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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,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 6DC3BC33CB3 for ; Tue, 28 Jan 2020 06:17:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2621E2173E for ; Tue, 28 Jan 2020 06:17:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=c-s.fr header.i=@c-s.fr header.b="lgZskWmS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2621E2173E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=c-s.fr Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C6D8E6B0006; Tue, 28 Jan 2020 01:17:39 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C1E806B0008; Tue, 28 Jan 2020 01:17:39 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B0D226B000A; Tue, 28 Jan 2020 01:17:39 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0138.hostedemail.com [216.40.44.138]) by kanga.kvack.org (Postfix) with ESMTP id 974416B0006 for ; Tue, 28 Jan 2020 01:17:39 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 4203B181AC9CC for ; Tue, 28 Jan 2020 06:17:39 +0000 (UTC) X-FDA: 76426036638.12.rifle89_25a1c02d8b727 X-HE-Tag: rifle89_25a1c02d8b727 X-Filterd-Recvd-Size: 5819 Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Tue, 28 Jan 2020 06:17:38 +0000 (UTC) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 486Gcc0WVCz9v22Q; Tue, 28 Jan 2020 07:17:36 +0100 (CET) Authentication-Results: localhost; dkim=pass reason="1024-bit key; insecure key" header.d=c-s.fr header.i=@c-s.fr header.b=lgZskWmS; dkim-adsp=pass; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id UkHPZqpb554O; Tue, 28 Jan 2020 07:17:35 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 486Gcb627Gz9v22N; Tue, 28 Jan 2020 07:17:35 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=c-s.fr; s=mail; t=1580192255; bh=+DPt49RKHi9mO1gnM2058SFaj+Fq0ceAMy7haYJU1NM=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=lgZskWmSj1VA5v5b98S9ZEmr7USU9rrof5MnKymq+rXgWJyl99vDSXQIZX47bFjeC /6k5GZov6uOPE4UU+Xi9hVhZlNd3ZPIeokTTE6E9eAr6ycFttvMUe986W6/vBNtjV8 Ykd6Kd6ETlhEILSsCQYi5j6eBswWvSBhAxwf3fzs= Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 8873F8B7C2; Tue, 28 Jan 2020 07:17:36 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id RqoGVOoiJ5M4; Tue, 28 Jan 2020 07:17:36 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id DC9498B75B; Tue, 28 Jan 2020 07:17:33 +0100 (CET) Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers To: Qian Cai , Anshuman Khandual Cc: Linux-MM , 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 , Ingo Molnar , 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: <012158b7-a40e-050f-cd1b-d6ce7faf042f@arm.com> From: Christophe Leroy Message-ID: <115c187b-73ce-30b2-0694-999db1f2183b@c-s.fr> Date: Tue, 28 Jan 2020 07:17:33 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: quoted-printable 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: Le 28/01/2020 =C3=A0 06:48, Qian Cai a =C3=A9crit=C2=A0: >=20 >=20 >> On Jan 27, 2020, at 11:58 PM, Anshuman Khandual wrote: >> >> As I had mentioned before, the test attempts to formalize page table h= elper semantics >> as expected from generic MM code paths and intend to catch deviations = when enabled on >> a given platform. How else should we test semantics errors otherwise ?= There are past >> examples of usefulness for this procedure on arm64 and on s390. I am w= ondering how >> else to prove the usefulness of a debug feature if these references ar= e not enough. >=20 > Not saying it will not be useful. As you mentioned it actually found a = bug or two in the past. The problem is that there is always a cost to mai= ntain something like this, and nobody knew how things could be broken eve= n for the isolated code you mentioned in the future given how complicated= the kernel code base is. I am not so positive that many developers would= enable this debug feature and use it on a regular basis from the informa= tion you gave so far. >=20 > On the other hand, it might just be good at maintaining this thing out = of tree by yourself anyway, because if there isn=E2=80=99t going to be us= ed by many developers, few people is going to contribute to this and even= noticed when it is broken. What=E2=80=99s the point of getting this merg= ed apart from being getting some meaningless credits? >=20 It is 'default y' so there is no much risk that it is forgotten, at=20 least all test suites run with 'allyes_defconfig' will trigger the test,=20 so I think it is really a good feature. Christophe