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Wed, 11 Sep 2024 22:55:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 00C2EC4CECF; Wed, 11 Sep 2024 22:55:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1726095348; bh=ONKVPueTm7R2PEVvV8+tCD9cNcEk3jCly02IRQlQKQg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eUiJEiIQGC8VjeuVStZGt08/gecMgGbA6/Fo846oN4XZsN1GacSC0O/e2hdwKqY4I V/cQVDeymgAllj1Ey5mMJHQl1F/GC7GV5Yt6Q1WeU4iNzkMzP+exjY7BAlreNrqbUd MWGJRxchhyh+qHR5c1CfTeuEUPL7RisF07YbyWGuaf8Ts0N+wzLm6Elp7VP/BNdyxf VykicW0iKU8O1umLdSKlIc8xTXa3wMnlJcDo37urOPv/YBpi5lcq0oyK5wK6Jca5Sj MiWZz7aL5NKXkn6LUXRrA2xKpGHMG3t/s9RmYdje9xUVzoo3EomMT39Xfa064Lmy0K CcQPMS1RGnEUQ== From: Danilo Krummrich To: ojeda@kernel.org, alex.gaynor@gmail.com, wedsonaf@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, benno.lossin@proton.me, a.hindborg@samsung.com, aliceryhl@google.com, akpm@linux-foundation.org Cc: daniel.almeida@collabora.com, faith.ekstrand@collabora.com, boris.brezillon@collabora.com, lina@asahilina.net, mcanal@igalia.com, zhiw@nvidia.com, cjia@nvidia.com, jhubbard@nvidia.com, airlied@redhat.com, ajanulgu@redhat.com, lyude@redhat.com, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-mm@kvack.org, Danilo Krummrich Subject: [PATCH v7 09/26] rust: alloc: implement kernel `Box` Date: Thu, 12 Sep 2024 00:52:45 +0200 Message-ID: <20240911225449.152928-10-dakr@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240911225449.152928-1-dakr@kernel.org> References: <20240911225449.152928-1-dakr@kernel.org> MIME-Version: 1.0 X-Stat-Signature: erraq419t8insw1cnft8acddwh7uo711 X-Rspamd-Queue-Id: E654020004 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1726095349-622548 X-HE-Meta: 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 jzXRwsx8 sVV/UAltCUCdRpB7WpYkyVerIMuAqKlrgZIFLZxxDN/GEyuOi+Dv+go8qp6jgVKGyhei+57aBltoNEQoH9KZYqDG++ERDoSwR6ZogwhxW1jJOMTigumwr3raJ9UG4Ifc15u2Zq7bQEjjIZK/kd5okbHI4iA2gzuRSkRFS5vfI6mwmmF8FlVLc1uA6Hh9t3QUv8Cz3ud6AepYhdUgagtvdnIXgzA+gJp7IJF14SgevpvUK8CZjPQxBgpzRdvwFd8cBI6x1HB6rtlefMHSn2M3xeQ/081XUQNYu51oYWzP4CjcKNBxf7SH/dP7uyg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: `Box` provides the simplest way to allocate memory for a generic type with one of the kernel's allocators, e.g. `Kmalloc`, `Vmalloc` or `KVmalloc`. In contrast to Rust's `Box` type, the kernel `Box` type considers the kernel's GFP flags for all appropriate functions, always reports allocation failures through `Result<_, AllocError>` and remains independent from unstable features. Signed-off-by: Danilo Krummrich Reviewed-by: Benno Lossin --- rust/kernel/alloc.rs | 6 + rust/kernel/alloc/kbox.rs | 465 ++++++++++++++++++++++++++++++++++++++ rust/kernel/prelude.rs | 2 +- 3 files changed, 472 insertions(+), 1 deletion(-) create mode 100644 rust/kernel/alloc/kbox.rs diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs index 7a405d6f3034..b1f28334b27a 100644 --- a/rust/kernel/alloc.rs +++ b/rust/kernel/alloc.rs @@ -5,6 +5,7 @@ #[cfg(not(any(test, testlib)))] pub mod allocator; pub mod box_ext; +pub mod kbox; pub mod vec_ext; #[cfg(any(test, testlib))] @@ -13,6 +14,11 @@ #[cfg(any(test, testlib))] pub use self::allocator_test as allocator; +pub use self::kbox::Box; +pub use self::kbox::KBox; +pub use self::kbox::KVBox; +pub use self::kbox::VBox; + /// Indicates an allocation error. #[derive(Copy, Clone, PartialEq, Eq, Debug)] pub