* (C) 2001, 2002, 2003, 2004 Rusty Russell
*
* This code is licenced under the GPL.
*/
#include <linux/sched/mm.h>
#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/scs.h>
#include <linux/percpu-rwsem.h>
#include <linux/cpuset.h>
#include <linux/random.h>
#include <trace/events/power.h>
#define CREATE_TRACE_POINTS
#include <trace/events/cpuhp.h>
#undef CREATE_TRACE_POINTS
#include "smpboot.h"
#define CPU_PAGE_SIZE_OFF_TWO 2
* 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;
}
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;
}
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:
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;
}
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);
}
EXPORT_SYMBOL_GPL(cpu_maps_update_begin);
void cpu_maps_update_done(void)
{
mutex_unlock(&cpu_add_remove_lock);
}
EXPORT_SYMBOL_GPL(cpu_maps_update_done);
* 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.dep_map, 0, 0, _THIS_IP_);
}
static void lockdep_release_cpus_lock(void)
{
rwsem_release(&cpu_hotplug_lock.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
* 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 broadcasted MCE observing CR4.MCE=0b on any
* core will shutdown the machine.
*/
return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
}
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;
}
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_ap_thread(st, true);
if (WARN_ON_ONCE((!cpu_online(cpu)))) {
return -ECANCELED;
}
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;
* Reset stale stack state from the last time this CPU was online.
*/
scs_task_reset(idle);
kasan_unpoison_task_stack(idle);
* 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();
ret = __cpu_up(cpu, idle);
irq_unlock_sparse();
if (ret) {
return ret;
}
return bringup_wait_for_ap(cpu);
}
static int finish_cpu(unsigned int cpu)
{
struct task_struct *idle = idle_thread_get(cpu);
struct mm_struct *mm = idle->active_mm;
* idle_task_exit() will have switched to &init_mm, now
* clean up any remaining active_mm state.
*/
if (mm != &init_mm) {
idle->active_mm = &init_mm;
}
mmdrop(mm);
return 0;
}
* 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);
}
}
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));
}
*
* Serialize hotplug trainwrecks outside of the cpu_hotplug_lock
* protected region.
*
* The operation is still serialized against concurrent CPU hotplug via
* cpu_add_remove_lock, i.e. CPU map protection. But it is _not_
* serialized against other hotplug related activity like adding or
* removing of state callbacks and state instances, which invoke either the
* startup or the teardown callback of the affected state.
*
* This is required for subsystems which are unfixable vs. CPU hotplug and
* evade lock inversion problems by scheduling work which has to be
* completed _before_ cpu_up()/_cpu_down() returns.
*
* Don't even think about adding anything to this for any new code or even
* drivers. It's only purpose is to keep existing lock order trainwrecks
* working.
*
* For cpu_down() there might be valid reasons to finish cleanups which are
* not required to be done under cpu_hotplug_lock, but that's a different
* story and would be not invoked via this.
*/
static void cpu_up_down_serialize_trainwrecks(bool tasks_frozen)
{
* cpusets delegate hotplug operations to a worker to "solve" the
* lock order problems. Wait for the worker, but only if tasks are
* _not_ frozen (suspend, hibernate) as that would wait forever.
*
* The wait is required because otherwise the hotplug operation
* returns with inconsistent state, which could even be observed in
* user space when a new CPU is brought up. The CPU plug uevent
* would be delivered and user space reacting on it would fail to
* move tasks to the newly plugged CPU up to the point where the
* work has finished because up to that point the newly plugged CPU
* is not assignable in cpusets/cgroups. On unplug that's not
* necessarily a visible issue, but it is still inconsistent state,
* which is the real problem which needs to be "fixed". This can't
* prevent the transient state between scheduling the work and
* returning from waiting for it.
