Re: [PATCH v8 3/3] xen/events: do some cleanups in evtchn_fifo_set_pending()

[Jürgen Groß <jgross@xxxxxxxx>]

On 27.11.20 14:27, Jan Beulich wrote:
> On 25.11.2020 11:51, Juergen Gross wrote:
> > --- a/xen/common/event_fifo.c
> > +++ b/xen/common/event_fifo.c
> > @@ -175,6 +175,18 @@ static void evtchn_fifo_set_pending(struct vcpu *v, struct 
> > evtchn *evtchn)
> >           return;
> >       }
> >   
> > +    /*
> > +     * Control block not mapped.  The guest must not unmask an
> > +     * event until the control block is initialized, so we can
> > +     * just drop the event.
> > +     */
> > +    if ( unlikely(!v->evtchn_fifo->control_block) )
> > +    {
> > +        printk(XENLOG_G_WARNING
> > +               "%pv has no FIFO event channel control block\n", v);
> > +        return;
> > +    }
> This results in bypassing the setting of PENDING and the possible
> call to evtchn_check_pollers(). It may in particular be the case
> that a very special purpose guest uses event channels just for
> waking up pollers, which - afaict - then doesn't require setting
> up a control block. To give an example, I could easily see an XTF
> test avoid that step if indeed it's unnecessary.
Okay, I can move the test after setting PENDING and do a "goto unlock"
instead of returning.


Juergen

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