6.16-stable review patch. If anyone has any objections, please let me know.
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From: Danilo Krummrich dakr@kernel.org
[ Upstream commit 22ab0641b939967f630d108e33a3582841ad6846 ]
drm::Device is allocated through __drm_dev_alloc() (which uses kmalloc()) and the driver private data, <T as drm::Driver>::Data, is initialized in-place.
Due to the order of fields in drm::Device
pub struct Device<T: drm::Driver> { dev: Opaquebindings::drm_device, data: T::Data, }
even with an arbitrary large alignment requirement of T::Data it can't happen that the size of Device is smaller than its alignment requirement.
However, let's not rely on this subtle circumstance and create a proper kmalloc() compatible Layout.
Fixes: 1e4b8896c0f3 ("rust: drm: add device abstraction") Reviewed-by: Alice Ryhl aliceryhl@google.com Link: https://lore.kernel.org/r/20250731154919.4132-3-dakr@kernel.org Signed-off-by: Danilo Krummrich dakr@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- rust/kernel/drm/device.rs | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs index 14c1aa402951..6c1fc33cdc68 100644 --- a/rust/kernel/drm/device.rs +++ b/rust/kernel/drm/device.rs @@ -5,6 +5,7 @@ //! C header: [`include/linux/drm/drm_device.h`](srctree/include/linux/drm/drm_device.h)
use crate::{ + alloc::allocator::Kmalloc, bindings, device, drm, drm::driver::AllocImpl, error::from_err_ptr, @@ -12,7 +13,7 @@ use crate::{ prelude::*, types::{ARef, AlwaysRefCounted, Opaque}, }; -use core::{mem, ops::Deref, ptr, ptr::NonNull}; +use core::{alloc::Layout, mem, ops::Deref, ptr, ptr::NonNull};
#[cfg(CONFIG_DRM_LEGACY)] macro_rules! drm_legacy_fields { @@ -96,6 +97,10 @@ impl<T: drm::Driver> Device<T> {
/// Create a new `drm::Device` for a `drm::Driver`. pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<ARef<Self>> { + // `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence ensure a `kmalloc()` + // compatible `Layout`. + let layout = Kmalloc::aligned_layout(Layout::new::<Self>()); + // SAFETY: // - `VTABLE`, as a `const` is pinned to the read-only section of the compilation, // - `dev` is valid by its type invarants, @@ -103,7 +108,7 @@ impl<T: drm::Driver> Device<T> { bindings::__drm_dev_alloc( dev.as_raw(), &Self::VTABLE, - mem::size_of::<Self>(), + layout.size(), mem::offset_of!(Self, dev), ) }