1 files changed, 39 insertions, 31 deletions

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 9b171c9dbe..f1275b61f8 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3684,56 +3684,64 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root)
     }
 }
 
-/*
- * If positive, discarding RAM is disabled. If negative, discarding RAM is
- * required to work and cannot be disabled.
- */
-static int ram_block_discard_disabled;
+static unsigned int ram_block_discard_required_cnt;
+static unsigned int ram_block_discard_disabled_cnt;
+static QemuMutex ram_block_discard_disable_mutex;
+
+static void ram_block_discard_disable_mutex_lock(void)
+{
+    static gsize initialized;
+
+    if (g_once_init_enter(&initialized)) {
+        qemu_mutex_init(&ram_block_discard_disable_mutex);
+        g_once_init_leave(&initialized, 1);
+    }
+    qemu_mutex_lock(&ram_block_discard_disable_mutex);
+}
+
+static void ram_block_discard_disable_mutex_unlock(void)
+{
+    qemu_mutex_unlock(&ram_block_discard_disable_mutex);
+}
 
 int ram_block_discard_disable(bool state)
 {
-    int old;
+    int ret = 0;
 
+    ram_block_discard_disable_mutex_lock();
     if (!state) {
-        qatomic_dec(&ram_block_discard_disabled);
-        return 0;
+        ram_block_discard_disabled_cnt--;
+    } else if (!ram_block_discard_required_cnt) {
+        ram_block_discard_disabled_cnt++;
+    } else {
+        ret = -EBUSY;
     }
-
-    do {
-        old = qatomic_read(&ram_block_discard_disabled);
-        if (old < 0) {
-            return -EBUSY;
-        }
-    } while (qatomic_cmpxchg(&ram_block_discard_disabled,
-                             old, old + 1) != old);
-    return 0;
+    ram_block_discard_disable_mutex_unlock();
+    return ret;
 }
 
 int ram_block_discard_require(bool state)
 {
-    int old;
+    int ret = 0;
 
+    ram_block_discard_disable_mutex_lock();
     if (!state) {
-        qatomic_inc(&ram_block_discard_disabled);
-        return 0;
+        ram_block_discard_required_cnt--;
+    } else if (!ram_block_discard_disabled_cnt) {
+        ram_block_discard_required_cnt++;
+    } else {
+        ret = -EBUSY;
     }
-
-    do {
-        old = qatomic_read(&ram_block_discard_disabled);
-        if (old > 0) {
-            return -EBUSY;
-        }
-    } while (qatomic_cmpxchg(&ram_block_discard_disabled,
-                             old, old - 1) != old);
-    return 0;
+    ram_block_discard_disable_mutex_unlock();
+    return ret;
 }
 
 bool ram_block_discard_is_disabled(void)
 {
-    return qatomic_read(&ram_block_discard_disabled) > 0;
+    return qatomic_read(&ram_block_discard_disabled_cnt);
 }
 
 bool ram_block_discard_is_required(void)
 {
-    return qatomic_read(&ram_block_discard_disabled) < 0;
+    return qatomic_read(&ram_block_discard_required_cnt);
 }