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#include <linux/balloon_compaction.h>
  31
  32/*
  33 * Balloon device works in 4K page units.  So each page is pointed to by
  34 * multiple balloon pages.  All memory counters in this driver are in balloon
  35 * page units.
  36 */
  37#define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
  38#define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
  39
  40struct virtio_balloon
  41{
  42        struct virtio_device *vdev;
  43        struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
  44
  45        /* Where the ballooning thread waits for config to change. */
  46        wait_queue_head_t config_change;
  47
  48        /* The thread servicing the balloon. */
  49        struct task_struct *thread;
  50
  51        /* Waiting for host to ack the pages we released. */
  52        wait_queue_head_t acked;
  53
  54        /* Number of balloon pages we've told the Host we're not using. */
  55        unsigned int num_pages;
  56        /*
  57         * The pages we've told the Host we're not using are enqueued
  58         * at vb_dev_info->pages list.
  59         * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
  60         * to num_pages above.
  61         */
  62        struct balloon_dev_info *vb_dev_info;
  63
  64        /* Synchronize access/update to this struct virtio_balloon elements */
  65        struct mutex balloon_lock;
  66
  67        /* The array of pfns we tell the Host about. */
  68        unsigned int num_pfns;
  69        u32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
  70
  71        /* Memory statistics */
  72        int need_stats_update;
  73        struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
  74};
  75
  76static struct virtio_device_id id_table[] = {
  77        { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
  78        { 0 },
  79};
  80
  81static u32 page_to_balloon_pfn(struct page *page)
  82{
  83        unsigned long pfn = page_to_pfn(page);
  84
  85        BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
  86        /* Convert pfn from Linux page size to balloon page size. */
  87        return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
  88}
  89
  90static struct page *balloon_pfn_to_page(u32 pfn)
  91{
  92        BUG_ON(pfn % VIRTIO_BALLOON_PAGES_PER_PAGE);
  93        return pfn_to_page(pfn / VIRTIO_BALLOON_PAGES_PER_PAGE);
  94}
  95
  96static void balloon_ack(struct virtqueue *vq)
  97{
  98        struct virtio_balloon *vb = vq->vdev->priv;
  99
 100        wake_up(&vb->acked);
 101}
 102
 103static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 104{
 105        struct scatterlist sg;
 106        unsigned int len;
 107
 108        sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 109
 110        /* We should always be able to add one buffer to an empty queue. */
 111        if (virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL) < 0)
 112                BUG();
 113        virtqueue_kick(vq);
 114
 115        /* When host has read buffer, this completes via balloon_ack */
 116        wait_event(vb->acked, virtqueue_get_buf(vq, &len));
 117}
 118
 119static void set_page_pfns(u32 pfns[], struct page *page)
 120{
 121        unsigned int i;
 122
 123        /* Set balloon pfns pointing at this page.
 124         * Note that the first pfn points at start of the page. */
 125        for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 126                pfns[i] = page_to_balloon_pfn(page) + i;
 127}
 128
 129static void fill_balloon(struct virtio_balloon *vb, size_t num)
 130{
 131        struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
 132
 133        /* We can only do one array worth at a time. */
 134        num = min(num, ARRAY_SIZE(vb->pfns));
 135
 136        mutex_lock(&vb->balloon_lock);
 137        for (vb->num_pfns = 0; vb->num_pfns < num;
 138             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 139                struct page *page = balloon_page_enqueue(vb_dev_info);
 140
 141                if (!page) {
 142                        dev_info_ratelimited(&vb->vdev->dev,
 143                                             "Out of puff! Can't get %u pages\n",
 144                                             VIRTIO_BALLOON_PAGES_PER_PAGE);
 145                        /* Sleep for at least 1/5 of a second before retry. */
 146                        msleep(200);
 147                        break;
 148                }
 149                set_page_pfns(vb->pfns + vb->num_pfns, page);
 150                vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 151                adjust_managed_page_count(page, -1);
 152        }
 153
 154        /* Did we get any? */
 155        if (vb->num_pfns != 0)
 156                tell_host(vb, vb->inflate_vq);
 157        mutex_unlock(&vb->balloon_lock);
 158}
 159
 160static void release_pages_by_pfn(const u32 pfns[], unsigned int num)
 161{
 162        unsigned int i;
 163
 164        /* Find pfns pointing at start of each page, get pages and free them. */
 165        for (i = 0; i < num; i += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 166                struct page *page = balloon_pfn_to_page(pfns[i]);
 167                balloon_page_free(page);
 168                adjust_managed_page_count(page, 1);
 169        }
 170}
 171
 172static void leak_balloon(struct virtio_balloon *vb, size_t num)
 173{
 174        struct page *page;
 175        struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
 176
 177        /* We can only do one array worth at a time. */
 178        num = min(num, ARRAY_SIZE(vb->pfns));
