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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 7EDE0C4332B for ; Wed, 3 Mar 2021 21:21:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5871A64EF6 for ; Wed, 3 Mar 2021 21:21:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376821AbhCCTnb (ORCPT ); Wed, 3 Mar 2021 14:43:31 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:60633 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240287AbhCCT1A (ORCPT ); Wed, 3 Mar 2021 14:27:00 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614799494; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zZak1YCTeDCL5z28NbOLP4nsAVAJ3AftCQx5HMPyNmg=; b=IHXoo81MZawOAha165i2gryWMZgBb5yiprXT6mOjPaBjbC02MZj3eezQDvwkyVho87NfYc xGdFqmMVNAyWLLwIMUozSjcYITh1/xxPCVJCtg0LL21yZJ3MsMXxP/TKoKJ0U0kQJI5NA0 DFJafWEHxVpFU0ame6JffjoUm9FS1Ic= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-191-qjA2q2YWP12qsw9B3FMcqA-1; Wed, 03 Mar 2021 14:24:50 -0500 X-MC-Unique: qjA2q2YWP12qsw9B3FMcqA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0B1EAC73A0; Wed, 3 Mar 2021 19:24:49 +0000 (UTC) Received: from [10.36.112.28] (ovpn-112-28.ams2.redhat.com [10.36.112.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4C14E60BFA; Wed, 3 Mar 2021 19:24:45 +0000 (UTC) Subject: Re: [PATCH V2 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory To: Catalin Marinas Cc: Anshuman Khandual , Will Deacon , 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 , linux-arm-kernel@lists.infradead.org References: <20210202123215.GA16868@willie-the-truck> <20210202123524.GB16868@willie-the-truck> <20210202125152.GC16868@willie-the-truck> <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> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <5c5eb731-a5b3-757b-fcf5-283eb268625b@redhat.com> Date: Wed, 3 Mar 2021 20:24:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210303190428.GB24035@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03.03.21 20:04, 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(). Indeed, it looks like a latent bug. > > 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. > Do you have access to that machine? We could identify which path is taken quite easily. > Another situation could be that pfn_valid() returns true when no memory > is mapped for that pfn. > >> As it happens early during boot, I doubt that some NVDIMMs that get detected >> and added early during boot as system RAM (via dax/kmem) are the problem. > > It is indeed very early, we can't even get the early console output. So even before any hotplug really happens. All sections should be early at that point I guess. > Debugging this is even harder as it's only misbehaving on a board we > don't have access to. > > On the logic in this patch, is the hot-added memory always covering a > full subsection? The arm64 pfn_valid() currently relies on > memblock_is_map_memory() but the patch changes it to > pfn_section_valid(). So if hot-added memory doesn't cover the full > subsection, it may return true even if the pfn is not mapped. Hotplugged System RAM always covers full sections. Hotplugged ZONE_DEVICE always covers full subsections. pfn_section_valid() properly handles both cases. (see generic pfn_valid()) -- Thanks, David / dhildenb