Re: [PATCH v3 16/18] KVM: x86/pmu: Ignore AnyThread bit if CPUID.0AH:EDX[15] is set

[Jim Mattson]

On Thu, Nov 5, 2026 at 5:50 PM Zide Chen <zide.chen@xxxxxxxxx> wrote:
>
> Intel PerfMon v5 introduces the ANYTHREAD_DEPRECATION capability
> (CPUID.0AH:EDX[15]) to indicate that AnyThread counting is deprecated
> and that writes to the AnyThread bit in IA32_PERFEVTSELx and
> IA32_FIXED_CTR_CTRL are ignored.
>
> Preserve the guest-written value in guest-visible state so that guest
> RDMSRs observe the AnyThread bit, but strip it before programming
> hardware to ensure cross-VM SMT isolation.
>
> Continue to inject #GP when ANYTHREAD_DEPRECATION is not present in the
> guest CPUID, e.g. for PerfMon v3/v4 guests or when the capability is
> not configured for a PerfMon v5+ guest.
>
> Advertise CPUID.0AH:EDX[15] only for PMU version 5+ guests, since the
> bit doesn't exist below version 5.
>
> Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>