linux-kernel - Re: [kvm-unit-tests Patch v2 4/5] x86: pmu: Support validation for Intel PMU fixed counter 3

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Message-ID: <CALMp9eQ4Xj5D-kgqVMKUNmdF37rLcMRXyDYdQU339sRCKZ7d9A@mail.gmail.com>
Date:   Tue, 31 Oct 2023 11:47:54 -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>
Subject: Re: [kvm-unit-tests Patch v2 4/5] x86: pmu: Support validation for
 Intel PMU fixed counter 3

On Tue, Oct 31, 2023 at 2:22 AM Dapeng Mi <dapeng1.mi@...ux.intel.com> wrote:
>
> Intel CPUs, like Sapphire Rapids, introduces a new fixed counter
> (fixed counter 3) to counter/sample topdown.slots event, but current
> code still doesn't cover this new fixed counter.
>
> So this patch adds code to validate this new fixed counter can count
> slots event correctly.

I'm not convinced that this actually validates anything.

Suppose, for example, that KVM used fixed counter 1 when the guest
asked for fixed counter 3. Wouldn't this test still pass?

> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  x86/pmu.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index 6bd8f6d53f55..404dc7b62ac2 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -47,6 +47,7 @@ struct pmu_event {
>         {"fixed 1", MSR_CORE_PERF_FIXED_CTR0, 10*N, 10.2*N},
>         {"fixed 2", MSR_CORE_PERF_FIXED_CTR0 + 1, 1*N, 500*N},
>         {"fixed 3", MSR_CORE_PERF_FIXED_CTR0 + 2, 0.1*N, 300*N},
> +       {"fixed 4", MSR_CORE_PERF_FIXED_CTR0 + 3, 1*N, 5000*N},
>  };
>
>  char *buf;
> --
> 2.34.1
>