Message-ID: <20251107193204.398657-3-lyude@redhat.com>
Date: Fri,  7 Nov 2025 14:23:54 -0500
From: Lyude Paul <lyude@...hat.com>
To: linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Cc: Danilo Krummrich <dakr@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	Daniel Almeida <daniel.almeida@...labora.com>,
	Asahi Lina <lina+kernel@...hilina.net>,
	Shankari Anand <shankari.ak0208@...il.com>,
	nouveau@...ts.freedesktop.org (open list:DRM DRIVER FOR NVIDIA GPUS [RUST])
Subject: [PATCH 2/2] rust/drm/gem: Use DeviceCtx with GEM objects

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@...hat.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      | 14 ++++----
 rust/kernel/drm/driver.rs      |  2 +-
 rust/kernel/drm/gem/mod.rs     | 66 ++++++++++++++++++++++------------
 7 files changed, 63 insertions(+), 37 deletions(-)

diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
index c78d69d5f045a..54245ee439042 100644
--- a/drivers/gpu/drm/nova/driver.rs
+++ b/drivers/gpu/drm/nova/driver.rs
@@ -59,7 +59,7 @@ fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> Result<Pin<KBo
 impl drm::Driver for NovaDriver {
     type Data = NovaData;
     type File = File;
-    type Object = gem::Object<NovaObject>;
+    type Object<Ctx: drm::DeviceCtx> = 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 2760ba4f3450b..14d275dc74ce7 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, DeviceCtx},
     prelude::*,
     sync::aref::ARef,
 };
@@ -19,21 +19,24 @@ 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: DeviceCtx>(_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: DeviceCtx>(
+        dev: &NovaDevice<Ctx>,
+        size: usize,
+    ) -> Result<ARef<gem::Object<Self, Ctx>>> {
         let aligned_size = size.next_multiple_of(1 << 12);
 
         if size == 0 || size > aligned_size {
             return Err(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 e3ea5ad85f49b..78fc08945e08e 100644
--- a/drivers/gpu/drm/tyr/driver.rs
+++ b/drivers/gpu/drm/tyr/driver.rs
@@ -187,7 +187,7 @@ 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::DeviceCtx> = 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..5e1403409f468 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::DeviceCtx;
 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: DeviceCtx>(_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 00072984930a3..227df6bf88c31 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -127,13 +127,13 @@ 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,
+        gem_create_object: T::Object::<AnyCtx>::ALLOC_OPS.gem_create_object,
+        prime_handle_to_fd: T::Object::<AnyCtx>::ALLOC_OPS.prime_handle_to_fd,
+        prime_fd_to_handle: T::Object::<AnyCtx>::ALLOC_OPS.prime_fd_to_handle,
+        gem_prime_import: T::Object::<AnyCtx>::ALLOC_OPS.gem_prime_import,
+        gem_prime_import_sg_table: T::Object::<AnyCtx>::ALLOC_OPS.gem_prime_import_sg_table,
+        dumb_create: T::Object::<AnyCtx>::ALLOC_OPS.dumb_create,
+        dumb_map_offset: T::Object::<AnyCtx>::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 fde0447566bef..4e8735e9018c4 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -104,7 +104,7 @@ pub trait Driver {
     type Data: Sync + Send;
 
     /// The type used to manage memory for this driver.
-    type Object: AllocImpl;
+    type Object<Ctx: drm::DeviceCtx>: 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 eb5f3feac8907..62ca11126e1c0 100644
--- a/rust/kernel/drm/gem/mod.rs
+++ b/rust/kernel/drm/gem/mod.rs
@@ -7,13 +7,16 @@
 use crate::{
     alloc::flags::*,
     bindings, drm,
-    drm::driver::{AllocImpl, AllocOps},
+    drm::{
+        device::{DeviceCtx, Registered},
+        driver::{AllocImpl, AllocOps},
+    },
     error::{to_result, Result},
     prelude::*,
     sync::aref::{ARef, AlwaysRefCounted},
     types::Opaque,
 };
-use core::{ops::Deref, ptr::NonNull};
+use core::{marker::PhantomData, ops::Deref, ptr::NonNull};
 
