linux-kernel - Re: [PATCH 0/3] x86_64/ftrace: Emulate calls from int3 when patching functions

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Date:   Wed, 8 May 2019 12:06:14 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, stable <stable@...r.kernel.org>
Subject: Re: [PATCH 0/3] x86_64/ftrace: Emulate calls from int3 when
 patching functions

On Wed, 8 May 2019 13:30:22 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> > To solve this, an int3_emulate_call() is created for x86_64 to allow
> > ftrace on x86_64 to emulate the call to ftrace_regs_caller() which will
> > make sure all the registered handlers to that function are still called.
> > And this keeps live kernel patching happy!  
> 
> Out of curiosity, would you have any idea to re-use these function for
> other use-case? Maybe kprobes can reuse it, but very limited use-case.

Yes, but only for x86_64.

> 
> > To mimimize the changes, and to avoid controversial patches, this
> > only changes x86_64. Due to the way x86_32 implements the regs->sp
> > the complexity of emulating calls on that platform is too much for
> > stable patches, and live kernel patching does not support x86_32 anyway.  
> 
> This series looks good to me.
> 
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks Masami!

-- Steve