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Linux/drivers/virtio/virtio_balloon.c

  1 /*
  2  * Virtio balloon implementation, inspired by Dor Laor and Marcelo
  3  * Tosatti's implementations.
  4  *
  5  *  Copyright 2008 Rusty Russell IBM Corporation
  6  *
  7  *  This program is free software; you can redistribute it and/or modify
  8  *  it under the terms of the GNU General Public License as published by
  9  *  the Free Software Foundation; either version 2 of the License, or
 10  *  (at your option) any later version.
 11  *
 12  *  This program is distributed in the hope that it will be useful,
 13  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 14  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 15  *  GNU General Public License for more details.
 16  *
 17  *  You should have received a copy of the GNU General Public License
 18  *  along with this program; if not, write to the Free Software
 19  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 20  */
 21 
 22 #include <linux/virtio.h>
 23 #include <linux/virtio_balloon.h>
 24 #include <linux/swap.h>
 25 #include <linux/kthread.h>
 26 #include <linux/freezer.h>
 27 #include <linux/delay.h>
 28 #include <linux/slab.h>
 29 #include <linux/module.h>
 30 #include <linux/balloon_compaction.h>
 31 #include <linux/oom.h>
 32 #include <linux/wait.h>
 33 
 34 /*
 35  * Balloon device works in 4K page units.  So each page is pointed to by
 36  * multiple balloon pages.  All memory counters in this driver are in balloon
 37  * page units.
 38  */
 39 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
 40 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
 41 #define OOM_VBALLOON_DEFAULT_PAGES 256
 42 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
 43 
 44 static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
 45 module_param(oom_pages, int, S_IRUSR | S_IWUSR);
 46 MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
 47 
 48 struct virtio_balloon {
 49         struct virtio_device *vdev;
 50         struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
 51 
 52         /* Where the ballooning thread waits for config to change. */
 53         wait_queue_head_t config_change;
 54 
 55         /* The thread servicing the balloon. */
 56         struct task_struct *thread;
 57 
 58         /* Waiting for host to ack the pages we released. */
 59         wait_queue_head_t acked;
 60 
 61         /* Number of balloon pages we've told the Host we're not using. */
 62         unsigned int num_pages;
 63         /*
 64          * The pages we've told the Host we're not using are enqueued
 65          * at vb_dev_info->pages list.
 66          * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
 67          * to num_pages above.
 68          */
 69         struct balloon_dev_info vb_dev_info;
 70 
 71         /* Synchronize access/update to this struct virtio_balloon elements */
 72         struct mutex balloon_lock;
 73 
 74         /* The array of pfns we tell the Host about. */
 75         unsigned int num_pfns;
 76         u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
 77 
 78         /* Memory statistics */
 79         int need_stats_update;
 80         struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 81 
 82         /* To register callback in oom notifier call chain */
 83         struct notifier_block nb;
 84 };
 85 
 86 static struct virtio_device_id id_table[] = {
 87         { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
 88         { 0 },
 89 };
 90 
 91 static u32 page_to_balloon_pfn(struct page *page)
 92 {
 93         unsigned long pfn = page_to_pfn(page);
 94 
 95         BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
 96         /* Convert pfn from Linux page size to balloon page size. */
 97         return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
 98 }
 99 
100 static struct page *balloon_pfn_to_page(u32 pfn)
101 {
102         BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
103         return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
104 }
105 
106 static void balloon_ack(struct virtqueue *vq)
107 {
108         struct virtio_balloon *vb = vq->vdev->priv;
109 
110         wake_up(&vb->acked);
111 }
112 
113 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
114 {
115         struct scatterlist sg;
116         unsigned int len;
117 
118         sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
119 
120         /* We should always be able to add one buffer to an empty queue. */
121         virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
122         virtqueue_kick(vq);
123 
124         /* When host has read buffer, this completes via balloon_ack */
125         wait_event(vb->acked, virtqueue_get_buf(vq, &len));
126 }
127 
128 static void set_page_pfns(u32 pfns[], struct page *page)
129 {
130         unsigned int i;
131 
132         /* Set balloon pfns pointing at this page.
133          * Note that the first pfn points at start of the page. */
134         for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
135                 pfns[i] = page_to_balloon_pfn(page) + i;
136 }
137 
138 static void fill_balloon(struct virtio_balloon *vb, size_t num)
139 {
140         struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
141 
142         /* We can only do one array worth at a time. */
143         num = min(num, ARRAY_SIZE(vb->pfns));
144 
145         mutex_lock(&vb->balloon_lock);
146         for (vb->num_pfns = 0; vb->num_pfns < num;
147              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
148                 struct page *page = balloon_page_enqueue(vb_dev_info);
149 
150                 if (!page) {
151                         dev_info_ratelimited(&vb->vdev->dev,
152                                              "Out of puff! Can't get %u pages\n",
153                                              VIRTIO_BALLOON_PAGES_PER_PAGE);
154                         /* Sleep for at least 1/5 of a second before retry. */
155                         msleep(200);
156                         break;
157                 }
158                 set_page_pfns(vb->pfns + vb->num_pfns, page);
159                 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
160                 if (!virtio_has_feature(vb->vdev,
161                                         VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
162                         adjust_managed_page_count(page, -1);
163         }
164 
165         /* Did we get any? */
166         if (vb->num_pfns != 0)
167                 tell_host(vb, vb->inflate_vq);
168         mutex_unlock(&vb->balloon_lock);
169 }
170 
171 static void release_pages_balloon(struct virtio_balloon *vb)
172 {
173         unsigned int i;
174 
175         /* Find pfns pointing at start of each page, get pages and free them. */
176         for (i = 0; i < vb->num_pfns; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
177                 struct page *page = balloon_pfn_to_page(vb->pfns[i]);
178                 if (!virtio_has_feature(vb->vdev,
179                                         VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
180                         adjust_managed_page_count(page, 1);
181                 put_page(page); /* balloon reference */
182         }
183 }
184 
185 static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
186 {
187         unsigned num_freed_pages;
188         struct page *page;
189         struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
190 
191         /* We can only do one array worth at a time. */
192         num = min(num, ARRAY_SIZE(vb->pfns));
193 
194         mutex_lock(&vb->balloon_lock);
195         for (vb->num_pfns = 0; vb->num_pfns < num;
196              vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
197                 page = balloon_page_dequeue(vb_dev_info);
198                 if (!page)
199                         break;
200                 set_page_pfns(vb->pfns + vb->num_pfns, page);
201                 vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
202         }
203 
204         num_freed_pages = vb->num_pfns;
205         /*
206          * Note that if
207          * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
208          * is true, we *have* to do it in this order
209          */
210         if (vb->num_pfns != 0)
211                 tell_host(vb, vb->deflate_vq);
212         release_pages_balloon(vb);
213         mutex_unlock(&vb->balloon_lock);
214         return num_freed_pages;
215 }
216 
217 static inline void update_stat(struct virtio_balloon *vb, int idx,
218                                u16 tag, u64 val)
219 {
220         BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
221         vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
222         vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
223 }
224 
225 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
226 
227 static void update_balloon_stats(struct virtio_balloon *vb)
228 {
229         unsigned long events[NR_VM_EVENT_ITEMS];
230         struct sysinfo i;
231         int idx = 0;
232 
233         all_vm_events(events);
234         si_meminfo(&i);
235 
236         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
237                                 pages_to_bytes(events[PSWPIN]));
238         update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
239                                 pages_to_bytes(events[PSWPOUT]));
240         update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
241         update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
242         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
243                                 pages_to_bytes(i.freeram));
244         update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
245                                 pages_to_bytes(i.totalram));
246 }
247 
248 /*
249  * While most virtqueues communicate guest-initiated requests to the hypervisor,
250  * the stats queue operates in reverse.  The driver initializes the virtqueue
251  * with a single buffer.  From that point forward, all conversations consist of
252  * a hypervisor request (a call to this function) which directs us to refill
253  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
254  * we notify our kthread which does the actual work via stats_handle_request().
