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It's quite normal for a device driver to start making use of its DRM device for tasks like creating GEM objects before userspace registration happens. This is an issue in rust though, since prior to userspace registration the device is only partly initialized. This means there's a plethora of DRM device operations we can't yet expose without opening up the door to UB if the DRM device in question isn't yet registered. Additionally, this isn't something we can reliably check at runtime. And even if we could, performing an operation which requires the device be registered when the device isn't actually registered is a programmer bug, meaning there's no real way to gracefully handle such a mistake at runtime. And even if that wasn't the case, it would be horrendously annoying and noisy to have to check if a device is registered constantly throughout a driver. In order to solve this, we first take inspiration from `kernel::device::DeviceContext` and introduce `kernel::drm::DeviceContext`. This provides us with a ZST type that we can generalize over to represent contexts where a device is known to have been registered with userspace at some point in time (`Registered`), along with contexts where we can't make such a guarantee (`Uninit`). It's important to note we intentionally do not provide a `DeviceContext` which represents an unregistered device. This is because there's no reasonable way to guarantee that a device with long-living references to itself will not be registered eventually with userspace. Instead, we provide a new-type for this: `UnregisteredDevice` which can provide a guarantee that the `Device` has never been registered with userspace. To ensure this, we modify `Registration` so that creating a new `Registration` requires passing ownership of an `UnregisteredDevice`. Signed-off-by: Lyude Paul Reviewed-by: Daniel Almeida --- V2: * Make sure that `UnregisteredDevice` is not thread-safe (since DRM device initialization is also not thread-safe) * Rename from AnyCtx to Uninit, I think this name actually makes a bit more sense. * Change assume_registered() to assume_ctx() Since it looks like in some situations, we'll want to update the DeviceContext of a object to the latest DeviceContext we know the Device to be in. * Rename Init to Uninit When we eventually add KMS support, we're going to have 3 different DeviceContexts - Uninit, Init, Registered. Additionally, aside from not being registered there are a number of portions of the rest of the Device which also aren't usable before at least the Init context - so the naming of Uninit makes this a little clearer. * s/DeviceContext/DeviceContext/ For consistency with the rest of the kernel * Drop as_ref::>() for now since I don't actually think we need this quite yet V3: * Get rid of drm_dev_ctx!, as we don't actually need to implement Send or Sync ourselves * Remove mention of C function in drm::device::Registration rustdoc * Add more documentation to the DeviceContext trait, go into detail about the various setup phases and such. * Add missing period to comment in `UnregisteredDevice::new()`. drivers/gpu/drm/nova/driver.rs | 8 +- drivers/gpu/drm/tyr/driver.rs | 10 +- rust/kernel/drm/device.rs | 179 +++++++++++++++++++++++++++------ rust/kernel/drm/driver.rs | 38 +++++-- rust/kernel/drm/mod.rs | 4 + 5 files changed, 193 insertions(+), 46 deletions(-) diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs index b1af0a099551d..99d6841b69cbc 100644 --- a/drivers/gpu/drm/nova/driver.rs +++ b/drivers/gpu/drm/nova/driver.rs @@ -21,7 +21,7 @@ pub(crate) struct NovaDriver { } =20 /// Convienence type alias for the DRM device type for this driver -pub(crate) type NovaDevice =3D drm::Device; +pub(crate) type NovaDevice =3D drm::Device; =20 #[pin_data] pub(crate) struct NovaData { @@ -56,10 +56,10 @@ impl auxiliary::Driver for NovaDriver { fn probe(adev: &auxiliary::Device, _info: &Self::IdInfo) -> impl= PinInit { let data =3D try_pin_init!(NovaData { adev: adev.into() }); =20 - let drm =3D drm::Device::::new(adev.as_ref(), data)?; - drm::Registration::new_foreign_owned(&drm, adev.as_ref(), 0)?; + let drm =3D drm::UnregisteredDevice::::new(adev.as_ref(), da= ta)?; + let drm =3D drm::Registration::new_foreign_owned(drm, adev.as_ref(= ), 0)?; =20 - Ok(Self { drm }) + Ok(Self { drm: drm.into() }) } } =20 diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs index 2a45d02888253..ac265a60f5667 100644 --- a/drivers/gpu/drm/tyr/driver.rs +++ b/drivers/gpu/drm/tyr/driver.rs @@ -30,7 +30,7 @@ pub(crate) type IoMem =3D kernel::io::mem::IoMem; =20 /// Convenience type alias for the DRM device type for this driver. -pub(crate) type TyrDevice =3D drm::Device; +pub(crate) type TyrDevice =3D drm::Device; =20 #[pin_data(PinnedDrop)] pub(crate) struct TyrDriver { @@ -133,10 +133,12 @@ fn probe( gpu_info, }); =20 - let tdev: ARef =3D drm::Device::new(pdev.as_ref(), data= )?; - drm::driver::Registration::new_foreign_owned(&tdev, pdev.as_ref(),= 0)?; + let tdev =3D drm::UnregisteredDevice::::new(pdev.as_ref(), d= ata)?; + let tdev =3D drm::driver::Registration::new_foreign_owned(tdev, pd= ev.as_ref(), 0)?; =20 - let driver =3D TyrDriver { device: tdev }; + let driver =3D TyrDriver { + device: tdev.into(), + }; =20 // We need this to be dev_info!() because dev_dbg!() does not work= at // all in Rust for now, and we need to see whether probe succeeded. diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs index 30116d78cabe0..f529bc7fc4032 100644 --- a/rust/kernel/drm/device.rs +++ b/rust/kernel/drm/device.rs @@ -10,7 +10,8 @@ device, // drm::{ self, - driver::AllocImpl, // + driver::AllocImpl, + private::Sealed, // }, error::from_err_ptr, prelude::*, @@ -18,10 +19,14 @@ ARef, AlwaysRefCounted, // }, - types::Opaque, + types::{ + NotThreadSafe, + Opaque, // + }, }; use core::{ alloc::Layout, + marker::PhantomData, mem, ops::Deref, ptr::{ @@ -61,26 +66,98 @@ macro_rules! drm_legacy_fields { } } =20 -/// A typed DRM device with a specific `drm::Driver` implementation. +/// A trait implemented by all possible contexts a [`Device`] can be used = in. +/// +/// Setting up a new [`Device`] is a multi-stage process. Each step of the= process that a user +/// interacts with in Rust has a respective [`DeviceContext`] typestate. F= or example, +/// `Device` would be a [`Device`] that reached the [`Regis= tered`] [`DeviceContext`]. +/// +/// Each stage of this process is described below: /// -/// The device is always reference-counted. +/// ```text +/// 1 2 3 +/// +--------------+ +------------------+ +-----------------------+ +/// |Device created| =E2=86=92 |Device initialized| =E2=86=92 |Registered = w/ userspace| +/// +--------------+ +------------------+ +-----------------------+ +/// (Uninit) (Registered) +/// ``` +/// +/// 1. The [`Device`] is in the [`Uninit`] context and is not guaranteed t= o be initialized or +/// registered with userspace. Only a limited subset of DRM core functi= onality is available. +/// 2. The [`Device`] is guaranteed to be fully initialized, but is not gu= aranteed to be registered +/// with userspace. All DRM core functionality which doesn't interact w= ith userspace is +/// available. We currently don't have a context for representing this. +/// 3. The [`Device`] is guaranteed to be fully initialized, and is guaran= teed to have been +/// registered with userspace at some point - thus putting it in the [`= Registered`] context. +/// +/// An important caveat of [`DeviceContext`] which must be kept in mind: w= hen used as a typestate +/// for a reference type, it can only guarantee that a [`Device`] reached = a particular stage in the +/// initialization process _at the time the reference was taken_. No guara= ntee is made in regards to +/// what stage of the process the [`Device`] is currently in. This means f= or instance that a +/// `&Device` may actually be registered with userspace, it jus= t wasn't known to be +/// registered at the time the reference was taken. +pub trait DeviceContext: Sealed + Send + Sync {} + +/// The [`DeviceContext`] of a [`Device`] that was registered with userspa= ce at some point. +/// +/// This represents a [`Device`] which is guaranteed to have been register= ed with userspace at +/// some point in time. Such a DRM device is guaranteed to have been fully= -initialized. +/// +/// Note: A device in this context is not guaranteed to remain registered = with userspace for its +/// entire lifetime, as this is impossible to guarantee at compile-time. /// /// # Invariants /// -/// `self.dev` is a valid instance of a `struct device`. -#[repr(C)] -pub struct Device { - dev: Opaque, - data: T::Data, +/// A [`Device`] in this [`DeviceContext`] is guaranteed to have been regi= stered with userspace +/// at some point in time. +pub struct Registered; + +impl Sealed for Registered {} +impl DeviceContext for Registered {} + +/// The [`DeviceContext`] of a [`Device`] that may be unregistered and par= tly uninitialized. +/// +/// A [`Device`] in this context is only guaranteed to be partly initializ= ed, and may or may not +/// be registered with userspace. Thus operations which depend on the [`De= vice`] being fully +/// initialized, or which depend on the [`Device`] being registered with u= serspace are not +/// available through this [`DeviceContext`]. +/// +/// A [`Device`] in this context can be used to create a +/// [`Registration`](drm::driver::Registration). +pub struct Uninit; + +impl Sealed for Uninit {} +impl DeviceContext for Uninit {} + +/// A [`Device`] which is known at compile-time to be unregistered with us= erspace. +/// +/// This type allows performing operations which are only safe to do befor= e userspace registration, +/// and can be used to create a [`Registration`](drm::driver::Registration= ) once the driver is ready +/// to register the device with userspace. +/// +/// Since DRM device initialization must be single-threaded, this object i= s not thread-safe. +/// +/// # Invariants +/// +/// The device in `self.0` is guaranteed to be a newly created [`Device`] = that has not yet been +/// registered with userspace until this type is dropped. +pub struct UnregisteredDevice(ARef>, Not= ThreadSafe); + +impl Deref for UnregisteredDevice { + type Target =3D Device; + + fn deref(&self) -> &Self::Target { + &self.0 + } } =20 -impl Device { +impl UnregisteredDevice { const VTABLE: bindings::drm_driver =3D drm_legacy_fields! { load: None, open: Some(drm::File::::open_callback), postclose: Some(drm::File::::postclose_callback), unload: None, - release: Some(Self::release), + release: Some(Device::::release), master_set: None, master_drop: None, debugfs_init: None, @@ -108,8 +185,10 @@ impl Device { =20 const GEM_FOPS: bindings::file_operations =3D drm::gem::create_fops(); =20 - /// Create a new `drm::Device` for a `drm::Driver`. - pub fn new(dev: &device::Device, data: impl PinInit) -= > Result> { + /// Create a new `UnregisteredDevice` for a `drm::Driver`. + /// + /// This can be used to create a [`Registration`](kernel::drm::Registr= ation). + pub fn new(dev: &device::Device, data: impl PinInit) -= > Result { // `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence en= sure a `kmalloc()` // compatible `Layout`. let layout =3D Kmalloc::aligned_layout(Layout::new::()); @@ -117,12 +196,12 @@ pub fn new(dev: &device::Device, data: impl PinInit) -> Result =3D unsafe { bindings::__drm_dev_alloc( dev.as_raw(), &Self::VTABLE, layout.size(), - mem::offset_of!(Self, dev), + mem::offset_of!(Device, dev), ) } .cast(); @@ -137,7 +216,7 @@ pub fn new(dev: &device::Device, data: impl PinInit) -> Result) -> Result { + dev: Opaque, + data: T::Data, + _ctx: PhantomData, +} =20 +impl Device { pub(crate) fn as_raw(&self) -> *mut bindings::drm_device { self.dev.get() } @@ -174,13 +284,13 @@ unsafe fn into_drm_device(ptr: NonNull) -> *mut= bindings::drm_device { /// /// # Safety /// - /// Callers must ensure that `ptr` is valid, non-null, and has a non-z= ero reference count, - /// i.e. it must be ensured that the reference count of the C `struct = drm_device` `ptr` points - /// to can't drop to zero, for the duration of this function call and = the entire duration when - /// the returned reference exists. - /// - /// Additionally, callers must ensure that the `struct device`, `ptr` = is pointing to, is - /// embedded in `Self`. + /// * Callers must ensure that `ptr` is valid, non-null, and has a non= -zero reference count, + /// i.e. it must be ensured that the reference count of the C `struc= t drm_device` `ptr` points + /// to can't drop to zero, for the duration of this function call an= d the entire duration when + /// the returned reference exists. + /// * Additionally, callers must ensure that the `struct device`, `ptr= ` is pointing to, is + /// embedded in `Self`. + /// * Callers promise that any type invariants of `C` will be upheld. #[doc(hidden)] pub unsafe fn from_raw<'a>(ptr: *const bindings::drm_device) -> &'a Se= lf { // SAFETY: By the safety requirements of this function `ptr` is a = valid pointer to a @@ -200,9 +310,20 @@ extern "C" fn release(ptr: *mut bindings::drm_device) { // - `this` is valid for dropping. unsafe { core::ptr::drop_in_place(this) }; } + + /// Change the [`DeviceContext`] for a [`Device`]. + /// + /// # Safety + /// + /// The caller promises that `self` fulfills all of the guarantees pro= vided by the given + /// [`DeviceContext`]. + pub(crate) unsafe fn assume_ctx(&self) -> &Devi= ce { + // SAFETY: The data layout is identical via our type invariants. + unsafe { mem::transmute(self) } + } } =20 -impl Deref for Device { +impl Deref for Device { type Target =3D T::Data; =20 fn deref(&self) -> &Self::Target { @@ -212,7 +333,7 @@ fn deref(&self) -> &Self::Target { =20 // SAFETY: DRM device objects are always reference counted and the get/put= functions // satisfy the requirements. -unsafe impl AlwaysRefCounted for Device { +unsafe impl AlwaysRefCounted for Device<= T, C> { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the= refcount is non-zero. unsafe { bindings::drm_dev_get(self.as_raw()) }; @@ -227,7 +348,7 @@ unsafe fn dec_ref(obj: NonNull) { } } =20 -impl AsRef for Device { +impl AsRef for Device { fn as_ref(&self) -> &device::Device { // SAFETY: `bindings::drm_device::dev` is valid as long as the DRM= device itself is valid, // which is guaranteed by the type invariant. @@ -236,8 +357,8 @@ fn as_ref(&self) -> &device::Device { } =20 // SAFETY: A `drm::Device` can be released from any thread. -unsafe impl Send for Device {} +unsafe impl Send for Device {} =20 // SAFETY: A `drm::Device` can be shared among threads because all immutab= le methods are protected // by the synchronization in `struct drm_device`. -unsafe impl Sync for Device {} +unsafe impl Sync for Device {} diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs index 5233bdebc9fcd..da9f1bfef1f14 100644 --- a/rust/kernel/drm/driver.rs +++ b/rust/kernel/drm/driver.rs @@ -13,6 +13,10 @@ prelude::*, sync::aref::ARef, // }; +use core::{ + mem, + ptr::NonNull, // +}; =20 /// Driver use the GEM memory manager. This should be set for all modern d= rivers. pub(crate) const FEAT_GEM: u32 =3D bindings::drm_driver_feature_DRIVER_GEM; @@ -123,31 +127,47 @@ pub trait Driver { pub struct Registration(ARef>); =20 impl Registration { - fn new(drm: &drm::Device, flags: usize) -> Result { + fn new(drm: drm::UnregisteredDevice, flags: usize) -> Result { // SAFETY: `drm.as_raw()` is valid by the invariants of `drm::Devi= ce`. to_result(unsafe { bindings::drm_dev_register(drm.as_raw(), flags)= })?; =20 - Ok(Self(drm.into())) + // SAFETY: We just called `drm_dev_register` above + let new =3D NonNull::from(unsafe { drm.assume_ctx() }); + + // Leak the ARef from UnregisteredDevice in preparation for transf= erring its ownership. + mem::forget(drm); + + // SAFETY: `drm`'s `Drop` constructor was never called, ensuring t= hat there remains at least + // one reference to the device - which we take ownership over here. + let new =3D unsafe { ARef::from_raw(new) }; + + Ok(Self(new)) } =20 - /// Registers a new [`Device`](drm::Device) with userspace. + /// Registers a new [`UnregisteredDevice`](drm::UnregisteredDevice) wi= th userspace. /// /// Ownership of the [`Registration`] object is passed to [`devres::re= gister`]. - pub fn new_foreign_owned( - drm: &drm::Device, - dev: &device::Device, + pub fn new_foreign_owned<'a>( + drm: drm::UnregisteredDevice, + dev: &'a device::Device, flags: usize, - ) -> Result + ) -> Result<&'a drm::Device> where T: 'static, { - if drm.as_ref().as_raw() !=3D dev.as_raw() { + let this_dev: &device::Device =3D drm.as_ref(); + if this_dev.as_raw() !=3D dev.as_raw() { return Err(EINVAL); } =20 let reg =3D Registration::::new(drm, flags)?; + let drm =3D NonNull::from(reg.device()); + + devres::register(dev, reg, GFP_KERNEL)?; =20 - devres::register(dev, reg, GFP_KERNEL) + // SAFETY: Since `reg` was passed to devres::register(), the devic= e now owns the lifetime + // of the DRM registration - ensuring that this references lives f= or at least as long as 'a. + Ok(unsafe { drm.as_ref() }) } =20 /// Returns a reference to the `Device` instance for this registration. diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs index 1b82b6945edf2..64a43cb0fe57c 100644 --- a/rust/kernel/drm/mod.rs +++ b/rust/kernel/drm/mod.rs @@ -9,6 +9,10 @@ pub mod ioctl; =20 pub use self::device::Device; +pub use self::device::DeviceContext; +pub use self::device::Registered; +pub use self::device::Uninit; +pub use self::device::UnregisteredDevice; pub use self::driver::Driver; pub use self::driver::DriverInfo; pub use self::driver::Registration; 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Thu, 22 Jan 2026 17:51:31 -0500 X-MC-Unique: TTC83R5rPseRm-Vi29HBwg-1 X-Mimecast-MFC-AGG-ID: TTC83R5rPseRm-Vi29HBwg_1769122290 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 01747180044D; Thu, 22 Jan 2026 22:51:30 +0000 (UTC) Received: from GoldenWind.redhat.com (unknown [10.22.89.232]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 090C130002D8; Thu, 22 Jan 2026 22:51:27 +0000 (UTC) From: Lyude Paul To: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org, Danilo Krummrich Cc: nouveau@lists.freedesktop.org, "Miguel Ojeda" , "Simona Vetter" , "Alice Ryhl" , "Shankari Anand" , "David Airlie" , "Benno Lossin" , "Asahi Lina" , "Daniel Almeida" , "Lyude Paul" Subject: [PATCH v3 2/3] rust/drm: Don't setup private driver data until registration Date: Thu, 22 Jan 2026 17:46:37 -0500 Message-ID: <20260122225057.3589500-3-lyude@redhat.com> In-Reply-To: <20260122225057.3589500-1-lyude@redhat.com> References: <20260122225057.3589500-1-lyude@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Content-Type: text/plain; charset="utf-8" Now that we have a DeviceContext that we can use to represent whether a Device is known to have been registered, we can make it so that drivers can create their Devices but wait until the registration phase to assign their private data to the Device. This is desirable as some drivers need to make use of the DRM device early on before finalizing their private driver data. As such, this change makes it so that the driver's private data can currently only be accessed through Device types and not Device. Signed-off-by: Lyude Paul --- drivers/gpu/drm/nova/driver.rs | 4 +-- drivers/gpu/drm/tyr/driver.rs | 4 +-- rust/kernel/drm/device.rs | 63 ++++++++++++++++++++-------------- rust/kernel/drm/driver.rs | 19 ++++++++-- 4 files changed, 58 insertions(+), 32 deletions(-) diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs index 99d6841b69cbc..8cea5f68c3b04 100644 --- a/drivers/gpu/drm/nova/driver.rs +++ b/drivers/gpu/drm/nova/driver.rs @@ -56,8 +56,8 @@ impl auxiliary::Driver for NovaDriver { fn probe(adev: &auxiliary::Device, _info: &Self::IdInfo) -> impl= PinInit { let data =3D try_pin_init!(NovaData { adev: adev.into() }); =20 - let drm =3D drm::UnregisteredDevice::::new(adev.as_ref(), da= ta)?; - let drm =3D drm::Registration::new_foreign_owned(drm, adev.as_ref(= ), 0)?; + let drm =3D drm::UnregisteredDevice::::new(adev.as_ref())?; + let drm =3D drm::Registration::new_foreign_owned(drm, adev.as_ref(= ), data, 0)?; =20 Ok(Self { drm: drm.into() }) } diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs index ac265a60f5667..e73c56659ea75 100644 --- a/drivers/gpu/drm/tyr/driver.rs +++ b/drivers/gpu/drm/tyr/driver.rs @@ -133,8 +133,8 @@ fn probe( gpu_info, }); =20 - let tdev =3D drm::UnregisteredDevice::::new(pdev.as_ref(), d= ata)?; - let tdev =3D drm::driver::Registration::new_foreign_owned(tdev, pd= ev.as_ref(), 0)?; + let tdev =3D drm::UnregisteredDevice::::new(pdev.as_ref())?; + let tdev =3D drm::driver::Registration::new_foreign_owned(tdev, pd= ev.as_ref(), data, 0)?; =20 let driver =3D TyrDriver { device: tdev.into(), diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs index f529bc7fc4032..0e81957cf8c28 100644 --- a/rust/kernel/drm/device.rs +++ b/rust/kernel/drm/device.rs @@ -26,13 +26,15 @@ }; use core::{ alloc::Layout, + cell::UnsafeCell, marker::PhantomData, - mem, - ops::Deref, - ptr::{ + mem::{ self, - NonNull, // + MaybeUninit, // }, + ops::Deref, + ptr::NonNull, + sync::atomic::*, }; =20 #[cfg(CONFIG_DRM_LEGACY)] @@ -141,7 +143,7 @@ impl DeviceContext for Uninit {} /// /// The device in `self.0` is guaranteed to be a newly created [`Device`] = that has not yet been /// registered with userspace until this type is dropped. -pub struct UnregisteredDevice(ARef>, Not= ThreadSafe); +pub struct UnregisteredDevice(pub(crate) ARef>, NotThreadSafe); =20 impl Deref for UnregisteredDevice { type Target =3D Device; @@ -188,7 +190,7 @@ impl UnregisteredDevice { /// Create a new `UnregisteredDevice` for a `drm::Driver`. /// /// This can be used to create a [`Registration`](kernel::drm::Registr= ation). - pub fn new(dev: &device::Device, data: impl PinInit) -= > Result { + pub fn