1 #include <linux/gfp.h>
2 #include <linux/highmem.h>
3 #include <linux/kernel.h>
4 #include <linux/mmdebug.h>
5 #include <linux/mm_types.h>
6 #include <linux/mm_inline.h>
7 #include <linux/pagemap.h>
8 #include <linux/rcupdate.h>
9 #include <linux/smp.h>
10 #include <linux/swap.h>
11 #include <linux/rmap.h>
12
13 #include <asm/pgalloc.h>
14 #include <asm/tlb.h>
15
16 #ifndef CONFIG_MMU_GATHER_NO_GATHER
17
18 static bool tlb_next_batch(struct mmu_gather *tlb)
19 {
20 struct mmu_gather_batch *batch;
21
22 /* Limit batching if we have delayed rmaps pending */
23 if (tlb->delayed_rmap && tlb->active != &tlb->local)
24 return false;
25
26 batch = tlb->active;
27 if (batch->next) {
28 tlb->active = batch->next;
29 return true;
30 }
31
32 if (tlb->batch_count == MAX_GATHER_BATCH_COUNT)
33 return false;
34
35 batch = (void *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
36 if (!batch)
37 return false;
38
39 tlb->batch_count++;
40 batch->next = NULL;
41 batch->nr = 0;
42 batch->max = MAX_GATHER_BATCH;
43
44 tlb->active->next = batch;
45 tlb->active = batch;
46
47 return true;
48 }
49
50 #ifdef CONFIG_SMP
51 static void tlb_flush_rmap_batch(struct mmu_gather_batch *batch, struct vm_area_struct *vma)
52 {
53 struct encoded_page **pages = batch->encoded_pages;
54
55 for (int i = 0; i < batch->nr; i++) {
56 struct encoded_page *enc = pages[i];
57
58 if (encoded_page_flags(enc) & ENCODED_PAGE_BIT_DELAY_RMAP) {
59 struct page *page = encoded_page_ptr(enc);
60 unsigned int nr_pages = 1;
61
62 if (unlikely(encoded_page_flags(enc) &
63 ENCODED_PAGE_BIT_NR_PAGES_NEXT))
64 nr_pages = encoded_nr_pages(pages[++i]);
65
66 folio_remove_rmap_ptes(page_folio(page), page, nr_pages,
67 vma);
68 }
69 }
70 }
71
72 /**
73 * tlb_flush_rmaps - do pending rmap removals after we have flushed the TLB
74 * @tlb: the current mmu_gather
75 * @vma: The memory area from which the pages are being removed.
76 *
77 * Note that because of how tlb_next_batch() above works, we will
78 * never start multiple new batches with pending delayed rmaps, so
79 * we only need to walk through the current active batch and the
80 * original local one.
81 */
82 void tlb_flush_rmaps(struct mmu_gather *tlb, struct vm_area_struct *vma)
83 {
84 if (!tlb->delayed_rmap)
85 return;
86
87 tlb_flush_rmap_batch(&tlb->local, vma);
88 if (tlb->active != &tlb->local)
89 tlb_flush_rmap_batch(tlb->active, vma);
90 tlb->delayed_rmap = 0;
91 }
92 #endif
93
94 /*
95 * We might end up freeing a lot of pages. Reschedule on a regular
96 * basis to avoid soft lockups in configurations without full
97 * preemption enabled. The magic number of 512 folios seems to work.
98 */
99 #define MAX_NR_FOLIOS_PER_FREE 512
100
101 static void __tlb_batch_free_encoded_pages(struct mmu_gather_batch *batch)
102 {
103 struct encoded_page **pages = batch->encoded_pages;
104 unsigned int nr, nr_pages;
105
106 while (batch->nr) {
107 if (!page_poisoning_enabled_static() && !want_init_on_free()) {
108 nr = min(MAX_NR_FOLIOS_PER_FREE, batch->nr);
109
110 /*
111 * Make sure we cover page + nr_pages, and don't leave
112 * nr_pages behind when capping the number of entries.
113 */
114 if (unlikely(encoded_page_flags(pages[nr - 1]) &
115 ENCODED_PAGE_BIT_NR_PAGES_NEXT))
116 nr++;
117 } else {
118 /*
119 * With page poisoning and init_on_free, the time it
120 * takes to free memory grows proportionally with the
121 * actual memory size. Therefore, limit based on the
122 * actual memory size and not the number of involved
123 * folios.
124 */
125 for (nr = 0, nr_pages = 0;
126 nr < batch->nr && nr_pages < MAX_NR_FOLIOS_PER_FREE;
127 nr++) {
128 if (unlikely(encoded_page_flags(pages[nr]) &
129 ENCODED_PAGE_BIT_NR_PAGES_NEXT))
130 nr_pages += encoded_nr_pages(pages[++nr]);
131 else
132 nr_pages++;
133 }
134 }
135
136 free_pages_and_swap_cache(pages, nr);
137 pages += nr;
138 batch->nr -= nr;
139
140 cond_resched();
141 }
142 }
143
144 static void tlb_batch_pages_flush(struct mmu_gather *tlb)
145 {
146 struct mmu_gather_batch *batch;
147
148 for (batch = &tlb->local; batch && batch->nr; batch = batch->next)
149 __tlb_batch_free_encoded_pages(batch);
150 tlb->active = &tlb->local;
151 }
152
153 static void tlb_batch_list_free(struct mmu_gather *tlb)
154 {
155 struct mmu_gather_batch *batch, *next;
156
157 for (batch = tlb->local.next; batch; batch = next) {
158 next = batch->next;
159 free_pages((unsigned long)batch, 0);
160 }
161 tlb->local.next = NULL;
162 }
163
164 static bool __tlb_remove_folio_pages_size(struct mmu_gather *tlb,
165 struct page *page, unsigned int nr_pages, bool delay_rmap,
166 int page_size)
167 {
168 int flags = delay_rmap ? ENCODED_PAGE_BIT_DELAY_RMAP : 0;
169 struct mmu_gather_batch *batch;
170
171 VM_BUG_ON(!tlb->end);
172
173 #ifdef CONFIG_MMU_GATHER_PAGE_SIZE
174 VM_WARN_ON(tlb->page_size != page_size);
175 VM_WARN_ON_ONCE(nr_pages != 1 && page_size != PAGE_SIZE);
176 VM_WARN_ON_ONCE(page_folio(page) != page_folio(page + nr_pages - 1));
177 #endif
178
179 batch = tlb->active;
180 /*
181 * Add the page and check if we are full. If so
182 * force a flush.
183 */
184 if (likely(nr_pages == 1)) {
185 batch->encoded_pages[batch->nr++] = encode_page(page, flags);
186 } else {
187 flags |= ENCODED_PAGE_BIT_NR_PAGES_NEXT;
188 batch->encoded_pages[batch->nr++] = encode_page(page, flags);
189 batch->encoded_pages[batch->nr++] = encode_nr_pages(nr_pages);
190 }
191 /*
192 * Make sure that we can always add another "page" + "nr_pages",
193 * requiring two entries instead of only a single one.
194 */
195 if (batch->nr >= batch->max - 1) {
196 if (!tlb_next_batch(tlb))
197 return true;
198 batch = tlb->active;
199 }
200 VM_BUG_ON_PAGE(batch->nr > batch->max - 1, page);
201
202 return false;
203 }
204
205 bool __tlb_remove_folio_pages(struct mmu_gather *tlb, struct page *page,
206 unsigned int nr_pages, bool delay_rmap)
207 {
208 return __tlb_remove_folio_pages_size(tlb, page, nr_pages, delay_rmap,
209 PAGE_SIZE);
210 }
211
212 bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
213 bool delay_rmap, int page_size)
214 {
215 return __tlb_remove_folio_pages_size(tlb, page, 1, delay_rmap, page_size);
216 }
217
218 #endif /* MMU_GATHER_NO_GATHER */
219
220 #ifdef CONFIG_MMU_GATHER_TABLE_FREE
221
222 static void __tlb_remove_table_free(struct mmu_table_batch *batch)
223 {
224 int i;
225
226 for (i = 0; i < batch->nr; i++)
227 __tlb_remove_table(batch->tables[i]);
228
229 free_page((unsigned long)batch);
230 }
231
232 #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
233
234 /*
235 * Semi RCU freeing of the page directories.
236 *
237 * This is needed by some architectures to implement software pagetable walkers.
238 *
239 * gup_fast() and other software pagetable walkers do a lockless page-table
240 * walk and therefore needs some synchronization with the freeing of the page
241 * directories. The chosen means to accomplish that is by disabling IRQs over
242 * the walk.
243 *
244 * Architectures that use IPIs to flush TLBs will then automagically DTRT,
245 * since we unlink the page, flush TLBs, free the page. Since the disabling of
246 * IRQs delays the completion of the TLB flush we can never observe an already
247 * freed page.
248 *
249 * Architectures that do not have this (PPC) need to delay the freeing by some
250 * other means, this is that means.
251 *
252 * What we do is batch the freed directory pages (tables) and RCU free them.
253 * We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
254 * holds off grace periods.
255 *
256 * However, in order to batch these pages we need to allocate storage, this
257 * allocation is deep inside the MM code and can thus easily fail on memory
258 * pressure. To guarantee progress we fall back to single table freeing, see
259 * the implementation of tlb_remove_table_one().
260 *
261 */
262
263 static void tlb_remove_table_smp_sync(void *arg)
264 {
265 /* Simply deliver the interrupt */
266 }
267
268 void tlb_remove_table_sync_one(void)
269 {
270 /*
271 * This isn't an RCU grace period and hence the page-tables cannot be
272 * assumed to be actually RCU-freed.
273 *
274 * It is however sufficient for software page-table walkers that rely on
275 * IRQ disabling.
276 */
277 smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
278 }
279
280 static void tlb_remove_table_rcu(struct rcu_head *head)
281 {
282 __tlb_remove_table_free(container_of(head, struct mmu_table_batch, rcu));
283 }
284
285 static void tlb_remove_table_free(struct mmu_table_batch *batch)
286 {
287 call_rcu(&batch->rcu, tlb_remove_table_rcu);
288 }
289
290 #else /* !CONFIG_MMU_GATHER_RCU_TABLE_FREE */
291
292 static void tlb_remove_table_free(struct mmu_table_batch *batch)
293 {
294 __tlb_remove_table_free(batch);
295 }
296
297 #endif /* CONFIG_MMU_GATHER_RCU_TABLE_FREE */
298
299 /*
300 * If we want tlb_remove_table() to imply TLB invalidates.
301 */
302 static inline void tlb_table_invalidate(struct mmu_gather *tlb)
303 {
304 if (tlb_needs_table_invalidate()) {
305 /*
306 * Invalidate page-table caches used by hardware walkers. Then
307 * we still need to RCU-sched wait while freeing the pages
308 * because software walkers can still be in-flight.
309 */
310 tlb_flush_mmu_tlbonly(tlb);
311 }
312 }
313
314 static void tlb_remove_table_one(void *table)
315 {
316 tlb_remove_table_sync_one();
317 __tlb_remove_table(table);
318 }
319
320 static void tlb_table_flush(struct mmu_gather *tlb)
321 {
322 struct mmu_table_batch **batch = &tlb->batch;
323
324 if (*batch) {
325 tlb_table_invalidate(tlb);
326 tlb_remove_table_free(*batch);
327 *batch = NULL;
328 }
329 }
330
331 void tlb_remove_table(struct mmu_gather *tlb, void *table)
332 {
333 struct mmu_table_batch **batch = &tlb->batch;
334
335 if (*batch == NULL) {
336 *batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
337 if (*batch == NULL) {
338 tlb_table_invalidate(tlb);
339 tlb_remove_table_one(table);
340 return;
341 }
342 (*batch)->nr = 0;
343 }
344
345 (*batch)->tables[(*batch)->nr++] = table;
346 if ((*batch)->nr == MAX_TABLE_BATCH)
347 tlb_table_flush(tlb);
348 }
349
350 static inline void tlb_table_init(struct mmu_gather *tlb)
351 {
352 tlb->batch = NULL;
353 }
354
