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`. Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx> --- rust/kernel/alloc.rs | 2 +- rust/kernel/alloc/allocator.rs | 89 +++++++++++++++++++++++++++++++++- 2 files changed, 89 insertions(+), 2 deletions(-) diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs index 6c21bd2edad9..535ed1527034 100644 --- a/rust/kernel/alloc.rs +++ b/rust/kernel/alloc.rs @@ -4,7 +4,7 @@ #[cfg(not(test))] #[cfg(not(testlib))] -mod allocator; +pub mod allocator; pub mod box_ext; pub mod vec_ext; diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs index e32182f91167..7a93442187a1 100644 --- a/rust/kernel/alloc/allocator.rs +++ b/rust/kernel/alloc/allocator.rs @@ -1,12 +1,28 @@ // SPDX-License-Identifier: GPL-2.0 //! Allocator support. +//! +//! Documentation for the kernel's memory allocators can found in the "Memory Allocation Guide" +//! linked below. For instance, this includes the concept of "get free page" (GFP) flags and the +//! typical application of the different kernel allocators. +//! +//! Reference: <https://docs.kernel.org/core-api/memory-allocation.html> use super::{flags::*, Flags}; use core::alloc::{GlobalAlloc, Layout}; use core::ptr; +use core::ptr::NonNull; -struct Kmalloc; +use crate::alloc::{AllocError, Allocator}; +use crate::bindings; + +/// 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 { @@ -36,6 +52,77 @@ pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: F unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 } } +/// # Invariants +/// +/// One of the following `krealloc`, `vrealloc`, `kvrealloc`. +struct ReallocFunc( + unsafe extern "C" fn(*const core::ffi::c_void, usize, u32) -> *mut core::ffi::c_void, +); + +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`]. + /// + /// # Guarantees + /// + /// This method has the same guarantees as `Allocator::realloc`. Additionally + /// - it accepts any pointer to a valid memory allocation allocated by this function. + /// - memory allocated by this function remains valid until it is passed to this function. + unsafe fn call( + &self, + ptr: Option<NonNull<u8>>, + layout: Layout, + flags: Flags, + ) -> Result<NonNull<[u8]>, AllocError> { + let size = aligned_size(layout); + let ptr = match ptr { + Some(ptr) => ptr.as_ptr(), + None => ptr::null(), + }; + + // SAFETY: + // - `self.0` is one of `krealloc`, `vrealloc`, `kvrealloc` and thus only requires that + // `ptr` is NULL or valid. + // - `ptr` is either NULL or valid by the safety requirements of this function. + // + // GUARANTEE: + // - `self.0` is one of `krealloc`, `vrealloc`, `kvrealloc`. + // - Those functions provide the guarantees of this function. + let raw_ptr = unsafe { + // If `size == 0` and `ptr != NULL` the memory behind the pointer is freed. + self.0(ptr.cast(), size, flags.0).cast() + }; + + let ptr = if size == 0 { + NonNull::dangling() + } else { + NonNull::new(raw_ptr).ok_or(AllocError)? + }; + + Ok(NonNull::slice_from_raw_parts(ptr, size)) + } +} + +// 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, + flags: Flags, + ) -> Result<NonNull<[u8]>, AllocError> { + // SAFETY: `ReallocFunc::call` has the same safety requirements as `Allocator::realloc`. + unsafe { ReallocFunc::KREALLOC.call(ptr, layout, flags) } + } +} + unsafe impl GlobalAlloc for Kmalloc { unsafe fn alloc(&self, layout: Layout) -> *mut u8 { // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety -- 2.46.0
