On Tue, 5 May 2015, Ian Campbell wrote:
> On Mon, 2015-04-27 at 17:32 +0100, Julien Grall wrote:
> > >> diff --git a/xen/include/asm-arm/event.h b/xen/include/asm-arm/event.h
> > >> index 5330dfe..0149d06 100644
> > >> --- a/xen/include/asm-arm/event.h
> > >> +++ b/xen/include/asm-arm/event.h
> > >> @@ -39,7 +39,12 @@ static inline int
> > >> local_events_need_delivery_nomask(void)
> > >>
> > >> static inline int local_events_need_delivery(void)
> > >> {
> > >> - if ( !vcpu_event_delivery_is_enabled(current) )
> > >> + struct vcpu *v = current;
> > >> +
> > >> + if ( unlikely(is_idle_vcpu(v)) )
> > >> + return 0;
> > >> +
> > >> + if ( !vcpu_event_delivery_is_enabled(v) )
> > >> return 0;
> > >> return local_events_need_delivery_nomask();
> > >> }
> > >
> > > Is it actually considered correct in Xen to call hypercall_preempt_check
> > > and/or local_events_need_delivery on the idle vcpu?
> >
> > It seems that the x86 version of hypercall_preempt_check is able to cope
> > with idle VCPU.
>
> AFAICT that's just a coincidence, since an idle vcpu won't ever have a
> pending up call.
>
> > Although, I'm not sure if there is path where
> > hypercall_preempt_check can be called on an idle VCPU (cc x86
> > maintainers for this purpose).
> >
> > > Shouldn't it be avoided and maybe a BUG_ON added here instead?
> >
> > This patch was the simple way to fix the bug. I have other ideas in mind
> > which require some rework in apply_p2m_changes.
> >
> > I'll wait to see what x86 maintainers think.
>
> I'm inclined to just go with this patch for now, unless Stefano is
> nacking it.
I won't nack it.
> One question first: What aspect of local_events_need_delivery relies on
> the vcpu not being an idle one? I suppose something is not initialised,
> but what.
>
> Ian.
>
>
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