Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

Pull virtio updates from Michael Tsirkin:

- vdpa sim refactoring

- virtio mem: Big Block Mode support

- misc cleanus, fixes

* tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost: (61 commits)
vdpa: Use simpler version of ida allocation
vdpa: Add missing comment for virtqueue count
uapi: virtio_ids: add missing device type IDs from OASIS spec
uapi: virtio_ids.h: consistent indentions
vhost scsi: fix error return code in vhost_scsi_set_endpoint()
virtio_ring: Fix two use after free bugs
virtio_net: Fix error code in probe()
virtio_ring: Cut and paste bugs in vring_create_virtqueue_packed()
tools/virtio: add barrier for aarch64
tools/virtio: add krealloc_array
tools/virtio: include asm/bug.h
vdpa/mlx5: Use write memory barrier after updating CQ index
vdpa: split vdpasim to core and net modules
vdpa_sim: split vdpasim_virtqueue's iov field in out_iov and in_iov
vdpa_sim: make vdpasim->buffer size configurable
vdpa_sim: use kvmalloc to allocate vdpasim->buffer
vdpa_sim: set vringh notify callback
vdpa_sim: add set_config callback in vdpasim_dev_attr
vdpa_sim: add get_config callback in vdpasim_dev_attr
vdpa_sim: make 'config' generic and usable for any device type
...

drivers/net/virtio_net.c

···
 			dev_err(&vdev->dev,
 				"device MTU appears to have changed it is now %d < %d",
 				mtu, dev->min_mtu);
+			err = -EINVAL;
 			goto free;
 		}
 

drivers/vdpa/Kconfig

···
 if VDPA
 
 config VDPA_SIM
-	tristate "vDPA device simulator"
+	tristate "vDPA device simulator core"
 	depends on RUNTIME_TESTING_MENU && HAS_DMA
 	select DMA_OPS
 	select VHOST_RING
-	select GENERIC_NET_UTILS
-	default n
 	help
-	  vDPA networking device simulator which loop TX traffic back
-	  to RX. This device is used for testing, prototyping and
-	  development of vDPA.
+	  Enable this module to support vDPA device simulators. These devices
+	  are used for testing, prototyping and development of vDPA.
+
+config VDPA_SIM_NET
+	tristate "vDPA simulator for networking device"
+	depends on VDPA_SIM
+	select GENERIC_NET_UTILS
+	help
+	  vDPA networking device simulator which loops TX traffic back to RX.
 
 config IFCVF
 	tristate "Intel IFC VF vDPA driver"
 	depends on PCI_MSI
-	default n
 	help
 	  This kernel module can drive Intel IFC VF NIC to offload
 	  virtio dataplane traffic to hardware.
···
 	tristate "vDPA driver for ConnectX devices"
 	select MLX5_VDPA
 	depends on MLX5_CORE
-	default n
 	help
 	  VDPA network driver for ConnectX6 and newer. Provides offloading
 	  of virtio net datapath such that descriptors put on the ring will

drivers/vdpa/ifcvf/ifcvf_main.c

···
 		return ret;
 	}
 
-	ret = pci_set_dma_mask(pdev, DMA_BIT_MASK(64));
+	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
 	if (ret) {
-		IFCVF_ERR(pdev, "No usable DMA confiugration\n");
-		return ret;
-	}
-
-	ret = pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(64));
-	if (ret) {
-		IFCVF_ERR(pdev,
-			  "No usable coherent DMA confiugration\n");
+		IFCVF_ERR(pdev, "No usable DMA configuration\n");
 		return ret;
 	}
 

drivers/vdpa/mlx5/net/mlx5_vnet.c

···
 static void mlx5_vdpa_handle_completions(struct mlx5_vdpa_virtqueue *mvq, int num)
 {
 	mlx5_cq_set_ci(&mvq->cq.mcq);
+
+	/* make sure CQ cosumer update is visible to the hardware before updating
+	 * RX doorbell record.
+	 */
+	dma_wmb();
 	rx_post(&mvq->vqqp, num);
 	if (mvq->event_cb.callback)
 		mvq->event_cb.callback(mvq->event_cb.private);

drivers/vdpa/vdpa.c

···
 	if (!vdev)
 		goto err;
 
-	err = ida_simple_get(&vdpa_index_ida, 0, 0, GFP_KERNEL);
+	err = ida_alloc(&vdpa_index_ida, GFP_KERNEL);
 	if (err < 0)
 		goto err_ida;
 

drivers/vdpa/vdpa_sim/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_VDPA_SIM) += vdpa_sim.o
+obj-$(CONFIG_VDPA_SIM_NET) += vdpa_sim_net.o

drivers/vdpa/vdpa_sim/vdpa_sim.c

···
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * VDPA networking device simulator.
+ * VDPA device simulator core.
  *
  * Copyright (c) 2020, Red Hat Inc. All rights reserved.
  *     Author: Jason Wang <[e-mail]>
···
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
-#include <linux/fs.h>
-#include <linux/poll.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
-#include <linux/wait.h>
-#include <linux/uuid.h>
-#include <linux/iommu.h>
 #include <linux/dma-map-ops.h>
-#include <linux/sysfs.h>
-#include <linux/file.h>
-#include <linux/etherdevice.h>
 #include <linux/vringh.h>
 #include <linux/vdpa.h>
-#include <linux/virtio_byteorder.h>
 #include <linux/vhost_iotlb.h>
-#include <uapi/linux/virtio_config.h>
-#include <uapi/linux/virtio_net.h>
+
+#include "vdpa_sim.h"
 
 #define DRV_VERSION  "0.1"
 #define DRV_AUTHOR   "Jason Wang <[e-mail]>"
-#define DRV_DESC     "vDPA Device Simulator"
+#define DRV_DESC     "vDPA Device Simulator core"
 #define DRV_LICENSE  "GPL v2"
 
 static int batch_mapping = 1;
 module_param(batch_mapping, int, 0444);
 MODULE_PARM_DESC(batch_mapping, "Batched mapping 1 -Enable; 0 - Disable");
 
-static char *macaddr;
-module_param(macaddr, charp, 0);
-MODULE_PARM_DESC(macaddr, "Ethernet MAC address");
-
-struct vdpasim_virtqueue {
-	struct vringh vring;
-	struct vringh_kiov iov;
-	unsigned short head;
-	bool ready;
-	u64 desc_addr;
-	u64 device_addr;
-	u64 driver_addr;
-	u32 num;
-	void *private;
-	irqreturn_t (*cb)(void *data);
-};
+static int max_iotlb_entries = 2048;
+module_param(max_iotlb_entries, int, 0444);
+MODULE_PARM_DESC(max_iotlb_entries,
+		 "Maximum number of iotlb entries. 0 means unlimited. (default: 2048)");
 
 #define VDPASIM_QUEUE_ALIGN PAGE_SIZE
 #define VDPASIM_QUEUE_MAX 256
-#define VDPASIM_DEVICE_ID 0x1
 #define VDPASIM_VENDOR_ID 0
-#define VDPASIM_VQ_NUM 0x2
-#define VDPASIM_NAME "vdpasim-netdev"
-
-static u64 vdpasim_features = (1ULL << VIRTIO_F_ANY_LAYOUT) |
-			      (1ULL << VIRTIO_F_VERSION_1)  |
-			      (1ULL << VIRTIO_F_ACCESS_PLATFORM) |
-			      (1ULL << VIRTIO_NET_F_MAC);
-
-/* State of each vdpasim device */
-struct vdpasim {
-	struct vdpa_device vdpa;
-	struct vdpasim_virtqueue vqs[VDPASIM_VQ_NUM];
-	struct work_struct work;
-	/* spinlock to synchronize virtqueue state */
-	spinlock_t lock;
-	struct virtio_net_config config;
-	struct vhost_iotlb *iommu;
-	void *buffer;
-	u32 status;
-	u32 generation;
-	u64 features;
-	/* spinlock to synchronize iommu table */
-	spinlock_t iommu_lock;
-};
-
-/* TODO: cross-endian support */
-static inline bool vdpasim_is_little_endian(struct vdpasim *vdpasim)
-{
-	return virtio_legacy_is_little_endian() ||
-		(vdpasim->features & (1ULL << VIRTIO_F_VERSION_1));
-}
-
-static inline u16 vdpasim16_to_cpu(struct vdpasim *vdpasim, __virtio16 val)
-{
-	return __virtio16_to_cpu(vdpasim_is_little_endian(vdpasim), val);
-}
-
-static inline __virtio16 cpu_to_vdpasim16(struct vdpasim *vdpasim, u16 val)
-{
-	return __cpu_to_virtio16(vdpasim_is_little_endian(vdpasim), val);
-}
-
-static struct vdpasim *vdpasim_dev;
 
 static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
 {
···
 	return vdpa_to_sim(vdpa);
 }
 
+static void vdpasim_vq_notify(struct vringh *vring)
+{
+	struct vdpasim_virtqueue *vq =
+		container_of(vring, struct vdpasim_virtqueue, vring);
+
+	if (!vq->cb)
+		return;
+
+	vq->cb(vq->private);
+}
+
 static void vdpasim_queue_ready(struct vdpasim *vdpasim, unsigned int idx)
 {
 	struct vdpasim_virtqueue *vq = &vdpasim->vqs[idx];
 
-	vringh_init_iotlb(&vq->vring, vdpasim_features,
+	vringh_init_iotlb(&vq->vring, vdpasim->dev_attr.supported_features,
 			  VDPASIM_QUEUE_MAX, false,
 			  (struct vring_desc *)(uintptr_t)vq->desc_addr,
 			  (struct vring_avail *)
 			  (uintptr_t)vq->driver_addr,
 			  (struct vring_used *)
 			  (uintptr_t)vq->device_addr);
+
+	vq->vring.notify = vdpasim_vq_notify;
 }
 
-static void vdpasim_vq_reset(struct vdpasim_virtqueue *vq)
+static void vdpasim_vq_reset(struct vdpasim *vdpasim,
+			     struct vdpasim_virtqueue *vq)
 {
 	vq->ready = false;
 	vq->desc_addr = 0;
···
 	vq->device_addr = 0;
 	vq->cb = NULL;
 	vq->private = NULL;
-	vringh_init_iotlb(&vq->vring, vdpasim_features, VDPASIM_QUEUE_MAX,
-			  false, NULL, NULL, NULL);
+	vringh_init_iotlb(&vq->vring, vdpasim->dev_attr.supported_features,
+			  VDPASIM_QUEUE_MAX, false, NULL, NULL, NULL);
+
+	vq->vring.notify = NULL;
 }
 
 static void vdpasim_reset(struct vdpasim *vdpasim)
 {
 	int i;
 
-	for (i = 0; i < VDPASIM_VQ_NUM; i++)
-		vdpasim_vq_reset(&vdpasim->vqs[i]);
+	for (i = 0; i < vdpasim->dev_attr.nvqs; i++)
+		vdpasim_vq_reset(vdpasim, &vdpasim->vqs[i]);
 
 	spin_lock(&vdpasim->iommu_lock);
 	vhost_iotlb_reset(vdpasim->iommu);
···
 	vdpasim->features = 0;
 	vdpasim->status = 0;
 	++vdpasim->generation;
-}
-
-static void vdpasim_work(struct work_struct *work)
-{
-	struct vdpasim *vdpasim = container_of(work, struct
-						 vdpasim, work);
-	struct vdpasim_virtqueue *txq = &vdpasim->vqs[1];
-	struct vdpasim_virtqueue *rxq = &vdpasim->vqs[0];
-	ssize_t read, write;
-	size_t total_write;
-	int pkts = 0;
-	int err;
-
-	spin_lock(&vdpasim->lock);
-
-	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
-		goto out;
-
-	if (!txq->ready || !rxq->ready)
-		goto out;
-
-	while (true) {
-		total_write = 0;
-		err = vringh_getdesc_iotlb(&txq->vring, &txq->iov, NULL,
-					   &txq->head, GFP_ATOMIC);
-		if (err <= 0)
-			break;
-
-		err = vringh_getdesc_iotlb(&rxq->vring, NULL, &rxq->iov,
-					   &rxq->head, GFP_ATOMIC);
-		if (err <= 0) {
-			vringh_complete_iotlb(&txq->vring, txq->head, 0);
-			break;
-		}
-
-		while (true) {
-			read = vringh_iov_pull_iotlb(&txq->vring, &txq->iov,
-						     vdpasim->buffer,
-						     PAGE_SIZE);
-			if (read <= 0)
-				break;
-
-			write = vringh_iov_push_iotlb(&rxq->vring, &rxq->iov,
-						      vdpasim->buffer, read);
-			if (write <= 0)
-				break;
-
-			total_write += write;
-		}
-
-		/* Make sure data is wrote before advancing index */
-		smp_wmb();
-
-		vringh_complete_iotlb(&txq->vring, txq->head, 0);
-		vringh_complete_iotlb(&rxq->vring, rxq->head, total_write);
-
-		/* Make sure used is visible before rasing the interrupt. */
-		smp_wmb();
-
-		local_bh_disable();
-		if (txq->cb)
-			txq->cb(txq->private);
-		if (rxq->cb)
-			rxq->cb(rxq->private);
-		local_bh_enable();
-
-		if (++pkts > 4) {
-			schedule_work(&vdpasim->work);
-			goto out;
-		}
-	}
-
-out:
-	spin_unlock(&vdpasim->lock);
 }
 
 static int dir_to_perm(enum dma_data_direction dir)
···
 	.free = vdpasim_free_coherent,
 };
 
