release/src-rt-6.x.4708/linux/linux-2.6.36/arch/x86/kernel/alternative.c

   1 #include <linux/module.h>
   2 #include <linux/sched.h>
   3 #include <linux/mutex.h>
   4 #include <linux/list.h>
   5 #include <linux/stringify.h>
   6 #include <linux/kprobes.h>
   7 #include <linux/mm.h>
   8 #include <linux/vmalloc.h>
   9 #include <linux/memory.h>
  10 #include <linux/stop_machine.h>
  11 #include <linux/slab.h>
  12 #include <asm/alternative.h>
  13 #include <asm/sections.h>
  14 #include <asm/pgtable.h>
  15 #include <asm/mce.h>
  16 #include <asm/nmi.h>
  17 #include <asm/vsyscall.h>
  18 #include <asm/cacheflush.h>
  19 #include <asm/tlbflush.h>
  20 #include <asm/io.h>
  21 #include <asm/fixmap.h>
  22
  23 #define MAX_PATCH_LEN (255-1)
  24
  25 #ifdef CONFIG_HOTPLUG_CPU
  26 static int smp_alt_once;
  27
  28 static int __init bootonly(char *str)
  29 {
  30         smp_alt_once = 1;
  31         return 1;
  32 }
  33 __setup("smp-alt-boot", bootonly);
  34 #else
  35 #define smp_alt_once 1
  36 #endif
  37
  38 static int __initdata_or_module debug_alternative;
  39
  40 static int __init debug_alt(char *str)
  41 {
  42         debug_alternative = 1;
  43         return 1;
  44 }
  45 __setup("debug-alternative", debug_alt);
  46
  47 static int noreplace_smp;
  48
  49 static int __init setup_noreplace_smp(char *str)
  50 {
  51         noreplace_smp = 1;
  52         return 1;
  53 }
  54 __setup("noreplace-smp", setup_noreplace_smp);
  55
  56 #ifdef CONFIG_PARAVIRT
  57 static int __initdata_or_module noreplace_paravirt = 0;
  58
  59 static int __init setup_noreplace_paravirt(char *str)
  60 {
  61         noreplace_paravirt = 1;
  62         return 1;
  63 }
  64 __setup("noreplace-paravirt", setup_noreplace_paravirt);
  65 #endif
  66
  67 #define DPRINTK(fmt, args...) if (debug_alternative) \
  68         printk(KERN_DEBUG fmt, args)
  69
  70 #if defined(GENERIC_NOP1) && !defined(CONFIG_X86_64)
  71 /* Use inline assembly to define this because the nops are defined
  72    as inline assembly strings in the include files and we cannot
  73    get them easily into strings. */
  74 asm("\t" __stringify(__INITRODATA_OR_MODULE) "\nintelnops: "
  75         GENERIC_NOP1 GENERIC_NOP2 GENERIC_NOP3 GENERIC_NOP4 GENERIC_NOP5 GENERIC_NOP6
  76         GENERIC_NOP7 GENERIC_NOP8
  77     "\t.previous");
  78 extern const unsigned char intelnops[];
  79 static const unsigned char *const __initconst_or_module
  80 intel_nops[ASM_NOP_MAX+1] = {
  81         NULL,
  82         intelnops,
  83         intelnops + 1,
  84         intelnops + 1 + 2,
  85         intelnops + 1 + 2 + 3,
  86         intelnops + 1 + 2 + 3 + 4,
  87         intelnops + 1 + 2 + 3 + 4 + 5,
  88         intelnops + 1 + 2 + 3 + 4 + 5 + 6,
  89         intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
  90 };
  91 #endif
  92
  93 #ifdef K8_NOP1
  94 asm("\t" __stringify(__INITRODATA_OR_MODULE) "\nk8nops: "
  95         K8_NOP1 K8_NOP2 K8_NOP3 K8_NOP4 K8_NOP5 K8_NOP6
  96         K8_NOP7 K8_NOP8
  97     "\t.previous");
  98 extern const unsigned char k8nops[];
  99 static const unsigned char *const __initconst_or_module
 100 k8_nops[ASM_NOP_MAX+1] = {
 101         NULL,
 102         k8nops,
 103         k8nops + 1,
 104         k8nops + 1 + 2,
 105         k8nops + 1 + 2 + 3,
