Merge branch 'for-4.6' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq

[deliverable/linux.git] / arch / x86 / kernel / smpboot.c

 /*
 *      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.
 *
 *      This code is released under the GNU General Public License version 2 or
 *      later.
 *
 *      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/module.h>
#include <linux/sched.h>
#include <linux/percpu.h>
#include <linux/bootmem.h>
#include <linux/err.h>
#include <linux/nmi.h>
#include <linux/tboot.h>
#include <linux/stackprotector.h>
#include <linux/gfp.h>
#include <linux/cpuidle.h>

#include <asm/acpi.h>
#include <asm/desc.h>
#include <asm/nmi.h>
#include <asm/irq.h>
#include <asm/idle.h>
#include <asm/realmode.h>
#include <asm/cpu.h>
#include <asm/numa.h>
#include <asm/pgtable.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/internal.h>
#include <asm/setup.h>
#include <asm/uv/uv.h>
#include <linux/mc146818rtc.h>
#include <asm/i8259.h>
#include <asm/realmode.h>
#include <asm/misc.h>

/* Number of siblings per CPU package */
int smp_num_siblings = 1;
EXPORT_SYMBOL(smp_num_siblings);

/* Last level cache ID of each logical CPU */
DEFINE_PER_CPU_READ_MOSTLY(u16, cpu_llc_id) = BAD_APICID;

/* 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);

DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);

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

/* Logical package management. We might want to allocate that dynamically */
static int *physical_to_logical_pkg __read_mostly;
static unsigned long *physical_package_map __read_mostly;;
static unsigned long *logical_package_map  __read_mostly;
static unsigned int max_physical_pkg_id __read_mostly;
unsigned int __max_logical_packages __read_mostly;
EXPORT_SYMBOL(__max_logical_packages);

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

        spin_lock_irqsave(&rtc_lock, flags);
        CMOS_WRITE(0xa, 0xf);
        spin_unlock_irqrestore(&rtc_lock, flags);
        local_flush_tlb();
        pr_debug("1.\n");
        *((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) =
                                                        start_eip >> 4;
        pr_debug("2.\n");
        *((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) =
                                                        start_eip & 0xf;
        pr_debug("3.\n");
}

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

        /*
         * Install writable page 0 entry to set BIOS data area.
         */
        local_flush_tlb();

        /*
         * Paranoid:  Set warm reset code and vector here back
         * to default values.
         */
        spin_lock_irqsave(&rtc_lock, flags);
        CMOS_WRITE(0, 0xf);
        spin_unlock_irqrestore(&rtc_lock, flags);

        *((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
}

/*
 * Report back to the Boot Processor during boot time or to the caller processor
 * during CPU online.
 */
static void smp_callin(void)
{
        int cpuid, phys_id;

        /*
         * If waken up by an INIT in an 82489DX configuration
         * cpu_callout_mask guarantees we don't get here before
         * an INIT_deassert IPI reaches our local APIC, so it is
         * now safe to touch our local APIC.
         */
        cpuid = smp_processor_id();

        /*
         * (This works even if the APIC is not enabled.)
         */
        phys_id = read_apic_id();

        /*
         * the boot CPU has finished the init stage and is spinning
         * on callin_map until we finish. We are free to set up this
         * CPU, first the APIC. (this is probably redundant on most
         * boards)
         */
        apic_ap_setup();

        /*
         * Save our processor parameters. Note: this information
         * is needed for clock calibration.
         */
        smp_store_cpu_info(cpuid);

        /*
         * Get our bogomips.
         * Update loops_per_jiffy in cpu_data. Previous call to
         * smp_store_cpu_info() stored a value that is close but not as
         * accurate as the value just calculated.
         */
        calibrate_delay();
        cpu_data(cpuid).loops_per_jiffy = loops_per_jiffy;
        pr_debug("Stack at about %p\n", &cpuid);

