On Tue, 1 Oct 2024 16:59:44 +0200
Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
> Implement `Allocator` for `KVmalloc`, an `Allocator` that tries to
> allocate memory wth `kmalloc` first and, on failure, falls back to
> `vmalloc`.
>
> All memory allocations made with `KVmalloc` end up in
> `kvrealloc_noprof()`; all frees in `kvfree()`.
>
> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
> ---
> rust/helpers/slab.c | 6 +++++
> rust/kernel/alloc/allocator.rs | 36 +++++++++++++++++++++++++++++
> rust/kernel/alloc/allocator_test.rs | 1 +
> 3 files changed, 43 insertions(+)
>
> diff --git a/rust/helpers/slab.c b/rust/helpers/slab.c
> index f043e087f9d6..a842bfbddcba 100644
> --- a/rust/helpers/slab.c
> +++ b/rust/helpers/slab.c
> @@ -7,3 +7,9 @@ rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
> {
> return krealloc(objp, new_size, flags);
> }
> +
> +void * __must_check __realloc_size(2)
> +rust_helper_kvrealloc(const void *p, size_t size, gfp_t flags)
> +{
> + return kvrealloc(p, size, flags);
> +}
> diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
> index f341e9ed5b7c..d0a8819c6741 100644
> --- a/rust/kernel/alloc/allocator.rs
> +++ b/rust/kernel/alloc/allocator.rs
> @@ -34,6 +34,15 @@
> /// For more details see [self].
> pub struct Vmalloc;
>
> +/// The kvmalloc kernel allocator.
> +///
> +/// `KVmalloc` attempts to allocate memory with `Kmalloc` first, but falls back to `Vmalloc` upon
> +/// failure. This allocator is typically used when the size for the requested allocation is not
> +/// known and may exceed the capabilities of `Kmalloc`.
> +///
> +/// For more details see [self].
> +pub struct KVmalloc;
> +
> /// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
> fn aligned_size(new_layout: Layout) -> usize {
> // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
> @@ -76,6 +85,9 @@ impl ReallocFunc {
> // INVARIANT: `vrealloc` satisfies the type invariants.
> const VREALLOC: Self = Self(bindings::vrealloc);
>
> + // INVARIANT: `kvrealloc` satisfies the type invariants.
> + const KVREALLOC: Self = Self(bindings::kvrealloc);
> +
> /// # Safety
> ///
> /// This method has the same safety requirements as [`Allocator::realloc`].
> @@ -203,6 +215,30 @@ unsafe fn realloc(
> }
> }
>
> +// SAFETY: `realloc` delegates to `ReallocFunc::call`, which guarantees that
> +// - memory remains valid until it is explicitly freed,
> +// - passing a pointer to a valid memory allocation is OK,
> +// - `realloc` satisfies the guarantees, since `ReallocFunc::call` has the same.
> +unsafe impl Allocator for KVmalloc {
> + #[inline]
> + unsafe fn realloc(
> + ptr: Option<NonNull<u8>>,
> + layout: Layout,
> + old_layout: Layout,
> + flags: Flags,
> + ) -> Result<NonNull<[u8]>, AllocError> {
> + // TODO: Support alignments larger than PAGE_SIZE.
> + if layout.align() > bindings::PAGE_SIZE {
> + pr_warn!("KVmalloc does not support alignments larger than PAGE_SIZE yet.\n");
> + return Err(AllocError);
> + }
> +
> + // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
> + // allocated with this `Allocator`.
> + unsafe { ReallocFunc::KVREALLOC.call(ptr, layout, old_layout, flags) }
> + }
> +}
> +
> #[global_allocator]
> static ALLOCATOR: Kmalloc = Kmalloc;
>
> diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
> index e7bf2982f68f..1b2642c547ec 100644
> --- a/rust/kernel/alloc/allocator_test.rs
> +++ b/rust/kernel/alloc/allocator_test.rs
> @@ -8,6 +8,7 @@
>
> pub struct Kmalloc;
> pub type Vmalloc = Kmalloc;
> +pub type KVmalloc = Kmalloc;
>
> unsafe impl Allocator for Kmalloc {
> unsafe fn realloc(
