linux-kernel - Re: [PATCH bpf-next v2] riscv, bpf: Add kfunc support for RV64

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Message-ID: <87h6vffqlo.fsf@all.your.base.are.belong.to.us>
Date:   Tue, 21 Feb 2023 08:02:43 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Pu Lehui <pulehui@...weicloud.com>, bpf@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf-next v2] riscv, bpf: Add kfunc support for RV64

Pu Lehui <pulehui@...weicloud.com> writes:

> On 2023/2/20 22:34, Björn Töpel wrote:
>> Pu Lehui <pulehui@...weicloud.com> writes:
>> 
>>> From: Pu Lehui <pulehui@...wei.com>
>>>
>>> As another important missing piece of RV64 JIT, kfunc allow bpf programs
>>> call kernel functions. For now, RV64 is sufficient to enable it.
>> 
>> Thanks Lehui!
>> 
>> Maybe we can reword/massage the commit message a bit? What do you think
>> about something like:
>> 
>> "Now that the BPF trampoline is supported by RISC-V, it is possible to
>> use BPF programs with kfunc calls.
>> 
>
> kfunc and bpf trampoline are functionally independent. kfunc [1], like 
> bpf helper functions, allows bpf programs to call exported kernel 
> functions, while bpf trampoline provides a more efficient way than 
> kprobe to act as a mediator between kernel functions and bpf programs, 
> and between bpf programs.
>
> In fact, it was already supported before the bpf trampoline 
> implementation, I just turned it on.

Good point. I guess my (incorrect) kfunc mental model was that
struct_ops and kfunc were tightly coupled. (Then again, w/o struct_ops
working kfunc is a bit half-working in my view.)

Fair enough. I'm still a bit confused about the commit message, but
happy with the patch.

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