Re: [PATCH 4/6] KVM: x86/pmu: [De]activate HG_ONLY PMCs at SVME changes and nested transitions

[Sean Christopherson <seanjc@google.com>]

On Wed, Jan 28, 2026, Jim Mattson wrote:
> On Thu, Jan 22, 2026 at 8:55 AM Sean Christopherson <seanjc@google.com> wrote:
> >
> > On Wed, Jan 21, 2026, Jim Mattson wrote:
> > > diff --git a/arch/x86/include/asm/kvm-x86-pmu-ops.h b/arch/x86/include/asm/kvm-x86-pmu-ops.h
> > > index f0aa6996811f..7b32796213a0 100644
> > > --- a/arch/x86/include/asm/kvm-x86-pmu-ops.h
> > > +++ b/arch/x86/include/asm/kvm-x86-pmu-ops.h
> > > @@ -26,6 +26,7 @@ KVM_X86_PMU_OP_OPTIONAL(cleanup)
> > >  KVM_X86_PMU_OP_OPTIONAL(write_global_ctrl)
> > >  KVM_X86_PMU_OP(mediated_load)
> > >  KVM_X86_PMU_OP(mediated_put)
> > > +KVM_X86_PMU_OP_OPTIONAL(set_pmc_eventsel_hw_enable)
> > >
> > >  #undef KVM_X86_PMU_OP
> > >  #undef KVM_X86_PMU_OP_OPTIONAL
> > > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > > index 833ee2ecd43f..1541c201285b 100644
> > > --- a/arch/x86/kvm/pmu.c
> > > +++ b/arch/x86/kvm/pmu.c
> > > @@ -1142,6 +1142,13 @@ void kvm_pmu_branch_retired(struct kvm_vcpu *vcpu)
> > >  }
> > >  EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_pmu_branch_retired);
> > >
> > > +void kvm_pmu_set_pmc_eventsel_hw_enable(struct kvm_vcpu *vcpu,
> > > +                                    unsigned long *bitmap, bool enable)
> > > +{
> > > +     kvm_pmu_call(set_pmc_eventsel_hw_enable)(vcpu, bitmap, enable);
> > > +}
> > > +EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_pmu_set_pmc_eventsel_hw_enable);
> >
> > Why bounce through a PMU op just to go from nested.c to pmu.c?  AFAICT, common
> > x86 code never calls kvm_pmu_set_pmc_eventsel_hw_enable(), just wire up calls
> > directly to amd_pmu_refresh_host_guest_eventsels().
> 
> It seemed that pmu.c deliberately didn't export anything. All accesses
> were via virtual function table. But maybe that was just happenstance.

Probably just happenstance?

> Should I create a separate pmu.h, or just throw the prototype into
> svm.h?

I say just throw it in svm.h.  We've had pmu_intel.h for a long time, and there's
hardly anything in there.  And somewhat surprisingly, only two things in vmx.h
that obviously could go in pmu_intel.h.

  void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu);
  int intel_pmu_create_guest_lbr_event(struct kvm_vcpu *vcpu);