split dev_queue

[cor.git] / kernel / cpu.c

/* CPU control.
 * (C) 2001, 2002, 2003, 2004 Rusty Russell
 *
 * This code is licenced under the GPL.
 */
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched/signal.h>
#include <linux/sched/hotplug.h>
#include <linux/sched/isolation.h>
#include <linux/sched/task.h>
#include <linux/sched/smt.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/rcupdate.h>
#include <linux/export.h>
#include <linux/bug.h>
#include <linux/kthread.h>
#include <linux/stop_machine.h>
#include <linux/mutex.h>
#include <linux/gfp.h>
#include <linux/suspend.h>
#include <linux/lockdep.h>
#include <linux/tick.h>
#include <linux/irq.h>
#include <linux/nmi.h>
#include <linux/smpboot.h>
#include <linux/relay.h>
#include <linux/slab.h>
#include <linux/percpu-rwsem.h>

#include <trace/events/power.h>
#define CREATE_TRACE_POINTS
#include <trace/events/cpuhp.h>

#include "smpboot.h"

/**
 * cpuhp_cpu_state - Per cpu hotplug state storage
 * @state:      The current cpu state
 * @target:     The target state
 * @thread:     Pointer to the hotplug thread
 * @should_run: Thread should execute
 * @rollback:   Perform a rollback
 * @single:     Single callback invocation
 * @bringup:    Single callback bringup or teardown selector
 * @cb_state:   The state for a single callback (install/uninstall)
 * @result:     Result of the operation
 * @done_up:    Signal completion to the issuer of the task for cpu-up
 * @done_down:  Signal completion to the issuer of the task for cpu-down
 */
struct cpuhp_cpu_state {
        enum cpuhp_state        state;
        enum cpuhp_state        target;
        enum cpuhp_state        fail;
#ifdef CONFIG_SMP
        struct task_struct      *thread;
        bool                    should_run;
        bool                    rollback;
        bool                    single;
        bool                    bringup;
        struct hlist_node       *node;
        struct hlist_node       *last;
        enum cpuhp_state        cb_state;
        int                     result;
        struct completion       done_up;
        struct completion       done_down;
#endif
};

static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
        .fail = CPUHP_INVALID,
};

#ifdef CONFIG_SMP
cpumask_t cpus_booted_once_mask;
#endif

#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);
static struct lockdep_map cpuhp_state_down_map =
        STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);


static inline void cpuhp_lock_acquire(bool bringup)
{
        lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
}

static inline void cpuhp_lock_release(bool bringup)
{
        lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
}
#else

static inline void cpuhp_lock_acquire(bool bringup) { }
static inline void cpuhp_lock_release(bool bringup) { }

#endif

/**
 * cpuhp_step - Hotplug state machine step
 * @name:       Name of the step
 * @startup:    Startup function of the step
 * @teardown:   Teardown function of the step
 * @cant_stop:  Bringup/teardown can't be stopped at this step
 */
struct cpuhp_step {
        const char              *name;
        union {
                int             (*single)(unsigned int cpu);
                int             (*multi)(unsigned int cpu,
                                         struct hlist_node *node);
        } startup;
        union {
                int             (*single)(unsigned int cpu);
                int             (*multi)(unsigned int cpu,
                                         struct hlist_node *node);
        } teardown;
        struct hlist_head       list;
        bool                    cant_stop;
        bool                    multi_instance;
};

static DEFINE_MUTEX(cpuhp_state_mutex);
static struct cpuhp_step cpuhp_hp_states[];

static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
{
        return cpuhp_hp_states + state;
}

/**
 * cpuhp_invoke_callback _ Invoke the callbacks for a given state
 * @cpu:        The cpu for which the callback should be invoked
 * @state:      The state to do callbacks for
 * @bringup:    True if the bringup callback should be invoked
 * @node:       For multi-instance, do a single entry callback for install/remove
 * @lastp:      For multi-instance rollback, remember how far we got
 *
 * Called from cpu hotplug and from the state register machinery.
 */
static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
                                 bool bringup, struct hlist_node *node,
                                 struct hlist_node **lastp)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        struct cpuhp_step *step = cpuhp_get_step(state);
        int (*cbm)(unsigned int cpu, struct hlist_node *node);
        int (*cb)(unsigned int cpu);
        int ret, cnt;

        if (st->fail == state) {
                st->fail = CPUHP_INVALID;

                if (!(bringup ? step->startup.single : step->teardown.single))
                        return 0;

                return -EAGAIN;
        }

        if (!step->multi_instance) {
                WARN_ON_ONCE(lastp && *lastp);
                cb = bringup ? step->startup.single : step->teardown.single;
                if (!cb)
                        return 0;
                trace_cpuhp_enter(cpu, st->target, state, cb);
                ret = cb(cpu);
                trace_cpuhp_exit(cpu, st->state, state, ret);
                return ret;
        }
        cbm = bringup ? step->startup.multi : step->teardown.multi;
        if (!cbm)
                return 0;

        /* Single invocation for instance add/remove */
        if (node) {
                WARN_ON_ONCE(lastp && *lastp);
                trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
                ret = cbm(cpu, node);
                trace_cpuhp_exit(cpu, st->state, state, ret);
                return ret;
        }

        /* State transition. Invoke on all instances */
        cnt = 0;
        hlist_for_each(node, &step->list) {
                if (lastp && node == *lastp)
                        break;

                trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
                ret = cbm(cpu, node);
                trace_cpuhp_exit(cpu, st->state, state, ret);
                if (ret) {
                        if (!lastp)
                                goto err;

                        *lastp = node;
                        return ret;
                }
                cnt++;
        }
        if (lastp)
                *lastp = NULL;
        return 0;
err:
        /* Rollback the instances if one failed */
        cbm = !bringup ? step->startup.multi : step->teardown.multi;
        if (!cbm)
                return ret;

        hlist_for_each(node, &step->list) {
                if (!cnt--)
                        break;

                trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
                ret = cbm(cpu, node);
                trace_cpuhp_exit(cpu, st->state, state, ret);
                /*
                 * Rollback must not fail,
                 */
                WARN_ON_ONCE(ret);
        }
        return ret;
}

#ifdef CONFIG_SMP
static bool cpuhp_is_ap_state(enum cpuhp_state state)
{
        /*
         * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
         * purposes as that state is handled explicitly in cpu_down.
         */
        return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
}

static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
{
        struct completion *done = bringup ? &st->done_up : &st->done_down;
        wait_for_completion(done);
}

static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
{
        struct completion *done = bringup ? &st->done_up : &st->done_down;
        complete(done);
}

/*
 * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
 */
static bool cpuhp_is_atomic_state(enum cpuhp_state state)
{
        return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
}

/* Serializes the updates to cpu_online_mask, cpu_present_mask */
static DEFINE_MUTEX(cpu_add_remove_lock);
bool cpuhp_tasks_frozen;
EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);

/*
 * The following two APIs (cpu_maps_update_begin/done) must be used when
 * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
 */
void cpu_maps_update_begin(void)
{
        mutex_lock(&cpu_add_remove_lock);
}

void cpu_maps_update_done(void)
{
        mutex_unlock(&cpu_add_remove_lock);
}

/*
 * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
 * Should always be manipulated under cpu_add_remove_lock
 */
static int cpu_hotplug_disabled;

