Re: [PATCH v3 2/2] RDMA/mlx5: get tph for p2p access when registering dma-buf mr

[fengchengwen <fengchengwen@huawei.com>]

On 5/13/2026 2:47 AM, Zhiping Zhang wrote:
> Query dma-buf TPH metadata when registering a dma-buf MR for peer to
> peer access and translate the raw steering tag into an mlx5 steering
> tag index. Factor mlx5_st_alloc_index() so callers that already have a
> raw steering tag can allocate the corresponding mlx5 index directly.
> Keep the DMAH path as the first priority and only fall back to dma-buf
> metadata when no DMAH is supplied.
> 
> Add pcie_tph_get_st_width() so the mlx5 IB driver can query the
> device's negotiated ST width without poking pci_dev::tph_req_type
> directly (that field is gated by CONFIG_PCIE_TPH and would otherwise
> break !CONFIG_PCIE_TPH builds). Pass the width to the dma-buf
> get_tph() callback so the exporter can return the value that matches
> the consumer's capability.

1\ Recommend the PCI/TPH modification be committed separately.
2\ How about rename it to pcie_tph_enabled_req_type() ? so we could
   use already defined macro:
#define   PCI_TPH_REQ_DISABLE		0x0 /* No TPH requests allowed */
#define   PCI_TPH_REQ_TPH_ONLY		0x1 /* TPH only requests allowed */
#define   PCI_TPH_REQ_EXT_TPH		0x3 /* Extended TPH requests allowed */

> 
> Pass the dma_buf pointer that the umem already resolved into
> get_tph_mr_dmabuf() instead of re-resolving the user-supplied fd.
> Re-resolving opens a TOCTOU where a concurrent dup2() can substitute a
> different dma_buf between umem creation and TPH lookup.
> 
> Track the per-MR ownership of the allocated mlx5 ST index on
> mlx5_ib_mr (dmabuf_st_index / dmabuf_st_owned) and release it once the
> firmware mkey no longer references it. Both the cached path
> (mlx5r_umr_revoke_mr_with_lock + ib_frmr_pool_push) and the
> destroy_mkey path call mlx5_ib_mr_put_dmabuf_st() so the ST index does
> not leak when the MR is reused from the FRMR pool.
> 
> Initialize ret in mlx5_st_create() so the cached steering-tag path
> returns success cleanly under clang builds.
> 
> Signed-off-by: Zhiping Zhang <zhipingz@meta.com>
> ---
>  drivers/infiniband/hw/mlx5/mlx5_ib.h          |  6 ++
>  drivers/infiniband/hw/mlx5/mr.c               | 72 ++++++++++++++++++-
>  .../net/ethernet/mellanox/mlx5/core/lib/st.c  | 27 ++++---
>  drivers/pci/tph.c                             | 20 ++++++
>  include/linux/mlx5/driver.h                   |  7 ++
>  include/linux/pci-tph.h                       |  2 +
>  6 files changed, 124 insertions(+), 10 deletions(-)
> 

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