Merge tag 'kvm-x86-misc-6.7' of https://github.com/kvm-x86/linux into HEAD

[thirdparty/kernel/stable.git] / arch / x86 / kernel / smpboot.c

// SPDX-License-Identifier: GPL-2.0-or-later
 /*
 *      x86 SMP booting functions
 *
 *      (c) 1995 Alan Cox, Building #3 <alan@lxorguk.ukuu.org.uk>
 *      (c) 1998, 1999, 2000, 2009 Ingo Molnar <mingo@redhat.com>
 *      Copyright 2001 Andi Kleen, SuSE Labs.
 *
 *      Much of the core SMP work is based on previous work by Thomas Radke, to
 *      whom a great many thanks are extended.
 *
 *      Thanks to Intel for making available several different Pentium,
 *      Pentium Pro and Pentium-II/Xeon MP machines.
 *      Original development of Linux SMP code supported by Caldera.
 *
 *      Fixes
 *              Felix Koop      :       NR_CPUS used properly
 *              Jose Renau      :       Handle single CPU case.
 *              Alan Cox        :       By repeated request 8) - Total BogoMIPS report.
 *              Greg Wright     :       Fix for kernel stacks panic.
 *              Erich Boleyn    :       MP v1.4 and additional changes.
 *      Matthias Sattler        :       Changes for 2.1 kernel map.
 *      Michel Lespinasse       :       Changes for 2.1 kernel map.
 *      Michael Chastain        :       Change trampoline.S to gnu as.
 *              Alan Cox        :       Dumb bug: 'B' step PPro's are fine
 *              Ingo Molnar     :       Added APIC timers, based on code
 *                                      from Jose Renau
 *              Ingo Molnar     :       various cleanups and rewrites
 *              Tigran Aivazian :       fixed "0.00 in /proc/uptime on SMP" bug.
 *      Maciej W. Rozycki       :       Bits for genuine 82489DX APICs
 *      Andi Kleen              :       Changed for SMP boot into long mode.
 *              Martin J. Bligh :       Added support for multi-quad systems
 *              Dave Jones      :       Report invalid combinations of Athlon CPUs.
 *              Rusty Russell   :       Hacked into shape for new "hotplug" boot process.
 *      Andi Kleen              :       Converted to new state machine.
 *      Ashok Raj               :       CPU hotplug support
 *      Glauber Costa           :       i386 and x86_64 integration
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/init.h>
#include <linux/smp.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/sched/topology.h>
#include <linux/sched/hotplug.h>
#include <linux/sched/task_stack.h>
#include <linux/percpu.h>
#include <linux/memblock.h>
#include <linux/err.h>
#include <linux/nmi.h>
#include <linux/tboot.h>
#include <linux/gfp.h>
#include <linux/cpuidle.h>
#include <linux/kexec.h>
#include <linux/numa.h>
#include <linux/pgtable.h>
#include <linux/overflow.h>
#include <linux/stackprotector.h>
#include <linux/cpuhotplug.h>
#include <linux/mc146818rtc.h>

#include <asm/acpi.h>
#include <asm/cacheinfo.h>
#include <asm/desc.h>
#include <asm/nmi.h>
#include <asm/irq.h>
#include <asm/realmode.h>
#include <asm/cpu.h>
#include <asm/numa.h>
#include <asm/tlbflush.h>
#include <asm/mtrr.h>
#include <asm/mwait.h>
#include <asm/apic.h>
#include <asm/io_apic.h>
#include <asm/fpu/api.h>
#include <asm/setup.h>
#include <asm/uv/uv.h>
#include <asm/microcode.h>
#include <asm/i8259.h>
#include <asm/misc.h>
#include <asm/qspinlock.h>
#include <asm/intel-family.h>
#include <asm/cpu_device_id.h>
#include <asm/spec-ctrl.h>
#include <asm/hw_irq.h>
#include <asm/stackprotector.h>
#include <asm/sev.h>

/* representing HT siblings of each logical CPU */
DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
EXPORT_PER_CPU_SYMBOL(cpu_sibling_map);

/* representing HT and core siblings of each logical CPU */
DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_map);
EXPORT_PER_CPU_SYMBOL(cpu_core_map);

/* representing HT, core, and die siblings of each logical CPU */
DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_die_map);
EXPORT_PER_CPU_SYMBOL(cpu_die_map);

/* Per CPU bogomips and other parameters */
DEFINE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info);
EXPORT_PER_CPU_SYMBOL(cpu_info);

/* CPUs which are the primary SMT threads */
struct cpumask __cpu_primary_thread_mask __read_mostly;

/* Representing CPUs for which sibling maps can be computed */
static cpumask_var_t cpu_sibling_setup_mask;

struct mwait_cpu_dead {
        unsigned int    control;
        unsigned int    status;
};

#define CPUDEAD_MWAIT_WAIT      0xDEADBEEF
#define CPUDEAD_MWAIT_KEXEC_HLT 0x4A17DEAD

/*
 * Cache line aligned data for mwait_play_dead(). Separate on purpose so
 * that it's unlikely to be touched by other CPUs.
 */
static DEFINE_PER_CPU_ALIGNED(struct mwait_cpu_dead, mwait_cpu_dead);

/* Logical package management. We might want to allocate that dynamically */
unsigned int __max_logical_packages __read_mostly;
EXPORT_SYMBOL(__max_logical_packages);
static unsigned int logical_packages __read_mostly;
static unsigned int logical_die __read_mostly;

/* Maximum number of SMT threads on any online core */
int __read_mostly __max_smt_threads = 1;

/* Flag to indicate if a complete sched domain rebuild is required */
bool x86_topology_update;

int arch_update_cpu_topology(void)
{
        int retval = x86_topology_update;

        x86_topology_update = false;
        return retval;
}

static unsigned int smpboot_warm_reset_vector_count;

static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
{
        unsigned long flags;

        spin_lock_irqsave(&rtc_lock, flags);
        if (!smpboot_warm_reset_vector_count++) {
                CMOS_WRITE(0xa, 0xf);
                *((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) = start_eip >> 4;
                *((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = start_eip & 0xf;
        }
        spin_unlock_irqrestore(&rtc_lock, flags);
}

static inline void smpboot_restore_warm_reset_vector(void)
{
        unsigned long flags;

        /*
         * Paranoid:  Set warm reset code and vector here back
         * to default values.
         */
        spin_lock_irqsave(&rtc_lock, flags);
        if (!--smpboot_warm_reset_vector_count) {
                CMOS_WRITE(0, 0xf);
                *((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
        }
        spin_unlock_irqrestore(&rtc_lock, flags);

}

/* Run the next set of setup steps for the upcoming CPU */
static void ap_starting(void)
{
        int cpuid = smp_processor_id();

        /* Mop up eventual mwait_play_dead() wreckage */
        this_cpu_write(mwait_cpu_dead.status, 0);
        this_cpu_write(mwait_cpu_dead.control, 0);

        /*
         * If woken up by an INIT in an 82489DX configuration the alive
         * synchronization guarantees that the CPU does not reach this
         * point before an INIT_deassert IPI reaches the local APIC, so it
         * is now safe to touch the local APIC.
         *
         * Set up this CPU, first the APIC, which is probably redundant on
         * most boards.
         */
        apic_ap_setup();

        /* Save the processor parameters. */
        smp_store_cpu_info(cpuid);

        /*
         * The topology information must be up to date before
         * notify_cpu_starting().
         */
        set_cpu_sibling_map(cpuid);

        ap_init_aperfmperf();

        pr_debug("Stack at about %p\n", &cpuid);

        wmb();

        /*
         * This runs the AP through all the cpuhp states to its target
         * state CPUHP_ONLINE.
         */
        notify_cpu_starting(cpuid);
}

static void ap_calibrate_delay(void)
{
        /*
         * Calibrate the delay loop and update loops_per_jiffy in cpu_data.
         * smp_store_cpu_info() stored a value that is close but not as
         * accurate as the value just calculated.
         *
         * As this is invoked after the TSC synchronization check,
         * calibrate_delay_is_known() will skip the calibration routine
         * when TSC is synchronized across sockets.
         */
        calibrate_delay();
        cpu_data(smp_processor_id()).loops_per_jiffy = loops_per_jiffy;
}

/*
 * Activate a secondary processor.
 */
static void notrace start_secondary(void *unused)
{
        /*
         * Don't put *anything* except direct CPU state initialization
         * before cpu_init(), SMP booting is too fragile that we want to
         * limit the things done here to the most necessary things.
         */
        cr4_init();

        /*
         * 32-bit specific. 64-bit reaches this code with the correct page
         * table established. Yet another historical divergence.
         */
        if (IS_ENABLED(CONFIG_X86_32)) {
                /* switch away from the initial page table */
                load_cr3(swapper_pg_dir);
                __flush_tlb_all();
        }

        cpu_init_exception_handling();

        /*
         * 32-bit systems load the microcode from the ASM startup code for
         * historical reasons.
         *
         * On 64-bit systems load it before reaching the AP alive
         * synchronization point below so it is not part of the full per
         * CPU serialized bringup part when "parallel" bringup is enabled.
         *
         * That's even safe when hyperthreading is enabled in the CPU as
         * the core code starts the primary threads first and leaves the
         * secondary threads waiting for SIPI. Loading microcode on
         * physical cores concurrently is a safe operation.
         *
         * This covers both the Intel specific issue that concurrent
         * microcode loading on SMT siblings must be prohibited and the
         * vendor independent issue`that microcode loading which changes
         * CPUID, MSRs etc. must be strictly serialized to maintain
         * software state correctness.
         */
        if (IS_ENABLED(CONFIG_X86_64))
                load_ucode_ap();

        /*
         * Synchronization point with the hotplug core. Sets this CPUs
         * synchronization state to ALIVE and spin-waits for the control CPU to
         * release this CPU for further bringup.
         */
        cpuhp_ap_sync_alive();

        cpu_init();
        fpu__init_cpu();
        rcu_cpu_starting(raw_smp_processor_id());
        x86_cpuinit.early_percpu_clock_init();

        ap_starting();

        /* Check TSC synchronization with the control CPU. */
        check_tsc_sync_target();

        /*
         * Calibrate the delay loop after the TSC synchronization check.
         * This allows to skip the calibration when TSC is synchronized
         * across sockets.
         */
        ap_calibrate_delay();

        speculative_store_bypass_ht_init();

        /*
         * Lock vector_lock, set CPU online and bring the vector
         * allocator online. Online must be set with vector_lock held
         * to prevent a concurrent irq setup/teardown from seeing a
         * half valid vector space.
         */
        lock_vector_lock();
        set_cpu_online(smp_processor_id(), true);
        lapic_online();
        unlock_vector_lock();
        x86_platform.nmi_init();

        /* enable local interrupts */
        local_irq_enable();

        x86_cpuinit.setup_percpu_clockev();

        wmb();
        cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
}

/**
 * topology_phys_to_logical_pkg - Map a physical package id to a logical
 * @phys_pkg:   The physical package id to map
 *
 * Returns logical package id or -1 if not found
 */
int topology_phys_to_logical_pkg(unsigned int phys_pkg)
{
        int cpu;

        for_each_possible_cpu(cpu) {
                struct cpuinfo_x86 *c = &cpu_data(cpu);

                if (c->initialized && c->phys_proc_id == phys_pkg)
                        return c->logical_proc_id;
        }
        return -1;
}
EXPORT_SYMBOL(topology_phys_to_logical_pkg);

/**
 * topology_phys_to_logical_die - Map a physical die id to logical
 * @die_id:     The physical die id to map
 * @cur_cpu:    The CPU for which the mapping is done
 *
 * Returns logical die id or -1 if not found
 */
static int topology_phys_to_logical_die(unsigned int die_id, unsigned int cur_cpu)
{
        int cpu, proc_id = cpu_data(cur_cpu).phys_proc_id;

        for_each_possible_cpu(cpu) {
                struct cpuinfo_x86 *c = &cpu_data(cpu);

                if (c->initialized && c->cpu_die_id == die_id &&
                    c->phys_proc_id == proc_id)
                        return c->logical_die_id;
        }
        return -1;
}

/**
 * topology_update_package_map - Update the physical to logical package map
 * @pkg:        The physical package id as retrieved via CPUID
 * @cpu:        The cpu for which this is updated
 */
int topology_update_package_map(unsigned int pkg, unsigned int cpu)
{
        int new;

        /* Already available somewhere? */
        new = topology_phys_to_logical_pkg(pkg);
        if (new >= 0)
                goto found;

        new = logical_packages++;
        if (new != pkg) {
                pr_info("CPU %u Converting physical %u to logical package %u\n",
                        cpu, pkg, new);
        }
found:
        cpu_data(cpu).logical_proc_id = new;
        return 0;
}
/**
 * topology_update_die_map - Update the physical to logical die map
 * @die:        The die id as retrieved via CPUID
 * @cpu:        The cpu for which this is updated
 */
int topology_update_die_map(unsigned int die, unsigned int cpu)
{
        int new;

        /* Already available somewhere? */
        new = topology_phys_to_logical_die(die, cpu);
        if (new >= 0)
                goto found;

        new = logical_die++;
        if (new != die) {
                pr_info("CPU %u Converting physical %u to logical die %u\n",
                        cpu, die, new);
        }
found:
        cpu_data(cpu).logical_die_id = new;
        return 0;
}

static void __init smp_store_boot_cpu_info(void)
{
        int id = 0; /* CPU 0 */
        struct cpuinfo_x86 *c = &cpu_data(id);

        *c = boot_cpu_data;
        c->cpu_index = id;
        topology_update_package_map(c->phys_proc_id, id);
        topology_update_die_map(c->cpu_die_id, id);
        c->initialized = true;
}

/*
 * The bootstrap kernel entry code has set these up. Save them for
 * a given CPU
 */
void smp_store_cpu_info(int id)
{
        struct cpuinfo_x86 *c = &cpu_data(id);

        /* Copy boot_cpu_data only on the first bringup */
        if (!c->initialized)
                *c = boot_cpu_data;
        c->cpu_index = id;
        /*
         * During boot time, CPU0 has this setup already. Save the info when
         * bringing up an AP.
         */
        identify_secondary_cpu(c);
        c->initialized = true;
}

static bool
topology_same_node(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
{
        int cpu1 = c->cpu_index, cpu2 = o->cpu_index;

        return (cpu_to_node(cpu1) == cpu_to_node(cpu2));
}

static bool
topology_sane(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o, const char *name)
{
        int cpu1 = c->cpu_index, cpu2 = o->cpu_index;

        return !WARN_ONCE(!topology_same_node(c, o),
                "sched: CPU #%d's %s-sibling CPU #%d is not on the same node! "
                "[node: %d != %d]. Ignoring dependency.\n",
                cpu1, name, cpu2, cpu_to_node(cpu1), cpu_to_node(cpu2));
}

#define link_mask(mfunc, c1, c2)                                        \
do {                                                                    \
        cpumask_set_cpu((c1), mfunc(c2));                               \
        cpumask_set_cpu((c2), mfunc(c1));                               \
} while (0)

static bool match_smt(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
{
        if (boot_cpu_has(X86_FEATURE_TOPOEXT)) {
                int cpu1 = c->cpu_index, cpu2 = o->cpu_index;

                if (c->phys_proc_id == o->phys_proc_id &&
                    c->cpu_die_id == o->cpu_die_id &&
                    per_cpu(cpu_llc_id, cpu1) == per_cpu(cpu_llc_id, cpu2)) {
                        if (c->cpu_core_id == o->cpu_core_id)
                                return topology_sane(c, o, "smt");

                        if ((c->cu_id != 0xff) &&
                            (o->cu_id != 0xff) &&
                            (c->cu_id == o->cu_id))
                                return topology_sane(c, o, "smt");
                }

        } else if (c->phys_proc_id == o->phys_proc_id &&
                   c->cpu_die_id == o->cpu_die_id &&
                   c->cpu_core_id == o->cpu_core_id) {
                return topology_sane(c, o, "smt");
        }

        return false;
}

static bool match_die(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
{
        if (c->phys_proc_id == o->phys_proc_id &&
            c->cpu_die_id == o->cpu_die_id)
                return true;
        return false;
}

static bool match_l2c(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
{
        int cpu1 = c->cpu_index, cpu2 = o->cpu_index;

        /* If the arch didn't set up l2c_id, fall back to SMT */
        if (per_cpu(cpu_l2c_id, cpu1) == BAD_APICID)
                return match_smt(c, o);

        /* Do not match if L2 cache id does not match: */
        if (per_cpu(cpu_l2c_id, cpu1) != per_cpu(cpu_l2c_id, cpu2))
                return false;

        return topology_sane(c, o, "l2c");
}

/*
 * Unlike the other levels, we do not enforce keeping a
 * multicore group inside a NUMA node.  If this happens, we will
 * discard the MC level of the topology later.
 */
static bool match_pkg(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
{
        if (c->phys_proc_id == o->phys_proc_id)
                return true;
        return false;
}

/*
 * Define intel_cod_cpu[] for Intel COD (Cluster-on-Die) CPUs.
 *
 * Any Intel CPU that has multiple nodes per package and does not
 * match intel_cod_cpu[] has the SNC (Sub-NUMA Cluster) topology.
 *
 * When in SNC mode, these CPUs enumerate an LLC that is shared
 * by multiple NUMA nodes. The LLC is shared for off-package data
 * access but private to the NUMA node (half of the package) for
 * on-package access. CPUID (the source of the information about
 * the LLC) can only enumerate the cache as shared or unshared,
 * but not this particular configuration.
 */

static const struct x86_cpu_id intel_cod_cpu[] = {
        X86_MATCH_INTEL_FAM6_MODEL(HASWELL_X, 0),       /* COD */
        X86_MATCH_INTEL_FAM6_MODEL(BROADWELL_X, 0),     /* COD */
        X86_MATCH_INTEL_FAM6_MODEL(ANY, 1),             /* SNC */
        {}
};

static bool match_llc(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
{
        const struct x86_cpu_id *id = x86_match_cpu(intel_cod_cpu);
        int cpu1 = c->cpu_index, cpu2 = o->cpu_index;
        bool intel_snc = id && id->driver_data;

        /* Do not match if we do not have a valid APICID for cpu: */
        if (per_cpu(cpu_llc_id, cpu1) == BAD_APICID)
                return false;

        /* Do not match if LLC id does not match: */
        if (per_cpu(cpu_llc_id, cpu1) != per_cpu(cpu_llc_id, cpu2))
                return false;

        /*
         * Allow the SNC topology without warning. Return of false
         * means 'c' does not share the LLC of 'o'. This will be
         * reflected to userspace.
         */
        if (match_pkg(c, o) && !topology_same_node(c, o) && intel_snc)
                return false;

        return topology_sane(c, o, "llc");
}


static inline int x86_sched_itmt_flags(void)
{
        return sysctl_sched_itmt_enabled ? SD_ASYM_PACKING : 0;
}

#ifdef CONFIG_SCHED_MC
static int x86_core_flags(void)
{
        return cpu_core_flags() | x86_sched_itmt_flags();
}
#endif
#ifdef CONFIG_SCHED_SMT
static int x86_smt_flags(void)
{
        return cpu_smt_flags();
}
#endif
#ifdef CONFIG_SCHED_CLUSTER
static int x86_cluster_flags(void)
{
        return cpu_cluster_flags() | x86_sched_itmt_flags();
}
#endif

static int x86_die_flags(void)
{
        if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
               return x86_sched_itmt_flags();

        return 0;
}

/*
 * Set if a package/die has multiple NUMA nodes inside.
 * AMD Magny-Cours, Intel Cluster-on-Die, and Intel
 * Sub-NUMA Clustering have this.
 */
static bool x86_has_numa_in_package;

static struct sched_domain_topology_level x86_topology[6];

static void __init build_sched_topology(void)
{
        int i = 0;

#ifdef CONFIG_SCHED_SMT
        x86_topology[i++] = (struct sched_domain_topology_level){
                cpu_smt_mask, x86_smt_flags, SD_INIT_NAME(SMT)
        };
#endif
#ifdef CONFIG_SCHED_CLUSTER
        x86_topology[i++] = (struct sched_domain_topology_level){
                cpu_clustergroup_mask, x86_cluster_flags, SD_INIT_NAME(CLS)
        };
#endif
#ifdef CONFIG_SCHED_MC
        x86_topology[i++] = (struct sched_domain_topology_level){
                cpu_coregroup_mask, x86_core_flags, SD_INIT_NAME(MC)
        };
#endif
        /*
         * When there is NUMA topology inside the package skip the DIE domain
         * since the NUMA domains will auto-magically create the right spanning
         * domains based on the SLIT.
         */
        if (!x86_has_numa_in_package) {
                x86_topology[i++] = (struct sched_domain_topology_level){
                        cpu_cpu_mask, x86_die_flags, SD_INIT_NAME(DIE)
                };
        }

        /*
         * There must be one trailing NULL entry left.
         */
        BUG_ON(i >= ARRAY_SIZE(x86_topology)-1);

        set_sched_topology(x86_topology);
}

void set_cpu_sibling_map(int cpu)
{
        bool has_smt = smp_num_siblings > 1;
        bool has_mp = has_smt || boot_cpu_data.x86_max_cores > 1;
        struct cpuinfo_x86 *c = &cpu_data(cpu);
        struct cpuinfo_x86 *o;
        int i, threads;

        cpumask_set_cpu(cpu, cpu_sibling_setup_mask);

        if (!has_mp) {
                cpumask_set_cpu(cpu, topology_sibling_cpumask(cpu));
                cpumask_set_cpu(cpu, cpu_llc_shared_mask(cpu));
                cpumask_set_cpu(cpu, cpu_l2c_shared_mask(cpu));
                cpumask_set_cpu(cpu, topology_core_cpumask(cpu));
                cpumask_set_cpu(cpu, topology_die_cpumask(cpu));
                c->booted_cores = 1;
                return;
        }

        for_each_cpu(i, cpu_sibling_setup_mask) {
                o = &cpu_data(i);

                if (match_pkg(c, o) && !topology_same_node(c, o))
                        x86_has_numa_in_package = true;

                if ((i == cpu) || (has_smt && match_smt(c, o)))
                        link_mask(topology_sibling_cpumask, cpu, i);

                if ((i == cpu) || (has_mp && match_llc(c, o)))
                        link_mask(cpu_llc_shared_mask, cpu, i);

                if ((i == cpu) || (has_mp && match_l2c(c, o)))
                        link_mask(cpu_l2c_shared_mask, cpu, i);

                if ((i == cpu) || (has_mp && match_die(c, o)))
                        link_mask(topology_die_cpumask, cpu, i);
        }

        threads = cpumask_weight(topology_sibling_cpumask(cpu));
        if (threads > __max_smt_threads)
                __max_smt_threads = threads;

        for_each_cpu(i, topology_sibling_cpumask(cpu))
                cpu_data(i).smt_active = threads > 1;

        /*
         * This needs a separate iteration over the cpus because we rely on all
         * topology_sibling_cpumask links to be set-up.
         */
        for_each_cpu(i, cpu_sibling_setup_mask) {
                o = &cpu_data(i);

                if ((i == cpu) || (has_mp && match_pkg(c, o))) {
                        link_mask(topology_core_cpumask, cpu, i);

                        /*
                         *  Does this new cpu bringup a new core?
                         */
                        if (threads == 1) {
                                /*
                                 * for each core in package, increment
                                 * the booted_cores for this new cpu
                                 */
                                if (cpumask_first(
                                    topology_sibling_cpumask(i)) == i)
                                        c->booted_cores++;
                                /*
                                 * increment the core count for all
                                 * the other cpus in this package
                                 */
                                if (i != cpu)
                                        cpu_data(i).booted_cores++;
                        } else if (i != cpu && !c->booted_cores)
                                c->booted_cores = cpu_data(i).booted_cores;
                }
        }
}

/* maps the cpu to the sched domain representing multi-core */
const struct cpumask *cpu_coregroup_mask(int cpu)
{
        return cpu_llc_shared_mask(cpu);
}

const struct cpumask *cpu_clustergroup_mask(int cpu)
{
        return cpu_l2c_shared_mask(cpu);
}

static void impress_friends(void)
{
        int cpu;
        unsigned long bogosum = 0;
        /*
         * Allow the user to impress friends.
         */
        pr_debug("Before bogomips\n");
        for_each_online_cpu(cpu)
                bogosum += cpu_data(cpu).loops_per_jiffy;

        pr_info("Total of %d processors activated (%lu.%02lu BogoMIPS)\n",
                num_online_cpus(),
                bogosum/(500000/HZ),
                (bogosum/(5000/HZ))%100);

        pr_debug("Before bogocount - setting activated=1\n");
}

/*
 * The Multiprocessor Specification 1.4 (1997) example code suggests
 * that there should be a 10ms delay between the BSP asserting INIT
 * and de-asserting INIT, when starting a remote processor.
 * But that slows boot and resume on modern processors, which include
 * many cores and don't require that delay.
 *
 * Cmdline "init_cpu_udelay=" is available to over-ride this delay.
 * Modern processor families are quirked to remove the delay entirely.
 */
#define UDELAY_10MS_DEFAULT 10000

static unsigned int init_udelay = UINT_MAX;

static int __init cpu_init_udelay(char *str)
{
        get_option(&str, &init_udelay);

        return 0;
}
early_param("cpu_init_udelay", cpu_init_udelay);

static void __init smp_quirk_init_udelay(void)
{
        /* if cmdline changed it from default, leave it alone */
        if (init_udelay != UINT_MAX)
                return;

        /* if modern processor, use no delay */
        if (((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) && (boot_cpu_data.x86 == 6)) ||
            ((boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) && (boot_cpu_data.x86 >= 0x18)) ||
            ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && (boot_cpu_data.x86 >= 0xF))) {
                init_udelay = 0;
                return;
        }
        /* else, use legacy delay */
        init_udelay = UDELAY_10MS_DEFAULT;
}

/*
 * Wake up AP by INIT, INIT, STARTUP sequence.
 */
static void send_init_sequence(int phys_apicid)
{
        int maxlvt = lapic_get_maxlvt();

        /* Be paranoid about clearing APIC errors. */
        if (APIC_INTEGRATED(boot_cpu_apic_version)) {
                /* Due to the Pentium erratum 3AP.  */
                if (maxlvt > 3)
                        apic_write(APIC_ESR, 0);
                apic_read(APIC_ESR);
        }

        /* Assert INIT on the target CPU */
        apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT, phys_apicid);
        safe_apic_wait_icr_idle();

        udelay(init_udelay);

        /* Deassert INIT on the target CPU */
        apic_icr_write(APIC_INT_LEVELTRIG | APIC_DM_INIT, phys_apicid);
        safe_apic_wait_icr_idle();
}

/*
 * Wake up AP by INIT, INIT, STARTUP sequence.
 */
static int wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
{
        unsigned long send_status = 0, accept_status = 0;
        int num_starts, j, maxlvt;

        preempt_disable();
        maxlvt = lapic_get_maxlvt();
        send_init_sequence(phys_apicid);

        mb();

        /*
         * Should we send STARTUP IPIs ?
         *
         * Determine this based on the APIC version.
         * If we don't have an integrated APIC, don't send the STARTUP IPIs.
         */
        if (APIC_INTEGRATED(boot_cpu_apic_version))
                num_starts = 2;
        else
                num_starts = 0;

        /*
         * Run STARTUP IPI loop.
         */
        pr_debug("#startup loops: %d\n", num_starts);

        for (j = 1; j <= num_starts; j++) {
                pr_debug("Sending STARTUP #%d\n", j);
                if (maxlvt > 3)         /* Due to the Pentium erratum 3AP.  */
                        apic_write(APIC_ESR, 0);
                apic_read(APIC_ESR);
                pr_debug("After apic_write\n");

                /*
                 * STARTUP IPI
                 */

                /* Target chip */
                /* Boot on the stack */
                /* Kick the second */
                apic_icr_write(APIC_DM_STARTUP | (start_eip >> 12),
                               phys_apicid);

                /*
                 * Give the other CPU some time to accept the IPI.
                 */
                if (init_udelay == 0)
                        udelay(10);
                else
                        udelay(300);

                pr_debug("Startup point 1\n");

                pr_debug("Waiting for send to finish...\n");
                send_status = safe_apic_wait_icr_idle();

                /*
                 * Give the other CPU some time to accept the IPI.
                 */
                if (init_udelay == 0)
                        udelay(10);
                else
                        udelay(200);

                if (maxlvt > 3)         /* Due to the Pentium erratum 3AP.  */
                        apic_write(APIC_ESR, 0);
                accept_status = (apic_read(APIC_ESR) & 0xEF);
                if (send_status || accept_status)
                        break;
        }
        pr_debug("After Startup\n");

        if (send_status)
                pr_err("APIC never delivered???\n");
        if (accept_status)
                pr_err("APIC delivery error (%lx)\n", accept_status);

        preempt_enable();
        return (send_status | accept_status);
}

/* reduce the number of lines printed when booting a large cpu count system */
static void announce_cpu(int cpu, int apicid)
{
        static int width, node_width, first = 1;
        static int current_node = NUMA_NO_NODE;
        int node = early_cpu_to_node(cpu);

        if (!width)
                width = num_digits(num_possible_cpus()) + 1; /* + '#' sign */

        if (!node_width)
                node_width = num_digits(num_possible_nodes()) + 1; /* + '#' */

        if (system_state < SYSTEM_RUNNING) {
                if (first)
                        pr_info("x86: Booting SMP configuration:\n");

                if (node != current_node) {
                        if (current_node > (-1))
                                pr_cont("\n");
                        current_node = node;

                        printk(KERN_INFO ".... node %*s#%d, CPUs:  ",
                               node_width - num_digits(node), " ", node);
                }

                /* Add padding for the BSP */
                if (first)
                        pr_cont("%*s", width + 1, " ");
                first = 0;

                pr_cont("%*s#%d", width - num_digits(cpu), " ", cpu);
        } else
                pr_info("Booting Node %d Processor %d APIC 0x%x\n",
                        node, cpu, apicid);
}

int common_cpu_up(unsigned int cpu, struct task_struct *idle)
{
        int ret;

        /* Just in case we booted with a single CPU. */
        alternatives_enable_smp();

        per_cpu(pcpu_hot.current_task, cpu) = idle;
        cpu_init_stack_canary(cpu, idle);

        /* Initialize the interrupt stack(s) */
        ret = irq_init_percpu_irqstack(cpu);
        if (ret)
                return ret;

#ifdef CONFIG_X86_32
        /* Stack for startup_32 can be just as for start_secondary onwards */
        per_cpu(pcpu_hot.top_of_stack, cpu) = task_top_of_stack(idle);
#endif
        return 0;
}

/*
 * NOTE - on most systems this is a PHYSICAL apic ID, but on multiquad
 * (ie clustered apic addressing mode), this is a LOGICAL apic ID.
 * Returns zero if startup was successfully sent, else error code from
 * ->wakeup_secondary_cpu.
 */
static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
{
        unsigned long start_ip = real_mode_header->trampoline_start;
        int ret;

#ifdef CONFIG_X86_64
        /* If 64-bit wakeup method exists, use the 64-bit mode trampoline IP */
        if (apic->wakeup_secondary_cpu_64)
                start_ip = real_mode_header->trampoline_start64;
#endif
        idle->thread.sp = (unsigned long)task_pt_regs(idle);
        initial_code = (unsigned long)start_secondary;

        if (IS_ENABLED(CONFIG_X86_32)) {
                early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu);
                initial_stack  = idle->thread.sp;
        } else if (!(smpboot_control & STARTUP_PARALLEL_MASK)) {
                smpboot_control = cpu;
        }

        /* Enable the espfix hack for this CPU */
        init_espfix_ap(cpu);

        /* So we see what's up */
        announce_cpu(cpu, apicid);

        /*
         * This grunge runs the startup process for
         * the targeted processor.
         */
        if (x86_platform.legacy.warm_reset) {

                pr_debug("Setting warm reset code and vector.\n");

                smpboot_setup_warm_reset_vector(start_ip);
                /*
                 * Be paranoid about clearing APIC errors.
                */
                if (APIC_INTEGRATED(boot_cpu_apic_version)) {
                        apic_write(APIC_ESR, 0);
                        apic_read(APIC_ESR);
                }
        }

        smp_mb();

        /*
         * Wake up a CPU in difference cases:
         * - Use a method from the APIC driver if one defined, with wakeup
         *   straight to 64-bit mode preferred over wakeup to RM.
         * Otherwise,
         * - Use an INIT boot APIC message
         */
        if (apic->wakeup_secondary_cpu_64)
                ret = apic->wakeup_secondary_cpu_64(apicid, start_ip);
        else if (apic->wakeup_secondary_cpu)
                ret = apic->wakeup_secondary_cpu(apicid, start_ip);
        else
                ret = wakeup_secondary_cpu_via_init(apicid, start_ip);

        /* If the wakeup mechanism failed, cleanup the warm reset vector */
        if (ret)
                arch_cpuhp_cleanup_kick_cpu(cpu);
        return ret;
}

int native_kick_ap(unsigned int cpu, struct task_struct *tidle)
{
        int apicid = apic->cpu_present_to_apicid(cpu);
        int err;

        lockdep_assert_irqs_enabled();

        pr_debug("++++++++++++++++++++=_---CPU UP  %u\n", cpu);

        if (apicid == BAD_APICID || !physid_isset(apicid, phys_cpu_present_map) ||
            !apic_id_valid(apicid)) {
                pr_err("%s: bad cpu %d\n", __func__, cpu);
                return -EINVAL;
        }

        /*
         * Save current MTRR state in case it was changed since early boot
         * (e.g. by the ACPI SMI) to initialize new CPUs with MTRRs in sync:
         */
        mtrr_save_state();

        /* the FPU context is blank, nobody can own it */
        per_cpu(fpu_fpregs_owner_ctx, cpu) = NULL;

        err = common_cpu_up(cpu, tidle);
        if (err)
                return err;

        err = do_boot_cpu(apicid, cpu, tidle);
        if (err)
                pr_err("do_boot_cpu failed(%d) to wakeup CPU#%u\n", err, cpu);

        return err;
}

int arch_cpuhp_kick_ap_alive(unsigned int cpu, struct task_struct *tidle)
{
        return smp_ops.kick_ap_alive(cpu, tidle);
}

void arch_cpuhp_cleanup_kick_cpu(unsigned int cpu)
{
        /* Cleanup possible dangling ends... */
        if (smp_ops.kick_ap_alive == native_kick_ap && x86_platform.legacy.warm_reset)
                smpboot_restore_warm_reset_vector();
}

void arch_cpuhp_cleanup_dead_cpu(unsigned int cpu)
{
        if (smp_ops.cleanup_dead_cpu)
                smp_ops.cleanup_dead_cpu(cpu);

        if (system_state == SYSTEM_RUNNING)
                pr_info("CPU %u is now offline\n", cpu);
}

void arch_cpuhp_sync_state_poll(void)
{
        if (smp_ops.poll_sync_state)
                smp_ops.poll_sync_state();
}

/**
 * arch_disable_smp_support() - Disables SMP support for x86 at boottime
 */
void __init arch_disable_smp_support(void)
{
        disable_ioapic_support();
}

/*
 * Fall back to non SMP mode after errors.
 *
 * RED-PEN audit/test this more. I bet there is more state messed up here.
 */
static __init void disable_smp(void)
{
        pr_info("SMP disabled\n");

        disable_ioapic_support();

        init_cpu_present(cpumask_of(0));
        init_cpu_possible(cpumask_of(0));

        if (smp_found_config)
                physid_set_mask_of_physid(boot_cpu_physical_apicid, &phys_cpu_present_map);
        else
                physid_set_mask_of_physid(0, &phys_cpu_present_map);
        cpumask_set_cpu(0, topology_sibling_cpumask(0));
        cpumask_set_cpu(0, topology_core_cpumask(0));
        cpumask_set_cpu(0, topology_die_cpumask(0));
}

static void __init smp_cpu_index_default(void)
{
        int i;
        struct cpuinfo_x86 *c;

        for_each_possible_cpu(i) {
                c = &cpu_data(i);
                /* mark all to hotplug */
                c->cpu_index = nr_cpu_ids;
        }
}

void __init smp_prepare_cpus_common(void)
{
        unsigned int i;

        smp_cpu_index_default();

        /*
         * Setup boot CPU information
         */
        smp_store_boot_cpu_info(); /* Final full version of the data */
        mb();

        for_each_possible_cpu(i) {
                zalloc_cpumask_var(&per_cpu(cpu_sibling_map, i), GFP_KERNEL);
                zalloc_cpumask_var(&per_cpu(cpu_core_map, i), GFP_KERNEL);
                zalloc_cpumask_var(&per_cpu(cpu_die_map, i), GFP_KERNEL);
                zalloc_cpumask_var(&per_cpu(cpu_llc_shared_map, i), GFP_KERNEL);
                zalloc_cpumask_var(&per_cpu(cpu_l2c_shared_map, i), GFP_KERNEL);
        }

        set_cpu_sibling_map(0);
}

#ifdef CONFIG_X86_64
/* Establish whether parallel bringup can be supported. */
bool __init arch_cpuhp_init_parallel_bringup(void)
{
        if (!x86_cpuinit.parallel_bringup) {
                pr_info("Parallel CPU startup disabled by the platform\n");
                return false;
        }

        smpboot_control = STARTUP_READ_APICID;
        pr_debug("Parallel CPU startup enabled: 0x%08x\n", smpboot_control);
        return true;
}
#endif

/*
 * Prepare for SMP bootup.
 * @max_cpus: configured maximum number of CPUs, It is a legacy parameter
 *            for common interface support.
 */
void __init native_smp_prepare_cpus(unsigned int max_cpus)
{
        smp_prepare_cpus_common();

        switch (apic_intr_mode) {
        case APIC_PIC:
        case APIC_VIRTUAL_WIRE_NO_CONFIG:
                disable_smp();
                return;
        case APIC_SYMMETRIC_IO_NO_ROUTING:
                disable_smp();
                /* Setup local timer */
                x86_init.timers.setup_percpu_clockev();
                return;
        case APIC_VIRTUAL_WIRE:
        case APIC_SYMMETRIC_IO:
                break;
        }

        /* Setup local timer */
        x86_init.timers.setup_percpu_clockev();

        pr_info("CPU0: ");
        print_cpu_info(&cpu_data(0));

        uv_system_init();

        smp_quirk_init_udelay();

        speculative_store_bypass_ht_init();

        snp_set_wakeup_secondary_cpu();
}

void arch_thaw_secondary_cpus_begin(void)
{
        set_cache_aps_delayed_init(true);
}

void arch_thaw_secondary_cpus_end(void)
{
        cache_aps_init();
}

/*
 * Early setup to make printk work.
 */
void __init native_smp_prepare_boot_cpu(void)
{
        int me = smp_processor_id();

        /* SMP handles this from setup_per_cpu_areas() */
        if (!IS_ENABLED(CONFIG_SMP))
                switch_gdt_and_percpu_base(me);

        native_pv_lock_init();
}

void __init calculate_max_logical_packages(void)
{
        int ncpus;

        /*
         * Today neither Intel nor AMD support heterogeneous systems so
         * extrapolate the boot cpu's data to all packages.
         */
        ncpus = cpu_data(0).booted_cores * topology_max_smt_threads();
        __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);
        pr_info("Max logical packages: %u\n", __max_logical_packages);
}

void __init native_smp_cpus_done(unsigned int max_cpus)
{
        pr_debug("Boot done\n");

        calculate_max_logical_packages();
        build_sched_topology();
        nmi_selftest();
        impress_friends();
        cache_aps_init();
}

static int __initdata setup_possible_cpus = -1;
static int __init _setup_possible_cpus(char *str)
{
        get_option(&str, &setup_possible_cpus);
        return 0;
}
early_param("possible_cpus", _setup_possible_cpus);


/*
 * cpu_possible_mask should be static, it cannot change as cpu's
 * are onlined, or offlined. The reason is per-cpu data-structures
 * are allocated by some modules at init time, and don't expect to
 * do this dynamically on cpu arrival/departure.
 * cpu_present_mask on the other hand can change dynamically.
 * In case when cpu_hotplug is not compiled, then we resort to current
 * behaviour, which is cpu_possible == cpu_present.
 * - Ashok Raj
 *
 * Three ways to find out the number of additional hotplug CPUs:
 * - If the BIOS specified disabled CPUs in ACPI/mptables use that.
 * - The user can overwrite it with possible_cpus=NUM
 * - Otherwise don't reserve additional CPUs.
 * We do this because additional CPUs waste a lot of memory.
 * -AK
 */
__init void prefill_possible_map(void)
{
        int i, possible;

        i = setup_max_cpus ?: 1;
        if (setup_possible_cpus == -1) {
                possible = num_processors;
#ifdef CONFIG_HOTPLUG_CPU
                if (setup_max_cpus)
                        possible += disabled_cpus;
#else
                if (possible > i)
                        possible = i;
#endif
        } else
                possible = setup_possible_cpus;

        total_cpus = max_t(int, possible, num_processors + disabled_cpus);

        /* nr_cpu_ids could be reduced via nr_cpus= */
        if (possible > nr_cpu_ids) {
                pr_warn("%d Processors exceeds NR_CPUS limit of %u\n",
                        possible, nr_cpu_ids);
                possible = nr_cpu_ids;
        }

#ifdef CONFIG_HOTPLUG_CPU
        if (!setup_max_cpus)
#endif
        if (possible > i) {
                pr_warn("%d Processors exceeds max_cpus limit of %u\n",
                        possible, setup_max_cpus);
                possible = i;
        }

        set_nr_cpu_ids(possible);

        pr_info("Allowing %d CPUs, %d hotplug CPUs\n",
                possible, max_t(int, possible - num_processors, 0));

        reset_cpu_possible_mask();

        for (i = 0; i < possible; i++)
                set_cpu_possible(i, true);
}

/* correctly size the local cpu masks */
void __init setup_cpu_local_masks(void)
{
        alloc_bootmem_cpumask_var(&cpu_sibling_setup_mask);
}

#ifdef CONFIG_HOTPLUG_CPU

/* Recompute SMT state for all CPUs on offline */
static void recompute_smt_state(void)
{
        int max_threads, cpu;

        max_threads = 0;
        for_each_online_cpu (cpu) {
                int threads = cpumask_weight(topology_sibling_cpumask(cpu));

                if (threads > max_threads)
                        max_threads = threads;
        }
        __max_smt_threads = max_threads;
}

static void remove_siblinginfo(int cpu)
{
        int sibling;
        struct cpuinfo_x86 *c = &cpu_data(cpu);

        for_each_cpu(sibling, topology_core_cpumask(cpu)) {
                cpumask_clear_cpu(cpu, topology_core_cpumask(sibling));
                /*/
                 * last thread sibling in this cpu core going down
                 */
                if (cpumask_weight(topology_sibling_cpumask(cpu)) == 1)
                        cpu_data(sibling).booted_cores--;
        }

        for_each_cpu(sibling, topology_die_cpumask(cpu))
                cpumask_clear_cpu(cpu, topology_die_cpumask(sibling));

        for_each_cpu(sibling, topology_sibling_cpumask(cpu)) {
                cpumask_clear_cpu(cpu, topology_sibling_cpumask(sibling));
                if (cpumask_weight(topology_sibling_cpumask(sibling)) == 1)
                        cpu_data(sibling).smt_active = false;
        }

        for_each_cpu(sibling, cpu_llc_shared_mask(cpu))
                cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling));
        for_each_cpu(sibling, cpu_l2c_shared_mask(cpu))
                cpumask_clear_cpu(cpu, cpu_l2c_shared_mask(sibling));
        cpumask_clear(cpu_llc_shared_mask(cpu));
        cpumask_clear(cpu_l2c_shared_mask(cpu));
        cpumask_clear(topology_sibling_cpumask(cpu));
        cpumask_clear(topology_core_cpumask(cpu));
        cpumask_clear(topology_die_cpumask(cpu));
        c->cpu_core_id = 0;
        c->booted_cores = 0;
        cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
        recompute_smt_state();
}

static void remove_cpu_from_maps(int cpu)
{
        set_cpu_online(cpu, false);
        numa_remove_cpu(cpu);
}

void cpu_disable_common(void)
{
        int cpu = smp_processor_id();

        remove_siblinginfo(cpu);

