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 X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC428C433E0 for ; Wed, 1 Jul 2020 17:09:37 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 91A5F2078A for ; Wed, 1 Jul 2020 17:09:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="GdDCVZus" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 91A5F2078A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=GxYpUqdvcFQ3Pae9S/XH59cxXkoXDWYW6Od9+66qPwQ=; b=GdDCVZustuiokBv7TluHsliJS vo+KxQwCBenSnSnWqW04GFjwi32AiMPuEzIZdyHr+wyZiB31npxru7k0+zLMN01NfGUreJw+lBlz7 GSsKqfGc7nSjpcpkEg50sxyXfwyByZBhoxUyBc4UIuAJ2g5lnCq3m/tcSL/x4nRjSiUPMjFt1j7P4 SWEoiwNRivKWIfg7drybVuRsYYmSyUtZbgOjsBpi5HbZltEHsIWpRBwO1sizBUXnL/GHJw9BHLw2R o6HObxl6gQrlB+6PBbe8qSYm3bnXVfMZyzucnkQQMH09LXI+rGt6fdD6Z9WnYTMDCRKq/vZIER5eN op9N490nQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqgCv-0006ZA-4t; Wed, 01 Jul 2020 17:07:37 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqgCt-0006YR-GB for linux-arm-kernel@lists.infradead.org; Wed, 01 Jul 2020 17:07:36 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 38EBF31B; Wed, 1 Jul 2020 10:07:33 -0700 (PDT) Received: from bakewell.cambridge.arm.com (unknown [10.37.8.41]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 572E33F73C; Wed, 1 Jul 2020 10:07:28 -0700 (PDT) Date: Wed, 1 Jul 2020 18:07:25 +0100 From: Dave P Martin To: Will Deacon Subject: Re: [PATCH 18/18] arm64: lto: Strengthen READ_ONCE() to acquire when CLANG_LTO=y Message-ID: <20200701170722.4rte5ssnmrn2uqzg@bakewell.cambridge.arm.com> References: <20200630173734.14057-1-will@kernel.org> <20200630173734.14057-19-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200630173734.14057-19-will@kernel.org> User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200701_130735_582539_5106DD8E X-CRM114-Status: GOOD ( 19.43 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , "Michael S. Tsirkin" , Peter Zijlstra , Catalin Marinas , Jason Wang , virtualization@lists.linux-foundation.org, Arnd Bergmann , Alan Stern , Sami Tolvanen , Matt Turner , kernel-team@android.com, Marco Elver , Kees Cook , "Paul E. McKenney" , Boqun Feng , Josh Triplett , Ivan Kokshaysky , linux-arm-kernel@lists.infradead.org, Richard Henderson , Nick Desaulniers , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jun 30, 2020 at 06:37:34PM +0100, Will Deacon wrote: > When building with LTO, there is an increased risk of the compiler > converting an address dependency headed by a READ_ONCE() invocation > into a control dependency and consequently allowing for harmful > reordering by the CPU. > > Ensure that such transformations are harmless by overriding the generic > READ_ONCE() definition with one that provides acquire semantics when > building with LTO. > > Signed-off-by: Will Deacon > --- > arch/arm64/include/asm/rwonce.h | 63 +++++++++++++++++++++++++++++++ > arch/arm64/kernel/vdso/Makefile | 2 +- > arch/arm64/kernel/vdso32/Makefile | 2 +- > 3 files changed, 65 insertions(+), 2 deletions(-) > create mode 100644 arch/arm64/include/asm/rwonce.h > > diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h > new file mode 100644 > index 000000000000..515e360b01a1 > --- /dev/null > +++ b/arch/arm64/include/asm/rwonce.h > @@ -0,0 +1,63 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Copyright (C) 2020 Google LLC. > + */ > +#ifndef __ASM_RWONCE_H > +#define __ASM_RWONCE_H > + > +#ifdef CONFIG_CLANG_LTO Don't we have a generic option for LTO that's not specific to Clang. Also, can you illustrate code that can only be unsafe with Clang LTO? [...] Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel