text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   *  linux/arch/arm/kernel/smp.c
   *
   *  Copyright (C) 2002 ARM Limited, All Rights Reserved.
   */
  #include <linux/module.h>
  #include <linux/delay.h>
  #include <linux/init.h>
  #include <linux/spinlock.h>
  #include <linux/sched/mm.h>
  #include <linux/sched/hotplug.h>
  #include <linux/sched/task_stack.h>
  #include <linux/interrupt.h>
  #include <linux/cache.h>
  #include <linux/profile.h>
  #include <linux/errno.h>
  #include <linux/mm.h>
  #include <linux/err.h>
  #include <linux/cpu.h>
  #include <linux/seq_file.h>
  #include <linux/irq.h>
  #include <linux/nmi.h>
  #include <linux/percpu.h>
  #include <linux/clockchips.h>
  #include <linux/completion.h>
  #include <linux/cpufreq.h>
  #include <linux/irq_work.h>
  #include <linux/kernel_stat.h>
  
  #include <linux/atomic.h>
  #include <asm/bugs.h>
  #include <asm/smp.h>
  #include <asm/cacheflush.h>
  #include <asm/cpu.h>
  #include <asm/cputype.h>
  #include <asm/exception.h>
  #include <asm/idmap.h>
  #include <asm/topology.h>
  #include <asm/mmu_context.h>
  #include <asm/procinfo.h>
  #include <asm/processor.h>
  #include <asm/sections.h>
  #include <asm/tlbflush.h>
  #include <asm/ptrace.h>
  #include <asm/smp_plat.h>
  #include <asm/virt.h>
  #include <asm/mach/arch.h>
  #include <asm/mpu.h>
  
  #define CREATE_TRACE_POINTS
  #include <trace/events/ipi.h>
  
  /*
   * as from 2.5, kernels no longer have an init_tasks structure
   * so we need some other way of telling a new secondary core
   * where to place its SVC stack
   */
  struct secondary_data secondary_data;
  
  enum ipi_msg_type {
  	IPI_WAKEUP,
  	IPI_TIMER,
  	IPI_RESCHEDULE,
  	IPI_CALL_FUNC,
  	IPI_CPU_STOP,
  	IPI_IRQ_WORK,
  	IPI_COMPLETION,
  	NR_IPI,
  	/*
  	 * CPU_BACKTRACE is special and not included in NR_IPI
  	 * or tracable with trace_ipi_*
  	 */
  	IPI_CPU_BACKTRACE = NR_IPI,
  	/*
  	 * SGI8-15 can be reserved by secure firmware, and thus may
  	 * not be usable by the kernel. Please keep the above limited
  	 * to at most 8 entries.
  	 */
  	MAX_IPI
  };
  
  static int ipi_irq_base __read_mostly;
  static int nr_ipi __read_mostly = NR_IPI;
  static struct irq_desc *ipi_desc[MAX_IPI] __read_mostly;
  
  static void ipi_setup(int cpu);
  
  static DECLARE_COMPLETION(cpu_running);
  
  static struct smp_operations smp_ops __ro_after_init;
  
  void __init smp_set_ops(const struct smp_operations *ops)
  {
  	if (ops)
  		smp_ops = *ops;
  };
  
  static unsigned long get_arch_pgd(pgd_t *pgd)
  {
  #ifdef CONFIG_ARM_LPAE
  	return __phys_to_pfn(virt_to_phys(pgd));
  #else
  	return virt_to_phys(pgd);
  #endif
  }
  
  #if defined(CONFIG_BIG_LITTLE) && defined(CONFIG_HARDEN_BRANCH_PREDICTOR)
  static int secondary_biglittle_prepare(unsigned int cpu)
  {
  	if (!cpu_vtable[cpu])
  		cpu_vtable[cpu] = kzalloc(sizeof(*cpu_vtable[cpu]), GFP_KERNEL);
  
  	return cpu_vtable[cpu] ? 0 : -ENOMEM;
  }
  
  static void secondary_biglittle_init(void)
  {
  	init_proc_vtable(lookup_processor(read_cpuid_id())->proc);
  }
  #else
  static int secondary_biglittle_prepare(unsigned int cpu)
  {
  	return 0;
  }
  
  static void secondary_biglittle_init(void)
  {
  }
  #endif
  
  int __cpu_up(unsigned int cpu, struct task_struct *idle)
  {
  	int ret;
  
  	if (!smp_ops.smp_boot_secondary)
  		return -ENOSYS;
  
  	ret = secondary_biglittle_prepare(cpu);
  	if (ret)
  		return ret;
  
  	/*
  	 * We need to tell the secondary core where to find
  	 * its stack and the page tables.
  	 */
  	secondary_data.stack = task_stack_page(idle) + THREAD_START_SP;
  #ifdef CONFIG_ARM_MPU
  	secondary_data.mpu_rgn_info = &mpu_rgn_info;
  #endif
  
  #ifdef CONFIG_MMU
  	secondary_data.pgdir = virt_to_phys(idmap_pgd);
  	secondary_data.swapper_pg_dir = get_arch_pgd(swapper_pg_dir);
  #endif
  	secondary_data.task = idle;
  	if (IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK))
  		task_thread_info(idle)->cpu = cpu;
  
  	sync_cache_w(&secondary_data);
  
  	/*
  	 * Now bring the CPU into our world.
  	 */
  	ret = smp_ops.smp_boot_secondary(cpu, idle);
  	if (ret == 0) {
  		/*
  		 * CPU was successfully started, wait for it
  		 * to come online or time out.
  		 */
  		wait_for_completion_timeout(&cpu_running,
  						 msecs_to_jiffies(1000));
  
  		if (!cpu_online(cpu)) {
  			pr_crit("CPU%u: failed to come online\n", cpu);
  			ret = -EIO;
  		}
  	} else {
  		pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
  	}
  
  
  	memset(&secondary_data, 0, sizeof(secondary_data));
  	return ret;
  }
  
  /* platform specific SMP operations */
  void __init smp_init_cpus(void)
  {
  	if (smp_ops.smp_init_cpus)
  		smp_ops.smp_init_cpus();
  }
  
  int platform_can_secondary_boot(void)
  {
  	return !!smp_ops.smp_boot_secondary;
  }
  
  int platform_can_cpu_hotplug(void)
  {
  #ifdef CONFIG_HOTPLUG_CPU
  	if (smp_ops.cpu_kill)
  		return 1;
  #endif
  
  	return 0;
  }
  
  #ifdef CONFIG_HOTPLUG_CPU
  static int platform_cpu_kill(unsigned int cpu)
  {
  	if (smp_ops.cpu_kill)
  		return smp_ops.cpu_kill(cpu);
  	return 1;
  }
  
  static int platform_cpu_disable(unsigned int cpu)
  {
  	if (smp_ops.cpu_disable)
  		return smp_ops.cpu_disable(cpu);
  
  	return 0;
  }
  
  int platform_can_hotplug_cpu(unsigned int cpu)
  {
  	/* cpu_die must be specified to support hotplug */
  	if (!smp_ops.cpu_die)
  		return 0;
  
  	if (smp_ops.cpu_can_disable)
  		return smp_ops.cpu_can_disable(cpu);
  
  	/*
  	 * By default, allow disabling all CPUs except the first one,
  	 * since this is special on a lot of platforms, e.g. because
  	 * of clock tick interrupts.
  	 */
  	return cpu != 0;
  }
  
  static void ipi_teardown(int cpu)
  {
  	int i;
  
  	if (WARN_ON_ONCE(!ipi_irq_base))
  		return;
  
  	for (i = 0; i < nr_ipi; i++)
  		disable_percpu_irq(ipi_irq_base + i);
  }
  
  /*
   * __cpu_disable runs on the processor to be shutdown.
   */
  int __cpu_disable(void)
  {
  	unsigned int cpu = smp_processor_id();
  	int ret;
  
  	ret = platform_cpu_disable(cpu);
  	if (ret)
  		return ret;
  
