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

["Yanjun.Zhu" <yanjun.zhu@linux.dev>]

On 3/25/26 8:00 AM, 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.

While the current patch set successfully introduces a generic buffer 
descriptor

infrastructure for CQ and QP creation, it raises the question of why

Memory Region (MR) allocation and registration have not been integrated 
into

this new ib_umem_list architecture.

Given that MRs often require complex memory backing—such as discrete 
dma-buf segments

from GPUs or fragmented user-space virtual addresses—extending the 
UVERBS_ATTR_BUFFERS

array model to MRs would seem like a natural evolution. This would 
provide a unified

UAPI for handling heterogeneous memory sources and eliminate the need 
for per-command

attributes when registering composite memory regions. Are there specific 
architectural

constraints or synchronization concerns that necessitated keeping MR 
registration on its legacy

path for now?

In short, I am wondering **whether this architecture can include MR 
(memory region) or not**.

As such, CQ/QP/MR can use the same architecture.

Zhu Yanjun

> Instead of adding per-command UAPI attributes for each new buffer
> type, a single UVERBS_ATTR_BUFFERS array attribute carries all buffer
> descriptors. Each descriptor specifies a buffer type and is indexed by
> per-command slot enums. A consumption check ensures userspace and
> driver agree on which buffers are used.
> The patchset:
> 1. Introduces the core ib_umem_list infrastructure and UAPI.
> 2. Factors out CQ buffer umem processing into a helper.
> 3. Integrates umem_list into CQ creation, with fallback to existing
>     per-attribute path.
> 4-7. Converts efa, mlx5, bnxt_re and mlx4 to use umem_list for CQ
>     buffer.
> 8. Removes the legacy umem field from struct ib_cq, now that all
>     drivers use umem_list for CQ buffer management.
> 9. Adds a consumption check verifying all umem_list buffers were
>     consumed by the driver after CQ creation.
> 10. Integrates umem_list into QP creation.
> 11. Converts mlx5 QP creation to use umem_list.
> 12-15. Extends CQ and QP with doorbell record buffer slots and
>     converts mlx5 to use them.
>
> Note this re-works the original patchset trying to handle this:
> https://lore.kernel.org/all/20260203085003.71184-1-jiri@resnulli.us/
> The code is so much different I'm sending this is a new patchset.
>
> Jiri Pirko (15):
>    RDMA/core: Introduce generic buffer descriptor infrastructure for umem
>    RDMA/uverbs: Push out CQ buffer umem processing into a helper
>    RDMA/uverbs: Integrate umem_list into CQ creation
>    RDMA/efa: Use umem_list for user CQ buffer
>    RDMA/mlx5: Use umem_list for user CQ buffer
>    RDMA/bnxt_re: Use umem_list for user CQ buffer
>    RDMA/mlx4: Use umem_list for user CQ buffer
>    RDMA/uverbs: Remove legacy umem field from struct ib_cq
>    RDMA/uverbs: Verify all umem_list buffers are consumed after CQ
>      creation
>    RDMA/uverbs: Integrate umem_list into QP creation
>    RDMA/mlx5: Use umem_list for QP buffers in create_qp
>    RDMA/uverbs: Add doorbell record buffer slot to CQ umem_list
>    RDMA/mlx5: Use umem_list for CQ doorbell record
>    RDMA/uverbs: Add doorbell record buffer slot to QP umem_list
>    RDMA/mlx5: Use umem_list for QP doorbell record
>
>   drivers/infiniband/core/core_priv.h           |   1 +
>   drivers/infiniband/core/umem.c                | 248 ++++++++++++++++++
>   drivers/infiniband/core/uverbs_cmd.c          |  18 +-
>   drivers/infiniband/core/uverbs_std_types_cq.c | 158 ++++++-----
>   drivers/infiniband/core/uverbs_std_types_qp.c |  26 +-
>   drivers/infiniband/core/verbs.c               |  26 +-
>   drivers/infiniband/hw/bnxt_re/ib_verbs.c      |  23 +-
>   drivers/infiniband/hw/efa/efa_verbs.c         |  17 +-
>   drivers/infiniband/hw/mlx4/cq.c               |  21 +-
>   drivers/infiniband/hw/mlx5/cq.c               |  40 ++-
>   drivers/infiniband/hw/mlx5/doorbell.c         |  41 ++-
>   drivers/infiniband/hw/mlx5/mlx5_ib.h          |   3 +-
>   drivers/infiniband/hw/mlx5/qp.c               |  76 ++++--
>   drivers/infiniband/hw/mlx5/srq.c              |   2 +-
>   include/rdma/ib_umem.h                        |  54 ++++
>   include/rdma/ib_verbs.h                       |   5 +-
>   include/rdma/uverbs_ioctl.h                   |  14 +
>   include/uapi/rdma/ib_user_ioctl_cmds.h        |  17 ++
>   include/uapi/rdma/ib_user_ioctl_verbs.h       |  27 ++
>   19 files changed, 651 insertions(+), 166 deletions(-)
>