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// 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;
use core::alloc::Layout;
use core::ptr;
use core::ptr::NonNull;
use crate::alloc::{AllocError, Allocator};
use crate::bindings;
use crate::pr_warn;
/// 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;
/// The virtually contiguous kernel allocator.
///
/// `Vmalloc` allocates pages from the page level allocator and maps them into the contiguous kernel
/// virtual space. It is typically used for large allocations. The memory allocated with this
/// allocator is not physically contiguous.
///
/// 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.
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`.
struct ReallocFunc(
unsafe extern "C" fn(*const crate::ffi::c_void, usize, u32) -> *mut crate::ffi::c_void,
);
impl ReallocFunc {
// INVARIANT: `krealloc` satisfies the type invariants.
const KREALLOC: Self = Self(bindings::krealloc);
// 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`].
///
/// # 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,
old_layout: Layout,
flags: Flags,
) -> Result<NonNull<[u8]>, AllocError> {
let size = aligned_size(layout);
let ptr = match ptr {
Some(ptr) => {
if old_layout.size() == 0 {
ptr::null()
} else {
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 {
crate::alloc::dangling_from_layout(layout)
} 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,
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: `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 Vmalloc {
#[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!("Vmalloc 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::VREALLOC.call(ptr, layout, old_layout, flags) }
}
}
// 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) }
}
}
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