linux-kernel - Re: instant reboot caused by 194a9749c73d650c0

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Date:   Mon, 16 Apr 2018 08:07:09 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: instant reboot caused by 194a9749c73d650c0


* Eric Dumazet <eric.dumazet@...il.com> wrote:

> Hi Kirill
> 
> For some reason, my hosts instantly crash at boot time, with absolutely no log on console.
> 
> Bisection pointed to :
> 
> $ git bisect bad
> 194a9749c73d650c0b1dfdee04fb0bdf0a888ba8 is the first bad commit
> commit 194a9749c73d650c0b1dfdee04fb0bdf0a888ba8
> Author: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Date:   Mon Mar 12 13:02:46 2018 +0300
> 
>     x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G

Could you please send your .config? These early boot problems are sometimes build 
and Kconfig environment sensitive.

A high level description of your hardware and the distro you are using would also 
be useful.

Kirill, I'm curious about this change:

-       /* Calculate address we are running at */
-       call    1f
-1:     popl    %edi
-       subl    $1b, %edi
+       /* Calculate address of paging_enabled() once we are executing in the 
trampoline */
+       leal    paging_enabled - trampoline_32bit_src + TRAMPOLINE_32BIT_CODE_OFFSET(%ecx), %eax

Here we change the calculation from a "discover where we are executing" method to 
a calculation method (which is fundamentally more fragile) - why?

Thanks,

	Ingo