~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/arch/s390/mm/fault.c

Version: ~ [ linux-5.19-rc3 ] ~ [ linux-5.18.5 ] ~ [ linux-5.17.15 ] ~ [ linux-5.16.20 ] ~ [ linux-5.15.48 ] ~ [ linux-5.14.21 ] ~ [ linux-5.13.19 ] ~ [ linux-5.12.19 ] ~ [ linux-5.11.22 ] ~ [ linux-5.10.123 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.199 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.248 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.284 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.319 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.302 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.9 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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 /*
 71  * Find out which address space caused the exception.
 72  */
 73 static enum fault_type get_fault_type(struct pt_regs *regs)
 74 {
 75         unsigned long trans_exc_code;
 76 
 77         trans_exc_code = regs->int_parm_long & 3;
 78         if (likely(trans_exc_code == 0)) {
 79                 /* primary space exception */
 80                 if (IS_ENABLED(CONFIG_PGSTE) &&
 81                     test_pt_regs_flag(regs, PIF_GUEST_FAULT))
 82                         return GMAP_FAULT;
 83                 if (current->thread.mm_segment == USER_DS)
 84                         return USER_FAULT;
 85                 return KERNEL_FAULT;
 86         }
 87         if (trans_exc_code == 2) {
 88                 /* secondary space exception */
 89                 if (current->thread.mm_segment & 1) {
 90                         if (current->thread.mm_segment == USER_DS_SACF)
 91                                 return USER_FAULT;
 92                         return KERNEL_FAULT;
 93                 }
 94                 return VDSO_FAULT;
 95         }
 96         if (trans_exc_code == 1) {
 97                 /* access register mode, not used in the kernel */
 98                 return USER_FAULT;
 99         }
100         /* home space exception -> access via kernel ASCE */
101         return KERNEL_FAULT;
102 }
103 
104 static int bad_address(void *p)
105 {
106         unsigned long dummy;
107 
108         return probe_kernel_address((unsigned long *)p, dummy);
109 }
110 
111 static void dump_pagetable(unsigned long asce, unsigned long address)
112 {
113         unsigned long *table = __va(asce & _ASCE_ORIGIN);
114 
115         pr_alert("AS:%016lx ", asce);
116         switch (asce & _ASCE_TYPE_MASK) {
117         case _ASCE_TYPE_REGION1:
118                 table += (address & _REGION1_INDEX) >> _REGION1_SHIFT;
119                 if (bad_address(table))
120                         goto bad;
121                 pr_cont("R1:%016lx ", *table);
122                 if (*table & _REGION_ENTRY_INVALID)
123                         goto out;
124                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
125                 /* fallthrough */
126         case _ASCE_TYPE_REGION2:
127                 table += (address & _REGION2_INDEX) >> _REGION2_SHIFT;
128                 if (bad_address(table))
129                         goto bad;
130                 pr_cont("R2:%016lx ", *table);
131                 if (*table & _REGION_ENTRY_INVALID)
132                         goto out;
133                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
134                 /* fallthrough */
135         case _ASCE_TYPE_REGION3:
136                 table += (address & _REGION3_INDEX) >> _REGION3_SHIFT;
137                 if (bad_address(table))
138                         goto bad;
139                 pr_cont("R3:%016lx ", *table);
140                 if (*table & (_REGION_ENTRY_INVALID | _REGION3_ENTRY_LARGE))
141                         goto out;
142                 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
143                 /* fallthrough */
144         case _ASCE_TYPE_SEGMENT:
145                 table += (address & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
146                 if (bad_address(table))
147                         goto bad;
148                 pr_cont("S:%016lx ", *table);
149                 if (*table & (_SEGMENT_ENTRY_INVALID | _SEGMENT_ENTRY_LARGE))
150                         goto out;
151                 table = (unsigned long *)(*table & _SEGMENT_ENTRY_ORIGIN);
152         }
153         table += (address & _PAGE_INDEX) >> _PAGE_SHIFT;
154         if (bad_address(table))
155                 goto bad;
156         pr_cont("P:%016lx ", *table);
157 out:
158         pr_cont("\n");
159         return;
160 bad:
161         pr_cont("BAD\n");
162 }
163 
164 static void dump_fault_info(struct pt_regs *regs)
165 {
166         unsigned long asce;
167 
