1 /****************************************************************************** 2 * balloon.c 3 * 4 * Xen balloon driver - enables returning/claiming memory to/from Xen. 5 * 6 * Copyright (c) 2003, B Dragovic 7 * Copyright (c) 2003-2004, M Williamson, K Fraser 8 * Copyright (c) 2005 Dan M. Smith, IBM Corporation 9 * 10 * This program is free software; you can redistribute it and/or 11 * modify it under the terms of the GNU General Public License version 2 12 * as published by the Free Software Foundation; or, when distributed 13 * separately from the Linux kernel or incorporated into other 14 * software packages, subject to the following license: 15 * 16 * Permission is hereby granted, free of charge, to any person obtaining a copy 17 * of this source file (the "Software"), to deal in the Software without 18 * restriction, including without limitation the rights to use, copy, modify, 19 * merge, publish, distribute, sublicense, and/or sell copies of the Software, 20 * and to permit persons to whom the Software is furnished to do so, subject to 21 * the following conditions: 22 * 23 * The above copyright notice and this permission notice shall be included in 24 * all copies or substantial portions of the Software. 25 * 26 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 27 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 28 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 29 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 30 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 31 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS 32 * IN THE SOFTWARE. 33 */ 34 35 #include <linux/kernel.h> 36 #include <linux/module.h> 37 #include <linux/sched.h> 38 #include <linux/errno.h> 39 #include <linux/mm.h> 40 #include <linux/bootmem.h> 41 #include <linux/pagemap.h> 42 #include <linux/highmem.h> 43 #include <linux/mutex.h> 44 #include <linux/list.h> 45 #include <linux/sysdev.h> 46 47 #include <asm/page.h> 48 #include <asm/pgalloc.h> 49 #include <asm/pgtable.h> 50 #include <asm/uaccess.h> 51 #include <asm/tlb.h> 52 53 #include <asm/xen/hypervisor.h> 54 #include <asm/xen/hypercall.h> 55 56 #include <xen/xen.h> 57 #include <xen/interface/xen.h> 58 #include <xen/interface/memory.h> 59 #include <xen/xenbus.h> 60 #include <xen/features.h> 61 #include <xen/page.h> 62 63 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10)) 64 65 #define BALLOON_CLASS_NAME "xen_memory" 66 67 struct balloon_stats { 68 /* We aim for 'current allocation' == 'target allocation'. */ 69 unsigned long current_pages; 70 unsigned long target_pages; 71 /* 72 * Drivers may alter the memory reservation independently, but they 73 * must inform the balloon driver so we avoid hitting the hard limit. 74 */ 75 unsigned long driver_pages; 76 /* Number of pages in high- and low-memory balloons. */ 77 unsigned long balloon_low; 78 unsigned long balloon_high; 79 }; 80 81 static DEFINE_MUTEX(balloon_mutex); 82 83 static struct sys_device balloon_sysdev; 84 85 static int register_balloon(struct sys_device *sysdev); 86 87 /* 88 * Protects atomic reservation decrease/increase against concurrent increases. 89 * Also protects non-atomic updates of current_pages and driver_pages, and 90 * balloon lists. 91 */ 92 static DEFINE_SPINLOCK(balloon_lock); 93 94 static struct balloon_stats balloon_stats; 95 96 /* We increase/decrease in batches which fit in a page */ 97 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)]; 98 99 #ifdef CONFIG_HIGHMEM 100 #define inc_totalhigh_pages() (totalhigh_pages++) 101 #define dec_totalhigh_pages() (totalhigh_pages--) 102 #else 103 #define inc_totalhigh_pages() do {} while(0) 104 #define dec_totalhigh_pages() do {} while(0) 105 #endif 106 107 /* List of ballooned pages, threaded through the mem_map array. */ 108 static LIST_HEAD(ballooned_pages); 109 110 /* Main work function, always executed in process context. */ 111 static void balloon_process(struct work_struct *work); 112 static DECLARE_WORK(balloon_worker, balloon_process); 113 static struct timer_list balloon_timer; 114 115 /* When ballooning out (allocating memory to return to Xen) we don't really 116 want the kernel to try too hard since that can trigger the oom killer. */ 117 #define GFP_BALLOON \ 118 (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC) 119 120 static void scrub_page(struct page *page) 121 { 122 #ifdef CONFIG_XEN_SCRUB_PAGES 123 clear_highpage(page); 124 #endif 125 } 126 127 /* balloon_append: add the given page to the balloon. */ 128 static void balloon_append(struct page *page) 129 { 130 /* Lowmem is re-populated first, so highmem pages go at list tail. */ 131 if (PageHighMem(page)) { 132 list_add_tail(&page->lru, &ballooned_pages); 133 balloon_stats.balloon_high++; 134 dec_totalhigh_pages(); 135 } else { 136 list_add(&page->lru, &ballooned_pages); 137 balloon_stats.balloon_low++; 138 } 139 140 totalram_pages--; 141 } 142 143 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */ 144 static struct page *balloon_retrieve(void) 145 { 146 struct page *page; 147 148 if (list_empty(&ballooned_pages)) 149 return NULL; 150 151 page = list_entry(ballooned_pages.next, struct page, lru); 152 list_del(&page->lru); 153 154 if (PageHighMem(page)) { 155 balloon_stats.balloon_high--; 156 inc_totalhigh_pages(); 157 } 158 else 159 balloon_stats.balloon_low--; 160 161 totalram_pages++; 162 163 return page; 164 } 165 166 static struct page *balloon_first_page(void) 167 { 168 if (list_empty(&ballooned_pages)) 169 return NULL; 170 return list_entry(ballooned_pages.next, struct page, lru); 171 } 172 173 static struct page *balloon_next_page(struct page *page) 174 { 175 struct list_head *next = page->lru.next; 176 if (next == &ballooned_pages) 177 return NULL; 178 return list_entry(next, struct page, lru); 179 } 180 181 static void balloon_alarm(unsigned long unused) 182 { 183 schedule_work(&balloon_worker); 184 } 185 186 static unsigned long current_target(void) 187 { 188 unsigned long target = balloon_stats.target_pages; 189 190 target = min(target, 191 balloon_stats.current_pages + 192 balloon_stats.balloon_low + 193 balloon_stats.balloon_high); 194 195 return target; 196 } 197 198 static int increase_reservation(unsigned long nr_pages) 199 { 200 unsigned long pfn, i, flags; 201 struct page *page; 202 long rc; 203 struct xen_memory_reservation reservation = { 204 .address_bits = 0, 205 .extent_order = 0, 206 .domid = DOMID_SELF 207 }; 208 209 if (nr_pages > ARRAY_SIZE(frame_list)) 210 nr_pages = ARRAY_SIZE(frame_list); 211 212 spin_lock_irqsave(&balloon_lock, flags); 213 214 page = balloon_first_page(); 215 for (i = 0; i < nr_pages; i++) { 216 BUG_ON(page == NULL); 217 frame_list[i] = page_to_pfn(page); 218 page = balloon_next_page(page); 219 } 220 221 set_xen_guest_handle(reservation.extent_start, frame_list); 222 reservation.nr_extents = nr_pages; 223 rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation); 224 if (rc < 0) 225 goto out; 226 227 for (i = 0; i < rc; i++) { 228 page = balloon_retrieve(); 229 BUG_ON(page == NULL); 230 231 pfn = page_to_pfn(page); 232 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) && 233 phys_to_machine_mapping_valid(pfn)); 234 235 set_phys_to_machine(pfn, frame_list[i]); 236 237 /* Link back into the page tables if not highmem. */ 238 if (pfn < max_low_pfn) { 239 int ret; 240 ret = HYPERVISOR_update_va_mapping( 241 (unsigned long)__va(pfn << PAGE_SHIFT), 242 mfn_pte(frame_list[i], PAGE_KERNEL), 243 0); 244 BUG_ON(ret); 245 } 246 247 /* Relinquish the page back to the allocator. */ 248 ClearPageReserved(page); 249 init_page_count(page); 250 __free_page(page); 251 } 252 253 balloon_stats.current_pages += rc; 254 255 out: 256 spin_unlock_irqrestore(&balloon_lock, flags); 257 258 return rc < 0 ? rc : rc != nr_pages; 259 } 260 261 static int decrease_reservation(unsigned long nr_pages) 262 { 263 unsigned long pfn, i, flags; 264 struct page *page; 265 int need_sleep = 0; 266 int ret; 267 struct xen_memory_reservation reservation = { 268 .address_bits = 0, 269 .extent_order = 0, 270 .domid = DOMID_SELF 271 }; 272 273 if (nr_pages > ARRAY_SIZE(frame_list)) 274 nr_pages = ARRAY_SIZE(frame_list); 275 276 for (i = 0; i < nr_pages; i++) { 277 if ((page = alloc_page(GFP_BALLOON)) == NULL) { 278 nr_pages = i; 279 need_sleep = 1; 280 break; 281 } 282 283 pfn = page_to_pfn(page); 284 frame_list[i] = pfn_to_mfn(pfn); 285 286 scrub_page(page); 287 288 if (!PageHighMem(page)) { 289 ret = HYPERVISOR_update_va_mapping( 290 (unsigned long)__va(pfn << PAGE_SHIFT), 291 __pte_ma(0), 0); 292 BUG_ON(ret); 293 } 294 295 } 296 297 /* Ensure that ballooned highmem pages don't have kmaps. */ 298 kmap_flush_unused(); 299 flush_tlb_all(); 300 301 spin_lock_irqsave(&balloon_lock, flags); 302 303 /* No more mappings: invalidate P2M and add to balloon. */ 304 for (i = 0; i < nr_pages; i++) { 305 pfn = mfn_to_pfn(frame_list[i]); 306 set_phys_to_machine(pfn, INVALID_P2M_ENTRY); 307 balloon_append(pfn_to_page(pfn)); 308 } 309 310 set_xen_guest_handle(reservation.extent_start, frame_list); 311 reservation.nr_extents = nr_pages; 312 ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation); 313 BUG_ON(ret != nr_pages); 314 315 balloon_stats.current_pages -= nr_pages; 316 317 spin_unlock_irqrestore(&balloon_lock, flags); 318 319 return need_sleep; 320 } 321 322 /* 323 * We avoid multiple worker processes conflicting via the balloon mutex. 324 * We may of course race updates of the target counts (which are protected 325 * by the balloon lock), or with changes to the Xen hard limit, but we will 326 * recover from these in time. 327 */ 328 static void balloon_process(struct work_struct *work) 329 { 330 int need_sleep = 0; 331 long credit; 332 333 mutex_lock(&balloon_mutex); 334 335 do { 336 credit = current_target() - balloon_stats.current_pages; 337 if (credit > 0) 338 need_sleep = (increase_reservation(credit) != 0); 339 if (credit < 0) 340 need_sleep = (decrease_reservation(-credit) != 0); 341 342 #ifndef CONFIG_PREEMPT 343 if (need_resched()) 344 schedule(); 345 #endif 346 } while ((credit != 0) && !need_sleep); 347 348 /* Schedule more work if there is some still to be done. */ 349 if (current_target() != balloon_stats.current_pages) 350 mod_timer(&balloon_timer, jiffies + HZ); 351 352 mutex_unlock(&balloon_mutex); 353 } 354 355 /* Resets the Xen limit, sets new target, and kicks off processing. */ 356 static void balloon_set_new_target(unsigned long target) 357 { 358 /* No need for lock. Not read-modify-write updates. */ 359 balloon_stats.target_pages = target; 360 schedule_work(&balloon_worker); 361 } 362 363 static struct xenbus_watch target_watch = 364 { 365 .node = "memory/target" 366 }; 367 368 /* React to a change in the target key */ 369 static void watch_target(struct xenbus_watch *watch, 370 const char **vec, unsigned int len) 371 { 372 unsigned long long new_target; 373 int err; 374 375 err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target); 376 if (err != 1) { 377 /* This is ok (for domain0 at least) - so just return */ 378 return; 379 } 380 381 /* The given memory/target value is in KiB, so it needs converting to 382 * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10. 383 */ 384 balloon_set_new_target(new_target >> (PAGE_SHIFT - 10)); 385 } 386 387 static int balloon_init_watcher(struct notifier_block *notifier, 388 unsigned long event, 389 void *data) 390 { 391 int err; 392 393 err = register_xenbus_watch(&target_watch); 394 if (err) 395 printk(KERN_ERR "Failed to set balloon watcher\n"); 396 397 return NOTIFY_DONE; 398 } 399 400 static struct notifier_block xenstore_notifier; 401 402 static int __init balloon_init(void) 403 { 404 unsigned long pfn; 405 struct page *page; 406 407 if (!xen_pv_domain()) 408 return -ENODEV; 409 410 pr_info("xen_balloon: Initialising balloon driver.