From: Jakub Kicinski <kuba@kernel.org>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Lorenz Bauer <lmb@cloudflare.com>,
Lorenzo Bianconi <lbianconi@redhat.com>,
Daniel Borkmann <daniel@iogearbox.net>,
John Fastabend <john.fastabend@gmail.com>,
netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: Redux: Backwards compatibility for XDP multi-buff
Date: Tue, 21 Sep 2021 15:54:43 -0700 [thread overview]
Message-ID: <20210921155443.507a8479@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <87o88l3oc4.fsf@toke.dk>
On Tue, 21 Sep 2021 18:06:35 +0200 Toke Høiland-Jørgensen wrote:
> 1. Do nothing. This would make it up to users / sysadmins to avoid
> anything breaking by manually making sure to not enable multi-buffer
> support while loading any XDP programs that will malfunction if
> presented with an mb frame. This will probably break in interesting
> ways, but it's nice and simple from an implementation PoV. With this
> we don't need the declaration discussed above either.
>
> 2. Add a check at runtime and drop the frames if they are mb-enabled and
> the program doesn't understand it. This is relatively simple to
> implement, but it also makes for difficult-to-understand issues (why
> are my packets suddenly being dropped?), and it will incur runtime
> overhead.
>
> 3. Reject loading of programs that are not MB-aware when running in an
> MB-enabled mode. This would make things break in more obvious ways,
> and still allow a userspace loader to declare a program "MB-aware" to
> force it to run if necessary. The problem then becomes at what level
> to block this?
>
> Doing this at the driver level is not enough: while a particular
> driver knows if it's running in multi-buff mode, we can't know for
> sure if a particular XDP program is multi-buff aware at attach time:
> it could be tail-calling other programs, or redirecting packets to
> another interface where it will be processed by a non-MB aware
> program.
>
> So another option is to make it a global toggle: e.g., create a new
> sysctl to enable multi-buffer. If this is set, reject loading any XDP
> program that doesn't support multi-buffer mode, and if it's unset,
> disable multi-buffer mode in all drivers. This will make it explicit
> when the multi-buffer mode is used, and prevent any accidental subtle
> malfunction of existing XDP programs. The drawback is that it's a
> mode switch, so more configuration complexity.
4. Add new program type, XDP_MB. Do not allow mixing of XDP vs XDP_MB
thru tail calls.
IMHO that's very simple and covers majority of use cases.
next prev parent reply other threads:[~2021-09-21 22:54 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-21 16:06 Redux: Backwards compatibility for XDP multi-buff Toke Høiland-Jørgensen
2021-09-21 17:31 ` Zvi Effron
2021-09-21 18:22 ` Toke Høiland-Jørgensen
2021-09-21 19:17 ` Zvi Effron
2021-09-21 22:14 ` Toke Høiland-Jørgensen
2021-09-21 23:10 ` Zvi Effron
2021-09-22 20:13 ` Toke Høiland-Jørgensen
2021-09-21 20:12 ` Alexei Starovoitov
2021-09-21 22:20 ` Toke Høiland-Jørgensen
2021-09-21 22:51 ` Jakub Kicinski
2021-09-22 20:01 ` Toke Høiland-Jørgensen
2021-09-22 21:23 ` Zvi Effron
2021-09-23 18:45 ` Toke Høiland-Jørgensen
2021-09-23 13:46 ` Jakub Kicinski
2021-09-27 12:43 ` Jesper Dangaard Brouer
2021-09-21 22:54 ` Jakub Kicinski [this message]
2021-09-22 20:02 ` Toke Høiland-Jørgensen
2021-09-22 21:11 ` Zvi Effron
2021-09-23 19:00 ` Toke Høiland-Jørgensen
2021-09-23 10:33 ` Lorenz Bauer
2021-09-23 12:59 ` Toke Høiland-Jørgensen
2021-09-24 10:18 ` Lorenz Bauer
2021-09-24 17:55 ` Zvi Effron
2021-09-24 19:38 ` Toke Høiland-Jørgensen
2021-09-28 8:47 ` Lorenz Bauer
2021-09-28 13:43 ` Toke Høiland-Jørgensen
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