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Linux/arch/s390/mm/fault.c

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  1 /*
  2  *  S390 version
  3  *    Copyright IBM Corp. 1999
  4  *    Author(s): Hartmut Penner (hp@de.ibm.com)
  5  *               Ulrich Weigand (uweigand@de.ibm.com)
  6  *
  7  *  Derived from "arch/i386/mm/fault.c"
  8  *    Copyright (C) 1995  Linus Torvalds
  9  */
 10 
 11 #include <linux/kernel_stat.h>
 12 #include <linux/perf_event.h>
 13 #include <linux/signal.h>
 14 #include <linux/sched.h>
 15 #include <linux/kernel.h>
 16 #include <linux/errno.h>
 17 #include <linux/string.h>
 18 #include <linux/types.h>
 19 #include <linux/ptrace.h>
 20 #include <linux/mman.h>
 21 #include <linux/mm.h>
 22 #include <linux/compat.h>
 23 #include <linux/smp.h>
 24 #include <linux/kdebug.h>
 25 #include <linux/init.h>
 26 #include <linux/console.h>
 27 #include <linux/module.h>
 28 #include <linux/hardirq.h>
 29 #include <linux/kprobes.h>
 30 #include <linux/uaccess.h>
 31 #include <linux/hugetlb.h>
 32 #include <asm/asm-offsets.h>
 33 #include <asm/pgtable.h>
 34 #include <asm/irq.h>
 35 #include <asm/mmu_context.h>
 36 #include <asm/facility.h>
 37 #include "../kernel/entry.h"
 38 
 39 #ifndef CONFIG_64BIT
 40 #define __FAIL_ADDR_MASK 0x7ffff000
 41 #define __SUBCODE_MASK 0x0200
 42 #define __PF_RES_FIELD 0ULL
 43 #else /* CONFIG_64BIT */
 44 #define __FAIL_ADDR_MASK -4096L
 45 #define __SUBCODE_MASK 0x0600
 46 #define __PF_RES_FIELD 0x8000000000000000ULL
 47 #endif /* CONFIG_64BIT */
 48 
 49 #define VM_FAULT_BADCONTEXT     0x010000
 50 #define VM_FAULT_BADMAP         0x020000
 51 #define VM_FAULT_BADACCESS      0x040000
 52 #define VM_FAULT_SIGNAL         0x080000
 53 #define VM_FAULT_PFAULT         0x100000
 54 
 55 static unsigned long store_indication __read_mostly;
 56 
 57 #ifdef CONFIG_64BIT
 58 static int __init fault_init(void)
 59 {
 60         if (test_facility(75))
 61                 store_indication = 0xc00;
 62         return 0;
 63 }
 64 early_initcall(fault_init);
 65 #endif
 66 
 67 static inline int notify_page_fault(struct pt_regs *regs)
 68 {
 69         int ret = 0;
 70 
 71         /* kprobe_running() needs smp_processor_id() */
 72         if (kprobes_built_in() && !user_mode(regs)) {
 73                 preempt_disable();
 74                 if (kprobe_running() && kprobe_fault_handler(regs, 14))
 75                         ret = 1;
 76                 preempt_enable();
 77         }
 78         return ret;
 79 }
 80 
 81 
 82 /*
 83  * Unlock any spinlocks which will prevent us from getting the
 84  * message out.
 85  */
 86 void bust_spinlocks(int yes)
 87 {
 88         if (yes) {
 89                 oops_in_progress = 1;
 90         } else {
 91                 int loglevel_save = console_loglevel;
 92                 console_unblank();
 93                 oops_in_progress = 0;
 94                 /*
 95                  * OK, the message is on the console.  Now we call printk()
 96                  * without oops_in_progress set so that printk will give klogd
 97                  * a poke.  Hold onto your hats...
 98                  */
 99                 console_loglevel = 15;
100                 printk(" ");
101                 console_loglevel = loglevel_save;
102         }
103 }
104 
105 /*
106  * Returns the address space associated with the fault.
