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Re: [Xen-devel] [RFC 12/19] xen/passthrough: iommu_deassign_device_dt: By default reassign device to nobody

On Thu, 2014-07-03 at 14:01 +0100, Julien Grall wrote:
> On 07/03/2014 01:53 PM, Ian Campbell wrote:
> > On Thu, 2014-07-03 at 13:07 +0100, Julien Grall wrote:
> >>>> If Xen reassigns the device to "nobody", it may receive some 
> >>>> global/context
> >>>> fault because the transaction has failed (indeed the context has been
> >>>> marked invalid).
> >>>
> >>> Can you describe here what happen in this case (I presume Xen tears down
> >>> the iommu to quiesce them somehow?)
> >>
> >> The SMMU drivers will mark the different Context Bank, S2CR, SMR as
> >> invalid. If the device is attempt to access the memory then, we will
> >> receive an interrupt in Xen.
> >>
> >> Actually it's only happen once, if the device is still enabled when the
> >> domain is shutdown.
> > 
> > My concern was with getting a storm of such interrupts after this point.
> > If it only happens once and any subsequent ones are damped by some means
> > then great.
> I guess, it can happen with a buggy device trying to access memory
> alone. But I don't think we should care about this case.

Ideally such a device wouldn't be able to DoS the rest of the system.

Does the SMMU not have a bit to say: deny all MMIO from this context
without raising an exception?


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