new(dev: &device::Device) -> Result { // `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence en= sure a `kmalloc()` // compatible `Layout`. let layout =3D Kmalloc::aligned_layout(Layout::new::()); @@ -207,22 +209,6 @@ pub fn new(dev: &device::Device, data: impl PinInit) -> Result) -> Result { dev: Opaque, - data: T::Data, + + /// Keeps track of whether we've initialized the device data yet. + pub(crate) data_is_init: AtomicBool, + + /// The Driver's private data. + /// + /// This must only be written to from [`drm::Registration::new`]. + pub(crate) data: UnsafeCell>, + _ctx: PhantomData, } =20 @@ -305,6 +299,21 @@ extern "C" fn release(ptr: *mut bindings::drm_device) { // SAFETY: `ptr` is a valid pointer to a `struct drm_device` and e= mbedded in `Self`. let this =3D unsafe { Self::from_drm_device(ptr) }; =20 + { + // SAFETY: + // - Since we are in release(), we are guaranteed that no one = else has access to `this`. + // - We confirmed above that `this` is a valid pointer to an i= nitialized `Self`. + let this =3D unsafe { &mut *this }; + if this.data_is_init.load(Ordering::Relaxed) { + // SAFETY: + // - Since we are in release(), we are guaranteed that no = one else has access to + // `this`. + // - We checked that the data is initialized above. + // - We do not use `data` any point after calling this fun= ction. + unsafe { (&mut *this.data.get()).assume_init_drop() }; + } + } + // SAFETY: // - When `release` runs it is guaranteed that there is no further= access to `this`. // - `this` is valid for dropping. @@ -323,11 +332,15 @@ pub(crate) unsafe fn assume_ctx(&self) -> &Device Deref for Device { +impl Deref for Device { type Target =3D T::Data; =20 fn deref(&self) -> &Self::Target { - &self.data + // SAFETY: + // - `data` is initialized before any `Device`s with the `Register= ed` context are available + // to the user. + // - `data` is only written to once in `Registration::new()`, so t= his read will never race. + unsafe { (&*self.data.get()).assume_init_ref() } } } =20 diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs index da9f1bfef1f14..a16605b407159 100644 --- a/rust/kernel/drm/driver.rs +++ b/rust/kernel/drm/driver.rs @@ -15,7 +15,8 @@ }; use core::{ mem, - ptr::NonNull, // + ptr::NonNull, + sync::atomic::*, // }; =20 /// Driver use the GEM memory manager. This should be set for all modern d= rivers. @@ -127,7 +128,18 @@ pub trait Driver { pub struct Registration(ARef>); =20 impl Registration { - fn new(drm: drm::UnregisteredDevice, flags: usize) -> Result { + fn new( + drm: drm::UnregisteredDevice, + data: impl PinInit, + flags: usize, + ) -> Result { + // SAFETY: + // - `raw_data` is a valid pointer to uninitialized memory. + // - `raw_data` will not move until it is dropped. + unsafe { data.__pinned_init(drm.0.data.get().cast()) }?; + + drm.data_is_init.store(true, Ordering::Relaxed); + // SAFETY: `drm.as_raw()` is valid by the invariants of `drm::Devi= ce`. to_result(unsafe { bindings::drm_dev_register(drm.as_raw(), flags)= })?; =20 @@ -150,6 +162,7 @@ fn new(drm: drm::UnregisteredDevice, flags: usize) -= > Result { pub fn new_foreign_owned<'a>( drm: drm::UnregisteredDevice, dev: &'a device::Device, + data: impl PinInit, flags: usize, ) -> Result<&'a drm::Device> where @@ -160,7 +173,7 @@ pub fn new_foreign_owned<'a>( return Err(EINVAL); 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Thu, 22 Jan 2026 22:51:35 +0000 (UTC) Received: from GoldenWind.redhat.com (unknown [10.22.89.232]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 3846830002D8; Thu, 22 Jan 2026 22:51:33 +0000 (UTC) From: Lyude Paul To: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org, Danilo Krummrich Cc: nouveau@lists.freedesktop.org, "Miguel Ojeda" , "Simona Vetter" , "Alice Ryhl" , "Shankari Anand" , "David Airlie" , "Benno Lossin" , "Asahi Lina" , "Daniel Almeida" , "Lyude Paul" Subject: [PATCH v3 3/3] rust/drm/gem: Use DeviceContext with GEM objects Date: Thu, 22 Jan 2026 17:46:38 -0500 Message-ID: <20260122225057.3589500-4-lyude@redhat.com> In-Reply-To: <20260122225057.3589500-1-lyude@redhat.com> References: <20260122225057.3589500-1-lyude@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Content-Type: text/plain; charset="utf-8" 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 --- 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 | 64 +++++++++++++++++++++++----------- 7 files changed, 63 insertions(+), 35 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, _info: &Self::Id= Info) -> impl PinInit; + type Object =3D gem::Object; =20 const INFO: drm::DriverInfo =3D INFO; =20 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 @@ =20 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 =3D NovaDriver; =20 - fn new(_dev: &NovaDevice, _size: usize) -> impl PinInit { + fn new(_dev: &NovaDevice, _size: usize) -> im= pl PinInit { try_pin_init!