[PATCH v5 4/4] rust/drm/gem: Use DeviceContext with GEM objects

Lyude Paul
2026-01-31T00:16:49Z

Now that we have the ability to represent the context in which a DRM device
is in at compile-time, we can start carrying around this context with GEM
object types in order to allow a driver to safely create GEM objects before
a DRM device has registered with userspace.

Signed-off-by: Lyude Paul <lyude@redhat.com>

---
V4:
* Add a comment to explain the Uninit DeviceContext usage in the GEM object
vtable (tl;dr: the DeviceContext is meaningless here)

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
drivers/gpu/drm/nova/driver.rs | 2 +-
drivers/gpu/drm/nova/gem.rs | 11 ++++---
drivers/gpu/drm/tyr/driver.rs | 2 +-
drivers/gpu/drm/tyr/gem.rs | 3 +-
rust/kernel/drm/device.rs | 18 ++++++-----
rust/kernel/drm/driver.rs | 2 +-
rust/kernel/drm/gem/mod.rs | 57 ++++++++++++++++++++++------------
7 files changed, 61 insertions(+), 34 deletions(-)

diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
index 8cea5f68c3b04..2c13261450406 100644
--- a/drivers/gpu/drm/nova/driver.rs
+++ b/drivers/gpu/drm/nova/driver.rs
@@ -67,7 +67,7 @@ fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<S
impl drm::Driver for NovaDriver {
type Data = NovaData;
type File = File;
- type Object = gem::Object<NovaObject>;
+ type Object<Ctx: drm::DeviceContext> = gem::Object<NovaObject, Ctx>;

const INFO: drm::DriverInfo = INFO;

diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
index 6ccfa5da57617..f6e98b9db58d8 100644
--- a/drivers/gpu/drm/nova/gem.rs
+++ b/drivers/gpu/drm/nova/gem.rs
@@ -2,7 +2,7 @@

use kernel::{
drm,
- drm::{gem, gem::BaseObject},
+ drm::{gem, gem::BaseObject, DeviceContext},
page,
prelude::*,
sync::aref::ARef,
@@ -20,20 +20,23 @@ pub(crate) struct NovaObject {}
impl gem::DriverObject for NovaObject {
type Driver = NovaDriver;

- fn new(_dev: &NovaDevice, _size: usize) -> impl PinInit<Self, Error> {
+ fn new<Ctx: DeviceContext>(_dev: &NovaDevice<Ctx>, _size: usize) -> impl PinInit<Self, Error> {
try_pin_init!(NovaObject {})
}
}

impl NovaObject {
/// Create a new DRM GEM object.
- pub(crate) fn new(dev: &NovaDevice, size: usize) -> Result<ARef<gem::Object<Self>>> {
+ pub(crate) fn new<Ctx: DeviceContext>(
+ dev: &NovaDevice<Ctx>,
+ size: usize,
+ ) -> Result<ARef<gem::Object<Self, Ctx>>> {
if size == 0 {
return Err(EINVAL);
}
let aligned_size = page::page_align(size).ok_or(EINVAL)?;

- gem::Object::new(dev, aligned_size)
+ gem::Object::<Self, Ctx>::new(dev, aligned_size)
}

/// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.
diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
index b574ee1c24587..170ffdfd92a18 100644
--- a/drivers/gpu/drm/tyr/driver.rs
+++ b/drivers/gpu/drm/tyr/driver.rs
@@ -177,7 +177,7 @@ fn drop(self: Pin<&mut Self>) {
impl drm::Driver for TyrDriver {
type Data = TyrData;
type File = File;
- type Object = drm::gem::Object<TyrObject>;
+ type Object<R: drm::DeviceContext> = drm::gem::Object<TyrObject, R>;

const INFO: drm::DriverInfo = INFO;

diff --git a/drivers/gpu/drm/tyr/gem.rs b/drivers/gpu/drm/tyr/gem.rs
index 1273bf89dbd5d..00804f8c14bd4 100644
--- a/drivers/gpu/drm/tyr/gem.rs
+++ b/drivers/gpu/drm/tyr/gem.rs
@@ -3,6 +3,7 @@
use crate::driver::TyrDevice;
use crate::driver::TyrDriver;
use kernel::drm::gem;
+use kernel::drm::DeviceContext;
use kernel::prelude::*;

