linux-kernel - Re: [PATCH v7 01/12] KVM: arm64: PMU: Introduce helpers to set the guest's PMU

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Date:   Mon, 16 Oct 2023 21:45:04 +0200
From:   Eric Auger <eauger@...hat.com>
To:     Raghavendra Rao Ananta <rananta@...gle.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Marc Zyngier <maz@...nel.org>
Cc:     Alexandru Elisei <alexandru.elisei@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Shaoqin Huang <shahuang@...hat.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v7 01/12] KVM: arm64: PMU: Introduce helpers to set the
 guest's PMU

Hi Reiji,

On 10/10/23 01:08, Raghavendra Rao Ananta wrote:
> From: Reiji Watanabe <reijiw@...gle.com>
> 
> Introduce new helper functions to set the guest's PMU
> (kvm->arch.arm_pmu) either to a default probed instance or to a
> caller requested one, and use it when the guest's PMU needs to
> be set. These helpers will make it easier for the following
> patches to modify the relevant code.
> 
> No functional change intended.
> 
> Signed-off-by: Reiji Watanabe <reijiw@...gle.com>
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
Reviewed-by: Eric Auger <eric.auger@...hat.com>

Eric
> ---
>  arch/arm64/kvm/pmu-emul.c | 50 +++++++++++++++++++++++++++------------
>  1 file changed, 35 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index 3afb281ed8d2..eb5dcb12dafe 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -874,6 +874,36 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq)
>  	return true;
>  }
>  
> +static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
> +{
> +	lockdep_assert_held(&kvm->arch.config_lock);
> +
> +	kvm->arch.arm_pmu = arm_pmu;
> +}
> +
> +/**
> + * kvm_arm_set_default_pmu - No PMU set, get the default one.
> + * @kvm: The kvm pointer
> + *
> + * The observant among you will notice that the supported_cpus
> + * mask does not get updated for the default PMU even though it
> + * is quite possible the selected instance supports only a
> + * subset of cores in the system. This is intentional, and
> + * upholds the preexisting behavior on heterogeneous systems
> + * where vCPUs can be scheduled on any core but the guest
> + * counters could stop working.
> + */
> +static int kvm_arm_set_default_pmu(struct kvm *kvm)
> +{
> +	struct arm_pmu *arm_pmu = kvm_pmu_probe_armpmu();
> +
> +	if (!arm_pmu)
> +		return -ENODEV;
> +
> +	kvm_arm_set_pmu(kvm, arm_pmu);
> +	return 0;
> +}
> +
>  static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
>  {
>  	struct kvm *kvm = vcpu->kvm;
> @@ -893,7 +923,7 @@ static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id)
>  				break;
>  			}
>  
> -			kvm->arch.arm_pmu = arm_pmu;
> +			kvm_arm_set_pmu(kvm, arm_pmu);
>  			cpumask_copy(kvm->arch.supported_cpus, &arm_pmu->supported_cpus);
>  			ret = 0;
>  			break;
> @@ -917,20 +947,10 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
>  		return -EBUSY;
>  
>  	if (!kvm->arch.arm_pmu) {
> -		/*
> -		 * No PMU set, get the default one.
> -		 *
> -		 * The observant among you will notice that the supported_cpus
> -		 * mask does not get updated for the default PMU even though it
> -		 * is quite possible the selected instance supports only a
> -		 * subset of cores in the system. This is intentional, and
> -		 * upholds the preexisting behavior on heterogeneous systems
> -		 * where vCPUs can be scheduled on any core but the guest
> -		 * counters could stop working.
> -		 */
> -		kvm->arch.arm_pmu = kvm_pmu_probe_armpmu();
> -		if (!kvm->arch.arm_pmu)
> -			return -ENODEV;
> +		int ret = kvm_arm_set_default_pmu(kvm);
> +
> +		if (ret)
> +			return ret;
>  	}
>  
>  	switch (attr->attr) {