        /* It's now safe to remove this processor from the online map */
        lock_vector_lock();
        remove_cpu_from_maps(cpu);
        unlock_vector_lock();
        fixup_irqs();
        lapic_offline();
}

int native_cpu_disable(void)
{
        int ret;

        ret = lapic_can_unplug_cpu();
        if (ret)
                return ret;

        cpu_disable_common();

        /*
         * Disable the local APIC. Otherwise IPI broadcasts will reach
         * it. It still responds normally to INIT, NMI, SMI, and SIPI
         * messages.
         *
         * Disabling the APIC must happen after cpu_disable_common()
         * which invokes fixup_irqs().
         *
         * Disabling the APIC preserves already set bits in IRR, but
         * an interrupt arriving after disabling the local APIC does not
         * set the corresponding IRR bit.
         *
         * fixup_irqs() scans IRR for set bits so it can raise a not
         * yet handled interrupt on the new destination CPU via an IPI
         * but obviously it can't do so for IRR bits which are not set.
         * IOW, interrupts arriving after disabling the local APIC will
         * be lost.
         */
        apic_soft_disable();

        return 0;
}

void play_dead_common(void)
{
        idle_task_exit();

        cpuhp_ap_report_dead();

        local_irq_disable();
}

/*
 * We need to flush the caches before going to sleep, lest we have
 * dirty data in our caches when we come back up.
 */
static inline void mwait_play_dead(void)
{
        struct mwait_cpu_dead *md = this_cpu_ptr(&mwait_cpu_dead);
        unsigned int eax, ebx, ecx, edx;
        unsigned int highest_cstate = 0;
        unsigned int highest_subcstate = 0;
        int i;

        if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
            boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
                return;
        if (!this_cpu_has(X86_FEATURE_MWAIT))
                return;
        if (!this_cpu_has(X86_FEATURE_CLFLUSH))
                return;
        if (__this_cpu_read(cpu_info.cpuid_level) < CPUID_MWAIT_LEAF)
                return;

        eax = CPUID_MWAIT_LEAF;
        ecx = 0;
        native_cpuid(&eax, &ebx, &ecx, &edx);

        /*
         * eax will be 0 if EDX enumeration is not valid.
         * Initialized below to cstate, sub_cstate value when EDX is valid.
         */
        if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED)) {
                eax = 0;
        } else {
                edx >>= MWAIT_SUBSTATE_SIZE;
                for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {
                        if (edx & MWAIT_SUBSTATE_MASK) {
                                highest_cstate = i;
                                highest_subcstate = edx & MWAIT_SUBSTATE_MASK;
                        }
                }
                eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
                        (highest_subcstate - 1);
        }

        /* Set up state for the kexec() hack below */
        md->status = CPUDEAD_MWAIT_WAIT;
        md->control = CPUDEAD_MWAIT_WAIT;

        wbinvd();

        while (1) {
                /*
                 * The CLFLUSH is a workaround for erratum AAI65 for
                 * the Xeon 7400 series.  It's not clear it is actually
                 * needed, but it should be harmless in either case.
                 * The WBINVD is insufficient due to the spurious-wakeup
                 * case where we return around the loop.
                 */
                mb();
                clflush(md);
                mb();
                __monitor(md, 0, 0);
                mb();
                __mwait(eax, 0);

                if (READ_ONCE(md->control) == CPUDEAD_MWAIT_KEXEC_HLT) {
                        /*
                         * Kexec is about to happen. Don't go back into mwait() as
                         * the kexec kernel might overwrite text and data including
                         * page tables and stack. So mwait() would resume when the
                         * monitor cache line is written to and then the CPU goes
                         * south due to overwritten text, page tables and stack.
                         *
                         * Note: This does _NOT_ protect against a stray MCE, NMI,
                         * SMI. They will resume execution at the instruction
                         * following the HLT instruction and run into the problem
                         * which this is trying to prevent.
                         */
                        WRITE_ONCE(md->status, CPUDEAD_MWAIT_KEXEC_HLT);
                        while(1)
                                native_halt();
                }
        }
}

/*
 * Kick all "offline" CPUs out of mwait on kexec(). See comment in
 * mwait_play_dead().
 */
void smp_kick_mwait_play_dead(void)
{
        u32 newstate = CPUDEAD_MWAIT_KEXEC_HLT;
        struct mwait_cpu_dead *md;
        unsigned int cpu, i;

        for_each_cpu_andnot(cpu, cpu_present_mask, cpu_online_mask) {
                md = per_cpu_ptr(&mwait_cpu_dead, cpu);

                /* Does it sit in mwait_play_dead() ? */
                if (READ_ONCE(md->status) != CPUDEAD_MWAIT_WAIT)
                        continue;

                /* Wait up to 5ms */
                for (i = 0; READ_ONCE(md->status) != newstate && i < 1000; i++) {
                        /* Bring it out of mwait */
                        WRITE_ONCE(md->control, newstate);
                        udelay(5);
                }

                if (READ_ONCE(md->status) != newstate)
                        pr_err_once("CPU%u is stuck in mwait_play_dead()\n", cpu);
        }
}

void __noreturn hlt_play_dead(void)
{
        if (__this_cpu_read(cpu_info.x86) >= 4)
                wbinvd();

        while (1)
                native_halt();
}

void native_play_dead(void)
{
        play_dead_common();
        tboot_shutdown(TB_SHUTDOWN_WFS);

        mwait_play_dead();
        if (cpuidle_play_dead())
                hlt_play_dead();
}

#else /* ... !CONFIG_HOTPLUG_CPU */
int native_cpu_disable(void)
{
        return -ENOSYS;
}

void native_play_dead(void)
{
        BUG();
}

#endif