1 files changed, 556 insertions, 181 deletions

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 04608a6502d7..0621878940ae 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -1,26 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*  Xenbus code for blkif backend
     Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au>
     Copyright (C) 2005 XenSource Ltd
 
-    This program is free software; you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation; either version 2 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
 
 */
 
-#include <stdarg.h>
+#define pr_fmt(fmt) "xen-blkback: " fmt
+
 #include <linux/module.h>
 #include <linux/kthread.h>
+#include <linux/pagemap.h>
 #include <xen/events.h>
 #include <xen/grant_table.h>
 #include "common.h"
 
+/* On the XenBus the max length of 'ring-ref%u'. */
+#define RINGREF_NAME_LEN (20)
+
 struct backend_info {
 	struct xenbus_device	*dev;
 	struct xen_blkif	*blkif;
@@ -33,14 +30,28 @@ struct backend_info {
 static struct kmem_cache *xen_blkif_cachep;
 static void connect(struct backend_info *);
 static int connect_ring(struct backend_info *);
-static void backend_changed(struct xenbus_watch *, const char **,
-			    unsigned int);
+static void backend_changed(struct xenbus_watch *, const char *,
+			    const char *);
+static void xen_blkif_free(struct xen_blkif *blkif);
+static void xen_vbd_free(struct xen_vbd *vbd);
 
 struct xenbus_device *xen_blkbk_xenbus(struct backend_info *be)
 {
 	return be->dev;
 }
 
+/*
+ * The last request could free the device from softirq context and
+ * xen_blkif_free() can sleep.
+ */
+static void xen_blkif_deferred_free(struct work_struct *work)
+{
+	struct xen_blkif *blkif;
+
+	blkif = container_of(work, struct xen_blkif, free_work);
+	xen_blkif_free(blkif);
+}
+
 static int blkback_name(struct xen_blkif *blkif, char *buf)
 {
 	char *devpath, *devname;
@@ -56,7 +67,7 @@ static int blkback_name(struct xen_blkif *blkif, char *buf)
 	else
 		devname  = devpath;
 
-	snprintf(buf, TASK_COMM_LEN, "blkback.%d.%s", blkif->domid, devname);
+	snprintf(buf, TASK_COMM_LEN, "%d.%s", blkif->domid, devname);
 	kfree(devpath);
 
 	return 0;
@@ -66,9 +77,11 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
 {
 	int err;
 	char name[TASK_COMM_LEN];
+	struct xen_blkif_ring *ring;
+	int i;
 
 	/* Not ready to connect? */
-	if (!blkif->irq || !blkif->vbd.bdev)
+	if (!blkif->rings || !blkif->rings[0].irq || !blkif->vbd.bdev_file)
 		return;
 
 	/* Already connected? */
@@ -86,121 +99,259 @@ static void xen_update_blkif_status(struct xen_blkif *blkif)
 		return;
 	}
 
-	err = filemap_write_and_wait(blkif->vbd.bdev->bd_inode->i_mapping);
+	err = sync_blockdev(file_bdev(blkif->vbd.bdev_file));
 	if (err) {
 		xenbus_dev_error(blkif->be->dev, err, "block flush");
 		return;
 	}
-	invalidate_inode_pages2(blkif->vbd.bdev->bd_inode->i_mapping);
+	invalidate_inode_pages2(blkif->vbd.bdev_file->f_mapping);
+
+	for (i = 0; i < blkif->nr_rings; i++) {
+		ring = &blkif->rings[i];
+		ring->xenblkd = kthread_run(xen_blkif_schedule, ring, "%s-%d", name, i);
+		if (IS_ERR(ring->xenblkd)) {
+			err = PTR_ERR(ring->xenblkd);
+			ring->xenblkd = NULL;
+			xenbus_dev_fatal(blkif->be->dev, err,
+					"start %s-%d xenblkd", name, i);
+			goto out;
+		}
+	}
+	return;
+
+out:
+	while (--i >= 0) {
+		ring = &blkif->rings[i];
+		kthread_stop(ring->xenblkd);
+	}
+	return;
+}
+
+static int xen_blkif_alloc_rings(struct xen_blkif *blkif)
+{
+	unsigned int r;
+
+	blkif->rings = kcalloc(blkif->nr_rings, sizeof(struct xen_blkif_ring),
+			       GFP_KERNEL);
+	if (!blkif->rings)
+		return -ENOMEM;
 
-	blkif->xenblkd = kthread_run(xen_blkif_schedule, blkif, "%s", name);
-	if (IS_ERR(blkif->xenblkd)) {
-		err = PTR_ERR(blkif->xenblkd);
-		blkif->xenblkd = NULL;
-		xenbus_dev_error(blkif->be->dev, err, "start xenblkd");
+	for (r = 0; r < blkif->nr_rings; r++) {
+		struct xen_blkif_ring *ring = &blkif->rings[r];
+
+		spin_lock_init(&ring->blk_ring_lock);
+		init_waitqueue_head(&ring->wq);
+		INIT_LIST_HEAD(&ring->pending_free);
+		INIT_LIST_HEAD(&ring->persistent_purge_list);
+		INIT_WORK(&ring->persistent_purge_work, xen_blkbk_unmap_purged_grants);
+		gnttab_page_cache_init(&ring->free_pages);
+
+		spin_lock_init(&ring->pending_free_lock);
+		init_waitqueue_head(&ring->pending_free_wq);
+		init_waitqueue_head(&ring->shutdown_wq);
+		ring->blkif = blkif;
+		ring->st_print = jiffies;
+		ring->active = true;
 	}
+
+	return 0;
 }
 
