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

[Edward Srouji]

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@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Signed-off-by: Edward Srouji <edwards@xxxxxxxxxx>
>
> 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@xxxxxxxxxx/
It adds 'select DMA_SHARED_BUFFER' to the infiniband Kconfig entry.