Re: [PATCH rdma-next v3 2/3] RDMA/uverbs: Add DMABUF object type and operations

[Edward Srouji <edwards@nvidia.com>]

On 2/23/2026 6:59 AM, Guenter Roeck wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Sun, Feb 01, 2026 at 04:34:05PM +0200, Edward Srouji wrote:
>> From: Yishai Hadas <yishaih@nvidia.com>
>>
>> Expose DMABUF functionality to userspace through the uverbs interface,
>> enabling InfiniBand/RDMA devices to export PCI based memory regions
>> (e.g. device memory) as DMABUF file descriptors. This allows
>> zero-copy sharing of RDMA memory with other subsystems that support the
>> dma-buf framework.
>>
>> A new UVERBS_OBJECT_DMABUF object type and allocation method were
>> introduced.
>>
>> During allocation, uverbs invokes the driver to supply the
>> rdma_user_mmap_entry associated with the given page offset (pgoff).
>>
>> Based on the returned rdma_user_mmap_entry, uverbs requests the driver
>> to provide the corresponding physical-memory details as well as the
>> driver’s PCI provider information.
>>
>> Using this information, dma_buf_export() is called; if it succeeds,
>> uobj->object is set to the underlying file pointer returned by the
>> dma-buf framework.
>>
>> The file descriptor number follows the standard uverbs allocation flow,
>> but the file pointer comes from the dma-buf subsystem, including its own
>> fops and private data.
>>
>> When an mmap entry is removed, uverbs iterates over its associated
>> DMABUFs, marks them as revoked, and calls dma_buf_move_notify() so that
>> their importers are notified.
>>
>> The same procedure applies during the disassociate flow; final cleanup
>> occurs when the application closes the file.
>>
>> Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
>> Signed-off-by: Edward Srouji <edwards@nvidia.com>
> 
> When trying to build powerpc:ppc64e_defconfig:
> 
> ERROR: modpost: "dma_resv_wait_timeout" [drivers/infiniband/core/ib_core.ko] undefined!
> ERROR: modpost: "dma_buf_move_notify" [drivers/infiniband/core/ib_core.ko] undefined!
> ERROR: modpost: "dma_resv_reset_max_fences" [drivers/infiniband/core/ib_core.ko] undefined!
> 
> The code now requires CONFIG_DMA_SHARED_BUFFER which is not enabled for
> this platform.
> 
> Guenter

A fix was already sent, which I believe solves your issue:
https://lore.kernel.org/linux-rdma/20260216121213.2088910-1-arnd@kernel.org/
It adds 'select DMA_SHARED_BUFFER' to the infiniband Kconfig entry.