Performance sorta hinges on it. It could be that the cheaper way the chipmakers deal with it is to phase out the 4core set and push the cores on a die higher, and to do that--incorporate an older core design into dedicated cores for untrusted code.

This would also require changes at the OS-makers to tag thread forks for trusted and untrusted behavior.

Essentially: instead of shutting down SMT for the entire machine, make the customer "prove" the code is safe for elevation or else it gets scheduled as non-SMT.