xenbus_client: Extend interface to support multi-page ring

Originally Xen PV drivers only use single-page ring to pass along
information. This might limit the throughput between frontend and
backend.

The patch extends Xenbus driver to support multi-page ring, which in
general should improve throughput if ring is the bottleneck. Changes to
various frontend / backend to adapt to the new interface are also
included.

Affected Xen drivers:
* blkfront/back
* netfront/back
* pcifront/back
* scsifront/back
* vtpmfront

The interface is documented, as before, in xenbus_client.c.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
Cc: Konrad Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

11 files changed, 324 insertions, 125 deletions

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index e3afe97280b1..ff3025922c14 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -193,7 +193,7 @@ fail:
         return ERR_PTR(-ENOMEM);
 }
 
-static int xen_blkif_map(struct xen_blkif *blkif, unsigned long shared_page,
+static int xen_blkif_map(struct xen_blkif *blkif, grant_ref_t gref,
                          unsigned int evtchn)
 {
         int err;
@@ -202,7 +202,8 @@ static int xen_blkif_map(struct xen_blkif *blkif, unsigned long shared_page,
         if (blkif->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, 1,
+                                     &blkif->blk_ring);
         if (err < 0)
                 return err;
 
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 37779e4c4585..2c61cf8c6f61 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1245,6 +1245,7 @@ static int setup_blkring(struct xenbus_device *dev,
                          struct blkfront_info *info)
 {
         struct blkif_sring *sring;
+        grant_ref_t gref;
         int err;
 
         info->ring_ref = GRANT_INVALID_REF;
@@ -1257,13 +1258,13 @@ static int setup_blkring(struct xenbus_device *dev,
         SHARED_RING_INIT(sring);
         FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
 
-        err = xenbus_grant_ring(dev, virt_to_mfn(info->ring.sring));
+        err = xenbus_grant_ring(dev, info->ring.sring, 1, &gref);
         if (err < 0) {
                 free_page((unsigned long)sring);
                 info->ring.sring = NULL;
                 goto fail;
         }
-        info->ring_ref = err;
+        info->ring_ref = gref;
 
         err = xenbus_alloc_evtchn(dev, &info->evtchn);
         if (err)
diff --git a/drivers/char/tpm/xen-tpmfront.c b/drivers/char/tpm/xen-tpmfront.c
index c3b4f5a5ac10..3111f2778079 100644
--- a/drivers/char/tpm/xen-tpmfront.c
+++ b/drivers/char/tpm/xen-tpmfront.c
@@ -193,6 +193,7 @@ static int setup_ring(struct xenbus_device *dev, struct tpm_private *priv)
         struct xenbus_transaction xbt;
         const char *message = NULL;
         int rv;
+        grant_ref_t gref;
 
         priv->shr = (void *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
         if (!priv->shr) {
@@ -200,11 +201,11 @@ static int setup_ring(struct xenbus_device *dev, struct tpm_private *priv)
                 return -ENOMEM;
         }
 
-        rv = xenbus_grant_ring(dev, virt_to_mfn(priv->shr));
+        rv = xenbus_grant_ring(dev, &priv->shr, 1, &gref);
         if (rv < 0)
                 return rv;
 
-        priv->ring_ref = rv;
+        priv->ring_ref = gref;
 
         rv = xenbus_alloc_evtchn(dev, &priv->evtchn);
         if (rv)
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index cab9f5257f57..99a49479843d 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1781,7 +1781,7 @@ int xenvif_map_frontend_rings(struct xenvif_queue *queue,
         int err = -ENOMEM;
 
         err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(queue->vif),
-                                     tx_ring_ref, &addr);
+                                     &tx_ring_ref, 1, &addr);
         if (err)
                 goto err;
 
@@ -1789,7 +1789,7 @@ int xenvif_map_frontend_rings(struct xenvif_queue *queue,
         BACK_RING_INIT(&queue->tx, txs, PAGE_SIZE);
 
         err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(queue->vif),
-                                     rx_ring_ref, &addr);
+                                     &rx_ring_ref, 1, &addr);
         if (err)
                 goto err;
 
