[crb002]

CPUs should have a single instruction that wipes branch prediction caches. I would have it off by default, and add to the C/C++ spec this as a standard library macro or pragma. Easy peasy.

You only need to wipe between syscalls that have side effects. Number crunching AVX heavy subroutines should never have to deal with safety once entered.

[ece]

This is what KPTI does, wipe caches, and if you did this often in user code, performance degradation would be all over the place. Also, heavy AVX routines that use encryption keys... would be great to attack.