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/workqueue.h>
26 #include <linux/delay.h>
27 #include <linux/slab.h>
28 #include <linux/module.h>
29 #include <linux/balloon_compaction.h>
30 #include <linux/wait.h>
31 #include <linux/mm.h>
32 #include <linux/mount.h>
33 #include <linux/magic.h>
34 
35 /*
36  * Balloon device works in 4K page units.  So each page is pointed to by
37  * multiple balloon pages.  All memory counters in this driver are in balloon
38  * page units.
39  */
40 #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
41 #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
42 #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
43 
44 #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
45 					     __GFP_NOMEMALLOC)
46 /* The order of free page blocks to report to host */
47 #define VIRTIO_BALLOON_FREE_PAGE_ORDER (MAX_ORDER - 1)
48 /* The size of a free page block in bytes */
49 #define VIRTIO_BALLOON_FREE_PAGE_SIZE \
50 	(1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
51 
52 #ifdef CONFIG_BALLOON_COMPACTION
53 static struct vfsmount *balloon_mnt;
54 #endif
55 
56 enum virtio_balloon_vq {
57 	VIRTIO_BALLOON_VQ_INFLATE,
58 	VIRTIO_BALLOON_VQ_DEFLATE,
59 	VIRTIO_BALLOON_VQ_STATS,
60 	VIRTIO_BALLOON_VQ_FREE_PAGE,
61 	VIRTIO_BALLOON_VQ_MAX
62 };
63 
64 enum virtio_balloon_config_read {
65 	VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0,
66 };
67 
68 struct virtio_balloon {
69 	struct virtio_device *vdev;
70 	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
71 
72 	/* Balloon's own wq for cpu-intensive work items */
73 	struct workqueue_struct *balloon_wq;
74 	/* The free page reporting work item submitted to the balloon wq */
75 	struct work_struct report_free_page_work;
76 
77 	/* The balloon servicing is delegated to a freezable workqueue. */
78 	struct work_struct update_balloon_stats_work;
79 	struct work_struct update_balloon_size_work;
80 
81 	/* Prevent updating balloon when it is being canceled. */
82 	spinlock_t stop_update_lock;
83 	bool stop_update;
84 	/* Bitmap to indicate if reading the related config fields are needed */
85 	unsigned long config_read_bitmap;
86 
87 	/* The list of allocated free pages, waiting to be given back to mm */
88 	struct list_head free_page_list;
89 	spinlock_t free_page_list_lock;
90 	/* The number of free page blocks on the above list */
91 	unsigned long num_free_page_blocks;
92 	/*
93 	 * The cmd id received from host.
94 	 * Read it via virtio_balloon_cmd_id_received to get the latest value
95 	 * sent from host.
96 	 */
97 	u32 cmd_id_received_cache;
98 	/* The cmd id that is actively in use */
99 	__virtio32 cmd_id_active;
100 	/* Buffer to store the stop sign */
101 	__virtio32 cmd_id_stop;
102 
103 	/* Waiting for host to ack the pages we released. */
104 	wait_queue_head_t acked;
105 
106 	/* Number of balloon pages we've told the Host we're not using. */
107 	unsigned int num_pages;
108 	/*
109 	 * The pages we've told the Host we're not using are enqueued
110 	 * at vb_dev_info->pages list.
111 	 * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
112 	 * to num_pages above.
113 	 */
114 	struct balloon_dev_info vb_dev_info;
115 
116 	/* Synchronize access/update to this struct virtio_balloon elements */
117 	struct mutex balloon_lock;
118 
119 	/* The array of pfns we tell the Host about. */
120 	unsigned int num_pfns;
121 	__virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
122 
123 	/* Memory statistics */
124 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
125 
126 	/* To register a shrinker to shrink memory upon memory pressure */
127 	struct shrinker shrinker;
128 };
129 
130 static struct virtio_device_id id_table[] = {
131 	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
132 	{ 0 },
133 };
134 
135 static u32 page_to_balloon_pfn(struct page *page)
136 {
137 	unsigned long pfn = page_to_pfn(page);
138 
139 	BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
140 	/* Convert pfn from Linux page size to balloon page size. */
141 	return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
142 }
143 
144 static void balloon_ack(struct virtqueue *vq)
145 {
146 	struct virtio_balloon *vb = vq->vdev->priv;
147 
148 	wake_up(&vb->acked);
149 }
150 
151 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
152 {
153 	struct scatterlist sg;
154 	unsigned int len;
155 
156 	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
157 
158 	/* We should always be able to add one buffer to an empty queue. */
159 	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
160 	virtqueue_kick(vq);
161 
162 	/* When host has read buffer, this completes via balloon_ack */
163 	wait_event(vb->acked, virtqueue_get_buf(vq, &len));
164 
165 }
166 
167 static void set_page_pfns(struct virtio_balloon *vb,
168 			  __virtio32 pfns[], struct page *page)
169 {
170 	unsigned int i;
171 
172 	/*
173 	 * Set balloon pfns pointing at this page.
