linux/drivers/virtio/virtio_balloon.c
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   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
  31/*
  32 * Balloon device works in 4K page units.  So each page is pointed to by
  33 * multiple balloon pages.  All memory counters in this driver are in balloon
  34 * page units.
  35 */
  36#define VIRTIO_BALLOON_PAGES_PER_PAGE (PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
  37
  38struct virtio_balloon
  39{
  40        struct virtio_device *vdev;
  41        struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
  42
  43        /* Where the ballooning thread waits for config to change. */
  44        wait_queue_head_t config_change;
  45
  46        /* The thread servicing the balloon. */
  47        struct task_struct *thread;
  48
  49        /* Waiting for host to ack the pages we released. */
  50        wait_queue_head_t acked;
  51
  52        /* Number of balloon pages we've told the Host we're not using. */
  53        unsigned int num_pages;
  54        /*
  55         * The pages we've told the Host we're not using.
  56         * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
  57         * to num_pages above.
  58         */
  59        struct list_head pages;
  60
  61        /* The array of pfns we tell the Host about. */
  62        unsigned int num_pfns;
  63        u32 pfns[256];
  64
  65        /* Memory statistics */
  66        int need_stats_update;
  67        struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
  68};
  69
  70static struct virtio_device_id id_table[] = {
  71        { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
  72        { 0 },
  73};
  74
  75static u32 page_to_balloon_pfn(struct page *page)
  76{
  77        unsigned long pfn = page_to_pfn(page);
  78
  79        BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
  80        /* Convert pfn from Linux page size to balloon page size. */
  81        return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
  82}
  83
  84static struct page *balloon_pfn_to_page(u32 pfn)
  85{
  86        BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
  87        return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
  88}
  89
  90static void balloon_ack(struct virtqueue *vq)
  91{
  92        struct virtio_balloon *vb = vq->vdev->priv;
  93
  94        wake_up(&vb->acked);
  95}
  96
  97static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
  98{
  99        struct scatterlist sg;
 100        unsigned int len;
 101
 102        sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 103
 104        /* We should always be able to add one buffer to an empty queue. */
 105        if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
 106                BUG();
 107        virtqueue_kick(vq);
 108
 109        /* When host has read buffer, this completes via balloon_ack */
 110        wait_event(vb->acked, virtqueue_get_buf(vq, &len));
 111}
 112
 113static void set_page_pfns(u32 pfns[], struct page *page)
 114{
 115        unsigned int i;
 116
 117        /* Set balloon pfns pointing at this page.
 118         * Note that the first pfn points at start of the page. */
 119        for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 120                pfns[i] = page_to_balloon_pfn(page) + i;
 121}
 122
 123static void fill_balloon(struct virtio_balloon *vb, size_t num)
 124{
 125        /* We can only do one array worth at a time. */
 126        num = min(num, ARRAY_SIZE(vb->pfns));
 127
 128        for (vb->num_pfns = 0; vb->num_pfns < num;
 129             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 130                struct page *page = alloc_page(GFP_HIGHUSER | __GFP_NORETRY |
 131                                        __GFP_NOMEMALLOC | __GFP_NOWARN);
 132                if (!page) {
 133                        if (printk_ratelimit())
 134                                dev_printk(KERN_INFO, &vb->vdev->dev,
 135                                           "Out of puff! Can't get %zu pages\n",
 136                                           num);
 137                        /* Sleep for at least 1/5 of a second before retry. */
 138                        msleep(200);
 139                        break;
 140                }
 141                set_page_pfns(vb->pfns + vb->num_pfns, page);
 142                vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 143                totalram_pages--;
 144                list_add(&page->lru, &vb->pages);
 145        }
 146
 147        /* Didn't get any?  Oh well. */
 148        if (vb->num_pfns == 0)
 149                return;
 150
 151        tell_host(vb, vb->inflate_vq);
 152}
 153
 154static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 155{
 156        unsigned int i;
 157
 158        /* Find pfns pointing at start of each page, get pages and free them. */
 159        for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 160                __free_page(balloon_pfn_to_page(pfns[i]));
 161                totalram_pages++;
 162        }
 163}
 164
 165static void leak_balloon(struct virtio_balloon *vb, size_t num)
 166{
 167        struct page *page;
 168
 169        /* We can only do one array worth at a time. */
 170        num = min(num, ARRAY_SIZE(vb->pfns));
 171
 172        for (vb->num_pfns = 0; vb->num_pfns < num;
