netdev - Re: [RFC PATCH net-next v6 05/15] netdev: support binding dma-buf to netdevice

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Message-Id: <037496c9-f06a-4946-b903-95d87d577b89@app.fastmail.com>
Date: Tue, 05 Mar 2024 22:42:07 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Mina Almasry" <almasrymina@...gle.com>
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Subject: Re: [RFC PATCH net-next v6 05/15] netdev: support binding dma-buf to netdevice

On Tue, Mar 5, 2024, at 21:00, Mina Almasry wrote:
> On Tue, Mar 5, 2024 at 1:05 AM Arnd Bergmann <arnd@...db.de> wrote:
>> On Tue, Mar 5, 2024, at 03:01, Mina Almasry wrote:
>
> A key goal of this patch series is that the kernel does not try to
> parse the skb frags that reside in the dma-buf for that precise
> reason. This is achieved using patch "net: add support for skbs with
> unreadable frags" which disables the kernel touching the payload in
> these skbs, and "tcp: RX path for devmem TCP" which implements a uapi
> where the kernel hands the data in the dmabuf to the userspace via a
> cmsg that gives the user a pointer to the data in the dmabuf (offset +
> size).
>
> So really AFACT the only restriction here is that the NIC should be
> able to DMA into the dmabuf that we're attaching, and dma_buf_attach()
> fails in this scenario so we're covered there.

Ok, makes sense. Thanks for the clarification.

     Arnd