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_HELO_NONE,SPF_PASS 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 1342FC2BA17 for ; Mon, 6 Apr 2020 17:16:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CEA0A249BC for ; Mon, 6 Apr 2020 17:15:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726536AbgDFRP7 (ORCPT ); Mon, 6 Apr 2020 13:15:59 -0400 Received: from mga05.intel.com ([192.55.52.43]:52103 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726491AbgDFRP7 (ORCPT ); Mon, 6 Apr 2020 13:15:59 -0400 IronPort-SDR: oe4/casutOdprL0GOao9Nx6c+QhRnYPVMuHhHUy4JRDhAPdw8IfqmCSu9Z4t3yGlDsO5ROakNL Ewir/UkPW9Cw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Apr 2020 10:15:59 -0700 IronPort-SDR: XvbhvgWzvOPJ3qs0Vu07U8bqvUowRe/V+/pIIHKAauAbqkFtJebCbyS/pOsCZU9mt765SWMLK+ RORiqy1IPYmQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,351,1580803200"; d="scan'208";a="250949282" Received: from yweiss1-mobl.ger.corp.intel.com (HELO localhost) ([10.252.49.159]) by orsmga003.jf.intel.com with ESMTP; 06 Apr 2020 10:15:57 -0700 Date: Mon, 6 Apr 2020 20:15:56 +0300 From: Jarkko Sakkinen To: Sean Christopherson Cc: linux-sgx@vger.kernel.org, Haitao Huang Subject: Re: [PATCH v2] x86/sgx: Fix deadlock and race conditions between fork() and EPC reclaim Message-ID: <20200406171556.GB20105@linux.intel.com> References: <20200403093550.104789-1-jarkko.sakkinen@linux.intel.com> <20200403234239.GJ2701@linux.intel.com> <20200404010948.GA24717@linux.intel.com> <20200406143638.GB21330@linux.intel.com> <20200406171027.GA20105@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200406171027.GA20105@linux.intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On Mon, Apr 06, 2020 at 08:10:29PM +0300, Jarkko Sakkinen wrote: > On Mon, Apr 06, 2020 at 07:36:38AM -0700, Sean Christopherson wrote: > > On Sat, Apr 04, 2020 at 04:12:02AM +0300, Jarkko Sakkinen wrote: > > > On Fri, Apr 03, 2020 at 04:42:39PM -0700, Sean Christopherson wrote: > > > > On Fri, Apr 03, 2020 at 12:35:50PM +0300, Jarkko Sakkinen wrote: > > > > > From: Sean Christopherson > > > > > @@ -221,12 +224,16 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm) > > > > > return ret; > > > > > } > > > > > > > > > > + /* > > > > > + * The page reclaimer uses list version for synchronization instead of > > > > > + * synchronize_scru() because otherwise we could conflict with > > > > > + * dup_mmap(). > > > > > + */ > > > > > spin_lock(&encl->mm_lock); > > > > > list_add_rcu(&encl_mm->list, &encl->mm_list); > > > > > > > > You dropped the smp_wmb(). > > > > > > As I said to you in my review x86 pipeline does not reorder writes. > > > > And as I pointed out in this thread, smp_wmb() is a _compiler_ barrier if > > and only if CONFIG_SMP=y. The compiler can reorder list_add_rcu() and > > mm_list_version++ because from it's perspective there is no dependency > > between the two. And that's entirely true except for the SMP case where > > the consumer of mm_list_version is relying on the list to be updated before > > the version changes. > > I see. > > So why not change the variable volatile given that x86 is the only > arch that this code gets used? Please note that I'm fully aware of https://www.kernel.org/doc/html/latest/process/volatile-considered-harmful.html Just wondering. Anyway, I'll add smp_wmb() back since it is safe play in terms of acceptance. /Jarkko