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Fri, 16 Apr 2021 17:04:58 +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 nfnIuGVT2LDV; Fri, 16 Apr 2021 17:04:58 +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 4FMKJB4wVtz9v3LK; Fri, 16 Apr 2021 17:04:58 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 0F4968B851; Fri, 16 Apr 2021 17:05:00 +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 gM_a9XKodz3W; Fri, 16 Apr 2021 17:04:59 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 7EF558B84C; Fri, 16 Apr 2021 17:04:58 +0200 (CEST) Subject: Re: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage() From: Christophe Leroy To: Steven Price , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , akpm@linux-foundation.org Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.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> Message-ID: Date: Fri, 16 Apr 2021 17:04:56 +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 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0F47890009E2 X-Stat-Signature: sgkyad4hug4obm1ysf5um954jw81x5x5 Received-SPF: none (csgroup.eu>: No applicable sender policy available) receiver=imf19; identity=mailfrom; envelope-from=""; helo=pegase1.c-s.fr; client-ip=93.17.236.30 X-HE-DKIM-Result: none/none X-HE-Tag: 1618585483-573783 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 16:40, Christophe Leroy a =C3=A9crit=C2=A0: >=20 >=20 > Le 16/04/2021 =C3=A0 15:00, Steven Price a =C3=A9crit=C2=A0: >> On 16/04/2021 12:08, Christophe Leroy wrote: >>> >>> >>> 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: >>>>>> To be honest I don't fully understand why powerpc requires the pag= e_size - it appears to be=20 >>>>>> using it purely to find "holes" in the calls to note_page(), but I= haven't worked out why such=20 >>>>>> holes would occur. >>>>> >>>>> I was indeed introduced for KASAN. We have a first commit=20 >>>>> https://github.com/torvalds/linux/commit/cabe8138 which uses page s= ize to detect whether it is=20 >>>>> a KASAN like stuff. >>>>> >>>>> Then came https://github.com/torvalds/linux/commit/b00ff6d8c as a f= ix. I can't remember what=20 >>>>> the problem was exactly, something around the use of hugepages for = kernel memory, came as part=20 >>>>> of the series=20 >>>>> https://patchwork.ozlabs.org/project/linuxppc-dev/cover/cover.15898= 66984.git.christophe.leroy@csgroup.eu/=20 >>>> >>>> >>>> >>>> >>>> >>>> Ah, that's useful context. So it looks like powerpc took a different= route to reducing the KASAN=20 >>>> output to x86. >>>> >>>> Given the generic ptdump code has handling for KASAN already it shou= ld be possible to drop that=20 >>>> from the powerpc arch code, which I think means we don't actually ne= ed to provide page size to=20 >>>> 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=20 >>> kasan_early_shadow_pte. But it doesn't take into account the powerpc = case where we have regular=20 >>> 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 y= ou have a similar check for=20 >> 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 a= nd it's going to cause=20 >> problems in the future. >> >=20 > I'm trying. I reverted the two commits b00ff6d8c and cabe8138. >=20 > At the moment, I don't get exactly what I expect: For linear memory I g= et one line for each 8M page=20 > whereas before reverting the patches I got one 16M line and one 112M li= ne. >=20 > And for KASAN shadow area I get two lines for the 2x 8M pages shadowing= linear mem then I get one 4M=20 > line for each PGDIR entry pointing to kasan_early_shadow_pte. >=20 > 0xf8000000-0xf87fffff 0x07000000=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 8M=C2=A0=C2=A0 huge=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 r= w=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 present > 0xf8800000-0xf8ffffff 0x07800000=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 8M=C2=A0=C2=A0 huge=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 r= w=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 present > 0xf9000000-0xf93fffff 0x01430000=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 4M=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 r=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 present ... > 0xfec00000-0xfeffffff 0x01430000=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 4M=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 r=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 present >=20 > Any idea ? >=20 I think the different with other architectures is here: } else if (flag !=3D st->current_flags || level !=3D st->level || addr >=3D st->marker[1].start_address || pa !=3D st->last_pa + PAGE_SIZE) { In addition to the checks everyone do, powerpc also checks "pa !=3D st->l= ast_pa + PAGE_SIZE". And it is definitely for that test that page_size argument add been added= . I see that other architectures except RISCV don't dump the physical addre= ss. But even RISCV doesn't=20 include that check. That physical address dump was added by commit aaa229529244 ("powerpc/mm:= Add physical address to=20 Linux page table dump") [https://github.com/torvalds/linux/commit/aaa2295= ] How do other architectures deal with the problem described by the commit = log of that patch ? Christophe