ptep_xchg_direct
pte_t ptep_xchg_direct(struct mm_struct *, unsigned long, pte_t *, pte_t);
pte = ptep_xchg_direct(vma->vm_mm, addr, ptep, pte_mkold(pte));
res = ptep_xchg_direct(vma->vm_mm, addr, ptep, __pte(_PAGE_INVALID));
ptep_xchg_direct(vma->vm_mm, addr, ptep, entry);
EXPORT_SYMBOL(ptep_xchg_direct);