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bh=BsPCLTZEaCquIBOJ6vNMgDVwuqLSKXr8k7CRbICgeWA=; b=Vc+5emaqJROq9y5q07LkEaSsjq/8OqCz/SNgX3Wuzehoy+In7/X5+4j3MA/49haYEbnREA pUD/YgRYHUWpptjzHwsDLgg6fg++vv4Us0Zb3Q6tu3njmZ50Brnx4lg9qDe5tKqDKSTnCv Y6U24wE8HvdRMhVrFYMWYXfISySvL2KtyZI2xiiNaAlj82LkoEcqanD/FaTnHvTPmQH0E3 mzPESVPTOCRZ4XBw34Ezm0Pw9Ux0MyxfwGifESWiNENvh91tx9+h8q/OWi6mNzjeDcVmW7 w5Esd9cD5zNQQ63gx1zcu0LY/CePwnQQEe2wd6hLDH3R5wS2l6P++bav564QwA== Message-ID: <52bc3f15-28da-4b40-917f-981f1f10d9b8@bootlin.com> Date: Fri, 28 Feb 2025 15:43:25 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 03/16] drm/vkms: Allow to configure multiple planes via configfs To: =?UTF-8?B?Sm9zw6kgRXhww7NzaXRv?= Cc: hamohammed.sa@gmail.com, simona@ffwll.ch, melissa.srw@gmail.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20250225175936.7223-1-jose.exposito89@gmail.com> <20250225175936.7223-4-jose.exposito89@gmail.com> Content-Language: en-US From: Louis Chauvet Autocrypt: addr=louis.chauvet@bootlin.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-GND-State: clean X-GND-Score: -100 X-GND-Cause: gggruggvucftvghtrhhoucdtuddrgeefvddrtddtgdeltdeiiecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfitefpfffkpdcuggftfghnshhusghstghrihgsvgenuceurghilhhouhhtmecufedtudenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhepkfffgggfuffvvehfhfgjtgfgsehtkeertddtvdejnecuhfhrohhmpefnohhuihhsucevhhgruhhvvghtuceolhhouhhishdrtghhrghuvhgvthessghoohhtlhhinhdrtghomheqnecuggftrfgrthhtvghrnhepkeeivedtfeegtdekheethedttddtfefhhfegjeeljeejleduvdfhudegvdekheevnecuffhomhgrihhnpegsohhothhlihhnrdgtohhmnecukfhppeeltddrkeelrdduieefrdduvdejnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehinhgvthepledtrdekledrudeifedruddvjedphhgvlhhopegludelvddrudeikedrtddrvddtngdpmhgrihhlfhhrohhmpehlohhuihhsrdgthhgruhhvvghtsegsohhothhlihhnrdgtohhmpdhnsggprhgtphhtthhopedutddprhgtphhtthhopehjohhsvgdrvgigphhoshhithhokeelsehgmhgrihhlrdgtohhmpdhrtghpthhtohephhgrmhhohhgrmhhmvggurdhsrgesghhmrghilhdrtghomhdprhgtphhtthhopehsihhmohhnrgesfhhffihllhdrtghhpdhrtghpthhtohepmhgvlhhishhsrgdrshhrfiesghhmrghilhdrtghomhdprhgtphhtthhopehmr ggrrhhtvghnrdhlrghnkhhhohhrshhtsehlihhnuhigrdhinhhtvghlrdgtohhmpdhrtghpthhtohepmhhrihhprghrugeskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepthiiihhmmhgvrhhmrghnnhesshhushgvrdguvgdprhgtphhtthhopegrihhrlhhivggusehgmhgrihhlrdgtohhm X-GND-Sasl: louis.chauvet@bootlin.com 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 > Co-developed-by: Louis Chauvet > Signed-off-by: Louis Chauvet > Signed-off-by: José Expósito > --- > 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