:
> > ---
> >  arch/x86/kvm/pmu.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> >
> > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > index 9ae07db6f0f6..290d407f339b 100644
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> > @@ -731,12 +731,38 @@ static inline bool cpl_is_matched(struct kvm_pmc *pmc)
> >         return (static_call(kvm_x86_get_cpl)(pmc->vcpu) == 0) ? select_os : select_user;
> >  }
> >
> > +static inline bool guest_pmu_is_enabled(struct kvm_pmu *pmu)
> > +{
> > +       /*
> > +        * Currently VMs do not have PMU settings in configs which defaults
> > +        * to "pmu=off".
> > +        *
> > +        * For Intel currently this means pmu->version will be 0.
> > +        * For AMD currently PMU cannot be disabled:
> 
> Isn't that what KVM_PMU_CAP_DISABLE is for?

Yeah, see my response.  KVM doesn't clear the metadata, so internally it looks
like the PMU is enabled even though it's effectively disabled from the guest's
perspective.