drm/nouveau: fix kernel-doc comments

[drm/drm-misc.git] / drivers / virtio / virtio_mem.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Virtio-mem device driver.
 *
 * Copyright Red Hat, Inc. 2020
 *
 * Author(s): David Hildenbrand <david@redhat.com>
 */

#include <linux/virtio.h>
#include <linux/virtio_mem.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/memory_hotplug.h>
#include <linux/memory.h>
#include <linux/hrtimer.h>
#include <linux/crash_dump.h>
#include <linux/mutex.h>
#include <linux/bitmap.h>
#include <linux/lockdep.h>
#include <linux/log2.h>
#include <linux/vmalloc.h>
#include <linux/suspend.h>

#include <acpi/acpi_numa.h>

static bool unplug_online = true;
module_param(unplug_online, bool, 0644);
MODULE_PARM_DESC(unplug_online, "Try to unplug online memory");

static bool force_bbm;
module_param(force_bbm, bool, 0444);
MODULE_PARM_DESC(force_bbm,
                "Force Big Block Mode. Default is 0 (auto-selection)");

static unsigned long bbm_block_size;
module_param(bbm_block_size, ulong, 0444);
MODULE_PARM_DESC(bbm_block_size,
                 "Big Block size in bytes. Default is 0 (auto-detection).");

/*
 * virtio-mem currently supports the following modes of operation:
 *
 * * Sub Block Mode (SBM): A Linux memory block spans 2..X subblocks (SB). The
 *   size of a Sub Block (SB) is determined based on the device block size, the
 *   pageblock size, and the maximum allocation granularity of the buddy.
 *   Subblocks within a Linux memory block might either be plugged or unplugged.
 *   Memory is added/removed to Linux MM in Linux memory block granularity.
 *
 * * Big Block Mode (BBM): A Big Block (BB) spans 1..X Linux memory blocks.
 *   Memory is added/removed to Linux MM in Big Block granularity.
 *
 * The mode is determined automatically based on the Linux memory block size
 * and the device block size.
 *
 * User space / core MM (auto onlining) is responsible for onlining added
 * Linux memory blocks - and for selecting a zone. Linux Memory Blocks are
 * always onlined separately, and all memory within a Linux memory block is
 * onlined to the same zone - virtio-mem relies on this behavior.
 */

/*
 * State of a Linux memory block in SBM.
 */
enum virtio_mem_sbm_mb_state {
        /* Unplugged, not added to Linux. Can be reused later. */
        VIRTIO_MEM_SBM_MB_UNUSED = 0,
        /* (Partially) plugged, not added to Linux. Error on add_memory(). */
        VIRTIO_MEM_SBM_MB_PLUGGED,
        /* Fully plugged, fully added to Linux, offline. */
        VIRTIO_MEM_SBM_MB_OFFLINE,
        /* Partially plugged, fully added to Linux, offline. */
        VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL,
        /* Fully plugged, fully added to Linux, onlined to a kernel zone. */
        VIRTIO_MEM_SBM_MB_KERNEL,
        /* Partially plugged, fully added to Linux, online to a kernel zone */
        VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL,
        /* Fully plugged, fully added to Linux, onlined to ZONE_MOVABLE. */
        VIRTIO_MEM_SBM_MB_MOVABLE,
        /* Partially plugged, fully added to Linux, onlined to ZONE_MOVABLE. */
        VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL,
        VIRTIO_MEM_SBM_MB_COUNT
};

/*
 * State of a Big Block (BB) in BBM, covering 1..X Linux memory blocks.
 */
enum virtio_mem_bbm_bb_state {
        /* Unplugged, not added to Linux. Can be reused later. */
        VIRTIO_MEM_BBM_BB_UNUSED = 0,
        /* Plugged, not added to Linux. Error on add_memory(). */
        VIRTIO_MEM_BBM_BB_PLUGGED,
        /* Plugged and added to Linux. */
        VIRTIO_MEM_BBM_BB_ADDED,
        /* All online parts are fake-offline, ready to remove. */
        VIRTIO_MEM_BBM_BB_FAKE_OFFLINE,
        VIRTIO_MEM_BBM_BB_COUNT
};

struct virtio_mem {
        struct virtio_device *vdev;

        /* We might first have to unplug all memory when starting up. */
        bool unplug_all_required;

        /* Workqueue that processes the plug/unplug requests. */
        struct work_struct wq;
        atomic_t wq_active;
        atomic_t config_changed;

        /* Virtqueue for guest->host requests. */
        struct virtqueue *vq;

        /* Wait for a host response to a guest request. */
        wait_queue_head_t host_resp;

        /* Space for one guest request and the host response. */
        struct virtio_mem_req req;
        struct virtio_mem_resp resp;

        /* The current size of the device. */
        uint64_t plugged_size;
        /* The requested size of the device. */
        uint64_t requested_size;

        /* The device block size (for communicating with the device). */
        uint64_t device_block_size;
        /* The determined node id for all memory of the device. */
        int nid;
        /* Physical start address of the memory region. */
        uint64_t addr;
        /* Maximum region size in bytes. */
        uint64_t region_size;

        /* The parent resource for all memory added via this device. */
        struct resource *parent_resource;
        /*
         * Copy of "System RAM (virtio_mem)" to be used for
         * add_memory_driver_managed().
         */
        const char *resource_name;
        /* Memory group identification. */
        int mgid;

        /*
         * We don't want to add too much memory if it's not getting onlined,
         * to avoid running OOM. Besides this threshold, we allow to have at
         * least two offline blocks at a time (whatever is bigger).
         */
#define VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD            (1024 * 1024 * 1024)
        atomic64_t offline_size;
        uint64_t offline_threshold;

        /* If set, the driver is in SBM, otherwise in BBM. */
        bool in_sbm;

        union {
                struct {
                        /* Id of the first memory block of this device. */
                        unsigned long first_mb_id;
                        /* Id of the last usable memory block of this device. */
                        unsigned long last_usable_mb_id;
                        /* Id of the next memory bock to prepare when needed. */
                        unsigned long next_mb_id;

                        /* The subblock size. */
                        uint64_t sb_size;
                        /* The number of subblocks per Linux memory block. */
                        uint32_t sbs_per_mb;

                        /*
                         * Some of the Linux memory blocks tracked as "partially
                         * plugged" are completely unplugged and can be offlined
                         * and removed -- which previously failed.
                         */
                        bool have_unplugged_mb;

                        /* Summary of all memory block states. */
                        unsigned long mb_count[VIRTIO_MEM_SBM_MB_COUNT];

                        /*
                         * One byte state per memory block. Allocated via
                         * vmalloc(). Resized (alloc+copy+free) on demand.
                         *
                         * With 128 MiB memory blocks, we have states for 512
                         * GiB of memory in one 4 KiB page.
                         */
                        uint8_t *mb_states;

                        /*
                         * Bitmap: one bit per subblock. Allocated similar to
                         * sbm.mb_states.
                         *
                         * A set bit means the corresponding subblock is
                         * plugged, otherwise it's unblocked.
                         *
                         * With 4 MiB subblocks, we manage 128 GiB of memory
                         * in one 4 KiB page.
                         */
                        unsigned long *sb_states;
                } sbm;

                struct {
                        /* Id of the first big block of this device. */
                        unsigned long first_bb_id;
                        /* Id of the last usable big block of this device. */
                        unsigned long last_usable_bb_id;
                        /* Id of the next device bock to prepare when needed. */
                        unsigned long next_bb_id;

                        /* Summary of all big block states. */
                        unsigned long bb_count[VIRTIO_MEM_BBM_BB_COUNT];

                        /* One byte state per big block. See sbm.mb_states. */
                        uint8_t *bb_states;

                        /* The block size used for plugging/adding/removing. */
                        uint64_t bb_size;
                } bbm;
        };

        /*
         * Mutex that protects the sbm.mb_count, sbm.mb_states,
         * sbm.sb_states, bbm.bb_count, and bbm.bb_states
         *
         * When this lock is held the pointers can't change, ONLINE and
         * OFFLINE blocks can't change the state and no subblocks will get
         * plugged/unplugged.
         *
         * In kdump mode, used to serialize requests, last_block_addr and
         * last_block_plugged.
         */
        struct mutex hotplug_mutex;
        bool hotplug_active;

        /* An error occurred we cannot handle - stop processing requests. */
        bool broken;

        /* Cached valued of is_kdump_kernel() when the device was probed. */
        bool in_kdump;

        /* The driver is being removed. */
        spinlock_t removal_lock;
        bool removing;

        /* Timer for retrying to plug/unplug memory. */
        struct hrtimer retry_timer;
        unsigned int retry_timer_ms;
#define VIRTIO_MEM_RETRY_TIMER_MIN_MS           50000
#define VIRTIO_MEM_RETRY_TIMER_MAX_MS           300000

        /* Memory notifier (online/offline events). */
        struct notifier_block memory_notifier;

        /* Notifier to block hibernation image storing/reloading. */
        struct notifier_block pm_notifier;

#ifdef CONFIG_PROC_VMCORE
        /* vmcore callback for /proc/vmcore handling in kdump mode */
        struct vmcore_cb vmcore_cb;
        uint64_t last_block_addr;
        bool last_block_plugged;
#endif /* CONFIG_PROC_VMCORE */

        /* Next device in the list of virtio-mem devices. */
        struct list_head next;
};

/*
 * We have to share a single online_page callback among all virtio-mem
 * devices. We use RCU to iterate the list in the callback.
 */
static DEFINE_MUTEX(virtio_mem_mutex);
static LIST_HEAD(virtio_mem_devices);

static void virtio_mem_online_page_cb(struct page *page, unsigned int order);
static void virtio_mem_fake_offline_going_offline(unsigned long pfn,
                                                  unsigned long nr_pages);
static void virtio_mem_fake_offline_cancel_offline(unsigned long pfn,
                                                   unsigned long nr_pages);
static void virtio_mem_retry(struct virtio_mem *vm);
static int virtio_mem_create_resource(struct virtio_mem *vm);
static void virtio_mem_delete_resource(struct virtio_mem *vm);

/*
 * Register a virtio-mem device so it will be considered for the online_page
 * callback.
 */
static int register_virtio_mem_device(struct virtio_mem *vm)
{
        int rc = 0;

        /* First device registers the callback. */
        mutex_lock(&virtio_mem_mutex);
        if (list_empty(&virtio_mem_devices))
                rc = set_online_page_callback(&virtio_mem_online_page_cb);
        if (!rc)
                list_add_rcu(&vm->next, &virtio_mem_devices);
        mutex_unlock(&virtio_mem_mutex);

        return rc;
}

/*
 * Unregister a virtio-mem device so it will no longer be considered for the
 * online_page callback.
 */
static void unregister_virtio_mem_device(struct virtio_mem *vm)
{
        /* Last device unregisters the callback. */
        mutex_lock(&virtio_mem_mutex);
        list_del_rcu(&vm->next);
        if (list_empty(&virtio_mem_devices))
                restore_online_page_callback(&virtio_mem_online_page_cb);
        mutex_unlock(&virtio_mem_mutex);

        synchronize_rcu();
}

/*
 * Calculate the memory block id of a given address.
 */
static unsigned long virtio_mem_phys_to_mb_id(unsigned long addr)
{
        return addr / memory_block_size_bytes();
}

/*
 * Calculate the physical start address of a given memory block id.
 */
static unsigned long virtio_mem_mb_id_to_phys(unsigned long mb_id)
{
        return mb_id * memory_block_size_bytes();
}

/*
 * Calculate the big block id of a given address.
 */
static unsigned long virtio_mem_phys_to_bb_id(struct virtio_mem *vm,
                                              uint64_t addr)
{
        return addr / vm->bbm.bb_size;
}

/*
 * Calculate the physical start address of a given big block id.
 */
static uint64_t virtio_mem_bb_id_to_phys(struct virtio_mem *vm,
                                         unsigned long bb_id)
{
        return bb_id * vm->bbm.bb_size;
}

/*
 * Calculate the subblock id of a given address.
 */
static unsigned long virtio_mem_phys_to_sb_id(struct virtio_mem *vm,
                                              unsigned long addr)
{
        const unsigned long mb_id = virtio_mem_phys_to_mb_id(addr);
        const unsigned long mb_addr = virtio_mem_mb_id_to_phys(mb_id);

        return (addr - mb_addr) / vm->sbm.sb_size;
}

/*
 * Set the state of a big block, taking care of the state counter.
 */
static void virtio_mem_bbm_set_bb_state(struct virtio_mem *vm,
                                        unsigned long bb_id,
                                        enum virtio_mem_bbm_bb_state state)
{
        const unsigned long idx = bb_id - vm->bbm.first_bb_id;
        enum virtio_mem_bbm_bb_state old_state;

        old_state = vm->bbm.bb_states[idx];
        vm->bbm.bb_states[idx] = state;

