linux-kernel - [PATCH] rust: Test page_align usize::MAX boundary edges

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Message-ID: <20251230094841.76830-1-bshephar@bne-home.net>
Date: Tue, 30 Dec 2025 19:48:41 +1000
From: bshephar@...-home.net
To: aliceryhl@...gle.com,
	lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com,
	ojeda@...nel.org,
	boqun.feng@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	lossin@...nel.org,
	a.hindborg@...nel.org,
	tmgross@...ch.edu,
	dakr@...nel.org
Cc: linux-mm@...ck.org,
	rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Brendan Shephard <bshephar@...-home.net>
Subject: [PATCH] rust: Test page_align usize::MAX boundary edges

From: Brendan Shephard <bshephar@...-home.net>

Update `page_align` doc tests to test `usize::MAX` boundaries
rather than arbitrary middle of `PAGE_SIZE`.

This patch is a follow-up of:
"[PATCH v8] rust: Return Option from page_align and ensure no usize overflow"

Signed-off-by: Brendan Shephard <bshephar@...-home.net>
---
 rust/kernel/page.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
index adecb200c654..d602d4231f56 100644
--- a/rust/kernel/page.rs
+++ b/rust/kernel/page.rs
@@ -45,9 +45,10 @@
 /// assert_eq!(page_align(0x1), Some(PAGE_SIZE));
 /// assert_eq!(page_align(PAGE_SIZE + 1), Some(2 * PAGE_SIZE));
 ///
-/// // Requested address causes overflow (returns `None`).
-/// let overflow_addr = usize::MAX - (PAGE_SIZE / 2);
-/// assert_eq!(page_align(overflow_addr), None);
+/// // Testing boundary conditions at the end of the address space.
+/// assert_eq!(page_align(usize::MAX - PAGE_SIZE + 1), Some(usize::MAX - PAGE_SIZE + 1));
+/// assert_eq!(page_align(usize::MAX - PAGE_SIZE + 2), None);
+/// assert_eq!(page_align(usize::MAX), None);
 /// ```
 #[inline(always)]
 pub const fn page_align(addr: usize) -> Option<usize> {

base-commit: 7acc70476f14661149774ab88d3fe23d83ba4249
-- 
2.52.0