-static const struct vdpa_config_ops vdpasim_net_config_ops;
-static const struct vdpa_config_ops vdpasim_net_batch_config_ops;
+static const struct vdpa_config_ops vdpasim_config_ops;
+static const struct vdpa_config_ops vdpasim_batch_config_ops;
 
-static struct vdpasim *vdpasim_create(void)
+struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr)
 {
 	const struct vdpa_config_ops *ops;
 	struct vdpasim *vdpasim;
 	struct device *dev;
-	int ret = -ENOMEM;
+	int i, ret = -ENOMEM;
 
 	if (batch_mapping)
-		ops = &vdpasim_net_batch_config_ops;
+		ops = &vdpasim_batch_config_ops;
 	else
-		ops = &vdpasim_net_config_ops;
+		ops = &vdpasim_config_ops;
 
-	vdpasim = vdpa_alloc_device(struct vdpasim, vdpa, NULL, ops, VDPASIM_VQ_NUM);
+	vdpasim = vdpa_alloc_device(struct vdpasim, vdpa, NULL, ops,
+				    dev_attr->nvqs);
 	if (!vdpasim)
 		goto err_alloc;
 
-	INIT_WORK(&vdpasim->work, vdpasim_work);
+	vdpasim->dev_attr = *dev_attr;
+	INIT_WORK(&vdpasim->work, dev_attr->work_fn);
 	spin_lock_init(&vdpasim->lock);
 	spin_lock_init(&vdpasim->iommu_lock);
 
···
 		goto err_iommu;
 	set_dma_ops(dev, &vdpasim_dma_ops);
 
-	vdpasim->iommu = vhost_iotlb_alloc(2048, 0);
+	vdpasim->config = kzalloc(dev_attr->config_size, GFP_KERNEL);
+	if (!vdpasim->config)
+		goto err_iommu;
+
+	vdpasim->vqs = kcalloc(dev_attr->nvqs, sizeof(struct vdpasim_virtqueue),
+			       GFP_KERNEL);
+	if (!vdpasim->vqs)
+		goto err_iommu;
+
+	vdpasim->iommu = vhost_iotlb_alloc(max_iotlb_entries, 0);
 	if (!vdpasim->iommu)
 		goto err_iommu;
 
-	vdpasim->buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	vdpasim->buffer = kvmalloc(dev_attr->buffer_size, GFP_KERNEL);
 	if (!vdpasim->buffer)
 		goto err_iommu;
 
-	if (macaddr) {
-		mac_pton(macaddr, vdpasim->config.mac);
-		if (!is_valid_ether_addr(vdpasim->config.mac)) {
-			ret = -EADDRNOTAVAIL;
-			goto err_iommu;
-		}
-	} else {
-		eth_random_addr(vdpasim->config.mac);
-	}
-
-	vringh_set_iotlb(&vdpasim->vqs[0].vring, vdpasim->iommu);
-	vringh_set_iotlb(&vdpasim->vqs[1].vring, vdpasim->iommu);
+	for (i = 0; i < dev_attr->nvqs; i++)
+		vringh_set_iotlb(&vdpasim->vqs[i].vring, vdpasim->iommu);
 
 	vdpasim->vdpa.dma_dev = dev;
-	ret = vdpa_register_device(&vdpasim->vdpa);
-	if (ret)
-		goto err_iommu;
 
 	return vdpasim;
 
···
 err_alloc:
 	return ERR_PTR(ret);
 }
+EXPORT_SYMBOL_GPL(vdpasim_create);
 
 static int vdpasim_set_vq_address(struct vdpa_device *vdpa, u16 idx,
 				  u64 desc_area, u64 driver_area,
···
 
 static u64 vdpasim_get_features(struct vdpa_device *vdpa)
 {
-	return vdpasim_features;
+	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
+
+	return vdpasim->dev_attr.supported_features;
 }
 
 static int vdpasim_set_features(struct vdpa_device *vdpa, u64 features)
 {
 	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
-	struct virtio_net_config *config = &vdpasim->config;
 
 	/* DMA mapping must be done by driver */
 	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)))
 		return -EINVAL;
 
-	vdpasim->features = features & vdpasim_features;
+	vdpasim->features = features & vdpasim->dev_attr.supported_features;
 
-	/* We generally only know whether guest is using the legacy interface
-	 * here, so generally that's the earliest we can set config fields.
-	 * Note: We actually require VIRTIO_F_ACCESS_PLATFORM above which
-	 * implies VIRTIO_F_VERSION_1, but let's not try to be clever here.
-	 */
-
-	config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
-	config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
 	return 0;
 }
 
···
 
 static u32 vdpasim_get_device_id(struct vdpa_device *vdpa)
 {
-	return VDPASIM_DEVICE_ID;
+	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
+
+	return vdpasim->dev_attr.id;
 }
 
 static u32 vdpasim_get_vendor_id(struct vdpa_device *vdpa)
···
 {
 	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
 
-	if (offset + len < sizeof(struct virtio_net_config))
-		memcpy(buf, (u8 *)&vdpasim->config + offset, len);
+	if (offset + len > vdpasim->dev_attr.config_size)
+		return;
+
+	if (vdpasim->dev_attr.get_config)
+		vdpasim->dev_attr.get_config(vdpasim, vdpasim->config);
+
+	memcpy(buf, vdpasim->config + offset, len);
 }
 
 static void vdpasim_set_config(struct vdpa_device *vdpa, unsigned int offset,
 			     const void *buf, unsigned int len)
 {
-	/* No writable config supportted by vdpasim */
+	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
+
+	if (offset + len > vdpasim->dev_attr.config_size)
+		return;
+
+	memcpy(vdpasim->config + offset, buf, len);
+
+	if (vdpasim->dev_attr.set_config)
+		vdpasim->dev_attr.set_config(vdpasim, vdpasim->config);
 }
 
 static u32 vdpasim_get_generation(struct vdpa_device *vdpa)
···
 	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
 
 	cancel_work_sync(&vdpasim->work);
-	kfree(vdpasim->buffer);
+	kvfree(vdpasim->buffer);
 	if (vdpasim->iommu)
 		vhost_iotlb_free(vdpasim->iommu);
+	kfree(vdpasim->vqs);
+	kfree(vdpasim->config);
 }
 
-static const struct vdpa_config_ops vdpasim_net_config_ops = {
+static const struct vdpa_config_ops vdpasim_config_ops = {
 	.set_vq_address         = vdpasim_set_vq_address,
 	.set_vq_num             = vdpasim_set_vq_num,
 	.kick_vq                = vdpasim_kick_vq,
···
 	.free                   = vdpasim_free,
 };
 
-static const struct vdpa_config_ops vdpasim_net_batch_config_ops = {
+static const struct vdpa_config_ops vdpasim_batch_config_ops = {
 	.set_vq_address         = vdpasim_set_vq_address,
 	.set_vq_num             = vdpasim_set_vq_num,
 	.kick_vq                = vdpasim_kick_vq,
···
 	.set_map                = vdpasim_set_map,
 	.free                   = vdpasim_free,
 };
-
-static int __init vdpasim_dev_init(void)
-{
-	vdpasim_dev = vdpasim_create();
-
-	if (!IS_ERR(vdpasim_dev))
-		return 0;
-
-	return PTR_ERR(vdpasim_dev);
-}
-
-static void __exit vdpasim_dev_exit(void)
-{
-	struct vdpa_device *vdpa = &vdpasim_dev->vdpa;
-
-	vdpa_unregister_device(vdpa);
-}
-
-module_init(vdpasim_dev_init)
-module_exit(vdpasim_dev_exit)
 
 MODULE_VERSION(DRV_VERSION);
 MODULE_LICENSE(DRV_LICENSE);

drivers/vdpa/vdpa_sim/vdpa_sim.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2020, Red Hat Inc. All rights reserved.
+ */
+
+#ifndef _VDPA_SIM_H
+#define _VDPA_SIM_H
+
+#include <linux/vringh.h>
+#include <linux/vdpa.h>
+#include <linux/virtio_byteorder.h>
+#include <linux/vhost_iotlb.h>
+#include <uapi/linux/virtio_config.h>
+
+#define VDPASIM_FEATURES	((1ULL << VIRTIO_F_ANY_LAYOUT) | \
+				 (1ULL << VIRTIO_F_VERSION_1)  | \
+				 (1ULL << VIRTIO_F_ACCESS_PLATFORM))
+
+struct vdpasim;
+
+struct vdpasim_virtqueue {
+	struct vringh vring;
+	struct vringh_kiov in_iov;
+	struct vringh_kiov out_iov;
+	unsigned short head;
+	bool ready;
+	u64 desc_addr;
+	u64 device_addr;
+	u64 driver_addr;
+	u32 num;
+	void *private;
+	irqreturn_t (*cb)(void *data);
+};
+
+struct vdpasim_dev_attr {
+	u64 supported_features;
+	size_t config_size;
+	size_t buffer_size;
+	int nvqs;
+	u32 id;
+
+	work_func_t work_fn;
+	void (*get_config)(struct vdpasim *vdpasim, void *config);
+	void (*set_config)(struct vdpasim *vdpasim, const void *config);
+};
+
+/* State of each vdpasim device */
+struct vdpasim {
+	struct vdpa_device vdpa;
+	struct vdpasim_virtqueue *vqs;
+	struct work_struct work;
+	struct vdpasim_dev_attr dev_attr;
+	/* spinlock to synchronize virtqueue state */
+	spinlock_t lock;
+	/* virtio config according to device type */
+	void *config;
+	struct vhost_iotlb *iommu;
+	void *buffer;
+	u32 status;
+	u32 generation;
+	u64 features;
+	/* spinlock to synchronize iommu table */
+	spinlock_t iommu_lock;
+};
+
+struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *attr);
+
+/* TODO: cross-endian support */
+static inline bool vdpasim_is_little_endian(struct vdpasim *vdpasim)
+{
+	return virtio_legacy_is_little_endian() ||
+		(vdpasim->features & (1ULL << VIRTIO_F_VERSION_1));
+}
+
+static inline u16 vdpasim16_to_cpu(struct vdpasim *vdpasim, __virtio16 val)
+{
+	return __virtio16_to_cpu(vdpasim_is_little_endian(vdpasim), val);
+}
+
+static inline __virtio16 cpu_to_vdpasim16(struct vdpasim *vdpasim, u16 val)
+{
+	return __cpu_to_virtio16(vdpasim_is_little_endian(vdpasim), val);
+}
+
+static inline u32 vdpasim32_to_cpu(struct vdpasim *vdpasim, __virtio32 val)
+{
+	return __virtio32_to_cpu(vdpasim_is_little_endian(vdpasim), val);
+}
+
+static inline __virtio32 cpu_to_vdpasim32(struct vdpasim *vdpasim, u32 val)
+{
+	return __cpu_to_virtio32(vdpasim_is_little_endian(vdpasim), val);
+}
+
+static inline u64 vdpasim64_to_cpu(struct vdpasim *vdpasim, __virtio64 val)
+{
+	return __virtio64_to_cpu(vdpasim_is_little_endian(vdpasim), val);
+}
+
+static inline __virtio64 cpu_to_vdpasim64(struct vdpasim *vdpasim, u64 val)
+{
+	return __cpu_to_virtio64(vdpasim_is_little_endian(vdpasim), val);
+}
+
+#endif