174 	 * Note that the first pfn points at start of the page.
175 	 */
176 	for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
177 		pfns[i] = cpu_to_virtio32(vb->vdev,
178 					  page_to_balloon_pfn(page) + i);
179 }
180 
181 static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
182 {
183 	unsigned num_allocated_pages;
184 	unsigned num_pfns;
185 	struct page *page;
186 	LIST_HEAD(pages);
187 
188 	/* We can only do one array worth at a time. */
189 	num = min(num, ARRAY_SIZE(vb->pfns));
190 
191 	for (num_pfns = 0; num_pfns < num;
192 	     num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
193 		struct page *page = balloon_page_alloc();
194 
195 		if (!page) {
196 			dev_info_ratelimited(&vb->vdev->dev,
197 					     "Out of puff! Can't get %u pages\n",
198 					     VIRTIO_BALLOON_PAGES_PER_PAGE);
199 			/* Sleep for at least 1/5 of a second before retry. */
200 			msleep(200);
201 			break;
202 		}
203 
204 		balloon_page_push(&pages, page);
205 	}
206 
207 	mutex_lock(&vb->balloon_lock);
208 
209 	vb->num_pfns = 0;
210 
211 	while ((page = balloon_page_pop(&pages))) {
212 		balloon_page_enqueue(&vb->vb_dev_info, page);
213 
214 		set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
215 		vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
216 		if (!virtio_has_feature(vb->vdev,
217 					VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
218 			adjust_managed_page_count(page, -1);
219 		vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
220 	}
221 
222 	num_allocated_pages = vb->num_pfns;
223 	/* Did we get any? */
224 	if (vb->num_pfns != 0)
225 		tell_host(vb, vb->inflate_vq);
226 	mutex_unlock(&vb->balloon_lock);
227 
228 	return num_allocated_pages;
229 }
230 
231 static void release_pages_balloon(struct virtio_balloon *vb,
232 				 struct list_head *pages)
233 {
234 	struct page *page, *next;
235 
236 	list_for_each_entry_safe(page, next, pages, lru) {
237 		if (!virtio_has_feature(vb->vdev,
238 					VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
239 			adjust_managed_page_count(page, 1);
240 		list_del(&page->lru);
241 		put_page(page); /* balloon reference */
242 	}
243 }
244 
245 static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
246 {
247 	unsigned num_freed_pages;
248 	struct page *page;
249 	struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
250 	LIST_HEAD(pages);
251 
252 	/* We can only do one array worth at a time. */
253 	num = min(num, ARRAY_SIZE(vb->pfns));
254 
255 	mutex_lock(&vb->balloon_lock);
256 	/* We can't release more pages than taken */
257 	num = min(num, (size_t)vb->num_pages);
258 	for (vb->num_pfns = 0; vb->num_pfns < num;
259 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
260 		page = balloon_page_dequeue(vb_dev_info);
261 		if (!page)
262 			break;
263 		set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
264 		list_add(&page->lru, &pages);
265 		vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
266 	}
267 
268 	num_freed_pages = vb->num_pfns;
269 	/*
270 	 * Note that if
271 	 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
272 	 * is true, we *have* to do it in this order
273 	 */
274 	if (vb->num_pfns != 0)
275 		tell_host(vb, vb->deflate_vq);
276 	release_pages_balloon(vb, &pages);
277 	mutex_unlock(&vb->balloon_lock);
278 	return num_freed_pages;
279 }
280 
281 static inline void update_stat(struct virtio_balloon *vb, int idx,
282 			       u16 tag, u64 val)
283 {
284 	BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
285 	vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
286 	vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
287 }
288 
289 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
290 
291 static unsigned int update_balloon_stats(struct virtio_balloon *vb)
292 {
293 	unsigned long events[NR_VM_EVENT_ITEMS];
294 	struct sysinfo i;
295 	unsigned int idx = 0;
296 	long available;
297 	unsigned long caches;
298 
299 	all_vm_events(events);
300 	si_meminfo(&i);
301 
302 	available = si_mem_available();
303 	caches = global_node_page_state(NR_FILE_PAGES);
304 
305 #ifdef CONFIG_VM_EVENT_COUNTERS
306 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
307 				pages_to_bytes(events[PSWPIN]));
308 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
309 				pages_to_bytes(events[PSWPOUT]));
310 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
311 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
312 #ifdef CONFIG_HUGETLB_PAGE
313 	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
314 		    events[HTLB_BUDDY_PGALLOC]);
315 	update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
316 		    events[HTLB_BUDDY_PGALLOC_FAIL]);
317 #endif
318 #endif
319 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
320 				pages_to_bytes(i.freeram));
321 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
322 				pages_to_bytes(i.totalram));
323 	update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
324 				pages_to_bytes(available));
325 	update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHES,
326 				pages_to_bytes(caches));
327 
328 	return idx;
329 }
330 
331 /*
332  * While most virtqueues communicate guest-initiated requests to the hypervisor,
333  * the stats queue operates in reverse.  The driver initializes the virtqueue
334  * with a single buffer.  From that point forward, all conversations consist of
335  * a hypervisor request (a call to this function) which directs us to refill
336  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
337  * we delegate the job to a freezable workqueue that will do the actual work via
338  * stats_handle_request().
339  */
340 static void stats_request(struct virtqueue *vq)
341 {
342 	struct virtio_balloon *vb = vq->vdev->priv;
343 
344 	spin_lock(&vb->stop_update_lock);
345 	if (!vb->stop_update)
346 		queue_work(system_freezable_wq, &vb->update_balloon_stats_work);
347 	spin_unlock(&vb->stop_update_lock);
348 }
349 
350 static void stats_handle_request(struct virtio_balloon *vb)
351 {
352 	struct virtqueue *vq;
353 	struct scatterlist sg;
354 	unsigned int len, num_stats;
355 
356 	num_stats = update_balloon_stats(vb);
357 
358 	vq = vb->stats_vq;
359 	if (!virtqueue_get_buf(vq, &len))
360 		return;
361 	sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
362 	virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
363 	virtqueue_kick(vq);
364 }
365 
366 static inline s64 towards_target(struct virtio_balloon *vb)
367 {
368 	s64 target;
369 	u32 num_pages;
370 
371 	virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
372 		     &num_pages);
373 
374 	/* Legacy balloon config space is LE, unlike all other devices. */
375 	if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
376 		num_pages = le32_to_cpu((__force __le32)num_pages);
377 
378 	target = num_pages;
379 	return target - vb->num_pages;
380 }
381 
382 /* Gives back @num_to_return blocks of free pages to mm. */
383 static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
384 					     unsigned long num_to_return)
385 {
386 	struct page *page;
387 	unsigned long num_returned;
388 
389 	spin_lock_irq(&vb->free_page_list_lock);
390 	for (num_returned = 0; num_returned < num_to_return; num_returned++) {
391 		page = balloon_page_pop(&vb->free_page_list);
392 		if (!page)
393 			break;
394 		free_pages((unsigned long)page_address(page),
395 			   VIRTIO_BALLOON_FREE_PAGE_ORDER);
396 	}
397 	vb->num_free_page_blocks -= num_returned;
398 	spin_unlock_irq(&vb->free_page_list_lock);
399 
400 	return num_returned;
401 }
402 
403 static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
404 {
405 	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
406 		return;
407 
408 	/* No need to queue the work if the bit was already set. */
409 	if (test_and_set_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
410 			     &vb->config_read_bitmap))
411 		return;
412 
413 	queue_work(vb->balloon_wq, &vb->report_free_page_work);
414 }
415 
416 static void virtballoon_changed(struct virtio_device *vdev)
417 {
418 	struct virtio_balloon *vb = vdev->priv;
419 	unsigned long flags;
420 
421 	spin_lock_irqsave(&vb->stop_update_lock, flags);
422 	if (!vb->stop_update) {
423 		queue_work(system_freezable_wq,
424 			   &vb->update_balloon_size_work);
425 		virtio_balloon_queue_free_page_work(vb);
426 	}
427 	spin_unlock_irqrestore(&vb->stop_update_lock, flags);
428 }
429 
430 static void update_balloon_size(struct virtio_balloon *vb)
431 {
432 	u32 actual = vb->num_pages;
433 
434 	/* Legacy balloon config space is LE, unlike all other devices. */
435 	if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
436 		actual = (__force u32)cpu_to_le32(actual);
437 
438 	virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
439 		      &actual);
440 }
441 
442 static void update_balloon_stats_func(struct work_struct *work)
443 {
444 	struct virtio_balloon *vb;
445 
446 	vb = container_of(work, struct virtio_balloon,
447 			  update_balloon_stats_work);
448 	stats_handle_request(vb);
449 }
450 
451 static void update_balloon_size_func(struct work_struct *work)
452 {
453 	struct virtio_balloon *vb;
454 	s64 diff;
455 
456 	vb = container_of(work, struct virtio_balloon,
457 			  update_balloon_size_work);
