vhost: fix range used in translate_desc()

vhost_iotlb_itree_first() requires `start` and `last` parameters
to search for a mapping that overlaps the range.

In translate_desc() we cyclically call vhost_iotlb_itree_first(),
incrementing `addr` by the amount already translated, so rightly
we move the `start` parameter passed to vhost_iotlb_itree_first(),
but we should hold the `last` parameter constant.

Let's fix it by saving the `last` parameter value before incrementing
`addr` in the loop.

Fixes: a9709d68 ("vhost: convert pre sorted vhost memory array to interval tree")
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20221109102503.18816-3-sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vhost.c

@@ -2053,7 +2053,7 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
 	struct vhost_dev *dev = vq->dev;
 	struct vhost_iotlb *umem = dev->iotlb ? dev->iotlb : dev->umem;
 	struct iovec *_iov;
-	u64 s = 0;
+	u64 s = 0, last = addr + len - 1;
 	int ret = 0;
 
 	while ((u64)len > s) {
@@ -2063,7 +2063,7 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
 			break;
 		}
 
-		map = vhost_iotlb_itree_first(umem, addr, addr + len - 1);
+		map = vhost_iotlb_itree_first(umem, addr, last);
 		if (map == NULL || map->start > addr) {
 			if (umem != dev->iotlb) {
 				ret = -EFAULT;