summaryrefslogtreecommitdiff
path: root/drivers/virtio/virtio_mem.c
blob: 0c2892ec68171d18e1578f3382922372d9b242fd (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
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Virtio-mem device driver.
 *
 * Copyright Red Hat, Inc. 2020
 *
 * Author(s): David Hildenbrand <david@redhat.com>
 */

#include <linux/virtio.h>
#include <linux/virtio_mem.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/memory_hotplug.h>
#include <linux/memory.h>
#include <linux/hrtimer.h>
#include <linux/crash_dump.h>
#include <linux/mutex.h>
#include <linux/bitmap.h>
#include <linux/lockdep.h>
#include <linux/log2.h>

#include <acpi/acpi_numa.h>

static bool unplug_online = true;
module_param(unplug_online, bool, 0644);
MODULE_PARM_DESC(unplug_online, "Try to unplug online memory");

static bool force_bbm;
module_param(force_bbm, bool, 0444);
MODULE_PARM_DESC(force_bbm,
		"Force Big Block Mode. Default is 0 (auto-selection)");

static unsigned long bbm_block_size;
module_param(bbm_block_size, ulong, 0444);
MODULE_PARM_DESC(bbm_block_size,
		 "Big Block size in bytes. Default is 0 (auto-detection).");

static bool bbm_safe_unplug = true;
module_param(bbm_safe_unplug, bool, 0444);
MODULE_PARM_DESC(bbm_safe_unplug,
	     "Use a safe unplug mechanism in BBM, avoiding long/endless loops");

/*
 * virtio-mem currently supports the following modes of operation:
 *
 * * Sub Block Mode (SBM): A Linux memory block spans 2..X subblocks (SB). The
 *   size of a Sub Block (SB) is determined based on the device block size, the
 *   pageblock size, and the maximum allocation granularity of the buddy.
 *   Subblocks within a Linux memory block might either be plugged or unplugged.
 *   Memory is added/removed to Linux MM in Linux memory block granularity.
 *
 * * Big Block Mode (BBM): A Big Block (BB) spans 1..X Linux memory blocks.
 *   Memory is added/removed to Linux MM in Big Block granularity.
 *
 * The mode is determined automatically based on the Linux memory block size
 * and the device block size.
 *
 * User space / core MM (auto onlining) is responsible for onlining added
 * Linux memory blocks - and for selecting a zone. Linux Memory Blocks are
 * always onlined separately, and all memory within a Linux memory block is
 * onlined to the same zone - virtio-mem relies on this behavior.
 */

/*
 * State of a Linux memory block in SBM.
 */
enum virtio_mem_sbm_mb_state {
	/* Unplugged, not added to Linux. Can be reused later. */
	VIRTIO_MEM_SBM_MB_UNUSED = 0,
	/* (Partially) plugged, not added to Linux. Error on add_memory(). */
	VIRTIO_MEM_SBM_MB_PLUGGED,
	/* Fully plugged, fully added to Linux, offline. */
	VIRTIO_MEM_SBM_MB_OFFLINE,
	/* Partially plugged, fully added to Linux, offline. */
	VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL,
	/* Fully plugged, fully added to Linux, onlined to a kernel zone. */
	VIRTIO_MEM_SBM_MB_KERNEL,
	/* Partially plugged, fully added to Linux, online to a kernel zone */
	VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL,
	/* Fully plugged, fully added to Linux, onlined to ZONE_MOVABLE. */
	VIRTIO_MEM_SBM_MB_MOVABLE,
	/* Partially plugged, fully added to Linux, onlined to ZONE_MOVABLE. */
	VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL,
	VIRTIO_MEM_SBM_MB_COUNT
};

/*
 * State of a Big Block (BB) in BBM, covering 1..X Linux memory blocks.
 */
enum virtio_mem_bbm_bb_state {
	/* Unplugged, not added to Linux. Can be reused later. */
	VIRTIO_MEM_BBM_BB_UNUSED = 0,
	/* Plugged, not added to Linux. Error on add_memory(). */
	VIRTIO_MEM_BBM_BB_PLUGGED,
	/* Plugged and added to Linux. */
	VIRTIO_MEM_BBM_BB_ADDED,
	/* All online parts are fake-offline, ready to remove. */
	VIRTIO_MEM_BBM_BB_FAKE_OFFLINE,
	VIRTIO_MEM_BBM_BB_COUNT
};

struct virtio_mem {
	struct virtio_device *vdev;

	/* We might first have to unplug all memory when starting up. */
	bool unplug_all_required;

	/* Workqueue that processes the plug/unplug requests. */
	struct work_struct wq;
	atomic_t wq_active;
	atomic_t config_changed;

	/* Virtqueue for guest->host requests. */
	struct virtqueue *vq;

	/* Wait for a host response to a guest request. */
	wait_queue_head_t host_resp;

	/* Space for one guest request and the host response. */
	struct virtio_mem_req req;
	struct virtio_mem_resp resp;

	/* The current size of the device. */
	uint64_t plugged_size;
	/* The requested size of the device. */
	uint64_t requested_size;

	/* The device block size (for communicating with the device). */
	uint64_t device_block_size;
	/* The determined node id for all memory of the device. */
	int nid;
	/* Physical start address of the memory region. */
	uint64_t addr;
	/* Maximum region size in bytes. */
	uint64_t region_size;

	/* The parent resource for all memory added via this device. */
	struct resource *parent_resource;
	/*
	 * Copy of "System RAM (virtio_mem)" to be used for
	 * add_memory_driver_managed().
	 */
	const char *resource_name;
	/* Memory group identification. */
	int mgid;

	/*
	 * We don't want to add too much memory if it's not getting onlined,
	 * to avoid running OOM. Besides this threshold, we allow to have at
	 * least two offline blocks at a time (whatever is bigger).
	 */
#define VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD		(1024 * 1024 * 1024)
	atomic64_t offline_size;
	uint64_t offline_threshold;

	/* If set, the driver is in SBM, otherwise in BBM. */
	bool in_sbm;

	union {
		struct {
			/* Id of the first memory block of this device. */
			unsigned long first_mb_id;
			/* Id of the last usable memory block of this device. */
			unsigned long last_usable_mb_id;
			/* Id of the next memory bock to prepare when needed. */
			unsigned long next_mb_id;

			/* The subblock size. */
			uint64_t sb_size;
			/* The number of subblocks per Linux memory block. */
			uint32_t sbs_per_mb;

			/* Summary of all memory block states. */
			unsigned long mb_count[VIRTIO_MEM_SBM_MB_COUNT];

			/*
			 * One byte state per memory block. Allocated via
			 * vmalloc(). Resized (alloc+copy+free) on demand.
			 *
			 * With 128 MiB memory blocks, we have states for 512
			 * GiB of memory in one 4 KiB page.
			 */
			uint8_t *mb_states;

			/*
			 * Bitmap: one bit per subblock. Allocated similar to
			 * sbm.mb_states.
			 *
			 * A set bit means the corresponding subblock is
			 * plugged, otherwise it's unblocked.
			 *
			 * With 4 MiB subblocks, we manage 128 GiB of memory
			 * in one 4 KiB page.
			 */
			unsigned long *sb_states;
		} sbm;

		struct {
			/* Id of the first big block of this device. */
			unsigned long first_bb_id;
			/* Id of the last usable big block of this device. */
			unsigned long last_usable_bb_id;
			/* Id of the next device bock to prepare when needed. */
			unsigned long next_bb_id;

			/* Summary of all big block states. */
			unsigned long bb_count[VIRTIO_MEM_BBM_BB_COUNT];

			/* One byte state per big block. See sbm.mb_states. */
			uint8_t *bb_states;

			/* The block size used for plugging/adding/removing. */
			uint64_t bb_size;
		} bbm;
	};

	/*
	 * Mutex that protects the sbm.mb_count, sbm.mb_states,
	 * sbm.sb_states, bbm.bb_count, and bbm.bb_states
	 *
	 * When this lock is held the pointers can't change, ONLINE and
	 * OFFLINE blocks can't change the state and no subblocks will get
	 * plugged/unplugged.
	 *
	 * In kdump mode, used to serialize requests, last_block_addr and
	 * last_block_plugged.
	 */
	struct mutex hotplug_mutex;
	bool hotplug_active;

	/* An error occurred we cannot handle - stop processing requests. */
	bool broken;

	/* Cached valued of is_kdump_kernel() when the device was probed. */
	bool in_kdump;

	/* The driver is being removed. */
	spinlock_t removal_lock;
	bool removing;

	/* Timer for retrying to plug/unplug memory. */
	struct hrtimer retry_timer;
	unsigned int retry_timer_ms;
#define VIRTIO_MEM_RETRY_TIMER_MIN_MS		50000
#define VIRTIO_MEM_RETRY_TIMER_MAX_MS		300000

	/* Memory notifier (online/offline events). */
	struct notifier_block memory_notifier;

#ifdef CONFIG_PROC_VMCORE
	/* vmcore callback for /proc/vmcore handling in kdump mode */
	struct vmcore_cb vmcore_cb;
	uint64_t last_block_addr;
	bool last_block_plugged;
#endif /* CONFIG_PROC_VMCORE */

	/* Next device in the list of virtio-mem devices. */
	struct list_head next;
};

/*
 * We have to share a single online_page callback among all virtio-mem
 * devices. We use RCU to iterate the list in the callback.
 */
static DEFINE_MUTEX(virtio_mem_mutex);
static LIST_HEAD(virtio_mem_devices);

static void virtio_mem_online_page_cb(struct page *page, unsigned int order);
static void virtio_mem_fake_offline_going_offline(unsigned long pfn,
						  unsigned long nr_pages);
static void virtio_mem_fake_offline_cancel_offline(unsigned long pfn,
						   unsigned long nr_pages);
static void virtio_mem_retry(struct virtio_mem *vm);
static int virtio_mem_create_resource(struct virtio_mem *vm);
static void virtio_mem_delete_resource(struct virtio_mem *vm);

/*
 * Register a virtio-mem device so it will be considered for the online_page
 * callback.
 */
static int register_virtio_mem_device(struct virtio_mem *vm)
{
	int rc = 0;

	/* First device registers the callback. */
	mutex_lock(&virtio_mem_mutex);
	if (list_empty(&virtio_mem_devices))
		rc = set_online_page_callback(&virtio_mem_online_page_cb);
	if (!rc)
		list_add_rcu(&vm->next, &virtio_mem_devices);
	mutex_unlock(&virtio_mem_mutex);

	return rc;
}

/*
 * Unregister a virtio-mem device so it will no longer be considered for the
 * online_page callback.
 */
static void unregister_virtio_mem_device(struct virtio_mem *vm)
{
	/* Last device unregisters the callback. */
	mutex_lock(&virtio_mem_mutex);
	list_del_rcu(&vm->next);
	if (list_empty(&virtio_mem_devices))
		restore_online_page_callback(&virtio_mem_online_page_cb);
	mutex_unlock(&virtio_mem_mutex);

	synchronize_rcu();
}

/*
 * Calculate the memory block id of a given address.
 */
static unsigned long virtio_mem_phys_to_mb_id(unsigned long addr)
{
	return addr / memory_block_size_bytes();
}

/*
 * Calculate the physical start address of a given memory block id.
 */
static unsigned long virtio_mem_mb_id_to_phys(unsigned long mb_id)
{
	return mb_id * memory_block_size_bytes();
}

/*
 * Calculate the big block id of a given address.
 */
static unsigned long virtio_mem_phys_to_bb_id(struct virtio_mem *vm,
					      uint64_t addr)
{
	return addr / vm->bbm.bb_size;
}

/*
 * Calculate the physical start address of a given big block id.
 */
static uint64_t virtio_mem_bb_id_to_phys(struct virtio_mem *vm,
					 unsigned long bb_id)
{
	return bb_id * vm->bbm.bb_size;
}

