1 /* Virtio balloon implementation, inspired by Dor Loar and Marcelo
2  * Tosatti's implementations.
3  *
4  *  Copyright 2008 Rusty Russell IBM Corporation
5  *
6  *  This program is free software; you can redistribute it and/or modify
7  *  it under the terms of the GNU General Public License as published by
8  *  the Free Software Foundation; either version 2 of the License, or
9  *  (at your option) any later version.
10  *
11  *  This program is distributed in the hope that it will be useful,
12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  *  GNU General Public License for more details.
15  *
16  *  You should have received a copy of the GNU General Public License
17  *  along with this program; if not, write to the Free Software
18  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
19  */
20 //#define DEBUG
21 #include <linux/virtio.h>
22 #include <linux/virtio_balloon.h>
23 #include <linux/swap.h>
24 #include <linux/kthread.h>
25 #include <linux/freezer.h>
26 #include <linux/delay.h>
27 #include <linux/slab.h>
28 
29 struct virtio_balloon
30 {
31 	struct virtio_device *vdev;
32 	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
33 
34 	/* Where the ballooning thread waits for config to change. */
35 	wait_queue_head_t config_change;
36 
37 	/* The thread servicing the balloon. */
38 	struct task_struct *thread;
39 
40 	/* Waiting for host to ack the pages we released. */
41 	struct completion acked;
42 
43 	/* Do we have to tell Host *before* we reuse pages? */
44 	bool tell_host_first;
45 
46 	/* The pages we've told the Host we're not using. */
47 	unsigned int num_pages;
48 	struct list_head pages;
49 
50 	/* The array of pfns we tell the Host about. */
51 	unsigned int num_pfns;
52 	u32 pfns[256];
53 
54 	/* Memory statistics */
55 	int need_stats_update;
56 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
57 };
58 
59 static struct virtio_device_id id_table[] = {
60 	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
61 	{ 0 },
62 };
63 
64 static u32 page_to_balloon_pfn(struct page *page)
65 {
66 	unsigned long pfn = page_to_pfn(page);
67 
68 	BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
69 	/* Convert pfn from Linux page size to balloon page size. */
70 	return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
71 }
72 
73 static void balloon_ack(struct virtqueue *vq)
74 {
75 	struct virtio_balloon *vb;
76 	unsigned int len;
77 
78 	vb = virtqueue_get_buf(vq, &len);
79 	if (vb)
80 		complete(&vb->acked);
81 }
82 
83 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
84 {
85 	struct scatterlist sg;
86 
87 	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
88 
89 	init_completion(&vb->acked);
90 
91 	/* We should always be able to add one buffer to an empty queue. */
92 	if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
93 		BUG();
94 	virtqueue_kick(vq);
95 
96 	/* When host has read buffer, this completes via balloon_ack */
97 	wait_for_completion(&vb->acked);
98 }
99 
100 static void fill_balloon(struct virtio_balloon *vb, size_t num)
101 {
102 	/* We can only do one array worth at a time. */
103 	num = min(num, ARRAY_SIZE(vb->pfns));
104 
105 	for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
106 		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
107 					__GFP_NOMEMALLOC | __GFP_NOWARN);
108 		if (!page) {
109 			if (printk_ratelimit())
110 				dev_printk(KERN_INFO, &vb->vdev->dev,
111 					   "Out of puff! Can't get %zu pages\n",
112 					   num);
113 			/* Sleep for at least 1/5 of a second before retry. */
114 			msleep(200);
115 			break;
116 		}
117 		vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
118 		totalram_pages--;
119 		vb->num_pages++;
120 		list_add(&page->lru, &vb->pages);
121 	}
122 
123 	/* Didn't get any?  Oh well. */
