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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
53enum fault_type {
54 KERNEL_FAULT,
55 USER_FAULT,
56 VDSO_FAULT,
57 GMAP_FAULT,
58};
59
60static unsigned long store_indication __read_mostly;
61
62static int __init fault_init(void)
63{
64 if (test_facility(75))
65 store_indication = 0xc00;
66 return 0;
67}
68early_initcall(fault_init);
69
70/*
71 * Find out which address space caused the exception.
72 */
73static 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
104static int bad_address(void *p)
105{
106 unsigned long dummy;
107
108 return probe_kernel_address((unsigned long *)p, dummy);
109}
110
111static 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);
157out:
158 pr_cont("\n");
159 return;
160bad:
161 pr_cont("BAD\n");
162}
163
164static 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
210int show_unhandled_signals = 1;
211
212void 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 */
233static 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
240const 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
252static 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
278static 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
291static 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
301static 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
321static 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 */
385static 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
454retry:
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;
539out_up:
540 up_read(&mm->mmap_sem);
541out:
542 return fault;
543}
544
545void 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}
580NOKPROBE_SYMBOL(do_protection_exception);
581
582void 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}
592NOKPROBE_SYMBOL(do_dat_exception);
593
594#ifdef CONFIG_PFAULT
595/*
596 * 'pfault' pseudo page faults routines.
597 */
598static int pfault_disable;
599
600static int __init nopfault(char *str)
601{
602 pfault_disable = 1;
603 return 1;
604}
605
606__setup("nopfault", nopfault);
607
608struct 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
619static 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
630int 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
648static struct pfault_refbk pfault_fini_refbk = {
649 .refdiagc = 0x258,
650 .reffcode = 1,
651 .refdwlen = 5,
652 .refversn = 2,
653};
654
655void 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
668static DEFINE_SPINLOCK(pfault_lock);
669static 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 */
694static 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);
764block:
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 }
773out:
774 spin_unlock(&pfault_lock);
775 put_task_struct(tsk);
776}
777
778static 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
795static 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
810out_pfault:
811 unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
812out_extint:
813 pfault_disable = 1;
814 return rc;
815}
816early_initcall(pfault_irq_init);
817
818#endif /* CONFIG_PFAULT */
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/extable.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/diag.h>
34#include <asm/pgtable.h>
35#include <asm/gmap.h>
36#include <asm/irq.h>
37#include <asm/mmu_context.h>
38#include <asm/facility.h>
39#include "../kernel/entry.h"
40
41#define __FAIL_ADDR_MASK -4096L
42#define __SUBCODE_MASK 0x0600
43#define __PF_RES_FIELD 0x8000000000000000ULL
44
45#define VM_FAULT_BADCONTEXT 0x010000
46#define VM_FAULT_BADMAP 0x020000
47#define VM_FAULT_BADACCESS 0x040000
48#define VM_FAULT_SIGNAL 0x080000
49#define VM_FAULT_PFAULT 0x100000
50
51static unsigned long store_indication __read_mostly;
52
53static int __init fault_init(void)
54{
55 if (test_facility(75))
56 store_indication = 0xc00;
57 return 0;
58}
59early_initcall(fault_init);
60
61static inline int notify_page_fault(struct pt_regs *regs)
62{
63 int ret = 0;
64
65 /* kprobe_running() needs smp_processor_id() */
66 if (kprobes_built_in() && !user_mode(regs)) {
67 preempt_disable();
68 if (kprobe_running() && kprobe_fault_handler(regs, 14))
69 ret = 1;
70 preempt_enable();
71 }
72 return ret;
73}
74
75
76/*
77 * Unlock any spinlocks which will prevent us from getting the
78 * message out.
79 */
80void bust_spinlocks(int yes)
81{
82 if (yes) {
83 oops_in_progress = 1;
84 } else {
85 int loglevel_save = console_loglevel;
86 console_unblank();
87 oops_in_progress = 0;
88 /*
89 * OK, the message is on the console. Now we call printk()
90 * without oops_in_progress set so that printk will give klogd
91 * a poke. Hold onto your hats...
