linux-kernel - Re: [PATCH RFC] MIPS: livepatch: Add LIVEPATCH basic code

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Date:   Wed, 10 Mar 2021 09:18:06 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Jinyang He <hejinyang@...ngson.cn>
cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Xuefeng Li <lixuefeng@...ngson.cn>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [PATCH RFC] MIPS: livepatch: Add LIVEPATCH basic code

Hi,

I cannot really comment on mips arch specifics but few words from the live 
patching perspective.

On Mon, 1 Mar 2021, Jinyang He wrote:

> Add the basic code of livepatch. livepatch is temporarily unavailable.
> Two core functions are missing, one is DYNAMIC_FTRACE_WITH_REGS, and
> another is save_stack_trace_tsk_reliable().
> `Huang Pei <huangpei@...ngson.cn>` is doing for ftrace. He will use
> `-fpatchable-function-entry` to achieve more complete ftrace.

DYNAMIC_FTRACE_WITH_ARGS has been introduced recently, so you might also 
look at that. As far as the live patching is concerned, 
DYNAMIC_FTRACE_WITH_ARGS is sufficient.

> save_stack_trace_tsk_reliable() currently has difficulties. This function
> may be improved in the future, but that seems to be a long time away.
> This is also the reason for delivering this RFC. Hope to get any help.

You may want to look at Documentation/livepatch/reliable-stacktrace.rst 
which nicely describes the requirements for the reliable stacktraces. 

Regards
Miroslav