 /// A type alias for retrieving a [`Driver`]s [`DriverFile`] implementation from its
 /// [`DriverObject`] implementation.
@@ -22,21 +25,30 @@
 /// [`DriverFile`]: drm::file::DriverFile
 pub type DriverFile<T> = drm::File<<<T as DriverObject>::Driver as drm::Driver>::File>;
 
+/// A type alias for retrieving the current [`AllocImpl`] for a given [`DriverObject`].
+///
+/// [`Driver`]: drm::Driver
+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 {
     /// Parent `Driver` for this object.
     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: DeviceCtx>(
+        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: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) -> Result {
+    fn open(_obj: &DriverAllocImpl<Self>, _file: &DriverFile<Self>) -> Result {
         Ok(())
     }
 
     /// Close a handle to an existing object, associated with a File.
-    fn close(_obj: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) {}
+    fn close(_obj: &DriverAllocImpl<Self>, _file: &DriverFile<Self>) {}
 }
 
 /// Trait that represents a GEM object subtype
@@ -62,9 +74,12 @@ 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(),
@@ -81,12 +96,12 @@ 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: DeviceCtx> IntoGEMObject for Object<T, Ctx> {
     fn as_raw(&self) -> *mut bindings::drm_gem_object {
         self.obj.get()
     }
@@ -94,7 +109,7 @@ 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) }
     }
 }
 
@@ -111,7 +126,7 @@ fn size(&self) -> usize {
     fn create_handle<D, F>(&self, file: &drm::File<F>) -> Result<u32>
     where
         Self: AllocImpl<Driver = D>,
-        D: drm::Driver<Object = Self, File = F>,
+        D: drm::Driver<Object<Registered> = Self, File = F>,
         F: drm::file::DriverFile<Driver = D>,
     {
         let mut handle: u32 = 0;
@@ -126,7 +141,7 @@ 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<Object = Self, File = F>,
+        D: drm::Driver<Object<Registered> = Self, File = F>,
         F: drm::file::DriverFile<Driver = D>,
     {
         // SAFETY: The arguments are all valid per the type invariants.
@@ -166,16 +181,18 @@ 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: DeviceCtx = Registered> {
     obj: Opaque<bindings::drm_gem_object>,
     #[pin]
     data: T,
+    _ctx: PhantomData<Ctx>,
 }
 
-impl<T: DriverObject> Object<T> {
+impl<T: DriverObject, Ctx: DeviceCtx> 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>),
@@ -195,11 +212,12 @@ 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,
         )?;
@@ -208,6 +226,8 @@ 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 never move out of `Self`.
@@ -221,13 +241,15 @@ 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) }
     }
 
@@ -253,7 +275,7 @@ 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::types::AlwaysRefCounted for Object<T> {
+unsafe impl<T: DriverObject, Ctx: DeviceCtx> crate::types::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()) };
@@ -268,9 +290,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) {
     }
 }
 
-impl<T: DriverObject> super::private::Sealed for Object<T> {}
+impl<T: DriverObject, Ctx: DeviceCtx> super::private::Sealed for Object<T, Ctx> {}
 
-impl<T: DriverObject> Deref for Object<T> {
+impl<T: DriverObject, Ctx: DeviceCtx> Deref for Object<T, Ctx> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -278,7 +300,7 @@ fn deref(&self) -> &Self::Target {
     }
 }
 
-impl<T: DriverObject> AllocImpl for Object<T> {
+impl<T: DriverObject, Ctx: DeviceCtx> AllocImpl for Object<T, Ctx> {
     type Driver = T::Driver;
 
     const ALLOC_OPS: AllocOps = AllocOps {
-- 
2.51.1

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