linux/drivers/virtio/virtio_balloon.c
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   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * Virtio balloon implementation, inspired by Dor Laor and Marcelo
   4 * Tosatti's implementations.
   5 *
   6 *  Copyright 2008 Rusty Russell IBM Corporation
   7 */
   8
   9#include <linux/virtio.h>
  10#include <linux/virtio_balloon.h>
  11#include <linux/swap.h>
  12#include <linux/workqueue.h>
  13#include <linux/delay.h>
  14#include <linux/slab.h>
  15#include <linux/module.h>
  16#include <linux/balloon_compaction.h>
  17#include <linux/wait.h>
  18#include <linux/mm.h>
  19#include <linux/mount.h>
  20#include <linux/magic.h>
  21#include <linux/pseudo_fs.h>
  22
  23/*
  24 * Balloon device works in 4K page units.  So each page is pointed to by
  25 * multiple balloon pages.  All memory counters in this driver are in balloon
  26 * page units.
  27 */
  28#define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
  29#define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
  30#define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
  31
  32#define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
  33                                             __GFP_NOMEMALLOC)
  34/* The order of free page blocks to report to host */
  35#define VIRTIO_BALLOON_FREE_PAGE_ORDER (MAX_ORDER - 1)
  36/* The size of a free page block in bytes */
  37#define VIRTIO_BALLOON_FREE_PAGE_SIZE \
  38        (1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
  39
  40#ifdef CONFIG_BALLOON_COMPACTION
  41static struct vfsmount *balloon_mnt;
  42#endif
  43
  44enum virtio_balloon_vq {
  45        VIRTIO_BALLOON_VQ_INFLATE,
  46        VIRTIO_BALLOON_VQ_DEFLATE,
  47        VIRTIO_BALLOON_VQ_STATS,
  48        VIRTIO_BALLOON_VQ_FREE_PAGE,
  49        VIRTIO_BALLOON_VQ_MAX
  50};
  51
  52enum virtio_balloon_config_read {
  53        VIRTIO_BALLOON_CONFIG_READ_CMD_ID = 0,
  54};
  55
  56struct virtio_balloon {
  57        struct virtio_device *vdev;
  58        struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
  59
  60        /* Balloon's own wq for cpu-intensive work items */
  61        struct workqueue_struct *balloon_wq;
  62        /* The free page reporting work item submitted to the balloon wq */
  63        struct work_struct report_free_page_work;
  64
  65        /* The balloon servicing is delegated to a freezable workqueue. */
  66        struct work_struct update_balloon_stats_work;
  67        struct work_struct update_balloon_size_work;
  68
  69        /* Prevent updating balloon when it is being canceled. */
  70        spinlock_t stop_update_lock;
  71        bool stop_update;
  72        /* Bitmap to indicate if reading the related config fields are needed */
  73        unsigned long config_read_bitmap;
  74
  75        /* The list of allocated free pages, waiting to be given back to mm */
  76        struct list_head free_page_list;
  77        spinlock_t free_page_list_lock;
  78        /* The number of free page blocks on the above list */
  79        unsigned long num_free_page_blocks;
  80        /*
  81         * The cmd id received from host.
  82         * Read it via virtio_balloon_cmd_id_received to get the latest value
  83         * sent from host.
  84         */
  85        u32 cmd_id_received_cache;
  86        /* The cmd id that is actively in use */
  87        __virtio32 cmd_id_active;
  88        /* Buffer to store the stop sign */
  89        __virtio32 cmd_id_stop;
  90
  91        /* Waiting for host to ack the pages we released. */
  92        wait_queue_head_t acked;
  93
  94        /* Number of balloon pages we've told the Host we're not using. */
  95        unsigned int num_pages;
  96        /*
  97         * The pages we've told the Host we're not using are enqueued
  98         * at vb_dev_info->pages list.
  99         * Each page on this list adds VIRTIO_BALLOON_PAGES_PER_PAGE
 100         * to num_pages above.
 101         */
 102        struct balloon_dev_info vb_dev_info;
 103
 104        /* Synchronize access/update to this struct virtio_balloon elements */
 105        struct mutex balloon_lock;
 106
 107        /* The array of pfns we tell the Host about. */
 108        unsigned int num_pfns;
 109        __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX];
 110
 111        /* Memory statistics */
 112        struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR];
 113
 114        /* To register a shrinker to shrink memory upon memory pressure */
 115        struct shrinker shrinker;
 116};
 117
 118static struct virtio_device_id id_table[] = {
 119        { VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID },
 120        { 0 },
 121};
 122
 123static u32 page_to_balloon_pfn(struct page *page)
 124{
 125        unsigned long pfn = page_to_pfn(page);
 126
 127        BUILD_BUG_ON(PAGE_SHIFT < VIRTIO_BALLOON_PFN_SHIFT);
 128        /* Convert pfn from Linux page size to balloon page size. */
 129        return pfn * VIRTIO_BALLOON_PAGES_PER_PAGE;
 130}
 131
 132static void balloon_ack(struct virtqueue *vq)
 133{
 134        struct virtio_balloon *vb = vq->vdev->priv;
 135
 136        wake_up(&vb->acked);
 137}
 138
 139static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
 140{
 141        struct scatterlist sg;
 142        unsigned int len;
 143
 144        sg_init_one(&sg, vb->pfns, sizeof(vb->pfns[0]) * vb->num_pfns);
 145
 146        /* We should always be able to add one buffer to an empty queue. */
 147        virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 148        virtqueue_kick(vq);
 149
 150        /* When host has read buffer, this completes via balloon_ack */
 151        wait_event(vb->acked, virtqueue_get_buf(vq, &len));
 152
 153}
 154
 155static void set_page_pfns(struct virtio_balloon *vb,
 156                          __virtio32 pfns[], struct page *page)
 157{
 158        unsigned int i;
 159
 160        /*
 161         * Set balloon pfns pointing at this page.