124 	if (vb->num_pfns == 0)
125 		return;
126 
127 	tell_host(vb, vb->inflate_vq);
128 }
129 
130 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
131 {
132 	unsigned int i;
133 
134 	for (i = 0; i < num; i++) {
135 		__free_page(pfn_to_page(pfns[i]));
136 		totalram_pages++;
137 	}
138 }
139 
140 static void leak_balloon(struct virtio_balloon *vb, size_t num)
141 {
142 	struct page *page;
143 
144 	/* We can only do one array worth at a time. */
145 	num = min(num, ARRAY_SIZE(vb->pfns));
146 
147 	for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
148 		page = list_first_entry(&vb->pages, struct page, lru);
149 		list_del(&page->lru);
150 		vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
151 		vb->num_pages--;
152 	}
153 
154 	if (vb->tell_host_first) {
155 		tell_host(vb, vb->deflate_vq);
156 		release_pages_by_pfn(vb->pfns, vb->num_pfns);
157 	} else {
158 		release_pages_by_pfn(vb->pfns, vb->num_pfns);
159 		tell_host(vb, vb->deflate_vq);
160 	}
161 }
162 
163 static inline void update_stat(struct virtio_balloon *vb, int idx,
164 			       u16 tag, u64 val)
165 {
166 	BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
167 	vb->stats[idx].tag = tag;
168 	vb->stats[idx].val = val;
169 }
170 
171 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
172 
173 static void update_balloon_stats(struct virtio_balloon *vb)
174 {
175 	unsigned long events[NR_VM_EVENT_ITEMS];
176 	struct sysinfo i;
177 	int idx = 0;
178 
179 	all_vm_events(events);
180 	si_meminfo(&i);
181 
182 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
183 				pages_to_bytes(events[PSWPIN]));
184 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
185 				pages_to_bytes(events[PSWPOUT]));
186 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
187 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
188 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
189 				pages_to_bytes(i.freeram));
190 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
191 				pages_to_bytes(i.totalram));
192 }
193 
194 /*
195  * While most virtqueues communicate guest-initiated requests to the hypervisor,
196  * the stats queue operates in reverse.  The driver initializes the virtqueue
197  * with a single buffer.  From that point forward, all conversations consist of
198  * a hypervisor request (a call to this function) which directs us to refill
199  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
200  * we notify our kthread which does the actual work via stats_handle_request().
201  */
202 static void stats_request(struct virtqueue *vq)
203 {
204 	struct virtio_balloon *vb;
205 	unsigned int len;
206 
207 	vb = virtqueue_get_buf(vq, &len);
208 	if (!vb)
209 		return;
210 	vb->need_stats_update = 1;
211 	wake_up(&vb->config_change);
212 }
213 
214 static void stats_handle_request(struct virtio_balloon *vb)
215 {
216 	struct virtqueue *vq;
217 	struct scatterlist sg;
218 
219 	vb->need_stats_update = 0;
220 	update_balloon_stats(vb);
221 
222 	vq = vb->stats_vq;
223 	sg_init_one(&sg, vb->stats, sizeof(vb->stats));
224 	if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
225 		BUG();
226 	virtqueue_kick(vq);
227 }
228 
229 static void virtballoon_changed(struct virtio_device *vdev)
230 {
231 	struct virtio_balloon *vb = vdev->priv;
232 
233 	wake_up(&vb->config_change);
234 }
235 
236 static inline s64 towards_target(struct virtio_balloon *vb)
237 {
238 	u32 v;
239 	vb->vdev->config->get(vb->vdev,
240 			      offsetof(struct virtio_balloon_config, num_pages),
241 			      &v, sizeof(v));
242 	return (s64)v - vb->num_pages;
243 }
244 
245 static void update_balloon_size(struct virtio_balloon *vb)
246 {
247 	__le32 actual = cpu_to_le32(vb->num_pages);
248 
249 	vb->vdev->config->set(vb->vdev,
250 			      offsetof(struct virtio_balloon_config, actual),
251 			      &actual, sizeof(actual));
252 }
253 
254 static int balloon(void *_vballoon)
255 {
256 	struct virtio_balloon *vb = _vballoon;
257 
258 	set_freezable();
259 	while (!kthread_should_stop()) {
260 		s64 diff;
261 
262 		try_to_freeze();
263 		wait_event_interruptible(vb->config_change,
264 					 (diff = towards_target(vb)) != 0
265 					 || vb->need_stats_update
266 					 || kthread_should_stop()
267 					 || freezing(current));
268 		if (vb->need_stats_update)
269 			stats_handle_request(vb);
270 		if (diff > 0)
271 			fill_balloon(vb, diff);
272 		else if (diff < 0)
273 			leak_balloon(vb, -diff);
274 		update_balloon_size(vb);
275 	}
276 	return 0;
277 }
278 
279 static int virtballoon_probe(struct virtio_device *vdev)
280 {
281 	struct virtio_balloon *vb;
282 	struct virtqueue *vqs[3];
283 	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
284 	const char *names[] = { "inflate", "deflate", "stats" };
285 	int err, nvqs;
286 
287 	vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
288 	if (!vb) {
289 		err = -ENOMEM;
290 		goto out;
291 	}
292 
293 	INIT_LIST_HEAD(&vb->pages);
294 	vb->num_pages = 0;
295 	init_waitqueue_head(&vb->config_change);
296 	vb->vdev = vdev;
297 	vb->need_stats_update = 0;
298 
299 	/* We expect two virtqueues: inflate and deflate,
300 	 * and optionally stat. */
301 	nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
302 	err = vdev->config->find_vqs(vdev, nvqs, vqs, callbacks, names);
303 	if (err)
304 		goto out_free_vb;
305 
306 	vb->inflate_vq = vqs[0];
307 	vb->deflate_vq = vqs[1];
308 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
309 		struct scatterlist sg;
310 		vb->stats_vq = vqs[2];
311 
312 		/*
313 		 * Prime this virtqueue with one buffer so the hypervisor can
314 		 * use it to signal us later.
315 		 */
316 		sg_init_one(&sg, vb->stats, sizeof vb->stats);
317 		if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb) < 0)
318 			BUG();
319 		virtqueue_kick(vb->stats_vq);
320 	}
321 
322 	vb->thread = kthread_run(balloon, vb, "vballoon");
323 	if (IS_ERR(vb->thread)) {
324 		err = PTR_ERR(vb->thread);
325 		goto out_del_vqs;
326 	}
327 
328 	vb->tell_host_first
329 		= virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
330 
331 	return 0;
332 
333 out_del_vqs:
334 	vdev->config->del_vqs(vdev);
335 out_free_vb:
336 	kfree(vb);
337 out:
338 	return err;
339 }
340 
341 static void __devexit virtballoon_remove(struct virtio_device *vdev)
342 {
343 	struct virtio_balloon *vb = vdev->priv;
344 
345 	kthread_stop(vb->thread);
346 
347 	/* There might be pages left in the balloon: free them. */
348 	while (vb->num_pages)
349 		leak_balloon(vb, vb->num_pages);
350 
351 	/* Now we reset the device so we can clean up the queues. */
352 	vdev->config->reset(vdev);
353 
354 	vdev->config->del_vqs(vdev);
355 	kfree(vb);
356 }
357 
358 static unsigned int features[] = {
359 	VIRTIO_BALLOON_F_MUST_TELL_HOST,
360 	VIRTIO_BALLOON_F_STATS_VQ,
361 };
362 
363 static struct virtio_driver virtio_balloon_driver = {
364 	.feature_table = features,
365 	.feature_table_size = ARRAY_SIZE(features),
366 	.driver.name =	KBUILD_MODNAME,
367 	.driver.owner =	THIS_MODULE,
368 	.id_table =	id_table,
369 	.probe =	virtballoon_probe,
370 	.remove =	__devexit_p(virtballoon_remove),
371 	.config_changed = virtballoon_changed,
372 };
373 
374 static int __init init(void)
375 {
376 	return register_virtio_driver(&virtio_balloon_driver);
377 }
378 
379 static void __exit fini(void)
380 {
381 	unregister_virtio_driver(&virtio_balloon_driver);
382 }
383 module_init(init);
384 module_exit(fini);
385 
386 MODULE_DEVICE_TABLE(virtio, id_table);
387 MODULE_DESCRIPTION("Virtio balloon driver");
388 MODULE_LICENSE("GPL");
389