xen/arm: Enable cpu_hotplug.c

Build cpu_hotplug for ARM and ARM64 guests.

Rename arch_(un)register_cpu to xen_(un)register_cpu and provide an
empty implementation on ARM and ARM64. On x86 just call
arch_(un)register_cpu as we are already doing.

Initialize cpu_hotplug on ARM.
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/arm/include/asm/xen/hypervisor.h

@@ -26,4 +26,14 @@ void __init xen_early_init(void);
 static inline void xen_early_init(void) { return; }
 #endif
 
+#ifdef CONFIG_HOTPLUG_CPU
+static inline void xen_arch_register_cpu(int num)
+{
+}
+
+static inline void xen_arch_unregister_cpu(int num)
+{
+}
+#endif
+
 #endif /* _ASM_ARM_XEN_HYPERVISOR_H */

arch/x86/include/asm/xen/hypervisor.h

@@ -57,4 +57,9 @@ static inline bool xen_x2apic_para_available(void)
 }
 #endif
 
+#ifdef CONFIG_HOTPLUG_CPU
+void xen_arch_register_cpu(int num);
+void xen_arch_unregister_cpu(int num);
+#endif
+
 #endif /* _ASM_X86_XEN_HYPERVISOR_H */

arch/x86/xen/enlighten.c

@@ -75,6 +75,7 @@
 #include <asm/mwait.h>
 #include <asm/pci_x86.h>
 #include <asm/pat.h>
+#include <asm/cpu.h>
 
 #ifdef CONFIG_ACPI
 #include <linux/acpi.h>
@@ -1899,3 +1900,17 @@ const struct hypervisor_x86 x86_hyper_xen = {
 	.set_cpu_features       = xen_set_cpu_features,
 };
 EXPORT_SYMBOL(x86_hyper_xen);
+
+#ifdef CONFIG_HOTPLUG_CPU
+void xen_arch_register_cpu(int num)
+{
+	arch_register_cpu(num);
+}
+EXPORT_SYMBOL(xen_arch_register_cpu);
+
+void xen_arch_unregister_cpu(int num)
+{
+	arch_unregister_cpu(num);
+}
+EXPORT_SYMBOL(xen_arch_unregister_cpu);
+#endif

drivers/xen/Makefile

-ifeq ($(filter y, $(CONFIG_ARM) $(CONFIG_ARM64)),)
 obj-$(CONFIG_HOTPLUG_CPU)		+= cpu_hotplug.o
-endif
 obj-$(CONFIG_X86)			+= fallback.o
 obj-y	+= grant-table.o features.o balloon.o manage.o preempt.o
 obj-y	+= events/

drivers/xen/cpu_hotplug.c

@@ -11,7 +11,7 @@
 static void enable_hotplug_cpu(int cpu)
 {
 	if (!cpu_present(cpu))
-		arch_register_cpu(cpu);
+		xen_arch_register_cpu(cpu);
 
 	set_cpu_present(cpu, true);
 }
@@ -19,7 +19,7 @@ static void enable_hotplug_cpu(int cpu)
 static void disable_hotplug_cpu(int cpu)
 {
 	if (cpu_present(cpu))
-		arch_unregister_cpu(cpu);
+		xen_arch_unregister_cpu(cpu);
 
 	set_cpu_present(cpu, false);
 }
@@ -102,7 +102,11 @@ static int __init setup_vcpu_hotplug_event(void)
 	static struct notifier_block xsn_cpu = {
 		.notifier_call = setup_cpu_watcher };
 
+#ifdef CONFIG_X86
 	if (!xen_pv_domain())
+#else
+	if (!xen_domain())
+#endif
 		return -ENODEV;
 
 	register_xenstore_notifier(&xsn_cpu);