[PATCH v3 00/10] 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 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

-- 
2.53.0