diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index 4a9be6ddf054..48e8461057ba 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -295,11 +295,10 @@ static int xen_initdom_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 			int pos;
 			u32 table_offset, bir;
 
-			pos = pci_find_capability(dev, PCI_CAP_ID_MSIX);
-
+			pos = dev->msix_cap;
 			pci_read_config_dword(dev, pos + PCI_MSIX_TABLE,
 					      &table_offset);
-			bir = (u8)(table_offset & PCI_MSIX_FLAGS_BIRMASK);
+			bir = (u8)(table_offset & PCI_MSIX_TABLE_BIR);
 
 			map_irq.table_base = pci_resource_start(dev, bir);
 			map_irq.entry_nr = msidesc->msi_attrib.entry_nr;
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 53d4f680c9b5..a492be2635ac 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -85,7 +85,29 @@
 
 EXPORT_SYMBOL_GPL(hypercall_page);
 
+/*
+ * Pointer to the xen_vcpu_info structure or
+ * &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info
+ * and xen_vcpu_setup for details. By default it points to share_info->vcpu_info
+ * but if the hypervisor supports VCPUOP_register_vcpu_info then it can point
+ * to xen_vcpu_info. The pointer is used in __xen_evtchn_do_upcall to
+ * acknowledge pending events.
+ * Also more subtly it is used by the patched version of irq enable/disable
+ * e.g. xen_irq_enable_direct and xen_iret in PV mode.
+ *
+ * The desire to be able to do those mask/unmask operations as a single
+ * instruction by using the per-cpu offset held in %gs is the real reason
+ * vcpu info is in a per-cpu pointer and the original reason for this
+ * hypercall.
+ *
+ */
 DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu);
+
+/*
+ * Per CPU pages used if hypervisor supports VCPUOP_register_vcpu_info
+ * hypercall. This can be used both in PV and PVHVM mode. The structure
+ * overrides the default per_cpu(xen_vcpu, cpu) value.
+ */
 DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info);
 
 enum xen_domain_type xen_domain_type = XEN_NATIVE;
@@ -157,6 +179,21 @@ static void xen_vcpu_setup(int cpu)
 
 	BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
 
+	/*
+	 * This path is called twice on PVHVM - first during bootup via
+	 * smp_init -> xen_hvm_cpu_notify, and then if the VCPU is being
+	 * hotplugged: cpu_up -> xen_hvm_cpu_notify.
+	 * As we can only do the VCPUOP_register_vcpu_info once lets
+	 * not over-write its result.
+	 *
+	 * For PV it is called during restore (xen_vcpu_restore) and bootup
+	 * (xen_setup_vcpu_info_placement). The hotplug mechanism does not
+	 * use this function.
+	 */
+	if (xen_hvm_domain()) {
+		if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
+			return;
+	}
 	if (cpu < MAX_VIRT_CPUS)
 		per_cpu(xen_vcpu,cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
 
@@ -172,7 +209,12 @@ static void xen_vcpu_setup(int cpu)
 
 	/* Check to see if the hypervisor will put the vcpu_info
 	   structure where we want it, which allows direct access via
-	   a percpu-variable. */
+	   a percpu-variable.
+	   N.B. This hypercall can _only_ be called once per CPU. Subsequent
+	   calls will error out with -EINVAL. This is due to the fact that
+	   hypervisor has no unregister variant and this hypercall does not
+	   allow to over-write info.mfn and info.offset.
+	 */
 	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);
 
 	if (err) {
@@ -387,6 +429,9 @@ static void __init xen_init_cpuid_mask(void)
 		cpuid_leaf1_edx_mask &=
 			~((1 << X86_FEATURE_APIC) |  /* disable local APIC */
 			  (1 << X86_FEATURE_ACPI));  /* disable ACPI */
+
+	cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_X2APIC % 32));
+
 	ax = 1;
 	cx = 0;
 	xen_cpuid(&ax, &bx, &cx, &dx);
@@ -1603,6 +1648,9 @@ void __ref xen_hvm_init_shared_info(void)
 	 * online but xen_hvm_init_shared_info is run at resume time too and
 	 * in that case multiple vcpus might be online. */
 	for_each_online_cpu(cpu) {
+		/* Leave it to be NULL. */
+		if (cpu >= MAX_VIRT_CPUS)
+			continue;
 		per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
 	}
 }
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 8b54603ce816..3002ec1bb71a 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -364,7 +364,7 @@ void __cpuinit xen_init_lock_cpu(int cpu)
 	int irq;
 	const char *name;
 
-	WARN(per_cpu(lock_kicker_irq, cpu) > 0, "spinlock on CPU%d exists on IRQ%d!\n",
+	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
 	     cpu, per_cpu(lock_kicker_irq, cpu));
 
 	/*
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index dd4d9cb86243..f03bf501527f 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -141,7 +141,7 @@ config XEN_GRANT_DEV_ALLOC
 
 config SWIOTLB_XEN
 	def_bool y
-	depends on PCI
+	depends on PCI && X86
 	select SWIOTLB
 
 config XEN_TMEM
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index d8cc8127f19c..6a6bbe4ede92 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -167,6 +167,8 @@ static void xen_irq_info_common_init(struct irq_info *info,
 	info->cpu = cpu;
 
 	evtchn_to_irq[evtchn] = irq;
+
+	irq_clear_status_flags(irq, IRQ_NOREQUEST|IRQ_NOAUTOEN);
 }
 
 static void xen_irq_info_evtchn_init(unsigned irq,
@@ -874,7 +876,6 @@ int bind_evtchn_to_irq(unsigned int evtchn)
 		struct irq_info *info = info_for_irq(irq);
 		WARN_ON(info == NULL || info->type != IRQT_EVTCHN);
 	}
-	irq_clear_status_flags(irq, IRQ_NOREQUEST|IRQ_NOAUTOEN);
 
 out:
 	mutex_unlock(&irq_mapping_update_lock);