linux-kernel - Re: [PATCH net-next v10 3/9] net: devmem: TCP tx netlink api

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Message-ID: <CAHS8izNUOO-X0WHFTMd3_yEjCDu4sPYADE1oDEtWTYFNNMB5wQ@mail.gmail.com>
Date: Wed, 23 Apr 2025 10:59:17 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Donald Hunter <donald.hunter@...il.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, io-uring@...r.kernel.org, 
	virtualization@...ts.linux.dev, kvm@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Andrew Lunn <andrew+netdev@...n.ch>, Jeroen de Borst <jeroendb@...gle.com>, 
	Harshitha Ramamurthy <hramamurthy@...gle.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Willem de Bruijn <willemb@...gle.com>, Jens Axboe <axboe@...nel.dk>, 
	Pavel Begunkov <asml.silence@...il.com>, David Ahern <dsahern@...nel.org>, 
	Neal Cardwell <ncardwell@...gle.com>, Stefan Hajnoczi <stefanha@...hat.com>, 
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	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez <eperezma@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, sdf@...ichev.me, dw@...idwei.uk, 
	Jamal Hadi Salim <jhs@...atatu.com>, Victor Nogueira <victor@...atatu.com>, 
	Pedro Tammela <pctammela@...atatu.com>, Samiullah Khawaja <skhawaja@...gle.com>
Subject: Re: [PATCH net-next v10 3/9] net: devmem: TCP tx netlink api

On Wed, Apr 23, 2025 at 5:11 AM Donald Hunter <donald.hunter@...il.com> wrote:
>
> Mina Almasry <almasrymina@...gle.com> writes:
>
> > From: Stanislav Fomichev <sdf@...ichev.me>
> >
> > Add bind-tx netlink call to attach dmabuf for TX; queue is not
> > required, only ifindex and dmabuf fd for attachment.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@...ichev.me>
> > Signed-off-by: Mina Almasry <almasrymina@...gle.com>
> >
> > ---
> >
> > v3:
> > - Fix ynl-regen.sh error (Simon).
> >
> > ---
> >  Documentation/netlink/specs/netdev.yaml | 12 ++++++++++++
> >  include/uapi/linux/netdev.h             |  1 +
> >  net/core/netdev-genl-gen.c              | 13 +++++++++++++
> >  net/core/netdev-genl-gen.h              |  1 +
> >  net/core/netdev-genl.c                  |  6 ++++++
> >  tools/include/uapi/linux/netdev.h       |  1 +
> >  6 files changed, 34 insertions(+)
> >
> > diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> > index f5e0750ab71db..c0ef6d0d77865 100644
> > --- a/Documentation/netlink/specs/netdev.yaml
> > +++ b/Documentation/netlink/specs/netdev.yaml
> > @@ -743,6 +743,18 @@ operations:
> >              - defer-hard-irqs
> >              - gro-flush-timeout
> >              - irq-suspend-timeout
> > +    -
> > +      name: bind-tx
> > +      doc: Bind dmabuf to netdev for TX
>
> nit: maybe add "for RX" to the bind-rx doc.
>

Thanks, will pull this with the next iteration.

> > +      attribute-set: dmabuf
>
> The bind-rx op has "flags: [ admin-perm ]", should bind-tx also?
>

The omission of admin-perm for tx is intentional.

Binding a dmabuf to an rx queue should and is a privileged operation,
because basically the application doing the binding is taking
ownership of this rx queue. For TX, no such queue ownership is being
taken. The TX binding just gives the netdevice access to the dmabuf
dma-addresses so the netdevice can send from there. It's very similar
to a normal dma-map with normal memory. There is no need for privilege
checks.

-- 
Thanks,
Mina