summaryrefslogtreecommitdiffstats
path: root/arch/x86/entry/entry_64.S
blob: d2a00c97e53f608ad67a4e24db1f5c64f1b9e880 (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
/* SPDX-License-Identifier: GPL-2.0 */
/*
 *  linux/arch/x86_64/entry.S
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 2000, 2001, 2002  Andi Kleen SuSE Labs
 *  Copyright (C) 2000  Pavel Machek <pavel@suse.cz>
 *
 * entry.S contains the system-call and fault low-level handling routines.
 *
 * Some of this is documented in Documentation/x86/entry_64.rst
 *
 * A note on terminology:
 * - iret frame:	Architecture defined interrupt frame from SS to RIP
 *			at the top of the kernel process stack.
 *
 * Some macro usage:
 * - SYM_FUNC_START/END:Define functions in the symbol table.
 * - idtentry:		Define exception entry points.
 */
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/cache.h>
#include <asm/errno.h>
#include <asm/asm-offsets.h>
#include <asm/msr.h>
#include <asm/unistd.h>
#include <asm/thread_info.h>
#include <asm/hw_irq.h>
#include <asm/page_types.h>
#include <asm/irqflags.h>
#include <asm/paravirt.h>
#include <asm/percpu.h>
#include <asm/asm.h>
#include <asm/smap.h>
#include <asm/pgtable_types.h>
#include <asm/export.h>
#include <asm/frame.h>
#include <asm/trapnr.h>
#include <asm/nospec-branch.h>
#include <linux/err.h>

#include "calling.h"

.code64
.section .entry.text, "ax"

#ifdef CONFIG_PARAVIRT
SYM_CODE_START(native_usergs_sysret64)
	UNWIND_HINT_EMPTY
	swapgs
	sysretq
SYM_CODE_END(native_usergs_sysret64)
#endif /* CONFIG_PARAVIRT */

/*
 * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers.
 *
 * This is the only entry point used for 64-bit system calls.  The
 * hardware interface is reasonably well designed and the register to
 * argument mapping Linux uses fits well with the registers that are
 * available when SYSCALL is used.
 *
 * SYSCALL instructions can be found inlined in libc implementations as
 * well as some other programs and libraries.  There are also a handful
 * of SYSCALL instructions in the vDSO used, for example, as a
 * clock_gettimeofday fallback.
 *
 * 64-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11,
 * then loads new ss, cs, and rip from previously programmed MSRs.
 * rflags gets masked by a value from another MSR (so CLD and CLAC
 * are not needed). SYSCALL does not save anything on the stack
 * and does not change rsp.
 *
 * Registers on entry:
 * rax  system call number
 * rcx  return address
 * r11  saved rflags (note: r11 is callee-clobbered register in C ABI)
 * rdi  arg0
 * rsi  arg1
 * rdx  arg2
 * r10  arg3 (needs to be moved to rcx to conform to C ABI)
 * r8   arg4
 * r9   arg5
 * (note: r12-r15, rbp, rbx are callee-preserved in C ABI)
 *
 * Only called from user space.
 *
 * When user can change pt_regs->foo always force IRET. That is because
 * it deals with uncanonical addresses better. SYSRET has trouble
 * with them due to bugs in both AMD and Intel CPUs.
 */

SYM_CODE_START(entry_SYSCALL_64)
	UNWIND_HINT_EMPTY

	swapgs
	/* tss.sp2 is scratch space. */
	movq	%rsp, PER_CPU_VAR(cpu_tss_rw + TSS_sp2)
	SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp

	/* Construct struct pt_regs on stack */
	pushq	$__USER_DS				/* pt_regs->ss */
	pushq	PER_CPU_VAR(cpu_tss_rw + TSS_sp2)	/* pt_regs->sp */
	pushq	%r11					/* pt_regs->flags */
	pushq	$__USER_CS				/* pt_regs->cs */
	pushq	%rcx					/* pt_regs->ip */
SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
	pushq	%rax					/* pt_regs->orig_ax */

	PUSH_AND_CLEAR_REGS rax=$-ENOSYS

	/* IRQs are off. */
	movq	%rax, %rdi
	movq	%rsp, %rsi
	call	do_syscall_64		/* returns with IRQs disabled */

	/*
	 * Try to use SYSRET instead of IRET if we're returning to
	 * a completely clean 64-bit userspace context.  If we're not,
	 * go to the slow exit path.
	 */
	movq	RCX(%rsp), %rcx
	movq	RIP(%rsp), %r11

	cmpq	%rcx, %r11	/* SYSRET requires RCX == RIP */
	jne	swapgs_restore_regs_and_return_to_usermode

	/*
	 * On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP
	 * in kernel space.  This essentially lets the user take over
	 * the kernel, since userspace controls RSP.
	 *
	 * If width of "canonical tail" ever becomes variable, this will need
	 * to be updated to remain correct on both old and new CPUs.
	 *
	 * Change top bits to match most significant bit (47th or 56th bit
	 * depending on paging mode) in the address.
	 */
#ifdef CONFIG_X86_5LEVEL
	ALTERNATIVE "shl $(64 - 48), %rcx; sar $(64 - 48), %rcx", \
		"shl $(64 - 57), %rcx; sar $(64 - 57), %rcx", X86_FEATURE_LA57
#else
	shl	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
	sar	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx
#endif

	/* If this changed %rcx, it was not canonical */
	cmpq	%rcx, %r11
	jne	swapgs_restore_regs_and_return_to_usermode

	cmpq	$__USER_CS, CS(%rsp)		/* CS must match SYSRET */
	jne	swapgs_restore_regs_and_return_to_usermode

	movq	R11(%rsp), %r11
	cmpq	%r11, EFLAGS(%rsp)		/* R11 == RFLAGS */
	jne	swapgs_restore_regs_and_return_to_usermode

