From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9C573E68154 for ; Tue, 17 Feb 2026 09:45:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D59026B0005; Tue, 17 Feb 2026 04:45:22 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D266A6B0089; Tue, 17 Feb 2026 04:45:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C2E776B008A; Tue, 17 Feb 2026 04:45:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id AB9676B0005 for ; Tue, 17 Feb 2026 04:45:22 -0500 (EST) Received: from smtpin25.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 4476D5E200 for ; Tue, 17 Feb 2026 09:45:22 +0000 (UTC) X-FDA: 84453465684.25.CFCD7E7 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf01.hostedemail.com (Postfix) with ESMTP id 9B93740008 for ; Tue, 17 Feb 2026 09:45:20 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=vfzdEU8P; spf=none (imf01.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=pass (policy=none) header.from=infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1771321520; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=xMgRdiAJqb3usCRSJ8lylhuVSY2ZK9m0DpJKEZWPmIo=; b=1OvUxsIv8iI+T7xEDO4p4gcSNCCAiM2Eba94xDTS4sjYgWrYAWZtPTJNwR4D9in2D2qm7K fkxm7C82i56f9CHM5lvBKBC7EOsi9NA08n/3oa3iHlYhv8W1XHu0JWR5YPs6wmucBeQEcV w/Zkt9hEva9N/eKfK4c0g4QA4xGSE6I= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=vfzdEU8P; spf=none (imf01.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=pass (policy=none) header.from=infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1771321520; a=rsa-sha256; cv=none; b=P5+5IvDVwaQC48FJFuvBR1lkN13L2FGT/y1XedQHjzemHH+aWbbTeKE59nYpLmdsofCA+Y EzqZe9ypf7ieHQ81Cmh5k7L5DYqI+Bjx1LSPtcKCZuOLlIA3qO3mDoFP0fIqjadvoNOOh1 Su+/VInx8nppkVn69M7t28gusaGRSkQ= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=xMgRdiAJqb3usCRSJ8lylhuVSY2ZK9m0DpJKEZWPmIo=; b=vfzdEU8PS31YLqCBPPTsHJKK6M Bu2Aofe2rrCYLrsMhtOAqEHczqxe7Uz5Cvtfe+RbqNdNUEY5oF35CfDenGMxMwUP+pKT4U44q7ks+ eeMq/TdZAd6W6g7FApjOV71LMTLvBRRMqeYQiCqvhNI4vrmp5R7FG0wIbfRzuPtITLQIn2FyBo+lT BzmjmiiFOvEg39fwySDUix3tCYxaeq82I0qSJHITsZCmiJCbkdfrEIfC2Nf9kw03brqHIG3KODg14 a2YrqiE04fHzgZXffdN7VAwlWi5pSI0eufTeiotNfINjXXmwJjXuwg697TeAcRADOJBoSy185DLvG f5fyFHpw==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vsHds-00000004Evt-1Xf8; Tue, 17 Feb 2026 09:45:16 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 3A261300CDE; Tue, 17 Feb 2026 10:45:15 +0100 (CET) Date: Tue, 17 Feb 2026 10:45:15 +0100 From: Peter Zijlstra To: Alice Ryhl Cc: Boqun Feng , Greg KH , Andreas Hindborg , Lorenzo Stoakes , "Liam R. 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: <20260217094515.GV1395266@noisy.programming.kicks-ass.net> References: <2026021313-embody-deprive-9da5@gregkh> <873434u3yq.fsf@kernel.org> <20260213142608.GV2995752@noisy.programming.kicks-ass.net> <2026021311-shorten-veal-532c@gregkh> <2026021326-stark-coastline-c5bc@gregkh> <20260217091348.GT1395266@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9B93740008 X-Stat-Signature: o6zxu6hi8mu3ot3dstsyhir4gufn6wpn X-Rspam-User: X-HE-Tag: 1771321520-551011 X-HE-Meta: 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 ecdE8q0z u4tPKc14n1ATL8fYc0zNpN4mEK4OjpKomo0J4L3H9rLDE1x7XCO/3esTVfvmH+DxmDrGnAPPO8Z3Hel/abMvq61wEVndFyGjTAhURy+orMLtdXFd1ynRXswE0tR4kBncB5EWTy1ytNSgxR6OnIrvPdiE0qUSqegeKxsiUyWGM65VWMuzjMAkZ6gdjxOnj1qqMOwLIEpGQvBLmC4B9DyhVu33bxYG3UzyoTsq914t5JRD8nDMNm9kQ/fzTataaFEjdEUM2LVpNuinTQW2A8rJ7OL7LdZgSzTbAfQ9j 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 09:33:40AM +0000, Alice Ryhl wrote: > On Tue, Feb 17, 2026 at 10:13:48AM +0100, Peter Zijlstra wrote: > > 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. > > movq is a valid implementation of 8 byte-wise copies. > > > Also, not a single atomic operation in sight. > > Relaxed atomics are just mov ops. They are not atomics at all. Somewhere along the line 'atomic' seems to have lost any and all meaning :-( It must be this C committee and their weasel speak for fear of reality that has infected everyone or somesuch. Anyway, all you really want is a normal memcpy and somehow Rust cannot provide? WTF?!