  #ifdef CONFIG_GENERIC_ARCH_TOPOLOGY
  	remove_cpu_topology(cpu);
  #endif
  
  	/*
  	 * Take this CPU offline.  Once we clear this, we can't return,
  	 * and we must not schedule until we're ready to give up the cpu.
  	 */
  	set_cpu_online(cpu, false);
  	ipi_teardown(cpu);
  
  	/*
  	 * OK - migrate IRQs away from this CPU
  	 */
  	irq_migrate_all_off_this_cpu();
  
  	/*
  	 * Flush user cache and TLB mappings, and then remove this CPU
  	 * from the vm mask set of all processes.
  	 *
  	 * Caches are flushed to the Level of Unification Inner Shareable
  	 * to write-back dirty lines to unified caches shared by all CPUs.
  	 */
  	flush_cache_louis();
  	local_flush_tlb_all();
  
  	return 0;
  }
  
  /*
   * called on the thread which is asking for a CPU to be shutdown -
   * waits until shutdown has completed, or it is timed out.
   */
  void __cpu_die(unsigned int cpu)
  {
  	if (!cpu_wait_death(cpu, 5)) {
  		pr_err("CPU%u: cpu didn't die\n", cpu);
  		return;
  	}
  	pr_debug("CPU%u: shutdown\n", cpu);
  
  	clear_tasks_mm_cpumask(cpu);
  	/*
  	 * platform_cpu_kill() is generally expected to do the powering off
  	 * and/or cutting of clocks to the dying CPU.  Optionally, this may
  	 * be done by the CPU which is dying in preference to supporting
  	 * this call, but that means there is _no_ synchronisation between
  	 * the requesting CPU and the dying CPU actually losing power.
  	 */
  	if (!platform_cpu_kill(cpu))
  		pr_err("CPU%u: unable to kill\n", cpu);
  }
  
  /*
   * Called from the idle thread for the CPU which has been shutdown.
   *
   * Note that we disable IRQs here, but do not re-enable them
   * before returning to the caller. This is also the behaviour
   * of the other hotplug-cpu capable cores, so presumably coming
   * out of idle fixes this.
   */
  void arch_cpu_idle_dead(void)
  {
  	unsigned int cpu = smp_processor_id();
  
  	idle_task_exit();
  
  	local_irq_disable();
  
  	/*
  	 * Flush the data out of the L1 cache for this CPU.  This must be
  	 * before the completion to ensure that data is safely written out
  	 * before platform_cpu_kill() gets called - which may disable
  	 * *this* CPU and power down its cache.
  	 */
  	flush_cache_louis();
  
  	/*
  	 * Tell __cpu_die() that this CPU is now safe to dispose of.  Once
  	 * this returns, power and/or clocks can be removed at any point
  	 * from this CPU and its cache by platform_cpu_kill().
  	 */
  	(void)cpu_report_death();
  
  	/*
  	 * Ensure that the cache lines associated with that completion are
  	 * written out.  This covers the case where _this_ CPU is doing the
  	 * powering down, to ensure that the completion is visible to the
  	 * CPU waiting for this one.
  	 */
  	flush_cache_louis();
  
  	/*
  	 * The actual CPU shutdown procedure is at least platform (if not
  	 * CPU) specific.  This may remove power, or it may simply spin.
  	 *
  	 * Platforms are generally expected *NOT* to return from this call,
  	 * although there are some which do because they have no way to
  	 * power down the CPU.  These platforms are the _only_ reason we
  	 * have a return path which uses the fragment of assembly below.
  	 *
  	 * The return path should not be used for platforms which can
  	 * power off the CPU.
  	 */
  	if (smp_ops.cpu_die)
  		smp_ops.cpu_die(cpu);
  
  	pr_warn("CPU%u: smp_ops.cpu_die() returned, trying to resuscitate\n",
  		cpu);
  
