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Linux/arch/s390/mm/fault.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  S390 version
  4  *    Copyright IBM Corp. 1999
  5  *    Author(s): Hartmut Penner (hp@de.ibm.com)
  6  *               Ulrich Weigand (uweigand@de.ibm.com)
  7  *
  8  *  Derived from "arch/i386/mm/fault.c"
  9  *    Copyright (C) 1995  Linus Torvalds
 10  */
 11 
 12 #include <linux/kernel_stat.h>
 13 #include <linux/perf_event.h>
 14 #include <linux/signal.h>
 15 #include <linux/sched.h>
 16 #include <linux/sched/debug.h>
 17 #include <linux/kernel.h>
 18 #include <linux/errno.h>
 19 #include <linux/string.h>
 20 #include <linux/types.h>
 21 #include <linux/ptrace.h>
 22 #include <linux/mman.h>
 23 #include <linux/mm.h>
 24 #include <linux/compat.h>
 25 #include <linux/smp.h>
 26 #include <linux/kdebug.h>
 27 #include <linux/init.h>
 28 #include <linux/console.h>
 29 #include <linux/extable.h>
 30 #include <linux/hardirq.h>
 31 #include <linux/kprobes.h>
 32 #include <linux/uaccess.h>
 33 #include <linux/hugetlb.h>
 34 #include <asm/asm-offsets.h>
 35 #include <asm/diag.h>
 36 #include <asm/pgtable.h>
 37 #include <asm/gmap.h>
 38 #include <asm/irq.h>
 39 #include <asm/mmu_context.h>
 40 #include <asm/facility.h>
 41 #include "../kernel/entry.h"
 42 
 43 #define __FAIL_ADDR_MASK -4096L
 44 #define __SUBCODE_MASK 0x0600
 45 #define __PF_RES_FIELD 0x8000000000000000ULL
 46 
 47 #define VM_FAULT_BADCONTEXT     0x010000
 48 #define VM_FAULT_BADMAP         0x020000
 49 #define VM_FAULT_BADACCESS      0x040000
 50 #define VM_FAULT_SIGNAL         0x080000
 51 #define VM_FAULT_PFAULT         0x100000
 52 
 53 enum fault_type {
 54         KERNEL_FAULT,
 55         USER_FAULT,
 56         VDSO_FAULT,
 57         GMAP_FAULT,
 58 };
 59 
 60 static unsigned long store_indication __read_mostly;
 61 
 62 static int __init fault_init(void)
 63 {
 64         if (test_facility(75))
 65                 store_indication = 0xc00;
 66         return 0;
 67 }
 68 early_initcall(fault_init);
 69 
 70 static inline int notify_page_fault(struct pt_regs *regs)
 71 {
 72         int ret = 0;
 73 
 74         /* kprobe_running() needs smp_processor_id() */
 75         if (kprobes_built_in() && !user_mode(regs)) {
 76                 preempt_disable();
 77                 if (kprobe_running() && kprobe_fault_handler(regs, 14))
 78                         ret = 1;
 79                 preempt_enable();
 80         }
 81         return ret;
 82 }
 83 
 84 
 85 /*
 86  * Unlock any spinlocks which will prevent us from getting the
 87  * message out.
 88  */
 89 void bust_spinlocks(int yes)
 90 {
 91         if (yes) {
 92                 oops_in_progress = 1;
 93         } else {
 94                 int loglevel_save = console_loglevel;
 95                 console_unblank();
 96                 oops_in_progress = 0;
 97                 /*
 98                  * OK, the message is on the console.  Now we call printk()
 99                  * without oops_in_progress set so that printk will give klogd
100                  * a poke.  Hold onto your hats...
101                  */
102                 console_loglevel = 15;
103                 printk(" ");
104                 console_loglevel = loglevel_save;
105         }
106 }
107 
108 /*
109  * Find out which address space caused the exception.
110  * Access register mode is impossible, ignore space == 3.
111  */
112 static inline enum fault_type get_fault_type(struct pt_regs *regs)
113 {
114         unsigned long trans_exc_code;
115 
116         trans_exc_code = regs->int_parm_long & 3;
117         if (likely(trans_exc_code == 0)) {
118                 /* primary space exception */
119                 if (IS_ENABLED(CONFIG_PGSTE) &&
120                     test_pt_regs_flag(regs, PIF_GUEST_FAULT))
121                         return GMAP_FAULT;
122                 if (current->thread.mm_segment == USER_DS)
123                         return USER_FAULT;
124                 return KERNEL_FAULT;
125         }
126         if (trans_exc_code == 2) {
127                 /* secondary space exception */
128                 if (current->thread.mm_segment & 1) {
129                         if (current->thread.mm_segment == USER_DS_SACF)
130                                 return USER_FAULT;
131                         return KERNEL_FAULT;
132                 }
133                 return VDSO_FAULT;
134         }
135         /* home space exception -> access via kernel ASCE */
136         return KERNEL_FAULT;
137 }
138 
139 static int bad_address(void *p)
140 {
141         unsigned long dummy;
142 
143         return probe_kernel_address((unsigned long *)p, dummy);
144 }
145 
146 static void dump_pagetable(unsigned long asce, unsigned long address)
147 {
148         unsigned long *table = __va(asce & _ASCE_ORIGIN);
149 
150         pr_alert("AS:%016lx ", asce);
151         switch (asce & _ASCE_TYPE_MASK) {
152         case _ASCE_TYPE_REGION1:
153                 table += (address & _REGION1_INDEX) >> _REGION1_SHIFT;
154                 if (bad_address(table))
155                         goto bad;
156                 pr_cont("R1:%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_REGION2:
162                 table += (address & _REGION2_INDEX) >> _REGION2_SHIFT;
163                 if (bad_address(table))
164                         goto bad;
165                 pr_cont("R2:%016lx ", *table);
166                 if (*table & _REGION_ENTRY_INVALID)
167                         goto out;
168                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
169                 /* fallthrough */
170         case _ASCE_TYPE_REGION3:
171                 table += (address & _REGION3_INDEX) >> _REGION3_SHIFT;
172                 if (bad_address(table))
173                         goto bad;
174                 pr_cont("R3:%016lx ", *table);
175                 if (*table & (_REGION_ENTRY_INVALID | _REGION3_ENTRY_LARGE))
176                         goto out;
177                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
178                 /* fallthrough */
179         case _ASCE_TYPE_SEGMENT:
180                 table += (address & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
181                 if (bad_address(table))
182                         goto bad;
183                 pr_cont("S:%016lx ", *table);
184                 if (*table & (_SEGMENT_ENTRY_INVALID | _SEGMENT_ENTRY_LARGE))
185                         goto out;
186                 table = (unsigned long *)(*table & _SEGMENT_ENTRY_ORIGIN);
187         }
188         table += (address & _PAGE_INDEX) >> _PAGE_SHIFT;
189         if (bad_address(table))
190                 goto bad;
191         pr_cont("P:%016lx ", *table);
192 out:
193         pr_cont("\n");
194         return;
195 bad:
196         pr_cont("BAD\n");
197 }
198 
199 static void dump_fault_info(struct pt_regs *regs)
200 {
201         unsigned long asce;
202 
203         pr_alert("Failing address: %016lx TEID: %016lx\n",
204                  regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
205         pr_alert("Fault in ");
206         switch (regs->int_parm_long & 3) {
207         case 3:
208                 pr_cont("home space ");
209                 break;
210         case 2:
211                 pr_cont("secondary space ");
212                 break;
213         case 1:
214                 pr_cont("access register ");
215                 break;
216         case 0:
217                 pr_cont("primary space ");
218                 break;
219         }
220         pr_cont("mode while using ");
221         switch (get_fault_type(regs)) {
222         case USER_FAULT:
223                 asce = S390_lowcore.user_asce;
224                 pr_cont("user ");
225                 break;
226         case VDSO_FAULT:
227                 asce = S390_lowcore.vdso_asce;
228                 pr_cont("vdso ");
229                 break;
230         case GMAP_FAULT:
231                 asce = ((struct gmap *) S390_lowcore.gmap)->asce;
232                 pr_cont("gmap ");
233                 break;
234         case KERNEL_FAULT:
235                 asce = S390_lowcore.kernel_asce;
236                 pr_cont("kernel ");
237                 break;
238         }
239         pr_cont("ASCE.\n");
240         dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
241 }
242 
243 int show_unhandled_signals = 1;
244 
245 void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault)
246 {
247         if ((task_pid_nr(current) > 1) && !show_unhandled_signals)
248                 return;
249         if (!unhandled_signal(current, signr))
250                 return;
251         if (!printk_ratelimit())
252                 return;
253         printk(KERN_ALERT "User process fault: interruption code %04x ilc:%d ",
254                regs->int_code & 0xffff, regs->int_code >> 17);
255         print_vma_addr(KERN_CONT "in ", regs->psw.addr);
256         printk(KERN_CONT "\n");
257         if (is_mm_fault)
258                 dump_fault_info(regs);
259         show_regs(regs);
260 }
261 
262 /*
263  * Send SIGSEGV to task.  This is an external routine
264  * to keep the stack usage of do_page_fault small.
265  */
266 static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
267 {
268         report_user_fault(regs, SIGSEGV, 1);
269         force_sig_fault(SIGSEGV, si_code,
270                         (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
271                         current);
272 }
273 
274 static noinline void do_no_context(struct pt_regs *regs)
275 {
276         const struct exception_table_entry *fixup;
277 
278         /* Are we prepared to handle this kernel fault?  */
279         fixup = search_exception_tables(regs->psw.addr);
280         if (fixup) {
281                 regs->psw.addr = extable_fixup(fixup);
282                 return;
283         }
284 
285         /*
286          * Oops. The kernel tried to access some bad page. We'll have to
287          * terminate things with extreme prejudice.
288          */
289         if (get_fault_type(regs) == KERNEL_FAULT)
290                 printk(KERN_ALERT "Unable to handle kernel pointer dereference"
291                        " in virtual kernel address space\n");
292         else
293                 printk(KERN_ALERT "Unable to handle kernel paging request"
294                        " in virtual user address space\n");
295         dump_fault_info(regs);
296         die(regs, "Oops");
297         do_exit(SIGKILL);
298 }
299 
300 static noinline void do_low_address(struct pt_regs *regs)
301 {
302         /* Low-address protection hit in kernel mode means
303            NULL pointer write access in kernel mode.  */
304         if (regs->psw.mask & PSW_MASK_PSTATE) {
305                 /* Low-address protection hit in user mode 'cannot happen'. */
306                 die (regs, "Low-address protection");
307                 do_exit(SIGKILL);
308         }
309 
310         do_no_context(regs);
311 }
312 
313 static noinline void do_sigbus(struct pt_regs *regs)
314 {
315         /*
316          * Send a sigbus, regardless of whether we were in kernel
317          * or user mode.
318          */
319         force_sig_fault(SIGBUS, BUS_ADRERR,
320                         (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK),
321                         current);
322 }
323 
324 static noinline int signal_return(struct pt_regs *regs)
325 {
326         u16 instruction;
327         int rc;
328 
329         rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
330         if (rc)
331                 return rc;
332         if (instruction == 0x0a77) {
333                 set_pt_regs_flag(regs, PIF_SYSCALL);
334                 regs->int_code = 0x00040077;
335                 return 0;
336         } else if (instruction == 0x0aad) {
337                 set_pt_regs_flag(regs, PIF_SYSCALL);
338                 regs->int_code = 0x000400ad;
339                 return 0;
340         }
341         return -EACCES;
342 }
343 
344 static noinline void do_fault_error(struct pt_regs *regs, int access, int fault)
345 {
346         int si_code;
347 
348         switch (fault) {
349         case VM_FAULT_BADACCESS:
350                 if (access == VM_EXEC && signal_return(regs) == 0)
351                         break;
352         case VM_FAULT_BADMAP:
353                 /* Bad memory access. Check if it is kernel or user space. */
354                 if (user_mode(regs)) {
355                         /* User mode accesses just cause a SIGSEGV */
356                         si_code = (fault == VM_FAULT_BADMAP) ?
357                                 SEGV_MAPERR : SEGV_ACCERR;
358                         do_sigsegv(regs, si_code);
359                         break;
360                 }
361         case VM_FAULT_BADCONTEXT:
362         case VM_FAULT_PFAULT:
363                 do_no_context(regs);
364                 break;
365         case VM_FAULT_SIGNAL:
366                 if (!user_mode(regs))
367                         do_no_context(regs);
368                 break;
369         default: /* fault & VM_FAULT_ERROR */
370                 if (fault & VM_FAULT_OOM) {
371                         if (!user_mode(regs))
372                                 do_no_context(regs);
373                         else
374                                 pagefault_out_of_memory();
375                 } else if (fault & VM_FAULT_SIGSEGV) {
376                         /* Kernel mode? Handle exceptions or die */
377                         if (!user_mode(regs))
378                                 do_no_context(regs);
379                         else
380                                 do_sigsegv(regs, SEGV_MAPERR);
381                 } else if (fault & VM_FAULT_SIGBUS) {
382                         /* Kernel mode? Handle exceptions or die */
383                         if (!user_mode(regs))
384                                 do_no_context(regs);
385                         else
386                                 do_sigbus(regs);
387                 } else
388                         BUG();
389                 break;
390         }
391 }
392 
393 /*
394  * This routine handles page faults.  It determines the address,
395  * and the problem, and then passes it off to one of the appropriate
396  * routines.
397  *
398  * interruption code (int_code):
399  *   04       Protection           ->  Write-Protection  (suprression)
400  *   10       Segment translation  ->  Not present       (nullification)
401  *   11       Page translation     ->  Not present       (nullification)
402  *   3b       Region third trans.  ->  Not present       (nullification)
403  */
404 static inline int do_exception(struct pt_regs *regs, int access)
405 {
406         struct gmap *gmap;
407         struct task_struct *tsk;
408         struct mm_struct *mm;
409         struct vm_area_struct *vma;
410         enum fault_type type;
411         unsigned long trans_exc_code;
412         unsigned long address;
413         unsigned int flags;
414         int fault;
415 
416         tsk = current;
417         /*
418          * The instruction that caused the program check has
419          * been nullified. Don't signal single step via SIGTRAP.
420          */
421         clear_pt_regs_flag(regs, PIF_PER_TRAP);
422 
423         if (notify_page_fault(regs))
424                 return 0;
425 
426         mm = tsk->mm;
427         trans_exc_code = regs->int_parm_long;
428 
429         /*
430          * Verify that the fault happened in user space, that
431          * we are not in an interrupt and that there is a 
432          * user context.
433          */
434         fault = VM_FAULT_BADCONTEXT;
435         type = get_fault_type(regs);
436         switch (type) {
437         case KERNEL_FAULT:
438                 goto out;
439         case VDSO_FAULT:
440                 fault = VM_FAULT_BADMAP;
441                 goto out;
442         case USER_FAULT:
443         case GMAP_FAULT:
444                 if (faulthandler_disabled() || !mm)
445                         goto out;
446                 break;
447         }
448 
449         address = trans_exc_code & __FAIL_ADDR_MASK;
450         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
451         flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
452         if (user_mode(regs))
453                 flags |= FAULT_FLAG_USER;
454         if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
455                 flags |= FAULT_FLAG_WRITE;
456         down_read(&mm->mmap_sem);
457 
458         gmap = NULL;
459         if (IS_ENABLED(CONFIG_PGSTE) && type == GMAP_FAULT) {
460                 gmap = (struct gmap *) S390_lowcore.gmap;
461                 current->thread.gmap_addr = address;
462                 current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
463                 current->thread.gmap_int_code = regs->int_code & 0xffff;
464                 address = __gmap_translate(gmap, address);
465                 if (address == -EFAULT) {
466                         fault = VM_FAULT_BADMAP;
467                         goto out_up;
468                 }
469                 if (gmap->pfault_enabled)
470                         flags |= FAULT_FLAG_RETRY_NOWAIT;
471         }
472 
473 retry:
474         fault = VM_FAULT_BADMAP;
475         vma = find_vma(mm, address);
476         if (!vma)
477                 goto out_up;
478 
479         if (unlikely(vma->vm_start > address)) {
480                 if (!(vma->vm_flags & VM_GROWSDOWN))
481                         goto out_up;
482                 if (expand_stack(vma, address))
483                         goto out_up;
484         }
485 
486         /*
487          * Ok, we have a good vm_area for this memory access, so
488          * we can handle it..
489          */
490         fault = VM_FAULT_BADACCESS;
491         if (unlikely(!(vma->vm_flags & access)))
492                 goto out_up;
493 
494         if (is_vm_hugetlb_page(vma))
495                 address &= HPAGE_MASK;
496         /*
497          * If for any reason at all we couldn't handle the fault,
498          * make sure we exit gracefully rather than endlessly redo
499          * the fault.
500          */
501         fault = handle_mm_fault(vma, address, flags);
502         /* No reason to continue if interrupted by SIGKILL. */
503         if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
504                 fault = VM_FAULT_SIGNAL;
505                 if (flags & FAULT_FLAG_RETRY_NOWAIT)
506                         goto out_up;
507                 goto out;
508         }
509         if (unlikely(fault & VM_FAULT_ERROR))
510                 goto out_up;
511 
512         /*
513          * Major/minor page fault accounting is only done on the
514          * initial attempt. If we go through a retry, it is extremely
515          * likely that the page will be found in page cache at that point.
516          */
517         if (flags & FAULT_FLAG_ALLOW_RETRY) {
518                 if (fault & VM_FAULT_MAJOR) {
519                         tsk->maj_flt++;
520                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
521                                       regs, address);
522                 } else {
523                         tsk->min_flt++;
524                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
525                                       regs, address);
526                 }
527                 if (fault & VM_FAULT_RETRY) {
528                         if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
529                             (flags & FAULT_FLAG_RETRY_NOWAIT)) {
530                                 /* FAULT_FLAG_RETRY_NOWAIT has been set,
531                                  * mmap_sem has not been released */
532                                 current->thread.gmap_pfault = 1;
533                                 fault = VM_FAULT_PFAULT;
534                                 goto out_up;
535                         }
536                         /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
537                          * of starvation. */
538                         flags &= ~(FAULT_FLAG_ALLOW_RETRY |
539                                    FAULT_FLAG_RETRY_NOWAIT);
540                         flags |= FAULT_FLAG_TRIED;
541                         down_read(&mm->mmap_sem);
542                         goto retry;
543                 }
544         }
545         if (IS_ENABLED(CONFIG_PGSTE) && gmap) {
546                 address =  __gmap_link(gmap, current->thread.gmap_addr,
547                                        address);
548                 if (address == -EFAULT) {
549                         fault = VM_FAULT_BADMAP;
550                         goto out_up;
551                 }
552                 if (address == -ENOMEM) {
553                         fault = VM_FAULT_OOM;
554                         goto out_up;
555                 }
556         }
557         fault = 0;
558 out_up:
559         up_read(&mm->mmap_sem);
560 out:
561         return fault;
562 }
563 
564 void do_protection_exception(struct pt_regs *regs)
565 {
566         unsigned long trans_exc_code;
567         int access, fault;
568 
569         trans_exc_code = regs->int_parm_long;
570         /*
571          * Protection exceptions are suppressing, decrement psw address.
572          * The exception to this rule are aborted transactions, for these
573          * the PSW already points to the correct location.
574          */
575         if (!(regs->int_code & 0x200))
576                 regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
577         /*
578          * Check for low-address protection.  This needs to be treated
579          * as a special case because the translation exception code
580          * field is not guaranteed to contain valid data in this case.
581          */
582         if (unlikely(!(trans_exc_code & 4))) {
583                 do_low_address(regs);
584                 return;
585         }
586         if (unlikely(MACHINE_HAS_NX && (trans_exc_code & 0x80))) {
587                 regs->int_parm_long = (trans_exc_code & ~PAGE_MASK) |
588                                         (regs->psw.addr & PAGE_MASK);
589                 access = VM_EXEC;
590                 fault = VM_FAULT_BADACCESS;
591         } else {
592                 access = VM_WRITE;
593                 fault = do_exception(regs, access);
594         }
595         if (unlikely(fault))
596                 do_fault_error(regs, access, fault);
597 }
598 NOKPROBE_SYMBOL(do_protection_exception);
599 
600 void do_dat_exception(struct pt_regs *regs)
601 {
602         int access, fault;
603 
604         access = VM_READ | VM_EXEC | VM_WRITE;
605         fault = do_exception(regs, access);
606         if (unlikely(fault))
607                 do_fault_error(regs, access, fault);
608 }
609 NOKPROBE_SYMBOL(do_dat_exception);
610 
611 #ifdef CONFIG_PFAULT 
612 /*
613  * 'pfault' pseudo page faults routines.
614  */
615 static int pfault_disable;
616 
617 static int __init nopfault(char *str)
618 {
619         pfault_disable = 1;
620         return 1;
621 }
622 
623 __setup("nopfault", nopfault);
624 
625 struct pfault_refbk {
626         u16 refdiagc;
627         u16 reffcode;
628         u16 refdwlen;
629         u16 refversn;
630         u64 refgaddr;
631         u64 refselmk;
632         u64 refcmpmk;
633         u64 reserved;
634 } __attribute__ ((packed, aligned(8)));
635 
636 int pfault_init(void)
637 {
638         struct pfault_refbk refbk = {
639                 .refdiagc = 0x258,
640                 .reffcode = 0,
641                 .refdwlen = 5,
642                 .refversn = 2,
643                 .refgaddr = __LC_LPP,
644                 .refselmk = 1ULL << 48,
645                 .refcmpmk = 1ULL << 48,
646                 .reserved = __PF_RES_FIELD };
647         int rc;
648 
649         if (pfault_disable)
650                 return -1;
651         diag_stat_inc(DIAG_STAT_X258);
652         asm volatile(
653                 "       diag    %1,%0,0x258\n"
654                 "0:     j       2f\n"
655                 "1:     la      %0,8\n"
656                 "2:\n"
657                 EX_TABLE(0b,1b)
658                 : "=d" (rc) : "a" (&refbk), "m" (refbk) : "cc");
659         return rc;
660 }
661 
662 void pfault_fini(void)
663 {
664         struct pfault_refbk refbk = {
665                 .refdiagc = 0x258,
666                 .reffcode = 1,
667                 .refdwlen = 5,
668                 .refversn = 2,
669         };
670 
671         if (pfault_disable)
672                 return;
673         diag_stat_inc(DIAG_STAT_X258);
674         asm volatile(
675                 "       diag    %0,0,0x258\n"
676                 "0:     nopr    %%r7\n"
677                 EX_TABLE(0b,0b)
678                 : : "a" (&refbk), "m" (refbk) : "cc");
679 }
680 
681 static DEFINE_SPINLOCK(pfault_lock);
682 static LIST_HEAD(pfault_list);
683 
684 #define PF_COMPLETE     0x0080
685 
686 /*
687  * The mechanism of our pfault code: if Linux is running as guest, runs a user
688  * space process and the user space process accesses a page that the host has
689  * paged out we get a pfault interrupt.
690  *
691  * This allows us, within the guest, to schedule a different process. Without
692  * this mechanism the host would have to suspend the whole virtual cpu until
693  * the page has been paged in.
694  *
695  * So when we get such an interrupt then we set the state of the current task
696  * to uninterruptible and also set the need_resched flag. Both happens within
697  * interrupt context(!). If we later on want to return to user space we
698  * recognize the need_resched flag and then call schedule().  It's not very
699  * obvious how this works...
700  *
701  * Of course we have a lot of additional fun with the completion interrupt (->
702  * host signals that a page of a process has been paged in and the process can
703  * continue to run). This interrupt can arrive on any cpu and, since we have
704  * virtual cpus, actually appear before the interrupt that signals that a page
705  * is missing.
706  */
707 static void pfault_interrupt(struct ext_code ext_code,
708                              unsigned int param32, unsigned long param64)
709 {
710         struct task_struct *tsk;
711         __u16 subcode;
712         pid_t pid;
713 
714         /*
715          * Get the external interruption subcode & pfault initial/completion
716          * signal bit. VM stores this in the 'cpu address' field associated
717          * with the external interrupt.
