* [PATCH v2] Revert "virtio: reject shm region if length is zero"
@ 2025-08-07 13:03 Igor Torrente
2025-08-08 11:26 ` Michael S. Tsirkin
0 siblings, 1 reply; 3+ messages in thread
From: Igor Torrente @ 2025-08-07 13:03 UTC (permalink / raw)
To: mst
Cc: sami.md.ko, virtualization, linux-kernel, eperezma, xuanzhuo,
jasowang, dmitry.osipenko, Igor Torrente
The commit 206cc44588f7 ("virtio: reject shm region if length is zero")
breaks the Virtio-gpu `host_visible` feature.
Right now in the Virtio-gpu code, `host_visible_region.len` is zero because
the struct comes directly from the `kzalloc` allocation. And Virtio-gpu
is 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.
As the Virtio-gpu relies on the previous behavior, this patch reverts
the offending commit.
Fixes: 206cc44588f7 ("virtio: reject shm region if length is zero` breaks the Virtio-gpu `host_visible")
This reverts commit 206cc44588f72b49ad4d7e21a7472ab2a72a83df.
Signed-off-by: Igor Torrente <igor.torrente@collabora.com>
---
v2: Improve the commit message (Michael S. Tsirkin)
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
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH v2] Revert "virtio: reject shm region if length is zero"
2025-08-07 13:03 [PATCH v2] Revert "virtio: reject shm region if length is zero" Igor Torrente
@ 2025-08-08 11:26 ` Michael S. Tsirkin
2025-08-08 15:21 ` Igor Torrente
0 siblings, 1 reply; 3+ messages in thread
From: Michael S. Tsirkin @ 2025-08-08 11:26 UTC (permalink / raw)
To: Igor Torrente
Cc: sami.md.ko, virtualization, linux-kernel, eperezma, xuanzhuo,
jasowang, dmitry.osipenko
On Thu, Aug 07, 2025 at 10:03:29AM -0300, Igor Torrente wrote:
> The commit 206cc44588f7 ("virtio: reject shm region if length is zero")
> breaks the Virtio-gpu `host_visible` feature.
>
> Right now in the Virtio-gpu code, `host_visible_region.len` is zero because
> the struct comes directly from the `kzalloc` allocation. And Virtio-gpu
> is 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.
>
> As the Virtio-gpu relies on the previous behavior, this patch reverts
> the offending commit.
>
> Fixes: 206cc44588f7 ("virtio: reject shm region if length is zero` breaks the Virtio-gpu `host_visible")
>
> This reverts commit 206cc44588f72b49ad4d7e21a7472ab2a72a83df.
>
> Signed-off-by: Igor Torrente <igor.torrente@collabora.com>
Fixes has to be adjacent to Signed-off-by.
But anyway, I already included v1 in my tree, pls check it out
and tell me if more fixes are needed.
> ---
> v2: Improve the commit message (Michael S. Tsirkin)
>
> 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
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v2] Revert "virtio: reject shm region if length is zero"
2025-08-08 11:26 ` Michael S. Tsirkin
@ 2025-08-08 15:21 ` Igor Torrente
0 siblings, 0 replies; 3+ messages in thread
From: Igor Torrente @ 2025-08-08 15:21 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: sami.md.ko, virtualization, linux-kernel, eperezma, xuanzhuo,
jasowang, dmitry.osipenko
---- El vie., 08 ago. 2025 08:26:08 -0300, Michael S. Tsirkin <mst@redhat.com> escribió ----
> On Thu, Aug 07, 2025 at 10:03:29AM -0300, Igor Torrente wrote:
> > The commit 206cc44588f7 ("virtio: reject shm region if length is zero")
> > breaks the Virtio-gpu `host_visible` feature.
> >
> > Right now in the Virtio-gpu code, `host_visible_region.len` is zero because
> > the struct comes directly from the `kzalloc` allocation. And Virtio-gpu
> > is 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.
> >
> > As the Virtio-gpu relies on the previous behavior, this patch reverts
> > the offending commit.
> >
> > Fixes: 206cc44588f7 ("virtio: reject shm region if length is zero` breaks the Virtio-gpu `host_visible")
> >
> > This reverts commit 206cc44588f72b49ad4d7e21a7472ab2a72a83df.
> >
> > Signed-off-by: Igor Torrente <igor.torrente@collabora.com>
>
>
> Fixes has to be adjacent to Signed-off-by.
Ohh, I will pay attention to this next time.
> But anyway, I already included v1 in my tree, pls check it out
> and tell me if more fixes are needed.
I tested here your branch, and it's working fine.
```
[ 0.298365] [drm] pci: virtio-gpu-pci detected at 0000:00:04.0
[ 0.298506] [drm] Host memory window: 0x200000000 +0x200000000
[ 0.298510] [drm] features: +virgl +edid +resource_blob +host_visible
```
```
Linux debian-arm64-vm-chromebook 6.16.0mst_virt_repo_linux-next+ #159 SMP PREEMPT_DYNAMIC Fri Aug 8 11:53:04 -03 2025 aarch64 GNU/Linux
```
Thanks for applying it,
---
Igor Torrente
>
> > ---
> > v2: Improve the commit message (Michael S. Tsirkin)
> >
> > 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
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2025-08-07 13:03 [PATCH v2] Revert "virtio: reject shm region if length is zero" Igor Torrente
2025-08-08 11:26 ` Michael S. Tsirkin
2025-08-08 15:21 ` Igor Torrente
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