*/
if (!tasks_frozen) {
cpuset_wait_for_hotplug();
}
}
#ifdef CONFIG_HOTPLUG_CPU
#ifndef arch_clear_mm_cpumask_cpu
#define arch_clear_mm_cpumask_cpu(cpu, mm) cpumask_clear_cpu(cpu, mm_cpumask(mm))
#endif
* 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;
}
arch_clear_mm_cpumask_cpu(cpu, t->mm);
task_unlock(t);
}
rcu_read_unlock();
}
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;
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--;
for (; st->state > target; st->state--) {
ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
* DYING must not fail!
*/
WARN_ON_ONCE(ret);
}
tick_handover_do_timer();
tick_offline_cpu(cpu);
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;
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) {
irq_unlock_sparse();
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);
irq_unlock_sparse();
hotplug_cpu__broadcast_tick_pull(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;
}
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_active_cpus() == 1 && cpu_active(cpu)) {
return -EBUSY;
}
if (!cpu_present(cpu)) {
return -EINVAL;
}
#ifdef CONFIG_CPU_ISOLATION_OPT
if (!tasks_frozen && !cpu_isolated(cpu) && num_online_uniso_cpus() == 1) {
return -EBUSY;
}
#endif
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();
cpu_up_down_serialize_trainwrecks(tasks_frozen);
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 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;
}
* cpu_device_down - Bring down a cpu device
* @dev: Pointer to the cpu device to offline
*
* This function is meant to be used by device core cpu subsystem only.
*
* Other subsystems should use remove_cpu() instead.
*/
int cpu_device_down(struct device *dev)
{
return cpu_down(dev->id, CPUHP_OFFLINE);
}
int remove_cpu(unsigned int cpu)
{
int ret;
lock_device_hotplug();
ret = device_offline(get_cpu_device(cpu));
unlock_device_hotplug();
return ret;
}
EXPORT_SYMBOL_GPL(remove_cpu);
void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
{
unsigned int cpu;
int error;
cpu_maps_update_begin();
* Make certain the cpu I'm about to reboot on is online.
*
* This is inline to what migrate_to_reboot_cpu() already do.
*/
if (!cpu_online(primary_cpu)) {
primary_cpu = cpumask_first(cpu_online_mask);
}
for_each_online_cpu(cpu)
{
if (cpu == primary_cpu) {
continue;
}
error = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
if (error) {
pr_err("Failed to offline CPU%d - error=%d", cpu, error);
break;
}
}
* Ensure all but the reboot CPU are offline.
*/
BUG_ON(num_online_cpus() > 1);
* Make sure the CPUs won't be enabled by someone else after this
* point. Kexec will reboot to a new kernel shortly resetting
* everything along the way.
*/
cpu_hotplug_disabled++;
cpu_maps_update_done();
}
#else
#define takedown_cpu NULL
#endif
* 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);
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
* 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);
if (state != CPUHP_AP_ONLINE_IDLE) {
return;
}
* Unpart the stopper thread before we start the idle loop (and start
* scheduling); this ensures the stopper task is always available.
*/
stop_machine_unpark(smp_processor_id());
st->state = CPUHP_AP_ONLINE_IDLE;
complete_ap_thread(st, true);
}
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 cpu_up() might have raced with another
* caller. Nothing to do.
*/
if (st->state >= target) {
goto out;
}
if (st->state == CPUHP_OFFLINE) {
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();
cpu_up_down_serialize_trainwrecks(tasks_frozen);
return ret;
}
static int 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;
}
* cpu_device_up - Bring up a cpu device
* @dev: Pointer to the cpu device to online
*
* This function is meant to be used by device core cpu subsystem only.
*
* Other subsystems should use add_cpu() instead.
*/
int cpu_device_up(struct device *dev)
{
return cpu_up(dev->id, CPUHP_ONLINE);
}
int add_cpu(unsigned int cpu)
{
int ret;
lock_device_hotplug();
ret = device_online(get_cpu_device(cpu));
unlock_device_hotplug();
return ret;
}
EXPORT_SYMBOL_GPL(add_cpu);
* bringup_hibernate_cpu - Bring up the CPU that we hibernated on
* @sleep_cpu: The cpu we hibernated on and should be brought up.
*
* On some architectures like arm64, we can hibernate on any CPU, but on
* wake up the CPU we hibernated on might be offline as a side effect of
* using maxcpus= for example.
