diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
index 92091de11113..55d106b5e31b 100644
--- a/arch/x86/include/asm/acpi.h
+++ b/arch/x86/include/asm/acpi.h
@@ -93,6 +93,9 @@ extern u8 acpi_sci_flags;
 extern int acpi_sci_override_gsi;
 void acpi_pic_sci_set_trigger(unsigned int, u16);
 
+extern int (*__acpi_register_gsi)(struct device *dev, u32 gsi,
+				  int trigger, int polarity);
+
 static inline void disable_acpi(void)
 {
 	acpi_disabled = 1;
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 031f0c238916..71232b941b6c 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -537,7 +537,8 @@ static int acpi_register_gsi_ioapic(struct device *dev, u32 gsi,
 	return gsi;
 }
 
-static int (*__acpi_register_gsi)(struct device *dev, u32 gsi, int trigger, int polarity) = acpi_register_gsi_pic;
+int (*__acpi_register_gsi)(struct device *dev, u32 gsi,
+			   int trigger, int polarity) = acpi_register_gsi_pic;
 
 /*
  * success: return IRQ number (>=0)
diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index 08e3cdccdfa8..3a4ab0b4dcca 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -53,6 +53,12 @@ static int xen_hvm_register_pirq(u32 gsi, int triggering)
 
 	return irq;
 }
+
+static int acpi_register_gsi_xen_hvm(struct device *dev, u32 gsi,
+				 int trigger, int polarity)
+{
+	return xen_hvm_register_pirq(gsi, trigger);
+}
 #endif
 
 #if defined(CONFIG_PCI_MSI)