Le 25/02/2025 à 18:59, José Expósito a écrit :
Create a default subgroup at /config/vkms/planes to allow to create as
many planes as required.
Reviewed-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
Co-developed-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
Signed-off-by: Louis Chauvet <louis.chauvet@xxxxxxxxxxx>
Signed-off-by: José Expósito <jose.exposito89@xxxxxxxxx>
---
Documentation/gpu/vkms.rst | 16 ++++-
drivers/gpu/drm/vkms/vkms_configfs.c | 87 ++++++++++++++++++++++++++++
2 files changed, 102 insertions(+), 1 deletion(-)
diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
index 423bdf86b5b1..bf23d0da33fe 100644
--- a/Documentation/gpu/vkms.rst
+++ b/Documentation/gpu/vkms.rst
@@ -71,6 +71,19 @@ By default, the instance is disabled::
cat /config/vkms/my-vkms/enabled
0
+And directories are created for each configurable item of the display pipeline::
+
+ tree /config/vkms/my-vkms
+ ├── enabled
+ └── planes
+
+To add items to the display pipeline, create one or more directories under the
+available paths.
+
+Start by creating one or more planes::
+
+ sudo mkdir /config/vkms/my-vkms/planes/plane0
+
Once you are done configuring the VKMS instance, enable it::
echo "1" | sudo tee /config/vkms/my-vkms/enabled
@@ -79,8 +92,9 @@ Finally, you can remove the VKMS instance disabling it::
echo "0" | sudo tee /config/vkms/my-vkms/enabled
-And removing the top level directory::
+And removing the top level directory and its subdirectories::
+ sudo rmdir /config/vkms/my-vkms/planes/*
sudo rmdir /config/vkms/my-vkms
Testing With IGT
diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 92512d52ddae..4f9d3341e6c0 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -16,6 +16,7 @@ static bool is_configfs_registered;
*
* @group: Top level configuration group that represents a VKMS device.
* Initialized when a new directory is created under "/config/vkms/"
+ * @planes_group: Default subgroup of @group at "/config/vkms/planes"
* @lock: Lock used to project concurrent access to the configuration attributes
* @config: Protected by @lock. Configuration of the VKMS device
* @enabled: Protected by @lock. The device is created or destroyed when this
@@ -23,16 +24,98 @@ static bool is_configfs_registered;
*/
struct vkms_configfs_device {
struct config_group group;
+ struct config_group planes_group;
struct mutex lock;
struct vkms_config *config;
bool enabled;
};
+/**
+ * struct vkms_configfs_plane - Configfs representation of a plane
+ *
+ * @group: Top level configuration group that represents a plane.
+ * Initialized when a new directory is created under "/config/vkms/planes"
+ * @dev: The vkms_configfs_device this plane belongs to
+ * @config: Configuration of the VKMS plane
+ */
+struct vkms_configfs_plane {
+ struct config_group group;
+ struct vkms_configfs_device *dev;
+ struct vkms_config_plane *config;
+};
+
#define device_item_to_vkms_configfs_device(item) \
container_of(to_config_group((item)), struct vkms_configfs_device, \
group)
+#define child_group_to_vkms_configfs_device(group) \
+ device_item_to_vkms_configfs_device((&(group)->cg_item)->ci_parent)
+
+#define plane_item_to_vkms_configfs_plane(item) \
+ container_of(to_config_group((item)), struct vkms_configfs_plane, group)
+
+static void plane_release(struct config_item *item)
+{
+ struct vkms_configfs_plane *plane;
+ struct mutex *lock;
+
+ plane = plane_item_to_vkms_configfs_plane(item);
+ lock = &plane->dev->lock;
+
+ guard(mutex)(lock);
+ vkms_config_destroy_plane(plane->config);
+ kfree(plane);
+}
I just found a flaw in our work: there is currently no way to forbid the
deletion of item/symlinks...
If you do:
modprobe vkms
cd /sys/kernel/config/vkms/
mkdir DEV
mkdir DEV/connectors/CON
mkdir DEV/planes/PLA
mkdir DEV/crtcs/CRT
mkdir DEV/encoders/ENC
ln -s DEV/crtcs/CRT DEV/planes/PLA/possible_crtcs/
ln -s DEV/crtcs/CRT DEV/encoders/ENC/possible_crtcs
ln -s DEV/encoders/ENC DEV/connectors/CON/possible_encoders
echo 1 > DEV/planes/PLA/type
tree
echo 1 > DEV/enabled
modetest -M vkms
=> everything fine
rm DEV/connectors/CON/possible_encoders/ENC
rmdir DEV/connectors/CON
modetest -M vkms
=> BUG: KASAN: slab-use-after-free
I see two solutions:
- we don't care and keep as is: if the device is enabled, and you delete
link/groups, it is your fault. As shown above: it can crash the kernel,
so it is a no-go.
- we care and we don't want to touch configfs: we need to implement a
kind of refcount for all vkms_config elements. Issue: non-trivial work,
may allow memory leaks/use after free...
- we care and we want to touch configfs: see my two patches (they apply
on the v1 of this series). This solution allows adding a check before
removing configfs item/group/link. I found it cleaner and way easier to
understand.
What do you think about my proposition? Do you have another idea?
+static struct configfs_item_operations plane_item_operations = {
+ .release = &plane_release,
+};
+
+static const struct config_item_type plane_item_type = {
+ .ct_item_ops = &plane_item_operations,
+ .ct_owner = THIS_MODULE,
+};
+
+static struct config_group *make_plane_group(struct config_group *group,
+ const char *name)
+{
+ struct vkms_configfs_device *dev;
+ struct vkms_configfs_plane *plane;
+
+ dev = child_group_to_vkms_configfs_device(group);
+
+ guard(mutex)(&dev->lock);
+
+ if (dev->enabled)
+ return ERR_PTR(-EBUSY);
+
+ plane = kzalloc(sizeof(*plane), GFP_KERNEL);
+ if (!plane)
+ return ERR_PTR(-ENOMEM);
+
+ plane->dev = dev;
+
+ plane->config = vkms_config_create_plane(dev->config);
+ if (IS_ERR(plane->config)) {
+ kfree(plane);
+ return ERR_CAST(plane->config);
+ }
+
+ config_group_init_type_name(&plane->group, name, &plane_item_type);
+
+ return &plane->group;
+}
+
+static struct configfs_group_operations planes_group_operations = {
+ .make_group = &make_plane_group,
+};
+
+static const struct config_item_type plane_group_type = {
+ .ct_group_ops = &planes_group_operations,
+ .ct_owner = THIS_MODULE,
+};
+
static ssize_t device_enabled_show(struct config_item *item, char *page)
{
struct vkms_configfs_device *dev;
@@ -125,6 +208,10 @@ static struct config_group *make_device_group(struct config_group *group,
config_group_init_type_name(&dev->group, name, &device_item_type);
mutex_init(&dev->lock);
+ config_group_init_type_name(&dev->planes_group, "planes",
+ &plane_group_type);
+ configfs_add_default_group(&dev->planes_group, &dev->group);
+
return &dev->group;
}
--
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
