According to this Mail in the Debian Mailing List, developer Henrique de Moraes Holschuh warns about using specific Intel CPUs with enabled Hyper Threading.
To be precise, the developers found a defect which could lead to “spurious errors, such as application and system misbehavior, data corruption, and data loss”.
Affected CPUs are Skylake and Kaby Lake series, the issue should not be limited to Linux but also occur on Windows and Macbook Pro. It seems that Intel already released a fix for this issue, as Intel already describes it in the errata SKZ7/SKW144/SKL150/SKX150/KBL095/KBW095 – “Short Loops Which Use AH/BH/CH/DH Registers May Cause Unpredictable System Behavior”.
For Debian or OpenSuse users, a Microcode update was already published, allowing you to continue to use Hyper Threading without any trouble. Using Ubuntu you can find a bug ticket here.
For Windows users, UEFI updates are usually the only way to update the microcode for the CPU. For some selected devices, however, they are also distributed via the Windows update. For Skylake chips with the signatures 0x406e3 and 0x506e3, the problem is corrected in the microcode version 0xb9 / 0xba or newer. There is no information on Skylake CPUs with the signature 0x50654 according to Debian.
Kaby-Lake CPUs with the signatures 0x806e9, 0x906e9 and Microcode version 0x48 are also affected.
Also some Macbook Pro from Apple from the year 2016 with the quad-core CPUs i7-6700HQ and i7-6820HQ are affected, possibly also some other devices. Even Apple creates EFI updates and publishes them to download, for Macbook Pro this has not happened by now.