        /*
         * This must be done before setting cpu_online_mask
         * or calling notify_cpu_starting.
         */
        set_cpu_sibling_map(raw_smp_processor_id());
        wmb();

        notify_cpu_starting(cpuid);

        /*
         * Allow the master to continue.
         */
        cpumask_set_cpu(cpuid, cpu_callin_mask);
}

static int cpu0_logical_apicid;
static int enable_start_cpu0;
/*
 * Activate a secondary processor.
 */
static void notrace start_secondary(void *unused)
{
        /*
         * Don't put *anything* before cpu_init(), SMP booting is too
         * fragile that we want to limit the things done here to the
         * most necessary things.
         */
        cpu_init();
        x86_cpuinit.early_percpu_clock_init();
        preempt_disable();
        smp_callin();

        enable_start_cpu0 = 0;

#ifdef CONFIG_X86_32
        /* switch away from the initial page table */
        load_cr3(swapper_pg_dir);
        __flush_tlb_all();
#endif

        /* otherwise gcc will move up smp_processor_id before the cpu_init */
        barrier();
        /*
         * Check TSC synchronization with the BP:
         */
        check_tsc_sync_target();

        /*
         * Lock vector_lock and initialize the vectors on this cpu
         * before setting the cpu online. We must set it online with
         * vector_lock held to prevent a concurrent setup/teardown
         * from seeing a half valid vector space.
         */
        lock_vector_lock();
        setup_vector_irq(smp_processor_id());
        set_cpu_online(smp_processor_id(), true);
        unlock_vector_lock();
        cpu_set_state_online(smp_processor_id());
        x86_platform.nmi_init();

        /* enable local interrupts */
        local_irq_enable();

        /* to prevent fake stack check failure in clock setup */
        boot_init_stack_canary();

        x86_cpuinit.setup_percpu_clockev();

        wmb();
        cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
}

int topology_update_package_map(unsigned int apicid, unsigned int cpu)
{
        unsigned int new, pkg = apicid >> boot_cpu_data.x86_coreid_bits;

        /* Called from early boot ? */
        if (!physical_package_map)
                return 0;

        if (pkg >= max_physical_pkg_id)
                return -EINVAL;

        /* Set the logical package id */
        if (test_and_set_bit(pkg, physical_package_map))
                goto found;

        if (pkg < __max_logical_packages) {
                set_bit(pkg, logical_package_map);
                physical_to_logical_pkg[pkg] = pkg;
                goto found;
        }
        new = find_first_zero_bit(logical_package_map, __max_logical_packages);
        if (new >= __max_logical_packages) {
                physical_to_logical_pkg[pkg] = -1;
                pr_warn("APIC(%x) Package %u exceeds logical package map\n",
                        apicid, pkg);
                return -ENOSPC;
        }
        set_bit(new, logical_package_map);
        pr_info("APIC(%x) Converting physical %u to logical package %u\n",
                apicid, pkg, new);
        physical_to_logical_pkg[pkg] = new;

found:
        cpu_data(cpu).logical_proc_id = physical_to_logical_pkg[pkg];
        return 0;
}

/**
 * topology_phys_to_logical_pkg - Map a physical package id to a logical
 *
 * Returns logical package id or -1 if not found
 */
int topology_phys_to_logical_pkg(unsigned int phys_pkg)
{
        if (phys_pkg >= max_physical_pkg_id)
                return -1;
        return physical_to_logical_pkg[phys_pkg];
}
EXPORT_SYMBOL(topology_phys_to_logical_pkg);

static void __init smp_init_package_map(void)
{
        unsigned int ncpus, cpu;
        size_t size;

        /*
         * Today neither Intel nor AMD support heterogenous systems. That
         * might change in the future....
         */
        ncpus = boot_cpu_data.x86_max_cores * smp_num_siblings;
        __max_logical_packages = DIV_ROUND_UP(nr_cpu_ids, ncpus);

