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 	/* The pages we've told the Host we're not using. */
44 	unsigned int num_pages;
45 	struct list_head pages;
46 
47 	/* The array of pfns we tell the Host about. */
48 	unsigned int num_pfns;
49 	u32 pfns[256];
50 
51 	/* Memory statistics */
52 	int need_stats_update;
53 	struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
54 };
55 
56 static struct virtio_device_id id_table[] = {
57 	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
58 	{ 0 },
59 };
60 
61 static u32 page_to_balloon_pfn(struct page *page)
62 {
63 	unsigned long pfn = page_to_pfn(page);
64 
65 	BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
66 	/* Convert pfn from Linux page size to balloon page size. */
67 	return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
68 }
69 
70 static void balloon_ack(struct virtqueue *vq)
71 {
72 	struct virtio_balloon *vb;
73 	unsigned int len;
74 
75 	vb = virtqueue_get_buf(vq, &len);
76 	if (vb)
77 		complete(&vb->acked);
78 }
79 
80 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
81 {
82 	struct scatterlist sg;
83 
84 	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
85 
86 	init_completion(&vb->acked);
87 
88 	/* We should always be able to add one buffer to an empty queue. */
89 	if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
90 		BUG();
91 	virtqueue_kick(vq);
92 
93 	/* When host has read buffer, this completes via balloon_ack */
94 	wait_for_completion(&vb->acked);
95 }
96 
97 static void fill_balloon(struct virtio_balloon *vb, size_t num)
98 {
99 	/* We can only do one array worth at a time. */
100 	num = min(num, ARRAY_SIZE(vb->pfns));
101 
102 	for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
103 		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
104 					__GFP_NOMEMALLOC | __GFP_NOWARN);
105 		if (!page) {
106 			if (printk_ratelimit())
107 				dev_printk(KERN_INFO, &vb->vdev->dev,
108 					   "Out of puff! Can't get %zu pages\n",
109 					   num);
110 			/* Sleep for at least 1/5 of a second before retry. */
111 			msleep(200);
112 			break;
113 		}
114 		vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
115 		totalram_pages--;
116 		vb->num_pages++;
117 		list_add(&page->lru, &vb->pages);
118 	}
119 
120 	/* Didn't get any?  Oh well. */
121 	if (vb->num_pfns == 0)
122 		return;
123 
124 	tell_host(vb, vb->inflate_vq);
125 }
126 
127 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
128 {
129 	unsigned int i;
130 
131 	for (i = 0; i < num; i++) {
132 		__free_page(pfn_to_page(pfns[i]));
133 		totalram_pages++;
134 	}
135 }
136 
137 static void leak_balloon(struct virtio_balloon *vb, size_t num)
138 {
139 	struct page *page;
140 
141 	/* We can only do one array worth at a time. */
142 	num = min(num, ARRAY_SIZE(vb->pfns));
143 
144 	for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
145 		page = list_first_entry(&vb->pages, struct page, lru);
146 		list_del(&page->lru);
147 		vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
148 		vb->num_pages--;
149 	}
150 
151 
152 	/*
153 	 * Note that if
154 	 * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
155 	 * is true, we *have* to do it in this order
156 	 */
157 	tell_host(vb, vb->deflate_vq);
158 	release_pages_by_pfn(vb->pfns, vb->num_pfns);
159 }
160 
161 static inline void update_stat(struct virtio_balloon *vb, int idx,
162 			       u16 tag, u64 val)
163 {
164 	BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
165 	vb->stats[idx].tag = tag;
166 	vb->stats[idx].val = val;
167 }
168 
169 #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
170 
171 static void update_balloon_stats(struct virtio_balloon *vb)
172 {
173 	unsigned long events[NR_VM_EVENT_ITEMS];
174 	struct sysinfo i;
175 	int idx = 0;
176 
177 	all_vm_events(events);
178 	si_meminfo(&i);
179 
180 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
181 				pages_to_bytes(events[PSWPIN]));
182 	update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
183 				pages_to_bytes(events[PSWPOUT]));
184 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
185 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
186 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
187 				pages_to_bytes(i.freeram));
188 	update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
189 				pages_to_bytes(i.totalram));
190 }
191 
192 /*
193  * While most virtqueues communicate guest-initiated requests to the hypervisor,
194  * the stats queue operates in reverse.  The driver initializes the virtqueue
195  * with a single buffer.  From that point forward, all conversations consist of
196  * a hypervisor request (a call to this function) which directs us to refill
197  * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
198  * we notify our kthread which does the actual work via stats_handle_request().
