[PATCH v4 0/3] vfio/dma-buf: add TPH support for peer-to-peer access

[Zhiping Zhang <zhipingz@meta.com>]

This series adds TLP Processing Hints (TPH) support to the VFIO dma-buf
export path, allowing importing drivers (e.g. mlx5) to use the
exporter's steering tag when performing peer-to-peer DMA into a
VFIO-owned device.

Patch 1 adds the dma-buf get_tph callback and the new vfio uAPI.
Patch 2 exposes the enabled TPH requester type through a small PCI/TPH
helper so callers don't reach into pci_dev internals.
Patch 3 wires up the mlx5 RDMA driver as a consumer.

Changes since v3:
  - vfio: TPH SET is now write-once per dma-buf; a second
    VFIO_DEVICE_FEATURE_DMA_BUF_TPH on the same dma-buf returns -EBUSY.
  - vfio: annotate priv->vdev with READ_ONCE/WRITE_ONCE across the
    cleanup, release, and feature-set paths to make the existing
    cleanup/release coordination explicit.
  - vfio uAPI: shrink steering_tag from __u16 to __u8 to match the
    8-bit ST width, and drop the trailing reserved[3] in
    struct vfio_device_feature_dma_buf_tph (struct is now 12 bytes).
  - Split the new PCI/TPH helper into its own patch (now patch 2) and
    rename it from pcie_tph_get_st_width() to
    pcie_tph_enabled_req_type(), exposing the enabled requester mode
    rather than just the ST width.
  - mlx5: release the allocated ST index before the MR is pushed back
    to the FRMR pool, so a reused MR cannot reference a freed firmware
    ST entry.
  - mlx5: free mlx5_st_idx_data when its refcount reaches zero, fixing
    a leak that accumulated across repeated alloc/dealloc cycles.
  - Initialize ret in mlx5_st_create() and mlx5_st_alloc_index_by_tag()
    to silence -Wsometimes-uninitialized warnings reported by the
    kernel test robot under clang.

Previous link:
v3: https://lore.kernel.org/linux-pci/20260512184755.4137227-1-zhipingz@meta.com/
v2: https://lore.kernel.org/linux-pci/20260430200704.352228-1-zhipingz@meta.com/

Zhiping Zhang (3):
  vfio: add dma-buf get_tph callback and DMA_BUF_TPH feature
  PCI/TPH: expose the enabled TPH requester type
  RDMA/mlx5: get tph for p2p access when registering dma-buf mr

 drivers/infiniband/hw/mlx5/mlx5_ib.h          |   6 +
 drivers/infiniband/hw/mlx5/mr.c               |  86 ++++++++++-
 .../net/ethernet/mellanox/mlx5/core/lib/st.c  |  28 ++--
 drivers/pci/tph.c                             |  12 ++
 drivers/vfio/pci/vfio_pci_core.c              |   3 +
 drivers/vfio/pci/vfio_pci_dmabuf.c            | 134 +++++++++++++++++-
 drivers/vfio/pci/vfio_pci_priv.h              |  12 ++
 include/linux/dma-buf.h                       |  21 +++
 include/linux/mlx5/driver.h                   |   7 +
 include/linux/pci-tph.h                       |   2 +
 include/uapi/linux/vfio.h                     |  35 +++++
 11 files changed, 327 insertions(+), 19 deletions(-)

-- 
2.53.0-Meta