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Re: [Xen-devel] [PATCH][RFC] pv-ops: fix shared irq device passthrough

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH][RFC] pv-ops: fix shared irq device passthrough
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 10 Nov 2009 10:44:59 -0800
Cc: "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, "'xen-devel@xxxxxxxxxxxxxxxxxxx'" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Han, Weidong" <weidong.han@xxxxxxxxx>, "'keir.fraser@xxxxxxxxxxxxx'" <keir.fraser@xxxxxxxxxxxxx>
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On 11/10/09 08:30, Konrad Rzeszutek Wilk wrote:
> With this patch you can share the PCI devices on the same IRQ, correct? Will
> this mean that you can assign to a guest a USB controller, while
> Dom0 has controller of the PCI NIC (and assuming that both of those
> share the same interrupt line)? If so, won't the Dom0 start throwing
> a fit b/c there are unhandled IRQs and eventually disable the IRQ line?
> Or even the guest decide that there are too many IRQs and decided to
> disable the IRQ line?

It would be easy to add a dummy handler which always returns IRQ_HANDLED
for every cross-domain shared interrupt to prevent this.  Of course that
would paper over any real spurious/screaming interrupt problem, but we
could add some extra logic into the dummy handler if necessary.

I merged the patch, and had to add the new parameter to
xen_allocate_pirq() in arch/x86/pci/xen.c.  I just made it 0 which
should have no functional difference from before, but I'll leave it to
you to decide what it really should be.


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