On Wed, Aug 06, 2025 at 03:34:55PM -0300, Igor Torrente wrote:
> 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
Pls go ahead and post the revert. We'll see what happens.
--
MST
