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[23.128.96.18]) by mx.google.com with ESMTP id p16si11955938edu.606.2021.04.19.09.04.01; Mon, 19 Apr 2021 09:04:25 -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; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=arm.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238955AbhDSOAt (ORCPT + 99 others); Mon, 19 Apr 2021 10:00:49 -0400 Received: from foss.arm.com ([217.140.110.172]:43492 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230021AbhDSOAs (ORCPT ); Mon, 19 Apr 2021 10:00:48 -0400 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 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/04/2021 14:14, 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: >>>> >>>> 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 ;) >> > > Looking at how the generic ptdump code handles KASAN, I'm a bit sceptic. > > IIUC, it is checking that kasan_early_shadow_pte is in the same page as > the pgtable referred by the PMD entry. But what happens if that PMD > entry is referring another pgtable which is inside the same page as > kasan_early_shadow_pte ? > > Shouldn't the test be > >     if (pmd_page_vaddr(val) == lm_alias(kasan_early_shadow_pte)) >         return note_kasan_page_table(walk, addr); Now I come to look at this code again, I think you're right. On arm64 this doesn't cause a problem - page tables are page sized and page aligned, so there couldn't be any non-KASAN pgtables sharing the page. Obviously that's not necessarily true of other architectures. Feel free to add a patch to your series ;) Steve