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Revert "virtio: reject shm region if length is zero"

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The commit 206cc44588 ("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: 206cc44588 ("virtio: reject shm region if length is zero")
Signed-off-by: Igor Torrente <igor.torrente@collabora.com>
Message-Id: <20250807124145.81816-1-igor.torrente@collabora.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Igor Torrente 2025-08-07 09:41:45 -03:00 committed by Michael S. Tsirkin
parent dd54bcf86c
commit ced17ee32a
1 changed files with 0 additions and 2 deletions
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2
include/linux/virtio_config.h
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@ -328,8 +328,6 @@ static inline
bool virtio_get_shm_region(struct virtio_device *vdev, bool virtio_get_shm_region(struct virtio_device *vdev,
struct virtio_shm_region *region, u8 id) struct virtio_shm_region *region, u8 id)
{ {
if (!region->len)
return false;
if (!vdev->config->get_shm_region) if (!vdev->config->get_shm_region)
return false; return false;
return vdev->config->get_shm_region(vdev, region, id); return vdev->config->get_shm_region(vdev, region, id);