ui/console: use exclusive mechanism directly

The previous commit (8bb93c6f99) using async_safe_run_on_cpu() doesn't
work on graphics sub-system which restrict which threads can do GUI
updates. Rather the special casing MacOS we just directly call the
helper and move all the exclusive handling into do_dafe_dpy_refresh().

The unfortunate bouncing of the BQL is to ensure there is no deadlock
as vCPUs waiting on the BQL are kicked into their quiescent state.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>

ui/console.c

@@ -1576,19 +1576,22 @@ bool dpy_gfx_check_format(QemuConsole *con,
 }
 
 /*
- * Safe DPY refresh for TCG guests. This runs when the TCG vCPUs are
- * quiescent so we can avoid races between dirty page tracking for
- * direct frame-buffer access by the guest.
+ * Safe DPY refresh for TCG guests. We use the exclusive mechanism to
+ * ensure the TCG vCPUs are quiescent so we can avoid races between
+ * dirty page tracking for direct frame-buffer access by the guest.
  *
  * This is a temporary stopgap until we've fixed the dirty tracking
  * races in display adapters.
  */
-static void do_safe_dpy_refresh(CPUState *cpu, run_on_cpu_data opaque)
+static void do_safe_dpy_refresh(DisplayChangeListener *dcl)
 {
-    DisplayChangeListener *dcl = opaque.host_ptr;
+    qemu_mutex_unlock_iothread();
+    start_exclusive();
     qemu_mutex_lock_iothread();
     dcl->ops->dpy_refresh(dcl);
     qemu_mutex_unlock_iothread();
+    end_exclusive();
+    qemu_mutex_lock_iothread();
 }
 
 static void dpy_refresh(DisplayState *s)
@@ -1598,8 +1601,7 @@ static void dpy_refresh(DisplayState *s)
     QLIST_FOREACH(dcl, &s->listeners, next) {
         if (dcl->ops->dpy_refresh) {
             if (tcg_enabled()) {
-                async_safe_run_on_cpu(first_cpu, do_safe_dpy_refresh,
-                                      RUN_ON_CPU_HOST_PTR(dcl));
+                do_safe_dpy_refresh(dcl);
             } else {
                 dcl->ops->dpy_refresh(dcl);
             }