From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E75573054EE for ; Fri, 7 Nov 2025 19:32:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762543950; cv=none; b=mq5UmQLCFmzkqBhEahMm0y+YLJIosipu2IQvktso16Mk1Wy0O+hdw0Vjcy+W/wQyLq1jRfi/HsXf3gUF7Z+N4aqiEcPZt1jg8/RLOmTMX1vpkvjz8gCWumPyksymOTIIKnxTd+UAvQm8l3QuRdXNcfav/H99tdgLuL99vSrNIIE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762543950; c=relaxed/simple; bh=hpYfuChdBxZ8aIvPC01mbDDCUm6HB8Cp304N2wi/dtU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OOnuRHP9WAz7LYQE+KwCm6QQDl9EFCYeo8Rp2RkQmFRnoTeXXzhemVrT5T0gFjgiwdoN75KqlpxpPuN95Vq/wj3VyKj59vnOu3yFCYL+AZ4rBUXYgQ/l6nmadsCyAv72mZWTw6q+yuJiZEnAsnuouXiJyOVT0yloWXsATymoX0U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Vi+8WU9+; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Vi+8WU9+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1762543946; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2w3HBCTCnyeGOWO+4tHcNTI3KzfddOfLp9dQjNEQkmE=; b=Vi+8WU9+MMKhlDZpUx0nWwl7oODZcgt9i048CI8grZ542VKNirc3EbaJKqn3qKyEotapkD asGOxTHCs2uHsnhvV4E9nwGnUq4UpW/r3aEvrvp7qJuzzWPJbBn5B0E7t6uQwOXGxqMJbs PrEIs5Wdb/Zcn8lGZUVNycJqESlif3k= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-404-MGuTFIVJOt-aQPn_B6JBGw-1; Fri, 07 Nov 2025 14:32:23 -0500 X-MC-Unique: MGuTFIVJOt-aQPn_B6JBGw-1 X-Mimecast-MFC-AGG-ID: MGuTFIVJOt-aQPn_B6JBGw_1762543940 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7DCAA180028A; Fri, 7 Nov 2025 19:32:20 +0000 (UTC) Received: from chopper.lan (unknown [10.22.81.9]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B420C1945110; Fri, 7 Nov 2025 19:32:15 +0000 (UTC) From: Lyude Paul To: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, dri-devel@lists.freedesktop.org Cc: Danilo Krummrich , Alice Ryhl , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Trevor Gross , nouveau@lists.freedesktop.org (open list:DRM DRIVER FOR NVIDIA GPUS [RUST]) Subject: [PATCH 1/2] rust: drm: Introduce DeviceCtx Date: Fri, 7 Nov 2025 14:23:53 -0500 Message-ID: <20251107193204.398657-2-lyude@redhat.com> In-Reply-To: <20251107193204.398657-1-lyude@redhat.com> References: <20251107193204.398657-1-lyude@redhat.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 One of the tricky things about DRM bindings in Rust is the fact that initialization of a DRM device is a multi-step process. 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::DeviceCtx` and introduce `kernel::drm::DeviceCtx`. 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 (`AnyCtx`). It's important to note we intentionally do not provide a `DeviceCtx` 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 --- drivers/gpu/drm/nova/driver.rs | 8 +- drivers/gpu/drm/tyr/driver.rs | 13 ++- rust/kernel/drm/device.rs | 167 +++++++++++++++++++++++++++------ rust/kernel/drm/driver.rs | 35 +++++-- rust/kernel/drm/mod.rs | 4 + 5 files changed, 181 insertions(+), 46 deletions(-) diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs index 91b7380f83ab4..c78d69d5f045a 100644 --- a/drivers/gpu/drm/nova/driver.rs +++ b/drivers/gpu/drm/nova/driver.rs @@ -13,7 +13,7 @@ pub(crate) struct NovaDriver { } /// Convienence type alias for the DRM device type for this driver -pub(crate) type NovaDevice = drm::Device; +pub(crate) type NovaDevice = drm::Device; #[pin_data] pub(crate) struct NovaData { @@ -48,10 +48,10 @@ impl auxiliary::Driver for NovaDriver { fn probe(adev: &auxiliary::Device, _info: &Self::IdInfo) -> Result>> { let data = try_pin_init!(NovaData { adev: adev.into() }); - let drm = drm::Device::::new(adev.as_ref(), data)?; - drm::Registration::new_foreign_owned(&drm, adev.as_ref(), 0)?; + let drm = drm::UnregisteredDevice::::new(adev.as_ref(), data)?; + let drm = drm::Registration::new_foreign_owned(drm, adev.as_ref(), 0)?; - Ok(KBox::new(Self { drm }, GFP_KERNEL)?.into()) + Ok(KBox::new(Self { drm: drm.into() }, GFP_KERNEL)?.into()) } } diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs index d5625dd1e41c8..e3ea5ad85f49b 100644 --- a/drivers/gpu/drm/tyr/driver.rs +++ b/drivers/gpu/drm/tyr/driver.rs @@ -30,7 +30,7 @@ pub(crate) type IoMem = kernel::io::mem::IoMem; /// Convenience type alias for the DRM device type for this driver. -pub(crate) type TyrDevice = drm::Device; +pub(crate) type TyrDevice = drm::Device; #[pin_data(PinnedDrop)] pub(crate) struct TyrDriver { @@ -140,10 +140,15 @@ fn probe( gpu_info, }); - let tdev: ARef = drm::Device::new(pdev.as_ref(), data)?; - drm::driver::Registration::new_foreign_owned(&tdev, pdev.as_ref(), 0)?; + let tdev = drm::UnregisteredDevice::::new(pdev.as_ref(), data)?; + let tdev = drm::driver::Registration::new_foreign_owned(tdev, pdev.as_ref(), 0)?; - let driver = KBox::pin_init(try_pin_init!(TyrDriver { device: tdev }), GFP_KERNEL)?; + let driver = KBox::pin_init( + try_pin_init!(TyrDriver { + device: tdev.into() + }), + GFP_KERNEL, + )?; // 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 3ce8f62a00569..00072984930a3 100644 --- a/rust/kernel/drm/device.rs +++ b/rust/kernel/drm/device.rs @@ -7,14 +7,14 @@ use crate::{ alloc::allocator::Kmalloc, bindings, device, drm, - drm::driver::AllocImpl, + drm::{driver::AllocImpl, private::Sealed}, error::from_err_ptr, error::Result, prelude::*, sync::aref::{ARef, AlwaysRefCounted}, types::Opaque, }; -use core::{alloc::Layout, mem, ops::Deref, ptr, ptr::NonNull}; +use core::{alloc::Layout, marker::PhantomData, mem, ops::Deref, ptr, ptr::NonNull}; #[cfg(CONFIG_DRM_LEGACY)] macro_rules! drm_legacy_fields { @@ -47,26 +47,83 @@ macro_rules! drm_legacy_fields { } } -/// A typed DRM device with a specific `drm::Driver` implementation. +macro_rules! drm_dev_ctx { + ( + $( #[$attrs:meta] )* + $name:ident + ) => { + $( #[$attrs] )* + pub struct $name; + + impl DeviceCtx for $name {} + impl Sealed for $name {} + + // SAFETY: All registration states are free of side-effects (e.g. no Drop) and are ZSTs, + // thus they are always thread-safe. + unsafe impl Send for $name {} + // SAFETY: All registration states are free of side-effects (e.g. no Drop) and are ZSTs, + // thus they are always thread-safe. + unsafe impl Sync for $name {} + }; +} + +/// A trait implemented by all possible contexts a [`Device`] can be used in. +pub trait DeviceCtx: Sealed + Send + Sync {} + +drm_dev_ctx! { + /// The [`DeviceCtx`] of a [`Device`] that was registered with userspace at some point. + /// + /// This represents a [`Device`] which is guaranteed to have been registered with userspace at + /// some point in time. Once a DRM device has registered itself with userspace, it is safe to + /// assume that the initialization process for the DRM device has completed. + /// + /// 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. However, any + /// userspace-dependent operations performed with an unregistered device in this [`DeviceCtx`] + /// are guaranteed to be no-ops. + /// + /// # Invariants + /// + /// A [`Device`] in this [`DeviceCtx`] is guaranteed to have called `drm_dev_register` once. + Registered +} + +drm_dev_ctx! { + /// The [`DeviceCtx`] of a [`Device`] that has no initialization or registration guarantees. + /// + /// A [`Device`] in this context could be in any state, pre or post registration, and is only + /// guaranteed to be minimally initialized. As such the operations which may be performed on + /// such [`Device`]s are more limited then in the [`Registered`] context. + AnyCtx +} + +/// A [`Device`] which is known at compile-time to be unregistered with userspace. /// -/// The device is always reference-counted. +/// This type allows performing operations which are only safe to do before userspace registration, +/// and can be used to create a [`Registration`](drm::driver::Registration) once the driver is ready +/// to register the device with userspace. /// /// # Invariants /// -/// `self.dev` is a valid instance of a `struct device`. -#[repr(C)] -pub struct Device { - dev: Opaque, - data: T::Data, +/// 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>); + +impl Deref for UnregisteredDevice { + type Target = Device; + + fn deref(&self) -> &Self::Target { + &self.0 + } } -impl Device { +impl UnregisteredDevice { const VTABLE: bindings::drm_driver = 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, @@ -94,8 +151,10 @@ impl Device { const GEM_FOPS: bindings::file_operations = drm::gem::create_fops(); - /// 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::Registration). + pub fn new(dev: &device::Device, data: impl PinInit) -> Result { // `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence ensure a `kmalloc()` // compatible `Layout`. let layout = Kmalloc::aligned_layout(Layout::new::()); @@ -103,12 +162,12 @@ pub fn new(dev: &device::Device, data: impl PinInit) -> Result = unsafe { bindings::__drm_dev_alloc( dev.as_raw(), &Self::VTABLE, layout.size(), - mem::offset_of!(Self, dev), + mem::offset_of!(Device, dev), ) } .cast(); @@ -123,7 +182,7 @@ pub fn new(dev: &device::Device, data: impl PinInit) -> Result) -> Result { + dev: Opaque, + data: T::Data, + _ctx: PhantomData, +} +impl Device { pub(crate) fn as_raw(&self) -> *mut bindings::drm_device { self.dev.get() } @@ -160,13 +250,13 @@ 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-zero 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 `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 promise that any type invariants of `Ctx` will be upheld. #[doc(hidden)] pub unsafe fn from_raw<'a>(ptr: *const bindings::drm_device) -> &'a Self { // SAFETY: By the safety requirements of this function `ptr` is a valid pointer to a @@ -188,7 +278,26 @@ extern "C" fn release(ptr: *mut bindings::drm_device) { } } -impl Deref for Device { +impl Device { + /// Assume the device has been fully initialized and registered with userspace. + /// + /// # Safety + /// + /// The caller promises that `drm_dev_register` has been called on this device. + pub(crate) unsafe fn assume_registered(&self) -> &Device { + // SAFETY: The data layout is identical via our type invariants. + unsafe { mem::transmute(self) } + } +} + +impl AsRef> for Device { + fn as_ref(&self) -> &Device { + // SAFETY: The data layout is identical via our type invariants. + unsafe { mem::transmute(self) } + } +} + +impl Deref for Device { type Target = T::Data; fn deref(&self) -> &Self::Target { @@ -198,7 +307,7 @@ fn deref(&self) -> &Self::Target { // 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 { 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()) }; @@ -213,7 +322,7 @@ unsafe fn dec_ref(obj: NonNull) { } } -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. @@ -222,8 +331,8 @@ fn as_ref(&self) -> &device::Device { } // SAFETY: A `drm::Device` can be released from any thread. -unsafe impl Send for Device {} +unsafe impl Send for Device {} // SAFETY: A `drm::Device` can be shared among threads because all immutable 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 f30ee4c6245cd..fde0447566bef 100644 --- a/rust/kernel/drm/driver.rs +++ b/rust/kernel/drm/driver.rs @@ -10,6 +10,7 @@ prelude::*, sync::aref::ARef, }; +use core::{mem, ptr::NonNull}; use macros::vtable; /// Driver use the GEM memory manager. This should be set for all modern drivers. @@ -122,30 +123,46 @@ pub trait Driver { impl Registration { /// Creates a new [`Registration`] and registers it. - 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::Device`. to_result(unsafe { bindings::drm_dev_register(drm.as_raw(), flags) })?; - Ok(Self(drm.into())) + // SAFETY: We just called `drm_dev_register` above + let new = NonNull::from(unsafe { drm.assume_registered() }); + + // Leak the ARef from UnregisteredDevice in preparation for transferring its ownership. + mem::forget(drm); + + // SAFETY: `drm`'s `Drop` constructor was never called, ensuring that there remains at least + // one reference to the device - which we take ownership over here. + let new = unsafe { ARef::from_raw(new) }; + + Ok(Self(new)) } - /// Same as [`Registration::new`}, but transfers ownership of the [`Registration`] to + /// Same as [`Registration::new`], but transfers ownership of the [`Registration`] to /// [`devres::register`]. - 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() != dev.as_raw() { + let this_dev: &device::Device = drm.as_ref(); + if this_dev.as_raw() != dev.as_raw() { return Err(EINVAL); } let reg = Registration::::new(drm, flags)?; + let drm = NonNull::from(reg.device()); + + devres::register(dev, reg, GFP_KERNEL)?; - devres::register(dev, reg, GFP_KERNEL) + // SAFETY: Since `reg` was passed to devres::register(), the device now owns the lifetime + // of the DRM registration - ensuring that this references lives for at least as long as 'a. + Ok(unsafe { drm.as_ref() }) } /// 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..90018edef3236 100644 --- a/rust/kernel/drm/mod.rs +++ b/rust/kernel/drm/mod.rs @@ -8,7 +8,11 @@ pub mod gem; pub mod ioctl; +pub use self::device::AnyCtx; pub use self::device::Device; +pub use self::device::DeviceCtx; +pub use self::device::Registered; +pub use self::device::UnregisteredDevice; pub use self::driver::Driver; pub use self::driver::DriverInfo; pub use self::driver::Registration; -- 2.51.1