718          */
719         subcode = ext_code.subcode;
720         if ((subcode & 0xff00) != __SUBCODE_MASK)
721                 return;
722         inc_irq_stat(IRQEXT_PFL);
723         /* Get the token (= pid of the affected task). */
724         pid = param64 & LPP_PID_MASK;
725         rcu_read_lock();
726         tsk = find_task_by_pid_ns(pid, &init_pid_ns);
727         if (tsk)
728                 get_task_struct(tsk);
729         rcu_read_unlock();
730         if (!tsk)
731                 return;
732         spin_lock(&pfault_lock);
733         if (subcode & PF_COMPLETE) {
734                 /* signal bit is set -> a page has been swapped in by VM */
735                 if (tsk->thread.pfault_wait == 1) {
736                         /* Initial interrupt was faster than the completion
737                          * interrupt. pfault_wait is valid. Set pfault_wait
738                          * back to zero and wake up the process. This can
739                          * safely be done because the task is still sleeping
740                          * and can't produce new pfaults. */
741                         tsk->thread.pfault_wait = 0;
742                         list_del(&tsk->thread.list);
743                         wake_up_process(tsk);
744                         put_task_struct(tsk);
745                 } else {
746                         /* Completion interrupt was faster than initial
747                          * interrupt. Set pfault_wait to -1 so the initial
748                          * interrupt doesn't put the task to sleep.
749                          * If the task is not running, ignore the completion
750                          * interrupt since it must be a leftover of a PFAULT
751                          * CANCEL operation which didn't remove all pending
752                          * completion interrupts. */
753                         if (tsk->state == TASK_RUNNING)
754                                 tsk->thread.pfault_wait = -1;
755                 }
756         } else {
757                 /* signal bit not set -> a real page is missing. */
758                 if (WARN_ON_ONCE(tsk != current))
759                         goto out;
760                 if (tsk->thread.pfault_wait == 1) {
761                         /* Already on the list with a reference: put to sleep */
762                         goto block;
763                 } else if (tsk->thread.pfault_wait == -1) {
764                         /* Completion interrupt was faster than the initial
765                          * interrupt (pfault_wait == -1). Set pfault_wait
766                          * back to zero and exit. */
767                         tsk->thread.pfault_wait = 0;
768                 } else {
769                         /* Initial interrupt arrived before completion
770                          * interrupt. Let the task sleep.
771                          * An extra task reference is needed since a different
772                          * cpu may set the task state to TASK_RUNNING again
773                          * before the scheduler is reached. */
774                         get_task_struct(tsk);
775                         tsk->thread.pfault_wait = 1;
776                         list_add(&tsk->thread.list, &pfault_list);
777 block:
778                         /* Since this must be a userspace fault, there
779                          * is no kernel task state to trample. Rely on the
780                          * return to userspace schedule() to block. */
781                         __set_current_state(TASK_UNINTERRUPTIBLE);
782                         set_tsk_need_resched(tsk);
783                         set_preempt_need_resched();
784                 }
785         }
786 out:
787         spin_unlock(&pfault_lock);
788         put_task_struct(tsk);
789 }
790 
791 static int pfault_cpu_dead(unsigned int cpu)
792 {
793         struct thread_struct *thread, *next;
794         struct task_struct *tsk;
795 
796         spin_lock_irq(&pfault_lock);
797         list_for_each_entry_safe(thread, next, &pfault_list, list) {
798                 thread->pfault_wait = 0;
799                 list_del(&thread->list);
800                 tsk = container_of(thread, struct task_struct, thread);
801                 wake_up_process(tsk);
802                 put_task_struct(tsk);
803         }
804         spin_unlock_irq(&pfault_lock);
805         return 0;
806 }
807 
808 static int __init pfault_irq_init(void)
809 {
810         int rc;
811 
812         rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
813         if (rc)
814                 goto out_extint;
815         rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
816         if (rc)
817                 goto out_pfault;
818         irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
819         cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead",
820                                   NULL, pfault_cpu_dead);
821         return 0;
822 
823 out_pfault:
824         unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
825 out_extint:
826         pfault_disable = 1;
827         return rc;
828 }
829 early_initcall(pfault_irq_init);
830 
831 #endif /* CONFIG_PFAULT */
832 

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