Re: [PATCH 09/10] KVM: x86: Setup Hyper-V TSC page before Xen PV clocks (during clock update)

[Paul Durrant]

On 21/01/2025 17:16, David Woodhouse wrote:
> On Tue, 2025-01-21 at 15:59 +0000, Paul Durrant wrote:
> > On 21/01/2025 15:44, Sean Christopherson wrote:
> > [snip]
> > > I think it's ok to keep the Hyper-V TSC page in this case.  It's not that the Xen
> > > PV clock is truly unstable, it's that some guests get tripped up by the STABLE
> > > flag.  A guest that can't handle the STABLE flag has bigger problems than the
> > > existence of a completely unrelated clock that is implied to be stable.
> >
> > Agreed.
> >
> > > > I don't know if anyone combines Xen and Hyper-V emulation capabilities for
> > > > the same guest on KVM though.)
> > >
> > > That someone would have to be quite "brave" :-D
> >
> > Maybe :-)
>
> Xen itself does offer some Hyper-V enlightenments, and we might
> reasonably expect KVM-based hypervisors to offer the same. We
> explicitly do account for the KVM CPUID leaves moving up to let the
> Hyper-V ones exist.
>
> I don't recall if Xen's Hyper-V support includes the TSC page though.

It does :-)