[PATCH v3 00/10] Add dmabuf read/write via io_uring

Pavel Begunkov
2026-04-29T15:26:19Z

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 from Intel.

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 bind it all, which also counts requests
using a dmabuf map and managing lifetimes, which is used to implement
map invalidation.

It was tested for GPU <-> NVMe transfers. Also, as it maintains a
long-term dma mapping, it helps with the IOMMU cost. The numbers
below are for udmabuf reads previously run by Anuj for different
IOMMU modes:

- 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

There are some liburing tests that can serve as an example:
git: https://github.com/isilence/liburing.git rw-dmabuf-tests-v3
url: https://github.com/isilence/liburing/tree/rw-dmabuf-tests-v3

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

v3: - 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

Pavel Begunkov (10):
file: add callback for creating long-term dmabuf maps
iov_iter: add iterator type for dmabuf maps
block: move bvec init into __bio_clone
block: introduce dma map backed bio type
lib: add dmabuf token infrastructure
block: forward create_dmabuf_token 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 dmabuf backed registered buffers

block/bio.c | 28 +++-
block/blk-merge.c | 14 ++
block/blk.h | 3 +-
block/fops.c | 16 ++
drivers/nvme/host/pci.c | 282 ++++++++++++++++++++++++++++++++
include/linux/bio.h | 19 ++-
include/linux/blk-mq.h | 9 +
include/linux/blk_types.h | 8 +-
include/linux/fs.h | 2 +
include/linux/io_dmabuf_token.h | 92 +++++++++++
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/rsrc.c | 266 +++++++++++++++++++++++++-----
io_uring/rsrc.h | 30 +++-
io_uring/rw.c | 4 +-
lib/Kconfig | 4 +
lib/Makefile | 2 +
lib/io_dmabuf_token.c | 272 ++++++++++++++++++++++++++++++
lib/iov_iter.c | 29 +++-
21 files changed, 1071 insertions(+), 59 deletions(-)
create mode 100644 include/linux/io_dmabuf_token.h
create mode 100644 lib/io_dmabuf_token.c

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2.53.0