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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45B22C00140 for ; Thu, 18 Aug 2022 16:40:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344862AbiHRQkt (ORCPT ); Thu, 18 Aug 2022 12:40:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58034 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344950AbiHRQko (ORCPT ); Thu, 18 Aug 2022 12:40:44 -0400 Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4D716BFAB4 for ; Thu, 18 Aug 2022 09:40:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1660840844; x=1692376844; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=llLrcHc/wK3CfmeEcVnkYQChSaB5jpfMLinYxM/52ds=; b=hFcBN1VrYHOudZFKwi9iquJO65AzlqyQeOWIS+eklaMwIPjBiY2KZTDh Cbd0x3jwX7IaohW+vNGC3VHe6fW0MJHX/jwzk4fzj81VWwMWxnMdgBGfK RhML5y/1xI40+YtL9ddvx7e0f9/puqZt/Jnyl1yw5F2yuq4tZlnO+E3th pfcK3PnV+Snk2pmwqsOeSoQvVa+ZUmTLfLwRZFtkABtBuVoMAPx4Kd3sD kznHD5RxIetYqtjAAvlOgNUkoOJifns2Sxlu9vzeLaJ4IQ0LGA16PptNy hNtqBQMz0Bqa3LhqQ3azFxD3gSUpTG2qKc+rMe+Yaw2MsTtsBWVoboHoc w==; X-IronPort-AV: E=McAfee;i="6500,9779,10443"; a="272582263" X-IronPort-AV: E=Sophos;i="5.93,247,1654585200"; d="scan'208";a="272582263" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Aug 2022 09:39:20 -0700 X-IronPort-AV: E=Sophos;i="5.93,247,1654585200"; d="scan'208";a="853473562" Received: from amalikya-mobl.amr.corp.intel.com (HELO [10.212.238.171]) ([10.212.238.171]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Aug 2022 09:39:20 -0700 Message-ID: <8a09b9d5-d5c6-7a1f-1e44-9525b5b18661@intel.com> Date: Thu, 18 Aug 2022 09:39:19 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v3 5/7] mm: Remember young/dirty bit for page migrations Content-Language: en-US To: Nadav Amit , Peter Xu Cc: "Huang, Ying" , Linux MM , LKML , Minchan Kim , David Hildenbrand , Andrew Morton , Hugh Dickins , Vlastimil Babka , Andrea Arcangeli , Andi Kleen , "Kirill A . Shutemov" , Dave Hansen References: <20220809220100.20033-1-peterx@redhat.com> <20220809220100.20033-6-peterx@redhat.com> <87pmh6dwdr.fsf@yhuang6-desk2.ccr.corp.intel.com> <5B21352C-2BE6-4070-BB6B-C1B7A5D4D225@gmail.com> From: Dave Hansen In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/15/22 14:03, Nadav Amit wrote: >> >> At least on x86, the hardware is not supposed to do so. The only case I >> remember (and sometimes misremembers) is with KNL erratum, which perhaps >> needs to be considered: >> >> https://lore.kernel.org/all/20160708001911.9A3FD2B6@viggo.jf.intel.com/ > I keep not remembering this erratum correctly. IIRC, the erratum says that > the access/dirty might be set, but it does not mean that a write is possible > after the PTE is cleared (i.e., the dirty/access might be set on the > non-present PTE, but the access itself would fail). So it is not an issue in > this case - losing A/D would not impact correctness since the access should > fail. > > Dave Hansen hates when I get confused with this one, but I cc him if he > wants to confirm. Right. The issue is strictly with the page walker setting Accessed/Dirty in a racy way. The TLB still has accurate contents at all times.