Even more Meltdown

Are you tired of hearing about Meltdown/Spectre yet?  Doesn’t matter!  The two sysctls for controlling mitigation in DragonFly have been renamed:

machdep.meltdown_mitigation
machdep.spectre_mitigation

They go to hopefully sensible defaults, but Matthew Dillon has done some testing to show the effects of each in various combinations.   (Update: more changes and tests.)  Note that this is not the final mitigation work; compilers (i.e. gcc) are being updated to include workarounds for this, so new gcc -> new compiler in DragonFly -> new defenses.  No silver bullet there, though.