netdev - Re: [PATCH net-next v19 03/13] netdev: support binding dma-buf to netdevice

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Message-ID: <CAHS8izPL4YdqFjkTpYavdxQn816=kkUv0xravQJF4Uno7Bn3ZQ@mail.gmail.com>
Date: Tue, 20 Aug 2024 00:01:02 -0400
From: Mina Almasry <almasrymina@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Taehee Yoo <ap420073@...il.com>, netdev@...r.kernel.org, 
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	Kaiyuan Zhang <kaiyuanz@...gle.com>, Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH net-next v19 03/13] netdev: support binding dma-buf to netdevice

On Mon, Aug 19, 2024 at 6:53 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 19 Aug 2024 00:44:27 +0900 Taehee Yoo wrote:
> > > @@ -9537,6 +9540,10 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
> > >                         NL_SET_ERR_MSG(extack, "Native and generic XDP can't be active at the same time");
> > >                         return -EEXIST;
> > >                 }
> > > +               if (dev_get_max_mp_channel(dev) != -1) {
> > > +                       NL_SET_ERR_MSG(extack, "XDP can't be installed on a netdev using memory providers");
> > > +                       return -EINVAL;
> > > +               }
> >
> > Should we consider virtual interfaces like bonding, bridge, etc?
> > Virtual interfaces as an upper interface of physical interfaces can
> > still install XDP prog.
> >
> > # ip link add bond0 type bond
> > # ip link set eth0 master bond0
> > # ip link set bond0 xdp pin /sys/fs/bpf/x/y
> > and
> > # ip link set bond0 xdpgeneric pin /sys/fs/bpf/x/y
> >
> > All virtual interfaces can install generic XDP prog.
> > The bonding interface can install native XDP prog.
>
> Good point. We may need some common helpers to place the checks for XDP.
> They are spread all over the place now.

Took a bit of a look here. Forgive me, I'm not that familiar with XDP
and virtual interfaces, so I'm a bit unsure what to do here.

For veth, it seems, the device behind the veth is stored in
veth_priv->peer, so it seems maybe a dev_get_max_mp_channel() check on
veth_priv->peer is the way to go to disable this for veth? I think we
need to do this check on creation of the veth and on the ndo_bpf of
veth.

For bonding, it seems we need to add mp channel check in bond_xdp_set,
and bond_enslave?

There are a few other drivers that define ndo_add_slave, seems a check
in br_add_slave is needed as well.

This seems like a potentially deep rabbit hole with a few checks to
add all of the place. Is this blocking the series? AFAICT if XDP fails
with mp-bound queues with a benign error, that seems fine to me; I
don't have a use case for memory providers + xdp yet. This should only
be blocking if someone can repro a very serious error (kernel crash)
or something with this combination.

I can try to add these checks locally and propose as a follow up
series. Let me know if I'm on the right track with figuring out how to
implement this, and, if you feel like it's blocking.

-- 
Thanks,
Mina