diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 1508e51..aac5fa6 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -109,8 +109,8 @@
 
 #define UV_BAU_MESSAGE			0xf5
 
-/* Xen vector callback to receive events in a HVM domain */
-#define XEN_HVM_EVTCHN_CALLBACK		0xf3
+/* Vector on which hypervisor callbacks will be delivered */
+#define HYPERVISOR_CALLBACK_VECTOR	0xf3
 
 /*
  * Local APIC timer IRQ vector is on a different priority level,
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 79ce568..c2934be 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -11,4 +11,8 @@
 
 extern struct ms_hyperv_info ms_hyperv;
 
+void hyperv_callback_vector(void);
+void hyperv_vector_handler(struct pt_regs *regs);
+void hv_register_vmbus_handler(int irq, irq_handler_t handler);
+
 #endif
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 0a630dd..a7d26d8 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -14,10 +14,15 @@
 #include <linux/time.h>
 #include <linux/clocksource.h>
 #include <linux/module.h>
+#include <linux/hardirq.h>
+#include <linux/interrupt.h>
 #include <asm/processor.h>
 #include <asm/hypervisor.h>
 #include <asm/hyperv.h>
 #include <asm/mshyperv.h>
+#include <asm/desc.h>
+#include <asm/idle.h>
+#include <asm/irq_regs.h>
 
 struct ms_hyperv_info ms_hyperv;
 EXPORT_SYMBOL_GPL(ms_hyperv);
@@ -30,6 +35,13 @@
 	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
 		return false;
 
+	/*
+	 * Xen emulates Hyper-V to support enlightened Windows.
+	 * Check to see first if we are on a Xen Hypervisor.
+	 */
+	if (xen_cpuid_base())
+		return false;
+
 	cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS,
 	      &eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]);
 
@@ -68,7 +80,14 @@
 	printk(KERN_INFO "HyperV: features 0x%x, hints 0x%x\n",
 	       ms_hyperv.features, ms_hyperv.hints);
 
-	clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
+	if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE)
+		clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
+#if IS_ENABLED(CONFIG_HYPERV)
+	/*
+	 * Setup the IDT for hypervisor callback.
+	 */
+	alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, hyperv_callback_vector);
+#endif
 }
 
 const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {
@@ -77,3 +96,36 @@
 	.init_platform		= ms_hyperv_init_platform,
 };
 EXPORT_SYMBOL(x86_hyper_ms_hyperv);
+
+#if IS_ENABLED(CONFIG_HYPERV)
+static int vmbus_irq = -1;
+static irq_handler_t vmbus_isr;
+
+void hv_register_vmbus_handler(int irq, irq_handler_t handler)
+{
+	vmbus_irq = irq;
+	vmbus_isr = handler;
+}
+
+void hyperv_vector_handler(struct pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+	struct irq_desc *desc;
+
+	irq_enter();
+	exit_idle();
+
+	desc = irq_to_desc(vmbus_irq);
+
+	if (desc)
+		generic_handle_irq_desc(vmbus_irq, desc);
+
+	irq_exit();
+	set_irq_regs(old_regs);
+}
+#else
+void hv_register_vmbus_handler(int irq, irq_handler_t handler)
+{
+}
+#endif
+EXPORT_SYMBOL_GPL(hv_register_vmbus_handler);
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 6ed91d9..8831176 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1091,11 +1091,18 @@
 	_ASM_EXTABLE(4b,9b)
 ENDPROC(xen_failsafe_callback)
 
-BUILD_INTERRUPT3(xen_hvm_callback_vector, XEN_HVM_EVTCHN_CALLBACK,
+BUILD_INTERRUPT3(xen_hvm_callback_vector, HYPERVISOR_CALLBACK_VECTOR,
 		xen_evtchn_do_upcall)
 
 #endif	/* CONFIG_XEN */
 
+#if IS_ENABLED(CONFIG_HYPERV)
+
+BUILD_INTERRUPT3(hyperv_callback_vector, HYPERVISOR_CALLBACK_VECTOR,
+	hyperv_vector_handler)
+
+#endif /* CONFIG_HYPERV */
+
 #ifdef CONFIG_FUNCTION_TRACER
 #ifdef CONFIG_DYNAMIC_FTRACE
 
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index cb3c591..048f224 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1454,11 +1454,16 @@
 	CFI_ENDPROC
 END(xen_failsafe_callback)
 
-apicinterrupt XEN_HVM_EVTCHN_CALLBACK \
+apicinterrupt HYPERVISOR_CALLBACK_VECTOR \
 	xen_hvm_callback_vector xen_evtchn_do_upcall
 
 #endif /* CONFIG_XEN */
 
+#if IS_ENABLED(CONFIG_HYPERV)
+apicinterrupt HYPERVISOR_CALLBACK_VECTOR \
+	hyperv_callback_vector hyperv_vector_handler
+#endif /* CONFIG_HYPERV */
+
 /*
  * Some functions should be protected against kprobes
  */
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index b38ef6d..64630f1 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -2,7 +2,7 @@
 
 config HYPERV
 	tristate "Microsoft Hyper-V client drivers"
-	depends on X86 && ACPI && PCI
+	depends on X86 && ACPI && PCI && X86_LOCAL_APIC
 	help
 	  Select this option to run Linux as a Hyper-V client operating
 	  system.
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 74d77df..22f77c5 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -1787,7 +1787,7 @@
 	int rc;
 	uint64_t callback_via;
 	if (xen_have_vector_callback) {
-		callback_via = HVM_CALLBACK_VECTOR(XEN_HVM_EVTCHN_CALLBACK);
+		callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
 		rc = xen_set_callback_via(callback_via);
 		if (rc) {
 			printk(KERN_ERR "Request for Xen HVM callback vector"
@@ -1798,8 +1798,9 @@
 		printk(KERN_INFO "Xen HVM callback vector for event delivery is "
 				"enabled\n");
 		/* in the restore case the vector has already been allocated */
-		if (!test_bit(XEN_HVM_EVTCHN_CALLBACK, used_vectors))
-			alloc_intr_gate(XEN_HVM_EVTCHN_CALLBACK, xen_hvm_callback_vector);
+		if (!test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors))
+			alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
+					xen_hvm_callback_vector);
 	}
 }
 #else