(NovaObject {}) } } =20 impl NovaObject { /// Create a new DRM GEM object. - pub(crate) fn new(dev: &NovaDevice, size: usize) -> Result>> { + pub(crate) fn new( + dev: &NovaDevice, + size: usize, + ) -> Result>> { if size =3D=3D 0 { return Err(EINVAL); } let aligned_size =3D page::page_align(size).ok_or(EINVAL)?; =20 - gem::Object::new(dev, aligned_size) + gem::Object::::new(dev, aligned_size) } =20 /// 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 e73c56659ea75..03e337d95521c 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 =3D TyrData; type File =3D File; - type Object =3D drm::gem::Object; + type Object =3D drm::gem::Object; =20 const INFO: drm::DriverInfo =3D INFO; =20 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::*; =20 /// GEM Object inner driver data @@ -12,7 +13,7 @@ pub(crate) struct TyrObject {} impl gem::DriverObject for TyrObject { type Driver =3D TyrDriver; =20 - fn new(_dev: &TyrDevice, _size: usize) -> impl PinInit { + fn new(_dev: &TyrDevice, _size: usize) -> imp= l PinInit { try_pin_init!(TyrObject {}) } } diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs index 0e81957cf8c28..4c03105e6a817 100644 --- a/rust/kernel/drm/device.rs +++ b/rust/kernel/drm/device.rs @@ -163,13 +163,13 @@ impl UnregisteredDevice { 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_s= g_table, - dumb_create: T::Object::ALLOC_OPS.dumb_create, - dumb_map_offset: T::Object::ALLOC_OPS.dumb_map_offset, + gem_create_object: T::Object::::ALLOC_OPS.gem_create_objec= t, + prime_handle_to_fd: T::Object::::ALLOC_OPS.prime_handle_to= _fd, + prime_fd_to_handle: T::Object::::ALLOC_OPS.prime_fd_to_han= dle, + gem_prime_import: T::Object::::ALLOC_OPS.gem_prime_import, + gem_prime_import_sg_table: T::Object::::ALLOC_OPS.gem_prim= e_import_sg_table, + dumb_create: T::Object::::ALLOC_OPS.dumb_create, + dumb_map_offset: T::Object::::ALLOC_OPS.dumb_map_offset, show_fdinfo: None, fbdev_probe: None, =20 diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs index a16605b407159..94ebaf19ac069 100644 --- a/rust/kernel/drm/driver.rs +++ b/rust/kernel/drm/driver.rs @@ -110,7 +110,7 @@ pub trait Driver { type Data: Sync + Send; =20 /// The type used to manage memory for this driver. - type Object: AllocImpl; + type Object: AllocImpl; =20 /// 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 b4199945db378..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, // }; @@ -33,21 +38,30 @@ /// [`DriverFile`]: drm::file::DriverFile pub type DriverFile =3D drm::File<<::Driver as drm::= Driver>::File>; =20 +/// A type alias for retrieving the current [`AllocImpl`] for a given [`Dr= iverObject`]. +/// +/// [`Driver`]: drm::Driver +pub type DriverAllocImpl =3D + <::Driver as drm::Driver>::Object; + /// GEM object functions, which must be implemented by drivers. pub trait DriverObject: Sync + Send + Sized { /// Parent `Driver` for this object. type Driver: drm::Driver; =20 /// Create a new driver data object for a GEM object of a given size. - fn new(dev: &drm::Device, size: usize) -> impl PinInit; + fn new( + dev: &drm::Device, + size: usize, + ) -> impl PinInit; =20 /// Open a new handle to an existing object, associated with a File. - fn open(_obj: &::Object, _file: &DriverFi= le) -> Result { + fn open(_obj: &DriverAllocImpl, _file: &DriverFile) -> Res= ult { Ok(()) } =20 /// Close a handle to an existing object, associated with a File. - fn close(_obj: &::Object, _file: &DriverF= ile) {} + fn close(_obj: &DriverAllocImpl, _file: &DriverFile) {} } =20 /// Trait that represents a GEM object subtype @@ -73,9 +87,12 @@ extern "C" fn open_callback( // SAFETY: `open_callback` is only ever called with a valid pointer to= a `struct drm_file`. let file =3D unsafe { DriverFile::::from_raw(raw_file) }; =20 - // SAFETY: `open_callback` is specified in the AllocOps structure for = `DriverObject`, - // ensuring that `raw_obj` is contained within a `DriverObject` - let