netdev - Re: [PATCH net-next] xsk: introduce xsk_dma

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Message-ID: <20230424082856.15c1e593@kernel.org>
Date:   Mon, 24 Apr 2023 08:28:56 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH net-next] xsk: introduce xsk_dma_ops

On Sun, 23 Apr 2023 09:54:28 +0800 Xuan Zhuo wrote:
> On Fri, 21 Apr 2023 06:50:59 -0700, Jakub Kicinski <kuba@...nel.org> wrote:
> > On Fri, 21 Apr 2023 15:31:04 +0800 Xuan Zhuo wrote:  
> > > I am not particularly familiar with dma-bufs. I want to know if this mechanism
> > > can solve the problem of virtio-net.
> > >
> > > I saw this framework, allowing the driver do something inside the ops of
> > > dma-bufs.
> > >
> > > If so, is it possible to propose a new patch based on dma-bufs?  
> >
> > I haven't looked in detail, maybe Olek has? AFAIU you'd need to rework
> > uAPI of XSK to allow user to pass in a dma-buf region rather than just
> > a user VA.  
> 
> This seems to be a big job. Can we first receive this patch.

To me it looks like a very obvious workaround for the fact that virtio
does not make normal use of the DMA API, and (for reasons which perhaps
due to my meager intellect I do not grasp) you are not allowed to fix
that. Regardless, we have a path forward so I vote "no" to the patch
under discussion.