/// GEM Object inner driver data
@@ -12,7 +13,7 @@ pub(crate) struct TyrObject {}
impl gem::DriverObject for TyrObject {
type Driver = TyrDriver;

- fn new(_dev: &TyrDevice, _size: usize) -> impl PinInit<Self, Error> {
+ fn new<Ctx: DeviceContext>(_dev: &TyrDevice<Ctx>, _size: usize) -> impl PinInit<Self, Error> {
try_pin_init!(TyrObject {})
}
}
diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
index a1d9b0e92f3fd..8dd1508c51cec 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -163,13 +163,17 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
master_set: None,
master_drop: None,
debugfs_init: None,
- gem_create_object: T::Object::ALLOC_OPS.gem_create_object,
- prime_handle_to_fd: T::Object::ALLOC_OPS.prime_handle_to_fd,
- prime_fd_to_handle: T::Object::ALLOC_OPS.prime_fd_to_handle,
- gem_prime_import: T::Object::ALLOC_OPS.gem_prime_import,
- gem_prime_import_sg_table: T::Object::ALLOC_OPS.gem_prime_import_sg_table,
- dumb_create: T::Object::ALLOC_OPS.dumb_create,
- dumb_map_offset: T::Object::ALLOC_OPS.dumb_map_offset,
+
+ // Ignore the Uninit DeviceContext below. It is only provided because it is required by the
+ // compiler, and it is not actually used by these functions.
+ gem_create_object: T::Object::<Uninit>::ALLOC_OPS.gem_create_object,
+ prime_handle_to_fd: T::Object::<Uninit>::ALLOC_OPS.prime_handle_to_fd,
+ prime_fd_to_handle: T::Object::<Uninit>::ALLOC_OPS.prime_fd_to_handle,
+ gem_prime_import: T::Object::<Uninit>::ALLOC_OPS.gem_prime_import,
+ gem_prime_import_sg_table: T::Object::<Uninit>::ALLOC_OPS.gem_prime_import_sg_table,
+ dumb_create: T::Object::<Uninit>::ALLOC_OPS.dumb_create,
+ dumb_map_offset: T::Object::<Uninit>::ALLOC_OPS.dumb_map_offset,
+
show_fdinfo: None,
fbdev_probe: None,

diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index cfb8884ece700..e6893f089733d 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -110,7 +110,7 @@ pub trait Driver {
type Data: Sync + Send;

/// The type used to manage memory for this driver.
- type Object: AllocImpl;
+ type Object<Ctx: drm::DeviceContext>: AllocImpl;

/// The type used to represent a DRM File (client)
type File: drm::file::DriverFile;
diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
index ad74c5159f725..3af9f52f8eda4 100644
--- a/rust/kernel/drm/gem/mod.rs
+++ b/rust/kernel/drm/gem/mod.rs
@@ -8,6 +8,10 @@
bindings,
drm::{
self,
+ device::{
+ DeviceContext,
+ Registered, //
+ },
driver::{
AllocImpl,
AllocOps, //
@@ -22,6 +26,7 @@
types::Opaque,
};
use core::{
+ marker::PhantomData,
ops::Deref,
ptr::NonNull, //
};
@@ -36,7 +41,8 @@
/// A type alias for retrieving the current [`AllocImpl`] for a given [`DriverObject`].
///
/// [`Driver`]: drm::Driver
-pub type DriverAllocImpl<T> = <<T as DriverObject>::Driver as drm::Driver>::Object;
+pub type DriverAllocImpl<T, Ctx = Registered> =
+ <<T as DriverObject>::Driver as drm::Driver>::Object<Ctx>;

