On 20/09/17 09:01, Herbert Xu wrote: > Harsh Jain <Harsh@xxxxxxxxxxx> 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; }
