i didn't say this at the time, but now that you mention inferno, i will.
if someone is seriously worried about TLB flushing on context switches,
likes setting up the MMU pretty much once-for-all,
thinks all threads should share all the address space, and absolutely
disdains user mode, he should be writing in limbo for
native inferno, where all of that is the usual state,
and indeed there is no other.  we're all in it together.