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 decriptor 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 return page; 129 } 130 EXPORT_SYMBOL_GPL(balloon_page_alloc); 131 132 /* 133 * balloon_page_enqueue - inserts a new page into the balloon page list. 134 * 135 * @b_dev_info: balloon device descriptor where we will insert a new page 136 * @page: new page to enqueue - allocated using balloon_page_alloc. 137 * 138 * Drivers must call this function to properly enqueue a new allocated balloon 139 * page before definitively removing the page from the guest system. 140 * 141 * Drivers must not call balloon_page_enqueue on pages that have been pushed to 142 * a list with balloon_page_push before removing them with balloon_page_pop. To 143 * enqueue a list of pages, use balloon_page_list_enqueue instead. 144 */ 145 void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, 146 struct page *page) 147 { 148 unsigned long flags; 149 150 spin_lock_irqsave(&b_dev_info->pages_lock, flags); 151 balloon_page_enqueue_one(b_dev_info, page); 152 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); 153 } 154 EXPORT_SYMBOL_GPL(balloon_page_enqueue); 155 156 /* 157 * balloon_page_dequeue - removes a page from balloon's page list and returns 158 * its address to allow the driver to release the page. 159 * @b_dev_info: balloon device decriptor where we will grab a page from. 160 * 161 * Driver must call this function to properly dequeue a previously enqueued page 162 * before definitively releasing it back to the guest system. 163 * 164 * Caller must perform its own accounting to ensure that this 165 * function is called only if some pages are actually enqueued. 166 * 167 * Note that this function may fail to dequeue some pages even if there are 168 * some enqueued pages - since the page list can be temporarily empty due to 169 * the compaction of isolated pages. 170 * 171 * TODO: remove the caller accounting requirements, and allow caller to wait 172 * until all pages can be dequeued. 173 * 174 * Return: struct page for the dequeued page, or NULL if no page was dequeued. 175 */ 176 struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) 177 { 178 unsigned long flags; 179 LIST_HEAD(pages); 180 int n_pages; 181 182 n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1); 183 184 if (n_pages != 1) { 185 /* 186 * If we are unable to dequeue a balloon page because the page 187 * list is empty and there are no isolated pages, then something 188 * went out of track and some balloon pages are lost. 189 * BUG() here, otherwise the balloon driver may get stuck in 190 * an infinite loop while attempting to release all its pages. 191 */ 192 spin_lock_irqsave(&b_dev_info->pages_lock, flags); 193 if (unlikely(list_empty(&b_dev_info->pages) && 194 !b_dev_info->isolated_pages)) 195 BUG(); 196 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); 197 return NULL; 198 } 199 return list_first_entry(&pages, struct page, lru); 200 } 201 EXPORT_SYMBOL_GPL(balloon_page_dequeue); 202 203 #ifdef CONFIG_BALLOON_COMPACTION 204 205 bool balloon_page_isolate(struct page *page, isolate_mode_t mode) 206 207 { 208 struct balloon_dev_info *b_dev_info = balloon_page_device(page); 209 unsigned long flags; 210 211 spin_lock_irqsave(&b_dev_info->pages_lock, flags); 212 list_del(&page->lru); 213 b_dev_info->isolated_pages++; 214 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); 215 216 return true; 217 } 218 219 void balloon_page_putback(struct page *page) 220 { 221 struct balloon_dev_info *b_dev_info = balloon_page_device(page); 222 unsigned long flags; 223 224 spin_lock_irqsave(&b_dev_info->pages_lock, flags); 225 list_add(&page->lru, &b_dev_info->pages); 226 b_dev_info->isolated_pages--; 227 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); 228 } 229 230 231 /* move_to_new_page() counterpart for a ballooned page */ 232 int balloon_page_migrate(struct address_space *mapping, 233 struct page *newpage, struct page *page, 234 enum migrate_mode mode) 235 { 236 struct balloon_dev_info *balloon = balloon_page_device(page); 237 238 /* 239 * We can not easily support the no copy case here so ignore it as it 240 * is unlikely to be used with balloon pages. See include/linux/hmm.h 241 * for a user of the MIGRATE_SYNC_NO_COPY mode. 242 */ 243 if (mode == MIGRATE_SYNC_NO_COPY) 244 return -EINVAL; 245 246 VM_BUG_ON_PAGE(!PageLocked(page), page); 247 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); 248 249 return balloon->migratepage(balloon, newpage, page, mode); 250 } 251 252 const struct address_space_operations balloon_aops = { 253 .migratepage = balloon_page_migrate, 254 .isolate_page = balloon_page_isolate, 255 .putback_page = balloon_page_putback, 256 }; 257 EXPORT_SYMBOL_GPL(balloon_aops); 258 259 #endif /* CONFIG_BALLOON_COMPACTION */ 260