linux-kernel - Re: [PATCH v6 01/20] KVM: x86/pmu: Don't allow exposing unsupported architectural events

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Date:   Sat, 4 Nov 2023 05:08:13 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Dapeng Mi <dapeng1.mi@...ux.intel.com>,
        Jinrong Liang <cloudliang@...cent.com>,
        Like Xu <likexu@...cent.com>,
        Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH v6 01/20] KVM: x86/pmu: Don't allow exposing unsupported
 architectural events

On Fri, Nov 3, 2023 at 5:02 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Hide architectural events that unsupported according to guest CPUID *or*
> hardware, i.e. don't let userspace advertise and potentially program
> unsupported architectural events.

The bitmask, pmu->available_event_types, is only used in
intel_hw_event_available(). As discussed
(https://lore.kernel.org/kvm/ZUU12-TUR_1cj47u@google.com/),
intel_hw_event_available() should go away.

> Note, KVM already limits the length of the reverse polarity field, only
> the mask itself is missing.
>
> Fixes: f5132b01386b ("KVM: Expose a version 2 architectural PMU to a guests")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/vmx/pmu_intel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 820d3e1f6b4f..1b13a472e3f2 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -533,7 +533,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>         pmu->counter_bitmask[KVM_PMC_GP] = ((u64)1 << eax.split.bit_width) - 1;
>         eax.split.mask_length = min_t(int, eax.split.mask_length,
>                                       kvm_pmu_cap.events_mask_len);
> -       pmu->available_event_types = ~entry->ebx &
> +       pmu->available_event_types = ~(entry->ebx | kvm_pmu_cap.events_mask) &
>                                         ((1ull << eax.split.mask_length) - 1);
>
>         if (pmu->version == 1) {
> --
> 2.42.0.869.gea05f2083d-goog
>