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=-7.8 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 94DCEC433DB for ; Tue, 2 Feb 2021 12:39:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 307CE64F5C for ; Tue, 2 Feb 2021 12:39:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 307CE64F5C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 6D98A6B0005; Tue, 2 Feb 2021 07:39:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 688706B006C; Tue, 2 Feb 2021 07:39:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 553456B006E; Tue, 2 Feb 2021 07:39:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0045.hostedemail.com [216.40.44.45]) by kanga.kvack.org (Postfix) with ESMTP id 3C7BB6B0005 for ; Tue, 2 Feb 2021 07:39:41 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id F258E1EE6 for ; Tue, 2 Feb 2021 12:39:40 +0000 (UTC) X-FDA: 77773284120.17.arm35_5f0d77b275ca Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin17.hostedemail.com (Postfix) with ESMTP id CA4F3180D0184 for ; Tue, 2 Feb 2021 12:39:40 +0000 (UTC) X-HE-Tag: arm35_5f0d77b275ca X-Filterd-Recvd-Size: 5302 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Tue, 2 Feb 2021 12:39:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612269579; 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=yEJntsm3uVvBSP7hH3XGK/+l1RDqeVkehzYxYBodVjU=; b=D6U8n/7+GRR6qyEa2+rH0wKRf8506ybKyeOXzo5GwlOVvclq59XyUi8y79RQlHutldD4z6 F4Re1twwk1HlO8YysekIxhg1YSwMsaoZ/iv1IUDZolArQXTzVHZYQnOV6j4FtZminZSizW 4GDZJEjvE97TYT9ymU06bOKldGxpdJ4= 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-125-obfjDlZcPCeTXibfYRwj9Q-1; Tue, 02 Feb 2021 07:39:36 -0500 X-MC-Unique: obfjDlZcPCeTXibfYRwj9Q-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 89D3A107ACE3; Tue, 2 Feb 2021 12:39:33 +0000 (UTC) Received: from [10.36.114.148] (ovpn-114-148.ams2.redhat.com [10.36.114.148]) by smtp.corp.redhat.com (Postfix) with ESMTP id E33495C230; Tue, 2 Feb 2021 12:39:30 +0000 (UTC) Subject: Re: [PATCH V2 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory To: Will Deacon , Anshuman Khandual Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Catalin Marinas , Ard Biesheuvel , Mark Rutland , James Morse , Robin Murphy , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Dan Williams , Mike Rapoport References: <1612239114-28428-1-git-send-email-anshuman.khandual@arm.com> <1612239114-28428-2-git-send-email-anshuman.khandual@arm.com> <20210202123215.GA16868@willie-the-truck> <20210202123524.GB16868@willie-the-truck> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Tue, 2 Feb 2021 13:39:29 +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: <20210202123524.GB16868@willie-the-truck> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02.02.21 13:35, Will Deacon wrote: > On Tue, Feb 02, 2021 at 12:32:15PM +0000, Will Deacon wrote: >> On Tue, Feb 02, 2021 at 09:41:53AM +0530, Anshuman Khandual wrote: >>> pfn_valid() validates a pfn but basically it checks for a valid struct page >>> backing for that pfn. It should always return positive for memory ranges >>> backed with struct page mapping. But currently pfn_valid() fails for all >>> ZONE_DEVICE based memory types even though they have struct page mapping. >>> >>> pfn_valid() asserts that there is a memblock entry for a given pfn without >>> MEMBLOCK_NOMAP flag being set. The problem with ZONE_DEVICE based memory is >>> that they do not have memblock entries. Hence memblock_is_map_memory() will >>> invariably fail via memblock_search() for a ZONE_DEVICE based address. This >>> eventually fails pfn_valid() which is wrong. memblock_is_map_memory() needs >>> to be skipped for such memory ranges. As ZONE_DEVICE memory gets hotplugged >>> into the system via memremap_pages() called from a driver, their respective >>> memory sections will not have SECTION_IS_EARLY set. >>> >>> Normal hotplug memory will never have MEMBLOCK_NOMAP set in their memblock >>> regions. Because the flag MEMBLOCK_NOMAP was specifically designed and set >>> for firmware reserved memory regions. memblock_is_map_memory() can just be >>> skipped as its always going to be positive and that will be an optimization >>> for the normal hotplug memory. Like ZONE_DEVICE based memory, all normal >>> hotplugged memory too will not have SECTION_IS_EARLY set for their sections >>> >>> Skipping memblock_is_map_memory() for all non early memory sections would >>> fix pfn_valid() problem for ZONE_DEVICE based memory and also improve its >>> performance for normal hotplug memory as well. >> >> Hmm. Although I follow your logic, this does seem to rely on an awful lot of >> assumptions to continue to hold true as the kernel evolves. In particular, >> how do we ensure that early sections are always fully backed with > > Sorry, typo here: ^^^ should be *non-early* sections. It might be a good idea to have a look at generic include/linux/mmzone.h:pfn_valid() As I expressed already, long term we should really get rid of the arm64 variant and rather special-case the generic one. Then we won't go out of sync - just as it happened with ZONE_DEVICE handling here. -- Thanks, David / dhildenb