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index e9b960f0ff32..13f5e7ff4bb5 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1486,6 +1486,7 @@ static int setup_netfront(struct xenbus_device *dev,
 {
         struct xen_netif_tx_sring *txs;
         struct xen_netif_rx_sring *rxs;
+        grant_ref_t gref;
         int err;
 
         queue->tx_ring_ref = GRANT_INVALID_REF;
@@ -1502,10 +1503,10 @@ static int setup_netfront(struct xenbus_device *dev,
         SHARED_RING_INIT(txs);
         FRONT_RING_INIT(&queue->tx, txs, PAGE_SIZE);
 
-        err = xenbus_grant_ring(dev, virt_to_mfn(txs));
+        err = xenbus_grant_ring(dev, txs, 1, &gref);
         if (err < 0)
                 goto grant_tx_ring_fail;
-        queue->tx_ring_ref = err;
+        queue->tx_ring_ref = gref;
 
         rxs = (struct xen_netif_rx_sring *)get_zeroed_page(GFP_NOIO | __GFP_HIGH);
         if (!rxs) {
@@ -1516,10 +1517,10 @@ static int setup_netfront(struct xenbus_device *dev,
         SHARED_RING_INIT(rxs);
         FRONT_RING_INIT(&queue->rx, rxs, PAGE_SIZE);
 
-        err = xenbus_grant_ring(dev, virt_to_mfn(rxs));
+        err = xenbus_grant_ring(dev, rxs, 1, &gref);
         if (err < 0)
                 goto grant_rx_ring_fail;
-        queue->rx_ring_ref = err;
+        queue->rx_ring_ref = gref;
 
         if (feature_split_evtchn)
                 err = setup_netfront_split(queue);
diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
index b1ffebec9b9e..7cfd2db02deb 100644
--- a/drivers/pci/xen-pcifront.c
+++ b/drivers/pci/xen-pcifront.c
@@ -777,12 +777,13 @@ static int pcifront_publish_info(struct pcifront_device *pdev)
 {
         int err = 0;
         struct xenbus_transaction trans;
+        grant_ref_t gref;
 
-        err = xenbus_grant_ring(pdev->xdev, virt_to_mfn(pdev->sh_info));
+        err = xenbus_grant_ring(pdev->xdev, pdev->sh_info, 1, &gref);
         if (err < 0)
                 goto out;
 
-        pdev->gnt_ref = err;
+        pdev->gnt_ref = gref;
 
         err = xenbus_alloc_evtchn(pdev->xdev, &pdev->evtchn);
         if (err)
diff --git a/drivers/scsi/xen-scsifront.c b/drivers/scsi/xen-scsifront.c
index 78d95069ac6a..fad22caf0eff 100644
--- a/drivers/scsi/xen-scsifront.c
+++ b/drivers/scsi/xen-scsifront.c
@@ -714,6 +714,7 @@ static int scsifront_alloc_ring(struct vscsifrnt_info *info)
 {
         struct xenbus_device *dev = info->dev;
         struct vscsiif_sring *sring;
+        grant_ref_t gref;
         int err = -ENOMEM;
 
         /***** Frontend to Backend ring start *****/
@@ -726,14 +727,14 @@ static int scsifront_alloc_ring(struct vscsifrnt_info *info)
         SHARED_RING_INIT(sring);
         FRONT_RING_INIT(&info->ring, sring, PAGE_SIZE);
 
-        err = xenbus_grant_ring(dev, virt_to_mfn(sring));
+        err = xenbus_grant_ring(dev, sring, 1, &gref);
         if (err < 0) {
                 free_page((unsigned long)sring);
                 xenbus_dev_fatal(dev, err,
                         "fail to grant shared ring (Front to Back)");
                 return err;
         }
-        info->ring_ref = err;
+        info->ring_ref = gref;
 
         err = xenbus_alloc_evtchn(dev, &info->evtchn);
         if (err) {
diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
index fe17c80ff4b7..98bc345f296e 100644
--- a/drivers/xen/xen-pciback/xenbus.c
+++ b/drivers/xen/xen-pciback/xenbus.c
@@ -113,7 +113,7 @@ static int xen_pcibk_do_attach(struct xen_pcibk_device *pdev, int gnt_ref,
                 "Attaching to frontend resources - gnt_ref=%d evtchn=%d\n",
                 gnt_ref, remote_evtchn);
 
