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1/*
2 * mm/balloon_compaction.c
3 *
4 * Common interface for making balloon pages movable by compaction.
5 *
6 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
7 */
8#include <linux/mm.h>
9#include <linux/slab.h>
10#include <linux/export.h>
11#include <linux/balloon_compaction.h>
12
13/*
14 * balloon_page_enqueue - allocates a new page and inserts it into the balloon
15 * page list.
16 * @b_dev_info: balloon device descriptor where we will insert a new page to
17 *
18 * Driver must call it to properly allocate a new enlisted balloon page
19 * before definitively removing it from the guest system.
20 * This function returns the page address for the recently enqueued page or
21 * NULL in the case we fail to allocate a new page this turn.
22 */
23struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
24{
25 unsigned long flags;
26 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
27 __GFP_NOMEMALLOC | __GFP_NORETRY);
28 if (!page)
29 return NULL;
30
31 /*
32 * Block others from accessing the 'page' when we get around to
33 * establishing additional references. We should be the only one
34 * holding a reference to the 'page' at this point.
35 */
36 BUG_ON(!trylock_page(page));
37 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
38 balloon_page_insert(b_dev_info, page);
39 __count_vm_event(BALLOON_INFLATE);
40 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
41 unlock_page(page);
42 return page;
43}
44EXPORT_SYMBOL_GPL(balloon_page_enqueue);
45
46/*
47 * balloon_page_dequeue - removes a page from balloon's page list and returns
48 * the its address to allow the driver release the page.
49 * @b_dev_info: balloon device decriptor where we will grab a page from.
50 *
51 * Driver must call it to properly de-allocate a previous enlisted balloon page
52 * before definetively releasing it back to the guest system.
53 * This function returns the page address for the recently dequeued page or
54 * NULL in the case we find balloon's page list temporarily empty due to
55 * compaction isolated pages.
56 */
57struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
58{
59 struct page *page, *tmp;
60 unsigned long flags;
61 bool dequeued_page;
62
63 dequeued_page = false;
64 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
65 list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
66 /*
67 * Block others from accessing the 'page' while we get around
68 * establishing additional references and preparing the 'page'
69 * to be released by the balloon driver.
70 */
71 if (trylock_page(page)) {
72#ifdef CONFIG_BALLOON_COMPACTION
73 if (!PagePrivate(page)) {
74 /* raced with isolation */
75 unlock_page(page);
76 continue;
77 }
78#endif
79 balloon_page_delete(page);
80 __count_vm_event(BALLOON_DEFLATE);
81 unlock_page(page);
82 dequeued_page = true;
83 break;
84 }
85 }
86 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
87
88 if (!dequeued_page) {
89 /*
90 * If we are unable to dequeue a balloon page because the page
91 * list is empty and there is no isolated pages, then something
92 * went out of track and some balloon pages are lost.
93 * BUG() here, otherwise the balloon driver may get stuck into
94 * an infinite loop while attempting to release all its pages.
95 */
96 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
97 if (unlikely(list_empty(&b_dev_info->pages) &&
98 !b_dev_info->isolated_pages))
99 BUG();
100 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
101 page = NULL;
102 }
103 return page;
104}
105EXPORT_SYMBOL_GPL(balloon_page_dequeue);
106
107#ifdef CONFIG_BALLOON_COMPACTION
108
109static inline void __isolate_balloon_page(struct page *page)
110{
111 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
112 unsigned long flags;
113
114 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
115 ClearPagePrivate(page);
116 list_del(&page->lru);
117 b_dev_info->isolated_pages++;
118 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
119}
120
121static inline void __putback_balloon_page(struct page *page)
122{
123 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
124 unsigned long flags;
125
126 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
127 SetPagePrivate(page);
128 list_add(&page->lru, &b_dev_info->pages);
129 b_dev_info->isolated_pages--;
130 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
131}
132
133/* __isolate_lru_page() counterpart for a ballooned page */
134bool balloon_page_isolate(struct page *page)
135{
136 /*
137 * Avoid burning cycles with pages that are yet under __free_pages(),
138 * or just got freed under us.
139 *
140 * In case we 'win' a race for a balloon page being freed under us and
141 * raise its refcount preventing __free_pages() from doing its job
142 * the put_page() at the end of this block will take care of
143 * release this page, thus avoiding a nasty leakage.
144 */
145 if (likely(get_page_unless_zero(page))) {
146 /*
147 * As balloon pages are not isolated from LRU lists, concurrent
148 * compaction threads can race against page migration functions
149 * as well as race against the balloon driver releasing a page.
150 *
151 * In order to avoid having an already isolated balloon page
152 * being (wrongly) re-isolated while it is under migration,
153 * or to avoid attempting to isolate pages being released by
154 * the balloon driver, lets be sure we have the page lock
155 * before proceeding with the balloon page isolation steps.
156 */
157 if (likely(trylock_page(page))) {
158 /*
159 * A ballooned page, by default, has PagePrivate set.
160 * Prevent concurrent compaction threads from isolating
161 * an already isolated balloon page by clearing it.
162 */
163 if (balloon_page_movable(page)) {
164 __isolate_balloon_page(page);
165 unlock_page(page);
166 return true;
167 }
168 unlock_page(page);
169 }
170 put_page(page);
171 }
172 return false;
173}
174
175/* putback_lru_page() counterpart for a ballooned page */
176void balloon_page_putback(struct page *page)
177{
178 /*
179 * 'lock_page()' stabilizes the page and prevents races against
180 * concurrent isolation threads attempting to re-isolate it.
181 */
182 lock_page(page);
183
184 if (__is_movable_balloon_page(page)) {
185 __putback_balloon_page(page);
186 /* drop the extra ref count taken for page isolation */
187 put_page(page);
188 } else {
189 WARN_ON(1);
190 dump_page(page, "not movable balloon page");
191 }
192 unlock_page(page);
193}
194
195/* move_to_new_page() counterpart for a ballooned page */
196int balloon_page_migrate(struct page *newpage,
197 struct page *page, enum migrate_mode mode)
198{
199 struct balloon_dev_info *balloon = balloon_page_device(page);
200 int rc = -EAGAIN;
201
202 VM_BUG_ON_PAGE(!PageLocked(page), page);
203 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
204
205 if (WARN_ON(!__is_movable_balloon_page(page))) {
206 dump_page(page, "not movable balloon page");
207 return rc;
208 }
209
210 if (balloon && balloon->migratepage)
211 rc = balloon->migratepage(balloon, newpage, page, mode);
212
213 return rc;
214}
215#endif /* CONFIG_BALLOON_COMPACTION */
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * mm/balloon_compaction.c
4 *
5 * Common interface for making balloon pages movable by compaction.
6 *
7 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
8 */
9#include <linux/mm.h>
10#include <linux/slab.h>
11#include <linux/export.h>
12#include <linux/balloon_compaction.h>
13
14static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
15 struct page *page)
16{
17 /*
18 * Block others from accessing the 'page' when we get around to
19 * establishing additional references. We should be the only one
20 * holding a reference to the 'page' at this point. If we are not, then
21 * memory corruption is possible and we should stop execution.
22 */
23 BUG_ON(!trylock_page(page));
24 balloon_page_insert(b_dev_info, page);
25 unlock_page(page);
26 __count_vm_event(BALLOON_INFLATE);
27}
28
29/**
30 * balloon_page_list_enqueue() - inserts a list of pages into the balloon page
31 * list.
32 * @b_dev_info: balloon device descriptor where we will insert a new page to
33 * @pages: pages to enqueue - allocated using balloon_page_alloc.
34 *
35 * Driver must call this function to properly enqueue balloon pages before
36 * definitively removing them from the guest system.
37 *
38 * Return: number of pages that were enqueued.
39 */
40size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
41 struct list_head *pages)
42{
43 struct page *page, *tmp;
44 unsigned long flags;
45 size_t n_pages = 0;
46
47 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
48 list_for_each_entry_safe(page, tmp, pages, lru) {
49 list_del(&page->lru);
50 balloon_page_enqueue_one(b_dev_info, page);
51 n_pages++;
52 }
53 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
54 return n_pages;
55}
56EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
57
58/**
59 * balloon_page_list_dequeue() - removes pages from balloon's page list and
60 * returns a list of the pages.
61 * @b_dev_info: balloon device decriptor where we will grab a page from.
62 * @pages: pointer to the list of pages that would be returned to the caller.
63 * @n_req_pages: number of requested pages.
64 *
65 * Driver must call this function to properly de-allocate a previous enlisted
66 * balloon pages before definitively releasing it back to the guest system.
67 * This function tries to remove @n_req_pages from the ballooned pages and
68 * return them to the caller in the @pages list.
69 *
70 * Note that this function may fail to dequeue some pages even if the balloon
71 * isn't empty - since the page list can be temporarily empty due to compaction
72 * of isolated pages.
73 *
74 * Return: number of pages that were added to the @pages list.
75 */
76size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
77 struct list_head *pages, size_t n_req_pages)
78{
79 struct page *page, *tmp;
80 unsigned long flags;
81 size_t n_pages = 0;
82
83 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
84 list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
85 if (n_pages == n_req_pages)
86 break;
87
88 /*
89 * Block others from accessing the 'page' while we get around to
90 * establishing additional references and preparing the 'page'
91 * to be released by the balloon driver.
92 */
93 if (!trylock_page(page))
94 continue;
95
96 if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&
97 PageIsolated(page)) {
98 /* raced with isolation */
99 unlock_page(page);
100 continue;
101 }
102 balloon_page_delete(page);
103 __count_vm_event(BALLOON_DEFLATE);
104 list_add(&page->lru, pages);
105 unlock_page(page);
106 n_pages++;
107 }
108 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
109
110 return n_pages;
111}
112EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
113
114/*
115 * balloon_page_alloc - allocates a new page for insertion into the balloon
116 * page list.