/*
 * Calculate the subblock id of a given address.
 */
static unsigned long virtio_mem_phys_to_sb_id(struct virtio_mem *vm,
					      unsigned long addr)
{
	const unsigned long mb_id = virtio_mem_phys_to_mb_id(addr);
	const unsigned long mb_addr = virtio_mem_mb_id_to_phys(mb_id);

	return (addr - mb_addr) / vm->sbm.sb_size;
}

/*
 * Set the state of a big block, taking care of the state counter.
 */
static void virtio_mem_bbm_set_bb_state(struct virtio_mem *vm,
					unsigned long bb_id,
					enum virtio_mem_bbm_bb_state state)
{
	const unsigned long idx = bb_id - vm->bbm.first_bb_id;
	enum virtio_mem_bbm_bb_state old_state;

	old_state = vm->bbm.bb_states[idx];
	vm->bbm.bb_states[idx] = state;

	BUG_ON(vm->bbm.bb_count[old_state] == 0);
	vm->bbm.bb_count[old_state]--;
	vm->bbm.bb_count[state]++;
}

/*
 * Get the state of a big block.
 */
static enum virtio_mem_bbm_bb_state virtio_mem_bbm_get_bb_state(struct virtio_mem *vm,
								unsigned long bb_id)
{
	return vm->bbm.bb_states[bb_id - vm->bbm.first_bb_id];
}

/*
 * Prepare the big block state array for the next big block.
 */
static int virtio_mem_bbm_bb_states_prepare_next_bb(struct virtio_mem *vm)
{
	unsigned long old_bytes = vm->bbm.next_bb_id - vm->bbm.first_bb_id;
	unsigned long new_bytes = old_bytes + 1;
	int old_pages = PFN_UP(old_bytes);
	int new_pages = PFN_UP(new_bytes);
	uint8_t *new_array;

	if (vm->bbm.bb_states && old_pages == new_pages)
		return 0;

	new_array = vzalloc(new_pages * PAGE_SIZE);
	if (!new_array)
		return -ENOMEM;

	mutex_lock(&vm->hotplug_mutex);
	if (vm->bbm.bb_states)
		memcpy(new_array, vm->bbm.bb_states, old_pages * PAGE_SIZE);
	vfree(vm->bbm.bb_states);
	vm->bbm.bb_states = new_array;
	mutex_unlock(&vm->hotplug_mutex);

	return 0;
}

#define virtio_mem_bbm_for_each_bb(_vm, _bb_id, _state) \
	for (_bb_id = vm->bbm.first_bb_id; \
	     _bb_id < vm->bbm.next_bb_id && _vm->bbm.bb_count[_state]; \
	     _bb_id++) \
		if (virtio_mem_bbm_get_bb_state(_vm, _bb_id) == _state)

#define virtio_mem_bbm_for_each_bb_rev(_vm, _bb_id, _state) \
	for (_bb_id = vm->bbm.next_bb_id - 1; \
	     _bb_id >= vm->bbm.first_bb_id && _vm->bbm.bb_count[_state]; \
	     _bb_id--) \
		if (virtio_mem_bbm_get_bb_state(_vm, _bb_id) == _state)

/*
 * Set the state of a memory block, taking care of the state counter.
 */
static void virtio_mem_sbm_set_mb_state(struct virtio_mem *vm,
					unsigned long mb_id, uint8_t state)
{
	const unsigned long idx = mb_id - vm->sbm.first_mb_id;
	uint8_t old_state;

	old_state = vm->sbm.mb_states[idx];
	vm->sbm.mb_states[idx] = state;

	BUG_ON(vm->sbm.mb_count[old_state] == 0);
	vm->sbm.mb_count[old_state]--;
	vm->sbm.mb_count[state]++;
}

/*
 * Get the state of a memory block.
 */
static uint8_t virtio_mem_sbm_get_mb_state(struct virtio_mem *vm,
					   unsigned long mb_id)
{
	const unsigned long idx = mb_id - vm->sbm.first_mb_id;

	return vm->sbm.mb_states[idx];
}

/*
 * Prepare the state array for the next memory block.
 */
static int virtio_mem_sbm_mb_states_prepare_next_mb(struct virtio_mem *vm)
{
	int old_pages = PFN_UP(vm->sbm.next_mb_id - vm->sbm.first_mb_id);
	int new_pages = PFN_UP(vm->sbm.next_mb_id - vm->sbm.first_mb_id + 1);
	uint8_t *new_array;

	if (vm->sbm.mb_states && old_pages == new_pages)
		return 0;

	new_array = vzalloc(new_pages * PAGE_SIZE);
	if (!new_array)
		return -ENOMEM;

	mutex_lock(&vm->hotplug_mutex);
	if (vm->sbm.mb_states)
		memcpy(new_array, vm->sbm.mb_states, old_pages * PAGE_SIZE);
	vfree(vm->sbm.mb_states);
	vm->sbm.mb_states = new_array;
	mutex_unlock(&vm->hotplug_mutex);

	return 0;
}

#define virtio_mem_sbm_for_each_mb(_vm, _mb_id, _state) \
	for (_mb_id = _vm->sbm.first_mb_id; \
	     _mb_id < _vm->sbm.next_mb_id && _vm->sbm.mb_count[_state]; \
	     _mb_id++) \
		if (virtio_mem_sbm_get_mb_state(_vm, _mb_id) == _state)

#define virtio_mem_sbm_for_each_mb_rev(_vm, _mb_id, _state) \
	for (_mb_id = _vm->sbm.next_mb_id - 1; \
	     _mb_id >= _vm->sbm.first_mb_id && _vm->sbm.mb_count[_state]; \
	     _mb_id--) \
		if (virtio_mem_sbm_get_mb_state(_vm, _mb_id) == _state)

/*
 * Calculate the bit number in the subblock bitmap for the given subblock
 * inside the given memory block.
 */
static int virtio_mem_sbm_sb_state_bit_nr(struct virtio_mem *vm,
					  unsigned long mb_id, int sb_id)
{
	return (mb_id - vm->sbm.first_mb_id) * vm->sbm.sbs_per_mb + sb_id;
}

/*
 * Mark all selected subblocks plugged.
 *
 * Will not modify the state of the memory block.
 */
static void virtio_mem_sbm_set_sb_plugged(struct virtio_mem *vm,
					  unsigned long mb_id, int sb_id,
					  int count)
{
	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

	__bitmap_set(vm->sbm.sb_states, bit, count);
}

/*
 * Mark all selected subblocks unplugged.
 *
 * Will not modify the state of the memory block.
 */
static void virtio_mem_sbm_set_sb_unplugged(struct virtio_mem *vm,
					    unsigned long mb_id, int sb_id,
					    int count)
{
	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

	__bitmap_clear(vm->sbm.sb_states, bit, count);
}

/*
 * Test if all selected subblocks are plugged.
 */
static bool virtio_mem_sbm_test_sb_plugged(struct virtio_mem *vm,
					   unsigned long mb_id, int sb_id,
					   int count)
{
	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

	if (count == 1)
		return test_bit(bit, vm->sbm.sb_states);

	/* TODO: Helper similar to bitmap_set() */
	return find_next_zero_bit(vm->sbm.sb_states, bit + count, bit) >=
	       bit + count;
}

/*
 * Test if all selected subblocks are unplugged.
 */
static bool virtio_mem_sbm_test_sb_unplugged(struct virtio_mem *vm,
					     unsigned long mb_id, int sb_id,
					     int count)
{
	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

	/* TODO: Helper similar to bitmap_set() */
	return find_next_bit(vm->sbm.sb_states, bit + count, bit) >=
	       bit + count;
}

/*
 * Find the first unplugged subblock. Returns vm->sbm.sbs_per_mb in case there is
 * none.
 */
static int virtio_mem_sbm_first_unplugged_sb(struct virtio_mem *vm,
					    unsigned long mb_id)
{
	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, 0);

	return find_next_zero_bit(vm->sbm.sb_states,
				  bit + vm->sbm.sbs_per_mb, bit) - bit;
}

/*
 * Prepare the subblock bitmap for the next memory block.
 */
static int virtio_mem_sbm_sb_states_prepare_next_mb(struct virtio_mem *vm)
{
	const unsigned long old_nb_mb = vm->sbm.next_mb_id - vm->sbm.first_mb_id;
	const unsigned long old_nb_bits = old_nb_mb * vm->sbm.sbs_per_mb;
	const unsigned long new_nb_bits = (old_nb_mb + 1) * vm->sbm.sbs_per_mb;
	int old_pages = PFN_UP(BITS_TO_LONGS(old_nb_bits) * sizeof(long));
	int new_pages = PFN_UP(BITS_TO_LONGS(new_nb_bits) * sizeof(long));
	unsigned long *new_bitmap, *old_bitmap;

	if (vm->sbm.sb_states && old_pages == new_pages)
		return 0;

	new_bitmap = vzalloc(new_pages * PAGE_SIZE);
	if (!new_bitmap)
		return -ENOMEM;

	mutex_lock(&vm->hotplug_mutex);
	if (vm->sbm.sb_states)
		memcpy(new_bitmap, vm->sbm.sb_states, old_pages * PAGE_SIZE);

	old_bitmap = vm->sbm.sb_states;
	vm->sbm.sb_states = new_bitmap;
	mutex_unlock(&vm->hotplug_mutex);

	vfree(old_bitmap);
	return 0;
}

/*
 * Test if we could add memory without creating too much offline memory -
 * to avoid running OOM if memory is getting onlined deferred.
 */
static bool virtio_mem_could_add_memory(struct virtio_mem *vm, uint64_t size)
{
	if (WARN_ON_ONCE(size > vm->offline_threshold))
		return false;

	return atomic64_read(&vm->offline_size) + size <= vm->offline_threshold;
}

/*
 * Try adding memory to Linux. Will usually only fail if out of memory.
 *
 * Must not be called with the vm->hotplug_mutex held (possible deadlock with
 * onlining code).
 *
 * Will not modify the state of memory blocks in virtio-mem.
 */
static int virtio_mem_add_memory(struct virtio_mem *vm, uint64_t addr,
				 uint64_t size)
{
	int rc;

	/*
	 * When force-unloading the driver and we still have memory added to
	 * Linux, the resource name has to stay.
	 */
	if (!vm->resource_name) {
		vm->resource_name = kstrdup_const("System RAM (virtio_mem)",
						  GFP_KERNEL);
		if (!vm->resource_name)
			return -ENOMEM;
	}

	dev_dbg(&vm->vdev->dev, "adding memory: 0x%llx - 0x%llx\n", addr,
		addr + size - 1);
	/* Memory might get onlined immediately. */
	atomic64_add(size, &vm->offline_size);
	rc = add_memory_driver_managed(vm->mgid, addr, size, vm->resource_name,
				       MHP_MERGE_RESOURCE | MHP_NID_IS_MGID);
	if (rc) {
		atomic64_sub(size, &vm->offline_size);
		dev_warn(&vm->vdev->dev, "adding memory failed: %d\n", rc);
		/*
		 * TODO: Linux MM does not properly clean up yet in all cases
		 * where adding of memory failed - especially on -ENOMEM.
		 */
	}
	return rc;
}

/*
 * See virtio_mem_add_memory(): Try adding a single Linux memory block.
 */
static int virtio_mem_sbm_add_mb(struct virtio_mem *vm, unsigned long mb_id)
{
	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
	const uint64_t size = memory_block_size_bytes();

	return virtio_mem_add_memory(vm, addr, size);
}

/*
 * See virtio_mem_add_memory(): Try adding a big block.
 */
static int virtio_mem_bbm_add_bb(struct virtio_mem *vm, unsigned long bb_id)
{
	const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
	const uint64_t size = vm->bbm.bb_size;

	return virtio_mem_add_memory(vm, addr, size);
}

/*
 * Try removing memory from Linux. Will only fail if memory blocks aren't
 * offline.
 *
 * Must not be called with the vm->hotplug_mutex held (possible deadlock with
 * onlining code).
 *
 * Will not modify the state of memory blocks in virtio-mem.
 */
static int virtio_mem_remove_memory(struct virtio_mem *vm, uint64_t addr,
				    uint64_t size)
{
	int rc;

	dev_dbg(&vm->vdev->dev, "removing memory: 0x%llx - 0x%llx\n", addr,
		addr + size - 1);
	rc = remove_memory(addr, size);
	if (!rc) {
		atomic64_sub(size, &vm->offline_size);
		/*
		 * We might have freed up memory we can now unplug, retry
		 * immediately instead of waiting.
		 */
		virtio_mem_retry(vm);
	} else {
		dev_dbg(&vm->vdev->dev, "removing memory failed: %d\n", rc);
	}
	return rc;
}