199  */
200 static void stats_request(struct virtqueue *vq)
201 {
202 	struct virtio_balloon *vb;
203 	unsigned int len;
204 
205 	vb = virtqueue_get_buf(vq, &len);
206 	if (!vb)
207 		return;
208 	vb->need_stats_update = 1;
209 	wake_up(&vb->config_change);
210 }
211 
212 static void stats_handle_request(struct virtio_balloon *vb)
213 {
214 	struct virtqueue *vq;
215 	struct scatterlist sg;
216 
217 	vb->need_stats_update = 0;
218 	update_balloon_stats(vb);
219 
220 	vq = vb->stats_vq;
221 	sg_init_one(&sg, vb->stats, sizeof(vb->stats));
222 	if (virtqueue_add_buf(vq, &sg, 1, 0, vb) < 0)
223 		BUG();
224 	virtqueue_kick(vq);
225 }
226 
227 static void virtballoon_changed(struct virtio_device *vdev)
228 {
229 	struct virtio_balloon *vb = vdev->priv;
230 
231 	wake_up(&vb->config_change);
232 }
233 
234 static inline s64 towards_target(struct virtio_balloon *vb)
235 {
236 	u32 v;
237 	vb->vdev->config->get(vb->vdev,
238 			      offsetof(struct virtio_balloon_config, num_pages),
239 			      &v, sizeof(v));
240 	return (s64)v - vb->num_pages;
241 }
242 
243 static void update_balloon_size(struct virtio_balloon *vb)
244 {
245 	__le32 actual = cpu_to_le32(vb->num_pages);
246 
247 	vb->vdev->config->set(vb->vdev,
248 			      offsetof(struct virtio_balloon_config, actual),
249 			      &actual, sizeof(actual));
250 }
251 
252 static int balloon(void *_vballoon)
253 {
254 	struct virtio_balloon *vb = _vballoon;
255 
256 	set_freezable();
257 	while (!kthread_should_stop()) {
258 		s64 diff;
259 
260 		try_to_freeze();
261 		wait_event_interruptible(vb->config_change,
262 					 (diff = towards_target(vb)) != 0
263 					 || vb->need_stats_update
264 					 || kthread_should_stop()
265 					 || freezing(current));
266 		if (vb->need_stats_update)
267 			stats_handle_request(vb);
268 		if (diff > 0)
269 			fill_balloon(vb, diff);
270 		else if (diff < 0)
271 			leak_balloon(vb, -diff);
272 		update_balloon_size(vb);
273 	}
274 	return 0;
275 }
276 
277 static int virtballoon_probe(struct virtio_device *vdev)
278 {
279 	struct virtio_balloon *vb;
280 	struct virtqueue *vqs[3];
281 	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
282 	const char *names[] = { "inflate", "deflate", "stats" };
283 	int err, nvqs;
284 
285 	vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
286 	if (!vb) {
287 		err = -ENOMEM;
288 		goto out;
289 	}
290 
291 	INIT_LIST_HEAD(&vb->pages);
292 	vb->num_pages = 0;
293 	init_waitqueue_head(&vb->config_change);
294 	vb->vdev = vdev;
295 	vb->need_stats_update = 0;
296 
297 	/* We expect two virtqueues: inflate and deflate,
298 	 * and optionally stat. */
299 	nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
300 	err = vdev->config->find_vqs(vdev, nvqs, vqs, callbacks, names);
301 	if (err)
302 		goto out_free_vb;
303 
304 	vb->inflate_vq = vqs[0];
305 	vb->deflate_vq = vqs[1];
306 	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
307 		struct scatterlist sg;
308 		vb->stats_vq = vqs[2];
309 
310 		/*
311 		 * Prime this virtqueue with one buffer so the hypervisor can
312 		 * use it to signal us later.
313 		 */
314 		sg_init_one(&sg, vb->stats, sizeof vb->stats);
315 		if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb) < 0)
316 			BUG();
317 		virtqueue_kick(vb->stats_vq);
318 	}
319 
320 	vb->thread = kthread_run(balloon, vb, "vballoon");
321 	if (IS_ERR(vb->thread)) {
322 		err = PTR_ERR(vb->thread);
323 		goto out_del_vqs;
324 	}
325 
326 	return 0;
327 
328 out_del_vqs:
329 	vdev->config->del_vqs(vdev);
330 out_free_vb:
331 	kfree(vb);
332 out:
333 	return err;
334 }
335 
336 static void __devexit virtballoon_remove(struct virtio_device *vdev)
337 {
338 	struct virtio_balloon *vb = vdev->priv;
339 
340 	kthread_stop(vb->thread);
341 
342 	/* There might be pages left in the balloon: free them. */
343 	while (vb->num_pages)
344 		leak_balloon(vb, vb->num_pages);
345 
346 	/* Now we reset the device so we can clean up the queues. */
347 	vdev->config->reset(vdev);
348 
349 	vdev->config->del_vqs(vdev);
350 	kfree(vb);
351 }
352 
353 static unsigned int features[] = {
354 	VIRTIO_BALLOON_F_MUST_TELL_HOST,
355 	VIRTIO_BALLOON_F_STATS_VQ,
356 };
357 
358 static struct virtio_driver virtio_balloon_driver = {
359 	.feature_table = features,
360 	.feature_table_size = ARRAY_SIZE(features),
361 	.driver.name =	KBUILD_MODNAME,
362 	.driver.owner =	THIS_MODULE,
363 	.id_table =	id_table,
364 	.probe =	virtballoon_probe,
365 	.remove =	__devexit_p(virtballoon_remove),
366 	.config_changed = virtballoon_changed,
367 };
368 
369 static int __init init(void)
370 {
371 	return register_virtio_driver(&virtio_balloon_driver);
372 }
373 
374 static void __exit fini(void)
375 {
376 	unregister_virtio_driver(&virtio_balloon_driver);
377 }
378 module_init(init);
379 module_exit(fini);
380 
381 MODULE_DEVICE_TABLE(virtio, id_table);
382 MODULE_DESCRIPTION("Virtio balloon driver");
383 MODULE_LICENSE("GPL");
384