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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.11.12 at 13:08, Dario Faggioli <dario.faggioli@xxxxxxxxxx> wrote:
> 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?

They are, but that only means Xen stays alive. Dom0 might
still not get a chance to run if there's a flood of them.

Jan


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