Re: [PATCH 2/2] drm/gpuvm: rust: add drm_gpuvm_exec support

["Onur Özkan" <work@onurozkan.dev>]

On Tue, 05 May 2026 13:29:37 +0000
Alice Ryhl <aliceryhl@google.com> wrote:

> This adds support for simple usage of drm_gpuvm_exec() for locking all
> of the dma reservations and adding fences to them. For more complex
> usage that does not involve locking all reservations, it is expected
> that the ww-mutex abstractions will be used instead.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/bindings/bindings_helper.h |  2 ++
>  rust/helpers/drm_gpuvm.c        |  6 ++++
>  rust/kernel/dma_buf/mod.rs      | 17 ++++++++++
>  rust/kernel/drm/gpuvm/mod.rs    | 71 +++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 96 insertions(+)
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 1124785e210b..3978682a6f2e 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -151,6 +151,8 @@ const vm_flags_t RUST_CONST_HELPER_VM_MIXEDMAP = VM_MIXEDMAP;
>  const vm_flags_t RUST_CONST_HELPER_VM_HUGEPAGE = VM_HUGEPAGE;
>  const vm_flags_t RUST_CONST_HELPER_VM_NOHUGEPAGE = VM_NOHUGEPAGE;
>  
> +const u32 RUST_CONST_HELPER_DRM_EXEC_INTERRUPTIBLE_WAIT = DRM_EXEC_INTERRUPTIBLE_WAIT;
> +
>  #if IS_ENABLED(CONFIG_GPU_BUDDY)
>  const unsigned long RUST_CONST_HELPER_GPU_BUDDY_RANGE_ALLOCATION = GPU_BUDDY_RANGE_ALLOCATION;
>  const unsigned long RUST_CONST_HELPER_GPU_BUDDY_TOPDOWN_ALLOCATION = GPU_BUDDY_TOPDOWN_ALLOCATION;
> diff --git a/rust/helpers/drm_gpuvm.c b/rust/helpers/drm_gpuvm.c
> index 4130b6325213..30fb1777fbf2 100644
> --- a/rust/helpers/drm_gpuvm.c
> +++ b/rust/helpers/drm_gpuvm.c
> @@ -23,4 +23,10 @@ bool rust_helper_drm_gpuvm_is_extobj(struct drm_gpuvm *gpuvm,
>  	return drm_gpuvm_is_extobj(gpuvm, obj);
>  }
>  
> +__rust_helper
> +void rust_helper_drm_gpuvm_exec_unlock(struct drm_gpuvm_exec *vm_exec)
> +{
> +	drm_gpuvm_exec_unlock(vm_exec);
> +}
> +
>  #endif // CONFIG_RUST_DRM_GPUVM
> diff --git a/rust/kernel/dma_buf/mod.rs b/rust/kernel/dma_buf/mod.rs
> index b66e747c35ad..234936ba8265 100644
> --- a/rust/kernel/dma_buf/mod.rs
> +++ b/rust/kernel/dma_buf/mod.rs
> @@ -5,3 +5,20 @@
>  pub mod dma_fence;
>  
>  pub use self::dma_fence::Fence;
> +
> +/// How the fences from a `dma_resv` obj are used.
> +///
> +/// Please see [the C-side documentation][dma_resv_usage] for more details.
> +///
> +/// [dma_resv_usage]: https://docs.kernel.org/driver-api/dma-buf.html#c.dma_resv_usage
> +#[repr(u32)]
> +pub enum DmaResvUsage {
> +    /// For in kernel memory management only (e.g. copying, clearing memory).
> +    Kernel = bindings::dma_resv_usage_DMA_RESV_USAGE_KERNEL,
> +    /// Implicit write synchronization for userspace submissions.
> +    Write = bindings::dma_resv_usage_DMA_RESV_USAGE_WRITE,
> +    /// Implicit read synchronization for userspace submissions.
> +    Read = bindings::dma_resv_usage_DMA_RESV_USAGE_READ,
> +    /// No implicit sync (e.g. preemption fences, page table updates, TLB flushes).
> +    Bookkeep = bindings::dma_resv_usage_DMA_RESV_USAGE_BOOKKEEP,
> +}
> diff --git a/rust/kernel/drm/gpuvm/mod.rs b/rust/kernel/drm/gpuvm/mod.rs
> index ae58f6f667c1..a52fb25f22ff 100644
> --- a/rust/kernel/drm/gpuvm/mod.rs
> +++ b/rust/kernel/drm/gpuvm/mod.rs
> @@ -16,6 +16,7 @@
>          Flags as AllocFlags, //
>      },
>      bindings,
> +    dma_buf::{DmaResvUsage, Fence},

This can be handled vertically.

