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=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 C14FBC433DB for ; Tue, 2 Feb 2021 12:40:46 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 868B964F4E for ; Tue, 2 Feb 2021 12:40:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 868B964F4E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=7A1Zo3uNNVmWjZIt6zSXJqlSr+WLi3ULusU/Cc4Y/P8=; b=xxswjOzb6/6cbt5tECt66HkKm xKme3Ep6ooC3y5FmgBwdHX9Vng7PQI+SeQr0Iw3R2eLPN4A3fI7lfCKE6hctHy8cRrrdC0hWSuynH hTO1m9WOr9Svj4/RSjiIjI1Fd8BF7eb8FRi4Dw42nh/me6QvQcFnDKW+dMX+TkPjEYzjc3MbF6UPi JiRy0KNZO2GrdGXf5NVuTub2t8unrLJ4zTNxW11Wz2zPhmHSpi46dXZzxJP5rKf8zYLu+8lmANM5c 9ws5n/qSAqKoKtxEFKwtBboY9zoIFOvfTSOunjKghZYRA9spReLipPOFIhe5jbknPa+x1UdI3zMKV blaPa4lUw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l6uy9-0002py-GJ; Tue, 02 Feb 2021 12:39:45 +0000 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l6uy6-0002oC-DB for linux-arm-kernel@lists.infradead.org; Tue, 02 Feb 2021 12:39:43 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612269580; 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=AszqWIS/4datUtjdT4HeWzxO//YlJVDx3qS4JYvPPSwRzP7Wd9Uehc50LERapwVCWe96G0 3Eb9tXeppl8v4vogYKwuW3zyk9/SWknj7Be3HDjY2pHhhTZQPSj36tWg2xpZICuh1jUQ/a lALM7XGlnGNDqZNnJ1SgyVhWDfpD2K4= 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 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-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210202_073942_516326_E62D4263 X-CRM114-Status: GOOD ( 19.49 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Catalin Marinas , 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 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel