[PATCH v4 00/14] Add dmabuf read/write via io_uring

[PATCH v4 00/14] Add dmabuf read/write via io_uring

[Pavel Begunkov]

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 good number of changes, and later was brough up
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 as well as Kanchan, Anuj and Nitesh did a lot of
testing and experimentation with different devices. Some 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 3-7: block layer support + prep patches
- Patches 8-9 implement NVMe support
- Patches 10-14 add io_uring support and uapi. Patch 14 specifically
  enables dma-buf support, the rest are preparation patches.

There are some liburing tests that can serve as an example:
git: https://github.com/isilence/liburing.git rw-dmabuf-tests-v4
url: https://github.com/isilence/liburing/tree/rw-dmabuf-tests-v4

[1] https://lore.kernel.org/io-uring/20220805162444.3985535-1-kbusch@fb.com/

v4: - 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 (1):
  nvme-pci: add SGL support for the dmabuf path

Pavel Begunkov (13):
  dma-buf: introduce initial file I/O infrastructure
  iov_iter: add iterator type for dmabuf maps
  block: rename bi_bvec_done
  block: always adjust bi_offset on bio_advance_iter
  block: move bvec init into __bio_clone
  block: introduce dma map backed bio type
  block: forward init_dma_buf_io_ctx to drivers
  nvme-pci: implement dma_token backed requests
  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

 Documentation/block/biovecs.rst |   8 +-
 block/bio.c                     |  30 ++-
 block/blk-merge.c               |  23 +-
 block/blk-mq-dma.c              |   2 +-
 block/blk.h                     |   2 +-
 block/fops.c                    |  16 ++
 drivers/block/loop.c            |   2 +-
 drivers/block/zloop.c           |   2 +-
 drivers/dma-buf/Makefile        |   2 +-
 drivers/dma-buf/dma-buf-io.c    | 275 ++++++++++++++++++++
 drivers/md/dm-io-rewind.c       |  16 +-
 drivers/md/dm-pcache/segment.c  |   4 +-
 drivers/nvdimm/btt.c            |   2 +-
 drivers/nvme/host/core.c        |  12 +
 drivers/nvme/host/nvme.h        |   2 +
 drivers/nvme/host/pci.c         | 448 +++++++++++++++++++++++++++++++-
 drivers/nvme/host/tcp.c         |   2 +-
 fs/btrfs/misc.h                 |   2 +-
 include/linux/bio.h             |  22 +-
 include/linux/blk-mq.h          |   7 +
 include/linux/blk_types.h       |  14 +-
 include/linux/blkdev.h          |   2 +
 include/linux/bvec.h            |  17 +-
 include/linux/dma-buf-io.h      |  91 +++++++
 include/linux/fs.h              |   2 +
 include/linux/io_uring_types.h  |   5 +
 include/linux/uio.h             |  11 +
 include/uapi/linux/io_uring.h   |  31 ++-
 io_uring/io_uring.c             |   3 +-
 io_uring/net.c                  |   4 +-
 io_uring/rsrc.c                 | 281 +++++++++++++++++---
 io_uring/rsrc.h                 |  45 +++-
 io_uring/rw.c                   |   6 +-
 lib/iov_iter.c                  |  31 ++-
 net/ceph/messenger.c            |   4 +-
 35 files changed, 1315 insertions(+), 111 deletions(-)
 create mode 100644 drivers/dma-buf/dma-buf-io.c
 create mode 100644 include/linux/dma-buf-io.h

-- 
2.54.0

[PATCH v4 01/14] dma-buf: introduce initial file I/O infrastructure

[Pavel Begunkov]

The goal is to be able to natively use dma-buf in the read-write / IO
path. This patch adds basic building blocks serving as a glue and API
between drivers and upper layer subsystems providing the uAPI. Later
patches implement it for NVMe raw block devices and expose it to the
user space via io_uring.

There are two main objects. struct dma_buf_io_ctx and struct
dma_buf_io_map. The ctx is used during initial registration and serves
as an interface between the upper layer user like io_uring and to the
importer subsystem / driver. The map represents the actual dma map
established for the target device[s] with dma_buf_map_attachment() and
stored in a device specific format. The context is created via a new
file operation ->init_dma_buf_io_ctx.

The ctx-map separation exists to support map invalidation (see
dma_buf_io_invalidate_mappings()). A ctx can create
multiple maps during its lifetime, but there can only be no more than
one (active) map attached to it. Invalidation drops the active map
if present, and the next map will only be attempted to be created
once there is a new request that wants to use the dma-buf IO ctx.

The primary task of the dma_buf_io_map object is to count requests
using it and to wait for their completion when we want to destroy the
DMA map. Invalidation is delayed by inserting a dma fence, which is
signaled when all flight requests are completed.

[un]mapping and any work with dma addresses is delegated to the
importer driver via an ops table stored in the ctx, see struct
dma_buf_io_ops. Only the target driver / subsystem knows about devices
it wants to use the dma-buf with, especially in case of multi-device
filesystems or stacking in the future.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 drivers/dma-buf/Makefile     |   2 +-
 drivers/dma-buf/dma-buf-io.c | 275 +++++++++++++++++++++++++++++++++++
 include/linux/dma-buf-io.h   |  91 ++++++++++++
 include/linux/fs.h           |   2 +
 4 files changed, 369 insertions(+), 1 deletion(-)
 create mode 100644 drivers/dma-buf/dma-buf-io.c
 create mode 100644 include/linux/dma-buf-io.h

diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index b25d7550bacf..523731b0f83e 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
-	 dma-fence-unwrap.o dma-resv.o dma-buf-mapping.o
+	 dma-fence-unwrap.o dma-resv.o dma-buf-mapping.o dma-buf-io.o
 obj-$(CONFIG_DMABUF_HEAPS)	+= dma-heap.o
 obj-$(CONFIG_DMABUF_HEAPS)	+= heaps/
 obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
diff --git a/drivers/dma-buf/dma-buf-io.c b/drivers/dma-buf/dma-buf-io.c
new file mode 100644
index 000000000000..5f545a1bcf32
--- /dev/null
+++ b/drivers/dma-buf/dma-buf-io.c
@@ -0,0 +1,275 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Common infrastructure for supporing dma-buf in the I/O path.
+ *
+ * Copyright (C) 2026 Pavel Begunkov <asml.silence@gmail.com>
+ */
+#include <linux/dma-buf-io.h>
+#include <linux/dma-resv.h>
+
+struct dma_buf_io_fence {
+	struct dma_fence base;
+	spinlock_t lock;
+};
+
+static const char *dma_buf_io_fence_drv_name(struct dma_fence *fence)
+{
+	/* default fence release kfree's the base pointer */
+	BUILD_BUG_ON(offsetof(struct dma_buf_io_fence, base));
+
+	return "dma-buf-io-ctx";
+}
+
+static const char *dma_buf_io_fence_timeline_name(struct dma_fence *fence)
+{
+	return "dma-buf-io-ctx";
+}
+
+const struct dma_fence_ops dma_buf_io_fence_ops = {
+	.get_driver_name = dma_buf_io_fence_drv_name,
+	.get_timeline_name = dma_buf_io_fence_timeline_name,
+};
+
+static void dma_buf_io_ctx_destroy_work(struct work_struct *work)
+{
+	struct dma_buf_io_ctx *ctx = container_of(work, struct dma_buf_io_ctx,
+						  release_work);
+
+	if (WARN_ON_ONCE(refcount_read(&ctx->refs)))
+		return;
+
+	ctx->dev_ops->release(ctx);
+	dma_buf_put(ctx->dmabuf);
+	kfree(ctx);
+}
+
+static void dma_buf_io_map_release_work(struct work_struct *work)
+{
+	struct dma_buf_io_map *map = container_of(work, struct dma_buf_io_map,
+						  release_work);
+	struct dma_buf_io_fence *fence = map->fence;
+	struct dma_buf_io_ctx *ctx = map->ctx;
+	struct dma_buf *dmabuf = ctx->dmabuf;
+
+	/* the release path must wait for fences */
+	if (WARN_ON_ONCE(refcount_read(&ctx->refs) == 0))
+		return;
+
+	/* Prevent from destoying the ctx while unmapping */
+	refcount_inc(&ctx->refs);
+
+	/*
+	 * There are no more requests using the map, we can signal the fence.
+	 * It should be done before taking the resv lock as someone could be
+	 * waiting for the fence while holding the lock.
+	 */
+	dma_fence_signal(&fence->base);
+
+	dma_resv_lock(dmabuf->resv, NULL);
+	ctx->dev_ops->unmap(ctx, map);
+	dma_resv_unlock(dmabuf->resv);
+
+	dma_fence_put(&fence->base);
+	percpu_ref_exit(&map->refs);
+	kfree(map);
+
+	if (refcount_dec_and_test(&ctx->refs)) {
+		/*
+		 * Destruction needs to wait for I/O and dma fences. Defer it to
+		 * simplify locking.
+		 */
+		INIT_WORK(&ctx->release_work, dma_buf_io_ctx_destroy_work);
+		queue_work(system_wq, &ctx->release_work);
+	}
+}
+
+static void dma_buf_io_map_refs_release(struct percpu_ref *ref)
+{
+	struct dma_buf_io_map *map = container_of(ref, struct dma_buf_io_map, refs);
+
+	/* might sleep, use a worker */
+	INIT_WORK(&map->release_work, dma_buf_io_map_release_work);
+	queue_work(system_wq, &map->release_work);
+}
+
+int dma_buf_io_init_map(struct dma_buf_io_ctx *ctx, struct dma_buf_io_map *map)
+{
+	struct dma_buf_io_fence *fence = NULL;
+	int ret;
+
+	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
+	if (!fence)
+		return -ENOMEM;
+
+	ret = percpu_ref_init(&map->refs, dma_buf_io_map_refs_release, 0, GFP_KERNEL);
+	if (ret) {
+		kfree(fence);
+		return ret;
+	}
+
+	spin_lock_init(&fence->lock);
+	dma_fence_init(&fence->base, &dma_buf_io_fence_ops, &fence->lock,
+			ctx->fence_ctx, atomic_inc_return(&ctx->fence_seq));
+	map->fence = fence;
+	map->ctx = ctx;
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_io_init_map, "DMA_BUF");
+
+struct dma_buf_io_map *dma_buf_io_create_map(struct dma_buf_io_ctx *ctx)
+{
+	struct dma_buf *dmabuf = ctx->dmabuf;
+	struct dma_buf_io_map *map;
+	long ret;
+
+retry:
+	/*
+	 * ->dmabuf_map() will be calling dma_buf_map_attachment(), for which
+	 * we'll need to wait for fences. Do a bit nicer and try to wait
+	 * without the resv lock first.
+	 */
+	ret = dma_resv_wait_timeout(dmabuf->resv, DMA_RESV_USAGE_KERNEL,
+				    true, MAX_SCHEDULE_TIMEOUT);
+	if (!ret)
+		ret = -EAGAIN;
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	ret = dma_resv_lock_interruptible(dmabuf->resv, NULL);
+	if (ret)
+		return ERR_PTR(ret);
+
+	map = dma_buf_io_get_map(ctx);
+	if (map) {
+		ret = 0;
+		goto out;
+	}
+
+	if (dma_resv_wait_timeout(dmabuf->resv, DMA_RESV_USAGE_KERNEL,
+				  true, 0) < 0) {
+		dma_resv_unlock(dmabuf->resv);
+		goto retry;
+	}
+
+	map = ctx->dev_ops->map(ctx);
+	if (IS_ERR(map)) {
+		ret = PTR_ERR(map);
+		goto out;
+	}
+
+	percpu_ref_get(&map->refs);
+	rcu_assign_pointer(ctx->map, map);
+out:
+	dma_resv_unlock(dmabuf->resv);
+	if (ret < 0)
+		return ERR_PTR(ret);
+	return map;
+}
+
+static void dma_buf_io_drop_map(struct dma_buf_io_ctx *ctx)
+{
+	struct dma_buf *dmabuf = ctx->dmabuf;
+	struct dma_buf_io_map *map;
+	int ret;
+
+	dma_resv_assert_held(dmabuf->resv);
+
+	map = rcu_dereference_protected(ctx->map,
+					dma_resv_held(dmabuf->resv));
+	if (!map)
+		return;
+	rcu_assign_pointer(ctx->map, NULL);
+
+	ret = dma_resv_reserve_fences(dmabuf->resv, 1);
+	if (WARN_ON_ONCE(ret)) {
+		struct dma_fence *fence = &map->fence->base;
+
+		dma_fence_get(fence);
+		percpu_ref_kill(&map->refs);
+		dma_fence_wait(fence, false);
+		dma_fence_put(fence);
+		return;
+	}
+
+	dma_resv_add_fence(dmabuf->resv, &map->fence->base,
+			   DMA_RESV_USAGE_KERNEL);
+	/*
+	 * Delay destruction until all inflight requests using the map are
+	 * gone. It'll also signal the fence then.
+	 */
+	percpu_ref_kill(&map->refs);
+}
+
+void dma_buf_io_invalidate_mappings(struct dma_buf_io_ctx *ctx)
+{
+	dma_buf_io_drop_map(ctx);
+}
+EXPORT_SYMBOL_NS_GPL(dma_buf_io_invalidate_mappings, "DMA_BUF");
+
+static void dma_buf_io_ctx_release_work(struct work_struct *work)
+{
+	struct dma_buf_io_ctx *ctx = container_of(work, struct dma_buf_io_ctx,
+						  release_work);
+	struct dma_buf *dmabuf = ctx->dmabuf;
+	long ret;
+
+	dma_resv_lock(dmabuf->resv, NULL);
+	/* Remove the last map, there should be no new ones going forward. */
+	dma_buf_io_drop_map(ctx);
+	dma_resv_unlock(dmabuf->resv);
+
+	/* Wait until all maps are destroyed. */
+	ret = dma_resv_wait_timeout(dmabuf->resv, DMA_RESV_USAGE_KERNEL,
+				    false, MAX_SCHEDULE_TIMEOUT);
+
+	if (WARN_ON_ONCE(ret <= 0))
+		return;
+	if (WARN_ON_ONCE(rcu_dereference_protected(ctx->map, true)))
+		return;
+
+	if (refcount_dec_and_test(&ctx->refs))
+		dma_buf_io_ctx_destroy_work(&ctx->release_work);
+}
+
+void dma_buf_io_ctx_release(struct dma_buf_io_ctx *ctx)
+{
+	/*
+	 * Destruction needs to wait for I/O and dma fences. Defer it to
+	 * simplify locking.
+	 */
+	INIT_WORK(&ctx->release_work, dma_buf_io_ctx_release_work);
+	queue_work(system_wq, &ctx->release_work);
+}
+
+int dma_buf_io_ctx_create(struct file *file,
+			   struct dma_buf_io_ctx *ctx,
+			   struct dma_buf *dmabuf,
+			   enum dma_data_direction dir)
+{
+	int ret;
+
+	if (!file->f_op->init_dma_buf_io_ctx)
+		return -EOPNOTSUPP;
+
+	memset(ctx, 0, sizeof(*ctx));
+	ctx->fence_ctx = dma_fence_context_alloc(1);
+	ctx->dir = dir;
+	ctx->dmabuf = dmabuf;
+	refcount_set(&ctx->refs, 1);
+	get_dma_buf(dmabuf);
+
+	ret = file->f_op->init_dma_buf_io_ctx(file, ctx);
+	if (ret) {
+		memset(ctx, 0, sizeof(*ctx));
+		dma_buf_put(dmabuf);
+		return ret;
+	}
+
+	if (WARN_ON_ONCE(!ctx->dev_ops ||
+			 !ctx->dev_ops->map ||
+			 !ctx->dev_ops->unmap ||
+			 !ctx->dev_ops->release))
+		return -EINVAL;
+
+	return ret;
+}
diff --git a/include/linux/dma-buf-io.h b/include/linux/dma-buf-io.h
new file mode 100644
index 000000000000..bcffc6202556
--- /dev/null
+++ b/include/linux/dma-buf-io.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __DMA_BUF_IO_H__
+#define __DMA_BUF_IO_H__
+
+#include <linux/dma-buf.h>
+
+struct dma_buf_io_fence;
+struct dma_buf_io_ctx;
+struct dma_buf_io_map;
+
+struct dma_buf_io_ops {
+	/*
+	 * Create a new map for the given ctx. Called with the reservation
+	 * lock held.
+	 */
+	struct dma_buf_io_map *(*map)(struct dma_buf_io_ctx *ctx);
+
+	/*
+	 * Clean up device specific parts of the @map. Called with the
+	 * reservation lock held.
+	 */
+	void (*unmap)(struct dma_buf_io_ctx *ctx, struct dma_buf_io_map *map);
+
+	/*
+	 * The user tries to destroy the ctx. Release all device specific
+	 * parts of the token.
+	 */
+	void (*release)(struct dma_buf_io_ctx *);
+};
+
+struct dma_buf_io_map {
+	/*
+	 * Counts attached requests and other users. Device specific unmapping
+	 * is deferred until all refs are dropped.
+	 */
+	struct percpu_ref		refs;
+
+	struct work_struct		release_work;
+	struct dma_buf_io_fence		*fence;
+	struct dma_buf_io_ctx		*ctx;
+};
+
+struct dma_buf_io_ctx {
+	struct dma_buf_io_map __rcu		*map;
+	struct dma_buf				*dmabuf;
+	enum dma_data_direction			dir;
+
+	atomic_t				fence_seq;
+	u64					fence_ctx;
+	struct work_struct			release_work;
+	refcount_t				refs;
+
+	void					*dev_priv;
+	const struct dma_buf_io_ops		*dev_ops;
+};
+
+int dma_buf_io_ctx_create(struct file *file,
+			   struct dma_buf_io_ctx *ctx,
+			   struct dma_buf *dmabuf,
+			   enum dma_data_direction dir);
+void dma_buf_io_ctx_release(struct dma_buf_io_ctx *ctx);
+
+struct dma_buf_io_map *dma_buf_io_create_map(struct dma_buf_io_ctx *ctx);
+
+static inline struct dma_buf_io_map *
+dma_buf_io_get_map(struct dma_buf_io_ctx *ctx)
+{
+	struct dma_buf_io_map *map;
+
+	guard(rcu)();
+
+	map = rcu_dereference(ctx->map);
+	if (unlikely(!map || !percpu_ref_tryget_live_rcu(&map->refs)))
+		return NULL;
+
+	return map;
+}
+
+static inline void dma_buf_io_map_drop(struct dma_buf_io_map *map)
+{
+	percpu_ref_put(&map->refs);
+}
+
+/*
+ * Device API
+ */
+
+void dma_buf_io_invalidate_mappings(struct dma_buf_io_ctx *ctx);
+int dma_buf_io_init_map(struct dma_buf_io_ctx *ctx, struct dma_buf_io_map *map);
+
+#endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index d10897b3a1e3..9fe349a279c7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1914,6 +1914,7 @@ struct dir_context {
 #define COPY_FILE_SPLICE		(1 << 0)
 
 struct io_uring_cmd;
+struct dma_buf_io_ctx;
 struct offset_ctx;
 
 typedef unsigned int __bitwise fop_flags_t;
@@ -1962,6 +1963,7 @@ struct file_operations {
 	int (*uring_cmd_iopoll)(struct io_uring_cmd *, struct io_comp_batch *,
 				unsigned int poll_flags);
 	int (*mmap_prepare)(struct vm_area_desc *);
+	int (*init_dma_buf_io_ctx)(struct file *, struct dma_buf_io_ctx *);
 } __randomize_layout;
 
 /* Supports async buffered reads */
-- 
2.54.0

Re: [PATCH v4 01/14] dma-buf: introduce initial file I/O infrastructure

[Christoph Hellwig]

The method name feels a bit convoluted, but given all the
previous discussions I don't care too strongly.  I'll leave
the dma-buf side review to those who understand it.

Re: [PATCH v4 01/14] dma-buf: introduce initial file I/O infrastructure

[Pavel Begunkov]

On 7/29/26 07:59, Christoph Hellwig wrote:
> The method name feels a bit convoluted, but given all the
> previous discussions I don't care too strongly.  I'll leave
> the dma-buf side review to those who understand it.

I assume you mean this:

+	int (*init_dma_buf_io_ctx)(struct file *, struct dma_buf_io_ctx *);

I agree, and all dma_buf_io_[ctx,map] look clunky, but I don't
see what I can drop out of the name. Suggestions? Maybe I at least
should make the fs op sth like "register_dma_buf".

-- 
Pavel Begunkov

Re: [PATCH v4 01/14] dma-buf: introduce initial file I/O infrastructure

[Christoph Hellwig]

On Wed, Jul 29, 2026 at 11:37:19AM +0100, Pavel Begunkov wrote:
> On 7/29/26 07:59, Christoph Hellwig wrote:
>> The method name feels a bit convoluted, but given all the
>> previous discussions I don't care too strongly.  I'll leave
>> the dma-buf side review to those who understand it.
>
> I assume you mean this:

Yes.

>
> +	int (*init_dma_buf_io_ctx)(struct file *, struct dma_buf_io_ctx *);
>
> I agree, and all dma_buf_io_[ctx,map] look clunky, but I don't
> see what I can drop out of the name. Suggestions? Maybe I at least
> should make the fs op sth like "register_dma_buf".

I just remember scares from the last discussion :)

register_dma_buf sounds fine to be, but unless I misremember there
were objections to that before.

>
> -- 
> Pavel Begunkov
---end quoted text---

Re: [PATCH v4 01/14] dma-buf: introduce initial file I/O infrastructure

[Pavel Begunkov]

On 7/29/26 12:28, Christoph Hellwig wrote:
> On Wed, Jul 29, 2026 at 11:37:19AM +0100, Pavel Begunkov wrote:
>> On 7/29/26 07:59, Christoph Hellwig wrote:
>>> The method name feels a bit convoluted, but given all the
>>> previous discussions I don't care too strongly.  I'll leave
>>> the dma-buf side review to those who understand it.
>>
>> I assume you mean this:
> 
> Yes.
> 
>>
>> +	int (*init_dma_buf_io_ctx)(struct file *, struct dma_buf_io_ctx *);
>>
>> I agree, and all dma_buf_io_[ctx,map] look clunky, but I don't
>> see what I can drop out of the name. Suggestions? Maybe I at least
>> should make the fs op sth like "register_dma_buf".
> 
> I just remember scares from the last discussion :)
> 
> register_dma_buf sounds fine to be, but unless I misremember there
> were objections to that before.
I'm going to respin the set in a couple of days, just going to
leave it as is unless we find better options.

-- 
Pavel Begunkov

[PATCH v4 02/14] iov_iter: add iterator type for dmabuf maps

[Pavel Begunkov]

Introduce a new iterator type for dmabuf maps. The map in an opaque
object with internals and format specific to the subsystem / driver, and
only it can use that subsystem / driver for issuing IO. The task of the
middle layers is to pass the map / iterator further down, maybe doing
basic splitting and length checking. The iterator can only be used by
operations of the file the associated map was created for.

Suggested-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/uio.h | 11 +++++++++++
 lib/iov_iter.c      | 29 +++++++++++++++++++++++------
 2 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index a9bc5b3067e3..6c31ec131a71 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -12,6 +12,7 @@
 
 struct page;
 struct folio_queue;
+struct dma_buf_io_map;
 
 typedef unsigned int __bitwise iov_iter_extraction_t;
 
@@ -29,6 +30,7 @@ enum iter_type {
 	ITER_FOLIOQ,
 	ITER_XARRAY,
 	ITER_DISCARD,
+	ITER_DMABUF_MAP,
 };
 
 #define ITER_SOURCE	1	// == WRITE
@@ -71,6 +73,7 @@ struct iov_iter {
 				const struct folio_queue *folioq;
 				struct xarray *xarray;
 				void __user *ubuf;
+				struct dma_buf_io_map *dmabuf_map;
 			};
 			size_t count;
 		};
@@ -155,6 +158,11 @@ static inline bool iov_iter_is_xarray(const struct iov_iter *i)
 	return iov_iter_type(i) == ITER_XARRAY;
 }
 
+static inline bool iov_iter_is_dmabuf_map(const struct iov_iter *i)
+{
+	return iov_iter_type(i) == ITER_DMABUF_MAP;
+}
+
 static inline unsigned char iov_iter_rw(const struct iov_iter *i)
 {
 	return i->data_source ? WRITE : READ;
@@ -300,6 +308,9 @@ void iov_iter_folio_queue(struct iov_iter *i, unsigned int direction,
 			  unsigned int first_slot, unsigned int offset, size_t count);
 void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray *xarray,
 		     loff_t start, size_t count);
+void iov_iter_dmabuf_map(struct iov_iter *i, unsigned int direction,
+			struct dma_buf_io_map *map,
+			loff_t off, size_t count);
 ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
 			size_t maxsize, unsigned maxpages, size_t *start);
 ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i, struct page ***pages,
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 273919b16161..6398b306d0e2 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -575,7 +575,8 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
 {
 	if (unlikely(i->count < size))
 		size = i->count;
-	if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i))) {
+	if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i)) ||
+	    unlikely(iov_iter_is_dmabuf_map(i))) {
 		i->iov_offset += size;
 		i->count -= size;
 	} else if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
@@ -631,7 +632,8 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
 		return;
 	}
 	unroll -= i->iov_offset;
-	if (iov_iter_is_xarray(i) || iter_is_ubuf(i)) {
+	if (iov_iter_is_xarray(i) || iter_is_ubuf(i) ||
+	    iov_iter_is_dmabuf_map(i)) {
 		BUG(); /* We should never go beyond the start of the specified
 			* range since we might then be straying into pages that
 			* aren't pinned.
@@ -775,6 +777,20 @@ void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
 }
 EXPORT_SYMBOL(iov_iter_xarray);
 
+void iov_iter_dmabuf_map(struct iov_iter *i, unsigned int direction,
+			 struct dma_buf_io_map *map,
+			 loff_t off, size_t count)
+{
+	WARN_ON(direction & ~(READ | WRITE));
+	*i = (struct iov_iter){
+		.iter_type = ITER_DMABUF_MAP,
+		.data_source = direction,
+		.dmabuf_map = map,
+		.count = count,
+		.iov_offset = off,
+	};
+}
+
 /**
  * iov_iter_discard - Initialise an I/O iterator that discards data
  * @i: The iterator to initialise.
@@ -841,7 +857,7 @@ static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i)
 
 unsigned long iov_iter_alignment(const struct iov_iter *i)
 {
-	if (likely(iter_is_ubuf(i))) {
+	if (likely(iter_is_ubuf(i)) || iov_iter_is_dmabuf_map(i)) {
 		size_t size = i->count;
 		if (size)
 			return ((unsigned long)i->ubuf + i->iov_offset) | size;
@@ -872,7 +888,7 @@ unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
 	size_t size = i->count;
 	unsigned k;
 
-	if (iter_is_ubuf(i))
+	if (iter_is_ubuf(i) || iov_iter_is_dmabuf_map(i))
 		return 0;
 
 	if (WARN_ON(!iter_is_iovec(i)))
@@ -1469,11 +1485,12 @@ EXPORT_SYMBOL_GPL(import_ubuf);
 void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
 {
 	if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i) &&
-			 !iter_is_ubuf(i)) && !iov_iter_is_kvec(i))
+			 !iter_is_ubuf(i) && !iov_iter_is_kvec(i) &&
+			 !iov_iter_is_dmabuf_map(i)))
 		return;
 	i->iov_offset = state->iov_offset;
 	i->count = state->count;
-	if (iter_is_ubuf(i))
+	if (iter_is_ubuf(i) || iov_iter_is_dmabuf_map(i))
 		return;
 	/*
 	 * For the *vec iters, nr_segs + iov is constant - if we increment
-- 
2.54.0

Re: [PATCH v4 02/14] iov_iter: add iterator type for dmabuf maps

[Christoph Hellwig]

On Tue, Jul 28, 2026 at 10:29:14PM +0100, Pavel Begunkov wrote:
> Introduce a new iterator type for dmabuf maps. The map in an opaque
> object with internals and format specific to the subsystem / driver, and
> only it can use that subsystem / driver for issuing IO. The task of the
> middle layers is to pass the map / iterator further down, maybe doing
> basic splitting and length checking. The iterator can only be used by
> operations of the file the associated map was created for.
> 
> Suggested-by: Keith Busch <kbusch@kernel.org>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

I'm also pretty sure I reviewed this and vairous other patches
before..

Re: [PATCH v4 02/14] iov_iter: add iterator type for dmabuf maps

[Pavel Begunkov]

On 7/29/26 07:59, Christoph Hellwig wrote:
> On Tue, Jul 28, 2026 at 10:29:14PM +0100, Pavel Begunkov wrote:
>> Introduce a new iterator type for dmabuf maps. The map in an opaque
>> object with internals and format specific to the subsystem / driver, and
>> only it can use that subsystem / driver for issuing IO. The task of the
>> middle layers is to pass the map / iterator further down, maybe doing
>> basic splitting and length checking. The iterator can only be used by
>> operations of the file the associated map was created for.
>>
>> Suggested-by: Keith Busch <kbusch@kernel.org>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> 
> Looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks,

> I'm also pretty sure I reviewed this and vairous other patches
> before..

There was a lot of shuffling, so I dropped the tag after a 10th
amendment to the patch as I didn't know whether you want to keep it.
I'll keep it all for v5 unless anything conceptual changes.

-- 
Pavel Begunkov

[PATCH v4 03/14] block: rename bi_bvec_done

[Pavel Begunkov]

struct bvec_iter::bi_bvec_done is used an offset in the current bvec,
let's rename it accordingly for better clarity. We're also going to use
it for non-bvec based iteration, so drop the "bvec" part.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 Documentation/block/biovecs.rst |  8 ++++----
 block/bio.c                     |  4 ++--
 block/blk-merge.c               |  8 ++++----
 block/blk-mq-dma.c              |  2 +-
 block/blk.h                     |  2 +-
 drivers/block/loop.c            |  2 +-
 drivers/block/zloop.c           |  2 +-
 drivers/md/dm-io-rewind.c       | 10 +++++-----
 drivers/md/dm-pcache/segment.c  |  4 ++--
 drivers/nvdimm/btt.c            |  2 +-
 drivers/nvme/host/tcp.c         |  2 +-
 fs/btrfs/misc.h                 |  2 +-
 include/linux/bvec.h            | 14 +++++++-------
 io_uring/net.c                  |  4 ++--
 lib/iov_iter.c                  |  2 +-
 net/ceph/messenger.c            |  4 ++--
 16 files changed, 36 insertions(+), 36 deletions(-)

diff --git a/Documentation/block/biovecs.rst b/Documentation/block/biovecs.rst
index 11126ed6f40f..49da2147b7d8 100644
--- a/Documentation/block/biovecs.rst
+++ b/Documentation/block/biovecs.rst
@@ -16,16 +16,16 @@ bv_len by the number of bytes completed in that biovec.
 In the new scheme of things, everything that must be mutated in order to
 partially complete a bio is segregated into struct bvec_iter: bi_sector,
 bi_size and bi_idx have been moved there; and instead of modifying bv_offset
-and bv_len, struct bvec_iter has bi_bvec_done, which represents the number of
+and bv_len, struct bvec_iter has bi_offset, which represents the number of
 bytes completed in the current bvec.
 
 There are a bunch of new helper macros for hiding the gory details - in
 particular, presenting the illusion of partially completed biovecs so that
-normal code doesn't have to deal with bi_bvec_done.
+normal code doesn't have to deal with bi_offset.
 
  * Driver code should no longer refer to biovecs directly; we now have
    bio_iovec() and bio_iter_iovec() macros that return literal struct biovecs,
-   constructed from the raw biovecs but taking into account bi_bvec_done and
+   constructed from the raw biovecs but taking into account bi_offset and
    bi_size.
 
    bio_for_each_segment() has been updated to take a bvec_iter argument
@@ -101,7 +101,7 @@ Other implications:
    I.e. instead of using bio_iovec_idx() (or bio->bi_iovec[bio->bi_idx]), you
    now use bio_iter_iovec(), which takes a bvec_iter and returns a
    literal struct bio_vec - constructed on the fly from the raw biovec but
-   taking into account bi_bvec_done (and bi_size).
+   taking into account bi_offset (and bi_size).
 
  * bi_vcnt can't be trusted or relied upon by driver code - i.e. anything that
    doesn't actually own the bio. The reason is twofold: firstly, it's not
diff --git a/block/bio.c b/block/bio.c
index 6a2f6fc3413e..bfaede30a54f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -229,7 +229,7 @@ void bio_init(struct bio *bio, struct block_device *bdev, struct bio_vec *table,
 	bio->bi_iter.bi_sector = 0;
 	bio->bi_iter.bi_size = 0;
 	bio->bi_iter.bi_idx = 0;
-	bio->bi_iter.bi_bvec_done = 0;
+	bio->bi_iter.bi_offset = 0;
 	bio->bi_end_io = NULL;
 	bio->bi_private = NULL;
 #ifdef CONFIG_BLK_CGROUP
@@ -1188,7 +1188,7 @@ void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter)
 
 	bio->bi_io_vec = (struct bio_vec *)iter->bvec;
 	bio->bi_iter.bi_idx = 0;
-	bio->bi_iter.bi_bvec_done = iter->iov_offset;
+	bio->bi_iter.bi_offset = iter->iov_offset;
 	bio->bi_iter.bi_size = iov_iter_count(iter);
 	bio_set_flag(bio, BIO_CLONED);
 }
diff --git a/block/blk-merge.c b/block/blk-merge.c
index ab1161ca69f1..258a726071d1 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -33,7 +33,7 @@ static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
 
 	bio_advance_iter(bio, &iter, iter.bi_size);
 
-	if (!iter.bi_bvec_done)
+	if (!iter.bi_offset)
 		idx = iter.bi_idx - 1;
 	else	/* in the middle of bvec */
 		idx = iter.bi_idx;
@@ -41,11 +41,11 @@ static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
 	*bv = bio->bi_io_vec[idx];
 
 	/*
-	 * iter.bi_bvec_done records actual length of the last bvec
+	 * iter.bi_offset records actual length of the last bvec
 	 * if this bio ends in the middle of one io vector
 	 */
-	if (iter.bi_bvec_done)
-		bv->bv_len = iter.bi_bvec_done;
+	if (iter.bi_offset)
+		bv->bv_len = iter.bi_offset;
 }
 
 static inline bool bio_will_gap(struct request_queue *q,
diff --git a/block/blk-mq-dma.c b/block/blk-mq-dma.c
index bfdb9ed70741..88fd9cbc951f 100644
--- a/block/blk-mq-dma.c
+++ b/block/blk-mq-dma.c
@@ -44,7 +44,7 @@ static bool blk_map_iter_next(struct request *req, struct blk_map_iter *iter,
 	 * one could be merged into it.  This typically happens when moving to
 	 * the next bio, but some callers also don't pack bvecs tight.
 	 */
-	while (!iter->iter.bi_size || !iter->iter.bi_bvec_done) {
+	while (!iter->iter.bi_size || !iter->iter.bi_offset) {
 		struct bio_vec next;
 
 		if (!__blk_map_iter_next(iter))
diff --git a/block/blk.h b/block/blk.h
index eaac05815cb0..50abfd932886 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -406,7 +406,7 @@ static inline bool bio_may_need_split(struct bio *bio,
 		return true;
 
 	bv = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
-	if (bio->bi_iter.bi_size > bv->bv_len - bio->bi_iter.bi_bvec_done)
+	if (bio->bi_iter.bi_size > bv->bv_len - bio->bi_iter.bi_offset)
 		return true;
 	if ((bv->bv_offset | bv->bv_len) & lim->dma_alignment)
 		return true;
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1faecef33009..0b125ccb2663 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -378,7 +378,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
 		iov_iter_bvec(&iter, rw,
 			__bvec_iter_bvec(rq->bio->bi_io_vec, rq->bio->bi_iter),
 			nr_bvec, blk_rq_bytes(rq));
-		iter.iov_offset = rq->bio->bi_iter.bi_bvec_done;
+		iter.iov_offset = rq->bio->bi_iter.bi_offset;
 	}
 	atomic_set(&cmd->ref, 2);
 
diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index 55eeb6aac0ea..6f4b44a1ee2f 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -553,7 +553,7 @@ static int zloop_do_rw(struct zloop_cmd *cmd)
 		iov_iter_bvec(&iter, rw,
 			__bvec_iter_bvec(rq->bio->bi_io_vec, rq->bio->bi_iter),
 					nr_bvec, blk_rq_bytes(rq));
-		iter.iov_offset = rq->bio->bi_iter.bi_bvec_done;
+		iter.iov_offset = rq->bio->bi_iter.bi_offset;
 	}
 
 	cmd->iocb.ki_pos = (cmd->sector - zone->start) << SECTOR_SHIFT;
diff --git a/drivers/md/dm-io-rewind.c b/drivers/md/dm-io-rewind.c
index 6155b0117c9d..04f3fc8aeb6f 100644
--- a/drivers/md/dm-io-rewind.c
+++ b/drivers/md/dm-io-rewind.c
@@ -16,12 +16,12 @@ static inline bool dm_bvec_iter_rewind(const struct bio_vec *bv,
 	int idx;
 
 	iter->bi_size += bytes;
-	if (bytes <= iter->bi_bvec_done) {
-		iter->bi_bvec_done -= bytes;
+	if (bytes <= iter->bi_offset) {
+		iter->bi_offset -= bytes;
 		return true;
 	}
 
