[PATCH RFC 04/18] rust: drm: gem: Add GEM object abstraction

Asahi Lina
2023-03-07T14:32:10Z

The DRM GEM subsystem is the DRM memory management subsystem used by
most modern drivers. Add a Rust abstraction to allow Rust DRM driver
implementations to use it.

Signed-off-by: Asahi Lina <lina@asahilina.net>
---
rust/bindings/bindings_helper.h | 1 +
rust/helpers.c | 23 +++
rust/kernel/drm/drv.rs | 4 +-
rust/kernel/drm/gem/mod.rs | 374 ++++++++++++++++++++++++++++++++++++++++
rust/kernel/drm/mod.rs | 1 +
5 files changed, 401 insertions(+), 2 deletions(-)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 7d7828faf89c..7183dfe6473f 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -9,6 +9,7 @@
#include <drm/drm_device.h>
#include <drm/drm_drv.h>
#include <drm/drm_file.h>
+#include <drm/drm_gem.h>
#include <drm/drm_ioctl.h>
#include <linux/delay.h>
#include <linux/device.h>
diff --git a/rust/helpers.c b/rust/helpers.c
index 73b2ce607f27..78ec4162b03b 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -18,6 +18,7 @@
* accidentally exposed.
*/

+#include <drm/drm_gem.h>
#include <linux/bug.h>
#include <linux/build_bug.h>
#include <linux/device.h>
@@ -374,6 +375,28 @@ void rust_helper_init_completion(struct completion *c)
}
EXPORT_SYMBOL_GPL(rust_helper_init_completion);

+#ifdef CONFIG_DRM
+
+void rust_helper_drm_gem_object_get(struct drm_gem_object *obj)
+{
+ drm_gem_object_get(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_object_get);
+
+void rust_helper_drm_gem_object_put(struct drm_gem_object *obj)
+{
+ drm_gem_object_put(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_object_put);
+
+__u64 rust_helper_drm_vma_node_offset_addr(struct drm_vma_offset_node *node)
+{
+ return drm_vma_node_offset_addr(node);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_vma_node_offset_addr);
+
+#endif
+
/*
* We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
* as the Rust `usize` type, so we can use it in contexts where Rust
diff --git a/rust/kernel/drm/drv.rs b/rust/kernel/drm/drv.rs
index 1dcb651e1417..c138352cb489 100644
--- a/rust/kernel/drm/drv.rs
+++ b/rust/kernel/drm/drv.rs
@@ -126,7 +126,7 @@ pub struct AllocOps {
}

