xref: /openbmc/linux/fs/dax.c (revision 60630924bb5af8751adcecc896e7763c3783ca89)
1  // SPDX-License-Identifier: GPL-2.0-only
2  /*
3   * fs/dax.c - Direct Access filesystem code
4   * Copyright (c) 2013-2014 Intel Corporation
5   * Author: Matthew Wilcox <matthew.r.wilcox@intel.com>
6   * Author: Ross Zwisler <ross.zwisler@linux.intel.com>
7   */
8  
9  #include <linux/atomic.h>
10  #include <linux/blkdev.h>
11  #include <linux/buffer_head.h>
12  #include <linux/dax.h>
13  #include <linux/fs.h>
14  #include <linux/genhd.h>
15  #include <linux/highmem.h>
16  #include <linux/memcontrol.h>
17  #include <linux/mm.h>
18  #include <linux/mutex.h>
19  #include <linux/pagevec.h>
20  #include <linux/sched.h>
21  #include <linux/sched/signal.h>
22  #include <linux/uio.h>
23  #include <linux/vmstat.h>
24  #include <linux/pfn_t.h>
25  #include <linux/sizes.h>
26  #include <linux/mmu_notifier.h>
27  #include <linux/iomap.h>
28  #include <asm/pgalloc.h>
29  
30  #define CREATE_TRACE_POINTS
31  #include <trace/events/fs_dax.h>
32  
33  static inline unsigned int pe_order(enum page_entry_size pe_size)
34  {
35  	if (pe_size == PE_SIZE_PTE)
36  		return PAGE_SHIFT - PAGE_SHIFT;
37  	if (pe_size == PE_SIZE_PMD)
38  		return PMD_SHIFT - PAGE_SHIFT;
39  	if (pe_size == PE_SIZE_PUD)
40  		return PUD_SHIFT - PAGE_SHIFT;
41  	return ~0;
42  }
43  
44  /* We choose 4096 entries - same as per-zone page wait tables */
45  #define DAX_WAIT_TABLE_BITS 12
46  #define DAX_WAIT_TABLE_ENTRIES (1 << DAX_WAIT_TABLE_BITS)
47  
48  /* The 'colour' (ie low bits) within a PMD of a page offset.  */
49  #define PG_PMD_COLOUR	((PMD_SIZE >> PAGE_SHIFT) - 1)
50  #define PG_PMD_NR	(PMD_SIZE >> PAGE_SHIFT)
51  
52  /* The order of a PMD entry */
53  #define PMD_ORDER	(PMD_SHIFT - PAGE_SHIFT)
54  
55  static wait_queue_head_t wait_table[DAX_WAIT_TABLE_ENTRIES];
56  
57  static int __init init_dax_wait_table(void)
58  {
59  	int i;
60  
61  	for (i = 0; i < DAX_WAIT_TABLE_ENTRIES; i++)
62  		init_waitqueue_head(wait_table + i);
63  	return 0;
64  }
65  fs_initcall(init_dax_wait_table);
66  
67  /*
68   * DAX pagecache entries use XArray value entries so they can't be mistaken
69   * for pages.  We use one bit for locking, one bit for the entry size (PMD)
70   * and two more to tell us if the entry is a zero page or an empty entry that
71   * is just used for locking.  In total four special bits.
72   *
73   * If the PMD bit isn't set the entry has size PAGE_SIZE, and if the ZERO_PAGE
74   * and EMPTY bits aren't set the entry is a normal DAX entry with a filesystem
75   * block allocation.
76   */
77  #define DAX_SHIFT	(4)
78  #define DAX_LOCKED	(1UL << 0)
79  #define DAX_PMD		(1UL << 1)
80  #define DAX_ZERO_PAGE	(1UL << 2)
81  #define DAX_EMPTY	(1UL << 3)
82  
83  static unsigned long dax_to_pfn(void *entry)
84  {
85  	return xa_to_value(entry) >> DAX_SHIFT;
86  }
87  
88  static void *dax_make_entry(pfn_t pfn, unsigned long flags)
89  {
90  	return xa_mk_value(flags | (pfn_t_to_pfn(pfn) << DAX_SHIFT));
91  }
92  
93  static bool dax_is_locked(void *entry)
94  {
95  	return xa_to_value(entry) & DAX_LOCKED;
96  }
97  
98  static unsigned int dax_entry_order(void *entry)
99  {
100  	if (xa_to_value(entry) & DAX_PMD)
101  		return PMD_ORDER;
102  	return 0;
103  }
104  
105  static unsigned long dax_is_pmd_entry(void *entry)
106  {
107  	return xa_to_value(entry) & DAX_PMD;
108  }
109  
110  static bool dax_is_pte_entry(void *entry)
111  {
112  	return !(xa_to_value(entry) & DAX_PMD);
113  }
114  
115  static int dax_is_zero_entry(void *entry)
116  {
117  	return xa_to_value(entry) & DAX_ZERO_PAGE;
118  }
119  
120  static int dax_is_empty_entry(void *entry)
121  {
122  	return xa_to_value(entry) & DAX_EMPTY;
123  }
124  
125  /*
126   * true if the entry that was found is of a smaller order than the entry
127   * we were looking for
128   */
129  static bool dax_is_conflict(void *entry)
130  {
131  	return entry == XA_RETRY_ENTRY;
132  }
133  
134  /*
135   * DAX page cache entry locking
136   */
137  struct exceptional_entry_key {
138  	struct xarray *xa;
139  	pgoff_t entry_start;
140  };
141  
142  struct wait_exceptional_entry_queue {
143  	wait_queue_entry_t wait;
144  	struct exceptional_entry_key key;
145  };
146  
147  /**
148   * enum dax_wake_mode: waitqueue wakeup behaviour
149   * @WAKE_ALL: wake all waiters in the waitqueue
150   * @WAKE_NEXT: wake only the first waiter in the waitqueue
151   */
152  enum dax_wake_mode {
153  	WAKE_ALL,
154  	WAKE_NEXT,
155  };
156  
157  static wait_queue_head_t *dax_entry_waitqueue(struct xa_state *xas,
158  		void *entry, struct exceptional_entry_key *key)
159  {
160  	unsigned long hash;
161  	unsigned long index = xas->xa_index;
162  
163  	/*
164  	 * If 'entry' is a PMD, align the 'index' that we use for the wait
165  	 * queue to the start of that PMD.  This ensures that all offsets in
166  	 * the range covered by the PMD map to the same bit lock.
167  	 */
168  	if (dax_is_pmd_entry(entry))
169  		index &= ~PG_PMD_COLOUR;
170  	key->xa = xas->xa;
171  	key->entry_start = index;
172  
173  	hash = hash_long((unsigned long)xas->xa ^ index, DAX_WAIT_TABLE_BITS);
174  	return wait_table + hash;
175  }
176  
177  static int wake_exceptional_entry_func(wait_queue_entry_t *wait,
178  		unsigned int mode, int sync, void *keyp)
179  {
180  	struct exceptional_entry_key *key = keyp;
181  	struct wait_exceptional_entry_queue *ewait =
182  		container_of(wait, struct wait_exceptional_entry_queue, wait);
183  
184  	if (key->xa != ewait->key.xa ||
185  	    key->entry_start != ewait->key.entry_start)
186  		return 0;
187  	return autoremove_wake_function(wait, mode, sync, NULL);
188  }
189  
190  /*
191   * @entry may no longer be the entry at the index in the mapping.
192   * The important information it's conveying is whether the entry at
193   * this index used to be a PMD entry.
194   */
195  static void dax_wake_entry(struct xa_state *xas, void *entry,
196  			   enum dax_wake_mode mode)
197  {
198  	struct exceptional_entry_key key;
199  	wait_queue_head_t *wq;
200  
201  	wq = dax_entry_waitqueue(xas, entry, &key);
202  
203  	/*
204  	 * Checking for locked entry and prepare_to_wait_exclusive() happens
205  	 * under the i_pages lock, ditto for entry handling in our callers.
206  	 * So at this point all tasks that could have seen our entry locked
207  	 * must be in the waitqueue and the following check will see them.
