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[23.128.96.18]) by mx.google.com with ESMTP id p8si6734487pgg.226.2021.04.16.07.43.23; Fri, 16 Apr 2021 07:43:35 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245105AbhDPOlx (ORCPT + 99 others); Fri, 16 Apr 2021 10:41:53 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:52168 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245411AbhDPOlV (ORCPT ); Fri, 16 Apr 2021 10:41:21 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4FMJmN2hxGz9vBnG; Fri, 16 Apr 2021 16:40:52 +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 4QkMRAzEi_DN; Fri, 16 Apr 2021 16:40:52 +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 4FMJmN11tvz9vBnC; Fri, 16 Apr 2021 16:40:52 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 781F48B84E; Fri, 16 Apr 2021 16:40:53 +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 D0sjjGIwO1la; Fri, 16 Apr 2021 16:40:53 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 91A338B84C; Fri, 16 Apr 2021 16:40:52 +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> <1102cda1-b00f-b6ef-6bf3-22068cc11510@arm.com> <6ff4816b-8ff6-19de-73a2-3fcadc003ccd@csgroup.eu> From: Christophe Leroy Message-ID: Date: Fri, 16 Apr 2021 16:40:52 +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 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 : >>>>> 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/ >>> >>> >>> >>> >>> 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 0xf9400000-0xf97fffff 0x01430000 4M r present 0xf9800000-0xf9bfffff 0x01430000 4M r present 0xf9c00000-0xf9ffffff 0x01430000 4M r present 0xfa000000-0xfa3fffff 0x01430000 4M r present 0xfa400000-0xfa7fffff 0x01430000 4M r present 0xfa800000-0xfabfffff 0x01430000 4M r present 0xfac00000-0xfaffffff 0x01430000 4M r present 0xfb000000-0xfb3fffff 0x01430000 4M r present 0xfb400000-0xfb7fffff 0x01430000 4M r present 0xfb800000-0xfbbfffff 0x01430000 4M r present 0xfbc00000-0xfbffffff 0x01430000 4M r present 0xfc000000-0xfc3fffff 0x01430000 4M r present 0xfc400000-0xfc7fffff 0x01430000 4M r present 0xfc800000-0xfcbfffff 0x01430000 4M r present 0xfcc00000-0xfcffffff 0x01430000 4M r present 0xfd000000-0xfd3fffff 0x01430000 4M r present 0xfd400000-0xfd7fffff 0x01430000 4M r present 0xfd800000-0xfdbfffff 0x01430000 4M r present 0xfdc00000-0xfdffffff 0x01430000 4M r present 0xfe000000-0xfe3fffff 0x01430000 4M r present 0xfe400000-0xfe7fffff 0x01430000 4M r present 0xfe800000-0xfebfffff 0x01430000 4M r present 0xfec00000-0xfeffffff 0x01430000 4M r present Any idea ? Christophe