xen/balloon: the balloon_lock is useless
[linux-2.6.git] / drivers / xen / balloon.c
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 static struct balloon_stats balloon_stats;
89
90 /* We increase/decrease in batches which fit in a page */
91 static unsigned long frame_list[PAGE_SIZE / sizeof(unsigned long)];
92
93 #ifdef CONFIG_HIGHMEM
94 #define inc_totalhigh_pages() (totalhigh_pages++)
95 #define dec_totalhigh_pages() (totalhigh_pages--)
96 #else
97 #define inc_totalhigh_pages() do {} while(0)
98 #define dec_totalhigh_pages() do {} while(0)
99 #endif
100
101 /* List of ballooned pages, threaded through the mem_map array. */
102 static LIST_HEAD(ballooned_pages);
103
104 /* Main work function, always executed in process context. */
105 static void balloon_process(struct work_struct *work);
106 static DECLARE_WORK(balloon_worker, balloon_process);
107 static struct timer_list balloon_timer;
108
109 /* When ballooning out (allocating memory to return to Xen) we don't really
110    want the kernel to try too hard since that can trigger the oom killer. */
111 #define GFP_BALLOON \
112         (GFP_HIGHUSER | __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC)
113
114 static void scrub_page(struct page *page)
115 {
116 #ifdef CONFIG_XEN_SCRUB_PAGES
117         clear_highpage(page);
118 #endif
119 }
120
121 /* balloon_append: add the given page to the balloon. */
122 static void __balloon_append(struct page *page)
123 {
124         /* Lowmem is re-populated first, so highmem pages go at list tail. */
125         if (PageHighMem(page)) {
126                 list_add_tail(&page->lru, &ballooned_pages);
127                 balloon_stats.balloon_high++;
128                 dec_totalhigh_pages();
129         } else {
130                 list_add(&page->lru, &ballooned_pages);
131                 balloon_stats.balloon_low++;
132         }
133 }
134
135 static void balloon_append(struct page *page)
136 {
137         __balloon_append(page);
138         totalram_pages--;
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         totalram_pages++;
160
161         return page;
162 }
163
164 static struct page *balloon_first_page(void)
165 {
166         if (list_empty(&ballooned_pages))
167                 return NULL;
168         return list_entry(ballooned_pages.next, struct page, lru);
169 }
170
171 static struct page *balloon_next_page(struct page *page)
172 {
173         struct list_head *next = page->lru.next;
174         if (next == &ballooned_pages)
175                 return NULL;
176         return list_entry(next, struct page, lru);
177 }
178
179 static void balloon_alarm(unsigned long unused)
180 {
181         schedule_work(&balloon_worker);
182 }
183
184 static unsigned long current_target(void)
185 {
186         unsigned long target = balloon_stats.target_pages;
187
188         target = min(target,
189                      balloon_stats.current_pages +
190                      balloon_stats.balloon_low +
191                      balloon_stats.balloon_high);
192
193         return target;
194 }
195
196 static int increase_reservation(unsigned long nr_pages)
197 {
198         unsigned long  pfn, i;
199         struct page   *page;
200         long           rc;
201         struct xen_memory_reservation reservation = {
202                 .address_bits = 0,
203                 .extent_order = 0,
204                 .domid        = DOMID_SELF
205         };
206
207         if (nr_pages > ARRAY_SIZE(frame_list))
208                 nr_pages = ARRAY_SIZE(frame_list);
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 < 0)
221                 goto out;
222
223         for (i = 0; i < rc; i++) {
224                 page = balloon_retrieve();
225                 BUG_ON(page == NULL);
226
227                 pfn = page_to_pfn(page);
228                 BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
229                        phys_to_machine_mapping_valid(pfn));
230
231                 set_phys_to_machine(pfn, frame_list[i]);
232
233                 /* Link back into the page tables if not highmem. */
234                 if (pfn < max_low_pfn) {
235                         int ret;
236                         ret = HYPERVISOR_update_va_mapping(
237                                 (unsigned long)__va(pfn << PAGE_SHIFT),
238                                 mfn_pte(frame_list[i], PAGE_KERNEL),
239                                 0);
240                         BUG_ON(ret);
241                 }
242
243                 /* Relinquish the page back to the allocator. */
244                 ClearPageReserved(page);
245                 init_page_count(page);
246                 __free_page(page);
247         }
248
249         balloon_stats.current_pages += rc;
250
251  out:
252         return rc < 0 ? rc : rc != nr_pages;
253 }
254
255 static int decrease_reservation(unsigned long nr_pages)
256 {
257         unsigned long  pfn, i;
258         struct page   *page;
259         int            need_sleep = 0;
260         int ret;
261         struct xen_memory_reservation reservation = {
262                 .address_bits = 0,
263                 .extent_order = 0,
264                 .domid        = DOMID_SELF
265         };
266
267         if (nr_pages > ARRAY_SIZE(frame_list))
268                 nr_pages = ARRAY_SIZE(frame_list);
269
270         for (i = 0; i < nr_pages; i++) {
271                 if ((page = alloc_page(GFP_BALLOON)) == NULL) {
272                         nr_pages = i;
273                         need_sleep = 1;
274                         break;
275                 }
276
277                 pfn = page_to_pfn(page);
278                 frame_list[i] = pfn_to_mfn(pfn);
279
280                 scrub_page(page);
281
282                 if (!PageHighMem(page)) {
283                         ret = HYPERVISOR_update_va_mapping(
284                                 (unsigned long)__va(pfn << PAGE_SHIFT),
285                                 __pte_ma(0), 0);
286                         BUG_ON(ret);
287                 }
288
289         }
290
291         /* Ensure that ballooned highmem pages don't have kmaps. */
292         kmap_flush_unused();
293         flush_tlb_all();
294
295         /* No more mappings: invalidate P2M and add to balloon. */
296         for (i = 0; i < nr_pages; i++) {
297                 pfn = mfn_to_pfn(frame_list[i]);
298                 set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
299                 balloon_append(pfn_to_page(pfn));
300         }
301
302         set_xen_guest_handle(reservation.extent_start, frame_list);
303         reservation.nr_extents   = nr_pages;
304         ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
305         BUG_ON(ret != nr_pages);
306
307         balloon_stats.current_pages -= nr_pages;
308
309         return need_sleep;
310 }
311
312 /*
313  * We avoid multiple worker processes conflicting via the balloon mutex.
314  * We may of course race updates of the target counts (which are protected
315  * by the balloon lock), or with changes to the Xen hard limit, but we will
316  * recover from these in time.
317  */
318 static void balloon_process(struct work_struct *work)
319 {
320         int need_sleep = 0;
321         long credit;
322
323         mutex_lock(&balloon_mutex);
324
325         do {
326                 credit = current_target() - balloon_stats.current_pages;
327                 if (credit > 0)
328                         need_sleep = (increase_reservation(credit) != 0);
329                 if (credit < 0)
330                         need_sleep = (decrease_reservation(-credit) != 0);
331
332 #ifndef CONFIG_PREEMPT
333                 if (need_resched())
334                         schedule();
335 #endif
336         } while ((credit != 0) && !need_sleep);
337
338         /* Schedule more work if there is some still to be done. */
339         if (current_target() != balloon_stats.current_pages)
340                 mod_timer(&balloon_timer, jiffies + HZ);
341
342         mutex_unlock(&balloon_mutex);
343 }
344
345 /* Resets the Xen limit, sets new target, and kicks off processing. */
346 static void balloon_set_new_target(unsigned long target)
347 {
348         /* No need for lock. Not read-modify-write updates. */
349         balloon_stats.target_pages = target;
350         schedule_work(&balloon_worker);
351 }
352
353 static struct xenbus_watch target_watch =
354 {
355         .node = "memory/target"
356 };
357
358 /* React to a change in the target key */
359 static void watch_target(struct xenbus_watch *watch,
360                          const char **vec, unsigned int len)
361 {
362         unsigned long long new_target;
363         int err;
364
365         err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
366         if (err != 1) {
367                 /* This is ok (for domain0 at least) - so just return */
368                 return;
369         }
370
371         /* The given memory/target value is in KiB, so it needs converting to
372          * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
373          */
374         balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
375 }
376
377 static int balloon_init_watcher(struct notifier_block *notifier,
378                                 unsigned long event,
379                                 void *data)
380 {
381         int err;
382
383         err = register_xenbus_watch(&target_watch);
384         if (err)
385                 printk(KERN_ERR "Failed to set balloon watcher\n");
386
387         return NOTIFY_DONE;
388 }
389
390 static struct notifier_block xenstore_notifier;
391
392 static int __init balloon_init(void)
393 {
394         unsigned long pfn;
395         struct page *page;
396
397         if (!xen_pv_domain())
398                 return -ENODEV;
399
400         pr_info("xen_balloon: Initialising balloon driver.\n");
401
402         balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
403         balloon_stats.target_pages  = balloon_stats.current_pages;
404         balloon_stats.balloon_low   = 0;
405         balloon_stats.balloon_high  = 0;
406         balloon_stats.driver_pages  = 0UL;
407
408         init_timer(&balloon_timer);
409         balloon_timer.data = 0;
410         balloon_timer.function = balloon_alarm;
411
412         register_balloon(&balloon_sysdev);
413
414         /* Initialise the balloon with excess memory space. */
415         for (pfn = PFN_UP(xen_extra_mem_start);
416              pfn < PFN_DOWN(xen_extra_mem_start + xen_extra_mem_size);
417              pfn++) {
418                 page = pfn_to_page(pfn);
419                 /* totalram_pages doesn't include the boot-time
420                    balloon extension, so don't subtract from it. */
421                 __balloon_append(page);
422         }
423
424         target_watch.callback = watch_target;
425         xenstore_notifier.notifier_call = balloon_init_watcher;
426
427         register_xenstore_notifier(&xenstore_notifier);
428
429         return 0;
430 }
431
432 subsys_initcall(balloon_init);
433
434 static void balloon_exit(void)
435 {
436     /* XXX - release balloon here */
437     return;
438 }
439
440 module_exit(balloon_exit);
441
442 #define BALLOON_SHOW(name, format, args...)                             \
443         static ssize_t show_##name(struct sys_device *dev,              \
444                                    struct sysdev_attribute *attr,       \
445                                    char *buf)                           \
446         {                                                               \
447                 return sprintf(buf, format, ##args);                    \
448         }                                                               \
449         static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
450
451 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
452 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
453 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
454 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
455
456 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
457                               char *buf)
458 {
459         return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
460 }
461
462 static ssize_t store_target_kb(struct sys_device *dev,
463                                struct sysdev_attribute *attr,
464                                const char *buf,
465                                size_t count)
466 {
467         char *endchar;
468         unsigned long long target_bytes;
469
470         if (!capable(CAP_SYS_ADMIN))
471                 return -EPERM;
472
473         target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
474
475         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
476
477         return count;
478 }
479
480 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
481                    show_target_kb, store_target_kb);
482
483
484 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
485                               char *buf)
486 {
487         return sprintf(buf, "%llu\n",
488                        (unsigned long long)balloon_stats.target_pages
489                        << PAGE_SHIFT);
490 }
491
492 static ssize_t store_target(struct sys_device *dev,
493                             struct sysdev_attribute *attr,
494                             const char *buf,
495                             size_t count)
496 {
497         char *endchar;
498         unsigned long long target_bytes;
499
500         if (!capable(CAP_SYS_ADMIN))
501                 return -EPERM;
502
503         target_bytes = memparse(buf, &endchar);
504
505         balloon_set_new_target(target_bytes >> PAGE_SHIFT);
506
507         return count;
508 }
509
510 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
511                    show_target, store_target);
512
513
514 static struct sysdev_attribute *balloon_attrs[] = {
515         &attr_target_kb,
516         &attr_target,
517 };
518
519 static struct attribute *balloon_info_attrs[] = {
520         &attr_current_kb.attr,
521         &attr_low_kb.attr,
522         &attr_high_kb.attr,
523         &attr_driver_kb.attr,
524         NULL
525 };
526
527 static struct attribute_group balloon_info_group = {
528         .name = "info",
529         .attrs = balloon_info_attrs,
530 };
531
532 static struct sysdev_class balloon_sysdev_class = {
533         .name = BALLOON_CLASS_NAME,
534 };
535
536 static int register_balloon(struct sys_device *sysdev)
537 {
538         int i, error;
539
540         error = sysdev_class_register(&balloon_sysdev_class);
541         if (error)
542                 return error;
543
544         sysdev->id = 0;
545         sysdev->cls = &balloon_sysdev_class;
546
547         error = sysdev_register(sysdev);
548         if (error) {
549                 sysdev_class_unregister(&balloon_sysdev_class);
550                 return error;
551         }
552
553         for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
554                 error = sysdev_create_file(sysdev, balloon_attrs[i]);
555                 if (error)
556                         goto fail;
557         }
558
559         error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
560         if (error)
561                 goto fail;
562
563         return 0;
564
565  fail:
566         while (--i >= 0)
567                 sysdev_remove_file(sysdev, balloon_attrs[i]);
568         sysdev_unregister(sysdev);
569         sysdev_class_unregister(&balloon_sysdev_class);
570         return error;
571 }
572
573 MODULE_LICENSE("GPL");