TLB_DIRTY
if (pte & PTE_PROT(TLB_DIRTY))
(pte & PTE_PROT(TLB_UNCACHABLE|TLB_DIRTY|TLB_REFTRAP));
#define pmap_clear_modify(pg) pmap_changebit(pg, 0, PTE_PROT(TLB_DIRTY))