From: Jesper Dangaard Brouer <brouer@redhat.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: bpf@vger.kernel.org, netdev@vger.kernel.org,
Daniel Borkmann <borkmann@iogearbox.net>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
maze@google.com, lmb@cloudflare.com, shaun@tigera.io,
Lorenzo Bianconi <lorenzo@kernel.org>,
marek@cloudflare.com, Jakub Kicinski <kuba@kernel.org>,
eyal.birger@gmail.com, colrack@gmail.com, brouer@redhat.com
Subject: Re: [PATCH bpf-next V11 5/7] bpf: drop MTU check when doing TC-BPF redirect to ingress
Date: Thu, 14 Jan 2021 17:14:29 +0100 [thread overview]
Message-ID: <20210114171429.1402ca3d@carbon> (raw)
In-Reply-To: <600008e5e2e80_1eeef20852@john-XPS-13-9370.notmuch>
On Thu, 14 Jan 2021 01:03:33 -0800
John Fastabend <john.fastabend@gmail.com> wrote:
> Jesper Dangaard Brouer wrote:
> > The use-case for dropping the MTU check when TC-BPF does redirect to
> > ingress, is described by Eyal Birger in email[0]. The summary is the
> > ability to increase packet size (e.g. with IPv6 headers for NAT64) and
> > ingress redirect packet and let normal netstack fragment packet as needed.
> >
> > [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/
> >
> > V9:
> > - Make net_device "up" (IFF_UP) check explicit in skb_do_redirect
> >
> > V4:
> > - Keep net_device "up" (IFF_UP) check.
> > - Adjustment to handle bpf_redirect_peer() helper
> >
> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> > ---
> > include/linux/netdevice.h | 31 +++++++++++++++++++++++++++++--
> > net/core/dev.c | 19 ++-----------------
> > net/core/filter.c | 14 +++++++++++---
> > 3 files changed, 42 insertions(+), 22 deletions(-)
> >
>
> [...]
>
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 3f2e593244ca..1908800b671c 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -2083,13 +2083,21 @@ static const struct bpf_func_proto bpf_csum_level_proto = {
> >
> > static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
> > {
> > - return dev_forward_skb(dev, skb);
>
> > + int ret = ____dev_forward_skb(dev, skb, false);
> > +
> > + if (likely(!ret)) {
> > + skb->protocol = eth_type_trans(skb, dev);
> > + skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
> > + ret = netif_rx(skb);
> > + }
> > +
> > + return ret;
>
> How about putting above block into a dev.c routine call it
>
> dev_forward_skb_nomtu(...)
>
> or something like that. Then we keep this code next to its pair
> with mtu check, dev_forward_skb().
>
> dev_forward_skb() also uses netif_rx_internal() looks like maybe we should
> just do the same here?
I love the idea. I'm coding it up and it looks much nicer. And yes we
obviously can use netif_rx_internal() once the code in core/dev.c
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2021-01-14 16:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-12 17:45 [PATCH bpf-next V11 0/7] bpf: New approach for BPF MTU handling Jesper Dangaard Brouer
2021-01-12 17:45 ` [PATCH bpf-next V11 1/7] bpf: Remove MTU check in __bpf_skb_max_len Jesper Dangaard Brouer
2021-01-14 8:18 ` John Fastabend
2021-01-12 17:45 ` [PATCH bpf-next V11 2/7] bpf: fix bpf_fib_lookup helper MTU check for SKB ctx Jesper Dangaard Brouer
2021-01-12 17:45 ` [PATCH bpf-next V11 3/7] bpf: bpf_fib_lookup return MTU value as output when looked up Jesper Dangaard Brouer
2021-01-12 17:45 ` [PATCH bpf-next V11 4/7] bpf: add BPF-helper for MTU checking Jesper Dangaard Brouer
2021-01-12 19:23 ` Andrii Nakryiko
2021-01-14 14:52 ` Jesper Dangaard Brouer
2021-01-14 15:33 ` Yonghong Song
2021-01-13 23:07 ` Daniel Borkmann
2021-01-14 14:36 ` Jesper Dangaard Brouer
2021-01-14 22:28 ` Daniel Borkmann
2021-01-18 11:04 ` Jesper Dangaard Brouer
2021-01-12 17:45 ` [PATCH bpf-next V11 5/7] bpf: drop MTU check when doing TC-BPF redirect to ingress Jesper Dangaard Brouer
2021-01-14 9:03 ` John Fastabend
2021-01-14 16:14 ` Jesper Dangaard Brouer [this message]
2021-01-12 17:45 ` [PATCH bpf-next V11 6/7] selftests/bpf: use bpf_check_mtu in selftest test_cls_redirect Jesper Dangaard Brouer
2021-01-12 17:45 ` [PATCH bpf-next V11 7/7] bpf/selftests: tests using bpf_check_mtu BPF-helper Jesper Dangaard Brouer
2021-01-12 19:29 ` Andrii Nakryiko
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