Commit 1b1a946d authored by Alice Ryhl's avatar Alice Ryhl Committed by Danilo Krummrich
Browse files

rust: alloc: specify the minimum alignment of each allocator 



The kernel's allocators sometimes provide a higher alignment than the
end-user requested, so add a new constant on the Allocator trait to let
the allocator specify what its minimum guaranteed alignment is.

This allows the ForeignOwnable trait to provide a more accurate value of
FOREIGN_ALIGN when using a pointer type such as Box, which will be
useful with certain collections such as XArray that store its own data
in the low bits of pointers.

Reviewed-by: default avatarBenno Lossin <lossin@kernel.org>
Signed-off-by: default avatarAlice Ryhl <aliceryhl@google.com>
Acked-by: default avatarLiam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250811-align-min-allocator-v2-1-3386cc94f4fc@google.com


[ Add helper for ARCH_KMALLOC_MINALIGN; remove cast to usize. - Danilo ]
Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
parent f87de691

rust/bindings/bindings_helper.h

+1 −0
Original line number Diff line number Diff line
@@ -84,6 +84,7 @@ 


/* `bindgen` gets confused at certain things. */

const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;

const size_t RUST_CONST_HELPER_ARCH_KMALLOC_MINALIGN = ARCH_KMALLOC_MINALIGN;

const size_t RUST_CONST_HELPER_PAGE_SIZE = PAGE_SIZE;

const gfp_t RUST_CONST_HELPER_GFP_ATOMIC = GFP_ATOMIC;

const gfp_t RUST_CONST_HELPER_GFP_KERNEL = GFP_KERNEL;

rust/kernel/alloc.rs

+8 −0
Original line number Diff line number Diff line
@@ -137,6 +137,14 @@ pub mod flags { 
/// - Implementers must ensure that all trait functions abide by the guarantees documented in the

///   `# Guarantees` sections.

pub unsafe trait Allocator {

    /// The minimum alignment satisfied by all allocations from this allocator.

    ///

    /// # Guarantees

    ///

    /// Any pointer allocated by this allocator is guaranteed to be aligned to `MIN_ALIGN` even if

    /// the requested layout has a smaller alignment.

    const MIN_ALIGN: usize;



    /// Allocate memory based on `layout` and `flags`.

    ///

    /// On success, returns a buffer represented as `NonNull<[u8]>` that satisfies the layout

rust/kernel/alloc/allocator.rs

+8 −0
Original line number Diff line number Diff line
@@ -17,6 +17,8 @@ 
use crate::bindings;

use crate::pr_warn;



const ARCH_KMALLOC_MINALIGN: usize = bindings::ARCH_KMALLOC_MINALIGN;



/// The contiguous kernel allocator.

///

/// `Kmalloc` is typically used for physically contiguous allocations up to page size, but also
@@ -128,6 +130,8 @@ unsafe fn call( 
// - 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 {

    const MIN_ALIGN: usize = ARCH_KMALLOC_MINALIGN;



    #[inline]

    unsafe fn realloc(

        ptr: Option<NonNull<u8>>,
@@ -145,6 +149,8 @@ unsafe fn realloc( 
// - passing a pointer to a valid memory allocation is OK,

// - `realloc` satisfies the guarantees, since `ReallocFunc::call` has the same.

unsafe impl Allocator for Vmalloc {

    const MIN_ALIGN: usize = kernel::page::PAGE_SIZE;



    #[inline]

    unsafe fn realloc(

        ptr: Option<NonNull<u8>>,
@@ -169,6 +175,8 @@ unsafe fn realloc( 
// - 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 {

    const MIN_ALIGN: usize = ARCH_KMALLOC_MINALIGN;



    #[inline]

    unsafe fn realloc(

        ptr: Option<NonNull<u8>>,