linux-kernel - Re: [PATCH 3/3] KVM: x86/pmu: Segregate Intel and AMD specific logic

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Date:   Wed, 2 Mar 2022 20:38:44 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     Like Xu <like.xu.linux@...il.com>, seanjc@...gle.com,
        dave.hansen@...ux.intel.com, peterz@...radead.org,
        alexander.shishkin@...ux.intel.com, eranian@...gle.com,
        daviddunn@...gle.com, ak@...ux.intel.com,
        kan.liang@...ux.intel.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, kim.phillips@....com,
        santosh.shukla@....com,
        "Paolo Bonzini - Distinguished Engineer (kernel-recipes.org) (KVM HoF)" 
        <pbonzini@...hat.com>
Subject: Re: [PATCH 3/3] KVM: x86/pmu: Segregate Intel and AMD specific logic

On Mon, Feb 21, 2022 at 2:02 AM Ravi Bangoria <ravi.bangoria@....com> wrote:
>
>
>
> On 21-Feb-22 1:27 PM, Like Xu wrote:
> > On 21/2/2022 3:31 pm, Ravi Bangoria wrote:
> >>   void reprogram_counter(struct kvm_pmu *pmu, int pmc_idx)
> >>   {
> >>       struct kvm_pmc *pmc = kvm_x86_ops.pmu_ops->pmc_idx_to_pmc(pmu, pmc_idx);
> >> +    bool is_intel = !strncmp(kvm_x86_ops.name, "kvm_intel", 9);
> >
> > How about using guest_cpuid_is_intel(vcpu)
>
> Yeah, that's better then strncmp().
>
> > directly in the reprogram_gp_counter() ?
>
> We need this flag in reprogram_fixed_counter() as well.

Explicit "is_intel" checks in any form seem clumsy, since we have
already put some effort into abstracting away the implementation
differences in struct kvm_pmu. It seems like these differences could
be handled by adding three masks to that structure: the "raw event
mask" (i.e. event selector and unit mask), the hsw_in_tx mask, and the
hsw_in_tx_checkpointed mask.

These changes should also be coordinated with Like's series that
eliminates all of the PERF_TYPE_HARDWARE nonsense.