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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
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


  reply index

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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