linux-kernel - Re: [PATCH v6 03/10] KVM: x86/pmu: Make part of the Intel v2 PMU MSRs handling x86 generic

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Date:   Fri, 2 Jun 2023 16:23:48 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 03/10] KVM: x86/pmu: Make part of the Intel v2 PMU MSRs
 handling x86 generic

On Tue, May 30, 2023, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> AMD PerfMonV2 defines three registers similar to part of the Intel
> v2 PMU registers, including the GLOBAL_CTRL, GLOBAL_STATUS and
> GLOBAL_OVF_CTRL MSRs. For better code reuse, this specific part of
> the handling can be extracted to make it generic for X86 as a straight
> code movement.
> 
> Specifically, the kvm_pmu_set/get_msr() handlers of GLOBAL_STATUS,
> GLOBAL_CTRL, GLOBAL_OVF_CTRL defined for Intel are moved to generic
> pmu.c and the callback function .pmc_is_globally_enabled is removed,
> which is very helpful to introduce the AMD PerfMonV2 code later.

Yeah, except this patch doesn't actually move anything.  *Some* of the common bits
show up in pmu.c, but the same bits in pmu_intel.c get left behind. 

> The new eponymous pmc_is_globally_enabled() works well as legacy AMD
> vPMU version is indexed as 1. Note that the specific *_is_valid_msr will
> continue to be used to avoid cross-vendor MSR access.

This should be two patches.  Moving the GLOBAL_CTRL stuff is logically separate
from moving the pmc_is_enabled() code.

> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
> @@ -213,6 +212,22 @@ static inline void reprogram_counters(struct kvm_pmu *pmu, u64 diff)
>  	kvm_make_request(KVM_REQ_PMU, pmu_to_vcpu(pmu));
>  }
>  
> +/*
> + * Check if a PMC is enabled by comparing it against global_ctrl bits.
> + *
> + * If the current version of vPMU doesn't have global_ctrl MSR,
> + * all vPMCs are enabled (return TRUE).
> + */
> +static inline bool pmc_is_globally_enabled(struct kvm_pmc *pmc)
> +{
> +	struct kvm_pmu *pmu = pmc_to_pmu(pmc);
> +
> +	if (pmu->version < 2)

Nah, we're not open coding this check, not after putting in the effort to squash
the mess of open coding on Intel.  Moving intel_pmu_has_perf_global_ctrl() is
trivial, and also allows moving the existence checks into kvm_pmu_is_valid_msr().