208  	 */
209  	if (waitqueue_active(wq))
210  		__wake_up(wq, TASK_NORMAL, mode == WAKE_ALL ? 0 : 1, &key);
211  }
212  
213  /*
214   * Look up entry in page cache, wait for it to become unlocked if it
215   * is a DAX entry and return it.  The caller must subsequently call
216   * put_unlocked_entry() if it did not lock the entry or dax_unlock_entry()
217   * if it did.  The entry returned may have a larger order than @order.
218   * If @order is larger than the order of the entry found in i_pages, this
219   * function returns a dax_is_conflict entry.
220   *
221   * Must be called with the i_pages lock held.
222   */
223  static void *get_unlocked_entry(struct xa_state *xas, unsigned int order)
224  {
225  	void *entry;
226  	struct wait_exceptional_entry_queue ewait;
227  	wait_queue_head_t *wq;
228  
229  	init_wait(&ewait.wait);
230  	ewait.wait.func = wake_exceptional_entry_func;
231  
232  	for (;;) {
233  		entry = xas_find_conflict(xas);
234  		if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
235  			return entry;
236  		if (dax_entry_order(entry) < order)
237  			return XA_RETRY_ENTRY;
238  		if (!dax_is_locked(entry))
239  			return entry;
240  
241  		wq = dax_entry_waitqueue(xas, entry, &ewait.key);
242  		prepare_to_wait_exclusive(wq, &ewait.wait,
243  					  TASK_UNINTERRUPTIBLE);
244  		xas_unlock_irq(xas);
245  		xas_reset(xas);
246  		schedule();
247  		finish_wait(wq, &ewait.wait);
248  		xas_lock_irq(xas);
249  	}
250  }
251  
252  /*
253   * The only thing keeping the address space around is the i_pages lock
254   * (it's cycled in clear_inode() after removing the entries from i_pages)
255   * After we call xas_unlock_irq(), we cannot touch xas->xa.
256   */
257  static void wait_entry_unlocked(struct xa_state *xas, void *entry)
258  {
259  	struct wait_exceptional_entry_queue ewait;
260  	wait_queue_head_t *wq;
261  
262  	init_wait(&ewait.wait);
263  	ewait.wait.func = wake_exceptional_entry_func;
264  
265  	wq = dax_entry_waitqueue(xas, entry, &ewait.key);
266  	/*
267  	 * Unlike get_unlocked_entry() there is no guarantee that this
268  	 * path ever successfully retrieves an unlocked entry before an
269  	 * inode dies. Perform a non-exclusive wait in case this path
270  	 * never successfully performs its own wake up.
271  	 */
272  	prepare_to_wait(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
273  	xas_unlock_irq(xas);
274  	schedule();
275  	finish_wait(wq, &ewait.wait);
276  }
277  
278  static void put_unlocked_entry(struct xa_state *xas, void *entry,
279  			       enum dax_wake_mode mode)
280  {
281  	if (entry && !dax_is_conflict(entry))
282  		dax_wake_entry(xas, entry, mode);
283  }
284  
285  /*
286   * We used the xa_state to get the entry, but then we locked the entry and
287   * dropped the xa_lock, so we know the xa_state is stale and must be reset
288   * before use.
289   */
290  static void dax_unlock_entry(struct xa_state *xas, void *entry)
291  {
292  	void *old;
293  
294  	BUG_ON(dax_is_locked(entry));
295  	xas_reset(xas);
296  	xas_lock_irq(xas);
297  	old = xas_store(xas, entry);
298  	xas_unlock_irq(xas);
299  	BUG_ON(!dax_is_locked(old));
300  	dax_wake_entry(xas, entry, WAKE_NEXT);
301  }
302  
303  /*
304   * Return: The entry stored at this location before it was locked.
305   */
306  static void *dax_lock_entry(struct xa_state *xas, void *entry)
307  {
308  	unsigned long v = xa_to_value(entry);
309  	return xas_store(xas, xa_mk_value(v | DAX_LOCKED));
310  }
311  
312  static unsigned long dax_entry_size(void *entry)
313  {
314  	if (dax_is_zero_entry(entry))
315  		return 0;
316  	else if (dax_is_empty_entry(entry))
317  		return 0;
318  	else if (dax_is_pmd_entry(entry))
319  		return PMD_SIZE;
320  	else
321  		return PAGE_SIZE;
322  }
323  
324  static unsigned long dax_end_pfn(void *entry)
325  {
326  	return dax_to_pfn(entry) + dax_entry_size(entry) / PAGE_SIZE;
327  }
328  
329  /*
330   * Iterate through all mapped pfns represented by an entry, i.e. skip
331   * 'empty' and 'zero' entries.
332   */
333  #define for_each_mapped_pfn(entry, pfn) \
334  	for (pfn = dax_to_pfn(entry); \
335  			pfn < dax_end_pfn(entry); pfn++)
336  
337  /*
338   * TODO: for reflink+dax we need a way to associate a single page with
339   * multiple address_space instances at different linear_page_index()
340   * offsets.
341   */
342  static void dax_associate_entry(void *entry, struct address_space *mapping,
343  		struct vm_area_struct *vma, unsigned long address)
344  {
345  	unsigned long size = dax_entry_size(entry), pfn, index;
346  	int i = 0;
347  
348  	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
349  		return;
350  
351  	index = linear_page_index(vma, address & ~(size - 1));
352  	for_each_mapped_pfn(entry, pfn) {
353  		struct page *page = pfn_to_page(pfn);
354  
355  		WARN_ON_ONCE(page->mapping);
356  		page->mapping = mapping;
357  		page->index = index + i++;
358  	}
359  }
360  
361  static void dax_disassociate_entry(void *entry, struct address_space *mapping,
362  		bool trunc)
363  {
364  	unsigned long pfn;
365  
366  	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
367  		return;
368  
369  	for_each_mapped_pfn(entry, pfn) {
370  		struct page *page = pfn_to_page(pfn);
371  
372  		WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
373  		WARN_ON_ONCE(page->mapping && page->mapping != mapping);
374  		page->mapping = NULL;
375  		page->index = 0;
376  	}
377  }
378  
379  static struct page *dax_busy_page(void *entry)
380  {
381  	unsigned long pfn;
382  
383  	for_each_mapped_pfn(entry, pfn) {
384  		struct page *page = pfn_to_page(pfn);
385  
386  		if (page_ref_count(page) > 1)
387  			return page;
388  	}
389  	return NULL;
390  }
391  
392  /*
393   * dax_lock_mapping_entry - Lock the DAX entry corresponding to a page
394   * @page: The page whose entry we want to lock
395   *
396   * Context: Process context.
397   * Return: A cookie to pass to dax_unlock_page() or 0 if the entry could
398   * not be locked.
399   */
400  dax_entry_t dax_lock_page(struct page *page)
401  {
402  	XA_STATE(xas, NULL, 0);
403  	void *entry;
404  
405  	/* Ensure page->mapping isn't freed while we look at it */
406  	rcu_read_lock();
407  	for (;;) {
408  		struct address_space *mapping = READ_ONCE(page->mapping);
409  
410  		entry = NULL;
411  		if (!mapping || !dax_mapping(mapping))
412  			break;
413  
414  		/*
415  		 * In the device-dax case there's no need to lock, a
416  		 * struct dev_pagemap pin is sufficient to keep the
417  		 * inode alive, and we assume we have dev_pagemap pin
418  		 * otherwise we would not have a valid pfn_to_page()
419  		 * translation.
420  		 */
421  		entry = (void *)~0UL;
422  		if (S_ISCHR(mapping->host->i_mode))
423  			break;
424  
425  		xas.xa = &mapping->i_pages;
426  		xas_lock_irq(&xas);
427  		if (mapping != page->mapping) {
428  			xas_unlock_irq(&xas);
429  			continue;
430  		}
431  		xas_set(&xas, page->index);
432  		entry = xas_load(&xas);
433  		if (dax_is_locked(entry)) {
434  			rcu_read_unlock();
435  			wait_entry_unlocked(&xas, entry);
436  			rcu_read_lock();
437  			continue;
438  		}
439  		dax_lock_entry(&xas, entry);
440  		xas_unlock_irq(&xas);
441  		break;
442  	}
443  	rcu_read_unlock();
444  	return (dax_entry_t)entry;
445  }
446  
447  void dax_unlock_page(struct page *page, dax_entry_t cookie)
448  {
449  	struct address_space *mapping = page->mapping;
450  	XA_STATE(xas, &mapping->i_pages, page->index);
451  
452  	if (S_ISCHR(mapping->host->i_mode))
453  		return;
454  
455  	dax_unlock_entry(&xas, (void *)cookie);
456  }
457  
458  /*
459   * Find page cache entry at given index. If it is a DAX entry, return it
460   * with the entry locked. If the page cache doesn't contain an entry at
461   * that index, add a locked empty entry.
