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 14:17 +0000, Jan Beulich wrote:
> > 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.
> > 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 don't think AMD's behaves much different, it's just that for the
> PPR case nothing is being done in that regard (and it's unclear
> whether or under what circumstances a high rate of these could
> occur).
> 
Indeed. I just double checked the code and yes, both faults and PPRs are
handled that way, and new interrupts are disabled until the tasklet
handles the request and re-enables them.

The difference, as Jan is saying, is there is no PPR equivalent of
disabling bus mastering that can ensure livelock safeness when it comes
to them.

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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