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Date: Wed, 4 Jul 2018 15:17:25 +0300
From: Vasily Averin <>
To: Solar Designer <>
Subject: Re: 32-bit syscall breakage in -431 kernel with KAISER

I've reported about microcode_ctl to Red Hat

On 07/03/2018 09:16 PM, Solar Designer wrote:
> On Tue, Jul 03, 2018 at 08:32:57PM +0300, Vasily Averin wrote:
>> 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?
> It's quite possible we never tested microcode_ctl on Owl.  It isn't part
> of Owl, even though there was intent to add it at some point.
> I enabled CONFIG_MICROCODE=m in our kernels in late 2016:
> * Sat Dec 10 2016 Solar Designer <> 2.6.18-408.el5.028stab120.1.owl5
> - Merged in Red Hat's CVE-2016-5195 "Dirty COW" fix from -416 (slightly
> different from the fix included in OpenVZ's 120.3 released earlier) while also
> keeping the mitigation introduced in owl4.
> - In the x86_64 config, enabled CONFIG_MICROCODE=m, CONFIG_NUMA=y and many
> many sensors (similar to RHEL's), bumped up CONFIG_NR_CPUS from 32 to 255.
> Tested many of these on a Dell PowerEdge R720xd with 2x E5-2660 v2 (NUMA, huge
> pages, some I2C sensors, 40 logical CPUs).
> IIRC, I intended to test it on that Dell machine mentioned in there, but
> it was already at Intel's latest microcode revision for its CPUs, so I
> did not.  I think I did test loading of the kernel module, though.
> Alexander

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