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

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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)
> 	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.

Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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