92 */
93 console_loglevel = 15;
94 printk(" ");
95 console_loglevel = loglevel_save;
96 }
97}
98
99/*
100 * Returns the address space associated with the fault.
101 * Returns 0 for kernel space and 1 for user space.
102 */
103static inline int user_space_fault(struct pt_regs *regs)
104{
105 unsigned long trans_exc_code;
106
107 /*
108 * The lowest two bits of the translation exception
109 * identification indicate which paging table was used.
110 */
111 trans_exc_code = regs->int_parm_long & 3;
112 if (trans_exc_code == 3) /* home space -> kernel */
113 return 0;
114 if (user_mode(regs))
115 return 1;
116 if (trans_exc_code == 2) /* secondary space -> set_fs */
117 return current->thread.mm_segment.ar4;
118 if (current->flags & PF_VCPU)
119 return 1;
120 return 0;
121}
122
123static int bad_address(void *p)
124{
125 unsigned long dummy;
126
127 return probe_kernel_address((unsigned long *)p, dummy);
128}
129
130static void dump_pagetable(unsigned long asce, unsigned long address)
131{
132 unsigned long *table = __va(asce & PAGE_MASK);
133
134 pr_alert("AS:%016lx ", asce);
135 switch (asce & _ASCE_TYPE_MASK) {
136 case _ASCE_TYPE_REGION1:
137 table = table + ((address >> 53) & 0x7ff);
138 if (bad_address(table))
139 goto bad;
140 pr_cont("R1:%016lx ", *table);
141 if (*table & _REGION_ENTRY_INVALID)
142 goto out;
143 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
144 /* fallthrough */
145 case _ASCE_TYPE_REGION2:
146 table = table + ((address >> 42) & 0x7ff);
147 if (bad_address(table))
148 goto bad;
149 pr_cont("R2:%016lx ", *table);
150 if (*table & _REGION_ENTRY_INVALID)
151 goto out;
152 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
153 /* fallthrough */
154 case _ASCE_TYPE_REGION3:
155 table = table + ((address >> 31) & 0x7ff);
156 if (bad_address(table))
157 goto bad;
158 pr_cont("R3:%016lx ", *table);
159 if (*table & (_REGION_ENTRY_INVALID | _REGION3_ENTRY_LARGE))
160 goto out;
161 table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
162 /* fallthrough */
163 case _ASCE_TYPE_SEGMENT:
164 table = table + ((address >> 20) & 0x7ff);
165 if (bad_address(table))
166 goto bad;
167 pr_cont("S:%016lx ", *table);
168 if (*table & (_SEGMENT_ENTRY_INVALID | _SEGMENT_ENTRY_LARGE))
169 goto out;
170 table = (unsigned long *)(*table & _SEGMENT_ENTRY_ORIGIN);
171 }
172 table = table + ((address >> 12) & 0xff);
173 if (bad_address(table))
174 goto bad;
175 pr_cont("P:%016lx ", *table);
176out:
177 pr_cont("\n");
178 return;
179bad:
180 pr_cont("BAD\n");
181}
182
183static void dump_fault_info(struct pt_regs *regs)
184{
185 unsigned long asce;
186
187 pr_alert("Failing address: %016lx TEID: %016lx\n",
188 regs->int_parm_long & __FAIL_ADDR_MASK, regs->int_parm_long);
189 pr_alert("Fault in ");
190 switch (regs->int_parm_long & 3) {
191 case 3:
192 pr_cont("home space ");
193 break;
194 case 2:
195 pr_cont("secondary space ");
196 break;
197 case 1:
198 pr_cont("access register ");
199 break;
200 case 0:
201 pr_cont("primary space ");
202 break;
203 }
204 pr_cont("mode while using ");
205 if (!user_space_fault(regs)) {
206 asce = S390_lowcore.kernel_asce;
207 pr_cont("kernel ");
208 }
209#ifdef CONFIG_PGSTE
210 else if ((current->flags & PF_VCPU) && S390_lowcore.gmap) {
211 struct gmap *gmap = (struct gmap *)S390_lowcore.gmap;
212 asce = gmap->asce;
213 pr_cont("gmap ");
214 }
215#endif
216 else {
217 asce = S390_lowcore.user_asce;
218 pr_cont("user ");
219 }
220 pr_cont("ASCE.\n");
221 dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);
222}
223
224int show_unhandled_signals = 1;
225
226void report_user_fault(struct pt_regs *regs, long signr, int is_mm_fault)
227{
228 if ((task_pid_nr(current) > 1) && !show_unhandled_signals)
229 return;
230 if (!unhandled_signal(current, signr))
231 return;
232 if (!printk_ratelimit())
233 return;
234 printk(KERN_ALERT "User process fault: interruption code %04x ilc:%d ",
235 regs->int_code & 0xffff, regs->int_code >> 17);
236 print_vma_addr(KERN_CONT "in ", regs->psw.addr);
237 printk(KERN_CONT "\n");
238 if (is_mm_fault)
239 dump_fault_info(regs);
240 show_regs(regs);
241}
242
243/*
244 * Send SIGSEGV to task. This is an external routine
245 * to keep the stack usage of do_page_fault small.
246 */
247static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
248{
249 struct siginfo si;
250
251 report_user_fault(regs, SIGSEGV, 1);
252 si.si_signo = SIGSEGV;
253 si.si_errno = 0;
254 si.si_code = si_code;
255 si.si_addr = (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK);
256 force_sig_info(SIGSEGV, &si, current);
257}
258
259static noinline void do_no_context(struct pt_regs *regs)
260{
261 const struct exception_table_entry *fixup;
262
263 /* Are we prepared to handle this kernel fault? */
264 fixup = search_exception_tables(regs->psw.addr);
265 if (fixup) {
266 regs->psw.addr = extable_fixup(fixup);
267 return;
268 }
269
270 /*
271 * Oops. The kernel tried to access some bad page. We'll have to
272 * terminate things with extreme prejudice.
273 */
274 if (!user_space_fault(regs))
275 printk(KERN_ALERT "Unable to handle kernel pointer dereference"
276 " in virtual kernel address space\n");
277 else
278 printk(KERN_ALERT "Unable to handle kernel paging request"
279 " in virtual user address space\n");
280 dump_fault_info(regs);
281 die(regs, "Oops");
282 do_exit(SIGKILL);
283}
284
285static noinline void do_low_address(struct pt_regs *regs)
286{
287 /* Low-address protection hit in kernel mode means
288 NULL pointer write access in kernel mode. */
289 if (regs->psw.mask & PSW_MASK_PSTATE) {
290 /* Low-address protection hit in user mode 'cannot happen'. */
291 die (regs, "Low-address protection");
292 do_exit(SIGKILL);
293 }
294
295 do_no_context(regs);
296}
297
298static noinline void do_sigbus(struct pt_regs *regs)
299{
300 struct task_struct *tsk = current;
301 struct siginfo si;
302
303 /*
304 * Send a sigbus, regardless of whether we were in kernel
305 * or user mode.
306 */
307 si.si_signo = SIGBUS;
308 si.si_errno = 0;
309 si.si_code = BUS_ADRERR;
310 si.si_addr = (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK);
311 force_sig_info(SIGBUS, &si, tsk);
312}
313
314static noinline void do_fault_error(struct pt_regs *regs, int fault)
315{
316 int si_code;
317
318 switch (fault) {
319 case VM_FAULT_BADACCESS:
320 case VM_FAULT_BADMAP:
321 /* Bad memory access. Check if it is kernel or user space. */
322 if (user_mode(regs)) {
323 /* User mode accesses just cause a SIGSEGV */
324 si_code = (fault == VM_FAULT_BADMAP) ?
325 SEGV_MAPERR : SEGV_ACCERR;
326 do_sigsegv(regs, si_code);
327 return;
328 }
329 case VM_FAULT_BADCONTEXT:
330 case VM_FAULT_PFAULT:
331 do_no_context(regs);
332 break;
333 case VM_FAULT_SIGNAL:
334 if (!user_mode(regs))
335 do_no_context(regs);
336 break;
337 default: /* fault & VM_FAULT_ERROR */
338 if (fault & VM_FAULT_OOM) {
339 if (!user_mode(regs))
340 do_no_context(regs);
341 else
342 pagefault_out_of_memory();
343 } else if (fault & VM_FAULT_SIGSEGV) {
344 /* Kernel mode? Handle exceptions or die */
345 if (!user_mode(regs))
346 do_no_context(regs);
347 else
348 do_sigsegv(regs, SEGV_MAPERR);
349 } else if (fault & VM_FAULT_SIGBUS) {
350 /* Kernel mode? Handle exceptions or die */
351 if (!user_mode(regs))
352 do_no_context(regs);
353 else
354 do_sigbus(regs);
355 } else
356 BUG();
357 break;
358 }
359}
360
361/*
362 * This routine handles page faults. It determines the address,
363 * and the problem, and then passes it off to one of the appropriate
364 * routines.
365 *
366 * interruption code (int_code):
367 * 04 Protection -> Write-Protection (suprression)
368 * 10 Segment translation -> Not present (nullification)
369 * 11 Page translation -> Not present (nullification)
370 * 3b Region third trans. -> Not present (nullification)
371 */
372static inline int do_exception(struct pt_regs *regs, int access)
373{
374#ifdef CONFIG_PGSTE
375 struct gmap *gmap;
376#endif
377 struct task_struct *tsk;
378 struct mm_struct *mm;
379 struct vm_area_struct *vma;
380 unsigned long trans_exc_code;
381 unsigned long address;
382 unsigned int flags;
383 int fault;
384
385 tsk = current;
386 /*
387 * The instruction that caused the program check has
388 * been nullified. Don't signal single step via SIGTRAP.
389 */
390 clear_pt_regs_flag(regs, PIF_PER_TRAP);
391
392 if (notify_page_fault(regs))
393 return 0;
394
395 mm = tsk->mm;
396 trans_exc_code = regs->int_parm_long;
397
398 /*
399 * Verify that the fault happened in user space, that
400 * we are not in an interrupt and that there is a
401 * user context.
402 */
403 fault = VM_FAULT_BADCONTEXT;
404 if (unlikely(!user_space_fault(regs) || faulthandler_disabled() || !mm))
405 goto out;
406
407 address = trans_exc_code & __FAIL_ADDR_MASK;
408 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
409 flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
410 if (user_mode(regs))
411 flags |= FAULT_FLAG_USER;
412 if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
413 flags |= FAULT_FLAG_WRITE;
414 down_read(&mm->mmap_sem);
415
416#ifdef CONFIG_PGSTE
417 gmap = (current->flags & PF_VCPU) ?
418 (struct gmap *) S390_lowcore.gmap : NULL;
419 if (gmap) {
420 current->thread.gmap_addr = address;
421 current->thread.gmap_write_flag = !!(flags & FAULT_FLAG_WRITE);
422 current->thread.gmap_int_code = regs->int_code & 0xffff;
423 address = __gmap_translate(gmap, address);
424 if (address == -EFAULT) {
425 fault = VM_FAULT_BADMAP;
426 goto out_up;
427 }
428 if (gmap->pfault_enabled)
429 flags |= FAULT_FLAG_RETRY_NOWAIT;
430 }
431#endif
432
433retry:
434 fault = VM_FAULT_BADMAP;
435 vma = find_vma(mm, address);
436 if (!vma)
437 goto out_up;
438
439 if (unlikely(vma->vm_start > address)) {
440 if (!(vma->vm_flags & VM_GROWSDOWN))
441 goto out_up;
442 if (expand_stack(vma, address))
443 goto out_up;
444 }
445
446 /*
447 * Ok, we have a good vm_area for this memory access, so
448 * we can handle it..
449 */
450 fault = VM_FAULT_BADACCESS;
451 if (unlikely(!(vma->vm_flags & access)))
452 goto out_up;
453
454 if (is_vm_hugetlb_page(vma))
455 address &= HPAGE_MASK;
456 /*
457 * If for any reason at all we couldn't handle the fault,
458 * make sure we exit gracefully rather than endlessly redo
459 * the fault.
460 */
461 fault = handle_mm_fault(vma, address, flags);
462 /* No reason to continue if interrupted by SIGKILL. */
463 if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
464 fault = VM_FAULT_SIGNAL;
465 goto out;
466 }
467 if (unlikely(fault & VM_FAULT_ERROR))
468 goto out_up;
469
470 /*
471 * Major/minor page fault accounting is only done on the
472 * initial attempt. If we go through a retry, it is extremely
473 * likely that the page will be found in page cache at that point.
474 */
475 if (flags & FAULT_FLAG_ALLOW_RETRY) {
476 if (fault & VM_FAULT_MAJOR) {
477 tsk->maj_flt++;
478 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
479 regs, address);
480 } else {
481 tsk->min_flt++;
482 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
483 regs, address);
484 }
485 if (fault & VM_FAULT_RETRY) {
486#ifdef CONFIG_PGSTE
487 if (gmap && (flags & FAULT_FLAG_RETRY_NOWAIT)) {
488 /* FAULT_FLAG_RETRY_NOWAIT has been set,
489 * mmap_sem has not been released */
490 current->thread.gmap_pfault = 1;
491 fault = VM_FAULT_PFAULT;
492 goto out_up;
493 }
494#endif
495 /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
496 * of starvation. */
497 flags &= ~(FAULT_FLAG_ALLOW_RETRY |
498 FAULT_FLAG_RETRY_NOWAIT);
499 flags |= FAULT_FLAG_TRIED;
500 down_read(&mm->mmap_sem);
501 goto retry;
502 }
503 }
504#ifdef CONFIG_PGSTE
505 if (gmap) {
506 address = __gmap_link(gmap, current->thread.gmap_addr,
507 address);
508 if (address == -EFAULT) {
509 fault = VM_FAULT_BADMAP;
510 goto out_up;
511 }
512 if (address == -ENOMEM) {
513 fault = VM_FAULT_OOM;
514 goto out_up;
515 }
516 }
517#endif
518 fault = 0;
519out_up:
520 up_read(&mm->mmap_sem);
521out:
522 return fault;
523}
524
525void do_protection_exception(struct pt_regs *regs)
526{
527 unsigned long trans_exc_code;
528 int fault;
529
530 trans_exc_code = regs->int_parm_long;
531 /*
532 * Protection exceptions are suppressing, decrement psw address.
533 * The exception to this rule are aborted transactions, for these
534 * the PSW already points to the correct location.
535 */
536 if (!(regs->int_code & 0x200))
537 regs->psw.addr = __rewind_psw(regs->psw, regs->int_code >> 16);
538 /*
539 * Check for low-address protection. This needs to be treated
540 * as a special case because the translation exception code
541 * field is not guaranteed to contain valid data in this case.
542 */
543 if (unlikely(!(trans_exc_code & 4))) {
544 do_low_address(regs);
545 return;
546 }
547 fault = do_exception(regs, VM_WRITE);
548 if (unlikely(fault))
549 do_fault_error(regs, fault);
550}
551NOKPROBE_SYMBOL(do_protection_exception);
552
553void do_dat_exception(struct pt_regs *regs)
554{
555 int access, fault;
556
557 access = VM_READ | VM_EXEC | VM_WRITE;
558 fault = do_exception(regs, access);
559 if (unlikely(fault))
560 do_fault_error(regs, fault);
561}
562NOKPROBE_SYMBOL(do_dat_exception);
563
564#ifdef CONFIG_PFAULT
565/*
566 * 'pfault' pseudo page faults routines.
567 */
568static int pfault_disable;
569
570static int __init nopfault(char *str)
571{
572 pfault_disable = 1;
573 return 1;
574}
575
576__setup("nopfault", nopfault);
577
578struct pfault_refbk {
579 u16 refdiagc;
580 u16 reffcode;
581 u16 refdwlen;
582 u16 refversn;
583 u64 refgaddr;
584 u64 refselmk;
585 u64 refcmpmk;
586 u64 reserved;
587} __attribute__ ((packed, aligned(8)));
588
589int pfault_init(void)
590{
591 struct pfault_refbk refbk = {
592 .refdiagc = 0x258,
593 .reffcode = 0,
594 .refdwlen = 5,
595 .refversn = 2,
596 .refgaddr = __LC_LPP,
597 .refselmk = 1ULL << 48,
598 .refcmpmk = 1ULL << 48,
599 .reserved = __PF_RES_FIELD };
600 int rc;
601
602 if (pfault_disable)
603 return -1;
604 diag_stat_inc(DIAG_STAT_X258);
605 asm volatile(
606 " diag %1,%0,0x258\n"
607 "0: j 2f\n"
608 "1: la %0,8\n"
609 "2:\n"
610 EX_TABLE(0b,1b)
611 : "=d" (rc) : "a" (&refbk), "m" (refbk) : "cc");
612 return rc;
613}
614
615void pfault_fini(void)
616{
617 struct pfault_refbk refbk = {
618 .refdiagc = 0x258,
619 .reffcode = 1,
620 .refdwlen = 5,
621 .refversn = 2,
622 };
623
624 if (pfault_disable)
625 return;
626 diag_stat_inc(DIAG_STAT_X258);
627 asm volatile(
628 " diag %0,0,0x258\n"
629 "0: nopr %%r7\n"
630 EX_TABLE(0b,0b)
631 : : "a" (&refbk), "m" (refbk) : "cc");
632}
633
634static DEFINE_SPINLOCK(pfault_lock);
635static LIST_HEAD(pfault_list);
636
637#define PF_COMPLETE 0x0080
638
639/*
640 * The mechanism of our pfault code: if Linux is running as guest, runs a user
641 * space process and the user space process accesses a page that the host has
642 * paged out we get a pfault interrupt.
643 *
644 * This allows us, within the guest, to schedule a different process. Without
645 * this mechanism the host would have to suspend the whole virtual cpu until
646 * the page has been paged in.
647 *
648 * So when we get such an interrupt then we set the state of the current task
649 * to uninterruptible and also set the need_resched flag. Both happens within
650 * interrupt context(!). If we later on want to return to user space we
651 * recognize the need_resched flag and then call schedule(). It's not very
652 * obvious how this works...
653 *
654 * Of course we have a lot of additional fun with the completion interrupt (->
655 * host signals that a page of a process has been paged in and the process can
656 * continue to run). This interrupt can arrive on any cpu and, since we have
657 * virtual cpus, actually appear before the interrupt that signals that a page
658 * is missing.
659 */
660static void pfault_interrupt(struct ext_code ext_code,
661 unsigned int param32, unsigned long param64)
662{
663 struct task_struct *tsk;
664 __u16 subcode;
665 pid_t pid;
666
667 /*
668 * Get the external interruption subcode & pfault initial/completion
669 * signal bit. VM stores this in the 'cpu address' field associated
670 * with the external interrupt.
671 */
672 subcode = ext_code.subcode;
673 if ((subcode & 0xff00) != __SUBCODE_MASK)
674 return;
675 inc_irq_stat(IRQEXT_PFL);
676 /* Get the token (= pid of the affected task). */
677 pid = param64 & LPP_PFAULT_PID_MASK;
678 rcu_read_lock();
679 tsk = find_task_by_pid_ns(pid, &init_pid_ns);
680 if (tsk)
681 get_task_struct(tsk);
682 rcu_read_unlock();
683 if (!tsk)
684 return;
685 spin_lock(&pfault_lock);
686 if (subcode & PF_COMPLETE) {
687 /* signal bit is set -> a page has been swapped in by VM */
688 if (tsk->thread.pfault_wait == 1) {
689 /* Initial interrupt was faster than the completion
690 * interrupt. pfault_wait is valid. Set pfault_wait
691 * back to zero and wake up the process. This can
692 * safely be done because the task is still sleeping
693 * and can't produce new pfaults. */
694 tsk->thread.pfault_wait = 0;
695 list_del(&tsk->thread.list);
696 wake_up_process(tsk);
697 put_task_struct(tsk);
698 } else {
699 /* Completion interrupt was faster than initial
700 * interrupt. Set pfault_wait to -1 so the initial
701 * interrupt doesn't put the task to sleep.
702 * If the task is not running, ignore the completion
703 * interrupt since it must be a leftover of a PFAULT
704 * CANCEL operation which didn't remove all pending
705 * completion interrupts. */
706 if (tsk->state == TASK_RUNNING)
707 tsk->thread.pfault_wait = -1;
708 }
709 } else {
710 /* signal bit not set -> a real page is missing. */
711 if (WARN_ON_ONCE(tsk != current))
712 goto out;
713 if (tsk->thread.pfault_wait == 1) {
714 /* Already on the list with a reference: put to sleep */
715 goto block;
716 } else if (tsk->thread.pfault_wait == -1) {
717 /* Completion interrupt was faster than the initial
718 * interrupt (pfault_wait == -1). Set pfault_wait
719 * back to zero and exit. */
720 tsk->thread.pfault_wait = 0;
721 } else {
722 /* Initial interrupt arrived before completion
723 * interrupt. Let the task sleep.
724 * An extra task reference is needed since a different
725 * cpu may set the task state to TASK_RUNNING again
726 * before the scheduler is reached. */
727 get_task_struct(tsk);
728 tsk->thread.pfault_wait = 1;
729 list_add(&tsk->thread.list, &pfault_list);
730block:
731 /* Since this must be a userspace fault, there
732 * is no kernel task state to trample. Rely on the
733 * return to userspace schedule() to block. */
734 __set_current_state(TASK_UNINTERRUPTIBLE);
735 set_tsk_need_resched(tsk);
736 set_preempt_need_resched();
737 }
738 }
739out:
740 spin_unlock(&pfault_lock);
741 put_task_struct(tsk);
742}
743
744static int pfault_cpu_dead(unsigned int cpu)
745{
746 struct thread_struct *thread, *next;
747 struct task_struct *tsk;
748
749 spin_lock_irq(&pfault_lock);
750 list_for_each_entry_safe(thread, next, &pfault_list, list) {
751 thread->pfault_wait = 0;
752 list_del(&thread->list);
753 tsk = container_of(thread, struct task_struct, thread);
754 wake_up_process(tsk);
755 put_task_struct(tsk);
756 }
757 spin_unlock_irq(&pfault_lock);
758 return 0;
759}
760
761static int __init pfault_irq_init(void)
762{
763 int rc;
764
765 rc = register_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
766 if (rc)
767 goto out_extint;
768 rc = pfault_init() == 0 ? 0 : -EOPNOTSUPP;
769 if (rc)
770 goto out_pfault;
771 irq_subclass_register(IRQ_SUBCLASS_SERVICE_SIGNAL);
772 cpuhp_setup_state_nocalls(CPUHP_S390_PFAULT_DEAD, "s390/pfault:dead",
773 NULL, pfault_cpu_dead);
774 return 0;
775
776out_pfault:
777 unregister_external_irq(EXT_IRQ_CP_SERVICE, pfault_interrupt);
778out_extint:
779 pfault_disable = 1;
780 return rc;
781}
782early_initcall(pfault_irq_init);
783
784#endif /* CONFIG_PFAULT */