Hi Gerd

While doing some testing with your brance, I reached that:

[  750.446449] kernel BUG at drivers/gpu/drm/virtio/virtgpu_vq.c:132!
[  750.447005] Call Trace:
[  750.447005]  [<ffffffffa00f3592>] virtio_gpu_alloc_cmd+0x22/0x50 [virtio_gpu]
[  750.447005]  [<ffffffffa00f4580>] virtio_gpu_cmd_context_create+0x30/0xa0 [virtio_gpu]

struct virtio_gpu_ctx_create {
        struct virtio_gpu_ctrl_hdr hdr;
        __le32 nlen;
        __le32 padding;
        char debug_name[64];
};

Is actually 96 bytes.

Perhaps that condition should be changed:
+       BUG_ON(size >= MAX_INLINE_CMD_SIZE);

--