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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 CFB2CC433E0 for ; Mon, 8 Mar 2021 11:29:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4B259651CA for ; Mon, 8 Mar 2021 11:29:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4B259651CA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9BFCD8D0023; Mon, 8 Mar 2021 06:29:44 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 970258D001D; Mon, 8 Mar 2021 06:29:44 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 85F0A8D0023; Mon, 8 Mar 2021 06:29:44 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0073.hostedemail.com [216.40.44.73]) by kanga.kvack.org (Postfix) with ESMTP id 693FC8D001D for ; Mon, 8 Mar 2021 06:29:44 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 3178E180AD83E for ; Mon, 8 Mar 2021 11:29:44 +0000 (UTC) X-FDA: 77896487088.17.05A59F6 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf23.hostedemail.com (Postfix) with ESMTP id A5191A0009E6 for ; Mon, 8 Mar 2021 11:29:42 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id AD39A651CD; Mon, 8 Mar 2021 11:29:39 +0000 (UTC) Date: Mon, 8 Mar 2021 11:29:37 +0000 From: Catalin Marinas To: David Hildenbrand Cc: Anshuman Khandual , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Will Deacon , Ard Biesheuvel , Mark Rutland , James Morse , Robin Murphy , =?iso-8859-1?B?Suly9G1l?= Glisse , Dan Williams , Mike Rapoport , Veronika Kabatova Subject: Re: [PATCH V3 1/2] arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory Message-ID: <20210308112936.GD15644@arm.com> References: <1614921898-4099-1-git-send-email-anshuman.khandual@arm.com> <1614921898-4099-2-git-send-email-anshuman.khandual@arm.com> <20210305181322.GI23855@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: A5191A0009E6 X-Stat-Signature: xagefga5zd5ycoc4ftmxatxsdzrj4q1e Received-SPF: none (kernel.org>: No applicable sender policy available) receiver=imf23; identity=mailfrom; envelope-from=""; helo=mail.kernel.org; client-ip=198.145.29.99 X-HE-DKIM-Result: none/none X-HE-Tag: 1615202982-992162 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 Fri, Mar 05, 2021 at 07:24:21PM +0100, David Hildenbrand wrote: > On 05.03.21 19:13, Catalin Marinas wrote: > > On Fri, Mar 05, 2021 at 10:54:57AM +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. > > > > > > Cc: Catalin Marinas > > > Cc: Will Deacon > > > Cc: Ard Biesheuvel > > > Cc: Robin Murphy > > > Cc: linux-arm-kernel@lists.infradead.org > > > Cc: linux-kernel@vger.kernel.org > > > Acked-by: David Hildenbrand > > > Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support") > > > Signed-off-by: Anshuman Khandual > > > --- > > > arch/arm64/mm/init.c | 12 ++++++++++++ > > > 1 file changed, 12 insertions(+) > > > > > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > > > index 0ace5e68efba..5920c527845a 100644 > > > --- a/arch/arm64/mm/init.c > > > +++ b/arch/arm64/mm/init.c > > > @@ -230,6 +230,18 @@ int pfn_valid(unsigned long pfn) > > > if (!valid_section(__pfn_to_section(pfn))) > > > return 0; > > > + > > > + /* > > > + * ZONE_DEVICE memory does not have the memblock entries. > > > + * memblock_is_map_memory() check for ZONE_DEVICE based > > > + * addresses will always fail. Even the normal hotplugged > > > + * memory will never have MEMBLOCK_NOMAP flag set in their > > > + * memblock entries. Skip memblock search for all non early > > > + * memory sections covering all of hotplug memory including > > > + * both normal and ZONE_DEVICE based. > > > + */ > > > + if (!early_section(__pfn_to_section(pfn))) > > > + return pfn_section_valid(__pfn_to_section(pfn), pfn); > > > > Would something like this work instead: > > > > if (online_device_section(ms)) > > return 1; > > > > to avoid the assumptions around early_section()? > > Please keep online section logic out of pfn valid logic. Tow different > things. (and rather not diverge too much from generic pfn_valid() - we want > to achieve the opposite in the long term, merging both implementations) I think I misread the code. I was looking for a new flag to check like SECTION_IS_DEVICE instead of assuming that !SECTION_IS_EARLY means device or mhp. Anyway, staring at this code for a bit more, I came to the conclusion that the logic in Anshuman's patches is fairly robust - we only need to check for memblock_is_map_memory() if early_section() as that's the only case where we can have MEMBLOCK_NOMAP. Maybe the comment above should be re-written a bit and avoid the ZONE_DEVICE and hotplugged memory details altogether. -- Catalin