/// Trait for memory manager implementations. Implemented internally.
-pub trait AllocImpl: Sealed {
+pub trait AllocImpl: Sealed + drm::gem::IntoGEMObject {
/// The C callback operations for this memory manager.
const ALLOC_OPS: AllocOps;
}
@@ -263,7 +263,7 @@ impl<T: Driver> Registration<T> {
drm,
registered: false,
vtable,
- fops: Default::default(), // TODO: GEM abstraction
+ fops: drm::gem::create_fops(),
_pin: PhantomPinned,
_p: PhantomData,
})
diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
new file mode 100644
index 000000000000..8a7d99613718
--- /dev/null
+++ b/rust/kernel/drm/gem/mod.rs
@@ -0,0 +1,374 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+//! DRM GEM API
+//!
+//! C header: [`include/linux/drm/drm_gem.h`](../../../../include/linux/drm/drm_gem.h)
+
+use alloc::boxed::Box;
+
+use crate::{
+ bindings,
+ drm::{device, drv, file},
+ error::{to_result, Result},
+ prelude::*,
+};
+use core::{mem, mem::ManuallyDrop, ops::Deref, ops::DerefMut};
+
+/// GEM object functions, which must be implemented by drivers.
+pub trait BaseDriverObject<T: BaseObject>: Sync + Send + Sized {
+ /// Create a new driver data object for a GEM object of a given size.
+ fn new(dev: &device::Device<T::Driver>, size: usize) -> Result<Self>;
+
+ /// Open a new handle to an existing object, associated with a File.
+ fn open(
+ _obj: &<<T as IntoGEMObject>::Driver as drv::Driver>::Object,
+ _file: &file::File<<<T as IntoGEMObject>::Driver as drv::Driver>::File>,
+ ) -> Result {
+ Ok(())
+ }
+
+ /// Close a handle to an existing object, associated with a File.
+ fn close(
+ _obj: &<<T as IntoGEMObject>::Driver as drv::Driver>::Object,
+ _file: &file::File<<<T as IntoGEMObject>::Driver as drv::Driver>::File>,
+ ) {
+ }
+}
+
+/// Trait that represents a GEM object subtype
+pub trait IntoGEMObject: Sized + crate::private::Sealed {
+ /// Owning driver for this type
+ type Driver: drv::Driver;
+
+ /// Returns a pointer to the raw `drm_gem_object` structure, which must be valid as long as
+ /// this owning object is valid.
+ fn gem_obj(&self) -> *mut bindings::drm_gem_object;
+
+ /// Returns a reference to the raw `drm_gem_object` structure, which must be valid as long as
+ /// this owning object is valid.
+ fn gem_ref(&self) -> &bindings::drm_gem_object {
+ // SAFETY: gem_obj() must be valid per the above requirement.
+ unsafe { &*self.gem_obj() }
+ }
+
+ /// Converts a pointer to a `drm_gem_object` into a pointer to this type.
+ fn from_gem_obj(obj: *mut bindings::drm_gem_object) -> *mut Self;
+}
+
+/// Trait which must be implemented by drivers using base GEM objects.
+pub trait DriverObject: BaseDriverObject<Object<Self>> {
+ /// Parent `Driver` for this object.
+ type Driver: drv::Driver;
+}
+
+unsafe extern "C" fn free_callback<T: DriverObject>(obj: *mut bindings::drm_gem_object) {
+ // SAFETY: All of our objects are Object<T>.
+ let this = crate::container_of!(obj, Object<T>, obj) as *mut Object<T>;
+
+ // SAFETY: The pointer we got has to be valid
+ unsafe { bindings::drm_gem_object_release(obj) };
+
+ // SAFETY: All of our objects are allocated via Box<>, and we're in the
+ // free callback which guarantees this object has zero remaining references,
+ // so we can drop it
+ unsafe { Box::from_raw(this) };
+}
+
+unsafe extern "C" fn open_callback<T: BaseDriverObject, U: BaseObject>(
+ raw_obj: *mut bindings::drm_gem_object,
+ raw_file: *mut bindings::drm_file,
+) -> core::ffi::c_int {
+ // SAFETY: The pointer we got has to be valid.
+ let file = unsafe {
+ file::File::<<<U as IntoGEMObject>::Driver as drv::Driver>::File>::from_raw(raw_file)
+ };
+ let obj =
+ <<<U as IntoGEMObject>::Driver as drv::Driver>::Object as IntoGEMObject>::from_gem_obj(
+ raw_obj,
+ );
+
+ // SAFETY: from_gem_obj() returns a valid pointer as long as the type is
+ // correct and the raw_obj we got is valid.
+ match T::open(unsafe { &*obj }, &file) {
+ Err(e) => e.to_kernel_errno(),
+ Ok(()) => 0,
+ }
+}
+
+unsafe extern "C" fn close_callback<T: BaseDriverObject, U: BaseObject>(
