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Howlett" , Miguel Ojeda , Boqun Feng , Gary Guo , =?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 v2] rust: page: add byte-wise atomic memory copy methods Message-ID: <2026021343-germicide-baritone-efe8@gregkh> References: <20260212-page-volatile-io-v2-1-a36cb97d15c2@kernel.org> <20260213095557.GS2995752@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260213095557.GS2995752@noisy.programming.kicks-ass.net> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 68D851C0015 X-Stat-Signature: 1un1i7dgkcdjkb1einx38d4jxgmq4rr1 X-Rspam-User: X-HE-Tag: 1770985107-311166 X-HE-Meta: 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 UQMNQT/h tpKIP/zqzhTY/MpMJ94Fa+ZE6hWHwXOHMI7MRGF43vv4dycmvTFA4OmMVqFTepm8/IAy5kuq+1UFDWyd94mtOITvo6xRxI4h57SqHjdUvANaC6J5HsMh4da34H0knPIF74CkmQWuzozUOHsfP65HKQ3HYJgyk0XQfYkMBKVdhrNmPr2Q6WlIbzaCsjeS7R6FOppY4fMzi9FNTAEFejwkA64aQOEOJC9nOao8ejKYxYRcZIL7+8/G9uvR8mTSdehK2n3wnPgvZhohn+DNyhvkHDvBk2dqontuhbYO53RUyC+fx2weSjwNhJC4A+mV7rJY3skWC/NRA4maYkzM3rtKLv86Z1fN3KAOoMMWZOulQhH1USM0Lrrtxw1sZ6156YgbQSFmrMi+gMJVWiNQ= 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 Fri, Feb 13, 2026 at 10:55:57AM +0100, Peter Zijlstra wrote: > 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. I too am totally confused when reading this patch, and the previous ones. Shouldn't the "normal" copy_from_user() stuff be used here correctly? Why is anything new needed? thanks, greg k-h