Index: /trunk/include/VBox/vmm/tm.h
===================================================================
--- /trunk/include/VBox/vmm/tm.h	(revision 54696)
+++ /trunk/include/VBox/vmm/tm.h	(revision 54697)
@@ -272,4 +272,5 @@
 VMMR3_INT_DECL(int)     TMR3CpuTickParavirtEnable(PVM pVM);
 VMMR3_INT_DECL(int)     TMR3CpuTickParavirtDisable(PVM pVM);
+VMMR3_INT_DECL(bool)    TMR3CpuTickIsFixedRateMonotonic(PVM pVM, bool fWithParavirtEnabled);
 /** @} */
 #endif /* IN_RING3 */
Index: /trunk/src/VBox/VMM/VMMR3/TM.cpp
===================================================================
--- /trunk/src/VBox/VMM/VMMR3/TM.cpp	(revision 54696)
+++ /trunk/src/VBox/VMM/VMMR3/TM.cpp	(revision 54697)
@@ -3200,7 +3200,6 @@
 
 
-#if 0
-/**
- * Check whether the host TSC is fixed rate & monotonic.
+/**
+ * Check whether the guest can be presented a fixed rate & monotonic TSC.
  *
  * @returns true if TSC is stable, false otherwise.
@@ -3213,7 +3212,9 @@
 VMMR3_INT_DECL(bool) TMR3CpuTickIsFixedRateMonotonic(PVM pVM, bool fWithParavirtEnabled)
 {
-    /** @todo */
-}
-#endif
+    /** @todo figure out what exactly we want here later. */
+    NOREF(fWithParavirtEnabled);
+    return (   tmR3HasFixedTSC(pVM)                                        /* Host has fixed-rate TSC. */
+            && g_pSUPGlobalInfoPage->u32Mode != SUPGIPMODE_ASYNC_TSC);     /* GIP thinks it's monotonic. */
+}