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                totalram_pages--;
 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                balloon_page_free(balloon_pfn_to_page(pfns[i]));
 167                totalram_pages++;
 168        }
 169}
 170
 171static void leak_balloon(struct virtio_balloon *vb, size_t num)
 172{
 173        struct page *page;
 174        struct balloon_dev_info *vb_dev_info = vb->vb_dev_info;
 175
 176        /* We can only do one array worth at a time. */
 177        num = min(num, ARRAY_SIZE(vb->pfns));
 178
 179        mutex_lock(&vb->balloon_lock);
 180        for (vb->num_pfns = 0; vb->num_pfns < num;
 181             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 182                page = balloon_page_dequeue(vb_dev_info);
 183                if (!page)
 184                        break;
 185                set_page_pfns(vb->pfns + vb->num_pfns, page);
 186                vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 187        }
 188
 189        /*
 190         * Note that if
 191         * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 192         * is true, we *have* to do it in this order
 193         */
 194        tell_host(vb, vb->deflate_vq);
 195        mutex_unlock(&vb->balloon_lock);
 196        release_pages_by_pfn(vb->pfns, vb->num_pfns);
 197}
 198
 199static inline void update_stat(struct virtio_balloon *vb, int idx,
 200                               u16 tag, u64 val)
 201{
 202        BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 203        vb->stats[idx].tag = tag;
 204        vb->stats[idx].val = val;
 205}
 206
 207#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 208
 209static void update_balloon_stats(struct virtio_balloon *vb)
 210{
 211        unsigned long events[NR_VM_EVENT_ITEMS];
 212        struct sysinfo i;
 213        int idx = 0;
 214
 215        all_vm_events(events);
 216        si_meminfo(&i);
 217
 218        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 219                                pages_to_bytes(events[PSWPIN]));
 220        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 221                                pages_to_bytes(events[PSWPOUT]));
 222        update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 223        update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 224        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 225                                pages_to_bytes(i.freeram));
 226        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 227                                pages_to_bytes(i.totalram));
 228}
 229
 230/*
 231 * While most virtqueues communicate guest-initiated requests to the hypervisor,
 232 * the stats queue operates in reverse.  The driver initializes the virtqueue
 233 * with a single buffer.  From that point forward, all conversations consist of
 234 * a hypervisor request (a call to this function) which directs us to refill
 235 * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 236 * we notify our kthread which does the actual work via stats_handle_request().
 237 */
 238static void stats_request(struct virtqueue *vq)
 239{
 240        struct virtio_balloon *vb = vq->vdev->priv;
 241
 242        vb->need_stats_update = 1;
 243        wake_up(&vb->config_change);
 244}
 245
 246static void stats_handle_request(struct virtio_balloon *vb)
 247{
 248        struct virtqueue *vq;
 249        struct scatterlist sg;
 250        unsigned int len;
 251
 252        vb->need_stats_update = 0;
 253        update_balloon_stats(vb);
 254
 255        vq = vb->stats_vq;
 256        if (!virtqueue_get_buf(vq, &len))
 257                return;
 258        sg_init_one(&sg, vb->stats, sizeof(vb->stats));
 259        if (virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL) < 0)
 260                BUG();
 261        virtqueue_kick(vq);
 262}
 263
 264static void virtballoon_changed(struct virtio_device *vdev)
 265{
 266        struct virtio_balloon *vb = vdev->priv;
 267
 268        wake_up(&vb->config_change);
 269}
 270
 271static inline s64 towards_target(struct virtio_balloon *vb)
 272{
 273        __le32 v;
 274        s64 target;
 275
 276        vb->vdev->config->get(vb->vdev,
 277                              offsetof(struct virtio_balloon_config, num_pages),
 278                              &v, sizeof(v));
 279        target = le32_to_cpu(v);
 280        return target - vb->num_pages;
 281}
 282
 283static void update_balloon_size(struct virtio_balloon *vb)
 284{
 285        __le32 actual = cpu_to_le32(vb->num_pages);
 286
 287        vb->vdev->config->set(vb->vdev,
 288                              offsetof(struct virtio_balloon_config, actual),
 289                              &actual, sizeof(actual));
 290}
 291
 292static int balloon(void *_vballoon)
 293{
 294        struct virtio_balloon *vb = _vballoon;
 295
 296        set_freezable();
 297        while (!kthread_should_stop()) {
 298                s64 diff;
 299
 300                try_to_freeze();
 301                wait_event_interruptible(vb->config_change,
 302                                         (diff = towards_target(vb)) != 0
 303                                         || vb->need_stats_update
 304                                         || kthread_should_stop()
 305                                         || freezing(current));
 306                if (vb->need_stats_update)
 307                        stats_handle_request(vb);
 308                if (diff > 0)
 309                        fill_balloon(vb, diff);
 310                else if (diff < 0)
 311                        leak_balloon(vb, -diff);
 312                update_balloon_size(vb);
 313        }
 314        return 0;
 315}
 316
 317static int init_vqs(struct virtio_balloon *vb)
 318{
 319        struct virtqueue *vqs[3];
 320        vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
 321        const char *names[] = { "inflate", "deflate", "stats" };
 322        int err, nvqs;
 323
 324        /*
 325         * We expect two virtqueues: inflate and deflate, and
 326         * optionally stat.