>      drm,
>      drm::gem::IntoGEMObject,
>      error::to_result,
> @@ -216,6 +217,30 @@ pub fn obtain(
>          Ok(GpuVmBoAlloc::new(self, obj, data)?.obtain())
>      }
>  
> +    /// Prepare this GPUVM.
> +    ///
> +    /// The parameter indicates how many fences to preallocate space for.
> +    #[inline]
> +    pub fn prepare(&self, num_fences: u32) -> impl PinInit<GpuVmExec<'_, T>, Error> {
> +        try_pin_init!(GpuVmExec {
> +            exec <- Opaque::try_ffi_init(|exec: *mut bindings::drm_gpuvm_exec| {
> +                // SAFETY: exec is valid but unused memory, so we can write.
> +                unsafe {
> +                    ptr::write_bytes(exec, 0u8, 1usize);
> +                    ptr::write(&raw mut (*exec).vm, self.as_raw());
> +                    ptr::write(&raw mut (*exec).flags, bindings::DRM_EXEC_INTERRUPTIBLE_WAIT);
> +                    ptr::write(&raw mut (*exec).num_fences, num_fences);
> +                }
> +
> +                // SAFETY: If successful, this `struct drm_gpuvm_exec` remains valid until this is
> +                // unlocked because it's pinned and unlocks it in drop. The contained pointer to
> +                // `self` remains valid because `GpuVmExec` borrows from `self`.
> +                to_result(unsafe { bindings::drm_gpuvm_exec_lock(exec) })
> +            }),
> +            _gpuvm: PhantomData,
> +        })
> +    }
> +
>      /// Clean up buffer objects that are no longer used.
>      #[inline]
>      pub fn deferred_cleanup(&self) {
> @@ -326,3 +351,49 @@ fn deref(&self) -> &GpuVm<T> {
>          &self.0
>      }
>  }
> +
> +/// The exec token for preparing the objects.
> +///
> +/// # Invariants
> +///
> +/// Owns a GPUVM exec context.
> +#[pin_data(PinnedDrop)]
> +pub struct GpuVmExec<'vm, T: DriverGpuVm> {
> +    #[pin]
> +    exec: Opaque<bindings::drm_gpuvm_exec>,
> +    _gpuvm: PhantomData<&'vm mut GpuVm<T>>,
> +}
> +
> +impl<'vm, T: DriverGpuVm> GpuVmExec<'vm, T> {
> +    /// Add a fence.
> +    ///
> +    /// The caller must ensure that the preallocated space for fences is sufficient.
> +    #[inline]
> +    pub fn resv_add_fence(
> +        &self,
> +        fence: &Fence,
> +        private_usage: DmaResvUsage,
> +        extobj_usage: DmaResvUsage,
> +    ) {
> +        // SAFETY: This method takes a refcount on the fence, so it's only required to be valid for
> +        // the duration of this method. If there is not enough space for the pre-allocated fence,
> +        // then this leads to a BUG_ON() but does not trigger UB.

Did you think about tracking the space of fences? We can store num_fences from
prepare and a counter added_fences then compare them in this function to avoid
this risk.

> +        unsafe {
> +            bindings::drm_gpuvm_resv_add_fence(
> +                (*self.exec.get()).vm,
> +                &raw mut (*self.exec.get()).exec,
> +                fence.as_raw(),
> +                private_usage as u32,
> +                extobj_usage as u32,
> +            )
> +        }
> +    }
> +}
> +
> +#[pinned_drop]
> +impl<'vm, T: DriverGpuVm> PinnedDrop for GpuVmExec<'vm, T> {
> +    fn drop(self: Pin<&mut Self>) {
> +        // SAFETY: We hold the lock, so it's safe to unlock.
> +        unsafe { bindings::drm_gpuvm_exec_unlock(self.exec.get()) };
> +    }
> +}
> 
> -- 
> 2.54.0.545.g6539524ca2-goog
>