107  * Returns 0 for kernel space and 1 for user space.
108  */
109 static inline int user_space_fault(struct pt_regs *regs)
110 {
111         unsigned long trans_exc_code;
112 
113         /*
114          * The lowest two bits of the translation exception
115          * identification indicate which paging table was used.
116          */
117         trans_exc_code = regs->int_parm_long & 3;
118         if (trans_exc_code == 3) /* home space -> kernel */
119                 return 0;
120         if (user_mode(regs))
121                 return 1;
122         if (trans_exc_code == 2) /* secondary space -> set_fs */
123                 return current->thread.mm_segment.ar4;
124         if (current->flags & PF_VCPU)
125                 return 1;
126         return 0;
127 }
128 
129 static int bad_address(void *p)
130 {
131         unsigned long dummy;
132 
133         return probe_kernel_address((unsigned long *)p, dummy);
134 }
135 
136 #ifdef CONFIG_64BIT
137 static void dump_pagetable(unsigned long asce, unsigned long address)
138 {
139         unsigned long *table = __va(asce & PAGE_MASK);
140 
141         pr_alert("AS:%016lx ", asce);
142         switch (asce & _ASCE_TYPE_MASK) {
143         case _ASCE_TYPE_REGION1:
144                 table = table + ((address >> 53) & 0x7ff);
145                 if (bad_address(table))
146                         goto bad;
147                 pr_cont("R1:%016lx ", *table);
148                 if (*table & _REGION_ENTRY_INVALID)
149                         goto out;
150                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
151                 /* fallthrough */
152         case _ASCE_TYPE_REGION2:
153                 table = table + ((address >> 42) & 0x7ff);
154                 if (bad_address(table))
155                         goto bad;
156                 pr_cont("R2:%016lx ", *table);
157                 if (*table & _REGION_ENTRY_INVALID)
158                         goto out;
159                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
160                 /* fallthrough */
161         case _ASCE_TYPE_REGION3:
162                 table = table + ((address >> 31) & 0x7ff);
163                 if (bad_address(table))
164                         goto bad;
165                 pr_cont("R3:%016lx ", *table);
166                 if (*table & (_REGION_ENTRY_INVALID | _REGION3_ENTRY_LARGE))
167                         goto out;
168                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
169                 /* fallthrough */
170         case _ASCE_TYPE_SEGMENT:
171                 table = table + ((address >> 20) & 0x7ff);
172                 if (bad_address(table))
173                         goto bad;
174                 pr_cont(KERN_CONT "S:%016lx ", *table);
175                 if (*table & (_SEGMENT_ENTRY_INVALID | _SEGMENT_ENTRY_LARGE))
176                         goto out;
177                 table = (unsigned long *)(*table & _SEGMENT_ENTRY_ORIGIN);
178         }
179         table = table + ((address >> 12) & 0xff);
180         if (bad_address(table))
181                 goto bad;
182         pr_cont("P:%016lx ", *table);
183 out:
184         pr_cont("\n");
185         return;
186 bad:
187         pr_cont("BAD\n");
188 }
189 
190 #else /* CONFIG_64BIT */
191 
192 static void dump_pagetable(unsigned long asce, unsigned long address)
193 {
194         unsigned long *table = __va(asce & PAGE_MASK);
195 
196         pr_alert("AS:%08lx ", asce);
197         table = table + ((address >> 20) & 0x7ff);
198         if (bad_address(table))
199                 goto bad;
200         pr_cont("S:%08lx ", *table);
201         if (*table & _SEGMENT_ENTRY_INVALID)
202                 goto out;
203         table = (unsigned long *)(*table & _SEGMENT_ENTRY_ORIGIN);
204         table = table + ((address >> 12) & 0xff);
205         if (bad_address(table))
206                 goto bad;
207         pr_cont("P:%08lx ", *table);
208 out:
209         pr_cont("\n");
210         return;
211 bad:
212         pr_cont("BAD\n");
213 }
214 
215 #endif /* CONFIG_64BIT */
216 
217 static void dump_fault_info(struct pt_regs *regs)
218 {
219         unsigned long asce;
220 
221         pr_alert("Fault in ");
222         switch (regs->int_parm_long & 3) {
223         case 3:
224                 pr_cont("home space ");
225                 break;
226         case 2:
227                 pr_cont("secondary space ");
228                 break;
229         case 1:
230                 pr_cont("access register ");
231                 break;
232         case 0:
233                 pr_cont("primary space ");
234                 break;
235         }
236         pr_cont("mode while using ");
237         if (!user_space_fault(regs)) {
238                 asce = S390_lowcore.kernel_asce;
239                 pr_cont("kernel ");
240         }
241 #ifdef CONFIG_PGSTE
242         else if ((current->flags & PF_VCPU) && S390_lowcore.gmap) {
243                 struct gmap *gmap = (struct gmap *)S390_lowcore.gmap;
244                 asce = gmap->asce;
245                 pr_cont("gmap ");
246         }
247 #endif
248         else {
249                 asce = S390_lowcore.user_asce;
250                 pr_cont("user ");
251         }
252         pr_cont("ASCE.\n");
253         dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
254 }
255 
256 static inline void report_user_fault(struct pt_regs *regs, long signr)
257 {
258         if ((task_pid_nr(current) > 1) && !show_unhandled_signals)
259                 return;
260         if (!unhandled_signal(current, signr))
261                 return;
262         if (!printk_ratelimit())
263                 return;
264         printk(KERN_ALERT "User process fault: interruption code 0x%X ",
265                regs->int_code);
266         print_vma_addr(KERN_CONT "in ", regs->psw.addr & PSW_ADDR_INSN);
267         printk(KERN_CONT "\n");
268         printk(KERN_ALERT "failing address: %016lx TEID: %016lx\n",
269                regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
270         dump_fault_info(regs);
271         show_regs(regs);
272 }
273 
274 /*
275  * Send SIGSEGV to task.  This is an external routine
276  * to keep the stack usage of do_page_fault small.
277  */
278 static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
279 {
280         struct siginfo si;
281 
282         report_user_fault(regs, SIGSEGV);
283         si.si_signo = SIGSEGV;
284         si.si_code = si_code;
285         si.si_addr = (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK);
286         force_sig_info(SIGSEGV, &si, current);
287 }
288 
289 static noinline void do_no_context(struct pt_regs *regs)
290 {
291         const struct exception_table_entry *fixup;
292         unsigned long address;
293 
294         /* Are we prepared to handle this kernel fault?  */
295         fixup = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
296         if (fixup) {
297                 regs->psw.addr = extable_fixup(fixup) | PSW_ADDR_AMODE;
298                 return;
299         }
300 
301         /*
302          * Oops. The kernel tried to access some bad page. We'll have to
303          * terminate things with extreme prejudice.
304          */
305         address = regs->int_parm_long & __FAIL_ADDR_MASK;
306         if (!user_space_fault(regs))
307                 printk(KERN_ALERT "Unable to handle kernel pointer dereference"
308                        " in virtual kernel address space\n");
309         else
310                 printk(KERN_ALERT "Unable to handle kernel paging request"
311                        " in virtual user address space\n");
312         printk(KERN_ALERT "failing address: %016lx TEID: %016lx\n",
313                regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
314         dump_fault_info(regs);
315         die(regs, "Oops");
316         do_exit(SIGKILL);
317 }
318 
319 static noinline void do_low_address(struct pt_regs *regs)
320 {
321         /* Low-address protection hit in kernel mode means
322            NULL pointer write access in kernel mode.  */
323         if (regs->psw.mask & PSW_MASK_PSTATE) {
324                 /* Low-address protection hit in user mode 'cannot happen'. */
325                 die (regs, "Low-address protection");
326                 do_exit(SIGKILL);
327         }
328 
329         do_no_context(regs);
330 }
331 
332 static noinline void do_sigbus(struct pt_regs *regs)
333 {
334         struct task_struct *tsk = current;
335         struct siginfo si;
336 
337         /*
338          * Send a sigbus, regardless of whether we were in kernel
339          * or user mode.