 327         */
 328        nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
 329        err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names);
 330        if (err)
 331                return err;
 332
 333        vb->inflate_vq = vqs[0];
 334        vb->deflate_vq = vqs[1];
 335        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 336                struct scatterlist sg;
 337                vb->stats_vq = vqs[2];
 338
 339                /*
 340                 * Prime this virtqueue with one buffer so the hypervisor can
 341                 * use it to signal us later.
 342                 */
 343                sg_init_one(&sg, vb->stats, sizeof vb->stats);
 344                if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
 345                    < 0)
 346                        BUG();
 347                virtqueue_kick(vb->stats_vq);
 348        }
 349        return 0;
 350}
 351
 352static const struct address_space_operations virtio_balloon_aops;
 353#ifdef CONFIG_BALLOON_COMPACTION
 354/*
 355 * virtballoon_migratepage - perform the balloon page migration on behalf of
 356 *                           a compation thread.     (called under page lock)
 357 * @mapping: the page->mapping which will be assigned to the new migrated page.
 358 * @newpage: page that will replace the isolated page after migration finishes.
 359 * @page   : the isolated (old) page that is about to be migrated to newpage.
 360 * @mode   : compaction mode -- not used for balloon page migration.
 361 *
 362 * After a ballooned page gets isolated by compaction procedures, this is the
 363 * function that performs the page migration on behalf of a compaction thread
 364 * The page migration for virtio balloon is done in a simple swap fashion which
 365 * follows these two macro steps:
 366 *  1) insert newpage into vb->pages list and update the host about it;
 367 *  2) update the host about the old page removed from vb->pages list;
 368 *
 369 * This function preforms the balloon page migration task.
 370 * Called through balloon_mapping->a_ops->migratepage
 371 */
 372int virtballoon_migratepage(struct address_space *mapping,
 373                struct page *newpage, struct page *page, enum migrate_mode mode)
 374{
 375        struct balloon_dev_info *vb_dev_info = balloon_page_device(page);
 376        struct virtio_balloon *vb;
 377        unsigned long flags;
 378
 379        BUG_ON(!vb_dev_info);
 380
 381        vb = vb_dev_info->balloon_device;
 382
 383        /*
 384         * In order to avoid lock contention while migrating pages concurrently
 385         * to leak_balloon() or fill_balloon() we just give up the balloon_lock
 386         * this turn, as it is easier to retry the page migration later.
 387         * This also prevents fill_balloon() getting stuck into a mutex
 388         * recursion in the case it ends up triggering memory compaction
 389         * while it is attempting to inflate the ballon.
 390         */
 391        if (!mutex_trylock(&vb->balloon_lock))
 392                return -EAGAIN;
 393
 394        /* balloon's page migration 1st step  -- inflate "newpage" */
 395        spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 396        balloon_page_insert(newpage, mapping, &vb_dev_info->pages);
 397        vb_dev_info->isolated_pages--;
 398        spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 399        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 400        set_page_pfns(vb->pfns, newpage);
 401        tell_host(vb, vb->inflate_vq);
 402
 403        /*
 404         * balloon's page migration 2nd step -- deflate "page"
 405         *
 406         * It's safe to delete page->lru here because this page is at
 407         * an isolated migration list, and this step is expected to happen here
 408         */
 409        balloon_page_delete(page);
 410        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 411        set_page_pfns(vb->pfns, page);
 412        tell_host(vb, vb->deflate_vq);
 413
 414        mutex_unlock(&vb->balloon_lock);
 415
 416        return MIGRATEPAGE_BALLOON_SUCCESS;
 417}
 418
 419/* define the balloon_mapping->a_ops callback to allow balloon page migration */
 420static const struct address_space_operations virtio_balloon_aops = {
 421                        .migratepage = virtballoon_migratepage,
 422};
 423#endif /* CONFIG_BALLOON_COMPACTION */
 424
 425static int virtballoon_probe(struct virtio_device *vdev)
 426{
 427        struct virtio_balloon *vb;
 428        struct address_space *vb_mapping;
 429        struct balloon_dev_info *vb_devinfo;
 430        int err;
 431
 432        vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
 433        if (!vb) {
 434                err = -ENOMEM;
 435                goto out;
 436        }
 437
 438        vb->num_pages = 0;
 439        mutex_init(&vb->balloon_lock);
 440        init_waitqueue_head(&vb->config_change);
 441        init_waitqueue_head(&vb->acked);
 442        vb->vdev = vdev;
 443        vb->need_stats_update = 0;
 444
 445        vb_devinfo = balloon_devinfo_alloc(vb);
 446        if (IS_ERR(vb_devinfo)) {
 447                err = PTR_ERR(vb_devinfo);
 448                goto out_free_vb;
 449        }
 450
 451        vb_mapping = balloon_mapping_alloc(vb_devinfo,
 452                                           (balloon_compaction_check()) ?
