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Date: Tue, 3 Jul 2018 20:32:57 +0300
From: Vasily Averin <>
To: Solar Designer <>
Subject: Re: 32-bit syscall breakage in -431 kernel with KAISER

Dear ALexander,
Do you observe host crash on start of microcode_ctl service?

I did not found the reason of crash-on boot on my test node,
now I think it was caused by some misconfiguration on our buildsystem.
I've recompiled kernel manually and successfully bootedit on my test node.
However then node was crashed on start of microcode_ctl service on host. 

I've found that on our kernel __cpuinit moves get_scattered_cpuid_extra() into init section,
but this function can be called lagally called after initialization,
from microcode_write() -> spec_ctrl_rescan_cpuid()

Issue was caused by CONFIG_HOTPLUG_CPU enabled on Red Hat but disabled on our kernels.
Therefore I afraid your kernel should be affected too.

Could you please clarify this question?

Thank you,
	Vasily Averin

On 06/29/2018 07:41 PM, Solar Designer wrote:
> Vasily,
> On Fri, Jun 29, 2018 at 07:08:02PM +0300, Vasily Averin wrote:
>> On 06/28/2018 05:11 PM, Vasily Averin wrote:
>>> On my test node I observe strange exception right on boot of 64-bit kernel, 
>>> it is not handles properly and writes 0 into EIP and it crashes the kernel.
>>> So I'm going to troubloeshoot qemu with gdb, hope it helps tofind the resoun of the trouble.
>> I have stable reproducer, but even with single-step and hardware breakpoints I still cannot intercept this mysterious exception.
>> it adds an extra frame on regular stack, changes EIP to 0, then generates page_fault an crashes.
>> Alexander,
>> could you please drop me your config for 64bit kernel?
> You can get our kernel configs here:
> Meanwhile, Chris who reported the problem on owl-users has confirmed
> that Pavel's fix works for him.
> Alexander

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