 106         k8nops + 1 + 2 + 3 + 4,
 107         k8nops + 1 + 2 + 3 + 4 + 5,
 108         k8nops + 1 + 2 + 3 + 4 + 5 + 6,
 109         k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 110 };
 111 #endif
 112
 113 #if defined(K7_NOP1) && !defined(CONFIG_X86_64)
 114 asm("\t" __stringify(__INITRODATA_OR_MODULE) "\nk7nops: "
 115         K7_NOP1 K7_NOP2 K7_NOP3 K7_NOP4 K7_NOP5 K7_NOP6
 116         K7_NOP7 K7_NOP8
 117     "\t.previous");
 118 extern const unsigned char k7nops[];
 119 static const unsigned char *const __initconst_or_module
 120 k7_nops[ASM_NOP_MAX+1] = {
 121         NULL,
 122         k7nops,
 123         k7nops + 1,
 124         k7nops + 1 + 2,
 125         k7nops + 1 + 2 + 3,
 126         k7nops + 1 + 2 + 3 + 4,
 127         k7nops + 1 + 2 + 3 + 4 + 5,
 128         k7nops + 1 + 2 + 3 + 4 + 5 + 6,
 129         k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 130 };
 131 #endif
 132
 133 #ifdef P6_NOP1
 134 asm("\t" __stringify(__INITRODATA_OR_MODULE) "\np6nops: "
 135         P6_NOP1 P6_NOP2 P6_NOP3 P6_NOP4 P6_NOP5 P6_NOP6
 136         P6_NOP7 P6_NOP8
 137     "\t.previous");
 138 extern const unsigned char p6nops[];
 139 static const unsigned char *const __initconst_or_module
 140 p6_nops[ASM_NOP_MAX+1] = {
 141         NULL,
 142         p6nops,
 143         p6nops + 1,
 144         p6nops + 1 + 2,
 145         p6nops + 1 + 2 + 3,
 146         p6nops + 1 + 2 + 3 + 4,
 147         p6nops + 1 + 2 + 3 + 4 + 5,
 148         p6nops + 1 + 2 + 3 + 4 + 5 + 6,
 149         p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 150 };
 151 #endif
 152
 153 #ifdef CONFIG_X86_64
 154
 155 extern char __vsyscall_0;
 156 static const unsigned char *const *__init_or_module find_nop_table(void)
 157 {
 158         if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
 159             boot_cpu_has(X86_FEATURE_NOPL))
 160                 return p6_nops;
 161         else
 162                 return k8_nops;
 163 }
 164
 165 #else /* CONFIG_X86_64 */
 166
 167 static const unsigned char *const *__init_or_module find_nop_table(void)
 168 {
 169         if (boot_cpu_has(X86_FEATURE_K8))
 170                 return k8_nops;
 171         else if (boot_cpu_has(X86_FEATURE_K7))
 172                 return k7_nops;
 173         else if (boot_cpu_has(X86_FEATURE_NOPL))
 174                 return p6_nops;
 175         else
 176                 return intel_nops;
 177 }
 178
 179 #endif /* CONFIG_X86_64 */
 180
 181 /* Use this to add nops to a buffer, then text_poke the whole buffer. */
 182 static void __init_or_module add_nops(void *insns, unsigned int len)
 183 {
 184         const unsigned char *const *noptable = find_nop_table();
 185
 186         while (len > 0) {
 187                 unsigned int noplen = len;
 188                 if (noplen > ASM_NOP_MAX)
 189                         noplen = ASM_NOP_MAX;
 190                 memcpy(insns, noptable[noplen], noplen);
 191                 insns += noplen;
 192                 len -= noplen;
 193         }
 194 }
 195
 196 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 197 extern s32 __smp_locks[], __smp_locks_end[];
 198 static void *text_poke_early(void *addr, const void *opcode, size_t len);
 199
 200 /* Replace instructions with better alternatives for this CPU type.
 201    This runs before SMP is initialized to avoid SMP problems with
 202    self modifying code. This implies that assymetric systems where
 203    APs have less capabilities than the boot processor are not handled.
 204    Tough. Make sure you disable such features by hand. */
 205
 206 void __init_or_module apply_alternatives(struct alt_instr *start,
 207                                          struct alt_instr *end)
 208 {
 209         struct alt_instr *a;
 210         u8 insnbuf[MAX_PATCH_LEN];
 211
 212         DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
 213         for (a = start; a < end; a++) {
 214                 u8 *instr = a->instr;
 215                 BUG_ON(a->replacementlen > a->instrlen);
 216                 BUG_ON(a->instrlen > sizeof(insnbuf));
 217                 BUG_ON(a->cpuid >= NCAPINTS*32);
 218                 if (!boot_cpu_has(a->cpuid))
 219                         continue;
 220 #ifdef CONFIG_X86_64
 221                 /* vsyscall code is not mapped yet. resolve it manually. */
 222                 if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) {
 223                         instr = __va(instr - (u8*)VSYSCALL_START + (u8*)__pa_symbol(&__vsyscall_0));
 224                         DPRINTK("%s: vsyscall fixup: %p => %p\n",
 225                                 __func__, a->instr, instr);
 226                 }
 227 #endif
 228                 memcpy(insnbuf, a->replacement, a->replacementlen);
 229                 if (*insnbuf == 0xe8 && a->replacementlen == 5)
 230                     *(s32 *)(insnbuf + 1) += a->replacement - a->instr;
 231                 add_nops(insnbuf + a->replacementlen,
 232                          a->instrlen - a->replacementlen);
 233                 text_poke_early(instr, insnbuf, a->instrlen);
 234         }
 235 }
 236
 237 #ifdef CONFIG_SMP
 238
 239 static void alternatives_smp_lock(const s32 *start, const s32 *end,
 240                                   u8 *text, u8 *text_end)
 241 {
 242         const s32 *poff;
 243
 244         mutex_lock(&text_mutex);
 245         for (poff = start; poff < end; poff++) {
 246                 u8 *ptr = (u8 *)poff + *poff;
 247
 248                 if (!*poff || ptr < text || ptr >= text_end)
 249                         continue;
 250                 /* turn DS segment override prefix into lock prefix */
 251                 if (*ptr == 0x3e)
 252                         text_poke(ptr, ((unsigned char []){0xf0}), 1);
 253         };
 254         mutex_unlock(&text_mutex);
 255 }
 256
 257 static void alternatives_smp_unlock(const s32 *start, const s32 *end,
 258                                     u8 *text, u8 *text_end)
 259 {
 260         const s32 *poff;
 261
 262         if (noreplace_smp)
 263                 return;
 264
 265         mutex_lock(&text_mutex);
 266         for (poff = start; poff < end; poff++) {
 267                 u8 *ptr = (u8 *)poff + *poff;
 268
 269                 if (!*poff || ptr < text || ptr >= text_end)
 270                         continue;
 271                 /* turn lock prefix into DS segment override prefix */
 272                 if (*ptr == 0xf0)
 273                         text_poke(ptr, ((unsigned char []){0x3E}), 1);
 274         };
 275         mutex_unlock(&text_mutex);
 276 }
 277
 278 struct smp_alt_module {
 279         /* what is this ??? */
 280         struct module   *mod;
 281         char            *name;
 282
 283         /* ptrs to lock prefixes */
 284         const s32       *locks;
 285         const s32       *locks_end;
 286
 287         /* .text segment, needed to avoid patching init code ;) */
 288         u8              *text;
 289         u8              *text_end;
 290
 291         struct list_head next;
 292 };
 293 static LIST_HEAD(smp_alt_modules);
 294 static DEFINE_MUTEX(smp_alt);
 295 static int smp_mode = 1;        /* protected by smp_alt */
 296
 297 void __init_or_module alternatives_smp_module_add(struct module *mod,
 298                                                   char *name,
 299                                                   void *locks, void *locks_end,
 300                                                   void *text,  void *text_end)
 301 {
 302         struct smp_alt_module *smp;
 303
 304         if (noreplace_smp)
 305                 return;
 306
 307         if (smp_alt_once) {
 308                 if (boot_cpu_has(X86_FEATURE_UP))
