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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,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 EE6E3C433B4 for ; Fri, 16 Apr 2021 15:18:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B354C61026 for ; Fri, 16 Apr 2021 15:18:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343653AbhDPPRo (ORCPT ); Fri, 16 Apr 2021 11:17:44 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:37762 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343531AbhDPPPx (ORCPT ); Fri, 16 Apr 2021 11:15:53 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4FMKXD004dz9v3Lf; Fri, 16 Apr 2021 17:15:23 +0200 (CEST) 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 WK3DlU5pFCvu; Fri, 16 Apr 2021 17:15:23 +0200 (CEST) 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 4FMKXC6BwFz9v3Ld; Fri, 16 Apr 2021 17:15:23 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 766108B84E; Fri, 16 Apr 2021 17:15:25 +0200 (CEST) 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 5GrWiUHi_Hri; Fri, 16 Apr 2021 17:15:25 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 5295F8B84C; Fri, 16 Apr 2021 17:15:24 +0200 (CEST) Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage() From: Christophe Leroy To: Steven Price , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , akpm@linux-foundation.org Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org References: <1ef6b954fb7b0f4dfc78820f1e612d2166c13227.1618506910.git.christophe.leroy@csgroup.eu> <41819925-3ee5-4771-e98b-0073e8f095cf@arm.com> <1102cda1-b00f-b6ef-6bf3-22068cc11510@arm.com> <6ff4816b-8ff6-19de-73a2-3fcadc003ccd@csgroup.eu> Message-ID: <10adad00-14de-61b6-ce2a-bdde23a34bcf@csgroup.eu> Date: Fri, 16 Apr 2021 17:15:23 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 16/04/2021 à 17:04, Christophe Leroy a écrit : > > > Le 16/04/2021 à 16:40, Christophe Leroy a écrit : >> >> >> Le 16/04/2021 à 15:00, Steven Price a écrit : >>> On 16/04/2021 12:08, Christophe Leroy wrote: >>>> >>>> >>>> Le 16/04/2021 à 12:51, Steven Price a écrit : >>>>> On 16/04/2021 11:38, Christophe Leroy wrote: >>>>>> >>>>>> >>>>>> Le 16/04/2021 à 11:28, Steven Price a écrit : >>>>>>> To be honest I don't fully understand why powerpc requires the page_size - it appears to be >>>>>>> using it purely to find "holes" in the calls to note_page(), but I haven't worked out why >>>>>>> such holes would occur. >>>>>> >>>>>> I was indeed introduced for KASAN. We have a first commit >>>>>> https://github.com/torvalds/linux/commit/cabe8138 which uses page size to detect whether it is >>>>>> a KASAN like stuff. >>>>>> >>>>>> Then came https://github.com/torvalds/linux/commit/b00ff6d8c as a fix. I can't remember what >>>>>> the problem was exactly, something around the use of hugepages for kernel memory, came as part >>>>>> of the series >>>>>> https://patchwork.ozlabs.org/project/linuxppc-dev/cover/cover.1589866984.git.christophe.leroy@csgroup.eu/ >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> Ah, that's useful context. So it looks like powerpc took a different route to reducing the >>>>> KASAN output to x86. >>>>> >>>>> Given the generic ptdump code has handling for KASAN already it should be possible to drop that >>>>> from the powerpc arch code, which I think means we don't actually need to provide page size to >>>>> notepage(). Hopefully that means more code to delete ;) >>>>> >>>> >>>> Yes ... and no. >>>> >>>> It looks like the generic ptdump handles the case when several pgdir entries points to the same >>>> kasan_early_shadow_pte. But it doesn't take into account the powerpc case where we have regular >>>> page tables where several (if not all) PTEs are pointing to the kasan_early_shadow_page . >>> >>> I'm not sure I follow quite how powerpc is different here. But could you have a similar check for >>> PTEs against kasan_early_shadow_pte as the other levels already have? >>> >>> I'm just worried that page_size isn't well defined in this interface and it's going to cause >>> problems in the future. >>> >> >> I'm trying. I reverted the two commits b00ff6d8c and cabe8138. >> >> At the moment, I don't get exactly what I expect: For linear memory I get one line for each 8M >> page whereas before reverting the patches I got one 16M line and one 112M line. >> >> And for KASAN shadow area I get two lines for the 2x 8M pages shadowing linear mem then I get one >> 4M line for each PGDIR entry pointing to kasan_early_shadow_pte. >> >> 0xf8000000-0xf87fffff 0x07000000         8M   huge        rw       present >> 0xf8800000-0xf8ffffff 0x07800000         8M   huge        rw       present >> 0xf9000000-0xf93fffff 0x01430000         4M               r        present > ... >> 0xfec00000-0xfeffffff 0x01430000         4M               r        present >> >> Any idea ? >> > > > I think the different with other architectures is here: > >     } else if (flag != st->current_flags || level != st->level || >            addr >= st->marker[1].start_address || >            pa != st->last_pa + PAGE_SIZE) { > > > In addition to the checks everyone do, powerpc also checks "pa != st->last_pa + PAGE_SIZE". > And it is definitely for that test that page_size argument add been added. By replacing that test by (pa - st->start_pa != addr - st->start_address) it works again. So we definitely don't need the real page size. > > I see that other architectures except RISCV don't dump the physical address. But even RISCV doesn't > include that check. > > That physical address dump was added by commit aaa229529244 ("powerpc/mm: Add physical address to > Linux page table dump") [https://github.com/torvalds/linux/commit/aaa2295] > > How do other architectures deal with the problem described by the commit log of that patch ? > > Christophe