arch/x86/mm/fault_32.c

   1 /*
   2  *  Copyright (C) 1995  Linus Torvalds
   3  */
   4
   5 #include <linux/signal.h>
   6 #include <linux/sched.h>
   7 #include <linux/kernel.h>
   8 #include <linux/errno.h>
   9 #include <linux/string.h>
  10 #include <linux/types.h>
  11 #include <linux/ptrace.h>
  12 #include <linux/mman.h>
  13 #include <linux/mm.h>
  14 #include <linux/smp.h>
  15 #include <linux/interrupt.h>
  16 #include <linux/init.h>
  17 #include <linux/tty.h>
  18 #include <linux/vt_kern.h>              /* For unblank_screen() */
  19 #include <linux/highmem.h>
  20 #include <linux/bootmem.h>              /* for max_low_pfn */
  21 #include <linux/vmalloc.h>
  22 #include <linux/module.h>
  23 #include <linux/kprobes.h>
  24 #include <linux/uaccess.h>
  25 #include <linux/kdebug.h>
  26
  27 #include <asm/system.h>
  28 #include <asm/desc.h>
  29 #include <asm/segment.h>
  30
  31 /*
  32  * Page fault error code bits
  33  *      bit 0 == 0 means no page found, 1 means protection fault
  34  *      bit 1 == 0 means read, 1 means write
  35  *      bit 2 == 0 means kernel, 1 means user-mode
  36  *      bit 3 == 1 means use of reserved bit detected
  37  *      bit 4 == 1 means fault was an instruction fetch
  38  */
  39 #define PF_PROT (1<<0)
  40 #define PF_WRITE        (1<<1)
  41 #define PF_USER (1<<2)
  42 #define PF_RSVD (1<<3)
  43 #define PF_INSTR        (1<<4)
  44
  45 extern void die(const char *, struct pt_regs *, long);
  46
  47 static inline int notify_page_fault(struct pt_regs *regs)
  48 {
  49 #ifdef CONFIG_KPROBES
  50         int ret = 0;
  51
  52         /* kprobe_running() needs smp_processor_id() */
  53         if (!user_mode_vm(regs)) {
  54                 preempt_disable();
  55                 if (kprobe_running() && kprobe_fault_handler(regs, 14))
  56                         ret = 1;
  57                 preempt_enable();
  58         }
  59
  60         return ret;
  61 #else
  62         return 0;
  63 #endif
  64 }
  65
  66 /*
  67  * Return EIP plus the CS segment base.  The segment limit is also
  68  * adjusted, clamped to the kernel/user address space (whichever is
  69  * appropriate), and returned in *eip_limit.
  70  *
  71  * The segment is checked, because it might have been changed by another
  72  * task between the original faulting instruction and here.
  73  *
  74  * If CS is no longer a valid code segment, or if EIP is beyond the
  75  * limit, or if it is a kernel address when CS is not a kernel segment,
  76  * then the returned value will be greater than *eip_limit.
  77  *
  78  * This is slow, but is very rarely executed.
  79  */
  80 static inline unsigned long get_segment_eip(struct pt_regs *regs,
  81                                             unsigned long *eip_limit)
  82 {
  83         unsigned long ip = regs->ip;
  84         unsigned seg = regs->cs & 0xffff;
  85         u32 seg_ar, seg_limit, base, *desc;
  86
  87         /* Unlikely, but must come before segment checks. */
  88         if (unlikely(regs->flags & VM_MASK)) {
  89                 base = seg << 4;
  90                 *eip_limit = base + 0xffff;
  91                 return base + (ip & 0xffff);
  92         }
  93
  94         /* The standard kernel/user address space limit. */
  95         *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg;
  96
  97         /* By far the most common cases. */
  98         if (likely(SEGMENT_IS_FLAT_CODE(seg)))
  99                 return ip;
 100
 101         /* Check the segment exists, is within the current LDT/GDT size,
 102            that kernel/user (ring 0..3) has the appropriate privilege,
 103            that it's a code segment, and get the limit. */
 104         __asm__ ("larl %3,%0; lsll %3,%1"
 105                  : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
 106         if ((~seg_ar & 0x9800) || ip > seg_limit) {
 107                 *eip_limit = 0;
 108                 return 1;        /* So that returned ip > *eip_limit. */
 109         }
 110
 111         /* Get the GDT/LDT descriptor base.
 112            When you look for races in this code remember that
 113            LDT and other horrors are only used in user space. */
 114         if (seg & (1<<2)) {
 115                 /* Must lock the LDT while reading it. */
 116                 mutex_lock(&current->mm->context.lock);
 117                 desc = current->mm->context.ldt;
 118                 desc = (void *)desc + (seg & ~7);
 119         } else {
 120                 /* Must disable preemption while reading the GDT. */
 121                 desc = (u32 *)get_cpu_gdt_table(get_cpu());
 122                 desc = (void *)desc + (seg & ~7);
 123         }
 124
 125         /* Decode the code segment base from the descriptor */
 126         base = get_desc_base((struct desc_struct *)desc);
 127
 128         if (seg & (1<<2))
 129                 mutex_unlock(&current->mm->context.lock);
 130         else
 131                 put_cpu();
 132
 133         /* Adjust EIP and segment limit, and clamp at the kernel limit.
 134            It's legitimate for segments to wrap at 0xffffffff. */
 135         seg_limit += base;
 136         if (seg_limit < *eip_limit && seg_limit >= base)
 137                 *eip_limit = seg_limit;
 138         return ip + base;
 139 }
 140
 141 /*
 142  * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
 143  * Check that here and ignore it.
 144  */
 145 static int __is_prefetch(struct pt_regs *regs, unsigned long addr)
 146 {
 147         unsigned long limit;
 148         unsigned char *instr = (unsigned char *)get_segment_eip(regs, &limit);
 149         int scan_more = 1;
 150         int prefetch = 0;
 151         int i;
 152
 153         for (i = 0; scan_more && i < 15; i++) {
 154                 unsigned char opcode;
 155                 unsigned char instr_hi;
 156                 unsigned char instr_lo;
 157
 158                 if (instr > (unsigned char *)limit)
 159                         break;
 160                 if (probe_kernel_address(instr, opcode))
 161                         break;
 162
 163                 instr_hi = opcode & 0xf0;
 164                 instr_lo = opcode & 0x0f;
 165                 instr++;
 166
 167                 switch (instr_hi) {
 168                 case 0x20:
 169                 case 0x30:
 170                         /*
 171                          * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
 172                          * In X86_64 long mode, the CPU will signal invalid
 173                          * opcode if some of these prefixes are present so
 174                          * X86_64 will never get here anyway
 175                          */
 176                         scan_more = ((instr_lo & 7) == 0x6);
 177                         break;
 178 #ifdef CONFIG_X86_64
 179                 case 0x40:
 180                         /*
 181                          * In AMD64 long mode 0x40..0x4F are valid REX prefixes
 182                          * Need to figure out under what instruction mode the
 183                          * instruction was issued. Could check the LDT for lm,
 184                          * but for now it's good enough to assume that long
 185                          * mode only uses well known segments or kernel.
 186                          */
 187                         scan_more = (!user_mode(regs)) || (regs->cs == __USER_CS);
 188                         break;
 189 #endif
 190                 case 0x60:
 191                         /* 0x64 thru 0x67 are valid prefixes in all modes. */
 192                         scan_more = (instr_lo & 0xC) == 0x4;
 193                         break;
 194                 case 0xF0:
 195                         /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
 196                         scan_more = !instr_lo || (instr_lo>>1) == 1;
 197                         break;
 198                 case 0x00:
 199                         /* Prefetch instruction is 0x0F0D or 0x0F18 */
 200                         scan_more = 0;
 201                         if (instr > (unsigned char *)limit)
 202                                 break;
 203                         if (probe_kernel_address(instr, opcode))
 204                                 break;
 205                         prefetch = (instr_lo == 0xF) &&
 206                                 (opcode == 0x0D || opcode == 0x18);
 207                         break;
 208                 default:
 209                         scan_more = 0;
 210                         break;
 211                 }
 212         }
 213         return prefetch;
 214 }
 215
 216 static inline int is_prefetch(struct pt_regs *regs, unsigned long addr,
 217                               unsigned long error_code)
 218 {
 219         if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
 220                      boot_cpu_data.x86 >= 6)) {
 221                 /* Catch an obscure case of prefetch inside an NX page. */
 222                 if (nx_enabled && (error_code & 16))
 223                         return 0;
 224                 return __is_prefetch(regs, addr);
 225         }
 226         return 0;
 227 }
 228
 229 static noinline void force_sig_info_fault(int si_signo, int si_code,
 230         unsigned long address, struct task_struct *tsk)
 231 {
 232         siginfo_t info;
 233
 234         info.si_signo = si_signo;
 235         info.si_errno = 0;
 236         info.si_code = si_code;
 237         info.si_addr = (void __user *)address;
 238         force_sig_info(si_signo, &info, tsk);
 239 }
 240
 241 void do_invalid_op(struct pt_regs *, unsigned long);
 242
 243 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
 244 {
 245         unsigned index = pgd_index(address);
 246         pgd_t *pgd_k;
 247         pud_t *pud, *pud_k;
 248         pmd_t *pmd, *pmd_k;
 249
 250         pgd += index;
 251         pgd_k = init_mm.pgd + index;
 252
 253         if (!pgd_present(*pgd_k))
 254                 return NULL;
 255
 256         /*
 257          * set_pgd(pgd, *pgd_k); here would be useless on PAE
 258          * and redundant with the set_pmd() on non-PAE. As would
 259          * set_pud.
 260          */
 261
 262         pud = pud_offset(pgd, address);
 263         pud_k = pud_offset(pgd_k, address);
 264         if (!pud_present(*pud_k))
 265                 return NULL;
 266
 267         pmd = pmd_offset(pud, address);
 268         pmd_k = pmd_offset(pud_k, address);
 269         if (!pmd_present(*pmd_k))
 270                 return NULL;
 271         if (!pmd_present(*pmd)) {
 272                 set_pmd(pmd, *pmd_k);
 273                 arch_flush_lazy_mmu_mode();
 274         } else
 275                 BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
 276         return pmd_k;
 277 }
 278
 279 /*
 280  * Handle a fault on the vmalloc or module mapping area
 281  *
 282  * This assumes no large pages in there.
 283  */
 284 static inline int vmalloc_fault(unsigned long address)
 285 {
 286         unsigned long pgd_paddr;
 287         pmd_t *pmd_k;
 288         pte_t *pte_k;
 289         /*
 290          * Synchronize this task's top level page-table
 291          * with the 'reference' page table.
 292          *
 293          * Do _not_ use "current" here. We might be inside
 294          * an interrupt in the middle of a task switch..
 295          */
 296         pgd_paddr = read_cr3();
 297         pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
 298         if (!pmd_k)
 299                 return -1;
 300         pte_k = pte_offset_kernel(pmd_k, address);
 301         if (!pte_present(*pte_k))
 302                 return -1;
 303         return 0;
 304 }
 305
 306 int show_unhandled_signals = 1;
 307
 308 /*
 309  * This routine handles page faults.  It determines the address,
 310  * and the problem, and then passes it off to one of the appropriate
 311  * routines.
 312  */
 313 void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 314 {
 315         struct task_struct *tsk;
 316         struct mm_struct *mm;
 317         struct vm_area_struct *vma;
 318         unsigned long address;
 319         int write, si_code;
 320         int fault;
 321
 322         /*
 323          * We can fault from pretty much anywhere, with unknown IRQ state.
 324          */
 325         trace_hardirqs_fixup();
 326
 327         /* get the address */
 328         address = read_cr2();
 329
 330         tsk = current;
 331
 332         si_code = SEGV_MAPERR;
 333
 334         /*
 335          * We fault-in kernel-space virtual memory on-demand. The
 336          * 'reference' page table is init_mm.pgd.
 337          *
 338          * NOTE! We MUST NOT take any locks for this case. We may
 339          * be in an interrupt or a critical region, and should
 340          * only copy the information from the master page table,
 341          * nothing more.
 342          *
 343          * This verifies that the fault happens in kernel space
 344          * (error_code & 4) == 0, and that the fault was not a
 345          * protection error (error_code & 9) == 0.
 346          */
 347         if (unlikely(address >= TASK_SIZE)) {
 348                 if (!(error_code & 0x0000000d) && vmalloc_fault(address) >= 0)
 349                         return;
 350                 if (notify_page_fault(regs))
 351                         return;
 352                 /*
 353                  * Don't take the mm semaphore here. If we fixup a prefetch
 354                  * fault we could otherwise deadlock.
 355                  */
 356                 goto bad_area_nosemaphore;
 357         }
 358
 359         if (notify_page_fault(regs))
 360                 return;
 361
 362         /* It's safe to allow irq's after cr2 has been saved and the vmalloc
 363            fault has been handled. */
 364         if (regs->flags & (X86_EFLAGS_IF|VM_MASK))
 365                 local_irq_enable();
 366
 367         mm = tsk->mm;
 368
 369         /*
 370          * If we're in an interrupt, have no user context or are running in an
 371          * atomic region then we must not take the fault.
 372          */
 373         if (in_atomic() || !mm)
 374                 goto bad_area_nosemaphore;
 375
 376         /* When running in the kernel we expect faults to occur only to
 377          * addresses in user space.  All other faults represent errors in the
 378          * kernel and should generate an OOPS.  Unfortunately, in the case of an
 379          * erroneous fault occurring in a code path which already holds mmap_sem
 380          * we will deadlock attempting to validate the fault against the
 381          * address space.  Luckily the kernel only validly references user
 382          * space from well defined areas of code, which are listed in the
 383          * exceptions table.
 384          *
 385          * As the vast majority of faults will be valid we will only perform
 386          * the source reference check when there is a possibility of a deadlock.
 387          * Attempt to lock the address space, if we cannot we then validate the
 388          * source.  If this is invalid we can skip the address space check,
 389          * thus avoiding the deadlock.
 390          */
 391         if (!down_read_trylock(&mm->mmap_sem)) {
 392                 if ((error_code & PF_USER) == 0 &&
 393                     !search_exception_tables(regs->ip))
 394                         goto bad_area_nosemaphore;
 395                 down_read(&mm->mmap_sem);
 396         }
 397
 398         vma = find_vma(mm, address);
 399         if (!vma)
 400                 goto bad_area;
 401         if (vma->vm_start <= address)
 402                 goto good_area;
 403         if (!(vma->vm_flags & VM_GROWSDOWN))
 404                 goto bad_area;
 405         if (error_code & PF_USER) {
 406                 /*
 407                  * Accessing the stack below %sp is always a bug.
 408                  * The large cushion allows instructions like enter
 409                  * and pusha to work.  ("enter $65535,$31" pushes
 410                  * 32 pointers and then decrements %sp by 65535.)
 411                  */
 412                 if (address + 65536 + 32 * sizeof(unsigned long) < regs->sp)
 413                         goto bad_area;
 414         }
 415         if (expand_stack(vma, address))
 416                 goto bad_area;
 417 /*
 418  * Ok, we have a good vm_area for this memory access, so
 419  * we can handle it..
 420  */
 421 good_area:
 422         si_code = SEGV_ACCERR;
 423         write = 0;
 424         switch (error_code & (PF_PROT|PF_WRITE)) {
 425         default:        /* 3: write, present */
 426                 /* fall through */
 427         case PF_WRITE:          /* write, not present */
 428                 if (!(vma->vm_flags & VM_WRITE))
 429                         goto bad_area;
 430                 write++;
 431                 break;
 432         case PF_PROT:           /* read, present */
 433                 goto bad_area;
 434         case 0:                 /* read, not present */
 435                 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
 436                         goto bad_area;
 437         }
 438
 439  survive:
 440         /*
 441          * If for any reason at all we couldn't handle the fault,
 442          * make sure we exit gracefully rather than endlessly redo
 443          * the fault.