	/*
	 * SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot
	 * restore RF properly. If the slowpath sets it for whatever reason, we
	 * need to restore it correctly.
	 *
	 * SYSRET can restore TF, but unlike IRET, restoring TF results in a
	 * trap from userspace immediately after SYSRET.  This would cause an
	 * infinite loop whenever #DB happens with register state that satisfies
	 * the opportunistic SYSRET conditions.  For example, single-stepping
	 * this user code:
	 *
	 *           movq	$stuck_here, %rcx
	 *           pushfq
	 *           popq %r11
	 *   stuck_here:
	 *
	 * would never get past 'stuck_here'.
	 */
	testq	$(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11
	jnz	swapgs_restore_regs_and_return_to_usermode

	/* nothing to check for RSP */

	cmpq	$__USER_DS, SS(%rsp)		/* SS must match SYSRET */
	jne	swapgs_restore_regs_and_return_to_usermode

	/*
	 * We win! This label is here just for ease of understanding
	 * perf profiles. Nothing jumps here.
	 */
syscall_return_via_sysret:
	/* rcx and r11 are already restored (see code above) */
	POP_REGS pop_rdi=0 skip_r11rcx=1

	/*
	 * Now all regs are restored except RSP and RDI.
	 * Save old stack pointer and switch to trampoline stack.
	 */
	movq	%rsp, %rdi
	movq	PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
	UNWIND_HINT_EMPTY

	pushq	RSP-RDI(%rdi)	/* RSP */
	pushq	(%rdi)		/* RDI */

	/*
	 * We are on the trampoline stack.  All regs except RDI are live.
	 * We can do future final exit work right here.
	 */
	STACKLEAK_ERASE_NOCLOBBER

	SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi

	popq	%rdi
	popq	%rsp
	USERGS_SYSRET64
SYM_CODE_END(entry_SYSCALL_64)

/*
 * %rdi: prev task
 * %rsi: next task
 */
.pushsection .text, "ax"
SYM_FUNC_START(__switch_to_asm)
	/*
	 * Save callee-saved registers
	 * This must match the order in inactive_task_frame
	 */
	pushq	%rbp
	pushq	%rbx
	pushq	%r12
	pushq	%r13
	pushq	%r14
	pushq	%r15

	/* switch stack */
	movq	%rsp, TASK_threadsp(%rdi)
	movq	TASK_threadsp(%rsi), %rsp

#ifdef CONFIG_STACKPROTECTOR
	movq	TASK_stack_canary(%rsi), %rbx
	movq	%rbx, PER_CPU_VAR(fixed_percpu_data) + stack_canary_offset
#endif

#ifdef CONFIG_RETPOLINE
	/*
	 * When switching from a shallower to a deeper call stack
	 * the RSB may either underflow or use entries populated
	 * with userspace addresses. On CPUs where those concerns
	 * exist, overwrite the RSB with entries which capture
	 * speculative execution to prevent attack.
	 */
	FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
#endif

	/* restore callee-saved registers */
	popq	%r15
	popq	%r14
	popq	%r13
	popq	%r12
	popq	%rbx
	popq	%rbp

	jmp	__switch_to
SYM_FUNC_END(__switch_to_asm)
.popsection

/*
 * A newly forked process directly context switches into this address.
 *
 * rax: prev task we switched from
 * rbx: kernel thread func (NULL for user thread)
 * r12: kernel thread arg
 */
.pushsection .text, "ax"
SYM_CODE_START(ret_from_fork)
	UNWIND_HINT_EMPTY
	movq	%rax, %rdi
	call	schedule_tail			/* rdi: 'prev' task parameter */

	testq	%rbx, %rbx			/* from kernel_thread? */
	jnz	1f				/* kernel threads are uncommon */

2:
	UNWIND_HINT_REGS
	movq	%rsp, %rdi
	call	syscall_return_slowpath	/* returns with IRQs disabled */
	jmp	swapgs_restore_regs_and_return_to_usermode

1:
	/* kernel thread */
	UNWIND_HINT_EMPTY
	movq	%r12, %rdi
	CALL_NOSPEC rbx
	/*
	 * A kernel thread is allowed to return here after successfully
	 * calling do_execve().  Exit to userspace to complete the execve()
	 * syscall.
	 */
	movq	$0, RAX(%rsp)
	jmp	2b
SYM_CODE_END(ret_from_fork)
.popsection

.macro DEBUG_ENTRY_ASSERT_IRQS_OFF
#ifdef CONFIG_DEBUG_ENTRY
	pushq %rax
	SAVE_FLAGS(CLBR_RAX)
	testl $X86_EFLAGS_IF, %eax
	jz .Lokay_\@
	ud2
.Lokay_\@:
	popq %rax
#endif
.endm

/**
 * idtentry_body - Macro to emit code calling the C function
 * @cfunc:		C function to be called
 * @has_error_code:	Hardware pushed error code on stack
 */
.macro idtentry_body cfunc has_error_code:req

	call	error_entry
	UNWIND_HINT_REGS

	movq	%rsp, %rdi			/* pt_regs pointer into 1st argument*/

	.if \has_error_code == 1
		movq	ORIG_RAX(%rsp), %rsi	/* get error code into 2nd argument*/
		movq	$-1, ORIG_RAX(%rsp)	/* no syscall to restart */
	.endif

	call	\cfunc

	jmp	error_return
.endm

/**
 * idtentry - Macro to generate entry stubs for simple IDT entries
 * @vector:		Vector number
 * @asmsym:		ASM symbol for the entry point
 * @cfunc:		C function to be called
 * @has_error_code:	Hardware pushed error code on stack
 *
 * The macro emits code to set up the kernel context for straight forward
 * and simple IDT entries. No IST stack, no paranoid entry checks.
 */
.macro idtentry vector asmsym cfunc has_error_code:req
SYM_CODE_START(\asmsym)
	UNWIND_HINT_IRET_REGS offset=\has_error_code*8
	ASM_CLAC

