arch/x86/kernel/reboot.c

   1 #include <linux/module.h>
   2 #include <linux/reboot.h>
   3 #include <linux/init.h>
   4 #include <linux/pm.h>
   5 #include <linux/efi.h>
   6 #include <acpi/reboot.h>
   7 #include <asm/io.h>
   8 #include <asm/apic.h>
   9 #include <asm/desc.h>
  10 #include <asm/hpet.h>
  11 #include <asm/pgtable.h>
  12 #include <asm/proto.h>
  13 #include <asm/reboot_fixups.h>
  14 #include <asm/reboot.h>
  15 #include <asm/pci_x86.h>
  16 #include <asm/virtext.h>
  17 #include <asm/cpu.h>
  18
  19 #ifdef CONFIG_X86_32
  20 # include <linux/dmi.h>
  21 # include <linux/ctype.h>
  22 # include <linux/mc146818rtc.h>
  23 #else
  24 # include <asm/iommu.h>
  25 #endif
  26
  27 #include <asm/apic.h>
  28
  29 /*
  30  * Power off function, if any
  31  */
  32 void (*pm_power_off)(void);
  33 EXPORT_SYMBOL(pm_power_off);
  34
  35 static const struct desc_ptr no_idt = {};
  36 static int reboot_mode;
  37 enum reboot_type reboot_type = BOOT_KBD;
  38 int reboot_force;
  39
  40 #if defined(CONFIG_X86_32) && defined(CONFIG_SMP)
  41 static int reboot_cpu = -1;
  42 #endif
  43
  44 /* This is set if we need to go through the 'emergency' path.
  45  * When machine_emergency_restart() is called, we may be on
  46  * an inconsistent state and won't be able to do a clean cleanup
  47  */
  48 static int reboot_emergency;
  49
  50 /* This is set by the PCI code if either type 1 or type 2 PCI is detected */
  51 bool port_cf9_safe = false;
  52
  53 /* reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old] | p[ci]
  54    warm   Don't set the cold reboot flag
  55    cold   Set the cold reboot flag
  56    bios   Reboot by jumping through the BIOS (only for X86_32)
  57    smp    Reboot by executing reset on BSP or other CPU (only for X86_32)
  58    triple Force a triple fault (init)
  59    kbd    Use the keyboard controller. cold reset (default)
  60    acpi   Use the RESET_REG in the FADT
  61    efi    Use efi reset_system runtime service
  62    pci    Use the so-called "PCI reset register", CF9
  63    force  Avoid anything that could hang.
  64  */
  65 static int __init reboot_setup(char *str)
  66 {
  67         for (;;) {
  68                 switch (*str) {
  69                 case 'w':
  70                         reboot_mode = 0x1234;
  71                         break;
  72
  73                 case 'c':
  74                         reboot_mode = 0;
  75                         break;
  76
  77 #ifdef CONFIG_X86_32
  78 #ifdef CONFIG_SMP
  79                 case 's':
  80                         if (isdigit(*(str+1))) {
  81                                 reboot_cpu = (int) (*(str+1) - '0');
  82                                 if (isdigit(*(str+2)))
  83                                         reboot_cpu = reboot_cpu*10 + (int)(*(str+2) - '0');
  84                         }
  85                                 /* we will leave sorting out the final value
  86                                    when we are ready to reboot, since we might not
  87                                    have set up boot_cpu_id or smp_num_cpu */
  88                         break;
  89 #endif /* CONFIG_SMP */
  90
  91                 case 'b':
  92 #endif
  93                 case 'a':
  94                 case 'k':
  95                 case 't':
  96                 case 'e':
  97                 case 'p':
  98                         reboot_type = *str;
  99                         break;
 100
 101                 case 'f':
 102                         reboot_force = 1;
 103                         break;
 104                 }
 105
 106                 str = strchr(str, ',');
 107                 if (str)
 108                         str++;
 109                 else
 110                         break;
 111         }
 112         return 1;
 113 }
 114
 115 __setup("reboot=", reboot_setup);
 116
 117
 118 #ifdef CONFIG_X86_32
 119 /*
 120  * Reboot options and system auto-detection code provided by
 121  * Dell Inc. so their systems "just work". :-)
 122  */
 123
 124 /*
 125  * Some machines require the "reboot=b"  commandline option,
 126  * this quirk makes that automatic.
