RE: [PATCH] cpufreq/amd-pstate: Bail out early in virtual machines and don't warn

[Michael Kelley]

From: Rong Zhang <i@xxxxxxxx> Sent: Thursday, July 16, 2026 11:29 AM
> 
> Hi K Prateek,
> 
> Thanks for reviewing this.
> 

[snip]

> 
> As Jason said:
> 
>    With Xen, the Xen hypervisor itself controls CPPC.  dom0
>    (xen_initial_domain()) doesn't need the amd-pstate driver.
> 
> I think we don't need to worry about Xen.
> 
> @Michael, if you have the time, could you test if Hyper-V exposes
> X86_FEATURE_HW_PSTATE (i.e., 0x80000007/edx bit 7)?

I checked a VM running on Hyper-V on an AMD Zen 2 (EPYC 7452),
and another on a Zen 4 (EPYC 9V74) processor. Neither has
X86_FEATURE_HW_PSTATE set. There are other variations that
could affect what a guest on Hyper-V sees, but these spot tests
are sufficient evidence that this flag does what we want for
Hyper-V guests.

Michael