/*
 * See virtio_mem_remove_memory(): Try removing a single Linux memory block.
 */
static int virtio_mem_sbm_remove_mb(struct virtio_mem *vm, unsigned long mb_id)
{
	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
	const uint64_t size = memory_block_size_bytes();

	return virtio_mem_remove_memory(vm, addr, size);
}

/*
 * Try offlining and removing memory from Linux.
 *
 * Must not be called with the vm->hotplug_mutex held (possible deadlock with
 * onlining code).
 *
 * Will not modify the state of memory blocks in virtio-mem.
 */
static int virtio_mem_offline_and_remove_memory(struct virtio_mem *vm,
						uint64_t addr,
						uint64_t size)
{
	int rc;

	dev_dbg(&vm->vdev->dev,
		"offlining and removing memory: 0x%llx - 0x%llx\n", addr,
		addr + size - 1);

	rc = offline_and_remove_memory(addr, size);
	if (!rc) {
		atomic64_sub(size, &vm->offline_size);
		/*
		 * We might have freed up memory we can now unplug, retry
		 * immediately instead of waiting.
		 */
		virtio_mem_retry(vm);
	} else {
		dev_dbg(&vm->vdev->dev,
			"offlining and removing memory failed: %d\n", rc);
	}
	return rc;
}

/*
 * See virtio_mem_offline_and_remove_memory(): Try offlining and removing
 * a single Linux memory block.
 */
static int virtio_mem_sbm_offline_and_remove_mb(struct virtio_mem *vm,
						unsigned long mb_id)
{
	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
	const uint64_t size = memory_block_size_bytes();

	return virtio_mem_offline_and_remove_memory(vm, addr, size);
}

/*
 * See virtio_mem_offline_and_remove_memory(): Try to offline and remove a
 * all Linux memory blocks covered by the big block.
 */
static int virtio_mem_bbm_offline_and_remove_bb(struct virtio_mem *vm,
						unsigned long bb_id)
{
	const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
	const uint64_t size = vm->bbm.bb_size;

	return virtio_mem_offline_and_remove_memory(vm, addr, size);
}

/*
 * Trigger the workqueue so the device can perform its magic.
 */
static void virtio_mem_retry(struct virtio_mem *vm)
{
	unsigned long flags;

	spin_lock_irqsave(&vm->removal_lock, flags);
	if (!vm->removing)
		queue_work(system_freezable_wq, &vm->wq);
	spin_unlock_irqrestore(&vm->removal_lock, flags);
}

static int virtio_mem_translate_node_id(struct virtio_mem *vm, uint16_t node_id)
{
	int node = NUMA_NO_NODE;

#if defined(CONFIG_ACPI_NUMA)
	if (virtio_has_feature(vm->vdev, VIRTIO_MEM_F_ACPI_PXM))
		node = pxm_to_node(node_id);
#endif
	return node;
}

/*
 * Test if a virtio-mem device overlaps with the given range. Can be called
 * from (notifier) callbacks lockless.
 */
static bool virtio_mem_overlaps_range(struct virtio_mem *vm, uint64_t start,
				      uint64_t size)
{
	return start < vm->addr + vm->region_size && vm->addr < start + size;
}

/*
 * Test if a virtio-mem device contains a given range. Can be called from
 * (notifier) callbacks lockless.
 */
static bool virtio_mem_contains_range(struct virtio_mem *vm, uint64_t start,
				      uint64_t size)
{
	return start >= vm->addr && start + size <= vm->addr + vm->region_size;
}

static int virtio_mem_sbm_notify_going_online(struct virtio_mem *vm,
					      unsigned long mb_id)
{
	switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
	case VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL:
	case VIRTIO_MEM_SBM_MB_OFFLINE:
		return NOTIFY_OK;
	default:
		break;
	}
	dev_warn_ratelimited(&vm->vdev->dev,
			     "memory block onlining denied\n");
	return NOTIFY_BAD;
}

static void virtio_mem_sbm_notify_offline(struct virtio_mem *vm,
					  unsigned long mb_id)
{
	switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
	case VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL:
	case VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL:
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL);
		break;
	case VIRTIO_MEM_SBM_MB_KERNEL:
	case VIRTIO_MEM_SBM_MB_MOVABLE:
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_OFFLINE);
		break;
	default:
		BUG();
		break;
	}
}

static void virtio_mem_sbm_notify_online(struct virtio_mem *vm,
					 unsigned long mb_id,
					 unsigned long start_pfn)
{
	const bool is_movable = is_zone_movable_page(pfn_to_page(start_pfn));
	int new_state;

	switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
	case VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL:
		new_state = VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL;
		if (is_movable)
			new_state = VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL;
		break;
	case VIRTIO_MEM_SBM_MB_OFFLINE:
		new_state = VIRTIO_MEM_SBM_MB_KERNEL;
		if (is_movable)
			new_state = VIRTIO_MEM_SBM_MB_MOVABLE;
		break;
	default:
		BUG();
		break;
	}
	virtio_mem_sbm_set_mb_state(vm, mb_id, new_state);
}

static void virtio_mem_sbm_notify_going_offline(struct virtio_mem *vm,
						unsigned long mb_id)
{
	const unsigned long nr_pages = PFN_DOWN(vm->sbm.sb_size);
	unsigned long pfn;
	int sb_id;

	for (sb_id = 0; sb_id < vm->sbm.sbs_per_mb; sb_id++) {
		if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
			continue;
		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
			       sb_id * vm->sbm.sb_size);
		virtio_mem_fake_offline_going_offline(pfn, nr_pages);
	}
}

static void virtio_mem_sbm_notify_cancel_offline(struct virtio_mem *vm,
						 unsigned long mb_id)
{
	const unsigned long nr_pages = PFN_DOWN(vm->sbm.sb_size);
	unsigned long pfn;
	int sb_id;

	for (sb_id = 0; sb_id < vm->sbm.sbs_per_mb; sb_id++) {
		if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
			continue;
		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
			       sb_id * vm->sbm.sb_size);
		virtio_mem_fake_offline_cancel_offline(pfn, nr_pages);
	}
}

static void virtio_mem_bbm_notify_going_offline(struct virtio_mem *vm,
						unsigned long bb_id,
						unsigned long pfn,
						unsigned long nr_pages)
{
	/*
	 * When marked as "fake-offline", all online memory of this device block
	 * is allocated by us. Otherwise, we don't have any memory allocated.
	 */
	if (virtio_mem_bbm_get_bb_state(vm, bb_id) !=
	    VIRTIO_MEM_BBM_BB_FAKE_OFFLINE)
		return;
	virtio_mem_fake_offline_going_offline(pfn, nr_pages);
}

static void virtio_mem_bbm_notify_cancel_offline(struct virtio_mem *vm,
						 unsigned long bb_id,
						 unsigned long pfn,
						 unsigned long nr_pages)
{
	if (virtio_mem_bbm_get_bb_state(vm, bb_id) !=
	    VIRTIO_MEM_BBM_BB_FAKE_OFFLINE)
		return;
	virtio_mem_fake_offline_cancel_offline(pfn, nr_pages);
}

/*
 * This callback will either be called synchronously from add_memory() or
 * asynchronously (e.g., triggered via user space). We have to be careful
 * with locking when calling add_memory().
 */
static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
					 unsigned long action, void *arg)
{
	struct virtio_mem *vm = container_of(nb, struct virtio_mem,
					     memory_notifier);
	struct memory_notify *mhp = arg;
	const unsigned long start = PFN_PHYS(mhp->start_pfn);
	const unsigned long size = PFN_PHYS(mhp->nr_pages);
	int rc = NOTIFY_OK;
	unsigned long id;

	if (!virtio_mem_overlaps_range(vm, start, size))
		return NOTIFY_DONE;

	if (vm->in_sbm) {
		id = virtio_mem_phys_to_mb_id(start);
		/*
		 * In SBM, we add memory in separate memory blocks - we expect
		 * it to be onlined/offlined in the same granularity. Bail out
		 * if this ever changes.
		 */
		if (WARN_ON_ONCE(size != memory_block_size_bytes() ||
				 !IS_ALIGNED(start, memory_block_size_bytes())))
			return NOTIFY_BAD;
	} else {
		id = virtio_mem_phys_to_bb_id(vm, start);
		/*
		 * In BBM, we only care about onlining/offlining happening
		 * within a single big block, we don't care about the
		 * actual granularity as we don't track individual Linux
		 * memory blocks.
		 */
		if (WARN_ON_ONCE(id != virtio_mem_phys_to_bb_id(vm, start + size - 1)))
			return NOTIFY_BAD;
	}

	/*
	 * Avoid circular locking lockdep warnings. We lock the mutex
	 * e.g., in MEM_GOING_ONLINE and unlock it in MEM_ONLINE. The
	 * blocking_notifier_call_chain() has it's own lock, which gets unlocked
	 * between both notifier calls and will bail out. False positive.
	 */
	lockdep_off();

	switch (action) {
	case MEM_GOING_OFFLINE:
		mutex_lock(&vm->hotplug_mutex);
		if (vm->removing) {
			rc = notifier_from_errno(-EBUSY);
			mutex_unlock(&vm->hotplug_mutex);
			break;
		}
		vm->hotplug_active = true;
		if (vm->in_sbm)
			virtio_mem_sbm_notify_going_offline(vm, id);
		else
			virtio_mem_bbm_notify_going_offline(vm, id,
							    mhp->start_pfn,
							    mhp->nr_pages);
		break;
	case MEM_GOING_ONLINE:
		mutex_lock(&vm->hotplug_mutex);
		if (vm->removing) {
			rc = notifier_from_errno(-EBUSY);
			mutex_unlock(&vm->hotplug_mutex);
			break;
		}
		vm->hotplug_active = true;
		if (vm->in_sbm)
			rc = virtio_mem_sbm_notify_going_online(vm, id);
		break;
	case MEM_OFFLINE:
		if (vm->in_sbm)
			virtio_mem_sbm_notify_offline(vm, id);

		atomic64_add(size, &vm->offline_size);
		/*
		 * Trigger the workqueue. Now that we have some offline memory,
		 * maybe we can handle pending unplug requests.
		 */
		if (!unplug_online)
			virtio_mem_retry(vm);

		vm->hotplug_active = false;
		mutex_unlock(&vm->hotplug_mutex);
		break;
	case MEM_ONLINE:
		if (vm->in_sbm)
			virtio_mem_sbm_notify_online(vm, id, mhp->start_pfn);

		atomic64_sub(size, &vm->offline_size);
		/*
		 * Start adding more memory once we onlined half of our
		 * threshold. Don't trigger if it's possibly due to our actipn
		 * (e.g., us adding memory which gets onlined immediately from
		 * the core).
		 */
		if (!atomic_read(&vm->wq_active) &&
		    virtio_mem_could_add_memory(vm, vm->offline_threshold / 2))
			virtio_mem_retry(vm);

		vm->hotplug_active = false;
		mutex_unlock(&vm->hotplug_mutex);
		break;
	case MEM_CANCEL_OFFLINE:
		if (!vm->hotplug_active)
			break;
		if (vm->in_sbm)
			virtio_mem_sbm_notify_cancel_offline(vm, id);
		else
			virtio_mem_bbm_notify_cancel_offline(vm, id,
							     mhp->start_pfn,
							     mhp->nr_pages);
		vm->hotplug_active = false;
		mutex_unlock(&vm->hotplug_mutex);
		break;
	case MEM_CANCEL_ONLINE:
		if (!vm->hotplug_active)
			break;
		vm->hotplug_active = false;
		mutex_unlock(&vm->hotplug_mutex);
		break;
	default:
		break;
	}

	lockdep_on();

	return rc;
}

/*
 * Set a range of pages PG_offline. Remember pages that were never onlined
 * (via generic_online_page()) using PageDirty().
 */
static void virtio_mem_set_fake_offline(unsigned long pfn,
					unsigned long nr_pages, bool onlined)
{
	page_offline_begin();
	for (; nr_pages--; pfn++) {
		struct page *page = pfn_to_page(pfn);