obj =3D unsafe { <::Object as IntoGEMObj= ect>::from_raw(raw_obj) }; + // SAFETY: + // * `open_callback` is specified in the AllocOps structure for `Drive= rObject`, ensuring that + // `raw_obj` is contained within a `DriverAllocImpl` + // * 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 =3D unsafe { IntoGEMObject::from_raw(raw_= obj) }; =20 match T::open(obj, file) { Err(e) =3D> e.to_errno(), @@ -92,12 +109,12 @@ extern "C" fn close_callback( =20 // SAFETY: `close_callback` is specified in the AllocOps structure for= `Object`, ensuring // that `raw_obj` is indeed contained within a `Object`. - let obj =3D unsafe { <::Object as IntoGEMObj= ect>::from_raw(raw_obj) }; + let obj: &DriverAllocImpl =3D unsafe { IntoGEMObject::from_raw(raw_= obj) }; =20 T::close(obj, file); } =20 -impl IntoGEMObject for Object { +impl IntoGEMObject for Object= { fn as_raw(&self) -> *mut bindings::drm_gem_object { self.obj.get() } @@ -105,7 +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` via the saf= ety contract of this // function - unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Objec= t, obj) } + unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Objec= t, obj) } } } =20 @@ -122,7 +139,7 @@ fn size(&self) -> usize { fn create_handle(&self, file: &drm::File) -> Result where Self: AllocImpl, - D: drm::Driver, + D: drm::Driver =3D Self, File =3D F>, F: drm::file::DriverFile, { let mut handle: u32 =3D 0; @@ -137,7 +154,7 @@ fn create_handle(&self, file: &drm::File) -> R= esult fn lookup_handle(file: &drm::File, handle: u32) -> Result> where Self: AllocImpl, - D: drm::Driver, + D: drm::Driver =3D Self, File =3D F>, F: drm::file::DriverFile, { // SAFETY: The arguments are all valid per the type invariants. @@ -177,16 +194,18 @@ impl 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 { +pub struct Object { obj: Opaque, #[pin] data: T, + _ctx: PhantomData, } =20 -impl Object { +impl Object { const OBJECT_FUNCS: bindings::drm_gem_object_funcs =3D bindings::drm_g= em_object_funcs { free: Some(Self::free_callback), open: Some(open_callback::), @@ -206,11 +225,12 @@ impl Object { }; =20 /// Create a new GEM object. - pub fn new(dev: &drm::Device, size: usize) -> Result> { + pub fn new(dev: &drm::Device, size: usize) -> Result> { let obj: Pin> =3D KBox::pin_init( try_pin_init!(Self { obj: Opaque::new(bindings::drm_gem_object::default()), data <- T::new(dev, size), + _ctx: PhantomData, }), GFP_KERNEL, )?; @@ -219,6 +239,8 @@ pub fn new(dev: &drm::Device, size: usize) -= > Result> { unsafe { (*obj.as_raw()).funcs =3D &Self::OBJECT_FUNCS }; =20 // SAFETY: The arguments are all valid per the type invariants. + // INVARIANT: We use `dev` for creating the GEM object, which is k= nown to be in state `Ctx` - + // ensuring that the GEM object's pointer to the DRM device is alw= ays in the same state. to_result(unsafe { bindings::drm_gem_object_init(dev.as_raw(), obj= .obj.get(), size) })?; =20 // SAFETY: We will never move out of `Self` as `ARef` is alw= ays treated as pinned. @@ -232,13 +254,15 @@ pub fn new(dev: &drm::Device, size: usize)= -> Result> { } =20 /// Returns the `Device` that owns this GEM object. - pub fn dev(&self) -> &drm::Device { + pub fn dev(&self) -> &drm::Device { // SAFETY: // - `struct drm_gem_object.dev` is initialized and valid for as l= ong as the GEM // object lives. // - The device we used for creating the gem object is passed as &= drm::Device to // Object::::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 `Ct= x` for the `Device` we + // return. unsafe { drm::Device::from_raw((*self.as_raw()).dev) } } =20 @@ -264,7 +288,7 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem= _object) { } =20 // SAFETY: Instances of `Object` are always reference-counted. -unsafe impl crate::sync::aref::AlwaysRefCounted for Objec= t { +unsafe impl AlwaysRefCounted for Obje= ct { 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()) }; @@ -279,9 +303,9 @@ unsafe fn dec_ref(obj: NonNull) { } } =20 -impl super::private::Sealed for Object {} +impl super::private::Sealed for Objec= t {} =20 -impl Deref for Object { +impl Deref for Object { type Target =3D T; =20 fn deref(&self) -> &Self::Target { @@ -289,7 +313,7 @@ fn deref(&self) -> &Self::Target { } } =20 -impl AllocImpl for Object { +impl AllocImpl for Object { type Driver =3D T::Driver; =20 const ALLOC_OPS: AllocOps =3D AllocOps { --=20 2.52.0