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 #include <linux/gfp.h> 47 48 #include <asm/page.h> 49 #include <asm/pgalloc.h> 50 #include <asm/pgtable.h> 51 #include <asm/uaccess.h> 52 #include <asm/tlb.h> 53 54 #include <asm/xen/hypervisor.h> 55 #include <asm/xen/hypercall.h> 56 57 #include <xen/xen.h> 58 #include <xen/interface/xen.h> 59 #include <xen/interface/memory.h> 60 #include <xen/xenbus.h> 61 #include <xen/features.h> 62 #include <xen/page.h> 63 64 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10)) 65 66 #define BALLOON_CLASS_NAME "xen_memory" 67 68 struct balloon_stats { 69 /* We aim for 'current allocation' == 'target allocation'. */ 70 unsigned long current_pages; 71 unsigned long target_pages; 72 /* 73 * Drivers may alter the memory reservation independently, but they 74 * must inform the balloon driver so we avoid hitting the hard limit. 75 */ 76 unsigned long driver_pages; 77 /* Number of pages in high- and low-memory balloons. */ 78 unsigned long balloon_low; 79 unsigned long balloon_high; 80 }; 81 82 static DEFINE_MUTEX(balloon_mutex); 83 84 static struct sys_device balloon_sysdev; 85 86 static int register_balloon(struct sys_device *sysdev); 87 88 /* 89 * Protects atomic reservation decrease/increase against concurrent increases. 90 * Also protects non-atomic updates of current_pages and driver_pages, and 91 * balloon lists. 92 */ 93 static DEFINE_SPINLOCK(balloon_lock); 94 95 static struct balloon_stats balloon_stats; 96 97 /* We increase/decrease in batches which fit in a page */ 98 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)]; 99 100 #ifdef CONFIG_HIGHMEM 101 #define inc_totalhigh_pages() (totalhigh_pages++) 102 #define dec_totalhigh_pages() (totalhigh_pages--) 103 #else 104 #define inc_totalhigh_pages() do {} while(0) 105 #define dec_totalhigh_pages() do {} while(0) 106 #endif 107 108 /* List of ballooned pages, threaded through the mem_map array. */ 109 static LIST_HEAD(ballooned_pages); 110 111 /* Main work function, always executed in process context. */ 112 static void balloon_process(struct work_struct *work); 113 static DECLARE_WORK(balloon_worker, balloon_process); 114 static struct timer_list balloon_timer; 115 116 /* When ballooning out (allocating memory to return to Xen) we don't really 117 want the kernel to try too hard since that can trigger the oom killer. */ 118 #define GFP_BALLOON \ 119 (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC) 120 121 static void scrub_page(struct page *page) 122 { 123 #ifdef CONFIG_XEN_SCRUB_PAGES 124 clear_highpage(page); 125 #endif 126 } 127 128 /* balloon_append: add the given page to the balloon. */ 129 static void balloon_append(struct page *page) 130 { 131 /* Lowmem is re-populated first, so highmem pages go at list tail. */ 132 if (PageHighMem(page)) { 133 list_add_tail(&page->lru, &ballooned_pages); 134 balloon_stats.balloon_high++; 135 dec_totalhigh_pages(); 136 } else { 137 list_add(&page->lru, &ballooned_pages); 138 balloon_stats.balloon_low++; 139 } 140 141 totalram_pages--; 142 } 143 144 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */ 145 static struct page *balloon_retrieve(void) 146 { 147 struct page *page; 148 149 if (list_empty(&ballooned_pages)) 150 return NULL; 151 152 page = list_entry(ballooned_pages.next, struct page, lru); 153 list_del(&page->lru); 154 155 if (PageHighMem(page)) { 156 balloon_stats.balloon_high--; 157 inc_totalhigh_pages(); 158 } 159 else 160 balloon_stats.balloon_low--; 161 162 totalram_pages++; 163 164 return page; 165 } 166 167 static struct page *balloon_first_page(void) 168 { 169 if (list_empty(&ballooned_pages)) 170 return NULL; 171 return list_entry(ballooned_pages.next, struct page, lru); 172 } 173 174 static struct page *balloon_next_page(struct page *page) 175 { 176 struct list_head *next = page->lru.next; 177 if (next == &ballooned_pages) 178 return NULL; 179 return list_entry(next, struct page, lru); 180 } 181 182 static void balloon_alarm(unsigned long unused) 183 { 184 schedule_work(&balloon_worker); 185 } 186 187 static unsigned long current_target(void) 188 { 189 unsigned long target = balloon_stats.target_pages; 190 191 target = min(target, 192 balloon_stats.current_pages + 193 balloon_stats.balloon_low + 194 balloon_stats.balloon_high); 195 196 return target; 197 } 198 199 static int increase_reservation(unsigned long nr_pages) 200 { 201 unsigned long pfn, i, flags; 202 struct page *page; 203 long rc; 204 struct xen_memory_reservation reservation = { 205 .address_bits = 0, 206 .extent_order = 0, 207 .domid = DOMID_SELF 208 }; 209 210 if (nr_pages > ARRAY_SIZE(frame_list)) 211 nr_pages = ARRAY_SIZE(frame_list); 212 213 spin_lock_irqsave(&balloon_lock, flags); 214 215 page = balloon_first_page(); 216 for (i = 0; i < nr_pages; i++) { 217 BUG_ON(page == NULL); 218 frame_list[i] = page_to_pfn(page); 219 page = balloon_next_page(page); 220 } 221 222 set_xen_guest_handle(reservation.extent_start, frame_list); 223 reservation.nr_extents = nr_pages; 224 rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation); 225 if (rc < 0) 226 goto out; 227 228 for (i = 0; i < rc; i++) { 229 page = balloon_retrieve(); 230 BUG_ON(page == NULL); 231 232 pfn = page_to_pfn(page); 233 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) && 234 phys_to_machine_mapping_valid(pfn)); 235 236 set_phys_to_machine(pfn, frame_list[i]); 237 238 /* Link back into the page tables if not highmem. */ 239 if (pfn < max_low_pfn) { 240 int ret; 241 ret = HYPERVISOR_update_va_mapping( 242 (unsigned long)__va(pfn << PAGE_SHIFT), 243 mfn_pte(frame_list[i], PAGE_KERNEL), 244 0); 245 BUG_ON(ret); 246 } 247 248 /* Relinquish the page back to the allocator. */ 249 ClearPageReserved(page); 250 init_page_count(page); 251 __free_page(page); 252 } 253 254 balloon_stats.current_pages += rc; 255 256 out: 257 spin_unlock_irqrestore(&balloon_lock, flags); 258 259 return rc < 0 ? rc : rc != nr_pages; 260 } 261 262 static int decrease_reservation(unsigned long nr_pages) 263 { 264 unsigned long pfn, i, flags; 265 struct page *page; 266 int need_sleep = 0; 267 int ret; 268 struct xen_memory_reservation reservation = { 269 .address_bits = 0, 270 .extent_order = 0, 271 .domid = DOMID_SELF 272 }; 273 274 if (nr_pages > ARRAY_SIZE(frame_list)) 275 nr_pages = ARRAY_SIZE(frame_list); 276 277 for (i = 0; i < nr_pages; i++) { 278 if ((page = alloc_page(GFP_BALLOON)) == NULL) { 279 nr_pages = i; 280 need_sleep = 1; 281 break; 282 } 283 284 pfn = page_to_pfn(page); 285 frame_list[i] = pfn_to_mfn(pfn); 286 287 scrub_page(page); 288 289 if (!PageHighMem(page)) { 290 ret = HYPERVISOR_update_va_mapping( 291 (unsigned long)__va(pfn << PAGE_SHIFT), 292 __pte_ma(0), 0); 293 BUG_ON(ret); 294 } 295 296 } 297 298 /* Ensure that ballooned highmem pages don't have kmaps. */ 299 kmap_flush_unused(); 300 flush_tlb_all(); 301 302 spin_lock_irqsave(&balloon_lock, flags); 303 304 /* No more mappings: invalidate P2M and add to balloon. */ 305 for (i = 0; i < nr_pages; i++) { 306 pfn = mfn_to_pfn(frame_list[i]); 307 set_phys_to_machine(pfn, INVALID_P2M_ENTRY); 308 balloon_append(pfn_to_page(pfn)); 309 } 310 311 set_xen_guest_handle(reservation.extent_start, frame_list); 312 reservation.nr_extents = nr_pages; 313 ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation); 314 BUG_ON(ret != nr_pages); 315 316 balloon_stats.current_pages -= nr_pages; 317 318 spin_unlock_irqrestore(&balloon_lock, flags); 319 320 return need_sleep; 321 } 322 323 /* 324 * We avoid multiple worker processes conflicting via the balloon mutex. 325 * We may of course race updates of the target counts (which are protected 326 * by the balloon lock), or with changes to the Xen hard limit, but we will 327 * recover from these in time. 328 */ 329 static void balloon_process(struct work_struct *work) 330 { 331 int need_sleep = 0; 332 long credit; 333 334 mutex_lock(&balloon_mutex); 335 336 do { 337 credit = current_target() - balloon_stats.current_pages; 338 if (credit > 0) 339 need_sleep = (increase_reservation(credit) != 0); 340 if (credit < 0) 341 need_sleep = (decrease_reservation(-credit) != 0); 342 343 #ifndef CONFIG_PREEMPT 344 if (need_resched()) 345 schedule(); 346 #endif 347 } while ((credit != 0) && !need_sleep); 348 349 /* Schedule more work if there is some still to be done. */ 350 if (current_target() != balloon_stats.current_pages) 351 mod_timer(&balloon_timer, jiffies + HZ); 352 353 mutex_unlock(&balloon_mutex); 354 } 355 356 /* Resets the Xen limit, sets new target, and kicks off processing. */ 357 static void balloon_set_new_target(unsigned long target) 358 { 359 /* No need for lock. Not read-modify-write updates. */ 360 balloon_stats.target_pages = target; 361 schedule_work(&balloon_worker); 362 } 363 364 static struct xenbus_watch target_watch = 365 { 366 .node = "memory/target" 367 }; 368 369 /* React to a change in the target key */ 370 static void watch_target(struct xenbus_watch *watch, 371 const char **vec, unsigned int len) 372 { 373 unsigned long long new_target; 374 int err; 375 376 err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target); 377 if (err != 1) { 378 /* This is ok (for domain0 at least) - so just return */ 379 return; 380 } 381 382 /* The given memory/target value is in KiB, so it needs converting to 383 * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10. 384 */ 385 balloon_set_new_target(new_target >> (PAGE_SHIFT - 10)); 386 } 387 388 static int balloon_init_watcher(struct notifier_block *notifier, 389 unsigned long event, 390 void *data) 391 { 392 int err; 393 394 err = register_xenbus_watch(&target_watch); 395 if (err) 396 printk(KERN_ERR "Failed to set balloon watcher\n"); 397 398 return NOTIFY_DONE; 399 } 400 401 static struct notifier_block xenstore_notifier; 402 403 static int __init balloon_init(void) 404 { 405 unsigned long pfn; 406 struct page *page; 407 408 if (!xen_pv_domain()) 409 return -ENODEV; 410 411 pr_info("xen_balloon: Initialising balloon driver.\n"); 412 413 balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn); 414 balloon_stats.target_pages = balloon_stats.current_pages; 415 balloon_stats.balloon_low = 0; 416 balloon_stats.balloon_high = 0; 417 balloon_stats.driver_pages = 0UL; 418 419 init_timer(&balloon_timer); 420 balloon_timer.data = 0; 421 balloon_timer.function = balloon_alarm; 422 423 register_balloon(&balloon_sysdev); 424 425 /* Initialise the balloon with excess memory space. */ 426 for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) { 427 page = pfn_to_page(pfn); 428 if (!PageReserved(page)) 429 balloon_append(page); 430 } 431 432 target_watch.callback = watch_target; 433 xenstore_notifier.notifier_call = balloon_init_watcher; 434 435 register_xenstore_notifier(&xenstore_notifier); 436 437 return 0; 438 } 439 440 subsys_initcall(balloon_init); 441 442 static void balloon_exit(void) 443 { 444 /* XXX - release balloon here */ 445 return; 446 } 447 448 module_exit(balloon_exit); 449 450 #define BALLOON_SHOW(name, format, args...) \ 451 static ssize_t show_##name(struct sys_device *dev, \ 452 struct sysdev_attribute *attr, \ 453 char *buf) \ 454 { \ 455 return sprintf(buf, format, ##args); \ 456 } \ 457 static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL) 458 459 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages)); 460 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low)); 461 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high)); 462 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages)); 463 464 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr, 465 char *buf) 466 { 467 return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages)); 468 } 469 470 static ssize_t store_target_kb(struct sys_device *dev, 471 struct sysdev_attribute *attr, 472 const char *buf, 473 size_t count) 474 { 475 char *endchar; 476 unsigned long long target_bytes; 477 478 if (!capable(CAP_SYS_ADMIN)) 479 return -EPERM; 480 481 target_bytes = simple_strtoull(buf, &endchar, 0) * 1024; 482 483 balloon_set_new_target(target_bytes >> PAGE_SHIFT); 484 485 return count; 486 } 487 488 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR, 489 show_target_kb, store_target_kb); 490 491 492 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr, 493 char *buf) 494 { 495 return sprintf(buf, "%llu\n", 496 (unsigned long long)balloon_stats.target_pages 497 << PAGE_SHIFT); 498 } 499 500 static ssize_t store_target(struct sys_device *dev, 501 struct sysdev_attribute *attr, 502 const char *buf, 503 size_t count) 504 { 505 char *endchar; 506 unsigned long long target_bytes; 507 508 if (!capable(CAP_SYS_ADMIN)) 509 return -EPERM; 510 511 target_bytes = memparse(buf, &endchar); 512 513 balloon_set_new_target(target_bytes >> PAGE_SHIFT); 514 515 return count; 516 } 517 518 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR, 519 show_target, store_target); 520 521 522 static struct sysdev_attribute *balloon_attrs[] = { 523 &attr_target_kb, 524 &attr_target, 525 }; 526 527 static struct attribute *balloon_info_attrs[] = { 528 &attr_current_kb.attr, 529 &attr_low_kb.attr, 530 &attr_high_kb.attr, 531 &attr_driver_kb.attr, 532 NULL 533 }; 534 535 static struct attribute_group balloon_info_group = { 536 .name = "info", 537 .attrs = balloon_info_attrs, 538 }; 539 540 static struct sysdev_class balloon_sysdev_class = { 541 .name = BALLOON_CLASS_NAME, 542 }; 543 544 static int register_balloon(struct sys_device *sysdev) 545 { 546 int i, error; 547 548 error = sysdev_class_register(&balloon_sysdev_class); 549 if (error) 550 return error; 551 552 sysdev->id = 0; 553 sysdev->cls = &balloon_sysdev_class; 554 555 error = sysdev_register(sysdev); 556 if (error) { 557 sysdev_class_unregister(&balloon_sysdev_class); 558 return error; 559 } 560 561 for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) { 562 error = sysdev_create_file(sysdev, balloon_attrs[i]); 563 if (error) 564 goto fail; 565 } 566 567 error = sysfs_create_group(&sysdev->kobj, &balloon_info_group); 568 if (error) 569 goto fail; 570 571 return 0; 572 573 fail: 574 while (--i >= 0) 575 sysdev_remove_file(sysdev, balloon_attrs[i]); 576 sysdev_unregister(sysdev); 577 sysdev_class_unregister(&balloon_sysdev_class); 578 return error; 579 } 580 581 MODULE_LICENSE("GPL"); 582