linux-kernel - Re: [Patch 1/2] KVM: x86/pmu: Add Intel CPUID-hinted TopDown slots event

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Date:   Tue, 31 Oct 2023 11:22:31 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhang Xiong <xiong.y.zhang@...el.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Like Xu <like.xu.linux@...il.com>,
        Dapeng Mi <dapeng1.mi@...el.com>, Like Xu <likexu@...cent.com>
Subject: Re: [Patch 1/2] KVM: x86/pmu: Add Intel CPUID-hinted TopDown slots event

On Tue, Oct 31, 2023 at 1:58 AM Dapeng Mi <dapeng1.mi@...ux.intel.com> wrote:
>
> This patch adds support for the architectural topdown slots event which
> is hinted by CPUID.0AH.EBX.

Can't a guest already program an event selector to count event select
0xa4, unit mask 1, unless the event is prohibited by
KVM_SET_PMU_EVENT_FILTER?

AFAICT, this change just enables event filtering based on
CPUID.0AH:EBX[bit 7] (though it's not clear to me why two independent
mechanisms are necessary for event filtering).