255  */
256 static void stats_request(struct virtqueue *vq)
257 {
258         struct virtio_balloon *vb = vq->vdev->priv;
259 
260         vb->need_stats_update = 1;
261         wake_up(&vb->config_change);
262 }
263 
264 static void stats_handle_request(struct virtio_balloon *vb)
265 {
266         struct virtqueue *vq;
267         struct scatterlist sg;
268         unsigned int len;
269 
270         vb->need_stats_update = 0;
271         update_balloon_stats(vb);
272 
273         vq = vb->stats_vq;
274         if (!virtqueue_get_buf(vq, &len))
275                 return;
276         sg_init_one(&sg, vb->stats, sizeof(vb->stats));
277         virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
278         virtqueue_kick(vq);
279 }
280 
281 static void virtballoon_changed(struct virtio_device *vdev)
282 {
283         struct virtio_balloon *vb = vdev->priv;
284 
285         wake_up(&vb->config_change);
286 }
287 
288 static inline s64 towards_target(struct virtio_balloon *vb)
289 {
290         s64 target;
291         u32 num_pages;
292 
293         virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
294                      &num_pages);
295 
296         /* Legacy balloon config space is LE, unlike all other devices. */
297         if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
298                 num_pages = le32_to_cpu((__force __le32)num_pages);
299 
300         target = num_pages;
301         return target - vb->num_pages;
302 }
303 
304 static void update_balloon_size(struct virtio_balloon *vb)
305 {
306         u32 actual = vb->num_pages;
307 
308         /* Legacy balloon config space is LE, unlike all other devices. */
309         if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
310                 actual = (__force u32)cpu_to_le32(actual);
311 
312         virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
313                       &actual);
314 }
315 
316 /*
317  * virtballoon_oom_notify - release pages when system is under severe
318  *                          memory pressure (called from out_of_memory())
319  * @self : notifier block struct
320  * @dummy: not used
321  * @parm : returned - number of freed pages
322  *
323  * The balancing of memory by use of the virtio balloon should not cause
324  * the termination of processes while there are pages in the balloon.
325  * If virtio balloon manages to release some memory, it will make the
326  * system return and retry the allocation that forced the OOM killer
327  * to run.
328  */
329 static int virtballoon_oom_notify(struct notifier_block *self,
330                                   unsigned long dummy, void *parm)
331 {
332         struct virtio_balloon *vb;
333         unsigned long *freed;
334         unsigned num_freed_pages;
335 
336         vb = container_of(self, struct virtio_balloon, nb);
337         if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
338                 return NOTIFY_OK;
339 
340         freed = parm;
341         num_freed_pages = leak_balloon(vb, oom_pages);
342         update_balloon_size(vb);
343         *freed += num_freed_pages;
344 
345         return NOTIFY_OK;
346 }
347 
348 static int balloon(void *_vballoon)
349 {
350         struct virtio_balloon *vb = _vballoon;
351         DEFINE_WAIT_FUNC(wait, woken_wake_function);
352 
353         set_freezable();
354         while (!kthread_should_stop()) {
355                 s64 diff;
356 
357                 try_to_freeze();
358 
359                 add_wait_queue(&vb->config_change, &wait);
360                 for (;;) {
361                         if ((diff = towards_target(vb)) != 0 ||
362                             vb->need_stats_update ||
363                             kthread_should_stop() ||
364                             freezing(current))
365                                 break;
366                         wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
367                 }
368                 remove_wait_queue(&vb->config_change, &wait);
369 
370                 if (vb->need_stats_update)
371                         stats_handle_request(vb);
372                 if (diff > 0)
373                         fill_balloon(vb, diff);
374                 else if (diff < 0)
375                         leak_balloon(vb, -diff);
376                 update_balloon_size(vb);
377 
378                 /*
379                  * For large balloon changes, we could spend a lot of time
380                  * and always have work to do.  Be nice if preempt disabled.
