Intel has issue errata to iron out stability issues with it’s hyperthreading bug on Skylake and KabyLake processors. It is unknown if the bug also affect earlier processors.

According to reports, such systems might experienced unpredictable system behaviour. It is unknown if the problem

Errata: SKZ7/SKW144/SKL150/SKX150/SKZ7/KBL095/KBW095 Short Loops Which Use AH/BH/CH/DH Registers May Cause Unpredictable System Behavior.

Problem: Under complex micro-architectural conditions, short loops of less than 64 instructions that use AH, BH, CH or DH registers as well as their corresponding wider register (e.g. RAX, EAX or AX for AH) may cause unpredictable system behavior. This can only happen when both logical processors on the same physical processor are active.

Implication: Due to this erratum, the system may experience unpredictable system behavior.

Intel has apparently issued microcode updates for Skylake and Kaby Lake processors to fix the problem. Manufacturers of the mainboards will need to get an UEFI update to fix it.

By Harry