462   *
463   * When requesting an entry with size DAX_PMD, grab_mapping_entry() will
464   * either return that locked entry or will return VM_FAULT_FALLBACK.
465   * This will happen if there are any PTE entries within the PMD range
466   * that we are requesting.
467   *
468   * We always favor PTE entries over PMD entries. There isn't a flow where we
469   * evict PTE entries in order to 'upgrade' them to a PMD entry.  A PMD
470   * insertion will fail if it finds any PTE entries already in the tree, and a
471   * PTE insertion will cause an existing PMD entry to be unmapped and
472   * downgraded to PTE entries.  This happens for both PMD zero pages as
473   * well as PMD empty entries.
474   *
475   * The exception to this downgrade path is for PMD entries that have
476   * real storage backing them.  We will leave these real PMD entries in
477   * the tree, and PTE writes will simply dirty the entire PMD entry.
478   *
479   * Note: Unlike filemap_fault() we don't honor FAULT_FLAG_RETRY flags. For
480   * persistent memory the benefit is doubtful. We can add that later if we can
481   * show it helps.
482   *
483   * On error, this function does not return an ERR_PTR.  Instead it returns
484   * a VM_FAULT code, encoded as an xarray internal entry.  The ERR_PTR values
485   * overlap with xarray value entries.
486   */
487  static void *grab_mapping_entry(struct xa_state *xas,
488  		struct address_space *mapping, unsigned int order)
489  {
490  	unsigned long index = xas->xa_index;
491  	bool pmd_downgrade;	/* splitting PMD entry into PTE entries? */
492  	void *entry;
493  
494  retry:
495  	pmd_downgrade = false;
496  	xas_lock_irq(xas);
497  	entry = get_unlocked_entry(xas, order);
498  
499  	if (entry) {
500  		if (dax_is_conflict(entry))
501  			goto fallback;
502  		if (!xa_is_value(entry)) {
503  			xas_set_err(xas, -EIO);
504  			goto out_unlock;
505  		}
506  
507  		if (order == 0) {
508  			if (dax_is_pmd_entry(entry) &&
509  			    (dax_is_zero_entry(entry) ||
510  			     dax_is_empty_entry(entry))) {
511  				pmd_downgrade = true;
512  			}
513  		}
514  	}
515  
516  	if (pmd_downgrade) {
517  		/*
518  		 * Make sure 'entry' remains valid while we drop
519  		 * the i_pages lock.
520  		 */
521  		dax_lock_entry(xas, entry);
522  
523  		/*
524  		 * Besides huge zero pages the only other thing that gets
525  		 * downgraded are empty entries which don't need to be
526  		 * unmapped.
527  		 */
528  		if (dax_is_zero_entry(entry)) {
529  			xas_unlock_irq(xas);
530  			unmap_mapping_pages(mapping,
531  					xas->xa_index & ~PG_PMD_COLOUR,
532  					PG_PMD_NR, false);
533  			xas_reset(xas);
534  			xas_lock_irq(xas);
535  		}
536  
537  		dax_disassociate_entry(entry, mapping, false);
538  		xas_store(xas, NULL);	/* undo the PMD join */
539  		dax_wake_entry(xas, entry, WAKE_ALL);
540  		mapping->nrpages -= PG_PMD_NR;
541  		entry = NULL;
542  		xas_set(xas, index);
543  	}
544  
545  	if (entry) {
546  		dax_lock_entry(xas, entry);
547  	} else {
548  		unsigned long flags = DAX_EMPTY;
549  
550  		if (order > 0)
551  			flags |= DAX_PMD;
552  		entry = dax_make_entry(pfn_to_pfn_t(0), flags);
553  		dax_lock_entry(xas, entry);
554  		if (xas_error(xas))
555  			goto out_unlock;
556  		mapping->nrpages += 1UL << order;
557  	}
558  
559  out_unlock:
560  	xas_unlock_irq(xas);
561  	if (xas_nomem(xas, mapping_gfp_mask(mapping) & ~__GFP_HIGHMEM))
562  		goto retry;
563  	if (xas->xa_node == XA_ERROR(-ENOMEM))
564  		return xa_mk_internal(VM_FAULT_OOM);
565  	if (xas_error(xas))
566  		return xa_mk_internal(VM_FAULT_SIGBUS);
567  	return entry;
568  fallback:
569  	xas_unlock_irq(xas);
570  	return xa_mk_internal(VM_FAULT_FALLBACK);
571  }
572  
573  /**
574   * dax_layout_busy_page_range - find first pinned page in @mapping
575   * @mapping: address space to scan for a page with ref count > 1
576   * @start: Starting offset. Page containing 'start' is included.
577   * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
578   *       pages from 'start' till the end of file are included.
579   *
580   * DAX requires ZONE_DEVICE mapped pages. These pages are never
581   * 'onlined' to the page allocator so they are considered idle when
582   * page->count == 1. A filesystem uses this interface to determine if
583   * any page in the mapping is busy, i.e. for DMA, or other
584   * get_user_pages() usages.
585   *
586   * It is expected that the filesystem is holding locks to block the
587   * establishment of new mappings in this address_space. I.e. it expects
588   * to be able to run unmap_mapping_range() and subsequently not race
589   * mapping_mapped() becoming true.
590   */
591  struct page *dax_layout_busy_page_range(struct address_space *mapping,
592  					loff_t start, loff_t end)
593  {
594  	void *entry;
595  	unsigned int scanned = 0;
596  	struct page *page = NULL;
597  	pgoff_t start_idx = start >> PAGE_SHIFT;
598  	pgoff_t end_idx;
599  	XA_STATE(xas, &mapping->i_pages, start_idx);
600  
601  	/*
602  	 * In the 'limited' case get_user_pages() for dax is disabled.
603  	 */
604  	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
605  		return NULL;
606  
607  	if (!dax_mapping(mapping) || !mapping_mapped(mapping))
608  		return NULL;
609  
610  	/* If end == LLONG_MAX, all pages from start to till end of file */
611  	if (end == LLONG_MAX)
612  		end_idx = ULONG_MAX;
613  	else
614  		end_idx = end >> PAGE_SHIFT;
615  	/*
616  	 * If we race get_user_pages_fast() here either we'll see the
617  	 * elevated page count in the iteration and wait, or
618  	 * get_user_pages_fast() will see that the page it took a reference
619  	 * against is no longer mapped in the page tables and bail to the
620  	 * get_user_pages() slow path.  The slow path is protected by
621  	 * pte_lock() and pmd_lock(). New references are not taken without
622  	 * holding those locks, and unmap_mapping_pages() will not zero the
623  	 * pte or pmd without holding the respective lock, so we are
624  	 * guaranteed to either see new references or prevent new
625  	 * references from being established.
626  	 */
627  	unmap_mapping_pages(mapping, start_idx, end_idx - start_idx + 1, 0);
628  
629  	xas_lock_irq(&xas);
630  	xas_for_each(&xas, entry, end_idx) {
631  		if (WARN_ON_ONCE(!xa_is_value(entry)))
632  			continue;
633  		if (unlikely(dax_is_locked(entry)))
634  			entry = get_unlocked_entry(&xas, 0);
635  		if (entry)
636  			page = dax_busy_page(entry);
637  		put_unlocked_entry(&xas, entry, WAKE_NEXT);
638  		if (page)
639  			break;
640  		if (++scanned % XA_CHECK_SCHED)
641  			continue;
642  
643  		xas_pause(&xas);
644  		xas_unlock_irq(&xas);
645  		cond_resched();
646  		xas_lock_irq(&xas);
647  	}
648  	xas_unlock_irq(&xas);
649  	return page;
650  }
651  EXPORT_SYMBOL_GPL(dax_layout_busy_page_range);
652  
653  struct page *dax_layout_busy_page(struct address_space *mapping)
654  {
655  	return dax_layout_busy_page_range(mapping, 0, LLONG_MAX);
656  }
657  EXPORT_SYMBOL_GPL(dax_layout_busy_page);
658  
659  static int __dax_invalidate_entry(struct address_space *mapping,
660  					  pgoff_t index, bool trunc)
661  {
662  	XA_STATE(xas, &mapping->i_pages, index);
663  	int ret = 0;
664  	void *entry;
665  
666  	xas_lock_irq(&xas);
667  	entry = get_unlocked_entry(&xas, 0);
668  	if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
669  		goto out;
670  	if (!trunc &&
671  	    (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY) ||
672  	     xas_get_mark(&xas, PAGECACHE_TAG_TOWRITE)))
673  		goto out;
674  	dax_disassociate_entry(entry, mapping, trunc);
675  	xas_store(&xas, NULL);
676  	mapping->nrpages -= 1UL << dax_entry_order(entry);
677  	ret = 1;
678  out:
679  	put_unlocked_entry(&xas, entry, WAKE_ALL);
680  	xas_unlock_irq(&xas);
681  	return ret;
682  }
683  
684  /*
685   * Delete DAX entry at @index from @mapping.  Wait for it
686   * to be unlocked before deleting it.
