1 // SPDX-License-Identifier: GPL-2.0 2 3 //! Implementation of the kernel's memory allocation infrastructure. 4 5 #[cfg(not(any(test, testlib)))] 6 pub mod allocator; 7 pub mod kbox; 8 pub mod kvec; 9 pub mod layout; 10 11 #[cfg(any(test, testlib))] 12 pub mod allocator_test; 13 14 #[cfg(any(test, testlib))] 15 pub use self::allocator_test as allocator; 16 17 pub use self::kbox::Box; 18 pub use self::kbox::KBox; 19 pub use self::kbox::KVBox; 20 pub use self::kbox::VBox; 21 22 pub use self::kvec::IntoIter; 23 pub use self::kvec::KVVec; 24 pub use self::kvec::KVec; 25 pub use self::kvec::VVec; 26 pub use self::kvec::Vec; 27 28 /// Indicates an allocation error. 29 #[derive(Copy, Clone, PartialEq, Eq, Debug)] 30 pub struct AllocError; 31 use core::{alloc::Layout, ptr::NonNull}; 32 33 /// Flags to be used when allocating memory. 34 /// 35 /// They can be combined with the operators `|`, `&`, and `!`. 36 /// 37 /// Values can be used from the [`flags`] module. 38 #[derive(Clone, Copy, PartialEq)] 39 pub struct Flags(u32); 40 41 impl Flags { 42 /// Get the raw representation of this flag. 43 pub(crate) fn as_raw(self) -> u32 { 44 self.0 45 } 46 47 /// Check whether `flags` is contained in `self`. 48 pub fn contains(self, flags: Flags) -> bool { 49 (self & flags) == flags 50 } 51 } 52 53 impl core::ops::BitOr for Flags { 54 type Output = Self; 55 fn bitor(self, rhs: Self) -> Self::Output { 56 Self(self.0 | rhs.0) 57 } 58 } 59 60 impl core::ops::BitAnd for Flags { 61 type Output = Self; 62 fn bitand(self, rhs: Self) -> Self::Output { 63 Self(self.0 & rhs.0) 64 } 65 } 66 67 impl core::ops::Not for Flags { 68 type Output = Self; 69 fn not(self) -> Self::Output { 70 Self(!self.0) 71 } 72 } 73 74 /// Allocation flags. 75 /// 76 /// These are meant to be used in functions that can allocate memory. 77 pub mod flags { 78 use super::Flags; 79 80 /// Zeroes out the allocated memory. 81 /// 82 /// This is normally or'd with other flags. 83 pub const __GFP_ZERO: Flags = Flags(bindings::__GFP_ZERO); 84 85 /// Allow the allocation to be in high memory. 86 /// 87 /// Allocations in high memory may not be mapped into the kernel's address space, so this can't 88 /// be used with `kmalloc` and other similar methods. 89 /// 90 /// This is normally or'd with other flags. 91 pub const __GFP_HIGHMEM: Flags = Flags(bindings::__GFP_HIGHMEM); 92 93 /// Users can not sleep and need the allocation to succeed. 94 /// 95 /// A lower watermark is applied to allow access to "atomic reserves". The current 96 /// implementation doesn't support NMI and few other strict non-preemptive contexts (e.g. 97 /// raw_spin_lock). The same applies to [`GFP_NOWAIT`]. 98 pub const GFP_ATOMIC: Flags = Flags(bindings::GFP_ATOMIC); 99 100 /// Typical for kernel-internal allocations. The caller requires ZONE_NORMAL or a lower zone 101 /// for direct access but can direct reclaim. 102 pub const GFP_KERNEL: Flags = Flags(bindings::GFP_KERNEL); 103 104 /// The same as [`GFP_KERNEL`], except the allocation is accounted to kmemcg. 105 pub const GFP_KERNEL_ACCOUNT: Flags = Flags(bindings::GFP_KERNEL_ACCOUNT); 106 107 /// For kernel allocations that should not stall for direct reclaim, start physical IO or 108 /// use any filesystem callback. It is very likely to fail to allocate memory, even for very 109 /// small allocations. 110 pub const GFP_NOWAIT: Flags = Flags(bindings::GFP_NOWAIT); 111 112 /// Suppresses allocation failure reports. 113 /// 114 /// This is normally or'd with other flags. 115 pub const __GFP_NOWARN: Flags = Flags(bindings::__GFP_NOWARN); 116 } 117 118 /// The kernel's [`Allocator`] trait. 119 /// 120 /// An implementation of [`Allocator`] can allocate, re-allocate and free memory buffers described 121 /// via [`Layout`]. 122 /// 123 /// [`Allocator`] is designed to be implemented as a ZST; [`Allocator`] functions do not operate on 124 /// an object instance. 125 /// 126 /// In order to be able to support `#[derive(SmartPointer)]` later on, we need to avoid a design 127 /// that requires an `Allocator` to be instantiated, hence its functions must not contain any kind 128 /// of `self` parameter. 129 /// 130 /// # Safety 131 /// 132 /// - A memory allocation returned from an allocator must remain valid until it is explicitly freed. 133 /// 134 /// - Any pointer to a valid memory allocation must be valid to be passed to any other [`Allocator`] 135 /// function of the same type. 136 /// 137 /// - Implementers must ensure that all trait functions abide by the guarantees documented in the 138 /// `# Guarantees` sections. 139 pub unsafe trait Allocator { 140 /// Allocate memory based on `layout` and `flags`. 141 /// 142 /// On success, returns a buffer represented as `NonNull<[u8]>` that satisfies the layout 143 /// constraints (i.e. minimum size and alignment as specified by `layout`). 144 /// 145 /// This function is equivalent to `realloc` when called with `None`. 146 /// 147 /// # Guarantees 148 /// 149 /// When the return value is `Ok(ptr)`, then `ptr` is 150 /// - valid for reads and writes for `layout.size()` bytes, until it is passed to 151 /// [`Allocator::free`] or [`Allocator::realloc`], 152 /// - aligned to `layout.align()`, 153 /// 154 /// Additionally, `Flags` are honored as documented in 155 /// <https://docs.kernel.org/core-api/mm-api.html#mm-api-gfp-flags>. 156 fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> { 157 // SAFETY: Passing `None` to `realloc` is valid by its safety requirements and asks for a 158 // new memory allocation. 159 unsafe { Self::realloc(None, layout, Layout::new::<()>(), flags) } 160 } 161 162 /// Re-allocate an existing memory allocation to satisfy the requested `layout`. 163 /// 164 /// If the requested size is zero, `realloc` behaves equivalent to `free`. 165 /// 166 /// If the requested size is larger than the size of the existing allocation, a successful call 167 /// to `realloc` guarantees that the new or grown buffer has at least `Layout::size` bytes, but 168 /// may also be larger. 169 /// 170 /// If the requested size is smaller than the size of the existing allocation, `realloc` may or 171 /// may not shrink the buffer; this is implementation specific to the allocator. 172 /// 173 /// On allocation failure, the existing buffer, if any, remains valid. 174 /// 175 /// The buffer is represented as `NonNull<[u8]>`. 176 /// 177 /// # Safety 178 /// 179 /// - If `ptr == Some(p)`, then `p` must point to an existing and valid memory allocation 180 /// created by this [`Allocator`]; if `old_layout` is zero-sized `p` does not need to be a 181 /// pointer returned by this [`Allocator`]. 182 /// - `ptr` is allowed to be `None`; in this case a new memory allocation is created and 183 /// `old_layout` is ignored. 184 /// - `old_layout` must match the `Layout` the allocation has been created with. 185 /// 186 /// # Guarantees 187 /// 188 /// This function has the same guarantees as [`Allocator::alloc`]. When `ptr == Some(p)`, then 189 /// it additionally guarantees that: 190 /// - the contents of the memory pointed to by `p` are preserved up to the lesser of the new 191 /// and old size, i.e. `ret_ptr[0..min(layout.size(), old_layout.size())] == 192 /// p[0..min(layout.size(), old_layout.size())]`. 193 /// - when the return value is `Err(AllocError)`, then `ptr` is still valid. 194 unsafe fn realloc( 195 ptr: Option<NonNull<u8>>, 196 layout: Layout, 197 old_layout: Layout, 198 flags: Flags, 199 ) -> Result<NonNull<[u8]>, AllocError>; 200 201 /// Free an existing memory allocation. 202 /// 203 /// # Safety 204 /// 205 /// - `ptr` must point to an existing and valid memory allocation created by this [`Allocator`]; 206 /// if `old_layout` is zero-sized `p` does not need to be a pointer returned by this 207 /// [`Allocator`]. 208 /// - `layout` must match the `Layout` the allocation has been created with. 209 /// - The memory allocation at `ptr` must never again be read from or written to. 210 unsafe fn free(ptr: NonNull<u8>, layout: Layout) { 211 // SAFETY: The caller guarantees that `ptr` points at a valid allocation created by this 212 // allocator. We are passing a `Layout` with the smallest possible alignment, so it is 213 // smaller than or equal to the alignment previously used with this allocation. 214 let _ = unsafe { Self::realloc(Some(ptr), Layout::new::<()>(), layout, Flags(0)) }; 215 } 216 } 217 218 /// Returns a properly aligned dangling pointer from the given `layout`. 219 pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> { 220 let ptr = layout.align() as *mut u8; 221 222 // SAFETY: `layout.align()` (and hence `ptr`) is guaranteed to be non-zero. 223 unsafe { NonNull::new_unchecked(ptr) } 224 } 225