linux-kernel - Re: [PATCH v12 01/11] x86: text_poke() may access uninitialized struct pages

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Message-ID: <20180625092229.GW2494@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Jun 2018 11:22:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, john.stultz@...aro.org,
        sboyd@...eaurora.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, hpa@...or.com, douly.fnst@...fujitsu.com,
        prarit@...hat.com, feng.tang@...el.com, pmladek@...e.com,
        gnomes@...rguk.ukuu.org.uk, linux-s390@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v12 01/11] x86: text_poke() may access uninitialized
 struct pages

On Mon, Jun 25, 2018 at 11:18:02AM +0200, Thomas Gleixner wrote:
> On Mon, 25 Jun 2018, Peter Zijlstra wrote:
> > On Mon, Jun 25, 2018 at 10:39:24AM +0200, Thomas Gleixner wrote:
> > > On Mon, 25 Jun 2018, Peter Zijlstra wrote:
> > > > I'm not entirely sure this is right.. Because not only do we need the
> > > > whole fixmap stuff working, we also need #DB and the IPI handlers set-up
> > > > and working.
> > > 
> > > IPI? That's early UP boot why would you need an IPI?
> > 
> > Because the way this is called is from __jump_label_transform() ->
> > text_poke_bp() -> text_poke() -> text_poke_early().
> > 
> > And if you look at text_poke_bp(), you'll note it relies on #DB and
> > on_each_cpu() IPIs.
> 
> on_each_cpu() resolves to a direct call on the current CPU and as there is
> no other CPU it does not matter. #DB might be a different story, haven't
> looked yet.

It _should_ all work.. but scary, who knows where this early stuff ends
up being used.