Merge tag 'for-5.3/dm-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/devic...

[linux-2.6-block.git] / drivers / misc / vmw_balloon.c

// SPDX-License-Identifier: GPL-2.0
/*
 * VMware Balloon driver.
 *
 * Copyright (C) 2000-2018, VMware, Inc. All Rights Reserved.
 *
 * This is VMware physical memory management driver for Linux. The driver
 * acts like a "balloon" that can be inflated to reclaim physical pages by
 * reserving them in the guest and invalidating them in the monitor,
 * freeing up the underlying machine pages so they can be allocated to
 * other guests.  The balloon can also be deflated to allow the guest to
 * use more physical memory. Higher level policies can control the sizes
 * of balloons in VMs in order to manage physical memory resources.
 */

//#define DEBUG
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/workqueue.h>
#include <linux/debugfs.h>
#include <linux/seq_file.h>
#include <linux/rwsem.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/mount.h>
#include <linux/balloon_compaction.h>
#include <linux/vmw_vmci_defs.h>
#include <linux/vmw_vmci_api.h>
#include <asm/hypervisor.h>

MODULE_AUTHOR("VMware, Inc.");
MODULE_DESCRIPTION("VMware Memory Control (Balloon) Driver");
MODULE_ALIAS("dmi:*:svnVMware*:*");
MODULE_ALIAS("vmware_vmmemctl");
MODULE_LICENSE("GPL");

static bool __read_mostly vmwballoon_shrinker_enable;
module_param(vmwballoon_shrinker_enable, bool, 0444);
MODULE_PARM_DESC(vmwballoon_shrinker_enable,
        "Enable non-cooperative out-of-memory protection. Disabled by default as it may degrade performance.");

/* Delay in seconds after shrink before inflation. */
#define VMBALLOON_SHRINK_DELAY          (5)

/* Maximum number of refused pages we accumulate during inflation cycle */
#define VMW_BALLOON_MAX_REFUSED         16

/* Magic number for the balloon mount-point */
#define BALLOON_VMW_MAGIC               0x0ba11007

/*
 * Hypervisor communication port definitions.
 */
#define VMW_BALLOON_HV_PORT             0x5670
#define VMW_BALLOON_HV_MAGIC            0x456c6d6f
#define VMW_BALLOON_GUEST_ID            1       /* Linux */

enum vmwballoon_capabilities {
        /*
         * Bit 0 is reserved and not associated to any capability.
         */
        VMW_BALLOON_BASIC_CMDS                  = (1 << 1),
        VMW_BALLOON_BATCHED_CMDS                = (1 << 2),
        VMW_BALLOON_BATCHED_2M_CMDS             = (1 << 3),
        VMW_BALLOON_SIGNALLED_WAKEUP_CMD        = (1 << 4),
        VMW_BALLOON_64_BIT_TARGET               = (1 << 5)
};

#define VMW_BALLOON_CAPABILITIES_COMMON (VMW_BALLOON_BASIC_CMDS \
                                        | VMW_BALLOON_BATCHED_CMDS \
                                        | VMW_BALLOON_BATCHED_2M_CMDS \
                                        | VMW_BALLOON_SIGNALLED_WAKEUP_CMD)

#define VMW_BALLOON_2M_ORDER            (PMD_SHIFT - PAGE_SHIFT)

/*
 * 64-bit targets are only supported in 64-bit
 */
#ifdef CONFIG_64BIT
#define VMW_BALLOON_CAPABILITIES        (VMW_BALLOON_CAPABILITIES_COMMON \
                                        | VMW_BALLOON_64_BIT_TARGET)
#else
#define VMW_BALLOON_CAPABILITIES        VMW_BALLOON_CAPABILITIES_COMMON
#endif

enum vmballoon_page_size_type {
        VMW_BALLOON_4K_PAGE,
        VMW_BALLOON_2M_PAGE,
        VMW_BALLOON_LAST_SIZE = VMW_BALLOON_2M_PAGE
};

#define VMW_BALLOON_NUM_PAGE_SIZES      (VMW_BALLOON_LAST_SIZE + 1)

static const char * const vmballoon_page_size_names[] = {
        [VMW_BALLOON_4K_PAGE]                   = "4k",
        [VMW_BALLOON_2M_PAGE]                   = "2M"
};

enum vmballoon_op {
        VMW_BALLOON_INFLATE,
        VMW_BALLOON_DEFLATE
};

enum vmballoon_op_stat_type {
        VMW_BALLOON_OP_STAT,
        VMW_BALLOON_OP_FAIL_STAT
};

#define VMW_BALLOON_OP_STAT_TYPES       (VMW_BALLOON_OP_FAIL_STAT + 1)

/**
 * enum vmballoon_cmd_type - backdoor commands.
 *
 * Availability of the commands is as followed:
 *
 * %VMW_BALLOON_CMD_START, %VMW_BALLOON_CMD_GET_TARGET and
 * %VMW_BALLOON_CMD_GUEST_ID are always available.
 *
 * If the host reports %VMW_BALLOON_BASIC_CMDS are supported then
 * %VMW_BALLOON_CMD_LOCK and %VMW_BALLOON_CMD_UNLOCK commands are available.
 *
 * If the host reports %VMW_BALLOON_BATCHED_CMDS are supported then
 * %VMW_BALLOON_CMD_BATCHED_LOCK and VMW_BALLOON_CMD_BATCHED_UNLOCK commands
 * are available.
 *
 * If the host reports %VMW_BALLOON_BATCHED_2M_CMDS are supported then
 * %VMW_BALLOON_CMD_BATCHED_2M_LOCK and %VMW_BALLOON_CMD_BATCHED_2M_UNLOCK
 * are supported.
 *
 * If the host reports  VMW_BALLOON_SIGNALLED_WAKEUP_CMD is supported then
 * VMW_BALLOON_CMD_VMCI_DOORBELL_SET command is supported.
 *
 * @VMW_BALLOON_CMD_START: Communicating supported version with the hypervisor.
 * @VMW_BALLOON_CMD_GET_TARGET: Gets the balloon target size.
 * @VMW_BALLOON_CMD_LOCK: Informs the hypervisor about a ballooned page.
 * @VMW_BALLOON_CMD_UNLOCK: Informs the hypervisor about a page that is about
 *                          to be deflated from the balloon.
 * @VMW_BALLOON_CMD_GUEST_ID: Informs the hypervisor about the type of OS that
 *                            runs in the VM.
 * @VMW_BALLOON_CMD_BATCHED_LOCK: Inform the hypervisor about a batch of
 *                                ballooned pages (up to 512).
 * @VMW_BALLOON_CMD_BATCHED_UNLOCK: Inform the hypervisor about a batch of
 *                                pages that are about to be deflated from the
 *                                balloon (up to 512).
 * @VMW_BALLOON_CMD_BATCHED_2M_LOCK: Similar to @VMW_BALLOON_CMD_BATCHED_LOCK
 *                                   for 2MB pages.
 * @VMW_BALLOON_CMD_BATCHED_2M_UNLOCK: Similar to
 *                                     @VMW_BALLOON_CMD_BATCHED_UNLOCK for 2MB
 *                                     pages.
 * @VMW_BALLOON_CMD_VMCI_DOORBELL_SET: A command to set doorbell notification
 *                                     that would be invoked when the balloon
 *                                     size changes.
 * @VMW_BALLOON_CMD_LAST: Value of the last command.
 */
enum vmballoon_cmd_type {
        VMW_BALLOON_CMD_START,
        VMW_BALLOON_CMD_GET_TARGET,
        VMW_BALLOON_CMD_LOCK,
        VMW_BALLOON_CMD_UNLOCK,
        VMW_BALLOON_CMD_GUEST_ID,
        /* No command 5 */
        VMW_BALLOON_CMD_BATCHED_LOCK = 6,
        VMW_BALLOON_CMD_BATCHED_UNLOCK,
        VMW_BALLOON_CMD_BATCHED_2M_LOCK,
        VMW_BALLOON_CMD_BATCHED_2M_UNLOCK,
        VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
        VMW_BALLOON_CMD_LAST = VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
};

#define VMW_BALLOON_CMD_NUM     (VMW_BALLOON_CMD_LAST + 1)

enum vmballoon_error_codes {
        VMW_BALLOON_SUCCESS,
        VMW_BALLOON_ERROR_CMD_INVALID,
        VMW_BALLOON_ERROR_PPN_INVALID,
        VMW_BALLOON_ERROR_PPN_LOCKED,
        VMW_BALLOON_ERROR_PPN_UNLOCKED,
        VMW_BALLOON_ERROR_PPN_PINNED,
        VMW_BALLOON_ERROR_PPN_NOTNEEDED,
        VMW_BALLOON_ERROR_RESET,
        VMW_BALLOON_ERROR_BUSY
};