-	bytes -= iter->bi_bvec_done;
+	bytes -= iter->bi_offset;
 	idx = iter->bi_idx - 1;
 
 	while (idx >= 0 && bytes && bytes > bv[idx].bv_len) {
@@ -32,13 +32,13 @@ static inline bool dm_bvec_iter_rewind(const struct bio_vec *bv,
 	if (WARN_ONCE(idx < 0 && bytes,
 		      "Attempted to rewind iter beyond bvec's boundaries\n")) {
 		iter->bi_size -= bytes;
-		iter->bi_bvec_done = 0;
+		iter->bi_offset = 0;
 		iter->bi_idx = 0;
 		return false;
 	}
 
 	iter->bi_idx = idx;
-	iter->bi_bvec_done = bv[idx].bv_len - bytes;
+	iter->bi_offset = bv[idx].bv_len - bytes;
 	return true;
 }
 
diff --git a/drivers/md/dm-pcache/segment.c b/drivers/md/dm-pcache/segment.c
index 7e9818701445..8f8816e1c539 100644
--- a/drivers/md/dm-pcache/segment.c
+++ b/drivers/md/dm-pcache/segment.c
@@ -14,7 +14,7 @@ int segment_copy_to_bio(struct pcache_segment *segment,
 
 	iov_iter_bvec(&iter, ITER_DEST, &bio->bi_io_vec[bio->bi_iter.bi_idx],
 			bio_segments(bio), bio->bi_iter.bi_size);
-	iter.iov_offset = bio->bi_iter.bi_bvec_done;
+	iter.iov_offset = bio->bi_iter.bi_offset;
 	if (bio_off)
 		iov_iter_advance(&iter, bio_off);
 
@@ -35,7 +35,7 @@ int segment_copy_from_bio(struct pcache_segment *segment,
 
 	iov_iter_bvec(&iter, ITER_SOURCE, &bio->bi_io_vec[bio->bi_iter.bi_idx],
 			bio_segments(bio), bio->bi_iter.bi_size);
-	iter.iov_offset = bio->bi_iter.bi_bvec_done;
+	iter.iov_offset = bio->bi_iter.bi_offset;
 	if (bio_off)
 		iov_iter_advance(&iter, bio_off);
 
diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index 7e1112960d7f..5d910a64503d 100644
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -1155,7 +1155,7 @@ static int btt_rw_integrity(struct btt *btt, struct bio_integrity_payload *bip,
 		bv = bvec_iter_bvec(bip->bip_vec, bip->bip_iter);
 		/*
 		 * The 'bv' obtained from bvec_iter_bvec has its .bv_len and
-		 * .bv_offset already adjusted for iter->bi_bvec_done, and we
+		 * .bv_offset already adjusted for iter->bi_offset, and we
 		 * can use those directly
 		 */
 
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index ba5c7b3e2a7c..ce03a0ea4ded 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -357,7 +357,7 @@ static void nvme_tcp_init_iter(struct nvme_tcp_request *req,
 		iov_iter_bvec(&req->iter, dir,
 			__bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter), nr_bvec,
 			bio->bi_iter.bi_size);
-		req->iter.iov_offset = bio->bi_iter.bi_bvec_done;
+		req->iter.iov_offset = bio->bi_iter.bi_offset;
 	}
 }
 
diff --git a/fs/btrfs/misc.h b/fs/btrfs/misc.h
index 694be6d0562a..802060943180 100644
--- a/fs/btrfs/misc.h
+++ b/fs/btrfs/misc.h
@@ -74,7 +74,7 @@ static inline struct bvec_iter init_bvec_iter_for_bio(struct bio *bio)
 		.bi_sector = 0,
 		.bi_size = bio_size,
 		.bi_idx = 0,
-		.bi_bvec_done = 0,
+		.bi_offset = 0,
 	};
 }
 
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index 92837e2743f1..fc566ee1c1ff 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -110,7 +110,7 @@ struct bvec_iter {
 	/*
 	 * Current offset in the bvec entry pointed to by `bi_idx`.
 	 */
-	unsigned int		bi_bvec_done;
+	unsigned int		bi_offset;
 } __packed __aligned(4);
 
 struct bvec_iter_all {
@@ -135,14 +135,14 @@ mp_bvec_iter_page(const struct bio_vec *bvecs, const struct bvec_iter iter)
 static __always_inline unsigned int
 mp_bvec_iter_len(const struct bio_vec *bvecs, const struct bvec_iter iter)
 {
-	return min(__bvec_iter_bvec(bvecs, iter)->bv_len - iter.bi_bvec_done,
+	return min(__bvec_iter_bvec(bvecs, iter)->bv_len - iter.bi_offset,
 			iter.bi_size);
 }
 
 static __always_inline unsigned int
 mp_bvec_iter_offset(const struct bio_vec *bvecs, const struct bvec_iter iter)
 {
-	return __bvec_iter_bvec(bvecs, iter)->bv_offset + iter.bi_bvec_done;
+	return __bvec_iter_bvec(bvecs, iter)->bv_offset + iter.bi_offset;
 }
 
 static __always_inline unsigned int
@@ -204,7 +204,7 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
 	}
 
 	iter->bi_size -= bytes;
-	bytes += iter->bi_bvec_done;
+	bytes += iter->bi_offset;
 
 	while (bytes && bytes >= bv[idx].bv_len) {
 		bytes -= bv[idx].bv_len;
@@ -212,7 +212,7 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
 	}
 
 	iter->bi_idx = idx;
-	iter->bi_bvec_done = bytes;
+	iter->bi_offset = bytes;
 	return true;
 }
 
@@ -223,13 +223,13 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
 static inline void bvec_iter_advance_single(const struct bio_vec *bv,
 				struct bvec_iter *iter, unsigned int bytes)
 {
-	unsigned int done = iter->bi_bvec_done + bytes;
+	unsigned int done = iter->bi_offset + bytes;
 
 	if (done == bv[iter->bi_idx].bv_len) {
 		done = 0;
 		iter->bi_idx++;
 	}
-	iter->bi_bvec_done = done;
+	iter->bi_offset = done;
 	iter->bi_size -= bytes;
 }
 
diff --git a/io_uring/net.c b/io_uring/net.c
index a74d15f7b7d2..439c99ad1884 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -1471,7 +1471,7 @@ static int io_sg_from_iter(struct sk_buff *skb,
 		return zerocopy_fill_skb_from_iter(skb, from, length);
 
 	bi.bi_size = min(from->count, length);
-	bi.bi_bvec_done = from->iov_offset;
+	bi.bi_offset = from->iov_offset;
 	bi.bi_idx = 0;
 
 	while (bi.bi_size && frag < MAX_SKB_FRAGS) {
@@ -1490,7 +1490,7 @@ static int io_sg_from_iter(struct sk_buff *skb,
 	from->bvec += bi.bi_idx;
 	from->nr_segs -= bi.bi_idx;
 	from->count -= copied;
-	from->iov_offset = bi.bi_bvec_done;
+	from->iov_offset = bi.bi_offset;
 
 	skb->data_len += copied;
 	skb->len += copied;
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 6398b306d0e2..146e5ed80c7c 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1642,7 +1642,7 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
 	}
 	bi.bi_idx = 0;
 	bi.bi_size = maxsize;
-	bi.bi_bvec_done = skip;
+	bi.bi_offset = skip;
 
 	maxpages = want_pages_array(pages, maxsize, skip, maxpages);
 
diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 34b3097b4c7b..9c1b6cf8c36f 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -762,7 +762,7 @@ static bool ceph_msg_data_bio_advance(struct ceph_msg_data_cursor *cursor,
 	if (!cursor->resid)
 		return false;   /* no more data */
 
-	if (!bytes || (it->iter.bi_size && it->iter.bi_bvec_done &&
+	if (!bytes || (it->iter.bi_size && it->iter.bi_offset &&
 		       page == bio_iter_page(it->bio, it->iter)))
 		return false;	/* more bytes to process in this segment */
 
@@ -817,7 +817,7 @@ static bool ceph_msg_data_bvecs_advance(struct ceph_msg_data_cursor *cursor,
 	if (!cursor->resid)
 		return false;   /* no more data */
 
-	if (!bytes || (cursor->bvec_iter.bi_bvec_done &&
+	if (!bytes || (cursor->bvec_iter.bi_offset &&
 		       page == bvec_iter_page(bvecs, cursor->bvec_iter)))
 		return false;	/* more bytes to process in this segment */
 
-- 
2.54.0

Re: [PATCH v4 03/14] block: rename bi_bvec_done

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH v4 04/14] block: always adjust bi_offset on bio_advance_iter

[Pavel Begunkov]

Extend bio_no_advance_iter() iteration to also increment the offset.
It's not currently needed because the currently listed request types
don't have a buffer, but will be useful once we add bios backed by
dma-buf, which don't have a bvec but work with a single range.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 drivers/md/dm-io-rewind.c |  6 ++++--
 include/linux/bio.h       | 12 ++++++++----
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-io-rewind.c b/drivers/md/dm-io-rewind.c
index 04f3fc8aeb6f..b22719c6411c 100644
--- a/drivers/md/dm-io-rewind.c
+++ b/drivers/md/dm-io-rewind.c
@@ -113,10 +113,12 @@ static inline void dm_bio_rewind_iter(const struct bio *bio,
 	iter->bi_sector -= bytes >> 9;
 
 	/* No advance means no rewind */
-	if (bio_no_advance_iter(bio))
+	if (bio_no_advance_iter(bio)) {
 		iter->bi_size += bytes;
-	else
+		iter->bi_offset -= bytes;
+	} else {
 		dm_bvec_iter_rewind(bio->bi_io_vec, iter, bytes);
+	}
 }
 
 /**
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 8f33f717b14f..dea9f567379d 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -113,11 +113,13 @@ static inline void bio_advance_iter(const struct bio *bio,
 {
 	iter->bi_sector += bytes >> 9;
 
-	if (bio_no_advance_iter(bio))
+	if (bio_no_advance_iter(bio)) {
 		iter->bi_size -= bytes;
-	else
+		iter->bi_offset += bytes;
+	} else {
 		bvec_iter_advance(bio->bi_io_vec, iter, bytes);
 		/* TODO: It is reasonable to complete bio with error here. */
+	}
 }
 
 /* @bytes should be less or equal to bvec[i->bi_idx].bv_len */
@@ -127,10 +129,12 @@ static inline void bio_advance_iter_single(const struct bio *bio,
 {
 	iter->bi_sector += bytes >> 9;
 
-	if (bio_no_advance_iter(bio))
+	if (bio_no_advance_iter(bio)) {
 		iter->bi_size -= bytes;
-	else
+		iter->bi_offset += bytes;
+	} else {
 		bvec_iter_advance_single(bio->bi_io_vec, iter, bytes);
+	}
 }
 
 void __bio_advance(struct bio *, unsigned bytes);
-- 
2.54.0

Re: [PATCH v4 04/14] block: always adjust bi_offset on bio_advance_iter

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH v4 05/14] block: move bvec init into __bio_clone

[Pavel Begunkov]

Consolidate bi_io_vec assignment for cloning in __bio_clone to keep any
further changes in one place.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 block/bio.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index bfaede30a54f..57c127aee116 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -860,6 +860,7 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
 	bio->bi_write_hint = bio_src->bi_write_hint;
 	bio->bi_write_stream = bio_src->bi_write_stream;
 	bio->bi_iter = bio_src->bi_iter;
+	bio->bi_io_vec = bio_src->bi_io_vec;
 
 	if (bio->bi_bdev) {
 		if (bio->bi_bdev == bio_src->bi_bdev &&
@@ -902,8 +903,6 @@ struct bio *bio_alloc_clone(struct block_device *bdev, struct bio *bio_src,
 		bio_put(bio);
 		return NULL;
 	}
-	bio->bi_io_vec = bio_src->bi_io_vec;
-
 	return bio;
 }
 EXPORT_SYMBOL(bio_alloc_clone);
@@ -923,7 +922,7 @@ int bio_init_clone(struct block_device *bdev, struct bio *bio,
 {
 	int ret;
 
-	bio_init(bio, bdev, bio_src->bi_io_vec, 0, bio_src->bi_opf);
+	bio_init(bio, bdev, NULL, 0, bio_src->bi_opf);
 	ret = __bio_clone(bio, bio_src, gfp);
 	if (ret)
 		bio_uninit(bio);
-- 
2.54.0

Re: [PATCH v4 05/14] block: move bvec init into __bio_clone

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH v4 06/14] block: introduce dma map backed bio type

[Pavel Begunkov]

Premapped buffers don't require a generic bio_vec since these have
already been dma mapped. Repurpose the bi_io_vec space to strore dmabuf
maps as they are mutually exclusive.

Suggested-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 block/bio.c               | 23 ++++++++++++++++++++++-
 block/blk-merge.c         | 15 +++++++++++++++
 block/fops.c              |  2 ++
 include/linux/bio.h       | 10 ++++++----
 include/linux/blk-mq.h    |  7 +++++++
 include/linux/blk_types.h | 14 +++++++++++++-
 include/linux/bvec.h      |  3 ++-
 7 files changed, 67 insertions(+), 7 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 57c127aee116..cc2bb9183c1a 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -860,7 +860,12 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
 	bio->bi_write_hint = bio_src->bi_write_hint;
 	bio->bi_write_stream = bio_src->bi_write_stream;
 	bio->bi_iter = bio_src->bi_iter;
-	bio->bi_io_vec = bio_src->bi_io_vec;
+
+	if (op_is_dmabuf(bio->bi_opf)) {
+		bio->bi_dmabuf_map = bio_src->bi_dmabuf_map;
+	} else {
+		bio->bi_io_vec = bio_src->bi_io_vec;
+	}
 
 	if (bio->bi_bdev) {
 		if (bio->bi_bdev == bio_src->bi_bdev &&
@@ -1192,6 +1197,17 @@ void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter)
 	bio_set_flag(bio, BIO_CLONED);
 }
 
+void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter)
+{
+	WARN_ON_ONCE(bio->bi_max_vecs);
+
+	bio->bi_dmabuf_map = iter->dmabuf_map;
+	bio->bi_vcnt = 0;
+	bio->bi_iter.bi_offset = iter->iov_offset;
+	bio->bi_iter.bi_size = iov_iter_count(iter);
+	bio->bi_opf |= REQ_NOMERGE | REQ_DMABUF;
+}
+
 /*
  * Aligns the bio size to the len_align_mask, releasing excessive bio vecs that
  * __bio_iov_iter_get_pages may have inserted, and reverts the trimmed length
@@ -1254,6 +1270,11 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
 		iov_iter_advance(iter, bio->bi_iter.bi_size);
 		return 0;
 	}
+	if (iov_iter_is_dmabuf_map(iter)) {
+		bio_dmabuf_map_set(bio, iter);
+		iov_iter_advance(iter, bio->bi_iter.bi_size);
+		return 0;
+	}
 
 	if (iov_iter_extract_will_pin(iter))
 		bio_set_flag(bio, BIO_PAGE_PINNED);
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 258a726071d1..6f0cabfe25ef 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -346,6 +346,20 @@ int bio_split_io_at(struct bio *bio, const struct queue_limits *lim,
 		len_align_mask |= (bc->bc_key->crypto_cfg.data_unit_size - 1);
 	}
 
+	if (op_is_dmabuf(bio->bi_opf)) {
+		/* single contiguous range into the dma-buf */
+		nsegs = 1;
+
+		if ((bio->bi_iter.bi_offset & start_align_mask) ||
+		    (bio->bi_iter.bi_size & len_align_mask))
+			return -EINVAL;
+		if (bio->bi_iter.bi_size > max_bytes) {
+			bytes = max_bytes;
+			goto split;
+		}
+		goto out;
+	}
+
 	bio_for_each_bvec(bv, bio, iter) {
 		if (bv.bv_offset & start_align_mask ||
 		    bv.bv_len & len_align_mask)
@@ -376,6 +390,7 @@ int bio_split_io_at(struct bio *bio, const struct queue_limits *lim,
 		bvprvp = &bvprv;
 	}
 
+out:
 	*segs = nsegs;
 	bio->bi_bvec_gap_bit = ffs(gaps);
 	return 0;
diff --git a/block/fops.c b/block/fops.c
index 15783a6180de..37d491f45015 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -348,6 +348,8 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
 		 * bio_iov_iter_get_pages() and set the bvec directly.
 		 */
 		bio_iov_bvec_set(bio, iter);
+	} else if (iov_iter_is_dmabuf_map(iter)) {
+		bio_dmabuf_map_set(bio, iter);
 	} else {
 		ret = blkdev_iov_iter_get_pages(bio, iter, bdev);
 		if (unlikely(ret))
diff --git a/include/linux/bio.h b/include/linux/bio.h
index dea9f567379d..c053e9444514 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -80,7 +80,8 @@ static inline bool bio_no_advance_iter(const struct bio *bio)
 {
 	return bio_op(bio) == REQ_OP_DISCARD ||
 	       bio_op(bio) == REQ_OP_SECURE_ERASE ||
-	       bio_op(bio) == REQ_OP_WRITE_ZEROES;
+	       bio_op(bio) == REQ_OP_WRITE_ZEROES ||
+	       op_is_dmabuf(bio->bi_opf);
 }
 
 static inline void *bio_data(struct bio *bio)
@@ -399,12 +400,12 @@ static inline void bio_wouldblock_error(struct bio *bio)
 
 /*
  * Calculate number of bvec segments that should be allocated to fit data
- * pointed by @iter. If @iter is backed by bvec it's going to be reused
- * instead of allocating a new one.
+ * pointed by @iter. If @iter is backed by a bvec or a dmabuf, the bvec array /
+ * the dma map are going to be reused, and so no extra allocation is required.
  */
 static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
 {
-	if (iov_iter_is_bvec(iter))
+	if (iov_iter_is_bvec(iter) || iov_iter_is_dmabuf_map(iter))
 		return 0;
 	return iov_iter_npages(iter, max_segs);
 }
@@ -484,6 +485,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
 		unsigned len_align_mask);
 
 void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter);
+void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter);
 void __bio_release_pages(struct bio *bio, bool mark_dirty);
 extern void bio_set_pages_dirty(struct bio *bio);
 extern void bio_check_pages_dirty(struct bio *bio);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index af878597afb8..7c7504c84e09 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -1017,6 +1017,13 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
 	return rq + 1;
 }
 
+static inline bool blk_mq_rq_is_dmabuf(struct request *rq)
+{
+	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
+		return false;
+	return rq->bio && op_is_dmabuf(rq->bio->bi_opf);
+}
+
 static inline struct blk_mq_hw_ctx *queue_hctx(struct request_queue *q, int id)
 {
 	struct blk_mq_hw_ctx *hctx;
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 8808ee76e73c..d605e31712d4 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -233,7 +233,12 @@ struct bio {
 	atomic_t		__bi_remaining;
 
 	/* The actual vec list, preserved by bio_reset() */
-	struct bio_vec		*bi_io_vec;
+	union {
+		struct bio_vec		*bi_io_vec;
+		/* Driver specific dma map, valid IFF REQ_DMABUF is set */
+		struct dma_buf_io_map	*bi_dmabuf_map;
+	};
+
 	struct bvec_iter	bi_iter;
 
 	union {
@@ -401,6 +406,7 @@ enum req_flag_bits {
 	__REQ_DRV,		/* for driver use */
 	__REQ_FS_PRIVATE,	/* for file system (submitter) use */
 	__REQ_ATOMIC,		/* for atomic write operations */
+	__REQ_DMABUF,		/* Using premmaped dma buffers */
 	/*
 	 * Command specific flags, keep last:
 	 */
@@ -433,6 +439,7 @@ enum req_flag_bits {
 #define REQ_DRV		(__force blk_opf_t)(1ULL << __REQ_DRV)
 #define REQ_FS_PRIVATE	(__force blk_opf_t)(1ULL << __REQ_FS_PRIVATE)
 #define REQ_ATOMIC	(__force blk_opf_t)(1ULL << __REQ_ATOMIC)
+#define REQ_DMABUF	(__force blk_opf_t)(1ULL << __REQ_DMABUF)
 
 #define REQ_NOUNMAP	(__force blk_opf_t)(1ULL << __REQ_NOUNMAP)
 
@@ -486,6 +493,11 @@ static inline bool op_is_discard(blk_opf_t op)
 	return (op & REQ_OP_MASK) == REQ_OP_DISCARD;
 }
 
+static inline bool op_is_dmabuf(blk_opf_t op)
+{
+	return op & REQ_DMABUF;
+}
+
 /*
  * Check if a bio or request operation is a zone management operation.
  */
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index fc566ee1c1ff..b63914ff56e3 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -108,7 +108,8 @@ struct bvec_iter {
 	unsigned int		bi_idx;
 
 	/*
-	 * Current offset in the bvec entry pointed to by `bi_idx`.
+	 * Current offset in the bvec entry pointed to by `bi_idx` or into
+	 * a dma-buf map.
 	 */
 	unsigned int		bi_offset;
 } __packed __aligned(4);
-- 
2.54.0

Re: [PATCH v4 06/14] block: introduce dma map backed bio type

[Christoph Hellwig]

> -	bio->bi_io_vec = bio_src->bi_io_vec;
> +
> +	if (op_is_dmabuf(bio->bi_opf)) {
> +		bio->bi_dmabuf_map = bio_src->bi_dmabuf_map;
> +	} else {
> +		bio->bi_io_vec = bio_src->bi_io_vec;
> +	}

No need for the braces.  But given that these are the fields why
even bother doing both sides and not rely on the union?

