Re: [Xen-devel] [PATCH] IOMMU: don't disable bus mastering on faults for devices used by Xen or Dom0

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Tue, 2012-11-06 at 13:58 +0000, Tim Deegan wrote:
> > It helps keeping Xen alive, but doesn't for any specific domain
> > (including Dom0).
> 
> Indeed.  (Intel) IOMMU interrupts are suppressed until the softirq
> handler acknowledges the error, but if the softirq handler doesn't
> disable the device, it will take another IOMMU interrupt immediately.
>
Right. I wasn't considering the possibility of this 'back-to-back'
variant of the thing.

> I thought the AMD side behaved eth same but clearly not -- I'll try to
> take a look at that later in the week.
> 
I think it does, or at least, I'm quite sure when I moved the fault
handling code in softiq context, I did it so that behavior was
consistent wrt both Intel and AMD (by explicitly silencing interrupts
until within the tasklet), at least for faults.

PPR came later and I moved them within the softirq as well after asking
AMD people, without having the possibility to test that myself.

So, to recap, feel free to check. Faults should behave as you're
describing, PPR I'm not sure. :-)

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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