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=ham 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 586C6C433ED for ; Fri, 16 Apr 2021 13:00:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D441B61166 for ; Fri, 16 Apr 2021 13:00:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D441B61166 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 28C4A6B0036; 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Fri, 16 Apr 2021 06:00:35 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9E1B33F85F; Fri, 16 Apr 2021 06:00:33 -0700 (PDT) Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage() To: Christophe Leroy , 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: Steven Price Message-ID: Date: Fri, 16 Apr 2021 14:00:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <6ff4816b-8ff6-19de-73a2-3fcadc003ccd@csgroup.eu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: B624141AD7B1 X-Stat-Signature: 8e1ion6onsjajmdr6o8cxah4xtyn1g3p Received-SPF: none (arm.com>: No applicable sender policy available) receiver=imf02; identity=mailfrom; envelope-from=""; helo=foss.arm.com; client-ip=217.140.110.172 X-HE-DKIM-Result: none/none X-HE-Tag: 1618578023-570506 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: On 16/04/2021 12:08, Christophe Leroy wrote: >=20 >=20 > Le 16/04/2021 =C3=A0 12:51, Steven Price a =C3=A9crit=C2=A0: >> On 16/04/2021 11:38, Christophe Leroy wrote: >>> >>> >>> Le 16/04/2021 =C3=A0 11:28, Steven Price a =C3=A9crit=C2=A0: >>>> 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 >>>>> --- >>>>> =C2=A0 arch/arm64/mm/ptdump.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 |=C2=A0 2 +- >>>>> =C2=A0 arch/riscv/mm/ptdump.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 |=C2=A0 2 +- >>>>> =C2=A0 arch/s390/mm/dump_pagetables.c |=C2=A0 3 ++- >>>>> =C2=A0 arch/x86/mm/dump_pagetables.c=C2=A0 |=C2=A0 2 +- >>>>> =C2=A0 include/linux/ptdump.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 |=C2=A0 2 +- >>>>> =C2=A0 mm/ptdump.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 16 ++++= ++++-------- >>>>> =C2=A0 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=20 >>>>> mm_walk *walk, >>>>> =C2=A0 { >>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct ptdump_state *st =3D walk->pr= ivate; >>>>> -=C2=A0=C2=A0=C2=A0 st->note_page(st, addr, 4, pte_val(kasan_early_= shadow_pte[0])); >>>>> +=C2=A0=C2=A0=C2=A0 st->note_page(st, addr, 4, pte_val(kasan_early_= shadow_pte[0]),=20 >>>>> PAGE_SIZE); >>>> >>>> I'm not completely sure what the page_size is going to be used for,=20 >>>> but note that KASAN presents an interesting case here. We short-cut=20 >>>> by detecting it's a KASAN region at a high level (PGD/P4D/PUD/PMD)=20 >>>> and instead of walking the tree down just call note_page() *once*=20 >>>> but with level=3D=3D4 because we know KASAN sets up the page table l= ike=20 >>>> that. >>>> >>>> However the one call actually covers a much larger region - so while= =20 >>>> PAGE_SIZE matches the level it doesn't match the region covered.=20 >>>> 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=20 >>> tested it with CONFIG_KASAN_VMALLOC selected. In this situation,=20 >>> since https://github.com/torvalds/linux/commit/af3d0a686 we don't=20 >>> 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=20 >>>> page_size - it appears to be using it purely to find "holes" in the=20 >>>> calls to note_page(), but I haven't worked out why such holes would=20 >>>> occur. >>> >>> I was indeed introduced for KASAN. We have a first commit=20 >>> https://github.com/torvalds/linux/commit/cabe8138 which uses page=20 >>> size to detect whether it is a KASAN like stuff. >>> >>> Then came https://github.com/torvalds/linux/commit/b00ff6d8c as a=20 >>> fix. I can't remember what the problem was exactly, something around=20 >>> the use of hugepages for kernel memory, came as part of the series=20 >>> https://patchwork.ozlabs.org/project/linuxppc-dev/cover/cover.1589866= 984.git.christophe.leroy@csgroup.eu/=20 >> >> >> >> Ah, that's useful context. So it looks like powerpc took a different=20 >> route to reducing the KASAN output to x86. >> >> Given the generic ptdump code has handling for KASAN already it should= =20 >> be possible to drop that from the powerpc arch code, which I think=20 >> means we don't actually need to provide page size to notepage().=20 >> Hopefully that means more code to delete ;) >> >=20 > Yes ... and no. >=20 > It looks like the generic ptdump handles the case when several pgdir=20 > entries points to the same kasan_early_shadow_pte. But it doesn't take=20 > into account the powerpc case where we have regular page tables where=20 > 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=20 have a similar check for PTEs against kasan_early_shadow_pte as the=20 other levels already have? I'm just worried that page_size isn't well defined in this interface and=20 it's going to cause problems in the future. Steve