drivers/vdpa/vdpa_sim/vdpa_sim_net.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * VDPA simulator for networking device.
+ *
+ * Copyright (c) 2020, Red Hat Inc. All rights reserved.
+ *     Author: Jason Wang <[e-mail]>
+ *
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/etherdevice.h>
+#include <linux/vringh.h>
+#include <linux/vdpa.h>
+#include <uapi/linux/virtio_net.h>
+
+#include "vdpa_sim.h"
+
+#define DRV_VERSION  "0.1"
+#define DRV_AUTHOR   "Jason Wang <[e-mail]>"
+#define DRV_DESC     "vDPA Device Simulator for networking device"
+#define DRV_LICENSE  "GPL v2"
+
+#define VDPASIM_NET_FEATURES	(VDPASIM_FEATURES | \
+				 (1ULL << VIRTIO_NET_F_MAC))
+
+#define VDPASIM_NET_VQ_NUM	2
+
+static char *macaddr;
+module_param(macaddr, charp, 0);
+MODULE_PARM_DESC(macaddr, "Ethernet MAC address");
+
+u8 macaddr_buf[ETH_ALEN];
+
+static struct vdpasim *vdpasim_net_dev;
+
+static void vdpasim_net_work(struct work_struct *work)
+{
+	struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
+	struct vdpasim_virtqueue *txq = &vdpasim->vqs[1];
+	struct vdpasim_virtqueue *rxq = &vdpasim->vqs[0];
+	ssize_t read, write;
+	size_t total_write;
+	int pkts = 0;
+	int err;
+
+	spin_lock(&vdpasim->lock);
+
+	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
+		goto out;
+
+	if (!txq->ready || !rxq->ready)
+		goto out;
+
+	while (true) {
+		total_write = 0;
+		err = vringh_getdesc_iotlb(&txq->vring, &txq->out_iov, NULL,
+					   &txq->head, GFP_ATOMIC);
+		if (err <= 0)
+			break;
+
+		err = vringh_getdesc_iotlb(&rxq->vring, NULL, &rxq->in_iov,
+					   &rxq->head, GFP_ATOMIC);
+		if (err <= 0) {
+			vringh_complete_iotlb(&txq->vring, txq->head, 0);
+			break;
+		}
+
+		while (true) {
+			read = vringh_iov_pull_iotlb(&txq->vring, &txq->out_iov,
+						     vdpasim->buffer,
+						     PAGE_SIZE);
+			if (read <= 0)
+				break;
+
+			write = vringh_iov_push_iotlb(&rxq->vring, &rxq->in_iov,
+						      vdpasim->buffer, read);
+			if (write <= 0)
+				break;
+
+			total_write += write;
+		}
+
+		/* Make sure data is wrote before advancing index */
+		smp_wmb();
+
+		vringh_complete_iotlb(&txq->vring, txq->head, 0);
+		vringh_complete_iotlb(&rxq->vring, rxq->head, total_write);
+
+		/* Make sure used is visible before rasing the interrupt. */
+		smp_wmb();
+
+		local_bh_disable();
+		if (vringh_need_notify_iotlb(&txq->vring) > 0)
+			vringh_notify(&txq->vring);
+		if (vringh_need_notify_iotlb(&rxq->vring) > 0)
+			vringh_notify(&rxq->vring);
+		local_bh_enable();
+
+		if (++pkts > 4) {
+			schedule_work(&vdpasim->work);
+			goto out;
+		}
+	}
+
+out:
+	spin_unlock(&vdpasim->lock);
+}
+
+static void vdpasim_net_get_config(struct vdpasim *vdpasim, void *config)
+{
+	struct virtio_net_config *net_config =
+		(struct virtio_net_config *)config;
+
+	net_config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
+	net_config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
+	memcpy(net_config->mac, macaddr_buf, ETH_ALEN);
+}
+
+static int __init vdpasim_net_init(void)
+{
+	struct vdpasim_dev_attr dev_attr = {};
+	int ret;
+
+	if (macaddr) {
+		mac_pton(macaddr, macaddr_buf);
+		if (!is_valid_ether_addr(macaddr_buf)) {
+			ret = -EADDRNOTAVAIL;
+			goto out;
+		}
+	} else {
+		eth_random_addr(macaddr_buf);
+	}
+
+	dev_attr.id = VIRTIO_ID_NET;
+	dev_attr.supported_features = VDPASIM_NET_FEATURES;
+	dev_attr.nvqs = VDPASIM_NET_VQ_NUM;
+	dev_attr.config_size = sizeof(struct virtio_net_config);
+	dev_attr.get_config = vdpasim_net_get_config;
+	dev_attr.work_fn = vdpasim_net_work;
+	dev_attr.buffer_size = PAGE_SIZE;
+
+	vdpasim_net_dev = vdpasim_create(&dev_attr);
+	if (IS_ERR(vdpasim_net_dev)) {
+		ret = PTR_ERR(vdpasim_net_dev);
+		goto out;
+	}
+
+	ret = vdpa_register_device(&vdpasim_net_dev->vdpa);
+	if (ret)
+		goto put_dev;
+
+	return 0;
+
+put_dev:
+	put_device(&vdpasim_net_dev->vdpa.dev);
+out:
+	return ret;
+}
+
+static void __exit vdpasim_net_exit(void)
+{
+	struct vdpa_device *vdpa = &vdpasim_net_dev->vdpa;
+
+	vdpa_unregister_device(vdpa);
+}
+
+module_init(vdpasim_net_init);
+module_exit(vdpasim_net_exit);
+
+MODULE_VERSION(DRV_VERSION);
+MODULE_LICENSE(DRV_LICENSE);
+MODULE_AUTHOR(DRV_AUTHOR);
+MODULE_DESCRIPTION(DRV_DESC);

drivers/vhost/scsi.c

···
 			if (!vhost_vq_is_setup(vq))
 				continue;
 
-			if (vhost_scsi_setup_vq_cmds(vq, vq->num))
+			ret = vhost_scsi_setup_vq_cmds(vq, vq->num);
+			if (ret)
 				goto destroy_vq_cmds;
 		}
 

drivers/vhost/vdpa.c

···
 		return -EFAULT;
 	if (vhost_vdpa_config_validate(v, &config))
 		return -EINVAL;
-	buf = kvzalloc(config.len, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
 
-	if (copy_from_user(buf, c->buf, config.len)) {
-		kvfree(buf);
-		return -EFAULT;
-	}
+	buf = vmemdup_user(c->buf, config.len);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
 
 	ops->set_config(vdpa, config.off, buf, config.len);
 

drivers/virtio/virtio_mem.c

···
 module_param(unplug_online, bool, 0644);
 MODULE_PARM_DESC(unplug_online, "Try to unplug online memory");
 
-enum virtio_mem_mb_state {
+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).");
+
+static bool bbm_safe_unplug = true;
+module_param(bbm_safe_unplug, bool, 0444);
+MODULE_PARM_DESC(bbm_safe_unplug,
+	     "Use a safe unplug mechanism in BBM, avoiding long/endless loops");
+
+/*
+ * 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_MB_STATE_UNUSED = 0,
+	VIRTIO_MEM_SBM_MB_UNUSED = 0,
 	/* (Partially) plugged, not added to Linux. Error on add_memory(). */
-	VIRTIO_MEM_MB_STATE_PLUGGED,
+	VIRTIO_MEM_SBM_MB_PLUGGED,
 	/* Fully plugged, fully added to Linux, offline. */
-	VIRTIO_MEM_MB_STATE_OFFLINE,
+	VIRTIO_MEM_SBM_MB_OFFLINE,
 	/* Partially plugged, fully added to Linux, offline. */
-	VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL,
+	VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL,
 	/* Fully plugged, fully added to Linux, online. */
-	VIRTIO_MEM_MB_STATE_ONLINE,
+	VIRTIO_MEM_SBM_MB_ONLINE,
 	/* Partially plugged, fully added to Linux, online. */
-	VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL,
-	VIRTIO_MEM_MB_STATE_COUNT
+	VIRTIO_MEM_SBM_MB_ONLINE_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 {
···
 
 	/* Workqueue that processes the plug/unplug requests. */
 	struct work_struct wq;
+	atomic_t wq_active;
 	atomic_t config_changed;
 
 	/* Virtqueue for guest->host requests. */
···
 
 	/* The device block size (for communicating with the device). */
 	uint64_t device_block_size;
-	/* The translated node id. NUMA_NO_NODE in case not specified. */
+	/* 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 subblock size. */
-	uint64_t subblock_size;
-	/* The number of subblocks per memory block. */
-	uint32_t nb_sb_per_mb;
-
-	/* Id of the first memory block of this device. */
-	unsigned long first_mb_id;
-	/* Id of the last memory block of this device. */
-	unsigned long last_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 parent resource for all memory added via this device. */
 	struct resource *parent_resource;
···
 	 */
 	const char *resource_name;
 
-	/* Summary of all memory block states. */
-	unsigned long nb_mb_state[VIRTIO_MEM_MB_STATE_COUNT];
-#define VIRTIO_MEM_NB_OFFLINE_THRESHOLD		10
-
 	/*
-	 * One byte state per memory block.
-	 *
-	 * Allocated via vmalloc(). When preparing new blocks, resized
-	 * (alloc+copy+free) when needed (crossing pages with the next mb).
-	 * (when crossing pages).
-	 *
-	 * With 128MB memory blocks, we have states for 512GB of memory in one
-	 * page.
+	 * 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).
 	 */
-	uint8_t *mb_state;
+#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;
+
+			/* 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;
+	};
 
 	/*
-	 * $nb_sb_per_mb bit per memory block. Handled similar to mb_state.
-	 *
-	 * With 4MB subblocks, we manage 128GB of memory in one page.
-	 */
-	unsigned long *sb_bitmap;
-
-	/*
-	 * Mutex that protects the nb_mb_state, mb_state, and sb_bitmap.
+	 * 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
···
 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);
 
 /*
  * Register a virtio-mem device so it will be considered for the online_page
···
 }
 
 /*
+ * 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,
···
 	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->subblock_size;
+	return (addr - mb_addr) / vm->sbm.sb_size;
 }
 
 /*
- * Set the state of a memory block, taking care of the state counter.
+ * Set the state of a big block, taking care of the state counter.
  */
-static void virtio_mem_mb_set_state(struct virtio_mem *vm, unsigned long mb_id,
-				    enum virtio_mem_mb_state state)
+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 = mb_id - vm->first_mb_id;
-	enum virtio_mem_mb_state old_state;
+	const unsigned long idx = bb_id - vm->bbm.first_bb_id;
+	enum virtio_mem_bbm_bb_state old_state;
 
-	old_state = vm->mb_state[idx];
-	vm->mb_state[idx] = state;
+	old_state = vm->bbm.bb_states[idx];
+	vm->bbm.bb_states[idx] = state;
 
-	BUG_ON(vm->nb_mb_state[old_state] == 0);
-	vm->nb_mb_state[old_state]--;
-	vm->nb_mb_state[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 memory block.
+ * Get the state of a big block.
  */
-static enum virtio_mem_mb_state virtio_mem_mb_get_state(struct virtio_mem *vm,
-							unsigned long mb_id)
+static enum virtio_mem_bbm_bb_state virtio_mem_bbm_get_bb_state(struct virtio_mem *vm,
+								unsigned long bb_id)
 {
-	const unsigned long idx = mb_id - vm->first_mb_id;
-
-	return vm->mb_state[idx];
+	return vm->bbm.bb_states[bb_id - vm->bbm.first_bb_id];
 }
 
 /*
- * Prepare the state array for the next memory block.
+ * Prepare the big block state array for the next big block.
  */
-static int virtio_mem_mb_state_prepare_next_mb(struct virtio_mem *vm)
+static int virtio_mem_bbm_bb_states_prepare_next_bb(struct virtio_mem *vm)
 {
-	unsigned long old_bytes = vm->next_mb_id - vm->first_mb_id + 1;
-	unsigned long new_bytes = vm->next_mb_id - vm->first_mb_id + 2;
+	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_mb_state;
+	uint8_t *new_array;
 
-	if (vm->mb_state && old_pages == new_pages)
+	if (vm->bbm.bb_states && old_pages == new_pages)
 		return 0;
 
-	new_mb_state = vzalloc(new_pages * PAGE_SIZE);
-	if (!new_mb_state)
+	new_array = vzalloc(new_pages * PAGE_SIZE);
+	if (!new_array)
 		return -ENOMEM;
 
 	mutex_lock(&vm->hotplug_mutex);
-	if (vm->mb_state)
-		memcpy(new_mb_state, vm->mb_state, old_pages * PAGE_SIZE);
-	vfree(vm->mb_state);
-	vm->mb_state = new_mb_state;
+	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_for_each_mb_state(_vm, _mb_id, _state) \
-	for (_mb_id = _vm->first_mb_id; \
-	     _mb_id < _vm->next_mb_id && _vm->nb_mb_state[_state]; \
-	     _mb_id++) \
-		if (virtio_mem_mb_get_state(_vm, _mb_id) == _state)
+#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_for_each_mb_state_rev(_vm, _mb_id, _state) \
-	for (_mb_id = _vm->next_mb_id - 1; \
-	     _mb_id >= _vm->first_mb_id && _vm->nb_mb_state[_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_mb_get_state(_vm, _mb_id) == _state)
+		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_mb_set_sb_plugged(struct virtio_mem *vm,
-					 unsigned long mb_id, int sb_id,
-					 int count)
+static void virtio_mem_sbm_set_sb_plugged(struct virtio_mem *vm,
+					  unsigned long mb_id, int sb_id,
+					  int count)
 {
-	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);
 
-	__bitmap_set(vm->sb_bitmap, bit, count);
+	__bitmap_set(vm->sbm.sb_states, bit, count);
 }
 
 /*
···
  *
  * Will not modify the state of the memory block.
  */
-static void virtio_mem_mb_set_sb_unplugged(struct virtio_mem *vm,
-					   unsigned long mb_id, int sb_id,
-					   int count)
+static void virtio_mem_sbm_set_sb_unplugged(struct virtio_mem *vm,
+					    unsigned long mb_id, int sb_id,
+					    int count)
 {
-	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);
 
-	__bitmap_clear(vm->sb_bitmap, bit, count);
+	__bitmap_clear(vm->sbm.sb_states, bit, count);
 }
 
 /*
  * Test if all selected subblocks are plugged.
  */
-static bool virtio_mem_mb_test_sb_plugged(struct virtio_mem *vm,
-					  unsigned long mb_id, int sb_id,
-					  int count)
+static bool virtio_mem_sbm_test_sb_plugged(struct virtio_mem *vm,
+					   unsigned long mb_id, int sb_id,
+					   int count)
 {
-	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, sb_id);
 
 	if (count == 1)
-		return test_bit(bit, vm->sb_bitmap);
+		return test_bit(bit, vm->sbm.sb_states);
 
 	/* TODO: Helper similar to bitmap_set() */
-	return find_next_zero_bit(vm->sb_bitmap, bit + count, bit) >=
+	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_mb_test_sb_unplugged(struct virtio_mem *vm,
-					    unsigned long mb_id, int sb_id,
-					    int count)
+static bool virtio_mem_sbm_test_sb_unplugged(struct virtio_mem *vm,
+					     unsigned long mb_id, int sb_id,
+					     int count)
 {
-	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb + sb_id;
+	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->sb_bitmap, bit + count, bit) >= bit + count;
+	return find_next_bit(vm->sbm.sb_states, bit + count, bit) >=
+	       bit + count;
 }
 
 /*
- * Find the first unplugged subblock. Returns vm->nb_sb_per_mb in case there is
+ * Find the first unplugged subblock. Returns vm->sbm.sbs_per_mb in case there is
  * none.
  */
-static int virtio_mem_mb_first_unplugged_sb(struct virtio_mem *vm,
+static int virtio_mem_sbm_first_unplugged_sb(struct virtio_mem *vm,
 					    unsigned long mb_id)
 {
-	const int bit = (mb_id - vm->first_mb_id) * vm->nb_sb_per_mb;
+	const int bit = virtio_mem_sbm_sb_state_bit_nr(vm, mb_id, 0);
 
-	return find_next_zero_bit(vm->sb_bitmap, bit + vm->nb_sb_per_mb, bit) -
-	       bit;
+	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_sb_bitmap_prepare_next_mb(struct virtio_mem *vm)
+static int virtio_mem_sbm_sb_states_prepare_next_mb(struct virtio_mem *vm)
 {
-	const unsigned long old_nb_mb = vm->next_mb_id - vm->first_mb_id;
-	const unsigned long old_nb_bits = old_nb_mb * vm->nb_sb_per_mb;
-	const unsigned long new_nb_bits = (old_nb_mb + 1) * vm->nb_sb_per_mb;
+	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_sb_bitmap, *old_sb_bitmap;
+	unsigned long *new_bitmap, *old_bitmap;
 
-	if (vm->sb_bitmap && old_pages == new_pages)
+	if (vm->sbm.sb_states && old_pages == new_pages)
 		return 0;
 
-	new_sb_bitmap = vzalloc(new_pages * PAGE_SIZE);
-	if (!new_sb_bitmap)
+	new_bitmap = vzalloc(new_pages * PAGE_SIZE);
+	if (!new_bitmap)
 		return -ENOMEM;
 
 	mutex_lock(&vm->hotplug_mutex);
-	if (new_sb_bitmap)
-		memcpy(new_sb_bitmap, vm->sb_bitmap, old_pages * PAGE_SIZE);
+	if (new_bitmap)
+		memcpy(new_bitmap, vm->sbm.sb_states, old_pages * PAGE_SIZE);
 
-	old_sb_bitmap = vm->sb_bitmap;
-	vm->sb_bitmap = new_sb_bitmap;
+	old_bitmap = vm->sbm.sb_states;
+	vm->sbm.sb_states = new_bitmap;
 	mutex_unlock(&vm->hotplug_mutex);
 
-	vfree(old_sb_bitmap);
+	vfree(old_bitmap);
 	return 0;
 }
 
 /*
- * Try to add a memory block to Linux. This will usually only fail
- * if out of memory.
+ * 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 the memory block.
+ * Will not modify the state of memory blocks in virtio-mem.
  */
-static int virtio_mem_mb_add(struct virtio_mem *vm, unsigned long mb_id)
+static int virtio_mem_add_memory(struct virtio_mem *vm, uint64_t addr,
+				 uint64_t size)
 {
-	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
-	int nid = vm->nid;
-
-	if (nid == NUMA_NO_NODE)
-		nid = memory_add_physaddr_to_nid(addr);
+	int rc;
 
 	/*
 	 * When force-unloading the driver and we still have memory added to
···
 			return -ENOMEM;
 	}
 
-	dev_dbg(&vm->vdev->dev, "adding memory block: %lu\n", mb_id);
-	return add_memory_driver_managed(nid, addr, memory_block_size_bytes(),
-					 vm->resource_name,
-					 MEMHP_MERGE_RESOURCE);
+	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->nid, addr, size, vm->resource_name,
+				       MEMHP_MERGE_RESOURCE);
+	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;
 }
 
 /*
- * Try to remove a memory block from Linux. Will only fail if the memory block
- * is not offline.
+ * 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 the memory block.
+ * Will not modify the state of memory blocks in virtio-mem.
  */
-static int virtio_mem_mb_remove(struct virtio_mem *vm, unsigned long mb_id)
+static int virtio_mem_remove_memory(struct virtio_mem *vm, uint64_t addr,
+				    uint64_t size)
 {
-	const uint64_t addr = virtio_mem_mb_id_to_phys(mb_id);
-	int nid = vm->nid;
+	int rc;
 
-	if (nid == NUMA_NO_NODE)
-		nid = memory_add_physaddr_to_nid(addr);
-
-	dev_dbg(&vm->vdev->dev, "removing memory block: %lu\n", mb_id);
-	return remove_memory(nid, addr, memory_block_size_bytes());
+	dev_dbg(&vm->vdev->dev, "removing memory: 0x%llx - 0x%llx\n", addr,
+		addr + size - 1);
+	rc = remove_memory(vm->nid, 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;
 }
 
 /*
- * Try to offline and remove a memory block from Linux.
+ * 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);
+}
+
+/*
+ * See virtio_mem_remove_memory(): Try to remove all Linux memory blocks covered
+ * by the big block.
+ */
+static int virtio_mem_bbm_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_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 the memory block.
+ * Will not modify the state of memory blocks in virtio-mem.
  */
-static int virtio_mem_mb_offline_and_remove(struct virtio_mem *vm,
-					    unsigned long mb_id)
+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(vm->nid, 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,
+			"offlining and removing memory failed: %d\n", rc);
+	}
+	return rc;
+}
+
+/*
+ * 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);
-	int nid = vm->nid;
+	const uint64_t size = memory_block_size_bytes();
 
-	if (nid == NUMA_NO_NODE)
-		nid = memory_add_physaddr_to_nid(addr);
+	return virtio_mem_offline_and_remove_memory(vm, addr, size);
+}
 
-	dev_dbg(&vm->vdev->dev, "offlining and removing memory block: %lu\n",
-		mb_id);
-	return offline_and_remove_memory(nid, addr, memory_block_size_bytes());
+/*
+ * 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);
 }
 
 /*
···
  * 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,
-				      unsigned long start, unsigned long size)
+static bool virtio_mem_overlaps_range(struct virtio_mem *vm, uint64_t start,
+				      uint64_t size)
 {
-	unsigned long dev_start = virtio_mem_mb_id_to_phys(vm->first_mb_id);
-	unsigned long dev_end = virtio_mem_mb_id_to_phys(vm->last_mb_id) +
-				memory_block_size_bytes();
-
-	return start < dev_end && dev_start < start + size;
+	return start < vm->addr + vm->region_size && vm->addr < start + size;
 }
 
 /*
- * Test if a virtio-mem device owns a memory block. Can be called from
+ * Test if a virtio-mem device contains a given range. Can be called from
  * (notifier) callbacks lockless.
  */
-static bool virtio_mem_owned_mb(struct virtio_mem *vm, unsigned long mb_id)
+static bool virtio_mem_contains_range(struct virtio_mem *vm, uint64_t start,
+				      uint64_t size)
 {
-	return mb_id >= vm->first_mb_id && mb_id <= vm->last_mb_id;
+	return start >= vm->addr && start + size <= vm->addr + vm->region_size;
 }
 
-static int virtio_mem_notify_going_online(struct virtio_mem *vm,
-					  unsigned long mb_id)
+static int virtio_mem_sbm_notify_going_online(struct virtio_mem *vm,
+					      unsigned long mb_id)
 {
-	switch (virtio_mem_mb_get_state(vm, mb_id)) {
-	case VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL:
-	case VIRTIO_MEM_MB_STATE_OFFLINE:
+	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;
···
 	return NOTIFY_BAD;
 }
 
-static void virtio_mem_notify_offline(struct virtio_mem *vm,
-				      unsigned long mb_id)
+static void virtio_mem_sbm_notify_offline(struct virtio_mem *vm,
+					  unsigned long mb_id)
 {
-	switch (virtio_mem_mb_get_state(vm, mb_id)) {
-	case VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL:
-		virtio_mem_mb_set_state(vm, mb_id,
-					VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);
+	switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
+	case VIRTIO_MEM_SBM_MB_ONLINE_PARTIAL:
+		virtio_mem_sbm_set_mb_state(vm, mb_id,
+					    VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL);
 		break;
-	case VIRTIO_MEM_MB_STATE_ONLINE:
-		virtio_mem_mb_set_state(vm, mb_id,
-					VIRTIO_MEM_MB_STATE_OFFLINE);
+	case VIRTIO_MEM_SBM_MB_ONLINE:
+		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)
+{
+	switch (virtio_mem_sbm_get_mb_state(vm, mb_id)) {
+	case VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL:
+		virtio_mem_sbm_set_mb_state(vm, mb_id,
+					VIRTIO_MEM_SBM_MB_ONLINE_PARTIAL);
+		break;
+	case VIRTIO_MEM_SBM_MB_OFFLINE:
+		virtio_mem_sbm_set_mb_state(vm, mb_id,
+					    VIRTIO_MEM_SBM_MB_ONLINE);
+		break;
+	default:
+		BUG();
+		break;
+	}
+}
+
+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)
+{
 	/*
-	 * Trigger the workqueue, maybe we can now unplug memory. Also,
-	 * when we offline and remove a memory block, this will re-trigger
-	 * us immediately - which is often nice because the removal of
-	 * the memory block (e.g., memmap) might have freed up memory
-	 * on other memory blocks we manage.
+	 * When marked as "fake-offline", all online memory of this device block
+	 * is allocated by us. Otherwise, we don't have any memory allocated.
 	 */
-	virtio_mem_retry(vm);
+	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_notify_online(struct virtio_mem *vm, unsigned long mb_id)
+static void virtio_mem_bbm_notify_cancel_offline(struct virtio_mem *vm,
+						 unsigned long bb_id,
+						 unsigned long pfn,
+						 unsigned long nr_pages)
 {
-	unsigned long nb_offline;
-
-	switch (virtio_mem_mb_get_state(vm, mb_id)) {
-	case VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL:
-		virtio_mem_mb_set_state(vm, mb_id,
-					VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL);
-		break;
-	case VIRTIO_MEM_MB_STATE_OFFLINE:
-		virtio_mem_mb_set_state(vm, mb_id, VIRTIO_MEM_MB_STATE_ONLINE);
-		break;
-	default:
-		BUG();
-		break;
-	}
-	nb_offline = vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] +
-		     vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL];
-
-	/* see if we can add new blocks now that we onlined one block */
-	if (nb_offline == VIRTIO_MEM_NB_OFFLINE_THRESHOLD - 1)
-		virtio_mem_retry(vm);
-}
-
-static void virtio_mem_notify_going_offline(struct virtio_mem *vm,
-					    unsigned long mb_id)
-{
-	const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
-	struct page *page;
-	unsigned long pfn;
-	int sb_id, i;
-
-	for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
-		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
-			continue;
-		/*
-		 * Drop our reference to the pages so the memory can get
-		 * offlined and add the unplugged pages to the managed
-		 * page counters (so offlining code can correctly subtract
-		 * them again).
-		 */
-		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
-			       sb_id * vm->subblock_size);
-		adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
-		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, "unplugged page referenced");
-		}
-	}
-}
-
-static void virtio_mem_notify_cancel_offline(struct virtio_mem *vm,
-					     unsigned long mb_id)
-{
-	const unsigned long nr_pages = PFN_DOWN(vm->subblock_size);
-	unsigned long pfn;
-	int sb_id, i;
-
-	for (sb_id = 0; sb_id < vm->nb_sb_per_mb; sb_id++) {
-		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
-			continue;
-		/*
-		 * Get the reference we dropped when going offline and
-		 * subtract the unplugged pages from the managed page
-		 * counters.
-		 */
-		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
-			       sb_id * vm->subblock_size);
-		adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
-		for (i = 0; i < nr_pages; i++)
-			page_ref_inc(pfn_to_page(pfn + i));
-	}
+	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);
 }
 
 /*
···
 	struct memory_notify *mhp = arg;
 	const unsigned long start = PFN_PHYS(mhp->start_pfn);
 	const unsigned long size = PFN_PHYS(mhp->nr_pages);
-	const unsigned long mb_id = virtio_mem_phys_to_mb_id(start);
 	int rc = NOTIFY_OK;
+	unsigned long id;
 
 	if (!virtio_mem_overlaps_range(vm, start, size))
 		return NOTIFY_DONE;
 
-	/*
-	 * Memory is onlined/offlined in memory block granularity. We cannot
-	 * cross virtio-mem device boundaries and memory block boundaries. 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;
+	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
···
 			break;
 		}
 		vm->hotplug_active = true;
-		virtio_mem_notify_going_offline(vm, mb_id);
+		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);
···
 			break;
 		}
 		vm->hotplug_active = true;
-		rc = virtio_mem_notify_going_online(vm, mb_id);
+		if (vm->in_sbm)
+			rc = virtio_mem_sbm_notify_going_online(vm, id);
 		break;
 	case MEM_OFFLINE:
-		virtio_mem_notify_offline(vm, mb_id);
+		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:
-		virtio_mem_notify_online(vm, mb_id);
+		if (vm->in_sbm)
+			virtio_mem_sbm_notify_online(vm, id);
+
+		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;
-		virtio_mem_notify_cancel_offline(vm, mb_id);
+		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;
···
  * (via generic_online_page()) using PageDirty().
  */
 static void virtio_mem_set_fake_offline(unsigned long pfn,
-					unsigned int nr_pages, bool onlined)
+					unsigned long nr_pages, bool onlined)
 {
 	for (; nr_pages--; pfn++) {
 		struct page *page = pfn_to_page(pfn);
···
  * (via generic_online_page()), clear PageDirty().
  */
 static void virtio_mem_clear_fake_offline(unsigned long pfn,
-					  unsigned int nr_pages, bool onlined)
+					  unsigned long nr_pages, bool onlined)
 {
 	for (; nr_pages--; pfn++) {
 		struct page *page = pfn_to_page(pfn);
···
  * Release a range of fake-offline pages to the buddy, effectively
  * fake-onlining them.
  */
-static void virtio_mem_fake_online(unsigned long pfn, unsigned int nr_pages)
+static void virtio_mem_fake_online(unsigned long pfn, unsigned long nr_pages)
 {
-	const int order = MAX_ORDER - 1;
-	int i;
+	const unsigned long max_nr_pages = MAX_ORDER_NR_PAGES;
+	unsigned long i;
 
 	/*
-	 * We are always called with subblock granularity, which is at least
-	 * aligned to MAX_ORDER - 1.
+	 * We are always called at least with MAX_ORDER_NR_PAGES
+	 * granularity/alignment (e.g., the way subblocks work). All pages
+	 * inside such a block are alike.
 	 */
-	for (i = 0; i < nr_pages; i += 1 << order) {
+	for (i = 0; i < nr_pages; i += max_nr_pages) {
 		struct page *page = pfn_to_page(pfn + i);
 
 		/*
···
 		 * alike.
 		 */
 		if (PageDirty(page)) {
-			virtio_mem_clear_fake_offline(pfn + i, 1 << order,
+			virtio_mem_clear_fake_offline(pfn + i, max_nr_pages,
 						      false);
-			generic_online_page(page, order);
+			generic_online_page(page, MAX_ORDER - 1);
 		} else {
-			virtio_mem_clear_fake_offline(pfn + i, 1 << order,
+			virtio_mem_clear_fake_offline(pfn + i, max_nr_pages,
 						      true);
-			free_contig_range(pfn + i, 1 << order);
-			adjust_managed_page_count(page, 1 << order);
+			free_contig_range(pfn + i, max_nr_pages);
+			adjust_managed_page_count(page, max_nr_pages);
 		}
 	}
+}
+
+/*
+ * Try to allocate a range, marking pages fake-offline, effectively
+ * fake-offlining them.
+ */
+static int virtio_mem_fake_offline(unsigned long pfn, unsigned long nr_pages)
+{
+	const bool is_movable = zone_idx(page_zone(pfn_to_page(pfn))) ==
+				ZONE_MOVABLE;
+	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++) {
+		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
+	 * and add the unplugged pages to the managed page counters (so
+	 * offlining code can correctly subtract them again).
+	 */
+	adjust_managed_page_count(pfn_to_page(pfn), nr_pages);
+	/* 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 we dropped when going offline and subtract the
+	 * unplugged pages from the managed page counters.
+	 */
+	adjust_managed_page_count(pfn_to_page(pfn), -nr_pages);
+	for (i = 0; i < nr_pages; i++)
+		page_ref_inc(pfn_to_page(pfn + i));
 }
 
 static void virtio_mem_online_page_cb(struct page *page, unsigned int order)
 {
 	const unsigned long addr = page_to_phys(page);
-	const unsigned long mb_id = virtio_mem_phys_to_mb_id(addr);
+	unsigned long id, sb_id;
 	struct virtio_mem *vm;
-	int sb_id;
+	bool do_online;
 
-	/*
-	 * We exploit here that subblocks have at least MAX_ORDER - 1
-	 * size/alignment and that this callback is is called with such a
-	 * size/alignment. So we cannot cross subblocks and therefore
-	 * also not memory blocks.
-	 */
 	rcu_read_lock();
 	list_for_each_entry_rcu(vm, &virtio_mem_devices, next) {
-		if (!virtio_mem_owned_mb(vm, mb_id))
+		if (!virtio_mem_contains_range(vm, addr, PFN_PHYS(1 << order)))
 			continue;
 
-		sb_id = virtio_mem_phys_to_sb_id(vm, addr);
-		/*
-		 * If plugged, online the pages, otherwise, set them fake
-		 * offline (PageOffline).
-		 */
-		if (virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+		if (vm->in_sbm) {
+			/*
+			 * We exploit here that subblocks have at least
+			 * MAX_ORDER_NR_PAGES size/alignment - so we cannot
+			 * cross subblocks within one call.
+			 */
+			id = virtio_mem_phys_to_mb_id(addr);
+			sb_id = virtio_mem_phys_to_sb_id(vm, addr);
+			do_online = virtio_mem_sbm_test_sb_plugged(vm, id,
+								   sb_id, 1);
+		} 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(page, order);
 		else
 			virtio_mem_set_fake_offline(PFN_DOWN(addr), 1 << order,
···
 		.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:
-		return -EAGAIN;
+		rc = -EAGAIN;
+		break;
 	case VIRTIO_MEM_RESP_BUSY:
-		return -ETXTBSY;
+		rc = -ETXTBSY;
+		break;
 	case VIRTIO_MEM_RESP_ERROR:
-		return -EINVAL;
+		rc = -EINVAL;
+		break;
 	default:
-		return -ENOMEM;
+		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,
···
 		.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:
-		return -ETXTBSY;
+		rc = -ETXTBSY;
+		break;
 	case VIRTIO_MEM_RESP_ERROR:
-		return -EINVAL;
+		rc = -EINVAL;
+		break;
 	default:
-		return -ENOMEM;
+		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:
···
 		atomic_set(&vm->config_changed, 1);
 		return 0;
 	case VIRTIO_MEM_RESP_BUSY:
-		return -ETXTBSY;
+		rc = -ETXTBSY;
+		break;
 	default:
-		return -ENOMEM;
+		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_mb_plug_sb(struct virtio_mem *vm, unsigned long mb_id,
-				 int sb_id, int count)
+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->subblock_size;
-	const uint64_t size = count * vm->subblock_size;
+			      sb_id * vm->sbm.sb_size;
+	const uint64_t size = count * vm->sbm.sb_size;
 	int rc;
-
-	dev_dbg(&vm->vdev->dev, "plugging memory block: %lu : %i - %i\n", mb_id,
-		sb_id, sb_id + count - 1);
 
 	rc = virtio_mem_send_plug_request(vm, addr, size);
 	if (!rc)
-		virtio_mem_mb_set_sb_plugged(vm, mb_id, sb_id, count);
+		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_mb_unplug_sb(struct virtio_mem *vm, unsigned long mb_id,
-				   int sb_id, int count)
+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->subblock_size;
-	const uint64_t size = count * vm->subblock_size;
+			      sb_id * vm->sbm.sb_size;
+	const uint64_t size = count * vm->sbm.sb_size;
 	int rc;
-
-	dev_dbg(&vm->vdev->dev, "unplugging memory block: %lu : %i - %i\n",
-		mb_id, sb_id, sb_id + count - 1);
 
 	rc = virtio_mem_send_unplug_request(vm, addr, size);
 	if (!rc)
-		virtio_mem_mb_set_sb_unplugged(vm, mb_id, sb_id, count);
+		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);
 }
 
 /*
···
  *
  * Note: can fail after some subblocks were unplugged.
  */
-static int virtio_mem_mb_unplug_any_sb(struct virtio_mem *vm,
-				       unsigned long mb_id, uint64_t *nb_sb)
+static int virtio_mem_sbm_unplug_any_sb(struct virtio_mem *vm,
+					unsigned long mb_id, uint64_t *nb_sb)
 {
 	int sb_id, count;
 	int rc;
 
-	sb_id = vm->nb_sb_per_mb - 1;
+	sb_id = vm->sbm.sbs_per_mb - 1;
 	while (*nb_sb) {
 		/* Find the next candidate subblock */
 		while (sb_id >= 0 &&
-		       virtio_mem_mb_test_sb_unplugged(vm, mb_id, sb_id, 1))
+		       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_mb_test_sb_plugged(vm, mb_id, sb_id - 1, 1)) {
+		       virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id - 1, 1)) {
 			count++;
 			sb_id--;
 		}
 
-		rc = virtio_mem_mb_unplug_sb(vm, mb_id, sb_id, count);
+		rc = virtio_mem_sbm_unplug_sb(vm, mb_id, sb_id, count);
 		if (rc)
 			return rc;
 		*nb_sb -= count;
···
  *
  * Note: can fail after some subblocks were unplugged.
  */
-static int virtio_mem_mb_unplug(struct virtio_mem *vm, unsigned long mb_id)
+static int virtio_mem_sbm_unplug_mb(struct virtio_mem *vm, unsigned long mb_id)
 {
-	uint64_t nb_sb = vm->nb_sb_per_mb;
+	uint64_t nb_sb = vm->sbm.sbs_per_mb;
 
-	return virtio_mem_mb_unplug_any_sb(vm, mb_id, &nb_sb);
+	return virtio_mem_sbm_unplug_any_sb(vm, mb_id, &nb_sb);
 }
 
 /*
  * Prepare tracking data for the next memory block.
  */
-static int virtio_mem_prepare_next_mb(struct virtio_mem *vm,
-				      unsigned long *mb_id)
+static int virtio_mem_sbm_prepare_next_mb(struct virtio_mem *vm,
+					  unsigned long *mb_id)
 {
 	int rc;
 
-	if (vm->next_mb_id > vm->last_usable_mb_id)
+	if (vm->sbm.next_mb_id > vm->sbm.last_usable_mb_id)
 		return -ENOSPC;
 
 	/* Resize the state array if required. */
-	rc = virtio_mem_mb_state_prepare_next_mb(vm);
+	rc = virtio_mem_sbm_mb_states_prepare_next_mb(vm);
 	if (rc)
 		return rc;
 
 	/* Resize the subblock bitmap if required. */
-	rc = virtio_mem_sb_bitmap_prepare_next_mb(vm);
+	rc = virtio_mem_sbm_sb_states_prepare_next_mb(vm);
 	if (rc)
 		return rc;
 
-	vm->nb_mb_state[VIRTIO_MEM_MB_STATE_UNUSED]++;
-	*mb_id = vm->next_mb_id++;
+	vm->sbm.mb_count[VIRTIO_MEM_SBM_MB_UNUSED]++;
+	*mb_id = vm->sbm.next_mb_id++;
 	return 0;
-}
-
-/*
- * Don't add too many blocks that are not onlined yet to avoid running OOM.
- */
-static bool virtio_mem_too_many_mb_offline(struct virtio_mem *vm)
-{
-	unsigned long nb_offline;
-
-	nb_offline = vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] +
-		     vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL];
-	return nb_offline >= VIRTIO_MEM_NB_OFFLINE_THRESHOLD;
 }
 
 /*
···
  *
  * Will modify the state of the memory block.
  */
-static int virtio_mem_mb_plug_and_add(struct virtio_mem *vm,
-				      unsigned long mb_id,
-				      uint64_t *nb_sb)
+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->nb_sb_per_mb);
-	int rc, rc2;
+	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_mb_plug_sb(vm, mb_id, 0, count);
+	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->nb_sb_per_mb)
-		virtio_mem_mb_set_state(vm, mb_id,
-					VIRTIO_MEM_MB_STATE_OFFLINE);
+	if (count == vm->sbm.sbs_per_mb)
+		virtio_mem_sbm_set_mb_state(vm, mb_id,
+					    VIRTIO_MEM_SBM_MB_OFFLINE);
 	else
-		virtio_mem_mb_set_state(vm, mb_id,
-					VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);
+		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_mb_add(vm, mb_id);
+	rc = virtio_mem_sbm_add_mb(vm, mb_id);
 	if (rc) {
-		enum virtio_mem_mb_state new_state = VIRTIO_MEM_MB_STATE_UNUSED;
+		int new_state = VIRTIO_MEM_SBM_MB_UNUSED;
 
-		dev_err(&vm->vdev->dev,
-			"adding memory block %lu failed with %d\n", mb_id, rc);
-		rc2 = virtio_mem_mb_unplug_sb(vm, mb_id, 0, count);
-
-		/*
-		 * TODO: Linux MM does not properly clean up yet in all cases
-		 * where adding of memory failed - especially on -ENOMEM.
-		 */
-		if (rc2)
-			new_state = VIRTIO_MEM_MB_STATE_PLUGGED;
-		virtio_mem_mb_set_state(vm, mb_id, new_state);
+		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;
 	}
 
···
  *
  * Note: Can fail after some subblocks were successfully plugged.
  */
-static int virtio_mem_mb_plug_any_sb(struct virtio_mem *vm, unsigned long mb_id,
-				     uint64_t *nb_sb, bool online)
+static int virtio_mem_sbm_plug_any_sb(struct virtio_mem *vm,
+				      unsigned long mb_id, uint64_t *nb_sb,
+				      bool online)
 {
 	unsigned long pfn, nr_pages;
 	int sb_id, count;
···
 		return -EINVAL;
 
 	while (*nb_sb) {
-		sb_id = virtio_mem_mb_first_unplugged_sb(vm, mb_id);
-		if (sb_id >= vm->nb_sb_per_mb)
+		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->nb_sb_per_mb &&
-		       !virtio_mem_mb_test_sb_plugged(vm, mb_id, sb_id + count,
-						      1))
+		       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_mb_plug_sb(vm, mb_id, sb_id, count);
+		rc = virtio_mem_sbm_plug_sb(vm, mb_id, sb_id, count);
 		if (rc)
 			return rc;
 		*nb_sb -= count;
···
 
 		/* fake-online the pages if the memory block is online */
 		pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
-			       sb_id * vm->subblock_size);
-		nr_pages = PFN_DOWN(count * vm->subblock_size);
+			       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_mb_test_sb_plugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+	if (virtio_mem_sbm_test_sb_plugged(vm, mb_id, 0, vm->sbm.sbs_per_mb)) {
 		if (online)
-			virtio_mem_mb_set_state(vm, mb_id,
-						VIRTIO_MEM_MB_STATE_ONLINE);
+			virtio_mem_sbm_set_mb_state(vm, mb_id,
+						    VIRTIO_MEM_SBM_MB_ONLINE);
 		else
-			virtio_mem_mb_set_state(vm, mb_id,
-						VIRTIO_MEM_MB_STATE_OFFLINE);
+			virtio_mem_sbm_set_mb_state(vm, mb_id,
+						    VIRTIO_MEM_SBM_MB_OFFLINE);
 	}
 
 	return 0;
 }
 
-/*
- * Try to plug the requested amount of memory.
- */
-static int virtio_mem_plug_request(struct virtio_mem *vm, uint64_t diff)
+static int virtio_mem_sbm_plug_request(struct virtio_mem *vm, uint64_t diff)
 {
-	uint64_t nb_sb = diff / vm->subblock_size;
+	uint64_t nb_sb = diff / vm->sbm.sb_size;
 	unsigned long mb_id;
 	int rc;
 
···
 	mutex_lock(&vm->hotplug_mutex);
 
 	/* Try to plug subblocks of partially plugged online blocks. */
-	virtio_mem_for_each_mb_state(vm, mb_id,
-				     VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL) {
-		rc = virtio_mem_mb_plug_any_sb(vm, mb_id, &nb_sb, true);
+	virtio_mem_sbm_for_each_mb(vm, mb_id,
+				   VIRTIO_MEM_SBM_MB_ONLINE_PARTIAL) {
+		rc = virtio_mem_sbm_plug_any_sb(vm, mb_id, &nb_sb, true);
 		if (rc || !nb_sb)
 			goto out_unlock;
 		cond_resched();
 	}
 
 	/* Try to plug subblocks of partially plugged offline blocks. */
-	virtio_mem_for_each_mb_state(vm, mb_id,
-				     VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {
-		rc = virtio_mem_mb_plug_any_sb(vm, mb_id, &nb_sb, false);
+	virtio_mem_sbm_for_each_mb(vm, mb_id,
+				   VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL) {
+		rc = virtio_mem_sbm_plug_any_sb(vm, mb_id, &nb_sb, false);
 		if (rc || !nb_sb)
 			goto out_unlock;
 		cond_resched();
···
 	mutex_unlock(&vm->hotplug_mutex);
 
 	/* Try to plug and add unused blocks */
-	virtio_mem_for_each_mb_state(vm, mb_id, VIRTIO_MEM_MB_STATE_UNUSED) {
-		if (virtio_mem_too_many_mb_offline(vm))
+	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_mb_plug_and_add(vm, mb_id, &nb_sb);
+		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_too_many_mb_offline(vm))
+		if (!virtio_mem_could_add_memory(vm, memory_block_size_bytes()))
 			return -ENOSPC;
 
-		rc = virtio_mem_prepare_next_mb(vm, &mb_id);
+		rc = virtio_mem_sbm_prepare_next_mb(vm, &mb_id);
 		if (rc)
 			return rc;
-		rc = virtio_mem_mb_plug_and_add(vm, mb_id, &nb_sb);
+		rc = virtio_mem_sbm_plug_and_add_mb(vm, mb_id, &nb_sb);
 		if (rc)
 			return rc;
 		cond_resched();
···
 }
 
 /*
+ * 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).
  *
···
  *
  * Note: Can fail after some subblocks were successfully unplugged.
  */
-static int virtio_mem_mb_unplug_any_sb_offline(struct virtio_mem *vm,
-					       unsigned long mb_id,
-					       uint64_t *nb_sb)
+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_mb_unplug_any_sb(vm, mb_id, nb_sb);
+	rc = virtio_mem_sbm_unplug_any_sb(vm, mb_id, nb_sb);
 
 	/* some subblocks might have been unplugged even on failure */
-	if (!virtio_mem_mb_test_sb_plugged(vm, mb_id, 0, vm->nb_sb_per_mb))
-		virtio_mem_mb_set_state(vm, mb_id,
-					VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL);
+	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_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+	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_mb_set_state(vm, mb_id,
-					VIRTIO_MEM_MB_STATE_UNUSED);
+		virtio_mem_sbm_set_mb_state(vm, mb_id,
+					    VIRTIO_MEM_SBM_MB_UNUSED);
 
 		mutex_unlock(&vm->hotplug_mutex);
-		rc = virtio_mem_mb_remove(vm, mb_id);
+		rc = virtio_mem_sbm_remove_mb(vm, mb_id);
 		BUG_ON(rc);
 		mutex_lock(&vm->hotplug_mutex);
 	}
···
  *
  * Will modify the state of the memory block.
  */
-static int virtio_mem_mb_unplug_sb_online(struct virtio_mem *vm,
-					  unsigned long mb_id, int sb_id,
-					  int count)
+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->subblock_size) * count;
+	const unsigned long nr_pages = PFN_DOWN(vm->sbm.sb_size) * count;
 	unsigned long start_pfn;
 	int rc;
 
 	start_pfn = PFN_DOWN(virtio_mem_mb_id_to_phys(mb_id) +
-			     sb_id * vm->subblock_size);
-	rc = alloc_contig_range(start_pfn, start_pfn + nr_pages,
-				MIGRATE_MOVABLE, GFP_KERNEL);
-	if (rc == -ENOMEM)
-		/* whoops, out of memory */
-		return rc;
-	if (rc)
-		return -EBUSY;
+			     sb_id * vm->sbm.sb_size);
 
-	/* Mark it as fake-offline before unplugging it */
-	virtio_mem_set_fake_offline(start_pfn, nr_pages, true);
-	adjust_managed_page_count(pfn_to_page(start_pfn), -nr_pages);
+	rc = virtio_mem_fake_offline(start_pfn, nr_pages);
+	if (rc)
+		return rc;
 
 	/* Try to unplug the allocated memory */
-	rc = virtio_mem_mb_unplug_sb(vm, mb_id, sb_id, count);
+	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;
 	}
 
-	virtio_mem_mb_set_state(vm, mb_id,
-				VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL);
+	virtio_mem_sbm_set_mb_state(vm, mb_id,
+				    VIRTIO_MEM_SBM_MB_ONLINE_PARTIAL);
 	return 0;
 }
 
···
  * 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_mb_unplug_any_sb_online(struct virtio_mem *vm,
-					      unsigned long mb_id,
-					      uint64_t *nb_sb)
+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->nb_sb_per_mb &&
-	    virtio_mem_mb_test_sb_plugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
-		rc = virtio_mem_mb_unplug_sb_online(vm, mb_id, 0,
-						    vm->nb_sb_per_mb);
+	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->nb_sb_per_mb;
+			*nb_sb -= vm->sbm.sbs_per_mb;
 			goto unplugged;
 		} else if (rc != -EBUSY)
 			return rc;
 	}
 
 	/* Fallback to single subblocks. */
-	for (sb_id = vm->nb_sb_per_mb - 1; sb_id >= 0 && *nb_sb; sb_id--) {
+	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_mb_test_sb_plugged(vm, mb_id, sb_id, 1))
+		       !virtio_mem_sbm_test_sb_plugged(vm, mb_id, sb_id, 1))
 			sb_id--;
 		if (sb_id < 0)
 			break;
 