  	/*
  	 * Do not return to the idle loop - jump back to the secondary
  	 * cpu initialisation.  There's some initialisation which needs
  	 * to be repeated to undo the effects of taking the CPU offline.
  	 */
  	__asm__("mov	sp, %0\n"
  	"	mov	fp, #0\n"
  	"	mov	r0, %1\n"
  	"	b	secondary_start_kernel"
  		:
  		: "r" (task_stack_page(current) + THREAD_SIZE - 8),
  		  "r" (current)
  		: "r0");
  }
  #endif /* CONFIG_HOTPLUG_CPU */
  
  /*
   * Called by both boot and secondaries to move global data into
   * per-processor storage.
   */
  static void smp_store_cpu_info(unsigned int cpuid)
  {
  	struct cpuinfo_arm *cpu_info = &per_cpu(cpu_data, cpuid);
  
  	cpu_info->loops_per_jiffy = loops_per_jiffy;
  	cpu_info->cpuid = read_cpuid_id();
  
  	store_cpu_topology(cpuid);
  	check_cpu_icache_size(cpuid);
  }
  
  /*
   * This is the secondary CPU boot entry.  We're using this CPUs
   * idle thread stack, but a set of temporary page tables.
   */
  asmlinkage void secondary_start_kernel(struct task_struct *task)
  {
  	struct mm_struct *mm = &init_mm;
  	unsigned int cpu;
  
  	set_current(task);
  
  	secondary_biglittle_init();
  
  	/*
  	 * The identity mapping is uncached (strongly ordered), so
  	 * switch away from it before attempting any exclusive accesses.
  	 */
  	cpu_switch_mm(mm->pgd, mm);
  	local_flush_bp_all();
  	enter_lazy_tlb(mm, current);
  	local_flush_tlb_all();
  
  	/*
  	 * All kernel threads share the same mm context; grab a
  	 * reference and switch to it.
  	 */
  	cpu = smp_processor_id();
  	mmgrab(mm);
  	current->active_mm = mm;
  	cpumask_set_cpu(cpu, mm_cpumask(mm));
  
  	cpu_init();
  
  #ifndef CONFIG_MMU
  	setup_vectors_base();
  #endif
  	pr_debug("CPU%u: Booted secondary processor\n", cpu);
  
  	trace_hardirqs_off();
  
  	/*
  	 * Give the platform a chance to do its own initialisation.
  	 */
  	if (smp_ops.smp_secondary_init)
  		smp_ops.smp_secondary_init(cpu);
  
  	notify_cpu_starting(cpu);
  
  	ipi_setup(cpu);
  
  	calibrate_delay();
  
  	smp_store_cpu_info(cpu);
  
  	/*
  	 * OK, now it's safe to let the boot CPU continue.  Wait for
  	 * the CPU migration code to notice that the CPU is online
  	 * before we continue - which happens after __cpu_up returns.
  	 */
  	set_cpu_online(cpu, true);
  
  	check_other_bugs();
  
  	complete(&cpu_running);
  
  	local_irq_enable();
  	local_fiq_enable();
  	local_abt_enable();
  
  	/*
  	 * OK, it's off to the idle thread for us
  	 */
  	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
  }
  
  void __init smp_cpus_done(unsigned int max_cpus)
  {
  	int cpu;
  	unsigned long bogosum = 0;
  
  	for_each_online_cpu(cpu)
  		bogosum += per_cpu(cpu_data, cpu).loops_per_jiffy;
  
  	printk(KERN_INFO "SMP: Total of %d processors activated "
  	       "(%lu.%02lu BogoMIPS).\n",
  	       num_online_cpus(),
  	       bogosum / (500000/HZ),
  	       (bogosum / (5000/HZ)) % 100);
  
  	hyp_mode_check();
  }
  
  void __init smp_prepare_boot_cpu(void)
  {
  	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
  }
  
  void __init smp_prepare_cpus(unsigned int max_cpus)
  {
  	unsigned int ncores = num_possible_cpus();
  
  	init_cpu_topology();
  
  	smp_store_cpu_info(smp_processor_id());
  
