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
fault_init(void)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
notify_page_fault(struct pt_regs * regs)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 */
bust_spinlocks(int yes)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 */
get_fault_type(struct pt_regs * regs)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
bad_address(void * p)139 static int bad_address(void *p)
140 {
141 unsigned long dummy;
142
143 return probe_kernel_address((unsigned long *)p, dummy);
144 }
145
dump_pagetable(unsigned long asce,unsigned long address)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
dump_fault_info(struct pt_regs * regs)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
report_user_fault(struct pt_regs * regs,long signr,int is_mm_fault)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 */
do_sigsegv(struct pt_regs * regs,int si_code)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
do_no_context(struct pt_regs * regs)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
do_low_address(struct pt_regs * regs)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
do_sigbus(struct pt_regs * regs)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
signal_return(struct pt_regs * regs)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
do_fault_error(struct pt_regs * regs,int access,vm_fault_t fault)344 static noinline void do_fault_error(struct pt_regs *regs, int access,
345 vm_fault_t fault)
346 {
347 int si_code;
348
349 switch (fault) {
350 case VM_FAULT_BADACCESS:
351 if (access == VM_EXEC && signal_return(regs) == 0)
352 break;
353 case VM_FAULT_BADMAP:
354 /* Bad memory access. Check if it is kernel or user space. */
355 if (user_mode(regs)) {
356 /* User mode accesses just cause a SIGSEGV */
357 si_code = (fault == VM_FAULT_BADMAP) ?
358 SEGV_MAPERR : SEGV_ACCERR;
359 do_sigsegv(regs, si_code);
360 break;
361 }
362 case VM_FAULT_BADCONTEXT:
363 case VM_FAULT_PFAULT:
364 do_no_context(regs);
365 break;
366 case VM_FAULT_SIGNAL:
367 if (!user_mode(regs))
368 do_no_context(regs);
369 break;
370 default: /* fault & VM_FAULT_ERROR */
371 if (fault & VM_FAULT_OOM) {
372 if (!user_mode(regs))
373 do_no_context(regs);
374 else
375 pagefault_out_of_memory();
376 } else if (fault & VM_FAULT_SIGSEGV) {
377 /* Kernel mode? Handle exceptions or die */
378 if (!user_mode(regs))
379 do_no_context(regs);
380 else
381 do_sigsegv(regs, SEGV_MAPERR);
382 } else if (fault & VM_FAULT_SIGBUS) {
383 /* Kernel mode? Handle exceptions or die */
384 if (!user_mode(regs))
385 do_no_context(regs);
386 else
387 do_sigbus(regs);
388 } else
389 BUG();
390 break;
391 }
392 }
393
394 /*
395 * This routine handles page faults. It determines the address,
396 * and the problem, and then passes it off to one of the appropriate
397 * routines.
398 *
399 * interruption code (int_code):
400 * 04 Protection -> Write-Protection (suprression)
401 * 10 Segment translation -> Not present (nullification)
402 * 11 Page translation -> Not present (nullification)
403 * 3b Region third trans. -> Not present (nullification)
404 */
do_exception(struct pt_regs * regs,int access)405 static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
406 {
407 struct gmap *gmap;
408 struct task_struct *tsk;
409 struct mm_struct *mm;
410 struct vm_area_struct *vma;
411 enum fault_type type;
412 unsigned long trans_exc_code;
413 unsigned long address;
414 unsigned int flags;
415 vm_fault_t fault;
416
417 tsk = current;
418 /*
419 * The instruction that caused the program check has
420 * been nullified. Don't signal single step via SIGTRAP.
421 */
422 clear_pt_regs_flag(regs, PIF_PER_TRAP);
423
424 if (notify_page_fault(regs))
425 return 0;
426
427 mm = tsk->mm;
428 trans_exc_code = regs->int_parm_long;
429
430 /*
431 * Verify that the fault happened in user space, that
432 * we are not in an interrupt and that there is a
433 * user context.
