Commit c0a3065d authored by Alexandre Courbot's avatar Alexandre Courbot Committed by Danilo Krummrich
Browse files

rust: dma: expose the count and size of CoherentAllocation 



These properties are very useful to have (and to be used by nova-core)
and should be accessible, hence add them.

Additionally, add type invariants for the size of an allocation.

Signed-off-by: default avatarAlexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250619-nova-frts-v6-2-ecf41ef99252@nvidia.com


[ Slightly extend the commit message. - Danilo ]
Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
parent 14371e58

rust/kernel/dma.rs

+26 −6
Original line number Diff line number Diff line
@@ -114,9 +114,11 @@ pub mod attrs { 
///

/// # Invariants

///

/// For the lifetime of an instance of [`CoherentAllocation`], the `cpu_addr` is a valid pointer

/// to an allocated region of coherent memory and `dma_handle` is the DMA address base of

/// the region.

/// - For the lifetime of an instance of [`CoherentAllocation`], the `cpu_addr` is a valid pointer

///   to an allocated region of coherent memory and `dma_handle` is the DMA address base of the

///   region.

/// - The size in bytes of the allocation is equal to `size_of::<T> * count`.

/// - `size_of::<T> * count` fits into a `usize`.

// TODO

//

// DMA allocations potentially carry device resources (e.g.IOMMU mappings), hence for soundness
@@ -179,9 +181,12 @@ pub fn alloc_attrs( 
        if ret.is_null() {

            return Err(ENOMEM);

        }

        // INVARIANT: We just successfully allocated a coherent region which is accessible for

        // INVARIANT:

        // - We just successfully allocated a coherent region which is accessible for

        //   `count` elements, hence the cpu address is valid. We also hold a refcounted reference

        //   to the device.

        // - The allocated `size` is equal to `size_of::<T> * count`.

        // - The allocated `size` fits into a `usize`.

        Ok(Self {

            dev: dev.into(),

            dma_handle,
@@ -201,6 +206,21 @@ pub fn alloc_coherent( 
        CoherentAllocation::alloc_attrs(dev, count, gfp_flags, Attrs(0))

    }



    /// Returns the number of elements `T` in this allocation.

    ///

    /// Note that this is not the size of the allocation in bytes, which is provided by

    /// [`Self::size`].

    pub fn count(&self) -> usize {

        self.count

    }



    /// Returns the size in bytes of this allocation.

    pub fn size(&self) -> usize {

        // INVARIANT: The type invariant of `Self` guarantees that `size_of::<T> * count` fits into

        // a `usize`.

        self.count * core::mem::size_of::<T>()

    }



    /// Returns the base address to the allocated region in the CPU's virtual address space.

    pub fn start_ptr(&self) -> *const T {

        self.cpu_addr