On Thu, Aug 07, 2025 at 09:41:45AM -0300, Igor Torrente wrote:
> This reverts commit 206cc44588f72b49ad4d7e21a7472ab2a72a83df.
>
No that's not enough. Explain the why not the what.
for example
-------
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.
To fix, revert the offending commit.
Fixes: 206cc44588f7 ("virtio: reject shm region if length is zero` breaks the Virtio-gpu `host_visible")
-------
> Signed-off-by: Igor Torrente <igor.torrente@xxxxxxxxxxxxx>
> ---
> include/linux/virtio_config.h | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index b3e1d30c765b..169c7d367fac 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -329,8 +329,6 @@ static inline
> bool virtio_get_shm_region(struct virtio_device *vdev,
> struct virtio_shm_region *region, u8 id)
> {
> - if (!region->len)
> - return false;
> if (!vdev->config->get_shm_region)
> return false;
> return vdev->config->get_shm_region(vdev, region, id);
> --
> 2.49.0
