From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH 07/20] iommu/amd: Remove special mapping code for dma_ops path Date: Tue, 12 Jul 2016 13:08:39 +0200 Message-ID: <20160712110839.GF12639@8bytes.org> References: <1467978311-28322-1-git-send-email-joro@8bytes.org> <1467978311-28322-8-git-send-email-joro@8bytes.org> <5784CCAB.8000007@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <5784CCAB.8000007@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Robin Murphy Cc: iommu@lists.linux-foundation.org, Vincent.Wan@amd.com, Joerg Roedel , linux-kernel@vger.kernel.org List-Id: iommu@lists.linux-foundation.org Hi Robin, On Tue, Jul 12, 2016 at 11:55:39AM +0100, Robin Murphy wrote: > > start = address; > > for (i = 0; i < pages; ++i) { > > - ret = dma_ops_domain_map(dma_dom, start, paddr, dir); > > - if (ret == DMA_ERROR_CODE) > > + ret = iommu_map_page(&dma_dom->domain, start, paddr, > > + PAGE_SIZE, prot, GFP_ATOMIC); > > I see that amd_iommu_map/unmap() takes a lock around calling > iommu_map/unmap_page(), but we don't appear to do that here. That seems > to suggest that either one is unsafe or the other is unnecessary. At this point no locking is required, because in this code path we know that we own the memory range and that nobody else is mapping that range. In the IOMMU-API path we can't make that assumption, so locking is required there. Both code-path use different types of domains, so there is also no chance that a domain is used in both code-paths (except when a dma-ops domain is set up). Joerg