 179
 180        mutex_lock(&vb->balloon_lock);
 181        for (vb->num_pfns = 0; vb->num_pfns < num;
 182             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 183                page = balloon_page_dequeue(vb_dev_info);
 184                if (!page)
 185                        break;
 186                set_page_pfns(vb->pfns + vb->num_pfns, page);
 187                vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 188        }
 189
 190        /*
 191         * Note that if
 192         * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 193         * is true, we *have* to do it in this order
 194         */
 195        if (vb->num_pfns != 0)
 196                tell_host(vb, vb->deflate_vq);
 197        mutex_unlock(&vb->balloon_lock);
 198        release_pages_by_pfn(vb->pfns, vb->num_pfns);
 199}
 200
 201static inline void update_stat(struct virtio_balloon *vb, int idx,
 202                               u16 tag, u64 val)
 203{
 204        BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 205        vb->stats[idx].tag = tag;
 206        vb->stats[idx].val = val;
 207}
 208
 209#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 210
 211static void update_balloon_stats(struct virtio_balloon *vb)
 212{
 213        unsigned long events[NR_VM_EVENT_ITEMS];
 214        struct sysinfo i;
 215        int idx = 0;
 216
 217        all_vm_events(events);
 218        si_meminfo(&i);
 219
 220        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 221                                pages_to_bytes(events[PSWPIN]));
 222        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 223                                pages_to_bytes(events[PSWPOUT]));
 224        update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 225        update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 226        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 227                                pages_to_bytes(i.freeram));
 228        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 229                                pages_to_bytes(i.totalram));
 230}
 231
 232/*
 233 * While most virtqueues communicate guest-initiated requests to the hypervisor,
 234 * the stats queue operates in reverse.  The driver initializes the virtqueue
 235 * with a single buffer.  From that point forward, all conversations consist of
 236 * a hypervisor request (a call to this function) which directs us to refill
 237 * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 238 * we notify our kthread which does the actual work via stats_handle_request().
 239 */
 240static void stats_request(struct virtqueue *vq)
 241{
 242        struct virtio_balloon *vb = vq->vdev->priv;
 243
 244        vb->need_stats_update = 1;
 245        wake_up(&vb->config_change);
 246}
 247
 248static void stats_handle_request(struct virtio_balloon *vb)
 249{
 250        struct virtqueue *vq;
 251        struct scatterlist sg;
 252        unsigned int len;
 253
 254        vb->need_stats_update = 0;
 255        update_balloon_stats(vb);
 256
 257        vq = vb->stats_vq;
 258        if (!virtqueue_get_buf(vq, &len))
 259                return;
 260        sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 261        if (virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL) < 0)
 262                BUG();
 263        virtqueue_kick(vq);
 264}
 265
 266static void virtballoon_changed(struct virtio_device *vdev)
 267{
 268        struct virtio_balloon *vb = vdev->priv;
 269
 270        wake_up(&vb->config_change);
 271}
 272
 273static inline s64 towards_target(struct virtio_balloon *vb)
 274{
 275        __le32 v;
 276        s64 target;
 277
 278        vb->vdev->config->get(vb->vdev,
 279                              offsetof(struct virtio_balloon_config, num_pages),
 280                              &v, sizeof(v));
 281        target = le32_to_cpu(v);
 282        return target - vb->num_pages;
 283}
 284
 285static void update_balloon_size(struct virtio_balloon *vb)
 286{
 287        __le32 actual = cpu_to_le32(vb->num_pages);
 288
 289        vb->vdev->config->set(vb->vdev,
 290                              offsetof(struct virtio_balloon_config, actual),
 291                              &actual, sizeof(actual));
 292}
 293
 294static int balloon(void *_vballoon)
 295{
 296        struct virtio_balloon *vb = _vballoon;
 297
 298        set_freezable();
 299        while (!kthread_should_stop()) {
 300                s64 diff;
 301
 302                try_to_freeze();
 303                wait_event_interruptible(vb->config_change,
 304                                         (diff = towards_target(vb)) != 0
 305                                         || vb->need_stats_update
 306                                         || kthread_should_stop()
 307                                         || freezing(current));
 308                if (vb->need_stats_update)
 309                        stats_handle_request(vb);
 310                if (diff > 0)
 311                        fill_balloon(vb, diff);
 312                else if (diff < 0)
 313                        leak_balloon(vb, -diff);
 314                update_balloon_size(vb);
 315        }
 316        return 0;
 317}
 318
 319static int init_vqs(struct virtio_balloon *vb)
 320{
 321        struct virtqueue *vqs[3];
 322        vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 323        const char *names[] = { "inflate", "deflate", "stats" };
 324        int err, nvqs;
 325
 326        /*
 327         * We expect two virtqueues: inflate and deflate, and
 328         * optionally stat.