		__SetPageOffline(page);
		if (!onlined) {
			SetPageDirty(page);
			/* FIXME: remove after cleanups */
			ClearPageReserved(page);
		}
	}
	page_offline_end();
}

/*
 * Clear PG_offline from a range of pages. If the pages were never onlined,
 * (via generic_online_page()), clear PageDirty().
 */
static void virtio_mem_clear_fake_offline(unsigned long pfn,
					  unsigned long nr_pages, bool onlined)
{
	for (; nr_pages--; pfn++) {
		struct page *page = pfn_to_page(pfn);

		__ClearPageOffline(page);
		if (!onlined)
			ClearPageDirty(page);
	}
}

/*
 * Release a range of fake-offline pages to the buddy, effectively
 * fake-onlining them.
 */
static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages)
{
	unsigned long order = MAX_ORDER - 1;
	unsigned long i;

	/*
	 * We might get called for ranges that don't cover properly aligned
	 * MAX_ORDER - 1 pages; however, we can only online properly aligned
	 * pages with an order of MAX_ORDER - 1 at maximum.
	 */
	while (!IS_ALIGNED(pfn | nr_pages, 1 << order))
		order--;

	for (i = 0; i < nr_pages; i += 1 << order) {
		struct page *page = pfn_to_page(pfn + i);

		/*
		 * If the page is PageDirty(), it was kept fake-offline when
		 * onlining the memory block. Otherwise, it was allocated
		 * using alloc_contig_range(). All pages in a subblock are
		 * alike.
		 */
		if (PageDirty(page)) {
			virtio_mem_clear_fake_offline(pfn + i, 1 << order, false);
			generic_online_page(page, order);
		} else {
			virtio_mem_clear_fake_offline(pfn + i, 1 << order, true);
			free_contig_range(pfn + i, 1 << order);
			adjust_managed_page_count(page, 1 << order);
		}
	}
}

/*
 * Try to allocate a range, marking pages fake-offline, effectively
 * fake-offlining them.
 */
static int virtio_mem_fake_offline(unsigned long pfn, unsigned long nr_pages)
{
	const bool is_movable = is_zone_movable_page(pfn_to_page(pfn));
	int rc, retry_count;

	/*
	 * TODO: We want an alloc_contig_range() mode that tries to allocate
	 * harder (e.g., dealing with temporarily pinned pages, PCP), especially
	 * with ZONE_MOVABLE. So for now, retry a couple of times with
	 * ZONE_MOVABLE before giving up - because that zone is supposed to give
	 * some guarantees.
	 */
	for (retry_count = 0; retry_count < 5; retry_count++) {
		rc = alloc_contig_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE,
					GFP_KERNEL);
		if (rc == -ENOMEM)
			/* whoops, out of memory */
			return rc;
		else if (rc && !is_movable)
			break;
		else if (rc)
			continue;

		virtio_mem_set_fake_offline(pfn, nr_pages, true);
		adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
		return 0;
	}

	return -EBUSY;
}

/*
 * Handle fake-offline pages when memory is going offline - such that the
 * pages can be skipped by mm-core when offlining.
 */
static void virtio_mem_fake_offline_going_offline(unsigned long pfn,
						  unsigned long nr_pages)
{
	struct page *page;
	unsigned long i;

	/*
	 * Drop our reference to the pages so the memory can get offlined
	 * and add the unplugged pages to the managed page counters (so
	 * offlining code can correctly subtract them again).
	 */
	adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
	/* Drop our reference to the pages so the memory can get offlined. */
	for (i = 0; i < nr_pages; i++) {
		page = pfn_to_page(pfn + i);
		if (WARN_ON(!page_ref_dec_and_test(page)))
			dump_page(page, "fake-offline page referenced");
	}
}

/*
 * Handle fake-offline pages when memory offlining is canceled - to undo
 * what we did in virtio_mem_fake_offline_going_offline().
 */
static void virtio_mem_fake_offline_cancel_offline(unsigned long pfn,
						   unsigned long nr_pages)
{
	unsigned long i;

	/*
	 * Get the reference we dropped when going offline and subtract the
	 * unplugged pages from the managed page counters.
	 */
	adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
	for (i = 0; i < nr_pages; i++)
		page_ref_inc(pfn_to_page(pfn + i));
}

static void virtio_mem_online_page(struct virtio_mem *vm,
				   struct page *page, unsigned int order)
{
	const unsigned long start = page_to_phys(page);
	const unsigned long end = start + PFN_PHYS(1 << order);
	unsigned long addr, next, id, sb_id, count;
	bool do_online;

	/*
	 * We can get called with any order up to MAX_ORDER - 1. If our
	 * subblock size is smaller than that and we have a mixture of plugged
	 * and unplugged subblocks within such a page, we have to process in
	 * smaller granularity. In that case we'll adjust the order exactly once
	 * within the loop.
	 */
	for (addr = start; addr < end; ) {
		next = addr + PFN_PHYS(1 << order);

		if (vm->in_sbm) {
			id = virtio_mem_phys_to_mb_id(addr);
			sb_id = virtio_mem_phys_to_sb_id(vm, addr);
			count = virtio_mem_phys_to_sb_id(vm, next - 1) - sb_id + 1;

			if (virtio_mem_sbm_test_sb_plugged(vm, id, sb_id, count)) {
				/* Fully plugged. */
				do_online = true;
			} else if (count == 1 ||
				   virtio_mem_sbm_test_sb_unplugged(vm, id, sb_id, count)) {
				/* Fully unplugged. */
				do_online = false;
			} else {
				/*
				 * Mixture, process sub-blocks instead. This
				 * will be at least the size of a pageblock.
				 * We'll run into this case exactly once.
				 */
				order = ilog2(vm->sbm.sb_size) - PAGE_SHIFT;
				do_online = virtio_mem_sbm_test_sb_plugged(vm, id, sb_id, 1);
				continue;
			}
		} else {
			/*
			 * If the whole block is marked fake offline, keep
			 * everything that way.
			 */
			id = virtio_mem_phys_to_bb_id(vm, addr);
			do_online = virtio_mem_bbm_get_bb_state(vm, id) !=
				    VIRTIO_MEM_BBM_BB_FAKE_OFFLINE;
		}

		if (do_online)
			generic_online_page(pfn_to_page(PFN_DOWN(addr)), order);
		else
			virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order,
						    false);
		addr = next;
	}
}

static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
{
	const unsigned long addr = page_to_phys(page);
	struct virtio_mem *vm;

	rcu_read_lock();
	list_for_each_entry_rcu(vm, &virtio_mem_devices, next) {
		/*
		 * Pages we're onlining will never cross memory blocks and,
		 * therefore, not virtio-mem devices.
		 */
		if (!virtio_mem_contains_range(vm, addr, PFN_PHYS(1 << order)))
			continue;

		/*
		 * virtio_mem_set_fake_offline() might sleep. We can safely
		 * drop the RCU lock at this point because the device
		 * cannot go away. See virtio_mem_remove() how races
		 * between memory onlining and device removal are handled.
		 */
		rcu_read_unlock();

		virtio_mem_online_page(vm, page, order);
		return;
	}
	rcu_read_unlock();

	/* not virtio-mem memory, but e.g., a DIMM. online it */
	generic_online_page(page, order);
}

static uint64_t virtio_mem_send_request(struct virtio_mem *vm,
					const struct virtio_mem_req *req)
{
	struct scatterlist *sgs[2], sg_req, sg_resp;
	unsigned int len;
	int rc;

	/* don't use the request residing on the stack (vaddr) */
	vm->req = *req;

	/* out: buffer for request */
	sg_init_one(&sg_req, &vm->req, sizeof(vm->req));
	sgs[0] = &sg_req;

	/* in: buffer for response */
	sg_init_one(&sg_resp, &vm->resp, sizeof(vm->resp));
	sgs[1] = &sg_resp;

	rc = virtqueue_add_sgs(vm->vq, sgs, 1, 1, vm, GFP_KERNEL);
	if (rc < 0)
		return rc;

	virtqueue_kick(vm->vq);

	/* wait for a response */
	wait_event(vm->host_resp, virtqueue_get_buf(vm->vq, &len));

	return virtio16_to_cpu(vm->vdev, vm->resp.type);
}

static int virtio_mem_send_plug_request(struct virtio_mem *vm, uint64_t addr,
					uint64_t size)
{
	const uint64_t nb_vm_blocks = size / vm->device_block_size;
	const struct virtio_mem_req req = {
		.type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_PLUG),
		.u.plug.addr = cpu_to_virtio64(vm->vdev, addr),
		.u.plug.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
	};
	int rc = -ENOMEM;

	if (atomic_read(&vm->config_changed))
		return -EAGAIN;

	dev_dbg(&vm->vdev->dev, "plugging memory: 0x%llx - 0x%llx\n", addr,
		addr + size - 1);

	switch (virtio_mem_send_request(vm, &req)) {
	case VIRTIO_MEM_RESP_ACK:
		vm->plugged_size += size;
		return 0;
	case VIRTIO_MEM_RESP_NACK:
		rc = -EAGAIN;
		break;
	case VIRTIO_MEM_RESP_BUSY:
		rc = -ETXTBSY;
		break;
	case VIRTIO_MEM_RESP_ERROR:
		rc = -EINVAL;
		break;
	default:
		break;
	}

	dev_dbg(&vm->vdev->dev, "plugging memory failed: %d\n", rc);
	return rc;
}

static int virtio_mem_send_unplug_request(struct virtio_mem *vm, uint64_t addr,
					  uint64_t size)
{
	const uint64_t nb_vm_blocks = size / vm->device_block_size;
	const struct virtio_mem_req req = {
		.type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_UNPLUG),
		.u.unplug.addr = cpu_to_virtio64(vm->vdev, addr),
		.u.unplug.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
	};
	int rc = -ENOMEM;

	if (atomic_read(&vm->config_changed))
		return -EAGAIN;

	dev_dbg(&vm->vdev->dev, "unplugging memory: 0x%llx - 0x%llx\n", addr,
		addr + size - 1);

	switch (virtio_mem_send_request(vm, &req)) {
	case VIRTIO_MEM_RESP_ACK:
		vm->plugged_size -= size;
		return 0;
	case VIRTIO_MEM_RESP_BUSY:
		rc = -ETXTBSY;
		break;
	case VIRTIO_MEM_RESP_ERROR:
		rc = -EINVAL;
		break;
	default:
		break;
	}

	dev_dbg(&vm->vdev->dev, "unplugging memory failed: %d\n", rc);
	return rc;
}

static int virtio_mem_send_unplug_all_request(struct virtio_mem *vm)
{
	const struct virtio_mem_req req = {
		.type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_UNPLUG_ALL),
	};
	int rc = -ENOMEM;

	dev_dbg(&vm->vdev->dev, "unplugging all memory");

	switch (virtio_mem_send_request(vm, &req)) {
	case VIRTIO_MEM_RESP_ACK:
		vm->unplug_all_required = false;
		vm->plugged_size = 0;
		/* usable region might have shrunk */
		atomic_set(&vm->config_changed, 1);
		return 0;
	case VIRTIO_MEM_RESP_BUSY:
		rc = -ETXTBSY;
		break;
	default:
		break;
	}

	dev_dbg(&vm->vdev->dev, "unplugging all memory failed: %d\n", rc);
	return rc;
}

/*
 * Plug selected subblocks. Updates the plugged state, but not the state
 * of the memory block.
 */
static int virtio_mem_sbm_plug_sb(struct virtio_mem *vm, unsigned long mb_id,
				  int sb_id, int count)
{
	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id) +
			      sb_id * vm->sbm.sb_size;
	const uint64_t size = count * vm->sbm.sb_size;
	int rc;

	rc = virtio_mem_send_plug_request(vm, addr, size);
	if (!rc)
		virtio_mem_sbm_set_sb_plugged(vm, mb_id, sb_id, count);
	return rc;
}

