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Date: Tue, 17 Feb 2026 10:13:48 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Boqun Feng <boqun@kernel.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
	Andreas Hindborg <a.hindborg@kernel.org>,
	Alice Ryhl <aliceryhl@google.com>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Miguel Ojeda <ojeda@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
	Gary Guo <gary@garyguo.net>,
	=?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
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	Mark Rutland <mark.rutland@arm.com>, linux-mm@kvack.org,
	rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] rust: page: add byte-wise atomic memory copy methods
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On Fri, Feb 13, 2026 at 08:19:17AM -0800, Boqun Feng wrote:
> Well, in standard C, technically memcpy() has the same problem as Rust's
> `core::ptr::copy()` and `core::ptr::copy_nonoverlapping()`, i.e. they
> are vulnerable to data races. Our in-kernel memcpy() on the other hand
> doesn't have this problem. Why? Because it's volatile byte-wise atomic
> per the implementation.

Look at arch/x86/lib/memcpy_64.S, plenty of movq variants there. Not
byte-wise. Also, not a single atomic operation in sight.