 127  */
 128 static int __init set_bios_reboot(const struct dmi_system_id *d)
 129 {
 130         if (reboot_type != BOOT_BIOS) {
 131                 reboot_type = BOOT_BIOS;
 132                 printk(KERN_INFO "%s series board detected. Selecting BIOS-method for reboots.\n", d->ident);
 133         }
 134         return 0;
 135 }
 136
 137 static struct dmi_system_id __initdata reboot_dmi_table[] = {
 138         {       /* Handle problems with rebooting on Dell E520's */
 139                 .callback = set_bios_reboot,
 140                 .ident = "Dell E520",
 141                 .matches = {
 142                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 143                         DMI_MATCH(DMI_PRODUCT_NAME, "Dell DM061"),
 144                 },
 145         },
 146         {       /* Handle problems with rebooting on Dell 1300's */
 147                 .callback = set_bios_reboot,
 148                 .ident = "Dell PowerEdge 1300",
 149                 .matches = {
 150                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
 151                         DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 1300/"),
 152                 },
 153         },
 154         {       /* Handle problems with rebooting on Dell 300's */
 155                 .callback = set_bios_reboot,
 156                 .ident = "Dell PowerEdge 300",
 157                 .matches = {
 158                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
 159                         DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 300/"),
 160                 },
 161         },
 162         {       /* Handle problems with rebooting on Dell Optiplex 745's SFF*/
 163                 .callback = set_bios_reboot,
 164                 .ident = "Dell OptiPlex 745",
 165                 .matches = {
 166                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 167                         DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
 168                 },
 169         },
 170         {       /* Handle problems with rebooting on Dell Optiplex 745's DFF*/
 171                 .callback = set_bios_reboot,
 172                 .ident = "Dell OptiPlex 745",
 173                 .matches = {
 174                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 175                         DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
 176                         DMI_MATCH(DMI_BOARD_NAME, "0MM599"),
 177                 },
 178         },
 179         {       /* Handle problems with rebooting on Dell Optiplex 745 with 0KW626 */
 180                 .callback = set_bios_reboot,
 181                 .ident = "Dell OptiPlex 745",
 182                 .matches = {
 183                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 184                         DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 745"),
 185                         DMI_MATCH(DMI_BOARD_NAME, "0KW626"),
 186                 },
 187         },
 188         {   /* Handle problems with rebooting on Dell Optiplex 330 with 0KP561 */
 189                 .callback = set_bios_reboot,
 190                 .ident = "Dell OptiPlex 330",
 191                 .matches = {
 192                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 193                         DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 330"),
 194                         DMI_MATCH(DMI_BOARD_NAME, "0KP561"),
 195                 },
 196         },
 197         {       /* Handle problems with rebooting on Dell 2400's */
 198                 .callback = set_bios_reboot,
 199                 .ident = "Dell PowerEdge 2400",
 200                 .matches = {
 201                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
 202                         DMI_MATCH(DMI_PRODUCT_NAME, "PowerEdge 2400"),
 203                 },
 204         },
 205         {       /* Handle problems with rebooting on Dell T5400's */
 206                 .callback = set_bios_reboot,
 207                 .ident = "Dell Precision T5400",
 208                 .matches = {
 209                         DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 210                         DMI_MATCH(DMI_PRODUCT_NAME, "Precision WorkStation T5400"),
 211                 },
 212         },
 213         {       /* Handle problems with rebooting on HP laptops */
 214                 .callback = set_bios_reboot,
 215                 .ident = "HP Compaq Laptop",
 216                 .matches = {
 217                         DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
 218                         DMI_MATCH(DMI_PRODUCT_NAME, "HP Compaq"),
 219                 },
 220         },
 221         { }
 222 };
 223
 224 static int __init reboot_init(void)
 225 {
 226         dmi_check_system(reboot_dmi_table);
 227         return 0;
 228 }
 229 core_initcall(reboot_init);
 230
 231 /* The following code and data reboots the machine by switching to real
 232    mode and jumping to the BIOS reset entry point, as if the CPU has
 233    really been reset.  The previous version asked the keyboard
 234    controller to pulse the CPU reset line, which is more thorough, but
 235    doesn't work with at least one type of 486 motherboard.  It is easy
 236    to stop this code working; hence the copious comments. */
 237 static const unsigned long long
 238 real_mode_gdt_entries [3] =
 239 {
 240         0x0000000000000000ULL,  /* Null descriptor */
 241         0x00009b000000ffffULL,  /* 16-bit real-mode 64k code at 0x00000000 */
 242         0x000093000100ffffULL   /* 16-bit real-mode 64k data at 0x00000100 */
 243 };
 244
 245 static const struct desc_ptr
 246 real_mode_gdt = { sizeof (real_mode_gdt_entries) - 1, (long)real_mode_gdt_entries },
 247 real_mode_idt = { 0x3ff, 0 };
 248
 249 /* This is 16-bit protected mode code to disable paging and the cache,
 250    switch to real mode and jump to the BIOS reset code.
 251
 252    The instruction that switches to real mode by writing to CR0 must be
 253    followed immediately by a far jump instruction, which set CS to a
 254    valid value for real mode, and flushes the prefetch queue to avoid
 255    running instructions that have already been decoded in protected
 256    mode.
 257
 258    Clears all the flags except ET, especially PG (paging), PE
 259    (protected-mode enable) and TS (task switch for coprocessor state
 260    save).  Flushes the TLB after paging has been disabled.  Sets CD and
 261    NW, to disable the cache on a 486, and invalidates the cache.  This
 262    is more like the state of a 486 after reset.  I don't know if
 263    something else should be done for other chips.
 264
 265    More could be done here to set up the registers as if a CPU reset had
 266    occurred; hopefully real BIOSs don't assume much. */
 267 static const unsigned char real_mode_switch [] =
 268 {
 269         0x66, 0x0f, 0x20, 0xc0,                 /*    movl  %cr0,%eax        */
 270         0x66, 0x83, 0xe0, 0x11,                 /*    andl  $0x00000011,%eax */
 271         0x66, 0x0d, 0x00, 0x00, 0x00, 0x60,     /*    orl   $0x60000000,%eax */
 272         0x66, 0x0f, 0x22, 0xc0,                 /*    movl  %eax,%cr0        */
 273         0x66, 0x0f, 0x22, 0xd8,                 /*    movl  %eax,%cr3        */
 274         0x66, 0x0f, 0x20, 0xc3,                 /*    movl  %cr0,%ebx        */
 275         0x66, 0x81, 0xe3, 0x00, 0x00, 0x00, 0x60,       /*    andl  $0x60000000,%ebx */
 276         0x74, 0x02,                             /*    jz    f                */
 277         0x0f, 0x09,                             /*    wbinvd                 */
 278         0x24, 0x10,                             /* f: andb  $0x10,al         */
 279         0x66, 0x0f, 0x22, 0xc0                  /*    movl  %eax,%cr0        */
 280 };
 281 static const unsigned char jump_to_bios [] =
 282 {
 283         0xea, 0x00, 0x00, 0xff, 0xff            /*    ljmp  $0xffff,$0x0000  */
 284 };
 285
 286 /*
 287  * Switch to real mode and then execute the code
 288  * specified by the code and length parameters.
 289  * We assume that length will aways be less that 100!
 290  */
 291 void machine_real_restart(const unsigned char *code, int length)
 292 {
 293         local_irq_disable();
 294
 295         /* Write zero to CMOS register number 0x0f, which the BIOS POST
 296            routine will recognize as telling it to do a proper reboot.  (Well
 297            that's what this book in front of me says -- it may only apply to
 298            the Phoenix BIOS though, it's not clear).  At the same time,
 299            disable NMIs by setting the top bit in the CMOS address register,
 300            as we're about to do peculiar things to the CPU.  I'm not sure if
 301            `outb_p' is needed instead of just `outb'.  Use it to be on the
 302            safe side.  (Yes, CMOS_WRITE does outb_p's. -  Paul G.)
 303          */
 304         spin_lock(&rtc_lock);
 305         CMOS_WRITE(0x00, 0x8f);
 306         spin_unlock(&rtc_lock);
 307
 308         /* Remap the kernel at virtual address zero, as well as offset zero
 309            from the kernel segment.  This assumes the kernel segment starts at
 310            virtual address PAGE_OFFSET. */
 311         memcpy(swapper_pg_dir, swapper_pg_dir + KERNEL_PGD_BOUNDARY,
 312                 sizeof(swapper_pg_dir [0]) * KERNEL_PGD_PTRS);
 313
 314         /*
 315          * Use `swapper_pg_dir' as our page directory.