struct AllocError; diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs new file mode 100644 index 000000000000..6188494f040d --- /dev/null +++ b/rust/kernel/alloc/kbox.rs @@ -0,0 +1,465 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Implementation of [`Box`]. + +#[allow(unused_imports)] // Used in doc comments. +use super::allocator::{KVmalloc, Kmalloc, Vmalloc}; +use super::{AllocError, Allocator, Flags}; +use core::fmt; +use core::marker::PhantomData; +use core::mem::ManuallyDrop; +use core::mem::MaybeUninit; +use core::ops::{Deref, DerefMut}; +use core::pin::Pin; +use core::ptr::NonNull; +use core::result::Result; + +use crate::init::{InPlaceInit, InPlaceWrite, Init, PinInit}; +use crate::types::ForeignOwnable; + +/// The kernel's [`Box`] type -- a heap allocation for a single value of type `T`. +/// +/// This is the kernel's version of the Rust stdlib's `Box`. There are several of differences, +/// for example no `noalias` attribute is emitted and partially moving out of a `Box` is not +/// supported. There are also several API differences, e.g. `Box` always requires an [`Allocator`] +/// implementation to be passed as generic, page [`Flags`] when allocating memory and all functions +/// that may allocate memory are fallible. +/// +/// `Box` works with any of the kernel's allocators, e.g. [`Kmalloc`], [`Vmalloc`] or [`KVmalloc`]. +/// There are aliases for `Box` with these allocators ([`KBox`], [`VBox`], [`KVBox`]). +/// +/// When dropping a [`Box`], the value is also dropped and the heap memory is automatically freed. +/// +/// # Examples +/// +/// ``` +/// let b = KBox::::new(24_u64, GFP_KERNEL)?; +/// +/// assert_eq!(*b, 24_u64); +/// # Ok::<(), Error>(()) +/// ``` +/// +/// ``` +/// # use kernel::bindings; +/// const SIZE: usize = bindings::KMALLOC_MAX_SIZE as usize + 1; +/// struct Huge([u8; SIZE]); +/// +/// assert!(KBox::::new_uninit(GFP_KERNEL | __GFP_NOWARN).is_err()); +/// ``` +/// +/// ``` +/// # use kernel::bindings; +/// const SIZE: usize = bindings::KMALLOC_MAX_SIZE as usize + 1; +/// struct Huge([u8; SIZE]); +/// +/// assert!(KVBox::::new_uninit(GFP_KERNEL).is_ok()); +/// ``` +/// +/// # Invariants +/// +/// `self.0` is always properly aligned and either points to memory allocated with `A` or, for +/// zero-sized types, is a dangling, well aligned pointer. +#[repr(transparent)] +pub struct Box(NonNull, PhantomData); + +/// Type alias for [`Box`] with a [`Kmalloc`] allocator. +/// +/// # Examples +/// +/// ``` +/// let b = KBox::new(24_u64, GFP_KERNEL)?; +/// +/// assert_eq!(*b, 24_u64); +/// # Ok::<(), Error>(()) +/// ``` +pub type KBox = Box; + +/// Type alias for [`Box`] with a [`Vmalloc`] allocator. +/// +/// # Examples +/// +/// ``` +/// let b = VBox::new(24_u64, GFP_KERNEL)?; +/// +/// assert_eq!(*b, 24_u64); +/// # Ok::<(), Error>(()) +/// ``` +pub type VBox = Box; + +/// Type alias for [`Box`] with a [`KVmalloc`] allocator. +/// +/// # Examples +/// +/// ``` +/// let b = KVBox::new(24_u64, GFP_KERNEL)?; +/// +/// assert_eq!(*b, 24_u64); +/// # Ok::<(), Error>(()) +/// ``` +pub type KVBox = Box; + +// SAFETY: `Box` is `Send` if `T` is `Send` because the `Box` owns a `T`. +unsafe impl Send for Box +where + T: Send + ?Sized, + A: Allocator, +{ +} + +// SAFETY: `Box` is `Sync` if `T` is `Sync` because the `Box` owns a `T`. +unsafe impl Sync for Box +where + T: Sync + ?Sized, + A: Allocator, +{ +} + +impl Box +where + T: ?Sized, + A: Allocator, +{ + /// Creates a new `Box` from a raw pointer. + /// + /// # Safety + /// + /// For non-ZSTs, `raw` must point at an allocation allocated with `A`that is sufficiently + /// aligned for and holds a valid `T`. The caller passes ownership of the allocation to the + /// `Box`. + /// + /// For ZSTs, `raw` must be a dangling, well aligned pointer. + #[inline] + pub const unsafe fn from_raw(raw: *mut T) -> Self { + // INVARIANT: Validity of `raw` is guaranteed by the safety preconditions of this function. + // SAFETY: By the safety preconditions of this function, `raw` is not a NULL pointer. + Self(unsafe { NonNull::new_unchecked(raw) }, PhantomData::) + } + + /// Consumes the `Box` and returns a raw pointer. + /// + /// This will not run the destructor of `T` and for non-ZSTs the allocation will stay alive + /// indefinitely. Use [`Box::from_raw`] to recover the [`Box`], drop the value and free the + /// allocation, if any. + /// + /// # Examples + /// + /// ``` + /// let x = KBox::new(24, GFP_KERNEL)?; + /// let ptr = KBox::into_raw(x); + /// let x = unsafe { KBox::from_raw(ptr) }; + /// + /// assert_eq!(*x, 24); + /// # Ok::<(), Error>(()) + /// ``` + #[inline] + pub fn into_raw(b: Self) -> *mut T { + let b = ManuallyDrop::new(b); + + b.0.as_ptr() + } + + /// Consumes and leaks the `Box` and returns a mutable reference. + /// + /// See [Box::into_raw] for more details. + #[inline] + pub fn leak<'a>(b: Self) -> &'a mut T { + // SAFETY: `Box::into_raw` always returns a properly aligned and dereferenceable pointer + // which points to an initialized instance of `T`. + unsafe { &mut *Box::into_raw(b) } + } +} + +impl Box, A> +where + A: Allocator, +{ + /// Converts a `Box, A>` to a `Box`. + /// + /// It is undefined behavior to call this function while the value inside of `b` is not yet + /// fully initialized. + /// + /// # Safety + /// + /// Callers must ensure that the value inside of `b` is in an initialized state. + pub unsafe fn assume_init(b: Self) -> Box { + let raw = Self::into_raw(b); + + // SAFETY: `raw` comes from a previous call to `Box::into_raw`. By the safety requirements + // of this function, the value inside the `Box` is in an initialized state. Hence, it is + // safe to reconstruct the `Box` as `Box`. + unsafe { Box::from_raw(raw.cast()) } + } + + /// Writes the value and converts to `Box`. + pub fn write(mut b: Self, value: T) -> Box { + (*b).write(value); + // SAFETY: We've just initialized `b`'s value. + unsafe { Self::assume_init(b) } + } +} + +impl Box +where + A: Allocator, +{ + fn is_zst() -> bool { + core::mem::size_of::() == 0 + } + + /// Creates a new `Box` and initializes its contents with `x`. + /// + /// New memory is allocated with `A`. The allocation may fail, in which case an error is + /// returned. For ZSTs no memory is allocated. + pub fn new(x: T, flags: Flags) -> Result { + let b = Self::new_uninit(flags)?; + Ok(Box::write(b, x)) + } + + /// Creates a new `Box` with uninitialized contents. + /// + /// New memory is allocated with `A`. The allocation may fail, in which case an error is + /// returned. For ZSTs no memory is allocated. + /// + /// # Examples + /// + /// ``` + /// let b = KBox::::new_uninit(GFP_KERNEL)?; + /// let b = KBox::write(b, 24); + /// + /// assert_eq!(*b, 24_u64); + /// # Ok::<(), Error>(()) + /// ``` + pub fn new_uninit(flags: Flags) -> Result, A>, AllocError> { + let ptr = if Self::is_zst() { + NonNull::dangling() + } else { + let layout = core::alloc::Layout::new::>(); + let ptr = A::alloc(layout, flags)?; + + ptr.cast() + }; + + // INVARIANT: `ptr` is either a dangling pointer or points to memory allocated with `A`, + // which is sufficient in size and alignment for storing a `T`. + Ok(Box(ptr, PhantomData::)) + } + + /// Constructs a new `Pin>`. If `T` does not implement [`Unpin`], then `x` will be + /// pinned in memory and can't be moved. + #[inline] + pub fn pin(x: T, flags: Flags) -> Result>, AllocError> + where + A: 'static, + { + Ok(Self::new(x, flags)?.into()) + } + + /// Forgets the contents (does not run the destructor), but keeps the allocation. + fn forget_contents(this: Self) -> Box, A> { + let ptr = Self::into_raw(this); + + // SAFETY: `ptr` is valid, because it came from `Box::into_raw`. + unsafe { Box::from_raw(ptr.cast()) } + } + + /// Drops the contents, but keeps the allocation. + /// + /// # Examples + /// + /// ``` + /// let value = KBox::new([0; 32], GFP_KERNEL)?; + /// assert_eq!(*value, [0; 32]); + /// let value = KBox::drop_contents(value); + /// // Now we can re-use `value`: + /// let value = KBox::write(value, [1; 32]); + /// assert_eq!(*value, [1; 32]); + /// # Ok::<(), Error>(()) + /// ``` + pub fn drop_contents(this: Self) -> Box, A> { + let ptr = this.0.as_ptr(); + + // SAFETY: `ptr` is valid, because it came from `this`. After this call we never access the + // value stored in `this` again. + unsafe { core::ptr::drop_in_place(ptr) }; + + Self::forget_contents(this) + } + + /// Moves the `Box`' value out of the `Box` and consumes the `Box`. + pub fn into_inner(b: Self) -> T { + // SAFETY: By the type invariant `&*b` is valid for `read`. + let value = unsafe { core::ptr::read(&*b) }; + let _ = Self::forget_contents(b); + value + } +} + +impl From> for Pin> +where + T: ?Sized, + A: Allocator, +{ + /// Converts a `Box` into a `Pin>`. If `T` does not implement [`Unpin`], then + /// `*b` will be pinned in memory and can't be moved. + /// + /// This moves `b` into `Pin` without moving `*b` or allocating and copying any memory. + fn from(b: Box) -> Self { + // SAFETY: The value wrapped inside a `Pin>` cannot be moved or replaced as long + // as `T` does not implement `Unpin`. + unsafe { Pin::new_unchecked(b) } + } +} + +impl InPlaceWrite for Box, A> +where + A: Allocator + 'static, +{ + type Initialized = Box; + + fn write_init(mut self, init: impl Init) -> Result { + let slot = self.as_mut_ptr(); + // SAFETY: When init errors/panics, slot will get deallocated but not dropped, + // slot is valid. + unsafe { init.__init(slot)? }; + // SAFETY: All fields have been initialized. + Ok(unsafe { Box::assume_init(self) }) + } + + fn write_pin_init(mut self, init: impl PinInit) -> Result, E> { + let slot = self.as_mut_ptr(); + // SAFETY: When init errors/panics, slot will get deallocated but not dropped, + // slot is valid and will not be moved, because we pin it later. + unsafe { init.