/*
 * VMware Balloon driver.
 *
 * Copyright (C) 2000-2014, VMware, Inc. All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; version 2 of the License and no later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 * NON INFRINGEMENT.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Maintained by:       Xavier Deguillard <xdeguillard@vmware.com>
 *                      Philip Moltmann <moltmann@vmware.com>
 */

/*
 * 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/io.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/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_VERSION("1.5.0.0-k");
MODULE_ALIAS("dmi:*:svnVMware*:*");
MODULE_ALIAS("vmware_vmmemctl");
MODULE_LICENSE("GPL");

/*
 * Various constants controlling rate of inflaint/deflating balloon,
 * measured in pages.
 */

/*
 * Rates of memory allocaton when guest experiences memory pressure
 * (driver performs sleeping allocations).
 */
#define VMW_BALLOON_RATE_ALLOC_MIN      512U
#define VMW_BALLOON_RATE_ALLOC_MAX      2048U
#define VMW_BALLOON_RATE_ALLOC_INC      16U

/*
 * When guest is under memory pressure, use a reduced page allocation
 * rate for next several cycles.
 */
#define VMW_BALLOON_SLOW_CYCLES         4

/*
 * Use __GFP_HIGHMEM to allow pages from HIGHMEM zone. We don't
 * allow wait (__GFP_RECLAIM) for NOSLEEP page allocations. Use
 * __GFP_NOWARN, to suppress page allocation failure warnings.
 */
#define VMW_PAGE_ALLOC_NOSLEEP          (__GFP_HIGHMEM|__GFP_NOWARN)

/*
 * Use GFP_HIGHUSER when executing in a separate kernel thread
 * context and allocation can sleep.  This is less stressful to
 * the guest memory system, since it allows the thread to block
 * while memory is reclaimed, and won't take pages from emergency
 * low-memory pools.
 */
#define VMW_PAGE_ALLOC_CANSLEEP         (GFP_HIGHUSER)

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

/*
 * 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),
};

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

#define VMW_BALLOON_2M_SHIFT            (9)
#define VMW_BALLOON_NUM_PAGE_SIZES      (2)

/*
 * Backdoor commands availability:
 *
 * START, GET_TARGET and GUEST_ID are always available,
 *
 * VMW_BALLOON_BASIC_CMDS:
 *      LOCK and UNLOCK commands,
 * VMW_BALLOON_BATCHED_CMDS:
 *      BATCHED_LOCK and BATCHED_UNLOCK commands.
 * VMW BALLOON_BATCHED_2M_CMDS:
 *      BATCHED_2M_LOCK and BATCHED_2M_UNLOCK commands,
 * VMW VMW_BALLOON_SIGNALLED_WAKEUP_CMD:
 *      VMW_BALLOON_CMD_VMCI_DOORBELL_SET command.
 */
#define VMW_BALLOON_CMD_START                   0
#define VMW_BALLOON_CMD_GET_TARGET              1
#define VMW_BALLOON_CMD_LOCK                    2
#define VMW_BALLOON_CMD_UNLOCK                  3
#define VMW_BALLOON_CMD_GUEST_ID                4
#define VMW_BALLOON_CMD_BATCHED_LOCK            6
#define VMW_BALLOON_CMD_BATCHED_UNLOCK          7
#define VMW_BALLOON_CMD_BATCHED_2M_LOCK         8
#define VMW_BALLOON_CMD_BATCHED_2M_UNLOCK       9
#define VMW_BALLOON_CMD_VMCI_DOORBELL_SET       10


/* error codes */
#define VMW_BALLOON_SUCCESS                     0
#define VMW_BALLOON_FAILURE                     -1
#define VMW_BALLOON_ERROR_CMD_INVALID           1
#define VMW_BALLOON_ERROR_PPN_INVALID           2
#define VMW_BALLOON_ERROR_PPN_LOCKED            3
#define VMW_BALLOON_ERROR_PPN_UNLOCKED          4
#define VMW_BALLOON_ERROR_PPN_PINNED            5
#define VMW_BALLOON_ERROR_PPN_NOTNEEDED         6
#define VMW_BALLOON_ERROR_RESET                 7
#define VMW_BALLOON_ERROR_BUSY                  8

#define VMW_BALLOON_SUCCESS_WITH_CAPABILITIES   (0x03000000)

