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Tue, 06 Oct 2026 18:32:35 -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 13/13] io_uring/rsrc: add dmabuf backed registered buffers Date: Wed, 7 Oct 2026 02:31:56 +0100 Message-ID: <5e9c68ce54227a530fe8db4fc48099ee6fba51ff.1791336002.git.asml.silence@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Implement dmabuf backed registered buffers. To register them, the user should specify IO_REGBUF_TYPE_DMABUF for the regitration and pass the desired dmabuf fd and a file for which it should be registered. >From there, it can be used with io_uring read/write requests IORING_OP_{READ,WRITE}_FIXED) as normal. The requests should be issued against the file specified during registration, and otherwise they'll be failed. The user should also be prepared to handle spurious -EAGAIN by reissuing the request. Internally, dmabuf registered buffers is an optin feature for io_uring request opcodes and they should pass a special flag on import to use it. Suggested-by: David Wei Suggested-by: Vishal Verma Suggested-by: Tushar Gohad Signed-off-by: Pavel Begunkov --- include/linux/io_uring_types.h | 5 +++ include/uapi/linux/io_uring.h | 6 ++- io_uring/Makefile | 1 + io_uring/dma-buf.c | 68 ++++++++++++++++++++++++++++++++++ io_uring/dma-buf.h | 67 +++++++++++++++++++++++++++++++++ io_uring/rsrc.c | 59 +++++++++++++++++++++++++++-- io_uring/rsrc.h | 5 +++ io_uring/rw.c | 33 ++++++++++++----- 8 files changed, 230 insertions(+), 14 deletions(-) create mode 100644 io_uring/dma-buf.c create mode 100644 io_uring/dma-buf.h diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h index 90fea94ad202..73cd11d173df 100644 --- a/include/linux/io_uring_types.h +++ b/include/linux/io_uring_types.h @@ -11,6 +11,7 @@ struct iou_loop_params; struct io_uring_bpf_ops; +struct dma_buf_io_map; enum { /* @@ -610,6 +611,7 @@ enum { REQ_F_IMPORT_BUFFER_BIT, REQ_F_SQE_COPIED_BIT, REQ_F_IOPOLL_BIT, + REQ_F_DMABUF_BIT, /* not a real bit, just to check we're not overflowing the space */ __REQ_F_LAST_BIT, @@ -705,6 +707,8 @@ enum { REQ_F_SQE_COPIED = IO_REQ_FLAG(REQ_F_SQE_COPIED_BIT), /* request must be iopolled to completion (set in ->issue()) */ REQ_F_IOPOLL = IO_REQ_FLAG(REQ_F_IOPOLL_BIT), + /* there is a dma map attached to request that needs to be dropped */ + REQ_F_DMABUF = IO_REQ_FLAG(REQ_F_DMABUF_BIT), }; struct io_tw_req { @@ -827,6 +831,7 @@ struct io_kiocb { /* custom credentials, valid IFF REQ_F_CREDS is set */ const struct cred *creds; struct io_wq_work work; + struct dma_buf_io_map *dmabuf_map; struct io_big_cqe { u64 extra1; diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h index abb590833a0f..b456f45fa8de 100644 --- a/include/uapi/linux/io_uring.h +++ b/include/uapi/linux/io_uring.h @@ -811,6 +811,7 @@ enum io_uring_rsrc_reg_flags { enum io_uring_regbuf_type { IO_REGBUF_TYPE_EMPTY, IO_REGBUF_TYPE_UADDR, + IO_REGBUF_TYPE_DMABUF, __IO_REGBUF_TYPE_MAX, }; @@ -820,7 +821,10 @@ struct io_uring_regbuf_desc { __u32 flags; __u64 size; __u64 uaddr; - __u64 __resv[7]; + + __s32 dmabuf_fd; + __s32 target_fd; + __u64 __resv[6]; }; /* Skip updating fd indexes set to this value in the fd table */ diff --git a/io_uring/Makefile b/io_uring/Makefile index