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Date: Fri, 13 Feb 2026 10:55:57 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andreas Hindborg <a.hindborg@kernel.org>
Cc: 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>,
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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
Message-ID: <20260213095557.GS2995752@noisy.programming.kicks-ass.net>
References: <20260212-page-volatile-io-v2-1-a36cb97d15c2@kernel.org>
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In-Reply-To: <20260212-page-volatile-io-v2-1-a36cb97d15c2@kernel.org>

On Thu, Feb 12, 2026 at 03:51:24PM +0100, Andreas Hindborg wrote:
> When copying data from buffers that are mapped to user space, it is
> impossible to guarantee absence of concurrent memory operations on those
> buffers. Copying data to/from `Page` from/to these buffers would be
> undefined behavior if no special considerations are made.
> 
> Add methods on `Page` to read and write the contents using byte-wise atomic
> operations.

I'm completely failing to understand. What!?

There is no such thing as an 'atomic' byte load, nor does it help one
whit against concurrent modification of the memory you're copying.