memory: Do not allocate FlatView in address_space_init

This creates a new AS object without any FlatView as
memory_region_transaction_commit() may want to reuse the empty FV.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20170921085110.25598-14-aik@ozlabs.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 67ace39b253ed5ae465275bc870f7e495547658b)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

1 files changed, 23 insertions, 6 deletions

diff --git a/memory.c b/memory.c
index f0c864206a..6914d87d0d 100644
--- a/memory.c
+++ b/memory.c
@@ -966,22 +966,37 @@ static void flatviews_reset(void)
 
 static void address_space_set_flatview(AddressSpace *as)
 {
-    FlatView *old_view = address_space_get_flatview(as);
+    FlatView *old_view = address_space_to_flatview(as);
     MemoryRegion *physmr = memory_region_get_flatview_root(as->root);
     FlatView *new_view = g_hash_table_lookup(flat_views, physmr);
 
     assert(new_view);
 
+    if (old_view == new_view) {
+        return;
+    }
+
+    if (old_view) {
+        flatview_ref(old_view);
+    }
+
     flatview_ref(new_view);
 
     if (!QTAILQ_EMPTY(&as->listeners)) {
-        address_space_update_topology_pass(as, old_view, new_view, false);
-        address_space_update_topology_pass(as, old_view, new_view, true);
+        FlatView tmpview = { .nr = 0 }, *old_view2 = old_view;
+
+        if (!old_view2) {
+            old_view2 = &tmpview;
+        }
+        address_space_update_topology_pass(as, old_view2, new_view, false);
+        address_space_update_topology_pass(as, old_view2, new_view, true);
     }
 
     /* Writes are protected by the BQL.  */
     atomic_rcu_set(&as->current_map, new_view);
-    flatview_unref(old_view);
+    if (old_view) {
+        flatview_unref(old_view);
+    }
 
     /* Note that all the old MemoryRegions are still alive up to this
      * point.  This relieves most MemoryListeners from the need to
@@ -989,7 +1004,9 @@ static void address_space_set_flatview(AddressSpace *as)
      * outside the iothread mutex, in which case precise reference
      * counting is necessary.
      */
-    flatview_unref(old_view);
+    if (old_view) {
+        flatview_unref(old_view);
+    }
 }
 
 void memory_region_transaction_begin(void)
@@ -2707,7 +2724,7 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
     as->ref_count = 1;
     as->root = root;
     as->malloced = false;
-    as->current_map = flatview_new(root);
+    as->current_map = NULL;
     as->ioeventfd_nb = 0;
     as->ioeventfds = NULL;
     QTAILQ_INIT(&as->listeners);