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

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Date:   Tue, 9 Nov 2021 23:16:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Guo Ren <guoren@...nel.org>, Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-csky@...r.kernel.org,
        linux-riscv@...ts.infradead.org, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Artem Kashkanov <artem.kashkanov@...el.com>,
        Like Xu <like.xu.linux@...il.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>
Subject: Re: [PATCH v3 15/16] KVM: arm64: Drop perf.c and fold its tiny bits
 of code into arm.c / pmu.c

On Mon, Oct 11, 2021, Marc Zyngier wrote:
> On Wed, 22 Sep 2021 01:05:32 +0100,
> Sean Christopherson <seanjc@...gle.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.