        BUG_ON(vm->bbm.bb_count[old_state] == 0);
        vm->bbm.bb_count[old_state]--;
        vm->bbm.bb_count[state]++;
}

/*
 * Get the state of a big block.
 */
static enum virtio_mem_bbm_bb_state virtio_mem_bbm_get_bb_state(struct virtio_mem *vm,
                                                                unsigned long bb_id)
{
        return vm->bbm.bb_states[bb_id - vm->bbm.first_bb_id];
}

/*
 * Prepare the big block state array for the next big block.
 */
static int virtio_mem_bbm_bb_states_prepare_next_bb(struct virtio_mem *vm)
{
        unsigned long old_bytes = vm->bbm.next_bb_id - vm->bbm.first_bb_id;
        unsigned long new_bytes = old_bytes + 1;
        int old_pages = PFN_UP(old_bytes);
        int new_pages = PFN_UP(new_bytes);
        uint8_t *new_array;

        if (vm->bbm.bb_states && old_pages == new_pages)
                return 0;

        new_array = vzalloc(new_pages * PAGE_SIZE);
        if (!new_array)
                return -ENOMEM;

        mutex_lock(&vm->hotplug_mutex);
        if (vm->bbm.bb_states)
                memcpy(new_array, vm->bbm.bb_states, old_pages * PAGE_SIZE);
        vfree(vm->bbm.bb_states);
        vm->bbm.bb_states = new_array;
        mutex_unlock(&vm->hotplug_mutex);

        return 0;
}

#define virtio_mem_bbm_for_each_bb(_vm, _bb_id, _state) \
        for (_bb_id = vm->bbm.first_bb_id; \
             _bb_id < vm->bbm.next_bb_id && _vm->bbm.bb_count[_state]; \
             _bb_id++) \
                if (virtio_mem_bbm_get_bb_state(_vm, _bb_id) == _state)

#define virtio_mem_bbm_for_each_bb_rev(_vm, _bb_id, _state) \
        for (_bb_id = vm->bbm.next_bb_id - 1; \
             _bb_id >= vm->bbm.first_bb_id && _vm->bbm.bb_count[_state]; \
             _bb_id--) \
                if (virtio_mem_bbm_get_bb_state(_vm, _bb_id) == _state)

/*
 * Set the state of a memory block, taking care of the state counter.
 */
static void virtio_mem_sbm_set_mb_state(struct virtio_mem *vm,
                                        unsigned long mb_id, uint8_t state)
{
        const unsigned long idx = mb_id - vm->sbm.first_mb_id;
        uint8_t old_state;

        old_state = vm->sbm.mb_states[idx];
        vm->sbm.mb_states[idx] = state;

        BUG_ON(vm->sbm.mb_count[old_state] == 0);
        vm->sbm.mb_count[old_state]--;
        vm->sbm.mb_count[state]++;
}

/*
 * Get the state of a memory block.
 */
static uint8_t virtio_mem_sbm_get_mb_state(struct virtio_mem *vm,
                                           unsigned long mb_id)
{
        const unsigned long idx = mb_id - vm->sbm.first_mb_id;

        return vm->sbm.mb_states[idx];
}

/*
 * Prepare the state array for the next memory block.
 */
static int virtio_mem_sbm_mb_states_prepare_next_mb(struct virtio_mem *vm)
{
        int old_pages = PFN_UP(vm->sbm.next_mb_id - vm->sbm.first_mb_id);
        int new_pages = PFN_UP(vm->sbm.next_mb_id - vm->sbm.first_mb_id + 1);
        uint8_t *new_array;

        if (vm->sbm.mb_states && old_pages == new_pages)
                return 0;

        new_array = vzalloc(new_pages * PAGE_SIZE);
        if (!new_array)
                return -ENOMEM;

        mutex_lock(&vm->hotplug_mutex);
        if (vm->sbm.mb_states)
                memcpy(new_array, vm->sbm.mb_states, old_pages * PAGE_SIZE);
        vfree(vm->sbm.mb_states);
        vm->sbm.mb_states = new_array;
        mutex_unlock(&vm->hotplug_mutex);

        return 0;
}

#define virtio_mem_sbm_for_each_mb(_vm, _mb_id, _state) \
        for (_mb_id = _vm->sbm.first_mb_id; \
             _mb_id < _vm->sbm.next_mb_id && _vm->sbm.mb_count[_state]; \
             _mb_id++) \
                if (virtio_mem_sbm_get_mb_state(_vm, _mb_id) == _state)

#define virtio_mem_sbm_for_each_mb_rev(_vm, _mb_id, _state) \
        for (_mb_id = _vm->sbm.next_mb_id - 1; \
             _mb_id >= _vm->sbm.first_mb_id && _vm->sbm.mb_count[_state]; \
             _mb_id--) \
                if (virtio_mem_sbm_get_mb_state(_vm, _mb_id) == _state)

/*
 * Calculate the bit number in the subblock bitmap for the given subblock
 * inside the given memory block.
 */
static int virtio_mem_sbm_sb_state_bit_nr(struct virtio_mem *vm,
                                          unsigned long mb_id, int sb_id)
{
        return (mb_id - vm->sbm.first_mb_id) * vm->sbm.sbs_per_mb + sb_id;
}

/*
 * Mark all selected subblocks plugged.
 *
 * Will not modify the state of the memory block.
 */
static void virtio_mem_sbm_set_sb_plugged(struct virtio_mem *vm,
                                          unsigned long mb_id, int sb_id,
                                          int count)
{
        const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

        __bitmap_set(vm->sbm.sb_states, bit, count);
}

/*
 * Mark all selected subblocks unplugged.
 *
 * Will not modify the state of the memory block.
 */
static void virtio_mem_sbm_set_sb_unplugged(struct virtio_mem *vm,
                                            unsigned long mb_id, int sb_id,
                                            int count)
{
        const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

        __bitmap_clear(vm->sbm.sb_states, bit, count);
}

/*
 * Test if all selected subblocks are plugged.
 */
static bool virtio_mem_sbm_test_sb_plugged(struct virtio_mem *vm,
                                           unsigned long mb_id, int sb_id,
                                           int count)
{
        const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

        if (count == 1)
                return test_bit(bit, vm->sbm.sb_states);

        /* TODO: Helper similar to bitmap_set() */
        return find_next_zero_bit(vm->sbm.sb_states, bit + count, bit) >=
               bit + count;
}

/*
 * Test if all selected subblocks are unplugged.
 */
static bool virtio_mem_sbm_test_sb_unplugged(struct virtio_mem *vm,
                                             unsigned long mb_id, int sb_id,
                                             int count)
{
        const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);

        /* TODO: Helper similar to bitmap_set() */
        return find_next_bit(vm->sbm.sb_states, bit + count, bit) >=
               bit + count;
}

/*
 * Find the first unplugged subblock. Returns vm->sbm.sbs_per_mb in case there is
 * none.
 */
static int virtio_mem_sbm_first_unplugged_sb(struct virtio_mem *vm,
                                            unsigned long mb_id)
{
        const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, 0);

        return find_next_zero_bit(vm->sbm.sb_states,
                                  bit + vm->sbm.sbs_per_mb, bit) - bit;
}

/*
 * Prepare the subblock bitmap for the next memory block.
 */
static int virtio_mem_sbm_sb_states_prepare_next_mb(struct virtio_mem *vm)
{
        const unsigned long old_nb_mb = vm->sbm.next_mb_id - vm->sbm.first_mb_id;
        const unsigned long old_nb_bits = old_nb_mb * vm->sbm.sbs_per_mb;
        const unsigned long new_nb_bits = (old_nb_mb + 1) * vm->sbm.sbs_per_mb;
        int old_pages = PFN_UP(BITS_TO_LONGS(old_nb_bits) * sizeof(long));
        int new_pages = PFN_UP(BITS_TO_LONGS(new_nb_bits) * sizeof(long));
        unsigned long *new_bitmap, *old_bitmap;

        if (vm->sbm.sb_states && old_pages == new_pages)
                return 0;

        new_bitmap = vzalloc(new_pages * PAGE_SIZE);
        if (!new_bitmap)
                return -ENOMEM;

        mutex_lock(&vm->hotplug_mutex);
        if (vm->sbm.sb_states)
                memcpy(new_bitmap, vm->sbm.sb_states, old_pages * PAGE_SIZE);

        old_bitmap = vm->sbm.sb_states;
        vm->sbm.sb_states = new_bitmap;
        mutex_unlock(&vm->hotplug_mutex);

        vfree(old_bitmap);
        return 0;
}

/*
 * Test if we could add memory without creating too much offline memory -
 * to avoid running OOM if memory is getting onlined deferred.
 */
static bool virtio_mem_could_add_memory(struct virtio_mem *vm, uint64_t size)
{
        if (WARN_ON_ONCE(size > vm->offline_threshold))
                return false;

        return atomic64_read(&vm->offline_size) + size <= vm->offline_threshold;
}

/*
 * Try adding memory to Linux. Will usually only fail if out of memory.
 *
 * Must not be called with the vm->hotplug_mutex held (possible deadlock with
 * onlining code).
 *
 * Will not modify the state of memory blocks in virtio-mem.
 */
static int virtio_mem_add_memory(struct virtio_mem *vm, uint64_t addr,
                                 uint64_t size)
{
        int rc;

        /*
         * When force-unloading the driver and we still have memory added to
         * Linux, the resource name has to stay.
         */
        if (!vm->resource_name) {
                vm->resource_name = kstrdup_const("System RAM (virtio_mem)",
                                                  GFP_KERNEL);
                if (!vm->resource_name)
                        return -ENOMEM;
        }

        dev_dbg(&vm->vdev->dev, "adding memory: 0x%llx - 0x%llx\n", addr,
                addr + size - 1);
        /* Memory might get onlined immediately. */
        atomic64_add(size, &vm->offline_size);
        rc = add_memory_driver_managed(vm->mgid, addr, size, vm->resource_name,
                                       MHP_MERGE_RESOURCE | MHP_NID_IS_MGID);
        if (rc) {
                atomic64_sub(size, &vm->offline_size);
                dev_warn(&vm->vdev->dev, "adding memory failed: %d\n", rc);
                /*
                 * TODO: Linux MM does not properly clean up yet in all cases
                 * where adding of memory failed - especially on -ENOMEM.
                 */
        }
        return rc;
}

/*
 * See virtio_mem_add_memory(): Try adding a single Linux memory block.
 */
static int virtio_mem_sbm_add_mb(struct virtio_mem *vm, unsigned long mb_id)
{
        const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
        const uint64_t size = memory_block_size_bytes();

        return virtio_mem_add_memory(vm, addr, size);
}

/*
 * See virtio_mem_add_memory(): Try adding a big block.
 */
static int virtio_mem_bbm_add_bb(struct virtio_mem *vm, unsigned long bb_id)
{
        const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
        const uint64_t size = vm->bbm.bb_size;

        return virtio_mem_add_memory(vm, addr, size);
}

/*
 * Try removing memory from Linux. Will only fail if memory blocks aren't
 * offline.
 *
 * Must not be called with the vm->hotplug_mutex held (possible deadlock with
 * onlining code).
 *
 * Will not modify the state of memory blocks in virtio-mem.
 */
static int virtio_mem_remove_memory(struct virtio_mem *vm, uint64_t addr,
                                    uint64_t size)
{
        int rc;

        dev_dbg(&vm->vdev->dev, "removing memory: 0x%llx - 0x%llx\n", addr,
                addr + size - 1);
        rc = remove_memory(addr, size);
        if (!rc) {
                atomic64_sub(size, &vm->offline_size);
                /*
                 * We might have freed up memory we can now unplug, retry
                 * immediately instead of waiting.
                 */
                virtio_mem_retry(vm);
        } else {
                dev_dbg(&vm->vdev->dev, "removing memory failed: %d\n", rc);
        }
        return rc;
}

/*
 * See virtio_mem_remove_memory(): Try removing a single Linux memory block.
 */
static int virtio_mem_sbm_remove_mb(struct virtio_mem *vm, unsigned long mb_id)
{
        const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
        const uint64_t size = memory_block_size_bytes();

        return virtio_mem_remove_memory(vm, addr, size);
}

/*
 * Try offlining and removing memory from Linux.
 *
 * Must not be called with the vm->hotplug_mutex held (possible deadlock with
 * onlining code).
 *
 * Will not modify the state of memory blocks in virtio-mem.
 */
static int virtio_mem_offline_and_remove_memory(struct virtio_mem *vm,
                                                uint64_t addr,
                                                uint64_t size)
{
        int rc;

        dev_dbg(&vm->vdev->dev,
                "offlining and removing memory: 0x%llx - 0x%llx\n", addr,
                addr + size - 1);

        rc = offline_and_remove_memory(addr, size);
        if (!rc) {
                atomic64_sub(size, &vm->offline_size);
                /*
                 * We might have freed up memory we can now unplug, retry
                 * immediately instead of waiting.
                 */
                virtio_mem_retry(vm);
                return 0;
        }
        dev_dbg(&vm->vdev->dev, "offlining and removing memory failed: %d\n", rc);
        /*
         * We don't really expect this to fail, because we fake-offlined all
         * memory already. But it could fail in corner cases.
         */
        WARN_ON_ONCE(rc != -ENOMEM && rc != -EBUSY);
        return rc == -ENOMEM ? -ENOMEM : -EBUSY;
}