#define VMW_BALLOON_SUCCESS_WITH_CAPABILITIES   (0x03000000)

#define VMW_BALLOON_CMD_WITH_TARGET_MASK                        \
        ((1UL << VMW_BALLOON_CMD_GET_TARGET)            |       \
         (1UL << VMW_BALLOON_CMD_LOCK)                  |       \
         (1UL << VMW_BALLOON_CMD_UNLOCK)                |       \
         (1UL << VMW_BALLOON_CMD_BATCHED_LOCK)          |       \
         (1UL << VMW_BALLOON_CMD_BATCHED_UNLOCK)        |       \
         (1UL << VMW_BALLOON_CMD_BATCHED_2M_LOCK)       |       \
         (1UL << VMW_BALLOON_CMD_BATCHED_2M_UNLOCK))

static const char * const vmballoon_cmd_names[] = {
        [VMW_BALLOON_CMD_START]                 = "start",
        [VMW_BALLOON_CMD_GET_TARGET]            = "target",
        [VMW_BALLOON_CMD_LOCK]                  = "lock",
        [VMW_BALLOON_CMD_UNLOCK]                = "unlock",
        [VMW_BALLOON_CMD_GUEST_ID]              = "guestType",
        [VMW_BALLOON_CMD_BATCHED_LOCK]          = "batchLock",
        [VMW_BALLOON_CMD_BATCHED_UNLOCK]        = "batchUnlock",
        [VMW_BALLOON_CMD_BATCHED_2M_LOCK]       = "2m-lock",
        [VMW_BALLOON_CMD_BATCHED_2M_UNLOCK]     = "2m-unlock",
        [VMW_BALLOON_CMD_VMCI_DOORBELL_SET]     = "doorbellSet"
};

enum vmballoon_stat_page {
        VMW_BALLOON_PAGE_STAT_ALLOC,
        VMW_BALLOON_PAGE_STAT_ALLOC_FAIL,
        VMW_BALLOON_PAGE_STAT_REFUSED_ALLOC,
        VMW_BALLOON_PAGE_STAT_REFUSED_FREE,
        VMW_BALLOON_PAGE_STAT_FREE,
        VMW_BALLOON_PAGE_STAT_LAST = VMW_BALLOON_PAGE_STAT_FREE
};

#define VMW_BALLOON_PAGE_STAT_NUM       (VMW_BALLOON_PAGE_STAT_LAST + 1)

enum vmballoon_stat_general {
        VMW_BALLOON_STAT_TIMER,
        VMW_BALLOON_STAT_DOORBELL,
        VMW_BALLOON_STAT_RESET,
        VMW_BALLOON_STAT_SHRINK,
        VMW_BALLOON_STAT_SHRINK_FREE,
        VMW_BALLOON_STAT_LAST = VMW_BALLOON_STAT_SHRINK_FREE
};

#define VMW_BALLOON_STAT_NUM            (VMW_BALLOON_STAT_LAST + 1)

static DEFINE_STATIC_KEY_TRUE(vmw_balloon_batching);
static DEFINE_STATIC_KEY_FALSE(balloon_stat_enabled);

struct vmballoon_ctl {
        struct list_head pages;
        struct list_head refused_pages;
        struct list_head prealloc_pages;
        unsigned int n_refused_pages;
        unsigned int n_pages;
        enum vmballoon_page_size_type page_size;
        enum vmballoon_op op;
};

/**
 * struct vmballoon_batch_entry - a batch entry for lock or unlock.
 *
 * @status: the status of the operation, which is written by the hypervisor.
 * @reserved: reserved for future use. Must be set to zero.
 * @pfn: the physical frame number of the page to be locked or unlocked.
 */
struct vmballoon_batch_entry {
        u64 status : 5;
        u64 reserved : PAGE_SHIFT - 5;
        u64 pfn : 52;
} __packed;

struct vmballoon {
        /**
         * @max_page_size: maximum supported page size for ballooning.
         *
         * Protected by @conf_sem
         */
        enum vmballoon_page_size_type max_page_size;

        /**
         * @size: balloon actual size in basic page size (frames).
         *
         * While we currently do not support size which is bigger than 32-bit,
         * in preparation for future support, use 64-bits.
         */
        atomic64_t size;

        /**
         * @target: balloon target size in basic page size (frames).
         *
         * We do not protect the target under the assumption that setting the
         * value is always done through a single write. If this assumption ever
         * breaks, we would have to use X_ONCE for accesses, and suffer the less
         * optimized code. Although we may read stale target value if multiple
         * accesses happen at once, the performance impact should be minor.
         */
        unsigned long target;

        /**
         * @reset_required: reset flag
         *
         * Setting this flag may introduce races, but the code is expected to
         * handle them gracefully. In the worst case, another operation will
         * fail as reset did not take place. Clearing the flag is done while
         * holding @conf_sem for write.
         */
        bool reset_required;

        /**
         * @capabilities: hypervisor balloon capabilities.
         *
         * Protected by @conf_sem.
         */
        unsigned long capabilities;

        /**
         * @batch_page: pointer to communication batch page.
         *
         * When batching is used, batch_page points to a page, which holds up to
         * %VMW_BALLOON_BATCH_MAX_PAGES entries for locking or unlocking.
         */
        struct vmballoon_batch_entry *batch_page;

        /**
         * @batch_max_pages: maximum pages that can be locked/unlocked.
         *
         * Indicates the number of pages that the hypervisor can lock or unlock
         * at once, according to whether batching is enabled. If batching is
         * disabled, only a single page can be locked/unlock on each operation.
         *
         * Protected by @conf_sem.
         */
        unsigned int batch_max_pages;

        /**
         * @page: page to be locked/unlocked by the hypervisor
         *
         * @page is only used when batching is disabled and a single page is
         * reclaimed on each iteration.
         *
         * Protected by @comm_lock.
         */
        struct page *page;

        /**
         * @shrink_timeout: timeout until the next inflation.
         *
         * After an shrink event, indicates the time in jiffies after which
         * inflation is allowed again. Can be written concurrently with reads,
         * so must use READ_ONCE/WRITE_ONCE when accessing.
         */
        unsigned long shrink_timeout;

        /* statistics */
        struct vmballoon_stats *stats;

#ifdef CONFIG_DEBUG_FS
        /* debugfs file exporting statistics */
        struct dentry *dbg_entry;
#endif

        /**
         * @b_dev_info: balloon device information descriptor.
         */
        struct balloon_dev_info b_dev_info;

        struct delayed_work dwork;

        /**
         * @huge_pages - list of the inflated 2MB pages.
         *
         * Protected by @b_dev_info.pages_lock .
         */
        struct list_head huge_pages;

        /**
         * @vmci_doorbell.
         *
         * Protected by @conf_sem.
         */
        struct vmci_handle vmci_doorbell;

        /**
         * @conf_sem: semaphore to protect the configuration and the statistics.
         */
        struct rw_semaphore conf_sem;

        /**
         * @comm_lock: lock to protect the communication with the host.
         *
         * Lock ordering: @conf_sem -> @comm_lock .
         */
        spinlock_t comm_lock;

        /**
         * @shrinker: shrinker interface that is used to avoid over-inflation.
         */
        struct shrinker shrinker;

        /**
         * @shrinker_registered: whether the shrinker was registered.
         *
         * The shrinker interface does not handle gracefully the removal of
         * shrinker that was not registered before. This indication allows to
         * simplify the unregistration process.
         */
        bool shrinker_registered;
};

static struct vmballoon balloon;

struct vmballoon_stats {
        /* timer / doorbell operations */
        atomic64_t general_stat[VMW_BALLOON_STAT_NUM];

        /* allocation statistics for huge and small pages */
        atomic64_t
               page_stat[VMW_BALLOON_PAGE_STAT_NUM][VMW_BALLOON_NUM_PAGE_SIZES];