/*
 * Unplug selected subblocks. Updates the plugged state, but not the state
 * of the memory block.
 */
static int virtio_mem_sbm_unplug_sb(struct virtio_mem *vm, unsigned long mb_id,
				    int sb_id, int count)
{
	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id) +
			      sb_id * vm->sbm.sb_size;
	const uint64_t size = count * vm->sbm.sb_size;
	int rc;

	rc = virtio_mem_send_unplug_request(vm, addr, size);
	if (!rc)
		virtio_mem_sbm_set_sb_unplugged(vm, mb_id, sb_id, count);
	return rc;
}

/*
 * Request to unplug a big block.
 *
 * Will not modify the state of the big block.
 */
static int virtio_mem_bbm_unplug_bb(struct virtio_mem *vm, unsigned long bb_id)
{
	const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
	const uint64_t size = vm->bbm.bb_size;

	return virtio_mem_send_unplug_request(vm, addr, size);
}

/*
 * Request to plug a big block.
 *
 * Will not modify the state of the big block.
 */
static int virtio_mem_bbm_plug_bb(struct virtio_mem *vm, unsigned long bb_id)
{
	const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
	const uint64_t size = vm->bbm.bb_size;

	return virtio_mem_send_plug_request(vm, addr, size);
}

/*
 * Unplug the desired number of plugged subblocks of a offline or not-added
 * memory block. Will fail if any subblock cannot get unplugged (instead of
 * skipping it).
 *
 * Will not modify the state of the memory block.
 *
 * Note: can fail after some subblocks were unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb_raw(struct virtio_mem *vm,
					    unsigned long mb_id, uint64_t *nb_sb)
{
	int sb_id, count;
	int rc;

	sb_id = vm->sbm.sbs_per_mb - 1;
	while (*nb_sb) {
		/* Find the next candidate subblock */
		while (sb_id >= 0 &&
		       virtio_mem_sbm_test_sb_unplugged(vm, mb_id, sb_id, 1))
			sb_id--;
		if (sb_id < 0)
			break;
		/* Try to unplug multiple subblocks at a time */
		count = 1;
		while (count < *nb_sb && sb_id > 0 &&
		       virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id - 1, 1)) {
			count++;
			sb_id--;
		}

		rc = virtio_mem_sbm_unplug_sb(vm, mb_id, sb_id, count);
		if (rc)
			return rc;
		*nb_sb -= count;
		sb_id--;
	}

	return 0;
}

/*
 * Unplug all plugged subblocks of an offline or not-added memory block.
 *
 * Will not modify the state of the memory block.
 *
 * Note: can fail after some subblocks were unplugged.
 */
static int virtio_mem_sbm_unplug_mb(struct virtio_mem *vm, unsigned long mb_id)
{
	uint64_t nb_sb = vm->sbm.sbs_per_mb;

	return virtio_mem_sbm_unplug_any_sb_raw(vm, mb_id, &nb_sb);
}

/*
 * Prepare tracking data for the next memory block.
 */
static int virtio_mem_sbm_prepare_next_mb(struct virtio_mem *vm,
					  unsigned long *mb_id)
{
	int rc;

	if (vm->sbm.next_mb_id > vm->sbm.last_usable_mb_id)
		return -ENOSPC;

	/* Resize the state array if required. */
	rc = virtio_mem_sbm_mb_states_prepare_next_mb(vm);
	if (rc)
		return rc;

	/* Resize the subblock bitmap if required. */
	rc = virtio_mem_sbm_sb_states_prepare_next_mb(vm);
	if (rc)
		return rc;

	vm->sbm.mb_count[VIRTIO_MEM_SBM_MB_UNUSED]++;
	*mb_id = vm->sbm.next_mb_id++;
	return 0;
}

/*
 * Try to plug the desired number of subblocks and add the memory block
 * to Linux.
 *
 * Will modify the state of the memory block.
 */
static int virtio_mem_sbm_plug_and_add_mb(struct virtio_mem *vm,
					  unsigned long mb_id, uint64_t *nb_sb)
{
	const int count = min_t(int, *nb_sb, vm->sbm.sbs_per_mb);
	int rc;

	if (WARN_ON_ONCE(!count))
		return -EINVAL;

	/*
	 * Plug the requested number of subblocks before adding it to linux,
	 * so that onlining will directly online all plugged subblocks.
	 */
	rc = virtio_mem_sbm_plug_sb(vm, mb_id, 0, count);
	if (rc)
		return rc;

	/*
	 * Mark the block properly offline before adding it to Linux,
	 * so the memory notifiers will find the block in the right state.
	 */
	if (count == vm->sbm.sbs_per_mb)
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_OFFLINE);
	else
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL);

	/* Add the memory block to linux - if that fails, try to unplug. */
	rc = virtio_mem_sbm_add_mb(vm, mb_id);
	if (rc) {
		int new_state = VIRTIO_MEM_SBM_MB_UNUSED;

		if (virtio_mem_sbm_unplug_sb(vm, mb_id, 0, count))
			new_state = VIRTIO_MEM_SBM_MB_PLUGGED;
		virtio_mem_sbm_set_mb_state(vm, mb_id, new_state);
		return rc;
	}

	*nb_sb -= count;
	return 0;
}

/*
 * Try to plug the desired number of subblocks of a memory block that
 * is already added to Linux.
 *
 * Will modify the state of the memory block.
 *
 * Note: Can fail after some subblocks were successfully plugged.
 */
static int virtio_mem_sbm_plug_any_sb(struct virtio_mem *vm,
				      unsigned long mb_id, uint64_t *nb_sb)
{
	const int old_state = virtio_mem_sbm_get_mb_state(vm, mb_id);
	unsigned long pfn, nr_pages;
	int sb_id, count;
	int rc;

	if (WARN_ON_ONCE(!*nb_sb))
		return -EINVAL;

	while (*nb_sb) {
		sb_id = virtio_mem_sbm_first_unplugged_sb(vm, mb_id);
		if (sb_id >= vm->sbm.sbs_per_mb)
			break;
		count = 1;
		while (count < *nb_sb &&
		       sb_id + count < vm->sbm.sbs_per_mb &&
		       !virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id + count, 1))
			count++;

		rc = virtio_mem_sbm_plug_sb(vm, mb_id, sb_id, count);
		if (rc)
			return rc;
		*nb_sb -= count;
		if (old_state == VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL)
			continue;

		/* fake-online the pages if the memory block is online */
		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
			       sb_id * vm->sbm.sb_size);
		nr_pages = PFN_DOWN(count * vm->sbm.sb_size);
		virtio_mem_fake_online(pfn, nr_pages);
	}

	if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, 0, vm->sbm.sbs_per_mb))
		virtio_mem_sbm_set_mb_state(vm, mb_id, old_state - 1);

	return 0;
}

static int virtio_mem_sbm_plug_request(struct virtio_mem *vm, uint64_t diff)
{
	const int mb_states[] = {
		VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL,
		VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL,
		VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL,
	};
	uint64_t nb_sb = diff / vm->sbm.sb_size;
	unsigned long mb_id;
	int rc, i;

	if (!nb_sb)
		return 0;

	/* Don't race with onlining/offlining */
	mutex_lock(&vm->hotplug_mutex);

	for (i = 0; i < ARRAY_SIZE(mb_states); i++) {
		virtio_mem_sbm_for_each_mb(vm, mb_id, mb_states[i]) {
			rc = virtio_mem_sbm_plug_any_sb(vm, mb_id, &nb_sb);
			if (rc || !nb_sb)
				goto out_unlock;
			cond_resched();
		}
	}

	/*
	 * We won't be working on online/offline memory blocks from this point,
	 * so we can't race with memory onlining/offlining. Drop the mutex.
	 */
	mutex_unlock(&vm->hotplug_mutex);

	/* Try to plug and add unused blocks */
	virtio_mem_sbm_for_each_mb(vm, mb_id, VIRTIO_MEM_SBM_MB_UNUSED) {
		if (!virtio_mem_could_add_memory(vm, memory_block_size_bytes()))
			return -ENOSPC;

		rc = virtio_mem_sbm_plug_and_add_mb(vm, mb_id, &nb_sb);
		if (rc || !nb_sb)
			return rc;
		cond_resched();
	}

	/* Try to prepare, plug and add new blocks */
	while (nb_sb) {
		if (!virtio_mem_could_add_memory(vm, memory_block_size_bytes()))
			return -ENOSPC;

		rc = virtio_mem_sbm_prepare_next_mb(vm, &mb_id);
		if (rc)
			return rc;
		rc = virtio_mem_sbm_plug_and_add_mb(vm, mb_id, &nb_sb);
		if (rc)
			return rc;
		cond_resched();
	}

	return 0;
out_unlock:
	mutex_unlock(&vm->hotplug_mutex);
	return rc;
}

/*
 * Plug a big block and add it to Linux.
 *
 * Will modify the state of the big block.
 */
static int virtio_mem_bbm_plug_and_add_bb(struct virtio_mem *vm,
					  unsigned long bb_id)
{
	int rc;

	if (WARN_ON_ONCE(virtio_mem_bbm_get_bb_state(vm, bb_id) !=
			 VIRTIO_MEM_BBM_BB_UNUSED))
		return -EINVAL;

	rc = virtio_mem_bbm_plug_bb(vm, bb_id);
	if (rc)
		return rc;
	virtio_mem_bbm_set_bb_state(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED);

	rc = virtio_mem_bbm_add_bb(vm, bb_id);
	if (rc) {
		if (!virtio_mem_bbm_unplug_bb(vm, bb_id))
			virtio_mem_bbm_set_bb_state(vm, bb_id,
						    VIRTIO_MEM_BBM_BB_UNUSED);
		else
			/* Retry from the main loop. */
			virtio_mem_bbm_set_bb_state(vm, bb_id,
						    VIRTIO_MEM_BBM_BB_PLUGGED);
		return rc;
	}
	return 0;
}

/*
 * Prepare tracking data for the next big block.
 */
static int virtio_mem_bbm_prepare_next_bb(struct virtio_mem *vm,
					  unsigned long *bb_id)
{
	int rc;

	if (vm->bbm.next_bb_id > vm->bbm.last_usable_bb_id)
		return -ENOSPC;

	/* Resize the big block state array if required. */
	rc = virtio_mem_bbm_bb_states_prepare_next_bb(vm);
	if (rc)
		return rc;

	vm->bbm.bb_count[VIRTIO_MEM_BBM_BB_UNUSED]++;
	*bb_id = vm->bbm.next_bb_id;
	vm->bbm.next_bb_id++;
	return 0;
}

static int virtio_mem_bbm_plug_request(struct virtio_mem *vm, uint64_t diff)
{
	uint64_t nb_bb = diff / vm->bbm.bb_size;
	unsigned long bb_id;
	int rc;

	if (!nb_bb)
		return 0;

	/* Try to plug and add unused big blocks */
	virtio_mem_bbm_for_each_bb(vm, bb_id, VIRTIO_MEM_BBM_BB_UNUSED) {
		if (!virtio_mem_could_add_memory(vm, vm->bbm.bb_size))
			return -ENOSPC;

		rc = virtio_mem_bbm_plug_and_add_bb(vm, bb_id);
		if (!rc)
			nb_bb--;
		if (rc || !nb_bb)
			return rc;
		cond_resched();
	}

	/* Try to prepare, plug and add new big blocks */
	while (nb_bb) {
		if (!virtio_mem_could_add_memory(vm, vm->bbm.bb_size))
			return -ENOSPC;

		rc = virtio_mem_bbm_prepare_next_bb(vm, &bb_id);
		if (rc)
			return rc;
		rc = virtio_mem_bbm_plug_and_add_bb(vm, bb_id);
		if (!rc)
			nb_bb--;
		if (rc)
			return rc;
		cond_resched();
	}

	return 0;
}

/*
 * Try to plug the requested amount of memory.
 */
static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
{
	if (vm->in_sbm)
		return virtio_mem_sbm_plug_request(vm, diff);
	return virtio_mem_bbm_plug_request(vm, diff);
}

