Re: [PATCH 00 of 14] swiotlb/x86: lay groundwork for xen dom0 use of swiotlb

[Jeremy Fitzhardinge <jeremy@goop.org>]

Becky Bruce wrote:
> 32-bit powerpc needs this support - I was actually about to push a 
> similar set of patches.  We have several processors that support 36 
> bits of physical address space and do not have any iommu capability.  
> The rest of the kernel support for those processors is now in place, 
> so swiotlb is the last piece of the puzzle for that to be fully 
> functional.  I need to take a closer look at this series to see 
> exactly what it's doing and how it differs from what I've been testing.
>
> So there is another immediate use case, and I'd really hate to see 
> this code duplicated.  It should be entirely possible to remove the 
> assumption that we can save off the VA of the original buffer, which 
> is the thing that precludes HIGHMEM support, and still have nice 
> readable, maintainable code.

Good, I'm glad I'm not just making things up ;)

The gist of the patch is to convert all the kernel virtual addresses 
into struct page+offset.  It's a fairly generic way to handle highmem 
systems, so it should work for you too.  Of course, if you have a 
cleaner patch to achieve the same result, then we evaluate that too.

    J