arm: kvm: implement CPU PM notifier

Upon CPU shutdown and consequent warm-reboot, the hypervisor CPU state
must be re-initialized. This patch implements a CPU PM notifier that
upon warm-boot calls a KVM hook to reinitialize properly the hypervisor
state so that the CPU can be safely resumed.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

arch/arm/kvm/arm.c

@@ -17,6 +17,7 @@
  */
 
 #include <linux/cpu.h>
+#include <linux/cpu_pm.h>
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/kvm_host.h>
@@ -853,6 +854,33 @@ static struct notifier_block hyp_init_cpu_nb = {
 	.notifier_call = hyp_init_cpu_notify,
 };
 
+#ifdef CONFIG_CPU_PM
+static int hyp_init_cpu_pm_notifier(struct notifier_block *self,
+				    unsigned long cmd,
+				    void *v)
+{
+	if (cmd == CPU_PM_EXIT) {
+		cpu_init_hyp_mode(NULL);
+		return NOTIFY_OK;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block hyp_init_cpu_pm_nb = {
+	.notifier_call = hyp_init_cpu_pm_notifier,
+};
+
+static void __init hyp_cpu_pm_init(void)
+{
+	cpu_pm_register_notifier(&hyp_init_cpu_pm_nb);
+}
+#else
+static inline void hyp_cpu_pm_init(void)
+{
+}
+#endif
+
 /**
  * Inits Hyp-mode on all online CPUs
  */
@@ -1013,6 +1041,8 @@ int kvm_arch_init(void *opaque)
 		goto out_err;
 	}
 
+	hyp_cpu_pm_init();
+
 	kvm_coproc_table_init();
 	return 0;
 out_err: