[PATCH] memory: Fix incorrect calls of log_global_start/stop

[Peter Xu <peterx@redhat.com>]

We should only call the log_global_start/stop when the global dirty track
bitmask changes from zero<->non-zero.

No real issue reported for this yet probably because no immediate user to
enable both dirty rate measurement and migration at the same time.  However
it'll be good to be prepared for it.

Fixes: 63b41db4bc ("memory: make global_dirty_tracking a bitmask")
Cc: Hyman Huang <huangy81@chinatelecom.cn>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 softmmu/memory.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/softmmu/memory.c b/softmmu/memory.c
index 7340e19ff5..81d4bf1454 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -2773,6 +2773,8 @@ static VMChangeStateEntry *vmstate_change;
 
 void memory_global_dirty_log_start(unsigned int flags)
 {
+    unsigned int old_flags = global_dirty_tracking;
+
     if (vmstate_change) {
         qemu_del_vm_change_state_handler(vmstate_change);
         vmstate_change = NULL;
@@ -2781,15 +2783,14 @@ void memory_global_dirty_log_start(unsigned int flags)
     assert(flags && !(flags & (~GLOBAL_DIRTY_MASK)));
     assert(!(global_dirty_tracking & flags));
     global_dirty_tracking |= flags;
-
     trace_global_dirty_changed(global_dirty_tracking);
 
-    MEMORY_LISTENER_CALL_GLOBAL(log_global_start, Forward);
-
-    /* Refresh DIRTY_MEMORY_MIGRATION bit.  */
-    memory_region_transaction_begin();
-    memory_region_update_pending = true;
-    memory_region_transaction_commit();
+    if (!old_flags) {
+        MEMORY_LISTENER_CALL_GLOBAL(log_global_start, Forward);
+        memory_region_transaction_begin();
+        memory_region_update_pending = true;
+        memory_region_transaction_commit();
+    }
 }
 
 static void memory_global_dirty_log_do_stop(unsigned int flags)
@@ -2800,12 +2801,12 @@ static void memory_global_dirty_log_do_stop(unsigned int flags)
 
     trace_global_dirty_changed(global_dirty_tracking);
 
-    /* Refresh DIRTY_MEMORY_MIGRATION bit.  */
-    memory_region_transaction_begin();
-    memory_region_update_pending = true;
-    memory_region_transaction_commit();
-
-    MEMORY_LISTENER_CALL_GLOBAL(log_global_stop, Reverse);
+    if (!global_dirty_tracking) {
+        memory_region_transaction_begin();
+        memory_region_update_pending = true;
+        memory_region_transaction_commit();
+        MEMORY_LISTENER_CALL_GLOBAL(log_global_stop, Reverse);
+    }
 }
 
 static void memory_vm_change_state_handler(void *opaque, bool running,
-- 
2.32.0