+/* Enable the persistent grants feature. */
+static bool feature_persistent = true;
+module_param(feature_persistent, bool, 0644);
+MODULE_PARM_DESC(feature_persistent, "Enables the persistent grants feature");
+
 static struct xen_blkif *xen_blkif_alloc(domid_t domid)
 {
 	struct xen_blkif *blkif;
 
+	BUILD_BUG_ON(MAX_INDIRECT_PAGES > BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST);
+
 	blkif = kmem_cache_zalloc(xen_blkif_cachep, GFP_KERNEL);
 	if (!blkif)
 		return ERR_PTR(-ENOMEM);
 
 	blkif->domid = domid;
-	spin_lock_init(&blkif->blk_ring_lock);
 	atomic_set(&blkif->refcnt, 1);
-	init_waitqueue_head(&blkif->wq);
 	init_completion(&blkif->drain_complete);
-	atomic_set(&blkif->drain, 0);
-	blkif->st_print = jiffies;
-	init_waitqueue_head(&blkif->waiting_to_free);
-	blkif->persistent_gnts.rb_node = NULL;
+
+	/*
+	 * Because freeing back to the cache may be deferred, it is not
+	 * safe to unload the module (and hence destroy the cache) until
+	 * this has completed. To prevent premature unloading, take an
+	 * extra module reference here and release only when the object
+	 * has been freed back to the cache.
+	 */
+	__module_get(THIS_MODULE);
+	INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
 
 	return blkif;
 }
 
-static int xen_blkif_map(struct xen_blkif *blkif, unsigned long shared_page,
-			 unsigned int evtchn)
+static int xen_blkif_map(struct xen_blkif_ring *ring, grant_ref_t *gref,
+			 unsigned int nr_grefs, unsigned int evtchn)
 {
 	int err;
+	struct xen_blkif *blkif = ring->blkif;
+	const struct blkif_common_sring *sring_common;
+	RING_IDX rsp_prod, req_prod;
+	unsigned int size;
 
 	/* Already connected through? */
-	if (blkif->irq)
+	if (ring->irq)
 		return 0;
 
-	err = xenbus_map_ring_valloc(blkif->be->dev, shared_page, &blkif->blk_ring);
+	err = xenbus_map_ring_valloc(blkif->be->dev, gref, nr_grefs,
+				     &ring->blk_ring);
 	if (err < 0)
 		return err;
 
+	sring_common = (struct blkif_common_sring *)ring->blk_ring;
+	rsp_prod = READ_ONCE(sring_common->rsp_prod);
+	req_prod = READ_ONCE(sring_common->req_prod);
+
 	switch (blkif->blk_protocol) {
 	case BLKIF_PROTOCOL_NATIVE:
 	{
-		struct blkif_sring *sring;
-		sring = (struct blkif_sring *)blkif->blk_ring;
-		BACK_RING_INIT(&blkif->blk_rings.native, sring, PAGE_SIZE);
+		struct blkif_sring *sring_native =
+			(struct blkif_sring *)ring->blk_ring;
+
+		BACK_RING_ATTACH(&ring->blk_rings.native, sring_native,
+				 rsp_prod, XEN_PAGE_SIZE * nr_grefs);
+		size = __RING_SIZE(sring_native, XEN_PAGE_SIZE * nr_grefs);
 		break;
 	}
 	case BLKIF_PROTOCOL_X86_32:
 	{
-		struct blkif_x86_32_sring *sring_x86_32;
-		sring_x86_32 = (struct blkif_x86_32_sring *)blkif->blk_ring;
-		BACK_RING_INIT(&blkif->blk_rings.x86_32, sring_x86_32, PAGE_SIZE);
+		struct blkif_x86_32_sring *sring_x86_32 =
+			(struct blkif_x86_32_sring *)ring->blk_ring;
+
+		BACK_RING_ATTACH(&ring->blk_rings.x86_32, sring_x86_32,
+				 rsp_prod, XEN_PAGE_SIZE * nr_grefs);
+		size = __RING_SIZE(sring_x86_32, XEN_PAGE_SIZE * nr_grefs);
 		break;
 	}
 	case BLKIF_PROTOCOL_X86_64:
 	{
-		struct blkif_x86_64_sring *sring_x86_64;
-		sring_x86_64 = (struct blkif_x86_64_sring *)blkif->blk_ring;
-		BACK_RING_INIT(&blkif->blk_rings.x86_64, sring_x86_64, PAGE_SIZE);
+		struct blkif_x86_64_sring *sring_x86_64 =
+			(struct blkif_x86_64_sring *)ring->blk_ring;
+
+		BACK_RING_ATTACH(&ring->blk_rings.x86_64, sring_x86_64,
+				 rsp_prod, XEN_PAGE_SIZE * nr_grefs);
+		size = __RING_SIZE(sring_x86_64, XEN_PAGE_SIZE * nr_grefs);
 		break;
 	}
 	default:
 		BUG();
 	}
 
