summaryrefslogtreecommitdiffstats
path: root/lib/iov_iter.c
blob: e0aa6b440ca5f4a4f3560100985e39c068c7a6a8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/export.h>
#include <linux/bvec.h>
#include <linux/fault-inject-usercopy.h>
#include <linux/uio.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/splice.h>
#include <linux/compat.h>
#include <linux/scatterlist.h>
#include <linux/instrumented.h>
#include <linux/iov_iter.h>

static __always_inline
size_t copy_to_user_iter(void __user *iter_to, size_t progress,
			 size_t len, void *from, void *priv2)
{
	if (should_fail_usercopy())
		return len;
	if (access_ok(iter_to, len)) {
		from += progress;
		instrument_copy_to_user(iter_to, from, len);
		len = raw_copy_to_user(iter_to, from, len);
	}
	return len;
}

static __always_inline
size_t copy_to_user_iter_nofault(void __user *iter_to, size_t progress,
				 size_t len, void *from, void *priv2)
{
	ssize_t res;

	if (should_fail_usercopy())
		return len;

	from += progress;
	res = copy_to_user_nofault(iter_to, from, len);
	return res < 0 ? len : res;
}

static __always_inline
size_t copy_from_user_iter(void __user *iter_from, size_t progress,
			   size_t len, void *to, void *priv2)
{
	size_t res = len;

	if (should_fail_usercopy())
		return len;
	if (access_ok(iter_from, len)) {
		to += progress;
		instrument_copy_from_user_before(to, iter_from, len);
		res = raw_copy_from_user(to, iter_from, len);
		instrument_copy_from_user_after(to, iter_from, len, res);
	}
	return res;
}

static __always_inline
size_t memcpy_to_iter(void *iter_to, size_t progress,
		      size_t len, void *from, void *priv2)
{
	memcpy(iter_to, from + progress, len);
	return 0;
}

static __always_inline
size_t memcpy_from_iter(void *iter_from, size_t progress,
			size_t len, void *to, void *priv2)
{
	memcpy(to + progress, iter_from, len);
	return 0;
}

/*
 * fault_in_iov_iter_readable - fault in iov iterator for reading
 * @i: iterator
 * @size: maximum length
 *
 * Fault in one or more iovecs of the given iov_iter, to a maximum length of
 * @size.  For each iovec, fault in each page that constitutes the iovec.
 *
 * Returns the number of bytes not faulted in (like copy_to_user() and
 * copy_from_user()).
 *
 * Always returns 0 for non-userspace iterators.
 */
size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t size)
{
	if (iter_is_ubuf(i)) {
		size_t n = min(size, iov_iter_count(i));
		n -= fault_in_readable(i->ubuf + i->iov_offset, n);
		return size - n;
	} else if (iter_is_iovec(i)) {
		size_t count = min(size, iov_iter_count(i));
		const struct iovec *p;
		size_t skip;

		size -= count;
		for (p = iter_iov(i), skip = i->iov_offset; count; p++, skip = 0) {
			size_t len = min(count, p->iov_len - skip);
			size_t ret;

			if (unlikely(!len))
				continue;
			ret = fault_in_readable(p->iov_base + skip, len);
			count -= len - ret;
			if (ret)
				break;
		}
		return count + size;
	}
	return 0;
}
EXPORT_SYMBOL(fault_in_iov_iter_readable);

/*
 * fault_in_iov_iter_writeable - fault in iov iterator for writing
 * @i: iterator
 * @size: maximum length
 *
 * Faults in the iterator using get_user_pages(), i.e., without triggering
 * hardware page faults.  This is primarily useful when we already know that
 * some or all of the pages in @i aren't in memory.
 *
 * Returns the number of bytes not faulted in, like copy_to_user() and
 * copy_from_user().
 *
 * Always returns 0 for non-user-space iterators.
 */
size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t size)
{
	if (iter_is_ubuf(i)) {
		size_t n = min(size, iov_iter_count(i));
		n -= fault_in_safe_writeable(i->ubuf + i->iov_offset, n);
		return size - n;
	} else if (iter_is_iovec(i)) {
		size_t count = min(size, iov_iter_count(i));
		const struct iovec *p;
		size_t skip;

		size -= count;
		for (p = iter_iov(i), skip = i->iov_offset; count; p++, skip = 0) {
			size_t len = min(count, p->iov_len - skip);
			size_t ret;

			if (unlikely(!len))
				continue;
			ret = fault_in_safe_writeable(p->iov_base + skip, len);
			count -= len - ret;
			if (ret)
				break;
		}
		return count + size;
	}
	return 0;
}
EXPORT_SYMBOL(fault_in_iov_iter_writeable);

void iov_iter_init(struct iov_iter *i, unsigned int direction,
			const struct iovec *iov, unsigned long nr_segs,
			size_t count)
{
	WARN_ON(direction & ~(READ | WRITE));
	*i = (struct iov_iter) {
		.iter_type = ITER_IOVEC,
		.copy_mc = false,
		.nofault = false,
		.data_source = direction,
		.__iov = iov,
		.nr_segs = nr_segs,
		.iov_offset = 0,
		.count = count
	};
}
EXPORT_SYMBOL(iov_iter_init);

size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
{
	if (WARN_ON_ONCE(i->data_source))
		return 0;
	if (user_backed_iter(i))
		might_fault();
	return iterate_and_advance(i, bytes, (void *)addr,
				   copy_to_user_iter, memcpy_to_iter);
}
EXPORT_SYMBOL(_copy_to_iter);

#ifdef CONFIG_ARCH_HAS_COPY_MC
static __always_inline
size_t copy_to_user_iter_mc(void __user *iter_to, size_t progress,
			    size_t len, void *from, void *priv2)
{
	if (access_ok(iter_to, len)) {
		from += progress;
		instrument_copy_to_user(iter_to, from, len);
		len = copy_mc_to_user(iter_to, from, len);
	}
	return len;
}

static __always_inline
size_t memcpy_to_iter_mc(void *iter_to, size_t progress,
			 size_t len, void *from, void *priv2)
{
	return copy_mc_to_kernel(iter_to, from + progress, len);
}