/*
 * See virtio_mem_offline_and_remove_memory(): Try offlining and removing
 * a single Linux memory block.
 */
static int virtio_mem_sbm_offline_and_remove_mb(struct virtio_mem *vm,
                                                unsigned long mb_id)
{
        const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
        const uint64_t size = memory_block_size_bytes();

        return virtio_mem_offline_and_remove_memory(vm, addr, size);
}

/*
 * Try (offlining and) removing memory from Linux in case all subblocks are
 * unplugged. Can be called on online and offline memory blocks.
 *
 * May modify the state of memory blocks in virtio-mem.
 */
static int virtio_mem_sbm_try_remove_unplugged_mb(struct virtio_mem *vm,
                                                  unsigned long mb_id)
{
        int rc;

        /*
         * Once all subblocks of a memory block were unplugged, offline and
         * remove it.
         */
        if (!virtio_mem_sbm_test_sb_unplugged(vm, mb_id, 0, vm->sbm.sbs_per_mb))
                return 0;

        /* offline_and_remove_memory() works for online and offline memory. */
        mutex_unlock(&vm->hotplug_mutex);
        rc = virtio_mem_sbm_offline_and_remove_mb(vm, mb_id);
        mutex_lock(&vm->hotplug_mutex);
        if (!rc)
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_UNUSED);
        return rc;
}

/*
 * See virtio_mem_offline_and_remove_memory(): Try to offline and remove a
 * all Linux memory blocks covered by the big block.
 */
static int virtio_mem_bbm_offline_and_remove_bb(struct virtio_mem *vm,
                                                unsigned long bb_id)
{
        const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
        const uint64_t size = vm->bbm.bb_size;

        return virtio_mem_offline_and_remove_memory(vm, addr, size);
}

/*
 * Trigger the workqueue so the device can perform its magic.
 */
static void virtio_mem_retry(struct virtio_mem *vm)
{
        unsigned long flags;

        spin_lock_irqsave(&vm->removal_lock, flags);
        if (!vm->removing)
                queue_work(system_freezable_wq, &vm->wq);
        spin_unlock_irqrestore(&vm->removal_lock, flags);
}

static int virtio_mem_translate_node_id(struct virtio_mem *vm, uint16_t node_id)
{
        int node = NUMA_NO_NODE;

#if defined(CONFIG_ACPI_NUMA)
        if (virtio_has_feature(vm->vdev, VIRTIO_MEM_F_ACPI_PXM))
                node = pxm_to_node(node_id);
#endif
        return node;
}

/*
 * Test if a virtio-mem device overlaps with the given range. Can be called
 * from (notifier) callbacks lockless.
 */
static bool virtio_mem_overlaps_range(struct virtio_mem *vm, uint64_t start,
                                      uint64_t size)
{
        return start < vm->addr + vm->region_size && vm->addr < start + size;
}

/*
 * Test if a virtio-mem device contains a given range. Can be called from
 * (notifier) callbacks lockless.
 */
static bool virtio_mem_contains_range(struct virtio_mem *vm, uint64_t start,
                                      uint64_t size)
{
        return start >= vm->addr && start + size <= vm->addr + vm->region_size;
}

static int virtio_mem_sbm_notify_going_online(struct virtio_mem *vm,
                                              unsigned long mb_id)
{
        switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
        case VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL:
        case VIRTIO_MEM_SBM_MB_OFFLINE:
                return NOTIFY_OK;
        default:
                break;
        }
        dev_warn_ratelimited(&vm->vdev->dev,
                             "memory block onlining denied\n");
        return NOTIFY_BAD;
}

static void virtio_mem_sbm_notify_offline(struct virtio_mem *vm,
                                          unsigned long mb_id)
{
        switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
        case VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL:
        case VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL:
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL);
                break;
        case VIRTIO_MEM_SBM_MB_KERNEL:
        case VIRTIO_MEM_SBM_MB_MOVABLE:
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_OFFLINE);
                break;
        default:
                BUG();
                break;
        }
}

static void virtio_mem_sbm_notify_online(struct virtio_mem *vm,
                                         unsigned long mb_id,
                                         unsigned long start_pfn)
{
        const bool is_movable = is_zone_movable_page(pfn_to_page(start_pfn));
        int new_state;

        switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
        case VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL:
                new_state = VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL;
                if (is_movable)
                        new_state = VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL;
                break;
        case VIRTIO_MEM_SBM_MB_OFFLINE:
                new_state = VIRTIO_MEM_SBM_MB_KERNEL;
                if (is_movable)
                        new_state = VIRTIO_MEM_SBM_MB_MOVABLE;
                break;
        default:
                BUG();
                break;
        }
        virtio_mem_sbm_set_mb_state(vm, mb_id, new_state);
}

static void virtio_mem_sbm_notify_going_offline(struct virtio_mem *vm,
                                                unsigned long mb_id)
{
        const unsigned long nr_pages = PFN_DOWN(vm->sbm.sb_size);
        unsigned long pfn;
        int sb_id;

        for (sb_id = 0; sb_id < vm->sbm.sbs_per_mb; sb_id++) {
                if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
                        continue;
                pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
                               sb_id * vm->sbm.sb_size);
                virtio_mem_fake_offline_going_offline(pfn, nr_pages);
        }
}

static void virtio_mem_sbm_notify_cancel_offline(struct virtio_mem *vm,
                                                 unsigned long mb_id)
{
        const unsigned long nr_pages = PFN_DOWN(vm->sbm.sb_size);
        unsigned long pfn;
        int sb_id;

        for (sb_id = 0; sb_id < vm->sbm.sbs_per_mb; sb_id++) {
                if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
                        continue;
                pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
                               sb_id * vm->sbm.sb_size);
                virtio_mem_fake_offline_cancel_offline(pfn, nr_pages);
        }
}

static void virtio_mem_bbm_notify_going_offline(struct virtio_mem *vm,
                                                unsigned long bb_id,
                                                unsigned long pfn,
                                                unsigned long nr_pages)
{
        /*
         * When marked as "fake-offline", all online memory of this device block
         * is allocated by us. Otherwise, we don't have any memory allocated.
         */
        if (virtio_mem_bbm_get_bb_state(vm, bb_id) !=
            VIRTIO_MEM_BBM_BB_FAKE_OFFLINE)
                return;
        virtio_mem_fake_offline_going_offline(pfn, nr_pages);
}

static void virtio_mem_bbm_notify_cancel_offline(struct virtio_mem *vm,
                                                 unsigned long bb_id,
                                                 unsigned long pfn,
                                                 unsigned long nr_pages)
{
        if (virtio_mem_bbm_get_bb_state(vm, bb_id) !=
            VIRTIO_MEM_BBM_BB_FAKE_OFFLINE)
                return;
        virtio_mem_fake_offline_cancel_offline(pfn, nr_pages);
}

/*
 * This callback will either be called synchronously from add_memory() or
 * asynchronously (e.g., triggered via user space). We have to be careful
 * with locking when calling add_memory().
 */
static int virtio_mem_memory_notifier_cb(struct notifier_block *nb,
                                         unsigned long action, void *arg)
{
        struct virtio_mem *vm = container_of(nb, struct virtio_mem,
                                             memory_notifier);
        struct memory_notify *mhp = arg;
        const unsigned long start = PFN_PHYS(mhp->start_pfn);
        const unsigned long size = PFN_PHYS(mhp->nr_pages);
        int rc = NOTIFY_OK;
        unsigned long id;

        if (!virtio_mem_overlaps_range(vm, start, size))
                return NOTIFY_DONE;

        if (vm->in_sbm) {
                id = virtio_mem_phys_to_mb_id(start);
                /*
                 * In SBM, we add memory in separate memory blocks - we expect
                 * it to be onlined/offlined in the same granularity. Bail out
                 * if this ever changes.
                 */
                if (WARN_ON_ONCE(size != memory_block_size_bytes() ||
                                 !IS_ALIGNED(start, memory_block_size_bytes())))
                        return NOTIFY_BAD;
        } else {
                id = virtio_mem_phys_to_bb_id(vm, start);
                /*
                 * In BBM, we only care about onlining/offlining happening
                 * within a single big block, we don't care about the
                 * actual granularity as we don't track individual Linux
                 * memory blocks.
                 */
                if (WARN_ON_ONCE(id != virtio_mem_phys_to_bb_id(vm, start + size - 1)))
                        return NOTIFY_BAD;
        }

        /*
         * Avoid circular locking lockdep warnings. We lock the mutex
         * e.g., in MEM_GOING_ONLINE and unlock it in MEM_ONLINE. The
         * blocking_notifier_call_chain() has it's own lock, which gets unlocked
         * between both notifier calls and will bail out. False positive.
         */
        lockdep_off();

        switch (action) {
        case MEM_GOING_OFFLINE:
                mutex_lock(&vm->hotplug_mutex);
                if (vm->removing) {
                        rc = notifier_from_errno(-EBUSY);
                        mutex_unlock(&vm->hotplug_mutex);
                        break;
                }
                vm->hotplug_active = true;
                if (vm->in_sbm)
                        virtio_mem_sbm_notify_going_offline(vm, id);
                else
                        virtio_mem_bbm_notify_going_offline(vm, id,
                                                            mhp->start_pfn,
                                                            mhp->nr_pages);
                break;
        case MEM_GOING_ONLINE:
                mutex_lock(&vm->hotplug_mutex);
                if (vm->removing) {
                        rc = notifier_from_errno(-EBUSY);
                        mutex_unlock(&vm->hotplug_mutex);
                        break;
                }
                vm->hotplug_active = true;
                if (vm->in_sbm)
                        rc = virtio_mem_sbm_notify_going_online(vm, id);
                break;
        case MEM_OFFLINE:
                if (vm->in_sbm)
                        virtio_mem_sbm_notify_offline(vm, id);

                atomic64_add(size, &vm->offline_size);
                /*
                 * Trigger the workqueue. Now that we have some offline memory,
                 * maybe we can handle pending unplug requests.
                 */
                if (!unplug_online)
                        virtio_mem_retry(vm);

                vm->hotplug_active = false;
                mutex_unlock(&vm->hotplug_mutex);
                break;
        case MEM_ONLINE:
                if (vm->in_sbm)
                        virtio_mem_sbm_notify_online(vm, id, mhp->start_pfn);

                atomic64_sub(size, &vm->offline_size);
                /*
                 * Start adding more memory once we onlined half of our
                 * threshold. Don't trigger if it's possibly due to our actipn
                 * (e.g., us adding memory which gets onlined immediately from
                 * the core).
                 */
                if (!atomic_read(&vm->wq_active) &&
                    virtio_mem_could_add_memory(vm, vm->offline_threshold / 2))
                        virtio_mem_retry(vm);

                vm->hotplug_active = false;
                mutex_unlock(&vm->hotplug_mutex);
                break;
        case MEM_CANCEL_OFFLINE:
                if (!vm->hotplug_active)
                        break;
                if (vm->in_sbm)
                        virtio_mem_sbm_notify_cancel_offline(vm, id);
                else
                        virtio_mem_bbm_notify_cancel_offline(vm, id,
                                                             mhp->start_pfn,
                                                             mhp->nr_pages);
                vm->hotplug_active = false;
                mutex_unlock(&vm->hotplug_mutex);
                break;
        case MEM_CANCEL_ONLINE:
                if (!vm->hotplug_active)
                        break;
                vm->hotplug_active = false;
                mutex_unlock(&vm->hotplug_mutex);
                break;
        default:
                break;
        }

        lockdep_on();

        return rc;
}

static int virtio_mem_pm_notifier_cb(struct notifier_block *nb,
                                     unsigned long action, void *arg)
{
        struct virtio_mem *vm = container_of(nb, struct virtio_mem,
                                             pm_notifier);
        switch (action) {
        case PM_HIBERNATION_PREPARE:
        case PM_RESTORE_PREPARE:
                /*
                 * When restarting the VM, all memory is unplugged. Don't
                 * allow to hibernate and restore from an image.
                 */
                dev_err(&vm->vdev->dev, "hibernation is not supported.\n");
                return NOTIFY_BAD;
        default:
                return NOTIFY_OK;
        }
}

/*
 * Set a range of pages PG_offline. Remember pages that were never onlined
 * (via generic_online_page()) using PageDirty().
 */
static void virtio_mem_set_fake_offline(unsigned long pfn,
                                        unsigned long nr_pages, bool onlined)
{
        page_offline_begin();
        for (; nr_pages--; pfn++) {
                struct page *page = pfn_to_page(pfn);

                if (!onlined)
                        /*
                         * Pages that have not been onlined yet were initialized
                         * to PageOffline(). Remember that we have to route them
                         * through generic_online_page().
                         */
                        SetPageDirty(page);
                else
                        __SetPageOffline(page);
                VM_WARN_ON_ONCE(!PageOffline(page));
        }
        page_offline_end();
}

/*
 * Clear PG_offline from a range of pages. If the pages were never onlined,
 * (via generic_online_page()), clear PageDirty().
 */
static void virtio_mem_clear_fake_offline(unsigned long pfn,
                                          unsigned long nr_pages, bool onlined)
{
        for (; nr_pages--; pfn++) {
                struct page *page = pfn_to_page(pfn);

                if (!onlined)
                        /* generic_online_page() will clear PageOffline(). */
                        ClearPageDirty(page);
                else
                        __ClearPageOffline(page);
        }
}

/*
 * Release a range of fake-offline pages to the buddy, effectively
 * fake-onlining them.
 */
static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages)
{
        unsigned long order = MAX_PAGE_ORDER;
        unsigned long i;

        /*
         * We might get called for ranges that don't cover properly aligned
         * MAX_PAGE_ORDER pages; however, we can only online properly aligned
         * pages with an order of MAX_PAGE_ORDER at maximum.
         */
        while (!IS_ALIGNED(pfn | nr_pages, 1 << order))
                order--;

        for (i = 0; i < nr_pages; i += 1 << order) {
                struct page *page = pfn_to_page(pfn + i);

                /*
                 * If the page is PageDirty(), it was kept fake-offline when
                 * onlining the memory block. Otherwise, it was allocated
                 * using alloc_contig_range(). All pages in a subblock are
                 * alike.
                 */
                if (PageDirty(page)) {
                        virtio_mem_clear_fake_offline(pfn + i, 1 << order, false);
                        generic_online_page(page, order);
                } else {
                        virtio_mem_clear_fake_offline(pfn + i, 1 << order, true);
                        free_contig_range(pfn + i, 1 << order);
                        adjust_managed_page_count(page, 1 << order);
                }
        }
}

/*
 * Try to allocate a range, marking pages fake-offline, effectively
 * fake-offlining them.
 */
static int virtio_mem_fake_offline(struct virtio_mem *vm, unsigned long pfn,
                                   unsigned long nr_pages)
{
        const bool is_movable = is_zone_movable_page(pfn_to_page(pfn));
        int rc, retry_count;

        /*
         * TODO: We want an alloc_contig_range() mode that tries to allocate
         * harder (e.g., dealing with temporarily pinned pages, PCP), especially
         * with ZONE_MOVABLE. So for now, retry a couple of times with
         * ZONE_MOVABLE before giving up - because that zone is supposed to give
         * some guarantees.
         */
        for (retry_count = 0; retry_count < 5; retry_count++) {
                /*
                 * If the config changed, stop immediately and go back to the
                 * main loop: avoid trying to keep unplugging if the device
                 * might have decided to not remove any more memory.
                 */
                if (atomic_read(&vm->config_changed))
                        return -EAGAIN;

                rc = alloc_contig_range(pfn, pfn + nr_pages, MIGRATE_MOVABLE,
                                        GFP_KERNEL);
                if (rc == -ENOMEM)
                        /* whoops, out of memory */
                        return rc;
                else if (rc && !is_movable)
                        break;
                else if (rc)
                        continue;

                virtio_mem_set_fake_offline(pfn, nr_pages, true);
                adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
                return 0;
        }

        return -EBUSY;
}

/*
 * Handle fake-offline pages when memory is going offline - such that the
 * pages can be skipped by mm-core when offlining.
 */
static void virtio_mem_fake_offline_going_offline(unsigned long pfn,
                                                  unsigned long nr_pages)
{
        struct page *page;
        unsigned long i;

        /* Drop our reference to the pages so the memory can get offlined. */
        for (i = 0; i < nr_pages; i++) {
                page = pfn_to_page(pfn + i);
                if (WARN_ON(!page_ref_dec_and_test(page)))
                        dump_page(page, "fake-offline page referenced");
        }
}

/*
 * Handle fake-offline pages when memory offlining is canceled - to undo
 * what we did in virtio_mem_fake_offline_going_offline().
 */
static void virtio_mem_fake_offline_cancel_offline(unsigned long pfn,
                                                   unsigned long nr_pages)
{
        unsigned long i;

        /*
         * Get the reference again that we dropped via page_ref_dec_and_test()
         * when going offline.
         */
        for (i = 0; i < nr_pages; i++)
                page_ref_inc(pfn_to_page(pfn + i));
}

static void virtio_mem_online_page(struct virtio_mem *vm,
                                   struct page *page, unsigned int order)
{
        const unsigned long start = page_to_phys(page);
        const unsigned long end = start + PFN_PHYS(1 << order);
        unsigned long addr, next, id, sb_id, count;
        bool do_online;

        /*
         * We can get called with any order up to MAX_PAGE_ORDER. If our subblock
         * size is smaller than that and we have a mixture of plugged and
         * unplugged subblocks within such a page, we have to process in
         * smaller granularity. In that case we'll adjust the order exactly once
         * within the loop.
         */
        for (addr = start; addr < end; ) {
                next = addr + PFN_PHYS(1 << order);

                if (vm->in_sbm) {
                        id = virtio_mem_phys_to_mb_id(addr);
                        sb_id = virtio_mem_phys_to_sb_id(vm, addr);
                        count = virtio_mem_phys_to_sb_id(vm, next - 1) - sb_id + 1;

                        if (virtio_mem_sbm_test_sb_plugged(vm, id, sb_id, count)) {
                                /* Fully plugged. */
                                do_online = true;
                        } else if (count == 1 ||
                                   virtio_mem_sbm_test_sb_unplugged(vm, id, sb_id, count)) {
                                /* Fully unplugged. */
                                do_online = false;
                        } else {
                                /*
                                 * Mixture, process sub-blocks instead. This
                                 * will be at least the size of a pageblock.
                                 * We'll run into this case exactly once.
                                 */
                                order = ilog2(vm->sbm.sb_size) - PAGE_SHIFT;
                                do_online = virtio_mem_sbm_test_sb_plugged(vm, id, sb_id, 1);
                                continue;
                        }
                } else {
                        /*
                         * If the whole block is marked fake offline, keep
                         * everything that way.
                         */
                        id = virtio_mem_phys_to_bb_id(vm, addr);
                        do_online = virtio_mem_bbm_get_bb_state(vm, id) !=
                                    VIRTIO_MEM_BBM_BB_FAKE_OFFLINE;
                }

                if (do_online)
                        generic_online_page(pfn_to_page(PFN_DOWN(addr)), order);
                else
                        virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order,
                                                    false);
                addr = next;
        }
}

static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
{
        const unsigned long addr = page_to_phys(page);
        struct virtio_mem *vm;

        rcu_read_lock();
        list_for_each_entry_rcu(vm, &virtio_mem_devices, next) {
                /*
                 * Pages we're onlining will never cross memory blocks and,
                 * therefore, not virtio-mem devices.
                 */
                if (!virtio_mem_contains_range(vm, addr, PFN_PHYS(1 << order)))
                        continue;

                /*
                 * virtio_mem_set_fake_offline() might sleep. We can safely
                 * drop the RCU lock at this point because the device
                 * cannot go away. See virtio_mem_remove() how races
                 * between memory onlining and device removal are handled.
                 */
                rcu_read_unlock();

                virtio_mem_online_page(vm, page, order);
                return;
        }
        rcu_read_unlock();

        /* not virtio-mem memory, but e.g., a DIMM. online it */
        generic_online_page(page, order);
}

static uint64_t virtio_mem_send_request(struct virtio_mem *vm,
                                        const struct virtio_mem_req *req)
{
        struct scatterlist *sgs[2], sg_req, sg_resp;
        unsigned int len;
        int rc;

        /* don't use the request residing on the stack (vaddr) */
        vm->req = *req;

        /* out: buffer for request */
        sg_init_one(&sg_req, &vm->req, sizeof(vm->req));
        sgs[0] = &sg_req;

        /* in: buffer for response */
        sg_init_one(&sg_resp, &vm->resp, sizeof(vm->resp));
        sgs[1] = &sg_resp;

        rc = virtqueue_add_sgs(vm->vq, sgs, 1, 1, vm, GFP_KERNEL);
        if (rc < 0)
                return rc;

        virtqueue_kick(vm->vq);

        /* wait for a response */
        wait_event(vm->host_resp, virtqueue_get_buf(vm->vq, &len));

        return virtio16_to_cpu(vm->vdev, vm->resp.type);
}

static int virtio_mem_send_plug_request(struct virtio_mem *vm, uint64_t addr,
                                        uint64_t size)
{
        const uint64_t nb_vm_blocks = size / vm->device_block_size;
        const struct virtio_mem_req req = {
                .type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_PLUG),
                .u.plug.addr = cpu_to_virtio64(vm->vdev, addr),
                .u.plug.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
        };
        int rc = -ENOMEM;

        if (atomic_read(&vm->config_changed))
                return -EAGAIN;

        dev_dbg(&vm->vdev->dev, "plugging memory: 0x%llx - 0x%llx\n", addr,
                addr + size - 1);

        switch (virtio_mem_send_request(vm, &req)) {
        case VIRTIO_MEM_RESP_ACK:
                vm->plugged_size += size;
                return 0;
        case VIRTIO_MEM_RESP_NACK:
                rc = -EAGAIN;
                break;
        case VIRTIO_MEM_RESP_BUSY:
                rc = -ETXTBSY;
                break;
        case VIRTIO_MEM_RESP_ERROR:
                rc = -EINVAL;
                break;
        default:
                break;
        }

        dev_dbg(&vm->vdev->dev, "plugging memory failed: %d\n", rc);
        return rc;
}

static int virtio_mem_send_unplug_request(struct virtio_mem *vm, uint64_t addr,
                                          uint64_t size)
{
        const uint64_t nb_vm_blocks = size / vm->device_block_size;
        const struct virtio_mem_req req = {
                .type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_UNPLUG),
                .u.unplug.addr = cpu_to_virtio64(vm->vdev, addr),
                .u.unplug.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
        };
        int rc = -ENOMEM;

        if (atomic_read(&vm->config_changed))
                return -EAGAIN;

        dev_dbg(&vm->vdev->dev, "unplugging memory: 0x%llx - 0x%llx\n", addr,
                addr + size - 1);

        switch (virtio_mem_send_request(vm, &req)) {
        case VIRTIO_MEM_RESP_ACK:
                vm->plugged_size -= size;
                return 0;
        case VIRTIO_MEM_RESP_BUSY:
                rc = -ETXTBSY;
                break;
        case VIRTIO_MEM_RESP_ERROR:
                rc = -EINVAL;
                break;
        default:
                break;
        }

        dev_dbg(&vm->vdev->dev, "unplugging memory failed: %d\n", rc);
        return rc;
}

static int virtio_mem_send_unplug_all_request(struct virtio_mem *vm)
{
        const struct virtio_mem_req req = {
                .type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_UNPLUG_ALL),
        };
        int rc = -ENOMEM;

        dev_dbg(&vm->vdev->dev, "unplugging all memory");

        switch (virtio_mem_send_request(vm, &req)) {
        case VIRTIO_MEM_RESP_ACK:
                vm->unplug_all_required = false;
                vm->plugged_size = 0;
                /* usable region might have shrunk */
                atomic_set(&vm->config_changed, 1);
                return 0;
        case VIRTIO_MEM_RESP_BUSY:
                rc = -ETXTBSY;
                break;
        default:
                break;
        }

        dev_dbg(&vm->vdev->dev, "unplugging all memory failed: %d\n", rc);
        return rc;
}

/*
 * Plug selected subblocks. Updates the plugged state, but not the state
 * of the memory block.
 */
static int virtio_mem_sbm_plug_sb(struct virtio_mem *vm, unsigned long mb_id,
                                  int sb_id, int count)
{
        const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id) +
                              sb_id * vm->sbm.sb_size;
        const uint64_t size = count * vm->sbm.sb_size;
        int rc;

        rc = virtio_mem_send_plug_request(vm, addr, size);
        if (!rc)
                virtio_mem_sbm_set_sb_plugged(vm, mb_id, sb_id, count);
        return rc;
}

/*
 * Unplug selected subblocks. Updates the plugged state, but not the state
 * of the memory block.
 */
static int virtio_mem_sbm_unplug_sb(struct virtio_mem *vm, unsigned long mb_id,
                                    int sb_id, int count)
{
        const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id) +
                              sb_id * vm->sbm.sb_size;
        const uint64_t size = count * vm->sbm.sb_size;
        int rc;

        rc = virtio_mem_send_unplug_request(vm, addr, size);
        if (!rc)
                virtio_mem_sbm_set_sb_unplugged(vm, mb_id, sb_id, count);
        return rc;
}

/*
 * Request to unplug a big block.
 *
 * Will not modify the state of the big block.
 */
static int virtio_mem_bbm_unplug_bb(struct virtio_mem *vm, unsigned long bb_id)
{
        const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
        const uint64_t size = vm->bbm.bb_size;

        return virtio_mem_send_unplug_request(vm, addr, size);
}

/*
 * Request to plug a big block.
 *
 * Will not modify the state of the big block.
 */
static int virtio_mem_bbm_plug_bb(struct virtio_mem *vm, unsigned long bb_id)
{
        const uint64_t addr = virtio_mem_bb_id_to_phys(vm, bb_id);
        const uint64_t size = vm->bbm.bb_size;

        return virtio_mem_send_plug_request(vm, addr, size);
}

/*
 * Unplug the desired number of plugged subblocks of a offline or not-added
 * memory block. Will fail if any subblock cannot get unplugged (instead of
 * skipping it).
 *
 * Will not modify the state of the memory block.
 *
 * Note: can fail after some subblocks were unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb_raw(struct virtio_mem *vm,
                                            unsigned long mb_id, uint64_t *nb_sb)
{
        int sb_id, count;
        int rc;

        sb_id = vm->sbm.sbs_per_mb - 1;
        while (*nb_sb) {
                /* Find the next candidate subblock */
                while (sb_id >= 0 &&
                       virtio_mem_sbm_test_sb_unplugged(vm, mb_id, sb_id, 1))
                        sb_id--;
                if (sb_id < 0)
                        break;
                /* Try to unplug multiple subblocks at a time */
                count = 1;
                while (count < *nb_sb && sb_id > 0 &&
                       virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id - 1, 1)) {
                        count++;
                        sb_id--;
                }

                rc = virtio_mem_sbm_unplug_sb(vm, mb_id, sb_id, count);
                if (rc)
                        return rc;
                *nb_sb -= count;
                sb_id--;
        }

        return 0;
}

/*
 * Unplug all plugged subblocks of an offline or not-added memory block.
 *
 * Will not modify the state of the memory block.
 *
 * Note: can fail after some subblocks were unplugged.
 */
static int virtio_mem_sbm_unplug_mb(struct virtio_mem *vm, unsigned long mb_id)
{
        uint64_t nb_sb = vm->sbm.sbs_per_mb;

        return virtio_mem_sbm_unplug_any_sb_raw(vm, mb_id, &nb_sb);
}

/*
 * Prepare tracking data for the next memory block.
 */
static int virtio_mem_sbm_prepare_next_mb(struct virtio_mem *vm,
                                          unsigned long *mb_id)
{
        int rc;

        if (vm->sbm.next_mb_id > vm->sbm.last_usable_mb_id)
                return -ENOSPC;

        /* Resize the state array if required. */
        rc = virtio_mem_sbm_mb_states_prepare_next_mb(vm);
        if (rc)
                return rc;

        /* Resize the subblock bitmap if required. */
        rc = virtio_mem_sbm_sb_states_prepare_next_mb(vm);
        if (rc)
                return rc;

        vm->sbm.mb_count[VIRTIO_MEM_SBM_MB_UNUSED]++;
        *mb_id = vm->sbm.next_mb_id++;
        return 0;
}

/*
 * Try to plug the desired number of subblocks and add the memory block
 * to Linux.
 *
 * Will modify the state of the memory block.
 */
static int virtio_mem_sbm_plug_and_add_mb(struct virtio_mem *vm,
                                          unsigned long mb_id, uint64_t *nb_sb)
{
        const int count = min_t(int, *nb_sb, vm->sbm.sbs_per_mb);
        int rc;

        if (WARN_ON_ONCE(!count))
                return -EINVAL;

        /*
         * Plug the requested number of subblocks before adding it to linux,
         * so that onlining will directly online all plugged subblocks.
         */
        rc = virtio_mem_sbm_plug_sb(vm, mb_id, 0, count);
        if (rc)
                return rc;

        /*
         * Mark the block properly offline before adding it to Linux,
         * so the memory notifiers will find the block in the right state.
         */
        if (count == vm->sbm.sbs_per_mb)
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_OFFLINE);
        else
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL);

        /* Add the memory block to linux - if that fails, try to unplug. */
        rc = virtio_mem_sbm_add_mb(vm, mb_id);
        if (rc) {
                int new_state = VIRTIO_MEM_SBM_MB_UNUSED;

                if (virtio_mem_sbm_unplug_sb(vm, mb_id, 0, count))
                        new_state = VIRTIO_MEM_SBM_MB_PLUGGED;
                virtio_mem_sbm_set_mb_state(vm, mb_id, new_state);
                return rc;
        }

        *nb_sb -= count;
        return 0;
}

/*
 * Try to plug the desired number of subblocks of a memory block that
 * is already added to Linux.
 *
 * Will modify the state of the memory block.
 *
 * Note: Can fail after some subblocks were successfully plugged.
 */
static int virtio_mem_sbm_plug_any_sb(struct virtio_mem *vm,
                                      unsigned long mb_id, uint64_t *nb_sb)
{
        const int old_state = virtio_mem_sbm_get_mb_state(vm, mb_id);
        unsigned long pfn, nr_pages;
        int sb_id, count;
        int rc;

        if (WARN_ON_ONCE(!*nb_sb))
                return -EINVAL;

        while (*nb_sb) {
                sb_id = virtio_mem_sbm_first_unplugged_sb(vm, mb_id);
                if (sb_id >= vm->sbm.sbs_per_mb)
                        break;
                count = 1;
                while (count < *nb_sb &&
                       sb_id + count < vm->sbm.sbs_per_mb &&
                       !virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id + count, 1))
                        count++;

                rc = virtio_mem_sbm_plug_sb(vm, mb_id, sb_id, count);
                if (rc)
                        return rc;
                *nb_sb -= count;
                if (old_state == VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL)
                        continue;

                /* fake-online the pages if the memory block is online */
                pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
                               sb_id * vm->sbm.sb_size);
                nr_pages = PFN_DOWN(count * vm->sbm.sb_size);
                virtio_mem_fake_online(pfn, nr_pages);
        }

        if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, 0, vm->sbm.sbs_per_mb))
                virtio_mem_sbm_set_mb_state(vm, mb_id, old_state - 1);

        return 0;
}

static int virtio_mem_sbm_plug_request(struct virtio_mem *vm, uint64_t diff)
{
        const int mb_states[] = {
                VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL,
                VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL,
                VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL,
        };
        uint64_t nb_sb = diff / vm->sbm.sb_size;
        unsigned long mb_id;
        int rc, i;

        if (!nb_sb)
                return 0;

        /* Don't race with onlining/offlining */
        mutex_lock(&vm->hotplug_mutex);

        for (i = 0; i < ARRAY_SIZE(mb_states); i++) {
                virtio_mem_sbm_for_each_mb(vm, mb_id, mb_states[i]) {
                        rc = virtio_mem_sbm_plug_any_sb(vm, mb_id, &nb_sb);
                        if (rc || !nb_sb)
                                goto out_unlock;
                        cond_resched();
                }
        }

        /*
         * We won't be working on online/offline memory blocks from this point,
         * so we can't race with memory onlining/offlining. Drop the mutex.
         */
        mutex_unlock(&vm->hotplug_mutex);

        /* Try to plug and add unused blocks */
        virtio_mem_sbm_for_each_mb(vm, mb_id, VIRTIO_MEM_SBM_MB_UNUSED) {
                if (!virtio_mem_could_add_memory(vm, memory_block_size_bytes()))
                        return -ENOSPC;

                rc = virtio_mem_sbm_plug_and_add_mb(vm, mb_id, &nb_sb);
                if (rc || !nb_sb)
                        return rc;
                cond_resched();
        }

        /* Try to prepare, plug and add new blocks */
        while (nb_sb) {
                if (!virtio_mem_could_add_memory(vm, memory_block_size_bytes()))
                        return -ENOSPC;

                rc = virtio_mem_sbm_prepare_next_mb(vm, &mb_id);
                if (rc)
                        return rc;
                rc = virtio_mem_sbm_plug_and_add_mb(vm, mb_id, &nb_sb);
                if (rc)
                        return rc;
                cond_resched();
        }

        return 0;
out_unlock:
        mutex_unlock(&vm->hotplug_mutex);
        return rc;
}

/*
 * Plug a big block and add it to Linux.
 *
 * Will modify the state of the big block.
 */
static int virtio_mem_bbm_plug_and_add_bb(struct virtio_mem *vm,
                                          unsigned long bb_id)
{
        int rc;

        if (WARN_ON_ONCE(virtio_mem_bbm_get_bb_state(vm, bb_id) !=
                         VIRTIO_MEM_BBM_BB_UNUSED))
                return -EINVAL;

        rc = virtio_mem_bbm_plug_bb(vm, bb_id);
        if (rc)
                return rc;
        virtio_mem_bbm_set_bb_state(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED);

        rc = virtio_mem_bbm_add_bb(vm, bb_id);
        if (rc) {
                if (!virtio_mem_bbm_unplug_bb(vm, bb_id))
                        virtio_mem_bbm_set_bb_state(vm, bb_id,
                                                    VIRTIO_MEM_BBM_BB_UNUSED);
                else
                        /* Retry from the main loop. */
                        virtio_mem_bbm_set_bb_state(vm, bb_id,
                                                    VIRTIO_MEM_BBM_BB_PLUGGED);
                return rc;
        }
        return 0;
}

/*
 * Prepare tracking data for the next big block.
 */
static int virtio_mem_bbm_prepare_next_bb(struct virtio_mem *vm,
                                          unsigned long *bb_id)
{
        int rc;

        if (vm->bbm.next_bb_id > vm->bbm.last_usable_bb_id)
                return -ENOSPC;

        /* Resize the big block state array if required. */
        rc = virtio_mem_bbm_bb_states_prepare_next_bb(vm);
        if (rc)
                return rc;

        vm->bbm.bb_count[VIRTIO_MEM_BBM_BB_UNUSED]++;
        *bb_id = vm->bbm.next_bb_id;
        vm->bbm.next_bb_id++;
        return 0;
}

static int virtio_mem_bbm_plug_request(struct virtio_mem *vm, uint64_t diff)
{
        uint64_t nb_bb = diff / vm->bbm.bb_size;
        unsigned long bb_id;
        int rc;

        if (!nb_bb)
                return 0;

        /* Try to plug and add unused big blocks */
        virtio_mem_bbm_for_each_bb(vm, bb_id, VIRTIO_MEM_BBM_BB_UNUSED) {
                if (!virtio_mem_could_add_memory(vm, vm->bbm.bb_size))
                        return -ENOSPC;

                rc = virtio_mem_bbm_plug_and_add_bb(vm, bb_id);
                if (!rc)
                        nb_bb--;
                if (rc || !nb_bb)
                        return rc;
                cond_resched();
        }

        /* Try to prepare, plug and add new big blocks */
        while (nb_bb) {
                if (!virtio_mem_could_add_memory(vm, vm->bbm.bb_size))
                        return -ENOSPC;

                rc = virtio_mem_bbm_prepare_next_bb(vm, &bb_id);
                if (rc)
                        return rc;
                rc = virtio_mem_bbm_plug_and_add_bb(vm, bb_id);
                if (!rc)
                        nb_bb--;
                if (rc)
                        return rc;
                cond_resched();
        }

        return 0;
}

/*
 * Try to plug the requested amount of memory.
 */
static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
{
        if (vm->in_sbm)
                return virtio_mem_sbm_plug_request(vm, diff);
        return virtio_mem_bbm_plug_request(vm, diff);
}

/*
 * Unplug the desired number of plugged subblocks of an offline memory block.
 * Will fail if any subblock cannot get unplugged (instead of skipping it).
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 *
 * Note: Can fail after some subblocks were successfully unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb_offline(struct virtio_mem *vm,
                                                unsigned long mb_id,
                                                uint64_t *nb_sb)
{
        int rc;

        rc = virtio_mem_sbm_unplug_any_sb_raw(vm, mb_id, nb_sb);

        /* some subblocks might have been unplugged even on failure */
        if (!virtio_mem_sbm_test_sb_plugged(vm, mb_id, 0, vm->sbm.sbs_per_mb))
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL);
        if (rc)
                return rc;

        if (virtio_mem_sbm_test_sb_unplugged(vm, mb_id, 0, vm->sbm.sbs_per_mb)) {
                /*
                 * Remove the block from Linux - this should never fail.
                 * Hinder the block from getting onlined by marking it
                 * unplugged. Temporarily drop the mutex, so
                 * any pending GOING_ONLINE requests can be serviced/rejected.
                 */
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_UNUSED);

                mutex_unlock(&vm->hotplug_mutex);
                rc = virtio_mem_sbm_remove_mb(vm, mb_id);
                BUG_ON(rc);
                mutex_lock(&vm->hotplug_mutex);
        }
        return 0;
}

/*
 * Unplug the given plugged subblocks of an online memory block.
 *
 * Will modify the state of the memory block.
 */
static int virtio_mem_sbm_unplug_sb_online(struct virtio_mem *vm,
                                           unsigned long mb_id, int sb_id,
                                           int count)
{
        const unsigned long nr_pages = PFN_DOWN(vm->sbm.sb_size) * count;
        const int old_state = virtio_mem_sbm_get_mb_state(vm, mb_id);
        unsigned long start_pfn;
        int rc;

        start_pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
                             sb_id * vm->sbm.sb_size);

        rc = virtio_mem_fake_offline(vm, start_pfn, nr_pages);
        if (rc)
                return rc;

        /* Try to unplug the allocated memory */
        rc = virtio_mem_sbm_unplug_sb(vm, mb_id, sb_id, count);
        if (rc) {
                /* Return the memory to the buddy. */
                virtio_mem_fake_online(start_pfn, nr_pages);
                return rc;
        }

        switch (old_state) {
        case VIRTIO_MEM_SBM_MB_KERNEL:
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL);
                break;
        case VIRTIO_MEM_SBM_MB_MOVABLE:
                virtio_mem_sbm_set_mb_state(vm, mb_id,
                                            VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL);
                break;
        }

        return 0;
}

/*
 * Unplug the desired number of plugged subblocks of an online memory block.
 * Will skip subblock that are busy.
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 *
 * Note: Can fail after some subblocks were successfully unplugged. Can
 *       return 0 even if subblocks were busy and could not get unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb_online(struct virtio_mem *vm,
                                               unsigned long mb_id,
                                               uint64_t *nb_sb)
{
        int rc, sb_id;

        /* If possible, try to unplug the complete block in one shot. */
        if (*nb_sb >= vm->sbm.sbs_per_mb &&
            virtio_mem_sbm_test_sb_plugged(vm, mb_id, 0, vm->sbm.sbs_per_mb)) {
                rc = virtio_mem_sbm_unplug_sb_online(vm, mb_id, 0,
                                                     vm->sbm.sbs_per_mb);
                if (!rc) {
                        *nb_sb -= vm->sbm.sbs_per_mb;
                        goto unplugged;
                } else if (rc != -EBUSY)
                        return rc;
        }

        /* Fallback to single subblocks. */
        for (sb_id = vm->sbm.sbs_per_mb - 1; sb_id >= 0 && *nb_sb; sb_id--) {
                /* Find the next candidate subblock */
                while (sb_id >= 0 &&
                       !virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
                        sb_id--;
                if (sb_id < 0)
                        break;

                rc = virtio_mem_sbm_unplug_sb_online(vm, mb_id, sb_id, 1);
                if (rc == -EBUSY)
                        continue;
                else if (rc)
                        return rc;
                *nb_sb -= 1;
        }

unplugged:
        rc = virtio_mem_sbm_try_remove_unplugged_mb(vm, mb_id);
        if (rc)
                vm->sbm.have_unplugged_mb = 1;
        /* Ignore errors, this is not critical. We'll retry later. */
        return 0;
}

/*
 * Unplug the desired number of plugged subblocks of a memory block that is
 * already added to Linux. Will skip subblock of online memory blocks that are
 * busy (by the OS). Will fail if any subblock that's not busy cannot get
 * unplugged.
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 *
 * Note: Can fail after some subblocks were successfully unplugged. Can
 *       return 0 even if subblocks were busy and could not get unplugged.
 */
static int virtio_mem_sbm_unplug_any_sb(struct virtio_mem *vm,
                                        unsigned long mb_id,
                                        uint64_t *nb_sb)
{
        const int old_state = virtio_mem_sbm_get_mb_state(vm, mb_id);

        switch (old_state) {
        case VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL:
        case VIRTIO_MEM_SBM_MB_KERNEL:
        case VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL:
        case VIRTIO_MEM_SBM_MB_MOVABLE:
                return virtio_mem_sbm_unplug_any_sb_online(vm, mb_id, nb_sb);
        case VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL:
        case VIRTIO_MEM_SBM_MB_OFFLINE:
                return virtio_mem_sbm_unplug_any_sb_offline(vm, mb_id, nb_sb);
        }
        return -EINVAL;
}

static int virtio_mem_sbm_unplug_request(struct virtio_mem *vm, uint64_t diff)
{
        const int mb_states[] = {
                VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL,
                VIRTIO_MEM_SBM_MB_OFFLINE,
                VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL,
                VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL,
                VIRTIO_MEM_SBM_MB_MOVABLE,
                VIRTIO_MEM_SBM_MB_KERNEL,
        };
        uint64_t nb_sb = diff / vm->sbm.sb_size;
        unsigned long mb_id;
        int rc, i;

        if (!nb_sb)
                return 0;

        /*
         * We'll drop the mutex a couple of times when it is safe to do so.
         * This might result in some blocks switching the state (online/offline)
         * and we could miss them in this run - we will retry again later.
         */
        mutex_lock(&vm->hotplug_mutex);

        /*
         * We try unplug from partially plugged blocks first, to try removing
         * whole memory blocks along with metadata. We prioritize ZONE_MOVABLE
         * as it's more reliable to unplug memory and remove whole memory
         * blocks, and we don't want to trigger a zone imbalances by
         * accidentially removing too much kernel memory.
         */
        for (i = 0; i < ARRAY_SIZE(mb_states); i++) {
                virtio_mem_sbm_for_each_mb_rev(vm, mb_id, mb_states[i]) {
                        rc = virtio_mem_sbm_unplug_any_sb(vm, mb_id, &nb_sb);
                        if (rc || !nb_sb)
                                goto out_unlock;
                        mutex_unlock(&vm->hotplug_mutex);
                        cond_resched();
                        mutex_lock(&vm->hotplug_mutex);
                }
                if (!unplug_online && i == 1) {
                        mutex_unlock(&vm->hotplug_mutex);
                        return 0;
                }
        }

        mutex_unlock(&vm->hotplug_mutex);
        return nb_sb ? -EBUSY : 0;
out_unlock:
        mutex_unlock(&vm->hotplug_mutex);
        return rc;
}

/*
 * Try to offline and remove a big block from Linux and unplug it. Will fail
 * with -EBUSY if some memory is busy and cannot get unplugged.
 *
 * Will modify the state of the memory block. Might temporarily drop the
 * hotplug_mutex.
 */
static int virtio_mem_bbm_offline_remove_and_unplug_bb(struct virtio_mem *vm,
                                                       unsigned long bb_id)
{
        const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));
        const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);
        unsigned long end_pfn = start_pfn + nr_pages;
        unsigned long pfn;
        struct page *page;
        int rc;

        if (WARN_ON_ONCE(virtio_mem_bbm_get_bb_state(vm, bb_id) !=
                         VIRTIO_MEM_BBM_BB_ADDED))
                return -EINVAL;

        /*
         * Start by fake-offlining all memory. Once we marked the device
         * block as fake-offline, all newly onlined memory will
         * automatically be kept fake-offline. Protect from concurrent
         * onlining/offlining until we have a consistent state.
         */
        mutex_lock(&vm->hotplug_mutex);
        virtio_mem_bbm_set_bb_state(vm, bb_id, VIRTIO_MEM_BBM_BB_FAKE_OFFLINE);

        for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
                page = pfn_to_online_page(pfn);
                if (!page)
                        continue;

                rc = virtio_mem_fake_offline(vm, pfn, PAGES_PER_SECTION);
                if (rc) {
                        end_pfn = pfn;
                        goto rollback;
                }
        }
        mutex_unlock(&vm->hotplug_mutex);

        rc = virtio_mem_bbm_offline_and_remove_bb(vm, bb_id);
        if (rc) {
                mutex_lock(&vm->hotplug_mutex);
                goto rollback;
        }

        rc = virtio_mem_bbm_unplug_bb(vm, bb_id);
        if (rc)
                virtio_mem_bbm_set_bb_state(vm, bb_id,
                                            VIRTIO_MEM_BBM_BB_PLUGGED);
        else
                virtio_mem_bbm_set_bb_state(vm, bb_id,
                                            VIRTIO_MEM_BBM_BB_UNUSED);
        return rc;

rollback:
        for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
                page = pfn_to_online_page(pfn);
                if (!page)
                        continue;
                virtio_mem_fake_online(pfn, PAGES_PER_SECTION);
        }
        virtio_mem_bbm_set_bb_state(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED);
        mutex_unlock(&vm->hotplug_mutex);
        return rc;
}

/*
 * Test if a big block is completely offline.
 */
static bool virtio_mem_bbm_bb_is_offline(struct virtio_mem *vm,
                                         unsigned long bb_id)
{
        const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));
        const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);
        unsigned long pfn;

        for (pfn = start_pfn; pfn < start_pfn + nr_pages;
             pfn += PAGES_PER_SECTION) {
                if (pfn_to_online_page(pfn))
                        return false;
        }

        return true;
}

/*
 * Test if a big block is completely onlined to ZONE_MOVABLE (or offline).
 */
static bool virtio_mem_bbm_bb_is_movable(struct virtio_mem *vm,
                                         unsigned long bb_id)
{
        const unsigned long start_pfn = PFN_DOWN(virtio_mem_bb_id_to_phys(vm, bb_id));
        const unsigned long nr_pages = PFN_DOWN(vm->bbm.bb_size);
        struct page *page;
        unsigned long pfn;

        for (pfn = start_pfn; pfn < start_pfn + nr_pages;
             pfn += PAGES_PER_SECTION) {
                page = pfn_to_online_page(pfn);
                if (!page)
                        continue;
                if (page_zonenum(page) != ZONE_MOVABLE)
                        return false;
        }

        return true;
}

static int virtio_mem_bbm_unplug_request(struct virtio_mem *vm, uint64_t diff)
{
        uint64_t nb_bb = diff / vm->bbm.bb_size;
        uint64_t bb_id;
        int rc, i;

        if (!nb_bb)
                return 0;

        /*
         * Try to unplug big blocks. Similar to SBM, start with offline
         * big blocks.
         */
        for (i = 0; i < 3; i++) {
                virtio_mem_bbm_for_each_bb_rev(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED) {
                        cond_resched();

                        /*
                         * As we're holding no locks, these checks are racy,
                         * but we don't care.
                         */
                        if (i == 0 && !virtio_mem_bbm_bb_is_offline(vm, bb_id))
                                continue;
                        if (i == 1 && !virtio_mem_bbm_bb_is_movable(vm, bb_id))
                                continue;
                        rc = virtio_mem_bbm_offline_remove_and_unplug_bb(vm, bb_id);
                        if (rc == -EBUSY)
                                continue;
                        if (!rc)
                                nb_bb--;
                        if (rc || !nb_bb)
                                return rc;
                }
                if (i == 0 && !unplug_online)
                        return 0;
        }

        return nb_bb ? -EBUSY : 0;
}

/*
 * Try to unplug the requested amount of memory.
 */
static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
{
        if (vm->in_sbm)
                return virtio_mem_sbm_unplug_request(vm, diff);
        return virtio_mem_bbm_unplug_request(vm, diff);
}

/*
 * Try to unplug all blocks that couldn't be unplugged before, for example,
 * because the hypervisor was busy. Further, offline and remove any memory
 * blocks where we previously failed.
 */
static int virtio_mem_cleanup_pending_mb(struct virtio_mem *vm)
{
        unsigned long id;
        int rc = 0;

        if (!vm->in_sbm) {
                virtio_mem_bbm_for_each_bb(vm, id,
                                           VIRTIO_MEM_BBM_BB_PLUGGED) {
                        rc = virtio_mem_bbm_unplug_bb(vm, id);
                        if (rc)
                                return rc;
                        virtio_mem_bbm_set_bb_state(vm, id,
                                                    VIRTIO_MEM_BBM_BB_UNUSED);
                }
                return 0;
        }

        virtio_mem_sbm_for_each_mb(vm, id, VIRTIO_MEM_SBM_MB_PLUGGED) {
                rc = virtio_mem_sbm_unplug_mb(vm, id);
                if (rc)
                        return rc;
                virtio_mem_sbm_set_mb_state(vm, id,
                                            VIRTIO_MEM_SBM_MB_UNUSED);
        }

        if (!vm->sbm.have_unplugged_mb)
                return 0;

