Index: sys/x86/x86/identcpu.c
===================================================================
--- sys/x86/x86/identcpu.c
+++ sys/x86/x86/identcpu.c
@@ -65,6 +65,7 @@
 #include <amd64/vmm/intel/vmx_controls.h>
 #include <x86/isa/icu.h>
 #include <x86/vmware.h>
+#include <x86/include/init.h>
 
 #ifdef __i386__
 #if !defined(CPU_DISABLE_SSE) && defined(I686_CPU)
@@ -1268,6 +1269,22 @@
 	NULL
 };
 
+#define HV_X64_MSR_TIME_REF_COUNT       0x40000020
+
+/* Wait "n" microseconds. */
+static void
+hyperv_delay(int n)
+{
+	uint64_t now, end;
+
+	/* The time counter has a fixed frequency of 10MHz */
+	now = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
+	end = now + n * 10;
+
+	while (now < end)
+		now = rdmsr(HV_X64_MSR_TIME_REF_COUNT);
+}
+
 static void
 identify_hypervisor(void)
 {
@@ -1294,8 +1311,12 @@
 			hv_vendor[12] = '\0';
 			if (strcmp(hv_vendor, "VMwareVMware") == 0)
 				vm_guest = VM_GUEST_VMWARE;
-			else if (strcmp(hv_vendor, "Microsoft Hv") == 0)
+			else if (strcmp(hv_vendor, "Microsoft Hv") == 0) {
 				vm_guest = VM_GUEST_HV;
+
+				/* Hyper-V's i8254 emulation is unreliable */
+				init_ops.early_delay = hyperv_delay;
+			}
 		}
 		return;
 	}