This was marked for stable, and honestly, nowhere in the discussion did I see any mention of just *how* bad the performance impact of this was.
When performance goes down by 50% on some loads, people need to start asking themselves whether it was worth it. It’s apparently better to just disable SMT entirely, which is what security-conscious people do anyway.
So why do that STIBP slow-down by default when the people who *really* care already disabled SMT?
I think we should use the same logic as for L1TF: we default to something that doesn’t kill performance. Warn once about it, and let the crazy people say “I’d rather take a 50% performance hit than worry about a theoretical issue”.