netdev - Re: [PATCH v3 bpf-next 02/18] bpf: Add bpf_arch_text

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Message-ID: <20191108091156.GG4114@hirez.programming.kicks-ass.net>
Date:   Fri, 8 Nov 2019 10:11:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     davem@...emloft.net, daniel@...earbox.net, x86@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v3 bpf-next 02/18] bpf: Add bpf_arch_text_poke() helper

On Thu, Nov 07, 2019 at 10:40:23PM -0800, Alexei Starovoitov wrote:
> Add bpf_arch_text_poke() helper that is used by BPF trampoline logic to patch
> nops/calls in kernel text into calls into BPF trampoline and to patch
> calls/nops inside BPF programs too.

This thing assumes the text is unused, right? That isn't spelled out
anywhere. The implementation is very much unsafe vs concurrent execution
of the text.