/*
 * Unplug the desired number of plugged subblocks of an offline memory block.
 * Will fail if any subblock cannot get unplugged (instead of skipping it).
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 *
 * Note: Can fail after some subblocks were successfully unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb_offline(struct virtio_mem *vm,
						unsigned long mb_id,
						uint64_t *nb_sb)
{
	int rc;

	rc = virtio_mem_sbm_unplug_any_sb_raw(vm, mb_id, nb_sb);

	/* some subblocks might have been unplugged even on failure */
	if (!virtio_mem_sbm_test_sb_plugged(vm, mb_id, 0, vm->sbm.sbs_per_mb))
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL);
	if (rc)
		return rc;

	if (virtio_mem_sbm_test_sb_unplugged(vm, mb_id, 0, vm->sbm.sbs_per_mb)) {
		/*
		 * Remove the block from Linux - this should never fail.
		 * Hinder the block from getting onlined by marking it
		 * unplugged. Temporarily drop the mutex, so
		 * any pending GOING_ONLINE requests can be serviced/rejected.
		 */
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_UNUSED);

		mutex_unlock(&vm->hotplug_mutex);
		rc = virtio_mem_sbm_remove_mb(vm, mb_id);
		BUG_ON(rc);
		mutex_lock(&vm->hotplug_mutex);
	}
	return 0;
}

/*
 * Unplug the given plugged subblocks of an online memory block.
 *
 * Will modify the state of the memory block.
 */
static int virtio_mem_sbm_unplug_sb_online(struct virtio_mem *vm,
					   unsigned long mb_id, int sb_id,
					   int count)
{
	const unsigned long nr_pages = PFN_DOWN(vm->sbm.sb_size) * count;
	const int old_state = virtio_mem_sbm_get_mb_state(vm, mb_id);
	unsigned long start_pfn;
	int rc;

	start_pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
			     sb_id * vm->sbm.sb_size);

	rc = virtio_mem_fake_offline(start_pfn, nr_pages);
	if (rc)
		return rc;

	/* Try to unplug the allocated memory */
	rc = virtio_mem_sbm_unplug_sb(vm, mb_id, sb_id, count);
	if (rc) {
		/* Return the memory to the buddy. */
		virtio_mem_fake_online(start_pfn, nr_pages);
		return rc;
	}

	switch (old_state) {
	case VIRTIO_MEM_SBM_MB_KERNEL:
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL);
		break;
	case VIRTIO_MEM_SBM_MB_MOVABLE:
		virtio_mem_sbm_set_mb_state(vm, mb_id,
					    VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL);
		break;
	}

	return 0;
}

/*
 * Unplug the desired number of plugged subblocks of an online memory block.
 * Will skip subblock that are busy.
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 *
 * Note: Can fail after some subblocks were successfully unplugged. Can
 *       return 0 even if subblocks were busy and could not get unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb_online(struct virtio_mem *vm,
					       unsigned long mb_id,
					       uint64_t *nb_sb)
{
	int rc, sb_id;

	/* If possible, try to unplug the complete block in one shot. */
	if (*nb_sb >= vm->sbm.sbs_per_mb &&
	    virtio_mem_sbm_test_sb_plugged(vm, mb_id, 0, vm->sbm.sbs_per_mb)) {
		rc = virtio_mem_sbm_unplug_sb_online(vm, mb_id, 0,
						     vm->sbm.sbs_per_mb);
		if (!rc) {
			*nb_sb -= vm->sbm.sbs_per_mb;
			goto unplugged;
		} else if (rc != -EBUSY)
			return rc;
	}

	/* Fallback to single subblocks. */
	for (sb_id = vm->sbm.sbs_per_mb - 1; sb_id >= 0 && *nb_sb; sb_id--) {
		/* Find the next candidate subblock */
		while (sb_id >= 0 &&
		       !virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
			sb_id--;
		if (sb_id < 0)
			break;

		rc = virtio_mem_sbm_unplug_sb_online(vm, mb_id, sb_id, 1);
		if (rc == -EBUSY)
			continue;
		else if (rc)
			return rc;
		*nb_sb -= 1;
	}

unplugged:
	/*
	 * Once all subblocks of a memory block were unplugged, offline and
	 * remove it. This will usually not fail, as no memory is in use
	 * anymore - however some other notifiers might NACK the request.
	 */
	if (virtio_mem_sbm_test_sb_unplugged(vm, mb_id, 0, vm->sbm.sbs_per_mb)) {
		mutex_unlock(&vm->hotplug_mutex);
		rc = virtio_mem_sbm_offline_and_remove_mb(vm, mb_id);
		mutex_lock(&vm->hotplug_mutex);
		if (!rc)
			virtio_mem_sbm_set_mb_state(vm, mb_id,
						    VIRTIO_MEM_SBM_MB_UNUSED);
	}

	return 0;
}

/*
 * Unplug the desired number of plugged subblocks of a memory block that is
 * already added to Linux. Will skip subblock of online memory blocks that are
 * busy (by the OS). Will fail if any subblock that's not busy cannot get
 * unplugged.
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 *
 * Note: Can fail after some subblocks were successfully unplugged. Can
 *       return 0 even if subblocks were busy and could not get unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb(struct virtio_mem *vm,
					unsigned long mb_id,
					uint64_t *nb_sb)
{
	const int old_state = virtio_mem_sbm_get_mb_state(vm, mb_id);

	switch (old_state) {
	case VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL:
	case VIRTIO_MEM_SBM_MB_KERNEL:
	case VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL:
	case VIRTIO_MEM_SBM_MB_MOVABLE:
		return virtio_mem_sbm_unplug_any_sb_online(vm, mb_id, nb_sb);
	case VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL:
	case VIRTIO_MEM_SBM_MB_OFFLINE:
		return virtio_mem_sbm_unplug_any_sb_offline(vm, mb_id, nb_sb);
	}
	return -EINVAL;
}

static int virtio_mem_sbm_unplug_request(struct virtio_mem *vm, uint64_t diff)
{
	const int mb_states[] = {
		VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL,
		VIRTIO_MEM_SBM_MB_OFFLINE,
		VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL,
		VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL,
		VIRTIO_MEM_SBM_MB_MOVABLE,
		VIRTIO_MEM_SBM_MB_KERNEL,
	};
	uint64_t nb_sb = diff / vm->sbm.sb_size;
	unsigned long mb_id;
	int rc, i;

	if (!nb_sb)
		return 0;

	/*
	 * We'll drop the mutex a couple of times when it is safe to do so.
	 * This might result in some blocks switching the state (online/offline)
	 * and we could miss them in this run - we will retry again later.
	 */
	mutex_lock(&vm->hotplug_mutex);

	/*
	 * We try unplug from partially plugged blocks first, to try removing
	 * whole memory blocks along with metadata. We prioritize ZONE_MOVABLE
	 * as it's more reliable to unplug memory and remove whole memory
	 * blocks, and we don't want to trigger a zone imbalances by
	 * accidentially removing too much kernel memory.
	 */
	for (i = 0; i < ARRAY_SIZE(mb_states); i++) {
		virtio_mem_sbm_for_each_mb_rev(vm, mb_id, mb_states[i]) {
			rc = virtio_mem_sbm_unplug_any_sb(vm, mb_id, &nb_sb);
			if (rc || !nb_sb)
				goto out_unlock;
			mutex_unlock(&vm->hotplug_mutex);
			cond_resched();
			mutex_lock(&vm->hotplug_mutex);
		}
		if (!unplug_online && i == 1) {
			mutex_unlock(&vm->hotplug_mutex);
			return 0;
		}
	}

	mutex_unlock(&vm->hotplug_mutex);
	return nb_sb ? -EBUSY : 0;
out_unlock:
	mutex_unlock(&vm->hotplug_mutex);
	return rc;
}

/*
 * Try to offline and remove a big block from Linux and unplug it. Will fail
 * with -EBUSY if some memory is busy and cannot get unplugged.
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 */
static int virtio_mem_bbm_offline_remove_and_unplug_bb(struct virtio_mem *vm,
						       unsigned long bb_id)
{
	const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));
	const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);
	unsigned long end_pfn = start_pfn + nr_pages;
	unsigned long pfn;
	struct page *page;
	int rc;

	if (WARN_ON_ONCE(virtio_mem_bbm_get_bb_state(vm, bb_id) !=
			 VIRTIO_MEM_BBM_BB_ADDED))
		return -EINVAL;

	if (bbm_safe_unplug) {
		/*
		 * Start by fake-offlining all memory. Once we marked the device
		 * block as fake-offline, all newly onlined memory will
		 * automatically be kept fake-offline. Protect from concurrent
		 * onlining/offlining until we have a consistent state.
		 */
		mutex_lock(&vm->hotplug_mutex);
		virtio_mem_bbm_set_bb_state(vm, bb_id,
					    VIRTIO_MEM_BBM_BB_FAKE_OFFLINE);

		for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
			page = pfn_to_online_page(pfn);
			if (!page)
				continue;

			rc = virtio_mem_fake_offline(pfn, PAGES_PER_SECTION);
			if (rc) {
				end_pfn = pfn;
				goto rollback_safe_unplug;
			}
		}
		mutex_unlock(&vm->hotplug_mutex);
	}

	rc = virtio_mem_bbm_offline_and_remove_bb(vm, bb_id);
	if (rc) {
		if (bbm_safe_unplug) {
			mutex_lock(&vm->hotplug_mutex);
			goto rollback_safe_unplug;
		}
		return rc;
	}

	rc = virtio_mem_bbm_unplug_bb(vm, bb_id);
	if (rc)
		virtio_mem_bbm_set_bb_state(vm, bb_id,
					    VIRTIO_MEM_BBM_BB_PLUGGED);
	else
		virtio_mem_bbm_set_bb_state(vm, bb_id,
					    VIRTIO_MEM_BBM_BB_UNUSED);
	return rc;

rollback_safe_unplug:
	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
		page = pfn_to_online_page(pfn);
		if (!page)
			continue;
		virtio_mem_fake_online(pfn, PAGES_PER_SECTION);
	}
	virtio_mem_bbm_set_bb_state(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED);
	mutex_unlock(&vm->hotplug_mutex);
	return rc;
}

/*
 * Test if a big block is completely offline.
 */
static bool virtio_mem_bbm_bb_is_offline(struct virtio_mem *vm,
					 unsigned long bb_id)
{
	const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));
	const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);
	unsigned long pfn;

	for (pfn = start_pfn; pfn < start_pfn + nr_pages;
	     pfn += PAGES_PER_SECTION) {
		if (pfn_to_online_page(pfn))
			return false;
	}

	return true;
}

/*
 * Test if a big block is completely onlined to ZONE_MOVABLE (or offline).
 */
static bool virtio_mem_bbm_bb_is_movable(struct virtio_mem *vm,
					 unsigned long bb_id)
{
	const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));
	const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);
	struct page *page;
	unsigned long pfn;

	for (pfn = start_pfn; pfn < start_pfn + nr_pages;
	     pfn += PAGES_PER_SECTION) {
		page = pfn_to_online_page(pfn);
		if (!page)
			continue;
		if (page_zonenum(page) != ZONE_MOVABLE)
			return false;
	}

	return true;
}

static int virtio_mem_bbm_unplug_request(struct virtio_mem *vm, uint64_t diff)
{
	uint64_t nb_bb = diff / vm->bbm.bb_size;
	uint64_t bb_id;
	int rc, i;

	if (!nb_bb)
		return 0;

	/*
	 * Try to unplug big blocks. Similar to SBM, start with offline
	 * big blocks.
	 */
	for (i = 0; i < 3; i++) {
		virtio_mem_bbm_for_each_bb_rev(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED) {
			cond_resched();

			/*
			 * As we're holding no locks, these checks are racy,
			 * but we don't care.
			 */
			if (i == 0 && !virtio_mem_bbm_bb_is_offline(vm, bb_id))
				continue;
			if (i == 1 && !virtio_mem_bbm_bb_is_movable(vm, bb_id))
				continue;
			rc = virtio_mem_bbm_offline_remove_and_unplug_bb(vm, bb_id);
			if (rc == -EBUSY)
				continue;
			if (!rc)
				nb_bb--;
			if (rc || !nb_bb)
				return rc;
		}
		if (i == 0 && !unplug_online)
			return 0;
	}

	return nb_bb ? -EBUSY : 0;
}

/*
 * Try to unplug the requested amount of memory.
 */
static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
{
	if (vm->in_sbm)
		return virtio_mem_sbm_unplug_request(vm, diff);
	return virtio_mem_bbm_unplug_request(vm, diff);
}

