linux-kernel - Re: [BUG?] ppc64le: fentry BPF not triggered after live patch (v6.14)

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Message-ID: <81b222ec-7635-411f-b72f-804284295edf@linux.ibm.com>
Date: Mon, 7 Apr 2025 13:52:27 +0530
From: Hari Bathini <hbathini@...ux.ibm.com>
To: Song Liu <song@...nel.org>, Naveen N Rao <naveen@...nel.org>
Cc: Jiri Olsa <olsajiri@...il.com>, Steven Rostedt <rostedt@...dmis.org>,
        Shung-Hsi Yu <shung-hsi.yu@...e.com>, bpf@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Vishal Chourasia <vishalc@...ux.ibm.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Michal Suchánek <msuchanek@...e.de>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-trace-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [BUG?] ppc64le: fentry BPF not triggered after live patch (v6.14)



On 04/04/25 12:03 am, Song Liu wrote:
> On Thu, Apr 3, 2025 at 8:30 AM Naveen N Rao <naveen@...nel.org> wrote:
> [...]
>>
>> We haven't addressed this particular interaction in the powerpc support
>> for ftrace direct and BPF trampolines. Right now, live patching takes
>> priority so we call the livepatch'ed function and skip further ftrace
>> direct calls.
>>
>> I'm curious if this works on arm64 with which we share support for
>> DYNAMIC_FTRACE_WITH_CALL_OPS.
> 
> We still need to land [1] for arm64 to support livepatch. In a quick test
> with [1], livepatch and bpf trampoline works together. I haven't looked
> into the arm64 JIT code, so I am not sure whether all the corner cases
> are properly handled.
> 
> [1] https://lore.kernel.org/live-patching/20250320171559.3423224-1-song@kernel.org/

Thanks for checking this on arm64, Song.
As Naveen pointed out, with out of line trampoline
on ppc64le, there are a few things to sort out with
regard to livepatch & BPF Trampoline interaction. Will
try and take a stab at it soon.

Thanks
Hari