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

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Date:	Thu, 18 Dec 2008 12:09:13 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Becky Bruce <beckyb@...nel.crashing.org>
CC:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	xen-devel@...ts.xensource.com, x86@...nel.org,
	ian.campbell@...rix.com, jbeulich@...ell.com, joerg.roedel@....com,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 00 of 14] swiotlb/x86: lay groundwork for xen dom0 use
 of swiotlb

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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