Re: [PATCH 3/5] kvm: kick vcpu when async_pf is resolved

[Paolo Bonzini <pbonzini@redhat.com>]

----- Original Message -----
> From: "Christian Borntraeger" <borntraeger@de.ibm.com>
> To: "Roman Kagan" <rkagan@virtuozzo.com>, "Radim Krčmář" <rkrcmar@redhat.com>, "Paolo Bonzini" <pbonzini@redhat.com>,
> kvm@vger.kernel.org
> Cc: "Denis Lunev" <den@virtuozzo.com>
> Sent: Friday, December 2, 2016 10:35:02 AM
> Subject: Re: [PATCH 3/5] kvm: kick vcpu when async_pf is resolved
> 
> On 12/02/2016 09:47 AM, Roman Kagan wrote:
> > When async_pf is ready the guest needs to be made aware of it ASAP,
> > because it may be holding off a higher priority task pending the
> > async_pf resolution in favor of a lower priority one.
> > 
> > In case async_pf's are harvested in vcpu context (x86) we have to not
> > only wake the vcpu up but kick it into host.
> > 
> > While at this, also replace the open-coded vcpu wakeup by the existing
> > helper.
> > 
> > Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
> > ---
> >  virt/kvm/async_pf.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> > index 9cced14..5f0a66c 100644
> > --- a/virt/kvm/async_pf.c
> > +++ b/virt/kvm/async_pf.c
> > @@ -105,8 +105,11 @@ static void async_pf_execute(struct work_struct *work)
> >  	 * This memory barrier pairs with prepare_to_wait's set_current_state()
> >  	 */
> >  	smp_mb();
> > -	if (swait_active(&vcpu->wq))
> > -		swake_up(&vcpu->wq);
> > +#ifdef CONFIG_KVM_ASYNC_PF_SYNC
> > +	kvm_vcpu_wake_up(vcpu);
> > +#else
> > +	kvm_vcpu_kick(vcpu);
> > +#endif
> 
> This will break s390, both functions are disabled for s390.
> On s390 do not want to kick the CPU for a completion. Instead we implement
> the kvm_async_page_present_sync call above and handle completion via an
> "pfault done" interrupt via the normal interrupt delivery.

Is there any reason (with this patch) to disable kvm_vcpu_wake_up on s390?
It was unused until now, but the patch makes sense as a cleanup.

Paolo