Re: [PATCH 14/15] KVM: x86/pmu: Advertise PerfMon version 5 on Intel hosts

[Mi, Dapeng]

On 7/24/2026 10:19 PM, Chen, Zide wrote:
>
> On 7/23/2026 10:20 PM, Jim Mattson wrote:
>> On Thu, Jul 23, 2026 at 4:25 PM Chen, Zide <zide.chen@xxxxxxxxx> wrote:
>>> Currently KVM always injects #GP when the AnyThread bit is set.
>>>
>>> kvm_pmu_refresh(): pmu->reserved_bits = 0xffffffff00200000ull;
>>>
>>> I understand the concern, but I'm not aware of a better solution for
>>> PMUv3/4. Silently ignoring AnyThread would deviate from the
>>> architectural behavior and, more importantly, may give the guest the
>>> false impression that AnyThread is supported. Supporting AnyThread, on
>>> the other hand, has cross-VM information leakage concerns.
>> Don't support versions 3 or 4; they aren't virtualizable. Hosts with
>> PMU versions 3 or 4 just get vPMU version 2.
> Yes, that sounds reasonable.

Yeah, that is our original implementation. It would be simpler. 


>
> PMUv3/v4 platforms (Nehalem, Westmere, Sandy Bridge, and Ivy Bridge) are
> quite old. In addition, the impact of exposing PMUv2 instead of PMUv3/v4
> should be minimal.
>