 173             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 174                page = list_first_entry(&vb->pages, struct page, lru);
 175                list_del(&page->lru);
 176                set_page_pfns(vb->pfns + vb->num_pfns, page);
 177                vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 178        }
 179
 180        /*
 181         * Note that if
 182         * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 183         * is true, we *have* to do it in this order
 184         */
 185        tell_host(vb, vb->deflate_vq);
 186        release_pages_by_pfn(vb->pfns, vb->num_pfns);
 187}
 188
 189static inline void update_stat(struct virtio_balloon *vb, int idx,
 190                               u16 tag, u64 val)
 191{
 192        BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 193        vb->stats[idx].tag = tag;
 194        vb->stats[idx].val = val;
 195}
 196
 197#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 198
 199static void update_balloon_stats(struct virtio_balloon *vb)
 200{
 201        unsigned long events[NR_VM_EVENT_ITEMS];
 202        struct sysinfo i;
 203        int idx = 0;
 204
 205        all_vm_events(events);
 206        si_meminfo(&i);
 207
 208        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 209                                pages_to_bytes(events[PSWPIN]));
 210        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 211                                pages_to_bytes(events[PSWPOUT]));
 212        update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 213        update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 214        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 215                                pages_to_bytes(i.freeram));
 216        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 217                                pages_to_bytes(i.totalram));
 218}
 219
 220/*
 221 * While most virtqueues communicate guest-initiated requests to the hypervisor,
 222 * the stats queue operates in reverse.  The driver initializes the virtqueue
 223 * with a single buffer.  From that point forward, all conversations consist of
 224 * a hypervisor request (a call to this function) which directs us to refill
 225 * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 226 * we notify our kthread which does the actual work via stats_handle_request().
 227 */
 228static void stats_request(struct virtqueue *vq)
 229{
 230        struct virtio_balloon *vb = vq->vdev->priv;
 231
 232        vb->need_stats_update = 1;
 233        wake_up(&vb->config_change);
 234}
 235
 236static void stats_handle_request(struct virtio_balloon *vb)
 237{
 238        struct virtqueue *vq;
 239        struct scatterlist sg;
 240        unsigned int len;
 241
 242        vb->need_stats_update = 0;
 243        update_balloon_stats(vb);
 244
 245        vq = vb->stats_vq;
 246        if (!virtqueue_get_buf(vq, &len))
 247                return;
 248        sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 249        if (virtqueue_add_buf(vq, &sg, 1, 0, vb, GFP_KERNEL) < 0)
 250                BUG();
 251        virtqueue_kick(vq);
 252}
 253
 254static void virtballoon_changed(struct virtio_device *vdev)
 255{
 256        struct virtio_balloon *vb = vdev->priv;
 257
 258        wake_up(&vb->config_change);
 259}
 260
 261static inline s64 towards_target(struct virtio_balloon *vb)
 262{
 263        __le32 v;
 264        s64 target;
 265
 266        vb->vdev->config->get(vb->vdev,
 267                              offsetof(struct virtio_balloon_config, num_pages),
 268                              &v, sizeof(v));
 269        target = le32_to_cpu(v);
 270        return target - vb->num_pages;
 271}
 272
 273static void update_balloon_size(struct virtio_balloon *vb)
 274{
 275        __le32 actual = cpu_to_le32(vb->num_pages);
 276
 277        vb->vdev->config->set(vb->vdev,
 278                              offsetof(struct virtio_balloon_config, actual),
 279                              &actual, sizeof(actual));
 280}
 281
 282static int balloon(void *_vballoon)
 283{
 284        struct virtio_balloon *vb = _vballoon;
 285
 286        set_freezable();
 287        while (!kthread_should_stop()) {
 288                s64 diff;
 289
 290                try_to_freeze();
 291                wait_event_interruptible(vb->config_change,
 292                                         (diff = towards_target(vb)) != 0
 293                                         || vb->need_stats_update
 294                                         || kthread_should_stop()
 295                                         || freezing(current));
 296                if (vb->need_stats_update)
 297                        stats_handle_request(vb);
 298                if (diff > 0)
 299                        fill_balloon(vb, diff);
 300                else if (diff < 0)
 301                        leak_balloon(vb, -diff);
 302                update_balloon_size(vb);
 303        }
 304        return 0;
 305}
 306
 307static int init_vqs(struct virtio_balloon *vb)
 308{
 309        struct virtqueue *vqs[3];
 310        vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 311        const char *names[] = { "inflate", "deflate", "stats" };
 312        int err, nvqs;
 313
 314        /*
 315         * We expect two virtqueues: inflate and deflate, and
 316         * optionally stat.