	.if \has_error_code == 0
		pushq	$-1			/* ORIG_RAX: no syscall to restart */
	.endif

	.if \vector == X86_TRAP_BP
		/*
		 * If coming from kernel space, create a 6-word gap to allow the
		 * int3 handler to emulate a call instruction.
		 */
		testb	$3, CS-ORIG_RAX(%rsp)
		jnz	.Lfrom_usermode_no_gap_\@
		.rept	6
		pushq	5*8(%rsp)
		.endr
		UNWIND_HINT_IRET_REGS offset=8
.Lfrom_usermode_no_gap_\@:
	.endif

	idtentry_body \cfunc \has_error_code

_ASM_NOKPROBE(\asmsym)
SYM_CODE_END(\asmsym)
.endm

/*
 * Interrupt entry/exit.
 *
 + The interrupt stubs push (vector) onto the stack, which is the error_code
 * position of idtentry exceptions, and jump to one of the two idtentry points
 * (common/spurious).
 *
 * common_interrupt is a hotpath, align it to a cache line
 */
.macro idtentry_irq vector cfunc
	.p2align CONFIG_X86_L1_CACHE_SHIFT
	idtentry \vector asm_\cfunc \cfunc has_error_code=1
.endm

/*
 * System vectors which invoke their handlers directly and are not
 * going through the regular common device interrupt handling code.
 */
.macro idtentry_sysvec vector cfunc
	idtentry \vector asm_\cfunc \cfunc has_error_code=0
.endm

/**
 * idtentry_mce_db - Macro to generate entry stubs for #MC and #DB
 * @vector:		Vector number
 * @asmsym:		ASM symbol for the entry point
 * @cfunc:		C function to be called
 *
 * The macro emits code to set up the kernel context for #MC and #DB
 *
 * If the entry comes from user space it uses the normal entry path
 * including the return to user space work and preemption checks on
 * exit.
 *
 * If hits in kernel mode then it needs to go through the paranoid
 * entry as the exception can hit any random state. No preemption
 * check on exit to keep the paranoid path simple.
 */
.macro idtentry_mce_db vector asmsym cfunc
SYM_CODE_START(\asmsym)
	UNWIND_HINT_IRET_REGS
	ASM_CLAC

	pushq	$-1			/* ORIG_RAX: no syscall to restart */

	/*
	 * If the entry is from userspace, switch stacks and treat it as
	 * a normal entry.
	 */
	testb	$3, CS-ORIG_RAX(%rsp)
	jnz	.Lfrom_usermode_switch_stack_\@

	/*
	 * paranoid_entry returns SWAPGS flag for paranoid_exit in EBX.
	 * EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS
	 */
	call	paranoid_entry

	UNWIND_HINT_REGS

	movq	%rsp, %rdi		/* pt_regs pointer */

	call	\cfunc

	jmp	paranoid_exit

	/* Switch to the regular task stack and use the noist entry point */
.Lfrom_usermode_switch_stack_\@:
	idtentry_body noist_\cfunc, has_error_code=0

_ASM_NOKPROBE(\asmsym)
SYM_CODE_END(\asmsym)
.endm

/*
 * Double fault entry. Straight paranoid. No checks from which context
 * this comes because for the espfix induced #DF this would do the wrong
 * thing.
 */
.macro idtentry_df vector asmsym cfunc
SYM_CODE_START(\asmsym)
	UNWIND_HINT_IRET_REGS offset=8
	ASM_CLAC

	/*
	 * paranoid_entry returns SWAPGS flag for paranoid_exit in EBX.
	 * EBX == 0 -> SWAPGS, EBX == 1 -> no SWAPGS
	 */
	call	paranoid_entry
	UNWIND_HINT_REGS

	movq	%rsp, %rdi		/* pt_regs pointer into first argument */
	movq	ORIG_RAX(%rsp), %rsi	/* get error code into 2nd argument*/
	movq	$-1, ORIG_RAX(%rsp)	/* no syscall to restart */
	call	\cfunc

	jmp	paranoid_exit

_ASM_NOKPROBE(\asmsym)
SYM_CODE_END(\asmsym)
.endm

/*
 * Include the defines which emit the idt entries which are shared
 * shared between 32 and 64 bit and emit the __irqentry_text_* markers
 * so the stacktrace boundary checks work.
 */
	.align 16
	.globl __irqentry_text_start
__irqentry_text_start:

#include <asm/idtentry.h>

	.align 16
	.globl __irqentry_text_end
__irqentry_text_end:

SYM_CODE_START_LOCAL(common_interrupt_return)
SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
#ifdef CONFIG_DEBUG_ENTRY
	/* Assert that pt_regs indicates user mode. */
	testb	$3, CS(%rsp)
	jnz	1f
	ud2
1:
#endif
	POP_REGS pop_rdi=0

	/*
	 * The stack is now user RDI, orig_ax, RIP, CS, EFLAGS, RSP, SS.
	 * Save old stack pointer and switch to trampoline stack.
	 */
	movq	%rsp, %rdi
	movq	PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
	UNWIND_HINT_EMPTY

	/* Copy the IRET frame to the trampoline stack. */
	pushq	6*8(%rdi)	/* SS */
	pushq	5*8(%rdi)	/* RSP */
	pushq	4*8(%rdi)	/* EFLAGS */
	pushq	3*8(%rdi)	/* CS */
	pushq	2*8(%rdi)	/* RIP */

	/* Push user RDI on the trampoline stack. */
	pushq	(%rdi)

	/*
	 * We are on the trampoline stack.  All regs except RDI are live.
	 * We can do future final exit work right here.
	 */
	STACKLEAK_ERASE_NOCLOBBER

	SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi

	/* Restore RDI. */
	popq	%rdi
	SWAPGS
	INTERRUPT_RETURN


SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)
#ifdef CONFIG_DEBUG_ENTRY
	/* Assert that pt_regs indicates kernel mode. */
	testb	$3, CS(%rsp)
	jz	1f
	ud2
1:
#endif
	POP_REGS
	addq	$8, %rsp	/* skip regs->orig_ax */
	/*
	 * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization
	 * when returning from IPI handler.
	 */
	INTERRUPT_RETURN

SYM_INNER_LABEL_ALIGN(native_iret, SYM_L_GLOBAL)
	UNWIND_HINT_IRET_REGS
	/*
	 * Are we returning to a stack segment from the LDT?  Note: in
	 * 64-bit mode SS:RSP on the exception stack is always valid.
	 */
#ifdef CONFIG_X86_ESPFIX64
	testb	$4, (SS-RIP)(%rsp)
	jnz	native_irq_return_ldt
#endif

SYM_INNER_LABEL(native_irq_return_iret, SYM_L_GLOBAL)
	/*
	 * This may fault.  Non-paranoid faults on return to userspace are
	 * handled by fixup_bad_iret.  These include #SS, #GP, and #NP.
	 * Double-faults due to espfix64 are handled in exc_double_fault.
	 * Other faults here are fatal.
	 */
	iretq

#ifdef CONFIG_X86_ESPFIX64
native_irq_return_ldt:
	/*
	 * We are running with user GSBASE.  All GPRs contain their user
	 * values.  We have a percpu ESPFIX stack that is eight slots
	 * long (see ESPFIX_STACK_SIZE).  espfix_waddr points to the bottom
	 * of the ESPFIX stack.
	 *
	 * We clobber RAX and RDI in this code.  We stash RDI on the
	 * normal stack and RAX on the ESPFIX stack.
	 *
	 * The ESPFIX stack layout we set up looks like this:
	 *
	 * --- top of ESPFIX stack ---
	 * SS
	 * RSP
	 * RFLAGS
	 * CS
	 * RIP  <-- RSP points here when we're done
	 * RAX  <-- espfix_waddr points here
	 * --- bottom of ESPFIX stack ---
	 */

	pushq	%rdi				/* Stash user RDI */
	SWAPGS					/* to kernel GS */
	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi	/* to kernel CR3 */

	movq	PER_CPU_VAR(espfix_waddr), %rdi
	movq	%rax, (0*8)(%rdi)		/* user RAX */
	movq	(1*8)(%rsp), %rax		/* user RIP */
	movq	%rax, (1*8)(%rdi)
	movq	(2*8)(%rsp), %rax		/* user CS */
	movq	%rax, (2*8)(%rdi)
	movq	(3*8)(%rsp), %rax		/* user RFLAGS */
	movq	%rax, (3*8)(%rdi)
	movq	(5*8)(%rsp), %rax		/* user SS */
	movq	%rax, (5*8)(%rdi)
	movq	(4*8)(%rsp), %rax		/* user RSP */
	movq	%rax, (4*8)(%rdi)
	/* Now RAX == RSP. */

	andl	$0xffff0000, %eax		/* RAX = (RSP & 0xffff0000) */

	/*
	 * espfix_stack[31:16] == 0.  The page tables are set up such that
	 * (espfix_stack | (X & 0xffff0000)) points to a read-only alias of
	 * espfix_waddr for any X.  That is, there are 65536 RO aliases of
	 * the same page.  Set up RSP so that RSP[31:16] contains the
	 * respective 16 bits of the /userspace/ RSP and RSP nonetheless
	 * still points to an RO alias of the ESPFIX stack.
	 */
	orq	PER_CPU_VAR(espfix_stack), %rax

	SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
	SWAPGS					/* to user GS */
	popq	%rdi				/* Restore user RDI */

	movq	%rax, %rsp
	UNWIND_HINT_IRET_REGS offset=8

	/*
	 * At this point, we cannot write to the stack any more, but we can
	 * still read.
	 */
	popq	%rax				/* Restore user RAX */

	/*
	 * RSP now points to an ordinary IRET frame, except that the page
	 * is read-only and RSP[31:16] are preloaded with the userspace
	 * values.  We can now IRET back to userspace.
	 */
	jmp	native_irq_return_iret
#endif
SYM_CODE_END(common_interrupt_return)
_ASM_NOKPROBE(common_interrupt_return)

/*
 * Reload gs selector with exception handling
 * edi:  new selector
 *
 * Is in entry.text as it shouldn't be instrumented.
 */
SYM_FUNC_START(asm_load_gs_index)
	FRAME_BEGIN
	swapgs
.Lgs_change:
	movl	%edi, %gs
2:	ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
	swapgs
	FRAME_END
	ret
SYM_FUNC_END(asm_load_gs_index)
EXPORT_SYMBOL(asm_load_gs_index)

	_ASM_EXTABLE(.Lgs_change, .Lbad_gs)
	.section .fixup, "ax"
	/* running with kernelgs */
SYM_CODE_START_LOCAL_NOALIGN(.Lbad_gs)
	swapgs					/* switch back to user gs */
.macro ZAP_GS
	/* This can't be a string because the preprocessor needs to see it. */
	movl $__USER_DS, %eax
	movl %eax, %gs
.endm
	ALTERNATIVE "", "ZAP_GS", X86_BUG_NULL_SEG
	xorl	%eax, %eax
	movl	%eax, %gs
	jmp	2b
SYM_CODE_END(.Lbad_gs)
	.previous

/*
 * rdi: New stack pointer points to the top word of the stack
 * rsi: Function pointer
 * rdx: Function argument (can be NULL if none)
 */
SYM_FUNC_START(asm_call_on_stack)
	/*
	 * Save the frame pointer unconditionally. This allows the ORC
	 * unwinder to handle the stack switch.
	 */
	pushq		%rbp
	mov		%rsp, %rbp