-	err = bind_interdomain_evtchn_to_irqhandler(blkif->domid, evtchn,
-						    xen_blkif_be_int, 0,
-						    "blkif-backend", blkif);
-	if (err < 0) {
-		xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
-		blkif->blk_rings.common.sring = NULL;
-		return err;
-	}
-	blkif->irq = err;
+	err = -EIO;
+	if (req_prod - rsp_prod > size)
+		goto fail;
+
+	err = bind_interdomain_evtchn_to_irqhandler_lateeoi(blkif->be->dev,
+			evtchn, xen_blkif_be_int, 0, "blkif-backend", ring);
+	if (err < 0)
+		goto fail;
+	ring->irq = err;
 
 	return 0;
+
+fail:
+	xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
+	ring->blk_rings.common.sring = NULL;
+	return err;
 }
 
-static void xen_blkif_disconnect(struct xen_blkif *blkif)
+static int xen_blkif_disconnect(struct xen_blkif *blkif)
 {
-	if (blkif->xenblkd) {
-		kthread_stop(blkif->xenblkd);
-		blkif->xenblkd = NULL;
-	}
+	struct pending_req *req, *n;
+	unsigned int j, r;
+	bool busy = false;
 
-	atomic_dec(&blkif->refcnt);
-	wait_event(blkif->waiting_to_free, atomic_read(&blkif->refcnt) == 0);
-	atomic_inc(&blkif->refcnt);
+	for (r = 0; r < blkif->nr_rings; r++) {
+		struct xen_blkif_ring *ring = &blkif->rings[r];
+		unsigned int i = 0;
 
-	if (blkif->irq) {
-		unbind_from_irqhandler(blkif->irq, blkif);
-		blkif->irq = 0;
-	}
+		if (!ring->active)
+			continue;
+
+		if (ring->xenblkd) {
+			kthread_stop(ring->xenblkd);
+			ring->xenblkd = NULL;
+			wake_up(&ring->shutdown_wq);
+		}
+
+		/* The above kthread_stop() guarantees that at this point we
+		 * don't have any discard_io or other_io requests. So, checking
+		 * for inflight IO is enough.
+		 */
+		if (atomic_read(&ring->inflight) > 0) {
+			busy = true;
+			continue;
+		}
+
+		if (ring->irq) {
+			unbind_from_irqhandler(ring->irq, ring);
+			ring->irq = 0;
+		}
 
-	if (blkif->blk_rings.common.sring) {
-		xenbus_unmap_ring_vfree(blkif->be->dev, blkif->blk_ring);
-		blkif->blk_rings.common.sring = NULL;
+		if (ring->blk_rings.common.sring) {
+			xenbus_unmap_ring_vfree(blkif->be->dev, ring->blk_ring);
+			ring->blk_rings.common.sring = NULL;
+		}
+
+		/* Remove all persistent grants and the cache of ballooned pages. */
+		xen_blkbk_free_caches(ring);
+
+		/* Check that there is no request in use */
+		list_for_each_entry_safe(req, n, &ring->pending_free, free_list) {
+			list_del(&req->free_list);
+
+			for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++)
+				kfree(req->segments[j]);
+
+			for (j = 0; j < MAX_INDIRECT_PAGES; j++)
+				kfree(req->indirect_pages[j]);
+
+			kfree(req);
+			i++;
+		}
+
+		BUG_ON(atomic_read(&ring->persistent_gnt_in_use) != 0);
+		BUG_ON(!list_empty(&ring->persistent_purge_list));
+		BUG_ON(!RB_EMPTY_ROOT(&ring->persistent_gnts));
+		BUG_ON(ring->free_pages.num_pages != 0);
+		BUG_ON(ring->persistent_gnt_c != 0);
+		WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));
+		ring->active = false;
 	}
+	if (busy)
+		return -EBUSY;
+
+	blkif->nr_ring_pages = 0;
+	/*
+	 * blkif->rings was allocated in connect_ring, so we should free it in
+	 * here.
+	 */
+	kfree(blkif->rings);
+	blkif->rings = NULL;
+	blkif->nr_rings = 0;
+
+	return 0;
 }
 
 static void xen_blkif_free(struct xen_blkif *blkif)
 {
-	if (!atomic_dec_and_test(&blkif->refcnt))
-		BUG();
+	WARN_ON(xen_blkif_disconnect(blkif));
+	xen_vbd_free(&blkif->vbd);
+	kfree(blkif->be->mode);
+	kfree(blkif->be);
+
+	/* Make sure everything is drained before shutting down */
 	kmem_cache_free(xen_blkif_cachep, blkif);
+	module_put(THIS_MODULE);
 }
 
 int __init xen_blkif_interface_init(void)
@@ -214,29 +365,48 @@ int __init xen_blkif_interface_init(void)
 	return 0;
 }
 
+void xen_blkif_interface_fini(void)
+{
+	kmem_cache_destroy(xen_blkif_cachep);
+	xen_blkif_cachep = NULL;
+}
+
 /*
  *  sysfs interface for VBD I/O requests
  */
 
-#define VBD_SHOW(name, format, args...)					\
+#define VBD_SHOW_ALLRING(name, format)					\
 	static ssize_t show_##name(struct device *_dev,			\
 				   struct device_attribute *attr,	\
 				   char *buf)				\
 	{								\
 		struct xenbus_device *dev = to_xenbus_device(_dev);	\
 		struct backend_info *be = dev_get_drvdata(&dev->dev);	\
+		struct xen_blkif *blkif = be->blkif;			\
+		unsigned int i;						\
+		unsigned long long result = 0;				\
 									\
-		return sprintf(buf, format, ##args);			\
+		if (!blkif->rings)				\
+			goto out;					\
+									\
+		for (i = 0; i < blkif->nr_rings; i++) {		\
+			struct xen_blkif_ring *ring = &blkif->rings[i];	\
+									\
+			result += ring->st_##name;			\
+		}							\
+									\
+out:									\
+		return sprintf(buf, format, result);			\
 	}								\
-	static DEVICE_ATTR(name, S_IRUGO, show_##name, NULL)
+	static DEVICE_ATTR(name, 0444, show_##name, NULL)
 
