reboot.c

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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/reboot.h>
#include <linux/init.h>
#include <linux/pm.h>
#include <linux/efi.h>
#include <linux/dmi.h>
#include <linux/sched.h>
#include <linux/tboot.h>
#include <linux/delay.h>
#include <acpi/reboot.h>
#include <asm/io.h>
#include <asm/apic.h>
#include <asm/desc.h>
#include <asm/hpet.h>
#include <asm/pgtable.h>
#include <asm/proto.h>
#include <asm/reboot_fixups.h>
#include <asm/reboot.h>
#include <asm/pci_x86.h>
#include <asm/virtext.h>
#include <asm/cpu.h>
#include <asm/nmi.h>
#include <asm/smp.h>

#include <linux/ctype.h>
#include <linux/mc146818rtc.h>
#include <asm/realmode.h>
#include <asm/x86_init.h>

/*
 * Power off function, if any
 */
void (*pm_power_off)(void);
EXPORT_SYMBOL(pm_power_off);

static const struct desc_ptr no_idt = {};
static int reboot_mode;
enum reboot_type reboot_type = BOOT_ACPI;
int reboot_force;

/*
 * This variable is used privately to keep track of whether or not
 * reboot_type is still set to its default value (i.e., reboot= hasn't
 * been set on the command line).  This is needed so that we can
 * suppress DMI scanning for reboot quirks.  Without it, it's
 * impossible to override a faulty reboot quirk without recompiling.
 */
static int reboot_default = 1;

#ifdef CONFIG_SMP
static int reboot_cpu = -1;
#endif

/*
 * This is set if we need to go through the 'emergency' path.
 * When machine_emergency_restart() is called, we may be on
 * an inconsistent state and won't be able to do a clean cleanup
 */
static int reboot_emergency;

/* This is set by the PCI code if either type 1 or type 2 PCI is detected */
bool port_cf9_safe = false;

/*
 * reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old] | p[ci]
 * warm   Don't set the cold reboot flag
 * cold   Set the cold reboot flag
 * bios   Reboot by jumping through the BIOS
 * smp    Reboot by executing reset on BSP or other CPU
 * triple Force a triple fault (init)
 * kbd    Use the keyboard controller. cold reset (default)
 * acpi   Use the RESET_REG in the FADT
 * efi    Use efi reset_system runtime service
 * pci    Use the so-called "PCI reset register", CF9
 * force  Avoid anything that could hang.
 */
static int __init reboot_setup(char *str)
{
    for (;;) {
        /*
         * Having anything passed on the command line via
         * reboot= will cause us to disable DMI checking
         * below.
         */
        reboot_default = 0;

        switch (*str) {
        case 'w':
            reboot_mode = 0x1234;
            break;

        case 'c':
            reboot_mode = 0;
            break;

#ifdef CONFIG_SMP
        case 's':
            if (isdigit(*(str+1))) {
                reboot_cpu = (int) (*(str+1) - '0');
                if (isdigit(*(str+2)))
                    reboot_cpu = reboot_cpu*10 + (int)(*(str+2) - '0');
            }
            /*
             * We will leave sorting out the final value
             * when we are ready to reboot, since we might not
             * have detected BSP APIC ID or smp_num_cpu
             */
            break;
#endif /* CONFIG_SMP */

        case 'b':
        case 'a':
        case 'k':
        case 't':
        case 'e':
        case 'p':
            reboot_type = *str;
            break;

        case 'f':
            reboot_force = 1;
            break;
        }

        str = strchr(str, ',');
        if (str)
            str++;
        else
            break;
    }
    return 1;
}

__setup("reboot=", reboot_setup);


/*
 * Reboot options and system auto-detection code provided by
 * Dell Inc. so their systems "just work". :-)
 */

/*
 * Some machines require the "reboot=b" or "reboot=k"  commandline options,
 * this quirk makes that automatic.
 */
static int __init set_bios_reboot(const struct dmi_system_id *d)
{
    if (reboot_type != BOOT_BIOS) {
        reboot_type = BOOT_BIOS;
        pr_info("%s series board detected. Selecting %s-method for reboots.\n",
            "BIOS", d->ident);
    }
    return 0;
}

void __noreturn machine_real_restart(unsigned int type)
{
    local_irq_disable();

    /*
     * Write zero to CMOS register number 0x0f, which the BIOS POST
     * routine will recognize as telling it to do a proper reboot.  (Well
     * that's what this book in front of me says -- it may only apply to
     * the Phoenix BIOS though, it's not clear).  At the same time,
     * disable NMIs by setting the top bit in the CMOS address register,
     * as we're about to do peculiar things to the CPU.  I'm not sure if
     * `outb_p' is needed instead of just `outb'.  Use it to be on the
     * safe side.  (Yes, CMOS_WRITE does outb_p's. -  Paul G.)
     */
    spin_lock(&rtc_lock);
    CMOS_WRITE(0x00, 0x8f);
    spin_unlock(&rtc_lock);

    /*
     * Switch back to the initial page table.
     */
#ifdef CONFIG_X86_32
    load_cr3(initial_page_table);
#else
    write_cr3(real_mode_header->trampoline_pgd);
#endif

    /* Jump to the identity-mapped low memory code */
#ifdef CONFIG_X86_32
    asm volatile("jmpl *%0" : :
             "rm" (real_mode_header->machine_real_restart_asm),
             "a" (type));
#else
    asm volatile("ljmpl *%0" : :
             "m" (real_mode_header->machine_real_restart_asm),
             "D" (type));
#endif
    unreachable();
}
#ifdef CONFIG_APM_MODULE
EXPORT_SYMBOL(machine_real_restart);
#endif

/*
 * Some Apple MacBook and MacBookPro's needs reboot=p to be able to reboot
 */
static int __init set_pci_reboot(const struct dmi_system_id *d)
{
    if (reboot_type != BOOT_CF9) {
        reboot_type = BOOT_CF9;
        pr_info("%s series board detected. Selecting %s-method for reboots.\n",
            "PCI", d->ident);
    }
    return 0;
}

static int __init set_kbd_reboot(const struct dmi_system_id *d)
{
    if (reboot_type != BOOT_KBD) {
        reboot_type = BOOT_KBD;
        pr_info("%s series board detected. Selecting %s-method for reboot.\n",
            "KBD", d->ident);
    }
    return 0;
}

/*
 * This is a single dmi_table handling all reboot quirks.
 */
static struct dmi_system_id __initdata reboot_dmi_table[] = {
    {   /* Handle problems with rebooting on Dell E520's */
        .callback = set_bios_reboot,
        .ident = "Dell E520",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Dell DM061"),
        },
    },
    {   /* Handle problems with rebooting on Dell 1300's */
        .callback = set_bios_reboot,
        .ident = "Dell PowerEdge 1300",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
            DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 1300/"),
        },
    },
    {   /* Handle problems with rebooting on Dell 300's */
        .callback = set_bios_reboot,
        .ident = "Dell PowerEdge 300",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
            DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 300/"),
        },
    },
    {   /* Handle problems with rebooting on Dell Optiplex 745's SFF */
        .callback = set_bios_reboot,
        .ident = "Dell OptiPlex 745",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
        },
    },
    {   /* Handle problems with rebooting on Dell Optiplex 745's DFF */
        .callback = set_bios_reboot,
        .ident = "Dell OptiPlex 745",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
            DMI_MATCH(DMI_BOARD_NAME, "0MM599"),
        },
    },
    {   /* Handle problems with rebooting on Dell Optiplex 745 with 0KW626 */
        .callback = set_bios_reboot,
        .ident = "Dell OptiPlex 745",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
            DMI_MATCH(DMI_BOARD_NAME, "0KW626"),
        },
    },
    {   /* Handle problems with rebooting on Dell Optiplex 330 with 0KP561 */
        .callback = set_bios_reboot,
        .ident = "Dell OptiPlex 330",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 330"),
            DMI_MATCH(DMI_BOARD_NAME, "0KP561"),
        },
    },
    {   /* Handle problems with rebooting on Dell Optiplex 360 with 0T656F */
        .callback = set_bios_reboot,
        .ident = "Dell OptiPlex 360",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 360"),
            DMI_MATCH(DMI_BOARD_NAME, "0T656F"),
        },
    },
    {   /* Handle problems with rebooting on Dell OptiPlex 760 with 0G919G */
        .callback = set_bios_reboot,
        .ident = "Dell OptiPlex 760",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 760"),
            DMI_MATCH(DMI_BOARD_NAME, "0G919G"),
        },
    },
    {   /* Handle problems with rebooting on Dell 2400's */
        .callback = set_bios_reboot,
        .ident = "Dell PowerEdge 2400",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
            DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 2400"),
        },
    },
    {   /* Handle problems with rebooting on Dell T5400's */
        .callback = set_bios_reboot,
        .ident = "Dell Precision T5400",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Precision WorkStation T5400"),
        },
    },
    {   /* Handle problems with rebooting on Dell T7400's */
        .callback = set_bios_reboot,
        .ident = "Dell Precision T7400",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Precision WorkStation T7400"),
        },
    },
    {   /* Handle problems with rebooting on HP laptops */
        .callback = set_bios_reboot,
        .ident = "HP Compaq Laptop",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
            DMI_MATCH(DMI_PRODUCT_NAME, "HP Compaq"),
        },
    },
    {   /* Handle problems with rebooting on Dell XPS710 */
        .callback = set_bios_reboot,
        .ident = "Dell XPS710",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Dell XPS710"),
        },
    },
    {   /* Handle problems with rebooting on Dell DXP061 */
        .callback = set_bios_reboot,
        .ident = "Dell DXP061",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Dell DXP061"),
        },
    },
    {   /* Handle problems with rebooting on Sony VGN-Z540N */
        .callback = set_bios_reboot,
        .ident = "Sony VGN-Z540N",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
            DMI_MATCH(DMI_PRODUCT_NAME, "VGN-Z540N"),
        },
    },
    {   /* Handle problems with rebooting on ASUS P4S800 */
        .callback = set_bios_reboot,
        .ident = "ASUS P4S800",
        .matches = {
            DMI_MATCH(DMI_BOARD_VENDOR, "ASUSTeK Computer INC."),
            DMI_MATCH(DMI_BOARD_NAME, "P4S800"),
        },
    },

    {   /* Handle reboot issue on Acer Aspire one */
        .callback = set_kbd_reboot,
        .ident = "Acer Aspire One A110",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
            DMI_MATCH(DMI_PRODUCT_NAME, "AOA110"),
        },
    },
    {   /* Handle problems with rebooting on Apple MacBook5 */
        .callback = set_pci_reboot,
        .ident = "Apple MacBook5",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "MacBook5"),
        },
    },
    {   /* Handle problems with rebooting on Apple MacBookPro5 */
        .callback = set_pci_reboot,
        .ident = "Apple MacBookPro5",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "MacBookPro5"),
        },
    },
    {   /* Handle problems with rebooting on Apple Macmini3,1 */
        .callback = set_pci_reboot,
        .ident = "Apple Macmini3,1",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Macmini3,1"),
        },
    },
    {   /* Handle problems with rebooting on the iMac9,1. */
        .callback = set_pci_reboot,
        .ident = "Apple iMac9,1",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "iMac9,1"),
        },
    },
    {   /* Handle problems with rebooting on the Latitude E6320. */
        .callback = set_pci_reboot,
        .ident = "Dell Latitude E6320",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E6320"),
        },
    },
    {   /* Handle problems with rebooting on the Latitude E5420. */
        .callback = set_pci_reboot,
        .ident = "Dell Latitude E5420",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E5420"),
        },
    },
    {   /* Handle problems with rebooting on the Latitude E6420. */
        .callback = set_pci_reboot,
        .ident = "Dell Latitude E6420",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E6420"),
        },
    },
    {   /* Handle problems with rebooting on the OptiPlex 990. */
        .callback = set_pci_reboot,
        .ident = "Dell OptiPlex 990",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 990"),
        },
    },
    {   /* Handle problems with rebooting on the Precision M6600. */
        .callback = set_pci_reboot,
        .ident = "Dell OptiPlex 990",
        .matches = {
            DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
            DMI_MATCH(DMI_PRODUCT_NAME, "Precision M6600"),
        },
    },
    { }
};

static int __init reboot_init(void)
{
    /*
     * Only do the DMI check if reboot_type hasn't been overridden
     * on the command line
     */
    if (reboot_default)
        dmi_check_system(reboot_dmi_table);
    return 0;
}
core_initcall(reboot_init);

static inline void kb_wait(void)
{
    int i;

    for (i = 0; i < 0x10000; i++) {
        if ((inb(0x64) & 0x02) == 0)
            break;
        udelay(2);
    }
}

static void vmxoff_nmi(int cpu, struct pt_regs *regs)
{
    cpu_emergency_vmxoff();
}

/* Use NMIs as IPIs to tell all CPUs to disable virtualization */
static void emergency_vmx_disable_all(void)
{
    /* Just make sure we won't change CPUs while doing this */
    local_irq_disable();

