OpenBSD is a widely-used variant of the Unix operating system. However, for security reasons, OpenBSD has turned off support for Intel's hyper-threading features.
In other words, in an OpenBSD environment configured with an Intel 64-bit processor, it is not possible to open more logical cores than the number of physical cores.
Mark Kettenis, maintainer of OpenBSD, said that SMT (Synchronous Multi-Threading) shares TLB (Transition Detection Buffer) and L1 cache among threads, which makes it easier to make regular attacks on the cache.
Kettenis stressed that they are very worried that this will lead to a Spectre (ghost) level vulnerability.
So, OpenBSD added new code 'hw.smt sysctl'.
Regarding the effect of turning off hyperthreading, Kettenis said that if it weren't for those rare code that was optimized for hyperthreading optimization, stopping it would have little effect on the daily workload.
