pmap_pte_reserve
pt_entry_t * const ptep = pmap_pte_reserve(pmap, va, flags);
pt_entry_t * const ptep = pmap_pte_reserve(pmap, va, 0);
pmap_pte_reserve(pmap_kernel(), virtual_end, 0);
pt_entry_t *pmap_pte_reserve(struct pmap *, vaddr_t, int);