168         pr_alert("Failing address: %016lx TEID: %016lx\n",
169                  regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
170         pr_alert("Fault in ");
171         switch (regs->int_parm_long & 3) {
172         case 3:
173                 pr_cont("home space ");
174                 break;
175         case 2:
176                 pr_cont("secondary space ");
177                 break;
178         case 1:
179                 pr_cont("access register ");
180                 break;
181         case 0:
182                 pr_cont("primary space ");
183                 break;
184         }
185         pr_cont("mode while using ");
186         switch (get_fault_type(regs)) {
187         case USER_FAULT:
188                 asce = S390_lowcore.user_asce;
189                 pr_cont("user ");
190                 break;
191         case VDSO_FAULT:
192                 asce = S390_lowcore.vdso_asce;
193                 pr_cont("vdso ");
194                 break;
195         case GMAP_FAULT:
196                 asce = ((struct gmap *) S390_lowcore.gmap)->asce;
197                 pr_cont("gmap ");
198                 break;
199         case KERNEL_FAULT:
200                 asce = S390_lowcore.kernel_asce;
201                 pr_cont("kernel ");
202                 break;
203         default:
204                 unreachable();
205         }
206         pr_cont("ASCE.\n");
207         dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
208 }
209 
210 int show_unhandled_signals = 1;
211 
212 void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault)
213 {
214         if ((task_pid_nr(current) > 1) && !show_unhandled_signals)
215                 return;
216         if (!unhandled_signal(current, signr))
217                 return;
218         if (!printk_ratelimit())
219                 return;
220         printk(KERN_ALERT "User process fault: interruption code %04x ilc:%d ",
221                regs->int_code & 0xffff, regs->int_code >> 17);
222         print_vma_addr(KERN_CONT "in ", regs->psw.addr);
223         printk(KERN_CONT "\n");
224         if (is_mm_fault)
225                 dump_fault_info(regs);
226         show_regs(regs);
227 }
228 
229 /*
230  * Send SIGSEGV to task.  This is an external routine
231  * to keep the stack usage of do_page_fault small.
232  */
233 static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
234 {
235         report_user_fault(regs, SIGSEGV, 1);
236         force_sig_fault(SIGSEGV, si_code,
237                         (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK));
238 }
239 
240 const struct exception_table_entry *s390_search_extables(unsigned long addr)
241 {
242         const struct exception_table_entry *fixup;
243 
244         fixup = search_extable(__start_dma_ex_table,
245                                __stop_dma_ex_table - __start_dma_ex_table,
246                                addr);
247         if (!fixup)
248                 fixup = search_exception_tables(addr);
249         return fixup;
250 }
251 
252 static noinline void do_no_context(struct pt_regs *regs)
253 {
254         const struct exception_table_entry *fixup;
255 
256         /* Are we prepared to handle this kernel fault?  */
257         fixup = s390_search_extables(regs->psw.addr);
258         if (fixup) {
259                 regs->psw.addr = extable_fixup(fixup);
260                 return;
261         }
262 
263         /*
264          * Oops. The kernel tried to access some bad page. We'll have to
265          * terminate things with extreme prejudice.
266          */
267         if (get_fault_type(regs) == KERNEL_FAULT)
268                 printk(KERN_ALERT "Unable to handle kernel pointer dereference"
269                        " in virtual kernel address space\n");
270         else
271                 printk(KERN_ALERT "Unable to handle kernel paging request"
272                        " in virtual user address space\n");
273         dump_fault_info(regs);
274         die(regs, "Oops");
275         do_exit(SIGKILL);
276 }
277 
278 static noinline void do_low_address(struct pt_regs *regs)
279 {
280         /* Low-address protection hit in kernel mode means
281            NULL pointer write access in kernel mode.  */
282         if (regs->psw.mask & PSW_MASK_PSTATE) {
283                 /* Low-address protection hit in user mode 'cannot happen'. */
284                 die (regs, "Low-address protection");
285                 do_exit(SIGKILL);
286         }
287 
288         do_no_context(regs);
289 }
290 
291 static noinline void do_sigbus(struct pt_regs *regs)
292 {
293         /*
294          * Send a sigbus, regardless of whether we were in kernel
295          * or user mode.