/// GEM object functions, which must be implemented by drivers.
pub trait DriverObject: Sync + Send + Sized {
@@ -44,7 +50,10 @@ pub trait DriverObject: Sync + Send + Sized {
type Driver: drm::Driver;

/// Create a new driver data object for a GEM object of a given size.
- fn new(dev: &drm::Device<Self::Driver>, size: usize) -> impl PinInit<Self, Error>;
+ fn new<Ctx: DeviceContext>(
+ dev: &drm::Device<Self::Driver, Ctx>,
+ size: usize,
+ ) -> impl PinInit<Self, Error>;

/// Open a new handle to an existing object, associated with a File.
fn open(_obj: &DriverAllocImpl<Self>, _file: &DriverFile<Self>) -> Result {
@@ -78,9 +87,12 @@ extern "C" fn open_callback<T: DriverObject>(
// SAFETY: `open_callback` is only ever called with a valid pointer to a `struct drm_file`.
let file = unsafe { DriverFile::<T>::from_raw(raw_file) };

- // SAFETY: `open_callback` is specified in the AllocOps structure for `DriverObject<T>`,
- // ensuring that `raw_obj` is contained within a `DriverObject<T>`
- let obj = unsafe { <<T::Driver as drm::Driver>::Object as IntoGEMObject>::from_raw(raw_obj) };
+ // SAFETY:
+ // * `open_callback` is specified in the AllocOps structure for `DriverObject`, ensuring that
+ // `raw_obj` is contained within a `DriverAllocImpl<T>`
+ // * It is only possible for `open_callback` to be called after device registration, ensuring
+ // that the object's device is in the `Registered` state.
+ let obj: &DriverAllocImpl<T> = unsafe { IntoGEMObject::from_raw(raw_obj) };

match T::open(obj, file) {
Err(e) => e.to_errno(),
@@ -97,12 +109,12 @@ extern "C" fn close_callback<T: DriverObject>(

// SAFETY: `close_callback` is specified in the AllocOps structure for `Object<T>`, ensuring
// that `raw_obj` is indeed contained within a `Object<T>`.
- let obj = unsafe { <<T::Driver as drm::Driver>::Object as IntoGEMObject>::from_raw(raw_obj) };
+ let obj: &DriverAllocImpl<T> = unsafe { IntoGEMObject::from_raw(raw_obj) };

T::close(obj, file);
}

-impl<T: DriverObject> IntoGEMObject for Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> IntoGEMObject for Object<T, Ctx> {
fn as_raw(&self) -> *mut bindings::drm_gem_object {
self.obj.get()
}
@@ -110,7 +122,7 @@ fn as_raw(&self) -> *mut bindings::drm_gem_object {
unsafe fn from_raw<'a>(self_ptr: *mut bindings::drm_gem_object) -> &'a Self {
// SAFETY: `obj` is guaranteed to be in an `Object<T>` via the safety contract of this
// function
- unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T>, obj) }
+ unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T, Ctx>, obj) }
}
}

@@ -127,7 +139,7 @@ fn size(&self) -> usize {
fn create_handle<D, F>(&self, file: &drm::File<F>) -> Result<u32>
where
Self: AllocImpl<Driver = D>,
- D: drm::Driver ,
+ D: drm::Driver<Object<Registered> = Self, File = F>,
F: drm::file::DriverFile<Driver = D>,
{
let mut handle: u32 = 0;
@@ -142,7 +154,7 @@ fn create_handle<D, F>(&self, file: &drm::File<F>) -> Result<u32>
fn lookup_handle<D, F>(file: &drm::File<F>, handle: u32) -> Result<ARef<Self>>
where
Self: AllocImpl<Driver = D>,
- D: drm::Driver ,
+ D: drm::Driver<Object<Registered> = Self, File = F>,
F: drm::file::DriverFile<Driver = D>,
{
// SAFETY: The arguments are all valid per the type invariants.
@@ -182,16 +194,18 @@ impl<T: IntoGEMObject> BaseObject for T {}
///
/// # Invariants
///
-/// - `self.obj` is a valid instance of a `struct drm_gem_object`.
+/// * `self.obj` is a valid instance of a `struct drm_gem_object`.
+/// * Any type invariants of `Ctx` apply to the parent DRM device for this GEM object.
#[repr(C)]
#[pin_data]
-pub struct Object<T: DriverObject + Send + Sync> {
+pub struct Object<T: DriverObject + Send + Sync, Ctx: DeviceContext = Registered> {
obj: Opaque<bindings::drm_gem_object>,
#[pin]
data: T,
+ _ctx: PhantomData<Ctx>,
}

-impl<T: DriverObject> Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> Object<T, Ctx> {
const OBJECT_FUNCS: bindings::drm_gem_object_funcs = bindings::drm_gem_object_funcs {
free: Some(Self::free_callback),
open: Some(open_callback::<T>),
@@ -211,11 +225,12 @@ impl<T: DriverObject> Object<T> {
};

/// Create a new GEM object.
- pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
+ pub fn new(dev: &drm::Device<T::Driver, Ctx>, size: usize) -> Result<ARef<Self>> {
let obj: Pin<KBox<Self>> = KBox::pin_init(
try_pin_init!(Self {
obj: Opaque::new(bindings::drm_gem_object::default()),
data <- T::new(dev, size),
+ _ctx: PhantomData,
}),
GFP_KERNEL,
)?;
@@ -224,6 +239,8 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
unsafe { (*obj.as_raw()).funcs = &Self::OBJECT_FUNCS };

// SAFETY: The arguments are all valid per the type invariants.
+ // INVARIANT: We use `dev` for creating the GEM object, which is known to be in state `Ctx` -
+ // ensuring that the GEM object's pointer to the DRM device is always in the same state.
to_result(unsafe { bindings::drm_gem_object_init(dev.as_raw(), obj.obj.get(), size) })?;

// SAFETY: We will never move out of `Self` as `ARef<Self>` is always treated as pinned.
@@ -237,13 +254,15 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
}

/// Returns the `Device` that owns this GEM object.
- pub fn dev(&self) -> &drm::Device<T::Driver> {
+ pub fn dev(&self) -> &drm::Device<T::Driver, Ctx> {
// SAFETY:
// - `struct drm_gem_object.dev` is initialized and valid for as long as the GEM
// object lives.
// - The device we used for creating the gem object is passed as &drm::Device<T::Driver> to
// Object::<T>::new(), so we know that `T::Driver` is the right generic parameter to use
// here.
+ // - Any type invariants of `Ctx` are upheld by using the same `Ctx` for the `Device` we
+ // return.
unsafe { drm::Device::from_raw((*self.as_raw()).dev) }
}

@@ -269,7 +288,7 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) {
}

// SAFETY: Instances of `Object<T>` are always reference-counted.
-unsafe impl<T: DriverObject> crate::sync::aref::AlwaysRefCounted for Object<T> {
+unsafe impl<T: DriverObject, Ctx: DeviceContext> AlwaysRefCounted for Object<T, Ctx> {
fn inc_ref(&self) {
// SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
unsafe { bindings::drm_gem_object_get(self.as_raw()) };
@@ -284,9 +303,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) {
}
}

-impl<T: DriverObject> super::private::Sealed for Object<T> {}
+impl<T: DriverObject, Ctx: DeviceContext> super::private::Sealed for Object<T, Ctx> {}

-impl<T: DriverObject> Deref for Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> Deref for Object<T, Ctx> {
type Target = T;

fn deref(&self) -> &Self::Target {
@@ -294,7 +313,7 @@ fn deref(&self) -> &Self::Target {
}
}

-impl<T: DriverObject> AllocImpl for Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> AllocImpl for Object<T, Ctx> {
type Driver = T::Driver;

const ALLOC_OPS: AllocOps = AllocOps {
--
2.52.0