"SMT (Simultanious Multi Threading) implementations typically share
TLBs and L1 caches between threads. This can make cache timing attacks a
lot easier and we strongly suspect that this will make several
spectre-class bugs exploitable. Especially on Intel's SMT implementation
which is better known as Hypter-threading. We really should not run
different security domains on different processor threads of the same
core."
"Note that SMT doesn't necessarily have a positive effect on
performance; it highly depends on the workload. In all likelyhood it
will actually slow down most workloads if you have a CPU with more than
two cores."
HT/SMT is disabled by default since 6.4
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