that interrupts be disabled and remain disabled until %cr2 is read.
Otherwise we can preempt and another process can fault, and by the
time we read %cr2, we see a different processes fault address. This
Greatly Confuses vm_fault() (to say the least). The i386 port has
got this marked as a bug workaround for a Cyrix CPU, which is what
lead me astray. Its actually necessary for preemption, regardless
of whether Cyrix cpus had a bug or not.
b3f7680e49