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Re: [Xen-devel] [PATCH v4 0/3] Set SMMU s2 input-size based on p2m tables

On Wed, 2015-05-06 at 19:17 +1000, Edgar E. Iglesias wrote:
> > Right, it seems like we may eventually need to introduce the possibility
> > of not sharing the p2m depending on the circumstances as is done on x86.
> Yes. How would that work in practice? I guess some of the guests memory space
> would not be DMA:able? or would we allow some kind of dynamic mapping
> driven from the guest?

For domU with passthrough enabled there would be a limitation on the
maximum usable IPA I suppose.

For dom0 it's a bit trickier, but I think the answer is basically that
on systems with insufficiently large SMMU support and peripherals or RAM
above the SMMU's limit we wouldn't be able to take advantage of the SMMU
protections and would be stuck with e.g. 1:1 mode. If it was only RAM
and not peripherals up high then perhaps we could trade off use of SMMU
vs dom0 RAM size.


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