        /* Monitor operations: total operations, and failures */
        atomic64_t ops[VMW_BALLOON_CMD_NUM][VMW_BALLOON_OP_STAT_TYPES];
};

static inline bool is_vmballoon_stats_on(void)
{
        return IS_ENABLED(CONFIG_DEBUG_FS) &&
                static_branch_unlikely(&balloon_stat_enabled);
}

static inline void vmballoon_stats_op_inc(struct vmballoon *b, unsigned int op,
                                          enum vmballoon_op_stat_type type)
{
        if (is_vmballoon_stats_on())
                atomic64_inc(&b->stats->ops[op][type]);
}

static inline void vmballoon_stats_gen_inc(struct vmballoon *b,
                                           enum vmballoon_stat_general stat)
{
        if (is_vmballoon_stats_on())
                atomic64_inc(&b->stats->general_stat[stat]);
}

static inline void vmballoon_stats_gen_add(struct vmballoon *b,
                                           enum vmballoon_stat_general stat,
                                           unsigned int val)
{
        if (is_vmballoon_stats_on())
                atomic64_add(val, &b->stats->general_stat[stat]);
}

static inline void vmballoon_stats_page_inc(struct vmballoon *b,
                                            enum vmballoon_stat_page stat,
                                            enum vmballoon_page_size_type size)
{
        if (is_vmballoon_stats_on())
                atomic64_inc(&b->stats->page_stat[stat][size]);
}

static inline void vmballoon_stats_page_add(struct vmballoon *b,
                                            enum vmballoon_stat_page stat,
                                            enum vmballoon_page_size_type size,
                                            unsigned int val)
{
        if (is_vmballoon_stats_on())
                atomic64_add(val, &b->stats->page_stat[stat][size]);
}

static inline unsigned long
__vmballoon_cmd(struct vmballoon *b, unsigned long cmd, unsigned long arg1,
                unsigned long arg2, unsigned long *result)
{
        unsigned long status, dummy1, dummy2, dummy3, local_result;

        vmballoon_stats_op_inc(b, cmd, VMW_BALLOON_OP_STAT);

        asm volatile ("inl %%dx" :
                "=a"(status),
                "=c"(dummy1),
                "=d"(dummy2),
                "=b"(local_result),
                "=S"(dummy3) :
                "0"(VMW_BALLOON_HV_MAGIC),
                "1"(cmd),
                "2"(VMW_BALLOON_HV_PORT),
                "3"(arg1),
                "4"(arg2) :
                "memory");

        /* update the result if needed */
        if (result)
                *result = (cmd == VMW_BALLOON_CMD_START) ? dummy1 :
                                                           local_result;

        /* update target when applicable */
        if (status == VMW_BALLOON_SUCCESS &&
            ((1ul << cmd) & VMW_BALLOON_CMD_WITH_TARGET_MASK))
                WRITE_ONCE(b->target, local_result);

        if (status != VMW_BALLOON_SUCCESS &&
            status != VMW_BALLOON_SUCCESS_WITH_CAPABILITIES) {
                vmballoon_stats_op_inc(b, cmd, VMW_BALLOON_OP_FAIL_STAT);
                pr_debug("%s: %s [0x%lx,0x%lx) failed, returned %ld\n",
                         __func__, vmballoon_cmd_names[cmd], arg1, arg2,
                         status);
        }

        /* mark reset required accordingly */
        if (status == VMW_BALLOON_ERROR_RESET)
                b->reset_required = true;

        return status;
}

static __always_inline unsigned long
vmballoon_cmd(struct vmballoon *b, unsigned long cmd, unsigned long arg1,
              unsigned long arg2)
{
        unsigned long dummy;

        return __vmballoon_cmd(b, cmd, arg1, arg2, &dummy);
}

/*
 * Send "start" command to the host, communicating supported version
 * of the protocol.
 */
static int vmballoon_send_start(struct vmballoon *b, unsigned long req_caps)
{
        unsigned long status, capabilities;

        status = __vmballoon_cmd(b, VMW_BALLOON_CMD_START, req_caps, 0,
                                 &capabilities);

        switch (status) {
        case VMW_BALLOON_SUCCESS_WITH_CAPABILITIES:
                b->capabilities = capabilities;
                break;
        case VMW_BALLOON_SUCCESS:
                b->capabilities = VMW_BALLOON_BASIC_CMDS;
                break;
        default:
                return -EIO;
        }

        /*
         * 2MB pages are only supported with batching. If batching is for some
         * reason disabled, do not use 2MB pages, since otherwise the legacy
         * mechanism is used with 2MB pages, causing a failure.
         */
        b->max_page_size = VMW_BALLOON_4K_PAGE;
        if ((b->capabilities & VMW_BALLOON_BATCHED_2M_CMDS) &&
            (b->capabilities & VMW_BALLOON_BATCHED_CMDS))
                b->max_page_size = VMW_BALLOON_2M_PAGE;


        return 0;
}

/**
 * vmballoon_send_guest_id - communicate guest type to the host.
 *
 * @b: pointer to the balloon.
 *
 * Communicate guest type to the host so that it can adjust ballooning
 * algorithm to the one most appropriate for the guest. This command
 * is normally issued after sending "start" command and is part of
 * standard reset sequence.
 *
 * Return: zero on success or appropriate error code.
 */
static int vmballoon_send_guest_id(struct vmballoon *b)
{
        unsigned long status;

        status = vmballoon_cmd(b, VMW_BALLOON_CMD_GUEST_ID,
                               VMW_BALLOON_GUEST_ID, 0);

        return status == VMW_BALLOON_SUCCESS ? 0 : -EIO;
}

/**
 * vmballoon_page_order() - return the order of the page
 * @page_size: the size of the page.
 *
 * Return: the allocation order.
 */
static inline
unsigned int vmballoon_page_order(enum vmballoon_page_size_type page_size)
{
        return page_size == VMW_BALLOON_2M_PAGE ? VMW_BALLOON_2M_ORDER : 0;
}

/**
 * vmballoon_page_in_frames() - returns the number of frames in a page.
 * @page_size: the size of the page.
 *
 * Return: the number of 4k frames.
 */
static inline unsigned int
vmballoon_page_in_frames(enum vmballoon_page_size_type page_size)
{
        return 1 << vmballoon_page_order(page_size);
}

/**
 * vmballoon_mark_page_offline() - mark a page as offline
 * @page: pointer for the page.
 * @page_size: the size of the page.
 */
static void
vmballoon_mark_page_offline(struct page *page,
                            enum vmballoon_page_size_type page_size)
{
        int i;

        for (i = 0; i < vmballoon_page_in_frames(page_size); i++)
                __SetPageOffline(page + i);
}

/**
 * vmballoon_mark_page_online() - mark a page as online
 * @page: pointer for the page.
 * @page_size: the size of the page.
 */
static void
vmballoon_mark_page_online(struct page *page,
                           enum vmballoon_page_size_type page_size)
{
        int i;

        for (i = 0; i < vmballoon_page_in_frames(page_size); i++)
                __ClearPageOffline(page + i);
}

/**
 * vmballoon_send_get_target() - Retrieve desired balloon size from the host.
 *
 * @b: pointer to the balloon.
 *
 * Return: zero on success, EINVAL if limit does not fit in 32-bit, as required
 * by the host-guest protocol and EIO if an error occurred in communicating with
 * the host.
 */
static int vmballoon_send_get_target(struct vmballoon *b)
{
        unsigned long status;
        unsigned long limit;

        limit = totalram_pages();

        /* Ensure limit fits in 32-bits if 64-bit targets are not supported */
        if (!(b->capabilities & VMW_BALLOON_64_BIT_TARGET) &&
            limit != (u32)limit)
                return -EINVAL;

        status = vmballoon_cmd(b, VMW_BALLOON_CMD_GET_TARGET, limit, 0);

        return status == VMW_BALLOON_SUCCESS ? 0 : -EIO;
}

/**
 * vmballoon_alloc_page_list - allocates a list of pages.
 *
 * @b: pointer to the balloon.
 * @ctl: pointer for the %struct vmballoon_ctl, which defines the operation.
 * @req_n_pages: the number of requested pages.
 *
 * Tries to allocate @req_n_pages. Add them to the list of balloon pages in
 * @ctl.pages and updates @ctl.n_pages to reflect the number of pages.
 *
 * Return: zero on success or error code otherwise.
 */
static int vmballoon_alloc_page_list(struct vmballoon *b,
                                     struct vmballoon_ctl *ctl,
                                     unsigned int req_n_pages)
{
        struct page *page;
        unsigned int i;

        for (i = 0; i < req_n_pages; i++) {
                /*
                 * First check if we happen to have pages that were allocated
                 * before. This happens when 2MB page rejected during inflation
                 * by the hypervisor, and then split into 4KB pages.
                 */
                if (!list_empty(&ctl->prealloc_pages)) {
                        page = list_first_entry(&ctl->prealloc_pages,
                                                struct page, lru);
                        list_del(&page->lru);
                } else {
                        if (ctl->page_size == VMW_BALLOON_2M_PAGE)
                                page = alloc_pages(__GFP_HIGHMEM|__GFP_NOWARN|
                                        __GFP_NOMEMALLOC, VMW_BALLOON_2M_ORDER);
                        else
                                page = balloon_page_alloc();

                        vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_ALLOC,
                                                 ctl->page_size);
                }

                if (page) {
                        vmballoon_mark_page_offline(page, ctl->page_size);
                        /* Success. Add the page to the list and continue. */
                        list_add(&page->lru, &ctl->pages);
                        continue;
                }

                /* Allocation failed. Update statistics and stop. */
                vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_ALLOC_FAIL,
                                         ctl->page_size);
                break;
        }

        ctl->n_pages = i;

        return req_n_pages == ctl->n_pages ? 0 : -ENOMEM;
}

/**
 * vmballoon_handle_one_result - Handle lock/unlock result for a single page.
 *
 * @b: pointer for %struct vmballoon.
 * @page: pointer for the page whose result should be handled.
 * @page_size: size of the page.
 * @status: status of the operation as provided by the hypervisor.
 */
static int vmballoon_handle_one_result(struct vmballoon *b, struct page *page,
                                       enum vmballoon_page_size_type page_size,
                                       unsigned long status)
{
        /* On success do nothing. The page is already on the balloon list. */
        if (likely(status == VMW_BALLOON_SUCCESS))
                return 0;

        pr_debug("%s: failed comm pfn %lx status %lu page_size %s\n", __func__,
                 page_to_pfn(page), status,
                 vmballoon_page_size_names[page_size]);

        /* Error occurred */
        vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_REFUSED_ALLOC,
                                 page_size);

        return -EIO;
}

/**
 * vmballoon_status_page - returns the status of (un)lock operation
 *
 * @b: pointer to the balloon.
 * @idx: index for the page for which the operation is performed.
 * @p: pointer to where the page struct is returned.
 *
 * Following a lock or unlock operation, returns the status of the operation for
 * an individual page. Provides the page that the operation was performed on on
 * the @page argument.
 *
 * Returns: The status of a lock or unlock operation for an individual page.
 */
static unsigned long vmballoon_status_page(struct vmballoon *b, int idx,
                                           struct page **p)
{
        if (static_branch_likely(&vmw_balloon_batching)) {
                /* batching mode */
                *p = pfn_to_page(b->batch_page[idx].pfn);
                return b->batch_page[idx].status;
        }

        /* non-batching mode */
        *p = b->page;

        /*
         * If a failure occurs, the indication will be provided in the status
         * of the entire operation, which is considered before the individual
         * page status. So for non-batching mode, the indication is always of
         * success.
         */
        return VMW_BALLOON_SUCCESS;
}

/**
 * vmballoon_lock_op - notifies the host about inflated/deflated pages.
 * @b: pointer to the balloon.
 * @num_pages: number of inflated/deflated pages.
 * @page_size: size of the page.
 * @op: the type of operation (lock or unlock).
 *
 * Notify the host about page(s) that were ballooned (or removed from the
 * balloon) so that host can use it without fear that guest will need it (or
 * stop using them since the VM does). Host may reject some pages, we need to
 * check the return value and maybe submit a different page. The pages that are
 * inflated/deflated are pointed by @b->page.
 *
 * Return: result as provided by the hypervisor.
 */
static unsigned long vmballoon_lock_op(struct vmballoon *b,
                                       unsigned int num_pages,
                                       enum vmballoon_page_size_type page_size,
                                       enum vmballoon_op op)
{
        unsigned long cmd, pfn;

        lockdep_assert_held(&b->comm_lock);

        if (static_branch_likely(&vmw_balloon_batching)) {
                if (op == VMW_BALLOON_INFLATE)
                        cmd = page_size == VMW_BALLOON_2M_PAGE ?
                                VMW_BALLOON_CMD_BATCHED_2M_LOCK :
                                VMW_BALLOON_CMD_BATCHED_LOCK;
                else
                        cmd = page_size == VMW_BALLOON_2M_PAGE ?
                                VMW_BALLOON_CMD_BATCHED_2M_UNLOCK :
                                VMW_BALLOON_CMD_BATCHED_UNLOCK;

                pfn = PHYS_PFN(virt_to_phys(b->batch_page));
        } else {
                cmd = op == VMW_BALLOON_INFLATE ? VMW_BALLOON_CMD_LOCK :
                                                  VMW_BALLOON_CMD_UNLOCK;
                pfn = page_to_pfn(b->page);

                /* In non-batching mode, PFNs must fit in 32-bit */
                if (unlikely(pfn != (u32)pfn))
                        return VMW_BALLOON_ERROR_PPN_INVALID;
        }

        return vmballoon_cmd(b, cmd, pfn, num_pages);
}

/**
 * vmballoon_add_page - adds a page towards lock/unlock operation.
 *
 * @b: pointer to the balloon.
 * @idx: index of the page to be ballooned in this batch.
 * @p: pointer to the page that is about to be ballooned.
 *
 * Adds the page to be ballooned. Must be called while holding @comm_lock.
 */
static void vmballoon_add_page(struct vmballoon *b, unsigned int idx,
                               struct page *p)
{
        lockdep_assert_held(&b->comm_lock);

        if (static_branch_likely(&vmw_balloon_batching))
                b->batch_page[idx] = (struct vmballoon_batch_entry)
                                        { .pfn = page_to_pfn(p) };
        else
                b->page = p;
}

/**
 * vmballoon_lock - lock or unlock a batch of pages.
 *
 * @b: pointer to the balloon.
 * @ctl: pointer for the %struct vmballoon_ctl, which defines the operation.
 *
 * Notifies the host of about ballooned pages (after inflation or deflation,
 * according to @ctl). If the host rejects the page put it on the
 * @ctl refuse list. These refused page are then released when moving to the
 * next size of pages.
 *
 * Note that we neither free any @page here nor put them back on the ballooned
 * pages list. Instead we queue it for later processing. We do that for several
 * reasons. First, we do not want to free the page under the lock. Second, it
 * allows us to unify the handling of lock and unlock. In the inflate case, the
 * caller will check if there are too many refused pages and release them.
 * Although it is not identical to the past behavior, it should not affect
 * performance.
 */
static int vmballoon_lock(struct vmballoon *b, struct vmballoon_ctl *ctl)
{
        unsigned long batch_status;
        struct page *page;
        unsigned int i, num_pages;

        num_pages = ctl->n_pages;
        if (num_pages == 0)
                return 0;

        /* communication with the host is done under the communication lock */
        spin_lock(&b->comm_lock);

        i = 0;
        list_for_each_entry(page, &ctl->pages, lru)
                vmballoon_add_page(b, i++, page);

        batch_status = vmballoon_lock_op(b, ctl->n_pages, ctl->page_size,
                                         ctl->op);

        /*
         * Iterate over the pages in the provided list. Since we are changing
         * @ctl->n_pages we are saving the original value in @num_pages and
         * use this value to bound the loop.
         */
        for (i = 0; i < num_pages; i++) {
                unsigned long status;

                status = vmballoon_status_page(b, i, &page);

                /*
                 * Failure of the whole batch overrides a single operation
                 * results.
                 */
                if (batch_status != VMW_BALLOON_SUCCESS)
                        status = batch_status;

                /* Continue if no error happened */
                if (!vmballoon_handle_one_result(b, page, ctl->page_size,
                                                 status))
                        continue;

                /*
                 * Error happened. Move the pages to the refused list and update
                 * the pages number.
                 */
                list_move(&page->lru, &ctl->refused_pages);
                ctl->n_pages--;
                ctl->n_refused_pages++;
        }

        spin_unlock(&b->comm_lock);

        return batch_status == VMW_BALLOON_SUCCESS ? 0 : -EIO;
}

/**
 * vmballoon_release_page_list() - Releases a page list
 *
 * @page_list: list of pages to release.
 * @n_pages: pointer to the number of pages.
 * @page_size: whether the pages in the list are 2MB (or else 4KB).
 *
 * Releases the list of pages and zeros the number of pages.
 */
static void vmballoon_release_page_list(struct list_head *page_list,
                                       int *n_pages,
                                       enum vmballoon_page_size_type page_size)
{
        struct page *page, *tmp;

        list_for_each_entry_safe(page, tmp, page_list, lru) {
                list_del(&page->lru);
                vmballoon_mark_page_online(page, page_size);
                __free_pages(page, vmballoon_page_order(page_size));
        }

        if (n_pages)
                *n_pages = 0;
}


/*
 * Release pages that were allocated while attempting to inflate the
 * balloon but were refused by the host for one reason or another.
 */
static void vmballoon_release_refused_pages(struct vmballoon *b,
                                            struct vmballoon_ctl *ctl)
{
        vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_REFUSED_FREE,
                                 ctl->page_size);

        vmballoon_release_page_list(&ctl->refused_pages, &ctl->n_refused_pages,
                                    ctl->page_size);
}