340          */
341         si.si_signo = SIGBUS;
342         si.si_errno = 0;
343         si.si_code = BUS_ADRERR;
344         si.si_addr = (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK);
345         force_sig_info(SIGBUS, &si, tsk);
346 }
347 
348 static noinline void do_fault_error(struct pt_regs *regs, int fault)
349 {
350         int si_code;
351 
352         switch (fault) {
353         case VM_FAULT_BADACCESS:
354         case VM_FAULT_BADMAP:
355                 /* Bad memory access. Check if it is kernel or user space. */
356                 if (user_mode(regs)) {
357                         /* User mode accesses just cause a SIGSEGV */
358                         si_code = (fault == VM_FAULT_BADMAP) ?
359                                 SEGV_MAPERR : SEGV_ACCERR;
360                         do_sigsegv(regs, si_code);
361                         return;
362                 }
363         case VM_FAULT_BADCONTEXT:
364         case VM_FAULT_PFAULT:
365                 do_no_context(regs);
366                 break;
367         case VM_FAULT_SIGNAL:
368                 if (!user_mode(regs))
369                         do_no_context(regs);
370                 break;
371         default: /* fault & VM_FAULT_ERROR */
372                 if (fault & VM_FAULT_OOM) {
373                         if (!user_mode(regs))
374                                 do_no_context(regs);
375                         else
376                                 pagefault_out_of_memory();
377                 } else if (fault & VM_FAULT_SIGSEGV) {
378                         /* Kernel mode? Handle exceptions or die */
379                         if (!user_mode(regs))
380                                 do_no_context(regs);
381                         else
382                                 do_sigsegv(regs, SEGV_MAPERR);
383                 } else if (fault & VM_FAULT_SIGBUS) {
384                         /* Kernel mode? Handle exceptions or die */
385                         if (!user_mode(regs))
386                                 do_no_context(regs);
387                         else
388                                 do_sigbus(regs);
389                 } else
390                         BUG();
391                 break;
392         }
393 }
394 
395 /*
396  * This routine handles page faults.  It determines the address,
397  * and the problem, and then passes it off to one of the appropriate
398  * routines.
399  *
400  * interruption code (int_code):
401  *   04       Protection           ->  Write-Protection  (suprression)
402  *   10       Segment translation  ->  Not present       (nullification)
403  *   11       Page translation     ->  Not present       (nullification)
404  *   3b       Region third trans.  ->  Not present       (nullification)
405  */
406 static inline int do_exception(struct pt_regs *regs, int access)
407 {
408 #ifdef CONFIG_PGSTE
409         struct gmap *gmap;
410 #endif
411         struct task_struct *tsk;
412         struct mm_struct *mm;
413         struct vm_area_struct *vma;
414         unsigned long trans_exc_code;
415         unsigned long address;
416         unsigned int flags;
417         int fault;
418 
419         tsk = current;
420         /*
421          * The instruction that caused the program check has
422          * been nullified. Don't signal single step via SIGTRAP.
423          */
424         clear_pt_regs_flag(regs, PIF_PER_TRAP);
425 
426         if (notify_page_fault(regs))
427                 return 0;
428 
429         mm = tsk->mm;
430         trans_exc_code = regs->int_parm_long;
431 
432         /*
433          * Verify that the fault happened in user space, that
434          * we are not in an interrupt and that there is a 
435          * user context.
436          */
437         fault = VM_FAULT_BADCONTEXT;
438         if (unlikely(!user_space_fault(regs) || in_atomic() || !mm))
439                 goto out;
440 
441         address = trans_exc_code & __FAIL_ADDR_MASK;
442         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
443         flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
444         if (user_mode(regs))
445                 flags |= FAULT_FLAG_USER;
446         if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
447                 flags |= FAULT_FLAG_WRITE;
448         down_read(&mm->mmap_sem);
449 
450 #ifdef CONFIG_PGSTE
451         gmap = (current->flags & PF_VCPU) ?
452                 (struct gmap *) S390_lowcore.gmap : NULL;
453         if (gmap) {
454                 current->thread.gmap_addr = address;
455                 address = __gmap_translate(gmap, address);
456                 if (address == -EFAULT) {
457                         fault = VM_FAULT_BADMAP;
458                         goto out_up;
459                 }
460                 if (gmap->pfault_enabled)
461                         flags |= FAULT_FLAG_RETRY_NOWAIT;
462         }
463 #endif
464 
465 retry:
466         fault = VM_FAULT_BADMAP;
467         vma = find_vma(mm, address);
468         if (!vma)
469                 goto out_up;
470 
471         if (unlikely(vma->vm_start > address)) {
472                 if (!(vma->vm_flags & VM_GROWSDOWN))
473                         goto out_up;
474                 if (expand_stack(vma, address))
475                         goto out_up;
476         }
477 
478         /*
479          * Ok, we have a good vm_area for this memory access, so
480          * we can handle it..
481          */
482         fault = VM_FAULT_BADACCESS;
483         if (unlikely(!(vma->vm_flags & access)))
484                 goto out_up;
485 
486         if (is_vm_hugetlb_page(vma))
487                 address &= HPAGE_MASK;
488         /*
489          * If for any reason at all we couldn't handle the fault,
490          * make sure we exit gracefully rather than endlessly redo
491          * the fault.
492          */
493         fault = handle_mm_fault(mm, vma, address, flags);
494         /* No reason to continue if interrupted by SIGKILL. */
495         if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
496                 fault = VM_FAULT_SIGNAL;
497                 if (flags & FAULT_FLAG_RETRY_NOWAIT)
498                         goto out_up;
499                 goto out;
500         }
501         if (unlikely(fault & VM_FAULT_ERROR))
502                 goto out_up;
503 
504         /*
505          * Major/minor page fault accounting is only done on the
506          * initial attempt. If we go through a retry, it is extremely
507          * likely that the page will be found in page cache at that point.
508          */
509         if (flags & FAULT_FLAG_ALLOW_RETRY) {
510                 if (fault & VM_FAULT_MAJOR) {
511                         tsk->maj_flt++;
512                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
513                                       regs, address);
514                 } else {
515                         tsk->min_flt++;
516                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
517                                       regs, address);
518                 }
519                 if (fault & VM_FAULT_RETRY) {
520 #ifdef CONFIG_PGSTE
521                         if (gmap && (flags & FAULT_FLAG_RETRY_NOWAIT)) {
522                                 /* FAULT_FLAG_RETRY_NOWAIT has been set,
523                                  * mmap_sem has not been released */
524                                 current->thread.gmap_pfault = 1;
525                                 fault = VM_FAULT_PFAULT;
526                                 goto out_up;
527                         }
528 #endif
529                         /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
530                          * of starvation. */
531                         flags &= ~(FAULT_FLAG_ALLOW_RETRY |
532                                    FAULT_FLAG_RETRY_NOWAIT);
533                         flags |= FAULT_FLAG_TRIED;
534                         down_read(&mm->mmap_sem);
535                         goto retry;
536                 }
537         }
538 #ifdef CONFIG_PGSTE
539         if (gmap) {
540                 address =  __gmap_link(gmap, current->thread.gmap_addr,
541                                        address);
542                 if (address == -EFAULT) {
543                         fault = VM_FAULT_BADMAP;
544                         goto out_up;
545                 }
546                 if (address == -ENOMEM) {
547                         fault = VM_FAULT_OOM;
548                         goto out_up;
549                 }
550         }
551 #endif
552         fault = 0;
553 out_up:
554         up_read(&mm->mmap_sem);
555 out:
556         return fault;
557 }
558 
559 void __kprobes do_protection_exception(struct pt_regs *regs)
560 {
561         unsigned long trans_exc_code;
562         int fault;
563 
564         trans_exc_code = regs->int_parm_long;
565         /*
566          * Protection exceptions are suppressing, decrement psw address.
567          * The exception to this rule are aborted transactions, for these
568          * the PSW already points to the correct location.
569          */
570         if (!(regs->int_code & 0x200))
571                 regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
572         /*
573          * Check for low-address protection.  This needs to be treated
574          * as a special case because the translation exception code
575          * field is not guaranteed to contain valid data in this case.
576          */
577         if (unlikely(!(trans_exc_code & 4))) {
578                 do_low_address(regs);
579                 return;
580         }
581         fault = do_exception(regs, VM_WRITE);
582         if (unlikely(fault))
583                 do_fault_error(regs, fault);
584 }
585 
586 void __kprobes do_dat_exception(struct pt_regs *regs)
587 {
588         int access, fault;
589 
590         access = VM_READ | VM_EXEC | VM_WRITE;
591         fault = do_exception(regs, access);
592         if (unlikely(fault))
593                 do_fault_error(regs, fault);
594 }
595 
596 #ifdef CONFIG_PFAULT 
597 /*
598  * 'pfault' pseudo page faults routines.
599  */
600 static int pfault_disable;
601 
602 static int __init nopfault(char *str)
603 {
604         pfault_disable = 1;
605         return 1;
606 }
607 
608 __setup("nopfault", nopfault);
609 
610 struct pfault_refbk {
611         u16 refdiagc;
612         u16 reffcode;
613         u16 refdwlen;
614         u16 refversn;
615         u64 refgaddr;
616         u64 refselmk;
617         u64 refcmpmk;
618         u64 reserved;
619 } __attribute__ ((packed, aligned(8)));
620 
621 int pfault_init(void)
622 {
623         struct pfault_refbk refbk = {
624                 .refdiagc = 0x258,
625                 .reffcode = 0,
626                 .refdwlen = 5,
627                 .refversn = 2,
628                 .refgaddr = __LC_CURRENT_PID,
629                 .refselmk = 1ULL << 48,
630                 .refcmpmk = 1ULL << 48,
631                 .reserved = __PF_RES_FIELD };
632         int rc;
633 
634         if (pfault_disable)
635                 return -1;
636         asm volatile(
637                 "       diag    %1,%0,0x258\n"
638                 "0:     j       2f\n"
639                 "1:     la      %0,8\n"
640                 "2:\n"
641                 EX_TABLE(0b,1b)
642                 : "=d" (rc) : "a" (&refbk), "m" (refbk) : "cc");
643         return rc;
644 }
645 
646 void pfault_fini(void)
647 {
648         struct pfault_refbk refbk = {
649                 .refdiagc = 0x258,
650                 .reffcode = 1,
651                 .refdwlen = 5,
652                 .refversn = 2,
653         };
654 
655         if (pfault_disable)
656                 return;
657         asm volatile(
658                 "       diag    %0,0,0x258\n"
659                 "0:\n"
660                 EX_TABLE(0b,0b)
661                 : : "a" (&refbk), "m" (refbk) : "cc");
662 }
663 
664 static DEFINE_SPINLOCK(pfault_lock);
665 static LIST_HEAD(pfault_list);
666 
667 static void pfault_interrupt(struct ext_code ext_code,
668                              unsigned int param32, unsigned long param64)
669 {
670         struct task_struct *tsk;
671         __u16 subcode;
672         pid_t pid;
673 
674         /*
675          * Get the external interruption subcode & pfault
676          * initial/completion signal bit. VM stores this 
677          * in the 'cpu address' field associated with the
678          * external interrupt. 