  	/*
  	 * are we trying to boot more cores than exist?
  	 */
  	if (max_cpus > ncores)
  		max_cpus = ncores;
  	if (ncores > 1 && max_cpus) {
  		/*
  		 * Initialise the present map, which describes the set of CPUs
  		 * actually populated at the present time. A platform should
  		 * re-initialize the map in the platforms smp_prepare_cpus()
  		 * if present != possible (e.g. physical hotplug).
  		 */
  		init_cpu_present(cpu_possible_mask);
  
  		/*
  		 * Initialise the SCU if there are more than one CPU
  		 * and let them know where to start.
  		 */
  		if (smp_ops.smp_prepare_cpus)
  			smp_ops.smp_prepare_cpus(max_cpus);
  	}
  }
  
  static const char *ipi_types[NR_IPI] __tracepoint_string = {
  	[IPI_WAKEUP]		= "CPU wakeup interrupts",
  	[IPI_TIMER]		= "Timer broadcast interrupts",
  	[IPI_RESCHEDULE]	= "Rescheduling interrupts",
  	[IPI_CALL_FUNC]		= "Function call interrupts",
  	[IPI_CPU_STOP]		= "CPU stop interrupts",
  	[IPI_IRQ_WORK]		= "IRQ work interrupts",
  	[IPI_COMPLETION]	= "completion interrupts",
  };
  
  static void smp_cross_call(const struct cpumask *target, unsigned int ipinr);
  
  void show_ipi_list(struct seq_file *p, int prec)
  {
  	unsigned int cpu, i;
  
  	for (i = 0; i < NR_IPI; i++) {
  		if (!ipi_desc[i])
  			continue;
  
  		seq_printf(p, "%*s%u: ", prec - 1, "IPI", i);
  
  		for_each_online_cpu(cpu)
  			seq_printf(p, "%10u ", irq_desc_kstat_cpu(ipi_desc[i], cpu));
  
  		seq_printf(p, " %s\n", ipi_types[i]);
  	}
  }
  
  void arch_send_call_function_ipi_mask(const struct cpumask *mask)
  {
  	smp_cross_call(mask, IPI_CALL_FUNC);
  }
  
  void arch_send_wakeup_ipi_mask(const struct cpumask *mask)
  {
  	smp_cross_call(mask, IPI_WAKEUP);
  }
  
  void arch_send_call_function_single_ipi(int cpu)
  {
  	smp_cross_call(cpumask_of(cpu), IPI_CALL_FUNC);
  }
  
  #ifdef CONFIG_IRQ_WORK
  void arch_irq_work_raise(void)
  {
  	if (arch_irq_work_has_interrupt())
  		smp_cross_call(cpumask_of(smp_processor_id()), IPI_IRQ_WORK);
  }
  #endif
  
  #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
  void tick_broadcast(const struct cpumask *mask)
  {
  	smp_cross_call(mask, IPI_TIMER);
  }
  #endif
  
  static DEFINE_RAW_SPINLOCK(stop_lock);
  
  /*
   * ipi_cpu_stop - handle IPI from smp_send_stop()
   */
  static void ipi_cpu_stop(unsigned int cpu)
  {
  	if (system_state <= SYSTEM_RUNNING) {
  		raw_spin_lock(&stop_lock);
  		pr_crit("CPU%u: stopping\n", cpu);
  		dump_stack();
  		raw_spin_unlock(&stop_lock);
  	}
  
  	set_cpu_online(cpu, false);
  
  	local_fiq_disable();
  	local_irq_disable();
  
  	while (1) {
  		cpu_relax();
  		wfe();
  	}
  }
  
  static DEFINE_PER_CPU(struct completion *, cpu_completion);
  
  int register_ipi_completion(struct completion *completion, int cpu)
  {
  	per_cpu(cpu_completion, cpu) = completion;
  	return IPI_COMPLETION;
  }
  
  static void ipi_complete(unsigned int cpu)
  {
  	complete(per_cpu(cpu_completion, cpu));
  }
  
  /*
   * Main handler for inter-processor interrupts
   */
  asmlinkage void __exception_irq_entry do_IPI(int ipinr, struct pt_regs *regs)
  {
  	handle_IPI(ipinr, regs);
  }
  
  static void do_handle_IPI(int ipinr)
  {
  	unsigned int cpu = smp_processor_id();
  
  	if ((unsigned)ipinr < NR_IPI)
  		trace_ipi_entry_rcuidle(ipi_types[ipinr]);
  
  	switch (ipinr) {
  	case IPI_WAKEUP:
  		break;
  
  #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
  	case IPI_TIMER:
  		tick_receive_broadcast();
  		break;
  #endif
  
  	case IPI_RESCHEDULE:
  		scheduler_ipi();
  		break;
  
  	case IPI_CALL_FUNC:
  		generic_smp_call_function_interrupt();
  		break;
  
  	case IPI_CPU_STOP:
  		ipi_cpu_stop(cpu);
  		break;
  
  #ifdef CONFIG_IRQ_WORK
  	case IPI_IRQ_WORK:
  		irq_work_run();
  		break;
  #endif
  
  	case IPI_COMPLETION:
  		ipi_complete(cpu);
  		break;
  
  	case IPI_CPU_BACKTRACE:
  		printk_deferred_enter();
  		nmi_cpu_backtrace(get_irq_regs());
  		printk_deferred_exit();
  		break;
  
  	default:
  		pr_crit("CPU%u: Unknown IPI message 0x%x\n",
  		        cpu, ipinr);
  		break;
  	}
  
  	if ((unsigned)ipinr < NR_IPI)
  		trace_ipi_exit_rcuidle(ipi_types[ipinr]);
  }
  
  /* Legacy version, should go away once all irqchips have been converted */
  void handle_IPI(int ipinr, struct pt_regs *regs)
  {
  	struct pt_regs *old_regs = set_irq_regs(regs);
  
  	irq_enter();
  	do_handle_IPI(ipinr);
  	irq_exit();
  
  	set_irq_regs(old_regs);
  }
  
  static irqreturn_t ipi_handler(int irq, void *data)
  {
  	do_handle_IPI(irq - ipi_irq_base);
  	return IRQ_HANDLED;
  }
  
  static void smp_cross_call(const struct cpumask *target, unsigned int ipinr)
  {
  	trace_ipi_raise_rcuidle(target, ipi_types[ipinr]);
  	__ipi_send_mask(ipi_desc[ipinr], target);
  }
  
  static void ipi_setup(int cpu)
  {
  	int i;
  
  	if (WARN_ON_ONCE(!ipi_irq_base))
  		return;
  
  	for (i = 0; i < nr_ipi; i++)
  		enable_percpu_irq(ipi_irq_base + i, 0);
  }
  
  void __init set_smp_ipi_range(int ipi_base, int n)
  {
  	int i;
  
  	WARN_ON(n < MAX_IPI);
  	nr_ipi = min(n, MAX_IPI);
  
  	for (i = 0; i < nr_ipi; i++) {
  		int err;
  
  		err = request_percpu_irq(ipi_base + i, ipi_handler,
  					 "IPI", &irq_stat);
  		WARN_ON(err);
  
  		ipi_desc[i] = irq_to_desc(ipi_base + i);
  		irq_set_status_flags(ipi_base + i, IRQ_HIDDEN);
  	}
  
  	ipi_irq_base = ipi_base;
  