    /*
     * We need to disable VMX on all CPUs before rebooting, otherwise
     * we risk hanging up the machine, because the CPU ignore INIT
     * signals when VMX is enabled.
     *
     * We can't take any locks and we may be on an inconsistent
     * state, so we use NMIs as IPIs to tell the other CPUs to disable
     * VMX and halt.
     *
     * For safety, we will avoid running the nmi_shootdown_cpus()
     * stuff unnecessarily, but we don't have a way to check
     * if other CPUs have VMX enabled. So we will call it only if the
     * CPU we are running on has VMX enabled.
     *
     * We will miss cases where VMX is not enabled on all CPUs. This
     * shouldn't do much harm because KVM always enable VMX on all
     * CPUs anyway. But we can miss it on the small window where KVM
     * is still enabling VMX.
     */
    if (cpu_has_vmx() && cpu_vmx_enabled()) {
        /* Disable VMX on this CPU. */
        cpu_vmxoff();

        /* Halt and disable VMX on the other CPUs */
        nmi_shootdown_cpus(vmxoff_nmi);

    }
}


void __attribute__((weak)) mach_reboot_fixups(void)
{
}

/*
 * Windows compatible x86 hardware expects the following on reboot:
 *
 * 1) If the FADT has the ACPI reboot register flag set, try it
 * 2) If still alive, write to the keyboard controller
 * 3) If still alive, write to the ACPI reboot register again
 * 4) If still alive, write to the keyboard controller again
 *
 * If the machine is still alive at this stage, it gives up. We default to
 * following the same pattern, except that if we're still alive after (4) we'll
 * try to force a triple fault and then cycle between hitting the keyboard
 * controller and doing that
 */
static void native_machine_emergency_restart(void)
{
    int i;
    int attempt = 0;
    int orig_reboot_type = reboot_type;

    if (reboot_emergency)
        emergency_vmx_disable_all();

    tboot_shutdown(TB_SHUTDOWN_REBOOT);

    /* Tell the BIOS if we want cold or warm reboot */
    *((unsigned short *)__va(0x472)) = reboot_mode;

    for (;;) {
        /* Could also try the reset bit in the Hammer NB */
        switch (reboot_type) {
        case BOOT_KBD:
            mach_reboot_fixups(); /* For board specific fixups */

            for (i = 0; i < 10; i++) {
                kb_wait();
                udelay(50);
                outb(0xfe, 0x64); /* Pulse reset low */
                udelay(50);
            }
            if (attempt == 0 && orig_reboot_type == BOOT_ACPI) {
                attempt = 1;
                reboot_type = BOOT_ACPI;
            } else {
                reboot_type = BOOT_TRIPLE;
            }
            break;

        case BOOT_TRIPLE:
            load_idt(&no_idt);
            __asm__ __volatile__("int3");

            reboot_type = BOOT_KBD;
            break;

        case BOOT_BIOS:
            machine_real_restart(MRR_BIOS);

            reboot_type = BOOT_KBD;
            break;

        case BOOT_ACPI:
            acpi_reboot();
            reboot_type = BOOT_KBD;
            break;

        case BOOT_EFI:
            if (efi_enabled)
                efi.reset_system(reboot_mode ?
                         EFI_RESET_WARM :
                         EFI_RESET_COLD,
                         EFI_SUCCESS, 0, NULL);
            reboot_type = BOOT_KBD;
            break;

        case BOOT_CF9:
            port_cf9_safe = true;
            /* Fall through */

        case BOOT_CF9_COND:
            if (port_cf9_safe) {
                u8 cf9 = inb(0xcf9) & ~6;
                outb(cf9|2, 0xcf9); /* Request hard reset */
                udelay(50);
                outb(cf9|6, 0xcf9); /* Actually do the reset */
                udelay(50);
            }
            reboot_type = BOOT_KBD;
            break;
        }
    }
}

void native_machine_shutdown(void)
{
    /* Stop the cpus and apics */
#ifdef CONFIG_SMP

    /* The boot cpu is always logical cpu 0 */
    int reboot_cpu_id = 0;

    /* See if there has been given a command line override */
    if ((reboot_cpu != -1) && (reboot_cpu < nr_cpu_ids) &&
        cpu_online(reboot_cpu))
        reboot_cpu_id = reboot_cpu;

    /* Make certain the cpu I'm about to reboot on is online */
    if (!cpu_online(reboot_cpu_id))
        reboot_cpu_id = smp_processor_id();

    /* Make certain I only run on the appropriate processor */
    set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));

