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 list_del(&page->lru);
98 balloon_page_finalize(page);
99 __count_vm_event(BALLOON_DEFLATE);
100 list_add(&page->lru, pages);
101 unlock_page(page);
102 dec_node_page_state(page, NR_BALLOON_PAGES);
103 n_pages++;
104 }
105 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
106
107 return n_pages;
108 }
109 EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
110
111 /*
112 * balloon_page_alloc - allocates a new page for insertion into the balloon
113 * page list.
114 *
115 * Driver must call this function to properly allocate a new balloon page.
116 * Driver must call balloon_page_enqueue before definitively removing the page
117 * from the guest system.
118 *
119 * Return: struct page for the allocated page or NULL on allocation failure.
120 */
balloon_page_alloc(void)121 struct page *balloon_page_alloc(void)
122 {
123 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
124 __GFP_NOMEMALLOC | __GFP_NORETRY |
125 __GFP_NOWARN);
126 return page;
127 }
128 EXPORT_SYMBOL_GPL(balloon_page_alloc);
129
130 /*
131 * balloon_page_enqueue - inserts a new page into the balloon page list.
132 *
133 * @b_dev_info: balloon device descriptor where we will insert a new page
134 * @page: new page to enqueue - allocated using balloon_page_alloc.
135 *
136 * Drivers must call this function to properly enqueue a new allocated balloon
137 * page before definitively removing the page from the guest system.
138 *
139 * Drivers must not call balloon_page_enqueue on pages that have been pushed to
140 * a list with balloon_page_push before removing them with balloon_page_pop. To
141 * enqueue a list of pages, use balloon_page_list_enqueue instead.
142 */
balloon_page_enqueue(struct balloon_dev_info * b_dev_info,struct page * page)143 void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
144 struct page *page)
145 {
146 unsigned long flags;
147
148 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
149 balloon_page_enqueue_one(b_dev_info, page);
150 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
151 }
152 EXPORT_SYMBOL_GPL(balloon_page_enqueue);
153
154 /*
155 * balloon_page_dequeue - removes a page from balloon's page list and returns
156 * its address to allow the driver to release the page.
157 * @b_dev_info: balloon device descriptor where we will grab a page from.
158 *
159 * Driver must call this function to properly dequeue a previously enqueued page
160 * before definitively releasing it back to the guest system.
161 *
162 * Caller must perform its own accounting to ensure that this
163 * function is called only if some pages are actually enqueued.
164 *
165 * Note that this function may fail to dequeue some pages even if there are
166 * some enqueued pages - since the page list can be temporarily empty due to
167 * the compaction of isolated pages.
168 *
169 * TODO: remove the caller accounting requirements, and allow caller to wait
170 * until all pages can be dequeued.
171 *
172 * Return: struct page for the dequeued page, or NULL if no page was dequeued.
173 */
balloon_page_dequeue(struct balloon_dev_info * b_dev_info)174 struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
175 {
176 unsigned long flags;
177 LIST_HEAD(pages);
178 int n_pages;
179
180 n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);
181
182 if (n_pages != 1) {
183 /*
184 * If we are unable to dequeue a balloon page because the page
185 * list is empty and there are no isolated pages, then something
186 * went out of track and some balloon pages are lost.
187 * BUG() here, otherwise the balloon driver may get stuck in
188 * an infinite loop while attempting to release all its pages.
189 */
190 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
191 if (unlikely(list_empty(&b_dev_info->pages) &&
192 !b_dev_info->isolated_pages))
193 BUG();
194 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
195 return NULL;
196 }
197 return list_first_entry(&pages, struct page, lru);
198 }
199 EXPORT_SYMBOL_GPL(balloon_page_dequeue);
200
201 #ifdef CONFIG_BALLOON_COMPACTION
202
balloon_page_isolate(struct page * page,isolate_mode_t mode)203 static bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
204
205 {
206 struct balloon_dev_info *b_dev_info = balloon_page_device(page);
207 unsigned long flags;
208
209 if (!b_dev_info)
210 return false;
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
balloon_page_putback(struct page * page)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 /* Isolated balloon pages cannot get deflated. */
226 if (WARN_ON_ONCE(!b_dev_info))
227 return;
228
229 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
230 list_add(&page->lru, &b_dev_info->pages);
231 b_dev_info->isolated_pages--;
232 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
233 }
234
235 /* move_to_new_page() counterpart for a ballooned page */
balloon_page_migrate(struct page * newpage,struct page * page,enum migrate_mode mode)236 static int balloon_page_migrate(struct page *newpage, struct page *page,
237 enum migrate_mode mode)
238 {
239 struct balloon_dev_info *balloon = balloon_page_device(page);
240
241 VM_BUG_ON_PAGE(!PageLocked(page), page);
242 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
243
244 /* Isolated balloon pages cannot get deflated. */
245 if (WARN_ON_ONCE(!balloon))
246 return -EAGAIN;
247
248 return balloon->migratepage(balloon, newpage, page, mode);
249 }
250
251 const struct movable_operations balloon_mops = {
252 .migrate_page = balloon_page_migrate,
253 .isolate_page = balloon_page_isolate,
254 .putback_page = balloon_page_putback,
255 };
256
balloon_init(void)257 static int __init balloon_init(void)
258 {
259 return set_movable_ops(&balloon_mops, PGTY_offline);
260 }
261 core_initcall(balloon_init);
262
263 #endif /* CONFIG_BALLOON_COMPACTION */
264