[PATCH for-8.1] vfio/display: Fix missing update to set backing fields

[Alex Williamson <alex.williamson@redhat.com>]

The below referenced commit renames scanout_width/height to
backing_width/height, but also promotes these fields in various portions
of the egl interface.  Meanwhile vfio dmabuf support has never used the
previous scanout fields and is therefore missed in the update.  This
results in a black screen when transitioning from ramfb to dmabuf display
when using Intel vGPU with these features.

Link: https://lists.gnu.org/archive/html/qemu-devel/2023-08/msg02726.html
Fixes: 9ac06df8b684 ("virtio-gpu-udmabuf: correct naming of QemuDmaBuf size properties")
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

This fixes a regression in dmabuf/EGL support for Intel GVT-g and
potentially the mbochs mdev driver as well.  Once validated by those
that understand dmabuf/EGL integration, I'd welcome QEMU maintainers to
take this directly for v8.1 or queue it as soon as possible for v8.1.1.

 hw/vfio/display.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/vfio/display.c b/hw/vfio/display.c
index bec864f482f4..837d9e6a309e 100644
--- a/hw/vfio/display.c
+++ b/hw/vfio/display.c
@@ -243,6 +243,8 @@ static VFIODMABuf *vfio_display_get_dmabuf(VFIOPCIDevice *vdev,
     dmabuf->dmabuf_id  = plane.dmabuf_id;
     dmabuf->buf.width  = plane.width;
     dmabuf->buf.height = plane.height;
+    dmabuf->buf.backing_width = plane.width;
+    dmabuf->buf.backing_height = plane.height;
     dmabuf->buf.stride = plane.stride;
     dmabuf->buf.fourcc = plane.drm_format;
     dmabuf->buf.modifier = plane.drm_format_mod;
-- 
2.40.1