diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index bb7d479..586b7ad 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -183,6 +183,10 @@
 }
 
 #define x2apic_supported()	(cpu_has_x2apic)
+static inline void x2apic_force_phys(void)
+{
+	x2apic_phys = 1;
+}
 #else
 static inline void check_x2apic(void)
 {
@@ -194,6 +198,9 @@
 {
 	return 0;
 }
+static inline void x2apic_force_phys(void)
+{
+}
 
 #define	x2apic_preenabled 0
 #define	x2apic_supported()	0
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 0b021c5..de039fc 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -49,6 +49,7 @@
 #include <asm/mtrr.h>
 #include <asm/smp.h>
 #include <asm/mce.h>
+#include <asm/kvm_para.h>
 
 unsigned int num_processors;
 
@@ -1361,52 +1362,76 @@
 }
 #endif /* CONFIG_X86_X2APIC */
 
-void __init enable_IR_x2apic(void)
+int __init enable_IR(void)
 {
 #ifdef CONFIG_INTR_REMAP
 	int ret;
-	unsigned long flags;
-	struct IO_APIC_route_entry **ioapic_entries = NULL;
 
 	ret = dmar_table_init();
 	if (ret) {
 		pr_debug("dmar_table_init() failed with %d:\n", ret);
-		goto ir_failed;
+		return 0;
 	}
 
 	if (!intr_remapping_supported()) {
 		pr_debug("intr-remapping not supported\n");
-		goto ir_failed;
+		return 0;
 	}
 
-
 	if (!x2apic_preenabled && skip_ioapic_setup) {
 		pr_info("Skipped enabling intr-remap because of skipping "
 			"io-apic setup\n");
-		return;
+		return 0;
 	}
 
+	if (enable_intr_remapping(x2apic_supported()))
+		return 0;
+
+	pr_info("Enabled Interrupt-remapping\n");
+
+	return 1;
+
+#endif
+	return 0;
+}
+
+void __init enable_IR_x2apic(void)
+{
+	unsigned long flags;
+	struct IO_APIC_route_entry **ioapic_entries = NULL;
+	int ret, x2apic_enabled = 0;
+
 	ioapic_entries = alloc_ioapic_entries();
 	if (!ioapic_entries) {
-		pr_info("Allocate ioapic_entries failed: %d\n", ret);
-		goto end;
+		pr_err("Allocate ioapic_entries failed\n");
+		goto out;
 	}
 
 	ret = save_IO_APIC_setup(ioapic_entries);
 	if (ret) {
 		pr_info("Saving IO-APIC state failed: %d\n", ret);
-		goto end;
+		goto out;
 	}
 
 	local_irq_save(flags);
-	mask_IO_APIC_setup(ioapic_entries);
 	mask_8259A();
+	mask_IO_APIC_setup(ioapic_entries);
 
-	ret = enable_intr_remapping(x2apic_supported());
-	if (ret)
-		goto end_restore;
+	ret = enable_IR();
+	if (!ret) {
+		/* IR is required if there is APIC ID > 255 even when running
+		 * under KVM
+		 */
+		if (max_physical_apicid > 255 || !kvm_para_available())
+			goto nox2apic;
+		/*
+		 * without IR all CPUs can be addressed by IOAPIC/MSI
+		 * only in physical mode
+		 */
+		x2apic_force_phys();
+	}
 
-	pr_info("Enabled Interrupt-remapping\n");
+	x2apic_enabled = 1;
 
 	if (x2apic_supported() && !x2apic_mode) {
 		x2apic_mode = 1;
@@ -1414,41 +1439,25 @@
 		pr_info("Enabled x2apic\n");
 	}
 
-end_restore:
-	if (ret)
-		/*
-		 * IR enabling failed
-		 */
+nox2apic:
+	if (!ret) /* IR enabling failed */
 		restore_IO_APIC_setup(ioapic_entries);
-
 	unmask_8259A();
 	local_irq_restore(flags);
 
-end:
+out:
 	if (ioapic_entries)
 		free_ioapic_entries(ioapic_entries);
 
-	if (!ret)
+	if (x2apic_enabled)
 		return;
 
-ir_failed:
 	if (x2apic_preenabled)
-		panic("x2apic enabled by bios. But IR enabling failed");
+		panic("x2apic: enabled by BIOS but kernel init failed.");
 	else if (cpu_has_x2apic)
-		pr_info("Not enabling x2apic,Intr-remapping\n");
-#else
-	if (!cpu_has_x2apic)
-		return;
-
-	if (x2apic_preenabled)
-		panic("x2apic enabled prior OS handover,"
-		      " enable CONFIG_X86_X2APIC, CONFIG_INTR_REMAP");
-#endif
-
-	return;
+		pr_info("Not enabling x2apic, Intr-remapping init failed.\n");
 }
 
-
 #ifdef CONFIG_X86_64
 /*
  * Detect and enable local APICs on non-SMP boards.
diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
index bc3e880..f3b1037 100644
--- a/arch/x86/kernel/apic/probe_64.c
+++ b/arch/x86/kernel/apic/probe_64.c
@@ -50,11 +50,11 @@
 void __init default_setup_apic_routing(void)
 {
 #ifdef CONFIG_X86_X2APIC
-	if (x2apic_mode && (apic != &apic_x2apic_phys &&
+	if (x2apic_mode
 #ifdef CONFIG_X86_UV
-		       apic != &apic_x2apic_uv_x &&
+		       && apic != &apic_x2apic_uv_x
 #endif
-		       apic != &apic_x2apic_cluster)) {
+		       ) {
 		if (x2apic_phys)
 			apic = &apic_x2apic_phys;
 		else