/**
 * _copy_mc_to_iter - copy to iter with source memory error exception handling
 * @addr: source kernel address
 * @bytes: total transfer length
 * @i: destination iterator
 *
 * The pmem driver deploys this for the dax operation
 * (dax_copy_to_iter()) for dax reads (bypass page-cache and the
 * block-layer). Upon #MC read(2) aborts and returns EIO or the bytes
 * successfully copied.
 *
 * The main differences between this and typical _copy_to_iter().
 *
 * * Typical tail/residue handling after a fault retries the copy
 *   byte-by-byte until the fault happens again. Re-triggering machine
 *   checks is potentially fatal so the implementation uses source
 *   alignment and poison alignment assumptions to avoid re-triggering
 *   hardware exceptions.
 *
 * * ITER_KVEC and ITER_BVEC can return short copies.  Compare to
 *   copy_to_iter() where only ITER_IOVEC attempts might return a short copy.
 *
 * Return: number of bytes copied (may be %0)
 */
size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
{
	if (WARN_ON_ONCE(i->data_source))
		return 0;
	if (user_backed_iter(i))
		might_fault();
	return iterate_and_advance(i, bytes, (void *)addr,
				   copy_to_user_iter_mc, memcpy_to_iter_mc);
}
EXPORT_SYMBOL_GPL(_copy_mc_to_iter);
#endif /* CONFIG_ARCH_HAS_COPY_MC */

static __always_inline
size_t memcpy_from_iter_mc(void *iter_from, size_t progress,
			   size_t len, void *to, void *priv2)
{
	return copy_mc_to_kernel(to + progress, iter_from, len);
}

static size_t __copy_from_iter_mc(void *addr, size_t bytes, struct iov_iter *i)
{
	if (unlikely(i->count < bytes))
		bytes = i->count;
	if (unlikely(!bytes))
		return 0;
	return iterate_bvec(i, bytes, addr, NULL, memcpy_from_iter_mc);
}

static __always_inline
size_t __copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
{
	if (unlikely(iov_iter_is_copy_mc(i)))
		return __copy_from_iter_mc(addr, bytes, i);
	return iterate_and_advance(i, bytes, addr,
				   copy_from_user_iter, memcpy_from_iter);
}

size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
{
	if (WARN_ON_ONCE(!i->data_source))
		return 0;

	if (user_backed_iter(i))
		might_fault();
	return __copy_from_iter(addr, bytes, i);
}
EXPORT_SYMBOL(_copy_from_iter);

static __always_inline
size_t copy_from_user_iter_nocache(void __user *iter_from, size_t progress,
				   size_t len, void *to, void *priv2)
{
	return __copy_from_user_inatomic_nocache(to + progress, iter_from, len);
}

size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
{
	if (WARN_ON_ONCE(!i->data_source))
		return 0;

	return iterate_and_advance(i, bytes, addr,
				   copy_from_user_iter_nocache,
				   memcpy_from_iter);
}
EXPORT_SYMBOL(_copy_from_iter_nocache);

#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
static __always_inline
size_t copy_from_user_iter_flushcache(void __user *iter_from, size_t progress,
				      size_t len, void *to, void *priv2)
{
	return __copy_from_user_flushcache(to + progress, iter_from, len);
}

static __always_inline
size_t memcpy_from_iter_flushcache(void *iter_from, size_t progress,
				   size_t len, void *to, void *priv2)
{
	memcpy_flushcache(to + progress, iter_from, len);
	return 0;
}

/**
 * _copy_from_iter_flushcache - write destination through cpu cache
 * @addr: destination kernel address
 * @bytes: total transfer length
 * @i: source iterator
 *
 * The pmem driver arranges for filesystem-dax to use this facility via
 * dax_copy_from_iter() for ensuring that writes to persistent memory
 * are flushed through the CPU cache. It is differentiated from
 * _copy_from_iter_nocache() in that guarantees all data is flushed for
 * all iterator types. The _copy_from_iter_nocache() only attempts to
 * bypass the cache for the ITER_IOVEC case, and on some archs may use
 * instructions that strand dirty-data in the cache.
 *
 * Return: number of bytes copied (may be %0)
 */
size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
{
	if (WARN_ON_ONCE(!i->data_source))
		return 0;

	return iterate_and_advance(i, bytes, addr,
				   copy_from_user_iter_flushcache,
				   memcpy_from_iter_flushcache);
}
EXPORT_SYMBOL_GPL(_copy_from_iter_flushcache);
#endif

static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
{
	struct page *head;
	size_t v = n + offset;

	/*
	 * The general case needs to access the page order in order
	 * to compute the page size.
	 * However, we mostly deal with order-0 pages and thus can
	 * avoid a possible cache line miss for requests that fit all
	 * page orders.
	 */
	if (n <= v && v <= PAGE_SIZE)
		return true;

	head = compound_head(page);
	v += (page - head) << PAGE_SHIFT;

	if (WARN_ON(n > v || v > page_size(head)))
		return false;
	return true;
}

size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
			 struct iov_iter *i)
{
	size_t res = 0;
	if (!page_copy_sane(page, offset, bytes))
		return 0;
	if (WARN_ON_ONCE(i->data_source))
		return 0;
	page += offset / PAGE_SIZE; // first subpage
	offset %= PAGE_SIZE;
	while (1) {
		void *kaddr = kmap_local_page(page);
		size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
		n = _copy_to_iter(kaddr + offset, n, i);
		kunmap_local(kaddr);
		res += n;
		bytes -= n;
		if (!bytes || !n)
			break;
		offset += n;
		if (offset == PAGE_SIZE) {
			page++;
			offset = 0;
		}
	}
	return res;
}
EXPORT_SYMBOL(copy_page_to_iter);

size_t copy_page_to_iter_nofault(struct page *page, unsigned offset, size_t bytes,
				 struct iov_iter *i)
{
	size_t res = 0;

	if (!page_copy_sane(page, offset, bytes))
		return 0;
	if (WARN_ON_ONCE(i->data_source))
		return 0;
	page += offset / PAGE_SIZE; // first subpage
	offset %= PAGE_SIZE;
	while (1) {
		void *kaddr = kmap_local_page(page);
		size_t n = min(bytes, (size_t)PAGE_SIZE - offset);

		n = iterate_and_advance(i, n, kaddr + offset,
					copy_to_user_iter_nofault,
					memcpy_to_iter);
		kunmap_local(kaddr);
		res += n;
		bytes -= n;
		if (!bytes || !n)
			break;
		offset += n;
		if (offset == PAGE_SIZE) {
			page++;
			offset = 0;
		}
	}
	return res;
}
EXPORT_SYMBOL(copy_page_to_iter_nofault);

size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
			 struct iov_iter *i)
{
	size_t res = 0;
	if (!page_copy_sane(page, offset, bytes))
		return 0;
	page += offset / PAGE_SIZE; // first subpage
	offset %= PAGE_SIZE;
	while (1) {
		void *kaddr = kmap_local_page(page);
		size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
		n = _copy_from_iter(kaddr + offset, n, i);
		kunmap_local(kaddr);
		res += n;
		bytes -= n;
		if (!bytes || !n)
			break;
		offset += n;
		if (offset == PAGE_SIZE) {
			page++;
			offset = 0;
		}
	}
	return res;
}
EXPORT_SYMBOL(copy_page_from_iter);

static __always_inline
size_t zero_to_user_iter(void __user *iter_to, size_t progress,
			 size_t len, void *priv, void *priv2)
{
	return clear_user(iter_to, len);
}

static __always_inline
size_t zero_to_iter(void *iter_to, size_t progress,
		    size_t len, void *priv, void *priv2)
{
	memset(iter_to, 0, len);
	return 0;
}

size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
{
	return iterate_and_advance(i, bytes, NULL,
				   zero_to_user_iter, zero_to_iter);
}
EXPORT_SYMBOL(iov_iter_zero);

size_t copy_page_from_iter_atomic(struct page *page, size_t offset,
		size_t bytes, struct iov_iter *i)
{
	size_t n, copied = 0;

	if (!page_copy_sane(page, offset, bytes))
		return 0;
	if (WARN_ON_ONCE(!i->data_source))
		return 0;

	do {
		char *p;

		n = bytes - copied;
		if (PageHighMem(page)) {
			page += offset / PAGE_SIZE;
			offset %= PAGE_SIZE;
			n = min_t(size_t, n, PAGE_SIZE - offset);
		}

		p = kmap_atomic(page) + offset;
		n = __copy_from_iter(p, n, i);
		kunmap_atomic(p);
		copied += n;
		offset += n;
	} while (PageHighMem(page) && copied != bytes && n > 0);

	return copied;
}
EXPORT_SYMBOL(copy_page_from_iter_atomic);

static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
{
	const struct bio_vec *bvec, *end;

	if (!i->count)
		return;
	i->count -= size;

	size += i->iov_offset;

	for (bvec = i->bvec, end = bvec + i->nr_segs; bvec < end; bvec++) {
		if (likely(size < bvec->bv_len))
			break;
		size -= bvec->bv_len;
	}
	i->iov_offset = size;
	i->nr_segs -= bvec - i->bvec;
	i->bvec = bvec;
}

static void iov_iter_iovec_advance(struct iov_iter *i, size_t size)
{
	const struct iovec *iov, *end;

	if (!i->count)
		return;
	i->count -= size;

	size += i->iov_offset; // from beginning of current segment
	for (iov = iter_iov(i), end = iov + i->nr_segs; iov < end; iov++) {
		if (likely(size < iov->iov_len))
			break;
		size -= iov->iov_len;
	}
	i->iov_offset = size;
	i->nr_segs -= iov - iter_iov(i);
	i->__iov = iov;
}

void iov_iter_advance(struct iov_iter *i, size_t size)
{
	if (unlikely(i->count < size))
		size = i->count;
	if (likely(iter_is_ubuf(i)) || unlikely(iov_iter_is_xarray(i))) {
		i->iov_offset += size;
		i->count -= size;
	} else if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i))) {
		/* iovec and kvec have identical layouts */
		iov_iter_iovec_advance(i, size);
	} else if (iov_iter_is_bvec(i)) {
		iov_iter_bvec_advance(i, size);
	} else if (iov_iter_is_discard(i)) {
		i->count -= size;
	}
}
EXPORT_SYMBOL(iov_iter_advance);

void iov_iter_revert(struct iov_iter *i, size_t unroll)
{
	if (!unroll)
		return;
	if (WARN_ON(unroll > MAX_RW_COUNT))
		return;
	i->count += unroll;
	if (unlikely(iov_iter_is_discard(i)))
		return;
	if (unroll <= i->iov_offset) {
		i->iov_offset -= unroll;
		return;
	}
	unroll -= i->iov_offset;
	if (iov_iter_is_xarray(i) || iter_is_ubuf(i)) {
		BUG(); /* We should never go beyond the start of the specified
			* range since we might then be straying into pages that
			* aren't pinned.
			*/
	} else if (iov_iter_is_bvec(i)) {
		const struct bio_vec *bvec = i->bvec;
		while (1) {
			size_t n = (--bvec)->bv_len;
			i->nr_segs++;
			if (unroll <= n) {
				i->bvec = bvec;
				i->iov_offset = n - unroll;
				return;
			}
			unroll -= n;
		}
	} else { /* same logics for iovec and kvec */
		const struct iovec *iov = iter_iov(i);
		while (1) {
			size_t n = (--iov)->iov_len;
			i->nr_segs++;
			if (unroll <= n) {
				i->__iov = iov;
				i->iov_offset = n - unroll;
				return;
			}
			unroll -= n;
		}
	}
}
EXPORT_SYMBOL(iov_iter_revert);

/*
 * Return the count of just the current iov_iter segment.
 */
size_t iov_iter_single_seg_count(const struct iov_iter *i)
{
	if (i->nr_segs > 1) {
		if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
			return min(i->count, iter_iov(i)->iov_len - i->iov_offset);
		if (iov_iter_is_bvec(i))
			return min(i->count, i->bvec->bv_len - i->iov_offset);
	}
	return i->count;
}
EXPORT_SYMBOL(iov_iter_single_seg_count);

void iov_iter_kvec(struct iov_iter *i, unsigned int direction,
			const struct kvec *kvec, unsigned long nr_segs,
			size_t count)
{
	WARN_ON(direction & ~(READ | WRITE));
	*i = (struct iov_iter){
		.iter_type = ITER_KVEC,
		.copy_mc = false,
		.data_source = direction,
		.kvec = kvec,
		.nr_segs = nr_segs,
		.iov_offset = 0,
		.count = count
	};
}
EXPORT_SYMBOL(iov_iter_kvec);

void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
			const struct bio_vec *bvec, unsigned long nr_segs,
			size_t count)
{
	WARN_ON(direction & ~(READ | WRITE));
	*i = (struct iov_iter){
		.iter_type = ITER_BVEC,
		.copy_mc = false,
		.data_source = direction,
		.bvec = bvec,
		.nr_segs = nr_segs,
		.iov_offset = 0,
		.count = count
	};
}
EXPORT_SYMBOL(iov_iter_bvec);

/**
 * iov_iter_xarray - Initialise an I/O iterator to use the pages in an xarray
 * @i: The iterator to initialise.
 * @direction: The direction of the transfer.
 * @xarray: The xarray to access.
 * @start: The start file position.
 * @count: The size of the I/O buffer in bytes.
 *
 * Set up an I/O iterator to either draw data out of the pages attached to an
 * inode or to inject data into those pages.  The pages *must* be prevented
 * from evaporation, either by taking a ref on them or locking them by the
 * caller.
 */
void iov_iter_xarray(struct iov_iter *i, unsigned int direction,
		     struct xarray *xarray, loff_t start, size_t count)
{
	BUG_ON(direction & ~1);
	*i = (struct iov_iter) {
		.iter_type = ITER_XARRAY,
		.copy_mc = false,
		.data_source = direction,
		.xarray = xarray,
		.xarray_start = start,
		.count = count,
		.iov_offset = 0
	};
}
EXPORT_SYMBOL(iov_iter_xarray);

/**
 * iov_iter_discard - Initialise an I/O iterator that discards data
 * @i: The iterator to initialise.
 * @direction: The direction of the transfer.
 * @count: The size of the I/O buffer in bytes.
 *
 * Set up an I/O iterator that just discards everything that's written to it.
 * It's only available as a READ iterator.
 */
void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count)
{
	BUG_ON(direction != READ);
	*i = (struct iov_iter){
		.iter_type = ITER_DISCARD,
		.copy_mc = false,
		.data_source = false,
		.count = count,
		.iov_offset = 0
	};
}
EXPORT_SYMBOL(iov_iter_discard);

static bool iov_iter_aligned_iovec(const struct iov_iter *i, unsigned addr_mask,
				   unsigned len_mask)
{
	size_t size = i->count;
	size_t skip = i->iov_offset;
	unsigned k;

	for (k = 0; k < i->nr_segs; k++, skip = 0) {
		const struct iovec *iov = iter_iov(i) + k;
		size_t len = iov->iov_len - skip;

		if (len > size)
			len = size;
		if (len & len_mask)
			return false;
		if ((unsigned long)(iov->iov_base + skip) & addr_mask)
			return false;

		size -= len;
		if (!size)
			break;
	}
	return true;
}

static bool iov_iter_aligned_bvec(const struct iov_iter *i, unsigned addr_mask,
				  unsigned len_mask)
{
	size_t size = i->count;
	unsigned skip = i->iov_offset;
	unsigned k;

	for (k = 0; k < i->nr_segs; k++, skip = 0) {
		size_t len = i->bvec[k].bv_len - skip;

		if (len > size)
			len = size;
		if (len & len_mask)
			return false;
		if ((unsigned long)(i->bvec[k].bv_offset + skip) & addr_mask)
			return false;

		size -= len;
		if (!size)
			break;
	}
	return true;
}

/**
 * iov_iter_is_aligned() - Check if the addresses and lengths of each segments
 * 	are aligned to the parameters.
 *
 * @i: &struct iov_iter to restore
 * @addr_mask: bit mask to check against the iov element's addresses
 * @len_mask: bit mask to check against the iov element's lengths
 *
 * Return: false if any addresses or lengths intersect with the provided masks
 */
bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
			 unsigned len_mask)
{
	if (likely(iter_is_ubuf(i))) {
		if (i->count & len_mask)
			return false;
		if ((unsigned long)(i->ubuf + i->iov_offset) & addr_mask)
			return false;
		return true;
	}

	if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
		return iov_iter_aligned_iovec(i, addr_mask, len_mask);

	if (iov_iter_is_bvec(i))
		return iov_iter_aligned_bvec(i, addr_mask, len_mask);

	if (iov_iter_is_xarray(i)) {
		if (i->count & len_mask)
			return false;
		if ((i->xarray_start + i->iov_offset) & addr_mask)
			return false;
	}

	return true;
}
EXPORT_SYMBOL_GPL(iov_iter_is_aligned);

static unsigned long iov_iter_alignment_iovec(const struct iov_iter *i)
{
	unsigned long res = 0;
	size_t size = i->count;
	size_t skip = i->iov_offset;
	unsigned k;

	for (k = 0; k < i->nr_segs; k++, skip = 0) {
		const struct iovec *iov = iter_iov(i) + k;
		size_t len = iov->iov_len - skip;
		if (len) {
			res |= (unsigned long)iov->iov_base + skip;
			if (len > size)
				len = size;
			res |= len;
			size -= len;
			if (!size)
				break;
		}
	}
	return res;
}

static unsigned long iov_iter_alignment_bvec(const struct iov_iter *i)
{
	unsigned res = 0;
	size_t size = i->count;
	unsigned skip = i->iov_offset;
	unsigned k;

	for (k = 0; k < i->nr_segs; k++, skip = 0) {
		size_t len = i->bvec[k].bv_len - skip;
		res |= (unsigned long)i->bvec[k].bv_offset + skip;
		if (len > size)
			len = size;
		res |= len;
		size -= len;
		if (!size)
			break;
	}
	return res;
}

unsigned long iov_iter_alignment(const struct iov_iter *i)
{
	if (likely(iter_is_ubuf(i))) {
		size_t size = i->count;
		if (size)
			return ((unsigned long)i->ubuf + i->iov_offset) | size;
		return 0;
	}

