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

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Subject: Re: [Xen-devel] Xen, IRQ-sharing and PCI passthrough
From: Florian Wagner <f_wagner@xxxxxxxxxx>
Date: Wed, 8 Jul 2009 08:35:13 +0200
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> Assuming your kernel has a call to irq_ignore_unhandled() out of
> note_interrupt(), [...]

Judging from my backtrace this seems to be the case, right?

> [...] there's nothing but using hardware's help (i.e. VT-d
> interrupt remapping) to get this addressed: The pv passthrough
> mechanism assumes that guests you assign physical devices to are well
> behaved, and your guest isn't (it fails to disable the interrupt at
> the device).

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

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.



Florian Wagner
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Syscomp Biochemische Dienstleistungen GmbH
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