Re: [PATCH v2 06/16] KVM: x86/pmu: Drop nr_arch_{gp,fixed}_counters from kvm_pmu

[Jim Mattson]

On Thu, Aug 27, 2026 at 3:48 PM Zide Chen <zide.chen@xxxxxxxxx> wrote:
>
> From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>
> This is a preparatory step toward fully bitmap-based PMU capability
> handling. Later patches switch KVM's view of host PMU capabilities from
> counter counts to counter bitmaps.
>
> Populate and use pmc_exists directly when walking guest-visible PMCs,
> instead of relying on pmu->nr_arch_{gp,fixed}_counters as intermediate
> state.
>
> Iterate counters via the newly added pmc_exists based helpers, and
> remove the now-redundant nr_arch_{gp,fixed}_counters fields from struct
> kvm_pmu.
>
> Note: {vmx,svm}_recalc_pmu_msr_intercepts() may leave stale intercepts
> on GP MSRs after CPUID narrowing. This corner case is resolved by the
> following patch: "KVM: x86/pmu: Switch to bitmask-based KVM PMU
> capabilities".

Are you saying that you are deliberately breaking bisection?!? Shame on you!

> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> Co-developed-by: Zide Chen <zide.chen@xxxxxxxxx>
> Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
> ---
> v2:
> - Fix AMD legacy PMU MSR intercept handling for guest PMU
>   narrowing reconfiguration by adding for_each_clear_bit_from().
> - Re-word the stale interception changelog part.
> ---
[ ... ]
> -       for (i = 0; i < pmu->nr_arch_fixed_counters; i++)
> +       kvm_for_each_fixed_counter(i, fixed_mask)
>                 vmx_set_intercept_for_msr(vcpu, MSR_CORE_PERF_FIXED_CTR0 + i,
>                                           MSR_TYPE_RW, intercept);
>         for ( ; i < kvm_pmu_cap.num_counters_fixed; i++)

Doesn't this potentially leave stale intercepts on FC MSRs after CPUID
narrowing as well?