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=-7.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,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 116E0C433E0 for ; Tue, 2 Feb 2021 12:35:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AD30764F5C for ; Tue, 2 Feb 2021 12:35:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AD30764F5C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 251996B0071; Tue, 2 Feb 2021 07:35:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1FFC76B0072; Tue, 2 Feb 2021 07:35:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0EF1C6B0073; Tue, 2 Feb 2021 07:35:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0038.hostedemail.com [216.40.44.38]) by kanga.kvack.org (Postfix) with ESMTP id EEF936B0071 for ; Tue, 2 Feb 2021 07:35:32 -0500 (EST) Received: from smtpin03.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id B3A62181AEF1D for ; Tue, 2 Feb 2021 12:35:32 +0000 (UTC) X-FDA: 77773273704.03.pets29_3d0a541275ca Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin03.hostedemail.com (Postfix) with ESMTP id 78AD228A4E8 for ; Tue, 2 Feb 2021 12:35:32 +0000 (UTC) X-HE-Tag: pets29_3d0a541275ca X-Filterd-Recvd-Size: 4047 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Tue, 2 Feb 2021 12:35:30 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id A521E64F4E; Tue, 2 Feb 2021 12:35:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612269329; bh=Lcs9qQjcI3+2E+x1vXYghwukVbPSnsQqMP3TbC6xXKY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dzVcaBeFdnOZb/0yfeoH1l1czXIQg2qJYtK/9bnIZ8qI1iQymFQtnaKGfsglLpFvf W3cwgWnsOauscsflpjeoKqoWo4k6EqXLsDVYHlhOe+pXTNw7KMRiTXTxb3YFCX99gm QDJma4uloSNVNzLyPJLDErq7kVMHaKGjNKD0k/hHGurksnoqIXhneV5vCoqErzy8uB imHHv49AA2y4C/tBMVIqSAeClXDRnPH6kkMnCmHC2QLfrmMPahhWUvVS0Sq9+TTfE3 fLZ060DZLXadKdcsn+BWAEulXbYhGFGGhgJyStCLIqISRlCq16c4J9qQmkyYMhxHw6 U0mVXq71oao3g== Date: Tue, 2 Feb 2021 12:35:24 +0000 From: Will Deacon To: 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 , =?iso-8859-1?B?Suly9G1l?= Glisse , Dan Williams , David Hildenbrand , Mike Rapoport Subject: Re: [PATCH V2 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Message-ID: <20210202123524.GB16868@willie-the-truck> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210202123215.GA16868@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) 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 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. Will