+static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
+ pte_t *pte, unsigned int flags)
+{
+ /* No page to get reference */
+ if (flags & FOLL_GET)
+ return -EFAULT;
+
+ if (flags & FOLL_TOUCH) {
+ pte_t entry = *pte;
+
+ if (flags & FOLL_WRITE)
+ entry = pte_mkdirty(entry);
+ entry = pte_mkyoung(entry);
+
+ if (!pte_same(*pte, entry)) {
+ set_pte_at(vma->vm_mm, address, pte, entry);
+ update_mmu_cache(vma, address, pte);
+ }
+ }
+
+ /* Proper page table entry exists, but no corresponding struct page */
+ return -EEXIST;
+}
+