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Re: [Xen-devel] [early RFC] ARM PCI Passthrough design document

Hi Stefano,

On 10/02/17 01:01, Stefano Stabellini wrote:
On Fri, 3 Feb 2017, Edgar E. Iglesias wrote:
A possible hack could be to allocate a chunk of DDR dedicated for PCI DMA.
PCI DMA devs could be locked in to only be able to access this mem + MSI 
Guests can still screw each other up but at least it becomes harder to 
read/write directly from each others OS memory.
It may not be worth the effort though....

Actually, we do have the swiotlb in Dom0, which can be used to bounce
DMA requests over a buffer that has been previously setup to be DMA safe
using an hypercall. That is how the swiotlb is used on x86. On ARM it is
used to issue cache flushes via hypercall, but it could be adapted to do
both. It would degrade performance, due to the additional memcpy, but it
would work, I believe.

A while ago, Globallogic suggested to use direct memory mapping for the guest to allow guest using DMA on platform not supporting SMMU.

I believe we can use the same trick on platform where SMMUs can not distinguish PCI devices.


Julien Grall

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