summaryrefslogtreecommitdiffstats
path: root/arch/x86/mm/tlb.c
blob: 03b6b4c2238daa6c5a97d6eb10c32fb825a9a077 (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
#include <linux/init.h>

#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/export.h>
#include <linux/cpu.h>
#include <linux/debugfs.h>

#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/nospec-branch.h>
#include <asm/cache.h>
#include <asm/apic.h>
#include <asm/uv/uv.h>

/*
 *	TLB flushing, formerly SMP-only
 *		c/o Linus Torvalds.
 *
 *	These mean you can really definitely utterly forget about
 *	writing to user space from interrupts. (Its not allowed anyway).
 *
 *	Optimizations Manfred Spraul <manfred@colorfullife.com>
 *
 *	More scalable flush, from Andi Kleen
 *
 *	Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi
 */

/*
 * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer which is
 * stored in cpu_tlb_state.last_user_mm_ibpb.
 */
#define LAST_USER_MM_IBPB	0x1UL

/*
 * We get here when we do something requiring a TLB invalidation
 * but could not go invalidate all of the contexts.  We do the
 * necessary invalidation by clearing out the 'ctx_id' which
 * forces a TLB flush when the context is loaded.
 */
static void clear_asid_other(void)
{
	u16 asid;

	/*
	 * This is only expected to be set if we have disabled
	 * kernel _PAGE_GLOBAL pages.
	 */
	if (!static_cpu_has(X86_FEATURE_PTI)) {
		WARN_ON_ONCE(1);
		return;
	}

	for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
		/* Do not need to flush the current asid */
		if (asid == this_cpu_read(cpu_tlbstate.loaded_mm_asid))
			continue;
		/*
		 * Make sure the next time we go to switch to
		 * this asid, we do a flush:
		 */
		this_cpu_write(cpu_tlbstate.ctxs[asid].ctx_id, 0);
	}
	this_cpu_write(cpu_tlbstate.invalidate_other, false);
}

atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);


static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
			    u16 *new_asid, bool *need_flush)
{
	u16 asid;

	if (!static_cpu_has(X86_FEATURE_PCID)) {
		*new_asid = 0;
		*need_flush = true;
		return;
	}

	if (this_cpu_read(cpu_tlbstate.invalidate_other))
		clear_asid_other();

	for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
		if (this_cpu_read(cpu_tlbstate.ctxs[asid].ctx_id) !=
		    next->context.ctx_id)
			continue;

		*new_asid = asid;
		*need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) <
			       next_tlb_gen);
		return;
	}

	/*
	 * We don't currently own an ASID slot on this CPU.
	 * Allocate a slot.
	 */
	*new_asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1;
	if (*new_asid >= TLB_NR_DYN_ASIDS) {
		*new_asid = 0;
		this_cpu_write(cpu_tlbstate.next_asid, 1);
	}
	*need_flush = true;
}

static void load_new_mm_cr3(pgd_t *pgdir, u16 new_asid, bool need_flush)
{
	unsigned long new_mm_cr3;

	if (need_flush) {
		invalidate_user_asid(new_asid);
		new_mm_cr3 = build_cr3(pgdir, new_asid);
	} else {
		new_mm_cr3 = build_cr3_noflush(pgdir, new_asid);
	}

	/*
	 * Caution: many callers of this function expect
	 * that load_cr3() is serializing and orders TLB
	 * fills with respect to the mm_cpumask writes.
	 */
	write_cr3(new_mm_cr3);
}

void leave_mm(int cpu)
{
	struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);

	/*
	 * It's plausible that we're in lazy TLB mode while our mm is init_mm.
	 * If so, our callers still expect us to flush the TLB, but there
	 * aren't any user TLB entries in init_mm to worry about.
	 *
	 * This needs to happen before any other sanity checks due to
	 * intel_idle's shenanigans.
	 */
	if (loaded_mm == &init_mm)
		return;

