linux-kernel - Re: [PATCH] KVM: arm64: build perf support only when enabled

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Date:   Thu, 22 Apr 2021 11:12:37 +0100
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Fuad Tabba <tabba@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        David Brazdil <dbrazdil@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: build perf support only when enabled

On Wed, Apr 21, 2021 at 02:56:16PM +0100, Marc Zyngier wrote:
> On Wed, 21 Apr 2021 14:49:01 +0100,
> Arnd Bergmann <arnd@...nel.org> wrote:
> > 
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > The perf_num_counters() function is only defined when CONFIG_PERF_EVENTS
> > is enabled:
> > 
> > arch/arm64/kvm/perf.c: In function 'kvm_perf_init':
> > arch/arm64/kvm/perf.c:58:43: error: implicit declaration of function 'perf_num_counters'; did you mean 'dec_mm_counter'? [-Werror=implicit-function-declaration]
> >    58 |         if (IS_ENABLED(CONFIG_ARM_PMU) && perf_num_counters() > 0
> >       |                                           ^~~~~~~~~~~~~~~~~
> > 
> > Use conditional compilation to disable this feature entirely when
> > CONFIG_PERF_EVENTS is disabled in the host.
> > 
> > Fixes: 6b5b368fccd7 ("KVM: arm64: Turn kvm_arm_support_pmu_v3() into a static key")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> > Not sure if this is the correct symbol to check for, but this is
> > one way to avoid the build failure.
> 
> I think a better way is to get rid of perf_num_counters() entirely,
> see [1]. If someone acks the second and last patches, I'll even take
> the whole series in (nudge nudge...).

Sorry, behind at the moment! Will get to it today.

Will