458 	diff = towards_target(vb);
459 
460 	if (diff > 0)
461 		diff -= fill_balloon(vb, diff);
462 	else if (diff < 0)
463 		diff += leak_balloon(vb, -diff);
464 	update_balloon_size(vb);
465 
466 	if (diff)
467 		queue_work(system_freezable_wq, work);
468 }
469 
470 static int init_vqs(struct virtio_balloon *vb)
471 {
472 	struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
473 	vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
474 	const char *names[VIRTIO_BALLOON_VQ_MAX];
475 	int err;
476 
477 	/*
478 	 * Inflateq and deflateq are used unconditionally. The names[]
479 	 * will be NULL if the related feature is not enabled, which will
480 	 * cause no allocation for the corresponding virtqueue in find_vqs.
481 	 */
482 	callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
483 	names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
484 	callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
485 	names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
486 	names[VIRTIO_BALLOON_VQ_STATS] = NULL;
487 	names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
488 
489 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
490 		names[VIRTIO_BALLOON_VQ_STATS] = "stats";
491 		callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
492 	}
493 
494 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
495 		names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
496 		callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
497 	}
498 
499 	err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
500 					 vqs, callbacks, names, NULL, NULL);
501 	if (err)
502 		return err;
503 
504 	vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
505 	vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
506 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
507 		struct scatterlist sg;
508 		unsigned int num_stats;
509 		vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
510 
511 		/*
512 		 * Prime this virtqueue with one buffer so the hypervisor can
513 		 * use it to signal us later (it can't be broken yet!).
514 		 */
515 		num_stats = update_balloon_stats(vb);
516 
517 		sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
518 		err = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb,
519 					   GFP_KERNEL);
520 		if (err) {
521 			dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
522 				 __func__);
523 			return err;
524 		}
525 		virtqueue_kick(vb->stats_vq);
526 	}
527 
528 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
529 		vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
530 
531 	return 0;
532 }
533 
534 static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb)
535 {
536 	if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
537 			       &vb->config_read_bitmap))
538 		virtio_cread(vb->vdev, struct virtio_balloon_config,
539 			     free_page_report_cmd_id,
540 			     &vb->cmd_id_received_cache);
541 
542 	return vb->cmd_id_received_cache;
543 }
544 
545 static int send_cmd_id_start(struct virtio_balloon *vb)
546 {
547 	struct scatterlist sg;
548 	struct virtqueue *vq = vb->free_page_vq;
549 	int err, unused;
550 
551 	/* Detach all the used buffers from the vq */
552 	while (virtqueue_get_buf(vq, &unused))
553 		;
554 
555 	vb->cmd_id_active = virtio32_to_cpu(vb->vdev,
556 					virtio_balloon_cmd_id_received(vb));
557 	sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active));
558 	err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL);
559 	if (!err)
560 		virtqueue_kick(vq);
561 	return err;
562 }
563 
564 static int send_cmd_id_stop(struct virtio_balloon *vb)
565 {
566 	struct scatterlist sg;
567 	struct virtqueue *vq = vb->free_page_vq;
568 	int err, unused;
569 
570 	/* Detach all the used buffers from the vq */
571 	while (virtqueue_get_buf(vq, &unused))
572 		;
573 
574 	sg_init_one(&sg, &vb->cmd_id_stop, sizeof(vb->cmd_id_stop));
575 	err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_stop, GFP_KERNEL);
576 	if (!err)
577 		virtqueue_kick(vq);
578 	return err;
579 }
580 
581 static int get_free_page_and_send(struct virtio_balloon *vb)
582 {
583 	struct virtqueue *vq = vb->free_page_vq;
584 	struct page *page;
585 	struct scatterlist sg;
586 	int err, unused;
587 	void *p;
588 
589 	/* Detach all the used buffers from the vq */
590 	while (virtqueue_get_buf(vq, &unused))
591 		;
592 
593 	page = alloc_pages(VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG,
594 			   VIRTIO_BALLOON_FREE_PAGE_ORDER);
595 	/*
596 	 * When the allocation returns NULL, it indicates that we have got all
597 	 * the possible free pages, so return -EINTR to stop.
