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Re: [Xen-devel] Does xc_map_foreign_pages() update IOMMU tables?

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Does xc_map_foreign_pages() update IOMMU tables?
From: Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 13 May 2010 14:09:45 +0200
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On 05/13/2010 02:00 PM, Keir Fraser wrote:
> On 13/05/2010 12:48, "Joanna Rutkowska" <joanna@xxxxxxxxxxxxxxxxxxxxxx>
> wrote:
>> Does the xc_map_foreign_pages() update also the IOMMU/VT-d tables so
>> that the mapped pages belong also to Dom0 (from the IOMMU point of view)?
> Seeing as how xc_map_foreign_pages() maps pages into a particular
> guest-process virtual address space, whereas IOMMU tables are a mapping from
> guest-physical address space, it's clear that x_m_f_p() cannot sensibly be
> having any effect on the IOMMU.
Interesting. That suggests the graphics drivers we tested do not use DMA
for XShmPutImage()...

Anyway, what would be the recommend way of updating IOMMU mappings in
this case? Would you consider patching of x_m_f_p() an acceptable
solution? (perhaps with some additional flag: "update_iommu")?


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