-		rc = virtio_mem_mb_unplug_sb_online(vm, mb_id, sb_id, 1);
+		rc = virtio_mem_sbm_unplug_sb_online(vm, mb_id, sb_id, 1);
 		if (rc == -EBUSY)
 			continue;
 		else if (rc)
···
 	 * remove it. This will usually not fail, as no memory is in use
 	 * anymore - however some other notifiers might NACK the request.
 	 */
-	if (virtio_mem_mb_test_sb_unplugged(vm, mb_id, 0, vm->nb_sb_per_mb)) {
+	if (virtio_mem_sbm_test_sb_unplugged(vm, mb_id, 0, vm->sbm.sbs_per_mb)) {
 		mutex_unlock(&vm->hotplug_mutex);
-		rc = virtio_mem_mb_offline_and_remove(vm, mb_id);
+		rc = virtio_mem_sbm_offline_and_remove_mb(vm, mb_id);
 		mutex_lock(&vm->hotplug_mutex);
 		if (!rc)
-			virtio_mem_mb_set_state(vm, mb_id,
-						VIRTIO_MEM_MB_STATE_UNUSED);
+			virtio_mem_sbm_set_mb_state(vm, mb_id,
+						    VIRTIO_MEM_SBM_MB_UNUSED);
 	}
 
 	return 0;
 }
 
-/*
- * Try to unplug the requested amount of memory.
- */
-static int virtio_mem_unplug_request(struct virtio_mem *vm, uint64_t diff)
+static int virtio_mem_sbm_unplug_request(struct virtio_mem *vm, uint64_t diff)
 {
-	uint64_t nb_sb = diff / vm->subblock_size;
+	uint64_t nb_sb = diff / vm->sbm.sb_size;
 	unsigned long mb_id;
 	int rc;
 
···
 	mutex_lock(&vm->hotplug_mutex);
 
 	/* Try to unplug subblocks of partially plugged offline blocks. */
-	virtio_mem_for_each_mb_state_rev(vm, mb_id,
-					 VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {
-		rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,
-							 &nb_sb);
+	virtio_mem_sbm_for_each_mb_rev(vm, mb_id,
+				       VIRTIO_MEM_SBM_MB_OFFLINE_PARTIAL) {
+		rc = virtio_mem_sbm_unplug_any_sb_offline(vm, mb_id, &nb_sb);
 		if (rc || !nb_sb)
 			goto out_unlock;
 		cond_resched();
 	}
 
 	/* Try to unplug subblocks of plugged offline blocks. */
-	virtio_mem_for_each_mb_state_rev(vm, mb_id,
-					 VIRTIO_MEM_MB_STATE_OFFLINE) {
-		rc = virtio_mem_mb_unplug_any_sb_offline(vm, mb_id,
-							 &nb_sb);
+	virtio_mem_sbm_for_each_mb_rev(vm, mb_id, VIRTIO_MEM_SBM_MB_OFFLINE) {
+		rc = virtio_mem_sbm_unplug_any_sb_offline(vm, mb_id, &nb_sb);
 		if (rc || !nb_sb)
 			goto out_unlock;
 		cond_resched();
···
 	}
 
 	/* Try to unplug subblocks of partially plugged online blocks. */
-	virtio_mem_for_each_mb_state_rev(vm, mb_id,
-					 VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL) {
-		rc = virtio_mem_mb_unplug_any_sb_online(vm, mb_id,
-							&nb_sb);
+	virtio_mem_sbm_for_each_mb_rev(vm, mb_id,
+				       VIRTIO_MEM_SBM_MB_ONLINE_PARTIAL) {
+		rc = virtio_mem_sbm_unplug_any_sb_online(vm, mb_id, &nb_sb);
 		if (rc || !nb_sb)
 			goto out_unlock;
 		mutex_unlock(&vm->hotplug_mutex);
···
 	}
 
 	/* Try to unplug subblocks of plugged online blocks. */
-	virtio_mem_for_each_mb_state_rev(vm, mb_id,
-					 VIRTIO_MEM_MB_STATE_ONLINE) {
-		rc = virtio_mem_mb_unplug_any_sb_online(vm, mb_id,
-							&nb_sb);
+	virtio_mem_sbm_for_each_mb_rev(vm, mb_id, VIRTIO_MEM_SBM_MB_ONLINE) {
+		rc = virtio_mem_sbm_unplug_any_sb_online(vm, mb_id, &nb_sb);
 		if (rc || !nb_sb)
 			goto out_unlock;
 		mutex_unlock(&vm->hotplug_mutex);
···
 }
 
 /*
+ * 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;
+
+	if (bbm_safe_unplug) {
+		/*
+		 * 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(pfn, PAGES_PER_SECTION);
+			if (rc) {
+				end_pfn = pfn;
+				goto rollback_safe_unplug;
+			}
+		}
+		mutex_unlock(&vm->hotplug_mutex);
+	}
+
+	rc = virtio_mem_bbm_offline_and_remove_bb(vm, bb_id);
+	if (rc) {
+		if (bbm_safe_unplug) {
+			mutex_lock(&vm->hotplug_mutex);
+			goto rollback_safe_unplug;
+		}
+		return rc;
+	}
+
+	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_safe_unplug:
+	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;
+}
+
+/*
+ * Try to remove a big block from Linux and unplug it. Will fail with
+ * -EBUSY if some memory is online.
+ *
+ * Will modify the state of the memory block.
+ */
+static int virtio_mem_bbm_remove_and_unplug_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_ADDED))
+		return -EINVAL;
+
+	rc = virtio_mem_bbm_remove_bb(vm, bb_id);
+	if (rc)
+		return -EBUSY;
+
+	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;
+}
+
+/*
+ * 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;
+}
+
+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;
+
+	if (!nb_bb)
+		return 0;
+
+	/* Try to unplug completely offline big blocks first. */
+	virtio_mem_bbm_for_each_bb_rev(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED) {
+		cond_resched();
+		/*
+		 * As we're holding no locks, this check is racy as memory
+		 * can get onlined in the meantime - but we'll fail gracefully.
+		 */
+		if (!virtio_mem_bbm_bb_is_offline(vm, bb_id))
+			continue;
+		rc = virtio_mem_bbm_remove_and_unplug_bb(vm, bb_id);
+		if (rc == -EBUSY)
+			continue;
+		if (!rc)
+			nb_bb--;
+		if (rc || !nb_bb)
+			return rc;
+	}
+
+	if (!unplug_online)
+		return 0;
+
+	/* Try to unplug any big blocks. */
+	virtio_mem_bbm_for_each_bb_rev(vm, bb_id, VIRTIO_MEM_BBM_BB_ADDED) {
+		cond_resched();
+		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;
+	}
+
+	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.
  */
 static int virtio_mem_unplug_pending_mb(struct virtio_mem *vm)
 {
-	unsigned long mb_id;
+	unsigned long id;
 	int rc;
 
-	virtio_mem_for_each_mb_state(vm, mb_id, VIRTIO_MEM_MB_STATE_PLUGGED) {
-		rc = virtio_mem_mb_unplug(vm, mb_id);
+	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_mb_set_state(vm, mb_id, VIRTIO_MEM_MB_STATE_UNUSED);
+		virtio_mem_sbm_set_mb_state(vm, id,
+					    VIRTIO_MEM_SBM_MB_UNUSED);
 	}
 
 	return 0;
···
 			usable_region_size, &usable_region_size);
 	end_addr = vm->addr + usable_region_size;
 	end_addr = min(end_addr, phys_limit);
-	vm->last_usable_mb_id = virtio_mem_phys_to_mb_id(end_addr) - 1;
+
+	if (vm->in_sbm)
+		vm->sbm.last_usable_mb_id =
+					 virtio_mem_phys_to_mb_id(end_addr) - 1;
+	else
+		vm->bbm.last_usable_bb_id =
+				     virtio_mem_phys_to_bb_id(vm, end_addr) - 1;
 
 	/* see if there is a request to change the size */
 	virtio_cread_le(vm->vdev, struct virtio_mem_config, requested_size,
···
 	if (vm->broken)
 		return;
 
+	atomic_set(&vm->wq_active, 1);
 retry:
 	rc = 0;
 
···
 			"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)
···
 static int virtio_mem_init(struct virtio_mem *vm)
 {
 	const uint64_t phys_limit = 1UL << MAX_PHYSMEM_BITS;
+	uint64_t sb_size, addr;
 	uint16_t node_id;
 
 	if (!vm->vdev->config->get) {
···
 	virtio_cread_le(vm->vdev, struct virtio_mem_config, region_size,
 			&vm->region_size);
 
-	/*
-	 * We always hotplug memory in memory block granularity. This way,
-	 * we have to wait for exactly one memory block to online.
-	 */
-	if (vm->device_block_size > memory_block_size_bytes()) {
-		dev_err(&vm->vdev->dev,
-			"The block size is not supported (too big).\n");
-		return -EINVAL;
-	}
+	/* 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);
 
 	/* bad device setup - warn only */
 	if (!IS_ALIGNED(vm->addr, memory_block_size_bytes()))
···
 			 "Some memory is not addressable. This can make some memory unusable.\n");
 
 	/*
-	 * Calculate the subblock size:
-	 * - At least MAX_ORDER - 1 / pageblock_order.
-	 * - At least the device block size.
-	 * In the worst case, a single subblock per memory block.
+	 * We want subblocks to span at least MAX_ORDER_NR_PAGES and
+	 * pageblock_nr_pages pages. This:
+	 * - Simplifies our page onlining code (virtio_mem_online_page_cb)
+	 *   and fake page onlining code (virtio_mem_fake_online).
+	 * - Is required for now for alloc_contig_range() to work reliably -
+	 *   it doesn't properly handle smaller granularity on ZONE_NORMAL.
 	 */
-	vm->subblock_size = PAGE_SIZE * 1ul << max_t(uint32_t, MAX_ORDER - 1,
-						     pageblock_order);
-	vm->subblock_size = max_t(uint64_t, vm->device_block_size,
-				  vm->subblock_size);
-	vm->nb_sb_per_mb = memory_block_size_bytes() / vm->subblock_size;
+	sb_size = max_t(uint64_t, MAX_ORDER_NR_PAGES,
+			pageblock_nr_pages) * PAGE_SIZE;
+	sb_size = max_t(uint64_t, vm->device_block_size, sb_size);
 
-	/* Round up to the next full memory block */
-	vm->first_mb_id = virtio_mem_phys_to_mb_id(vm->addr - 1 +
-						   memory_block_size_bytes());
-	vm->next_mb_id = vm->first_mb_id;
-	vm->last_mb_id = virtio_mem_phys_to_mb_id(vm->addr +
-			 vm->region_size) - 1;
+	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 = vm->addr + 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 = vm->addr + 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;
+	}
+
+	/* 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);
+	/* In BBM, we also want at least two big blocks. */
+	vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
+				      vm->offline_threshold);
 
 	dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
 	dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size);
···
 		 (unsigned long long)vm->device_block_size);
 	dev_info(&vm->vdev->dev, "memory block size: 0x%lx",
 		 memory_block_size_bytes());
-	dev_info(&vm->vdev->dev, "subblock size: 0x%llx",
-		 (unsigned long long)vm->subblock_size);
-	if (vm->nid != NUMA_NO_NODE)
+	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);
+	if (vm->nid != NUMA_NO_NODE && IS_ENABLED(CONFIG_NUMA))
 		dev_info(&vm->vdev->dev, "nid: %d", vm->nid);
 
 	return 0;
···
 	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)
···
 	cancel_work_sync(&vm->wq);
 	hrtimer_cancel(&vm->retry_timer);
 
-	/*
-	 * After we unregistered our callbacks, user space can online partially
-	 * plugged offline blocks. Make sure to remove them.
-	 */
-	virtio_mem_for_each_mb_state(vm, mb_id,
-				     VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL) {
-		rc = virtio_mem_mb_remove(vm, mb_id);
-		BUG_ON(rc);
-		virtio_mem_mb_set_state(vm, mb_id, VIRTIO_MEM_MB_STATE_UNUSED);
+	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.
+		 */
 	}
-	/*
-	 * 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);
···
 	 * the system. And there is no way to stop the driver/device from going
 	 * away. Warn at least.
 	 */
-	if (vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] ||
-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL] ||
-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE] ||
-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL]) {
+	if (virtio_mem_has_memory_added(vm)) {
 		dev_warn(&vdev->dev, "device still has system memory added\n");
 	} else {
 		virtio_mem_delete_resource(vm);
···
 	}
 
 	/* remove all tracking data - no locking needed */
-	vfree(vm->mb_state);
-	vfree(vm->sb_bitmap);
+	if (vm->in_sbm) {
+		vfree(vm->sbm.mb_states);
+		vfree(vm->sbm.sb_states);
+	} else {
+		vfree(vm->bbm.bb_states);
+	}
 
