linux-kernel - [RFC v2 11/11] io_uring/rsrc: implement dmabuf regbuf import

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Message-ID: <44e4ad8c4bd72856379c368e4303090c44c9e98e.1763725388.git.asml.silence@gmail.com>
Date: Sun, 23 Nov 2025 22:51:31 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: linux-block@...r.kernel.org,
	io-uring@...r.kernel.org
Cc: Vishal Verma <vishal1.verma@...el.com>,
	tushar.gohad@...el.com,
	Keith Busch <kbusch@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Pavel Begunkov <asml.silence@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org,
	linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org,
	David Wei <dw@...idwei.uk>
Subject: [RFC v2 11/11] io_uring/rsrc: implement dmabuf regbuf import

Allow importing dmabuf backed registered buffers. It's an opt-in feature
for requests and they need to pass a flag allowing it. Furthermore,
the import will fail if the request's file doesn't match the file for
which the buffer for registered. This way, it's also limited to files
that support the feature by implementing the corresponding file op.
Enable it for read/write requests.

Suggested-by: David Wei <dw@...idwei.uk>
Suggested-by: Vishal Verma <vishal1.verma@...el.com>
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 io_uring/rsrc.c | 36 +++++++++++++++++++++++++++++-------
 io_uring/rsrc.h | 16 +++++++++++++++-
 io_uring/rw.c   |  4 ++--
 3 files changed, 46 insertions(+), 10 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 7dfebf459dd0..a5d88dae536e 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1201,9 +1201,27 @@ 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_dmabuf(struct io_kiocb *req,
+			   int ddir, struct iov_iter *iter,
 			   struct io_mapped_ubuf *imu,
-			   u64 buf_addr, size_t len)
+			   size_t len, size_t offset)
+{
+	struct io_regbuf_dma *db = imu->priv;
+
+	if (!len)
+		return -EFAULT;
+	if (req->file != db->target_file)
+		return -EBADF;
+
+	iov_iter_dma_token(iter, ddir, db->token, offset, len);
+	return 0;
+}
+
+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,
+			   unsigned import_flags)
 {
 	const struct bio_vec *bvec;
 	size_t folio_mask;
@@ -1219,8 +1237,11 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
 
 	offset = buf_addr - imu->ubuf;
 
-	if (imu->flags & IO_IMU_F_DMA)
-		return -EOPNOTSUPP;
+	if (imu->flags & IO_IMU_F_DMA) {
+		if (!(import_flags & IO_REGBUF_IMPORT_ALLOW_DMA))
+			return -EFAULT;
+		return io_import_dmabuf(req, ddir, iter, imu, len, offset);
+	}
 	if (imu->flags & IO_IMU_F_KBUF)
 		return io_import_kbuf(ddir, iter, imu, len, offset);
 
@@ -1274,16 +1295,17 @@ inline struct io_rsrc_node *io_find_buf_node(struct io_kiocb *req,
 	return NULL;
 }
 
-int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
+int __io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
 			u64 buf_addr, size_t len, int ddir,
-			unsigned issue_flags)
+			unsigned issue_flags, unsigned import_flags)
 {
 	struct io_rsrc_node *node;
 
 	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,
+				import_flags);
 }
 
 /* Lock two rings at once. The rings must be different! */
diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index 280d3988abf3..e0eafce976f3 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -33,6 +33,10 @@ enum {
 	IO_IMU_F_DMA			= 2,
 };
 
+enum {
+	IO_REGBUF_IMPORT_ALLOW_DMA		= 1,
+};
+
 struct io_mapped_ubuf {
 	u64		ubuf;
 	unsigned int	len;
@@ -66,9 +70,19 @@ int io_rsrc_data_alloc(struct io_rsrc_data *data, unsigned nr);
 
 struct io_rsrc_node *io_find_buf_node(struct io_kiocb *req,
 				      unsigned issue_flags);
+int __io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
+			u64 buf_addr, size_t len, int ddir,
+			unsigned issue_flags, unsigned import_flags);
+
+static inline
 int io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
 			u64 buf_addr, size_t len, int ddir,
-			unsigned issue_flags);
+			unsigned issue_flags)
+{
+	return __io_import_reg_buf(req, iter, buf_addr, len, ddir,
+				   issue_flags, 0);
+}
+
 int io_import_reg_vec(int ddir, struct iov_iter *iter,
 			struct io_kiocb *req, struct iou_vec *vec,
 			unsigned nr_iovs, unsigned issue_flags);
diff --git a/io_uring/rw.c b/io_uring/rw.c
index a3eb4e7bf992..0d9d99695801 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -374,8 +374,8 @@ static int io_init_rw_fixed(struct io_kiocb *req, unsigned int issue_flags,
 	if (io->bytes_done)
 		return 0;
 
-	ret = io_import_reg_buf(req, &io->iter, rw->addr, rw->len, ddir,
-				issue_flags);
+	ret = __io_import_reg_buf(req, &io->iter, rw->addr, rw->len, ddir,
+				  issue_flags, IO_REGBUF_IMPORT_ALLOW_DMA);
 	iov_iter_save_state(&io->iter, &io->iter_state);
 	return ret;
 }
-- 
2.52.0