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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 210C9C5ACB3 for ; Thu, 16 Nov 2023 10:36:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345037AbjKPKg4 (ORCPT ); Thu, 16 Nov 2023 05:36:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54654 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230315AbjKPKgz (ORCPT ); Thu, 16 Nov 2023 05:36:55 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E4A51B8 for ; Thu, 16 Nov 2023 02:36:50 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 47AA51595; Thu, 16 Nov 2023 02:37:36 -0800 (PST) Received: from [10.1.35.163] (XHFQ2J9959.cambridge.arm.com [10.1.35.163]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1F8C23F6C4; Thu, 16 Nov 2023 02:36:47 -0800 (PST) Message-ID: Date: Thu, 16 Nov 2023 10:36:45 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 01/14] mm: Batch-copy PTE ranges during fork() Content-Language: en-GB To: David Hildenbrand , kernel test robot , Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Zenghui Yu , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Andrew Morton , Anshuman Khandual , Matthew Wilcox , Yu Zhao , Mark Rutland , Kefeng Wang , John Hubbard , Zi Yan Cc: oe-kbuild-all@lists.linux.dev, Linux Memory Management List , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20231115163018.1303287-2-ryan.roberts@arm.com> <202311160516.kHhfmjvl-lkp@intel.com> <4e8d329c-eda6-4ff8-bb56-8924bb4583b2@redhat.com> From: Ryan Roberts In-Reply-To: <4e8d329c-eda6-4ff8-bb56-8924bb4583b2@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/11/2023 10:12, David Hildenbrand wrote: > On 16.11.23 11:07, Ryan Roberts wrote: >> Hi All, >> >> Hoping for some guidance below! >> >> >> On 15/11/2023 21:26, kernel test robot wrote: >>> Hi Ryan, >>> >>> kernel test robot noticed the following build errors: >>> >>> [auto build test ERROR on akpm-mm/mm-everything] >>> [also build test ERROR on linus/master v6.7-rc1 next-20231115] >>> [cannot apply to arm64/for-next/core efi/next] >>> [If your patch is applied to the wrong git tree, kindly drop us a note. >>> And when submitting patch, we suggest to use '--base' as documented in >>> https://git-scm.com/docs/git-format-patch#_base_tree_information] >>> >>> url:    >>> https://github.com/intel-lab-lkp/linux/commits/Ryan-Roberts/mm-Batch-copy-PTE-ranges-during-fork/20231116-010123 >>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git >>> mm-everything >>> patch link:    >>> https://lore.kernel.org/r/20231115163018.1303287-2-ryan.roberts%40arm.com >>> patch subject: [PATCH v2 01/14] mm: Batch-copy PTE ranges during fork() >>> config: arm-randconfig-002-20231116 >>> (https://download.01.org/0day-ci/archive/20231116/202311160516.kHhfmjvl-lkp@intel.com/config) >>> compiler: arm-linux-gnueabi-gcc (GCC) 13.2.0 >>> reproduce (this is a W=1 build): >>> (https://download.01.org/0day-ci/archive/20231116/202311160516.kHhfmjvl-lkp@intel.com/reproduce) >>> >>> If you fix the issue in a separate patch/commit (i.e. not just a new version of >>> the same patch/commit), kindly add following tags >>> | Reported-by: kernel test robot >>> | Closes: >>> https://lore.kernel.org/oe-kbuild-all/202311160516.kHhfmjvl-lkp@intel.com/ >>> >>> All errors (new ones prefixed by >>): >>> >>>     mm/memory.c: In function 'folio_nr_pages_cont_mapped': >>>>> mm/memory.c:969:16: error: implicit declaration of function 'pte_pgprot'; >>>>> did you mean 'ptep_get'? [-Werror=implicit-function-declaration] >>>       969 |         prot = pte_pgprot(pte_mkold(pte_mkclean(ptent))); >>>           |                ^~~~~~~~~~ >>>           |                ptep_get >>>     cc1: some warnings being treated as errors >> >> It turns out that pte_pgprot() is not universal; its only implemented by >> architectures that select CONFIG_HAVE_IOREMAP_PROT (currently arc, arm64, >> loongarch, mips, powerpc, s390, sh, x86). >> >> I'm using it in core-mm to help calculate the number of "contiguously mapped" >> pages within a folio (note that's not the same as arm64's notion of >> contpte-mapped. I just want to know that there are N physically contiguous pages >> mapped virtually contiguously with the same permissions). And I'm using >> pte_pgprot() to extract the permissions for each pte to compare. It's important >> that we compare the permissions because just because the pages belongs to the >> same folio doesn't imply they are mapped with the same permissions; think >> mprotect()ing a sub-range. >> >> I don't have a great idea for how to fix this - does anyone have any thoughts? > > KIS :) fork() operates on individual VMAs if I am not daydreaming. > > Just check for the obvious pte_write()/dirty/ and you'll be fine. Yes, that seems much simpler! I think we might have to be careful about the uffd wp bit too? I think that's it - are there any other exotic bits that might need to be considered? > > If your code tries to optimize "between VMAs", you really shouldn't be doing > that at this point. No I'm not doing that; It's one VMA at a time. > > If someone did an mprotect(), there are separate VMAs, and you shouldn't be > looking at the PTEs belonging to a different VMA. > Yep understood, thanks.