-        err = xenbus_map_ring_valloc(pdev->xdev, gnt_ref, &vaddr);
+        err = xenbus_map_ring_valloc(pdev->xdev, &gnt_ref, 1, &vaddr);
         if (err < 0) {
                 xenbus_dev_fatal(pdev->xdev, err,
                                 "Error mapping other domain page in ours.");
diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c
index 2eab75892c23..db42b59b0162 100644
--- a/drivers/xen/xen-scsiback.c
+++ b/drivers/xen/xen-scsiback.c
@@ -809,7 +809,7 @@ static int scsiback_init_sring(struct vscsibk_info *info, grant_ref_t ring_ref,
         if (info->irq)
                 return -1;
 
-        err = xenbus_map_ring_valloc(info->dev, ring_ref, &area);
+        err = xenbus_map_ring_valloc(info->dev, &ring_ref, 1, &area);
         if (err)
                 return err;
 
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index ca744102b666..96b2011d25f3 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -52,17 +52,25 @@
 struct xenbus_map_node {
         struct list_head next;
         union {
-                struct vm_struct *area; /* PV */
-                struct page *page;     /* HVM */
+                struct {
+                        struct vm_struct *area;
+                } pv;
+                struct {
+                        struct page *pages[XENBUS_MAX_RING_PAGES];
+                        void *addr;
+                } hvm;
         };
-        grant_handle_t handle;
+        grant_handle_t handles[XENBUS_MAX_RING_PAGES];
+        unsigned int   nr_handles;
 };
 
 static DEFINE_SPINLOCK(xenbus_valloc_lock);
 static LIST_HEAD(xenbus_valloc_pages);
 
 struct xenbus_ring_ops {
-        int (*map)(struct xenbus_device *dev, int gnt, void **vaddr);
+        int (*map)(struct xenbus_device *dev,
+                   grant_ref_t *gnt_refs, unsigned int nr_grefs,
+                   void **vaddr);
         int (*unmap)(struct xenbus_device *dev, void *vaddr);
 };
 
@@ -355,17 +363,39 @@ static void xenbus_switch_fatal(struct xenbus_device *dev, int depth, int err,
 /**
  * xenbus_grant_ring
  * @dev: xenbus device
- * @ring_mfn: mfn of ring to grant
-
- * Grant access to the given @ring_mfn to the peer of the given device.  Return
- * a grant reference on success, or -errno on error. On error, the device will
- * switch to XenbusStateClosing, and the error will be saved in the store.
+ * @vaddr: starting virtual address of the ring
+ * @nr_pages: number of pages to be granted
+ * @grefs: grant reference array to be filled in
+ *
+ * Grant access to the given @vaddr to the peer of the given device.
+ * Then fill in @grefs with grant references.  Return 0 on success, or
+ * -errno on error.  On error, the device will switch to
+ * XenbusStateClosing, and the error will be saved in the store.
  */
-int xenbus_grant_ring(struct xenbus_device *dev, unsigned long ring_mfn)
+int xenbus_grant_ring(struct xenbus_device *dev, void *vaddr,
+                      unsigned int nr_pages, grant_ref_t *grefs)
 {
-        int err = gnttab_grant_foreign_access(dev->otherend_id, ring_mfn, 0);
-        if (err < 0)
-                xenbus_dev_fatal(dev, err, "granting access to ring page");
+        int err;
+        int i, j;
+
+        for (i = 0; i < nr_pages; i++) {
+                unsigned long addr = (unsigned long)vaddr +
+                        (PAGE_SIZE * i);
+                err = gnttab_grant_foreign_access(dev->otherend_id,
+                                                  virt_to_mfn(addr), 0);
+                if (err < 0) {
+                        xenbus_dev_fatal(dev, err,
+                                         "granting access to ring page");
+                        goto fail;
+                }
+                grefs[i] = err;
+        }
+
+        return 0;
+
+fail:
+        for (j = 0; j < i; j++)
+                gnttab_end_foreign_access_ref(grefs[j], 0);
         return err;
 }
 EXPORT_SYMBOL_GPL(xenbus_grant_ring);
@@ -419,62 +449,130 @@ EXPORT_SYMBOL_GPL(xenbus_free_evtchn);
 /**
  * xenbus_map_ring_valloc
  * @dev: xenbus device
- * @gnt_ref: grant reference
+ * @gnt_refs: grant reference array
+ * @nr_grefs: number of grant references
  * @vaddr: pointer to address to be filled out by mapping
  *
- * Based on Rusty Russell's skeleton driver's map_page.
- * Map a page of memory into this domain from another domain's grant table.
- * xenbus_map_ring_valloc allocates a page of virtual address space, maps the
- * page to that address, and sets *vaddr to that address.
- * Returns 0 on success, and GNTST_* (see xen/include/interface/grant_table.h)
- * or -ENOMEM on error. If an error is returned, device will switch to
+ * Map @nr_grefs pages of memory into this domain from another
+ * domain's grant table.  xenbus_map_ring_valloc allocates @nr_grefs
+ * pages of virtual address space, maps the pages to that address, and
+ * sets *vaddr to that address.  Returns 0 on success, and GNTST_*
+ * (see xen/include/interface/grant_table.h) or -ENOMEM / -EINVAL on
+ * error. If an error is returned, device will switch to
  * XenbusStateClosing and the error message will be saved in XenStore.
  */
-int xenbus_map_ring_valloc(struct xenbus_device *dev, int gnt_ref, void **vaddr)
+int xenbus_map_ring_valloc(struct xenbus_device *dev, grant_ref_t *gnt_refs,
+                           unsigned int nr_grefs, void **vaddr)
 {
-        return ring_ops->map(dev, gnt_ref, vaddr);
+        return ring_ops->map(dev, gnt_refs, nr_grefs, vaddr);
 }
 EXPORT_SYMBOL_GPL(xenbus_map_ring_valloc);
 
+/* N.B. sizeof(phys_addr_t) doesn't always equal to sizeof(unsigned
+ * long), e.g. 32-on-64.  Caller is responsible for preparing the
+ * right array to feed into this function */
+static int __xenbus_map_ring(struct xenbus_device *dev,
+                             grant_ref_t *gnt_refs,
+                             unsigned int nr_grefs,
+                             grant_handle_t *handles,
+                             phys_addr_t *addrs,
+                             unsigned int flags,
+                             bool *leaked)
+{
+        struct gnttab_map_grant_ref map[XENBUS_MAX_RING_PAGES];
+        struct gnttab_unmap_grant_ref unmap[XENBUS_MAX_RING_PAGES];
+        int i, j;
+        int err = GNTST_okay;
+
+        if (nr_grefs > XENBUS_MAX_RING_PAGES)
+                return -EINVAL;
+
+        for (i = 0; i < nr_grefs; i++) {
+                memset(&map[i], 0, sizeof(map[i]));
+                gnttab_set_map_op(&map[i], addrs[i], flags, gnt_refs[i],
+                                  dev->otherend_id);
+                handles[i] = INVALID_GRANT_HANDLE;
+        }
+
+        gnttab_batch_map(map, i);
+
+        for (i = 0; i < nr_grefs; i++) {
+                if (map[i].status != GNTST_okay) {
+                        err = map[i].status;
+                        xenbus_dev_fatal(dev, map[i].status,
+                                         "mapping in shared page %d from domain %d",
+                                         gnt_refs[i], dev->otherend_id);
+                        goto fail;
+                } else
+                        handles[i] = map[i].handle;
+        }
+
+        return GNTST_okay;
+
+ fail:
+        for (i = j = 0; i < nr_grefs; i++) {
+                if (handles[i] != INVALID_GRANT_HANDLE) {
+                        memset(&unmap[j], 0, sizeof(unmap[j]));
+                        gnttab_set_unmap_op(&unmap[j], (phys_addr_t)addrs[i],
+                                            GNTMAP_host_map, handles[i]);
+                        j++;
+                }
+        }
+
+        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap, j))
+                BUG();
+
+        *leaked = false;
+        for (i = 0; i < j; i++) {
+                if (unmap[i].status != GNTST_okay) {
+                        *leaked = true;
+                        break;
+                }
+        }
+
+        return err;
+}
+
 static int xenbus_map_ring_valloc_pv(struct xenbus_device *dev,
-                                     int gnt_ref, void **vaddr)
+                                     grant_ref_t *gnt_refs,
+                                     unsigned int nr_grefs,
+                                     void **vaddr)
 {
-        struct gnttab_map_grant_ref op = {
-                .flags = GNTMAP_host_map | GNTMAP_contains_pte,
-                .ref   = gnt_ref,
-                .dom   = dev->otherend_id,
-        };
         struct xenbus_map_node *node;
         struct vm_struct *area;
-        pte_t *pte;
+        pte_t *ptes[XENBUS_MAX_RING_PAGES];
+        phys_addr_t phys_addrs[XENBUS_MAX_RING_PAGES];
+        int err = GNTST_okay;
+        int i;
+        bool leaked;
 
         *vaddr = NULL;
 
+        if (nr_grefs > XENBUS_MAX_RING_PAGES)
+                return -EINVAL;
+
         node = kzalloc(sizeof(*node), GFP_KERNEL);
         if (!node)
                 return -ENOMEM;
 
-        area = alloc_vm_area(PAGE_SIZE, &pte);
+        area = alloc_vm_area(PAGE_SIZE * nr_grefs, ptes);
         if (!area) {
                 kfree(node);
                 return -ENOMEM;
         }
 
-        op.host_addr = arbitrary_virt_to_machine(pte).maddr;
+        for (i = 0; i < nr_grefs; i++)
+                phys_addrs[i] = arbitrary_virt_to_machine(ptes[i]).maddr;
 
-        gnttab_batch_map(&op, 1);
-
-        if (op.status != GNTST_okay) {
-                free_vm_area(area);
-                kfree(node);
-                xenbus_dev_fatal(dev, op.status,
-                                 "mapping in shared page %d from domain %d",
-                                 gnt_ref, dev->otherend_id);
-                return op.status;
-        }
+        err = __xenbus_map_ring(dev, gnt_refs, nr_grefs, node->handles,
+                                phys_addrs,
+                                GNTMAP_host_map | GNTMAP_contains_pte,
+                                &leaked);
+        if (err)
+                goto failed;
 
-        node->handle = op.handle;
-        node->area = area;
+        node->nr_handles = nr_grefs;
+        node->pv.area = area;
 
         spin_lock(&xenbus_valloc_lock);
         list_add(&node->next, &xenbus_valloc_pages);
@@ -482,14 +580,33 @@ static int xenbus_map_ring_valloc_pv(struct xenbus_device *dev,
 
         *vaddr = area->addr;
         return 0;
+
+failed:
+        if (!leaked)
+                free_vm_area(area);
+        else
+                pr_alert("leaking VM area %p size %u page(s)", area, nr_grefs);
+
+        kfree(node);
+        return err;
 }
 
 static int xenbus_map_ring_valloc_hvm(struct xenbus_device *dev,
-                                      int gnt_ref, void **vaddr)
+                                      grant_ref_t *gnt_ref,
+                                      unsigned int nr_grefs,
+                                      void **vaddr)
 {
         struct xenbus_map_node *node;
+        int i;
         int err;
         void *addr;
+        bool leaked = false;
+        /* Why do we need two arrays? See comment of __xenbus_map_ring */
+        phys_addr_t phys_addrs[XENBUS_MAX_RING_PAGES];
+        unsigned long addrs[XENBUS_MAX_RING_PAGES];
+
+        if (nr_grefs > XENBUS_MAX_RING_PAGES)
+                return -EINVAL;
 
         *vaddr = NULL;
 
@@ -497,15 +614,32 @@ static int xenbus_map_ring_valloc_hvm(struct xenbus_device *dev,
         if (!node)
                 return -ENOMEM;
 
-        err = alloc_xenballooned_pages(1, &node->page, false /* lowmem */);
+        err = alloc_xenballooned_pages(nr_grefs, node->hvm.pages,
+                                       false /* lowmem */);
         if (err)
                 goto out_err;
 
-        addr = pfn_to_kaddr(page_to_pfn(node->page));
+        for (i = 0; i < nr_grefs; i++) {
+                unsigned long pfn = page_to_pfn(node->hvm.pages[i]);
+                phys_addrs[i] = (unsigned long)pfn_to_kaddr(pfn);
+                addrs[i] = (unsigned long)pfn_to_kaddr(pfn);
+        }
+
+        err = __xenbus_map_ring(dev, gnt_ref, nr_grefs, node->handles,
+                                phys_addrs, GNTMAP_host_map, &leaked);
+        node->nr_handles = nr_grefs;
 
-        err = xenbus_map_ring(dev, gnt_ref, &node->handle, addr);
         if (err)
-                goto out_err_free_ballooned_pages;
+                goto out_free_ballooned_pages;
+
+        addr = vmap(node->hvm.pages, nr_grefs, VM_MAP | VM_IOREMAP,
+                    PAGE_KERNEL);
+        if (!addr) {
+                err = -ENOMEM;
+                goto out_xenbus_unmap_ring;
+        }
+
+        node->hvm.addr = addr;
 
         spin_lock(&xenbus_valloc_lock);
         list_add(&node->next, &xenbus_valloc_pages);
@@ -514,8 +648,16 @@ static int xenbus_map_ring_valloc_hvm(struct xenbus_device *dev,
         *vaddr = addr;
         return 0;
 
- out_err_free_ballooned_pages:
-        free_xenballooned_pages(1, &node->page);
+ out_xenbus_unmap_ring:
+        if (!leaked)
+                xenbus_unmap_ring(dev, node->handles, node->nr_handles,
+                                  addrs);
+        else
+                pr_alert("leaking %p size %u page(s)",
+                         addr, nr_grefs);
+ out_free_ballooned_pages:
+        if (!leaked)
+                free_xenballooned_pages(nr_grefs, node->hvm.pages);
  out_err:
         kfree(node);
         return err;
@@ -525,35 +667,37 @@ static int xenbus_map_ring_valloc_hvm(struct xenbus_device *dev,
 /**
  * xenbus_map_ring
  * @dev: xenbus device
- * @gnt_ref: grant reference
- * @handle: pointer to grant handle to be filled
- * @vaddr: address to be mapped to
+ * @gnt_refs: grant reference array
+ * @nr_grefs: number of grant reference
+ * @handles: pointer to grant handle to be filled
+ * @vaddrs: addresses to be mapped to
+ * @leaked: fail to clean up a failed map, caller should not free vaddr
  *
- * Map a page of memory into this domain from another domain's grant table.
+ * Map pages of memory into this domain from another domain's grant table.
  * xenbus_map_ring does not allocate the virtual address space (you must do
- * this yourself!). It only maps in the page to the specified address.
+ * this yourself!). It only maps in the pages to the specified address.
  * Returns 0 on success, and GNTST_* (see xen/include/interface/grant_table.h)
- * or -ENOMEM on error. If an error is returned, device will switch to
- * XenbusStateClosing and the error message will be saved in XenStore.
+ * or -ENOMEM / -EINVAL on error. If an error is returned, device will switch to
+ * XenbusStateClosing and the first error message will be saved in XenStore.
+ * Further more if we fail to map the ring, caller should check @leaked.
+ * If @leaked is not zero it means xenbus_map_ring fails to clean up, caller
+ * should not free the address space of @vaddr.
  */
-int xenbus_map_ring(struct xenbus_device *dev, int gnt_ref,
-                    grant_handle_t *handle, void *vaddr)
+int xenbus_map_ring(struct xenbus_device *dev, grant_ref_t *gnt_refs,
+                    unsigned int nr_grefs, grant_handle_t *handles,
+                    unsigned long *vaddrs, bool *leaked)
 {
-        struct gnttab_map_grant_ref op;
-
-        gnttab_set_map_op(&op, (unsigned long)vaddr, GNTMAP_host_map, gnt_ref,
-                          dev->otherend_id);
+        phys_addr_t phys_addrs[XENBUS_MAX_RING_PAGES];
+        int i;
 
-        gnttab_batch_map(&op, 1);
+        if (nr_grefs > XENBUS_MAX_RING_PAGES)
+                return -EINVAL;
 
-        if (op.status != GNTST_okay) {
-                xenbus_dev_fatal(dev, op.status,
-                                 "mapping in shared page %d from domain %d",
-                                 gnt_ref, dev->otherend_id);
-        } else
-                *handle = op.handle;
+        for (i = 0; i < nr_grefs; i++)
+                phys_addrs[i] = (unsigned long)vaddrs[i];
 
-        return op.status;
+        return __xenbus_map_ring(dev, gnt_refs, nr_grefs, handles,
+                                 phys_addrs, GNTMAP_host_map, leaked);
 }
 EXPORT_SYMBOL_GPL(xenbus_map_ring);
 
