Merge tag 'smp_urgent_for_v6.10_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull smp fixes from Borislav Petkov:

 - Fix "nosmp" and "maxcpus=0" after the parallel CPU bringup work went
   in and broke them

 - Make sure CPU hotplug dynamic prepare states are actually executed

* tag 'smp_urgent_for_v6.10_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  cpu: Fix broken cmdline "nosmp" and "maxcpus=0"
  cpu/hotplug: Fix dynstate assignment in __cpuhp_setup_state_cpuslocked()

Author: torvalds

kernel/cpu.c

@@ -1859,6 +1859,9 @@ static inline bool cpuhp_bringup_cpus_parallel(unsigned int ncpus) { return fals
 
 void __init bringup_nonboot_cpus(unsigned int max_cpus)
 {
+	if (!max_cpus)
+		return;
+
 	/* Try parallel bringup optimization if enabled */
 	if (cpuhp_bringup_cpus_parallel(max_cpus))
 		return;
@@ -2446,7 +2449,7 @@ EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
  * The caller needs to hold cpus read locked while calling this function.
  * Return:
  *   On success:
- *      Positive state number if @state is CPUHP_AP_ONLINE_DYN;
+ *      Positive state number if @state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN;
  *      0 for all other states
  *   On failure: proper (negative) error code
  */
@@ -2469,7 +2472,7 @@ int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
 	ret = cpuhp_store_callbacks(state, name, startup, teardown,
 				    multi_instance);
 
-	dynstate = state == CPUHP_AP_ONLINE_DYN;
+	dynstate = state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN;
 	if (ret > 0 && dynstate) {
 		state = ret;
 		ret = 0;
@@ -2500,8 +2503,8 @@ int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
 out:
 	mutex_unlock(&cpuhp_state_mutex);
 	/*
-	 * If the requested state is CPUHP_AP_ONLINE_DYN, return the
-	 * dynamically allocated state in case of success.
+	 * If the requested state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN,
+	 * return the dynamically allocated state in case of success.
 	 */
 	if (!ret && dynstate)
 		return state;