xref: /linux/drivers/virtio/virtio_balloon.c (revision ae7f6711d6231c9ba54feb5ba9856c3775e482f8)
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 
28 struct virtio_balloon
29 {
30 	struct virtio_device *vdev;
31 	struct virtqueue *inflate_vq, *deflate_vq;
32 
33 	/* Where the ballooning thread waits for config to change. */
34 	wait_queue_head_t config_change;
35 
36 	/* The thread servicing the balloon. */
37 	struct task_struct *thread;
38 
39 	/* Waiting for host to ack the pages we released. */
40 	struct completion acked;
41 
42 	/* Do we have to tell Host *before* we reuse pages? */
43 	bool tell_host_first;
44 
45 	/* The pages we've told the Host we're not using. */
46 	unsigned int num_pages;
47 	struct list_head pages;
48 
49 	/* The array of pfns we tell the Host about. */
50 	unsigned int num_pfns;
51 	u32 pfns[256];
52 };
53 
54 static struct virtio_device_id id_table[] = {
55 	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
56 	{ 0 },
57 };
58 
59 static u32 page_to_balloon_pfn(struct page *page)
60 {
61 	unsigned long pfn = page_to_pfn(page);
62 
63 	BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
64 	/* Convert pfn from Linux page size to balloon page size. */
65 	return pfn >> (PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT);
66 }
67 
68 static void balloon_ack(struct virtqueue *vq)
69 {
70 	struct virtio_balloon *vb;
71 	unsigned int len;
72 
73 	vb = vq->vq_ops->get_buf(vq, &len);
74 	if (vb)
75 		complete(&vb->acked);
76 }
77 
78 static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
79 {
80 	struct scatterlist sg;
81 
82 	sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
83 
84 	init_completion(&vb->acked);
85 
86 	/* We should always be able to add one buffer to an empty queue. */
87 	if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
88 		BUG();
89 	vq->vq_ops->kick(vq);
90 
91 	/* When host has read buffer, this completes via balloon_ack */
92 	wait_for_completion(&vb->acked);
93 }
94 
95 static void fill_balloon(struct virtio_balloon *vb, size_t num)
96 {
97 	/* We can only do one array worth at a time. */
98 	num = min(num, ARRAY_SIZE(vb->pfns));
99 
100 	for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
101 		struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY);
102 		if (!page) {
103 			if (printk_ratelimit())
104 				dev_printk(KERN_INFO, &vb->vdev->dev,
105 					   "Out of puff! Can't get %zu pages\n",
106 					   num);
107 			/* Sleep for at least 1/5 of a second before retry. */
108 			msleep(200);
109 			break;
110 		}
111 		vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
112 		totalram_pages--;
113 		vb->num_pages++;
114 		list_add(&page->lru, &vb->pages);
115 	}
116 
117 	/* Didn't get any?  Oh well. */
118 	if (vb->num_pfns == 0)
119 		return;
120 
121 	tell_host(vb, vb->inflate_vq);
122 }
123 
124 static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
125 {
126 	unsigned int i;
127 
128 	for (i = 0; i < num; i++) {
129 		__free_page(pfn_to_page(pfns[i]));
130 		totalram_pages++;
131 	}
132 }
133 
134 static void leak_balloon(struct virtio_balloon *vb, size_t num)
135 {
136 	struct page *page;
137 
138 	/* We can only do one array worth at a time. */
139 	num = min(num, ARRAY_SIZE(vb->pfns));
140 
141 	for (vb->num_pfns = 0; vb->num_pfns < num; vb->num_pfns++) {
142 		page = list_first_entry(&vb->pages, struct page, lru);
143 		list_del(&page->lru);
144 		vb->pfns[vb->num_pfns] = page_to_balloon_pfn(page);
145 		vb->num_pages--;
146 	}
147 
148 	if (vb->tell_host_first) {
149 		tell_host(vb, vb->deflate_vq);
150 		release_pages_by_pfn(vb->pfns, vb->num_pfns);
151 	} else {
152 		release_pages_by_pfn(vb->pfns, vb->num_pfns);
