Hello,
The commit `206cc44588f7 virtio: reject shm region if length is zero` breaks the Virtio-gpu `host_visible` feature.
As you can see in the snippet below, host_visible_region is zero because of the `kzalloc`.
It's using the `vm_get_shm_region` (drivers/virtio/virtio_mmio.c:536) to read the `addr` and `len` from qemu/crosvm.
```
drivers/gpu/drm/virtio/virtgpu_kms.c
132 vgdev = drmm_kzalloc(dev, sizeof(struct virtio_gpu_device), GFP_KERNEL);
[...]
177 if (virtio_get_shm_region(vgdev->vdev, &vgdev->host_visible_region,
178 VIRTIO_GPU_SHM_ID_HOST_VISIBLE)) {
```
Now it always fails.
I don't know exactly what issue this patch is trying to solve, but right now Virtio-gpu relies upon the previous behavior.
Can we just revert it?
BR,
----
Igor Torrente