434 */
435 fault = VM_FAULT_BADCONTEXT;
436 type = get_fault_type(regs);
437 switch (type) {
438 case KERNEL_FAULT:
439 goto out;
440 case VDSO_FAULT:
441 fault = VM_FAULT_BADMAP;
442 goto out;
443 case USER_FAULT:
444 case GMAP_FAULT:
445 if (faulthandler_disabled() || !mm)
446 goto out;
447 break;
448 }
449
450 address = trans_exc_code & __FAIL_ADDR_MASK;
451 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
452 flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
453 if (user_mode(regs))
454 flags |= FAULT_FLAG_USER;
455 if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
456 flags |= FAULT_FLAG_WRITE;
457 down_read(&mm->mmap_sem);
458
459 gmap = NULL;
460 if (IS_ENABLED(CONFIG_PGSTE) && type == GMAP_FAULT) {
461 gmap = (struct gmap *) S390_lowcore.gmap;
462 current->thread.gmap_addr = address;
463 current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
464 current->thread.gmap_int_code = regs->int_code & 0xffff;
465 address = __gmap_translate(gmap, address);
466 if (address == -EFAULT) {
467 fault = VM_FAULT_BADMAP;
468 goto out_up;
469 }
470 if (gmap->pfault_enabled)
471 flags |= FAULT_FLAG_RETRY_NOWAIT;
472 }
473
474 retry:
475 fault = VM_FAULT_BADMAP;
476 vma = find_vma(mm, address);
477 if (!vma)
478 goto out_up;
479
480 if (unlikely(vma->vm_start > address)) {
481 if (!(vma->vm_flags & VM_GROWSDOWN))
482 goto out_up;
483 if (expand_stack(vma, address))
484 goto out_up;
485 }
486
487 /*
488 * Ok, we have a good vm_area for this memory access, so
489 * we can handle it..
490 */
491 fault = VM_FAULT_BADACCESS;
492 if (unlikely(!(vma->vm_flags & access)))
493 goto out_up;
494
495 if (is_vm_hugetlb_page(vma))
496 address &= HPAGE_MASK;
497 /*
498 * If for any reason at all we couldn't handle the fault,
499 * make sure we exit gracefully rather than endlessly redo
500 * the fault.
501 */
502 fault = handle_mm_fault(vma, address, flags);
503 /* No reason to continue if interrupted by SIGKILL. */
504 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
505 fault = VM_FAULT_SIGNAL;
506 if (flags & FAULT_FLAG_RETRY_NOWAIT)
507 goto out_up;
508 goto out;
509 }
510 if (unlikely(fault & VM_FAULT_ERROR))
511 goto out_up;
512
513 /*
514 * Major/minor page fault accounting is only done on the
515 * initial attempt. If we go through a retry, it is extremely
516 * likely that the page will be found in page cache at that point.
517 */
518 if (flags & FAULT_FLAG_ALLOW_RETRY) {
519 if (fault & VM_FAULT_MAJOR) {
520 tsk->maj_flt++;
521 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
522 regs, address);
523 } else {
524 tsk->min_flt++;
525 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
526 regs, address);
527 }
528 if (fault & VM_FAULT_RETRY) {
529 if (IS_ENABLED(CONFIG_PGSTE) && gmap &&
530 (flags & FAULT_FLAG_RETRY_NOWAIT)) {
531 /* FAULT_FLAG_RETRY_NOWAIT has been set,
532 * mmap_sem has not been released */
533 current->thread.gmap_pfault = 1;
534 fault = VM_FAULT_PFAULT;
535 goto out_up;
536 }
537 /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
538 * of starvation. */
539 flags &= ~(FAULT_FLAG_ALLOW_RETRY |
540 FAULT_FLAG_RETRY_NOWAIT);
541 flags |= FAULT_FLAG_TRIED;
542 down_read(&mm->mmap_sem);
543 goto retry;
544 }
545 }
546 if (IS_ENABLED(CONFIG_PGSTE) && gmap) {
547 address = __gmap_link(gmap, current->thread.gmap_addr,
548 address);
549 if (address == -EFAULT) {
550 fault = VM_FAULT_BADMAP;
551 goto out_up;
552 }
553 if (address == -ENOMEM) {
554 fault = VM_FAULT_OOM;
555 goto out_up;
556 }
557 }
558 fault = 0;
559 out_up:
560 up_read(&mm->mmap_sem);
561 out:
562 return fault;
563 }
564
do_protection_exception(struct pt_regs * regs)565 void do_protection_exception(struct pt_regs *regs)
566 {
567 unsigned long trans_exc_code;
568 int access;
569 vm_fault_t fault;
570
571 trans_exc_code = regs->int_parm_long;
572 /*
573 * Protection exceptions are suppressing, decrement psw address.
574 * The exception to this rule are aborted transactions, for these
575 * the PSW already points to the correct location.
576 */
577 if (!(regs->int_code & 0x200))
578 regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
579 /*
580 * Check for low-address protection. This needs to be treated
581 * as a special case because the translation exception code
582 * field is not guaranteed to contain valid data in this case.
