Re: [PATCH v3 15/16] KVM: arm64: Drop perf.c and fold its tiny bits of code into arm.c / pmu.c

[Sean Christopherson <seanjc@google.com>]

On Mon, Oct 11, 2021, Marc Zyngier wrote:
> On Wed, 22 Sep 2021 01:05:32 +0100,
> Sean Christopherson <seanjc@google.com> wrote:
> > diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> > index 864b9997efb2..42270676498d 100644
> > --- a/include/kvm/arm_pmu.h
> > +++ b/include/kvm/arm_pmu.h
> > @@ -14,6 +14,7 @@
> >  #define ARMV8_PMU_MAX_COUNTER_PAIRS	((ARMV8_PMU_MAX_COUNTERS + 1) >> 1)
> >  
> >  DECLARE_STATIC_KEY_FALSE(kvm_arm_pmu_available);
> > +void kvm_pmu_init(void);
> >  
> >  static __always_inline bool kvm_arm_support_pmu_v3(void)
> >  {
> 
> Note that this patch is now conflicting with e840f42a4992 ("KVM:
> arm64: Fix PMU probe ordering"), which was merged in -rc4. Moving the
> static key definition to arch/arm64/kvm/pmu-emul.c and getting rid of
> kvm_pmu_init() altogether should be enough to resolve it.

Defining kvm_arm_pmu_available in pmu-emul.c doesn't work as-is because pmu-emul.c
depends on CONFIG_HW_PERF_EVENTS=y.  Since pmu-emul.c is the only path that enables
the key, my plan is to add a prep match to bury kvm_arm_pmu_available behind the
existing #ifdef CONFIG_HW_PERF_EVENTS in arm_pmu.h and add a stub
for kvm_arm_support_pmu_v3().  The only ugly part is that the KVM_NVHE_ALIAS() also
gains an #ifdef, but that doesn't seem too bad.