/* Batch page description */

/*
 * Layout of a page in the batch page:
 *
 * +-------------+----------+--------+
 * |             |          |        |
 * | Page number | Reserved | Status |
 * |             |          |        |
 * +-------------+----------+--------+
 * 64  PAGE_SHIFT          6         0
 *
 * The reserved field should be set to 0.
 */
#define VMW_BALLOON_BATCH_MAX_PAGES     (PAGE_SIZE / sizeof(u64))
#define VMW_BALLOON_BATCH_STATUS_MASK   ((1UL << 5) - 1)
#define VMW_BALLOON_BATCH_PAGE_MASK     (~((1UL << PAGE_SHIFT) - 1))

struct vmballoon_batch_page {
        u64 pages[VMW_BALLOON_BATCH_MAX_PAGES];
};

static u64 vmballoon_batch_get_pa(struct vmballoon_batch_page *batch, int idx)
{
        return batch->pages[idx] & VMW_BALLOON_BATCH_PAGE_MASK;
}

static int vmballoon_batch_get_status(struct vmballoon_batch_page *batch,
                                int idx)
{
        return (int)(batch->pages[idx] & VMW_BALLOON_BATCH_STATUS_MASK);
}

static void vmballoon_batch_set_pa(struct vmballoon_batch_page *batch, int idx,
                                u64 pa)
{
        batch->pages[idx] = pa;
}


#define VMWARE_BALLOON_CMD(cmd, arg1, arg2, result)             \
({                                                              \
        unsigned long __status, __dummy1, __dummy2, __dummy3;   \
        __asm__ __volatile__ ("inl %%dx" :                      \
                "=a"(__status),                                 \
                "=c"(__dummy1),                                 \
                "=d"(__dummy2),                                 \
                "=b"(result),                                   \
                "=S" (__dummy3) :                               \
                "0"(VMW_BALLOON_HV_MAGIC),                      \
                "1"(VMW_BALLOON_CMD_##cmd),                     \
                "2"(VMW_BALLOON_HV_PORT),                       \
                "3"(arg1),                                      \
                "4" (arg2) :                                    \
                "memory");                                      \
        if (VMW_BALLOON_CMD_##cmd == VMW_BALLOON_CMD_START)     \
                result = __dummy1;                              \
        result &= -1UL;                                         \
        __status & -1UL;                                        \
})

#ifdef CONFIG_DEBUG_FS
struct vmballoon_stats {
        unsigned int timer;
        unsigned int doorbell;

        /* allocation statistics */
        unsigned int alloc[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int alloc_fail[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int sleep_alloc;
        unsigned int sleep_alloc_fail;
        unsigned int refused_alloc[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int refused_free[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int free[VMW_BALLOON_NUM_PAGE_SIZES];

        /* monitor operations */
        unsigned int lock[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int lock_fail[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int unlock[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int unlock_fail[VMW_BALLOON_NUM_PAGE_SIZES];
        unsigned int target;
        unsigned int target_fail;
        unsigned int start;
        unsigned int start_fail;
        unsigned int guest_type;
        unsigned int guest_type_fail;
        unsigned int doorbell_set;
        unsigned int doorbell_unset;
};

#define STATS_INC(stat) (stat)++
#else
#define STATS_INC(stat)
#endif

struct vmballoon;

struct vmballoon_ops {
        void (*add_page)(struct vmballoon *b, int idx, struct page *p);
        int (*lock)(struct vmballoon *b, unsigned int num_pages,
                        bool is_2m_pages, unsigned int *target);
        int (*unlock)(struct vmballoon *b, unsigned int num_pages,
                        bool is_2m_pages, unsigned int *target);
};

struct vmballoon_page_size {
        /* list of reserved physical pages */
        struct list_head pages;

        /* transient list of non-balloonable pages */
        struct list_head refused_pages;
        unsigned int n_refused_pages;
};

struct vmballoon {
        struct vmballoon_page_size page_sizes[VMW_BALLOON_NUM_PAGE_SIZES];

        /* supported page sizes. 1 == 4k pages only, 2 == 4k and 2m pages */
        unsigned supported_page_sizes;

        /* balloon size in pages */
        unsigned int size;
        unsigned int target;

        /* reset flag */
        bool reset_required;

        /* adjustment rates (pages per second) */
        unsigned int rate_alloc;

        /* slowdown page allocations for next few cycles */
        unsigned int slow_allocation_cycles;

        unsigned long capabilities;

        struct vmballoon_batch_page *batch_page;
        unsigned int batch_max_pages;
        struct page *page;

        const struct vmballoon_ops *ops;

#ifdef CONFIG_DEBUG_FS
        /* statistics */
        struct vmballoon_stats stats;

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

        struct sysinfo sysinfo;

        struct delayed_work dwork;

        struct vmci_handle vmci_doorbell;
};

static struct vmballoon balloon;

/*
 * Send "start" command to the host, communicating supported version
 * of the protocol.
 */
static bool vmballoon_send_start(struct vmballoon *b, unsigned long req_caps)
{
        unsigned long status, capabilities, dummy = 0;
        bool success;