> +void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter)
> +{
> +	WARN_ON_ONCE(bio->bi_max_vecs);
> +
> +	bio->bi_dmabuf_map = iter->dmabuf_map;
> +	bio->bi_vcnt = 0;
> +	bio->bi_iter.bi_offset = iter->iov_offset;
> +	bio->bi_iter.bi_size = iov_iter_count(iter);
> +	bio->bi_opf |= REQ_NOMERGE | REQ_DMABUF;

This seems to be largely copied from bio_iov_bvec_set, but misses
the REQ_CLONE there that we should probably set as well to indicate
that the data descriptor is not owned (although not setting it is
not really a bug).

What about merging these two into a single and easier to use interface
like this:

diff --git a/block/bio.c b/block/bio.c
index cc2bb9183c1a..25393bdd119d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -860,12 +860,9 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
 	bio->bi_write_hint = bio_src->bi_write_hint;
 	bio->bi_write_stream = bio_src->bi_write_stream;
 	bio->bi_iter = bio_src->bi_iter;
-
-	if (op_is_dmabuf(bio->bi_opf)) {
-		bio->bi_dmabuf_map = bio_src->bi_dmabuf_map;
-	} else {
-		bio->bi_io_vec = bio_src->bi_io_vec;
-	}
+	static_assert(offsetof(struct bio, bi_io_vec) ==
+		      offsetof(struct bio, bi_dmabuf_map));
+	bio->bi_io_vec = bio_src->bi_io_vec;
 
 	if (bio->bi_bdev) {
 		if (bio->bi_bdev == bio_src->bi_bdev &&
@@ -1186,26 +1183,21 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
 }
 EXPORT_SYMBOL_GPL(__bio_release_pages);
 
-void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter)
+bool bio_iov_iter_set(struct bio *bio, const struct iov_iter *iter)
 {
 	WARN_ON_ONCE(bio->bi_max_vecs);
 
+	if (!iov_iter_is_bvec(iter) && !iov_iter_is_dmabuf_map(iter))
+		return false;
+
 	bio->bi_io_vec = (struct bio_vec *)iter->bvec;
 	bio->bi_iter.bi_idx = 0;
 	bio->bi_iter.bi_offset = iter->iov_offset;
 	bio->bi_iter.bi_size = iov_iter_count(iter);
 	bio_set_flag(bio, BIO_CLONED);
-}
-
-void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter)
-{
-	WARN_ON_ONCE(bio->bi_max_vecs);
-
-	bio->bi_dmabuf_map = iter->dmabuf_map;
-	bio->bi_vcnt = 0;
-	bio->bi_iter.bi_offset = iter->iov_offset;
-	bio->bi_iter.bi_size = iov_iter_count(iter);
-	bio->bi_opf |= REQ_NOMERGE | REQ_DMABUF;
+	if (iov_iter_is_dmabuf_map(iter))
+		bio->bi_opf |= REQ_NOMERGE | REQ_DMABUF;
+	return true;
 }
 
 /*
@@ -1265,13 +1257,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
 	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
 		return -EIO;
 
-	if (iov_iter_is_bvec(iter)) {
-		bio_iov_bvec_set(bio, iter);
-		iov_iter_advance(iter, bio->bi_iter.bi_size);
-		return 0;
-	}
-	if (iov_iter_is_dmabuf_map(iter)) {
-		bio_dmabuf_map_set(bio, iter);
+	if (bio_iov_iter_set(bio, iter)) {
 		iov_iter_advance(iter, bio->bi_iter.bi_size);
 		return 0;
 	}
diff --git a/block/blk-map.c b/block/blk-map.c
index d1d6bbe0ecf1..34816e6e64de 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -473,7 +473,7 @@ static int blk_rq_map_user_bvec(struct request *rq, const struct iov_iter *iter)
 	bio = blk_rq_map_bio_alloc(rq, 0, GFP_KERNEL);
 	if (!bio)
 		return -ENOMEM;
-	bio_iov_bvec_set(bio, iter);
+	bio_iov_iter_set(bio, iter);
 
 	ret = blk_rq_append_bio(rq, bio);
 	if (ret)
diff --git a/block/fops.c b/block/fops.c
index d83cdbab65a6..97fb124a19b2 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -340,17 +340,12 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
 	bio->bi_end_io = blkdev_bio_end_io_async;
 	bio->bi_ioprio = iocb->ki_ioprio;
 
-	if (iov_iter_is_bvec(iter)) {
-		/*
-		 * Users don't rely on the iterator being in any particular
-		 * state for async I/O returning -EIOCBQUEUED, hence we can
-		 * avoid expensive iov_iter_advance(). Bypass
-		 * bio_iov_iter_get_pages() and set the bvec directly.
-		 */
-		bio_iov_bvec_set(bio, iter);
-	} else if (iov_iter_is_dmabuf_map(iter)) {
-		bio_dmabuf_map_set(bio, iter);
-	} else {
+	/*
+	 * Users don't rely on the iterator being in any particular state for
+	 * async I/O returning -EIOCBQUEUED, hence we can avoid the expensive
+	 * iov_iter_advance() if we could set the bvec/dmabuf directly.
+	 */
+	if (!bio_iov_iter_set(bio, iter)) {
 		ret = blkdev_iov_iter_get_pages(bio, iter, bdev);
 		if (unlikely(ret))
 			goto out_bio_put;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index c053e9444514..1eff02a843ef 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -484,8 +484,7 @@ int bdev_rw_virt(struct block_device *bdev, sector_t sector, void *data,
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
 		unsigned len_align_mask);
 
-void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter);
-void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter);
+bool bio_iov_iter_set(struct bio *bio, const struct iov_iter *iter);
 void __bio_release_pages(struct bio *bio, bool mark_dirty);
 extern void bio_set_pages_dirty(struct bio *bio);
 extern void bio_check_pages_dirty(struct bio *bio);

Re: [PATCH v4 06/14] block: introduce dma map backed bio type

[Pavel Begunkov]

On 7/29/26 08:07, Christoph Hellwig wrote:
>> -	bio->bi_io_vec = bio_src->bi_io_vec;
>> +
>> +	if (op_is_dmabuf(bio->bi_opf)) {
>> +		bio->bi_dmabuf_map = bio_src->bi_dmabuf_map;
>> +	} else {
>> +		bio->bi_io_vec = bio_src->bi_io_vec;
>> +	}
> 
> No need for the braces.  

Got it,

But given that these are the fields why
> even bother doing both sides and not rely on the union?

Compiles into the same, but comparing to a comment makes
the compiler to check it for us if anything happens.

Noticed static_assert() below, that works as well, though I
think the current version is nicer b/c it preserves assignment
types for the compiler. Strict aliasing is obviously not a
thing, so don't have a strong opinion.

>> +void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter)
>> +{
>> +	WARN_ON_ONCE(bio->bi_max_vecs);
>> +
>> +	bio->bi_dmabuf_map = iter->dmabuf_map;
>> +	bio->bi_vcnt = 0;
>> +	bio->bi_iter.bi_offset = iter->iov_offset;
>> +	bio->bi_iter.bi_size = iov_iter_count(iter);
>> +	bio->bi_opf |= REQ_NOMERGE | REQ_DMABUF;
> 
> This seems to be largely copied from bio_iov_bvec_set, but misses
> the REQ_CLONE there that we should probably set as well to indicate
> that the data descriptor is not owned (although not setting it is
> not really a bug).
> 
> What about merging these two into a single and easier to use interface
> like this:

No opinion on this, I can add it, probably as another prep patch.


> diff --git a/block/bio.c b/block/bio.c
> index cc2bb9183c1a..25393bdd119d 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -860,12 +860,9 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp)
>   	bio->bi_write_hint = bio_src->bi_write_hint;
>   	bio->bi_write_stream = bio_src->bi_write_stream;
>   	bio->bi_iter = bio_src->bi_iter;
> -
> -	if (op_is_dmabuf(bio->bi_opf)) {
> -		bio->bi_dmabuf_map = bio_src->bi_dmabuf_map;
> -	} else {
> -		bio->bi_io_vec = bio_src->bi_io_vec;
> -	}
> +	static_assert(offsetof(struct bio, bi_io_vec) ==
> +		      offsetof(struct bio, bi_dmabuf_map));
> +	bio->bi_io_vec = bio_src->bi_io_vec;
>   
>   	if (bio->bi_bdev) {
>   		if (bio->bi_bdev == bio_src->bi_bdev &&
> @@ -1186,26 +1183,21 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
>   }
>   EXPORT_SYMBOL_GPL(__bio_release_pages);
>   
> -void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter)
> +bool bio_iov_iter_set(struct bio *bio, const struct iov_iter *iter)
>   {
>   	WARN_ON_ONCE(bio->bi_max_vecs);
>   
> +	if (!iov_iter_is_bvec(iter) && !iov_iter_is_dmabuf_map(iter))
> +		return false;
> +
>   	bio->bi_io_vec = (struct bio_vec *)iter->bvec;
>   	bio->bi_iter.bi_idx = 0;
>   	bio->bi_iter.bi_offset = iter->iov_offset;
>   	bio->bi_iter.bi_size = iov_iter_count(iter);
>   	bio_set_flag(bio, BIO_CLONED);
> -}
> -
> -void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter)
> -{
> -	WARN_ON_ONCE(bio->bi_max_vecs);
> -
> -	bio->bi_dmabuf_map = iter->dmabuf_map;
> -	bio->bi_vcnt = 0;
> -	bio->bi_iter.bi_offset = iter->iov_offset;
> -	bio->bi_iter.bi_size = iov_iter_count(iter);
> -	bio->bi_opf |= REQ_NOMERGE | REQ_DMABUF;
> +	if (iov_iter_is_dmabuf_map(iter))
> +		bio->bi_opf |= REQ_NOMERGE | REQ_DMABUF;
> +	return true;
>   }
>   
>   /*
> @@ -1265,13 +1257,7 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
>   	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
>   		return -EIO;
>   
> -	if (iov_iter_is_bvec(iter)) {
> -		bio_iov_bvec_set(bio, iter);
> -		iov_iter_advance(iter, bio->bi_iter.bi_size);
> -		return 0;
> -	}
> -	if (iov_iter_is_dmabuf_map(iter)) {
> -		bio_dmabuf_map_set(bio, iter);
> +	if (bio_iov_iter_set(bio, iter)) {
>   		iov_iter_advance(iter, bio->bi_iter.bi_size);
>   		return 0;
>   	}
> diff --git a/block/blk-map.c b/block/blk-map.c
> index d1d6bbe0ecf1..34816e6e64de 100644
> --- a/block/blk-map.c
> +++ b/block/blk-map.c
> @@ -473,7 +473,7 @@ static int blk_rq_map_user_bvec(struct request *rq, const struct iov_iter *iter)
>   	bio = blk_rq_map_bio_alloc(rq, 0, GFP_KERNEL);
>   	if (!bio)
>   		return -ENOMEM;
> -	bio_iov_bvec_set(bio, iter);
> +	bio_iov_iter_set(bio, iter);
>   
>   	ret = blk_rq_append_bio(rq, bio);
>   	if (ret)
> diff --git a/block/fops.c b/block/fops.c
> index d83cdbab65a6..97fb124a19b2 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -340,17 +340,12 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
>   	bio->bi_end_io = blkdev_bio_end_io_async;
>   	bio->bi_ioprio = iocb->ki_ioprio;
>   
> -	if (iov_iter_is_bvec(iter)) {
> -		/*
> -		 * Users don't rely on the iterator being in any particular
> -		 * state for async I/O returning -EIOCBQUEUED, hence we can
> -		 * avoid expensive iov_iter_advance(). Bypass
> -		 * bio_iov_iter_get_pages() and set the bvec directly.
> -		 */
> -		bio_iov_bvec_set(bio, iter);
> -	} else if (iov_iter_is_dmabuf_map(iter)) {
> -		bio_dmabuf_map_set(bio, iter);
> -	} else {
> +	/*
> +	 * Users don't rely on the iterator being in any particular state for
> +	 * async I/O returning -EIOCBQUEUED, hence we can avoid the expensive
> +	 * iov_iter_advance() if we could set the bvec/dmabuf directly.
> +	 */
> +	if (!bio_iov_iter_set(bio, iter)) {
>   		ret = blkdev_iov_iter_get_pages(bio, iter, bdev);
>   		if (unlikely(ret))
>   			goto out_bio_put;
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index c053e9444514..1eff02a843ef 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -484,8 +484,7 @@ int bdev_rw_virt(struct block_device *bdev, sector_t sector, void *data,
>   int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
>   		unsigned len_align_mask);
>   
> -void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter);
> -void bio_dmabuf_map_set(struct bio *bio, struct iov_iter *iter);
> +bool bio_iov_iter_set(struct bio *bio, const struct iov_iter *iter);
>   void __bio_release_pages(struct bio *bio, bool mark_dirty);
>   extern void bio_set_pages_dirty(struct bio *bio);
>   extern void bio_check_pages_dirty(struct bio *bio);

-- 
Pavel Begunkov

[PATCH v4 07/14] block: forward init_dma_buf_io_ctx to drivers

[Pavel Begunkov]

Add a simple proxy implementation of init_dma_buf_io_ctx() forwarding
the call to a new struct block_device_operations operation.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 block/fops.c           | 14 ++++++++++++++
 include/linux/blkdev.h |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/block/fops.c b/block/fops.c
index 37d491f45015..d83cdbab65a6 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -926,6 +926,19 @@ static int blkdev_mmap_prepare(struct vm_area_desc *desc)
 	return generic_file_mmap_prepare(desc);
 }
 
+static int blkdev_init_dma_buf_io_ctx(struct file *file,
+				      struct dma_buf_io_ctx *ctx)
+{
+	struct block_device *bdev = file_bdev(file);
+	struct gendisk *disk = bdev->bd_disk;
+
+	if (!(file->f_flags & O_DIRECT))
+		return -EINVAL;
+	if (!disk->fops->init_dma_buf_io_ctx)
+		return -EINVAL;
+	return disk->fops->init_dma_buf_io_ctx(bdev, ctx);
+}
+
 const struct file_operations def_blk_fops = {
 	.open		= blkdev_open,
 	.release	= blkdev_release,
@@ -944,6 +957,7 @@ const struct file_operations def_blk_fops = {
 	.fallocate	= blkdev_fallocate,
 	.uring_cmd	= blkdev_uring_cmd,
 	.fop_flags	= FOP_BUFFER_RASYNC,
+	.init_dma_buf_io_ctx = blkdev_init_dma_buf_io_ctx,
 };
 
 static __init int blkdev_init(void)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9213a5716f95..9f4c92e51dc9 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1682,6 +1682,8 @@ struct block_device_operations {
 	/* returns the length of the identifier or a negative errno: */
 	int (*get_unique_id)(struct gendisk *disk, u8 id[16],
 			enum blk_unique_id id_type);
+	int (*init_dma_buf_io_ctx)(struct block_device *,
+				   struct dma_buf_io_ctx *);
 	struct module *owner;
 	const struct pr_ops *pr_ops;
 
-- 
2.54.0

Re: [PATCH v4 07/14] block: forward init_dma_buf_io_ctx to drivers

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH v4 08/14] nvme-pci: implement dma_token backed requests

[Pavel Begunkov]

Enable BIO_DMABUF_MAP backed requests. It creates a prp list for the
dmabuf when it's mapped, which is then used to initialise requests.