/*
 * Try to unplug all blocks that couldn't be unplugged before, for example,
 * because the hypervisor was busy.
 */
static int virtio_mem_unplug_pending_mb(struct virtio_mem *vm)
{
	unsigned long id;
	int rc;

	if (!vm->in_sbm) {
		virtio_mem_bbm_for_each_bb(vm, id,
					   VIRTIO_MEM_BBM_BB_PLUGGED) {
			rc = virtio_mem_bbm_unplug_bb(vm, id);
			if (rc)
				return rc;
			virtio_mem_bbm_set_bb_state(vm, id,
						    VIRTIO_MEM_BBM_BB_UNUSED);
		}
		return 0;
	}

	virtio_mem_sbm_for_each_mb(vm, id, VIRTIO_MEM_SBM_MB_PLUGGED) {
		rc = virtio_mem_sbm_unplug_mb(vm, id);
		if (rc)
			return rc;
		virtio_mem_sbm_set_mb_state(vm, id,
					    VIRTIO_MEM_SBM_MB_UNUSED);
	}

	return 0;
}

/*
 * Update all parts of the config that could have changed.
 */
static void virtio_mem_refresh_config(struct virtio_mem *vm)
{
	const struct range pluggable_range = mhp_get_pluggable_range(true);
	uint64_t new_plugged_size, usable_region_size, end_addr;

	/* the plugged_size is just a reflection of what _we_ did previously */
	virtio_cread_le(vm->vdev, struct virtio_mem_config, plugged_size,
			&new_plugged_size);
	if (WARN_ON_ONCE(new_plugged_size != vm->plugged_size))
		vm->plugged_size = new_plugged_size;

	/* calculate the last usable memory block id */
	virtio_cread_le(vm->vdev, struct virtio_mem_config,
			usable_region_size, &usable_region_size);
	end_addr = min(vm->addr + usable_region_size - 1,
		       pluggable_range.end);

	if (vm->in_sbm) {
		vm->sbm.last_usable_mb_id = virtio_mem_phys_to_mb_id(end_addr);
		if (!IS_ALIGNED(end_addr + 1, memory_block_size_bytes()))
			vm->sbm.last_usable_mb_id--;
	} else {
		vm->bbm.last_usable_bb_id = virtio_mem_phys_to_bb_id(vm,
								     end_addr);
		if (!IS_ALIGNED(end_addr + 1, vm->bbm.bb_size))
			vm->bbm.last_usable_bb_id--;
	}
	/*
	 * If we cannot plug any of our device memory (e.g., nothing in the
	 * usable region is addressable), the last usable memory block id will
	 * be smaller than the first usable memory block id. We'll stop
	 * attempting to add memory with -ENOSPC from our main loop.
	 */

	/* see if there is a request to change the size */
	virtio_cread_le(vm->vdev, struct virtio_mem_config, requested_size,
			&vm->requested_size);

	dev_info(&vm->vdev->dev, "plugged size: 0x%llx", vm->plugged_size);
	dev_info(&vm->vdev->dev, "requested size: 0x%llx", vm->requested_size);
}

/*
 * Workqueue function for handling plug/unplug requests and config updates.
 */
static void virtio_mem_run_wq(struct work_struct *work)
{
	struct virtio_mem *vm = container_of(work, struct virtio_mem, wq);
	uint64_t diff;
	int rc;

	if (unlikely(vm->in_kdump)) {
		dev_warn_once(&vm->vdev->dev,
			     "unexpected workqueue run in kdump kernel\n");
		return;
	}

	hrtimer_cancel(&vm->retry_timer);

	if (vm->broken)
		return;

	atomic_set(&vm->wq_active, 1);
retry:
	rc = 0;

	/* Make sure we start with a clean state if there are leftovers. */
	if (unlikely(vm->unplug_all_required))
		rc = virtio_mem_send_unplug_all_request(vm);

	if (atomic_read(&vm->config_changed)) {
		atomic_set(&vm->config_changed, 0);
		virtio_mem_refresh_config(vm);
	}

	/* Unplug any leftovers from previous runs */
	if (!rc)
		rc = virtio_mem_unplug_pending_mb(vm);

	if (!rc && vm->requested_size != vm->plugged_size) {
		if (vm->requested_size > vm->plugged_size) {
			diff = vm->requested_size - vm->plugged_size;
			rc = virtio_mem_plug_request(vm, diff);
		} else {
			diff = vm->plugged_size - vm->requested_size;
			rc = virtio_mem_unplug_request(vm, diff);
		}
	}

	switch (rc) {
	case 0:
		vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
		break;
	case -ENOSPC:
		/*
		 * We cannot add any more memory (alignment, physical limit)
		 * or we have too many offline memory blocks.
		 */
		break;
	case -ETXTBSY:
		/*
		 * The hypervisor cannot process our request right now
		 * (e.g., out of memory, migrating);
		 */
	case -EBUSY:
		/*
		 * We cannot free up any memory to unplug it (all plugged memory
		 * is busy).
		 */
	case -ENOMEM:
		/* Out of memory, try again later. */
		hrtimer_start(&vm->retry_timer, ms_to_ktime(vm->retry_timer_ms),
			      HRTIMER_MODE_REL);
		break;
	case -EAGAIN:
		/* Retry immediately (e.g., the config changed). */
		goto retry;
	default:
		/* Unknown error, mark as broken */
		dev_err(&vm->vdev->dev,
			"unknown error, marking device broken: %d\n", rc);
		vm->broken = true;
	}

	atomic_set(&vm->wq_active, 0);
}

static enum hrtimer_restart virtio_mem_timer_expired(struct hrtimer *timer)
{
	struct virtio_mem *vm = container_of(timer, struct virtio_mem,
					     retry_timer);

	virtio_mem_retry(vm);
	vm->retry_timer_ms = min_t(unsigned int, vm->retry_timer_ms * 2,
				   VIRTIO_MEM_RETRY_TIMER_MAX_MS);
	return HRTIMER_NORESTART;
}

static void virtio_mem_handle_response(struct virtqueue *vq)
{
	struct virtio_mem *vm = vq->vdev->priv;

	wake_up(&vm->host_resp);
}

static int virtio_mem_init_vq(struct virtio_mem *vm)
{
	struct virtqueue *vq;

	vq = virtio_find_single_vq(vm->vdev, virtio_mem_handle_response,
				   "guest-request");
	if (IS_ERR(vq))
		return PTR_ERR(vq);
	vm->vq = vq;

	return 0;
}

static int virtio_mem_init_hotplug(struct virtio_mem *vm)
{
	const struct range pluggable_range = mhp_get_pluggable_range(true);
	uint64_t unit_pages, sb_size, addr;
	int rc;

	/* bad device setup - warn only */
	if (!IS_ALIGNED(vm->addr, memory_block_size_bytes()))
		dev_warn(&vm->vdev->dev,
			 "The alignment of the physical start address can make some memory unusable.\n");
	if (!IS_ALIGNED(vm->addr + vm->region_size, memory_block_size_bytes()))
		dev_warn(&vm->vdev->dev,
			 "The alignment of the physical end address can make some memory unusable.\n");
	if (vm->addr < pluggable_range.start ||
	    vm->addr + vm->region_size - 1 > pluggable_range.end)
		dev_warn(&vm->vdev->dev,
			 "Some device memory is not addressable/pluggable. This can make some memory unusable.\n");

	/* Prepare the offline threshold - make sure we can add two blocks. */
	vm->offline_threshold = max_t(uint64_t, 2 * memory_block_size_bytes(),
				      VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD);

	/*
	 * alloc_contig_range() works reliably with pageblock
	 * granularity on ZONE_NORMAL, use pageblock_nr_pages.
	 */
	sb_size = PAGE_SIZE * pageblock_nr_pages;
	sb_size = max_t(uint64_t, vm->device_block_size, sb_size);

	if (sb_size < memory_block_size_bytes() && !force_bbm) {
		/* SBM: At least two subblocks per Linux memory block. */
		vm->in_sbm = true;
		vm->sbm.sb_size = sb_size;
		vm->sbm.sbs_per_mb = memory_block_size_bytes() /
				     vm->sbm.sb_size;

		/* Round up to the next full memory block */
		addr = max_t(uint64_t, vm->addr, pluggable_range.start) +
		       memory_block_size_bytes() - 1;
		vm->sbm.first_mb_id = virtio_mem_phys_to_mb_id(addr);
		vm->sbm.next_mb_id = vm->sbm.first_mb_id;
	} else {
		/* BBM: At least one Linux memory block. */
		vm->bbm.bb_size = max_t(uint64_t, vm->device_block_size,
					memory_block_size_bytes());

		if (bbm_block_size) {
			if (!is_power_of_2(bbm_block_size)) {
				dev_warn(&vm->vdev->dev,
					 "bbm_block_size is not a power of 2");
			} else if (bbm_block_size < vm->bbm.bb_size) {
				dev_warn(&vm->vdev->dev,
					 "bbm_block_size is too small");
			} else {
				vm->bbm.bb_size = bbm_block_size;
			}
		}

		/* Round up to the next aligned big block */
		addr = max_t(uint64_t, vm->addr, pluggable_range.start) +
		       vm->bbm.bb_size - 1;
		vm->bbm.first_bb_id = virtio_mem_phys_to_bb_id(vm, addr);
		vm->bbm.next_bb_id = vm->bbm.first_bb_id;

		/* Make sure we can add two big blocks. */
		vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
					      vm->offline_threshold);
	}

	dev_info(&vm->vdev->dev, "memory block size: 0x%lx",
		 memory_block_size_bytes());
	if (vm->in_sbm)
		dev_info(&vm->vdev->dev, "subblock size: 0x%llx",
			 (unsigned long long)vm->sbm.sb_size);
	else
		dev_info(&vm->vdev->dev, "big block size: 0x%llx",
			 (unsigned long long)vm->bbm.bb_size);

	/* create the parent resource for all memory */
	rc = virtio_mem_create_resource(vm);
	if (rc)
		return rc;

	/* use a single dynamic memory group to cover the whole memory device */
	if (vm->in_sbm)
		unit_pages = PHYS_PFN(memory_block_size_bytes());
	else
		unit_pages = PHYS_PFN(vm->bbm.bb_size);
	rc = memory_group_register_dynamic(vm->nid, unit_pages);
	if (rc < 0)
		goto out_del_resource;
	vm->mgid = rc;

	/*
	 * If we still have memory plugged, we have to unplug all memory first.
	 * Registering our parent resource makes sure that this memory isn't
	 * actually in use (e.g., trying to reload the driver).
	 */
	if (vm->plugged_size) {
		vm->unplug_all_required = true;
		dev_info(&vm->vdev->dev, "unplugging all memory is required\n");
	}

	/* register callbacks */
	vm->memory_notifier.notifier_call = virtio_mem_memory_notifier_cb;
	rc = register_memory_notifier(&vm->memory_notifier);
	if (rc)
		goto out_unreg_group;
	rc = register_virtio_mem_device(vm);
	if (rc)
		goto out_unreg_mem;

	return 0;
out_unreg_mem:
	unregister_memory_notifier(&vm->memory_notifier);
out_unreg_group:
	memory_group_unregister(vm->mgid);
out_del_resource:
	virtio_mem_delete_resource(vm);
	return rc;
}

