Re: [PATCH 2/2] rust: drm: Add GPUVM abstraction

Charalampos Mitrodimas
2025-03-24T18:29:34Z

Daniel Almeida <daniel.almeida@collabora.com> writes:

> +/// The object returned after a call to [`GpuVm::lock`].
> +///
> +/// This object has access to operations that modify the VM's interval tree.
> +pub struct LockedGpuVm<'a, T: DriverGpuVm> {
> + gpuvm: &'a GpuVm<T>,
> +}
> +
> +impl<T: DriverGpuVm> LockedGpuVm<'_, T> {
> + /// Finds the [`GpuVmBo`] object that connects `obj` to this VM.
> + ///
> + /// If found, increases the reference count of the GpuVmBo object
> + /// accordingly.
> + pub fn find_bo(&mut self, obj: &DriverObject<T>) -> Option<ARef<GpuVmBo<T>>> {
> + // SAFETY: LockedGpuVm implies the right locks are held.
> + let p = unsafe {
> + bindings::drm_gpuvm_bo_find(
> + self.gpuvm.gpuvm() as *mut _,
> + obj.gem_obj() as *const _ as *mut _,
> + )
> + };
> + if p.is_null() {
> + None
> + } else {
> + // SAFETY: All the drm_gpuvm_bo objects in this GpuVm are always allocated by us as GpuVmBo<T>.
> + let p = unsafe { crate::container_of!(p, GpuVmBo<T>, bo) as *mut GpuVmBo<T> };
> + // SAFETY: We checked for NULL above, and the types ensure that
> + // this object was created by vm_bo_alloc_callback<T>.
> + Some(unsafe { ARef::from_raw(NonNull::new_unchecked(p)) })
> + }

Hi Daniel,

This is mostly eye candy—maybe we can simplify it to just:
if p.is_null() {
return None;
}

// SAFETY: All the drm_gpuvm_bo objects in this GpuVm are always allocated by us as GpuVmBo<T>.
let p = unsafe { crate::container_of!(p, GpuVmBo<T>, bo) as *mut GpuVmBo<T> };
// SAFETY: We checked for NULL above, and the types ensure that
// this object was created by vm_bo_alloc_callback<T>.
Some(unsafe { ARef::from_raw(NonNull::new_unchecked(p)) })

Same with `fn obtain_bo`?

--
C. Mitrodimas

> + }
> +
> + /// Obtains the [`GpuVmBo`] object that connects `obj` to this VM.
> + ///
> + /// This connection is unique, so an instane of [`GpuVmBo`] will be
> + /// allocated for `obj` once, and that instance will be returned from that
> + /// point forward.
> + pub fn obtain_bo(&mut self, obj: &DriverObject<T>) -> Result<ARef<GpuVmBo<T>>> {
> + // SAFETY: LockedGpuVm implies the right locks are held.
> + let p = unsafe {
> + bindings::drm_gpuvm_bo_obtain(
> + self.gpuvm.gpuvm() as *mut _,
> + obj.gem_obj() as *const _ as *mut _,
> + )
> + };
> + if p.is_null() {
> + Err(ENOMEM)
> + } else {
> + // SAFETY: Container invariant is guaranteed for GpuVmBo objects for this GpuVm.
> + let p = unsafe { crate::container_of!(p, GpuVmBo<T>, bo) as *mut GpuVmBo<T> };
> + // SAFETY: We checked for NULL above, and the types ensure that
> + // this object was created by vm_bo_alloc_callback<T>.
> + Ok(unsafe { ARef::from_raw(NonNull::new_unchecked(p)) })
> + }
> + }