598 	 */
599 	if (!page)
600 		return -EINTR;
601 
602 	p = page_address(page);
603 	sg_init_one(&sg, p, VIRTIO_BALLOON_FREE_PAGE_SIZE);
604 	/* There is always 1 entry reserved for the cmd id to use. */
605 	if (vq->num_free > 1) {
606 		err = virtqueue_add_inbuf(vq, &sg, 1, p, GFP_KERNEL);
607 		if (unlikely(err)) {
608 			free_pages((unsigned long)p,
609 				   VIRTIO_BALLOON_FREE_PAGE_ORDER);
610 			return err;
611 		}
612 		virtqueue_kick(vq);
613 		spin_lock_irq(&vb->free_page_list_lock);
614 		balloon_page_push(&vb->free_page_list, page);
615 		vb->num_free_page_blocks++;
616 		spin_unlock_irq(&vb->free_page_list_lock);
617 	} else {
618 		/*
619 		 * The vq has no available entry to add this page block, so
620 		 * just free it.
621 		 */
622 		free_pages((unsigned long)p, VIRTIO_BALLOON_FREE_PAGE_ORDER);
623 	}
624 
625 	return 0;
626 }
627 
628 static int send_free_pages(struct virtio_balloon *vb)
629 {
630 	int err;
631 	u32 cmd_id_active;
632 
633 	while (1) {
634 		/*
635 		 * If a stop id or a new cmd id was just received from host,
636 		 * stop the reporting.
637 		 */
638 		cmd_id_active = virtio32_to_cpu(vb->vdev, vb->cmd_id_active);
639 		if (unlikely(cmd_id_active !=
640 			     virtio_balloon_cmd_id_received(vb)))
641 			break;
642 
643 		/*
644 		 * The free page blocks are allocated and sent to host one by
645 		 * one.
646 		 */
647 		err = get_free_page_and_send(vb);
648 		if (err == -EINTR)
649 			break;
650 		else if (unlikely(err))
651 			return err;
652 	}
653 
654 	return 0;
655 }
656 
657 static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
658 {
659 	int err;
660 	struct device *dev = &vb->vdev->dev;
661 
662 	/* Start by sending the received cmd id to host with an outbuf. */
663 	err = send_cmd_id_start(vb);
664 	if (unlikely(err))
665 		dev_err(dev, "Failed to send a start id, err = %d\n", err);
666 
667 	err = send_free_pages(vb);
668 	if (unlikely(err))
669 		dev_err(dev, "Failed to send a free page, err = %d\n", err);
670 
671 	/* End by sending a stop id to host with an outbuf. */
672 	err = send_cmd_id_stop(vb);
673 	if (unlikely(err))
674 		dev_err(dev, "Failed to send a stop id, err = %d\n", err);
675 }
676 
677 static void report_free_page_func(struct work_struct *work)
678 {
679 	struct virtio_balloon *vb = container_of(work, struct virtio_balloon,
680 						 report_free_page_work);
681 	u32 cmd_id_received;
682 
683 	cmd_id_received = virtio_balloon_cmd_id_received(vb);
684 	if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
685 		/* Pass ULONG_MAX to give back all the free pages */
686 		return_free_pages_to_mm(vb, ULONG_MAX);
687 	} else if (cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP &&
688 		   cmd_id_received !=
689 		   virtio32_to_cpu(vb->vdev, vb->cmd_id_active)) {
690 		virtio_balloon_report_free_page(vb);
691 	}
692 }
693 
694 #ifdef CONFIG_BALLOON_COMPACTION
695 /*
696  * virtballoon_migratepage - perform the balloon page migration on behalf of
697  *			     a compation thread.     (called under page lock)
698  * @vb_dev_info: the balloon device
699  * @newpage: page that will replace the isolated page after migration finishes.
700  * @page   : the isolated (old) page that is about to be migrated to newpage.
701  * @mode   : compaction mode -- not used for balloon page migration.
702  *
703  * After a ballooned page gets isolated by compaction procedures, this is the
704  * function that performs the page migration on behalf of a compaction thread
705  * The page migration for virtio balloon is done in a simple swap fashion which
706  * follows these two macro steps:
707  *  1) insert newpage into vb->pages list and update the host about it;
708  *  2) update the host about the old page removed from vb->pages list;
709  *
710  * This function preforms the balloon page migration task.
711  * Called through balloon_mapping->a_ops->migratepage
712  */
713 static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
714 		struct page *newpage, struct page *page, enum migrate_mode mode)
715 {
716 	struct virtio_balloon *vb = container_of(vb_dev_info,
717 			struct virtio_balloon, vb_dev_info);
718 	unsigned long flags;
719 
720 	/*
721 	 * In order to avoid lock contention while migrating pages concurrently
722 	 * to leak_balloon() or fill_balloon() we just give up the balloon_lock
723 	 * this turn, as it is easier to retry the page migration later.
724 	 * This also prevents fill_balloon() getting stuck into a mutex
725 	 * recursion in the case it ends up triggering memory compaction
726 	 * while it is attempting to inflate the ballon.
727 	 */
728 	if (!mutex_trylock(&vb->balloon_lock))
729 		return -EAGAIN;
730 
731 	get_page(newpage); /* balloon reference */
732 
733 	/* balloon's page migration 1st step  -- inflate "newpage" */
734 	spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
735 	balloon_page_insert(vb_dev_info, newpage);
736 	vb_dev_info->isolated_pages--;
737 	__count_vm_event(BALLOON_MIGRATE);
738 	spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
739 	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
740 	set_page_pfns(vb, vb->pfns, newpage);
741 	tell_host(vb, vb->inflate_vq);
742 
743 	/* balloon's page migration 2nd step -- deflate "page" */
744 	spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
745 	balloon_page_delete(page);
746 	spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
747 	vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
748 	set_page_pfns(vb, vb->pfns, page);
749 	tell_host(vb, vb->deflate_vq);
750 
751 	mutex_unlock(&vb->balloon_lock);
752 
753 	put_page(page); /* balloon reference */
754 
755 	return MIGRATEPAGE_SUCCESS;
756 }
757 
758 static struct dentry *balloon_mount(struct file_system_type *fs_type,
759 		int flags, const char *dev_name, void *data)
760 {
761 	static const struct dentry_operations ops = {
762 		.d_dname = simple_dname,
763 	};
764 
765 	return mount_pseudo(fs_type, "balloon-kvm:", NULL, &ops,
766 				BALLOON_KVM_MAGIC);
767 }
768 
769 static struct file_system_type balloon_fs = {
770 	.name           = "balloon-kvm",
771 	.mount          = balloon_mount,
772 	.kill_sb        = kill_anon_super,
773 };
774 
775 #endif /* CONFIG_BALLOON_COMPACTION */
776 
777 static unsigned long shrink_free_pages(struct virtio_balloon *vb,
778 				       unsigned long pages_to_free)
779 {
780 	unsigned long blocks_to_free, blocks_freed;
781 
782 	pages_to_free = round_up(pages_to_free,
783 				 1 << VIRTIO_BALLOON_FREE_PAGE_ORDER);
784 	blocks_to_free = pages_to_free >> VIRTIO_BALLOON_FREE_PAGE_ORDER;
785 	blocks_freed = return_free_pages_to_mm(vb, blocks_to_free);
786 
787 	return blocks_freed << VIRTIO_BALLOON_FREE_PAGE_ORDER;
788 }
789 
790 static unsigned long shrink_balloon_pages(struct virtio_balloon *vb,
791 					  unsigned long pages_to_free)
792 {
793 	unsigned long pages_freed = 0;
794 
795 	/*
796 	 * One invocation of leak_balloon can deflate at most
797 	 * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it
798 	 * multiple times to deflate pages till reaching pages_to_free.
