6.12-stable review patch. If anyone has any objections, please let me know.
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From: Danilo Krummrich dakr@kernel.org
[ Upstream commit fde578c86281f27b182680c7642836a0dbbd0be7 ]
aligned_size() dates back to when Rust did support kmalloc() only, but is now used in ReallocFunc::call() and hence for all allocators.
However, the additional padding applied by aligned_size() is only required by the kmalloc() allocator backend.
Hence, replace aligned_size() with Kmalloc::aligned_layout() and use it for the affected allocators, i.e. kmalloc() and kvmalloc(), only.
While at it, make Kmalloc::aligned_layout() public, such that Rust abstractions, which have to call subsystem specific kmalloc() based allocation primitives directly, can make use of it.
Fixes: 8a799831fc63 ("rust: alloc: implement `ReallocFunc`") Reviewed-by: Alice Ryhl aliceryhl@google.com Link: https://lore.kernel.org/r/20250731154919.4132-2-dakr@kernel.org [ Remove `const` from Kmalloc::aligned_layout(). - Danilo ] Signed-off-by: Danilo Krummrich dakr@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- rust/kernel/alloc/allocator.rs | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-)
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs index 439985e29fbc..e4cd29100007 100644 --- a/rust/kernel/alloc/allocator.rs +++ b/rust/kernel/alloc/allocator.rs @@ -43,17 +43,6 @@ pub struct Vmalloc; /// 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. - let layout = new_layout.pad_to_align(); - - // Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()` - // which together with the slab guarantees means the `krealloc` will return a properly aligned - // object (see comments in `kmalloc()` for more information). - layout.size() -} - /// # Invariants /// /// One of the following: `krealloc`, `vrealloc`, `kvrealloc`. @@ -87,7 +76,7 @@ impl ReallocFunc { old_layout: Layout, flags: Flags, ) -> Result<NonNull<[u8]>, AllocError> { - let size = aligned_size(layout); + let size = layout.size(); let ptr = match ptr { Some(ptr) => { if old_layout.size() == 0 { @@ -122,6 +111,17 @@ impl ReallocFunc { } }
+impl Kmalloc { + /// Returns a [`Layout`] that makes [`Kmalloc`] fulfill the requested size and alignment of + /// `layout`. + pub fn aligned_layout(layout: Layout) -> Layout { + // Note that `layout.size()` (after padding) is guaranteed to be a multiple of + // `layout.align()` which together with the slab guarantees means that `Kmalloc` will return + // a properly aligned object (see comments in `kmalloc()` for more information). + layout.pad_to_align() + } +} + // 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, @@ -134,6 +134,8 @@ unsafe impl Allocator for Kmalloc { old_layout: Layout, flags: Flags, ) -> Result<NonNull<[u8]>, AllocError> { + let layout = Kmalloc::aligned_layout(layout); + // SAFETY: `ReallocFunc::call` has the same safety requirements as `Allocator::realloc`. unsafe { ReallocFunc::KREALLOC.call(ptr, layout, old_layout, flags) } } @@ -175,6 +177,10 @@ unsafe impl Allocator for KVmalloc { old_layout: Layout, flags: Flags, ) -> Result<NonNull<[u8]>, AllocError> { + // `KVmalloc` may use the `Kmalloc` backend, hence we have to enforce a `Kmalloc` + // compatible layout. + let layout = Kmalloc::aligned_layout(layout); + // 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");