Re: [Xen-devel] Re: ATI radeon fails with "iommu=soft swiotlb=force" (seen on RV730/RV740 and RS780/RS800)

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Jeremy Fitzhardinge <jeremy@xxxxxxxx> 05.10.09 21:09 >>>
>vmalloc_32 is a general problem.  The only clean way I can see to make
>it work under Xen is to make sure all the pages in the DMA32 zone are
>really under 4G in machine addresses.  But that doesn't scale very well

Why? Just adding a hook in vmalloc.c would do.

>if you have more than one domain wanting to use vmalloc_32 for hardware
>access (or a few small domains).

That's why noted that doing this for the whole zone is likely overkill.

>I'm wondering if the "proper" fix is to introduce a vmalloc_dma() call
>which allocates the pages with the proper DMA API calls them maps them
>together in the vmalloc space, and then start migrating drivers over to
>this new API (ie as needed when people report Xen problems).  That would
>be more generally correct, but perhaps it would be a bit more cumbersome
>because it would have to return both the vaddr of the vmapping, and the
>dma_addr_t array, so that vfree_dma() can make the proper
>dma_free_coherent calls.

Hmm, yes, but the more cumbersome an API is to use, the less likely it
is that people would want to adopt using it (or that it would be mergable
in the first place)).

Jan


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