        /*
         * Possibly larger than what we need as the number of apic ids per
         * package can be smaller than the actual used apic ids.
         */
        max_physical_pkg_id = DIV_ROUND_UP(MAX_LOCAL_APIC, ncpus);
        size = max_physical_pkg_id * sizeof(unsigned int);
        physical_to_logical_pkg = kmalloc(size, GFP_KERNEL);
        memset(physical_to_logical_pkg, 0xff, size);
        size = BITS_TO_LONGS(max_physical_pkg_id) * sizeof(unsigned long);
        physical_package_map = kzalloc(size, GFP_KERNEL);
        size = BITS_TO_LONGS(__max_logical_packages) * sizeof(unsigned long);
        logical_package_map = kzalloc(size, GFP_KERNEL);

        pr_info("Max logical packages: %u\n", __max_logical_packages);

        for_each_present_cpu(cpu) {
                unsigned int apicid = apic->cpu_present_to_apicid(cpu);

                if (apicid == BAD_APICID || !apic->apic_id_valid(apicid))
                        continue;
                if (!topology_update_package_map(apicid, cpu))
                        continue;
                pr_warn("CPU %u APICId %x disabled\n", cpu, apicid);
                per_cpu(x86_bios_cpu_apicid, cpu) = BAD_APICID;
                set_cpu_possible(cpu, false);
                set_cpu_present(cpu, false);
        }
}

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;
        smp_init_package_map();
}

/*
 * 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);

        *c = boot_cpu_data;
        c->cpu_index = id;
        /*
         * During boot time, CPU0 has this setup already. Save the info when
         * bringing up AP or offlined CPU0.
         */
        identify_secondary_cpu(c);
}

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 &&
                    per_cpu(cpu_llc_id, cpu1) == per_cpu(cpu_llc_id, cpu2) &&
                    c->compute_unit_id == o->compute_unit_id)
                        return topology_sane(c, o, "smt");

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

        return false;
}

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

        if (per_cpu(cpu_llc_id, cpu1) != BAD_APICID &&
            per_cpu(cpu_llc_id, cpu1) == per_cpu(cpu_llc_id, cpu2))
                return topology_sane(c, o, "llc");

        return false;
}

/*
 * 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_die(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
{
        if (c->phys_proc_id == o->phys_proc_id)
                return true;
        return false;
}

static struct sched_domain_topology_level numa_inside_package_topology[] = {
#ifdef CONFIG_SCHED_SMT
        { cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },
#endif
#ifdef CONFIG_SCHED_MC
        { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
#endif
        { NULL, },
};
/*
 * set_sched_topology() sets the topology internal to a CPU.  The
 * NUMA topologies are layered on top of it to build the full
 * system topology.
 *
 * If NUMA nodes are observed to occur within a CPU package, this
 * function should be called.  It forces the sched domain code to
 * only use the SMT level for the CPU portion of the topology.
 * This essentially falls back to relying on NUMA information
 * from the SRAT table to describe the entire system topology
 * (except for hyperthreads).
 */
static void primarily_use_numa_for_topology(void)
{
        set_sched_topology(numa_inside_package_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;

        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, topology_core_cpumask(cpu));
                c->booted_cores = 1;
                return;
        }

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

                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);

        }

        /*
         * 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_die(c, o))) {
                        link_mask(topology_core_cpumask, cpu, i);

                        /*
                         *  Does this new cpu bringup a new core?
                         */
                        if (cpumask_weight(
                            topology_sibling_cpumask(cpu)) == 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;
                }
                if (match_die(c, o) && !topology_same_node(c, o))
                        primarily_use_numa_for_topology();
        }
}

/* maps the cpu to the sched domain representing multi-core */
const struct cpumask *cpu_coregroup_mask(int cpu)
{
        return cpu_llc_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_possible_cpu(cpu)
                if (cpumask_test_cpu(cpu, cpu_callout_mask))
                        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");
}

void __inquire_remote_apic(int apicid)
{
        unsigned i, regs[] = { APIC_ID >> 4, APIC_LVR >> 4, APIC_SPIV >> 4 };
        const char * const names[] = { "ID", "VERSION", "SPIV" };
        int timeout;
        u32 status;

        pr_info("Inquiring remote APIC 0x%x...\n", apicid);

        for (i = 0; i < ARRAY_SIZE(regs); i++) {
                pr_info("... APIC 0x%x %s: ", apicid, names[i]);

                /*
                 * Wait for idle.
                 */
                status = safe_apic_wait_icr_idle();
                if (status)
                        pr_cont("a previous APIC delivery may have failed\n");

                apic_icr_write(APIC_DM_REMRD | regs[i], apicid);

                timeout = 0;
                do {
                        udelay(100);
                        status = apic_read(APIC_ICR) & APIC_ICR_RR_MASK;
                } while (status == APIC_ICR_RR_INPROG && timeout++ < 1000);

                switch (status) {
                case APIC_ICR_RR_VALID:
                        status = apic_read(APIC_RRR);
                        pr_cont("%08x\n", status);
                        break;
                default:
                        pr_cont("failed\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_AMD) && (boot_cpu_data.x86 >= 0xF))) {
                init_udelay = 0;
                return;
        }
        /* else, use legacy delay */
        init_udelay = UDELAY_10MS_DEFAULT;
}

/*
 * Poke the other CPU in the eye via NMI to wake it up. Remember that the normal
 * INIT, INIT, STARTUP sequence will reset the chip hard for us, and this
 * won't ... remember to clear down the APIC, etc later.
 */
int
wakeup_secondary_cpu_via_nmi(int apicid, unsigned long start_eip)
{
        unsigned long send_status, accept_status = 0;
        int maxlvt;

        /* Target chip */
        /* Boot on the stack */
        /* Kick the second */
        apic_icr_write(APIC_DM_NMI | apic->dest_logical, apicid);

        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.
         */
        udelay(200);
        if (APIC_INTEGRATED(apic_version[boot_cpu_physical_apicid])) {
                maxlvt = lapic_get_maxlvt();
                if (maxlvt > 3)                 /* Due to the Pentium erratum 3AP.  */
                        apic_write(APIC_ESR, 0);
                accept_status = (apic_read(APIC_ESR) & 0xEF);
        }
        pr_debug("NMI sent\n");

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

        return (send_status | accept_status);
}

static int
wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
{
        unsigned long send_status = 0, accept_status = 0;
        int maxlvt, num_starts, j;

        maxlvt = lapic_get_maxlvt();

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

        pr_debug("Asserting INIT\n");

        /*
         * Turn INIT on target chip
         */
        /*
         * Send IPI
         */
        apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT,
                       phys_apicid);

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

        udelay(init_udelay);

        pr_debug("Deasserting INIT\n");

        /* Target chip */
        /* Send IPI */
        apic_icr_write(APIC_INT_LEVELTRIG | APIC_DM_INIT, phys_apicid);

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

        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(apic_version[phys_apicid]))
                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);

        return (send_status | accept_status);
}

void smp_announce(void)
{
        int num_nodes = num_online_nodes();

        printk(KERN_INFO "x86: Booted up %d node%s, %d CPUs\n",
               num_nodes, (num_nodes > 1 ? "s" : ""), num_online_cpus());
}

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

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

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

        if (cpu == 1)
                printk(KERN_INFO "x86: Booting SMP configuration:\n");

        if (system_state == SYSTEM_BOOTING) {
                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 (cpu == 1)
                        pr_cont("%*s", width + 1, " ");

                pr_cont("%*s#%d", width - num_digits(cpu), " ", cpu);

        } else
                pr_info("Booting Node %d Processor %d APIC 0x%x\n",
                        node, cpu, apicid);
}

static int wakeup_cpu0_nmi(unsigned int cmd, struct pt_regs *regs)
{
        int cpu;

        cpu = smp_processor_id();
        if (cpu == 0 && !cpu_online(cpu) && enable_start_cpu0)
                return NMI_HANDLED;

        return NMI_DONE;
}

/*
 * Wake up AP by INIT, INIT, STARTUP sequence.
 *
 * Instead of waiting for STARTUP after INITs, BSP will execute the BIOS
 * boot-strap code which is not a desired behavior for waking up BSP. To
 * void the boot-strap code, wake up CPU0 by NMI instead.
 *
 * This works to wake up soft offlined CPU0 only. If CPU0 is hard offlined
 * (i.e. physically hot removed and then hot added), NMI won't wake it up.
 * We'll change this code in the future to wake up hard offlined CPU0 if
 * real platform and request are available.
 */
static int
wakeup_cpu_via_init_nmi(int cpu, unsigned long start_ip, int apicid,
               int *cpu0_nmi_registered)
{
        int id;
        int boot_error;

        preempt_disable();

        /*
         * Wake up AP by INIT, INIT, STARTUP sequence.
         */
        if (cpu) {
                boot_error = wakeup_secondary_cpu_via_init(apicid, start_ip);
                goto out;
        }

        /*
         * Wake up BSP by nmi.
         *
         * Register a NMI handler to help wake up CPU0.
         */
        boot_error = register_nmi_handler(NMI_LOCAL,
                                          wakeup_cpu0_nmi, 0, "wake_cpu0");

        if (!boot_error) {
                enable_start_cpu0 = 1;
                *cpu0_nmi_registered = 1;
                if (apic->dest_logical == APIC_DEST_LOGICAL)
                        id = cpu0_logical_apicid;
                else
                        id = apicid;
                boot_error = wakeup_secondary_cpu_via_nmi(id, start_ip);
        }

out:
        preempt_enable();

        return boot_error;
}

void common_cpu_up(unsigned int cpu, struct task_struct *idle)
{
        /* Just in case we booted with a single CPU. */
        alternatives_enable_smp();

        per_cpu(current_task, cpu) = idle;

#ifdef CONFIG_X86_32
        /* Stack for startup_32 can be just as for start_secondary onwards */
        irq_ctx_init(cpu);
        per_cpu(cpu_current_top_of_stack, cpu) =
                (unsigned long)task_stack_page(idle) + THREAD_SIZE;
#else
        clear_tsk_thread_flag(idle, TIF_FORK);
        initial_gs = per_cpu_offset(cpu);
#endif
}

/*
 * 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 CPU booted OK, else error code from
 * ->wakeup_secondary_cpu.
 */
static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
{
        volatile u32 *trampoline_status =
                (volatile u32 *) __va(real_mode_header->trampoline_status);
        /* start_ip had better be page-aligned! */
        unsigned long start_ip = real_mode_header->trampoline_start;

        unsigned long boot_error = 0;
        int cpu0_nmi_registered = 0;
        unsigned long timeout;

        idle->thread.sp = (unsigned long) (((struct pt_regs *)
                          (THREAD_SIZE +  task_stack_page(idle))) - 1);

        early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
        initial_code = (unsigned long)start_secondary;
        stack_start  = idle->thread.sp;

        /*
         * Enable the espfix hack for this CPU
        */
#ifdef CONFIG_X86_ESPFIX64
        init_espfix_ap(cpu);
#endif

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

        /*
         * This grunge runs the startup process for
         * the targeted processor.
         */

        if (get_uv_system_type() != UV_NON_UNIQUE_APIC) {

                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(apic_version[boot_cpu_physical_apicid])) {
                        apic_write(APIC_ESR, 0);
                        apic_read(APIC_ESR);
                }
        }

        /*
         * AP might wait on cpu_callout_mask in cpu_init() with
         * cpu_initialized_mask set if previous attempt to online
         * it timed-out. Clear cpu_initialized_mask so that after
         * INIT/SIPI it could start with a clean state.
         */
        cpumask_clear_cpu(cpu, cpu_initialized_mask);
        smp_mb();

        /*
         * Wake up a CPU in difference cases:
         * - Use the method in the APIC driver if it's defined
         * Otherwise,
         * - Use an INIT boot APIC message for APs or NMI for BSP.
         */
        if (apic->wakeup_secondary_cpu)
                boot_error = apic->wakeup_secondary_cpu(apicid, start_ip);
        else
                boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
                                                     &cpu0_nmi_registered);

        if (!boot_error) {
                /*
                 * Wait 10s total for first sign of life from AP
                 */
                boot_error = -1;
                timeout = jiffies + 10*HZ;
                while (time_before(jiffies, timeout)) {
                        if (cpumask_test_cpu(cpu, cpu_initialized_mask)) {
                                /*
                                 * Tell AP to proceed with initialization
                                 */
                                cpumask_set_cpu(cpu, cpu_callout_mask);
                                boot_error = 0;
                                break;
                        }
                        schedule();
                }
        }

        if (!boot_error) {
                /*
                 * Wait till AP completes initial initialization
                 */
                while (!cpumask_test_cpu(cpu, cpu_callin_mask)) {
                        /*
                         * Allow other tasks to run while we wait for the
                         * AP to come online. This also gives a chance
                         * for the MTRR work(triggered by the AP coming online)
                         * to be completed in the stop machine context.
                         */
                        schedule();
                }
        }

        /* mark "stuck" area as not stuck */
        *trampoline_status = 0;

        if (get_uv_system_type() != UV_NON_UNIQUE_APIC) {
                /*
                 * Cleanup possible dangling ends...
                 */
                smpboot_restore_warm_reset_vector();
        }
        /*
         * Clean up the nmi handler. Do this after the callin and callout sync
         * to avoid impact of possible long unregister time.
         */
        if (cpu0_nmi_registered)
                unregister_nmi_handler(NMI_LOCAL, "wake_cpu0");

        return boot_error;
}

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

        WARN_ON(irqs_disabled());

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

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

        /*
         * Already booted CPU?
         */
        if (cpumask_test_cpu(cpu, cpu_callin_mask)) {
                pr_debug("do_boot_cpu %d Already started\n", cpu);
                return -ENOSYS;
        }

        /*
         * 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();

        /* x86 CPUs take themselves offline, so delayed offline is OK. */
        err = cpu_check_up_prepare(cpu);
        if (err && err != -EBUSY)
                return err;

        /* the FPU context is blank, nobody can own it */
        __cpu_disable_lazy_restore(cpu);

        common_cpu_up(cpu, tidle);

        /*
         * We 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();

        err = do_boot_cpu(apicid, cpu, tidle);

        if (err) {
                irq_unlock_sparse();
                pr_err("do_boot_cpu failed(%d) to wakeup CPU#%u\n", err, cpu);
                return -EIO;
        }

        /*
         * Check TSC synchronization with the AP (keep irqs disabled
         * while doing so):
         */
        local_irq_save(flags);
        check_tsc_sync_source(cpu);
        local_irq_restore(flags);

        while (!cpu_online(cpu)) {
                cpu_relax();
                touch_nmi_watchdog();
        }

        irq_unlock_sparse();

        return 0;
}

/**
 * arch_disable_smp_support() - disables SMP support for x86 at runtime
 */
void 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));
}

enum {
        SMP_OK,
        SMP_NO_CONFIG,
        SMP_NO_APIC,
        SMP_FORCE_UP,
};

/*
 * Various sanity checks.
 */
static int __init smp_sanity_check(unsigned max_cpus)
{
        preempt_disable();

