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Howlett" , Miguel Ojeda , Boqun Feng , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Trevor Gross , Danilo Krummrich , Will Deacon , Mark Rutland , linux-mm@kvack.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] rust: page: add byte-wise atomic memory copy methods Message-ID: <20260218102045.GD1282955@noisy.programming.kicks-ass.net> References: <20260213-page-volatile-io-v3-1-d60487b04d40@kernel.org> <67aea464d25c8cafb3113eea62c8221b@garyguo.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <67aea464d25c8cafb3113eea62c8221b@garyguo.net> X-Stat-Signature: 6qkaywjha3n7kbzhs8us9g6iwputiaig X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: E5CB0100002 X-HE-Tag: 1771410050-233250 X-HE-Meta: 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 XeFzUZbT +stRG4iBqJWe4lFZJrC8DLhq1QjSwAUfK+dZk/KFF3BGFEgtmmlXXJvjzZsxV6uUDd/lhcxCYxcFYXiqtHrP11FaClitUNCaNPOZqrmw/xDzlduXS74FWgBbugmRKwB8ZuWTOSzRPRSBXieXIbYSyU2ADhKzmhFTCJPbXXtndzOqSmE/WeeJ9e3y3RivFonzvyf9IXyc0FoA5B4FT3gbogIEHspn6Jcb9yjPcwAJfiNvdoPSQqCAxblQhH9FGsbacn2klcE3h4tLuZBxr+4Dd3YSibsyOQb/s5qHn2iq1UQ1sezazYH3W7vut0qhqnOGZ4VuL35pfju0O76I= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Feb 17, 2026 at 11:10:15PM +0000, Gary Guo wrote: > If we have this in stable, I think it's sufficient for LKMM. However > for Rust/C11 MM says that volatile ops are not atomic and use them for > concurrency is UB. > > I recall in last Rust all hands the vibe at discussion is that it's > desirable to define volatile as being byte-wise atomic, so if that > actually happens, this would indeed be what we want (but I think > semantics w.r.t. mixed-size atomics need to be figured out first). I would strongly suggest for volatile to be single-copy 'atomic' for any naturally aligned word sized access. This is what we have with GCC/Clang. If you pick anything else, you're explicitly creation interoperability issues.