linux/drivers/misc/vmw_balloon.c
<<
>>
Prefs
   1/*
   2 * VMware Balloon driver.
   3 *
   4 * Copyright (C) 2000-2014, VMware, Inc. All Rights Reserved.
   5 *
   6 * This program is free software; you can redistribute it and/or modify it
   7 * under the terms of the GNU General Public License as published by the
   8 * Free Software Foundation; version 2 of the License and no later version.
   9 *
  10 * This program is distributed in the hope that it will be useful, but
  11 * WITHOUT ANY WARRANTY; without even the implied warranty of
  12 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  13 * NON INFRINGEMENT.  See the GNU General Public License for more
  14 * details.
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * along with this program; if not, write to the Free Software
  18 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19 *
  20 * Maintained by:       Xavier Deguillard <xdeguillard@vmware.com>
  21 *                      Philip Moltmann <moltmann@vmware.com>
  22 */
  23
  24/*
  25 * This is VMware physical memory management driver for Linux. The driver
  26 * acts like a "balloon" that can be inflated to reclaim physical pages by
  27 * reserving them in the guest and invalidating them in the monitor,
  28 * freeing up the underlying machine pages so they can be allocated to
  29 * other guests.  The balloon can also be deflated to allow the guest to
  30 * use more physical memory. Higher level policies can control the sizes
  31 * of balloons in VMs in order to manage physical memory resources.
  32 */
  33
  34//#define DEBUG
  35#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  36
  37#include <linux/types.h>
  38#include <linux/kernel.h>
  39#include <linux/mm.h>
  40#include <linux/vmalloc.h>
  41#include <linux/sched.h>
  42#include <linux/module.h>
  43#include <linux/workqueue.h>
  44#include <linux/debugfs.h>
  45#include <linux/seq_file.h>
  46#include <linux/vmw_vmci_defs.h>
  47#include <linux/vmw_vmci_api.h>
  48#include <asm/hypervisor.h>
  49
  50MODULE_AUTHOR("VMware, Inc.");
  51MODULE_DESCRIPTION("VMware Memory Control (Balloon) Driver");
  52MODULE_VERSION("1.5.0.0-k");
  53MODULE_ALIAS("dmi:*:svnVMware*:*");
  54MODULE_ALIAS("vmware_vmmemctl");
  55MODULE_LICENSE("GPL");
  56
  57/*
  58 * Various constants controlling rate of inflaint/deflating balloon,
  59 * measured in pages.
  60 */
  61
  62/*
  63 * Rates of memory allocaton when guest experiences memory pressure
  64 * (driver performs sleeping allocations).
  65 */
  66#define VMW_BALLOON_RATE_ALLOC_MIN      512U
  67#define VMW_BALLOON_RATE_ALLOC_MAX      2048U
  68#define VMW_BALLOON_RATE_ALLOC_INC      16U
  69
  70/*
  71 * When guest is under memory pressure, use a reduced page allocation
  72 * rate for next several cycles.
  73 */
  74#define VMW_BALLOON_SLOW_CYCLES         4
  75
  76/*
  77 * Use __GFP_HIGHMEM to allow pages from HIGHMEM zone. We don't
  78 * allow wait (__GFP_RECLAIM) for NOSLEEP page allocations. Use
  79 * __GFP_NOWARN, to suppress page allocation failure warnings.
  80 */
  81#define VMW_PAGE_ALLOC_NOSLEEP          (__GFP_HIGHMEM|__GFP_NOWARN)
  82
  83/*
  84 * Use GFP_HIGHUSER when executing in a separate kernel thread
  85 * context and allocation can sleep.  This is less stressful to
  86 * the guest memory system, since it allows the thread to block
  87 * while memory is reclaimed, and won't take pages from emergency
  88 * low-memory pools.
  89 */
  90#define VMW_PAGE_ALLOC_CANSLEEP         (GFP_HIGHUSER)
  91
  92/* Maximum number of refused pages we accumulate during inflation cycle */
  93#define VMW_BALLOON_MAX_REFUSED         16
  94
  95/*
  96 * Hypervisor communication port definitions.
  97 */
  98#define VMW_BALLOON_HV_PORT             0x5670
  99#define VMW_BALLOON_HV_MAGIC            0x456c6d6f
 100#define VMW_BALLOON_GUEST_ID            1       /* Linux */
 101
 102enum vmwballoon_capabilities {
 103        /*
 104         * Bit 0 is reserved and not associated to any capability.
 105         */
 106        VMW_BALLOON_BASIC_CMDS                  = (1 << 1),
 107        VMW_BALLOON_BATCHED_CMDS                = (1 << 2),
 108        VMW_BALLOON_BATCHED_2M_CMDS             = (1 << 3),
 109        VMW_BALLOON_SIGNALLED_WAKEUP_CMD        = (1 << 4),
 110};
 111
 112#define VMW_BALLOON_CAPABILITIES        (VMW_BALLOON_BASIC_CMDS \
 113                                        | VMW_BALLOON_BATCHED_CMDS \
 114                                        | VMW_BALLOON_BATCHED_2M_CMDS \
 115                                        | VMW_BALLOON_SIGNALLED_WAKEUP_CMD)
 116
 117#define VMW_BALLOON_2M_SHIFT            (9)
 118#define VMW_BALLOON_NUM_PAGE_SIZES      (2)
 119
 120/*
 121 * Backdoor commands availability:
 122 *
 123 * START, GET_TARGET and GUEST_ID are always available,
 124 *
 125 * VMW_BALLOON_BASIC_CMDS:
 126 *      LOCK and UNLOCK commands,
 127 * VMW_BALLOON_BATCHED_CMDS:
 128 *      BATCHED_LOCK and BATCHED_UNLOCK commands.
 129 * VMW BALLOON_BATCHED_2M_CMDS:
 130 *      BATCHED_2M_LOCK and BATCHED_2M_UNLOCK commands,
 131 * VMW VMW_BALLOON_SIGNALLED_WAKEUP_CMD:
 132 *      VMW_BALLOON_CMD_VMCI_DOORBELL_SET command.