#if !defined(CONFIG_X86_BIGSMP) && defined(CONFIG_X86_32)
        if (def_to_bigsmp && nr_cpu_ids > 8) {
                unsigned int cpu;
                unsigned nr;

                pr_warn("More than 8 CPUs detected - skipping them\n"
                        "Use CONFIG_X86_BIGSMP\n");

                nr = 0;
                for_each_present_cpu(cpu) {
                        if (nr >= 8)
                                set_cpu_present(cpu, false);
                        nr++;
                }

                nr = 0;
                for_each_possible_cpu(cpu) {
                        if (nr >= 8)
                                set_cpu_possible(cpu, false);
                        nr++;
                }

                nr_cpu_ids = 8;
        }
#endif

        if (!physid_isset(hard_smp_processor_id(), phys_cpu_present_map)) {
                pr_warn("weird, boot CPU (#%d) not listed by the BIOS\n",
                        hard_smp_processor_id());

                physid_set(hard_smp_processor_id(), phys_cpu_present_map);
        }

        /*
         * If we couldn't find an SMP configuration at boot time,
         * get out of here now!
         */
        if (!smp_found_config && !acpi_lapic) {
                preempt_enable();
                pr_notice("SMP motherboard not detected\n");
                return SMP_NO_CONFIG;
        }

        /*
         * Should not be necessary because the MP table should list the boot
         * CPU too, but we do it for the sake of robustness anyway.
         */
        if (!apic->check_phys_apicid_present(boot_cpu_physical_apicid)) {
                pr_notice("weird, boot CPU (#%d) not listed by the BIOS\n",
                          boot_cpu_physical_apicid);
                physid_set(hard_smp_processor_id(), phys_cpu_present_map);
        }
        preempt_enable();

        /*
         * If we couldn't find a local APIC, then get out of here now!
         */
        if (APIC_INTEGRATED(apic_version[boot_cpu_physical_apicid]) &&
            !cpu_has_apic) {
                if (!disable_apic) {
                        pr_err("BIOS bug, local APIC #%d not detected!...\n",
                                boot_cpu_physical_apicid);
                        pr_err("... forcing use of dummy APIC emulation (tell your hw vendor)\n");
                }
                return SMP_NO_APIC;
        }

        /*
         * If SMP should be disabled, then really disable it!
         */
        if (!max_cpus) {
                pr_info("SMP mode deactivated\n");
                return SMP_FORCE_UP;
        }

        return SMP_OK;
}

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;
        }
}

/*
 * Prepare for SMP bootup.  The MP table or ACPI has been read
 * earlier.  Just do some sanity checking here and enable APIC mode.
 */
void __init native_smp_prepare_cpus(unsigned int max_cpus)
{
        unsigned int i;

        smp_cpu_index_default();

        /*
         * Setup boot CPU information
         */
        smp_store_boot_cpu_info(); /* Final full version of the data */
        cpumask_copy(cpu_callin_mask, cpumask_of(0));
        mb();

        current_thread_info()->cpu = 0;  /* needed? */
        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_llc_shared_map, i), GFP_KERNEL);
        }
        set_cpu_sibling_map(0);

        switch (smp_sanity_check(max_cpus)) {
        case SMP_NO_CONFIG:
                disable_smp();
                if (APIC_init_uniprocessor())
                        pr_notice("Local APIC not detected. Using dummy APIC emulation.\n");
                return;
        case SMP_NO_APIC:
                disable_smp();
                return;
        case SMP_FORCE_UP:
                disable_smp();
                apic_bsp_setup(false);
                return;
        case SMP_OK:
                break;
        }

        default_setup_apic_routing();

        if (read_apic_id() != boot_cpu_physical_apicid) {
                panic("Boot APIC ID in local APIC unexpected (%d vs %d)",
                     read_apic_id(), boot_cpu_physical_apicid);
                /* Or can we switch back to PIC here? */
        }

        cpu0_logical_apicid = apic_bsp_setup(false);

        pr_info("CPU%d: ", 0);
        print_cpu_info(&cpu_data(0));

        if (is_uv_system())
                uv_system_init();

        set_mtrr_aps_delayed_init();

        smp_quirk_init_udelay();
}

void arch_enable_nonboot_cpus_begin(void)
{
        set_mtrr_aps_delayed_init();
}

void arch_enable_nonboot_cpus_end(void)
{
        mtrr_aps_init();
}

/*
 * Early setup to make printk work.
 */
void __init native_smp_prepare_boot_cpu(void)
{
        int me = smp_processor_id();
        switch_to_new_gdt(me);
        /* already set me in cpu_online_mask in boot_cpu_init() */
        cpumask_set_cpu(me, cpu_callout_mask);
        cpu_set_state_online(me);
}

