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 16D6CC433E0 for ; Fri, 5 Mar 2021 04:22:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C792765009 for ; Fri, 5 Mar 2021 04:22:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229759AbhCEEWC (ORCPT ); Thu, 4 Mar 2021 23:22:02 -0500 Received: from foss.arm.com ([217.140.110.172]:47460 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229463AbhCEEWB (ORCPT ); Thu, 4 Mar 2021 23:22:01 -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 31FACD6E; Thu, 4 Mar 2021 20:22:01 -0800 (PST) Received: from [10.163.68.69] (unknown [10.163.68.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9A69C3F73B; Thu, 4 Mar 2021 20:21:56 -0800 (PST) Subject: Re: [PATCH V2 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory To: Will Deacon , David Hildenbrand Cc: Catalin Marinas , Mark Rutland , linux-kernel@vger.kernel.org, Mike Rapoport , linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , James Morse , Dan Williams , Robin Murphy , Ard Biesheuvel , vkabatov@redhat.com, linux-arm-kernel@lists.infradead.org References: <4d8f5156-8628-5531-1485-322ad92aa15c@redhat.com> <0e649f28-4d54-319d-f876-8a93870cda7f@arm.com> <20210205185552.GA23216@willie-the-truck> <20210211115354.GB29894@willie-the-truck> <23e5eb93-a39c-c68e-eac1-c5ccf9036079@arm.com> <20210303190428.GB24035@arm.com> <20210303212406.GB20055@willie-the-truck> <9872a864-15b1-12a7-6aac-0e68554bc744@redhat.com> <20210304093559.GB20721@willie-the-truck> From: Anshuman Khandual Message-ID: <023088a4-c5aa-7a24-f9dd-ecd2b11dcae6@arm.com> Date: Fri, 5 Mar 2021 09:52:30 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210304093559.GB20721@willie-the-truck> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/4/21 3:06 PM, Will Deacon wrote: > On Thu, Mar 04, 2021 at 09:12:31AM +0100, David Hildenbrand wrote: >> On 04.03.21 04:31, Anshuman Khandual wrote: >>> On 3/4/21 2:54 AM, Will Deacon wrote: >>>> On Wed, Mar 03, 2021 at 07:04:33PM +0000, Catalin Marinas wrote: >>>>> On Thu, Feb 11, 2021 at 01:35:56PM +0100, David Hildenbrand wrote: >>>>>> On 11.02.21 13:10, Anshuman Khandual wrote: >>>>>>> On 2/11/21 5:23 PM, Will Deacon wrote: >>>>>>>> ... and dropped. These patches appear to be responsible for a boot >>>>>>>> regression reported by CKI: >>>>>>> >>>>>>> Ahh, boot regression ? These patches only change the behaviour >>>>>>> for non boot memory only. >>>>>>> >>>>>>>> https://lore.kernel.org/r/cki.8D1CB60FEC.K6NJMEFQPV@redhat.com >>>>>>> >>>>>>> Will look into the logs and see if there is something pointing to >>>>>>> the problem. >>>>>> >>>>>> It's strange. One thing I can imagine is a mis-detection of early sections. >>>>>> However, I don't see that happening: >>>>>> >>>>>> In sparse_init_nid(), we: >>>>>> 1. Initialize the memmap >>>>>> 2. Set SECTION_IS_EARLY | SECTION_HAS_MEM_MAP via >>>>>> sparse_init_one_section() >>>>>> >>>>>> Only hotplugged sections (DIMMs, dax/kmem) set SECTION_HAS_MEM_MAP without >>>>>> SECTION_IS_EARLY - which is correct, because these are not early. >>>>>> >>>>>> So once we know that we have valid_section() -- SECTION_HAS_MEM_MAP is set >>>>>> -- early_section() should be correct. >>>>>> >>>>>> Even if someone would be doing a pfn_valid() after >>>>>> memblocks_present()->memory_present() but before >>>>>> sparse_init_nid(), we should be fine (!valid_section() -> return 0). >>>>> >>>>> I couldn't figure out how this could fail with Anshuman's patches. >>>>> Will's suspicion is that some invalid/null pointer gets dereferenced >>>>> before being initialised but the only case I see is somewhere in >>>>> pfn_section_valid() (ms->usage) if valid_section() && !early_section(). >>>>> >>>>> Assuming that we do get a valid_section(ms) && !early_section(ms), is >>>>> there a case where ms->usage is not initialised? I guess races with >>>>> section_deactivate() are not possible this early. >>>>> >>>>> Another situation could be that pfn_valid() returns true when no memory >>>>> is mapped for that pfn. >>>> >>>> The case I wondered about was __pfn_to_section() with a bogus pfn, since >>>> with patch 2/2 we call that *before* checking that pfn_to_section_nr() is >>>> sane. >>> >>> Right, that is problematic. __pfn_to_section() should not be called without >>> first validating pfn_to_section_nr(), as it could cause out-of-bound access >>> on mem_section buffer. Will fix that order but as there is no test scenario >>> which is definitive for this reported regression, how should we ensure that >>> it fixes the problem ? >> >> Oh, right, I missed that in patch #2. (and when comparing to generic >> pfn_valid()). >> >> I thought bisecting pointed at patch #1, that's why I didn't even have >> another look at patch #2. Makes sense. > > I don't think we ever bisected it beyond these two patches, so it could > be either of them. Anshuman -- please work with Veronika on this, as she > has access to the problematic machine and was really helpful in debugging > this last time. Sure, will respin the patch series with a fix for [PATCH 2/2] as discussed and then follow up with Veronika to recreate the problem.