linux-kernel - Re: [PATCH bpf-next v1 0/4] Support bpf trampoline for RV64

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Message-ID: <8735763pcu.fsf@all.your.base.are.belong.to.us>
Date:   Thu, 16 Feb 2023 10:56:49 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Pu Lehui <pulehui@...weicloud.com>, bpf@...r.kernel.org,
        linux-riscv@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>
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>,
        Palmer Dabbelt <palmer@...belt.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Guo Ren <guoren@...nel.org>,
        Luke Nelson <luke.r.nels@...il.com>,
        Xi Wang <xi.wang@...il.com>, Pu Lehui <pulehui@...wei.com>,
        Pu Lehui <pulehui@...weicloud.com>
Subject: Re: [PATCH bpf-next v1 0/4] Support bpf trampoline for RV64

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

> BPF trampoline is the critical infrastructure of the bpf
> subsystem, acting as a mediator between kernel functions
> and BPF programs. Numerous important features, such as
> using ebpf program for zero overhead kernel introspection,
> rely on this key component. We can't wait to support bpf
> trampoline on RV64. Since RV64 does not support ftrace
> direct call yet, the current RV64 bpf trampoline is only
> used in bpf context.
>
> As most of riscv cpu support unaligned memory accesses,
> we temporarily use patch [1] to facilitate testing. The
> test results are as follow, and test_verifier with no
> new failure ceses.
>
> - fexit_bpf2bpf:OK
> - dummy_st_ops:OK
> - xdp_bpf2bpf:OK
>
> [1] https://lore.kernel.org/linux-riscv/20210916130855.4054926-2-chenhuang5@huawei.com/
>
> v1:
> - Remove the logic of bpf_arch_text_poke supported for
>   kernel functions. (Kuohai and Björn)
> - Extend patch_text for multiple instructions. (Björn)
> - Fix OOB issue when image too big. (Björn)

This series is ready to go in as is.

@Palmer I'd like to take this series via the bpf-next tree (as usual),
but note that there are some non-BPF changes as well, related to text
poking.

@Lehui I'd like to see two follow-up patches:

1. Enable kfunc for RV64, by adding:
 | bool bpf_jit_supports_kfunc_call(void)
 | {
 |         return true;
 | }

2. Remove the checkpatch warning on patch 4:
 | WARNING: kfree(NULL) is safe and this check is probably not required
 | #313: FILE: arch/riscv/net/bpf_jit_comp64.c:984:
 | +	if (branches_off)
 | +		kfree(branches_off);


For the series:

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