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=-20.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, 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 AC9A0C43460 for ; Fri, 16 Apr 2021 10:38:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B232610CD for ; Fri, 16 Apr 2021 10:38:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241147AbhDPKjB (ORCPT ); Fri, 16 Apr 2021 06:39:01 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:39660 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240931AbhDPKis (ORCPT ); Fri, 16 Apr 2021 06:38:48 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4FMCNW3tv5z9v4WN; Fri, 16 Apr 2021 12:38:19 +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 TGx8rBpOGfLa; Fri, 16 Apr 2021 12:38:19 +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 4FMCNW2yYgz9v4WM; Fri, 16 Apr 2021 12:38:19 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 8FD108B83B; Fri, 16 Apr 2021 12:38:20 +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 gxbf4EojfzU4; Fri, 16 Apr 2021 12:38:20 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 6CE338B83A; Fri, 16 Apr 2021 12:38:19 +0200 (CEST) Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage() To: Steven Price , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , akpm@linux-foundation.org Cc: linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-mm@kvack.org References: <1ef6b954fb7b0f4dfc78820f1e612d2166c13227.1618506910.git.christophe.leroy@csgroup.eu> <41819925-3ee5-4771-e98b-0073e8f095cf@arm.com> From: Christophe Leroy Message-ID: Date: Fri, 16 Apr 2021 12:38:18 +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: <41819925-3ee5-4771-e98b-0073e8f095cf@arm.com> 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 11:28, Steven Price a écrit : > On 15/04/2021 18:18, Christophe Leroy wrote: >> In order to support large pages on powerpc, notepage() >> needs to know the page size of the page. >> >> Add a page_size argument to notepage(). >> >> Signed-off-by: Christophe Leroy >> --- >>   arch/arm64/mm/ptdump.c         |  2 +- >>   arch/riscv/mm/ptdump.c         |  2 +- >>   arch/s390/mm/dump_pagetables.c |  3 ++- >>   arch/x86/mm/dump_pagetables.c  |  2 +- >>   include/linux/ptdump.h         |  2 +- >>   mm/ptdump.c                    | 16 ++++++++-------- >>   6 files changed, 14 insertions(+), 13 deletions(-) >> > [...] >> diff --git a/mm/ptdump.c b/mm/ptdump.c >> index da751448d0e4..61cd16afb1c8 100644 >> --- a/mm/ptdump.c >> +++ b/mm/ptdump.c >> @@ -17,7 +17,7 @@ static inline int note_kasan_page_table(struct mm_walk *walk, >>   { >>       struct ptdump_state *st = walk->private; >> -    st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0])); >> +    st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0]), PAGE_SIZE); > > I'm not completely sure what the page_size is going to be used for, but note that KASAN presents an > interesting case here. We short-cut by detecting it's a KASAN region at a high level > (PGD/P4D/PUD/PMD) and instead of walking the tree down just call note_page() *once* but with > level==4 because we know KASAN sets up the page table like that. > > However the one call actually covers a much larger region - so while PAGE_SIZE matches the level it > doesn't match the region covered. AFAICT this will lead to odd results if you enable KASAN on powerpc. Hum .... I successfully tested it with KASAN, I now realise that I tested it with CONFIG_KASAN_VMALLOC selected. In this situation, since https://github.com/torvalds/linux/commit/af3d0a686 we don't have any common shadow page table anymore. I'll test again without CONFIG_KASAN_VMALLOC. > > 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/ Christophe