Index: /trunk/include/iprt/asm.h
===================================================================
--- /trunk/include/iprt/asm.h	(revision 25670)
+++ /trunk/include/iprt/asm.h	(revision 25671)
@@ -4362,5 +4362,5 @@
                            "S" (pu64));
 #   else /* !PIC */
-    __asm__ __volatile__("cmpxchg8b %1\n\t"
+    __asm__ __volatile__("lock; cmpxchg8b %1\n\t"
                          : "=A" (u64),
                            "+m" (*pu64)
Index: /trunk/src/VBox/Runtime/common/asm/ASMAtomicUoReadU64.asm
===================================================================
--- /trunk/src/VBox/Runtime/common/asm/ASMAtomicUoReadU64.asm	(revision 25670)
+++ /trunk/src/VBox/Runtime/common/asm/ASMAtomicUoReadU64.asm	(revision 25671)
@@ -64,5 +64,5 @@
         xor     ecx, ecx
         xor     ebx, ebx
-        cmpxchg8b [edi]
+        lock cmpxchg8b [edi]
 
         pop     edi