-VBD_SHOW(oo_req,  "%llu\n", be->blkif->st_oo_req);
-VBD_SHOW(rd_req,  "%llu\n", be->blkif->st_rd_req);
-VBD_SHOW(wr_req,  "%llu\n", be->blkif->st_wr_req);
-VBD_SHOW(f_req,  "%llu\n", be->blkif->st_f_req);
-VBD_SHOW(ds_req,  "%llu\n", be->blkif->st_ds_req);
-VBD_SHOW(rd_sect, "%llu\n", be->blkif->st_rd_sect);
-VBD_SHOW(wr_sect, "%llu\n", be->blkif->st_wr_sect);
+VBD_SHOW_ALLRING(oo_req,  "%llu\n");
+VBD_SHOW_ALLRING(rd_req,  "%llu\n");
+VBD_SHOW_ALLRING(wr_req,  "%llu\n");
+VBD_SHOW_ALLRING(f_req,  "%llu\n");
+VBD_SHOW_ALLRING(ds_req,  "%llu\n");
+VBD_SHOW_ALLRING(rd_sect, "%llu\n");
+VBD_SHOW_ALLRING(wr_sect, "%llu\n");
 
 static struct attribute *xen_vbdstat_attrs[] = {
 	&dev_attr_oo_req.attr,
@@ -249,11 +419,23 @@ static struct attribute *xen_vbdstat_attrs[] = {
 	NULL
 };
 
-static struct attribute_group xen_vbdstat_group = {
+static const struct attribute_group xen_vbdstat_group = {
 	.name = "statistics",
 	.attrs = xen_vbdstat_attrs,
 };
 
+#define VBD_SHOW(name, format, args...)					\
+	static ssize_t show_##name(struct device *_dev,			\
+				   struct device_attribute *attr,	\
+				   char *buf)				\
+	{								\
+		struct xenbus_device *dev = to_xenbus_device(_dev);	\
+		struct backend_info *be = dev_get_drvdata(&dev->dev);	\
+									\
+		return sprintf(buf, format, ##args);			\
+	}								\
+	static DEVICE_ATTR(name, 0444, show_##name, NULL)
+
 VBD_SHOW(physical_device, "%x:%x\n", be->major, be->minor);
 VBD_SHOW(mode, "%s\n", be->mode);
 
@@ -288,12 +470,11 @@ static void xenvbd_sysfs_delif(struct xenbus_device *dev)
 	device_remove_file(&dev->dev, &dev_attr_physical_device);
 }
 
-
 static void xen_vbd_free(struct xen_vbd *vbd)
 {
-	if (vbd->bdev)
-		blkdev_put(vbd->bdev, vbd->readonly ? FMODE_READ : FMODE_WRITE);
-	vbd->bdev = NULL;
+	if (vbd->bdev_file)
+		fput(vbd->bdev_file);
+	vbd->bdev_file = NULL;
 }
 
 static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
@@ -301,8 +482,7 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
 			  int cdrom)
 {
 	struct xen_vbd *vbd;
-	struct block_device *bdev;
-	struct request_queue *q;
+	struct file *bdev_file;
 
 	vbd = &blkif->vbd;
 	vbd->handle   = handle;
@@ -311,45 +491,44 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle,
 
 	vbd->pdevice  = MKDEV(major, minor);
 
-	bdev = blkdev_get_by_dev(vbd->pdevice, vbd->readonly ?
-				 FMODE_READ : FMODE_WRITE, NULL);
+	bdev_file = bdev_file_open_by_dev(vbd->pdevice, vbd->readonly ?
+				 BLK_OPEN_READ : BLK_OPEN_WRITE, NULL, NULL);
 
-	if (IS_ERR(bdev)) {
-		DPRINTK("xen_vbd_create: device %08x could not be opened.\n",
+	if (IS_ERR(bdev_file)) {
+		pr_warn("xen_vbd_create: device %08x could not be opened\n",
 			vbd->pdevice);
 		return -ENOENT;
 	}
 
-	vbd->bdev = bdev;
-	if (vbd->bdev->bd_disk == NULL) {
-		DPRINTK("xen_vbd_create: device %08x doesn't exist.\n",
+	vbd->bdev_file = bdev_file;
+	if (file_bdev(vbd->bdev_file)->bd_disk == NULL) {
+		pr_warn("xen_vbd_create: device %08x doesn't exist\n",
 			vbd->pdevice);
 		xen_vbd_free(vbd);
 		return -ENOENT;
 	}
 	vbd->size = vbd_sz(vbd);
 
-	if (vbd->bdev->bd_disk->flags & GENHD_FL_CD || cdrom)
+	if (cdrom || disk_to_cdi(file_bdev(vbd->bdev_file)->bd_disk))
 		vbd->type |= VDISK_CDROM;
-	if (vbd->bdev->bd_disk->flags & GENHD_FL_REMOVABLE)
+	if (file_bdev(vbd->bdev_file)->bd_disk->flags & GENHD_FL_REMOVABLE)
 		vbd->type |= VDISK_REMOVABLE;
 
-	q = bdev_get_queue(bdev);
-	if (q && q->flush_flags)
+	if (bdev_write_cache(file_bdev(bdev_file)))
 		vbd->flush_support = true;
-
-	if (q && blk_queue_secdiscard(q))
+	if (bdev_max_secure_erase_sectors(file_bdev(bdev_file)))
 		vbd->discard_secure = true;
 
-	DPRINTK("Successful creation of handle=%04x (dom=%u)\n",
+	pr_debug("Successful creation of handle=%04x (dom=%u)\n",
 		handle, blkif->domid);
 	return 0;
 }
-static int xen_blkbk_remove(struct xenbus_device *dev)
+
+static void xen_blkbk_remove(struct xenbus_device *dev)
 {
 	struct backend_info *be = dev_get_drvdata(&dev->dev);
 
-	DPRINTK("");
+	pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id);
 
 	if (be->major || be->minor)
 		xenvbd_sysfs_delif(dev);
@@ -360,17 +539,14 @@ static int xen_blkbk_remove(struct xenbus_device *dev)
 		be->backend_watch.node = NULL;
 	}
 
+	dev_set_drvdata(&dev->dev, NULL);
+
 	if (be->blkif) {
 		xen_blkif_disconnect(be->blkif);
-		xen_vbd_free(&be->blkif->vbd);
-		xen_blkif_free(be->blkif);
-		be->blkif = NULL;
-	}
 
-	kfree(be->mode);
-	kfree(be);
-	dev_set_drvdata(&dev->dev, NULL);
-	return 0;
+		/* Put the reference we set in xen_blkif_alloc(). */
+		xen_blkif_put(be->blkif);
+	}
 }
 
 int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt,
@@ -393,20 +569,22 @@ static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info
 	struct xen_blkif *blkif = be->blkif;
 	int err;
 	int state = 0;
-	struct block_device *bdev = be->blkif->vbd.bdev;
-	struct request_queue *q = bdev_get_queue(bdev);
+	struct block_device *bdev = file_bdev(be->blkif->vbd.bdev_file);
 
-	if (blk_queue_discard(q)) {
+	if (!xenbus_read_unsigned(dev->nodename, "discard-enable", 1))
+		return;
+
+	if (bdev_max_discard_sectors(bdev)) {
 		err = xenbus_printf(xbt, dev->nodename,
 			"discard-granularity", "%u",
-			q->limits.discard_granularity);
+			bdev_discard_granularity(bdev));
 		if (err) {
 			dev_warn(&dev->dev, "writing discard-granularity (%d)", err);
 			return;
 		}
 		err = xenbus_printf(xbt, dev->nodename,
 			"discard-alignment", "%u",
-			q->limits.discard_alignment);
+			bdev_discard_alignment(bdev));
 		if (err) {
 			dev_warn(&dev->dev, "writing discard-alignment (%d)", err);
 			return;
@@ -426,6 +604,7 @@ static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info
 	if (err)
 		dev_warn(&dev->dev, "writing feature-discard (%d)", err);
 }
+
 int xen_blkbk_barrier(struct xenbus_transaction xbt,
 		      struct backend_info *be, int state)
 {
@@ -451,6 +630,10 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
 	int err;
 	struct backend_info *be = kzalloc(sizeof(struct backend_info),
 					  GFP_KERNEL);
+
+	/* match the pr_debug in xen_blkbk_remove */
+	pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id);
+
 	if (!be) {
 		xenbus_dev_fatal(dev, -ENOMEM,
 				 "allocating backend structure");
@@ -467,14 +650,34 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
 		goto fail;
 	}
 
+	err = xenbus_printf(XBT_NIL, dev->nodename,
+			    "feature-max-indirect-segments", "%u",
+			    MAX_INDIRECT_SEGMENTS);
+	if (err)
+		dev_warn(&dev->dev,
+			 "writing %s/feature-max-indirect-segments (%d)",
+			 dev->nodename, err);
+
+	/* Multi-queue: advertise how many queues are supported by us.*/
+	err = xenbus_printf(XBT_NIL, dev->nodename,
+			    "multi-queue-max-queues", "%u", xenblk_max_queues);
+	if (err)
+		pr_warn("Error writing multi-queue-max-queues\n");
+
 	/* setup back pointer */
 	be->blkif->be = be;
 
-	err = xenbus_watch_pathfmt(dev, &be->backend_watch, backend_changed,
+	err = xenbus_watch_pathfmt(dev, &be->backend_watch, NULL,
+				   backend_changed,
 				   "%s/%s", dev->nodename, "physical-device");
 	if (err)
 		goto fail;
 
+	err = xenbus_printf(XBT_NIL, dev->nodename, "max-ring-page-order", "%u",
+			    xen_blkif_max_ring_order);
+	if (err)
+		pr_warn("%s write out 'max-ring-page-order' failed\n", __func__);
+
 	err = xenbus_switch_state(dev, XenbusStateInitWait);
 	if (err)
 		goto fail;
@@ -482,19 +685,18 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
 	return 0;
 
 fail:
-	DPRINTK("failed");
+	pr_warn("%s failed\n", __func__);
 	xen_blkbk_remove(dev);
 	return err;
 }
 
-
 /*
  * Callback received when the hotplug scripts have placed the physical-device
  * node.  Read it and the mode node, and create a vbd.  If the frontend is
  * ready, connect.
  */
 static void backend_changed(struct xenbus_watch *watch,
-			    const char **vec, unsigned int len)
+			    const char *path, const char *token)
 {
 	int err;
 	unsigned major;
@@ -506,7 +708,7 @@ static void backend_changed(struct xenbus_watch *watch,
 	unsigned long handle;
 	char *device_type;
 
-	DPRINTK("");
+	pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id);
 
 	err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x",
 			   &major, &minor);
@@ -525,7 +727,7 @@ static void backend_changed(struct xenbus_watch *watch,
 
 	if (be->major | be->minor) {
 		if (be->major != major || be->minor != minor)
-			pr_warn(DRV_PFX "changing physical device (from %x:%x to %x:%x) not supported.\n",
+			pr_warn("changing physical device (from %x:%x to %x:%x) not supported.\n",
 				be->major, be->minor, major, minor);
 		return;
 	}
@@ -545,9 +747,12 @@ static void backend_changed(struct xenbus_watch *watch,
 	}
 
 	/* Front end dir is a number, which is used as the handle. */
-	err = strict_strtoul(strrchr(dev->otherend, '/') + 1, 0, &handle);
-	if (err)
+	err = kstrtoul(strrchr(dev->otherend, '/') + 1, 0, &handle);
+	if (err) {
+		kfree(be->mode);
+		be->mode = NULL;
 		return;
+	}
 
 	be->major = major;
 	be->minor = minor;
@@ -576,7 +781,6 @@ static void backend_changed(struct xenbus_watch *watch,
 	}
 }
 
-
 /*
  * Callback received when the frontend's state changes.
  */
@@ -586,13 +790,12 @@ static void frontend_changed(struct xenbus_device *dev,
 	struct backend_info *be = dev_get_drvdata(&dev->dev);
 	int err;
 
-	DPRINTK("%s", xenbus_strstate(frontend_state));
+	pr_debug("%s %p %s\n", __func__, dev, xenbus_strstate(frontend_state));
 
 	switch (frontend_state) {
 	case XenbusStateInitialising:
 		if (dev->state == XenbusStateClosed) {
-			pr_info(DRV_PFX "%s: prepare for reconnect\n",
-				dev->nodename);
+			pr_info("%s: prepare for reconnect\n", dev->nodename);
 			xenbus_switch_state(dev, XenbusStateInitWait);
 		}
 		break;
@@ -611,11 +814,21 @@ static void frontend_changed(struct xenbus_device *dev,
 		 * Enforce precondition before potential leak point.
 		 * xen_blkif_disconnect() is idempotent.
 		 */
-		xen_blkif_disconnect(be->blkif);
+		err = xen_blkif_disconnect(be->blkif);
+		if (err) {
+			xenbus_dev_fatal(dev, err, "pending I/O");
+			break;
+		}
 
 		err = connect_ring(be);
-		if (err)
+		if (err) {
+			/*
+			 * Clean up so that memory resources can be used by
+			 * other devices. connect_ring reported already error.
+			 */
+			xen_blkif_disconnect(be->blkif);
 			break;
+		}
 		xen_update_blkif_status(be->blkif);
 		break;
 
@@ -628,7 +841,8 @@ static void frontend_changed(struct xenbus_device *dev,
 		xenbus_switch_state(dev, XenbusStateClosed);
 		if (xenbus_dev_is_online(dev))
 			break;
-		/* fall through if not online */
+		fallthrough;
+		/* if not online */
 	case XenbusStateUnknown:
 		/* implies xen_blkif_disconnect() via xen_blkbk_remove() */
 		device_unregister(&dev->dev);
@@ -641,9 +855,27 @@ static void frontend_changed(struct xenbus_device *dev,
 	}
 }
 
+/* Once a memory pressure is detected, squeeze free page pools for a while. */
+static unsigned int buffer_squeeze_duration_ms = 10;
+module_param_named(buffer_squeeze_duration_ms,
+		buffer_squeeze_duration_ms, int, 0644);
+MODULE_PARM_DESC(buffer_squeeze_duration_ms,
+"Duration in ms to squeeze pages buffer when a memory pressure is detected");
 
-/* ** Connection ** */
+/*
+ * Callback received when the memory pressure is detected.
+ */
+static void reclaim_memory(struct xenbus_device *dev)
+{
+	struct backend_info *be = dev_get_drvdata(&dev->dev);
+
+	if (!be)
+		return;
+	be->blkif->buffer_squeeze_end = jiffies +
+		msecs_to_jiffies(buffer_squeeze_duration_ms);
+}
 
+/* ** Connection ** */
 
 /*
  * Write the physical details regarding the block device to the store, and
@@ -655,7 +887,7 @@ static void connect(struct backend_info *be)
 	int err;
 	struct xenbus_device *dev = be->dev;
 
-	DPRINTK("%s", dev->otherend);
+	pr_debug("%s %s\n", __func__, dev->otherend);
 
 	/* Supply the information about the device the frontend needs */
 again:
@@ -672,7 +904,8 @@ again:
 
 	xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support);
 
-	err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u", 1);
+	err = xenbus_printf(xbt, dev->nodename, "feature-persistent", "%u",
+			be->blkif->vbd.feature_gnt_persistent_parm);
 	if (err) {
 		xenbus_dev_fatal(dev, err, "writing %s/feature-persistent",
 				 dev->nodename);
@@ -697,13 +930,19 @@ again:
 		goto abort;
 	}
 	err = xenbus_printf(xbt, dev->nodename, "sector-size", "%lu",
-			    (unsigned long)
-			    bdev_logical_block_size(be->blkif->vbd.bdev));
+			    (unsigned long)bdev_logical_block_size(
+					file_bdev(be->blkif->vbd.bdev_file)));
 	if (err) {
 		xenbus_dev_fatal(dev, err, "writing %s/sector-size",
 				 dev->nodename);
 		goto abort;
 	}
+	err = xenbus_printf(xbt, dev->nodename, "physical-sector-size", "%u",
+			    bdev_physical_block_size(
+					file_bdev(be->blkif->vbd.bdev_file)));
+	if (err)
+		xenbus_dev_error(dev, err, "writing %s/physical-sector-size",
+				 dev->nodename);
 
 	err = xenbus_transaction_end(xbt, 0);
 	if (err == -EAGAIN)
@@ -721,84 +960,220 @@ again:
 	xenbus_transaction_end(xbt, 1);
 }
 
-
-static int connect_ring(struct backend_info *be)
+/*
+ * Each ring may have multi pages, depends on "ring-page-order".
+ */
+static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir)
 {
-	struct xenbus_device *dev = be->dev;
-	unsigned long ring_ref;
-	unsigned int evtchn;
-	unsigned int pers_grants;
-	char protocol[64] = "";
-	int err;
+	unsigned int ring_ref[XENBUS_MAX_RING_GRANTS];
+	struct pending_req *req, *n;
+	int err, i, j;
+	struct xen_blkif *blkif = ring->blkif;
+	struct xenbus_device *dev = blkif->be->dev;
+	unsigned int nr_grefs, evtchn;
+
+	err = xenbus_scanf(XBT_NIL, dir, "event-channel", "%u",
+			  &evtchn);
+	if (err != 1) {
+		err = -EINVAL;
+		xenbus_dev_fatal(dev, err, "reading %s/event-channel", dir);
+		return err;
+	}
+
+	nr_grefs = blkif->nr_ring_pages;
+
+	if (unlikely(!nr_grefs)) {
+		WARN_ON(true);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < nr_grefs; i++) {
+		char ring_ref_name[RINGREF_NAME_LEN];
+
+		if (blkif->multi_ref)
+			snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
+		else {
+			WARN_ON(i != 0);
+			snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref");
+		}
 
-	DPRINTK("%s", dev->otherend);
+		err = xenbus_scanf(XBT_NIL, dir, ring_ref_name,
+				   "%u", &ring_ref[i]);
 
-	err = xenbus_gather(XBT_NIL, dev->otherend, "ring-ref", "%lu",
-			    &ring_ref, "event-channel", "%u", &evtchn, NULL);
+		if (err != 1) {
+			err = -EINVAL;
+			xenbus_dev_fatal(dev, err, "reading %s/%s",
+					 dir, ring_ref_name);
+			return err;
+		}
+	}
+
+	err = -ENOMEM;
+	for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) {
+		req = kzalloc(sizeof(*req), GFP_KERNEL);
+		if (!req)
+			goto fail;
+		list_add_tail(&req->free_list, &ring->pending_free);
+		for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
+			req->segments[j] = kzalloc(sizeof(*req->segments[0]), GFP_KERNEL);
+			if (!req->segments[j])
+				goto fail;
+		}
+		for (j = 0; j < MAX_INDIRECT_PAGES; j++) {
+			req->indirect_pages[j] = kzalloc(sizeof(*req->indirect_pages[0]),
+							 GFP_KERNEL);
+			if (!req->indirect_pages[j])
+				goto fail;
+		}
+	}
+
+	/* Map the shared frame, irq etc. */
+	err = xen_blkif_map(ring, ring_ref, nr_grefs, evtchn);
 	if (err) {
-		xenbus_dev_fatal(dev, err,
-				 "reading %s/ring-ref and event-channel",
-				 dev->otherend);
-		return err;
+		xenbus_dev_fatal(dev, err, "mapping ring-ref port %u", evtchn);
+		goto fail;
 	}
 
-	be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
-	err = xenbus_gather(XBT_NIL, dev->otherend, "protocol",
-			    "%63s", protocol, NULL);
-	if (err)
-		strcpy(protocol, "unspecified, assuming native");
+	return 0;
+
+fail:
+	list_for_each_entry_safe(req, n, &ring->pending_free, free_list) {
+		list_del(&req->free_list);
+		for (j = 0; j < MAX_INDIRECT_SEGMENTS; j++) {
+			if (!req->segments[j])
+				break;
+			kfree(req->segments[j]);
+		}
+		for (j = 0; j < MAX_INDIRECT_PAGES; j++) {
+			if (!req->indirect_pages[j])
+				break;
+			kfree(req->indirect_pages[j]);
+		}
+		kfree(req);
+	}
+	return err;
+}
+
+static int connect_ring(struct backend_info *be)
+{
+	struct xenbus_device *dev = be->dev;
+	struct xen_blkif *blkif = be->blkif;
+	char protocol[64] = "";
+	int err, i;
+	char *xspath;
+	size_t xspathsize;
+	const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */
+	unsigned int requested_num_queues = 0;
+	unsigned int ring_page_order;
+
+	pr_debug("%s %s\n", __func__, dev->otherend);
+
+	blkif->blk_protocol = BLKIF_PROTOCOL_DEFAULT;
+	err = xenbus_scanf(XBT_NIL, dev->otherend, "protocol",
+			   "%63s", protocol);
+	if (err <= 0)
+		strcpy(protocol, "unspecified, assuming default");
 	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_NATIVE))
-		be->blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
+		blkif->blk_protocol = BLKIF_PROTOCOL_NATIVE;
 	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_32))
-		be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_32;
+		blkif->blk_protocol = BLKIF_PROTOCOL_X86_32;
 	else if (0 == strcmp(protocol, XEN_IO_PROTO_ABI_X86_64))
-		be->blkif->blk_protocol = BLKIF_PROTOCOL_X86_64;
+		blkif->blk_protocol = BLKIF_PROTOCOL_X86_64;
 	else {
 		xenbus_dev_fatal(dev, err, "unknown fe protocol %s", protocol);
-		return -1;
+		return -ENOSYS;
 	}
-	err = xenbus_gather(XBT_NIL, dev->otherend,
-			    "feature-persistent", "%u",
-			    &pers_grants, NULL);
-	if (err)
-		pers_grants = 0;
-
-	be->blkif->vbd.feature_gnt_persistent = pers_grants;
-	be->blkif->vbd.overflow_max_grants = 0;
 
-	pr_info(DRV_PFX "ring-ref %ld, event-channel %d, protocol %d (%s) %s\n",
-		ring_ref, evtchn, be->blkif->blk_protocol, protocol,
-		pers_grants ? "persistent grants" : "");
+	blkif->vbd.feature_gnt_persistent_parm = feature_persistent;
+	blkif->vbd.feature_gnt_persistent =
+		blkif->vbd.feature_gnt_persistent_parm &&
+		xenbus_read_unsigned(dev->otherend, "feature-persistent", 0);
+
+	blkif->vbd.overflow_max_grants = 0;
+
+	/*
+	 * Read the number of hardware queues from frontend.
+	 */
+	requested_num_queues = xenbus_read_unsigned(dev->otherend,
+						    "multi-queue-num-queues",
+						    1);
+	if (requested_num_queues > xenblk_max_queues
+	    || requested_num_queues == 0) {
+		/* Buggy or malicious guest. */
+		xenbus_dev_fatal(dev, err,
+				"guest requested %u queues, exceeding the maximum of %u.",
+				requested_num_queues, xenblk_max_queues);
+		return -ENOSYS;
+	}
+	blkif->nr_rings = requested_num_queues;
+	if (xen_blkif_alloc_rings(blkif))
+		return -ENOMEM;
 
-	/* Map the shared frame, irq etc. */
-	err = xen_blkif_map(be->blkif, ring_ref, evtchn);
-	if (err) {
-		xenbus_dev_fatal(dev, err, "mapping ring-ref %lu port %u",
-				 ring_ref, evtchn);
+	pr_info("%s: using %d queues, protocol %d (%s) %s\n", dev->nodename,
+		 blkif->nr_rings, blkif->blk_protocol, protocol,
+		 blkif->vbd.feature_gnt_persistent ? "persistent grants" : "");
+
+	err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u",
+			   &ring_page_order);
+	if (err != 1) {
+		blkif->nr_ring_pages = 1;
+		blkif->multi_ref = false;
+	} else if (ring_page_order <= xen_blkif_max_ring_order) {
+		blkif->nr_ring_pages = 1 << ring_page_order;
+		blkif->multi_ref = true;
+	} else {
+		err = -EINVAL;
+		xenbus_dev_fatal(dev, err,
+				 "requested ring page order %d exceed max:%d",
+				 ring_page_order,
+				 xen_blkif_max_ring_order);
 		return err;
 	}
 
+	if (blkif->nr_rings == 1)
+		return read_per_ring_refs(&blkif->rings[0], dev->otherend);
+	else {
+		xspathsize = strlen(dev->otherend) + xenstore_path_ext_size;
+		xspath = kmalloc(xspathsize, GFP_KERNEL);
+		if (!xspath) {
+			xenbus_dev_fatal(dev, -ENOMEM, "reading ring references");
+			return -ENOMEM;
+		}
+
+		for (i = 0; i < blkif->nr_rings; i++) {
+			memset(xspath, 0, xspathsize);
+			snprintf(xspath, xspathsize, "%s/queue-%u", dev->otherend, i);
+			err = read_per_ring_refs(&blkif->rings[i], xspath);
+			if (err) {
+				kfree(xspath);
+				return err;
+			}
+		}
+		kfree(xspath);
+	}
 	return 0;
 }
 
-
-/* ** Driver Registration ** */
-
-
 static const struct xenbus_device_id xen_blkbk_ids[] = {
 	{ "vbd" },
 	{ "" }
 };
 
-
-static DEFINE_XENBUS_DRIVER(xen_blkbk, ,
+static struct xenbus_driver xen_blkbk_driver = {
+	.ids  = xen_blkbk_ids,
 	.probe = xen_blkbk_probe,
 	.remove = xen_blkbk_remove,
-	.otherend_changed = frontend_changed
-);
-
+	.otherend_changed = frontend_changed,
+	.allow_rebind = true,
+	.reclaim_memory = reclaim_memory,
+};
 
 int xen_blkif_xenbus_init(void)
 {
 	return xenbus_register_backend(&xen_blkbk_driver);
 }
+
+void xen_blkif_xenbus_fini(void)
+{
+	xenbus_unregister_driver(&xen_blkbk_driver);
+}