linux-kernel - Re: [PATCH RFC net-next v1 5/5] net: devmem: Implement TX path

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Message-ID: <6798ee97c73e1_987d9294d6@willemb.c.googlers.com.notmuch>
Date: Tue, 28 Jan 2025 09:49:59 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Mina Almasry <almasrymina@...gle.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 linux-doc@...r.kernel.org, 
 virtualization@...ts.linux.dev, 
 kvm@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, 
 "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, 
 Donald Hunter <donald.hunter@...il.com>, 
 Jonathan Corbet <corbet@....net>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 David Ahern <dsahern@...nel.org>, 
 "Michael S. Tsirkin" <mst@...hat.com>, 
 Jason Wang <jasowang@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
 Eugenio Pérez <eperezma@...hat.com>, 
 Stefan Hajnoczi <stefanha@...hat.com>, 
 Stefano Garzarella <sgarzare@...hat.com>, 
 Shuah Khan <shuah@...nel.org>, 
 Kaiyuan Zhang <kaiyuanz@...gle.com>, 
 Pavel Begunkov <asml.silence@...il.com>, 
 Willem de Bruijn <willemb@...gle.com>, 
 Samiullah Khawaja <skhawaja@...gle.com>, 
 Stanislav Fomichev <sdf@...ichev.me>, 
 Joe Damato <jdamato@...tly.com>, 
 dw@...idwei.uk
Subject: Re: [PATCH RFC net-next v1 5/5] net: devmem: Implement TX path

> > > +struct net_devmem_dmabuf_binding *
> > > +net_devmem_get_sockc_binding(struct sock *sk, struct sockcm_cookie *sockc)
> > > +{
> > > +     struct net_devmem_dmabuf_binding *binding;
> > > +     int err = 0;
> > > +
> > > +     binding = net_devmem_lookup_dmabuf(sockc->dmabuf_id);
> >
> > This lookup is from global xarray net_devmem_dmabuf_bindings.
> >
> > Is there a check that the socket is sending out through the device
> > to which this dmabuf was bound with netlink? Should there be?
> > (e.g., SO_BINDTODEVICE).
> >
> 
> Yes, I think it may be an issue if the user triggers a send from a
> different netdevice, because indeed when we bind a dmabuf we bind it
> to a specific netdevice.
> 
> One option is as you say to require TX sockets to be bound and to
> check that we're bound to the correct netdev. I also wonder if I can
> make this work without SO_BINDTODEVICE, by querying the netdev the
> sock is currently trying to send out on and doing a check in the
> tcp_sendmsg. I'm not sure if this is possible but I'll give it a look.

I was a bit quick on mentioning SO_BINDTODEVICE. Agreed that it is
vastly preferable to not require that, but infer the device from
the connected TCP sock.