linux-kernel - Re: [PATCH v3 12/16] KVM: Move x86's perf guest info callbacks to generic KVM

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Date:   Mon, 11 Oct 2021 16:33:31 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Sean Christopherson <seanjc@...gle.com>
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 12/16] KVM: Move x86's perf guest info callbacks to generic KVM

On Mon, 11 Oct 2021 15:46:25 +0100,
Sean Christopherson <seanjc@...gle.com> wrote:
> 
> On Mon, Oct 11, 2021, Marc Zyngier wrote:
> > On Wed, 22 Sep 2021 01:05:29 +0100, Sean Christopherson <seanjc@...gle.com> wrote:
> > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > > index ed940aec89e0..828b6eaa2c56 100644
> > > --- a/arch/arm64/include/asm/kvm_host.h
> > > +++ b/arch/arm64/include/asm/kvm_host.h
> > > @@ -673,6 +673,14 @@ int io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa);
> > >  void kvm_perf_init(void);
> > >  void kvm_perf_teardown(void);
> > >  
> > > +#ifdef CONFIG_GUEST_PERF_EVENTS
> > > +static inline bool kvm_arch_pmi_in_guest(struct kvm_vcpu *vcpu)
> > 
> > Pardon my x86 ignorance, what is PMI? PMU Interrupt?
> 
> Ya, Performance Monitoring Interrupt.  I didn't realize the term wasn't
> common perf terminology.  Maybe kvm_arch_perf_events_in_guest() to be
> less x86-centric?

Up to you. I would be happy with just a comment.

> 
> > > +{
> > > +	/* Any callback while a vCPU is loaded is considered to be in guest. */
> > > +	return !!vcpu;
> > > +}
> > > +#endif
> > 
> > Do you really need this #ifdef?
> 
> Nope, should compile fine without it, though simply dropping the #ifdef
> would make make the semantics of the function wrong, even if nothing
> consumes it.  Tweak it to use IS_ENABLED()?
> 
> 	return IS_ENABLED(CONFIG_GUEST_PERF_EVENTS) && !!vcpu;

LGTM.

	M.

-- 
Without deviation from the norm, progress is not possible.