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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 v3] rust: page: add byte-wise atomic memory copy methods Message-ID: <20260213112837.GT2995752@noisy.programming.kicks-ass.net> References: <20260213-page-volatile-io-v3-1-d60487b04d40@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260213-page-volatile-io-v3-1-d60487b04d40@kernel.org> X-Rspamd-Queue-Id: 19EE88000B X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 4e4a6icgiab1sf6z3y8swu117636qh1z X-HE-Tag: 1770982123-656289 X-HE-Meta: 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 87n6bL6K nRAV2Ob6kMomURO5P4OI86p1i74sRlHK0kRuqdtTI2llTORuWnHeldA10niyFKKiw4DJJ6bg8M2DLuHvw5ij/DMoPB271XCkwh4HyQZ9hqjkrd7CAML3XUuCtgkRUFAJdmg+0xQTCwYOXLj8De/XSJsK6PKLzXrOqYX3hb8p/xsLPey2/nSl0+QrSKxQlDwIsA5KsByOzkbHzPxamBRonqAjzHtsfMQywHp0n0V+f+OesM0T/fay0DtX5ReCYYLYFGrHYGoUO3llQCOTIEPrcRKmovjeqZ5xz8Dnn 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 07:42:53AM +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. > > Also improve clarity by specifying additional requirements on > `read_raw`/`write_raw` methods regarding concurrent operations on involved > buffers. > + /// - Callers must ensure that this call does not race with a write to the source page that > + /// overlaps with this read. Yeah, but per the bit above, its user mapped, you *CANNOT* ensure this. And same comment as for v2, none of this makes sense. Byte loads are not magically atomic. And they don't actually fix anything. NAK