xen/x86: Move irq allocation from Xen smp_op.cpu_up()

Commit ce0d3c0a ("genirq: Revert sparse irq locking around
__cpu_up() and move it to x86 for now") reverted irq locking
introduced by commit a8994181 ("hotplug: Prevent alloc/free
of irq descriptors during cpu up/down") because of Xen allocating
irqs in both of its cpu_up ops.

We can move those allocations into CPU notifiers so that original
patch can be reinstated.
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

arch/x86/xen/enlighten.c

@@ -140,6 +140,8 @@ RESERVE_BRK(shared_info_page_brk, PAGE_SIZE);
 __read_mostly int xen_have_vector_callback;
 EXPORT_SYMBOL_GPL(xen_have_vector_callback);
 
+static struct notifier_block xen_cpu_notifier;
+
 /*
  * Point at some empty memory to start with. We map the real shared_info
  * page as soon as fixmap is up and running.
@@ -1627,6 +1629,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
 	xen_initial_gdt = &per_cpu(gdt_page, 0);
 
 	xen_smp_init();
+	register_cpu_notifier(&xen_cpu_notifier);
 
 #ifdef CONFIG_ACPI_NUMA
 	/*
@@ -1820,21 +1823,53 @@ static void __init init_hvm_pv_info(void)
 	xen_domain_type = XEN_HVM_DOMAIN;
 }
 
-static int xen_hvm_cpu_notify(struct notifier_block *self, unsigned long action,
+static int xen_cpu_notify(struct notifier_block *self, unsigned long action,
 			 void *hcpu)
 {
 	int cpu = (long)hcpu;
+	int rc;
+
 	switch (action) {
 	case CPU_UP_PREPARE:
+		if (xen_hvm_domain()) {
+			/*
+			 * This can happen if CPU was offlined earlier and
+			 * offlining timed out in common_cpu_die().
+			 */
+			if (cpu_report_state(cpu) == CPU_DEAD_FROZEN) {
+				xen_smp_intr_free(cpu);
+				xen_uninit_lock_cpu(cpu);
+			}
+
 			if (cpu_acpi_id(cpu) != U32_MAX)
 				per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);
 			else
 				per_cpu(xen_vcpu_id, cpu) = cpu;
 			xen_vcpu_setup(cpu);
-		if (xen_have_vector_callback) {
-			if (xen_feature(XENFEAT_hvm_safe_pvclock))
+		}
+
+		if (xen_pv_domain() ||
+		    (xen_have_vector_callback &&
+		     xen_feature(XENFEAT_hvm_safe_pvclock)))
 			xen_setup_timer(cpu);
+
+		rc = xen_smp_intr_init(cpu);
+		if (rc) {
+			WARN(1, "xen_smp_intr_init() for CPU %d failed: %d\n",
+			     cpu, rc);
+			return NOTIFY_BAD;
 		}
+
+		break;
+	case CPU_ONLINE:
+		xen_init_lock_cpu(cpu);
+		break;
+	case CPU_UP_CANCELED:
+		xen_smp_intr_free(cpu);
+		if (xen_pv_domain() ||
+		    (xen_have_vector_callback &&
+		     xen_feature(XENFEAT_hvm_safe_pvclock)))
+			xen_teardown_timer(cpu);
 		break;
 	default:
 		break;
@@ -1842,8 +1877,8 @@ static int xen_hvm_cpu_notify(struct notifier_block *self, unsigned long action,
 	return NOTIFY_OK;
 }
 
-static struct notifier_block xen_hvm_cpu_notifier = {
-	.notifier_call	= xen_hvm_cpu_notify,
+static struct notifier_block xen_cpu_notifier = {
+	.notifier_call	= xen_cpu_notify,
 };
 
 #ifdef CONFIG_KEXEC_CORE
@@ -1875,7 +1910,7 @@ static void __init xen_hvm_guest_init(void)
 	if (xen_feature(XENFEAT_hvm_callback_vector))
 		xen_have_vector_callback = 1;
 	xen_hvm_smp_init();
-	register_cpu_notifier(&xen_hvm_cpu_notifier);
+	register_cpu_notifier(&xen_cpu_notifier);
 	xen_unplug_emulated_devices();
 	x86_init.irqs.intr_init = xen_init_IRQ;
 	xen_hvm_init_time_ops();

arch/x86/xen/smp.c

@@ -115,7 +115,7 @@ asmlinkage __visible void cpu_bringup_and_idle(int cpu)
 	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
 }
 