/**
 * vmballoon_change - retrieve the required balloon change
 *
 * @b: pointer for the balloon.
 *
 * Return: the required change for the balloon size. A positive number
 * indicates inflation, a negative number indicates a deflation.
 */
static int64_t vmballoon_change(struct vmballoon *b)
{
        int64_t size, target;

        size = atomic64_read(&b->size);
        target = READ_ONCE(b->target);

        /*
         * We must cast first because of int sizes
         * Otherwise we might get huge positives instead of negatives
         */

        if (b->reset_required)
                return 0;

        /* consider a 2MB slack on deflate, unless the balloon is emptied */
        if (target < size && target != 0 &&
            size - target < vmballoon_page_in_frames(VMW_BALLOON_2M_PAGE))
                return 0;

        /* If an out-of-memory recently occurred, inflation is disallowed. */
        if (target > size && time_before(jiffies, READ_ONCE(b->shrink_timeout)))
                return 0;

        return target - size;
}

/**
 * vmballoon_enqueue_page_list() - Enqueues list of pages after inflation.
 *
 * @b: pointer to balloon.
 * @pages: list of pages to enqueue.
 * @n_pages: pointer to number of pages in list. The value is zeroed.
 * @page_size: whether the pages are 2MB or 4KB pages.
 *
 * Enqueues the provides list of pages in the ballooned page list, clears the
 * list and zeroes the number of pages that was provided.
 */
static void vmballoon_enqueue_page_list(struct vmballoon *b,
                                        struct list_head *pages,
                                        unsigned int *n_pages,
                                        enum vmballoon_page_size_type page_size)
{
        unsigned long flags;

        if (page_size == VMW_BALLOON_4K_PAGE) {
                balloon_page_list_enqueue(&b->b_dev_info, pages);
        } else {
                /*
                 * Keep the huge pages in a local list which is not available
                 * for the balloon compaction mechanism.
                 */
                spin_lock_irqsave(&b->b_dev_info.pages_lock, flags);
                list_splice_init(pages, &b->huge_pages);
                __count_vm_events(BALLOON_INFLATE, *n_pages *
                                  vmballoon_page_in_frames(VMW_BALLOON_2M_PAGE));
                spin_unlock_irqrestore(&b->b_dev_info.pages_lock, flags);
        }

        *n_pages = 0;
}

/**
 * vmballoon_dequeue_page_list() - Dequeues page lists for deflation.
 *
 * @b: pointer to balloon.
 * @pages: list of pages to enqueue.
 * @n_pages: pointer to number of pages in list. The value is zeroed.
 * @page_size: whether the pages are 2MB or 4KB pages.
 * @n_req_pages: the number of requested pages.
 *
 * Dequeues the number of requested pages from the balloon for deflation. The
 * number of dequeued pages may be lower, if not enough pages in the requested
 * size are available.
 */
static void vmballoon_dequeue_page_list(struct vmballoon *b,
                                        struct list_head *pages,
                                        unsigned int *n_pages,
                                        enum vmballoon_page_size_type page_size,
                                        unsigned int n_req_pages)
{
        struct page *page, *tmp;
        unsigned int i = 0;
        unsigned long flags;

        /* In the case of 4k pages, use the compaction infrastructure */
        if (page_size == VMW_BALLOON_4K_PAGE) {
                *n_pages = balloon_page_list_dequeue(&b->b_dev_info, pages,
                                                     n_req_pages);
                return;
        }

        /* 2MB pages */
        spin_lock_irqsave(&b->b_dev_info.pages_lock, flags);
        list_for_each_entry_safe(page, tmp, &b->huge_pages, lru) {
                list_move(&page->lru, pages);
                if (++i == n_req_pages)
                        break;
        }

        __count_vm_events(BALLOON_DEFLATE,
                          i * vmballoon_page_in_frames(VMW_BALLOON_2M_PAGE));
        spin_unlock_irqrestore(&b->b_dev_info.pages_lock, flags);
        *n_pages = i;
}

/**
 * vmballoon_split_refused_pages() - Split the 2MB refused pages to 4k.
 *
 * If inflation of 2MB pages was denied by the hypervisor, it is likely to be
 * due to one or few 4KB pages. These 2MB pages may keep being allocated and
 * then being refused. To prevent this case, this function splits the refused
 * pages into 4KB pages and adds them into @prealloc_pages list.
 *
 * @ctl: pointer for the %struct vmballoon_ctl, which defines the operation.
 */
static void vmballoon_split_refused_pages(struct vmballoon_ctl *ctl)
{
        struct page *page, *tmp;
        unsigned int i, order;

        order = vmballoon_page_order(ctl->page_size);

        list_for_each_entry_safe(page, tmp, &ctl->refused_pages, lru) {
                list_del(&page->lru);
                split_page(page, order);
                for (i = 0; i < (1 << order); i++)
                        list_add(&page[i].lru, &ctl->prealloc_pages);
        }
        ctl->n_refused_pages = 0;
}

/**
 * vmballoon_inflate() - Inflate the balloon towards its target size.
 *
 * @b: pointer to the balloon.
 */
static void vmballoon_inflate(struct vmballoon *b)
{
        int64_t to_inflate_frames;
        struct vmballoon_ctl ctl = {
                .pages = LIST_HEAD_INIT(ctl.pages),
                .refused_pages = LIST_HEAD_INIT(ctl.refused_pages),
                .prealloc_pages = LIST_HEAD_INIT(ctl.prealloc_pages),
                .page_size = b->max_page_size,
                .op = VMW_BALLOON_INFLATE
        };

        while ((to_inflate_frames = vmballoon_change(b)) > 0) {
                unsigned int to_inflate_pages, page_in_frames;
                int alloc_error, lock_error = 0;

                VM_BUG_ON(!list_empty(&ctl.pages));
                VM_BUG_ON(ctl.n_pages != 0);

                page_in_frames = vmballoon_page_in_frames(ctl.page_size);

                to_inflate_pages = min_t(unsigned long, b->batch_max_pages,
                                         DIV_ROUND_UP_ULL(to_inflate_frames,
                                                          page_in_frames));

                /* Start by allocating */
                alloc_error = vmballoon_alloc_page_list(b, &ctl,
                                                        to_inflate_pages);

                /* Actually lock the pages by telling the hypervisor */
                lock_error = vmballoon_lock(b, &ctl);

                /*
                 * If an error indicates that something serious went wrong,
                 * stop the inflation.
                 */
                if (lock_error)
                        break;

                /* Update the balloon size */
                atomic64_add(ctl.n_pages * page_in_frames, &b->size);

                vmballoon_enqueue_page_list(b, &ctl.pages, &ctl.n_pages,
                                            ctl.page_size);

                /*
                 * If allocation failed or the number of refused pages exceeds
                 * the maximum allowed, move to the next page size.
                 */
                if (alloc_error ||
                    ctl.n_refused_pages >= VMW_BALLOON_MAX_REFUSED) {
                        if (ctl.page_size == VMW_BALLOON_4K_PAGE)
                                break;

                        /*
                         * Split the refused pages to 4k. This will also empty
                         * the refused pages list.
                         */
                        vmballoon_split_refused_pages(&ctl);
                        ctl.page_size--;
                }

                cond_resched();
        }

        /*
         * Release pages that were allocated while attempting to inflate the
         * balloon but were refused by the host for one reason or another,
         * and update the statistics.
         */
        if (ctl.n_refused_pages != 0)
                vmballoon_release_refused_pages(b, &ctl);

        vmballoon_release_page_list(&ctl.prealloc_pages, NULL, ctl.page_size);
}

/**
 * vmballoon_deflate() - Decrease the size of the balloon.
 *
 * @b: pointer to the balloon
 * @n_frames: the number of frames to deflate. If zero, automatically
 * calculated according to the target size.
 * @coordinated: whether to coordinate with the host
 *
 * Decrease the size of the balloon allowing guest to use more memory.
 *
 * Return: The number of deflated frames (i.e., basic page size units)
 */
static unsigned long vmballoon_deflate(struct vmballoon *b, uint64_t n_frames,
                                       bool coordinated)
{
        unsigned long deflated_frames = 0;
        unsigned long tried_frames = 0;
        struct vmballoon_ctl ctl = {
                .pages = LIST_HEAD_INIT(ctl.pages),
                .refused_pages = LIST_HEAD_INIT(ctl.refused_pages),
                .page_size = VMW_BALLOON_4K_PAGE,
                .op = VMW_BALLOON_DEFLATE
        };