381                  */
382                 cond_resched();
383         }
384         return 0;
385 }
386 
387 static int init_vqs(struct virtio_balloon *vb)
388 {
389         struct virtqueue *vqs[3];
390         vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
391         static const char * const names[] = { "inflate", "deflate", "stats" };
392         int err, nvqs;
393 
394         /*
395          * We expect two virtqueues: inflate and deflate, and
396          * optionally stat.
397          */
398         nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
399         err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
400         if (err)
401                 return err;
402 
403         vb->inflate_vq = vqs[0];
404         vb->deflate_vq = vqs[1];
405         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
406                 struct scatterlist sg;
407                 vb->stats_vq = vqs[2];
408 
409                 /*
410                  * Prime this virtqueue with one buffer so the hypervisor can
411                  * use it to signal us later (it can't be broken yet!).
412                  */
413                 sg_init_one(&sg, vb->stats, sizeof vb->stats);
414                 if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
415                     < 0)
416                         BUG();
417                 virtqueue_kick(vb->stats_vq);
418         }
419         return 0;
420 }
421 
422 #ifdef CONFIG_BALLOON_COMPACTION
423 /*
424  * virtballoon_migratepage - perform the balloon page migration on behalf of
425  *                           a compation thread.     (called under page lock)
426  * @vb_dev_info: the balloon device
427  * @newpage: page that will replace the isolated page after migration finishes.
428  * @page   : the isolated (old) page that is about to be migrated to newpage.
429  * @mode   : compaction mode -- not used for balloon page migration.
430  *
431  * After a ballooned page gets isolated by compaction procedures, this is the
432  * function that performs the page migration on behalf of a compaction thread
433  * The page migration for virtio balloon is done in a simple swap fashion which
434  * follows these two macro steps:
435  *  1) insert newpage into vb->pages list and update the host about it;
436  *  2) update the host about the old page removed from vb->pages list;
437  *
438  * This function preforms the balloon page migration task.
439  * Called through balloon_mapping->a_ops->migratepage
440  */
441 static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
442                 struct page *newpage, struct page *page, enum migrate_mode mode)
443 {
444         struct virtio_balloon *vb = container_of(vb_dev_info,
445                         struct virtio_balloon, vb_dev_info);
446         unsigned long flags;
447 
448         /*
449          * In order to avoid lock contention while migrating pages concurrently
450          * to leak_balloon() or fill_balloon() we just give up the balloon_lock
451          * this turn, as it is easier to retry the page migration later.
452          * This also prevents fill_balloon() getting stuck into a mutex
453          * recursion in the case it ends up triggering memory compaction
454          * while it is attempting to inflate the ballon.
455          */
456         if (!mutex_trylock(&vb->balloon_lock))
457                 return -EAGAIN;
458 
459         get_page(newpage); /* balloon reference */
460 
461         /* balloon's page migration 1st step  -- inflate "newpage" */
462         spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
463         balloon_page_insert(vb_dev_info, newpage);
464         vb_dev_info->isolated_pages--;
465         __count_vm_event(BALLOON_MIGRATE);
466         spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
467         vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
468         set_page_pfns(vb->pfns, newpage);
469         tell_host(vb, vb->inflate_vq);
470 
471         /* balloon's page migration 2nd step -- deflate "page" */
472         balloon_page_delete(page);
473         vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
474         set_page_pfns(vb->pfns, page);
475         tell_host(vb, vb->deflate_vq);
476 
477         mutex_unlock(&vb->balloon_lock);
478 
479         put_page(page); /* balloon reference */
