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

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Message-ID: <20070718174736.0baf6d0e@the-village.bc.nu>
Date:	Wed, 18 Jul 2007 17:47:36 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"Dor Laor" <dor.laor@...ranet.com>
Cc:	"Or Sagi" <ors@...is.com>, <kvm-devel@...ts.sourceforge.net>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [kvm-devel] [RFC] Deferred interrupt handling.

> 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

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