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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: Jakub Kicinski <kuba@kernel.org>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	bpf@vger.kernel.org, netdev@vger.kernel.org,
	Daniel Borkmann <borkmann@iogearbox.net>,
	maze@google.com, lmb@cloudflare.com, shaun@tigera.io,
	Lorenzo Bianconi <lorenzo@kernel.org>,
	marek@cloudflare.com, eyal.birger@gmail.com
Subject: Re: [PATCH bpf-next V3 0/6] bpf: New approach for BPF MTU handling
Date: Fri, 9 Oct 2020 14:07:44 -0700	[thread overview]
Message-ID: <20201009210744.xa55r6sanggqv5ou@ast-mbp> (raw)
In-Reply-To: <5f80ccca63d9_ed74208f8@john-XPS-13-9370.notmuch>

On Fri, Oct 09, 2020 at 01:49:14PM -0700, John Fastabend wrote:
> Jakub Kicinski wrote:
> > On Thu, 08 Oct 2020 16:08:57 +0200 Jesper Dangaard Brouer wrote:
> > > V3: Drop enforcement of MTU in net-core, leave it to drivers
> > 
> > Sorry for being late to the discussion.
> > 
> > I absolutely disagree. We had cases in the past where HW would lock up
> > if it was sent a frame with bad geometry.
> > 
> > We will not be sprinkling validation checks across the drivers because
> > some reconfiguration path may occasionally yield a bad packet, or it's
> > hard to do something right with BPF.
> 
> This is a driver bug then. As it stands today drivers may get hit with
> skb with MTU greater than set MTU as best I can tell. Generally I
> expect drivers use MTU to configure RX buffers not sure how it is going
> to be used on TX side? Any examples? I just poked around through the
> driver source to see and seems to confirm its primarily for RX side
> configuration with some drivers throwing the event down to the firmware
> for something that I can't see in the code?
> 
> I'm not suggestiong sprinkling validation checks across the drivers.
> I'm suggesting if the drivers hang we fix them.

+1

I've seen HW that hangs when certain sizes of the packet.
Like < 68 byte TX where size is one specific constant.
I don't think it's a job of the stack or the driver to deal with that.
It's firmware/hw bug.

  reply	other threads:[~2020-10-09 21:07 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-08 14:08 [PATCH bpf-next V3 0/6] bpf: New approach for BPF MTU handling Jesper Dangaard Brouer
2020-10-08 14:09 ` [PATCH bpf-next V3 1/6] bpf: Remove MTU check in __bpf_skb_max_len Jesper Dangaard Brouer
2020-10-09 16:12   ` Daniel Borkmann
2020-10-09 18:26     ` Maciej Żenczykowski
2020-10-10 10:25     ` Jesper Dangaard Brouer
2020-10-08 14:09 ` [PATCH bpf-next V3 2/6] bpf: bpf_fib_lookup return MTU value as output when looked up Jesper Dangaard Brouer
2020-10-09  4:05   ` David Ahern
2020-10-08 14:09 ` [PATCH bpf-next V3 3/6] bpf: add BPF-helper for MTU checking Jesper Dangaard Brouer
2020-10-09 23:29   ` Maciej Żenczykowski
2020-10-21 11:32     ` Jesper Dangaard Brouer
2020-10-12 15:54   ` Lorenz Bauer
2020-10-08 14:09 ` [PATCH bpf-next V3 4/6] bpf: make it possible to identify BPF redirected SKBs Jesper Dangaard Brouer
2020-10-09 16:47   ` Daniel Borkmann
2020-10-09 18:33     ` Maciej Żenczykowski
2020-10-10 11:09       ` Jesper Dangaard Brouer
2020-10-12 21:04         ` Maciej Żenczykowski
2020-10-08 14:09 ` [PATCH bpf-next V3 5/6] bpf: drop MTU check when doing TC-BPF redirect to ingress Jesper Dangaard Brouer
2020-10-09 23:17   ` Maciej Żenczykowski
2020-10-08 14:09 ` [PATCH bpf-next V3 6/6] net: inline and splitup is_skb_forwardable Jesper Dangaard Brouer
2020-10-09 16:33 ` [PATCH bpf-next V3 0/6] bpf: New approach for BPF MTU handling Jakub Kicinski
2020-10-09 20:49   ` John Fastabend
2020-10-09 21:07     ` Alexei Starovoitov [this message]
2020-10-09 21:57       ` Maciej Żenczykowski
2020-10-09 23:00     ` Jakub Kicinski
2020-10-10 10:44       ` Jesper Dangaard Brouer
2020-10-10 16:32         ` Jakub Kicinski
2020-10-10 23:52           ` John Fastabend
2020-10-11 23:30             ` Jakub Kicinski
2020-10-13 20:40           ` Jesper Dangaard Brouer
2020-10-13 23:07             ` Jakub Kicinski
2020-10-13 23:37               ` Alexei Starovoitov
2020-10-13 23:54                 ` Maciej Żenczykowski

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