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rust: alloc: implement Allocator for Kmalloc

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Implement `Allocator` for `Kmalloc`, the kernel's default allocator,
typically used for objects smaller than page size.

All memory allocations made with `Kmalloc` end up in `krealloc()`.

It serves as allocator for the subsequently introduced types `KBox` and
`KVec`.

Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20241004154149.93856-7-dakr@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Danilo Krummrich 2024-10-04 17:41:10 +02:00 committed by Miguel Ojeda
parent a87a36f0bf
commit a34822d1c4
1 changed files with 28 additions and 3 deletions
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31
rust/kernel/alloc/allocator.rs
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@ -13,10 +13,16 @@
use core::ptr;
use core::ptr::NonNull;
use crate::alloc::AllocError;
use crate::alloc::{AllocError, Allocator};
use crate::bindings;
struct Kmalloc;
/// The contiguous kernel allocator.
///
/// `Kmalloc` is typically used for physically contiguous allocations up to page size, but also
/// supports larger allocations up to `bindings::KMALLOC_MAX_SIZE`, which is hardware specific.
///
/// For more details see [self].
pub struct Kmalloc;
/// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
fn aligned_size(new_layout: Layout) -> usize {
@ -53,8 +59,10 @@ struct ReallocFunc(
unsafe extern "C" fn(*const core::ffi::c_void, usize, u32) -> *mut core::ffi::c_void,
);
#[expect(dead_code)]
impl ReallocFunc {
// INVARIANT: `krealloc` satisfies the type invariants.
const KREALLOC: Self = Self(bindings::krealloc);
/// # Safety
///
/// This method has the same safety requirements as [`Allocator::realloc`].
@ -106,6 +114,23 @@ unsafe fn call(
}
}
// 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 Kmalloc {
#[inline]
unsafe fn realloc(
ptr: Option<NonNull<u8>>,
layout: Layout,
old_layout: Layout,
flags: Flags,
) -> Result<NonNull<[u8]>, AllocError> {
// SAFETY: `ReallocFunc::call` has the same safety requirements as `Allocator::realloc`.
unsafe { ReallocFunc::KREALLOC.call(ptr, layout, old_layout, flags) }
}
}
// SAFETY: TODO.
unsafe impl GlobalAlloc for Kmalloc {
unsafe fn alloc(&self, layout: Layout) -> *mut u8 {