  	/* Setup the boot CPU immediately */
  	ipi_setup(smp_processor_id());
  }
  
  void smp_send_reschedule(int cpu)
  {
  	smp_cross_call(cpumask_of(cpu), IPI_RESCHEDULE);
  }
  
  void smp_send_stop(void)
  {
  	unsigned long timeout;
  	struct cpumask mask;
  
  	cpumask_copy(&mask, cpu_online_mask);
  	cpumask_clear_cpu(smp_processor_id(), &mask);
  	if (!cpumask_empty(&mask))
  		smp_cross_call(&mask, IPI_CPU_STOP);
  
  	/* Wait up to one second for other CPUs to stop */
  	timeout = USEC_PER_SEC;
  	while (num_online_cpus() > 1 && timeout--)
  		udelay(1);
  
  	if (num_online_cpus() > 1)
  		pr_warn("SMP: failed to stop secondary CPUs\n");
  }
  
  /* In case panic() and panic() called at the same time on CPU1 and CPU2,
   * and CPU 1 calls panic_smp_self_stop() before crash_smp_send_stop()
   * CPU1 can't receive the ipi irqs from CPU2, CPU1 will be always online,
   * kdump fails. So split out the panic_smp_self_stop() and add
   * set_cpu_online(smp_processor_id(), false).
   */
  void panic_smp_self_stop(void)
  {
  	pr_debug("CPU %u will stop doing anything useful since another CPU has paniced\n",
  	         smp_processor_id());
  	set_cpu_online(smp_processor_id(), false);
  	while (1)
  		cpu_relax();
  }
  
  /*
   * not supported here
   */
  int setup_profiling_timer(unsigned int multiplier)
  {
  	return -EINVAL;
  }
  
  #ifdef CONFIG_CPU_FREQ
  
  static DEFINE_PER_CPU(unsigned long, l_p_j_ref);
  static DEFINE_PER_CPU(unsigned long, l_p_j_ref_freq);
  static unsigned long global_l_p_j_ref;
  static unsigned long global_l_p_j_ref_freq;
  
  static int cpufreq_callback(struct notifier_block *nb,
  					unsigned long val, void *data)
  {
  	struct cpufreq_freqs *freq = data;
  	struct cpumask *cpus = freq->policy->cpus;
  	int cpu, first = cpumask_first(cpus);
  	unsigned int lpj;
  
  	if (freq->flags & CPUFREQ_CONST_LOOPS)
  		return NOTIFY_OK;
  
  	if (!per_cpu(l_p_j_ref, first)) {
  		for_each_cpu(cpu, cpus) {
  			per_cpu(l_p_j_ref, cpu) =
  				per_cpu(cpu_data, cpu).loops_per_jiffy;
  			per_cpu(l_p_j_ref_freq, cpu) = freq->old;
  		}
  
  		if (!global_l_p_j_ref) {
  			global_l_p_j_ref = loops_per_jiffy;
  			global_l_p_j_ref_freq = freq->old;
  		}
  	}
  
  	if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
  	    (val == CPUFREQ_POSTCHANGE && freq->old > freq->new)) {
  		loops_per_jiffy = cpufreq_scale(global_l_p_j_ref,
  						global_l_p_j_ref_freq,
  						freq->new);
  
  		lpj = cpufreq_scale(per_cpu(l_p_j_ref, first),
  				    per_cpu(l_p_j_ref_freq, first), freq->new);
  		for_each_cpu(cpu, cpus)
  			per_cpu(cpu_data, cpu).loops_per_jiffy = lpj;
  	}
  	return NOTIFY_OK;
  }
  
  static struct notifier_block cpufreq_notifier = {
  	.notifier_call  = cpufreq_callback,
  };
  
  static int __init register_cpufreq_notifier(void)
  {
  	return cpufreq_register_notifier(&cpufreq_notifier,
  						CPUFREQ_TRANSITION_NOTIFIER);
  }
  core_initcall(register_cpufreq_notifier);
  
  #endif
  
  static void raise_nmi(cpumask_t *mask)
  {
  	__ipi_send_mask(ipi_desc[IPI_CPU_BACKTRACE], mask);
  }
  
  void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
  {
  	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_nmi);
  }
  