c54e328d1410..965bb60e9f7b 100644 --- a/io_uring/Makefile +++ b/io_uring/Makefile @@ -26,3 +26,4 @@ obj-$(CONFIG_PROC_FS) += fdinfo.o obj-$(CONFIG_IO_URING_MOCK_FILE) += mock_file.o obj-$(CONFIG_IO_URING_BPF) += bpf_filter.o obj-$(CONFIG_IO_URING_BPF_OPS) += bpf-ops.o +obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o diff --git a/io_uring/dma-buf.c b/io_uring/dma-buf.c new file mode 100644 index 000000000000..f40c9d87ed8a --- /dev/null +++ b/io_uring/dma-buf.c @@ -0,0 +1,68 @@ +#include "dma-buf.h" + +static inline void io_release_dmabuf(void *priv) +{ + struct io_buf_dma *bd = priv; + + fput(bd->target_file); + dma_buf_io_ctx_release(bd->ctx); + kfree(bd); +} + +int io_register_dmabuf(struct io_ring_ctx *ctx, + struct io_uring_regbuf_desc *desc, + struct io_mapped_ubuf *imu) +{ + struct io_buf_dma *bd = NULL; + struct file *target_file = NULL; + struct dma_buf *dmabuf = NULL; + int ret; + + if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER)) + return -EOPNOTSUPP; + if (ctx->flags & IORING_SETUP_IOPOLL) + return -EOPNOTSUPP; + if (desc->uaddr || desc->size) + return -EINVAL; + + bd = kzalloc(sizeof(*bd), GFP_KERNEL); + if (!bd) + return -ENOMEM; + + target_file = fget(desc->target_fd); + if (!target_file) { + ret = -EBADF; + goto err; + } + dmabuf = dma_buf_get(desc->dmabuf_fd); + if (IS_ERR(dmabuf)) { + ret = PTR_ERR(dmabuf); + dmabuf = NULL; + goto err; + } + ret = io_validate_user_buf_range(0, dmabuf->size); + if (ret) + goto err; + + ret = dma_buf_io_ctx_create(target_file, dmabuf, DMA_BIDIRECTIONAL, + &bd->ctx); + if (ret) + goto err; + + bd->target_file = target_file; + imu->len = dmabuf->size; + imu->release = io_release_dmabuf; + imu->priv = bd; + imu->flags = IO_REGBUF_F_DMABUF; + imu->dir = IO_BUF_DEST | IO_BUF_SOURCE; + dma_buf_put(dmabuf); + return 0; +err: + kfree(bd); + if (target_file) + fput(target_file); + if (dmabuf) + dma_buf_put(dmabuf); + return ret; +} + diff --git a/io_uring/dma-buf.h b/io_uring/dma-buf.h new file mode 100644 index 000000000000..10d2efdd8c9f --- /dev/null +++ b/io_uring/dma-buf.h @@ -0,0 +1,67 @@ +// SPDX-License-Identifier: GPL-2.0 +#ifndef IOU_DMA_BUF_H +#define IOU_DMA_BUF_H + +#include +#include + +#include "rsrc.h" + +struct io_buf_dma { + struct dma_buf_io_ctx *ctx; + struct file *target_file; +}; + +static inline void io_detach_dmabuf_map(struct io_kiocb *req) +{ + if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER)) + return; + if (!(req->flags & REQ_F_DMABUF) || !req->dmabuf_map) + return; + dma_buf_io_map_drop(req->dmabuf_map); + req->dmabuf_map = NULL; +} + +static inline int io_attach_dmabuf_map(struct io_kiocb *req, + struct iov_iter *iter, + unsigned issue_flags) +{ + bool nowait = issue_flags & IO_URING_F_NONBLOCK; + struct dma_buf_io_map *map; + struct io_buf_dma *bd; + + if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER)) + return -EOPNOTSUPP; + if (!(req->flags & REQ_F_DMABUF)) + return 0; + + bd = req->buf_node->buf->priv; + map = dma_buf_io_get_map(bd->ctx, nowait); + if (unlikely(IS_ERR(map))) + return PTR_ERR(map); + req->dmabuf_map = map; + iter->dmabuf_map = map; + return 0; +} + +static inline int io_import_dmabuf_map(struct io_kiocb *req, + int ddir, struct iov_iter *iter, + struct io_mapped_ubuf *imu, + size_t len, size_t offset) +{ + struct io_buf_dma *bd = imu->priv; + + if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER)) + return -EOPNOTSUPP; + if (req->file != bd->target_file) + return -EBADF; + req->flags |= REQ_F_DMABUF; + iov_iter_dmabuf_map(iter, ddir, NULL, offset, len); + return 0; +} + +int io_register_dmabuf(struct io_ring_ctx *ctx, + struct io_uring_regbuf_desc *desc, + struct io_mapped_ubuf *imu); + +#endif /* IOU_DMA_BUF_H */ diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c index 6e4fe70b316f..d6f7cbf731eb 100644 --- a/io_uring/rsrc.c +++ b/io_uring/rsrc.c @@ -10,6 +10,7 @@ #include #include #include +#include #include @@ -19,6 +20,7 @@ #include "rsrc.h" #include "memmap.h" #include "register.h" +#include "dma-buf.h" struct io_rsrc_update { struct file *file; @@ -898,6 +900,38 @@ bool io_check_coalesce_buffer(struct page **page_array, int nr_pages, return true; } +static struct io_rsrc_node *io_register_dmabuf_desc(struct io_ring_ctx *ctx, + struct io_uring_regbuf_desc *desc) +{ + struct io_rsrc_node *node = NULL; + struct io_mapped_ubuf *imu = NULL; + int ret; + + node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER); + if (!node) + return ERR_PTR(-ENOMEM); + + imu = io_alloc_imu(ctx, 0); + if (!imu) { + ret = -ENOMEM; + goto err; + } + memset(imu, 0, sizeof(*imu)); + refcount_set(&imu->refs, 1); + + ret = io_register_dmabuf(ctx, desc, imu); + if (ret) + goto err; + node->buf = imu; + return node; +err: + if (imu) + io_free_imu(ctx, imu); + if (node) + io_cache_free(&ctx->node_cache, node); + return ERR_PTR(ret); +} + static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx, struct io_uring_regbuf_desc *desc) { @@ -916,6 +950,12 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx, if (!mem_is_zero(&desc->__resv, sizeof(desc->__resv)) || desc->flags) return ERR_PTR(-EINVAL); + if (desc->type == IO_REGBUF_TYPE_DMABUF) + return io_register_dmabuf_desc(ctx, desc); + + if (desc->dmabuf_fd || desc->target_fd) + return ERR_PTR(-EINVAL); + if (desc->type == IO_REGBUF_TYPE_EMPTY) { if (uaddr || size) return ERR_PTR(-EFAULT); @@ -1240,9 +1280,12 @@ static int io_import_kbuf(int ddir, struct iov_iter *iter, return 0; } -static int io_import_fixed(int ddir, struct iov_iter *iter, +static int io_import_fixed(struct io_kiocb *req, + int ddir, struct iov_iter *iter, struct io_mapped_ubuf *imu, - u64 buf_addr, size_t len) + u64 buf_addr, size_t len, + unsigned issue_flags, + unsigned import_flags) { const struct bio_vec *bvec; size_t folio_mask; @@ -1262,6 +1305,11 @@ static int io_import_fixed(int ddir, struct iov_iter *iter, offset = buf_addr - imu->ubuf; + if (imu->flags & IO_REGBUF_F_DMABUF) { + if (!(import_flags & IO_REGBUF_IMPORT_ALLOW_DMABUF)) + return -EFAULT; + return io_import_dmabuf_map(req, ddir, iter, imu, len, offset); + } if (imu->flags & IO_REGBUF_F_KBUF) return io_import_kbuf(ddir, iter, imu, len, offset); @@ -1324,7 +1372,8 @@ int __io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter, node = io_find_buf_node(req, issue_flags); if (!node) return -EFAULT; - return io_import_fixed(ddir, iter, node->buf, buf_addr, len); + return io_import_fixed(req, ddir, iter, node->buf, buf_addr, len, + issue_flags, import_flags); } static