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h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PDtho+oYVDPTVKfgrOYdPw3jXqlofGentNAB3BvW8FIz6GKIOqc/MLY2PP8qmSEGo U2oKYtPaRWtpNl30Odn9jYRNhvl8fEVOTsFJzjaaj9KRW31LKPXIZ2BsxptY+ky8Vo 1MI0cou3urUefGbFR/0o4iaG051OKEew7Ibqmy5sBH4Nptf/j0Krt3jTAMYGAjEs61 WM0Q1/lGrvFb6Dkr1l4eDY9N6NE9TaCfw3bL+nQPsCBe4+Zm6ecazzgYnw5siuwGdO zB/Q3t1SxZWSOIUn/S10Eanp/GhZ6wczC6iInsUfZK1ihE0HStVfJNE4Egl+Kxoj19 6XF7cwiwcMAyQ== Date: Fri, 30 Aug 2024 00:04:38 +0200 From: Danilo Krummrich To: Benno Lossin Cc: ojeda@kernel.org, alex.gaynor@gmail.com, wedsonaf@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, a.hindborg@samsung.com, aliceryhl@google.com, akpm@linux-foundation.org, 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 Subject: Re: [PATCH v6 04/26] rust: alloc: implement `Allocator` for `Kmalloc` Message-ID: References: <20240816001216.26575-1-dakr@kernel.org> <20240816001216.26575-5-dakr@kernel.org> <2dd02834-b2b6-4ff6-9e29-43c9d77b69e2@proton.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2dd02834-b2b6-4ff6-9e29-43c9d77b69e2@proton.me> X-Stat-Signature: 4j14fdxucsm49rned9er6mhutwmpnq9u X-Rspamd-Queue-Id: 8D282A0008 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1724969089-597316 X-HE-Meta: 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 BIhA/unq r6MNFnGDk17MVJ7IgIN3DkZgQPnl/vKb5Y8/hTDtuxx1kh5UZGqR+/6yhJ4Hu28F7cGpg2gQVJru54NLlYk0qL8gogkFYGX17gscxcn7dAwF4+UlfRvT0xoNToG1ziQ/DQvAcA1Wbh7ekFfi3kHX+DssT3chEntAdbbFKgd34Nxd0rhwhwBPoRlI8je9hoWMXr1E8PawZHPhon1F2yDDFC+LpSvD+pAUzhczNBNJWNDwEyR9TooovGReLwntGP3vD04jYP3sVnqypKLszRPmIKR35iMu5geN+y6GVQ7w12kIyS3uYdQ1M1BopOg5cpfiU1s8fYhdneRP17sA= 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: On Thu, Aug 29, 2024 at 06:32:42PM +0000, Benno Lossin wrote: > On 16.08.24 02:10, Danilo Krummrich wrote: > > 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 > > --- > > rust/kernel/alloc.rs | 2 +- > > rust/kernel/alloc/allocator.rs | 72 +++++++++++++++++++++++++++++++++- > > 2 files changed, 72 insertions(+), 2 deletions(-) > > > > diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs > > index 9932f21b0539..477dbe3c5a2f 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..78e7d5488843 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: > > Thanks, this nice. > > > > > 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. > > Does putting a link here work? (I guess we don't yet export the bindings > documentation, so it will probably fail... When we decide to enable it, > we should create an issue to add missing links) > > > +/// > > +/// 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 +52,60 @@ 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`]. > > + unsafe fn call( > > + &self, > > + ptr: Option>, > > + layout: Layout, > > + flags: Flags, > > + ) -> Result, AllocError> { > > + let size = aligned_size(layout); > > + let ptr = match ptr { > > + Some(ptr) => ptr.as_ptr(), > > + None => ptr::null(), > > + }; > > + > > + // SAFETY: `ptr` is either NULL or valid by the safety requirements of this function. > > You need some justification as to why calling the three allowed > functions here. What kind of justification do I need? Can you please share some more details on what you think is missing here? > > > + 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)) > > + } > > +} > > + > > +unsafe impl Allocator for Kmalloc { > > Missing SAFETY comment. Yeah, I think we came across this in an earlier version of the series. I asked you about the content and usefulness of a comment here, since I'd just end up re-iterating what the `Allocator` trait documentation says. IIRC, you replied that you want to think of something that'd make sense to add here. What do you think should be written here? > > --- > Cheers, > Benno > > > + #[inline] > > + unsafe fn realloc( > > + ptr: Option>, > > + layout: Layout, > > + flags: Flags, > > + ) -> Result, 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 > > >