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

[Zhiping Zhang <zhipingz@meta.com>]

On Tue, May 12, 2026 at 6:49 PM fengchengwen <fengchengwen@huawei.com> wrote:
>
> >
> 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 */
>

Hi Chengwen,
  Thanks for the great suggestions.
  1. Splitting the PCI/TPH helper change into a separate prep patch
sounds reasonable.
  2. I see your point about exposing the enabled TPH request type! I
want to take one
      more pass over the overall flow and switch to that if I don’t
find any issues.

  Zhiping

> >
> > 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(-)
> >
>
> ...