linux-kernel - Re: [PATCH v3 6/6] KVM: arm64: Reload PMCNTENSET

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Message-ID: <Z9H7RYEI_cPwNe7h@linux.dev>
Date: Wed, 12 Mar 2025 14:23:17 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Andrew Jones <drjones@...hat.com>,
	Shannon Zhao <shannon.zhao@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, devel@...nix.com
Subject: Re: [PATCH v3 6/6] KVM: arm64: Reload PMCNTENSET_EL0

On Wed, Mar 12, 2025 at 08:56:00PM +0900, Akihiko Odaki wrote:
> Disable counters that are no longer included in PMCNTENSET_EL0. It is
> not necessary to enable counters included in PMCNTENSET_EL0 because
> kvm_pmu_handle_pmcr() does so if appropriate.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>  arch/arm64/kvm/pmu-emul.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index 2d19c6048091..b14655dda6db 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -831,6 +831,8 @@ void kvm_vcpu_reload_pmu(struct kvm_vcpu *vcpu)
>  {
>  	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
>  
> +	kvm_pmu_disable_counter_mask(vcpu, ~__vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
> +

Just so this function appears consistent, can we move this after the
point where the mask is applied?

There's no functional impact of course since PMCR_EL0.N can only be
changed before the VM is started, i.e. not possible to have running
counters >= N.

Thanks,
Oliver