799 	 */
800 	while (vb->num_pages && pages_to_free) {
801 		pages_freed += leak_balloon(vb, pages_to_free) /
802 					VIRTIO_BALLOON_PAGES_PER_PAGE;
803 		pages_to_free -= pages_freed;
804 	}
805 	update_balloon_size(vb);
806 
807 	return pages_freed;
808 }
809 
810 static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
811 						  struct shrink_control *sc)
812 {
813 	unsigned long pages_to_free, pages_freed = 0;
814 	struct virtio_balloon *vb = container_of(shrinker,
815 					struct virtio_balloon, shrinker);
816 
817 	pages_to_free = sc->nr_to_scan * VIRTIO_BALLOON_PAGES_PER_PAGE;
818 
819 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
820 		pages_freed = shrink_free_pages(vb, pages_to_free);
821 
822 	if (pages_freed >= pages_to_free)
823 		return pages_freed;
824 
825 	pages_freed += shrink_balloon_pages(vb, pages_to_free - pages_freed);
826 
827 	return pages_freed;
828 }
829 
830 static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
831 						   struct shrink_control *sc)
832 {
833 	struct virtio_balloon *vb = container_of(shrinker,
834 					struct virtio_balloon, shrinker);
835 	unsigned long count;
836 
837 	count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
838 	count += vb->num_free_page_blocks >> VIRTIO_BALLOON_FREE_PAGE_ORDER;
839 
840 	return count;
841 }
842 
843 static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
844 {
845 	unregister_shrinker(&vb->shrinker);
846 }
847 
848 static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
849 {
850 	vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
851 	vb->shrinker.count_objects = virtio_balloon_shrinker_count;
852 	vb->shrinker.seeks = DEFAULT_SEEKS;
853 
854 	return register_shrinker(&vb->shrinker);
855 }
856 
857 static int virtballoon_probe(struct virtio_device *vdev)
858 {
859 	struct virtio_balloon *vb;
860 	__u32 poison_val;
861 	int err;
862 
863 	if (!vdev->config->get) {
864 		dev_err(&vdev->dev, "%s failure: config access disabled\n",
865 			__func__);
866 		return -EINVAL;
867 	}
868 
869 	vdev->priv = vb = kzalloc(sizeof(*vb), GFP_KERNEL);
870 	if (!vb) {
871 		err = -ENOMEM;
872 		goto out;
873 	}
874 
875 	INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
876 	INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
877 	spin_lock_init(&vb->stop_update_lock);
878 	mutex_init(&vb->balloon_lock);
879 	init_waitqueue_head(&vb->acked);
880 	vb->vdev = vdev;
881 
882 	balloon_devinfo_init(&vb->vb_dev_info);
883 
884 	err = init_vqs(vb);
885 	if (err)
886 		goto out_free_vb;
887 
888 #ifdef CONFIG_BALLOON_COMPACTION
889 	balloon_mnt = kern_mount(&balloon_fs);
890 	if (IS_ERR(balloon_mnt)) {
891 		err = PTR_ERR(balloon_mnt);
892 		goto out_del_vqs;
893 	}
894 
895 	vb->vb_dev_info.migratepage = virtballoon_migratepage;
896 	vb->vb_dev_info.inode = alloc_anon_inode(balloon_mnt->mnt_sb);
897 	if (IS_ERR(vb->vb_dev_info.inode)) {
898 		err = PTR_ERR(vb->vb_dev_info.inode);
899 		kern_unmount(balloon_mnt);
900 		goto out_del_vqs;
901 	}
902 	vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
903 #endif
904 	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
905 		/*
906 		 * There is always one entry reserved for cmd id, so the ring
907 		 * size needs to be at least two to report free page hints.
908 		 */
909 		if (virtqueue_get_vring_size(vb->free_page_vq) < 2) {
910 			err = -ENOSPC;
911 			goto out_del_vqs;
912 		}
913 		vb->balloon_wq = alloc_workqueue("balloon-wq",
914 					WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
915 		if (!vb->balloon_wq) {
916 			err = -ENOMEM;
917 			goto out_del_vqs;
918 		}
919 		INIT_WORK(&vb->report_free_page_work, report_free_page_func);
920 		vb->cmd_id_received_cache = VIRTIO_BALLOON_CMD_ID_STOP;
921 		vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
922 						  VIRTIO_BALLOON_CMD_ID_STOP);
923 		vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
924 						  VIRTIO_BALLOON_CMD_ID_STOP);
925 		vb->num_free_page_blocks = 0;
926 		spin_lock_init(&vb->free_page_list_lock);
927 		INIT_LIST_HEAD(&vb->free_page_list);
928 		if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
929 			memset(&poison_val, PAGE_POISON, sizeof(poison_val));
930 			virtio_cwrite(vb->vdev, struct virtio_balloon_config,
931 				      poison_val, &poison_val);
932 		}
933 	}
934 	/*
935 	 * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
936 	 * shrinker needs to be registered to relieve memory pressure.
