linux-kernel - Re: [PATCH for-next 0/3] EFA dmabuf memory regions

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Date:   Tue, 26 Oct 2021 09:10:26 +0300
From:   Gal Pressman <gal.pressman@...ux.dev>
To:     Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Oded Gabbay <ogabbay@...ana.ai>,
        Tomer Tayar <ttayar@...ana.ai>,
        Yossi Leybovich <sleybo@...zon.com>,
        Alexander Matushevsky <matua@...zon.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Jianxin Xiong <jianxin.xiong@...el.com>,
        Firas Jahjah <firasj@...zon.com>
Subject: Re: [PATCH for-next 0/3] EFA dmabuf memory regions

On 12/10/2021 15:09, Gal Pressman wrote:
> Hey all,
>
> This is a followup to my previous RFCs [1][2], which now adds a new api
> to the RDMA subsystem that allows drivers to get a pinned dmabuf memory
> region without requiring an implementation of the move_notify callback.
> The new api makes use of the dynamic attachment api implemented in the
> RDMA subsystem, but calls dma_buf_pin() in order to make sure that the
> callback will not be called, as suggested by Christian.
>
> As explained in the previous RFC, move_notify requires the RDMA device
> to support on-demand-paging (ODP) which is not common on most devices
> (only supported by mlx5).
>
> While the dynamic requirement makes sense for certain GPUs, some devices
> (such as habanalabs) have device memory that is always "pinned" and do
> not need/use the move_notify operation.
>
> Patch #1 changes the dmabuf documentation to make it clear that pinning
> does not necessarily mean the memory must be moved to system memory, it
> is up to the exporter to decide.
> Patch #2 adds the RDMA api that allows drivers to get pinned dmabuf
> memory regions.
> Patch #3 adds the EFA implementation of the dmabuf importer.
>
> The motivation of this submission is to use habanalabs as the dmabuf
> exporter, and EFA as the importer to allow for peer2peer access through
> libibverbs.
>
> [1] https://lore.kernel.org/linux-rdma/20210818074352.29950-1-galpress@amazon.com/
> [2] https://lore.kernel.org/linux-rdma/20211007104301.76693-1-galpress@amazon.com/
>
> Thanks


Hey Jason, did you get a chance to take a look?