Hyperthreading in Skylake and Kaby Lake seems to be broken and should be disabled in BIOS/UEFI.

My Laptop is also affected by this bug, but I will try to update the microcode. Since I’m running Arch Linux I should get the update rather fast.

UPDATE

Gosh, this bug is serious. For now I disabled hyperthreading completely. Hope a fix will be available (if even possible?).