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Tue, 06 Oct 2026 18:32:12 -0700 (PDT) Received: from 127.mynet ([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a17f6538b7sm21183615e9.13.2026.10.06.18.32.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Oct 2026 18:32:11 -0700 (PDT) From: Pavel Begunkov To: linux-block@vger.kernel.org Cc: asml.silence@gmail.com, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, Christoph Hellwig , Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= , Keith Busch , Sagi Grimberg , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , Jens Axboe , Nitesh Shetty , Kanchan Joshi , Anuj Gupta , Tushar Gohad , William Power , Matthew Brost , Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , dm-devel@lists.linux.dev Subject: [PATCH v8 00/13] Add dmabuf read/write via io_uring Date: Wed, 7 Oct 2026 02:31:43 +0100 Message-ID: X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The patch set allows to register a dmabuf to an io_uring instance for a specified file and use it with io_uring read / write requests. The infrastructure is not tied to io_uring and there could be more users in the future. A similar idea was attempted some years ago by Keith [1], from where I borrowed a number of changes. Later it was brough back up to life by Tushar and Vishal. It's an opt-in feature for files, and they need to implement a new file operation to use it. Only NVMe block devices are supported in this series. The user API is built on top of io_uring's "registered buffers", where a dmabuf is registered in a special way, but after it can be used as any other "registered buffer" with IORING_OP_{READ,WRITE}_FIXED requests. It's created via a new file operation and the resulted map is then passed through the I/O stack in a new iterator type. There is some additional infrastructure to glue it together, count requests, manage lifetime and implement invalidation. Tushar, William, Phil did a lot of testing and experimentation on various devices with previous versions of the patch set, and I've received lots of help from Anuj, Kanchan and Nitesh with investigations, testing, and patching. Earlier benchmarks by Anuj for IOMMU optimisations with udmabuf showed: STRICT: before = 570 KIOPS, after = 5.01 MIOPS LAZY: before = 1.93 MIOPS, after = 5.01 MIOPS PASSTHROUGH: before = 5.01 MIOPS, after = 5.01 MIOPS # Patch set structure: - Patches 1-2 introduce internal API and infrastructure mediating io_uring and target subsystem / devices - Patches 3-5: block layer support + prep patches - Patches 6-8 implement NVMe support - Patches 9-13 add io_uring support and uapi. There are some liburing tests that can serve as an example: git: https://github.com/isilence/liburing.git rw-dmabuf-tests-v8 url: https://github.com/isilence/liburing/tree/rw-dmabuf-tests-v8 The patches are based on Jens' for-next. Also available as a branch: git: https://github.com/isilence/linux.git rw-dmabuf-v8 url: https://github.com/isilence/linux/tree/rw-dmabuf-v8 [1] https://lore.kernel.org/io-uring/20220805162444.3985535-1-kbusch@fb.com/ v8: - fix blkdev_buffered_write() returning 0 - fix kvmalloc-kfree mismatch - fix invalidation hang - remove cpu dma sync as unnecessary for dev-to-dev transfers - move nvme dma-buf code into a new file - tighten dma-buf [re]export around io_uring issue - simplify dma-buf-io locking/sync as proposed by Matthew Brost v7: - refcount *_io_ctx - wait rcu grace period for ctx->map before freeing maps - increment map counters under dma resv lock - more comments about bio splitting - make ->unmap responsible for freeing maps to match ->map - replace dma_sync_single* with full table sync - detach dma-buf on nvme reset after cancel nvme_cancel_tagset v6: - remove fences and wait on invalidation synchronously - report all map requests are detached earlier, outside of wq - handle nvme removal - gate nvme_free_descriptors() on iod->nr_descriptors - fix error handling in nvme_rq_setup_dmabuf_map() - fix iov_iter_alignment() - relax the 1G io_uring registered dma-buf limit - fix type overflow issue in bio split - allocate struct dma_buf_io_ctx inside the dma-buf-io code - harden block checks against dma-buf + buffered io v5: - Reject dma-buf with buffered IO for raw bdev - Add lim->max_segments bio splitting - Add bio_iov_iter_set() helper - Fix io_uring uapi validation - Other minor changes NVMe: - Rename nvme_pci_sgl_set_data() to nvme_pci_dma_iter_set_sgl(), split into its own prep patch. - Convert segment walk loops to do-while. - Drop adjacent segment coalescing logic. - Drop first_dma/first_len from nvme_pci_dmabuf_sgl_nents() - Remove entries > NVME_MAX_SEGS bailout; moving to the block layer. - Factor SGL vs PRP decision making into a helper. v4: - https://lore.kernel.org/all/cover.1785274111.git.asml.silence@gmail.com/ - Add sgl support from Anuj - Move it under drivers/dma-buf/ and rename - Fix mis-sized allocations - Fix io_uring re-import mishandling - Drop map before io_uring "task work" - Move blk-mq callback to block_device_operations - Convert bio flag to REQ_OP* - Other small changes v3: https://lore.kernel.org/io-uring/cover.1777475843.git.asml.silence@gmail.com/ - Rework io_uring registration - Move token/map infrastructure code out of blk-mq - Simplify callbacks: remove a separate blk-mq table, which was mostly just forwarding calls (to nvme). - Don't skip dma sync depending on request direction - Fix a couple of hangs - Rename s/dma/dmabuf/ - Other small changes v2: - Don't pass raw dma addresses, wrap it into a driver specific object - Split into two objects: token and map - Implement move_notify Anuj Gupta (2): nvme-pci: rename nvme_pci_sgl_set_data to nvme_pci_dma_iter_set_sgl nvme-pci: add SGL support for the dmabuf path Pavel Begunkov (11): block: always adjust bi_offset on bio_advance_iter block: introduce dma map backed bio type block: add dma-buf support for raw bdev nvme-pci: implement dma-buf backed requests nvme seaparate file nvme sgl fixup io_uring/rsrc: introduce buf registration structure io_uring/rsrc: extend buffer update io_uring/rsrc: add uncloneable regbuf flag io_uring/rsrc: add regbuf import flags io_uring/rsrc: add dmabuf backed registered buffers block/bio.c | 15 +- block/blk-merge.c | 50 +++++++ block/fops.c | 24 +++- drivers/md/dm-io-rewind.c | 6 +- drivers/nvme/host/Makefile | 1 + drivers/nvme/host/core.c | 12 ++ drivers/nvme/host/nvme.h | 2 + drivers/nvme/host/pci-dmabuf.c | 164 ++++++++++++++++++++++ drivers/nvme/host/pci-dmabuf.h | 73 ++++++++++ drivers/nvme/host/pci.c | 249 ++++++++++++++++++++++++++++++++- include/linux/bio.h | 21 +-- include/linux/blk-mq.h | 7 + include/linux/blk_types.h | 14 +- include/linux/blkdev.h | 2 + include/linux/bvec.h | 3 +- include/linux/io_uring_types.h | 5 + include/uapi/linux/io_uring.h | 31 +++- io_uring/Makefile | 1 + io_uring/dma-buf.c | 68 +++++++++ io_uring/dma-buf.h | 67 +++++++++ io_uring/rsrc.c | 172 +++++++++++++++++------ io_uring/rsrc.h | 32 ++++- io_uring/rw.c | 33 +++-- 23 files changed, 974 insertions(+), 78 deletions(-) create mode 100644 drivers/nvme/host/pci-dmabuf.c create mode 100644 drivers/nvme/host/pci-dmabuf.h create mode 100644 io_uring/dma-buf.c create mode 100644 io_uring/dma-buf.h -- 2.54.0