 162         * Note that the first pfn points at start of the page.
 163         */
 164        for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++)
 165                pfns[i] = cpu_to_virtio32(vb->vdev,
 166                                          page_to_balloon_pfn(page) + i);
 167}
 168
 169static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
 170{
 171        unsigned num_allocated_pages;
 172        unsigned num_pfns;
 173        struct page *page;
 174        LIST_HEAD(pages);
 175
 176        /* We can only do one array worth at a time. */
 177        num = min(num, ARRAY_SIZE(vb->pfns));
 178
 179        for (num_pfns = 0; num_pfns < num;
 180             num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 181                struct page *page = balloon_page_alloc();
 182
 183                if (!page) {
 184                        dev_info_ratelimited(&vb->vdev->dev,
 185                                             "Out of puff! Can't get %u pages\n",
 186                                             VIRTIO_BALLOON_PAGES_PER_PAGE);
 187                        /* Sleep for at least 1/5 of a second before retry. */
 188                        msleep(200);
 189                        break;
 190                }
 191
 192                balloon_page_push(&pages, page);
 193        }
 194
 195        mutex_lock(&vb->balloon_lock);
 196
 197        vb->num_pfns = 0;
 198
 199        while ((page = balloon_page_pop(&pages))) {
 200                balloon_page_enqueue(&vb->vb_dev_info, page);
 201
 202                set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
 203                vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
 204                if (!virtio_has_feature(vb->vdev,
 205                                        VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 206                        adjust_managed_page_count(page, -1);
 207                vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
 208        }
 209
 210        num_allocated_pages = vb->num_pfns;
 211        /* Did we get any? */
 212        if (vb->num_pfns != 0)
 213                tell_host(vb, vb->inflate_vq);
 214        mutex_unlock(&vb->balloon_lock);
 215
 216        return num_allocated_pages;
 217}
 218
 219static void release_pages_balloon(struct virtio_balloon *vb,
 220                                 struct list_head *pages)
 221{
 222        struct page *page, *next;
 223
 224        list_for_each_entry_safe(page, next, pages, lru) {
 225                if (!virtio_has_feature(vb->vdev,
 226                                        VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 227                        adjust_managed_page_count(page, 1);
 228                list_del(&page->lru);
 229                put_page(page); /* balloon reference */
 230        }
 231}
 232
 233static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
 234{
 235        unsigned num_freed_pages;
 236        struct page *page;
 237        struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info;
 238        LIST_HEAD(pages);
 239
 240        /* We can only do one array worth at a time. */
 241        num = min(num, ARRAY_SIZE(vb->pfns));
 242
 243        mutex_lock(&vb->balloon_lock);
 244        /* We can't release more pages than taken */
 245        num = min(num, (size_t)vb->num_pages);
 246        for (vb->num_pfns = 0; vb->num_pfns < num;
 247             vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 248                page = balloon_page_dequeue(vb_dev_info);
 249                if (!page)
 250                        break;
 251                set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
 252                list_add(&page->lru, &pages);
 253                vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE;
 254        }
 255
 256        num_freed_pages = vb->num_pfns;
 257        /*
 258         * Note that if
 259         * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
 260         * is true, we *have* to do it in this order
 261         */
 262        if (vb->num_pfns != 0)
 263                tell_host(vb, vb->deflate_vq);
 264        release_pages_balloon(vb, &pages);
 265        mutex_unlock(&vb->balloon_lock);
 266        return num_freed_pages;
 267}
 268
 269static inline void update_stat(struct virtio_balloon *vb, int idx,
 270                               u16 tag, u64 val)
 271{
 272        BUG_ON(idx >= VIRTIO_BALLOON_S_NR);
 273        vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag);
 274        vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val);
 275}
 276
 277#define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
 278
 279static unsigned int update_balloon_stats(struct virtio_balloon *vb)
 280{
 281        unsigned long events[NR_VM_EVENT_ITEMS];
 282        struct sysinfo i;
 283        unsigned int idx = 0;
 284        long available;
 285        unsigned long caches;
 286
 287        all_vm_events(events);
 288        si_meminfo(&i);
 289
 290        available = si_mem_available();
 291        caches = global_node_page_state(NR_FILE_PAGES);
 292
 293#ifdef CONFIG_VM_EVENT_COUNTERS
 294        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
 295                                pages_to_bytes(events[PSWPIN]));
 296        update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
 297                                pages_to_bytes(events[PSWPOUT]));
 298        update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT, events[PGMAJFAULT]);
 299        update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT, events[PGFAULT]);
 300#ifdef CONFIG_HUGETLB_PAGE
