[Resend PATCH v1 1/3] cpu/smt: add a notifier to notify the SMT changes

[Wenyou Yang <WenYou.Yang@amd.com>]

Add the notifier chain to notify the cpu SMT status changes

Signed-off-by: Wenyou Yang <WenYou.Yang@amd.com>
---
 include/linux/cpu.h |  5 +++++
 kernel/cpu.c        | 11 ++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 314802f98b9d..9a842317fe2d 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -213,6 +213,11 @@ enum cpuhp_smt_control {
 	CPU_SMT_NOT_IMPLEMENTED,
 };
 
+enum cpuhp_smt_status {
+	SMT_ENABLED,
+	SMT_DISABLED,
+};
+
 #if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT)
 extern enum cpuhp_smt_control cpu_smt_control;
 extern void cpu_smt_disable(bool force);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6c0a92ca6bb5..accae0fa9868 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -89,6 +89,9 @@ static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
 cpumask_t cpus_booted_once_mask;
 #endif
 
+RAW_NOTIFIER_HEAD(smt_notifier_head);
+EXPORT_SYMBOL(smt_notifier_head);
+
 #if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
 static struct lockdep_map cpuhp_state_up_map =
 	STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
@@ -2281,8 +2284,10 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
 		 */
 		cpuhp_offline_cpu_device(cpu);
 	}
-	if (!ret)
+	if (!ret) {
 		cpu_smt_control = ctrlval;
+		raw_notifier_call_chain(&smt_notifier_head, SMT_DISABLED, NULL);
+	}
 	cpu_maps_update_done();
 	return ret;
 }
@@ -2303,7 +2308,11 @@ int cpuhp_smt_enable(void)
 		/* See comment in cpuhp_smt_disable() */
 		cpuhp_online_cpu_device(cpu);
 	}
+	if (!ret)
+		raw_notifier_call_chain(&smt_notifier_head, SMT_ENABLED, NULL);
+
 	cpu_maps_update_done();
+
 	return ret;
 }
 #endif
-- 
2.39.2