Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 1937 insertions, 0 deletions

diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
new file mode 100644
index 0000000000..9ce9b9e0e9
--- /dev/null
+++ b/drivers/misc/vmw_balloon.c
@@ -0,0 +1,1937 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * VMware Balloon driver.
+ *
+ * Copyright (C) 2000-2018, VMware, Inc. All Rights Reserved.
+ *
+ * This is VMware physical memory management driver for Linux. The driver
+ * acts like a "balloon" that can be inflated to reclaim physical pages by
+ * reserving them in the guest and invalidating them in the monitor,
+ * freeing up the underlying machine pages so they can be allocated to
+ * other guests.  The balloon can also be deflated to allow the guest to
+ * use more physical memory. Higher level policies can control the sizes
+ * of balloons in VMs in order to manage physical memory resources.
+ */
+
+//#define DEBUG
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/types.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/workqueue.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/rwsem.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/balloon_compaction.h>
+#include <linux/vmw_vmci_defs.h>
+#include <linux/vmw_vmci_api.h>
+#include <asm/hypervisor.h>
+
+MODULE_AUTHOR("VMware, Inc.");
+MODULE_DESCRIPTION("VMware Memory Control (Balloon) Driver");
+MODULE_ALIAS("dmi:*:svnVMware*:*");
+MODULE_ALIAS("vmware_vmmemctl");
+MODULE_LICENSE("GPL");
+
+static bool __read_mostly vmwballoon_shrinker_enable;
+module_param(vmwballoon_shrinker_enable, bool, 0444);
+MODULE_PARM_DESC(vmwballoon_shrinker_enable,
+	"Enable non-cooperative out-of-memory protection. Disabled by default as it may degrade performance.");
+
+/* Delay in seconds after shrink before inflation. */
+#define VMBALLOON_SHRINK_DELAY		(5)
+
+/* Maximum number of refused pages we accumulate during inflation cycle */
+#define VMW_BALLOON_MAX_REFUSED		16
+
+/* Magic number for the balloon mount-point */
+#define BALLOON_VMW_MAGIC		0x0ba11007
+
+/*
+ * Hypervisor communication port definitions.
+ */
+#define VMW_BALLOON_HV_PORT		0x5670
+#define VMW_BALLOON_HV_MAGIC		0x456c6d6f
+#define VMW_BALLOON_GUEST_ID		1	/* Linux */
+
+enum vmwballoon_capabilities {
+	/*
+	 * Bit 0 is reserved and not associated to any capability.
+	 */
+	VMW_BALLOON_BASIC_CMDS			= (1 << 1),
+	VMW_BALLOON_BATCHED_CMDS		= (1 << 2),
+	VMW_BALLOON_BATCHED_2M_CMDS		= (1 << 3),
+	VMW_BALLOON_SIGNALLED_WAKEUP_CMD	= (1 << 4),
+	VMW_BALLOON_64_BIT_TARGET		= (1 << 5)
+};
+
+#define VMW_BALLOON_CAPABILITIES_COMMON	(VMW_BALLOON_BASIC_CMDS \
+					| VMW_BALLOON_BATCHED_CMDS \
+					| VMW_BALLOON_BATCHED_2M_CMDS \
+					| VMW_BALLOON_SIGNALLED_WAKEUP_CMD)
+
+#define VMW_BALLOON_2M_ORDER		(PMD_SHIFT - PAGE_SHIFT)
+
+/*
+ * 64-bit targets are only supported in 64-bit
+ */
+#ifdef CONFIG_64BIT
+#define VMW_BALLOON_CAPABILITIES	(VMW_BALLOON_CAPABILITIES_COMMON \
+					| VMW_BALLOON_64_BIT_TARGET)
+#else
+#define VMW_BALLOON_CAPABILITIES	VMW_BALLOON_CAPABILITIES_COMMON
+#endif
+
+enum vmballoon_page_size_type {
+	VMW_BALLOON_4K_PAGE,
+	VMW_BALLOON_2M_PAGE,
+	VMW_BALLOON_LAST_SIZE = VMW_BALLOON_2M_PAGE
+};
+
+#define VMW_BALLOON_NUM_PAGE_SIZES	(VMW_BALLOON_LAST_SIZE + 1)
+
+static const char * const vmballoon_page_size_names[] = {
+	[VMW_BALLOON_4K_PAGE]			= "4k",
+	[VMW_BALLOON_2M_PAGE]			= "2M"
+};
+
+enum vmballoon_op {
+	VMW_BALLOON_INFLATE,
+	VMW_BALLOON_DEFLATE
+};
+
+enum vmballoon_op_stat_type {
+	VMW_BALLOON_OP_STAT,
+	VMW_BALLOON_OP_FAIL_STAT
+};
+
+#define VMW_BALLOON_OP_STAT_TYPES	(VMW_BALLOON_OP_FAIL_STAT + 1)
+
+/**
+ * enum vmballoon_cmd_type - backdoor commands.
+ *
+ * Availability of the commands is as followed:
+ *
+ * %VMW_BALLOON_CMD_START, %VMW_BALLOON_CMD_GET_TARGET and
+ * %VMW_BALLOON_CMD_GUEST_ID are always available.
+ *
+ * If the host reports %VMW_BALLOON_BASIC_CMDS are supported then
+ * %VMW_BALLOON_CMD_LOCK and %VMW_BALLOON_CMD_UNLOCK commands are available.
+ *
+ * If the host reports %VMW_BALLOON_BATCHED_CMDS are supported then
+ * %VMW_BALLOON_CMD_BATCHED_LOCK and VMW_BALLOON_CMD_BATCHED_UNLOCK commands
+ * are available.
+ *
+ * If the host reports %VMW_BALLOON_BATCHED_2M_CMDS are supported then
+ * %VMW_BALLOON_CMD_BATCHED_2M_LOCK and %VMW_BALLOON_CMD_BATCHED_2M_UNLOCK
+ * are supported.
+ *
+ * If the host reports  VMW_BALLOON_SIGNALLED_WAKEUP_CMD is supported then
+ * VMW_BALLOON_CMD_VMCI_DOORBELL_SET command is supported.
+ *
+ * @VMW_BALLOON_CMD_START: Communicating supported version with the hypervisor.
+ * @VMW_BALLOON_CMD_GET_TARGET: Gets the balloon target size.
+ * @VMW_BALLOON_CMD_LOCK: Informs the hypervisor about a ballooned page.
+ * @VMW_BALLOON_CMD_UNLOCK: Informs the hypervisor about a page that is about
+ *			    to be deflated from the balloon.
+ * @VMW_BALLOON_CMD_GUEST_ID: Informs the hypervisor about the type of OS that
+ *			      runs in the VM.
+ * @VMW_BALLOON_CMD_BATCHED_LOCK: Inform the hypervisor about a batch of
+ *				  ballooned pages (up to 512).
+ * @VMW_BALLOON_CMD_BATCHED_UNLOCK: Inform the hypervisor about a batch of
+ *				  pages that are about to be deflated from the
+ *				  balloon (up to 512).
+ * @VMW_BALLOON_CMD_BATCHED_2M_LOCK: Similar to @VMW_BALLOON_CMD_BATCHED_LOCK
+ *				     for 2MB pages.
+ * @VMW_BALLOON_CMD_BATCHED_2M_UNLOCK: Similar to
+ *				       @VMW_BALLOON_CMD_BATCHED_UNLOCK for 2MB
+ *				       pages.
+ * @VMW_BALLOON_CMD_VMCI_DOORBELL_SET: A command to set doorbell notification
+ *				       that would be invoked when the balloon
+ *				       size changes.
+ * @VMW_BALLOON_CMD_LAST: Value of the last command.
+ */
+enum vmballoon_cmd_type {
+	VMW_BALLOON_CMD_START,
+	VMW_BALLOON_CMD_GET_TARGET,
+	VMW_BALLOON_CMD_LOCK,
+	VMW_BALLOON_CMD_UNLOCK,
+	VMW_BALLOON_CMD_GUEST_ID,
+	/* No command 5 */
+	VMW_BALLOON_CMD_BATCHED_LOCK = 6,
+	VMW_BALLOON_CMD_BATCHED_UNLOCK,
+	VMW_BALLOON_CMD_BATCHED_2M_LOCK,
+	VMW_BALLOON_CMD_BATCHED_2M_UNLOCK,
+	VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
+	VMW_BALLOON_CMD_LAST = VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
+};
+
+#define VMW_BALLOON_CMD_NUM	(VMW_BALLOON_CMD_LAST + 1)
+
+enum vmballoon_error_codes {
+	VMW_BALLOON_SUCCESS,
+	VMW_BALLOON_ERROR_CMD_INVALID,
+	VMW_BALLOON_ERROR_PPN_INVALID,
+	VMW_BALLOON_ERROR_PPN_LOCKED,
+	VMW_BALLOON_ERROR_PPN_UNLOCKED,
+	VMW_BALLOON_ERROR_PPN_PINNED,
+	VMW_BALLOON_ERROR_PPN_NOTNEEDED,
+	VMW_BALLOON_ERROR_RESET,
+	VMW_BALLOON_ERROR_BUSY
+};
+
+#define VMW_BALLOON_SUCCESS_WITH_CAPABILITIES	(0x03000000)
+
+#define VMW_BALLOON_CMD_WITH_TARGET_MASK			\
+	((1UL << VMW_BALLOON_CMD_GET_TARGET)		|	\
+	 (1UL << VMW_BALLOON_CMD_LOCK)			|	\
+	 (1UL << VMW_BALLOON_CMD_UNLOCK)		|	\
+	 (1UL << VMW_BALLOON_CMD_BATCHED_LOCK)		|	\
+	 (1UL << VMW_BALLOON_CMD_BATCHED_UNLOCK)	|	\
+	 (1UL << VMW_BALLOON_CMD_BATCHED_2M_LOCK)	|	\
+	 (1UL << VMW_BALLOON_CMD_BATCHED_2M_UNLOCK))
+
+static const char * const vmballoon_cmd_names[] = {
+	[VMW_BALLOON_CMD_START]			= "start",
+	[VMW_BALLOON_CMD_GET_TARGET]		= "target",
+	[VMW_BALLOON_CMD_LOCK]			= "lock",
+	[VMW_BALLOON_CMD_UNLOCK]		= "unlock",
+	[VMW_BALLOON_CMD_GUEST_ID]		= "guestType",
+	[VMW_BALLOON_CMD_BATCHED_LOCK]		= "batchLock",
+	[VMW_BALLOON_CMD_BATCHED_UNLOCK]	= "batchUnlock",
+	[VMW_BALLOON_CMD_BATCHED_2M_LOCK]	= "2m-lock",
+	[VMW_BALLOON_CMD_BATCHED_2M_UNLOCK]	= "2m-unlock",
+	[VMW_BALLOON_CMD_VMCI_DOORBELL_SET]	= "doorbellSet"
+};
+
+enum vmballoon_stat_page {
+	VMW_BALLOON_PAGE_STAT_ALLOC,
+	VMW_BALLOON_PAGE_STAT_ALLOC_FAIL,
+	VMW_BALLOON_PAGE_STAT_REFUSED_ALLOC,
+	VMW_BALLOON_PAGE_STAT_REFUSED_FREE,
+	VMW_BALLOON_PAGE_STAT_FREE,
+	VMW_BALLOON_PAGE_STAT_LAST = VMW_BALLOON_PAGE_STAT_FREE
+};
+
+#define VMW_BALLOON_PAGE_STAT_NUM	(VMW_BALLOON_PAGE_STAT_LAST + 1)
+
+enum vmballoon_stat_general {
+	VMW_BALLOON_STAT_TIMER,
+	VMW_BALLOON_STAT_DOORBELL,
+	VMW_BALLOON_STAT_RESET,
+	VMW_BALLOON_STAT_SHRINK,
+	VMW_BALLOON_STAT_SHRINK_FREE,
+	VMW_BALLOON_STAT_LAST = VMW_BALLOON_STAT_SHRINK_FREE
+};
+
+#define VMW_BALLOON_STAT_NUM		(VMW_BALLOON_STAT_LAST + 1)
+
+static DEFINE_STATIC_KEY_TRUE(vmw_balloon_batching);
+static DEFINE_STATIC_KEY_FALSE(balloon_stat_enabled);
+
+struct vmballoon_ctl {
+	struct list_head pages;
+	struct list_head refused_pages;
+	struct list_head prealloc_pages;
+	unsigned int n_refused_pages;
+	unsigned int n_pages;
+	enum vmballoon_page_size_type page_size;
+	enum vmballoon_op op;
+};
+
+/**
+ * struct vmballoon_batch_entry - a batch entry for lock or unlock.
+ *
+ * @status: the status of the operation, which is written by the hypervisor.
+ * @reserved: reserved for future use. Must be set to zero.
+ * @pfn: the physical frame number of the page to be locked or unlocked.
+ */
+struct vmballoon_batch_entry {
+	u64 status : 5;
+	u64 reserved : PAGE_SHIFT - 5;
+	u64 pfn : 52;
+} __packed;
+
+struct vmballoon {
+	/**
+	 * @max_page_size: maximum supported page size for ballooning.
+	 *
+	 * Protected by @conf_sem
+	 */
+	enum vmballoon_page_size_type max_page_size;
+
+	/**
+	 * @size: balloon actual size in basic page size (frames).
+	 *
+	 * While we currently do not support size which is bigger than 32-bit,
+	 * in preparation for future support, use 64-bits.
+	 */
+	atomic64_t size;
+
+	/**
+	 * @target: balloon target size in basic page size (frames).
+	 *
+	 * We do not protect the target under the assumption that setting the
+	 * value is always done through a single write. If this assumption ever
+	 * breaks, we would have to use X_ONCE for accesses, and suffer the less
+	 * optimized code. Although we may read stale target value if multiple
+	 * accesses happen at once, the performance impact should be minor.
+	 */
+	unsigned long target;
+
+	/**
+	 * @reset_required: reset flag
+	 *
+	 * Setting this flag may introduce races, but the code is expected to
+	 * handle them gracefully. In the worst case, another operation will
+	 * fail as reset did not take place. Clearing the flag is done while
+	 * holding @conf_sem for write.
+	 */
+	bool reset_required;
+
+	/**
+	 * @capabilities: hypervisor balloon capabilities.
+	 *
+	 * Protected by @conf_sem.
+	 */
+	unsigned long capabilities;
+
+	/**
+	 * @batch_page: pointer to communication batch page.
+	 *
+	 * When batching is used, batch_page points to a page, which holds up to
+	 * %VMW_BALLOON_BATCH_MAX_PAGES entries for locking or unlocking.
+	 */
+	struct vmballoon_batch_entry *batch_page;
+
+	/**
+	 * @batch_max_pages: maximum pages that can be locked/unlocked.
+	 *
+	 * Indicates the number of pages that the hypervisor can lock or unlock
+	 * at once, according to whether batching is enabled. If batching is
+	 * disabled, only a single page can be locked/unlock on each operation.
+	 *
+	 * Protected by @conf_sem.
+	 */
+	unsigned int batch_max_pages;
+
+	/**
+	 * @page: page to be locked/unlocked by the hypervisor
+	 *
+	 * @page is only used when batching is disabled and a single page is
+	 * reclaimed on each iteration.
+	 *
+	 * Protected by @comm_lock.
+	 */
+	struct page *page;
+
+	/**
+	 * @shrink_timeout: timeout until the next inflation.
+	 *
+	 * After an shrink event, indicates the time in jiffies after which
+	 * inflation is allowed again. Can be written concurrently with reads,
+	 * so must use READ_ONCE/WRITE_ONCE when accessing.
+	 */
+	unsigned long shrink_timeout;
+
+	/* statistics */
+	struct vmballoon_stats *stats;
+
+	/**
+	 * @b_dev_info: balloon device information descriptor.
+	 */
+	struct balloon_dev_info b_dev_info;
+
+	struct delayed_work dwork;
+
+	/**
+	 * @huge_pages - list of the inflated 2MB pages.
+	 *
+	 * Protected by @b_dev_info.pages_lock .
+	 */
+	struct list_head huge_pages;
+
+	/**
+	 * @vmci_doorbell.
+	 *
+	 * Protected by @conf_sem.
+	 */
+	struct vmci_handle vmci_doorbell;
+
+	/**
+	 * @conf_sem: semaphore to protect the configuration and the statistics.
+	 */
+	struct rw_semaphore conf_sem;
+
+	/**
+	 * @comm_lock: lock to protect the communication with the host.
+	 *
+	 * Lock ordering: @conf_sem -> @comm_lock .
+	 */
+	spinlock_t comm_lock;
+
+	/**
+	 * @shrinker: shrinker interface that is used to avoid over-inflation.
+	 */
+	struct shrinker shrinker;
+
+	/**
+	 * @shrinker_registered: whether the shrinker was registered.
+	 *
+	 * The shrinker interface does not handle gracefully the removal of
+	 * shrinker that was not registered before. This indication allows to
+	 * simplify the unregistration process.
+	 */
+	bool shrinker_registered;
+};
+
+static struct vmballoon balloon;
+
+struct vmballoon_stats {
+	/* timer / doorbell operations */
+	atomic64_t general_stat[VMW_BALLOON_STAT_NUM];
+
+	/* allocation statistics for huge and small pages */
+	atomic64_t
+	       page_stat[VMW_BALLOON_PAGE_STAT_NUM][VMW_BALLOON_NUM_PAGE_SIZES];
+
+	/* Monitor operations: total operations, and failures */
+	atomic64_t ops[VMW_BALLOON_CMD_NUM][VMW_BALLOON_OP_STAT_TYPES];
+};
+
+static inline bool is_vmballoon_stats_on(void)
+{
+	return IS_ENABLED(CONFIG_DEBUG_FS) &&
+		static_branch_unlikely(&balloon_stat_enabled);
+}
+
+static inline void vmballoon_stats_op_inc(struct vmballoon *b, unsigned int op,
+					  enum vmballoon_op_stat_type type)
+{
+	if (is_vmballoon_stats_on())
+		atomic64_inc(&b->stats->ops[op][type]);
+}
+
+static inline void vmballoon_stats_gen_inc(struct vmballoon *b,
+					   enum vmballoon_stat_general stat)
+{
+	if (is_vmballoon_stats_on())
+		atomic64_inc(&b->stats->general_stat[stat]);
+}
+
+static inline void vmballoon_stats_gen_add(struct vmballoon *b,
+					   enum vmballoon_stat_general stat,
+					   unsigned int val)
+{
+	if (is_vmballoon_stats_on())
+		atomic64_add(val, &b->stats->general_stat[stat]);
+}
+
+static inline void vmballoon_stats_page_inc(struct vmballoon *b,
+					    enum vmballoon_stat_page stat,
+					    enum vmballoon_page_size_type size)
+{
+	if (is_vmballoon_stats_on())
+		atomic64_inc(&b->stats->page_stat[stat][size]);
+}
+
+static inline void vmballoon_stats_page_add(struct vmballoon *b,
+					    enum vmballoon_stat_page stat,
+					    enum vmballoon_page_size_type size,
+					    unsigned int val)
+{
+	if (is_vmballoon_stats_on())
+		atomic64_add(val, &b->stats->page_stat[stat][size]);
+}
+
+static inline unsigned long
+__vmballoon_cmd(struct vmballoon *b, unsigned long cmd, unsigned long arg1,
+		unsigned long arg2, unsigned long *result)
+{
+	unsigned long status, dummy1, dummy2, dummy3, local_result;
+
+	vmballoon_stats_op_inc(b, cmd, VMW_BALLOON_OP_STAT);
+
+	asm volatile ("inl %%dx" :
+		"=a"(status),
+		"=c"(dummy1),
+		"=d"(dummy2),
+		"=b"(local_result),
+		"=S"(dummy3) :
+		"0"(VMW_BALLOON_HV_MAGIC),
+		"1"(cmd),
+		"2"(VMW_BALLOON_HV_PORT),
+		"3"(arg1),
+		"4"(arg2) :
+		"memory");
+
+	/* update the result if needed */
+	if (result)
+		*result = (cmd == VMW_BALLOON_CMD_START) ? dummy1 :
+							   local_result;
+
+	/* update target when applicable */
+	if (status == VMW_BALLOON_SUCCESS &&
+	    ((1ul << cmd) & VMW_BALLOON_CMD_WITH_TARGET_MASK))
+		WRITE_ONCE(b->target, local_result);
+
+	if (status != VMW_BALLOON_SUCCESS &&
+	    status != VMW_BALLOON_SUCCESS_WITH_CAPABILITIES) {
+		vmballoon_stats_op_inc(b, cmd, VMW_BALLOON_OP_FAIL_STAT);
+		pr_debug("%s: %s [0x%lx,0x%lx) failed, returned %ld\n",
+			 __func__, vmballoon_cmd_names[cmd], arg1, arg2,
+			 status);
+	}
+
+	/* mark reset required accordingly */
+	if (status == VMW_BALLOON_ERROR_RESET)
+		b->reset_required = true;
+
+	return status;
+}
+
+static __always_inline unsigned long
+vmballoon_cmd(struct vmballoon *b, unsigned long cmd, unsigned long arg1,
+	      unsigned long arg2)
+{
+	unsigned long dummy;
+
+	return __vmballoon_cmd(b, cmd, arg1, arg2, &dummy);
+}
+
+/*
+ * Send "start" command to the host, communicating supported version
+ * of the protocol.
+ */
+static int vmballoon_send_start(struct vmballoon *b, unsigned long req_caps)
+{
+	unsigned long status, capabilities;
+
+	status = __vmballoon_cmd(b, VMW_BALLOON_CMD_START, req_caps, 0,
+				 &capabilities);
+
+	switch (status) {
+	case VMW_BALLOON_SUCCESS_WITH_CAPABILITIES:
+		b->capabilities = capabilities;
+		break;
+	case VMW_BALLOON_SUCCESS:
+		b->capabilities = VMW_BALLOON_BASIC_CMDS;
+		break;
+	default:
+		return -EIO;
+	}
+
+	/*
+	 * 2MB pages are only supported with batching. If batching is for some
+	 * reason disabled, do not use 2MB pages, since otherwise the legacy
+	 * mechanism is used with 2MB pages, causing a failure.
+	 */
+	b->max_page_size = VMW_BALLOON_4K_PAGE;
+	if ((b->capabilities & VMW_BALLOON_BATCHED_2M_CMDS) &&
+	    (b->capabilities & VMW_BALLOON_BATCHED_CMDS))
+		b->max_page_size = VMW_BALLOON_2M_PAGE;
+
+
+	return 0;
+}
+
+/**
+ * vmballoon_send_guest_id - communicate guest type to the host.
+ *
+ * @b: pointer to the balloon.
+ *
+ * Communicate guest type to the host so that it can adjust ballooning
+ * algorithm to the one most appropriate for the guest. This command
+ * is normally issued after sending "start" command and is part of
+ * standard reset sequence.
+ *
+ * Return: zero on success or appropriate error code.
+ */
+static int vmballoon_send_guest_id(struct vmballoon *b)
+{
+	unsigned long status;
+
+	status = vmballoon_cmd(b, VMW_BALLOON_CMD_GUEST_ID,
+			       VMW_BALLOON_GUEST_ID, 0);
+
+	return status == VMW_BALLOON_SUCCESS ? 0 : -EIO;
+}
+
+/**
+ * vmballoon_page_order() - return the order of the page
+ * @page_size: the size of the page.
+ *
+ * Return: the allocation order.
+ */
+static inline
+unsigned int vmballoon_page_order(enum vmballoon_page_size_type page_size)
+{
+	return page_size == VMW_BALLOON_2M_PAGE ? VMW_BALLOON_2M_ORDER : 0;
+}
+
+/**
+ * vmballoon_page_in_frames() - returns the number of frames in a page.
+ * @page_size: the size of the page.
+ *
+ * Return: the number of 4k frames.
+ */
+static inline unsigned int
+vmballoon_page_in_frames(enum vmballoon_page_size_type page_size)
+{
+	return 1 << vmballoon_page_order(page_size);
+}
+
+/**
+ * vmballoon_mark_page_offline() - mark a page as offline
+ * @page: pointer for the page.
+ * @page_size: the size of the page.
+ */
+static void
+vmballoon_mark_page_offline(struct page *page,
+			    enum vmballoon_page_size_type page_size)
+{
+	int i;
+
+	for (i = 0; i < vmballoon_page_in_frames(page_size); i++)
+		__SetPageOffline(page + i);
+}
+
+/**
+ * vmballoon_mark_page_online() - mark a page as online
+ * @page: pointer for the page.
+ * @page_size: the size of the page.
+ */
+static void
+vmballoon_mark_page_online(struct page *page,
+			   enum vmballoon_page_size_type page_size)
+{
+	int i;
+
+	for (i = 0; i < vmballoon_page_in_frames(page_size); i++)
+		__ClearPageOffline(page + i);
+}
+
+/**
+ * vmballoon_send_get_target() - Retrieve desired balloon size from the host.
+ *
+ * @b: pointer to the balloon.
+ *
+ * Return: zero on success, EINVAL if limit does not fit in 32-bit, as required
+ * by the host-guest protocol and EIO if an error occurred in communicating with
+ * the host.
+ */
+static int vmballoon_send_get_target(struct vmballoon *b)
+{
+	unsigned long status;
+	unsigned long limit;
+
+	limit = totalram_pages();
+
+	/* Ensure limit fits in 32-bits if 64-bit targets are not supported */
+	if (!(b->capabilities & VMW_BALLOON_64_BIT_TARGET) &&
+	    limit != (u32)limit)
+		return -EINVAL;
+
+	status = vmballoon_cmd(b, VMW_BALLOON_CMD_GET_TARGET, limit, 0);
+
+	return status == VMW_BALLOON_SUCCESS ? 0 : -EIO;
+}
+
+/**
+ * vmballoon_alloc_page_list - allocates a list of pages.
+ *
+ * @b: pointer to the balloon.
+ * @ctl: pointer for the %struct vmballoon_ctl, which defines the operation.
+ * @req_n_pages: the number of requested pages.
+ *
+ * Tries to allocate @req_n_pages. Add them to the list of balloon pages in
+ * @ctl.pages and updates @ctl.n_pages to reflect the number of pages.
+ *
+ * Return: zero on success or error code otherwise.
+ */
+static int vmballoon_alloc_page_list(struct vmballoon *b,
+				     struct vmballoon_ctl *ctl,
+				     unsigned int req_n_pages)
+{
+	struct page *page;
+	unsigned int i;
+
+	for (i = 0; i < req_n_pages; i++) {
+		/*
+		 * First check if we happen to have pages that were allocated
+		 * before. This happens when 2MB page rejected during inflation
+		 * by the hypervisor, and then split into 4KB pages.
+		 */
+		if (!list_empty(&ctl->prealloc_pages)) {
+			page = list_first_entry(&ctl->prealloc_pages,
+						struct page, lru);
+			list_del(&page->lru);
+		} else {
+			if (ctl->page_size == VMW_BALLOON_2M_PAGE)
+				page = alloc_pages(__GFP_HIGHMEM|__GFP_NOWARN|
+					__GFP_NOMEMALLOC, VMW_BALLOON_2M_ORDER);
+			else
+				page = balloon_page_alloc();
+
+			vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_ALLOC,
+						 ctl->page_size);
+		}
+
+		if (page) {
+			/* Success. Add the page to the list and continue. */
+			list_add(&page->lru, &ctl->pages);
+			continue;
+		}
+
+		/* Allocation failed. Update statistics and stop. */
+		vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_ALLOC_FAIL,
+					 ctl->page_size);
+		break;
+	}
+
+	ctl->n_pages = i;
+
+	return req_n_pages == ctl->n_pages ? 0 : -ENOMEM;
+}
+
+/**
+ * vmballoon_handle_one_result - Handle lock/unlock result for a single page.
+ *
+ * @b: pointer for %struct vmballoon.
+ * @page: pointer for the page whose result should be handled.
+ * @page_size: size of the page.
+ * @status: status of the operation as provided by the hypervisor.
+ */
+static int vmballoon_handle_one_result(struct vmballoon *b, struct page *page,
+				       enum vmballoon_page_size_type page_size,
+				       unsigned long status)
+{
+	/* On success do nothing. The page is already on the balloon list. */
+	if (likely(status == VMW_BALLOON_SUCCESS))
+		return 0;
+
+	pr_debug("%s: failed comm pfn %lx status %lu page_size %s\n", __func__,
+		 page_to_pfn(page), status,
+		 vmballoon_page_size_names[page_size]);
+
+	/* Error occurred */
+	vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_REFUSED_ALLOC,
+				 page_size);
+
+	return -EIO;
+}
+
+/**
+ * vmballoon_status_page - returns the status of (un)lock operation
+ *
+ * @b: pointer to the balloon.
+ * @idx: index for the page for which the operation is performed.
+ * @p: pointer to where the page struct is returned.
+ *
+ * Following a lock or unlock operation, returns the status of the operation for
+ * an individual page. Provides the page that the operation was performed on on
+ * the @page argument.
+ *
+ * Returns: The status of a lock or unlock operation for an individual page.
+ */
+static unsigned long vmballoon_status_page(struct vmballoon *b, int idx,
+					   struct page **p)
+{
+	if (static_branch_likely(&vmw_balloon_batching)) {
+		/* batching mode */
+		*p = pfn_to_page(b->batch_page[idx].pfn);
+		return b->batch_page[idx].status;
+	}
+
+	/* non-batching mode */
+	*p = b->page;
+
+	/*
+	 * If a failure occurs, the indication will be provided in the status
+	 * of the entire operation, which is considered before the individual
+	 * page status. So for non-batching mode, the indication is always of
+	 * success.
+	 */
+	return VMW_BALLOON_SUCCESS;
+}
+
+/**
+ * vmballoon_lock_op - notifies the host about inflated/deflated pages.
+ * @b: pointer to the balloon.
+ * @num_pages: number of inflated/deflated pages.
+ * @page_size: size of the page.
+ * @op: the type of operation (lock or unlock).
+ *
+ * Notify the host about page(s) that were ballooned (or removed from the
+ * balloon) so that host can use it without fear that guest will need it (or
+ * stop using them since the VM does). Host may reject some pages, we need to
+ * check the return value and maybe submit a different page. The pages that are
+ * inflated/deflated are pointed by @b->page.
+ *
+ * Return: result as provided by the hypervisor.
+ */
+static unsigned long vmballoon_lock_op(struct vmballoon *b,
+				       unsigned int num_pages,
+				       enum vmballoon_page_size_type page_size,
+				       enum vmballoon_op op)
+{
+	unsigned long cmd, pfn;
+
+	lockdep_assert_held(&b->comm_lock);
+
+	if (static_branch_likely(&vmw_balloon_batching)) {
+		if (op == VMW_BALLOON_INFLATE)
+			cmd = page_size == VMW_BALLOON_2M_PAGE ?
+				VMW_BALLOON_CMD_BATCHED_2M_LOCK :
+				VMW_BALLOON_CMD_BATCHED_LOCK;
+		else
+			cmd = page_size == VMW_BALLOON_2M_PAGE ?
+				VMW_BALLOON_CMD_BATCHED_2M_UNLOCK :
+				VMW_BALLOON_CMD_BATCHED_UNLOCK;
+
+		pfn = PHYS_PFN(virt_to_phys(b->batch_page));
+	} else {
+		cmd = op == VMW_BALLOON_INFLATE ? VMW_BALLOON_CMD_LOCK :
+						  VMW_BALLOON_CMD_UNLOCK;
+		pfn = page_to_pfn(b->page);
+
+		/* In non-batching mode, PFNs must fit in 32-bit */
+		if (unlikely(pfn != (u32)pfn))
+			return VMW_BALLOON_ERROR_PPN_INVALID;
+	}
+
+	return vmballoon_cmd(b, cmd, pfn, num_pages);
+}
+
+/**
+ * vmballoon_add_page - adds a page towards lock/unlock operation.
+ *
+ * @b: pointer to the balloon.
+ * @idx: index of the page to be ballooned in this batch.
+ * @p: pointer to the page that is about to be ballooned.
+ *
+ * Adds the page to be ballooned. Must be called while holding @comm_lock.
+ */
+static void vmballoon_add_page(struct vmballoon *b, unsigned int idx,
+			       struct page *p)
+{
+	lockdep_assert_held(&b->comm_lock);
+
+	if (static_branch_likely(&vmw_balloon_batching))
+		b->batch_page[idx] = (struct vmballoon_batch_entry)
+					{ .pfn = page_to_pfn(p) };
+	else
+		b->page = p;
+}
+
+/**
+ * vmballoon_lock - lock or unlock a batch of pages.
+ *
+ * @b: pointer to the balloon.
+ * @ctl: pointer for the %struct vmballoon_ctl, which defines the operation.
+ *
+ * Notifies the host of about ballooned pages (after inflation or deflation,
+ * according to @ctl). If the host rejects the page put it on the
+ * @ctl refuse list. These refused page are then released when moving to the
+ * next size of pages.
+ *
+ * Note that we neither free any @page here nor put them back on the ballooned
+ * pages list. Instead we queue it for later processing. We do that for several
+ * reasons. First, we do not want to free the page under the lock. Second, it
+ * allows us to unify the handling of lock and unlock. In the inflate case, the
+ * caller will check if there are too many refused pages and release them.
+ * Although it is not identical to the past behavior, it should not affect
+ * performance.
+ */
+static int vmballoon_lock(struct vmballoon *b, struct vmballoon_ctl *ctl)
+{
+	unsigned long batch_status;
+	struct page *page;
+	unsigned int i, num_pages;
+
+	num_pages = ctl->n_pages;
+	if (num_pages == 0)
+		return 0;
+
+	/* communication with the host is done under the communication lock */
+	spin_lock(&b->comm_lock);
+
+	i = 0;
+	list_for_each_entry(page, &ctl->pages, lru)
+		vmballoon_add_page(b, i++, page);
+
+	batch_status = vmballoon_lock_op(b, ctl->n_pages, ctl->page_size,
+					 ctl->op);
+
+	/*
+	 * Iterate over the pages in the provided list. Since we are changing
+	 * @ctl->n_pages we are saving the original value in @num_pages and
+	 * use this value to bound the loop.
+	 */
+	for (i = 0; i < num_pages; i++) {
+		unsigned long status;
+
+		status = vmballoon_status_page(b, i, &page);
+
+		/*
+		 * Failure of the whole batch overrides a single operation
+		 * results.
+		 */
+		if (batch_status != VMW_BALLOON_SUCCESS)
+			status = batch_status;
+
+		/* Continue if no error happened */
+		if (!vmballoon_handle_one_result(b, page, ctl->page_size,
+						 status))
+			continue;
+
+		/*
+		 * Error happened. Move the pages to the refused list and update
+		 * the pages number.
+		 */
+		list_move(&page->lru, &ctl->refused_pages);
+		ctl->n_pages--;
+		ctl->n_refused_pages++;
+	}
+
+	spin_unlock(&b->comm_lock);
+
+	return batch_status == VMW_BALLOON_SUCCESS ? 0 : -EIO;
+}
+
+/**
+ * vmballoon_release_page_list() - Releases a page list
+ *
+ * @page_list: list of pages to release.
+ * @n_pages: pointer to the number of pages.
+ * @page_size: whether the pages in the list are 2MB (or else 4KB).
+ *
+ * Releases the list of pages and zeros the number of pages.
+ */
+static void vmballoon_release_page_list(struct list_head *page_list,
+				       int *n_pages,
+				       enum vmballoon_page_size_type page_size)
+{
+	struct page *page, *tmp;
+
+	list_for_each_entry_safe(page, tmp, page_list, lru) {
+		list_del(&page->lru);
+		__free_pages(page, vmballoon_page_order(page_size));
+	}
+
+	if (n_pages)
+		*n_pages = 0;
+}
+
+
+/*
+ * Release pages that were allocated while attempting to inflate the
+ * balloon but were refused by the host for one reason or another.
+ */
+static void vmballoon_release_refused_pages(struct vmballoon *b,
+					    struct vmballoon_ctl *ctl)
+{
+	vmballoon_stats_page_inc(b, VMW_BALLOON_PAGE_STAT_REFUSED_FREE,
+				 ctl->page_size);
+
+	vmballoon_release_page_list(&ctl->refused_pages, &ctl->n_refused_pages,
+				    ctl->page_size);
+}
+
+/**
+ * vmballoon_change - retrieve the required balloon change
+ *
+ * @b: pointer for the balloon.
+ *
+ * Return: the required change for the balloon size. A positive number
+ * indicates inflation, a negative number indicates a deflation.
+ */
+static int64_t vmballoon_change(struct vmballoon *b)
+{
+	int64_t size, target;
+
+	size = atomic64_read(&b->size);
+	target = READ_ONCE(b->target);
+
+	/*
+	 * We must cast first because of int sizes
+	 * Otherwise we might get huge positives instead of negatives
+	 */
+
+	if (b->reset_required)
+		return 0;
+
+	/* consider a 2MB slack on deflate, unless the balloon is emptied */
+	if (target < size && target != 0 &&
+	    size - target < vmballoon_page_in_frames(VMW_BALLOON_2M_PAGE))
+		return 0;
+
+	/* If an out-of-memory recently occurred, inflation is disallowed. */
+	if (target > size && time_before(jiffies, READ_ONCE(b->shrink_timeout)))
+		return 0;
+
+	return target - size;
+}
+
+/**
+ * vmballoon_enqueue_page_list() - Enqueues list of pages after inflation.
+ *
+ * @b: pointer to balloon.
+ * @pages: list of pages to enqueue.
+ * @n_pages: pointer to number of pages in list. The value is zeroed.
+ * @page_size: whether the pages are 2MB or 4KB pages.
+ *
+ * Enqueues the provides list of pages in the ballooned page list, clears the
+ * list and zeroes the number of pages that was provided.
+ */
+static void vmballoon_enqueue_page_list(struct vmballoon *b,
+					struct list_head *pages,
+					unsigned int *n_pages,
+					enum vmballoon_page_size_type page_size)
+{
+	unsigned long flags;
+	struct page *page;
+
+	if (page_size == VMW_BALLOON_4K_PAGE) {
+		balloon_page_list_enqueue(&b->b_dev_info, pages);
+	} else {
+		/*
+		 * Keep the huge pages in a local list which is not available
+		 * for the balloon compaction mechanism.
+		 */
+		spin_lock_irqsave(&b->b_dev_info.pages_lock, flags);
+
+		list_for_each_entry(page, pages, lru) {
+			vmballoon_mark_page_offline(page, VMW_BALLOON_2M_PAGE);
+		}
+
+		list_splice_init(pages, &b->huge_pages);
+		__count_vm_events(BALLOON_INFLATE, *n_pages *
+				  vmballoon_page_in_frames(VMW_BALLOON_2M_PAGE));
+		spin_unlock_irqrestore(&b->b_dev_info.pages_lock, flags);
+	}
+
+	*n_pages = 0;
+}
+
+/**
+ * vmballoon_dequeue_page_list() - Dequeues page lists for deflation.
+ *
+ * @b: pointer to balloon.
+ * @pages: list of pages to enqueue.
+ * @n_pages: pointer to number of pages in list. The value is zeroed.
+ * @page_size: whether the pages are 2MB or 4KB pages.
+ * @n_req_pages: the number of requested pages.
+ *
+ * Dequeues the number of requested pages from the balloon for deflation. The
+ * number of dequeued pages may be lower, if not enough pages in the requested
+ * size are available.
+ */
+static void vmballoon_dequeue_page_list(struct vmballoon *b,
+					struct list_head *pages,
+					unsigned int *n_pages,
+					enum vmballoon_page_size_type page_size,
+					unsigned int n_req_pages)
+{
+	struct page *page, *tmp;
+	unsigned int i = 0;
+	unsigned long flags;
+
+	/* In the case of 4k pages, use the compaction infrastructure */
+	if (page_size == VMW_BALLOON_4K_PAGE) {
+		*n_pages = balloon_page_list_dequeue(&b->b_dev_info, pages,
+						     n_req_pages);
+		return;
+	}
+
+	/* 2MB pages */
+	spin_lock_irqsave(&b->b_dev_info.pages_lock, flags);
+	list_for_each_entry_safe(page, tmp, &b->huge_pages, lru) {
+		vmballoon_mark_page_online(page, VMW_BALLOON_2M_PAGE);
+
+		list_move(&page->lru, pages);
+		if (++i == n_req_pages)
+			break;
+	}
+
+	__count_vm_events(BALLOON_DEFLATE,
+			  i * vmballoon_page_in_frames(VMW_BALLOON_2M_PAGE));
+	spin_unlock_irqrestore(&b->b_dev_info.pages_lock, flags);
+	*n_pages = i;
+}
+
+/**
+ * vmballoon_split_refused_pages() - Split the 2MB refused pages to 4k.
+ *
+ * If inflation of 2MB pages was denied by the hypervisor, it is likely to be
+ * due to one or few 4KB pages. These 2MB pages may keep being allocated and
+ * then being refused. To prevent this case, this function splits the refused
+ * pages into 4KB pages and adds them into @prealloc_pages list.
+ *
+ * @ctl: pointer for the %struct vmballoon_ctl, which defines the operation.
+ */
+static void vmballoon_split_refused_pages(struct vmballoon_ctl *ctl)
+{
+	struct page *page, *tmp;
+	unsigned int i, order;
+
+	order = vmballoon_page_order(ctl->page_size);
+
+	list_for_each_entry_safe(page, tmp, &ctl->refused_pages, lru) {
+		list_del(&page->lru);
+		split_page(page, order);
+		for (i = 0; i < (1 << order); i++)
+			list_add(&page[i].lru, &ctl->prealloc_pages);
+	}
+	ctl->n_refused_pages = 0;
+}
+
+/**
+ * vmballoon_inflate() - Inflate the balloon towards its target size.
+ *
+ * @b: pointer to the balloon.
+ */
+static void vmballoon_inflate(struct vmballoon *b)
+{
+	int64_t to_inflate_frames;
+	struct vmballoon_ctl ctl = {
+		.pages = LIST_HEAD_INIT(ctl.pages),
+		.refused_pages = LIST_HEAD_INIT(ctl.refused_pages),
+		.prealloc_pages = LIST_HEAD_INIT(ctl.prealloc_pages),
+		.page_size = b->max_page_size,
+		.op = VMW_BALLOON_INFLATE
+	};
+
+	while ((to_inflate_frames = vmballoon_change(b)) > 0) {
+		unsigned int to_inflate_pages, page_in_frames;
+		int alloc_error, lock_error = 0;
+
+		VM_BUG_ON(!list_empty(&ctl.pages));
+		VM_BUG_ON(ctl.n_pages != 0);
+
+		page_in_frames = vmballoon_page_in_frames(ctl.page_size);
+
+		to_inflate_pages = min_t(unsigned long, b->batch_max_pages,
+					 DIV_ROUND_UP_ULL(to_inflate_frames,
+							  page_in_frames));
+
+		/* Start by allocating */
+		alloc_error = vmballoon_alloc_page_list(b, &ctl,
+							to_inflate_pages);
+
+		/* Actually lock the pages by telling the hypervisor */
+		lock_error = vmballoon_lock(b, &ctl);
+
+		/*
+		 * If an error indicates that something serious went wrong,
+		 * stop the inflation.
+		 */
+		if (lock_error)
+			break;
+
+		/* Update the balloon size */
+		atomic64_add(ctl.n_pages * page_in_frames, &b->size);
+
+		vmballoon_enqueue_page_list(b, &ctl.pages, &ctl.n_pages,
+					    ctl.page_size);
+
+		/*
+		 * If allocation failed or the number of refused pages exceeds
+		 * the maximum allowed, move to the next page size.
+		 */
+		if (alloc_error ||
+		    ctl.n_refused_pages >= VMW_BALLOON_MAX_REFUSED) {
+			if (ctl.page_size == VMW_BALLOON_4K_PAGE)
+				break;
+
+			/*
+			 * Split the refused pages to 4k. This will also empty
+			 * the refused pages list.
+			 */
+			vmballoon_split_refused_pages(&ctl);
+			ctl.page_size--;
+		}
+
+		cond_resched();
+	}
+
+	/*
+	 * Release pages that were allocated while attempting to inflate the
+	 * balloon but were refused by the host for one reason or another,
+	 * and update the statistics.
+	 */
+	if (ctl.n_refused_pages != 0)
+		vmballoon_release_refused_pages(b, &ctl);
+
+	vmballoon_release_page_list(&ctl.prealloc_pages, NULL, ctl.page_size);
+}
+
+/**
+ * vmballoon_deflate() - Decrease the size of the balloon.
+ *
+ * @b: pointer to the balloon
+ * @n_frames: the number of frames to deflate. If zero, automatically
+ * calculated according to the target size.
+ * @coordinated: whether to coordinate with the host
+ *
+ * Decrease the size of the balloon allowing guest to use more memory.
+ *
+ * Return: The number of deflated frames (i.e., basic page size units)
+ */
+static unsigned long vmballoon_deflate(struct vmballoon *b, uint64_t n_frames,
+				       bool coordinated)
+{
+	unsigned long deflated_frames = 0;
+	unsigned long tried_frames = 0;
+	struct vmballoon_ctl ctl = {
+		.pages = LIST_HEAD_INIT(ctl.pages),
+		.refused_pages = LIST_HEAD_INIT(ctl.refused_pages),
+		.page_size = VMW_BALLOON_4K_PAGE,
+		.op = VMW_BALLOON_DEFLATE
+	};
+
+	/* free pages to reach target */
+	while (true) {
+		unsigned int to_deflate_pages, n_unlocked_frames;
+		unsigned int page_in_frames;
+		int64_t to_deflate_frames;
+		bool deflated_all;
+
+		page_in_frames = vmballoon_page_in_frames(ctl.page_size);
+
+		VM_BUG_ON(!list_empty(&ctl.pages));
+		VM_BUG_ON(ctl.n_pages);
+		VM_BUG_ON(!list_empty(&ctl.refused_pages));
+		VM_BUG_ON(ctl.n_refused_pages);
+
+		/*
+		 * If we were requested a specific number of frames, we try to
+		 * deflate this number of frames. Otherwise, deflation is
+		 * performed according to the target and balloon size.
+		 */
+		to_deflate_frames = n_frames ? n_frames - tried_frames :
+					       -vmballoon_change(b);
+
+		/* break if no work to do */
+		if (to_deflate_frames <= 0)
+			break;
+
+		/*
+		 * Calculate the number of frames based on current page size,
+		 * but limit the deflated frames to a single chunk
+		 */
+		to_deflate_pages = min_t(unsigned long, b->batch_max_pages,
+					 DIV_ROUND_UP_ULL(to_deflate_frames,
+							  page_in_frames));
+
+		/* First take the pages from the balloon pages. */
+		vmballoon_dequeue_page_list(b, &ctl.pages, &ctl.n_pages,
+					    ctl.page_size, to_deflate_pages);
+
+		/*
+		 * Before pages are moving to the refused list, count their
+		 * frames as frames that we tried to deflate.
+		 */
+		tried_frames += ctl.n_pages * page_in_frames;
+
+		/*
+		 * Unlock the pages by communicating with the hypervisor if the
+		 * communication is coordinated (i.e., not pop). We ignore the
+		 * return code. Instead we check if all the pages we manage to
+		 * unlock all the pages. If we failed, we will move to the next
+		 * page size, and would eventually try again later.
+		 */
+		if (coordinated)
+			vmballoon_lock(b, &ctl);
+
+		/*
+		 * Check if we deflated enough. We will move to the next page
+		 * size if we did not manage to do so. This calculation takes
+		 * place now, as once the pages are released, the number of
+		 * pages is zeroed.
+		 */
+		deflated_all = (ctl.n_pages == to_deflate_pages);
+
+		/* Update local and global counters */
+		n_unlocked_frames = ctl.n_pages * page_in_frames;
+		atomic64_sub(n_unlocked_frames, &b->size);
+		deflated_frames += n_unlocked_frames;
+
+		vmballoon_stats_page_add(b, VMW_BALLOON_PAGE_STAT_FREE,
+					 ctl.page_size, ctl.n_pages);
+
+		/* free the ballooned pages */
+		vmballoon_release_page_list(&ctl.pages, &ctl.n_pages,
+					    ctl.page_size);
+
+		/* Return the refused pages to the ballooned list. */
+		vmballoon_enqueue_page_list(b, &ctl.refused_pages,
+					    &ctl.n_refused_pages,
+					    ctl.page_size);
+
+		/* If we failed to unlock all the pages, move to next size. */
+		if (!deflated_all) {
+			if (ctl.page_size == b->max_page_size)
+				break;
+			ctl.page_size++;
+		}
+
+		cond_resched();
+	}
+
+	return deflated_frames;
+}
+
+/**
+ * vmballoon_deinit_batching - disables batching mode.
+ *
+ * @b: pointer to &struct vmballoon.
+ *
+ * Disables batching, by deallocating the page for communication with the
+ * hypervisor and disabling the static key to indicate that batching is off.
+ */
+static void vmballoon_deinit_batching(struct vmballoon *b)
+{
+	free_page((unsigned long)b->batch_page);
+	b->batch_page = NULL;
+	static_branch_disable(&vmw_balloon_batching);
+	b->batch_max_pages = 1;
+}
+
+/**
+ * vmballoon_init_batching - enable batching mode.
+ *
+ * @b: pointer to &struct vmballoon.
+ *
+ * Enables batching, by allocating a page for communication with the hypervisor
+ * and enabling the static_key to use batching.
+ *
+ * Return: zero on success or an appropriate error-code.
+ */
+static int vmballoon_init_batching(struct vmballoon *b)
+{
+	struct page *page;
+
+	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	if (!page)
+		return -ENOMEM;
+
+	b->batch_page = page_address(page);
+	b->batch_max_pages = PAGE_SIZE / sizeof(struct vmballoon_batch_entry);
+
+	static_branch_enable(&vmw_balloon_batching);
+
+	return 0;
+}
+
+/*
+ * Receive notification and resize balloon
+ */
+static void vmballoon_doorbell(void *client_data)
+{
+	struct vmballoon *b = client_data;
+
+	vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_DOORBELL);
+
+	mod_delayed_work(system_freezable_wq, &b->dwork, 0);
+}
+
+/*
+ * Clean up vmci doorbell
+ */
+static void vmballoon_vmci_cleanup(struct vmballoon *b)
+{
+	vmballoon_cmd(b, VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
+		      VMCI_INVALID_ID, VMCI_INVALID_ID);
+
+	if (!vmci_handle_is_invalid(b->vmci_doorbell)) {
+		vmci_doorbell_destroy(b->vmci_doorbell);
+		b->vmci_doorbell = VMCI_INVALID_HANDLE;
+	}
+}
+
+/**
+ * vmballoon_vmci_init - Initialize vmci doorbell.
+ *
+ * @b: pointer to the balloon.
+ *
+ * Return: zero on success or when wakeup command not supported. Error-code
+ * otherwise.
+ *
+ * Initialize vmci doorbell, to get notified as soon as balloon changes.
+ */
+static int vmballoon_vmci_init(struct vmballoon *b)
+{
+	unsigned long error;
+
+	if ((b->capabilities & VMW_BALLOON_SIGNALLED_WAKEUP_CMD) == 0)
+		return 0;
+
+	error = vmci_doorbell_create(&b->vmci_doorbell, VMCI_FLAG_DELAYED_CB,
+				     VMCI_PRIVILEGE_FLAG_RESTRICTED,
+				     vmballoon_doorbell, b);
+
+	if (error != VMCI_SUCCESS)
+		goto fail;
+
+	error =	__vmballoon_cmd(b, VMW_BALLOON_CMD_VMCI_DOORBELL_SET,
+				b->vmci_doorbell.context,
+				b->vmci_doorbell.resource, NULL);
+
+	if (error != VMW_BALLOON_SUCCESS)
+		goto fail;
+
+	return 0;
+fail:
+	vmballoon_vmci_cleanup(b);
+	return -EIO;
+}
+
+/**
+ * vmballoon_pop - Quickly release all pages allocate for the balloon.
+ *
+ * @b: pointer to the balloon.
+ *
+ * This function is called when host decides to "reset" balloon for one reason
+ * or another. Unlike normal "deflate" we do not (shall not) notify host of the
+ * pages being released.
+ */
+static void vmballoon_pop(struct vmballoon *b)
+{
+	unsigned long size;
+
+	while ((size = atomic64_read(&b->size)))
+		vmballoon_deflate(b, size, false);
+}
+
+/*
+ * Perform standard reset sequence by popping the balloon (in case it
+ * is not  empty) and then restarting protocol. This operation normally
+ * happens when host responds with VMW_BALLOON_ERROR_RESET to a command.
+ */
+static void vmballoon_reset(struct vmballoon *b)
+{
+	int error;
+
+	down_write(&b->conf_sem);
+
+	vmballoon_vmci_cleanup(b);
+
+	/* free all pages, skipping monitor unlock */
+	vmballoon_pop(b);
+
+	if (vmballoon_send_start(b, VMW_BALLOON_CAPABILITIES))
+		goto unlock;
+
+	if ((b->capabilities & VMW_BALLOON_BATCHED_CMDS) != 0) {
+		if (vmballoon_init_batching(b)) {
+			/*
+			 * We failed to initialize batching, inform the monitor
+			 * about it by sending a null capability.
+			 *
+			 * The guest will retry in one second.
+			 */
+			vmballoon_send_start(b, 0);
+			goto unlock;
+		}
+	} else if ((b->capabilities & VMW_BALLOON_BASIC_CMDS) != 0) {
+		vmballoon_deinit_batching(b);
+	}
+
+	vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_RESET);
+	b->reset_required = false;
+
+	error = vmballoon_vmci_init(b);
+	if (error)
+		pr_err_once("failed to initialize vmci doorbell\n");
+
+	if (vmballoon_send_guest_id(b))
+		pr_err_once("failed to send guest ID to the host\n");
+
+unlock:
+	up_write(&b->conf_sem);
+}
+
+/**
+ * vmballoon_work - periodic balloon worker for reset, inflation and deflation.
+ *
+ * @work: pointer to the &work_struct which is provided by the workqueue.
+ *
+ * Resets the protocol if needed, gets the new size and adjusts balloon as
+ * needed. Repeat in 1 sec.
+ */
+static void vmballoon_work(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct vmballoon *b = container_of(dwork, struct vmballoon, dwork);
+	int64_t change = 0;
+
+	if (b->reset_required)
+		vmballoon_reset(b);
+
+	down_read(&b->conf_sem);
+
+	/*
+	 * Update the stats while holding the semaphore to ensure that
+	 * @stats_enabled is consistent with whether the stats are actually
+	 * enabled
+	 */
+	vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_TIMER);
+
+	if (!vmballoon_send_get_target(b))
+		change = vmballoon_change(b);
+
+	if (change != 0) {
+		pr_debug("%s - size: %llu, target %lu\n", __func__,
+			 atomic64_read(&b->size), READ_ONCE(b->target));
+
+		if (change > 0)
+			vmballoon_inflate(b);
+		else  /* (change < 0) */
+			vmballoon_deflate(b, 0, true);
+	}
+
+	up_read(&b->conf_sem);
+
+	/*
+	 * We are using a freezable workqueue so that balloon operations are
+	 * stopped while the system transitions to/from sleep/hibernation.
+	 */
+	queue_delayed_work(system_freezable_wq,
+			   dwork, round_jiffies_relative(HZ));
+
+}
+
+/**
+ * vmballoon_shrinker_scan() - deflate the balloon due to memory pressure.
+ * @shrinker: pointer to the balloon shrinker.
+ * @sc: page reclaim information.
+ *
+ * Returns: number of pages that were freed during deflation.
+ */
+static unsigned long vmballoon_shrinker_scan(struct shrinker *shrinker,
+					     struct shrink_control *sc)
+{
+	struct vmballoon *b = &balloon;
+	unsigned long deflated_frames;
+
+	pr_debug("%s - size: %llu", __func__, atomic64_read(&b->size));
+
+	vmballoon_stats_gen_inc(b, VMW_BALLOON_STAT_SHRINK);
+
+	/*
+	 * If the lock is also contended for read, we cannot easily reclaim and
+	 * we bail out.
+	 */
+	if (!down_read_trylock(&b->conf_sem))
+		return 0;
+
+	deflated_frames = vmballoon_deflate(b, sc->nr_to_scan, true);
+
+	vmballoon_stats_gen_add(b, VMW_BALLOON_STAT_SHRINK_FREE,
+				deflated_frames);
+
+	/*
+	 * Delay future inflation for some time to mitigate the situations in
+	 * which balloon continuously grows and shrinks. Use WRITE_ONCE() since
+	 * the access is asynchronous.
+	 */
+	WRITE_ONCE(b->shrink_timeout, jiffies + HZ * VMBALLOON_SHRINK_DELAY);
+
+	up_read(&b->conf_sem);
+
+	return deflated_frames;
+}
+
+/**
+ * vmballoon_shrinker_count() - return the number of ballooned pages.
+ * @shrinker: pointer to the balloon shrinker.
+ * @sc: page reclaim information.
+ *
+ * Returns: number of 4k pages that are allocated for the balloon and can
+ *	    therefore be reclaimed under pressure.
+ */
+static unsigned long vmballoon_shrinker_count(struct shrinker *shrinker,
+					      struct shrink_control *sc)
+{
+	struct vmballoon *b = &balloon;
+
+	return atomic64_read(&b->size);
+}
+
+static void vmballoon_unregister_shrinker(struct vmballoon *b)
+{
+	if (b->shrinker_registered)
+		unregister_shrinker(&b->shrinker);
+	b->shrinker_registered = false;
+}
+
+static int vmballoon_register_shrinker(struct vmballoon *b)
+{
+	int r;
+
+	/* Do nothing if the shrinker is not enabled */
+	if (!vmwballoon_shrinker_enable)
+		return 0;
+
+	b->shrinker.scan_objects = vmballoon_shrinker_scan;
+	b->shrinker.count_objects = vmballoon_shrinker_count;
+	b->shrinker.seeks = DEFAULT_SEEKS;
+
+	r = register_shrinker(&b->shrinker, "vmw-balloon");
+
+	if (r == 0)
+		b->shrinker_registered = true;
+
+	return r;
+}
+
+/*
+ * DEBUGFS Interface
+ */
+#ifdef CONFIG_DEBUG_FS
+
+static const char * const vmballoon_stat_page_names[] = {
+	[VMW_BALLOON_PAGE_STAT_ALLOC]		= "alloc",
+	[VMW_BALLOON_PAGE_STAT_ALLOC_FAIL]	= "allocFail",
+	[VMW_BALLOON_PAGE_STAT_REFUSED_ALLOC]	= "errAlloc",
+	[VMW_BALLOON_PAGE_STAT_REFUSED_FREE]	= "errFree",
+	[VMW_BALLOON_PAGE_STAT_FREE]		= "free"
+};
+
+static const char * const vmballoon_stat_names[] = {
+	[VMW_BALLOON_STAT_TIMER]		= "timer",
+	[VMW_BALLOON_STAT_DOORBELL]		= "doorbell",
+	[VMW_BALLOON_STAT_RESET]		= "reset",
+	[VMW_BALLOON_STAT_SHRINK]		= "shrink",
+	[VMW_BALLOON_STAT_SHRINK_FREE]		= "shrinkFree"
+};
+
+static int vmballoon_enable_stats(struct vmballoon *b)
+{
+	int r = 0;
+
+	down_write(&b->conf_sem);
+
+	/* did we somehow race with another reader which enabled stats? */
+	if (b->stats)
+		goto out;
+
+	b->stats = kzalloc(sizeof(*b->stats), GFP_KERNEL);
+
+	if (!b->stats) {
+		/* allocation failed */
+		r = -ENOMEM;
+		goto out;
+	}
+	static_key_enable(&balloon_stat_enabled.key);
+out:
+	up_write(&b->conf_sem);
+	return r;
+}
+
+/**
+ * vmballoon_debug_show - shows statistics of balloon operations.
+ * @f: pointer to the &struct seq_file.
+ * @offset: ignored.
+ *
+ * Provides the statistics that can be accessed in vmmemctl in the debugfs.
+ * To avoid the overhead - mainly that of memory - of collecting the statistics,
+ * we only collect statistics after the first time the counters are read.
+ *
+ * Return: zero on success or an error code.
+ */
+static int vmballoon_debug_show(struct seq_file *f, void *offset)
+{
+	struct vmballoon *b = f->private;
+	int i, j;
+
+	/* enables stats if they are disabled */
+	if (!b->stats) {
+		int r = vmballoon_enable_stats(b);
+
+		if (r)
+			return r;
+	}
+
+	/* format capabilities info */
+	seq_printf(f, "%-22s: %#16x\n", "balloon capabilities",
+		   VMW_BALLOON_CAPABILITIES);
+	seq_printf(f, "%-22s: %#16lx\n", "used capabilities", b->capabilities);
+	seq_printf(f, "%-22s: %16s\n", "is resetting",
+		   b->reset_required ? "y" : "n");
+
+	/* format size info */
+	seq_printf(f, "%-22s: %16lu\n", "target", READ_ONCE(b->target));
+	seq_printf(f, "%-22s: %16llu\n", "current", atomic64_read(&b->size));
+
+	for (i = 0; i < VMW_BALLOON_CMD_NUM; i++) {
+		if (vmballoon_cmd_names[i] == NULL)
+			continue;
+
+		seq_printf(f, "%-22s: %16llu (%llu failed)\n",
+			   vmballoon_cmd_names[i],
+			   atomic64_read(&b->stats->ops[i][VMW_BALLOON_OP_STAT]),
+			   atomic64_read(&b->stats->ops[i][VMW_BALLOON_OP_FAIL_STAT]));
+	}
+
+	for (i = 0; i < VMW_BALLOON_STAT_NUM; i++)
+		seq_printf(f, "%-22s: %16llu\n",
+			   vmballoon_stat_names[i],
+			   atomic64_read(&b->stats->general_stat[i]));
+
+	for (i = 0; i < VMW_BALLOON_PAGE_STAT_NUM; i++) {
+		for (j = 0; j < VMW_BALLOON_NUM_PAGE_SIZES; j++)
+			seq_printf(f, "%-18s(%s): %16llu\n",
+				   vmballoon_stat_page_names[i],
+				   vmballoon_page_size_names[j],
+				   atomic64_read(&b->stats->page_stat[i][j]));
+	}
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(vmballoon_debug);
+
+static void __init vmballoon_debugfs_init(struct vmballoon *b)
+{
+	debugfs_create_file("vmmemctl", S_IRUGO, NULL, b,
+			    &vmballoon_debug_fops);
+}
+
+static void __exit vmballoon_debugfs_exit(struct vmballoon *b)
+{
+	static_key_disable(&balloon_stat_enabled.key);
+	debugfs_lookup_and_remove("vmmemctl", NULL);
+	kfree(b->stats);
+	b->stats = NULL;
+}
+
+#else
+
+static inline void vmballoon_debugfs_init(struct vmballoon *b)
+{
+}
+
+static inline void vmballoon_debugfs_exit(struct vmballoon *b)
+{
+}
+
+#endif	/* CONFIG_DEBUG_FS */
+
+
+#ifdef CONFIG_BALLOON_COMPACTION
+/**
+ * vmballoon_migratepage() - migrates a balloon page.
+ * @b_dev_info: balloon device information descriptor.
+ * @newpage: the page to which @page should be migrated.
+ * @page: a ballooned page that should be migrated.
+ * @mode: migration mode, ignored.
+ *
+ * This function is really open-coded, but that is according to the interface
+ * that balloon_compaction provides.
+ *
+ * Return: zero on success, -EAGAIN when migration cannot be performed
+ *	   momentarily, and -EBUSY if migration failed and should be retried
+ *	   with that specific page.
+ */
+static int vmballoon_migratepage(struct balloon_dev_info *b_dev_info,
+				 struct page *newpage, struct page *page,
+				 enum migrate_mode mode)
+{
+	unsigned long status, flags;
+	struct vmballoon *b;
+	int ret;
+
+	b = container_of(b_dev_info, struct vmballoon, b_dev_info);
+
+	/*
+	 * If the semaphore is taken, there is ongoing configuration change
+	 * (i.e., balloon reset), so try again.
+	 */
+	if (!down_read_trylock(&b->conf_sem))
+		return -EAGAIN;
+
+	spin_lock(&b->comm_lock);
+	/*
+	 * We must start by deflating and not inflating, as otherwise the
+	 * hypervisor may tell us that it has enough memory and the new page is
+	 * not needed. Since the old page is isolated, we cannot use the list
+	 * interface to unlock it, as the LRU field is used for isolation.
+	 * Instead, we use the native interface directly.
+	 */
+	vmballoon_add_page(b, 0, page);
+	status = vmballoon_lock_op(b, 1, VMW_BALLOON_4K_PAGE,
+				   VMW_BALLOON_DEFLATE);
+
+	if (status == VMW_BALLOON_SUCCESS)
+		status = vmballoon_status_page(b, 0, &page);
+
+	/*
+	 * If a failure happened, let the migration mechanism know that it
+	 * should not retry.
+	 */
+	if (status != VMW_BALLOON_SUCCESS) {
+		spin_unlock(&b->comm_lock);
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+
+	/*
+	 * The page is isolated, so it is safe to delete it without holding
+	 * @pages_lock . We keep holding @comm_lock since we will need it in a
+	 * second.
+	 */
+	balloon_page_delete(page);
+
+	put_page(page);
+
+	/* Inflate */
+	vmballoon_add_page(b, 0, newpage);
+	status = vmballoon_lock_op(b, 1, VMW_BALLOON_4K_PAGE,
+				   VMW_BALLOON_INFLATE);
+
+	if (status == VMW_BALLOON_SUCCESS)
+		status = vmballoon_status_page(b, 0, &newpage);
+
+	spin_unlock(&b->comm_lock);
+
+	if (status != VMW_BALLOON_SUCCESS) {
+		/*
+		 * A failure happened. While we can deflate the page we just
+		 * inflated, this deflation can also encounter an error. Instead
+		 * we will decrease the size of the balloon to reflect the
+		 * change and report failure.
+		 */
+		atomic64_dec(&b->size);
+		ret = -EBUSY;
+	} else {
+		/*
+		 * Success. Take a reference for the page, and we will add it to
+		 * the list after acquiring the lock.
+		 */
+		get_page(newpage);
+		ret = MIGRATEPAGE_SUCCESS;
+	}
+
+	/* Update the balloon list under the @pages_lock */
+	spin_lock_irqsave(&b->b_dev_info.pages_lock, flags);
+
+	/*
+	 * On inflation success, we already took a reference for the @newpage.
+	 * If we succeed just insert it to the list and update the statistics
+	 * under the lock.
+	 */
+	if (ret == MIGRATEPAGE_SUCCESS) {
+		balloon_page_insert(&b->b_dev_info, newpage);
+		__count_vm_event(BALLOON_MIGRATE);
+	}
+
+	/*
+	 * We deflated successfully, so regardless to the inflation success, we
+	 * need to reduce the number of isolated_pages.
+	 */
+	b->b_dev_info.isolated_pages--;
+	spin_unlock_irqrestore(&b->b_dev_info.pages_lock, flags);
+
+out_unlock:
+	up_read(&b->conf_sem);
+	return ret;
+}
+
+/**
+ * vmballoon_compaction_init() - initialized compaction for the balloon.
+ *
+ * @b: pointer to the balloon.
+ *
+ * If during the initialization a failure occurred, this function does not
+ * perform cleanup. The caller must call vmballoon_compaction_deinit() in this
+ * case.
+ *
+ * Return: zero on success or error code on failure.
+ */
+static __init void vmballoon_compaction_init(struct vmballoon *b)
+{
+	b->b_dev_info.migratepage = vmballoon_migratepage;
+}
+
+#else /* CONFIG_BALLOON_COMPACTION */
+static inline void vmballoon_compaction_init(struct vmballoon *b)
+{
+}
+#endif /* CONFIG_BALLOON_COMPACTION */
+
+static int __init vmballoon_init(void)
+{
+	int error;
+
+	/*
+	 * Check if we are running on VMware's hypervisor and bail out
+	 * if we are not.
+	 */
+	if (x86_hyper_type != X86_HYPER_VMWARE)
+		return -ENODEV;
+
+	INIT_DELAYED_WORK(&balloon.dwork, vmballoon_work);
+
+	error = vmballoon_register_shrinker(&balloon);
+	if (error)
+		goto fail;
+
+	/*
+	 * Initialization of compaction must be done after the call to
+	 * balloon_devinfo_init() .
+	 */
+	balloon_devinfo_init(&balloon.b_dev_info);
+	vmballoon_compaction_init(&balloon);
+
+	INIT_LIST_HEAD(&balloon.huge_pages);
+	spin_lock_init(&balloon.comm_lock);
+	init_rwsem(&balloon.conf_sem);
+	balloon.vmci_doorbell = VMCI_INVALID_HANDLE;
+	balloon.batch_page = NULL;
+	balloon.page = NULL;
+	balloon.reset_required = true;
+
+	queue_delayed_work(system_freezable_wq, &balloon.dwork, 0);
+
+	vmballoon_debugfs_init(&balloon);
+
+	return 0;
+fail:
+	vmballoon_unregister_shrinker(&balloon);
+	return error;
+}
+
+/*
+ * Using late_initcall() instead of module_init() allows the balloon to use the
+ * VMCI doorbell even when the balloon is built into the kernel. Otherwise the
+ * VMCI is probed only after the balloon is initialized. If the balloon is used
+ * as a module, late_initcall() is equivalent to module_init().
+ */
+late_initcall(vmballoon_init);
+
+static void __exit vmballoon_exit(void)
+{
+	vmballoon_unregister_shrinker(&balloon);
+	vmballoon_vmci_cleanup(&balloon);
+	cancel_delayed_work_sync(&balloon.dwork);
+
+	vmballoon_debugfs_exit(&balloon);
+
+	/*
+	 * Deallocate all reserved memory, and reset connection with monitor.
+	 * Reset connection before deallocating memory to avoid potential for
+	 * additional spurious resets from guest touching deallocated pages.
+	 */
+	vmballoon_send_start(&balloon, 0);
+	vmballoon_pop(&balloon);
+}
+module_exit(vmballoon_exit);