687   */
688  int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index)
689  {
690  	int ret = __dax_invalidate_entry(mapping, index, true);
691  
692  	/*
693  	 * This gets called from truncate / punch_hole path. As such, the caller
694  	 * must hold locks protecting against concurrent modifications of the
695  	 * page cache (usually fs-private i_mmap_sem for writing). Since the
696  	 * caller has seen a DAX entry for this index, we better find it
697  	 * at that index as well...
698  	 */
699  	WARN_ON_ONCE(!ret);
700  	return ret;
701  }
702  
703  /*
704   * Invalidate DAX entry if it is clean.
705   */
706  int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
707  				      pgoff_t index)
708  {
709  	return __dax_invalidate_entry(mapping, index, false);
710  }
711  
712  static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_dev,
713  			     sector_t sector, struct page *to, unsigned long vaddr)
714  {
715  	void *vto, *kaddr;
716  	pgoff_t pgoff;
717  	long rc;
718  	int id;
719  
720  	rc = bdev_dax_pgoff(bdev, sector, PAGE_SIZE, &pgoff);
721  	if (rc)
722  		return rc;
723  
724  	id = dax_read_lock();
725  	rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
726  	if (rc < 0) {
727  		dax_read_unlock(id);
728  		return rc;
729  	}
730  	vto = kmap_atomic(to);
731  	copy_user_page(vto, (void __force *)kaddr, vaddr, to);
732  	kunmap_atomic(vto);
733  	dax_read_unlock(id);
734  	return 0;
735  }
736  
737  /*
738   * By this point grab_mapping_entry() has ensured that we have a locked entry
739   * of the appropriate size so we don't have to worry about downgrading PMDs to
740   * PTEs.  If we happen to be trying to insert a PTE and there is a PMD
741   * already in the tree, we will skip the insertion and just dirty the PMD as
742   * appropriate.
743   */
744  static void *dax_insert_entry(struct xa_state *xas,
745  		struct address_space *mapping, struct vm_fault *vmf,
746  		void *entry, pfn_t pfn, unsigned long flags, bool dirty)
747  {
748  	void *new_entry = dax_make_entry(pfn, flags);
749  
750  	if (dirty)
751  		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
752  
753  	if (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE)) {
754  		unsigned long index = xas->xa_index;
755  		/* we are replacing a zero page with block mapping */
756  		if (dax_is_pmd_entry(entry))
757  			unmap_mapping_pages(mapping, index & ~PG_PMD_COLOUR,
758  					PG_PMD_NR, false);
759  		else /* pte entry */
760  			unmap_mapping_pages(mapping, index, 1, false);
761  	}
762  
763  	xas_reset(xas);
764  	xas_lock_irq(xas);
765  	if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
766  		void *old;
767  
768  		dax_disassociate_entry(entry, mapping, false);
769  		dax_associate_entry(new_entry, mapping, vmf->vma, vmf->address);
770  		/*
771  		 * Only swap our new entry into the page cache if the current
772  		 * entry is a zero page or an empty entry.  If a normal PTE or
773  		 * PMD entry is already in the cache, we leave it alone.  This
774  		 * means that if we are trying to insert a PTE and the
775  		 * existing entry is a PMD, we will just leave the PMD in the
776  		 * tree and dirty it if necessary.
777  		 */
778  		old = dax_lock_entry(xas, new_entry);
779  		WARN_ON_ONCE(old != xa_mk_value(xa_to_value(entry) |
780  					DAX_LOCKED));
781  		entry = new_entry;
782  	} else {
783  		xas_load(xas);	/* Walk the xa_state */
784  	}
785  
786  	if (dirty)
787  		xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
788  
789  	xas_unlock_irq(xas);
790  	return entry;
791  }
792  
793  static inline
794  unsigned long pgoff_address(pgoff_t pgoff, struct vm_area_struct *vma)
795  {
796  	unsigned long address;
797  
798  	address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
799  	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
800  	return address;
801  }
802  
803  /* Walk all mappings of a given index of a file and writeprotect them */
804  static void dax_entry_mkclean(struct address_space *mapping, pgoff_t index,
805  		unsigned long pfn)
806  {
807  	struct vm_area_struct *vma;
808  	pte_t pte, *ptep = NULL;
809  	pmd_t *pmdp = NULL;
810  	spinlock_t *ptl;
811  
812  	i_mmap_lock_read(mapping);
813  	vma_interval_tree_foreach(vma, &mapping->i_mmap, index, index) {
814  		struct mmu_notifier_range range;
815  		unsigned long address;
816  
817  		cond_resched();
818  
819  		if (!(vma->vm_flags & VM_SHARED))
820  			continue;
821  
822  		address = pgoff_address(index, vma);
823  
824  		/*
825  		 * follow_invalidate_pte() will use the range to call
826  		 * mmu_notifier_invalidate_range_start() on our behalf before
827  		 * taking any lock.
828  		 */
829  		if (follow_invalidate_pte(vma->vm_mm, address, &range, &ptep,
830  					  &pmdp, &ptl))
831  			continue;
832  
833  		/*
834  		 * No need to call mmu_notifier_invalidate_range() as we are
835  		 * downgrading page table protection not changing it to point
836  		 * to a new page.
837  		 *
838  		 * See Documentation/vm/mmu_notifier.rst
839  		 */
840  		if (pmdp) {
841  #ifdef CONFIG_FS_DAX_PMD
842  			pmd_t pmd;
843  
844  			if (pfn != pmd_pfn(*pmdp))
845  				goto unlock_pmd;
846  			if (!pmd_dirty(*pmdp) && !pmd_write(*pmdp))
847  				goto unlock_pmd;
848  
849  			flush_cache_page(vma, address, pfn);
850  			pmd = pmdp_invalidate(vma, address, pmdp);
851  			pmd = pmd_wrprotect(pmd);
852  			pmd = pmd_mkclean(pmd);
853  			set_pmd_at(vma->vm_mm, address, pmdp, pmd);
854  unlock_pmd:
855  #endif
856  			spin_unlock(ptl);
857  		} else {
858  			if (pfn != pte_pfn(*ptep))
859  				goto unlock_pte;
860  			if (!pte_dirty(*ptep) && !pte_write(*ptep))
861  				goto unlock_pte;
862  
863  			flush_cache_page(vma, address, pfn);
864  			pte = ptep_clear_flush(vma, address, ptep);
865  			pte = pte_wrprotect(pte);
866  			pte = pte_mkclean(pte);
867  			set_pte_at(vma->vm_mm, address, ptep, pte);
868  unlock_pte:
869  			pte_unmap_unlock(ptep, ptl);
870  		}
871  
872  		mmu_notifier_invalidate_range_end(&range);
873  	}
874  	i_mmap_unlock_read(mapping);
875  }
876  
877  static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
878  		struct address_space *mapping, void *entry)
879  {
880  	unsigned long pfn, index, count;
881  	long ret = 0;
882  
883  	/*
884  	 * A page got tagged dirty in DAX mapping? Something is seriously
885  	 * wrong.
886  	 */
887  	if (WARN_ON(!xa_is_value(entry)))
888  		return -EIO;
889  
890  	if (unlikely(dax_is_locked(entry))) {
891  		void *old_entry = entry;
892  
893  		entry = get_unlocked_entry(xas, 0);
894  
895  		/* Entry got punched out / reallocated? */
896  		if (!entry || WARN_ON_ONCE(!xa_is_value(entry)))
897  			goto put_unlocked;
898  		/*
899  		 * Entry got reallocated elsewhere? No need to writeback.
