Re: [Xen-devel] [PATCH v9 12/12] xen/arm: gic_events_need_delivery and irq priorities

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 06/18/2014 01:51 PM, Stefano Stabellini wrote:
> On Wed, 18 Jun 2014, Julien Grall wrote:
>> On 06/18/2014 11:36 AM, Ian Campbell wrote:
>>> AIUI there is no relationship here with "xen/arm: make accesses to
>>> desc->status flags atomic" which fixes an issue which already present
>>> before this series.
>>
>> The error was not really there before. We were "safe" because the flags
>> were cleared before EOIing the IRQ.
>>
>> Here, we are clearing after EOIing (it has been made by the guest). So
>> this race condition can happen more often.
> 
> However considering that when IRQ_GUEST is set, IRQ_INPROGRESS is only
> read by irq.c, I think the window for errors is extremely small.
> 
> That doesn't mean we should expose ourselves to risks, so I still
> recommend we apply "make accesses to desc->status flags atomic".

FYI, with my upcoming device passthrough series, I rely of
IRQ_INPROGRESS in release_irq to know if we need to EOI an IRQ routed to
the guest.

So this series is definitely necessary, otherwise we loose the interrupt
for ever.

Regards,

-- 
Julien Grall

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