Messages in this thread | | | Date | Mon, 29 Sep 2008 12:30:44 +0300 | From | Muli Ben-Yehuda <> | Subject | Re: [PATCH 9/9] x86/iommu: use dma_ops_list in get_dma_ops |
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On Sun, Sep 28, 2008 at 09:13:33PM +0200, Joerg Roedel wrote:
> I think we should try to build a paravirtualized IOMMU for KVM > guests. It should work this way: We reserve a configurable amount > of contiguous guest physical memory and map it dma contiguous using > some kind of hardware IOMMU. This is possible with all hardare > IOMMUs we have in the field by now, also Calgary and GART. The guest > does dma_coherent allocations from this memory directly and is done. > For map_single and map_sg > the guest can do bounce buffering. We avoid nearly all pvdma hypercalls > with this approach, keep guest swapping working and solve also the > problems with device dma_masks and guest memory that is not contigous on > the host side.
I'm not sure I follow, but if I understand correctly with this approach the guest could only DMA into buffers that fall within the range you allocated for DMA and mapped. Isn't that a pretty nasty limitation? The guest would need to bounce-bufer every frame that happened to not fall inside that range, with the resulting loss of performance.
Cheers, Muli -- The First Workshop on I/O Virtualization (WIOV '08) Dec 2008, San Diego, CA, http://www.usenix.org/wiov08/ xxx SYSTOR 2009---The Israeli Experimental Systems Conference http://www.haifa.il.ibm.com/conferences/systor2009/
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