x86 pmap.c:
	pmap_kenter_pa() does shootdown if PG_V and PG_U are set,
	says it shouldn't happen.  (kenter_pa shouldn' be used on
	an existing mapping?

	pmap_kremove() does the same, but it should happen

	pmap_ldt_xcall() does, don't think we do?

	pmap_load()/pmap_dump do, what about us in a similar place?

	pmap_zero_page()/pmap_copy_page() do.

	pmap_remove() does

	pmap_page_remove()

	pmap_clear_attrs()/pmap_write_protect() do, which are backends
	for pmap_clear_modify/pmap_clear_reference/pmap_page_protect

	pmap_unwire

	pmap_enter_ma

	pmap_update() does around shootdowns

	pmap_growkernel() does 


amd64/machdep.c:

	cpu_reset() does while clearing out page tables

i386/kvm86.c:
	
	kvm86_bioscall() do while calling the bios