Suggested-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 drivers/nvme/host/core.c |  12 ++
 drivers/nvme/host/nvme.h |   2 +
 drivers/nvme/host/pci.c  | 259 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 273 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 453c1f0b2dd0..ce66a1843bec 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2676,6 +2676,17 @@ static int nvme_report_zones(struct gendisk *disk, sector_t sector,
 #define nvme_report_zones	NULL
 #endif /* CONFIG_BLK_DEV_ZONED */
 
+static int nvme_init_dma_buf_io_ctx(struct block_device *bdev,
+				    struct dma_buf_io_ctx *ctx)
+{
+	struct nvme_ns *ns = bdev->bd_disk->private_data;
+	struct nvme_ctrl *ctrl = ns->ctrl;
+
+	if (!ctrl->ops->init_dma_buf_io_ctx)
+		return -EINVAL;
+	return ctrl->ops->init_dma_buf_io_ctx(ctrl, ctx);
+}
+
 const struct block_device_operations nvme_bdev_ops = {
 	.owner		= THIS_MODULE,
 	.ioctl		= nvme_ioctl,
@@ -2686,6 +2697,7 @@ const struct block_device_operations nvme_bdev_ops = {
 	.get_unique_id	= nvme_get_unique_id,
 	.report_zones	= nvme_report_zones,
 	.pr_ops		= &nvme_pr_ops,
+	.init_dma_buf_io_ctx = nvme_init_dma_buf_io_ctx,
 };
 
 static int nvme_wait_ready(struct nvme_ctrl *ctrl, u32 mask, u32 val,
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 824651cc898d..034c31af8fec 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -652,6 +652,8 @@ struct nvme_ctrl_ops {
 	int (*get_address)(struct nvme_ctrl *ctrl, char *buf, int size);
 	void (*print_device_info)(struct nvme_ctrl *ctrl);
 	bool (*supports_pci_p2pdma)(struct nvme_ctrl *ctrl);
+	int (*init_dma_buf_io_ctx)(struct nvme_ctrl *ctrl,
+				   struct dma_buf_io_ctx *ctx);
 	unsigned long (*get_virt_boundary)(struct nvme_ctrl *ctrl, bool is_admin);
 };
 
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 69932d640b53..f1b67c191892 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -27,6 +27,8 @@
 #include <linux/io-64-nonatomic-lo-hi.h>
 #include <linux/io-64-nonatomic-hi-lo.h>
 #include <linux/sed-opal.h>
+#include <linux/dma-buf-io.h>
+#include <linux/dma-resv.h>
 
 #include "trace.h"
 #include "nvme.h"
@@ -393,6 +395,13 @@ struct nvme_queue {
 	struct completion delete_done;
 };
 
+struct nvme_dmabuf_map {
+	struct dma_buf_io_map base;
+	struct sg_table *sgt;
+	unsigned nr_entries;
+	dma_addr_t dma_list[];
+};
+
 /* bits for iod->flags */
 enum nvme_iod_flags {
 	/* this command has been aborted by the timeout handler */
@@ -859,6 +868,138 @@ static void nvme_free_descriptors(struct request *req)
 	}
 }
 
+static inline struct nvme_dmabuf_map *
+to_nvme_dmabuf_map(struct dma_buf_io_map *map)
+{
+	return container_of(map, struct nvme_dmabuf_map, base);
+}
+
+static void nvme_dmabuf_map_sync_for_cpu(struct nvme_dev *nvme_dev,
+					 struct request *req)
+{
+	struct device *dev = nvme_dev->dev;
+	enum dma_data_direction dma_dir;
+	struct bio *bio = req->bio;
+	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
+	dma_addr_t *dma_list = map->dma_list;
+	unsigned offset = bio->bi_iter.bi_offset;
+	unsigned map_idx = offset / NVME_CTRL_PAGE_SIZE;
+	int length = blk_rq_payload_bytes(req) +
+		     (offset & (NVME_CTRL_PAGE_SIZE - 1));
+
+	dma_dir = rq_data_dir(req) == READ ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
+
+	while (length > 0) {
+		dma_sync_single_for_cpu(dev, dma_list[map_idx++],
+					NVME_CTRL_PAGE_SIZE, dma_dir);
+		length -= NVME_CTRL_PAGE_SIZE;
+	}
+}
+
+static void nvme_dmabuf_map_sync_for_device(struct nvme_dev *nvme_dev,
+					    struct request *req)
+{
+	struct device *dev = nvme_dev->dev;
+	enum dma_data_direction dma_dir;
+	struct bio *bio = req->bio;
+	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
+	dma_addr_t *dma_list = map->dma_list;
+	unsigned offset = bio->bi_iter.bi_offset;
+	unsigned map_idx = offset / NVME_CTRL_PAGE_SIZE;
+	int length = blk_rq_payload_bytes(req) +
+		     (offset & (NVME_CTRL_PAGE_SIZE - 1));
+
+	dma_dir = rq_data_dir(req) == READ ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
+
+	while (length > 0) {
+		dma_sync_single_for_device(dev, dma_list[map_idx++],
+					   NVME_CTRL_PAGE_SIZE, dma_dir);
+		length -= NVME_CTRL_PAGE_SIZE;
+	}
+}
+
+static void nvme_rq_clean_dmabuf_map(struct nvme_dev *dev,
+				      struct request *req)
+{
+	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
+
+	nvme_dmabuf_map_sync_for_cpu(dev, req);
+
+	if (!(iod->flags & IOD_SINGLE_SEGMENT))
+		nvme_free_descriptors(req);
+}
+
+static blk_status_t nvme_rq_setup_dmabuf_map(struct request *req,
+					     struct nvme_queue *nvmeq)
+{
+	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
+	struct bio *bio = req->bio;
+	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
+	unsigned bvec_done = bio->bi_iter.bi_offset;
+	unsigned map_idx = bvec_done / NVME_CTRL_PAGE_SIZE;
+	unsigned offset = bvec_done & (NVME_CTRL_PAGE_SIZE - 1);
+	int length = blk_rq_payload_bytes(req) - (NVME_CTRL_PAGE_SIZE - offset);
+	dma_addr_t *dma_list = map->dma_list;
+	u64 prp1_dma = dma_list[map_idx++] + offset;
+	u64 dma_addr, prp2_dma;
+	dma_addr_t prp_dma;
+	__le64 *prp_list;
+	unsigned i;
+
+	nvme_dmabuf_map_sync_for_device(nvmeq->dev, req);
+
+	if (length <= 0) {
+		prp2_dma = 0;
+		goto done;
+	}
+
+	if (length <= NVME_CTRL_PAGE_SIZE) {
+		prp2_dma = dma_list[map_idx];
+		goto done;
+	}
+
+	if (DIV_ROUND_UP(length, NVME_CTRL_PAGE_SIZE) <=
+	    NVME_SMALL_POOL_SIZE / sizeof(__le64))
+		iod->flags |= IOD_SMALL_DESCRIPTOR;
+
+	prp_list = dma_pool_alloc(nvme_dma_pool(nvmeq, iod), GFP_ATOMIC,
+			&prp_dma);
+	if (!prp_list)
+		return BLK_STS_RESOURCE;
+
+	iod->descriptors[iod->nr_descriptors++] = prp_list;
+	prp2_dma = prp_dma;
+	i = 0;
+	for (;;) {
+		if (i == NVME_CTRL_PAGE_SIZE >> 3) {
+			__le64 *old_prp_list = prp_list;
+
+			prp_list = dma_pool_alloc(nvmeq->descriptor_pools.large,
+					GFP_ATOMIC, &prp_dma);
+			if (!prp_list)
+				goto free_prps;
+			iod->descriptors[iod->nr_descriptors++] = prp_list;
+			prp_list[0] = old_prp_list[i - 1];
+			old_prp_list[i - 1] = cpu_to_le64(prp_dma);
+			i = 1;
+		}
+
+		dma_addr = dma_list[map_idx++];
+		prp_list[i++] = cpu_to_le64(dma_addr);
+
+		length -= NVME_CTRL_PAGE_SIZE;
+		if (length <= 0)
+			break;
+	}
+done:
+	iod->cmd.common.dptr.prp1 = cpu_to_le64(prp1_dma);
+	iod->cmd.common.dptr.prp2 = cpu_to_le64(prp2_dma);
+	return BLK_STS_OK;
+free_prps:
+	nvme_free_descriptors(req);
+	return BLK_STS_RESOURCE;
+}
+
 static void nvme_free_prps(struct request *req, unsigned int attrs)
 {
 	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
@@ -937,6 +1078,11 @@ static void nvme_unmap_data(struct request *req)
 	struct device *dma_dev = nvmeq->dev->dev;
 	unsigned int attrs = 0;
 
+	if (blk_mq_rq_is_dmabuf(req)) {
+		nvme_rq_clean_dmabuf_map(nvmeq->dev, req);
+		return;
+	}
+
 	if (iod->flags & IOD_SINGLE_SEGMENT) {
 		static_assert(offsetof(union nvme_data_ptr, prp1) ==
 				offsetof(union nvme_data_ptr, sgl.addr));
@@ -1251,6 +1397,9 @@ static blk_status_t nvme_map_data(struct request *req)
 	struct blk_dma_iter iter;
 	blk_status_t ret;
 
+	if (blk_mq_rq_is_dmabuf(req))
+		return nvme_rq_setup_dmabuf_map(req, nvmeq);
+
 	/*
 	 * Try to skip the DMA iterator for single segment requests, as that
 	 * significantly improves performances for small I/O sizes.
@@ -2269,6 +2418,112 @@ static int nvme_create_queue(struct nvme_queue *nvmeq, int qid, bool polled)
 	return result;
 }
 
+#if defined(CONFIG_DMA_SHARED_BUFFER)
+static void nvme_dmabuf_invalidate_mappings(struct dma_buf_attachment *attach)
+{
+	struct dma_buf_io_ctx *ctx = attach->importer_priv;
+
+	dma_buf_io_invalidate_mappings(ctx);
+}
+
+const struct dma_buf_attach_ops nvme_dmabuf_importer_ops = {
+	.invalidate_mappings	= nvme_dmabuf_invalidate_mappings,
+	.allow_peer2peer	= true,
+};
+
+static struct dma_buf_io_map *nvme_dma_buf_io_map(struct dma_buf_io_ctx *ctx)
+{
+	unsigned nr_entries = ctx->dmabuf->size / NVME_CTRL_PAGE_SIZE;
+	struct dma_buf_attachment *attach = ctx->dev_priv;
+	unsigned long tmp, i = 0;
+	struct nvme_dmabuf_map *map;
+	struct scatterlist *sg;
+	struct sg_table *sgt;
+	int ret;
+
+	dma_resv_assert_held(ctx->dmabuf->resv);
+
+	map = kmalloc_flex(*map, dma_list, nr_entries);
+	if (!map)
+		return ERR_PTR(-ENOMEM);
+
+	sgt = dma_buf_map_attachment(attach, ctx->dir);
+	if (IS_ERR(sgt)) {
+		ret = PTR_ERR(sgt);
+		sgt = NULL;
+		goto err;
+	}
+
+	for_each_sgtable_dma_sg(sgt, sg, tmp) {
+		dma_addr_t dma_addr = sg_dma_address(sg);
+		unsigned long sg_len = sg_dma_len(sg);
+
+		if (sg_len % NVME_CTRL_PAGE_SIZE) {
+			ret = -EINVAL;
+			goto err;
+		}
+
+		while (sg_len) {
+			map->dma_list[i++] = dma_addr;
+			dma_addr += NVME_CTRL_PAGE_SIZE;
+			sg_len -= NVME_CTRL_PAGE_SIZE;
+		}
+	}
+
+	ret = dma_buf_io_init_map(ctx, &map->base);
+	if (ret)
+		goto err;
+	map->nr_entries = nr_entries;
+	map->sgt = sgt;
+	return &map->base;
+err:
+	if (sgt)
+		dma_buf_unmap_attachment(attach, sgt, ctx->dir);
+	kfree(map);
+	return ERR_PTR(ret);
+}
+
+static void nvme_dma_buf_io_unmap(struct dma_buf_io_ctx *ctx,
+				  struct dma_buf_io_map *map_base)
+{
+	struct dma_buf_attachment *attach = ctx->dev_priv;
+	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(map_base);
+
+	dma_resv_assert_held(ctx->dmabuf->resv);
+
+	dma_buf_unmap_attachment(attach, map->sgt, ctx->dir);
+}
+
+static void nvme_dma_buf_io_release(struct dma_buf_io_ctx *ctx)
+{
+	struct dma_buf_attachment *attach = ctx->dev_priv;
+
+	dma_buf_detach(ctx->dmabuf, attach);
+}
+
+const struct dma_buf_io_ops nvme_dma_buf_io_ops = {
+	.map		= nvme_dma_buf_io_map,
+	.unmap		= nvme_dma_buf_io_unmap,
+	.release	= nvme_dma_buf_io_release,
+};
+
+static int nvme_pci_init_dma_buf_io_ctx(struct nvme_ctrl *ctrl,
+					struct dma_buf_io_ctx *ctx)
+{
+	struct dma_buf_attachment *attach;
+	struct nvme_dev *dev = to_nvme_dev(ctrl);
+
+	attach = dma_buf_dynamic_attach(ctx->dmabuf, dev->dev,
+					&nvme_dmabuf_importer_ops, ctx);
+	if (IS_ERR(attach))
+		return PTR_ERR(attach);
+
+	ctx->dev_priv = attach;
+	ctx->dev_ops = &nvme_dma_buf_io_ops;
+	return 0;
+}
+#endif
+
 static const struct blk_mq_ops nvme_mq_admin_ops = {
 	.queue_rq	= nvme_queue_rq,
 	.complete	= nvme_pci_complete_rq,
@@ -3563,6 +3818,9 @@ static const struct nvme_ctrl_ops nvme_pci_ctrl_ops = {
 	.print_device_info	= nvme_pci_print_device_info,
 	.supports_pci_p2pdma	= nvme_pci_supports_pci_p2pdma,
 	.get_virt_boundary	= nvme_pci_get_virt_boundary,
+#if defined(CONFIG_DMA_SHARED_BUFFER)
+	.init_dma_buf_io_ctx	= nvme_pci_init_dma_buf_io_ctx,
+#endif
 };
 
 static int nvme_dev_map(struct nvme_dev *dev)
@@ -4327,5 +4585,6 @@ MODULE_AUTHOR("Matthew Wilcox <willy@linux.intel.com>");
 MODULE_LICENSE("GPL");
 MODULE_VERSION("1.0");
 MODULE_DESCRIPTION("NVMe host PCIe transport driver");
+MODULE_IMPORT_NS("DMA_BUF");
 module_init(nvme_init);
 module_exit(nvme_exit);
-- 
2.54.0

Re: [PATCH v4 08/14] nvme-pci: implement dma_token backed requests

[Christoph Hellwig]

> +static int nvme_init_dma_buf_io_ctx(struct block_device *bdev,
> +				    struct dma_buf_io_ctx *ctx)

Please stick to two-tab indents for function declaration continuation
for the nvme code to keep the code easy to maintain.

> +#if defined(CONFIG_DMA_SHARED_BUFFER)

This should be good old #ifdef.  Same in a few other places over
the series.

Modulo these minor nits the patch looks good.

Re: [PATCH v4 08/14] nvme-pci: implement dma_token backed requests

[Pavel Begunkov]

On 7/29/26 08:10, Christoph Hellwig wrote:
>> +static int nvme_init_dma_buf_io_ctx(struct block_device *bdev,
>> +				    struct dma_buf_io_ctx *ctx)
> 
> Please stick to two-tab indents for function declaration continuation
> for the nvme code to keep the code easy to maintain.
> 
>> +#if defined(CONFIG_DMA_SHARED_BUFFER)
> 
> This should be good old #ifdef.  Same in a few other places over
> the series.

Going to apply both for v5, thanks.

> Modulo these minor nits the patch looks good.

-- 
Pavel Begunkov

[PATCH v4 09/14] nvme-pci: add SGL support for the dmabuf path

[Pavel Begunkov]

From: Anuj Gupta <anuj20.g@samsung.com>

Add SGL support in addition to PRP for dmabuf-backed requests,
coalescing the mapping's sg_table into NVMe SGL data descriptors.

Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
[pavel: rebased]
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 drivers/nvme/host/pci.c | 191 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 187 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index f1b67c191892..cbb321fb7c50 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -1287,12 +1287,18 @@ static blk_status_t nvme_pci_setup_data_prp(struct request *req,
 	return BLK_STS_IOERR;
 }
 
+static void nvme_pci_sgl_set_data_addr(struct nvme_sgl_desc *sge,
+				       dma_addr_t addr, u32 len)
+{
+	sge->addr = cpu_to_le64(addr);
+	sge->length = cpu_to_le32(len);
+	sge->type = NVME_SGL_FMT_DATA_DESC << 4;
+}
+
 static void nvme_pci_sgl_set_data(struct nvme_sgl_desc *sge,
 		struct blk_dma_iter *iter)
 {
-	sge->addr = cpu_to_le64(iter->addr);
-	sge->length = cpu_to_le32(iter->len);
-	sge->type = NVME_SGL_FMT_DATA_DESC << 4;
+	nvme_pci_sgl_set_data_addr(sge, iter->addr, iter->len);
 }
 
 static void nvme_pci_sgl_set_seg(struct nvme_sgl_desc *sge,
@@ -1303,6 +1309,158 @@ static void nvme_pci_sgl_set_seg(struct nvme_sgl_desc *sge,
 	sge->type = NVME_SGL_FMT_LAST_SEG_DESC << 4;
 }
 
+static unsigned int nvme_pci_dmabuf_sgl_nents(struct request *req,
+					      dma_addr_t *first_dma,
+					      u32 *first_len)
+{
+	struct bio *bio = req->bio;
+	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
+	struct scatterlist *sg;
+	unsigned long tmp;
+	size_t offset = bio->bi_iter.bi_offset;
+	size_t remaining = blk_rq_payload_bytes(req);
+	dma_addr_t last_end = 0;
+	unsigned int nents = 0;
+	dma_addr_t dma = 0;
+	u32 len = 0;
+	bool have = false;
+
+	for_each_sgtable_dma_sg(map->sgt, sg, tmp) {
+		size_t sg_len = sg_dma_len(sg);
+		dma_addr_t addr = sg_dma_address(sg);
+
+		if (!remaining)
+			break;
+		if (offset >= sg_len) {
+			offset -= sg_len;
+			continue;
+		}
+
+		addr += offset;
+		sg_len -= offset;
+		offset = 0;
+
+		while (sg_len && remaining) {
+			u32 chunk = min_t(size_t, remaining, sg_len);
+
+			if (!have || last_end != addr) {
+				nents++;
+				if (nents == 1) {
+					dma = addr;
+					len = chunk;
+				}
+			} else if (nents == 1) {
+				len += chunk;
+			}
+
+			have = true;
+			last_end = addr + chunk;
+			addr += chunk;
+			sg_len -= chunk;
+			remaining -= chunk;
+		}
+	}
+
+	if (unlikely(remaining))
+	       return 0;
+
+	*first_dma = dma;
+	*first_len = len;
+	return nents;
+}
+
+static blk_status_t nvme_rq_setup_dmabuf_sgl(struct request *req,
+					     struct nvme_queue *nvmeq,
+					     unsigned int entries,
+					     dma_addr_t first_dma, u32 first_len)
+{
+	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
+	struct bio *bio = req->bio;
+	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
+	size_t length = blk_rq_payload_bytes(req);
+	struct nvme_sgl_desc *sg_list = NULL;
+	dma_addr_t sgl_dma = 0, last_end = 0;
+	unsigned int mapped = 0;
+	unsigned long tmp;
+	struct scatterlist *sg;
+	size_t offset, remaining;
+	bool have = false;
+
+	if (!entries)
+		return BLK_STS_IOERR;
+	if (entries > NVME_MAX_SEGS)
+		return BLK_STS_AGAIN;
+
+	iod->cmd.common.flags = NVME_CMD_SGL_METABUF;
+	iod->total_len = length;
+
+	nvme_dmabuf_map_sync_for_device(nvmeq->dev, req);
+
+	if (entries == 1) {
+		nvme_pci_sgl_set_data_addr(&iod->cmd.common.dptr.sgl, first_dma,
+					   first_len);
+		return BLK_STS_OK;
+	}
+
+	if (entries <= NVME_SMALL_POOL_SIZE / sizeof(*sg_list))
+		iod->flags |= IOD_SMALL_DESCRIPTOR;
+
+	sg_list = dma_pool_alloc(nvme_dma_pool(nvmeq, iod), GFP_ATOMIC,
+				 &sgl_dma);
+	if (!sg_list)
+		return BLK_STS_RESOURCE;
+	iod->descriptors[iod->nr_descriptors++] = sg_list;
+
+	offset = bio->bi_iter.bi_offset;
+	remaining = length;
+
+	for_each_sgtable_dma_sg(map->sgt, sg, tmp) {
+		size_t sg_len = sg_dma_len(sg);
+		dma_addr_t addr = sg_dma_address(sg);
+
+		if (!remaining)
+			break;
+		if (offset >= sg_len) {
+			offset -= sg_len;
+			continue;
+		}
+
+		addr += offset;
+		sg_len -= offset;
+		offset = 0;
+
+		while (sg_len && remaining) {
+			u32 chunk = min_t(size_t, remaining, sg_len);
+
+			if (have && last_end == addr) {
+				u32 old = le32_to_cpu(sg_list[mapped - 1].length);
+
+				sg_list[mapped - 1].length = cpu_to_le32(old + chunk);
+			} else {
+				if (WARN_ON_ONCE(mapped == entries))
+					goto err_free;
+				nvme_pci_sgl_set_data_addr(&sg_list[mapped++],
+							   addr, chunk);
+			}
+			have = true;
+			last_end = addr + chunk;
+			addr += chunk;
+			sg_len -= chunk;
+			remaining -= chunk;
+		}
+	}
+
+	if (unlikely(remaining))
+		goto err_free;
+
+	nvme_pci_sgl_set_seg(&iod->cmd.common.dptr.sgl, sgl_dma, mapped);
+	return BLK_STS_OK;
+err_free:
+	iod->nr_descriptors--;
+	dma_pool_free(nvme_dma_pool(nvmeq, iod), sg_list, sgl_dma);
+	return BLK_STS_IOERR;
+}
+
 static blk_status_t nvme_pci_setup_data_sgl(struct request *req,
 		struct blk_dma_iter *iter)
 {
@@ -1397,8 +1555,33 @@ static blk_status_t nvme_map_data(struct request *req)
 	struct blk_dma_iter iter;
 	blk_status_t ret;
 
