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=-10.3 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=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 32F7BC43460 for ; Mon, 19 Apr 2021 14:00:21 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A6B8861006 for ; Mon, 19 Apr 2021 14:00:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A6B8861006 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 151986B007D; Mon, 19 Apr 2021 10:00:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0D7456B007E; Mon, 19 Apr 2021 10:00:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E91176B0080; Mon, 19 Apr 2021 10:00:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0185.hostedemail.com [216.40.44.185]) by kanga.kvack.org (Postfix) with ESMTP id C8EE46B007D for ; Mon, 19 Apr 2021 10:00:19 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 8813C8249980 for ; Mon, 19 Apr 2021 14:00:19 +0000 (UTC) X-FDA: 78049276158.21.DD5A545 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf20.hostedemail.com (Postfix) with ESMTP id 4FA572BEE for ; Mon, 19 Apr 2021 14:00:12 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0FCD231B; Mon, 19 Apr 2021 07:00:18 -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 3FBAA3F7D7; Mon, 19 Apr 2021 07:00:16 -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> <627ee414-2f78-94e3-b77b-1013f52e77e3@csgroup.eu> From: Steven Price Message-ID: <4a76fbda-aa9d-867b-e2eb-a1951780aeec@arm.com> Date: Mon, 19 Apr 2021 15:00:14 +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: <627ee414-2f78-94e3-b77b-1013f52e77e3@csgroup.eu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4FA572BEE X-Stat-Signature: ksnedftpbzyt34hbuah7h6q9xa5wbak6 Received-SPF: none (arm.com>: No applicable sender policy available) receiver=imf20; identity=mailfrom; envelope-from=""; helo=foss.arm.com; client-ip=217.140.110.172 X-HE-DKIM-Result: none/none X-HE-Tag: 1618840812-266618 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 19/04/2021 14:14, 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: >>>> >>>> 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 > Looking at how the generic ptdump code handles KASAN, I'm a bit sceptic= . >=20 > IIUC, it is checking that kasan_early_shadow_pte is in the same page as= =20 > the pgtable referred by the PMD entry. But what happens if that PMD=20 > entry is referring another pgtable which is inside the same page as=20 > kasan_early_shadow_pte ? >=20 > Shouldn't the test be >=20 > =C2=A0=C2=A0=C2=A0=C2=A0if (pmd_page_vaddr(val) =3D=3D lm_alias(kasan_= early_shadow_pte)) > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return note_kasan_page_tabl= e(walk, addr); Now I come to look at this code again, I think you're right. On arm64=20 this doesn't cause a problem - page tables are page sized and page=20 aligned, so there couldn't be any non-KASAN pgtables sharing the page.=20 Obviously that's not necessarily true of other architectures. Feel free to add a patch to your series ;) Steve