Index: sys/dev/hyperv/vmbus/hv_hv.c
===================================================================
--- sys/dev/hyperv/vmbus/hv_hv.c
+++ sys/dev/hyperv/vmbus/hv_hv.c
@@ -36,6 +36,7 @@
 #include <sys/kernel.h>
 #include <sys/malloc.h>
 #include <sys/pcpu.h>
+#include <sys/proc.h>
 #include <sys/timetc.h>
 #include <machine/bus.h>
 #include <machine/md_var.h>
@@ -77,6 +78,12 @@
 	return (now);
 }
 
+static void
+hv_idle_hook(sbintime_t sbt)
+{
+	rdmsr(HV_X64_MSR_GUEST_IDLE);
+}
+
 /**
  * @brief Invoke the specified hypercall
  */
@@ -172,7 +179,7 @@
 	hv_vmbus_g_context.hypercall_page = virt_addr;
 
 	hv_et_init();
-	
+
 	return (0);
 
 	cleanup:
@@ -510,6 +517,10 @@
 		/* Register virtual timecount */
 		tc_init(&hv_timecounter);
 	}
+
+	if (hyperv_features & HV_FEATURE_MSR_GUEST_IDLE) {
+		cpu_idle_hook = hv_idle_hook;
+	}
 }
 SYSINIT(hyperv_initialize, SI_SUB_HYPERVISOR, SI_ORDER_FIRST, hyperv_init,
     NULL);
Index: sys/dev/hyperv/vmbus/hv_vmbus_priv.h
===================================================================
--- sys/dev/hyperv/vmbus/hv_vmbus_priv.h
+++ sys/dev/hyperv/vmbus/hv_vmbus_priv.h
@@ -619,6 +619,7 @@
 #define HV_X64_MSR_SINT14     (0x4000009E)
 #define HV_X64_MSR_SINT15     (0x4000009F)
 
+#define HV_X64_MSR_GUEST_IDLE (0x400000F0)
 /*
  * Synthetic Timer MSRs. Four timers per vcpu.
  */