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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 6B9AFC433F4 for ; Fri, 31 Aug 2018 15:53:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3115220837 for ; Fri, 31 Aug 2018 15:53:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3115220837 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729241AbeHaUBJ (ORCPT ); Fri, 31 Aug 2018 16:01:09 -0400 Received: from mga09.intel.com ([134.134.136.24]:44719 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727957AbeHaUBI (ORCPT ); Fri, 31 Aug 2018 16:01:08 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 31 Aug 2018 08:53:01 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,312,1531810800"; d="scan'208";a="259697793" Received: from 2b52.sc.intel.com ([143.183.136.52]) by fmsmga006.fm.intel.com with ESMTP; 31 Aug 2018 08:53:00 -0700 Message-ID: <1535730524.501.13.camel@intel.com> Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW From: Yu-cheng Yu To: Dave Hansen , Peter Zijlstra , Jann Horn Cc: the arch/x86 maintainers , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , ravi.v.shankar@intel.com, vedvyas.shanbhogue@intel.com Date: Fri, 31 Aug 2018 08:48:44 -0700 In-Reply-To: References: <1535649960.26689.15.camel@intel.com> <33d45a12-513c-eba2-a2de-3d6b630e928e@linux.intel.com> <1535651666.27823.6.camel@intel.com> <1535660494.28258.36.camel@intel.com> <1535662366.28781.6.camel@intel.com> <20180831095300.GF24124@hirez.programming.kicks-ass.net> <1535726032.32537.0.camel@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2018-08-31 at 07:47 -0700, Dave Hansen wrote: > On 08/31/2018 07:33 AM, Yu-cheng Yu wrote: > > > > Please use the form: > > > > pte_t new_pte, pte = READ_ONCE(*ptep); > > do { > > new_pte = /* ... */; > > } while (!try_cmpxchg(ptep, &pte, new_pte); > It's probably also worth doing some testing to see if you can detect > the > cost of the cmpxchg.  It's definitely more than the old code. > > A loop that does mprotect(PROT_READ) followed by > mprotect(PROT_READ|PROT_WRITE) should do it. I created the test, https://github.com/yyu168/cet-smoke-test/blob/quick/quick/mprotect_ben ch.c then realized this won't work. To trigger a race in ptep_set_wrprotect(), we need to fork from one of three pthread siblings. Or do we measure only how much this affects fork? If there is no racing, the effect should be minimal. Yu-cheng From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Date: Fri, 31 Aug 2018 08:48:44 -0700 Message-ID: <1535730524.501.13.camel@intel.com> References: <1535649960.26689.15.camel@intel.com> <33d45a12-513c-eba2-a2de-3d6b630e928e@linux.intel.com> <1535651666.27823.6.camel@intel.com> <1535660494.28258.36.camel@intel.com> <1535662366.28781.6.camel@intel.com> <20180831095300.GF24124@hirez.programming.kicks-ass.net> <1535726032.32537.0.camel@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Dave Hansen , Peter Zijlstra , Jann Horn Cc: the arch/x86 maintainers , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , ravi.v.shankar@intel.com, vedvya List-Id: linux-api@vger.kernel.org On Fri, 2018-08-31 at 07:47 -0700, Dave Hansen wrote: > On 08/31/2018 07:33 AM, Yu-cheng Yu wrote: > > > > Please use the form: > > > > pte_t new_pte, pte = READ_ONCE(*ptep); > > do { > > new_pte = /* ... */; > > } while (!try_cmpxchg(ptep, &pte, new_pte); > It's probably also worth doing some testing to see if you can detect > the > cost of the cmpxchg.  It's definitely more than the old code. > > A loop that does mprotect(PROT_READ) followed by > mprotect(PROT_READ|PROT_WRITE) should do it. I created the test, https://github.com/yyu168/cet-smoke-test/blob/quick/quick/mprotect_ben ch.c then realized this won't work. To trigger a race in ptep_set_wrprotect(), we need to fork from one of three pthread siblings. Or do we measure only how much this affects fork? If there is no racing, the effect should be minimal. Yu-cheng From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id B60B36B57BA for ; Fri, 31 Aug 2018 11:53:02 -0400 (EDT) Received: by mail-pg1-f199.google.com with SMTP id x2-v6so7038867pgp.4 for ; Fri, 31 Aug 2018 08:53:02 -0700 (PDT) Received: from mga17.intel.com (mga17.intel.com. [192.55.52.151]) by mx.google.com with ESMTPS id e11-v6si9910279plb.373.2018.08.31.08.53.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 31 Aug 2018 08:53:01 -0700 (PDT) Message-ID: <1535730524.501.13.camel@intel.com> Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW From: Yu-cheng Yu Date: Fri, 31 Aug 2018 08:48:44 -0700 In-Reply-To: References: <1535649960.26689.15.camel@intel.com> <33d45a12-513c-eba2-a2de-3d6b630e928e@linux.intel.com> <1535651666.27823.6.camel@intel.com> <1535660494.28258.36.camel@intel.com> <1535662366.28781.6.camel@intel.com> <20180831095300.GF24124@hirez.programming.kicks-ass.net> <1535726032.32537.0.camel@intel.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen , Peter Zijlstra , Jann Horn Cc: the arch/x86 maintainers , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , ravi.v.shankar@intel.com, vedvyas.shanbhogue@intel.com On Fri, 2018-08-31 at 07:47 -0700, Dave Hansen wrote: > On 08/31/2018 07:33 AM, Yu-cheng Yu wrote: > > > > Please use the form: > > > > pte_t new_pte, pte = READ_ONCE(*ptep); > > do { > > new_pte = /* ... */; > > } while (!try_cmpxchg(ptep, &pte, new_pte); > It's probably also worth doing some testing to see if you can detect > the > cost of the cmpxchg.A A It's definitely more than the old code. > > A loop that does mprotect(PROT_READ) followed by > mprotect(PROT_READ|PROT_WRITE) should do it. I created the test, https://github.com/yyu168/cet-smoke-test/blob/quick/quick/mprotect_ben ch.c then realized this won't work. To trigger a race in ptep_set_wrprotect(), we need to fork from one of three pthread siblings. Or do we measure only how much this affects fork? If there is no racing, the effect should be minimal. Yu-cheng