	/* iovec and kvec have identical layouts */
	if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
		return iov_iter_alignment_iovec(i);

	if (iov_iter_is_bvec(i))
		return iov_iter_alignment_bvec(i);

	if (iov_iter_is_xarray(i))
		return (i->xarray_start + i->iov_offset) | i->count;

	return 0;
}
EXPORT_SYMBOL(iov_iter_alignment);

unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
{
	unsigned long res = 0;
	unsigned long v = 0;
	size_t size = i->count;
	unsigned k;

	if (iter_is_ubuf(i))
		return 0;

	if (WARN_ON(!iter_is_iovec(i)))
		return ~0U;

	for (k = 0; k < i->nr_segs; k++) {
		const struct iovec *iov = iter_iov(i) + k;
		if (iov->iov_len) {
			unsigned long base = (unsigned long)iov->iov_base;
			if (v) // if not the first one
				res |= base | v; // this start | previous end
			v = base + iov->iov_len;
			if (size <= iov->iov_len)
				break;
			size -= iov->iov_len;
		}
	}
	return res;
}
EXPORT_SYMBOL(iov_iter_gap_alignment);

static int want_pages_array(struct page ***res, size_t size,
			    size_t start, unsigned int maxpages)
{
	unsigned int count = DIV_ROUND_UP(size + start, PAGE_SIZE);

	if (count > maxpages)
		count = maxpages;
	WARN_ON(!count);	// caller should've prevented that
	if (!*res) {
		*res = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
		if (!*res)
			return 0;
	}
	return count;
}

static ssize_t iter_xarray_populate_pages(struct page **pages, struct xarray *xa,
					  pgoff_t index, unsigned int nr_pages)
{
	XA_STATE(xas, xa, index);
	struct page *page;
	unsigned int ret = 0;

	rcu_read_lock();
	for (page = xas_load(&xas); page; page = xas_next(&xas)) {
		if (xas_retry(&xas, page))
			continue;

		/* Has the page moved or been split? */
		if (unlikely(page != xas_reload(&xas))) {
			xas_reset(&xas);
			continue;
		}

		pages[ret] = find_subpage(page, xas.xa_index);
		get_page(pages[ret]);
		if (++ret == nr_pages)
			break;
	}
	rcu_read_unlock();
	return ret;
}

static ssize_t iter_xarray_get_pages(struct iov_iter *i,
				     struct page ***pages, size_t maxsize,
				     unsigned maxpages, size_t *_start_offset)
{
	unsigned nr, offset, count;
	pgoff_t index;
	loff_t pos;

	pos = i->xarray_start + i->iov_offset;
	index = pos >> PAGE_SHIFT;
	offset = pos & ~PAGE_MASK;
	*_start_offset = offset;

	count = want_pages_array(pages, maxsize, offset, maxpages);
	if (!count)
		return -ENOMEM;
	nr = iter_xarray_populate_pages(*pages, i->xarray, index, count);
	if (nr == 0)
		return 0;

	maxsize = min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
	i->iov_offset += maxsize;
	i->count -= maxsize;
	return maxsize;
}

/* must be done on non-empty ITER_UBUF or ITER_IOVEC one */
static unsigned long first_iovec_segment(const struct iov_iter *i, size_t *size)
{
	size_t skip;
	long k;

	if (iter_is_ubuf(i))
		return (unsigned long)i->ubuf + i->iov_offset;

	for (k = 0, skip = i->iov_offset; k < i->nr_segs; k++, skip = 0) {
		const struct iovec *iov = iter_iov(i) + k;
		size_t len = iov->iov_len - skip;

		if (unlikely(!len))
			continue;
		if (*size > len)
			*size = len;
		return (unsigned long)iov->iov_base + skip;
	}
	BUG(); // if it had been empty, we wouldn't get called
}

/* must be done on non-empty ITER_BVEC one */
static struct page *first_bvec_segment(const struct iov_iter *i,
				       size_t *size, size_t *start)
{
	struct page *page;
	size_t skip = i->iov_offset, len;

	len = i->bvec->bv_len - skip;
	if (*size > len)
		*size = len;
	skip += i->bvec->bv_offset;
	page = i->bvec->bv_page + skip / PAGE_SIZE;
	*start = skip % PAGE_SIZE;
	return page;
}

static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
		   struct page ***pages, size_t maxsize,
		   unsigned int maxpages, size_t *start)
{
	unsigned int n, gup_flags = 0;

	if (maxsize > i->count)
		maxsize = i->count;
	if (!maxsize)
		return 0;
	if (maxsize > MAX_RW_COUNT)
		maxsize = MAX_RW_COUNT;

	if (likely(user_backed_iter(i))) {
		unsigned long addr;
		int res;

		if (iov_iter_rw(i) != WRITE)
			gup_flags |= FOLL_WRITE;
		if (i->nofault)
			gup_flags |= FOLL_NOFAULT;

		addr = first_iovec_segment(i, &maxsize);
		*start = addr % PAGE_SIZE;
		addr &= PAGE_MASK;
		n = want_pages_array(pages, maxsize, *start, maxpages);
		if (!n)
			return -ENOMEM;
		res = get_user_pages_fast(addr, n, gup_flags, *pages);
		if (unlikely(res <= 0))
			return res;
		maxsize = min_t(size_t, maxsize, res * PAGE_SIZE - *start);
		iov_iter_advance(i, maxsize);
		return maxsize;
	}
	if (iov_iter_is_bvec(i)) {
		struct page **p;
		struct page *page;

		page = first_bvec_segment(i, &maxsize, start);
		n = want_pages_array(pages, maxsize, *start, maxpages);
		if (!n)
			return -ENOMEM;
		p = *pages;
		for (int k = 0; k < n; k++)
			get_page(p[k] = page + k);
		maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start);
		i->count -= maxsize;
		i->iov_offset += maxsize;
		if (i->iov_offset == i->bvec->bv_len) {
			i->iov_offset = 0;
			i->bvec++;
			i->nr_segs--;
		}
		return maxsize;
	}
	if (iov_iter_is_xarray(i))
		return iter_xarray_get_pages(i, pages, maxsize, maxpages, start);
	return -EFAULT;
}

ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
		size_t maxsize, unsigned maxpages, size_t *start)
{
	if (!maxpages)
		return 0;
	BUG_ON(!pages);

	return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages, start);
}
EXPORT_SYMBOL(iov_iter_get_pages2);

ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i,
		struct page ***pages, size_t maxsize, size_t *start)
{
	ssize_t len;