-	if (blk_mq_rq_is_dmabuf(req))
+	if (blk_mq_rq_is_dmabuf(req)) {
+		if (use_sgl != SGL_UNSUPPORTED) {
+			dma_addr_t first_dma;
+			u32 first_len;
+			unsigned int entries;
+
+			entries = nvme_pci_dmabuf_sgl_nents(req, &first_dma,
+							    &first_len);
+
+			if (use_sgl == SGL_FORCED) {
+				ret = nvme_rq_setup_dmabuf_sgl(req, nvmeq,
+								entries, first_dma, first_len);
+				return ret == BLK_STS_AGAIN ? BLK_STS_IOERR : ret;
+			}
+
+			if (sgl_threshold && entries &&
+			    DIV_ROUND_UP(blk_rq_payload_bytes(req), entries) >=
+			    sgl_threshold) {
+				ret = nvme_rq_setup_dmabuf_sgl(req, nvmeq,
+								entries, first_dma, first_len);
+				if (ret != BLK_STS_AGAIN)
+					return ret;
+			}
+		}
+
 		return nvme_rq_setup_dmabuf_map(req, nvmeq);
+	}
 
 	/*
 	 * Try to skip the DMA iterator for single segment requests, as that
-- 
2.54.0

Re: [PATCH v4 09/14] nvme-pci: add SGL support for the dmabuf path

[Christoph Hellwig]

On Tue, Jul 28, 2026 at 10:29:21PM +0100, Pavel Begunkov wrote:
> From: Anuj Gupta <anuj20.g@samsung.com>
> 
> Add SGL support in addition to PRP for dmabuf-backed requests,
> coalescing the mapping's sg_table into NVMe SGL data descriptors.
> 
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> [pavel: rebased]
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  drivers/nvme/host/pci.c | 191 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 187 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index f1b67c191892..cbb321fb7c50 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -1287,12 +1287,18 @@ static blk_status_t nvme_pci_setup_data_prp(struct request *req,
>  	return BLK_STS_IOERR;
>  }
>  
> +static void nvme_pci_sgl_set_data_addr(struct nvme_sgl_desc *sge,
> +				       dma_addr_t addr, u32 len)
> +{
> +	sge->addr = cpu_to_le64(addr);
> +	sge->length = cpu_to_le32(len);
> +	sge->type = NVME_SGL_FMT_DATA_DESC << 4;
> +}
> +
>  static void nvme_pci_sgl_set_data(struct nvme_sgl_desc *sge,
>  		struct blk_dma_iter *iter)
>  {
> -	sge->addr = cpu_to_le64(iter->addr);
> -	sge->length = cpu_to_le32(iter->len);
> -	sge->type = NVME_SGL_FMT_DATA_DESC << 4;
> +	nvme_pci_sgl_set_data_addr(sge, iter->addr, iter->len);
>  }

The naming is a bit confusing (and me passing the iter to
nvme_pci_sgl_set_data is probably at faul for that).  So maybe
spin out a prep patch to rename the old nvme_pci_sgl_set_data
to nvme_pci_dma_iter_set_sgl or so, and then add the new one
as nvme_pci_sgl_set_data (as before the dma_iter conversion).

>
> +static unsigned int nvme_pci_dmabuf_sgl_nents(struct request *req,
> +					      dma_addr_t *first_dma,
> +					      u32 *first_len)

This is a really good example why the aligning to the opening braces
produces totally unreadble code..

But I also don't understand what the use case for this function
is to start with.  struct sg_table tells us how many segments
exist on the DMA side in the nents member, which should be just
fine for the SGL threshold calculation.

> +{
> +	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
> +	struct bio *bio = req->bio;
> +	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
> +	size_t length = blk_rq_payload_bytes(req);
> +	struct nvme_sgl_desc *sg_list = NULL;
> +	dma_addr_t sgl_dma = 0, last_end = 0;
> +	unsigned int mapped = 0;
> +	unsigned long tmp;
> +	struct scatterlist *sg;
> +	size_t offset, remaining;
> +	bool have = false;
> +
> +	if (!entries)
> +		return BLK_STS_IOERR;
> +	if (entries > NVME_MAX_SEGS)
> +		return BLK_STS_AGAIN;

Given that the block layer enforced data in rw/command and the
max_segments limit, why do we need the extra check here?

> +			continue;
> +		}
> +
> +		addr += offset;
> +		sg_len -= offset;
> +		offset = 0;
> +
> +		while (sg_len && remaining) {

These can't be false on the first iteration, so maybe turn this into
a do {} while loop?

> +			u32 chunk = min_t(size_t, remaining, sg_len);
> +
> +			if (have && last_end == addr) {
> +				u32 old = le32_to_cpu(sg_list[mapped - 1].length);
> +
> +				sg_list[mapped - 1].length = cpu_to_le32(old + chunk);

Overly long line.

> +			} else {
> +				if (WARN_ON_ONCE(mapped == entries))
> +					goto err_free;
> +				nvme_pci_sgl_set_data_addr(&sg_list[mapped++],
> +							   addr, chunk);
> +			}

Why do we need this merging?  dma_map_sg should have already done
any interesting merging, or am I missing something?

> +		if (use_sgl != SGL_UNSUPPORTED) {
> +			dma_addr_t first_dma;
> +			u32 first_len;
> +			unsigned int entries;
> +
> +			entries = nvme_pci_dmabuf_sgl_nents(req, &first_dma,
> +							    &first_len);
> +
> +			if (use_sgl == SGL_FORCED) {
> +				ret = nvme_rq_setup_dmabuf_sgl(req, nvmeq,
> +								entries, first_dma, first_len);
> +				return ret == BLK_STS_AGAIN ? BLK_STS_IOERR : ret;
> +			}
> +
> +			if (sgl_threshold && entries &&
> +			    DIV_ROUND_UP(blk_rq_payload_bytes(req), entries) >=
> +			    sgl_threshold) {
> +				ret = nvme_rq_setup_dmabuf_sgl(req, nvmeq,
> +								entries, first_dma, first_len);
> +				if (ret != BLK_STS_AGAIN)
> +					return ret;
> +			}
> +		}

Various overly long lines.  Please factor out a helper for the
decisions to use sgl vs not instead of open coding it here.

Re: [PATCH v4 09/14] nvme-pci: add SGL support for the dmabuf path

[Anuj Gupta/Anuj Gupta]

>> +static void nvme_pci_sgl_set_data_addr(struct nvme_sgl_desc *sge,
>> +				       dma_addr_t addr, u32 len)
>> +{
>> +	sge->addr = cpu_to_le64(addr);
>> +	sge->length = cpu_to_le32(len);
>> +	sge->type = NVME_SGL_FMT_DATA_DESC << 4;
>> +}
>> +
>>   static void nvme_pci_sgl_set_data(struct nvme_sgl_desc *sge,
>>   		struct blk_dma_iter *iter)
>>   {
>> -	sge->addr = cpu_to_le64(iter->addr);
>> -	sge->length = cpu_to_le32(iter->len);
>> -	sge->type = NVME_SGL_FMT_DATA_DESC << 4;
>> +	nvme_pci_sgl_set_data_addr(sge, iter->addr, iter->len);
>>   }
> 
> The naming is a bit confusing (and me passing the iter to
> nvme_pci_sgl_set_data is probably at faul for that).  So maybe
> spin out a prep patch to rename the old nvme_pci_sgl_set_data
> to nvme_pci_dma_iter_set_sgl or so, and then add the new one
> as nvme_pci_sgl_set_data (as before the dma_iter conversion).
>

Thanks for the detailed review! Will split the rename into a prep patch.

>>
>> +static unsigned int nvme_pci_dmabuf_sgl_nents(struct request *req,
>> +					      dma_addr_t *first_dma,
>> +					      u32 *first_len)
> 
> This is a really good example why the aligning to the opening braces
> produces totally unreadble code..
> 
> But I also don't understand what the use case for this function
> is to start with.  struct sg_table tells us how many segments
> exist on the DMA side in the nents member, which should be just
> fine for the SGL threshold calculation.

sg_table->nents covers the entire exported buffer (<=1GiB), while a
request only covers a subrange[bi_offset, bi_offset+payload). Using
nents would overcount the request's segments.

> 
>> +{
>> +	struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
>> +	struct bio *bio = req->bio;
>> +	struct nvme_dmabuf_map *map = to_nvme_dmabuf_map(bio->bi_dmabuf_map);
>> +	size_t length = blk_rq_payload_bytes(req);
>> +	struct nvme_sgl_desc *sg_list = NULL;
>> +	dma_addr_t sgl_dma = 0, last_end = 0;
>> +	unsigned int mapped = 0;
>> +	unsigned long tmp;
>> +	struct scatterlist *sg;
>> +	size_t offset, remaining;
>> +	bool have = false;
>> +
>> +	if (!entries)
>> +		return BLK_STS_IOERR;
>> +	if (entries > NVME_MAX_SEGS)
>> +		return BLK_STS_AGAIN;
> 
> Given that the block layer enforced data in rw/command and the
> max_segments limit, why do we need the extra check here?

A dmabuf bio reports nsegs=1 (bio_split_io_at) to the block layer, so 
max_segments isn't enforced against the SG entries actually spanned by 
the request. Hence the explicit check.

> 
>> +			continue;
>> +		}
>> +
>> +		addr += offset;
>> +		sg_len -= offset;
>> +		offset = 0;
>> +
>> +		while (sg_len && remaining) {
> 
> These can't be false on the first iteration, so maybe turn this into
> a do {} while loop?

Will do.

> 
>> +			u32 chunk = min_t(size_t, remaining, sg_len);
>> +
>> +			if (have && last_end == addr) {
>> +				u32 old = le32_to_cpu(sg_list[mapped - 1].length);
>> +
>> +				sg_list[mapped - 1].length = cpu_to_le32(old + chunk);
> 
> Overly long line.
> 
>> +			} else {
>> +				if (WARN_ON_ONCE(mapped == entries))
>> +					goto err_free;
>> +				nvme_pci_sgl_set_data_addr(&sg_list[mapped++],
>> +							   addr, chunk);
>> +			}
> 
> Why do we need this merging?  dma_map_sg should have already done
> any interesting merging, or am I missing something?

Will drop it.

Re: [PATCH v4 09/14] nvme-pci: add SGL support for the dmabuf path

[Christoph Hellwig]

On Wed, Jul 29, 2026 at 03:47:23PM +0530, Anuj Gupta/Anuj Gupta wrote:
> > But I also don't understand what the use case for this function
> > is to start with.  struct sg_table tells us how many segments
> > exist on the DMA side in the nents member, which should be just
> > fine for the SGL threshold calculation.
> 
> sg_table->nents covers the entire exported buffer (<=1GiB), while a
> request only covers a subrange[bi_offset, bi_offset+payload). Using
> nents would overcount the request's segments.

Urgg, yes.

> >> +	if (!entries)
> >> +		return BLK_STS_IOERR;
> >> +	if (entries > NVME_MAX_SEGS)
> >> +		return BLK_STS_AGAIN;
> > 
> > Given that the block layer enforced data in rw/command and the
> > max_segments limit, why do we need the extra check here?
> 
> A dmabuf bio reports nsegs=1 (bio_split_io_at) to the block layer, so 
> max_segments isn't enforced against the SG entries actually spanned by 
> the request. Hence the explicit check.

We'll need to expose the actual nsegs to the block layer and split
based on that.  Otherwise I/O might work or fail based on the device
capabilities.

Re: [PATCH v4 09/14] nvme-pci: add SGL support for the dmabuf path

[Pavel Begunkov]

On 7/29/26 12:31, Christoph Hellwig wrote:
> On Wed, Jul 29, 2026 at 03:47:23PM +0530, Anuj Gupta/Anuj Gupta wrote:
>>> But I also don't understand what the use case for this function
>>> is to start with.  struct sg_table tells us how many segments
>>> exist on the DMA side in the nents member, which should be just
>>> fine for the SGL threshold calculation.
>>
>> sg_table->nents covers the entire exported buffer (<=1GiB), while a
>> request only covers a subrange[bi_offset, bi_offset+payload). Using
>> nents would overcount the request's segments.
> 
> Urgg, yes.
> 
>>>> +	if (!entries)
>>>> +		return BLK_STS_IOERR;
>>>> +	if (entries > NVME_MAX_SEGS)
>>>> +		return BLK_STS_AGAIN;
>>>
>>> Given that the block layer enforced data in rw/command and the
>>> max_segments limit, why do we need the extra check here?
>>
>> A dmabuf bio reports nsegs=1 (bio_split_io_at) to the block layer, so
>> max_segments isn't enforced against the SG entries actually spanned by
>> the request. Hence the explicit check.
> 
> We'll need to expose the actual nsegs to the block layer and split
> based on that.  Otherwise I/O might work or fail based on the device
> capabilities.

It was exposed in early version as I was passing a [{dma,len}, ...]
array, but we moved from that. Maybe I should put the minimum
segment size in the map structure, and (possibly over) split using
that for now? Keith had this chunk in his patches:

+		int offset = offset_in_page(bio->bi_iter.bi_bvec_done);
+
+		nsegs = ALIGN(bio->bi_iter.bi_size + offset, PAGE_SIZE) >>
+								PAGE_SHIFT;
+		if (bio->bi_iter.bi_size > max_bytes) {
+			bytes = max_bytes;
+			nsegs = (bytes + offset) >> PAGE_SHIFT;
+		} else if (nsegs > lim->max_segments) {
+			nsegs = lim->max_segments;
+			bytes = PAGE_SIZE * nsegs - offset;
+		} else {
+			*segs = nsegs;
+			return NULL;
+		}

-- 
Pavel Begunkov

Re: [PATCH v4 09/14] nvme-pci: add SGL support for the dmabuf path

[Christoph Hellwig]

On Wed, Jul 29, 2026 at 12:45:47PM +0100, Pavel Begunkov wrote:
> It was exposed in early version as I was passing a [{dma,len}, ...]
> array, but we moved from that. Maybe I should put the minimum
> segment size in the map structure, and (possibly over) split using
> that for now? Keith had this chunk in his patches:
>
> +		int offset = offset_in_page(bio->bi_iter.bi_bvec_done);
> +
> +		nsegs = ALIGN(bio->bi_iter.bi_size + offset, PAGE_SIZE) >>
> +								PAGE_SHIFT;
> +		if (bio->bi_iter.bi_size > max_bytes) {
> +			bytes = max_bytes;
> +			nsegs = (bytes + offset) >> PAGE_SHIFT;
> +		} else if (nsegs > lim->max_segments) {
> +			nsegs = lim->max_segments;
> +			bytes = PAGE_SIZE * nsegs - offset;
> +		} else {
> +			*segs = nsegs;
> +			return NULL;
> +		}

This seems very pessimistic, especially for the case of the registration
only having a single segment, which I'd expect to be fairly common due
to P2P bar mappings, huge pages or IOMMU coalescing.  So at very least
we'd want to special case that, but in an idea world the caller would
be required to provide a useful nr_segments for the I/O.

Re: [PATCH v4 09/14] nvme-pci: add SGL support for the dmabuf path

[Pavel Begunkov]

On 7/29/26 12:55, Christoph Hellwig wrote:
> On Wed, Jul 29, 2026 at 12:45:47PM +0100, Pavel Begunkov wrote:
>> It was exposed in early version as I was passing a [{dma,len}, ...]
>> array, but we moved from that. Maybe I should put the minimum
>> segment size in the map structure, and (possibly over) split using
>> that for now? Keith had this chunk in his patches:
>>
>> +		int offset = offset_in_page(bio->bi_iter.bi_bvec_done);
>> +
>> +		nsegs = ALIGN(bio->bi_iter.bi_size + offset, PAGE_SIZE) >>
>> +								PAGE_SHIFT;
>> +		if (bio->bi_iter.bi_size > max_bytes) {
>> +			bytes = max_bytes;
>> +			nsegs = (bytes + offset) >> PAGE_SHIFT;
>> +		} else if (nsegs > lim->max_segments) {
>> +			nsegs = lim->max_segments;
>> +			bytes = PAGE_SIZE * nsegs - offset;
>> +		} else {
>> +			*segs = nsegs;
>> +			return NULL;
>> +		}
> 
> This seems very pessimistic, especially for the case of the registration
> only having a single segment, which I'd expect to be fairly common due
> to P2P bar mappings, huge pages or IOMMU coalescing.  So at very least

Agree that PAGE_SIZE is too pessimistic, but I'd calculate it from
the sg table on registration and use here. Not ideal but should cover
most common cases like huge pages.

> we'd want to special case that, but in an idea world the caller would
> be required to provide a useful nr_segments for the I/O.

