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

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.


Julien Grall

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