This helps to simplify failure paths of vhost_virtqueue_start()
a lot. We also need to zero-out pointers on unmap, to not try
to unmap invalid pointers.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Reviewed-by: Raphael Norwitz <raphael.s.norwitz@gmail.com>
---
 hw/virtio/vhost.c | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index be2245cc7e..db6ea42f9b 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -472,14 +472,20 @@ static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr,
     }
 }
 
-static void vhost_memory_unmap(struct vhost_dev *dev, void *buffer,
+static void vhost_memory_unmap(struct vhost_dev *dev, void **buffer,
                                hwaddr len, int is_write,
                                hwaddr access_len)
 {
+    if (!*buffer) {
+        return;
+    }
+
     if (!vhost_dev_has_iommu(dev)) {
-        address_space_unmap(dev->vdev->dma_as, buffer, len, is_write,
+        address_space_unmap(dev->vdev->dma_as, *buffer, len, is_write,
                             access_len);
     }
+
+    *buffer = NULL;
 }
 
 static int vhost_verify_ring_part_mapping(void *ring_hva,
@@ -1315,33 +1321,33 @@ int vhost_virtqueue_start(struct vhost_dev *dev,
     vq->desc = vhost_memory_map(dev, a, l, false);
     if (!vq->desc) {
         r = -ENOMEM;
-        goto fail_alloc_desc;
+        goto fail;
     }
     vq->avail_size = l = virtio_queue_get_avail_size(vdev, idx);
     vq->avail_phys = a = virtio_queue_get_avail_addr(vdev, idx);
     vq->avail = vhost_memory_map(dev, a, l, false);
     if (!vq->avail) {
         r = -ENOMEM;
-        goto fail_alloc_avail;
+        goto fail;
     }
     vq->used_size = l = virtio_queue_get_used_size(vdev, idx);
     vq->used_phys = a = virtio_queue_get_used_addr(vdev, idx);
     vq->used = vhost_memory_map(dev, a, l, true);
     if (!vq->used) {
         r = -ENOMEM;
-        goto fail_alloc_used;
+        goto fail;
     }
 
     r = vhost_virtqueue_set_addr(dev, vq, vhost_vq_index, dev->log_enabled);
     if (r < 0) {
-        goto fail_alloc;
+        goto fail;
     }
 
     file.fd = event_notifier_get_fd(virtio_queue_get_host_notifier(vvq));
     r = dev->vhost_ops->vhost_set_vring_kick(dev, &file);
     if (r) {
         VHOST_OPS_DEBUG(r, "vhost_set_vring_kick failed");
-        goto fail_kick;
+        goto fail;
     }
 
     /* Clear and discard previous events if any. */
@@ -1361,24 +1367,19 @@ int vhost_virtqueue_start(struct vhost_dev *dev,
         file.fd = -1;
         r = dev->vhost_ops->vhost_set_vring_call(dev, &file);
         if (r) {
-            goto fail_vector;
+            goto fail;
         }
     }
 
     return 0;
 
-fail_vector:
-fail_kick:
-fail_alloc:
-    vhost_memory_unmap(dev, vq->used, virtio_queue_get_used_size(vdev, idx),
+fail:
+    vhost_memory_unmap(dev, &vq->used, virtio_queue_get_used_size(vdev, idx),
                        0, 0);
-fail_alloc_used:
-    vhost_memory_unmap(dev, vq->avail, virtio_queue_get_avail_size(vdev, idx),
+    vhost_memory_unmap(dev, &vq->avail, virtio_queue_get_avail_size(vdev, idx),
                        0, 0);
-fail_alloc_avail:
-    vhost_memory_unmap(dev, vq->desc, virtio_queue_get_desc_size(vdev, idx),
+    vhost_memory_unmap(dev, &vq->desc, virtio_queue_get_desc_size(vdev, idx),
                        0, 0);
-fail_alloc_desc:
     return r;
 }
 
@@ -1425,11 +1426,11 @@ static int do_vhost_virtqueue_stop(struct vhost_dev *dev,
                                                 vhost_vq_index);
     }
 
-    vhost_memory_unmap(dev, vq->used, virtio_queue_get_used_size(vdev, idx),
+    vhost_memory_unmap(dev, &vq->used, virtio_queue_get_used_size(vdev, idx),
                        1, virtio_queue_get_used_size(vdev, idx));
-    vhost_memory_unmap(dev, vq->avail, virtio_queue_get_avail_size(vdev, idx),
+    vhost_memory_unmap(dev, &vq->avail, virtio_queue_get_avail_size(vdev, idx),
                        0, virtio_queue_get_avail_size(vdev, idx));
-    vhost_memory_unmap(dev, vq->desc, virtio_queue_get_desc_size(vdev, idx),
+    vhost_memory_unmap(dev, &vq->desc, virtio_queue_get_desc_size(vdev, idx),
                        0, virtio_queue_get_desc_size(vdev, idx));
     return r;
 }
-- 
2.48.1