pud_deref
return __pa(pud_deref(pud)) >> PAGE_SHIFT;
return (pmd_t *) pud_deref(pud) + pmd_index(address);
vmem_free_pages(pud_deref(pudp_get(pud)), CRST_ALLOC_ORDER, NULL);
vmem_free_pages(pud_deref(entry), get_order(PUD_SIZE), altmap);