Re: [Xen-devel] irq_guest_eoi_timer interaction with MSI

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 14/11/08 09:28, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> So we'd add a pirq-indexed bitmap to mitigate that. Whether we use
>> PHYSDEVOP_irq_eoi or EVTCHNOP_unmask, we need a new shared-memory bitmap,
>> right? Might as well use irq_eoi and index by pirq, I'd say.
> 
> Hmm, I'm still not convinced: With what you propose, it's unclear to me who
> would when clear the bit in that bitmap for the 'temporarily masked' case.
> Anyway, unless you get to implement your version earlier (and thus
> convince me that things will work out correctly), I'll try to get implemented
> what I would think should be appropriate here once I find time to do so.

Perhaps if we go your route we can make PHYSDEVOP_irq_eoi obsolete? It's
only really called where we also do an unmask, and it's pointless to have
two hypercalls where one will do. So a guest that detects the new bitmap
could then know it only needs to unmask-by-hypercall, rather than use
PHYSDEVOP_irq_eoi at all.

That would at least make me happier about your approach. :-)

 -- Keir



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