 453                                           &virtio_balloon_aops : NULL);
 454        if (IS_ERR(vb_mapping)) {
 455                /*
 456                 * IS_ERR(vb_mapping) && PTR_ERR(vb_mapping) == -EOPNOTSUPP
 457                 * This means !CONFIG_BALLOON_COMPACTION, otherwise we get off.
 458                 */
 459                err = PTR_ERR(vb_mapping);
 460                if (err != -EOPNOTSUPP)
 461                        goto out_free_vb_devinfo;
 462        }
 463
 464        vb->vb_dev_info = vb_devinfo;
 465
 466        err = init_vqs(vb);
 467        if (err)
 468                goto out_free_vb_mapping;
 469
 470        vb->thread = kthread_run(balloon, vb, "vballoon");
 471        if (IS_ERR(vb->thread)) {
 472                err = PTR_ERR(vb->thread);
 473                goto out_del_vqs;
 474        }
 475
 476        return 0;
 477
 478out_del_vqs:
 479        vdev->config->del_vqs(vdev);
 480out_free_vb_mapping:
 481        balloon_mapping_free(vb_mapping);
 482out_free_vb_devinfo:
 483        balloon_devinfo_free(vb_devinfo);
 484out_free_vb:
 485        kfree(vb);
 486out:
 487        return err;
 488}
 489
 490static void remove_common(struct virtio_balloon *vb)
 491{
 492        /* There might be pages left in the balloon: free them. */
 493        while (vb->num_pages)
 494                leak_balloon(vb, vb->num_pages);
 495        update_balloon_size(vb);
 496
 497        /* Now we reset the device so we can clean up the queues. */
 498        vb->vdev->config->reset(vb->vdev);
 499
 500        vb->vdev->config->del_vqs(vb->vdev);
 501}
 502
 503static void virtballoon_remove(struct virtio_device *vdev)
 504{
 505        struct virtio_balloon *vb = vdev->priv;
 506
 507        kthread_stop(vb->thread);
 508        remove_common(vb);
 509        balloon_mapping_free(vb->vb_dev_info->mapping);
 510        balloon_devinfo_free(vb->vb_dev_info);
 511        kfree(vb);
 512}
 513
 514#ifdef CONFIG_PM
 515static int virtballoon_freeze(struct virtio_device *vdev)
 516{
 517        struct virtio_balloon *vb = vdev->priv;
 518
 519        /*
 520         * The kthread is already frozen by the PM core before this
 521         * function is called.
 522         */
 523
 524        remove_common(vb);
 525        return 0;
 526}
 527
 528static int virtballoon_restore(struct virtio_device *vdev)
 529{
 530        struct virtio_balloon *vb = vdev->priv;
 531        int ret;
 532
 533        ret = init_vqs(vdev->priv);
 534        if (ret)
 535                return ret;
 536
 537        fill_balloon(vb, towards_target(vb));
 538        update_balloon_size(vb);
 539        return 0;
 540}
 541#endif
 542
 543static unsigned int features[] = {
 544        VIRTIO_BALLOON_F_MUST_TELL_HOST,
 545        VIRTIO_BALLOON_F_STATS_VQ,
 546};
 547
 548static struct virtio_driver virtio_balloon_driver = {
 549        .feature_table = features,
 550        .feature_table_size = ARRAY_SIZE(features),
 551        .driver.name =  KBUILD_MODNAME,
 552        .driver.owner = THIS_MODULE,
 553        .id_table =     id_table,
 554        .probe =        virtballoon_probe,
 555        .remove =       virtballoon_remove,
 556        .config_changed = virtballoon_changed,
 557#ifdef CONFIG_PM
 558        .freeze =       virtballoon_freeze,
 559        .restore =      virtballoon_restore,
 560#endif
 561};
 562
 563module_virtio_driver(virtio_balloon_driver);
 564MODULE_DEVICE_TABLE(virtio, id_table);
 565MODULE_DESCRIPTION("Virtio balloon driver");
 566MODULE_LICENSE("GPL");
 567
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