In June of this year, OpenBSD announced plans to disable Hyper-Threading support for Intel CPUs due to concerns about more Spectre variants. On August 23, OpenBSD founder Theo de Raadt announced on the mailing list that OpenBSD-current (6.4) would officially disable the Hyper-Threading feature of Intel processors.
Theo de Raadt said that Intel processors have recently exploded two hardware bugs: TLBleed and T1TF (aka Foreshadow). Resolving these vulnerabilities requires updating microcode, plus software-related scenarios, and turning off hyperthreading. Hyperthreading is flawed by sharing resources and lack of security between the two CPU instances. He expects more bugs related to Hyper-Threading in the future, so he decided to disable Hyper-Threading by default in OpenBSD 6.4 and encouraged users of 6.2 and 6.3 to turn off Hyper-Threading in the machine’s BIOS.
Hyper-Threading is an Intel proprietary implementation of simultaneous multi-threading technology that allows processors to perform concurrent operations at different cores of the CPU. Intel processors have been adding this feature since 2002 and are enabled by default, which the chip giant says will improve performance.