        STATS_INC(b->stats.start);

        status = VMWARE_BALLOON_CMD(START, req_caps, dummy, capabilities);

        switch (status) {
        case VMW_BALLOON_SUCCESS_WITH_CAPABILITIES:
                b->capabilities = capabilities;
                success = true;
                break;
        case VMW_BALLOON_SUCCESS:
                b->capabilities = VMW_BALLOON_BASIC_CMDS;
                success = true;
                break;
        default:
                success = false;
        }

        if (b->capabilities & VMW_BALLOON_BATCHED_2M_CMDS)
                b->supported_page_sizes = 2;
        else
                b->supported_page_sizes = 1;

        if (!success) {
                pr_debug("%s - failed, hv returns %ld\n", __func__, status);
                STATS_INC(b->stats.start_fail);
        }
        return success;
}

static bool vmballoon_check_status(struct vmballoon *b, unsigned long status)
{
        switch (status) {
        case VMW_BALLOON_SUCCESS:
                return true;

        case VMW_BALLOON_ERROR_RESET:
                b->reset_required = true;
                /* fall through */

        default:
                return false;
        }
}

/*
 * 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.
 */
static bool vmballoon_send_guest_id(struct vmballoon *b)
{
        unsigned long status, dummy = 0;

        status = VMWARE_BALLOON_CMD(GUEST_ID, VMW_BALLOON_GUEST_ID, dummy,
                                dummy);

        STATS_INC(b->stats.guest_type);

        if (vmballoon_check_status(b, status))
                return true;

        pr_debug("%s - failed, hv returns %ld\n", __func__, status);
        STATS_INC(b->stats.guest_type_fail);
        return false;
}

static u16 vmballoon_page_size(bool is_2m_page)
{
        if (is_2m_page)
                return 1 << VMW_BALLOON_2M_SHIFT;

        return 1;
}

/*
 * Retrieve desired balloon size from the host.
 */
static bool vmballoon_send_get_target(struct vmballoon *b, u32 *new_target)
{
        unsigned long status;
        unsigned long target;
        unsigned long limit;
        unsigned long dummy = 0;
        u32 limit32;

        /*
         * si_meminfo() is cheap. Moreover, we want to provide dynamic
         * max balloon size later. So let us call si_meminfo() every
         * iteration.
         */
        si_meminfo(&b->sysinfo);
        limit = b->sysinfo.totalram;

        /* Ensure limit fits in 32-bits */
        limit32 = (u32)limit;
        if (limit != limit32)
                return false;

        /* update stats */
        STATS_INC(b->stats.target);

        status = VMWARE_BALLOON_CMD(GET_TARGET, limit, dummy, target);
        if (vmballoon_check_status(b, status)) {
                *new_target = target;
                return true;
        }

        pr_debug("%s - failed, hv returns %ld\n", __func__, status);
        STATS_INC(b->stats.target_fail);
        return false;
}

/*
 * Notify the host about allocated page so that host can use it without
 * fear that guest will need it. Host may reject some pages, we need to
 * check the return value and maybe submit a different page.
 */
static int vmballoon_send_lock_page(struct vmballoon *b, unsigned long pfn,
                                unsigned int *hv_status, unsigned int *target)
{
        unsigned long status, dummy = 0;
        u32 pfn32;

        pfn32 = (u32)pfn;
        if (pfn32 != pfn)
                return -1;

        STATS_INC(b->stats.lock[false]);

        *hv_status = status = VMWARE_BALLOON_CMD(LOCK, pfn, dummy, *target);
        if (vmballoon_check_status(b, status))
                return 0;

        pr_debug("%s - ppn %lx, hv returns %ld\n", __func__, pfn, status);
        STATS_INC(b->stats.lock_fail[false]);
        return 1;
}

static int vmballoon_send_batched_lock(struct vmballoon *b,
                unsigned int num_pages, bool is_2m_pages, unsigned int *target)
{
        unsigned long status;
        unsigned long pfn = PHYS_PFN(virt_to_phys(b->batch_page));

        STATS_INC(b->stats.lock[is_2m_pages]);

        if (is_2m_pages)
                status = VMWARE_BALLOON_CMD(BATCHED_2M_LOCK, pfn, num_pages,
                                *target);
        else
                status = VMWARE_BALLOON_CMD(BATCHED_LOCK, pfn, num_pages,
                                *target);

        if (vmballoon_check_status(b, status))
                return 0;

        pr_debug("%s - batch ppn %lx, hv returns %ld\n", __func__, pfn, status);
        STATS_INC(b->stats.lock_fail[is_2m_pages]);
        return 1;
}

/*
 * Notify the host that guest intends to release given page back into
 * the pool of available (to the guest) pages.
 */
static bool vmballoon_send_unlock_page(struct vmballoon *b, unsigned long pfn,
                                                        unsigned int *target)
{
        unsigned long status, dummy = 0;
        u32 pfn32;

        pfn32 = (u32)pfn;
        if (pfn32 != pfn)
                return false;

        STATS_INC(b->stats.unlock[false]);

        status = VMWARE_BALLOON_CMD(UNLOCK, pfn, dummy, *target);
        if (vmballoon_check_status(b, status))
                return true;

        pr_debug("%s - ppn %lx, hv returns %ld\n", __func__, pfn, status);
        STATS_INC(b->stats.unlock_fail[false]);
        return false;
}

static bool vmballoon_send_batched_unlock(struct vmballoon *b,
                unsigned int num_pages, bool is_2m_pages, unsigned int *target)
{
        unsigned long status;
        unsigned long pfn = PHYS_PFN(virt_to_phys(b->batch_page));

        STATS_INC(b->stats.unlock[is_2m_pages]);

        if (is_2m_pages)
                status = VMWARE_BALLOON_CMD(BATCHED_2M_UNLOCK, pfn, num_pages,
                                *target);
        else
                status = VMWARE_BALLOON_CMD(BATCHED_UNLOCK, pfn, num_pages,
                                *target);

        if (vmballoon_check_status(b, status))
                return true;

        pr_debug("%s - batch ppn %lx, hv returns %ld\n", __func__, pfn, status);
        STATS_INC(b->stats.unlock_fail[is_2m_pages]);
        return false;
}

static struct page *vmballoon_alloc_page(gfp_t flags, bool is_2m_page)
{
        if (is_2m_page)
                return alloc_pages(flags, VMW_BALLOON_2M_SHIFT);

        return alloc_page(flags);
}

static void vmballoon_free_page(struct page *page, bool is_2m_page)
{
        if (is_2m_page)
                __free_pages(page, VMW_BALLOON_2M_SHIFT);
        else
                __free_page(page);
}

/*
 * Quickly release all pages allocated for 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)
{
        struct page *page, *next;
        unsigned is_2m_pages;

        for (is_2m_pages = 0; is_2m_pages < VMW_BALLOON_NUM_PAGE_SIZES;
                        is_2m_pages++) {
                struct vmballoon_page_size *page_size =
                                &b->page_sizes[is_2m_pages];
                u16 size_per_page = vmballoon_page_size(is_2m_pages);

                list_for_each_entry_safe(page, next, &page_size->pages, lru) {
                        list_del(&page->lru);
                        vmballoon_free_page(page, is_2m_pages);
                        STATS_INC(b->stats.free[is_2m_pages]);
                        b->size -= size_per_page;
                        cond_resched();
                }
        }

        /* Clearing the batch_page unconditionally has no adverse effect */
        free_page((unsigned long)b->batch_page);
        b->batch_page = NULL;
}

/*
 * Notify the host of a ballooned page. If host rejects the page put it on the
 * refuse list, those refused page are then released at the end of the
 * inflation cycle.
 */
static int vmballoon_lock_page(struct vmballoon *b, unsigned int num_pages,
                                bool is_2m_pages, unsigned int *target)
{
        int locked, hv_status;
        struct page *page = b->page;
        struct vmballoon_page_size *page_size = &b->page_sizes[false];

        /* is_2m_pages can never happen as 2m pages support implies batching */

        locked = vmballoon_send_lock_page(b, page_to_pfn(page), &hv_status,
                                                                target);
        if (locked > 0) {
                STATS_INC(b->stats.refused_alloc[false]);

                if (hv_status == VMW_BALLOON_ERROR_RESET ||
                                hv_status == VMW_BALLOON_ERROR_PPN_NOTNEEDED) {
                        vmballoon_free_page(page, false);
                        return -EIO;
                }

                /*
                 * Place page on the list of non-balloonable pages
                 * and retry allocation, unless we already accumulated
                 * too many of them, in which case take a breather.
                 */
                if (page_size->n_refused_pages < VMW_BALLOON_MAX_REFUSED) {
                        page_size->n_refused_pages++;
                        list_add(&page->lru, &page_size->refused_pages);
                } else {
                        vmballoon_free_page(page, false);
                }
                return -EIO;
        }

        /* track allocated page */
        list_add(&page->lru, &page_size->pages);