296          */
297         force_sig_fault(SIGBUS, BUS_ADRERR,
298                         (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK));
299 }
300 
301 static noinline int signal_return(struct pt_regs *regs)
302 {
303         u16 instruction;
304         int rc;
305 
306         rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
307         if (rc)
308                 return rc;
309         if (instruction == 0x0a77) {
310                 set_pt_regs_flag(regs, PIF_SYSCALL);
311                 regs->int_code = 0x00040077;
312                 return 0;
313         } else if (instruction == 0x0aad) {
314                 set_pt_regs_flag(regs, PIF_SYSCALL);
315                 regs->int_code = 0x000400ad;
316                 return 0;
317         }
318         return -EACCES;
319 }
320 
321 static noinline void do_fault_error(struct pt_regs *regs, int access,
322                                         vm_fault_t fault)
323 {
324         int si_code;
325 
326         switch (fault) {
327         case VM_FAULT_BADACCESS:
328                 if (access == VM_EXEC && signal_return(regs) == 0)
329                         break;
330                 /* fallthrough */
331         case VM_FAULT_BADMAP:
332                 /* Bad memory access. Check if it is kernel or user space. */
333                 if (user_mode(regs)) {
334                         /* User mode accesses just cause a SIGSEGV */
335                         si_code = (fault == VM_FAULT_BADMAP) ?
336                                 SEGV_MAPERR : SEGV_ACCERR;
337                         do_sigsegv(regs, si_code);
338                         break;
339                 }
340                 /* fallthrough */
341         case VM_FAULT_BADCONTEXT:
342                 /* fallthrough */
343         case VM_FAULT_PFAULT:
344                 do_no_context(regs);
345                 break;
346         case VM_FAULT_SIGNAL:
347                 if (!user_mode(regs))
348                         do_no_context(regs);
349                 break;
350         default: /* fault & VM_FAULT_ERROR */
351                 if (fault & VM_FAULT_OOM) {
352                         if (!user_mode(regs))
353                                 do_no_context(regs);
354                         else
355                                 pagefault_out_of_memory();
356                 } else if (fault & VM_FAULT_SIGSEGV) {
357                         /* Kernel mode? Handle exceptions or die */
358                         if (!user_mode(regs))
359                                 do_no_context(regs);
360                         else
361                                 do_sigsegv(regs, SEGV_MAPERR);
362                 } else if (fault & VM_FAULT_SIGBUS) {
363                         /* Kernel mode? Handle exceptions or die */
364                         if (!user_mode(regs))
365                                 do_no_context(regs);
366                         else
367                                 do_sigbus(regs);
368                 } else
369                         BUG();
370                 break;
371         }
372 }
373 
374 /*
375  * This routine handles page faults.  It determines the address,
376  * and the problem, and then passes it off to one of the appropriate
377  * routines.
378  *
379  * interruption code (int_code):
380  *   04       Protection           ->  Write-Protection  (suprression)
381  *   10       Segment translation  ->  Not present       (nullification)
382  *   11       Page translation     ->  Not present       (nullification)
383  *   3b       Region third trans.  ->  Not present       (nullification)
384  */
385 static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
386 {
387         struct gmap *gmap;
388         struct task_struct *tsk;
389         struct mm_struct *mm;
390         struct vm_area_struct *vma;
391         enum fault_type type;
392         unsigned long trans_exc_code;
393         unsigned long address;
394         unsigned int flags;
395         vm_fault_t fault;
396 
397         tsk = current;
398         /*
399          * The instruction that caused the program check has
400          * been nullified. Don't signal single step via SIGTRAP.
401          */
402         clear_pt_regs_flag(regs, PIF_PER_TRAP);
403 
404         if (kprobe_page_fault(regs, 14))
405                 return 0;
406 
407         mm = tsk->mm;
408         trans_exc_code = regs->int_parm_long;
409 
410         /*
411          * Verify that the fault happened in user space, that
412          * we are not in an interrupt and that there is a 
413          * user context.
414          */
415         fault = VM_FAULT_BADCONTEXT;
416         type = get_fault_type(regs);
417         switch (type) {
418         case KERNEL_FAULT:
419                 goto out;
420         case VDSO_FAULT:
421                 fault = VM_FAULT_BADMAP;
422                 goto out;
423         case USER_FAULT:
424         case GMAP_FAULT:
425                 if (faulthandler_disabled() || !mm)
426                         goto out;
427                 break;
428         }
429 
430         address = trans_exc_code & __FAIL_ADDR_MASK;
431         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
432         flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
433         if (user_mode(regs))
434                 flags |= FAULT_FLAG_USER;
435         if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
436                 flags |= FAULT_FLAG_WRITE;
437         down_read(&mm->mmap_sem);
438 
439         gmap = NULL;
440         if (IS_ENABLED(CONFIG_PGSTE) && type == GMAP_FAULT) {
441                 gmap = (struct gmap *) S390_lowcore.gmap;
442                 current->thread.gmap_addr = address;
443                 current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
444                 current->thread.gmap_int_code = regs->int_code & 0xffff;
445                 address = __gmap_translate(gmap, address);
446                 if (address == -EFAULT) {
447                         fault = VM_FAULT_BADMAP;
448                         goto out_up;
449                 }
450                 if (gmap->pfault_enabled)
451                         flags |= FAULT_FLAG_RETRY_NOWAIT;
452         }
453 
454 retry:
455         fault = VM_FAULT_BADMAP;
456         vma = find_vma(mm, address);
457         if (!vma)
458                 goto out_up;
459 
460         if (unlikely(vma->vm_start > address)) {
461                 if (!(vma->vm_flags & VM_GROWSDOWN))
462                         goto out_up;
463                 if (expand_stack(vma, address))
464                         goto out_up;
465         }
466 
467         /*
468          * Ok, we have a good vm_area for this memory access, so
469          * we can handle it..
470          */
471         fault = VM_FAULT_BADACCESS;
472         if (unlikely(!(vma->vm_flags & access)))
473                 goto out_up;
474 
475         if (is_vm_hugetlb_page(vma))
476                 address &= HPAGE_MASK;
477         /*
478          * If for any reason at all we couldn't handle the fault,
479          * make sure we exit gracefully rather than endlessly redo
480          * the fault.
481          */
482         fault = handle_mm_fault(vma, address, flags);
483         /* No reason to continue if interrupted by SIGKILL. */
484         if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
485                 fault = VM_FAULT_SIGNAL;
486                 if (flags & FAULT_FLAG_RETRY_NOWAIT)
487                         goto out_up;
488                 goto out;
489         }
490         if (unlikely(fault & VM_FAULT_ERROR))
491                 goto out_up;
492 
493         /*
494          * Major/minor page fault accounting is only done on the
495          * initial attempt. If we go through a retry, it is extremely
496          * likely that the page will be found in page cache at that point.
497          */
498         if (flags & FAULT_FLAG_ALLOW_RETRY) {
499                 if (fault & VM_FAULT_MAJOR) {
500                         tsk->maj_flt++;
501                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
502                                       regs, address);
503                 } else {
504                         tsk->min_flt++;
505                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
506                                       regs, address);
507                 }
508                 if (fault & VM_FAULT_RETRY) {
509                         if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
510                             (flags & FAULT_FLAG_RETRY_NOWAIT)) {
511                                 /* FAULT_FLAG_RETRY_NOWAIT has been set,
512                                  * mmap_sem has not been released */
513                                 current->thread.gmap_pfault = 1;
514                                 fault = VM_FAULT_PFAULT;
515                                 goto out_up;
516                         }
517                         /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
518                          * of starvation. */
519                         flags &= ~(FAULT_FLAG_ALLOW_RETRY |
520                                    FAULT_FLAG_RETRY_NOWAIT);
521                         flags |= FAULT_FLAG_TRIED;
522                         down_read(&mm->mmap_sem);
523                         goto retry;
524                 }
525         }
526         if (IS_ENABLED(CONFIG_PGSTE) && gmap) {
527                 address =  __gmap_link(gmap, current->thread.gmap_addr,
528                                        address);
529                 if (address == -EFAULT) {
530                         fault = VM_FAULT_BADMAP;
531                         goto out_up;
532                 }
533                 if (address == -ENOMEM) {
534                         fault = VM_FAULT_OOM;
535                         goto out_up;
536                 }
537         }
538         fault = 0;
539 out_up:
540         up_read(&mm->mmap_sem);
541 out:
542         return fault;
543 }
544 
545 void do_protection_exception(struct pt_regs *regs)
546 {
547         unsigned long trans_exc_code;
548         int access;
549         vm_fault_t fault;
550 
551         trans_exc_code = regs->int_parm_long;
552         /*
553          * Protection exceptions are suppressing, decrement psw address.
554          * The exception to this rule are aborted transactions, for these
555          * the PSW already points to the correct location.
556          */
557         if (!(regs->int_code & 0x200))
558                 regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
559         /*
560          * Check for low-address protection.  This needs to be treated
561          * as a special case because the translation exception code
562          * field is not guaranteed to contain valid data in this case.
563          */
564         if (unlikely(!(trans_exc_code & 4))) {
565                 do_low_address(regs);
566                 return;
567         }
568         if (unlikely(MACHINE_HAS_NX && (trans_exc_code & 0x80))) {
569                 regs->int_parm_long = (trans_exc_code & ~PAGE_MASK) |
570                                         (regs->psw.addr & PAGE_MASK);
571                 access = VM_EXEC;
572                 fault = VM_FAULT_BADACCESS;
573         } else {
574                 access = VM_WRITE;
575                 fault = do_exception(regs, access);
576         }
577         if (unlikely(fault))
578                 do_fault_error(regs, access, fault);
579 }
580 NOKPROBE_SYMBOL(do_protection_exception);
581 
582 void do_dat_exception(struct pt_regs *regs)
583 {
584         int access;
585         vm_fault_t fault;
586 
587         access = VM_READ | VM_EXEC | VM_WRITE;
588         fault = do_exception(regs, access);
589         if (unlikely(fault))
590                 do_fault_error(regs, access, fault);
591 }
592 NOKPROBE_SYMBOL(do_dat_exception);
593 
594 #ifdef CONFIG_PFAULT 
595 /*
596  * 'pfault' pseudo page faults routines.
597  */
598 static int pfault_disable;
599 
600 static int __init nopfault(char *str)
601 {
602         pfault_disable = 1;
603         return 1;
604 }
605 
606 __setup("nopfault", nopfault);
607 
608 struct pfault_refbk {
609         u16 refdiagc;
610         u16 reffcode;
611         u16 refdwlen;
612         u16 refversn;
613         u64 refgaddr;
614         u64 refselmk;
615         u64 refcmpmk;
616         u64 reserved;
617 } __attribute__ ((packed, aligned(8)));
618 
619 static struct pfault_refbk pfault_init_refbk = {
620         .refdiagc = 0x258,
621         .reffcode = 0,
622         .refdwlen = 5,
623         .refversn = 2,
624         .refgaddr = __LC_LPP,
625         .refselmk = 1ULL << 48,
626         .refcmpmk = 1ULL << 48,
627         .reserved = __PF_RES_FIELD
628 };
629 
630 int pfault_init(void)
631 {
632         int rc;
633 
634         if (pfault_disable)
635                 return -1;
636         diag_stat_inc(DIAG_STAT_X258);
637         asm volatile(
638                 "       diag    %1,%0,0x258\n"
639                 "0:     j       2f\n"
640                 "1:     la      %0,8\n"
641                 "2:\n"
642                 EX_TABLE(0b,1b)
643                 : "=d" (rc)
644                 : "a" (&pfault_init_refbk), "m" (pfault_init_refbk) : "cc");
645         return rc;
646 }
647 
648 static struct pfault_refbk pfault_fini_refbk = {
649         .refdiagc = 0x258,
650         .reffcode = 1,
651         .refdwlen = 5,
652         .refversn = 2,
653 };
654 
655 void pfault_fini(void)
656 {
657 
658         if (pfault_disable)
659                 return;
660         diag_stat_inc(DIAG_STAT_X258);
661         asm volatile(
662                 "       diag    %0,0,0x258\n"
663                 "0:     nopr    %%r7\n"
664                 EX_TABLE(0b,0b)
665                 : : "a" (&pfault_fini_refbk), "m" (pfault_fini_refbk) : "cc");
666 }
667 
668 static DEFINE_SPINLOCK(pfault_lock);
669 static LIST_HEAD(pfault_list);
670 
671 #define PF_COMPLETE     0x0080
672 
673 /*
674  * The mechanism of our pfault code: if Linux is running as guest, runs a user
675  * space process and the user space process accesses a page that the host has
676  * paged out we get a pfault interrupt.
677  *
678  * This allows us, within the guest, to schedule a different process. Without
679  * this mechanism the host would have to suspend the whole virtual cpu until
680  * the page has been paged in.
681  *
682  * So when we get such an interrupt then we set the state of the current task
683  * to uninterruptible and also set the need_resched flag. Both happens within
684  * interrupt context(!). If we later on want to return to user space we
685  * recognize the need_resched flag and then call schedule().  It's not very
686  * obvious how this works...
687  *
688  * Of course we have a lot of additional fun with the completion interrupt (->
689  * host signals that a page of a process has been paged in and the process can
690  * continue to run). This interrupt can arrive on any cpu and, since we have
691  * virtual cpus, actually appear before the interrupt that signals that a page
692  * is missing.