900  		 * We have to compare pfns as we must not bail out due to
901  		 * difference in lockbit or entry type.
902  		 */
903  		if (dax_to_pfn(old_entry) != dax_to_pfn(entry))
904  			goto put_unlocked;
905  		if (WARN_ON_ONCE(dax_is_empty_entry(entry) ||
906  					dax_is_zero_entry(entry))) {
907  			ret = -EIO;
908  			goto put_unlocked;
909  		}
910  
911  		/* Another fsync thread may have already done this entry */
912  		if (!xas_get_mark(xas, PAGECACHE_TAG_TOWRITE))
913  			goto put_unlocked;
914  	}
915  
916  	/* Lock the entry to serialize with page faults */
917  	dax_lock_entry(xas, entry);
918  
919  	/*
920  	 * We can clear the tag now but we have to be careful so that concurrent
921  	 * dax_writeback_one() calls for the same index cannot finish before we
922  	 * actually flush the caches. This is achieved as the calls will look
923  	 * at the entry only under the i_pages lock and once they do that
924  	 * they will see the entry locked and wait for it to unlock.
925  	 */
926  	xas_clear_mark(xas, PAGECACHE_TAG_TOWRITE);
927  	xas_unlock_irq(xas);
928  
929  	/*
930  	 * If dax_writeback_mapping_range() was given a wbc->range_start
931  	 * in the middle of a PMD, the 'index' we use needs to be
932  	 * aligned to the start of the PMD.
933  	 * This allows us to flush for PMD_SIZE and not have to worry about
934  	 * partial PMD writebacks.
935  	 */
936  	pfn = dax_to_pfn(entry);
937  	count = 1UL << dax_entry_order(entry);
938  	index = xas->xa_index & ~(count - 1);
939  
940  	dax_entry_mkclean(mapping, index, pfn);
941  	dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE);
942  	/*
943  	 * After we have flushed the cache, we can clear the dirty tag. There
944  	 * cannot be new dirty data in the pfn after the flush has completed as
945  	 * the pfn mappings are writeprotected and fault waits for mapping
946  	 * entry lock.
947  	 */
948  	xas_reset(xas);
949  	xas_lock_irq(xas);
950  	xas_store(xas, entry);
951  	xas_clear_mark(xas, PAGECACHE_TAG_DIRTY);
952  	dax_wake_entry(xas, entry, WAKE_NEXT);
953  
954  	trace_dax_writeback_one(mapping->host, index, count);
955  	return ret;
956  
957   put_unlocked:
958  	put_unlocked_entry(xas, entry, WAKE_NEXT);
959  	return ret;
960  }
961  
962  /*
963   * Flush the mapping to the persistent domain within the byte range of [start,
964   * end]. This is required by data integrity operations to ensure file data is
965   * on persistent storage prior to completion of the operation.
966   */
967  int dax_writeback_mapping_range(struct address_space *mapping,
968  		struct dax_device *dax_dev, struct writeback_control *wbc)
969  {
970  	XA_STATE(xas, &mapping->i_pages, wbc->range_start >> PAGE_SHIFT);
971  	struct inode *inode = mapping->host;
972  	pgoff_t end_index = wbc->range_end >> PAGE_SHIFT;
973  	void *entry;
974  	int ret = 0;
975  	unsigned int scanned = 0;
976  
977  	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
978  		return -EIO;
979  
980  	if (mapping_empty(mapping) || wbc->sync_mode != WB_SYNC_ALL)
981  		return 0;
982  
983  	trace_dax_writeback_range(inode, xas.xa_index, end_index);
984  
985  	tag_pages_for_writeback(mapping, xas.xa_index, end_index);
986  
987  	xas_lock_irq(&xas);
988  	xas_for_each_marked(&xas, entry, end_index, PAGECACHE_TAG_TOWRITE) {
989  		ret = dax_writeback_one(&xas, dax_dev, mapping, entry);
990  		if (ret < 0) {
991  			mapping_set_error(mapping, ret);
992  			break;
993  		}
994  		if (++scanned % XA_CHECK_SCHED)
995  			continue;
996  
997  		xas_pause(&xas);
998  		xas_unlock_irq(&xas);
999  		cond_resched();
1000  		xas_lock_irq(&xas);
1001  	}
1002  	xas_unlock_irq(&xas);
1003  	trace_dax_writeback_range_done(inode, xas.xa_index, end_index);
1004  	return ret;
1005  }
1006  EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
1007  
1008  static sector_t dax_iomap_sector(const struct iomap *iomap, loff_t pos)
1009  {
1010  	return (iomap->addr + (pos & PAGE_MASK) - iomap->offset) >> 9;
1011  }
1012  
1013  static int dax_iomap_pfn(const struct iomap *iomap, loff_t pos, size_t size,
1014  			 pfn_t *pfnp)
1015  {
1016  	const sector_t sector = dax_iomap_sector(iomap, pos);
1017  	pgoff_t pgoff;
1018  	int id, rc;
1019  	long length;
1020  
1021  	rc = bdev_dax_pgoff(iomap->bdev, sector, size, &pgoff);
1022  	if (rc)
1023  		return rc;
1024  	id = dax_read_lock();
1025  	length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
1026  				   NULL, pfnp);
1027  	if (length < 0) {
1028  		rc = length;
1029  		goto out;
1030  	}
1031  	rc = -EINVAL;
1032  	if (PFN_PHYS(length) < size)
1033  		goto out;
1034  	if (pfn_t_to_pfn(*pfnp) & (PHYS_PFN(size)-1))
1035  		goto out;
1036  	/* For larger pages we need devmap */
1037  	if (length > 1 && !pfn_t_devmap(*pfnp))
1038  		goto out;
1039  	rc = 0;
1040  out:
1041  	dax_read_unlock(id);
1042  	return rc;
1043  }
1044  
1045  /*
1046   * The user has performed a load from a hole in the file.  Allocating a new
1047   * page in the file would cause excessive storage usage for workloads with
1048   * sparse files.  Instead we insert a read-only mapping of the 4k zero page.
1049   * If this page is ever written to we will re-fault and change the mapping to
1050   * point to real DAX storage instead.