679          */
680         subcode = ext_code.subcode;
681         if ((subcode & 0xff00) != __SUBCODE_MASK)
682                 return;
683         inc_irq_stat(IRQEXT_PFL);
684         /* Get the token (= pid of the affected task). */
685         pid = sizeof(void *) == 4 ? param32 : param64;
686         rcu_read_lock();
687         tsk = find_task_by_pid_ns(pid, &init_pid_ns);
688         if (tsk)
689                 get_task_struct(tsk);
690         rcu_read_unlock();
691         if (!tsk)
692                 return;
693         spin_lock(&pfault_lock);
694         if (subcode & 0x0080) {
695                 /* signal bit is set -> a page has been swapped in by VM */
696                 if (tsk->thread.pfault_wait == 1) {
697                         /* Initial interrupt was faster than the completion
698                          * interrupt. pfault_wait is valid. Set pfault_wait
699                          * back to zero and wake up the process. This can
700                          * safely be done because the task is still sleeping
701                          * and can't produce new pfaults. */
702                         tsk->thread.pfault_wait = 0;
703                         list_del(&tsk->thread.list);
704                         wake_up_process(tsk);
705                         put_task_struct(tsk);
706                 } else {
707                         /* Completion interrupt was faster than initial
708                          * interrupt. Set pfault_wait to -1 so the initial
709                          * interrupt doesn't put the task to sleep.
710                          * If the task is not running, ignore the completion
711                          * interrupt since it must be a leftover of a PFAULT
712                          * CANCEL operation which didn't remove all pending
713                          * completion interrupts. */
714                         if (tsk->state == TASK_RUNNING)
715                                 tsk->thread.pfault_wait = -1;
716                 }
717         } else {
718                 /* signal bit not set -> a real page is missing. */
719                 if (WARN_ON_ONCE(tsk != current))
720                         goto out;
721                 if (tsk->thread.pfault_wait == 1) {
722                         /* Already on the list with a reference: put to sleep */
723                         __set_task_state(tsk, TASK_UNINTERRUPTIBLE);
724                         set_tsk_need_resched(tsk);
725                 } else if (tsk->thread.pfault_wait == -1) {
726                         /* Completion interrupt was faster than the initial
727                          * interrupt (pfault_wait == -1). Set pfault_wait
728                          * back to zero and exit. */
729                         tsk->thread.pfault_wait = 0;
730                 } else {
731                         /* Initial interrupt arrived before completion
732                          * interrupt. Let the task sleep.
733                          * An extra task reference is needed since a different
734                          * cpu may set the task state to TASK_RUNNING again
735                          * before the scheduler is reached. */
736                         get_task_struct(tsk);
737                         tsk->thread.pfault_wait = 1;
738                         list_add(&tsk->thread.list, &pfault_list);
739                         __set_task_state(tsk, TASK_UNINTERRUPTIBLE);
740                         set_tsk_need_resched(tsk);
741                 }
742         }
743 out:
744         spin_unlock(&pfault_lock);
745         put_task_struct(tsk);
746 }
747 
748 static int pfault_cpu_notify(struct notifier_block *self, unsigned long action,
749                              void *hcpu)
750 {
751         struct thread_struct *thread, *next;
752         struct task_struct *tsk;
753 
754         switch (action & ~CPU_TASKS_FROZEN) {
755         case CPU_DEAD:
756                 spin_lock_irq(&pfault_lock);
757                 list_for_each_entry_safe(thread, next, &pfault_list, list) {
758                         thread->pfault_wait = 0;
759                         list_del(&thread->list);
760                         tsk = container_of(thread, struct task_struct, thread);
761                         wake_up_process(tsk);
762                         put_task_struct(tsk);
763                 }
764                 spin_unlock_irq(&pfault_lock);
765                 break;
766         default:
767                 break;
768         }
769         return NOTIFY_OK;
770 }
771 
772 static int __init pfault_irq_init(void)
773 {
774         int rc;
775 
776         rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
777         if (rc)
778                 goto out_extint;
779         rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
780         if (rc)
781                 goto out_pfault;
782         irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
783         hotcpu_notifier(pfault_cpu_notify, 0);
784         return 0;
785 
786 out_pfault:
787         unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
788 out_extint:
789         pfault_disable = 1;
790         return rc;
791 }
792 early_initcall(pfault_irq_init);
793 
794 #endif /* CONFIG_PFAULT */
795 

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