RE: [kvm-devel] [RFC] Deferred interrupt handling.

[Dor Laor]

>Alan Cox wrote:
>>> What if we will force the specific device to the end of the list.
>Once
>>> IRQ_NONE was returned by the other devices, we will mask the irq,
>>> forward the irq to the guest, issue a timer for 1msec. Motivation:
>>> 1msec is long enough for the guest to ack the irq + host unmask the
>irq
>>>
>>
>> It makes no difference. The deadlock isn't fixable by timing hacks.
>> Consider the following sequence
>>
>>
>> 	Guest0	-	blocked on I/O
>>
>> 	IRQ14 from your hardware
>> 		Block IRQ14
>> 		Sent to guest (guest is blocked)
>>
>> 	IRQ14 from hard disk
>> 		Ignored (as blocked)
>>


But now the timer will pop and the hard disk will get its irq.
The guest will be released right after.

>> 	Deadlock
>>
>
>IMO the only reasonable solution is to disallow interrupt forwarding
>with shared irqs.  If someone later comes up with a bright idea, we can
>implement it.  Otherwise the problem will solve itself with hardware
>moving to msi.
>

I though of that but the problem is that we'd like to use it with
current hardware
devices that are shared.
:(
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