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
balloon_page_enqueue_one(struct balloon_dev_info * b_dev_info,struct page * page)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 inc_node_page_state(page, NR_BALLOON_PAGES);
28 }
29
30 /**
31 * balloon_page_list_enqueue() - inserts a list of pages into the balloon page
32 * list.
33 * @b_dev_info: balloon device descriptor where we will insert a new page to
34 * @pages: pages to enqueue - allocated using balloon_page_alloc.
35 *
36 * Driver must call this function to properly enqueue balloon pages before
37 * definitively removing them from the guest system.
38 *
39 * Return: number of pages that were enqueued.
40 */
balloon_page_list_enqueue(struct balloon_dev_info * b_dev_info,struct list_head * pages)41 size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
42 struct list_head *pages)
43 {
44 struct page *page, *tmp;
45 unsigned long flags;
46 size_t n_pages = 0;
47
48 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
49 list_for_each_entry_safe(page, tmp, pages, lru) {
50 list_del(&page->lru);
51 balloon_page_enqueue_one(b_dev_info, page);
52 n_pages++;
53 }
54 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
55 return n_pages;
56 }
57 EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
58
59 /**
60 * balloon_page_list_dequeue() - removes pages from balloon's page list and
61 * returns a list of the pages.
62 * @b_dev_info: balloon device descriptor where we will grab a page from.
63 * @pages: pointer to the list of pages that would be returned to the caller.
64 * @n_req_pages: number of requested pages.
65 *
66 * Driver must call this function to properly de-allocate a previous enlisted
67 * balloon pages before definitively releasing it back to the guest system.
68 * This function tries to remove @n_req_pages from the ballooned pages and
69 * return them to the caller in the @pages list.
70 *
71 * Note that this function may fail to dequeue some pages even if the balloon
72 * isn't empty - since the page list can be temporarily empty due to compaction
73 * of isolated pages.
74 *
75 * Return: number of pages that were added to the @pages list.
76 */
balloon_page_list_dequeue(struct balloon_dev_info * b_dev_info,struct list_head * pages,size_t n_req_pages)77 size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
78 struct list_head *pages, size_t n_req_pages)
79 {
80 struct page *page, *tmp;
81 unsigned long flags;
82 size_t n_pages = 0;
83
84 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
85 list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
86 if (n_pages == n_req_pages)
87 break;
88
89 /*
90 * Block others from accessing the 'page' while we get around to
91 * establishing additional references and preparing the 'page'
92 * to be released by the balloon driver.
93 */
94 if (!trylock_page(page))
95 continue;
96
97 if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&
98 PageIsolated(page)) {
99 /* raced with isolation */
100 unlock_page(page);
101 continue;
102 }
103 balloon_page_delete(page);
104 __count_vm_event(BALLOON_DEFLATE);
105 list_add(&page->lru, pages);
106 unlock_page(page);
107 dec_node_page_state(page, NR_BALLOON_PAGES);
108 n_pages++;
109 }
110 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
111
112 return n_pages;
113 }
114 EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
115
116 /*
117 * balloon_page_alloc - allocates a new page for insertion into the balloon
118 * page list.
119 *
120 * Driver must call this function to properly allocate a new balloon page.
121 * Driver must call balloon_page_enqueue before definitively removing the page
122 * from the guest system.
123 *
124 * Return: struct page for the allocated page or NULL on allocation failure.
125 */
balloon_page_alloc(void)126 struct page *balloon_page_alloc(void)
127 {
128 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
129 __GFP_NOMEMALLOC | __GFP_NORETRY |
130 __GFP_NOWARN);
131 return page;
132 }
133 EXPORT_SYMBOL_GPL(balloon_page_alloc);
134
135 /*
136 * balloon_page_enqueue - inserts a new page into the balloon page list.
137 *
138 * @b_dev_info: balloon device descriptor where we will insert a new page
139 * @page: new page to enqueue - allocated using balloon_page_alloc.
