netdev - Re: [PATCH v13 bpf-next 10/10] selftests/bpf: tests for using dynptrs to parse skb and xdp buffers

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Message-ID: <CAADnVQKUqagMC3ELf9mW+RwQsxogtFFJ7fQNp9btq-Hcd9O+ag@mail.gmail.com>
Date:   Fri, 10 Mar 2023 09:43:59 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Joanne Koong <joannelkoong@...il.com>,
        bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Toke Høiland-Jørgensen <toke@...nel.org>
Subject: Re: [PATCH v13 bpf-next 10/10] selftests/bpf: tests for using dynptrs
 to parse skb and xdp buffers

On Thu, Mar 9, 2023 at 9:12 PM Stanislav Fomichev <sdf@...gle.com> wrote:
>
> >
> > and I'm wondering whether you meant bpf_prog_dev_bound_match(), and
> > whether it protects against the ABA problem, i.e., if
> > __bpf_offload_dev_netdev_unregister() is called twice, and we get
> > aux->offload and aux->offload->netdev at the same addresses?
>
> Yes, the comment is talking about bpf_prog_dev_bound_match during attach time.
> When __bpf_offload_dev_netdev_unregister races with our prog load
> (which is being loaded for some specific netdev),
> bpf_prog_dev_bound_match check during attach time should render this
> program un-attach-able / unusable (since the original netdev, for
> which this prog has been loaded, is gone).
>
> But going back to s390 issue: so basically, rewriting imm for kfuncs
> early in the verifier prevents jit from being able to call
> bpf_jit_find_kfunc_model? Did I get that correctly?
> Adding kfunc_desc seems like a nice hack, but I liked your previous
> series which pushed that imm resolution down to the jits better :-(

Me too. All I was saying is to do without hacking through all JITs.
More or less what v2 version was doing instead all-arch change in v3.