 133 */
 134#define VMW_BALLOON_CMD_START                   0
 135#define VMW_BALLOON_CMD_GET_TARGET              1
 136#define VMW_BALLOON_CMD_LOCK                    2
 137#define VMW_BALLOON_CMD_UNLOCK                  3
 138#define VMW_BALLOON_CMD_GUEST_ID                4
 139#define VMW_BALLOON_CMD_BATCHED_LOCK            6
 140#define VMW_BALLOON_CMD_BATCHED_UNLOCK          7
 141#define VMW_BALLOON_CMD_BATCHED_2M_LOCK         8
 142#define VMW_BALLOON_CMD_BATCHED_2M_UNLOCK       9
 143#define VMW_BALLOON_CMD_VMCI_DOORBELL_SET       10
 144
 145
 146/* error codes */
 147#define VMW_BALLOON_SUCCESS                     0
 148#define VMW_BALLOON_FAILURE                     -1
 149#define VMW_BALLOON_ERROR_CMD_INVALID           1
 150#define VMW_BALLOON_ERROR_PPN_INVALID           2
 151#define VMW_BALLOON_ERROR_PPN_LOCKED            3
 152#define VMW_BALLOON_ERROR_PPN_UNLOCKED          4
 153#define VMW_BALLOON_ERROR_PPN_PINNED            5
 154#define VMW_BALLOON_ERROR_PPN_NOTNEEDED         6
 155#define VMW_BALLOON_ERROR_RESET                 7
 156#define VMW_BALLOON_ERROR_BUSY                  8
 157
 158#define VMW_BALLOON_SUCCESS_WITH_CAPABILITIES   (0x03000000)
 159
 160/* Batch page description */
 161
 162/*
 163 * Layout of a page in the batch page:
 164 *
 165 * +-------------+----------+--------+
 166 * |             |          |        |
 167 * | Page number | Reserved | Status |
 168 * |             |          |        |
 169 * +-------------+----------+--------+
 170 * 64  PAGE_SHIFT          6         0
 171 *
 172 * The reserved field should be set to 0.
 173 */
 174#define VMW_BALLOON_BATCH_MAX_PAGES     (PAGE_SIZE / sizeof(u64))
 175#define VMW_BALLOON_BATCH_STATUS_MASK   ((1UL << 5) - 1)
 176#define VMW_BALLOON_BATCH_PAGE_MASK     (~((1UL << PAGE_SHIFT) - 1))
 177
 178struct vmballoon_batch_page {
 179        u64 pages[VMW_BALLOON_BATCH_MAX_PAGES];
 180};
 181
 182static u64 vmballoon_batch_get_pa(struct vmballoon_batch_page *batch, int idx)
 183{
 184        return batch->pages[idx] & VMW_BALLOON_BATCH_PAGE_MASK;
 185}
 186
 187static int vmballoon_batch_get_status(struct vmballoon_batch_page *batch,
 188                                int idx)
 189{
 190        return (int)(batch->pages[idx] & VMW_BALLOON_BATCH_STATUS_MASK);
 191}
 192
 193static void vmballoon_batch_set_pa(struct vmballoon_batch_page *batch, int idx,
 194                                u64 pa)
 195{
 196        batch->pages[idx] = pa;
 197}
 198
 199
 200#define VMWARE_BALLOON_CMD(cmd, arg1, arg2, result)             \
 201({                                                              \
 202        unsigned long __status, __dummy1, __dummy2, __dummy3;   \
 203        __asm__ __volatile__ ("inl %%dx" :                      \
 204                "=a"(__status),                                 \
 205                "=c"(__dummy1),                                 \
 206                "=d"(__dummy2),                                 \
 207                "=b"(result),                                   \
 208                "=S" (__dummy3) :                               \
 209                "0"(VMW_BALLOON_HV_MAGIC),                      \
 210                "1"(VMW_BALLOON_CMD_##cmd),                     \
 211                "2"(VMW_BALLOON_HV_PORT),                       \
 212                "3"(arg1),                                      \
 213                "4" (arg2) :                                    \
 214                "memory");                                      \
 215        if (VMW_BALLOON_CMD_##cmd == VMW_BALLOON_CMD_START)     \
 216                result = __dummy1;                              \
 217        result &= -1UL;                                         \
 218        __status & -1UL;                                        \
 219})
 220
 221#ifdef CONFIG_DEBUG_FS
 222struct vmballoon_stats {
 223        unsigned int timer;
 224        unsigned int doorbell;
 225
 226        /* allocation statistics */
 227        unsigned int alloc[VMW_BALLOON_NUM_PAGE_SIZES];
 228        unsigned int alloc_fail[VMW_BALLOON_NUM_PAGE_SIZES];
 229        unsigned int sleep_alloc;
 230        unsigned int sleep_alloc_fail;
 231        unsigned int refused_alloc[VMW_BALLOON_NUM_PAGE_SIZES];
 232        unsigned int refused_free[VMW_BALLOON_NUM_PAGE_SIZES];
 233        unsigned int free[VMW_BALLOON_NUM_PAGE_SIZES];
 234
 235        /* monitor operations */
 236        unsigned int lock[VMW_BALLOON_NUM_PAGE_SIZES];
 237        unsigned int lock_fail[VMW_BALLOON_NUM_PAGE_SIZES];
 238        unsigned int unlock[VMW_BALLOON_NUM_PAGE_SIZES];
 239        unsigned int unlock_fail[VMW_BALLOON_NUM_PAGE_SIZES];
 240        unsigned int target;
 241        unsigned int target_fail;
 242        unsigned int start;
 243        unsigned int start_fail;
 244        unsigned int guest_type;
 245        unsigned int guest_type_fail;
 246        unsigned int doorbell_set;
 247        unsigned int doorbell_unset;
 248};
 249
 250#define STATS_INC(stat) (stat)++
 251#else
 252#define STATS_INC(stat)
 253#endif
 254
 255struct vmballoon;
 256
 257struct vmballoon_ops {
 258        void (*add_page)(struct vmballoon *b, int idx, struct page *p);
 259        int (*lock)(struct vmballoon *b, unsigned int num_pages,
 260                        bool is_2m_pages, unsigned int *target);
 261        int (*unlock)(struct vmballoon *b, unsigned int num_pages,
 262                        bool is_2m_pages, unsigned int *target);
 263};
 264
 265struct vmballoon_page_size {
 266        /* list of reserved physical pages */
 267        struct list_head pages;
 268
 269        /* transient list of non-balloonable pages */
 270        struct list_head refused_pages;
 271        unsigned int n_refused_pages;
 272};
 273
 274struct vmballoon {
 275        struct vmballoon_page_size page_sizes[VMW_BALLOON_NUM_PAGE_SIZES];
 276
 277        /* supported page sizes. 1 == 4k pages only, 2 == 4k and 2m pages */
 278        unsigned supported_page_sizes;
 279
 280        /* balloon size in pages */
 281        unsigned int size;
 282        unsigned int target;
 283
 284        /* reset flag */
 285        bool reset_required;
 286
 287        /* adjustment rates (pages per second) */
 288        unsigned int rate_alloc;
 289
 290        /* slowdown page allocations for next few cycles */
 291        unsigned int slow_allocation_cycles;
 292
 293        unsigned long capabilities;
 294
 295        struct vmballoon_batch_page *batch_page;
 296        unsigned int batch_max_pages;
 297        struct page *page;
 298
 299        const struct vmballoon_ops *ops;
 300
 301#ifdef CONFIG_DEBUG_FS
 302        /* statistics */
 303        struct vmballoon_stats stats;
 304
 305        /* debugfs file exporting statistics */
 306        struct dentry *dbg_entry;
 307#endif
 308
 309        struct sysinfo sysinfo;
 310
 311        struct delayed_work dwork;
 312
 313        struct vmci_handle vmci_doorbell;
 314};
 315
 316static struct vmballoon balloon;
 317
 318/*
 319 * Send "start" command to the host, communicating supported version
 320 * of the protocol.