117 *
118 * Driver must call this function to properly allocate a new balloon page.
119 * Driver must call balloon_page_enqueue before definitively removing the page
120 * from the guest system.
121 *
122 * Return: struct page for the allocated page or NULL on allocation failure.
123 */
124struct page *balloon_page_alloc(void)
125{
126 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
127 __GFP_NOMEMALLOC | __GFP_NORETRY |
128 __GFP_NOWARN);
129 return page;
130}
131EXPORT_SYMBOL_GPL(balloon_page_alloc);
132
133/*
134 * balloon_page_enqueue - inserts a new page into the balloon page list.
135 *
136 * @b_dev_info: balloon device descriptor where we will insert a new page
137 * @page: new page to enqueue - allocated using balloon_page_alloc.
138 *
139 * Drivers must call this function to properly enqueue a new allocated balloon
140 * page before definitively removing the page from the guest system.
141 *
142 * Drivers must not call balloon_page_enqueue on pages that have been pushed to
143 * a list with balloon_page_push before removing them with balloon_page_pop. To
144 * enqueue a list of pages, use balloon_page_list_enqueue instead.
145 */
146void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
147 struct page *page)
148{
149 unsigned long flags;
150
151 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
152 balloon_page_enqueue_one(b_dev_info, page);
153 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
154}
155EXPORT_SYMBOL_GPL(balloon_page_enqueue);
156
157/*
158 * balloon_page_dequeue - removes a page from balloon's page list and returns
159 * its address to allow the driver to release the page.
160 * @b_dev_info: balloon device decriptor where we will grab a page from.
161 *
162 * Driver must call this function to properly dequeue a previously enqueued page
163 * before definitively releasing it back to the guest system.
164 *
165 * Caller must perform its own accounting to ensure that this
166 * function is called only if some pages are actually enqueued.
167 *
168 * Note that this function may fail to dequeue some pages even if there are
169 * some enqueued pages - since the page list can be temporarily empty due to
170 * the compaction of isolated pages.
171 *
172 * TODO: remove the caller accounting requirements, and allow caller to wait
173 * until all pages can be dequeued.
174 *
175 * Return: struct page for the dequeued page, or NULL if no page was dequeued.
176 */
177struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
178{
179 unsigned long flags;
180 LIST_HEAD(pages);
181 int n_pages;
182
183 n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);
184
185 if (n_pages != 1) {
186 /*
187 * If we are unable to dequeue a balloon page because the page
188 * list is empty and there are no isolated pages, then something
189 * went out of track and some balloon pages are lost.
190 * BUG() here, otherwise the balloon driver may get stuck in
191 * an infinite loop while attempting to release all its pages.
192 */
193 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
194 if (unlikely(list_empty(&b_dev_info->pages) &&
195 !b_dev_info->isolated_pages))
196 BUG();
197 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
198 return NULL;
199 }
200 return list_first_entry(&pages, struct page, lru);
201}
202EXPORT_SYMBOL_GPL(balloon_page_dequeue);
203
204#ifdef CONFIG_BALLOON_COMPACTION
205
206bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
207
208{
209 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
210 unsigned long flags;
211
212 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
213 list_del(&page->lru);
214 b_dev_info->isolated_pages++;
215 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
216
217 return true;
218}
219
220void balloon_page_putback(struct page *page)
221{
222 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
223 unsigned long flags;
224
225 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
226 list_add(&page->lru, &b_dev_info->pages);
227 b_dev_info->isolated_pages--;
228 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
229}
230
231
232/* move_to_new_page() counterpart for a ballooned page */
233int balloon_page_migrate(struct address_space *mapping,
234 struct page *newpage, struct page *page,
235 enum migrate_mode mode)
236{
237 struct balloon_dev_info *balloon = balloon_page_device(page);
238
239 /*
240 * We can not easily support the no copy case here so ignore it as it
241 * is unlikely to be used with balloon pages. See include/linux/hmm.h
242 * for a user of the MIGRATE_SYNC_NO_COPY mode.
243 */
244 if (mode == MIGRATE_SYNC_NO_COPY)
245 return -EINVAL;
246
247 VM_BUG_ON_PAGE(!PageLocked(page), page);
248 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
249
250 return balloon->migratepage(balloon, newpage, page, mode);
251}
252
253const struct address_space_operations balloon_aops = {
254 .migratepage = balloon_page_migrate,
255 .isolate_page = balloon_page_isolate,
256 .putback_page = balloon_page_putback,
257};
258EXPORT_SYMBOL_GPL(balloon_aops);
259
260#endif /* CONFIG_BALLOON_COMPACTION */