@@ -579,14 +723,15 @@ EXPORT_SYMBOL_GPL(xenbus_unmap_ring_vfree);
 static int xenbus_unmap_ring_vfree_pv(struct xenbus_device *dev, void *vaddr)
 {
         struct xenbus_map_node *node;
-        struct gnttab_unmap_grant_ref op = {
-                .host_addr = (unsigned long)vaddr,
-        };
+        struct gnttab_unmap_grant_ref unmap[XENBUS_MAX_RING_PAGES];
         unsigned int level;
+        int i;
+        bool leaked = false;
+        int err;
 
         spin_lock(&xenbus_valloc_lock);
         list_for_each_entry(node, &xenbus_valloc_pages, next) {
-                if (node->area->addr == vaddr) {
+                if (node->pv.area->addr == vaddr) {
                         list_del(&node->next);
                         goto found;
                 }
@@ -601,22 +746,41 @@ static int xenbus_unmap_ring_vfree_pv(struct xenbus_device *dev, void *vaddr)
                 return GNTST_bad_virt_addr;
         }
 
-        op.handle = node->handle;
-        op.host_addr = arbitrary_virt_to_machine(
-                lookup_address((unsigned long)vaddr, &level)).maddr;
+        for (i = 0; i < node->nr_handles; i++) {
+                unsigned long addr;
+
+                memset(&unmap[i], 0, sizeof(unmap[i]));
+                addr = (unsigned long)vaddr + (PAGE_SIZE * i);
+                unmap[i].host_addr = arbitrary_virt_to_machine(
+                        lookup_address(addr, &level)).maddr;
+                unmap[i].dev_bus_addr = 0;
+                unmap[i].handle = node->handles[i];
+        }
 
-        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1))
+        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap, i))
                 BUG();
 
-        if (op.status == GNTST_okay)
-                free_vm_area(node->area);
+        err = GNTST_okay;
+        leaked = false;
+        for (i = 0; i < node->nr_handles; i++) {
+                if (unmap[i].status != GNTST_okay) {
+                        leaked = true;
+                        xenbus_dev_error(dev, unmap[i].status,
+                                         "unmapping page at handle %d error %d",
+                                         node->handles[i], unmap[i].status);
+                        err = unmap[i].status;
+                        break;
+                }
+        }
+
+        if (!leaked)
+                free_vm_area(node->pv.area);
         else
-                xenbus_dev_error(dev, op.status,
-                                 "unmapping page at handle %d error %d",
-                                 node->handle, op.status);
+                pr_alert("leaking VM area %p size %u page(s)",
+                         node->pv.area, node->nr_handles);
 
         kfree(node);
-        return op.status;
+        return err;
 }
 
 static int xenbus_unmap_ring_vfree_hvm(struct xenbus_device *dev, void *vaddr)
@@ -624,10 +788,12 @@ static int xenbus_unmap_ring_vfree_hvm(struct xenbus_device *dev, void *vaddr)
         int rv;
         struct xenbus_map_node *node;
         void *addr;
+        unsigned long addrs[XENBUS_MAX_RING_PAGES];
+        int i;
 
         spin_lock(&xenbus_valloc_lock);
         list_for_each_entry(node, &xenbus_valloc_pages, next) {
-                addr = pfn_to_kaddr(page_to_pfn(node->page));
+                addr = node->hvm.addr;
                 if (addr == vaddr) {
                         list_del(&node->next);
                         goto found;
@@ -643,12 +809,16 @@ static int xenbus_unmap_ring_vfree_hvm(struct xenbus_device *dev, void *vaddr)
                 return GNTST_bad_virt_addr;
         }
 
-        rv = xenbus_unmap_ring(dev, node->handle, addr);
+        for (i = 0; i < node->nr_handles; i++)
+                addrs[i] = (unsigned long)pfn_to_kaddr(page_to_pfn(node->hvm.pages[i]));
 
