balloon.c revision 95170b2e23d4e98843b4833d27fae7bf0910e19c
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#include <asm/e820.h> 54 55#include <asm/xen/hypervisor.h> 56#include <asm/xen/hypercall.h> 57 58#include <xen/xen.h> 59#include <xen/interface/xen.h> 60#include <xen/interface/memory.h> 61#include <xen/xenbus.h> 62#include <xen/features.h> 63#include <xen/page.h> 64 65#define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10)) 66 67#define BALLOON_CLASS_NAME "xen_memory" 68 69struct balloon_stats { 70 /* We aim for 'current allocation' == 'target allocation'. */ 71 unsigned long current_pages; 72 unsigned long target_pages; 73 /* Number of pages in high- and low-memory balloons. */ 74 unsigned long balloon_low; 75 unsigned long balloon_high; 76}; 77 78static DEFINE_MUTEX(balloon_mutex); 79 80static struct sys_device balloon_sysdev; 81 82static int register_balloon(struct sys_device *sysdev); 83 84static struct balloon_stats balloon_stats; 85 86/* We increase/decrease in batches which fit in a page */ 87static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)]; 88 89#ifdef CONFIG_HIGHMEM 90#define inc_totalhigh_pages() (totalhigh_pages++) 91#define dec_totalhigh_pages() (totalhigh_pages--) 92#else 93#define inc_totalhigh_pages() do {} while(0) 94#define dec_totalhigh_pages() do {} while(0) 95#endif 96 97/* List of ballooned pages, threaded through the mem_map array. */ 98static LIST_HEAD(ballooned_pages); 99 100/* Main work function, always executed in process context. */ 101static void balloon_process(struct work_struct *work); 102static DECLARE_DELAYED_WORK(balloon_worker, balloon_process); 103 104/* When ballooning out (allocating memory to return to Xen) we don't really 105 want the kernel to try too hard since that can trigger the oom killer. */ 106#define GFP_BALLOON \ 107 (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC) 108 109static void scrub_page(struct page *page) 110{ 111#ifdef CONFIG_XEN_SCRUB_PAGES 112 clear_highpage(page); 113#endif 114} 115 116/* balloon_append: add the given page to the balloon. */ 117static void __balloon_append(struct page *page) 118{ 119 /* Lowmem is re-populated first, so highmem pages go at list tail. */ 120 if (PageHighMem(page)) { 121 list_add_tail(&page->lru, &ballooned_pages); 122 balloon_stats.balloon_high++; 123 dec_totalhigh_pages(); 124 } else { 125 list_add(&page->lru, &ballooned_pages); 126 balloon_stats.balloon_low++; 127 } 128} 129 130static void balloon_append(struct page *page) 131{ 132 __balloon_append(page); 133 totalram_pages--; 134} 135 136/* balloon_retrieve: rescue a page from the balloon, if it is not empty. */ 137static struct page *balloon_retrieve(void) 138{ 139 struct page *page; 140 141 if (list_empty(&ballooned_pages)) 142 return NULL; 143 144 page = list_entry(ballooned_pages.next, struct page, lru); 145 list_del(&page->lru); 146 147 if (PageHighMem(page)) { 148 balloon_stats.balloon_high--; 149 inc_totalhigh_pages(); 150 } 151 else 152 balloon_stats.balloon_low--; 153 154 totalram_pages++; 155 156 return page; 157} 158 159static struct page *balloon_first_page(void) 160{ 161 if (list_empty(&ballooned_pages)) 162 return NULL; 163 return list_entry(ballooned_pages.next, struct page, lru); 164} 165 166static struct page *balloon_next_page(struct page *page) 167{ 168 struct list_head *next = page->lru.next; 169 if (next == &ballooned_pages) 170 return NULL; 171 return list_entry(next, struct page, lru); 172} 173 174static unsigned long current_target(void) 175{ 176 unsigned long target = balloon_stats.target_pages; 177 178 target = min(target, 179 balloon_stats.current_pages + 180 balloon_stats.balloon_low + 181 balloon_stats.balloon_high); 182 183 return target; 184} 185 186static int increase_reservation(unsigned long nr_pages) 187{ 188 unsigned long pfn, i; 189 struct page *page; 190 long rc; 191 struct xen_memory_reservation reservation = { 192 .address_bits = 0, 193 .extent_order = 0, 194 .domid = DOMID_SELF 195 }; 196 197 if (nr_pages > ARRAY_SIZE(frame_list)) 198 nr_pages = ARRAY_SIZE(frame_list); 199 200 page = balloon_first_page(); 201 for (i = 0; i < nr_pages; i++) { 202 BUG_ON(page == NULL); 203 frame_list[i] = page_to_pfn(page); 204 page = balloon_next_page(page); 205 } 206 207 set_xen_guest_handle(reservation.extent_start, frame_list); 208 reservation.nr_extents = nr_pages; 209 rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation); 210 if (rc < 0) 211 goto out; 212 213 for (i = 0; i < rc; i++) { 214 page = balloon_retrieve(); 215 BUG_ON(page == NULL); 216 217 pfn = page_to_pfn(page); 218 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) && 219 phys_to_machine_mapping_valid(pfn)); 220 221 set_phys_to_machine(pfn, frame_list[i]); 222 223 /* Link back into the page tables if not highmem. */ 224 if (pfn < max_low_pfn) { 225 int ret; 226 ret = HYPERVISOR_update_va_mapping( 227 (unsigned long)__va(pfn << PAGE_SHIFT), 228 mfn_pte(frame_list[i], PAGE_KERNEL), 229 0); 230 BUG_ON(ret); 231 } 232 233 /* Relinquish the page back to the allocator. */ 234 ClearPageReserved(page); 235 init_page_count(page); 236 __free_page(page); 237 } 238 239 balloon_stats.current_pages += rc; 240 241 out: 242 return rc < 0 ? rc : rc != nr_pages; 243} 244 245static int decrease_reservation(unsigned long nr_pages) 246{ 247 unsigned long pfn, i; 248 struct page *page; 249 int need_sleep = 0; 250 int ret; 251 struct xen_memory_reservation reservation = { 252 .address_bits = 0, 253 .extent_order = 0, 254 .domid = DOMID_SELF 255 }; 256 257 if (nr_pages > ARRAY_SIZE(frame_list)) 258 nr_pages = ARRAY_SIZE(frame_list); 259 260 for (i = 0; i < nr_pages; i++) { 261 if ((page = alloc_page(GFP_BALLOON)) == NULL) { 262 nr_pages = i; 263 need_sleep = 1; 264 break; 265 } 266 267 pfn = page_to_pfn(page); 268 frame_list[i] = pfn_to_mfn(pfn); 269 270 scrub_page(page); 271 272 if (!PageHighMem(page)) { 273 ret = HYPERVISOR_update_va_mapping( 274 (unsigned long)__va(pfn << PAGE_SHIFT), 275 __pte_ma(0), 0); 276 BUG_ON(ret); 277 } 278 279 } 280 281 /* Ensure that ballooned highmem pages don't have kmaps. */ 282 kmap_flush_unused(); 283 flush_tlb_all(); 284 285 /* No more mappings: invalidate P2M and add to balloon. */ 286 for (i = 0; i < nr_pages; i++) { 287 pfn = mfn_to_pfn(frame_list[i]); 288 set_phys_to_machine(pfn, INVALID_P2M_ENTRY); 289 balloon_append(pfn_to_page(pfn)); 290 } 291 292 set_xen_guest_handle(reservation.extent_start, frame_list); 293 reservation.nr_extents = nr_pages; 294 ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation); 295 BUG_ON(ret != nr_pages); 296 297 balloon_stats.current_pages -= nr_pages; 298 299 return need_sleep; 300} 301 302/* 303 * We avoid multiple worker processes conflicting via the balloon mutex. 304 * We may of course race updates of the target counts (which are protected 305 * by the balloon lock), or with changes to the Xen hard limit, but we will 306 * recover from these in time. 307 */ 308static void balloon_process(struct work_struct *work) 309{ 310 int need_sleep = 0; 311 long credit; 312 313 mutex_lock(&balloon_mutex); 314 315 do { 316 credit = current_target() - balloon_stats.current_pages; 317 if (credit > 0) 318 need_sleep = (increase_reservation(credit) != 0); 319 if (credit < 0) 320 need_sleep = (decrease_reservation(-credit) != 0); 321 322#ifndef CONFIG_PREEMPT 323 if (need_resched()) 324 schedule(); 325#endif 326 } while ((credit != 0) && !need_sleep); 327 328 /* Schedule more work if there is some still to be done. */ 329 if (current_target() != balloon_stats.current_pages) 330 schedule_delayed_work(&balloon_worker, HZ); 331 332 mutex_unlock(&balloon_mutex); 333} 334 335/* Resets the Xen limit, sets new target, and kicks off processing. */ 336static void balloon_set_new_target(unsigned long target) 337{ 338 /* No need for lock. Not read-modify-write updates. */ 339 balloon_stats.target_pages = target; 340 schedule_delayed_work(&balloon_worker, 0); 341} 342 343static struct xenbus_watch target_watch = 344{ 345 .node = "memory/target" 346}; 347 348/* React to a change in the target key */ 349static void watch_target(struct xenbus_watch *watch, 350 const char **vec, unsigned int len) 351{ 352 unsigned long long new_target; 353 int err; 354 355 err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target); 356 if (err != 1) { 357 /* This is ok (for domain0 at least) - so just return */ 358 return; 359 } 360 361 /* The given memory/target value is in KiB, so it needs converting to 362 * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10. 363 */ 364 balloon_set_new_target(new_target >> (PAGE_SHIFT - 10)); 365} 366 367static int balloon_init_watcher(struct notifier_block *notifier, 368 unsigned long event, 369 void *data) 370{ 371 int err; 372 373 err = register_xenbus_watch(&target_watch); 374 if (err) 375 printk(KERN_ERR "Failed to set balloon watcher\n"); 376 377 return NOTIFY_DONE; 378} 379 380static struct notifier_block xenstore_notifier; 381 382static int __init balloon_init(void) 383{ 384 unsigned long pfn, extra_pfn_end; 385 struct page *page; 386 387 if (!xen_pv_domain()) 388 return -ENODEV; 389 390 pr_info("xen_balloon: Initialising balloon driver.\n"); 391 392 balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn); 393 balloon_stats.target_pages = balloon_stats.current_pages; 394 balloon_stats.balloon_low = 0; 395 balloon_stats.balloon_high = 0; 396 397 register_balloon(&balloon_sysdev); 398 399 /* 400 * Initialise the balloon with excess memory space. We need 401 * to make sure we don't add memory which doesn't exist or 402 * logically exist. The E820 map can be trimmed to be smaller 403 * than the amount of physical memory due to the mem= command 404 * line parameter. And if this is a 32-bit non-HIGHMEM kernel 405 * on a system with memory which requires highmem to access, 406 * don't try to use it. 407 */ 408 extra_pfn_end = min(min(max_pfn, e820_end_of_ram_pfn()), 409 (unsigned long)PFN_DOWN(xen_extra_mem_start + xen_extra_mem_size)); 410 for (pfn = PFN_UP(xen_extra_mem_start); 411 pfn < extra_pfn_end; 412 pfn++) { 413 page = pfn_to_page(pfn); 414 /* totalram_pages doesn't include the boot-time 415 balloon extension, so don't subtract from it. */ 416 __balloon_append(page); 417 } 418 419 target_watch.callback = watch_target; 420 xenstore_notifier.notifier_call = balloon_init_watcher; 421 422 register_xenstore_notifier(&xenstore_notifier); 423 424 return 0; 425} 426 427subsys_initcall(balloon_init); 428 429static void balloon_exit(void) 430{ 431 /* XXX - release balloon here */ 432 return; 433} 434 435module_exit(balloon_exit); 436 437#define BALLOON_SHOW(name, format, args...) \ 438 static ssize_t show_##name(struct sys_device *dev, \ 439 struct sysdev_attribute *attr, \ 440 char *buf) \ 441 { \ 442 return sprintf(buf, format, ##args); \ 443 } \ 444 static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL) 445 446BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages)); 447BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low)); 448BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high)); 449 450static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr, 451 char *buf) 452{ 453 return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages)); 454} 455 456static ssize_t store_target_kb(struct sys_device *dev, 457 struct sysdev_attribute *attr, 458 const char *buf, 459 size_t count) 460{ 461 char *endchar; 462 unsigned long long target_bytes; 463 464 if (!capable(CAP_SYS_ADMIN)) 465 return -EPERM; 466 467 target_bytes = simple_strtoull(buf, &endchar, 0) * 1024; 468 469 balloon_set_new_target(target_bytes >> PAGE_SHIFT); 470 471 return count; 472} 473 474static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR, 475 show_target_kb, store_target_kb); 476 477 478static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr, 479 char *buf) 480{ 481 return sprintf(buf, "%llu\n", 482 (unsigned long long)balloon_stats.target_pages 483 << PAGE_SHIFT); 484} 485 486static ssize_t store_target(struct sys_device *dev, 487 struct sysdev_attribute *attr, 488 const char *buf, 489 size_t count) 490{ 491 char *endchar; 492 unsigned long long target_bytes; 493 494 if (!capable(CAP_SYS_ADMIN)) 495 return -EPERM; 496 497 target_bytes = memparse(buf, &endchar); 498 499 balloon_set_new_target(target_bytes >> PAGE_SHIFT); 500 501 return count; 502} 503 504static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR, 505 show_target, store_target); 506 507 508static struct sysdev_attribute *balloon_attrs[] = { 509 &attr_target_kb, 510 &attr_target, 511}; 512 513static struct attribute *balloon_info_attrs[] = { 514 &attr_current_kb.attr, 515 &attr_low_kb.attr, 516 &attr_high_kb.attr, 517 NULL 518}; 519 520static struct attribute_group balloon_info_group = { 521 .name = "info", 522 .attrs = balloon_info_attrs, 523}; 524 525static struct sysdev_class balloon_sysdev_class = { 526 .name = BALLOON_CLASS_NAME, 527}; 528 529static int register_balloon(struct sys_device *sysdev) 530{ 531 int i, error; 532 533 error = sysdev_class_register(&balloon_sysdev_class); 534 if (error) 535 return error; 536 537 sysdev->id = 0; 538 sysdev->cls = &balloon_sysdev_class; 539 540 error = sysdev_register(sysdev); 541 if (error) { 542 sysdev_class_unregister(&balloon_sysdev_class); 543 return error; 544 } 545 546 for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) { 547 error = sysdev_create_file(sysdev, balloon_attrs[i]); 548 if (error) 549 goto fail; 550 } 551 552 error = sysfs_create_group(&sysdev->kobj, &balloon_info_group); 553 if (error) 554 goto fail; 555 556 return 0; 557 558 fail: 559 while (--i >= 0) 560 sysdev_remove_file(sysdev, balloon_attrs[i]); 561 sysdev_unregister(sysdev); 562 sysdev_class_unregister(&balloon_sysdev_class); 563 return error; 564} 565 566MODULE_LICENSE("GPL"); 567