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

[Jim Mattson]

On Tue, Oct 31, 2023 at 2:22 AM Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> ---
>  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
>