I actually dug this up from my notes to undo it because it is a limited attack and my work computer could use the extra power, and/or it behaves less well without using it.
But to force Linux not to use hyperthreading, as it is an attack surface for high sensitive situations, even on computers where you can’t disable it from the BIOS (ideal case):
GRUB_CMDLINE_LINUX_DEFAULT(where N is # of cores)
- Then run
update-gruband reboot! 😀