+#ifdef CONFIG_HOTPLUG_SMT
+
+static const char *smt_states[] = {
+ [CPU_SMT_ENABLED] = "on",
+ [CPU_SMT_DISABLED] = "off",
+ [CPU_SMT_FORCE_DISABLED] = "forceoff",
+ [CPU_SMT_NOT_SUPPORTED] = "notsupported",
+};
+
+static ssize_t
+show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ return snprintf(buf, PAGE_SIZE - 2, "%s\n", smt_states[cpu_smt_control]);
+}
+
+static void cpuhp_offline_cpu_device(unsigned int cpu)
+{
+ struct device *dev = get_cpu_device(cpu);
+
+ dev->offline = true;
+ /* Tell user space about the state change */
+ kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
+}
+
+static void cpuhp_online_cpu_device(unsigned int cpu)
+{
+ struct device *dev = get_cpu_device(cpu);
+
+ dev->offline = false;
+ /* Tell user space about the state change */
+ kobject_uevent(&dev->kobj, KOBJ_ONLINE);
+}
+
+int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
+{
+ int cpu, ret = 0;
+
+ cpu_maps_update_begin();
+ for_each_online_cpu(cpu) {
+ if (topology_is_primary_thread(cpu))
+ continue;
+ ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
+ if (ret)
+ break;
+ /*
+ * As this needs to hold the cpu maps lock it's impossible
+ * to call device_offline() because that ends up calling
+ * cpu_down() which takes cpu maps lock. cpu maps lock
+ * needs to be held as this might race against in kernel
+ * abusers of the hotplug machinery (thermal management).
+ *
+ * So nothing would update device:offline state. That would
+ * leave the sysfs entry stale and prevent onlining after
+ * smt control has been changed to 'off' again. This is
+ * called under the sysfs hotplug lock, so it is properly
+ * serialized against the regular offline usage.
+ */
+ cpuhp_offline_cpu_device(cpu);
+ }
+ if (!ret) {
+ cpu_smt_control = ctrlval;
+ arch_smt_update();
+ }
+ cpu_maps_update_done();
+ return ret;
+}
+
+int cpuhp_smt_enable(void)
+{
+ int cpu, ret = 0;
+
+ cpu_maps_update_begin();
+ cpu_smt_control = CPU_SMT_ENABLED;
+ arch_smt_update();
+ for_each_present_cpu(cpu) {
+ /* Skip online CPUs and CPUs on offline nodes */
+ if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
+ continue;
+ ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
+ if (ret)
+ break;
+ /* See comment in cpuhp_smt_disable() */
+ cpuhp_online_cpu_device(cpu);
+ }
+ cpu_maps_update_done();
+ return ret;
+}
+
+static ssize_t
+store_smt_control(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ int ctrlval, ret;
+
+ if (sysfs_streq(buf, "on"))
+ ctrlval = CPU_SMT_ENABLED;
+ else if (sysfs_streq(buf, "off"))
+ ctrlval = CPU_SMT_DISABLED;
+ else if (sysfs_streq(buf, "forceoff"))
+ ctrlval = CPU_SMT_FORCE_DISABLED;
+ else
+ return -EINVAL;
+
+ if (cpu_smt_control == CPU_SMT_FORCE_DISABLED)
+ return -EPERM;
+
+ if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
+ return -ENODEV;
+
+ ret = lock_device_hotplug_sysfs();
+ if (ret)
+ return ret;
+
+ if (ctrlval != cpu_smt_control) {
+ switch (ctrlval) {
+ case CPU_SMT_ENABLED:
+ ret = cpuhp_smt_enable();
+ break;
+ case CPU_SMT_DISABLED:
+ case CPU_SMT_FORCE_DISABLED:
+ ret = cpuhp_smt_disable(ctrlval);
+ break;
+ }
+ }
+
+ unlock_device_hotplug();
+ return ret ? ret : count;
+}
+static DEVICE_ATTR(control, 0644, show_smt_control, store_smt_control);
+
+static ssize_t
+show_smt_active(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ bool active = topology_max_smt_threads() > 1;
+
+ return snprintf(buf, PAGE_SIZE - 2, "%d\n", active);
+}
+static DEVICE_ATTR(active, 0444, show_smt_active, NULL);
+
+static struct attribute *cpuhp_smt_attrs[] = {
+ &dev_attr_control.attr,
+ &dev_attr_active.attr,
+ NULL
+};
+
+static const struct attribute_group cpuhp_smt_attr_group = {
+ .attrs = cpuhp_smt_attrs,
+ .name = "smt",
+ NULL
+};
+
+static int __init cpu_smt_state_init(void)
+{
+ return sysfs_create_group(&cpu_subsys.dev_root->kobj,
+ &cpuhp_smt_attr_group);
+}
+
+#else
+static inline int cpu_smt_state_init(void) { return 0; }
+#endif
+