+ raw_obj: *mut bindings::drm_gem_object,
+ raw_file: *mut bindings::drm_file,
+) {
+ // SAFETY: The pointer we got has to be valid.
+ let file = unsafe {
+ file::File::<<<U as IntoGEMObject>::Driver as drv::Driver>::File>::from_raw(raw_file)
+ };
+ let obj =
+ <<<U as IntoGEMObject>::Driver as drv::Driver>::Object as IntoGEMObject>::from_gem_obj(
+ raw_obj,
+ );
+
+ // SAFETY: from_gem_obj() returns a valid pointer as long as the type is
+ // correct and the raw_obj we got is valid.
+ T::close(unsafe { &*obj }, &file);
+}
+
+impl<T: DriverObject> IntoGEMObject for Object<T> {
+ type Driver = T::Driver;
+
+ fn gem_obj(&self) -> *mut bindings::drm_gem_object {
+ &self.obj as *const _ as *mut _
+ }
+
+ fn from_gem_obj(obj: *mut bindings::drm_gem_object) -> *mut Object<T> {
+ crate::container_of!(obj, Object<T>, obj) as *mut Object<T>
+ }
+}
+
+/// Base operations shared by all GEM object classes
+pub trait BaseObject: IntoGEMObject {
+ /// Returns the size of the object in bytes.
+ fn size(&self) -> usize {
+ self.gem_ref().size
+ }
+
+ /// Creates a new reference to the object.
+ fn reference(&self) -> ObjectRef<Self> {
+ // SAFETY: Having a reference to an Object implies holding a GEM reference
+ unsafe {
+ bindings::drm_gem_object_get(self.gem_obj());
+ }
+ ObjectRef {
+ ptr: self as *const _,
+ }
+ }
+
+ /// Creates a new handle for the object associated with a given `File`
+ /// (or returns an existing one).
+ fn create_handle(
+ &self,
+ file: &file::File<<<Self as IntoGEMObject>::Driver as drv::Driver>::File>,
+ ) -> Result<u32> {
+ let mut handle: u32 = 0;
+ // SAFETY: The arguments are all valid per the type invariants.
+ to_result(unsafe {
+ bindings::drm_gem_handle_create(file.raw() as *mut _, self.gem_obj(), &mut handle)
+ })?;
+ Ok(handle)
+ }
+
+ /// Looks up an object by its handle for a given `File`.
+ fn lookup_handle(
+ file: &file::File<<<Self as IntoGEMObject>::Driver as drv::Driver>::File>,
+ handle: u32,
+ ) -> Result<ObjectRef<Self>> {
+ // SAFETY: The arguments are all valid per the type invariants.
+ let ptr = unsafe { bindings::drm_gem_object_lookup(file.raw() as *mut _, handle) };
+
+ if ptr.is_null() {
+ Err(ENOENT)
+ } else {
+ Ok(ObjectRef {
+ ptr: ptr as *const _,
+ })
+ }
+ }
+
+ /// Creates an mmap offset to map the object from userspace.
+ fn create_mmap_offset(&self) -> Result<u64> {
+ // SAFETY: The arguments are valid per the type invariant.
+ to_result(unsafe {
+ // TODO: is this threadsafe?
+ bindings::drm_gem_create_mmap_offset(self.gem_obj())
+ })?;
+ Ok(unsafe {
+ bindings::drm_vma_node_offset_addr(&self.gem_ref().vma_node as *const _ as *mut _)
+ })
+ }
+}
+
+impl<T: IntoGEMObject> BaseObject for T {}
+
+/// A base GEM object.
+#[repr(C)]
+pub struct Object<T: DriverObject> {
+ obj: bindings::drm_gem_object,
+ // The DRM core ensures the Device exists as long as its objects exist, so we don't need to
+ // manage the reference count here.
+ dev: ManuallyDrop<device::Device<T::Driver>>,
+ inner: T,
+}
+
+impl<T: DriverObject> Object<T> {
+ /// The size of this object's structure.
+ pub const SIZE: usize = mem::size_of::<Self>();
+
+ const OBJECT_FUNCS: bindings::drm_gem_object_funcs = bindings::drm_gem_object_funcs {
+ free: Some(free_callback::<T>),
+ open: Some(open_callback::<T, Object<T>>),
+ close: Some(close_callback::<T, Object<T>>),
+ print_info: None,
+ export: None,
+ pin: None,
+ unpin: None,
+ get_sg_table: None,
+ vmap: None,
+ vunmap: None,
+ mmap: None,
+ vm_ops: core::ptr::null_mut(),
+ };
+
+ /// Create a new GEM object.
+ pub fn new(dev: &device::Device<T::Driver>, size: usize) -> Result<UniqueObjectRef<Self>> {
+ let mut obj: Box<Self> = Box::try_new(Self {
+ // SAFETY: This struct is expected to be zero-initialized
+ obj: unsafe { mem::zeroed() },
+ // SAFETY: The drm subsystem guarantees that the drm_device will live as long as
+ // the GEM object lives, so we can conjure a reference out of thin air.
+ dev: ManuallyDrop::new(unsafe { device::Device::from_raw(dev.ptr) }),
+ inner: T::new(dev, size)?,
+ })?;