 309                         alternatives_smp_unlock(locks, locks_end,
 310                                                 text, text_end);
 311                 return;
 312         }
 313
 314         smp = kzalloc(sizeof(*smp), GFP_KERNEL);
 315         if (NULL == smp)
 316                 return; /* we'll run the (safe but slow) SMP code then ... */
 317
 318         smp->mod        = mod;
 319         smp->name       = name;
 320         smp->locks      = locks;
 321         smp->locks_end  = locks_end;
 322         smp->text       = text;
 323         smp->text_end   = text_end;
 324         DPRINTK("%s: locks %p -> %p, text %p -> %p, name %s\n",
 325                 __func__, smp->locks, smp->locks_end,
 326                 smp->text, smp->text_end, smp->name);
 327
 328         mutex_lock(&smp_alt);
 329         list_add_tail(&smp->next, &smp_alt_modules);
 330         if (boot_cpu_has(X86_FEATURE_UP))
 331                 alternatives_smp_unlock(smp->locks, smp->locks_end,
 332                                         smp->text, smp->text_end);
 333         mutex_unlock(&smp_alt);
 334 }
 335
 336 void __init_or_module alternatives_smp_module_del(struct module *mod)
 337 {
 338         struct smp_alt_module *item;
 339
 340         if (smp_alt_once || noreplace_smp)
 341                 return;
 342
 343         mutex_lock(&smp_alt);
 344         list_for_each_entry(item, &smp_alt_modules, next) {
 345                 if (mod != item->mod)
 346                         continue;
 347                 list_del(&item->next);
 348                 mutex_unlock(&smp_alt);
 349                 DPRINTK("%s: %s\n", __func__, item->name);
 350                 kfree(item);
 351                 return;
 352         }
 353         mutex_unlock(&smp_alt);
 354 }
 355
 356 void alternatives_smp_switch(int smp)
 357 {
 358         struct smp_alt_module *mod;
 359
 360 #ifdef CONFIG_LOCKDEP
 361         /*
 362          * Older binutils section handling bug prevented
 363          * alternatives-replacement from working reliably.
 364          *
 365          * If this still occurs then you should see a hang
 366          * or crash shortly after this line:
 367          */
 368         printk("lockdep: fixing up alternatives.\n");
 369 #endif
 370
 371         if (noreplace_smp || smp_alt_once)
 372                 return;
 373         BUG_ON(!smp && (num_online_cpus() > 1));
 374
 375         mutex_lock(&smp_alt);
 376
 377         /*
 378          * Avoid unnecessary switches because it forces JIT based VMs to
 379          * throw away all cached translations, which can be quite costly.
 380          */
 381         if (smp == smp_mode) {
 382                 /* nothing */
 383         } else if (smp) {
 384                 printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
 385                 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 386                 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 387                 list_for_each_entry(mod, &smp_alt_modules, next)
 388                         alternatives_smp_lock(mod->locks, mod->locks_end,
 389                                               mod->text, mod->text_end);
 390         } else {
 391                 printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 392                 set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 393                 set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 394                 list_for_each_entry(mod, &smp_alt_modules, next)
 395                         alternatives_smp_unlock(mod->locks, mod->locks_end,
 396                                                 mod->text, mod->text_end);
 397         }
 398         smp_mode = smp;
 399         mutex_unlock(&smp_alt);
 400 }
 401
 402 /* Return 1 if the address range is reserved for smp-alternatives */
 403 int alternatives_text_reserved(void *start, void *end)
 404 {
 405         struct smp_alt_module *mod;
 406         const s32 *poff;
 407         u8 *text_start = start;
 408         u8 *text_end = end;
 409
 410         list_for_each_entry(mod, &smp_alt_modules, next) {
 411                 if (mod->text > text_end || mod->text_end < text_start)
 412                         continue;
 413                 for (poff = mod->locks; poff < mod->locks_end; poff++) {
 414                         const u8 *ptr = (const u8 *)poff + *poff;
 415
 416                         if (text_start <= ptr && text_end > ptr)
 417                                 return 1;
