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Re: [Xen-devel] VP problematic for backend drivers on IA64?

On Tue, Jan 24, 2006 at 04:02:36PM -0800, Magenheimer, Dan (HP Labs Fort 
Collins) wrote:

> Actually, after thinking about this, it's a bit
> more complicated because of the possibility that a DMA may
> address more than one page.  If so, a simple DMA may need to be
> translated into a scatter-gather (or a scatter-gather into
> a more complex scatter-gather).
> Not impossible, obviously because Xen/x86 handles this -- by
> changing Linux, correct?

Correct. Specifically, it's handled by Xen's version of swiotlb.c.

> Do hardware IOMMU's in general handle this complication?

Yes. You can use a HW IOMMU to map a scatter-gather list of machine
pages into a contigous range in the IO space. It can also do the
reverse, but that's less interesting.

> E.g. is there a cleanly defined interface that can be applied
> to a VP domain "Xen IOMMU"?

I'm not sure what you're asking here?

Muli Ben-Yehuda
http://www.mulix.org | http://mulix.livejournal.com/

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