+
+ obj.obj.funcs = &Self::OBJECT_FUNCS;
+ to_result(unsafe {
+ bindings::drm_gem_object_init(dev.raw() as *mut _, &mut obj.obj, size)
+ })?;
+
+ let obj_ref = UniqueObjectRef {
+ ptr: Box::leak(obj),
+ };
+
+ Ok(obj_ref)
+ }
+
+ /// Returns the `Device` that owns this GEM object.
+ pub fn dev(&self) -> &device::Device<T::Driver> {
+ &self.dev
+ }
+}
+
+impl<T: DriverObject> crate::private::Sealed for Object<T> {}
+
+impl<T: DriverObject> Deref for Object<T> {
+ type Target = T;
+
+ fn deref(&self) -> &Self::Target {
+ &self.inner
+ }
+}
+
+impl<T: DriverObject> DerefMut for Object<T> {
+ fn deref_mut(&mut self) -> &mut Self::Target {
+ &mut self.inner
+ }
+}
+
+impl<T: DriverObject> drv::AllocImpl for Object<T> {
+ const ALLOC_OPS: drv::AllocOps = drv::AllocOps {
+ gem_create_object: None,
+ prime_handle_to_fd: Some(bindings::drm_gem_prime_handle_to_fd),
+ prime_fd_to_handle: Some(bindings::drm_gem_prime_fd_to_handle),
+ gem_prime_import: None,
+ gem_prime_import_sg_table: None,
+ gem_prime_mmap: Some(bindings::drm_gem_prime_mmap),
+ dumb_create: None,
+ dumb_map_offset: None,
+ dumb_destroy: None,
+ };
+}
+
+/// A reference-counted shared reference to a base GEM object.
+pub struct ObjectRef<T: IntoGEMObject> {
+ // Invariant: the pointer is valid and initialized, and this ObjectRef owns a reference to it.
+ ptr: *const T,
+}
+
+/// SAFETY: GEM object references are safe to share between threads.
+unsafe impl<T: IntoGEMObject> Send for ObjectRef<T> {}
+unsafe impl<T: IntoGEMObject> Sync for ObjectRef<T> {}
+
+impl<T: IntoGEMObject> Clone for ObjectRef<T> {
+ fn clone(&self) -> Self {
+ self.reference()
+ }
+}
+
+impl<T: IntoGEMObject> Drop for ObjectRef<T> {
+ fn drop(&mut self) {
+ // SAFETY: Having an ObjectRef implies holding a GEM reference.
+ // The free callback will take care of deallocation.
+ unsafe {
+ bindings::drm_gem_object_put((*self.ptr).gem_obj());
+ }
+ }
+}
+
+impl<T: IntoGEMObject> Deref for ObjectRef<T> {
+ type Target = T;
+
+ fn deref(&self) -> &Self::Target {
+ // SAFETY: The pointer is valid per the invariant
+ unsafe { &*self.ptr }
+ }
+}
+
+/// A unique reference to a base GEM object.
+pub struct UniqueObjectRef<T: IntoGEMObject> {
+ // Invariant: the pointer is valid and initialized, and this ObjectRef owns the only reference
+ // to it.
+ ptr: *mut T,
+}
+
+impl<T: IntoGEMObject> UniqueObjectRef<T> {
+ /// Downgrade this reference to a shared reference.
+ pub fn into_ref(self) -> ObjectRef<T> {
+ let ptr = self.ptr as *const _;
+ core::mem::forget(self);
+
+ ObjectRef { ptr }
+ }
+}
+
+impl<T: IntoGEMObject> Drop for UniqueObjectRef<T> {
+ fn drop(&mut self) {
+ // SAFETY: Having a UniqueObjectRef implies holding a GEM
+ // reference. The free callback will take care of deallocation.
+ unsafe {
+ bindings::drm_gem_object_put((*self.ptr).gem_obj());
+ }
+ }
+}
+
+impl<T: IntoGEMObject> Deref for UniqueObjectRef<T> {
+ type Target = T;
+
+ fn deref(&self) -> &Self::Target {
+ // SAFETY: The pointer is valid per the invariant
+ unsafe { &*self.ptr }
+ }
+}
+
+impl<T: IntoGEMObject> DerefMut for UniqueObjectRef<T> {
+ fn deref_mut(&mut self) -> &mut Self::Target {
+ // SAFETY: The pointer is valid per the invariant
+ unsafe { &mut *self.ptr }
+ }
+}
+
+pub(super) fn create_fops() -> bindings::file_operations {
+ bindings::file_operations {
+ owner: core::ptr::null_mut(),
+ open: Some(bindings::drm_open),
+ release: Some(bindings::drm_release),
+ unlocked_ioctl: Some(bindings::drm_ioctl),
+ #[cfg(CONFIG_COMPAT)]
+ compat_ioctl: Some(bindings::drm_compat_ioctl),
+ #[cfg(not(CONFIG_COMPAT))]
+ compat_ioctl: None,
+ poll: Some(bindings::drm_poll),
+ read: Some(bindings::drm_read),
+ llseek: Some(bindings::noop_llseek),
+ mmap: Some(bindings::drm_gem_mmap),
+ ..Default::default()
+ }
+}
diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
index a767942d0b52..c44760a1332f 100644
--- a/rust/kernel/drm/mod.rs
+++ b/rust/kernel/drm/mod.rs
@@ -5,4 +5,5 @@
pub mod device;
pub mod drv;
pub mod file;
+pub mod gem;
pub mod ioctl;

--
2.35.1