From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:32994 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726111AbgA1RrR (ORCPT ); Tue, 28 Jan 2020 12:47:17 -0500 Date: Tue, 28 Jan 2020 17:47:09 +0000 From: Catalin Marinas Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers Message-ID: <20200128174709.GK655507@arrakis.emea.arm.com> References: <1580174873-18117-1-git-send-email-anshuman.khandual@arm.com> <14882A91-17DE-4ABD-ABF2-08E7CCEDF660@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <14882A91-17DE-4ABD-ABF2-08E7CCEDF660@lca.pw> Sender: linux-s390-owner@vger.kernel.org List-ID: To: Qian Cai Cc: Anshuman Khandual , Mark Rutland , linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Peter Zijlstra , James Hogan , Tetsuo Handa , Heiko Carstens , Michal Hocko , linux-mm@kvack.org, Dave Hansen , Paul Mackerras , sparclinux@vger.kernel.org, Thomas Gleixner , linux-s390@vger.kernel.org, Michael Ellerman , x86@kernel.org, Russell King - ARM Linux , Matthew Wilcox , Steven Price , Jason Gunthorpe , Gerald Schaefer , linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Ingo Molnar , Kees Cook , Masahiro Yamada , Mark Brown , "Kirill A . Shutemov" , Dan Williams , Vlastimil Babka , Christophe Leroy , Sri Krishna chowdary , Ard Biesheuvel , Greg Kroah-Hartman , linux-mips@vger.kernel.org, Ralf Baechle , linux-kernel@vger.kernel.org, Paul Burton , Mike Rapoport , Vineet Gupta , Martin Schwidefsky , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" On Mon, Jan 27, 2020 at 09:11:53PM -0500, Qian Cai wrote: > On Jan 27, 2020, at 8:28 PM, Anshuman Khandual wrote: > > This adds tests which will validate architecture page table helpers and > > other accessors in their compliance with expected generic MM semantics. > > This will help various architectures in validating changes to existing > > page table helpers or addition of new ones. [...] > What’s the value of this block of new code? It only supports x86 and > arm64 which are supposed to be good now. Did those tests ever find any > regression or this is almost only useful for new architectures which > only happened once in a few years? The primary goal here is not finding regressions but having clearly defined semantics of the page table accessors across architectures. x86 and arm64 are a good starting point and other architectures will be enabled as they are aligned to the same semantics. See for example this past discussion: https://lore.kernel.org/linux-mm/20190628102003.GA56463@arrakis.emea.arm.com/ These tests should act as the 'contract' between the generic mm code and the architecture port. Without clear semantics, some bugs may be a lot subtler than a boot failure. FTR, I fully support this patch (and I should get around to review it properly; thanks for the reminder ;)). -- Catalin