 444          */
 445         fault = handle_mm_fault(mm, vma, address, write);
 446         if (unlikely(fault & VM_FAULT_ERROR)) {
 447                 if (fault & VM_FAULT_OOM)
 448                         goto out_of_memory;
 449                 else if (fault & VM_FAULT_SIGBUS)
 450                         goto do_sigbus;
 451                 BUG();
 452         }
 453         if (fault & VM_FAULT_MAJOR)
 454                 tsk->maj_flt++;
 455         else
 456                 tsk->min_flt++;
 457
 458         /*
 459          * Did it hit the DOS screen memory VA from vm86 mode?
 460          */
 461         if (regs->flags & VM_MASK) {
 462                 unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
 463                 if (bit < 32)
 464                         tsk->thread.screen_bitmap |= 1 << bit;
 465         }
 466         up_read(&mm->mmap_sem);
 467         return;
 468
 469 /*
 470  * Something tried to access memory that isn't in our memory map..
 471  * Fix it, but check if it's kernel or user first..
 472  */
 473 bad_area:
 474         up_read(&mm->mmap_sem);
 475
 476 bad_area_nosemaphore:
 477         /* User mode accesses just cause a SIGSEGV */
 478         if (error_code & PF_USER) {
 479                 /*
 480                  * It's possible to have interrupts off here.
 481                  */
 482                 local_irq_enable();
 483
 484                 /*
 485                  * Valid to do another page fault here because this one came
 486                  * from user space.
 487                  */
 488                 if (is_prefetch(regs, address, error_code))
 489                         return;
 490
 491                 if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
 492                     printk_ratelimit()) {
 493                         printk("%s%s[%d]: segfault at %08lx ip %08lx "
 494                             "sp %08lx error %lx\n",
 495                             task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
 496                             tsk->comm, task_pid_nr(tsk), address, regs->ip,
 497                             regs->sp, error_code);
 498                 }
 499                 tsk->thread.cr2 = address;
 500                 /* Kernel addresses are always protection faults */
 501                 tsk->thread.error_code = error_code | (address >= TASK_SIZE);
 502                 tsk->thread.trap_no = 14;
 503                 force_sig_info_fault(SIGSEGV, si_code, address, tsk);
 504                 return;
 505         }
 506
 507 #ifdef CONFIG_X86_F00F_BUG
 508         /*
 509          * Pentium F0 0F C7 C8 bug workaround.
 510          */
 511         if (boot_cpu_data.f00f_bug) {
 512                 unsigned long nr;
 513
 514                 nr = (address - idt_descr.address) >> 3;
 515
 516                 if (nr == 6) {
 517                         do_invalid_op(regs, 0);
 518                         return;
 519                 }
 520         }
 521 #endif
 522
 523 no_context:
 524         /* Are we prepared to handle this kernel fault?  */
 525         if (fixup_exception(regs))
 526                 return;
 527
 528         /*
 529          * Valid to do another page fault here, because if this fault
 530          * had been triggered by is_prefetch fixup_exception would have
 531          * handled it.
 532          */
 533         if (is_prefetch(regs, address, error_code))
 534                 return;
 535
 536 /*
 537  * Oops. The kernel tried to access some bad page. We'll have to
 538  * terminate things with extreme prejudice.
 539  */
 540
 541         bust_spinlocks(1);
 542
 543         if (oops_may_print()) {
 544                 __typeof__(pte_val(__pte(0))) page;
 545
 546 #ifdef CONFIG_X86_PAE
 547                 if (error_code & 16) {
 548                         pte_t *pte = lookup_address(address);
 549
 550                         if (pte && pte_present(*pte) && !pte_exec_kernel(*pte))
 551                                 printk(KERN_CRIT "kernel tried to execute "
 552                                         "NX-protected page - exploit attempt? "
 553                                         "(uid: %d)\n", current->uid);
 554                 }
 555 #endif
 556                 if (address < PAGE_SIZE)
 557                         printk(KERN_ALERT "BUG: unable to handle kernel NULL "
 558                                         "pointer dereference");
 559                 else
 560                         printk(KERN_ALERT "BUG: unable to handle kernel paging"
 561                                         " request");
 562                 printk(" at virtual address %08lx\n", address);
 563                 printk(KERN_ALERT "printing ip: %08lx ", regs->ip);
 564
 565                 page = read_cr3();
 566                 page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
 567 #ifdef CONFIG_X86_PAE
 568                 printk("*pdpt = %016Lx ", page);
 569                 if ((page >> PAGE_SHIFT) < max_low_pfn
 570                     && page & _PAGE_PRESENT) {
 571                         page &= PAGE_MASK;
 572                         page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT)
 573                                                                  & (PTRS_PER_PMD - 1)];
 574                         printk(KERN_CONT "*pde = %016Lx ", page);
 575                         page &= ~_PAGE_NX;
 576                 }
 577 #else
 578                 printk("*pde = %08lx ", page);
 579 #endif
 580
 581                 /*
 582                  * We must not directly access the pte in the highpte
 583                  * case if the page table is located in highmem.