	/*
	 * The unwinder relies on the word at the top of the new stack
	 * page linking back to the previous RSP.
	 */
	mov		%rsp, (%rdi)
	mov		%rdi, %rsp
	/* Move the argument to the right place */
	mov		%rdx, %rdi

1:
	.pushsection .discard.instr_begin
	.long 1b - .
	.popsection

	CALL_NOSPEC	rsi

2:
	.pushsection .discard.instr_end
	.long 2b - .
	.popsection

	/* Restore the previous stack pointer from RBP. */
	leaveq
	ret
SYM_FUNC_END(asm_call_on_stack)

#ifdef CONFIG_XEN_PV
/*
 * A note on the "critical region" in our callback handler.
 * We want to avoid stacking callback handlers due to events occurring
 * during handling of the last event. To do this, we keep events disabled
 * until we've done all processing. HOWEVER, we must enable events before
 * popping the stack frame (can't be done atomically) and so it would still
 * be possible to get enough handler activations to overflow the stack.
 * Although unlikely, bugs of that kind are hard to track down, so we'd
 * like to avoid the possibility.
 * So, on entry to the handler we detect whether we interrupted an
 * existing activation in its critical region -- if so, we pop the current
 * activation and restart the handler using the previous one.
 *
 * C calling convention: exc_xen_hypervisor_callback(struct *pt_regs)
 */
SYM_CODE_START_LOCAL(exc_xen_hypervisor_callback)

/*
 * Since we don't modify %rdi, evtchn_do_upall(struct *pt_regs) will
 * see the correct pointer to the pt_regs
 */
	UNWIND_HINT_FUNC
	movq	%rdi, %rsp			/* we don't return, adjust the stack frame */
	UNWIND_HINT_REGS

	call	xen_pv_evtchn_do_upcall

	jmp	error_return
SYM_CODE_END(exc_xen_hypervisor_callback)

/*
 * Hypervisor uses this for application faults while it executes.
 * We get here for two reasons:
 *  1. Fault while reloading DS, ES, FS or GS
 *  2. Fault while executing IRET
 * Category 1 we do not need to fix up as Xen has already reloaded all segment
 * registers that could be reloaded and zeroed the others.
 * Category 2 we fix up by killing the current process. We cannot use the
 * normal Linux return path in this case because if we use the IRET hypercall
 * to pop the stack frame we end up in an infinite loop of failsafe callbacks.
 * We distinguish between categories by comparing each saved segment register
 * with its current contents: any discrepancy means we in category 1.
 */
SYM_CODE_START(xen_failsafe_callback)
	UNWIND_HINT_EMPTY
	movl	%ds, %ecx
	cmpw	%cx, 0x10(%rsp)
	jne	1f
	movl	%es, %ecx
	cmpw	%cx, 0x18(%rsp)
	jne	1f
	movl	%fs, %ecx
	cmpw	%cx, 0x20(%rsp)
	jne	1f
	movl	%gs, %ecx
	cmpw	%cx, 0x28(%rsp)
	jne	1f
	/* All segments match their saved values => Category 2 (Bad IRET). */
	movq	(%rsp), %rcx
	movq	8(%rsp), %r11
	addq	$0x30, %rsp
	pushq	$0				/* RIP */
	UNWIND_HINT_IRET_REGS offset=8
	jmp	asm_exc_general_protection
1:	/* Segment mismatch => Category 1 (Bad segment). Retry the IRET. */
	movq	(%rsp), %rcx
	movq	8(%rsp), %r11
	addq	$0x30, %rsp
	UNWIND_HINT_IRET_REGS
	pushq	$-1 /* orig_ax = -1 => not a system call */
	PUSH_AND_CLEAR_REGS
	ENCODE_FRAME_POINTER
	jmp	error_return
SYM_CODE_END(xen_failsafe_callback)
#endif /* CONFIG_XEN_PV */

/*
 * Save all registers in pt_regs, and switch gs if needed.
 * Use slow, but surefire "are we in kernel?" check.
 * Return: ebx=0: need swapgs on exit, ebx=1: otherwise
 */
SYM_CODE_START_LOCAL(paranoid_entry)
	UNWIND_HINT_FUNC
	cld
	PUSH_AND_CLEAR_REGS save_ret=1
	ENCODE_FRAME_POINTER 8
	movl	$1, %ebx
	movl	$MSR_GS_BASE, %ecx
	rdmsr
	testl	%edx, %edx
	js	1f				/* negative -> in kernel */
	SWAPGS
	xorl	%ebx, %ebx

1:
	/*
	 * Always stash CR3 in %r14.  This value will be restored,
	 * verbatim, at exit.  Needed if paranoid_entry interrupted
	 * another entry that already switched to the user CR3 value
	 * but has not yet returned to userspace.
	 *
	 * This is also why CS (stashed in the "iret frame" by the
	 * hardware at entry) can not be used: this may be a return
	 * to kernel code, but with a user CR3 value.
	 */
	SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14

	/*
	 * The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an
	 * unconditional CR3 write, even in the PTI case.  So do an lfence
	 * to prevent GS speculation, regardless of whether PTI is enabled.
	 */
	FENCE_SWAPGS_KERNEL_ENTRY

	ret
SYM_CODE_END(paranoid_entry)

