netdev - Re: [PATCH bpf-next] libbpf: fix AF_XDP helper program to support kernels without the JMP32 eBPF instruction class

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Message-ID: <c02dbf12-f1ae-8cb1-13fc-a7bb2fbff3aa@intel.com>
Date:   Fri, 20 Dec 2019 08:20:48 +0100
From:   Björn Töpel <bjorn.topel@...el.com>
To:     Alex Forster <aforster@...udflare.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next] libbpf: fix AF_XDP helper program to support
 kernels without the JMP32 eBPF instruction class

On 2019-12-19 23:29, Alex Forster wrote:
>> I though af_xdp landed after jmp32 ?
> 
> They were indeed pretty close together, but AF_XDP became usable in
> late 2018 with either 4.18 or 4.19. JMP32 landed in early 2019 with
> 5.1.
>

Correct, but is anyone really using AF_XDP pre-5.1?

The rationale for doing JMP32:
https://lore.kernel.org/bpf/87v9sip0i8.fsf@toke.dk/

I think going forward, a route where different AF_XDP programs is loaded
based on what currently running kernel supports. "Every s^Hcycle is
sacred", and we're actually paying for the extra checks.

Then again, failing to load is still pretty bad. :-) Thanks for fixing this.


Acked-by: Björn Töpel <bjorn.topel@...el.com>


> Alex Forster
>