 584                  * And let's rather not kmap-atomic the pte, just in case
 585                  * it's allocated already.
 586                  */
 587                 if ((page >> PAGE_SHIFT) < max_low_pfn
 588                     && (page & _PAGE_PRESENT)
 589                     && !(page & _PAGE_PSE)) {
 590                         page &= PAGE_MASK;
 591                         page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT)
 592                                                                  & (PTRS_PER_PTE - 1)];
 593                         printk("*pte = %0*Lx ", sizeof(page)*2, (u64)page);
 594                 }
 595
 596                 printk("\n");
 597         }
 598
 599         tsk->thread.cr2 = address;
 600         tsk->thread.trap_no = 14;
 601         tsk->thread.error_code = error_code;
 602         die("Oops", regs, error_code);
 603         bust_spinlocks(0);
 604         do_exit(SIGKILL);
 605
 606 /*
 607  * We ran out of memory, or some other thing happened to us that made
 608  * us unable to handle the page fault gracefully.
 609  */
 610 out_of_memory:
 611         up_read(&mm->mmap_sem);
 612         if (is_global_init(tsk)) {
 613                 yield();
 614                 down_read(&mm->mmap_sem);
 615                 goto survive;
 616         }
 617         printk("VM: killing process %s\n", tsk->comm);
 618         if (error_code & 4)
 619                 do_group_exit(SIGKILL);
 620         goto no_context;
 621
 622 do_sigbus:
 623         up_read(&mm->mmap_sem);
 624
 625         /* Kernel mode? Handle exceptions or die */
 626         if (!(error_code & PF_USER))
 627                 goto no_context;
 628
 629         /* User space => ok to do another page fault */
 630         if (is_prefetch(regs, address, error_code))
 631                 return;
 632
 633         tsk->thread.cr2 = address;
 634         tsk->thread.error_code = error_code;
 635         tsk->thread.trap_no = 14;
 636         force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
 637 }
 638
 639 void vmalloc_sync_all(void)
 640 {
 641         /*
 642          * Note that races in the updates of insync and start aren't
 643          * problematic: insync can only get set bits added, and updates to
 644          * start are only improving performance (without affecting correctness
 645          * if undone).
 646          */
 647         static DECLARE_BITMAP(insync, PTRS_PER_PGD);
 648         static unsigned long start = TASK_SIZE;
 649         unsigned long address;
 650
 651         if (SHARED_KERNEL_PMD)
 652                 return;
 653
 654         BUILD_BUG_ON(TASK_SIZE & ~PGDIR_MASK);
 655         for (address = start; address >= TASK_SIZE; address += PGDIR_SIZE) {
 656                 if (!test_bit(pgd_index(address), insync)) {
 657                         unsigned long flags;
 658                         struct page *page;
 659
 660                         spin_lock_irqsave(&pgd_lock, flags);
 661                         for (page = pgd_list; page; page =
 662                                         (struct page *)page->index)
 663                                 if (!vmalloc_sync_one(page_address(page),
 664                                                                 address)) {
 665                                         BUG_ON(page != pgd_list);
 666                                         break;
 667                                 }
 668                         spin_unlock_irqrestore(&pgd_lock, flags);
 669                         if (!page)
 670                                 set_bit(pgd_index(address), insync);
 671                 }
 672                 if (address == start && test_bit(pgd_index(address), insync))
 673                         start = address + PGDIR_SIZE;
 674         }
 675 }