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Date: Mon, 17 Nov 2008 09:15:48 +0000 From: "Jan Beulich" <jbeulich@...ell.com> To: "Jeremy Fitzhardinge" <jeremy@...p.org> Cc: "Ian Campbell" <ian.campbell@...rix.com>, "Ingo Molnar" <mingo@...e.hu>, "the arch/x86 maintainers" <x86@...nel.org>, "Xen-devel" <xen-devel@...ts.xensource.com>, <linux-kernel@...r.kernel.org> Subject: Re: [Xen-devel] [PATCH 03 of 38] swiotlb: allow architectures tooverrideswiotlb pool allocation >>> Jeremy Fitzhardinge <jeremy@...p.org> 14.11.08 20:33 >>> >Jan Beulich wrote: >> Not directly related to this patch alone, but to the combined set of changes >> to swiotlb: I don't see any handling of CONFIG_HIGHMEM here (or at least >> a note that this a known limitation needing work). I mention this because >> this was the largest part of the changes I had posted long ago to make >> lib/swiotlb.c Xen-ready, and which got rejected due to their ugliness. >> > >Was that Andi's objection on the grounds that he didn't think that Xen >should need swiotlb at all? No, Tony Luck actually merged it, but someone else (I don't recall who it was) requested it to be reverted again. >I have to admit I didn't follow that thread very closely (or threads, as >I seem to remember). Do you have a pointer to the pertinent bits? http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=51099005ab8e09d68a13fea8d55bc739c1040ca6 >> While perhaps less intrusive to take care of, I also didn't see an equivalent >> of the range_straddles_page_boundary() logic, without which I can't see >> how this would work in the common case. >> >Could you be more specific? The swiotlb allocation should be machine >contiguous and so there's no stradding required, but I think I'm missing >your point. The question is whether a multi-page piece of memory must be funneled through the swiotlb in the first place. In native code, checking whether the first/last byte satisfies the address_needs_mapping() check is sufficient, but in Xen you also need to check whether the known to be physically contiguous pages are also machine-contiguous. Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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