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[Xen-devel] Re: [PATCH 00 of 14] swiotlb/x86: lay groundwork for xen dom

To: Becky Bruce <beckyb@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 00 of 14] swiotlb/x86: lay groundwork for xen dom0 use of swiotlb
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Thu, 18 Dec 2008 12:09:13 -0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, ian.campbell@xxxxxxxxxx, joerg.roedel@xxxxxxx, x86@xxxxxxxxxx, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx>, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>
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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


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