1051   */
1052  static vm_fault_t dax_load_hole(struct xa_state *xas,
1053  		struct address_space *mapping, void **entry,
1054  		struct vm_fault *vmf)
1055  {
1056  	struct inode *inode = mapping->host;
1057  	unsigned long vaddr = vmf->address;
1058  	pfn_t pfn = pfn_to_pfn_t(my_zero_pfn(vaddr));
1059  	vm_fault_t ret;
1060  
1061  	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
1062  			DAX_ZERO_PAGE, false);
1063  
1064  	ret = vmf_insert_mixed(vmf->vma, vaddr, pfn);
1065  	trace_dax_load_hole(inode, vmf, ret);
1066  	return ret;
1067  }
1068  
1069  #ifdef CONFIG_FS_DAX_PMD
1070  static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
1071  		const struct iomap *iomap, void **entry)
1072  {
1073  	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
1074  	unsigned long pmd_addr = vmf->address & PMD_MASK;
1075  	struct vm_area_struct *vma = vmf->vma;
1076  	struct inode *inode = mapping->host;
1077  	pgtable_t pgtable = NULL;
1078  	struct page *zero_page;
1079  	spinlock_t *ptl;
1080  	pmd_t pmd_entry;
1081  	pfn_t pfn;
1082  
1083  	zero_page = mm_get_huge_zero_page(vmf->vma->vm_mm);
1084  
1085  	if (unlikely(!zero_page))
1086  		goto fallback;
1087  
1088  	pfn = page_to_pfn_t(zero_page);
1089  	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
1090  			DAX_PMD | DAX_ZERO_PAGE, false);
1091  
1092  	if (arch_needs_pgtable_deposit()) {
1093  		pgtable = pte_alloc_one(vma->vm_mm);
1094  		if (!pgtable)
1095  			return VM_FAULT_OOM;
1096  	}
1097  
1098  	ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
1099  	if (!pmd_none(*(vmf->pmd))) {
1100  		spin_unlock(ptl);
1101  		goto fallback;
1102  	}
1103  
1104  	if (pgtable) {
1105  		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
1106  		mm_inc_nr_ptes(vma->vm_mm);
1107  	}
1108  	pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
1109  	pmd_entry = pmd_mkhuge(pmd_entry);
1110  	set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
1111  	spin_unlock(ptl);
1112  	trace_dax_pmd_load_hole(inode, vmf, zero_page, *entry);
1113  	return VM_FAULT_NOPAGE;
1114  
1115  fallback:
1116  	if (pgtable)
1117  		pte_free(vma->vm_mm, pgtable);
1118  	trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
1119  	return VM_FAULT_FALLBACK;
1120  }
1121  #else
1122  static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
1123  		const struct iomap *iomap, void **entry)
1124  {
1125  	return VM_FAULT_FALLBACK;
1126  }
1127  #endif /* CONFIG_FS_DAX_PMD */
1128  
1129  s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
1130  {
1131  	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
1132  	pgoff_t pgoff;
1133  	long rc, id;
1134  	void *kaddr;
1135  	bool page_aligned = false;
1136  	unsigned offset = offset_in_page(pos);
1137  	unsigned size = min_t(u64, PAGE_SIZE - offset, length);
1138  
1139  	if (IS_ALIGNED(sector << SECTOR_SHIFT, PAGE_SIZE) &&
1140  	    (size == PAGE_SIZE))
1141  		page_aligned = true;
1142  
1143  	rc = bdev_dax_pgoff(iomap->bdev, sector, PAGE_SIZE, &pgoff);
1144  	if (rc)
1145  		return rc;
1146  
1147  	id = dax_read_lock();
1148  
1149  	if (page_aligned)
1150  		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
1151  	else
1152  		rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
1153  	if (rc < 0) {
1154  		dax_read_unlock(id);
1155  		return rc;
1156  	}
1157  
1158  	if (!page_aligned) {
1159  		memset(kaddr + offset, 0, size);
1160  		dax_flush(iomap->dax_dev, kaddr + offset, size);
1161  	}
1162  	dax_read_unlock(id);
1163  	return size;
1164  }
1165  
1166  static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
1167  		struct iov_iter *iter)
1168  {
1169  	const struct iomap *iomap = &iomi->iomap;
1170  	loff_t length = iomap_length(iomi);
1171  	loff_t pos = iomi->pos;
1172  	struct block_device *bdev = iomap->bdev;
1173  	struct dax_device *dax_dev = iomap->dax_dev;
1174  	loff_t end = pos + length, done = 0;
1175  	ssize_t ret = 0;
1176  	size_t xfer;
1177  	int id;
1178  
1179  	if (iov_iter_rw(iter) == READ) {
1180  		end = min(end, i_size_read(iomi->inode));
1181  		if (pos >= end)
1182  			return 0;
1183  
1184  		if (iomap->type == IOMAP_HOLE || iomap->type == IOMAP_UNWRITTEN)
1185  			return iov_iter_zero(min(length, end - pos), iter);
1186  	}
1187  
1188  	if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
1189  		return -EIO;
1190  
1191  	/*
1192  	 * Write can allocate block for an area which has a hole page mapped
1193  	 * into page tables. We have to tear down these mappings so that data
1194  	 * written by write(2) is visible in mmap.
1195  	 */
1196  	if (iomap->flags & IOMAP_F_NEW) {
1197  		invalidate_inode_pages2_range(iomi->inode->i_mapping,
1198  					      pos >> PAGE_SHIFT,
1199  					      (end - 1) >> PAGE_SHIFT);
1200  	}
1201  
1202  	id = dax_read_lock();
1203  	while (pos < end) {
1204  		unsigned offset = pos & (PAGE_SIZE - 1);
1205  		const size_t size = ALIGN(length + offset, PAGE_SIZE);
1206  		const sector_t sector = dax_iomap_sector(iomap, pos);
1207  		ssize_t map_len;
1208  		pgoff_t pgoff;
1209  		void *kaddr;
1210  
1211  		if (fatal_signal_pending(current)) {
1212  			ret = -EINTR;
1213  			break;
1214  		}
1215  
1216  		ret = bdev_dax_pgoff(bdev, sector, size, &pgoff);
1217  		if (ret)
1218  			break;
1219  
1220  		map_len = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size),
1221  				&kaddr, NULL);
1222  		if (map_len < 0) {
1223  			ret = map_len;
1224  			break;
1225  		}
1226  
1227  		map_len = PFN_PHYS(map_len);
1228  		kaddr += offset;
1229  		map_len -= offset;
1230  		if (map_len > end - pos)
1231  			map_len = end - pos;
1232  
1233  		/*
1234  		 * The userspace address for the memory copy has already been
1235  		 * validated via access_ok() in either vfs_read() or
1236  		 * vfs_write(), depending on which operation we are doing.
1237  		 */
1238  		if (iov_iter_rw(iter) == WRITE)
1239  			xfer = dax_copy_from_iter(dax_dev, pgoff, kaddr,
1240  					map_len, iter);
1241  		else
1242  			xfer = dax_copy_to_iter(dax_dev, pgoff, kaddr,
1243  					map_len, iter);
1244  
1245  		pos += xfer;
1246  		length -= xfer;
1247  		done += xfer;
1248  
1249  		if (xfer == 0)
1250  			ret = -EFAULT;
1251  		if (xfer < map_len)
1252  			break;
1253  	}
1254  	dax_read_unlock(id);
1255  
1256  	return done ? done : ret;
1257  }
1258  
1259  /**
1260   * dax_iomap_rw - Perform I/O to a DAX file
1261   * @iocb:	The control block for this I/O
1262   * @iter:	The addresses to do I/O from or to
1263   * @ops:	iomap ops passed from the file system
1264   *
1265   * This function performs read and write operations to directly mapped
1266   * persistent memory.  The callers needs to take care of read/write exclusion
1267   * and evicting any page cache pages in the region under I/O.
1268   */
1269  ssize_t
1270  dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
1271  		const struct iomap_ops *ops)
1272  {
1273  	struct iomap_iter iomi = {
1274  		.inode		= iocb->ki_filp->f_mapping->host,
1275  		.pos		= iocb->ki_pos,
1276  		.len		= iov_iter_count(iter),
1277  	};
1278  	loff_t done = 0;
1279  	int ret;
1280  
1281  	if (iov_iter_rw(iter) == WRITE) {
1282  		lockdep_assert_held_write(&iomi.inode->i_rwsem);
1283  		iomi.flags |= IOMAP_WRITE;
1284  	} else {
1285  		lockdep_assert_held(&iomi.inode->i_rwsem);
1286  	}
1287  
1288  	if (iocb->ki_flags & IOCB_NOWAIT)
1289  		iomi.flags |= IOMAP_NOWAIT;
1290  
1291  	while ((ret = iomap_iter(&iomi, ops)) > 0)
1292  		iomi.processed = dax_iomap_iter(&iomi, iter);
1293  
1294  	done = iomi.pos - iocb->ki_pos;
1295  	iocb->ki_pos = iomi.pos;
1296  	return done ? done : ret;
1297  }
1298  EXPORT_SYMBOL_GPL(dax_iomap_rw);
1299  
1300  static vm_fault_t dax_fault_return(int error)
1301  {
1302  	if (error == 0)
1303  		return VM_FAULT_NOPAGE;
1304  	return vmf_error(error);
1305  }
1306  
1307  /*
1308   * MAP_SYNC on a dax mapping guarantees dirty metadata is
1309   * flushed on write-faults (non-cow), but not read-faults.
1310   */
1311  static bool dax_fault_is_synchronous(unsigned long flags,
1312  		struct vm_area_struct *vma, const struct iomap *iomap)
1313  {
1314  	return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
1315  		&& (iomap->flags & IOMAP_F_DIRTY);
1316  }
1317  
1318  /*
1319   * When handling a synchronous page fault and the inode need a fsync, we can
1320   * insert the PTE/PMD into page tables only after that fsync happened. Skip
1321   * insertion for now and return the pfn so that caller can insert it after the
1322   * fsync is done.
