linux-kernel - Re: [PATCH v2] rust: page: add Rust version of PAGE

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Message-ID: <81e9b289-b95c-4671-b442-1a0ac3dae466@nvidia.com>
Date: Mon, 21 Oct 2024 11:20:03 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>, "Matthew Wilcox (Oracle)"
	<willy@...radead.org>
CC: Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>, Björn Roy Baron
	<bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>,
	<linux-mm@...ck.org>, <rust-for-linux@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] rust: page: add Rust version of PAGE_ALIGN

On 10/16/24 4:34 AM, Alice Ryhl wrote:
> This is a useful for helper for working with indices into buffers that
> consist of several pages. I forgot to include it when I added PAGE_SIZE
> and PAGE_MASK for the same purpose in commit fc6e66f4696b ("rust: add
> abstraction for `struct page`").
> 
> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> Changes in v2:
> - Make the function const.
> - Address integer overflow in docs.
> - Link to v1: https://lore.kernel.org/r/20241015-page-align-v1-1-68fbd8b6d10c@google.com
> ---
>   rust/kernel/page.rs | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
> index 208a006d587c..9ef01929e7d0 100644
> --- a/rust/kernel/page.rs
> +++ b/rust/kernel/page.rs
> @@ -20,6 +20,15 @@
>   /// A bitmask that gives the page containing a given address.
>   pub const PAGE_MASK: usize = !(PAGE_SIZE - 1);
>   
> +/// Round up the given number to the next multiple of `PAGE_SIZE`.
> +///
> +/// It is incorrect to pass an address where the next multiple of `PAGE_SIZE` doesn't fit in a
> +/// `usize`.
> +pub const fn page_align(addr: usize) -> usize {
> +    // Brackets around PAGE_SIZE-1 to avoid triggering overflow sanitizers in the wrong cases.

Silly nit, but I did start looking for brackets that aren't there, so:

s/Brackets/parentheses/


> +    (addr + (PAGE_SIZE - 1)) & PAGE_MASK
> +}
> +
>   /// A pointer to a page that owns the page allocation.
>   ///
>   /// # Invariants
> 
> ---
> base-commit: 8d8f785ceb21b9a0de11e05b811cc52d6fa79318
> change-id: 20241015-page-align-7e5fa4c751be
> 
> Best regards,

thanks,
-- 
John Hubbard