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Re: [Xen-devel] [PATCH] xen/arm: Let the IOMMU be accessible by Dom0 if forcibly disabled in Xen

On 08.08.19 14:01, Roger Pau Monné wrote:

Hi, Roger.

On Thu, Aug 08, 2019 at 01:53:23PM +0300, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

Don't skip IOMMU nodes when creating DT for Dom0 if IOMMU has been
forcibly disabled in bootargs (e.g. "iommu=0") in order to let
the IOMMU be accessible by DOM0.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
I have heard there is a "possible" case when the IOMMU could be accessible by 
So, I think, for this to work we need to create corresponding DT nodes in the DT
at least.
dom0 on ARM being an autotranslated guest I'm not sure how it's going
to program the DMA remapping in the iommu, since it doesn't know the
mfns of the memory it uses at all, hence I don't see the point in
exposing the hardware iommu to dom0 unless there's some emulation done
to make dom0 able to access it.

Currently, Dom0 on ARM is always 1:1 mapped (gfn == mfn). However, I don't really know how long this assumption it is going to be true.

Being honest, I don't need this use-case at the moment. I have experimented with the code which creates DT nodes for Dom0 a bit, and recollected

about the possibility for the IOMMU to be accessible by Dom0. If this patch doesn't have any real value, I would be ok to just drop it.

Thanks, Roger.


Oleksandr Tyshchenko

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