1323   */
1324  static vm_fault_t dax_fault_synchronous_pfnp(pfn_t *pfnp, pfn_t pfn)
1325  {
1326  	if (WARN_ON_ONCE(!pfnp))
1327  		return VM_FAULT_SIGBUS;
1328  	*pfnp = pfn;
1329  	return VM_FAULT_NEEDDSYNC;
1330  }
1331  
1332  static vm_fault_t dax_fault_cow_page(struct vm_fault *vmf,
1333  		const struct iomap_iter *iter)
1334  {
1335  	sector_t sector = dax_iomap_sector(&iter->iomap, iter->pos);
1336  	unsigned long vaddr = vmf->address;
1337  	vm_fault_t ret;
1338  	int error = 0;
1339  
1340  	switch (iter->iomap.type) {
1341  	case IOMAP_HOLE:
1342  	case IOMAP_UNWRITTEN:
1343  		clear_user_highpage(vmf->cow_page, vaddr);
1344  		break;
1345  	case IOMAP_MAPPED:
1346  		error = copy_cow_page_dax(iter->iomap.bdev, iter->iomap.dax_dev,
1347  					  sector, vmf->cow_page, vaddr);
1348  		break;
1349  	default:
1350  		WARN_ON_ONCE(1);
1351  		error = -EIO;
1352  		break;
1353  	}
1354  
1355  	if (error)
1356  		return dax_fault_return(error);
1357  
1358  	__SetPageUptodate(vmf->cow_page);
1359  	ret = finish_fault(vmf);
1360  	if (!ret)
1361  		return VM_FAULT_DONE_COW;
1362  	return ret;
1363  }
1364  
1365  /**
1366   * dax_fault_iter - Common actor to handle pfn insertion in PTE/PMD fault.
1367   * @vmf:	vm fault instance
1368   * @iter:	iomap iter
1369   * @pfnp:	pfn to be returned
1370   * @xas:	the dax mapping tree of a file
1371   * @entry:	an unlocked dax entry to be inserted
1372   * @pmd:	distinguish whether it is a pmd fault
1373   */
1374  static vm_fault_t dax_fault_iter(struct vm_fault *vmf,
1375  		const struct iomap_iter *iter, pfn_t *pfnp,
1376  		struct xa_state *xas, void **entry, bool pmd)
1377  {
1378  	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
1379  	const struct iomap *iomap = &iter->iomap;
1380  	size_t size = pmd ? PMD_SIZE : PAGE_SIZE;
1381  	loff_t pos = (loff_t)xas->xa_index << PAGE_SHIFT;
1382  	bool write = vmf->flags & FAULT_FLAG_WRITE;
1383  	bool sync = dax_fault_is_synchronous(iter->flags, vmf->vma, iomap);
1384  	unsigned long entry_flags = pmd ? DAX_PMD : 0;
1385  	int err = 0;
1386  	pfn_t pfn;
1387  
1388  	if (!pmd && vmf->cow_page)
1389  		return dax_fault_cow_page(vmf, iter);
1390  
1391  	/* if we are reading UNWRITTEN and HOLE, return a hole. */
1392  	if (!write &&
1393  	    (iomap->type == IOMAP_UNWRITTEN || iomap->type == IOMAP_HOLE)) {
1394  		if (!pmd)
1395  			return dax_load_hole(xas, mapping, entry, vmf);
1396  		return dax_pmd_load_hole(xas, vmf, iomap, entry);
1397  	}
1398  
1399  	if (iomap->type != IOMAP_MAPPED) {
1400  		WARN_ON_ONCE(1);
1401  		return pmd ? VM_FAULT_FALLBACK : VM_FAULT_SIGBUS;
1402  	}
1403  
1404  	err = dax_iomap_pfn(&iter->iomap, pos, size, &pfn);
1405  	if (err)
1406  		return pmd ? VM_FAULT_FALLBACK : dax_fault_return(err);
1407  
1408  	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn, entry_flags,
1409  				  write && !sync);
1410  
1411  	if (sync)
1412  		return dax_fault_synchronous_pfnp(pfnp, pfn);
1413  
1414  	/* insert PMD pfn */
1415  	if (pmd)
1416  		return vmf_insert_pfn_pmd(vmf, pfn, write);
1417  
1418  	/* insert PTE pfn */
1419  	if (write)
1420  		return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
1421  	return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
1422  }
1423  
1424  static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
1425  			       int *iomap_errp, const struct iomap_ops *ops)
1426  {
1427  	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
1428  	XA_STATE(xas, &mapping->i_pages, vmf->pgoff);
1429  	struct iomap_iter iter = {
1430  		.inode		= mapping->host,
1431  		.pos		= (loff_t)vmf->pgoff << PAGE_SHIFT,
1432  		.len		= PAGE_SIZE,
1433  		.flags		= IOMAP_FAULT,
1434  	};
1435  	vm_fault_t ret = 0;
1436  	void *entry;
1437  	int error;
1438  
1439  	trace_dax_pte_fault(iter.inode, vmf, ret);
1440  	/*
1441  	 * Check whether offset isn't beyond end of file now. Caller is supposed
1442  	 * to hold locks serializing us with truncate / punch hole so this is
1443  	 * a reliable test.
1444  	 */
1445  	if (iter.pos >= i_size_read(iter.inode)) {
1446  		ret = VM_FAULT_SIGBUS;
1447  		goto out;
1448  	}
1449  
1450  	if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
1451  		iter.flags |= IOMAP_WRITE;
1452  
1453  	entry = grab_mapping_entry(&xas, mapping, 0);
1454  	if (xa_is_internal(entry)) {
1455  		ret = xa_to_internal(entry);
1456  		goto out;
1457  	}
1458  
1459  	/*
1460  	 * It is possible, particularly with mixed reads & writes to private
1461  	 * mappings, that we have raced with a PMD fault that overlaps with
1462  	 * the PTE we need to set up.  If so just return and the fault will be
1463  	 * retried.
1464  	 */
1465  	if (pmd_trans_huge(*vmf->pmd) || pmd_devmap(*vmf->pmd)) {
1466  		ret = VM_FAULT_NOPAGE;
1467  		goto unlock_entry;
1468  	}
1469  
1470  	while ((error = iomap_iter(&iter, ops)) > 0) {
1471  		if (WARN_ON_ONCE(iomap_length(&iter) < PAGE_SIZE)) {
1472  			iter.processed = -EIO;	/* fs corruption? */
1473  			continue;
1474  		}
1475  
1476  		ret = dax_fault_iter(vmf, &iter, pfnp, &xas, &entry, false);
1477  		if (ret != VM_FAULT_SIGBUS &&
1478  		    (iter.iomap.flags & IOMAP_F_NEW)) {
1479  			count_vm_event(PGMAJFAULT);
1480  			count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
1481  			ret |= VM_FAULT_MAJOR;
1482  		}
1483  
1484  		if (!(ret & VM_FAULT_ERROR))
1485  			iter.processed = PAGE_SIZE;
1486  	}
1487  
1488  	if (iomap_errp)
1489  		*iomap_errp = error;
1490  	if (!ret && error)
1491  		ret = dax_fault_return(error);
1492  
1493  unlock_entry:
1494  	dax_unlock_entry(&xas, entry);
1495  out:
1496  	trace_dax_pte_fault_done(iter.inode, vmf, ret);
1497  	return ret;
1498  }
1499  
1500  #ifdef CONFIG_FS_DAX_PMD
1501  static bool dax_fault_check_fallback(struct vm_fault *vmf, struct xa_state *xas,
1502  		pgoff_t max_pgoff)
1503  {
1504  	unsigned long pmd_addr = vmf->address & PMD_MASK;
1505  	bool write = vmf->flags & FAULT_FLAG_WRITE;
1506  
1507  	/*
1508  	 * Make sure that the faulting address's PMD offset (color) matches
1509  	 * the PMD offset from the start of the file.  This is necessary so
1510  	 * that a PMD range in the page table overlaps exactly with a PMD
1511  	 * range in the page cache.