/*
 * "Paranoid" exit path from exception stack.  This is invoked
 * only on return from non-NMI IST interrupts that came
 * from kernel space.
 *
 * We may be returning to very strange contexts (e.g. very early
 * in syscall entry), so checking for preemption here would
 * be complicated.  Fortunately, we there's no good reason
 * to try to handle preemption here.
 *
 * On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it)
 */
SYM_CODE_START_LOCAL(paranoid_exit)
	UNWIND_HINT_REGS
	testl	%ebx, %ebx			/* swapgs needed? */
	jnz	.Lparanoid_exit_no_swapgs
	/* Always restore stashed CR3 value (see paranoid_entry) */
	RESTORE_CR3	scratch_reg=%rbx save_reg=%r14
	SWAPGS_UNSAFE_STACK
	jmp	restore_regs_and_return_to_kernel
.Lparanoid_exit_no_swapgs:
	/* Always restore stashed CR3 value (see paranoid_entry) */
	RESTORE_CR3	scratch_reg=%rbx save_reg=%r14
	jmp restore_regs_and_return_to_kernel
SYM_CODE_END(paranoid_exit)

/*
 * Save all registers in pt_regs, and switch GS if needed.
 */
SYM_CODE_START_LOCAL(error_entry)
	UNWIND_HINT_FUNC
	cld
	PUSH_AND_CLEAR_REGS save_ret=1
	ENCODE_FRAME_POINTER 8
	testb	$3, CS+8(%rsp)
	jz	.Lerror_kernelspace

	/*
	 * We entered from user mode or we're pretending to have entered
	 * from user mode due to an IRET fault.
	 */
	SWAPGS
	FENCE_SWAPGS_USER_ENTRY
	/* We have user CR3.  Change to kernel CR3. */
	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax

.Lerror_entry_from_usermode_after_swapgs:
	/* Put us onto the real thread stack. */
	popq	%r12				/* save return addr in %12 */
	movq	%rsp, %rdi			/* arg0 = pt_regs pointer */
	call	sync_regs
	movq	%rax, %rsp			/* switch stack */
	ENCODE_FRAME_POINTER
	pushq	%r12
	ret

.Lerror_entry_done_lfence:
	FENCE_SWAPGS_KERNEL_ENTRY
.Lerror_entry_done:
	ret

	/*
	 * There are two places in the kernel that can potentially fault with
	 * usergs. Handle them here.  B stepping K8s sometimes report a
	 * truncated RIP for IRET exceptions returning to compat mode. Check
	 * for these here too.
	 */
.Lerror_kernelspace:
	leaq	native_irq_return_iret(%rip), %rcx
	cmpq	%rcx, RIP+8(%rsp)
	je	.Lerror_bad_iret
	movl	%ecx, %eax			/* zero extend */
	cmpq	%rax, RIP+8(%rsp)
	je	.Lbstep_iret
	cmpq	$.Lgs_change, RIP+8(%rsp)
	jne	.Lerror_entry_done_lfence

	/*
	 * hack: .Lgs_change can fail with user gsbase.  If this happens, fix up
	 * gsbase and proceed.  We'll fix up the exception and land in
	 * .Lgs_change's error handler with kernel gsbase.
	 */
	SWAPGS
	FENCE_SWAPGS_USER_ENTRY
	jmp .Lerror_entry_done

.Lbstep_iret:
	/* Fix truncated RIP */
	movq	%rcx, RIP+8(%rsp)
	/* fall through */

.Lerror_bad_iret:
	/*
	 * We came from an IRET to user mode, so we have user
	 * gsbase and CR3.  Switch to kernel gsbase and CR3:
	 */
	SWAPGS
	FENCE_SWAPGS_USER_ENTRY
	SWITCH_TO_KERNEL_CR3 scratch_reg=%rax

	/*
	 * Pretend that the exception came from user mode: set up pt_regs
	 * as if we faulted immediately after IRET.
	 */
	mov	%rsp, %rdi
	call	fixup_bad_iret
	mov	%rax, %rsp
	jmp	.Lerror_entry_from_usermode_after_swapgs
SYM_CODE_END(error_entry)

SYM_CODE_START_LOCAL(error_return)
	UNWIND_HINT_REGS
	DEBUG_ENTRY_ASSERT_IRQS_OFF
	testb	$3, CS(%rsp)
	jz	restore_regs_and_return_to_kernel
	jmp	swapgs_restore_regs_and_return_to_usermode
SYM_CODE_END(error_return)

/*
 * Runs on exception stack.  Xen PV does not go through this path at all,
 * so we can use real assembly here.
 *
 * Registers:
 *	%r14: Used to save/restore the CR3 of the interrupted context
 *	      when PAGE_TABLE_ISOLATION is in use.  Do not clobber.
 */
SYM_CODE_START(asm_exc_nmi)
	UNWIND_HINT_IRET_REGS

	/*
	 * We allow breakpoints in NMIs. If a breakpoint occurs, then
	 * the iretq it performs will take us out of NMI context.
	 * This means that we can have nested NMIs where the next
	 * NMI is using the top of the stack of the previous NMI. We
	 * can't let it execute because the nested NMI will corrupt the
	 * stack of the previous NMI. NMI handlers are not re-entrant
	 * anyway.
	 *
	 * To handle this case we do the following:
	 *  Check the a special location on the stack that contains
	 *  a variable that is set when NMIs are executing.
	 *  The interrupted task's stack is also checked to see if it
	 *  is an NMI stack.
	 *  If the variable is not set and the stack is not the NMI
	 *  stack then:
	 *    o Set the special variable on the stack
	 *    o Copy the interrupt frame into an "outermost" location on the
	 *      stack
	 *    o Copy the interrupt frame into an "iret" location on the stack
	 *    o Continue processing the NMI
	 *  If the variable is set or the previous stack is the NMI stack:
	 *    o Modify the "iret" location to jump to the repeat_nmi
	 *    o return back to the first NMI
	 *
	 * Now on exit of the first NMI, we first clear the stack variable
	 * The NMI stack will tell any nested NMIs at that point that it is
	 * nested. Then we pop the stack normally with iret, and if there was
	 * a nested NMI that updated the copy interrupt stack frame, a
	 * jump will be made to the repeat_nmi code that will handle the second
	 * NMI.
	 *
	 * However, espfix prevents us from directly returning to userspace
	 * with a single IRET instruction.  Similarly, IRET to user mode
	 * can fault.  We therefore handle NMIs from user space like
	 * other IST entries.
	 */

