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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 3B7A0C10DCE for ; Fri, 6 Mar 2020 09:41:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 18BEA2073D for ; Fri, 6 Mar 2020 09:41:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726212AbgCFJlT (ORCPT ); Fri, 6 Mar 2020 04:41:19 -0500 Received: from foss.arm.com ([217.140.110.172]:58604 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725927AbgCFJlT (ORCPT ); Fri, 6 Mar 2020 04:41:19 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 18BC231B; Fri, 6 Mar 2020 01:41:19 -0800 (PST) Received: from [10.1.195.32] (e112269-lin.cambridge.arm.com [10.1.195.32]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 664A33F6C4; Fri, 6 Mar 2020 01:41:18 -0800 (PST) Subject: Re: [PATCH] mm: Correct guards for non_swap_entry() To: Andrew Morton Cc: "linux-kernel@vger.kernel.org" , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Arnd Bergmann , Dan Williams References: <20200305130550.22693-1-steven.price@arm.com> <20200305194431.7fe10d760d9921d0eff106c1@linux-foundation.org> From: Steven Price Message-ID: Date: Fri, 6 Mar 2020 09:41:16 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200305194431.7fe10d760d9921d0eff106c1@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/03/2020 03:44, Andrew Morton wrote: > On Thu, 5 Mar 2020 13:05:50 +0000 Steven Price wrote: > >> If CONFIG_DEVICE_PRIVATE is defined, but neither CONFIG_MEMORY_FAILURE nor >> CONFIG_MIGRATION, then non_swap_entry() will return 0, meaning that the >> condition (non_swap_entry(entry) && is_device_private_entry(entry)) in >> zap_pte_range() will never be true even if the entry is a device private >> one. >> >> Equally any other code depending on non_swap_entry() will not function >> as expected. > > What are the user-visible runtime effects of this change? > > Is a cc:stable needed? > I originally spotted this just by looking at the code, I haven't actually observed any problems. Looking a bit more closely it appears that actually this situation (currently at least) cannot occur: DEVICE_PRIVATE depends on ZONE_DEVICE ZONE_DEVICE depends on MEMORY_HOTREMOVE MEMORY_HOTREMOVE depends on MIGRATION So there's probably no need to back port. Steve