355 #else /* !CONFIG_MMU_GATHER_TABLE_FREE */
356
357 static inline void tlb_table_flush(struct mmu_gather *tlb) { }
358 static inline void tlb_table_init(struct mmu_gather *tlb) { }
359
360 #endif /* CONFIG_MMU_GATHER_TABLE_FREE */
361
362 static void tlb_flush_mmu_free(struct mmu_gather *tlb)
363 {
364 tlb_table_flush(tlb);
365 #ifndef CONFIG_MMU_GATHER_NO_GATHER
366 tlb_batch_pages_flush(tlb);
367 #endif
368 }
369
370 void tlb_flush_mmu(struct mmu_gather *tlb)
371 {
372 tlb_flush_mmu_tlbonly(tlb);
373 tlb_flush_mmu_free(tlb);
374 }
375
376 static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
377 bool fullmm)
378 {
379 tlb->mm = mm;
380 tlb->fullmm = fullmm;
381
382 #ifndef CONFIG_MMU_GATHER_NO_GATHER
383 tlb->need_flush_all = 0;
384 tlb->local.next = NULL;
385 tlb->local.nr = 0;
386 tlb->local.max = ARRAY_SIZE(tlb->__pages);
387 tlb->active = &tlb->local;
388 tlb->batch_count = 0;
389 #endif
390 tlb->delayed_rmap = 0;
391
392 tlb_table_init(tlb);
393 #ifdef CONFIG_MMU_GATHER_PAGE_SIZE
394 tlb->page_size = 0;
395 #endif
396
397 __tlb_reset_range(tlb);
398 inc_tlb_flush_pending(tlb->mm);
399 }
400
401 /**
402 * tlb_gather_mmu - initialize an mmu_gather structure for page-table tear-down
403 * @tlb: the mmu_gather structure to initialize
404 * @mm: the mm_struct of the target address space
405 *
406 * Called to initialize an (on-stack) mmu_gather structure for page-table
407 * tear-down from @mm.
408 */
409 void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm)
410 {
411 __tlb_gather_mmu(tlb, mm, false);
412 }
413
414 /**
415 * tlb_gather_mmu_fullmm - initialize an mmu_gather structure for page-table tear-down
416 * @tlb: the mmu_gather structure to initialize
417 * @mm: the mm_struct of the target address space
418 *
419 * In this case, @mm is without users and we're going to destroy the
420 * full address space (exit/execve).
421 *
422 * Called to initialize an (on-stack) mmu_gather structure for page-table
423 * tear-down from @mm.
424 */
425 void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm)
426 {
427 __tlb_gather_mmu(tlb, mm, true);
428 }
429
430 /**
431 * tlb_finish_mmu - finish an mmu_gather structure
432 * @tlb: the mmu_gather structure to finish
433 *
434 * Called at the end of the shootdown operation to free up any resources that
435 * were required.
436 */
437 void tlb_finish_mmu(struct mmu_gather *tlb)
438 {
439 /*
440 * If there are parallel threads are doing PTE changes on same range
441 * under non-exclusive lock (e.g., mmap_lock read-side) but defer TLB
442 * flush by batching, one thread may end up seeing inconsistent PTEs
443 * and result in having stale TLB entries. So flush TLB forcefully
444 * if we detect parallel PTE batching threads.
445 *
446 * However, some syscalls, e.g. munmap(), may free page tables, this
447 * needs force flush everything in the given range. Otherwise this
448 * may result in having stale TLB entries for some architectures,
449 * e.g. aarch64, that could specify flush what level TLB.
450 */
451 if (mm_tlb_flush_nested(tlb->mm)) {
452 /*
453 * The aarch64 yields better performance with fullmm by
454 * avoiding multiple CPUs spamming TLBI messages at the
455 * same time.
456 *
457 * On x86 non-fullmm doesn't yield significant difference
458 * against fullmm.
459 */
460 tlb->fullmm = 1;
461 __tlb_reset_range(tlb);
462 tlb->freed_tables = 1;
463 }
464
465 tlb_flush_mmu(tlb);
466
467 #ifndef CONFIG_MMU_GATHER_NO_GATHER
468 tlb_batch_list_free(tlb);
469 #endif
470 dec_tlb_flush_pending(tlb->mm);
471 }
472
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