+/* Clears any mapping for user virtual address UPAGE in page
+ directory PD.
+ UPAGE need not already be mapped. */
+void
+pagedir_clear_page (uint32_t *pd, void *upage)
+{
+ uint32_t *pte = lookup_page (pd, upage, false);
+ if (pte != NULL && *pte != 0)
+ {
+ *pte = 0;
+
+ if (active_pd () == pd)
+ {
+ /* We cleared a page-table entry in the active page
+ table, so we have to invalidate the TLB. See
+ [IA32-v3], section 3.11. */
+ pagedir_activate (pd);
+ }
+ }
+
+}
+
+/* Returns true if the PTE for user virtual page UPAGE in PD is
+ dirty, that is, if the page has been modified since the PTE
+ was installed.
+ Returns false if PD contains no PDE for UPAGE. */
+bool
+pagedir_test_dirty (uint32_t *pd, const void *upage)
+{
+ uint32_t *pte = lookup_page (pd, (void *) upage, false);
+ return pte != NULL && (*pte & PG_D) != 0;
+}
+
+/* Returns true if the PTE for user virtual page UPAGE in PD has
+ been accessed recently, that is, between the time the PTE was
+ installed and the last time it was cleared.
+ Returns false if PD contains no PDE for UPAGE. */
+bool
+pagedir_test_accessed (uint32_t *pd, const void *upage)
+{
+ uint32_t *pte = lookup_page (pd, (void *) upage, false);
+ return pte != NULL && (*pte & PG_A) != 0;
+}
+
+/* Returns true if the PTE for user virtual page UPAGE in PD has
+ been accessed recently, and then resets the accessed bit for
+ that page.
+ Returns false and has no effect if PD contains no PDE for
+ UPAGE. */
+bool
+pagedir_test_accessed_and_clear (uint32_t *pd, const void *upage)
+{
+ uint32_t *pte = lookup_page (pd, (void *) upage, false);
+ if (pte != NULL)
+ {
+ bool accessed = (*pte & PG_A) != 0;
+ *pte &= ~(uint32_t) PG_A;
+ return accessed;
+ }
+ else
+ return false;
+}
+