int io_buffer_acct_cloned_hpages(struct io_ring_ctx *ctx, @@ -1751,7 +1800,9 @@ int __io_import_reg_vec(int ddir, struct iov_iter *iter, iovec_off = vec->nr - nr_iovs; iov = vec->iovec + iovec_off; - if (imu->flags & IO_REGBUF_F_KBUF) { + if (imu->flags & IO_REGBUF_F_DMABUF) { + return -EOPNOTSUPP; + } else if (imu->flags & IO_REGBUF_F_KBUF) { int ret = io_kern_bvec_size(iov, nr_iovs, imu, &nr_segs); if (unlikely(ret)) diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h index 351995b61e68..d893cc5e580a 100644 --- a/io_uring/rsrc.h +++ b/io_uring/rsrc.h @@ -28,6 +28,11 @@ struct io_rsrc_node { enum { IO_REGBUF_F_KBUF = 1 << 0, IO_REGBUF_F_UNCLONEABLE = 1 << 1, + IO_REGBUF_F_DMABUF = 1 << 3, +}; + +enum { + IO_REGBUF_IMPORT_ALLOW_DMABUF = 1 << 1, }; struct io_mapped_ubuf { diff --git a/io_uring/rw.c b/io_uring/rw.c index 999d9a1cc5a5..d33b925a848e 100644 --- a/io_uring/rw.c +++ b/io_uring/rw.c @@ -23,6 +23,7 @@ #include "rsrc.h" #include "poll.h" #include "rw.h" +#include "dma-buf.h" static void io_complete_rw(struct kiocb *kiocb, long res); static void io_complete_rw_iopoll(struct kiocb *kiocb, long res); @@ -358,13 +359,18 @@ static int io_init_rw_fixed(struct io_kiocb *req, unsigned int issue_flags, struct io_async_rw *io = req->async_data; int ret; - if (io->bytes_done) - return 0; + if (!io->bytes_done) { + ret = __io_import_reg_buf(req, &io->iter, rw->addr, rw->len, ddir, + issue_flags, IO_REGBUF_IMPORT_ALLOW_DMABUF); + if (ret) + return ret; + iov_iter_save_state(&io->iter, &io->iter_state); + } - ret = io_import_reg_buf(req, &io->iter, rw->addr, rw->len, ddir, - issue_flags); - iov_iter_save_state(&io->iter, &io->iter_state); - return ret; + ret = io_attach_dmabuf_map(req, &io->iter, issue_flags); + if (ret) + return ret; + return 0; } int io_prep_read_fixed(struct io_kiocb *req, const struct io_uring_sqe *sqe) @@ -577,6 +583,8 @@ static void io_complete_rw(struct kiocb *kiocb, long res) struct io_rw *rw = container_of(kiocb, struct io_rw, kiocb); struct io_kiocb *req = cmd_to_io_kiocb(rw); + io_detach_dmabuf_map(req); + /* ring owner may block in freeze_super() before task_work runs */ if (kiocb->ki_flags & IOCB_WRITE) io_req_end_write(req); @@ -698,7 +706,7 @@ static ssize_t loop_rw_iter(int ddir, struct io_rw *rw, struct iov_iter *iter) !(kiocb->ki_filp->f_flags & O_NONBLOCK)) return -EAGAIN; if ((req->flags & REQ_F_BUF_NODE) && - (req->buf_node->buf->flags & IO_REGBUF_F_KBUF)) + (req->buf_node->buf->flags & (IO_REGBUF_F_KBUF|IO_REGBUF_F_DMABUF))) return -EFAULT; ppos = io_kiocb_ppos(kiocb); @@ -1226,7 +1234,10 @@ int io_read_fixed(struct io_kiocb *req, unsigned int issue_flags) if (unlikely(ret)) return ret; - return io_read(req, issue_flags); + ret = io_read(req, issue_flags); + if (ret != -EIOCBQUEUED) + io_detach_dmabuf_map(req); + return ret; } int io_write_fixed(struct io_kiocb *req, unsigned int issue_flags) @@ -1237,7 +1248,11 @@ int io_write_fixed(struct io_kiocb *req, unsigned int issue_flags) if (unlikely(ret)) return ret; - return io_write(req, issue_flags); + ret = io_write(req, issue_flags); + if (ret != -EIOCBQUEUED) + io_detach_dmabuf_map(req); + return ret; + } void io_rw_fail(struct io_kiocb *req) -- 2.54.0