- in tlb_flush_all(), don't skip TLB entries with the high bit on,
I was confused about which MMU register it was using. it's also fine
to use the last hardware context.
- in pmap_create(), don't allocate a hardware context for the new pmap.
it's unnecessary, and when this would cause us to recycle all the contexts,
it would result in the current process's context being set to 0
(ie. the kernel's context). the current process could then return to
userspace without going through the context-switch code (and thus without
having a hardware context reallocated). this would lead to user mappings
being entered in the kernel's context later, causing all sorts of trouble.
add some assertions to catch this kind of thing.
0d8f526f58