	*pages = NULL;

	len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start);
	if (len <= 0) {
		kvfree(*pages);
		*pages = NULL;
	}
	return len;
}
EXPORT_SYMBOL(iov_iter_get_pages_alloc2);

static int iov_npages(const struct iov_iter *i, int maxpages)
{
	size_t skip = i->iov_offset, size = i->count;
	const struct iovec *p;
	int npages = 0;

	for (p = iter_iov(i); size; skip = 0, p++) {
		unsigned offs = offset_in_page(p->iov_base + skip);
		size_t len = min(p->iov_len - skip, size);

		if (len) {
			size -= len;
			npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
			if (unlikely(npages > maxpages))
				return maxpages;
		}
	}
	return npages;
}

static int bvec_npages(const struct iov_iter *i, int maxpages)
{
	size_t skip = i->iov_offset, size = i->count;
	const struct bio_vec *p;
	int npages = 0;

	for (p = i->bvec; size; skip = 0, p++) {
		unsigned offs = (p->bv_offset + skip) % PAGE_SIZE;
		size_t len = min(p->bv_len - skip, size);

		size -= len;
		npages += DIV_ROUND_UP(offs + len, PAGE_SIZE);
		if (unlikely(npages > maxpages))
			return maxpages;
	}
	return npages;
}

int iov_iter_npages(const struct iov_iter *i, int maxpages)
{
	if (unlikely(!i->count))
		return 0;
	if (likely(iter_is_ubuf(i))) {
		unsigned offs = offset_in_page(i->ubuf + i->iov_offset);
		int npages = DIV_ROUND_UP(offs + i->count, PAGE_SIZE);
		return min(npages, maxpages);
	}
	/* iovec and kvec have identical layouts */
	if (likely(iter_is_iovec(i) || iov_iter_is_kvec(i)))
		return iov_npages(i, maxpages);
	if (iov_iter_is_bvec(i))
		return bvec_npages(i, maxpages);
	if (iov_iter_is_xarray(i)) {
		unsigned offset = (i->xarray_start + i->iov_offset) % PAGE_SIZE;
		int npages = DIV_ROUND_UP(offset + i->count, PAGE_SIZE);
		return min(npages, maxpages);
	}
	return 0;
}
EXPORT_SYMBOL(iov_iter_npages);

const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
{
	*new = *old;
	if (iov_iter_is_bvec(new))
		return new->bvec = kmemdup(new->bvec,
				    new->nr_segs * sizeof(struct bio_vec),
				    flags);
	else if (iov_iter_is_kvec(new) || iter_is_iovec(new))
		/* iovec and kvec have identical layout */
		return new->__iov = kmemdup(new->__iov,
				   new->nr_segs * sizeof(struct iovec),
				   flags);
	return NULL;
}
EXPORT_SYMBOL(dup_iter);

static __noclone int copy_compat_iovec_from_user(struct iovec *iov,
		const struct iovec __user *uvec, unsigned long nr_segs)
{
	const struct compat_iovec __user *uiov =
		(const struct compat_iovec __user *)uvec;
	int ret = -EFAULT, i;

	if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
		return -EFAULT;

	for (i = 0; i < nr_segs; i++) {
		compat_uptr_t buf;
		compat_ssize_t len;

		unsafe_get_user(len, &uiov[i].iov_len, uaccess_end);
		unsafe_get_user(buf, &uiov[i].iov_base, uaccess_end);

		/* check for compat_size_t not fitting in compat_ssize_t .. */
		if (len < 0) {
			ret = -EINVAL;
			goto uaccess_end;
		}
		iov[i].iov_base = compat_ptr(buf);
		iov[i].iov_len = len;
	}

	ret = 0;
uaccess_end:
	user_access_end();
	return ret;
}

static __noclone int copy_iovec_from_user(struct iovec *iov,
		const struct iovec __user *uiov, unsigned long nr_segs)
{
	int ret = -EFAULT;

	if (!user_access_begin(uiov, nr_segs * sizeof(*uiov)))
		return -EFAULT;

	do {
		void __user *buf;
		ssize_t len;

		unsafe_get_user(len, &uiov->iov_len, uaccess_end);
		unsafe_get_user(buf, &uiov->iov_base, uaccess_end);

		/* check for size_t not fitting in ssize_t .. */
		if (unlikely(len < 0)) {
			ret = -EINVAL;
			goto uaccess_end;
		}
		iov->iov_base = buf;
		iov->iov_len = len;

		uiov++; iov++;
	} while (--nr_segs);

	ret = 0;
uaccess_end:
	user_access_end();
	return ret;
}

struct iovec *iovec_from_user(const struct iovec __user *uvec,
		unsigned long nr_segs, unsigned long fast_segs,
		struct iovec *fast_iov, bool compat)
{
	struct iovec *iov = fast_iov;
	int ret;

	/*
	 * SuS says "The readv() function *may* fail if the iovcnt argument was
	 * less than or equal to 0, or greater than {IOV_MAX}.  Linux has
	 * traditionally returned zero for zero segments, so...
	 */
	if (nr_segs == 0)
		return iov;
	if (nr_segs > UIO_MAXIOV)
		return ERR_PTR(-EINVAL);
	if (nr_segs > fast_segs) {
		iov = kmalloc_array(nr_segs, sizeof(struct iovec), GFP_KERNEL);
		if (!iov)
			return ERR_PTR(-ENOMEM);
	}

	if (unlikely(compat))
		ret = copy_compat_iovec_from_user(iov, uvec, nr_segs);
	else
		ret = copy_iovec_from_user(iov, uvec, nr_segs);
	if (ret) {
		if (iov != fast_iov)
			kfree(iov);
		return ERR_PTR(ret);
	}

	return iov;
}

/*
 * Single segment iovec supplied by the user, import it as ITER_UBUF.
 */
static ssize_t __import_iovec_ubuf(int type, const struct iovec __user *uvec,
				   struct iovec **iovp, struct iov_iter *i,
				   bool compat)
{
	struct iovec *iov = *iovp;
	ssize_t ret;

	if (compat)
		ret = copy_compat_iovec_from_user(iov, uvec, 1);
	else
		ret = copy_iovec_from_user(iov, uvec, 1);
	if (unlikely(ret))
		return ret;

	ret = import_ubuf(type, iov->iov_base, iov->iov_len, i);
	if (unlikely(ret))
		return ret;
	*iovp = NULL;
	return i->count;
}

ssize_t __import_iovec(int type, const struct iovec __user *uvec,
		 unsigned nr_segs, unsigned fast_segs, struct iovec **iovp,
		 struct iov_iter *i, bool compat)
{
	ssize_t total_len = 0;
	unsigned long seg;
	struct iovec *iov;

	if (nr_segs == 1)
		return __import_iovec_ubuf(type, uvec, iovp, i, compat);

	iov = iovec_from_user(uvec, nr_segs, fast_segs, *iovp, compat);
	if (IS_ERR(iov)) {
		*iovp = NULL;
		return PTR_ERR(iov);
	}