*/
int bringup_hibernate_cpu(unsigned int sleep_cpu)
{
int ret;
if (!cpu_online(sleep_cpu)) {
pr_info("Hibernated on a CPU that is offline! Bringing CPU up.\n");
ret = cpu_up(sleep_cpu, CPUHP_ONLINE);
if (ret) {
pr_err("Failed to bring hibernate-CPU up!\n");
return ret;
}
}
return 0;
}
void bringup_nonboot_cpus(unsigned int setup_max_cpus)
{
unsigned int cpu;
for_each_present_cpu(cpu)
{
if (num_online_cpus() >= setup_max_cpus) {
break;
}
if (!cpu_online(cpu)) {
cpu_up(cpu, CPUHP_ONLINE);
}
}
}
#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 freeze_secondary_cpus() users are
* supposed to do thaw_secondary_cpus() on the failure path.
*/
cpu_hotplug_disabled++;
cpu_maps_update_done();
return error;
}
void __weak arch_thaw_secondary_cpus_begin(void)
{
}
void __weak arch_thaw_secondary_cpus_end(void)
{
}
void thaw_secondary_cpus(void)
{
int cpu, error;
cpu_maps_update_begin();
_cpu_hotplug_enable();
if (cpumask_empty(frozen_cpus)) {
goto out;
}
pr_info("Enabling non-boot CPUs ...\n");
arch_thaw_secondary_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_thaw_secondary_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
int __boot_cpu_id;
#endif
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_RANDOM_PREPARE] = {
.name = "random:prepare",
.startup.single = random_prepare_cpu,
.teardown.single = NULL,
},
[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,
},
[CPUHP_BRINGUP_CPU] =
{
.name = "cpu:bringup",
.startup.single = bringup_cpu,
.teardown.single = finish_cpu,
.cant_stop = true,
},
[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,
},
[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,
},
* 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,
},
[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_RANDOM_ONLINE] = {
.name = "random:online",
.startup.single = random_online_cpu,
.teardown.single = NULL,
},
[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
[CPUHP_AP_ACTIVE] =
{
.name = "sched:active",
.startup.single = sched_cpu_activate,
.teardown.single = sched_cpu_deactivate,
},
#endif
[CPUHP_ONLINE] =
{
.name = "online",
.startup.single = NULL,
.teardown.single = NULL,
},
};
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)
{
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;
for_each_present_cpu(cpu)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
int cpustate = st->state;
if (cpu >= failedcpu) {
break;
}
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);
#ifdef CONFIG_HOTPLUG_SMT
static void cpuhp_offline_cpu_device(unsigned int cpu)
{
struct device *dev = get_cpu_device(cpu);
dev->offline = true;
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;
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)
{
if (cpu_online(cpu) || !node_online(cpu_to_node(cpu))) {
continue;
}
ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
if (ret) {
break;
}
cpuhp_online_cpu_device(cpu);
}
cpu_maps_update_done();
return ret;
}
#endif
#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 = cpu_up(dev->id, target);
} else {
ret = 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 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
static ssize_t _store_smt_control(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
return -ENODEV;
}
#endif
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 - CPU_PAGE_SIZE_OFF_TWO, "%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 - CPU_PAGE_SIZE_OFF_TWO, "%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
* 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.
*/
#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);
#ifdef CONFIG_CPU_ISOLATION_OPT
struct cpumask __cpu_isolated_mask __read_mostly;
EXPORT_SYMBOL(__cpu_isolated_mask);
#endif
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);
}
#ifdef CONFIG_CPU_ISOLATION_OPT
void init_cpu_isolated(const struct cpumask *src)
{
cpumask_copy(&__cpu_isolated_mask, src);
}
#endif
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();
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);
bool cpu_mitigations_off(void)
{
return cpu_mitigations == CPU_MITIGATIONS_OFF;
}
EXPORT_SYMBOL_GPL(cpu_mitigations_off);
bool cpu_mitigations_auto_nosmt(void)
{
return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
}
EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt);