memory: add ref/unref calls

Add ref/unref calls at the following places:

- places where memory regions are stashed by a listener and
  used outside the BQL (including in Xen or KVM).

- memory_region_find callsites

- creation of aliases and containers (only the aliased/contained
  region gets a reference to avoid loops)

- around calls to del_subregion/add_subregion, where the region
  could disappear after the first call

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

memory.c

@@ -148,6 +148,7 @@ static bool memory_listener_match(MemoryListener *listener,
         }                                                               \
     } while (0)
 
+/* No need to ref/unref .mr, the FlatRange keeps it alive.  */
 #define MEMORY_LISTENER_UPDATE_REGION(fr, as, dir, callback)            \
     MEMORY_LISTENER_CALL(callback, dir, (&(MemoryRegionSection) {       \
         .mr = (fr)->mr,                                                 \
@@ -263,11 +264,17 @@ static void flatview_insert(FlatView *view, unsigned pos, FlatRange *range)
     memmove(view->ranges + pos + 1, view->ranges + pos,
             (view->nr - pos) * sizeof(FlatRange));
     view->ranges[pos] = *range;
+    memory_region_ref(range->mr);
     ++view->nr;
 }
 
 static void flatview_destroy(FlatView *view)
 {
+    int i;
+
+    for (i = 0; i < view->nr; i++) {
+        memory_region_unref(view->ranges[i].mr);
+    }
     g_free(view->ranges);
 }
 
@@ -709,6 +716,11 @@ static void memory_region_destructor_ram(MemoryRegion *mr)
     qemu_ram_free(mr->ram_addr);
 }
 
+static void memory_region_destructor_alias(MemoryRegion *mr)
+{
+    memory_region_unref(mr->alias);
+}
+
 static void memory_region_destructor_ram_from_ptr(MemoryRegion *mr)
 {
     qemu_ram_free_from_ptr(mr->ram_addr);
@@ -964,6 +976,8 @@ void memory_region_init_alias(MemoryRegion *mr,
                               uint64_t size)
 {
     memory_region_init(mr, owner, name, size);
+    memory_region_ref(orig);
+    mr->destructor = memory_region_destructor_alias;
     mr->alias = orig;
     mr->alias_offset = offset;
 }
@@ -1342,6 +1356,7 @@ static void memory_region_add_subregion_common(MemoryRegion *mr,
     memory_region_transaction_begin();
 
     assert(!subregion->parent);
+    memory_region_ref(subregion);
     subregion->parent = mr;
     subregion->addr = offset;
     QTAILQ_FOREACH(other, &mr->subregions, subregions_link) {
@@ -1404,6 +1419,7 @@ void memory_region_del_subregion(MemoryRegion *mr,
     assert(subregion->parent == mr);
     subregion->parent = NULL;
     QTAILQ_REMOVE(&mr->subregions, subregion, subregions_link);
+    memory_region_unref(subregion);
     memory_region_update_pending |= mr->enabled && subregion->enabled;
     memory_region_transaction_commit();
 }
@@ -1431,12 +1447,14 @@ void memory_region_set_address(MemoryRegion *mr, hwaddr addr)
     }
 
     memory_region_transaction_begin();
+    memory_region_ref(mr);
     memory_region_del_subregion(parent, mr);
     if (may_overlap) {
         memory_region_add_subregion_overlap(parent, addr, mr, priority);
     } else {
         memory_region_add_subregion(parent, addr, mr);
     }
+    memory_region_unref(mr);
     memory_region_transaction_commit();
 }
 
@@ -1484,6 +1502,7 @@ bool memory_region_present(MemoryRegion *parent, hwaddr addr)
     if (!mr) {
         return false;
     }
+    memory_region_unref(mr);
     return true;
 }
 
@@ -1523,6 +1542,8 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
     ret.size = range.size;
     ret.offset_within_address_space = int128_get64(range.start);
     ret.readonly = fr->readonly;
+    memory_region_ref(ret.mr);
+
     return ret;
 }