	/* Warn if we're not lazy. */
	WARN_ON(!this_cpu_read(cpu_tlbstate.is_lazy));

	switch_mm(NULL, &init_mm, NULL);
}
EXPORT_SYMBOL_GPL(leave_mm);

void switch_mm(struct mm_struct *prev, struct mm_struct *next,
	       struct task_struct *tsk)
{
	unsigned long flags;

	local_irq_save(flags);
	switch_mm_irqs_off(prev, next, tsk);
	local_irq_restore(flags);
}

static void sync_current_stack_to_mm(struct mm_struct *mm)
{
	unsigned long sp = current_stack_pointer;
	pgd_t *pgd = pgd_offset(mm, sp);

	if (pgtable_l5_enabled()) {
		if (unlikely(pgd_none(*pgd))) {
			pgd_t *pgd_ref = pgd_offset_k(sp);

			set_pgd(pgd, *pgd_ref);
		}
	} else {
		/*
		 * "pgd" is faked.  The top level entries are "p4d"s, so sync
		 * the p4d.  This compiles to approximately the same code as
		 * the 5-level case.
		 */
		p4d_t *p4d = p4d_offset(pgd, sp);

		if (unlikely(p4d_none(*p4d))) {
			pgd_t *pgd_ref = pgd_offset_k(sp);
			p4d_t *p4d_ref = p4d_offset(pgd_ref, sp);

			set_p4d(p4d, *p4d_ref);
		}
	}
}

static inline unsigned long mm_mangle_tif_spec_ib(struct task_struct *next)
{
	unsigned long next_tif = task_thread_info(next)->flags;
	unsigned long ibpb = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_IBPB;

	return (unsigned long)next->mm | ibpb;
}

static void cond_ibpb(struct task_struct *next)
{
	if (!next || !next->mm)
		return;

	/*
	 * Both, the conditional and the always IBPB mode use the mm
	 * pointer to avoid the IBPB when switching between tasks of the
	 * same process. Using the mm pointer instead of mm->context.ctx_id
	 * opens a hypothetical hole vs. mm_struct reuse, which is more or
	 * less impossible to control by an attacker. Aside of that it
	 * would only affect the first schedule so the theoretically
	 * exposed data is not really interesting.
	 */
	if (static_branch_likely(&switch_mm_cond_ibpb)) {
		unsigned long prev_mm, next_mm;

		/*
		 * This is a bit more complex than the always mode because
		 * it has to handle two cases:
		 *
		 * 1) Switch from a user space task (potential attacker)
		 *    which has TIF_SPEC_IB set to a user space task
		 *    (potential victim) which has TIF_SPEC_IB not set.
		 *
		 * 2) Switch from a user space task (potential attacker)
		 *    which has TIF_SPEC_IB not set to a user space task
		 *    (potential victim) which has TIF_SPEC_IB set.
		 *
		 * This could be done by unconditionally issuing IBPB when
		 * a task which has TIF_SPEC_IB set is either scheduled in
		 * or out. Though that results in two flushes when:
		 *
		 * - the same user space task is scheduled out and later
		 *   scheduled in again and only a kernel thread ran in
		 *   between.
		 *
		 * - a user space task belonging to the same process is
		 *   scheduled in after a kernel thread ran in between
		 *
		 * - a user space task belonging to the same process is
		 *   scheduled in immediately.
		 *
		 * Optimize this with reasonably small overhead for the
		 * above cases. Mangle the TIF_SPEC_IB bit into the mm
		 * pointer of the incoming task which is stored in
		 * cpu_tlbstate.last_user_mm_ibpb for comparison.
		 */
		next_mm = mm_mangle_tif_spec_ib(next);
		prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_ibpb);

		/*
		 * Issue IBPB only if the mm's are different and one or
		 * both have the IBPB bit set.
		 */
		if (next_mm != prev_mm &&
		    (next_mm | prev_mm) & LAST_USER_MM_IBPB)
			indirect_branch_prediction_barrier();

		this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, next_mm);
	}

	if (static_branch_unlikely(&switch_mm_always_ibpb)) {
		/*
		 * Only flush when switching to a user space task with a
		 * different context than the user space task which ran
		 * last on this CPU.
		 */
		if (this_cpu_read(cpu_tlbstate.last_user_mm) != next->mm) {
			indirect_branch_prediction_barrier();
			this_cpu_write(cpu_tlbstate.last_user_mm, next->mm);
		}
	}
}

void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
			struct task_struct *tsk)
{
	struct mm_struct *real_prev = this_cpu_read(cpu_tlbstate.loaded_mm);
	u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
	bool was_lazy = this_cpu_read(cpu_tlbstate.is_lazy);
	unsigned cpu = smp_processor_id();
	u64 next_tlb_gen;
	bool need_flush;
	u16 new_asid;

	/*
	 * NB: The scheduler will call us with prev == next when switching
	 * from lazy TLB mode to normal mode if active_mm isn't changing.
	 * When this happens, we don't assume that CR3 (and hence
	 * cpu_tlbstate.loaded_mm) matches next.
	 *
	 * NB: leave_mm() calls us with prev == NULL and tsk == NULL.
	 */

	/* We don't want flush_tlb_func_* to run concurrently with us. */
	if (IS_ENABLED(CONFIG_PROVE_LOCKING))
		WARN_ON_ONCE(!irqs_disabled());

	/*
	 * Verify that CR3 is what we think it is.  This will catch
	 * hypothetical buggy code that directly switches to swapper_pg_dir
	 * without going through leave_mm() / switch_mm_irqs_off() or that
	 * does something like write_cr3(read_cr3_pa()).
	 *
	 * Only do this check if CONFIG_DEBUG_VM=y because __read_cr3()
	 * isn't free.
	 */
#ifdef CONFIG_DEBUG_VM
	if (WARN_ON_ONCE(__read_cr3() != build_cr3(real_prev->pgd, prev_asid))) {
		/*
		 * If we were to BUG here, we'd be very likely to kill
		 * the system so hard that we don't see the call trace.
		 * Try to recover instead by ignoring the error and doing
		 * a global flush to minimize the chance of corruption.
		 *
		 * (This is far from being a fully correct recovery.
		 *  Architecturally, the CPU could prefetch something
		 *  back into an incorrect ASID slot and leave it there
		 *  to cause trouble down the road.  It's better than
		 *  nothing, though.)
		 */
		__flush_tlb_all();
	}
#endif
	this_cpu_write(cpu_tlbstate.is_lazy, false);

	/*
	 * The membarrier system call requires a full memory barrier and
	 * core serialization before returning to user-space, after
	 * storing to rq->curr. Writing to CR3 provides that full
	 * memory barrier and core serializing instruction.
	 */
	if (real_prev == next) {
		VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
			   next->context.ctx_id);

		/*
		 * Even in lazy TLB mode, the CPU should stay set in the
		 * mm_cpumask. The TLB shootdown code can figure out from
		 * from cpu_tlbstate.is_lazy whether or not to send an IPI.
		 */
		if (WARN_ON_ONCE(real_prev != &init_mm &&
				 !cpumask_test_cpu(cpu, mm_cpumask(next))))
			cpumask_set_cpu(cpu, mm_cpumask(next));

		/*
		 * If the CPU is not in lazy TLB mode, we are just switching
		 * from one thread in a process to another thread in the same
		 * process. No TLB flush required.
		 */
		if (!was_lazy)
			return;

		/*
		 * Read the tlb_gen to check whether a flush is needed.
		 * If the TLB is up to date, just use it.
		 * The barrier synchronizes with the tlb_gen increment in
		 * the TLB shootdown code.
		 */
		smp_mb();
		next_tlb_gen = atomic64_read(&next->context.tlb_gen);
		if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) ==
				next_tlb_gen)
			return;

		/*
		 * TLB contents went out of date while we were in lazy
		 * mode. Fall through to the TLB switching code below.
		 */
		new_asid = prev_asid;
		need_flush = true;
	} else {
		/*
		 * Avoid user/user BTB poisoning by flushing the branch
		 * predictor when switching between processes. This stops
		 * one process from doing Spectre-v2 attacks on another.
		 */
		cond_ibpb(tsk);

		if (IS_ENABLED(CONFIG_VMAP_STACK)) {
			/*
			 * If our current stack is in vmalloc space and isn't
			 * mapped in the new pgd, we'll double-fault.  Forcibly
			 * map it.
			 */
			sync_current_stack_to_mm(next);
		}

		/*
		 * Stop remote flushes for the previous mm.
		 * Skip kernel threads; we never send init_mm TLB flushing IPIs,
		 * but the bitmap manipulation can cause cache line contention.
		 */
		if (real_prev != &init_mm) {
			VM_WARN_ON_ONCE(!cpumask_test_cpu(cpu,
						mm_cpumask(real_prev)));
			cpumask_clear_cpu(cpu, mm_cpumask(real_prev));
		}

		/*
		 * Start remote flushes and then read tlb_gen.
		 */
		if (next != &init_mm)
			cpumask_set_cpu(cpu, mm_cpumask(next));
		next_tlb_gen = atomic64_read(&next->context.tlb_gen);

		choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush);

		/* Let nmi_uaccess_okay() know that we're changing CR3. */
		this_cpu_write(cpu_tlbstate.loaded_mm, LOADED_MM_SWITCHING);
		barrier();
	}

	if (need_flush) {
		this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id);
		this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen);
		load_new_mm_cr3(next->pgd, new_asid, true);

		/*
		 * NB: This gets called via leave_mm() in the idle path
		 * where RCU functions differently.  Tracing normally
		 * uses RCU, so we need to use the _rcuidle variant.
		 *
		 * (There is no good reason for this.  The idle code should
		 *  be rearranged to call this before rcu_idle_enter().)
		 */
		trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
	} else {
		/* The new ASID is already up to date. */
		load_new_mm_cr3(next->pgd, new_asid, false);

		/* See above wrt _rcuidle. */
		trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, 0);
	}

	/* Make sure we write CR3 before loaded_mm. */
	barrier();

	this_cpu_write(cpu_tlbstate.loaded_mm, next);
	this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid);

	if (next != real_prev) {
		load_mm_cr4(next);
		switch_ldt(real_prev, next);
	}
}

/*
 * Please ignore the name of this function.  It should be called
 * switch_to_kernel_thread().
 *
 * enter_lazy_tlb() is a hint from the scheduler that we are entering a
 * kernel thread or other context without an mm.  Acceptable implementations
 * include doing nothing whatsoever, switching to init_mm, or various clever
 * lazy tricks to try to minimize TLB flushes.
 *
 * The scheduler reserves the right to call enter_lazy_tlb() several times
 * in a row.  It will notify us that we're going back to a real mm by
 * calling switch_mm_irqs_off().
 */
void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
{
	if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm)
		return;

	this_cpu_write(cpu_tlbstate.is_lazy, true);
}

/*
 * Call this when reinitializing a CPU.  It fixes the following potential
 * problems:
 *
 * - The ASID changed from what cpu_tlbstate thinks it is (most likely
 *   because the CPU was taken down and came back up with CR3's PCID
 *   bits clear.  CPU hotplug can do this.
 *
 * - The TLB contains junk in slots corresponding to inactive ASIDs.
 *
 * - The CPU went so far out to lunch that it may have missed a TLB
 *   flush.
 */
void initialize_tlbstate_and_flush(void)
{
	int i;
	struct mm_struct *mm = this_cpu_read(cpu_tlbstate.loaded_mm);
	u64 tlb_gen = atomic64_read(&init_mm.context.tlb_gen);
	unsigned long cr3 = __read_cr3();

	/* Assert that CR3 already references the right mm. */
	WARN_ON((cr3 & CR3_ADDR_MASK) != __pa(mm->pgd));

	/*
	 * Assert that CR4.PCIDE is set if needed.  (CR4.PCIDE initialization
	 * doesn't work like other CR4 bits because it can only be set from
	 * long mode.)
	 */
	WARN_ON(boot_cpu_has(X86_FEATURE_PCID) &&
		!(cr4_read_shadow() & X86_CR4_PCIDE));

	/* Force ASID 0 and force a TLB flush. */
	write_cr3(build_cr3(mm->pgd, 0));

	/* Reinitialize tlbstate. */
	this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, LAST_USER_MM_IBPB);
	this_cpu_write(cpu_tlbstate.loaded_mm_asid, 0);
	this_cpu_write(cpu_tlbstate.next_asid, 1);
	this_cpu_write(cpu_tlbstate.ctxs[0].ctx_id, mm->context.ctx_id);
	this_cpu_write(cpu_tlbstate.ctxs[0].tlb_gen, tlb_gen);

	for (i = 1; i < TLB_NR_DYN_ASIDS; i++)
		this_cpu_write(cpu_tlbstate.ctxs[i].ctx_id, 0);
}

/*
 * flush_tlb_func_common()'s memory ordering requirement is that any
 * TLB fills that happen after we flush the TLB are ordered after we
 * read active_mm's tlb_gen.  We don't need any explicit barriers
 * because all x86 flush operations are serializing and the
 * atomic64_read operation won't be reordered by the compiler.
 */
static void flush_tlb_func_common(const struct flush_tlb_info *f,
				  bool local, enum tlb_flush_reason reason)
{
	/*
	 * We have three different tlb_gen values in here.  They are:
	 *
	 * - mm_tlb_gen:     the latest generation.
	 * - local_tlb_gen:  the generation that this CPU has already caught
	 *                   up to.
	 * - f->new_tlb_gen: the generation that the requester of the flush
	 *                   wants us to catch up to.
	 */
	struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
	u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
	u64 mm_tlb_gen = atomic64_read(&loaded_mm->context.tlb_gen);
	u64 local_tlb_gen = this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen);

	/* This code cannot presently handle being reentered. */
	VM_WARN_ON(!irqs_disabled());

	if (unlikely(loaded_mm == &init_mm))
		return;

	VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].ctx_id) !=
		   loaded_mm->context.ctx_id);

	if (this_cpu_read(cpu_tlbstate.is_lazy)) {
		/*
		 * We're in lazy mode.  We need to at least flush our
		 * paging-structure cache to avoid speculatively reading
		 * garbage into our TLB.  Since switching to init_mm is barely
		 * slower than a minimal flush, just switch to init_mm.
		 *
		 * This should be rare, with native_flush_tlb_others skipping
		 * IPIs to lazy TLB mode CPUs.
		 */
		switch_mm_irqs_off(NULL, &init_mm, NULL);
		return;
	}

	if (unlikely(local_tlb_gen == mm_tlb_gen)) {
		/*
		 * There's nothing to do: we're already up to date.  This can
		 * happen if two concurrent flushes happen -- the first flush to
		 * be handled can catch us all the way up, leaving no work for
		 * the second flush.
		 */
		trace_tlb_flush(reason, 0);
		return;
	}

	WARN_ON_ONCE(local_tlb_gen > mm_tlb_gen);
	WARN_ON_ONCE(f->new_tlb_gen > mm_tlb_gen);

	/*
	 * If we get to this point, we know that our TLB is out of date.
	 * This does not strictly imply that we need to flush (it's
	 * possible that f->new_tlb_gen <= local_tlb_gen), but we're
	 * going to need to flush in the very near future, so we might
	 * as well get it over with.
	 *
	 * The only question is whether to do a full or partial flush.
	 *
	 * We do a partial flush if requested and two extra conditions
	 * are met:
	 *
	 * 1. f->new_tlb_gen == local_tlb_gen + 1.  We have an invariant that
	 *    we've always done all needed flushes to catch up to
	 *    local_tlb_gen.  If, for example, local_tlb_gen == 2 and
	 *    f->new_tlb_gen == 3, then we know that the flush needed to bring
	 *    us up to date for tlb_gen 3 is the partial flush we're
	 *    processing.
	 *
	 *    As an example of why this check is needed, suppose that there
	 *    are two concurrent flushes.  The first is a full flush that
	 *    changes context.tlb_gen from 1 to 2.  The second is a partial
	 *    flush that changes context.tlb_gen from 2 to 3.  If they get
	 *    processed on this CPU in reverse order, we'll see
	 *     local_tlb_gen == 1, mm_tlb_gen == 3, and end != TLB_FLUSH_ALL.
	 *    If we were to use __flush_tlb_one_user() and set local_tlb_gen to
	 *    3, we'd be break the invariant: we'd update local_tlb_gen above
	 *    1 without the full flush that's needed for tlb_gen 2.
	 *
	 * 2. f->new_tlb_gen == mm_tlb_gen.  This is purely an optimiation.
	 *    Partial TLB flushes are not all that much cheaper than full TLB
	 *    flushes, so it seems unlikely that it would be a performance win
	 *    to do a partial flush if that won't bring our TLB fully up to
	 *    date.  By doing a full flush instead, we can increase
	 *    local_tlb_gen all the way to mm_tlb_gen and we can probably
	 *    avoid another flush in the very near future.
	 */
	if (f->end != TLB_FLUSH_ALL &&
	    f->new_tlb_gen == local_tlb_gen + 1 &&
	    f->new_tlb_gen == mm_tlb_gen) {
		/* Partial flush */
		unsigned long nr_invalidate = (f->end - f->start) >> f->stride_shift;
		unsigned long addr = f->start;

