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
14 static 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 */
40 size_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 }
56 EXPORT_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 descriptor 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 */
76 size_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 }
112 EXPORT_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 */
124 struct 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 }
131 EXPORT_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 */
146 void 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 }
155 EXPORT_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 descriptor 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 */
177 struct 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 }
202 EXPORT_SYMBOL_GPL(balloon_page_dequeue);
203
204 #ifdef CONFIG_BALLOON_COMPACTION
205
206 static bool 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
220 static void 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 /* move_to_new_page() counterpart for a ballooned page */
232 static int balloon_page_migrate(struct page *newpage, struct page *page,
233 enum migrate_mode mode)
234 {
235 struct balloon_dev_info *balloon = balloon_page_device(page);
236
237 VM_BUG_ON_PAGE(!PageLocked(page), page);
238 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
239
240 return balloon->migratepage(balloon, newpage, page, mode);
241 }
242
243 const struct movable_operations balloon_mops = {
244 .migrate_page = balloon_page_migrate,
245 .isolate_page = balloon_page_isolate,
246 .putback_page = balloon_page_putback,
247 };
248 EXPORT_SYMBOL_GPL(balloon_mops);
249
250 #endif /* CONFIG_BALLOON_COMPACTION */
251
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