Re: [PATCH v3 40/41] x86/tsc: Add standalone helper for getting CPU frequency from CPUID

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

On Sat, 2026-05-16 at 09:42 +0200, Paolo Bonzini wrote:
> On 5/15/26 21:19, Sean Christopherson wrote:
> > Extract the guts of cpu_khz_from_cpuid() to a standalone helper that
> > doesn't restrict the usage to Intel CPUs.  This will allow sharing the
> > core logic with kvmclock, as (a) CPUID.0x16 may be enumerated alongside
> > kvmclock, and (b) KVM generally doesn't restrict CPUID based on vendor.
> 
> Even for native there's no real reason to restrict to Intel, I think.
> native_calibrate_tsc() only limits itself because historically (prior to 
> commit 604dc9170f24, "x86/tsc: Use CPUID.0x16 to calculate missing 
> crystal frequency", 2019-05-09) it used a hardcoded table of crystal 
> frequencies.
> 
> Of course paranoia applies, but for virtualization, if the leaf exists 
> there is no reason not to trust it.

Agreed.

Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>

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