153 		tell_host(vb, vb->deflate_vq);
154 	}
155 }
156 
157 static void virtballoon_changed(struct virtio_device *vdev)
158 {
159 	struct virtio_balloon *vb = vdev->priv;
160 
161 	wake_up(&vb->config_change);
162 }
163 
164 static inline s64 towards_target(struct virtio_balloon *vb)
165 {
166 	u32 v;
167 	vb->vdev->config->get(vb->vdev,
168 			      offsetof(struct virtio_balloon_config, num_pages),
169 			      &v, sizeof(v));
170 	return (s64)v - vb->num_pages;
171 }
172 
173 static void update_balloon_size(struct virtio_balloon *vb)
174 {
175 	__le32 actual = cpu_to_le32(vb->num_pages);
176 
177 	vb->vdev->config->set(vb->vdev,
178 			      offsetof(struct virtio_balloon_config, actual),
179 			      &actual, sizeof(actual));
180 }
181 
182 static int balloon(void *_vballoon)
183 {
184 	struct virtio_balloon *vb = _vballoon;
185 
186 	set_freezable();
187 	while (!kthread_should_stop()) {
188 		s64 diff;
189 
190 		try_to_freeze();
191 		wait_event_interruptible(vb->config_change,
192 					 (diff = towards_target(vb)) != 0
193 					 || kthread_should_stop()
194 					 || freezing(current));
195 		if (diff > 0)
196 			fill_balloon(vb, diff);
197 		else if (diff < 0)
198 			leak_balloon(vb, -diff);
199 		update_balloon_size(vb);
200 	}
201 	return 0;
202 }
203 
204 static int virtballoon_probe(struct virtio_device *vdev)
205 {
206 	struct virtio_balloon *vb;
207 	struct virtqueue *vqs[2];
208 	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack };
209 	const char *names[] = { "inflate", "deflate" };
210 	int err;
211 
212 	vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
213 	if (!vb) {
214 		err = -ENOMEM;
215 		goto out;
216 	}
217 
218 	INIT_LIST_HEAD(&vb->pages);
219 	vb->num_pages = 0;
220 	init_waitqueue_head(&vb->config_change);
221 	vb->vdev = vdev;
222 
223 	/* We expect two virtqueues. */
224 	err = vdev->config->find_vqs(vdev, 2, vqs, callbacks, names);
225 	if (err)
226 		goto out_free_vb;
227 
228 	vb->inflate_vq = vqs[0];
229 	vb->deflate_vq = vqs[1];
230 
231 	vb->thread = kthread_run(balloon, vb, "vballoon");
232 	if (IS_ERR(vb->thread)) {
233 		err = PTR_ERR(vb->thread);
234 		goto out_del_vqs;
235 	}
236 
237 	vb->tell_host_first
238 		= virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
239 
240 	return 0;
241 
242 out_del_vqs:
243 	vdev->config->del_vqs(vdev);
244 out_free_vb:
245 	kfree(vb);
246 out:
247 	return err;
248 }
249 
250 static void __devexit virtballoon_remove(struct virtio_device *vdev)
251 {
252 	struct virtio_balloon *vb = vdev->priv;
253 
254 	kthread_stop(vb->thread);
255 
256 	/* There might be pages left in the balloon: free them. */
257 	while (vb->num_pages)
258 		leak_balloon(vb, vb->num_pages);
259 
260 	/* Now we reset the device so we can clean up the queues. */
261 	vdev->config->reset(vdev);
262 
263 	vdev->config->del_vqs(vdev);
264 	kfree(vb);
265 }
266 
267 static unsigned int features[] = { VIRTIO_BALLOON_F_MUST_TELL_HOST };
268 
269 static struct virtio_driver virtio_balloon_driver = {
270 	.feature_table = features,
271 	.feature_table_size = ARRAY_SIZE(features),
272 	.driver.name =	KBUILD_MODNAME,
273 	.driver.owner =	THIS_MODULE,
274 	.id_table =	id_table,
275 	.probe =	virtballoon_probe,
276 	.remove =	__devexit_p(virtballoon_remove),
277 	.config_changed = virtballoon_changed,
278 };
279 
280 static int __init init(void)
281 {
282 	return register_virtio_driver(&virtio_balloon_driver);
283 }
284 
285 static void __exit fini(void)
286 {
287 	unregister_virtio_driver(&virtio_balloon_driver);
288 }
289 module_init(init);
290 module_exit(fini);
291 
292 MODULE_DEVICE_TABLE(virtio, id_table);
293 MODULE_DESCRIPTION("Virtio balloon driver");
294 MODULE_LICENSE("GPL");
295