Index: /trunk/src/VBox/VMM/VMMR3/PGM.cpp
===================================================================
--- /trunk/src/VBox/VMM/VMMR3/PGM.cpp	(revision 65984)
+++ /trunk/src/VBox/VMM/VMMR3/PGM.cpp	(revision 65985)
@@ -3687,5 +3687,5 @@
         case PGMMODE_AMD64_NX:
         case PGMMODE_AMD64:
-            GCPhysCR3 = CPUMGetGuestCR3(pVCpu) & UINT64_C(0xfffffffffffff000); /** @todo define this mask! */
+            GCPhysCR3 = CPUMGetGuestCR3(pVCpu) & X86_CR3_AMD64_PAGE_MASK;
             rc = PGM_GST_NAME_AMD64(Enter)(pVCpu, GCPhysCR3);
             switch (pVCpu->pgm.s.enmShadowMode)