virtio-gpu-udmabuf: create udmabuf for blob even when iov_cnt == 1

There were often cases where a scanout blob sometimes has just 1 entry
that is linked to many pages in it. So just checking whether iov_cnt is 1
is not enough for screening small, non-scanout blobs. Therefore adding
iov_len check as well to make sure it creates an udmabuf only for a scanout
blob, which is at least bigger than one page size.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Marc-André Lureau <marcandre.lureau@redhat.com>
Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20230621222704.29932-1-dongwon.kim@intel.com>

hw/display/virtio-gpu-udmabuf.c

@@ -132,7 +132,8 @@ void virtio_gpu_init_udmabuf(struct virtio_gpu_simple_resource *res)
     void *pdata = NULL;
 
     res->dmabuf_fd = -1;
-    if (res->iov_cnt == 1) {
+    if (res->iov_cnt == 1 &&
+        res->iov[0].iov_len < 4096) {
         pdata = res->iov[0].iov_base;
     } else {
         virtio_gpu_create_udmabuf(res);