linux-kernel - Re: [PATCH v2 0/2] Take ARCH_KMALLOC_MINALIGN into account for build-time XArray check

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Message-ID: <87ldnqf06r.fsf@t14s.mail-host-address-is-not-set>
Date: Mon, 11 Aug 2025 15:38:20 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>, Lorenzo Stoakes
 <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Danilo Krummrich
 <dakr@...nel.org>, Matthew Wilcox <willy@...radead.org>, Tamir Duberstein
 <tamird@...il.com>, Miguel Ojeda <ojeda@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn
 Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>,
 Trevor Gross <tmgross@...ch.edu>, linux-mm@...ck.org,
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, Alice Ryhl
 <aliceryhl@...gle.com>
Subject: Re: [PATCH v2 0/2] Take ARCH_KMALLOC_MINALIGN into account for
 build-time XArray check

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> The Rust bindings for XArray include a build-time check to ensure that
> you can only use the XArray with pointers that are 4-byte aligned.
> Because of that, there is currently a build failure if you attempt to
> create an XArray<KBox<T>> where T is a 1-byte or 2-byte aligned type.
> However, this error is incorrect as KBox<_> is guaranteed to be a
> pointer that comes from kmalloc, and kmalloc always produces pointers
> that are at least 4-byte aligned.
>
> To fix this, we augment the compile-time logic that computes the
> alignment of KBox<_> to take the minimum alignment of its allocator into
> account.
>
> Intended to land through alloc-next under the RUST [ALLOC] entry.
>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>

Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>

Best regards,
Andreas Hindborg