PxD_FLAG_PRESENT
set_pud(pud, __pud((PxD_FLAG_PRESENT | PxD_FLAG_VALID) +
set_pmd(pmd, __pmd((PxD_FLAG_PRESENT | PxD_FLAG_VALID)
#define pmd_present(x) (pmd_flag(x) & PxD_FLAG_PRESENT)
#define pud_present(x) (pud_flag(x) & PxD_FLAG_PRESENT)