Revert "vfs: Delete the associated dentry when deleting a file"

[thirdparty/linux.git] / drivers / hv / hv_balloon.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2012, Microsoft Corporation.
 *
 * Author:
 *   K. Y. Srinivasan <kys@microsoft.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/mman.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <linux/memory_hotplug.h>
#include <linux/memory.h>
#include <linux/notifier.h>
#include <linux/percpu_counter.h>

#include <linux/hyperv.h>

#define CREATE_TRACE_POINTS
#include "hv_trace_balloon.h"

/*
 * We begin with definitions supporting the Dynamic Memory protocol
 * with the host.
 *
 * Begin protocol definitions.
 */



/*
 * Protocol versions. The low word is the minor version, the high word the major
 * version.
 *
 * History:
 * Initial version 1.0
 * Changed to 0.1 on 2009/03/25
 * Changes to 0.2 on 2009/05/14
 * Changes to 0.3 on 2009/12/03
 * Changed to 1.0 on 2011/04/05
 */

#define DYNMEM_MAKE_VERSION(Major, Minor) ((__u32)(((Major) << 16) | (Minor)))
#define DYNMEM_MAJOR_VERSION(Version) ((__u32)(Version) >> 16)
#define DYNMEM_MINOR_VERSION(Version) ((__u32)(Version) & 0xff)

enum {
        DYNMEM_PROTOCOL_VERSION_1 = DYNMEM_MAKE_VERSION(0, 3),
        DYNMEM_PROTOCOL_VERSION_2 = DYNMEM_MAKE_VERSION(1, 0),
        DYNMEM_PROTOCOL_VERSION_3 = DYNMEM_MAKE_VERSION(2, 0),

        DYNMEM_PROTOCOL_VERSION_WIN7 = DYNMEM_PROTOCOL_VERSION_1,
        DYNMEM_PROTOCOL_VERSION_WIN8 = DYNMEM_PROTOCOL_VERSION_2,
        DYNMEM_PROTOCOL_VERSION_WIN10 = DYNMEM_PROTOCOL_VERSION_3,

        DYNMEM_PROTOCOL_VERSION_CURRENT = DYNMEM_PROTOCOL_VERSION_WIN10
};



/*
 * Message Types
 */

enum dm_message_type {
        /*
         * Version 0.3
         */
        DM_ERROR                        = 0,
        DM_VERSION_REQUEST              = 1,
        DM_VERSION_RESPONSE             = 2,
        DM_CAPABILITIES_REPORT          = 3,
        DM_CAPABILITIES_RESPONSE        = 4,
        DM_STATUS_REPORT                = 5,
        DM_BALLOON_REQUEST              = 6,
        DM_BALLOON_RESPONSE             = 7,
        DM_UNBALLOON_REQUEST            = 8,
        DM_UNBALLOON_RESPONSE           = 9,
        DM_MEM_HOT_ADD_REQUEST          = 10,
        DM_MEM_HOT_ADD_RESPONSE         = 11,
        DM_VERSION_03_MAX               = 11,
        /*
         * Version 1.0.
         */
        DM_INFO_MESSAGE                 = 12,
        DM_VERSION_1_MAX                = 12
};


/*
 * Structures defining the dynamic memory management
 * protocol.
 */

union dm_version {
        struct {
                __u16 minor_version;
                __u16 major_version;
        };
        __u32 version;
} __packed;


union dm_caps {
        struct {
                __u64 balloon:1;
                __u64 hot_add:1;
                /*
                 * To support guests that may have alignment
                 * limitations on hot-add, the guest can specify
                 * its alignment requirements; a value of n
                 * represents an alignment of 2^n in mega bytes.
                 */
                __u64 hot_add_alignment:4;
                __u64 reservedz:58;
        } cap_bits;
        __u64 caps;
} __packed;

union dm_mem_page_range {
        struct  {
                /*
                 * The PFN number of the first page in the range.
                 * 40 bits is the architectural limit of a PFN
                 * number for AMD64.
                 */
                __u64 start_page:40;
                /*
                 * The number of pages in the range.
                 */
                __u64 page_cnt:24;
        } finfo;
        __u64  page_range;
} __packed;



/*
 * The header for all dynamic memory messages:
 *
 * type: Type of the message.
 * size: Size of the message in bytes; including the header.
 * trans_id: The guest is responsible for manufacturing this ID.
 */

struct dm_header {
        __u16 type;
        __u16 size;
        __u32 trans_id;
} __packed;

/*
 * A generic message format for dynamic memory.
 * Specific message formats are defined later in the file.
 */

struct dm_message {
        struct dm_header hdr;
        __u8 data[]; /* enclosed message */
} __packed;


/*
 * Specific message types supporting the dynamic memory protocol.
 */

/*
 * Version negotiation message. Sent from the guest to the host.
 * The guest is free to try different versions until the host
 * accepts the version.
 *
 * dm_version: The protocol version requested.
 * is_last_attempt: If TRUE, this is the last version guest will request.
 * reservedz: Reserved field, set to zero.
 */

struct dm_version_request {
        struct dm_header hdr;
        union dm_version version;
        __u32 is_last_attempt:1;
        __u32 reservedz:31;
} __packed;

/*
 * Version response message; Host to Guest and indicates
 * if the host has accepted the version sent by the guest.
 *
 * is_accepted: If TRUE, host has accepted the version and the guest
 * should proceed to the next stage of the protocol. FALSE indicates that
 * guest should re-try with a different version.
 *
 * reservedz: Reserved field, set to zero.
 */

struct dm_version_response {
        struct dm_header hdr;
        __u64 is_accepted:1;
        __u64 reservedz:63;
} __packed;

/*
 * Message reporting capabilities. This is sent from the guest to the
 * host.
 */

struct dm_capabilities {
        struct dm_header hdr;
        union dm_caps caps;
        __u64 min_page_cnt;
        __u64 max_page_number;
} __packed;

/*
 * Response to the capabilities message. This is sent from the host to the
 * guest. This message notifies if the host has accepted the guest's
 * capabilities. If the host has not accepted, the guest must shutdown
 * the service.
 *
 * is_accepted: Indicates if the host has accepted guest's capabilities.
 * reservedz: Must be 0.
 */

struct dm_capabilities_resp_msg {
        struct dm_header hdr;
        __u64 is_accepted:1;
        __u64 reservedz:63;
} __packed;

/*
 * This message is used to report memory pressure from the guest.
 * This message is not part of any transaction and there is no
 * response to this message.
 *
 * num_avail: Available memory in pages.
 * num_committed: Committed memory in pages.
 * page_file_size: The accumulated size of all page files
 *                 in the system in pages.
 * zero_free: The nunber of zero and free pages.
 * page_file_writes: The writes to the page file in pages.
 * io_diff: An indicator of file cache efficiency or page file activity,
 *          calculated as File Cache Page Fault Count - Page Read Count.
 *          This value is in pages.
 *
 * Some of these metrics are Windows specific and fortunately
 * the algorithm on the host side that computes the guest memory
 * pressure only uses num_committed value.
 */

struct dm_status {
        struct dm_header hdr;
        __u64 num_avail;
        __u64 num_committed;
        __u64 page_file_size;
        __u64 zero_free;
        __u32 page_file_writes;
        __u32 io_diff;
} __packed;


/*
 * Message to ask the guest to allocate memory - balloon up message.
 * This message is sent from the host to the guest. The guest may not be
 * able to allocate as much memory as requested.
 *
 * num_pages: number of pages to allocate.
 */

struct dm_balloon {
        struct dm_header hdr;
        __u32 num_pages;
        __u32 reservedz;
} __packed;


/*
 * Balloon response message; this message is sent from the guest
 * to the host in response to the balloon message.
 *
 * reservedz: Reserved; must be set to zero.
 * more_pages: If FALSE, this is the last message of the transaction.
 * if TRUE there will atleast one more message from the guest.
 *
 * range_count: The number of ranges in the range array.
 *
 * range_array: An array of page ranges returned to the host.
 *
 */

struct dm_balloon_response {
        struct dm_header hdr;
        __u32 reservedz;
        __u32 more_pages:1;
        __u32 range_count:31;
        union dm_mem_page_range range_array[];
} __packed;

/*
 * Un-balloon message; this message is sent from the host
 * to the guest to give guest more memory.
 *
 * more_pages: If FALSE, this is the last message of the transaction.
 * if TRUE there will atleast one more message from the guest.
 *
 * reservedz: Reserved; must be set to zero.
 *
 * range_count: The number of ranges in the range array.
 *
 * range_array: An array of page ranges returned to the host.
 *
 */

struct dm_unballoon_request {
        struct dm_header hdr;
        __u32 more_pages:1;
        __u32 reservedz:31;
        __u32 range_count;
        union dm_mem_page_range range_array[];
} __packed;

/*
 * Un-balloon response message; this message is sent from the guest
 * to the host in response to an unballoon request.
 *
 */

struct dm_unballoon_response {
        struct dm_header hdr;
} __packed;


/*
 * Hot add request message. Message sent from the host to the guest.
 *
 * mem_range: Memory range to hot add.
 *
 * On Linux we currently don't support this since we cannot hot add
 * arbitrary granularity of memory.
 */

struct dm_hot_add {
        struct dm_header hdr;
        union dm_mem_page_range range;
} __packed;

/*
 * Hot add response message.
 * This message is sent by the guest to report the status of a hot add request.
 * If page_count is less than the requested page count, then the host should
 * assume all further hot add requests will fail, since this indicates that
 * the guest has hit an upper physical memory barrier.
 *
 * Hot adds may also fail due to low resources; in this case, the guest must
 * not complete this message until the hot add can succeed, and the host must
 * not send a new hot add request until the response is sent.
 * If VSC fails to hot add memory DYNMEM_NUMBER_OF_UNSUCCESSFUL_HOTADD_ATTEMPTS
 * times it fails the request.
 *
 *
 * page_count: number of pages that were successfully hot added.
 *
 * result: result of the operation 1: success, 0: failure.
 *
 */

struct dm_hot_add_response {
        struct dm_header hdr;
        __u32 page_count;
        __u32 result;
} __packed;

/*
 * Types of information sent from host to the guest.
 */

enum dm_info_type {
        INFO_TYPE_MAX_PAGE_CNT = 0,
        MAX_INFO_TYPE
};


/*
 * Header for the information message.
 */

struct dm_info_header {
        enum dm_info_type type;
        __u32 data_size;
} __packed;

/*
 * This message is sent from the host to the guest to pass
 * some relevant information (win8 addition).
 *
 * reserved: no used.
 * info_size: size of the information blob.
 * info: information blob.
 */

struct dm_info_msg {
        struct dm_header hdr;
        __u32 reserved;
        __u32 info_size;
        __u8  info[];
};

/*
 * End protocol definitions.
 */

/*
 * State to manage hot adding memory into the guest.
 * The range start_pfn : end_pfn specifies the range
 * that the host has asked us to hot add. The range
 * start_pfn : ha_end_pfn specifies the range that we have
 * currently hot added. We hot add in multiples of 128M
 * chunks; it is possible that we may not be able to bring
 * online all the pages in the region. The range
 * covered_start_pfn:covered_end_pfn defines the pages that can
 * be brough online.
 */

struct hv_hotadd_state {
        struct list_head list;
        unsigned long start_pfn;
        unsigned long covered_start_pfn;
        unsigned long covered_end_pfn;
        unsigned long ha_end_pfn;
        unsigned long end_pfn;
        /*
         * A list of gaps.
         */
        struct list_head gap_list;
};

struct hv_hotadd_gap {
        struct list_head list;
        unsigned long start_pfn;
        unsigned long end_pfn;
};

struct balloon_state {
        __u32 num_pages;
        struct work_struct wrk;
};

struct hot_add_wrk {
        union dm_mem_page_range ha_page_range;
        union dm_mem_page_range ha_region_range;
        struct work_struct wrk;
};

static bool hot_add = true;
static bool do_hot_add;
/*
 * Delay reporting memory pressure by
 * the specified number of seconds.
 */
static uint pressure_report_delay = 45;

/*
 * The last time we posted a pressure report to host.
 */
static unsigned long last_post_time;

module_param(hot_add, bool, (S_IRUGO | S_IWUSR));
MODULE_PARM_DESC(hot_add, "If set attempt memory hot_add");

module_param(pressure_report_delay, uint, (S_IRUGO | S_IWUSR));
MODULE_PARM_DESC(pressure_report_delay, "Delay in secs in reporting pressure");
static atomic_t trans_id = ATOMIC_INIT(0);

static int dm_ring_size = (5 * PAGE_SIZE);

/*
 * Driver specific state.
 */

enum hv_dm_state {
        DM_INITIALIZING = 0,
        DM_INITIALIZED,
        DM_BALLOON_UP,
        DM_BALLOON_DOWN,
        DM_HOT_ADD,
        DM_INIT_ERROR
};


static __u8 recv_buffer[PAGE_SIZE];
static __u8 *send_buffer;
#define PAGES_IN_2M     512
#define HA_CHUNK (32 * 1024)

struct hv_dynmem_device {
        struct hv_device *dev;
        enum hv_dm_state state;
        struct completion host_event;
        struct completion config_event;

        /*
         * Number of pages we have currently ballooned out.
         */
        unsigned int num_pages_ballooned;
        unsigned int num_pages_onlined;
        unsigned int num_pages_added;

        /*
         * State to manage the ballooning (up) operation.
         */
        struct balloon_state balloon_wrk;

        /*
         * State to execute the "hot-add" operation.
         */
        struct hot_add_wrk ha_wrk;

        /*
         * This state tracks if the host has specified a hot-add
         * region.
         */
        bool host_specified_ha_region;

        /*
         * State to synchronize hot-add.
         */
        struct completion  ol_waitevent;
        bool ha_waiting;
        /*
         * This thread handles hot-add
         * requests from the host as well as notifying
         * the host with regards to memory pressure in
         * the guest.
         */
        struct task_struct *thread;

        /*
         * Protects ha_region_list, num_pages_onlined counter and individual
         * regions from ha_region_list.
         */
        spinlock_t ha_lock;

        /*
         * A list of hot-add regions.
         */
        struct list_head ha_region_list;

        /*
         * We start with the highest version we can support
         * and downgrade based on the host; we save here the
         * next version to try.
         */
        __u32 next_version;

        /*
         * The negotiated version agreed by host.
         */
        __u32 version;
};

static struct hv_dynmem_device dm_device;

static void post_status(struct hv_dynmem_device *dm);

#ifdef CONFIG_MEMORY_HOTPLUG
static inline bool has_pfn_is_backed(struct hv_hotadd_state *has,
                                     unsigned long pfn)
{
        struct hv_hotadd_gap *gap;

        /* The page is not backed. */
        if ((pfn < has->covered_start_pfn) || (pfn >= has->covered_end_pfn))
                return false;

        /* Check for gaps. */
        list_for_each_entry(gap, &has->gap_list, list) {
                if ((pfn >= gap->start_pfn) && (pfn < gap->end_pfn))
                        return false;
        }

        return true;
}

static unsigned long hv_page_offline_check(unsigned long start_pfn,
                                           unsigned long nr_pages)
{
        unsigned long pfn = start_pfn, count = 0;
        struct hv_hotadd_state *has;
        bool found;

        while (pfn < start_pfn + nr_pages) {
                /*
                 * Search for HAS which covers the pfn and when we find one
                 * count how many consequitive PFNs are covered.
                 */
                found = false;
                list_for_each_entry(has, &dm_device.ha_region_list, list) {
                        while ((pfn >= has->start_pfn) &&
                               (pfn < has->end_pfn) &&
                               (pfn < start_pfn + nr_pages)) {
                                found = true;
                                if (has_pfn_is_backed(has, pfn))
                                        count++;
                                pfn++;
                        }
                }

                /*
                 * This PFN is not in any HAS (e.g. we're offlining a region
                 * which was present at boot), no need to account for it. Go
                 * to the next one.
                 */
                if (!found)
                        pfn++;
        }

        return count;
}

static int hv_memory_notifier(struct notifier_block *nb, unsigned long val,
                              void *v)
{
        struct memory_notify *mem = (struct memory_notify *)v;
        unsigned long flags, pfn_count;

        switch (val) {
        case MEM_ONLINE:
        case MEM_CANCEL_ONLINE:
                if (dm_device.ha_waiting) {
                        dm_device.ha_waiting = false;
                        complete(&dm_device.ol_waitevent);
                }
                break;

        case MEM_OFFLINE:
                spin_lock_irqsave(&dm_device.ha_lock, flags);
                pfn_count = hv_page_offline_check(mem->start_pfn,
                                                  mem->nr_pages);
                if (pfn_count <= dm_device.num_pages_onlined) {
                        dm_device.num_pages_onlined -= pfn_count;
                } else {
                        /*
                         * We're offlining more pages than we managed to online.
                         * This is unexpected. In any case don't let
                         * num_pages_onlined wrap around zero.
                         */
                        WARN_ON_ONCE(1);
                        dm_device.num_pages_onlined = 0;
                }
                spin_unlock_irqrestore(&dm_device.ha_lock, flags);
                break;
        case MEM_GOING_ONLINE:
        case MEM_GOING_OFFLINE:
        case MEM_CANCEL_OFFLINE:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block hv_memory_nb = {
        .notifier_call = hv_memory_notifier,
        .priority = 0
};

/* Check if the particular page is backed and can be onlined and online it. */
static void hv_page_online_one(struct hv_hotadd_state *has, struct page *pg)
{
        if (!has_pfn_is_backed(has, page_to_pfn(pg))) {
                if (!PageOffline(pg))
                        __SetPageOffline(pg);
                return;
        }
        if (PageOffline(pg))
                __ClearPageOffline(pg);

        /* This frame is currently backed; online the page. */
        __online_page_set_limits(pg);
        __online_page_increment_counters(pg);
        __online_page_free(pg);

        lockdep_assert_held(&dm_device.ha_lock);
        dm_device.num_pages_onlined++;
}

static void hv_bring_pgs_online(struct hv_hotadd_state *has,
                                unsigned long start_pfn, unsigned long size)
{
        int i;

        pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn);
        for (i = 0; i < size; i++)
                hv_page_online_one(has, pfn_to_page(start_pfn + i));
}

static void hv_mem_hot_add(unsigned long start, unsigned long size,
                                unsigned long pfn_count,
                                struct hv_hotadd_state *has)
{
        int ret = 0;
        int i, nid;
        unsigned long start_pfn;
        unsigned long processed_pfn;
        unsigned long total_pfn = pfn_count;
        unsigned long flags;

        for (i = 0; i < (size/HA_CHUNK); i++) {
                start_pfn = start + (i * HA_CHUNK);

                spin_lock_irqsave(&dm_device.ha_lock, flags);
                has->ha_end_pfn +=  HA_CHUNK;

                if (total_pfn > HA_CHUNK) {
                        processed_pfn = HA_CHUNK;
                        total_pfn -= HA_CHUNK;
                } else {
                        processed_pfn = total_pfn;
                        total_pfn = 0;
                }

                has->covered_end_pfn +=  processed_pfn;
                spin_unlock_irqrestore(&dm_device.ha_lock, flags);

                init_completion(&dm_device.ol_waitevent);
                dm_device.ha_waiting = !memhp_auto_online;

                nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
                ret = add_memory(nid, PFN_PHYS((start_pfn)),
                                (HA_CHUNK << PAGE_SHIFT));

                if (ret) {
                        pr_err("hot_add memory failed error is %d\n", ret);
                        if (ret == -EEXIST) {
                                /*
                                 * This error indicates that the error
                                 * is not a transient failure. This is the
                                 * case where the guest's physical address map
                                 * precludes hot adding memory. Stop all further
                                 * memory hot-add.
                                 */
                                do_hot_add = false;
                        }
                        spin_lock_irqsave(&dm_device.ha_lock, flags);
                        has->ha_end_pfn -= HA_CHUNK;
                        has->covered_end_pfn -=  processed_pfn;
                        spin_unlock_irqrestore(&dm_device.ha_lock, flags);
                        break;
                }

                /*
                 * Wait for the memory block to be onlined when memory onlining
                 * is done outside of kernel (memhp_auto_online). Since the hot
                 * add has succeeded, it is ok to proceed even if the pages in
                 * the hot added region have not been "onlined" within the
                 * allowed time.
                 */
                if (dm_device.ha_waiting)
                        wait_for_completion_timeout(&dm_device.ol_waitevent,
                                                    5*HZ);
                post_status(&dm_device);
        }
}

static void hv_online_page(struct page *pg, unsigned int order)
{
        struct hv_hotadd_state *has;
        unsigned long flags;
        unsigned long pfn = page_to_pfn(pg);

        spin_lock_irqsave(&dm_device.ha_lock, flags);
        list_for_each_entry(has, &dm_device.ha_region_list, list) {
                /* The page belongs to a different HAS. */
                if ((pfn < has->start_pfn) ||
                                (pfn + (1UL << order) > has->end_pfn))
                        continue;

                hv_bring_pgs_online(has, pfn, 1UL << order);
                break;
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);
}

static int pfn_covered(unsigned long start_pfn, unsigned long pfn_cnt)
{
        struct hv_hotadd_state *has;
        struct hv_hotadd_gap *gap;
        unsigned long residual, new_inc;
        int ret = 0;
        unsigned long flags;

        spin_lock_irqsave(&dm_device.ha_lock, flags);
        list_for_each_entry(has, &dm_device.ha_region_list, list) {
                /*
                 * If the pfn range we are dealing with is not in the current
                 * "hot add block", move on.
                 */
                if (start_pfn < has->start_pfn || start_pfn >= has->end_pfn)
                        continue;

                /*
                 * If the current start pfn is not where the covered_end
                 * is, create a gap and update covered_end_pfn.
                 */
                if (has->covered_end_pfn != start_pfn) {
                        gap = kzalloc(sizeof(struct hv_hotadd_gap), GFP_ATOMIC);
                        if (!gap) {
                                ret = -ENOMEM;
                                break;
                        }

                        INIT_LIST_HEAD(&gap->list);
                        gap->start_pfn = has->covered_end_pfn;
                        gap->end_pfn = start_pfn;
                        list_add_tail(&gap->list, &has->gap_list);

                        has->covered_end_pfn = start_pfn;
                }

                /*
                 * If the current hot add-request extends beyond
                 * our current limit; extend it.
                 */
                if ((start_pfn + pfn_cnt) > has->end_pfn) {
                        residual = (start_pfn + pfn_cnt - has->end_pfn);
                        /*
                         * Extend the region by multiples of HA_CHUNK.
                         */
                        new_inc = (residual / HA_CHUNK) * HA_CHUNK;
                        if (residual % HA_CHUNK)
                                new_inc += HA_CHUNK;

                        has->end_pfn += new_inc;
                }

                ret = 1;
                break;
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);

        return ret;
}

static unsigned long handle_pg_range(unsigned long pg_start,
                                        unsigned long pg_count)
{
        unsigned long start_pfn = pg_start;
        unsigned long pfn_cnt = pg_count;
        unsigned long size;
        struct hv_hotadd_state *has;
        unsigned long pgs_ol = 0;
        unsigned long old_covered_state;
        unsigned long res = 0, flags;

        pr_debug("Hot adding %lu pages starting at pfn 0x%lx.\n", pg_count,
                pg_start);

        spin_lock_irqsave(&dm_device.ha_lock, flags);
        list_for_each_entry(has, &dm_device.ha_region_list, list) {
                /*
                 * If the pfn range we are dealing with is not in the current
                 * "hot add block", move on.
                 */
                if (start_pfn < has->start_pfn || start_pfn >= has->end_pfn)
                        continue;

                old_covered_state = has->covered_end_pfn;

                if (start_pfn < has->ha_end_pfn) {
                        /*
                         * This is the case where we are backing pages
                         * in an already hot added region. Bring
                         * these pages online first.
                         */
                        pgs_ol = has->ha_end_pfn - start_pfn;
                        if (pgs_ol > pfn_cnt)
                                pgs_ol = pfn_cnt;

                        has->covered_end_pfn +=  pgs_ol;
                        pfn_cnt -= pgs_ol;
                        /*
                         * Check if the corresponding memory block is already
                         * online. It is possible to observe struct pages still
                         * being uninitialized here so check section instead.
                         * In case the section is online we need to bring the
                         * rest of pfns (which were not backed previously)
                         * online too.
                         */
                        if (start_pfn > has->start_pfn &&
                            online_section_nr(pfn_to_section_nr(start_pfn)))
                                hv_bring_pgs_online(has, start_pfn, pgs_ol);

                }

                if ((has->ha_end_pfn < has->end_pfn) && (pfn_cnt > 0)) {
                        /*
                         * We have some residual hot add range
                         * that needs to be hot added; hot add
                         * it now. Hot add a multiple of
                         * of HA_CHUNK that fully covers the pages
                         * we have.
                         */
                        size = (has->end_pfn - has->ha_end_pfn);
                        if (pfn_cnt <= size) {
                                size = ((pfn_cnt / HA_CHUNK) * HA_CHUNK);
                                if (pfn_cnt % HA_CHUNK)
                                        size += HA_CHUNK;
                        } else {
                                pfn_cnt = size;
                        }
                        spin_unlock_irqrestore(&dm_device.ha_lock, flags);
                        hv_mem_hot_add(has->ha_end_pfn, size, pfn_cnt, has);
                        spin_lock_irqsave(&dm_device.ha_lock, flags);
                }
                /*
                 * If we managed to online any pages that were given to us,
                 * we declare success.
                 */
                res = has->covered_end_pfn - old_covered_state;
                break;
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);

        return res;
}

static unsigned long process_hot_add(unsigned long pg_start,
                                        unsigned long pfn_cnt,
                                        unsigned long rg_start,
                                        unsigned long rg_size)
{
        struct hv_hotadd_state *ha_region = NULL;
        int covered;
        unsigned long flags;

        if (pfn_cnt == 0)
                return 0;

        if (!dm_device.host_specified_ha_region) {
                covered = pfn_covered(pg_start, pfn_cnt);
                if (covered < 0)
                        return 0;

                if (covered)
                        goto do_pg_range;
        }

        /*
         * If the host has specified a hot-add range; deal with it first.
         */

        if (rg_size != 0) {
                ha_region = kzalloc(sizeof(struct hv_hotadd_state), GFP_KERNEL);
                if (!ha_region)
                        return 0;

                INIT_LIST_HEAD(&ha_region->list);
                INIT_LIST_HEAD(&ha_region->gap_list);

                ha_region->start_pfn = rg_start;
                ha_region->ha_end_pfn = rg_start;
                ha_region->covered_start_pfn = pg_start;
                ha_region->covered_end_pfn = pg_start;
                ha_region->end_pfn = rg_start + rg_size;

                spin_lock_irqsave(&dm_device.ha_lock, flags);
                list_add_tail(&ha_region->list, &dm_device.ha_region_list);
                spin_unlock_irqrestore(&dm_device.ha_lock, flags);
        }

do_pg_range:
        /*
         * Process the page range specified; bringing them
         * online if possible.
         */
        return handle_pg_range(pg_start, pfn_cnt);
}

#endif

static void hot_add_req(struct work_struct *dummy)
{
        struct dm_hot_add_response resp;
#ifdef CONFIG_MEMORY_HOTPLUG
        unsigned long pg_start, pfn_cnt;
        unsigned long rg_start, rg_sz;
#endif
        struct hv_dynmem_device *dm = &dm_device;

        memset(&resp, 0, sizeof(struct dm_hot_add_response));
        resp.hdr.type = DM_MEM_HOT_ADD_RESPONSE;
        resp.hdr.size = sizeof(struct dm_hot_add_response);

#ifdef CONFIG_MEMORY_HOTPLUG
        pg_start = dm->ha_wrk.ha_page_range.finfo.start_page;
        pfn_cnt = dm->ha_wrk.ha_page_range.finfo.page_cnt;

        rg_start = dm->ha_wrk.ha_region_range.finfo.start_page;
        rg_sz = dm->ha_wrk.ha_region_range.finfo.page_cnt;

        if ((rg_start == 0) && (!dm->host_specified_ha_region)) {
                unsigned long region_size;
                unsigned long region_start;

                /*
                 * The host has not specified the hot-add region.
                 * Based on the hot-add page range being specified,
                 * compute a hot-add region that can cover the pages
                 * that need to be hot-added while ensuring the alignment
                 * and size requirements of Linux as it relates to hot-add.
                 */
                region_start = pg_start;
                region_size = (pfn_cnt / HA_CHUNK) * HA_CHUNK;
                if (pfn_cnt % HA_CHUNK)
                        region_size += HA_CHUNK;

                region_start = (pg_start / HA_CHUNK) * HA_CHUNK;

                rg_start = region_start;
                rg_sz = region_size;
        }

        if (do_hot_add)
                resp.page_count = process_hot_add(pg_start, pfn_cnt,
                                                rg_start, rg_sz);

        dm->num_pages_added += resp.page_count;
#endif
        /*
         * The result field of the response structure has the
         * following semantics:
         *
         * 1. If all or some pages hot-added: Guest should return success.
         *
         * 2. If no pages could be hot-added:
         *
         * If the guest returns success, then the host
         * will not attempt any further hot-add operations. This
         * signifies a permanent failure.
         *
         * If the guest returns failure, then this failure will be
         * treated as a transient failure and the host may retry the
         * hot-add operation after some delay.
         */
        if (resp.page_count > 0)
                resp.result = 1;
        else if (!do_hot_add)
                resp.result = 1;
        else
                resp.result = 0;

        if (!do_hot_add || (resp.page_count == 0))
                pr_err("Memory hot add failed\n");

        dm->state = DM_INITIALIZED;
        resp.hdr.trans_id = atomic_inc_return(&trans_id);
        vmbus_sendpacket(dm->dev->channel, &resp,
                        sizeof(struct dm_hot_add_response),
                        (unsigned long)NULL,
                        VM_PKT_DATA_INBAND, 0);
}

static void process_info(struct hv_dynmem_device *dm, struct dm_info_msg *msg)
{
        struct dm_info_header *info_hdr;

        info_hdr = (struct dm_info_header *)msg->info;

        switch (info_hdr->type) {
        case INFO_TYPE_MAX_PAGE_CNT:
                if (info_hdr->data_size == sizeof(__u64)) {
                        __u64 *max_page_count = (__u64 *)&info_hdr[1];

                        pr_info("Max. dynamic memory size: %llu MB\n",
                                (*max_page_count) >> (20 - PAGE_SHIFT));
                }

                break;
        default:
                pr_warn("Received Unknown type: %d\n", info_hdr->type);
        }
}

static unsigned long compute_balloon_floor(void)
{
        unsigned long min_pages;
        unsigned long nr_pages = totalram_pages();
#define MB2PAGES(mb) ((mb) << (20 - PAGE_SHIFT))
        /* Simple continuous piecewiese linear function:
         *  max MiB -> min MiB  gradient
         *       0         0
         *      16        16
         *      32        24
         *     128        72    (1/2)
         *     512       168    (1/4)
         *    2048       360    (1/8)
         *    8192       744    (1/16)
         *   32768      1512    (1/32)
         */
        if (nr_pages < MB2PAGES(128))
                min_pages = MB2PAGES(8) + (nr_pages >> 1);
        else if (nr_pages < MB2PAGES(512))
                min_pages = MB2PAGES(40) + (nr_pages >> 2);
        else if (nr_pages < MB2PAGES(2048))
                min_pages = MB2PAGES(104) + (nr_pages >> 3);
        else if (nr_pages < MB2PAGES(8192))
                min_pages = MB2PAGES(232) + (nr_pages >> 4);
        else
                min_pages = MB2PAGES(488) + (nr_pages >> 5);
#undef MB2PAGES
        return min_pages;
}

/*
 * Post our status as it relates memory pressure to the
 * host. Host expects the guests to post this status
 * periodically at 1 second intervals.
 *
 * The metrics specified in this protocol are very Windows
 * specific and so we cook up numbers here to convey our memory
 * pressure.
 */

static void post_status(struct hv_dynmem_device *dm)
{
        struct dm_status status;
        unsigned long now = jiffies;
        unsigned long last_post = last_post_time;

        if (pressure_report_delay > 0) {
                --pressure_report_delay;
                return;
        }

        if (!time_after(now, (last_post_time + HZ)))
                return;

        memset(&status, 0, sizeof(struct dm_status));
        status.hdr.type = DM_STATUS_REPORT;
        status.hdr.size = sizeof(struct dm_status);
        status.hdr.trans_id = atomic_inc_return(&trans_id);

        /*
         * The host expects the guest to report free and committed memory.
         * Furthermore, the host expects the pressure information to include
         * the ballooned out pages. For a given amount of memory that we are
         * managing we need to compute a floor below which we should not
         * balloon. Compute this and add it to the pressure report.
         * We also need to report all offline pages (num_pages_added -
         * num_pages_onlined) as committed to the host, otherwise it can try
         * asking us to balloon them out.
         */
        status.num_avail = si_mem_available();
        status.num_committed = vm_memory_committed() +
                dm->num_pages_ballooned +
                (dm->num_pages_added > dm->num_pages_onlined ?
                 dm->num_pages_added - dm->num_pages_onlined : 0) +
                compute_balloon_floor();

        trace_balloon_status(status.num_avail, status.num_committed,
                             vm_memory_committed(), dm->num_pages_ballooned,
                             dm->num_pages_added, dm->num_pages_onlined);
        /*
         * If our transaction ID is no longer current, just don't
         * send the status. This can happen if we were interrupted
         * after we picked our transaction ID.
         */
        if (status.hdr.trans_id != atomic_read(&trans_id))
                return;

        /*
         * If the last post time that we sampled has changed,
         * we have raced, don't post the status.
         */
        if (last_post != last_post_time)
                return;

        last_post_time = jiffies;
        vmbus_sendpacket(dm->dev->channel, &status,
                                sizeof(struct dm_status),
                                (unsigned long)NULL,
                                VM_PKT_DATA_INBAND, 0);

}

static void free_balloon_pages(struct hv_dynmem_device *dm,
                         union dm_mem_page_range *range_array)
{
        int num_pages = range_array->finfo.page_cnt;
        __u64 start_frame = range_array->finfo.start_page;
        struct page *pg;
        int i;

        for (i = 0; i < num_pages; i++) {
                pg = pfn_to_page(i + start_frame);
                __ClearPageOffline(pg);
                __free_page(pg);
                dm->num_pages_ballooned--;
        }
}



static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
                                        unsigned int num_pages,
                                        struct dm_balloon_response *bl_resp,
                                        int alloc_unit)
{
        unsigned int i, j;
        struct page *pg;

        if (num_pages < alloc_unit)
                return 0;

        for (i = 0; (i * alloc_unit) < num_pages; i++) {
                if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) >
                        PAGE_SIZE)
                        return i * alloc_unit;

                /*
                 * We execute this code in a thread context. Furthermore,
                 * we don't want the kernel to try too hard.
                 */
                pg = alloc_pages(GFP_HIGHUSER | __GFP_NORETRY |
                                __GFP_NOMEMALLOC | __GFP_NOWARN,
                                get_order(alloc_unit << PAGE_SHIFT));

                if (!pg)
                        return i * alloc_unit;

                dm->num_pages_ballooned += alloc_unit;

                /*
                 * If we allocatted 2M pages; split them so we
                 * can free them in any order we get.
                 */

                if (alloc_unit != 1)
                        split_page(pg, get_order(alloc_unit << PAGE_SHIFT));

                /* mark all pages offline */
                for (j = 0; j < (1 << get_order(alloc_unit << PAGE_SHIFT)); j++)
                        __SetPageOffline(pg + j);

                bl_resp->range_count++;
                bl_resp->range_array[i].finfo.start_page =
                        page_to_pfn(pg);
                bl_resp->range_array[i].finfo.page_cnt = alloc_unit;
                bl_resp->hdr.size += sizeof(union dm_mem_page_range);

        }

        return num_pages;
}

static void balloon_up(struct work_struct *dummy)
{
        unsigned int num_pages = dm_device.balloon_wrk.num_pages;
        unsigned int num_ballooned = 0;
        struct dm_balloon_response *bl_resp;
        int alloc_unit;
        int ret;
        bool done = false;
        int i;
        long avail_pages;
        unsigned long floor;

        /* The host balloons pages in 2M granularity. */
        WARN_ON_ONCE(num_pages % PAGES_IN_2M != 0);

        /*
         * We will attempt 2M allocations. However, if we fail to
         * allocate 2M chunks, we will go back to 4k allocations.
         */
        alloc_unit = 512;

        avail_pages = si_mem_available();
        floor = compute_balloon_floor();

        /* Refuse to balloon below the floor, keep the 2M granularity. */
        if (avail_pages < num_pages || avail_pages - num_pages < floor) {
                pr_warn("Balloon request will be partially fulfilled. %s\n",
                        avail_pages < num_pages ? "Not enough memory." :
                        "Balloon floor reached.");

                num_pages = avail_pages > floor ? (avail_pages - floor) : 0;
                num_pages -= num_pages % PAGES_IN_2M;
        }

        while (!done) {
                bl_resp = (struct dm_balloon_response *)send_buffer;
                memset(send_buffer, 0, PAGE_SIZE);
                bl_resp->hdr.type = DM_BALLOON_RESPONSE;
                bl_resp->hdr.size = sizeof(struct dm_balloon_response);
                bl_resp->more_pages = 1;

                num_pages -= num_ballooned;
                num_ballooned = alloc_balloon_pages(&dm_device, num_pages,
                                                    bl_resp, alloc_unit);

                if (alloc_unit != 1 && num_ballooned == 0) {
                        alloc_unit = 1;
                        continue;
                }

                if (num_ballooned == 0 || num_ballooned == num_pages) {
                        pr_debug("Ballooned %u out of %u requested pages.\n",
                                num_pages, dm_device.balloon_wrk.num_pages);

                        bl_resp->more_pages = 0;
                        done = true;
                        dm_device.state = DM_INITIALIZED;
                }

                /*
                 * We are pushing a lot of data through the channel;
                 * deal with transient failures caused because of the
                 * lack of space in the ring buffer.
                 */

                do {
                        bl_resp->hdr.trans_id = atomic_inc_return(&trans_id);
                        ret = vmbus_sendpacket(dm_device.dev->channel,
                                                bl_resp,
                                                bl_resp->hdr.size,
                                                (unsigned long)NULL,
                                                VM_PKT_DATA_INBAND, 0);

                        if (ret == -EAGAIN)
                                msleep(20);
                        post_status(&dm_device);
                } while (ret == -EAGAIN);

                if (ret) {
                        /*
                         * Free up the memory we allocatted.
                         */
                        pr_err("Balloon response failed\n");

                        for (i = 0; i < bl_resp->range_count; i++)
                                free_balloon_pages(&dm_device,
                                                 &bl_resp->range_array[i]);

                        done = true;
                }
        }

}

static void balloon_down(struct hv_dynmem_device *dm,
                        struct dm_unballoon_request *req)
{
        union dm_mem_page_range *range_array = req->range_array;
        int range_count = req->range_count;
        struct dm_unballoon_response resp;
        int i;
        unsigned int prev_pages_ballooned = dm->num_pages_ballooned;

        for (i = 0; i < range_count; i++) {
                free_balloon_pages(dm, &range_array[i]);
                complete(&dm_device.config_event);
        }

        pr_debug("Freed %u ballooned pages.\n",
                prev_pages_ballooned - dm->num_pages_ballooned);

        if (req->more_pages == 1)
                return;

        memset(&resp, 0, sizeof(struct dm_unballoon_response));
        resp.hdr.type = DM_UNBALLOON_RESPONSE;
        resp.hdr.trans_id = atomic_inc_return(&trans_id);
        resp.hdr.size = sizeof(struct dm_unballoon_response);

        vmbus_sendpacket(dm_device.dev->channel, &resp,
                                sizeof(struct dm_unballoon_response),
                                (unsigned long)NULL,
                                VM_PKT_DATA_INBAND, 0);

        dm->state = DM_INITIALIZED;
}

static void balloon_onchannelcallback(void *context);

static int dm_thread_func(void *dm_dev)
{
        struct hv_dynmem_device *dm = dm_dev;

        while (!kthread_should_stop()) {
                wait_for_completion_interruptible_timeout(
                                                &dm_device.config_event, 1*HZ);
                /*
                 * The host expects us to post information on the memory
                 * pressure every second.
                 */
                reinit_completion(&dm_device.config_event);
                post_status(dm);
        }

        return 0;
}


static void version_resp(struct hv_dynmem_device *dm,
                        struct dm_version_response *vresp)
{
        struct dm_version_request version_req;
        int ret;

        if (vresp->is_accepted) {
                /*
                 * We are done; wakeup the
                 * context waiting for version
                 * negotiation.
                 */
                complete(&dm->host_event);
                return;
        }
        /*
         * If there are more versions to try, continue
         * with negotiations; if not
         * shutdown the service since we are not able
         * to negotiate a suitable version number
         * with the host.
         */
        if (dm->next_version == 0)
                goto version_error;

        memset(&version_req, 0, sizeof(struct dm_version_request));
        version_req.hdr.type = DM_VERSION_REQUEST;
        version_req.hdr.size = sizeof(struct dm_version_request);
        version_req.hdr.trans_id = atomic_inc_return(&trans_id);
        version_req.version.version = dm->next_version;
        dm->version = version_req.version.version;

        /*
         * Set the next version to try in case current version fails.
         * Win7 protocol ought to be the last one to try.
         */
        switch (version_req.version.version) {
        case DYNMEM_PROTOCOL_VERSION_WIN8:
                dm->next_version = DYNMEM_PROTOCOL_VERSION_WIN7;
                version_req.is_last_attempt = 0;
                break;
        default:
                dm->next_version = 0;
                version_req.is_last_attempt = 1;
        }

        ret = vmbus_sendpacket(dm->dev->channel, &version_req,
                                sizeof(struct dm_version_request),
                                (unsigned long)NULL,
                                VM_PKT_DATA_INBAND, 0);

        if (ret)
                goto version_error;

        return;

version_error:
        dm->state = DM_INIT_ERROR;
        complete(&dm->host_event);
}

static void cap_resp(struct hv_dynmem_device *dm,
                        struct dm_capabilities_resp_msg *cap_resp)
{
        if (!cap_resp->is_accepted) {
                pr_err("Capabilities not accepted by host\n");
                dm->state = DM_INIT_ERROR;
        }
        complete(&dm->host_event);
}

static void balloon_onchannelcallback(void *context)
{
        struct hv_device *dev = context;
        u32 recvlen;
        u64 requestid;
        struct dm_message *dm_msg;
        struct dm_header *dm_hdr;
        struct hv_dynmem_device *dm = hv_get_drvdata(dev);
        struct dm_balloon *bal_msg;
        struct dm_hot_add *ha_msg;
        union dm_mem_page_range *ha_pg_range;
        union dm_mem_page_range *ha_region;

        memset(recv_buffer, 0, sizeof(recv_buffer));
        vmbus_recvpacket(dev->channel, recv_buffer,
                         PAGE_SIZE, &recvlen, &requestid);

        if (recvlen > 0) {
                dm_msg = (struct dm_message *)recv_buffer;
                dm_hdr = &dm_msg->hdr;

                switch (dm_hdr->type) {
                case DM_VERSION_RESPONSE:
                        version_resp(dm,
                                 (struct dm_version_response *)dm_msg);
                        break;

                case DM_CAPABILITIES_RESPONSE:
                        cap_resp(dm,
                                 (struct dm_capabilities_resp_msg *)dm_msg);
                        break;

                case DM_BALLOON_REQUEST:
                        if (dm->state == DM_BALLOON_UP)
                                pr_warn("Currently ballooning\n");
                        bal_msg = (struct dm_balloon *)recv_buffer;
                        dm->state = DM_BALLOON_UP;
                        dm_device.balloon_wrk.num_pages = bal_msg->num_pages;
                        schedule_work(&dm_device.balloon_wrk.wrk);
                        break;

                case DM_UNBALLOON_REQUEST:
                        dm->state = DM_BALLOON_DOWN;
                        balloon_down(dm,
                                 (struct dm_unballoon_request *)recv_buffer);
                        break;

                case DM_MEM_HOT_ADD_REQUEST:
                        if (dm->state == DM_HOT_ADD)
                                pr_warn("Currently hot-adding\n");
                        dm->state = DM_HOT_ADD;
                        ha_msg = (struct dm_hot_add *)recv_buffer;
                        if (ha_msg->hdr.size == sizeof(struct dm_hot_add)) {
                                /*
                                 * This is a normal hot-add request specifying
                                 * hot-add memory.
                                 */
                                dm->host_specified_ha_region = false;
                                ha_pg_range = &ha_msg->range;
                                dm->ha_wrk.ha_page_range = *ha_pg_range;
                                dm->ha_wrk.ha_region_range.page_range = 0;
                        } else {
                                /*
                                 * Host is specifying that we first hot-add
                                 * a region and then partially populate this
                                 * region.
                                 */
                                dm->host_specified_ha_region = true;
                                ha_pg_range = &ha_msg->range;
                                ha_region = &ha_pg_range[1];
                                dm->ha_wrk.ha_page_range = *ha_pg_range;
                                dm->ha_wrk.ha_region_range = *ha_region;
                        }
                        schedule_work(&dm_device.ha_wrk.wrk);
                        break;

                case DM_INFO_MESSAGE:
                        process_info(dm, (struct dm_info_msg *)dm_msg);
                        break;

                default:
                        pr_warn("Unhandled message: type: %d\n", dm_hdr->type);

                }
        }

}

static int balloon_probe(struct hv_device *dev,
                        const struct hv_vmbus_device_id *dev_id)
{
        int ret;
        unsigned long t;
        struct dm_version_request version_req;
        struct dm_capabilities cap_msg;

#ifdef CONFIG_MEMORY_HOTPLUG
        do_hot_add = hot_add;
#else
        do_hot_add = false;
#endif

        /*
         * First allocate a send buffer.
         */

        send_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!send_buffer)
                return -ENOMEM;

        ret = vmbus_open(dev->channel, dm_ring_size, dm_ring_size, NULL, 0,
                        balloon_onchannelcallback, dev);

        if (ret)
                goto probe_error0;

        dm_device.dev = dev;
        dm_device.state = DM_INITIALIZING;
        dm_device.next_version = DYNMEM_PROTOCOL_VERSION_WIN8;
        init_completion(&dm_device.host_event);
        init_completion(&dm_device.config_event);
        INIT_LIST_HEAD(&dm_device.ha_region_list);
        spin_lock_init(&dm_device.ha_lock);
        INIT_WORK(&dm_device.balloon_wrk.wrk, balloon_up);
        INIT_WORK(&dm_device.ha_wrk.wrk, hot_add_req);
        dm_device.host_specified_ha_region = false;

        dm_device.thread =
                 kthread_run(dm_thread_func, &dm_device, "hv_balloon");
        if (IS_ERR(dm_device.thread)) {
                ret = PTR_ERR(dm_device.thread);
                goto probe_error1;
        }

#ifdef CONFIG_MEMORY_HOTPLUG
        set_online_page_callback(&hv_online_page);
        register_memory_notifier(&hv_memory_nb);
#endif

        hv_set_drvdata(dev, &dm_device);
        /*
         * Initiate the hand shake with the host and negotiate
         * a version that the host can support. We start with the
         * highest version number and go down if the host cannot
         * support it.
         */
        memset(&version_req, 0, sizeof(struct dm_version_request));
        version_req.hdr.type = DM_VERSION_REQUEST;
        version_req.hdr.size = sizeof(struct dm_version_request);
        version_req.hdr.trans_id = atomic_inc_return(&trans_id);
        version_req.version.version = DYNMEM_PROTOCOL_VERSION_WIN10;
        version_req.is_last_attempt = 0;
        dm_device.version = version_req.version.version;

        ret = vmbus_sendpacket(dev->channel, &version_req,
                                sizeof(struct dm_version_request),
                                (unsigned long)NULL,
                                VM_PKT_DATA_INBAND, 0);
        if (ret)
                goto probe_error2;

        t = wait_for_completion_timeout(&dm_device.host_event, 5*HZ);
        if (t == 0) {
                ret = -ETIMEDOUT;
                goto probe_error2;
        }

        /*
         * If we could not negotiate a compatible version with the host
         * fail the probe function.
         */
        if (dm_device.state == DM_INIT_ERROR) {
                ret = -ETIMEDOUT;
                goto probe_error2;
        }

        pr_info("Using Dynamic Memory protocol version %u.%u\n",
                DYNMEM_MAJOR_VERSION(dm_device.version),
                DYNMEM_MINOR_VERSION(dm_device.version));

        /*
         * Now submit our capabilities to the host.
         */
        memset(&cap_msg, 0, sizeof(struct dm_capabilities));
        cap_msg.hdr.type = DM_CAPABILITIES_REPORT;
        cap_msg.hdr.size = sizeof(struct dm_capabilities);
        cap_msg.hdr.trans_id = atomic_inc_return(&trans_id);

        cap_msg.caps.cap_bits.balloon = 1;
        cap_msg.caps.cap_bits.hot_add = 1;

        /*
         * Specify our alignment requirements as it relates
         * memory hot-add. Specify 128MB alignment.
         */
        cap_msg.caps.cap_bits.hot_add_alignment = 7;

        /*
         * Currently the host does not use these
         * values and we set them to what is done in the
         * Windows driver.
         */
        cap_msg.min_page_cnt = 0;
        cap_msg.max_page_number = -1;

        ret = vmbus_sendpacket(dev->channel, &cap_msg,
                                sizeof(struct dm_capabilities),
                                (unsigned long)NULL,
                                VM_PKT_DATA_INBAND, 0);
        if (ret)
                goto probe_error2;

        t = wait_for_completion_timeout(&dm_device.host_event, 5*HZ);
        if (t == 0) {
                ret = -ETIMEDOUT;
                goto probe_error2;
        }

        /*
         * If the host does not like our capabilities,
         * fail the probe function.
         */
        if (dm_device.state == DM_INIT_ERROR) {
                ret = -ETIMEDOUT;
                goto probe_error2;
        }

        dm_device.state = DM_INITIALIZED;
        last_post_time = jiffies;

        return 0;

probe_error2:
#ifdef CONFIG_MEMORY_HOTPLUG
        restore_online_page_callback(&hv_online_page);
#endif
        kthread_stop(dm_device.thread);

probe_error1:
        vmbus_close(dev->channel);
probe_error0:
        kfree(send_buffer);
        return ret;
}

static int balloon_remove(struct hv_device *dev)
{
        struct hv_dynmem_device *dm = hv_get_drvdata(dev);
        struct hv_hotadd_state *has, *tmp;
        struct hv_hotadd_gap *gap, *tmp_gap;
        unsigned long flags;

        if (dm->num_pages_ballooned != 0)
                pr_warn("Ballooned pages: %d\n", dm->num_pages_ballooned);

        cancel_work_sync(&dm->balloon_wrk.wrk);
        cancel_work_sync(&dm->ha_wrk.wrk);

        vmbus_close(dev->channel);
        kthread_stop(dm->thread);
        kfree(send_buffer);
#ifdef CONFIG_MEMORY_HOTPLUG
        restore_online_page_callback(&hv_online_page);
        unregister_memory_notifier(&hv_memory_nb);
#endif
        spin_lock_irqsave(&dm_device.ha_lock, flags);
        list_for_each_entry_safe(has, tmp, &dm->ha_region_list, list) {
                list_for_each_entry_safe(gap, tmp_gap, &has->gap_list, list) {
                        list_del(&gap->list);
                        kfree(gap);
                }
                list_del(&has->list);
                kfree(has);
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);

        return 0;
}

static const struct hv_vmbus_device_id id_table[] = {
        /* Dynamic Memory Class ID */
        /* 525074DC-8985-46e2-8057-A307DC18A502 */
        { HV_DM_GUID, },
        { },
};

MODULE_DEVICE_TABLE(vmbus, id_table);

static  struct hv_driver balloon_drv = {
        .name = "hv_balloon",
        .id_table = id_table,
        .probe =  balloon_probe,
        .remove =  balloon_remove,
        .driver = {
                .probe_type = PROBE_PREFER_ASYNCHRONOUS,
        },
};

static int __init init_balloon_drv(void)
{

        return vmbus_driver_register(&balloon_drv);
}

module_init(init_balloon_drv);

MODULE_DESCRIPTION("Hyper-V Balloon");
MODULE_LICENSE("GPL");