		while (addr < f->end) {
			__flush_tlb_one_user(addr);
			addr += 1UL << f->stride_shift;
		}
		if (local)
			count_vm_tlb_events(NR_TLB_LOCAL_FLUSH_ONE, nr_invalidate);
		trace_tlb_flush(reason, nr_invalidate);
	} else {
		/* Full flush. */
		local_flush_tlb();
		if (local)
			count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
		trace_tlb_flush(reason, TLB_FLUSH_ALL);
	}

	/* Both paths above update our state to mm_tlb_gen. */
	this_cpu_write(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen, mm_tlb_gen);
}

static void flush_tlb_func_local(void *info, enum tlb_flush_reason reason)
{
	const struct flush_tlb_info *f = info;

	flush_tlb_func_common(f, true, reason);
}

static void flush_tlb_func_remote(void *info)
{
	const struct flush_tlb_info *f = info;

	inc_irq_stat(irq_tlb_count);

	if (f->mm && f->mm != this_cpu_read(cpu_tlbstate.loaded_mm))
		return;

	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
	flush_tlb_func_common(f, false, TLB_REMOTE_SHOOTDOWN);
}

static bool tlb_is_not_lazy(int cpu, void *data)
{
	return !per_cpu(cpu_tlbstate.is_lazy, cpu);
}

void native_flush_tlb_others(const struct cpumask *cpumask,
			     const struct flush_tlb_info *info)
{
	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
	if (info->end == TLB_FLUSH_ALL)
		trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
	else
		trace_tlb_flush(TLB_REMOTE_SEND_IPI,
				(info->end - info->start) >> PAGE_SHIFT);

	if (is_uv_system()) {
		/*
		 * This whole special case is confused.  UV has a "Broadcast
		 * Assist Unit", which seems to be a fancy way to send IPIs.
		 * Back when x86 used an explicit TLB flush IPI, UV was
		 * optimized to use its own mechanism.  These days, x86 uses
		 * smp_call_function_many(), but UV still uses a manual IPI,
		 * and that IPI's action is out of date -- it does a manual
		 * flush instead of calling flush_tlb_func_remote().  This
		 * means that the percpu tlb_gen variables won't be updated
		 * and we'll do pointless flushes on future context switches.
		 *
		 * Rather than hooking native_flush_tlb_others() here, I think
		 * that UV should be updated so that smp_call_function_many(),
		 * etc, are optimal on UV.
		 */
		unsigned int cpu;

		cpu = smp_processor_id();
		cpumask = uv_flush_tlb_others(cpumask, info);
		if (cpumask)
			smp_call_function_many(cpumask, flush_tlb_func_remote,
					       (void *)info, 1);
		return;
	}

	/*
	 * If no page tables were freed, we can skip sending IPIs to
	 * CPUs in lazy TLB mode. They will flush the CPU themselves
	 * at the next context switch.
	 *
	 * However, if page tables are getting freed, we need to send the
	 * IPI everywhere, to prevent CPUs in lazy TLB mode from tripping
	 * up on the new contents of what used to be page tables, while
	 * doing a speculative memory access.
	 */
	if (info->freed_tables)
		smp_call_function_many(cpumask, flush_tlb_func_remote,
			       (void *)info, 1);
	else
		on_each_cpu_cond_mask(tlb_is_not_lazy, flush_tlb_func_remote,
				(void *)info, 1, GFP_ATOMIC, cpumask);
}

