Re: [PATCH v6 8/8] KVM: selftests: Add PERF_METRICS and fixed counter 3 tests

[Jim Mattson]

On Mon, Jul 13, 2026 at 10:28 PM Mi, Dapeng <dapeng1.mi@xxxxxxxxxxxxxxx> wrote:
>
>
> On 7/14/2026 1:11 PM, Jim Mattson wrote:
> > On Mon, Jul 13, 2026 at 12:12 AM Mi, Dapeng <dapeng1.mi@xxxxxxxxxxxxxxx> wrote:
> >
> >> rdpmc is the preferable way to read PMU counters since the better
> >> performance than rdmsr, and most of current code regardless of kernel or
> >> user-space already use rdpmc to read PMC counters. If we set the rdpmc to
> >> interception by default, then it may cause extra performance hit.
> >>
> >> Currently I didn't hear there is any plan to extend the rdpmc to support
> >> more types for Intel platforms ...
> > Is Intel willing to commit to that?
>
> I'm afraid not. :(

Then, KVM must always intercept RDPMC.

> rdpmc is still possible to be extended to support more types in the future,
> but recently we don't see such requirements.

That's no comfort.

An alternative would be for Intel to provide a way for KVM to query
which types of PMC are supported in ECX[31:16], before or concurrently
with any microarchitecture that supports more types than CPUs support
today.