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 32015C433E0 for ; Mon, 25 Jan 2021 22:18:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AF847207B7 for ; Mon, 25 Jan 2021 22:18:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AF847207B7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D57736B00C2; Mon, 25 Jan 2021 17:18:43 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D06786B00C3; Mon, 25 Jan 2021 17:18:43 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C1C406B00C4; Mon, 25 Jan 2021 17:18:43 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0202.hostedemail.com [216.40.44.202]) by kanga.kvack.org (Postfix) with ESMTP id AAA306B00C2 for ; Mon, 25 Jan 2021 17:18:43 -0500 (EST) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 770501EE6 for ; Mon, 25 Jan 2021 22:18:43 +0000 (UTC) X-FDA: 77745712926.08.pipe43_4d05ec127589 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id 57ADE1819E764 for ; Mon, 25 Jan 2021 22:18:43 +0000 (UTC) X-HE-Tag: pipe43_4d05ec127589 X-Filterd-Recvd-Size: 3594 Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Mon, 25 Jan 2021 22:18:41 +0000 (UTC) IronPort-SDR: AuHdj54IFN8xbht+scmWllpjCgzeqAeiRvtkS+EDlKRKbt1Lmg/BPlGl1i1kiv7UzJA+HQYSqC pRJkXhHejUbQ== X-IronPort-AV: E=McAfee;i="6000,8403,9875"; a="158988406" X-IronPort-AV: E=Sophos;i="5.79,374,1602572400"; d="scan'208";a="158988406" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jan 2021 14:18:39 -0800 IronPort-SDR: DugOZsV+ToMjSGqjsXLvGijFi0PtI0XJE4I4LV/dYgGFrabp02LiqxEDb9/wwuIe3v5gJVNFfF HGVTIeRsiaLA== X-IronPort-AV: E=Sophos;i="5.79,374,1602572400"; d="scan'208";a="393535238" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.212.60.232]) ([10.212.60.232]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jan 2021 14:18:38 -0800 Subject: Re: [PATCH v17 11/26] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY to _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> <20201229213053.16395-12-yu-cheng.yu@intel.com> <20210125182709.GC23290@zn.tnic> <8084836b-4990-90e8-5c9a-97a920f0239e@intel.com> <20210125215558.GK23070@zn.tnic> From: "Yu, Yu-cheng" Message-ID: Date: Mon, 25 Jan 2021 14:18:37 -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: <20210125215558.GK23070@zn.tnic> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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: On 1/25/2021 1:55 PM, Borislav Petkov wrote: > On Mon, Jan 25, 2021 at 01:27:51PM -0800, Yu, Yu-cheng wrote: >>> Maybe I'm missing something but those two can happen outside of the >>> loop, no? Or is *ptep somehow changing concurrently while the loop is >>> doing the CMPXCHG and you need to recreate it each time? >>> >>> IOW, you can generate upfront and do the empty loop... >> >> *ptep can change concurrently. > > Care to elaborate? > For example, when a thread reads a W=1, D=0 PTE and before changing it to W=0,D=0, another thread could have written to the page and the PTE is W=1, D=1 now. When try_cmpxchg() detects the difference, old_pte is read again.