693  */
694 static void pfault_interrupt(struct ext_code ext_code,
695                              unsigned int param32, unsigned long param64)
696 {
697         struct task_struct *tsk;
698         __u16 subcode;
699         pid_t pid;
700 
701         /*
702          * Get the external interruption subcode & pfault initial/completion
703          * signal bit. VM stores this in the 'cpu address' field associated
704          * with the external interrupt.
705          */
706         subcode = ext_code.subcode;
707         if ((subcode & 0xff00) != __SUBCODE_MASK)
708                 return;
709         inc_irq_stat(IRQEXT_PFL);
710         /* Get the token (= pid of the affected task). */
711         pid = param64 & LPP_PID_MASK;
712         rcu_read_lock();
713         tsk = find_task_by_pid_ns(pid, &init_pid_ns);
714         if (tsk)
715                 get_task_struct(tsk);
716         rcu_read_unlock();
717         if (!tsk)
718                 return;
719         spin_lock(&pfault_lock);
720         if (subcode & PF_COMPLETE) {
721                 /* signal bit is set -> a page has been swapped in by VM */
722                 if (tsk->thread.pfault_wait == 1) {
723                         /* Initial interrupt was faster than the completion
724                          * interrupt. pfault_wait is valid. Set pfault_wait
725                          * back to zero and wake up the process. This can
726                          * safely be done because the task is still sleeping
727                          * and can't produce new pfaults. */
728                         tsk->thread.pfault_wait = 0;
729                         list_del(&tsk->thread.list);
730                         wake_up_process(tsk);
731                         put_task_struct(tsk);
732                 } else {
733                         /* Completion interrupt was faster than initial
734                          * interrupt. Set pfault_wait to -1 so the initial
735                          * interrupt doesn't put the task to sleep.
736                          * If the task is not running, ignore the completion
737                          * interrupt since it must be a leftover of a PFAULT
738                          * CANCEL operation which didn't remove all pending
739                          * completion interrupts. */
740                         if (tsk->state == TASK_RUNNING)
741                                 tsk->thread.pfault_wait = -1;
742                 }
743         } else {
744                 /* signal bit not set -> a real page is missing. */
745                 if (WARN_ON_ONCE(tsk != current))
746                         goto out;
747                 if (tsk->thread.pfault_wait == 1) {
748                         /* Already on the list with a reference: put to sleep */
749                         goto block;
750                 } else if (tsk->thread.pfault_wait == -1) {
751                         /* Completion interrupt was faster than the initial
752                          * interrupt (pfault_wait == -1). Set pfault_wait
753                          * back to zero and exit. */
754                         tsk->thread.pfault_wait = 0;
755                 } else {
756                         /* Initial interrupt arrived before completion
757                          * interrupt. Let the task sleep.
758                          * An extra task reference is needed since a different
759                          * cpu may set the task state to TASK_RUNNING again
760                          * before the scheduler is reached. */
761                         get_task_struct(tsk);
762                         tsk->thread.pfault_wait = 1;
763                         list_add(&tsk->thread.list, &pfault_list);
764 block:
765                         /* Since this must be a userspace fault, there
766                          * is no kernel task state to trample. Rely on the
767                          * return to userspace schedule() to block. */
768                         __set_current_state(TASK_UNINTERRUPTIBLE);
769                         set_tsk_need_resched(tsk);
770                         set_preempt_need_resched();
771                 }
772         }
773 out:
774         spin_unlock(&pfault_lock);
775         put_task_struct(tsk);
776 }
777 
778 static int pfault_cpu_dead(unsigned int cpu)
779 {
780         struct thread_struct *thread, *next;
781         struct task_struct *tsk;
782 
783         spin_lock_irq(&pfault_lock);
784         list_for_each_entry_safe(thread, next, &pfault_list, list) {
785                 thread->pfault_wait = 0;
786                 list_del(&thread->list);
787                 tsk = container_of(thread, struct task_struct, thread);
788                 wake_up_process(tsk);
789                 put_task_struct(tsk);
790         }
791         spin_unlock_irq(&pfault_lock);
792         return 0;
793 }
794 
795 static int __init pfault_irq_init(void)
796 {
797         int rc;
798 
799         rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
800         if (rc)
801                 goto out_extint;
802         rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
803         if (rc)
804                 goto out_pfault;
805         irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
806         cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead",
807                                   NULL, pfault_cpu_dead);
808         return 0;
809 
810 out_pfault:
811         unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
812 out_extint:
813         pfault_disable = 1;
814         return rc;
815 }
816 early_initcall(pfault_irq_init);
817 
818 #endif /* CONFIG_PFAULT */
819 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp