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Date: Mon, 25 Jun 2018 11:22:29 +0200
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v12 01/11] x86: text_poke() may access uninitialized
 struct pages
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, linux@armlinux.org.uk, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, john.stultz@linaro.org, sboyd@codeaurora.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, douly.fnst@cn.fujitsu.com, prarit@redhat.com, feng.tang@intel.com, pmladek@suse.com, gnomes@lxorguk.ukuu.org.uk, linux-s390@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>
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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.