Index: /trunk/src/VBox/Additions/WINNT/Graphics/Video/mp/wddm/VBoxMPWddm.cpp
===================================================================
--- /trunk/src/VBox/Additions/WINNT/Graphics/Video/mp/wddm/VBoxMPWddm.cpp	(revision 55244)
+++ /trunk/src/VBox/Additions/WINNT/Graphics/Video/mp/wddm/VBoxMPWddm.cpp	(revision 55245)
@@ -904,5 +904,6 @@
      * Estimate max 4KB per command.
      */
-    ULONG cbCmdVbva = VBOXCMDVBVA_BUFFERSIZE(4096);
+    //ULONG cbCmdVbva = VBOXCMDVBVA_BUFFERSIZE(4096);
+    ULONG cbCmdVbva = RT_MIN(_4M, cbAvailable / 4); /* <- temporary fix against ring buffer overflow. */
 
     if (cbCmdVbva >= cbAvailable)