Re: 4.17.0-rc1 doesn't boot.

From: Dave Hansen
Date: Tue Apr 17 2018 - 12:48:28 EST

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:
> 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

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.