        /*
         * Let's retry (offlining and) removing completely unplugged Linux
         * memory blocks.
         */
        vm->sbm.have_unplugged_mb = false;

        mutex_lock(&vm->hotplug_mutex);
        virtio_mem_sbm_for_each_mb(vm, id, VIRTIO_MEM_SBM_MB_MOVABLE_PARTIAL)
                rc |= virtio_mem_sbm_try_remove_unplugged_mb(vm, id);
        virtio_mem_sbm_for_each_mb(vm, id, VIRTIO_MEM_SBM_MB_KERNEL_PARTIAL)
                rc |= virtio_mem_sbm_try_remove_unplugged_mb(vm, id);
        virtio_mem_sbm_for_each_mb(vm, id, VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL)
                rc |= virtio_mem_sbm_try_remove_unplugged_mb(vm, id);
        mutex_unlock(&vm->hotplug_mutex);

        if (rc)
                vm->sbm.have_unplugged_mb = true;
        /* Ignore errors, this is not critical. We'll retry later. */
        return 0;
}

/*
 * Update all parts of the config that could have changed.
 */
static void virtio_mem_refresh_config(struct virtio_mem *vm)
{
        const struct range pluggable_range = mhp_get_pluggable_range(true);
        uint64_t new_plugged_size, usable_region_size, end_addr;

        /* the plugged_size is just a reflection of what _we_ did previously */
        virtio_cread_le(vm->vdev, struct virtio_mem_config, plugged_size,
                        &new_plugged_size);
        if (WARN_ON_ONCE(new_plugged_size != vm->plugged_size))
                vm->plugged_size = new_plugged_size;

        /* calculate the last usable memory block id */
        virtio_cread_le(vm->vdev, struct virtio_mem_config,
                        usable_region_size, &usable_region_size);
        end_addr = min(vm->addr + usable_region_size - 1,
                       pluggable_range.end);

        if (vm->in_sbm) {
                vm->sbm.last_usable_mb_id = virtio_mem_phys_to_mb_id(end_addr);
                if (!IS_ALIGNED(end_addr + 1, memory_block_size_bytes()))
                        vm->sbm.last_usable_mb_id--;
        } else {
                vm->bbm.last_usable_bb_id = virtio_mem_phys_to_bb_id(vm,
                                                                     end_addr);
                if (!IS_ALIGNED(end_addr + 1, vm->bbm.bb_size))
                        vm->bbm.last_usable_bb_id--;
        }
        /*
         * If we cannot plug any of our device memory (e.g., nothing in the
         * usable region is addressable), the last usable memory block id will
         * be smaller than the first usable memory block id. We'll stop
         * attempting to add memory with -ENOSPC from our main loop.
         */

        /* see if there is a request to change the size */
        virtio_cread_le(vm->vdev, struct virtio_mem_config, requested_size,
                        &vm->requested_size);

        dev_info(&vm->vdev->dev, "plugged size: 0x%llx", vm->plugged_size);
        dev_info(&vm->vdev->dev, "requested size: 0x%llx", vm->requested_size);
}

/*
 * Workqueue function for handling plug/unplug requests and config updates.
 */
static void virtio_mem_run_wq(struct work_struct *work)
{
        struct virtio_mem *vm = container_of(work, struct virtio_mem, wq);
        uint64_t diff;
        int rc;

        if (unlikely(vm->in_kdump)) {
                dev_warn_once(&vm->vdev->dev,
                             "unexpected workqueue run in kdump kernel\n");
                return;
        }

        hrtimer_cancel(&vm->retry_timer);

        if (vm->broken)
                return;

        atomic_set(&vm->wq_active, 1);
retry:
        rc = 0;

        /* Make sure we start with a clean state if there are leftovers. */
        if (unlikely(vm->unplug_all_required))
                rc = virtio_mem_send_unplug_all_request(vm);

        if (atomic_read(&vm->config_changed)) {
                atomic_set(&vm->config_changed, 0);
                virtio_mem_refresh_config(vm);
        }

        /* Cleanup any leftovers from previous runs */
        if (!rc)
                rc = virtio_mem_cleanup_pending_mb(vm);

        if (!rc && vm->requested_size != vm->plugged_size) {
                if (vm->requested_size > vm->plugged_size) {
                        diff = vm->requested_size - vm->plugged_size;
                        rc = virtio_mem_plug_request(vm, diff);
                } else {
                        diff = vm->plugged_size - vm->requested_size;
                        rc = virtio_mem_unplug_request(vm, diff);
                }
        }

        /*
         * Keep retrying to offline and remove completely unplugged Linux
         * memory blocks.
         */
        if (!rc && vm->in_sbm && vm->sbm.have_unplugged_mb)
                rc = -EBUSY;

        switch (rc) {
        case 0:
                vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
                break;
        case -ENOSPC:
                /*
                 * We cannot add any more memory (alignment, physical limit)
                 * or we have too many offline memory blocks.
                 */
                break;
        case -ETXTBSY:
                /*
                 * The hypervisor cannot process our request right now
                 * (e.g., out of memory, migrating);
                 */
        case -EBUSY:
                /*
                 * We cannot free up any memory to unplug it (all plugged memory
                 * is busy).
                 */
        case -ENOMEM:
                /* Out of memory, try again later. */
                hrtimer_start(&vm->retry_timer, ms_to_ktime(vm->retry_timer_ms),
                              HRTIMER_MODE_REL);
                break;
        case -EAGAIN:
                /* Retry immediately (e.g., the config changed). */
                goto retry;
        default:
                /* Unknown error, mark as broken */
                dev_err(&vm->vdev->dev,
                        "unknown error, marking device broken: %d\n", rc);
                vm->broken = true;
        }

        atomic_set(&vm->wq_active, 0);
}

static enum hrtimer_restart virtio_mem_timer_expired(struct hrtimer *timer)
{
        struct virtio_mem *vm = container_of(timer, struct virtio_mem,
                                             retry_timer);

        virtio_mem_retry(vm);
        vm->retry_timer_ms = min_t(unsigned int, vm->retry_timer_ms * 2,
                                   VIRTIO_MEM_RETRY_TIMER_MAX_MS);
        return HRTIMER_NORESTART;
}

static void virtio_mem_handle_response(struct virtqueue *vq)
{
        struct virtio_mem *vm = vq->vdev->priv;

        wake_up(&vm->host_resp);
}

static int virtio_mem_init_vq(struct virtio_mem *vm)
{
        struct virtqueue *vq;

        vq = virtio_find_single_vq(vm->vdev, virtio_mem_handle_response,
                                   "guest-request");
        if (IS_ERR(vq))
                return PTR_ERR(vq);
        vm->vq = vq;

        return 0;
}

static int virtio_mem_init_hotplug(struct virtio_mem *vm)
{
        const struct range pluggable_range = mhp_get_pluggable_range(true);
        uint64_t unit_pages, sb_size, addr;
        int rc;

        /* bad device setup - warn only */
        if (!IS_ALIGNED(vm->addr, memory_block_size_bytes()))
                dev_warn(&vm->vdev->dev,
                         "The alignment of the physical start address can make some memory unusable.\n");
        if (!IS_ALIGNED(vm->addr + vm->region_size, memory_block_size_bytes()))
                dev_warn(&vm->vdev->dev,
                         "The alignment of the physical end address can make some memory unusable.\n");
        if (vm->addr < pluggable_range.start ||
            vm->addr + vm->region_size - 1 > pluggable_range.end)
                dev_warn(&vm->vdev->dev,
                         "Some device memory is not addressable/pluggable. This can make some memory unusable.\n");

        /* Prepare the offline threshold - make sure we can add two blocks. */
        vm->offline_threshold = max_t(uint64_t, 2 * memory_block_size_bytes(),
                                      VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD);

        /*
         * alloc_contig_range() works reliably with pageblock
         * granularity on ZONE_NORMAL, use pageblock_nr_pages.
         */
        sb_size = PAGE_SIZE * pageblock_nr_pages;
        sb_size = max_t(uint64_t, vm->device_block_size, sb_size);

        if (sb_size < memory_block_size_bytes() && !force_bbm) {
                /* SBM: At least two subblocks per Linux memory block. */
                vm->in_sbm = true;
                vm->sbm.sb_size = sb_size;
                vm->sbm.sbs_per_mb = memory_block_size_bytes() /
                                     vm->sbm.sb_size;

                /* Round up to the next full memory block */
                addr = max_t(uint64_t, vm->addr, pluggable_range.start) +
                       memory_block_size_bytes() - 1;
                vm->sbm.first_mb_id = virtio_mem_phys_to_mb_id(addr);
                vm->sbm.next_mb_id = vm->sbm.first_mb_id;
        } else {
                /* BBM: At least one Linux memory block. */
                vm->bbm.bb_size = max_t(uint64_t, vm->device_block_size,
                                        memory_block_size_bytes());

                if (bbm_block_size) {
                        if (!is_power_of_2(bbm_block_size)) {
                                dev_warn(&vm->vdev->dev,
                                         "bbm_block_size is not a power of 2");
                        } else if (bbm_block_size < vm->bbm.bb_size) {
                                dev_warn(&vm->vdev->dev,
                                         "bbm_block_size is too small");
                        } else {
                                vm->bbm.bb_size = bbm_block_size;
                        }
                }

                /* Round up to the next aligned big block */
                addr = max_t(uint64_t, vm->addr, pluggable_range.start) +
                       vm->bbm.bb_size - 1;
                vm->bbm.first_bb_id = virtio_mem_phys_to_bb_id(vm, addr);
                vm->bbm.next_bb_id = vm->bbm.first_bb_id;

                /* Make sure we can add two big blocks. */
                vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
                                              vm->offline_threshold);
        }

        dev_info(&vm->vdev->dev, "memory block size: 0x%lx",
                 memory_block_size_bytes());
        if (vm->in_sbm)
                dev_info(&vm->vdev->dev, "subblock size: 0x%llx",
                         (unsigned long long)vm->sbm.sb_size);
        else
                dev_info(&vm->vdev->dev, "big block size: 0x%llx",
                         (unsigned long long)vm->bbm.bb_size);

        /* create the parent resource for all memory */
        rc = virtio_mem_create_resource(vm);
        if (rc)
                return rc;

        /* use a single dynamic memory group to cover the whole memory device */
        if (vm->in_sbm)
                unit_pages = PHYS_PFN(memory_block_size_bytes());
        else
                unit_pages = PHYS_PFN(vm->bbm.bb_size);
        rc = memory_group_register_dynamic(vm->nid, unit_pages);
        if (rc < 0)
                goto out_del_resource;
        vm->mgid = rc;

        /*
         * If we still have memory plugged, we have to unplug all memory first.
         * Registering our parent resource makes sure that this memory isn't
         * actually in use (e.g., trying to reload the driver).
         */
        if (vm->plugged_size) {
                vm->unplug_all_required = true;
                dev_info(&vm->vdev->dev, "unplugging all memory is required\n");
        }

        /* register callbacks */
        vm->memory_notifier.notifier_call = virtio_mem_memory_notifier_cb;
        rc = register_memory_notifier(&vm->memory_notifier);
        if (rc)
                goto out_unreg_group;
        /* Block hibernation as early as possible. */
        vm->pm_notifier.priority = INT_MAX;
        vm->pm_notifier.notifier_call = virtio_mem_pm_notifier_cb;
        rc = register_pm_notifier(&vm->pm_notifier);
        if (rc)
                goto out_unreg_mem;
        rc = register_virtio_mem_device(vm);
        if (rc)
                goto out_unreg_pm;

        return 0;
out_unreg_pm:
        unregister_pm_notifier(&vm->pm_notifier);
out_unreg_mem:
        unregister_memory_notifier(&vm->memory_notifier);
out_unreg_group:
        memory_group_unregister(vm->mgid);
out_del_resource:
        virtio_mem_delete_resource(vm);
        return rc;
}

