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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@suse.de>, Pavel Machek <pavel@ucw.cz>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, shuzzle@mailbox.org
Subject: Re: Fwd: [Bug 150021] New: kernel panic: "kernel tried to execute NX-protected page" when resuming from hibernate to disk
Date: Thu, 28 Jul 2016 01:29:49 +0200
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On Thursday, July 28, 2016 01:20:53 AM Rafael J. Wysocki wrote:
> On Wednesday, July 27, 2016 05:17:38 PM Josh Poimboeuf wrote:
> > On Thu, Jul 28, 2016 at 12:12:15AM +0200, Rafael J. Wysocki wrote:
> > > On Wednesday, July 27, 2016 12:59:18 PM Josh Poimboeuf wrote:
> > > > Hm... I have a theory, but I'm not sure about it.  I noticed that
> > > > x86_acpi_enter_sleep_state(),
> > > 
> > > I think you mean x86_acpi_suspend_lowlevel().
> > 
> > Oops!
> > 
> > > > which is involved in suspend, overwrites
> > > > several global variables (e.g, initial_code) which are used by the CPU
> > > > boot code in head_64.S.  But surprisingly, it doesn't restore those
> > > > variables to their original values after it resumes.
> > > 
> > > Is the head_64.S code also used to bring up offline CPUs?
> > 
> > Yes.
> 
> OK
> 
> So it is really interesting why and how that stuff works for everybody.
> 
> Basically, CPU online should fail after a suspend-resume cycle, but it
> doesn't most of the time AFAICS.

do_boot_cpu() restores those values, so I think we're safe from that angle.

That should apply to the CPU online during resume from hibernation too.

Thanks,
Rafael