480 
481         return MIGRATEPAGE_SUCCESS;
482 }
483 #endif /* CONFIG_BALLOON_COMPACTION */
484 
485 static int virtballoon_probe(struct virtio_device *vdev)
486 {
487         struct virtio_balloon *vb;
488         int err;
489 
490         if (!vdev->config->get) {
491                 dev_err(&vdev->dev, "%s failure: config access disabled\n",
492                         __func__);
493                 return -EINVAL;
494         }
495 
496         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
497         if (!vb) {
498                 err = -ENOMEM;
499                 goto out;
500         }
501 
502         vb->num_pages = 0;
503         mutex_init(&vb->balloon_lock);
504         init_waitqueue_head(&vb->config_change);
505         init_waitqueue_head(&vb->acked);
506         vb->vdev = vdev;
507         vb->need_stats_update = 0;
508 
509         balloon_devinfo_init(&vb->vb_dev_info);
510 #ifdef CONFIG_BALLOON_COMPACTION
511         vb->vb_dev_info.migratepage = virtballoon_migratepage;
512 #endif
513 
514         err = init_vqs(vb);
515         if (err)
516                 goto out_free_vb;
517 
518         vb->nb.notifier_call = virtballoon_oom_notify;
519         vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
520         err = register_oom_notifier(&vb->nb);
521         if (err < 0)
522                 goto out_oom_notify;
523 
524         virtio_device_ready(vdev);
525 
526         vb->thread = kthread_run(balloon, vb, "vballoon");
527         if (IS_ERR(vb->thread)) {
528                 err = PTR_ERR(vb->thread);
529                 goto out_del_vqs;
530         }
531 
532         return 0;
533 
534 out_del_vqs:
535         unregister_oom_notifier(&vb->nb);
536 out_oom_notify:
537         vdev->config->del_vqs(vdev);
538 out_free_vb:
539         kfree(vb);
540 out:
541         return err;
542 }
543 
544 static void remove_common(struct virtio_balloon *vb)
545 {
546         /* There might be pages left in the balloon: free them. */
547         while (vb->num_pages)
548                 leak_balloon(vb, vb->num_pages);
549         update_balloon_size(vb);
550 
551         /* Now we reset the device so we can clean up the queues. */
552         vb->vdev->config->reset(vb->vdev);
553 
554         vb->vdev->config->del_vqs(vb->vdev);
555 }
556 
557 static void virtballoon_remove(struct virtio_device *vdev)
558 {
559         struct virtio_balloon *vb = vdev->priv;
560 
561         unregister_oom_notifier(&vb->nb);
562         kthread_stop(vb->thread);
563         remove_common(vb);
564         kfree(vb);
565 }
566 
567 #ifdef CONFIG_PM_SLEEP
568 static int virtballoon_freeze(struct virtio_device *vdev)
569 {
570         struct virtio_balloon *vb = vdev->priv;
571 
572         /*
573          * The kthread is already frozen by the PM core before this
574          * function is called.
575          */
576 
577         remove_common(vb);
578         return 0;
579 }
580 
581 static int virtballoon_restore(struct virtio_device *vdev)
582 {
583         struct virtio_balloon *vb = vdev->priv;
584         int ret;
585 
586         ret = init_vqs(vdev->priv);
587         if (ret)
588                 return ret;
589 
590         virtio_device_ready(vdev);
591 
592         fill_balloon(vb, towards_target(vb));
593         update_balloon_size(vb);
594         return 0;
595 }
596 #endif
597 
598 static unsigned int features[] = {
599         VIRTIO_BALLOON_F_MUST_TELL_HOST,
600         VIRTIO_BALLOON_F_STATS_VQ,
601         VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
602 };
603 
604 static struct virtio_driver virtio_balloon_driver = {
605         .feature_table = features,
606         .feature_table_size = ARRAY_SIZE(features),
607         .driver.name =  KBUILD_MODNAME,
608         .driver.owner = THIS_MODULE,
609         .id_table =     id_table,
610         .probe =        virtballoon_probe,
611         .remove =       virtballoon_remove,
612         .config_changed = virtballoon_changed,
613 #ifdef CONFIG_PM_SLEEP
614         .freeze =       virtballoon_freeze,
615         .restore =      virtballoon_restore,
616 #endif
617 };
618 
619 module_virtio_driver(virtio_balloon_driver);
620 MODULE_DEVICE_TABLE(virtio, id_table);
621 MODULE_DESCRIPTION("Virtio balloon driver");
622 MODULE_LICENSE("GPL");
623 

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