_DESCTYPE_MASK
#define pmd_bad(pmd) ((pmd_val(pmd) & _DESCTYPE_MASK) != _PAGE_TABLE)
#define pud_bad(pud) ((pud_val(pud) & _DESCTYPE_MASK) != _PAGE_TABLE)
if ((pmd & _DESCTYPE_MASK) == _PAGE_PRESENT) {
int pmd_type = pmd_val(*pmd_dir) & _DESCTYPE_MASK;