 316          */
 317         load_cr3(swapper_pg_dir);
 318
 319         /* Write 0x1234 to absolute memory location 0x472.  The BIOS reads
 320            this on booting to tell it to "Bypass memory test (also warm
 321            boot)".  This seems like a fairly standard thing that gets set by
 322            REBOOT.COM programs, and the previous reset routine did this
 323            too. */
 324         *((unsigned short *)0x472) = reboot_mode;
 325
 326         /* For the switch to real mode, copy some code to low memory.  It has
 327            to be in the first 64k because it is running in 16-bit mode, and it
 328            has to have the same physical and virtual address, because it turns
 329            off paging.  Copy it near the end of the first page, out of the way
 330            of BIOS variables. */
 331         memcpy((void *)(0x1000 - sizeof(real_mode_switch) - 100),
 332                 real_mode_switch, sizeof (real_mode_switch));
 333         memcpy((void *)(0x1000 - 100), code, length);
 334
 335         /* Set up the IDT for real mode. */
 336         load_idt(&real_mode_idt);
 337
 338         /* Set up a GDT from which we can load segment descriptors for real
 339            mode.  The GDT is not used in real mode; it is just needed here to
 340            prepare the descriptors. */
 341         load_gdt(&real_mode_gdt);
 342
 343         /* Load the data segment registers, and thus the descriptors ready for
 344            real mode.  The base address of each segment is 0x100, 16 times the
 345            selector value being loaded here.  This is so that the segment
 346            registers don't have to be reloaded after switching to real mode:
 347            the values are consistent for real mode operation already. */
 348         __asm__ __volatile__ ("movl $0x0010,%%eax\n"
 349                                 "\tmovl %%eax,%%ds\n"
 350                                 "\tmovl %%eax,%%es\n"
 351                                 "\tmovl %%eax,%%fs\n"
 352                                 "\tmovl %%eax,%%gs\n"
 353                                 "\tmovl %%eax,%%ss" : : : "eax");
 354
 355         /* Jump to the 16-bit code that we copied earlier.  It disables paging
 356            and the cache, switches to real mode, and jumps to the BIOS reset
 357            entry point. */
 358         __asm__ __volatile__ ("ljmp $0x0008,%0"
 359                                 :
 360                                 : "i" ((void *)(0x1000 - sizeof (real_mode_switch) - 100)));
 361 }
 362 #ifdef CONFIG_APM_MODULE
 363 EXPORT_SYMBOL(machine_real_restart);
 364 #endif
 365
 366 #endif /* CONFIG_X86_32 */
 367
 368 static inline void kb_wait(void)
 369 {
 370         int i;
 371
 372         for (i = 0; i < 0x10000; i++) {
 373                 if ((inb(0x64) & 0x02) == 0)
 374                         break;
 375                 udelay(2);
 376         }
 377 }
 378
 379 static void vmxoff_nmi(int cpu, struct die_args *args)
 380 {
 381         cpu_emergency_vmxoff();
 382 }
 383
 384 /* Use NMIs as IPIs to tell all CPUs to disable virtualization
 385  */
 386 static void emergency_vmx_disable_all(void)
 387 {
 388         /* Just make sure we won't change CPUs while doing this */
 389         local_irq_disable();
 390
 391         /* We need to disable VMX on all CPUs before rebooting, otherwise
 392          * we risk hanging up the machine, because the CPU ignore INIT
 393          * signals when VMX is enabled.
 394          *
 395          * We can't take any locks and we may be on an inconsistent
 396          * state, so we use NMIs as IPIs to tell the other CPUs to disable
 397          * VMX and halt.
 398          *
 399          * For safety, we will avoid running the nmi_shootdown_cpus()
 400          * stuff unnecessarily, but we don't have a way to check
 401          * if other CPUs have VMX enabled. So we will call it only if the
 402          * CPU we are running on has VMX enabled.
 403          *
 404          * We will miss cases where VMX is not enabled on all CPUs. This
 405          * shouldn't do much harm because KVM always enable VMX on all
 406          * CPUs anyway. But we can miss it on the small window where KVM
 407          * is still enabling VMX.
 408          */
 409         if (cpu_has_vmx() && cpu_vmx_enabled()) {
 410                 /* Disable VMX on this CPU.
