A critical flaw has been found in Intel’s Skylake and Kaby Lake’s Hyperthreading

This flaw was discovered and highlighted by Linux Debian.org, who states that Skylake and Kaby Lake CPUs can “in some situations, dangerously misbehave when hyper-threading is enabled” with this behaviour resulting in “application and system misbehaviour, data corruption, and data loss”.

Right now the only fix for this issue is to disable Hyperthreading on Skylake and Kaby Lake CPUs, though given the fact that this issue only presents itself on select/rare workloads no gamers or general consumers should be affected or concerned by this issue.  

Below is a brief description of how this issue works, with Intel noting that this can be worked around with future microcode updates. 

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 (eg RAX, EAX or AX for AH) may cause unpredictable system behaviour. This can only happen when both logical processors on the same physical processor are active.

This issue is known to Intel, though at this time it is unknown when UEFI or BIOS fixes will be available to the Intel motherboards. Right now only a minimal number of consumers are affected by this issue, though it is certainly concerning to find such a flaw in Intel’s modern CPU designs. 

You can join the discussion on Intel’s Hyperthreading bug under certain workloads on the OC3D Forums.