More rambling idea...

Can MIPS use KSEG0 store for USPACE? 

Benefit;
- cpu_switch_resume() will go.  no TLB hardwiring necessary.   
Downside;
- physically contiguous memory is mandated.
- conflict severely to MI VM effect of its own USPACE management
scheme.
 
Some modern processors have MIPS-like way to handle memory
store without MMU intervention. It's a sharp contrast to i386/m68k.
VM makes efforts to wire/unwire USPACE to make sure the range
safe for some critical operations.  Since when u. was removed,
USPACE is a genuine kernel space entity and it's not necessarily
to impose VM's full care.  I can not estimate how large this change
will affect MI NetBSD arena.  Thoughts?

Toru Nishimura/ALKYL Technology