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Mon, 19 Apr 2021 15:14:17 +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 yKDNb47P5hGT; Mon, 19 Apr 2021 15:14:17 +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 4FP6j53cN4z9txv7; Mon, 19 Apr 2021 15:14:17 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 866238B7B4; Mon, 19 Apr 2021 15:14:22 +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 CgC9R0HVBL9q; Mon, 19 Apr 2021 15:14:22 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id AB4DA8B7BD; Mon, 19 Apr 2021 15:14:21 +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> From: Christophe Leroy Message-ID: <627ee414-2f78-94e3-b77b-1013f52e77e3@csgroup.eu> Date: Mon, 19 Apr 2021 15:14:21 +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: <1102cda1-b00f-b6ef-6bf3-22068cc11510@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr X-Rspamd-Queue-Id: 9560080192E9 X-Stat-Signature: ws9qqhke6o5tdd397a5jk4c77ccgwryw X-Rspamd-Server: rspam02 Received-SPF: none (csgroup.eu>: No applicable sender policy available) receiver=imf08; identity=mailfrom; envelope-from=""; helo=pegase1.c-s.fr; client-ip=93.17.236.30 X-HE-DKIM-Result: none/none X-HE-Tag: 1618838046-64766 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: 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 page_s= ize - it appears to be using=20 >>> it purely to find "holes" in the calls to note_page(), but I haven't = worked out why such holes=20 >>> would occur. >> >> I was indeed introduced for KASAN. We have a first commit=20 >> https://github.com/torvalds/linux/commit/cabe8138 which uses page size= to detect whether it is a=20 >> KASAN like stuff. >> >> Then came https://github.com/torvalds/linux/commit/b00ff6d8c as a fix.= I can't remember what the=20 >> problem was exactly, something around the use of hugepages for kernel = memory, came as part of the=20 >> series=20 >> https://patchwork.ozlabs.org/project/linuxppc-dev/cover/cover.15898669= 84.git.christophe.leroy@csgroup.eu/=20 >=20 >=20 > Ah, that's useful context. So it looks like powerpc took a different ro= ute to reducing the KASAN=20 > output to x86. >=20 > Given the generic ptdump code has handling for KASAN already it should = be possible to drop that from=20 > the powerpc arch code, which I think means we don't actually need to pr= ovide page size to=20 > notepage(). Hopefully that means more code to delete ;) >=20 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 t= he pgtable referred by the=20 PMD entry. But what happens if that PMD entry is referring another pgtabl= e which is inside the same=20 page as kasan_early_shadow_pte ? Shouldn't the test be if (pmd_page_vaddr(val) =3D=3D lm_alias(kasan_early_shadow_pte)) return note_kasan_page_table(walk, addr); Christophe