From:   =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
To:     Pu Lehui <pulehui@huaweicloud.com>, bpf@vger.kernel.org,
        linux-riscv@lists.infradead.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Palmer Dabbelt <palmer@rivosinc.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        Guo Ren <guoren@kernel.org>,
        Luke Nelson <luke.r.nels@gmail.com>,
        Xi Wang <xi.wang@gmail.com>, Pu Lehui <pulehui@huawei.com>,
        Pu Lehui <pulehui@huaweicloud.com>
Subject: Re: [PATCH bpf-next v1 0/4] Support bpf trampoline for RV64
In-Reply-To: <20230215135205.1411105-1-pulehui@huaweicloud.com>
References: <20230215135205.1411105-1-pulehui@huaweicloud.com>
Date:   Thu, 16 Feb 2023 10:56:49 +0100
Message-ID: <8735763pcu.fsf@all.your.base.are.belong.to.us>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
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Precedence: bulk

Pu Lehui <pulehui@huaweicloud.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-chenhuan=
g5@huawei.com/
>
> v1:
> - Remove the logic of bpf_arch_text_poke supported for
>   kernel functions. (Kuohai and Bj=C3=B6rn)
> - Extend patch_text for multiple instructions. (Bj=C3=B6rn)
> - Fix OOB issue when image too big. (Bj=C3=B6rn)

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: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>
Acked-by: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>