linux-kernel - Re: [PATCH v2 1/6] KVM: x86/pmu: Setup pmc->eventsel for fixed PMCs

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Date:   Mon, 6 Dec 2021 11:57:35 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <likexu@...cent.com>
Subject: Re: [PATCH v2 1/6] KVM: x86/pmu: Setup pmc->eventsel for fixed PMCs

On Mon, Nov 29, 2021 at 11:42 PM Like Xu <like.xu.linux@...il.com> wrote:
>
> From: Like Xu <likexu@...cent.com>
>
> The current pmc->eventsel for fixed counter is underutilised. The
> pmc->eventsel can be setup for all known available fixed counters
> since we have mapping between fixed pmc index and
> the intel_arch_events array.
>
> Either gp or fixed counter, it will simplify the later checks for
> consistency between eventsel and perf_hw_id.
>
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>  arch/x86/kvm/vmx/pmu_intel.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 1b7456b2177b..b7ab5fd03681 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -459,6 +459,21 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>         return 1;
>  }
>
> +static void setup_fixed_pmc_eventsel(struct kvm_pmu *pmu)
> +{
> +       size_t size = ARRAY_SIZE(fixed_pmc_events);
> +       struct kvm_pmc *pmc;
> +       u32 event;
> +       int i;
> +
> +       for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
> +               pmc = &pmu->fixed_counters[i];
> +               event = fixed_pmc_events[array_index_nospec(i, size)];
How do we know that i < size? For example, Ice Lake supports 4 fixed
counters, but fixed_pmc_events only has three entries.
> +               pmc->eventsel = (intel_arch_events[event].unit_mask << 8) |
> +                       intel_arch_events[event].eventsel;
> +       }
> +}
> +
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