Index: /trunk/src/VBox/Devices/PC/DevIoApic.cpp
===================================================================
--- /trunk/src/VBox/Devices/PC/DevIoApic.cpp	(revision 38849)
+++ /trunk/src/VBox/Devices/PC/DevIoApic.cpp	(revision 38850)
@@ -596,5 +596,4 @@
      * Initialize the state data.
      */
-
     s->pDevInsR3 = pDevIns;
     s->pDevInsR0 = PDMDEVINS_2_R0PTR(pDevIns);
@@ -602,4 +601,8 @@
     ioapic_reset(s);
     s->id = cCpus;
+
+    /* PDM provides locking via the IOAPIC helpers. */
+    rc = PDMDevHlpSetDeviceCritSect(pDevIns, PDMDevHlpCritSectGetNop(pDevIns));
+    AssertRCReturn(rc, rc);
 
     /*