937 	 */
938 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
939 		err = virtio_balloon_register_shrinker(vb);
940 		if (err)
941 			goto out_del_balloon_wq;
942 	}
943 	virtio_device_ready(vdev);
944 
945 	if (towards_target(vb))
946 		virtballoon_changed(vdev);
947 	return 0;
948 
949 out_del_balloon_wq:
950 	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
951 		destroy_workqueue(vb->balloon_wq);
952 out_del_vqs:
953 	vdev->config->del_vqs(vdev);
954 out_free_vb:
955 	kfree(vb);
956 out:
957 	return err;
958 }
959 
960 static void remove_common(struct virtio_balloon *vb)
961 {
962 	/* There might be pages left in the balloon: free them. */
963 	while (vb->num_pages)
964 		leak_balloon(vb, vb->num_pages);
965 	update_balloon_size(vb);
966 
967 	/* Now we reset the device so we can clean up the queues. */
968 	vb->vdev->config->reset(vb->vdev);
969 
970 	vb->vdev->config->del_vqs(vb->vdev);
971 }
972 
973 static void virtballoon_remove(struct virtio_device *vdev)
974 {
975 	struct virtio_balloon *vb = vdev->priv;
976 
977 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
978 		virtio_balloon_unregister_shrinker(vb);
979 	spin_lock_irq(&vb->stop_update_lock);
980 	vb->stop_update = true;
981 	spin_unlock_irq(&vb->stop_update_lock);
982 	cancel_work_sync(&vb->update_balloon_size_work);
983 	cancel_work_sync(&vb->update_balloon_stats_work);
984 
985 	if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
986 		cancel_work_sync(&vb->report_free_page_work);
987 		destroy_workqueue(vb->balloon_wq);
988 	}
989 
990 	remove_common(vb);
991 #ifdef CONFIG_BALLOON_COMPACTION
992 	if (vb->vb_dev_info.inode)
993 		iput(vb->vb_dev_info.inode);
994 
995 	kern_unmount(balloon_mnt);
996 #endif
997 	kfree(vb);
998 }
999 
1000 #ifdef CONFIG_PM_SLEEP
1001 static int virtballoon_freeze(struct virtio_device *vdev)
1002 {
1003 	struct virtio_balloon *vb = vdev->priv;
1004 
1005 	/*
1006 	 * The workqueue is already frozen by the PM core before this
1007 	 * function is called.
1008 	 */
1009 	remove_common(vb);
1010 	return 0;
1011 }
1012 
1013 static int virtballoon_restore(struct virtio_device *vdev)
1014 {
1015 	struct virtio_balloon *vb = vdev->priv;
1016 	int ret;
1017 
1018 	ret = init_vqs(vdev->priv);
1019 	if (ret)
1020 		return ret;
1021 
1022 	virtio_device_ready(vdev);
1023 
1024 	if (towards_target(vb))
1025 		virtballoon_changed(vdev);
1026 	update_balloon_size(vb);
1027 	return 0;
1028 }
1029 #endif
1030 
1031 static int virtballoon_validate(struct virtio_device *vdev)
1032 {
1033 	if (!page_poisoning_enabled())
1034 		__virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
1035 
1036 	__virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);
1037 	return 0;
1038 }
1039 
1040 static unsigned int features[] = {
1041 	VIRTIO_BALLOON_F_MUST_TELL_HOST,
1042 	VIRTIO_BALLOON_F_STATS_VQ,
1043 	VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
1044 	VIRTIO_BALLOON_F_FREE_PAGE_HINT,
1045 	VIRTIO_BALLOON_F_PAGE_POISON,
1046 };
1047 
1048 static struct virtio_driver virtio_balloon_driver = {
1049 	.feature_table = features,
1050 	.feature_table_size = ARRAY_SIZE(features),
1051 	.driver.name =	KBUILD_MODNAME,
1052 	.driver.owner =	THIS_MODULE,
1053 	.id_table =	id_table,
1054 	.validate =	virtballoon_validate,
1055 	.probe =	virtballoon_probe,
1056 	.remove =	virtballoon_remove,
1057 	.config_changed = virtballoon_changed,
1058 #ifdef CONFIG_PM_SLEEP
1059 	.freeze	=	virtballoon_freeze,
1060 	.restore =	virtballoon_restore,
1061 #endif
1062 };
1063 
1064 module_virtio_driver(virtio_balloon_driver);
1065 MODULE_DEVICE_TABLE(virtio, id_table);
1066 MODULE_DESCRIPTION("Virtio balloon driver");
1067 MODULE_LICENSE("GPL");
1068