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

Sean Christopherson
2023-11-09T23:05:42Z

On Thu, Nov 09, 2023, Jim Mattson wrote:
> On Thu, Nov 9, 2023 at 10:24 AM Konstantin Khorenko <khorenko@virtuozzo.com> 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.