#ifdef CONFIG_HOTPLUG_CPU

DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);

void cpus_read_lock(void)
{
        percpu_down_read(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_lock);

int cpus_read_trylock(void)
{
        return percpu_down_read_trylock(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_trylock);

void cpus_read_unlock(void)
{
        percpu_up_read(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_unlock);

void cpus_write_lock(void)
{
        percpu_down_write(&cpu_hotplug_lock);
}

void cpus_write_unlock(void)
{
        percpu_up_write(&cpu_hotplug_lock);
}

void lockdep_assert_cpus_held(void)
{
        /*
         * We can't have hotplug operations before userspace starts running,
         * and some init codepaths will knowingly not take the hotplug lock.
         * This is all valid, so mute lockdep until it makes sense to report
         * unheld locks.
         */
        if (system_state < SYSTEM_RUNNING)
                return;

        percpu_rwsem_assert_held(&cpu_hotplug_lock);
}

static void lockdep_acquire_cpus_lock(void)
{
        rwsem_acquire(&cpu_hotplug_lock.rw_sem.dep_map, 0, 0, _THIS_IP_);
}

static void lockdep_release_cpus_lock(void)
{
        rwsem_release(&cpu_hotplug_lock.rw_sem.dep_map, _THIS_IP_);
}

/*
 * Wait for currently running CPU hotplug operations to complete (if any) and
 * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
 * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
 * hotplug path before performing hotplug operations. So acquiring that lock
 * guarantees mutual exclusion from any currently running hotplug operations.
 */
void cpu_hotplug_disable(void)
{
        cpu_maps_update_begin();
        cpu_hotplug_disabled++;
        cpu_maps_update_done();
}
EXPORT_SYMBOL_GPL(cpu_hotplug_disable);

static void __cpu_hotplug_enable(void)
{
        if (WARN_ONCE(!cpu_hotplug_disabled, "Unbalanced cpu hotplug enable\n"))
                return;
        cpu_hotplug_disabled--;
}

void cpu_hotplug_enable(void)
{
        cpu_maps_update_begin();
        __cpu_hotplug_enable();
        cpu_maps_update_done();
}
EXPORT_SYMBOL_GPL(cpu_hotplug_enable);

#else

static void lockdep_acquire_cpus_lock(void)
{
}

static void lockdep_release_cpus_lock(void)
{
}

#endif  /* CONFIG_HOTPLUG_CPU */

/*
 * Architectures that need SMT-specific errata handling during SMT hotplug
 * should override this.
 */
void __weak arch_smt_update(void) { }

#ifdef CONFIG_HOTPLUG_SMT
enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;

void __init cpu_smt_disable(bool force)
{
        if (!cpu_smt_possible())
                return;

        if (force) {
                pr_info("SMT: Force disabled\n");
                cpu_smt_control = CPU_SMT_FORCE_DISABLED;
        } else {
                pr_info("SMT: disabled\n");
                cpu_smt_control = CPU_SMT_DISABLED;
        }
}

/*
 * The decision whether SMT is supported can only be done after the full
 * CPU identification. Called from architecture code.
 */
void __init cpu_smt_check_topology(void)
{
        if (!topology_smt_supported())
                cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
}

static int __init smt_cmdline_disable(char *str)
{
        cpu_smt_disable(str && !strcmp(str, "force"));
        return 0;
}
early_param("nosmt", smt_cmdline_disable);

static inline bool cpu_smt_allowed(unsigned int cpu)
{
        if (cpu_smt_control == CPU_SMT_ENABLED)
                return true;

        if (topology_is_primary_thread(cpu))
                return true;

        /*
         * On x86 it's required to boot all logical CPUs at least once so
         * that the init code can get a chance to set CR4.MCE on each
         * CPU. Otherwise, a broadacasted MCE observing CR4.MCE=0b on any
         * core will shutdown the machine.
         */
        return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
}

/* Returns true if SMT is not supported of forcefully (irreversibly) disabled */
bool cpu_smt_possible(void)
{
        return cpu_smt_control != CPU_SMT_FORCE_DISABLED &&
                cpu_smt_control != CPU_SMT_NOT_SUPPORTED;
}
EXPORT_SYMBOL_GPL(cpu_smt_possible);
#else
static inline bool cpu_smt_allowed(unsigned int cpu) { return true; }
#endif

static inline enum cpuhp_state
cpuhp_set_state(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
        enum cpuhp_state prev_state = st->state;

        st->rollback = false;
        st->last = NULL;

        st->target = target;
        st->single = false;
        st->bringup = st->state < target;

        return prev_state;
}

static inline void
cpuhp_reset_state(struct cpuhp_cpu_state *st, enum cpuhp_state prev_state)
{
        st->rollback = true;

        /*
         * If we have st->last we need to undo partial multi_instance of this
         * state first. Otherwise start undo at the previous state.
         */
        if (!st->last) {
                if (st->bringup)
                        st->state--;
                else
                        st->state++;
        }

        st->target = prev_state;
        st->bringup = !st->bringup;
}

/* Regular hotplug invocation of the AP hotplug thread */
static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
{
        if (!st->single && st->state == st->target)
                return;

        st->result = 0;
        /*
         * Make sure the above stores are visible before should_run becomes
         * true. Paired with the mb() above in cpuhp_thread_fun()
         */
        smp_mb();
        st->should_run = true;
        wake_up_process(st->thread);
        wait_for_ap_thread(st, st->bringup);
}

static int cpuhp_kick_ap(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
        enum cpuhp_state prev_state;
        int ret;

        prev_state = cpuhp_set_state(st, target);
        __cpuhp_kick_ap(st);
        if ((ret = st->result)) {
                cpuhp_reset_state(st, prev_state);
                __cpuhp_kick_ap(st);
        }

        return ret;
}

static int bringup_wait_for_ap(unsigned int cpu)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

        /* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
        wait_for_ap_thread(st, true);
        if (WARN_ON_ONCE((!cpu_online(cpu))))
                return -ECANCELED;

        /* Unpark the stopper thread and the hotplug thread of the target cpu */
        stop_machine_unpark(cpu);
        kthread_unpark(st->thread);

        /*
         * SMT soft disabling on X86 requires to bring the CPU out of the
         * BIOS 'wait for SIPI' state in order to set the CR4.MCE bit.  The
         * CPU marked itself as booted_once in notify_cpu_starting() so the
         * cpu_smt_allowed() check will now return false if this is not the
         * primary sibling.
         */
        if (!cpu_smt_allowed(cpu))
                return -ECANCELED;

        if (st->target <= CPUHP_AP_ONLINE_IDLE)
                return 0;

        return cpuhp_kick_ap(st, st->target);
}

static int bringup_cpu(unsigned int cpu)
{
        struct task_struct *idle = idle_thread_get(cpu);
        int ret;

        /*
         * Some architectures have to walk the irq descriptors to
         * setup the vector space for the cpu which comes online.
         * Prevent irq alloc/free across the bringup.
         */
        irq_lock_sparse();

        /* Arch-specific enabling code. */
        ret = __cpu_up(cpu, idle);
        irq_unlock_sparse();
        if (ret)
                return ret;
        return bringup_wait_for_ap(cpu);
}

/*
 * Hotplug state machine related functions
 */

static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
{
        for (st->state--; st->state > st->target; st->state--)
                cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
}

static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
{
        if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
                return true;
        /*
         * When CPU hotplug is disabled, then taking the CPU down is not
         * possible because takedown_cpu() and the architecture and
         * subsystem specific mechanisms are not available. So the CPU
         * which would be completely unplugged again needs to stay around
         * in the current state.
         */
        return st->state <= CPUHP_BRINGUP_CPU;
}

static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                              enum cpuhp_state target)
{
        enum cpuhp_state prev_state = st->state;
        int ret = 0;

        while (st->state < target) {
                st->state++;
                ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
                if (ret) {
                        if (can_rollback_cpu(st)) {
                                st->target = prev_state;
                                undo_cpu_up(cpu, st);
                        }
                        break;
                }
        }
        return ret;
}

/*
 * The cpu hotplug threads manage the bringup and teardown of the cpus
 */
static void cpuhp_create(unsigned int cpu)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

        init_completion(&st->done_up);
        init_completion(&st->done_down);
}

static int cpuhp_should_run(unsigned int cpu)
{
        struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

        return st->should_run;
}

/*
 * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
 * callbacks when a state gets [un]installed at runtime.
 *
 * Each invocation of this function by the smpboot thread does a single AP
 * state callback.
 *
 * It has 3 modes of operation:
 *  - single: runs st->cb_state
 *  - up:     runs ++st->state, while st->state < st->target
 *  - down:   runs st->state--, while st->state > st->target
 *
 * When complete or on error, should_run is cleared and the completion is fired.
 */
static void cpuhp_thread_fun(unsigned int cpu)
{
        struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
        bool bringup = st->bringup;
        enum cpuhp_state state;

        if (WARN_ON_ONCE(!st->should_run))
                return;

        /*
         * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
         * that if we see ->should_run we also see the rest of the state.
         */
        smp_mb();

        /*
         * The BP holds the hotplug lock, but we're now running on the AP,
         * ensure that anybody asserting the lock is held, will actually find
         * it so.
         */
        lockdep_acquire_cpus_lock();
        cpuhp_lock_acquire(bringup);

        if (st->single) {
                state = st->cb_state;
                st->should_run = false;
        } else {
                if (bringup) {
                        st->state++;
                        state = st->state;
                        st->should_run = (st->state < st->target);
                        WARN_ON_ONCE(st->state > st->target);
                } else {
                        state = st->state;
                        st->state--;
                        st->should_run = (st->state > st->target);
                        WARN_ON_ONCE(st->state < st->target);
                }
        }

        WARN_ON_ONCE(!cpuhp_is_ap_state(state));

        if (cpuhp_is_atomic_state(state)) {
                local_irq_disable();
                st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
                local_irq_enable();

                /*
                 * STARTING/DYING must not fail!
                 */
                WARN_ON_ONCE(st->result);
        } else {
                st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
        }

        if (st->result) {
                /*
                 * If we fail on a rollback, we're up a creek without no
                 * paddle, no way forward, no way back. We loose, thanks for
                 * playing.
                 */
                WARN_ON_ONCE(st->rollback);
                st->should_run = false;
        }

        cpuhp_lock_release(bringup);
        lockdep_release_cpus_lock();

        if (!st->should_run)
                complete_ap_thread(st, bringup);
}

/* Invoke a single callback on a remote cpu */
static int
cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
                         struct hlist_node *node)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int ret;

        if (!cpu_online(cpu))
                return 0;

        cpuhp_lock_acquire(false);
        cpuhp_lock_release(false);

        cpuhp_lock_acquire(true);
        cpuhp_lock_release(true);

        /*
         * If we are up and running, use the hotplug thread. For early calls
         * we invoke the thread function directly.
         */
        if (!st->thread)
                return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);

        st->rollback = false;
        st->last = NULL;

        st->node = node;
        st->bringup = bringup;
        st->cb_state = state;
        st->single = true;

        __cpuhp_kick_ap(st);

        /*
         * If we failed and did a partial, do a rollback.
         */
        if ((ret = st->result) && st->last) {
                st->rollback = true;
                st->bringup = !bringup;

                __cpuhp_kick_ap(st);
        }

        /*
         * Clean up the leftovers so the next hotplug operation wont use stale
         * data.
         */
        st->node = st->last = NULL;
        return ret;
}

static int cpuhp_kick_ap_work(unsigned int cpu)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        enum cpuhp_state prev_state = st->state;
        int ret;

        cpuhp_lock_acquire(false);
        cpuhp_lock_release(false);

        cpuhp_lock_acquire(true);
        cpuhp_lock_release(true);

        trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
        ret = cpuhp_kick_ap(st, st->target);
        trace_cpuhp_exit(cpu, st->state, prev_state, ret);

        return ret;
}

static struct smp_hotplug_thread cpuhp_threads = {
        .store                  = &cpuhp_state.thread,
        .create                 = &cpuhp_create,
        .thread_should_run      = cpuhp_should_run,
        .thread_fn              = cpuhp_thread_fun,
        .thread_comm            = "cpuhp/%u",
        .selfparking            = true,
};

void __init cpuhp_threads_init(void)
{
        BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
        kthread_unpark(this_cpu_read(cpuhp_state.thread));
}

#ifdef CONFIG_HOTPLUG_CPU
/**
 * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
 * @cpu: a CPU id
 *
 * This function walks all processes, finds a valid mm struct for each one and
 * then clears a corresponding bit in mm's cpumask.  While this all sounds
 * trivial, there are various non-obvious corner cases, which this function
 * tries to solve in a safe manner.
 *
 * Also note that the function uses a somewhat relaxed locking scheme, so it may
 * be called only for an already offlined CPU.
 */
void clear_tasks_mm_cpumask(int cpu)
{
        struct task_struct *p;

        /*
         * This function is called after the cpu is taken down and marked
         * offline, so its not like new tasks will ever get this cpu set in
         * their mm mask. -- Peter Zijlstra
         * Thus, we may use rcu_read_lock() here, instead of grabbing
         * full-fledged tasklist_lock.
         */
        WARN_ON(cpu_online(cpu));
        rcu_read_lock();
        for_each_process(p) {
                struct task_struct *t;

                /*
                 * Main thread might exit, but other threads may still have
                 * a valid mm. Find one.
                 */
                t = find_lock_task_mm(p);
                if (!t)
                        continue;
                cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
                task_unlock(t);
        }
        rcu_read_unlock();
}

/* Take this CPU down. */
static int take_cpu_down(void *_param)
{
        struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
        enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
        int err, cpu = smp_processor_id();
        int ret;

        /* Ensure this CPU doesn't handle any more interrupts. */
        err = __cpu_disable();
        if (err < 0)
                return err;

        /*
         * We get here while we are in CPUHP_TEARDOWN_CPU state and we must not
         * do this step again.
         */
        WARN_ON(st->state != CPUHP_TEARDOWN_CPU);
        st->state--;
        /* Invoke the former CPU_DYING callbacks */
        for (; st->state > target; st->state--) {
                ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
                /*
                 * DYING must not fail!
                 */
                WARN_ON_ONCE(ret);
        }

        /* Give up timekeeping duties */
        tick_handover_do_timer();
        /* Remove CPU from timer broadcasting */
        tick_offline_cpu(cpu);
        /* Park the stopper thread */
        stop_machine_park(cpu);
        return 0;
}

static int takedown_cpu(unsigned int cpu)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int err;

        /* Park the smpboot threads */
        kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);

        /*
         * Prevent irq alloc/free while the dying cpu reorganizes the
         * interrupt affinities.
         */
        irq_lock_sparse();

        /*
         * So now all preempt/rcu users must observe !cpu_active().
         */
        err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
        if (err) {
                /* CPU refused to die */
                irq_unlock_sparse();
                /* Unpark the hotplug thread so we can rollback there */
                kthread_unpark(per_cpu_ptr(&cpuhp_state, cpu)->thread);
                return err;
        }
        BUG_ON(cpu_online(cpu));

        /*
         * The teardown callback for CPUHP_AP_SCHED_STARTING will have removed
         * all runnable tasks from the CPU, there's only the idle task left now
         * that the migration thread is done doing the stop_machine thing.
         *
         * Wait for the stop thread to go away.
         */
        wait_for_ap_thread(st, false);
        BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);

        /* Interrupts are moved away from the dying cpu, reenable alloc/free */
        irq_unlock_sparse();

        hotplug_cpu__broadcast_tick_pull(cpu);
        /* This actually kills the CPU. */
        __cpu_die(cpu);

        tick_cleanup_dead_cpu(cpu);
        rcutree_migrate_callbacks(cpu);
        return 0;
}

static void cpuhp_complete_idle_dead(void *arg)
{
        struct cpuhp_cpu_state *st = arg;

        complete_ap_thread(st, false);
}

void cpuhp_report_idle_dead(void)
{
        struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

        BUG_ON(st->state != CPUHP_AP_OFFLINE);
        rcu_report_dead(smp_processor_id());
        st->state = CPUHP_AP_IDLE_DEAD;
        /*
         * We cannot call complete after rcu_report_dead() so we delegate it
         * to an online cpu.
         */
        smp_call_function_single(cpumask_first(cpu_online_mask),
                                 cpuhp_complete_idle_dead, st, 0);
}

static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)
{
        for (st->state++; st->state < st->target; st->state++)
                cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
}

static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
                                enum cpuhp_state target)
{
        enum cpuhp_state prev_state = st->state;
        int ret = 0;

        for (; st->state > target; st->state--) {
                ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
                if (ret) {
                        st->target = prev_state;
                        if (st->state < prev_state)
                                undo_cpu_down(cpu, st);
                        break;
                }
        }
        return ret;
}

/* Requires cpu_add_remove_lock to be held */
static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
                           enum cpuhp_state target)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int prev_state, ret = 0;

        if (num_online_cpus() == 1)
                return -EBUSY;

        if (!cpu_present(cpu))
                return -EINVAL;

        cpus_write_lock();

        cpuhp_tasks_frozen = tasks_frozen;

        prev_state = cpuhp_set_state(st, target);
        /*
         * If the current CPU state is in the range of the AP hotplug thread,
         * then we need to kick the thread.
         */
        if (st->state > CPUHP_TEARDOWN_CPU) {
                st->target = max((int)target, CPUHP_TEARDOWN_CPU);
                ret = cpuhp_kick_ap_work(cpu);
                /*
                 * The AP side has done the error rollback already. Just
                 * return the error code..
                 */
                if (ret)
                        goto out;

                /*
                 * We might have stopped still in the range of the AP hotplug
                 * thread. Nothing to do anymore.
                 */
                if (st->state > CPUHP_TEARDOWN_CPU)
                        goto out;

                st->target = target;
        }
        /*
         * The AP brought itself down to CPUHP_TEARDOWN_CPU. So we need
         * to do the further cleanups.
         */
        ret = cpuhp_down_callbacks(cpu, st, target);
        if (ret && st->state == CPUHP_TEARDOWN_CPU && st->state < prev_state) {
                cpuhp_reset_state(st, prev_state);
                __cpuhp_kick_ap(st);
        }

out:
        cpus_write_unlock();
        /*
         * Do post unplug cleanup. This is still protected against
         * concurrent CPU hotplug via cpu_add_remove_lock.
         */
        lockup_detector_cleanup();
        arch_smt_update();
        return ret;
}

static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
{
        if (cpu_hotplug_disabled)
                return -EBUSY;
        return _cpu_down(cpu, 0, target);
}

static int do_cpu_down(unsigned int cpu, enum cpuhp_state target)
{
        int err;

        cpu_maps_update_begin();
        err = cpu_down_maps_locked(cpu, target);
        cpu_maps_update_done();
        return err;
}

int cpu_down(unsigned int cpu)
{
        return do_cpu_down(cpu, CPUHP_OFFLINE);
}
EXPORT_SYMBOL(cpu_down);

#else
#define takedown_cpu            NULL
#endif /*CONFIG_HOTPLUG_CPU*/

/**
 * notify_cpu_starting(cpu) - Invoke the callbacks on the starting CPU
 * @cpu: cpu that just started
 *
 * It must be called by the arch code on the new cpu, before the new cpu
 * enables interrupts and before the "boot" cpu returns from __cpu_up().
 */
void notify_cpu_starting(unsigned int cpu)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
        int ret;

        rcu_cpu_starting(cpu);  /* Enables RCU usage on this CPU. */
        cpumask_set_cpu(cpu, &cpus_booted_once_mask);
        while (st->state < target) {
                st->state++;
                ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
                /*
                 * STARTING must not fail!
                 */
                WARN_ON_ONCE(ret);
        }
}

/*
 * Called from the idle task. Wake up the controlling task which brings the
 * stopper and the hotplug thread of the upcoming CPU up and then delegates
 * the rest of the online bringup to the hotplug thread.
 */
void cpuhp_online_idle(enum cpuhp_state state)
{
        struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

        /* Happens for the boot cpu */
        if (state != CPUHP_AP_ONLINE_IDLE)
                return;

        st->state = CPUHP_AP_ONLINE_IDLE;
        complete_ap_thread(st, true);
}

/* Requires cpu_add_remove_lock to be held */
static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        struct task_struct *idle;
        int ret = 0;

        cpus_write_lock();

        if (!cpu_present(cpu)) {
                ret = -EINVAL;
                goto out;
        }

        /*
         * The caller of do_cpu_up might have raced with another
         * caller. Ignore it for now.
         */
        if (st->state >= target)
                goto out;

        if (st->state == CPUHP_OFFLINE) {
                /* Let it fail before we try to bring the cpu up */
                idle = idle_thread_get(cpu);
                if (IS_ERR(idle)) {
                        ret = PTR_ERR(idle);
                        goto out;
                }
        }

        cpuhp_tasks_frozen = tasks_frozen;

        cpuhp_set_state(st, target);
        /*
         * If the current CPU state is in the range of the AP hotplug thread,
         * then we need to kick the thread once more.
         */
        if (st->state > CPUHP_BRINGUP_CPU) {
                ret = cpuhp_kick_ap_work(cpu);
                /*
                 * The AP side has done the error rollback already. Just
                 * return the error code..
                 */
                if (ret)
                        goto out;
        }

        /*
         * Try to reach the target state. We max out on the BP at
         * CPUHP_BRINGUP_CPU. After that the AP hotplug thread is
         * responsible for bringing it up to the target state.
         */
        target = min((int)target, CPUHP_BRINGUP_CPU);
        ret = cpuhp_up_callbacks(cpu, st, target);
out:
        cpus_write_unlock();
        arch_smt_update();
        return ret;
}

static int do_cpu_up(unsigned int cpu, enum cpuhp_state target)
{
        int err = 0;

        if (!cpu_possible(cpu)) {
                pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n",
                       cpu);
#if defined(CONFIG_IA64)
                pr_err("please check additional_cpus= boot parameter\n");
#endif
                return -EINVAL;
        }

        err = try_online_node(cpu_to_node(cpu));
        if (err)
                return err;

        cpu_maps_update_begin();

        if (cpu_hotplug_disabled) {
                err = -EBUSY;
                goto out;
        }
        if (!cpu_smt_allowed(cpu)) {
                err = -EPERM;
                goto out;
        }

        err = _cpu_up(cpu, 0, target);
out:
        cpu_maps_update_done();
        return err;
}

int cpu_up(unsigned int cpu)
{
        return do_cpu_up(cpu, CPUHP_ONLINE);
}
EXPORT_SYMBOL_GPL(cpu_up);

#ifdef CONFIG_PM_SLEEP_SMP
static cpumask_var_t frozen_cpus;

int freeze_secondary_cpus(int primary)
{
        int cpu, error = 0;

        cpu_maps_update_begin();
        if (primary == -1) {
                primary = cpumask_first(cpu_online_mask);
                if (!housekeeping_cpu(primary, HK_FLAG_TIMER))
                        primary = housekeeping_any_cpu(HK_FLAG_TIMER);
        } else {
                if (!cpu_online(primary))
                        primary = cpumask_first(cpu_online_mask);
        }

        /*
         * We take down all of the non-boot CPUs in one shot to avoid races
         * with the userspace trying to use the CPU hotplug at the same time
         */
        cpumask_clear(frozen_cpus);

        pr_info("Disabling non-boot CPUs ...\n");
        for_each_online_cpu(cpu) {
                if (cpu == primary)
                        continue;

                if (pm_wakeup_pending()) {
                        pr_info("Wakeup pending. Abort CPU freeze\n");
                        error = -EBUSY;
                        break;
                }

                trace_suspend_resume(TPS("CPU_OFF"), cpu, true);
                error = _cpu_down(cpu, 1, CPUHP_OFFLINE);
                trace_suspend_resume(TPS("CPU_OFF"), cpu, false);
                if (!error)
                        cpumask_set_cpu(cpu, frozen_cpus);
                else {
                        pr_err("Error taking CPU%d down: %d\n", cpu, error);
                        break;
                }
        }

        if (!error)
                BUG_ON(num_online_cpus() > 1);
        else
                pr_err("Non-boot CPUs are not disabled\n");

        /*
         * Make sure the CPUs won't be enabled by someone else. We need to do
         * this even in case of failure as all disable_nonboot_cpus() users are
         * supposed to do enable_nonboot_cpus() on the failure path.
         */
        cpu_hotplug_disabled++;

        cpu_maps_update_done();
        return error;
}

void __weak arch_enable_nonboot_cpus_begin(void)
{
}

void __weak arch_enable_nonboot_cpus_end(void)
{
}

void enable_nonboot_cpus(void)
{
        int cpu, error;

        /* Allow everyone to use the CPU hotplug again */
        cpu_maps_update_begin();
        __cpu_hotplug_enable();
        if (cpumask_empty(frozen_cpus))
                goto out;

        pr_info("Enabling non-boot CPUs ...\n");

        arch_enable_nonboot_cpus_begin();

        for_each_cpu(cpu, frozen_cpus) {
                trace_suspend_resume(TPS("CPU_ON"), cpu, true);
                error = _cpu_up(cpu, 1, CPUHP_ONLINE);
                trace_suspend_resume(TPS("CPU_ON"), cpu, false);
                if (!error) {
                        pr_info("CPU%d is up\n", cpu);
                        continue;
                }
                pr_warn("Error taking CPU%d up: %d\n", cpu, error);
        }

        arch_enable_nonboot_cpus_end();

        cpumask_clear(frozen_cpus);
out:
        cpu_maps_update_done();
}

static int __init alloc_frozen_cpus(void)
{
        if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
                return -ENOMEM;
        return 0;
}
core_initcall(alloc_frozen_cpus);

/*
 * When callbacks for CPU hotplug notifications are being executed, we must
 * ensure that the state of the system with respect to the tasks being frozen
 * or not, as reported by the notification, remains unchanged *throughout the
 * duration* of the execution of the callbacks.
 * Hence we need to prevent the freezer from racing with regular CPU hotplug.
 *
 * This synchronization is implemented by mutually excluding regular CPU
 * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
 * Hibernate notifications.
 */
static int
cpu_hotplug_pm_callback(struct notifier_block *nb,
                        unsigned long action, void *ptr)
{
        switch (action) {

        case PM_SUSPEND_PREPARE:
        case PM_HIBERNATION_PREPARE:
                cpu_hotplug_disable();
                break;

        case PM_POST_SUSPEND:
        case PM_POST_HIBERNATION:
                cpu_hotplug_enable();
                break;

        default:
                return NOTIFY_DONE;
        }

        return NOTIFY_OK;
}


static int __init cpu_hotplug_pm_sync_init(void)
{
        /*
         * cpu_hotplug_pm_callback has higher priority than x86
         * bsp_pm_callback which depends on cpu_hotplug_pm_callback
         * to disable cpu hotplug to avoid cpu hotplug race.
         */
        pm_notifier(cpu_hotplug_pm_callback, 0);
        return 0;
}
core_initcall(cpu_hotplug_pm_sync_init);

#endif /* CONFIG_PM_SLEEP_SMP */

int __boot_cpu_id;

#endif /* CONFIG_SMP */

/* Boot processor state steps */
static struct cpuhp_step cpuhp_hp_states[] = {
        [CPUHP_OFFLINE] = {
                .name                   = "offline",
                .startup.single         = NULL,
                .teardown.single        = NULL,
        },
#ifdef CONFIG_SMP
        [CPUHP_CREATE_THREADS]= {
                .name                   = "threads:prepare",
                .startup.single         = smpboot_create_threads,
                .teardown.single        = NULL,
                .cant_stop              = true,
        },
        [CPUHP_PERF_PREPARE] = {
                .name                   = "perf:prepare",
                .startup.single         = perf_event_init_cpu,
                .teardown.single        = perf_event_exit_cpu,
        },
        [CPUHP_WORKQUEUE_PREP] = {
                .name                   = "workqueue:prepare",
                .startup.single         = workqueue_prepare_cpu,
                .teardown.single        = NULL,
        },
        [CPUHP_HRTIMERS_PREPARE] = {
                .name                   = "hrtimers:prepare",
                .startup.single         = hrtimers_prepare_cpu,
                .teardown.single        = hrtimers_dead_cpu,
        },
        [CPUHP_SMPCFD_PREPARE] = {
                .name                   = "smpcfd:prepare",
                .startup.single         = smpcfd_prepare_cpu,
                .teardown.single        = smpcfd_dead_cpu,
        },
        [CPUHP_RELAY_PREPARE] = {
                .name                   = "relay:prepare",
                .startup.single         = relay_prepare_cpu,
                .teardown.single        = NULL,
        },
        [CPUHP_SLAB_PREPARE] = {
                .name                   = "slab:prepare",
                .startup.single         = slab_prepare_cpu,
                .teardown.single        = slab_dead_cpu,
        },
        [CPUHP_RCUTREE_PREP] = {
                .name                   = "RCU/tree:prepare",
                .startup.single         = rcutree_prepare_cpu,
                .teardown.single        = rcutree_dead_cpu,
        },
        /*
         * On the tear-down path, timers_dead_cpu() must be invoked
         * before blk_mq_queue_reinit_notify() from notify_dead(),
         * otherwise a RCU stall occurs.
         */
        [CPUHP_TIMERS_PREPARE] = {
                .name                   = "timers:prepare",
                .startup.single         = timers_prepare_cpu,
                .teardown.single        = timers_dead_cpu,
        },
        /* Kicks the plugged cpu into life */
        [CPUHP_BRINGUP_CPU] = {
                .name                   = "cpu:bringup",
                .startup.single         = bringup_cpu,
                .teardown.single        = NULL,
                .cant_stop              = true,
        },
        /* Final state before CPU kills itself */
        [CPUHP_AP_IDLE_DEAD] = {
                .name                   = "idle:dead",
        },
        /*
         * Last state before CPU enters the idle loop to die. Transient state
         * for synchronization.
         */
        [CPUHP_AP_OFFLINE] = {
                .name                   = "ap:offline",
                .cant_stop              = true,
        },
        /* First state is scheduler control. Interrupts are disabled */
        [CPUHP_AP_SCHED_STARTING] = {
                .name                   = "sched:starting",
                .startup.single         = sched_cpu_starting,
                .teardown.single        = sched_cpu_dying,
        },
        [CPUHP_AP_RCUTREE_DYING] = {
                .name                   = "RCU/tree:dying",
                .startup.single         = NULL,
                .teardown.single        = rcutree_dying_cpu,
        },
        [CPUHP_AP_SMPCFD_DYING] = {
                .name                   = "smpcfd:dying",
                .startup.single         = NULL,
                .teardown.single        = smpcfd_dying_cpu,
        },
        /* Entry state on starting. Interrupts enabled from here on. Transient
         * state for synchronsization */
        [CPUHP_AP_ONLINE] = {
                .name                   = "ap:online",
        },
        /*
         * Handled on controll processor until the plugged processor manages
         * this itself.
         */
        [CPUHP_TEARDOWN_CPU] = {
                .name                   = "cpu:teardown",
                .startup.single         = NULL,
                .teardown.single        = takedown_cpu,
                .cant_stop              = true,
        },
        /* Handle smpboot threads park/unpark */
        [CPUHP_AP_SMPBOOT_THREADS] = {
                .name                   = "smpboot/threads:online",
                .startup.single         = smpboot_unpark_threads,
                .teardown.single        = smpboot_park_threads,
        },
        [CPUHP_AP_IRQ_AFFINITY_ONLINE] = {
                .name                   = "irq/affinity:online",
                .startup.single         = irq_affinity_online_cpu,
                .teardown.single        = NULL,
        },
        [CPUHP_AP_PERF_ONLINE] = {
                .name                   = "perf:online",
                .startup.single         = perf_event_init_cpu,
                .teardown.single        = perf_event_exit_cpu,
        },
        [CPUHP_AP_WATCHDOG_ONLINE] = {
                .name                   = "lockup_detector:online",
                .startup.single         = lockup_detector_online_cpu,
                .teardown.single        = lockup_detector_offline_cpu,
        },
        [CPUHP_AP_WORKQUEUE_ONLINE] = {
                .name                   = "workqueue:online",
                .startup.single         = workqueue_online_cpu,
                .teardown.single        = workqueue_offline_cpu,
        },
        [CPUHP_AP_RCUTREE_ONLINE] = {
                .name                   = "RCU/tree:online",
                .startup.single         = rcutree_online_cpu,
                .teardown.single        = rcutree_offline_cpu,
        },
#endif
        /*
         * The dynamically registered state space is here
         */

#ifdef CONFIG_SMP
        /* Last state is scheduler control setting the cpu active */
        [CPUHP_AP_ACTIVE] = {
                .name                   = "sched:active",
                .startup.single         = sched_cpu_activate,
                .teardown.single        = sched_cpu_deactivate,
        },
#endif

        /* CPU is fully up and running. */
        [CPUHP_ONLINE] = {
                .name                   = "online",
                .startup.single         = NULL,
                .teardown.single        = NULL,
        },
};

/* Sanity check for callbacks */
static int cpuhp_cb_check(enum cpuhp_state state)
{
        if (state <= CPUHP_OFFLINE || state >= CPUHP_ONLINE)
                return -EINVAL;
        return 0;
}

/*
 * Returns a free for dynamic slot assignment of the Online state. The states
 * are protected by the cpuhp_slot_states mutex and an empty slot is identified
 * by having no name assigned.
 */
static int cpuhp_reserve_state(enum cpuhp_state state)
{
        enum cpuhp_state i, end;
        struct cpuhp_step *step;

        switch (state) {
        case CPUHP_AP_ONLINE_DYN:
                step = cpuhp_hp_states + CPUHP_AP_ONLINE_DYN;
                end = CPUHP_AP_ONLINE_DYN_END;
                break;
        case CPUHP_BP_PREPARE_DYN:
                step = cpuhp_hp_states + CPUHP_BP_PREPARE_DYN;
                end = CPUHP_BP_PREPARE_DYN_END;
                break;
        default:
                return -EINVAL;
        }

        for (i = state; i <= end; i++, step++) {
                if (!step->name)
                        return i;
        }
        WARN(1, "No more dynamic states available for CPU hotplug\n");
        return -ENOSPC;
}

static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
                                 int (*startup)(unsigned int cpu),
                                 int (*teardown)(unsigned int cpu),
                                 bool multi_instance)
{
        /* (Un)Install the callbacks for further cpu hotplug operations */
        struct cpuhp_step *sp;
        int ret = 0;

        /*
         * If name is NULL, then the state gets removed.
         *
         * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
         * the first allocation from these dynamic ranges, so the removal
         * would trigger a new allocation and clear the wrong (already
         * empty) state, leaving the callbacks of the to be cleared state
         * dangling, which causes wreckage on the next hotplug operation.
         */
        if (name && (state == CPUHP_AP_ONLINE_DYN ||
                     state == CPUHP_BP_PREPARE_DYN)) {
                ret = cpuhp_reserve_state(state);
                if (ret < 0)
                        return ret;
                state = ret;
        }
        sp = cpuhp_get_step(state);
        if (name && sp->name)
                return -EBUSY;

        sp->startup.single = startup;
        sp->teardown.single = teardown;
        sp->name = name;
        sp->multi_instance = multi_instance;
        INIT_HLIST_HEAD(&sp->list);
        return ret;
}

static void *cpuhp_get_teardown_cb(enum cpuhp_state state)
{
        return cpuhp_get_step(state)->teardown.single;
}

/*
 * Call the startup/teardown function for a step either on the AP or
 * on the current CPU.
 */
static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup,
                            struct hlist_node *node)
{
        struct cpuhp_step *sp = cpuhp_get_step(state);
        int ret;

        /*
         * If there's nothing to do, we done.
         * Relies on the union for multi_instance.
         */
        if ((bringup && !sp->startup.single) ||
            (!bringup && !sp->teardown.single))
                return 0;
        /*
         * The non AP bound callbacks can fail on bringup. On teardown
         * e.g. module removal we crash for now.
         */
#ifdef CONFIG_SMP
        if (cpuhp_is_ap_state(state))
                ret = cpuhp_invoke_ap_callback(cpu, state, bringup, node);
        else
                ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
#else
        ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
#endif
        BUG_ON(ret && !bringup);
        return ret;
}

/*
 * Called from __cpuhp_setup_state on a recoverable failure.
 *
 * Note: The teardown callbacks for rollback are not allowed to fail!
 */
static void cpuhp_rollback_install(int failedcpu, enum cpuhp_state state,
                                   struct hlist_node *node)
{
        int cpu;

        /* Roll back the already executed steps on the other cpus */
        for_each_present_cpu(cpu) {
                struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                int cpustate = st->state;

                if (cpu >= failedcpu)
                        break;

                /* Did we invoke the startup call on that cpu ? */
                if (cpustate >= state)
                        cpuhp_issue_call(cpu, state, false, node);
        }
}

int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
                                          struct hlist_node *node,
                                          bool invoke)
{
        struct cpuhp_step *sp;
        int cpu;
        int ret;

        lockdep_assert_cpus_held();

        sp = cpuhp_get_step(state);
        if (sp->multi_instance == false)
                return -EINVAL;

        mutex_lock(&cpuhp_state_mutex);

        if (!invoke || !sp->startup.multi)
                goto add_node;

        /*
         * Try to call the startup callback for each present cpu
         * depending on the hotplug state of the cpu.
         */
        for_each_present_cpu(cpu) {
                struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                int cpustate = st->state;

                if (cpustate < state)
                        continue;

                ret = cpuhp_issue_call(cpu, state, true, node);
                if (ret) {
                        if (sp->teardown.multi)
                                cpuhp_rollback_install(cpu, state, node);
                        goto unlock;
                }
        }
add_node:
        ret = 0;
        hlist_add_head(node, &sp->list);
unlock:
        mutex_unlock(&cpuhp_state_mutex);
        return ret;
}

int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
                               bool invoke)
{
        int ret;

        cpus_read_lock();
        ret = __cpuhp_state_add_instance_cpuslocked(state, node, invoke);
        cpus_read_unlock();
        return ret;
}
EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);

/**
 * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
 * @state:              The state to setup
 * @invoke:             If true, the startup function is invoked for cpus where
 *                      cpu state >= @state
 * @startup:            startup callback function
 * @teardown:           teardown callback function
 * @multi_instance:     State is set up for multiple instances which get
 *                      added afterwards.
 *
 * The caller needs to hold cpus read locked while calling this function.
 * Returns:
 *   On success:
 *      Positive state number if @state is CPUHP_AP_ONLINE_DYN
 *      0 for all other states
 *   On failure: proper (negative) error code
 */
int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
                                   const char *name, bool invoke,
                                   int (*startup)(unsigned int cpu),
                                   int (*teardown)(unsigned int cpu),
                                   bool multi_instance)
{
        int cpu, ret = 0;
        bool dynstate;

        lockdep_assert_cpus_held();

        if (cpuhp_cb_check(state) || !name)
                return -EINVAL;

        mutex_lock(&cpuhp_state_mutex);

        ret = cpuhp_store_callbacks(state, name, startup, teardown,
                                    multi_instance);

        dynstate = state == CPUHP_AP_ONLINE_DYN;
        if (ret > 0 && dynstate) {
                state = ret;
                ret = 0;
        }

        if (ret || !invoke || !startup)
                goto out;

        /*
         * Try to call the startup callback for each present cpu
         * depending on the hotplug state of the cpu.
         */
        for_each_present_cpu(cpu) {
                struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                int cpustate = st->state;

                if (cpustate < state)
                        continue;

                ret = cpuhp_issue_call(cpu, state, true, NULL);
                if (ret) {
                        if (teardown)
                                cpuhp_rollback_install(cpu, state, NULL);
                        cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
                        goto out;
                }
        }
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 (!ret && dynstate)
                return state;
        return ret;
}
EXPORT_SYMBOL(__cpuhp_setup_state_cpuslocked);

int __cpuhp_setup_state(enum cpuhp_state state,
                        const char *name, bool invoke,
                        int (*startup)(unsigned int cpu),
                        int (*teardown)(unsigned int cpu),
                        bool multi_instance)
{
        int ret;

        cpus_read_lock();
        ret = __cpuhp_setup_state_cpuslocked(state, name, invoke, startup,
                                             teardown, multi_instance);
        cpus_read_unlock();
        return ret;
}
EXPORT_SYMBOL(__cpuhp_setup_state);

int __cpuhp_state_remove_instance(enum cpuhp_state state,
                                  struct hlist_node *node, bool invoke)
{
        struct cpuhp_step *sp = cpuhp_get_step(state);
        int cpu;

        BUG_ON(cpuhp_cb_check(state));

        if (!sp->multi_instance)
                return -EINVAL;

        cpus_read_lock();
        mutex_lock(&cpuhp_state_mutex);

        if (!invoke || !cpuhp_get_teardown_cb(state))
                goto remove;
        /*
         * Call the teardown callback for each present cpu depending
         * on the hotplug state of the cpu. This function is not
         * allowed to fail currently!
         */
        for_each_present_cpu(cpu) {
                struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                int cpustate = st->state;

                if (cpustate >= state)
                        cpuhp_issue_call(cpu, state, false, node);
        }

remove:
        hlist_del(node);
        mutex_unlock(&cpuhp_state_mutex);
        cpus_read_unlock();

        return 0;
}
EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);

/**
 * __cpuhp_remove_state_cpuslocked - Remove the callbacks for an hotplug machine state
 * @state:      The state to remove
 * @invoke:     If true, the teardown function is invoked for cpus where
 *              cpu state >= @state
 *
 * The caller needs to hold cpus read locked while calling this function.
 * The teardown callback is currently not allowed to fail. Think
 * about module removal!
 */
void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke)
{
        struct cpuhp_step *sp = cpuhp_get_step(state);
        int cpu;

        BUG_ON(cpuhp_cb_check(state));

        lockdep_assert_cpus_held();

        mutex_lock(&cpuhp_state_mutex);
        if (sp->multi_instance) {
                WARN(!hlist_empty(&sp->list),
                     "Error: Removing state %d which has instances left.\n",
                     state);
                goto remove;
        }

        if (!invoke || !cpuhp_get_teardown_cb(state))
                goto remove;

        /*
         * Call the teardown callback for each present cpu depending
         * on the hotplug state of the cpu. This function is not
         * allowed to fail currently!
         */
        for_each_present_cpu(cpu) {
                struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
                int cpustate = st->state;

                if (cpustate >= state)
                        cpuhp_issue_call(cpu, state, false, NULL);
        }
remove:
        cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
        mutex_unlock(&cpuhp_state_mutex);
}
EXPORT_SYMBOL(__cpuhp_remove_state_cpuslocked);

void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
{
        cpus_read_lock();
        __cpuhp_remove_state_cpuslocked(state, invoke);
        cpus_read_unlock();
}
EXPORT_SYMBOL(__cpuhp_remove_state);

#if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
static ssize_t show_cpuhp_state(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);

        return sprintf(buf, "%d\n", st->state);
}
static DEVICE_ATTR(state, 0444, show_cpuhp_state, NULL);

static ssize_t write_cpuhp_target(struct device *dev,
                                  struct device_attribute *attr,
                                  const char *buf, size_t count)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
        struct cpuhp_step *sp;
        int target, ret;

        ret = kstrtoint(buf, 10, &target);
        if (ret)
                return ret;

#ifdef CONFIG_CPU_HOTPLUG_STATE_CONTROL
        if (target < CPUHP_OFFLINE || target > CPUHP_ONLINE)
                return -EINVAL;
#else
        if (target != CPUHP_OFFLINE && target != CPUHP_ONLINE)
                return -EINVAL;
#endif

        ret = lock_device_hotplug_sysfs();
        if (ret)
                return ret;

        mutex_lock(&cpuhp_state_mutex);
        sp = cpuhp_get_step(target);
        ret = !sp->name || sp->cant_stop ? -EINVAL : 0;
        mutex_unlock(&cpuhp_state_mutex);
        if (ret)
                goto out;

        if (st->state < target)
                ret = do_cpu_up(dev->id, target);
        else
                ret = do_cpu_down(dev->id, target);
out:
        unlock_device_hotplug();
        return ret ? ret : count;
}

static ssize_t show_cpuhp_target(struct device *dev,
                                 struct device_attribute *attr, char *buf)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);

        return sprintf(buf, "%d\n", st->target);
}
static DEVICE_ATTR(target, 0644, show_cpuhp_target, write_cpuhp_target);


static ssize_t write_cpuhp_fail(struct device *dev,
                                struct device_attribute *attr,
                                const char *buf, size_t count)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
        struct cpuhp_step *sp;
        int fail, ret;

        ret = kstrtoint(buf, 10, &fail);
        if (ret)
                return ret;

        if (fail < CPUHP_OFFLINE || fail > CPUHP_ONLINE)
                return -EINVAL;

        /*
         * Cannot fail STARTING/DYING callbacks.
         */
        if (cpuhp_is_atomic_state(fail))
                return -EINVAL;