#ifdef CONFIG_PROC_VMCORE
static int virtio_mem_send_state_request(struct virtio_mem *vm, uint64_t addr,
					 uint64_t size)
{
	const uint64_t nb_vm_blocks = size / vm->device_block_size;
	const struct virtio_mem_req req = {
		.type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_STATE),
		.u.state.addr = cpu_to_virtio64(vm->vdev, addr),
		.u.state.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
	};
	int rc = -ENOMEM;

	dev_dbg(&vm->vdev->dev, "requesting state: 0x%llx - 0x%llx\n", addr,
		addr + size - 1);

	switch (virtio_mem_send_request(vm, &req)) {
	case VIRTIO_MEM_RESP_ACK:
		return virtio16_to_cpu(vm->vdev, vm->resp.u.state.state);
	case VIRTIO_MEM_RESP_ERROR:
		rc = -EINVAL;
		break;
	default:
		break;
	}

	dev_dbg(&vm->vdev->dev, "requesting state failed: %d\n", rc);
	return rc;
}

static bool virtio_mem_vmcore_pfn_is_ram(struct vmcore_cb *cb,
					 unsigned long pfn)
{
	struct virtio_mem *vm = container_of(cb, struct virtio_mem,
					     vmcore_cb);
	uint64_t addr = PFN_PHYS(pfn);
	bool is_ram;
	int rc;

	if (!virtio_mem_contains_range(vm, addr, PAGE_SIZE))
		return true;
	if (!vm->plugged_size)
		return false;

	/*
	 * We have to serialize device requests and access to the information
	 * about the block queried last.
	 */
	mutex_lock(&vm->hotplug_mutex);

	addr = ALIGN_DOWN(addr, vm->device_block_size);
	if (addr != vm->last_block_addr) {
		rc = virtio_mem_send_state_request(vm, addr,
						   vm->device_block_size);
		/* On any kind of error, we're going to signal !ram. */
		if (rc == VIRTIO_MEM_STATE_PLUGGED)
			vm->last_block_plugged = true;
		else
			vm->last_block_plugged = false;
		vm->last_block_addr = addr;
	}

	is_ram = vm->last_block_plugged;
	mutex_unlock(&vm->hotplug_mutex);
	return is_ram;
}
#endif /* CONFIG_PROC_VMCORE */

static int virtio_mem_init_kdump(struct virtio_mem *vm)
{
#ifdef CONFIG_PROC_VMCORE
	dev_info(&vm->vdev->dev, "memory hot(un)plug disabled in kdump kernel\n");
	vm->vmcore_cb.pfn_is_ram = virtio_mem_vmcore_pfn_is_ram;
	register_vmcore_cb(&vm->vmcore_cb);
	return 0;
#else /* CONFIG_PROC_VMCORE */
	dev_warn(&vm->vdev->dev, "disabled in kdump kernel without vmcore\n");
	return -EBUSY;
#endif /* CONFIG_PROC_VMCORE */
}

static int virtio_mem_init(struct virtio_mem *vm)
{
	uint16_t node_id;

	if (!vm->vdev->config->get) {
		dev_err(&vm->vdev->dev, "config access disabled\n");
		return -EINVAL;
	}

	/* Fetch all properties that can't change. */
	virtio_cread_le(vm->vdev, struct virtio_mem_config, plugged_size,
			&vm->plugged_size);
	virtio_cread_le(vm->vdev, struct virtio_mem_config, block_size,
			&vm->device_block_size);
	virtio_cread_le(vm->vdev, struct virtio_mem_config, node_id,
			&node_id);
	vm->nid = virtio_mem_translate_node_id(vm, node_id);
	virtio_cread_le(vm->vdev, struct virtio_mem_config, addr, &vm->addr);
	virtio_cread_le(vm->vdev, struct virtio_mem_config, region_size,
			&vm->region_size);

	/* Determine the nid for the device based on the lowest address. */
	if (vm->nid == NUMA_NO_NODE)
		vm->nid = memory_add_physaddr_to_nid(vm->addr);

	dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
	dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size);
	dev_info(&vm->vdev->dev, "device block size: 0x%llx",
		 (unsigned long long)vm->device_block_size);
	if (vm->nid != NUMA_NO_NODE && IS_ENABLED(CONFIG_NUMA))
		dev_info(&vm->vdev->dev, "nid: %d", vm->nid);

	/*
	 * We don't want to (un)plug or reuse any memory when in kdump. The
	 * memory is still accessible (but not exposed to Linux).
	 */
	if (vm->in_kdump)
		return virtio_mem_init_kdump(vm);
	return virtio_mem_init_hotplug(vm);
}

static int virtio_mem_create_resource(struct virtio_mem *vm)
{
	/*
	 * When force-unloading the driver and removing the device, we
	 * could have a garbage pointer. Duplicate the string.
	 */
	const char *name = kstrdup(dev_name(&vm->vdev->dev), GFP_KERNEL);

	if (!name)
		return -ENOMEM;

	/* Disallow mapping device memory via /dev/mem completely. */
	vm->parent_resource = __request_mem_region(vm->addr, vm->region_size,
						   name, IORESOURCE_SYSTEM_RAM |
						   IORESOURCE_EXCLUSIVE);
	if (!vm->parent_resource) {
		kfree(name);
		dev_warn(&vm->vdev->dev, "could not reserve device region\n");
		dev_info(&vm->vdev->dev,
			 "reloading the driver is not supported\n");
		return -EBUSY;
	}

	/* The memory is not actually busy - make add_memory() work. */
	vm->parent_resource->flags &= ~IORESOURCE_BUSY;
	return 0;
}

static void virtio_mem_delete_resource(struct virtio_mem *vm)
{
	const char *name;

	if (!vm->parent_resource)
		return;

	name = vm->parent_resource->name;
	release_resource(vm->parent_resource);
	kfree(vm->parent_resource);
	kfree(name);
	vm->parent_resource = NULL;
}

static int virtio_mem_range_has_system_ram(struct resource *res, void *arg)
{
	return 1;
}

static bool virtio_mem_has_memory_added(struct virtio_mem *vm)
{
	const unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;

	return walk_iomem_res_desc(IORES_DESC_NONE, flags, vm->addr,
				   vm->addr + vm->region_size, NULL,
				   virtio_mem_range_has_system_ram) == 1;
}

static int virtio_mem_probe(struct virtio_device *vdev)
{
	struct virtio_mem *vm;
	int rc;

	BUILD_BUG_ON(sizeof(struct virtio_mem_req) != 24);
	BUILD_BUG_ON(sizeof(struct virtio_mem_resp) != 10);

	vdev->priv = vm = kzalloc(sizeof(*vm), GFP_KERNEL);
	if (!vm)
		return -ENOMEM;

	init_waitqueue_head(&vm->host_resp);
	vm->vdev = vdev;
	INIT_WORK(&vm->wq, virtio_mem_run_wq);
	mutex_init(&vm->hotplug_mutex);
	INIT_LIST_HEAD(&vm->next);
	spin_lock_init(&vm->removal_lock);
	hrtimer_init(&vm->retry_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	vm->retry_timer.function = virtio_mem_timer_expired;
	vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
	vm->in_kdump = is_kdump_kernel();

	/* register the virtqueue */
	rc = virtio_mem_init_vq(vm);
	if (rc)
		goto out_free_vm;

	/* initialize the device by querying the config */
	rc = virtio_mem_init(vm);
	if (rc)
		goto out_del_vq;

	virtio_device_ready(vdev);

	/* trigger a config update to start processing the requested_size */
	if (!vm->in_kdump) {
		atomic_set(&vm->config_changed, 1);
		queue_work(system_freezable_wq, &vm->wq);
	}

	return 0;
out_del_vq:
	vdev->config->del_vqs(vdev);
out_free_vm:
	kfree(vm);
	vdev->priv = NULL;

	return rc;
}

static void virtio_mem_deinit_hotplug(struct virtio_mem *vm)
{
	unsigned long mb_id;
	int rc;

	/*
	 * Make sure the workqueue won't be triggered anymore and no memory
	 * blocks can be onlined/offlined until we're finished here.
	 */
	mutex_lock(&vm->hotplug_mutex);
	spin_lock_irq(&vm->removal_lock);
	vm->removing = true;
	spin_unlock_irq(&vm->removal_lock);
	mutex_unlock(&vm->hotplug_mutex);

	/* wait until the workqueue stopped */
	cancel_work_sync(&vm->wq);
	hrtimer_cancel(&vm->retry_timer);

	if (vm->in_sbm) {
		/*
		 * After we unregistered our callbacks, user space can online
		 * partially plugged offline blocks. Make sure to remove them.
		 */
		virtio_mem_sbm_for_each_mb(vm, mb_id,
					   VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL) {
			rc = virtio_mem_sbm_remove_mb(vm, mb_id);
			BUG_ON(rc);
			virtio_mem_sbm_set_mb_state(vm, mb_id,
						    VIRTIO_MEM_SBM_MB_UNUSED);
		}
		/*
		 * After we unregistered our callbacks, user space can no longer
		 * offline partially plugged online memory blocks. No need to
		 * worry about them.
		 */
	}

	/* unregister callbacks */
	unregister_virtio_mem_device(vm);
	unregister_memory_notifier(&vm->memory_notifier);

	/*
	 * There is no way we could reliably remove all memory we have added to
	 * the system. And there is no way to stop the driver/device from going
	 * away. Warn at least.
	 */
	if (virtio_mem_has_memory_added(vm)) {
		dev_warn(&vm->vdev->dev,
			 "device still has system memory added\n");
	} else {
		virtio_mem_delete_resource(vm);
		kfree_const(vm->resource_name);
		memory_group_unregister(vm->mgid);
	}

	/* remove all tracking data - no locking needed */
	if (vm->in_sbm) {
		vfree(vm->sbm.mb_states);
		vfree(vm->sbm.sb_states);
	} else {
		vfree(vm->bbm.bb_states);
	}
}

static void virtio_mem_deinit_kdump(struct virtio_mem *vm)
{
#ifdef CONFIG_PROC_VMCORE
	unregister_vmcore_cb(&vm->vmcore_cb);
#endif /* CONFIG_PROC_VMCORE */
}

static void virtio_mem_remove(struct virtio_device *vdev)
{
	struct virtio_mem *vm = vdev->priv;

	if (vm->in_kdump)
		virtio_mem_deinit_kdump(vm);
	else
		virtio_mem_deinit_hotplug(vm);

	/* reset the device and cleanup the queues */
	virtio_reset_device(vdev);
	vdev->config->del_vqs(vdev);

	kfree(vm);
	vdev->priv = NULL;
}

static void virtio_mem_config_changed(struct virtio_device *vdev)
{
	struct virtio_mem *vm = vdev->priv;

	if (unlikely(vm->in_kdump))
		return;

	atomic_set(&vm->config_changed, 1);
	virtio_mem_retry(vm);
}

#ifdef CONFIG_PM_SLEEP
static int virtio_mem_freeze(struct virtio_device *vdev)
{
	/*
	 * When restarting the VM, all memory is usually unplugged. Don't
	 * allow to suspend/hibernate.
	 */
	dev_err(&vdev->dev, "save/restore not supported.\n");
	return -EPERM;
}

static int virtio_mem_restore(struct virtio_device *vdev)
{
	return -EPERM;
}
#endif

static unsigned int virtio_mem_features[] = {
#if defined(CONFIG_NUMA) && defined(CONFIG_ACPI_NUMA)
	VIRTIO_MEM_F_ACPI_PXM,
#endif
	VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE,
};

static const struct virtio_device_id virtio_mem_id_table[] = {
	{ VIRTIO_ID_MEM, VIRTIO_DEV_ANY_ID },
	{ 0 },
};

static struct virtio_driver virtio_mem_driver = {
	.feature_table = virtio_mem_features,
	.feature_table_size = ARRAY_SIZE(virtio_mem_features),
	.driver.name = KBUILD_MODNAME,
	.driver.owner = THIS_MODULE,
	.id_table = virtio_mem_id_table,
	.probe = virtio_mem_probe,
	.remove = virtio_mem_remove,
	.config_changed = virtio_mem_config_changed,
#ifdef CONFIG_PM_SLEEP
	.freeze	=	virtio_mem_freeze,
	.restore =	virtio_mem_restore,
#endif
};

module_virtio_driver(virtio_mem_driver);
MODULE_DEVICE_TABLE(virtio, virtio_mem_id_table);
MODULE_AUTHOR("David Hildenbrand <david@redhat.com>");
MODULE_DESCRIPTION("Virtio-mem driver");
MODULE_LICENSE("GPL");