 411                  */
 412                 cpu_vmxoff();
 413
 414                 /* Halt and disable VMX on the other CPUs */
 415                 nmi_shootdown_cpus(vmxoff_nmi);
 416
 417         }
 418 }
 419
 420
 421 void __attribute__((weak)) mach_reboot_fixups(void)
 422 {
 423 }
 424
 425 static void native_machine_emergency_restart(void)
 426 {
 427         int i;
 428
 429         if (reboot_emergency)
 430                 emergency_vmx_disable_all();
 431
 432         /* Tell the BIOS if we want cold or warm reboot */
 433         *((unsigned short *)__va(0x472)) = reboot_mode;
 434
 435         for (;;) {
 436                 /* Could also try the reset bit in the Hammer NB */
 437                 switch (reboot_type) {
 438                 case BOOT_KBD:
 439                         mach_reboot_fixups(); /* for board specific fixups */
 440
 441                         for (i = 0; i < 10; i++) {
 442                                 kb_wait();
 443                                 udelay(50);
 444                                 outb(0xfe, 0x64); /* pulse reset low */
 445                                 udelay(50);
 446                         }
 447
 448                 case BOOT_TRIPLE:
 449                         load_idt(&no_idt);
 450                         __asm__ __volatile__("int3");
 451
 452                         reboot_type = BOOT_KBD;
 453                         break;
 454
 455 #ifdef CONFIG_X86_32
 456                 case BOOT_BIOS:
 457                         machine_real_restart(jump_to_bios, sizeof(jump_to_bios));
 458
 459                         reboot_type = BOOT_KBD;
 460                         break;
 461 #endif
 462
 463                 case BOOT_ACPI:
 464                         acpi_reboot();
 465                         reboot_type = BOOT_KBD;
 466                         break;
 467
 468                 case BOOT_EFI:
 469                         if (efi_enabled)
 470                                 efi.reset_system(reboot_mode ?
 471                                                  EFI_RESET_WARM :
 472                                                  EFI_RESET_COLD,
 473                                                  EFI_SUCCESS, 0, NULL);
 474                         reboot_type = BOOT_KBD;
 475                         break;
 476
 477                 case BOOT_CF9:
 478                         port_cf9_safe = true;
 479                         /* fall through */
 480
 481                 case BOOT_CF9_COND:
 482                         if (port_cf9_safe) {
 483                                 u8 cf9 = inb(0xcf9) & ~6;
 484                                 outb(cf9|2, 0xcf9); /* Request hard reset */
 485                                 udelay(50);
 486                                 outb(cf9|6, 0xcf9); /* Actually do the reset */
 487                                 udelay(50);
 488                         }
 489                         reboot_type = BOOT_KBD;
 490                         break;
 491                 }
 492         }
 493 }
 494
 495 void native_machine_shutdown(void)
 496 {
 497         /* Stop the cpus and apics */
 498 #ifdef CONFIG_SMP
 499
 500         /* The boot cpu is always logical cpu 0 */
 501         int reboot_cpu_id = 0;
 502
 503 #ifdef CONFIG_X86_32
 504         /* See if there has been given a command line override */
 505         if ((reboot_cpu != -1) && (reboot_cpu < nr_cpu_ids) &&
 506                 cpu_online(reboot_cpu))
 507                 reboot_cpu_id = reboot_cpu;
 508 #endif
 509
 510         /* Make certain the cpu I'm about to reboot on is online */
 511         if (!cpu_online(reboot_cpu_id))
 512                 reboot_cpu_id = smp_processor_id();
 513
 514         /* Make certain I only run on the appropriate processor */
 515         set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));
 516
 517         /* O.K Now that I'm on the appropriate processor,
 518          * stop all of the others.
 519          */
 520         smp_send_stop();
 521 #endif
 522
 523         lapic_shutdown();
 524
 525 #ifdef CONFIG_X86_IO_APIC
 526         disable_IO_APIC();
 527 #endif
 528
 529 #ifdef CONFIG_HPET_TIMER
 530         hpet_disable();
 531 #endif
 532
 533 #ifdef CONFIG_X86_64
 534         pci_iommu_shutdown();
 535 #endif
 536 }
 537
 538 static void __machine_emergency_restart(int emergency)
 539 {
 540         reboot_emergency = emergency;
 541         machine_ops.emergency_restart();
 542 }
 543
 544 static void native_machine_restart(char *__unused)
 545 {
 546         printk("machine restart\n");
 547
 548         if (!reboot_force)
 549                 machine_shutdown();
 550         __machine_emergency_restart(0);
 551 }
 552
 553 static void native_machine_halt(void)
 554 {
 555         /* stop other cpus and apics */
 556         machine_shutdown();
 557
 558         /* stop this cpu */
 559         stop_this_cpu(NULL);
 560 }
 561
 562 static void native_machine_power_off(void)
 563 {
 564         if (pm_power_off) {
 565                 if (!reboot_force)
 566                         machine_shutdown();
 567                 pm_power_off();
 568         }
 569 }
 570
 571 struct machine_ops machine_ops = {
 572         .power_off = native_machine_power_off,
 573         .shutdown = native_machine_shutdown,
 574         .emergency_restart = native_machine_emergency_restart,
 575         .restart = native_machine_restart,
 576         .halt = native_machine_halt,
 577 #ifdef CONFIG_KEXEC
 578         .crash_shutdown = native_machine_crash_shutdown,
 579 #endif
 580 };
 581
 582 void machine_power_off(void)
 583 {
 584         machine_ops.power_off();
 585 }
 586
 587 void machine_shutdown(void)
 588 {
 589         machine_ops.shutdown();
 590 }
 591
 592 void machine_emergency_restart(void)
 593 {
 594         __machine_emergency_restart(1);
 595 }
 596
 597 void machine_restart(char *cmd)
 598 {
 599         machine_ops.restart(cmd);
 600 }
 601
 602 void machine_halt(void)
 603 {
 604         machine_ops.halt();
 605 }
 606
 607 #ifdef CONFIG_KEXEC
 608 void machine_crash_shutdown(struct pt_regs *regs)
 609 {
 610         machine_ops.crash_shutdown(regs);
 611 }
 612 #endif
 613
 614
 615 #if defined(CONFIG_SMP)
 616
 617 /* This keeps a track of which one is crashing cpu. */
 618 static int crashing_cpu;
 619 static nmi_shootdown_cb shootdown_callback;
 620
 621 static atomic_t waiting_for_crash_ipi;
 622
 623 static int crash_nmi_callback(struct notifier_block *self,
 624                         unsigned long val, void *data)
 625 {
 626         int cpu;
 627
 628         if (val != DIE_NMI_IPI)
 629                 return NOTIFY_OK;
 630
 631         cpu = raw_smp_processor_id();
 632
 633         /* Don't do anything if this handler is invoked on crashing cpu.
 634          * Otherwise, system will completely hang. Crashing cpu can get
 635          * an NMI if system was initially booted with nmi_watchdog parameter.
 636          */
 637         if (cpu == crashing_cpu)
 638                 return NOTIFY_STOP;
 639         local_irq_disable();
 640
 641         shootdown_callback(cpu, (struct die_args *)data);
 642
 643         atomic_dec(&waiting_for_crash_ipi);
 644         /* Assume hlt works */
 645         halt();
 646         for (;;)
 647                 cpu_relax();
 648
 649         return 1;
 650 }
 651
 652 static void smp_send_nmi_allbutself(void)
 653 {
 654         apic->send_IPI_allbutself(NMI_VECTOR);
 655 }
 656
 657 static struct notifier_block crash_nmi_nb = {
 658         .notifier_call = crash_nmi_callback,
 659 };
 660
 661 /* Halt all other CPUs, calling the specified function on each of them
 662  *
 663  * This function can be used to halt all other CPUs on crash
 664  * or emergency reboot time. The function passed as parameter
 665  * will be called inside a NMI handler on all CPUs.
 666  */
 667 void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 668 {
 669         unsigned long msecs;
 670         local_irq_disable();
 671
 672         /* Make a note of crashing cpu. Will be used in NMI callback.*/
 673         crashing_cpu = safe_smp_processor_id();
 674
 675         shootdown_callback = callback;
 676
 677         atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
 678         /* Would it be better to replace the trap vector here? */
 679         if (register_die_notifier(&crash_nmi_nb))
 680                 return;         /* return what? */
 681         /* Ensure the new callback function is set before sending
 682          * out the NMI
 683          */
 684         wmb();
 685
 686         smp_send_nmi_allbutself();
 687
 688         msecs = 1000; /* Wait at most a second for the other cpus to stop */
 689         while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
 690                 mdelay(1);
 691                 msecs--;
 692         }
 693
 694         /* Leave the nmi callback set */
 695 }
 696 #else /* !CONFIG_SMP */
 697 void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 698 {
 699         /* No other CPUs to shoot down */
 700 }
 701 #endif