Index: /trunk/include/iprt/x86.h
===================================================================
--- /trunk/include/iprt/x86.h	(revision 48356)
+++ /trunk/include/iprt/x86.h	(revision 48357)
@@ -973,4 +973,9 @@
 /** Get FSB clock status (Intel-specific). */
 #define MSR_IA32_FSB_CLOCK_STS              0xCD
+
+/** C0 Maximum Frequency Clock Count */
+#define MSR_IA32_MPERF                      0xE7
+/** C0 Actual Frequency Clock Count */
+#define MSR_IA32_APERF                      0xE8
 
 /** MTRR Capabilities. */
Index: /trunk/src/VBox/VMM/VMMAll/CPUMAllRegs.cpp
===================================================================
--- /trunk/src/VBox/VMM/VMMAll/CPUMAllRegs.cpp	(revision 48356)
+++ /trunk/src/VBox/VMM/VMMAll/CPUMAllRegs.cpp	(revision 48357)
@@ -1144,4 +1144,6 @@
         case MSR_IA32_PMC1:
         case MSR_IA32_PLATFORM_ID:          /* fam/mod >= 6_01 */
+        case MSR_IA32_MPERF:                /* intel_pstate depends on this but does a validation test */
+        case MSR_IA32_APERF:                /* intel_pstate depends on this but does a validation test */
         /*case MSR_IA32_BIOS_UPDT_TRIG: - write-only? */
         case MSR_RAPL_POWER_UNIT: