xref: /openbmc/linux/drivers/xen/balloon.c (revision d5532ee7) 
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 	totalram_pages--;
135 }
136 
137 /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
138 static struct page *balloon_retrieve(void)
139 {
140 	struct page *page;
141 
142 	if (list_empty(&ballooned_pages))
143 		return NULL;
144 
145 	page = list_entry(ballooned_pages.next, struct page, lru);
146 	list_del(&page->lru);
147 
148 	if (PageHighMem(page)) {
149 		balloon_stats.balloon_high--;
150 		inc_totalhigh_pages();
151 	}
152 	else
153 		balloon_stats.balloon_low--;
154 
155 	totalram_pages++;
156 
157 	return page;
158 }
159 
160 static struct page *balloon_first_page(void)
161 {
162 	if (list_empty(&ballooned_pages))
163 		return NULL;
164 	return list_entry(ballooned_pages.next, struct page, lru);
165 }
166 
167 static struct page *balloon_next_page(struct page *page)
168 {
169 	struct list_head *next = page->lru.next;
170 	if (next == &ballooned_pages)
171 		return NULL;
172 	return list_entry(next, struct page, lru);
173 }
174 
175 static void balloon_alarm(unsigned long unused)
176 {
177 	schedule_work(&balloon_worker);
178 }
179 
180 static unsigned long current_target(void)
181 {
182 	unsigned long target = balloon_stats.target_pages;
183 
184 	target = min(target,
185 		     balloon_stats.current_pages +
186 		     balloon_stats.balloon_low +
187 		     balloon_stats.balloon_high);
188 
189 	return target;
190 }
191 
192 static int increase_reservation(unsigned long nr_pages)
193 {
194 	unsigned long  pfn, i, flags;
195 	struct page   *page;
196 	long           rc;
197 	struct xen_memory_reservation reservation = {
198 		.address_bits = 0,
199 		.extent_order = 0,
200 		.domid        = DOMID_SELF
201 	};
202 
203 	if (nr_pages > ARRAY_SIZE(frame_list))
204 		nr_pages = ARRAY_SIZE(frame_list);
205 
206 	spin_lock_irqsave(&xen_reservation_lock, flags);
207 
208 	page = balloon_first_page();
209 	for (i = 0; i < nr_pages; i++) {
210 		BUG_ON(page == NULL);
211 		frame_list[i] = page_to_pfn(page);
212 		page = balloon_next_page(page);
213 	}
214 
215 	set_xen_guest_handle(reservation.extent_start, frame_list);
216 	reservation.nr_extents = nr_pages;
217 	rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
218 	if (rc < 0)
219 		goto out;
220 
221 	for (i = 0; i < rc; i++) {
222 		page = balloon_retrieve();
223 		BUG_ON(page == NULL);
224 
225 		pfn = page_to_pfn(page);
226 		BUG_ON(!xen_feature(XENFEAT_auto_translated_physmap) &&
227 		       phys_to_machine_mapping_valid(pfn));
228 
229 		set_phys_to_machine(pfn, frame_list[i]);
230 
231 		/* Link back into the page tables if not highmem. */
232 		if (pfn < max_low_pfn) {
233 			int ret;
234 			ret = HYPERVISOR_update_va_mapping(
235 				(unsigned long)__va(pfn << PAGE_SHIFT),
236 				mfn_pte(frame_list[i], PAGE_KERNEL),
237 				0);
238 			BUG_ON(ret);
239 		}
240 
241 		/* Relinquish the page back to the allocator. */
242 		ClearPageReserved(page);
243 		init_page_count(page);
244 		__free_page(page);
245 	}
246 
247 	balloon_stats.current_pages += rc;
248 
249  out:
250 	spin_unlock_irqrestore(&xen_reservation_lock, flags);
251 
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, flags;
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 	spin_lock_irqsave(&xen_reservation_lock, flags);
296 
297 	/* No more mappings: invalidate P2M and add to balloon. */
298 	for (i = 0; i < nr_pages; i++) {
299 		pfn = mfn_to_pfn(frame_list[i]);
300 		set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
301 		balloon_append(pfn_to_page(pfn));
302 	}
303 
304 	set_xen_guest_handle(reservation.extent_start, frame_list);
305 	reservation.nr_extents   = nr_pages;
306 	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
307 	BUG_ON(ret != nr_pages);
308 
309 	balloon_stats.current_pages -= nr_pages;
310 
311 	spin_unlock_irqrestore(&xen_reservation_lock, flags);
312 
313 	return need_sleep;
314 }
315 
316 /*
317  * We avoid multiple worker processes conflicting via the balloon mutex.
318  * We may of course race updates of the target counts (which are protected
319  * by the balloon lock), or with changes to the Xen hard limit, but we will
320  * recover from these in time.
321  */
322 static void balloon_process(struct work_struct *work)
323 {
324 	int need_sleep = 0;
325 	long credit;
326 
327 	mutex_lock(&balloon_mutex);
328 
329 	do {
330 		credit = current_target() - balloon_stats.current_pages;
331 		if (credit > 0)
332 			need_sleep = (increase_reservation(credit) != 0);
333 		if (credit < 0)
334 			need_sleep = (decrease_reservation(-credit) != 0);
335 
336 #ifndef CONFIG_PREEMPT
337 		if (need_resched())
338 			schedule();
339 #endif
340 	} while ((credit != 0) && !need_sleep);
341 
342 	/* Schedule more work if there is some still to be done. */
343 	if (current_target() != balloon_stats.current_pages)
344 		mod_timer(&balloon_timer, jiffies + HZ);
345 
346 	mutex_unlock(&balloon_mutex);
347 }
348 
349 /* Resets the Xen limit, sets new target, and kicks off processing. */
350 static void balloon_set_new_target(unsigned long target)
351 {
352 	/* No need for lock. Not read-modify-write updates. */
353 	balloon_stats.target_pages = target;
354 	schedule_work(&balloon_worker);
355 }
356 
357 static struct xenbus_watch target_watch =
358 {
359 	.node = "memory/target"
360 };
361 
362 /* React to a change in the target key */
363 static void watch_target(struct xenbus_watch *watch,
364 			 const char **vec, unsigned int len)
365 {
366 	unsigned long long new_target;
367 	int err;
368 
369 	err = xenbus_scanf(XBT_NIL, "memory", "target", "%llu", &new_target);
370 	if (err != 1) {
371 		/* This is ok (for domain0 at least) - so just return */
372 		return;
373 	}
374 
375 	/* The given memory/target value is in KiB, so it needs converting to
376 	 * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
377 	 */
378 	balloon_set_new_target(new_target >> (PAGE_SHIFT - 10));
379 }
380 
381 static int balloon_init_watcher(struct notifier_block *notifier,
382 				unsigned long event,
383 				void *data)
384 {
385 	int err;
386 
387 	err = register_xenbus_watch(&target_watch);
388 	if (err)
389 		printk(KERN_ERR "Failed to set balloon watcher\n");
390 
391 	return NOTIFY_DONE;
392 }
393 
394 static struct notifier_block xenstore_notifier;
395 
396 static int __init balloon_init(void)
397 {
398 	unsigned long pfn;
399 	struct page *page;
400 
401 	if (!xen_pv_domain())
402 		return -ENODEV;
403 
404 	pr_info("xen_balloon: Initialising balloon driver.\n");
405 
406 	balloon_stats.current_pages = min(xen_start_info->nr_pages, max_pfn);
407 	balloon_stats.target_pages  = balloon_stats.current_pages;
408 	balloon_stats.balloon_low   = 0;
409 	balloon_stats.balloon_high  = 0;
410 	balloon_stats.driver_pages  = 0UL;
411 
412 	init_timer(&balloon_timer);
413 	balloon_timer.data = 0;
414 	balloon_timer.function = balloon_alarm;
415 
416 	register_balloon(&balloon_sysdev);
417 
418 	/* Initialise the balloon with excess memory space. */
419 	for (pfn = xen_start_info->nr_pages; pfn < max_pfn; pfn++) {
420 		page = pfn_to_page(pfn);
421 		if (!PageReserved(page))
422 			balloon_append(page);
423 	}
424 
425 	target_watch.callback = watch_target;
426 	xenstore_notifier.notifier_call = balloon_init_watcher;
427 
428 	register_xenstore_notifier(&xenstore_notifier);
429 
430 	return 0;
431 }
432 
433 subsys_initcall(balloon_init);
434 
435 static void balloon_exit(void)
436 {
437     /* XXX - release balloon here */
438     return;
439 }
440 
441 module_exit(balloon_exit);
442 
443 #define BALLOON_SHOW(name, format, args...)				\
444 	static ssize_t show_##name(struct sys_device *dev,		\
445 				   struct sysdev_attribute *attr,	\
446 				   char *buf)				\
447 	{								\
448 		return sprintf(buf, format, ##args);			\
449 	}								\
450 	static SYSDEV_ATTR(name, S_IRUGO, show_##name, NULL)
451 
452 BALLOON_SHOW(current_kb, "%lu\n", PAGES2KB(balloon_stats.current_pages));
453 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
454 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
455 BALLOON_SHOW(driver_kb, "%lu\n", PAGES2KB(balloon_stats.driver_pages));
456 
457 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute *attr,
458 			      char *buf)
459 {
460 	return sprintf(buf, "%lu\n", PAGES2KB(balloon_stats.target_pages));
461 }
462 
463 static ssize_t store_target_kb(struct sys_device *dev,
464 			       struct sysdev_attribute *attr,
465 			       const char *buf,
466 			       size_t count)
467 {
468 	char *endchar;
469 	unsigned long long target_bytes;
470 
471 	if (!capable(CAP_SYS_ADMIN))
472 		return -EPERM;
473 
474 	target_bytes = simple_strtoull(buf, &endchar, 0) * 1024;
475 
476 	balloon_set_new_target(target_bytes >> PAGE_SHIFT);
477 
478 	return count;
479 }
480 
481 static SYSDEV_ATTR(target_kb, S_IRUGO | S_IWUSR,
482 		   show_target_kb, store_target_kb);
483 
484 
485 static ssize_t show_target(struct sys_device *dev, struct sysdev_attribute *attr,
486 			      char *buf)
487 {
488 	return sprintf(buf, "%llu\n",
489 		       (unsigned long long)balloon_stats.target_pages
490 		       << PAGE_SHIFT);
491 }
492 
493 static ssize_t store_target(struct sys_device *dev,
494 			    struct sysdev_attribute *attr,
495 			    const char *buf,
496 			    size_t count)
497 {
498 	char *endchar;
499 	unsigned long long target_bytes;
500 
501 	if (!capable(CAP_SYS_ADMIN))
502 		return -EPERM;
503 
504 	target_bytes = memparse(buf, &endchar);
505 
506 	balloon_set_new_target(target_bytes >> PAGE_SHIFT);
507 
508 	return count;
509 }
510 
511 static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
512 		   show_target, store_target);
513 
514 
515 static struct sysdev_attribute *balloon_attrs[] = {
516 	&attr_target_kb,
517 	&attr_target,
518 };
519 
520 static struct attribute *balloon_info_attrs[] = {
521 	&attr_current_kb.attr,
522 	&attr_low_kb.attr,
523 	&attr_high_kb.attr,
524 	&attr_driver_kb.attr,
525 	NULL
526 };
527 
528 static struct attribute_group balloon_info_group = {
529 	.name = "info",
530 	.attrs = balloon_info_attrs,
531 };
532 
533 static struct sysdev_class balloon_sysdev_class = {
534 	.name = BALLOON_CLASS_NAME,
535 };
536 
537 static int register_balloon(struct sys_device *sysdev)
538 {
539 	int i, error;
540 
541 	error = sysdev_class_register(&balloon_sysdev_class);
542 	if (error)
543 		return error;
544 
545 	sysdev->id = 0;
546 	sysdev->cls = &balloon_sysdev_class;
547 
548 	error = sysdev_register(sysdev);
549 	if (error) {
550 		sysdev_class_unregister(&balloon_sysdev_class);
551 		return error;
552 	}
553 
554 	for (i = 0; i < ARRAY_SIZE(balloon_attrs); i++) {
555 		error = sysdev_create_file(sysdev, balloon_attrs[i]);
556 		if (error)
557 			goto fail;
558 	}
559 
560 	error = sysfs_create_group(&sysdev->kobj, &balloon_info_group);
561 	if (error)
562 		goto fail;
563 
564 	return 0;
565 
566  fail:
567 	while (--i >= 0)
568 		sysdev_remove_file(sysdev, balloon_attrs[i]);
569 	sysdev_unregister(sysdev);
570 	sysdev_class_unregister(&balloon_sysdev_class);
571 	return error;
572 }
573 
574 MODULE_LICENSE("GPL");
575