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