linux-kernel - Re: [RFC][PATCH] x86/ftrace: Have ftrace trampolines turn read-only at the end of system boot up

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Date:   Fri, 1 May 2020 09:24:04 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC][PATCH] x86/ftrace: Have ftrace trampolines turn read-only
 at the end of system boot up

On Fri, 1 May 2020 00:17:06 -0500
Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> > Would it be easier to just call a new __text_poke_bp() which skips the
> > SYSTEM_BOOTING check, since you know the trampoline will always be
> > read-only?
> > 
> > Like:  
> 
> early_trace_init() is called after mm_init(), so I thought it might
> work, but I guess not:

Yeah, I was about to say that this happens before mm_init() ;-)

It's why we already have magic for enabling function tracing the first time.

Do you see anything wrong with this current solution? It probably needs
more comments, but I wanted to get acceptance on the logic before I go and
pretty it up and send a non RFC patch.

-- Steve