To date, unwiring a fictitious page has produced a panic. The reason

being that PHYS_TO_VM_PAGE() returns the wrong vm_page for fictitious
pages but unwiring uses PHYS_TO_VM_PAGE().  The resulting panic
reported an unexpected wired count.  Rather than attempting to fix
PHYS_TO_VM_PAGE(), this fix takes advantage of the properties of
fictitious pages.  Specifically, fictitious pages will never be
completely unwired.  Therefore, we can keep a fictitious page's wired
count forever set to one and thereby avoid the use of
PHYS_TO_VM_PAGE() when we know that we're working with a fictitious
page, just not which one.

In collaboration with: green@, tegge@
PR: kern/29915

sys/vm/vm_extern.h

@@ -69,8 +69,8 @@ void swapout_procs(int);
 int useracc(void *, int, int);
 int vm_fault(vm_map_t, vm_offset_t, vm_prot_t, int);
 void vm_fault_copy_entry(vm_map_t, vm_map_t, vm_map_entry_t, vm_map_entry_t);
-void vm_fault_unwire(vm_map_t, vm_offset_t, vm_offset_t);
+void vm_fault_unwire(vm_map_t, vm_offset_t, vm_offset_t, boolean_t);
-int vm_fault_wire(vm_map_t, vm_offset_t, vm_offset_t, boolean_t);
+int vm_fault_wire(vm_map_t, vm_offset_t, vm_offset_t, boolean_t, boolean_t);
 void vm_forkproc(struct thread *, struct proc *, struct thread *, int);
 void vm_waitproc(struct proc *);
 int vm_mmap(vm_map_t, vm_offset_t *, vm_size_t, vm_prot_t, vm_prot_t, int, void *, vm_ooffset_t);

sys/vm/vm_fault.c

@@ -1038,10 +1038,8 @@ vm_fault_quick(caddr_t v, int prot)
  *	Wire down a range of virtual addresses in a map.
  */
 int
-vm_fault_wire(map, start, end, user_wire)
+vm_fault_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
-	vm_map_t map;
+    boolean_t user_wire, boolean_t fictitious)
-	vm_offset_t start, end;
-	boolean_t user_wire;
 {
 	vm_offset_t va;
 	int rv;
@@ -1057,7 +1055,7 @@ vm_fault_wire(map, start, end, user_wire)
 		    user_wire ? VM_FAULT_USER_WIRE : VM_FAULT_CHANGE_WIRING);
 		if (rv) {
 			if (va != start)
-				vm_fault_unwire(map, start, va);
+				vm_fault_unwire(map, start, va, fictitious);
 			return (rv);
 		}
 	}
@@ -1070,9 +1068,8 @@ vm_fault_wire(map, start, end, user_wire)
  *	Unwire a range of virtual addresses in a map.
  */
 void
-vm_fault_unwire(map, start, end)
+vm_fault_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
-	vm_map_t map;
+    boolean_t fictitious)
-	vm_offset_t start, end;
 {
 	vm_paddr_t pa;
 	vm_offset_t va;
@@ -1090,9 +1087,11 @@ vm_fault_unwire(map, start, end)
 		pa = pmap_extract(pmap, va);
 		if (pa != 0) {
 			pmap_change_wiring(pmap, va, FALSE);
-			vm_page_lock_queues();
+			if (!fictitious) {
-			vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
+				vm_page_lock_queues();
-			vm_page_unlock_queues();
+				vm_page_unwire(PHYS_TO_VM_PAGE(pa), 1);
+				vm_page_unlock_queues();
+			}
 		}
 	}
 	if (pmap != kernel_pmap)

sys/vm/vm_map.c

@@ -1726,7 +1726,9 @@ vm_map_unwire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 				/*
 				 * Retain the map lock.
 				 */
-				vm_fault_unwire(map, entry->start, entry->end);
+				vm_fault_unwire(map, entry->start, entry->end,
+				    entry->object.vm_object != NULL &&
+				    entry->object.vm_object->type == OBJT_DEVICE);
 			}
 		}
 		KASSERT(entry->eflags & MAP_ENTRY_IN_TRANSITION,
@@ -1758,7 +1760,7 @@ vm_map_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 	vm_offset_t saved_end, saved_start;
 	unsigned int last_timestamp;
 	int rv;
-	boolean_t need_wakeup, result, user_wire;
+	boolean_t fictitious, need_wakeup, result, user_wire;
 
 	user_wire = (flags & VM_MAP_WIRE_USER) ? TRUE : FALSE;
 	vm_map_lock(map);
@@ -1834,13 +1836,15 @@ vm_map_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 			entry->wired_count++;
 			saved_start = entry->start;
 			saved_end = entry->end;
+			fictitious = entry->object.vm_object != NULL &&
+			    entry->object.vm_object->type == OBJT_DEVICE;
 			/*
 			 * Release the map lock, relying on the in-transition
 			 * mark.
 			 */
 			vm_map_unlock(map);
 			rv = vm_fault_wire(map, saved_start, saved_end,
-			    user_wire);
+			    user_wire, fictitious);
 			vm_map_lock(map);
 			if (last_timestamp + 1 != map->timestamp) {
 				/*
@@ -1924,7 +1928,9 @@ vm_map_wire(vm_map_t map, vm_offset_t start, vm_offset_t end,
 				/*
 				 * Retain the map lock.
 				 */
-				vm_fault_unwire(map, entry->start, entry->end);
+				vm_fault_unwire(map, entry->start, entry->end,
+				    entry->object.vm_object != NULL &&
+				    entry->object.vm_object->type == OBJT_DEVICE);
 			}
 		}
 		KASSERT(entry->eflags & MAP_ENTRY_IN_TRANSITION,
@@ -2048,7 +2054,9 @@ vm_map_sync(
 static void
 vm_map_entry_unwire(vm_map_t map, vm_map_entry_t entry)
 {
-	vm_fault_unwire(map, entry->start, entry->end);
+	vm_fault_unwire(map, entry->start, entry->end,
+	    entry->object.vm_object != NULL &&
+	    entry->object.vm_object->type == OBJT_DEVICE);
 	entry->wired_count = 0;
 }
 

sys/vm/vm_page.c

@@ -1167,6 +1167,8 @@ vm_page_wire(vm_page_t m)
 	 */
 	s = splvm();
 	mtx_assert(&vm_page_queue_mtx, MA_OWNED);
+	if (m->flags & PG_FICTITIOUS)
+		return;
 	if (m->wire_count == 0) {
 		if ((m->flags & PG_UNMANAGED) == 0)
 			vm_pageq_remove(m);
@@ -1212,6 +1214,8 @@ vm_page_unwire(vm_page_t m, int activate)
 
 	s = splvm();
 	mtx_assert(&vm_page_queue_mtx, MA_OWNED);
+	if (m->flags & PG_FICTITIOUS)
+		return;
 	if (m->wire_count > 0) {
 		m->wire_count--;
 		if (m->wire_count == 0) {