-static void xen_smp_intr_free(unsigned int cpu)
+void xen_smp_intr_free(unsigned int cpu)
 {
 	if (per_cpu(xen_resched_irq, cpu).irq >= 0) {
 		unbind_from_irqhandler(per_cpu(xen_resched_irq, cpu).irq, NULL);
@@ -159,7 +159,7 @@ static void xen_smp_intr_free(unsigned int cpu)
 		per_cpu(xen_pmu_irq, cpu).name = NULL;
 	}
 };
-static int xen_smp_intr_init(unsigned int cpu)
+int xen_smp_intr_init(unsigned int cpu)
 {
 	int rc;
 	char *resched_name, *callfunc_name, *debug_name, *pmu_name;
@@ -475,8 +475,6 @@ static int xen_cpu_up(unsigned int cpu, struct task_struct *idle)
 	common_cpu_up(cpu, idle);
 
 	xen_setup_runstate_info(cpu);
-	xen_setup_timer(cpu);
-	xen_init_lock_cpu(cpu);
 
 	/*
 	 * PV VCPUs are always successfully taken down (see 'while' loop
@@ -495,10 +493,6 @@ static int xen_cpu_up(unsigned int cpu, struct task_struct *idle)
 
 	xen_pmu_init(cpu);
 
-	rc = xen_smp_intr_init(cpu);
-	if (rc)
-		return rc;
-
 	rc = HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL);
 	BUG_ON(rc);
 
@@ -769,47 +763,12 @@ static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
 	xen_init_lock_cpu(0);
 }
 
-static int xen_hvm_cpu_up(unsigned int cpu, struct task_struct *tidle)
-{
-	int rc;
-
-	/*
-	 * This can happen if CPU was offlined earlier and
-	 * offlining timed out in common_cpu_die().
-	 */
-	if (cpu_report_state(cpu) == CPU_DEAD_FROZEN) {
-		xen_smp_intr_free(cpu);
-		xen_uninit_lock_cpu(cpu);
-	}
-
-	/*
-	 * xen_smp_intr_init() needs to run before native_cpu_up()
-	 * so that IPI vectors are set up on the booting CPU before
-	 * it is marked online in native_cpu_up().
-	*/
-	rc = xen_smp_intr_init(cpu);
-	WARN_ON(rc);
-	if (!rc)
-		rc =  native_cpu_up(cpu, tidle);
-
-	/*
-	 * We must initialize the slowpath CPU kicker _after_ the native
-	 * path has executed. If we initialized it before none of the
-	 * unlocker IPI kicks would reach the booting CPU as the booting
-	 * CPU had not set itself 'online' in cpu_online_mask. That mask
-	 * is checked when IPIs are sent (on HVM at least).
-	 */
-	xen_init_lock_cpu(cpu);
-	return rc;
-}
-
 void __init xen_hvm_smp_init(void)
 {
 	if (!xen_have_vector_callback)
 		return;
 	smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
 	smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
-	smp_ops.cpu_up = xen_hvm_cpu_up;
 	smp_ops.cpu_die = xen_cpu_die;
 	smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
 	smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;

arch/x86/xen/smp.h

 #ifndef _XEN_SMP_H
 
+#ifdef CONFIG_SMP
 extern void xen_send_IPI_mask(const struct cpumask *mask,
 			      int vector);
 extern void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
@@ -8,6 +9,18 @@ extern void xen_send_IPI_allbutself(int vector);
 extern void xen_send_IPI_all(int vector);
 extern void xen_send_IPI_self(int vector);
 
+extern int xen_smp_intr_init(unsigned int cpu);
+extern void xen_smp_intr_free(unsigned int cpu);
+
+#else /* CONFIG_SMP */
+
+static inline int xen_smp_intr_init(unsigned int cpu)
+{
+	return 0;
+}
+static inline void xen_smp_intr_free(unsigned int cpu) {}
+#endif /* CONFIG_SMP */
+
 #ifdef CONFIG_XEN_PVH
 extern void xen_pvh_early_cpu_init(int cpu, bool entry);
 #else