From: Joerg Roedel Subject: Re: [PATCH] iommu/vt-d: Fix scatterlist offset handling Date: Fri, 6 Oct 2017 16:43:09 +0200 Message-ID: <20171006144309.GA30803@8bytes.org> References: <644c3e01654f8bd48d669c36e424959d6ef0e27e.1506607370.git.robin.murphy@arm.com> <1507035334.29211.105.camel@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Woodhouse , ashok.raj@intel.com, leedom@chelsio.com, Harsh@chelsio.com, herbert@gondor.apana.org.au, iommu@lists.linux-foundation.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: Robin Murphy Return-path: Received: from 8bytes.org ([81.169.241.247]:39360 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751491AbdJFOnL (ORCPT ); Fri, 6 Oct 2017 10:43:11 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-crypto-owner@vger.kernel.org List-ID: On Tue, Oct 03, 2017 at 07:05:17PM +0100, Robin Murphy wrote: > Now, there are indeed plenty of drivers and subsystems which do work on > lists of explicitly single pages - anything doing some variant of > "addr = kmap_atomic(sg_page(sg)) + sg->offset;" is easy to spot - but I > don't think DMA API implementations are in a position to make any kind > of assumption; nearly all of them just shut up and handle sg->length > bytes from sg_phys(sg) without questioning the caller, and I reckon > that's exactly what they should be doing. I agree with that, it is not explicitly forbidden to have an sg->offset > PAGE_SIZE and most IOMMU drivers handle this case. So this is a problem I'd like to see resolved in the VT-d driver too. If nobody comes up with a correct fix soon I'll apply this one and rip out the large-page support from __domain_mapping() to make it work. Speaking of __domain_mapping(), this function is a big unmaintainable mess which should be split and rewritten. A clean and maintainable rewrite can alse re-add the large-page support. Regards, Joerg