	/*
	 * According to the Single Unix Specification we should return EINVAL if
	 * an element length is < 0 when cast to ssize_t or if the total length
	 * would overflow the ssize_t return value of the system call.
	 *
	 * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
	 * overflow case.
	 */
	for (seg = 0; seg < nr_segs; seg++) {
		ssize_t len = (ssize_t)iov[seg].iov_len;

		if (!access_ok(iov[seg].iov_base, len)) {
			if (iov != *iovp)
				kfree(iov);
			*iovp = NULL;
			return -EFAULT;
		}

		if (len > MAX_RW_COUNT - total_len) {
			len = MAX_RW_COUNT - total_len;
			iov[seg].iov_len = len;
		}
		total_len += len;
	}

	iov_iter_init(i, type, iov, nr_segs, total_len);
	if (iov == *iovp)
		*iovp = NULL;
	else
		*iovp = iov;
	return total_len;
}

/**
 * import_iovec() - Copy an array of &struct iovec from userspace
 *     into the kernel, check that it is valid, and initialize a new
 *     &struct iov_iter iterator to access it.
 *
 * @type: One of %READ or %WRITE.
 * @uvec: Pointer to the userspace array.
 * @nr_segs: Number of elements in userspace array.
 * @fast_segs: Number of elements in @iov.
 * @iovp: (input and output parameter) Pointer to pointer to (usually small
 *     on-stack) kernel array.
 * @i: Pointer to iterator that will be initialized on success.
 *
 * If the array pointed to by *@iov is large enough to hold all @nr_segs,
 * then this function places %NULL in *@iov on return. Otherwise, a new
 * array will be allocated and the result placed in *@iov. This means that
 * the caller may call kfree() on *@iov regardless of whether the small
 * on-stack array was used or not (and regardless of whether this function
 * returns an error or not).
 *
 * Return: Negative error code on error, bytes imported on success
 */
ssize_t import_iovec(int type, const struct iovec __user *uvec,
		 unsigned nr_segs, unsigned fast_segs,
		 struct iovec **iovp, struct iov_iter *i)
{
	return __import_iovec(type, uvec, nr_segs, fast_segs, iovp, i,
			      in_compat_syscall());
}
EXPORT_SYMBOL(import_iovec);

int import_ubuf(int rw, void __user *buf, size_t len, struct iov_iter *i)
{
	if (len > MAX_RW_COUNT)
		len = MAX_RW_COUNT;
	if (unlikely(!access_ok(buf, len)))
		return -EFAULT;

	iov_iter_ubuf(i, rw, buf, len);
	return 0;
}
EXPORT_SYMBOL_GPL(import_ubuf);

/**
 * iov_iter_restore() - Restore a &struct iov_iter to the same state as when
 *     iov_iter_save_state() was called.
 *
 * @i: &struct iov_iter to restore
 * @state: state to restore from
 *
 * Used after iov_iter_save_state() to bring restore @i, if operations may
 * have advanced it.
 *
 * Note: only works on ITER_IOVEC, ITER_BVEC, and ITER_KVEC
 */
void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
{
	if (WARN_ON_ONCE(!iov_iter_is_bvec(i) && !iter_is_iovec(i) &&
			 !iter_is_ubuf(i)) && !iov_iter_is_kvec(i))
		return;
	i->iov_offset = state->iov_offset;
	i->count = state->count;
	if (iter_is_ubuf(i))
		return;
	/*
	 * For the *vec iters, nr_segs + iov is constant - if we increment
	 * the vec, then we also decrement the nr_segs count. Hence we don't
	 * need to track both of these, just one is enough and we can deduct
	 * the other from that. ITER_KVEC and ITER_IOVEC are the same struct
	 * size, so we can just increment the iov pointer as they are unionzed.
	 * ITER_BVEC _may_ be the same size on some archs, but on others it is
	 * not. Be safe and handle it separately.
	 */
	BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
	if (iov_iter_is_bvec(i))
		i->bvec -= state->nr_segs - i->nr_segs;
	else
		i->__iov -= state->nr_segs - i->nr_segs;
	i->nr_segs = state->nr_segs;
}

/*
 * Extract a list of contiguous pages from an ITER_XARRAY iterator.  This does not
 * get references on the pages, nor does it get a pin on them.
 */
static ssize_t iov_iter_extract_xarray_pages(struct iov_iter *i,
					     struct page ***pages, size_t maxsize,
					     unsigned int maxpages,
					     iov_iter_extraction_t extraction_flags,
					     size_t *offset0)
{
	struct page *page, **p;
	unsigned int nr = 0, offset;
	loff_t pos = i->xarray_start + i->iov_offset;
	pgoff_t index = pos >> PAGE_SHIFT;
	XA_STATE(xas, i->xarray, index);

	offset = pos & ~PAGE_MASK;
	*offset0 = offset;

	maxpages = want_pages_array(pages, maxsize, offset, maxpages);
	if (!maxpages)
		return -ENOMEM;
	p = *pages;

	rcu_read_lock();
	for (page = xas_load(&xas); page; page = xas_next(&xas)) {
		if (xas_retry(&xas, page))
			continue;

		/* Has the page moved or been split? */
		if (unlikely(page != xas_reload(&xas))) {
			xas_reset(&xas);
			continue;
		}

		p[nr++] = find_subpage(page, xas.xa_index);
		if (nr == maxpages)
			break;
	}
	rcu_read_unlock();

	maxsize = min_t(size_t, nr * PAGE_SIZE - offset, maxsize);
	iov_iter_advance(i, maxsize);
	return maxsize;
}

/*
 * Extract a list of contiguous pages from an ITER_BVEC iterator.  This does
 * not get references on the pages, nor does it get a pin on them.
 */
static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
					   struct page ***pages, size_t maxsize,
					   unsigned int maxpages,
					   iov_iter_extraction_t extraction_flags,
					   size_t *offset0)
{
	struct page **p, *page;
	size_t skip = i->iov_offset, offset, size;
	int k;

	for (;;) {
		if (i->nr_segs == 0)
			return 0;
		size = min(maxsize, i->bvec->bv_len - skip);
		if (size)
			break;
		i->iov_offset = 0;
		i->nr_segs--;
		i->bvec++;
		skip = 0;
	}

	skip += i->bvec->bv_offset;
	page = i->bvec->bv_page + skip / PAGE_SIZE;
	offset = skip % PAGE_SIZE;
	*offset0 = offset;

	maxpages = want_pages_array(pages, size, offset, maxpages);
	if (!maxpages)
		return -ENOMEM;
	p = *pages;
	for (k = 0; k < maxpages; k++)
		p[k] = page + k;

	size = min_t(size_t, size, maxpages * PAGE_SIZE - offset);
	iov_iter_advance(i, size);
	return size;
}

/*
 * Extract a list of virtually contiguous pages from an ITER_KVEC iterator.
 * This does not get references on the pages, nor does it get a pin on them.
 */
static ssize_t iov_iter_extract_kvec_pages(struct iov_iter *i,
					   struct page ***pages, size_t maxsize,
					   unsigned int maxpages,
					   iov_iter_extraction_t extraction_flags,
					   size_t *offset0)
{
	struct page **p, *page;
	const void *kaddr;
	size_t skip = i->iov_offset, offset, len, size;
	int k;

	for (;;) {
		if (i->nr_segs == 0)
			return 0;
		size = min(maxsize, i->kvec->iov_len - skip);
		if (size)
			break;
		i->iov_offset = 0;
		i->nr_segs--;
		i->kvec++;
		skip = 0;
	}

	kaddr = i->kvec->iov_base + skip;
	offset = (unsigned long)kaddr & ~PAGE_MASK;
	*offset0 = offset;

	maxpages = want_pages_array(pages, size, offset, maxpages);
	if (!maxpages)
		return -ENOMEM;
	p = *pages;

	kaddr -= offset;
	len = offset + size;
	for (k = 0; k < maxpages; k++) {
		size_t seg = min_t(size_t, len, PAGE_SIZE);

		if (is_vmalloc_or_module_addr(kaddr))
			page = vmalloc_to_page(kaddr);
		else
			page = virt_to_page(kaddr);

		p[k] = page;
		len -= seg;
		kaddr += PAGE_SIZE;
	}

	size = min_t(size_t, size, maxpages * PAGE_SIZE - offset);
	iov_iter_advance(i, size);
	return size;
}

/*
 * Extract a list of contiguous pages from a user iterator and get a pin on
 * each of them.  This should only be used if the iterator is user-backed
 * (IOBUF/UBUF).
 *
 * It does not get refs on the pages, but the pages must be unpinned by the
 * caller once the transfer is complete.
 *
 * This is safe to be used where background IO/DMA *is* going to be modifying
 * the buffer; using a pin rather than a ref makes forces fork() to give the
 * child a copy of the page.
 */
static ssize_t iov_iter_extract_user_pages(struct iov_iter *i,
					   struct page ***pages,
					   size_t maxsize,
					   unsigned int maxpages,
					   iov_iter_extraction_t extraction_flags,
					   size_t *offset0)
{
	unsigned long addr;
	unsigned int gup_flags = 0;
	size_t offset;
	int res;

	if (i->data_source == ITER_DEST)
		gup_flags |= FOLL_WRITE;
	if (extraction_flags & ITER_ALLOW_P2PDMA)
		gup_flags |= FOLL_PCI_P2PDMA;
	if (i->nofault)
		gup_flags |= FOLL_NOFAULT;

	addr = first_iovec_segment(i, &maxsize);
	*offset0 = offset = addr % PAGE_SIZE;
	addr &= PAGE_MASK;
	maxpages = want_pages_array(pages, maxsize, offset, maxpages);
	if (!maxpages)
		return -ENOMEM;
	res = pin_user_pages_fast(addr, maxpages, gup_flags, *pages);
	if (unlikely(res <= 0))
		return res;
	maxsize = min_t(size_t, maxsize, res * PAGE_SIZE - offset);
	iov_iter_advance(i, maxsize);
	return maxsize;
}

/**
 * iov_iter_extract_pages - Extract a list of contiguous pages from an iterator
 * @i: The iterator to extract from
 * @pages: Where to return the list of pages
 * @maxsize: The maximum amount of iterator to extract
 * @maxpages: The maximum size of the list of pages
 * @extraction_flags: Flags to qualify request
 * @offset0: Where to return the starting offset into (*@pages)[0]
 *
 * Extract a list of contiguous pages from the current point of the iterator,
 * advancing the iterator.  The maximum number of pages and the maximum amount
 * of page contents can be set.
 *
 * If *@pages is NULL, a page list will be allocated to the required size and
 * *@pages will be set to its base.  If *@pages is not NULL, it will be assumed
 * that the caller allocated a page list at least @maxpages in size and this
 * will be filled in.
 *
 * @extraction_flags can have ITER_ALLOW_P2PDMA set to request peer-to-peer DMA
 * be allowed on the pages extracted.
 *
 * The iov_iter_extract_will_pin() function can be used to query how cleanup
 * should be performed.
 *
 * Extra refs or pins on the pages may be obtained as follows:
 *
 *  (*) If the iterator is user-backed (ITER_IOVEC/ITER_UBUF), pins will be
 *      added to the pages, but refs will not be taken.
 *      iov_iter_extract_will_pin() will return true.
 *
 *  (*) If the iterator is ITER_KVEC, ITER_BVEC or ITER_XARRAY, the pages are
 *      merely listed; no extra refs or pins are obtained.
 *      iov_iter_extract_will_pin() will return 0.
 *
 * Note also:
 *
 *  (*) Use with ITER_DISCARD is not supported as that has no content.
 *
 * On success, the function sets *@pages to the new pagelist, if allocated, and
 * sets *offset0 to the offset into the first page.
 *
 * It may also return -ENOMEM and -EFAULT.
 */
ssize_t iov_iter_extract_pages(struct iov_iter *i,
			       struct page ***pages,
			       size_t maxsize,
			       unsigned int maxpages,
			       iov_iter_extraction_t extraction_flags,
			       size_t *offset0)
{
	maxsize = min_t(size_t, min_t(size_t, maxsize, i->count), MAX_RW_COUNT);
	if (!maxsize)
		return 0;

	if (likely(user_backed_iter(i)))
		return iov_iter_extract_user_pages(i, pages, maxsize,
						   maxpages, extraction_flags,
						   offset0);
	if (iov_iter_is_kvec(i))
		return iov_iter_extract_kvec_pages(i, pages, maxsize,
						   maxpages, extraction_flags,
						   offset0);
	if (iov_iter_is_bvec(i))
		return iov_iter_extract_bvec_pages(i, pages, maxsize,
						   maxpages, extraction_flags,
						   offset0);
	if (iov_iter_is_xarray(i))
		return iov_iter_extract_xarray_pages(i, pages, maxsize,
						     maxpages, extraction_flags,
						     offset0);
	return -EFAULT;
}
EXPORT_SYMBOL_GPL(iov_iter_extract_pages);