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 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 */ 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 __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 */ 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 */ 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 205 206 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 } 219 220 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 } 230 231 232 /* move_to_new_page() counterpart for a ballooned page */ 233 static 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 } 252 253 const struct address_space_operations balloon_aops = { 254 .migratepage = balloon_page_migrate, 255 .isolate_page = balloon_page_isolate, 256 .putback_page = balloon_page_putback, 257 }; 258 EXPORT_SYMBOL_GPL(balloon_aops); 259 260 #endif /* CONFIG_BALLOON_COMPACTION */ 261