Re: [PATCH v3 31/41] x86/tsc: Pass KNOWN_FREQ and RELIABLE as params to registration

[Woodhouse, David]

On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote:
> Add a "tsc_properties" set of flags and use it to annotate whether the
> TSC operates at a known and/or reliable frequency when registering a
> paravirtual TSC calibration routine.  Currently, each PV flow manually
> sets the associated feature flags, but often in haphazard fashion that
> makes it difficult for unfamiliar readers to see the properties of the
> TSC when running under a particular hypervisor.
> 
> The other, bigger issue with manually setting the feature flags is that
> it decouples the flags from the calibration routine.  E.g. in theory, PV
> code could mark the TSC as having a known frequency, but then have its
> PV calibration discarded in favor of a method that doesn't use that known
> frequency.  Passing the TSC properties along with the calibration routine
> will allow adding sanity checks to guard against replacing a "better"
> calibration routine with a "worse" routine.
> 
> As a bonus, the flags also give developers working on new PV code a heads
> up that they should at least mark the TSC as having a known frequency.
> 
> Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> Tested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>

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