Re: [PATCH v8 7/8] KVM: x86/pmu: Emulate RDPMC on performance metrics

[Chen, Zide]

On 8/18/2026 2:24 PM, Andi Kleen wrote:
> On Tue, Aug 18, 2026 at 01:30:32PM -0500, Chen, Zide wrote:
>>
>>
>> On 8/18/2026 12:41 PM, Andi Kleen wrote:
>>> On Mon, Aug 17, 2026 at 11:31:41AM -0700, Zide Chen wrote:
>>>> If the host has the PERF_METRICS capability but it's not present on
>>>> the guest, RDPMC interception must be enabled and KVM should inject
>>>> an #GP when the guest attempts a PERF_METRICS RDPMC.
>>>>
>>>> If the guest has PERF_METRICS but RDPMC interception is enabled for
>>>> other reasons, KVM needs to emulate RDPMC with type 0x2000.
>>>>
>>>> For simplicity, Metrics Clear Mode is not supported.
>>>
>>> But is the bit cleared in PERF_CAPABILITIES? And would 
>>> the enable bit fault?
>>
>> Currently KVM doesn't advertise
>> IA32_PERF_CAPABILITIES.RDPMC_METRICS_CLEAR[19].
> 
> Thanks.
> 
> How about the fault for the enable bit?

Yes, KVM always injects a #GP if the guest writes
IA32_FIXED_CTR_CTRL.METRICS_CLEAR_EN[bit 14].

> 
>>> It would be better to just support it, metrics clear is actually useful.
>>
>> Sure, I'll add it.
> 
> I guess it could be a follow-on patch, no need to hold up this one.

OK.