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

From: Daniel Borkmann <daniel@iogearbox.net>
To: Xu Kuohai <xukuohai@huaweicloud.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>,
	Florent Revest <revest@chromium.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
	Alexei Starovoitov <ast@kernel.org>,
	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>, Zi Shen Lim <zlim.lnx@gmail.com>,
	Pasha Tatashin <pasha.tatashin@soleen.com>,
	Ard Biesheuvel <ardb@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Guo Ren <guoren@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH bpf-next v2 0/4] Add ftrace direct call for arm64
Date: Thu, 22 Sep 2022 20:01:16 +0200	[thread overview]
Message-ID: <f1e14934-dc54-9bf7-501a-89affdb7371e@iogearbox.net> (raw)
In-Reply-To: <20220913162732.163631-1-xukuohai@huaweicloud.com>

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