        /* update balloon size */
        b->size++;

        return 0;
}

static int vmballoon_lock_batched_page(struct vmballoon *b,
                unsigned int num_pages, bool is_2m_pages, unsigned int *target)
{
        int locked, i;
        u16 size_per_page = vmballoon_page_size(is_2m_pages);

        locked = vmballoon_send_batched_lock(b, num_pages, is_2m_pages,
                        target);
        if (locked > 0) {
                for (i = 0; i < num_pages; i++) {
                        u64 pa = vmballoon_batch_get_pa(b->batch_page, i);
                        struct page *p = pfn_to_page(pa >> PAGE_SHIFT);

                        vmballoon_free_page(p, is_2m_pages);
                }

                return -EIO;
        }

        for (i = 0; i < num_pages; i++) {
                u64 pa = vmballoon_batch_get_pa(b->batch_page, i);
                struct page *p = pfn_to_page(pa >> PAGE_SHIFT);
                struct vmballoon_page_size *page_size =
                                &b->page_sizes[is_2m_pages];

                locked = vmballoon_batch_get_status(b->batch_page, i);

                switch (locked) {
                case VMW_BALLOON_SUCCESS:
                        list_add(&p->lru, &page_size->pages);
                        b->size += size_per_page;
                        break;
                case VMW_BALLOON_ERROR_PPN_PINNED:
                case VMW_BALLOON_ERROR_PPN_INVALID:
                        if (page_size->n_refused_pages
                                        < VMW_BALLOON_MAX_REFUSED) {
                                list_add(&p->lru, &page_size->refused_pages);
                                page_size->n_refused_pages++;
                                break;
                        }
                        /* Fallthrough */
                case VMW_BALLOON_ERROR_RESET:
                case VMW_BALLOON_ERROR_PPN_NOTNEEDED:
                        vmballoon_free_page(p, is_2m_pages);
                        break;
                default:
                        /* This should never happen */
                        WARN_ON_ONCE(true);
                }
        }

        return 0;
}

/*
 * Release the page allocated for the balloon. Note that we first notify
 * the host so it can make sure the page will be available for the guest
 * to use, if needed.
 */
static int vmballoon_unlock_page(struct vmballoon *b, unsigned int num_pages,
                bool is_2m_pages, unsigned int *target)
{
        struct page *page = b->page;
        struct vmballoon_page_size *page_size = &b->page_sizes[false];

        /* is_2m_pages can never happen as 2m pages support implies batching */

        if (!vmballoon_send_unlock_page(b, page_to_pfn(page), target)) {
                list_add(&page->lru, &page_size->pages);
                return -EIO;
        }

        /* deallocate page */
        vmballoon_free_page(page, false);
        STATS_INC(b->stats.free[false]);

        /* update balloon size */
        b->size--;

        return 0;
}

static int vmballoon_unlock_batched_page(struct vmballoon *b,
                                unsigned int num_pages, bool is_2m_pages,
                                unsigned int *target)
{
        int locked, i, ret = 0;
        bool hv_success;
        u16 size_per_page = vmballoon_page_size(is_2m_pages);

        hv_success = vmballoon_send_batched_unlock(b, num_pages, is_2m_pages,
                        target);
        if (!hv_success)
                ret = -EIO;

        for (i = 0; i < num_pages; i++) {
                u64 pa = vmballoon_batch_get_pa(b->batch_page, i);
                struct page *p = pfn_to_page(pa >> PAGE_SHIFT);
                struct vmballoon_page_size *page_size =
                                &b->page_sizes[is_2m_pages];

                locked = vmballoon_batch_get_status(b->batch_page, i);
                if (!hv_success || locked != VMW_BALLOON_SUCCESS) {
                        /*
                         * That page wasn't successfully unlocked by the
                         * hypervisor, re-add it to the list of pages owned by
                         * the balloon driver.
                         */
                        list_add(&p->lru, &page_size->pages);
                } else {
                        /* deallocate page */
                        vmballoon_free_page(p, is_2m_pages);
                        STATS_INC(b->stats.free[is_2m_pages]);

                        /* update balloon size */
                        b->size -= size_per_page;
                }
        }

        return ret;
}

/*
 * 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,
                bool is_2m_pages)
{
        struct page *page, *next;
        struct vmballoon_page_size *page_size =
                        &b->page_sizes[is_2m_pages];

        list_for_each_entry_safe(page, next, &page_size->refused_pages, lru) {
                list_del(&page->lru);
                vmballoon_free_page(page, is_2m_pages);
                STATS_INC(b->stats.refused_free[is_2m_pages]);
        }

        page_size->n_refused_pages = 0;
}

static void vmballoon_add_page(struct vmballoon *b, int idx, struct page *p)
{
        b->page = p;
}

static void vmballoon_add_batched_page(struct vmballoon *b, int idx,
                                struct page *p)
{
        vmballoon_batch_set_pa(b->batch_page, idx,
                        (u64)page_to_pfn(p) << PAGE_SHIFT);
}

