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[159.2.239.150]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93be0cc67e6sm187224885a.5.2026.09.18.10.05.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2026 10:05:25 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1x7c1c-00000001zVZ-3Nwz; Fri, 18 Sep 2026 14:05:24 -0300 Date: Fri, 18 Sep 2026 14:05:24 -0300 From: Jason Gunthorpe To: Thomas =?utf-8?Q?Hellstr=C3=B6m?= Cc: Leon Romanovsky , Bjorn Helgaas , Logan Gunthorpe , Chaitanya Kulkarni , Greg Kroah-Hartman , Jens Axboe , Alex Williamson , Ankit Agrawal , Jonathan Corbet , Shuah Khan , "Joerg Roedel (AMD)" , Will Deacon , Robin Murphy , Randy Dunlap , Sumit Semwal , Christian =?utf-8?B?S8O2bmln?= , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, iommu@lists.linux.dev, Tushar Dave , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-rdma@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v6 18/18] RDMA/mlx5: Ask P2PDMA whether ATS takes a direct peer-to-peer route Message-ID: <20260918170524.GH11599@ziepe.ca> References: <20260914-fix-p2p-acs-v4-0-v6-0-5ef07ec9ef06@nvidia.com> <20260914-fix-p2p-acs-v4-0-v6-18-5ef07ec9ef06@nvidia.com> <321890690ce83d1943b2f678bd9bee9b8c895b66.camel@linux.intel.com> <20260918121500.GV13683@unreal> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Sep 18, 2026 at 03:42:28PM +0200, Thomas Hellström wrote: > > 1) Xe attachment check if pci_p2pdma_distance() returns OK for the > path. Then Xe always sets up dma-addresses using dma_map_resource(). Open coding pci_p2pdma_distance() in drivers is a hack. Using dma_map_resource() like this was never "allowed". We've fixed things so these hacks are not needed, the drivers need to move over to things like dma_buf_phys_vec_to_sgt() and the hmm helpers to use the DMA API correctly. > 1a) Let's say the importer (Xe) has ATS enabled, and the exporter is > supposed to map dma_addresses. > In between there is a switch that allows direct traffic. > Now with your patch series, How would the exporter know that Xe has ATS > enabled and therefore should return IOVA mappings rather than the BUS > addresses representing the shortcut. The thing that does the DMA map must be aware of what PCI TLPs the PCIe initiator will use to compute the proper P2P mapping mode. ATS always needs an IOVA but that still doesn't mean the P2P will work. > It seems to me that a pci-device settable flag "ATS always enabled" > should be enough to fix both issues? It should be be per-mapping to support the NIC workflow that isn't a global operation. Jason