From: Robin Murphy Subject: Re: DMA error when sg->offset value is greater than PAGE_SIZE in Intel IOMMU Date: Wed, 20 Sep 2017 11:12:08 +0100 Message-ID: <26992a1e-edb3-ed78-ce8e-31e0739d75f4@arm.com> References: <20170920080151.GA3348@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: leedom@chelsio.com, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, linux-crypto@vger.kernel.org, dwmw2@infradead.org To: Herbert Xu , Harsh Jain Return-path: In-Reply-To: <20170920080151.GA3348@gondor.apana.org.au> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On 20/09/17 09:01, Herbert Xu wrote: > Harsh Jain wrote: >> >> While debugging DMA mapping error in chelsio crypto driver we observed that when scatter/gather list received by driver has some entry with page->offset > 4096 (PAGE_SIZE). It starts giving DMA error.  Without IOMMU it works fine. > > This is not a bug. The network stack can and will feed us such > SG lists. > >> 2) It cannot be driver's responsibilty to update received sg entries to adjust offset and page >> because we are not the only one who directly uses received sg list. > > No the driver must deal with this. Having said that, if we can > improve our driver helper interface to make this easier then we > should do that too. What we certainly shouldn't do is to take a > whack-a-mole approach like this patch does. AFAICS this is entirely on intel-iommu - from a brief look it appears that all the IOVA calculations would handle the offset correctly, but then __domain_mapping() blindly uses sg_page() for the physical address, so if offset is larger than a page it would end up with the DMA mapping covering the wrong part of the buffer. Does the diff below help? Robin. ----->8----- diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c index b3914fce8254..2ed43d928135 100644 --- a/drivers/iommu/intel-iommu.c +++ b/drivers/iommu/intel-iommu.c @@ -2253,7 +2253,7 @@ static int __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn, sg_res = aligned_nrpages(sg->offset, sg->length); sg->dma_address = ((dma_addr_t)iov_pfn << VTD_PAGE_SHIFT) + sg->offset; sg->dma_length = sg->length; - pteval = page_to_phys(sg_page(sg)) | prot; + pteval = (sg_phys(sg) & PAGE_MASK) | prot; phys_pfn = pteval >> VTD_PAGE_SHIFT; }