 321 */
 322static bool vmballoon_send_start(struct vmballoon *b, unsigned long req_caps)
 323{
 324        unsigned long status, capabilities, dummy = 0;
 325        bool success;
 326
 327        STATS_INC(b->stats.start);
 328
 329        status = VMWARE_BALLOON_CMD(START, req_caps, dummy, capabilities);
 330
 331        switch (status) {
 332        case VMW_BALLOON_SUCCESS_WITH_CAPABILITIES:
 333                b->capabilities = capabilities;
 334                success = true;
 335                break;
 336        case VMW_BALLOON_SUCCESS:
 337                b->capabilities = VMW_BALLOON_BASIC_CMDS;
 338                success = true;
 339                break;
 340        default:
 341                success = false;
 342        }
 343
 344        if (b->capabilities & VMW_BALLOON_BATCHED_2M_CMDS)
 345                b->supported_page_sizes = 2;
 346        else
 347                b->supported_page_sizes = 1;
 348
 349        if (!success) {
 350                pr_debug("%s - failed, hv returns %ld\n", __func__, status);
 351                STATS_INC(b->stats.start_fail);
 352        }
 353        return success;
 354}
 355
 356static bool vmballoon_check_status(struct vmballoon *b, unsigned long status)
 357{
 358        switch (status) {
 359        case VMW_BALLOON_SUCCESS:
 360                return true;
 361
 362        case VMW_BALLOON_ERROR_RESET:
 363                b->reset_required = true;
 364                /* fall through */
 365
 366        default:
 367                return false;
 368        }
 369}
 370
 371/*
 372 * Communicate guest type to the host so that it can adjust ballooning
 373 * algorithm to the one most appropriate for the guest. This command
 374 * is normally issued after sending "start" command and is part of
 375 * standard reset sequence.
 376 */
 377static bool vmballoon_send_guest_id(struct vmballoon *b)
 378{
 379        unsigned long status, dummy = 0;
 380
 381        status = VMWARE_BALLOON_CMD(GUEST_ID, VMW_BALLOON_GUEST_ID, dummy,
 382                                dummy);
 383
 384        STATS_INC(b->stats.guest_type);
 385
 386        if (vmballoon_check_status(b, status))
 387                return true;
 388
 389        pr_debug("%s - failed, hv returns %ld\n", __func__, status);
 390        STATS_INC(b->stats.guest_type_fail);
 391        return false;
 392}
 393
 394static u16 vmballoon_page_size(bool is_2m_page)
 395{
 396        if (is_2m_page)
 397                return 1 << VMW_BALLOON_2M_SHIFT;
 398
 399        return 1;
 400}
 401
 402/*
 403 * Retrieve desired balloon size from the host.
 404 */
 405static bool vmballoon_send_get_target(struct vmballoon *b, u32 *new_target)
 406{
 407        unsigned long status;
 408        unsigned long target;
 409        unsigned long limit;
 410        unsigned long dummy = 0;
 411        u32 limit32;
 412
 413        /*
 414         * si_meminfo() is cheap. Moreover, we want to provide dynamic
 415         * max balloon size later. So let us call si_meminfo() every
 416         * iteration.
 417         */
 418        si_meminfo(&b->sysinfo);
 419        limit = b->sysinfo.totalram;
 420
 421        /* Ensure limit fits in 32-bits */
 422        limit32 = (u32)limit;
 423        if (limit != limit32)
 424                return false;
 425
 426        /* update stats */
 427        STATS_INC(b->stats.target);
 428
 429        status = VMWARE_BALLOON_CMD(GET_TARGET, limit, dummy, target);
 430        if (vmballoon_check_status(b, status)) {
 431                *new_target = target;
 432                return true;
 433        }
 434
 435        pr_debug("%s - failed, hv returns %ld\n", __func__, status);
 436        STATS_INC(b->stats.target_fail);
 437        return false;
 438}
 439
 440/*
 441 * Notify the host about allocated page so that host can use it without
 442 * fear that guest will need it. Host may reject some pages, we need to
 443 * check the return value and maybe submit a different page.
 444 */
 445static int vmballoon_send_lock_page(struct vmballoon *b, unsigned long pfn,
 446                                unsigned int *hv_status, unsigned int *target)
 447{
 448        unsigned long status, dummy = 0;
 449        u32 pfn32;
 450
 451        pfn32 = (u32)pfn;
 452        if (pfn32 != pfn)
 453                return -1;
 454
 455        STATS_INC(b->stats.lock[false]);
 456
 457        *hv_status = status = VMWARE_BALLOON_CMD(LOCK, pfn, dummy, *target);
 458        if (vmballoon_check_status(b, status))
 459                return 0;
 460
 461        pr_debug("%s - ppn %lx, hv returns %ld\n", __func__, pfn, status);
 462        STATS_INC(b->stats.lock_fail[false]);
 463        return 1;
 464}
 465
 466static int vmballoon_send_batched_lock(struct vmballoon *b,
 467                unsigned int num_pages, bool is_2m_pages, unsigned int *target)
 468{
 469        unsigned long status;
 470        unsigned long pfn = page_to_pfn(b->page);
 471
 472        STATS_INC(b->stats.lock[is_2m_pages]);
 473
 474        if (is_2m_pages)
 475                status = VMWARE_BALLOON_CMD(BATCHED_2M_LOCK, pfn, num_pages,
 476                                *target);
 477        else
 478                status = VMWARE_BALLOON_CMD(BATCHED_LOCK, pfn, num_pages,
 479                                *target);
 480
 481        if (vmballoon_check_status(b, status))
 482                return 0;
 483
 484        pr_debug("%s - batch ppn %lx, hv returns %ld\n", __func__, pfn, status);
 485        STATS_INC(b->stats.lock_fail[is_2m_pages]);
 486        return 1;
 487}
 488
 489/*
 490 * Notify the host that guest intends to release given page back into
 491 * the pool of available (to the guest) pages.
