Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2166 insertions, 0 deletions

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
new file mode 100644
index 0000000000..e000fa3b9f
--- /dev/null
+++ b/drivers/hv/hv_balloon.c
@@ -0,0 +1,2166 @@
+// 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/cleanup.h>
+#include <linux/kernel.h>
+#include <linux/jiffies.h>
+#include <linux/mman.h>
+#include <linux/debugfs.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/count_zeros.h>
+#include <linux/memory_hotplug.h>
+#include <linux/memory.h>
+#include <linux/notifier.h>
+#include <linux/percpu_counter.h>
+#include <linux/page_reporting.h>
+
+#include <linux/hyperv.h>
+#include <asm/hyperv-tlfs.h>
+
+#include <asm/mshyperv.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 number 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.
+ *
+ */
+
+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 allow_hibernation;
+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;
+extern unsigned int page_reporting_order;
+#define HV_MAX_FAILURES	2
+
+/*
+ * The last time we posted a pressure report to host.
+ */
+static unsigned long last_post_time;
+
+static int hv_hypercall_multi_failure;
+
+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 = VMBUS_RING_SIZE(16 * 1024);
+
+/*
+ * 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[HV_HYP_PAGE_SIZE];
+static __u8 balloon_up_send_buffer[HV_HYP_PAGE_SIZE];
+#define PAGES_IN_2M (2 * 1024 * 1024 / PAGE_SIZE)
+#define HA_CHUNK (128 * 1024 * 1024 / PAGE_SIZE)
+
+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;
+	/*
+	 * 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;
+
+	struct page_reporting_dev_info pr_dev_info;
+
+	/*
+	 * Maximum number of pages that can be hot_add-ed
+	 */
+	__u64 max_dynamic_page_count;
+};
+
+static struct hv_dynmem_device dm_device;
+
+static void post_status(struct hv_dynmem_device *dm);
+
+static void enable_page_reporting(void);
+
+static void disable_page_reporting(void);
+
+#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 pfn_count;
+
+	switch (val) {
+	case MEM_ONLINE:
+	case MEM_CANCEL_ONLINE:
+		complete(&dm_device.ol_waitevent);
+		break;
+
+	case MEM_OFFLINE:
+		scoped_guard(spinlock_irqsave, &dm_device.ha_lock) {
+			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;
+			}
+		}
+		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. */
+	generic_online_page(pg, 0);
+
+	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;
+
+	for (i = 0; i < (size/HA_CHUNK); i++) {
+		start_pfn = start + (i * HA_CHUNK);
+
+		scoped_guard(spinlock_irqsave, &dm_device.ha_lock) {
+			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;
+		}
+
+		reinit_completion(&dm_device.ol_waitevent);
+
+		nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
+		ret = add_memory(nid, PFN_PHYS((start_pfn)),
+				(HA_CHUNK << PAGE_SHIFT), MHP_MERGE_RESOURCE);
+
+		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;
+			}
+			scoped_guard(spinlock_irqsave, &dm_device.ha_lock) {
+				has->ha_end_pfn -= HA_CHUNK;
+				has->covered_end_pfn -=  processed_pfn;
+			}
+			break;
+		}
+
+		/*
+		 * Wait for memory to get onlined. If the kernel onlined the
+		 * memory when adding it, this will return directly. Otherwise,
+		 * it will wait for user space to online the memory. This helps
+		 * to avoid adding memory faster than it is getting onlined. As
+		 * adding succeeded, it is ok to proceed even if the memory was
+		 * not onlined in time.
+		 */
+		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 pfn = page_to_pfn(pg);
+
+	guard(spinlock_irqsave)(&dm_device.ha_lock);
+	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;
+	}
+}
+
+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;
+
+	guard(spinlock_irqsave)(&dm_device.ha_lock);
+	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;
+	}
+
+	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
+			 * 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;
+
+	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;
+
+		scoped_guard(spinlock_irqsave, &dm_device.ha_lock) {
+			list_add_tail(&ha_region->list, &dm_device.ha_region_list);
+		}
+	}
+
+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_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) {
+		if (!allow_hibernation)
+			pr_err("Memory hot add failed\n");
+		else
+			pr_info("Ignore hot-add request!\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 - HV_HYP_PAGE_SHIFT));
+			dm->max_dynamic_page_count = *max_page_count;
+		}
+
+		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;
+}
+
+/*
+ * Compute total committed memory pages
+ */
+
+static unsigned long get_pages_committed(struct hv_dynmem_device *dm)
+{
+	return 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();
+}
+
+/*
+ * 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;
+	unsigned long num_pages_avail, num_pages_committed;
+
+	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.
+	 */
+	num_pages_avail = si_mem_available();
+	num_pages_committed = get_pages_committed(dm);
+
+	trace_balloon_status(num_pages_avail, num_pages_committed,
+			     vm_memory_committed(), dm->num_pages_ballooned,
+			     dm->num_pages_added, dm->num_pages_onlined);
+
+	/* Convert numbers of pages into numbers of HV_HYP_PAGEs. */
+	status.num_avail = num_pages_avail * NR_HV_HYP_PAGES_IN_PAGE;
+	status.num_committed = num_pages_committed * NR_HV_HYP_PAGES_IN_PAGE;
+
+	/*
+	 * 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--;
+		adjust_managed_page_count(pg, 1);
+	}
+}
+
+
+
+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;
+
+	for (i = 0; i < num_pages / alloc_unit; i++) {
+		if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) >
+			HV_HYP_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 < alloc_unit; j++) {
+			__SetPageOffline(pg + j);
+			adjust_managed_page_count(pg + j, -1);
+		}
+
+		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 i * alloc_unit;
+}
+
+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;
+
+	/*
+	 * We will attempt 2M allocations. However, if we fail to
+	 * allocate 2M chunks, we will go back to PAGE_SIZE allocations.
+	 */
+	alloc_unit = PAGES_IN_2M;
+
+	avail_pages = si_mem_available();
+	floor = compute_balloon_floor();
+
+	/* Refuse to balloon below the floor. */
+	if (avail_pages < num_pages || avail_pages - num_pages < floor) {
+		pr_info("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;
+	}
+
+	while (!done) {
+		memset(balloon_up_send_buffer, 0, HV_HYP_PAGE_SIZE);
+		bl_resp = (struct dm_balloon_response *)balloon_up_send_buffer;
+		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);
+		/*
+		 * disable free page reporting if multiple hypercall
+		 * failure flag set. It is not done in the page_reporting
+		 * callback context as that causes a deadlock between
+		 * page_reporting_process() and page_reporting_unregister()
+		 */
+		if (hv_hypercall_multi_failure >= HV_MAX_FAILURES) {
+			pr_err("Multiple failures in cold memory discard hypercall, disabling page reporting\n");
+			disable_page_reporting();
+			/* Reset the flag after disabling reporting */
+			hv_hypercall_multi_failure = 0;
+		}
+	}
+
+	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,
+			 HV_HYP_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 (allow_hibernation) {
+				pr_info("Ignore balloon-up request!\n");
+				break;
+			}
+
+			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:
+			if (allow_hibernation) {
+				pr_info("Ignore balloon-down request!\n");
+				break;
+			}
+
+			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_ratelimited("Unhandled message: type: %d\n", dm_hdr->type);
+
+		}
+	}
+
+}
+
+#define HV_LARGE_REPORTING_ORDER	9
+#define HV_LARGE_REPORTING_LEN (HV_HYP_PAGE_SIZE << \
+		HV_LARGE_REPORTING_ORDER)
+static int hv_free_page_report(struct page_reporting_dev_info *pr_dev_info,
+		    struct scatterlist *sgl, unsigned int nents)
+{
+	unsigned long flags;
+	struct hv_memory_hint *hint;
+	int i, order;
+	u64 status;
+	struct scatterlist *sg;
+
+	WARN_ON_ONCE(nents > HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES);
+	WARN_ON_ONCE(sgl->length < (HV_HYP_PAGE_SIZE << page_reporting_order));
+	local_irq_save(flags);
+	hint = *this_cpu_ptr(hyperv_pcpu_input_arg);
+	if (!hint) {
+		local_irq_restore(flags);
+		return -ENOSPC;
+	}
+
+	hint->type = HV_EXT_MEMORY_HEAT_HINT_TYPE_COLD_DISCARD;
+	hint->reserved = 0;
+	for_each_sg(sgl, sg, nents, i) {
+		union hv_gpa_page_range *range;
+
+		range = &hint->ranges[i];
+		range->address_space = 0;
+		order = get_order(sg->length);
+		/*
+		 * Hyper-V expects the additional_pages field in the units
+		 * of one of these 3 sizes, 4Kbytes, 2Mbytes or 1Gbytes.
+		 * This is dictated by the values of the fields page.largesize
+		 * and page_size.
+		 * This code however, only uses 4Kbytes and 2Mbytes units
+		 * and not 1Gbytes unit.
+		 */
+
+		/* page reporting for pages 2MB or higher */
+		if (order >= HV_LARGE_REPORTING_ORDER ) {
+			range->page.largepage = 1;
+			range->page_size = HV_GPA_PAGE_RANGE_PAGE_SIZE_2MB;
+			range->base_large_pfn = page_to_hvpfn(
+					sg_page(sg)) >> HV_LARGE_REPORTING_ORDER;
+			range->page.additional_pages =
+				(sg->length / HV_LARGE_REPORTING_LEN) - 1;
+		} else {
+			/* Page reporting for pages below 2MB */
+			range->page.basepfn = page_to_hvpfn(sg_page(sg));
+			range->page.largepage = false;
+			range->page.additional_pages =
+				(sg->length / HV_HYP_PAGE_SIZE) - 1;
+		}
+
+	}
+
+	status = hv_do_rep_hypercall(HV_EXT_CALL_MEMORY_HEAT_HINT, nents, 0,
+				     hint, NULL);
+	local_irq_restore(flags);
+	if (!hv_result_success(status)) {
+
+		pr_err("Cold memory discard hypercall failed with status %llx\n",
+				status);
+		if (hv_hypercall_multi_failure > 0)
+			hv_hypercall_multi_failure++;
+
+		if (hv_result(status) == HV_STATUS_INVALID_PARAMETER) {
+			pr_err("Underlying Hyper-V does not support order less than 9. Hypercall failed\n");
+			pr_err("Defaulting to page_reporting_order %d\n",
+					pageblock_order);
+			page_reporting_order = pageblock_order;
+			hv_hypercall_multi_failure++;
+			return -EINVAL;
+		}
+
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void enable_page_reporting(void)
+{
+	int ret;
+
+	if (!hv_query_ext_cap(HV_EXT_CAPABILITY_MEMORY_COLD_DISCARD_HINT)) {
+		pr_debug("Cold memory discard hint not supported by Hyper-V\n");
+		return;
+	}
+
+	BUILD_BUG_ON(PAGE_REPORTING_CAPACITY > HV_MEMORY_HINT_MAX_GPA_PAGE_RANGES);
+	dm_device.pr_dev_info.report = hv_free_page_report;
+	/*
+	 * We let the page_reporting_order parameter decide the order
+	 * in the page_reporting code
+	 */
+	dm_device.pr_dev_info.order = 0;
+	ret = page_reporting_register(&dm_device.pr_dev_info);
+	if (ret < 0) {
+		dm_device.pr_dev_info.report = NULL;
+		pr_err("Failed to enable cold memory discard: %d\n", ret);
+	} else {
+		pr_info("Cold memory discard hint enabled with order %d\n",
+				page_reporting_order);
+	}
+}
+
+static void disable_page_reporting(void)
+{
+	if (dm_device.pr_dev_info.report) {
+		page_reporting_unregister(&dm_device.pr_dev_info);
+		dm_device.pr_dev_info.report = NULL;
+	}
+}
+
+static int ballooning_enabled(void)
+{
+	/*
+	 * Disable ballooning if the page size is not 4k (HV_HYP_PAGE_SIZE),
+	 * since currently it's unclear to us whether an unballoon request can
+	 * make sure all page ranges are guest page size aligned.
+	 */
+	if (PAGE_SIZE != HV_HYP_PAGE_SIZE) {
+		pr_info("Ballooning disabled because page size is not 4096 bytes\n");
+		return 0;
+	}
+
+	return 1;
+}
+
+static int hot_add_enabled(void)
+{
+	/*
+	 * Disable hot add on ARM64, because we currently rely on
+	 * memory_add_physaddr_to_nid() to get a node id of a hot add range,
+	 * however ARM64's memory_add_physaddr_to_nid() always return 0 and
+	 * DM_MEM_HOT_ADD_REQUEST doesn't have the NUMA node information for
+	 * add_memory().
+	 */
+	if (IS_ENABLED(CONFIG_ARM64)) {
+		pr_info("Memory hot add disabled on ARM64\n");
+		return 0;
+	}
+
+	return 1;
+}
+
+static int balloon_connect_vsp(struct hv_device *dev)
+{
+	struct dm_version_request version_req;
+	struct dm_capabilities cap_msg;
+	unsigned long t;
+	int ret;
+
+	/*
+	 * max_pkt_size should be large enough for one vmbus packet header plus
+	 * our receive buffer size. Hyper-V sends messages up to
+	 * HV_HYP_PAGE_SIZE bytes long on balloon channel.
+	 */
+	dev->channel->max_pkt_size = HV_HYP_PAGE_SIZE * 2;
+
+	ret = vmbus_open(dev->channel, dm_ring_size, dm_ring_size, NULL, 0,
+			 balloon_onchannelcallback, dev);
+	if (ret)
+		return ret;
+
+	/*
+	 * 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 out;
+
+	t = wait_for_completion_timeout(&dm_device.host_event, 5*HZ);
+	if (t == 0) {
+		ret = -ETIMEDOUT;
+		goto out;
+	}
+
+	/*
+	 * If we could not negotiate a compatible version with the host
+	 * fail the probe function.
+	 */
+	if (dm_device.state == DM_INIT_ERROR) {
+		ret = -EPROTO;
+		goto out;
+	}
+
+	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);
+
+	/*
+	 * When hibernation (i.e. virtual ACPI S4 state) is enabled, the host
+	 * currently still requires the bits to be set, so we have to add code
+	 * to fail the host's hot-add and balloon up/down requests, if any.
+	 */
+	cap_msg.caps.cap_bits.balloon = ballooning_enabled();
+	cap_msg.caps.cap_bits.hot_add = hot_add_enabled();
+
+	/*
+	 * 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 out;
+
+	t = wait_for_completion_timeout(&dm_device.host_event, 5*HZ);
+	if (t == 0) {
+		ret = -ETIMEDOUT;
+		goto out;
+	}
+
+	/*
+	 * If the host does not like our capabilities,
+	 * fail the probe function.
+	 */
+	if (dm_device.state == DM_INIT_ERROR) {
+		ret = -EPROTO;
+		goto out;
+	}
+
+	return 0;
+out:
+	vmbus_close(dev->channel);
+	return ret;
+}
+
+/*
+ * DEBUGFS Interface
+ */
+#ifdef CONFIG_DEBUG_FS
+
+/**
+ * hv_balloon_debug_show - shows statistics of balloon operations.
+ * @f: pointer to the &struct seq_file.
+ * @offset: ignored.
+ *
+ * Provides the statistics that can be accessed in hv-balloon in the debugfs.
+ *
+ * Return: zero on success or an error code.
+ */
+static int hv_balloon_debug_show(struct seq_file *f, void *offset)
+{
+	struct hv_dynmem_device *dm = f->private;
+	char *sname;
+
+	seq_printf(f, "%-22s: %u.%u\n", "host_version",
+				DYNMEM_MAJOR_VERSION(dm->version),
+				DYNMEM_MINOR_VERSION(dm->version));
+
+	seq_printf(f, "%-22s:", "capabilities");
+	if (ballooning_enabled())
+		seq_puts(f, " enabled");
+
+	if (hot_add_enabled())
+		seq_puts(f, " hot_add");
+
+	seq_puts(f, "\n");
+
+	seq_printf(f, "%-22s: %u", "state", dm->state);
+	switch (dm->state) {
+	case DM_INITIALIZING:
+			sname = "Initializing";
+			break;
+	case DM_INITIALIZED:
+			sname = "Initialized";
+			break;
+	case DM_BALLOON_UP:
+			sname = "Balloon Up";
+			break;
+	case DM_BALLOON_DOWN:
+			sname = "Balloon Down";
+			break;
+	case DM_HOT_ADD:
+			sname = "Hot Add";
+			break;
+	case DM_INIT_ERROR:
+			sname = "Error";
+			break;
+	default:
+			sname = "Unknown";
+	}
+	seq_printf(f, " (%s)\n", sname);
+
+	/* HV Page Size */
+	seq_printf(f, "%-22s: %ld\n", "page_size", HV_HYP_PAGE_SIZE);
+
+	/* Pages added with hot_add */
+	seq_printf(f, "%-22s: %u\n", "pages_added", dm->num_pages_added);
+
+	/* pages that are "onlined"/used from pages_added */
+	seq_printf(f, "%-22s: %u\n", "pages_onlined", dm->num_pages_onlined);
+
+	/* pages we have given back to host */
+	seq_printf(f, "%-22s: %u\n", "pages_ballooned", dm->num_pages_ballooned);
+
+	seq_printf(f, "%-22s: %lu\n", "total_pages_committed",
+				get_pages_committed(dm));
+
+	seq_printf(f, "%-22s: %llu\n", "max_dynamic_page_count",
+				dm->max_dynamic_page_count);
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(hv_balloon_debug);
+
+static void  hv_balloon_debugfs_init(struct hv_dynmem_device *b)
+{
+	debugfs_create_file("hv-balloon", 0444, NULL, b,
+			&hv_balloon_debug_fops);
+}
+
+static void  hv_balloon_debugfs_exit(struct hv_dynmem_device *b)
+{
+	debugfs_lookup_and_remove("hv-balloon", NULL);
+}
+
+#else
+
+static inline void hv_balloon_debugfs_init(struct hv_dynmem_device  *b)
+{
+}
+
+static inline void hv_balloon_debugfs_exit(struct hv_dynmem_device *b)
+{
+}
+
+#endif	/* CONFIG_DEBUG_FS */
+
+static int balloon_probe(struct hv_device *dev,
+			 const struct hv_vmbus_device_id *dev_id)
+{
+	int ret;
+
+	allow_hibernation = hv_is_hibernation_supported();
+	if (allow_hibernation)
+		hot_add = false;
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+	do_hot_add = hot_add;
+#else
+	do_hot_add = false;
+#endif
+	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;
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+	set_online_page_callback(&hv_online_page);
+	init_completion(&dm_device.ol_waitevent);
+	register_memory_notifier(&hv_memory_nb);
+#endif
+
+	hv_set_drvdata(dev, &dm_device);
+
+	ret = balloon_connect_vsp(dev);
+	if (ret != 0)
+		goto connect_error;
+
+	enable_page_reporting();
+	dm_device.state = DM_INITIALIZED;
+
+	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_error;
+	}
+
+	hv_balloon_debugfs_init(&dm_device);
+
+	return 0;
+
+probe_error:
+	dm_device.state = DM_INIT_ERROR;
+	dm_device.thread  = NULL;
+	disable_page_reporting();
+	vmbus_close(dev->channel);
+connect_error:
+#ifdef CONFIG_MEMORY_HOTPLUG
+	unregister_memory_notifier(&hv_memory_nb);
+	restore_online_page_callback(&hv_online_page);
+#endif
+	return ret;
+}
+
+static void 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;
+
+	if (dm->num_pages_ballooned != 0)
+		pr_warn("Ballooned pages: %d\n", dm->num_pages_ballooned);
+
+	hv_balloon_debugfs_exit(dm);
+
+	cancel_work_sync(&dm->balloon_wrk.wrk);
+	cancel_work_sync(&dm->ha_wrk.wrk);
+
+	kthread_stop(dm->thread);
+
+	/*
+	 * This is to handle the case when balloon_resume()
+	 * call has failed and some cleanup has been done as
+	 * a part of the error handling.
+	 */
+	if (dm_device.state != DM_INIT_ERROR) {
+		disable_page_reporting();
+		vmbus_close(dev->channel);
+#ifdef CONFIG_MEMORY_HOTPLUG
+		unregister_memory_notifier(&hv_memory_nb);
+		restore_online_page_callback(&hv_online_page);
+#endif
+	}
+
+	guard(spinlock_irqsave)(&dm_device.ha_lock);
+	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);
+	}
+}
+
+static int balloon_suspend(struct hv_device *hv_dev)
+{
+	struct hv_dynmem_device *dm = hv_get_drvdata(hv_dev);
+
+	tasklet_disable(&hv_dev->channel->callback_event);
+
+	cancel_work_sync(&dm->balloon_wrk.wrk);
+	cancel_work_sync(&dm->ha_wrk.wrk);
+
+	if (dm->thread) {
+		kthread_stop(dm->thread);
+		dm->thread = NULL;
+		vmbus_close(hv_dev->channel);
+	}
+
+	tasklet_enable(&hv_dev->channel->callback_event);
+
+	return 0;
+
+}
+
+static int balloon_resume(struct hv_device *dev)
+{
+	int ret;
+
+	dm_device.state = DM_INITIALIZING;
+
+	ret = balloon_connect_vsp(dev);
+
+	if (ret != 0)
+		goto out;
+
+	dm_device.thread =
+		 kthread_run(dm_thread_func, &dm_device, "hv_balloon");
+	if (IS_ERR(dm_device.thread)) {
+		ret = PTR_ERR(dm_device.thread);
+		dm_device.thread = NULL;
+		goto close_channel;
+	}
+
+	dm_device.state = DM_INITIALIZED;
+	return 0;
+close_channel:
+	vmbus_close(dev->channel);
+out:
+	dm_device.state = DM_INIT_ERROR;
+	disable_page_reporting();
+#ifdef CONFIG_MEMORY_HOTPLUG
+	unregister_memory_notifier(&hv_memory_nb);
+	restore_online_page_callback(&hv_online_page);
+#endif
+	return ret;
+}
+
+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,
+	.suspend = balloon_suspend,
+	.resume = balloon_resume,
+	.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");