 317         */
 318        nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 319        err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
 320        if (err)
 321                return err;
 322
 323        vb->inflate_vq = vqs[0];
 324        vb->deflate_vq = vqs[1];
 325        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 326                struct scatterlist sg;
 327                vb->stats_vq = vqs[2];
 328
 329                /*
 330                 * Prime this virtqueue with one buffer so the hypervisor can
 331                 * use it to signal us later.
 332                 */
 333                sg_init_one(&sg, vb->stats, sizeof vb->stats);
 334                if (virtqueue_add_buf(vb->stats_vq, &sg, 1, 0, vb, GFP_KERNEL)
 335                    < 0)
 336                        BUG();
 337                virtqueue_kick(vb->stats_vq);
 338        }
 339        return 0;
 340}
 341
 342static int virtballoon_probe(struct virtio_device *vdev)
 343{
 344        struct virtio_balloon *vb;
 345        int err;
 346
 347        vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 348        if (!vb) {
 349                err = -ENOMEM;
 350                goto out;
 351        }
 352
 353        INIT_LIST_HEAD(&vb->pages);
 354        vb->num_pages = 0;
 355        init_waitqueue_head(&vb->config_change);
 356        init_waitqueue_head(&vb->acked);
 357        vb->vdev = vdev;
 358        vb->need_stats_update = 0;
 359
 360        err = init_vqs(vb);
 361        if (err)
 362                goto out_free_vb;
 363
 364        vb->thread = kthread_run(balloon, vb, "vballoon");
 365        if (IS_ERR(vb->thread)) {
 366                err = PTR_ERR(vb->thread);
 367                goto out_del_vqs;
 368        }
 369
 370        return 0;
 371
 372out_del_vqs:
 373        vdev->config->del_vqs(vdev);
 374out_free_vb:
 375        kfree(vb);
 376out:
 377        return err;
 378}
 379
 380static void remove_common(struct virtio_balloon *vb)
 381{
 382        /* There might be pages left in the balloon: free them. */
 383        while (vb->num_pages)
 384                leak_balloon(vb, vb->num_pages);
 385        update_balloon_size(vb);
 386
 387        /* Now we reset the device so we can clean up the queues. */
 388        vb->vdev->config->reset(vb->vdev);
 389
 390        vb->vdev->config->del_vqs(vb->vdev);
 391}
 392
 393static void __devexit virtballoon_remove(struct virtio_device *vdev)
 394{
 395        struct virtio_balloon *vb = vdev->priv;
 396
 397        kthread_stop(vb->thread);
 398        remove_common(vb);
 399        kfree(vb);
 400}
 401
 402#ifdef CONFIG_PM
 403static int virtballoon_freeze(struct virtio_device *vdev)
 404{
 405        struct virtio_balloon *vb = vdev->priv;
 406
 407        /*
 408         * The kthread is already frozen by the PM core before this
 409         * function is called.
 410         */
 411
 412        remove_common(vb);
 413        return 0;
 414}
 415
 416static int virtballoon_restore(struct virtio_device *vdev)
 417{
 418        struct virtio_balloon *vb = vdev->priv;
 419        int ret;
 420
 421        ret = init_vqs(vdev->priv);
 422        if (ret)
 423                return ret;
 424
 425        fill_balloon(vb, towards_target(vb));
 426        update_balloon_size(vb);
 427        return 0;
 428}
 429#endif
 430
 431static unsigned int features[] = {
 432        VIRTIO_BALLOON_F_MUST_TELL_HOST,
 433        VIRTIO_BALLOON_F_STATS_VQ,
 434};
 435
 436static struct virtio_driver virtio_balloon_driver = {
 437        .feature_table = features,
 438        .feature_table_size = ARRAY_SIZE(features),
 439        .driver.name =  KBUILD_MODNAME,
 440        .driver.owner = THIS_MODULE,
 441        .id_table =     id_table,
 442        .probe =        virtballoon_probe,
 443        .remove =       __devexit_p(virtballoon_remove),
 444        .config_changed = virtballoon_changed,
 445#ifdef CONFIG_PM
 446        .freeze =       virtballoon_freeze,
 447        .restore =      virtballoon_restore,
 448#endif
 449};
 450
 451static int __init init(void)
 452{
 453        return register_virtio_driver(&virtio_balloon_driver);
 454}
 455
 456static void __exit fini(void)
 457{
 458        unregister_virtio_driver(&virtio_balloon_driver);
 459}
 460module_init(init);
 461module_exit(fini);
 462
 463MODULE_DEVICE_TABLE(virtio, id_table);
 464MODULE_DESCRIPTION("Virtio balloon driver");
 465MODULE_LICENSE("GPL");
 466
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