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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 04A2DC433E6 for ; Thu, 21 Jan 2021 21:42:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B317423A5C for ; Thu, 21 Jan 2021 21:42:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727741AbhAUVlr (ORCPT ); Thu, 21 Jan 2021 16:41:47 -0500 Received: from mga07.intel.com ([134.134.136.100]:49386 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727369AbhAUVlb (ORCPT ); Thu, 21 Jan 2021 16:41:31 -0500 IronPort-SDR: OGhMR9Rk/bgECFutorlR+55TQQLiyl5C7hVx35FZf8eTbKrQzIn96rvNOqElguH7raWHtuL6L+ SNWEJvgg209g== X-IronPort-AV: E=McAfee;i="6000,8403,9871"; a="243425919" X-IronPort-AV: E=Sophos;i="5.79,365,1602572400"; d="scan'208";a="243425919" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Jan 2021 13:40:50 -0800 IronPort-SDR: u+JpUjjQSXfUXGLMAXw5NU/pwznQ/bNs8S+w5N5NH/wdP5atFQQCvDp7F07Fk3vKwlzciE8b70 SLxX92CVOZxg== X-IronPort-AV: E=Sophos;i="5.79,365,1602572400"; d="scan'208";a="571851418" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.209.46.254]) ([10.209.46.254]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Jan 2021 13:40:47 -0800 Subject: Re: [PATCH v17 08/26] x86/mm: Introduce _PAGE_COW To: Borislav Petkov Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu References: <20201229213053.16395-1-yu-cheng.yu@intel.com> <20201229213053.16395-9-yu-cheng.yu@intel.com> <20210121184405.GE32060@zn.tnic> <20210121204113.GG32060@zn.tnic> From: "Yu, Yu-cheng" Message-ID: <56a7b904-dddc-d92c-b74f-552f9738b8ac@intel.com> Date: Thu, 21 Jan 2021 13:40:46 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210121204113.GG32060@zn.tnic> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On 1/21/2021 12:41 PM, Borislav Petkov wrote: > On Thu, Jan 21, 2021 at 12:16:23PM -0800, Yu, Yu-cheng wrote: >> It clears _PAGE_DIRTY and sets _PAGE_COW. That is, >> >> if (pte.pte & _PAGE_DIRTY) { >> pte.pte &= ~_PAGE_DIRTY; >> pte.pte |= _PAGE_COW; >> } >> >> So, shifting makes resulting code more efficient. > > Efficient for what? Is this a hot path? > > If not, I'd take readable code any day of the week. > Ok, I will change it to the more readable code as stated earlier. -- Yu-cheng