Re: [PATCH 1/5] KVM: arm64: Divorce the perf code from oprofile helpers

From: Will Deacon <will@kernel.org>
To: Marc Zyngier <maz@kernel.org>
Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
	linux-sh@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
	Rich Felker <dalias@libc.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Peter Zijlstra <peterz@infradead.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	nathan@kernel.org, Viresh Kumar <viresh.kumar@linaro.org>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	kernel-team@android.com
Subject: Re: [PATCH 1/5] KVM: arm64: Divorce the perf code from oprofile helpers
Date: Thu, 22 Apr 2021 11:43:27 +0100	[thread overview]
Message-ID: <20210422104327.GC1442@willie-the-truck> (raw)
In-Reply-To: <20210414134409.1266357-2-maz@kernel.org>

On Wed, Apr 14, 2021 at 02:44:05PM +0100, Marc Zyngier wrote:
> KVM/arm64 is the sole user of perf_num_counters(), and really
> could do without it. Stop using the obsolete API by relying on
> the existing probing code.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/perf.c     | 7 +------
>  arch/arm64/kvm/pmu-emul.c | 2 +-
>  include/kvm/arm_pmu.h     | 4 ++++
>  3 files changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/kvm/perf.c b/arch/arm64/kvm/perf.c
> index 739164324afe..b8b398670ef2 100644
> --- a/arch/arm64/kvm/perf.c
> +++ b/arch/arm64/kvm/perf.c
> @@ -50,12 +50,7 @@ static struct perf_guest_info_callbacks kvm_guest_cbs = {
>  
>  int kvm_perf_init(void)
>  {
> -	/*
> -	 * Check if HW_PERF_EVENTS are supported by checking the number of
> -	 * hardware performance counters. This could ensure the presence of
> -	 * a physical PMU and CONFIG_PERF_EVENT is selected.
> -	 */
> -	if (IS_ENABLED(CONFIG_ARM_PMU) && perf_num_counters() > 0)
> +	if (kvm_pmu_probe_pmuver() != 0xf)

Took me a while to figure out that this returns 0xf if the hardware has a
PMUVer of 0x0, so it's all good:

Acked-by: Will Deacon <will@kernel.org>

Will