 301        update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGALLOC,
 302                    events[HTLB_BUDDY_PGALLOC]);
 303        update_stat(vb, idx++, VIRTIO_BALLOON_S_HTLB_PGFAIL,
 304                    events[HTLB_BUDDY_PGALLOC_FAIL]);
 305#endif
 306#endif
 307        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
 308                                pages_to_bytes(i.freeram));
 309        update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
 310                                pages_to_bytes(i.totalram));
 311        update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
 312                                pages_to_bytes(available));
 313        update_stat(vb, idx++, VIRTIO_BALLOON_S_CACHES,
 314                                pages_to_bytes(caches));
 315
 316        return idx;
 317}
 318
 319/*
 320 * While most virtqueues communicate guest-initiated requests to the hypervisor,
 321 * the stats queue operates in reverse.  The driver initializes the virtqueue
 322 * with a single buffer.  From that point forward, all conversations consist of
 323 * a hypervisor request (a call to this function) which directs us to refill
 324 * the virtqueue with a fresh stats buffer.  Since stats collection can sleep,
 325 * we delegate the job to a freezable workqueue that will do the actual work via
 326 * stats_handle_request().
 327 */
 328static void stats_request(struct virtqueue *vq)
 329{
 330        struct virtio_balloon *vb = vq->vdev->priv;
 331
 332        spin_lock(&vb->stop_update_lock);
 333        if (!vb->stop_update)
 334                queue_work(system_freezable_wq, &vb->update_balloon_stats_work);
 335        spin_unlock(&vb->stop_update_lock);
 336}
 337
 338static void stats_handle_request(struct virtio_balloon *vb)
 339{
 340        struct virtqueue *vq;
 341        struct scatterlist sg;
 342        unsigned int len, num_stats;
 343
 344        num_stats = update_balloon_stats(vb);
 345
 346        vq = vb->stats_vq;
 347        if (!virtqueue_get_buf(vq, &len))
 348                return;
 349        sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
 350        virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
 351        virtqueue_kick(vq);
 352}
 353
 354static inline s64 towards_target(struct virtio_balloon *vb)
 355{
 356        s64 target;
 357        u32 num_pages;
 358
 359        virtio_cread(vb->vdev, struct virtio_balloon_config, num_pages,
 360                     &num_pages);
 361
 362        /* Legacy balloon config space is LE, unlike all other devices. */
 363        if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 364                num_pages = le32_to_cpu((__force __le32)num_pages);
 365
 366        target = num_pages;
 367        return target - vb->num_pages;
 368}
 369
 370/* Gives back @num_to_return blocks of free pages to mm. */
 371static unsigned long return_free_pages_to_mm(struct virtio_balloon *vb,
 372                                             unsigned long num_to_return)
 373{
 374        struct page *page;
 375        unsigned long num_returned;
 376
 377        spin_lock_irq(&vb->free_page_list_lock);
 378        for (num_returned = 0; num_returned < num_to_return; num_returned++) {
 379                page = balloon_page_pop(&vb->free_page_list);
 380                if (!page)
 381                        break;
 382                free_pages((unsigned long)page_address(page),
 383                           VIRTIO_BALLOON_FREE_PAGE_ORDER);
 384        }
 385        vb->num_free_page_blocks -= num_returned;
 386        spin_unlock_irq(&vb->free_page_list_lock);
 387
 388        return num_returned;
 389}
 390
 391static void virtio_balloon_queue_free_page_work(struct virtio_balloon *vb)
 392{
 393        if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 394                return;
 395
 396        /* No need to queue the work if the bit was already set. */
 397        if (test_and_set_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
 398                             &vb->config_read_bitmap))
 399                return;
 400
 401        queue_work(vb->balloon_wq, &vb->report_free_page_work);
 402}
 403
 404static void virtballoon_changed(struct virtio_device *vdev)
 405{
 406        struct virtio_balloon *vb = vdev->priv;
 407        unsigned long flags;
 408
 409        spin_lock_irqsave(&vb->stop_update_lock, flags);
 410        if (!vb->stop_update) {
 411                queue_work(system_freezable_wq,
 412                           &vb->update_balloon_size_work);
 413                virtio_balloon_queue_free_page_work(vb);
 414        }
 415        spin_unlock_irqrestore(&vb->stop_update_lock, flags);
 416}
 417
 418static void update_balloon_size(struct virtio_balloon *vb)
 419{
 420        u32 actual = vb->num_pages;
 421
 422        /* Legacy balloon config space is LE, unlike all other devices. */
 423        if (!virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1))
 424                actual = (__force u32)cpu_to_le32(actual);
 425
 426        virtio_cwrite(vb->vdev, struct virtio_balloon_config, actual,
 427                      &actual);
 428}
 429
 430static void update_balloon_stats_func(struct work_struct *work)
 431{
 432        struct virtio_balloon *vb;
 433
 434        vb = container_of(work, struct virtio_balloon,
 435                          update_balloon_stats_work);
 436        stats_handle_request(vb);
 437}
 438
 439static void update_balloon_size_func(struct work_struct *work)
 440{
 441        struct virtio_balloon *vb;
 442        s64 diff;
 443
 444        vb = container_of(work, struct virtio_balloon,
 445                          update_balloon_size_work);
 446        diff = towards_target(vb);