+        rv = xenbus_unmap_ring(dev, node->handles, node->nr_handles,
+                               addrs);
         if (!rv)
-                free_xenballooned_pages(1, &node->page);
+                vunmap(vaddr);
         else
-                WARN(1, "Leaking %p\n", vaddr);
+                WARN(1, "Leaking %p, size %u page(s)\n", vaddr,
+                     node->nr_handles);
 
         kfree(node);
         return rv;
@@ -657,29 +827,44 @@ static int xenbus_unmap_ring_vfree_hvm(struct xenbus_device *dev, void *vaddr)
 /**
  * xenbus_unmap_ring
  * @dev: xenbus device
- * @handle: grant handle
- * @vaddr: addr to unmap
+ * @handles: grant handle array
+ * @nr_handles: number of handles in the array
+ * @vaddrs: addresses to unmap
  *
- * Unmap a page of memory in this domain that was imported from another domain.
+ * Unmap memory in this domain that was imported from another domain.
  * Returns 0 on success and returns GNTST_* on error
  * (see xen/include/interface/grant_table.h).
  */
 int xenbus_unmap_ring(struct xenbus_device *dev,
-                      grant_handle_t handle, void *vaddr)
+                      grant_handle_t *handles, unsigned int nr_handles,
+                      unsigned long *vaddrs)
 {
-        struct gnttab_unmap_grant_ref op;
+        struct gnttab_unmap_grant_ref unmap[XENBUS_MAX_RING_PAGES];
+        int i;
+        int err;
 
-        gnttab_set_unmap_op(&op, (unsigned long)vaddr, GNTMAP_host_map, handle);
+        if (nr_handles > XENBUS_MAX_RING_PAGES)
+                return -EINVAL;
 
-        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1))
+        for (i = 0; i < nr_handles; i++)
+                gnttab_set_unmap_op(&unmap[i], vaddrs[i],
+                                    GNTMAP_host_map, handles[i]);
+
+        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap, i))
                 BUG();
 
-        if (op.status != GNTST_okay)
-                xenbus_dev_error(dev, op.status,
-                                 "unmapping page at handle %d error %d",
-                                 handle, op.status);
+        err = GNTST_okay;
+        for (i = 0; i < nr_handles; i++) {
+                if (unmap[i].status != GNTST_okay) {
+                        xenbus_dev_error(dev, unmap[i].status,
+                                         "unmapping page at handle %d error %d",
+                                         handles[i], unmap[i].status);
+                        err = unmap[i].status;
+                        break;
+                }
+        }
 
-        return op.status;
+        return err;
 }
 EXPORT_SYMBOL_GPL(xenbus_unmap_ring);
 
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index b0f1c9e5d687..289c0b5f08fe 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -46,6 +46,10 @@
 #include <xen/interface/io/xenbus.h>
 #include <xen/interface/io/xs_wire.h>
 
+#define XENBUS_MAX_RING_PAGE_ORDER 4
+#define XENBUS_MAX_RING_PAGES      (1U << XENBUS_MAX_RING_PAGE_ORDER)
+#define INVALID_GRANT_HANDLE       (~0U)
+
 /* Register callback to watch this node. */
 struct xenbus_watch
 {
@@ -199,15 +203,19 @@ int xenbus_watch_pathfmt(struct xenbus_device *dev, struct xenbus_watch *watch,
                          const char *pathfmt, ...);
 
 int xenbus_switch_state(struct xenbus_device *dev, enum xenbus_state new_state);
-int xenbus_grant_ring(struct xenbus_device *dev, unsigned long ring_mfn);
-int xenbus_map_ring_valloc(struct xenbus_device *dev,
-                           int gnt_ref, void **vaddr);
-int xenbus_map_ring(struct xenbus_device *dev, int gnt_ref,
-                           grant_handle_t *handle, void *vaddr);
+int xenbus_grant_ring(struct xenbus_device *dev, void *vaddr,
+                      unsigned int nr_pages, grant_ref_t *grefs);
+int xenbus_map_ring_valloc(struct xenbus_device *dev, grant_ref_t *gnt_refs,
+                           unsigned int nr_grefs, void **vaddr);
+int xenbus_map_ring(struct xenbus_device *dev,
+                    grant_ref_t *gnt_refs, unsigned int nr_grefs,
+                    grant_handle_t *handles, unsigned long *vaddrs,
+                    bool *leaked);
 
 int xenbus_unmap_ring_vfree(struct xenbus_device *dev, void *vaddr);
 int xenbus_unmap_ring(struct xenbus_device *dev,
-                      grant_handle_t handle, void *vaddr);
+                      grant_handle_t *handles, unsigned int nr_handles,
+                      unsigned long *vaddrs);
 
 int xenbus_alloc_evtchn(struct xenbus_device *dev, int *port);
 int xenbus_free_evtchn(struct xenbus_device *dev, int port);