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Date: Tue, 17 Jan 2017 14:44:54 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Stafford Horne <shorne@gmail.com>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kees Cook <keescook@chromium.org>, Jessica Yu <jeyu@redhat.com>,
        Petr Mladek <pmladek@suse.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Yang Shi <yang.shi@linaro.org>, Tejun Heo <tj@kernel.org>,
        Prarit Bhargava <prarit@redhat.com>,
        Yaowei Bai <baiyaowei@cmss.chinamobile.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: Re: [PATCH -next] init/main: Init jump_labels before they are used
 to build zonelists
Message-ID: <20170117134454.GB6515@twins.programming.kicks-ass.net>
References: <20170117125624.8535-1-shorne@gmail.com>
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On Tue, Jan 17, 2017 at 02:07:36PM +0100, Vlastimil Babka wrote:

> Anyway I'm not sure if this patch is safe. Hopefully Peter can judge
> this better...
> 
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Signed-off-by: Stafford Horne <shorne@gmail.com>
> > ---
> >  init/main.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/init/main.c b/init/main.c
> > index 8b1adb6e..d1ca7cb 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -513,6 +513,7 @@ asmlinkage __visible void __init start_kernel(void)
> >  	boot_cpu_state_init();
> >  	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
> >  
> > +	jump_label_init();
> >  	build_all_zonelists(NULL, NULL);
> >  	page_alloc_init();
> >  
> > @@ -526,8 +527,6 @@ asmlinkage __visible void __init start_kernel(void)
> >  		parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
> >  			   NULL, set_init_arg);
> >  
> > -	jump_label_init();
> > -

Urgh, that means auditing all archs that implement this. The thing
you're looking for is if the self-modifying code cruft can be done that
early.

x86 looks to be fine, because this is after setup_arch() which is
required for ideal_nops[] to be initialied and we use text_poke_early()
which doesn't really need anything else.

I've not gone through the other arches...