\n"); 411 412 balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn); 413 balloon_stats.target_pages = balloon_stats.current_pages; 414 balloon_stats.balloon_low = 0; 415 balloon_stats.balloon_high = 0; 416 balloon_stats.driver_pages = 0UL; 417 418 init_timer(&balloon_timer); 419 balloon_timer.data = 0; 420 balloon_timer.function = balloon_alarm; 421 422 register_balloon(&balloon_sysdev); 423 424 /* Initialise the balloon with excess memory space. */ 425 for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) { 426 page = pfn_to_page(pfn); 427 if (!PageReserved(page)) 428 balloon_append(page); 429 } 430 431 target_watch.callback = watch_target; 432 xenstore_notifier.notifier_call = balloon_init_watcher; 433 434 register_xenstore_notifier(&xenstore_notifier); 435 436 return 0; 437 } 438 439 subsys_initcall(balloon_init); 440 441 static void balloon_exit(void) 442 { 443 /* XXX - release balloon here */ 444 return; 445 } 446 447 module_exit(balloon_exit); 448 449 #define BALLOON_SHOW(name, format, args...) \ 450 static ssize_t show_##name(struct sys_device *dev, \ 451 struct sysdev_attribute *attr, \ 452 char *buf) \ 453 { \ 454 return sprintf(buf, format, ##args); \ 455 } \ 456 static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL) 457 458 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages)); 459 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low)); 460 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high)); 461 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages)); 462 463 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr, 464 char *buf) 465 { 466 return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages)); 467 } 468 469 static ssize_t store_target_kb(struct sys_device *dev, 470 struct sysdev_attribute *attr, 471 const char *buf, 472 size_t count) 473 { 474 char *endchar; 475 unsigned long long target_bytes; 476 477 if (!capable(CAP_SYS_ADMIN)) 478 return -EPERM; 479 480 target_bytes = simple_strtoull(buf, &endchar, 0) * 1024; 481 482 balloon_set_new_target(target_bytes >> PAGE_SHIFT); 483 484 return count; 485 } 486 487 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR, 488 show_target_kb, store_target_kb); 489 490 491 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr, 492 char *buf) 493 { 494 return sprintf(buf, "%llu\n", 495 (unsigned long long)balloon_stats.target_pages 496 << PAGE_SHIFT); 497 } 498 499 static ssize_t store_target(struct sys_device *dev, 500 struct sysdev_attribute *attr, 501 const char *buf, 502 size_t count) 503 { 504 char *endchar; 505 unsigned long long target_bytes; 506 507 if (!capable(CAP_SYS_ADMIN)) 508 return -EPERM; 509 510 target_bytes = memparse(buf, &endchar); 511 512 balloon_set_new_target(target_bytes >> PAGE_SHIFT); 513 514 return count; 515 } 516 517 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR, 518 show_target, store_target); 519 520 521 static struct sysdev_attribute *balloon_attrs[] = { 522 &attr_target_kb, 523 &attr_target, 524 }; 525 526 static struct attribute *balloon_info_attrs[] = { 527 &attr_current_kb.attr, 528 &attr_low_kb.attr, 529 &attr_high_kb.attr, 530 &attr_driver_kb.attr, 531 NULL 532 }; 533 534 static struct attribute_group balloon_info_group = { 535 .name = "info", 536 .attrs = balloon_info_attrs, 537 }; 538 539 static struct sysdev_class balloon_sysdev_class = { 540 .name = BALLOON_CLASS_NAME, 541 }; 542 543 static int register_balloon(struct sys_device *sysdev) 544 { 545 int i, error; 546 547 error = sysdev_class_register(&balloon_sysdev_class); 548 if (error) 549 return error; 550 551 sysdev->id = 0; 552 sysdev->cls = &balloon_sysdev_class; 553 554 error = sysdev_register(sysdev); 555 if (error) { 556 sysdev_class_unregister(&balloon_sysdev_class); 557 return error; 558 } 559 560 for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) { 561 error = sysdev_create_file(sysdev, balloon_attrs[i]); 562 if (error) 563 goto fail; 564 } 565 566 error = sysfs_create_group(&sysdev->kobj, &balloon_info_group); 567 if (error) 568 goto fail; 569 570 return 0; 571 572 fail: 573 while (--i >= 0) 574 sysdev_remove_file(sysdev, balloon_attrs[i]); 575 sysdev_unregister(sysdev); 576 sysdev_class_unregister(&balloon_sysdev_class); 577 return error; 578 } 579 580 MODULE_LICENSE("GPL"); 581