        /*
         * Cannot fail anything that doesn't have callbacks.
         */
        mutex_lock(&cpuhp_state_mutex);
        sp = cpuhp_get_step(fail);
        if (!sp->startup.single && !sp->teardown.single)
                ret = -EINVAL;
        mutex_unlock(&cpuhp_state_mutex);
        if (ret)
                return ret;

        st->fail = fail;

        return count;
}

static ssize_t show_cpuhp_fail(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);

        return sprintf(buf, "%d\n", st->fail);
}

static DEVICE_ATTR(fail, 0644, show_cpuhp_fail, write_cpuhp_fail);

static struct attribute *cpuhp_cpu_attrs[] = {
        &dev_attr_state.attr,
        &dev_attr_target.attr,
        &dev_attr_fail.attr,
        NULL
};

static const struct attribute_group cpuhp_cpu_attr_group = {
        .attrs = cpuhp_cpu_attrs,
        .name = "hotplug",
        NULL
};

static ssize_t show_cpuhp_states(struct device *dev,
                                 struct device_attribute *attr, char *buf)
{
        ssize_t cur, res = 0;
        int i;

        mutex_lock(&cpuhp_state_mutex);
        for (i = CPUHP_OFFLINE; i <= CPUHP_ONLINE; i++) {
                struct cpuhp_step *sp = cpuhp_get_step(i);

                if (sp->name) {
                        cur = sprintf(buf, "%3d: %s\n", i, sp->name);
                        buf += cur;
                        res += cur;
                }
        }
        mutex_unlock(&cpuhp_state_mutex);
        return res;
}
static DEVICE_ATTR(states, 0444, show_cpuhp_states, NULL);

static struct attribute *cpuhp_cpu_root_attrs[] = {
        &dev_attr_states.attr,
        NULL
};

static const struct attribute_group cpuhp_cpu_root_attr_group = {
        .attrs = cpuhp_cpu_root_attrs,
        .name = "hotplug",
        NULL
};

#ifdef CONFIG_HOTPLUG_SMT

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;
        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;
        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;
}

#else /* !CONFIG_HOTPLUG_SMT */
static ssize_t
__store_smt_control(struct device *dev, struct device_attribute *attr,
                    const char *buf, size_t count)
{
        return -ENODEV;
}
#endif /* 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",
        [CPU_SMT_NOT_IMPLEMENTED]       = "notimplemented",
};

static ssize_t
show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
{
        const char *state = smt_states[cpu_smt_control];

        return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
}

static ssize_t
store_smt_control(struct device *dev, struct device_attribute *attr,
                  const char *buf, size_t count)
{
        return __store_smt_control(dev, attr, buf, 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)
{
        return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_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_sysfs_init(void)
{
        return sysfs_create_group(&cpu_subsys.dev_root->kobj,
                                  &cpuhp_smt_attr_group);
}

static int __init cpuhp_sysfs_init(void)
{
        int cpu, ret;

        ret = cpu_smt_sysfs_init();
        if (ret)
                return ret;

        ret = sysfs_create_group(&cpu_subsys.dev_root->kobj,
                                 &cpuhp_cpu_root_attr_group);
        if (ret)
                return ret;

        for_each_possible_cpu(cpu) {
                struct device *dev = get_cpu_device(cpu);

                if (!dev)
                        continue;
                ret = sysfs_create_group(&dev->kobj, &cpuhp_cpu_attr_group);
                if (ret)
                        return ret;
        }
        return 0;
}
device_initcall(cpuhp_sysfs_init);
#endif /* CONFIG_SYSFS && CONFIG_HOTPLUG_CPU */

/*
 * cpu_bit_bitmap[] is a special, "compressed" data structure that
 * represents all NR_CPUS bits binary values of 1<<nr.
 *
 * It is used by cpumask_of() to get a constant address to a CPU
 * mask value that has a single bit set only.
 */

/* cpu_bit_bitmap[0] is empty - so we can back into it */
#define MASK_DECLARE_1(x)       [x+1][0] = (1UL << (x))
#define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
#define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
#define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)

const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {

        MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
        MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
#if BITS_PER_LONG > 32
        MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
        MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
#endif
};
EXPORT_SYMBOL_GPL(cpu_bit_bitmap);

const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
EXPORT_SYMBOL(cpu_all_bits);

#ifdef CONFIG_INIT_ALL_POSSIBLE
struct cpumask __cpu_possible_mask __read_mostly
        = {CPU_BITS_ALL};
#else
struct cpumask __cpu_possible_mask __read_mostly;
#endif
EXPORT_SYMBOL(__cpu_possible_mask);

struct cpumask __cpu_online_mask __read_mostly;
EXPORT_SYMBOL(__cpu_online_mask);

struct cpumask __cpu_present_mask __read_mostly;
EXPORT_SYMBOL(__cpu_present_mask);

struct cpumask __cpu_active_mask __read_mostly;
EXPORT_SYMBOL(__cpu_active_mask);

atomic_t __num_online_cpus __read_mostly;
EXPORT_SYMBOL(__num_online_cpus);

void init_cpu_present(const struct cpumask *src)
{
        cpumask_copy(&__cpu_present_mask, src);
}

void init_cpu_possible(const struct cpumask *src)
{
        cpumask_copy(&__cpu_possible_mask, src);
}

void init_cpu_online(const struct cpumask *src)
{
        cpumask_copy(&__cpu_online_mask, src);
}

void set_cpu_online(unsigned int cpu, bool online)
{
        /*
         * atomic_inc/dec() is required to handle the horrid abuse of this
         * function by the reboot and kexec code which invoke it from
         * IPI/NMI broadcasts when shutting down CPUs. Invocation from
         * regular CPU hotplug is properly serialized.
         *
         * Note, that the fact that __num_online_cpus is of type atomic_t
         * does not protect readers which are not serialized against
         * concurrent hotplug operations.
         */
        if (online) {
                if (!cpumask_test_and_set_cpu(cpu, &__cpu_online_mask))
                        atomic_inc(&__num_online_cpus);
        } else {
                if (cpumask_test_and_clear_cpu(cpu, &__cpu_online_mask))
                        atomic_dec(&__num_online_cpus);
        }
}

/*
 * Activate the first processor.
 */
void __init boot_cpu_init(void)
{
        int cpu = smp_processor_id();

        /* Mark the boot cpu "present", "online" etc for SMP and UP case */
        set_cpu_online(cpu, true);
        set_cpu_active(cpu, true);
        set_cpu_present(cpu, true);
        set_cpu_possible(cpu, true);

#ifdef CONFIG_SMP
        __boot_cpu_id = cpu;
#endif
}

/*
 * Must be called _AFTER_ setting up the per_cpu areas
 */
void __init boot_cpu_hotplug_init(void)
{
#ifdef CONFIG_SMP
        cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
#endif
        this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
}

/*
 * These are used for a global "mitigations=" cmdline option for toggling
 * optional CPU mitigations.
 */
enum cpu_mitigations {
        CPU_MITIGATIONS_OFF,
        CPU_MITIGATIONS_AUTO,
        CPU_MITIGATIONS_AUTO_NOSMT,
};

static enum cpu_mitigations cpu_mitigations __ro_after_init =
        CPU_MITIGATIONS_AUTO;

static int __init mitigations_parse_cmdline(char *arg)
{
        if (!strcmp(arg, "off"))
                cpu_mitigations = CPU_MITIGATIONS_OFF;
        else if (!strcmp(arg, "auto"))
                cpu_mitigations = CPU_MITIGATIONS_AUTO;
        else if (!strcmp(arg, "auto,nosmt"))
                cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT;
        else
                pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n",
                        arg);

        return 0;
}
early_param("mitigations", mitigations_parse_cmdline);

/* mitigations=off */
bool cpu_mitigations_off(void)
{
        return cpu_mitigations == CPU_MITIGATIONS_OFF;
}
EXPORT_SYMBOL_GPL(cpu_mitigations_off);

/* mitigations=auto,nosmt */
bool cpu_mitigations_auto_nosmt(void)
{
        return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
}
EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt);