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[142.68.128.5]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7b32acb0496sm718091885a.89.2024.11.13.10.41.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Nov 2024 10:41:30 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1tBIIz-000000011lJ-0zht; Wed, 13 Nov 2024 14:41:29 -0400 Date: Wed, 13 Nov 2024 14:41:29 -0400 From: Jason Gunthorpe To: Christoph Hellwig Cc: Robin Murphy , Leon Romanovsky , Jens Axboe , Joerg Roedel , Will Deacon , Sagi Grimberg , Keith Busch , Bjorn Helgaas , Logan Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , Marek Szyprowski , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Andrew Morton , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, matthew.brost@intel.com, Thomas.Hellstrom@linux.intel.com, brian.welty@intel.com, himal.prasad.ghimiray@intel.com, krishnaiah.bommu@intel.com, niranjana.vishwanathapura@intel.com Subject: Re: [PATCH v1 00/17] Provide a new two step DMA mapping API Message-ID: <20241113184129.GA173265@ziepe.ca> References: <20241105195357.GI35848@ziepe.ca> <20241107083256.GA9071@lst.de> <20241107132808.GK35848@ziepe.ca> <20241107135025.GA14996@lst.de> <20241108150226.GM35848@ziepe.ca> <20241108150500.GA10102@lst.de> <20241108152537.GN35848@ziepe.ca> <20241108152956.GA12130@lst.de> <20241108153846.GO35848@ziepe.ca> <20241112060108.GA10056@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241112060108.GA10056@lst.de> X-Rspamd-Queue-Id: 9702620006 X-Stat-Signature: trzk3zk3u5gcsn8kj4numh1jcd1134rf X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1731523247-54253 X-HE-Meta: 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 z5Ot/jYF ZPSDpElodowEMrXYjPEdk7m9zaNfGwDWTIoDbc9wGDNZVDvbSMAuePKLwOJA0J8WyHqoRoqgnPp+upV1mWJ5TBnH+hGcobMjRLSQsSKpaetondF9LCVKWfXYmUBftW0xZ5/eX5h3IfZkOj07BeFpRVZllLsRYDTwZ9GC+56hZ00uDtrbwaSpbSyss21SX9yLhOQks0k3T1xVBtjClTBPT+92DFTxsTInzb35J6w/LXBTkSMr0tn8yUYXvQ3zvPSbhAqdGyQKDNMrelIsfOvUDKoL0mpYuN4ScpqSf X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Nov 12, 2024 at 07:01:08AM +0100, Christoph Hellwig wrote: > On Fri, Nov 08, 2024 at 11:38:46AM -0400, Jason Gunthorpe wrote: > > > > What I'm thinking about is replacing code like the above with something like: > > > > > > > > if (p2p_provider) > > > > return DMA_MAPPING_ERROR; > > > > > > > > And the caller is the one that would have done is_pci_p2pdma_page() > > > > and either passes p2p_provider=NULL or page->pgmap->p2p_provider. > > > > > > And where do you get that one from? > > > > Which one? > > The p2p_provider thing (whatever that will actually be). p2p_provider would be splitting out the information in pci_p2pdma_pagemap to it's own type: struct pci_p2pdma_pagemap { struct pci_dev *provider; u64 bus_offset; That is the essential information to compute PCI_P2PDMA_MAP_*. For example when blk_rq_dma_map_iter_start() calls pci_p2pdma_state(), it has this information from page->pgmap. It would still have the information via the pgmap when we split it out of the pci_p2pdma_pagemap. Since everything doing a dma map has to do the pci_p2pdma_state() to compute PCI_P2PDMA_MAP_* every dma mapping operation has already got the provider. Since everything is uniform within a mapping operation the provider is constant for the whole map. For future non-struct page cases the provider comes along with the address list from whatever created the address list in the first place. Looking at dmabuf for example, I expect dmabuf to provide a new data structure which is a list of lists: [[provider GPU: [mmio_addr1,mmio_addr2,mmio_addr3], [provider NULL: [cpu_addr1, cpu_addr2, ...], .. ] And each uniform group would be dma map'd on its own using the embedded provider instead of page->pgmap. Jason