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 }
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  */
balloon_page_list_enqueue(struct balloon_dev_info * b_dev_info,struct list_head * pages)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  */
balloon_page_list_dequeue(struct balloon_dev_info * b_dev_info,struct list_head * pages,size_t n_req_pages)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  */
balloon_page_alloc(void)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  */
balloon_page_enqueue(struct balloon_dev_info * b_dev_info,struct page * page)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  */
balloon_page_dequeue(struct balloon_dev_info * b_dev_info)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 
balloon_page_isolate(struct page * page,isolate_mode_t mode)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 
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 	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 */
balloon_page_migrate(struct page * newpage,struct page * page,enum migrate_mode mode)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 	/*
238 	 * We can not easily support the no copy case here so ignore it as it
239 	 * is unlikely to be used with balloon pages. See include/linux/hmm.h
240 	 * for a user of the MIGRATE_SYNC_NO_COPY mode.
241 	 */
242 	if (mode == MIGRATE_SYNC_NO_COPY)
243 		return -EINVAL;
244 
245 	VM_BUG_ON_PAGE(!PageLocked(page), page);
246 	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
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 EXPORT_SYMBOL_GPL(balloon_mops);
257 
258 #endif /* CONFIG_BALLOON_COMPACTION */
259