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Re: [Xen-devel] [PATCH v3 10/13] xen/iommu: smmu: Check for duplicate stream IDs when registering master devices

On 20/02/15 12:35, Ian Campbell wrote:
> On Fri, 2015-01-30 at 18:49 +0000, Julien Grall wrote:
>> From: Andreas Herrmann <andreas.herrmann@xxxxxxxxxxx>
>> If DT information lists one stream ID twice for the master devices of
>> an SMMU this can cause a multi match when stream ID matching is used.
>> For stream ID indexing this might trigger an overwrite of an S2CR that
>> is already in use.
>> So better check for duplicates when DT information is parsed.
>> Taken from the linux ML:
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-January/226099.html
>> Cc: Andreas Herrmann <herrmann.der.user@xxxxxxxxxxxxxx>
>> Signed-off-by: Andreas Herrmann <andreas.herrmann@xxxxxxxxxxx>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> I think you were going to drop this one as it is not strictly required?
> I'm still not entirely clear on the motivation for this patch, looking
> at the v2 thread I see "But, the developer made have written by mistake
> twice the streamid for the device." which I think you were saying that
> the DT might, hypothetically, be wrong and have duplicated IDs, is that
> right?
> Is it a hypothetical problem or have we seen it in a real device-tree?

It's an hypothetical problem. The algo on the next patch won't work
correctly otherwise.

I may need to rework a bit the next patch if we drop it.


Julien Grall

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