/*
 * Inflate the balloon towards its target size. Note that we try to limit
 * the rate of allocation to make sure we are not choking the rest of the
 * system.
 */
static void vmballoon_inflate(struct vmballoon *b)
{
        unsigned rate;
        unsigned int allocations = 0;
        unsigned int num_pages = 0;
        int error = 0;
        gfp_t flags = VMW_PAGE_ALLOC_NOSLEEP;
        bool is_2m_pages;

        pr_debug("%s - size: %d, target %d\n", __func__, b->size, b->target);

        /*
         * First try NOSLEEP page allocations to inflate balloon.
         *
         * If we do not throttle nosleep allocations, we can drain all
         * free pages in the guest quickly (if the balloon target is high).
         * As a side-effect, draining free pages helps to inform (force)
         * the guest to start swapping if balloon target is not met yet,
         * which is a desired behavior. However, balloon driver can consume
         * all available CPU cycles if too many pages are allocated in a
         * second. Therefore, we throttle nosleep allocations even when
         * the guest is not under memory pressure. OTOH, if we have already
         * predicted that the guest is under memory pressure, then we
         * slowdown page allocations considerably.
         */

        /*
         * Start with no sleep allocation rate which may be higher
         * than sleeping allocation rate.
         */
        if (b->slow_allocation_cycles) {
                rate = b->rate_alloc;
                is_2m_pages = false;
        } else {
                rate = UINT_MAX;
                is_2m_pages =
                        b->supported_page_sizes == VMW_BALLOON_NUM_PAGE_SIZES;
        }

        pr_debug("%s - goal: %d, no-sleep rate: %u, sleep rate: %d\n",
                 __func__, b->target - b->size, rate, b->rate_alloc);

        while (!b->reset_required &&
                b->size + num_pages * vmballoon_page_size(is_2m_pages)
                < b->target) {
                struct page *page;

                if (flags == VMW_PAGE_ALLOC_NOSLEEP)
                        STATS_INC(b->stats.alloc[is_2m_pages]);
                else
                        STATS_INC(b->stats.sleep_alloc);

                page = vmballoon_alloc_page(flags, is_2m_pages);
                if (!page) {
                        STATS_INC(b->stats.alloc_fail[is_2m_pages]);

                        if (is_2m_pages) {
                                b->ops->lock(b, num_pages, true, &b->target);

                                /*
                                 * ignore errors from locking as we now switch
                                 * to 4k pages and we might get different
                                 * errors.
                                 */

                                num_pages = 0;
                                is_2m_pages = false;
                                continue;
                        }

                        if (flags == VMW_PAGE_ALLOC_CANSLEEP) {
                                /*
                                 * CANSLEEP page allocation failed, so guest
                                 * is under severe memory pressure. Quickly
                                 * decrease allocation rate.
                                 */
                                b->rate_alloc = max(b->rate_alloc / 2,
                                                    VMW_BALLOON_RATE_ALLOC_MIN);
                                STATS_INC(b->stats.sleep_alloc_fail);
                                break;
                        }

                        /*
                         * NOSLEEP page allocation failed, so the guest is
                         * under memory pressure. Let us slow down page
                         * allocations for next few cycles so that the guest
                         * gets out of memory pressure. Also, if we already
                         * allocated b->rate_alloc pages, let's pause,
                         * otherwise switch to sleeping allocations.
                         */
                        b->slow_allocation_cycles = VMW_BALLOON_SLOW_CYCLES;

                        if (allocations >= b->rate_alloc)
                                break;

                        flags = VMW_PAGE_ALLOC_CANSLEEP;
                        /* Lower rate for sleeping allocations. */
                        rate = b->rate_alloc;
                        continue;
                }

                b->ops->add_page(b, num_pages++, page);
                if (num_pages == b->batch_max_pages) {
                        error = b->ops->lock(b, num_pages, is_2m_pages,
                                        &b->target);
                        num_pages = 0;
                        if (error)
                                break;
                }

                cond_resched();

                if (allocations >= rate) {
                        /* We allocated enough pages, let's take a break. */
                        break;
                }
        }

        if (num_pages > 0)
                b->ops->lock(b, num_pages, is_2m_pages, &b->target);

        /*
         * We reached our goal without failures so try increasing
         * allocation rate.
         */
        if (error == 0 && allocations >= b->rate_alloc) {
                unsigned int mult = allocations / b->rate_alloc;

                b->rate_alloc =
                        min(b->rate_alloc + mult * VMW_BALLOON_RATE_ALLOC_INC,
                            VMW_BALLOON_RATE_ALLOC_MAX);
        }

        vmballoon_release_refused_pages(b, true);
        vmballoon_release_refused_pages(b, false);
}

