linux-kernel - Re: [PATCH bpf-next v2 0/4] Add ftrace direct call for arm64

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Date:   Thu, 22 Sep 2022 20:01:16 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Xu Kuohai <xukuohai@...weicloud.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Florent Revest <revest@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        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>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Marc Zyngier <maz@...nel.org>, Guo Ren <guoren@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH bpf-next v2 0/4] Add ftrace direct call for arm64

On 9/13/22 6:27 PM, Xu Kuohai wrote:
> This series adds ftrace direct call for arm64, which is required to attach
> bpf trampoline to fentry.
> 
> Although there is no agreement on how to support ftrace direct call on arm64,
> no patch has been posted except the one I posted in [1], so this series
> continues the work of [1] with the addition of long jump support. Now ftrace
> direct call works regardless of the distance between the callsite and custom
> trampoline.
> 
> [1] https://lore.kernel.org/bpf/20220518131638.3401509-2-xukuohai@huawei.com/
> 
> v2:
> - Fix compile and runtime errors caused by ftrace_rec_arch_init
> 
> v1: https://lore.kernel.org/bpf/20220913063146.74750-1-xukuohai@huaweicloud.com/
> 
> Xu Kuohai (4):
>    ftrace: Allow users to disable ftrace direct call
>    arm64: ftrace: Support long jump for ftrace direct call
>    arm64: ftrace: Add ftrace direct call support
>    ftrace: Fix dead loop caused by direct call in ftrace selftest

Given there's just a tiny fraction touching BPF JIT and most are around core arm64,
it probably makes sense that this series goes via Catalin/Will through arm64 tree
instead of bpf-next if it looks good to them. Catalin/Will, thoughts (Ack + bpf-next
could work too, but I'd presume this just results in merge conflicts)?

>   arch/arm64/Kconfig                |   2 +
>   arch/arm64/Makefile               |   4 +
>   arch/arm64/include/asm/ftrace.h   |  35 ++++--
>   arch/arm64/include/asm/patching.h |   2 +
>   arch/arm64/include/asm/ptrace.h   |   6 +-
>   arch/arm64/kernel/asm-offsets.c   |   1 +
>   arch/arm64/kernel/entry-ftrace.S  |  39 ++++--
>   arch/arm64/kernel/ftrace.c        | 198 ++++++++++++++++++++++++++++--
>   arch/arm64/kernel/patching.c      |  14 +++
>   arch/arm64/net/bpf_jit_comp.c     |   4 +
>   include/linux/ftrace.h            |   2 +
>   kernel/trace/Kconfig              |   7 +-
>   kernel/trace/ftrace.c             |   9 +-
>   kernel/trace/trace_selftest.c     |   2 +
>   14 files changed, 296 insertions(+), 29 deletions(-)

Thanks,
Daniel