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Fri, 16 Apr 2021 12:38:19 +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 TGx8rBpOGfLa; Fri, 16 Apr 2021 12:38:19 +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 4FMCNW2yYgz9v4WM; Fri, 16 Apr 2021 12:38:19 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 8FD108B83B; Fri, 16 Apr 2021 12:38:20 +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 gxbf4EojfzU4; Fri, 16 Apr 2021 12:38:20 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 6CE338B83A; Fri, 16 Apr 2021 12:38:19 +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> From: Christophe Leroy Message-ID: Date: Fri, 16 Apr 2021 12:38:18 +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: <41819925-3ee5-4771-e98b-0073e8f095cf@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 4DFD7F2 X-Stat-Signature: toscyonfitqp3sixdjzqx8o6m4ypzg65 Received-SPF: none (csgroup.eu>: No applicable sender policy available) receiver=imf12; identity=mailfrom; envelope-from=""; helo=pegase1.c-s.fr; client-ip=93.17.236.30 X-HE-DKIM-Result: none/none X-HE-Tag: 1618569496-971102 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 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 mm_wa= lk *walk, >> =C2=A0 { >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct ptdump_state *st =3D walk->priva= te; >> -=C2=A0=C2=A0=C2=A0 st->note_page(st, addr, 4, pte_val(kasan_early_sha= dow_pte[0])); >> +=C2=A0=C2=A0=C2=A0 st->note_page(st, addr, 4, pte_val(kasan_early_sha= dow_pte[0]), PAGE_SIZE); >=20 > I'm not completely sure what the page_size is going to be used for, but= note that KASAN presents an=20 > interesting case here. We short-cut by detecting it's a KASAN region at= a high level=20 > (PGD/P4D/PUD/PMD) and instead of walking the tree down just call note_p= age() *once* but with=20 > level=3D=3D4 because we know KASAN sets up the page table like that. >=20 > However the one call actually covers a much larger region - so while PA= GE_SIZE matches the level it=20 > doesn't match the region covered. 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 tested= it with=20 CONFIG_KASAN_VMALLOC selected. In this situation, since=20 https://github.com/torvalds/linux/commit/af3d0a686 we don't have any comm= on shadow page table anymore. I'll test again without CONFIG_KASAN_VMALLOC. >=20 > To be honest I don't fully understand why powerpc requires the page_siz= e - it appears to be using it=20 > purely to find "holes" in the calls to note_page(), but I haven't worke= d 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 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 mem= ory, came as part of the=20 series=20 https://patchwork.ozlabs.org/project/linuxppc-dev/cover/cover.1589866984.= git.christophe.leroy@csgroup.eu/ Christophe