Re: [PATCH v2 04/11] KVM: x86: Process "guest stopped request" once per guest time update

[Paul Durrant]

On 01/02/2025 01:38, Sean Christopherson wrote:
> Handle "guest stopped" requests once per guest time update in preparation
> of restoring KVM's historical behavior of setting PVCLOCK_GUEST_STOPPED
> for kvmclock and only kvmclock.  For now, simply move the code to minimize
> the probability of an unintentional change in functionally.
>
> Note, in practice, all clocks are guaranteed to see the request (or not)
> even though each PV clock processes the request individual, as KVM holds
> vcpu->mutex (blocks KVM_KVMCLOCK_CTRL) and it should be impossible for
> KVM's suspend notifier to run while KVM is handling requests.  And because
> the helper updates the reference flags, all subsequent PV clock updates
> will pick up PVCLOCK_GUEST_STOPPED.
>
> Note #2, once PVCLOCK_GUEST_STOPPED is restricted to kvmclock, the
> horrific #ifdef will go away.

:-)

> Cc: Paul Durrant <pdurrant@xxxxxxxxxx>
> Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>   arch/x86/kvm/x86.c | 17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)

Reviewed-by: Paul Durrant <paul@xxxxxxx>