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

[Julien Grall <julien.grall@xxxxxxxxxx>]

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 
> > doorbell.
> > 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.
Cheers,

--
Julien Grall

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