1 files changed, 23 insertions, 13 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 0e2ade648aff..7b9b38a12d25 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -6,7 +6,6 @@
 #include <linux/virtio_blk.h>
 #include <linux/scatterlist.h>
 
-#define VIRTIO_MAX_SG   (3+MAX_PHYS_SEGMENTS)
 #define PART_BITS 4
 
 static int major, index;
@@ -26,8 +25,11 @@ struct virtio_blk
 
         mempool_t *pool;
 
+        /* What host tells us, plus 2 for header & tailer. */
+        unsigned int sg_elems;
+
         /* Scatterlist: can be too big for stack. */
-        struct scatterlist sg[VIRTIO_MAX_SG];
+        struct scatterlist sg[/*sg_elems*/];
 };
 
 struct virtblk_req
@@ -97,8 +99,6 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
         if (blk_barrier_rq(vbr->req))
                 vbr->out_hdr.type |= VIRTIO_BLK_T_BARRIER;
 
-        /* This init could be done at vblk creation time */
-        sg_init_table(vblk->sg, VIRTIO_MAX_SG);
         sg_set_buf(&vblk->sg[0], &vbr->out_hdr, sizeof(vbr->out_hdr));
         num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
         sg_set_buf(&vblk->sg[num+1], &vbr->status, sizeof(vbr->status));
@@ -130,7 +130,7 @@ static void do_virtblk_request(struct request_queue *q)
 
         while ((req = elv_next_request(q)) != NULL) {
                 vblk = req->rq_disk->private_data;
-                BUG_ON(req->nr_phys_segments > ARRAY_SIZE(vblk->sg));
+                BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems);
 
                 /* If this request fails, stop queue and wait for something to
                    finish to restart it. */
@@ -196,12 +196,22 @@ static int virtblk_probe(struct virtio_device *vdev)
         int err;
         u64 cap;
         u32 v;
-        u32 blk_size;
+        u32 blk_size, sg_elems;
 
         if (index_to_minor(index) >= 1 << MINORBITS)
                 return -ENOSPC;
 
-        vdev->priv = vblk = kmalloc(sizeof(*vblk), GFP_KERNEL);
+        /* We need to know how many segments before we allocate. */
+        err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
+                                offsetof(struct virtio_blk_config, seg_max),
+                                &sg_elems);
+        if (err)
+                sg_elems = 1;
+
+        /* We need an extra sg elements at head and tail. */
+        sg_elems += 2;
+        vdev->priv = vblk = kmalloc(sizeof(*vblk) +
+                                    sizeof(vblk->sg[0]) * sg_elems, GFP_KERNEL);
         if (!vblk) {
                 err = -ENOMEM;
                 goto out;
@@ -210,6 +220,8 @@ static int virtblk_probe(struct virtio_device *vdev)
         INIT_LIST_HEAD(&vblk->reqs);
         spin_lock_init(&vblk->lock);
         vblk->vdev = vdev;
+        vblk->sg_elems = sg_elems;
+        sg_init_table(vblk->sg, vblk->sg_elems);
 
         /* We expect one virtqueue, for output. */
         vblk->vq = vdev->config->find_vq(vdev, 0, blk_done);
@@ -277,6 +289,10 @@ static int virtblk_probe(struct virtio_device *vdev)
         }
         set_capacity(vblk->disk, cap);
 
+        /* We can handle whatever the host told us to handle. */
+        blk_queue_max_phys_segments(vblk->disk->queue, vblk->sg_elems-2);
+        blk_queue_max_hw_segments(vblk->disk->queue, vblk->sg_elems-2);
+
         /* No real sector limit. */
         blk_queue_max_sectors(vblk->disk->queue, -1U);
 
@@ -290,12 +306,6 @@ static int virtblk_probe(struct virtio_device *vdev)
         else
                 blk_queue_max_segment_size(vblk->disk->queue, -1UL);
 
-        err = virtio_config_val(vdev, VIRTIO_BLK_F_SEG_MAX,
-                                offsetof(struct virtio_blk_config, seg_max),
-                                &v);
-        if (!err)
-                blk_queue_max_hw_segments(vblk->disk->queue, v);
-
         /* Host can optionally specify the block size of the device */
         err = virtio_config_val(vdev, VIRTIO_BLK_F_BLK_SIZE,
                                 offsetof(struct virtio_blk_config, blk_size),