	ASM_CLAC

	/* Use %rdx as our temp variable throughout */
	pushq	%rdx

	testb	$3, CS-RIP+8(%rsp)
	jz	.Lnmi_from_kernel

	/*
	 * NMI from user mode.  We need to run on the thread stack, but we
	 * can't go through the normal entry paths: NMIs are masked, and
	 * we don't want to enable interrupts, because then we'll end
	 * up in an awkward situation in which IRQs are on but NMIs
	 * are off.
	 *
	 * We also must not push anything to the stack before switching
	 * stacks lest we corrupt the "NMI executing" variable.
	 */

	swapgs
	cld
	FENCE_SWAPGS_USER_ENTRY
	SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx
	movq	%rsp, %rdx
	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
	UNWIND_HINT_IRET_REGS base=%rdx offset=8
	pushq	5*8(%rdx)	/* pt_regs->ss */
	pushq	4*8(%rdx)	/* pt_regs->rsp */
	pushq	3*8(%rdx)	/* pt_regs->flags */
	pushq	2*8(%rdx)	/* pt_regs->cs */
	pushq	1*8(%rdx)	/* pt_regs->rip */
	UNWIND_HINT_IRET_REGS
	pushq   $-1		/* pt_regs->orig_ax */
	PUSH_AND_CLEAR_REGS rdx=(%rdx)
	ENCODE_FRAME_POINTER

	/*
	 * At this point we no longer need to worry about stack damage
	 * due to nesting -- we're on the normal thread stack and we're
	 * done with the NMI stack.
	 */

	movq	%rsp, %rdi
	movq	$-1, %rsi
	call	exc_nmi

	/*
	 * Return back to user mode.  We must *not* do the normal exit
	 * work, because we don't want to enable interrupts.
	 */
	jmp	swapgs_restore_regs_and_return_to_usermode

.Lnmi_from_kernel:
	/*
	 * Here's what our stack frame will look like:
	 * +---------------------------------------------------------+
	 * | original SS                                             |
	 * | original Return RSP                                     |
	 * | original RFLAGS                                         |
	 * | original CS                                             |
	 * | original RIP                                            |
	 * +---------------------------------------------------------+
	 * | temp storage for rdx                                    |
	 * +---------------------------------------------------------+
	 * | "NMI executing" variable                                |
	 * +---------------------------------------------------------+
	 * | iret SS          } Copied from "outermost" frame        |
	 * | iret Return RSP  } on each loop iteration; overwritten  |
	 * | iret RFLAGS      } by a nested NMI to force another     |
	 * | iret CS          } iteration if needed.                 |
	 * | iret RIP         }                                      |
	 * +---------------------------------------------------------+
	 * | outermost SS          } initialized in first_nmi;       |
	 * | outermost Return RSP  } will not be changed before      |
	 * | outermost RFLAGS      } NMI processing is done.         |
	 * | outermost CS          } Copied to "iret" frame on each  |
	 * | outermost RIP         } iteration.                      |
	 * +---------------------------------------------------------+
	 * | pt_regs                                                 |
	 * +---------------------------------------------------------+
	 *
	 * The "original" frame is used by hardware.  Before re-enabling
	 * NMIs, we need to be done with it, and we need to leave enough
	 * space for the asm code here.
	 *
	 * We return by executing IRET while RSP points to the "iret" frame.
	 * That will either return for real or it will loop back into NMI
	 * processing.
	 *
	 * The "outermost" frame is copied to the "iret" frame on each
	 * iteration of the loop, so each iteration starts with the "iret"
	 * frame pointing to the final return target.
	 */

	/*
	 * Determine whether we're a nested NMI.
	 *
	 * If we interrupted kernel code between repeat_nmi and
	 * end_repeat_nmi, then we are a nested NMI.  We must not
	 * modify the "iret" frame because it's being written by
	 * the outer NMI.  That's okay; the outer NMI handler is
	 * about to about to call exc_nmi() anyway, so we can just
	 * resume the outer NMI.
	 */

	movq	$repeat_nmi, %rdx
	cmpq	8(%rsp), %rdx
	ja	1f
	movq	$end_repeat_nmi, %rdx
	cmpq	8(%rsp), %rdx
	ja	nested_nmi_out
1:

	/*
	 * Now check "NMI executing".  If it's set, then we're nested.
	 * This will not detect if we interrupted an outer NMI just
	 * before IRET.
	 */
	cmpl	$1, -8(%rsp)
	je	nested_nmi

	/*
	 * Now test if the previous stack was an NMI stack.  This covers
	 * the case where we interrupt an outer NMI after it clears
	 * "NMI executing" but before IRET.  We need to be careful, though:
	 * there is one case in which RSP could point to the NMI stack
	 * despite there being no NMI active: naughty userspace controls
	 * RSP at the very beginning of the SYSCALL targets.  We can
	 * pull a fast one on naughty userspace, though: we program
	 * SYSCALL to mask DF, so userspace cannot cause DF to be set
	 * if it controls the kernel's RSP.  We set DF before we clear
	 * "NMI executing".
	 */
	lea	6*8(%rsp), %rdx
	/* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp)) */
	cmpq	%rdx, 4*8(%rsp)
	/* If the stack pointer is above the NMI stack, this is a normal NMI */
	ja	first_nmi

	subq	$EXCEPTION_STKSZ, %rdx
	cmpq	%rdx, 4*8(%rsp)
	/* If it is below the NMI stack, it is a normal NMI */
	jb	first_nmi

	/* Ah, it is within the NMI stack. */

	testb	$(X86_EFLAGS_DF >> 8), (3*8 + 1)(%rsp)
	jz	first_nmi	/* RSP was user controlled. */

	/* This is a nested NMI. */

nested_nmi:
	/*
	 * Modify the "iret" frame to point to repeat_nmi, forcing another
	 * iteration of NMI handling.
	 */
	subq	$8, %rsp
	leaq	-10*8(%rsp), %rdx
	pushq	$__KERNEL_DS
	pushq	%rdx
	pushfq
	pushq	$__KERNEL_CS
	pushq	$repeat_nmi

	/* Put stack back */
	addq	$(6*8), %rsp

nested_nmi_out:
	popq	%rdx

	/* We are returning to kernel mode, so this cannot result in a fault. */
	iretq

first_nmi:
	/* Restore rdx. */
	movq	(%rsp), %rdx

	/* Make room for "NMI executing". */
	pushq	$0

	/* Leave room for the "iret" frame */
	subq	$(5*8), %rsp

	/* Copy the "original" frame to the "outermost" frame */
	.rept 5
	pushq	11*8(%rsp)
	.endr
	UNWIND_HINT_IRET_REGS

	/* Everything up to here is safe from nested NMIs */

#ifdef CONFIG_DEBUG_ENTRY
	/*
	 * For ease of testing, unmask NMIs right away.  Disabled by
	 * default because IRET is very expensive.
	 */
	pushq	$0		/* SS */
	pushq	%rsp		/* RSP (minus 8 because of the previous push) */
	addq	$8, (%rsp)	/* Fix up RSP */
	pushfq			/* RFLAGS */
	pushq	$__KERNEL_CS	/* CS */
	pushq	$1f		/* RIP */
	iretq			/* continues at repeat_nmi below */
	UNWIND_HINT_IRET_REGS
1:
#endif

repeat_nmi:
	/*
	 * If there was a nested NMI, the first NMI's iret will return
	 * here. But NMIs are still enabled and we can take another
	 * nested NMI. The nested NMI checks the interrupted RIP to see
	 * if it is between repeat_nmi and end_repeat_nmi, and if so
	 * it will just return, as we are about to repeat an NMI anyway.
	 * This makes it safe to copy to the stack frame that a nested
	 * NMI will update.
	 *
	 * RSP is pointing to "outermost RIP".  gsbase is unknown, but, if
	 * we're repeating an NMI, gsbase has the same value that it had on
	 * the first iteration.  paranoid_entry will load the kernel
	 * gsbase if needed before we call exc_nmi().  "NMI executing"
	 * is zero.
	 */
	movq	$1, 10*8(%rsp)		/* Set "NMI executing". */

	/*
	 * Copy the "outermost" frame to the "iret" frame.  NMIs that nest
	 * here must not modify the "iret" frame while we're writing to
	 * it or it will end up containing garbage.
	 */
	addq	$(10*8), %rsp
	.rept 5
	pushq	-6*8(%rsp)
	.endr
	subq	$(5*8), %rsp
end_repeat_nmi:

	/*
	 * Everything below this point can be preempted by a nested NMI.
	 * If this happens, then the inner NMI will change the "iret"
	 * frame to point back to repeat_nmi.
	 */
	pushq	$-1				/* ORIG_RAX: no syscall to restart */

	/*
	 * Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit
	 * as we should not be calling schedule in NMI context.
	 * Even with normal interrupts enabled. An NMI should not be
	 * setting NEED_RESCHED or anything that normal interrupts and
	 * exceptions might do.
	 */
	call	paranoid_entry
	UNWIND_HINT_REGS

	movq	%rsp, %rdi
	movq	$-1, %rsi
	call	exc_nmi

	/* Always restore stashed CR3 value (see paranoid_entry) */
	RESTORE_CR3 scratch_reg=%r15 save_reg=%r14

	testl	%ebx, %ebx			/* swapgs needed? */
	jnz	nmi_restore
nmi_swapgs:
	SWAPGS_UNSAFE_STACK
nmi_restore:
	POP_REGS

	/*
	 * Skip orig_ax and the "outermost" frame to point RSP at the "iret"
	 * at the "iret" frame.
	 */
	addq	$6*8, %rsp

	/*
	 * Clear "NMI executing".  Set DF first so that we can easily
	 * distinguish the remaining code between here and IRET from
	 * the SYSCALL entry and exit paths.
	 *
	 * We arguably should just inspect RIP instead, but I (Andy) wrote
	 * this code when I had the misapprehension that Xen PV supported
	 * NMIs, and Xen PV would break that approach.
	 */
	std
	movq	$0, 5*8(%rsp)		/* clear "NMI executing" */

	/*
	 * iretq reads the "iret" frame and exits the NMI stack in a
	 * single instruction.  We are returning to kernel mode, so this
	 * cannot result in a fault.  Similarly, we don't need to worry
	 * about espfix64 on the way back to kernel mode.
	 */
	iretq
SYM_CODE_END(asm_exc_nmi)

#ifndef CONFIG_IA32_EMULATION
/*
 * This handles SYSCALL from 32-bit code.  There is no way to program
 * MSRs to fully disable 32-bit SYSCALL.
 */
SYM_CODE_START(ignore_sysret)
	UNWIND_HINT_EMPTY
	mov	$-ENOSYS, %eax
	sysretl
SYM_CODE_END(ignore_sysret)
#endif

.pushsection .text, "ax"
SYM_CODE_START(rewind_stack_do_exit)
	UNWIND_HINT_FUNC
	/* Prevent any naive code from trying to unwind to our caller. */
	xorl	%ebp, %ebp

	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rax
	leaq	-PTREGS_SIZE(%rax), %rsp
	UNWIND_HINT_REGS

	call	do_exit
SYM_CODE_END(rewind_stack_do_exit)
.popsection