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 10:19 +0000, Jan Beulich wrote:
> > This check is really there to stop a mad device from hosing the system
> > rather than to contain a malicious OS, and a properly out-of-control
> > device needs to be stopped or it will livelock Xen with iommu faults.
> > In a uniprocessor system, dom0 might never get the chance to fix it.
> 
> If that's the main goal, then on the AMD side the code may not do
> what you want it to: PPR log entries, causing interrupts too, don't
> get limited/suppressed in any way, yet are obviously to some
> extent under guest control.
> 
IIRC, PPR are dealt with in softirq context too, aren't they?

> But yes, for the purpose here limiting the fault rate in some way
> (with a slightly higher limit for Dom0 than DomU-s) would indeed
> be the better route.
> 
BTW, yes, independently from the above and for what it counts, I agree
with this.

Regards,
Dario

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

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