linux-kernel - Re: [PATCH 2/5] KVM: x86/pmu: Add a helper to check if pmc has PEBS mode enabled

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Date:   Wed, 24 May 2023 13:54:23 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Ravi Bangoria <ravi.bangoria@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] KVM: x86/pmu: Add a helper to check if pmc has PEBS
 mode enabled

On Fri, Mar 10, 2023, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> Add a helper to check if pmc has PEBS mode enabled so that more new
> code may reuse this part and opportunistically drop a pmu reference.
> 
> No functional change intended.
> 
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>  arch/x86/kvm/pmu.c | 3 +--
>  arch/x86/kvm/pmu.h | 7 +++++++
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index d1c89a6625a0..01a6b7ffa9b1 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -191,7 +191,6 @@ static int pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type, u64 config,
>  				 bool exclude_user, bool exclude_kernel,
>  				 bool intr)
>  {
> -	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
>  	struct perf_event *event;
>  	struct perf_event_attr attr = {
>  		.type = type,
> @@ -203,7 +202,7 @@ static int pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type, u64 config,
>  		.exclude_kernel = exclude_kernel,
>  		.config = config,
>  	};
> -	bool pebs = test_bit(pmc->idx, (unsigned long *)&pmu->pebs_enable);
> +	bool pebs = pebs_is_enabled(pmc);
>  
>  	attr.sample_period = get_sample_period(pmc, pmc->counter);
>  
> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
> index cff0651b030b..db4262fe8814 100644
> --- a/arch/x86/kvm/pmu.h
> +++ b/arch/x86/kvm/pmu.h
> @@ -189,6 +189,13 @@ static inline void kvm_pmu_request_counter_reprogram(struct kvm_pmc *pmc)
>  	kvm_make_request(KVM_REQ_PMU, pmc->vcpu);
>  }
>  
> +static inline bool pebs_is_enabled(struct kvm_pmc *pmc)

pebs_is_enabled() is a bit too generic, e.g. at a glance I would expect it to return
true if PEBS as a whole is enabled.  What about something like pmc_is_pebs() or
pmc_is_pebs_enabled()?