 	/* reset the device and cleanup the queues */
 	vdev->config->reset(vdev);

drivers/virtio/virtio_ring.c

···
 	vq->num_added = 0;
 	vq->packed_ring = true;
 	vq->use_dma_api = vring_use_dma_api(vdev);
-	list_add_tail(&vq->vq.list, &vdev->vqs);
 #ifdef DEBUG
 	vq->in_use = false;
 	vq->last_add_time_valid = false;
···
 			cpu_to_le16(vq->packed.event_flags_shadow);
 	}
 
+	list_add_tail(&vq->vq.list, &vdev->vqs);
 	return &vq->vq;
 
 err_desc_extra:
···
 err_desc_state:
 	kfree(vq);
 err_vq:
-	vring_free_queue(vdev, event_size_in_bytes, device, ring_dma_addr);
+	vring_free_queue(vdev, event_size_in_bytes, device, device_event_dma_addr);
 err_device:
-	vring_free_queue(vdev, event_size_in_bytes, driver, ring_dma_addr);
+	vring_free_queue(vdev, event_size_in_bytes, driver, driver_event_dma_addr);
 err_driver:
 	vring_free_queue(vdev, ring_size_in_bytes, ring, ring_dma_addr);
 err_ring:
···
 	vq->last_used_idx = 0;
 	vq->num_added = 0;
 	vq->use_dma_api = vring_use_dma_api(vdev);
-	list_add_tail(&vq->vq.list, &vdev->vqs);
 #ifdef DEBUG
 	vq->in_use = false;
 	vq->last_add_time_valid = false;
···
 	memset(vq->split.desc_state, 0, vring.num *
 			sizeof(struct vring_desc_state_split));
 
+	list_add_tail(&vq->vq.list, &vdev->vqs);
 	return &vq->vq;
 }
 EXPORT_SYMBOL_GPL(__vring_new_virtqueue);

include/linux/vdpa.h

···
  * @config: the configuration ops for this device.
  * @index: device index
  * @features_valid: were features initialized? for legacy guests
+ * @nvqs: maximum number of supported virtqueues
  */
 struct vdpa_device {
 	struct device dev;

include/uapi/linux/virtio_ids.h

···
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE. */
 
-#define VIRTIO_ID_NET		1 /* virtio net */
-#define VIRTIO_ID_BLOCK		2 /* virtio block */
-#define VIRTIO_ID_CONSOLE	3 /* virtio console */
-#define VIRTIO_ID_RNG		4 /* virtio rng */
-#define VIRTIO_ID_BALLOON	5 /* virtio balloon */
-#define VIRTIO_ID_RPMSG		7 /* virtio remote processor messaging */
-#define VIRTIO_ID_SCSI		8 /* virtio scsi */
-#define VIRTIO_ID_9P		9 /* 9p virtio console */
-#define VIRTIO_ID_RPROC_SERIAL 11 /* virtio remoteproc serial link */
-#define VIRTIO_ID_CAIF	       12 /* Virtio caif */
-#define VIRTIO_ID_GPU          16 /* virtio GPU */
-#define VIRTIO_ID_INPUT        18 /* virtio input */
-#define VIRTIO_ID_VSOCK        19 /* virtio vsock transport */
-#define VIRTIO_ID_CRYPTO       20 /* virtio crypto */
-#define VIRTIO_ID_IOMMU        23 /* virtio IOMMU */
-#define VIRTIO_ID_MEM          24 /* virtio mem */
-#define VIRTIO_ID_FS           26 /* virtio filesystem */
-#define VIRTIO_ID_PMEM         27 /* virtio pmem */
-#define VIRTIO_ID_MAC80211_HWSIM 29 /* virtio mac80211-hwsim */
+#define VIRTIO_ID_NET			1 /* virtio net */
+#define VIRTIO_ID_BLOCK			2 /* virtio block */
+#define VIRTIO_ID_CONSOLE		3 /* virtio console */
+#define VIRTIO_ID_RNG			4 /* virtio rng */
+#define VIRTIO_ID_BALLOON		5 /* virtio balloon */
+#define VIRTIO_ID_IOMEM			6 /* virtio ioMemory */
+#define VIRTIO_ID_RPMSG			7 /* virtio remote processor messaging */
+#define VIRTIO_ID_SCSI			8 /* virtio scsi */
+#define VIRTIO_ID_9P			9 /* 9p virtio console */
+#define VIRTIO_ID_MAC80211_WLAN		10 /* virtio WLAN MAC */
+#define VIRTIO_ID_RPROC_SERIAL		11 /* virtio remoteproc serial link */
+#define VIRTIO_ID_CAIF			12 /* Virtio caif */
+#define VIRTIO_ID_MEMORY_BALLOON	13 /* virtio memory balloon */
+#define VIRTIO_ID_GPU			16 /* virtio GPU */
+#define VIRTIO_ID_CLOCK			17 /* virtio clock/timer */
+#define VIRTIO_ID_INPUT			18 /* virtio input */
+#define VIRTIO_ID_VSOCK			19 /* virtio vsock transport */
+#define VIRTIO_ID_CRYPTO		20 /* virtio crypto */
+#define VIRTIO_ID_SIGNAL_DIST		21 /* virtio signal distribution device */
+#define VIRTIO_ID_PSTORE		22 /* virtio pstore device */
+#define VIRTIO_ID_IOMMU			23 /* virtio IOMMU */
+#define VIRTIO_ID_MEM			24 /* virtio mem */
+#define VIRTIO_ID_FS			26 /* virtio filesystem */
+#define VIRTIO_ID_PMEM			27 /* virtio pmem */
+#define VIRTIO_ID_MAC80211_HWSIM	29 /* virtio mac80211-hwsim */
 
 #endif /* _LINUX_VIRTIO_IDS_H */

mm/memory_hotplug.c

···
 }
 EXPORT_SYMBOL_GPL(remove_memory);
 
+static int try_offline_memory_block(struct memory_block *mem, void *arg)
+{
+	uint8_t online_type = MMOP_ONLINE_KERNEL;
+	uint8_t **online_types = arg;
+	struct page *page;
+	int rc;
+
+	/*
+	 * Sense the online_type via the zone of the memory block. Offlining
+	 * with multiple zones within one memory block will be rejected
+	 * by offlining code ... so we don't care about that.
+	 */
+	page = pfn_to_online_page(section_nr_to_pfn(mem->start_section_nr));
+	if (page && zone_idx(page_zone(page)) == ZONE_MOVABLE)
+		online_type = MMOP_ONLINE_MOVABLE;
+
+	rc = device_offline(&mem->dev);
+	/*
+	 * Default is MMOP_OFFLINE - change it only if offlining succeeded,
+	 * so try_reonline_memory_block() can do the right thing.
+	 */
+	if (!rc)
+		**online_types = online_type;
+
+	(*online_types)++;
+	/* Ignore if already offline. */
+	return rc < 0 ? rc : 0;
+}
+
+static int try_reonline_memory_block(struct memory_block *mem, void *arg)
+{
+	uint8_t **online_types = arg;
+	int rc;
+
+	if (**online_types != MMOP_OFFLINE) {
+		mem->online_type = **online_types;
+		rc = device_online(&mem->dev);
+		if (rc < 0)
+			pr_warn("%s: Failed to re-online memory: %d",
+				__func__, rc);
+	}
+
+	/* Continue processing all remaining memory blocks. */
+	(*online_types)++;
+	return 0;
+}
+
 /*
- * Try to offline and remove a memory block. Might take a long time to
- * finish in case memory is still in use. Primarily useful for memory devices
- * that logically unplugged all memory (so it's no longer in use) and want to
- * offline + remove the memory block.
+ * Try to offline and remove memory. Might take a long time to finish in case
+ * memory is still in use. Primarily useful for memory devices that logically
+ * unplugged all memory (so it's no longer in use) and want to offline + remove
+ * that memory.
  */
 int offline_and_remove_memory(int nid, u64 start, u64 size)
 {
-	struct memory_block *mem;
-	int rc = -EINVAL;
+	const unsigned long mb_count = size / memory_block_size_bytes();
+	uint8_t *online_types, *tmp;
+	int rc;
 
 	if (!IS_ALIGNED(start, memory_block_size_bytes()) ||
-	    size != memory_block_size_bytes())
-		return rc;
-
-	lock_device_hotplug();
-	mem = find_memory_block(__pfn_to_section(PFN_DOWN(start)));
-	if (mem)
-		rc = device_offline(&mem->dev);
-	/* Ignore if the device is already offline. */
-	if (rc > 0)
-		rc = 0;
+	    !IS_ALIGNED(size, memory_block_size_bytes()) || !size)
+		return -EINVAL;
 
 	/*
-	 * In case we succeeded to offline the memory block, remove it.
+	 * We'll remember the old online type of each memory block, so we can
+	 * try to revert whatever we did when offlining one memory block fails
+	 * after offlining some others succeeded.
+	 */
+	online_types = kmalloc_array(mb_count, sizeof(*online_types),
+				     GFP_KERNEL);
+	if (!online_types)
+		return -ENOMEM;
+	/*
+	 * Initialize all states to MMOP_OFFLINE, so when we abort processing in
+	 * try_offline_memory_block(), we'll skip all unprocessed blocks in
+	 * try_reonline_memory_block().
+	 */
+	memset(online_types, MMOP_OFFLINE, mb_count);
+
+	lock_device_hotplug();
+
+	tmp = online_types;
+	rc = walk_memory_blocks(start, size, &tmp, try_offline_memory_block);
+
+	/*
+	 * In case we succeeded to offline all memory, remove it.
 	 * This cannot fail as it cannot get onlined in the meantime.
 	 */
 	if (!rc) {
 		rc = try_remove_memory(nid, start, size);
-		WARN_ON_ONCE(rc);
+		if (rc)
+			pr_err("%s: Failed to remove memory: %d", __func__, rc);
+	}
+
+	/*
+	 * Rollback what we did. While memory onlining might theoretically fail
+	 * (nacked by a notifier), it barely ever happens.
+	 */
+	if (rc) {
+		tmp = online_types;
+		walk_memory_blocks(start, size, &tmp,
+				   try_reonline_memory_block);
 	}
 	unlock_device_hotplug();
 
+	kfree(online_types);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(offline_and_remove_memory);

tools/virtio/asm/barrier.h

···
 # define mb() abort()
 # define dma_rmb() abort()
 # define dma_wmb() abort()
+#elif defined(__aarch64__)
+#define dmb(opt) asm volatile("dmb " #opt : : : "memory")
+#define virt_mb() __sync_synchronize()
+#define virt_rmb() dmb(ishld)
+#define virt_wmb() dmb(ishst)
+#define virt_store_mb(var, value)  do { WRITE_ONCE(var, value); dmb(ish); } while (0)
+/* Weak barriers should be used. If not - it's a bug */
+# define mb() abort()
+# define dma_rmb() abort()
+# define dma_wmb() abort()
 #else
 #error Please fill in barrier macros
 #endif

tools/virtio/linux/bug.h

···
 #ifndef BUG_H
 #define BUG_H
 
+#include <asm/bug.h>
+
 #define BUG_ON(__BUG_ON_cond) assert(!(__BUG_ON_cond))
 
 #define BUILD_BUG_ON(x)

tools/virtio/linux/kernel.h

···
 
 #include <linux/compiler.h>
 #include <linux/types.h>
+#include <linux/overflow.h>
 #include <linux/list.h>
 #include <linux/printk.h>
 #include <linux/bug.h>
···
 #  define unlikely(x)	(__builtin_expect(!!(x), 0))
 # endif
 
+static inline void *krealloc_array(void *p, size_t new_n, size_t new_size, gfp_t gfp)
+{
+	size_t bytes;
+
+	if (unlikely(check_mul_overflow(new_n, new_size, &bytes)))
+		return NULL;
+
+	return krealloc(p, bytes, gfp);
+}
+
 #define pr_err(format, ...) fprintf (stderr, format, ## __VA_ARGS__)
 #ifdef DEBUG
 #define pr_debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)
···
 #endif
 #define dev_err(dev, format, ...) fprintf (stderr, format, ## __VA_ARGS__)
 #define dev_warn(dev, format, ...) fprintf (stderr, format, ## __VA_ARGS__)
-
-#define WARN_ON_ONCE(cond) (unlikely(cond) ? fprintf (stderr, "WARNING\n") : 0)
 
 #define min(x, y) ({				\
 	typeof(x) _min1 = (x);			\