 492 */
 493static bool vmballoon_send_unlock_page(struct vmballoon *b, unsigned long pfn,
 494                                                        unsigned int *target)
 495{
 496        unsigned long status, dummy = 0;
 497        u32 pfn32;
 498
 499        pfn32 = (u32)pfn;
 500        if (pfn32 != pfn)
 501                return false;
 502
 503        STATS_INC(b->stats.unlock[false]);
 504
 505        status = VMWARE_BALLOON_CMD(UNLOCK, pfn, dummy, *target);
 506        if (vmballoon_check_status(b, status))
 507                return true;
 508
 509        pr_debug("%s - ppn %lx, hv returns %ld\n", __func__, pfn, status);
 510        STATS_INC(b->stats.unlock_fail[false]);
 511        return false;
 512}
 513
 514static bool vmballoon_send_batched_unlock(struct vmballoon *b,
 515                unsigned int num_pages, bool is_2m_pages, unsigned int *target)
 516{
 517        unsigned long status;
 518        unsigned long pfn = page_to_pfn(b->page);
 519
 520        STATS_INC(b->stats.unlock[is_2m_pages]);
 521
 522        if (is_2m_pages)
 523                status = VMWARE_BALLOON_CMD(BATCHED_2M_UNLOCK, pfn, num_pages,
 524                                *target);
 525        else
 526                status = VMWARE_BALLOON_CMD(BATCHED_UNLOCK, pfn, num_pages,
 527                                *target);
 528
 529        if (vmballoon_check_status(b, status))
 530                return true;
 531
 532        pr_debug("%s - batch ppn %lx, hv returns %ld\n", __func__, pfn, status);
 533        STATS_INC(b->stats.unlock_fail[is_2m_pages]);
 534        return false;
 535}
 536
 537static struct page *vmballoon_alloc_page(gfp_t flags, bool is_2m_page)
 538{
 539        if (is_2m_page)
 540                return alloc_pages(flags, VMW_BALLOON_2M_SHIFT);
 541
 542        return alloc_page(flags);
 543}
 544
 545static void vmballoon_free_page(struct page *page, bool is_2m_page)
 546{
 547        if (is_2m_page)
 548                __free_pages(page, VMW_BALLOON_2M_SHIFT);
 549        else
 550                __free_page(page);
 551}
 552
 553/*
 554 * Quickly release all pages allocated for the balloon. This function is
 555 * called when host decides to "reset" balloon for one reason or another.
 556 * Unlike normal "deflate" we do not (shall not) notify host of the pages
 557 * being released.
 558 */
 559static void vmballoon_pop(struct vmballoon *b)
 560{
 561        struct page *page, *next;
 562        unsigned is_2m_pages;
 563
 564        for (is_2m_pages = 0; is_2m_pages < VMW_BALLOON_NUM_PAGE_SIZES;
 565                        is_2m_pages++) {
 566                struct vmballoon_page_size *page_size =
 567                                &b->page_sizes[is_2m_pages];
 568                u16 size_per_page = vmballoon_page_size(is_2m_pages);
 569
 570                list_for_each_entry_safe(page, next, &page_size->pages, lru) {
 571                        list_del(&page->lru);
 572                        vmballoon_free_page(page, is_2m_pages);
 573                        STATS_INC(b->stats.free[is_2m_pages]);
 574                        b->size -= size_per_page;
 575                        cond_resched();
 576                }
 577        }
 578
 579        if (b->batch_page) {
 580                vunmap(b->batch_page);
 581                b->batch_page = NULL;
 582        }
 583
 584        if (b->page) {
 585                __free_page(b->page);
 586                b->page = NULL;
 587        }
 588}
 589
 590/*
 591 * Notify the host of a ballooned page. If host rejects the page put it on the
 592 * refuse list, those refused page are then released at the end of the
 593 * inflation cycle.
 594 */
 595static int vmballoon_lock_page(struct vmballoon *b, unsigned int num_pages,
 596                                bool is_2m_pages, unsigned int *target)
 597{
 598        int locked, hv_status;
 599        struct page *page = b->page;
 600        struct vmballoon_page_size *page_size = &b->page_sizes[false];
 601
 602        /* is_2m_pages can never happen as 2m pages support implies batching */
 603
 604        locked = vmballoon_send_lock_page(b, page_to_pfn(page), &hv_status,
 605                                                                target);
 606        if (locked > 0) {
 607                STATS_INC(b->stats.refused_alloc[false]);
 608
 609                if (hv_status == VMW_BALLOON_ERROR_RESET ||
 610                                hv_status == VMW_BALLOON_ERROR_PPN_NOTNEEDED) {
 611                        vmballoon_free_page(page, false);
 612                        return -EIO;
 613                }
 614
 615                /*
 616                 * Place page on the list of non-balloonable pages
 617                 * and retry allocation, unless we already accumulated
 618                 * too many of them, in which case take a breather.
