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 #include <xen/interface/xen.h>
56 #include <xen/interface/memory.h>
57 #include <xen/xenbus.h>
58 #include <xen/features.h>
59 #include <xen/page.h>
60
61 #define PAGES2KB(_p) ((_p)<<(PAGE_SHIFT-10))
62
63 #define BALLOON_CLASS_NAME "xen_memory"
64
65 struct balloon_stats {
66 /* We aim for 'current allocation' == 'target allocation'. */
67 unsigned long current_pages;
68 unsigned long target_pages;
69 /* We may hit the hard limit in Xen. If we do then we remember it. */
70 unsigned long hard_limit;
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
141 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
142 static struct page *balloon_retrieve(void)
143 {
144 struct page *page;
145
146 if (list_empty(&ballooned_pages))
147 return NULL;
148
149 page = list_entry(ballooned_pages.next, struct page, lru);
150 list_del(&page->lru);
151
152 if (PageHighMem(page)) {
153 balloon_stats.balloon_high--;
154 inc_totalhigh_pages();
155 }
156 else
157 balloon_stats.balloon_low--;
158
159 return page;
160 }
161
162 static struct page *balloon_first_page(void)
163 {
164 if (list_empty(&ballooned_pages))
165 return NULL;
166 return list_entry(ballooned_pages.next, struct page, lru);
167 }
168
169 static struct page *balloon_next_page(struct page *page)
170 {
171 struct list_head *next = page->lru.next;
172 if (next == &ballooned_pages)
173 return NULL;
174 return list_entry(next, struct page, lru);
175 }
176
177 static void balloon_alarm(unsigned long unused)
178 {
179 schedule_work(&balloon_worker);
180 }
181
182 static unsigned long current_target(void)
183 {
184 unsigned long target = min(balloon_stats.target_pages, balloon_stats.hard_limit);
185
186 target = min(target,
187 balloon_stats.current_pages +
188 balloon_stats.balloon_low +
189 balloon_stats.balloon_high);
190
191 return target;
192 }
193
194 static int increase_reservation(unsigned long nr_pages)
195 {
196 unsigned long pfn, i, flags;
197 struct page *page;
198 long rc;
199 struct xen_memory_reservation reservation = {
200 .address_bits = 0,
201 .extent_order = 0,
202 .domid = DOMID_SELF
203 };
204
205 if (nr_pages > ARRAY_SIZE(frame_list))
206 nr_pages = ARRAY_SIZE(frame_list);
207
208 spin_lock_irqsave(&balloon_lock, flags);
209
210 page = balloon_first_page();
211 for (i = 0; i < nr_pages; i++) {
212 BUG_ON(page == NULL);
213 frame_list[i] = page_to_pfn(page);;
214 page = balloon_next_page(page);
215 }
216
217 set_xen_guest_handle(reservation.extent_start, frame_list);
218 reservation.nr_extents = nr_pages;
219 rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
220 if (rc < nr_pages) {
221 if (rc > 0) {
222 int ret;
223
224 /* We hit the Xen hard limit: reprobe. */
225 reservation.nr_extents = rc;
226 ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation,
227 &reservation);
228 BUG_ON(ret != rc);
229 }
230 if (rc >= 0)
231 balloon_stats.hard_limit = (balloon_stats.current_pages + rc -
232 balloon_stats.driver_pages);
233 goto out;
234 }
235
236 for (i = 0; i < nr_pages; i++) {
237 page = balloon_retrieve();
238 BUG_ON(page == NULL);
239
240 pfn = page_to_pfn(page);
241 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
242 phys_to_machine_mapping_valid(pfn));
243
244 set_phys_to_machine(pfn, frame_list[i]);
245
246 /* Link back into the page tables if not highmem. */
247 if (pfn < max_low_pfn) {
248 int ret;
249 ret = HYPERVISOR_update_va_mapping(
250 (unsigned long)__va(pfn << PAGE_SHIFT),
251 mfn_pte(frame_list[i], PAGE_KERNEL),
252 0);
253 BUG_ON(ret);
254 }
255
256 /* Relinquish the page back to the allocator. */
257 ClearPageReserved(page);
258 init_page_count(page);
259 __free_page(page);
260 }
261
262 balloon_stats.current_pages += nr_pages;
263 totalram_pages = balloon_stats.current_pages;
264
265 out:
266 spin_unlock_irqrestore(&balloon_lock, flags);
267
268 return 0;
269 }
270
271 static int decrease_reservation(unsigned long nr_pages)
272 {
273 unsigned long pfn, i, flags;
274 struct page *page;
275 int need_sleep = 0;
276 int ret;
277 struct xen_memory_reservation reservation = {
278 .address_bits = 0,
279 .extent_order = 0,
280 .domid = DOMID_SELF
281 };
282
283 if (nr_pages > ARRAY_SIZE(frame_list))
284 nr_pages = ARRAY_SIZE(frame_list);
285
286 for (i = 0; i < nr_pages; i++) {
287 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
288 nr_pages = i;
289 need_sleep = 1;
290 break;
291 }
292
293 pfn = page_to_pfn(page);
294 frame_list[i] = pfn_to_mfn(pfn);
295
296 scrub_page(page);
297
298 if (!PageHighMem(page)) {
299 ret = HYPERVISOR_update_va_mapping(
300 (unsigned long)__va(pfn << PAGE_SHIFT),
301 __pte_ma(0), 0);
302 BUG_ON(ret);
303 }
304
305 }
306
307 /* Ensure that ballooned highmem pages don't have kmaps. */
308 kmap_flush_unused();
309 flush_tlb_all();
310
311 spin_lock_irqsave(&balloon_lock, flags);
312
313 /* No more mappings: invalidate P2M and add to balloon. */
314 for (i = 0; i < nr_pages; i++) {
315 pfn = mfn_to_pfn(frame_list[i]);
316 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
317 balloon_append(pfn_to_page(pfn));
318 }
319
320 set_xen_guest_handle(reservation.extent_start, frame_list);
321 reservation.nr_extents = nr_pages;
322 ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
323 BUG_ON(ret != nr_pages);
324
325 balloon_stats.current_pages -= nr_pages;
326 totalram_pages = balloon_stats.current_pages;
327
328 spin_unlock_irqrestore(&balloon_lock, flags);
329
330 return need_sleep;
331 }
332
333 /*
334 * We avoid multiple worker processes conflicting via the balloon mutex.
335 * We may of course race updates of the target counts (which are protected
336 * by the balloon lock), or with changes to the Xen hard limit, but we will
337 * recover from these in time.
338 */
339 static void balloon_process(struct work_struct *work)
340 {
341 int need_sleep = 0;
342 long credit;
343
344 mutex_lock(&balloon_mutex);
345
346 do {
347 credit = current_target() - balloon_stats.current_pages;
348 if (credit > 0)
349 need_sleep = (increase_reservation(credit) != 0);
350 if (credit < 0)
351 need_sleep = (decrease_reservation(-credit) != 0);
352
353 #ifndef CONFIG_PREEMPT
354 if (need_resched())
355 schedule();
356 #endif
357 } while ((credit != 0) && !need_sleep);
358
359 /* Schedule more work if there is some still to be done. */
360 if (current_target() != balloon_stats.current_pages)
361 mod_timer(&balloon_timer, jiffies + HZ);
362
363 mutex_unlock(&balloon_mutex);
364 }
365
366 /* Resets the Xen limit, sets new target, and kicks off processing. */
367 static void balloon_set_new_target(unsigned long target)
368 {
369 /* No need for lock. Not read-modify-write updates. */
370 balloon_stats.hard_limit = ~0UL;
371 balloon_stats.target_pages = target;
372 schedule_work(&balloon_worker);
373 }
374
375 static struct xenbus_watch target_watch =
376 {
377 .node = "memory/target"
378 };
379
380 /* React to a change in the target key */
381 static void watch_target(struct xenbus_watch *watch,
382 const char **vec, unsigned int len)
383 {
384 unsigned long long new_target;
385 int err;
386
387 err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
388 if (err != 1) {
389 /* This is ok (for domain0 at least) - so just return */
390 return;
391 }
392
393 /* The given memory/target value is in KiB, so it needs converting to
394 * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
395 */
396 balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
397 }
398
399 static int balloon_init_watcher(struct notifier_block *notifier,
400 unsigned long event,
401 void *data)
402 {
403 int err;
404
405 err = register_xenbus_watch(&target_watch);
406 if (err)
407 printk(KERN_ERR "Failed to set balloon watcher\n");
408
409 return NOTIFY_DONE;
410 }
411
412 static struct notifier_block xenstore_notifier;
413
414 static int __init balloon_init(void)
415 {
416 unsigned long pfn;
417 struct page *page;
418
419 if (!xen_pv_domain())
420 return -ENODEV;
421
422 pr_info("xen_balloon: Initialising balloon driver.\n");
423
424 balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
425 totalram_pages = balloon_stats.current_pages;
426 balloon_stats.target_pages = balloon_stats.current_pages;
427 balloon_stats.balloon_low = 0;
428 balloon_stats.balloon_high = 0;
429 balloon_stats.driver_pages = 0UL;
430 balloon_stats.hard_limit = ~0UL;
431
432 init_timer(&balloon_timer);
433 balloon_timer.data = 0;
434 balloon_timer.function = balloon_alarm;
435
436 register_balloon(&balloon_sysdev);
437
438 /* Initialise the balloon with excess memory space. */
439 for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
440 page = pfn_to_page(pfn);
441 if (!PageReserved(page))
442 balloon_append(page);
443 }
444
445 target_watch.callback = watch_target;
446 xenstore_notifier.notifier_call = balloon_init_watcher;
447
448 register_xenstore_notifier(&xenstore_notifier);
449
450 return 0;
451 }
452
453 subsys_initcall(balloon_init);
454
455 static void balloon_exit(void)
456 {
457 /* XXX - release balloon here */
458 return;
459 }
460
461 module_exit(balloon_exit);
462
463 #define BALLOON_SHOW(name, format, args...) \
464 static ssize_t show_##name(struct sys_device *dev, \
465 struct sysdev_attribute *attr, \
466 char *buf) \
467 { \
468 return sprintf(buf, format, ##args); \
469 } \
470 static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
471
472 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
473 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
474 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
475 BALLOON_SHOW(hard_limit_kb,
476 (balloon_stats.hard_limit!=~0UL) ? "%lu\n" : "???\n",
477 (balloon_stats.hard_limit!=~0UL) ? PAGES2KB(balloon_stats.hard_limit) : 0);
478 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
479
480 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
481 char *buf)
482 {
483 return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
484 }
485
486 static ssize_t store_target_kb(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 = simple_strtoull(buf, &endchar, 0) * 1024;
498
499 balloon_set_new_target(target_bytes >> PAGE_SHIFT);
500
501 return count;
502 }
503
504 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
505 show_target_kb, store_target_kb);
506
507
508 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
509 char *buf)
510 {
511 return sprintf(buf, "%llu\n",
512 (unsigned long long)balloon_stats.target_pages
513 << PAGE_SHIFT);
514 }
515
516 static ssize_t store_target(struct sys_device *dev,
517 struct sysdev_attribute *attr,
518 const char *buf,
519 size_t count)
520 {
521 char *endchar;
522 unsigned long long target_bytes;
523
524 if (!capable(CAP_SYS_ADMIN))
525 return -EPERM;
526
527 target_bytes = memparse(buf, &endchar);
528
529 balloon_set_new_target(target_bytes >> PAGE_SHIFT);
530
531 return count;
532 }
533
534 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
535 show_target, store_target);
536
537
538 static struct sysdev_attribute *balloon_attrs[] = {
539 &attr_target_kb,
540 &attr_target,
541 };
542
543 static struct attribute *balloon_info_attrs[] = {
544 &attr_current_kb.attr,
545 &attr_low_kb.attr,
546 &attr_high_kb.attr,
547 &attr_hard_limit_kb.attr,
548 &attr_driver_kb.attr,
549 NULL
550 };
551
552 static struct attribute_group balloon_info_group = {
553 .name = "info",
554 .attrs = balloon_info_attrs,
555 };
556
557 static struct sysdev_class balloon_sysdev_class = {
558 .name = BALLOON_CLASS_NAME,
559 };
560
561 static int register_balloon(struct sys_device *sysdev)
562 {
563 int i, error;
564
565 error = sysdev_class_register(&balloon_sysdev_class);
566 if (error)
567 return error;
568
569 sysdev->id = 0;
570 sysdev->cls = &balloon_sysdev_class;
571
572 error = sysdev_register(sysdev);
573 if (error) {
574 sysdev_class_unregister(&balloon_sysdev_class);
575 return error;
576 }
577
578 for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
579 error = sysdev_create_file(sysdev, balloon_attrs[i]);
580 if (error)
581 goto fail;
582 }
583
584 error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
585 if (error)
586 goto fail;
587
588 return 0;
589
590 fail:
591 while (--i >= 0)
592 sysdev_remove_file(sysdev, balloon_attrs[i]);
593 sysdev_unregister(sysdev);
594 sysdev_class_unregister(&balloon_sysdev_class);
595 return error;
596 }
597
598 MODULE_LICENSE("GPL");
599
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