virtio-gpu has special code path that bypassed vIOMMU protection.  So
for now let's disable iommu_platform for the device until we fully
support that (if needed).

After the patch, both virtio-vga and virtio-gpu won't allow to boot with
iommu_platform parameter set.

CC: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/display/virtio-gpu-pci.c | 8 +++++++-
 hw/display/virtio-gpu.c     | 5 +++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/hw/display/virtio-gpu-pci.c b/hw/display/virtio-gpu-pci.c
index ef92c4ad6f..3519dc80b1 100644
--- a/hw/display/virtio-gpu-pci.c
+++ b/hw/display/virtio-gpu-pci.c
@@ -28,10 +28,16 @@ static void virtio_gpu_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
     VirtIOGPU *g = &vgpu->vdev;
     DeviceState *vdev = DEVICE(&vgpu->vdev);
     int i;
+    Error *local_error = NULL;
 
     qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
     virtio_pci_force_virtio_1(vpci_dev);
-    object_property_set_bool(OBJECT(vdev), true, "realized", errp);
+    object_property_set_bool(OBJECT(vdev), true, "realized", &local_error);
+
+    if (local_error) {
+        error_propagate(errp, local_error);
+        return;
+    }
 
     for (i = 0; i < g->conf.max_outputs; i++) {
         object_property_set_link(OBJECT(g->scanout[i].con),
diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
index 274e365713..6658f6c6a6 100644
--- a/hw/display/virtio-gpu.c
+++ b/hw/display/virtio-gpu.c
@@ -1173,6 +1173,11 @@ static void virtio_gpu_device_realize(DeviceState *qdev, Error **errp)
     Error *local_err = NULL;
     int i;
 
+    if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {
+        error_setg(errp, "virtio-gpu does not support vIOMMU yet");
+        return;
+    }
+
     if (g->conf.max_outputs > VIRTIO_GPU_MAX_SCANOUTS) {
         error_setg(errp, "invalid max_outputs > %d", VIRTIO_GPU_MAX_SCANOUTS);
         return;
-- 
2.14.3