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

        nmi_selftest();
        impress_friends();
        setup_ioapic_dest();
        mtrr_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 dont 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;

        /* no processor from mptable or madt */
        if (!num_processors)
                num_processors = 1;

        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 %d\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;
        }

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

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

        nr_cpu_ids = possible;
}

#ifdef CONFIG_HOTPLUG_CPU

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_sibling_cpumask(cpu))
                cpumask_clear_cpu(cpu, topology_sibling_cpumask(sibling));
        for_each_cpu(sibling, cpu_llc_shared_mask(cpu))
                cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling));
        cpumask_clear(cpu_llc_shared_mask(cpu));
        cpumask_clear(topology_sibling_cpumask(cpu));
        cpumask_clear(topology_core_cpumask(cpu));
        c->phys_proc_id = 0;
        c->cpu_core_id = 0;
        cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
}

static void remove_cpu_from_maps(int cpu)
{
        set_cpu_online(cpu, false);
        cpumask_clear_cpu(cpu, cpu_callout_mask);
        cpumask_clear_cpu(cpu, cpu_callin_mask);
        /* was set by cpu_init() */
        cpumask_clear_cpu(cpu, cpu_initialized_mask);
        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();
}

int native_cpu_disable(void)
{
        int ret;

        ret = check_irq_vectors_for_cpu_disable();
        if (ret)
                return ret;

        clear_local_APIC();
        cpu_disable_common();

        return 0;
}

int common_cpu_die(unsigned int cpu)
{
        int ret = 0;

        /* We don't do anything here: idle task is faking death itself. */

        /* They ack this in play_dead() by setting CPU_DEAD */
        if (cpu_wait_death(cpu, 5)) {
                if (system_state == SYSTEM_RUNNING)
                        pr_info("CPU %u is now offline\n", cpu);
        } else {
                pr_err("CPU %u didn't die...\n", cpu);
                ret = -1;
        }

        return ret;
}

void native_cpu_die(unsigned int cpu)
{
        common_cpu_die(cpu);
}

void play_dead_common(void)
{
        idle_task_exit();
        reset_lazy_tlbstate();
        amd_e400_remove_cpu(raw_smp_processor_id());

        /* Ack it */
        (void)cpu_report_death();

        /*
         * With physical CPU hotplug, we should halt the cpu
         */
        local_irq_disable();
}

static bool wakeup_cpu0(void)
{
        if (smp_processor_id() == 0 && enable_start_cpu0)
                return true;

        return false;
}

/*
 * 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)
{
        unsigned int eax, ebx, ecx, edx;
        unsigned int highest_cstate = 0;
        unsigned int highest_subcstate = 0;
        void *mwait_ptr;
        int i;

        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);
        }

        /*
         * This should be a memory location in a cache line which is
         * unlikely to be touched by other processors.  The actual
         * content is immaterial as it is not actually modified in any way.
         */
        mwait_ptr = &current_thread_info()->flags;

        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(mwait_ptr);
                mb();
                __monitor(mwait_ptr, 0, 0);
                mb();
                __mwait(eax, 0);
                /*
                 * If NMI wants to wake up CPU0, start CPU0.
                 */
                if (wakeup_cpu0())
                        start_cpu0();
        }
}

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

        while (1) {
                native_halt();
                /*
                 * If NMI wants to wake up CPU0, start CPU0.
                 */
                if (wakeup_cpu0())
                        start_cpu0();
        }
}

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

        mwait_play_dead();      /* Only returns on failure */
        if (cpuidle_play_dead())
                hlt_play_dead();
}

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

void native_cpu_die(unsigned int cpu)
{
        /* We said "no" in __cpu_disable */
        BUG();
}

void native_play_dead(void)
{
        BUG();
}

#endif