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Re: [Xen-devel] Xen, IRQ-sharing and PCI passthrough

To: Florian Wagner <f_wagner@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Xen, IRQ-sharing and PCI passthrough
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 08 Jul 2009 08:31:29 +0100
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On 08/07/2009 07:35, "Florian Wagner" <f_wagner@xxxxxxxxxx> wrote:

> Do I understand this correctly: For safe operation of a virtual machine
> using PCI passthrough and shared interrupts a well behaved operating
> system in the vm is necessary. That is an OS that shuts down the mapped
> devices correctly before turning off (unload kernel module).
> So what am I to to in the case that someone issues a "xm destroy" on
> such a vm? There is no way to cleanly shutdown in such a situation, is
> there?
> That's quite a risk for system stability of the host. One thoughtless
> "xm destroy" and the whole host is crashed, requiring at a minimum a
> cold reset or even a reinstall.

We're probably missing a device reset somewhere during domain destruction.
Or it may be happening too late. Still there is a limit to VM isolation when
IRQs are shared. The best bet is to use MSI, if one of your devices supports
it. That would require Xen 3.4.

 -- Keir

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