Re: [PATCH rdma-next v5 00/15] RDMA: Introduce generic buffer descriptor infrastructure for umem

[Leon Romanovsky <leon@kernel.org>]

On Sun, May 17, 2026 at 08:29:51AM +0200, Jiri Pirko wrote:
> From: Jiri Pirko <jiri@nvidia.com>
> 
> This patchset introduces a generic buffer descriptor infrastructure
> for passing memory buffers (dma-buf or user VA) to uverbs commands,
> and wires it up for CQ and QP creation in the uverbs core, efa, mlx5,
> bnxt_re and mlx4 drivers.
> 
> Instead of adding ad-hoc per-buffer UAPI attributes for each new buffer
> type, each command declares dedicated UVERBS_ATTR_UMEM attributes that
> carry one buffer descriptor each. Each descriptor specifies a buffer
> type, covering both VA and dma-buf. A consumption check ensures
> userspace and driver agree on which attributes are used.
> 
> The patchset:
> 1-2,4. Plumbing: rename ib_umem_get() to ib_umem_get_va() and re-route
>    it through the new central ib_umem_get(); no behaviour change.
> 3. Introduces the core buffer descriptor infrastructure and UAPI.
> 5. Factors out CQ buffer umem processing into a helper.
> 6. Adds the CQ buffer UMEM attribute and driver wrappers.
> 7-10. Converts efa, mlx5, bnxt_re and mlx4 to use the new CQ helpers,
>    with drivers taking umem ownership.
> 11. Removes the legacy umem field from struct ib_cq, now that all
>    drivers use the new helpers.
> 12. Adds optional whole-QP, RQ and SQ UMEM attributes to QP creation.
> 13. Converts mlx5 QP creation to use the new attributes.
> 14-15. Adds mlx5 driver-namespace UMEM attributes for CQ and QP
>    doorbell records.
> 
> ---
> Based on top of: https://lore.kernel.org/all/0-v1-045258567bd6+9fe-ib_uverbs_support_ko_jgg@nvidia.com/

The overall approach looks sane to me.

I have a few minor comments, mostly related to how I expect the
ib_umem_get_*() helpers to be used:

1. We should hide the ib_umem_get() function and export only
   ib_umem_get_va(), ib_umem_get_attr(), and
   ib_umem_get_attr_or_va(). I do not want to see drivers relying on
   ib_umem_get() again.

2. Pass a struct uverbs_attr_bundle *attrs instead of struct ib_udata
   *udata to ib_umem_get().

3. Consider simplifying ib_umem_get() further by passing in the desc.
   I am not fully convinced it helps, but it could allow handling
   va_fallback outside of ib_umem_get().
 
Thanks