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 C2A9DC433E0 for ; Tue, 26 Jan 2021 16:43:59 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3C41C229C9 for ; Tue, 26 Jan 2021 16:43:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3C41C229C9 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 52E7B8D00F2; Tue, 26 Jan 2021 11:43:58 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 4DEE98D00B0; Tue, 26 Jan 2021 11:43:58 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3CD8D8D00F2; Tue, 26 Jan 2021 11:43:58 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0156.hostedemail.com [216.40.44.156]) by kanga.kvack.org (Postfix) with ESMTP id 27F188D00B0 for ; Tue, 26 Jan 2021 11:43:58 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id E05E0180AD80F for ; Tue, 26 Jan 2021 16:43:57 +0000 (UTC) X-FDA: 77748498114.21.part49_090c67e2758f Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id A3AA7180442CD for ; Tue, 26 Jan 2021 16:43:57 +0000 (UTC) X-HE-Tag: part49_090c67e2758f X-Filterd-Recvd-Size: 4055 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by imf42.hostedemail.com (Postfix) with ESMTP for ; Tue, 26 Jan 2021 16:43:56 +0000 (UTC) IronPort-SDR: 51BbinREehW+62I4lhY6ATXfPknSwUejQq9Aw51d813IEeUxkg+BaexoNB4GdQq6Tgit1vdK2O /P2ms+SbhIoA== X-IronPort-AV: E=McAfee;i="6000,8403,9876"; a="180077736" X-IronPort-AV: E=Sophos;i="5.79,375,1602572400"; d="scan'208";a="180077736" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Jan 2021 08:43:54 -0800 IronPort-SDR: eGwpQ92J/sX81sqArYH6+QIHP+J0S4EMZTaaYIKsSJxcLe0QKMCKSSF3yj0bW41zDIEqCl3g42 x8Jj9aQHSdrg== X-IronPort-AV: E=Sophos;i="5.79,375,1602572400"; d="scan'208";a="504585840" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.212.153.84]) ([10.212.153.84]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Jan 2021 08:43:51 -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: Peter Zijlstra , 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 , 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> From: "Yu, Yu-cheng" Message-ID: <2f69ab09-57e8-6da0-07ab-5b885758fc27@intel.com> Date: Tue, 26 Jan 2021 08:43:51 -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: 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 1/26/2021 1:40 AM, Peter Zijlstra wrote: > On Tue, Jan 26, 2021 at 09:46:36AM +0100, Peter Zijlstra wrote: >> On Mon, Jan 25, 2021 at 07:27:09PM +0100, Borislav Petkov wrote: >> >>>> + pte_t old_pte, new_pte; >>>> + >>>> + do { >>>> + old_pte = READ_ONCE(*ptep); >>>> + new_pte = pte_wrprotect(old_pte); >>> >>> 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... >>> >>>> + >>>> + } while (!try_cmpxchg(&ptep->pte, &old_pte.pte, new_pte.pte)); >>>> + >>>> + return; >>>> + } >> >> Empty loop would be wrong, but that wants to be written like: >> >> old_pte = READ_ONCE(*ptep); >> do { >> new_pte = pte_wrprotect(old_pte); >> } while (try_cmpxchg(&ptep->pte, &old_pte.pte, new_pte.pte)); > > ! went missing, too early, moar wake-up juice. > >> Since try_cmpxchg() will update old_pte on failure. Thanks Peter! I will fix that. -- Yu-cheng