 619                 */
 620                if (page_size->n_refused_pages < VMW_BALLOON_MAX_REFUSED) {
 621                        page_size->n_refused_pages++;
 622                        list_add(&page->lru, &page_size->refused_pages);
 623                } else {
 624                        vmballoon_free_page(page, false);
 625                }
 626                return -EIO;
 627        }
 628
 629        /* track allocated page */
 630        list_add(&page->lru, &page_size->pages);
 631
 632        /* update balloon size */
 633        b->size++;
 634
 635        return 0;
 636}
 637
 638static int vmballoon_lock_batched_page(struct vmballoon *b,
 639                unsigned int num_pages, bool is_2m_pages, unsigned int *target)
 640{
 641        int locked, i;
 642        u16 size_per_page = vmballoon_page_size(is_2m_pages);
 643
 644        locked = vmballoon_send_batched_lock(b, num_pages, is_2m_pages,
 645                        target);
 646        if (locked > 0) {
 647                for (i = 0; i < num_pages; i++) {
 648                        u64 pa = vmballoon_batch_get_pa(b->batch_page, i);
 649                        struct page *p = pfn_to_page(pa >> PAGE_SHIFT);
 650
 651                        vmballoon_free_page(p, is_2m_pages);
 652                }
 653
 654                return -EIO;
 655        }
 656
 657        for (i = 0; i < num_pages; i++) {
 658                u64 pa = vmballoon_batch_get_pa(b->batch_page, i);
 659                struct page *p = pfn_to_page(pa >> PAGE_SHIFT);
 660                struct vmballoon_page_size *page_size =
 661                                &b->page_sizes[is_2m_pages];
 662
 663                locked = vmballoon_batch_get_status(b->batch_page, i);
 664
 665                switch (locked) {
 666                case VMW_BALLOON_SUCCESS:
 667                        list_add(&p->lru, &page_size->pages);
 668                        b->size += size_per_page;
 669                        break;
 670                case VMW_BALLOON_ERROR_PPN_PINNED:
 671                case VMW_BALLOON_ERROR_PPN_INVALID:
 672                        if (page_size->n_refused_pages
 673                                        < VMW_BALLOON_MAX_REFUSED) {
 674                                list_add(&p->lru, &page_size->refused_pages);
 675                                page_size->n_refused_pages++;
 676                                break;
 677                        }
 678                        /* Fallthrough */
 679                case VMW_BALLOON_ERROR_RESET:
 680                case VMW_BALLOON_ERROR_PPN_NOTNEEDED:
 681                        vmballoon_free_page(p, is_2m_pages);
 682                        break;
 683                default:
 684                        /* This should never happen */
 685                        WARN_ON_ONCE(true);
 686                }
 687        }
 688
 689        return 0;
 690}
 691
 692/*
 693 * Release the page allocated for the balloon. Note that we first notify
 694 * the host so it can make sure the page will be available for the guest
 695 * to use, if needed.
 696 */
 697static int vmballoon_unlock_page(struct vmballoon *b, unsigned int num_pages,
 698                bool is_2m_pages, unsigned int *target)
 699{
 700        struct page *page = b->page;
 701        struct vmballoon_page_size *page_size = &b->page_sizes[false];
 702
 703        /* is_2m_pages can never happen as 2m pages support implies batching */
 704
 705        if (!vmballoon_send_unlock_page(b, page_to_pfn(page), target)) {
 706                list_add(&page->lru, &page_size->pages);
 707                return -EIO;
 708        }
 709
 710        /* deallocate page */
 711        vmballoon_free_page(page, false);
 712        STATS_INC(b->stats.free[false]);
 713
 714        /* update balloon size */
 715        b->size--;
 716
 717        return 0;
 718}
 719
 720static int vmballoon_unlock_batched_page(struct vmballoon *b,
 721                                unsigned int num_pages, bool is_2m_pages,
 722                                unsigned int *target)
 723{
 724        int locked, i, ret = 0;
 725        bool hv_success;
 726        u16 size_per_page = vmballoon_page_size(is_2m_pages);
 727
 728        hv_success = vmballoon_send_batched_unlock(b, num_pages, is_2m_pages,
 729                        target);
 730        if (!hv_success)
 731                ret = -EIO;
 732
 733        for (i = 0; i < num_pages; i++) {
 734                u64 pa = vmballoon_batch_get_pa(b->batch_page, i);
 735                struct page *p = pfn_to_page(pa >> PAGE_SHIFT);
 736                struct vmballoon_page_size *page_size =
 737                                &b->page_sizes[is_2m_pages];
 738
 739                locked = vmballoon_batch_get_status(b->batch_page, i);
 740                if (!hv_success || locked != VMW_BALLOON_SUCCESS) {
 741                        /*
 742                         * That page wasn't successfully unlocked by the
 743                         * hypervisor, re-add it to the list of pages owned by
 744                         * the balloon driver.
 745                         */
 746                        list_add(&p->lru, &page_size->pages);
 747                } else {
 748                        /* deallocate page */
 749                        vmballoon_free_page(p, is_2m_pages);
 750                        STATS_INC(b->stats.free[is_2m_pages]);
 751
 752                        /* update balloon size */
 753                        b->size -= size_per_page;
 754                }
 755        }
 756
 757        return ret;
 758}
 759
 760/*
 761 * Release pages that were allocated while attempting to inflate the
 762 * balloon but were refused by the host for one reason or another.
 763 */
 764static void vmballoon_release_refused_pages(struct vmballoon *b,
 765                bool is_2m_pages)
 766{
 767        struct page *page, *next;
 768        struct vmballoon_page_size *page_size =
 769                        &b->page_sizes[is_2m_pages];
 770
 771        list_for_each_entry_safe(page, next, &page_size->refused_pages, lru) {
 772                list_del(&page->lru);
 773                vmballoon_free_page(page, is_2m_pages);
 774                STATS_INC(b->stats.refused_free[is_2m_pages]);
 775        }
 776
 777        page_size->n_refused_pages = 0;
 778}
 779
 780static void vmballoon_add_page(struct vmballoon *b, int idx, struct page *p)
 781{
 782        b->page = p;
 783}
 784
 785static void vmballoon_add_batched_page(struct vmballoon *b, int idx,
 786                                struct page *p)
 787{
 788        vmballoon_batch_set_pa(b->batch_page, idx,
 789                        (u64)page_to_pfn(p) << PAGE_SHIFT);
 790}
 791
 792/*
 793 * Inflate the balloon towards its target size. Note that we try to limit
 794 * the rate of allocation to make sure we are not choking the rest of the
 795 * system.
 796 */
 797static void vmballoon_inflate(struct vmballoon *b)
 798{
 799        unsigned rate;
 800        unsigned int allocations = 0;
 801        unsigned int num_pages = 0;
 802        int error = 0;
 803        gfp_t flags = VMW_PAGE_ALLOC_NOSLEEP;
 804        bool is_2m_pages;
 805
 806        pr_debug("%s - size: %d, target %d\n", __func__, b->size, b->target);
 807
 808        /*
 809         * First try NOSLEEP page allocations to inflate balloon.