/*
 * See Documentation/x86/tlb.txt for details.  We choose 33
 * because it is large enough to cover the vast majority (at
 * least 95%) of allocations, and is small enough that we are
 * confident it will not cause too much overhead.  Each single
 * flush is about 100 ns, so this caps the maximum overhead at
 * _about_ 3,000 ns.
 *
 * This is in units of pages.
 */
static unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;

void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
				unsigned long end, unsigned int stride_shift,
				bool freed_tables)
{
	int cpu;

	struct flush_tlb_info info __aligned(SMP_CACHE_BYTES) = {
		.mm = mm,
		.stride_shift = stride_shift,
		.freed_tables = freed_tables,
	};

	cpu = get_cpu();

	/* This is also a barrier that synchronizes with switch_mm(). */
	info.new_tlb_gen = inc_mm_tlb_gen(mm);

	/* Should we flush just the requested range? */
	if ((end != TLB_FLUSH_ALL) &&
	    ((end - start) >> stride_shift) <= tlb_single_page_flush_ceiling) {
		info.start = start;
		info.end = end;
	} else {
		info.start = 0UL;
		info.end = TLB_FLUSH_ALL;
	}

	if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
		VM_WARN_ON(irqs_disabled());
		local_irq_disable();
		flush_tlb_func_local(&info, TLB_LOCAL_MM_SHOOTDOWN);
		local_irq_enable();
	}

	if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids)
		flush_tlb_others(mm_cpumask(mm), &info);

	put_cpu();
}


static void do_flush_tlb_all(void *info)
{
	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
	__flush_tlb_all();
}

void flush_tlb_all(void)
{
	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
	on_each_cpu(do_flush_tlb_all, NULL, 1);
}

static void do_kernel_range_flush(void *info)
{
	struct flush_tlb_info *f = info;
	unsigned long addr;

	/* flush range by one by one 'invlpg' */
	for (addr = f->start; addr < f->end; addr += PAGE_SIZE)
		__flush_tlb_one_kernel(addr);
}

void flush_tlb_kernel_range(unsigned long start, unsigned long end)
{

	/* Balance as user space task's flush, a bit conservative */
	if (end == TLB_FLUSH_ALL ||
	    (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
		on_each_cpu(do_flush_tlb_all, NULL, 1);
	} else {
		struct flush_tlb_info info;
		info.start = start;
		info.end = end;
		on_each_cpu(do_kernel_range_flush, &info, 1);
	}
}

void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
{
	struct flush_tlb_info info = {
		.mm = NULL,
		.start = 0UL,
		.end = TLB_FLUSH_ALL,
	};

	int cpu = get_cpu();

	if (cpumask_test_cpu(cpu, &batch->cpumask)) {
		VM_WARN_ON(irqs_disabled());
		local_irq_disable();
		flush_tlb_func_local(&info, TLB_LOCAL_SHOOTDOWN);
		local_irq_enable();
	}

	if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids)
		flush_tlb_others(&batch->cpumask, &info);

	cpumask_clear(&batch->cpumask);

	put_cpu();
}

static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
			     size_t count, loff_t *ppos)
{
	char buf[32];
	unsigned int len;

	len = sprintf(buf, "%ld\n", tlb_single_page_flush_ceiling);
	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}

static ssize_t tlbflush_write_file(struct file *file,
		 const char __user *user_buf, size_t count, loff_t *ppos)
{
	char buf[32];
	ssize_t len;
	int ceiling;

	len = min(count, sizeof(buf) - 1);
	if (copy_from_user(buf, user_buf, len))
		return -EFAULT;

	buf[len] = '\0';
	if (kstrtoint(buf, 0, &ceiling))
		return -EINVAL;

	if (ceiling < 0)
		return -EINVAL;

	tlb_single_page_flush_ceiling = ceiling;
	return count;
}

static const struct file_operations fops_tlbflush = {
	.read = tlbflush_read_file,
	.write = tlbflush_write_file,
	.llseek = default_llseek,
};

static int __init create_tlb_single_page_flush_ceiling(void)
{
	debugfs_create_file("tlb_single_page_flush_ceiling", S_IRUSR | S_IWUSR,
			    arch_debugfs_dir, NULL, &fops_tlbflush);
	return 0;
}
late_initcall(create_tlb_single_page_flush_ceiling);