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From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Marek Zavodsky <marek.zavodsky@gmail.com>
Cc: "Daniel Borkmann" <daniel@iogearbox.net>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Lorenz Bauer" <lmb@cloudflare.com>,
	"Maciej Żenczykowski" <maze@google.com>,
	"Saeed Mahameed" <saeed@kernel.org>,
	"Daniel Borkmann" <borkmann@iogearbox.net>,
	"Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
	BPF-dev-list <bpf@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"Lorenzo Bianconi" <lorenzo.bianconi@redhat.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Shaun Crampton" <shaun@tigera.io>,
	"David Miller" <davem@davemloft.net>,
	"Marek Majkowski" <marek@cloudflare.com>
Subject: Re: BPF redirect API design issue for BPF-prog MTU feedback?
Date: Mon, 21 Sep 2020 23:17:16 +0200
Message-ID: <CA+FuTSdx_a+DGG5dSFRB3wkowwNb1ZXHFed=qA3sj5y6U3VtiA@mail.gmail.com> (raw)
In-Reply-To: <CAG0p+LmqDXCJVygVtqvmsd2v4A=HRZdsGU3mSY0G=tGr2DoUvQ@mail.gmail.com>

On Mon, Sep 21, 2020 at 6:22 PM Marek Zavodsky <marek.zavodsky@gmail.com> wrote:
>
> Hi guys,
>
> My kernel knowledge is small, but I experienced this (similar) issue
> with packet encapsulation (not a redirect), therefore modifying the
> redirect branch would not help in my case.
>
> I'm working on a TC program to do GUE encap/decap (IP + UDP + GUE,
> outer header has extra 52B).
> There are no issues with small packets. But when I use curl to
> download big file HTTP server chunks data randomly. Some packets have
> MTU size, others are even bigger. Big packets are not an issue,
> however MTU sized packets fail on bpf_skb_adjust_room with -524
> (ENOTSUPP).

This is a related, but different, unresolved issue at the boundary of
GSO packets. Packets that are not GSO, but would exceed MTU once
encapsulated, will cause adjust room to fail:

            (!shrink && (skb->len + len_diff_abs > len_max &&
                         !skb_is_gso(skb))))
                return -ENOTSUPP;

As admin, this can be addressed by setting a lower route MTU on routes
that may be encapsulated. But that is not very obvious or transparent.

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-17 12:38 Jesper Dangaard Brouer
2020-09-17 12:54 ` Maciej Żenczykowski
2020-09-17 19:11   ` Saeed Mahameed
2020-09-18 10:00     ` Jesper Dangaard Brouer
2020-09-18 10:34       ` Toke Høiland-Jørgensen
2020-09-18 23:06       ` Maciej Żenczykowski
2020-09-21 10:37         ` Lorenz Bauer
2020-09-21 12:49           ` Jesper Dangaard Brouer
2020-09-21 15:08             ` Daniel Borkmann
2020-09-21 16:21               ` Marek Zavodsky
2020-09-21 21:17                 ` Willem de Bruijn [this message]
2020-09-22  9:15                   ` Jesper Dangaard Brouer
2020-09-21 16:26               ` Jesper Dangaard Brouer
2020-09-22  6:56                 ` Eyal Birger
2020-09-21 18:04               ` John Fastabend
2020-10-06 11:45                 ` Jesper Dangaard Brouer
2020-09-21 10:42   ` Lorenz Bauer

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