 810         *
 811         * If we do not throttle nosleep allocations, we can drain all
 812         * free pages in the guest quickly (if the balloon target is high).
 813         * As a side-effect, draining free pages helps to inform (force)
 814         * the guest to start swapping if balloon target is not met yet,
 815         * which is a desired behavior. However, balloon driver can consume
 816         * all available CPU cycles if too many pages are allocated in a
 817         * second. Therefore, we throttle nosleep allocations even when
 818         * the guest is not under memory pressure. OTOH, if we have already
 819         * predicted that the guest is under memory pressure, then we
 820         * slowdown page allocations considerably.
 821         */
 822
 823        /*
 824         * Start with no sleep allocation rate which may be higher
 825         * than sleeping allocation rate.
 826         */
 827        if (b->slow_allocation_cycles) {
 828                rate = b->rate_alloc;
 829                is_2m_pages = false;
 830        } else {
 831                rate = UINT_MAX;
 832                is_2m_pages =
 833                        b->supported_page_sizes == VMW_BALLOON_NUM_PAGE_SIZES;
 834        }
 835
 836        pr_debug("%s - goal: %d, no-sleep rate: %u, sleep rate: %d\n",
 837                 __func__, b->target - b->size, rate, b->rate_alloc);
 838
 839        while (!b->reset_required &&
 840                b->size + num_pages * vmballoon_page_size(is_2m_pages)
 841                < b->target) {
 842                struct page *page;
 843
 844                if (flags == VMW_PAGE_ALLOC_NOSLEEP)
 845                        STATS_INC(b->stats.alloc[is_2m_pages]);
 846                else
 847                        STATS_INC(b->stats.sleep_alloc);
 848
 849                page = vmballoon_alloc_page(flags, is_2m_pages);
 850                if (!page) {
 851                        STATS_INC(b->stats.alloc_fail[is_2m_pages]);
 852
 853                        if (is_2m_pages) {
 854                                b->ops->lock(b, num_pages, true, &b->target);
 855
 856                                /*
 857                                 * ignore errors from locking as we now switch
 858                                 * to 4k pages and we might get different
 859                                 * errors.
 860                                 */
 861
 862                                num_pages = 0;
 863                                is_2m_pages = false;
 864                                continue;
 865                        }
 866
 867                        if (flags == VMW_PAGE_ALLOC_CANSLEEP) {
 868                                /*
 869                                 * CANSLEEP page allocation failed, so guest
 870                                 * is under severe memory pressure. Quickly
 871                                 * decrease allocation rate.
 872                                 */
 873                                b->rate_alloc = max(b->rate_alloc / 2,
 874                                                    VMW_BALLOON_RATE_ALLOC_MIN);
 875                                STATS_INC(b->stats.sleep_alloc_fail);
 876                                break;
 877                        }
 878
 879                        /*
 880                         * NOSLEEP page allocation failed, so the guest is
 881                         * under memory pressure. Let us slow down page
 882                         * allocations for next few cycles so that the guest
 883                         * gets out of memory pressure. Also, if we already
 884                         * allocated b->rate_alloc pages, let's pause,
 885                         * otherwise switch to sleeping allocations.
 886                         */
 887                        b->slow_allocation_cycles = VMW_BALLOON_SLOW_CYCLES;
 888
 889                        if (allocations >= b->rate_alloc)
 890                                break;
 891
 892                        flags = VMW_PAGE_ALLOC_CANSLEEP;
 893                        /* Lower rate for sleeping allocations. */
 894                        rate = b->rate_alloc;
 895                        continue;
 896                }
 897
 898                b->ops->add_page(b, num_pages++, page);
 899                if (num_pages == b->batch_max_pages) {
 900                        error = b->ops->lock(b, num_pages, is_2m_pages,
 901                                        &b->target);
 902                        num_pages = 0;
 903                        if (error)
 904                                break;
 905                }
 906
 907                cond_resched();
 908
 909                if (allocations >= rate) {
 910                        /* We allocated enough pages, let's take a break. */
 911                        break;
 912                }
 913        }
 914
 915        if (num_pages > 0)
 916                b->ops->lock(b, num_pages, is_2m_pages, &b->target);
 917
 918        /*
 919         * We reached our goal without failures so try increasing
 920         * allocation rate.
 921         */
 922        if (error == 0 && allocations >= b->rate_alloc) {
 923                unsigned int mult = allocations / b->rate_alloc;
 924
 925                b->rate_alloc =
 926                        min(b->rate_alloc + mult * VMW_BALLOON_RATE_ALLOC_INC,
 927                            VMW_BALLOON_RATE_ALLOC_MAX);
 928        }
 929
 930        vmballoon_release_refused_pages(b, true);
 931        vmballoon_release_refused_pages(b, false);
 932}
 933
 934/*
 935 * Decrease the size of the balloon allowing guest to use more memory.