Not sure we can do it in the straightforward way from the abstraction
perspective, mapping are hidden from io_uring, and there could be
multi-device files with differently shaped IOMMU mappings at some
point. We'll surely need readv/writev support later, so maybe we can
improve while doing that as it'd mean passing a {off,len} of some
sort from io_uring.

-- 
Pavel Begunkov

[PATCH v4 10/14] io_uring/rsrc: introduce buf registration structure

[Pavel Begunkov]

In preparation to following changes, instead of passing an iovec for
buffer registration introduce a new structure. It'll be moved to uapi
later, but for now it's initialised early from a user provided iovec.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rsrc.c | 47 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 15 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 8d0f2ee24e0c..8af371ba6c06 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -27,8 +27,13 @@ struct io_rsrc_update {
 	u32				offset;
 };
 
+struct io_uring_regbuf_desc {
+	__u64 uaddr;
+	__u64 size;
+};
+
 static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
-						   struct iovec *iov);
+						   struct io_uring_regbuf_desc *desc);
 
 static int hpage_acct_ref(struct io_ring_ctx *ctx, struct page *hpage,
 			  bool *acct_new)
@@ -81,6 +86,15 @@ static bool hpage_acct_unref(struct io_ring_ctx *ctx, struct page *hpage)
 
 #define IO_CACHED_BVECS_SEGS	32
 
+static void io_iov_to_regbuf_desc(const struct iovec *iov,
+				  struct io_uring_regbuf_desc *desc)
+{
+	*desc = (struct io_uring_regbuf_desc) {
+		.uaddr = (u64)(uintptr_t)iov->iov_base,
+		.size = iov->iov_len,
+	};
+}
+
 int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
 {
 	unsigned long page_limit, cur_pages, new_pages;
@@ -381,6 +395,7 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 		return -EINVAL;
 
 	for (done = 0; done < nr_args; done++) {
+		struct io_uring_regbuf_desc desc;
 		struct io_rsrc_node *node;
 		u64 tag = 0;
 
@@ -394,7 +409,9 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 			err = -EFAULT;
 			break;
 		}
-		node = io_sqe_buffer_register(ctx, iov);
+
+		io_iov_to_regbuf_desc(iov, &desc);
+		node = io_sqe_buffer_register(ctx, &desc);
 		if (IS_ERR(node)) {
 			err = PTR_ERR(node);
 			break;
@@ -853,26 +870,26 @@ bool io_check_coalesce_buffer(struct page **page_array, int nr_pages,
 }
 
 static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
-						   struct iovec *iov)
+						   struct io_uring_regbuf_desc *desc)
 {
+	unsigned long uaddr = (unsigned long)desc->uaddr;
+	size_t size = desc->size;
 	struct io_mapped_ubuf *imu = NULL;
 	struct page **pages = NULL;
 	struct io_rsrc_node *node;
 	unsigned long off;
-	size_t size;
 	int ret, nr_pages, i;
 	struct io_imu_folio_data data;
 	bool coalesced = false;
 
-	if (!iov->iov_base) {
-		if (iov->iov_len)
+	if (!uaddr) {
+		if (size)
 			return ERR_PTR(-EFAULT);
 		/* remove the buffer without installing a new one */
 		return NULL;
 	}
 
-	ret = io_validate_user_buf_range((unsigned long)iov->iov_base,
-					 iov->iov_len);
+	ret = io_validate_user_buf_range(uaddr, size);
 	if (ret)
 		return ERR_PTR(ret);
 
@@ -881,8 +898,7 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 		return ERR_PTR(-ENOMEM);
 
 	ret = -ENOMEM;
-	pages = io_pin_pages((unsigned long) iov->iov_base, iov->iov_len,
-				&nr_pages);
+	pages = io_pin_pages(uaddr, size, &nr_pages);
 	if (IS_ERR(pages)) {
 		ret = PTR_ERR(pages);
 		pages = NULL;
@@ -904,10 +920,9 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 	if (ret)
 		goto done;
 
-	size = iov->iov_len;
 	/* store original address for later verification */
-	imu->ubuf = (unsigned long) iov->iov_base;
-	imu->len = iov->iov_len;
+	imu->ubuf = uaddr;
+	imu->len = size;
 	imu->folio_shift = PAGE_SHIFT;
 	imu->release = io_release_ubuf;
 	imu->priv = imu;
@@ -917,7 +932,7 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 		imu->folio_shift = data.folio_shift;
 	refcount_set(&imu->refs, 1);
 
-	off = (unsigned long)iov->iov_base & ~PAGE_MASK;
+	off = uaddr & ~PAGE_MASK;
 	if (coalesced)
 		off += data.first_folio_page_idx << PAGE_SHIFT;
 
@@ -969,6 +984,7 @@ int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
 		memset(iov, 0, sizeof(*iov));
 
 	for (i = 0; i < nr_args; i++) {
+		struct io_uring_regbuf_desc desc;
 		struct io_rsrc_node *node;
 		u64 tag = 0;
 
@@ -992,7 +1008,8 @@ int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
 			}
 		}
 
-		node = io_sqe_buffer_register(ctx, iov);
+		io_iov_to_regbuf_desc(iov, &desc);
+		node = io_sqe_buffer_register(ctx, &desc);
 		if (IS_ERR(node)) {
 			ret = PTR_ERR(node);
 			break;
-- 
2.54.0

[PATCH v4 11/14] io_uring/rsrc: extend buffer update

[Pavel Begunkov]

We need to pass more information to buffer registration than we can fit
into a single struct iovec. This patch allows users to optionally pass
struct io_uring_regbuf_desc. Apart from having more space for future use
cases, it also introduces registration types.

Currently, the type can be either of IO_REGBUF_TYPE_UADDR, which mirrors
the iovec path, or IO_REGBUF_TYPE_EMPTY for leaving a buffer table slot
empty. The next patch introduces a dmabuf backed type, and can be useful
for other extensions like splicing a list of user addresses (i.e.
iovec[]), interoperability with zcrx, kernel allocated memory like was
brough up by Cristoph. Note, the type only represents a registration
option, which is distinct from how io_uring internally stores it.

The flags field is not used yet but always useful to have, e.g. we can
encode read-only / write-only restrictions using it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/uapi/linux/io_uring.h | 27 +++++++++++++-
 io_uring/rsrc.c               | 69 ++++++++++++++++++++++-------------
 2 files changed, 69 insertions(+), 27 deletions(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 909fb7aea638..98b259901185 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -790,13 +790,38 @@ struct io_uring_rsrc_update {
 
 struct io_uring_rsrc_update2 {
 	__u32 offset;
-	__u32 resv;
+	__u32 flags;
 	__aligned_u64 data;
 	__aligned_u64 tags;
 	__u32 nr;
 	__u32 resv2;
 };
 
+/* struct io_uring_rsrc_update2::flags */
+enum io_uring_rsrc_reg_flags {
+	/*
+	 * Use the extended descriptor format for buffer updates,
+	 * see struct io_uring_regbuf_desc
+	 */
+	IORING_RSRC_UPDATE_EXTENDED		= 1U << 1,
+};
+
+/* Buffer registration type, passed in struct io_uring_regbuf_desc::type */
+enum io_uring_regbuf_type {
+	IO_REGBUF_TYPE_EMPTY,
+	IO_REGBUF_TYPE_UADDR,
+
+	__IO_REGBUF_TYPE_MAX,
+};
+
+struct io_uring_regbuf_desc {
+	__u32 type; /* enum io_uring_regbuf_type */
+	__u32 flags;
+	__u64 size;
+	__u64 uaddr;
+	__u64 __resv[7];
+};
+
 /* Skip updating fd indexes set to this value in the fd table */
 #define IORING_REGISTER_FILES_SKIP	(-2)
 
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 8af371ba6c06..24fc3232a66a 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -27,11 +27,6 @@ struct io_rsrc_update {
 	u32				offset;
 };
 
-struct io_uring_regbuf_desc {
-	__u64 uaddr;
-	__u64 size;
-};
-
 static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 						   struct io_uring_regbuf_desc *desc);
 
@@ -90,9 +85,12 @@ static void io_iov_to_regbuf_desc(const struct iovec *iov,
 				  struct io_uring_regbuf_desc *desc)
 {
 	*desc = (struct io_uring_regbuf_desc) {
+		.type = IO_REGBUF_TYPE_UADDR,
 		.uaddr = (u64)(uintptr_t)iov->iov_base,
 		.size = iov->iov_len,
 	};
+	if (!desc->uaddr)
+		desc->type = IO_REGBUF_TYPE_EMPTY;
 }
 
 int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
@@ -323,6 +321,8 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 		return -ENXIO;
 	if (up->offset + nr_args > ctx->file_table.data.nr)
 		return -EINVAL;
+	if (up->flags)
+		return -EINVAL;
 
 	for (done = 0; done < nr_args; done++) {
 		u64 tag = 0;
@@ -382,9 +382,8 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 				   struct io_uring_rsrc_update2 *up,
 				   unsigned int nr_args)
 {
+	bool extended = up->flags & IORING_RSRC_UPDATE_EXTENDED;
 	u64 __user *tags = u64_to_user_ptr(up->tags);
-	struct iovec fast_iov, *iov;
-	struct iovec __user *uvec;
 	u64 user_data = up->data;
 	__u32 done;
 	int i, err;
@@ -393,29 +392,49 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 		return -ENXIO;
 	if (up->offset + nr_args > ctx->buf_table.nr)
 		return -EINVAL;
+	if (up->flags & ~IORING_RSRC_UPDATE_EXTENDED)
+		return -EINVAL;
 
 	for (done = 0; done < nr_args; done++) {
 		struct io_uring_regbuf_desc desc;
 		struct io_rsrc_node *node;
 		u64 tag = 0;
 
-		uvec = u64_to_user_ptr(user_data);
-		iov = iovec_from_user(uvec, 1, 1, &fast_iov, io_is_compat(ctx));
-		if (IS_ERR(iov)) {
-			err = PTR_ERR(iov);
-			break;
-		}
 		if (tags && copy_from_user(&tag, &tags[done], sizeof(tag))) {
 			err = -EFAULT;
 			break;
 		}
 
-		io_iov_to_regbuf_desc(iov, &desc);
+		if (extended) {
+			if (copy_from_user(&desc, u64_to_user_ptr(user_data),
+					   sizeof(desc))) {
+				err = -EFAULT;
+				break;
+			}
+			user_data += sizeof(desc);
+		} else {
+			struct iovec __user *uvec = u64_to_user_ptr(user_data);
+			struct iovec fast_iov, *iov;
+
+			if (io_is_compat(ctx))
+				user_data += sizeof(struct compat_iovec);
+			else
+				user_data += sizeof(struct iovec);
+
+			iov = iovec_from_user(uvec, 1, 1, &fast_iov, io_is_compat(ctx));
+			if (IS_ERR(iov)) {
+				err = PTR_ERR(iov);
+				break;
+			}
+			io_iov_to_regbuf_desc(iov, &desc);
+		}
+
 		node = io_sqe_buffer_register(ctx, &desc);
 		if (IS_ERR(node)) {
 			err = PTR_ERR(node);
 			break;
 		}
+
 		if (tag) {
 			if (!node) {
 				err = -EINVAL;
@@ -426,10 +445,6 @@ static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
 		i = array_index_nospec(up->offset + done, ctx->buf_table.nr);
 		io_reset_rsrc_node(ctx, &ctx->buf_table, i);
 		ctx->buf_table.nodes[i] = node;
-		if (io_is_compat(ctx))
-			user_data += sizeof(struct compat_iovec);
-		else
-			user_data += sizeof(struct iovec);
 	}
 	return done ? done : err;
 }
@@ -464,7 +479,7 @@ int io_register_files_update(struct io_ring_ctx *ctx, void __user *arg,
 	memset(&up, 0, sizeof(up));
 	if (copy_from_user(&up, arg, sizeof(struct io_uring_rsrc_update)))
 		return -EFAULT;
-	if (up.resv || up.resv2)
+	if (up.resv2)
 		return -EINVAL;
 	return __io_register_rsrc_update(ctx, IORING_RSRC_FILE, &up, nr_args);
 }
@@ -478,7 +493,7 @@ int io_register_rsrc_update(struct io_ring_ctx *ctx, void __user *arg,
 		return -EINVAL;
 	if (copy_from_user(&up, arg, sizeof(up)))
 		return -EFAULT;
-	if (!up.nr || up.resv || up.resv2)
+	if (!up.nr || up.resv2)
 		return -EINVAL;
 	return __io_register_rsrc_update(ctx, type, &up, up.nr);
 }
@@ -578,12 +593,9 @@ int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
 	struct io_uring_rsrc_update2 up2;
 	int ret;
 
+	memset(&up2, 0, sizeof(up2));
 	up2.offset = up->offset;
 	up2.data = up->arg;
-	up2.nr = 0;
-	up2.tags = 0;
-	up2.resv = 0;
-	up2.resv2 = 0;
 
 	if (up->offset == IORING_FILE_INDEX_ALLOC) {
 		ret = io_files_update_with_index_alloc(req, issue_flags);
@@ -882,8 +894,13 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 	struct io_imu_folio_data data;
 	bool coalesced = false;
 
-	if (!uaddr) {
-		if (size)
+	if (desc->type >= __IO_REGBUF_TYPE_MAX)
+		return ERR_PTR(-EINVAL);
+	if (!mem_is_zero(&desc->__resv, sizeof(desc->__resv)))
+		return ERR_PTR(-EINVAL);
+
+	if (desc->type == IO_REGBUF_TYPE_EMPTY) {
+		if (uaddr || size)
 			return ERR_PTR(-EFAULT);
 		/* remove the buffer without installing a new one */
 		return NULL;
-- 
2.54.0

Re: [PATCH v4 11/14] io_uring/rsrc: extend buffer update

[Anuj Gupta/Anuj Gupta]

On 7/29/2026 2:59 AM, Pavel Begunkov wrote:
> @@ -882,8 +894,13 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
>   	struct io_imu_folio_data data;
>   	bool coalesced = false;
>   
> -	if (!uaddr) {
> -		if (size)
> +	if (desc->type >= __IO_REGBUF_TYPE_MAX)
> +		return ERR_PTR(-EINVAL);
> +	if (!mem_is_zero(&desc->__resv, sizeof(desc->__resv)))
> +		return ERR_PTR(-EINVAL);

desc->flags  isn't validated here, unlike __resv. nonzero flags should 
be rejected too?

> +
> +	if (desc->type == IO_REGBUF_TYPE_EMPTY) {
> +		if (uaddr || size)
>   			return ERR_PTR(-EFAULT);
>   		/* remove the buffer without installing a new one */
>   		return NULL;

Re: [PATCH v4 11/14] io_uring/rsrc: extend buffer update

[Pavel Begunkov]

On 7/29/26 14:31, Anuj Gupta/Anuj Gupta wrote:
> On 7/29/2026 2:59 AM, Pavel Begunkov wrote:
>> @@ -882,8 +894,13 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
>>    	struct io_imu_folio_data data;
>>    	bool coalesced = false;
>>    
>> -	if (!uaddr) {
>> -		if (size)
>> +	if (desc->type >= __IO_REGBUF_TYPE_MAX)
>> +		return ERR_PTR(-EINVAL);
>> +	if (!mem_is_zero(&desc->__resv, sizeof(desc->__resv)))
>> +		return ERR_PTR(-EINVAL);
> 
> desc->flags  isn't validated here, unlike __resv. nonzero flags should
> be rejected too?

good catch

-- 
Pavel Begunkov

[PATCH v4 12/14] io_uring/rsrc: add uncloneable regbuf flag

[Pavel Begunkov]

It's hard to implement cloning if the internal structure needs to be
mutable and/or relies on other ring resources. In preparation to such
buffer types, add a flag indicating that the buffer can't be cloned. It
might be possible to add cloning in the future for them, but that would
likely need reallocating the structure and reacquiring resources in case
by case manner.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rsrc.c | 5 +++++
 io_uring/rsrc.h | 3 ++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 24fc3232a66a..d57e8a0380b5 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1381,6 +1381,11 @@ static int io_clone_buffers(struct io_ring_ctx *ctx, struct io_ring_ctx *src_ctx
 		if (!src_node) {
 			dst_node = NULL;
 		} else {
+			if (src_node->buf->flags & IO_REGBUF_F_UNCLONEABLE) {
+				io_rsrc_data_free(ctx, &data);
+				return -ENOMEM;
+			}
+
 			dst_node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER);
 			if (!dst_node) {
 				io_rsrc_data_free(ctx, &data);
diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index 98ae8ef51009..83aa86e6f320 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -29,7 +29,8 @@ enum {
 };
 
 enum {
-	IO_REGBUF_F_KBUF		= 1,
+	IO_REGBUF_F_KBUF		= 1 << 0,
+	IO_REGBUF_F_UNCLONEABLE		= 1 << 1,
 };
 
 struct io_mapped_ubuf {
-- 
2.54.0

[PATCH v4 13/14] io_uring/rsrc: add regbuf import flags

[Pavel Begunkov]

We'll have special registered buffer types that can't be used with all
opcodes and need special handling. Add separate flags to control
registered buffer import, which will be used to specify what kind of
buffers the caller can handle.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rsrc.c |  8 ++++----
 io_uring/rsrc.h | 24 ++++++++++++++++++++----
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index d57e8a0380b5..05877b4c0ee5 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1245,9 +1245,9 @@ 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;
 
@@ -1656,9 +1656,9 @@ static int io_kern_bvec_size(struct iovec *iov, unsigned nr_iovs,
 	return 0;
 }
 
-int io_import_reg_vec(int ddir, struct iov_iter *iter,
+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)
+			unsigned nr_iovs, unsigned issue_flags, unsigned import_flags)
 {
 	struct io_rsrc_node *node;
 	struct io_mapped_ubuf *imu;
diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index 83aa86e6f320..f12abaf63270 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -65,12 +65,28 @@ 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,
+int __io_import_reg_buf(struct io_kiocb *req, struct iov_iter *iter,
 			u64 buf_addr, size_t len, int ddir,
-			unsigned issue_flags);
-int io_import_reg_vec(int ddir, struct iov_iter *iter,
+			unsigned issue_flags, unsigned import_flags);
+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);
+			unsigned nr_iovs, 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)
+{
+	return __io_import_reg_buf(req, iter, buf_addr, len, ddir, issue_flags, 0);
+}
+
+static inline 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)
+{
+	return __io_import_reg_vec(ddir, iter, req, vec, nr_iovs, issue_flags, 0);
+}
+
 int io_prep_reg_iovec(struct io_kiocb *req, struct iou_vec *iv,
 			const struct iovec __user *uvec, size_t uvec_segs);
 
-- 
2.54.0

[PATCH v4 14/14] io_uring/rsrc: add dmabuf backed registered buffers

[Pavel Begunkov]