140 *
141 * Drivers must call this function to properly enqueue a new allocated balloon
142 * page before definitively removing the page from the guest system.
143 *
144 * Drivers must not call balloon_page_enqueue on pages that have been pushed to
145 * a list with balloon_page_push before removing them with balloon_page_pop. To
146 * enqueue a list of pages, use balloon_page_list_enqueue instead.
147 */
balloon_page_enqueue(struct balloon_dev_info * b_dev_info,struct page * page)148 void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
149 struct page *page)
150 {
151 unsigned long flags;
152
153 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
154 balloon_page_enqueue_one(b_dev_info, page);
155 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
156 }
157 EXPORT_SYMBOL_GPL(balloon_page_enqueue);
158
159 /*
160 * balloon_page_dequeue - removes a page from balloon's page list and returns
161 * its address to allow the driver to release the page.
162 * @b_dev_info: balloon device descriptor where we will grab a page from.
163 *
164 * Driver must call this function to properly dequeue a previously enqueued page
165 * before definitively releasing it back to the guest system.
166 *
167 * Caller must perform its own accounting to ensure that this
168 * function is called only if some pages are actually enqueued.
169 *
170 * Note that this function may fail to dequeue some pages even if there are
171 * some enqueued pages - since the page list can be temporarily empty due to
172 * the compaction of isolated pages.
173 *
174 * TODO: remove the caller accounting requirements, and allow caller to wait
175 * until all pages can be dequeued.
176 *
177 * Return: struct page for the dequeued page, or NULL if no page was dequeued.
178 */
balloon_page_dequeue(struct balloon_dev_info * b_dev_info)179 struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
180 {
181 unsigned long flags;
182 LIST_HEAD(pages);
183 int n_pages;
184
185 n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);
186
187 if (n_pages != 1) {
188 /*
189 * If we are unable to dequeue a balloon page because the page
190 * list is empty and there are no isolated pages, then something
191 * went out of track and some balloon pages are lost.
192 * BUG() here, otherwise the balloon driver may get stuck in
193 * an infinite loop while attempting to release all its pages.
194 */
195 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
196 if (unlikely(list_empty(&b_dev_info->pages) &&
197 !b_dev_info->isolated_pages))
198 BUG();
199 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
200 return NULL;
201 }
202 return list_first_entry(&pages, struct page, lru);
203 }
204 EXPORT_SYMBOL_GPL(balloon_page_dequeue);
205
206 #ifdef CONFIG_BALLOON_COMPACTION
207
balloon_page_isolate(struct page * page,isolate_mode_t mode)208 static bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
209
210 {
211 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
212 unsigned long flags;
213
214 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
215 list_del(&page->lru);
216 b_dev_info->isolated_pages++;
217 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
218
219 return true;
220 }
221
balloon_page_putback(struct page * page)222 static void balloon_page_putback(struct page *page)
223 {
224 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
225 unsigned long flags;
226
227 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
228 list_add(&page->lru, &b_dev_info->pages);
229 b_dev_info->isolated_pages--;
230 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
231 }
232
233 /* move_to_new_page() counterpart for a ballooned page */
balloon_page_migrate(struct page * newpage,struct page * page,enum migrate_mode mode)234 static int balloon_page_migrate(struct page *newpage, struct page *page,
235 enum migrate_mode mode)
236 {
237 struct balloon_dev_info *balloon = balloon_page_device(page);
238
239 VM_BUG_ON_PAGE(!PageLocked(page), page);
240 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
241
242 return balloon->migratepage(balloon, newpage, page, mode);
243 }
244
245 const struct movable_operations balloon_mops = {
246 .migrate_page = balloon_page_migrate,
247 .isolate_page = balloon_page_isolate,
248 .putback_page = balloon_page_putback,
249 };
250 EXPORT_SYMBOL_GPL(balloon_mops);
251
252 #endif /* CONFIG_BALLOON_COMPACTION */
253