linux-kernel - [PATCH rdma-next v2 0/3] RDMA: Add support for exporting dma-buf file descriptors

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Message-ID: <20260121-dmabuf-export-v2-0-6381183bcc3d@nvidia.com>
Date: Wed, 21 Jan 2026 23:42:10 +0200
From: Edward Srouji <edwards@...dia.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>, "Sumit
 Semwal" <sumit.semwal@...aro.org>, Christian König
	<christian.koenig@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<linux-media@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	<linaro-mm-sig@...ts.linaro.org>, Yishai Hadas <yishaih@...dia.com>, "Edward
 Srouji" <edwards@...dia.com>
Subject: [PATCH rdma-next v2 0/3] RDMA: Add support for exporting dma-buf
 file descriptors

This patch series introduces dma-buf export support for RDMA/InfiniBand
devices, enabling userspace applications to export RDMA PCI-backed
memory regions (such as device memory or mlx5 UAR pages) as dma-buf file
descriptors.

This allows PCI device memory to be shared with other kernel subsystems
(e.g., graphics or media) or between userspace processes, via the 
standard dma-buf interface, avoiding unnecessary copies and enabling
efficient peer-to-peer (P2P) DMA transfers. See [1] for background on
dma-buf.

As part of this series, we introduce a new uverbs object of type FD for 
dma-buf export, along with the corresponding APIs for allocation and 
teardown. This object encapsulates all attributes required to export a
dma-buf.

The implementation enforces P2P-only mappings and properly manages
resource lifecycle, including:
- Cleanup during driver removal or RDMA context destruction.
- Revocation via dma_buf_move_notify() when the underlying mmap entries
  are removed.
- Refactors common cleanup logic for reuse across FD uobject types.

The infrastructure is generic within uverbs, allowing individual drivers
to easily integrate and supply their vendor-specific implementation.

The mlx5 driver is the first consumer of this new API, providing:
- Initialization of PCI peer-to-peer DMA support.
- mlx5-specific implementations of the mmap_get_pfns and 
  pgoff_to_mmap_entry device operations required for dma-buf export.

[1] https://docs.kernel.org/driver-api/dma-buf.html

Signed-off-by: Yishai Hadas <yishaih@...dia.com>
Signed-off-by: Edward Srouji <edwards@...dia.com>
---
Changes in v2:
- Split the FD uobject refactoring into a separate patch
  ("RDMA: Add support for exporting dma-buf file descriptors")
- Remove redundant revoked check from attach callback. It is checked
  during map
- Add pin callback that returns -EOPNOTSUPP to explicitly refuse pinned
  importers
- Wait for pending fences after dma_buf_move_notify() using
  dma_resv_wait_timeout() to ensure hardware has completed all in-flight
  operations before proceeding
- Link to v1: https://lore.kernel.org/r/20260108-dmabuf-export-v1-0-6d47d46580d3@nvidia.com

---
Yishai Hadas (3):
      RDMA/uverbs: Support external FD uobjects
      RDMA/uverbs: Add DMABUF object type and operations
      RDMA/mlx5: Implement DMABUF export ops

 drivers/infiniband/core/Makefile                  |   1 +
 drivers/infiniband/core/device.c                  |   2 +
 drivers/infiniband/core/ib_core_uverbs.c          |  22 +++
 drivers/infiniband/core/rdma_core.c               |  63 ++++----
 drivers/infiniband/core/rdma_core.h               |   1 +
 drivers/infiniband/core/uverbs.h                  |  10 ++
 drivers/infiniband/core/uverbs_std_types_dmabuf.c | 176 ++++++++++++++++++++++
 drivers/infiniband/core/uverbs_uapi.c             |   1 +
 drivers/infiniband/hw/mlx5/main.c                 |  72 +++++++++
 include/rdma/ib_verbs.h                           |   9 ++
 include/rdma/uverbs_types.h                       |   1 +
 include/uapi/rdma/ib_user_ioctl_cmds.h            |  10 ++
 12 files changed, 342 insertions(+), 26 deletions(-)
---
base-commit: 325e3b5431ddd27c5f93156b36838a351e3b2f72
change-id: 20260108-dmabuf-export-0d598058dd1e

Best regards,
-- 
Edward Srouji <edwards@...dia.com>