        /* free pages to reach target */
        while (true) {
                unsigned int to_deflate_pages, n_unlocked_frames;
                unsigned int page_in_frames;
                int64_t to_deflate_frames;
                bool deflated_all;

                page_in_frames = vmballoon_page_in_frames(ctl.page_size);

                VM_BUG_ON(!list_empty(&ctl.pages));
                VM_BUG_ON(ctl.n_pages);
                VM_BUG_ON(!list_empty(&ctl.refused_pages));
                VM_BUG_ON(ctl.n_refused_pages);

                /*
                 * If we were requested a specific number of frames, we try to
                 * deflate this number of frames. Otherwise, deflation is
                 * performed according to the target and balloon size.
                 */
                to_deflate_frames = n_frames ? n_frames - tried_frames :
                                               -vmballoon_change(b);

                /* break if no work to do */
                if (to_deflate_frames <= 0)
                        break;

                /*
                 * Calculate the number of frames based on current page size,
                 * but limit the deflated frames to a single chunk
                 */
                to_deflate_pages = min_t(unsigned long, b->batch_max_pages,
                                         DIV_ROUND_UP_ULL(to_deflate_frames,
                                                          page_in_frames));

                /* First take the pages from the balloon pages. */
                vmballoon_dequeue_page_list(b, &ctl.pages, &ctl.n_pages,
                                            ctl.page_size, to_deflate_pages);

                /*
                 * Before pages are moving to the refused list, count their
                 * frames as frames that we tried to deflate.
                 */
                tried_frames += ctl.n_pages * page_in_frames;

                /*
                 * Unlock the pages by communicating with the hypervisor if the
                 * communication is coordinated (i.e., not pop). We ignore the
                 * return code. Instead we check if all the pages we manage to
                 * unlock all the pages. If we failed, we will move to the next
                 * page size, and would eventually try again later.
                 */
                if (coordinated)
                        vmballoon_lock(b, &ctl);

                /*
                 * Check if we deflated enough. We will move to the next page
                 * size if we did not manage to do so. This calculation takes
                 * place now, as once the pages are released, the number of
                 * pages is zeroed.
                 */
                deflated_all = (ctl.n_pages == to_deflate_pages);

                /* Update local and global counters */
                n_unlocked_frames = ctl.n_pages * page_in_frames;
                atomic64_sub(n_unlocked_frames, &b->size);
                deflated_frames += n_unlocked_frames;

                vmballoon_stats_page_add(b, VMW_BALLOON_PAGE_STAT_FREE,
                                         ctl.page_size, ctl.n_pages);

                /* free the ballooned pages */
                vmballoon_release_page_list(&ctl.pages, &ctl.n_pages,
                                            ctl.page_size);

                /* Return the refused pages to the ballooned list. */
                vmballoon_enqueue_page_list(b, &ctl.refused_pages,
                                            &ctl.n_refused_pages,
                                            ctl.page_size);

                /* If we failed to unlock all the pages, move to next size. */
                if (!deflated_all) {
                        if (ctl.page_size == b->max_page_size)
                                break;
                        ctl.page_size++;
                }

                cond_resched();
        }

        return deflated_frames;
}

/**
 * vmballoon_deinit_batching - disables batching mode.
 *
 * @b: pointer to &struct vmballoon.
 *
 * Disables batching, by deallocating the page for communication with the
 * hypervisor and disabling the static key to indicate that batching is off.
 */
static void vmballoon_deinit_batching(struct vmballoon *b)
{
        free_page((unsigned long)b->batch_page);
        b->batch_page = NULL;
        static_branch_disable(&vmw_balloon_batching);
        b->batch_max_pages = 1;
}

/**
 * vmballoon_init_batching - enable batching mode.
 *
 * @b: pointer to &struct vmballoon.
 *
 * Enables batching, by allocating a page for communication with the hypervisor
 * and enabling the static_key to use batching.
 *
 * Return: zero on success or an appropriate error-code.
 */
static int vmballoon_init_batching(struct vmballoon *b)
{
        struct page *page;

        page = alloc_page(GFP_KERNEL | __GFP_ZERO);
        if (!page)
                return -ENOMEM;

        b->batch_page = page_address(page);
        b->batch_max_pages = PAGE_SIZE / sizeof(struct vmballoon_batch_entry);

        static_branch_enable(&vmw_balloon_batching);

        return 0;
}

/*
 * Receive notification and resize balloon
 */
static void vmballoon_doorbell(void *client_data)
{
        struct vmballoon *b = client_data;

        vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_DOORBELL);

        mod_delayed_work(system_freezable_wq, &b->dwork, 0);
}

/*
 * Clean up vmci doorbell
 */
static void vmballoon_vmci_cleanup(struct vmballoon *b)
{
        vmballoon_cmd(b, VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
                      VMCI_INVALID_ID, VMCI_INVALID_ID);

        if (!vmci_handle_is_invalid(b->vmci_doorbell)) {
                vmci_doorbell_destroy(b->vmci_doorbell);
                b->vmci_doorbell = VMCI_INVALID_HANDLE;
        }
}

/**
 * vmballoon_vmci_init - Initialize vmci doorbell.
 *
 * @b: pointer to the balloon.
 *
 * Return: zero on success or when wakeup command not supported. Error-code
 * otherwise.
 *
 * Initialize vmci doorbell, to get notified as soon as balloon changes.
 */
static int vmballoon_vmci_init(struct vmballoon *b)
{
        unsigned long error;

        if ((b->capabilities & VMW_BALLOON_SIGNALLED_WAKEUP_CMD) == 0)
                return 0;

        error = vmci_doorbell_create(&b->vmci_doorbell, VMCI_FLAG_DELAYED_CB,
                                     VMCI_PRIVILEGE_FLAG_RESTRICTED,
                                     vmballoon_doorbell, b);

        if (error != VMCI_SUCCESS)
                goto fail;

        error = __vmballoon_cmd(b, VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
                                b->vmci_doorbell.context,
                                b->vmci_doorbell.resource, NULL);

        if (error != VMW_BALLOON_SUCCESS)
                goto fail;

        return 0;
fail:
        vmballoon_vmci_cleanup(b);
        return -EIO;
}

/**
 * vmballoon_pop - Quickly release all pages allocate for the balloon.
 *
 * @b: pointer to the balloon.
 *
 * This function is called when host decides to "reset" balloon for one reason
 * or another. Unlike normal "deflate" we do not (shall not) notify host of the
 * pages being released.
 */
static void vmballoon_pop(struct vmballoon *b)
{
        unsigned long size;

        while ((size = atomic64_read(&b->size)))
                vmballoon_deflate(b, size, false);
}

/*
 * Perform standard reset sequence by popping the balloon (in case it
 * is not  empty) and then restarting protocol. This operation normally
 * happens when host responds with VMW_BALLOON_ERROR_RESET to a command.
 */
static void vmballoon_reset(struct vmballoon *b)
{
        int error;

        down_write(&b->conf_sem);

        vmballoon_vmci_cleanup(b);

        /* free all pages, skipping monitor unlock */
        vmballoon_pop(b);

        if (vmballoon_send_start(b, VMW_BALLOON_CAPABILITIES))
                goto unlock;

        if ((b->capabilities & VMW_BALLOON_BATCHED_CMDS) != 0) {
                if (vmballoon_init_batching(b)) {
                        /*
                         * We failed to initialize batching, inform the monitor
                         * about it by sending a null capability.
                         *
                         * The guest will retry in one second.
                         */
                        vmballoon_send_start(b, 0);
                        goto unlock;
                }
        } else if ((b->capabilities & VMW_BALLOON_BASIC_CMDS) != 0) {
                vmballoon_deinit_batching(b);
        }

        vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_RESET);
        b->reset_required = false;

        error = vmballoon_vmci_init(b);
        if (error)
                pr_err("failed to initialize vmci doorbell\n");

        if (vmballoon_send_guest_id(b))
                pr_err("failed to send guest ID to the host\n");

unlock:
        up_write(&b->conf_sem);
}

/**
 * vmballoon_work - periodic balloon worker for reset, inflation and deflation.
 *
 * @work: pointer to the &work_struct which is provided by the workqueue.
 *
 * Resets the protocol if needed, gets the new size and adjusts balloon as
 * needed. Repeat in 1 sec.
 */
static void vmballoon_work(struct work_struct *work)
{
        struct delayed_work *dwork = to_delayed_work(work);
        struct vmballoon *b = container_of(dwork, struct vmballoon, dwork);
        int64_t change = 0;

        if (b->reset_required)
                vmballoon_reset(b);

        down_read(&b->conf_sem);