583 */
584 if (unlikely(!(trans_exc_code & 4))) {
585 do_low_address(regs);
586 return;
587 }
588 if (unlikely(MACHINE_HAS_NX && (trans_exc_code & 0x80))) {
589 regs->int_parm_long = (trans_exc_code & ~PAGE_MASK) |
590 (regs->psw.addr & PAGE_MASK);
591 access = VM_EXEC;
592 fault = VM_FAULT_BADACCESS;
593 } else {
594 access = VM_WRITE;
595 fault = do_exception(regs, access);
596 }
597 if (unlikely(fault))
598 do_fault_error(regs, access, fault);
599 }
600 NOKPROBE_SYMBOL(do_protection_exception);
601
do_dat_exception(struct pt_regs * regs)602 void do_dat_exception(struct pt_regs *regs)
603 {
604 int access;
605 vm_fault_t fault;
606
607 access = VM_READ | VM_EXEC | VM_WRITE;
608 fault = do_exception(regs, access);
609 if (unlikely(fault))
610 do_fault_error(regs, access, fault);
611 }
612 NOKPROBE_SYMBOL(do_dat_exception);
613
614 #ifdef CONFIG_PFAULT
615 /*
616 * 'pfault' pseudo page faults routines.
617 */
618 static int pfault_disable;
619
nopfault(char * str)620 static int __init nopfault(char *str)
621 {
622 pfault_disable = 1;
623 return 1;
624 }
625
626 __setup("nopfault", nopfault);
627
628 struct pfault_refbk {
629 u16 refdiagc;
630 u16 reffcode;
631 u16 refdwlen;
632 u16 refversn;
633 u64 refgaddr;
634 u64 refselmk;
635 u64 refcmpmk;
636 u64 reserved;
637 } __attribute__ ((packed, aligned(8)));
638
pfault_init(void)639 int pfault_init(void)
640 {
641 struct pfault_refbk refbk = {
642 .refdiagc = 0x258,
643 .reffcode = 0,
644 .refdwlen = 5,
645 .refversn = 2,
646 .refgaddr = __LC_LPP,
647 .refselmk = 1ULL << 48,
648 .refcmpmk = 1ULL << 48,
649 .reserved = __PF_RES_FIELD };
650 int rc;
651
652 if (pfault_disable)
653 return -1;
654 diag_stat_inc(DIAG_STAT_X258);
655 asm volatile(
656 " diag %1,%0,0x258\n"
657 "0: j 2f\n"
658 "1: la %0,8\n"
659 "2:\n"
660 EX_TABLE(0b,1b)
661 : "=d" (rc) : "a" (&refbk), "m" (refbk) : "cc");
662 return rc;
663 }
664
pfault_fini(void)665 void pfault_fini(void)
666 {
667 struct pfault_refbk refbk = {
668 .refdiagc = 0x258,
669 .reffcode = 1,
670 .refdwlen = 5,
671 .refversn = 2,
672 };
673
674 if (pfault_disable)
675 return;
676 diag_stat_inc(DIAG_STAT_X258);
677 asm volatile(
678 " diag %0,0,0x258\n"
679 "0: nopr %%r7\n"
680 EX_TABLE(0b,0b)
681 : : "a" (&refbk), "m" (refbk) : "cc");
682 }
683
684 static DEFINE_SPINLOCK(pfault_lock);
685 static LIST_HEAD(pfault_list);
686
687 #define PF_COMPLETE 0x0080
688
689 /*
690 * The mechanism of our pfault code: if Linux is running as guest, runs a user
691 * space process and the user space process accesses a page that the host has
692 * paged out we get a pfault interrupt.
693 *
694 * This allows us, within the guest, to schedule a different process. Without
695 * this mechanism the host would have to suspend the whole virtual cpu until
696 * the page has been paged in.
697 *
698 * So when we get such an interrupt then we set the state of the current task
699 * to uninterruptible and also set the need_resched flag. Both happens within
700 * interrupt context(!). If we later on want to return to user space we
701 * recognize the need_resched flag and then call schedule(). It's not very
702 * obvious how this works...
703 *
704 * Of course we have a lot of additional fun with the completion interrupt (->
705 * host signals that a page of a process has been paged in and the process can
706 * continue to run). This interrupt can arrive on any cpu and, since we have
707 * virtual cpus, actually appear before the interrupt that signals that a page
708 * is missing.
709 */
pfault_interrupt(struct ext_code ext_code,unsigned int param32,unsigned long param64)710 static void pfault_interrupt(struct ext_code ext_code,
711 unsigned int param32, unsigned long param64)
712 {
713 struct task_struct *tsk;
714 __u16 subcode;
715 pid_t pid;
716
717 /*
718 * Get the external interruption subcode & pfault initial/completion
719 * signal bit. VM stores this in the 'cpu address' field associated
720 * with the external interrupt.
721 */
722 subcode = ext_code.subcode;
723 if ((subcode & 0xff00) != __SUBCODE_MASK)
724 return;
725 inc_irq_stat(IRQEXT_PFL);
726 /* Get the token (= pid of the affected task). */
727 pid = param64 & LPP_PID_MASK;
728 rcu_read_lock();
729 tsk = find_task_by_pid_ns(pid, &init_pid_ns);
730 if (tsk)
731 get_task_struct(tsk);
732 rcu_read_unlock();
733 if (!tsk)
734 return;
735 spin_lock(&pfault_lock);
736 if (subcode & PF_COMPLETE) {
737 /* signal bit is set -> a page has been swapped in by VM */
738 if (tsk->thread.pfault_wait == 1) {
739 /* Initial interrupt was faster than the completion
740 * interrupt. pfault_wait is valid. Set pfault_wait
741 * back to zero and wake up the process. This can
742 * safely be done because the task is still sleeping
743 * and can't produce new pfaults. */
744 tsk->thread.pfault_wait = 0;
745 list_del(&tsk->thread.list);
746 wake_up_process(tsk);
747 put_task_struct(tsk);
748 } else {
749 /* Completion interrupt was faster than initial
750 * interrupt. Set pfault_wait to -1 so the initial
751 * interrupt doesn't put the task to sleep.
752 * If the task is not running, ignore the completion
753 * interrupt since it must be a leftover of a PFAULT
754 * CANCEL operation which didn't remove all pending
755 * completion interrupts. */
756 if (tsk->state == TASK_RUNNING)
757 tsk->thread.pfault_wait = -1;
758 }
759 } else {
760 /* signal bit not set -> a real page is missing. */
761 if (WARN_ON_ONCE(tsk != current))
762 goto out;
763 if (tsk->thread.pfault_wait == 1) {
764 /* Already on the list with a reference: put to sleep */
765 goto block;
766 } else if (tsk->thread.pfault_wait == -1) {
767 /* Completion interrupt was faster than the initial
768 * interrupt (pfault_wait == -1). Set pfault_wait
769 * back to zero and exit. */
770 tsk->thread.pfault_wait = 0;
771 } else {
772 /* Initial interrupt arrived before completion
773 * interrupt. Let the task sleep.
774 * An extra task reference is needed since a different
775 * cpu may set the task state to TASK_RUNNING again
776 * before the scheduler is reached. */
777 get_task_struct(tsk);
778 tsk->thread.pfault_wait = 1;
779 list_add(&tsk->thread.list, &pfault_list);
780 block:
781 /* Since this must be a userspace fault, there
782 * is no kernel task state to trample. Rely on the
783 * return to userspace schedule() to block. */
784 __set_current_state(TASK_UNINTERRUPTIBLE);
785 set_tsk_need_resched(tsk);
786 set_preempt_need_resched();
787 }
788 }
789 out:
790 spin_unlock(&pfault_lock);
791 put_task_struct(tsk);
792 }
793
pfault_cpu_dead(unsigned int cpu)794 static int pfault_cpu_dead(unsigned int cpu)
795 {
796 struct thread_struct *thread, *next;
797 struct task_struct *tsk;
798
799 spin_lock_irq(&pfault_lock);
800 list_for_each_entry_safe(thread, next, &pfault_list, list) {
801 thread->pfault_wait = 0;
802 list_del(&thread->list);
803 tsk = container_of(thread, struct task_struct, thread);
804 wake_up_process(tsk);
805 put_task_struct(tsk);
806 }
807 spin_unlock_irq(&pfault_lock);
808 return 0;
809 }
810
pfault_irq_init(void)811 static int __init pfault_irq_init(void)
812 {
813 int rc;
814
815 rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
816 if (rc)
817 goto out_extint;
818 rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
819 if (rc)
820 goto out_pfault;
821 irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
822 cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead",
823 NULL, pfault_cpu_dead);
824 return 0;
825
826 out_pfault:
827 unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
828 out_extint:
829 pfault_disable = 1;
830 return rc;
831 }
832 early_initcall(pfault_irq_init);
833
834 #endif /* CONFIG_PFAULT */
835
