Re: [Xen-devel] Question about swiotlb-xen driver

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 3 Dec 2013, Stefano Stabellini wrote:
> On Tue, 3 Dec 2013, Ian Campbell wrote:
> > On Tue, 2013-12-03 at 16:11 +0200, Andrii Tseglytskyi wrote:
> > > Hi Stefano,
> > > 
> > > 
> > > Could you please answer, is swiotlb-xen driver designed to work on
> > > DomU kernel? 
> > 
> > No. DomU device assignment will require an IOMMU I'm afraid.
> 
> The swiotlb-xen driver is designed to make DMA transactions safe in Dom0
> as we don't have IOMMU support in Xen yet.

FYI you could modify it to run in a DomU without too much trouble, but I
wouldn't recommend it because:

- you would still need to trust the DomU as much as you trust Dom0
because it could read/write all the RAM via DMA. At this point you loose
most of the benefit of running the driver in a separate VM.

- It would be slow because you would need to bounce all the DMA requests
on the swiotlb buffer (this could be worked around with another 1:1
mapping, but at this point you loose even more flexibility, your DomU
wouldn't probably be able even to restart).

So yes, it is only for Dom0 at the moment :-)

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