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 <dw@davidwei.uk>
Suggested-by: Vishal Verma <vishal1.verma@intel.com>
Suggested-by: Tushar Gohad <tushar.gohad@intel.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/io_uring_types.h |   5 +
 include/uapi/linux/io_uring.h  |   6 +-
 io_uring/io_uring.c            |   3 +-
 io_uring/rsrc.c                | 168 ++++++++++++++++++++++++++++++++-
 io_uring/rsrc.h                |  18 ++++
 io_uring/rw.c                  |   6 +-
 6 files changed, 198 insertions(+), 8 deletions(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index a2c623a67a25..f90586d353c1 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -10,6 +10,7 @@
 
 struct iou_loop_params;
 struct io_uring_bpf_ops;
+struct dma_buf_io_map;
 
 enum {
 	/*
@@ -594,6 +595,7 @@ enum {
 	REQ_F_IMPORT_BUFFER_BIT,
 	REQ_F_SQE_COPIED_BIT,
 	REQ_F_IOPOLL_BIT,
+	REQ_F_DROP_DMABUF_BIT,
 
 	/* not a real bit, just to check we're not overflowing the space */
 	__REQ_F_LAST_BIT,
@@ -689,6 +691,8 @@ 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_DROP_DMABUF	= IO_REQ_FLAG(REQ_F_DROP_DMABUF_BIT),
 };
 
 struct io_tw_req {
@@ -811,6 +815,7 @@ 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 98b259901185..c39297e8beb6 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -810,6 +810,7 @@ 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,
 };
@@ -819,7 +820,10 @@ 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/io_uring.c b/io_uring/io_uring.c
index 1279e27c2c6d..cb88d19c8fb2 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -109,7 +109,7 @@
 
 #define IO_REQ_CLEAN_SLOW_FLAGS (REQ_F_REFCOUNT | IO_REQ_LINK_FLAGS | \
 				 REQ_F_REISSUE | REQ_F_POLLED | \
-				 IO_REQ_CLEAN_FLAGS)
+				 IO_REQ_CLEAN_FLAGS | REQ_F_DROP_DMABUF)
 
 #define IO_TCTX_REFS_CACHE_NR	(1U << 10)
 
@@ -1125,6 +1125,7 @@ static void io_free_batch_list(struct io_ring_ctx *ctx,
 				io_queue_next(req);
 			if (unlikely(req->flags & IO_REQ_CLEAN_FLAGS))
 				io_clean_op(req);
+			io_req_drop_dmabuf(req);
 		}
 		io_put_file(req);
 		io_req_put_rsrc_nodes(req);
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 05877b4c0ee5..d23dbb0dd6b8 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -10,6 +10,7 @@
 #include <linux/compat.h>
 #include <linux/io_uring.h>
 #include <linux/io_uring/cmd.h>
+#include <linux/dma-buf-io.h>
 
 #include <uapi/linux/io_uring.h>
 
@@ -881,6 +882,95 @@ bool io_check_coalesce_buffer(struct page **page_array, int nr_pages,
 	return true;
 }
 
+struct io_regbuf_dma {
+	struct dma_buf_io_ctx		ctx;
+	struct file			*target_file;
+};
+
+static void io_release_reg_dmabuf(void *priv)
+{
+	struct io_regbuf_dma *db = priv;
+
+	fput(db->target_file);
+	dma_buf_io_ctx_release(&db->ctx);
+}
+
+static struct io_rsrc_node *io_register_dmabuf(struct io_ring_ctx *ctx,
+						struct io_uring_regbuf_desc *desc)
+{
+	struct io_rsrc_node *node = NULL;
+	struct io_mapped_ubuf *imu = NULL;
+	struct io_regbuf_dma *regbuf = NULL;
+	struct file *target_file = NULL;
+	struct dma_buf *dmabuf = NULL;
+	int ret;
+
+	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
+		return ERR_PTR(-EOPNOTSUPP);
+	if (ctx->flags & IORING_SETUP_IOPOLL)
+		return ERR_PTR(-EOPNOTSUPP);
+	if (desc->uaddr || desc->size)
+		return ERR_PTR(-EINVAL);
+
+	ret = -ENOMEM;
+	node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER);
+	if (!node)
+		return ERR_PTR(-ENOMEM);
+	imu = io_alloc_imu(ctx, 0);
+	if (!imu)
+		goto err;
+	regbuf = kzalloc(sizeof(*regbuf), GFP_KERNEL);
+	if (!regbuf)
+		goto err;
+
+	ret = -EBADF;
+	target_file = fget(desc->target_fd);
+	if (!target_file)
+		goto err;
+
+	dmabuf = dma_buf_get(desc->dmabuf_fd);
+	if (IS_ERR(dmabuf)) {
+		ret = PTR_ERR(dmabuf);
+		dmabuf = NULL;
+		goto err;
+	}
+	if (dmabuf->size > SZ_1G) {
+		ret = -EINVAL;
+		goto err;
+	}
+
+	ret = dma_buf_io_ctx_create(target_file, &regbuf->ctx, dmabuf,
+				    DMA_BIDIRECTIONAL);
+	if (ret)
+		goto err;
+
+	regbuf->target_file = target_file;
+	imu->nr_bvecs = 1;
+	imu->ubuf = 0;
+	imu->len = dmabuf->size;
+	imu->folio_shift = 0;
+	imu->release = io_release_reg_dmabuf;
+	imu->priv = regbuf;
+	imu->flags = IO_REGBUF_F_DMABUF;
+	imu->dir = IO_IMU_DEST | IO_IMU_SOURCE;
+	refcount_set(&imu->refs, 1);
+	node->buf = imu;
+	dma_buf_put(dmabuf);
+	return node;
+err:
+	kfree(regbuf);
+	if (imu)
+		io_free_imu(ctx, imu);
+	if (node)
+		io_cache_free(&ctx->node_cache, node);
+	if (target_file)
+		fput(target_file);
+	if (dmabuf)
+		dma_buf_put(dmabuf);
+	return ERR_PTR(ret);
+}
+
+
 static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 						   struct io_uring_regbuf_desc *desc)
 {
@@ -899,6 +989,12 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
 	if (!mem_is_zero(&desc->__resv, sizeof(desc->__resv)))
 		return ERR_PTR(-EINVAL);
 
+	if (desc->type == IO_REGBUF_TYPE_DMABUF)
+		return io_register_dmabuf(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);
@@ -1170,9 +1266,64 @@ static int io_import_kbuf(int ddir, struct iov_iter *iter,
 	return 0;
 }
 
-static int io_import_fixed(int ddir, struct iov_iter *iter,
+void io_drop_dmabuf_node(struct io_kiocb *req)
+{
+	struct io_mapped_ubuf *imu;
+
+	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
+		return;
+	if (WARN_ON_ONCE(req->buf_node->type != IORING_RSRC_BUFFER))
+		return;
+	imu = req->buf_node->buf;
+	if (WARN_ON_ONCE(!(imu->flags & IO_REGBUF_F_DMABUF)))
+		return;
+	dma_buf_io_map_drop(req->dmabuf_map);
+	req->flags &= ~REQ_F_DROP_DMABUF;
+}
+
+static int io_import_dmabuf(struct io_kiocb *req,
+			   int ddir, struct iov_iter *iter,
+			   struct io_mapped_ubuf *imu,
+			   size_t len, size_t offset,
+			   unsigned issue_flags)
+{
+	struct io_regbuf_dma *db = imu->priv;
+	struct dma_buf_io_map *map;
+
+	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
+		return -EOPNOTSUPP;
+	if (!len)
+		return -EFAULT;
+	if (req->file != db->target_file)
+		return -EBADF;
+
+	if (req->flags & REQ_F_DROP_DMABUF) {
+		map = req->dmabuf_map;
+		goto init_iter;
+	}
+
+	map = dma_buf_io_get_map(&db->ctx);
+	if (unlikely(!map)) {
+		if (!(issue_flags & IO_URING_F_IOWQ))
+			return -EAGAIN;
+		map = dma_buf_io_create_map(&db->ctx);
+		if (IS_ERR(map))
+			return PTR_ERR(map);
+	}
+
+	req->dmabuf_map = map;
+	req->flags |= REQ_F_DROP_DMABUF;
+init_iter:
+	iov_iter_dmabuf_map(iter, ddir, map, 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)
+			   u64 buf_addr, size_t len,
+			   unsigned issue_flags,
+			   unsigned import_flags)
 {
 	const struct bio_vec *bvec;
 	size_t folio_mask;
@@ -1192,6 +1343,12 @@ 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(req, ddir, iter, imu, len, offset,
+					issue_flags);
+	}
 	if (imu->flags & IO_REGBUF_F_KBUF)
 		return io_import_kbuf(ddir, iter, imu, len, offset);
 
@@ -1254,7 +1411,8 @@ 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,
@@ -1676,7 +1834,9 @@ 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 f12abaf63270..3cb9b57f159b 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -31,6 +31,11 @@ enum {
 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 {
@@ -173,4 +178,17 @@ static inline void io_alloc_cache_vec_kasan(struct iou_vec *iv)
 		io_vec_free(iv);
 }
 
+void io_drop_dmabuf_node(struct io_kiocb *req);
+
+static inline void io_req_drop_dmabuf(struct io_kiocb *req)
+{
+	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
+		return;
+	if (!(req->flags & REQ_F_DROP_DMABUF))
+		return;
+	if (WARN_ON_ONCE(!(req->flags & REQ_F_BUF_NODE)))
+		return;
+	io_drop_dmabuf_node(req);
+}
+
 #endif
diff --git a/io_uring/rw.c b/io_uring/rw.c
index 95038cfda615..11ff7b5a1164 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -380,8 +380,8 @@ 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_DMABUF);
 	iov_iter_save_state(&io->iter, &io->iter_state);
 	return ret;
 }
@@ -591,6 +591,8 @@ 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_req_drop_dmabuf(req);
+
 	__io_complete_rw_common(req, res);
 	io_req_set_res(req, io_fixup_rw_res(req, res), 0);
 	req->io_task_work.func = io_req_rw_complete;
-- 
2.54.0

Re: [PATCH v4 14/14] io_uring/rsrc: add dmabuf backed registered buffers

[Anuj Gupta/Anuj Gupta]

On 7/29/2026 2:59 AM, Pavel Begunkov wrote:
> +static struct io_rsrc_node *io_register_dmabuf(struct io_ring_ctx *ctx,
> +						struct io_uring_regbuf_desc *desc)
> +{
> +	struct io_rsrc_node *node = NULL;
> +	struct io_mapped_ubuf *imu = NULL;
> +	struct io_regbuf_dma *regbuf = NULL;
> +	struct file *target_file = NULL;
> +	struct dma_buf *dmabuf = NULL;
> +	int ret;
> +
> +	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
> +		return ERR_PTR(-EOPNOTSUPP);
> +	if (ctx->flags & IORING_SETUP_IOPOLL)
> +		return ERR_PTR(-EOPNOTSUPP);
> +	if (desc->uaddr || desc->size)
> +		return ERR_PTR(-EINVAL);
> +
> +	ret = -ENOMEM;
> +	node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER);
> +	if (!node)
> +		return ERR_PTR(-ENOMEM);
> +	imu = io_alloc_imu(ctx, 0);
> +	if (!imu)
> +		goto err;
> +	regbuf = kzalloc(sizeof(*regbuf), GFP_KERNEL);
> +	if (!regbuf)
> +		goto err;
> +
> +	ret = -EBADF;
> +	target_file = fget(desc->target_fd);
> +	if (!target_file)
> +		goto err;
> +
> +	dmabuf = dma_buf_get(desc->dmabuf_fd);
> +	if (IS_ERR(dmabuf)) {
> +		ret = PTR_ERR(dmabuf);
> +		dmabuf = NULL;
> +		goto err;
> +	}
> +	if (dmabuf->size > SZ_1G) {
> +		ret = -EINVAL;
> +		goto err;
> +	}
> +
> +	ret = dma_buf_io_ctx_create(target_file, &regbuf->ctx, dmabuf,
> +				    DMA_BIDIRECTIONAL);
> +	if (ret)
> +		goto err;
> +
> +	regbuf->target_file = target_file;
> +	imu->nr_bvecs = 1;

There is no bvec backing a dmabuf imu - should this be 0?

> +	imu->ubuf = 0;
> +	imu->len = dmabuf->size;
> +	imu->folio_shift = 0;
> +	imu->release = io_release_reg_dmabuf;
> +	imu->priv = regbuf;
> +	imu->flags = IO_REGBUF_F_DMABUF;
> +	imu->dir = IO_IMU_DEST | IO_IMU_SOURCE;
> +	refcount_set(&imu->refs, 1);
> +	node->buf = imu;
> +	dma_buf_put(dmabuf);
> +	return node;
> +err:
> +	kfree(regbuf);
> +	if (imu)
> +		io_free_imu(ctx, imu);
> +	if (node)
> +		io_cache_free(&ctx->node_cache, node);
> +	if (target_file)
> +		fput(target_file);
> +	if (dmabuf)
> +		dma_buf_put(dmabuf);
> +	return ERR_PTR(ret);
> +}
> +
> +

nit: extra newline here

> +static int io_import_dmabuf(struct io_kiocb *req,
> +			   int ddir, struct iov_iter *iter,
> +			   struct io_mapped_ubuf *imu,
> +			   size_t len, size_t offset,
> +			   unsigned issue_flags)
> +{
> +	struct io_regbuf_dma *db = imu->priv;
> +	struct dma_buf_io_map *map;
> +
> +	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
> +		return -EOPNOTSUPP;
> +	if (!len)
> +		return -EFAULT;
> +	if (req->file != db->target_file)
> +		return -EBADF;
> +
> +	if (req->flags & REQ_F_DROP_DMABUF) {
> +		map = req->dmabuf_map;
> +		goto init_iter;
> +	}

O_DIRECT is checked only during registration; we should recheck
(file->f_flags & O_DIRECT) per request.

Re: [PATCH v4 14/14] io_uring/rsrc: add dmabuf backed registered buffers

[Pavel Begunkov]

On 7/29/26 14:30, Anuj Gupta/Anuj Gupta wrote:
> On 7/29/2026 2:59 AM, Pavel Begunkov wrote:
>> +static struct io_rsrc_node *io_register_dmabuf(struct io_ring_ctx *ctx,
>> +						struct io_uring_regbuf_desc *desc)
>> +{
>> +	struct io_rsrc_node *node = NULL;
>> +	struct io_mapped_ubuf *imu = NULL;
>> +	struct io_regbuf_dma *regbuf = NULL;
>> +	struct file *target_file = NULL;
>> +	struct dma_buf *dmabuf = NULL;
>> +	int ret;
>> +
>> +	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
>> +		return ERR_PTR(-EOPNOTSUPP);
>> +	if (ctx->flags & IORING_SETUP_IOPOLL)
>> +		return ERR_PTR(-EOPNOTSUPP);
>> +	if (desc->uaddr || desc->size)
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	ret = -ENOMEM;
>> +	node = io_rsrc_node_alloc(ctx, IORING_RSRC_BUFFER);
>> +	if (!node)
>> +		return ERR_PTR(-ENOMEM);
>> +	imu = io_alloc_imu(ctx, 0);
>> +	if (!imu)
>> +		goto err;
>> +	regbuf = kzalloc(sizeof(*regbuf), GFP_KERNEL);
>> +	if (!regbuf)
>> +		goto err;
>> +
>> +	ret = -EBADF;
>> +	target_file = fget(desc->target_fd);
>> +	if (!target_file)
>> +		goto err;
>> +
>> +	dmabuf = dma_buf_get(desc->dmabuf_fd);
>> +	if (IS_ERR(dmabuf)) {
>> +		ret = PTR_ERR(dmabuf);
>> +		dmabuf = NULL;
>> +		goto err;
>> +	}
>> +	if (dmabuf->size > SZ_1G) {
>> +		ret = -EINVAL;
>> +		goto err;
>> +	}
>> +
>> +	ret = dma_buf_io_ctx_create(target_file, &regbuf->ctx, dmabuf,
>> +				    DMA_BIDIRECTIONAL);
>> +	if (ret)
>> +		goto err;
>> +
>> +	regbuf->target_file = target_file;
>> +	imu->nr_bvecs = 1;
> 
> There is no bvec backing a dmabuf imu - should this be 0?

Doesn't really matter as it's not used. It's 1 to say that
it's just 1 contig segment, but I can just zero it to avoid
confusion.

> 
>> +	imu->ubuf = 0;
>> +	imu->len = dmabuf->size;
>> +	imu->folio_shift = 0;
>> +	imu->release = io_release_reg_dmabuf;
>> +	imu->priv = regbuf;
>> +	imu->flags = IO_REGBUF_F_DMABUF;
>> +	imu->dir = IO_IMU_DEST | IO_IMU_SOURCE;
>> +	refcount_set(&imu->refs, 1);
>> +	node->buf = imu;
>> +	dma_buf_put(dmabuf);
>> +	return node;
>> +err:
>> +	kfree(regbuf);
>> +	if (imu)
>> +		io_free_imu(ctx, imu);
>> +	if (node)
>> +		io_cache_free(&ctx->node_cache, node);
>> +	if (target_file)
>> +		fput(target_file);
>> +	if (dmabuf)
>> +		dma_buf_put(dmabuf);
>> +	return ERR_PTR(ret);
>> +}
>> +
>> +
> 
> nit: extra newline here
> 
>> +static int io_import_dmabuf(struct io_kiocb *req,
>> +			   int ddir, struct iov_iter *iter,
>> +			   struct io_mapped_ubuf *imu,
>> +			   size_t len, size_t offset,
>> +			   unsigned issue_flags)
>> +{
>> +	struct io_regbuf_dma *db = imu->priv;
>> +	struct dma_buf_io_map *map;
>> +
>> +	if (!IS_ENABLED(CONFIG_DMA_SHARED_BUFFER))
>> +		return -EOPNOTSUPP;
>> +	if (!len)
>> +		return -EFAULT;
>> +	if (req->file != db->target_file)
>> +		return -EBADF;
>> +
>> +	if (req->flags & REQ_F_DROP_DMABUF) {
>> +		map = req->dmabuf_map;
>> +		goto init_iter;
>> +	}
> 
> O_DIRECT is checked only during registration; we should recheck
> (file->f_flags & O_DIRECT) per request.

Nobody should be able to clear O_DIRECT, unless I missed something?
And fwiw, io_uring wouldn't be the right place to do it.

-- 
Pavel Begunkov

Re: [PATCH v4 00/14] Add dmabuf read/write via io_uring

[Christoph Hellwig]

Might help to say this applies to Jens' for-next branch for those trying
to apply the patches..

Re: [PATCH v4 00/14] Add dmabuf read/write via io_uring

[Pavel Begunkov]

On 7/29/26 07:54, Christoph Hellwig wrote:
> Might help to say this applies to Jens' for-next branch for those trying
> to apply the patches..

Ah yes, and there is a branch as well:
git: https://github.com/isilence/linux.git rw-dmabuf-v4
url: https://github.com/isilence/linux/tree/rw-dmabuf-v4

-- 
Pavel Begunkov