    /*
     * O.K Now that I'm on the appropriate processor, stop all of the
     * others. Also disable the local irq to not receive the per-cpu
     * timer interrupt which may trigger scheduler's load balance.
     */
    local_irq_disable();
    stop_other_cpus();
#endif

    lapic_shutdown();

#ifdef CONFIG_X86_IO_APIC
    disable_IO_APIC();
#endif

#ifdef CONFIG_HPET_TIMER
    hpet_disable();
#endif

#ifdef CONFIG_X86_64
    x86_platform.iommu_shutdown();
#endif
}

static void __machine_emergency_restart(int emergency)
{
    reboot_emergency = emergency;
    machine_ops.emergency_restart();
}

static void native_machine_restart(char *__unused)
{
    pr_notice("machine restart\n");

    if (!reboot_force)
        machine_shutdown();
    __machine_emergency_restart(0);
}

static void native_machine_halt(void)
{
    /* Stop other cpus and apics */
    machine_shutdown();

    tboot_shutdown(TB_SHUTDOWN_HALT);

    stop_this_cpu(NULL);
}

static void native_machine_power_off(void)
{
    if (pm_power_off) {
        if (!reboot_force)
            machine_shutdown();
        pm_power_off();
    }
    /* A fallback in case there is no PM info available */
    tboot_shutdown(TB_SHUTDOWN_HALT);
}

struct machine_ops machine_ops = {
    .power_off = native_machine_power_off,
    .shutdown = native_machine_shutdown,
    .emergency_restart = native_machine_emergency_restart,
    .restart = native_machine_restart,
    .halt = native_machine_halt,
#ifdef CONFIG_KEXEC
    .crash_shutdown = native_machine_crash_shutdown,
#endif
};

void machine_power_off(void)
{
    machine_ops.power_off();
}

void machine_shutdown(void)
{
    machine_ops.shutdown();
}

void machine_emergency_restart(void)
{
    __machine_emergency_restart(1);
}

void machine_restart(char *cmd)
{
    machine_ops.restart(cmd);
}

void machine_halt(void)
{
    machine_ops.halt();
}

#ifdef CONFIG_KEXEC
void machine_crash_shutdown(struct pt_regs *regs)
{
    machine_ops.crash_shutdown(regs);
}
#endif


#if defined(CONFIG_SMP)

/* This keeps a track of which one is crashing cpu. */
static int crashing_cpu;
static nmi_shootdown_cb shootdown_callback;

static atomic_t waiting_for_crash_ipi;

static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
{
    int cpu;

    cpu = raw_smp_processor_id();

    /*
     * Don't do anything if this handler is invoked on crashing cpu.
     * Otherwise, system will completely hang. Crashing cpu can get
     * an NMI if system was initially booted with nmi_watchdog parameter.
     */
    if (cpu == crashing_cpu)
        return NMI_HANDLED;
    local_irq_disable();

    shootdown_callback(cpu, regs);

    atomic_dec(&waiting_for_crash_ipi);
    /* Assume hlt works */
    halt();
    for (;;)
        cpu_relax();

    return NMI_HANDLED;
}

static void smp_send_nmi_allbutself(void)
{
    apic->send_IPI_allbutself(NMI_VECTOR);
}

/*
 * Halt all other CPUs, calling the specified function on each of them
 *
 * This function can be used to halt all other CPUs on crash
 * or emergency reboot time. The function passed as parameter
 * will be called inside a NMI handler on all CPUs.
 */
void nmi_shootdown_cpus(nmi_shootdown_cb callback)
{
    unsigned long msecs;
    local_irq_disable();

    /* Make a note of crashing cpu. Will be used in NMI callback. */
    crashing_cpu = safe_smp_processor_id();

    shootdown_callback = callback;

    atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
    /* Would it be better to replace the trap vector here? */
    if (register_nmi_handler(NMI_LOCAL, crash_nmi_callback,
                 NMI_FLAG_FIRST, "crash"))
        return;     /* Return what? */
    /*
     * Ensure the new callback function is set before sending
     * out the NMI
     */
    wmb();

    smp_send_nmi_allbutself();

    msecs = 1000; /* Wait at most a second for the other cpus to stop */
    while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
        mdelay(1);
        msecs--;
    }

    /* Leave the nmi callback set */
}
#else /* !CONFIG_SMP */
void nmi_shootdown_cpus(nmi_shootdown_cb callback)
{
    /* No other CPUs to shoot down */
}
#endif