 936 */
 937static void vmballoon_deflate(struct vmballoon *b)
 938{
 939        unsigned is_2m_pages;
 940
 941        pr_debug("%s - size: %d, target %d\n", __func__, b->size, b->target);
 942
 943        /* free pages to reach target */
 944        for (is_2m_pages = 0; is_2m_pages < b->supported_page_sizes;
 945                        is_2m_pages++) {
 946                struct page *page, *next;
 947                unsigned int num_pages = 0;
 948                struct vmballoon_page_size *page_size =
 949                                &b->page_sizes[is_2m_pages];
 950
 951                list_for_each_entry_safe(page, next, &page_size->pages, lru) {
 952                        if (b->reset_required ||
 953                                (b->target > 0 &&
 954                                        b->size - num_pages
 955                                        * vmballoon_page_size(is_2m_pages)
 956                                < b->target + vmballoon_page_size(true)))
 957                                break;
 958
 959                        list_del(&page->lru);
 960                        b->ops->add_page(b, num_pages++, page);
 961
 962                        if (num_pages == b->batch_max_pages) {
 963                                int error;
 964
 965                                error = b->ops->unlock(b, num_pages,
 966                                                is_2m_pages, &b->target);
 967                                num_pages = 0;
 968                                if (error)
 969                                        return;
 970                        }
 971
 972                        cond_resched();
 973                }
 974
 975                if (num_pages > 0)
 976                        b->ops->unlock(b, num_pages, is_2m_pages, &b->target);
 977        }
 978}
 979
 980static const struct vmballoon_ops vmballoon_basic_ops = {
 981        .add_page = vmballoon_add_page,
 982        .lock = vmballoon_lock_page,
 983        .unlock = vmballoon_unlock_page
 984};
 985
 986static const struct vmballoon_ops vmballoon_batched_ops = {
 987        .add_page = vmballoon_add_batched_page,
 988        .lock = vmballoon_lock_batched_page,
 989        .unlock = vmballoon_unlock_batched_page
 990};
 991
 992static bool vmballoon_init_batching(struct vmballoon *b)
 993{
 994        b->page = alloc_page(VMW_PAGE_ALLOC_NOSLEEP);
 995        if (!b->page)
 996                return false;
 997
 998        b->batch_page = vmap(&b->page, 1, VM_MAP, PAGE_KERNEL);
 999        if (!b->batch_page) {
1000                __free_page(b->page);
1001                return false;
1002        }
1003
1004        return true;
1005}
1006
1007/*
1008 * Receive notification and resize balloon
1009 */
1010static void vmballoon_doorbell(void *client_data)
1011{
1012        struct vmballoon *b = client_data;
1013
1014        STATS_INC(b->stats.doorbell);
1015
1016        mod_delayed_work(system_freezable_wq, &b->dwork, 0);
1017}
1018
1019/*
1020 * Clean up vmci doorbell
1021 */
1022static void vmballoon_vmci_cleanup(struct vmballoon *b)
1023{
1024        int error;
1025
1026        VMWARE_BALLOON_CMD(VMCI_DOORBELL_SET, VMCI_INVALID_ID,
1027                        VMCI_INVALID_ID, error);
1028        STATS_INC(b->stats.doorbell_unset);
1029
1030        if (!vmci_handle_is_invalid(b->vmci_doorbell)) {
1031                vmci_doorbell_destroy(b->vmci_doorbell);
1032                b->vmci_doorbell = VMCI_INVALID_HANDLE;
1033        }
1034}
1035
1036/*
1037 * Initialize vmci doorbell, to get notified as soon as balloon changes
1038 */
1039static int vmballoon_vmci_init(struct vmballoon *b)
1040{
1041        int error = 0;
1042
1043        if ((b->capabilities & VMW_BALLOON_SIGNALLED_WAKEUP_CMD) != 0) {
1044                error = vmci_doorbell_create(&b->vmci_doorbell,
1045                                VMCI_FLAG_DELAYED_CB,
1046                                VMCI_PRIVILEGE_FLAG_RESTRICTED,
1047                                vmballoon_doorbell, b);
1048
1049                if (error == VMCI_SUCCESS) {
1050                        VMWARE_BALLOON_CMD(VMCI_DOORBELL_SET,
1051                                        b->vmci_doorbell.context,
1052                                        b->vmci_doorbell.resource, error);
1053                        STATS_INC(b->stats.doorbell_set);
1054                }
1055        }
1056
1057        if (error != 0) {
1058                vmballoon_vmci_cleanup(b);
1059
1060                return -EIO;
1061        }
1062
1063        return 0;
1064}
1065
1066/*
1067 * Perform standard reset sequence by popping the balloon (in case it
1068 * is not  empty) and then restarting protocol. This operation normally
1069 * happens when host responds with VMW_BALLOON_ERROR_RESET to a command.
1070 */
1071static void vmballoon_reset(struct vmballoon *b)
1072{
1073        int error;
1074
1075        vmballoon_vmci_cleanup(b);
1076
1077        /* free all pages, skipping monitor unlock */
1078        vmballoon_pop(b);
1079
1080        if (!vmballoon_send_start(b, VMW_BALLOON_CAPABILITIES))
1081                return;
1082
1083        if ((b->capabilities & VMW_BALLOON_BATCHED_CMDS) != 0) {
1084                b->ops = &vmballoon_batched_ops;
1085                b->batch_max_pages = VMW_BALLOON_BATCH_MAX_PAGES;
1086                if (!vmballoon_init_batching(b)) {
1087                        /*
1088                         * We failed to initialize batching, inform the monitor
1089                         * about it by sending a null capability.
1090                         *
1091                         * The guest will retry in one second.
1092                         */
1093                        vmballoon_send_start(b, 0);
1094                        return;
1095                }
1096        } else if ((b->capabilities & VMW_BALLOON_BASIC_CMDS) != 0) {
1097                b->ops = &vmballoon_basic_ops;
1098                b->batch_max_pages = 1;
1099        }
1100
1101        b->reset_required = false;
1102
1103        error = vmballoon_vmci_init(b);
1104        if (error)
1105                pr_err("failed to initialize vmci doorbell\n");
1106
1107        if (!vmballoon_send_guest_id(b))
1108                pr_err("failed to send guest ID to the host\n");
1109}
1110
1111/*
1112 * Balloon work function: reset protocol, if needed, get the new size and
1113 * adjust balloon as needed. Repeat in 1 sec.
1114 */
1115static void vmballoon_work(struct work_struct *work)
1116{
1117        struct delayed_work *dwork = to_delayed_work(work);
1118        struct vmballoon *b = container_of(dwork, struct vmballoon, dwork);
1119        unsigned int target;
1120
1121        STATS_INC(b->stats.timer);
1122
1123        if (b->reset_required)
1124                vmballoon_reset(b);
1125
1126        if (b->slow_allocation_cycles > 0)
1127                b->slow_allocation_cycles--;
1128
1129        if (!b->reset_required && vmballoon_send_get_target(b, &target)) {
1130                /* update target, adjust size */
1131                b->target = target;
1132
1133                if (b->size < target)
1134                        vmballoon_inflate(b);
1135                else if (target == 0 ||
1136                                b->size > target + vmballoon_page_size(true))
1137                        vmballoon_deflate(b);
1138        }
1139
1140        /*
1141         * We are using a freezable workqueue so that balloon operations are
1142         * stopped while the system transitions to/from sleep/hibernation.
