there's still something funny going on with interrupts being masked
in kthreads.  in my profiling runs I was seeing that preempt() and
ltsleep() were showing up as taking a lot of time, even though they
were only called a few times.  I tried printing the ipl info returned
by calling splhigh() in uvm_aio_aiodone() (which is only every called
in the aiodoned kthread), and it was 0x1.  putting a call to spl0()
at the top of uvm_aiodone_daemon() changed that value to 0xff01
(which is what I would expect it to be when interrupts are fully
enabled), and the time reported for preempt() and ltsleep() went
way down.  so even though the status register for process 0 is
initialized to the right value in mach_init() (at least in the pmax
port, which is what I've been testing), something is going wrong later.
could someone more familiar with this code take a look?

-Chuck