netdev - Re: [PATCH v3 2/9] virtio-net: set up xdp for multi buffer packets

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Message-ID: <CACGkMEsBe=_uNFB_6K_obqcnnaJi6ME22-j7cgXwSCTV85BKQw@mail.gmail.com>
Date:   Mon, 9 Jan 2023 16:56:37 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Heng Qi <hengqi@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v3 2/9] virtio-net: set up xdp for multi buffer packets

On Mon, Jan 9, 2023 at 10:48 AM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
>
>
> 在 2023/1/3 下午2:40, Heng Qi 写道:
> > When the xdp program sets xdp.frags, which means it can process
> > multi-buffer packets over larger MTU, so we continue to support xdp.
> > But for single-buffer xdp, we should keep checking for MTU.
> >
> > Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> > Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >   drivers/net/virtio_net.c | 10 ++++++----
> >   1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 443aa7b8f0ad..60e199811212 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -3074,7 +3074,9 @@ static int virtnet_restore_guest_offloads(struct virtnet_info *vi)
> >   static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> >                          struct netlink_ext_ack *extack)
> >   {
> > -     unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
> > +     unsigned int room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
> > +                                        sizeof(struct skb_shared_info));
> > +     unsigned int max_sz = PAGE_SIZE - room - ETH_HLEN;
>
> Hi Jason, I've updated the calculation of 'max_sz' in this patch instead
> of a separate bugfix, since doing so also seemed clear.

Sure, I will review it with this series no later than the end of this week.

Thanks

>
> Thanks.
>
> >       struct virtnet_info *vi = netdev_priv(dev);
> >       struct bpf_prog *old_prog;
> >       u16 xdp_qp = 0, curr_qp;
> > @@ -3095,9 +3097,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> >               return -EINVAL;
> >       }
> >
> > -     if (dev->mtu > max_sz) {
> > -             NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP");
> > -             netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
> > +     if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) {
> > +             NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP without frags");
> > +             netdev_warn(dev, "single-buffer XDP requires MTU less than %u\n", max_sz);
> >               return -EINVAL;
> >       }
> >
>