 447
 448        if (!diff)
 449                return;
 450
 451        if (diff > 0)
 452                diff -= fill_balloon(vb, diff);
 453        else
 454                diff += leak_balloon(vb, -diff);
 455        update_balloon_size(vb);
 456
 457        if (diff)
 458                queue_work(system_freezable_wq, work);
 459}
 460
 461static int init_vqs(struct virtio_balloon *vb)
 462{
 463        struct virtqueue *vqs[VIRTIO_BALLOON_VQ_MAX];
 464        vq_callback_t *callbacks[VIRTIO_BALLOON_VQ_MAX];
 465        const char *names[VIRTIO_BALLOON_VQ_MAX];
 466        int err;
 467
 468        /*
 469         * Inflateq and deflateq are used unconditionally. The names[]
 470         * will be NULL if the related feature is not enabled, which will
 471         * cause no allocation for the corresponding virtqueue in find_vqs.
 472         */
 473        callbacks[VIRTIO_BALLOON_VQ_INFLATE] = balloon_ack;
 474        names[VIRTIO_BALLOON_VQ_INFLATE] = "inflate";
 475        callbacks[VIRTIO_BALLOON_VQ_DEFLATE] = balloon_ack;
 476        names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
 477        names[VIRTIO_BALLOON_VQ_STATS] = NULL;
 478        names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 479
 480        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 481                names[VIRTIO_BALLOON_VQ_STATS] = "stats";
 482                callbacks[VIRTIO_BALLOON_VQ_STATS] = stats_request;
 483        }
 484
 485        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 486                names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "free_page_vq";
 487                callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
 488        }
 489
 490        err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
 491                                         vqs, callbacks, names, NULL, NULL);
 492        if (err)
 493                return err;
 494
 495        vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
 496        vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
 497        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
 498                struct scatterlist sg;
 499                unsigned int num_stats;
 500                vb->stats_vq = vqs[VIRTIO_BALLOON_VQ_STATS];
 501
 502                /*
 503                 * Prime this virtqueue with one buffer so the hypervisor can
 504                 * use it to signal us later (it can't be broken yet!).
 505                 */
 506                num_stats = update_balloon_stats(vb);
 507
 508                sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
 509                err = virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb,
 510                                           GFP_KERNEL);
 511                if (err) {
 512                        dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
 513                                 __func__);
 514                        return err;
 515                }
 516                virtqueue_kick(vb->stats_vq);
 517        }
 518
 519        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 520                vb->free_page_vq = vqs[VIRTIO_BALLOON_VQ_FREE_PAGE];
 521
 522        return 0;
 523}
 524
 525static u32 virtio_balloon_cmd_id_received(struct virtio_balloon *vb)
 526{
 527        if (test_and_clear_bit(VIRTIO_BALLOON_CONFIG_READ_CMD_ID,
 528                               &vb->config_read_bitmap))
 529                virtio_cread(vb->vdev, struct virtio_balloon_config,
 530                             free_page_report_cmd_id,
 531                             &vb->cmd_id_received_cache);
 532
 533        return vb->cmd_id_received_cache;
 534}
 535
 536static int send_cmd_id_start(struct virtio_balloon *vb)
 537{
 538        struct scatterlist sg;
 539        struct virtqueue *vq = vb->free_page_vq;
 540        int err, unused;
 541
 542        /* Detach all the used buffers from the vq */
 543        while (virtqueue_get_buf(vq, &unused))
 544                ;
 545
 546        vb->cmd_id_active = virtio32_to_cpu(vb->vdev,
 547                                        virtio_balloon_cmd_id_received(vb));
 548        sg_init_one(&sg, &vb->cmd_id_active, sizeof(vb->cmd_id_active));
 549        err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_active, GFP_KERNEL);
 550        if (!err)
 551                virtqueue_kick(vq);
 552        return err;
 553}
 554
 555static int send_cmd_id_stop(struct virtio_balloon *vb)
 556{
 557        struct scatterlist sg;
 558        struct virtqueue *vq = vb->free_page_vq;
 559        int err, unused;
 560
 561        /* Detach all the used buffers from the vq */
 562        while (virtqueue_get_buf(vq, &unused))
 563                ;
 564
 565        sg_init_one(&sg, &vb->cmd_id_stop, sizeof(vb->cmd_id_stop));
 566        err = virtqueue_add_outbuf(vq, &sg, 1, &vb->cmd_id_stop, GFP_KERNEL);
 567        if (!err)
 568                virtqueue_kick(vq);
 569        return err;
 570}
 571
 572static int get_free_page_and_send(struct virtio_balloon *vb)
 573{
 574        struct virtqueue *vq = vb->free_page_vq;
 575        struct page *page;
 576        struct scatterlist sg;
 577        int err, unused;
 578        void *p;
 579
 580        /* Detach all the used buffers from the vq */
 581        while (virtqueue_get_buf(vq, &unused))
 582                ;
 583
 584        page = alloc_pages(VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG,
 585                           VIRTIO_BALLOON_FREE_PAGE_ORDER);
 586        /*
 587         * When the allocation returns NULL, it indicates that we have got all
 588         * the possible free pages, so return -EINTR to stop.
 589         */
 590        if (!page)
 591                return -EINTR;
 592
 593        p = page_address(page);
 594        sg_init_one(&sg, p, VIRTIO_BALLOON_FREE_PAGE_SIZE);
 595        /* There is always 1 entry reserved for the cmd id to use. */
 596        if (vq->num_free > 1) {
 597                err = virtqueue_add_inbuf(vq, &sg, 1, p, GFP_KERNEL);
 598                if (unlikely(err)) {
 599                        free_pages((unsigned long)p,
 600                                   VIRTIO_BALLOON_FREE_PAGE_ORDER);
 601                        return err;
 602                }
 603                virtqueue_kick(vq);
 604                spin_lock_irq(&vb->free_page_list_lock);
 605                balloon_page_push(&vb->free_page_list, page);
 606                vb->num_free_page_blocks++;
 607                spin_unlock_irq(&vb->free_page_list_lock);
 608        } else {
 609                /*
 610                 * The vq has no available entry to add this page block, so
 611                 * just free it.
 612                 */
 613                free_pages((unsigned long)p, VIRTIO_BALLOON_FREE_PAGE_ORDER);
 614        }
 615
 616        return 0;
 617}
 618
 619static int send_free_pages(struct virtio_balloon *vb)
 620{
 621        int err;
 622        u32 cmd_id_active;
 623
 624        while (1) {
 625                /*
 626                 * If a stop id or a new cmd id was just received from host,
 627                 * stop the reporting.
 628                 */
 629                cmd_id_active = virtio32_to_cpu(vb->vdev, vb->cmd_id_active);
 630                if (unlikely(cmd_id_active !=
 631                             virtio_balloon_cmd_id_received(vb)))
 632                        break;
 633
 634                /*
 635                 * The free page blocks are allocated and sent to host one by
 636                 * one.
 637                 */
 638                err = get_free_page_and_send(vb);
 639                if (err == -EINTR)
 640                        break;
 641                else if (unlikely(err))
 642                        return err;
 643        }
 644
 645        return 0;
 646}
 647
 648static void virtio_balloon_report_free_page(struct virtio_balloon *vb)
 649{
 650        int err;
 651        struct device *dev = &vb->vdev->dev;
 652
 653        /* Start by sending the received cmd id to host with an outbuf. */
 654        err = send_cmd_id_start(vb);
 655        if (unlikely(err))
 656                dev_err(dev, "Failed to send a start id, err = %d\n", err);
 657
 658        err = send_free_pages(vb);
 659        if (unlikely(err))
 660                dev_err(dev, "Failed to send a free page, err = %d\n", err);
 661
 662        /* End by sending a stop id to host with an outbuf. */
 663        err = send_cmd_id_stop(vb);
 664        if (unlikely(err))
 665                dev_err(dev, "Failed to send a stop id, err = %d\n", err);
 666}
 667
 668static void report_free_page_func(struct work_struct *work)
 669{
 670        struct virtio_balloon *vb = container_of(work, struct virtio_balloon,
 671                                                 report_free_page_work);
 672        u32 cmd_id_received;
 673
 674        cmd_id_received = virtio_balloon_cmd_id_received(vb);
 675        if (cmd_id_received == VIRTIO_BALLOON_CMD_ID_DONE) {
 676                /* Pass ULONG_MAX to give back all the free pages */
 677                return_free_pages_to_mm(vb, ULONG_MAX);
 678        } else if (cmd_id_received != VIRTIO_BALLOON_CMD_ID_STOP &&
 679                   cmd_id_received !=
 680                   virtio32_to_cpu(vb->vdev, vb->cmd_id_active)) {
 681                virtio_balloon_report_free_page(vb);
 682        }
 683}
 684
 685#ifdef CONFIG_BALLOON_COMPACTION
 686/*
 687 * virtballoon_migratepage - perform the balloon page migration on behalf of
 688 *                           a compation thread.     (called under page lock)
 689 * @vb_dev_info: the balloon device
 690 * @newpage: page that will replace the isolated page after migration finishes.
