[CentOS-devel] Broken hyperthreading on Intel Skylake and Kaby Lake processors

Wed Jun 28 19:16:07 UTC 2017
Phil Perry <phil at elrepo.org>

On 28/06/17 10:06, Laurentiu Pancescu wrote:
> On 27/06/17 23:17, Tru Huynh wrote:
>> But there is this changelog from the debian team:
>> http://metadata.ftp-master.debian.org/changelogs/non-free/i/intel-microcode/unstable_changelog 
>>
> 
> FWIW, Fedora also updated its microcode to version 20170511 on May 23rd, 
> according to their changelog.  Not sure if it would work to just get the 
> microcode files from their package (until RH releases an updated 
> version).  Disabling hyperthreading feels less experimental, at a 
> moderate cost in performance.
> 
> Laurențiu
> 
> [1] https://apps.fedoraproject.org/packages/microcode_ctl/

I downloaded the latest microcode archive from Intel here:

https://downloadcenter.intel.com/download/26798/Linux-Processor-Microcode-Data-File

and unpacked the intel-ucode folder into /usr/lib/firmware/intel-ucode/ 
overwriting the files provided by the microcode_ctl package.

To manually force an update without rebooting, do:

echo 1 > /sys/devices/system/cpu/microcode/reload

dmesg then shows the microcode has been updated:

[693680.818073] microcode: CPU0 sig=0x506e3, pf=0x2, revision=0xa0
[693680.818944] microcode: CPU0 updated to revision 0xba, date = 2017-04-09
[693680.818993] microcode: CPU1 sig=0x506e3, pf=0x2, revision=0xa0
[693680.819861] microcode: CPU1 updated to revision 0xba, date = 2017-04-09
[693680.819946] microcode: CPU2 sig=0x506e3, pf=0x2, revision=0xa0
[693680.820788] microcode: CPU2 updated to revision 0xba, date = 2017-04-09
[693680.820834] microcode: CPU3 sig=0x506e3, pf=0x2, revision=0xa0
[693680.821622] microcode: CPU3 updated to revision 0xba, date = 2017-04-09

I haven't rebooted, but I'm assuming the new microcode files will get 
written upon reboot.

I've not experienced any issues since manually updating as described 
above so I'm not waiting on Red Hat for an update.