/*
 * Decrease the size of the balloon allowing guest to use more memory.
 */
static void vmballoon_deflate(struct vmballoon *b)
{
        unsigned is_2m_pages;

        pr_debug("%s - size: %d, target %d\n", __func__, b->size, b->target);

        /* free pages to reach target */
        for (is_2m_pages = 0; is_2m_pages < b->supported_page_sizes;
                        is_2m_pages++) {
                struct page *page, *next;
                unsigned int num_pages = 0;
                struct vmballoon_page_size *page_size =
                                &b->page_sizes[is_2m_pages];

                list_for_each_entry_safe(page, next, &page_size->pages, lru) {
                        if (b->reset_required ||
                                (b->target > 0 &&
                                        b->size - num_pages
                                        * vmballoon_page_size(is_2m_pages)
                                < b->target + vmballoon_page_size(true)))
                                break;

                        list_del(&page->lru);
                        b->ops->add_page(b, num_pages++, page);

                        if (num_pages == b->batch_max_pages) {
                                int error;

                                error = b->ops->unlock(b, num_pages,
                                                is_2m_pages, &b->target);
                                num_pages = 0;
                                if (error)
                                        return;
                        }

                        cond_resched();
                }

                if (num_pages > 0)
                        b->ops->unlock(b, num_pages, is_2m_pages, &b->target);
        }
}

static const struct vmballoon_ops vmballoon_basic_ops = {
        .add_page = vmballoon_add_page,
        .lock = vmballoon_lock_page,
        .unlock = vmballoon_unlock_page
};

static const struct vmballoon_ops vmballoon_batched_ops = {
        .add_page = vmballoon_add_batched_page,
        .lock = vmballoon_lock_batched_page,
        .unlock = vmballoon_unlock_batched_page
};

static bool vmballoon_init_batching(struct vmballoon *b)
{
        struct page *page;

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

        b->batch_page = page_address(page);
        return true;
}

/*
 * Receive notification and resize balloon

 */
static void vmballoon_doorbell(void *client_data)
{
        struct vmballoon *b = client_data;

        STATS_INC(b->stats.doorbell);

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

/*
 * Clean up vmci doorbell
 */
static void vmballoon_vmci_cleanup(struct vmballoon *b)
{
        int error;

        VMWARE_BALLOON_CMD(VMCI_DOORBELL_SET, VMCI_INVALID_ID,
                        VMCI_INVALID_ID, error);
        STATS_INC(b->stats.doorbell_unset);

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

/*
 * Initialize vmci doorbell, to get notified as soon as balloon changes
 */
static int vmballoon_vmci_init(struct vmballoon *b)
{
        int error = 0;

        if ((b->capabilities & VMW_BALLOON_SIGNALLED_WAKEUP_CMD) != 0) {
                error = vmci_doorbell_create(&b->vmci_doorbell,
                                VMCI_FLAG_DELAYED_CB,
                                VMCI_PRIVILEGE_FLAG_RESTRICTED,
                                vmballoon_doorbell, b);

                if (error == VMCI_SUCCESS) {
                        VMWARE_BALLOON_CMD(VMCI_DOORBELL_SET,
                                        b->vmci_doorbell.context,
                                        b->vmci_doorbell.resource, error);
                        STATS_INC(b->stats.doorbell_set);
                }
        }

        if (error != 0) {
                vmballoon_vmci_cleanup(b);

                return -EIO;
        }

        return 0;
}

/*
 * 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;

        vmballoon_vmci_cleanup(b);

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

        if (!vmballoon_send_start(b, VMW_BALLOON_CAPABILITIES))
                return;

        if ((b->capabilities & VMW_BALLOON_BATCHED_CMDS) != 0) {
                b->ops = &vmballoon_batched_ops;
                b->batch_max_pages = VMW_BALLOON_BATCH_MAX_PAGES;
                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);
                        return;
                }
        } else if ((b->capabilities & VMW_BALLOON_BASIC_CMDS) != 0) {
                b->ops = &vmballoon_basic_ops;
                b->batch_max_pages = 1;
        }

        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");
}

/*
 * Balloon work function: reset protocol, if needed, get the new size and
 * adjust 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);
        unsigned int target;

        STATS_INC(b->stats.timer);

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

        if (b->slow_allocation_cycles > 0)
                b->slow_allocation_cycles--;

        if (!b->reset_required && vmballoon_send_get_target(b, &target)) {
                /* update target, adjust size */
                b->target = target;

                if (b->size < target)
                        vmballoon_inflate(b);
                else if (target == 0 ||
                                b->size > target + vmballoon_page_size(true))
                        vmballoon_deflate(b);
        }