#ifdef CONFIG_PROC_VMCORE
static int virtio_mem_send_state_request(struct virtio_mem *vm, uint64_t addr,
                                         uint64_t size)
{
        const uint64_t nb_vm_blocks = size / vm->device_block_size;
        const struct virtio_mem_req req = {
                .type = cpu_to_virtio16(vm->vdev, VIRTIO_MEM_REQ_STATE),
                .u.state.addr = cpu_to_virtio64(vm->vdev, addr),
                .u.state.nb_blocks = cpu_to_virtio16(vm->vdev, nb_vm_blocks),
        };
        int rc = -ENOMEM;

        dev_dbg(&vm->vdev->dev, "requesting state: 0x%llx - 0x%llx\n", addr,
                addr + size - 1);

        switch (virtio_mem_send_request(vm, &req)) {
        case VIRTIO_MEM_RESP_ACK:
                return virtio16_to_cpu(vm->vdev, vm->resp.u.state.state);
        case VIRTIO_MEM_RESP_ERROR:
                rc = -EINVAL;
                break;
        default:
                break;
        }

        dev_dbg(&vm->vdev->dev, "requesting state failed: %d\n", rc);
        return rc;
}

static bool virtio_mem_vmcore_pfn_is_ram(struct vmcore_cb *cb,
                                         unsigned long pfn)
{
        struct virtio_mem *vm = container_of(cb, struct virtio_mem,
                                             vmcore_cb);
        uint64_t addr = PFN_PHYS(pfn);
        bool is_ram;
        int rc;

        if (!virtio_mem_contains_range(vm, addr, PAGE_SIZE))
                return true;
        if (!vm->plugged_size)
                return false;

        /*
         * We have to serialize device requests and access to the information
         * about the block queried last.
         */
        mutex_lock(&vm->hotplug_mutex);

        addr = ALIGN_DOWN(addr, vm->device_block_size);
        if (addr != vm->last_block_addr) {
                rc = virtio_mem_send_state_request(vm, addr,
                                                   vm->device_block_size);
                /* On any kind of error, we're going to signal !ram. */
                if (rc == VIRTIO_MEM_STATE_PLUGGED)
                        vm->last_block_plugged = true;
                else
                        vm->last_block_plugged = false;
                vm->last_block_addr = addr;
        }

        is_ram = vm->last_block_plugged;
        mutex_unlock(&vm->hotplug_mutex);
        return is_ram;
}
#endif /* CONFIG_PROC_VMCORE */

static int virtio_mem_init_kdump(struct virtio_mem *vm)
{
#ifdef CONFIG_PROC_VMCORE
        dev_info(&vm->vdev->dev, "memory hot(un)plug disabled in kdump kernel\n");
        vm->vmcore_cb.pfn_is_ram = virtio_mem_vmcore_pfn_is_ram;
        register_vmcore_cb(&vm->vmcore_cb);
        return 0;
#else /* CONFIG_PROC_VMCORE */
        dev_warn(&vm->vdev->dev, "disabled in kdump kernel without vmcore\n");
        return -EBUSY;
#endif /* CONFIG_PROC_VMCORE */
}

static int virtio_mem_init(struct virtio_mem *vm)
{
        uint16_t node_id;

        if (!vm->vdev->config->get) {
                dev_err(&vm->vdev->dev, "config access disabled\n");
                return -EINVAL;
        }

        /* Fetch all properties that can't change. */
        virtio_cread_le(vm->vdev, struct virtio_mem_config, plugged_size,
                        &vm->plugged_size);
        virtio_cread_le(vm->vdev, struct virtio_mem_config, block_size,
                        &vm->device_block_size);
        virtio_cread_le(vm->vdev, struct virtio_mem_config, node_id,
                        &node_id);
        vm->nid = virtio_mem_translate_node_id(vm, node_id);
        virtio_cread_le(vm->vdev, struct virtio_mem_config, addr, &vm->addr);
        virtio_cread_le(vm->vdev, struct virtio_mem_config, region_size,
                        &vm->region_size);

        /* Determine the nid for the device based on the lowest address. */
        if (vm->nid == NUMA_NO_NODE)
                vm->nid = memory_add_physaddr_to_nid(vm->addr);

        dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
        dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size);
        dev_info(&vm->vdev->dev, "device block size: 0x%llx",
                 (unsigned long long)vm->device_block_size);
        if (vm->nid != NUMA_NO_NODE && IS_ENABLED(CONFIG_NUMA))
                dev_info(&vm->vdev->dev, "nid: %d", vm->nid);

        /*
         * We don't want to (un)plug or reuse any memory when in kdump. The
         * memory is still accessible (but not exposed to Linux).
         */
        if (vm->in_kdump)
                return virtio_mem_init_kdump(vm);
        return virtio_mem_init_hotplug(vm);
}

static int virtio_mem_create_resource(struct virtio_mem *vm)
{
        /*
         * When force-unloading the driver and removing the device, we
         * could have a garbage pointer. Duplicate the string.
         */
        const char *name = kstrdup(dev_name(&vm->vdev->dev), GFP_KERNEL);

        if (!name)
                return -ENOMEM;

        /* Disallow mapping device memory via /dev/mem completely. */
        vm->parent_resource = __request_mem_region(vm->addr, vm->region_size,
                                                   name, IORESOURCE_SYSTEM_RAM |
                                                   IORESOURCE_EXCLUSIVE);
        if (!vm->parent_resource) {
                kfree(name);
                dev_warn(&vm->vdev->dev, "could not reserve device region\n");
                dev_info(&vm->vdev->dev,
                         "reloading the driver is not supported\n");
                return -EBUSY;
        }

        /* The memory is not actually busy - make add_memory() work. */
        vm->parent_resource->flags &= ~IORESOURCE_BUSY;
        return 0;
}

static void virtio_mem_delete_resource(struct virtio_mem *vm)
{
        const char *name;

        if (!vm->parent_resource)
                return;

        name = vm->parent_resource->name;
        release_resource(vm->parent_resource);
        kfree(vm->parent_resource);
        kfree(name);
        vm->parent_resource = NULL;
}

static int virtio_mem_range_has_system_ram(struct resource *res, void *arg)
{
        return 1;
}

static bool virtio_mem_has_memory_added(struct virtio_mem *vm)
{
        const unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;

        return walk_iomem_res_desc(IORES_DESC_NONE, flags, vm->addr,
                                   vm->addr + vm->region_size, NULL,
                                   virtio_mem_range_has_system_ram) == 1;
}

static int virtio_mem_probe(struct virtio_device *vdev)
{
        struct virtio_mem *vm;
        int rc;

        BUILD_BUG_ON(sizeof(struct virtio_mem_req) != 24);
        BUILD_BUG_ON(sizeof(struct virtio_mem_resp) != 10);

        vdev->priv = vm = kzalloc(sizeof(*vm), GFP_KERNEL);
        if (!vm)
                return -ENOMEM;

        init_waitqueue_head(&vm->host_resp);
        vm->vdev = vdev;
        INIT_WORK(&vm->wq, virtio_mem_run_wq);
        mutex_init(&vm->hotplug_mutex);
        INIT_LIST_HEAD(&vm->next);
        spin_lock_init(&vm->removal_lock);
        hrtimer_init(&vm->retry_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        vm->retry_timer.function = virtio_mem_timer_expired;
        vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
        vm->in_kdump = is_kdump_kernel();

        /* register the virtqueue */
        rc = virtio_mem_init_vq(vm);
        if (rc)
                goto out_free_vm;

        /* initialize the device by querying the config */
        rc = virtio_mem_init(vm);
        if (rc)
                goto out_del_vq;

        virtio_device_ready(vdev);

        /* trigger a config update to start processing the requested_size */
        if (!vm->in_kdump) {
                atomic_set(&vm->config_changed, 1);
                queue_work(system_freezable_wq, &vm->wq);
        }

        return 0;
out_del_vq:
        vdev->config->del_vqs(vdev);
out_free_vm:
        kfree(vm);
        vdev->priv = NULL;

        return rc;
}

static void virtio_mem_deinit_hotplug(struct virtio_mem *vm)
{
        unsigned long mb_id;
        int rc;

        /*
         * Make sure the workqueue won't be triggered anymore and no memory
         * blocks can be onlined/offlined until we're finished here.
         */
        mutex_lock(&vm->hotplug_mutex);
        spin_lock_irq(&vm->removal_lock);
        vm->removing = true;
        spin_unlock_irq(&vm->removal_lock);
        mutex_unlock(&vm->hotplug_mutex);

        /* wait until the workqueue stopped */
        cancel_work_sync(&vm->wq);
        hrtimer_cancel(&vm->retry_timer);

        if (vm->in_sbm) {
                /*
                 * After we unregistered our callbacks, user space can online
                 * partially plugged offline blocks. Make sure to remove them.
                 */
                virtio_mem_sbm_for_each_mb(vm, mb_id,
                                           VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL) {
                        rc = virtio_mem_sbm_remove_mb(vm, mb_id);
                        BUG_ON(rc);
                        virtio_mem_sbm_set_mb_state(vm, mb_id,
                                                    VIRTIO_MEM_SBM_MB_UNUSED);
                }
                /*
                 * After we unregistered our callbacks, user space can no longer
                 * offline partially plugged online memory blocks. No need to
                 * worry about them.
                 */
        }

        /* unregister callbacks */
        unregister_virtio_mem_device(vm);
        unregister_pm_notifier(&vm->pm_notifier);
        unregister_memory_notifier(&vm->memory_notifier);

        /*
         * There is no way we could reliably remove all memory we have added to
         * the system. And there is no way to stop the driver/device from going
         * away. Warn at least.
         */
        if (virtio_mem_has_memory_added(vm)) {
                dev_warn(&vm->vdev->dev,
                         "device still has system memory added\n");
        } else {
                virtio_mem_delete_resource(vm);
                kfree_const(vm->resource_name);
                memory_group_unregister(vm->mgid);
        }

        /* remove all tracking data - no locking needed */
        if (vm->in_sbm) {
                vfree(vm->sbm.mb_states);
                vfree(vm->sbm.sb_states);
        } else {
                vfree(vm->bbm.bb_states);
        }
}

static void virtio_mem_deinit_kdump(struct virtio_mem *vm)
{
#ifdef CONFIG_PROC_VMCORE
        unregister_vmcore_cb(&vm->vmcore_cb);
#endif /* CONFIG_PROC_VMCORE */
}

static void virtio_mem_remove(struct virtio_device *vdev)
{
        struct virtio_mem *vm = vdev->priv;

        if (vm->in_kdump)
                virtio_mem_deinit_kdump(vm);
        else
                virtio_mem_deinit_hotplug(vm);

        /* reset the device and cleanup the queues */
        virtio_reset_device(vdev);
        vdev->config->del_vqs(vdev);

        kfree(vm);
        vdev->priv = NULL;
}

static void virtio_mem_config_changed(struct virtio_device *vdev)
{
        struct virtio_mem *vm = vdev->priv;

        if (unlikely(vm->in_kdump))
                return;

        atomic_set(&vm->config_changed, 1);
        virtio_mem_retry(vm);
}

#ifdef CONFIG_PM_SLEEP
static int virtio_mem_freeze(struct virtio_device *vdev)
{
        struct virtio_mem *vm = vdev->priv;

        /*
         * We block hibernation using the PM notifier completely. The workqueue
         * is already frozen by the PM core at this point, so we simply
         * reset the device and cleanup the queues.
         */
        if (pm_suspend_target_state != PM_SUSPEND_TO_IDLE &&
            vm->plugged_size &&
            !virtio_has_feature(vm->vdev, VIRTIO_MEM_F_PERSISTENT_SUSPEND)) {
                dev_err(&vm->vdev->dev,
                        "suspending with plugged memory is not supported\n");
                return -EPERM;
        }

        virtio_reset_device(vdev);
        vdev->config->del_vqs(vdev);
        vm->vq = NULL;
        return 0;
}

static int virtio_mem_restore(struct virtio_device *vdev)
{
        struct virtio_mem *vm = vdev->priv;
        int ret;

        ret = virtio_mem_init_vq(vm);
        if (ret)
                return ret;
        virtio_device_ready(vdev);

        /* Let's check if anything changed. */
        virtio_mem_config_changed(vdev);
        return 0;
}
#endif

static unsigned int virtio_mem_features[] = {
#if defined(CONFIG_NUMA) && defined(CONFIG_ACPI_NUMA)
        VIRTIO_MEM_F_ACPI_PXM,
#endif
        VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE,
        VIRTIO_MEM_F_PERSISTENT_SUSPEND,
};

static const struct virtio_device_id virtio_mem_id_table[] = {
        { VIRTIO_ID_MEM, VIRTIO_DEV_ANY_ID },
        { 0 },
};

static struct virtio_driver virtio_mem_driver = {
        .feature_table = virtio_mem_features,
        .feature_table_size = ARRAY_SIZE(virtio_mem_features),
        .driver.name = KBUILD_MODNAME,
        .id_table = virtio_mem_id_table,
        .probe = virtio_mem_probe,
        .remove = virtio_mem_remove,
        .config_changed = virtio_mem_config_changed,
#ifdef CONFIG_PM_SLEEP
        .freeze =       virtio_mem_freeze,
        .restore =      virtio_mem_restore,
#endif
};

module_virtio_driver(virtio_mem_driver);
MODULE_DEVICE_TABLE(virtio, virtio_mem_id_table);
MODULE_AUTHOR("David Hildenbrand <david@redhat.com>");
MODULE_DESCRIPTION("Virtio-mem driver");
MODULE_LICENSE("GPL");