 691 * @page   : the isolated (old) page that is about to be migrated to newpage.
 692 * @mode   : compaction mode -- not used for balloon page migration.
 693 *
 694 * After a ballooned page gets isolated by compaction procedures, this is the
 695 * function that performs the page migration on behalf of a compaction thread
 696 * The page migration for virtio balloon is done in a simple swap fashion which
 697 * follows these two macro steps:
 698 *  1) insert newpage into vb->pages list and update the host about it;
 699 *  2) update the host about the old page removed from vb->pages list;
 700 *
 701 * This function preforms the balloon page migration task.
 702 * Called through balloon_mapping->a_ops->migratepage
 703 */
 704static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
 705                struct page *newpage, struct page *page, enum migrate_mode mode)
 706{
 707        struct virtio_balloon *vb = container_of(vb_dev_info,
 708                        struct virtio_balloon, vb_dev_info);
 709        unsigned long flags;
 710
 711        /*
 712         * In order to avoid lock contention while migrating pages concurrently
 713         * to leak_balloon() or fill_balloon() we just give up the balloon_lock
 714         * this turn, as it is easier to retry the page migration later.
 715         * This also prevents fill_balloon() getting stuck into a mutex
 716         * recursion in the case it ends up triggering memory compaction
 717         * while it is attempting to inflate the ballon.
 718         */
 719        if (!mutex_trylock(&vb->balloon_lock))
 720                return -EAGAIN;
 721
 722        get_page(newpage); /* balloon reference */
 723
 724        /* balloon's page migration 1st step  -- inflate "newpage" */
 725        spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 726        balloon_page_insert(vb_dev_info, newpage);
 727        vb_dev_info->isolated_pages--;
 728        __count_vm_event(BALLOON_MIGRATE);
 729        spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 730        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 731        set_page_pfns(vb, vb->pfns, newpage);
 732        tell_host(vb, vb->inflate_vq);
 733
 734        /* balloon's page migration 2nd step -- deflate "page" */
 735        spin_lock_irqsave(&vb_dev_info->pages_lock, flags);
 736        balloon_page_delete(page);
 737        spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags);
 738        vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE;
 739        set_page_pfns(vb, vb->pfns, page);
 740        tell_host(vb, vb->deflate_vq);
 741
 742        mutex_unlock(&vb->balloon_lock);
 743
 744        put_page(page); /* balloon reference */
 745
 746        return MIGRATEPAGE_SUCCESS;
 747}
 748
 749static int balloon_init_fs_context(struct fs_context *fc)
 750{
 751        return init_pseudo(fc, BALLOON_KVM_MAGIC) ? 0 : -ENOMEM;
 752}
 753
 754static struct file_system_type balloon_fs = {
 755        .name           = "balloon-kvm",
 756        .init_fs_context = balloon_init_fs_context,
 757        .kill_sb        = kill_anon_super,
 758};
 759
 760#endif /* CONFIG_BALLOON_COMPACTION */
 761
 762static unsigned long shrink_free_pages(struct virtio_balloon *vb,
 763                                       unsigned long pages_to_free)
 764{
 765        unsigned long blocks_to_free, blocks_freed;
 766
 767        pages_to_free = round_up(pages_to_free,
 768                                 1 << VIRTIO_BALLOON_FREE_PAGE_ORDER);
 769        blocks_to_free = pages_to_free >> VIRTIO_BALLOON_FREE_PAGE_ORDER;
 770        blocks_freed = return_free_pages_to_mm(vb, blocks_to_free);
 771
 772        return blocks_freed << VIRTIO_BALLOON_FREE_PAGE_ORDER;
 773}
 774
 775static unsigned long leak_balloon_pages(struct virtio_balloon *vb,
 776                                          unsigned long pages_to_free)
 777{
 778        return leak_balloon(vb, pages_to_free * VIRTIO_BALLOON_PAGES_PER_PAGE) /
 779                VIRTIO_BALLOON_PAGES_PER_PAGE;
 780}
 781
 782static unsigned long shrink_balloon_pages(struct virtio_balloon *vb,
 783                                          unsigned long pages_to_free)
 784{
 785        unsigned long pages_freed = 0;
 786
 787        /*
 788         * One invocation of leak_balloon can deflate at most
 789         * VIRTIO_BALLOON_ARRAY_PFNS_MAX balloon pages, so we call it
 790         * multiple times to deflate pages till reaching pages_to_free.
 791         */
 792        while (vb->num_pages && pages_freed < pages_to_free)
 793                pages_freed += leak_balloon_pages(vb,
 794                                                  pages_to_free - pages_freed);
 795
 796        update_balloon_size(vb);
 797
 798        return pages_freed;
 799}
 800
 801static unsigned long virtio_balloon_shrinker_scan(struct shrinker *shrinker,
 802                                                  struct shrink_control *sc)
 803{
 804        unsigned long pages_to_free, pages_freed = 0;
 805        struct virtio_balloon *vb = container_of(shrinker,
 806                                        struct virtio_balloon, shrinker);
 807
 808        pages_to_free = sc->nr_to_scan;
 809
 810        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 811                pages_freed = shrink_free_pages(vb, pages_to_free);
 812
 813        if (pages_freed >= pages_to_free)
 814                return pages_freed;
 815
 816        pages_freed += shrink_balloon_pages(vb, pages_to_free - pages_freed);
 817
 818        return pages_freed;
 819}
 820
 821static unsigned long virtio_balloon_shrinker_count(struct shrinker *shrinker,
 822                                                   struct shrink_control *sc)
 823{
 824        struct virtio_balloon *vb = container_of(shrinker,
 825                                        struct virtio_balloon, shrinker);
 826        unsigned long count;
 827
 828        count = vb->num_pages / VIRTIO_BALLOON_PAGES_PER_PAGE;
 829        count += vb->num_free_page_blocks << VIRTIO_BALLOON_FREE_PAGE_ORDER;
 830
 831        return count;
 832}
 833
 834static void virtio_balloon_unregister_shrinker(struct virtio_balloon *vb)
 835{
 836        unregister_shrinker(&vb->shrinker);
 837}
 838
 839static int virtio_balloon_register_shrinker(struct virtio_balloon *vb)
 840{
 841        vb->shrinker.scan_objects = virtio_balloon_shrinker_scan;
 842        vb->shrinker.count_objects = virtio_balloon_shrinker_count;
 843        vb->shrinker.seeks = DEFAULT_SEEKS;
 844
 845        return register_shrinker(&vb->shrinker);
 846}
 847
 848static int virtballoon_probe(struct virtio_device *vdev)
 849{
 850        struct virtio_balloon *vb;
 851        __u32 poison_val;
 852        int err;
 853
 854        if (!vdev->config->get) {
 855                dev_err(&vdev->dev, "%s failure: config access disabled\n",
 856                        __func__);
 857                return -EINVAL;
 858        }
 859
 860        vdev->priv = vb = kzalloc(sizeof(*vb), GFP_KERNEL);
 861        if (!vb) {
 862                err = -ENOMEM;
 863                goto out;
 864        }
 865
 866        INIT_WORK(&vb->update_balloon_stats_work, update_balloon_stats_func);
 867        INIT_WORK(&vb->update_balloon_size_work, update_balloon_size_func);
 868        spin_lock_init(&vb->stop_update_lock);
 869        mutex_init(&vb->balloon_lock);
 870        init_waitqueue_head(&vb->acked);
 871        vb->vdev = vdev;
 872
 873        balloon_devinfo_init(&vb->vb_dev_info);
 874
 875        err = init_vqs(vb);
 876        if (err)
 877                goto out_free_vb;
 878
 879#ifdef CONFIG_BALLOON_COMPACTION
 880        balloon_mnt = kern_mount(&balloon_fs);
 881        if (IS_ERR(balloon_mnt)) {
 882                err = PTR_ERR(balloon_mnt);
 883                goto out_del_vqs;
 884        }
 885
 886        vb->vb_dev_info.migratepage = virtballoon_migratepage;
 887        vb->vb_dev_info.inode = alloc_anon_inode(balloon_mnt->mnt_sb);
 888        if (IS_ERR(vb->vb_dev_info.inode)) {
 889                err = PTR_ERR(vb->vb_dev_info.inode);
 890                kern_unmount(balloon_mnt);
 891                goto out_del_vqs;
 892        }
 893        vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
 894#endif
 895        if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 896                /*
 897                 * There is always one entry reserved for cmd id, so the ring
 898                 * size needs to be at least two to report free page hints.
 899                 */
 900                if (virtqueue_get_vring_size(vb->free_page_vq) < 2) {
 901                        err = -ENOSPC;
 902                        goto out_del_vqs;
 903                }
 904                vb->balloon_wq = alloc_workqueue("balloon-wq",
 905                                        WQ_FREEZABLE | WQ_CPU_INTENSIVE, 0);
 906                if (!vb->balloon_wq) {
 907                        err = -ENOMEM;
 908                        goto out_del_vqs;
 909                }
 910                INIT_WORK(&vb->report_free_page_work, report_free_page_func);
 911                vb->cmd_id_received_cache = VIRTIO_BALLOON_CMD_ID_STOP;
 912                vb->cmd_id_active = cpu_to_virtio32(vb->vdev,
 913                                                  VIRTIO_BALLOON_CMD_ID_STOP);
 914                vb->cmd_id_stop = cpu_to_virtio32(vb->vdev,
 915                                                  VIRTIO_BALLOON_CMD_ID_STOP);
 916                spin_lock_init(&vb->free_page_list_lock);
 917                INIT_LIST_HEAD(&vb->free_page_list);
 918                if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) {
 919                        memset(&poison_val, PAGE_POISON, sizeof(poison_val));
 920                        virtio_cwrite(vb->vdev, struct virtio_balloon_config,
 921                                      poison_val, &poison_val);
 922                }
 923        }
 924        /*
 925         * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a
 926         * shrinker needs to be registered to relieve memory pressure.
 927         */
 928        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
 929                err = virtio_balloon_register_shrinker(vb);
 930                if (err)
 931                        goto out_del_balloon_wq;
 932        }
 933        virtio_device_ready(vdev);
 934
 935        if (towards_target(vb))
 936                virtballoon_changed(vdev);
 937        return 0;
 938
 939out_del_balloon_wq:
 940        if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT))
 941                destroy_workqueue(vb->balloon_wq);
 942out_del_vqs:
 943        vdev->config->del_vqs(vdev);
 944out_free_vb:
 945        kfree(vb);
 946out:
 947        return err;
 948}
 949
 950static void remove_common(struct virtio_balloon *vb)
 951{
 952        /* There might be pages left in the balloon: free them. */
 953        while (vb->num_pages)
 954                leak_balloon(vb, vb->num_pages);
 955        update_balloon_size(vb);
 956
 957        /* Now we reset the device so we can clean up the queues. */
 958        vb->vdev->config->reset(vb->vdev);
 959
 960        vb->vdev->config->del_vqs(vb->vdev);
 961}
 962
 963static void virtballoon_remove(struct virtio_device *vdev)
 964{
 965        struct virtio_balloon *vb = vdev->priv;
 966
 967        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
 968                virtio_balloon_unregister_shrinker(vb);
 969        spin_lock_irq(&vb->stop_update_lock);
 970        vb->stop_update = true;
 971        spin_unlock_irq(&vb->stop_update_lock);
 972        cancel_work_sync(&vb->update_balloon_size_work);
 973        cancel_work_sync(&vb->update_balloon_stats_work);
 974
 975        if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
 976                cancel_work_sync(&vb->report_free_page_work);
 977                destroy_workqueue(vb->balloon_wq);
 978        }
 979
 980        remove_common(vb);
 981#ifdef CONFIG_BALLOON_COMPACTION
 982        if (vb->vb_dev_info.inode)
 983                iput(vb->vb_dev_info.inode);
 984
 985        kern_unmount(balloon_mnt);
 986#endif
 987        kfree(vb);
 988}
 989
 990#ifdef CONFIG_PM_SLEEP
 991static int virtballoon_freeze(struct virtio_device *vdev)
 992{
 993        struct virtio_balloon *vb = vdev->priv;
 994
 995        /*
 996         * The workqueue is already frozen by the PM core before this
 997         * function is called.
 998         */
 999        remove_common(vb);
1000        return 0;
1001}
1002
1003static int virtballoon_restore(struct virtio_device *vdev)
1004{
1005        struct virtio_balloon *vb = vdev->priv;
1006        int ret;
1007
1008        ret = init_vqs(vdev->priv);
1009        if (ret)
1010                return ret;
1011
1012        virtio_device_ready(vdev);
1013
1014        if (towards_target(vb))
1015                virtballoon_changed(vdev);
1016        update_balloon_size(vb);
1017        return 0;
1018}
1019#endif
1020
1021static int virtballoon_validate(struct virtio_device *vdev)
1022{
1023        if (!page_poisoning_enabled())
1024                __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON);
1025
1026        __virtio_clear_bit(vdev, VIRTIO_F_IOMMU_PLATFORM);
1027        return 0;
1028}
1029
1030static unsigned int features[] = {
1031        VIRTIO_BALLOON_F_MUST_TELL_HOST,
1032        VIRTIO_BALLOON_F_STATS_VQ,
1033        VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
1034        VIRTIO_BALLOON_F_FREE_PAGE_HINT,
1035        VIRTIO_BALLOON_F_PAGE_POISON,
1036};
1037
1038static struct virtio_driver virtio_balloon_driver = {
1039        .feature_table = features,
1040        .feature_table_size = ARRAY_SIZE(features),
1041        .driver.name =  KBUILD_MODNAME,
1042        .driver.owner = THIS_MODULE,
1043        .id_table =     id_table,
1044        .validate =     virtballoon_validate,
1045        .probe =        virtballoon_probe,
1046        .remove =       virtballoon_remove,
1047        .config_changed = virtballoon_changed,
1048#ifdef CONFIG_PM_SLEEP
1049        .freeze =       virtballoon_freeze,
1050        .restore =      virtballoon_restore,
1051#endif
1052};
1053
1054module_virtio_driver(virtio_balloon_driver);
1055MODULE_DEVICE_TABLE(virtio, id_table);
1056MODULE_DESCRIPTION("Virtio balloon driver");
1057MODULE_LICENSE("GPL");
1058