__pinned_init(slot)? }; + // SAFETY: All fields have been initialized. + Ok(unsafe { Box::assume_init(self) }.into()) + } +} + +impl InPlaceInit for Box +where + A: Allocator + 'static, +{ + type PinnedSelf = Pin; + + #[inline] + fn try_pin_init(init: impl PinInit, flags: Flags) -> Result, E> + where + E: From, + { + Box::<_, A>::new_uninit(flags)?.write_pin_init(init) + } + + #[inline] + fn try_init(init: impl Init, flags: Flags) -> Result + where + E: From, + { + Box::<_, A>::new_uninit(flags)?.write_init(init) + } +} + +impl ForeignOwnable for Box +where + A: Allocator, +{ + type Borrowed<'a> = &'a T; + + fn into_foreign(self) -> *const core::ffi::c_void { + Box::into_raw(self) as _ + } + + unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self { + // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous + // call to `Self::into_foreign`. + unsafe { Box::from_raw(ptr as _) } + } + + unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T { + // SAFETY: The safety requirements of this method ensure that the object remains alive and + // immutable for the duration of 'a. + unsafe { &*ptr.cast() } + } +} + +impl ForeignOwnable for Pin> +where + A: Allocator, +{ + type Borrowed<'a> = Pin<&'a T>; + + fn into_foreign(self) -> *const core::ffi::c_void { + // SAFETY: We are still treating the box as pinned. + Box::into_raw(unsafe { Pin::into_inner_unchecked(self) }) as _ + } + + unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self { + // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous + // call to `Self::into_foreign`. + unsafe { Pin::new_unchecked(Box::from_raw(ptr as _)) } + } + + unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Pin<&'a T> { + // SAFETY: The safety requirements for this function ensure that the object is still alive, + // so it is safe to dereference the raw pointer. + // The safety requirements of `from_foreign` also ensure that the object remains alive for + // the lifetime of the returned value. + let r = unsafe { &*ptr.cast() }; + + // SAFETY: This pointer originates from a `Pin>`. + unsafe { Pin::new_unchecked(r) } + } +} + +impl Deref for Box +where + T: ?Sized, + A: Allocator, +{ + type Target = T; + + fn deref(&self) -> &T { + // SAFETY: `self.0` is always properly aligned, dereferenceable and points to an initialized + // instance of `T`. + unsafe { self.0.as_ref() } + } +} + +impl DerefMut for Box +where + T: ?Sized, + A: Allocator, +{ + fn deref_mut(&mut self) -> &mut T { + // SAFETY: `self.0` is always properly aligned, dereferenceable and points to an initialized + // instance of `T`. + unsafe { self.0.as_mut() } + } +} + +impl fmt::Debug for Box +where + T: ?Sized + fmt::Debug, + A: Allocator, +{ + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + fmt::Debug::fmt(&**self, f) + } +} + +impl Drop for Box +where + T: ?Sized, + A: Allocator, +{ + fn drop(&mut self) { + let size = core::mem::size_of_val::(self); + + // SAFETY: The pointer in `self.0` is guaranteed to be valid by the type invariant. + unsafe { core::ptr::drop_in_place::(self.deref_mut()) }; + + if size != 0 { + // SAFETY: As `size` is not zero, `self.0` was previously allocated with `A`. + unsafe { A::free(self.0.cast()) }; + } + } +} diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs index 4571daec0961..a9210634a8c3 100644 --- a/rust/kernel/prelude.rs +++ b/rust/kernel/prelude.rs @@ -14,7 +14,7 @@ #[doc(no_inline)] pub use core::pin::Pin; -pub use crate::alloc::{box_ext::BoxExt, flags::*, vec_ext::VecExt}; +pub use crate::alloc::{box_ext::BoxExt, flags::*, vec_ext::VecExt, KBox, KVBox, VBox}; #[doc(no_inline)] pub use alloc::{boxed::Box, vec::Vec};