Re: [PATCH v2] KVM x86/xen: add an override for PVCLOCK_TSC_STABLE_BIT

[Paul Durrant]

On 31/10/2023 23:06, David Woodhouse wrote:
[snip]
> >                  mutex_lock(&kvm->lock);
> >                  if (!kvm->created_vcpus) {
> >                          kvm->arch.force_tsc_unstable = true;
> >                          r = 0;
> >                  }
> >                  mutex_unlock(&kvm->lock);
> >
> > So that it would be blatantly obvious that there's no race with checking a per-VM
> > flag without any lock/RCU protections.
>
> Makes sense. Although TBH if the VMM wants to flip this bit on and off
> at runtime while the guest clocks are being updated, it deserves what
> it gets. It's not a problem for KVM.

The first version of the patch that used an attribute requested a clock 
update when the attribute was set. I dropped that in this version but I 
think it'd best to re-instate it.

  Paul