        /*
         * 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));
}

/*
 * DEBUGFS Interface
 */
#ifdef CONFIG_DEBUG_FS

static int vmballoon_debug_show(struct seq_file *f, void *offset)
{
        struct vmballoon *b = f->private;
        struct vmballoon_stats *stats = &b->stats;

        /* format capabilities info */
        seq_printf(f,
                   "balloon capabilities:   %#4x\n"
                   "used capabilities:      %#4lx\n"
                   "is resetting:           %c\n",
                   VMW_BALLOON_CAPABILITIES, b->capabilities,
                   b->reset_required ? 'y' : 'n');

        /* format size info */
        seq_printf(f,
                   "target:             %8d pages\n"
                   "current:            %8d pages\n",
                   b->target, b->size);

        /* format rate info */
        seq_printf(f,
                   "rateSleepAlloc:     %8d pages/sec\n",
                   b->rate_alloc);

        seq_printf(f,
                   "\n"
                   "timer:              %8u\n"
                   "doorbell:           %8u\n"
                   "start:              %8u (%4u failed)\n"
                   "guestType:          %8u (%4u failed)\n"
                   "2m-lock:            %8u (%4u failed)\n"
                   "lock:               %8u (%4u failed)\n"
                   "2m-unlock:          %8u (%4u failed)\n"
                   "unlock:             %8u (%4u failed)\n"
                   "target:             %8u (%4u failed)\n"
                   "prim2mAlloc:        %8u (%4u failed)\n"
                   "primNoSleepAlloc:   %8u (%4u failed)\n"
                   "primCanSleepAlloc:  %8u (%4u failed)\n"
                   "prim2mFree:         %8u\n"
                   "primFree:           %8u\n"
                   "err2mAlloc:         %8u\n"
                   "errAlloc:           %8u\n"
                   "err2mFree:          %8u\n"
                   "errFree:            %8u\n"
                   "doorbellSet:        %8u\n"
                   "doorbellUnset:      %8u\n",
                   stats->timer,
                   stats->doorbell,
                   stats->start, stats->start_fail,
                   stats->guest_type, stats->guest_type_fail,
                   stats->lock[true],  stats->lock_fail[true],
                   stats->lock[false],  stats->lock_fail[false],
                   stats->unlock[true], stats->unlock_fail[true],
                   stats->unlock[false], stats->unlock_fail[false],
                   stats->target, stats->target_fail,
                   stats->alloc[true], stats->alloc_fail[true],
                   stats->alloc[false], stats->alloc_fail[false],
                   stats->sleep_alloc, stats->sleep_alloc_fail,
                   stats->free[true],
                   stats->free[false],
                   stats->refused_alloc[true], stats->refused_alloc[false],
                   stats->refused_free[true], stats->refused_free[false],
                   stats->doorbell_set, stats->doorbell_unset);

        return 0;
}

static int vmballoon_debug_open(struct inode *inode, struct file *file)
{
        return single_open(file, vmballoon_debug_show, inode->i_private);
}

static const struct file_operations vmballoon_debug_fops = {
        .owner          = THIS_MODULE,
        .open           = vmballoon_debug_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static int __init vmballoon_debugfs_init(struct vmballoon *b)
{
        int error;

        b->dbg_entry = debugfs_create_file("vmmemctl", S_IRUGO, NULL, b,
                                           &vmballoon_debug_fops);
        if (IS_ERR(b->dbg_entry)) {
                error = PTR_ERR(b->dbg_entry);
                pr_err("failed to create debugfs entry, error: %d\n", error);
                return error;
        }

        return 0;
}

static void __exit vmballoon_debugfs_exit(struct vmballoon *b)
{
        debugfs_remove(b->dbg_entry);
}

#else

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

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

#endif  /* CONFIG_DEBUG_FS */

static int __init vmballoon_init(void)
{
        int error;
        unsigned is_2m_pages;
        /*
         * 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;

        for (is_2m_pages = 0; is_2m_pages < VMW_BALLOON_NUM_PAGE_SIZES;
                        is_2m_pages++) {
                INIT_LIST_HEAD(&balloon.page_sizes[is_2m_pages].pages);
                INIT_LIST_HEAD(&balloon.page_sizes[is_2m_pages].refused_pages);
        }

        /* initialize rates */
        balloon.rate_alloc = VMW_BALLOON_RATE_ALLOC_MAX;

        INIT_DELAYED_WORK(&balloon.dwork, vmballoon_work);

        error = vmballoon_debugfs_init(&balloon);
        if (error)
                return error;

        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);

        return 0;
}
module_init(vmballoon_init);

static void __exit vmballoon_exit(void)
{
        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);
}
module_exit(vmballoon_exit);