1143         */
1144        queue_delayed_work(system_freezable_wq,
1145                           dwork, round_jiffies_relative(HZ));
1146}
1147
1148/*
1149 * DEBUGFS Interface
1150 */
1151#ifdef CONFIG_DEBUG_FS
1152
1153static int vmballoon_debug_show(struct seq_file *f, void *offset)
1154{
1155        struct vmballoon *b = f->private;
1156        struct vmballoon_stats *stats = &b->stats;
1157
1158        /* format capabilities info */
1159        seq_printf(f,
1160                   "balloon capabilities:   %#4x\n"
1161                   "used capabilities:      %#4lx\n"
1162                   "is resetting:           %c\n",
1163                   VMW_BALLOON_CAPABILITIES, b->capabilities,
1164                   b->reset_required ? 'y' : 'n');
1165
1166        /* format size info */
1167        seq_printf(f,
1168                   "target:             %8d pages\n"
1169                   "current:            %8d pages\n",
1170                   b->target, b->size);
1171
1172        /* format rate info */
1173        seq_printf(f,
1174                   "rateSleepAlloc:     %8d pages/sec\n",
1175                   b->rate_alloc);
1176
1177        seq_printf(f,
1178                   "\n"
1179                   "timer:              %8u\n"
1180                   "doorbell:           %8u\n"
1181                   "start:              %8u (%4u failed)\n"
1182                   "guestType:          %8u (%4u failed)\n"
1183                   "2m-lock:            %8u (%4u failed)\n"
1184                   "lock:               %8u (%4u failed)\n"
1185                   "2m-unlock:          %8u (%4u failed)\n"
1186                   "unlock:             %8u (%4u failed)\n"
1187                   "target:             %8u (%4u failed)\n"
1188                   "prim2mAlloc:        %8u (%4u failed)\n"
1189                   "primNoSleepAlloc:   %8u (%4u failed)\n"
1190                   "primCanSleepAlloc:  %8u (%4u failed)\n"
1191                   "prim2mFree:         %8u\n"
1192                   "primFree:           %8u\n"
1193                   "err2mAlloc:         %8u\n"
1194                   "errAlloc:           %8u\n"
1195                   "err2mFree:          %8u\n"
1196                   "errFree:            %8u\n"
1197                   "doorbellSet:        %8u\n"
1198                   "doorbellUnset:      %8u\n",
1199                   stats->timer,
1200                   stats->doorbell,
1201                   stats->start, stats->start_fail,
1202                   stats->guest_type, stats->guest_type_fail,
1203                   stats->lock[true],  stats->lock_fail[true],
1204                   stats->lock[false],  stats->lock_fail[false],
1205                   stats->unlock[true], stats->unlock_fail[true],
1206                   stats->unlock[false], stats->unlock_fail[false],
1207                   stats->target, stats->target_fail,
1208                   stats->alloc[true], stats->alloc_fail[true],
1209                   stats->alloc[false], stats->alloc_fail[false],
1210                   stats->sleep_alloc, stats->sleep_alloc_fail,
1211                   stats->free[true],
1212                   stats->free[false],
1213                   stats->refused_alloc[true], stats->refused_alloc[false],
1214                   stats->refused_free[true], stats->refused_free[false],
1215                   stats->doorbell_set, stats->doorbell_unset);
1216
1217        return 0;
1218}
1219
1220static int vmballoon_debug_open(struct inode *inode, struct file *file)
1221{
1222        return single_open(file, vmballoon_debug_show, inode->i_private);
1223}
1224
1225static const struct file_operations vmballoon_debug_fops = {
1226        .owner          = THIS_MODULE,
1227        .open           = vmballoon_debug_open,
1228        .read           = seq_read,
1229        .llseek         = seq_lseek,
1230        .release        = single_release,
1231};
1232
1233static int __init vmballoon_debugfs_init(struct vmballoon *b)
1234{
1235        int error;
1236
1237        b->dbg_entry = debugfs_create_file("vmmemctl", S_IRUGO, NULL, b,
1238                                           &vmballoon_debug_fops);
1239        if (IS_ERR(b->dbg_entry)) {
1240                error = PTR_ERR(b->dbg_entry);
1241                pr_err("failed to create debugfs entry, error: %d\n", error);
1242                return error;
1243        }
1244
1245        return 0;
1246}
1247
1248static void __exit vmballoon_debugfs_exit(struct vmballoon *b)
1249{
1250        debugfs_remove(b->dbg_entry);
1251}
1252
1253#else
1254
1255static inline int vmballoon_debugfs_init(struct vmballoon *b)
1256{
1257        return 0;
1258}
1259
1260static inline void vmballoon_debugfs_exit(struct vmballoon *b)
1261{
1262}
1263
1264#endif  /* CONFIG_DEBUG_FS */
1265
1266static int __init vmballoon_init(void)
1267{
1268        int error;
1269        unsigned is_2m_pages;
1270        /*
1271         * Check if we are running on VMware's hypervisor and bail out
1272         * if we are not.
1273         */
1274        if (x86_hyper != &x86_hyper_vmware)
1275                return -ENODEV;
1276
1277        for (is_2m_pages = 0; is_2m_pages < VMW_BALLOON_NUM_PAGE_SIZES;
1278                        is_2m_pages++) {
1279                INIT_LIST_HEAD(&balloon.page_sizes[is_2m_pages].pages);
1280                INIT_LIST_HEAD(&balloon.page_sizes[is_2m_pages].refused_pages);
1281        }
1282
1283        /* initialize rates */
1284        balloon.rate_alloc = VMW_BALLOON_RATE_ALLOC_MAX;
1285
1286        INIT_DELAYED_WORK(&balloon.dwork, vmballoon_work);
1287
1288        error = vmballoon_debugfs_init(&balloon);
1289        if (error)
1290                return error;
1291
1292        balloon.vmci_doorbell = VMCI_INVALID_HANDLE;
1293        balloon.batch_page = NULL;
1294        balloon.page = NULL;
1295        balloon.reset_required = true;
1296
1297        queue_delayed_work(system_freezable_wq, &balloon.dwork, 0);
1298
1299        return 0;
1300}
1301module_init(vmballoon_init);
1302
1303static void __exit vmballoon_exit(void)
1304{
1305        vmballoon_vmci_cleanup(&balloon);
1306        cancel_delayed_work_sync(&balloon.dwork);
1307
1308        vmballoon_debugfs_exit(&balloon);
1309
1310        /*
1311         * Deallocate all reserved memory, and reset connection with monitor.
1312         * Reset connection before deallocating memory to avoid potential for
1313         * additional spurious resets from guest touching deallocated pages.
1314         */
1315        vmballoon_send_start(&balloon, 0);
1316        vmballoon_pop(&balloon);
1317}
1318module_exit(vmballoon_exit);
1319