TLB_DIRTY
if ((pte & PTE_PROT(TLB_DIRTY)) == 0)
(pte & PTE_PROT(TLB_UNCACHEABLE|TLB_DIRTY|TLB_REFTRAP));
#define pmap_clear_modify(pg) pmap_changebit(pg, 0, PTE_PROT(TLB_DIRTY))
#define pmap_is_modified(pg) pmap_testbit(pg, PTE_PROT(TLB_DIRTY))
#define PVF_MOD PTE_PROT(TLB_DIRTY) /* pg/mp is modified */