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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 5930EECE58E for ; Tue, 8 Oct 2019 08:07:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 33F82217D7 for ; Tue, 8 Oct 2019 08:07:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730533AbfJHIH1 (ORCPT ); Tue, 8 Oct 2019 04:07:27 -0400 Received: from foss.arm.com ([217.140.110.172]:57944 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730292AbfJHIH1 (ORCPT ); Tue, 8 Oct 2019 04:07:27 -0400 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 EFB621570; Tue, 8 Oct 2019 01:07:25 -0700 (PDT) Received: from [10.162.40.139] (p8cg001049571a15.blr.arm.com [10.162.40.139]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B53E83F6C4; Tue, 8 Oct 2019 01:07:12 -0700 (PDT) Subject: Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers To: Ingo Molnar Cc: linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Greg Kroah-Hartman , Thomas Gleixner , Mike Rapoport , Jason Gunthorpe , Dan Williams , Peter Zijlstra , Michal Hocko , Mark Rutland , Mark Brown , Steven Price , Ard Biesheuvel , Masahiro Yamada , Kees Cook , Tetsuo Handa , Matthew Wilcox , Sri Krishna chowdary , Dave Hansen , Russell King - ARM Linux , Michael Ellerman , Paul Mackerras , Martin Schwidefsky , Heiko Carstens , "David S. Miller" , Vineet Gupta , James Hogan , Paul Burton , Ralf Baechle , "Kirill A . Shutemov" , Gerald Schaefer , Christophe Leroy , linux-snps-arc@lists.infradead.org, linux-mips@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org References: <1570427124-21887-1-git-send-email-anshuman.khandual@arm.com> <1570427124-21887-3-git-send-email-anshuman.khandual@arm.com> <20191007130617.GB56546@gmail.com> From: Anshuman Khandual Message-ID: <916f2dd7-6b05-065b-da75-3dbcad1f804d@arm.com> Date: Tue, 8 Oct 2019 13:37:36 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20191007130617.GB56546@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On 10/07/2019 06:36 PM, Ingo Molnar wrote: > > * Anshuman Khandual wrote: > >> This adds a test module which will validate architecture page table helpers >> and accessors regarding compliance with generic MM semantics expectations. >> This will help various architectures in validating changes to the existing >> page table helpers or addition of new ones. >> >> Test page table and memory pages creating it's entries at various level are >> all allocated from system memory with required alignments. If memory pages >> with required size and alignment could not be allocated, then all depending >> individual tests are skipped. > >> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h >> index 52e5f5f2240d..b882792a3999 100644 >> --- a/arch/x86/include/asm/pgtable_64_types.h >> +++ b/arch/x86/include/asm/pgtable_64_types.h >> @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void) >> #define pgtable_l5_enabled() 0 >> #endif /* CONFIG_X86_5LEVEL */ >> >> +#define mm_p4d_folded(mm) (!pgtable_l5_enabled()) >> + >> extern unsigned int pgdir_shift; >> extern unsigned int ptrs_per_p4d; > > Any deep reason this has to be a macro instead of proper C? > >> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug >> index 327b3ebf23bf..683131b1ee7d 100644 >> --- a/mm/Kconfig.debug >> +++ b/mm/Kconfig.debug >> @@ -117,3 +117,18 @@ config DEBUG_RODATA_TEST >> depends on STRICT_KERNEL_RWX >> ---help--- >> This option enables a testcase for the setting rodata read-only. >> + >> +config DEBUG_ARCH_PGTABLE_TEST >> + bool "Test arch page table helpers for semantics compliance" >> + depends on MMU >> + depends on DEBUG_KERNEL >> + depends on !(ARM || IA64) > > Please add a proper enabling switch for architectures to opt in. Sure, will do. > > Please also add it to Documentation/features/list-arch.sh so that it's > listed as a 'TODO' entry on architectures where the tests are not enabled > yet. Will do. > >> + help >> + This options provides a kernel module which can be used to test >> + architecture page table helper functions on various platform in >> + verifying if they comply with expected generic MM semantics. This >> + will help architectures code in making sure that any changes or >> + new additions of these helpers will still conform to generic MM >> + expected semantics. > > Typos and grammar fixed: > > help > This option provides a kernel module which can be used to test > architecture page table helper functions on various platforms in > verifying if they comply with expected generic MM semantics. This > will help architecture code in making sure that any changes or > new additions of these helpers still conform to expected > semantics of the generic MM. Sure, will update except the 'kernel module' part. Thank you. > > Also, more fundamentally: isn't a kernel module too late for such a debug Its not a kernel module any more, my bad that the description has still these words left on from previous versions, will fix it. The test now gets invoked through a late_initcall(). > check, should something break due to a core MM change? Have these debug > checks caught any bugs or inconsistencies before? Gerald Schaefer had reported earlier about a bug found on s390 with this test. https://lkml.org/lkml/2019/9/4/1718 > > Why not call this as some earlier MM debug check, after enabling paging > but before executing user-space binaries or relying on complex MM ops > within the kernel, called at a stage when those primitives are all > expected to work fine? At minimum we need buddy allocator to be initialized for the allocations to work. Just after pgtable_init() or kmem_cache_init() in mm_init() will be a good place ? > > It seems to me that arch_pgtable_tests_init) won't even context-switch > normally, right? Not sure whether I got this. Why would you expect it to context switch ? > > Finally, instead of inventing yet another randomly named .config debug > switch, please fit it into the regular MM debug options which go along > the CONFIG_DEBUG_VM* naming scheme. > > Might even make sense to enable these new debug checks by default if > CONFIG_DEBUG_VM=y, that way we'll get a *lot* more debug coverage than > some random module somewhere that few people will know about, let alone > run. All the configs with respect to memory debugging is generated from lib/Kconfig.debug after fetching all that is in "mm/Kconfig.debug". There are only three configs which depend on CONFIG_DEBUG_VM like a package. 1. CONFIG_DEBUG_VM_VMACACHE 2. CONFIG_DEBUG_VM_RB 3. CONFIG_DEBUG_VM_PGFLAGS 4. CONFIG_DEBUG_VM_PGTABLE [proposed for this] Before that, just trying to understand whether the reason of making this arch page table test as part of DEBUG_VM_* package than a just a stand alone config as many others, is that it is directly related to virtual memory enablement in kernel. Or is there something else I am missing. But this looks better and will make this depend on a selectable arch config like ARCH_HAS_DEBUG_VM_PGTABLE or something. > > Thanks, > > Ingo >