        /*
         * Update the stats while holding the semaphore to ensure that
         * @stats_enabled is consistent with whether the stats are actually
         * enabled
         */
        vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_TIMER);

        if (!vmballoon_send_get_target(b))
                change = vmballoon_change(b);

        if (change != 0) {
                pr_debug("%s - size: %llu, target %lu\n", __func__,
                         atomic64_read(&b->size), READ_ONCE(b->target));

                if (change > 0)
                        vmballoon_inflate(b);
                else  /* (change < 0) */
                        vmballoon_deflate(b, 0, true);
        }

        up_read(&b->conf_sem);

        /*
         * We are using a freezable workqueue so that balloon operations are
         * stopped while the system transitions to/from sleep/hibernation.
         */
        queue_delayed_work(system_freezable_wq,
                           dwork, round_jiffies_relative(HZ));

}

/**
 * vmballoon_shrinker_scan() - deflate the balloon due to memory pressure.
 * @shrinker: pointer to the balloon shrinker.
 * @sc: page reclaim information.
 *
 * Returns: number of pages that were freed during deflation.
 */
static unsigned long vmballoon_shrinker_scan(struct shrinker *shrinker,
                                             struct shrink_control *sc)
{
        struct vmballoon *b = &balloon;
        unsigned long deflated_frames;

        pr_debug("%s - size: %llu", __func__, atomic64_read(&b->size));

        vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_SHRINK);

        /*
         * If the lock is also contended for read, we cannot easily reclaim and
         * we bail out.
         */
        if (!down_read_trylock(&b->conf_sem))
                return 0;

        deflated_frames = vmballoon_deflate(b, sc->nr_to_scan, true);

        vmballoon_stats_gen_add(b, VMW_BALLOON_STAT_SHRINK_FREE,
                                deflated_frames);

        /*
         * Delay future inflation for some time to mitigate the situations in
         * which balloon continuously grows and shrinks. Use WRITE_ONCE() since
         * the access is asynchronous.
         */
        WRITE_ONCE(b->shrink_timeout, jiffies + HZ * VMBALLOON_SHRINK_DELAY);

        up_read(&b->conf_sem);

        return deflated_frames;
}

/**
 * vmballoon_shrinker_count() - return the number of ballooned pages.
 * @shrinker: pointer to the balloon shrinker.
 * @sc: page reclaim information.
 *
 * Returns: number of 4k pages that are allocated for the balloon and can
 *          therefore be reclaimed under pressure.
 */
static unsigned long vmballoon_shrinker_count(struct shrinker *shrinker,
                                              struct shrink_control *sc)
{
        struct vmballoon *b = &balloon;

        return atomic64_read(&b->size);
}

static void vmballoon_unregister_shrinker(struct vmballoon *b)
{
        if (b->shrinker_registered)
                unregister_shrinker(&b->shrinker);
        b->shrinker_registered = false;
}

static int vmballoon_register_shrinker(struct vmballoon *b)
{
        int r;

        /* Do nothing if the shrinker is not enabled */
        if (!vmwballoon_shrinker_enable)
                return 0;

        b->shrinker.scan_objects = vmballoon_shrinker_scan;
        b->shrinker.count_objects = vmballoon_shrinker_count;
        b->shrinker.seeks = DEFAULT_SEEKS;

        r = register_shrinker(&b->shrinker);

        if (r == 0)
                b->shrinker_registered = true;

        return r;
}

/*
 * DEBUGFS Interface
 */
#ifdef CONFIG_DEBUG_FS

static const char * const vmballoon_stat_page_names[] = {
        [VMW_BALLOON_PAGE_STAT_ALLOC]           = "alloc",
        [VMW_BALLOON_PAGE_STAT_ALLOC_FAIL]      = "allocFail",
        [VMW_BALLOON_PAGE_STAT_REFUSED_ALLOC]   = "errAlloc",
        [VMW_BALLOON_PAGE_STAT_REFUSED_FREE]    = "errFree",
        [VMW_BALLOON_PAGE_STAT_FREE]            = "free"
};

static const char * const vmballoon_stat_names[] = {
        [VMW_BALLOON_STAT_TIMER]                = "timer",
        [VMW_BALLOON_STAT_DOORBELL]             = "doorbell",
        [VMW_BALLOON_STAT_RESET]                = "reset",
        [VMW_BALLOON_STAT_SHRINK]               = "shrink",
        [VMW_BALLOON_STAT_SHRINK_FREE]          = "shrinkFree"
};

static int vmballoon_enable_stats(struct vmballoon *b)
{
        int r = 0;

        down_write(&b->conf_sem);

        /* did we somehow race with another reader which enabled stats? */
        if (b->stats)
                goto out;

        b->stats = kzalloc(sizeof(*b->stats), GFP_KERNEL);

        if (!b->stats) {
                /* allocation failed */
                r = -ENOMEM;
                goto out;
        }
        static_key_enable(&balloon_stat_enabled.key);
out:
        up_write(&b->conf_sem);
        return r;
}

/**
 * vmballoon_debug_show - shows statistics of balloon operations.
 * @f: pointer to the &struct seq_file.
 * @offset: ignored.
 *
 * Provides the statistics that can be accessed in vmmemctl in the debugfs.
 * To avoid the overhead - mainly that of memory - of collecting the statistics,
 * we only collect statistics after the first time the counters are read.
 *
 * Return: zero on success or an error code.
 */
static int vmballoon_debug_show(struct seq_file *f, void *offset)
{
        struct vmballoon *b = f->private;
        int i, j;

        /* enables stats if they are disabled */
        if (!b->stats) {
                int r = vmballoon_enable_stats(b);

                if (r)
                        return r;
        }

        /* format capabilities info */
        seq_printf(f, "%-22s: %#16x\n", "balloon capabilities",
                   VMW_BALLOON_CAPABILITIES);
        seq_printf(f, "%-22s: %#16lx\n", "used capabilities", b->capabilities);
        seq_printf(f, "%-22s: %16s\n", "is resetting",
                   b->reset_required ? "y" : "n");

        /* format size info */
        seq_printf(f, "%-22s: %16lu\n", "target", READ_ONCE(b->target));
        seq_printf(f, "%-22s: %16llu\n", "current", atomic64_read(&b->size));

        for (i = 0; i < VMW_BALLOON_CMD_NUM; i++) {
                if (vmballoon_cmd_names[i] == NULL)
                        continue;

                seq_printf(f, "%-22s: %16llu (%llu failed)\n",
                           vmballoon_cmd_names[i],
                           atomic64_read(&b->stats->ops[i][VMW_BALLOON_OP_STAT]),
                           atomic64_read(&b->stats->ops[i][VMW_BALLOON_OP_FAIL_STAT]));
        }

        for (i = 0; i < VMW_BALLOON_STAT_NUM; i++)
                seq_printf(f, "%-22s: %16llu\n",
                           vmballoon_stat_names[i],
                           atomic64_read(&b->stats->general_stat[i]));

        for (i = 0; i < VMW_BALLOON_PAGE_STAT_NUM; i++) {
                for (j = 0; j < VMW_BALLOON_NUM_PAGE_SIZES; j++)
                        seq_printf(f, "%-18s(%s): %16llu\n",
                                   vmballoon_stat_page_names[i],
                                   vmballoon_page_size_names[j],
                                   atomic64_read(&b->stats->page_stat[i][j]));
        }

        return 0;
}

DEFINE_SHOW_ATTRIBUTE(vmballoon_debug);

static void __init vmballoon_debugfs_init(struct vmballoon *b)
{
        b->dbg_entry = debugfs_create_file("vmmemctl", S_IRUGO, NULL, b,
                                           &vmballoon_debug_fops);
}

static void __exit vmballoon_debugfs_exit(struct vmballoon *b)
{
        static_key_disable(&balloon_stat_enabled.key);
        debugfs_remove(b->dbg_entry);
        kfree(b->stats);
        b->stats = NULL;
}

#else

static inline void vmballoon_debugfs_init(struct vmballoon *b)
{
}

static inline void vmballoon_debugfs_exit(struct vmballoon *b)
{
}

#endif  /* CONFIG_DEBUG_FS */


#ifdef CONFIG_BALLOON_COMPACTION

static struct dentry *vmballoon_mount(struct file_system_type *fs_type,
                                      int flags, const char *dev_name,
                                      void *data)
{
        static const struct dentry_operations ops = {
                .d_dname = simple_dname,
        };

        return mount_pseudo(fs_type, "balloon-vmware:", NULL, &ops,
                            BALLOON_VMW_MAGIC);
}

static struct file_system_type vmballoon_fs = {
        .name           = "balloon-vmware",
        .mount          = vmballoon_mount,
        .kill_sb        = kill_anon_super,
};

static struct vfsmount *vmballoon_mnt;

/**
 * vmballoon_migratepage() - migrates a balloon page.
 * @b_dev_info: balloon device information descriptor.
 * @newpage: the page to which @page should be migrated.
 * @page: a ballooned page that should be migrated.
 * @mode: migration mode, ignored.
 *
 * This function is really open-coded, but that is according to the interface
 * that balloon_compaction provides.
 *
 * Return: zero on success, -EAGAIN when migration cannot be performed
 *         momentarily, and -EBUSY if migration failed and should be retried
 *         with that specific page.
 */
static int vmballoon_migratepage(struct balloon_dev_info *b_dev_info,
                                 struct page *newpage, struct page *page,
                                 enum migrate_mode mode)
{
        unsigned long status, flags;
        struct vmballoon *b;
        int ret;

        b = container_of(b_dev_info, struct vmballoon, b_dev_info);

        /*
         * If the semaphore is taken, there is ongoing configuration change
         * (i.e., balloon reset), so try again.
         */
        if (!down_read_trylock(&b->conf_sem))
                return -EAGAIN;

        spin_lock(&b->comm_lock);
        /*
         * We must start by deflating and not inflating, as otherwise the
         * hypervisor may tell us that it has enough memory and the new page is
         * not needed. Since the old page is isolated, we cannot use the list
         * interface to unlock it, as the LRU field is used for isolation.
         * Instead, we use the native interface directly.
         */
        vmballoon_add_page(b, 0, page);
        status = vmballoon_lock_op(b, 1, VMW_BALLOON_4K_PAGE,
                                   VMW_BALLOON_DEFLATE);

        if (status == VMW_BALLOON_SUCCESS)
                status = vmballoon_status_page(b, 0, &page);

        /*
         * If a failure happened, let the migration mechanism know that it
         * should not retry.
         */
        if (status != VMW_BALLOON_SUCCESS) {
                spin_unlock(&b->comm_lock);
                ret = -EBUSY;
                goto out_unlock;
        }

        /*
         * The page is isolated, so it is safe to delete it without holding
         * @pages_lock . We keep holding @comm_lock since we will need it in a
         * second.
         */
        balloon_page_delete(page);

        put_page(page);

        /* Inflate */
        vmballoon_add_page(b, 0, newpage);
        status = vmballoon_lock_op(b, 1, VMW_BALLOON_4K_PAGE,
                                   VMW_BALLOON_INFLATE);

        if (status == VMW_BALLOON_SUCCESS)
                status = vmballoon_status_page(b, 0, &newpage);

        spin_unlock(&b->comm_lock);

        if (status != VMW_BALLOON_SUCCESS) {
                /*
                 * A failure happened. While we can deflate the page we just
                 * inflated, this deflation can also encounter an error. Instead
                 * we will decrease the size of the balloon to reflect the
                 * change and report failure.
                 */
                atomic64_dec(&b->size);
                ret = -EBUSY;
        } else {
                /*
                 * Success. Take a reference for the page, and we will add it to
                 * the list after acquiring the lock.
                 */
                get_page(newpage);
                ret = MIGRATEPAGE_SUCCESS;
        }

        /* Update the balloon list under the @pages_lock */
        spin_lock_irqsave(&b->b_dev_info.pages_lock, flags);

        /*
         * On inflation success, we already took a reference for the @newpage.
         * If we succeed just insert it to the list and update the statistics
         * under the lock.
         */
        if (ret == MIGRATEPAGE_SUCCESS) {
                balloon_page_insert(&b->b_dev_info, newpage);
                __count_vm_event(BALLOON_MIGRATE);
        }

        /*
         * We deflated successfully, so regardless to the inflation success, we
         * need to reduce the number of isolated_pages.
         */
        b->b_dev_info.isolated_pages--;
        spin_unlock_irqrestore(&b->b_dev_info.pages_lock, flags);

out_unlock:
        up_read(&b->conf_sem);
        return ret;
}

/**
 * vmballoon_compaction_deinit() - removes compaction related data.
 *
 * @b: pointer to the balloon.
 */
static void vmballoon_compaction_deinit(struct vmballoon *b)
{
        if (!IS_ERR(b->b_dev_info.inode))
                iput(b->b_dev_info.inode);

        b->b_dev_info.inode = NULL;
        kern_unmount(vmballoon_mnt);
        vmballoon_mnt = NULL;
}

/**
 * vmballoon_compaction_init() - initialized compaction for the balloon.
 *
 * @b: pointer to the balloon.
 *
 * If during the initialization a failure occurred, this function does not
 * perform cleanup. The caller must call vmballoon_compaction_deinit() in this
 * case.
 *
 * Return: zero on success or error code on failure.
 */
static __init int vmballoon_compaction_init(struct vmballoon *b)
{
        vmballoon_mnt = kern_mount(&vmballoon_fs);
        if (IS_ERR(vmballoon_mnt))
                return PTR_ERR(vmballoon_mnt);

        b->b_dev_info.migratepage = vmballoon_migratepage;
        b->b_dev_info.inode = alloc_anon_inode(vmballoon_mnt->mnt_sb);

        if (IS_ERR(b->b_dev_info.inode))
                return PTR_ERR(b->b_dev_info.inode);

        b->b_dev_info.inode->i_mapping->a_ops = &balloon_aops;
        return 0;
}

#else /* CONFIG_BALLOON_COMPACTION */

static void vmballoon_compaction_deinit(struct vmballoon *b)
{
}

static int vmballoon_compaction_init(struct vmballoon *b)
{
        return 0;
}

#endif /* CONFIG_BALLOON_COMPACTION */

static int __init vmballoon_init(void)
{
        int error;

        /*
         * Check if we are running on VMware's hypervisor and bail out
         * if we are not.
         */
        if (x86_hyper_type != X86_HYPER_VMWARE)
                return -ENODEV;

        INIT_DELAYED_WORK(&balloon.dwork, vmballoon_work);

        error = vmballoon_register_shrinker(&balloon);
        if (error)
                goto fail;

        /*
         * Initialization of compaction must be done after the call to
         * balloon_devinfo_init() .
         */
        balloon_devinfo_init(&balloon.b_dev_info);
        error = vmballoon_compaction_init(&balloon);
        if (error)
                goto fail;

        INIT_LIST_HEAD(&balloon.huge_pages);
        spin_lock_init(&balloon.comm_lock);
        init_rwsem(&balloon.conf_sem);
        balloon.vmci_doorbell = VMCI_INVALID_HANDLE;
        balloon.batch_page = NULL;
        balloon.page = NULL;
        balloon.reset_required = true;

        queue_delayed_work(system_freezable_wq, &balloon.dwork, 0);

        vmballoon_debugfs_init(&balloon);

        return 0;
fail:
        vmballoon_unregister_shrinker(&balloon);
        vmballoon_compaction_deinit(&balloon);
        return error;
}

/*
 * Using late_initcall() instead of module_init() allows the balloon to use the
 * VMCI doorbell even when the balloon is built into the kernel. Otherwise the
 * VMCI is probed only after the balloon is initialized. If the balloon is used
 * as a module, late_initcall() is equivalent to module_init().
 */
late_initcall(vmballoon_init);

static void __exit vmballoon_exit(void)
{
        vmballoon_unregister_shrinker(&balloon);
        vmballoon_vmci_cleanup(&balloon);
        cancel_delayed_work_sync(&balloon.dwork);

        vmballoon_debugfs_exit(&balloon);

        /*
         * Deallocate all reserved memory, and reset connection with monitor.
         * Reset connection before deallocating memory to avoid potential for
         * additional spurious resets from guest touching deallocated pages.
         */
        vmballoon_send_start(&balloon, 0);
        vmballoon_pop(&balloon);

        /* Only once we popped the balloon, compaction can be deinit */
        vmballoon_compaction_deinit(&balloon);
}
module_exit(vmballoon_exit);