On Fri, 2026-05-15 at 12:19 -0700, Sean Christopherson wrote:
> Register the Hyper-V reference counter (refcounter) callbacks for saving
> and restoring its PV sched_clock, if and only if the refcounter is
> actually being used for sched_clock.  Currently, Hyper-V overrides the
> save/restore hooks if the reference TSC available, whereas the Hyper-V
> refcounter code only overrides sched_clock if the reference TSC is
> available *and* it's not invariant.  The flaw is effectively papered over
> by invoking the "old" save/restore callbacks as part of save/restore, but
> that's unnecessary and fragile.
> 
> To avoid introducing more complexity, and to allow for additional cleanups
> of the PV sched_clock code, move the save/restore hooks and logic into
> hyperv_timer.c and simply wire up the hooks when overriding sched_clock
> itself.
> 
> Note, while the Hyper-V refcounter code is intended to be architecture
> neutral, CONFIG_PARAVIRT is firmly x86-only, i.e. adding a small amount of
> x86 specific code (which will be reduced in future cleanups) doesn't
> meaningfully pollute generic code.
> 
> Reviewed-by: Michael Kelley <[email protected]>
> Tested-by: Michael Kelley <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>

Reviewed-by: David Woodhouse <[email protected]>

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