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=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 40337C433E0 for ; Mon, 1 Feb 2021 09:34:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DEA4664EAB for ; Mon, 1 Feb 2021 09:34:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232814AbhBAJe1 (ORCPT ); Mon, 1 Feb 2021 04:34:27 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:46129 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232773AbhBAJeY (ORCPT ); Mon, 1 Feb 2021 04:34:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612171977; 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=TRJgwth9GyqyyQWIRdUel3dkprdXQQtXGasEdO9dd+4=; b=JdPVyIcqPs1kiri/P/wdF3Z4Wcj8fYXt5pF0wHQZhfbEUONGYQs0bjYS8ja8EO8l5ZOc7E ZikDD02+szSQcl686tMe2vzi3/+/pdwITLrkyu2RtAzQXNpYCTTN8seVUE5W6rY3biqPzp BWB8lyRUNhXQDmdpmx0DbpB3o9exUpU= 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-10-AK_YxLelMz630S1tQGjELQ-1; Mon, 01 Feb 2021 04:32:53 -0500 X-MC-Unique: AK_YxLelMz630S1tQGjELQ-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 E6304801AF1; Mon, 1 Feb 2021 09:32:50 +0000 (UTC) Received: from [10.36.115.24] (ovpn-115-24.ams2.redhat.com [10.36.115.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id DBD9260C66; Mon, 1 Feb 2021 09:32:45 +0000 (UTC) To: Mike Rapoport , Andrew Morton Cc: Andrea Arcangeli , Baoquan He , Borislav Petkov , Chris Wilson , "H. Peter Anvin" , Ingo Molnar , Linus Torvalds , =?UTF-8?Q?=c5=81ukasz_Majczak?= , Mel Gorman , Michal Hocko , Mike Rapoport , Qian Cai , "Sarvela, Tomi P" , Thomas Gleixner , Vlastimil Babka , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org References: <20210130221035.4169-1-rppt@kernel.org> <20210130221035.4169-2-rppt@kernel.org> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v4 1/2] x86/setup: always add the beginning of RAM as memblock.memory Message-ID: <56e2c568-b121-8860-a6b0-274ace46d835@redhat.com> Date: Mon, 1 Feb 2021 10:32:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210130221035.4169-2-rppt@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.01.21 23:10, Mike Rapoport wrote: > From: Mike Rapoport > > The physical memory on an x86 system starts at address 0, but this is not > always reflected in e820 map. For example, the BIOS can have e820 entries > like > > [ 0.000000] BIOS-provided physical RAM map: > [ 0.000000] BIOS-e820: [mem 0x0000000000001000-0x000000000009ffff] usable > > or > > [ 0.000000] BIOS-provided physical RAM map: > [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] reserved > [ 0.000000] BIOS-e820: [mem 0x0000000000001000-0x0000000000057fff] usable > > In either case, e820__memblock_setup() won't add the range 0x0000 - 0x1000 > to memblock.memory and later during memory map initialization this range is > left outside any zone. > > With SPARSEMEM=y there is always a struct page for pfn 0 and this struct > page will have it's zone link wrong no matter what value will be set there. > > To avoid this inconsistency, add the beginning of RAM to memblock.memory. > Limit the added chunk size to match the reserved memory to avoid > registering memory that may be used by the firmware but never reserved at > e820__memblock_setup() time. > > Fixes: bde9cfa3afe4 ("x86/setup: don't remove E820_TYPE_RAM for pfn 0") > Signed-off-by: Mike Rapoport > Cc: stable@vger.kernel.org > --- > arch/x86/kernel/setup.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index 3412c4595efd..67c77ed6eef8 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -727,6 +727,14 @@ static void __init trim_low_memory_range(void) > * Kconfig help text for X86_RESERVE_LOW. > */ > memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE)); > + > + /* > + * Even if the firmware does not report the memory at address 0 as > + * usable, inform the generic memory management about its existence > + * to ensure it is a part of ZONE_DMA and the memory map for it is > + * properly initialized. > + */ > + memblock_add(0, ALIGN(reserve_low, PAGE_SIZE)); > } > > /* > I think, to make that code more robust, and to not rely on archs to do the right thing, we should do something like 1) Make sure in free_area_init() that each PFN with a memmap (i.e., falls into a partial present section) is spanned by a zone; that would include PFN 0 in this case. 2) In init_zone_unavailable_mem(), similar to round_up(max_pfn, PAGES_PER_SECTION) handling, consider range [round_down(min_pfn, PAGES_PER_SECTION), min_pfn - 1] which would handle in the x86-64 case [0..0] and, therefore, initialize PFN 0. Also, I think the special-case of PFN 0 is analogous to the round_up(max_pfn, PAGES_PER_SECTION) handling in init_zone_unavailable_mem(): who guarantees that these PFN above the highest present PFN are actually spanned by a zone? I'd suggest going through all zone ranges in free_area_init() first, dealing with zones that have "not section aligned start/end", clamping them up/down if required such that no holes within a section are left uncovered by a zone. -- Thanks, David / dhildenb