 418                 }
 419         }
 420
 421         return 0;
 422 }
 423 #endif
 424
 425 #ifdef CONFIG_PARAVIRT
 426 void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
 427                                      struct paravirt_patch_site *end)
 428 {
 429         struct paravirt_patch_site *p;
 430         char insnbuf[MAX_PATCH_LEN];
 431
 432         if (noreplace_paravirt)
 433                 return;
 434
 435         for (p = start; p < end; p++) {
 436                 unsigned int used;
 437
 438                 BUG_ON(p->len > MAX_PATCH_LEN);
 439                 /* prep the buffer with the original instructions */
 440                 memcpy(insnbuf, p->instr, p->len);
 441                 used = pv_init_ops.patch(p->instrtype, p->clobbers, insnbuf,
 442                                          (unsigned long)p->instr, p->len);
 443
 444                 BUG_ON(used > p->len);
 445
 446                 /* Pad the rest with nops */
 447                 add_nops(insnbuf + used, p->len - used);
 448                 text_poke_early(p->instr, insnbuf, p->len);
 449         }
 450 }
 451 extern struct paravirt_patch_site __start_parainstructions[],
 452         __stop_parainstructions[];
 453 #endif  /* CONFIG_PARAVIRT */
 454
 455 void __init alternative_instructions(void)
 456 {
 457         /* The patching is not fully atomic, so try to avoid local interruptions
 458            that might execute the to be patched code.
 459            Other CPUs are not running. */
 460         stop_nmi();
 461
 462         /*
 463          * Don't stop machine check exceptions while patching.
 464          * MCEs only happen when something got corrupted and in this
 465          * case we must do something about the corruption.
 466          * Ignoring it is worse than a unlikely patching race.
 467          * Also machine checks tend to be broadcast and if one CPU
 468          * goes into machine check the others follow quickly, so we don't
 469          * expect a machine check to cause undue problems during to code
 470          * patching.
 471          */
 472
 473         apply_alternatives(__alt_instructions, __alt_instructions_end);
 474
 475         /* switch to patch-once-at-boottime-only mode and free the
 476          * tables in case we know the number of CPUs will never ever
 477          * change */
 478 #ifdef CONFIG_HOTPLUG_CPU
 479         if (num_possible_cpus() < 2)
 480                 smp_alt_once = 1;
 481 #endif
 482
 483 #ifdef CONFIG_SMP
 484         if (smp_alt_once) {
 485                 if (1 == num_possible_cpus()) {
 486                         printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 487                         set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 488                         set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 489
 490                         alternatives_smp_unlock(__smp_locks, __smp_locks_end,
 491                                                 _text, _etext);
 492                 }
 493         } else {
 494                 alternatives_smp_module_add(NULL, "core kernel",
 495                                             __smp_locks, __smp_locks_end,
 496                                             _text, _etext);
 497
 498                 /* Only switch to UP mode if we don't immediately boot others */
 499                 if (num_present_cpus() == 1 || setup_max_cpus <= 1)
 500                         alternatives_smp_switch(0);
 501         }
 502 #endif
 503         apply_paravirt(__parainstructions, __parainstructions_end);
 504
 505         if (smp_alt_once)
 506                 free_init_pages("SMP alternatives",
 507                                 (unsigned long)__smp_locks,
 508                                 (unsigned long)__smp_locks_end);
 509
 510         restart_nmi();
 511 }
 512
 513 /**
 514  * text_poke_early - Update instructions on a live kernel at boot time
 515  * @addr: address to modify
 516  * @opcode: source of the copy
 517  * @len: length to copy
 518  *
 519  * When you use this code to patch more than one byte of an instruction
 520  * you need to make sure that other CPUs cannot execute this code in parallel.
 521  * Also no thread must be currently preempted in the middle of these
 522  * instructions. And on the local CPU you need to be protected again NMI or MCE
 523  * handlers seeing an inconsistent instruction while you patch.
 524  */
 525 static void *__init_or_module text_poke_early(void *addr, const void *opcode,
 526                                               size_t len)
 527 {
 528         unsigned long flags;
 529         local_irq_save(flags);
 530         memcpy(addr, opcode, len);
 531         sync_core();
 532         local_irq_restore(flags);
 533         /* Could also do a CLFLUSH here to speed up CPU recovery; but
 534            that causes hangs on some VIA CPUs. */
 535         return addr;
 536 }
 537
 538 /**
 539  * text_poke - Update instructions on a live kernel
 540  * @addr: address to modify
 541  * @opcode: source of the copy
 542  * @len: length to copy
 543  *
 544  * Only atomic text poke/set should be allowed when not doing early patching.
 545  * It means the size must be writable atomically and the address must be aligned
 546  * in a way that permits an atomic write. It also makes sure we fit on a single
 547  * page.
 548  *
 549  * Note: Must be called under text_mutex.
 550  */
 551 void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
 552 {
 553         unsigned long flags;
 554         char *vaddr;
 555         struct page *pages[2];
 556         int i;
 557
 558         if (!core_kernel_text((unsigned long)addr)) {
 559                 pages[0] = vmalloc_to_page(addr);
 560                 pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
 561         } else {
 562                 pages[0] = virt_to_page(addr);
 563                 WARN_ON(!PageReserved(pages[0]));
 564                 pages[1] = virt_to_page(addr + PAGE_SIZE);
 565         }
 566         BUG_ON(!pages[0]);
 567         local_irq_save(flags);
 568         set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
 569         if (pages[1])
 570                 set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
 571         vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
 572         memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
 573         clear_fixmap(FIX_TEXT_POKE0);
 574         if (pages[1])
 575                 clear_fixmap(FIX_TEXT_POKE1);
 576         local_flush_tlb();
 577         sync_core();
 578         /* Could also do a CLFLUSH here to speed up CPU recovery; but
 579            that causes hangs on some VIA CPUs. */
 580         for (i = 0; i < len; i++)
 581                 BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
 582         local_irq_restore(flags);
 583         return addr;
 584 }
 585
 586 /*
 587  * Cross-modifying kernel text with stop_machine().
 588  * This code originally comes from immediate value.
 589  */
 590 static atomic_t stop_machine_first;
 591 static int wrote_text;
 592
 593 struct text_poke_params {
 594         void *addr;
 595         const void *opcode;
 596         size_t len;
 597 };
 598
 599 static int __kprobes stop_machine_text_poke(void *data)
 600 {
 601         struct text_poke_params *tpp = data;
 602
 603         if (atomic_dec_and_test(&stop_machine_first)) {
 604                 text_poke(tpp->addr, tpp->opcode, tpp->len);
 605                 smp_wmb();      /* Make sure other cpus see that this has run */
 606                 wrote_text = 1;
 607         } else {
 608                 while (!wrote_text)
 609                         cpu_relax();
 610                 smp_mb();       /* Load wrote_text before following execution */
 611         }
 612
 613         flush_icache_range((unsigned long)tpp->addr,
 614                            (unsigned long)tpp->addr + tpp->len);
 615         return 0;
 616 }
 617
 618 /**
 619  * text_poke_smp - Update instructions on a live kernel on SMP
 620  * @addr: address to modify
 621  * @opcode: source of the copy
 622  * @len: length to copy
 623  *
 624  * Modify multi-byte instruction by using stop_machine() on SMP. This allows
 625  * user to poke/set multi-byte text on SMP. Only non-NMI/MCE code modifying
 626  * should be allowed, since stop_machine() does _not_ protect code against
 627  * NMI and MCE.
 628  *
 629  * Note: Must be called under get_online_cpus() and text_mutex.
 630  */
 631 void *__kprobes text_poke_smp(void *addr, const void *opcode, size_t len)
 632 {
 633         struct text_poke_params tpp;
 634
 635         tpp.addr = addr;
 636         tpp.opcode = opcode;
 637         tpp.len = len;
 638         atomic_set(&stop_machine_first, 1);
 639         wrote_text = 0;
 640         stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
 641         return addr;
 642 }