1512  	 */
1513  	if ((vmf->pgoff & PG_PMD_COLOUR) !=
1514  	    ((vmf->address >> PAGE_SHIFT) & PG_PMD_COLOUR))
1515  		return true;
1516  
1517  	/* Fall back to PTEs if we're going to COW */
1518  	if (write && !(vmf->vma->vm_flags & VM_SHARED))
1519  		return true;
1520  
1521  	/* If the PMD would extend outside the VMA */
1522  	if (pmd_addr < vmf->vma->vm_start)
1523  		return true;
1524  	if ((pmd_addr + PMD_SIZE) > vmf->vma->vm_end)
1525  		return true;
1526  
1527  	/* If the PMD would extend beyond the file size */
1528  	if ((xas->xa_index | PG_PMD_COLOUR) >= max_pgoff)
1529  		return true;
1530  
1531  	return false;
1532  }
1533  
1534  static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
1535  			       const struct iomap_ops *ops)
1536  {
1537  	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
1538  	XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_ORDER);
1539  	struct iomap_iter iter = {
1540  		.inode		= mapping->host,
1541  		.len		= PMD_SIZE,
1542  		.flags		= IOMAP_FAULT,
1543  	};
1544  	vm_fault_t ret = VM_FAULT_FALLBACK;
1545  	pgoff_t max_pgoff;
1546  	void *entry;
1547  	int error;
1548  
1549  	if (vmf->flags & FAULT_FLAG_WRITE)
1550  		iter.flags |= IOMAP_WRITE;
1551  
1552  	/*
1553  	 * Check whether offset isn't beyond end of file now. Caller is
1554  	 * supposed to hold locks serializing us with truncate / punch hole so
1555  	 * this is a reliable test.
1556  	 */
1557  	max_pgoff = DIV_ROUND_UP(i_size_read(iter.inode), PAGE_SIZE);
1558  
1559  	trace_dax_pmd_fault(iter.inode, vmf, max_pgoff, 0);
1560  
1561  	if (xas.xa_index >= max_pgoff) {
1562  		ret = VM_FAULT_SIGBUS;
1563  		goto out;
1564  	}
1565  
1566  	if (dax_fault_check_fallback(vmf, &xas, max_pgoff))
1567  		goto fallback;
1568  
1569  	/*
1570  	 * grab_mapping_entry() will make sure we get an empty PMD entry,
1571  	 * a zero PMD entry or a DAX PMD.  If it can't (because a PTE
1572  	 * entry is already in the array, for instance), it will return
1573  	 * VM_FAULT_FALLBACK.
1574  	 */
1575  	entry = grab_mapping_entry(&xas, mapping, PMD_ORDER);
1576  	if (xa_is_internal(entry)) {
1577  		ret = xa_to_internal(entry);
1578  		goto fallback;
1579  	}
1580  
1581  	/*
1582  	 * It is possible, particularly with mixed reads & writes to private
1583  	 * mappings, that we have raced with a PTE fault that overlaps with
1584  	 * the PMD we need to set up.  If so just return and the fault will be
1585  	 * retried.
1586  	 */
1587  	if (!pmd_none(*vmf->pmd) && !pmd_trans_huge(*vmf->pmd) &&
1588  			!pmd_devmap(*vmf->pmd)) {
1589  		ret = 0;
1590  		goto unlock_entry;
1591  	}
1592  
1593  	iter.pos = (loff_t)xas.xa_index << PAGE_SHIFT;
1594  	while ((error = iomap_iter(&iter, ops)) > 0) {
1595  		if (iomap_length(&iter) < PMD_SIZE)
1596  			continue; /* actually breaks out of the loop */
1597  
1598  		ret = dax_fault_iter(vmf, &iter, pfnp, &xas, &entry, true);
1599  		if (ret != VM_FAULT_FALLBACK)
1600  			iter.processed = PMD_SIZE;
1601  	}
1602  
1603  unlock_entry:
1604  	dax_unlock_entry(&xas, entry);
1605  fallback:
1606  	if (ret == VM_FAULT_FALLBACK) {
1607  		split_huge_pmd(vmf->vma, vmf->pmd, vmf->address);
1608  		count_vm_event(THP_FAULT_FALLBACK);
1609  	}
1610  out:
1611  	trace_dax_pmd_fault_done(iter.inode, vmf, max_pgoff, ret);
1612  	return ret;
1613  }
1614  #else
1615  static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
1616  			       const struct iomap_ops *ops)
1617  {
1618  	return VM_FAULT_FALLBACK;
1619  }
1620  #endif /* CONFIG_FS_DAX_PMD */
1621  
1622  /**
1623   * dax_iomap_fault - handle a page fault on a DAX file
1624   * @vmf: The description of the fault
1625   * @pe_size: Size of the page to fault in
1626   * @pfnp: PFN to insert for synchronous faults if fsync is required
1627   * @iomap_errp: Storage for detailed error code in case of error
1628   * @ops: Iomap ops passed from the file system
1629   *
1630   * When a page fault occurs, filesystems may call this helper in
1631   * their fault handler for DAX files. dax_iomap_fault() assumes the caller
1632   * has done all the necessary locking for page fault to proceed
1633   * successfully.
1634   */
1635  vm_fault_t dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
1636  		    pfn_t *pfnp, int *iomap_errp, const struct iomap_ops *ops)
1637  {
1638  	switch (pe_size) {
1639  	case PE_SIZE_PTE:
1640  		return dax_iomap_pte_fault(vmf, pfnp, iomap_errp, ops);
1641  	case PE_SIZE_PMD:
1642  		return dax_iomap_pmd_fault(vmf, pfnp, ops);
1643  	default:
1644  		return VM_FAULT_FALLBACK;
1645  	}
1646  }
1647  EXPORT_SYMBOL_GPL(dax_iomap_fault);
1648  
1649  /*
1650   * dax_insert_pfn_mkwrite - insert PTE or PMD entry into page tables
1651   * @vmf: The description of the fault
1652   * @pfn: PFN to insert
1653   * @order: Order of entry to insert.
1654   *
1655   * This function inserts a writeable PTE or PMD entry into the page tables
1656   * for an mmaped DAX file.  It also marks the page cache entry as dirty.
1657   */
1658  static vm_fault_t
1659  dax_insert_pfn_mkwrite(struct vm_fault *vmf, pfn_t pfn, unsigned int order)
1660  {
1661  	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
1662  	XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, order);
1663  	void *entry;
1664  	vm_fault_t ret;
1665  
1666  	xas_lock_irq(&xas);
1667  	entry = get_unlocked_entry(&xas, order);
1668  	/* Did we race with someone splitting entry or so? */
1669  	if (!entry || dax_is_conflict(entry) ||
1670  	    (order == 0 && !dax_is_pte_entry(entry))) {
1671  		put_unlocked_entry(&xas, entry, WAKE_NEXT);
1672  		xas_unlock_irq(&xas);
1673  		trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
1674  						      VM_FAULT_NOPAGE);
1675  		return VM_FAULT_NOPAGE;
1676  	}
1677  	xas_set_mark(&xas, PAGECACHE_TAG_DIRTY);
1678  	dax_lock_entry(&xas, entry);
1679  	xas_unlock_irq(&xas);
1680  	if (order == 0)
1681  		ret = vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
1682  #ifdef CONFIG_FS_DAX_PMD
1683  	else if (order == PMD_ORDER)
1684  		ret = vmf_insert_pfn_pmd(vmf, pfn, FAULT_FLAG_WRITE);
1685  #endif
1686  	else
1687  		ret = VM_FAULT_FALLBACK;
1688  	dax_unlock_entry(&xas, entry);
1689  	trace_dax_insert_pfn_mkwrite(mapping->host, vmf, ret);
1690  	return ret;
1691  }
1692  
1693  /**
1694   * dax_finish_sync_fault - finish synchronous page fault
1695   * @vmf: The description of the fault
1696   * @pe_size: Size of entry to be inserted
1697   * @pfn: PFN to insert
1698   *
1699   * This function ensures that the file range touched by the page fault is
1700   * stored persistently on the media and handles inserting of appropriate page
1701   * table entry.
1702   */
1703  vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
1704  		enum page_entry_size pe_size, pfn_t pfn)
1705  {
1706  	int err;
1707  	loff_t start = ((loff_t)vmf->pgoff) << PAGE_SHIFT;
1708  	unsigned int order = pe_order(pe_size);
1709  	size_t len = PAGE_SIZE << order;
1710  
1711  	err = vfs_fsync_range(vmf->vma->vm_file, start, start + len - 1, 1);
1712  	if (err)
1713  		return VM_FAULT_SIGBUS;
1714  	return dax_insert_pfn_mkwrite(vmf, pfn, order);
1715  }
1716  EXPORT_SYMBOL_GPL(dax_finish_sync_fault);
1717