Re: [PATCH v7 06/12] KVM: arm64: PMU: Add a helper to read the number of counters

[Oliver Upton <oliver.upton@linux.dev>]

On Mon, Oct 09, 2023 at 11:08:52PM +0000, Raghavendra Rao Ananta wrote:
> Add a helper, kvm_arm_get_num_counters(), to read the number
> of counters from the arm_pmu associated to the VM. Make the
> function global as upcoming patches will be interested to
> know the value while setting the PMCR.N of the guest from
> userspace.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
>  arch/arm64/kvm/pmu-emul.c | 17 +++++++++++++++++
>  include/kvm/arm_pmu.h     |  6 ++++++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index a161d6266a5c..84aa8efd9163 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -873,6 +873,23 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq)
>  	return true;
>  }
>  
> +/**
> + * kvm_arm_get_num_counters - Get the number of general-purpose PMU counters.
> + * @kvm: The kvm pointer
> + */
> +int kvm_arm_get_num_counters(struct kvm *kvm)

nit: the naming suggests this returns the configured number of PMCs, not
the limit.

Maybe kvm_arm_pmu_get_max_counters()?

> +{
> +	struct arm_pmu *arm_pmu = kvm->arch.arm_pmu;
> +
> +	lockdep_assert_held(&kvm->arch.config_lock);
> +
> +	/*
> +	 * The arm_pmu->num_events considers the cycle counter as well.
> +	 * Ignore that and return only the general-purpose counters.
> +	 */
> +	return arm_pmu->num_events - 1;
> +}
> +
>  static void kvm_arm_set_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
>  {
>  	lockdep_assert_held(&kvm->arch.config_lock);
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index cd980d78b86b..672f3e9d7eea 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -102,6 +102,7 @@ void kvm_vcpu_pmu_resync_el0(void);
>  
>  u8 kvm_arm_pmu_get_pmuver_limit(void);
>  int kvm_arm_set_default_pmu(struct kvm *kvm);
> +int kvm_arm_get_num_counters(struct kvm *kvm);
>  
>  u64 kvm_vcpu_read_pmcr(struct kvm_vcpu *vcpu);
>  #else
> @@ -181,6 +182,11 @@ static inline int kvm_arm_set_default_pmu(struct kvm *kvm)
>  	return -ENODEV;
>  }
>  
> +static inline int kvm_arm_get_num_counters(struct kvm *kvm)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline u64 kvm_vcpu_read_pmcr(struct kvm_vcpu *vcpu)
>  {
>  	return 0;
> -- 
> 2.42.0.609.gbb76f46606-goog
> 

-- 
Thanks,
Oliver