 329         */
 330        nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 331        err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
 332        if (err)
 333                return err;
 334
 335        vb->inflate_vq = vqs[0];
 336        vb->deflate_vq = vqs[1];
 337        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 338                struct scatterlist sg;
 339                vb->stats_vq = vqs[2];
 340
 341                /*
 342                 * Prime this virtqueue with one buffer so the hypervisor can
 343                 * use it to signal us later.
 344                 */
 345                sg_init_one(&sg, vb->stats, sizeof vb->stats);
 346                if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
 347                    < 0)
 348                        BUG();
 349                virtqueue_kick(vb->stats_vq);
 350        }
 351        return 0;
 352}
 353
 354static const struct address_space_operations virtio_balloon_aops;
 355#ifdef CONFIG_BALLOON_COMPACTION
 356/*
 357 * virtballoon_migratepage - perform the balloon page migration on behalf of
 358 *                           a compation thread.     (called under page lock)
 359 * @mapping: the page->mapping which will be assigned to the new migrated page.
 360 * @newpage: page that will replace the isolated page after migration finishes.
 361 * @page   : the isolated (old) page that is about to be migrated to newpage.
 362 * @mode   : compaction mode -- not used for balloon page migration.
 363 *
 364 * After a ballooned page gets isolated by compaction procedures, this is the
 365 * function that performs the page migration on behalf of a compaction thread
 366 * The page migration for virtio balloon is done in a simple swap fashion which
 367 * follows these two macro steps:
 368 *  1) insert newpage into vb->pages list and update the host about it;
 369 *  2) update the host about the old page removed from vb->pages list;
 370 *
 371 * This function preforms the balloon page migration task.
 372 * Called through balloon_mapping->a_ops->migratepage
 373 */
 374int virtballoon_migratepage(struct address_space *mapping,
 375                struct page *newpage, struct page *page, enum migrate_mode mode)
 376{
 377        struct balloon_dev_info *vb_dev_info = balloon_page_device(page);
 378        struct virtio_balloon *vb;
 379        unsigned long flags;
 380
 381        BUG_ON(!vb_dev_info);
 382
 383        vb = vb_dev_info->balloon_device;
 384
 385        /*
 386         * In order to avoid lock contention while migrating pages concurrently
 387         * to leak_balloon() or fill_balloon() we just give up the balloon_lock
 388         * this turn, as it is easier to retry the page migration later.
 389         * This also prevents fill_balloon() getting stuck into a mutex
 390         * recursion in the case it ends up triggering memory compaction
 391         * while it is attempting to inflate the ballon.
 392         */
 393        if (!mutex_trylock(&vb->balloon_lock))
 394                return -EAGAIN;
 395
 396        /* balloon's page migration 1st step  -- inflate "newpage" */
 397        spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 398        balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
 399        vb_dev_info->isolated_pages--;
 400        spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 401        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 402        set_page_pfns(vb->pfns, newpage);
 403        tell_host(vb, vb->inflate_vq);
 404
 405        /*
 406         * balloon's page migration 2nd step -- deflate "page"
 407         *
 408         * It's safe to delete page->lru here because this page is at
 409         * an isolated migration list, and this step is expected to happen here
 410         */
 411        balloon_page_delete(page);
 412        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 413        set_page_pfns(vb->pfns, page);
 414        tell_host(vb, vb->deflate_vq);
 415
 416        mutex_unlock(&vb->balloon_lock);
 417
 418        return MIGRATEPAGE_BALLOON_SUCCESS;
 419}
 420
 421/* define the balloon_mapping->a_ops callback to allow balloon page migration */
 422static const struct address_space_operations virtio_balloon_aops = {
 423                        .migratepage = virtballoon_migratepage,
 424};
 425#endif /* CONFIG_BALLOON_COMPACTION */
 426
 427static int virtballoon_probe(struct virtio_device *vdev)
 428{
 429        struct virtio_balloon *vb;
 430        struct address_space *vb_mapping;
 431        struct balloon_dev_info *vb_devinfo;
 432        int err;
 433
 434        vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 435        if (!vb) {
 436                err = -ENOMEM;
 437                goto out;
 438        }
 439
 440        vb->num_pages = 0;
 441        mutex_init(&vb->balloon_lock);
 442        init_waitqueue_head(&vb->config_change);
 443        init_waitqueue_head(&vb->acked);
 444        vb->vdev = vdev;
 445        vb->need_stats_update = 0;
 446
 447        vb_devinfo = balloon_devinfo_alloc(vb);
 448        if (IS_ERR(vb_devinfo)) {
 449                err = PTR_ERR(vb_devinfo);
 450                goto out_free_vb;
 451        }
 452
 453        vb_mapping = balloon_mapping_alloc(vb_devinfo,
 454                                           (balloon_compaction_check()) ?
 455                                           &virtio_balloon_aops : NULL);
 456        if (IS_ERR(vb_mapping)) {
 457                /*
 458                 * IS_ERR(vb_mapping) && PTR_ERR(vb_mapping) == -EOPNOTSUPP
 459                 * This means !CONFIG_BALLOON_COMPACTION, otherwise we get off.
 460                 */
 461                err = PTR_ERR(vb_mapping);
 462                if (err != -EOPNOTSUPP)
 463                        goto out_free_vb_devinfo;
 464        }
 465
 466        vb->vb_dev_info = vb_devinfo;
 467
 468        err = init_vqs(vb);
 469        if (err)
 470                goto out_free_vb_mapping;
 471
 472        vb->thread = kthread_run(balloon, vb, "vballoon");
 473        if (IS_ERR(vb->thread)) {
 474                err = PTR_ERR(vb->thread);
 475                goto out_del_vqs;
 476        }
 477
 478        return 0;
 479
 480out_del_vqs:
 481        vdev->config->del_vqs(vdev);
 482out_free_vb_mapping:
 483        balloon_mapping_free(vb_mapping);
 484out_free_vb_devinfo:
 485        balloon_devinfo_free(vb_devinfo);
 486out_free_vb:
 487        kfree(vb);
 488out:
 489        return err;
 490}
 491
 492static void remove_common(struct virtio_balloon *vb)
 493{
 494        /* There might be pages left in the balloon: free them. */
 495        while (vb->num_pages)
 496                leak_balloon(vb, vb->num_pages);
 497        update_balloon_size(vb);
 498
 499        /* Now we reset the device so we can clean up the queues. */
 500        vb->vdev->config->reset(vb->vdev);
 501
 502        vb->vdev->config->del_vqs(vb->vdev);
 503}
 504
 505static void virtballoon_remove(struct virtio_device *vdev)
 506{
 507        struct virtio_balloon *vb = vdev->priv;
 508
 509        kthread_stop(vb->thread);
 510        remove_common(vb);
 511        balloon_mapping_free(vb->vb_dev_info->mapping);
 512        balloon_devinfo_free(vb->vb_dev_info);
 513        kfree(vb);
 514}
 515
 516#ifdef CONFIG_PM
 517static int virtballoon_freeze(struct virtio_device *vdev)
 518{
 519        struct virtio_balloon *vb = vdev->priv;
 520
 521        /*
 522         * The kthread is already frozen by the PM core before this
 523         * function is called.
 524         */
 525
 526        remove_common(vb);
 527        return 0;
 528}
 529
 530static int virtballoon_restore(struct virtio_device *vdev)
 531{
 532        struct virtio_balloon *vb = vdev->priv;
 533        int ret;
 534
 535        ret = init_vqs(vdev->priv);
 536        if (ret)
 537                return ret;
 538
 539        fill_balloon(vb, towards_target(vb));
 540        update_balloon_size(vb);
 541        return 0;
 542}
 543#endif
 544
 545static unsigned int features[] = {
 546        VIRTIO_BALLOON_F_MUST_TELL_HOST,
 547        VIRTIO_BALLOON_F_STATS_VQ,
 548};
 549
 550static struct virtio_driver virtio_balloon_driver = {
 551        .feature_table = features,
 552        .feature_table_size = ARRAY_SIZE(features),
 553        .driver.name =  KBUILD_MODNAME,
 554        .driver.owner = THIS_MODULE,
 555        .id_table =     id_table,
 556        .probe =        virtballoon_probe,
 557        .remove =       virtballoon_remove,
 558        .config_changed = virtballoon_changed,
 559#ifdef CONFIG_PM
 560        .freeze =       virtballoon_freeze,
 561        .restore =      virtballoon_restore,
 562#endif
 563};
 564
 565module_virtio_driver(virtio_balloon_driver);
 566MODULE_DEVICE_TABLE(virtio, id_table);
 567MODULE_DESCRIPTION("Virtio balloon driver");
 568MODULE_LICENSE("GPL");
 569
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