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 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 */
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 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 */
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
206static 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
220static 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
232/* move_to_new_page() counterpart for a ballooned page */
233static int 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 */
261