linux-kernel - Re: 4.17.0-rc1 doesn't boot.

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Message-ID: <017d65c5-748b-eeae-a020-fa4473f4507c@linux.intel.com>
Date:   Tue, 17 Apr 2018 09:48:07 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Mike Galbraith <efault@....de>, Borislav Petkov <bp@...en8.de>,
        Jörg Otte <jrg.otte@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Aaro Koskinen <aaro.koskinen@...ia.com>
Subject: Re: 4.17.0-rc1 doesn't boot.

On 04/17/2018 09:00 AM, Mike Galbraith wrote:
> On Tue, 2018-04-17 at 17:31 +0200, Borislav Petkov wrote:
>> On Tue, Apr 17, 2018 at 05:21:30PM +0200, Jörg Otte wrote:
>>> finished bisection.
>>> 39114b7a743e6759bab4d96b7d9651d44d17e3f9 is the first bad commit
>>> (x86/pti: Never implicitly clear _PAGE_GLOBAL for kernel image).
>>
>> Looks like you're not the only one:
>>
>> http://marc.info/?i=20180417150130.GA11166@ak-laptop.emea.nsn-net.net
> 
> I'm hitting this too, but only with PREEMPT_RT.  I put a bandaid on it
> (tell pti_kernel_image_global_ok() to return true for PREEMPT_RT) while
> waiting to see if it was really really as non-rt as it appeared to be.

It looks like pti_init() is too early for
change_page_attr()/set_memory_nonglobal() because they look for
irqs_off().  This *should* be OK in practice because we only need to
flush the boot CPU, not the others.  That's what ends up causing the
BUG_ON().

But, there's apparently something else going on too because things don't
boot even with that BUG_ON() backed out.

The good news is that its easy to reproduce.